BOPP film with improved stiffness/toughness balance

Abstract

The present invention relates to a new biaxially oriented polypropylene (BOPP) film, a process for the preparation of such film as well as the use of a polypropylene for the preparation of such film and an article comprising such film.

Claims

1. A biaxially oriented polypropylene (BOPP) film comprising a polypropylene (PP), wherein the biaxially oriented polypropylene (BOPP) film has a) a modulus of elasticity in transverse direction (TD) of at least 5 000 N/mm.sup.2, and b) an elongation at break in machine direction (MD) of at least 170%, and wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having i) a melting temperature (T.sub.m) measured by differential scanning calorimetry (DSC) in the range of from 164 to 169 C., ii) a xylene cold soluble fraction (XCS) determined at 25 C. according to ISO 16152 in the range of from 1.0 to 3.5 wt %, and iii) a content of ethylene units in the range of from 0.01 to 0.5 wt %, based on the total weight of the random polypropylene copolymer (C-PP).

2. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the biaxially oriented polypropylene (BOPP) film has a) a modulus of elasticity in machine direction (MD) of at least 2 000 N/mm.sup.2, and/or b) an elongation at break in transverse direction (TD) of at least 46%.

3. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the biaxially oriented polypropylene (BOPP) film has a tensile strength in machine direction (MD) of at least 110 N/mm.sup.2 and/or a tensile strength in transverse direction (TD) of at least 300 N/mm.sup.2.

4. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having a) a crystallization temperature (T.sub.c) measured by differential scanning calorimetry (DSC) of at least 115 C., and/or b) a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of 7.0 g/10min, and/or c) an mmmm pentad content of 95.0% determined by .sup.13C NMR spectroscopy, and/or d) 2,1 erythro regio-defect content of below 1.0% determined by .sup.13C NMR spectroscopy.

5. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having a) a crystallization temperature (T.sub.c) measured by differential scanning calorimetry (DSC) of at least 118 C., and/or b) a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of 7.0 g/10 min, c) an mmmm pentad content of 95.0 to 98.0% determined by .sup.13C NMR spectroscopy, and/or d) 2,1 erythro regio-defect content of below 0.5% determined by .sup.13C NMR spectroscopy.

6. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having a comonomer corrected meso sequence length (MSL4) in the range of from 130 to 250 as determined by the following formula (IV)
MSL4=(((1(fE*5))*[mmmm])/(((1(fE*5))*0.5*[mmmr])+(0.5*2*fE)))+4 (IV).

7. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having a ratio of weight average molecular weight (M.sub.w) to number average molecular weight (M.sub.n) [M.sub.w/M.sub.n] of at least 4.0.

8. The biaxially oriented polypropylene (BOPP) film according to claim 7, wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having a ratio of weight average molecular weight (M.sub.w) to number average molecular weight (M.sub.n) [M.sub.w/M.sub.n] of at least 5.0.

9. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the polypropylene (PP) is a random polypropylene copolymer (C-PP) having a polydispersity index of 2.5.

10. The biaxially oriented polypropylene (BOPP) film according to claim 1, wherein the biaxially oriented polypropylene (BOPP) film has a) a draw ratio in machine direction (MD) of 3.0 and/or b) a draw ratio in transverse direction (TD) of 6.0.

11. The biaxially oriented polypropylene (BOPP) film according to claim 10, wherein the biaxially oriented polypropylene (BOPP) film has a) a draw ratio in machine direction (MD) of 4.0, and/or b) a draw ratio in transverse direction (TD) of 7.0.

12. A process for the preparation of a biaxially oriented polypropylene (BOPP) film according to claim 1, the process comprising at least the steps of i) providing a polypropylene (PP) which is a random polypropylene copolymer (C-PP) having a) a crystallization temperature (T.sub.c) measured by differential scanning calorimetry (DSC) of at least 115 C., and/or b) a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of 7.0 g/10 min, and/or c) an mmmm pentad content of 95.0% determined by .sup.13C NMR spectroscopy, and/or d) 2,1 erythro regio-defect content of below 1.0% determined by .sup.13C NMR spectroscopy, and ii) stretching the polypropylene (PP) of step i) in machine direction (MD) and transverse direction (TD), wherein the stretching in machine direction (MD) and transverse direction (TD) is carried out in consecutive steps.

13. The process according to claim 12, wherein the polypropylene (PP) has a) a drawing temperature (T.sub.draw) when drawn in transverse direction in the range of the inequation (II),
Tm25TdrawTm+10(II), wherein Tdraw is the drawing temperature (T.sub.draw) in C. of the first segment of the drawing zone (DZT) in the oven where the polypropylene (PP) is drawn in transverse direction, wherein further this first segment of the drawing zone (DZT) is defined as the zone where the draw ratio of the drawn polypropylene (PP) is at least 1.1; and Tm is the melting temperature (T.sub.m) of the polypropylene (PP) in C.; and optionally b) a drawing temperature (T.sub.draw) when drawn in transverse direction in the range of the inequation (III),
TmTdrawTm+18(III), wherein Tdraw is the drawing temperature (T.sub.draw) in C. of the heating zone (HZT) in the oven where the polypropylene (PP) is drawn in transverse direction, wherein further the heating zone (HZT) is the zone upstream to the drawing zone (DZT); and Tm is the melting temperature (T.sub.m) of the polypropylene (PP) in C.

14. The process according to claim 12, wherein the polypropylene (PP) has a drawing temperature (T.sub.draw) when stretched in machine direction in the range of the inequation (I)
Tm50TdrawTm15(I), wherein Tdraw is the drawing temperature (T.sub.draw) in C., wherein the drawing temperature (T.sub.draw) is defined as the temperature (in C.) of the first roll (R1) of two successive rolls (R1, R2) of all rolls in the oven consecutively arranged in machine direction where the polypropylene (PP) is drawn in machine direction, wherein further said two successive rolls (R1, R2) when locking in machine direction have as the first pair of successive rolls for the first time a roll speed difference of at least 20 m/min; and Tm is the melting temperature (T.sub.m) of the polypropylene (PP) in C.

15. The process according to claim 12, wherein step b) is carried out in that the polypropylene (PP) of step a) is stretched a) in machine direction (MD) with a draw ratio of 3.0 and/or b) in transverse direction (TD) with a draw ratio of 6.0.

16. An article comprising a biaxially oriented polypropylene (BOPP) film as defined in claim 1.

Description

EXAMPLES

(1) A. Measuring Methods

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

(3) Quantification of Ethylene Content by NMR Spectroscopy

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

(5) Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probehead at 125 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) along with chromium (III) acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225 and Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128). A total of 6144 (6 k) transients were acquired per spectra. Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present.

(6) Characteristic signals corresponding to the incorporation of ethylene were observed (Cheng, H. N., Macromolecules 17 (1984), 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer:
fE=(E/(P+E)

(7) The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) through integration of multiple signals across the whole spectral region in the .sup.13C{.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

(8) For systems with very low ethylene content where only isolated ethylene in PPEPP sequences were observed the method of Wang et. al. was modified reducing the influence of integration of sites that are no longer present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:
E=0.5(S+S+S+0.5(S+S))

(9) Through the use of this set of sites the corresponding integral equation becomes:
E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))
using the same notation used in the article of Wang et. al. (Wang, W-J., Zhu, S.,

(10) Macromolecules 33 (2000), 1157). Equations used for absolute propylene content were not modified.

(11) The mole percent comonomer incorporation was calculated from the mole fraction:
C2 [mol %]=100*fE

(12) The weight percent comonomer incorporation was calculated from the mole fraction:
C2 [wt %]=100*(fE*28.06)/((fE*28.06)+((1fE)*42.08))
Quantification of Microstructure by NMR Spectroscopy

(13) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity, tacticity distribution and content of regio-defects of the polymers.

(14) Quantitative .sup.13C{.sup.1H} NMR spectra recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm selective excitation probehead at 125 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2). This setup was chosen primarily for the high resolution needed for tacticity distribution quantification (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443, Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251). Standard single-pulse excitation was employed utilising the NOE and bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225 and Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251). A total of 8192 (8 k) transients were acquired per spectra.

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

(16) The tacticity distribution was quantified through integration of the methyl region between 23.6 and 19.7 ppm correcting for any sites not related to the stereo sequences of interest. (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443, and Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251). Characteristic signals corresponding isolated ethylene incorporation were observed (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157 and Cheng, H. N., Macromolecules 17 (1984), 1950). Characteristic signals corresponding to the presence of regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253) were not observed. With characteristic signals corresponding to regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253) or ethylene incorporation (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157 and Cheng, H. N., Macromolecules 17 (1984), 1950) observed the influence of regio-defects on the quantification of the tacticity distribution was corrected for by subtraction of representative integrals from integrals corresponding to specific steric n-ad sequences.

(17) The presence of copolymerised ethylene in the form of isolated ethylene incorporation was indicated by the presence of the S, T and S sites at 37.9, 30.9 and 24.5 ppm respectively and confirmed by the presence of other characteristic sites.

(18) The amount of isolated ethylene incorporation was quantified using the average integral (E) of the two characteristic methylene signals named S and S accounting the number of sites per unit and corrected using an empirically determined correction factor (f):
E=f*0.5*(0.5*S+S)

(19) The empirical correction factor was need as these signals are not directly quantitative with respect to the methyl signals under the given experimental conditions due to their different NOE and spin-lattice relaxation times.

(20) Characteristic signals corresponding to other forms of ethylene incorporation were not observed (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157 and Cheng, H. N., Macromolecules 17 (1984), 1950).

(21) The pentad tacticity distribution was determined through direct separate integration of each methyl signal from a given steric pentad followed by normalisation to the sum of methyl signals from all steric pentads. The relative content of a specific steric pentad was reported as the mole fraction or percentage of a given steric pentad xxxx with respect to all steric pentads:
[xxxx]=xxxx/(mmmm+mmmr+rmmr+mmrr+xmrx+mrmr+rrrr+mrrr+mrrm)
where xmrx represents the combined integral of both mmrm and rmrr as signal from these steric pentads are not commonly resolved. The pentad isotacticity was thus given by:
[mmmm]=mmmm/(mmmm+mmmr+rmmr+mmrr+xmrx+mrmr+rrrr+mm+mrrm)

(22) When appropriate integrals were corrected for the presence of sites not directly associated with steric pentads.

(23) Specifically the following corrections were applied to the raw integrals (xxxx) to account for the presence of sites not directly associated with steric pentads:
xmrx=xmrxE

(24) The amount of primary inserted propene (p) was quantified based on the integral of all signals in the methyl region (CH3) from 23.6 to 19.7 ppm with correction for other species included in the integral not related to primary insertion and for primary insertion signals excluded from this region such that:
p=CH3

(25) The average length of stereo sequences consisting of four or more monomer unites with like tacticity accounting for the presence of comonomer, i.e. the comonomer corrected meso sequence length determined from the pentad tacticity distribution (MSL4), was calculated using the mole fractions of the mmmm and mmmr steric pentads and mole fraction of the ethylene content (fE) as determined by the .sup.13C NMR spectroscopy method for ethylene comonomer content determination:
MSL4=(((1(fE*5))*[mmmm])/(((1(fE*5))*0.5*[mmmr])+(0.5*2*fE)))+4

(26) It should be noted that the equation for MSL4 is identical to that for MSL4 when the comonomer content is zero. That is if fE=0 then MSL4=MSL4=4+2 [mmmm]/[mmmr].

(27) Rheology: Dynamic rheological measurements were carried out with Rheometrics RDA-II QC on compression moulded samples under nitrogen atmosphere at 200 C. using 25 mmdiameter plate and plate geometry. The oscillatory shear experiments were done within the linear viscoelastic range of strain at frequencies from 0.01 to 500 rad/s. (ISO 6721-10)

(28) The values of storage modulus (G), loss modulus (G), complex modulus (G*) and complex viscosity (*) were obtained as a function of frequency ().

(29) The Zero shear viscosity (.sub.0) was calculated using complex fluidity defined as the reciprocal of complex viscosity. Its real and imaginary part are thus defined by
f()=()/[().sup.2+().sup.2] and
f()=()/[().sup.2+().sup.2]

(30) From the following equations
=G/ and =G/
f()=G()*/[G().sup.2+G().sup.2]
f()=G()*/[G().sup.2+G().sup.2]
The polydispersity index, PI,

(31) PI=10.sup.5/G.sub.c, is calculated from the cross-over point of G() and G(), for which G(.sub.c)=G(.sub.c)=G.sub.c holds.

(32) Melt Flow Rate (MFR.sub.2)

(33) The melt flow rates were 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 standardized to ISO 1133 extrudes within 10 minutes at a temperature of 230 C. under a load of 2.16 kg.

(34) The Xylene Solubles (XCS, Wt.-%): Content of xylene cold solubles (XCS) is determined at 25 C. according ISO 16152; first edition; 2005-07-01.

(35) 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.

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

(37) Tensile strength in machine and transverse direction were determined according to ISO 527-3 at 23 C. on the biaxially oriented films. Testing was performed at a cross head speed of 1 mm/min.

(38) Elongation at break in machine and transverse direction were determined according to ISO 527-3 at 23 C. on the biaxially oriented films. Testing was performed at a cross head speed of 1 mm/min.

(39) Modulus of Elasticity in machine and transverse direction were determined according to ISO 527-3 at 23 C. on the biaxially oriented films. Testing was performed at a cross head speed of 1 mm/min.

(40) Number Average Molecular Weight (M.sub.n), Weight Average Molecular Weight (M.sub.w)

(41) Molecular weight averages Mw and Mn were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3 Olexis and 1 Olexis Guard columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 160 C. and at a constant flow rate of 1 mL/min 200 L of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11 500 kg/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D 6474-99. All samples were prepared by dissolving 5.0-9.0 mg of polymer in 8 mL (at 160 C.) of stabilized TCB (same as mobile phase) for 2.5 hours for PP or 3 hours for PE at max. 160 C. under continuous gentle shaking in the autosampler of the GPC instrument.

(42) B. Examples

(43) The catalyst used in the polymerization process for examples IE1 and IE2 has been produced as follows: First, 0.1 mol of MgCl.sub.23 EtOH was suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution was cooled to the temperature of 15 C. and 300 ml of cold TiCl.sub.4 was added while maintaining the temperature at said level. Then, the temperature of the slurry was increased slowly to 20 C. At this temperature, 0.02 mol of dioctylphthalate (DOP) was added to the slurry. After the addition of the phthalate, the temperature was raised to 135 C. during 90 minutes and the slurry was allowed to stand for 60 minutes. Then, another 300 ml of TiCl.sub.4 was added and the temperature was kept at 135 C. for 120 minutes. After this, the catalyst was filtered from the liquid and washed six times with 300 ml heptane at 80 C. Then, the solid catalyst component was filtered and dried. Catalyst and its preparation concept is described in general e.g. in patent publications EP491566, EP591224 and EP586390. As co-catalyst triethyl-aluminium (TEAL) and as donor dicyclo pentyl dimethoxy silane (D-donor) was used. The aluminium to donor ratio is indicated in table 1.

(44) As additives 0.56 wt. % of a mixture of 1.3 parts of Calicium Stearate (Ceasit FI from Bearlocher), 80.7 parts of Pentaerythrityl-tetrakis(3-(3,5-di-tert. butyl-4-hydroxyphenyl)-propionate (Irganox 1010 from BASF AG) and 18.0 parts of 2,6-di-tert. butyl-4-methyl phenol (Ionol CP from Oxiris Chemicals) were added to the polymers.

(45) TABLE-US-00001 TABLE 1 Preparation of examples IE1 and IE2 Example IE1 IE2 Ti in cat [wt.-%] 1.8 1.8 TEAL/Ti [mol/mol] 154 154 TEAL/Donor [mol/mol] 16 16 Prepoly Reactor Temp. [ C.] 30 30 H2/C3 [mol/kmol] 0.589 0.589 Loop Reactor Temp. [ C.] 85 85 H2/C3 [mol/kmol] 1.489 1.489 split [wt.-%] 39.3 39.3 MFR.sub.2 [g/10 min] 3.05 3.05 GPR 1 Reactor Temp. [ C.] 85 85 H2/C3 [mol/kmol] 17 17 split [wt.-%] 54.2 54.2 MFR.sub.2 [g/10 min] 2.8 2.8 MFR.sub.2 produced in GPR1 [g/10 min] 2.65 2.65 GPR 2 Reactor Temp. [ C.] 90 90 H2/C3 [mol/kmol] 20 20 C2/C3 [mol/kmol] 2.5 split [wt.-%] 6.5 6.5 MFR.sub.2 [g/10 min] 2.8 2.8 MFR.sub.2 produced in GPR2 [g/10 min] 2.8 2.8

(46) The properties of the unstretched inventive examples IE1 and IE2 as well as of a comparative example CE1 are summarized in Table 2.

(47) TABLE-US-00002 TABLE 2 Properties of unstretched polypropylene samples Examples Unit CE1 IE1 IE2 C2 [mol %] 0 0 0.2 MFR.sub.2 [g/10 min] 2.2 3.5 3.5 XS [wt %] 3.3 1.6 1.6 mmmm [%] 92.3 97.2 97.2 T.sub.m [ C.] 159.5 166.0 164.0 T.sub.c [ C.] 111.3 124.6 124.6 PI [Pas.sup.1] 4.3 3.4 3.4 M.sub.w/M.sub.n [] 6.1 6.2 6.2 MSL4 [monomers] 100 210 146

(48) As comparative example CE1, a commercial propylene homopolymer (available as HB311BF from Borealis AG, Austria) has been used.

(49) A biaxially oriented polypropylene (BOPP) film comprising either the inventive example IE1, the inventive example IE2 or the comparative example CE1 was prepared by using a BOPP pilot line of Brckner Maschinenbau. The used BOPP pilot line closely resembles the tenter frame technology of full scale commercial lines, comprising of (i) a casting unit to create a sheet of un-oriented film, (ii) a machine orientation section to stretch the cast film in machine direction (MD) (machine orientation operation (MDO)) and (iii) a heated oven for the transverse orientation operation (TDO), yielding the BOPP film.

(50) In Table 3, the applied settings for the preparation of the present BOPP film are outlined.

(51) TABLE-US-00003 TABLE 3 Settings for the BOPP film preparation Length of Strain Temperature speed relevant Draw rate [ C.] [m/min] drawing section ratio () Melt 260.sup. 15 cm.sup.a 4 2 s.sup.1 Cast 90 13 n.a. 0 MDO 137.sup.b 13 .fwdarw. 60 5 mm.sup.c 4.6 ~6 s.sup.1 TDO1 170 to 176 60 4.1 m.sup.d 1.0 0.0 TDO2 164.sup.e 60 0.8 m.sup.f 1.1-2.7 1 s.sup.1 TDO3 160-164 60 3.3 m.sup.g 1.1-9.0 1 s.sup.1 .sup.adistance between chill roll and die exit, .sup.btemperature of the first roll (R1) of the two successive rolls (R1, R2) = [T.sub.draw], .sup.cdistance between last heating roll and first drawing roll .sup.dthe length of the heating zone .sup.etemperature of the first segment of the drawing zone (DZT) = T.sub.draw .sup.flength of the first segment of the drawing zone (DZT) .sup.gthe total length of the drawing zone (DZT) MDO drawing in machine direction [T.sub.draw] TDO1 drawin in transverse direction: heating zone (HZT) [T.sub.draw] TDO2 drawin in transverse direction: first segment of the drawing zone (DZT) [T.sub.draw] TDO3 drawin in transverse direction: total drawing zone (DZT)

(52) Each resin was extruded through a T-die (die-gap 1 mm) and was cast onto the chill roll which was set to 90 C. The melt, before contacting the chill roll, was drawn in air by a factor 4, at a Hencky strain rate of approximately 2 s.sup.1, as achieved by the difference in melt output rate and take up speed (13 m/min) A final cast film thickness of 250 m was obtained. This cast film was continuously fed to the MDO unit.

(53) The MDO unit of the Bruckner pilot BOPP line was composed of 12 rolls, of which the first 7 rolls are used to heat the cast film to the MD stretching temperature (137 C.). Rolls 8-12 were run at 60 m/min, providing the MDO drawing by a factor of 4.6 (.sub.MDO). The final rolls of the MDO unit anneal the MDO film at 126 C. The very small gap width between roll 7 and 8 (5-10 mm) causes a very high strain rate of 6 s.sup.1. Table 4 lists the temperature of each MDO roll.

(54) TABLE-US-00004 TABLE 4 Temperatures of MDO rolls Roll # 1 2 3 4 5 6 7 8 9 10 11 12 Temperature [ C.] 88 94 102 108 114 120 137 135 110 110 126 126

(55) The drawing of the MDO film in TD direction and its transport in MD direction along the length of the TDO oven was accomplished by two counter rotating belts, which run on both sides of the TDO oven, both equipped with several, equidistant clamps. The clamps of each belt, before they enter the TDO oven, automatically open and then close to grab the MDO film which is continuously fed into the TDO oven consisting of a heating-, drawing-, relaxation- and annealing-zone. Each zone is further segmented into shorter sections which can be set to a selected temperature. The temperatures in the TDO oven were typically adjusted to temperatures between 140 and 175 C.

(56) The TDO drawing was accomplished by the increase of the transversal belt-to-belt distance in the drawing zone. The belt-to-belt distance increases linearly, providing a non-constant (decreasing) TD drawing rate of the MDO film. The initial strain rate, calculated from length of the drawing section (3.3 m), line speed (60 m/min) and TD drawing ratio (9) is 1 s.sup.1. This is a typical strain rate for full scale lines. In the relaxation zone of the TDO oven, the draw ratio was slightly reduced, via a small decrease in the belt-to-belt TD-distance. The TDO film was collected on a cardboard mandrel and stored for further analyses.

(57) The properties of the biaxially oriented polypropylene (BOPP) films prepared from the polypropylenes of the inventive examples IE1 and IE2 and comparative example CE1 are summarized in Table 5.

(58) TABLE-US-00005 TABLE 5 Biaxially oriented polypropylene (BOPP) films Tensile Elongation Modulus of strength at break Elasticity Tdraw'in MD TD MD TD MD TD TD [N/mm.sup.2] [N/mm.sup.2] [%] [%] [N/mm.sup.2] [N/mm.sup.2] CE1 166 C. 105 244 167 43 1787 3462 IE1 164 C. 178 415 186 48 2509 5557 IE1 170 C. 162 401 194 54 2493 5352 IE2 164 C. 147 365 220 55 2309 5257 IE2 170 C. 120 310 200 63 2100 5100

(59) As can be gathered from the measured details outlined in Table 5, the inventive BOPP film has favourable film properties compared to prior art biaxially oriented polypropylene (BOPP) films. In particular, it can be gathered that the inventive BOPP films show a better balanced mechanical property profile. For example, the inventive BOPP films show higher stiffness, i.e. modulus of elasticity, and toughness, i.e. elongation at break, than films made with polypropylenes of the prior art.