Specification
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“A THERMOSETTING EPOXY RESIN, A COMPOSITE MATERIAL, A METHOD
OF FORMING A COMPOSITE MATERIAL ARTICLE, A MOULD AND A
METHOD OF MAKING A MOULD”
AIRBUS OPERATIONS LIMITED, New Filton House, Bristol BS99 7AR, United
Kingdom, a company incorporated in United Kingdom,
The following specification particularly describes the invention and the manner in
which it is to be performed.
A THERMOSETTING EPOXY RESIN, A COMPOSITE
MATERIAL, A METHOD OF FORMING A COMPOSITE
MATERIAL ARTICLE, A MOULD AND A METHOD OF
5 MAKING A MOULD
FIELD OF THE INVENTION
The present invention relates to the field of thermosetting composite materials.
In particular, the invention relates to the field of microwave curing of thermosetting
10 composite materials.
BACKGROUND OF THE INVENTION
The thermal curing of fibre/epoxy composites in a single-sided mould is an
established industrial technique. The thermal curing is performed by applying thermal
15 energy, normally by hot air convection in an oven or autoclave. This process is slow
and a lot of energy is used to heat the air and equipment. The hot air must
subsequently be vented and the hot equipment cooled. Also, because the equipment
takes time to reach the relevant temperature, there is more time for the tool face to
expand due to thermal expansion. That can introduce error in the shape of the final
20 article.
It is known to use electromagnetic energy to cure epoxy resins in a shorter
time. The advantage of using electromagnetic energy, for example radio wave or
microwave energy to cure the epoxy resin is that only the epoxy itself is heated,
25 resulting in a significant energy saving. Also, because the mould itself does not
become too hot, due to the shorter curing time tolerance errors due to thermal
expansion are reduced.
One example of microwave curing a thermoset polymer is shown in US Patent
30 No.4626642 in the name of General Motors Corporation. In that case a thermoset
polymer is used as an adhesive in securing automotive plastics components together.
The thermoset polymer comprises an epoxy with added steel or aluminium fibres or
powder. Graphite fibres are described as an alternative additive.
2
Japanese Patent Publication No.5-79208 describes a method of microwave
curing a reinforced plastic comprising an epoxy resin and a Kevlar fibre. US Patent
No.6566414 describes adding microwave exothermic accelerators. That document
concerns it 5 self with application of the resin composition to asphalt, concrete, slate etc.
It is an object of the invention to provide an improved thermosetting epoxy
resin.
10 According to a first aspect of the invention there is provided a thermosetting
epoxy resin including particles of magnetite and particles of conductive carbon
material.
The combination of a conductive carbon material, for example graphite
15 powder and magnetite has a beneficial and synergistic effect not seen in the single
substance additive epoxies in the prior art. In particular, magnetite acts as an effective
microwave susceptor above a critical temperature whilst carbon susceptors act from a
lower temperature. By combining the two substances into a thermosetting epoxy
resin, a resin material is provided which has good susceptibility to microwave heating
20 from a cold start through to a thermosetting temperature.
It is an object of the invention to provide an improved composite material.
According to a second aspect of the invention there is provided a composite
25 material comprising a thermosetting epoxy resin matrix including particles of
magnetite and laid-up carbon fibre reinforcement.
The carbon fibre reinforcement material provides the low temperature
microwave susceptibility whilst the inclusion of particles of magnetite in the
30 thermosetting epoxy resin provides the microwave susceptibility at higher
temperatures. Additional conductive carbon material could be added to the epoxy
resin if necessary.
3
It is an object of the invention to provide an improved method of forming a
composite material article.
According to a third aspect of the invention there is provided a method of
forming a composite material a 5 rticle comprising the steps of providing a matrix
material comprising at least a thermosetting epoxy resin including magnetite particles,
providing a mould of substantially microwave transparent material, providing a
carbon fibre reinforcement material, laying-up the matrix material and the
reinforcement material in the mould and applying microwave radiation to the laid-up
10 material to effect thermosetting of the resin.
In that way microwave heating of the resin effects thermosetting and the
present of magnetite particles together with the presence of the carbon fibre
reinforcement material provides the synergistic microwave susceptor effect of the
15 combination of carbon and magnetite described above.
According to a fourth aspect of the invention there is provided a mould for
moulding a composite material article comprising a mould body formed of material
which is substantially transparent to microwave radiation and a tool face having
20 microwave susceptors on or adjacent the working surface thereof.
In that way, when a composite material is laid-up on the mould and microwave
energy is applied, minimal microwave energy is absorbed by the mould itself but by
providing microwave suspectors on or adjacent the mould surface, microwave energy
25 will be absorbed locally and local heating will occur which encourages thermosetting
of at least the outer mould line of the composite material.
According to a fifth aspect of the invention there is provided a method of
making a mould for moulding a composite material article comprising the steps of
30 providing a mould body of substantially microwave transparent material, providing a
tool face and incorporating into the tool face or applying to the working surface of the
tool face, microwave radiation absorbing material.
4
Further advantages of the invention are set out in the claims appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the various aspects of the invention will now be described in
detail, by 5 way of example, and with reference to the accompanying drawings, in
which:-
Figs.1a and 1b are schematic representations of the matrix and reinforcement
phases of a fibre reinforced composite material,
10
Fig.2 is a schematic representation of the composite material,
Fig.3 is a schematic sectional view through a mould in accordance with the
invention,
15
Fig.4 is a schematic sectional view through another mould in accordance with
the invention, and
Fig.5 is a schematic sectional view through the mould of Fig.4 shown with a
20 composite material laid-up on the mould.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In Figs.1a and 1b the separate matrix and reinforcement phases of a carbon
fibre composite material are shown. The matrix phase 10 comprises a thermosetting
25 epoxy resin having magnetite particles 12 dispersed therein in the range 1-5% by
volume. The magnetite particles are preferably sized in the range 5-100 nanometres.
The resin and magnetite mix can be formed by providing an initial master
batch of resin with a high concentration of magnetite powder which is subsequently
30 mixed into a greater volume of resin to provide the preferred proportion of magnetite
by volume in the resin.
5
Fig.1b shows a carbon fibre reinforcing phase 14 of the composite carbon fibre
material. The carbon fibre reinforcement phase is typically made from graphite fibre
which is formed into a yarn and then woven in a variety of different patterns.
The c 5 omposite carbon fibre/epoxy material occurs when the carbon fibre
reinforcement phase 14 is combined with the epoxy matrix phase. The combination of
those two can occur prior to moulding, for example in a so-called “pre-preg” process.
Alternatively, the combination of the epoxy with the carbon fibre can occur when
laying-up material in a mould.
10
It is noted that by applying microwave radiation to the aforementioned carbon
fibre/epoxy/magnetite material, the graphite filaments in the carbon fibre act from
cold as a microwave susceptor, by which it is meant that they absorb microwave
energy and convert that energy to heat, heating the epoxy matrix material which
15 surrounds the carbon fibre. That, in turn, heats the magnetite powders and, after a
certain amount of heating, the magnetite particles also act as microwave susceptors.
The synergist combination of magnetite and carbon fibre in reasonably close thermal
proximity is particularly useful in the application of thermosetting epoxy resin by
application of microwave energy. By providing microwave susceptors in the
20 composite material, the amount of microwave energy that is required to be applied to
a particular composite material mould is reduced.
Although it is expected that the carbon fibre which exists in the composite
material will be sufficient to act as a microwave suspector from cold, it may be
25 necessary to add additional carbon either in the form of graphite powder or carbon
nanotubes. In that case, the additional carbon material added into the thermosetting
epoxy resin shall comprise a proportion by volume in the range 0.5% to 2%. Graphite
powder in the form of carbon black of 10-60nm could be used. Carbon nanotubes
with a diameter of 5-20nm and a length of 1-100nm could be used.
30
It is preferred that the total, by volume, of microwave susceptor additives to
the epoxy resin should be no more than 5%.
6
Turning to Fig.3, a mould 18 comprises a mould base body 20 and a mould
tool face 22 mounted on the mould base body 20. The mould tool face 22 has an outer
surface 24, against which the outer mould line of a composite carbon fibre reinforced
material will lie.
5
In the embodiment of Fig.3, the mould base body 20 is formed from a material
which is relatively transparent to microwaves, by which we mean microwave energy
is not readily absorbed by the material of the mould base body 20. Typically, the
microwave transparent material will comprise a ceramic material. Most particularly a
ceramic fibre material wil 10 l form the mould base body 20. The mould tool face 22 is
formed from a material which includes, most preferably at or adjacent the surface 24,
a proportion of microwave susceptors, as described above.
In the example shown in Fig.3, the mould tool face 22 is formed from a
15 silicate/basalt fibre material with the addition of a microwave susceptor. The
microwave susceptor could be graphite or a ferrite material, such as magnetite. That
susceptor can be introduced into the silicate fibre by mixing when creating the mould
tool face 22.
20 In Fig.4 a mould 18 is shown which is substantially similar to the mould in
Fig.3 and parts corresponding to parts in Fig.3 carry the same reference numerals.
As in the mould 18 of Fig.3, the mould 18 of Fig.4 comprises a mould base
body 20 formed of a microwave transparent material, as described in relation to Fig.3.
25 In Fig.4, the mould 18 has a mould tool face 22 mounted on the mould base body 20.
In this case, the mould tool face 22 is also formed from a material which is
substantially transparent to microwaves. In the mould 18 of Fig.4, the mould surface
24 has a coating 26 which includes a proportion of microwave suspector material.
The coating 26 or can be applied by dusting the mould surface 24, by powder coating
30 the mould surface 24 or by painting an emulsion of a carrier and the microwave
suspector material. The advantage of the Fig.4 arrangement is the application of
microwave energy to the mould 18 results in local heating only where the microwave
susceptor material 26 is applied, ie at the surface 24 of the tool face 22 where the heat
7
is most required to effect thermosetting. The remainder of the tool does not absorb
microwave energy. In previous moulding arrangement, the mould 18 would be
arranged in an autoclave and the entire autoclave and mould would need to be heated
to reach the thermosetting temperature of the epoxy. In the present case, the mould is
arranged inside a large 5 microwave system and microwave energy is not absorbed by
the rest of the mould. The great proportion of the microwave energy is absorbed by
the microwave susceptible material which coats the surface of the mould and by the
microwave susceptors in the carbon fibre reinforced composite material.
10 Fig.5 shows the mould of Fig.4 with a composite material comprising carbon
fibre reinforcing material and an epoxy matrix with magnetite particles therein.
When the carbon fibre composite is laid-up on the mould, microwave energy is
applied and the mould base body 20 and mould tool face 22 absorb little microwave
15 radiation. Microwave susceptors, for example magnetite and/or graphite in the layer
26 coating the surface of the tool face 22, and the graphite and magnetite particles in
the carbon fibre reinforced matrix absorb microwave energy and convert that to heat
which acts to thermoset the epoxy matrix material.
20 The frequency of microwave radiation applied to the mould is preferably
2.45GHz (approximately), which is the typical frequency of a domestic microwave
oven.
8
8
Claims
1. A thermosetting epoxy resin including particles of magnetite and particles of
5 conductive carbon material.
2. A thermosetting epoxy resin according to claim 1 in which the particles of
magnetite have a size in the range 5-100 nanometres.
10 3. A thermosetting epoxy resin according to claim 1 or 2 in which the conductive
carbon material comprises graphite powder.
4. A thermosetting epoxy resin according to claim 1 or 2 in which the conductive
carbon material comprises carbon nano tubes.
15
5. A thermosetting epoxy resin according to any preceding claim in which the
conductive carbon material comprises a mixture of graphite powder and carbon nano
tubes.
20 6. A thermosetting epoxy resin according to any preceding claim in which the
particles of magnetite are provided in the amount of 1% to 5% by volume to volume
of the resin, most preferably 3% to 5%.
7. A thermosetting epoxy resin according to any preceding claim in which the
25 particles of conductive carbon material are provided in the amount 0.5% to 5% by
volume to volume of resin, most preferably 0.5% to 2%.
8. A thermosetting epoxy resin according to any preceding claim in which the
particles of magnetite and conductive carbon material together form no more than 5%
30 by volume to volume of resin.
9. A composite material comprising a thermosetting epoxy resin matrix including
particles of magnetite and carbon fibre reinforcement.
9
10. A composite material according to claim 9 formed as a pre-preg material.
11. A composite material according to claim 9 or 10 further including particles of
5 conductive carbon material.
12. A composite material according to claim 9, 10 or 11, in which the particles of
magnetite have a size in the range 5-100 nanometres.
10 13. A composite material according to claim 11, in which the conductive carbon
material comprises graphite powder.
14. A composite material according to claim 11, in which the conductive carbon
material comprises carbon nano tubes.
15
15. A composite material according to claim 11, in which the conductive carbon
material comprises a mixture of graphite powder and carbon nano tubes.
16. A composite material according to any preceding claim, in which the particles of
20 magnetite are provided in the amount of 1% to 5% by volume to volume of the resin,
most preferably 3% to 5%.
17. A composite material according to any of claims 11 or 13 to 15, in which the
particles of conductive carbon material are provided in the amount 0.5% to 5% by
25 volume to volume of resin, most preferably 0.5% to 2%.
18. A composite material according to any of claims 11 or 13 to 15, in which the
particles of magnetite and conductive carbon material together form no more than 5%
by volume to volume of resin.
30
19. A method of forming a composite material article comprising the steps of
providing a matrix material comprising at least a thermosetting epoxy resin and
magnetite particles, providing a mould of substantially microwave transparent
10
material, providing a carbon fibre reinforcement material, laying up the matrix
material and the reinforcement material in the mould and applying microwave
radiation to the laid-up material to effect thermosetting of the resin.
20. A mould for moulding a co 5 mposite material article comprising a mould body
formed of material which is substantially transparent to microwave radiation and a
tool face having microwave radiation absorbing material on or adjacent the working
surface thereof.
10 21. A method of making a mould for moulding a composite material article
comprising the steps of providing a mould body of substantially microwave
transparent material, providing a tool face and incorporating into the tool face or
applying to the working surface of the tool face, microwave radiation absorbing
material.
15
22. A method of making a mould according to claim 21, in which the step of
applying microwave radiation absorbing material to the working surface of the tool
face comprises coating the working surface of the tool face with microwave radiation
absorbent material, either by painting, by powder coating or by dusting before
20 moulding.
23. A method of making a mould for moulding a composite article according to
claim 22 in which the step of incorporating microwave radiation absorbing material
into the tool face comprises adding microwave radiation absorbing material into a
25 ceramic used to forming the tool face.
24. A method of forming a composite material article, a mould for moulding a
composite material article and the method of making a mould for moulding the
composite material article according to any of claims 19 to 23 in which the mould
30 body of substantially microwave transparent material comprises a silicate ceramic.
11
25. A mould or a method of making a mould for moulding a composite material
article, according to any of claims 20 to 23, in which the microwave radiation
absorbing material comprises one or both of particles of magnetic or conductive
carbon material.
5
12
Prakash Nama
Of Global IP Services
Attorney for the Applicant
Registration Number: IN/PA-1085
12
A THERMOSETTING EPOXY RESIN, A COMPOSITE
MATERIAL, A METHOD OF FORMING A COMPOSITE
MATERIAL ARTICLE, A MOULD AND A METHOD OF
MAKING A MOULD
