Multilayer, coextruded polyolefin film and manufacture thereof on triple bubble lines

1 . A biaxially oriented, coextruded, multilayer packaging film comprising at least the following layers:

an outer heat sealable layer a) comprising polymers selected from the group of ethylene-alpha-olefin copolymers, polybutylene (PB), ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers, ethylene butyl acrylate copolymers (EBA) and mixtures thereof, the total amount of ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers and ethylene butyl acrylate copolymers (EBA) in the heat sealable layer being not higher than 30% by weight based on the total weight of the film;

an inner gas barrier layer b) comprising ethylene-vinyl alcohol (EVOH), wherein the EVOH content is comprised between 3% and 25% by weight based on the total weight of the film; and

an outer layer c) comprising one or more polyolefins,

wherein the film:

has a gloss value at 60° higher than 100 g.u. measured in accordance to ASTM D2457,

comprises at least 90% by weight of one or more polyolefins based on the total weight of the film,

does not contain any polyamide or polyester, and

has at least one of the following features:

elastic modulus higher than 4000 kg/cm 2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.;

elongation at break of at most 200% in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.;

tensile strength at break higher than 500 kg/cm 2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.

2 . The film of claim 1 , wherein the film does not contain any polymers other than polyolefins, ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers, ethylene butyl acrylate copolymers (EBA) and EVOH.

3 . The film of claim 1 , wherein the heat sealable layer a) comprises ethylene(meth)acrylate and/or (meth)acrylic acid copolymers and wherein:

said ethylene(meth)acrylate copolymers are selected from ethylene C 1 -C 4 alkyl (meth)acrylate copolymers, ethylene methyl (meth)acrylate copolymers, ethylene ethyl (meth)acrylate copolymers and ethylene-butyl (meth)acrylate copolymers, and/or

said(meth)acrylic acid copolymers are in form of ionomers.

4 . The film of claim 1 , wherein the polyolefins in the outer layer c) are selected from the group consisting of:

ethylene polymers, long chain branching polyethylene (PE), HDPE or MDPE, LLDPE,

propylene polymers, polypropylene (PP),

copolymers of ethylene and propylene (EP), and mixtures thereof.

5 . The film of claim 1 , wherein

the ratio between the elastic moduli measured in LD and in TD and/or

the ratio between the elongations at break measured in LD and in TD and/or

the ratio between the tensile strengths at break measured in LD and in TD, varies at most of ±25% with respect to the unit.

6 . The film of claim 1 having either:

i) a free shrink lower than 15% in both LD and TD, measured at 120° C. in oil according to ASTM D2732 and, a maximum shrink tension, measured according to the method of the present description, not higher than 25 kg/cm 2 both in LD and in TD; or

ii) a free shrink higher than 20% in both LD and TD, measured at 85° C. in water according to ASTM D2732 or higher than 15% in both LD and TD, measured at 120° C. in oil according to ASTM D2732 and, a maximum shrink tension, measured according to the method of the present description, not higher than 35 kg/cm 2 both in LD and in TD.

7 . The film of claim 1 , further comprising an inner layer d), directly adhered to the outer heat sealant layer a), the layer d) consisting essentially of polymers selected from the group consisting of polyolefins, ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers, ethylene butyl acrylate copolymers (EBA) and mixtures thereof, wherein the total amount of EVA, ethylene(meth)acrylate/(meth)acrylic acid copolymers and EBA in the film is not higher than 30% by weight based on the total weight of the film, and, optionally, comprising at least 5% by weight of polybutylene based on the total weight of layer d).

8 . The film of claim 1 , having a total thickness comprised between 4 and 120 microns.

9 . The film of claim 1 , wherein the film is not crosslinked.

10 . The film of claim 1 being a first film and heat-sealed to itself or heat sealed to a second film to form a flexible container, the second film, if of a different composition from the first film, the second film being a polyolefin based film.

11 . The film according to claim 10 further comprising a product, placed into said flexible container, optionally wherein the product is placed on a rigid or semi-rigid support.

12 . A package comprising a biaxially oriented, coextruded, multilayer packaging film comprising at least the following layers:

an outer heat sealable layer a) comprising polymers selected from the group of ethylene-alpha-olefin copolymers, polybutylene (PB), ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers, ethylene butyl acrylate copolymers (EBA) and mixtures thereof, the total amount of ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers and ethylene butyl acrylate copolymers (EBA) in the heat sealable layer being not higher than 30% by weight based on the total weight of the film;

an inner gas barrier layer b) comprising ethylene-vinyl alcohol (EVOH), wherein the EVOH content is comprised between 3% and 25% by weight based on the total weight of the film; and

an outer layer c) comprising one or more polyolefins,

wherein the film:

has a gloss value at 60° higher than 100 g.u. measured in accordance to ASTM D2457,

comprises at least 90% by weight of one or more polyolefins based on the total weight of the film,

does not contain any polyamide or polyester, and

has at least one of the following features:

elastic modulus higher than 4000 kg/cm 2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.;

elongation at break of at most 200% in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.;

tensile strength at break higher than 500 kg/cm 2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.,

and a product packaged therein.

13 . The package according to claim 12 comprising a rigid or semi-rigid support, the product placed onto said support, and the multilayer packaging film having a free shrink lower than 15% in both longitudinal direction (LD) and transverse direction (TD), measured at 120° C. in oil according to ASTM D2732,

wherein the outer heat sealable layer a) of the film is in contact with or faces the product, and the film is hermetically sealed onto said support.

14 . The package according to claim 13 wherein the support is selected from PET, APET, PP and PE.

15 . The package of claim 12 comprising a product and the multilayer packaging film wrapped around such product, wherein the film has:

i) a free shrink higher than 20% in both longitudinal direction (LD) and transverse direction (TD), measured at 85° C. in water according to ASTM D2732 or

ii) a free shrink higher than 15% in both LD and TD, measured at 120° C. in oil according to ASTM D2732 and wherein the outer heat sealable layer a) of the film is in contact with or faces the product.

16 . The package according to claim 12 comprising a rigid or semi-rigid support, the product placed onto said support and the multilayer packaging film wrapped around both said support and said product, wherein the wrapped film has a free shrink lower than 15% in both longitudinal direction (LD) and transverse direction (TD), measured at 120° C. in oil according to ASTM D2732 and wherein the outer heat sealable layer a) of the film is in contact with or faces the product.

17 . The package according to claim 12 wherein the packaged product is a food product selected from the group consisting of fresh red meat, processed meat, fish, poultry, cheese, fruits and vegetables.

18 . A triple bubble process for manufacturing a biaxially oriented, coextruded, multilayer packaging film, such process comprising, in order, the steps of:

i) co-extruding through a round die the melted thermoplastic polymers of the film, to form a co-extruded multilayer tube comprising at least layers a), b) and c),

ii) cooling the co-extruded multilayer tube to a temperature below the lowest melting point of the thermoplastic polymers, and passing it through deflate rolls, providing a flat tube ( 6 ),

iii) moving the tube through a couple of pinch rolls ( 5 ) and pre-heating the tube to a temperature comprised between 80° C. and 130° C. through pre-heating ovens ( 1 , 2 ) emitting infrared radiation (IR),

iv) further heating the pre-heated tube to keep its temperature between 80° C. and 130° C. through heating orientation oven(s) ( 3 ) emitting infrared radiation (IR), while biaxially orienting the tube by longitudinally pulling it through a couple of deflate rolls and transversally expanding it by blowing a gas in the multilayer tube, with an orientation ratio, in both the longitudinal direction and the transverse direction, comprised between 2.5:1 and 6:1, thus providing a biaxially oriented tube ( 8 ),

v) cooling the oriented tube ( 8 ), passing it through a series of converging rolls and lay-flattening it,

vi) optionally bringing the temperature of the lay flattened film to a temperature between 40° C. and 60° C.,

vii) heat-setting the tube by longitudinally lifting it up through a couple of pinch rolls and by blowing a gas in the tube, while heating it at a temperature comprised between 60° C. to 150° C.,

viii) passing the heat-set tube through a series of converging rolls, lay-flattening it and winding it;

wherein:

in step iii) and step iv) the wavelength of the IR radiation emitted by the pre-heating ovens ( 1 , 2 ) and by the heating orientation oven(s) ( 3 ) matches the absorbance wavelength of the polyolefins; and

optionally, in step iv) the pre-heated tube ( 7 ) passes through an additional couple of pinch rolls ( 4 ) positioned between the pre-heating ovens ( 1 , 2 ) and the heating orientation oven(s) ( 3 );

the multilayer packaging film comprising at least the following layers:

an outer heat sealable layer a) comprising polymers selected from the group of ethylene-alpha-olefin copolymers, polybutylene (PB), ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers, ethylene butyl acrylate copolymers (EBA) and mixtures thereof, the total amount of ethylene vinyl acetate copolymers (EVA), ethylene(meth)acrylate/(meth)acrylic acid copolymers and ethylene butyl acrylate copolymers (EBA) in the heat sealable layer being not higher than 30% by weight based on the total weight of the film;

an inner gas barrier layer b) comprising ethylene-vinyl alcohol (EVOH), wherein the EVOH content is comprised between 3% and 25% by weight based on the total weight of the film; and

an outer layer c) comprising one or more polyolefins,

wherein the film:

has a gloss value at 60° higher than 100 g.u. measured in accordance to ASTM D2457,

comprises at least 90% by weight of one or more polyolefins based on the total weight of the film,

does not contain any polyamide or polyester, and

has at least one of the following features:

elastic modulus higher than 4000 kg/cm 2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.;

elongation at break of at most 200% in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.;

tensile strength at break higher than 500 kg/cm 2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.

19 . The process of claim 18 further comprising the step of thermoforming the multilayer packaging film to form a thermoformed support.