Propylene-based terpolymers for films

Abstract

A terpolymer containing propylene, ethylene and an alpha olefins of formula CH2=CHZ wherein Z is an hydrocarbon group having from 2 to 10 carbon atoms wherein: (i) the content of ethylene derived units ranges from 0.5 wt % to 5.0 wt %; (ii) the content of alpha olefin derived units ranges from 1.0 wt % to 5.0 wt %; (iii) the area of the DSC curve after the peak of the melting point (Tm) represents more than 22%; of the total area of the DSC curve; (iv) the polydispersity index (PI) ranges from 2.0 to 7.0.

Claims

1. A film comprising a propylene, ethylene and 1-hexene terpolymer comprising: (i) an ethylene content of 1.0-3.0 wt %; (ii) a 1-hexene content of 2.0-4.0 wt %; (iii) an area of a differential scanning calorimetry (DSC) curve after the peak of the melting point (T.sub.m) of greater than about 22% of the total area of the DSC curve; and (iv) a polydispersity index (PI) of 2.0-7.0; wherein the film comprises a melt flow rate (ISO 1133, 230° C., 2.16 kg) of no greater than 6.3 g/10 min and a haze value as measured on a 50 μm cast film of no greater than 0.4%.

2. The film of claim 1, wherein the area of the DSC curve after the peak of the melting point (Tm) comprises greater than 25% of the total area of the DSC curve.

3. The film of claim 1, wherein the area of the DSC curve between the peak of the melting point (Tm) and Tm+5° C. is lower than 19% of the total area of the DSC curve.

4. The film of claim 1, wherein the amount (Wt %) of alpha-olefin (C.sub.6), the amount (Wt %) of ethylene (C.sub.2) and the melting point (T.sub.m) of the terpolymer fulfill the following relationship (1):
Tm>157−(C.sub.2+0.8C.sub.6)*6[[+157]]  (1).

5. The film of claim 1, having a seal initiation temperature (SIT) ranging from 90-120° C.

6. The film of claim 1, having the crystallization temperature ranging from 70-100° C.

7. The film of claim 1, wherein the film is a biaxially oriented film (BOPP).

Description

EXAMPLES

(1) The following examples are given to illustrate the present invention without limiting purpose.

(2) Characterization Methods

(3) Melting temperature, crystallization temperature and partial area percentage determination: Determined by differential scanning calorimetry (DSC). A sample weighting 6±1 mg, is heated to 220±1° C. at a rate of 20° C./min and kept at 220±1° C. for 2 minutes in nitrogen stream and it is thereafter cooled at a rate of 20° C./min to 40 ±2° C., thereby kept at this temperature for 2 min to crystallise the sample. Then, the sample is again fused at a temperature rise rate of 20° C./min up to 220° C.±1. The melting scan is recorded, a thermogram is obtained, and, from this, melting temperatures and crystallization temperatures are read.

(4) For partial area calculation the same melting peak considered for Tm calculation is used.

(5) A baseline to the peak is built by joining the peak initiation and end temperatures at which the endothermic peak begins and ends to deviate from the relatively straight baseline.

(6) Partial area is calculated by taking as starting point the Tm temperature and as end point the peak end temperature.

(7) Results are expressed in percentage of total area.

(8) Melt Flow Rate: Determined according to the method ISO 1133 (230° C., 2.16 kg).

(9) Solubility in xylene: Determined as follows.

(10) 2.5 g of polymer and 250 ml of xylene are introduced in a glass flask equipped with a refrigerator and a magnetical stirrer. The temperature is raised in 30 minutes at 135° C. The so obtained clear solution is then kept under reflux and stirring for further 30 minutes. The closed flask is kept in thermostatic water bath at 25° C. for 30 minutes. The so formed solid is filtered on quick filtering paper. 100 ml of the filtered liquid is poured in a previously weighed aluminium container, which is heated on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 70° C. under vacuum until constant weight is obtained. The weight percentage of polymer soluble in xylene at room temperature is then calculated.

(11) 1-hexene and ethylene content: Determined by .sup.13C-NMR spectroscopy in terpolymers:

(12) NMR analysis. .sup.13C NMR spectra are acquired on an AV-600 spectrometer operating at 150.91 MHz in the Fourier transform mode at 120° C. The peak of the propylene CH was used as internal reference at 28.83. The .sup.13C NMR spectrum is acquired using the following parameters:

(13) TABLE-US-00001 Spectral width (SW) 60 ppm Spectrum centre (O1) 30 ppm Decoupling sequence WALTZ 65_64pl Pulse program .sup.(1) ZGPG Pulse Length (P1) .sup.(2)\ for 90° Total number of points (TD) 32K Relaxation Delay .sup.(2) 15 s Number of transients .sup.(3) 1500

(14) The total amount of 1-hexene and ethylene as molar percent is calculated from diad using the following relations:
[P]=PP+0.5PH+0.5PE
[H]=HH+0.5PH
[E]=EE+0.5PE

(15) Assignments of the .sup.13C NMR spectrum of propylene/1-hexene/ethylene copolymers have been calculated according to the following table:

(16) TABLE-US-00002 Area Chemical Shift Assignments Sequence 1 46.93-46.00 S.sub.αα PP 2 44.50-43.82 S.sub.αα PH 3 41.34-4.23  S.sub.αα HH 4 38.00-37.40 S.sub.αγ + S.sub.αδ PE 5 35.70-35.0  4B.sub.4 H 6 35.00-34.53 S.sub.αγ + S.sub.αδ HE 7 33.75 33.20 CH H 8 33.24 T.sub.δδ EPE 9 30.92 T.sub.βδ PPE 10 30.76 S.sub.γγ XEEX 11 30.35 S.sub.γδ XEEE 12 29.95 S.sub.δδ EEE 13 29.35 3B.sub.4 H 14 28.94-28.38 CH P 15 27.43-27.27 S.sub.βδ XEE 16 24.67-24.53 S.sub.ββ XEX 17 23.44-23.35 2B.sub.4 H 18 21.80-19.90 CH.sub.3 P 19 14.22 CH.sub.3 H

(17) Polydispersity Index (PI): Determined at a temperature of 200° C. by using a parallel plates rheometer model RMS-800 marketed by RHEOMETRICS (USA), operating at an oscillation frequency which increases from 0.1 rad/sec to 100 rad/sec. From the crossover modulus one can derive the P.I. by way of the equation:
P.I.=10.sup.5/Gc
in which Gc is the crossover modulus which is defined as the value (expressed in Pa) at which G′=G″ wherein G′ is the storage modulus and G″ is the loss modulus.

(18) Seal Initiation Temperature (SIT)

(19) Preparation of the Film Specimens

(20) Some films with a thickness of 50 μm are prepared by extruding each test composition ina a single screw Collin extruder (length/diameter ratio of screw 1:25) at a film drawing speed of 7 m/min and a melt temperature do 210-250° C. Each resulting film is superimposed on a 1000 μm thick film of a propylene homopolymer having a xylene insoluble fraction of 97 wt % and a MFR L of 2 g/10 min. The superimposed films are bonded to each other in a Carver press at 200° C. under a 9000 kg load, which is maintained for 5 minutes. The resulting laminates are stretched longitudinally and transversally, i.e. biaxially, by a factor 6 with a TOM Long film stretcher at 150° C., thus obtaining a 20 μm thick film (18 μm homopolymer+2 μm test).

(21) 2×5 cm specimens are cut from the films.

(22) Determination of the SIT

(23) For each test two of the above specimens are superimposed in alignment, the adjacent layers being layers of the particular test composition. The superimposed specimens are sealed along one of the 2 cm sides with a Brugger Feinmechanik Sealer, model HSG-ETK 745. Sealing time is 5 seconds at a pressure of 0.1 N/mm.sup.2 The sealing temperature is increased of 2° C. for each seal, starting from about 10° C. less than the melting temperature of the test composition. The sealed samples are left to cool and then their unsealed ends are attached to an Instron machine where they are tested at a traction speed of 50 mm/min.

(24) The SIT. is the minimum sealing temperature at which the seal does not break when a load of at least 2 Newtons is applied in the said test conditions.

(25) Haze on Film

(26) Determined on 50 μm thick cast films of the test composition. The measurement was carried out on a 50×50 mm portion cut from the central zone of the film.

(27) The instrument used for the test was a Gardner photometer with Haze-meter UX-10 equipped with a G.E. 1209 lamp and filter C. The instrument calibration was made by carrying out a measurement in the absence of the sample (0% Haze) and a measurement with intercepted light beam (100% Haze).

(28) Gloss on Film

(29) Determined on the same specimens as for the Haze.

(30) The instrument used for the test was a model 1020 Zehntner photometer for incident measurements. The calibration was made by carrying out a measurement at incidence angle of 60° on black glass having a standard Gloss of 96.2% and a measurement at an incidence angle of 45° on black glass having a standard Gloss of 55.4%.

Example 1 and Comparative Example 2

(31) A copolymer is prepared by polymerising propylene, ethylene and hexene-1 in the presence of a catalyst under continuous conditions in a plant comprising a polymerisation apparatus as described in EP 1 012 195.

(32) The catalyst is sent to the polymerisation apparatus that comprises two interconnected cylindrical reactors, riser and downcomer. Fast fluidisation conditions are established in the riser by recycling gas from the gas-solid separator.

(33) In examples 1 the gas composition in the two reactor legs has been differentiated by using the “barrier” feed according to what described in EP 1 012 195. This stream is propylene fed in the larger upper part of the downcomer. In comparative example 2 the barrier feed has not been used.

(34) The catalyst employed comprises a catalyst component prepared by analogy with example 5 of EP-A-728 769 but using microspheroidal MgCl.sub.2.Math.1.7C.sub.2H.sub.5OH instead of MgCl.sub.2.Math.2.1C.sub.2H.sub.5OH. Such catalyst component is used with dicyclopentyl dimethoxy silane (DCPMS) as external donor and with triethylaluminium (TEA).

(35) The polymer particles exiting the reactor are subjected to a steam treatment to remove the reactive monomers and volatile substances and then dried. The main operative conditions are indicated in Table 1. The characteristics of the produced polymers are indicated in Table 3.

(36) TABLE-US-00003 TABLE 1 Examples 1 2* TEA/solid catalyst 10 5 component, g/g TEA/DCPMS, g/g 4 4 C.sub.6/(C.sub.3 + C.sub.6), mol/mol Riser 0.039 0.034 C.sub.6/(C.sub.3 + C.sub.6), mol/mol Downcomer 0.084 0.034 C.sub.2/(C.sub.3 + C.sub.2), mol/mol Riser 0.02 0.015 C.sub.2/(C.sub.3 + C.sub.2), Downcomer 0.006 0.015 mol/mol C2 ethylene; C3 propylene; C6 1-hexene *comparative

(37) The Examples haven been added to additives and peroxides according to table 2. Then the polymer mixture is placed in a twin screw extruder Berstorff (L/D=33) and extruded in the following operating conditions: temperature of feeding part: 190-210° C.; melt temperature: 235-245° C.; temperature of die part: 210° C.; flow rate: 15 kg/h; rotational speed of the screw: 250 rpm.

(38) TABLE-US-00004 TABLE 2 examples 1 2* Irganox 1010 wt % 0.05 0.05 Calcium stearate wt % 0.05 0.05 Irgafos 168 wt % 0.1 0.1 Luperox 101 wt % 0.027 0.025 *Comparative

(39) Preparation of BOPP Film:

(40) From pellet samples of the obtained polypropylenes, several plaques 950 nm to 1050 nm thick with size 60 mm×60 mm were obtained via compression moulding. By a film stretcher kept at 150±5° C. 5 specimen with the listed dimensions were simultaneously oriented at a fixed stretch ratio of 7 times in machine direction and 7 times in transverse machine direction. Final film thickness of the biaxially oriented film is around 20 nm.

(41) TABLE-US-00005 TABLE 3 Example 1 2* MFR g/10 min 6.3 6.4 C6 NMR % 3.4 2.8 C2 NMR % 1.9 1.5 PI 4.2 4 XS % 12 8 Tm ° C. 134.5 134.1 Tc ° C. 88.3 91.3 SIT on BOPP ° C. 105 112 Haze on film % 0.4 1 Area of the DSC after the % 28 19 melting point (Tm) Area of the DSC between the % 12 12 melting point (Tm) and Tm + 5° C. C2 ethylene; C3 propylene; C6 1-hexene; XS xylene solubles *comparative

(42) The terpolymer of comparative example 2 has the same melting point of the terpolymer of example 1 but different comonomers content. The Area of the DSC after the melting point (Tm) is lower than 22% and even in this case the sit of the terpolymers of the invention is considerably lower.

(43) To the terpolymer of example 1, 0.25 wt % of NX8500e (a clarifying agent of Millichen) has been added. And a blow molded bottle has been produced. The haze, top load and Izod at 4° C. has been measured on the bottle giving respectively 14%; 381 kJ/m.sup.2 and 83 kJ/m.sup.2