PROPYLENE RANDOM COPOLYMER COMPOSITION WITH REDUCED SEALING INITIATION TEMPERATURE

Abstract

The present invention is directed to a polyolefin composition which is suitable as sealing layer of a multilayer film providing improved, i.e. reduced sealing initiation temperature. The polyolefin composition comprises a random copolymer of propylene and a polymer of 1-butene. The present invention is also directed to oriented and non-oriented films comprising the polyolefin composition and to the use of a polymer of 1-butene in a polyolefin composition comprising a random copolymer of propylene for reducing the sealing initiation temperature of an oriented or non-oriented film comprising the polyolefin composition. The present invention allows the application of a random copolymer of propylene based polyolefin composition as sealing layer of a multilayer film for higher speed packaging lines and at the same time also provides good hot tack and optical properties.

Claims

1. A polyolefin composition comprising: (A) a random copolymer of propylene with one or more monomers selected from ethylene and a C.sub.4-C.sub.12-alpha-olefin having: a comonomer content of 1.0 to 10 wt % based on the weight of the random copolymer of propylene, and (B) a polymer of 1-butene having a weight average molecular weight M.sub.w of 100,000 to 300,000 g/mol, and a molecular weight distribution M.sub.w/M.sub.n of below 6.0.

2. The polyolefin composition according to claim 1, wherein the random copolymer of propylene has a xylene cold soluble content of below 10 wt %.

3. The polyolefin composition according to claim 1, wherein the random copolymer of propylene has a comonomer content of 2.0 to 10 wt %, based on the weight of the random copolymer of propylene.

4. The polyolefin composition according to claim 1, wherein the comonomer in the random copolymer of propylene is ethylene and there is only one comonomer and/or the polymer of 1-butene is a copolymer of: 1-butene with one or more comonomers whereby the content of 1-butene is between 1 wt % and <50 wt % based on the weight of the copolymer.

5. The polyolefin composition according to claim 1, wherein the random copolymer of propylene has a melt flow rate MFR.sub.2 of 1.0 to 50 g/10 min as measured at 230 C. (2.16 kg) according to ISO 1133.

6. The polyolefin composition according to claim 1, wherein the random copolymer of propylene exhibits two melting temperatures T.sub.m which differ from each other as determined by differential scanning calorimetry according to ISO 11357-3.

7. The polyolefin composition according to claim 6, wherein the two melting temperatures T.sub.m of the random copolymer of propylene differ from each other by at least 4.0 C.

8. The polyolefin composition according to claim 1, wherein the polymer of 1-butene has a melt flow rate MFR.sub.2 of between 2.0 g/10 min and 10 g/10 min as measured at 190 C. (2.16 kg) according to ISO 1133.

9. The polyolefin composition according to claim 1, wherein the polymer of 1-butene has a weight average molecular weight M.sub.w of 150,000 to 250,000 g/mol.

10. The polyolefin composition according to claim 1, wherein the polymer of 1-butene has a molecular weight distribution M.sub.w/M.sub.n of below 4.5.

11. The polyolefin composition according to claim 1, wherein the amount of the random copolymer of propylene is at least 80 wt % and/or the amount of the polymer of 1-butene is at least 1.0 wt %, and the amount of the polymer of 1-butene is at most 15 wt %, based on the weight of the polyolefin composition and/or the amount of the random copolymer of propylene is between 80 wt % and 99 wt %, based on the weight of the polyolefin composition and/or the amount of the polymer of 1-butene is between 1.0 to 20 wt %, based on the weight of the polyolefin composition of the present invention.

12. The polyolefin composition according to claim 1, wherein the weight ratio between the polymer of 1-butene and the random copolymer of propylene is 0.01-0.25.

13. A film, comprising a polyolefin composition according to claim 1.

14. A multilayered film comprising a film according to claim 13, as a sealing layer and at least one further film layers.

15. (canceled)

Description

EXAMPLES

1. Definitions/Measuring Methods

[0195] 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.

[0196] Calculation of comonomer content of the second propylene ethylene random copolymer fraction (R-PP2):

[00001]$\frac{C\left(R.Math..Math.2\right)-w\left(\mathrm{PP}.Math..Math.1\right)C\left(\mathrm{PP}.Math..Math.1\right)}{w\left(\mathrm{PP}.Math..Math.2\right)}=C\left(\mathrm{PP}.Math..Math.2\right)$

wherein [0197] w(PP1) is the weight fraction of the propylene ethylene random copolymer fraction (R-PP1), i.e. the product of the first reactor (R1), based on the weight of R-PP; [0198] w(PP2) is the weight fraction of the propylene ethylene random copolymer fraction (R-PP2), i.e. of the polymer produced in the second reactor (R2), based on the weight of R-PP [0199] C(PP1) is the comonomer content [in wt %] of the propylene ethylene random copolymer fraction (R-PP1), i.e. of the product of the first reactor (R1), [0200] C(R2) is the comonomer content [in wt %] of the product obtained in the second reactor (R2), i.e. the propylene ethylene random copolymer (R-PP), [0201] C(PP2) is the calculated comonomer content [in wt %] of the the propylene ethylene random copolymer fraction (R-PP2).

[0202] Calculation of the xylene cold soluble (XCS) content of the propylene ethylene random copolymer fraction (R-PP2):

[00002]$\frac{\mathrm{XS}\left(R.Math..Math.2\right)-w\left(\mathrm{PP}.Math..Math.1\right)\mathrm{XS}\left(\mathrm{PP}.Math..Math.1\right)}{w\left(\mathrm{PP}.Math..Math.2\right)}=\mathrm{XS}\left(\mathrm{PP}.Math..Math.2\right)$

wherein [0203] w(PP1) is the weight fraction of the propylene ethylene random copolymer fraction (R-PP1), i.e. the product of the first reactor (R1), [0204] w(PP2) is the weight fraction of the propylene ethylene random copolymer fraction (R-PP2), i.e. of the polymer produced in the second reactor (R2), [0205] XS(PP1) is the xylene cold soluble (XCS) content [in wt %] of the propylene ethylene random copolymer fraction (R-PP1), i.e. of the product of the first reactor (R1), [0206] XS(R2) is the xylene cold soluble (XCS) content [in wt %] of the product obtained in the second reactor (R2), i.e. the propylene ethylene random copolymer (R-PP), [0207] XS(PP2) is the calculated xylene cold soluble (XCS) content [in wt %] of the propylene ethylene random copolymer fraction (R-PP2).

[0208] Calculation of melt flow rate MFR.sub.2 (230 C.) of the propylene ethylene random copolymer fraction (R-PP2):

[00003]$\mathrm{MFR}\left(\mathrm{PP}.Math..Math.2\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(\mathrm{PP}\right)\right)-w\left(\mathrm{PP}.Math..Math.1\right)\log \left(\mathrm{MFR}\left(\mathrm{PP}.Math..Math.1\right)\right)}{w\left(\mathrm{PP}.Math..Math.2\right)}\right]}$

wherein [0209] w(PP1) is the weight fraction of the propylene ethylene random copolymer fraction (R-PP1), i.e. the product of the first reactor (R1), [0210] w(PP2) is the weight fraction of the propylene ethylene random copolymer fraction (R-PP2), i.e. of the polymer produced in the second reactor (R2), [0211] MFR(PP1) is the melt flow rate MFR.sub.2 (230 C.) [in g/10 min] of the propylene ethylene random copolymer fraction (R-PP1), [0212] MFR(PP) is the melt flow rate MFR.sub.2 (230 C.) [in g/10 min] of the product obtained in the second reactor (R2), i.e. the propylene ethylene random copolymer (R-PP), [0213] MFR(PP2) is the calculated melt flow rate MFR.sub.2 (230 C.) [in g/10 min] of the propylene ethylene random copolymer fraction (R-PP2).

[0214] Density is measured according to ISO 1183-1method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

[0215] MFR is measured according to ISO 1133 (2.16 kg load), at 230 C. for random copolymer of propylene, at 190 C. for polymer of 1-butene.

[0216] Ethylene content/Comonomer content is measured with Fourier transform infrared spectroscopy (FTIR) calibrated with .sup.13C-NMR. When measuring the ethylene content in polypropylene, a thin film of the sample (thickness about 0.3 mm) was prepared by hot-pressing. The area of absorption peaks 720 and 733 cm.sup.1 was measured with Bruker Tensor 27 FTIR spectrometer. The method was calibrated by ethylene content data measured by .sup.13C-NMR. The presence or absence of a comonomer, e.g. ethylene, in a polymer of 1-butene was identified from the presence or absence of additional absorption in FTIR, for ethylene at 730 cm.sup.1.

[0217] The xylene cold solubles (XCS, wt %): Content of xylene cold solubles (XCS) is determined at 25 C. according ISO 16152; first edition; 2005-07-01

[0218] Melting temperature T.sub.m, crystallization temperature T.sub.c: measured with Mettler TA820 differential scanning calorimetry (DSC) on 5 to 10 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10 C./min in the temperature range of +23 to +210 C. Crystallization temperature and enthalpy are determined from the cooling step, while melting temperature and melting enthalpy are determined from the second heating step.

[0219] The glass transition temperature T.sub.g is determined by dynamic mechanical analysis according to ISO 6721-7. The measurements are done in torsion mode on compression moulded samples (40101 mm.sup.3) between 100 C. and +150 C. with a heating rate of 2 C./min and a frequency of 1 Hz.

[0220] Tensile test for film: ASTM D882

[0221] Flexural Modulus Test for Base Resin or Pellet Thereof:

[0222] ISO 178. The test specimens have a dimension of 80104.0 mm.sup.3 (lengthwidththickness), and were prepared by injection molding according to EN ISO 1873-2. The length of the span between the supports was 64 mm, the test speed was 2 mm/min and the force was 100 N.

[0223] Number average molecular weight (M.sub.n), weight average molecular weight (M.sub.w) and polydispersity (M.sub.w/M.sub.n) are determined by Gel Permeation Chromatography (GPC) according to the following method:

[0224] The weight average molecular weight Mw and the polydispersity (M.sub.w/M.sub.n, wherein M.sub.n is the number average molecular weight and M.sub.w is the weight average molecular weight) is measured by a method based on ISO 16014-1:2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument, equipped with refractive index detector and online viscometer was used with 3TSK-gel columns (GMHXL-HT) from TosoHaas and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg/L 2,6-di tert butyl-4-methyl-phenol) as solvent at 145 C. and at a constant flow rate of 1 mL/min. 216.5 L of sample solution were injected per analysis. The column set was calibrated using relative calibration with 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11 500 kg/mol and a set of well characterized broad polypropylene standards. All samples were prepared by dissolving 5-10 mg of polymer in 10 mL (at 160 C.) of stabilized TCB (same as mobile phase) and keeping for 3 hours with continuous shaking prior sampling in into the GPC instrument.

[0225] Film thickness was measured according to ISO 4593.

[0226] Transparency, haze and clarity: All optical parameters are measured on 30 m thick cast films. Transparency, haze and clarity were determined according to ASTM D 1003.

[0227] Gloss is measured on 30 m thick cast film according to DIN 67530/ISO 2813 at an angle of 60.

[0228] Sealing initiation temperature (SIT) is the sealing temperature at which a heat seal of significant strength is produced, here a seal force of 5 N, measured on Otto Brugger in line with ASTM F 2029 and ASTM F 88 in following conditions: Seal width 25 mm, seal pressure 3 bars, 1 second dwell time, 2 heated flat jaws, seal force 5 N, peel speed 100 mm/s, test speed 250 mm/min.

[0229] Hot tack is measured on DTC in line with ASTM F 1921 in the following conditions: 3 bars, sealing time 1 second, cooling time 0.1 second (release), 2 teflonized jaws, hot tack force 1 N, peel speed 200 mm/s, sealing pressure 0.25 N/mm.sup.2, dwell/sealing time 1 second, delay time 100 ms; test/peel speed 200 mm/s; flat jaws covered with teflon tape.

2. Examples

a) Preparation of a Propylene Ethylene Random Copolymer (R-PP) According to the Present Invention:

[0230] The catalyst used in the polymerization processes of the examples is the catalyst as prepared in Example 8 of WO 2004/029112 A1 (see pages 22-23), except that diethylaluminum chloride is used as an aluminum compound instead of triethylaluminum.

[0231] An external donor, dicyclopentyldimethoxy silane, is used. The ratio of aluminum to donor is 7.5. Polypropylene is copolymerized with ethylene in a pilot bimodal multireactor system for polymerization mode consisting of a pre-polymerization, a loop reactor and a gas reactor, with a catalyst of the above-described system and under the polymerization conditions as indicated in Table 1. The technical features of the obtained random copolymer of propylene and ethylene are listed in Table 2.

[0232] In Table 1, H.sub.2/C.sub.3/mol/kmol means the feed ratio of H.sub.2/C.sub.3, and C.sub.2/C.sub.3/mol/kmol means the feed ratio of C.sub.2/C.sub.3. The volume of the pre-polymerization reactor is very small, and production rate is much less than that in loop reactor and gas reactor. In this case, R-PP1 means the sum of copolymers as produced in pre-polymerization reactor and loop reactor, and R-PP2 means the fraction as produced in gas reactor.

[0233] The technical features of the final copolymer product and two fractions (R-PP1 & R-PP2) as produced in different reactors are listed in Table 2. The C.sub.2-content, XS and MFR.sub.2 of the 45% fraction (R-PP1) of the final copolymer and the respective technical features of the final copolymer are obtained by directly testing the products of the loop reactor and the gas reactor (i.e. the last reactor), respectively. The C.sub.2-content, XS and MFR.sub.2 of the 55% fraction (R-PP2) are obtained by calculation according to the calculation equations as indicated under Definitions/Measuring Methods above.

TABLE-US-00001 TABLE 1 Polymerization conditions of propylene ethylene random copolymer (R-PP) Total production/kg/h 60 Prepolymerization Temperature/ C. 30 Pressure/bar 55 Donor/g/t 40 H.sub.2 feed/g/h 2.5 C.sub.2 feed/g/h 300 Loop Reactor Temperature/ C. 70 Production/kg/h 25 Pressure/bar 55 C.sub.2-content/wt % 3.4 C.sub.2/C.sub.3 ratio/mol/kmol 8.55 C.sub.2 feed/g/h 600 H.sub.2/C.sub.3 in Loop/mol/kmol 4 MFR.sub.2 at 230 C. 8 Split/% 45 Gas Phase Reactor C.sub.2/C.sub.3/mol/kmol 28 C.sub.2-content/wt % 4.2 H.sub.2/C.sub.3/mol/kmol 42 MFR.sub.2 at 230 C. 8 Temperature/ C. 85 Pressure/bar 21 Split/% 55

TABLE-US-00002 TABLE 2 Technical features of the final propylene ethylene random copolymer (R-PP) and two fractions as produced in different reactors 45% fraction Final (prepolymerization 55% fraction product and loop reactor) (gas phase reactor) (R-PP) C.sub.2/wt % 3.4 4.9 4.2 MFR.sub.2/g/10 min 8.0 8.0 8.0 XCS wt % 5.0 8.6 7.0 T.sub.m/ C. 137 T.sub.m/ C. 146

b) Preparation of Polyolefin Compositions

[0234] After polymerization, the copolymer is pelletized in an extruder. The formulation contains regular additives such as a normal acid scavenger (e.g. Ca stearate), antioxidants (e.g. Irganox 1010, Irgafos 168), anti-slip agent and anti-blocking agents (e.g. synthetic silica) in conventionally used amounts.

[0235] In the inventive example, Example 2, at this step also 10 wt % of Tafmer BL2491M is added to the polyolefin composition.

[0236] Tafmer BL2491M is a polymer of 1-butene having a weight average molecular weight of 197,000 g/mol as determined by GPC and a molecular weight distribution M.sub.w/M.sub.n of 2.7. Tafmer BL2491M is commercially available from Mitsui.

[0237] In the reference example, Example 1, no polymer of 1-butene is added.

c) Preparation of Cast Films

[0238] The compositions of Examples 1 and 2, respectively, are extruded in a cast machine to obtain a 30 m 3-layer film with the following setup.

[0239] Core layer: HD601CF, a propylene homopolymer having an MFR.sub.2 (230 C.) of 8.0 g/10 min and a melting temperature T.sub.m of 164 C. It is commercially available from Borouge/Borealis.

[0240] Non-sealable skin layer: RD265CF, a propylene random copolymer having an MFR.sub.2 (230 C.) of 8.0 g/10 min and a melting temperature T.sub.m of 151 C. It is commercially available from Borouge/Borealis.

[0241] Sealable skin layer: polyolefin composition as described above for Examples 1 (MFR.sub.2, 230 C., 2.16 kg of 8.0 g/10 min) and 2 (MFR.sub.2, 230 C., 2.16 kg of 8.1 g/10 min) COLLIN cast configuration for 30 m 3-layer film (6-18-6 m)

[0242] Sealable skin layer on the chill roll side

[0243] No corona treatment

[0244] Table 3 shows the properties of the respective cast films of Examples 1 and 2.

TABLE-US-00003 TABLE 3 Example 1 Example 2 SIT/ C. 112 104 Hot tack/ C. 94 73 Haze/% 3.0 2.6 Gloss at 60 137.0 136.7

[0245] As can be seen from the values of Example 2, the sealing initiation temperature (SIT) is very much reduced by 8 C. with addition of only 10 wt % of the polymer of 1-butene of the invention. This strong improvement enables to provide a highly feasible alternative to higher speed packaging lines which are demanding with respect of the choice of the polymer material. In addition, hot tack is improved as well and optical properties like haze and gloss are comparable to the reference, i.e. still very good. Haze is even slightly improved.