Polymer film for in-mould labelling

Abstract

The invention relates to a multi-layered, opaque, biaxially-oriented polyolefin film with a thickness of less than 150 mum and which comprises f. a base layer that contains vacuoles and at least one polymer of at least one olefin, g. an inner intermediate layer that contains at least one polymer of at least one olefin, h. an outer intermediate layer that contains at least one polymer of at least one olefin, i. an inner cover layer which is in contact with the inner intermediate layer and contains 5-70 wt. % of at least one polyethylene and 30-95 wt. % of at least one propylene polymer, and j. an outer cover layer which is in contact with the outer intermediate layer and contains 5-70 wt. % of at least one polyethylene and 30-95% of at least one propylene polymer, each amount indication relating to the weight of the layer in question, and characterised in that said outer intermediate layer has a thickness of 0.5 to 5 mum and contains 4.5 to 30 wt. % of pigments, preferably Tau[Iota]Omicron2, in that the outer cover layer has a thickness of >0 to <2 mum, and in that the film has a gloss on either side of less than 50 gloss units measured according to DIN EN ISO 2813 at an angle of 60 DEG and at a temperature of 25 DEG C.

Claims

1. A multi-layered, opaque, biaxially oriented polyolefin film with a thickness of less than 150 μm, comprising a. a vacuole-containing base layer containing at least one polymer of at least one olefin, b. an inner intermediate layer containing at least one polymer of at least one olefin, c. an outer intermediate layer containing at least one polymer of at least one olefin, d. an inner cover layer, which is in contact with the inner intermediate layer, and e. an outer cover layer, which is in contact with the outer intermediate layer, wherein the specified quantities relate to the weight of the respective layer, wherein the outer intermediate layer has a thickness from 0.5 to 10 μm, wherein the inner cover layer and the outer cover layer, in each case independently of one another, contain 15-55% by weight of at least one polyethylene polymer and also 45-85% by weight of at least one propylene polymer, and the outer cover layer has a thickness from >0 to <10 μm and the film on both sides has a gloss of less than 50 gloss units measured in accordance with DIN EN ISO 2813 at an angle of 60° and at a temperature of 25° C.

2. The film according to claim 1, wherein the film on both sides has a gloss of than less than 40 gloss units measured in accordance with DIN EN ISO 2813 at an angle of 60° and at a temperature of 25° C. and said the pigment is TiO2.

3. The film according to claim 1, wherein the inner cover layer and the outer cover layer, each independently of one another, contain HDPE or MDPE.

4. The film according to claim 1, wherein the inner cover layer and the outer cover layer, each independently of one another, contain at least one ethylene-propylene copolymer, at least one propylene-butylene copolymer or at least one ethyl ene-propyl ene-butyl ene terpolymer.

5. The film according to claim 1, wherein the inner cover layer has a seal initiation temperature from 80 to 110° C.

6. The film according to claim 1, wherein the inner intermediate layer and the outer intermediate layer each contain at least one propylene homopolymer.

7. The film according to claim 1, wherein the inner intermediate layer and the outer intermediate layer each contain at least 70% by weight of at least one propylene homopolymer.

8. The film according to claim 1, wherein the base layer has a density of <0.6 g/cm.sup.3, and contains at least 70% by weight of a highly isotactic or highly crystalline propylene homopolymer.

9. The film according to claim 1, wherein the base layer has a density of preferably <0.55 g/cm.sup.3, and contains at least 70% by weight of a highly isotactic or highly crystalline propylene homopolymer.

10. The film according to claim 1, wherein the base layer contains at least 70% by weight of at least one highly isotactic or highly crystalline propylene polymer and the film has a thickness of <60 μm.

11. The film according to claim 1, wherein the thickness of the inner cover layer lies in the range from 0.1 to 10.0 μm.

12. The film according to claim 1, wherein the density of the film lies in a range from 0.2 to 0.80 g/cm.sup.3.

13. The film according to claim 1, wherein the film on both sides has a surface roughness Rz in a range of 2.0-6 μm with a cutoff of 0.25 mm.

14. The film according to claim 1, wherein the film on both sides has a surface roughness Rz in a range of 2.0-6 μm with a cutoff of 0.25 mm, and Rz values of the inner and the outer surface differ by at most 2 μm.

15. The film according to claim 1, wherein the separation force for destacking of the film is less than 20 N measured from a film side against a film side.

16. An in-mould label which comprises the film according to claim 1.

17. The film according to claim 1, wherein the outer cover layer has a thickness from >0 to <2 μm.

Description

EXAMPLE 1

(1) Following the coextrusion method, a five-layered preliminary film was extruded from a flat film die. This preliminary film was drawn off on a chill roll, solidified and then oriented in the longitudinal and transverse direction and lastly fixed. The surface of the outer cover layer was pre-treated by means of corona in order to increase the surface tension. The five-layered film had a layered structure constituted by inner cover layer/inner intermediate layer/base layer/outer intermediate layer/outer cover layer. The individual layers of the film had the following composition:

(2) Inner Cover Layer (2.3 μm):

(3) 65% by weight ethylene-propylene copolymer with a melting point of 135° C. and a melt flow index of 7.3 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(4) 35% by weight polyethylene with a density of 0.934 g/cm.sup.3 and a melt flow index (190° C. and 21.6 kg) of 14.5 g/10 min.

(5) Inner Intermediate Layer (4.0 μm)

(6) 99.88% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% (in relation to 100% PP), a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(7) 0.12% by weight erucic acid amide (ESA)

(8) Base Layer (40.2 μm)

(9) 85.95% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (in relation to 100% PP) and a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(10) 14% by weight calcium carbonate with a mean particle diameter of 3.5 μm

(11) 0.05% by weight erucic acid amide (ESA)

(12) Outer Intermediate Layer (2.7 μm)

(13) 94% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (based on 100% PP), a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(14) 6% by weight TiO.sub.2 with a mean particle diameter from 0.1 to 0.3 μm

(15) Outer Cover Layer (0.8 μm):

(16) 70% by weight ethylene-propylene copolymer with a melting point of 135° C. and melt flow index of 7.3 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(17) 30% by weight polyethylene with a density of 0.934 g/cm.sup.3 and a melt flow index (190° C. and 21.6 kg) of 14.5 g/10 min

(18) All layers of the film additionally contained stabiliser and neutralising agent in conventional quantities.

(19) More specifically, the following conditions and temperatures during production of the film were selected: extrusion: extrusion temperature approximately 250° C. chill roll: temperature 25° C., longitudinal stretching: T 120° C. longitudinal stretching by a factor of 4.8 transverse stretching: T=155° transverse stretching by a factor of 8 fixing T=133° C.

(20) The film was surface-treated on the surface of the outer cover layer by means of corona. The film had a density of 0.56 g/cm.sup.3 and a thickness of 50 μm.

EXAMPLE 2

(21) A film according to Example 1 was produced with the following deviating layer thicknesses. The thickness of the outer cover layer was 0.5 μm, and the thickness of the outer intermediate layer was 2.1 μm. The thicknesses of the other layers and also the composition of all layers remained unchanged.

EXAMPLE 3

(22) A film according to Example 1 was produced with the following deviating composition of the individual layers:

(23) Inner Cover Layer (1.5 μm):

(24) 35% by weight ethylene-propylene copolymer with a melting point of 135° C. and a melt flow index of 7.3 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(25) 35% by weight polyethylene with a density of 0.934 g/cm.sup.3 and a melt flow index (190° C. and 21.6 kg) of 14.5 g/10 min.

(26) 30% by weight ethylene-propylene-butylene copolymer with a melting point of 135° C. and a melt flow index of 5.5 g/10 min at 230° and 2.16 kg load (ISO 1133)

(27) Inner Intermediate Layer (4.3 μm)

(28) 99.88% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (based on 100% PP), a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(29) 0.12% by weight erucic acid amide (ESA)

(30) Base Layer (41.3 μm)

(31) 84.95% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (based on 100% PP) and a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(32) 15% by weight calcium carbonate with a mean particle diameter of 3.5 μm

(33) 0.05% by weight erucic acid amide (ESA)

(34) Outer Intermediate Layer (2.3 μm)

(35) 94% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (based on 100% PP), a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(36) 6% by weight TiO.sub.2 with a mean particle diameter from 0.1 to 0.3 μm

(37) Outer Cover Layer (0.6 μm):

(38) 60% by weight ethylene-propylene-butylene copolymer with a melting point of 135° C. and melt flow index of 5.5 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(39) 20% by weight ethylene-propylene copolymer with a melting point of 135° C. and a melt flow index of 7.3 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(40) 20% by weight polyethylene with a density of 0.934 g/cm.sup.3 and a melt flow index (190° C. and 21.6 kg) of 14.5 g/10 min.

(41) All the layers of the film additionally contained stabiliser and neutralising agent in conventional quantities.

COMPARATIVE EXAMPLE 1

(42) A film according to Example 1 was produced with the following deviating composition of the individual layers:

(43) Inner Cover Layer (0.5 μm):

(44) 100% by weight ethylene-propylene copolymer with a melting point of 135° C. and a melt flow index of 7.3 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(45) Inner Intermediate Layer (3.6 μm)

(46) 100% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (in relation to 100% PP), a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(47) Base Layer (39.1 μm)

(48) 89% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (in relation to 100% PP) and a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(49) 8.6% by weight calcium carbonate with a mean particle diameter of 3.5 μm

(50) 2.4% by weight TiO.sub.2 with a mean particle diameter from 0.1 to 0.3 μm

(51) Outer Intermediate Layer (6.3 μm)

(52) 96.4% by weight propylene homopolymer (PP) with an n-heptane soluble proportion of 4.5% by weight (based on 100% PP), a melting point of 165° C. and a melt flow index of 3.2 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(53) 3.6% by weight TiO.sub.2 with a mean particle diameter from 0.1 to 0.3 μm

(54) Outer Cover Layer (0.5 μm):

(55) 10% by weight ethylene-propylene copolymer with a melting point of 135° C. and a melt flow index of 7.3 g/10 min at 230° C. and 2.16 kg load (ISO 1133)

(56) 5% by weight polyethylene with a density of 0.937 g/cm.sup.3 and a melt flow index (190° C. and 21.6 kg) of 14.5 g/10 min

(57) 85% by weight ethylene-propylene-butylene copolymer with a melting point of 135° C. and a melt flow index of 5.5 g/10 min at 230° and 2.16 kg load (ISO 1133)

(58) All layers of the film additionally contained stabiliser and neutralising agent in conventional quantities.

COMPARATIVE EXAMPLE 2

(59) A film was produced as described in Example 1. In contrast to Example 1, no TiO.sub.2 was added to the outer intermediate layer. The content of propylene homopolymer was increased accordingly to 100% by weight. The rest of the composition and the method conditions during production. of the film remained unchanged.

(60) The roughness of this film results primarily from the thin matt cover layer and to a small extent from the vacuole-containing base layer and is Rz 1.9 μm, and the gloss is 58 units. The separation force is approximately 25 N. The destackability of the film is poor. This structure corresponds approximately to Comparative Example 2 of WO2009/052921.

COMPARATIVE EXAMPLE 3

(61) A film was produced as described in Example 1. In contrast to Example 1, the layer thickness of the outer cover layer was increased to approximately 2.8 μm. In addition, no TiO.sub.2 was added to the outer intermediate layer. The content of propylene homopolymer in the intermediate layer was increased accordingly to 100% by weight. The rest of the composition and the method conditions during production. of the film remained unchanged.

(62) The roughness of this film increases due to the thicker matt layer compared to Example 2 to Rz to approximately 3.5 μm, and the gloss is 30 units. The separation force however is approximately 20 N. The destacking behaviour compared to Comparative Example 2 is thus improved by the thicker matt layer, however it was demonstrated that the destackability is not optimal without the inner roughness by TiO.sub.2 in the intermediate layer.

COMPARATIVE EXAMPLE 4

(63) A film was produced as described in Comparative Example 3. In contrast to Comparative Example 3, the layer thickness of the outer intermediate layer was increased to approximately 7 μm. This structure thus corresponds approximately to the films according to WO2009/052921 (Example 2). The rest of the composition and the method conditions during production of the film remained unchanged.

(64) The roughness of this film decreases due to the thicker TiO.sub.2-free outer intermediate layer compared to Comparative Example 3 to Rz approximately 2.5 μm, and the gloss is 51 units. The separation force is 26 N. The destacking behaviour compared to Comparative Example 2 and 3 is thus impaired by the thicker TiO.sub.2-free outer intermediate layer. Here, there was no inner roughness.

COMPARATIVE EXAMPLE 5

(65) A film was produced as described in Example 1. In contrast to Example 1, no PE was added to the outer cover layer. The content of propylene-ethylene copolymer was increased accordingly to 100% by weight. The rest of the composition and the method conditions during production of the film remained unchanged. The film demonstrates a low roughness of Rz approximately 1.5 μm and poor destackability due to the lack of a matt layer. The separation force is 25 N. The inner roughness caused by the intermediate layer with a high TiO.sub.2 content of 6% by weight does not solve the problem. Gloss is 70 units.

COMPARATIVE EXAMPLE 6

(66) A film was produced as described in Example 1. In contrast to Example 1, the outer intermediate layer was omitted, that is to say a four-layered film was produced. No polyethylene was added to the outer cover layer. The content of propylene-ethylene copolymer was increased accordingly to 100% by weight. The layer thickness of the outer cover layer was increased to 1.5 μm. The rest of the composition and the method conditions during production of the film remained unchanged. Gloss is 57 units. Due to the vacuole-containing base layer, the film demonstrates a roughness of Rz approximately 3.1 μm, but still a very poor destackability. The separation force is 30 N. The inner roughness caused by the base layer with a thin copolymer cover layer indeed increases the roughness values, but this inner roughness alone cannot solve the problem. This example additionally proves that films with comparable roughness Rz nevertheless may have different destacking behaviour.

(67) The results of the measurements of the separation force on these films are summarised in the following table. For measurements 3 and 5 the respective outer cover layers were placed one on top of the other during the separation force measurement in order to examine the destacking behaviour of these surfaces relative to one another.

(68) TABLE-US-00001 TABLE Gloss Rz Gloss Rz Separation Measurement Upper film/film side [GE] [μm] Lower film/film side [GE] [μm] force [N] 1 Example 1/inner 16 3.4 Example 1/outer cover 16 3.3 11 cover layer layer 2 Example 2/inner 16 3.4 Example 2/outer cover 30 4.2 11 cover layer layer 3 Example 2/outer 30 4.2 Example 3/outer cover 30 4.2 13 cover layer layer 4 Example 3/outer 36 2.6 Example 4/outer cover 28 2.2 12 cover layer layer 5 Comparative 56 1.7 Comparative 56 1.7 20 Example 1/outer Example/outer cover layer cover layer 6 Comparative Example 16 3.4 Comparative Example 58 1.9 25 2/inner cover layer 2/outer cover layer 7 Comparative Example 16 3.4 Comparative Example 30 3.5 20 3/inner cover layer 3/outer cover layer 8 Comparative Example 16 3.4 Comparative Example 51 2.5 26 4/inner cover layer 4/outer cover layer 9 Comparative Example 16 3.4 Comparative Example 70 1.5 25 5/inner cover layer 5/outer cover layer 10 Comparative Example 16 3.4 Comparative Example 57 3.1 30 6/inner cover layer 6/outer cover layer