U.S. patent application number 15/911799 was filed with the patent office on 2018-09-13 for piezoelectric composite and method of forming same.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Kwok Pong Chan, Matthew Harvey Krohn.
Application Number | 20180261757 15/911799 |
Document ID | / |
Family ID | 53015963 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180261757 |
Kind Code |
A1 |
Krohn; Matthew Harvey ; et
al. |
September 13, 2018 |
PIEZOELECTRIC COMPOSITE AND METHOD OF FORMING SAME
Abstract
A piezoelectric composite for use in an ultrasonic transducer
and a method of forming the same is provided. The composite has a
piezoelectric ceramic component and a hydrophobic polymer component
arranged to form a 1-3, 2-2, or 3-3 composite type. In one
embodiment, the hydrophobic polymer is selected to polymerize at a
moderate temperature.
Inventors: |
Krohn; Matthew Harvey;
(Lewistown, PA) ; Chan; Kwok Pong; (Troy,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
|
Family ID: |
53015963 |
Appl. No.: |
15/911799 |
Filed: |
March 5, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14260844 |
Apr 24, 2014 |
9911912 |
|
|
15911799 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 5/5419 20130101;
C08L 51/085 20130101; B06B 1/0622 20130101; C08L 63/00 20130101;
H01L 41/183 20130101; C08G 59/24 20130101; C08G 59/306 20130101;
C08G 77/14 20130101; C08K 5/5415 20130101; C08L 83/06 20130101;
B06B 1/06 20130101; H01L 41/37 20130101; C08G 59/223 20130101; C08L
63/00 20130101; C08K 5/5415 20130101; C08K 5/5419 20130101; C08L
51/085 20130101 |
International
Class: |
H01L 41/18 20060101
H01L041/18; C08L 51/08 20060101 C08L051/08; B06B 1/06 20060101
B06B001/06; C08K 5/5415 20060101 C08K005/5415; C08K 5/5419 20060101
C08K005/5419; C08G 77/14 20060101 C08G077/14; C08L 83/06 20060101
C08L083/06; C08L 63/00 20060101 C08L063/00; C08G 59/30 20060101
C08G059/30; C08G 59/24 20060101 C08G059/24; C08G 59/22 20060101
C08G059/22; H01L 41/37 20060101 H01L041/37 |
Claims
1. A piezoelectric composite comprising a plurality of
piezoelectric ceramic components and a hydrophobic polymer
component, wherein the plurality of piezoelectric ceramic
components and the hydrophobic polymer component are arranged to
form a composite type selected from the group consisting of a 1-3
composite type, a 2-2 composite type, and a 3-3 composite type.
2. The piezoelectric composite as recited in claim 1, wherein the
hydrophobic polymer component is a polymerization product of a
reaction mixture comprising a siloxane epoxide monomer and a
photoacid generator.
3. The piezoelectric composite as recited in claim 1, wherein the
hydrophobic polymer is a polymerization product of a reaction
mixture comprising an epoxide monomer and photoacid generator.
4. The piezoelectric composite as recited in claim 1, wherein the
hydrophobic polymer is a polymerization product of a reaction
mixture comprising a neat epoxide monomer and photoacid
generator.
5. The piezoelectric composite as recited in claim 4, wherein the
photoacid generator is present in the reaction mixture at a
concentration between 0.25% by weight and 3% by weight.
6. The piezoelectric composite as recited in claim 1, wherein the
hydrophobic polymer is a polymerization product of a reaction
mixture comprising an epoxide monomer, photoacid generator, and an
epoxide toughening monomer that is different than the epoxide
monomer.
7. The piezoelectric composite as recited in claim 6, wherein the
epoxide toughening monomer comprises a plurality of
dimethylsiloxane moieties and at least one epoxide moiety.
8. The piezoelectric composite as recited in claim 6, wherein the
epoxide toughening monomer is present in the reaction mixture at a
concentration between 0.25% by weight and 40% by weight.
9. The piezoelectric composite as recited in claim 1, wherein the
hydrophobic polymer is a polymerization product of a reaction
mixture comprising an epoxide monomer, photoacid generator, an
epoxide toughening monomer that is different than the epoxide
monomer, and an adhesion promoter.
10. The piezoelectric composite as recited in claim 9, wherein the
adhesion promoter is present in the reaction mixture at a
concentration between 0.25% by weight and 6% by weight.
11. The piezoelectric composite as recited in claim 1, wherein the
hydrophobic polymer component has less than a 4% change in mass
when tested according to ASTM Standard D 570-98(2010)e1.
12. The piezoelectric composite as recited in claim 1, wherein the
piezoelectric composite type is a 1-3 composite type.
13. The piezoelectric composite as recited in claim 12, wherein the
plurality of piezoelectric ceramic components are posts having a
length-to-width aspect ratio of at least 2.5 to 1.
14. The piezoelectric composite as recited in claim 1, wherein the
plurality of piezoelectric ceramic components and the hydrophobic
polymer component are arranged such that the plurality of
piezoelectric ceramic components occupies between 20% and 80% by
volume of the piezoelectric composite.
15. The piezoelectric composite as recited in claim 14, wherein the
plurality of piezoelectric ceramic components and the hydrophobic
polymer component are arranged such that the hydrophobic polymer
component occupies between 20% and 80% by volume of the
piezoelectric composite.
16. A method of forming a piezoelectric composite, the method
comprising steps of: dicing a ceramic to form a plurality of
piezoelectric ceramic components, wherein the step of dicing forms
grooves between each piezoelectric ceramic component while leaving
each piezoelectric ceramic component monolithically joined to a
back plate; filling the grooves with a reaction mixture comprising
a photoacid generator and an epoxide monomer selected to provide a
hydrophobic polymer component; initiating a polymerization reaction
in the reaction mixture; and permitting the polymerization reaction
to cure to form the hydrophobic polymer component within the
grooves, thereby forming a piezoelectric composite.
17. The method as recited in claim 16, wherein the step of
initiating and the step of permitting are both performed between
20.degree. C. and 30.degree. C.
18. The method as recited in claim 16, further comprising grinding
a top portion of the piezoelectric composite.
19. The method as recited in claim 16, wherein the step of
initiating the polymerization reaction comprises exposing the
reaction mixture to ultraviolet light.
20. An ultrasonic transducer comprising: a piezoelectric composite
comprising a plurality of piezoelectric ceramic components and a
hydrophobic polymer component, wherein the plurality of
piezoelectric ceramic components and the hydrophobic polymer
component are arranged to form a composite type selected from the
group consisting of a 1-3 composite type, a 2-2 composite type and
a 3-3 composite type; a printed circuit board providing an
electrical connection between the plurality of piezoelectric
ceramic components and a cable; a substrate contacting terminal
ends of the plurality of piezoelectric ceramic components to
provide an acoustic energy transmission window; and a case, joined
to the substrate to encase the piezoelectric composite and the
printed circuit board, wherein the cable provides an electrical
connection outside of the case.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to piezoelectric
composites and, in particular, to 1-3, 2-2 and 3-3 piezoelectric
composites for use in moist environments.
[0002] Conventional ultrasonic transducers are constructed from one
or more piezoelectric elements. One type of ultrasonic transducer
element is a piezoelectric composite comprising piezoelectric
ceramic material surrounded by a piezoelectrically passive polymer
matrix. Ultrasonic transducers formed from these piezoelectric
composites can experience an unusually short lifetime, when the
ultrasonic transducers are used in moist or underwater
environments. These ultrasonic transducers show a reduction in gain
early in their operational life. The use of what most would
consider a watertight case is not effective due to the construction
of the ultrasonic probes. Probe construction often requires use of
multiple types of materials with different thermal expansion
coefficients, which can lead to the formation of interface
dis-bonds during manufacturing and/or operation. In addition, the
front surface of the probe is designed to maximize acoustic
transmission and is often very thin which allows water to quickly
diffuse to the piezoelectric material. It is therefore desirable to
provide an improved piezoelectric composite that addresses at least
some of these shortcomings.
[0003] The discussion above is merely provided for general
background information and is not intended to be used as an aid in
determining the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE INVENTION
[0004] A piezoelectric composite for use in an ultrasonic
transducer and a method of forming the same is provided. The
composite has a piezoelectric ceramic component and a hydrophobic
polymer component arranged to form a 1-3, 2-2, or 3-3 composite
type. In one embodiment, the hydrophobic polymer is selected to
polymerize at a moderate temperature. An advantage that may be
realized in the practice of some disclosed embodiments of the
piezoelectric composite is the composite resists reductions in gain
and/or has a longer operational lifetime in moist or underwater
environments.
[0005] In a first embodiment, a piezoelectric composite is
provided. The piezoelectric composite comprises a plurality of
piezoelectric ceramic components and a hydrophobic polymer
component. The plurality of piezoelectric ceramic components and
the hydrophobic polymer component are arranged to form a composite
type selected from the group consisting of a 1-3 composite type, a
2-2 composite type, and a 3-3 composite type.
[0006] In a second embodiment, a method of forming a piezoelectric
composite is provided. The method comprises steps of dicing a
ceramic to form a plurality of piezoelectric ceramic components,
wherein the step of dicing forms grooves between each piezoelectric
ceramic component while leaving each piezoelectric ceramic
component monolithically joined to a back plate. The grooves are
filled with a reaction mixture comprising a photoacid generator and
an epoxide monomer selected to provide a hydrophobic polymer
component. A polymerization reaction is initiated in the reaction
mixture. The polymerization reaction cures to form the hydrophobic
polymer component within the grooves, thereby forming a
piezoelectric composite.
[0007] In a third embodiment, an ultrasonic transducer is provided.
The ultrasonic transducer comprises a piezoelectric composite
comprising a plurality of piezoelectric ceramic components and a
hydrophobic polymer component, wherein the plurality of
piezoelectric ceramic components and the hydrophobic polymer
component are arranged to form a composite type selected from the
group consisting of a 1-3 composite type, a 2-2 composite type and
a 3-3 composite type. The ultrasonic transducer comprises a printed
circuit board that provides an electrical connection between the
plurality of piezoelectric ceramic components and a cable, a
substrate contacting terminal ends of the plurality of
piezoelectric ceramic components to provide an acoustic energy
transmission window, and a case, joined to the substrate to encase
the piezoelectric composite and the printed circuit board, wherein
the cable provides an electrical connection outside of the
case.
[0008] This brief description of the invention is intended only to
provide a brief overview of subject matter disclosed herein
according to one or more illustrative embodiments, and does not
serve as a guide to interpreting the claims or to define or limit
the scope of the invention, which is defined only by the appended
claims. This brief description is provided to introduce an
illustrative selection of concepts in a simplified form that are
further described below in the detailed description. This brief
description is not intended to identify key features or essential
features of the claimed subject matter, nor is it intended to be
used as an aid in determining the scope of the claimed subject
matter. The claimed subject matter is not limited to
implementations that solve any or all disadvantages noted in the
background.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] So that the manner in which the features of the invention
can be understood, a detailed description of the invention may be
had by reference to certain embodiments, some of which are
illustrated in the accompanying drawings. It is to be noted,
however, that the drawings illustrate only certain embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the scope of the invention encompasses other equally
effective embodiments. The drawings are not necessarily to scale,
emphasis generally being placed upon illustrating the features of
certain embodiments of the invention. In the drawings, like
numerals are used to indicate like parts throughout the various
views. Thus, for further understanding of the invention, reference
can be made to the following detailed description, read in
connection with the drawings in which:
[0010] FIG. 1 is a perspective view of an exemplary piezoelectric
composite after the it has been filled with a polymer, which is
cured;
[0011] FIG. 2 is a perspective view of an exemplary piezoelectric
composite after a grinding operation;
[0012] FIG. 3 is a cross section view of an exemplary ultrasonic
transducer;
[0013] FIG. 4 is a schematic depiction of a 1-3 composite type;
[0014] FIG. 5 is a schematic depiction of a 2-2 composite type;
[0015] FIG. 6 and FIG. 7 are schematic depictions of two views of a
3-3 composite type;
[0016] FIG. 8 is a graph depicting reductions in gain in decibels
(dB) as a function of time for an ultrasonic transducer immersed
underwater;
[0017] FIG. 9 is a graph depicting change in array length of
ultrasonic transducers as a function of time when exposed to humid
conditions;
[0018] FIG. 10 is a graph depicting heat flow in a non-hydrophobic
piezoelectric composite as a function of temperature; and
[0019] FIG. 11 is a graph depicting change in mass as a function of
time for two polymer components that are used in piezoelectric
composites.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Some piezoelectric composite probes have been found to
experience gain loss during operation, which leads to shortened
operational lifetimes. Without wishing to be bound by any
particular theory, intrusion of water into the piezoelectric
composite appears to be responsible for this shortcoming and, for
reasons related to the probe construction, a watertight casing does
not consistently solve this lifetime problem. This disclosure
provides piezoelectric composites having 1-3, 2-2 and 3-3
arrangements for addressing at least some of these problems.
[0021] The delicate nature of 1-3, 2-2 and 3-3 composite types,
used in ultrasonic probes, raises certain processing concerns. To
address some of these concerns, the grooves between each of the
plurality of piezoelectric ceramic components are filled with a
filler polymer (e.g. an epoxy) that serves several purposes. The
filler polymer omits air from between the plurality of
piezoelectric ceramic components that could result in breakdown
during the application of an electric field to the piezoelectric
components. Electric fields are used to invoke a mechanical
displacement of the piezoelectric material, which generates the
acoustic pressure. Electric fields are also used to align the
dipoles in the piezoelectric materials, which improves the
perceived piezoelectric response. The filler polymer also keeps the
plurality of piezoelectric ceramic components in position during
the grinding operation and otherwise adds toughness to the system
during its operational lifetime. The filler polymer also functions
as a mask during the sputtering operation and thereby prevents the
thin layer of the electrode material from being deposited on the
sides of the plurality of piezoelectric ceramic components. It also
acts as a support for the electrode material allowing for lateral
electrical connection between the piezoelectric ceramic components
of the piezoelectric composite.
[0022] While the filler polymer is a desirable component, use of
the filler polymer introduces further complications into the
fabrication of the piezoelectric composite. Most filler polymers
and piezoelectric ceramic components have very different
coefficients of thermal expansion (CTE). It is therefore
problematic to use a filler polymer that is thermally cured above
room temperature, as the increased temperatures would cause the
polymer component and the piezoelectric ceramic component to
expand/contract at different rates, which will lead to stresses and
mechanical deformation. A polymer component that cures at or near
room temperature is often selected for the manufacturing of
piezoelectric composites, but the use of some types of polymer
components produces a piezoelectric composite that experiences
reduction in gain and shortened operational lifetime. In addition,
because piezoelectric composites are relatively thin (0.1 to 5 mm)
relative to their lateral dimensions (6 to 150 mm), they are very
susceptible to interaction with water (short diffusion dimensions).
The polymer components used to fill piezoelectric composites can
often show exaggerated effects relative to their bulk properties
due to a small thickness dimension.
[0023] FIG. 1 is a perspective view of an exemplary piezoelectric
composite 100 comprising a plurality of piezoelectric ceramic
components 102 and a hydrophobic polymer component 104. In the
exemplary embodiment of FIG. 1, the piezoelectric ceramic
components 102 and the hydrophobic polymer component 104 are
arranged as a 1-3 composite type, wherein the piezoelectric ceramic
components 102 have one degree of connectivity (the Z axis) and the
hydrophobic polymer component 104 has three degrees of connectivity
(the X, Y and Z axes). The piezoelectric ceramic components 102 may
be made, for example, by sequential dicing and grinding operations.
In the dicing operation, a series of grooves are cut in a ceramic
along two perpendicular axes (e.g., the X and Y axis). The grooves
are cut to a sufficient depth in the direction of the Z axis so as
to leave a back plate 106 joined to the plurality of piezoelectric
ceramic components 102. The grooves between each of the plurality
of piezoelectric ceramic components 102 are then filled with a
reaction mixture that, after curing, produces the hydrophobic
polymer component 104. After curing, the back plate 106 may be
removed by, for example, grinding. The grooves have a dimension
such that about 20% to about 80% by volume of the piezoelectric
composite 100 is occupied by the plurality of piezoelectric ceramic
components 102 with the balance of the volume being the hydrophobic
polymer component 104. In other embodiments, the piezoelectric
composite 100 comprises about 30% to about 60% by volume of the
plurality of piezoelectric ceramic components 102 with the balance
of the volume being the hydrophobic polymer component 104. In other
embodiments, the piezoelectric composite 100 comprises about 30% by
volume of the plurality of piezoelectric ceramic components 102
with the balance being the hydrophobic polymer component 104. In
other embodiments, the piezoelectric composite 100 comprises about
20% to about 70% by volume of the plurality of piezoelectric
ceramic component 102 with the balance being the hydrophobic
polymer component 104 mixed with an inorganic powder, such as
silica or alumina. In the grinding operation, a terminal end of the
piezoelectric composite 100 is removed until a desired thickness
has been achieved. In one embodiment of a 1-3 composite type, after
the grinding operation, the piezoelectric ceramic components 102
are posts that have a length-to-width aspect ratio of at least 2.5
to 1 and, in one embodiment, about 5 to 1. In some embodiments, a
thin layer of an electrode material is deposited on the
piezoelectric composite 100 by, for example, sputtering. FIG. 2 is
a depiction of a piezoelectric composite after the grinding
operation has been completed and the back plate has been
removed.
[0024] FIG. 3 is a cross section view of an exemplary ultrasonic
transducer 300 that comprises the piezoelectric composite 100. The
piezoelectric composite 100 is mounted such that the piezoelectric
composite 100 contacts a substrate 302. The piezoelectric composite
100 is connected to a printed circuit board (PCB) 304 by wires 316.
The wires 316 include electrically hot wires and at least one
ground wire. The space between the piezoelectric composite 100 and
the printed circuit board 304 may be filled with a dampening
material that inhibits ultrasonic energy. The piezoelectric
composite 100 has been segmented into an array by cutting
deactivation cuts 314 into the piezoelectric composite 100. The
printed circuit board 304 is connected to a cable 306 by wires 308
and the piezoelectric composite 100 is sealed between a case 310
and the substrate 302. In some embodiments, a lower surface 312 of
the substrate 302 is then subjected to a grinding operation to
produce a suitably thin layer to provide an acoustic window that is
designed to maximize the transmitted ultrasonic energy.
[0025] As shown in FIGS. 4-7, the piezoelectric ceramic component
and the hydrophobic polymer component are arranged as different
composite types. FIG. 4 is a schematic depiction of a 1-3 composite
type, wherein a piezoelectric ceramic component 402 has one degree
of connectivity (the Z axis) and a hydrophobic polymer component
404 has three degrees of connectivity (the X, Y and Z axes). FIG. 5
is a schematic depiction of a 2-2 composite type wherein a
piezoelectric ceramic component 502 has two degrees of connectivity
(the X and Y axes) and a hydrophobic polymer component 504 has two
degrees of connectivity (the X and Y axes). FIG. 6 and FIG. 7 are
schematic depictions of two views of a 3-3 composite type, wherein
a piezoelectric ceramic component 602 and a hydrophobic polymer
component 604 both have three degrees of connectivity (the X, Y and
Z axes).
[0026] In certain applications, it is desirable to use an
ultrasonic transducer in a moist environment or even immersed
underwater. It is in this environment where the shortened lifetime
and reductions in gain are most pronounced. The use of a watertight
case to protect the piezoelectric composite formed using a
non-hydrophobic epoxy has not produced a piezoelectric transducer
that is suitable for commercial use. For example, FIG. 8 is a graph
depicting reduction in gain in decibels (dB) as a function of time
for two ultrasonic transducers immersed underwater. Line 800 shows
the response of a "water-tight" ultrasonic transducer made using a
non-hydrophobic epoxy sold under the brand name EPO-TEK.RTM. 301 by
Epoxy Technologies, Inc. As shown in line 800 of FIG. 8, the
water-tight ultrasonic transducer made using a non-hydrophobic
epoxy experienced rapidly reduced gain during water immersion and
began to plateau at a 5 dB to 6 dB loss after about five to ten
days. Many such water-tight probes showed complete failure within
three to six months of their operational life. In some extreme
cases (see line 804, where the piezoelectric composite is formed
from a non-hydrophobic epoxy) complete failure of the probe occurs
within the first thirty days of operation.
[0027] In contrast with line 800, line 802 shows the response of an
ultrasonic transducer made using a hydrophobic polymer component
made according to the present disclosure. Line 800 and line 802
were both generated by immersion of the respective ultrasonic
transducer in water. As shown in line 802 of FIG. 8, the ultrasonic
transducer made using a hydrophobic polymer component showed no
substantial reduction in gain after twenty days of water immersion.
The probes formed using hydrophobic polymer components showed
improved alignment and fit as well as stable thermal
properties.
[0028] As shown in FIG. 9, in addition to the reductions in gain,
water-tight probes formed using non-hydrophobic epoxies (line 900)
also experience issues with alignment and fit (due to swelling
caused by water adsorption) relative to probes formed using
hydrophobic polymer components (line 902). FIG. 10 is a graph
illustrating of the effect of humidity on piezoelectric composites
formed using a non-hydrophobic polymer component. Line 1002 shows
the response of a piezoelectric composite made using a
non-hydrophobic polymer component directly after curing. Line 1002
shows a step glass transition when heated. After exposure to a
humid environment (32.degree. C. at 70% relative humidity for 46
hours) the response of the material is significantly altered (see
line 1000). The thermal properties are particularly relevant over
temperature region 1004 (below about 60.degree. C.) which includes
the typical operating temperatures for ultrasonic transducers.
Probes formed using non-hydrophobic epoxies showed an enthalpic
relaxation peak 1006 that is not present directly after curing. A
dip 1008 in line 1000 is indicative of the removal of water from
the probe formed using non-hydrophobic epoxy.
[0029] A variety of hydrophobic polymer components may be used but
the delicate nature of 1-3, 2-2 and 3-3 composite types should be
taken into consideration. In one embodiment, the hydrophobic
polymer component is a polymerization product of a reaction mixture
comprising an epoxide monomer and a photoacid generator via
cationic ring opening polymerization mechanism. Irradiation of the
photoacid generator with light initiates polymerization at a
moderate temperature (e.g. 20-30.degree. C.). In one embodiment,
the moderate temperature is near room temperature (e.g.
20-25.degree. C.). In one embodiment, the polymerization is
initiated in an undiluted (neat) reaction mixture. The use of a
hydrophobic epoxide monomer in the absence of a nucleophilic curing
agent (e.g. an amine) permits the generation of a hydrophobic
polymer component with low hydroxyl concentration and high
hydrophobicity.
[0030] A variety of hydrophobic epoxide monomers can be used to
produce the hydrophobic polymer component. The term "hydrophobic
polymer" refers to a substance that experiences a low change in
mass when tested according to ASTM Standard D 570-98(2010)e1
"Standard Test Method for Water Absorption of Plastics." In one
embodiment, the change in mass is less than 4% after ten days of
water exposure. In one embodiment, the change in mass is less than
2% after ten days of water exposure. In another embodiment, the
change in mass is less than 1% after ten days of water exposure. In
yet another embodiment, the change in mass is less than 0.5% after
ten days of water exposure. FIG. 11 is a graph depicting change in
mass as a function of time for a hydrophobic polymer component
(line 1100) and a non-hydrophobic polymer component (line 1102).
Table 1 provides several examples of hydrophobic epoxide monomers.
Entries 1-4 are examples of siloxane epoxide monomers while example
5 is an example of an ester epoxide monomer.
TABLE-US-00001 TABLE 1 Examples of Hydrophobic Epoxide Monomers
Entry Name Structure 1 1,3-bis-[2-(3,4-epoxy-
cyclohexyl)-ethyl]-1,1,3,3- tetramethyl-disiloxane ##STR00001## 2
1,3-Bis(3-(2,3- epoxypropoxy)propyl) tetramethyldisiloxane
##STR00002## 3 1,1,3,5,5-Pentamethyl-1,5- bis[3-(2-
oxiranylmethoxy)propyl]-3- phenyltrisiloxane ##STR00003## 4
1,3-bis-[2-(3,4-epoxy- cyclohexyl)-ethyl]-1,1,3,3-
tetramethyl-disiloxane ##STR00004## 5 3,4-Epoxycyclohexylmethyl-
3,4- epoxycyclohexanecarboxylate ##STR00005##
[0031] Numerous photoacid generators may be used to initiate the
polymerization reaction. Several examples of photoacid generators
are provided in Table 2.
TABLE-US-00002 TABLE 2 Examples of Photoacid Generators Entry Name
Structure 1 p- (octyloxyphenyl)phenyliodonium hexafluoroantimonate
##STR00006## 2 p-isopropyl-2'- methyldiphenyliodonium
Tetrakis(pentafluorophenyl) borate ##STR00007## 3 Triarylsulfonium
hexafluoroantimonate salts, mixed ##STR00008## ##STR00009##
[0032] In one embodiment, the reaction mixture comprises between
97% and 99.75% (wt.) neat epoxide monomer and between 0.25% and 3%
(wt.) photoacid generator. In one such embodiment, the reaction
mixture consists essentially of 97% (wt.) and 99.75% (wt.) neat
epoxide monomer with the balance being photoacid generator. In
another embodiment, the reaction mixture further comprises an
epoxide toughening monomer and/or an adhesion promoter. In one such
embodiment, the reaction mixture comprises between 60% (wt.) and
99.75% (wt.) neat epoxide monomer, between 0.25% (wt.) and 3% (wt.)
photoacid generator, between 0.25% (wt.) and 40% (wt.) epoxide
toughening monomer and between 0% (wt.) and 6% (wt.) adhesion
promoter. In one such embodiment, between 0.25% (wt.) and 6% (wt.)
of the adhesion promoter is present.
[0033] Epoxide toughening monomers are resins that increase the
flexibility of the resulting hydrophobic polymer component, which
helps deter crack growth and failure of piezoelectric composites.
Several examples of epoxide toughening monomers are provided in
Table 3 wherein the epoxide toughening monomer comprises
dimethylsiloxane moieties and at least one epoxysiloxane moiety.
Other epoxide toughening monomers are also suitable. Epoxide
toughening monomers generally decrease the amount of cross-linking
and lower the glass transition temperature (Tg) relative to a
corresponding hydrophobic polymer component that omits the epoxide
toughening monomer.
TABLE-US-00003 TABLE 3 Examples of Epoxide Toughening Monomers
##STR00010## Epoxycyclohexylethylmethylsiloxane--dimethylsiloxane
copolymers Mole % (epoxycyclohexyl)- Molecular weight Viscosity
Entry ethylmethylsiloxane (g per mole) (centistokes) 1 2-3%
18,000-20,000 650-800 2 3-4% 18,000-20,000 650-850 3 8-10%
10,000-12,000 300-450
[0034] Adhesion promoters include alkoxyl silanes containing an
epoxide moiety. Epoxide moieties include glycidyl and/or
3,4-epoxycyclohexyl groups. Table 4 provides examples of several
adhesion promoters.
TABLE-US-00004 TABLE 4 Examples of Adhesion promoters Entry Name
Structure 1 2-(3,4- epoxycyclohexyl)ethyltrimethoxysilane
##STR00011## 2 2-(3,4- epoxycyclohexyl)ethyltriethoxysilane
##STR00012## 3 (3-glycidoxypropyl)trimethoxysilane ##STR00013## 4
(3-glycidoxypropyl)triethoxysilane ##STR00014##
[0035] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *