CA1104741A - Composition of a styrene resin, and a pre-compounded polymer system comprising a polyolefin and a selectively hydrogenated block copolymer of a vinyl aromatic compound and an olefinic elastomer - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

There are provided compositions comprising (a) a poly-styrene resin; and (b) a precompounded polymer system com-prising an olefinic resin and a selectively hydrogenated elastomeric block copolymer resin alone, or in further combination with a styrene resin; and, (c) optionally, a hydrogenated elastomeric block copolymer resin. The use of (a) and (b) together provided high impact strength without the delamination problems experience with the known combinations of (a) and (c).

Description

~ 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.

~ 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 ~ 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 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~

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.

O r ~r I u o o u~

c~ o o q l ~ O 0 5 O ~-1 ~1 ul . n u X ~ ~1 rl ,1 0~
O In Ul U~ ~
~ ~JI In ~ o ~ o --11 [` N ~ -1 ~1 ~ ~I N ~r . n~ ,,.
~` ~ O
O O
~; ~1 I ~ o ~ O
Ll ~') rl O COO
O ~ I O Ul O a~
O
~ ~ O
~1 a) Ln u~ ct) O 1`
O C O ~ N N
O
~ ~ ~`I O
11') . . 1-~ 0 '~

~ ~r o Ul . , o ,1 ~ r. 0 0 ~r 3 .Y
a.~ ~ ~~ ~ ~ Q~
~1 hC: A h 1~

Q u~ O ~ 4~ rl ~1 ~ Oal~ ~ o~ o~
~1 ~ ~3a) Iq h ~ a) u1 S-l Ul ~ h ~h O ~ 1~ ~ O~ Irq ul O O 1 ~ ~ ~ r h .a) X ,1 a~ h a)al G~ E3 ~ ~ 1 Ei O ~ 0~ ~ P
Q ~ a O ~ ~ 1~ d O Ql ~ ~
E~ >1 ~ ~ Q~ O Id . _l O .-1 -O ~ ~ O ~ O IJ ~ 3 0~1 0 ~
O ~ 0 ~ Ql U~ C .4 V Pi X O ~ H rl ~~r~

O~.q o o. ~a ~r I ~ 1` ~
o t`
$ u~ ~
co O r~
r') ¦ Noo ~
o o rt ` '~J O
N ~O a) r-l r-l N ~3 o o oi~ ~ u~
~~ ~ o r~
r~
o o u~
o o . u~
o l ~ ri ~ o o O tQ
o o ~ ~s o ~In ,~ ,~
t~) ¦ N ,~

O U~
It~ N ,C U~
` t~ O
~¦ N ,f~
o O U~
111 (~I rC tl~
01 0~
N ,~
g U~
r~ ~ ~ O
r~
~ U
U U:) .C
~ ~ ~
C) ~ Q~
r~ O D

' e X ~ ~ ~ ~ u ~J

~ 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.

Claims (10)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A high impact strength thermoplastic composition consisting essentially of 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 polyethylene or a poly-.alpha.-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 block copolymer of a vinyl aromatic compound (A)n and (A)1n and an olefin block (B), of the A-B-A1; A-(B-A-B)n-A; A(BA)nB;
(A)4B; B(A)4; or B[(AB)nB]4 type, wherein n is an integer of from 1 to 10, and optionally, (c) a selectively hydrogenated elastomeric block copolymer of one of the types set forth in (b).

2. A composition as defined in claim 1 wherein component (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).

3. A composition as defined in claim 1 wherein component (b) comprises from 80 to 20 parts by weight and component (c) from 20 to 80 parts by weight of the total weight of (b) and (c).
4. A composition as defined in claim 1 wherein component (a) is a styrene resin having at least 25% of the polymer units derived from a vinyl aromatic compound of the formula:

Claim 4 Cont'd wherein R is hydrogen, alkyl of from 1 to 4 carbon atoms or halogen; Z is hydrogen, alkyl of from 1 to 4 carbon atoms or vinyl; and p is an integer of from 1 to 5.

5. A composition as defined in Claim 4 wherein styrene resin is a styrene homopolymer resin.

6. A composition as defined in Claim 1 wherein, in components (b) and (c), (A) and (A)1 are selected from styrene, .alpha.-methyl styrene, vinyl toluene, vinyl xylene and vinyl naphthalene and (B) is selected from butadiene, isoprene, 1,3-pentadiene or 2,3-dimethylbutadiene.

7. A composition as defined in Claim 6 wherein, in components (b) and (c), (A) is a styrene block, (B), is an olefin block, and (A)1 is a styrene block.

8. A composition as defined in Claim 7 wherein, in components (b) and (c), terminal blocks (A) and (A)1 have molecular weights of 2,000 to 100,000, respectively, and center block (B) has a molecular weight of from 25,000 to 1,000,000.

9. A composition as defined in Claim 1 wherein, in component (b), said olefinic resin is polyethylene, poly-propylene, or an ethylene-propylene copolymer.

10. A composition as defined in Claim 1 wherein, in component (b), the styrene resin comprises a styrene homopolymer.