U.S. patent application number 10/771692 was filed with the patent office on 2005-08-04 for dynamic seal using vulcanization of fluorocarbon elastomers.
Invention is credited to Alajbegovic, Vahidin, Berdichevsky, Alexander, Park, Edward Hosung.
Application Number | 20050167928 10/771692 |
Document ID | / |
Family ID | 34679366 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050167928 |
Kind Code |
A1 |
Park, Edward Hosung ; et
al. |
August 4, 2005 |
Dynamic seal using vulcanization of fluorocarbon elastomers
Abstract
A dynamic seal assembly for installation between first and
second relatively rotating members, comprising a ring for fixed
engagement with said first member and an annular seal extending
radially from said ring and configured to slidably engage said
second member, wherein said radial seal has a thickness, and a
length that is from about 1 to about 15 times greater than said
thickness. In various embodiments, the seal is formed of a rubber
composition comprising a vulcanized fluorocarbon elastomer
dispersed in a matrix of a thermoplastic polymeric material. In
various embodiments, the matrix forms a continuous phase and the
vulcanized elastomeric material is in the form of particles forming
a non-continuous phase. The compositions may be made by combining a
curative, an uncured fluorocarbon elastomer, and a thermoplastic
material, and heating the mixture to effect vulcanization of the
elastomeric material, while applying mechanical energy.
Inventors: |
Park, Edward Hosung;
(Saline, MI) ; Berdichevsky, Alexander;
(Farmington Hills, MI) ; Alajbegovic, Vahidin;
(Novi, MI) |
Correspondence
Address: |
FREUDENBERG-NOK GENERAL PARTNERSHIP
LEGAL DEPARTMENT
47690 EAST ANCHOR COURT
PLYMOUTH
MI
48170-2455
US
|
Family ID: |
34679366 |
Appl. No.: |
10/771692 |
Filed: |
February 4, 2004 |
Current U.S.
Class: |
277/560 |
Current CPC
Class: |
C08J 3/246 20130101;
F16J 15/3284 20130101; F16J 15/3252 20130101; F16J 15/3244
20130101 |
Class at
Publication: |
277/560 |
International
Class: |
F16J 015/32 |
Claims
What is claimed is:
1. A dynamic seal assembly for installation between first and
second relatively rotating members, said assembly comprising: a
ring for fixed engagement with said first member and an annular
seal extending radially from said ring and configured to slidably
engage said second member, wherein said radial seal has a
thickness, and a length that is from about 1 to about 15 times
greater than said thickness.
2. A dynamic seal assembly according to claim 1, wherein said
length is from about 5 to about 15 times greater than said
thickness.
3. A dynamic seal assembly according to claim 2, wherein said
length is from about 5 to about 12 times greater than said
thickness.
4. A dynamic seal according to claim 1, wherein said radial seal is
comprises a cured fluorocarbon elastomer dispersed in a matrix
comprising a thermoplastic material.
5. A dynamic seal according to claim 4, wherein said cured
fluorocarbon elastomer is present as a discrete phase or a phase
co-continuous with said matrix, and wherein said radial seal has a
tan-delta of less than 1.0.
6. A dynamic seal according to claim 4, wherein the radial seal is
made by a process comprising the step of dynamically vulcanizing a
fluorocarbon elastomer in the presence of a thermoplastic
material.
7. A dynamic seal according to claim 4, wherein the hardness of
said annular seal is Shore A 50 or greater, the tensile strength of
the seal is 4 MPa or greater, the modulus at 100% of the article is
at least about 4 MPa, and the elongation at break of the article is
10% or greater.
8. A dynamic seal according to claim 4, wherein said cured
fluorocarbon elastomer is present at a level of at least about 35%
by weight based on the total weight of said cured fluorocarbon
elastomer and said thermoplastic polymer.
9. A dynamic seal according to claim 8, wherein said cured
fluorocarbon elastomer is present at a level of at least about 50%
by weight based on said total weight.
10. A dynamic seal according to claim 4, wherein said thermoplastic
material is a thermoplastic elastomeric material comprising an
amorphous polymer having a glass transition temperature of at least
about -40.degree. C.
11. A dynamic seal according to claim 4, wherein said thermoplastic
material is a reactive oligomer material which comprises a
semi-crystalline polymer having a melting point of at least about
80.degree. C.
12. A dynamic seal according to claim 4, wherein said fluorocarbon
elastomer is selected from the group consisting of VDF/HFP,
VDF/HFP/TFE, VDF/PFVE/TFE, TFE/Pr, TFE/Pr/VDF, TFE/Et/PFVE/VDF,
TFE/Et:PFVE, TFE/PFVE; and mixtures thereof.
13. A dynamic seal according to claim 1, wherein said radial seal
is made by a process comprising the steps of: (a) combining an
uncured or partially cured fluorocarbon elastomer, a curative agent
capable of reacting with the fluorocarbon elastomer to effect cure,
and a thermoplastic material; (b) mixing the combination; (c)
applying heat to the combination during the mixing step; and (d)
forming the seal by subjecting the composition to one of blow
molding, compressive molding, injection molding, or extrusion.
14. A dynamic seal according to claim 1 wherein the radial seal is
made by a process comprising made by a process comprising the steps
of: (a) mixing the elastomer and thermoplastic components in the
presence of the curative agent; (b) heating during mixing to effect
cure of the elastomeric components; and (c) injection molding the
composition.
15. A dynamic seal according to claim 1, wherein said first member
is a housing, and said second member is a rotating shaft.
16. A method for making a dynamic seal comprising: (a) forming a
mixture by combining a curative, an uncured or partially cured
elastomeric material, and a thermoplastic material; and (b) heating
the mixture at a temperature and for a time sufficient to effect
vulcanization of the elastomeric material, wherein mechanical
energy is applied to mix the mixture during the heating step;
wherein the elastomeric material comprises a fluorocarbon
elastomer; and wherein the thermoplastic material comprises a
non-fluorine-containing polymeric material; and (c) injection
molding the mixture.
17. A method according to claim 16, wherein said fluorocarbon
elastomer is selected from the group consisting of: VDF/HFP,
VDF/HFP/TFE, VDF/PFVE/TFE, TFE/Pr, TFE/Pr/VDF, TFE/Et/PFVE/VDF,
TFE/Et:PFVE, TFE/PFVE; and mixtures thereof.
18. A dynamic seal assembly for installation between an inner
rotating shaft and an outer housing comprising: an annular radial
seal extending from said non-rotating housing into sliding contact
with said shaft, said annular radial seal being configured to
slidably engage said shaft, said radial seal having a thickness,
and a length which is from about 1 to about 15 times greater than
said thickness, said annular radial seal further comprising a flat
bearing surface which contacts the rotating shaft.
19. A dynamic seal assembly according to claim 18, wherein said
length is from about 5 to about 15 times greater than said
thickness.
20. A dynamic seal assembly according to claim 19, wherein said
length is from about 5 to about 12 times greater than said
thickness.
21. A dynamic seal according to claim 18 wherein said flat bearing
surface comprises a variegated surface.
22. A dynamic seal according to claim 21, wherein said variegated
surface is a helical spiral groove.
23. A dynamic seal according to claim 18, wherein said annular seal
comprises a reinforcing bead.
24. A dynamic seal according to claim 18, wherein said annular seal
comprises a pair of suspension flanges and a spring disposed
between the suspension flanges.
25. A dynamic seal according to claim 18, wherein the annular seal
is formed of a material having a tangent delta of less than about
1.0.
26. A dynamic seal according to claim 18, wherein said annular seal
is formed of a material having a ratio of loss modulus to storage
modulus which is less than about 0.1.
Description
INTRODUCTION
[0001] This invention relates to seals, and more particularly
relates to annular seals of the type to be mounted on a rotating
shaft, such as, a wheel oil seal installed between a rotating shaft
and outer surrounding stationary housing of a motor vehicle.
[0002] Dynamic gaskets are typically formed of cured elastomeric
materials have a desirable set of physical properties typical of
the elastomeric state. These gaskets typically show a high tendency
to return to their original sized and shape following removal of a
deforming force, and they retain physical properties after repeated
cycles of stretching, including strain levels up to 1000%. Based on
these properties, the materials are generally useful for making
dynamic seal such as seals and gaskets.
[0003] Because they are formed of thermoset materials, gaskets
formed of cured elastomeric materials can not generally be
processed by conventional thermoplastic techniques such as
injection molding, extrusion, or blow molding. Rather, articles
must be fashioned from elastomeric materials by high temperature
curing and compression molding. Although these and other rubber
compounding operations are conventional and known, they
nevertheless tend to be more expensive and require higher capital
investment than the relatively simpler thermoplastic processing
techniques. Another drawback is that scrap generated in the
manufacturing process is difficult to recycle and reuse, which
further adds to the cost of manufacturing such articles.
[0004] In today's automobile engines, the high temperatures of use
have led to the development of a new generation of lubricants
containing a high level of basic materials such as amines. Seals
are often in contact with such fluids during use, and are subject
to a wide variety of challenging environmental conditions,
including exposure to high temperature, contact with corrosive
chemicals, and high wear conditions during normal use. Accordingly,
it is desirable to make seals from materials that combine
elastomeric properties and stability or resistance to the
environmental conditions.
[0005] To meet the demands of the new lubricant technology, seals
using fluorocarbon elastomers have been developed that are highly
resistant to the basic compounds found in the lubricating oils and
greases. Specifically seals formed of cured elastomers based on
copolymers of tetrafluoroethylene and propylene have met great
commercial success. As a thermoset material, the cured fluorocarbon
rubber is subject to the processing disadvantages noted above.
[0006] It would be desirable to provide an elastomeric or rubber
composition seal that would combine a high level of chemical
resistance with the advantages of thermoplastic processability. It
would further be desirable to provide methods for formulating
chemically resistant rubbers having such advantageous
properties.
SUMMARY
[0007] The present invention provides dynamic seal assemblies for
installation between first and second relatively rotating members,
comprising: a ring for fixed engagement with said first member and
an annular seal extending radially from said ring and configured to
slidably engage said second member, wherein said radial seal has a
thickness and a length that is from about 1 to about 15 times
greater than said thickness. In various embodiments, the assembly
comprises a dynamic seal for installation between an inner rotating
shaft and outer non-rotating housing comprising. The seal has a
first ring for fixed engagement with the housing including an
annular radial seal extending from the first ring into sliding
contact with the shaft. The annular radial seal, which is
configured to slidably engage the rotating shaft has a thickness
and a length being greater than and less than about 15 times
greater than the thickness.
[0008] In one embodiment of the invention, the seal is made of a
processable rubber composition containing a vulcanized elastomeric
material dispersed in a matrix of a thermoplastic polymeric
material. The elastomeric material comprises a synthetic,
non-crystalline fluorine-containing polymeric material that
exhibits elastomeric properties when crosslinked or vulcanized. In
a preferred embodiment, the material contains repeating units
derived from tetrafluoroethylene, at least one C.sub.2-4 olefin,
and optionally one or more additional fluorine-containing monomers.
In another, the material contains repeating units derived from
vinylidene fluoride, hexafluoropropylene, and optional other
fluorine-containing monomers. In one embodiment the matrix forms a
continuous phase and the vulcanized elastomeric material is in the
form of particles forming a non-continuous phase.
[0009] A method for making a dynamic seal rubber composition
comprises combining a curative, an elastomeric material as
described above, and a thermoplastic material, and heating the
mixture at a temperature and for a time sufficient to effect
vulcanization of the elastomeric material, while mechanical energy
is applied to mix the mixture during the heating step. The
thermoplastic material comprises a polymeric material that softens
and flows upon heating. The dynamic seals may be readily formed
from the rubber compositions according to conventional
thermoplastic processes such as blow molding, injection molding,
and extrusion.
[0010] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating embodiments of the invention, are
intended for purposes of illustration only and are not intended to
limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIGS. 1a and 1b are perspective views of a dynamic seal in
accordance with the teachings of the present invention;
[0012] FIGS. 2a and 2b are perspective views of a dynamic seal in
accordance with a second embodiment of the present invention;
[0013] FIGS. 3a and 3b are perspective views of a dynamic seal in
accordance with third embodiment of the present invention;
[0014] FIGS. 4a and 4b are perspective views of a dynamic seal in
accordance with a fourth embodiment of the present invention;
[0015] FIGS. 5a and 5b are perspective views of a dynamic seal in
accordance with a fifth embodiment of the present invention;
and
[0016] FIGS. 6a-6e are graphs describing material properties of
various materials.
[0017] It should be noted that the figures set forth herein are
intended to exemplify the general characteristics of the apparatus,
materials and methods among those of this invention, for the
purpose of the description of such embodiments herein. These
figures may not precisely reflect the characteristics of any given
embodiment, and are not necessarily intended to define or limit
specific embodiments within the scope of this invention.
DESCRIPTION
[0018] The following definitions and non-limiting guidelines must
be considered in reviewing the description of this invention set
forth herein.
[0019] The headings (such as "Introduction" and "Summary,") used
herein are intended only for general organization of topics within
the disclosure of the invention, and are not intended to limit the
disclosure of the invention or any aspect thereof. In particular,
subject matter disclosed in the "Introduction" may include aspects
of technology within the scope of the invention, and may not
constitute a recitation of prior art. Subject matter disclosed in
the "Summary" is not an exhaustive or complete disclosure of the
entire scope of the invention or any embodiments thereof.
[0020] The citation of references herein does not constitute an
admission that those references are prior art or have any relevance
to the patentability of the invention disclosed herein. Any
discussion of the content of references cited in the Introduction
is intended merely to provide a general summary of assertions made
by the authors of the references, and does not constitute an
admission as to the accuracy of the content of such references. All
references cited in the Description section of this specification
are hereby incorporated by reference in their entirety.
[0021] The description and specific examples, while indicating
embodiments of the invention, are intended for purposes of
illustration only and are not intended to limit the scope of the
invention. Moreover, recitation of multiple embodiments having
stated features is not intended to exclude other embodiments having
additional features, or other embodiments incorporating different
combinations of the stated features.
[0022] As used herein, the words "preferred" and "preferably" refer
to embodiments of the invention that afford certain benefits, under
certain circumstances. However, other embodiments may also be
preferred, under the same or other circumstances. Furthermore, the
recitation of one or more preferred embodiments does not imply that
other embodiments are not useful, and is not intended to exclude
other embodiments from the scope of the invention.
[0023] As used herein, the word "include," and its variants, is
intended to be non-limiting, such that recitation of items in a
list is not to the exclusion of other like items that may also be
useful in the materials, compositions, devices, and methods of this
invention.
[0024] FIGS. 1a and 1b are perspective views of one embodiment of a
dynamic seal 10 in accordance with the teachings of the present
invention. The dynamic seal 10 has a first ring 12 for fixed
engagement with the housing 14 which is coupled to an annular
radial seal 16 extending from the first ring 12 into sliding
contact with the shaft 18. The annular radial seal 16, which is
configured to slidably engage the rotating shaft 18, has a
thickness T and a length L that is from about 1 to about 15 times
greater than the thickness. Optionally, L is from about 3 to about
15 times greater than T, optionally from about 5 to about 12 times
greater than T, optionally from about 5 to about 10 times greater
than T.
[0025] In various embodiments, the dynamic seal 10 is formed of a
processable rubber compositions comprising a vulcanized elastomeric
material dispersed in a matrix. The vulcanized elastomeric material
is the product of vulcanizing, crosslinking, or curing a
fluorocarbon elastomer. The matrix is made of a thermoplastic
material containing at least one containing thermoplastic polymer.
The processable rubber compositions may be processed by
conventional thermoplastic techniques to form dynamic seal having
physical properties that make them useful in a number of
applications calling for elastomeric properties.
[0026] As seen in FIG. 1b, the dynamic seal 10 can have a flat
bearing surface 20 which interfaces with the rotating shaft 18.
Additionally shown is an optional reinforcement bead 22 which
increases the bearing force of the seal against the rotating shaft
18. The length of the bearing surface 20 is between 1 and 99%, and
preferably 25-75% of the length.
[0027] As can be seen in FIG. 2b, the dynamic seal 10b an have a
bearing surface 20b which is substantially variegated. In this
regard, a spiral groove 24 is formed onto a portion of the flat
bearing surface 20b. It is envisioned that there can be between 5
and 200 grooves per inch, and these grooves would cover between 10
and 90%, and preferably 25-75% of the flat bearing surface. The
number of spiral grooves which contact with the shaft surface is
between 1 and 10, and preferably between 1 and 3 grooves in contact
with the shaft.
[0028] FIGS. 3a and 3b represent another embodiment of the dynamic
seal. Shown is a flange portion having a pair of suspension flanges
24. Disposed between the suspension flanges 24 is a spring
reinforcement member 26. The spring reinforcement member 26
functions to increase the coupling force between the bearing
surface 20b and the rotating shaft 18.
[0029] FIGS. 4a-5b represent alternate dynamic seal 10c and 10d. As
can be seen, the seals can have varying length to width ratios.
Specifically, the length per width ratio of the seal is greater
than 1 to about 15, and preferably about 5 to 12, and most
preferably 8 to 10. Additionally, the dynamic seals need not have a
reinforcing rib or variegated bearing surface.
[0030] In particular preferred embodiments, a dynamic seal 10 is
made from the processable compositions typically exhibit a Shore A
hardness of 50 or more, preferably Shore A 70 or more, typically in
the range of Shore A 70 to Shore A 90. In addition or
alternatively, the tensile strength of the dynamic seal will
preferably be 4 MPa or greater, preferably 8 MPa or greater,
typically about 8-13 MPa.
[0031] In still other embodiments, the dynamic seal 10 has a
modulus at 100% of at least 2 MPa, preferably at least about 4 MPa,
and typically in the range of about 4-8 MPa. In other embodiments,
elongation at break of articles made from the processable
compositions of the invention will be 10% or greater, preferably at
least about 50%, more preferably at least about 150%, and typically
in the range of 150-300%. Dynamic seal 10 of the invention may be
characterized as having at least one of hardness, tensile strength,
modulus, and elongation at break in the above noted ranges.
[0032] In various embodiments, the dynamic seal 10 is formed of a
rubber composition comprising two-phases, where the matrix forms a
continuous phase, and the vulcanized elastomeric material is in the
form of particles forming a non-continuous, disperse, or discrete
phase. In another aspect, the dynamic seal 10 is formed of
elastomeric material and the matrix form co-continuous phases. The
compositions of the elastomeric material contains 35% by weight or
more, and preferably 40% by weight or more of the elastomer phase,
based on the total weight of elastomer and thermoplastic material.
Optionally, the compositions contains 50% by weight or more of the
elastomer phase. The elastomer phase may be present in the form of
particles in a continuous thermoplastic phase, as a 3-D network
forming a co-continuous phase with the thermoplastic material, or
as a mixture of both. The particles or 3-D network of the elastomer
phase preferably have minimum dimensions of 10 .mu.m or less, and
more preferably 1 .mu.m or less.
[0033] The dynamic seal 10 may be formed of a rubber composition
which is made by dynamic vulcanization of a fluorocarbon elastomer
in the presence of a thermoplastic component. In this regard, the
method for producing a dynamic seal is provided. The formation of
the seal begins with combining a curative agent, an elastomeric
material, and a thermoplastic material to form a mixture. The
mixture is heated at a temperature and for a time sufficient to
effect vulcanization or cure of the fluorocarbon elastomer in the
presence of the thermoplastic material. Mechanical energy is
applied to the mixture of elastomeric material, curative agent and
thermoplastic material during the heating step. The elastomer and
thermoplastic components in the presence of a curative agent and
heating during the mixing to effect cure of the elastomeric
component. Alternatively, the elastomeric material and
thermoplastic material may be mixed for a time and at a shear rate
sufficient to form a dispersion of the elastomeric material in a
continuous or co-continuous thermoplastic phase. Thereafter, a
curative agent may be added to the dispersion of elastomeric
material and thermoplastic material while continuing the mixing.
Finally, the dispersion is heated while continuing to mix to
produce the processable rubber composition of the invention.
[0034] The desired properties of polymeric materials for dynamic
shaft seal are the ratio of recovery time to real time and the
ratio of loss modulus to storage modulus, which is described as
tangent delta. Ideally, the ratio of recovery time to real time
should be less than 1 to function as dynamic shaft seal without
leakage. The ratio of loss modulus to storage modulus changes with
changes in temperature. Typically, cured elastomers show the less
than 1 for dynamic seal; however, plastic polymeric materials
exhibit equal to 1 or greater. PTFE is one of the plastic materials
used for dynamic seal, and it functions as a dynamic seal even
though the ratio is greater than 1. The long and curved lip design
tend to compensate the lack of desired property to prevent
"bellmouthing" behavior which leads to leakage.
[0035] At the same token, the ratio of loss modulus to storage
modulus is desirable to be less that 0.1. The ratio is typically
described as a tangent delta value with DMTA (Dynamic Mechanical
Thermal Analyzer). Again, the elastomeric materials usually show
less than 0.1 value; however, plastic materials exhibit equal or
greater than 0.1 due to more viscosity contribution than
elastomeric contribution of typical visco-elastic behavior of
plastic materials. The typical value of PTFE plastic is greater
than 0.1, especially at the phase transition temperatures
(20.degree., 120.degree., etc.). However, the long and curved lip
design tend to compensate to prevent "bellmouthing" behavior. TPU
and TPE type thermoplastic materials according to the present
invention can function as dynamic seal by applying proper design to
compensate for the lack of desired material properties, which could
cause for leakage due to "bellmouthing" properties of plastic-like
materials. The long and curved lip design, and associated
reinforcement structure at the end of lip seal, and loading of
spring at the tip of the lip seal features proposed to compensate
for the lack of desirable material properties for dynamic seal
applications. In this regard, it is preferable that the ratio of
loss modulus to storage modulus of the material used in the seal is
less than 10, and most preferably less than 1.0.
[0036] FIGS. 6a-6c represent material properties of the materials
used to form the dynamic seal of the present invention.
Specifically, shown is the value of tan-delta as a function of
temperature. For comparison with thermoplastic and elastomeric
material, FIGS. 6d and 6e are provided.
[0037] FIG. 6a represents testing of the material used to form the
seal of the present invention. This material is formed of 70.0 pphn
Dyneon FE5840; 30.0 pphn Dyneon BRE 7231X; 25.0 pphn Dyneon
THV815X; 6.0 pphn Rhenofit CF; 3.0 pphn Elastomag 170; 1.0 pphn
Kemamide 5221; and 10.0 pphn Austin Black.
[0038] The compositions of the invention are preferably processable
by conventional plastic processing techniques. In another
embodiment, dynamic seal is provided comprising the cured,
fluorocarbon elastomers dispersed in a thermoplastic matrix.
Preferred fluorocarbon elastomers include commercially available
copolymers of one or more fluorine containing monomers, chiefly
vinylidene fluoride (VDF), hexafluoropropylene (HFP),
tetrafluoroethylene (TFE), and perfluorovinyl ethers (PFVE).
Preferred PFVE include those with a C.sub.1-8 perfluoroalkyl group,
preferably perfluoroalkyl groups with 1 to 6 carbons, and
particularly perfluoromethyl vinyl ether and perfluoropropyl vinyl
ether. In addition, the copolymers may also contain repeating units
derived from olefins such as ethylene (Et) and propylene (Pr). The
copolymers may also contain relatively minor amounts of cure site
monomers (CSM), discussed further below. Preferred copolymer
fluorocarbon elastomers include VDF/HFP, VDF/HFP/CSM, VDF/HFP/TFE,
VDF/HFP/TFE/CSM, VDF/PFVE/TFE/CSM, TFE/Pr, TFE/Pr/VDF,
TFE/Et/PFVE/VDF/CSM, TFE/Et/PFVE/CSM and TFE/PFVE/CSM. The
elastomer designation gives the monomers from which the elastomer
gums are synthesized. The elastomer gums have viscosities that give
a Mooney viscosity in the range generally of 15-160 (ML1+10, large
rotor at 121.degree. C.), which can be selected for a combination
of flow and physical properties. Elastomer suppliers include Dyneon
(3M), Asahi Glass Fluoropolymers, Solvay/Ausimont, Dupont, and
Daikin.
[0039] In one embodiment, the elastomeric material is described as
a copolymer of tetrafluoroethylene and at least one C.sub.2-4
olefin. As such, the elastomeric material comprises repeating units
derived from tetrafluoroethylene and at least one C.sub.2-4 olefin.
Optionally, the elastomeric material may contain repeating units
derived from one or more additional fluorine-containing
monomers.
[0040] In a preferred embodiment, the elastomeric material
comprises repeating units derived from 10-90 mole %
tetrafluoroethylene, 10-90 mole % C.sub.2-4 olefin, and up to 30
mole % of one or more additional fluorine-containing monomers.
Preferably, the repeating units are derived from 25-90 mole %
tetrafluoroethylene and 10-75 mole % C.sub.2-4 olefin. In another
preferred embodiment, the repeating units are derived from 45-65
mole % tetrafluoroethylene and 20-55 mole % C.sub.2-4 olefin.
[0041] In another embodiment, the elastomeric materials are curable
fluorocarbon elastomers containing repeating units derived from
fluoromonomers vinylidene fluoride (VDF) and hexafluoropropylene
(HFP). In some embodiments, the elastomers further contain
repeating units derived from tetrafluoroethylene. The elastomeric
materials may be cured or crosslinked as described below to provide
cured materials with rubber-like properties.
[0042] Chemically, in this embodiment the elastomeric material is
made of copolymers of VDF and HFP, or of terpolymers of VDF, HFP,
and tetrafluoroethylene (TFE), with optional cure site monomers. In
preferred embodiments, they contain about 66 to about 70% by weight
fluorine. The elastomers are commercially available, and are
exemplified by the Viton.RTM. A, Viton.RTM. B, and Viton.RTM. F
series of elastomers from DuPont Dow Elastomers. Grades are
commercially available containing the gum polymers alone, or as
curative-containing pre-compounds.
[0043] In another embodiment, the elastomers can be described
chemically as copolymers of TFE and PFVE, optionally as a
terpolymer with VDF. The elastomer may further contain repeating
units derived from cure site monomers. The fluorocarbon elastomeric
materials used to make the processable rubber compositions of the
invention may typically be prepared by free radical emulsion
polymerization of a monomer mixture containing the desired molar
ratios of starting monomers. Initiators are typically organic or
inorganic peroxide compounds, and the emulsifying agent is
typically a fluorinated acid soap. The molecular weight of the
polymer formed may be controlled by the relative amounts of
initiators used compared to the monomer level and the choice of
transfer agent if any. Typical transfer agents include carbon
tetrachloride, methanol, and acetone. The emulsion polymerization
may be conducted under batch or continuous conditions.
[0044] The thermoplastic material making up the matrix includes at
least one component that is a thermoplastic polymer. This
thermoplastic material can be a fluorine containing a non-fluorine
containing thermoplastic. The polymeric material softens and flows
upon heating. In one aspect, a thermoplastic material is one the
melt viscosity of which can be measured, such as by ASTM D-1238 or
D-2116, at a temperature above its melting point.
[0045] The thermoplastic material of the invention may be selected
to provide enhanced properties of the rubber/thermoplastic
combination at elevated temperatures, preferably above 80.degree.
C. and more preferably at about 150.degree. C. and higher. Such
thermoplastics include those that maintain physical properties,
such as at least one of tensile strength, modulus, and elongation
at break to an acceptable degree at the elevated temperature. In a
preferred embodiment, the thermoplastics possess physical
properties at the elevated temperatures that are superior (i.e.
higher tensile strength, higher modulus, and/or higher elongation
at break) to those of the cured fluorocarbon elastomer (rubber) at
a comparable temperature.
[0046] The thermoplastic polymeric material used in the invention
may be a reactive oligomer type thermoplastic. Thermoplastic
oligomer polymerized at the elevated temperature (150-250.degree.
C.) to form high molecular weight thermoplastics. Cyclic oligomer
from Cyclics Corporation is one example. It becomes polybutyelene
terephtalate (PBT) when polymerized, a thermoplastic polyester.
[0047] The thermoplastic polymeric material used in the invention
may be a thermoplastic elastomer. Thermoplastic elastomers have
some physical properties of rubber, such as softness, flexibility
and resilience, but may be processed like thermoplastics. A
transition from a melt to a solid rubber-like composition occurs
fairly rapidly upon cooling. This is in contrast to conventional
elastomers, which harden slowly upon heating. Thermoplastic
elastomers may be processed on conventional plastic equipment such
as injection molders and extruders. Scrap may generally be readily
recycled.
[0048] Thermoplastic elastomers have a multi-phase structure,
wherein the phases are generally intimately mixed. In many cases,
the phases are held together by graft or block copolymerization. At
least one phase is made of a material that is hard at room
temperature but fluid upon heating. Another phase is a softer
material that is rubber like at room temperature.
[0049] Many thermoplastic elastomers are known. Non-limiting
examples of A-B-A type thermoplastic elastomers include
polystyrene/polysiloxane/poly- styrene,
polystyrene/polyethylene-co-butylene/polystyrene,
polystyrene/polybutadiene polystyrene,
polystyrene/polyisoprene/polystyre- ne,
poly-.alpha.-methylstyrene/polybutadiene/poly-a-methylstyrene,
poly-.alpha.-methyl
styrene/polyisoprene/poly-.alpha.-methylstyrene, and
polyethylene/polyethylene-co-butylene/polyethylene.
[0050] Non-limiting examples of thermoplastic elastomers having a
(A-B).sub.n repeating structure include polyamide/polyether,
polysulfone/polydimethylsiloxane, polyurethane/polyester,
polyurethane/polyether, polyester/polyether,
polycarbonate/polydimethylsi- loxane, and polycarbonate/polyether.
Among the most common commercially available thermoplastic
elastomers are those that contain polystyrene as the hard segment.
Triblock elastomers are available with polystyrene as the hard
segment and either polybutadiene, polyisoprene, or
polyethylene-co-butylene as the soft segment. Similarly, styrene
butadiene repeating co-polymers are commercially available, as well
as polystyrene/polyisoprene repeating polymers.
[0051] The thermoplastic polymeric material may also be selected
from among solid, generally high molecular weight, plastic
materials. Preferably, the materials are crystalline or
semi-crystalline polymers, and more preferably have a crystallinity
of at least 25 percent as measured by differential scanning
calorimetry. Amorphous polymers with a suitably high glass
transition temperature are also acceptable as the thermoplastic
polymeric material. The thermoplastic also preferably has a melt
temperature in the range from about 80.degree. C. to about
350.degree. C., or glass transition temperature in the range of
-40.degree. to about 300.degree. C., but the melt temperature
should generally be lower than the decomposition temperature of the
thermoplastic vulcanizate.
[0052] Non-limiting examples of thermoplastic polymers include
polyolefins, polyesters, nylons, polycarbonates,
styrene-acrylonitrile copolymers, polyethylene terephthalate,
polybutylene terephthalate, polyamides, polystyrene, polystyrene
derivatives, polyphenylene oxide, polyoxymethylene, and
fluorine-containing thermoplastics.
[0053] Polyolefins are formed by polymerizing .alpha.-olefins such
as, but not limited to, ethylene, propylene, 1-butene, 1-hexene,
1-octene, 2-methyl-1-propene, 3-methyl-1-pentene,
4-methyl-1-pentene, 5-methyl-1-hexene, and mixtures thereof.
Copolymers of ethylene and propylene or ethylene or propylene with
another a-olefin such as 1-butene, 1-hexene, 1-octene,
2-methyl-1-propene, 3-methyl-1-pentene, 4-methyl-1-pentene,
5-methyl-1-hexene or mixtures thereof are also contemplated. These
homopolymers and copolymers, and blends of them, may be
incorporated as the thermoplastic polymeric material of the
invention.
[0054] Polyester thermoplastics contain repeating ester linking
units in the polymer backbone. In one embodiment, they contain
repeating units derived from low molecular weight diols and low
molecular weight aromatic diacids. Non-limiting examples include
the commercially available grades of polyethylene terephthalate and
polybutylene terephthalate. Alternatively, the polyesters may be
based on aliphatic diols and aliphatic diacids. Exemplary are the
copolymers of ethylene glycol or butanediol with adipic acid. In
another embodiment, the thermoplastic polyesters are polylactones,
prepared by polymerizing a monomer containing both hydroxyl and
carboxyl functionality. Polycaprolactone is a non-limiting example
of this class of thermoplastic polyester.
[0055] Polyamide thermoplastics contain repeating amide linkages in
the polymer backbone. In one embodiment, the polyamides contain
repeating units derived from diamine and diacid monomers such as
the well known nylon 66, a polymer of hexamethylene diamine and
adipic acid. Other nylons have structures resulting from varying
the size of the diamine and diacid components. Non-limiting
examples include nylon 610, nylon 612, nylon 46, and nylon 6/66
copolymer. In another embodiment, the polyamides have a structure
resulting from polymerizing a monomer with both amine and carboxyl
functionality. Non-limiting examples include nylon 6
(polycaprolactam), nylon 11, and nylon 12.
[0056] Other polyamides made from diamine and diacid components
include the high temperature aromatic polyamides containing
repeating units derived from diamines and aromatic diacids such as
terephthalic acid. Commercially available examples of these include
PA6T (a copolymer of hexanediamine and terephthalic acid), and PA9T
(a copolymer of nonanediamine and terephthalic acid), sold by
Kuraray under the Genestar tradename. For some applications, the
melting point of some aromatic polyamides may be higher than
optimum for thermoplastic processing. In such cases, the melting
point may be lowered by preparing appropriate copolymers. In a
non-limiting example, in the case of PA6T, which has a melting
temperature of about 370.degree. C., it is possible to in effect
lower the melting point to below a moldable temperature of
320.degree. C. by including an effective amount of a non-aromatic
diacid such as adipic acid when making the polymer.
[0057] Other non-limiting examples of high temperature
thermoplastics include polyphenylene sulfide, liquid crystal
polymers, and high temperature polyimides. Liquid crystal polymers
are based chemically on linear polymers containing repeating linear
aromatic rings. Because of the aromatic structure, the materials
form domains in the nematic melt state with a characteristic
spacing detectable by x-ray diffraction methods. Examples of
materials include copolymers of hydroxybenzoic acid, or copolymers
of ethylene glycol and linear aromatic diesters such as
terephthalic acid or naphthalene dicarboxylic acid.
[0058] High temperature thermoplastic polyimides include the
polymeric reaction products of aromatic dianhydrides and aromatic
diamines. They are commercially available from a number of sources.
Exemplary is a copolymer of 1,4-benzenediamine and
1,2,4,5-benzenetetracarboxylic acid dianhydride.
[0059] In a preferred embodiment, the matrix comprises at least one
non-fluorine containing thermoplastic, such as those described
above. Thermoplastic fluorine-containing polymers may be selected
from a wide range of polymers and commercial products. The polymers
are melt processable--they soften and flow when heated, and can be
readily processed in thermoplastic techniques such as injection
molding, extrusion, compression molding, and blow molding. The
materials are readily recyclable by melting and re-processing.
[0060] The thermoplastic polymers may be fully fluorinated or
partially fluorinated. Fully fluorinated thermoplastic polymers
include copolymers of tetrafluoroethylene and perfluoroalkyl vinyl
ethers. The perfluoroalkyl group is preferably of 1 to 6 carbon
atoms. Other examples of copolymers are PFA (copolymer of TFE and
perfluoropropyl vinyl ether) and MFA (copolymer of TFE and
perfluoromethyl vinyl ether). Other examples of fully fluorinated
thermoplastic polymers include copolymers of TFE with
perfluoroolefins of 3 to 8 carbon atoms. Non-limiting examples
include FEP (copolymer of TFE and hexafluoropropylene).
[0061] Partially fluorinated thermoplastic polymers include E-TFE
(copolymer of ethylene and TFE), E-CTFE (copolymer of ethylene and
chlorotrifluoroethylene), and PVDF (polyvinylidene fluoride). A
number of thermoplastic copolymers of vinylidene fluoride are also
suitable thermoplastic polymers for use in the invention. These
include, without limitation, copolymers with perfluoroolefins such
as hexafluoropropylene, and copolymers with
chlorotrifluoroethylene.
[0062] Thermoplastic terpolymers may also be used. These include
thermoplastic terpolymers of TFE, HFP, and vinylidene fluoride.
These and other fluorine-containing thermoplastic materials are
commercially available. Suppliers include Dyneon (3M), Daikin,
Asahi Glass Fluoroplastics, Solvay/Ausimont and DuPont
[0063] Useful curative agents include diamines, peroxides, and
polyol/onium salt combinations. Diamine curatives have been known
since the 1950's. Diamine curatives are relatively slow curing, but
offer advantages in several areas. Such curatives are commercially
available, for example as Diak-1 from DuPont Dow Elastomers.
[0064] Heating and mixing or mastication at vulcanization
temperatures are generally adequate to complete the vulcanization
reaction in a few minutes or less, but if shorter vulcanization
times are desired, higher temperatures and/or higher shear may be
used. A suitable range of vulcanization temperature is from about
the melting temperature of the thermoplastic material (typically
120.degree. C.) to about 300.degree. C or more. Typically, the
range is from about 150.degree. C. to about 250.degree. C. A
preferred range of vulcanization temperatures is from about
180.degree. C. to about 220.degree. C. It is preferred that mixing
continue without interruption until vulcanization occurs or is
complete.
[0065] If appreciable curing is allowed after mixing has stopped,
an unprocessable thermoplastic vulcanizate may be obtained. In this
case, a kind of post curing step may be carried out to complete the
curing process. In some embodiments, the post curing takes the form
of continuing to mix the elastomer and thermoplastic during a
cool-down period.
[0066] After dynamic vulcanization, a homogeneous mixture is
obtained, wherein the rubber is in the form of small dispersed
particles essentially of an average particle size smaller than
about 50 .mu.m, preferably of an average particle size smaller than
about 25 .mu.m. More typically and preferably, the particles have
an average size of about 10 .mu.m or less, preferably about 5 .mu.m
or less, and more preferably about 1 .mu.m or less. In other
embodiments, even when the average particle size is larger, there
will be a significant number of cured elastomer particles less than
1 .mu.m in size dispersed in the thermoplastic matrix.
[0067] The size of the particles referred to above may be equated
to the diameter of spherical particles, or to the diameter of a
sphere of equivalent volume. It is to be understood that not all
particles will be spherical. Some particles will be fairly
isotropic so that a size approximating a sphere diameter may be
readily determined. Other particles may be anisotropic in that one
or two dimensions may be longer than another dimension. In such
cases, the preferred particle sizes referred to above correspond to
the shortest of the dimensions of the particles.
[0068] In some embodiments, the cured elastomeric material is in
the form of particles forming a dispersed, discrete, or
non-continuous phase wherein the particles are separated from one
another by the continuous phase made up of the thermoplastic
matrix. Such structures are expected to be more favored at
relatively lower loadings of cured elastomer, i.e. where the
thermoplastic material takes up a relatively higher volume of the
compositions. In other embodiments, the cured material may be in
the form of a co-continuous phase with the thermoplastic material.
Such structures are believed to be favored at relatively higher
volume of the cured elastomer. At intermediate elastomer loadings,
the structure of the two-phase compositions may take on an
intermediate state in that some of the cured elastomer may be in
the form of discrete particles and some may be in the form.
* * * * *