POLYMER FILM FOR IN-MOLD LABELING

Abstract

The invention relates to an opaque multilayer biaxially oriented polypropylene film comprising at least one vacuole-containing base layer and a printable outer cover layer and an inner matte cover layer, the inner cover layer containing at least two incompatible polymers and having a surface roughness Rz of at least 2.0 μm at a cut-off of 25 μm. The inner matte cover layer contains a polydialkylsiloxane having a viscosity of 100,000 to 500,000 mm.sup.2/s and the surface of this inner cover layer is surface treated by means of corona or the inner cover layer contains a siloxane-modified polyolefin.

Claims

1. An opaque multilayer biaxially oriented polypropylene film comprising at least one vacuole-containing base layer and a printable outer cover layer and an inner matte cover layer, the inner cover layer containing at least two incompatible polymers and having a surface roughness Rz of at least 2.0 μm at a cut-off of 25 μm, characterized in that the inner matte cover layer contains a polydialkylsiloxane which has a viscosity of 100,000 to 500,000 mm.sup.2/s and the surface of this inner cover layer is surface treated by means of corona treated or the inner cover layer contains a siloxane-modified polyolefin.

2. The film according to claim 1, characterized in that the mixture of incompatible polymers contains at least one polyethylene and one propylene polymer.

3. The film according to claim 1 or 2, characterized in that the polyethylene is an HDPE or an MDPE and the polypropylene polymer is a propylene copolymer or propylene terpolymer or a propylene homopolymer.

4. The film according to any one of claims 1 to 3, characterized in that the inner cover layer contains >0.5% by weight of polydialkylsiloxane, based on the weight of the inner cover layer.

5. The film according to any one of claims 1 to 4, characterized in that the polydialkylsiloxane has a viscosity of 150,000 to 400,000 mm.sup.2/s.

6. The film according to any one of claims 1 to 5, characterized in that the inner cover layer contains >0.5% by weight of a siloxane-modified polyolefin, based on the weight of the inner cover layer.

7. The film according to one or more of claims 1 to 6, characterized in that the thickness of the inner cover layer is 0.5 to 5 μm.

8. The film according to one or more of claims 1 to 7, characterized in that the inner cover layer additionally contains anti-blocking agents, preferably crosslinked silicones or crosslinked polymethyl methacrylate particles.

9. The film according to one or more of claims 1 to 8, characterized in that the outer cover layer is composed of propylene polymers and has a gloss of 15 to 40.

10. The film according to one or more of claims 1 to 8, characterized in that the outer cover layer contains propylene polymers and an incompatible polyethylene and surface roughness Rz in a range of 2.0-6 μm at a cut-off of 0.25 mm and the Rz values of the inner and outer surface differ by a maximum of 2 μm.

11. The film according to one or more of claims 1 to 8, characterized in that the film additionally has an inner intermediate layer and an outer intermediate layer and the outer intermediate layer has a thickness of 0.5 to 5 μm and contains 4.5 to 30% by weight of pigments, preferably TiO.sub.2.

12. A use of a film according to any one of claims 1 to 11 in sheet-fed offset printing, characterized in that the sheets are printed and stacked.

13. A use of a film according to any one of claims 1 to 11 as an in-mold label in the deep drawing process.

14. The use according to claim 13, characterized in that the inner cover layer has a seal initiation temperature of 80 to 110° C.

Description

EXAMPLE 1 (ONE SIDE MATTE, 1.5% PDMS)

[0129] After the co-extrusion process, a five-layer prefilm was extruded from a slot die. This prefilm was drawn off on a chill roll, solidified and then oriented in the longitudinal and transverse directions and finally fixed. The surface of the outer and inner cover layers was pretreated by means of corona. The five-layered film had a layer construction of inner cover layer/inner intermediate layer/base layer/outer intermediate layer/outer cover layer. The individual layers of the film had the following composition: [0130] inner cover layer I (2.3 μm): [0131] ˜60% by weight of ethylene-propylene copolymer having 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) [0132] ˜38.5% by weight MDPE having an MFI of 14.4 g/10 min (21.6 kg and 190° C.), density of 0.937 g/ccm3 and a melting point of 126° C. [0133] 1.5% by weight polydimethylsiloxane having a viscosity of 300,000 mm.sup.2/s. [0134] 0.33% by weight SiO.sub.2 as an anti-blocking agent having a mean particle size of 5 μm [0135] inner intermediate layer I (4.0 μm) [0136] 99.88% by weight of propylene homopolymer having 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) [0137] 0.12% by weight of erucic acid amide (ESA) [0138] base layer (40.2 μm) [0139] 85.95% by weight of propylene homopolymer (PP) having 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) [0140] 14% by weight calcium carbonate having a mean particle diameter of 3.5 μm [0141] 0.05% by weight of erucic acid amide (ESA) [0142] outer intermediate layer II (3.0 μm) [0143] 94% by weight of propylene homopolymer (PP) having 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) [0144] 6% by weight TiO.sub.2 having an average particle diameter of 0.1 to 0.3 μm outer cover layer II (0.8 μm): [0145] ˜100% by weight of ethylene-propylene copolymer having 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)

[0146] All layers of the film additionally contained stabilizer and neutralizing agent in conventional amounts.

[0147] More specifically, the following conditions and temperatures were selected in the production of the film: [0148] Extrusion: Extrusion temperature about 250° C. [0149] Chill roll: Temperature 25° C. [0150] Longitudinal stretching: T=120° C. [0151] Longitudinal stretching by a factor of 4.8 [0152] Transverse stretching: T=155° C. [0153] Transverse stretching by a factor of 8 [0154] Fixation T=133° C.

[0155] The film was surface treated on both surfaces by means of corona. The film had an opaque appearance and a density of 0.56 g/cm.sup.3 and a thickness of 50 μm.

EXAMPLE 2 (ONE SIDE MATTE, 1% PDMS)

[0156] A film was produced according to Example 1, in contrast to Example 1, the content of polydimethylsiloxane was reduced to 1% by weight. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

EXAMPLE 3 (ONE SIDE MATTE, 2% PDMS)

[0157] A film was produced according to Example 1, in contrast to Example 1, the content of polydimethylsiloxane was reduced to 2% by weight. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

EXAMPLE 4 (TWO SIDE MATTE, 1.5% PDMS)

[0158] A film was produced according to Example 1, in contrast to Example 1, the composition of the outer cover layer was changed. The outer cover layer now had the same composition as the inner cover layer, in addition, the thickness of the inner cover layer was reduced to 1.5 μm. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

EXAMPLE 5 (TWO SIDE MATTE, 1.5% PDMS WITHOUT INNER ZWS)

[0159] A film was produced according to Example 3, in contrast to Example 3, the inner intermediate layer was omitted, thus producing a four-layered film. The thickness of the base layer was increased by 4 μm to obtain a film of comparable thickness. The thicknesses of the other layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

EXAMPLE 6 (ONE SIDE MATTE, 1.5% PDMS+TAFMER)

[0160] A film was produced according to Example 1, in contrast to Example 1, the composition of the inner cover layer was changed. A polymer having a low melting point was additionally added to the inner cover layer. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged. [0161] inner cover layer I (2.3 μm): [0162] ˜20% by weight of ethylene-propylene copolymer having 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) [0163] ˜40% by weight C3C4 copolymer Tafmer XM7070 [0164] ˜38.5% by weightMDPE having an MFI of 14.4 g/10 min (21.6 kg and 190° C.), density of 0.937 g/ccm3 and a melting point of 126° C. [0165] 1.5% by weight polydimethylsiloxane having a viscosity of 300,000 mm.sup.2/s. [0166] 0.33% by weight SiO.sub.2 as an anti-blocking agent having a mean particle size of 5 μm

COMPARATIVE EXAMPLE 1 (ONE SIDE MATTE, WITHOUT PDMS)

[0167] A film was produced according to Example 1, in contrast to Example 1, the composition of the inner cover layer was changed. The inner cover layer now contained no polydialkylsiloxane. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

COMPARATIVE EXAMPLE 2 (ONE SIDE MATTE, 1.5% PDMS WITH LOW VISCOSITY)

[0168] A film was produced according to Example 1, in contrast to Example 1, the composition of the inner cover layer I was changed. In contrast to Example 1, instead of the polydimethylsiloxane having a viscosity of 300,000 mm.sup.2/s, a polydimethylsiloxane having a viscosity of 30,000 mm.sup.2/s was used in the same amount. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

COMPARATIVE EXAMPLE 3 (ONE SIDE MATTE, 1.5% PDMS WITHOUT CORONA)

[0169] A film was produced according to Example 1, in contrast to Example 1, no surface treatment of the inner cover layer was performed. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

COMPARATIVE EXAMPLE 4 (TWO SIDE GLOSS, 1.5% PDMS WITHOUT MDPE)

[0170] A film was produced as described in Example 1. In contrast to Example 1, no MDPE was added to the inner cover layer. The content of propylene polymer was correspondingly increased to ˜98% by weight. The other composition and process conditions in the production of the film were not changed. [0171] ˜98% by weight of ethylene-propylene copolymer having 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) [0172] 1.5% by weight polydimethylsiloxane having a viscosity of 300,000 mm.sup.2/s. [0173] 0.33% by weight SiO.sub.2 as an anti-blocking agent having a mean particle size of 5 μm

COMPARATIVE EXAMPLE 5 (ONE SIDE MATTE, ESA INSTEAD OF PDMS)

[0174] A film was produced according to Example 1, in contrast to Example 1, the composition of the inner cover layer I was changed. In contrast to Example 1, no polydimethylsiloxane was used, but instead, an erucic acid amide was used in an amount of 0.5% by weight. The thicknesses of the layers, and the composition of all other layers, and the conditions during the production of the film remained unchanged.

[0175] The films according to the examples and the comparative examples were initially stored under different conditions for different periods and then examined with regard to their properties. Subsequently, the films were printed by sheet-fed printing process. The printed sheets were stacked. The printed sheets were then separated, the respective labels punched out of the sheet and the labels stacked in turn.

[0176] The stacked labels were then used in the injection molding process and in the deep drawing process as labels. The results are summarized in the table below.

[0177] The use according to the invention is described in detail below:

[0178] The films according to the examples and the comparative examples were cut into large-sized sheets of 70 cm×70 cm and stacked. The individual sheets were printed with a 4-fold repeat and the printed sheets were stacked. The repeats were punched out as individual labels from the printed sheets, stacked and finally provided on a labeling machine. The labels were used to label deep-drawn and injection-molded containers.

[0179] The films according to Examples 1 to 5 could be printed at high speed in the sheet-fed printing process and the printed sheets could be separated without ink transfer. The speed could be increased to up to 10,000 sheets per hour when printing the sheets. The labels which were punched from the sheets could also be easily stacked and unstacked and showed a good adhesion to the container. Optically flawless labeled containers were produced in this way.

[0180] The films according to the comparative examples could not be processed at this speed, both the printing and the labeling process speed had to be reduced (see table). Despite reduced speed, false or double feed disturbances occurred to varying degrees, which sometimes required the printing process or the labeling process to be interrupted.

TABLE-US-00001 TABLE Sheet-fed Adhesion to printing process Sheet stack the container Printability V Run Ink transfer/ Injec- Deep of the Example Film structure Max process destackability tion draw outside 1 one side matte, 1.5% PDMS ++ ++ None/+++ +++ + +++ 2 one side matte, 1.0% PDMS ++ ++ barely visible/++ +++ + +++ 3 one side matte, 2.0% PDMS +++ +++ None/+++ +++ + ++ 4 two side matte, 1.5% PDMS +++ +++ None/++++ +++ + ++* 5 two side matte, 1.5% PDMS ++ ++ None/++ +++ + ++* without inner ZWS 6 one side matte, 1.5% PDMS + ++ ++ None/+++ +++ ++ +++ Tafmer VB 1 one side matte, without PDMS +/− +/− Very clear/− +++ + +++ VB 2 one side matte, 1.5% PDMS ++ ++ None/− ++ + −− with low viscosity VB 3 one side matte, 1.5% PDMS +++ +++ Clear/++ ++ + −−− without corona VB 4 two side gloss, 1.5% PDMS + + None/−− +++ Blow +++ without MDPE VB 5 one side matte, ESA instead +/− +/− Clear/−** ++ − ++ of PDMS *lower gloss **erratic