U.S. patent application number 11/591204 was filed with the patent office on 2007-03-08 for elastomeric compositions containing fluoropolymer blends.
This patent application is currently assigned to Freudenberg-NOK General Partnership. Invention is credited to Edward Hosung Park.
Application Number | 20070055020 11/591204 |
Document ID | / |
Family ID | 34933467 |
Filed Date | 2007-03-08 |
United States Patent
Application |
20070055020 |
Kind Code |
A1 |
Park; Edward Hosung |
March 8, 2007 |
Elastomeric compositions containing fluoropolymer blends
Abstract
Processable rubber compositions contain a vulcanized
fluorocarbon elastomer dispersed in a thermoplastic matrix
comprising a fully fluorinated polymer and a partially fluorinated
polymer. The processing temperature is below the melting point of
the fully fluorinated polymer. The compositions are made by
combining a curative, uncured fluorocarbon elastomer, a fully
fluorinated thermoplastic, and a partially fluorinated
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. Shaped articles such as seals,
gaskets, O-rings, and hoses may be readily formed from the rubber
compositions according to conventional thermoplastic processes such
as blow molding, injection molding, and extrusion.
Inventors: |
Park; Edward Hosung;
(Saline, MI) |
Correspondence
Address: |
FREUDENBERG-NOK GENERAL PARTNERSHIP;LEGAL DEPARTMENT
47690 EAST ANCHOR COURT
PLYMOUTH
MI
48170-2455
US
|
Assignee: |
Freudenberg-NOK General
Partnership
Plymouth
MI
|
Family ID: |
34933467 |
Appl. No.: |
11/591204 |
Filed: |
November 1, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10813527 |
Mar 30, 2004 |
7135527 |
|
|
11591204 |
Nov 1, 2006 |
|
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Current U.S.
Class: |
525/199 |
Current CPC
Class: |
C08L 2205/03 20130101;
C08L 2205/02 20130101; C08J 2327/12 20130101; C08L 27/18 20130101;
C08L 27/20 20130101; C08L 2666/04 20130101; C08L 2666/04 20130101;
C08L 2666/04 20130101; C08L 2666/04 20130101; C08L 27/12 20130101;
C08L 27/16 20130101; C08L 27/16 20130101; C08L 27/20 20130101; C08L
27/18 20130101; C08L 27/12 20130101; C08J 3/24 20130101 |
Class at
Publication: |
525/199 |
International
Class: |
C08L 27/12 20060101
C08L027/12 |
Claims
1.-14. (canceled)
15. A processable rubber composition comprising a cured
fluorocarbon elastomer dispersed in a thermoplastic matrix, wherein
the thermoplastic matrix comprises a fully fluorinated
thermoplastic melt-processable polymer and a partially fluorinated
thermoplastic melt-processable polymer; the cured fluorocarbon
elastomer is present as a discrete phase or a phase co-continuous
with the matrix; and the dimensions of the elastomer phase are less
than 10 .mu.m, as measured by atomic force microscopy on
cryogenically microtomed cross-sections of shaped articles formed
from the processable rubber composition.
16. A composition according to claim 15, wherein the dimensions of
the elastomer phase are less than or equal to 1 .mu.m.
17. A composition according to claim 15, wherein the cured
fluorocarbon elastomer is present at least in part as particles
dispersed in a continuous thermoplastic phase.
18. A composition according to claim 15, wherein the cured
fluorocarbon elastomer is present at least in part in a dispersed
phase co-continuous with the thermoplastic phase.
19. A composition according to claim 15, wherein the composition
exhibits a single melting temperature of less than 290.degree.
C.
20. A composition according to claim 15, wherein the composition
exhibits a single melting temperature of less than 250.degree.
C.
21. A composition according to claim 15, wherein the ratio of the
weight of the fully fluorinated polymer to the weight of the
partially fluorinated polymer in the matrix ranges from 1:9 to
9:1.
22. A composition according to claim 21, wherein the ratio of the
weight of the fully fluorinated polymer to the weight of the
partially fluorinated polymer in the matrix ranges from 1:2 to
2:1.
23. A method for making a processable rubber composition
comprising: mixing an elastomeric component and a thermoplastic
component in the presence of a curative agent, and heating during
mixing to effect cure of the elastomeric component wherein the
elastomeric material comprises a fluorocarbon elastomer; and
wherein the thermoplastic material is a fluoroplastic blend
comprising a fully fluorinated thermoplastic melt-processable
polymer and a partially fluorinated thermoplastic melt-processable
polymer.
24. A method according to claim 23, comprising forming a mixture by
combining the curative, an uncured or partially cured elastomeric
material, and the thermoplastic material; and 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.
25. A method according to claim 23 comprising: mixing the
elastomeric material and the thermoplastic material for a time and
at a shear rate sufficient to form a dispersion of the elastomeric
material in a continuous thermoplastic phase; adding a curative to
the dispersion while continuing the mixing; and heating the
dispersion while continuing to mix the curative, elastomeric
material, and thermoplastic material.
26. A method according to claim 23, wherein the ratio of the weight
of the fully fluorinated polymer to the weight of the partially
fluorinated polymer in the matrix ranges from 1:9 to 9:1.
27. A method according to claim 26, wherein the ratio of the weight
of the fully fluorinated polymer to the weight of the partially
fluorinated polymer in the matrix ranges from 1:2 to 2:1.
28. A method according to claim 23, wherein the fluorocarbon
elastomer comprises repeating units derived from vinylidene
fluoride and hexafluoropropylene.
29. A method according to claim 28, wherein the fluorocarbon
elastomer further comprises repeating units derived from
tetrafluoroethylene.
30. A method according to claim 23, wherein the 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.
31. A method according to claim 30, wherein the fluorocarbon
elastomer also comprises cure site monomers.
32. A method according to claim 23, wherein the curative comprises
a polyol.
33. A method according to claim 23, wherein the curative comprises
a peroxide.
34. A method according to claim 23, wherein the thermoplastic
material comprises a fully fluorinated polymer selected from the
group consisting of PFA, MFA and FEP, and a partially fluorinated
polymer selected from the group consisting of polyvinylidene
fluoride and copolymers of vinylidene fluoride.
35. A method according to claim 23, comprising a continuous
process.
36. A method according to claim 35, carried out in a twin screw
extruder.
37. A method according to claim 23, comprising a batch process.
38. A method according to claim 23, wherein the composition
comprises at least about 35 parts by weight vulcanized elastomeric
material per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined.
39. A method according to claim 23, wherein the combination
comprises at least about 50 parts by weight vulcanized elastomeric
material per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined.
40. A shaped article comprising a cured fluorocarbon elastomer
dispersed in a matrix comprising a thermoplastic material, wherein
the thermoplastic material comprises from about 10 to about 90% by
weight of a fully fluorinated thermoplastic melt-processable
polymer and from about 10 to about 90% by weight of a partially
fluorinated thermoplastic polymer.
41. A shaped article according to claim 40, wherein the hardness of
the article is Shore A 50 or greater, the tensile strength of the
article is 4 MPa or greater, the modulus at 100% of the article is
4 MPa or greater, or the elongation at break of the article is 10%
or greater.
42. A shaped article according to claim 40, wherein the cured
fluorocarbon elastomer is present at a level of at least 35% by
weight based on the total weight of cured fluorocarbon elastomer
and thermoplastic polymer.
43. A shaped article according to claim 40 wherein the cured
fluorocarbon elastomer is present at a level of at least 50% by
weight based on the total weight of cured fluorocarbon elastomer
and thermoplastic polymer.
44. A method according to claim 40, wherein the 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.
45. A seal according to claim 40.
46. An O-ring according to claim 40.
47. A gasket according to claim 40.
48. A hose according to claim 38.
49. A method for reducing costs of a manufacturing process for
making shaped rubber articles from a processable rubber
composition, comprising recycling scrap material generated during
the manufacturing process to make new shaped articles comprising
the processable rubber composition, wherein the processable rubber
composition is the product of dynamic vulcanization of a
fluorocarbon elastomer in the presence of a thermoplastic material,
wherein the thermoplastic material comprises from about 10 to about
90% by weight of a fully fluorinated thermoplastic polymer and from
about 10 to about 90% by weight of a partially fluorinated
thermoplastic polymer.
50. A method according to claim 49, wherein the manufacturing
process comprises forming the shaped articles by a thermoplastic
processing technique.
51. A method according to claim 49, wherein the thermoplastic
processing technique is selected from the group consisting of blow
molding, injection molding, compression molding, and extrusion.
52. A method according to claim 49, wherein recycling comprises
melting the scrap material at a temperature below the melting point
of the fully fluorinated polymer.
53. A method according to claim 49, wherein recycling comprising
melting the scrap material at a temperature below 250.degree.
C.
54. A process of manufacturing shaped plastic articles, comprising
preparing a processable rubber composition by dynamically
vulcanizing a fluorocarbon elastomer in the presence of a
fluoroplastic blend comprising a fully fluorinated melt-processable
polymer and a partially fluorinated melt-processable polymer;
melting the rubber composition; and fabricating the shaped article
from the molten rubber composition with a thermoplastic processing
technique.
55. A method according to claim 54, comprising melting the rubber
at a temperature below the melting temperature of the fully
fluorinated polymer.
56. A method according to claim 54, comprising melting the rubber
at a temperature below 280.degree. C., wherein the fluoroplastic
blend comprises more than 65% by weight fluorine.
57. A method according to claim 54, comprising injection molding
the molten rubber composition.
58. A method according to claim 54, comprising extruding the molten
rubber composition.
59. A processable rubber composition comprising a cured
fluorocarbon elastomer dispersed in a matrix comprising a
thermoplastic material, wherein: the thermoplastic material
comprises a fully fluorinated melt-processable thermoplastic
polymer and a partially fluorinated melt-processable thermoplastic
polymer; the cured fluorocarbon elastomer is present at a level of
greater than or equal to 35% by weight based on the total weight of
cured fluorocarbon elastomer and thermoplastic material; and the
dimensions of the cured fluorocarbon elastomer are less than 10
.mu.m, as measured by atomic force microscopy on cryogenically
microtomed cross-sections of shaped articles formed from the
processable rubber composition.
60. A processable rubber composition according to claim 59, wherein
the dimensions are less than 1 .mu.m.
61. A method for making a processable rubber composition
comprising: mixing an elastomeric component and the thermoplastic
material in the presence of a curative agent; and heating during
mixing to effect cure of the elastomeric component, wherein the
elastomeric component comprises a fluorocarbon elastomer; wherein
said rubber composition comprises a cured fluorocarbon elastomer
dispersed in a matrix comprising a thermoplastic material, wherein
the thermoplastic material comprises a fully fluorinated
melt-processable thermoplastic polymer and a partially fluorinated
melt-processable thermoplastic polymer; and the cured fluorocarbon
elastomer is present at a level of greater than or equal to 35% by
weight based on the total weight of cured fluorocarbon elastomer
and thermoplastic material.
62. A method according to claim 61, comprising forming a mixture by
combining the curative, an uncured or partially cured fluorocarbon
elastomer and the thermoplastic material; and heating the mixture
at a temperature and for a time sufficient to effect vulcanization
of the elastomer, wherein mechanical energy is applied to mix the
mixture during the heating step.
63. A method according to claim 61, comprising: mixing the
elastomeric component and the thermoplastic material for a time and
at a shear rate sufficient to form a dispersion of the elastomeric
material in a continuous thermoplastic phase; adding a curative to
the dispersion while continuing the mixing; and heating the
dispersion while continuing to mix the curative, elastomeric
material, and thermoplastic material.
64. A shaped article made by thermoplastic processing of a
processable rubber composition comprising a cured fluorocarbon
elastomer dispersed in a matrix comprising a thermoplastic
material, wherein: the thermoplastic material comprises a fully
fluorinated melt-processable thermoplastic polymer and a partially
fluorinated melt-processable thermoplastic polymer; and the cured
fluorocarbon elastomer is present at a level of greater than or
equal to 35% by weight based on the total weight of cured
fluorocarbon elastomer and thermoplastic material.
65. A shaped article according to claim 64, wherein the hardness of
the article is Shore A 50 or greater, the tensile strength of the
article is 4 MPa or greater, the modulus at 100% of the article is
4 MPa or greater, or the elongation at break of the article is 10%
or greater.
66. A shaped article according to claim 64, wherein the
thermoplastic material comprises from about 10 to about 90% by
weight of a fully fluorinated thermoplastic polymer and from about
10 to about 90% by weight of a partially fluorinated thermoplastic
polymer.
67. A shaped article according to claim 64 wherein the cured
fluorocarbon elastomer is present at a level of at least 50% by
weight based on the total weight of cured fluorocarbon elastomer
and thermoplastic polymer.
68. A shaped article according to claim 64, wherein the
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.
69. A seal according to claim 64.
70. An O-ring according to claim 64.
71. A gasket according to claim 64.
72. A hose according to claim 64.
73. A process of manufacturing a shaped plastic article, comprising
preparing a processable rubber composition by dynamically
vulcanizing a fluorocarbon elastomer in the presence of the
fluoroplastic material; melting the rubber composition; and
fabricating the shaped article from the molten rubber composition
with a thermoplastic processing technique; wherein said processable
rubber composition comprises a cured fluorocarbon elastomer
dispersed in a matrix comprising a thermoplastic material, wherein:
the thermoplastic material comprises a fully fluorinated
melt-processable thermoplastic polymer and a partially fluorinated
melt-processable thermoplastic polymer; and the cured fluorocarbon
elastomer is present at a level of greater than or equal to 35% by
weight based on the total weight of cured fluorocarbon elastomer
and thermoplastic material.
74. A method according to claim 73, comprising melting the rubber
composition at a temperature below the melting temperature of the
fully fluorinated polymer.
75. A method according to claim 73, comprising melting the rubber
at a temperature below 280.degree. C., wherein the fluoroplastic
blend comprises more than 65% by weight fluorine.
76. A method according to claim 73, comprising injection molding
the molten rubber composition.
77. A method according to claim 73, comprising extruding the molten
rubber composition.
78. A processable rubber composition comprising a cured
fluorocarbon elastomer dispersed in a matrix comprising a
thermoplastic material, wherein: the thermoplastic material
comprises a fully fluorinated melt-processable thermoplastic
polymer and a partially fluorinated melt-processable thermoplastic
polymer; the cured fluorocarbon elastomer is present at a level of
50%-80% by weight based on the total weight of cured fluorocarbon
elastomer and thermoplastic material; and the dimensions of the
elastomer phase are less than 10 .mu.m, as measured by atomic force
microscopy on cryogenically microtomed cross-sections of shaped
articles formed from the processable rubber composition, and
wherein the composition exhibits a single melting temperature of
less than 250.degree. C.
79. A composition according to claim 78, wherein the ratio of the
weight of the fully fluorinated polymer to the weight of the
partially fluorinated polymer in the matrix ranges from 1:2 to
2:1.
80. A composition according to claim 78, wherein the fluorocarbon
elastomer comprises repeating units derived from vinylidene
fluoride and hexafluoropropylene.
81. A composition according to claim 80, wherein the fluorocarbon
elastomer further comprises repeating units derived from
tetrafluoroethylene.
82. A composition according to claim 78, wherein the 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.
83. A composition according to claim 82, wherein the fluorocarbon
elastomer also comprises cure site monomers.
84. A composition according to claim 78, wherein the thermoplastic
material comprises a fully fluorinated polymer selected from the
group consisting of PFA, MFA and FEP, and a partially fluorinated
polymer selected from the group consisting of polyvinylidene
fluoride and copolymers of vinylidene fluoride.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/813,527 filed on Mar. 30, 2004, the disclosure of which
is incorporated herein by reference.
INTRODUCTION
[0002] The present invention relates to fluorine containing
elastomer compositions.
[0003] Cured elastomers or rubbers have a variety of physical
properties useful for applications in molded articles. Among the
properties are a high degree of flexibility, elasticity, and
resistance to compression set. As such they find use in a variety
of applications, such as seals and gaskets. Uncured elastomers or
rubbers are in the form of a resin or gum. To obtain a molded
article with suitable elastomeric properties, the uncured resins
are crosslinked or cured with a variety of crosslinking agents.
[0004] For conventional elastomers, cure is generally carried out
in a mold under conditions of temperature and pressure suitable for
forming a cured or partially cured article. Because the curing
reaction produces a thermoset material, conventional rubber
compositions cannot be processed after the elastomer is cured.
[0005] Dynamically vulcanized rubbers are prepared by carrying out
the crosslinking reaction while the elastomer is stirred or mixed
together with a thermoplastic material. The resulting composition
may be further melt processed, even after cure of the elastomer is
complete. Molded articles made from the compositions have
elastomeric properties, yet the compositions may be thermally or
melt processed according to conventional thermoplastic
techniques.
[0006] In thermoplastic techniques, a processable composition is
first melted and then held above the melting temperature for quite
a time before shaped articles are fabricated. The processing
temperature depends on the melt behavior of the compositions, which
is largely determined by the thermoplastic material. Thermoplastics
with a high fluorine content are preferred for some applications
due to the high chemical stability of the composition. Such high
fluorine thermoplastics are characterized by relatively high
melting temperatures.
[0007] During processing, the cured elastomer is subject to a high
temperature, which may be above a temperature at which the cured
elastomer is stable. Prolonged exposure to high temperatures can
degrade a cured elastomer. A drawback of using fluorinated
thermoplastics in such processable compositions is that their
melting point is generally higher than the stability range of the
cured elastomer. The melting temperature can be lowered by using a
partially fluorinated polymer, but the lower fluorine content may
lead to having solvent resistance and other properties below the
preferred levels for the application.
[0008] It would be desirable to provide compositions that exhibit a
high level of solvent resistance and other properties, along with
highly developed elastomeric properties.
SUMMARY
[0009] A processable rubber composition comprises a cured
fluorocarbon elastomer dispersed in a matrix comprising a
thermoplastic material. The thermoplastic material is a
fluoroplastic blend containing a fully fluorinated thermoplastic
polymer and a partially fluorinated thermoplastic polymer. In
various embodiments, the cured elastomer makes up 35% by weight or
more of the composition. The composition preferably exhibits a
single melting temperature, as determined for example by
differential scanning calorimetry, which is below that of the high
melting fully fluorinated polymer of the fluoroplastic blend. At
the same time, the fluorine content of the thermoplastic is above
60%, and preferably above 65%.
[0010] Methods for making the processable rubber composition
involve mixing an elastomeric component and a thermoplastic
component in the presence of a curative agent and heating during
mixing to effect cure of the elastomeric component. In preferred
embodiments, the elastomeric component is a fluorocarbon elastomer
and the thermoplastic component is a fluoroplastic blend as
described above. Shaped articles may be made by melt processing the
rubber compositions with conventional thermoplastic techniques.
Such techniques involve melting and processing the rubber
compositions at temperatures below the melting point of the fully
fluorinated polymer, and preferably below 280.degree. C.
[0011] Suitable fluorocarbon elastomers include those that are
curable with phenol or peroxide curing agents, and those designated
as FKM, FFKM, and FTPM. The fluoroplastic blend preferably contains
a fully fluorinated polymer selected from the group consisting of
PFA, MFA, and FEP, and a partially fluorinated polymer selected
from the group consisting of polyvinylidene fluoride, copolymers of
vinylidene fluoride, ETFE, and ECTFE.
DETAILED DESCRIPTION
[0012] The following description of the preferred embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0013] 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.
[0014] 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. All
references cited in the Description section of this specification
are hereby incorporated by reference in their entirety.
[0015] 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. Specific Examples are provided
for illustrative purposes of how to make, use and practice the
compositions and methods of this invention and, unless explicitly
stated otherwise, are not intended to be a representation that
given embodiments of this invention have, or have not, been made or
tested.
[0016] 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.
[0017] 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.
[0018] The terms "elastomeric material, elastomer" and the like
refer to chemical compositions that possess, or can be modified
(i.e. cured or crosslinked) to possess elastomeric properties.
According to context, the terms refer to an uncured or partially
cured material, in which elastomeric properties are not fully
developed, or to a cured rubber-like material, with fully developed
elastomeric properties. At some points in the specification, the
terms are used with adjectives such as "cured, partially cured, or
uncured" for clarity.
[0019] The terms "curing agent, curative, curative agent," and the
like are used interchangeably to designate the chemical compound or
composition that reacts with the (uncured) elastomer to form a
cured elastomer and to develop the elastomeric properties of the
cured product. According to context it is used to refer to a formal
curing initiator (e.g. a radical initiator such as a peroxide) as
well as a crosslinking agent that may be used in conjunction with
the initiator (e.g. triallylisocyanurate). At some points, the term
"curing system" or the like is used to refer to a combination of
initiator and crosslinker and optional additional components used
in the curing. It is to be understood that often the curing system
is provided by an elastomer supplier (and may be incorporated into
the elastomer), and may be used according to the manufacturer's
instructions.
[0020] According to one embodiment of the invention, a processable
rubber composition is provided comprising a cured fluorocarbon
elastomer dispersed in a matrix comprising a thermoplastic
material, wherein the thermoplastic material comprises a fully
fluorinated thermoplastic polymer and a partially fluorinated
thermoplastic polymer and the cured fluorocarbon elastomer is
present at a level of greater than or equal to 35% by weight based
on the total weight of cured fluorocarbon elastomer and
thermoplastic material. In various embodiments, the cured elastomer
is 40% or more, or 50% or more by weight of the total.
[0021] In another aspect, a processable rubber composition is
provided comprising a cured fluorocarbon elastomer dispersed in a
thermoplastic matrix, wherein the thermoplastic matrix comprises a
fully fluorinated thermoplastic polymer and a partially fluorinated
thermoplastic polymer and the cured fluorocarbon elastomer is
present as a discrete phase or a phase co-continuous with the
matrix. The dimensions of the elastomer phase are less than 10
.mu.m, as measured by atomic force microscopy on cryogenically
microtomed cross-sections of shaped articles formed from the
processable rubber composition. In various embodiments, the
dimensions are less than 1 .mu.m.
[0022] In another embodiment, methods for making a processable
rubber composition are provided comprising mixing an elastomeric
component and a thermoplastic component in the presence of a
curative agent and heating during mixing to effect cure of the
elastomeric component, wherein the elastomeric material comprises a
fluorocarbon elastomer; and the thermoplastic material is a
fluoroplastic blend comprising a fully fluorinated thermoplastic
polymer and a partially fluorinated thermoplastic polymer.
[0023] The compositions of the invention are based on a
fluoroplastic blend comprising a fully fluorinated polymer and a
partially fluorinated polymer. The fluoroplastic blend preferably
contains 10-90% by weight of the fully fluorinated polymer, and
10-90% by weight of the partially fluorinated polymer. The weight
ratio of the fully fluorinated polymer to the partially fluorinated
polymer preferably ranges from 1:9 to 9:1. The compositions
preferably exhibit a single melt temperature below 305.degree. C.,
and preferably below 250.degree. C. They may be melt processed and
fabricated into shaped articles with thermoplastic techniques
operating below the melting temperature of the fully fluorinated
polymer of the fluoroplastic blend.
[0024] In one aspect, the method is carried out by forming a
mixture by combining the curative, an uncured or partially cured
elastomeric material, and the thermoplastic material and 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. In
another aspect, the method comprises mixing the elastomeric
material and the thermoplastic material for a time and at a shear
rate sufficient to form a dispersion of the elastomeric material in
a continuous thermoplastic phase, adding a curative to the
dispersion while continuing the mixing, and heating the dispersion
while continuing to mix the curative, elastomeric material, and
thermoplastic material.
[0025] A shaped article is also provided, comprising a cured
fluorocarbon elastomer dispersed in a matrix comprising a
thermoplastic material, wherein the thermoplastic material
comprises 10-90% by weight of a fully fluorinated thermoplastic
polymer and 10-90% by weight of a partially fluorinated
thermoplastic polymer. In preferred embodiments, the hardness of
the article is Shore A 50 or greater, preferably about 60 to about
80 Shore A; the tensile strength of the article is 4 MPa or
greater, preferably about 5 to about 7 MPa; the modulus at 100% of
the article is 4 MPa or greater, preferably about 6 to about 8 MPa;
or the elongation at break of the article is 10% or greater,
preferably about 100% to about 200%. Non-limiting examples are
molded seals, gaskets, and o-rings, as well as extruded hoses.
Shaped articles are made by further processing of the rubber
compositions described above at temperatures below the melting
point of the fully fluorinated polymer.
[0026] In another embodiment, a method for reducing costs of a
manufacturing process for making shaped rubber articles from a
processable rubber composition comprises recycling scrap material
generated during the manufacturing process to make new shaped
articles comprising the processable rubber composition, wherein the
rubber composition is as described above. The manufacturing
processes include conventional thermoplastic techniques such as
blow molding, injection molding, and extrusion. The recycling step
involves melting the processable composition at a temperature that
is lower than the melting temperature of the fully fluorinated
polymer in the thermoplastic material.
[0027] Fluorocarbon elastomers are curable compositions based on
fluorine-containing polymers. Various types of fluoroelastomers may
be used. One classification of fluoroelastomers is given in ASTM-D
1418, "Standard practice for rubber and rubber
latices-nomenclature". The designation FKM is given for
fluoro-rubbers that utilize vinylidene fluoride as a co-monomer.
Several varieties of FKM fluoroelastomers are commercially
available. A first variety may be chemically described as a
copolymer of hexafluoropropylene and vinylidene fluoride. These FKM
elastomers tend to have an advantageous combination of overall
properties. Some commercial embodiments are available with about
66% by weight fluorine. Another type of FKM elastomer may be
chemically described as a terpolymer of tetrafluoroethylene,
hexafluoropropylene, and vinylidene fluoride. Such elastomers tend
to have high heat resistance and good resistance to aromatic
solvents. They are commercially available with, for example
68-69.5% by weight fluorine. Another FKM elastomer is chemically
described as a terpolymer of tetrafluoroethylene, a fluorinated
vinyl ether, and vinylidene fluoride. Such elastomers tend to have
improved low temperature performance. They are available with
62-68% by weight fluorine. A fourth type of FKM elastomer is
described as a terpolymer of tetrafluoroethylene, propylene, and
vinylidene fluoride. Such FKM elastomers tend to have improved base
resistance. Some commercial embodiments contain about 67% weight
fluorine. A fifth type of FKM elastomer may be described as a
pentapolymer of tetrafluoroethylene, hexafluoropropylene, ethylene,
a fluorinated vinyl ether and vinylidene fluoride. Such elastomers
typically have improved base resistance and have improved low
temperature performance.
[0028] Another category of fluorocarbon elastomers is designated as
FFKM. These elastomers may be designated as perfluoroelastomers
because the polymers are completely fluorinated and contain no
carbon hydrogen bond. As a group, the FFKM fluoroelastomers tend to
have superior fluid resistance. They were originally introduced by
DuPont under the Kalrez.RTM. trade name. Additional suppliers
include Daikin and Ausimont.
[0029] A third category of fluorocarbon elastomer is designated as
FTPM. Typical of this category are the copolymers of propylene and
tetrafluoroethylene. The category is characterized by a high
resistance to basic materials such as amines.
[0030] 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. In various embodiments, 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.
[0031] 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.
[0032] In various embodiments, the molar ratio of
tetrafluoroethylene units to C.sub.2-4 olefin repeating units is
from 60:40 to 40:60. In another embodiment, the elastomeric
material comprises alternating units of C.sub.2-4 olefins and
tetrafluoroethylene. In such polymers the molar ratio of
tetrafluoroethylene to C.sub.2-4 olefin is approximately 50:50.
[0033] In another embodiment, the elastomeric materials are
provided as block copolymers having an A-B-A structure, wherein A
represents a block of poly-tetrafluoroethylene and B represents a
block of polyolefin.
[0034] A preferred C.sub.2-4 olefin is propylene. Elastomeric
materials based on copolymers of tetrafluoroethylene and propylene
are commercially available, for example from Asahi under the
Aflas.RTM. trade name.
[0035] A preferred additional monomer in the vulcanized elastomeric
material is vinylidene difluoride. Other fluorine-containing
monomers that may be used in the elastomeric materials of the
invention include without limitation, perfluoroalkyl vinyl
compounds, perfluoroalkyl vinylidene compounds, and perfluoroalkoxy
vinyl compounds. Hexafluoropropylene (HFP) is an example of
perfluoroalkyl vinyl monomer. Perfluoromethyl vinyl ether is an
example of a preferred perfluoroalkoxy vinyl monomer. For example,
rubbers based on copolymers of tetrafluoroethylene, ethylene, and
perfluoromethyl vinyl ether are commercially available from Dupont
under the Viton.RTM. ETP trade name.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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. Such fluoroelastomers are commercially available as
noted above.
[0040] In various embodiments, the fluoroelastomers of the
composition of the invention also comprise at least one halogenated
cure site or a reactive double bond resulting from the presence of
a copolymerized unit of a non-conjugated diene. In various
embodiments, the fluorocarbon elastomers contain up to 5 mole % and
preferably up to 3 mole % of repeating units derived from the
so-called cure site monomers.
[0041] The cure site monomers are preferably selected from the
group consisting of brominated, chlorinated, and iodinated olefins;
brominated, chlorinated, and iodinated unsaturated ethers; and
non-conjugated dienes. Halogenated cure sites may be copolymerized
cure site monomers or halogen atoms that are present at terminal
positions of the fluoroelastomer polymer chain. The cure site
monomers, reactive double bonds or halogenated end groups are
capable of reacting to form crosslinks.
[0042] The brominated cure site monomers may contain other
halogens, preferably fluorine. Examples are bromotrifluoroethylene,
4-bromo-3,3,4,4-tetrafluorobutene-1 and others such as vinyl
bromide, 1-bromo-2,2-difluoroethylene, perfluoroalkyl bromide,
4-bromo-1,1,2-trifluorobutene,
4-bromo-1,1,3,3,4,4,-hexafluorobutene,
4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene,
6-bromo-5,5,6,6-tetrafluorohexene, 4-bromoperfluorobutene-1 and
3,3-difluoroallyl bromide. Brominated unsaturated ether cure site
monomers useful in the invention include ethers such as
2-bromo-perfluoroethyl perfluorovinyl ether and fluorinated
compounds of the class CF.sub.2 Br--R.sub.f--O--CF.dbd.CF.sub.2
(R.sub.f is perfluoroalkylene), such as CF.sub.2 BrCF.sub.2
O--CF.dbd.CF.sub.2, and fluorovinyl ethers of the class
ROCF.dbd.CFBr or ROCBr.dbd.CF.sub.2, where R is a lower alkyl group
or fluoroalkyl group, such as CH.sub.3OCF.dbd.CFBr or CF.sub.3
CH.sub.2 OCF.dbd.CFBr.
[0043] Iodinated olefins may also be used as cure site monomers.
Suitable iodinated monomers include iodinated olefins of the
formula: CHR.dbd.CH-Z-CH.sub.2CHR--I, wherein R is --H or
--CH.sub.3; Z is a C.sub.1-C.sub.18 (per)fluoroalkylene radical,
linear or branched, optionally containing one or more ether oxygen
atoms, or a (per)fluoropolyoxyalkylene radical as disclosed in U.S.
Pat. No. 5,674,959. Other examples of useful iodinated cure site
monomers are unsaturated ethers of the formula: I(CH.sub.2 CF.sub.2
CF.sub.2).sub.nOCF.dbd.CF.sub.2 and ICH.sub.2 CF.sub.2
O[CF(CF.sub.3)CF.sub.2 O].sub.n CF.dbd.CF.sub.2, and the like,
wherein n=1-3, such as disclosed in U.S. Pat. No. 5,717,036. In
addition, suitable iodinated cure site monomers including
iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1;
3-chloro-4-iodo-3,4,4-trifluorobutene;
2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane;
2-iodo-1-(perfluorovinyloxy)-1,1,2,2-tetrafluoroethylene; 1,1,2,3,3
3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane; 2-iodoethyl vinyl
ether; 3,3,4,5,5,5-hexafluoro-4-iodopentene; and
iodotrifluoroethylene are disclosed in U.S. Pat. No. 4,694,045.
[0044] Examples of non-conjugated diene cure site monomers include
1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene and others, such as
those disclosed in Canadian Patent 2,067,891. A suitable triene is
8-methyl-4-ethylidene-1,7-octadiene.
[0045] Of the cure site monomers listed above, preferred compounds
include 4-bromo-3,3,4,4-tetrafluorobutene-1;
4-iodo-3,3,4,4-tetrafluorobutene-1; and bromotrifluoroethylene.
[0046] Additionally, or alternatively, iodine, bromine or mixtures
thereof may be present at the fluoroelastomer chain ends as a
result of the use of chain transfer or molecular weight regulating
agents during preparation of the fluoroelastomers. Such agents
include iodine-containing compounds that result in bound iodine at
one or both ends of the polymer molecules. Methylene iodide;
1,4-diiodoperfluoro-n-butane; and
1,6-diiodo-3,3,4,4,tetrafluorohexane are representative of such
agents. Other iodinated chain transfer agents include
1,3-diiodoperfluoropropane; 1,4-diiodoperfluorobutane;
1,6-diiodoperfluorohexane; 1,3-diiodo-2-chloroperfluoropropane;
1,2-di(iododifluoromethyl)perfluorocyclobutane;
monoiodoperfluoroethane; monoiodoperfluorobutane; and
2-iodo-1-hydroperfluoroethane. Particularly preferred are
diiodinated chain transfer agents. Examples of brominated chain
transfer agents include 1-bromo-2-iodoperfluoroethane;
1-bromo-3-iodoperfluoropropane; 1-iodo-2-bromo-1,1-difluoroethane
and others such as disclosed in U.S. Pat. No. 5,151,492.
[0047] Additionally, or alternatively, iodine, bromine or mixtures
thereof may be present at the fluoroelastomer chain ends as a
result of the use of chain transfer or molecular weight regulating
agents during preparation of the fluoroelastomers. Such agents
include iodine-containing compounds that result in bound iodine at
one or both ends of the polymer molecules. Methylene iodide;
1,4-diiodoperfluoro-n-butane; and
1,6-diiodo-3,3,4,4,tetrafluorohexane are representative of such
agents. Other iodinated chain transfer agents include
1,3-diiodoperfluoropropane; 1,4-diiodoperfluorobutane;
1,6-diiodoperfluorohexane; 1,3-diiodo-2-chloroperfluoropropane;
1,2-di(iododifluoromethyl)perfluorocyclobutane;
monoiodoperfluoroethane; monoiodoperfluorobutane; and
2-iodo-1-hydroperfluoroethane. Particularly preferred are
diiodinated chain transfer agents. Examples of brominated chain
transfer agents include 1-bromo-2-iodoperfluoroethane;
1-bromo-3-iodoperfluoropropane; 1-iodo-2-bromo-1,1-difluoroethane
and others such as disclosed in U.S. Pat. No. 5,151,492.
[0048] Other cure monomers may be used that introduce low levels,
preferably less than or equal about 5 mole %, more preferably less
than or equal about 3 mole %, of functional groups such as epoxy,
carboxylic acid, carboxylic acid halide, carboxylic ester,
carboxylate salts, sulfonic acid groups, sulfonic acid alkyl
esters, and sulfonic acid salts. such monomers and cure are
described for example in Kamiya et al., U.S. Pat. No.
5,354,811.
[0049] Fluorocarbon elastomers based on cure site monomers are
commercially available. Non-limiting examples include Viton GF,
GLT-305, GLT-505, GBL-200, and GBL-900 grades from DuPont. Others
include the G-900 and LT series from Daikin, the FX series and the
RE series from NOK, and Tecnoflon P457 and P757 from Solvay.
[0050] The fluorocarbon elastomers are dynamically vulcanized in
the presence of a fluoroplastic blend. The blend contains a fully
fluorinated polymer and a partially fluorinated polymer such as a
thermoplastic homo- or copolymer of vinylidene fluoride. The blend
may contain minor amounts of a non-fluorine containing polymer, but
the amount is limited by the requirement that the blend remain
compatible, giving a homogeneous thermoplastic phase, and
exhibiting the melting point behavior discussed below. In various
embodiments, the ratio of fully fluorinated to partially
fluorinated polymers in the fluoroplastic blend ranges from 9:1 to
1:9. In various embodiments, the blend comprises from about 10 to
about 90 parts, from about 20 to about 80 parts, from about 25
parts to about 75 parts, from about 33 to about 67 parts, from
about 40 to about 60 parts, or about 50 parts of one of the
components, with the other component present at a level to bring it
up to 100 parts. In embodiments where no other polymers are present
in the fluoroplastic blend except the fully fluorinated and
partially fluorinated polymers, the parts correspond to % by weight
of the total weight of the fluoroplastic blend.
[0051] In another aspect, the fluoroplastic blend comprises two
fluoropolymers, one with greater than 65 wt % fluorine content, the
other with less than 65 wt % fluorine content. The two
fluoropolymers are present in the same ratios as stated above. In a
preferred embodiment, the polymer with greater than 65% fluorine is
fully fluorinated.
[0052] As discussed below, processable rubber compositions made
from the fluoroplastic blend exhibit a DSC melting temperature
lower than that of the fully fluorinated polymer of the blend. In
various embodiments, the DSC melting temperature is below
305.degree. C., below 290.degree. C., below 260.degree. C., or
below 250.degree. C. In a preferred embodiment, the melting
temperature is below 240.degree. C. Thus, in various embodiments,
the processable rubber compositions will have a melting point of
less than 305.degree. C. and a continuous phase with a fluorine
content of greater than 60 wt %. Preferably the fluorine content
will be greater than 65 wt % and a melting point below 290.degree.
C., below 260.degree. C., or preferably below 250.degree. C. In
another preferred embodiment, the compositions exhibit a melting
point below 240.degree. C.
[0053] 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.
Commercial embodiments are available which contain 59 to 76% by
weight fluorine.
[0054] Fully fluorinated thermoplastic polymers include copolymers
of tetrafluoroethylene and perfluoroalkyl vinyl ethers. The
perfluoroalkyl group is preferably of 1 to 6 carbon atoms. 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 perfluoro olefins of 3 to 8 carbon atoms.
Non-limiting examples include FEP (copolymer of TFE and
hexafluoropropylene).
[0055] 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. Thermoplastic terpolymers may also be
used. These include thermoplastic terpolymers of TFE, HFP, and
vinylidene fluoride. Fully fluorinated fluoroplastics are
characterized by relatively high melting points, when compared to
the vinylidene fluoride based thermoplastics that are also included
in the fluoroplastic blend of the invention. As examples, PFA has a
melting point of about 305.degree. C., MFA has a melting point of
280-290.degree. C., and FEP has a melting point of about
260-290.degree. C. The melting point of individual grades depends
on the exact structure, processing conditions, and other factors,
but the values given here are representative. A consequence of a
high melting point is that thermoplastic processing techniques,
such as blow molding, injection molding, and extrusion need to be
carried out at temperatures above the relatively high melting
point. In the case of thermoplastic processing of compositions
containing a cured elastomer, the elastomer is exposed for extended
periods of time to the relatively temperature required to melt the
thermoplastic and make it flow. Many elastomers are adversely
affected by the high temperatures, and suffer degradation.
[0056] Partially fluorinated fluoroplastics such as the vinylidene
fluoride homo- and copolymers described above have relatively lower
melting points than the fully fluorinated fluoroplastics. For
example, polyvinylidene fluoride has a melting point of about
160-170.degree. C. Some copolymer thermoplastics have an even lower
melting point, due to the presence of a small amount of co-monomer.
For example, a vinylidene fluoride copolymer with a small amount of
hexafluoropropylene, exemplified in a commercial embodiment such as
the Kynar Flex series, exhibits a melting point in the range of
about 105-160.degree. C., and typically about 130.degree. C. These
low melting points lead to advantages in thermoplastic processing,
as lower temperatures of melting lead to lower energy costs and
avoidance of the problem of degradation of cured elastomers in the
compositions. One drawback of the partially fluorinated polymers
for some applications is their relatively low fluorine content.
Polyvinylidene fluoride has only about 59% by fluorine, while the
fully fluorinated polymers have fluorine content from about 71%
(MFA) to about 76% (FEP). In some applications, a higher fluorine
content is desirable for contributing to increased solvent
resistance and other properties.
[0057] The fluoroplastic blend provides advantages over
compositions consisting of mostly partially fluorinated polymers,
in that the fluorine content of the blend is higher, which leads to
better solvent resistance and other properties in shaped articles
made from the compositions. The fluorine content of the blend is
essentially the weighted average of the fluorine contents of the
individual components. As a non-limiting example, a 50/50 blend of
FEP (76% F) and polyvinylidene fluoride (59% F) is about (59+76)/2,
or 67.5% fluorine.
[0058] Processable rubber compositions of the invention that
contain the fluoroplastic blend as the continuous phase preferably
exhibit a single melting temperature, when measured for example by
differential scanning calorimetry (DSC). Advantageously, the
melting of the blend is intermediate between that of the fully
fluorinated and partially fluorinated polymers. For example, the
DSC melting point of dynamic vulcanizate made from 50/50 PVDF (mp
160.degree. C.) and PFA (mp 305.degree. C.) was about 235.degree.
C. Because such compositions can be subsequently processed at lower
temperatures than the melting point of the fully fluorinated
polymer, degradation temperatures of the cured fluoroelastomers can
be avoided in subsequent thermoplastic processing of the
compositions.
[0059] In a preferred embodiment, a fluorocarbon elastomer is cured
in the presence of a mixture of a fully fluorinated and partially
fluorinated thermoplastic polymer (i.e., the "fluoroplastic blend"
described above) to form a dynamic vulcanizate containing particles
of cured fluoroelastomer. The dynamic vulcanization is preferably
carried out at a temperature above the melting point of the higher
melting component, i.e. the fully fluorinated polymer. This exposes
the curing and cured fluoroelastomer to relatively high
temperatures, but only for a brief period of time required to cure
the elastomer. After the processable rubber composition is thus
formed, it can be subsequently processed in thermoplastic
techniques at a temperature at or slightly above (for example, 10
to 30.degree. C. higher) the DSC melting point exhibited by the
composition, which is lower than that of the fully fluorinated
polymer.
[0060] Useful curative agents include diamines, peroxides, and
polyol/onium salt combinations. 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.
[0061] Peroxide curative contains an organic peroxide. The peroxide
is believed to function by first extracting a hydrogen or halogen
atom from the fluorocarbon elastomer to create a free radical that
can be crosslinked. The peroxide curative preferably also contains
a crosslinker. In various embodiment, the crosslinker contains at
least two sites of olefinic unsaturation, which react with the free
radical on the fluorocarbon elastomer molecule generated by the
reaction of peroxide.
[0062] A wide range of organic peroxides is known and commercially
available. The organic peroxides are activated over a wide range of
temperatures. The activation temperature of the peroxides may be
described in a parameter known as half-life. Typically values for
half-lives of, for example, 0.1 hours, 1 hour, and 10 hours are
given in degrees centigrade. For example a T.sub.1/2 at 0.1 hours
of 143.degree. C. indicates that at that temperature, half of the
peroxide will decompose within 0.1 hours. Organic peroxides with a
T.sub.1/2 at 0.1 hours from 118.degree. C. to 228.degree. C. are
commercially available. The T.sub.1/2 values indicate the kinetics
of the initial reaction in crosslinking the fluorocarbon
elastomers, that is decomposition of the peroxide to form a radical
containing intermediate.
[0063] In some embodiments, the T.sub.1/2 of the organic peroxide
may be matched to the temperature of the molten material into which
the peroxide is to be added. Non-limiting examples of commercially
available organic peroxides for initiating the cure of fluorocarbon
elastomers include butyl 4,4-di-(tert-butylperoxy)valerate;
tert-butyl peroxybenzoate; di-tert-amyl peroxide; dicumyl peroxide;
di-(tert-butylperoxyisopropyl)benzene;
2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; tert-butyl cumyl
peroxide; 2,5,-dimethyl-2,5-di(tert-butylperoxy)hexyne-3;
di-tert-butyl peroxide;
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane;
1,1,3,3-tetramethylbutyl hydroperoxide; diisopropylbenzene
monohydroperoxide; cumyl hydroperoxide; tert-butyl hydroperoxide;
tert-amyl hydroperoxide; tert-butyl peroxyisobutyrate; tert-amyl
peroxyacetate; tert-butylperoxy stearyl carbonate;
di(1-hydroxycyclohexyl)peroxide; ethyl
3,3-di(tert-butylperoxy)butyrate; and tert-butyl 3-isopropenylcumyl
peroxide.
[0064] One or more crosslinking co-agents may be combined with the
peroxide. Non-limiting examples include triallyl cyanurate;
triallyl isocyanurate; tri(methallyl)-isocyanurate;
tris(diallylamine)-s-triazine, triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraallyl
terephthalamide; N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbornene-2-methylene)cyanurate. The crosslinking coagents
contain at least two sites of olefinic unsaturation. These sites of
unsaturation react with the free radical generated on the
fluorocarbon elastomer molecule and crosslink the elastomer. A
commonly used crosslinking agent is triallylisocyanurate
(TAIC).
[0065] Suitable onium salts are described, for example, in U.S.
Pat. Nos. 4,233,421; 4,912,171; and 5,262,490. Examples include
triphenylbenzyl phosphonium chloride, tributyl alkyl phosphonium
chloride, tributyl benzyl ammonium chloride, tetrabutyl ammonium
bromide, and triarylsulfonium chloride.
[0066] Another class of useful onium salts is represented by the
following formula: ##STR1## where [0067] Q is nitrogen or
phosphorus; [0068] Z is a hydrogen atom or [0069] is a substituted
or unsubstituted, cyclic or acyclic alkyl group having from 4 to
about 20 carbon atoms that is terminated with a group of the
formula --COOA where A is a hydrogen atom or a NH.sub.4.sup.+
cation or Z is a group of the formula [0070] --CY.sub.2 COOR' where
Y is a hydrogen or halogen atom, or is a substituted or
unsubstituted alkyl or aryl group having from 1 to about 6 carbon
atoms that may optionally contain one or more quaternary
heteroatoms and where R' is a hydrogen atom, a NH.sub.4.sup.+
cation, an alkyl group, or is an acyclic anhydride, e.g., a group
of the formula --COR where R is an alkyl group or is a group that
itself contains organo-onium (i.e., giving a bis-organo-onium);
preferably R' is hydrogen; Z may also be a substituted or
unsubstituted, cyclic or acyclic alkyl group having from 4 to about
20 carbon atoms that is terminated with a group of the formula
--COOA where A is a hydrogen atom or is a NH.sub.4.sup.+0 cation;
[0071] R.sub.1, R.sub.2, and R.sub.3 are each, independently, a
hydrogen atom or an alkyl, aryl, alkenyl, or any combination
thereof, each R.sub.1, R.sub.2, and R.sub.3 can be substituted with
chlorine, fluorine, bromine, cyano, --OR'', or --COOR'' where R''
is a C.sub.1 to C.sub.20 alkyl, aryl, aralkyl, or alkenyl, and any
pair of the R.sub.1, R.sub.2, and R.sub.3 groups can be connected
with each other and with Q to form a heterocyclic ring; one or more
of the R.sub.1, R.sub.2, and R.sub.3 groups may also be a group of
the formula Z where Z is as defined above; [0072] X is an organic
or inorganic anion (for example, without limitation, halide,
sulfate, acetate, phosphate, phosphonate, hydroxide, alkoxide,
phenoxide, or bisphenoxide); and [0073] n is a number equal to the
valence of the anion X.
[0074] The polyol crosslinking agents may be any of those
polyhydroxy compounds known in the art to function as a
crosslinking agent or co-curative for fluoroelastomers, such as
those polyhydroxy compounds disclosed in U.S. Pat. No. 4,259,463
(Moggi et al.), U.S. Pat. No. 3,876,654 (Pattison), U.S. Pat. No.
4,233,421 (Worm), and U.S. Defensive Publication T107,801
(Nersasian). Preferred polyols include aromatic polyhydroxy
compounds, aliphatic polyhydroxy compounds, and phenol resins.
[0075] Representative aromatic polyhydroxy compounds include any
one of the following: di-, tri-, and tetrahydroxybenzenes,
-naphthalenes, and -anthracenes, and bisphenols of the formula
##STR2## wherein A is a difunctional aliphatic, cycloaliphatic, or
aromatic radical of 1 to 13 carbon atoms, or a thio, oxy, carbonyl,
or sulfonyl radical, A is optionally substituted with at least one
chlorine or fluorine atom, x is 0 or 1, n is 1 or 2, and any
aromatic ring of the polyhydroxy compound is optionally substituted
with at least one atom of chlorine, fluorine, or bromine atom, or
carboxyl or an acyl radical (e.g., --COR, where R is H or a C.sub.1
to C.sub.8 alkyl, aryl or cycloalkyl group) or alkyl radical with,
for example, 1 to 8 carbon atoms. It will be understood from the
above bisphenol formula III that the --OH groups can be attached in
any position (other than number one) in either ring. Blends of two
or more such compounds can also be used. A preferred bisphenol
compound is Bisphenol AF, which is
2,2-bis(4-hydroxyphenyl)hexafluoropropane. Other non-limiting
examples include 4,4'-dihydroxydiphenyl sulfone (Bisphenol S) and
2,2-bis(4-hydroxyphenyl)propane (Bisphenol A). Aromatic polyhydroxy
compound, such as hydroquinone may also be used as curative agents.
Further non-limiting examples include catechol, resorcinol,
2-methyl resorcinol, 5-methyl resorcinol, 2-methyl hydroquinone,
2,5-dimethyl hydroquinone, and 2-t-butyl hydroquinone,
1,5-dihydroxynaphthalene and 9,10-dihydroxyanthracene.
[0076] Aliphatic polyhydroxy compounds may also be used as a polyol
curative. Examples include fluoroaliphatic diols, e.g.
1,1,6,6-tetrahydrooctafluorohexanediol, and others such as those
described in U.S. Pat. No. 4,358,559 (Holcomb et al.) and
references cited therein. Derivatives of polyhydroxy compounds can
also be used such as those described in U.S. Pat. No. 4,446,270
(Guenthner et al.) and include, for example,
2-(4-allyloxyphenyl)-2-(4-hydroxyphenyl)propane. Mixtures of two or
more of the polyhydroxy compounds can be used.
[0077] Phenol resins capable of crosslinking a rubber polymer can
be employed as the polyol curative agent. Reference to phenol resin
may include mixtures of these resins, as described in U.S. Pat.
Nos. 2,972,600 and 3,287,440. These phenolic resins can be used to
obtain the desired level of cure without the use of other curatives
or curing agents.
[0078] Phenol resin curatives can be made by the condensation of
alkyl substituted phenols or unsubstituted phenols with aldehydes,
preferably formaldehydes, in an alkaline medium or by condensation
of bi-functional phenoldialcohols. The alkyl substituents of the
alkyl substituted phenols typically contain 1 to about 10 carbon
atoms. Dimethylolphenols or phenolic resins, substituted in
para-positions with alkyl groups containing 1 to about 10 carbon
atoms, are preferred. Useful commercially available phenol resins
include alkylphenol-formaldehyde resin, and bromomethylated
alkylphenol-formaldehyde resins.
[0079] In one embodiment, phenol resin curative agents may be
represented by the general formula ##STR3## where Q is a divalent
radical selected from the group consisting of --CH.sub.2-- and
--CH.sub.2--O--CH.sub.2--; m is zero or a positive integer from 1
to 20 and R' is hydrogen or an organic radical. Preferably, Q is
the divalent radical --CH.sub.2--O--CH.sub.2--, m is zero or a
positive integer from 1 to 10, and R' is hydrogen or an organic
radical having less than 20 carbon atoms. In another embodiment,
preferably m is zero or a positive integer from 1 to 5 and R' is an
organic radical having between 4 and 12 carbon atoms. Other
preferred phenol resins are also defined in U.S. Pat. No.
5,952,425.
[0080] The cured fluorocarbon elastomer compositions of the
invention are prepared by a process of dynamic vulcanization.
Dynamic vulcanization is a vulcanization or a curing process for a
rubber (here a fluorocarbon elastomer) contained in a thermoplastic
composition, wherein the curable rubber is vulcanized under
conditions of sufficiently high shear at a temperature above the
melting point of the thermoplastic component. In this way, the
rubber is simultaneously crosslinked and dispersed within the
thermoplastic matrix. Dynamic vulcanization may be carried out by
applying mechanical energy to mix the elastomeric and thermoplastic
components at elevated temperature in the presence of a curative in
conventional mixing equipment, such as roll mills, Moriyama mixers,
Banbury mixers, Brabender mixers, continuous mixers, mixing
extruders such as single and twin-screw extruders, and the like. An
advantageous characteristic of dynamically cured compositions is
that, not withstanding that the elastomeric component is fully
cured, the composition can be processed and reprocessed by
conventional plastic processing techniques such as extrusion,
injection molding, and compression molding. Scrap or flashing can
also be salvaged and reprocessed with thermoplastic techniques.
[0081] The vulcanized elastomeric material that results from the
process of dynamic vulcanization is generally present as small
particles within a continuous thermoplastic polymer matrix. A
co-continuous morphology is also possible depending on the amount
of elastomeric material relative to thermoplastic material, the
cure system, the mechanism of cure and the amount and degree of
mixing.
[0082] After dynamic vulcanization, a homogeneous mixture is
obtained wherein the cured fluoroelastomer is in the form of
dispersed particles having an average particle smaller than about
50 micrometers, preferably of an average particle size smaller than
about 25 micrometers. The particle size may be determined from maps
prepared by atomic force microscopy on cryogenically microtomed
cross-sections of shaped articles formed from the processable
rubber composition.
[0083] Typically, the particles have an average size of 10
micrometers or less, more preferably 5 micrometers or less as
measured with the atomic force microscopy technique. In some
embodiments, the particles have an average size of 1 micrometer or
less. In other embodiments, even when the average particle size is
higher, there will be a significant number of cured elastomer
particles with a diameter of less than 1 micron dispersed in the
thermoplastic matrix.
[0084] In various embodiments, masterbatches of peroxide are
prepared for use as the curative to be added to the dynamically
vulcanizing system. To make the masterbatch, one can combine a
peroxide cure initiator, a fluorocarbon elastomer, and optionally a
crosslinking agent. In preferred embodiments, the masterbatch
contains from about 5 to about 50% by weight of the peroxide. The
masterbatches may be conveniently prepared by combining the
ingredients in conventional mixers such as Banbury mixers, and the
like. They may also be compounded on screw mixers such as
twin-screw extruders. The masterbatches containing fluorocarbon
elastomer and peroxide may be added to molten mixtures during the
dynamic vulcanization processing batch mixtures or in continuous
mixers such as twin-screw extruders.
[0085] The fluorocarbon elastomer of the peroxide masterbatch may
be chosen to be compatible with mixing in the fluorocarbon
elastomer during the dynamic vulcanization process. In typical
dynamic vulcanization processes, a fluorocarbon elastomer is mixed
together in a molten thermoplastic material. The temperature is
typically 10-30.degree. C. higher than the melting point of the
thermoplastic. Adding the peroxide curing agent, optionally along
with a crosslinking agent containing multiple sites of olefinic
unsaturation, in the form of a masterbatch allows for faster
incorporation of the peroxide curing agent into the elastomer phase
of the dynamic vulcanizate. It is also believed that the
fluorocarbon elastomer component of the masterbatch protects the
peroxide from bumping and volatilization upon addition to the
molten mixture.
[0086] In one embodiment, the fluorocarbon elastomer of the
peroxide masterbatch and that of the molten mixture are selected to
be the same. In this way, the masterbatch containing the peroxide
is immediately compatible with the fluorocarbon elastomer of the
dynamic vulcanizate. By using the masterbatch method, a portion of
the fluorocarbon elastomer to be cured in the dynamic vulcanization
process is added along with the peroxide. Recipes for the dynamic
vulcanizations, along with the charges of fluorocarbon elastomer
during the different steps of the dynamic vulcanization process,
can be designed and calculated depending on the concentration of
the fluorocarbon elastomer in the masterbatch.
[0087] The masterbatch can contain a wide range of peroxide
concentrations, but it is usually preferred to make masterbatches
having from about 5% up to about 50% by weight peroxide. In some
embodiments, it will be desirable to add peroxide in the master
batch process in as little fluorocarbon elastomer as possible, so
as to achieve desired properties in the fully cured dynamic
vulcanizate. In other embodiments, it may be desirable to add more
of the fluorocarbon elastomer into the dynamic vulcanization
process after the initial melt blending of the fluorocarbon
elastomer and the thermoplastic. In these cases, masterbatches
having peroxide concentrations toward the lower end of the
preferred range may be used.
[0088] The masterbatch is blended under conditions such that the
blending temperature does not exceed a temperature at which the
peroxide would act to cure the fluorocarbon elastomer. Typically,
the masterbatch may be blended at temperatures up to 100.degree.
C., in order to provide a mixture of low enough viscosity for
efficient blending. A preferred temperature range for blending of
the masterbatch is 80-100.degree. C. For reactive elastomers, it
may be desirable to blend at 80.degree. C. or less.
[0089] In a preferred embodiment, plasticizers, extender oils,
synthetic processing oils, or a combination thereof may be used in
the compositions of the invention. The type of processing oil
selected will typically be consistent with that ordinarily used in
conjunction with the specific rubber or rubbers present in the
composition. The extender oils may include, but are not limited to,
aromatic, naphthenic, and paraffinic extender oils. Preferred
synthetic processing oils include polylinear .alpha.-olefins. The
extender oils may also include organic esters, alkyl ethers, or
combinations thereof. As disclosed in U.S. Pat. No. 5,397,832, it
has been found that the addition of certain low to medium molecular
weight organic esters and alkyl ether esters to the compositions of
the invention lowers the Tg of the thermoplastic and rubber
components, and of the overall composition, and improves the low
temperatures properties, particularly flexibility and strength.
These organic esters and alkyl ether esters generally have a
molecular weight that is generally less than about 10,000.
Particularly suitable esters include monomeric and oligomeric
materials having an average molecular weight below about 2000, and
preferably below about 600. In one embodiment, the esters may be
either aliphatic mono- or diesters or alternatively oligomeric
aliphatic esters or alkyl ether esters.
[0090] In addition to the elastomeric material, the thermoplastic
polymeric material, and curative, the processable rubber
compositions of this invention may include other additives such as
stabilizers processing aids, curing accelerators, fillers,
pigments, adhesives, tackifiers, and waxes. The properties of the
compositions and articles of the invention may be modified, either
before or after vulcanization, by the addition of ingredients that
are conventional in the compounding of rubber, thermoplastics, and
blends thereof.
[0091] A wide variety of processing aids may be used, including
plasticizers and mold release agents. Non-limiting examples of
processing aids include Caranuba wax, phthalate ester plasticizers
such as dioctylphthalate (DOP) and dibutylphthalate silicate (DBS),
fatty acid salts such zinc stearate and sodium stearate,
polyethylene wax, and keramide. In some embodiments, high
temperature processing aids are preferred. Such include, without
limitation, linear fatty alcohols such as blends of
C.sub.10-C.sub.28 alcohols, organosilicones, and functionalized
perfluoropolyethers. In some embodiments, the compositions contain
about 1 to about 15% by weight processing aids, preferably about 5
to about 10% by weight.
[0092] Acid acceptor compounds are commonly used as curing
accelerators or curing stabilizers. Preferred acid acceptor
compounds include oxides and hydroxides of divalent metals.
Non-limiting examples include Ca(OH).sub.2, MgO, CaO, and ZnO.
[0093] Non-limiting examples of fillers include both organic and
inorganic fillers such as, barium sulfate, zinc sulfide, carbon
black, silica, titanium dioxide, clay, talc, fiber glass, fumed
silica and discontinuous fibers such as mineral fibers, wood
cellulose fibers, carbon fiber, boron fiber, and aramid fiber
(Kevlar). Some non-limiting examples of processing additives
include stearic acid and lauric acid. The addition of carbon black,
extender oil, or both, preferably prior to dynamic vulcanization,
is particularly preferred. Non-limiting examples of carbon black
fillers include SAF black, HAF black, SRP black and Austin black.
Carbon black improves the tensile strength, and an extender oil can
improve processability, the resistance to oil swell, heat
stability, hysteresis, cost, and permanent set. In a preferred
embodiment, fillers such as carboxy block may make up to about 40%
by weight of the total weight of the compositions of the invention.
Preferably, the compositions comprise 1-40 weight % of filler. In
other embodiments, the filler makes up 10 to 25 weight % of the
compositions.
[0094] The vulcanized elastomeric material, also referred to herein
generically as a "rubber," is generally present as small particles
within a continuous thermoplastic polymer matrix. A co-continuous
morphology is also possible depending on the amount of elastomeric
material relative to thermoplastic material, the cure system, and
the mechanism and degree of cure of the elastomer and the amount
and degree of mixing. Preferably, the elastomeric material is fully
crosslinked/cured.
[0095] Full crosslinking can be achieved by adding an appropriate
curative or curative system to a blend of thermoplastic material
and elastomeric material, and vulcanizing or curing the rubber to
the desired degree under vulcanizing conditions. In a preferred
embodiment, the elastomer is crosslinked by the process of dynamic
vulcanization. The term dynamic vulcanization refers to a
vulcanization or curing process for a rubber (here a fluorocarbon
elastomer) contained in a thermoplastic composition (here the
fluoroplastic blend), wherein the curable rubber is vulcanized
under conditions of sufficiently high shear at a temperature above
the melting point of the thermoplastic component. The rubber is
thus simultaneously crosslinked and dispersed within the
thermoplastic matrix. Dynamic vulcanization is effected by applying
mechanical energy to mix the elastomeric and thermoplastic
components at elevated temperature in the presence of a curative in
conventional mixing equipment such as roll mills, Moriyama mixers,
Banbury mixers, Brabender mixers, continuous mixers, mixing
extruders such as single and twin-screw extruders, and the like. An
advantageous characteristic of dynamically cured compositions is
that, notwithstanding the fact that the elastomeric component is
fully cured, the compositions can be processed and reprocessed by
conventional plastic processing techniques such as extrusion,
injection molding and compression molding. Scrap or flashing can be
salvaged and reprocessed. One advantage of the compositions of the
invention is that they can be processed at relatively lower
temperatures than can compositions made with a single fully
fluorinated thermoplastic polymer.
[0096] 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, which is up
to about 300.degree. C. or more. It is preferred that mixing
continue without interruption until vulcanization occurs or is
complete.
[0097] 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.
[0098] 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.
[0099] 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.
[0100] 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 of a
co-continuous phase.
[0101] The homogenous nature of the compositions, the small
particle size indicative of a large surface area of contact between
the phases, and the ability of the compositions to be formed into
shaped articles having sufficient hardness, tensile strength,
modulus, elongation at break, or compression set to be useful in
industrial applications, indicate a relatively high degree of
compatibility between the elastomer and thermoplastic phases.
[0102] The progress of the vulcanization may be followed by
monitoring mixing torque or mixing energy requirements during
mixing. The mixing torque or mixing energy curve generally goes
through a maximum after which mixing can be continued somewhat
longer to improve the fabricability of the blend. In certain
embodiment, additional ingredients are added after the dynamic
vulcanization is complete. The stabilizer package is preferably
added to the thermoplastic vulcanizate after vulcanization has been
essentially completed, i.e., the curative has been essentially
consumed.
[0103] The processable rubber compositions of the invention may be
manufactured in a batch process or a continuous process. In a batch
process, predetermined charges of elastomeric material,
fluoroplastic blend, and curative agents are added to a mixing
apparatus. In a typical batch procedure, the elastomeric material
and fluoroplastic blend are first mixed, blended, masticated or
otherwise physically combined until a desired particle size of
elastomeric material is provided in a continuous phase of
thermoplastic material. When the structure of the elastomeric
material is as desired, a curative agent may be added while
continuing to apply mechanical energy to mix the elastomeric
material and fluoroplastic blend. Curing is effected by heating or
continuing to heat the mixing combination of fluoroplastic blend
and elastomeric material in the presence of the curative agent.
When cure is complete, the processable rubber composition may be
removed from the reaction vessel (mixing chamber) for further
processing.
[0104] It is preferred to mix the elastomeric material and
fluoroplastic blend at a temperature where the thermoplastic
material softens and flows. If such a temperature is below that at
which the curative agent is activated, the curative agent may be a
part of the mixture during the initial particle dispersion step of
the batch process. In some embodiments, a curative is combined with
the elastomeric material and fluoroplastic blend at a temperature
below the curing temperature. When the desired dispersion is
achieved, the temperature may be increased to effect cure. In one
embodiment, commercially available elastomeric materials are used
that contain a curative pre-formulated into the elastomer. However,
if the curative agent is activated at the temperature of initial
mixing (which will generally be the case with the relatively high
melting fully fluorinated polymers used in the fluoroplastic blend,
it is preferred to leave out the curative until the desired
particle size distribution of the elastomeric material in the
thermoplastic matrix is achieved. In another embodiment, curative
is added after the elastomeric material and fluoroplastic blend are
mixed. In a preferred embodiment, the curative agent is added to a
mixture of elastomeric particles in the fluoroplastic blend while
the entire mixture continues to be mechanically stirred, agitated
or otherwise mixed.
[0105] Continuous processes may also be used to prepare the
processable rubber compositions of the invention. In a preferred
embodiment, a twin screw extruder apparatus, either co-rotation or
counter-rotation screw type, is provided with ports for material
addition and reaction chambers made up of modular components of the
twin screw apparatus. In a typical continuous procedure, the
fluoroplastic blend and elastomeric material are combined by
inserting them into the screw extruder together from a first hopper
using a feeder (loss-in-weight or volumetric feeder). Temperature
and screw parameters may be adjusted to provide a proper
temperature and shear to effect the desired mixing and particle
size distribution of an uncured elastomeric component in a
thermoplastic material matrix. The duration of mixing may be
controlled by providing a longer or shorter length of extrusion
apparatus or by controlling the speed of screw rotation for the
mixture of elastomeric material and thermoplastic material to go
through during the mixing phase. The degree of mixing may also be
controlled by the mixing screw element configuration in the screw
shaft, such as intensive, medium or mild screw designs. Then, at a
downstream port, by using side feeder (loss-in-weight or volumetric
feeder), the curative agent may be added continuously to the
mixture of fluoroplastic blend and elastomeric material as it
continues to travel down the twin screw extrusion pathway.
Downstream of the curative additive port, the mixing parameters and
transit time may be varied as described above. By adjusting the
shear rate, temperature, duration of mixing, mixing screw element
configuration, as well as the time of adding the curative agent,
processable rubber compositions of the invention may be made in a
continuous process. As in the batch process, the elastomeric
material may be commercially formulated to contain a curative
agent, generally a phenol or phenol resin curative.
[0106] The compositions and articles of the invention will contain
a sufficient amount of vulcanized elastomeric material ("rubber")
to form a rubbery composition of matter, that is, they will exhibit
a desirable combination of flexibility, softness, and compression
set. Preferably, the compositions should comprise at least about 25
parts by weight rubber, preferably at least about 35 parts by
weight rubber, more preferably at least about 40 parts by weight
rubber, even more preferably at least about 45 parts by weight
rubber, and still more preferably at least about 50 parts by weight
rubber per 100 parts by weight of the rubber and thermoplastic
polymer combined. The amount of cured rubber within the
thermoplastic vulcanizate is generally from about 5 to about 95
percent by weight, preferably from about 35 to about 95 percent by
weight, more preferably from about 40 to about 90 weight percent,
and more preferably from about 50 to about 80 percent by weight of
the total weight of the rubber and the thermoplastic polymer
combined.
[0107] The amount of fluoroplastic blend within the processable
rubber compositions of the invention is generally from about 5 to
about 95 percent by weight, preferably from about 10 to about 65
percent by weight and more preferably from about 20 to about 50
percent by weight of the total weight of the rubber and the
fluoroplastic blend combined.
[0108] As noted above, the processable rubber compositions and
shaped articles of the invention include a cured rubber and a
thermoplastic polymer comprising or consisting essentially of the
fluoroplastic blend described herein. Preferably, the thermoplastic
vulcanizate is a homogeneous mixture wherein the rubber is in the
form of finely-divided and well-dispersed rubber particles within a
non-vulcanized matrix. It should be understood, however, that the
thermoplastic vulcanizates of the this invention are not limited to
those containing discrete phases inasmuch as the compositions of
this invention may also include other morphologies such as
co-continuous morphologies. In especially preferred embodiments,
the rubber particles have an average particle size smaller than
about 50 .mu.m, more preferably smaller than about 25 .mu.m, even
more preferably smaller than about 10 .mu.m or less, and still more
preferably smaller than about 5 .mu.m.
[0109] Advantageously, the shaped articles of the invention are
rubber-like materials that, unlike conventional rubbers, can be
processed and recycled like thermoplastic materials. These
materials are preferably rubber-like to the extent that they will
retract to less than 1.5 times their original length within one
minute after being stretched at room temperature to twice its
original length and held for one minute before release, as defined
in ASTM D1566. Also, these materials preferably satisfy the tensile
set requirements set forth in ASTM D412, and they also satisfy the
elastic requirements for compression set per ASTM D395.
[0110] In various embodiments, the cured dynamic vulcanizates of
the invention may be made in batch, semi-batch, or continuous
processes through the use of peroxide masterbatches to deliver the
curing agents to vulcanize the fluorocarbon elastomers. For
example, melt processable fluoroelastomer compositions may be made
by blending a fluoroplastic blend and a fluorocarbon elastomer to
form a first mixture, at a temperature above a temperature at which
the thermoplastic will flow sufficiently, to form a dispersion of
the fluorocarbon elastomer. Such temperature may be referred to as
a melt flow temperature. Next, a second mixture (masterbatch) is
provided that contains a fluorocarbon elastomer and preferably
greater than about 5% by weight of an organic peroxide. The
masterbatch is formulated and manufactured at a temperature below
that at which the peroxide would activate to initiate crosslinking
of the fluorocarbon elastomer. The first mixture and the second
mixtures are then combined and blended together while heating at a
temperature and for a time sufficient to effect cure of the
fluorocarbon elastomer in the first and second mixtures.
[0111] The process may also be carried out continuously, for
example in extrusion mixers such as a twin-screw extruder. In one
embodiment, a solid blend of an uncured fluorocarbon elastomer and
a fluoroplastic blend is delivered to a first feeder of a first
twin-screw extrusion apparatus. The solid blend is injected into
the barrel of the extruder, with the barrel heated above a
temperature at which the thermoplastic will melt and flow, to
produce a dispersion of the fluorocarbon elastomer in the
thermoplastic. For example, the barrel may be heated above the
crystalline melting temperature of the thermoplastic material. In
preferred embodiments, the temperature is 10.degree., 20.degree. or
30.degree. C. higher than the melting temperature of the
thermoplastic. The solid blend is then mixed in the twin-screw
extruder to form a homogeneous melt blend. A peroxide masterbatch
containing greater or equal to 5% by weight of an organic peroxide
is then delivered to a second feeder and injected into the barrel
of the twin-screw extruder at a point downstream of the first
feeder. The peroxide masterbatch and the homogeneous melt blend in
the barrel are then further mixed while continuing to heat for a
time and at a temperature sufficient to effect cure of the
fluorocarbon elastomers. The cured dynamic vulcanizate may then be
extruded from the twin-screw extrusion apparatus.
[0112] In an alternate embodiment, the peroxide masterbatch may be
delivered to the second feeder with a twin-screw extrusion
apparatus that blends the organic peroxide, fluorocarbon elastomer,
and optional crosslinking agent at a temperature less than that
which would activate the peroxide to cure the elastomer. In this
way, it is possible to continuously feed a fluorocarbon elastomer
and the fluoroplastic blend at a first feeder port, and a curing
agent and fluorocarbon elastomer at a second port downstream from
the first.
[0113] After extrusion from the mixing apparatus, the dynamically
vulcanized strand may be cooled in a water bath and chopped into
pellets for later use.
EXAMPLES
[0114] Examples 1-3 illustrate recipes for making moldable
compositions of the invention. They can be made by either batch or
continuous processes.
[0115] In a batch process, processable rubber compositions are
compounded in a batch mixer such as a Banbury mixer, Moriyama
mixer, and a Brabender with an internal mixing attachment. The high
temperature fluoroplastic (e.g. PFA, with a melting point of about
335.degree. C.) and the low temperature fluoroplastic (e.g. Kynar
Flex 2500-20, a copolymer of vinylidene fluoride and HFP with a
melting point of about 115.degree. C.) are melted together at
350-380.degree. C. and stirred for 10-15 minutes until a
homogeneous fluoroplastic blend is obtained. A fluorinated
processing aid (e.g. Tecnoflon FPA-1) and optional compatibilizing
agent are added during the mixing stage to improve mixing
efficiency. Fluorocarbon elastomer is then added to the mixer, and
continuously mixed with the thermoplastic blend for 10-15 minutes
at a rotor speed of 50 rpm. Then the other ingredients are added.
If the elastomers are not cure incorporated, curing agent may also
be added at this time. Stirring continues for an additional time
required to achieve full cure of the elastomer, as determined for
example by reaching a steady state torque reading in the mixer. The
composition is then discharged from the batch mixer and granulated
to make small size pellets for use in subsequent fabrication
processes, such as injection molding, compression molding, blow
molding, single layer extrusion, multi-layer extrusion, insert
molding, and the like.
[0116] A continuous process is carried out in a twin-screw
extruder. Pellets of the high temperature fluoroplastic and the low
temperature fluoroplastic are mixed separately and added to the
extruder hopper. The pellets are fed into the barrel, which is
heated to 350-380.degree. C., along with the processing and
optional compatibilizing agent. The plastic mixture is melted in
the melting zone of the extruder barrel, compressed in the
compression zone, and mixed in the first mixing zone. Fluorocarbon
elastomer (as chopped pellets) is fed into the barrel from a first
side feeding zone hopper, which is downstream of the first mixing
zone. The elastomer pellets are melted in the barrel and mixed with
the molten fluoroplastic mixture as the screws are rotated to push
the molten plastic/elastomer mixture into the second mixing zone.
The rest of the ingredients are added at a second side feeding zone
that is downstream of the second mixing zone. Typical residence
time is about 10-15 minutes in the barrel at a screw speed of
150-200 rpm. The temperature is maintained at 350-380.degree. C.
The cured elastomer/fluoroplastic blend is extruded through a 1-3
mm diameter strand die and is quenched by cooling in a water bath
before passing through a strand pelletizer. The pellets may be
processed by a wide variety of thermoplastic techniques into molded
articles. The material may also be formed into plaques for the
measurement of physical properties.
[0117] In Examples 1-3, the following materials are used:
[0118] Tecnoflon FOR 50HS and FOR 80HS are no (low) post cure
bisphenol curable fluorocarbon elastomers from Solvay, with
bisphenol curing agent formulated into the resin.
[0119] Kynar Flex 2500-20 is a vinylidene fluoride/HFP copolymer
based thermoplastic from Atofina Chemicals.
[0120] Elastomag 170 is a magnesium hydroxide powder from Rohm and
Haas.
[0121] MT Black is a carbon black filler.
[0122] Struktol WS-280 is a processing aid from Struktol.
[0123] Tecnoflon FPA-1 is a high temperature processing aid from
Solvay.
[0124] Fluorel FE 5840 is a high fluorine (70% F) cure incorporated
fluoroelastomer from Dyneon.
[0125] Dyneon BRE 7231X is a base resistant cure incorporated
fluoroelastomer from Dyneon. It is based on a terpolymer of TFE,
propylene, and vinylidene fluoride.
[0126] PFA is a copolymer of TFE and perfluoropropyl vinyl
ether.
[0127] Rhenofit CF is a calcium hydroxide from Rhein Chemie.
[0128] Austin Black is a carbon black filler.
Example 1
[0129] TABLE-US-00001 Ex 1a Ex 1b Ex 1c Ex 1d Ex 1e Ingredient phr
phr phr phr phr Fluorel FE5840 70.0 70.0 70.0 70.0 70.0 Dyneon BRE
7231X 30.0 30.0 30.0 30.0 30.0 Kynar Flex 2500-20 10.0 30.0 50.0
70.0 90.0 PFA 90.0 70.0 50.0 30.0 10.0 Rhenofit CF 6.0 6.0 6.0 6.0
6.0 Elastomag 170 3.0 3.0 3.0 3.0 3.0 Struktol WS-280 1.0 1.0 1.0
1.0 1.0 Austin Black 10.00 10.00 10.00 10.00 10.00 Tecnoflon FPA-1
1.00 1.00 1.00 1.00 1.00 melting point 240 240 241 240 239 (DSC),
.degree. C.
[0130] The melting point of the compositions of Example 1 is
determined by differential scanning calorimetry. A sample of the
moldable rubber composition is heated above 260.degree. C., and the
endothermic heat flow is measured on cooling to determine the DSC
melting point. Shaped articles are prepared by thermoplastic
processing the compositions. The compositions are heated to about
260-270.degree. C. (about 20-30.degree. C. above the DSC melting
temperature) and made into shaped articles by thermoplastic
techniques such as extrusion, injection molding, compression
molding, insertion molding, and thermoforming.
Example 2
[0131] TABLE-US-00002 Ex 4a Ex 4b Ex 4c Ex 4d Ex 4e Ingredient phr
phr phr phr phr Fluorel FE5840 70.0 70.0 70.0 70.0 70.0 Dyneon BRE
7231X 30.0 30.0 30.0 30.0 30.0 Kynar Flex 2500-20 5.0 10.0 12.5
15.0 20.0 PFA 20.0 15.0 12.5 10.0 5.0 Rhenofit CF 6.0 6.0 6.0 6.0
6.0 Elastomag 170 3.0 3.0 3.0 3.0 3.0 Struktol WS-280 1.0 1.0 1.0
1.0 1.0 Austin Black 10.00 10.00 10.00 10.00 10.00 Tecnoflon FPA-1
1.00 1.00 1.00 1.00 1.00
Example 3
[0132] TABLE-US-00003 Ex 5a Ex 5b Ex 5c Ex 5d Ex 5e Ingredient phr
phr phr phr phr Tecnoflon FOR 80HS 100.0 100.0 100.0 100.0 100.0
Kynar Flex 2500-20 5.0 10.0 12.5 10.0 5.0 PFA 20.0 15.0 12.5 10.0
5.0 Elastomag 170 (MgO) 3.0 3.0 3.0 3.0 3.0 MT Black (N990) 30.00
30.00 30.00 30.00 30.00 Struktol WS-280 1.00 1.00 1.00 1.00 1.00
Tecnoflon FPA-1 1.00 1.00 .00 1.00 1.00
[0133] Molded articles prepared from the cured compositions of
Examples 2 and are prepared by conventional plastic processing
techniques.
[0134] Although the invention has been described in light of
various embodiments including those currently considered to be the
most advantageous or preferred for carrying out the invention, it
is to be understood that the invention is not limited to the
disclosed embodiments. Rather, variations and modifications that
will occur to one of skill in the art upon reading the disclosure
are intended to be within the scope of the invention, which is
defined in the appended claims.
* * * * *