Polypropylene composition for tapes

Abstract

The invention relates to a polypropylene composition comprising a propylene homopolymer or propylene-ethylene copolymer having an ethylene content of at most 1.0 wt % based on the propylene-ethylene copolymer, wherein the amount of propylene homopolymer or propylene-ethylene copolymer is at least 98 wt %, for example at least 98.5 wt %, preferably at least 99 wt %, more preferably at least 99.5, for example at least 99.75 wt % based on the polypropylene composition, wherein the polypropylene composition has a melt flow rate in the range of 0.70 to 2.4 dg/min as measured according to IS01 133 (2.16 kg/230° C.), an Mw/Mn in the range from 7.0 to 13.0, wherein Mw stands for the weight average molecular weight and Mn stands for the number average weight, an Mz/Mn is in the range from 20 to 50, wherein Mz stands for the z-average molecular weight and wherein Mw, Mn and Mz are measured according to ASTM D6474-12.

Claims

1. A tape prepared from a polypropylene composition comprising a propylene homopolymer or propylene-ethylene copolymer having an ethylene content of at most 1.0 wt % based on the propylene-ethylene copolymer, wherein an amount of propylene homopolymer or propylene-ethylene copolymer is at least 98 wt %, based on the polypropylene composition, wherein the polypropylene composition has a melt flow rate in the range of 0.70 to 2.4 dg/min as measured according to ISO1133 (2.16 kg/230° C.); an Mw/Mn in the range from 8.0 to 13.0, wherein Mw stands for the weight average molecular weight and Mn stands for the number average weight; and an Mz/Mn is in the range from 20 to 50, wherein Mz stands for the z-average molecular weight, and wherein Mw, Mn and Mz are measured according to ASTM D6474-12.

2. A process for the preparation of the tapes of claim 1 comprising the step of providing the polypropylene composition; and extruding the polypropylene composition.

3. The tape according to claim 1, wherein the tape is a strapping tape.

4. The tape according to claim 1, wherein the polypropylene composition has a melt flow rate in the range of 0.70 to 2.3 dg/min as measured according to ISO1133 (2.16 kg/230° C.).

5. The tape according to claim 1, wherein the polypropylene composition has an amount of xylene soluble amount (XS) as measured according to ASTM D 5492-10 in the range from 0.5 to 3.5 wt %.

6. The tape according to claim 1, wherein the polypropylene composition has a pentad isotacticity of at least 94% based on the composition, wherein the isotacticity is determined using .sup.13C NMR.

7. The tape according to claim 1, wherein the polypropylene composition has a MWD divided by the gelcount 500 of at least 0.9 wherein MWD is calculated by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn) and wherein Mw and Mn are measured according to ASTM D6474-12 and wherein the gelcount 500 stands for the gelcount of all particles having an equivalent diameter of at least 500 μm.

8. The tape according to claim 1, wherein the polypropylene composition is unimodal.

9. The tape according to claim 1, wherein the polypropylene composition further comprises additives, and wherein sum of the amount of additives and the amount of propylene homopolymer or propylene-ethylene copolymer is 100 wt % based on the polypropylene composition.

10. The tape according to claim 1, wherein the polypropylene composition has a flexural modulus in parallel orientation of at least 1800 MPa, as measured according to ASTM D790-10.

11. The tape according to claim 1, wherein the polypropylene composition has an Izod notched impact strength in parallel orientation of at least 2.5 kJ/m.sup.2 as measured at 23° C. according to ISO 180 4A.

12. The tape according to claim 1, wherein the polypropylene composition has an Mz/Mw is in the range from 2.7 to 4.5.

13. The tape according to claim 1, wherein the amount of propylene homopolymer or propylene-ethylene copolymer is at least 99.75 wt %, based on the polypropylene composition.

14. The tape according to claim 13, wherein the tape has a thickness of 20 microns to 100 microns.

15. The tape according to claim 1, wherein the polypropylene composition has an Mw/Mn in the range from 9.0 to 13.0.

Description

EXAMPLES

Example 1

(1) Step A) Butyl Grignard Formation

(2) A 1.7 L stirred flask, fitted with a reflux condenser and a funnel, was filled with magnesium powder (40.0 g, 1.65 mol). The flask was brought under nitrogen. The magnesium was dried at 80° C. for 2 hours under nitrogen purge, after which dibutyl ether (200 ml), iodine (0.05 g) and n-chlorobutane (10 ml) were successively added and stirred at 120 rpm. The temperature was maintained at 80° C. and a mixture of n-chlorobutane (146 ml) and dibutyl ether (1180 ml) was slowly added over 3 hours. The reaction mixture was stirred for another 3 hours at 80° C. Then the stirring and heating were stopped and the small amount of solid material was allowed to settle for 24 hours. By decanting the colourless solution above the precipitate, a solution of butylmagnesiumchloride with a concentration of 0.90 mol Mg/L was obtained.

(3) Step B) Preparation of the First Intermediate Reaction Product

(4) The solution of reaction product of step A (500 ml, 0.45 mol Mg) and 260 ml of a solution of tetraethoxysilane (TES) in dibutyl ether (DBE), (47 ml of TES and 213 ml of DBE), were cooled to 5° C., and then were fed simultaneously to a mixing device (minimixer) of 0.45 ml volume equipped with a stirrer and jacket. The minimixer was cooled to 5° C. by means of cold water circulating in the minimixer's jacket. The stirring speed in the minimixer was 1000 rpm. From the mixing device, the mixed components were directly dosed into a 1.3 liter reactor fitted with blade stirrer and containing 350 ml of dibutyl ether. The dosing temperature of the reactor was 35° C. and the dosing time was 360 min. The stirring speed in the reactor was 250 rpm at the beginning of dosing and was gradually increased up to 450 rpm at the end of dosing stage. On completion of the dosing, the reaction mixture was heated up to 60° C. in 30 minutes and held at this temperature for 1 hour. Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting. The solid substance was washed three times using with 700 ml of heptane at a reactor temperature of 50° C. for three times. A pale yellow solid substance, reaction product B (the solid first intermediate reaction product; the support), was obtained upon drying with a nitrogen purge. The average particle size of support was 20 microns.

(5) Step C) Preparation of the Second Intermediate Reaction Product

(6) In inert nitrogen atmosphere at 20° C. in a 1000 ml glass flask equipped with a mechanical agitator was filled with 50 g of reaction product B, dispersed in 500 ml of heptane and stirred at 250 rpm. Subsequently, a solution of 2.7 ml ethanol (EtOH/Mg=0.1) in 20 ml heptane was dosed under stirring during 1 hour. After keeping the reaction mixture at 20° C. for 30 minutes, a solution of 9.5 ml titanium tetraethoxide (TET/Mg=0.1) in 20 ml of heptane was added for 1 hour. The slurry was slowly allowed to warm up to 30° C. over 30 minutes and held at that temperature for another 2 hours. Finally, the supernatant liquid was decanted from the solid reaction product (the second intermediate reaction product C; first activated support) which was washed once with 500 ml of heptane at 30° C. and dried using a nitrogen purge.

(7) Step D) Preparation of the Third Intermediate Reaction Product

(8) In inert nitrogen atmosphere at 25° C. in a 1000 ml glass flask equipped with a mechanical agitator was filled with 50 g of second intermediate reaction product C dispersed in 500 ml of heptane and stirred at 250 rpm. Subsequently, a solution of 6.3 ml ethanol (EtOH/Mg=0.3), 20.8 ml of toluene and 37.5 ml of heptane was dosed at 25° C. under stirring during 1 hour. The slurry was slowly allowed to warm up to 30° C. over 30 minutes and held at that temperature for another 3 hours. Finally, the supernatant liquid was decanted from the solid reaction product (the third intermediate reaction product D; second activated support) which was washed once with 500 ml of heptane at 25° C. and dried using a nitrogen purge.

(9) Preparation of the Catalyst H

(10) Steps A-D) are carried out as in Example 1. Step E) is carried out as follows.

(11) A 300 ml reactor-filter flask was brought under nitrogen and 125 mL of titanium tetrachloride was added, then 5.5 g of second activated support in 15 ml of heptane was added to the reactor. The contents of the reactor were stirred for 60 minutes at room 25° C. Then, 1.78 ml of ethylbenzoate, EB (EB/Mg=0.30 molar ratio) in 4 ml of chlorobenzene was added to the reactor in 30 minutes. Temperature of reaction mixture was increased to 115° C. and then the reaction mixture was stirred at 115° C. for 90 minutes (I stage of catalyst preparation). The contents of the flask were filtered, after which the solid product was washed with chlorobenzene (125 ml) at 100 to 105° C. for 20 minutes. Then, the contents of the flask were filtered. A mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added to the reactor. The reaction mixture was stirred at 115° C. for 60 minutes (II stage of catalyst preparation). Then, the contents of the flask were filtered. A mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added to the reactor. Then, 0.51 g of 4-[benzoyl(methyl)amino]pentan-yl benzoate (AB/Mg=0.04) in 4 ml of chlorobenzene was added to the reactor in 10 minutes. The reaction mixture was stirred at 115° C. for 30 minutes (III stage of catalyst preparation). Then, the contents of the flask were filtered. A mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added to the reactor. The reaction mixture was stirred at 115° C. for 30 minutes (IV stage of catalyst preparation). Then, the contents of the flask were filtered. The solid product obtained was washed five times with 125 ml of heptane starting at 60° C. with 5 minutes stirring per wash prior to filtration. The temperature was gradually reduced from 60 to 25° C. during the washings. Finally, the solid product obtained was dried using a nitrogen purge at a temperature of 25° C. for 2 hours. The composition of the solid catalyst H produced is given in Table 1.

(12) TABLE-US-00001 TABLE 1 Composition of solid catalyst H d50 Mg Ti ID Activator (EB) EtO Catalyst Example [μm] [%] [%] [%] [%] [%] H 8 22.16 19.65 2.40 8.41 6.68 1.48

(13) Catalyst CE

(14) Catalyst CE is prepared according to the method disclosed in U.S. Pat. No. 4,866,022, hereby incorporated by reference. This patent discloses a catalyst component comprising a product obtained by: (a) forming a solution of a magnesium-containing species from a magnesium carbonate or a magnesium carboxylate; (b) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane having a formula: R.sub.nSiR′.sub.4-n, wherein n=0 to 4 and wherein R is hydrogen or an alkyl, a haloalkyl or aryl radical containing one to about ten carbon atoms or a halosilyl radical or haloalkylsilyl radical containing one to about eight carbon atoms, and R′ is OR or a halogen; (c) reprecipitating such solid particles from a mixture containing a cyclic ether; and (d) treating the reprecipitated particles with a transition metal compound and an electron donor. This process for preparing a catalyst is incorporated into the present application by reference.

(15) The process was performed in one horizontally stirred gas-phase reactor with downstream powder processing units (=degassing & catalyst deactivation) for powder collection.

(16) The reactor was operated at an average of 70° C. at 25 bar. H2/C3 ratios in both reactors were controlled such to obtain a powder having the desired melt flow rate (MFR).

(17) The catalyst was dosed through a nozzle to the reactor. Cocatalyst (triethylaluminium, TEN) and External Donor (DIPDMS or DiBDMS) were dosed via a separate nozzle to the reactor (as a premixed mixture) and in ratio to the catalyst flow.

(18) The process conditions as given in Table 2 were used:

(19) TABLE-US-00002 TABLE 2 Process conditions. Al/Mg Al/Si Si/Ti H.sub.2/C.sub.3 catalyst donor (mol/mol) (mol/mol) (mol/mol) (mol/mol) Example 1 H DiPDMS 4 7 8 0.009 Comparative CE DiBDMS 4 12 5 0.0008 example 1 (CE1) DiPDMS: di-(isopropyl)-dimethoxysilane DiBDMS: di(isobutyl)-dimethoxysilane

(20) The powder was collected and granulate was prepared by melt-mixing the powder with the appropriate additives in a single screw extruder. The additives (antioxidants, acid scavengers) were used in an amount of 1400 ppm based on the powder and mixed prior to dosing to the extruder. The temperature profile in the extruder was 20-20-30-50-100-170-220-220-240° C., at a throughput of 13 kg/h at 200 rpm.

(21) Methods

(22) All of the below properties were measured on the granulate.

(23) Mz, Mn, Mw

(24) Mw, Mn and Mz were all measured in accordance with ASTM D6474-12 (Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by High Temperature Gel Permeation Chromatography). Mw stands for the weight average molecular weight and Mn stands for the number average weight. Mz stands for the z-average molecular weight.

(25) In addition to the method specified by ASTM D6474-12, the method was performed using a configuration in which a Polymer Char IR5 infrared concentration detector and a Polymer Char online viscosity detector was used to gain ‘absolute’ or accurate molar masses. Three columns of Polymer Laboratories 13 μm PLgel Olexis, 300×7.5 mm were used in series with 1,2,4-trichlorobenzene stabilized with 1 g/L butylhydroxytoluene (also known as 2,6-di-tert-butyl-4-methylphenol or BHT) as eluens. The molar mass was determined based on a calibration using linear PE standards (narrow and broad (Mw/Mn=4 to 15)) in the range of 0.5-2800 kg/mol. Samples of polymer granules were mixed with Tris (2,4-di-tert-butylphenyl)phosphite (Irgafos 168) and 1,1,3-Tris (2-methyl-4-hydroxy-5-tert-butylphenyl)butane (Topanol CA) in a weight ratio sample:Irgafos:Topanol of 1:1:1, after which the mixture thus obtained was dissolved in 1,2,4-trichlorobenzene stabilized with 1 g/L BHT until the concentration of the mixture in 1,2,3-trichlorobenzene stabilized with 1 g/L BHT was 0.03 wt %.

(26) Xylene Solubles (XS) XS, wt % is xylene solubles, measured according to ASTM D 5492-10. 1 gram of polymer and 100 ml of xylene are introduced in a glass flask equipped with a magnetic stirrer. The temperature is raised up to the boiling point of the solvent. The so obtained clear solution is then kept under reflux and stirring for further 15 min. Heating is stopped and the isolating plate between heating and flask is removed. Cooling takes places with stirring for 5 min. The closed flask is then kept for 30 min in a thermostatic water bath at 25° C. for 30 min. The so formed solid is filtered on filtering paper. 25 ml of the filtered liquid is poured in a previously weighed aluminium container, which is heated in a stove of 140° C. for at least 2 hours, under nitrogen flow and vacuum, to remove the solvent by evaporation. The container is then kept in an oven at 140° C. under vacuum until constant weight is obtained. The weight percentage of polymer soluble in xylene at room temperature is then calculated.

(27) Pentad Isotacticity

(28) 175 mg of the polypropylene granules was dissolved in 3 ml at 130° C. in deuterated tetrachloroethylene (C.sub.2D.sub.2Cl.sub.4) containing 2,6-Di-tert-butyl-4-methylphenol (BHT) (5 mg BHT in 200 ml C.sub.2D.sub.2Cl.sub.4). The .sup.13C NMR spectrum was recorded on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe head operating at 125° C. The isotacticity of the mmmm pentad levels was determined from the .sup.13C NMR spectrum in % based on the total pentad amount.

(29) Melt Flow Rate (MFR)

(30) For purpose of the invention the melt flow rate is the melt flow rate as measured according to ISO1133 (2.16 kg/230° C.).

(31) Tm and Tc Measurement

(32) The crystallization temperature, the crystallinity and the melting temperature are measured according to ASTM D3418-08 at a heating rate of 10° C./min in DSC. The sample is heated up to 200° C. (first heating) and then cooled at a cooling rate 10° C./min of (to measure the crystallization temperature Tc) and then heated a second time at a heating rate of 10° C./min (second heating) to measure the melting temperature (Tm). For the determination of Tc and Tm, a 5 mg polymer sample was measured.

(33) Production of Films

(34) The granulate obtained was processed into single-layer films having a thickness of 25 μm by using a ME-20 extruder and a CR-7 cast film system obtainable from Optical Control Systems GmbH. The extruder was operated at a screw speed of 50 rpm, with a temperature profile along the extruder screw of 190° C. in the material feed zone to 250° C. in the die zone. The extruder was equipped with a slit die. The width of the die opening was 100 mm. The die gap was in the range from 0.50 to 1.0 mm.

(35) The cast film system comprised a dual chrome plated steel chill roll system having a temperature control system. The chill roll was operated at a temperature of 20° C. The cast film system comprised two rubber nip rolls to pull the film. The speed of the cast film system was controlled by the nip rolls to produce film at a speed of 7.6 m/min.

(36) Gel Content Determination

(37) The gel content was determined via on-line measurement of the film in the cast film system using an FSA-100 film surface analyser obtainable from Optical Control Systems GmbH software version 6.3.4.2, wherein the surface analyser is positioned between the chill roll system and the nip rolls. The film surface analyser comprised a CCD line scan camera with a resolution of 50 μm. The smallest defects that could be identified accordingly had a dimension of 50 μm length and 50 μm width. The film surface analyser comprised halogen based illumination system. A continuous image of the film surface was thus produced. The determination of defects was performed using image recognition software provided by Optical Control Systems GmbH integrated with the FSA-100 film surface analyser. A film sample with a total surface size of 10.0 m.sup.2 was tested.

(38) The number of gels having an equivalent diameter of >100 μm, >200 μm and of >500 μm and of >900 μm were reported.

(39) Flex. Modulus (parallel orientation).

(40) For purpose of the present invention, stiffness of the granulate is determined by measuring the flexural modulus according to ASTM D790-10. Flexural modulus was determined on 3.2 mm thick specimens according to ISO37/2, parallel orientation.

(41) Izod Notched Impact Strength (Parallel Orientation)

(42) For purpose of the present invention, impact strength is determined by measuring the Izod notched impact strength of the granulate at 23° C. according to ISO 180 4A, Test geometry: 65*12.7*3.2 mm, notch 45° according to ISO 37/2 parallel orientation.

(43) Conclusion

(44) As can be seen from Table 3, the polypropylene compositions of the invention show a lower gel count and have a higher stiffness and maintain their impact strength, which allows for the preparation of thinner tapes without decreasing the properties of the tape.

(45) In particular, when a phthalate free external donor is used, the polypropylene composition of the invention could be suitably used for applications where consumer acceptance of phthalate containing products is low, for example in food and medical applications.

(46) TABLE-US-00003 TABLE 3 Results Example IE1 CE1 Mw (kDa) 460 440 Mn (kDa) 48 75 Mz (kDa) 1400 1100 Mz/Mw 3.1 2.6 Mz/Mn 29.2 14.7 MWD = Mw/Mn 9.6 5.9 XS (wt %) 2.1 2.3 Pentad isotacticity (%) 96.0 94.1 Tm (2.sup.nd heating), (° C.) 163.3 162.0 Tc (2.sup.nd cooling), ° C. 111.8 111.7 MFR (g/10 min) 1.3 1.0 properties Gel count >200 μm 2.10 49 Gel count >500 μm 0.3 7.8 Gel count >900 μm 0.2 2.1 MWD/gelcount >500 μm 32 0.76 Cumulative gel count is 49.7 170.2 gel county >100 μm flex modulus (parallel 1934 1742 orientation) (MPa) Izod notched Impact strength 3.2 3.4 (parallel orientation) (kJ/m.sup.2)