Multi-layer biaxially oriented polymer film

Abstract

A multi-layer biaxially oriented polymer film comprising a core layer (CL) and at least one sealing layer (SL), said sealing layer(s) (SL) comprise(s) a propylene copolymer composition (P) having a comonomer content in the range of 3.0 to 8.0 wt.-%, the comonomers are C.sub.5 to C.sub.12 -olefins, said propylene copolymer composition (P) 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. A multi-layer biaxially oriented polymer film comprising: (a) a core layer (CL) 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) (c1) has a comonomer content in the range of 3.0 to 8.0 wt. %, the comonomer is C.sub.6 alpha olefin, (c2) comprises a polypropylene (A) and a propylene copolymer (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 comonomer is C.sub.6 alpha olefin, and said propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt. %, the comonomer is C.sub.6 alpha olefin, (c3) 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); (c4) has a melting temperature Tm determined by differential scanning calorimetry (DSC) of at least 135 C.; and (c5) has a heat sealing initiation temperature (SIT) of equal or below 115 C.; and (c6) has a xylene soluble content (XCS) determined at 25 C. according to ISO 16152 of below 20.0 wt. %; and (c7) is free of any elastomeric component.

2. A multi-layer biaxially oriented polymer film according to claim 1, wherein the sealing layer (SL) and/or the propylene copolymer composition (P) has/have a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 2.0 to 50.0 g/10 min.

3. A multi-layer biaxially oriented polymer film according to claim 1, wherein the sealing layer (SL) and/or the propylene copolymer composition (P) has/have: a molecular weight distribution (MWD) measured by gel permeation chromatography (GPC) of at least 2.5.

4. A multi-layer biaxially oriented polymer film according to claim 1, wherein: (a) the comonomer content in the polypropylene (A) is lower compared to the comonomer content in the propylene copolymer (B), and/or (b) com (P)com (A) is at least 1.0, wherein com (A) is the comonomer content of the polypropylene (A) given in weight percent [wt. %], com (P) is the comonomer content of the propylene copolymer composition (P) given in weight percent [wt. %].

5. A multi-layer biaxially oriented polymer film according to claim 1, wherein the sealing layer (SL) and/or the propylene copolymer composition (P) fulfill(s) the equation (I):
TmSIT22 C.(I) wherein Tm is the melting temperature of the sealing layer (SL) and/or of the propylene copolymer composition (P) determined by differential scanning calorimetry (DSC) and given in centigrade [ C.], SIT is the heat sealing initiation temperature (SIT) given in centigrade [ C.] of the sealing layer (SL) and/or of the propylene copolymer composition (P).

6. A multi-layer biaxially oriented polymer film according to claim 1, wherein the polypropylene (A) of the propylene copolymer composition (P): (a) is a propylene copolymer (C-A) with a comonomer content in the range of 0.5 to below 4.0 wt. %, and/or (b) has a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of at least 1.5 g/10 min, and/or (c) has a xylene soluble content (XCS) of below 2.5 wt. %.

7. A multi-layer biaxially oriented polymer film according to claim 1, wherein said core layer (CL) comprises a propylene homopolymer.

8. A multi-layer biaxially oriented polymer film according to claim 1, wherein said core layer (CL) is a polypropylene (PP) or a propylene homopolymer (H-PP) having: (a) a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 1.0 to 15.0 g/10 min, and/or (b) a melting temperature Tm determined by differential scanning calorimetry (DSC) of at least 155 C.

9. A multi-layer biaxially oriented polymer film according to claim 1, wherein: (a) core layer (CL) has a thickness in the range of 5 to 80 m, and/or (b) the sealing layer (SL) has a thickness in the range of 0.2 to 15 m.

10. A multi-layer biaxially oriented polymer film according to claim 1, wherein said multi-layer biaxially oriented polymer film comprises three layers, namely the core layer (CL), the sealing layer (SL) and at least one of: (a) an outer layer (OL) being a polyolefin (PO), or (b) a further sealing layer (SL), or (c) a metal layer (ML), wherein the multi-layer biaxially oriented polymer film has the stacking order: (a1) sealing layer (SL)-core layer (CL) outer layer (OL), or (b1) sealing layer (SL)-core layer (CL)-sealing layer (SL), or (c1) sealing layer (SL)-core layer (CL)-a metal layer (ML).

Description

EXAMPLES

(1) A. Measuring Methods

(2) 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.

(3) Quantification of Microstructure by NMR Spectroscopy

(4) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity, regio-regularity and comonomer content of the polymers.

(5) 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.

(6) 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.

(7) 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.

(8) 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.

(9) 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

(10) 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. 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)

(11) 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

(12) Calculation of comonomer content of the propylene copolymer (B):

(13) $\frac{C\left(P\right)-w\left(A\right)\mathrm{xC}\left(A\right)}{w\left(B\right)}=C\left(B\right)$
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

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

(15) 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.

(16) Melt Flow Rate (MFR)

(17) 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 MFR.sub.2 (230 C.) of the propylene copolymer (B):

(18) $MFR\left(B\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(P\right)\right)-w\left(A\right)\log \left(MFR\left(A\right)\right)}{w\left(B\right)}\right]}$
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 %)

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

(20) Hexane Solubles

(21) FDA section 177.1520

(22) 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.

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

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

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

(26) 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.

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

(28) 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.

(29) 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.

(30) 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

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

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

(33) 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.

(34) 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:

(35) Specimen width: 25 mm

(36) Seal Pressure: 0.66 N/mm.sup.2

(37) Seal Time: 1 sec

(38) Cool time: 30 sec

(39) Peel Speed: 42 mm/sec

(40) Start temperature: 80 C.

(41) End temperature: 150 C.

(42) 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. Sealing Strength is the force measured at the temperature defined in Table 2.

(43) Hot Tack Force:

(44) 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:

(45) Specimen width: 25 mm

(46) Seal Pressure: 1.2 N/mm.sup.2

(47) Seal Time: 0.5 sec

(48) Cool time: 0.2 sec

(49) Peel Speed: 200 mm/sec

(50) Start temperature: 90 C.

(51) End temperature: 140 C.

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

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

(54) Gloss was determined on the multi-layered films according to DIN 67530-1982 at an angle of 20.

(55) Transparency, haze and clarity were determined on the multi-layered films according to ASTM D1003-00

B. Examples

(56) 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.

(57) TABLE-US-00001 TABLE 1 Preparation of the propylene copolymer composition (P) P1 P2 P3 Loop MFR.sub.2 [g/10 min] 4.6 3.4 4.0 C6 [wt.-%] 0.0 1.2 1.2 XCS [wt.-%] <1.5 <1.5 <1.5 GPR C6 [wt.-%] 5.5 5.9 7.4 Split Loop/GPR [%] 39/61 47/53 45/55 FINAL C6 [wt.-%] 3.2 3.6 4.4 XCS [wt.-%] 2 2.3 5.5 HHS [wt.-%] 0.7 0.8 0.9 MFR.sub.2 [g/10 min] 8.6 8.2 7.9 Mw [kg/mol] 226 224 210 MWD [] 3.0 2.9 2.9 SIT [ C.] nm nm 102 Tm [ C.] 148 141 141 Tc [ C.] 111 97 100 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 soluble SIT Sealing 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 nm not measured P4 is the commercial propylene-ethylene-1-butene terpolymer TD210BF of Borealis AG having a melt flow rate MFR.sub.2 (230 C.) of 6 g/10 min, a melting temperature Tm of 131 C. and a MWD of 4.9 H-PP is the commercial polypropylene homopolymer HC101BF of Borealis AG having a melt flow rate MFR.sub.2 (230 C.) of 3.2 g/10 min, a melting temperature Tm of 161 C.

(58) Three layer biaxial oriented polymer films were produced on a BOPP pilot line. In the first step a three layer cast film was co-extruded by a flat t-shaped die with a die width of 300 mm. The film thickness of the co-extruded film was in the range of 800 m to 900 m. The melt temperature of the core layer (H-PP) was in the range of 255 C. to 260 C. The melt temperature of the sealing layer and the opposite layer (same polymer as the sealing layer) was in the range of 260 C. to 265 C. The produced three layer film was casted on a chill roll and cooled by a water bath with a temperature of 19 C. to 22 C. The temperature of the chill roll was in the range of 23 C. to 24 C. The contact of the co-extruded film to the chill roll was supported by an air knife with an air temperature of 35 C. to 39 C.

(59) In a second step the casted film was longitudinal stretched by two pairs of temperature controlled rolls at a temperature at 109 C. to 111 C. The total stretching ratio in machine direction was 1:4.5. Afterwards the film was stretched in transverse direction in a tenter with mechanical clips at temperature higher as 150 C. Typical temperature in the stretching zone of the tenter was 165 C. to 170 C. The stretching ratio of the three layer film in traverse direction was 1:8.0. In a further zone the film was relaxed to a stretching ratio of 1:7.5 at temperature of 144 C. to 147 C. The final film sped was 63 m/min.

(60) Afterwards the opposite layer to the sealing layer was corona treated for identification of the sealing layer at the following film testing.

(61) In the final film structure of the produced three layer BOPP film the sealing layer and the opposite corona treated layer each had a thickness of 0.5 m to 1.8 m (see table 2) and the thickness of the core layer was 22 m to 24 m. The thickness of the three layers was controlled by the throughput of the three corresponding extruders.

(62) For the core layer (CL) H-PP has been used, whereas for the sealing layers (SL) one of the polymers P1 to P4 have been used.

(63) TABLE-US-00002 TABLE 2 Properties of the multi-layer biaxially oriented polymer film CE1 CE2 IE1A IE1B IE2A IE2B IE3A IE3B P4 P4 P1 P1 P2 P2 P3 P3 LT [m] 1.2 0.5 1.5 0.6 1.4 0.7 1.8 0.7 HTF [N] 3.6 3.2 4.0 4.0 n.a. n.a. 6.2 4.0 HT-IT [ C.] 98 102 93 94 n.a. n.a. 85 88 SS (A) [N] 1.6 1.6 1.6 1.6 1.5 2.5 6.8 4.7 SS (B) [N] 3.3 3.0 3.9 3.6 3.9 6.3 9.2 5.4 SIT [ C.] 110 110 110 110 110 105 100 100 T [%] 93.7 93.7 93.7 93.7 93.7 93.7 93.8 93.7 H [%] 1.1 0.9 0.6 0.6 0.8 0.5 0.9 0.4 C [%] 97.6 98.2 97.4 98.2 97.1 98.2 97.7 98.2 LT Layer thickness of the sealing layers determined by Scanning Electron Microscopy SIT is the heat sealing initiation temperature HTF is the hot tack force HT-IT Hot Tack initiation temperature at F>1N (see page 32) SS(A) is the sealing strength at 105 C. SS(B) is the sealing strength at 110 C. T Transparency H Haze C Clarity