POLYOLEFIN COMPOSITION FOR NON-ORIENTED FILM WITH IMRPOVED OXYGEN BARRIER PROPERTY

Abstract

The present invention is directed to a polyolefin composition suitable for producing a non-oriented film with improved oxygen barrier property, and to such a non-oriented film. The polyolefin composition comprises a propylene homo-or copolymer, a hydrocarbon resin and optionally a nucleating agent. The present invention is also directed to the use of a hydrocarbon resin in a non-oriented film comprising a propylene homo- or copolymer for improving oxygen barrier property of said non-oriented film. The present invention allows the application of a polypropylene based non-oriented film like a cast film (CPP) for packaging of sensitive food.

Claims

1. A polyolefin composition comprising: (A) a propylene homo- or copolymer with an MFR.sub.2 of 0.5-80 g/10 min as measured in accordance with ISO 1133, and (B) a hydrocarbon resin product comprising a hydrocarbon resin, wherein the hydrocarbon resin has: a weight average molecular weight of 500-5,000 g/mol, or a melt viscosity of 80-400 mPa.Math.s at 200 C. as measured according to ASTM D-3236, or a softening point of 200 C. or less as measured according to ASTM E-28, or by any combination thereof.

2. The polyolefin composition according to claim 1, further comprising: (C) a nucleating agent.

3. The polyolefin composition according to claim 2, wherein the nucleating agent (C) is a polymeric alpha-nucleating agent.

4. The polyolefin composition according to claim 1, wherein component (A) is a propylene copolymer and the comonomer in component (A) is ethylene and/or a C.sub.4-C.sub.8--olefin, and the comonomer content is less than 7.5 mol. % based on the propylene copolymer.

5. The polyolefin composition according to claim 1, wherein component (A) is a propylene homopolymer.

6. The polyolefin composition according to claim 1, wherein the propylene homo- or copolymer (A) has a melting temperature (T.sub.m) of at least 150.0 C. as measured by differential scanning calorimetry (DSC).

7. The polyolefin composition according to claim 1, wherein the propylene homo- or copolymer (A) has: a flexural modulus of at least 1,400 MPa as measured according to ISO 178, and/or a Vicat softening temperature of at least 140 C. as measured according to ISO 306.

8. The polyolefin composition according to claim 1, wherein the amount of the hydrocarbon resin product (B) is 1-40 wt. % based on the entire polyolefin composition.

9. The polyolefin composition according to claim 1, with the proviso that the composition does not comprise a blend of a polypropylene polymer having an MFR.sub.2 of 2.9 g/10 min, 15 wt. % of a dicyclopentadiene based hydrocarbon resin having a softening point of 140 C., and 180 ppm of a nucleating agent.

10. The polyolefin composition according to claim 1, with the proviso that the composition does not comprise a blend of a propylene homopolymer having a density of 0.91 g/cm.sup.3 and a melt index of 2.0 g/10 min, 15 wt. % of a fully hydrogenated hydrocarbon resin having a softening point of 125 C., and 3,000 ppm of 1,3:2,4-dibenzylidene sorbitol.

11. The polyolefin composition according to claim 1, with the proviso that the composition does not comprise a blend comprising a propylene ethylene random copolymer having a melt index at 230 C. and 2.16 kg load of 7.2 g/10 min, 0.3 wt.-% or 1.0 wt. % of a hydrocarbon resin, and 0.05 wt. % of calcium stearate.

12. The polyolefin composition according to claim 1, with the proviso that the composition does not comprise a blend of 83.3 wt. % of a polypropylene, 14.7 wt. % of a hydrocarbon resin, 0.08 wt. % of a nucleating agent, and 1.92 wt. % of a low density polyethylene.

13. An article comprising a polyolefin composition according to claim 1.

14. The article according to claim 13, wherein the article is a non-oriented film.

15. The article according to claim 14, wherein the cast film is obtained from the polyolefin composition in a cast film production process, wherein the chill roll has a temperature of 20-90 C.

Description

EXAMPLES

[0165] 1. Definitions/Measuring Methods

[0166] 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. MFR.sub.2 is measured at 230 C. with a load of 2.16 kg according to ISO 1133.

[0167] Pentad isotacticity (mmmm) is determined by .sup.13C NMR spectroscopy as defined below. Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the stereo-regularity (tacticity) and regio-regularity of the polymers.

[0168] 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.

[0169] For polypropylene homopolymers approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary 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 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; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 11289). A total of 8192 (8k) transients were acquired per spectra.

[0170] Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0171] For polypropylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0172] The tacticity distribution was quantified through integration of the methyl region between 23.6-19.7 ppm correcting for any sites not related to the stereo sequences of interest (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromoleucles 30 (1997) 6251).

[0173] Specifically the influence of regio defects and comonomer on the quantification of the tacticity distribution was corrected for by subtraction of representative regio defect and comonomer integrals from the specific integral regions of the stereo sequences.

[0174] The isotacticity was determined at the pentad level and reported as the percentage of isotactic pentad (mmmm) sequences with respect to all pentad sequences:

[mmmm] %=100*(mmmm/sum of all pentads)

[0175] The presence of 2,1 erythro regio defects was indicated by the presence of the two methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic sites.

[0176] Characteristic signals corresponding to other types of regio defects were not observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

[0177] The amount of 2,1 erythro regio defects was quantified using the average integral of the two characteristic methyl sites at 17.7 and 17.2 ppm:

P.sub.21e=I.sub.e6+I.sub.e8)/2

[0178] The amount of 1,2 primary inserted propene was quantified based on the methyl region with correction undertaken for sites included in this region not related to primary insertion and for primary insertion sites excluded from this region:

P.sub.12=I.sub.CH3+P.sub.12e

[0179] The total amount of propene was quantified as the sum of primary inserted propene and all other present regio defects:

P.sub.total=P.sub.12+P.sub.21e

[0180] The mole percent of 2,1 erythro regio defects was quantified with respect to all propene:

[21e] mol %=100*(P.sub.21e/P.sub.total)

[0181] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.

[0182] 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 as described in G. Singh, A. Kothari, V. Gupta, Polymer Testing 2009, 28(5), 475.

[0183] 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 as described in Z. Zhou, R. Kuemmerle, X. Qiu, D. Redwine, R. Cong, A. Taha, D. Baugh, B. Winniford, J. Mag. Reson. 187 (2007) 225 and V. Busico, P. Carbonniere, R. Cipullo, C. Pellecchia, J. Severn, G. Talarico, Macromol. Rapid Commun. 2007, 28, 1128. A total of 6144 (6 k) transients were acquired per spectra.

[0184] 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.

[0185] With characteristic signals corresponding to 2,1 erythro regio defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) the correction for the influence of the regio defects on determined properties was required. Characteristic signals corresponding to other types of regio defects were not observed.

[0186] Characteristic signals corresponding to the incorporation of ethylene were observed (as described in Cheng, H. N., Macromolecules 1984, 17, 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer.

[0187] The comonomer fraction was quantified using the method of W-J. Wang and S. Zhu, Macromolecules 2000, 33 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.

[0188] The mole percent comonomer incorporation was calculated from the mole fraction.

[0189] The weight percent comonomer incorporation was calculated from the mole fraction.

[0190] Vicat softening temperature: Softening point for soft plastics can be measured according to ISO 306:2013 standard method; on specimen type plaque 2402404 mm, conditioning time 96 hrs or more, heating rate 50 K/h, load 10 N.

[0191] Softening point is measured according to ASTM-E28.

[0192] Melting temperature (T.sub.m), crystallization temperature (T.sub.cr), and degree of crystallinity: The melting temperature of the used polymers was measured in accordance with ASTM D3418. T.sub.m and T.sub.cr were measured with Mettler TA820 differential scanning calorimetry (DSC) on 3+/0.5 mg samples. Both crystallization and melting curves were obtained during 10 C./min cooling and heating scans between 10 to 200 C. Melting and crystallization temperatures were taken as the peaks of endotherms and exotherms. The degree of crystallinity was calculated by comparison with heat of fusion of a perfectly crystalline polymer of the same polymer type, e.g. for polyethylene, 290 J/g.

[0193] 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 (40.Math.10.Math.1 mm.sup.3) between 100 C. and +150 C. with a heating rate of 2 C./min and a frequency of 1 Hz.

[0194] Flexural Modulus: The flexural modulus is determined according to ISO 178. The test specimens having a dimension of 80104.0 mm.sup.3 (lengthwidththickness) are prepared by injection moulding according to EN ISO 1873-2. The specimens are conditioned at 23 C. and 50% relative humidity. The length of the span between the supports is 64 mm, the test speed is 2 mm/min and the force is 100 N.

[0195] Content of xylene cold solubles (XCS) is determined at 25 C. according to ISO 16152; first edition; 2005-07-01.

[0196] 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:

[0197] 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 3 TSK-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.

[0198] Melt viscosity is measured according to ASTM D-3236.

[0199] Transparency, haze and clarity: All optical parameters are measured on 40 m thick cast films. Transparency, haze and clarity were determined according to ASTM D 1003.

[0200] Gloss is measured on 40 m thick cast film according to DIN 67530 at an angle of 60.

[0201] Tensile test (modulus, strength and extension at break) is measured at 23 C. according to ISO 527-1 (with a specimen Type 2, 15 mm width at cross head speed 1 mm/min) and ISO 527-3 (with a specimen Type 2, 15 mm width at a speed of 200 mm/min) using 40 m thick cast film.

[0202] Oxygen barrier property, i.e. oxygen transmission rate, is determined on cast films having a thickness of 40 m. The specimen is mounted as a sealed semi-barrier between two chambers at ambient atmospheric pressure. One chamber is slowly purged by a stream of nitrogen and hydrogen gas mixture (2% H.sub.2 in N.sub.2) at a given temperature and relative humidity and the other chamber is purged by a stream of oxygen at the same temperature and relative humidity as the N.sub.2 stream. As oxygen gas permeates through the film into the nitrogen carrier gas, it is transported to the coulometric detector where it produces an electrical current, the magnitude of which is proportional to the amount of oxygen flowing into the detector per unit time. The oxygen transmission rate test is performed as per ASTM D 3985, at 23 C. and 0% relative humidity, with using 10 sccm of N.sub.2/H.sub.2 and O.sub.2 (99.999%) gases and a film surface area of 1 cm.sup.2.

[0203] 2. Examples

[0204] In the following inventive examples (IE) and comparative examples (CE) the following compounds are used.

[0205] HD915CF, is a propylene homopolymer containing 200 ppm or less of a nucleating agent. It has an MFR.sub.2 of 8 g/10 min, a melting temperature of 164-170 C., a flexural modulus of 2,100 MPa and a Vicat softening temperature of 158 C.

[0206] HD601CF, is a propylene homopolymer. The polymer does not comprise any nucleating agent. HD601CF has an MFR.sub.2 of 8 g/10 min, a melting temperature of 164 C., a flexural modulus of 1,450 MPa and a Vicat softening temperature of 154 C.

[0207] HD915CF and HD601CF are commercially available by Borealis AG or Borouge, respectively.

[0208] Arkon P-125 is a fully hydrogenated hydrocarbon resin and is commercially available by Arakawa Chemical Industries, Ltd., Japan. The hydrocarbon resin has a softening point of 125 C. (ASTM E-28), a weight average molecular weight M.sub.w of 1300 g/mol and a melt viscosity of 300 mPa.Math.s at 200 C. as measured according to ASTM D-3236.

[0209] Constab MA930PP is a master batch containing 60 wt.-% of a fully hydrogenated hydrocarbon resin and is commercially available by Constab Polyolefin Additives GmbH. The hydrocarbon resin has a softening point of 150 C. (ASTM E-28), a weight average molecular weight M.sub.w of 800 g/mol and a melt viscosity of 200 mPa.Math.s at 200 C. as measured according to ASTM D-3236.

[0210] HPN20E is an alpha-nucleating agent commercially available by Milliken Chemical.

[0211] Preparation of the Cast Film Samples.

[0212] Cast films having a thickness of around 40 m are produced on Collin equipment with different chill roll (CR) temperatures from the propylene homopolymers after compounding with a hydrocarbon resin (product) and/or an alpha-nucleating agent, if any.

[0213] Monolayer films are cast coextruded (three extruders are fed with the same product with structure 1/2/1).

[0214] Total thickness: 40 m

[0215] Total throughput: 6 kg/h

[0216] Melt temperature: 210-220 C., depended on the test sample

[0217] Chill roll temperature depends from the trial, from 20 to 50 C. as indicated in Table 1 below.

[0218] The melt pressure is reduced in case of inventive examples. The more component (B), the more the melt pressure is reduced.

[0219] The following tables illustrate the films which were produced according to the inventive examples (IE) and comparative examples (CI) and also the obtained properties.

[0220] In the following tables the following abbreviations are used and units apply: [0221] P1 for polymer 1, HD601CF [0222] P2 for polymer 2, HD915CF [0223] HR1 for hydrocarbon resin product 1, Arkon P-125, amount 10 or 20 wt.-% [0224] HR2 for hydrocarbon resin product 2, Constab MA930PP, amount 10 or 20 wt.-% [0225] NA for nucleating agent, HPN20E, amount 500 or 1,000 ppm [0226] CRT for chill roll temperature [0227] TH for thickness of the cast film [0228] OTR oxygen transmission rate, average values of three measurements, SD for standard deviation; values calculated for a 40.0 m thick film and values calculated for a 1 mm thick film [0229] HZ for haze [0230] GL for gloss [0231] TM for tensile modulus; MD for machine direction, TD for transverse direction

TABLE-US-00001 TABLE 1 Composition and properties of cast films OTR/ml/m.sup.2 .Math. d TM/MPa Polyolefin composition CRT/ C. TH/m 1 mm film HZ GL MD/TD CE1 P1 20 42.0 93 0.1 153 966/939 CE2 P1 35 42.3 98 CE3 P1 50 43.3 94 CE4 P2 20 40.0 86 CE5 P2 35 40.5 85 CE6 P2 50 41.0 74 4.8 132 CE7 P1 NA 500 50 39.1 68 CE8 P1 NA 1,000 50 39.3 72 CE9 P2 NA 500 50 39.9 64 CE10 P2 NA 1,000 50 39.8 63 3.3 137 IE1 P2 HR1 10 NA 500 50 41.2 59 IE2 P2 HR1 10 50 38.2 59 IE3 P2 HR1 20 50 37.8 50 0.6 152 1670/1610 IE4 P2 HR2 10 50 37.3 58 IE5 P2 HR2 20 50 41.6 48 1.3 144 1450/1420

[0232] The overview given by Table 1 demonstrates the powerful performance of the present invention as indicated by the inventive examples. In the inventive examples the oxygen transmission rate is very much reduced to values which are comparable to BOPP films at same thickness. Nevertheless, good optical properties are retained and mechanical (i.e. tensile modulus) properties are improved. This provides the possibility to pack more sensitive food. Alternatively, the thickness of films can be reduced or extra lamination omitted while keeping the same oxygen transmission rate.

[0233] The presence of the hydrocarbon resin allows to process the polypropylene based cast film (CPP) at higher chill roll temperature, i.e. without producing hazy films. As can be seen from examples CE1-CE3, without any nucleating agent present, the increase in chill roll temperature does not affect oxygen transmission rate while examples CE4-CE6, with a nucleating agent, show that there is an effect on oxygen transmission rate in case the chill roll temperature is higher, i.e. 50 C. The skilled person knows, however, that chill roll temperatures above 30 C. result in hazy films. This is confirmed by the performance of CE6. Addition of a nucleating agent as additive (CE7-CE10) also reduces, i.e. improves, oxygen transmission rate (compare CE3 with CE7 and CE8), or further improves oxygen transmission rate (compare CE6 with CE9 and CE10), respectively. However, hazy films are produced as confirmed by the performance of CE10.

[0234] Addition of a hydrocarbon resins further improves oxygen transmission rate (compare CE9 with IE1). The effect on oxygen transmission rate increases with increasing amount of hydrocarbon resin (compare IE2 with IE3 and IE4 with IE5). These films with very much improved oxygen transmission rate show acceptable optical properties and boosted tensile modulus (see IE3 and IE5). The inventive films also have excellent processability.

[0235] The use of a hydrocarbon resin in a cast film comprising a propylene homo- or copolymer according to one aspect of the present invention improves oxygen barrier property of said cast film by reducing the oxygen transmission rate of said cast film by at least 15% based on the same cast film apart from not comprising said hydrocarbon resin (compare CE6 with IE2, reduction of OTR by 20%; compare CE6 with IE3, reduction of OTR by 32%; compare CE6 with IE5, reduction of OTR by 35%).

[0236] Following Table 2 shows the same examples and cast films as Table 1, however, additional information as regards oxygen transmission rate values measured is provided.

TABLE-US-00002 TABLE 2 Composition and properties of cast films OTR/ml/m.sup.2 .Math. d Polyolefin composition TH/m average SD 40 m 1 mm CE1 P1 42.0 2214 182 2325 93 CE2 P1 42.3 2313 305 2446 98 CE3 P1 43.3 2175 272 2354 94 CE4 P2 40.0 2154 72 2154 86 CE5 P2 40.5 2110 93 2136 85 CE6 P2 41.0 1813 43 1858 74 CE7 P1 NA 500 39.1 1748 11 1709 68 CE8 P1 NA 1,000 39.3 1820 83 1788 72 CE9 P2 NA 500 39.9 1598 28 1594 64 CE10 P2 NA 1,000 39.8 1586 6.4 1578 63 IE1 P2 HR1 10 NA 500 41.2 1436 37 1479 59 IE2 P2 HR1 10 38.2 1554 43 1484 59 IE3 P2 HR1 20 37.8 1333 45 1260 50 IE4 P2 HR2 10 37.3 1552 32 1447 58 IE5 P2 HR2 20 41.6 1165 52 1212 48