Sealable and easy opening polyester films

1 . A fully thermoplastic heat sealable, optionally oriented, multilayer polyester based film comprising at least the following layers:

1) A heat-sealable polyester based outer layer;

2) An inner layer placed between layer 1) and layer 3) comprising at least 80 wt % of one or more polyesters and between 1 wt % and 20 wt % with respect to the total weight of the layer of one or more further polymers selected from the group consisting of polyolefins, ethylene vinyl acetate copolymers (EVA), ethylene (meth)acrylate/(meth)acrylic acid copolymers and mixtures thereof; and

3) A polyester based layer;

wherein the multilayer polyester based film is heat shrinkable with a percentage of free shrink at 120° C. of at least 15% in longitudinal and/or transverse direction, measured in oil according to ASTM D 2732; and

wherein the multilayer polyester based film has either:

i. an in/in seal opening force of between 850 g/inch and 1500 g/inch sealed over the entirety of the range from 110° C. to 160° C.; or

ii. an in/out seal opening force of between 800 g/inch and 1800 g/inch sealed over the entirety of the range from 150° C. to 190° C.;

opening force being measured by having film specimens having dimensions of 2.54 cm of width and about 15-20 cm of length, cut along the machine direction being sealed on itself with the heat-sealable polyester based outer layer facing each other for in/in seals or heat-sealed on itself with the heat-sealable polyester based outer layer facing an outer layer opposite the heat-sealable polyester based outer layer for in/out seals;

hot bar sealing along the transverse direction with a sealing time of 1 second at the temperature listed above in i. and ii., the specimens fixed into the lower jaw and into the upper jaw of a dynamometer; the test area positioned in the middle of the two jaws of the dynamometer; the measure force applied for the opening of 0.8 cm of the seal in g/inch;

dynamometer conditions set as follows:

equipment: Instron 5564,

starting jaw distance: 5 cm,

crosshead speed: 300 mm/min,

seal width: 0.8 cm.

2 . The heat sealable film according to claim 1 wherein layer 2) adheres to layer 1) and to layer 3).

3 . The heat sealable film according to claim 1 , wherein said layer 2) comprises at least 85 wt %, of one or more polyesters and wherein said layer 2) comprises between 1 wt % and 10 wt % of one or more further polymers selected from the group consisting of polyolefins, ethylene vinyl acetate copolymers (EVA), ethylene (meth)acrylate/(meth)acrylic acid copolymers and mixtures thereof.

4 . The heat sealable film according to any one of claim 1 , wherein said polyolefins comprised in layer 2) are selected from the group consisting of ethylene polymers, propylene polymers, butylene polymers and mixtures thereof.

5 . The heat sealable film according to claim 4 wherein said ethylene polymers are selected from the group of ethylene copolymers, ethylene alpha olefin copolymers, ethylene (C 4 -C 10 ) alpha olefin copolymers, and linear low density polyethylene (LLDPE) and/or said propylene polymers are selected from propylene copolymers, or propylene alpha olefin copolymers and/or said butylene polymers are selected from butylene copolymers, or butylene alpha olefin copolymers.

6 . The heat sealable film according to claim 1 , wherein said polyolefins comprised in layer 2) are modified polyolefins, anhydride modified polyolefins, or maleic anhydride modified polyolefins.

7 . The heat sealable film according to claim 1 wherein said ethylene (meth)acrylate copolymers comprise members 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, ethylene methylacrylate copolymers, and ionomers.

8 . The heat sealable film according to claim 7 , wherein said ethylene (meth)acrylate copolymers are ethylene methylacrylate copolymers comprising between 5 and 40 wt % of methyl acrylate.

9 . The heat sealable film according to claim 1 , wherein said ethylene (meth)acrylate/(meth)acrylic acid copolymers are modified ethylene (meth)acrylate/(meth)acrylic acid copolymers, anhydride modified ethylene (meth)acrylate/(meth)acrylic acid copolymers, or maleic anhydride modified ethylene (meth)acrylate/(meth)acrylic acid copolymers.

10 . The heat sealable film according to claim 1 , wherein said one or more polyesters comprised in layer 2) are selected from the group consisting of poly(ethylene terephthalate) (PET), glycol-modified poly(ethylene terephthalate) (PETG) and a mixture of PET and PETG.

11 . The heat sealable film according to claim 1 , wherein the heat sealable layer 1) comprises at least 90 wt % of one or more polyesters.

12 . The heat sealable film according to claim 1 , wherein the film comprises an outer layer of the film, opposite to the heat sealable layer 1), said outer layer comprising at least 90 wt % of one or more polyesters.

13 . The heat sealable film according to claim 12 , wherein said outer layer is layer 3).

14 . The heat sealable film according to claim 1 , wherein the overall composition of the film comprises at least 75 wt % of polyesters, polyesters of aromatic dicarboxylic acids, or polyesters of terephthalic acid.

15 . The heat sealable film according to claim 1 wherein layer 3) has a thickness of at least 20% of the total thickness of the film.

16 . The heat sealable film according to claim 1 wherein: (i) the heat-sealable layer 1) has a thickness comprised between 0.5 and 15 microns; and/or (ii) layer 2) has a thickness comprised between 1 and 15 microns; and/or (iii) layer 3) has a thickness comprised between 5 and 60 microns.

17 . The heat sealable film according to claim 1 , which is biaxially oriented, with an orientation ratio between about 2:1 and about 5:1 in both longitudinal and transverse direction.

18 . The heat sealable film according to claim 1 , wherein layer 3) is an inner layer, comprising at least 90 wt % of one or more polyesters.

19 . The heat sealable film according to claim 1 wherein the film has a Dopack value of at least 0.25 when sealed onto a Silver Plastic APET 1826 tray, using a Sealpac A7 machine with a 1826 OC (Outside Cut) tool, equipped with a rounded seal bar (w=4 mm; r=8 mm), at a sealing temperature of 140° C.

20 . A package comprising a container, a product placed into said container and a lid made of a heat sealable film, wherein the heat-sealable layer of the film is in contact with faces or faces the product, the film being hermetically sealed onto said container, wherein the container is selected from CPET, APET, APET/CPET and RPET containers, the heat sealable film comprising at least the following layers:

1) a heat-sealable polyester based outer layer,

2) an inner layer placed between layer 1) and layer 3) comprising at least 80 wt % of one or more polyesters and between 1 wt % and 20 wt % with respect to the total weight of the layer of one or more further polymers selected from the group consisting of polyolefins, ethylene vinyl acetate copolymers (EVA), ethylene (meth)acrylate/(meth)acrylic acid copolymers and mixtures thereof; and

3) a polyester based layer,

wherein the multilayer polyester based film is heat shrinkable with a percentage of free shrink at 120° C. of at least 15% in longitudinal and/or transverse direction, measured in oil according to ASTM D 2735; and

wherein the heat sealable film has either:

i. an in/in seal opening force of between 850 g/inch and 1500 g/inch sealed over the entirety of the range from 110° C. to 160° C.; or

ii. an in/out seal opening force of between 800 g/inch and 1800 g/inch sealed over the entirety of the range from 150° C. to 190° C.;

opening force being measured by having film specimens having dimensions of 2.54 cm of width and about 15-20 cm of length, cut along the machine direction being sealed on itself with the heat-sealable polyester based outer layer facing each other for in/in seals or heat-sealed on itself with heat-sealable polyester based outer layer facing an outer layer opposite the heat-sealable polyester based outer layer for in/out seals, hot bar sealing along the transverse direction with a sealing time of 1 second at the temperature listed above in i. and ii., the specimens fixed into the lower jaw and into the upper jaw of a dynamometer, the test area positioned in the middle of the two jaws of the dynamometer, the measure force applied for the opening of 0.8 cm of the seal in g/inch,

dynamometer conditions set as follows:

equipment: Instron 5564

starting jaw distance: 5 cm,

crosshead speed: 300 mm/min,

seal width: 0.8 cm.

21 . A flexible container obtainable by heat-sealing a heat-sealable film onto itself, or by heat-sealing two films, of which at least one is a heat sealable film, wherein the heat sealable film comprises at least the following layers:

1) a heat-sealable polyester based outer layer,

2) an inner layer placed between layer 1) and layer 3) comprising at least 80 wt % of one or more polyesters and between 1 wt % and 20 wt % with respect to the total weight of the layer of one or more further polymers selected from the group consisting of polyolefins, ethylene vinyl acetate copolymers (EVA), ethylene (meth)acrylate/(meth)acrylic acid copolymers and mixtures thereof; and

3) a polyester based layer,

wherein the multilayer polyester based film is heat shrinkable with a percentage of free shrink at 120° C. of at least 15% in longitudinal and/or transverse direction, measured in oil according to ASTM D 2735; and

wherein the heat sealable film has either:

i. an in/in seal opening force of between 850 g/inch and 1500 g/inch sealed over the entirety of the range from 110° C. to 160° C.; or

ii. an in/out seal opening force of between 800 g/inch and 1800 g/inch sealed over the entirety of the range from 150° C. to 190° C.;

opening force being measured by having film specimens having dimensions of 2.54 cm of width and about 15-20 cm of length, cut along the machine direction being sealed on itself with the heat-sealable polyester based outer layer facing each other for in/in seals or heat-sealed on itself with heat-sealable polyester based outer layer facing an outer layer opposite the heat-sealable polyester based outer layer for in/out seals, hot bar sealing along the transverse direction with a sealing time of 1 second at the temperature listed above in i. and ii., the specimens fixed into the lower jaw and into the upper jaw of a dynamometer, the test area positioned in the middle of the two jaws of the dynamometer, the measure force applied for the opening of 0.8 cm of the seal in g/inch,

dynamometer conditions set as follows:

equipment: Instron 5564

starting jaw distance: 5 cm,

crosshead speed: 300 mm/min,

seal width: 0.8 cm.