WO1998031744A1

WO1998031744A1 - Impact polypropylene composition having high impact resistance and stiffness

Info

Publication number: WO1998031744A1
Application number: PCT/US1998/000870
Authority: WO
Inventors: Henry Wu-Hsiang Yang
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1997-01-21
Filing date: 1998-01-16
Publication date: 1998-07-23

Abstract

A novel impact polypropylene composition, and a masterbatch composition useful for the production of same, said composition having improved properties and comprising (A) isotactic polypropylene, (B) ethylene-propylene rubber, (C) high density polyethylene, and (D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene. The impact polypropylene composition offers the ability to simultaneously improve both the low temperature Gardner impact resistance and stiffness of both lower flow and higher flow isotactic polypropylene (i-PP) relative to ICP's which are blends of only (B) and (A).

Description

TITLE: IMPACT POLYPROPYLENE COMPOSITION HAVING HIGH IMPACT RESISTANCE AND STIFFNESS

FIELD OF THE INVENTION

This invention relates to impact polypropylene compositions, and more specifically to impact polypropylene compositions having improved low temperature Gardner impact strength and, at the same time, improved stiffness.

BACKGROUND OF THE INVENTION

Isotactic polypropylene (hereinafter "i-PP"), while having many useful properties, is known to possess relatively poor low temperature impact resistance. To overcome this deficiency, polypropylene impact blends are employed. Polypropylene impact blends, also referred to as "impact copolymers," or "ICP's," include blends of i-PP and substantially amorphous ethylene-propylene rubbers (EPR) or ethylene-propylene-diene terpolymers (also known as "EPDM"). As is well known, the addition of certain types of rubber components in minor amounts to i-PP results in polypropylene impact blends having good overall mechanical property balances, particularly improved impact strengths, as compared to unmodified polypropylenes. Such polypropylene impact blends are thus particularly useful in the manufacture of molded and extruded articles, such as containers, filament rods, automotive parts, and the like, in accordance with conventional molding and/or extrusion techniques.

Unfortunately, however, the addition of EPR or EPDM to i-PP, while improving low temperature impact properties, results in a decease in the stiffness of the polypropylene and parts molded therefrom. Therefore, the improvement in impact properties offered by ICP's is obtained at the expense of stiffness. Since high stiffness in molded polypropylene pans is also a desirable property, affecting for example the stress that a molded part can endure without significant deformation, workers in the art have sought to improve both the stiffness and impact strength of ICP's relative to unmodified i-PP and ICP's consisting essentially of EPR or EPDM and i-PP.

By way of example, it is known to replace some of the rubber in EPR- or EPDM-modified polypropylenes with higher density polymers, in particular high density polyethylene (HDPE). For example, U.S. Pat. No. 3,256,367 discloses that polypropylene compositions having impact strengths and stiffness improved over polypropylene or rubber-modified polypropylene are obtained by the incorporation of a polyethylene having a density above 0.93 g/cc into polypropylene-rubber compositions. As described in the patent, the blends comprise 50 to 96% by weight of a polypropylene having a melt flow at 230 °F and 44 psi less than 12 g/10 min., 2 to 25% by weight of certain polyethylenes, particularly high density polyethylenes, as exemplified, and 2 to 25% by weight of certain types of amorphous ethylene/propylene copolymer or polyisobutylene elastomers.

Incorporation of high density polyethylene into rubber-modified polypropylenes has been reported to achieve other beneficial results. For example, U.S. 4,319,004 describes a ternary molding composition containing an ethylene- propylene copolymer, a propylene polymer, and polyethylene. Preferred formulations according to the invention contain 40-45% by weight of the ethylene-propylene copolymer (a), 35-58% by weight of the propylene polymer (b) and 5-20% by weight of polyethylene. The third component (c), i.e. polyethylene, is said to surprisingly raise the notch impact strength at low temperatures and to have a positive effect on the shrinkage after removal from the mold. A high-density polyethylene is said to be preferably utilized in this embodiment. While the foregoing references describe certain improvements in ICP's, there is still a need for an impact polypropylene composition capable of higher stiffness, higher impact, or, if possible, both higher stiffness and impact at the same time. In U.S. Patent No. 3,256,367, the incorporation of HDPE into ICP's to simultaneously improve both impact resistance and stiffness has been described only for ICP's based on higher molecular weight (lower MFR) polypropylenes, typically those having MFR below about 12 g/10 min. However, polypropylenes with MFR greater than about 20g/10 min. are preferred in the manufacture of certain injection molded parts, for example automotive interior trim, where, because of the large part size or part complexity, a highly fluid polymer melt is desired in order to achieve optimal mold filling and part uniformity. To be useful in service, such parts also require a good balance of low temperature Gardner impact resistance and stiffness. Thus, it would be highly desirable to be able to improve the properties of ICP's based on such high flow polypropylenes by the addition of high density polyethylene or by other means. Unfortunately, applicant has found that the prior art method of adding HDPE to ICP blends of i-PP and EPR to improve stiffness and low temperature impact strength, as measured by Gardner impact, is not satisfactory for higher MFR ICP's. The higher MFR ICP's do not respond to HDPE in the same way as lower MFR ICP's. HDPE addition to higher MFR ICP's improves the stiffness of such blends, but the low temperature Gardner impact strength does not improve, or it even worsens relative to the unmodified ICP. Thus a need still exists for an ICP composition which can provide simultaneously improved low temperature Gardner impact strength and stiffness in both lower MFR and higher MFR applications. Further, a need exists for a masterbatch composition which can improve the low temperature Gardner impact resistance and stiffness of both lower flow and higher flow i-PP relative to ICP's which are blends of only rubber and i-PP. SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a novel impact polypropylene composition, comprising: (A) isotactic polypropylene; (B) ethylene-propylene rubber; (C) high density polyethylene; and (D) an ethylene- propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene. In accordance with one embodiment, there is provided an impact polypropylene composition which offers the capability of simultaneously improving both the low temperature Gardner impact resistance and stiffness of both lower MFR and higher MFR isotactic polypropylene (i-PP) relative to ICP', said composition comprising:

(A) isotactic polypropylene;

(B) ethylene-propylene rubber; (C) high density polyethylene; and

(D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene, wherein: the amount of (A) is about 60 to about 90 percent by weight of the combined weight of (A), (B), (C), and (D); the amount of (B) is about 8 to about 35 percent by weight of the combined weight of (A), (B), (C), and (D); the weight ratio of (C) to (B) is in the range of 0.1 to 0.95; and the amount of (D) is about 1 to about 20 percent by weight of the combined weight of (A), (B), (C), and (D).

In accordance with yet another embodiment, there is provided a masterbatch composition, useful for the production of certain impact polypropylene compositions of the present invention, said masterbatch composition comprising components (B), (C), and (D) above, as follows: (B) ethylene-propylene rubber; (C) high density polyethylene; and (D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene, wherein: the amount of (B) is about to about 50 percent to about 90 percent by weight of the combined weight of (B), (C), and (D); the weight ratio of (C) to (B) is in the range of 0.1 to 0.95; and the amount of (D) is about 1 to about 45 percent by weight of the combined weight of (B), (C), and (D).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to polypropylene impact blends, also referred to as "impact copolymers," or "ICP's," which include blends of i-PP and substantially amorphous ethylene-propylene rubbers (EPR). Sometimes certain copolymers of ethylene and propylene are also referred to in the art as impact copolymers or ICP's, but it will be understood that in this patent specification "impact copolymer" and "ICP" refer to blends comprising i-PP and EPR. Components suitable for use in the compositions of the invention include the following.

Isotactic Polypropylene (Component A^

Any isotactic polypropylene (i-PP) conventionally employed in preparing polypropylene impact blends having a melt flow rate (MFR) of from about 0.001 to about 500 g/ 10 min. (230°C, 2160 g load as per ASTM D 1238 ) can be used in the compositions of this invention. Preferably, the isotactic polypropylene will have an MFR of from about 0.01 to about 200 g/10 min., more preferably from about 20 to about 200 g/10 min., and still more preferably from about 80 to about 200 g/10 min. As used in this specification, unless otherwise indicated, the term "about" means that the indicated values need not be exact, and they may be 10% greater or lower than the value shown. Normally, solid isotactic polypropylenes are preferably employed in the impact polypropylene composition of the present invention, i.e., polypropylenes of greater than 90% hot heptane insolubles. The particular density of the polypropylene is not critical. Preferred isotactic polypropylenes are normally crystalline and have densities ranging from about 0.90 to about 0.94 g/cc. Moreover, the blends of the invention can include several polypropylenes having different melt flow rates to provide a polypropylene impact blend having mechanical property characteristics as desired. As used herein, the term "isotactic polypropylene" is meant to include homopolypropylene, as well as copolymers of propylene and ethylene containing up to 8 weight percent of polymerized ethylene or other alpha-olefins.

Ethylene-Propylene Rubber (Component B^

The ethylene-propylene rubbers (EPR) useful for the impact polypropylene compositions of the present invention are substantially amorphous random elastomeric copolymers of ethylene and propylene, with or without a copolymerizable diene, which have a weight average molecular weight of about 50,000 to about 1 ,000,000, preferably about 100,000 to about 500,000, and a polymerized ethylene content of about 35 weight percent to about 70 weight percent. The term "elastomer" and its derivatives will be used interchangeably with the term "rubber" and its corresponding derivatives.

Examples of ethylene-propylene rubbers (EPR) which are particularly useful in the present invention include saturated ethylene-propylene binary copolymer rubbers (EPM) and ethylene-propylene-non-conjugated diene terpolymer rubbers (EPDM), having the above-mentioned characteristics and containing about 1 to about 5 weight percent of a diene such as 5-ethylidene-2- norborene, 5-methylene-2-norborene, 1,4 -hexadiene, dicyclopentadiene (DCPD), and the like. As used in this patent specification and in the appended claims, the term "ethylene-propylene rubber" (abbreviated as "EPR") is intended to encompass all of the aforementioned rubber types, namely EPR, EPM, or EPDM, as well as mixtures thereof. All of these relatively high ethylene-containing elastomers, and the methods for making them, are well known and the EPR's are readily available commercially.

While any of the EPR's described above may be advantageously employed in the instant invention, lower Tg (glass transition temperature) EPR's are preferred. This is because lower Tg EPR's perform better in simple binary mixtures of i-PP and EPR. For example, the Izod and Gardner impact properties of ICP's which consist of 80% by weight i-PP and 20 % by weight EPR are significantly improved by lowering the Tg of the EPR. As the Tg of such binary blends of i-PP and EPR decreases from about -37 to about -50°C, the Gardner impact measured at -29° C increases. At the same time, stiffness, as measured by the heat distortion temperature(HDT) and flexural modulus, remain essentially unchanged. Thus the most preferred EPR's of the present invention will have the lowest Tg achievable for a given EPR.

The Tg of a polymer can be conveniently measured by methods well known in the art, for example by differential scanning calorimetry (DSC) or dynamic mechanical thermal analysis (DMT A) techniques. As used herein, Tg will be understood to refer to the value for Tg obtained using the DMTA method based the tan δ peak, which is well known in the art.

The Tg of an EPR can be readily controlled by varying its ethylene content. The lowest Tg for commercially produced EPR's, about -50°C, occurs within a range of from about 35 to about 70 weight percent ethylene. Above this range, Tg increases due to the development of polyethylene crystallinity. In a similar fashion, Tg also increases due to the development of polypropylene crystallinity as ethylene content drops below this range. Those skilled in the art will understand that the relationship between Tg and ethylene content is readily measurable and is a continuous, smooth-curve function. There is, therefore, no well-defined point above or below which the Tg abruptly changes as ethylene content changes. Also, the catalyst used to produce the EPR will determine the ethylene content required to give the lowest Tg value. For example, when vanadium-based or metallocene-based single site catalysts are used, the EPR having the lowest Tg will have an ethylene content of about 45-55 weight percent, the Tg being in this case about -50 °C. On the other hand, with traditional Ziegler-Natta titanium-based catalysts, which are usually multi-sited, the EPR having the lowest Tg will have an ethylene content of about 65-68 weight percent and a Tg of about -47 °C.

Therefore, in a preferred embodiment, the EPR of the present invention will have a polymerized ethylene content of from about 35 to about 70 percent by weight, where the term "about" is used to indicate that variation above 70 percent or below 35 percent is acceptable, so long as the Tg of the EPR is within 5 degrees of the minimum value obtainable with the catalyst being employed. It will be apparent to the skilled artisan that the minimum Tg obtainable with a given catalyst and polymerization system can be determined by varying the ethylene content in the copolymer and observing the resultant Tg, all of which can be accomplished, as noted above, using methods well known in the art.

High Density Polyethylene (Component O

High density polyethylenes, traditionally known as "HDPE," are defined herein to include those polyethylenes where the density is equal to or above 0.940 g/cc. The high-density polyethylenes usable as the high density polyethylene (hereinafter HDPE) component in the present invention are commercially available and include those having a density of 0.940 g/cc or greater, preferably 0.945 g/cc or greater, more preferably, 0.950 g/cc or greater, and most preferably 0.955 g/cc or greater. Such HDPE's generally include ethylene homopolymers and copolymers of ethylene with alpha-olefins (preferably having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms). Preferable alpha-olefins are propylene, butene- 1 , hexene- 1 , 4-methy Ipentene- 1 , and octene- 1. Processes for making such polymers are well known in the art and include, for example, gas phase, slurry, and solution polymerization processes. The melt index of the HDPE determined under the conditions E according to ASTM D 1238 method, is generally 0.10 to 300 g/10 min., preferably 0.1 to 100 g/10 min., more preferably, 0.1 to 10 g/10 min. The molecular weight distribution (MWD) of the HDPE is not critical, although if the melt index of the HDPE is particularly low, it may be more desirable to use broader MWD HDPE's that are more shear-thinning and less viscous under extrusion conditions in order to facilitate melt mixing. Such polyethylenes, often referred to as broad molecular weight distribution high molecular weight HDPE (BMWD HMW-HDPE)are well known in the art and are commercially available. An HDPE of this type that has been found to be suitable is Exxon HDZ-126, which has a melt index, as defined above, of about 0.35 g/10 min. and a density of 0.957 g/cc.

Eτhylene-Propylene Copolvmer (Component D^{^}l

The ethylene-propylene copolymer (hereinafter referred to either as "ethylene-propylene copolymer" or "EPC") of the present invention comprises from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene. Preferably, the ethylene- propylene copolymer will have a polymerized ethylene content of about 14% to about 27% by weight, and more preferably about 14% to about 20% by weight. The weight average molecular weight (Mw) of the ethylene-propylene copolymer is preferably in the range of from about 50,000 to about 500,000, more preferably from about 75,000 to about 300,000, and most preferably from about 100,000 to about 200,000.

The ethylene-propylene copolymer (EPC) of the invention may be prepared using metallocene or conventional Ziegler-Natta type catalysts. In either case, the polymerization may be carried out in gas phase, solution, or slurry polymerization processes. For example, a satisfactory process for preparing the ethylene-propylene copolymer comprises contacting ethylene and propylene monomers, under polymerization conditions and in such a ratio as to give the desired polymerized composition, with a metallocene catalyst which yields isotactic polypropylene having a tacticity greater than about 80 percent. Such metallocene catalysts are known in the art, and methods for their preparation and use are also known. For example, U.S. 5,391,629 describes a suitable metallocene catalyst for making the inventive EPC, namely activated dimethylsilanyl bis(indenyl) hafnium dimethyl, which can be used in known solution polymerization processes.

Alternatively, the inventive EPC may be prepared using a conventional Ziegler-Natta catalyst which can yield similar isotactic polypropylenes. A suitable conventional Ziegler-Natta catalyst for preparing the EPC of the present invention is commercially available from Toho Titanium Co., Ltd. (Japan) and has the commercial designation Toho 301 C.

The MWD of the ethylene-propylene copolymer may be broad or narrow.

Typically, when the ethylene-propylene copolymer is prepared using a metallocene catalyst, the MWD will be narrow and on the order of 2.0-2.5. If the ethylene-propylene copolymer is prepared using certain Ziegler-Natta catalysts, for example the titanium catalyst available from Toho, the MWD will be on the order of 2.5 to 5.5. Tnventive Compositions and Methods for Their Preparation

The impact polypropylene compositions of the invention can be prepared by mixing the ethylene-propylene copolymer, EPR, high density polyethylene, and polypropylene components in any order using conventional hot processing equipment well-known in the art, such as Banbury or Brabender mixers, roll mills, screw extruders, and the like, or by solution blending. However, when the components are mixed by melt compounding, it is highly preferred to premix the EPR and HDPE components, either in the presence or absence of the ethylene- propylene copolymer, before they are added to the i-PP. While not wishing to be bound by theory, applicant believes that the HDPE in i-PP/EPR/HDPE blends functions by forming a subinclusion in the EPR rubber particles. When HDPE and EPR are pre-mixed the HDPE is thought to be subincluded in the EPR. Because of the subinclusion, it is further believed that when the mixture is let down into i-PP, the HDPE is present as a core particle located inside the EPR rubber particles. On the other hand, if i-PP, EPR, and HDPE are simultaneously placed in a melt mixer and compounded, it is thought that not all of the HDPE will be inside of the EPR, and some will exist as separate domains within the i-PP matrix.

As noted above, the impact polypropylene compositions of the present invention may also be prepared by solution blending, using, for example, hot xylene to dissolve all of the components. When solution blending is employed, all of the components may be simultaneously dissolved in an appropriate solvent followed by recovery of the mixture from the solution. The impact polypropylene composition may be recovered by precipitation of the dissolved components by the addition of a non-solvent, such as isopropanol, or it may be recovered by evaporation of the solvent. Thus, in one embodiment, the novel polypropylene impact compositions of the present invention may be prepared by combining, by any of the methods discussed above, (A) isotactic polypropylene; (B) ethylene-propylene rubber; (C) high density polyethylene; and (D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30% by weight, preferably from about 14% to about 27% by weight, and more preferably about 14%) to about 20%) by weight of polymerized ethylene, and from about 90 to about 70 weight percent polymerized propylene.

Applicant has found that although any ratios of the components (A), (B),

(C), and (D) may be employed to produce the impact polypropylene compositions of the present invention, it is preferable to keep the weight ratio of HDPE (Component C) to EPR (Component B) less than 1.0. When ratios of 1.0 or greater are employed, only stiffness is improved. At weight ratios of (C)/(B) less than 1.0 both impact and stiffness can be improved. Thus, in a preferred embodiment, the ratio by weight of the high density polyethylene (C) to the ethylene-propylene rubber (B) is from 0.1 to 0.95, preferably from 0.2 to 0.8, more preferably from 0.4 to 0.7, and most preferably from 0.5 to 0.7.

As is well known, the MFR of the impact polypropylene compositions itself will depend upon the MFR's of the individual components of the composition and the relative amounts in which they are blended. In one embodiment the impact polypropylene composition of the invention will have an MFR greater than about 25 g/10 min.

In accordance with another embodiment of the invention, there is provided an impact polypropylene composition which offers the capability of simultaneously improving both the low temperature Gardner impact resistance and stiffness of both lower MFR and higher MFR isotactic polypropylene (i-PP) relative to ICP', said composition comprising (A) isotactic polypropylene; (B) ethylene-propylene rubber; (C) high density polyethylene; and (D) an ethylene- propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene. In this embodiment, the amount of (A) is about 60 to about 90 percent by weight of the combined weight of (A), (B), (C), and (D), preferably about 65 to about 85 percent by weight, and most preferably about 68 to about 82 percent by weight. The amount of (B) is about 8 to about 35 percent by weight of the combined weight of (A), (B), (C), and (D), preferably about 10 to about 30 percent by weight, and most preferably about 15 to about 25 percent by weight. The weight ratio of (C) to (B) is in the range of 0.1 to 0.95, preferably 0.2 to 0.8, more preferably from 0.4 to 0.7, and most preferably from 0.5 to 0.7. The amount of (D) is about 1 to about 20 percent by weight of the combined weight of (A), (B), (C), and (D), preferably about 2 to about 10 percent by weight, and most preferably about 3 to about 5 percent by weight.

In yet another embodiment, the present invention is a masterbatch composition, useful for the production of certain impact polypropylene compositions of the present invention. The masterbatch composition comprises EPR (B), HDPE (C), and EPC (D) as follows: the amount of (B) is about 50 percent to about 90 percent by weight of the combined weight of (B), (C), and

(D); the weight ratio of (C) to (B) is in the range of 0.1 to 0.95; and the amount of (D) is about 1 to about 45 percent by weight of the combined weight of (B), (C), and (D).

The components (B), (C), and (D) used for preparing the masterbatch composition of the invention are the same as components (B), (C), and (D) described above for preparation of the impact polypropylene compositions of the invention. Also, the methods of combining the components of the masterbatch are identical to those described above for the preparation of the impact polypropylene composition of the invention. Normally, the masterbatch will exist in pellet or crumb form, and may comprise other additives, such as fillers, antioxidants, and processing aids, which are added to improve processability of the compositions containing the masterbatch, and nucleating agents, such as sodium benzoate, which improves stiffness of the finished goods.

The inventive masterbatch, once formed, offers a convenient and flexible method for making certain impact polypropylene composition of the invention. For example, producers of impact resistant molded parts may add any desired amount of the inventive master batch to any i-PP in order to produce the desired level of impact and stiffness improvement required for the producer' s particular application. The inventive masterbatch may be combined with i-PP to form the impact polypropylene composition of the invention using any of the means normally employed for letting down masterbatches into base polymers. Such means include, for example, continuous on-line blending using a side-feed extruder in the primary extrusion process, thus forming a melt blend directly, or by pre-mixing by tumble blending to form a dry blend, which is then extruded to form a melt blended composition.

If desired, the polypropylene impact compositions and the masterbatch compositions of the invention may also include antioxidants, stabilizers, antifogging agents, processing agents, nucleating agents, and other property- modifying additives, in normal and conventional amounts. Moreover, the blends can include pigments, fillers, and colorants in conventional amounts for producing products not requiring clarity. The impact blends of the invention are particularly useful in producing molded and/or extruded parts of surprisingly good stiffness and low temperature Gardner impact balance by employment of conventional injection molding, blow molding and/or extrusion techniques. More particularly, the preferred blends have extremely good melt flow rheologies for use in the injection molding techniques, in particular for the molding of automotive trim parts such as bumpers, interior trims, instrument panels, and the like, while at the same time possessing a surprisingly good balance of stiffness and low temperature Gardner impact strength.

EXAMPLES

The following examples more particularly illustrate the nature of the invention but are not intended to be limiting thereof. In the following examples, the mechanical evaluations were made employing the following tests:

Comparative Examples C1-C2 and Examples 3-4

Comparative Examples 1 and 2 (Cl and C2) illustrate prior art compositions based on only i-PP and EPR or i-PP, EPR, and HDPE. Examples 3 and 4 illustrate compositions of the present invention. Examples Cl, C2, 3, and 4 used the same components, but in different weight percents, as indicated in Table 1. Component (A), the i-PP, was a commercial i-PP homopolymer having an MFR = 3.5 g/lOmin. Component (B), the EPR, was Vistalon®-457 (V-457), which is commercially available from Exxon Chemical Company (Vistalon is a registered trademark of Exxon Corporation). V-457 has a Tg of -50°C and a polymerized ethylene content of about 43.7 weight percent. Example Cl employs an 80/20 (weight weight) i-PP/V-457 mixing ratio, as a reference point. In examples C2, 3, and 4, a portion of Component (B) was replaced by either Component (C), which was HDPE (HDZ-126, a product of Exxon Chemical Component (C), which was HDPE (HDZ-126, a product of Exxon Chemical Company, MI = 0.35 g/10 min., density = 0.957 g/cc) or a combination of Component (C) and Component (D) (the ethylene-propylene copolymer (EPC)).

Component (D), reference number 19257-97/98, was synthesized as follows: a 2-liter autoclave reactor equipped with a jacket temperature controller was used. 800 ml of toluene was charged into the reactor and cooled to -10°C by circulating chilled isopropyl alcohol through the reactor jacket. A separate container was used to prepare a constant pressure (120 psi) gas mixture of 30 mole percent ethylene and 70 mole percent propylene. In a separate 10 ml. catalyst vial, 25 mg. (0.05 mmole) of dimethylsilanyl bis(indenyl) hafnium dimethyl was dissolved in 3 ml. of toluene and then activated with 40 mg. (0.05 mmole) of N,N- dimethyl anilinium tetrakis(pentafluorophenyl)boron. The activated catalyst solution was then cannulated into the reactor and agitated for 2 minutes before the monomer source was opened to the reactor. The reaction was run for 10 minutes and the monomer source was closed. At the end of the 10 minutes, the excess of monomer mixture in the reactor was discharged and the polymer made was recovered in a chilled methanol. The polymer was dried in a vacuum oven set at 40°C. After it was dried, the polymer weighted 56 g. Fourier Transform Infrared Spectroscopy (FTIR analysis) indicated the polymer contains 16 weight percent ethylene. Gel Permeation Chromatography (GPC analysis) indicated Mw = 115,000 and Mn = 59,000.

All the compositions of Examples Cl, C2, 3, and 4 were prepared using a Banbury mixer. The composition components were combined in a single step, and the combination was melt homogenized in the Banbury mixer at 200 °C. Each composition contained a standard package of nucleating and stabilizing agents, as follows: 2,000 ppm sodium benzoate, 400 ppm magnesium aluminum hydroxy carbonate (such as DHT4A, which is commercially available from Kyowa Chemical, Ltd. (Japan); 500 ppm tris (4-t-butyl-3-hydroxy-2,6-dimethyl)- s-triazine-2,4,6-(lH, 3H, 5H)-trione (such as Cyanox® 1790, which is commercially available from Cytec Industries, Inc. (Cyanox is a registered trademark of the American Cyanamid Company)); and 500 ppm bis (2,4-di-t- butylphenyl) pentaerythritol diphosphite (such as Ultranox® 626, which is commercially available from GE Specialty Chemicals, Inc. (Ultranox is a registered trademark of GE Specialty Chemicals, Inc.)). Compression molded disks for the Gardner impact tests were then prepared with the melt homogenized compositions, and injection molded bars (by the lab scale Butler injection machine) were also prepared for the Izod, HDT and the flexural modulus tests. The mixing recipe for each composition and the corresponding test results are set forth in Table 1.

Table 1.

Comparative Examples C4-C8 and Example 9

In comparative examples C4-C8 and Example 9, Component (A) was a high MFR i-PP homopolymer having an MFR of 83 g/lOmin. The high flow i-PP was prepared using a titanium catalyst available from Toho Titanium Co., Ltd. (Japan) and having the commercial designation Toho 30 lC. The polymerization was conducted in a bulk propylene polymerization reactor using methods well known in the art.

Component (D), the EPC, reference number 20439- 18, was also prepared using Toho 301C catalyst as follows: a 5-liter gas mixing tank was used to prepared an Initial Monomer Mixture (IMM) which contains 9 mole percent ethylene and 90 mole percent propylene. Another 5-liter tank was also used to prepare a Make-up Monomer Mixture (MMM) which contained 22 mole percent ethylene and 78 mole percent propylene. The polymerization was conducted in a 2-liter autoclave reactor. The reactor was charged with 1 liter of hexene. In a separate vial, 1.5 mmole of triethyl aluminum, 0.15 mmole of tetraethoxy silane, and 0.15 mmole of dicyclopentyl dimethoxy silane was mixed into 5 ml. of hexane and then the solution was cannulated into the reactor and stirred for 2 minutes. 5 psi of hydrogen was charged into the reactor and then the reactor was heated to 70°C. The IMM was then opened to the reactor and controlled to 80 psi under agitation. 0.01 gm of prepolymerized TOHO 301C catalyst in mineral oil was charged into the reactor with 250 ml. of hexane under pressure. The IMM was closed and MMM was opened to the reactor and controlled to the same 80 psi and let it reacted for 2 hours. At the end of 2 hours, the excess of monomer was vented and the polymer solution was poured into chilled methanol to recover the polymer. After dried in an vacuum oven set at 50°C, the polymer weighed 90 gm, and C-13 nmr analysis indicated 27 wt.% ethylene. The intrinsic viscosity measured in decalin at 135°C was 2.8 dl/g, and GPC analysis indicated Mw = 197,000 and Mn = 50,000. Component (B) was also prepared with Toho 301C catalyst using the polymerization procedure described above for Component (D), except that the concentrations of monomers were adjusted to give an EPR having an ethylene content of 37 weight percent. The intrinsic viscosity measured in decalin at 135 °C was 5.0 dl/g.

Component (C) was the same HDPE employed in comparative examples Cl and C2 and examples 3 and 4 above.

In all of the examples C4-C8 and Example 9, all of the components set forth in Table 2 for each example were first dissolved in hot xylene, and the standard additive package described above in examples Cl, C2, 3, and 4 was added to the hot xylene solutions. The compositions were then isolated from their respective solutions by precipitation in cold methanol, and each was then placed in a Brabender mixer and melt homogenized by mixing at 200 °C. Each of the melt homogenized compositions was then molded and tested as described in examples Cl, C2, 3, and 4. The recipes and test results for each composition are set forth in Table 2.

Comparative examples C4-C7 show that prior art approaches to simultaneously improve the low temperature Gardner impact resistance and stiffness, when applied to high MFR ICP's, are not effective. While replacement of EPR with HDPE does improve stiffness, Gardner impact strength at -29 °C and Izod impact strength are not improved, or are actually worsened. In contrast,

Example 9 shows that by employing the composition of the present invention, i.e., by replacing some of the EPR/HDPE mixture with EPC, the low temperature Gardner impact strength and stiffness of the high MFR ICP can surprisingly be simultaneously improved. These findings are completely unexpected based on the teachings of the prior art. Table 2,

Claims

I claim:

1. An impact polypropylene composition, comprising:

(A) an isotactic polypropylene;

(B) an ethylene-propylene rubber;

(C) a high density polyethylene; and

(D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene.

2. An impact polypropylene composition comprising:

(A) isotactic polypropylene;

(B) ethylene-propylene rubber;

(C) high density polyethylene; and (D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene, wherein the amount of (A) is about 60 to about 90 percent by weight of the combined weight of (A), (B), (C), and (D), the amount of (B) is about 8 to about 35 percent by weight of the combined weight of (A), (B), (C), and (D), the weight ratio of (C) to

(B) is in the range of 0.1 to 0.95, and the amount of (D) is about 1 to about 20 percent by weight of the combined weight of (A), (B), (C), and (D).

3. The composition according to claims 1 or 2 wherein (A) has an MFR of from about 20 to about 200 g/10 min.

4. The composition according to claims 1 or 2 wherein (A) has an MFR of from about 80 to about 200 g/10 min.

5. The composition according to claims 1 or 2 wherein (B) has a polymerized ethylene content of from about 35 to about 70 percent by weight.

6. The composition according to claims 1 or 2 wherein (D) has a weight average molecular weight in the range of from about 100,000 to about 200,000.

7. The composition according to claims 1 or 2 wherein said ethylene- propylene copolymer has a polydispersity of from about 2 to about 5.5.

8. The composition according to claims 1 or 2 wherein said ethylene- propylene copolymer has a polydispersity of from about 2 to about 2.5.

9. The composition according to claims 1 or 2 wherein said composition exhibits an MFR greater than about 25 g/10 min.

10. A masterbatch composition for the production of impact resistance polypropylene comprising:

(B) ethylene-propylene rubber;

(C) high density polyethylene; and (D) an ethylene-propylene copolymer, said ethylene-propylene copolymer comprising from about 10 to about 30 weight percent polymerized ethylene and from about 90 to about 70 weight percent polymerized propylene, wherein the amount of (B) is about 50 percent to about 90 percent by weight of the combined weight of (B), (C), and (D); the weight ratio of (C) to (B) is in the range of 0.1 to 0.95; and the amount of (D) is about 1 to about 45 percent by weight of the combined weight of (B), (C), and (D).