Method for producing a multi-layer composite film, multi-layer composite film, and use thereof

A method for producing a multilayered composite film, the method comprising at least the following steps:

• a step of coextruding at least four layers, including the first layer, the second layer, the third layer and a fourth layer;
• wherein:
• the first layer forms an outward surface of the composite film;
• the third layer forms a surface of the composite film facing or coming in contact with a good to be packaged;
• and
• the second layer is disposed between the first layer and the third layer;
• the fourth layer is disposed between the first layer and the third layer, preferably between the first layer and the second layer;
• wherein the second layer consists of a single layer or a plurality of layers;
• wherein the fourth layer consists of a single layer or a plurality of layers;
• a step of stretching the coextruded composite film;
• and
• a step of relaxing the stretched composite film;
• wherein the stretching is bi-axial;
• wherein a stretch factor in the machine direction or longitudinal direction is at least 2.0;
• wherein a stretch factor in the transversal direction is at least 2.0;
• wherein the sum of the stretch factor in the machine direction and the stretch factor in the transversal direction is at least 5.0;
• wherein the composite film has a temperature of 70 to 130° C. during stretching;
• wherein a relaxation factor in the machine direction is more than 0.00;
• wherein a relaxation factor in the transversal direction is more than 0.00;
• wherein the sum of the relaxation factor in the machine direction and of the relaxation factor in the transversal direction is at least 0.05;
• wherein the composite film has a temperature of 60 to 180° C. during relaxation;
• wherein a dwell time during relaxation is at least 2 seconds;
• wherein a dwell time during relaxation is at most 30 seconds, or the duration of relaxation is at most 30 seconds;
• wherein a residual stretch factor in the machine direction is at most 5.0;
• wherein a residual stretch factor in the transversal direction is at most 5.0;
• wherein the first layer comprises a thermoplastic resin having a density of greater than 1.00 g/cm3;
• wherein the fourth layer or the plurality of the fourth layers each comprises a thermoplastic resin having a density of less than 1.00 g/cm3;
• wherein the second layer or the plurality of the second layers each comprises a thermoplastic resin having a density of greater than 1.00 g/cm3;
• and
• wherein the third layer comprises a thermoplastic resin having a density of less than 0.95 g/cm3.

A multilayered, coextruded, biaxially stretched, and relaxed composite film, comprising at least a first layer, a second layer and a third layer, wherein:

• the first layer forms an outward surface of the composite film;
• the third layer forms a surface of the composite film facing or coming in contact with a good to be packaged;
• and
• the second layer is disposed between the first layer and the third layer;
• wherein the second layer consists of a single layer or a plurality of layers;
• wherein a residual stretch factor of the composite film in a machine direction is at most 5.0;
• wherein a residual stretch factor of the composite film in a transversal direction is at most 5.0;
• wherein the first layer comprises a thermoplastic resin having a density of greater than 1.00 g/cm3;
• wherein the second layer or the plurality of the plurality of the second layers each comprises a thermoplastic resin having a density of greater than 1.00 g/cm3;
• and
• wherein the third layer comprises a thermoplastic resin having a density of less than 0.95 g/cm3.