CA1133176A

CA1133176A - High impact melt-flowable dual continuum melt mixed polymer blends of polypropylene polyethylene, and ethylene-propylene rubber

Info

Publication number: CA1133176A
Application number: CA342,914A
Authority: CA
Inventors: Terrence Huff
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1979-01-31
Filing date: 1980-01-02
Publication date: 1982-10-05
Also published as: AU5505880A; AU528326B2; JPS55104334A; EP0015066A1; EP0015066B1; US4221882A; DE3064554D1

Abstract

ABSTRACT OF THE DISCLOSURE
Malt mixed,malt-flowable blends of polypropylene, at least about 30% polyethylene and from about 4 to about 11% ethylene-propylene copolymer rubber, and method for making same, are disclosed. Such blends posses higher low temperature Izod and Gardner impact strength than conventional impact polypropylene blends, while having a comparable or higher flexural modulus.

Description

~33~7~i 1 This inventlon relates to a melt-flowable high-

2 impact melt-mixed blend of polypropylene and polyethylene,

3 preferably high density polyethylene, believed to have an

4 interpenetrating network structure which is stabilized against collapse during molding by inclusion of minor amounts 6 of an ethylene-propylene copolymer elastomer.
7 Ternary blends of low density polyethylene (LDPE), 8 polypropylene (PP) and monoolefin polymer rubbers having 9 improved impact strengths and optical clarity have been dis-closed previously in U.S. Patent No. 4,088,714 and Patent 11 No. 4,087,485, respectively. Patent No. 4,088,714 discloses 12 that the impact properties of poIypropylene (PP) and cross-13 linkable Iow density polyethylene (LDPE) blends could be 14 significantIy improved by addition of an ethylene-propylene copolymer elastomer (EPR) to the blend, in an amount such 16 that the ratio of elastomer to the cross-linkable low 17 density polyethylene (LDPE~ was approximately one to one, 18 and curing the elastomer with the cross~linkable LDPE to 19 fDrm a discontinuous, tightly cross-linked phase of elastomer and LDPE which is in~imately dispersed in a continuous phase 21 of PP- Although a tightly cross-linked phase of EPR and 22 LDPE-is not itself melt flowable, it was found that by being 23 intimately dispersed in a continuous phase of PP which was 24 mèlt flowable, the total blend assumed a beneficial melt flowable characteristic. In U.S. Patent No. 4,087,485 it 26 was disclosed that an impact polypropylene blend having sur-27 prisingly good optical properties may be formulated by par-28 tially curing an EPR with a cross-linkable LDPE in the 29 presence of polypropylene, wherein the polypropyIene component comprises about 70 to 95 percent of the total mixture.

' ~3~6 -- 2 ~

1 Although such blends of PP and LDPE had an excel-2 lent balance of overall mechanical properties as compared to 3 previous PP-LDPE blends, this improvement depended upon the 4 achievement of crosslinking of the EPR with the LDPE. Addi-S tionally, the employment of a LDPE does not permit the 6 achievement of as high a tensile strength, flexural modulus 7 or impact strength in the final blend as could be achieved 8 if a high density polyethylene (HDPE) could be used.
9 Certain binary blends of HDPE and PP have been previously formulated which have a good balance of low 11 temperature impact strength (Izod) and flexural modulus.
12 Such blends, which exhibit these good mechanical properties 13 when the relative concentrations of PP to HDPE is about 1:1 14 to 2:1, have proved unsatisfactory for molding large fin-ished parts wherein t~e molding process employs high 16 temperatures and pressure, e.g. in injection molding. Parts 17 molded ~rom such binary blends of PP/HDPE have failed due to 18 delamination of the two phases. Additionally, although 19 binary blends of PP and ~DPE have good Izod impact and ~0 flexural modulus properties, it: has been found that their 21 Gardner impact strengths are exceptionally poor.
22 Studies of the morphology of melt mixed binary 23 blends of PP and HDPE, wherein the relative ratio of PP/HDPE
24 is about 1:1 to about 2:1, indicate that upon melt mixing an interconnected three dimensional continuum network of ~DPE
26 interlocked with an interconnected three dimensional con-27 tinuum network of PP, a dual continuum structure, may be 28 formed. This interpenetrating interlocked network structure 29 is believed to account for the good Izod impact-flexural 30 properties observed in parts molded from such blends, but is 31 relatively unstable under shear in the melt state thereby 32 providing for a good melt rheology.
33 The delamination observed in finished parts which 34 have been molded ~rom such PP/HDPE binary blends is believed 35 to stem from a disruption of this dual continuum network 36 structure which occurs in the molding process. Heat and 37 pressure encountered in the molding process causes the 1 interlocking dual continuum network structure to collapse.
2 Upon collapse the blend structure is believed to assume a 3 machine oriented fibrous tape-like dispersion wherein a 4 multiplicity of tape-like structure of HDPE and PP become interlayered, one upon the other, within the molded part.
6 Molding processes convert the internal structure of melt 7 mixed blend from that of an interlocked dual continuum to 8 that of machine oriented separate layers along which, due g to the poor interfacial bonding which exist between HDPE
and PP, surface deLamination may occur in finished molded 11 parts, presumably occuring along the HDPE~PP interface.
12 Previous workers have included monoolefin polymer 13 rubbers, e.g. ethylene-propylene copolymer elastomers (EPR) 14 and the like in certain binary blends of HDPE and PP to improve the mechanical properties of such blends. Blends of 16 monoolefin polymer rubbers, e.g., ethylene-propylene co-17 polymer elastomers and ethylene, propylene and copolymeriz-18 able polyene terpolymer elastomers, with polyolefins, e.g., 19 high density polyethylene, polypropylene and the like, which can be processed and fabricatecl by methods used for thermo-21 plastics and have elastomeric properties without requiring 22 vulcanization are well-known. Furthermore, thermoplastic 23 elastomer blends of partially cured monoolefin copolymer 24 rubbers and certain polyolefins are known. See, for example, U.S. Patent Nos. 3,758,642 and 3,806,588. It is disclosed 26 in both of these prior art patents that the partial curing 27 of the monoolefin copolymer rubber is essential to produce 28 a blend which has the characteristics of a thermoplastic 29 resin, i.e., which can be reprocessed, while also having elastomeric characteristics.
31 Rnown thermoplastic elastomer blends of monoolefin 32 polymer rubbers and polyolefin resins suffer from a disad-33 vantage of having less than desirable overall balance of 34 mechanical and physical properties, such as low resiliency, tensile strength, stiffness, surface hardness, and/or high 36 heat distortion, permanent or tension set, etc. Furthermore, 37 many known blends, including blends prepared in accordance /

~33~

with the teachings of the above mentioned U.S. Patent Nos.
3,758,643 and 3,806,558 or U~S. Paten~ No. 3,835,201, have less than desirable melt rheologies, e.g , high viscosity at high shear rates and the high melt temperatures normally used i~ injection moldlng. Such undesirable characteristics restrict the use of such known thermoplastic elastomer blends in the manufacture of many types of flexible molded or extruded articles. This is particularly evident ln the manufacture of flexible body components for the automotive industry. For such a use, a thermoplastic elastomer is requlred which has such characteristics as relatively low viscoslty at high shear rates at melt temperatures for use in high-speed injection molding or extrusion techniques to provide flexible body com-ponents having high resiliency, tensile strength, flexural modulus, etc" along with low permanent set, heat distortion and the like.
The addition of EPR to certain PP/HDPE blends has also been proposed to overcome certain processing problems.
U.S. Patent No. 3,256,366 teaches a method whereby a vulcaniz-ing agent/ such as a peroxide may be intimately mlxed with a high or low density PE, wlthout encountering the prevulcaniza-tion problems inherent in such mixing, by premixing the PE
with between 10~ to 70% hy weight, of a rubbery copolymer such as EPR which acts as a diluent. Patent No. 3,256,366 addition-ally discloses that up to 30~ of PP may be mixed with the PE/EPR blend tQ improve the mechanical properties of a finished vulcanized article formed there~rom.
A recent effort to develop a low EPR content PP
and PE blend with improved impact resistance is disclosed in German Offenlegungsschrift 2,801,217 to Mitsui. This dis-closure describes a three step polymerization process wherein lsotactic PP is prepared in the first step. In a second step ethylene-propylene rubber i~ polymerized ln the presence of the PP of step one, forming a PP-EPR block copolymer. Finally~
PE is prepared in a third step, in the presence of the PP-EPR
of step two, to produce a finished high impact block copolymer ~33~7~

1 blend comprising about 35.2 mol. ~ PE, 4.85 mol. ~ amorphous 2 polymer (EPR) and the remainder (59.95 mol. %) PP. From this 3 disclosure it appears that block copolymerization is required 4 to produce a high impact formulation with a yood balance of other mechanical properties.
6 Patent No. 3,256,367 discloses that the impact strengths, stiffness and heat resistance properties of PP/EPR
8 blends may be improved by the addition of a HDPE component 9 in a PP:HDPE ratio of from about 2:1 to about 48:1 and preferably 3.25:1 to 23:1. The combined amount of EPR and 11 HDPE is preferably maintained at less than 35% by weight in, 12 order to produce a mixture of desirable flexural character-13 istics. The ratio of EPR/HDPE is generally one or greater.
14 At a EPR/HDPE ratios of about 1.0 or greater, the flexural modulus of such mixtures falls off rapidly as the concentra-16 tion of combined EPR and HDPE increases, especially as it 17 exceeds 33~. Yet, when an EPR/HDPE ratio of less than one 18 is employed the 0C Izod impact strength is significantly 19 worse. The rapid loss in low temperature impact strengths which occur at EPR/HDPE ratios less than one re~uires, in 21 order to maintain good low temperature impact properties, 22 the employment of the more expensive EPR in order to keep 23 the EPR/HDPE ratio grea~er than one.
24 A ternary blend of ethylene propylene and ethylene propylene rubber is disclosed in U.S. Patent 3,137,672 26 wherein 0.5 to 3 wt. ~ of EPR is incorporated into the blend 27 as an aid for dispersing finely divided solid additives~
28 The blends contain 30 to 60% polypropylene, balance poly-29 ethylene and EPR.
It is desirable in impact polypropylene formula-31 tions to achieve a high level of low temperature impact 32 strength while maintaining a high room temperature flexural 33 modulus. Such combination of properties are exhibited by 34 melt mixed blends of PP and HDPE wherein the respective ratio of such components is from about 1:1 to about 2:1. However, 36 such blends alone cannot be used to produce satisfactory 37 molded parts because of the occurrence of delamination in 1 such parts and because falling weight, low temperature im-2 pact strength is unaccep-tably poor.
3 It has now been found that a melt-flowable blend 4 of PP and HDPE presumed to possess a dual continuum struc-

5 ture may be stabilized against loss of this structure and

6 delamination in parts molded from such blend by inclusion

7 of a minor amount of an EPR copolymer in the blend prior to 3 melt fabrication. The addition of such amounts of EPR also 9 produces significantly improved low temperature Gardner im-10 pact strengths.
11 The EPR acts to stabilize the dual continuum 12 structure of such blends against collapse when subjected to 13 the heat and pressure of molding processes. It is believed 14 that the EPR incorporates itself, during melt mixing, between 15 the PP~HDP~ interfaces of the dual continuum structure and 16 functions as a molecular glue to improve interfacial bonding.
17 Incorporation of such amounts of EPR into blends 18 of PP/HDPE wherein the PP:HDPE ratio is 1:1 or greater prior 19 to melt fabrication allows such material to be used to make 20 molded parts which have impacts strengths equal to or higher 21 than parts molded from conventional impact polypropylene 22 formulations (i.e., PP-EPR-HDPE at EPR/HDPE > 1.0). Parts 23 molded from blends of this invention have equal or higher 24 heat distortion properties and have also been found to be 25 resistant to stress whitening upon impact loading as compared 26 to conventional impact grades of polypropylene.
27 In applications, such as films, packaging materials 28 and the like, requiring heat-sealable blends having good 29 clarity the HDPE component may be replaced with a LDPE.
30 Blends of LDPE and PP also form a dual continuum structure 31 upon melt mixing which may be stabilized by inclusion of 32 minor but effective amounts of EPR. As compared to conven-33 tional PP/LDPE, blends, blends stabilized in accordance with 34 this invention also exhibit a good balance of flexural 35 modulus and impact strengths, although these propexties, in 36 molded test pieces, are not as great as those exhibited by 37 blends of this invention which employ a HDPE component.

`S ~1 '' ' ,41 t ~

1 In the practice of this invention, the impact 2 PP/HDPE blends of the invention employ a ratio, by weight, 3 of PP to the combined amount of PE and EPR of from about 1 4 to about 2. The polyethylene component should have a density of about at least about .919 g/cc. The ethylene-propylene 6 copolymer rubber included in the blend is contained in an 7 amount which by weight percent of the total mixture ranges

8 from about 3.5 to 11 percent. The EPR should have an ethylene

9 content which is equal to or exceeds 30 percent. On a weight percent basis of the final blend, blends within the scope of this invention comprise about 45-67 percent polypropylene, 12 about 30-45 percent polyethylene and 3.5-11 percent of 13 ethylene-propylene copolymer.
14 In order to achieve the good balance of low tempera-ture impact strength and room temperature flexural modulus, 16 it is believed necessary to employ a ratio of polypropylene 17 to polyethylene which will produce an interlocked dual con-18 tinuum network structure in the blend upon melt mixing. Since 19 a high density poIyethylene is preferred in most applications, hereafter the polyethylene component will be generally re-21 ferred to as HDPE. The preferred minimum ratio of PP to the 22 combined amount of HDPE and EPR for this purpose is about 1, 23 and the highest ratio which has been found to be satisfactory 24 is about 2Ø The necessary ratio has been found to depend, at least in part, upon the melt flow rate (MFR) of the PP
26 which is used. Where the PP has a melt flow rate of one or 27 less (a fractional MFR polypropylene) it has been f~und that 28 at least 30 percent by weight HDPE based upon the entire 29 blend should be employed and at least about 4 percent by weight EPR, based upon the entire blends should be used to 31 stabilize the dual continuum structure. In this case the 32 ratio of PP to the combined HDPE and EPR may range from about 33 1.0 to about 2Ø When the PP component has a melt flow rate 34 greater than about 1 it has been found that at least about 37 percent by weight HDPE based upon the entire blend should be 36 employed and at least about 5.5 percent by weight EPR based 37 upon the entlre blend should be used. Thus where the PP has ' ~3~

1 a melt flow rate greater than 1 the ratio of PP to the com-2 bined HDPE and EPR may range from about 1.0 to about 1.55.
3 Additionally, slnce it is desirable to minimize 4 the amount of EPR required - the most expensive component of the blend - the melt flow rate of the PP and the melt index 6 (MI) of the HDPE should be comparable. To be comparable the 7 MI of the polyethylene component should be around one half 8 of the numerical value of the MFR of the PP component.
9 Generally, the minimum amounts discussed above apply only when the HDPE melt index r~te is comparable to the melt flow 11 rate of the PP component. As the difference in the melt in-12 dex of the HDPE and the PP components becomes greater it 13 becomes necessary to employ higher concentrations of HDPE
14 and EPR in the blend in order to maintain a given level of mechanical properties.
16 The polypropylene useful in the blends of this 17 invention are normally solid isotactic polypxopylenesr i.e., 18 polypropylenes of greater than 90 percent hot heptane in-19 solubles, having a melt flow rate (MFR) of from about 0.3 to about 35 g/10 minutes (230C, 2160 g load). The particular 21 density of the~polypropylene is not critical. As known, 22 such isotactic polypropylenes are normally crystalline and ~3 have density ranges from about 0.89 to about 0.91 g/cc.
2~ Preferably, a polypropylene having a melt flow rate of about 0.3 to about 12.0 is employed. Within this range the MFR is 26 selected in dependance upon the processing steps for which 27 the blend is designed. For example, where the blend is 28 designed for injection molding, the PP should have a MFR
29 greater than 3; if designed for sheet extruding, thermo-forming or stamping the MFR should be less than l. Moreover, 31 the blends of the invention can include more than one poly-32 propylene component, i.e., several polypropylenes having 33 different melt flow rates, whereby the resulting blends have 34 melt flow rates within the above ranges.
The polyethylenes which are useful in this inven-36 tion are those normally solid polymers having a density g 1 greater than 0.919 g/cc and a melt index (MI) of from about 2 0.1 to about 20 g/10 minutes, (190C at 2160 g load). Except 3 for blends that are designed for special applications which 4 require good heat sealability and clarity properties and therefore require the use of a LDPE component, it is pre-6 ferred to employ a HDPE in order to produce blends having 7 a high flexural modulus and impact strength. Thus, the 8 preferred polyethylenes have densities greater than about 9 0.950 g/cc and may have a MI between 0.1 to about 100.
Since the impact strength of the blend will vary inversely 11 with the melt index of the HDPE, the MI will usually be from 12 about 0.1 to about 20. Since the best balance between flex-13 ural modulus and impact strength occurs when the MI of the 14 HDPE is from about 0.1 and about 5.0, this range is preferred.
The most preferred range is from about 0.3 to about 3.0 16 Such polyethylenes and methods for making same are well 17 known and the materials are readily available commercially.
18 The ethyIene-propylene copolymer rubber employed 19 in the blend of this invention is an ethylene-propylene elastomer which has a Mooney viscosity greater than 20 ML
21 (1 + 8) at 212Fj r and, generally, between the range of 20 22 to about 120 and preferably from about 35 to 60. The per-23 centage of ethylene in such rubber should be greater than 30 24 percent by weight and, preferably, about 40 to 60 weight percent, although the particular amount has not been found 26 to be particularly crucial to the invention. Generally, 27 EPR's having a narrow molecular weight distribution will 28 produce blends having between 1exural moduli than EPR's 29 having broad molecular weight distributions. Such EPR
copoIymers and methods for making same are well known and 31 are readily available commercially from a number of manu-32 facturers. Therefore, such rubbers will not be discussed in 33 detail, except to point out that any EPR copolymer having 34 the above identified characteristics may be employed in this 35 invention.
36 In the practice of this invention, a ratio of PP

33L~6 1 to the combined amount of HDPE and EPR of from about 1 to 2 about 2.0 has been found suitable to produce significantly 3 improved low tempexature impact strength while maintaining 4 a good high temperature flexural modulus. The amount of EPR
which should be incorporated within the blend to stabilize 6 the dual continuum melt mix structure depends upon the par-7 ticular combination of properties desired in the final mix.
8 Increasing the EPR amount increases the low temperature im-9 pact strength at the expense of some loss in flexural modulus and, conversely, decreasing the amount of EPR in-11 creases flexural modulus at the expense of low temperature 12 impact strength. Although the inclusion of any amount of 13 EPR which ranges between about 4.0 to about 11 percent by 14 weight of the total mixture tends to stabilize the dual continuum struc~ure against collapse when submitted to the 16 molding process, the rubber component is the more expensive 17 component o~ the blend, therefore it is preferred to use an 18 EPR concentration which ranges from about 4.0 to about 8 19 percent as giving the best trade-off between cost versus improved mechanical properties.
21 Other components such as colorants, stabilizers, 22 antioxidants, fillers and the like may be included within 23 the composition of these blends without adversely affecting 24 the mechanical prop~rties. Dual continuum blends made in ~5 acc~rdance with this invention have been stablliæed with 2~ distearyl thiodipropionate (DSTDP) as an antioxidant and 27 IR 1010 and/or DSTDP as a thermal or processing stabilizer 28 to prevent molecular weight degradation during processing 29 with no adverse effect upon the mechanical pxoperties.
Carbon black has been added to such blends without serious 31 adverse effect. Specific examples of stabiliæers have been 32 mentioned as an illustration that other combinations of 33 conventional additives could be used.
34 Generally, to produce the melt mixed dual con~
tinuum blends of this invention it is necessary to mi~ the 36 EPR with at least one of the two other components, PP or ~33~'76 1 PE, by a high shear mixing method. This premixture may 2 then be mixed with the remaining component by a low shear 3 mixing method. Although the order of mixing is not critical, 4 it is preferred to mix the EPR component with the PP by a high shear mixing method, with the HDPE component, as virgin 6 stock or as a mixture with PP, melt mixed by low shear 7 mixing.
8 In a preferred blending method a total preblend 9 batch of PP and EPR are premixed in a Banbury mixer, Farrel Continuous mixer or a Twin Screw Extruder. The mixing 11 temperature is normally about 204C (400F), and mixing is 12 continued until the EPR is well dispersed in the PP phase.
13 This total preblend batch is then pelletized or powdered and 14 mixed with an appropriate amount of virgin HDPE, and melt mixed as an extruder letdown, normally at about 204C ~400F).
16 Alternatively, a masterbatch of EPR and PP may be prepared 17 by blending EPR with a first portion of PP and the melt mix 18 blend prepared as an extruder letdown of this masterbatch l9 with a~mixture of a second portion of PP and HDPE. No significant differences in the mechanical properties of 21 the final blend has been observed when the EPR is premixed 22 with the total amount of PP as compared to when the EPR is 23 premixed with a first portion of PP and the master-~atch 24 is subsequently melt mixed with the final portion of PP and HDPE.
26 In the total preblend method, for example, a mix-27 ture of ao percent by weight polypropylene is mixed with 28 20 percent by weight of an ethylene-propylene copolymer and 29 is blended in a Banbury for about 4 minutes at 204C (400F).
After blending, the preblend is dumped, sheeted, cooled and 31 chopped to pellet size. Subsequently 55 percent by weight 32 of the preblend PP/EPR is added to 45 percent by weight of 33 a high density polyethylene to make up a pellet mixture which 34 is suitable for melt mixing in an extruder letdown ~at about 204C (400F) with a 100 mesh screen pack in place. The 36 final melt mixed blend, comprising 44 percent PP, 45 percent ~33~

1 HDPE and 11 percent EPR is then ready to be used for molding 2 parts.
3 The PP, HDPE and EPR blends may be processed into 4 molded parts in their virgin state, as a regrind or as a mix-5 ture of virgin and regrind stock.
6 The following tables more particularly illustrate the 7 nature of the invention and the composition of the blends and 8 are not intended to be limitations thereon. In the following 9 examples, the mechanical property evaluations were made

10 employing the following ~ests:

.. .. ..
13 ~elt Processability Melt Flow Rate D 1238L
14 StiffnesS Flexural Modulus D 790 I.A.
15 Strength Properties Tensile & Elongation D 638 16 at yield and fail Speed C
17 Impact Strength Room Temperature Notched 18 Izod D 256 19 Unnotchecl Izod at 1, -20, 21 Gardner at 0F Falling 22 dart tes~a 23 (a) Gardner impact tester used; data reduction by the Bruceton 24 staircase design.
25 Test specimens for the above mechanical property evaluations 26 were produced on an HPM in~ection molding machine, 350 tons 27 capacity, Egan 2" Reciproscrew feed.

29 A total preblend of 1634g polypropylene (E-115, 30 Exxon Chemical Co., 5 MFR homopolymer) and 409g. of an 31 ethylene-propylene copolymer rubber (Exxon Chemical Co., 40 wt.
32 ~ ethylene content) were mixed in a Banbury mixer for 4 minutes 33 at 400F. After mixing the Banbury pig was chopped to pellet 34 size. A pelIet blend comprising 8.25 lbs. of the PP/EPR pre-35 blend and 6.75 lbs. of a polyethylene component (MI-0.3, 36 density=0.960) was prepared and melt mixed as an extruder let-37 down at about 400F as the set temperature in all extruder 1 20nes, with a 100 mesh screen pack. The dual continuum blend 2 so produced comprised 118 EPR, 45% PE and 44% PP, by weight.

4 A masterbatch of PP/EPR of 2.7 lbs. polypropylene 5 (E-115) and 1.8 lbs. EPR (MD 714A, 50 wt.% ethylene content) 6 were mixed in a Banbury mixer for 4 minutes at 400F. The 7 Banbury pig was pelletized. A pellet blend of 2.1 lbs. of 8 the PP/EPR masterbatch, 4.7 lbs. PE (MI=0.3, density=0.960) 9 and 5.9 lbs. PP (E-115) was melt mixed as an extruder letdown 10 at about 400F with 100 mesh screens. The dual continuum ll blend produced comprised, 6.6% EPR, 37.0% PE and 56.4% PP, by 12 weight.
13 ~able I reports the properties of the melt mixed 14 blends of Examples 1 and 2 and compares them with the prop-15 erties of conventional impact PP/PE blends containing EPR.
16 Additionally, the properties of binary melt mixed blends of 17 PP/PE are reported for comparison. Unless indicated to the 18 contrary~ ~he compositions reported in Table I were formulated 19 with the following components:
EPR - (V404), 40 Mooney viscosity (1~8(a) 212F), 21 ethylene content 40 wt.%;
22 PE - (A60003) Allied Chemical Co., MI=0.3, density-23 0.960; and 24 PP - (E-I15) Exxon Chemical Co., MF~=5.0, homopoly-mer.
26 Table I illustrates the-significant improvement in 27 the impact properties of PP formulations made in accordanc~
28 with this invention. The formulations of Example 1 and 2 29 exhibit greatly increased Gardner impact strengths compared to 30 conventional blends A, B, and C. The increase in impact 31 strengths achievable by the addition of minor amounts of EPR
32 is clearly evident upon comparison to the binary blends which 33 contain no EPR. In comparison to the convention blends, 34 Examples 1 and 2 have a comparable flexural modulus. The 35 effect of maintaining the PP/HDPE ~ EPR ratio within the pre-36 ferred range of 1-2 is illustrated by comparison of Examples 1 1 and 2, Example 1 having a ratio below one has a flexural 2 modulus significantly less than Example 2.
3 The examples set forth in the following tables were 4 formulated in accordance with the masterbatch method.
Tables II, IIIand IV illustrate the relationship 6 between the MFR of the PP component and the minimum amounts 7 of EPR and HDPE, by weight of the total blend, necessary to 8 the formulation of blends having improved impact strengths 9 and good flexural modulus.
Table II illustrates blends formulated with a PP

11 component having a melt flow rate greater than one. When a

12 MFRjl PP is employed the minimum total amount of EPR + HDPE

13 should be about 40~ by weight or greater. Thus, in examples

14 3-7, a dramatic increase in the impact properties occurs

15 between samples 5 and 6. The minimum amount of EPR needed,

16 when HDPE is held at 37~, is shown by samples 8-11 to fall

17 between 4 and 6% as evidenced by the dramatic increase exhib-

18 ited in ~he Gardner impact strengths between these limits, with

19 the preferred minimum falling at about 5.5%.
Table III illustrates that when a fractional MFR
21 grade PP is employed, as when a thermoforming blend is desired, 22 that to achieve improved impact properties the minimum total 23 concen~tration of EPR+HDPE must be about 30~ or greater, as 24 evidenGed by the increased Gardner impact strength between 25 samples 13 and 14.
26 Table IV illustrates the more precise limits for 27 obtaining a desirable property balance in dual continuum blends 28 containing a fractional MFR grade PP as having a minimum total 29 concentration of EPR+HDPE of 34~ or greater, wherein the 30 minimum amount of HDPE is 30~ and the minimum amount of EPR
31 i5 3.5%.
32 Table V illustrates the rapid fall off of flexural 33 modulus that occurs in conventional impact blends which 34 employ EPR and HDPE in a ratio of 1 or greater when the total 35 concentration of EPR+HDPE begins to exceed about 33~ of the 36 total blend.

1 When samples 24-29 of Table V are contrasted with 2 the dual continuum blends of this invention, samples 6, 7,10, 3 11, 14, 15, 16, 17 and 18, it is apparent that it is not 4 possible to obtain a comparable balance of good flexural 5 modulus and low temperature impact strength with a convention 6 blend as can be achieved by the dual continuum blends of the 7 present invention.
8 In conventional blends where EPR and HDPE, at a 9 EPR-HDPE ratio of one or greater, are employed to improve 10 impact strength, the flexural modulus falls off rapidly as 11 the EPR~HDPE exceeds 33%. On the other hand, as illustrated 12 by Table VI where the combined total of EPR+HDPE is kept 13 below about 34% any attempt to decrease the amount of the 14 more expensive EPR component that decreases the EPR/HDPE
15 below 1.0 causes a rapid all off in the low temperature 16 impact strength of the blend.
17 Applican~ has surprisingly found that a good balance 18 bet~een flexural modulus and low temperature impact strength 19 may be achieved at EPR/HDPE ratios less than 1 and ~PR~HDPE

20 total concentrations greater than about 34%.

21 No surface delamination has been obser~ed to occur

22 in large parts molded from the blends of the present invention.

23 EXAMPLE 36

24 A dual continuum blend was prepared with a low

25 density polyethylene, in replacement of HDPE, according to the

26 masterbatch procedure set orth in Example 2. The EPR was

27 V-404, PP was E-115, and the LDPE ~Jas LD 102 having an MI of

28 6.5 and a density of 0.922 g/cc. The composition comprised

29 5 . 6% EPR, 37.0% LDPE and 57.4% PP by weight. Test specimens

30 were prepared by injection molding and by film extruding.

31 The injection molded specimen had the following properties:

32 MFR 7.8

33 Flexural Modulus (psi x 10 ) 104

34 Tensile, yield (psi) 2949 % Elongation, yield 19.4 36 R. T. Notched Izod (ft-lbs/inch) 4.0 3~7~

1 Unnotched Izod at 0F 37.5 2 Gardner Impact at 0F 31 3 (96 mil disk), inch-lbs.
4 Pentane Extractables 6.8 The film extruded specimen had the following properties as 6 compared to films produced from Amoco 6011 random copolymer;
7 polypropylene (E 115); and a dual continuum blend prepared 8 with a HDPE component comprising 37~ HDPE~ 5.5% EPR and 57.5 9 PP (film impact strength conducted according to ASTM D 1709-10 62T): HDPE Example 11 Properties Amoco 6011 E-115 Dual Continuum 36 12 Impact @ RT (Kg-13 Cm) (3 mil film) 26 9 6 39 14 Impact @ 0F (Kg-15 Cm) (3 mil film) 5 2 4 10 16 As can be seen from the above data~ a dual continuum 17 blend formulated with LDPE has significantly improved impact 18 properties when extruded into a film, compared to conventional 19 film making formulations, but relatively poor low temperature 20 Gardner impact strengths when used in injection molding.
21 Conversely, a dual continuum blend formulated with ~DPE has 22 poor film impact strengths but, as has been illustrated by 23 previous examples,~significa~lyimprov~d impact strength when 24 used to make injection molded parts.

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TABLE I I I
2 EX~lPLE NO~ 12 13 14 15 16 3 EPR, wt. ~6 10 10 10 10 10 4 Polyethylene4,wt. % -- 10 20 30 40 Polypropylene6, wt. 96 90 80 70 60 50 6 Ratio: PP/HDPEfEPR -- 4.00 2.33 1,50 1.00 8 Flex. Mod. x 10 3 140 . 0133 . 0125 . 0115 . 0 106 . 0 9 ~qFR 2.7 1.0 1.0 0.79 û.75 Tensile, Yield 3904 3?28 3687 3629 3470 11 % ~long., Yield 20 . 3 21. 6 21. 3 21. 5 22 O 2 12 Tensile, Fail 13 ~6 Elong., Fail 14 R.T. Notch, Izod 3. 2 15. 2 16 . 5 16. 6 16 ~ 6 Unnotched I zod, 16 at 0 F
17 --20F 12 . 9 20. 6 36. 7 DNB DNB
1 8 --4 0 ~
19 Gardner at 0F 43+7 22+4 151+2 183+21 >240 t96 mil disks) .. _ . .. . .. _ . . ... _ . . _ 21 3. V-404 22 4. EHM 6003 23 6. E-612 ~3 I` O ~ ~ o ' In U) OD ~ I I. , ~ I +l ~
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.i 2 EXAMPLE NO . 24 25 26 27 28 29 3 E~R, wt.% 6.7 10.0 13.4 17.4 20.0 24.0 4 Polyethylene4, wto % 5 ~ 9 8~ 9 11~ 7 15.2 17.5 21.0 5 PolypropyleneS, wt.% 87~4 81.1 74.9 67.4 62.5 55.0 6 Ratio: PP/HDPE+EPR 6.94 4.29 2.98 2.07 1.67 lo 22 8 Flex. ~od. x lQ 3167 154 135 114 107 90 9 MFR 4.5 4.1 4.3 3.7 3.0 2.7 10 Tensile, Yield 4279 3928 3472 3096 2978 2604 11 % Elong., ~ield- ~ 14~ 3 16.3 15 ~ 1 16. 819 ~ 7 22 ~ 7 12 Tensile, Fail 13 % Elong., Fail -- ~- ~~ ~~ ~~
14 R.T. Notch, Izod ~ 1.4 1.3 2.3 DNB DNB DNB
l$ Unnotched Izod, 16 a~ 0F 18~ 9 30- 9 DNB DNB DNB DNB
17 - 20F 14.4 20.4 32 DNB DNB DNB
18 - 40F 12.4 16.7 28 43 47 DNB
19 Gardner at 0~F 22+6 95+29 127+8 230+6 >240 >240 20 (96 ~ mil disks ?
21 HDT at 66~ (C) ~~ ~~ 87 82 77 74 _ .
22 3. V-404 ~3 4. EHM 6003 24 5. E-115 2 EX~PLE NO. , 30 31 32 33 34 35 3 EPR , wt.% 9 6 3 18 12 6 4 Polyethylene4, wt.~ 3 6 9 6 12 18 5 Polypropyl ne5, wt.% 88 88 88 76 76 76 6 Ratio: PP~HDPE+EPR 7.33 7.33 7.333.17 3.17 3.17 : .
7 P~OPERTIES
8 Flex. Mod. x 10 3181 195 207 137 153178 ~ 9 MFR ~ 4.7 4.4 4O5 3.9 3.73.6 : ~ 10 Tensile, Yield 4377 47005004 3546 39094511 Elong., Yield12.9 12.413.1 14.2 14.714.2 12 Tensile, Fail -- . -- ~~ -~ ~~ ~~
13 ~ Elong., Fail -- -- -- -- ~- ~-14 R.T. Notch, Izod 0.9 0.9 0.9 1.8 1.71.4 Unn~tched I ZGd, 16 at 0F 19.7 17.811.3 37.3 34.825.7 17 -20F 15.7 12.8 7.8 27.3 26.915.2 18 -40F 13.3 9.6 7.2 24.2 18.910.2 _..r~.
19 Gardner at 0F 80+5 12+41+0.1 123_6 114+6 12+2 (96 mil disks) :

21 3. V-40~
22 4. FHM 6003 23 5. E-115

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A melt-flowable, high impact strength, melt mixed blend of polypropylene ethylene-propylene copolymer rubber and polyethylene wherein the ratio by weight of the polypropy-lene component to the combined polyethylene and ethylene-propylene copolymer rubber components is from about 1.0 to about 2.0; and the polyethylene component is at least about 30% by weight of the total blend and the ethylene-propylene copolymer rubber component is present from at least about 4% to about 11% by weight of the total blend.

2. The high impact blend of claim 1, wherein said ethylene-propylene copolymer rubber component is present from at least about 4% to about 8% by weight of the total blend.

3. The high impact blend of claim 1, wherein said polyethylene-component has a density of at least about 0.950 g/cc.

4. The high impact blend of claim 3, wherein said polyethylene component has a melt index of from about 0.1 to about 20.

5. The high impact blend of claim 4, wherein when said polypropylene component has a melt flow rate greater than 1 the polyethylene component is at least about 37% by weight of the total blend and said ethylene-propylene copoly-mer rubber component is at least about 5.5% by weight of the total blend.

6. The high impact blend of claim 5, wherein said polyethylene component has a melt index of from about 1 to about 5.

7. The high impact blend of claim 1, wherein said ethylene-propylene copolymer rubber has a mooney viscosity greater than 20 and an ethylene content greater than 30% by weight.

8. The high impact blend of claim 7, wherein the ethylene content is between about 40 to about 60% by weight.

9. The high impact blend of claim 7, wherein said polypropylene component has a melt flow rate of from about 0.3 to about 12Ø

10. The high impact blend of claim 1, suitable for film applications, wherein said polyethylene component has a density of from about 0.910 to about 0.929 g/cc, and a melt index of from about 0.3 to about 20.

11. A pellet mixture for making melt mixed melt-flowable, high impact strength blends, comprising:
a pelletized blend, of a polypropylene com-ponent and an ethylene-propylene copolymer rubber component, produced by high shear mixing; and a pelletized polyethylene component; wherein said pelletized blend of polypropylene and ethylene-propylene is mixed with said pelletized polyethylene in proportions sufficient to produce a total pellet mixture wherein the ratio by weight of polypropylene to the total amount of polyethylene and ethylene-propylene copolymer rubber is from about 1.0 to about 2.0, the polyethylene is at least about 30% by weight of the pellet mixture, and the ethylene-propylene copolymer rubber is from at least about 4% to about 11% by weight of the pellet mixture.

12. A process for making a melt-flowable high impact melt mixed blend of polypropylene, ethylene-propylene copolymer rubber and polyethylene, comprising the steps of:
(a) high shear mixing of a polypropylene com-ponent with an ethylene-propylene copoly-mer rubber component; and (b) melt mixing the polypropylene and ethylene-propylene copolymer rubber of (a) with a poly-ethylene component to form a final blend of from about 4 to about 11% by weight EPR, at least about 30% by weight of PE; wherein the ratio by weight of PP to the combined EPR and PE is from about 1 to about 2.

13. A process for making a melt-flowable high impact melt mixed blend of polypropylene, ethylene-propylene copolymer rubber and polyethylene, comprising the steps of:
(a) high shear mixing of a first portion of poly-propylene with an ethylene-propylene copolymer rubber component; and (b) melt mixing the polypropylene and ethylene-propylene copolymer rubber of (a) with a second portion of polypropylene and a polyethylene component to form a final blend of from about 4 to about 11% by weight EPR, at least about 30% by weight PE; wherein the ratio by weight of PP to the combined amount of EPR and PE is from about 1 to about 2.

14. The high impact blend of claim 1, wherein said polyethylene component has a density of at least about 0.919 g/cc.