Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITIONS OF RUBBER AND POLYETHYLENE
The present invention relates to melt~processable
compositions of ru~ber and polyethylene and especially to
such compositions in which the rubber is ground scrap rubber
obtained from, for instance, used automobile tires.
Some motor vehicles, especially trucks and other
large vehicles, have rubber mudflaps near the rear of the
wheels of the vehicle. These mudflaps are intended to
deflect downwards water, mud, sand, stones and the like that
are thrown up by the wheels of the vehicle as the vehicle
travels along a road, thereby reducing the safety hazards of
flying objects and the annoyance to motorists of spray of
water, mud and the like.
Mudflaps are normally made from rubber compositions
using compression vulcanization processesO Whil~ such
processes have produced commercially-acceptable products, it
is believed that other fabrication processes ofer the
potential of greater versatility, faster cycle times, better
economics and/or improved properties.
Mudflaps and similar products may be manufactured
from thermoplastic polymers such as polyethylene, poly- -
propylene and polyvinyl chloride by melt-forming processes
e.g. injection moulding and sheet extrusion. However, such
products tend to lack the appearance and flexibility of
rubber that is often expected by consumers.
Mudflaps and similar products may al~o be manufac-
tured from blends of powdered rubber and polyethylene. The
resultant products have the appearance and feel of rubber but
have a lower resistance to flexural cracking than products
made from polyethylene or rubber only~
It has now been found that rubber-like articles of
improved physical properties may be manufactured from
compositions of rubber and polyethylene.
Accordingly, the present invention provides a melt
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processable composition comprising:
(a) 30 to 90% by weight of a linear low density
polyethylene, said polyethylene having a density of less than
0.915 g/cm3, and;
(b) 10 to 70% by weight of ground vulcanized
rubber of a particle size of less than about 1.5 mm.
The present invention also provides a process for
forming an article having the appearance of rubber, said
process comprising (i) feeding to melt processing apparatus a
composition comprising:
(a) 30 to 90~ by weight of a linear low density
polyethylene, said polyethylene having a density of less than
0.915 g/cm3, and;
(b) 10 to 70% by weight of ground vu~lcanized
rubber of a particle size of less than about 1~.5 mm,
(ii) admixing said composition wi~hin said
apparatus under melt conditions; and
(iii) forming the resultant admixed molten
composition into an article.
In preferred embodiments of the composition and
process of the present invention, the rubber is ground scrap
rubber, especially ground scrap rubber obtained from
automobile tires.
In a further embodiment, the rubber particles have
been coated with 2000 ~o 10 000 ppm, based on the weight of
rubber, of an organic cross linking agent, especi~lly an
organic peroxide cross-linking agentO
The composition of the present invention is
comprised of polyethylene and rubber. The polyethylene is a
linear low density polyethylene having a density of less
than 0.915 g/cm3 and especially in the range of about 0.880
g~cm3 to 0.915 g/cm3~ Such polyethylenes may be copolymers
of ethylene with an alpha-olefin homologue of ethylene e.g. a
C4 - Clo alpha-olefin, examples of which are butene 1,
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hexene-l and octene-l. Alternatively, the polyethylene may
be a copolymer of ethylene with more than one alpha-olefin
homologue of ethylene e.g. polymers of ethylene with more
than one C3 - Clo alpha-olefin e.g. more than one of
propylene, butene-l, hexene-l and octene~l. The molecular
weight of the polyethylene may be varied over a wide range,
depending in particular on the intended end-use of articles
fabricated from the composition of polyethylene and rubber,
and the proportion of polyethylene in the compositionO An
example of a polyethylene of the type described above is DFDA _-
1137 polyethylene which has density of 0.906 g/cm and a meltindex of 0.8 dg/min. and i5 available from Vnion Carbide
Corporation of Danbury, Conn., U.S.A. ~-
The rubber of the composition is a groùnd
vulcanized rubber. The rubber should be ground -to a particle
size that will facilitate adequate mixing of the polyethylene
and rubber during processing of the composition. Thus the
particle sizes that may be used will depend for-instance on
the mixing capabilities of the melt processing apparatus,
e.g. injection moulding apparatus or extrusion apparatus.
The intended end-use of art}cles formed from the composition
may also be a factor because the homogeneity of the
composition as formed into an article may affect the
properties of that article. The particle size of the rubber
should be less than 1.5 mm, especially less than 1.0 mm and
in particular less than 0.5 mm. The rubber should be
classified so that all, or at least essentially all, of the
rubber has a particle size of less than 1.5 mm; larger
particles tend to have detrimental effects on properties of
the resultant products.
In a preferred embodiment, the ground vulcanized
rubber is obtained from automobile tires or the like,
especially scrap automobile tires. Such tires may be ground
to a suitable particle size for the compositions of the
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present inventioll. Techniques for grinding rubber are known
in the art.
In embodiments of the present invention, the
compositions may also contain an organic cross-linking agent,
especially an organic peroxide cross-linking agent coated
onto the surface of the rubber particles. Any such cross-
linking agent must be coated onto the particles of the ground
rubber prior to the admixing of rubber and polyethylene;
addition of peroxide into the compositions in the form of a
concentrate or directly compounding peroxide into the
polyethylene does not result in significant improvements in
flex life of the product and/or results in processing
difficulties e.g. due to cross-linking of the polymer. It is
preferred that the coating of the particles be carried out in
a uniform manner, to improve the uniformity of ~ke resultant
product. For instance~ the coating may be applied using a
solution of cross~linking agent and inert solvent by admixing
the solution and rubber particles and subsequently removing
the solvent. In a preferred method~ the coating may be
applied using a Henschel* mixer.
The amount of the cross-linking agent may be about
2000 to 10 000 ppm, especially 2500 to 6000 ppm, based on the
amount of rubber. The preferred cross-linking agents are
organic peroxide cross-linking agents, especially a bis(tertO
alkyl peroxyalkyl~benzene, dicumyl peroxide and/or an
acetylenic diperoxy compound. For instance, the cross-link-
ing agent may be 2,5-dimethyl-2,5~di(t-butylperoxy) hexyne-3
which is available commercially under the trade mark Lupersol 6
130 from Pennwalt Corp, of Buffalo, New York, U.S.A. Alter-
natively, the cross-linking agent may be 2,5-dimethyl-2,5 bis
(tertbutyl peroxyisopropyl) benzene which is available
commercially under the trade mark Vulcup from Hercules
Incorporated. A co-curing agent may also be incorporated
into the composition in association with the cross-linking
agent. Examples of co-curing agents include triallyl
* denotes trade mark
.~.a,~ 33~3~
cyanurate/ triallyl isocyanurate and 1,2-po:Lybutadiene.
The compositions of the present invention may also
contain stabili~ers e.g. antioxidants and/or ultra violet
stabili~ers, pigments, fillers and the like, as is known for
rubber compositions.
The compositions contain 30 to 90% by weight of the
linear low density polyethylene and 10 to 70% by weight of
the rubber. In preferred embodiments the compositions
contain 40 to 60% by weight of polyethylene and 40 to 60% by
weight of rubber. However, it is to be understood that the
relative amounts of polyethylene and rubber, and the type of
polyethylene, will depend in particular on the properties
required in the articles fabricated from the compositions.
The compositions of the present invention are
particularly intended for use in an injection mo~lding or a
sheet extrusion process, especially for the manufacture of
articles that have the appearance of being fabricated from
rubber. Such articles include mudflaps and other protective
devices for use on motor vehicles, especially trucks and
other large vehicles.
In an injection moulding process, the compositions
are admixed under melt conditions. Although the compositions
could be so admixed prior to being fed to the injection
moulding apparatus, it is preferred that the admixing occur
in the injection moulding apparatus immediately prior to
injection of the admixed composition into the mould of the
apparatus. The amount of admixing should be sufficient to
provide a degree of homogenei~y in tha moulded article
subsequently obtained that is commensurate with the intended
end-use of the article; homogeneity is one factor that is
pertinent to the properties of the moulded article, Thus,
apart from the mixing characteristics of the injection
moulding apparatus, matters such as the particle si~e of the
components of the co~position, the relative particle sizes
between different components and the uniformity of the
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particle si~es e.g. particle size distribution, of the
components may be important with respect to the propertles oP
the articles that are obtained. Such factors will be
understood by those skilled in the art.
The compositions of the present invention are also
intended for use in melt processes other than injection
moulding. For instance, the compositions may be fed to
extrusion apparatus, especially extrusion apparatus for the
manufacture of sheet products. Mixing characteristics of the
extrusion apparatus, particle sizes of the components of the
compositions, relative particle sizes between different
components and the uniformity of the particle sizes, e.g.
particle size distribution, may be important with respect to
the properties of the articles that are obtained~
Articles fabricated from the compositi~ons of the
present invention may be used in a variety of end uses. In
particular, the articles may be in the form of mudflaps for
vehicles~
The present invention is illustrated by the
following examples.
Example I
A number of compositions of the present invention
and comparative compositions were prepared. The polyethylene
was in the form of pellets. The ru~ber was obtained from
scrap automobile tires and had been ground to a particle size
of 1~0 mm. Organic peroxide, if present, had heen coated
onto the rubber particles, prior to admixing of rubber and
polyethylene, in a Henschel mixer.
To test the properties of such compositions;
so-called "tensile bars" were prepared. These tensile bars
had a length of 130 mm, a width of 13 mm and a thickness of 3
mm, and were moulded on an Engel* injection moulding machine
from a dry blend of polyethylene pellets and rubber powder.
In preparing the sample tensile bars, the melt temperature
used was 220C, which was selected so as to acti~ate any
* denotes trade mark
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organic peroxide present in the composition being moulded
while maintaining decomposition of the rubber at an
acceptable level. The screw speed and back pre~sure on the
injection moulding apparatus were both set at the maximum ~or
the apparatus to maximize the decyree of polymer/rubber
homogeneity. Mould closure time was kept to a minimum to
reduce any tendency for the rubber to decompose~
The injection moulded tensile bars were subjected
to the following tests:
(a) Flex test ..... The bars were flexed to 90
degrees on each side of the axis of the bars, at ambient
temperature and at a rate of 42 cycles/minute. The bars were
considered to have failed when a crack of more than 3 mm in
length had appeared at the point of flexure of t~he bars.
(b) Notched Flex test .... The proced~.re described
above for the flex test was repeated except that a slit
having a depth of 3 mm was cut into one side of the bars at
the point of fle~ureO The bars were considered.to have
failed when this cut had grown by 3 mm in length.
(c) Tensile Impact test .~. Type L tensile impact
bars were cut from the injection moulded bars, according to
the procedure of ASTM D-1822-68. The tensile impact test was
carried out at -40C.
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~ N:l.* 1 2 3 ~ 5 6 7 8 9
P~y~e* 100 50 50 100 SO 50 0 50 50
fp~rts ~ WE~iÇht)
Rut~er 0 50 50 0 50 50 100 50 50
(E~rtS ~ wei~ht)
C~nic Pe~a~ O 0 3000 0 0 3~00 0 0 3000
~m)
Elex~;t>21 ~00>21 OCO>21 000 3001000 3175>21 ~0050~0 I~DO
N~td~d Flex ~st>31 00018 000>31 000900 300 900; >21 ~
;~ 0 ~s; l~ 4 14 ao ~; 21 - -
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* Note: (i) Runs 1, 4 to 7 and 9 are comparative runs
~ii) In Runs 1 to 3, 8 and 9, the polyethylene was
an ethylene/butene-l/oetena-l terpolymer
having a density of 0.9102 g/cm3 and a melt
index of 1.6 dg/min.
In Runs 4 ~o 6, the polyethylene was an
ethylene/butene-l copolymer having a density
of 0.924 g/cm3 and a melt index of 5.1
dg/min.
tiii) The organic peroxide was Lupersol 130.
(iv) The samples of Run 7 were prepared by
compression moulding, not by injection
moulding.
(v) In Run 8, the polyethylene and ru~ber were
poorly mixed.
~vi) In Run 9~ the particle size of the rubber was
2.0 mm.
Runs 2 and 5 show the improvement in properties
that is obtained when a lower density polyethylene is used.
Runs 2 and 3 and Runs 5 and 6 show the effects of the
addition of organic peroxide on the flex life of articles
moulded from the compositions. Runs 1, 3 and 7 show that the
flex life of articles moulded from polyethylene and
peroxide-treated rubber may be as good as articles injection
moulded from polyethylene or compression moulded from
rubber.
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