Multi-layer cast film

Abstract

A multi-layer polymer film comprising a core layer and a sealing layer, said sealing layer comprises a propylene copolymer composition, said propylene copolymer composition has a comonomer content in the range of 3.0 to 8.0 wt.-%, the comonomers are C.sub.5 to C.sub.12 -olefins, comprises a polypropylene (A) and a polypropylene (B) in the weight ratio [(A)/(B)] of 20/80 to 80/20, wherein said polypropylene (A) has a comonomer content of equal or below 4.0 wt.-%, the comonomers are C.sub.5 to C.sub.12 -olefins, and said propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt.-%, the comonomers are C.sub.5 to C.sub.12 -olefins.

Claims

1. Process for producing a multi-layer polymer film comprising: providing a core layer (CL) selected from the group consisting of polyvinyl alcohols, polyacrylates, polyamides, poly(ethylene terephthalate), polyolefins (PO) and mixtures thereof, a sealing layer (SL), and optionally an outer (OL), a further sealing layer (SL) or a metal layer (ML) wherein: (a) the core layer (CL); (a1) is coated on the one side with a propylene copolymer composition (P) obtaining a sealing layer (SL); and (a2) optionally; (a2-i) is on the other side coated with a polyolefin (PO) obtaining an outer layer (OL); or (a2-ii) is on the other side coated with a propylene copolymer composition (P) obtaining a second sealing layer (SL); or (a2-iii) is on the other side metallized obtaining a metal layer (ML), wherein; (b) said propylene copolymer composition (P); (b1) has a comonomer content in the range of 3.0 to 8.0 wt. %, the comonomer is C.sub.6 -olefin, (b2) comprises a polypropylene (A) and a polypropylene (B) in the weight ratio [(A)/(B)] of 35/65 to 50/50, wherein said polypropylene (A) is a propylene homopolymer (H-A) or a propylene copolymer (C-A) having a comonomer content of below 4.0 wt. %, the comonomers are C.sub.5 to C.sub.12 -olefins, and said propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt. %, the comonomer is C.sub.6 -olefin, and (b3) fulfills the ratio MFR (A)/MFR (P)<1.0 wherein MFR(A) is the melt flow rate MFR.sub.2 (230 C.) [g/10 min] measured according to ISO 1133 of the polypropylene (A), MFR(P) is the melt flow rate MFR.sub.2 (230 C.) [g/10 min] measured according to ISO 1133 of the propylene copolymer composition (P), and (b4) has a xylene soluble content (XCS) determined at 25 C. according to ISO 16152 of below 16.0 wt. %; (b5) a melting temperature Tm determined by differential scanning calorimetry (DSC) of at least 135 C., and (b6) a heat sealing temperature (SIT) of equal or below 115 C., and (b7) is free of any elastomeric polymer component, and wherein the multilayer polymer film is cast and not subjected to a stretching step.

2. Process according to claim 1, wherein polymer layers of the multilayer polymer film are coextruded on a cast film line.

3. Process according to claim 1, wherein the propylene copolymer composition (P) and/or the polyolefin (PO) has/have (a) a core layer (CL) being selected from the group consisting of polyvinyl alcohols, polyacrylates, polyamides, poly(ethylene terephthalate), polyolefins (PO) and mixtures thereof, and (b) a sealing layer (SL), said sealing layer (SL) comprises a propylene copolymer composition (P), said propylene copolymer composition (P).

4. Process according to claim 2, wherein molten polymers are extruded through slot extrusion dies onto a chill roll to cool the polymers to a solid cast film of at least two layers.

5. Process according to claim 2, wherein melts for the core layer (CL) and the propylene copolymer composition (P) for the sealing layer (SL) are coextruded through flat-film multilayer die, and taken off the resultant multi-layer polymer film over one or more rolls for solidification.

6. Process according to claim 2, wherein melts for the core layer (CL), the propylene copolymer composition (P) for the sealing layer (SL) and the polymer for the outer layer (OL) are coextruded through flat-film multilayer die, and taken off the resultant multi-layer polymer film over one or more rolls for solidification.

7. Process according to claim 2, wherein melts for the core layer (CL), the propylene copolymer composition (P) for the sealing layer (SL) and the polymer for a further sealing layer (SL) are coextruded through flat-film multilayer die, and taken off the resultant multi-layer polymer film over one or more rolls for solidification.

8. Process according to claim 5, wherein the take-off roll or the rolls, by means of which the extruded film is cooled and solidified, are kept at a temperature from 10 to 50 C.

9. Process according to claim 5, wherein the take-off roll or the rolls, by means of which the extruded film is cooled and solidified, are kept at a temperature from 15 to 40 C.

10. Process according to claim 5, wherein the take-off roll or the rolls, by means of which the extruded film is cooled and solidified, are kept at a temperature from 10 to 50 C.

11. Process according to claim 1, wherein the multi-layer film is corona-treated or flame-treated.

12. Process according to claim 11, wherein the corona treatment or flame treatment is carried out by passing the film between two conductor elements serving as electrodes with high voltage.

13. Process according to claim 12, wherein the high voltage is an alternating voltage.

Description

EXAMPLES

A. 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.

Quantification of Microstructure by NMR Spectroscopy

(2) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity, regio-regularity and comonomer content of the polymers. 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. Standard single-pulse excitation was employed utilising the NOE at short recycle delays (as described in Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004, 37, 813, and in Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006, 207, 382) and the RS-HEPT decoupling scheme (as described in Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239, and in Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 2007, 45, S1, S198). A total of 1024 (1 k) transients were acquired per spectra.

(3) 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. The tacticity distribution was quantified through integration of the methyl region in the .sup.13C{.sup.1H} spectra, correcting for any signal not related to the primary (1, 2) inserted propene stereo sequences, as described in Busico, V., Cipullo, R., Prog. Polym. Sci. 2001, 26, 443 and in Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 1997, 30, 6251.

(4) Characteristic signals corresponding to regio defects were observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253). The influence of regio defects on the quantification of the tacticity distribution was corrected for by subtraction of representative regio defect integrals from specific integrals of the stereo sequences.

(5) The isotacticity was determined at the triad level and reported as the percentage of isotactic triad mm with respect to all triad sequences:
% mm=(mm/(mm+mr+rr))*100

(6) Characteristic signals corresponding to the incorporation of 1-hexene were observed, and the 1-hexene content was calculated as the mole percent of 1-hexene in the polymer, H (mol %), according to:
[H]=H.sub.tot/(P.sub.tot+H.sub.tot)
where:
H.sub.tot=I(B.sub.4)/2+I(B.sub.4)2
where I( B.sub.4) is the integral of the B.sub.4 sites at 44.1 ppm, which identifies the isolated 1-hexene incorporated in PPHPP sequences, and I(B.sub.4) is the integral of the B.sub.4 sites at 41.6 ppm, which identifies the consecutively incorporated 1-hexene in PPHHPP sequences.

(7) P.sub.tot=Integral of all CH3 areas on the methyl region with correction applied for underestimation of other propene units not accounted for in this region and overestimation due to other sites found in this region.
and H(mol %)=100[H]
which is then converted into wt % using the correlation
H(wt %)=(100H mol %84.16)/(H mol %84.16+(100H mol %)42.08)

(8) A statistical distribution is suggested from the relationship between the content of hexene present in isolated (PPHPP) and consecutive (PPHHPP) incorporated comonomer sequences:
[HH]<[H].sup.2

Calculation of Comonomer Content of the Propylene Copolymer (B)

(9) $\frac{C\left(P\right)-w\left(A\right)C\left(A\right)}{w\left(B\right)}=C\left(B\right)$
wherein w(A) is the weight fraction of the polypropylene (A), w(B) is the weight fraction of the propylene copolymer (B), C(A) is the comonomer content [in wt.-%] measured by .sup.13C NMR spectroscopy of the polypropylene (A), i.e. of the product of the first reactor (R1), C(P) is the comonomer content [in wt.-%] measured by .sup.13C NMR spectroscopy of the propylene copolymer composition (P)], C(B) is the calculated comonomer content [in wt.-%] of the the propylene copolymer (B)

Mw, Mn, MWD

(10) Mw/Mn/MWD are measured by Gel Permeation Chromatography (GPC) according to the following method:

(11) The weight average molecular weight (Mw), the number average molecular weight (Mn), and the molecular weight distribution (MWD=Mw/Mn) 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 viscosimeter is 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 are injected per analysis. The column set is 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 are prepared by dissolving 5 to 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.

Melt Flow Rate (MFR)

(12) The melt flow rates are measured with a load of 2.16 kg (MFR.sub.2) at 230 C. The melt flow rate is that quantity of polymer in grams which the test apparatus standardised to ISO 1133 extrudes within 10 minutes at a temperature of 230 C. under a load of 2.16 kg.

Calculation of Melt Flow Rate MFR2 (230 C.) of the Propylene Copolymer (B)

(13) $\mathrm{MFR}\left(B\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(P\right)\right)-w\left(A\right)\log \left(\mathrm{MFR}\left(A\right)\right)}{w\left(B\right)}\right]}$
wherein w(A) is the weight fraction of the polypropylene (A), w(B) is the weight fraction of the propylene copolymer (B), MFR(A) is the melt flow rate MFR.sub.2 (230 C.) [in g/10 min] measured according ISO 1133 of the polypropylene (A), MFR(P) is the melt flow rate MFR.sub.2 (230 C.) [in g/10 min] measured according ISO 1133 of the propylene copolymer composition (P), MFR(B) is the calculated melt flow rate MFR.sub.2 (230 C.) [in g/10 min] of the propylene copolymer (B).

Xylene Cold Soluble Fraction (XCS wt %)

(14) Content of xylene cold solubles (XCS) is determined at 25 C. according ISO 16152; first edition; 2005 Jul. 1.

Hexane Solubles

FDA Section 177.1520

(15) 1 g of a polymer film of 100 m thickness is added to 400 ml hexane at 50 C. for 2 hours while stirring with a reflux cooler.

(16) After 2 hours the mixture is immediately filtered on a filter paper No 41.

(17) The precipitate is collected in an aluminium recipient and the residual hexane is evaporated on a steam bath under N.sub.2 flow.

(18) The amount of hexane solubles is determined by the formula
((wt. sample+wt. crucible)(wt crucible))/(wt. sample).Math.100.

(19) Melting temperature T.sub.m, crystallization temperature T.sub.c is measured with Mettler TA820 differential scanning calorimetry (DSC) on 5-10 mg samples. Both crystallization and melting curves were obtained during 10 C./min cooling and heating scans between 30 C. and 225 C. Melting and crystallization temperatures were taken as the peaks of endotherms and exotherms.

(20) Also the melt- and crystallization enthalpy (Hm and Hc) were measured by the DSC method according to ISO 11357-3.

(21) Porosity: BET with N.sub.2 gas, ASTM 4641, apparatus Micromeritics Tristar 3000; sample preparation: at a temperature of 50 C., 6 hours in vacuum.

(22) Surface area: BET with N.sub.2 gas ASTM D 3663, apparatus Micromeritics Tristar 3000: sample preparation at a temperature of 50 C., 6 hours in vacuum.

(23) Mean particle size is measured with Coulter Counter LS200 at room temperature with n-heptane as medium; particle sizes below 100 nm by transmission electron microscopy.

Sealing Initiation Temperature (SIT); Sealing End Temperature (SET), Sealing Range

(24) The method determines the sealing temperature range (sealing range) of polypropylene films. The sealing temperature range is the temperature range, in which the films can be sealed according to conditions given below.

(25) The lower limit (heat sealing initiation temperature (SIT)) is the sealing temperature at which a sealing strength of >1 N is achieved. The upper limit (sealing end temperature (SET)) is reached, when the films stick to the sealing device.

(26) The sealing range is determined on a DTC Hot tack tester Model 52-F/201 with a film of 25 m thickness with the following further parameters: Specimen width: 25 mm Seal Pressure: 0.66 N/mm.sup.2 Seal Time: 1 sec Cool time: 30 sec Peel Speed: 42 mm/sec Start temperature: 80 C. End temperature: 150 C.

(27) Specimen is sealed sealing layer (SL) to sealing layer (SL) at each sealbar temperature and seal strength (force) is determined at each step. All values of the SIT and SET were measured on the multi-layer film, like the three layer film as used in the examples. In cases where the SIT and SET refer to the propylene copolymer composition (P) or the sealing layer (SL) as such the SIT and SET were measured on a monolayer cast film of the propylene copolymer composition (P) and the sealing layer (SL), respectively, having a thickness of 100 m as described in application No. 10 160 631.7. and application No. 10 160 611.9.

Hot Tack Force

(28) The hot tack force is determined on a DTC Hot tack tester Model 52-F/201 with a film of 25 m thickness with the following further parameters: Specimen width: 25 mm Seal Pressure: 1.2 N/mm.sup.2 Seal Time: 0.5 sec Cool time: 0.2 sec Peel Speed: 200 mm/sec Start temperature: 90 C. End temperature: 140 C.

(29) The maximum hot tack force, i.e the maximum of a force/temperature diagram is determined and reported.

(30) Hot tack initiation temperature: is determined from the hot tack curve at the point where the force exceeds 1 N

(31) Gloss was determined on the multi-layerd films according to DIN 67530 at an angle of 20 C.

(32) Transparency, haze and clarity were determined on the multi-layerd films according to ASTM D 1003-00.

B. Examples

(33) The propylene copolymer compositions (P) of table 1 have been produced in a Borstar PP pilot plant in a two-step polymerization process starting in a bulk-phase loop reactor followed by polymerization in a gas phase reactor, varying the molecular weight as well as hexene content by appropriate hydrogen and comonomer feeds. The catalyst used in the polymerization process was a metallocene catalyst as described in example 10 of WO 2010/052263 A1.

(34) TABLE-US-00001 TABLE 1 Preparation of the propylene copolymer composition (P) P1 P2 P3 Loop MFR.sub.2 [g/10 4.0 4.3 4.1 min] C6 [wt.-%] 1.2 0.0 3.5 XCS [wt.-%] <1.5 <1.5 <1.5 GPR C6 [wt.-%] 7.4 5.8 6.6 Split [%] 45/55 34/66 58/42 Loop/GPR FINAL C6 [wt.-%] 4.8 3.8 5.3 XCS [wt.-%] 15.4 1.9 11.0 HHS [wt.-%] 0.9 0.8 1.0 MFR.sub.2 [g/10 7.9 10.0 11.0 min] Mw [kg/mol] 210 211 nm MWD [] 2.9 3.0 nm SIT [ C.] 102 108 98 Tm [ C.] 141 149 126 Tc [ C.] 100.4 101.2 90.9 Loop defines the polypropylene (A) GPR defines the propylene copolymer (B) Final defines the propylene copolymer (P) C6 is 1-hexene content HHS hexane hot solubles nm not measured SIT Sealing as initiation temperature measured on a monolayer film [100 m] as described in application No. 10 160 631.7. and application No. 10 160 611.9 P4 is the commercial propylene-ethylene-1-butene terpolymer TD215BF of Borealis AG having a melt flow rate MFR.sub.2 (230 C.) of 6 g/10 min, a melting temperature Tm of 130 C.. P5 is the commercial propylene-ethylene-1-butene terpolymer TD220BF of Borealis AG having a melt flow rate MFR.sub.2 (230 C.) of 6 g/10 min, a melting temperature Tm of 132 C.. P6 is the commercial random ethylene-propylene copolymer RE239CF of Borealis AG having a melt flow rate MFR.sub.2 (230 C.) of 11 g/10 min, a melting temperature Tm of 140 C.. H-PP is the commercial polypropylene homopolymer HD234CF of Borealis AG having a melt flow rate MFR.sub.2 (230 C.) of 8 g/10 min, a melting temperature Tm of 162 C..

(35) Three layer films were produced at three layer coex line, the film structure was OL-CL-SL with a core layer of 33 m (CL) and an outer layer of 8.5 m (OL) and one sealing layer (SL) of 8.5 m. For the core layer (CL) and the outer layer (OL) H-PP has been used, whereas for the sealing layer (SL) one of the polymers P1 to P6 have been used. The melt temperature of the polymers was in the range of 247 C. to 252 C. in the extruder die. The throughput for all three layer was in sum 60 kg/h. The take of speed of the film was 27.5 m/min to 31 m/min as a film width of 60 cm. The temperature of the chill roll was in the range of 13 C. to 20 C. The temperature of the water bath was in the range of 15 C. to 20 C.

(36) TABLE-US-00002 TABLE 2 Properties of the multi-layer polymer film CE1 CE2 CE3 IE1 IE2 IE3 P4 P5 P6 P1 P2 P3 SIT [ C.] 105 106 112 104 107 99 SET [ C.] 140 140 140 140 140 140 SET SIT [ C.] 35 34 28 36 33 41 HTF [N] 7.4 6.9 7 5.9 4.7 7.3 ST [ C.] 115 120 135 120 110 115 T [%] 93.7 93.7 93.6 93.7 93.7 93.7 H [%] 1.7 2.2 2.6 1.6 1.9 1.6 C [%] 96.7 96.4 95.9 97.2 97.1 97 TH [M] 49 50 50 50 51 50 G [%] 139.9 139.8 135.6 142 141.5 142.9 SIT is the heat sealing initiation temperature SET is the heat sealing end temperature SET SIT is the difference of SET and SIT ST is the sealing temperature HTF is the hot tack force T Transparancy H Haze C Clarity TH Thickness G Gloss 20