Note: Descriptions are shown in the official language in which they were submitted.
~ 8CH-2704
This invention relates to novel resin compositions
and more particularly, to polymer compositions comprising a
styrene resin, a precompounded blend of an olefinic resin and
a hydrogenated elastomeric block copolymer of a vinyl aromatic
compound and an olefinic elastomer, alone, or in further
,~. o~
combination with a styrene resin and, op~ically, a hydro-
genated elastomeric block copolymer of a vinyl aromatic
compound and an olefinic elastomer.
The brittleness and lack of impact strength of parts
molded from styrene resins is a matter of common knowledge
and experience. These problems have been overcome in the
art by blending rubber into the styrene resins, or by
forming resins in which polystyrene is grafted onto a
rubbery backbone of, e.g., styrene butadiene random compolymer.
Unfortunately, such high impact polystyrene weathers poorly
and is unsuitable for out~of-doors applications.
Many manufactures of high impact polystyrenes have
been trying to make them from saturated, e.g., selectively
hydrogenated rubbers. In such rubbers, the olefinic
unsaturation has been reduced, but the aromatic unsaturation
is largely unaffected. These approaches have involved, e.g.,
an interpolymerization route which is the technique normally
used to produce grafted polystyrenebutadiene backbone resins.
To do this, polybutadiene is dissolved in styrene monomer
and after about a 7-8% styrene conversion, a phase inversion
takes place in which the continuous phase polybutadiene
is styrene monomer becomes the dispersed phase under strong
stirring. A type of micelle in a polystyrene + styrene
monomer phase is formed, the "micelles" looking like
droplets. In this way, emulsified rubber particles grafted
and partly cross-linked are formed, of which about 2/3
is polystyrene occlusion and about 1/3 ~ is rubber. ;-
~ ~ 8CH-2704
This is to say that with a rubber loading of, typically,
10~ by weight, the volume percent of rubber, in the form
of particles is 30-40~. This particular phenomenon causes
a great improvement in impact resistance, e.g. 0.4 ft. lbs./
inch of notch in the Izod test rises to 2.5 ft. lbs./in.
notch. Unfortunately, however, there is a high reduction
in stiffness E from 31,000 to 18,000 and in tensile yield
strength, of from 530 to 195 kgf./cm2. Also flowability
is strongly impaired by the great volume fraction of "non-
flowing" rubber particles. In any event, the backbone is
unsaturated and this causes poor resistance to attack by
oxygen, ozone, heat and ultraviolet light.
A number of workers in this art have also tried to
use the so-called EPDM rubbers, e.g., ethylene~propylene
diene terpolymers to toughen styrene resins by the technique
mentioned above. A difficulty with this is to find useful
main chain and grafting reaction conditions. The saturated
rubber doesn't contain enough reaction sites for proper
grafting and cross-linking. This causes the particles to
become large (10-20~) and weak~ During extrusion and
injection molding these particles can easily be disrupted
by the shear forces involved during melt flow, resulting
in a rather dull surface appearance.
Lunk, U.S. patent No. 3,810,957 dated May 14, 1974,
has disclosed blends of selectively hydrogenated block
copolymers and polystyrene. This blending, e.g., by
milling, extruding or Banbury mixing of a polystyrene resin
with a selectively hydrogenated poly(monovinyl aromatic
hydrocarbon)-poly(conjugated diene)-poly(monovinyl
aromatic hydrocarbon) block copolymer produces high
impact thermoplastic molding compositions which have
greatly improved weathering resistance.
-- 2 --
~ 741 8CH-2704
e .~ ~ Unfortunately, such compositions do
produce molded articles which give delamination problems
due to the large amounts of saturated rubber needed to
obtain reasonable impact levels.
In Canadian application, Serial No. 291,749 dated
November 25, 1977, a major improvement is disclosed in
providing high impact strength combinations of polyphenylene
ether resins and styrene resins. The improvement comprises
adding to the combination a precompounded easily dispersible
polymer system, e.g., a polyolefin combined with a rubbery
block copolymer, and an additional amount of a rubbery
block copolymer.
It has now been discovered that styrene resins per se
can be remarkably improved in terms of impact strength
and processing improvement by intimately admixing them
with a precompounded easily dispersible polymer system and,
if desired, an additional amount of a hydrogenated block
copolymer.
The resulting compositions show no tendency to delamin-
ate. They also have a high heat distortion temperature,
high gloss; high strength in tension, high stiffness; high
creep resistance; high ultraviolet resistance; high aging
resistance; high heat resistance during processing; and
good flowability.
It is believed that the surprising efficiency of the
system is attributable to the special features of system
(b). System (b~ consists of a precompounded mixture of
a selectively hydrogenated vinyl aromatic-olefin-vinyl
aromatic block copolymer and an olefinic resin, e.g., .
polyethylene, polypropylen, ethylene/propylene copolymers,
and the like, at a ratio of 20/80 to 80/20, by weight.
In any case, dispersibility in component (b) can be
:~G~7~1 8CH-2704
furt:her improved by adding polystyrene, and especially
homopolymers of styrene, as a dispersing aid in an amount
of up to 100 parts by weight of resinous components, and
up to about 10~ by weight of other dispersing aids, such as
hydrocarbon resins can also be included.
The new compositions may also be reinforced, e.g.,
with fibrous glass, and rendered flame retardant with
flame retardant additives to extend their field of use in
molded products.
According to the present invention, there are provided
high impact strength thermoplastic compositions com-
prising an intimate blend of:
(a) a styrene resin; and
(b) a precompounded composition comprising from 80
to 20 parts by weight of an olefinic resin comprising poly-
ethylene or a poly-a -olefin resin, alone or in further
combination with a minor, effective amount of a styrene
resin and correspondingly from 20 to 80 parts by weight
of a selectively hydrogenated linear, sequential or radial
teleblock copolymer of a vinyl aromatic compound (A)n and
(A) n and an olefinic elastomer (s)~ of the A-B-A
A-(s-A-B)nA; (A(BA)n (A)4B; B(A)4; or B[(AB)n B]4 type,
wherein n is an integer of 1 to 10; and, optionally,
(c) a selectively hydrogenated elastomeric block
copolymer of one of the types set forth in (b).
Preferred compositions will be those in which com-
ponent (a) comprises from 99 to 60 parts by weight and
component (b) comprises from 1 to 40 parts by weight and
component)c) comprises from 0 to 20 parts by weight of
the total weight of components (a), (b) and (c). In
particularly preferred compositions, component (b) com-
prises from 80 to 20 parts by weight and component (c) from
74~ 8CH-2704
20 to 80 parts by weight of the total weight of (b) and (c).
With respect to component (a), as is disclosed in the
above-mentioned Lunk patent, the styrene resins most suit-
able are polymer of vinyl aromatic hydrocarbons prepared by
polymerizing at ieast one alkenylaromatic hydrocarbon of
the benzene series and include the polymers of styrene and
ring-substituted styrene wherein the aromatic nucleus is
substituted with one or more alkyl groups preferably con-
taining from 1 to 4 carbon atoms such as methyl or ethyl
or with a halogen group such as a chloro group. Examples
of such monomers are styrene, vinyl toluene, vinyl xylene,
vinyl ethyl benzene, and divinyl benzene. Suitable
monomers also include chain-substituted styrenes such as
alphamethyl styrene. Preferably, these polymers have an
intrinsic viscosity of from 0.5 to 1.5, especially in the
range of 0.6 to 1.0 dl./g., as determined using a 0.25 g.
/100 ml. solution in toluene at 30C.
The styrene resins most preferred are those having at
least 25% by weight polymer units derived from vinyl aromatic
monomer having the formula:
RC = CH2
(z)p
wherein R is hydrogen, alkyl of 1 to 4 carbon atoms or
halogen; Z is a member selected from the class consisting
of vinyl; hydrogen, or alkyl of from 1 to 4 carbon atoms;
and p is from 1 to 5. The preferred styrene resins for
purposes of this invention are polystyrene homopolymers.
With respect to components(b) and (c) the hydrogenated
block copolymers are may be means known in the art and they
-- 5 --
~ 8C~-270
are commercially available.
Prior to hydrogenation, the end blocks of these copoly-
mers comprise homopolymers or copolymers preferably pre~
pared from alkenyl aromatic hydrocarbons and particularly
vinyl aromatic hydrocarbons wherein the aromatic moiety
may be either monocyclic or polycyclic. Typical monomers
include styrene, alpha methyl styrene, vinyl xylene, ethyl
vinyl xylene, vinyl naphthalene, and the like, or mixtures
thereof. The end blocks (A) and (A)l, may be the same or
different. They are preferably selected from styrene, a-
methyl styrene, vinyl toluene, vinyl xylene, vinyl naphth-
alene, especially styrene, The center block (B) may be
derived from, for example, butadiene, isoprene, 1,3-
pentadiene, 2,3-dimethyl butadiene, and the like, and it may
have a linear, sequential or teleradial structure.
The selectively hydrogenated linear block copolymers
are described in Haefele et al, U.S. 3,333,024 dated
July 25, 1967, and also in the above-mentioned Luke patent.
The ratio of the copolymers and the average molecular
weights can vary broadly although the molecular weight of
center block should be greater than that of the combined
terminal blocks. It is preferred to form terminal blocks
A having average molecular weights of 2,000 to 100,000 and
center block B, e.g., a hydrogenated polybutadiene block
with an average molecular weight of 25,000 to 1,000,000.
Still more preferably, the terminal blocks have average
molecular weights of 8,000 to 60,000 while the hydrogenated
polybutadiene polymer blocks has an average molecular
weight between 50,0Q0 and 300,000. The terminal blocks will
preferably comprise 2 to 60% by weight, or more, preferably,
15 to 40% by weight, of the total block polymer. The
preferred copolymers will be those formed from a copolymer
~4~4~ 8Cl~-2704
having a hydrogenated/saturated polybutadiene center block
where 5 to 55%, or more, preferably, 30 to 50% of the
butadient carbon atoms, are vinyl side chains.
The hydrogenated copolymers will have the average un-
saturation reduced to less than 20% of the original value.
It is preferred to have the unsaturation of the center block
B reduce to 10%, or less, preferably, 5% of its original
value.
The block copolymers are formed by techniques well known
to those skilled in the art. Hydrogenation may be con-
ducted utilizing a variety of hydrogenation catalysts such
as nickel e~ kieselguhr, Raney nickel, copper chromite,
molybdenum sulfide and finely divided platinum or other
noble metals on a low surface area carrier.
Hydrogenation may be conducted at any desired tempera-
ture or pressure, from atmospheric to 300 psig, the usual
range being between 100 and 1,000 psig at temperatures
from 75F. to 600F~ for times between 0.1 and 24 hours,
preferably, from 0.2 to 8 hours.
Hydrogenated block copolymers such as Kraton G - 6500,
Kraton G - 6521, Karton G - 1650 and Kraton G - 1652 from
Shell Chemical Company, Polymers Division, have been found
useable according to the present invention. Kraton G -
1650 is preferred. Also useable are the so-called hydrogenated
Solprenes of Phillips, especially the product designated
Solprene - 512.
The radial teleblock copolymers of which the Solprenes
are typical examples can be characterized as having at least
three polymer branches with each branch of the radial block
polymer comprising terminal non-elastomeric segments, e.g.
(A) and ~Al) as defined hereinabove. The branches of the
radial block polymer contain a terminal non-elastomeric
~ 8CH-2704
segment attached to an elastomeric polymer segment, e.g.
(B) as defined above. These are described in Marrs, U.S.
patent No. 3,753,936 dated August 21, 1973 and in Zelinski
U.S. patent No. 3,281,383 dated October 25, 1966, and they
are selectively hydrogenated by procedures known per se.
In any event, the term "selective hydrogenation" is used
herein to contemplate polymers in which the elastomeric
blocks (B) have been hydrogenated, but the non-elastomeric
blocks (A) and (A ) have been left unhydrogenated, i.e.,
aromatic.
As is mentioned above, other additives may be present
in the compositions, such as pigments, e.g., titanium
dioxide.
With respect to component (b), a variety of polyole-
fins can be used with the block copolymer to form the premix.
In general, it is preferred to use polyethylene or a poly
~-olefin or a copolymer of~ -olefin or a copolymer of ~-
olefins, the ~-olefin having from 3 to 8 carbon atoms.
These can be made by known precedures and are readily
available from a number of sources. Especially preferred
are polyethylene or polypropylene and their copolymers and
block copolymers, e.g., ethylene-propylene copolymer, etc.
The amount of elastomeric block copolymer, and poly-
olefins and polystyrene dispersing agent, if used, combined,
added to the styrene resin will vary from 1 to 40% by weight
of the composition.
Of course, other additives may be present in the
compositions, such as plasticizers, pigments, flame re-
tardants, and the like, in amounts varying between about 1
and 100 parts by weight of the total resinous components (a),
(b) and (c) in the composition. The above-stated ranges for
amounts of the polystyrene resin (a), the precompounded blend
~ 4~ 8CH-2704
of polyolefin and the hydrogenated elastomeric block copolymer
resin (b) and the hydrogenated elastomeric block copolymer
resin (c), if present, is based solely upon such resinous
components in the polymer blend and excludes other additives.
Among the features of this invention are reinforced
compositions containing reinforcing amounts of reinforcements,
such as powders, whiskers, fibers or platelets of metals,
e.g., aluminum, bronze, iron or nickel, and non-metals, e.g.,
carbon filaments, acicular CaSiO3, asbestos, Tio2, titanate
whiskers, glass flakes, and the like. Such reinforcements
will be present in an amount of, e.g. 2 to 90% by weight,
preferably 10 to 60% by weight. Especially preferred
as reinforcement is fibrous glass.
The method of forming the polymer composition is not
critical, so long as component (b) is precompounded. Any
prior art blending technique is generally suitable. The
preferred method comprises blending the polymers and any
additives, such as reinforcements in powder, granular and
filamentous form -- as the case may be -- extruding the
blend and chopping into pellets suitable for molding to shape
by means conventionally used to mold normally solid thermo-
plastic compositions.
The following examples are set forth as further de-
scription of the invention, but are not to be construde as
limiting the invention thereto.
The formulations are produced by a general procedure
comprising mechanically blending then co-extruding in a twin
screw Werner Pfleiderer (WP) extruder at 220-240F. and
molding into test pieces in a reciprocating screw injection
molding machine at about 220 C. (cylinder) and 60C (mold).
To make component (b~, the block copolymer and the olefinic
resin are masterbatched by precompounding at 400F. in a twin
~ 41 8CH-2704
screw WP or in an adequate rubber processing machine first.
The ]physical tests are carried out by the following procesures:
Izod impact strength on l/8" notched speimens; falling dart
impact tests on 1/8" disc specimens; tensile strength and
stifEness on ASTM type l bars, drawing rate 0.5 cm./min.;
E modulus with an extentiometer on ASTM type l bars, drawing
rate of 0.5 cm./min., flow length at 240C. and 0.3 cm.
thickness at constant injection rate and pressure; heat
distortion temperature at 266 psi; and apparent melt viscosity
at 1500 sec. 1 and 540 F.
., . . ~
4~ 8 CH - 2 7 0 4
EXAMPLES 1-4
The following formulations are prepared, molded and tested:
Table 1. - Compositions of Styrene Resin and Premix of
Hydrogenated Block Copolymer and Polyolefin
-
Example lA* 1 2 3 4
Composition (parts by weight)
Styrene homopolymera 85 90 80 70 60
/ Hydrogenated styrene-
butadienebstyrene block
j copolymer -- 2.5 5.0 7.5 10
d~ Ethylene ~ropylene
copolymer -- 2.5 5.0 7.5 10
~Styrene homopolymer -- 5.0 10.0 15 20
Hydrogenated styrene-
butadienebstyrene block
copolymer 15 -- -- -- --
Properties ;
Heat Distortion temp.,
oC. 92 93 92 91 90
Melt viscosity, poise 1,910 1,700 1,725 1,920 1,850
Izod impact, ft. lbs./
in. notch 2.5 0.95 1.45 1.55 2.4
Falling dart impact,
kg. -m. 2.5 0.5 0.8 1.5 2.75
Tensile yield strength, 400 495 430 368 320
kg.-m.
E modulus kgf./cm25,10028,800 26,200 24,000 20,600
Surface appearancehigh high high high high
gloss gloss gloss gloss gloss
* Control
a Hoechst N 7000 high heat crystal
b Shell Chemical Kraton G 1650
~ "
c BA-616 Huls Chemical Co.
d Premix
4~
8CH-2704
The compositions prepared with precompounded resins in
accordance with this invention are seen to retain their
properties over a wide range of rubber contents and to
provide excellent impact resistance even at low block copolymer
contents.
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~ 7~1 8CH-2704
The foregoing data demonstrate that high impact poly-
styrene can be obtained according to this invention with
excellent retention of all other important properties.
Obviously, many variations will suggest themselves to
those skilled in this art in light of the above, detailed
description. All such variations are within the full
intended scope of the appended claims.
The instant application discloses, but does not
claim, subject matter disclosed and claimed in the related ~`
commonly assigned Canadian Application Serial No. 291,749, filed
November 25, 1977.
- 15 -
