Multilayer film

1. A bi-axially orientated polypropylene film, having a thickness comprised between 10 μm and 120 μm, obtained by means of flat die co-extrusion and sequential stretching respectively in a machine direction and in a direction transverse to the machine direction, and suitable to make packing, flexible packages, laminated products and labels, wherein the film comprises:

a base layer based on polypropylene and having an outer face and an inner face,

an outer tie layer adjacent to the outer face of the base layer and based on copolymers of olefins comprising polar comonomers like vinyl acetates, alkyl acrylates, alkyl methacrylates, acrylic acid or maleic anhydride;

an outer skin layer, adjacent to an outer face of the outer tie layer, and based on polyamide,

wherein said outer skin layer comprises a blend of an amorphous polyamide and a semicrystalline polyamide, said blend comprising 25% to 75% (by weight) of amorphous polyamide and 75% to 25% (by weight) of semicrystalline polyamide.

2. The film as in claim 1 , further comprising an inner skin layer, opposite the outer skin layer, comprising propylene homopolymer, copolymer, or terpolymer, alpha-olefine copolymers comprising ethylene or propylene comonomers, propylene or ethylene elastomer, polyethylene, or blends thereof.

3. The film as in claim 2 , further comprising an inner tie layer, disposed between said base layer and said inner skin layer, comprising propylene homopolymer or copolymer.

4. The film as in claim 1 , further comprising an inner tie layer based on copolymers of olefins comprising polar comonomers like vinyl acetates, alkyl acrylates, alkyl methacrylates, acrylic acid or maleic anhydride, adjacent to the inner face of the base layer, and an inner skin layer, based on polyamide, adjacent on an inner face of the inner tie layer, wherein said inner skin layer based on polyamide comprises a blend of 25% to 75% (by weight) amorphous polyamide and 75% to 25% (by weight) semicrystalline polyamide.

5. The film as in claim 1 , comprising an inner tie layer, adjacent to the inner face of the base layer, and comprising propylene copolymer, or terpolymer, or C2 C3 plastomers, or blends thereof, and an inner skin layer, adjacent to a inner face of the inner tie layer and comprising propylene homopolymer, copolymer, or terpolymer, alpha-olefine copolymers comprising ethylene or propylene comonomers, propylene or ethylene elastomer, polyethylene, or blends thereof.

6. The film as in claim 5 , comprising an inner coating layer, adjacent to an inner face of said inner skin layer and based on aliphatic polyurethane or a poly aziridin, or EVA resin.

7. The film ad in claim 1 , comprising an inner tie layer, adjacent to the inner face of the base layer, and comprising propylene homopolymer, and an inner skin layer, adjacent to a inner face of the inner tie layer, based on a blend of polypropylene copolymers modified with maleic anhydride.

8. The film as in claim 7 , comprising an inner coating layer, adjacent to an inner face of said inner skin layer and comprising aliphatic polyurethane.

9. The film as in claim 1 , wherein said outer tie layer is based on copolymers of ethylene with polar comonomers like vinyl acetate, methyl acrylate, butyl acrylate or acrylic acid or maleic anhydride, or graft copolymers of any of these comonomers with polyolefins.

10. The film as in claim 1 , wherein said outer skin layer is treated with flame, corona, or plasma.

11. The film as in claim 1 , wherein said outer skin layer is coated with metal, metal oxide, organic or inorganic lacquers, or a combination thereof.

12. The film as in claim 1 , wherein said base layer comprises at least one of fillers, voiding agents, hard resins, additives.

13. The film as in claim 1 , wherein said outer skin layer has a thickness comprised between about 0.3 μm and 10 μm.

14. The film as in claim 1 , wherein said outer skin layer has a thickness comprised between about 0.3 μm and 1 μm.

15. The film as in claim 1 , wherein said film has a shrinkage at 130° C. of less than 7% in both machine direction and transverse direction.

16. A method to make a bi-axially orientated polypropylene film having a thickness comprised between 10 μm and 120 μm and suitable to make packing, flexible packages, laminated products and labels, comprising the following steps:

a first co-extrusion step, by means of a flat die extrusion unit, to make a co-extruded intermediate product in the form of a film,

a second step of stretching in the machine direction and

a third step of stretching in a direction transverse to the machine direction, of the intermediate product, so as to determine the desired bi-axially orientated structure and define the final thickness of each of the layers;

wherein the first co-extrusion step provides to extrude an intermediate product formed at least by a base layer based on polypropylene and having an outer face and an inner face, an outer tie layer adjacent to the outer face of the base layer, and based on copolymers of olefins comprising polar comonomers like vinyl acetates, alkyl acrylates, alkyl methacrylates, acrylic acid or maleic anhydride, and an outer skin layer, adjacent to an outer face of the outer tie layer, and based on polyamide, wherein, to extrude said outer skin layer, it provides to use a blend of an amorphous polyamide and a semicrystalline polyamide, said blend comprising 25% to 75% (by weight) of amorphous polyamide and 75% to 25% (by weight) of semicrystalline polyamide, and

wherein said second and third steps of stretching provide to stretch the intermediate product by a factor 3 to 6 in the machine direction and subsequently by a factor 7 to 12 in the direction transverse to the machine direction.