U.S. patent application number 10/485449 was filed with the patent office on 2004-11-25 for welding techniques for polymer or polymer composite components.
Invention is credited to Beehag, Andrew, Hou, Meng, Yuan, Qiang.
Application Number | 20040231790 10/485449 |
Document ID | / |
Family ID | 3830687 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040231790 |
Kind Code |
A1 |
Hou, Meng ; et al. |
November 25, 2004 |
Welding techniques for polymer or polymer composite components
Abstract
A process for bonding a semi-crystalline or crystalline
thermoplastic polymer to a thermosetting polymer component, the
process including selecting compatible semi-crystalline
thermoplastic polymer and uncured thermosetting polymer components
wherein the curing temperature of the uncured thermosetting polymer
components is above the melting temperature of the semi-crystalline
thermoplastic polymer. The process includes locating the
thermoplastic polymer in contact with the uncured thermosetting
polymer component and heating the thermoplastic polymer and uncured
thermosetting polymer or thermosetting polymer composite component
to the curing temperature of the thermosetting polymer, where the
uncured thermosetting polymer components and the thermoplastic
polymer are able to at least partly interpenetrate before the
thermosetting polymer cures. The thermoplastic polymer and cured
thermosetting polymer component are then cooled such that the
thermoplastic polymer is very strongly bonded to the cured
thermosetting polymer component.
Inventors: |
Hou, Meng; (New South Wales,
AU) ; Beehag, Andrew; (New South Wales, AU) ;
Yuan, Qiang; (New South Wales, AU) |
Correspondence
Address: |
David A Fahah
Sheldon & Mak
9th Floor
225 South Lake Avenue
Pasadena
CA
91101
US
|
Family ID: |
3830687 |
Appl. No.: |
10/485449 |
Filed: |
June 25, 2004 |
PCT Filed: |
July 31, 2002 |
PCT NO: |
PCT/AU02/01014 |
Current U.S.
Class: |
156/307.1 ;
156/308.2; 156/309.6; 428/98 |
Current CPC
Class: |
B29C 66/712 20130101;
B29C 66/43441 20130101; B29C 66/524 20130101; B29C 66/73793
20130101; B29C 65/006 20130101; B29C 66/474 20130101; C08J 5/12
20130101; B29C 66/1122 20130101; B29C 66/73115 20130101; B29C
66/91945 20130101; B29C 66/7394 20130101; B29C 66/73775 20130101;
B29C 66/91933 20130101; B29C 65/4815 20130101; Y10T 428/31909
20150401; B29C 66/341 20130101; B29C 66/71 20130101; B29C 66/73771
20130101; B29C 66/73773 20130101; B29C 66/73941 20130101; B29C
66/112 20130101; B29C 66/73751 20130101; B29C 66/0342 20130101;
B29C 65/18 20130101; B29C 65/02 20130101; B29C 66/131 20130101;
B29C 66/73117 20130101; Y10T 428/24 20150115; B29C 66/721 20130101;
B29C 66/7212 20130101; B29C 66/7254 20130101; B29C 66/7392
20130101; B29C 65/5057 20130101; B29C 66/72141 20130101; B29C
66/7212 20130101; B29K 2307/04 20130101; B29C 66/7212 20130101;
B29K 2309/08 20130101; B29C 66/71 20130101; B29K 2063/00 20130101;
B29C 66/71 20130101; B29K 2027/16 20130101 |
Class at
Publication: |
156/307.1 ;
156/309.6; 156/308.2; 428/098 |
International
Class: |
B32B 031/26; B32B
007/04; B32B 027/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2001 |
AU |
PR 6731 |
Claims
1. A process for bonding a semi-crystalline or crystalline
thermoplastic polymer to a thermosetting polymer component, the
process including: selecting compatible semi-crystalline
thermoplastic polymer and uncured thermosetting polymer components
wherein the curing temperature of the uncured thermosetting polymer
component is above the melting temperature of the semi-crystalline
thermoplastic polymer, locating the thermoplastic polymer in
contact with the uncured thermosetting polymer component; heating
the thermoplastic polymer and uncured thermosetting polymer or
thermosetting polymer composite component to the curing temperature
of the thermosetting polymer, where the uncured thermosetting
polymer components and the thermoplastic polymer are able to at
least partly interpenetrate before the thermosetting polymer cures;
and cooling the thermoplastic polymer and cured thermosetting
polymer component such that the thermoplastic polymer is very
strongly bonded to the cured thermosetting polymer component.
2. A process according to claim 1, wherein the thermosetting
polymer component is a thermosetting polymer.
3. A process according to claim 1, wherein the thermosetting
polymer component is initially uncured and forms part of a
thermosetting polymer composite.
4. A process according to claim 3, wherein the thermoplastic
polymer and the uncured thermosetting polymer part of the
thermosetting polymer composite are able to, when heated, at least
partly interpenetrate before the thermosetting polymer cures,
thereby bonding the thermoplastic polymer to the thermosetting
polymer composite.
5. A process for bonding a semi-crystalline or crystalline
thermoplastic polymer to a thermosetting polymer component, the
process including: selecting compatible semi-crystalline
thermoplastic polymer and uncured thermosetting polymer components
wherein the uncured thermosetting polymer component can migrate
into the semi-crystalline thermoplastic polymer at or below the
curing temperature of the thermosetting component; locating the
thermoplastic polymer in contact with the uncured thermosetting
polymer component; heating the thermoplastic polymer and uncured
thermosetting polymer or thermosetting polymer composite component
to the curing temperature of the thermosetting polymer, where the
uncured thermosetting polymer components and the thermoplastic
polymer are able to at least partly interpenetrate before the
thermosetting polymer cures; and cooling the thermoplastic polymer
and cured thermosetting polymer component such that the
thermoplastic polymer is very strongly bonded to the cured
thermosetting polymer component.
6. A process according to claim 5, wherein the curing temperature
of the thermosetting component is below the melting temperature of
the semi-crystalline thermoplastic polymer.
7. A process according to claim 5 or 6, wherein the thermosetting
polymer component is a thermosetting polymer.
8. A process according to claim 5 or 6, wherein the thermosetting
polymer component is initially uncured and forms part of a
thermosetting polymer composite.
9. A process according to claim 8, wherein the thermoplastic
polymer and the uncured thermosetting polymer part of the
thermosetting polymer composite are able to, when heated, at least
partly interpenetrate before the thermosetting polymer cures,
thereby bonding the thermoplastic polymer to the thermosetting
polymer composite.
10. A process according to any proceeding claim, wherein the
thermoplastic polymer is a thermoplastic polymer component or a
component with a compatible thermoplastic polymer surface.
11. A process according to any proceeding claim, wherein the
thermoplastic polymer is one of either pure polyvinylidene fluoride
(PVDF), or a thermoplastic polymer containing PVDF in combination
with other polymers and/or additives.
12. A process according to any preceding claim, wherein the
thermoplastic polymer contains a small amount a lightweight fabric
scrim.
13. A process according to any one of claims 1 to 11, wherein the
thermoplastic polymer contains material allowing electrical
conductivity or localised heating, such as ferromagnetic particles
or other electrically conductive material.
14. A process according to any preceding claim, wherein the
thermoplastic polymer is in the form of a film or powder, or is
coated directly onto the surface of a mould or tool.
15. A process according to any preceding claim, wherein the
thermosetting polymer is a resin/hardener mixture cured at an
elevated temperature.
16. A process according to any preceding claim, wherein the
thermosetting polymer is an epoxy or a bismaleimide.
17. A cured thermosetting polymer or thermosetting polymer
composite component with a thermoplastic surface made in accordance
with any preceding claim.
18. A process for welding a thermosetting polymer or thermosetting
polymer composite component with a thermoplastic surface formed in
accordance with the process defined in any one of claims 1 to 16,
to a second component having a thermoplastic surface, the process
including: locating and holding the thermoplastic surface of the
thermosetting polymer component or thermosetting polymer composite
in intimate contact with the thermoplastic surface of the second
component; heating the respective thermoplastic surfaces to a
temperature above the melting temperature of the thermoplastics for
a time such that the thermoplastic surfaces become molten and
welding of the adjacent thermoplastic surfaces occurs; and cooling
the molten thermoplastic to produce a strong bond between the
thermosetting or thermosetting composite components and the second
component.
19. A process according to claim 18, wherein the second component
is a thermosetting polymer or thermosetting polymer composite
component having a thermoplastic surface.
20. A process according to claim 19, wherein the second component
is formed in accordance with any one of claims 1 to 16.
21. A process according to claim 18, wherein the second component
is a thermoplastic polymer or thermoplastic polymer composite, or
any other component having a suitable thermoplastic surface.
22. A process according to any one of claims 18 to 21, wherein the
flow of the molten thermoplastic surfaces is increased by raising
the temperature and/or applying more pressure to the two components
during heating, or allowing additional process time.
23. A process according to any one of claims 18 to 22, further
including adding further layers of semi-crystalline or crystalline
thermoplastic material between the thermoplastic surfaces as
required to fill gaps or provide high thermoplastic polymer
flow.
24. A process according to claim 23, wherein the step of heating
also includes heating the additional thermoplastics material to a
temperature above the melting temperature of the thermoplastic for
a time such that the thermoplastic layers become molten and fuse
together.
25. A process according to any one of claims 18 to 24, wherein
welding takes place at a temperature below the glass transition
temperature of the cured thermosetting polymer or thermosetting
polymer composite component.
26. A thermosetting polymer or thermosetting polymer composite
component having a thermoplastic surface formed in accordance with
the process defined in any one of claims 1 to 16 welded to a second
component having a thermoplastic surface in accordance with the
process defined in any one of claims 18 to 25.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from International Patent
Application PCT/AU02/01014, entitled "Welding techniques for
polymer or polymer composite components" filed Jul. 31, 2002 which
claims priority from Australian Patent Application PR6731 entitled
"Welding techniques for polymer or polymer composite components,"
filed Jul. 31, 2001, the contents of which are incorporated by
reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to the creation of a new
functional surface on a polymer or polymer composite component. In
particular, the invention relates to altering the surface of a
thermosetting polymer or thermosetting polymer composite. The
invention also relates to a method for the formation of a joint
between a thermosetting polymer or thermosetting polymer composite
component, having a modified functional surface, and a second
component.
BACKGROUND OF THE INVENTION
[0003] Thermoplastic polymers (thermoplastics) are one of the major
classes of polymer material. A solid thermoplastic polymer can
typically be heated to soften and ultimately melt it, and then
cooled to return it to its solid state. These temperature-induced
changes are mostly fully-reversible. Thermoplastics can be divided
into two broad groups: "amorphous thermoplastics" and
"semi-crystalline thermoplastics". In solid amorphous
thermoplastics all of the polymer chains are arranged in a random
or disordered state: none of the polymer chains are arranged in a
crystalline structure. In solid semi-crystalline thermoplastics the
structure is mixed: in some portions of the material the polymer
chains are arranged in a ordered crystalline structure, and in some
portions the chains are in an amorphous state. "Crystalline
thermoplastics" have a higher proportion of crystallinity, but
still have some amorphous portions. For the purpose of this
discussion, crystalline thermoplastics will be grouped with
semi-crystalline thermoplastics, and the term "semi-crystalline
thermoplastic" will also include "crystalline thermoplastic". In
addition for the purpose of this discussion, "amorphous polymers"
or "amorphous thermoplastics" and "semi-crystalline polymers" or
"semi-crystalline thermoplastics" refer to types of thermoplastic
polymer material, rather than to the local microstructure of any
portion of thermoplastic polymer material.
[0004] Amorphous thermoplastics are characterised by a glass
transition temperature (T.sub.g) above which, with further heating,
progressive softening occurs. At temperatures substantially higher
than the glass transition temperature these thermoplastics behave
like a high viscosity liquid. The service temperature of amorphous
thermoplastics is below their glass transition temperature. They
are also as a class generally susceptible to chemical attack and
fluid absorption.
[0005] Semi-crystalline thermoplastics have a distinctive melting
temperature (T.sub.m), above which the material melts and behaves
as a liquid. With further increases in temperature the viscosity
falls off quickly. Semi-crystalline thermoplastics also have a
characteristic glass transition temperature, often well below the
melting temperature, due to their amorphous portions. Whether the
semi-crystalline thermoplastic is above or below its glass
transition temperature also influences some properties of these
thermoplastics. However semicrystalline thermoplastics can often be
used at service temperatures well above their glass transition
temperature, because their crystalline portions are very rigid.
Typically, semi-crystalline thermoplastics absorb less fluid than
amorphous materials.
[0006] In both amorphous thermoplastics and semi-crystalline
thermoplastics, changes induced by heating or cooling are normally
fully reversible, unless the decomposition temperature, typically
much higher than either the glass transition temperature or the
melting temperature, is exceeded.
[0007] Thermosetting polymers are a second class of polymer that
includes epoxide (often called epoxy), bismaleimide and vinyl ester
polymers. An addition-polymerisation thermosetting polymer such as
epoxy prior to curing consists of (as a minimum) a resin (monomer)
and a hardener, which react together to produce a temperature for
epoxies) above which considerable softening of the thermosetting
polymer occurs, and the thermosetting polymer behaves like a
rubber. (Further heating does not melt the polymer--instead it
typically starts to decompose at higher temperatures.) This is
critical for subsequent processing such as high-temperature joining
of components that contain a thermosetting polymer (e.g. a carbon
fibre/epoxy composite), as dimensional distortion of the components
can occur when the glass transition temperature of the
thermosetting polymer is approached or exceeded.
[0008] Composite materials are a class of material which consist of
at least two constituent materials, intimately joined together,
which together behave as one material with different, usually
superior, properties to either of the constituent materials.
Polymer composites consist of polymers, either thermosetting or
thermoplastic, reinforced by fibre or particulate reinforcement.
Well-known polymer composites include glass fibre reinforced
polyester resin, and carbon fibre reinforced epoxy. Both these use
thermosetting polymers as the matrix, and are therefore often
called thermosefting composites.
[0009] One major difference between thermoplastic and thermosetting
polymers is that thermoplastics can be melted and resolidified by
raising and lowering temperature, whereas thermosetting polymers
cannot. This characteristic has been utilised for the welding of
thermoplastics and thermoplastic composites, whereas thermosetting
polymers or thermosetting composites cannot be joined simply in
this fashion.
[0010] Thermosetting polymer components with thermoplastic surfaces
are attractive, some advantages being enabling the enhanced surface
properties of the thermoplastic and potentially for welding of
similarly surfaced components. Normally this would be done by an
adhesive bonding process. In an adhesive bonding process, the
adhesive is brought into contact with the component, must flow and
wet the component, and is then solidified in situ. It is quite
common to make an adhesive joint between a thermosetting polymer
and a thermoplastic polymer. In the most common method an uncured
thermosetting polymer such as an epoxy is used as the adhesive,
brought into contact with a solid thermoplastic polymer, and
subsequently cured. This could be done as part of the process to
cure a thermosetting composite component. Alternatively, a
thermoplastic polymer can be used as the adhesive, by heating it to
melt it and bringing it into contact with a cured thermosetting
component. The thermoplastic resin is subsequently cooled.
[0011] In both these situations, it is difficult to generate strong
adhesive bonds between the thermosetting polymer and thermoplastic
polymer. Where the thermoplastic is used as the adhesive, the joint
relies on weak secondary chemical bonds and is therefore itself
weak. Where an uncured thermosetting polymer functions as the
adhesive, on a thermoplastic surface, there are generally few sites
for the formation of the higher strength primary chemical bonds.
These bonds can be encouraged by surface treatment of the
thermoplastic, either with a chemical agent or by physical means
such as plasma treatment. This can be time-consuming and expensive,
may not provide sufficiently high strength or reliability for a
critical application such as the assembly of aircraft components,
and may still be subject to chemical attack.
[0012] However, a better method of achieving high strength
attachment between thermosetting and thermoplastic polymers is by
the formation of a semi-interpenetrating polymer network. These
provide a form of mechanical interlock between the polymer chains
of different polymers (in this case thermosetting and thermoplastic
polymers) by having the chains of one polymer interpenetrating the
other.
[0013] Previously, amorphous thermoplastic materials have been
joined to thermosetting composites by formation of an
interpenetrating polymer network during the curing of the
thermosetting composite by encouraging the liquid, uncured
components (monomer and hardener) of the thermosetting polymer to
migrate into the amorphous thermoplastic before the thermosetting
polymer cures, utilising the low solvent resistance of the
amorphous thermoplastic. This migration into the amorphous
thermoplastic would normally occur below the glass transition
temperature of the thermoplastic, at which condition the material
is solid. This effectively gives the cured thermosetting composite
a thermoplastic surface, with the ability to join to a
similarly-surfaced material under increased temperature and some
joining pressure.
[0014] The above process, and the amorphous thermoplastic required
for it, has several disadvantages. Firstly, the low solvent
resistance required for the amorphous thermoplastic used in this
process means that the surface and any joint formed from this
surface is likely to be susceptible to solvent attack.
[0015] Secondly, with this process there is an inherent difficulty
in attempting to select materials which will allow easy and
efficient surfacing and welding processes as well as provide a high
service temperature in the subsequent welded joint. In order to
join two components with amorphous thermoplastic surfaces, the
glass transition temperature of the thermoplastic has to be
substantially exceeded, possibly by at least 50.degree. C., to
obtain a high quality joint in a reasonable time. As a result, the
glass transition temperature of the underlying thermosetting
polymer is typically exceeded, which leads to reduced stiffness and
dimensional instability of the component. Dimensional change of the
components is likely, unless adequate tooling is used to support
the component at the joining temperature, especially as high
pressures may need to be applied to the joint in order to obtain
good contact and sufficient flow for consistent high-quality
joints. If a sufficiently high temperature is required for the
joining process, degradation of the thermosetting polymer or
thermosetting composite can also occur. If a high-temperature
amorphous thermoplastic is chosen as the surfacing/welding material
in order to boost the service temperature of the weld, the
surfacing and welding processes must in general be conducted at
higher temperatures, risking dimensional change or degradation of
the thermosetting composite. If a lower-temperature amorphous
thermoplastic is chosen for easy surfacing and welding, the service
temperature is likely to be unacceptably low. Finally, joining to a
high-temperature amorphous thermoplastic often requires special
long and/or complex cure cycles, for example cure cycles including
dwell times below the normal curing temperature, in order to have
the thermosetting monomer and hardener penetrate to a depth
sufficient for adhesive strength. This may add many hours to the
manufacturing time of a component, resulting in increased costs of
production.
[0016] U.S. Pat. No. 5,643,390 describes a process of bonding a
thermoplastic layer to a thermoset composite. The described method
involves "selecting a thermoplastic material and a thermosetting
monomer wherein said thermosetting monomer has similar solubility
parameters to that of said thermoplastic material". "Similar
solubility parameters" is defined in terms of Hildebrand solubility
theory, which is not suitable for the description of polymers with
substantial polar and/or hydrogen bonding forces.
[0017] This US patent is directed to the use of amorphous
thermoplastics. The patent advises that the mobility of penetrants
in semi-crystalline polymers is extremely small, and this prevents
the formation of an interpenetrating network to provide adhesive
strength. There is also no discussion of the compatibility of
semi-crystalline thermoplastic polymers.
[0018] In contrast, the present invention is a process which
utilises semi-crystalline polymers, advantageously allowing easier
surfacing and subsequent welding, and not compromising the solvent
resistance of the subsequent welded joint.
[0019] U.S. Pat. No. 5,667,881 describes a method for fabricating
an integral thermoset/thermoplastic composite joint. The described
method requires that the thermoplastic and thermoset resins must be
mutually partially miscible, or mutually miscible between 10 and
60%. The patent also states that the cure temperature does not
significantly exceed the glass transition temperature of the
thermoplastic resin. At such temperatures the thermoplastic polymer
is solid or has an extremely high viscosity, and migration of the
uncured thermoset polymer into an amorphous thermoplastic polymer,
and formation of a semi-interpenetrating network is quite slow.
This is confirmed by the long cure cycles mentioned in the
patent.
[0020] Further, the invention described in U.S. Pat. No. 5,667,881
relates to the formation of an integral joint with a prefabricated
thermoplastic article, which places constraints on the type of
article that may be attached using this technique, when compared to
the formation of a functional thermoplastic surface.
[0021] The present invention advantageously alleviates at least
some of the disadvantages of the processes described above, and
provides an improved process for forming a thermoplastic surface on
a thermosetting polymer or thermosetting polymer composite.
[0022] A further advantage of the present invention is an improved
process for joining a thermosetting polymer or thermosetting
polymer composite component, having a thermoplastic surface, to a
second component with a suitable thermoplastic surface.
SUMMARY OF THE INVENTION
[0023] In a first aspect, the invention provides a process for
bonding a semi-crystalline or crystalline thermoplastic polymer to
a thermosetting polymer component, the process including:
[0024] selecting compatible semi-crystalline thermoplastic polymer
and uncured thermosetting polymer components wherein the curing
temperature of the uncured thermosetting polymer component is above
the melting temperature of the semi-crystalline thermoplastic
polymer, locating the thermoplastic polymer in contact with the
uncured thermosetting polymer component;
[0025] heating the thermoplastic polymer and uncured thermosetting
polymer or thermosetting polymer composite component to the curing
temperature of the thermosetting polymer, where the uncured
thermosetting polymer components and the thermoplastic polymer are
able to at least partly interpenetrate before the thermosetting
polymer cures; and
[0026] cooling the thermoplastic polymer and cured thermosetting
polymer component such that the thermoplastic polymer is very
strongly bonded to the cured thermosetting polymer component.
[0027] In a second aspect, the invention provides a process for
bonding a semi-crystalline or crystalline thermoplastic polymer to
a thermosetting polymer component, the process including:
[0028] selecting compatible semi-crystalline thermoplastic polymer
and uncured thermosetting polymer components wherein the uncured
thermosetting polymer components can migrate into the
semi-crystalline thermoplastic polymer at or below the curing
temperature of the thermosetting component;
[0029] locating the thermoplastic polymer in contact with the
uncured thermosetting polymer component;
[0030] heating the thermoplastic polymer and uncured thermosetting
polymer or thermosetting polymer composite component to the curing
temperature of the thermosetting polymer, where the uncured
thermosetting polymer components and the thermoplastic polymer are
able to at least partly interpenetrate before the thermosetting
polymer cures; and
[0031] cooling the thermoplastic polymer and cured thermosetting
polymer component such that the thermoplastic polymer is very
strongly bonded to the cured thermosetting polymer component.
[0032] In the second aspect of the invention, the curing
temperature of the thermosetting component may be below the melting
temperature of the semi-crystalline thermoplastic polymer.
[0033] In either of the above embodiments of the invention, the
thermosetting polymer component may be a thermosetting polymer or a
thermosetting polymer composite. When the thermosetting polymer
component is a composite, the thermoplastic polymer and the uncured
thermosetting polymer part of the thermosetting polymer composite
are able to, when heated, at least partly interpenetrate before the
thermosetting polymer cures, thereby bonding the thermoplastic
polymer to the thermosetting polymer composite.
[0034] The compatibility of the thermoplastic and thermosetting
components indicates the ability of the thermoplastic and
thermosetting components to interpenetrate through close matching
of their respective solubilities.
[0035] Advantageously, the thermoplastic polymer may be a
thermoplastic polymer component or a component of any sort with a
compatible thermoplastic polymer surface.
[0036] It will be appreciated that, with the interpenetration
between the thermoplastic and thermoset resins, the thermoplastic
polymer surface is very strongly bonded to the thermosetting
polymer or thermosetting polymer composite. This ensures that the
thermoplastic surface cannot be readily removed from the
thermosetting polymer or thermosetting polymer composite.
[0037] It will be appreciated that a cured thermosetting polymer or
thermosetting polymer composite with a thermoplastic surface made
according to the first or second aspect of the invention may be
bonded to a further section of thermosetting polymer or
thermosetting polymer composite by a second curing process
conducted according to the first or second aspect of the
invention.
[0038] Preferably, the thermoplastic polymer is polyvinylidene
fluoride (PVDF), either pure PVDF or containing the PVDF in
combination with other polymers and/or conventional additives.
[0039] Additionally, the thermoplastic polymer may contain a small
amount of additional material, such as a lightweight fabric scrim.
Alternatively, the thermoplastic polymer may contain a small amount
of material allowing electrical conductivity or localised heating,
such as ferromagnetic particles or other electrically conductive
material.
[0040] The thermoplastic polymer may be in the form of a film or
powder, or coated directly onto the surface of a mould or tool.
Additional material, which does not adhere to the thermoplastic,
may be located adjacent to the thermoplastic film during
manufacture to improve the surface quality of thermoplastic after
manufacturing.
[0041] The thickness of thermoplastic may be varied on the surface
of the component.
[0042] The thermosetting polymer is preferably a resin/hardener
mixture cured at an appropriate elevated temperature. In the case
of a thermosetting polymer composite, the composite is a suitable
thermosetting polymer reinforced with one or more other materials.
More preferably the thermosetting polymer is an epoxy or a
bismaleimide.
[0043] The third aspect of the invention takes advantage of the
fact that the first or second aspect of the invention provides a
cured thermosetting polymer or cured thermosetting polymer
composite with a semi-crystalline or crystalline thermoplastic
surface.
[0044] Accordingly, the third aspect of the invention provides a
process for joining a thermosetting polymer or thermosetting
polymer composite component with a thermoplastic surface made in
accordance with the first or second aspect of the invention, to a
second component having a thermoplastic surface, the process
including:
[0045] locating and holding the thermoplastic surface of the
thermosetting polymer component or thermosetting polymer composite
in intimate contact with the thermoplastic surface of the second
component;
[0046] heating the respective thermoplastic surfaces to a
temperature above the melting temperature of the thermoplastics for
a time such that the thermoplastic surfaces become molten and
welding of the adjacent thermoplastic surfaces occurs; and
[0047] cooling the molten thermoplastic to produce a strong bond
between the thermosetting or thermosetting composite components and
the second component.
[0048] Advantageously, the thermoplastic surface of the
thermosetting polymer composite component is formed in accordance
with either the first or second aspects of the invention.
[0049] The thermosetting polymer component may be a thermosetting
polymer or a thermosetting polymer composite.
[0050] Preferably, the second component is a thermosetting polymer
or thermosetting polymer composite component having a thermoplastic
surface such that the process of the third aspect of the invention
may be used to form a joint between two thermosetting polymers or
thermosetting composite components with thermoplastic surfaces.
[0051] Alternatively, the second component may be a thermoplastic
polymer or thermoplastic polymer composite, or any other component
having a suitable thermoplastic surface.
[0052] The molten thermoplastic surfaces provide high thermoplastic
polymer flow when placed in intimate contact, thereby filling any
undulations in the opposed surfaces. The flow can be increased by
raising the temperature and/or applying more pressure to the two
components during heating or allowing additional process time.
[0053] The process may further include adding further layers of
semi-crystalline or crystalline thermoplastic material between the
thermoplastic surfaces as required to fill gaps or provide high
thermoplastic polymer flow. Where additional thermoplastic material
is used, the step of heating also includes heating the additional
thermoplastics material to a temperature above the melting
temperature of the thermoplastic for a time such that the
thermoplastic layers become molten and fuse together.
[0054] Reheating the welded thermoplastic layers also allows for
the components to be dismantled and reassembled as required. They
may then be welded again in the same manner described above, with
extra thermoplastic material added between the modified
thermoplastic surfaces if insufficient thermoplastic material has
been retained on the separated components.
[0055] Reheating the welded thermoplastic layers also allows for
the components to be put through the welding process again, or
rewelded, to improve the weld in selected areas.
[0056] Preferably, welding takes place at a temperature below the
glass transition temperature of the cured thermosetting polymer or
polymer composite component. Alternatively welding takes place at a
temperature not significantly overheating the thermosetting
polymer.
[0057] The thermosetting composite components may include inserts,
foam or honeycomb core, other thermoplastic subcomponents or films,
or any other material that can be incorporated as an integral part
of a largely thermoset composite component.
[0058] The invention also extends to thermosetting components
having a thermoplastic surface made in accordance with either the
first or second aspects of the invention. Advantageously, the
preferred features of the process of the first and second aspects
of the invention apply, as appropriate, to the component formed
from the process.
[0059] The invention further extends to products made in accordance
with the third aspect of the invention. Advantageously, the
preferred features of the process of the third aspect of the
invention apply, as appropriate, to the products formed from the
process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] The invention will now be described, by way of example only,
with reference to the accompanying drawings in which:
[0061] FIG. 1 illustrates the relationship of a reinforced
thermosetting polymer, a thermoplastic layer, and the
semi-interpenetrating network (SIPN) formed therebetween;
[0062] FIG. 2 is a schematic illustration showing the joining of
two thermosetting polymer components according to an embodiment of
the present invention;
[0063] FIG. 3 is a schematic illustration showing the joining of
two thermosetting polymer components according to an embodiment of
the present invention;
[0064] FIG. 4 illustrates a Hansen solubility diagram for a
polymer, which can be used determine the suitability of a solvent
for a particular polymer.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0065] In a first embodiment of the invention, and with reference
to FIG. 1, a semi-crystalline or crystalline thermoplastic layer 10
is bonded to the surface of a thermosetting polymer 12 or
thermosetting composite component during the curing of the
thermosetting component to form a semi-interpenetrating polymer
network 14. This is achieved by selecting a semi-crystalline
thermoplastic 10 which is compatible with the chosen thermosetting
monomers. Determination of suitable material combinations can be
made using thermodynamic and solubility criteria, which will be
discussed in the following section.
[0066] Polymer Thermodynamics and Solubility Criteria
[0067] The selection of compatible materials requires a close
matching of several solubility parameters. The principle of
material selection for a compatible amorphous thermoplastic is
based on the Gibb's free energy of mixing (.DELTA.G.sub.m), which
states that
.DELTA.G.sub.m=.DELTA.H.sub.m-T.DELTA.S.sub.m.ltoreq.0 (1)
[0068] where .DELTA.H.sub.m is enthalpy of mixing, T is temperature
and .DELTA.S.sub.m is entropy of mixing. The Hildebrand-Scatchard
equation can then be used to determine the enthalpy of mixing
as
.DELTA.H.sub.m=V.PHI..sub.b(.delta..sub.b-.delta..sub.b).sup.2
(2)
[0069] where .delta..sub.a and .delta..sub.b are the solubility
parameters (also known as the Hildebrand parameters) of the two
species considered, e.g. amorphous polymer and monomer or
hardener.
[0070] However, the use of the Hildebrand-Scatchard equation
(Equation (2) above) is inadequate for the class of
high-performance semi-crystalline thermoplastics that would be most
favourable for joining applications, as intermolecular forces such
as polar forces greatly affect the solubility behaviour of these
polymers. The use of Hansen parameters which take account of
dispersion, polar and hydrogen bonding forces is recommended as a
more suitable approach for these polymers (See AFM Barton "CRC
Handbook of Solubility Parameters and Other Cohesion Parameters",
CRC Press, Boca Raton, 1983). The application of these parameters
provides a reasonable guide for polymer-solvent compatibility. A
radius of compatibility for polymer b is defined by radius .sup.bR,
as shown in the solubility chart in FIG. 4. The Hansen solubility
parameters for dispersion (.delta..sub.d), polar (.delta..sub.p)
and hydrogen bonding forces (.delta..sub.h) for any solvent a can
be determined and plotted on the chart. Where the point on the
solubility chart locating the three Hansen parameters for solvent a
(.sup.a.delta..sub.d, .sup.a.delta..sub.d, and .sup.a.delta..sub.d)
lies within the sphere defined by .sup.bR, the polymer is soluble
in the solvent, i.e.
[4(.sup.a.delta..sub.d-.sup.b.delta..sub.d).sup.2+(.sup.a.delta..sub.p-.su-
p.b.delta..sub.p).sup.2+(.sup.a.delta..sub.h-.sup.b.delta..sub.h).sup.2].s-
up.1/2<.sup.bR (3)
[0071] where the solvent in this case is the monomer or hardener,
and .sup.bR is determined by standard experiments using common
solvents of known Hansen parameters.
[0072] An advantageous feature of the first and second aspects of
the current invention is the alteration of the "effective
solubility parameter" of the semi-crystalline thermoplastic 10.
This is achieved by bringing the thermoplastic 10 and
monomer/hardener 12 to a sufficiently high temperature. In general
terms, solvents cannot migrate effectively through the solid
crystalline portion of polymers, due to insufficient free energy to
overcome the heat of fusion of the crystalline portion of the
polymer. Through increased temperature of the system, the heat of
fusion is overcome. Under these circumstances the monomer and
hardener are able to migrate through the polymer, whereas
previously the polymer was insoluble. Hence the "effective
solubility parameter" of the polymer is altered through the
addition of heat.
[0073] Therefore one way to provide for rapid formation of a
semi-interpenetrating polymer network 14 is to alter the "effective
solubility parameter" of the semi-crystalline thermoplastic 10 by
curing the thermosetting polymer 12 above the melting temperature
of the semi-crystalline thermoplastic 10. However, a second
possibility also exists, as described in relation to the second
aspect of the invention. Through careful matching of the
monomer/hardener 12 and thermoplastic solubility properties, and at
a suitable temperature, the presence of the thermoset monomer,
acting as a solvent, can overcome the heat of fusion of the
crystalline polymer, thus lowering the "melt" temperature to an
"effective melting temperature" which depends on the
monomer/hardener involved. Under these circumstances the monomer
and hardener are able to migrate through the polymer below the
normal melting temperature. This is demonstrated in the
experimental discussion within this document.
[0074] It should be noted that the melting temperature or lower
"effective melting temperature" described here would be a minimum
processing temperature, and that standard curing conditions for the
thermosetting polymer may impose a higher processing
temperature.
[0075] Material Selection and Surface Integration
[0076] A semi-crystalline thermoplastic material 10 selected
according to the above criteria may be integrated successfully, by
the formation of a substantial semi-interpenetrating polymer
network (SIPN) 14, onto the surface of a thermosetting polymer or
thermosetting polymer composite 12. An aspect of that process is
the selection of a thermosetting polymer and a thermoplastic with a
solubility determined by the use of Hansen parameters, and the
selection of a curing temperature/time cycle such that the
thermosetting monomer and hardener are able to migrate sufficiently
into the molten semi-crystalline polymer, or into the crystalline
component of the thermoplastic polymer by overcoming the heat of
fusion of the crystalline component.
[0077] During processing the crystalline portion of the
thermoplastic polymer in contact with the monomer and hardener
"melts", allowing rapid discrete mixing of the uncured
thermosetting resin and thermoplastic resin. Following cure of the
component, the thermoplastic film 10 is intimately bonded to the
component 12 through the entanglement of molecular chains in the
region of the original surfaces thereby forming a
semi-interpenetrating polymer network 14 between the thermosetting
resin and the thermoplastic resin.
[0078] Advantageously, when the above thermodynamic and solubility
compatibility criteria have been met, the bonding process may
typically take place without any alteration to the manufacturer's
recommended curing cycle for the thermosetting polymer.
[0079] Further selection criteria may also be applied for the
benefit of the subsequent process of welding thermosetting polymer
or thermosetting polymer composites 16, 18, whereby the melting
point of the semi-crystalline thermoplastic polymer (T.sub.m) 20 is
below the glass transition temperature (T.sub.g) of the cured
thermosetting polymer or thermosetting polymer composite 16, 18.
The discussion below is directed to this circumstance, but it will
be appreciated that the invention is not restricted to this
material selection, but rather that additional advantages would
result from such an appropriate selection.
[0080] Welding Technology
[0081] The above thermodynamic discussion relates to the selection
of a semi-crystalline thermoplastic for integration of
thermoplastic material onto the surface of a thermosetting polymer
or thermosetting polymer composite. The selection of a
semi-crystalline thermoplastic material with a melting temperature
below the T.sub.g of the cured thermosetting polymer or polymer
composite component, as in the first aspect of the invention,
allows distinct advantages in the welding of two largely
thermosetting composite components.
[0082] In accordance with a third embodiment of the invention, a
thermosetting polymer or thermosetting composite component 16 with
a semi-crystalline thermoplastic surface 20 formed in accordance
with the first or second aspect of the invention may be joined to a
second component 18 having a suitable thermoplastic surface 22,
under external heat and pressure (heat platen 24), as illustrated
in FIG. 2. Alternatively, a heating element 26 as shown
schematically in FIG. 3, or other material allowing heat to be
focused on the welding line, can be used to join two components 16,
18.
[0083] The second component may also be a thermosetting polymer or
thermosetting composite component with a semi-crystalline
thermoplastic surface, and the discussion below is directed to this
circumstance, but it will be appreciated that the third embodiment
of the invention is not so restricted and extends broadly to the
formation of a joint between a thermosetting polymer or
thermosetting composite component with a semi-crystalline
thermoplastic surface formed in accordance with the first or second
of aspect of the invention and any other component with a suitable
thermoplastic surface.
[0084] The inclusion of a thermoplastic polymer surface of a
thermosetting polymer or thermosetting composite component enables
joining of two components made largely of different thermosetting
polymers or thermosetting polymer composites or other materials but
with similar surface materials.
[0085] The process of welding the thermoplastic layers takes place
under applied heat and, in most circumstances, pressure. The
thermoplastic layers are heated to a temperature above the melting
temperature of the thermoplastic and below the glass transition
temperature of the thermosetting polymer or thermosetting composite
components. When the thermoplastic has a melting temperature lower
than the glass transition temperature of the thermosetting
components that are to be joined, the components may in the right
circumstances be joined without the use of supporting tooling, with
no permanent distortion of the components occurring during joining.
Furthermore degradation of the thermosetting polymer or composite
is unlikely when exposed to a temperature below the glass
transition temperature of the thermosetting polymer for a moderate
period of time. This reduces or eliminates the need for expensive
or sophisticated systems to focus heating on the joint only.
[0086] Further, since the welding process occurs above the melt
temperature of the semi-crystalline or crystalline thermoplastic,
the thermoplastic flows considerably during welding, even under
very low welding pressures. This degree of flow above their melt
temperature is an intrinsic advantage of semi-crystalline
thermoplastic polymers in this application. Such flow allows the
thermoplastic to fill small undulations in the surface of the
components or small gaps between the components due to normal
manufacturing tolerances, and is very important for a practical
welding process. This reduces the cost of tooling for such
operations and reduces the possibility that the largely thermoset
composite components will become distorted during the process.
[0087] The invention also allows simple unwelding and separation of
any welded components. The components, or the welded region
thereof, can be heated to a temperature above the melt temperature
of the semi-crystalline or crystalline thermoplastic. An advantage
of the current invention is that the thermosetting polymer or
thermosetting composite components can be separated with external
heat applied near the joint, and there is no requirement for an
embedded element. At this temperature range little force is needed
to separate the components. As each component will retain most of
its thermoplastic surface layer, due to the formation in the
surfacing process of a semi-interpenetrating polymer network, the
separated components may subsequently be welded again in the same
manner described above. If necessary, an extra layer or layers of
semi-crystalline or crystalline thermoplastic material may be added
between the modified thermoplastic surfaces if insufficient
thermoplastic material has been retained on the separated
components.
[0088] Alternatively, if desired, at this temperature range the
components may be put through the welding process again, or
rewelded, to improve the weld in selected areas.
[0089] While the majority of the above description relates to the
surfacing of thermosetting composites with semi-crystalline or
crystalline thermoplastic film for the purpose of subsequently
joining thermosetting components, the generation of a thermoplastic
functional semi-crystalline polymer surface intimately bonded to a
thermosetting polymer or composite component may also provide
additional distinct advantages such as improved chemical
resistance, reduced water absorption, improved wear and erosion
resistance, improved surface appearance, improved frictional
properties, improved surface electrical properties, improved fire
resistance or reduced smoke generation due to fire, improved UV
resistance, improved surface cracking resistance, improved
biocompatibility, improved ability to be sterilised or reduced
notch sensitivity. In particular, the process of the first or
second aspect of this invention may be used to provide strongly
bonded erosion resistant surfaces for carbon fibre/epoxy
composites.
[0090] It will also be appreciated that, the present invention
provides an opportunity for the integration of a semi-crystalline
polymer on the surface of a thermoplastic or thermoplastic
composite based on a different thermoplastic polymer. In this
circumstance, the provision of different surface properties or the
ability to join components under different welding conditions to
that required for the thermoplastic parent material would be
enabled through this technique. Furthermore this technique would
allow a class of thermoplastic or thermoplastic composite materials
to be joined to thermosetting or thermosetting composite materials
having a semi-crystalline polymer surface as discussed above.
[0091] Experimental Discussion
[0092] Surfacing Process
[0093] Two separate composite panels with a semi-crystalline
polymer surface were manufactured. First, a single layer of PVDF
semi-crystalline thermoplastic film with a melting point of
approximately 170.degree. C. (127 .mu.m thickness) was placed on a
stack of preimpregnated plain woven fabric comprising T300 carbon
fibre and Hexcel F593 epoxy resin. The film was cleaned with
isopropyl alcohol prior to placing on the stack. The stack was
placed on a flat tool, and enclosed within a vacuum bag. The air
within the vacuum bag was evacuated, and the stack subsequently
cured at 177.degree. C. and 0.63 MPa external pressure for 120
minutes. After curing, the thermoplastic layer was fully integrated
with the composite substrate. A second panel was manufactured with
a single 127 .mu.m layer of PVDF semi-crystalline thermoplastic
film placed on a stack of preimpregnated satin fabric consisting of
glass fibre and Hexcel F155. The film was cleaned with isopropyl
alcohol prior to placing on the stack. The stack was placed on a
flat tool, and enclosed within a vacuum bag. The air within the
vacuum bag was evacuated, and the stack subsequently cured at
127.degree. C. and 0.32 MPa external pressure for 120 minutes.
After curing the thermoplastic surface layer was fully integrated
with the composite substrate.
[0094] Joining Process
[0095] Two composite components with identical thermosetting
composite substrates and thermoplastic surfaces were cleaned with
isopropyl alcohol and the thermoplastic surfaces placed in contact
with each other. The T300/F593 and GF/F155 epoxy composites had
bondlines heated to 185.degree. C. and applied pressure of 0.1 Mpa
for 20 minutes. Upon holding the components at the required
temperature and pressure, whereby complete healing has occurred,
the components were cooled while pressure was maintained. Upon
cooling to room temperature, the components were welded
together.
[0096] Bond Strength
[0097] Bond strengths were determined using a single-lap-shear
bonding test specimen, with a width of 25 mm and joint length of
12.5 mm. Specimens were tested at ambient conditions at a speed of
1.25 mm/min. An average bond strength of 29.1 MPa was observed for
the T300/F593 epoxy composite. This compares to an average bond
strength of 24.4 MPa observed for otherwise identical specimens
bonded using epoxy adhesive film. Additionally, an average bond
strength of 27.6 MPa was observed for the glass fibre/F155 epoxy
composite.
[0098] Pressure Requirements
[0099] Trials using various welding pressures indicate that
high-quality welds can be made using pressures from 50 kPa to 1
MPa. A preferred pressure is between 100 kPa and 350 kPa. However,
the applied pressure is not necessary for ensuring welding, but
rather is used to bring the adjacent thermoplastic polymer surfaces
into full and intimate contact, and to ensure some polymer flow. In
manufacturing practice, minor fluctuations in dimensional tolerance
are overcome by the use of pressure. In the case of this
thermoplastic joining, no additional pressure is required other
than to bring the surfaces into contact with each other, which
allows the polymer chains to migrate across the original surface
and thereby heal the joint. Higher pressures (1 MPa and greater)
may also be used to force entrapped air from the joint. It should
be noted that welding pressure may squeeze some of the
thermoplastic out of the immediate joint area.
[0100] Joining Time
[0101] The ability of the polymer to heal itself, and the time
taken to do so, where molecular chains cross the original join line
and become entangled with the polymer chains from the adjacent
surface, is dependent on the temperature of the thermoplastic
surface, i.e. the activity level of the polymer chains.
[0102] It will be understood that the invention disclosed and
defined in this specification extends to all alternative
combinations of two or more of the individual features mentioned or
evident from the text or drawings. All of these different
combinations constitute various alternative aspects of the
invention.
* * * * *