GAS-BARRIER HEAT-SHRINKABLE FILM
The present invention refers to a versatile gas-barrier multilayer heat-shrinkable thermoplastic film that, by minimal variations in its manufacturing process, becomes suitable for the manufacture of packages, called “Flowpack”, on horizontal form-fill-seal (HFFS) machines, of tray-lidded packages or of shrinkable packaging bags. This film comprises a first outer sealant layer, a second outer polyester layer, an inner barrier layer, no polyamide or polyester inner layer(s), no polyolefin layers positioned between the barrier layer and the sealant layer and at least a polyolefin bulk layer of specific relative thickness placed between the inner barrier layer and the outer polyester layer.
1 . A multilayer asymmetrical heat-shrinkable gas-barrier thermoplastic packaging film comprising
an outer sealant layer (B),
an inner gas-barrier layer (A),
an outer layer (C) comprising a major proportion of polyester(s),
at least an inner layer (D), positioned between the gas barrier layer (A) and the outer layer (C), comprising a major proportion of polyolefin(s) and/or of ethylene-vinyl acetate copolymer(s),
no inner layer comprising a major proportion of polyamide(s) or polyester(s),
no inner layer positioned between the gas barrier layer (A) and the sealant layer (B) comprising a major proportion of polyolefin(s),
wherein the thickness ratio in percentage of the inner layer (D) with respect to the total thickness of the film is from 15 to 50% and the total thickness of the film is lower than 80 microns.
2 . (canceled)
3 . The film according to claim 2 comprising
no inner layer comprising polyamide(s) or polyester(s), and
no inner layer positioned between the gas barrier layer (A) and the sealant layer (B) comprising polyolefin(s).
4 . The film according to claim 1 , wherein the thickness ratio in percentage of the inner layer (D) with respect to the total thickness of the film is from 15 to 35%.
5 . The film according to claim 1 wherein:
the sealant layer (B) comprises one or more resins selected among polyolefins, modified polyolefins and their blends; and/or
the barrier layer (A) comprises at least an EVOH resin, in amount of at least 70% by weight with respect to the layer weight; and/or
the outer layer (C) comprises a major proportion of aromatic polyesters; and/or
the inner layer (D) comprises a resin selected from ethylene homopolymers, ethylene-alpha-olefin copolymers ethylene-vinyl acetate copolymers, polypropylene homopolymers, propylene-ethylene co-polymers, propylene-ethylene-butene copolymers, propylene-butene-ethylene copolymers and their blends.
6 . The film according to claim 1 wherein layer (B) and/or layer (D) comprise a major proportion of a LLDPE.
7 . The film according to claim 1 wherein the outer polyester layer (C) comprises a blend of polyesters comprising one or more PETG(s) in amount from 30% to 50% by weight with respect to the weight of the polyester blend.
8 . The film according to claim 1 wherein
the sealant layer (B) comprises polyolefins or their blends in major proportion, in amount higher than 60% by weight with respect to layer (B) weight; and/or
the outer layer (C) comprises polyester(s) in amount higher than 60% by weight with respect to layer (C) weight.
9 . The film according to claim 1 wherein the thickness ratio in percentage of
the sealant layer (B) is at most 45%; and/or
the barrier layer (A) is from 4% to 30%; and/or
the outer layer (C) is from 3% to 25%; and/or
the inner layer (D) is from 15% to 35%,
with respect to the total thickness of the film.
10 . The film according to claim 1 further comprising at least a tie layer (E), wherein the tie layer (E) has a thickness ratio in percentage lower than 15% with respect to the total thickness of the film.
11 . The film according to claim 1 wherein the sequence of layers is selected among B/A/D/C, B/A/D/E/C, B/E/A/D/C, B/E/A/D/E/C, B/E/A/E/D/E/C, B/F/A/D/C, B/F/A/D/E/C, B/F/E/A/D/C, B/F/E/A/D/E/C and B/F/E/A/E/D/E/C.
12 . The film according to claim 1 , obtainable according to the process of claim 15 , said film being characterized by
a haze value between 1% and 15% measured according to standard ASTM D 1003; and/or
a gloss value (60° angle) higher than 100 g.u., measured according to standard ASTM D 2457.
13 . The film according to claim 1 suitable for Flowpack packaging applications, characterized by
a maximum shrink tension, measured according to the test method herein reported, lower than 45 kg/cm 2 both in the longitudinal and transverse directions and/or higher than 15 kg/cm 2 both in the longitudinal and transverse directions; and/or
a residual shrink tension at 5° C., measured according to the test method herein reported, lower than 45 Kg/cm 2 both in the longitudinal and transverse directions and/or higher than 25 Kg/cm 2 ; and/or
a free shrink in the longitudinal direction, measured at 85° C. in water according to ASTM D 2732, higher than 5%, and/or lower than 30%; and/or
a free shrink in the transverse direction, measured at 85° C. in water according to ASTM D 2732, higher than 5% and/or lower than 30%; and/or
a difference between the free shrink values in the longitudinal direction and transverse directions, measured at 85° C. in water according to ASTM D 2732, lower than 15%; and/or
an elastic modulus, measured according to ASTM D 882, in the range 8000 to 14000 kg/cm 2 in each of the longitudinal and transverse directions; and/or
an elongation at break, measured according to ASTM D882, in the range 70 to 140% in each of the longitudinal and transverse directions; and/or
a tensile at break, measured according to ASTM D882, in the range 700 to 1200 kg/cm 2 in each of the longitudinal and transverse directions; and/or
a curling, measured according to the test method herein reported, not higher than 20% in each one of the longitudinal and transverse directions and/or not higher than 10% in the transverse direction,
wherein said film is obtainable according to the process of claim 16 .
14 . The film according to claim 1 suitable for tray lidding packaging applications, characterized by:
a maximum shrink tension, measured according to the test method herein reported, lower than 25 kg/cm 2 both in the longitudinal and transverse directions and/or higher than 7 kg/cm 2 both in the longitudinal and transverse directions; and/or
a residual shrink tension at 5° C., measured according to the test method herein reported, lower than 36 Kg/cm 2 both in the longitudinal and transverse directions and/or higher than 25 Kg/cm 2 ; and/or
a free shrink in the longitudinal direction, measured at 85° C. in water according to ASTM D 2732, higher than 5%; and/or
a free shrink in the transverse direction, measured at 85° C. in water according to ASTM D 2732, higher than 3%, and/or lower than 10%; and/or
a difference between the free shrink values in the longitudinal direction and transverse directions, measured at 85° C. in water according to ASTM D 2732, lower than 10%; and/or
an elastic modulus, measured according to ASTM D 882, in the range 8000 to 14000 kg/cm 2 in each of the longitudinal and transverse directions; and/or
an elongation at break, measured according to ASTM D 882, in the range 70 to 160% in each of the longitudinal and transverse directions; and/or
a tensile at break, measured according to ASTM D 882, in the range 700 to 1200 kg/cm 2 in each of the longitudinal and transverse directions; and/or
a curling, measured according to the test method herein reported, not higher than 10%, in each one of the longitudinal and transverse directions,
wherein said film is obtainable according to the process of claim 17 .
15 . A process for manufacturing the films according to claim 1 comprising the steps of:
a) coextruding the resins and/or blends of resins of the various layers through a round or flat extrusion die, thus obtaining a tube or sheet;
b) quenching the tube or sheet at temperature comprised between 5 and 25° C.;
c) cross-linking the tube or sheet;
d) heating the tube or sheet at an orientation temperature comprised between 85° C. and 160° C.;
e) simultaneously or sequentially biaxially stretching the heated tube or sheet at a stretching ratio of at least 2.5:1 and of at most 5:1 in each one of the transverse (TD) and longitudinal (LD) directions;
f) annealing the stretched tube or sheet by heating it at a temperature from 45° C. to 105° C.;
g) cooling the annealed tube or sheet at a temperature lower than 40° C.
16 . The manufacturing process according to claim 15 for manufacturing a film for Flowpack packaging applications wherein the annealing step f) is performed at a temperature of at most 80° C.
17 . The manufacturing process according to claim 15 for manufacturing a film for Tray Lidding packaging applications wherein the annealing step f) is performed at a temperature higher than 80° C.
18 . (canceled)
19 . A packaging process, which is a Flowpack packaging process on a horizontal form-fill-seal (HFFS) machine and which comprises:
(a) providing a film according to claim 1 ,
(b) running the film through a former thus forming a tube,
(c) inserting a product, optionally placed in a container, into the tube,
(d) sealing the tube longitudinally,
(e) sealing and cutting the tube transversally at the beginning and at the end of the package, optionally gas-flushing the tube before closing it, and
(f) heat-shrinking the package.
20 . (canceled)
21 . A packaging process which is a tray lidding packaging process and which comprises:
(I) providing a tray with a heat-sealable rim,
(II) loading said tray with the product to be packaged,
(III) applying a lid on top of said tray,
(IV) heat-sealing said lid to the tray rim, optionally modifying the atmosphere between said lid and said tray, thus providing a package, and
(V) heat shrinking the package, simultaneously or subsequently to the sealing step, in which the lid is a film according to of claim 1 .
22 . (canceled)
23 . (canceled)
24 . (canceled)
25 . The use of the film according to claim 1 in a tray lidding packaging process, where the film is used in combination with an innermost gas-permeable packaging film, or in the manufacture of shrinkable flexible containers.
26 . The film according to claim 5 wherein the sealant layer (B) is selected from ethylene homopolymers, ethylene co-polymers, propylene homopolymers, propylene co-polymers and blends thereof.