PROCESS FOR PRODUCING FIBROUS MATERIAL PRE-IMPREGNATED
WITH THERMOSETTING POLYMER
The present invention relates to a process for
manufacturing a pre-impregnated fibrous material and
the uses of such fibrous materials.
The expression "fibrous materials" is understood to
mean an assembly of reinforcing fibers which may be
10 either short fibers such as felts or nonwovens that may
be in the form of strips, sheets, braids, rovings or
fragments, or continuous fibers such as for example in
2D fabrics, UD fibers or nonwovens.
15 The fibers that may be incorporated into the
composition of the material are more especially carbon
fibers, glass fibers, mineral fibers such as basalt,
silicon carbide, polymer-based fibers, plant fibers,
cellulose fibers such as viscose, flax, hemp, silk,
20 sisal, used alone or as a mixture.
The invention relates more particularly to the
manufacture of fibrous materials impregnated by a
thermosetting polymer, otherwise known as a
25 thermosetting resin (the two terms meaning the same
thing) or a blend of thermosetting polymers (or resins)
and the uses of such materials referred to as preimpregnated
fibrous materials, for the manufacture of
composite materials that are used for producing three-
30 dimensional (3D) parts.
Indeed, fibrous materials pre-impregnated with a
polymer are used in the manufacture of structural parts
for machines, in particular moveable machines, with a
35 view to lightening them while giving them a mechanical
strength comparable to that obtained with metal
structural parts and/or to ensure thermal protection
and/or to ensure the discharging of electrostatic
charges. These fibrous materials may be impregnated
with a thermoplastic polymer or with a thermosetting
polymer.
5 The pre-impregnated fibrous materials may also contain
conductive nanofillers of carbon origin such as carbon
nanotubes (or CNTs), carbon black, nanofibers or
graphenes, more particularly carbon nanotubes (CNTs).
10 The presence of carbon nanotubes in the fibrous
material makes it possible to improve the mechanical
and/or thermal and/or electrical properties of the
mechanical parts based on said material.
15 Thus, the pre-impregnated fibrous materials form light
materials that provide a mechanical strength comparable
to metal, giving an increase in the electrical and/or
thermal resistance of the mechanical part produced in
order to ensure the discharging of the heat and/or of
20 the electrostatic charge. These materials are
particularly suitable for the simple production of any
three-dimensional, commonly symbolized by 3D,
mechanical structure, in particular for motor vehicles,
aeronautics, the nautical field, railroad transport,
25 sport or aerospace.
The invention applies to the production of parts having
a 3D structure, such as in particular aircraft wings,
the fuselage of an aircraft, the hull of a boat, the
30 side members or spoilers of a motor vehicle or else
brake disks, a cylinder body or steering wheels, using
pre-impregnated fibrous materials.
In the manufacture of fibrous materials impregnated by
35 a thermosetting resin (that is to say by a
thermosetting polymer) or a blend of thermosetting
polymers, the impregnation takes place at the melting
temperature Tm of the resin as the minimum temperature
or at a higher temperature. This temperature Tm varies
depending on the resins used. After the step of
impregnating the material, the resin is in a stable
state which enables a shaping of the material for the
5 manufacture of three-dimensional parts. The shaping may
be carried out just after impregnation or subsequently.
The curing agent or element for the activation of the
crosslinking reaction which has been introduced into
the thermosetting resin remains inactive as long as its
10 reaction temperature is not reached. This temperature
is above the glass transition temperature Tg of the
(crosslinked) resin and is above the melting
temperature Tm (of the resin before crosslinking) if it
exists. For the production of parts having a three-
15 dimensional structure, the fibrous materials are shaped
and heated at a temperature at least equal to the glass
transition temperature Tg of the resin. The resin is
converted to a thermoset resin and the part thus takes
on its final shape.
20
To date, when nanofillers such as CNTs are introduced
into the thermosetting resin, they are in fact
dispersed in the base formulation of the resin, that is
to say in the thermosetting resin or resin composition
25 containing the curing agent.
The Applicant has observed in this case that the
presence in the resin of nanofillers, in particular
such as CNTs, poses several technical problems to be
30 solved. Firstly, the dry handling thereof in the form
of a pulverulent powder of nanometer size presents
risks for health, safety and the environment in general
for users in plants for producing pre-impregnated
fibrous materials. Secondly, the introduction of these
35 nanofj.llers, in particular CNTs, leads to the formation
of aggregates, requiring the use of particular, very
high shear mixers in order to break them up with a risk
of heating and premature crosslinking of the resin in
the presence of the curing agent. Similarly, these
nanofillers, due to their size (large specific surface
area) and their interactions with the resin, lead to a
significant increase in the viscosity of the medium.
This significantly limits the amount of nanof illers, in
particular the amount of CNTs, which it is possible to
incorporate into a thermosetting resin that already
contains the curing agent, without using the particular
methods of high-shear dispersion with the cited
drawbacks.
Failing a solution to the cited problems, the presence
in the resin of nanofillers, such as CNTs, gives rise
to a formation of under-crosslinked domains that
15 contribute to the reduction of the glass transition
temperature Tg of the resin with respect to the
temperature specified by the manufacturers and,
consequently, a modification with reduction of the
thermomechanical performances directly linked to the
20 Tg, and of the electrical performances (conductivity)
via the heterogeneity of the material. One of the
reasons or possible explanations is that the portion of
thermosetting resin remains adsorbed on the surface of
the CNTs and therefore it is no longer available to the
25 crosslinking reaction in order to participate in the
crosslinked network. The formation of under-crosslinked
domains then contributes to the reduction of the glass
transition temperature and of the thermomechanical
performances (Auad et al., Poly. Engin. Sci. 2010,
30 183-190).
The objective of the present invention is to overcome
this problem. It makes it possible to avoid the
formation of under-crosslinked domains and to maintain
35 a high glass transition temperature Tg of the
thermosetting resin (thermosetting polymer or blend of
thermosetting polymers).
For this purpose, it is proposed according to the
invention to use a mixture containing nanofillers, in
particular carbon nanotubes and the curing agent, that
is to say nanofillers predispersed separately in the
5 curing agent, in order to introduce the carbon
nanotubes, by means of this mixture, into the fibrous
material, more specifically by the final impregnation
of this material.
10 Thus, according to the invention, the nanofillers are
introduced into the thermosetting polymer, not alone,
but by means of the nanofillers/curing agent mixture.
In accordance with the invention, the
nanofillers/curing agent mixture may be introduced
15 directly into the thermosetting polymer before
impregnation of the fibrous material or else may be
incorporated into the fibrous material during the
impregnation.
20 The nanofillers/curing agent mixture may be in the form
of a fluid, powder, fibers or film, depending on the
curing agent and on the amount of nanofillers. When the
nanofillers/curing agent mixture is incorporated into
the fibrous material before impregnation, this mixture
25 will preferably be produced either in the form of
fibers, or in the form of a film, or in the form of a
powder. Thus, when the nanofillers/curing agent mixture
is in the form of fibers, these fibers will
advantageously be in the assembly of fibers forming the
30 fibrous material. When the mixture is in the form of a
powder, it will be deposited on the fibrous material.
When the mixture is in the form of a film, it will
advantageously be deposited on the fibrous material.
The fibrous material thus obtained is then impregnated
35 by the thermosetting polymer. It is furthermore
apparent to the Applicant that this invention could
also be applied to carbon-based conductive nanofillers
other than carbon nanotubes and in particular to carbon
black, to carbon nanofibers or to graphenes, which are
also capable of posing safety problems due to their
pulverulent nature and which have an ability to confer
improved conductive or mechanical properties on the
5 materials into which they are incorporated.
One subject of the present invention is more
particularly a process for manufacturing a fibrous
material comprising an assembly of one or more fibers,
10 composed of carbon fibers or glass fibers or plant
fibers or mineral fibers or cellulose fibers or
polymer-based fibers, used alone or as a mixture,
impregnated by a thermosetting polymer or a blend of
thermosetting polymers containing a curing agent and
15 nanofillers of carbon origin such as carbon nanotubes
(CNTs), carbon black, carbon nanofibers or graphenes,
mainly characterized in that a mixture containing the
nanofillers of carbon origin such as CNTs and the
curing agent (nanofillers predispersed in said curing
20 agent) is used in order to introduce said nanofillers
into the fibrous material. The nanofillers of carbon
origin/curing agent mixture advantageously comprises a
content of nanofillers of between 10% and 60%,
preferably of between 20% and 50%, relative to the
25 total weight of the mixture.
The nanofillers of carbon origin/curing agent mixture
may also comprise a crosslinking catalyst or
accelerator. Various types of crosslinkings and, as a
30 function thereof, corresponding curing agents may be
considered according to the present invention, for
example :
- by polycondensation or by polyaddition between two
co-reactive functions with the curing agent being
that of the 2 components which is the least
viscous and/or has the lower molecular weight,
with a possibility of a crosslinking reaction that
is accelerated by catalysis (presence of a
catalyst) ; or
- by radical crosslinking via opening of
ethylenically unsaturated groups, the curing agent
being, in this case, the radical initiator, of
peroxide type, including hydroperoxide, with the
optional presence of an accelerator for the
decomposition of the peroxide, such as a tertiary
amine or CO*+ or ~ es~alt+s.
10
In one preferred exemplary embodiment, the nanofillers
of organic origin, hereinafter referred to as
nanofillers, consist of carbon nanotubes (CNTs).
15 The expression "thermosetting resin" is considered to
mean the main multifunctional resin of a two-component
(2K) system that can be crosslinked by condensation,
addition or by opening of ethylenically unsaturated
groups via a radical route or via other ionic or other
20 crosslinking routes. The other reactive component of
this system corresponds to the definition of curing
agent according to the invention which corresponds to
the least viscous and/or lower molecular weight
component in said two-component system. In the case
25 where the thermosetting resin comprises crosslinkable
ethylenically unsaturated groups, said curing agent is,
for example, a radical initiator, in particular a
peroxide initiator, which term signifies, for the
invention, either a peroxide or a hydroperoxide. With a
30 hydroperoxide type initiator, decomposition
accelerators may be used, such as tertiary amines and
cobalt (2+) or iron ( 2 + ) salts.
The term "curing agent" is understood, within the
35 meaning of the present invention, to mean a compound
capable of giving rise to a chemical crosslinking and
of resulting in a three-dimensional polymer network, by
means of irreversible crosslinking bonds of covalent
type, which once obtained can no longer be converted by
the action of heat, with said three-dimensional network
being infusible by heating and insoluble in a solvent.
This compound is therefore firstly a crosslinking agent
5 for said thermosetting resin. This compound is in
general the least viscous and/or lower molecular weight
compound, in particular among the two components of a
two-component crosslinkable system.
10 The curing agent is therefore an often polyfunctional
compound bearing, for example, amine, anhydride or
alcohol or isocyanate or epoxy functions that are
reactive with respect to co-reactive functions borne by
a thermosetting resin. The expression "thermosetting
15 resin" is understood, within the meaning of the present
invention, to mean a polymer that can be chemically
crosslinked by a curing agent, into a thermoset resin
which has a three-dimensional structure and is
infusible and insoluble, which once obtained can no
20 longer be converted by the action of heat. In other
words, a thermosetting resin, once the threedimensional
polymer network is formed, becomes a
thermoset polymer network which will no longer flow
under the effect of heat (absence of creep), even with
25 a supply of shearing (via shear) mechanical energy.
The thermosetting resins to be crosslinked using the
curing agent according to the invention comprise: epoxy
resins, polyesters and unsaturated polyesters, vinyl
30 esters, phenolic resins, polyurethanes, cyanoacrylates
and polyimides such as bismaleimide resins, aminoplasts
(resulting from the reaction of an amine such as
melamine with an aldehyde such as glyoxal or
formaldehyde) and mixtures thereof, without this list
35 being limiting. It should be noted that the unsaturated
polyesters, vinyl esters or acrylated multifunctional
resins crosslink by opening at least two ethylenically
unsaturated groups in the presence of a radical
initiator which, in this case, acts as curing agent, in
general in the presence of an ethylenic comonomer such
as acrylic or vinylaromatic monomers. The preferred
radical initiator is of peroxide type, this term
5 including peroxides and hydroperoxides. The
decomposition of the peroxide initiator, and in
particular of the hydroperoxide initiator, may be
accelerated in the presence of a decomposition
accelerator such as a tertiary amine or a cobalt (*+) or
10 iron ( 2 f ) salt.
The impregnation may be carried out by placing,
according to a first option, the fibrous material in a
fluid bath of thermosetting polymer(s) into which the
15 nanofillers/curing agent mixture (nanofillers
predispersed in the curing agent) is introduced or has
been introduced.
The impregnation may also be carried out by placing the
20 fibrous material in a fluidized bed, the thermosetting
polymer or the blend of thermosetting polymers being in
powder form, and also the nanofillers/curing agent
mixture.
25 The impregnation may also be carried out by directly
extruding a stream of thermosetting polymer containing
the nanofillers/curing agent mixture over the fibrous
material which is in the form of a sheet or strip or
braid.
30
It is also possible to envisage the pre-impregnation of
the fibrous material with the curing agent/nanofillers
mixture before the deposition of the thermosetting
polymer (resin) .
35
Furthermore, in another exemplary embodiment, the
impregnation consists in:
i) using at least two series of different fibers, a
first series of continuous fibers forming the
reinforcing fibers of said material and a second
series of fibers consisting of (uncrosslinked)
thermosetting polymer containing the
nanofillers/curing agent mixture and having a
melting temperature Tm;
ii) placing the two series of fibers in contact with
one another; then
10 iii) heating the set of the two series of fibers to a
temperature at least equal to the melting
temperature Tm of the thermosetting fibers and
leaving the set to cool to ambient temperature,
the melting temperature Tm being below the
reaction temperature of the curing agent and below
the melting temperature of the fibers of the first
series.
The reinforcing fibers constituting the first series
20 may be mineral fibers or organic fibers of
thermoplastic or thermosetting polymer or else a
mixture of mineral fibers and organic fibers of
thermoplastic or thermosetting polymer.
25 The invention also relates to an appliance for
implementing the process in which the impregnation
consists in using two series of fibers, the
impregnation of the reinforcing fibers forming the
first series taking place directly by melting at a
30 temperature Tm of the thermosetting polymer fibers
which have been brought into contact.
Advantageously, the appliance comprises a line for
continuous formation of said material in the form of at
35 least one calibrated and homogeneous strip made of
(mineral or organic) reinforcing fibers impregnated
with thermosetting polymer, comprising the device for
positioning at least one set of two series of fibers
used to form a strip, so as to place the two series of
fibers in contact with one another, this device being
provided with a first calendering device and comprising
a shaping device, provided with a second calendering
5 device, provided with two rolls comprising at least one
pressing section of desired width, in order to obtain,
via pressure, a strip that is calibrated in width
during its passage through the rolls.
10 When the two series of fibers are heated at the melting
temperature Tm of the thermosetting polymer fiber, they
are also shaped in order to obtain a homogeneous
material having a shape and dimensions calibrated in
the form of a strip.
15
For the simultaneous formation of several widthcalibrated
and homogeneous strips of pre-impregnated
fibrous material, the appliance comprises inlets for
several sets of two series of fibers and several
20 sections for shaping and width-calibrating the strips.
The invention also relates to the uses of fibrous
materials pre-impregnated by a composition containing a
thermosetting polymer or a blend of thermosetting
25 polymers and a mixture of nanofillers, such as carbon
nanotubes, and of curing agent, for the manufacture of
parts having a three-dimensional structure.
This use comprises a step of shaping the pre-
30 impregnated fibrous materials, combined with a heating
of said materials to a temperature at least equal to
the glass transition temperature Tg of the
thermosetting polymer, in order to activate the
reaction of the curing agent, that is to say to
35 crosslink the polymer in order to render the
composition thermoset (i.e. crosslinked) and give the
part its final shape.
In practice, several methods may be used for the
manufacture of three-dimensional (3D) parts.
In one example, the shaping of the fibrous materials
5 may consist in positioning the pre-impregnated fibrous
materials on a preform, in staggered rows and so that
they are at least partly superposed until the desired
thickness is obtained and in heating by means of a
laser which also makes it possible to adjust the
10 positioning of the fibrous materials relative to the
preform, the preform then being removed.
According to other examples, the shaping of the preimpregnated
materials is carried out by one of the
15 following known techniques:
- calendering,
- laminating,
- pultrusion,
- low-pressure injection molding (RTM) or else,
20 - the technique of filament winding,
- infusion,
- thermocompression,
- RIM or S-RIM.
25 Other distinctive features and advantages of the
invention will appear clearly on reading the
description which is provided below and which is given
by way of illustrative and nonlimiting example and with
regard to the figures in which:
30
- figure 1 represents the diagram of an appliance
for implementing the process in the case where the
impregnation is carried out by melting a series of
thermosetting fibers, in contact with a series of
35 reinforcing fibers;
- figure 2 represents the diagram of a half-furnace
with the groove for placing the fibers;
- figure 3 represents the diagram of the calendering
rolls with the complementary elements for
calibrating and shaping the material in the form
of a strip;
5 - figure 4 represents the diagram of a half-furnace
with several grooves for placing the fibers;
- figure 5 represents the diagram of the calendering
rolls with several complementary elements for
calibrating and shaping the material into several
strips.
In the remainder of this description, the expression
"nanofiller of carbon origin", intended to be mixed
with the curing agent according to the invention,
15 denotes a filler comprising at least one element from
the group formed of carbon nanotubes, carbon
nanofibers, carbon black, graphenes, graphite or a
mixture thereof in any proportions. Preferably, the
size of the particles of these nanofillers does not
20 exceed 150 nm, it being possible for these particles to
be in the form of aggregates of particles that do not
exceed 10 pm (microns) . The nanofillers of carbon
origin are referred to hereinbelow as nanofillers.
25 According to the invention, it is proposed to introduce
nanofillers such as carbon nanotubes (CNTs) by means of
a mixture containing a reactive compound that makes it
possible to achieve the crosslinking of the
thermosetting resin and the nanofillers when this
30 (resin) is heated at a temperature at least equal to
the crosslinking temperature. In a known manner, the
reactive compound comprises at least one curing agent
or a composition of curing agents. It may also comprise
an accelerator or a catalyst. Reference will
35 subsequently be made, for simplicity, to curing agent.
I) The nanofillers/curing agent mixture:
The mixture contains nanofillers and the curing agent
or a combination of curing agents, chosen as a function
5 of the resin used in a known manner for a person
skilled in the art. Thus, the nanofillers/curing agent
mixture may comprise additives, for example compounds
which will be inert with respect to the crosslinking
reaction (such as solvents) or on the contrary reactive
10 solvents or diluents that will control the crosslinking
reaction by adjusting certain mechanical properties of
the final thermoset resin, and also catalysts or
accelerators that make it possible to accelerate the
crosslinking of the reactive components.
15
As additives to the nanofillers/curing agent mixture,
it is possible to have a thermoplastic polymer or a
thermoplastic polymer blend, such as for example a
polyamide (PA), a polyetherimide (PEI) or a solid
20 epoxy.
When an accelerator or a catalyst is present in the
mixture, it is also chosen in a known manner for a
person skilled in the art as a function of the resin
25 used.
The nanofillers of carbon origin/curing agent mixture
advantageously comprises a content of nanofillers of
between 10% and 60%, preferably of between 20% and 50%,
30 relative to the total weight of the mixture.
Carbon nanotubes (CNTs) have particular crystalline
structures, of tubular shape, that are hollow and
closed off, composed of atoms positioned regularly as
35 pentagons, hexagons and/or heptagons, obtained from
carbon. CNTs in general consist of one or more rolled
graphite sheets. A distinction is thus made between
single-walled nanotubes (or SWNTs) and multiwalled
nanotubes (or MWNTs). Double-walled nanotubes may
especially be prepared as described by Flahaut et al.
in Chem. Comm. (2003), 1442. Multiwalled nanotubes may,
for their part, be prepared as described in document
5 WO 03/02456. It is preferred, according to the
invention, to use multiwalled CNTs.
The carbon nanotubes used according to the invention
customarily have a mean diameter ranging from 0.1 to
10 200 nm, preferably from 0.1 to 100 nm, more preferably
from 0.4 to 50 nm and better still from 1 to 30 nm, and
advantageously a length of more than 0.1 pm and
advantageously of from 0.1 to 20 p, for example around
6 p. Their length/diameter ratio is advantageously
15 greater than 10 and usually greater than 100. These
nanotubes therefore comprise, in particular, what are
known as VGCF (vapor grown carbon fiber) nanotubes.
Their specific surface area is for example between 100
and 300 m2/g and their bulk density may in particular be
20 between 0.01 and 0.5 g/cm3 and more preferably between
0.07 and 0.2 g/cm3. The multiwalled carbon nanotubes may
for example comprise from 5 to 15 sheets and more
preferably from 7 to 10 sheets.
25 An example of raw carbon nanotubes is the trade name
~ra~histren~CtlOhO~ f rom Arkema.
Carbon nanofibers, like carbon nanotubes, are
nanofilaments produced by chemical vapor deposition
30 (CVD) from a carbon-based source which is decomposed
over a catalyst comprising a transition metal (Fe, Ni,
Co, Cu) in the presence of hydrogen, at temperatures
from 500°C to 1200"~. However, these two carbon-based
fillers differ due to their structure (I. Martin-Gullon
35 et al., Carbon 44 (2006) 1572-1580). Specifically,
carbon nanotubes consist of one or more graphene sheets
wound concentrically about the axis of the fiber in
order to form a cylinder having a diameter of from 10
to 100 nm. In contrast, carbon nanofibers are composed
of relatively organized graphitic regions (or
turbostratic stacks), the planes of which are inclined
at variable angles with respect to the axis of the
5 fiber. These stacks may take the form of platelets,
herringbones or stacked cups in order to form
structures that have a diameter ranging generally from
100 nm to 500 nm, or even more.
10 Furthermore, carbon black is a colloidal carbon-based
material manufactured industrially by incomplete
combustion of heavy petroleum products, which is in the
form of spheres of carbon and aggregates of these
spheres, the dimensions of which are generally between
15 10 and 1000 nm.
Graphenes are isolated and individualized sheets of
graphite, but very often assemblies comprising between
one and a few tens of sheets are referred to as
20 graphenes. Unlike carbon nanotubes, they have a more or
less planar structure, with corrugations due to thermal
agitation that are even greater when the number of
sheets is reduced. A distinction is made between FLGs
(few layer graphenes), NGP (nanosized graphene plates),
25 CNS (carbon nanosheets) , and GNRs (graphene
nanoribbons) .
Graphite is characterized by a crystalline structure
composed of carbon atoms organized in regular planes of
30 hexagons. Graphite is available for example under the
brands Timrex or Ensaco.
The curing agent is chosen as a function of the nature
of the thermosetting resin and of its method of
35 crosslinking (or its reactivity) in a two-component
reactive (in fact co-reactive) system, for example by
(poly) condensation or by (poly)a ddition or by
crosslinking via the opening of ethylenically
unsaturated groups via a radical route or
(crosslinkable) by other routes. If the thermosetting
resin bears functions that are reactive by condensation
or by addition, said curing agent bears co-reactive
5 functions, that is to say functions capable of reacting
with the functions borne by said thermosetting resin,
respectively by condensation and addition. The
thermosetting resin and the curing agent thus form a
two-component reactive system having a mean reactive
10 functionality of greater than 2 in order to be
crosslinkable. In the case of thermosetting resins that
are crosslinkable via the opening of ethylenically
unsaturated groups via a radical crosslinking route or
another route, at least two ethylenically unsaturated
15 groups per polymer chain are present. In this case, the
curing agents may for example be radical initiators,
such as the family of peroxide compounds which may be
peroxides or hydroperoxides. The latter may break down
into free radicals, either by raising the temperature
20 (via a thermal effect), but also at low temperature by
the use of a reducing agent which is an accelerator of
the radical decomposition of the initiator and is
commonly known as an accelerator in thermosetting
(crosslinkable) compositions of this type.
25
Therefore, as a function of the thermosetting resins and
reactive functions borne, the curing agents that can be
used according to the invention may comprise amines,
derivatives obtained by reaction of urea with a
30 polyamine, acid anhydrides, organic acids, polyols and
mixtures thereof, without this list being limiting.
As amines that can be used, mention may be made of
aliphatic amines such as cyclohexylamine, linear
35 ethylene polyamines such as ethylenediamine,
diethylenetriamine (DETA), triethylenetetramine (TETA)
and tetraethylenepentamine (TEPA), cycloaliphatic amines
such as 1,2-diaminocyclohexane, isophorone diamine,
N, N 1 -disopropyl isophorone diamine and hexamine,
aromatic amines such as benzylamine, diethyltoluenediamine
(DETDA) , metaphenylenediamine (MPDA) I
diaminodiphenylmethane (DDM), diaminodiphenylsulfone
5 (DDS), dicyanodiamide (DICY such as Dyhard lOOSF from
AlzChem) , 4,4' -diaminodiphenylsulf one, 4,4' -methylenedianiline,
4,4'-methy1enebis(ortho-ch1oroani1ine)
(MBOCA) , and oligomers of polyamines (for example
Epikure 3164 from Resolution).
10
As derivatives obtained by the reaction of urea with a
polyamine, mention may be made of 1- (2-
aminoethyl) imidazolidone, also known as 1- (2-aminoethy1)
imidazolidin-2-one (UDETA) , 1- (Z-hydroxy-
15 ethy1)imidazolidone (HE101 I 1- (2- [ (2-aminoethyl)
amino] ethyl) imidazolidone (UTETA) , 1- [ (2- {2- [ (2-
aminoethyl)amino]ethyl}amino)ethyl]imidazolidone
(UTEPA), N-(6-aminohexyl)-N'-(6-rnethyl-4-0~0-1,4-
dihydropyrimidin-2-yl) urea (UPy) .
20
As anhydrides, mention may be made of phthalic
anhydrides and derivatives such as phthalic anhydride,
dichlorophthalic anhydride, tetrachlorophthalic
anhydride, tetrahydrophthalic anhydride, methyl
25 hexahydrophthalic anhydride (MHHPA) , methyl
tetrahydrophthalic anhydride (MTHPA, such as Aradur 917
from Huntsman), methyl hexahydrophthalic anhydride
(HHPA), methyl nadic anhydride (MNA), dodecenyl
succinic anhydride (DDSA) and maleic anhydride.
30
As organic acids, mention may be made of organic acids
such as oxalic, succinic, citric, tartaric, adipic,
sebacic, perchloric and phosphoric acids, disulfonic
acids such as m-benzenedisulfonic acid, P-
35 toluenesulfonic acid, methanedisulfonyl chloride or
methanedisulfonic acid.
As organic phosphates, mention may be made of
monomethyl orthophosphate, monoethyl orthophosphate,
mono-n-butyl orthophosphate and monoamyl
orthophosphate.
5
As polyols that can be used as curing agents in particular
with isocyanate resins, mention may be made of glycerol,
ethylene glycol, trimethylolpropane, pentaerythritol,
polyether polyols, for example those obtained by
10 condensation of an alkylene oxide or of a mixture of
alkylene oxides with glycerol, ethylene glycol,
trimethylolpropane, pentaerythritol and polyester polyols,
for example those obtained from polycarboxylic acids, in
particular oxalic acid, malonic acid, succinic acid,
15 adipic acid, maleic acid, fumaric acid, isophthalic acid,
and terephthalic acid, with glycerol, ethylene glycol,
trimethylolpropane and pentaerythritol.
The polyether polyols obtained by addition of alkylene
20 oxides, in particular ethylene oxide and/or propylene
oxide, to aromatic amines, in particular the mixture of
2,4- and 2,6-toluenediamine, are also suitable.
As other compounds that may be used as curing agents
25 according to the invention, mention may also be made of
isocyanates such as bis-4-phenyldiisocyanate, phenolic
derivatives such as the product DEH 85 from Dow,
adducts of ethylene oxide or propylene oxide with a
pol yamine such as DETA, for example
30 hydroxyethyldiethylenetriamine, the polyether amines
sold by Huntsman under the trade name ~ effam ineR D-2000
and T-403, the DGEBA-aliphatic amines adducts with an
excess of amine functions relative to the glycidyl
functions, polyamidoamines, for example versamidB 140
35 from Cognis Corp., and EpikureB 3090 from Hexion,
polyamides such as EpikureR 3090 and EpikureR 3100-ET-
60 from Hexion, the amidoarnines obtained by
condensation between a fatty acid and a polyamine such
as ~ncamide@-26 0an~d ~nc amide@ 501 from Air Products,
f' lexibilized" polyamides such as ~~ikure@31 64 from
Hexion, polymercaptans such as capcurem 3830-8 1 from
Cognis Corp., Mannich bases obtained by reaction
5 between (poly)a mine, formaldehyde and (alkyl)p henols
such as ~~ikure' 190, 195 and 197 from Hexion,
ketimines, for example ~~ikure3@5 02 from Hexion, epoxy
resin base polyols that can crosslink polyisocyanates,
for example ~~ikote' 1007 and 1009 from Hexion.
10
As another compound that may be used as a curing agent,
in particular for thermosetting resins containing
ethylenically unsaturated groups, mention may also be
made of organic peroxides/hydroperoxides with their
15 matrices (often organic solvents since peroxides are
never packaged pure), as mentioned below. For example,
cumene hydroperoxide (~u~erox' CU5OVE from Arkema
containing 50% of organic solvents) may be chosen.
20 Catalyst and accelerator
The catalyst is chosen from: substituted benzoic acids
such as salicylic, 5-chlorobenzoic or acetylsalicylic
acids. Sulphone-containing (or sulfonic) acids such as
25 m-benzenedisulfonic acid.
The accelerator (in particular the accelerator for
decomposition of a hydroperoxide) may be chosen from:
tertiary amines such as dimethylaminoethyl phenol (DMP),
30 benzyldimethyl aniline (BDMA), monoethyl amine associated
with boron trifluoride (MEA-BF3), imidazoles such as 2-
ethyl-4-methylimidazole, and metal alcoholates.
11) The thermosetting polymers also referred to as
35 thermosettina resins
The expression "thermosetting polymers" or else
"thermosetting resin" is understood to mean a material
that is generally liquid at ambient temperature or has
a low melting point which is capable of being cured,
generally in the presence of a curing agent, under the
effect of heat, an accelerator, a catalyst or a
5 combination of these elements, in order to obtain a
thermoset resin. This (thermoset resin) consists of a
material containing polymer chains of variable length
bonded together by covalent bonds so as to form a
three-dimensional network. Regarding its properties,
10 this thermoset resin is infusible and insoluble. It may
be softened by heating it above its glass transition
temperature (Tg) but exhibits no creep and once a shape
has been given to it, it cannot be subsequently
reshaped by heating.
The thermosettinu ~olvmers are chosen from:
- unsaturated polyesters, epoxy resins, vinyl
esters, phenolic resins, polyurethanes,
20 cyanoacrylates, multifunctional acrylate resins
and polyimides, such as bismaleimide resins,
aminoplasts (resulting from the reaction of an
amine such as melamine with an aldehyde such as
glyoxal or formaldehyde) and mixtures thereof.
25
Among the thermosetting resins, those comprising epoxy,
acid or isocyanate units are preferred, such as those
which lead to thermoset networks of epoxy, polyester or
polyurethane type being obtained by reaction with a
30 curing agent bearing respectively an amine, acid or
alcohol function. More particularly still, the
invention applies to thermosetting epoxy (or
epoxidized) resins that are crosslinkable in the
presence of a curing agent of amine (including
35 polyamine, polyamide amine and polyether amine) type or
of anhydride type.
Regarding epoxy resins to be crosslinked using the
curing agent according to the invention, mention may be
made, by way of example, of epoxidized resins having a
functionality, defined as the number of epoxide (or
5 oxirane) functions per molecule, at least equal to 2,
such as bisphenol A diglycidyl ether, butadiene
diepoxide, 3,4-epoxycyclohexylmethyl 3,4-
epoxycyclohexanecarboxylate, vinylcyclohexene dioxide,
4,4'-di(l,2-epoxyethy1)diphenyl ether, 4,4'- (1,2-
10 epoxyethyl)biphenyl, 2,2-bis(3,4-epoxycyclohexyl)
propane, resorcinol diglycidyl ether,
phloroglucinol diglycidyl ether, bis (2,3-
epoxycyclopentyl)ether, 2- (3,4-epoxy)c yclohexane-5,5-
spiro (3,4-epoxy)c yclohexane-m-dioxane, bis (3,4-epoxy-6 -
15 methylcyclohexyl) adipate, N, Nf -m-phenylenebis (4,5-
epoxy-1,2-cyclohexane-dicarboxamide), a diepoxy
compound containing a hydantoin ring. Such resins may
generally be represented by the formula:
20
in which R3 is a group of formula -CH2-0-R4-0-CH2- in
which R4 is a divalent group chosen from alkylene
groups having from 2 to 12 carbon atoms and those
comprising at least one substituted or unsubstituted
25 aliphatic or aromatic ring.
Use may also be made of polyepoxidized resins
comprising three or more epoxide groups per molecule,
such as for example p-aminophenol triglycidyl ether,
30 polyaryl glycidyl ethers, 1,3,5-tri (l,2-epoxy) benzene,
2,2',4,4'-tetraglycidoxybenzophenone, tet raglycidoxytetraphenylethane,
the polyglycidyl ether of the
phenol/formaldehyde resin of novolac type
(polyepoxidized novalacs), epoxidized polybutadiene,
35 glycerol triglycidyl ether, trimethylolpropane
triglycidyl ether and tetraglycidyl-4,4'-diaminodiphenylmethane.
The epoxy resins generally require as curing agent an
5 acid anhydride or an amine.
The saturated polyester and unsaturated polyester
resins are obtained by reaction of a polyacid (or
corresponding anhydride) with a polyol. Said polyacid
10 is saturated for the saturated polyesters and
ethylenically unsaturated for the unsaturated
polyesters. Mention may be made, as polyacid, of:
succinic acid, pentanedioic acid, adipic acid, maleic
acid (unsaturated), fumaric acid (unsaturated),
15 itaconic acid (unsaturated) and also the anhydrides of
these acids, heptanedioic acid, octanedioic acid,
azelaic acid, sebacic acid, undecanedioic acid,
dodecanedioic acid, brassylic acid, tetradecanedioic
acid, hexadecanedioic acid, octadecanedioic acid,
20 octadecenedioic acid, eicosanedioic acid, docosanedioic
acid and fatty acid dimers containing 36 carbon atoms
(C36) or CS4 fatty acid trimers.
The fatty acid dimers or trimers mentioned above are
25 (dimerized/trimerized) fatty acid oligomers obtained by
oligomerization or polymerization of unsaturated
monobasic fatty acids comprising a Cl8 long hydrocarbonbased
chain (such as linoleic acid and oleic acid), as
described in particular in document EP 0 471 566.
30
When the diacid is cycloaliphatic, it may comprise the
following carbon-based backbones: norbornylmethane,
cyclohexylmethane, dicyclohexylmethane, dicyclohexylpropane,
di(methylcyclohexyl), di (methylcyclo-
35 hexyl) propane.
When the diacid is aromatic, it is chosen from phthalic
acid, terephthalic acid, isophthalic acid,
tetrahydrophthalic acid, trimellitic acid and
naphthalenic (or naphthenic) diacids, and also the
corresponding anhydrides of these acids.
5 Among the polyols, compounds of which the molecule
comprises at least two hydroxyl groups which make it
possible to react with polyacids in order to obtain
polyesters, mention may be made of ethylene glycol,
propylene glycol, butylene glycol, 1,6-hexamethylene
10 glycol, diethylene glycol, dipropylene glycol,
neopentyl glycol, triethylene glycol, glycerol,
trimethylolethane, trimethylolpropane, pentaerythritol,
1,3-trimethylene glycol, 1,4-tetramethylene glycol,
1,8-octamethylene glycol, 1, 10-decamethylene glycol,
15 1,4-cyclohexanedimethanol, polyether diols such as PEG,
PPG or PTMG, carboxylic diacid units such as
terephthalic acid and glycol (ethanediol) or butanediol
units.
20 Unsaturated polyesters resulting from the
polymerization by condensation of dicarboxylic acids
containing an ethylenically unsaturated compound (such
as maleic anhydride or fumaric acid) and of glycols
such as propylene glycol are preferred. They are
25 generally cured in dilution in a reactive monomer such
as styrene, by reaction of the latter with the
unsaturated groups present on the polyester chain,
generally with the aid of a curing agent chosen from
organic peroxides including hydroperoxides, either via
30 a thermal effect (heating), or in the presence of a
decomposition accelerator of tertiary amine or cobalt
(2+) salt, such as cobalt octoate, or iron (2+) salt
type -
35 The vinyl esters comprise the products of the reaction
of epoxides with (meth)acrylic acid. They may be cured
after dissolving in styrene (in a manner similar to the
polyester resins) using organic peroxides, like the
unsaturated polyesters.
As regards the isocyanate resins to be crosslinked
5 according to the invention, mention may be made of
hexamethylene diisocyanate (HMDI) ,
trimethylhexamethylene diisocyanates (TMDIs) such as
2,2,4-trimethylhexamethylene diisocyanate and 2,4,4-
trimethylhexamethylene diisocyanate, undecane
10 triisocyanates (UNTIs), 2-methylpentane diisocyanate,
isophorone diisocyanate, norbornane diisocyanate
(NBDI) I 1,3-bis(isocyanatomethyl)cyclohexane
(hydrogenated XDI) , 4,4'-bis(isocyanatocyc1ohexyl)
methane (H12MDI), 2,4- or 2,6-toluene
15 diisocyanate (TDI), diphenylmethane diisocyanates
(MDIs) , 1,5-naphthalene diisocyanate (NDI) , p-phenylene
diisocyanate (PPDI) , adducts comprising at least two
isocyanate functions and that are formed by
condensation between compounds comprising at least two
20 isocyanate functions among those mentioned and
compounds bearing other functions that react with the
isocyanate functions, such as for example hydroxyl,
thiol or amine functions. More particularly, as
thermosetting resins bearing isocyanate functions,
25 mention may be made of isocyanate-terminated
prepolymers resulting from the reaction of a
diisocyanate in excess and of a diol or of an oligomer
(polyether, polyester) diol or resulting from a
diisocyanate in excess and a diamine or an oligomer
30 diamine (polyether-amine, polyamide-amine) .
Among the polyisocyanates, mention may be made of
modified polyisocyanates such as those containing
carbodiimide groups, urethane groups, isocyanurate
35 groups, urea groups or biurea groups.
Polyols that make it possible to react with the
polyisocyanates are used as curing agents for obtaining
polyurethanes and polyamines in order to obtain
polyureas.
111) The fibers of the fibrous materials
5
The fibers constituting the fibrous materials may be
mineral or organic fibers, such as for example carbon
fibers, glass fibers, mineral fibers such as basalt,
silicon carbide, polymer-based fibers, for example such
10 as aromatic polyamides or aramids or polyolefins,
cellulose fibers such as viscose, plant fibers such as
flax, hemp, silk, and sisal, used alone or as a
mixture.
15 Examples of processes for impregnating the fibrous
material
The impregnation may be carried out by placing the
fibrous material in a fluid bath of thermosetting
20 polymer(s), into which the nanofillers/curing agent
mixture is introduced. The term "fluid" is understood,
within the meaning of the present invention, to mean a
medium which flows under its own weight and which has
no specific shape (unlike a solid), for instance a
25 liquid which may be more or less viscous or a powder
put into suspension in a gas (for example air)
generally known under the term "fluidized bed".
When the fibrous materials are in the form of a strip
30 or sheet, they may be put into circulation in the
fluid, for example liquid, bath of thermosetting
polymer.
The impregnation may be carried out according to a
35 fluidized-bed impregnation process in which the polymer
composition, namely the polymer or the blend of
polymers containing the nanofillers/curing agent
mixture, is in powder form. For this, the fibrous
materials are passed into fluidized bed impregnating
baths of polymer particles containing the
nanofillers/curing agent mixture and these
impregnations are optionally dried and may be heated in
5 order to complete the impregnation of the polymer on
the fibers or fabrics, and calendered if necessary.
It is also possible to deposit the polymer containing
the nanofillers/curing agent mixture and that is in
10 powder form, directly onto the fibrous materials placed
flat on a vibrating support, in order to enable the
distribution of the powder over the fibrous materials.
As another variant, it is possible to directly extrude
15 a stream of polymer containing the nanofillers/curing
agent mixture onto the fibrous material that is in the
form of a sheet or strip or braid and to carry out a
calendering operation.
20 When the nanofillers/curing agent mixture is introduced
directly into the fibrous material, the impregnation
may be carried out by placing the fibrous material in a
fluidized bed, with the thermosetting polymer or the
blend of thermosetting polymers that is in powder form.
25 The impregnation may be carried out by placing the
fibrous material in a fluid bath of thermosetting
polymer(s) or else by depositing a film of
thermosetting polymer on the fibrous material, then
calendering and heating.
30
In the case where the nanofillers/curing agent mixture
is introduced directly in powder form after grinding
into the fibrous material, the assembly may rest on a
vibrating plate for example in order to distribute the
35 powder properly. The impregnation step is
advantageously carried out by depositing a film of
thermosetting polymer on the fibrous material, then
calendering and heating.
According to another example, the fibrous material is
formed from a first series of fibers constituting the
mineral or organic reinforcing fibers and from a second
5 series of thermosetting polymer fibers containing the
nanofillers/curing agent mixture, having a melting
temperature Tm (before crosslinking) below the melting
temperature of the fibers of the first series and below
the glass transition temperature Tg of the (crosslinked)
10 thermosetting polymer. The two series of fibers are
brought into contact and the impregnation is carried out
by heating up to the melting temperature Tm of the second
series of fibers (thermoset polymer fibers).
15 The thermosetting polymers (or resins) that are
incorporated into the composition of the thermosetting
fibers according to this exemplary embodiment are
chosen from: unsaturated polyesters, epoxy resins,
vinyl esters, multifunctional acrylate monomers or
20 oligomers (MFA), (multifunctional) acrylic/acrylate
resins, phenolic resins, polyurethanes, cyanoacrylates
and polyimides, such as bismaleimide resins,
aminoplasts (resulting from the reaction of an amine
such as melamine with an aldehyde such as glyoxal or
25 formaldehyde) and mixtures thereof.
Example of an appliance for manufacturing a fibrous
material in the case where the impregnation is carried
out by melting fibers of a thermosetting polymer or of
30 a blend of thermosetting polymers
In this exemplary embodiment of a pre-impregnated
material, when the two series of fibers are heated at
the melting temperature Tm of the fibers of the second
35 series, they are also shaped in order to obtain a
homogeneous material of calibrated shape and dimensions
with the appliance as described below.
The positioning of the two series of fibers and the
shaping of the material impregnated with molten
thermosetting fibers (fibers from the second series)
are advantageously carried out by a system comprising
5 the implementation of calendering operations.
Preferably, several successive calendering operations
are carried out in order to refine the shaping of the
material and to obtain a defect-free homogeneous
10 material, that is to say a homogeneous material without
granularity and without air bubbles.
Preferably, the appliance illustrated by the diagram
from figure 1 comprises a line for the continuous
15 formation of said material in the form of a calibrated
and homogeneous strip of reinforcing fibers, for
example mineral reinforcing fibers, impregnated with
thermosetting polymer according to the invention. The
continuous formation line comprises a device for
20 positioning the two series of fibers equipped with a
first calendering device.
According to one embodiment, the appliance comprises a
line L for continuous formation of the material in the
25 form of a calibrated and homogeneous strip, described
below in connection with figures 1, 2 and 3.
In one embodiment variant, the line L for continuous
formation of the material is designed to simultaneously
30 form several calibrated and homogeneous strips, as will
be described in connection with figures 4 and 5.
This continuous formation line L comprises:
- a device 100 for positioning the fibers which is
35 equipped with:
- a device 104 for unwinding the fibers, this
device 104 comprises reels 141 of fibers for
the fibers of the first series and reels 142
for the fibers of the second series. In
practice, there are as many reels as fibers and
a pay-out device 143;
- a preheating device 105; it comprises two halffurnaces
with horizontal opening, and infrared
ramps. Its length is 1 m. The maximum
temperature that can be reached is 600"~. The
passage groove 13 has a cross section of
40 x 40 mm approximately;
- a calendering device 106; it comprises two rolls
as illustrated in figure 3, having a diameter of
100 mm, a width of 100 mrn and a polished chromeplated
surface with Ra less than 0.1 micron. The
surface of the rolls 15 and 17 possesses male and
female elements 16 and 18. The shape of these
elements is suitable for fitting one inside the
other, by pressure, so as to calibrate the strip
10 in terms of width, when it passes through the
rolls. Preferably, the width of the strip is from
3 mrn to a few tens of mrn and for example 6 mm.
This device comprises electric heating providing
a maximum temperature at around 260°c, a
cartridge heater with a rotating supply manifold
and control via a thermocouple probe at the
surface, a self-aligning bearing and a gap that
can be adjusted from 0 to 2 mm by a nut and bolt,
a synchronous drive of the two rolls via a chain
or timing belt, a gear motor with brushless
servomotor making it possible to have a maximum
30 line speed of 30 m/minute and an electrical
synchronization with the haul-off line;
- a shaping device 150 equipped with:
- a heating device 110 identical to the
preheating device 105. The temperature of this
device is controlled in order to reach' the
melting temperature Tm of the thermoplastic
polymer fibers. The half-furnace 11 comprises a
passage groove 13 represented in figure 4,
- a second calendering device 115;
- a third calendering device 116;
- these calendering devices are identical to the
first calendering device 106. The details of
5 the structure of the roll are illustrated in
the diagram of figure 3;
- a cooling device 117: it is in the form of a 1 m
long tank made of stainless steel into which the
strip is introduced and submerged in cold water
if necessary (the strip is represented as dotted
lines in the crossing of the tank). It comprises
a compressed air dryer and a water refrigeration
unit of approximately 3 kW;
- a device 118 for controlling the winding and
15 supporting the strip that prevents vibrations
and that performs movements from top to bottom
over a height corresponding to the width of the
winding reels 300;
- a winding device 300: this device comprises
20 several flat reels in the form of flat spools
such as 301, 302, having a diameter of around
600 mm. The flat spools are superposed about a
vertical axis XX as they are filled. Provision
is made to store 10 to 20 flat spools with an
interlayer between them. The passage from one
flat spool 301 to the next 302 is carried out
manually. The synchronization with haul-off of
the strip is carried out by a control pad. The
tension is controlled by the counterweight of
30 the pad;
- a haul-off line 350 makes it possible to pull
off the strip continuously. It comprises
elastomer rolls and makes it possible to exert a
set pressure via a pneumatic cylinder. It is
synchronized electrically with the calendering
devices.
The continuous formation line L is managed via a
control station 400, of computer type with a display
screen. This station 400 is connected via a network for
example to the various electric control devices of the
5 line: electric motors, variable speed drives and speed
and temperature regulators, motor of the haul-off line
in order to enable the various synchronizations
necessary for the continuous operation of the line L.
This control station also makes it possible to record
10 all the parameters for the management of the automatic
operations and synchronization.
In the case where the reinforcing fibers 1 used have a
coating (or sizing) layer, the coating layer may be
15 removed if necessary, that is to say in the event of
incompatibility with the thermosetting polymer fibers
according to the invention to be melted. The coating
layer will be removed before the two series of fibers
1, 2 are brought into contact. For this purpose,
20 provision may be made for the fibers of the two series
to arrive via two separate pay-out devices, so that the
desizing is carried out on the reinforcing fibers
before contact between the two series of fibers or
provision may be made for the desizing of the
25 reinforcing fibers to be carried out in a furnace, such
as the furnace 105, before the two series of fibers are
brought into contact in the furnace 105.
In addition, in order to obtain improved melting and
30 impregnation, it is possible to use a heating device
110 of laser type instead of an infrared furnace. In
the case of laser heating, the laser device is arranged
so that the laser beam arrives in the longitudinal axis
of the fibers (of the tape), that is to say the haul-
35 axis. Thus, the heating is direct and therefore
concentrated on the fibers.
Preferably, the heating device 110 is of induction or
microwave heating type.
Specifically, an induction or microwave heating device
5 is particularly suitable when electrically conductive
fibers are present in the assembly or when electrically
conductive fillers such as CNTs are present in the preimpregnated
material. This is because, in the case of
induction or microwave heating, the electrical
10 conductivity of the latter is employed and contributes
to curing at the core being obtained and to a better
homogeneity of the fibrous material. The thermal
conduction of the fibers of the assembly or of the CNT
fillers present in the pre-impregnated fibrous material
15 also contributes, with this type of heating, to a
curing at the core which improves the homogeneity of
the material.
Microwave or induction heating, very particularly
suitable in the presence of fillers such as carbon
nanotubes CNTs in the pre-impregnated material, makes
it possible to obtain a better dispersion/distribution
of the CNTs within the material, resulting in the
physicochemical properties having a better homogeneity
and, consequently, the final product having better
properties overall.
The pre-impregnated fibrous materials of a
composition containing a thermosetting polymer or a
30 blend of thermosetting polymers and a CNT/curing
agent mixture according to the invention are
particularly suitable for the manufacture of threedimensional
parts.
35 For this, the materials are shaped and heated at a
temperature at least equal to the glass transition
temperature Tg of the thermosetting polymer, in order
to activate the reaction of the curing agent, that is
to say to crosslink the polymer in order to render the
composition thermoset and give the part its final
shape.
5 In practice, several methods can be used for the
manufacture of three-dimensional parts.
In one example, the shaping of the fibrous materials
may consist in positioning the pre-impregnated fibrous
10 materials on a preform, in staggered rows and so that
they are at least partly superposed until the desired
thickness is obtained and in heating by means of a
laser which also makes it possible to adjust the
positioning of the fibrous materials relative to the
15 preform, the preform then being removed.
In another example, the pultrusion method is used. The
fibrous material, which is in the form of
unidirectional fibers or strips of fabrics, is placed
20 in a bath of thermosetting resin(s) that is then passed
into a heated die where the shaping and the
crosslinking (the curing) take place.
According to other examples, the shaping of the preimpregnated
materials is carried out by one of the
following known techniques:
- calendering,
- laminating,
- the pultrusion technique,
- low-pressure injection molding (RTM) or else,
- the technique of filament winding,
- infusion,
- thermocompression,
- RIM or S-RIM.
It is thus possible to produce parts having a twodimensional
and three-dimensional structure such as,
for example, aircraft wings, the fuselage of an
aircraft, the hull of a boat, the side members or
spoilers of a motor vehicle or else brake disks,
cylinders or steering wheels.
5 In practice, the fibrous material may be heated by
laser heating or a plasma torch or nitrogen torch or an
infrared oven or else by microwaves or by induction.
Advantageously the heating is carried out by induction
or by microwaves.
10
This is because the conductivity properties of the preimpregnated
material containing conductive fibers
and/or filled with conductive particles such as CNTs
are advantageous in combination with induction or
15 microwave heating since then the electrical
conductivity is employed and contributes to curing at
the core being obtained and to better homogeneity of
the fibrous material. The thermal conduction of the
fillers such as CNTs present in the pre-impregnated
20 fibrous material also contributes, with this type of
heating, to curing at the core which improves the
homogeneity of the substrate.
Induction heating is obtained, for example, by exposing
25 the substrate to an alternating electromagnetic field
using a high frequency unit of 650 kHz to 1 MHz.
Microwave heating is obtained, for example, by exposing
the substrate to a hyperfrequency electromagnetic field
30 using a hyperfrequency generator of 2 to 3 GHz.
The Tg may be measured by dynamic mechanical analysis
(DMA) at a frequency of 1 Hz and with a rise in
temperature of 2°C per minute and with a stabilization
35 time of 30 seconds every 2 " b~ef ore the measurement.
The Tm may be measured by DSC (differential scanning
calorimetry) .
Experimental section
Example 1 is presented in order to illustrate the
present invention.
5
Example 1: Preparation of an epoxy-amine thermosetting
composite according to the invention.
In a first step, a curing agent/CNT mixture is prepared
10 with a polyamine curing agent according to the
following procedure:
Introduced into the first feed hopper of a BUSS@ MDK 46
co-kneader (L/D = ll), equipped with an extrusion screw
15 and a granulating device are ~ra~histren~th' ClOO
carbon nanotubes from Arkema. The curing agent of the
type of a mixture of polyamines (~radur@ 5052 from
Huntsman) is injected in liquid form at ambient
temperature into the second zone of the co-kneader.
20 After kneading, at the outlet of the take-up extruder a
solid mixture is obtained exiting the die, containing
25% of CNTs and 75% of curing agent. This mixture is
then used as is or after dilution in the same curing
agent, depending on the targeted CNT content, for the
25 manufacture of an epoxy-amine/glass fibers composite,
by infusion. . .
A few minutes before the infusion step, the curing
agent/CNT (1% CNT) liquid mixture is introduced into
30 the thermosetting resin (Araldite LY 5052 from
Huntsman) with a weight ratio of 38 parts of curing
agent per 100 parts of resin. The mixing is carried out
using a blade mixer at ambient temperature and at a
speed of 100 rpm for a few seconds.
35
The reactive mixture containing three components
(thermosetting resin - curing agent - CNTs) is then
infused under vacuum into a three-dimensional network
of glass fibers, consisting of a stack of 8
two-dimensional plies (fabrics) of glass fibers. After
curing of the resin obtained after 1 hour at ambient
temperature, a composite is obtained composed of
5 50 vol% of glass fibers and 50 vol% of CNT-filled
thermoset resin.

CLAIMS
1. A process for manufacturing a fibrous material
5 comprising an assembly of one or more fibers,
composed of carbon fibers or glass fibers or plant
fibers or mineral fibers or cellulose fibers or
polymer-based fibers, used alone or as a mixture,
impregnated by a thermosetting polymer or a blend
of thermosetting polymers containing a curing
agent and nanofillers of carbon origin such as
carbon nanotubes (CNTs), characterized in that a
mixture containing the nanofillers of carbon
origin and the curing agent is used in order to
15 introduce said nanofillers into the fibrous
material.
2. The process for manufacturing a fibrous material
comprising an assembly of one or more fibers as
20 claimed in claim 1, characterized in that the
nanofillers/curing agent mixture is in the form of
fluid, fibers, powder or film.
3. The process for manufacturing a fibrous material
25 comprising an assembly of one or more fibers as
claimed in claim 1, characterized in that the
nanofillers/curing agent mixture is introduced
directly into the thermosetting polymer or the
blend of thermosetting polymers used to impregnate
30 the fibrous material.
4. The process for manufacturing a fibrous material
comprising an assembly of one or more fibers as
claimed in claim 1, characterized in that the
nanofillers/curing agent mixture is introduced
into the fibrous material before impregnation, in
the form of fibers incorporated into the assembly
of fibers of said material or in the form of a
film deposited on the material or in the form of
powder deposited on said material.
5. The process for manufacturing a fibrous material
5 as claimed in any one of the preceding claims,
characterized in that the nanofillers of carbon
origin/curing agent mixture advantageously
comprises a content of nanofillers of between 10%
and 60%, preferably between 20% and 50%, relative
10 to the total weight of the mixture.
6. The process for manufacturing a fibrous material
as claimed in any one of the preceding claims,
characterized in that the nanofillers of carbon
origin consist of carbon nanotubes or carbon
nanofibers or carbon black or graphenes or
graphite or a mixture thereof.
7. The process for manufacturing a fibrous material
20 as claimed in any one of the preceding claims,
characterized in that the curing agent is selected
from amines, derivatives obtained by reaction of
urea with a polyamine, acid anhydrides, organic
acids, organic phosphates, polyols, and radical
25 initiators such as peroxides or hydroperoxides.
8. The process for manufacturing a fibrous material
as claimed in any one of the preceding claims,
characterized in that the nanofillers/curing agent
mixture comprises one or more additives such as an
accelerator or a catalyst or else a thermoplastic
polymer or a blend of thermoplastic polymers.
9. The process for manufacturing a fibrous material
35 as claimed in claim 8, characterized in that the
catalyst is selected from: substituted benzoic
acids such as salicylic acid, 5-chlorobenzoic acid
or acetylsalicylic acid, sulfone-containing acids
such as m-benzenedisulfonic acid and the
accelerator is selected from: tertiary amines such
as dimethylaminoethylphenol (DMP), benzyldimethyl
aniline (BDMA), monoethylamine associated with
5 boron trifluoride (MEA-BF3), imidazoles such as 2-
ethyl-4-methylimidazole, and metal alcoholates.
10. The process for manufacturing a fibrous material
as claimed in any one of the preceding claims,
10 characterized in that the thermosetting polymer is
selected from: unsaturated polyesters, epoxy
resins, vinyl esters, multifunctional acrylate
monomers or oligomers, acrylic/acrylate resins,
phenolic resins, polyurethanes, cyanoacrylates and
polyimides, such as bismaleimide resins,
aminoplasts (resulting from the reaction of an
amine such as melamine with an aldehyde such as
glyoxal or formaldehyde) and mixtures thereof.
20 11. The process for manufacturing a fibrous material
as claimed in any one of the preceding claims,
characterized in that the impregnation is carried
out by placing the fibrous material in a fluid
bath of thermosetting polymer(s), into which the
25 nanofillers/curing agent mixture is introduced.
12. The process for manufacturing a fibrous material
as claimed in claim 3, characterized in that the
impregnation is carried out by placing the fibrous
material in a fluidized bed with the thermosetting
polymer or the blend of thermosetting polymers
that is in powder form and also the
nanofillers/curing agent mixture.
35 13. The process for manufacturing a fibrous material
as claimed in claim 3, characterized in that the
impregnation is carried out by directly extruding
a stream of thermosetting polymer containing the
nanofillers/curing agent mixture over the fibrous
material which is in the form of a sheet or strip
or braid.
5 14. The process for manufacturing a fibrous material
as claimed in claim 4, characterized in that the
nanofillers/curing agent mixture is introduced
directly into the fibrous material, the
impregnation being carried out by placing the
fibrous material in a fluidized bed with the
thermosetting polymer or the blend of
thermosetting polymers in powder form or by
placing the fibrous material in a fluid bath of
thermosetting polymer(s) or by depositing a film
15 of thermosetting polymer on the fibrous material,
followed by calendering and heating.
15. The process for manufacturing a fibrous material
as claimed in any one of claims 1 to 10,
20 characterized in that it consists in i) using at
least two series of different fibers, a first
series of continuous fibers forming the
reinforcing fibers of said material and a second
series of thermosetting polymer fibers containing
the nanofillers/curing agent mixture and having a
melting temperature Tm; ii) placing the two series
of fibers in contact with one another, then iii)
heating the set of the two series of fibers to a
temperature at least equal to the melting
temperature Tm of the thermosetting fibers and
leaving the set to cool to ambient temperature,
the melting temperature Tm being below the
reaction temperature of the curing agent and below
the melting temperature of the fibers of the first
35 series.
16. The process for manufacturing a fibrous material
as claimed in claim 15, characterized in that the
reinforcing fibers constituting the first series
are mineral fibers or organic fibers of
thermoplastic or thermosetting polymer.
5 17. An appliance for implementing the process as
claimed in claim 15, characterized in that it
comprises a line (L) for continuous formation of
said material in the form of at least one
calibrated and homogeneous strip (20) made of
(mineral or organic) reinforcing fibers
impregnated with thermosetting polymer, comprising
the device (100) for positioning the two series of
fibers (1, 2) used to form a strip, so as to place
the two series of fibers in contact with one
15 another, this device being provided with a first
calendering device (106) and comprising a shaping
device (150), provided with a second calendering
device (115), provided with two rolls comprising
at least one pressing section of desired width, in
order to obtain, via pressure, a strip that is
calibrated in width during its passage through the
rolls.
18. The appliance for implementing the process as
25 claimed in claim 15, characterized in that a line
- ( L ) for continuous formation of the fibrous
material comprises inlets for several sets of two
series of fibers and several shaping and widthcalibrating
sections so as to simultaneously form
several calibrated and homogeneous strips of preimpregnated
fibrous material.
19. The use of pre-impregnated fibrous materials
obtained by a process as claimed in any one of
35 claims 1 to 16, for the manufacture of parts
having a three-dimensional structure,
characterized in that it comprises a step of
shaping the pre-impregnated fibrous materials
combined with a heating of these materials to a
temperature at least equal to the glass transition
temperature Tg of the thermosetting polymer, in
, order to activate the reaction of the curing
5 agent, that is to-say to crosslink the polymer in
order to render the composition thermoset and give
he partLits final shape.
20. The use of pre-impregnated fibrous materials for
the manufacture of three-dimensional parts as
claimed in claim 19, characterized in that said
shaping of the fibrous materials consists in
positioning the pre-impregnated fibrous materials
on a preform, in staggered rows and so that they
are at least partly superposed until the desired
thickness is obtained and in heating by means of a
laser which also makes it possible to adjust the
positioning of the fibrous materials relative to
the preform, the preform then being removed.
21. The use of pre-impregnated fibrous materials for
the manufacture of three-dimensional parts as
claimed in claim 19, characterized in that the
shaping of the pre-impregnated materials is
carried out by one of the following known
techniques:
- calendering,
- laminating,
- the pultrusion technique,
- low-pressulre injection molding (RTM) or else,
- the technique of filament winding,
- infusion,
- thermocompression,
- RIM or S-RIM.