U.S. patent application number 12/719083 was filed with the patent office on 2010-09-02 for method of making and using shape memory polymer patches.
This patent application is currently assigned to Cornerstone Research Group, Inc.. Invention is credited to Frank Auffinger, Thomas Joseph Barnell, Sean Patrick Garrigan, Patrick Joseph Hood, Richard Douglas Hreha, Tat Hung Tong, Benjamin John Vining.
Application Number | 20100221523 12/719083 |
Document ID | / |
Family ID | 42470670 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100221523 |
Kind Code |
A1 |
Hood; Patrick Joseph ; et
al. |
September 2, 2010 |
METHOD OF MAKING AND USING SHAPE MEMORY POLYMER PATCHES
Abstract
A method of repairing a composite component having a damaged
area including: laying a composite patch over the damaged area;
activating the shape memory polymer resin to easily and quickly
mold said patch to said damaged area; deactivating said shape
memory polymer so that said composite patch retains the molded
shape; and bonding said composite patch to said damaged part.
Inventors: |
Hood; Patrick Joseph;
(Bellbrook, OH) ; Garrigan; Sean Patrick;
(Beavercreek, OH) ; Auffinger; Frank; (Hamilton,
OH) ; Tong; Tat Hung; (Bellbrook, OH) ;
Vining; Benjamin John; (Dayton, OH) ; Hreha; Richard
Douglas; (Beavercreek, OH) ; Barnell; Thomas
Joseph; (Dayton, OH) |
Correspondence
Address: |
CORNERSTONE RESEARCH GROUP, INC.
2750 INDIAN RIPPLE ROAD
DAYTON
OH
45440
US
|
Assignee: |
Cornerstone Research Group,
Inc.
Dayton
OH
|
Family ID: |
42470670 |
Appl. No.: |
12/719083 |
Filed: |
March 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11611184 |
Dec 15, 2006 |
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12719083 |
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11569902 |
Sep 8, 2008 |
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11611184 |
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12090760 |
Apr 18, 2008 |
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11569902 |
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Current U.S.
Class: |
428/318.4 ;
156/320; 428/304.4 |
Current CPC
Class: |
Y10T 428/287 20150115;
Y10T 428/2817 20150115; Y10T 428/249953 20150401; Y10T 428/249987
20150401; Y10T 428/1462 20150115; Y10T 442/2738 20150401; Y10T
428/2848 20150115; B29C 73/10 20130101 |
Class at
Publication: |
428/318.4 ;
428/304.4; 156/320 |
International
Class: |
B32B 3/26 20060101
B32B003/26; B29C 65/02 20060101 B29C065/02; B29C 65/48 20060101
B29C065/48 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This application was made in part with government support
under contract number NNK05OA29C awarded by the National
Aeronautics and Space Administration (NASA). The U.S. government
has certain rights in the invention.
Claims
1. A product comprising: a thermo-reversible dry adhesive
comprising: a first layer comprising a dry adhesive; a second layer
comprising a shape memory polymer; wherein the thermo-reversible
dry adhesive has a first shape at a first temperature and a second
shape at a second temperature with a load applied.
2. The product of claim 1, wherein the dry adhesive comprises a
soft dry adhesive.
3. The product of claim 1, wherein the shape memory polymer
comprises a shape memory polymer foam comprising at least one of an
epoxy, a polyurethane or a crosslinked vinyl polymer.
4. A product as set forth in claim 1 wherein the shape memory
polymer comprises: at least one of a rigid epoxy or a flexible
epoxy; and at least one of a crosslinking agent or a catalytic
curing agent; wherein the rigid epoxy is an aromatic epoxy having
at least two epoxide groups, the flexible epoxy is an aliphatic
epoxy having at least two epoxide groups, and the crosslinking
agent is one of a multi-amine, an organic multi-carboxylic acid, or
an anhydride.
5. A product as set forth in claim 2, wherein the soft dry adhesive
comprises: at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two
epoxide groups, the flexible epoxy is an aliphatic epoxy having at
least two epoxide groups, and the crosslinking agent is one of a
multi-amine, an organic multi-carboxylic acid, or an anhydride.
6. A product as set forth in claim 1 further comprising at least
one substrate wherein the thermo-reversible dry adhesive is
positioned on top of the at least one substrate with the first
layer in contact with the at least one substrate.
7. A product as set forth in claim 6 wherein the pull-off force of
the thermo-reversible dry adhesive with the curved structure is
about 0 to 50 N/cm2 for one of the at least one substrate.
8. A product as set forth in claim 6 wherein the pull-off force of
the thermo-reversible dry adhesive with the relatively flat
structure is about 10 to about 200 N/cm2 for one of the at least
one substrate.
9. A product as set forth in claim 1 wherein the at least one
substrate comprises at least one of an automotive body trim piece,
a sign, a picture, an automotive side molding, or a surface
decorative film.
10. A product as set forth in claim 9 wherein the at least one
substrate comprises one of stainless steel, glass, aluminum alloy
5657, polypropylene, or Teflon.
11. A product as set forth in claim 1, wherein the dry adhesive is
grafted to the shape memory polymer to form a single layer.
12. A method comprising: providing a thermo-reversible dry adhesive
comprising at least one dry adhesive layer and at least one shape
memory polymer layer; heating the thermo-reversible dry adhesive to
a temperature higher than the glass transition temperature of the
shape memory polymer layer; imposing a load on the
thermo-reversible dry adhesive while cooling to a temperature below
the glass transition temperature of the shape memory polymer layer,
so that the dry adhesive layer substantially conforms to a
corresponding topography of an underlying substrate to form a
strong adhesive bond to the underlying substrate; and releasing the
thermo-reversible dry adhesive from the underlying substrate by
heating the thermo-reversible dry adhesive to a temperature above
the glass transition temperature of the shape memory polymer to
cause the shape memory polymer to revert to its original shape,
therein causing the dry adhesive layer to return to its original
shape.
13. A method as set forth in claim 12 wherein the load is about 1
N/cm2 to about 20 N/cm2.
14. A method as set forth in claim 12 wherein the glass transition
temperature of the shape memory polymer is about 25 to about
200.degree. C.
15. A method as set forth in claim 12 wherein the glass transition
temperature of the dry adhesive is about -90 to about 200.degree.
C.
16. A method comprising: forming a thermo-reversible dry adhesive
comprising: forming a first layer by curing a first component, a
second component, and a third component; forming a second layer
over the first layer comprising pouring a mixture of a fourth
component and a fifth component over the first layer and curing the
second layer; and post-curing the first and second layers to form
the thermo-reversible adhesive having a curved structure at a first
temperature and having a relatively flat structure at a second
temperature with a load applied.
17. A method as set forth in claim 16 wherein the first component,
the second component, and the third component comprise: at least
one of a rigid epoxy or a flexible epoxy; and at least one of a
crosslinking agent or a catalytic curing agent; wherein the rigid
epoxy is an aromatic epoxy having at least two epoxide groups, the
flexible epoxy is an aliphatic epoxy having at least two epoxide
groups, and the crosslinking agent is one of a multi-amine, an
organic multi-carboxylic acid, or an anhydride.
18. A method as set forth in claim 16 wherein the first component,
the second component, and the third component comprise an aromatic
diepoxy, an aliphatic diepoxy, and a diamine.
19. A method as set forth in claim 18, wherein the aromatic diepoxy
comprises diglycidyl ether of bisphenol A epoxy monomer with an
approximate epoxy equivalent weight of 180; wherein the aliphatic
epoxy comprises NGDE; and wherein the diamine comprises
poly(propylene glycol)bis(2-aminopropyl)ether with an average
molecular weight of 230.
20. A method as set forth in claim 16, wherein the fourth component
and the fifth component comprise an aliphatic diepoxy and a
diamine, and wherein the components are present in an amount
sufficient to provide, upon curing of the second layer, a soft
epoxy dry adhesive layer having a glass transition temperature of
-90.degree. C. to 200.degree. C. and having a pull-off strength of
1-200 N/cm2.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. Utility application Ser. No.
11/611,184 filed Dec. 15, 2006 which is a continuation of U.S.
Utility application Ser. No. 11/569,902 filed Dec. 1, 2006, which
is a national stage entry from PCT application PCT/US2005/019842
filed Jun. 4, 2005, which all claim priority benefit of U.S.
Provisional Patent Application Ser. No. 60/577,003 filed Jun. 4,
2004. Additionally this application is a continuation of U.S.
Utility application Ser. No. 12/090,760 filed Apr. 18, 2008, which
is a national stage entry from PCT/US2006/062179 filed Dec. 15,
2006 which further claims priority from a U.S. Provisional Patent
Application Ser. No. 60/750,502 filed Dec. 15, 2005.
BACKGROUND OF THE INVENTION
[0003] 1. Patches Background
[0004] The present invention generally relates to the repair of
components made from material such as metals, composites, wood,
plastics, glass and other materials. It is to be appreciated that
the present invention has general and specific industrial
application in the repair of various materials. The term
"composite" is commonly used in industry to identify components
produced by impregnating a fibrous material with a thermoplastic or
thermosetting resin to form laminates or layers.
[0005] Generally, polymers and polymer composites have the
advantages of weight saving, high specific mechanical properties,
and good corrosion resistance which make them indispensable
materials in all areas of manufacturing. Nevertheless,
manufacturing costs are sometime detrimental, since they can
represent a considerable part of the total costs and are made even
more costly by the inability to quickly and easily repair these
materials without requiring a complete, and expensive, total
replacement. Furthermore, the production of complex shaped parts is
still a challenge for the composite industry. The limited potential
for complex shape forming offered by advanced composite materials
leaves little scope for design freedom in order to improve
mechanical performance and/or integrate supplementary functions.
This has been one of the primary limitations for a wider use of
advanced composites in cost-sensitive large volume applications.
Additionally, the nature of composite materials does not lend
itself to easy repair, especially on cheap, mass produced items and
repair kits for more expensive, specialty items (such as in the
aeronautic industry) are bulky, expensive, and require long time to
complete the repair.
[0006] Shape memory polymers (SMPs) and shape memory alloys (SMAs)
were first developed about 20 years ago and have been the subject
of commercial development in the last 10 years. SMPs are polymers
that derive their name from their inherent ability to return to
their original "memorized" shape after undergoing a shape
deformation. SMPs that have been preformed can be deformed to any
desired shape below or above its glass transition temperature
(T.sub.g). If it is below the T.sub.g, this process is called cold
deformation. When deformation of the SMP occurs above its T.sub.g,
the process is denoted as warm deformation. In either case the SMP
must remain below, or be quenched to below, the T.sub.g while
maintained in the desired deformed shape to "lock" in the
deformation. Once the deformation is locked in, the polymer network
cannot return to a relaxed state due to thermal barriers. The SMP
will hold its deformed shape indefinitely until it is heated above
its T.sub.g, whereat the SMP stored mechanical strain is released
and the SMP returns to its performed state.
[0007] SMPs are not simply elastomers, nor simply plastics. They
exhibit characteristics of both materials, depending on their
temperature. While rigid, an SMP demonstrates the
strength-to-weight ratio of a rigid polymer; however, normal rigid
polymers under thermal stimulus simply flow or melt into a random
new shape, and they have no "memorized" shape to which they can
return. While heated and pliable, an SMP has the flexibility of a
high-quality, dynamic elastomer, tolerating up to 400% elongation
or more; however, unlike normal elastomers, an SMP can be reshaped
or returned quickly to its memorized shape and subsequently cooled
into a rigid plastic.
[0008] Several known polymer types exhibit shape memory properties.
Probably the best known and best researched polymer types
exhibiting shape memory polymer properties are polyurethane
polymers. Gordon, Proc of First Intl. Conf. Shape Memory and
Superelastic Tech., 115-120 (1994) and Tobushi et al., Proc of
First Intl. Conf. Shape Memory and Superelastic Tech., 109-114
(1994) exemplify studies directed to properties and application of
shape memory polyurethanes. Another polymeric system based on
crosslinking polyethylene homopolymer was reported by S. Ota,
Radiat. Phys. Chem. 18, 81 (1981). A styrene-butadiene
thermoplastic copolymer system was also described by Japan Kokai,
JP 63-179955 to exhibit shape memory properties. Polyisoprene was
also claimed to exhibit shape memory properties in Japan Kokai JP
62-192440. Another known polymeric system, disclosed by Kagami et
al., Macromol. Rapid Communication, 17, 539-543 (1996), is the
class of copolymers of stearyl acrylate and acrylic acid or methyl
acrylate. Other SMP polymers known in the art include articles
formed of norbornene or dimethaneoctahydronapthalene homopolymers
or copolymers, set forth in U.S. Pat. No. 4,831,094. Additionally,
styrene copolymer based SMPs are disclosed in U.S. Pat. No.
6,759,481 which is incorporated herein by reference.
[0009] Modern aircraft are perhaps one of the largest users of
composite materials. Composites are widely used in the aerospace
industry to provide aircraft components such as fuselages, wings
and tail fins, doors and so on. This is because composite
components have the physical attribute of being relatively
lightweight while at the same time having high structural strength
in comparison to metals. Such composite components typically are of
a sandwich construction. When damage occurs to such structures, for
example by impacted damage from a flying stone or other debris or
from a dropped tool, a damage crater, crack, or hole will be formed
in the object concerned.
[0010] The general approach to repair damage is to remove the
damaged part from the aircraft, and repair the damage by using an
electric blanket with a vacuum bag. A "prepreg" formed of a layer
of fibrous material impregnated with uncured resin is laid over the
area to be repaired. The electric blanket applies heat to that area
to cure the prepreg. The vacuum bag holds the electric blanket in
position over the repair area while at the same time applying a
compaction force to the prepreg.
[0011] Repairs using this approach are not however always
satisfactory. This is because the inconsistency of the heat
provided by the electric blanket leads to unreliability in the
curing. Also, the use of vacuum bag compaction is not very
effective in removing air from the prepreg so that the repaired
area is not necessarily void free. Additionally, it normally takes
a long amount of time to remove, repair, replace, and test the
damaged component on an aircraft. Finally, the majority of time in
using these methods typically involves waiting for the resin in the
composite material and filler to cure. If this cure cycle was
eliminated not only would there be a vast reduction in time but
also in the emissions and use of chemicals, eliminating the cleanup
and disposal of said chemicals.
[0012] A similar method of repair to such composite structures
generally entails a lightweight composite filler material being
inserted into the crater in a thixotropic state to protrude
slightly from the outer surface. The filler is then allowed to
harden and cure. It is then abraided flush with the surface of the
structure. A patch of fiber reinforced composite material in either
cured or more generally uncured state is then adhered to the
surface of the structure over the filled crater using a separate
adhesive and the patch is then bonded in position using both vacuum
and heat. The vacuum is normally applied using an airtight sheet of
material placed over the repair and temporarily sealed to the
structure using a bead of adhesive around its periphery. A vacuum
is then created under the sheet to try to ensure that any air
bubbles are expelled from underneath the patch and to ensure good
bonding. At the same time a heater blanket positioned inside or
outside of the vacuum bag will apply heat to the repair to effect
hardening and curing of the adhesive which is normally a curable
resin.
[0013] Multi-layered repair patches are also known in the art and
these repair patches have been used both for repairing holes in
drywall material as well as repairing holes in automobile bodies.
U.S. Pat. Nos. 5,075,149 issued to Owens et al. ("Owens"),
4,707,391 issued to Hoffmann ("Hoffmann '391") and 4,135,017 issued
to Hoffmann ("Hoffmann '017") are all directed to multi-layer
repair patches.
[0014] Owens discloses a three-layered patch with a metal plate
disclosed between two polyester sheets. The metal plate is held in
place between the two polyester sheets with a semi-solid adhesive
such as urethane. The semi-solid adhesive fixedly attaches the two
polyester sheets together as well as fixedly attaching the
reinforcing metal plate between the two sheets. Owens is not useful
for repairs which require the application of bonding material or
plaster to the repair patch because the bonding material or plaster
cannot readily pass through the mesh due to the presence of the
urethane adhesive. Additionally, the patch cannot be molded
quickly, on-site, without additional time and equipment.
[0015] Hoffmann '391 discloses a two-layer patch including a
perforated metal plate with an outer fiberglass mesh attached to
one side of the plate. A glue or adhesive coating is applied to the
surface of the plate that is attached to the surface to be repaired
and an additional adhesive coating is applied to the inward-facing
surface of the fiberglass mesh to attach the mesh to the metal
plate as well as to attach the mesh to the surface under
repair.
[0016] Hoffmann '017 also discloses a two-layer patch. An inner
metal plate is covered with adhesive that secures one surface of
the plate to the surface under repair. An outer plate cover is
laminated onto the exterior side of the metal plate by means of a
layer of adhesive applied to the inward-facing side of the plate
cover.
[0017] Both of these methods employ metal plates in the final patch
with limits the ability of these patches to be easily and quickly
molded to the damaged part on-site. Additionally, the use of metal
eliminates some of the weight saving advantages of a pure composite
repair patch.
[0018] Additionally, the repairs alone in these methods can take
approximately four hours or more to complete, mainly due to the
time necessary to allow curing of the filler and adhesive. When
taking into account the time to remove the damaged parts, mold the
patch to the damaged area, and replace the part, the time involved
increases. In addition, despite the use of vacuum equipment to
attempt to expel all air entrapped under the patch, the complete
absence of such entrapment cannot be guaranteed and non-destructive
testing may need to be carried out to ensure the structural
integrity of the repair. With aircraft downtime often running at
$US100,000.00 per hour it will be appreciated that enormous
potential savings are possible when employing the method of the
instant invention.
[0019] Additionally, if mass produced items, such as car hoods,
bumpers, and other manufactured parts are damaged, it is oftentimes
less expensive to replace the entire part than to repair it,
although such parts are often expensive themselves. Thus there is a
need for a cheap, quick, and effective method of repairing such
mass produced parts and for quickly and reliably repairing aircraft
and other high end parts.
[0020] 2. Epoxy Background
[0021] Shape memory materials are materials capable of distortion
above their glass transition temperatures (T.sub.gs), storing such
distortion at temperatures below their T.sub.g as potential
mechanical energy in the material, and release this energy when
heated again to above the T.sub.g, returning to their original
"memory" shape.
[0022] The first materials known to have these properties were
shape memory metal alloys (SMAs), including TiNi (Nitinol), CuZnAl,
and FeNiAl alloys. These materials have been proposed for various
uses, including vascular stents, medical guide wires, orthodontic
wires, vibration dampers, pipe couplings, electrical connectors,
thermostats, actuators, eyeglass frames, and brassiere underwires.
With a temperature change of as little as 10.degree. C., these
alloys can exert a stress as large as 415 MPa when applied against
a resistance to changing its shape from its deformed shape.
However, these materials have not yet been widely used, in part
because they are relatively expensive.
[0023] Shape memory polymers (SMPs) are being developed to replace
or augment the use of SMAs, in part because the polymers are light
weight, high in shape recovery ability, easy to manipulate, and
economical as compared with SMAs. SMPs are materials capable of
distortion above their glass transition temperature (T.sub.g),
storing such distortion at temperatures below their T.sub.g as
potential mechanical energy in the polymer, and release this energy
when heated to temperatures above their T.sub.g, returning to their
original memory shape. When the polymer is heated to near its
transition state it becomes soft and malleable and can be deformed
under resistances of approximately 1 MPa modulus. When the
temperature is decreased below its T.sub.g, the deformed shape is
fixed by the higher rigidity of the material at a lower temperature
while, at the same time, the mechanical energy expended on the
material during deformation will be stored. Thus, favorable
properties for SMPs will closely link to the network architecture
and to the sharpness of the transition separating the rigid and
rubbery states.
[0024] Heretofore, numerous polymers have been found to have
particularly attractive shape memory effects, most notably the
polyurethanes, polynorbornene, styrene-butadiene copolymers, and
cross-linked polyethylene.
[0025] In literature, SMPs are generally characterized as phase
segregated linear block co-polymers having a hard segment and a
soft segment, see for example, U.S. Pat. No. 6,720,402 issued to
Langer and Lendlein on Apr. 13, 2004. As described in Langer, the
hard segment is typically crystalline, with a defined melting
point, and the soft segment is typically amorphous, with a defined
glass transition temperature. In some embodiments, however, the
hard segment is amorphous and has a glass transition temperature
rather than a melting point. In other embodiments, the soft segment
is crystalline and has a melting point rather than a glass
transition temperature. The melting point or glass transition
temperature of the soft segment is substantially less than the
melting point or glass transition temperature of the hard segment.
Examples of polymers used to prepare hard and soft segments of
known SMPs include various polyacrylates, polyamides,
polysiloxanes, polyurethanes, polyethers, polyether amides,
polyurethane/ureas, polyether esters, and urethane/butadiene
copolymers.
[0026] The limitations with these are other existing shape memory
polymers lie in the thermal characteristics and tolerances of the
material. The T.sub.g of a material may be too low for the
conditions in which the system will reside, leading to the material
being incapable of activation. An example of such a situation is an
environment with an ambient temperature exceeding the transition
temperature of the SMP; such a climate would not allow the polymer
to efficiently make use of its rigid phase. Additionally, current
organic systems from which SMPs are synthesized are not capable of
operating in adverse environments that degrade polymeric materials.
An example of such an environment is low earth orbit, where intense
radiation and highly reactive atomic oxygen destroy most organic
materials.
[0027] Applications for a shape memory material capable of
withstanding these harsh conditions as well as higher thermal loads
include, but are not limited to; morphing aerospace structures and
space compatible polymers capable of self-actuation and
dampening.
[0028] As discussed in Langer, SMP can be reshaped and reformed
multiple times without losing its mechanical or chemical
properties. When the SMP described by Langer is heated above the
melting point or glass transition temperature of the hard segment,
the material can be shaped. This (original) shape can be memorized
by cooling the SMP below the melting point or glass transition
temperature of the hard segment. When the shaped SMP is cooled
below the melting point or glass transition temperature of the soft
segment while the shape is deformed, a new (temporary) shape is
fixed. The original shape is recovered by heating the material
above the melting point or glass transition temperature of the soft
segment but below the melting point or glass transition temperature
of the hard segment. The recovery of the original shape, which is
induced by an increase in temperature, is called the thermal shape
memory effect. Properties that describe the shape memory
capabilities of a material are the shape recovery of the original
shape and the shape fixity of the temporary shape.
[0029] Conventional shape memory polymers generally are segmented
polyurethanes and have hard segments that include aromatic
moieties. U.S. Pat. No. 5,145,935 to Hayashi, for example,
discloses a shape memory polyurethane elastomer molded article
formed from a polyurethane elastomer polymerized from of a
difunctional diisocyanate, a difunctional polyol, and a
difunctional chain extender.
[0030] Examples of additional polymers used to prepare hard and
soft segments of known SMPs include various polyethers,
polyacrylates, polyamides, polysiloxanes, polyurethanes, polyether
amides, polyurethane/ureas, polyether esters, and
urethane/butadiene copolymers. See, for example, U.S. Pat. No.
5,506,300 to Ward et al.; U.S. Pat. No. 5,145,935 to Hayashi; and
U.S. Pat. No. 5,665,822 to Bitler et al.
[0031] Several physical properties of SMPs other than the ability
to memorize shape are significantly altered in response to external
changes in temperature and stress, particularly at the melting
point or glass transition temperature of the soft segment. These
properties include the elastic modulus, hardness, flexibility,
vapor permeability, damping, index of refraction, and dielectric
constant. The elastic modulus (the ratio of the stress in a body to
the corresponding strain) of an SMP can change by a factor of up to
200 when heated above the melting point or glass transition
temperature of the soft segment. Also, the hardness of the material
changes dramatically when the soft segment is at or above its
melting point or glass transition temperature. When the material is
heated to a temperature above the melting point or glass transition
temperature of the soft segment, the damping ability can be up to
five times higher than a conventional rubber product. The material
can readily recover to its original molded shape following numerous
thermal cycles, and can be heated above the melting point of the
hard segment and reshaped and cooled to fix a new original
shape.
[0032] Recently, SMPs have been created using reactions of
different polymers to eliminate the need for a hard and soft
segment, creating instead, a single piece of SMP. The advantages of
a polymer consisting of a single crosslinked network, instead of
multiple networks are obvious to those of skill in the art. The
presently disclosed invention uses this new method of creating
SMPs. U.S. Pat. No. 6,759,481 discloses such a SMP using a reaction
of styrene, a vinyl compound, a multifunctional crosslinking agent
and an initiator to create a styrene based SMP.
[0033] The industrial use of SMPs has been limited because of their
low transition temperatures. Epoxy resins are a unique class of
material which possesses attractive thermal and mechanical
properties. Epoxy resins polymerize thermally producing a highly
dense crosslinked network. Typically these thermoset epoxy networks
are rigid and have low strain capability. By altering this network
system, it is possible to produce a lightly crosslinked network
still possessing many of the original materials properties but with
the functionality of a shape memory polymer. Currently there is no
epoxy based SMP available.
[0034] High temperature, high toughness thermoset resins with shape
memory characteristics are not currently available. Other high
temperature, high toughness, thermoset resins do not have shape
memory. Typically, epoxy resins do not exhibit the shape memory
effect mentioned above. In order to exhibit this shape memory
effect epoxy resins must be crosslinked in a manner different from
normal epoxy resins. It is this new method of crosslinking epoxy
resins that is highly sought after.
[0035] It is the object of the present invention to provide a
preformed and cured patch and a method to quickly and cheaply
permanently repair any number of items with composite materials
which retain similar or greater mechanical properties of the parts
repaired. Another object is to provide a method for quickly and
cheaply joining two parts together in order to form a larger part
which retains similar mechanical properties of the original parts.
These and other objects of the present invention will become
apparent from the following specification.
SUMMARY OF THE INVENTION
[0036] According to a first aspect of the invention there is
provided a patch of fiber reinforced shape memory polymer resin
composite material for attachment to a surface of a fiber
reinforced plastics composite, metal, wood, or plastic structure
over an area of damage to the structure, the patch defining an
outer surface, a bonding surface opposed thereto and a peripheral
edge, the patch including fiber reinforcement and shape memory
polymer resin as the matrix material with said matrix material
being in a substantially final state of hardness. The patch may
conveniently include a final protective coating applied to the
outer surface thereof. The process according to the first aspect is
primarily to be used for temporary or cosmetic repair of
manufactured parts.
[0037] This patch and process reduces the time to repair composite
parts and other material and eliminates the creation of volatile
components that must not be released into the environment as per
EPA requirements during the repair process. The combination of both
of these factors makes this process highly transferable into mass
production of patches for high-performance composites at an
affordable price and for the mass production of patches for use in
lower performance items as well. Additionally the patch can be
molded on site by hand, without the use of significant amounts of
equipment or special orders to pre-mold the composite patch to
match the specific damaged area. Another benefit is that by using
shape memory polymer as the resin the damaged part does not need to
be removed from the larger component, for example removing the wing
from the airplane, in order to mold the patch and repair the
damage.
[0038] The patch, according to the first aspect of the invention,
will typically be in some predetermined memorized geometric shape,
typically a flat square or rectangle, but can be in any desired
preformed shape. In order to mold the patch to the desired shape,
the shape memory polymer resin is activated, typically using heat
to raise the temperature of the shape memory polymer resin above
its activation temperature or light to activate the shape memory
polymer, at which point the shape memory polymer resin, and the
entire composite part, become soft and can be mechanically
deformed, typically by hand, to the desired shape. Once the
composite part has cooled below the activation temperature of the
shape memory polymer resin or has been deactivated by light, the
composite part will retain the new, deformed shape, and can be
bonded to the damaged part with adhesives.
[0039] Bonding the patch to the damaged part is typically
accomplished with some form of adhesive. While some adhesives may
require heat curing, choosing the correct shape memory polymer to
use as the resin matrix will prevent this curing from causing the
composite material to become soft again, and lose its molded shape,
especially if using a light activated shape memory polymer resin.
This presents little difficulty as curing the adhesive may include
raising the temperature thereof to a temperature less than
substantially 100.degree. C. where there is a large availability of
shape memory polymers whose activation temperatures are above
100.degree. C. It will be appreciated that adhesive cure
temperatures could be as high as 180.degree. C., but repairs in the
field are likely to be more sound if a lower curing temperature
resin is used to avoid the possibility damage to the composite
patch or further damage to the part being repaired. Additionally,
certain formulations and types of shape memory polymer can be made
with a transition temperature well in excess of 180.degree. C. such
that high cure temperatures for most adhesives are of little
concern. Where the adhesive is a curable resin the method may
include the step of curing the adhesive for a period less than one
hour. Such a short curing time can dramatically shorten the overall
repair time according to the method of the invention, especially
when only the adhesive and not the resin in the patch requires
curing. Furthermore, some adhesives, such as pressure sensitive
adhesives, require no curing, thus eliminating this concern.
[0040] Manufacture of the patch according to the invention includes
creating a cured composite patch within a shape memory polymer
resin matrix. The patch is preformed to a predetermined, memorized
shape. The composite patch may be of any required thickness and any
suitable number of layers of fibrous material within a shape memory
polymer resin matrix, one or more, in order to give the required
structural strength in particular circumstances.
[0041] It will be appreciated that when carrying out the repair
method of the invention all the normal preparatory work may be done
to the damaged area in the usual way, for example thorough drying
thereof, abrasion and cleaning of the surface to be repaired and
debris and sharp edge removal. Best results for the repair are
likely to be obtained when the liquid adhesive is painted onto all
contact areas with a brush or the like to ensure good adhesion.
[0042] The method of the invention thus enables the use of the
patch according to the first aspect of the invention in a manner
which avoids the use of a separate filler material which must be
separately hardened and abraded flush with the surface to be
repaired prior to the application of the patch thereto with, again,
a separate adhesive. Additionally, the method of the inventions
enables use of a patch without any curing of the resin employed in
the composite patch. Overall time savings for repairs according to
the method of the invention are expected to be at least three hours
over prior art methods.
[0043] A second aspect of the invention allows for the permanent
repair of manufactured parts including high strength applications
of airplane parts and boat hulls. According to the second aspect of
the invention there is provided a patch of fiber reinforced shape
memory polymer resin composite material for attachment to a surface
of a fiber reinforced plastics composite, metal, wood, or plastic
structure over an area of damage to the structure, the patch
defining an outer surface, a bonding surface opposed thereto and a
peripheral edge, the patch including fiber reinforcement and shape
memory polymer resin as the matrix material with said matrix
material being in a substantially final state of hardness. The
patch may conveniently include a final protective coating applied
to the outer surface thereof.
[0044] A second aspect of the invention allows for the quick and
easy permanent repair of composite parts or other material.
According to the second aspect a part has been damaged and requires
permanent repair. Typically the damaged section will have damage to
the composite part and potentially damage to the underlying layers.
Since the majority of time in repairing composite parts and other
manufactured components with composite patches involves the curing
of the composite eliminating this step will significantly reduce
the amount of time and effort spent in repair. It is to be
appreciated that the initial steps of creating a seamless
transition phase between the damaged and undamaged sections of the
part can be accomplished by normal means. Additionally, repair to
the underlying filler, foam, or other material can be accomplished
in a normal means.
[0045] Once the damaged area has been removed and a transition area
has been created, smoothed, machined, cleaned, and otherwise
prepared for repair, a preformed composite patch within a shape
memory polymer resin matrix can be used. After activating the
patch's shape memory polymer with either heat or light (or other
electromagnetic radiation), the patch is then formed and molded
into the damaged area either manually or with other means of
assistance. Once the composite patch has been molded to the damaged
area deactivate the shape memory polymer by letting it cool below
its transition temperature or exposing it to light or other
electromagnetic radiation. When the patch is hard, simply bond the
composite material to the damaged part, clean and machine the patch
to remove any excess patch material to ensure it is flush and level
with the damaged part, and sand, finish, and coat if necessary with
standard methods.
[0046] This patch and process reduces the time of composite repair
and eliminates the creation of VOC (volatile components that must
be not be released into the environment as per EPA requirements)
during the repair process. The combination of both of these factors
makes this process highly transferable into mass production of
high-performance composites at an affordable price. Additionally,
it is to be appreciated that this method of repair requires no
curing time for the composite patch and eliminates the need to wait
for any layer to cure before proceeding with the repair, thus
significantly reducing the time to permanently repair a damaged
part.
[0047] Another aspect of the invention allows the joining of two
parts to create a single, larger part without the use of expensive
welding, molding, or other methods that use expensive chemicals or
require other controls to prevent discharge of chemicals and
vapors. By placing two or more parts of similar or dissimilar shape
or size in juxtaposition and using the patch to connect the parts,
a larger part can be created. Once the patch is soft from
activation of the shape memory polymer resin is can be molded to
ensure a tight connection between two parts, even if the parts are
of significant geometries. Once bonded to the individual parts, the
larger part can be used.
[0048] Another embodiment is the repairing of material with a piece
of shape memory polymer. This method is best used in processes
where high strength is less preferable to other desires. This is
accomplished in a manner similar to the composite patch.
[0049] Additional embodiments of the present invention include the
use of other means of molding the composite patch and bonding said
patch to the damaged part.
[0050] The epoxy based shape memory polymers (SMPs) that are
described in this application are well adapted for industrial use
in making SMP Molds, as set forth in U.S. Pat. No. 6,986,855 issued
to Hood and Havens on Jan. 17, 2006, or for use in other industrial
and manufacturing processes.
[0051] As previously stated, SMPs are a unique class of polymers
that can harden and soften quickly and repetitively on demand. This
feature provides the ability to soften temporarily, change shape,
and harden to a solid structural shape in various new highly
detailed shapes and forms.
[0052] SMPs have a very narrow temperature span in which they
transition from hard to soft and back again. Additionally it is
possible to manufacture the SMP such that the activation of the SMP
occurs over a very narrow temperature range, typically less than 5
degrees Celsius. This narrow glass transition temperature (T.sub.g)
range is a key property that allows a SMP to maintain full
structural rigidity up to the specifically designed activation
temperature. SMPs possessing these properties, such as described
here, are particularly useful in applications that will change
shape at some stage but need the structure to stay rigid at higher
operating temperatures, typically greater than 0.degree. C., such
as morphing aerospace structures and SMP molding processes.
[0053] In accordance with the present invention, the SMPs disclosed
are a reaction product of at least one reagent containing two
active amino-hydrogen or two active phenolic-hydrogen with at least
one multifunctional cross linking reagent which contains at least
three or more active amino- or phenolic-hydrogen or is a reagent
containing at least three glycidyl ether moieties which is then
further mixed with at least one diglycidyl ether reagent whereupon
the resulting mixture is cured and has a glass transition
temperature higher than 0.degree. C. This reaction creates
crosslinking between the monomers and polymers such that during
polymerization they form a crosslinked thermoset network.
[0054] Therefore it is an object of the present disclosure to
provide an epoxy-based polymer containing a crosslinked thermoset
network which exhibits the shape memory effect described above
which is useful in making the shape memory polymer patches.
[0055] Other objects, features and advantages of the invention will
be apparent from the following detailed description taken in
connection with the examples and accompanying drawings and are
within the scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a perspective view of a typical pipe with a
damaged area.
[0057] FIG. 2 is a perspective view of a shape memory polymer
composite patch.
[0058] FIG. 3 is a perspective view of a typical pipe with damage
repaired by the shape memory polymer composite patch.
[0059] FIG. 4 is a perspective view of a typical pipe with damage
at or near a wall, floor, or ceiling.
[0060] FIG. 5 is a perspective view of a typical pipe with damage
at or near a wall, floor, or ceiling repaired by the shape memory
polymer composite patch.
[0061] FIG. 6 is a perspective view of two short pieces of pipes
that are to be joined together.
[0062] FIG. 7 is a perspective view of the single long pipe created
from the two shorter pipes joined by the shape memory polymer
composite patch.
[0063] FIG. 8 is a perspective view of two flat pieces that are to
be joined together.
[0064] FIG. 9 is a perspective view of a single piece created from
the two smaller pieces joined by two sheets of shape memory polymer
composite patch.
[0065] FIG. 10 is a perspective view of a section of a boat that
has a damaged area.
[0066] FIG. 11 is a sectional view of the same damaged area showing
the fiberglass coating and damaged area.
[0067] FIG. 12 is a perspective view of the shape memory polymer
composite patch with slightly angled sides for a better fit of the
patch.
[0068] FIG. 13 is a sectional view of the damaged area after the
damage area has been removed and a transition area from undamaged
to damaged area has been created.
[0069] FIG. 14 is a sectional view of the of the damaged area ready
for repair and the soft composite patch that is ready for molding
into the damaged area.
[0070] FIG. 15 is a sectional view of the of the boat hull with the
composite patch essentially repairing the damaged area with some
excess patch material extending beyond the original hull.
[0071] FIG. 16 is a sectional view of the machined and sanded patch
so that the patch and the original hull are flush.
[0072] FIG. 17 is a perspective view of the hull fully repaired by
the shape memory polymer composite patch.
DETAILED DESCRIPTION OF THE INVENTION
SMP Patch
[0073] Referring to the drawings in greater detail, the method of
the invention herein is directed to fabricating and using a
composite patch with a Shape Memory Polymer (SMP) resin matrix or
other shape memory material in the manufacture of castable
composite parts.
[0074] Examples 1 and 2 below describe the exemplary methods of
creating pre-form shape memory polymer (SMP) composite parts. In
general, the preferred SMP is a styrene copolymer based SMP as
disclosed in U.S. Pat. No. 6,759,481, however, other types of SMPs
such as cyanate ester, polyurethane, polyethylene homopolymer,
styrene-butadiene, polyisoprene, copolymers of stearyl acrylate and
acrylic acid or methyl acrylate, norbornene or
dimethaneoctahydronapthalene homopolymers or copolymers, malemide
and other materials are within the scope of the present
invention.
Example 1
[0075] A polymeric reaction mixture was formulated by mixing vinyl
neodecanoate (10%), divinyl benzene (0.8%), and styrene (85.2%) in
random order to yield a clear solution. Benzoyl peroxide paste (4%)
which is 50% benzoyl peroxide, was then added to the resulting
solution (all composition % are by weight). The resulting solution
was kept cold in a refrigerator before use. To prepare the shape
memory polymer resin matrix composite sheet, a piece of 3D weave
carbon fiber is placed on a glass sheet, ensuring that there are no
stray fibers and the carbon fiber piece is smooth. Next, pour some
of the polymeric reaction mixture onto the carbon fiber. Use a
plastic squeegee or plastic spreader to spread the resin evenly
over the entire surface of the fabric. Thoroughly remove air
bubbles and straighten the fabric. Place bleeder and breather
fabric on top of the resin soaked carbon fiber. Then place the
entire system in a high temperature vacuum bag with a vacuum valve
stem and apply vacuum thoroughly, ensuring that there are no leaks.
Cure the composite part with the following cycle: 1) A one-hour
linear ramp to 75.degree. C. in an oven, autoclave, or other form
of controlled heating device; 2) A three-hour hold at 75.degree.
C.; 3) A three-hour linear ramp to 90.degree. C.; 4) A two-hour
linear ramp to 110.degree. C.; 5) A one-hour linear ramp to
20.degree. C. After curing, remove from oven and allow to cool.
Remove vacuum bag, bleeder fabric, breather fabric, and glass
plates from composite.
Example 2
[0076] A polymeric reaction mixture was formulated by mixing vinyl
neodecanoate (10%), divinyl benzene (0.8%), and styrene (55.2%) in
random order to form a colorless solution. Polystyrene granules
(30%) were then added to the resulting solution. The resulting
mixture was then allowed to sit at room temperature with occasional
stirring until all the polystyrene granules were dissolved to give
a clear, viscous solution. Benzoyl peroxide (4%) which is 50%
benzoyl peroxide was then added to the resulting solution (all
composition % are by weight). The resulting polymeric reaction
mixture is continually stirred at or near 25.degree. C., not to
exceed 30.degree. C. until a clear solution is achieved which can
take 2 hours or more. The resulting solution is kept cold in a
refrigerator before use. To prepare the shape memory polymer resin
matrix composite sheet, a piece of 3D weave carbon fiber is placed
on a glass sheet, ensuring that there are no stray fibers and the
carbon fiber piece is smooth. Next, pour some of the polymeric
reaction mixture onto the carbon fiber. Use a plastic squeegee or
plastic spreader to spread the resin evenly over the entire surface
of the fabric. Thoroughly remove air bubbles and straighten the
fabric. Place bleeder and breather fabric on top of the resin
soaked carbon fiber. Then place the entire system in a high
temperature vacuum bag with a vacuum valve stem and apply vacuum
thoroughly, ensuring that there are no leaks. Cure the composite
part with the following cycle: 1) A one-hour linear ramp to
75.degree. C. in an oven, autoclave, or other form of controlled
heating device; 2) A three-hour hold at 75.degree. C.; 3) A
three-hour linear ramp to 90.degree. C.; 4) A two-hour linear ramp
to 110.degree. C.; 5) A one hour linear ramp to 20.degree. C. After
curing, remove from oven and allow to cool. Remove vacuum bag,
bleeder fabric, breather fabric, and glass plates from
composite.
[0077] To achieve more than one fabric layer simply soak two or
more layers of fabric in the shape memory polymer and stack on top
of each other. The use of other fabrics such as carbon nano-fibers,
spandex, chopped fiber, random fiber mat, fabric of any material,
continuous fiber, fiberglass, or other type of textile fabric can
be used to replace carbon fiber in the above examples. In Example 2
it is essential that while mixing after the addition of benzyl
peroxide that the temperature of the resin be maintained below
30.degree. C. as the mixture may become hot and explosive. Mixing
in a cold water or ice bath ensures the temperature will not exceed
30.degree. C. It can take two hours or more to fully mix.
[0078] Additionally, once cured, the shape memory polymer composite
can be deformed for easy storage, shipping, or immediate use. If
deformed for storage or shipping, simply activating the shape
memory polymer resin will restore the composite part to its
original, memorized shape.
[0079] The method of repairing all types of components and the
composite patch joining system all utilize the same common
features. The following description therefore relates to all of
these features.
[0080] FIG. 1 shows a typical pipe, 2, with a crack, 4. FIG. 2
shows a flat, essentially square piece of shape memory polymer
resin composite, 6. After activation, the shape memory polymer
resin in 6 will become soft and can be easily molded to a variety
of shapes. In the present example, a technician, wearing gloves,
can easily mechanically deform 6 to cover the crack 4 and follow
the curvature of the pipe 2 as seen in FIG. 3 where the deformed
patch, 8, covers the crack and essentially replicates the shape of
the pipe. After bonding the patch to the pipe with an adhesive the
pipe is repaired and can continue with normal operations.
[0081] This process of patching various holes, cracks, leaks, and
other damages is not limited to simple shapes. FIG. 4 shows a
larger hole, 12, at the joint between a pipe, 10, and the ground,
wall, or ceiling. Again, after activation, the shape memory polymer
resin in 6 will become
[0082] Additionally these repairs can be conducted not only by
composite material but also by pure shape memory polymer resins
which undergo the same activation, deformation, and bonding as seen
in the above description.
[0083] Another embodiment of the invention is the ability to join
two or more parts together easily in order to form larger parts.
FIG. 6 shows two short pipes, 16 and 18. If it is desired to create
a larger pipe from these two it may be very difficult or time
consuming to weld or otherwise join these pipes. Using a composite
patch or patch of shape memory material a single pipe can easily be
made out of 16 and 18 as shown in FIG. 7. After placing 16 and 18
end to end in order to form a single pipe, the shape memory polymer
resin composite or pure shape memory polymer patch is activated and
deformed around the pipe in order to effect a joining of the pipes
with the deformed patch, 20. After bonding the patch to the pipes a
new long pipe, 22, is created. This entire process can be quick and
reduces the emission and use of typically bonding or welding tools
that create fire and chemical hazards upon use.
[0084] This embodiment is not limited to pipes and can be used to
join other geometric shapes together. FIG. 8 shows flat panels, 24
and 26, that may joined. FIG. 9 shows that with the use of two
patches, 28 and 30, the flat panels can quickly be joined without
deforming the patches or deforming the panels so that patches can
match the minor changes in the shape of the boards. After bonding
the patches to the panels, a new larger panel, 32, is created.
[0085] Another exemplary embodiment provides a means of permanent
repair for manufactured parts that can significantly reduce the
time required for repair. In FIG. 10 there is shown a section of a
boat hull that has suffered damage, 38. The boat hull is made of a
fiberglass outer layer, 36, and a filler or foam inner layer, 34.
FIG. 11 shows a sectional view of the damaged hull, 38, with the
outer fiberglass layer, 36, damaged from a piece of debris. While
no damage is shown to the filler or foam inner layer, 34, if such
damage present, this damage could be repaired with normal methods.
FIG. 12 shows a composite patch material, 40, made by the process
of Example 1 above except that fiberglass, instead of carbon fiber,
is used as the fibrous material. In order to repair the damaged
area, 38, shown in FIGS. 10 and 11, the damaged area must be
removed, as shown at 42 in FIG. 13, and a clean, smooth transition
area is created, shown as 43. As shown in FIG. 13 the boat hull has
been machined to create transition regions, 43, on all sides of the
damaged area from undamaged fiberglass composite structure to the
area to be repaired, 42.
[0086] Once the surface has been prepared for repair using normal
methods, the shape memory polymer composite patch, 40, is activated
by raising its temperature above its T.sub.g. As shown in FIG. 14
the composite patch is then initially deformed, 44, into a shape
that will make it easier to mold into the damaged area, 42, and the
transition area, 43. While the temperature of the composite patch
is above its T.sub.g, the composite patch is formed and molded into
the damaged area, 42, and surrounded by the transition area, 43, so
that the entire damaged area and transition area are essentially
covered by the patch. As shown in FIG. 15 the now molded composite
patch, 46, has been placed so as to essentially cover the entire
damaged area. Additionally, the molded patch, because of its soft
and pliable state while heated, is able to fill in most gaps and
crevices and completely replicate the entire damaged area and
machined transition area. As previously noted, this process
requires no cure time as the composite patch is already in an
essentially cured state. Once the patch has been molded to the
desired area, simply allow the patch to cool below its T.sub.g to
return the patch to a hard, rigid state. This process should only
take a few minutes.
[0087] The composite patch can be bonded to the original part with
a variety of systems discussed below. Once cooled and bonded to the
original part it is possible that there will be some excess
material that will rise above and/or not be flush with the
original, undamaged surface, as shown at 47 in FIG. 15. This excess
material can be removed through sanding or other machine processes
as shown in FIG. 16 where the final surface, 48, of the composite
patch, 46, is now flush with the original part. FIG. 17 shows a
final view of the patch, 50, used to fully repair the damaged area,
38, in FIG. 10. The composite patch is now flush with the surface
and may be coated or painted as desired. It is to be appreciated
that these repairs can be conducted not only by composite material
but also by pure shape memory polymer resins which undergo the same
activation, deformation, and bonding as seen in the above
descriptions. It is also to be appreciated that this method of
permanent repair can also be used for airplane parts, car parts,
and any other manufactured part that can be repaired using
composite material.
[0088] In order to bond the composite patch to a variety of
systems, the adhesive must be chosen very carefully. There are a
variety of commercially-available adhesive systems for use in
bonding shape memory polymer composite patches to different
substrates. The wide range of adhesives will aid in developing
different patch systems for different applications. Some adhesives
are aerospace compatible, while others can only be used for ground
applications or mass produced items. Cryogenic compatible adhesives
are also available for use in repairing cryogenic pipes and tanks.
These adhesives can be divided into two categories: thermally cured
adhesives and pressure sensitive adhesives. The thermally cured
adhesives chosen can be cured at or above the transition
temperature of the shape memory polymer composite as pressure and
heat are applied to cure the adhesive, and the patch is soft and
easily formed around the area to be patched. The pressure sensitive
adhesives are effective for quick repairs in sealing spaces that
contain different environments such as the inside of pressure
vessels and gas or liquid conduits. These adhesives allow for a
quick "bandage-type" approach until a more permanent solution could
be achieved. The following adhesives could be used for various
applications, but is not intended to limit adhesives within the
scope of the present invention to only those listed below:
Thermally Cured Adhesives
[0089] LORD Corporation Products [0090] 310 A/B Epoxy Adhesive
[0091] 7542 A/E Urethane Adhesive
[0092] 3M Products [0093] Scotch-Weld AF 563K Film Adhesive [0094]
Scotch-Weld AF 163-2 Film Adhesive [0095] Scotch-Weld EC 3333 B/A
2-Part Paste Adhesive [0096] Scotch-Weld EC 3448 Paste Adhesive
(1-Part)
[0097] Loctite Products [0098] Hysol.RTM. EA 9309.3 NA Epoxy Paste
Adhesive [0099] Hysol.RTM. 615 [0100] Hysol.RTM. U-05FL [0101]
Hysol.RTM. EA 9361 Epoxy Paste Adhesive [0102] Hysol.RTM. EA 9628
Epoxy Film Adhesive [0103] Hysol.RTM. EA 9695 Epoxy Film Adhesive
[0104] Hysol.RTM. EA 9696 Epoxy Film Adhesive
Pressure Sensitive
[0105] 3M Products [0106] 9244 Structural Bonding Tape [0107] 468
MPR Structural Bonding Tape [0108] 9485 PC High-Performance
Adhesive Transfer Tape
[0109] Budnick Converting, Inc. Products [0110] P02--Multi-purpose
Double-Coated Splicing & Mounting [0111] 1198--UHA Adhesive
Transfer [0112] P50--Multi-purpose Double-Coated Cloth Tape
[0113] The thermally cured adhesives can be applied by: 1) forming
the shape memory polymer composite patch around the area to be
bonded (without adhesive); 2) applying adhesive to the patch; and
then 3) bonding the preformed patch to the damaged area through
thermal cure. This approach is the easiest and cleanest method for
using paste-type adhesives. This method may be enhanced by using
vacuum pressure during thermal cure and choosing an adhesive that
has a cure temperature above the transition temperature of the
shape memory polymer composite used for the patch. This would allow
for a more intimate interface between the patch and the substrate
during cure. This helps promote distributed load transfer through
the adhesive.
[0114] Pressure adhesives are applied to the shape memory polymer
composite patch manually with the backing paper left intact. When
repair is desired, 1) the patch/adhesive combination is heated
above the transition temperature of the composite patch, 2) the
backing paper is removed and 3) the patch is formed manually or
with assistance and adhered simultaneously to the substrate. This
method of adhesive application prior to use enables very fast
repair scenarios. Additionally for light or electromagnetic
radiation activated shape memory polymer composites, the patch
adhesive combination is activated by application of said
electromagnetic radiation, the patch is formed manually or with
other mechanical assistance to the substrate and deactivated with
electromagnetic radiation.
[0115] The following are examples of the process of bonding shape
memory polymer composites to substrates according to all aspects of
the invention:
Example 3
[0116] In order to bond a shape memory polymer composite patch to
fiberglass, the area around the damaged portion of a part or the
area near the portion of the part to be joined to another, the
applicable area is scuff sanded and solvent wiped to ensure a
clean, smooth bonding surface. Additionally, scuff sand and solvent
wipe the side of the patch to be bonded to the substrate. Using
3M's 9485 PC High-Performance Adhesive Transfer Tape, apply the
tape to the patch manually leaving the backing on the adhesive.
Using the patch from Example 1 heat the patch above its transition
temperature in an oven which is at or near 90.degree. C. Remove the
patch/adhesive from the oven, peel away the adhesive backing and
form patch to fiberglass surface manually or with assistance of a
vacuum pad or bagging.
Example 4
[0117] In order to bond a shape memory polymer composite patch to
stainless steel the area around the damaged portion of a part or
the area near the portion of the part to be joined to another is
scuff sanded and solvent wiped to ensure a clean, smooth bonding
surface. Additionally scuff sand and solvent wipe the side of the
patch to be bonded to the substrate to ensure a smooth bonding
surface. Apply a thin, even layer of Loctite HYSOL U05-FL paste
adhesive to repair area on stainless steel. Using the patch from
Example 1 heat the patch above its transition temperature. Form
patch to repair surface manually or with a heating blanket using
vacuum pressure. Cure adhesive according to manufacturers
recommendations using temperature controller connected to the
heating blanket or other method. Remove vacuum blanket after
cure.
[0118] The bonding of the shape memory polymer composite patch can
be done to various other substrates, metal cans, car fenders, other
composite parts, using the method of Example 3 above. The methods
described above are useful and one method should be chosen over the
other method depending on the application. Thermally cured
adhesives should generally be used for higher strength applications
where time-to-repair is less critical such as airplane parts,
load-bearing structural parts, and other parts with high strength
or other mechanical properties as described in Example 4 above.
Pressure sensitive adhesives should generally be used for lower
strength applications where time-to-repair is more critical or the
cost or strength is not as important such as leaking pipes or
simple cosmetic repairs. After bonding with the correct adhesive
and composite patch, the repaired part may be used normally. This
includes flowing liquids or gasses through pipes at normal
operating temperatures and pressures.
[0119] Because of the properties inherent in shape memory polymers,
composites utilizing shape memory polymer as the resin matrix can
be temporarily softened, reshaped, and rapidly hardened in
real-time to function in a variety of structural configurations.
They can be fabricated with nearly any type of fabric, and creative
reinforcements can result in dramatic shape changes in functional
structures and they are machinable.
[0120] Therefore, it can readily be seen that the present invention
provides a quick and easy way to utilize composite and shape memory
polymer technology to create a patch that has the flexibility of
duct tape with the performance of composites and similar metal
substances.
[0121] It is therefore apparent that one exemplary embodiment of
the invention provides a method for repairing manufactured parts of
the type having a damaged area thereof. A repair material is
preformed into a desired shape. The repair material may comprise,
for example, a shape memory polymer. The shape memory polymer is
activated so that the preformed repair material becomes soft, and
it is then deformed into a shape adapted for the repair function.
The shape memory polymer is then deactivated while maintaining the
polymer in its deformed state. Thereafter, the deformed shape
memory polymer is bonded to the damaged area of the manufactured
part.
[0122] The repair material may comprise a composite material formed
from at least one layer of fibrous material in combination with a
shape memory polymer. In one form, the fibrous material may be
embedded within the shape memory polymer or, the fibrous material
can be impregnated with the shape memory polymer.
[0123] The fibrous material may be chosen from carbon nanofibers,
carbon fiber, spandex, chopped fiber, random fiber mat, fabric of
any material, continuous fiber, fiberglass, or other types of
textile fibers, yarns, and fabrics. For example, the fibrous
material may be present in the form of a flat woven article, a
two-dimensional weave, or a three-dimensional weave.
[0124] The shape memory polymer may be selected from a host of
polymer types including styrene, cyanate esters, maleamide
polymers, epoxy polymers, or vinyl ester polymers. In some cases,
the shape memory polymer will be a thermoset resin.
[0125] The repair material may include a thermal energy generation
means embedded therein. Such thermal energy generation means may
comprise, for example, thermally conductive fibers or electrical
conductors.
[0126] In another exemplary embodiment of the invention, activation
of the shape memory polymer is achieved by heating the polymer
above its transition temperature. The heating may, for example, be
effected by inductive heating, hot air, or by heat lamps.
Additionally, when the repair material comprises a thermal energy
generation means embedded therein, it may be activated by applying
electrical current to the thermal energy generation means.
[0127] In yet another exemplary embodiment of the invention,
activation of the shape memory polymer may be achieved by
application of electromagnetic radiation such as in the form of
visible light or ultraviolet light.
[0128] The deformation step may be achieved via mechanical means
such as by pressing in a press mold or by extruding the material
through a rolling die mold.
[0129] In one exemplary embodiment of the invention, the shape
memory polymer is deactivated by reducing the temperature thereof
to below its activation temperature. This can be accomplished while
the polymer is being press molded so that during the press molding,
the polymer is maintained at a temperature below its activation
temperature. Further, the deactivation of the shape memory polymer
may be achieved by application of electromagnetic radiation such as
visible light or ultraviolet light thereto.
[0130] The manufactured part may be composed of any material, such
as metal, wood, plastic, glass, or in itself may be a composite
part or similar material. The bonding step in accordance with the
invention may be achieved via a host of conventional means such as
via thermally cured adhesives or pressure sensitive adhesives.
[0131] In addition to shape memory polymers, other shape memory
materials such as shape memory alloys may be mentioned as being
effective.
[0132] Another aspect of the invention comprises joining a
plurality of parts together via use of the shape memory materials.
Here, the parts are juxtaposed so that at least one joint or
joinder area is formed. A preformed shape memory material such as a
shape memory polymer is provided and activated. The shape memory
material is then applied to the joint or joinder area and deformed
into a desired shape. The shape memory material is deactivated
while maintaining it in its deformed shape. The deformed shape is
then bonded to the joint area to effect joinder of the parts
together.
[0133] Epoxy SMP
[0134] Generally, shape memory polymers (SMPs) are comprised of two
essential components; the back bone polymer, which is comprised of
monomeric constituents that undergo polymerization to produce
polymers possessing specific glass transition temperatures
(T.sub.gs), and a crosslinking agent. The mixture of monomers can
be formulated so that the glass transition temperatures can be
tuned to meet different operational needs for specific
applications.
[0135] In general, shape memory polymer (SMP) can be made with any
polymer system by introduction of a small, but specific amount of
crosslinking agent into the material. However, the exact chemistry
to introduce this crosslinking into the material varies with
different polymers. In the case of epoxy SMP, this can be achieved
by using amine and phenol reagents that form linear polymer chain
with the diepoxide (e.g. Bisphenol A diglycidyl ether, which is the
most commonly available epoxy resin) and cured with small amount of
crosslinking multifunctional amine, phenol or glycidyl ether
reagents. In contrast, common epoxy resins are normally cured with
stoichiometric amount of diamine crosslinking reagents. The use of
these amine reagents ensures there is enough flexibility between
the crosslinking points within the polymer materials, and this
flexibility or mobility is what imparts the materials with shape
memory properties.
[0136] The crosslink density is crucial in controlling the
elongation and transition temperature ("T.sub.g") of epoxy SMP. For
most applications, the highest crosslink density possible is
desired in order to maximize the T.sub.g and thereby the use of the
material. A relatively low crosslink density is required in SMP
materials to allow movement of epoxy chains, increasing elongation
and shape memory properties. However, if too few crosslinkers are
present, the material behaves as a thermoplastic, irreversibly
deforming at elevated temperatures. Therefore one must be careful
to find the optimum crosslink density that allows for maximum
elongation with full retention of original form.
[0137] Crosslink density is defined as the number of moles of
crosslinker divided by the total moles of the resin system. In
formulation, balanced stoichiometry must be used, meaning that all
reactive epoxide groups must have one active amino-hydrogen or
phenolic-hydrogen to react with. Therefore, the monomers containing
two active amino-hydrogen or phenolic-hydrogen serve as chain
extenders while the multifunctional-amines, phenols, or glycidyl
ethers serve as crosslinkers. In formulation, two equations must be
solved simultaneously: one balancing all reactive groups and the
other defining the crosslink density. Depending on the curing
agents and epoxies used, crosslink densities ranging from 0.2 mol %
to 10 mol % based on total number of moles.
[0138] Dissolving thermoplastics in epoxy resins is often performed
to increase toughness. Often, solvents or kneading machines are
used to adequately blend thermoplastics and epoxy resins. One
approach that can be taken with epoxy SMP is in situ
polymerization, where a thermoplastic modifier is polymerized
during the cure of the epoxy resin. The thermoplastic polymerizes
via a free-radical addition mechanism, while the epoxy polymerizes
in an epoxide ring-opening reaction. This allows simple mixing of
the two low viscosity resins: the thermoplastic monomers and the
epoxy resin system. The T.sub.g of the original epoxy formulation
is affected depending on the thermoplastic used and degree of
polymerization. Styrene and acrylate monomers can used together and
independently to tailor the T.sub.g of the material. The loading of
initiator can also be modified to control the chain length of the
thermoplastic molecules. The presence of the thermoplastic phase
does not hinder the elongation of the epoxy matrix. Any loading is
possible, although visible phase separation occurs above 10 weight
percent for polystyrene systems.
[0139] All reagents that used to produce the epoxy-based SMP are
commercially available; some are available in bulk scale. Some
examples of reagents are as follows.
[0140] Amine reagents can be 2-amino-3-picoline,
2-amino-6-picoline, 2-aminopyridine, 3-aminopyridine,
4-aminophenol, 2-aminothiazole, 8-aminoquinoline, 8-naphthylamine,
ethanolamine, o-anisidine, 2'-(2-aminoethoxy)ethanol, benzylamine,
or propylamine, piperazine and substituted piperazines, e.g.,
2-(methylamido)piperazine, 2-methylpiperazine,
2,5-dimethylpiperazine, 2,6-dimethylpiperazine, aniline and
substituted anilines, e.g., 4-(methylamido)aniline,
4-methoxyaniline (p-anisidine), 3-methoxyaniline (m-anisidine),
2-methoxyaniline (o-anisidine), 4-butylaniline, 2-sec-butylaniline,
2-tert-butylaniline, 4-sec-butylaniline, 4-tert-butylaniline,
5-tert-butyl-2-methoxyaniline, 3,4-dimethoxyaniline,
3,4-dimethylaniline; alkyl amines and substituted alkyl amines,
e.g., propylamine, butylamine, tert-butylamine, sec-butylamine,
benzylamine; alkanol amines, e.g., 2-aminoethanol and
1-aminopropan-2-ol; and aromatic and aliphatic secondary diamines,
e.g., 1,4-bis(methylamino)benzene, 1,2-bis(methylamino)ethane and
N,N'-bis(2-hydroxyethyl)ethylenediamine,
N,N'-dibenzylethylenedimaine; and other aromatic amines, e.g.,
2-aminobenothiazole, 3-amino-5-methylpyrazole,
2-amino-6-methylpyridine, 3-aminophenol, 2-amino-3-picoline,
4-aminopyridine, 3-aminopyridine, 2-aminpyridine, 3-aminoquinoline,
5-aminoquinoline, 2-aminothiophenol.
[0141] Multifunctional cross-linking reagents can be
Bis-(4-glycidyloxyphenyl)methane (Bisphenol F),
diglycidyl-1,2-cyclohexanedicarboxylate, resorcinol diglycidyl
ether, or N,N-diglycidylaniline, tris(2,3-epoxypropyl)
isocyanurate, glycerol propoxylate triglycidyl ether,
3,5-diethyltoluene-2,4-diamine and 3,5-diethyltoluene-2,6-diamine,
methylenedianiline, diethylenetriamine, and
tris(2-aminoethyl)amine.
[0142] In addition to using reagents containing active amino
groups, it is also possible to use diphenol reagents containing
active phenolic groups to produce epoxy-based SMP, some examples of
these diphenol reagents are as follows: Hydroquinone,
methylhydroquinone, resorcinol, catechol,
4,4'-(9-fluorenylidene)diphenol, 2,7-dihydroxynaphthalene and
bisphenol A.
[0143] In addition it is possible to tune the mechanical properties
such as toughness and T.sub.g of the epoxy SMP using
thermopolastic. Thermoplastics are dissolved in epoxy resin systems
to increase toughness, enhance self-healing properties, and modify
other material properties. By incorporation the following
commercial thermoplastics in epoxy SMP resin the mechanical and
chemical properties of the final SMP can be tailored to specific
design and environmental requirements: polystyrene, polysulfone,
and polymethyl methacrylate. The following thermoplastics, and
their copolymers, also have potential use in epoxy SMP:
Polyacrylonitrile, Polybutylacrylate, Polymethylmethacrylate,
Polybutadiene, Polyoxymethylene (acetal), High impact polystyrene,
Polyamide, Polybutylene terephthalate, Polycarbonate, Polyethylene,
Polyethylene terephthalate, Polyetheretherketone, Polyetherimide,
Polyethersulfone, Polyphthalamide, Polyphenylene ether,
Polyphenylene sulfide, Polystyrene, Polysulfone, Polyurethane,
Polyester, and Poly(styrene-acrylonitrile).
[0144] The current material system shows a great degree of strain
(i.e. elongation) above T.sub.g as compared to those epoxy system
that were published. The materials also show good stability
significantly at least 60.degree. C. above T.sub.g, unlike the
published material system which continues to cure above T.sub.g
which leads to change of material properties each time the material
is heated.
[0145] Several samples of the epoxy-based SMP were prepared, using
either aniline, aminoethanol, p-anisidine, m-anisidine,
3-aminopyridine, 4-tert-butylcatechol, resorcinol, hydroquinone,
bisphenol A as the reagents to react with methylenedianiline and
bisphenol A diglycidyl ether. For aniline-based epoxy SMP,
crosslinker content from about 0.5 mol % to 10 mol % was
formulated.
[0146] The invention will now be further described with reference
to a number of specific examples which are to be regarded solely as
illustrative and not as restricting the scope of the invention.
Example 1
[0147] As an example, 1.08 g aniline (amine reagent) was mixed with
0.066 g of methylenedianline (crosslinking diamine). The resulting
solution was mixed with 4.17 g of bisphenol A diglycidyl ether to
form an homogeneous solution. This solution was then injected into
a glass mold, made with two, 2''.times.2'' glass with a Viton
O-ring sandwiched in between, by syringe. The resulting material
was cured in an oven pre-heated to 125.degree. C. for 18 hours.
This resulted in a clear solid shape memory polymer at room
temperature that has a glass transition temperature (Tg) of about
104.degree. C. The resulting material was also tough, as revealed
by its resistance to cutting by razor blade hitting with a hammer,
and with large elongation above its T.sub.g, and excellent shape
recovery. The rubbery modulus of this material was also
significantly higher than the styrene-based SMP.
Example 2
[0148] For a resin system with a T.sub.g of 103.degree. C.,
Bisphenol A diglycidyl ether at 78.94% weight is mixed with aniline
at 19.88% weight and DETDA (major isomers:
3,5-diethyltoluene-2,4-diamine and 3,5-diethyltoluene-2,6-diamine)
at 1.19% weight. All components are miscible liquids and are easily
combined through mechanical mixing.
Example 3
[0149] For a resin system with a T.sub.g of 60.degree. C.,
diglycidyl ether of Bisphenol A at 45.32% weight and 1,4-butanediol
diglycidyl ether at 31.38% weight are mixed with aniline at 21.99%
weight and DETDA (major isomers: 3,5-diethyltoluene-2,4-diamine and
3,5-diethyltoluene-2,6-diamine) at 1.31% weight. All components are
miscible liquids and are easily combined through mechanical
mixing.
[0150] While the amount of crosslinking reagents used can vary from
0.01 mol % to 10 mol % or more, it is particularly preferred to
keep the amount between 0.2 mol % to 7.0 mol %. The amount of
phenol or amine reagents will vary stoichiometrically with the
epoxide reagents and each can vary from 35 mol % to 65 mol %. It is
particularly preferred that both are in the range of 45 mol % to 55
mol %.
[0151] The glass transition temperature of the shape memory polymer
can be also be tailored by altering the mixture of mono- and
multi-functional amine reagents and the multifunctional epoxy
resins. The transition temperature can also be tailored by the
combination of different reagents and resins such that more than
one reagent or resin is added to a single mixture. The resulting
formulations all showed the ability to withstand strains from at
least from 0-60% of their original size before critical deformation
occurred. Additionally, some formulations showed the ability to
expand 0-700% of their original size before critical deformation
occurred.
[0152] Finally, additional catalytic elements may be used to assist
the reaction and lower the final cure temperature of the
epoxy-based SMP. Some catalysts that could be used are:
bis(triphenylphosphoranylidene) ammonium chloride,
bis(triphenylphosphoranylidene) ammonium bromide, and
bis(triphenuylphosphoranylidene) ammonium acetate.
[0153] The shape memory phenomenon in the vicinity of T.sub.g and
the ability to set the value of T.sub.g, by varying the
composition, over a very broad range of temperatures allows
contemplation of numerous applications in varied uses including,
but not limited to, molds for contact lenses manufacturing, molds
for composite manufacturing, structural deployment devices for
remote systems, games and toys, domestic articles, arts and
ornamentation units, medical and paramedical instruments and
devices, thermo-sensitive instruments and security devices, office
equipment, garden equipment, educative articles, tricks, jokes and
novelty items, building accessories, hygiene accessories,
automotive accessories, films and sheets for retractable housings
and packaging, coupling material for pipes of different diameters,
building games accessories, folding games, scale model accessories,
bath toys, boots and shoes inserts, skiing accessories,
suction-devices for vacuum cleaners, pastry-making accessories,
camping articles, adaptable coat hangers, retractable films and
nets, sensitive window blinds, isolation and blocking joints,
fuses, alarm devices, sculpture accessories, adaptable hairdressing
accessories, plates for braille that can be erased, medical
prosthesis, orthopedic devices, furniture, deformable rulers,
recoverable printing matrix, formable casts/braces, shoes,
form-fitting spandex, form-fitting clothes, self-ironing clothes,
self-fluffing pillows, deployable structures, space deployable
structures, satellites, and pipe replacements for underground
applications.
[0154] Although this invention has been described with respect to
certain preferred embodiments, it will be appreciated that a wide
variety of equivalents may be substituted for those specific
elements shown and described herein, all without departing from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *