Polypropylene impact copolymers with low haze

Abstract

The present invention provides an in-reactor solution that avoids costly blending and the use of metallocene elastomers. The inventive Ziegler-Natta polypropylene composition also includes additional components that may improve properties relative to a metallocene catalyzed elastomers. The invention is a clear impact polypropylene composition that is made in-reactor with Ziegler-Natta catalyst, and is suitable for a wide range of processes. Unlike other clear impact copolymers, it does not rely on high-shear processes or compounding with elastomers. The invention uses conventional polypropylene reactor technology to produce these compositions.

Claims

1. A propylene impact copolymer comprising: (a) a matrix comprising a polypropylene homopolymer or a propylene/alpha-olefin random copolymer which comprises more than 50 wt. % of units derived from propylene monomer; and (b) a dispersed phase comprising an ethylene-propylene copolymer, wherein the dispersed phase has a melting point between 100 C. and 124 C., and an enthalpy greater than 11 J/g, the dispersed phase having a molar ratio of ethylene moiety/(ethylene moiety plus propylene moiety) greater than 0.82, wherein the propylene impact copolymer has a haze value less than 30% in a 50 mil plaque, and a haze value less than 15% in a 20 mil plaque.

2. The propylene impact copolymer of claim 1, having a Gardner impact value greater than 200 in-lbs.

3. The propylene impact copolymer of claim 1, catalyzed with a Ziegler-Natta catalyst.

4. The propylene impact copolymer of claim 1, having 10 wt. % or less xylene solubles.

5. A manufactured article comprising (a) a matrix comprising a polypropylene homopolymer or a propylene/alpha-olefin random copolymer which comprises more than 50 wt. % of units derived from propylene monomer; and (b) a dispersed phase comprising an ethylene-propylene copolymer, wherein the dispersed phase has a melting point between 100 C. and 124 C., and an enthalpy greater than 11 J/g, the dispersed phase having a molar ratio of ethylene moiety/(ethylene moiety plus propylene moiety) greater than 0.82, wherein the manufactured article has a haze value less than 30% in a 50 mil plaque, and a haze value less than 15% in a 20 mil plaque.

6. The manufactured article of claim 5, catalyzed with a Ziegler-Natta catalyst.

7. The manufactured article of claim 5 is a thermoformed container.

8. The manufactured article of claim 5 is a blow molded container.

9. The manufactured article of claim 5 is an injection molded container.

10. A process to produce a propylene impact copolymer comprising the steps of: (a) one or more matrix phase polymerization steps, occurring in one or more liquid phase reactors; (b) one or more dispersed phase polymerization steps, occurring in one or more gas phase reactors; and (c) at least one de-gassing step, the propylene impact copolymer comprising: (1) a matrix comprising a polypropylene homopolymer or a propylene/alpha-olefin random copolymer which comprises more than 50 wt.% of units derived from propylene monomer; and (2) a dispersed phase comprising an ethylene-propylene copolymer, wherein the dispersed phase has a melting point between 100 C. and 124 C., and an enthalpy greater than 11 J/g, the dispersed phase having a molar ratio of ethylene moiety/(ethylene moiety plus propylene moiety) greater than 0.82, wherein the propylene impact copolymer has a haze value less than 30% in a 50 mil plaque, and a haze value less than 15% in a 20 mil plaque.

11. The propylene impact copolymer produced by the process of claim 10, having a Gardner impact value greater than 200 in-lbs.

12. The propylene impact copolymer produced by the process of claim 10, catalyzed with a Ziegler-Natta catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts haze values as a function of the molar gas phase ratio.

(2) FIG. 2 depicts haze values of inventive and comparative examples.

(3) FIG. 3 depicts flexural modulus values of inventive and comparative examples.

(4) FIG. 4 depicts Gardner impact values of inventive and comparative examples.

(5) FIG. 5 depicts melt values of inventive and comparative examples.

(6) FIG. 6 depicts melt values of inventive and comparative examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) For purposes of the description hereinafter, it is to be understood that the embodiments described herein may assume alternative variations and embodiments. It is also to be understood that the specific articles, compositions, and/or processes described herein are exemplary and should not be considered as limiting.

(8) As used herein, haze generally refers to an appearance cause by scattered light upon passing through a film or sheet of a material that can produce a smoky or translucent field. The haze of the present invention is measured using ASTM D1003-97, wherein haze plaques were molded at two thicknesses: 50 and 20 mil.

(9) As used herein, clarity generally refers to the amount of luminous transmittance described according to and measured per ASTM D1003 on a 20 mil plaque.

(10) As used herein, flexural modulus (expressed in units of PSI) is the one percent secant modulus, which is further described according to and measured per ASTM D790 at 230 C.

(11) As used herein, the melt flow rate (MFR; units of g/10 min or dg/min) is described according to and measured per ASTM D1238 using a load of 2.16 kg at 230 C.

(12) As used herein, notched Izod impact strength (expressed in ft-lbs/in) was measured at 23 C. as described according to and measured per ASTM D256.

(13) As used herein, Gardner Impact was measured at 0, 4, and 23 C. according to ASTM D5420-10 in the GC configuration. It is expressed in in-lbs.

(14) As used herein, molar phase gas ratio (or molar gas ratio) refers to the quantity of ethylene in a dispersed phase polymerization step and, thus, the dispersed phase. It is defined by the equation:
Molar Gas Ratio=mol C2/(mol C2+mol C3)
where C2 is ethylene, and C3 is propylene.

(15) As used herein, differential scanning calorimetry (or DSC) describes a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. About 5 to 10 mg of a sheet of the polymer pressed at approximately 200 C. is removed with a punch die and placed in a light aluminum pan (about 50 mg) and crimped shut. The thermal behavior was investigated using the following profile: The samples were heated to 200 C. and held isothermal for 3 minutes in order to remove any previous thermal history. The cooling and second heating curves were recorded in the temperature range of 20 C. to 200 C. using a scan rate of 10 C./min.

(16) Catalysts employed in the polymerization of -olefins may be characterized as supported catalysts or unsupported catalysts, sometimes referred to as homogeneous catalysts. The so-called conventional Ziegler-Natta catalysts are stereospecific complexes formed from a transition metal halide and a metal alkyl or hydride, such as titanium tetrachloride supported on an active magnesium dichloride. A supported catalyst component includes, but is not necessarily limited to, titanium tetrachloride supported on an active anhydrous magnesium dihalide, such as magnesium dichloride or magnesium dibromide. A supported catalyst component may be employed in conjunction with a co-catalyst such as an alkylaluminum compound, for example, triethylaluminum (TEAL). The Ziegler-Natta catalysts may also incorporate an electron donor compound that may take the form of various amines, phosphenes, esters, aldehydes, and alcohols.

(17) Single site catalyzed polyolefins can differ from Ziegler-Natta catalyzed polyolefins in terms of molecular structure, particularly molecular weight and co-monomer distribution. The single site catalysts, such as metallocene catalysts, can create polyolefins with a narrow molecular weight distribution.

(18) Metallocene catalysts are coordination compounds or cyclopentadienyl groups coordinated with transition metals through i-bonding. Metallocene catalysts are often employed as unsupported or homogeneous catalysts, although they also may be employed in supported catalyst components. With respect to the metallocene random copolymers, this term denotes polymers obtained by copolymerizing ethylene and an -olefin, such as propylene, butene, hexene or octene, in the presence of a monosite catalyst generally consisting of an atom of a metal which may, for example, be zirconium or titanium, and of two cyclic alkyl molecules bonded to the metal. More specifically, the metallocene catalysts are usually composed of two cyclopentadiene-type rings bonded to the metal.

(19) The impact modifying components in this composition were made using a heterogeneous Ziegler-Natta catalyst. Therefore, it is expected that several compositions exist in the impact modifying component.

(20) It was unexpected that ZN-catalyzed PP would produce a dispersed phase component that avoids significant haze in the final composition. The present invention prefers high ethylene content to achieve a product having both high impact resistance and low haze. Examples with comparisons are found in the attached Tables 1-4 and FIGS. 1-6.

(21) TABLE-US-00001 TABLE 1 wt. % C2 External C2/(C2 + C3) (Tot- Example Type Process Catalyst Donor molar MFR IR) Haze (20 mil) Haze (50 mil) 1 Comparative Lab Pilot Plant ZN-118 P 0.82 8.8 20.8 99 n/a 2 Comparative Lab Pilot Plant ZN-118 D 0.43 11.3 7.5 99 n/a 3 Comparative Lab Pilot Plant ZN-118 D 0.55 8.9 13.1 99 n/a 4 Comparative Lab Pilot Plant ZN-118 D 0.65 4.9 16.3 99 n/a 5 Comparative Lab Pilot Plant ZN-118 D 0.75 2.7 22.2 99 n/a 6 Comparative Lab Pilot Plant ZN-118 D 0.82 2.7 23.5 99 n/a 7 Comparative Lab Pilot Plant ZN-118 D 0.85 3.8 17.1 80 n/a 8 Inventive Lab Pilot Plant ZN-118 D 0.88 2.8 22.2 <20 n/a 9 Inventive Lab Pilot Plant ZN-118 D 0.90 n/m 9.3 11 n/a 10 Inventive Lab Pilot Plant ZN-118 D 0.90 3.1 20.4 14 n/a 13 Inventive Lab Pilot Plant ZN-118 D 0.92 3.0 20.5 10 n/a 14 Inventive Lab Pilot Plant ZN-118 D 0.95 0.5 29.2 20 n/a

(22) TABLE-US-00002 TABLE 2 ASTM ASTM D1003 Molar Gas D1003 Haze, Clarity, 20 mil First DSC Second DSC DMTA PP DMTA PE Ratio 20 mil plaque Melting Melting Transition Transition Sample C.sub.2/(C.sub.2 + C.sub.3) plaque (%) (%) Point ( C.) Point (Peak, C.) (Peak, C.) Example 2 0.43 99.50 31.00 n/a 165.00 8.00 54.00 Example 3 0.55 99.00 16.00 119.00 165.00 7.00 54.00 Example 4 0.65 98.00 10.00 119.00 165.00 9.00 53.00 Example 5 0.75 96.00 13.00 119.00 165,00 8.00 50.00 Example 6 0.82 80.00 47.00 119.00 165.00 7.00 45.00 Inventive 0.90 11.00 93.00 119.00 165.00 10.00 Absent Example 9 Comparative Example 18 12.00 92.00 99.00 165.00 10.00 Absent Example 18

(23) TABLE-US-00003 TABLE 3 wt. % C2/(C2 + C2 External C3) (Tot- Qualitative Haze Haze Example Type Process Catalyst Donor molar MFR IR) Optics (20 mil) (50 mil) 15 Inventive SPHERIPOL Pilot Plant ZN-111 D 0.90 1.6 24 Clear 12 30 16 Inventive SPHERIPOL Commercial ZN-118 D 0.90 2 18 Clear 10 26 Plant

(24) TABLE-US-00004 TABLE 4 Dis- Flexural Notched persed Modulus Izod Notched DTU Haze, 4 C. Phase MFR (1% (23 C., Izod Rockwell L at 60 50 mil Gardner Exam- Content (dg/ secant, ft-lbs/ Break Hardness 66 psi Gloss disk Impact ple Type Material Description (%) min) psi) in) Type (R Scale) ( C.) (%) (%) (in-lbs) 16 Inventive Inventive In-Reactor 20 2.0 141,000 8 Non- 82 70 87 26 207 Example 16 ICP break 17 Com- D334 Compounded 20 2.0 138,000 11 Non- 82 83 93 18 227 parative Formulation break 18 Com- INSPIRE Compounded 20 2.0 218,000 10 Non- 98 111 90 23 246 parative 117 Formulation break 19 Com- TI4020 In-Reactor 20 2.0 180,000 10 Non- 82 n/a 90 100 200 parative ICP break 20 Com- FT021N Homopolymer 0 2.0 230,000 0.6 Complete n/a n/a 90 25 10 parative Break

(25) As shown in FIG. 1, an inventive ZN-catalyzed PP can demonstrate a substantial reduction in haze when the molar gas ratio is in excess of 0.82.

(26) As shown in FIGS. 2-4, the physical properties of the inventive compositions are comparable or superior to other compositions known in the art, without any additional compounding step or the addition of metallocene elastomers.

(27) As shown in FIGS. 5 and 6, one major physical property difference between the inventive sample and the compounded compositions (e.g., Comparative 18) is the first DSC melting point of the inventive samples is 119 C. whereas the compounded compositions have a first melting point of 99 C.

(28) In an embodiment of the invention, it is hypothesized that this invention is clear despite the heterogeneity in the impact modifying component, because that component has an average refractive index of approximately 1.50, which is similar to that of polypropylene. Dispersed phases are able to allow light to pass through articles made from this material with only limited loss due to diffraction.

(29) In an embodiment of the invention, the propylene impact copolymer may be made using one or more matrix phase polymerization steps, occurring in one or more gas phase reactors; one or more dispersed phase polymerization steps, occurring in one or more liquid phase reactors; and at least one de-gassing step.

(30) Thus, the inventors have achieved an improved and commercially practicable method of producing a high C2 content in-reactor grade in liquid monomer slurry.

(31) In contrast, U.S. Pat. No. 6,015,854 teaches that without gas phase technology, the preparation of the materials of its invention would not be practicable commercially, because of the large amounts of propylene monomer present in the bulk or liquid monomer slurry process; that monomer must be removed to achieve the desired high ethylene contents in the reaction product in the second reactor. With a diluent process, propylene would be dissolved in the diluent within the first reactor, and portions of the diluent would have to be removed to purge the system of much of the propylene prior to the introduction of the first stage polymer and catalyst species into the second reactor (see U.S. Pat. No. 6,015,854 at column 5, lines 38-48).

(32) Using TA analytical software, a baseline was drawn on the second heating curve. The baseline extended from 20 C. to 170 C. Perpendicular lines (called perpendicular drops in the TA software) were placed at 110 C. and 130 C. and were used as integration limits. The integration limits were placed at 20 C., 130 C., 110 C., 115 C. and 170 C. Integrations were performed to obtain three distinct areas. Area 1 is defined as the area under the DSC curve (enthalpy of melting) between 110 C. and 130 C. Area 2 is defined as the area under the DSC curve (enthalpy of melting) between 115 C. and 130 C. Area 3 is the area between 120 C. and 130 C. Further results are shown in Table 5, below.

(33) TABLE-US-00005 TABLE 5 Integration Integration Integration Limits: Limits: Limits: Xylene First Second 110 to 130 115 to 130 120 to 130 Total Solubles Melting Melting Area 1 Area 2 Area 3 Area X Area Y Area Z Area i Area j Area k Area Matrix Type (%) Peak Peak (J/g) (J/g) (J/g) (J/g) (J/g) (J/g) (J/g) (J/g) (J/g) (J/g) Homopolymer Matrix (Matrix contains about 0% ethylene) hpp Inventive 2.0 122.0 165.0 14.6 13.4 81.9 17.7 11.3 83.1 21.9 7.1 83.1 112.0 matrix hpp Inventive 2.0 122.0 165.0 18.8 17.6 79.1 22.6 14.6 80.1 27.5 9.7 80.1 117.4 matrix hpp Comparative 10.5 120.0 165.0 11.5 11.2 74.4 15.3 10.0 76.8 18.9 6.4 76.8 102.1 matrix Low Blush hpp Comparative 13.0 118.0 165.0 5.1 5.5 76.1 7.1 4.6 77.1 8.8 2.9 77.1 88.8 matrix Standard Impact Random Copolymer Matrix (Matrix contains about 2% ethylene) RCP Inventive 6.9 125.0 152.0 19.5 23.3 56.3 24.2 20.5 56.6 29.0 15.8 56.6 101.4 matrix RCP Comparative 3.7 98.4 152.0 22.6 14.7 55.0 25.2 12.7 55.7 28.4 9.6 55.7 93.7 matrix Metallocene Blend

(34) While the present invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications, which are within the true spirit and scope of the present invention.