Note: Descriptions are shown in the official language in which they were submitted.
CA 02558900 2006-09-07
BLENDS OF HXNBR AND LOW MOONEY HNBR
FIELD OF THE INVENTION
The present invention relates to polymer blends of low Mooney hydrogenated
nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene
rubber. The
present invention also relates to a process to prepare blends of low Mooney
hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite
butadiene
rubber.
The present invention further relates to rubber compounds containing polymer
blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated
carboxylated nitrite butadiene rubber. In addition the present invention
relates to
shaped articles containing rubber compounds based on polymer blends of low
Mooney
hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite
butadiene
rubber.
The polymer blends according to the present invention have improved
processability characteristics and the compounds containing the polymer blends
have
excellent mechanical strength retention at elevated temperatures, improved low
temperature properties and enhanced hot air/chemical resistance.
BACKGROUND OF THE INVENTION
Hydrogenated nitrite rubber (HNBR), prepared by the selective hydrogenation of
acrylonitrile-butadiene rubber (nitrite rubber; NBR, a co-polymer containing
at least one
conjugated diene, at least one unsaturated nitrite and optionally further co-
monomers),
is a specialty rubber which has very good heat resistance, excellent ozone and
chemical resistance, and excellent oil resistance. Coupled with the high level
of
mechanical properties of the rubber (in particular the high resistance to
abrasion) it is
not surprising that NBR and HNBR has found widespread use in the automotive
(seals,
hoses, bearing pads) oil (stators, well head seals, valve
plates), electrical (cable sheathing), mechanical engineering (wheels,
rollers) and
shipbuilding (pipe seals, couplings) industries, amongst others.
Commercially available NBR and HNBR have a Mooney viscosity in the range of
from 55 to 105, a molecular weight in the range of from 200,000 to 500,000
g/mol, and
for the HNBR a polydispersity greater than 3.0 and a residual double bond
(RDB)
CA 02558900 2006-09-07
POS 1203 CA
content in the range of from 1 to 18% (by IR spectroscopy).
One limitation in processing NBR and HNBR is the relatively high Mooney
viscosity. In principle, NBR and HNBR having a lower molecular weight and
lower
Mooney viscosity would have better processability. Attempts have been made to
reduce the molecular weight of the polymer by mastication (mechanical
breakdown) and
by chemical means (for example, using strong acid), but such methods have the
disadvantages that they result in the introduction of functional groups (such
as
carboxylic acid and ester groups) into the polymer, and the altering of the
micro-
structure of the polymer. This results in disadvantageous changes in the
properties of
the polymer. In addition, these types of approaches, by their very nature,
produce
polymers having a broad molecular weight distribution.
A, optionally hydrogenated, nitrite rubber having a low Mooney (<55) and
improved processability, but which has the same microstructure as those
rubbers which
are currently available, is difficult to manufacture using current
technologies. The
hydrogenation of NBR to produce HNBR results in an even bigger increase in the
Mooney viscosity of the raw polymer. This Mooney Increase Ratio (MIR) is
generally
around 2, depending upon the polymer grade, hydrogenation level and nature of
the
feedstock. Furthermore, limitations associated with the production of NBR
itself dictate
the low viscosity range for the HNBR feedstock.
Karl Ziegler's discovery of the high effectiveness of certain metal salts, in
combination with main group alkylating agents, to promote olefin
polymerization under
mild conditions has had a significant impact on chemical research and
production to
date. It was discovered early on that some "Ziegler-type" catalysts not only
promote the
coordination-insertion mechanism but also affect an entirely different
chemical process
that is the mutual exchange (or metathesis) reaction of alkenes.
Acyclic diene metathesis (or ADMET) is catalyzed by a great variety of
transition
metal complexes as well as non-metallic systems. Heterogeneous catalyst
systems
based on metal oxides, sulfides or metal salts were originally used for the
metathesis of
olefins. However, the limited stability (especially towards hetero-
substituents) and the
lack of selectivity resulting from the numerous active sites and side
reactions are major
drawbacks of the heterogeneous systems.
Homogeneous systems have also been devised and used to effect olefin
metathesis. These systems offer significant activity and control advantages
over the
2
CA 02558900 2006-09-07
POS 1203 CA
heterogeneous catalyst systems. For example, certain Rhodium based complexes
are
effective catalysts for the metathesis of electron-rich olefins.
The discovery that certain metal-alkylidene complexes are capable of
catalyzing
the metathesis of olefins triggered the development of a new generation of
well-defined,
highly active, single-site catalysts. Amongst these, Bis-
(tricyclohexylphosphine)
benzylidene ruthenium dichloride (commonly know as Grubb's catalyst) has been
widely
used, due to its remarkable insensitivity to air and moisture and high
tolerance towards
various functional groups. Unlike the molybdenum-based metathesis catalysts,
this
ruthenium carbene catalyst is stable to acids, alcohols, aldehydes and
quaternary
amine salts and can be used in a variety of solvents (C6H6, CH2CI2, THF, t
BuOH).
The use of transition-metal catalyzed alkene metathesis has since enjoyed
increasing attention as a synthetic method. The most commonly-used catalysts
are
based on Mo, W and Ru. Research efforts have been mainly focused on the
synthesis
of small molecules, but the application of olefin metathesis to polymer
synthesis has
allowed the preparation of new polymeric material with unprecedented
properties (such
as highly stereoregular poly-norbornadiene).
The utilization of olefin metathesis as a means to produce low molecular
weight
compounds from unsaturated elastomers has received growing interest. The use
of an
appropriate catalyst allows the cross-metathesis of the unsaturation of the
polymer with
the co-olefin. The end result is the cleavage of the polymer chain at the
unsaturation
sites and the generation of polymer fragments having lower molecular weights.
In
addition, another effect of this process is the "homogenizing" of the polymer
chain
lengths, resulting in a reduction of the polydispersity. From an application
and
processing stand point, a narrow molecular weight distribution of the raw
polymer
results in improved physical properties of the vulcanized rubber, while the
lower
molecular weight provides good processing behavior.
The so-called "depolymerization" of copolymers of 1,3-butadiene with a variety
of
co-monomers (styrene, propene, divinylbenzene and ethylvinylbenzene,
acrylonitrile,
vinyltrimethylsilane and divinyldimethyl- silane) in the presence of classical
Mo and W
catalyst system has been investigated. Similarly, the degradation of a nitrite
rubber
using WC16 and SnMe4 or PhC=CH co-catalyst was reported in 1988. However, the
focus of such research was to produce only low molecular fragments which could
be
characterized by conventional chemical means and contains no teaching with
respect to
3
CA 02558900 2006-09-07
POS 1203 CA
the preparation of low molecular weight nitrite rubber polymers. Furthermore,
such
processes are non-controlled and produce a wide range of products.
The catalytic depolymerization of 1,4-polybutadiene in the presence of
substituted olefins or ethylene (as chain transfer agents) in the presence of
well-defined
Grubb's or Schrock's catalysts is also possible. The use of Molybdenum or
Tungsten
compounds of the general structural formula {M(=NR~)(OR2)2(=CHR); M = Mo, W}
to
produce low molecular weight polymers or oligomers from gelled polymers
containing
internal unsaturation along the polymer backbone was claimed in U.S. Patent
No.
5,446,102. Again, however, the process disclosed is non-controlled, and
there is no teaching with respect to the preparation of low molecular weight
nitrite rubber
polymers.
International Applications PCT/CA02/00966, PCT/CA02/00965, and WO-
03/002613-A1 and Co-pending Canadian Patent Application. No.2,462,011 disclose
that hydrogenated and non-hydrogenated nitrite rubber having lower molecular
weights
and narrower molecular weight distributions than those known in the art can be
prepared by the olefin metathesis of nitrite butadiene rubber, optionally
followed by
hydrogenation of the resulting metathesized NBR. Currently, some of the lowest
Mooney viscosity products are currently available from LANXESS Corporation.
Hydrogenated carboxylated acrylonitrile-butadiene rubber (HXNBR) is known to
provide vulcanizates possessing outstanding mechanical properties (tensile,
elongation
and tear) combined with excellent property retention at high temperatures. In
addition,
vulcanizates containing HXNBR exhibit excellent abrasion resistance, adhesive
strength
as well as improved hot air aging resistance over carboxylated nitrite. HXNBR
thrives in
severe end use environments such as oil well (packer and drill bit seals) and
roll
(printing and paper-making) applications.
SUMMARY OF THE INVENTION
The present invention relates to polymer blends of low Mooney hydrogenated
nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene
rubber. The
present invention also relates to a process to prepare blends of low Mooney
hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite
butadiene
rubber.
The present invention further relates to rubber compounds containing polymer
4
CA 02558900 2006-09-07
POS 1203 CA
blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated
carboxylated nitrite butadiene rubber. In addition the present invention
relates to
shaped articles containing rubber compounds based on polymer blends of low
Mooney
hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite
butadiene
rubber.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates the compound Mooney viscosity of blended compounds of low
Mooney HNBR and HNXBR.
Figure 2 illustrates the Mooney scorch of blended compounds of low Mooney HNBR
and HNXBR.
Figure 3 illustrates the injection moldability of blended compounds of low
Mooney
HNBR and HNXBR.
Figure 4 illustrates the hardness of blended compounds of low Mooney HNBR and
HNXBR.
Figure 5 illustrates the stress as 100% elongation of blended compounds of low
Mooney
HNBR and HNXBR.
Figure 6 illustrates the elongation at break of blended compounds of low
Mooney HNBR
and HNXBR.
Figure 7 illustrates the tensile strength of blended compounds of low Mooney
HNBR
and HNXBR.
Figure 8 illustrates the tear resistance of blended compounds of low Mooney
HNBR and
HNXBR.
Figure 9 illustrates the temperature retraction of blended compounds of low
Mooney
HNBR and HNXBR.
Figure 10 illustrates the hardness and stress strain changes of blended
compounds of
low Mooney HNBR and HNXBR.
Figure 11 illustrates the hot air heat resistance under compression of blended
compounds of low Mooney HNBR and HNXBR.
Figure 12 illustrates the immersion aging resistance to lithium grease of
blended
compounds of low Mooney HNBR and HNXBR.
5
CA 02558900 2006-09-07
POS 1203 CA
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described for purposes of illustration and
not
limitation. Except in the operating examples, or where otherwise indicated,
all numbers
expressing quantities, percentages, and so forth in the specification are to
be
understood as being modified in all instances by the term "about." Also, all
ranges
include any combination of the maximum and minimum points disclosed and
include
any intermediate ranges therein, which may or may not be specifically
enumerated
herein.
The low Mooney hydrogenated nitrite rubbers useful in the present invention
and
processes for making them are known in the art and are the subject of U.S.
Patent Nos.
6,673,881, 6,780,939 and 6,841,623 the disclosure of which is incorporated by
reference for the purpose of Jurisdictions allowing for this feature. Such
rubbers are
formed by the olefin metathesis of nitrite butadiene rubber with a Ru
metathesis
catalyst, such as a Grubb's catalyst, followed optionally by hydrogenation of
the
resulting metathesized NBR.
Low Mooney hydrogenated nitrite rubbers useful in the present invention have a
Mooney viscosity (ML(1 +4) @ 100°C) of between 1 and 55, preferably
between 5 and
50, more preferably between 20 and 45 and most preferably between 15-40.
As used throughout this specification, the term "nitrite rubber" is intended
to have
a broad meaning and is meant to encompass a copolymer having (a) repeating
units
derived from at least one conjugated diene, (b) at least one alpha,beta-
unsaturated
nitrite and optionally (c) repeating units derived from at least one further
monomer.
As used throughout this specification, term, hydrogenated carboxylated nitrite
rubber is intended to have a broad meaning and is meant to encompass a
hydrogenated copolymer having (a) repeating units derived from at least one
conjugated diene, (b) at least one alpha, beta-unsaturated nitrite and (c)
repeating
unites derived from monomers
selected from the group consisting of conjugated dienes, unsaturated
carboxylic acids
and alkyl esters of unsaturated carboxylic acids.
The conjugated diene may be any known conjugated diene in particular a C4-C6
conjugated diene. Preferred conjugated dienes are butadiene, isoprene,
piperylene,
2,3-dimethyl butadiene and mixtures thereof. Even more preferred C4-C6
conjugated
6
CA 02558900 2006-09-07
POS 1203 CA
dienes are butadiene,
isoprene and mixtures thereof. The most preferred C4-C6 conjugated diene is
butadiene.
The alpha,beta-unsaturated nitrite may be any known alpha,beta-unsaturated
nitrite, in particular a C3-C5 alpha,beta-unsaturated nitrite. Preferred C3-CS
alpha,beta-
unsaturated nitrites are acrylonitrile, methacrylonitrile, ethacrylonitrile
and mixtures
thereof. The most preferred C3-C5 alpha,beta-unsaturated nitrite is
acrylonitrile.
The unsaturated carboxylic acid may be any known unsaturated carboxylic acid
copolymerizable with the other monomers, in particular a C3-C~6 alpha,beta-
unsaturated
carboxylic acid. Preferred unsaturated carboxylic acids are acrylic acid,
methacrylic
acid, itaconic acid and malefic acid and mixtures thereof.
The alkyl ester of an unsaturated carboxylic acid may be any known alkyl ester
of
an unsaturated carboxylic acid copolymerizable with the other monomers, in
particular
an alkyl ester of an C3-C~6 alpha,beta-unsaturated carboxylic acid. Preferred
alkyl ester
of an unsaturated carboxylic acid are alkyl esters of acrylic acid,
methacrylic acid,
itaconic acid and malefic acid and mixtures thereof, in particular butyl
acrylate, methyl
acrylate, 2-ethylhexyl acrylate and octyl acrylate. Preferred alkyl esters
include methyl,
ethyl, propyl, and butyl esters.
Hydrogenated in this invention is preferably understood by more than 50 % of
the
residual double bonds (RDB) present in the starting nitrite polymer/NBR being
hydrogenated, preferably more than 90 % of the RDB are hydrogenated, more
preferably more than 95 % of the RDB are
hydrogenated and most preferably more than 99 % of the RDB are hydrogenated.
An antioxidant may be useful in the preparation of polymers blends and
compounds containing polymer blends according to the present invention.
Examples of
suitable antioxidants include p-dicumyl diphenylamine (Naugard~ 445),
Vulkanox~ DDA
(a diphenylamine derivative), Vulkanox~ ZMB2 (zinc salt of methylmercapto
benzimidazole), Vulkanox~ HS (polymerized 1,2-dihydro-2,2,4-trimethyl
quinoline) and
Irganox~ 1035 (thiodiethylene bis(3,5-di-tert.-butyl-4-hydroxy) hydrocinnamate
or
thiodiethylene bis(3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate supplied
by Ciba-
Geigy.
Suitable peroxide curatives useful in the preparation of polymer blends and
7
CA 02558900 2006-09-07
POS 1203 CA
compounds containing polymer blends according to the present invention include
dicumyl peroxide, di-tert.-butyl peroxide, benzoyl peroxide, 2,2'-bis (tert.-
butylperoxy
diisopropylbenzene (Vulcup 40KE), benzoyl peroxide, 2,5-dimethyl-2,5-di(tert-
butylperoxy)-hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, (2,5-
bis(tert.-
butylperoxy)-2,5-dimethyl hexane and the like can be used. The high
temperature of
the polyamide melt influences the selection, however. The best suited curing
agents
are readily accessible by means of few preliminary experiments. A preferred
peroxide
curing agent is commercially available under the trademark Vulcup 40KE. The
peroxide
curing agent is suitably used in an amount of 0.2 to 7 parts per hundred parts
of rubber
(phr), preferably 1 to 3 phr. Too much peroxide may lead to undesirably
violent
reaction. Sulphur, sulphur-containing compounds and resins can also be used as
curatives.
Vulcanizing co-agents can also be used in the preparation of compounds
according to the present invention. Mention is made of triallyl isocyanurate
(TAIC),
commercially available under the trademark DIAK 7 from DuPont or N,N'-m-
phenylene
dimaleimide know as HVA-2 (DuPont Dow), triallyl cyanurate (TAC) or liquid
polybutadiene known as Ricon~ D 153 (supplied by Ricon Resins). Amounts can be
equivalent to the peroxide curative or less, preferably equal.
Crosslinking density can further be increased by the addition of an activator
such
as zinc peroxide (50% on an inert carrier) using Struktol~ ZP 1014 in
combination with
the peroxide. Amounts can be between 0.2 to 7 phr, preferably 1 to 3 phr.
It is possible to achieve further crosslinking by using curatives used with
carboxylated polymers such as: amines, epoxies, isocyanates, carbodiimides,
aziridines, or any other additive that can form a derivative of a carboxyl
group.
The ratio of hydrogenated carboxylated nitrite rubber to low Mooney
hydrogenated nitrite rubber can vary between wide limits, preferably 95 parts
to 5 parts
by weight (phr) to 5 parts to 95 parts by weight. More preferably. 75 parts to
25 parts
by weight to 25 parts to 75 parts by weight. The ratio of HXNBR to low Mooney
HNBR
can vary and can be optimized by simple experimentation by one skilled in the
art.
It is possible to include processing oils and extenders or plasticizers in the
compound according to the present invention. Suitable plasticizers include
those well
known for use with nitrite polymers such as the phthalate compounds, the
phosphate
compounds, the adipate compounds, the alkyl carbitol formal compounds, the
8
CA 02558900 2006-09-07
POS 1203 CA
coumarone-indene resins and the like. An example is the plasticizer
commercially
available under the trademark Plasthall~ 810, or Plasthall~ TOTM (trioctyl
trimellitate) or
TP-95 (di-(butoxy-ethoxy-ethyl) adipate supplied by Morton International. The
plasticizer should be a material that is stable at high temperature and will
not exude
from the compound.
It is also possible to use a mixture of another elastomer in the compound of
the
present invention, for example, a carboxylated nitrite rubber (XNBR), a
hydrogenated
nitrite rubber (HNBR) or a nitrite rubber (NBR), a vinyl acetate rubber (EVM)
or a
ethylene/acrylate rubber (AEM). Suitable XNBR's are commercially available
from
Lanxess Deutschland GmbH under the trademark Krynac~ and suitable HNBR's are
commercially available from Lanxess Deutschland GmbH under the trademark
Therban~ and suitable NBR's are available from Lanxess Deutschland GmbH under
the
trademark Perbunan~. EVM is commercially available from Lanxess Deutschland
GmbH
under the trademark Levapren~. Vamac~ D an ethylene acrylic elastomer is
commercially available from DuPont.
The present inventive compound can also contain at least one filler. The
filler
may be an active or inactive filler or a mixture thereof. The filler may be
added to the
compound in an amount from 1 to 200 phr, preferably 10 - 120 phr, most
preferably 20 -
80 phr. Suitable fillers include:
- highly dispersed silicas, prepared e.g. by the precipitation of silicate
solutions or
the flame hydrolysis of silicon halides, with specific surface areas of in the
range of from
5 to 1000 m2/g, and with primary particle sizes of in the range of from 10 to
400 nm;
the silicas can optionally also be present as mixed oxides with other metal
oxides such
as those of AI, Mg, Ca, Ba, Zn, Zr and Ti;
- synthetic silicates, such as aluminum silicate and alkaline earth metal
silicate
like magnesium silicate or calcium silicate, with BET specific surface areas
in the range
of from 20 to 400 m2/g and primary particle diameters in the range of from 10
to 400
nm;
- natural silicates, such as kaolin and other naturally occurring silica;
- glass fibers and glass fiber products (matting, extrudates) or glass
microspheres;
- carbon blacks; the carbon blacks to be used here are prepared by the lamp
black, furnace black or gas black process and have preferably BET (DIN 66 131)
9
CA 02558900 2006-09-07
POS 1203 CA
specific surface areas in the range of from 20 to 200 m2/g, e.g. SAF, ISAF,
HAF, FEF or
GPF carbon blacks;
- rubber gels, especially those based on polybutadiene, butadiene/styrene
copolymers, butadiene/acrylonitrile copolymers and polychloroprene;
or mixtures thereof.
Examples of preferred mineral fillers include silica, silicates, clay such as
bentonite, gypsum, alumina, titanium dioxide, talc, mixtures of these, and the
like.
These mineral particles have hydroxyl groups on their surface, rendering them
hydrophilic and oleophobic. This exacerbates the difficulty of achieving good
interaction
between the filler particles and the rubber. For many purposes, the preferred
mineral is
silica, especially silica made by carbon dioxide precipitation of sodium
silicate.
Dried amorphous silica particles suitable for use in accordance with the
invention
may have a mean agglomerate particle size in the range of from 1 to 100
microns,
preferably between 10 and 50 microns and most preferably between 10 and 25
microns.
It is preferred that less than 10 percent by volume of the agglomerate
particles are
below 5 microns or over 50 microns in size. A suitable amorphous dried silica
moreover
usually has a BET surface area, measured in accordance with DIN (Deutsche
Industrie
Norm) 66131, of in the range of from 50 and 450 square meters per gram and a
DBP
absorption, as measured in accordance with DIN 53601, of in the range of from
150 and
400 grams per 100 grams of silica, and a drying loss, as measured according to
DIN
ISO 787/11, of in the range of from 0 to 10 percent by weight. Suitable silica
fillers are
available under the trademarks HiSil~ 210, HiSil~ 233 and HISiI~ 243 from PPG
Industries Inc. Also suitable are Vulkasil S and Vulkasil N, from Lanxess
Deutschland
GmbH.
The compound according to the present invention can contain further auxiliary
products suitable for use with rubbers, such as reaction accelerators,
vulcanizing
accelerators, vulcanizing acceleration auxiliaries, antioxidants, foaming
agents, anti-
aging agents, heat stabilizers, light stabilizers, ozone stabilizers,
processing aids,
plasticizers, tackifiers, blowing agents, dyestuffs, pigments, waxes,
extenders, organic
acids, inhibitors, metal oxides, and activators such as triethanolamine,
polyethylene
glycol, hexanetriol, etc., which are known to the rubber industry. The rubber
aids are
used in conventional amounts, which depend inter alia on the intended use.
Conventional amounts include from 0.1 to 50 wt.%, based on rubber. Preferably
the
CA 02558900 2006-09-07
POS 1203 CA
compound contains in the range of 0.1 to 20 phr of an organic fatty acid as an
auxiliary
product, preferably a unsaturated fatty acid having one, two or more carbon
double
bonds in the molecule which more preferably includes 10% by weight or more of
a
conjugated diene acid having at least one conjugated carbon-carbon double bond
in its
molecule. Preferably those fatty acids have in the range of from 8-22 carbon
atoms,
more preferably 12-18. Examples include stearic acid, palmitic acid and oleic
acid and
their calcium-, zinc-, magnesium-, potassium- and ammonium salts. Preferably
the
compound includes in the range of 5 to 50 phr of an acrylate as an auxiliary
product.
Suitable acrylates are known from EP-A1-0 319 320, U.S. Patent Nos. 5,208,294
and
4,983,678. Reference is made to zinc acrylate, zinc diacrylate or zinc
dimethacrylate or
a liquid acrylate, such as trimethylolpropanetrimethacrylate (TRIM),
butanedioldi-
methacrylate (BDMA) and ethylenglycoldimethacrylate (EDMA). It might be
advantageous to use a combination of different acrylates and/or metal salts
thereof. Of
particular advantage is often to use metal acrylates in combination with a
Scorch-
retarder such as sterically hindered phenols (e.g. methyl-substituted
aminoalkylphenols,
in particular 2,6-di-tert.-butyl-4-dimethylaminomethylphenol). It is possible
to incorporate
other known additives or compounding agents in the compound according to the
present invention.
The ingredients of the final polymer blend can be mixed together, suitably at
an
elevated temperature that may range from 25°C to 200°C. Normally
the mixing time
does not exceed one hour and a time in the range from 2 to 30 minutes is
usually
adequate. If the polymer blend is prepared without solvent or was recovered
from the
solution, the mixing can be suitably carried out in an internal mixer such as
a Banbury
mixer, or a Haake or Brabender miniature internal mixer. A two-roll mill mixer
also
provides a good dispersion of the additives within the elastomer. An extruder
also
provides good mixing, and permits shorter mixing times. It is possible to
carry out the
mixing in two or more stages, and the mixing can be done in different
apparatus, for
example one stage in an internal mixer and one stage in an extruder. However,
it
should be taken care that no unwanted pre-crosslinking (= scorch) occurs
during the
mixing stage. For compounding and vulcanization see also: Encyclopedia of
Polymer
Science and Engineering, Vol. 4, p. 66 et seq. (Compounding) and Vol. 17, p.
666 et
seq. (Vulcanization).
The invention is further illustrated but is not intended to be limited by the
11
CA 02558900 2006-09-07
POS 1203 CA
following examples in which all parts and percentages are by weight unless
otherwise
specified.
EXAMPLES
The peroxide cured HXNBR and/or HXNBR and low Mooney HNBR blend recipes used
for this investigation is tabulated in Table I. The control formulation
contains 100%
HXNBR. HNBR-AT (34% ACN, < 0.9% RDB, 39 MU) is then blended into HXNBR at
three different levels: 25/75, 50/50 and 75/25.
Table I: Standard HXNBR formulation used with the blend ratios
INGREDIENT PHRS
Exam 1e 9 2 3 4
HXNBR 100 75 50 25
HNBR-AT 0 25 50 75
CARBON BLACK N660 50
ODA 0.5
ODPA 1.5
TOTM 5
ZINC PEROXIDE 50% 7
TAIC 1.5
PEROXIDE 40% 7.5
TOTAL PHRS 173
List of compound ingredients and testing fluids
HXNBR = Therban XT VP KA 8889 (33% ACN, 3.5% RDB, 5% carboxylic acid and 77
MU (100°C)) available from LANXESS Deutschland GmbH.
HNBR-AT = Low Mooney HNBR Therban AT VP KA 8966 (34% ACN, < 0.9% RDB and
39 MU (100°C)) available from LANXESS Deutschland GmbH.
ODA = Octadecyl amine = Armeen 18D from Akzo Nobel
ODPA = p-dicumyl diphenylamine = Naugard 445 from Chemtura.
CARBON BLACK = N660 from Cabot.
TOTM = trioctyl trimellitate (Plasthall) from C.P. Hall.
ZINC PEROXIDE (Zn02) = 50% active zinc peroxide preparation, Struktol ZP 1014,
available from Struktol.
12
CA 02558900 2006-09-07
POS 1203 CA
TAIC = triallyl isocyanurate (Disk#7) from DuPont.
PEROXIDE = bis (t-butyl-peroxy) diisopropylbenzene (40% on Burgess clay) =
Vulcup
40KE from Geo Chemicals.
Lithium grease = Motomaster constant velocity joint grease (meets GM
specification
7843867).
A laboratory BR-82 internal mixer (1.6 L capacity) was used for first stage
mixing.
The rotor speed was set at 55 rpm and cooling carryied out at 30°C. All
ingredients
except the peroxide were added to the mixer. At time 0 min, HXNBR and HNBR
were
added to the mixer and allowed to mix for 1 minute. At this time, the carbon
black, ODA,
ODPA and zinc peroxide were added to the mix. Mixing continued for an
additional 1
minute at which time a sweep was performed. After an additional one minute of
mixing,
the TAIC and TOTM were added and the whole batch was allowed to mix for an
extra 2
minutes then discharged from the mixer. The peroxide was added and
incorporated
during the second stage on a 10" by 20" two roll mill cooled at 30°C.
The processability and final compound properties of the HNBR blends were
measured in accordance with the ensuing list of ASTM procedures:
Mooney Viscosity and Scorch - ASTM D1646-81
Capillary Rheometer - ASTM D5099-93 A (except barrel inside diameter = 19 mm
and
barrel length = 25.4 mm).
Hardness - ASTM D2240
Stress Strain - ASTM D412 A
Tear Resistance - ASTM D624
Temperature Retraction - ASTM D1329
Hot air aging resistance - ASTM D573
Compression Set - ASTM D395 B
Fluid Resistance - ASTM D471
Figure 1 clearly shows that the systematic and progressive blending of low
Mooney HNBR-AT into HXNBR brings about a substantial lowering of the compound
Mooney viscosity. Compound Mooney values decrease by up to 20 MU in the cases
where the blend ratio is 25/75. Compound Mooney viscosities in the range of 50
to 60
are desirable for injection moldable products.
13
CA 02558900 2006-09-07
POS 1203 CA
Mooney scorch is often an issue with carboxylated elastomers. The use of a
slow
release dispersion of zinc peroxide alleviates this issue in 100% HXNBR,
however, as
can be seen from the data in Figure 2, low Mooney HNBR-AT addition will help
to
prolong the safety period before vulcanization. Longer scorch safety is
advantageous
in injection molding in the case of long channels and intricate die designs
which require
good flow for complete mold filling.
A capillary rheometer (Monsanto Processability Tester) possessing a barrel LlD
of 30 and a die diameter of 0.0754 cm was employed to explore the injection
moldability
of the compounds in the higher shear rate zone. In Figure 3, the barrel
pressure is
plotted as a function of shear rate. It is observed that increasing the
concentration of
low Mooney HNBR-AT in the blend will help in decreasing barrel pressure,
meaning that
for the same barrel pressure, a low Mooney HNBR-AT blend will flow quicker
through
the capillary compared to the HXNBR compound alone. Barrel pressures became
unreliable in the 3000 s-1 range of the rheometer as the 1000 bar range limit
of the
apparatus was attained. Nevertheless, the trends observed in the lower shear
rate
range of the rheometer are favourable towards the use of low Mooney HNBR-AT
rich
blends for lower barrel pressures and/or quicker flow behavior.
Hardnesses (A-2 type) were measured at 23, 100 and 150°C (Figure
4). The
highest hardnesses were obtained on the HXNBR compounds as low Mooney HNBR-
AT addition progressively lowered hardness values. Improved retention of
hardness at
elevated temperature testing was observed with the low Mooney HNBR-AT rich
compounds compared with the control compound (ex. 1 ).
In Figure 5, stress at 100% elongation data are presented at 23, 100 and
150°C.
The stress data in figure 5 mirror the trends observed in the hardness values
of Figure
4. Low Mooney HNBR-AT addition to HXNBR causes a decrease in stiffness values
at
room temperature. The low Mooney HNBR-AT rich compounds display the least
change in stiffness upon elevated temperature testing.
In Figure 6, elongation to break values increase with low Mooney HNBR-AT
addition. Here it is observed that the best elongation at higher temperatures
is seen
with the HXNBR rich blends.
In Figure 7, it is illustrated that extraordinary high tensile strengths of
over 25
MPa are possible using HXNBR (ex. 1 ). Blending in low Mooney HNBR-AT brings
about a slight decrease in tensile strength, but only by about 1 - 3 MPa. A
drop in
14
CA 02558900 2006-09-07
POS 1203 CA
tensile strength is noted during the elevated temperature testing, however
values of 8 -
13 MPa are possible at 150°C. Excellent mechanical property retention
at elevated
temperatures is crucial for proper functioning of parts which provide good
sealing
behavior.
Tear resistance by using die B or die C cut specimens was measured at room
temperature in Figure 8. The excellent tear strength of HXNBR is observed.
Blending
in low Mooney HNBR-AT has only a moderate effect in decreasing the tear
strength as
excellent values are retained up to the 25/75 blend ratio.
As shown by the temperature retraction data in Figure 9, the low temperature
resistance slightly improves upon HNBR-AT addition. HXNBR contains 33% ACN
whereas low Mooney HNBR-AT contains 34% ACN. As its level predominantly
determines the low temperature behavior in HNBRs (low ACN levels provide
improved
low temperature characteristics), it is a clear advantage that low Mooney HNBR-
AT rich
blends display improved low temperature properties.
The hardness and stress strain data changes upon exposing die C dumbbell
samples to hot air at 135°C for 504 hours are depicted in Figure 10. In
all cases,
hardening and stiffening takes place with corresponding loss of elongation. It
is clear
however, that elongation loss can be lessened by adding more low Mooney HNBR-
AT.
The hot air heat resistance under compression at 135°C and for 70, 168
and 504
hours is presented in Figure 11. The trends are readily apparent. Progressive
low
Mooney HNBR-AT addition causes a lowering of unwanted set due to compression.
Immersion aging resistance to lithium grease (Figure 12) was carried out on
specimens aged for 168 hrs at 135°C. Property change in terms of
hardness, tensile,
elongation and volume swell is reported. Lithium based constant velocity joint
grease
resistance is improved in the low Mooney HNBR-AT rich blends as witnessed by
the
lower tensile and hardness changes as well as better elongation retention as a
function
of immersion aging.
Although the invention has been described in detail in the foregoing for the
purpose of illustration, it is to be understood that such detail is solely for
that purpose
and that variations can be made therein by those skilled in the art without
departing
from the spirit and scope of the invention except as it may be limited by the
claims.
