Monoaxially oriented multilayer cast film

Abstract

Multilayer cast film, which is oriented in machine direction and comprises at least one outer layer, one core layer and one sealing layer, as well as its use in retort stand up pouches.

Claims

1. A multilayer cast film oriented in machine direction, the multilayer cast film comprises at least three layers A, B and C, wherein a) layer A is an outer layer comprising a heterophasic propylene copolymer, wherein the heterophasic propylene copolymer of layer A comprises a-a) 75 to 95 wt % of a polypropylene matrix (PP-M) with an MFR.sub.2 (ISO 1133, 230 C., 2.16 kg) of 0.5 to 30.0 g/10 min being a homopolymer or a copolymer which has a comonomer content of less than 10.0 wt %, a-b) 5 to 25 wt % of a propylene/alpha-olefin rubber (EPR) with at least 50 wt % propylene having an intrinsic viscosity (IV) of 0.8 to 2.5 dl/g, and a-c) 0.0001 to 1 wt % of an alpha-nucleating agent (NA); b) layer B is a core layer comprising a high isotacticity polypropylene homopolymer, wherein the high isotacticity polypropylene homopolymer of layer B is characterized by (b-i) an isotacticity expressed in mmmm pentads of at least 96 mol %, measured by means of 13 C-NMR, (b-ii) a decaline soluble content of 2.0 wt % or below, and (b-iii) polydispersity index (PI) of at least 5.5; and c) layer C is a sealing layer comprising a propylene based random copolymer or a propylene based terpolymer, optionally in combination with a heterophasic propylene copolymer, wherein the propylene based random copolymer or terpolymer of layer C comprises (c-i) 80.0 to 98.0 wt % of propylene, (c-ii) up to 5.0 wt % of ethylene, and (c-iii) 1.5 to 20.0 wt % of an alpha-olefin having 4 to 20 carbon atoms, wherein the sum of (c-i), (c-ii), (c-iii) is 100 wt % and the amount of ethylene (c-ii), if present, is lower than the amount of alpha-olefin (c-iii), wherein the machine direction oriented multilayer cast film has (i) a tensile modulus measured according to ISO 527-3 on a 50 m film in machine direction of at least 2600 MPa and in transverse direction of at least 1200 MPa, (ii) a haze value measured according to ASTM D1003 on a 50 m film of at most 5.5%, and (iii) a shrinkage measured according to the method as described in the experimental parton a 50 m film after 10 minutes at 100 C. in machine direction of at most 3.0%.

2. The multilayer cast film oriented in machine direction according to claim 1, wherein the copolymer or terpolymer of layer C has been visbroken.

3. The multilayer cast film oriented in machine direction according to claim 2, wherein A: the propylene/alpha-olefin rubber (EPR) of the heterophasic propylene copolymer of layer A is a propylene/ethylene rubber and the heterophasic propylene copolymer is alpha nucleated by a reactor technique, and wherein a catalyst used for preparing the heterophasic propylene copolymer is prepolymerized with at least one vinyl compound, B: the high isotacticity polypropylene homopolymer of layer B has a melting point of at least 162 C., and C: the propylene based random copolymer is a propylene-1-butene random copolymer and the propylene based terpolymer is a propylene-ethylene-1-butene terpolymer with an ethylene content of 0.5 to 5.0 wt %.

4. The multilayer cast film oriented in machine direction according claim 1, wherein the multilayer case film has a thickness of 100 to 600 microns before orientation and after being stretched in machine direction with a draw ratio of 1:3 up to 1:12 has a thickness of 15 to 150 microns.

5. The multilayer cast film oriented in machine direction according claim 1, wherein the multilayer cast film is suitable for being treated with a steam sterilization step at a temperature of above 110 C.

6. A laminate comprising a multilayer case film oriented in machine direction, wherein the multilayer cast film comprises at least three layers A, B and C, wherein a) layer A is an outer layer comprising a heterophasic propylene copolymer, wherein the heterophasic propylene copolymer of layer A comprises a-a) 75 to 95 wt % of a polypropylene matrix (PP-M) with an MFR.sub.2 (ISO 1133, 230 C., 2.16 kg) of 0.5 to 30.0 g/10 min being a homopolymer or a copolymer which has a comonomer content of less than 10.0 wt %, a-b) 5 to 25 wt % of a propylene/alpha-olefin rubber (EPR) with at least 50 wt % propylene having an intrinsic viscosity (IV) of 0.8 to 2.5 dl/g, and a-c) 0.0001 to 1 wt % of an alpha-nucleating agent (NA); b) layer B is a core layer comprising a high isotacticity polypropylene homopolymer, wherein the high isotacticity polypropylene homopolymer of layer B is characterized by (b-i) an isotacticity expressed in mmmm pentads of at least 96 mol%, measured by means of 13C-NMR, (b-ii) a decaline soluble content of 2.0 wt % or below, and (b-iii) polydispersity index (PI) of at least 5.5; and c) layer C is a sealing layer comprising a propylene based random copolymer or a propylene based terpolymer, optionally in combination with a heterophasic propylene copolymer, wherein the propylene based random copolymer or terpolymer of layer C comprises (c-i) 80.0 to 98.0 wt % of propylene, (c-ii) up to 5.0 wt % of ethylene, and (c-iii) 1.5 to 20.0 wt % of an alpha-olefin having 4 to 20 carbon atoms, wherein the sum of (c-i), (c-ii) and (c-iii) is 100 wt % and the amount of ethylene (c-ii), if present, is lower than the amount of alpha-olefin (c-iii), wherein the machine direction oriented multilayer cast film has (i) a tensile modulus measured according to ISO 527-3 on a 50 m film in machine direction of at least 2600 MPa and in transverse direction of at least 1200 MPa, (ii) a haze value measured according to ASTM D1003 on a 50 m film of at most 5.5%, and (iii) a shrinkage measured in analogy to ISO 11501 on a 50 m film after 10 minutes at 100 C. in machine direction of at most 3.0%, wherein the shrinkage is measured by putting 10 pieces of film on a talcum bed in an oven with the selected temperature.

7. A retortable stand up pouch comprising a multilayer case film oriented in machine direction, wherein the multilayer cast film comprises at least three layers A, B and C, wherein a) layer A is an outer layer comprising a heterophasic propylene copolymer, wherein the heterophasic propylene copolymer of layer A comprises a-a) 75 to 95 wt % of a polypropylene matrix (PP-M) with an MFR.sub.2 (ISO 1133, 230 C., 2.16 kg) of 0.5 to 30.0 g/10 min being a homopolymer or a copolymer which has a comonomer content of less than 10.0 wt %, a-b) 5 to 25 wt % of a propylene/alpha-olefin rubber (EPR) with at least 50 wt % propylene having an intrinsic viscosity (IV) of 0.8 to 2.5 dl/g, and a-c) 0.0001 to 1 wt % of an alpha-nucleating agent (NA); b) layer B is a core layer comprising a high isotacticity polypropylene homopolymer wherein the high isotacticity polypropylene homopolymer of layer B is characterized by (b-i) an isotacticity expressed in mmmm pentads of at least 96 mol %, measured by means of 13C-NMR, (b-ii) a decaline soluble content of 2.0 wt % or below, and b-iii) polydispersity index (PI) of at least 5.5; and c) layer C is a sealing layer comprising a propylene based random copolymer or a propylene based terpolymer, optionally in combination with a heterophasic propylene copolymer, wherein the propylene based random copolymer or terpolymer of layer C comprises (c-i) 80.0 to 98.0 wt % of propylene, (c-ii) up to 5.0 wt % of ethylene, and (c-iii) 1.5 to 20.0 wt % of an alpha-olefin having 4 to 20 carbon atoms, wherein the sum of (c-i), (c-ii) and (c-iii) is 100 wt % and the amount of ethylene (c-ii), if present, is lower than the amount of alpha-olefin (c-iii), wherein the machine direction oriented multilayer cast film has (i) a tensile modulus measured according to ISO 527-3 on a 50 m film in machine direction of at least 2600 MPa and in transverse direction of at least 1200 MPa, (ii) a haze value measured according to ASTM D1003 on a 50 m film of at most 5.5%, and (iii) a shrinkage measured in analogy to ISO 11501 on a 50 m film after 10 minutes at 100 C. in machine direction of at most 3.0%, wherein the shrinkage is measured by putting 10 pieces of film on a talcum bed in an oven with the selected temperature.

8. The multilayer cast film oriented in machine direction according to claim 1, having a seal strength of at least 40 N/15 mm before and after steam sterilization at 121 C. for 30 min, between the multilayer cast film and a further layer comprising Al-foil-layer, wherein the laminate structure is 12m oriented polyester (PET)/9m Al-layer 50 m machine direction oriented multilayer cast film, and the laminate has been sealed at 170 C.

9. The multilayer cast film oriented in machine direction according to claim 1 having a seal strength of at least 45 N/15 mm before steam sterilization at 121 C. for 30 min and at least 32 N/15 mm after steam sterilization at 121 C. for 30 min between the multilayer cast film and a further layer comprising oriented polyamide, wherein the laminate structure of 12m oriented polyester (PET)/15m oriented polyamide layer (OPA)/50 m machine direction oriented multilayer cast film, and the laminate has been sealed at 200 C.

10. The multilayer cast film oriented in machine direction according to claim 8, having a seal strength between the multilayer cast film and the further layer of at least 45 N/15 mm before and after steam sterilization at 121 C. for 30 min.

11. The multilayer cast film oriented in machine direction according to claim 9, having a seal strength between the multilayer cast film and the further layer of at least 50 N/15 mm before steam sterilization at 121 C. for 30 minutes.

12. The multilayer cast film oriented in machine direction according to claim 9, having a seal strength between the multilayer cast film and the further layer of at least 35 N/15 mm after steam sterilization at 121 C. for 30 minutes.

13. The multilayer cast film oriented in machine direction according to claim 9, having a seal strength between the multilayer cast film and the further layer of at least 50 N/15 mm before steam sterilization at 121 C. for 30 minutes and at least 35 N/15 mm after steam sterilization at 121 C. for 30 minutes.

Description

INVENTIVE EXAMPLES IE-1 AND IE-2

(1) Layer A) and optional in Layer C): heterophasic propylene copolymer, Borpact BC918CF, distributed by Borealis)

(2) The copolymer has an ethylene content of 2.4 wt % and a xylene soluble fraction (EPR content) at RT of 14 wt %. The MFR.sub.2 (230 C.; 2.16 kg) is 3.0 g/10 min. The density is 905 kg/m.sup.3 and the melting point 167 C. The polymer is nucleated by the BNT-technology) and contains 0.0004 wt % of poly(vinylcyclohexane) as alpha-nucleating agent. Layer B) high isotacticity polypropylene homopolymer (HIPP) was prepared according to Example 1 of EP 1883659 and had the following properties:

(3) MFR.sub.2 (230 C.; 2.16 kg) of 3.6 g/10 min; mmmm pentad of 97.65%; XCS of 1.3%, PI of 6.1, MWD of 8, Tm of 163.5 C. Layer C): commercial propylene-ethylene-1-butene terpolymer Borseal TD220BF of Borealis having a melt flow rate MFR.sub.2 (230 C.) of 6 g/10 min, a melting temperature Tm of 132 C.

IE-1:

(4) Layer A: 100 wt % of BC918CF (thickness: 10% of total film) Layer B: 100 wt % of HC110BF (thickness: 80% of total film) Layer C: 100 wt % of TD220BF (thickness: 10% of total film)

IE-2:

(5) Layer A: 100 wt % of BC918CF (thickness: 10% of total film) Layer B: 100 wt % of HC110BF (thickness: 80% of total film) Layer C: 75 wt % of TD220BF+25 wt % of BC918CF (thickness: 10% of total film)

COMPARATIVE EXAMPLES CE-1, CE-2 AND CE-3

(6) Additional Polymers Used:

(7) BA110CF: heterophasic propylene-ethylene impact copolymer (distributed by Borealis) with MFR.sub.2 (230 C./2.16 kg) of 0.85 g/10 min, a melting temperature Tm of 166 C., an ethylene content of 8 wt %, XCS of 16.7 wt.-%, and a density of 910 kg/cm.sup.3. The ethylene content of the XCS is 40 wt %.

(8) BE170CF: heterophasic propylene-ethylene copolymer (distributed by Borealis) with MFR.sub.2 (230 C./2.16 kg) of 13.0 g/10 min, a melting temperature Tm of 164 C., an ethylene content of 8.2 wt %, XCS of 17.0 wt %.

CE-1:

(9) Layer A: 30 wt % of BA110CF+40 wt % of BC918CF+30 wt % of BE170CF (thickness: 10% of total film) Layer B: 30 wt % of BA110CF+40 wt % of BC918CF+30 wt % of BE170CF (thickness: 80% of total film) Layer C: 75 wt % of TD220BF+25 wt % of BC918CF (thickness: 10% of total film)

CE-2:

(10) Layer A: 30 wt % of BA110CF+40 wt % of HC110BF+30 wt % of BEI 70CF (thickness: 10% of total film) Layer B: 30 wt % of BA110CF+40 wt % of HC110BF+30 wt % of BE170CF (thickness: 80% of total film) Layer C: 75 wt % of TD220BF+25 wt % of BC918CF (thickness: 10% of total film)

CE-3:

(11) Layer A: 100 wt % of HC110BF (thickness: 10% of total film) Layer B: 30 wt % of BA110CF+40 wt % of HC110BF+30wt % of BE170CF (thickness: 80% of total film) Layer C: 75 wt % of TD220BF+25wt % of BC918CF (thickness: 10% of total film)

(12) Production of Films

(13) Three layer films were produced at three layer coextusion cast film line, the film structure was A-B-C with a split of the layers: core layer (B) 80%, outer layer (A) 10% and one sealing layer (C) 10%.

(14) 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 layers 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. The obtained three-layer film had a thickness of 250 m.

(15) Orientation Process

(16) The machine direction orientation was performed on a commercially available MDO unit. The unit consists of preheating, drawing, annealing, and cooling sections, with each set at specific temperatures to optimize the performance of the unit and produce films with the desired properties.

(17) Orientation is achieved by reheating the non-oriented polypropylene film at a temperature of 105 C., the stretching was done at 125 C., cooling and annealing was done at 110 down to 40 C.

(18) Inlet speed was 10 m/min, outlet speed was then 50 m/min. Drawdown ratio (DDR) was around 1:5, thus yielding a 25 m MDO film.

(19) While one part of the film was used for primary testing of mechanics and optics, another part was used for preparing the laminates, which were also subjected to a steam sterilization step at 121 C. for 30 minutes. All results of the mechanical and optical characterization are summarized in Table 1.

(20) Sterilization Process

(21) The sterilization was done by subjecting the laminates to saturated steam of 121 C. for 30 minutes.

(22) Lamination Process

(23) Two Laminate Structures were Prepared:

(24) 12 m PET-layer/9 m Al-foil-layer/50 m MDO film according to the invention and 12 m PET-layer/15 m OPA-layer/50 m MDO film according to the invention

(25) Commercially available standard 12 m PET-films, 15 m OPA-films and 9 m Al-foil were used besides the MDO film according to the invention

(26) The lamination step was done on a commercially available lamination machine. As adhesive between the layers a commercially available two component solvent-based polyurethane adhesive from H. B. Fuller was used.

(27) TABLE-US-00001 TABLE 1 Property unit IE-1 IE-2 CE-1 CE-2 CE-3 Film thickness m 53 61 55 60 55 Tensile test MD Tensile Modulus MPa 3195 3135 2298 2442 2548 Tensile Strain at Yield % 33 30 33 33 30 Tensile Strain at Break % 34 35 34 39 30 Tensile test TD Tensile Modulus MPa 1438 1541 980 1139 1171 Tensile Strain at Yield % 5 5 7 6 4 Optics Transparency % 94.7 94.7 94.7 94.6 94.6 Haze % 4.4 4.1 12.9 12.5 6.0 Clarity % 96.6 96.7 91.3 88.0 89.3 SIT Initial Sealing Temp. C. 132 138 138 138 138 Shrinkage 100 C. MD % 2.3 2.7 5.0 4.1 3.3 150 C. MD % 11.0 11.4 20.5 13.2 15.1 Seal Strength Structure PET/AL/PP 170 C./1 s before sterilization N/15 65.6 48.1 51.9 52.6 46.6 mm After sterilization N/15 46.3 49.7 29.0 33.8 34.3 mm Structure PET/OPA/PP 200 C./1 s before sterilization N/15 57.8 51.0 33.0 36.5 35.2 mm After sterilization N/15 42.5 35.8 28.3 24.6 30.9 mm

(28) From Table 1 it can be easily seen that the PP sealing films according to the present invention have improved Tensile Modulus in machine direction as well as transverse direction as well as improved optics (e.g. lower haze).

(29) Furthermore the shrinkage of the PP sealing films according to the present invention is clearly lower compared to the comparative film structures.

(30) Additionally the Seal Strength in the different lamination structures is improved by using the MDO 3-layer cast film according to the invention as sealing layer.