U.S. patent application number 10/284396 was filed with the patent office on 2004-05-06 for porous polymeric membrane toughened composites.
Invention is credited to Thompson, Samuel A..
Application Number | 20040084304 10/284396 |
Document ID | / |
Family ID | 32174863 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040084304 |
Kind Code |
A1 |
Thompson, Samuel A. |
May 6, 2004 |
POROUS POLYMERIC MEMBRANE TOUGHENED COMPOSITES
Abstract
Composites comprising porous polymeric membrane films meeting
the following equation: 75 MPa<(longitudinal membrane tensile
modulus+transverse membrane tensile modulus)/2, wherein at least a
portion of the porosity of the membrane is imbibed with resin and
methods for making the same. The composites have unusually high
resistance to fracture and catastrophic failure.
Inventors: |
Thompson, Samuel A.;
(Wilmington, DE) |
Correspondence
Address: |
Allan M. Wheatcraft, Esquire
W. L. Gore & Associates, Inc.
551 Paper Mill Road
Newark
DE
19714-9206
US
|
Family ID: |
32174863 |
Appl. No.: |
10/284396 |
Filed: |
October 30, 2002 |
Current U.S.
Class: |
204/296 ;
174/126.2; 257/701; 257/702; 428/304.4; 428/306.6; 428/307.3;
428/308.4; 428/315.5; 428/316.6; 428/317.1; 428/320.2; 428/322.7;
428/421; 428/900; 89/36.02; 89/36.05 |
Current CPC
Class: |
Y10S 428/90 20130101;
Y10T 428/249953 20150401; F41H 5/0471 20130101; Y10T 428/249958
20150401; Y10T 428/249956 20150401; Y10T 428/249994 20150401; Y10T
428/249955 20150401; F41H 5/02 20130101; Y10T 428/249978 20150401;
H05K 2201/015 20130101; Y10T 428/249999 20150401; Y10T 428/3154
20150401; H05K 2201/0116 20130101; Y10T 428/249981 20150401; F41H
5/08 20130101; H05K 1/0353 20130101; Y10T 428/249982 20150401 |
Class at
Publication: |
204/296 ;
428/306.6; 428/304.4; 428/308.4; 428/307.3; 428/315.5; 428/316.6;
428/317.1; 428/320.2; 428/322.7; 428/421; 428/900; 089/036.05;
089/036.02; 257/701; 257/702; 174/126.2 |
International
Class: |
C25B 013/00; C25C
007/04; B32B 003/00; B32B 003/06; B32B 003/26; B32B 005/14; B32B
007/12; B32B 027/00; H01B 005/00; H01L 023/053; H01L 023/12; H01L
023/14; F41H 005/08; F41H 005/02 |
Claims
What is claimed is:
1. A composite comprising a porous polymeric membrane, wherein the
porosity of the membrane is at least partially filled with resin,
the resin having a room temperature flexural modulus of greater
than about 1 GPa, and wherein the membrane satisfies the following
equation: 75 MPa<(longitudinal membrane tensile
modulus+transverse membrane tensile modulus)/2.
2. The composite of claim 1, wherein the resin comprises a material
selected from the group consisting of metals, metalloids, ceramics,
polymeric materials, and combinations thereof.
3. The composite of claim 1, wherein the resin comprises polymeric
material.
4. The composite of claim 3, wherein the polymeric material
comprises thermoplastic polymer.
5. The composite of claim 3, wherein the polymeric material
comprises. thermoset polymer.
6. The composite of claim 3, wherein the ratio of the room
temperature flexural modulus of the resin to the room temperature
flexural modulus of the composite, measured in the direction of the
higher of the transverse and longitudinal moduli, is greater than
or equal to about 1.
7. The composite of claim 3, further including at least one filler
material.
8. The composite of claim 1, wherein the membrane comprises a
material selected from the group consisting of vinyl polymers,
styrenes, acrylates, methacrylates, polyethylenes, polypropylenes,
polyacrylonitriles, polyacrylamides, poly vinyl chlorides,
fluoropolymers, condensation polymers, polysulfones, polyimides,
polyamides, polycarbonates, polysulfides, polyesters,
polyanhydrides, polyacetals, polyurethanes, polyureas, cellulose,
cellulose derivatives, polysaccharides, pectinic polymers and
derivatives, alginic polymers and derivatives, chitins and
derivatives, phenolics, aldehyde polymers, polysiloxanes and
derivatives, and combinations thereof.
9. The composite of claim 8, wherein the fluoropolymer is
polytetraflouroethylene.
10. The composite of claim 9, wherein the polytetraflouroethylene
is expanded polytetrafluoroethylene.
11. The composite of claim 10, wherein the expanded
polytetraflouroethylene is substantially void of nodal
material.
12. The composite of claim 1, wherein the composite is joined to
one or more metal layers in the form of a laminate.
13. The composite of claim 12, wherein the one or more metals are
selected from the group consisting of aluminum, copper, gold, tin,
silver, lead and combinations thereof.
14. The composite of claim 1, wherein the composite is joined to
one or more capacitance layer materials.
15. The composite of claim 1, wherein the composite is a layer of a
laminate.
16. The composite of claim 15, wherein the composite is an
interface adhesive layer in the laminate.
17. The composite of claim 15, wherein the composite is an outer
layer on the laminate.
18. The composite of claim 15, wherein the laminate additionally
includes at least one layer of a material selected from metal and
capacitance materials.
19. The composite of claim 18, wherein the metal is selected from
the group consisting of aluminum, copper, gold, tin, silver, lead
and combinations thereof.
20. A printed circuit board comprising the composite of claim
1.
21. An electronic substrate comprising the composite of claim
1.
22. A chip package substrate comprising the composite of claim
1.
23. A silicon wafer comprising the composite of claim 1.
24. A composite comprising a porous polymeric membrane, wherein the
porosity of the membrane is at least partially filled with resin
and the membrane satisfies the following equation: 75
MPa<(longitudinal membrane tensile modulus+transverse membrane
tensile modulus)/2, and wherein the ratio of the room temperature
flexural modulus of the resin to the room temperature flexural
modulus of the composite, measured in the direction of the higher
of the transverse and longitudinal moduli, is greater than or equal
to about 1.
25. The composite of claim 24, wherein the resin comprises a
material selected from the group consisting of metals, metalloids,
ceramics, polymeric materials, and combinations thereof.
26. The composite of claim 24, wherein the resin comprises
polymeric material.
27. The composite of claim 26, wherein the polymeric material
comprises thermoplastic polymer.
28. The composite of claim 26, wherein the polymeric material
comprises thermoset polymer.
29. The composite of claim 24, further including at least one
filler material.
30. The composite of claim 24, wherein the membrane comprises a
material selected from the group consisting of vinyl polymers,
styrenes, acrylates, methacrylates, polyethylenes, polypropylenes,
polyacrylonitriles, polyacrylamides, poly vinyl chlorides,
fluoropolymers, condensation polymers, polysulfones, polyimides,
polyamides, polycarbonates, polysulfides, polyesters,
polyanhydrides, polyacetals, polyurethanes, polyureas, cellulose,
cellulose derivatives, polysaccharides, pectinic polymers and
derivatives, alginic polymers and derivatives, chitins and
derivatives, phenolics, aldehyde polymers, polysiloxanes and
derivatives, and combinations thereof.
31. The composite of claim 30, wherein the fluoropolymer is
polytetrafluoroethylene.
32. The composite of claim 31, wherein the polytetrafluoroethylene
is expanded polytetrafluoroethylene.
33. The composite of claim 32, wherein the expanded
polytetrafluoroethylene is substantially void of nodal
material.
34. The composite of claim 24, wherein the composite is joined to
one or more metal layers in the form of a laminate.
35. The composite of claim 34, wherein the one or more metals are
selected from the group consisting of aluminum, copper, gold, tin,
silver, lead, and combinations thereof.
36. The composite of claim 24, wherein the composite is joined to
one or more capacitance layer materials.
37. The composite of claim 24, wherein the composite is a layer of
a laminate.
38. The composite of claim 37, wherein the composite is an
interface adhesive layer in the laminate.
39. The composite of claim 37, wherein the composite is an outer
layer on the laminate.
40. The composite of claim 37, wherein the laminate additionally
includes at least one layer of a material selected from metal and
capacitance materials.
41. The composite of claim 37, wherein the metal is selected from
the group consisting of aluminum, copper, gold, tin, silver, lead,
and combinations thereof.
42. The composite of claim 41, wherein the metal is copper.
43. A printed circuit board comprising the composite of claim
24.
44. An electronic substrate comprising the composite of claim
24.
45. A chip package substrate comprising the composite of claim
24.
46. A silicon wafer comprising the composite of claim 24.
47. The composite of claim 1, wherein the resin exhibits brittle
failure.
48. The composite of claim 1, wherein the glass transition
temperature of the resin is equal to the glass transition
temperature of the composite.
49. The composite of claim 24, wherein the resin exhibits brittle
failure.
50. A composite comprising a porous expanded
polytetrafluoroethylene membrane, wherein the porosity of the
membrane is at least partially filled with resin, the resin having
a room temperature flexural modulus of greater than about 1 GPa,
and wherein the membrane satisfies the following equation: 75
MPa<(longitudinal membrane tensile modulus+transverse membrane
tensile modulus)/2.
51. The composite of claim 50, wherein the resin comprises a
material selected from the group consisting of metals, metalloids,
ceramics, polymeric materials, and combinations thereof.
52. The composite of claim 51, wherein the resin comprises
polymeric material.
53. The composite of claim 52, wherein the polymeric material
comprises thermoplastic polymer.
54. The composite of claim 52, wherein the polymeric material
comprises thermoset polymer.
55. The composite of claim 50, wherein the ratio of the room
temperature flexural modulus of the resin to the room temperature
modulus of the composite, measured in the direction of the higher
of the transverse and longitudinal moduli, is greater than or equal
to about 1.
56. The composite of claim 50, further including at least one
filler material.
57. The composite of claim 50, wherein the membrane is
substantially void of nodal material.
58. The composite of claim 50, wherein the composite is joined to
one or more metal layers in the form of a laminate.
59. The composite of claim 58, wherein the one or more metals are
selected from the group consisting of aluminum, copper, gold, tin,
silver, lead and combinations thereof.
60. The composite of claim 50, wherein the composite is joined to
one or more capacitance layer materials.
61. The composite of claim 50, wherein the composite is a layer of
a laminate.
62. The composite of claim 61, wherein the composite is an
interface adhesive layer in the composite.
63. The composite of claim 61, wherein the composite is an outer
layer on the laminate.
64. The composite of claim 61, wherein the laminate additionally
includes at least one layer of a material selected from metal and
capacitance materials.
65. The composite of claim 61, wherein the metal is selected from
the group consisting of aluminum, copper, gold, tin, silver, lead
and combinations thereof.
66. A printed circuit board comprising the composite of claim
50.
67. An electronic substrate comprising the composite of claim
50.
68. A chip package substrate comprising the composite of claim
50.
69. A silicon wafer comprising the composite of claim 50.
70. The composite of claim 50, wherein the resin exhibits brittle
failure.
71. The composite of claim 50, wherein the glass transition
temperature of the resin is equal to the glass transition
temperature of the composite.
72. The composite of claim 50, wherein the ratio of the room
temperature flexural modulus of the resin divided by the room
temperature flexural modulus of the composite measured in the
direction parallel to the higher modulus direction of the membrane
is greater than about 1.
73. An electronic chip package comprising a laminated substrate,
wherein the laminated substrate includes at least one conductive
layer and at least one dielectric layer bonded to the conductive
layer, the dielectric layer comprising a porous, expanded
polytetrafluoroethylene membrane wherein the porosity of the
membrane is at least partially filled with resin, the resin has a
room temperature flexural modulus of greater than about 1 GPa, and
the membrane satisfies the following equation: 75
MPa<(longitudinal membrane tensile modulus+transverse membrane
tensile modulus)/2.
74. The electronic chip package of claim 73, further comprising
alternating layers of the at least one conductive layer and the at
least one dielectric layer.
75. The electronic chip package of claim 74, further comprising at
least one via therein.
76. The electronic chip package of claim 73, wherein the resin
comprises polymeric material.
77. The electronic chip package of claim 76, wherein the polymeric
material comprises thermoplastic polymer.
78. The electronic chip package of claim 76, wherein the polymeric
material comprises thermoset polymer.
79. The electronic chip package of claim 76, wherein the conductive
layer comprises a material selected from the group consisting of
aluminum, copper, gold, tin, silver, lead, and combinations
thereof.
80. The electronic chip package of claim 79, wherein the conductive
layer comprises copper.
81. The electronic chip package of claim 76, wherein the expanded
polytetraflouroethylene membrane is substantially void of nodal
material.
82. The electronic chip package of claim 76, wherein the ratio of
the room temperature flexural modulus of the resin to the room
temperature flexural modulus of the composite, measured in the
direction of the higher of the transverse and longitudinal moduli,
is greater than or equal to 1.
83. The composite of claim 1, wherein the composite is laminated to
at least one layer of high modulus fiber containing material.
84. The composite of claim 83, wherein the high modulus fiber is
selected from the group consisting of glass fiber, carbon fiber,
ceramic fiber, and combinations thereof.
85. The composite of claim 24, wherein the composite is laminated
to at least one layer of high modulus fiber containing
material.
86. The composite of claim 85, wherein the high modulus fiber is
selected from the group consisting of glass fiber, carbon fiber,
ceramic fiber, and combinations thereof.
87. The composite of claim 50, wherein the composite is laminated
to at least one layer of high modulus fiber containing
material.
88. The composite of claim 87, wherein the high modulus fiber is
selected from the group consisting of glass fiber, carbon fiber,
ceramic fiber, and combinations thereof.
89. A sporting goods article comprising the composite of claim
1.
90. A sporting goods article comprising the composite of claim
24.
91. An aerospace part comprising the composite of claim 1.
92. An aerospace part comprising the composite of claim 24.
93. The sporting goods article of claim 89, wherein the sporting
goods article is selected from the group consisting of fishing
equipment, hunting equipment, golf equipment, tennis equipment,
skiing equipment, track and field equipment, basketball equipment,
football equipment, soccer equipment, lacrosse equipment, and
hockey equipment.
94. The sporting goods article of claim 90, wherein the sporting
goods article is selected from the group consisting of fishing
equipment, hunting equipment, golf equipment, tennis equipment,
skiing equipment, track and field equipment, basketball equipment,
football equipment, soccer equipment, lacrosse equipment, and
hockey equipment.
95. The aerospace part of claim 91, wherein the aerospace part is
selected from the group consisting of aircraft panels, safety
devices, fan blades, control surfaces, and struts.
96. The aerospace part of claim 92, wherein the aerospace part is
selected from the group consisting of aircraft panels, safety
devices, fan blades, control surfaces, and struts.
97. The composite of claim 24, wherein the resin has a room
temperature flexural modulus of greater than about 1 GPa.
98. An armor material comprising the composite of claim 1, wherein
the armor material is selected from the group consisting of body
armor and vehicle armor.
99. An armor material comprising the composite of claim 24, wherein
the armor material is selected from the group consisting of body
armor and vehicle armor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to the use of certain porous polymeric
membranes to toughen composite structures.
[0003] 2. Description of Related Art
[0004] Toughness is a term used to refer to a material's ability to
adapt to, and ability to handle, stress. Tougher materials
withstand greater stress prior to failure. Toughness often also
implies failure that is more ductile in nature and
non-catastrophic, characterized by inelastic and energy absorbing
processes preceding failure. Frequently used metrics for toughness
include but are not limited to fracture energy measurements, impact
energy measurements, strength, puncture strength, impact strength,
and strength after impact.
[0005] Related art in toughened composites includes rubber
toughening of polymers, and composite reinforcement with fibrous
material (chopped or continuous glass, aramid fibers, carbon
fibers, etc.).
[0006] Rubber toughening is a term applied to materials toughened
by the presence of a second and discrete rubber phase in a
polymeric matrix. These rubber domains are believed to act as
stress concentrators, acting to dissipate stress on a microscopic
level and increase matrix toughness. Toughness is used herein to
describe the ability to absorb energy in a non catastrophic manner.
The rubber domains are typically generated by either a phase
separation phenomenon or by addition of individual rubber
particles. When added as individual rubber particles these
particles are often in the form of core-shell rubbers where an
outer shell is present over the rubber core. The shell is typically
made from a material having a glass transition temperature above
room temperature. The shell functions to prevent clumping and aid
in dispersion. Rubber toughening can be accompanied by a drop in
matrix glass transition temperature, a drop in resin modulus, or
both simultaneously. Rubber toughening typically loses its
effectiveness as the Tg of thermoset resins increases above
150.degree. C. as a result of the high cross-link density and
inability of molecules to move without breakage in response to
stress.
[0007] Thermoplastics that have been rubber toughened to enable
applications beyond those available to the brittle neat polymer
include polyvinyl chloride, polystyrene, acetal polymers including
polyoxymethylene. Thermoset resins that have been rubber toughened
include epoxy resins of low glass transition temperature.
[0008] Other polymers better known for their inherent toughness
have also been enhanced by rubber toughening. Rubber toughened
polycarbonate, and nylon, fall into this group.
[0009] Composite reinforcement in the traditional sense typically
means increasing the overall stiffness of the matrix such that a
composite can carry greater load with less deflection than the neat
resin matrix. This reinforcement also often acts to increase the
toughness of the material in that significantly more energy is
required to generate a catastrophic failure than that of the neat
resin matrix. Reinforcement is typically accomplished by addition
of high modulus fibers such as glass, aramid, ceramic, or carbon
fibers. These fibers typically fall in the 1-20 um diameter range.
The coarseness of the fibrous reinforcement can limit applications,
as for example in electronics where feature size can be on the
order of one to several microns. To effectively boost stiffness and
toughness in a polymeric composite the fibrous reinforcement is
typically bonded to the resin to facilitate stress transfer from
resin to fiber. This bond can be mechanical as in interlocking on a
rough surface like that of carbon fiber, or it can be chemical as
in covalent interaction between resin and fiber surface. This
bonding is often enhanced with a reactive surface treatment to
improve mechanical performance.
[0010] The prior art also discloses the use of
polytetrafluoroethylene (PTFE) as composite reinforcement.
[0011] For example, it is known to prepare fibers from expanded
PTFE, the fibers are used to produce fabrics that are then
impregnated with thermosetting resins for use in printed circuit
boards. These structures are not membrane structures and the fibers
reinforce the resin on a macroscopic scale.
[0012] Also known is the use of fibrillated PTFE mixed with
thermoplastic materials as well as thermosetting resins, wherein
the fibrillated PTFE is discontinuous.
[0013] Composites have also been formed by the addition of
fibrillated PTFE to a molybdenum disulfide and thermoplastic
elastomer blend for improved abrasion resistance, solvent
resistance and useful life and strength. Again, in such composites
the PTFE is discontinuous.
[0014] The prior art also shows composites of fluorine containing
elastomer and a fibrillated PTFE. The PTFE is discontinuous.
[0015] U.S. Pat. No. 3,953,566 to Gore discloses production of a
form of PTFE known as expanded polytetrafluoroethylene (ePTFE),
which is a porous membrane film of interconnected voids formed by
nodes and fibrils. The void space in the ePTFE material comprises
at least 50% of the volume, and frequently more than 70%. ePTFE is
often a higher strength material than PTFE, and it is also an
excellent dielectric material.
[0016] The use of such ePTFE porous membrane films to form
composites is also known. For example, U.S. Pat. No. 5,753,358 to
Korleski discloses an adhesive composite material comprising an
ePTFE material having interconnected nodes and fibrils, wherein at
least a portion of the void content of the material is imbibed with
a particulate filled resin adhesive.
[0017] U.S. Pat. No. 4,784,901 to Hatakeyama et al. discloses
flexible printed circuit board base materials comprising a sheet of
porous, ePTFE impregnated with a bismaleimide-triazine resin. The
sheet of porous, ePTFE comprises interconnected nodes and fibrils
and voids.
[0018] U.S. Pat. No. 5,547,551 to Bahar et al. discloses ultra-thin
composite membranes which include a base material and an ion
exchange resin. The base material is a membrane which is defined by
a thickness of less than 1 mil (0.025 mm) and a microstructure
characterized by nodes and fibrils and voids, or in an alternative
embodiment, by fibrils and voids with no nodes present. The ion
exchange resin substantially impregnates the membrane such that the
membrane is essentially air impermeable. Bahar discusses the
improved performance of ion exchange membranes containing ePTFE
over ion exchange resins without ePTFE. Important performance
criteria discussed are uniformity and occlusiveness as in free of
pin holes and air impermeability, mechanical integrity, and long
term chemical stability. The membranes operate in the water swollen
state where the ion exchange resin is highly swollen, soft and
rubbery. Bahar indicates that a preferred base material is an
expanded PTFE made in accordance with the teachings of U.S. Pat.
No. 3,593,566.
[0019] U.S. Pat. No. 5,476,589 to Bacino discloses a non-woven web
that is a thin, porous polytetrafluoroethylene membrane consisting
essentially of a non-woven web having a microstructure of
substantially only microfibrils fused at crossover points. The
non-woven web is unusually strong, unusually thin, has unusually
small pore sizes, but a very high air flow-through. It has a pore
size between 0.05 and 0.4 micrometers; a bubble point between 10
and 60 psi; a pore size distribution value between 1.05 and 1.20; a
ball burst strength between 0.9 and 17 pounds/force; and air flow
of between 20 Frazier and 10 Gurley seconds; a thickness between
1.0 and 25.4 micrometers; and a fiber diameter ranging between 5
and 200 nm.
[0020] U.S. Pat. No. 5,288,547 to Elmes et al. discloses a process
for preparing a composite using a porous membrane film component
that enhances toughness in the obtained composite. Elmes et al.
teach that the thermoplastic membrane dissolves into the composite
and that it would be undesirable to not have the thermoplastic
membrane dissolve into the composite. Elmes et al. also state that
a weak resin-thermoplastic interface is a problem as it has a
negative effect on composite performance.
[0021] The entire disclosure of each of the above U.S. Patents is
hereby incorporated by reference.
[0022] Moreover, MICROLAM.RTM. 410 Dielectric and MICROLAM.RTM. 610
Dielectric are two commercially available products available from
W. L. Gore & Associates, Newark, Del. These products are
composites of thermoset resins and ePTFE porous membranes.
MICROLAM.RTM. 410 Dielectric also contains a large volume fraction
of inorganic filler and the membrane component generally has a
maximum tensile modulus of 133 MPa and a tensile modulus of 1 MPa
at 90 degrees from the direction of the maximum tensile modulus.
FIG. 5 is an SEM of the type of membrane used in this product.
MICROLAM.RTM. 610 Dielectric has a membrane component which
generally has a maximum tensile modulus of 76 MPa and a tensile
modulus of 16 MPa at 90 degrees from the direction of the maximum
tensile modulus. FIG. 6 is an SEM of the type of membrane used in
this product.
[0023] It is also known to produce materials including
substantially node-free ePTFE membranes having the porosity at
least partially imbibed with fluorinated ethylene propylene
("FEP"). FEP has a room temperature flexural modulus of about 0.5
to 0.7 GPa. Node free membranes imbibed with FEP typically exhibit
a room temperature flexural modulus ratio of FEP/FEP-membrane
composite of about 0.6.
SUMMARY OF THE INVENTION
[0024] The invention relates to the use of porous polymeric
membrane films in composites such that these membranes provide
substantially improved resistance to fracture and catastrophic
failure in the composite. As used herein "composite" means a body
comprising two or more distinct materials. This toughening, in
contrast to traditional rubber toughening is independent of the
glass transition of the resin used. As used herein "porous
polymeric membrane film" means a porous polymeric film, the pores
of which are substantially interconnected. The porous polymeric
membrane film is insoluble in that it remains intact and
undissolved during processing of the composite.
[0025] The porous polymeric membrane film satisfies the following
equation:
75 MPa<(longitudinal membrane tensile modulus+transverse
membrane tensile modulus)/2.
[0026] In an aspect of the invention the composites include resin
having a room temperature (23.degree. C.) flexural modulus of
greater than about 1 GPa imbibed into at least a portion of the
porosity of the membrane. The resin can be any suitable inorganic
or organic material or a combination thereof which has a room
temperature flexural modulus of greater than about 1 GPa. Suitable
inorganic materials include, for example, metals, metalloids, and
ceramics. Suitable organic materials include, for example,
polymeric materials.
[0027] In a further aspect of the invention, the ratio of the room
temperature flexural modulus of the resin to the room temperature
flexural modulus of the composite, measured in the direction of the
higher of the transverse and longitudinal moduli, is greater than
or equal to about 1.
[0028] Toughening with such a membrane structure does not affect
the glass transition temperature (Tg) of the resin. Moreover, the
Tg of the final composite is the same as the Tg of the neat resin
without membrane. The impact on composite flexural and tensile
modulus will depend upon the volume fraction of the membrane and
the flexural and tensile moduli of the matrix and membrane. Because
the membrane is a distinct and separate phase from the matrix, in
contrast with rubber toughening, lowering of the flexural or
tensile modulus by incomplete phase separation cannot occur.
[0029] It has been unexpectedly discovered that when used in a
composite structure, porous polymeric membrane structures according
to the invention contribute significantly to the fracture toughness
of the composite. In an aspect of the invention the membrane
structure is an expanded polytetrafluoroethylene membrane that has
minimal material present in non-fibrillar form, termed "nodes". In
a further aspect of the invention the membrane is substantially
void of nodal material. Isotropic fibril orientation is preferred
when stress may be loaded from multiple directions. When stress is
anisotropic it is preferred that the greater number of fibrils be
parallel to the direction of maximum stress. When multiple layer
structures are contemplated, cross plying of the layers may be
desirable to maximize performance. One measure of fibril
orientation and density is the membrane tensile modulus. Membranes
having higher moduli are preferred.
[0030] Unlike traditional high modulus fiber reinforcements (e.g.,
glass, carbon, etc.), the membranes of this invention have
substantially non-linear, membrane-like structures. In the specific
case of expanded polytetrafluoroethylene membranes the membrane
does not readily wet or bond to other materials. Contrary to what
the prior art teaches in the selection of a toughener or
reinforcement material, the membranes of the invention unexpectedly
provide enhanced composite performance.
[0031] Traditional reinforcements also provide for and act by
substantially increasing the modulus in the composite over that of
the neat resin alone. Carbon, graphite, glass, ceramic, and aramid
fibers for example can increase the modulus of the composite by
greater than a factor of 10.
[0032] In an aspect of the invention, composite room temperature
flexural moduli measured in the direction of the higher of the
membrane transverse and longitudinal moduli, are typically lower
than the room temperature flexural modulus of the resin component
alone.
DESCRIPTION OF THE DRAWINGS
[0033] The present invention should become apparent from the
following description when considered in conjunction with the
accompanying drawings, in which:
[0034] FIG. 1 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 1.
[0035] FIG. 2 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 2.
[0036] FIG. 3 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 3.
[0037] FIG. 4 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 4.
[0038] FIG. 5 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 5.
[0039] FIG. 6 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 6.
[0040] FIG. 7 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Comparative
Example 7.
[0041] FIG. 8 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Example 1.
[0042] FIG. 9 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Example 2.
[0043] FIG. 10 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Example 3.
[0044] FIG. 11 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Example 4.
[0045] FIG. 12 is a Scanning Electron Micrograph taken at
2000.times.magnification of the membrane used in Example 5.
[0046] FIG. 13 is a Scanning Electron Micrograph taken at
2500.times.magnification of the membrane used in Example 6.
[0047] FIG. 14 is a Scanning Electron Micrograph taken at
1000.times.magnification of the membrane used in Example 10.
[0048] FIG. 15 is a graph plotting composite Kq value versus
membrane modulus for several Examples of the invention and several
Comparatives Examples.
[0049] FIG. 16 is a graph plotting composite Kq value versus
membrane modulus for several Examples of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] The invention relates to the use of specific porous
polymeric membrane films in combination with resin to provide
toughening in composites, the composite structures themselves, the
method of making these composites, and their use in articles and
applications of commerce.
[0051] As stated above, the resin can be any suitable inorganic or
organic material or a combination thereof. In an aspect of the
invention, the resin has a room temperature flexural modulus of
greater than about 1 GPa. Suitable inorganic materials include, for
example, metals, metalloids, and ceramics. Suitable organic
materials include, for example, polymeric materials. If the resin
is an organic material it may also include non-polymeric
components, such as inorganic materials. For example, if an organic
material such as a polymeric material is used, the polymeric
material can also include (e.g., be combined with, mixed with, or
have dispersed therein) a ceramic and/or metal and/or metalloid
material. The resin, whether inorganic, organic, or a combination
thereof, has a room temperature flexural modulus of greater than
about 1 GPa. It should be understood that as used herein "resin"
includes all of the materials present in the resin component of the
composite. Thus, it is possible that when the resin is a
combination of two or more components, one of the components of the
resin (e.g. a polymeric material) could have a room temperature
flexural modulus of less than about 1 GPa, but if the combination
of the two components (e.g. combination of polymeric material and
ceramic filler) results in a material having a room temperature
flexural modulus of greater than about 1 GPa, then the resin is
according to the invention.
[0052] It has been unexpectedly found that composites with
desirable properties can be produced by imbibing a resin having a
room temperature flexural modulus of greater than about 1 GPa into
at least a portion of the porosity of a high tensile modulus porous
polymeric membrane film.
[0053] In a further aspect of the invention the ratio of the room
temperature flexural modulus of the resin to the room temperature
flexural modulus of the composite, measured in the direction of the
higher of the membrane transverse and longitudinal moduli, is
greater than or equal to about 1. In this aspect of the invention
the room temperature flexural modulus of the resin may or may not
be greater than about 1 GPa.
[0054] The porous polymeric membrane film meets the following
equation:
75 MPa<(longitudinal membrane tensile modulus +transverse
membrane tensile modulus)/2.
[0055] Membranes satisfying 100 MPa<(longitudinal membrane
tensile modulus+transverse membrane tensile modulus)/2 are more
preferred. Membranes satisfying 150 MPa<(longitudinal membrane
tensile modulus+transverse membrane tensile modulus)/2 are even
more preferred. Membranes satisfying 250 MPa<(longitudinal
membrane tensile modulus+transverse membrane tensile modulus)/2 are
even more preferred. Membranes satisfying 300 MPa<(longitudinal
membrane tensile modulus+transverse membrane tensile modulus)/2 are
even more preferred. Membranes satisfying 400 MPa<(longitudinal
membrane tensile modulus+transverse membrane tensile modulus)/2 are
most preferred. Membranes having tensile moduli>200 MPa in all
directions are the most preferred.
[0056] The membrane may contain organic and inorganic components.
Membranes comprising polymeric materials are preferred. Membranes
comprising stretched polymers are preferred. Membranes comprising
expanded PTFE are the most preferred. The polymeric membrane may
comprise virtually any polymeric material, for example vinyl
polymers, styrene, acrylate, methacrylate, polyethylenes,
polypropylenes, polyacrylonitrile, polyacrylamide, poly vinyl
chloride, fluoropolymers including PTFE, condensation polymers,
polysulfone, polyimides, polyamides, polycarbonates, polysulfides,
polyesters, polyanhydrides, polyacetals, polyurethanes, polyurea,
cellulose, cellulose derivatives, polysaccharides, pectinic
polymers and derivatives, alginic polymers and derivatives, chitin
and derivatives, phenolics, aldehyde polymers, polysiloxanes,
derivatives, copolymers and blends thereof.
[0057] The porous polymeric membrane film may be made by known
methods. Preferred are ePTFE membranes having minimal nodal
material. Most preferred are node-free ePTFE membranes. Such ePTFE
membranes can be made, for example, according to the teachings of
U.S. Pat. No. 5,476,589 to Bacino. Such membranes are formed
through biaxial expansion of PTFE so as to create a membrane that
is highly fibrillated--essentially eliminating coarse nodal
structure. As a result, the structure comprises an extremely strong
web of fine fibrils intersecting at fibril cross-over points.
Representative of such structures can be seen in the S.E.M. of FIG.
13. Large node structures, such as those described and illustrated
in U.S. Pat. No. 3,953,566, to Gore, are absent from such membrane
films. Representative of structures formed according to the
teachings of U.S. Pat. No. 3,953,566 can be seen in the S.E.M. of
FIG. 6 where large nodes and fibrils are clearly seen.
[0058] The expanded PTFE material according to U.S. Pat. No.
5,476,589 may be made in the following manner. A PTFE fine powder
that has a low amorphous content and a degree of crystallization of
at least 98% is used as the raw material. Suitable PTFE fine
powders include, for example, FLUON.RTM. CD-123 and FLUON.RTM. CD-1
fine powders available from ICI Americas, Inc., and TEFLON.RTM.
fine powders available from E.I. duPont de Nemours and Co., Inc.
The PTFE fine powder is first coagulated and then lubricated with a
hydrocarbon extrusion aid, preferably an odorless mineral spirit
such as ISOPAR.RTM. K (available from Exxon Corp.). The lubricated
powder is compressed into cylinders and extruded in a ram extruder
to form tapes. Two or more layers of tape can be stacked together
and compressed between two rolls. The tape or tapes are compressed
between rolls to an appropriate thickness, e.g., 0.1 to 1 mm, or
so. The wet tape is stretched traversely to 1.5 to 5 times its
original width. The extrusion aid is driven off with heat.
[0059] The dried tape is then expanded longitudinally between banks
of rolls in a space heated to a temperature that is below the
polymer melting point (327.degree. C.). The longitudinal expansion
is such that the ratio of speed of the second bank of rolls to the
first bank of rolls is 10-100 to 1. The longitudinal expansion is
repeated at a 1-1.5 to 1 ratio.
[0060] Next, the tape, after the longitudinal expansion, is
expanded traversely at a temperature that is less than 327.degree.
C. to at least 1.5 times and preferably to 6 to 15 times the input
width of the original extrudate while restraining the membrane from
longitudinal contraction. While still under constraint, the
membrane is preferably heated to above the polymer melting point
(327.degree. C.) and is then cooled.
[0061] Particularly preferred membranes are such node-free ePTFE
membranes having a high density of fibrils oriented in the
direction of maximum stress in the intended composite body.
Isotropic fibril orientation is preferred when stress may be loaded
from multiple directions.
[0062] The ePTFE membranes may have any suitable void content. In
an aspect of the invention the membrane can have a void content of
from about 1% to about 99.5% by volume. In a further aspect of the
invention, the void content can be from about 50% to about 90%.
With a preferred void content of from about 70-90%.
[0063] The membrane may optionally facilitate or be treated to
facilitate bonding to the resin component. Example treatments
include corona, plasma, chemical oxidation, etc.
[0064] To form the composites of the invention resin is imbibed
into at least a portion of the porosity of the membrane. Polymeric
resins are preferred and include thermoplastic resins, thermoset
resins, and combinations or mixtures thereof. In an aspect of the
invention the resin is polymeric and has a glass transition
temperature in the amorphous component of >80.degree. C.
[0065] Suitable thermoplastic resins include, for example, vinyl
polymers, styrene, acrylate, methacrylate, certain polyethylenes,
polypropylenes, polyacrylonitrile, polyacrylamide, poly vinyl
chloride, certain fluoropolymers, and combinations thereof.
Moreover, suitable thermoset resins include, for example, epoxy,
cyanate ester, bis maleimide, phenolics, unsaturated resins such as
unsaturated polyesters, hydrosilation resins,
polydicyclopentadiene, polyurethanes, polysulfide, acetylenic
resins, polyanhydrides, melamine, alkyds, ureas, isocyanates, and
combinations thereof. Particularly preferred polymeric resins
include thermoset resins including epoxy resins, cyanate esters,
and combinations thereof.
[0066] The resins may also include one or more suitable filler
materials. In an aspect of the invention the filler is dispersed
evenly in the resin. Filler materials can be in any suitable form,
such as particulate or fiber form. The filler can be any suitable
inorganic and/or organic material or combinations thereof. For
example, metals and alloys such as, but not limited to, nickel,
copper, aluminum, silicon, solder, silver, gold, metal-plated
materials such as silver-plated copper, silver-plated nickel,
silver-plated glass, etc., are useful. Moreover, inorganics such as
BaTiO.sub.3, SrTiO.sub.3, SiO.sub.2, Al2O.sub.3, BN, ZnO,
TiO.sub.2, MnO, CuO, Sb.sub.2O.sub.3, WC, fused silica, fumed
silica, amorphous fused silica, sol-gel silica, sol-gel titanates,
mixed titanates, lithium-containing ceramics, hollow glass
microspheres, carbon-based materials such as carbon, activated
charcoal, carbon black, ketchem black, diamond powder, etc., are
also useful. Particularly preferred fillers include BaTiO.sub.2,
SiO.sub.2, Al.sub.2O.sub.3, ZnO, TiO.sub.2, nickel and solder.
[0067] The selection of optional filler (and the amount thereof)
will depend on the desired properties of the final composite body.
For example, by selecting the proper filler, composite properties
such as conductivity, resistivity, modulus, strength, impact
behavior, thermal expansion, damping, weather resistance, wear
resistance, weight (either increase or decrease final weight of
composite), lubricity, friction, color, finish, sound
reflection--absorption--amplification, insulation, toughness, etc.,
may be controlled.
[0068] Fillers may optionally be surface treated to improve
composite performance. Examples of suitable surface treatments
include but are not limited to silanes, zirconates and titanates
and the like. These agents may act as wetting agents, processing
aids, flame retardants, colorants, etc.
[0069] Generally, it is desirable to fill as much of the membrane
porosity with resin as is possible. Preferably, the porosity is
essentially filled with resin. However, desirable composites can be
formed which include a substantial amount of porosity. In this
regard, preferred void contents of the final composite may range
from about 0% to about 70% by volume.
[0070] Any suitable method or process may be used to imbibe the
membrane with resin. For example, resin may be imbibed into the
membrane by one or more combinations of solvent impregnation, melt
impregnation, monomer infiltration, and film lamination. Imbibing
may be assisted by solvent, temperature, pressure, and vacuum and
any combination thereof designed to aid in getting the resin into
the membrane.
[0071] The form of the composite and method of manufacture of
articles can be in any of the forms and methods known in the art,
for example sheet molding, prepreg lay-up, compression molding,
thermoforming, tape wrap, extrusion and molding starting with
particulated membrane and/or particulated membrane-resin composite,
injection molding of resin or resin monomer into membrane preforms,
stamping, pultrusion, machining, etc. In one embodiment the
composite form is in sheets that are subsequently sheet molded into
articles. In yet another embodiment the resin-membrane composite
preform is particulated by grinding, cutting, cryogenic grinding,
or any other means of preparing small composite pieces, and then
fed into a mold via powder metering or through an extruder into a
mold to make a final part. Heat and pressure may optionally be
applied to flow the resin and/or provide thermal energy for curing
chemistries. In yet another embodiment membrane particulate is
combined with resin to make a molded article. In a preferred
embodiment articles are made from sheets of resin-membrane
composite combined with the use of heat and pressure.
[0072] Once the composite is formed, the composite will have many
end uses that will now be apparent to the skilled artisan. The
composite will be useful in electronics applications, such as a
dielectric material. Thus, it may be desirable to laminate, or
otherwise join, the composite to one or more metal layers (such as
aluminum, copper, gold, tin, silver, lead, etc.). Moreover, it may
be desirable to laminate, or otherwise join, the composite to one
or more capacitance layers (for example, ceramic filled
polymers).
[0073] The composite is also useful in combination with one or more
layers of high modulus fiber containing materials, such as glass
fibers, carbon fibers, and ceramic fibers. In this regard, the
composite of the invention can be laminated to, for example, a
layer of a high modulus fiber containing material to add toughness
to such a material. Such laminates are particularly useful as
structural materials, as well as in aerospace applications, defense
applications, and sporting goods applications.
[0074] For example, fishing, hunting, golf, tennis, skiing, track
and field, basketball, football, soccer, lacrosse, and hockey
related sporting goods materials such as rods, bows, arrow shafts,
clubs, rackets, sticks, skis and poles, javelins, helmets, pole
vault poles, backstops, and posts can be fabricated using the
composites of the invention. Thus, the present invention includes
sporting goods equipment comprising composites of the invention.
Aerospace materials applications include, for example, interior and
exterior aircraft-panels, flight critical parts, non-flight
critical parts, safety devices, fan blades, control surfaces,
struts, and the like can also be fabricated using the composites of
the invention. Thus, the present invention includes aerospace parts
comprising composites of the invention. Defense materials
applications include structural members, armor panels for personal
or vehicle defense (e.g., body armor plate apparel such as vest
armor and helmet armor, vehicle armor such as armor plating for
personnel carrier and tank sacrificial armor tiles), and military
equipment housings.
[0075] Further, it may be desirable to laminate together two or
more of the inventive composites to form relatively thicker
composites. Moreover, in an aspect of the invention, the composite
can be used as an inner layer of a composite structure. The
composite can serve as an interface adhesive layer, adhering
together two layers in a composite structure, such as a laminate.
Moreover, the composite can serve as an outer layer of a laminate.
Thus, the invention also provides a novel laminate comprising at
least one layer of the composite described above. In such
embodiments the composites of the invention are particularly
attractive due to their toughness. Specifically, during the
lamination process an operator will, generally, handle the
composite material (for example, a dielectric material) to be
laminated to, for example, a copper substrate. A potential problem
with this procedure is that currently used dielectric materials are
known to have a propensity to crack prior to, or during, lamination
and during end use due to stress induced chemically, mechanically,
thermally, or combinations thereof. This can result in lower
production efficiencies, wasted materials, failed parts, etc. By
providing the toughened composites of the invention, the cracking
problem will be greatly reduced.
[0076] End uses for the composites of the invention include, for
example, use in electronic applications, prepreg, cores, thin
cores, and ultra thin cores used in electronic substrates, printed
circuit boards, chip package substrates, silicon wafers, and outer
layer on composite structures. In an aspect of the invention the
composite can be used in forming electronic chip packages, which
are well known to the skilled artisan. Such electronic chip
packages comprise a laminated substrate having at least one
conductive layer and at least one dielectric layer bonded to the
conductive layer. Such packages can include a multitude of
alternating conductive/dielectric layers and can additionally
include one or more vias therein.
[0077] Further applications for the composites include, for
example, use in stress bearing applications including but not
limited to civil engineering, automotive, marine, trains, home and
commercial appliance, radome, construction, manufacturing,
furnishings, filtration, toys, dental including dental implants,
medical including medical implants, wire wrapping, and like
industries.
[0078] Properties enhanced include but are not limited to strength,
toughness, impact resistance, damage resistance, damage tolerance,
abrasion resistance, puncture resistance, etc.
[0079] Although the membrane enhances the toughness of resins
across the spectrum from those that are very brittle to those that
are extremely tough, in one preferred embodiment of this invention
the membrane is used to enhance the toughness of resins that
exhibit brittle failure in the absence of the membrane. Brittle
failure is defined as a fracture failure characterized by a
substantially linear stress strain curve until failure or a
characteristically smooth and substantially featureless fracture
surface. Enhanced toughness in these brittle materials greatly
increases the latitude with which these materials can be applied in
articles of commerce, enabling the use of lower cost, lower
molecular weight and easier to process resin components.
EXAMPLES
Examples 1-9 and Comparative Examples 1-7
[0080] Expanded PTFE membranes were impregnated with resin A or B
as noted in Tables 1 and 2. The composites were formed as follows.
A prepreg was laid up unidirectionally to prepare 1/8" (0.32 cm)
thick plaques as described below, cured, and then fracture
specimens cut from these plaques and fracture energy measured in
three point bend configuration following a modified ASTM D5045.
Specifically, specimen dimensions were 2.5"(6.4 cm).times.0.5"(1.27
cm).times.0.125"(0.32 cm) with a central precrack of approximately
40-60% of the 0.5" dimension. Prior to testing a fresh razor blade
was used to scribe a sharp crack into the specimen. Kq was
calculated using equation A1.4.3 in ASTM D 5045 using peak load in
the stress strain curve as Kq. Kq is a measure of the stress
intensity required for crack advancement. Testing was performed in
a three-point bend configuration with a span of 2.0" (5.08 cm) and
a cross-head speed of 0.1 mm/sec. Kq was measured in longitudinal
and transverse directions on the plaque and indicated by crack
direction in x and y direction, respectively. Membrane tensile
modulus was also measured in longitudinal and transverse
directions.
[0081] Membranes used in Examples 1-9 (according to the invention)
are characterized as having small nodes and /or being substantially
node-free membrane structures and further described by membrane
tensile modulus, as set forth in Table 2. Membranes used in the
Comparative Examples 1-7 (not according to the invention) are
characterized as having node and fibril membrane structures and
further described by membrane tensile modulus, as set forth in
Table 1. Impregnation of the membranes was accomplished by running
the membrane through a methyl ethyl ketone solution of the
respective resin followed by drying off of the solvent in an air
circulation oven. Plaques were prepared by laying up the prepreg
inside a 1/8" thick frame mold maintaining membrane direction in
each ply. The mold was covered with PTFE film on both sides and
pressed at 200 psi (1.378 KPa) until cured. After curing the PTFE
film was removed from both sides of the composite. Cure cycle for
resin A was 2 hours at 350.degree. F. (177.degree. C.). Cure cycle
for Resin B was 1 hour at 350.degree. F. (177.degree. C.) followed
by 2 hours at 435.degree. F. (244.degree. C.).
[0082] Resin A included the ingredients below and had a Tg of
130.degree. C. and a room temperature flexural modulus of 2.96 GPa.
Room temperature flexural modulus of Resin A was measured using a 3
point bend test geometry on a Rheometrics Solid Analyzer RSA II.
The sample was tested over a frequency range of 0.1 to 15 Hz. The
reported flexural modulus was taken as the modulus at 1 Hz. The
sample was measured using a strain of 0.02%. All testing was done
at ambient conditions.
1 Percent by Ingredient weight Supplier DER 538 A80 94.6 Eastech,
Philadelphia PA Epoxy resin XB4399A70 3.2 Vantico, Brewster NY
Muhifunctional epoxy resin 2 methyl imidazole 0.1 Fisher
Scientific, Pittsburgh, PA Dicyan diamide 2 Sigma Aldrich,
Milwaukee, WI FC430 0.1 3M, Saint Paul MN Surfactant
[0083] Resin B included the ingredients below and had a Tg of
215.degree. C. and a room temperature flexural modulus of 4.9 GPa.
The room temperature modulus of resin B was measured using strain
gauges on a sample measuring about 1/8" thick, about 1/2" wide, and
about 11/4" long. Measurement conditions followed ASTM D790 with an
adjusted span of 1".
2 Ingredient Percent by weight Supplier PT30 49.2 Lonza, Fairlawn,
NJ Cyanate ester resin GY2600 9.5 Vantico, Brewster NY Epoxy resin
ECN 1871 37.8 Ciba Geigy, Brewster NY Epxoy novolac resin Irganox
1010 1.5 Ciba Geigy, Brewster NY Antioxidant Ba-59P 2 Great Lakes
Chemical, West Flame Lafayette IN retardant
[0084] Tables 1 and 2 list the corresponding Figure showing an SEM
of the membrane used, the composite Kq for each of the composites
formed, the membrane tensile moduli data, the resin used to form
the composite, and the weight percent of ePTFE in the
composite.
3TABLE 1 Membrane SEM Composite K.sub.q Tensile Weight % Example of
Membrane MPa(M).sup.0.5 Modulus MPa Resin ePTFE Comparative X =
3.70 +/- 0.06 Longitudinal: 14 A 49 Example 1 Y = 3.42 +/- 0.12
Transverse: 57 Comparative X = 3.20 +/- 0.07 Longitudinal: 12 A 27
Example 2 Y = 3.11 +/- 0.08 Transverse: 96 Comparative X = 2.08 +/-
0.04 Longitudinal: 73 A 16 Example 3 Y = 2.74 +/- 0.05 Transverse:
7 Comparative X = 1.94 +/- 0.05 Longitudinal: 119 A 19 Example 4 Y
= 3.08 +/- 0.09 Transverse: 6 Comparative X = 2.11 +/- 0.04
Longitudinal: 133 A 27 Example 5 Y = 3.31 +/- 0.08 Transverse: 1
Comparative X = 3.27 +/- 0.09 Longitudinal: 16 A 35 Example 6 Y =
2.98 +/- 0.02 Transverse: 76 Comparative X = 3.06 +/- 0.04
Longitudinal: 86 A 32 Example 7 Y = 4.41 +/- 0.11 Transverse:
29
[0085]
4TABLE 2 Membrane SEM Composite K.sub.q Tensile modulus Weight %
Example of Membrane MPa(M).sup.0.5 MPa Resin ePTFE Example 1 X =
2.89 +/- 0.03 Longitudinal: A 33 Y = 5.85 +/- 0.09 257 Transverse:
6 Example 2 X = 2.79 +/- 0.03 Longitudinal: A 18 Y = 6.28 +/- 0.66
393 Transverse: 4 Example 3 X = 6.14 +/- 0.19 Longitudinal: 85 A 29
Y = 2.85 +/- 0.03 Transverse: 429 Example 4 X = 3.60 +/- 0.03
Longitudinal: A 25 Y = 5.99 +/- 0.13 286 Transverse: 21 Example 5 X
= 4.66 +/- 0.12 Longitudinal: A 25 Y = 3.42 +/- 0.09 143
Transverse: 96 Example 6 X = 8.90 +/- 0.32 Longitudinal: A 34 Y =
4.64 +/- 0.12 805 Transverse: 82 Example 7 -- X = 1.90 +/- 0.06
Longitudinal: B 27 Y = 3.41 +/- 0.16 320 Transverse: 16 Example 8
-- X = 3.97 +/- 0.22 Longitudinal: B 37 Y = 3.65 +/- 0.12 128
Transverse: 293 Example 9 -- X = 2.64 +/- 0.13 Longitudinal: B 37 Y
= 3.99 +/- 0.23 262 Transverse: 131
[0086] The ePTFE membranes were characterized as to tensile modulus
as follows. Specimens were die cut to 15 mm.times.165 mm strips.
Tensile tests were carried out on an Instron tensile strength
tester. Machine parameters were set as follows. Cross head speed:
508 mm/minute. Full scale load range: 0.1 kN. Grip distance: 50 mm.
Testing was conducted at ambient conditions. Young's modulus was
calculated with automatically defined limits (Series IX automated
Materials Testing System software). Sample thickness was measured
using a Kafer FZ1000/30 snap gauge. Measurements were taken in at
least four areas of each specimen.
[0087] FIG. 15 is a plot of composite Kq values versus membrane
modulus values for each composite formed using Resin A.
[0088] FIG. 16 is a plot of composite Kq values versus membrane
modulus values for each composite formed using Resin B.
[0089] The above examples show that using membranes according to
the invention results in composites having surprisingly high
toughness.
Example 10
[0090] Resin B, used in Examples 7, 8 and 9 (and having a room
temperature flexural modulus of 4.9 GPa), was imbibed into an
expanded PTFE membrane having a transverse tensile modulus of 119
MPa and a longitudinal tensile modulus of 56 MPa. FIG. 14 is a
Scanning Electron Micrograph taken at 1000.times.magnification of
the membrane used in this Example. The resin was imbibed into the
porosity of the membrane substantially as described in Examples 1-9
and Comparative Examples 1-7, to obtain a composite body. The room
temperature flexural modulus of the composite was 4.5 GPa (as
measured parallel to the membrane transverse direction). The room
temperature flexural modulus of the composite was measured using
the same method as was used to measure the room temperature
flexural modulus of Resin A, above. Thus, this example demonstrates
formation of a composite where the ratio of the resin room
temperature flexural modulus to the composite room temperature
flexural modulus (measured parallel to the membrane transverse
direction) is greater than 1.
Examples 11 and 12
[0091] ePTFE Membranes prepared as described in U.S. Pat. No.
5,476,589 were impregnated with polystyrene using a solution in
methyl ethyl ketone. Each membrane was impregnated by running the
membrane through the polymer solution followed by drying off of the
solvent. Polystyrene content was 70 +/-10% by weight of the final
composite. Plaques were prepared by laying up prepreg inside of a
1/8" thick frame mold. The mold was covered with PTFE film on both
sides and pressed at 200 psi (1.378 KPa). The thermal cycle was
200.degree. C. for 1 hour for Example 11 (low molecular weight
polystyrene (a blend of Mw=200,000 and 4,000)) and 250.degree. C.
for 1 hour for Example 12 (high molecular weight polystyrene (a Mw
of 280,000)). As used herein Mw is weight average molecular weight.
Both polystyrenes were obtained from Aldrich Chemical Company,
Milwaukee, Wis. and are available as Aldrich Cat# 33, 165-1 and
Aldrich Cat# 18, 242-7, respectively.
[0092] The ePTFE membrane used for each composite had a
longitudinal membrane tensile modulus of 241 MPa and a transverse
tensile modulus of 65 MPa. The room temperature flexural modulus of
the high molecular weight polystyrene was measured to be 3.8 GPa
while that of the composite was measured to be 3.2 GPa parallel to
the membrane transverse direction and 3.5 GPa parallel to the
membrane longitudinal direction. Room temperature flexural modulus
was measured using the same method as was used to measure the room
temperature flexural modulus of Resin A, above. Kq measurements
were made as described in the earlier Examples. Toughness data for
each example is set forth in Table 3.
5TABLE 3 Kq Kq Composite - Y Composite - X direction (90 degrees
Example Kq Neat resin direction to the X-direction) Example 11 0.12
+/- 0.02 1.2 +/- 0.18 2.6 +/- 0.45 MPa(m) 0.5 MPa(m) 0.5 MPa(m) 0.5
Example 12 2.2 +/- 0.26 3.5 +/- 0.16 4.2 +/- 0.32 MPa(m) 0.5 MPa(m)
0.5 MPa(m) 0.5
[0093] The above example demonstrates that using membranes
according to the invention results in composites having
surprisingly high toughness.
Examples 13 and 14 and Comparative Example 8
[0094] 900 um thick test laminate were prepared using commercially
available MICROLAM.RTM. 410 Dielectric, available from W. L. Gore
and Associates, Inc., Elkton, Md. The laminate were prepared from
stacked layers of MICROLAM.RTM. 410 Dielectric, pressed under 325
psi (2.24 KPa) and cured at 350.degree. F. (177.degree. C.) for 1
hour followed by 435.degree. F. (224.degree. C.) for 2 hours.
Specimens measuring 50 mm.times.12.5 mm were cut from the laminate.
Comparative Example 8 contained only layers of MICROLAM.RTM. 410
Dielectric. Examples 13 and 14 contained single outer plies of high
modulus ePTFE membrane, with the remainder being layers of
MICROLAM.RTM. 410 Dielectric. Examples 13 and 14 were prepared by
pressing the outer ePTFE layer with the inner MICROLAM.RTM. 410
Dielectric layers during lamination. During lamination, some of the
the resin from the MICROLAM.RTM. 410 Dielectric infiltrated at
least some of the porosity of the outer layer membrane. The resin
component of the MICROLAM.RTM. 410 Dielectric that infiltrated some
of the outer layer membrane porosity is essentially the same as
Resin B, above, and had a room temperature flexural modulus of
about 4.9 GPa. In Example 13 the outer layer membrane had a
longitudinal tensile modulus of 805 MPa and a transverse tensile
modulus of 82 MPa. In Example 14 the outer layer membrane had a
longitudinal tensile modulus of 570 MPa and a transverse tensile
modulus of 22 MPa. Thus, the outer layers of Example 13 and Example
14 are composites according to the invention.
[0095] Test specimens from each of Comparative Example 8 and
Examples 13 and 14 were then loaded in three point bend at a cross
head speed of 0.1 mm/minute and a span of 2.54 cm. Flexural
strength was calculated using peak load. Strength was calculated as
follows and data is listed in Table 4:
strength=3 PL/2 bd.sup.2
[0096] Where P=peak load, L=span, b=specimen width, d=specimen
depth.
6TABLE 4 Flexural Strength Flexural Strength (measured with sample
long (measured at 90 degrees from axis parallel to the longitudinal
membrane Example longitudinal membrane direction) Number direction)
(MPa) (MPa) Comparative 111 (+/- 3) 86 (+/- 5) Example 8 Example 13
126 (+/- 4) 118 (+/- 9) Example 14 124 (+/- 6) 110 (+/- 4)
[0097] These examples demonstrate that composites according to the
invention can be used as an outer layer in laminates to toughen
such laminates.
[0098] While particular embodiments of the present invention have
been illustrated and described herein, the present invention should
not be limited to such illustrations and descriptions. It should be
apparent that changes and modifications may be incorporated and
embodied as part of the present invention within the scope of the
following claims.
* * * * *