MULTILAYER FILM

Abstract

The invention relates to a stretchable multilayer film comprising in the following order a. a first outer layer comprising at least 98 wt % of a linear low density polyethylene, b. a first inner layer, c. a second inner layer, d. a third inner layer and e a second outer layer comprising 70% to 30 wt % of a linear low density polyethylene and 30 to 70 wt % very low density polyethylene (VLDPE), wherein at least one of the inner layers comprises at least 98 wt % of a propylene homopolymer or 98 wt % of a propylene ethylene copolymer and wherein the other inner layer(s) comprise(s) at least 98 wt % of a linear low density polyethylene.

Claims

1. Stretchable multilayer film comprising in the following order a. a first outer layer comprising at least 98 wt % of a linear low density polyethylene b. a first inner layer c. a second inner layer d. a third inner layer e. a second outer layer comprising 70 wt % to 30 wt % of a linear low density polyethylene and 30 to 70 wt % very low density polyethylene (VLDPE), wherein at least one of the inner layers comprises at least 98 wt % of a propylene homopolymer or 98 wt % of a propylene ethylene copolymer and wherein the other inner layer(s) comprise(s) at least 98 wt % of a linear low density polyethylene.

2. Stretchable multilayer film comprising in the following order a. a first outer layer consisting essentially of a linear low density polyethylene b. a first inner layer c. a second inner layer d. a third inner layer e. a second outer layer comprising 70 wt % to 30 wt % of a linear low density polyethylene and 30 wt % to 70 wt % of a very low density polyethylene (VLDPE), wherein at least one of the inner layers consists essentially of a propylene homopolymer or consists essentially of a propylene ethylene copolymer and wherein the other inner layer(s) consist essentially of a linear low density polyethylene.

3. Multilayer film according to claim 1, wherein the propylene ethylene copolymer used is a propylene ethylene copolymer having an amount of ethylene in the propylene copolymer in the range from 1 to 5 wt %, based on the propylene ethylene copolymer.

4. Multilayer film according to claim 1, wherein the density of the linear low density polyethylene in the inner layer(s) is from 917 to 920 kg/m.sup.3 and preferably wherein the melt flow index of the linear low density polyethylene in the inner layer(s) ranges from 1.8 to 4.5 g/10 min.

5. Multilayer film according to claim 1, wherein the thickness of the multilayer film is in the range from 15 to 25 microns.

6. Multilayer film according to claim 1, comprising one or more further layers which layers each individually comprise at least 98 wt % of a propylene homopolymer and/or at least 98 wt % of a propylene ethylene copolymer and/or at least 98 wt % of a linear low density polyethylene.

7. Multilayer film according to claim 1, wherein the first outer layer comprises linear low density polyethylene, wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene or ethylene and 1-hexene or ethylene and 1-octene. wherein at least one of the inner layers comprises a propylene homopolymer or a propylene ethylene copolymer, wherein at least one of the inner layers comprises linear low density polyethylene wherein the linear low density polyethylene is produced using a metallocene catalyst wherein at least one of the inner layers comprises a linear low density polyethylene wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene or ethylene and 1-hexene or ethylene and 1-octene wherein the second outer layer comprises very low density polyethylene and linear low density polyethylene, wherein the VLDPE is a low density polyethylene copolymer comprising ethylene and 1-hexene or ethylene and 1-octene, and wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene or ethylene and 1-hexene or ethylene and 1-octene.

8. Multilayer film according to claim 7 comprising a. a first outer layer comprising at least 98 wt % of a linear low density polyethylene, wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene b. a first inner layer c. a second inner layer d. a third inner layer e. a second outer layer comprising 70 wt % to 30 wt % of a linear low density polyethylene and 30 wt % to 70 wt % VLDPE, wherein at least one of the inner layers comprises at least 98 wt % of a propylene ethylene copolymer and wherein the other inner layer(s) comprise(s) at least 98 wt % of a linear low density polyethylene, wherein at least one of the inner layers comprises a linear low density polyethylene wherein the linear low density polyethylene is produced using a metallocene catalyst and optionally wherein at least one of the inner layers comprises at least 98 wt % of a linear low density polyethylene, wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene wherein the second outer layer comprises very low density polyethylene and linear low density polyethylene, wherein the VLDPE is a low density polyethylene copolymer comprising ethylene and 1-hexene and wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene.

9. Multilayer film according to claim 1, comprising, a. a first outer layer comprising at least 98 wt % of a linear low density polyethylene, wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene b. a first inner layer c. a second inner layer d. a third inner layer e. a second outer layer comprising 70 wt % to 30 wt % of a linear low density polyethylene and 30 wt % to 70 wt % VLDPE, wherein at least one of the inner layers comprises at least 98 wt % of a propylene ethylene copolymer and wherein the other inner layer(s) comprise(s) at least 98 wt % of a linear low density polyethylene, wherein the linear low density polyethylene comprises ethylene and 1-hexene wherein the second outer layer comprises very low density polyethylene and linear low density polyethylene, wherein the VLDPE is a low density polyethylene copolymer comprising ethylene and 1-hexene and wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene.

10. Multilayer film according to claim 1, comprising a. a first outer layer comprising at least 98 wt % of a linear low density polyethylene, wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene b. a first inner layer c. a second inner layer d. a third inner layer e. a second outer layer comprising 70 wt % to 30 wt % of a linear low density polyethylene and 30 wt % to 70 wt % VLDPE, wherein at least one of the inner layers comprises at least 98 wt % of a propylene ethylene copolymer and wherein the other inner layer(s) comprise(s) at least 98 wt % of a linear low density polyethylene, wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene wherein the second outer layer comprises very low density polyethylene and linear low density polyethylene, wherein the VLDPE is a low density polyethylene copolymer comprising ethylene and 1-hexene and wherein the linear low density polyethylene is a low density polyethylene copolymer comprising ethylene and 1-butene.

11. Multilayer film according to claim 1, wherein the first outer layer constitutes from 10 wt % to 20 wt % of the multi-layer film, wherein the second outer layer constitutes from 10 wt % to 20 wt % of the multi-layer film, wherein the inner layer(s) comprising the propylene ethylene copolymer constitute(s) from 5 to 35 wt % of the multi-layer film, and wherein the inner layer(s) comprising a linear low density polyethylene constitute from 25 wt % to 75 wt % of the multilayer film.

12. Multilayer film according to claim 1, wherein each layer in the multilayer film comprises an amount of additives of 0 to 2 wt % based on the total weight of the layer.

13. Process for the preparation of the multilayer film of claim 1, wherein the multilayer film is prepared by a cast film extrusion process.

14. Process for wrapping an object which comprises a plurality of individual articles, comprising i) obtaining the multilayer film of claim 1, ii) stretching and wrapping said multilayer film around said object in order to obtain a wrapped object.

15. Object comprising a plurality of individual articles, wherein the object is stretch wrapped by the multilayer film of claim 1.

Description

EXAMPLES

Structure 1

[0096] Structure 1 highlights a stretchable multilayer film consisting of

a. a first outer layer comprising at least 99.5 wt % of a linear low density polyethylene having a melt flow index in the range from 2.5 to 3 g/10 min and having a density in the range from 917 to 920 kg/m.sup.3 and wherein the linear low density polyethylene comprises ethylene and 1-butene
b. a first inner layer comprising at least 99.5 wt % of a propylene ethylene copolymer having a melt flow index in the range from 7 to 9 g/10 min and having a density in the range from 902 to 908 kg/m.sup.3
wherein the amount of ethylene in the propylene ethylene copolymer is 3-5 wt % based on the propylene ethylene copolymer
c. a second inner layer comprising at least 99.5 wt % of a linear low density polyethylene having a melt flow index in the range from 3 to 4 g/10 min and having a density in the range from 917 to 920 kg/m.sup.3, wherein the linear low density polyethylene is produced using a metallocene catalyst and wherein the linear low density polyethylene comprises ethylene and 1-hexene
d. a third inner layer comprising at least 99.5 wt % of a linear low density polyethylene comprising ethylene and 1-butene, wherein the linear low density polyethylene has a melt flow index in the range from 2.5 to 3 g/10 min and having a density in the range from 917 to 920 kg/m.sup.3
e a second outer layer comprising 70% to 30 wt % of a linear low density polyethylene comprising ethylene and 1-butene and having a melt flow index in the range from 2.5 to 3 g/10 min and having a density in the range from 917-920 kg/m.sup.3
and 30 to 70 wt % of a very low density polyethylene comprising ethylene and 1-hexene, having a melt flow index in the range from 3 to 5 g/10 min and a having a density in the range from 900 to 910, preferably from 900 to 905 kg/m.sup.3,
wherein the first outer layer constitutes from 10 to 20 wt % of the multi-layer film, for example around 15 wt %
wherein the second outer layer constitutes from 10 to 20 wt % of the multi-layer film, for example around 15 wt %
the inner layer comprising the propylene ethylene copolymer constitutes from 5 to 15 wt %, for example from 10 to 15 wt %
and the inner layers comprising a linear low density polyethylene constitute from 45 to 75 wt % of the multi-layer film, for example around 60 wt %,
preferably wherein the thickness of the multi-layer film is 15 to 17 m (micron).

[0097] Preferably, the multi-layer film mentioned above, comprises the layers in the order as mentioned.

Structure 2

[0098] Structure 2 highlights a stretchable multilayer film consisting of

a. a first outer layer comprising at least 99.5 wt % of a linear low density polyethylene having a melt flow index in the range from 2.5 to 3 g/10 min and having a density in the range from 917 to 920 kg/m.sup.3 and wherein the linear low density polyethylene comprises ethylene and 1-butene
b. a first inner layer comprising at least 99.5 wt % of a propylene ethylene copolymer having a melt flow index in the range from 7 to 9 g/10 min and having a density in the range from 902 to 908 kg/m.sup.3, wherein the amount of ethylene in the propylene ethylene copolymer is 3-5 wt % based on the propylene ethylene copolymer
c. a second inner layer comprising at least 99.5 wt % of a linear low density polyethylene having a melt flow index in the range from 2 to 3 g/10 min and having a density in the range from 917 to 920 kg/m.sup.3, wherein the linear low density polyethylene is produced using a Ziegler Natta catalyst and wherein the linear low density polyethylene comprises ethylene and 1-hexene
d. a third inner layer comprising at least 99.5 wt % of a propylene ethylene copolymer having a melt flow index in the range from 7 to 9 g/10 min and having a density in the range from 902 to 908 kg/m.sup.3, wherein the amount of ethylene in the propylene ethylene copolymer is 3-5 wt % based on the propylene ethylene copolymer
e a second outer layer comprising 70% to 30 wt % of a linear low density polyethylene comprising ethylene and 1-butene having a melt flow index in the range from 2.5 to 3 g/10 min and having a density in the range from 917-920 kg/m.sup.3
and 30 to 70 wt % of a very low density polyethylene comprising ethylene and 1-hexene, having a melt flow index in the range from 3 to 5 g/10 min and a having a density in the range from 900 to 910, preferably from 900 to 905 kg/m.sup.3,
wherein the first outer layer constitutes from 10 to 20 wt % of the multi-layer film, for example around 15 wt %
wherein the second outer layer constitutes from 10 to 20 wt % of the multi-layer film, for example around 15 wt %
the inner layers comprising the propylene ethylene copolymer constitutes from 10 to 35 wt %, for example around 30 wt %
and the inner layer comprising the linear low density polyethylene constitute from 30 to 60 wt % of the multi-layer film, for example around 40 wt %,
preferably wherein the thickness of the multi-layer film is 15 to 17 m (micron).

[0099] Preferably, the multi-layer film mentioned above, comprises the layers in the order as mentioned.

Production of Structures 1 and 2 and Comparative Reference Structures 1 and 2

[0100] Two 5-layers film structures were produced: structure 1 and structure 2.

[0101] Structure 1 was produced on SML cast line equipped with 2500 mm wide flat die and five extruders to provide the layers of the film structure. Extruders were set with barrier screws L/D=30 and distribution dimension was 90/120/120/120/90 mm. Total film thickness was in between 15 m-17 m. The flat die was set with gap of 0.8 mm. The overall throughput was 800 kg/h with chill roll speed at 360 m/min. Barrel temperature profiles were ramped from 100 C. at the feed section to 260 C. at the die. Chill roll water inlet temperature was 25 C. at first chill roll and 27 C. at second one. The line was equipped with thickness profile measurement and contact winder.

[0102] The materials used and their melt flow index as determined using ISO1133:2011 (2.16 kg/10 min at 190 C.) and their density are indicated in Table 1 below.

TABLE-US-00001 TABLE 1 Materials used in the 5-layer structure 1. MFI [2.16 kg/10 min Density abbreviation Grade Polymer type at 190 C.] [kg/m3] C4-LLDPE SABICLLDPE LLDPE 2.8 918 318BE C6-mLLDPE ExxonMobil LLDPE 3.5 918 3518CB produced using a metallocene catalyst Random PP SABIC621P PP.sub.(ethylene content 4 wt. %) 8.0 905 C6-VLDPE Attane 4607G VLDPE 4.0 904 C4: 1-butene as comonomer C6: 1-hexene as comonomer

TABLE-US-00002 TABLE 2 Summarize the layers distribution of film structure 1 and its comparative example reference structure 1. Layer distribution (wt % based on total Layer Polymer type film) Structure 1 Layer 1 C4-LLDPE 15% Layer 2 Random PP 10% Layer 3 C6-mLLDPE 30% Layer 4 C4-LLDPE 30% Layer 5 C4-LLDPE + 15% C6-VLDPE Comparative example of structure 1 Layer 1 C4-LLDPE 15% Layer 2 C4-LLDPE 20% Layer 3 C6-mLLDPE 30% Layer 4 C4-LLDPE 20% Layer 5 C4-LLDPE + 15% C6-VLDPE

[0103] Structure 2 was produced on a cast line owned by Colines equipped with 1500 mm wide flat die and four extruders to provide the layers of the film structure. Extruders were set with barrier screws L/D=30 and distribution dimension was 90/120/160/90 mm. Total film thickness was in between 15 m-17 m. The flat die was set with gap of 0.8 mm. The overall throughput was 500 kg/h with chill roll speed at 400 m/min. Barrel temperature profiles were ramped from 90 C. at the feed section to 260 C. at the die. Chill roll water inlet temperature was 25 C. The line was equipped with thickness profile measurement and contact winder.

[0104] The materials used and their melt flow index as determined using ISO1133:2011 (2.16 kg/10 min at 190 C.) and their density are indicated in Table 1 below.

TABLE-US-00003 TABLE 3 Materials used in the 5-layer film of structure 2. MFI [2.16 kg/ 10 min Density Abbreviation Grade Polymer type at 190 C.] [kg/m3] C4-LLDPE SABICLLDPE LLDPE 2.8 918 318BE C6-LLDPE SABICLLDPE LLDPE 2.2 918 6218BE Random PP SABIC621P PP.sub.(ethylene 4%) 8.0 905 C6-VLDPE Attane 4607G VLDPE 4.0 904 C4: 1-butene as comonomer C6: 1-hexene as comonomer

TABLE-US-00004 TABLE 4 Summarize the layers distribution of film structure 2 and its comparative example reference structure 2. Layer distribution (wt % based on layer Polymer type total film) Structure 2 Layer 1 C4-LLDPE 15% Layer 2 Random PP 14% Layer 3 C6-LLDPE 42% Layer 4 Random PP 14% Layer 5 C4-LLDPE + 15% C6-VLDPE Reference structure 2 Layer 1 C4-LLDPE 15% Layer 2 C6-LLDPE 20% Layer 3 C6-LLDPE 30% Layer 4 C6-LLDPE 20% Layer 5 C4-LLDPE + 15% C6-VLDPE

TABLE-US-00005 TABLE 5 Measurements Reference Reference Film property Norm structure 1 Structure 1 structure 2 Structure 2 Holding Force (kg) HIGHLIGHT 25 28 26 29 method Stretch-ability (%) HIGHLIGHT 250 250 250 200 method Impact resistance ASTM 5.6 5.73 3.34 4.18 (g/m) D1709-04 Tear resistance TD ASTM 194 198 475 584 (kJ/m.sup.2) D1922-00a Haze ASTM good good 1.8 1.4 D1003-07 Gloss (45) ASTM good good 91 92 D2457-03 good: Good optical properties as determined visually, because of this, the haze and gloss values were not determined. TD transverse direction (perpendicular to the direction of the extrusion)

How Holding Force was Measured (HIGHLIGHT Method).

[0105] In order to measure holding force a tailor made instrument produced by company HIGHLIGHT Industries Ltd was used using the conditions recommended by the manufacturer. This instrument, which is very well known in the stretch market and recognized as a reference method worldwide, is able to determine the holding force that a stretch film can provide on unitized goods after being stretched to a desired level. The interesting thing is that this instrument can measure the holding force and stretch-ability on real shape stretch film, providing measurements directly related to the film application in use. The instruments comprise two driven rollers where stretch film is elongated at a certain stretching level, on real dimensions (film width 500 mm-750 mm). The rollers are also able to measure the force necessary to elongate the stretch film, as a result the instruments determines the holding force (by the ultimate force) at a specific stretching value (here 250% stretch). The holding force measured as described predicts the force of containment that a stretch film applies to unitized goods.

CONCLUSION

[0106] As can be seen from the above table, by using the multilayer films according to the invention, i.e. those multilayer films comprising an inner layer comprising at least 98 wt % of propylene ethylene copolymer, holding force is improved as well as tear resistance in transverse direction. Additionally, optical properties are maintained and stretchability is sufficient for power stretch film applications, such as the stretch wrapping of (sparkling) beverages in (plastic) bottles.

[0107] Impact resistance of structure 1 and of comparative structure 1 are comparable. The good impact resistance of these structures is due to the presence of a layer comprising at least 98 wt % of LLDPE produced by polymerization in the presence of a metallocene catalyst.

[0108] Surprisingly, when this layer was absent (and the only LLDPEs present were a C4 and a C-6 LLDPE, which are known to have a lesser impact resistance), an inner layer comprising at least 98 wt % of propylene ethylene copolymer significantly improved the impact resistance of the multilayer film. (Compare the impact resistance of structure 2 to the impact resistance of reference structure 2).

[0109] This finding offers the possibility to produce multilayer stretch films based on C4 and/or C6-LLDPE (which are more cost effective than LLDPEs produced using a metallocene catalyst), while obtaining an impact resistance comparable to that of a multilayer stretch film containing an LLDPE produced using a metallocene catalyst (also indicated herein as mLLDPE).