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

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/cm2 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/cm2 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.

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/cm2 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/cm2 in both the longitudinal direction (LD) and the transverse direction (TD), measured in accordance to ASTM D 882 at 23° C.