Note: Descriptions are shown in the official language in which they were submitted.
CA 02330897 2001-O1-12
Docket No. 196600221CPA
METHOD FOR MANUFACTURE OF ELASTOMERIC ALLOYS USING RECYCLED
RUBBERS
Cross Reference to Related Application
This application is a continuation-in-part of U.S. patent application Serial
No. 08/992,547 filed December 17, 1997.
Field of the Invention
1 o The present invention is directed to a mEahod of preparing blend
thermoplastic compositions using particles of recycled vulcanized, or
crosslinked,
rubber and to the compositions made by the mEahod and articles formed from
these
compositions. The thermoplastic compositions produced by the method may be
formed into many products, including automotive and industrial components.
Background and Summary of the Invention
Both manufacturers and the general public have placed an emphasis in
recent years on recycling materials. Recycling rnaterials is desirable from
the
standpoint of reducing waste that must be landfi!led, burned, or otherwise
discarded.
It has become desirable for manufacturers to include recycled plastic or
recycled
2 o rubber content in the manufacture of articles. In some instances, recycled
materials
may also offer a cost advantage over virgin materials.
Recycling of thermoset polymeric materials, however, has faced serious
difficulties in the preparation of materials for recycling and in maintaining
desired
properties for the articles that incorporate recycled material. One avenue for
2 s recycling crosslinked rubbers has been the use of ground crosslinked
rubber as a
filler in new thermoset polymeric materials. Ground crosslinked rubber may be
CA 02330897 2001-O1-12
produced in mesh sizes of from 10 to over 30(), with a typical range being
about 40-
80 mesh. The ground crosslinked rubber has commonly been recycled by adding it
to uncrosslinked rubber and then vulcanizing the blend rubber. In general, it
has
been reported in literature that blends cannot include more than about 10%
recycled
rubber without suffering a significant decrease in properties, including
surface
roughness. Mixtures including up to 30% ground crosslinked rubber in new
rubber
have been reported to have somewhat lower tE:nsile strength as compared to
virgin
rubber.
One solution to the problem of how to incorporate larger amounts of recycled
1 o rubber without a decrease in properties is to chemically treat the
recycled rubber.
Stosky reported in "Innovation in the Development and Use of Recycled Rubber,"
Paper No. 42, Rubber Division, American Chemical Society (May 6-9, 1997) that
chemically treated recycled rubber could be incorporated in amounts of up to
75% in
a blend with virgin rubber, resulting in a material having equivalent or even
superior
5 performance as compared to virgin rubber. The chemical treatment appears to
involve a surface treatment that allows for crosslinks between the ground
crosslinked rubber and the virgin thermosetting material. Another method of
recycling rubber involves de-vulcanizing the rubber by physical or chemical
means.
De-vulcanized rubber may be mixed with virgin material, re-molded, and then re-
2 o vulcanized along with the new material to produ<;ed a crosslinked blend. A
process
of treating ground crosslinked rubber with a caustic gas to allow bonding with
other
polymers has also been reported.
These methods, however, involve added reactions and manufacturing steps
that make recycling of materials more expensive. Moreover, these methods are
2 s directed to thermoset materials only. Thus, the need remains for a
relatively simple
2
CA 02330897 2001-O1-12
and effective means of recycling cured rubber scrap into new articles,
particularly
articles formed from thermoplastic compositions.
The present invention provides a method of recycling a cured EPDM
terpolymer or EPR copolymer rubber, or mixtures including these rubbers, by
blending the recycle rubber into a thermoplastic material such as a
thermoplastic
polyolefin or resin or an olefin or vulcanizate ttoermoplastic elastomer to
form a
blend composition. The blend compositions comprise ground crosslinked rubber
having a particle size of about 80 mesh or smaller, preferably of about 120
mesh or
smaller. (The mesh size is inversely proportional to the particle size.) The
1 o compositions prepared according to the methods of the invention may
include a
surprisingly high level of recycle rubber without adverse effect on physical
or
aesthetic properties. Thus, the blend thermoplastic materials produced may
comprise up to about 70% by weight of the ground crosslinked rubber, based
upon
the total weight of the blend material. The thermoplastic blend materials of
the
invention may also comprise a compatibilizer.
Detailed Description
The term "ground crosslinked rubber" as used in relation to the methods and
compositions of the invention refers to at least partially crosslinked or
vulcanized
rubber that has been reduced to particles. Preferably, the rubber is fully
crosslinked;
2 o i.e., the crosslinking has been carried to an extent that formation of
further
crosslinks, if possible, would not substantially improve the physical
properties of the
rubber. The particle size of the recycle ground crosslinked rubber of the
invention is
about 80 mesh or smaller, preferably about 120 rnesh or smaller, and it is
especially
preferred that the particle size be about 200 mesh or smaller.
3
CA 02330897 2001-O1-12
The ground crosslinked rubber particles may be prepared by a number of
methods. In one method, the rubber is swelled with solvent and then ground to
a
fine particle size. The rubber may be ground cryogenically. In a preferred
procedure, the recycled rubber particles are prepared according to the
procedure in
Rouse, U.S. Pat. No. 5,411,215, incorporated herein by reference. In this
procedure, the rubber is ground as a 10% by v~reight slurry in water of 10
mesh
particles in a series of grinding mills having progressively finer grinding
stone.
The rubbers that may be recycled in the methods and compositions of the
invention are ethylene propylene rubber (also known as EPM or EPR), ethylene
1o propylene diene monomer rubber (EPDM), and mixtures and blends of these.
The
rubbers will be collectively referred to herein as EPDM. Mixtures and blends
of
EPDM with other rubbers may also be used, as well as elastomeric alloys that
include these rubbers. The rubber compound, which includes the rubber and any
additives, may also typically include up to about 50% additives, preferably up
to
about 15% additives, based upon the weight of the rubber compound. Example of
useful additives include, without limitation, accelerators, oils, colorants
and fillers,
especially carbon black.
The ground crosslinked rubber is mixed with a thermoplastic component. The
thermoplastic component is preferably a polyoleflnic material. Among preferred
2 o materials are homopolymers of ethylene, propylene, and butylene, and
copolymers
that include one or more of these monomers. In a particularly preferred
embodiment, the recycled ground crosslinked rubber is ethylene propylene diene
monomer rubber and the thermoplastic component is selected from polyethylene,
polypropylene, ethylene copolymers, propylene copolymers, polyethylene
2s propylene) copolymers, and combinations of these. In a particularly
preferred
4
CA 02330897 2001-O1-12
embodiment, the rubber particles comprise EF'DM rubber that is at least
partially
cured, preferably fully cured, and the thermoplastic composition comprises
polypropylene.
Alternatively, the thermoplastic component can be a thermoplastic elastomer
such as an olefinic thermoplastic elastomer, i.e., a TPO, or an olefinic
vulcanizate
elastomer, i.e., a TPV.
The ground crosslinked rubber particles can be included in the thermoplastic
composition in amounts of up to about 70% by weight, and preferably up to
about
60% by weight, based upon the total weight of the blend thermoplastic
composition.
1o Preferably, at least about 5% by weight of the recycle ground crosslinked
rubber is
included. The amount of ground rubber that is included is determined based
upon
the particular application and can readily be del:ermined by straightforward
testing.
The compositions of the invention may also include a compatibilizer.
Generally speaking, a compatibilizer is required where the thermoplastic
component
15 consists essentially of a polyolefinic material, but may not be required
where the
thermoplastic component is a TPO or a TPV. Useful compatibilizers are
plasticizers
and oils that are used to improve physical properties of the blend. It is
particularly
preferred to include as a compatibilizer a paraffinic oil or derivative of a
paraffinic oil.
A compatibilizer is included in amounts of at least about 1 % by weight of the
blend.
2 o It is preferred to include at least about 10% by weight compatibilizer,
based upon the
total weight of the blend thermoplastic material. Preferably, no more than
about
25% by weight of compatibilizer is included in thc: compositions of the
invention.
Customary additives such as lubricants, fillers, pigments, plasticizers,
surface-
modifying additives, UV absorbers, antioxidants, hindered amine or amide light
2 s stabilizers, and so on may be added to the thermoplastic composition along
with the
CA 02330897 2001-O1-12
a m
ground crosslinked rubber and compatibilizer. Blends, particularly blends
containing
EPDM rubber that has not been pigmented, can be colored to a desired color.
For
instance, an automotive component formed from the blend may be colored to
complement the color of a vehicle body to which it is to be attached.
In general, there must be enough of the thermoplastic material to hold the
alloy together. There should also be adequate dispersion or distribution of
the
rubber particles in the thermoplastic resin medium. When the blend
thermoplastic
material is used in an injection molding operation, the blend thermoplastic
material
may include up to about 70% by weight, preferably up to about 60%, of the
rubber
i o particles. When lower compression set (as may be measured by ASTM 395) is
needed, the amount of rubber is higher; however, lower levels of rubber are
included
when surface properties, such as surface smoothness, are important. When the
blend thermoplastic material is to be extruded, a lower weight percentage of
rubber
particles, such as less than about 40% by weight, may be used to obtain better
15 surface smoothness.
The invention embraces a broad range with respect to levels of the rubber
particles that may be included in the blend compositions, and the particular
percentage by weight of rubber particles may be chosen to suit the article to
be
manufactured from the blend. In general, the compression set improves, or
2o decreases, with higher levels of the rubber particles. Tensile properties,
however,
are generally better with lower levels of rubber particles in the blend
thermoplastic
material. Thus, it is necessary to balance the levels of the thermoplastic and
the
rubber particles in the thermoplastic material in viE~w of the properties
required for
the ultimate article that is to be made from it. The blend thermoplastic
materials of
25 the invention typically have hardnesses of about 60 Shore A, and hardnesses
of up
6
CA 02330897 2001-O1-12
o
to about 60 Shore D are possible. When the rubber particles are included in
higher'
amounts, it is preferred that the molding or shaping conditions be controlled
so that
the surface of the part being formed is the thermoplastic component of the
blend.
The blend thermoplastic material of the invention is particularly useful as a
replacement for conventional rubber materials. The blend thermoplastic
material
offers several advantages over materials that are presently available. First,
the
materials are less expensive due to the utilization of recycled rubber.
Secondly, the
blend thermoplastic materials, like other thermoplastic compositions, may be
re-
melted and reformed. In addition, the process by which the blend thermoplastic
to materials of the invention is manufactured is more straightforward and less
sensitive
to manufacturing conditions as compared to manufacture of rubbers containing
recycled rubber. Moreover, the present blend thermoplastic material may be
prepared using the equipment usually employed in preparing thermoplastic
blends
rather than the specialized equipment required for dynamic vulcanization.
15 The blend thermoplastic materials of the invention may be prepared by
mixing
the thermoplastic composition, additives, including compatibilizer, and the
rubber
particles in either a continuous or batch process. Such processes may be
carried
out using, for example and without limitation, twin screw extruders, Buss
extruders,
continuous milling lines, or with a high-shear or low-shear mixer. The mixture
may
2 o then be extruded and pelletized according to usual methods. The pellets
may be
either packaged for future use or used immediately in a process of forming an
article. The pellets or blends of the invention may be formed into articles
according
to any of the methods known in the art for thermal processing of thermoplastic
resin
compositions. For example, compression molding, vacuum molding, injection
25 molding, thermoforming, blow molding, calendering, casting, extrusion,
filament
CA 02330897 2001-O1-12
winding, laminating, rotational or slush molding, transfer molding, lay-up or
contact
molding, stamping, and combinations of these methods may be used with the
blend
thermoplastic materials.
The blend thermoplastic materials of the invention may be formed into many
s different kinds of articles. In particular, the blend thermoplastic
materials of the
invention may be formed into seals, seal extensions, and other automotive
components. Articles that need low compression set are particularly suited for
the
blend materials of the invention.
It will be appreciated by those skilled in the art that the blend of the
present
to invention can be itself added to an additional thermoplastic material to
form a
second blend. For example, it has been found that the blend of the present
invention can be added to a TPO or a TPV to rE:duce the cost of the TPO or TPV
without significant degradation of physical propE:rties. The blend comprising
a
ground crosslinked rubber having an average particle size of about 80 mesh or
15 smaller, a thermoplastic olefinic material and a c:ompatibilizer can be
combined with
a TPO or a TPV in proportion by weight of from about 5% to about 70% of blend
to
about 95% to about 30% of TPO or TPV, preferably from about 10% to about 40%
of
blend to about 90% to about 60% of TPO or TPV.
The invention is further described and illustrated by the following examples.
2 o The examples are intended to be instructive and do not in any way limit
the scope of
the invention as described and claimed.
EXAMPLES
Example 1.
2S
Parts by Weight
s
CA 02330897 2001-O1-12
Recycle ground EPDM, 200 mesh 100
W110 polypropylene (available from Rexene
Products Co., Dallas, TX) 60
Flexon 885 Paraffinic Oil (available from Exxon
Chemical Co., Houston, TX ) 30
Silica FK500LS (available from Degussa Corp.,
Ridgefield Park, NJ) 3
Antioxidant 0.2
Lubricant 0.4
to
Example 2.
Parts by Weiqht
Recycle ground EPDM, 120 mesh 100
3T1A polypropylene (available from Rexene
15 Products Co., Dallas, TX) 234
Flexon 885 Paraffinic Oil (available from Exxon
Chemical Co., Houston, TX ) 50
Silica FK500LS (available from Degussa Corp.,
Ridgefieid Park, NJ) 3
2 o Antioxidant
0.2
Lubricant
0.4
Example 3.
Parts by Weioht
2 s Recycle ground EPDM, 120 mesh 100
9
CA 02330897 2001-O1-12
o
W110 polypropylene (available from Rexene
Products Co., Dallas, TX) 67
Flexon 885 Paraffinic Oil (available from Exxon
Chemical Co., Houston, TX ) 25
Silica FK500LS (available from Degussa Corp.,
Ridgefield Park, NJ)
Antioxidant 0.2
Lubricant 0.4
1o The ingredient of the examples were mixed in a low shear mixer, then
extruded and pelletized. Plaques of 6'x6' were injection molded from the
compositions of Examples 1-3 and from several commercially available
materials.
The plaques were tested to compare the properties of the compositions of the
invention to the properties of the commercially available materials. (The
SANTOPRENE materials are available from Advanced Elastomer Systems, Akron,
OH; the MULTIBASE material is available from Multibase Co., Inc. Copley, OH.)
The results of the testing are set out in Table 1.
to
CA 02330897 2001-O1-12
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