Polypropylene composition combining low sealing initiation temperature and high melting temperature

Abstract

The invention relates to a polypropylene composition which combines low sealing initiation temperature (SIT) and high melting point (Tm), thus having a broad sealing window.

Claims

1. Polypropylene composition that is a binary blend comprising two propylene polymer fractions PPF1 and PPF2 in specific amounts: a) 30 to 50 wt % of propylene polymer fraction PPF1 that is a propylene copolymer comprising propylene monomer and 1.50 to 7.00 mol % of one comonomer selected from C.sub.4-C.sub.10 alpha-olefin, and b) 70 to 50 wt % of propylene polymer fraction PPF2 that is a propylene terpolymer comprising propylene monomer, 0.30 to 3.00 mol % of ethylene comonomer and 3.50 to 12.00 mol % of one comonomer selected from C.sub.4-C.sub.10 alpha-olefin, wherein the polypropylene composition: i. has a melting temperature (Tm) in a range of 135 to 160° C. as determined by DSC according to ISO 11357, ii. satisfies the equation:
Delta=Tm−SIT wherein Delta is in a range of 30 to 43° C., and wherein Tm is melting temperature, in ° C., of the polypropylene composition, SIT is sealing initiation temperature, in ° C., of the polypropylene composition, as calculated from pellets via DSC analysis, wherein amounts of PPF1 and PPF2 being are relative to a total sum of the propylene polymer fractions PPF1 and PPF2, and wherein the polypropylene composition has an amount of xylene soluble (XS) in a range of 3 to 15 wt %, as determined at 25° C. according ISO 16152; 5.sup.th edition; 2005-07-01.

2. Polypropylene composition according to claim 1, wherein the polypropylene composition has an MFR.sub.2 in a range of 3.0 to 10.0 g/10 min, as measured at 230° C. under a load of 2.16 kg according to ISO 1133.

3. Polypropylene composition according to claim 1, wherein the propylene polymer fraction PPF1 is a propylene copolymer comprising 1-butene (C.sub.4) and the propylene polymer fraction PPF2 is a propylene terpolymer comprising ethylene comonomer and 1-butene (C.sub.4).

4. Process for producing the polypropylene composition according to claim 1, by a sequential polymerisation process comprising at least two reactors connected in series, said process comprising the steps: a) polymerising in a first reactor that is a slurry reactor propylene and one comonomer selected from C.sub.4-C.sub.10 alpha-olefin and obtaining a propylene polymer fraction PPF1, b) transferring the propylene polymer fraction PPF1 and unreacted comonomers of a reactor (R-1) into a second reactor (R-2) that is a gas-phase reactor-1 (GPR-1), c) polymerising in the gas-phase reactor-1 (GPR-1) propylene, ethylene and one comonomer selected from C.sub.4-C.sub.10 alpha-olefin in the presence of the propylene polymer fraction PPF1, and obtaining a propylene polymer fraction PPF2, that is a propylene terpolymer, said propylene polymer fraction PPF2 and the propylene polymer fraction PPF1 forming the polypropylene composition, d) recovering the polypropylene composition.

5. A film comprising the polypropylene composition according to claim 1.

6. The film according to claim 5 wherein said film is a blown film or a cast film.

7. The film according to claim 5, wherein said film is a multilayer film.

Description

EXAMPLES

I. Measuring Methods

(1) The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples, unless otherwise defined.

(2) a) Melt Flow Rate

(3) The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability and hence the processability of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR.sub.2 of polypropylene is determined at a temperature of 230° C. and under a load of 2.16 kg.

(4) b) Melt Flow Rate (MFR.sub.2) for the Propylene Terpolymer (PPF2)

(5) The MFR.sub.2 for the propylene terpolymer (PPF2) is calculated using the below formula:
In(MFR.sub.2 of the polypropylene composition)=x(In(MFR.sub.2 of the propylene copolymer (PPF1)))+(1−x)(In(MFR.sub.2 of the propylene terpolymer (PPF2)));
wherein MFR.sub.2 of the polypropylene composition means the MFR.sub.2 of the PP composition according to the present invention and wherein
x=the weight ratio (wt) of the propylene copolymer (PPF1) based on the combined weight of the propylene copolymer (PPF1) and the weight of the propylene terpolymer (PPF2) which is in total=1.

(6) c) Melting Temperature

(7) The melting temperature, Tm, is determined by differential scanning calorimetry (DSC) according to ISO 11357-3 with a TA-Instruments 2920 Dual-Cell with RSC refrigeration apparatus and data station. A heating and cooling rate of 10° C./min is applied in a heat/cool/heat cycle between +23 and +210° C. The melting temperature (Tm) is being determined in the second heating step.

(8) d) Xylene Cold Soluble Fraction (XS, wt %)

(9) The amount of the polymer soluble in xylene is determined at 25.0° C. according to ISO 16152; 5.sup.th edition; 2005 Jul. 1.

(10) e) Comonomer Content

(11) Quantitative .sup.13C{.sup.1H} NMR spectra recorded in the molten-state using a Bruker Advance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 7 mm magic-angle spinning (MAS) probehead at 180° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was packed into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz. This setup was chosen primarily for the high sensitivity needed for rapid identification and accurate quantification {klimke06, parkinson07, castignolles09}. Standard single-pulse excitation was employed utilising the NOE at short recycle delays of 3 s {pollard04, klimke06} and the RS-HEPT decoupling scheme {fillip05, griffin07}. A total of 1024 (1 k) transients were acquired per spectra.

(12) Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. All chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

(13) Characteristic signals corresponding to the incorporation of 1-butene were observed and the comonomer content quantified in the following way. The amount isolated 1-butene incorporated in PBP sequences was quantified using the integral of the αB2 sites at 43.6 ppm accounting for the number of reporting sites per comonomer:
B=I.sub.αB2/2

(14) The amount consecutively incorporated 1-butene in PBBP sequences was quantified using the integral of the ααB2 site at 40.5 ppm accounting for the number of reporting sites per comonomer:
BB=2*I.sub.ααB2

(15) The total 1-butene content was calculated based on the sum of isolated and consecutively incorporated 1-butene:
Btotal=B+BB

(16) Characteristic signals corresponding to the incorporation of ethylene were observed and the comonomer content quantified in the following way. The amount isolated ethylene incorporated in PEP sequences was quantified using the integral of the Sαγ sites at 37.9 ppm accounting for the number of reporting sites per comonomer:
E=I.sub.Sαγ/2

(17) When characteristic signals corresponding to consecutive ethylene incorporation in PEEP sequences were observed the amount of such consecutively incorporated ethylene was quantified using the integral of S.sub.βδ sites at 27 ppm accounting for the number of reporting sites per comonomer:
EE=I.sub.Sβδ

(18) With no sites indicative of consecutive ethylene incorporation in PEEE sequences observed the total ethylene comonomer content was calculated as:
Etotal=E+EE

(19) Characteristic signals corresponding to regio defects were not observed {resconi00}.

(20) The amount of propene was quantified based on the main Sαα methylene sites at 46.7 ppm and compensating for the relative amount of methylene unit of propene in PBP, PBBP, PEP and PEEP sequences not accounted for:
Ptotal=I.sub.Sαα+B+BB/2+E+EE/2

(21) The total mole fraction of 1-butene in the polymer was then calculated as:
fB=(Btotal/(Etotal+Ptotal+Btotal)

(22) The total mole fraction of ethylene in the polymer was then calculated as:
fE=(Etotal/(Etotal+Ptotal+Btotal)

(23) The mole percent comonomer incorporation was calculated from the mole fractions:
B[mol %]=100*fB
E[mol %]=100*fE

(24) The weight percent comonomer incorporation was calculated from the mole fractions:
B[wt %]=100*(fB*56.11)/((fE*28.05)+(fB*56.11)+((1−(fE+fB))*42.08))
E[wt %]=100*(fE*28.05)/((fE*28.05)+(fB*56.11)+((1−(fE+fB))*42.08)).
klimke06
Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382.
parkinson07
Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128.
pollard04
Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813.
filip05
Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239
griffin07
Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 2007 45, S1, S198
castignolles09
Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373
busico01
Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443
busico97
Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromoleucles 30 (1997) 6251
zhou07
Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225
busico07
Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128
resconi00
Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253

(25) The comonomer content of the propylene terpolymer (PPF2) is calculated using the below formula:
Comonomer content of the polypropylene composition=x(Comonomer content of the propylene copolymer (PPF1))+(1−x)(Comonomer content of the propylene terpolymer (PPF2)).
x=the weight ratio (wt) of the propylene copolymer (PPF1) based on the combined weight of the propylene copolymer (PPF1) and the weight of the propylene terpolymer (PPF2) which is in total =1.

(26) f) Sealing Initiation Temperature (SIT), Sealing Range

(27) Differential Scanning calorimetry (DSC) experiments were run on a TA Instruments Q2000 device calibrated with Indium, Zinc, and Tin according to ISO 11357/1. The measurements were run under nitrogen atmosphere (50 mL min−1) on 5±0.5 mg samples in a heat/cool/heat cycle with a scan rate of 10° C./min between −30° C. and 225° C. according to ISO 11357/3. Melting (Tm) and crystallisation (Tc) temperatures were taken as the peaks of the endotherms and exotherms in the cooling cycle and the second heating cycle respectively.

(28) The Sealing Initiation Temperature (SIT) was predicted by analyzing the second heating scan according to the following procedure: the first limit for integration was set at 16° C., the second limit at Tm+20° C., and the total melting enthalpy was registered. The temperature T1 is defined as the temperature at which 19% of this melting enthalpy with the abovementioned limits for integration was obtained. The parameter SIT is finally calculated as:
SIT=1.0596×T1+3.8501

II. Inventive and Comparative Examples

(29) a) Catalyst Preparation

(30) 3.4 litre of 2-ethylhexanol and 810 ml of propylene glycol butyl monoether (in a molar ratio 4/1) were added to a 20.0 I reactor. Then 7.8 litre of a 20.0% solution in toluene of BEM (butyl ethyl magnesium) provided by Crompton GmbH, were slowly added to the well stirred alcohol mixture. During the addition the temperature was kept at 10.0° C. After addition the temperature of the reaction mixture was raised to 60.0° C. and mixing was continued at this temperature for 30 minutes. Finally after cooling to room temperature the obtained Mg-alkoxide was transferred to a storage vessel.

(31) 21.2 g of Mg alkoxide prepared above was mixed with 4.0 ml bis(2-ethylhexyl) citraconate for 5 min. After mixing the obtained Mg complex was used immediately in the preparation of the catalyst component.

(32) 19.5 ml of titanium tetrachloride was placed in a 300 ml reactor equipped with a mechanical stirrer at 25.0° C. Mixing speed was adjusted to 170 rpm. 26.0 g of Mg-complex prepared above was added within 30 minutes keeping the temperature at 25.0° C. 3.0 ml of Viscoplex® 1-254 and 1.0 ml of a toluene solution with 2 mg Necadd 447™ was added. Then 24.0 ml of heptane was added to form an emulsion. Mixing was continued for 30 minutes at 25.0° C., after which the reactor temperature was raised to 90.0° C. within 30 minutes. The reaction mixture was stirred for a further 30 minutes at 90.0° C. Afterwards stirring was stopped and the reaction mixture was allowed to settle for 15 minutes at 90.0° C. The solid material was washed 5 times: washings were made at 80.0° C. under stirring for 30 min with 170 rpm. After stirring was stopped the reaction mixture was allowed to settle for 20-30 minutes and followed by siphoning.

(33) Wash 1: washing was made with a mixture of 100 ml of toluene and 1 ml donor

(34) Wash 2: washing was made with a mixture of 30 ml of TiCl4 and 1 ml of donor.

(35) Wash 3: washing was made with 100 ml of toluene.

(36) Wash 4: washing was made with 60 ml of heptane.

(37) Wash 5: washing was made with 60 ml of heptane under 10 minutes stirring.

(38) Afterwards stirring was stopped and the reaction mixture was allowed to settle for 10 minutes while decreasing the temperature to 70° C. with subsequent siphoning, followed by N.sub.2 sparging for 20 minutes to yield an air sensitive powder.

(39) b) Inventive Examples (IE1 and IE2)

(40) The inventive examples (IE) were produced in a pilot plant with a prepolymerisation reactor, one slurry loop reactor and one gas phase reactor. The solid catalyst component described above was used for the inventive examples IE1 and IE2 along with triethylaluminium (TEAL) as co-catalyst and dicyclo pentyl dimethoxy silane (D-donor) as external donor.

(41) c) Comparative Examples (CE1, CE2 and CE3)

(42) CE-1 is a C.sub.2C.sub.4 propylene terpolymer having a narrow molecular weight distribution, MFR.sub.2 of 6.0 g/10 min and melting point of 130° C., seal initiation temperature (SIT) of 103° C. and is manufactured and distributed by Borealis under the Trade name TD315BF.

(43) CE-2 is a C.sub.2C.sub.4 propylene terpolymer having a medium molecular weight distribution, MFR.sub.2 of 6.0 g/10 min and melting point of 130° C., seal initiation temperature (SIT) of 103° C. and is manufactured and distributed by Borealis under the Trade name TD210BF.

(44) CE-3 is a C.sub.2C.sub.4 propylene terpolymer having a medium molecular weight distribution, MFR.sub.2 of 6 g/10 min and melting point of 130° C., seal initiation temperature (SIT) of 103° C. and is manufactured and distributed by Borealis under the Trade name TD215BF.

(45) TABLE-US-00001 TABLE 1 Polymerisation conditions. IE-1 IE2 Loop (propylene polymer fraction PPF1) Temperature [° C.] 70 70 Pressure [kPa] 5340 5225 Residence time [h] 0.47 0.50 Split [%] 46 39 H.sub.2/C.sub.3 ratio [mol/kmol] 0.91 0.60 C.sub.4/C.sub.3 ratio [mol/kmol] 123 88 MFR.sub.2 [g/10 min] 5.6 4.9 C.sub.4 content [mol %] 4.0 3.8 GPR 1 (propylene polymer fraction PPF2) Temperature [° C.] 80 75 Pressure [kPa] 2500 2400 Residence time [h] 1.82 2.3 Split [%] 54 61 H.sub.2/C.sub.3 ratio [mol/kmol] 10.1 14.9 C.sub.2/C.sub.3 ratio [mol/kmol] 15.2 12 C.sub.4/C.sub.3 ratio [mol/kmol] 203 143.9 MFR.sub.2 GPR 1 [g/10 min] 5.4 5.8 C.sub.2 content [mol %] 2.7 2.0 C.sub.4 content [mol %] 8.3 8.2 Polypropylene composition MFR.sub.2 [g/10 min] 5.6 5.4 XS [wt %] 10.1 14.8 C.sub.4 content total [mol %] 6.3 6.4 C.sub.2 content total [mol %] 1.5 1.2 Melting point [° C.] 144.0 140.7

(46) TABLE-US-00002 TABLE 2 Melting temperature (Tm), Seal initiation temperature (SIT) and Delta values of inventive examples (IE1, IE2) and comparative examples (CE1, CE2, CE3). IE1 IE2 CE1 CE2 CE3 Tm 143.5 140.7 129.8 132.8 131.3 SIT [° C.] 102.5 102.0 101.0 106.0 106.0 Delta (Tm-SIT) 41.0 38.7 29.0 27.0 25.0

(47) From Table 2 it can be derived that the polypropylene compositions according to the invention present higher melting temperature (Tm) values and higher Delta (Tm−SIT) values than the comparative examples.