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EP-4427923-B1 - BIAXIALLY ORIENTED POLYPROPYLENE-BASED MULTILAYER FILM

EP4427923B1EP 4427923 B1EP4427923 B1EP 4427923B1EP-4427923-B1

Inventors

  • WANG, JINGBO
  • FAWAZ, Joel
  • GAHLEITNER, MARKUS
  • BERNREITNER, KLAUS
  • NIEDERSUESS, PETER
  • ORTNER, STEFAN

Dates

Publication Date
20260506
Application Date
20230307

Claims (15)

  1. Biaxially oriented polypropylene-based multilayer film comprising at least a core layer (CL), a first outer layer (OL1) and a second outer layer (OL2), wherein the first and the second outer layers (OL1) and (OL2) comprise 70.0 to 100.0 wt.-%, based on the total weight of the respective outer layer, of a metallocene catalysed ethylene-propylene-1-butene terpolymer (mC2C3C4) base resin having • an ethylene (C2) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 0.7 to 2.0 wt.-% with respect to the total weight of the mC2C3C4 base resin; • a 1-butene (C4) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 4.0 to 7.8 wt.-% with respect to the total weight of the mC2C3C4 base resin; • a propylene (C3) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 90.2 to 96.0 wt.-% with respect to the total weight of the mC2C3C4 base resin; whereby the units derived from ethylene, propylene and butene add up to 100 wt.-%, and • a melt flow rate MFR 2 (230 °C / 2.16 kg) measured according to ISO 1133 in the range from 3.0 to 10.0 g/10 min; • a xylene cold soluble (XCS) content in the range of 2.0 to 5.0 wt.-%, determined at 25 °C according ISO 16152, based on the total wiegt of the mC2C3C4 base resin; • a melting temperature T m as determined by DSC according to ISO 11357 in the range from 120 to 129 °C; • a crystallization temperature T c as determined by DSC according to ISO 11357 in the range from 80 to 110 °C and • a number of 2,1 regio-defects measured by 13 C-NMR analysis (as described in the experimental part) in the range of 0.10 to 1.5 mol-% and whereby the mC2C3C4 base resin consists of (i) 30.0 to 60.0 wt.-%, based on the total weight of the mC2C3C4 base resin, of a first polymer component (TERPO-1) having • a melt flow rate MFR 2 (230 °C / 2.16 kg) measured according to ISO 1133 in the range from 1.0 to 10.0 g/10 min; • an ethylene (C2) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 0.7 to 1.3 wt.-% with respect to the total weight of the first polymer component (TERPO-1) and • a 1-butene (C4) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 4.0 to 6.0 wt.-% with respect to the total weight of the first polymer component (TERPO-1); and (ii) 40.0 to 70.0 wt.-% based on the total weight of the mC2C3C4 base resin, of a second polymer component (TERPO-2) having • a melt flow rate MFR 2 (230 °C / 2.16 kg) measured according to ISO 1133 in the range from 10.0 to 20.0 g/10 min; • an ethylene (C2) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 1.3 to 2.0 wt.-% with respect to the total weight of the second polymer component (TERPO-2) and • a 1-butene (C4) content measured by 13 C-NMR analysis (as described in the experimental part) in the range of 6.0 to 10.0 wt.-% with respect to the total weight of the second polymer component (TERPO-2) and (iii) optionally one or more additives, selected from the group consisting of slip agents, anti-block agents, UV stabilizers, antistatic agents, alpha-nucleating agents, antioxidants and mixtures thereof; whereby the core layer (CL) is a polypropylene-based layer and whereby the biaxially oriented polypropylene-based multilayer film has a sealing initiation temperature measured on a 25µm biaxially oriented test cast film as described in the experimental part in the range of 80 to 105 °C.
  2. The biaxially oriented polypropylene-based multilayer film according to claim 1, wherein the mC2C3C4 base resin comprises two polymer fractions (TERPO-1) and (TERPO-2), whereby the fraction (TERPO-1) is present in an amount of from 40.0 to 58.0 wt.-%, preferably from 45.0 to 55.0 wt.-%, based on the total weight of the mC2C3C4 base resin, and the fraction (TERPO-2) is thus present in an amount of from 60.0 to 52.0 wt.-%, preferably from 55.0 to 45.0 wt.-%, based on the total weight of the mC2C3C4 base resin.
  3. The biaxially oriented polypropylene-based multilayer film according to claim 1 or 2, wherein the fraction (TERPO-1) of the mC2C3C4 base resin has an ethylene content, based on the total weight of the fraction (TERPO-1), in the range of 0.7 to 1.2 wt.-%, preferably of 0.8 to 1.2 wt.-%, and the fraction (TERPO-2) has an ethylene content, based on the total weight of the fraction (TERPO-2), in the range of 1.3 to 1.9 wt.-%, preferably of 1.4 to 1.9 wt.-%, whereby the ethylene content of fraction (TERPO-1) is lower than the ethylene content of fraction (TERPO-2) and wherein the 1-butene content of fraction (TERPO-1) of the mC2C3C4 base resin, based on the total weight of the fraction (TERPO-1), is in the range of 4.1 to 6.0 wt.-%, preferably 4.1 to 5.9 wt.-%, and the fraction (TERPO-2) has an 1-butene content, based on the total weight of the fraction (TERPO-2), in the range of 6.5 to 9.5 wt.-%, preferably of 7.0 to 9.0 wt.-%, whereby the ethylene content of fraction (TERPO-1) is lower than the ethylene content of fraction (TERPO-2).
  4. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein fraction (TERPO-1) has a melt flow rate MFR 2 (230 °C/2.16 kg) measured according to ISO 1133 in the range of from 2.0 to 9.5 g/10 min, preferably from 2.5 to 9.0 g/10 min, and that fraction (TERPO-2) has a melt flow rate MFR 2 (230 °C/2.16 kg) measured according to ISO 1133 in the range of from 10.5 to 19.0 g/10 min, more preferably 11.0 to 18.0 g/10 min, whereby the MFR 2 of fraction (TERPO-1) is lower than the MFR 2 of fraction (TERPO-2).
  5. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the mC2C3C4 base resin has an ethylene (C2) content in the range of 0.8 to 1.9 wt.-%, preferably 0.9 to 1.8 wt.-% and more preferably 1.0 to 1.8 wt.-%, with respect to the total weight of the mC2C3C4 base resin and a 1-butene (C4) content in the range of 4.1 to 7.7 wt.-%, preferably 4.2 to 7.6 wt.-%, with respect to the total weight of the mC2C3C4 base resin.
  6. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the mC2C3C4 base resin has a melt flow rate MFR 2 (230 °C / 2.16 kg) measured according to ISO 1133 in the range of 4.5 to 9.5 g/10min, preferably 5.0 to 9.0 g/10 min and more preferably 5.5 to 8.5 g/ 10 min or a xylene cold soluble (XCS) content as determined according to ISO 16152 in the range of 2.5 to 4.8 wt.-%, preferably from 2.8 to 4.5 wt.-%, based on the weight of the mC2C3C4 base resin.
  7. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the mC2C3C4 base resin has a melting temperature T m as determined by DSC according to ISO 11357 in the range of 122 to 128 °C and a crystallization temperature T c as determined by DSC according to ISO 11357 in the range of 82 to 105 °C, preferably 85 to 100 °C and more preferably 86 to 90°C.
  8. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the outer layers (OL1) and (OL2) consist of the mC2C3C4 base resin as defined in any of the claims 1 to 7.
  9. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the core layer (CL) comprises, preferably consists of a propylene homopolymer (H-PP).
  10. The biaxially oriented polypropylene-based multilayer film according to claim 9, wherein the propylene homopolymer (H-PP) is characterized by a xylene soluble content (XCS) as determined according to ISO 16152 of below 5.0 wt.-%, more preferably below 4.0 wt.-%, still more preferably below 3.5 wt.-% and/or a melting temperature Tm (measured with DSC) of at least 145 °C, more preferably at least 150 °C, still more preferably at least 160 °C.
  11. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the film may further comprise one or two tie layers (TL1) and (TL2), whereby the optional tie layers are located between the core layer (CL) and one or both of the outer layers (OL1) and/or (OL2).
  12. The biaxially oriented polypropylene-based multilayer film according to claim 11, wherein the tie layers (TL1) and (TL2) are made of a polypropylene based polymer, preferably of the same propylene based polymer and more preferably of the same polypropylene based polymer as used for the core layer (CL), even more preferably of the same propylene homopolymer as used for the core layer (CL).
  13. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the thickness of the layers after biaxial orientation is for each outer layer: 0.3 µm to 3.0 µm, preferably 0.4 µm to 2.0 µm, more preferably 0.5 µm to 1.5 µm, whereby preferably, both outer layers have the same thickness; the core layer: 5 µm to 40 µm, preferably 10 µm to 35 µm, more preferably 15 µm to 25 µm; and each tie layers, if present: 1.0 µm to 5 µm, preferably 1.5 µm to 4.5 µm, more preferably 2.0 µm to 4.50 µm, whereby preferably, both tie layers have the same thickness and whereby the total thickness of the BOPP film is 8 µm to 80 µm, preferably 10 µm to 60 µm, more preferably 15 µm to 40 µm.
  14. The biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, wherein the film is characterized by a sealing initiation temperature determined as described in the experimental part on a BOPP film with a thickness of 25 µm in the range of 90 to 104 °C, and more preferably in the range of 100 °C to 104 °C
  15. Use of the biaxially oriented polypropylene-based multilayer film according to any of the preceding claims, as packing material, in particular as a packing material for food and/or non-food products like textiles, flowers, pet food, detergents and protective films for cardboard boxes containing tobacco product or perfumes.

Description

The present invention relates to a polypropylene-based multilayer film, which is biaxially oriented, a process for manufacturing the biaxially oriented multilayer film and to its use in flexible packaging. Polypropylene-based resins have been widely used in the food packaging field because they have excellent tensile strength, rigidity, transparency and the like, and are additionally advantageous due to their non-toxicity and odorlessness. Generally, they are used in the form of cast films (CPP), biaxially oriented films (BOPP) or water-quenched tubular films (TQPP). Biaxially oriented polypropylene (BOPP) films are films stretched in both machine and transverse directions, producing molecular chain orientation in two directions. Biaxially oriented polypropylene-based (BOPP) multilayer films are commonly used in packaging industry, including food packaging. Typically, this application comprises a sealing layer, which provides the necessary sealing performance for hermetically closing a packaging system. However, such a sealing layer is directly in contact with the food packed, therefore the cleanness, e.g. the low content of extractables, is very important. Films for food packaging are typically transparent, or, more general, shall furthermore have good optical properties, like low haze to provide an attractive appearance. Polypropylenes according to state of art technology are based on the Ziegler-Natta type catalyst technology, i.e. titanium-centred heterogeneous catalysts with aluminium alkyl activation. Thus, the sealing layer is typically a Ziegler-Natta catalysed propylene - ethylene - butene terpolymer. WO 2009/019169 A1, for example, describes a process for providing Ziegler-Natta derived PP terpolymers suitable for blown film comprising at least 8 wt.-% of total comonomer units with the comonomer units being derived from ethylene and C4 to C8 alpha olefins by way of using 1,3-diether internal donor catalyst. According to WO 2009/019169 A1, an optimal balance of properties shall be observed when an ethylene content of lower than 2.5 wt.-% is combined with a butene-1 content of higher than 10 wt.-%, whereby alternatively when ethylene content is higher than 2.5 wt.-%, butene content should be lower than 10 wt.-%. A composition having an ethylene content of 1.2 wt.-% and 11.3 wt.-% butene, i.e. a C4/C2 (wt/wt) ratio of 9.4 resulted in a SIT of 107.4 °C and 0.2 % haze (1mm plaque) In the last decades this solution served the needs sufficiently. Due to the change of market requirements, such terpolymers have however somehow reached their limit, e.g. the sealing initiation temperature is not low enough, optics are not as good as required. Metallocene catalyst derived PP terpolymers have also already been described for sealing applications. For instance, EP 20193414 A discloses bimodal C2C3C4 terpolymers made by polymerization in a loop reactor, followed by a gas phase reactor in the presence of a metallocene catalyst. The terpolymers were used to make cast films after their MFR2 (ISO1133, 2.16 kg, 230 °C) of 2.0 g/10 min reached after polymerization has been adjusted by visbreaking to a final MFR2 (ISO1133, 2.16 kg, 230 °C) in the range of 11.0 to 14.0 g/10 min. BOPP films are in principle mentioned, but not demonstrated. WO 2022167368 A discloses films made from a blend of a C2C3C4 terpolymer and a C3C4 random copolymer upgrading resin. The C2C3C4 terpolymers is made by polymerization in a loop reactor, followed by a gas phase reactor in the presence of a metallocene catalyst, whereby a quite high amount of polymer was produced in the gas phase reactor, i.e. 59.0 wt.-%, related to the final polymer. According to claim 1 the terpolymer can have a xylene cold soluble (XCS) content in the range of 5.0 to 25.0 wt.-%, preferably 15.0 to 19.0 wt.-% determined at 25 °C according ISO 16152. The terpolymer used in the Examples has a quite high amount of xylene cold soluble (XCS) fraction of 17.1 wt.-%. EP 1358252 B1 (Basell) claims a bioriented polypropylene film (BOPP) wherein at least one layer comprises a propylene random copolymer containing at least 0.8% by weight of ethylene or a propylene polymer composition comprising a propylene random copolymer containing at least 0.8% by weight of one or more comonomers selected from ethylene and C4 -C10 α-olefins, said random copolymer or polymer composition having the following features: (1) a melting temperature of 155 °C or higher measured by DSC with a temperature variation of 20°C per minute; (2) a content of fraction soluble in xylene at room temperature (at 25 °C) lower than 3% by weight, and a value of the ratio of the polymer fraction collected by TREF method disclosed in the characterization section in the temperature range from 25°C to 95°C to the fraction soluble in xylene at room temperature higher than 8 wt.-%/wt.-%; and (3) a Melt Flow Rate (230°C, 2.16 Kg load) from 1 to 10 g/10min. Sealing related properties are not mentioned. WO 2021110615 relates t