A HEAT-SEALABLE PACKAGING FILM

Abstract

A heat-sealable packaging film, comprising a base film mainly comprising polyethylene terephthalate, the base film forming a layer of the packaging film; and a heat seal layer mainly comprising an IPA-modified copolyester; wherein the heat seal layer has been extrusion coated on the base film so that the heat seal layer material forms an exterior, amorphous, and heat- sealable heat seal layer.

Claims

1. A method of manufacture of a heat-sealable packaging film, comprising: providing a base film mainly comprising polyethylene terephthalate (PET), the base film forming a layer of the heat-sealable packaging film; providing a heat seal layer material mainly comprising an at least semi-crystallized and isophthalic acid modified copolyester comprising at least 5 weight% isophthalic acid; and extrusion coating the heat seal layer material on the base film, wherein, in the heat-sealable packaging film, the heat seal layer material forms a heat seal layer that is exterior, amorphous, and heat-sealable.

2. The method of claim 1, further comprising: providing a tie layer material mainly comprising a thermoplastic polymer, wherein the extrusion coating involves coextrusion coating the tie layer material and the heat seal layer material on the base film, wherein, in the heat-sealable packaging film, the heat seal layer material forms the heat seal layer and the tie layer material forms a tie layer disposed between the base film and the heat seal layer.

3. The method of claim 1, wherein the at least semi-crystallized and isophthalic acid modified copolyester has an isophthalic acid content of 5 to 15 weight%.

4. The method of claim 1, wherein the heat seal layer material has a melting point T.sub.m according to ASTM D3418 from 200 to 240° C.

5. The method of claim 1, wherein the heat seal layer material of the heat-sealable packaging film has a recrystallization temperature of equal to or above 70° C. and equal to or below 180° C.

6. The method of claim 1, wherein the heat seal layer material has a crystallinity according to ASTM D1505 above or equal to 30 %.

7. The method of claim 1, wherein the heat seal layer material is provided as a solid, granular material.

8. The method of claim 1, wherein the heat seal layer material has a copolyester concentration of more than 99 vol%.

9. The method of claim 2, wherein the thermoplastic polymer of the tie layer material is a polyolefin.

10. The method of claim 1, wherein the extrusion coating is performed in an extruder that comprises a worm or a screw, wherein the heat seal layer material is heated to above 100° C. before an entry into the worm or the screw, at the entry into the worm or the screw, or both.

11. The method of claim 1, wherein the base film has a thickness of 23 to 50 .Math.m, and the heat seal layer material is extrusion coated in a total grammage of 8 to 20 g/m.sup.2.

12. The method of claim 1, wherein the heat seal layer material is cooled by more than 200° C./s during or after the extrusion coating.

13. The method of claim 1, wherein the base film, the heat seal layer, or both, do not comprise glycol-modified PET (PET-G).

14. The method of claim 1, further comprising: drying the heat seal layer material at a temperature above 110° C. before the extrusion coating.

15. A method of manufacture of a package, comprising: providing a base film mainly comprising polyethylene terephthalate (PET), the base film forming a layer of a heat-sealable packaging film; providing a heat seal layer material mainly comprising an at least semi-crystallized and isophthalic acid modified copolyester comprising at least 5 weight% isophthalic acid; extrusion coating the heat seal layer material on the base film, wherein, in the heat-sealable packaging film, the heat seal layer material forms a heat seal layer that is exterior, amorphous, and heat-sealable; and heat-sealing the heat-sealable packaging film to an object, wherein the heat seal layer faces the object.

16. A heat-sealable packaging film, comprising: a base film mainly comprising polyethylene terephthalate, the base film forming a layer of the heat-sealable packaging film; and a heat seal layer mainly comprising an isophthalic acid modified copolyester comprising at least 5 weight% isophthalic acid; wherein the heat seal layer is formed by a heat seal layer material that has been extrusion coated on the base film, and wherein the heat seal layer is exterior, amorphous, and heat-sealable .

17. The heat-sealable packaging film of claim 16, wherein the heat-sealable packaging film does not comprise a polyurethane (PU) based adhesive between the base film and the heat seal layer.

18. The heat-sealable packaging film of claim 16, wherein the base film, the heat seal layer, or both, do not comprise glycol-modified PET (PET-G).

19. A package, comprising: a sheet or lid of a packaging film; and an object, wherein: the packaging film comprises: a base film mainly comprising polyethylene terephthalate, the base film forming a layer of the packaging film, and a heat seal layer mainly comprising an isophthalic acid modified copolyester comprising at least 5 weight% isophthalic acid, wherein the heat seal layer is formed by a heat seal layer material that has been extrusion coated on the base film, and wherein the heat seal layer is exterior, amorphous, and heat-sealable, the packaging film is heat-sealed to the object with the heat seal layer facing the object, and the package comprises a packaged product.

20. The package of claim 19, wherein the packaged product comprises a foodstuff product and/or a pharmaceutical product.

21. The heat-sealable packaging film of claim 16, wherein the heat-sealable packaging film is configured to produce a waste material during a recycling process, and wherein the waste material is configured to dry at temperatures above 100° C.

22. The method of claim 2, wherein the base film has a thickness of 23 to 50 .Math.m, and the heat seal layer material and the tie layer material are coextrusion coated in a total grammage of 8 to 20 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] In the schematic drawings:

[0118] FIG. 1 shows a side view of a first example of the heat-sealable packaging films of the present disclosure;

[0119] FIG. 2 shows a side view of a second example of the heat-sealable packaging films of the present disclosure;

[0120] FIG. 3 shows a side view of a third example of the heat-sealable packaging films of the present disclosure;

[0121] FIG. 4 shows a side view of a fourth example of the heat-sealable packaging films of the present disclosure; and

[0122] FIG. 5 shows a perspective view of a cup and a lid punched from the packaging film of FIG. 2.

DETAILED DESCRIPTION

[0123] FIGS. 1 to 4 show first to fourth examples, respectively, of heat-sealable, flexible packaging films 1a to 1d of the present disclosure. The packaging films 1a to 1d have been manufactured according to examples of methods of the present disclosure. In the following, the same refence signs will be applied to designate identical or corresponding features of each of the packaging films 1a to 1d.

[0124] The films 1a to 1d can be used as lids for containers, see also below and FIG. 5, or other packaging applications where a heat-sealable, potentially flexible, packaging film is relevant to apply.

[0125] Each of the packaging films 1a to 1d comprises a base film 2 of extruded BOPET, the base film 2 forming a layer of each of the packaging films 1a to 1d. An exterior, amorphous, and heat-sealable heat seal layer 3 mainly is of an IPA-modified copolyester comprising about 10 weight% IPA. The heat seal layer 3 has been extrusion coated on the base film so that an initial or start material for the heat seal layer 3 after manufacture of the packaging films 1a to 1d forms the heat seal layer 3.

[0126] The packaging films 1b to 1d of FIGS. 2 to 4, respectively, also include a coextrusion coating tie layer 4 of a thermoplastic polymer. In manufacture of the packaging films 1b to 1d, the tie layer 4 and the heat seal layer 3 have been coextrusion coated on the base film so that, in the manufactured packaging films 1b to 1d, a start material for the heat seal layer 3 forms the exterior, amorphous, and heat-sealable heat seal layer 3 and a start material for the tie layer 4 is disposed between the base film 2 and the heat-seal layer 3. Consequentially, no adhesive or glue layer is present in the packaging films 1a to 1d.

[0127] Each of the packaging films 1a to 1d is manufactured by an associated example of the methods according to the present disclosure. First, the base film 2 is provided or manufactured, potentially manufactured in a previous process, and the heat seal layer material is provided. The heat seal layer material is provided as a substantially opaque, whitish, solid, granular material. The heat seal layer start material comprises the semi-crystallized and IPA-modified copolyester comprising at least 5 weight% isophthalic acid. Then, the heat seal layer material is extrusion coated on the base film 2 so that, in the manufactured packaging film 1a to 1d, the heat seal layer material forms the exterior, amorphous, and heat-sealable heat seal layer 3.

[0128] Each of the methods of manufacture of the packaging films 1b to 1d further comprises providing a coextrusion coating tie layer material of a thermoplastic polymer, wherein the extrusion coating involves coextrusion coating the tie layer material and the heat seal layer material on the base film 3 so that, in the associated manufactured packaging film 1a to 1d, the heat seal layer material forms the exterior, amorphous, and heat-sealable heat seal layer 3 and the tie layer material forms the tie layer 4 disposed between the base film 2 and the heat-seal layer 3. The packaging sheets 1c and 1d also include a second, further tie layer 5, which has been coextrusion coated together with the tie layer 4 and the heat seal layer 3. A not shown extrusion coating primer can be applied to the surface of the base film 2 facing the heat seal layer 3 before the (co-)extrusion coating of the heat seal layer 3 and, where relevant, the one or two tie layers 4, 5. The primer may be selected among the above-mentioned options.

[0129] The heat seal layer material can have a melting point T.sub.m of about 230° C. In the (co-)extrusion coating process, the heat seal layer material is heated to its T.sub.m so that it is on a melted and amorphous form. In the manufactured packaging films 1a to 1d the heat seal layer material is in an amorphous, solid form. The heat seal layer material can have a relative density of 1.37 g/m.sup.3, a bulk density of 0.84 g/m.sup.3, and a specific density crystalline above 1.3 or 1.35, such as 1.39, g/m.sup.3. The heat seal layer material can have a crystallinity according to ASTM D1505 of about 48 %.

[0130] The heat seal layer material can be (co-)extrusion coated at a temperature thereof at about 275° C. Coextrusion coating is performed in an extruder, which comprises a feedblock, and a temperature of the heat seal layer material in the feedblock or a temperature set in the feedblock can be 260° C. During the coextrusion coating, the (co-)extrusion coated heat seal layer 3, and the potential tie layer(s) 4 and 5, are quenched to allow the heat seal layer material 3 to substantially maintain its amorphous form in the manufactured packaging films 1a to 1d, which allows the manufactured heat seal layer 3 to be heat-sealable.

[0131] The copolyester of the heat seal layer material can, for example, be Selenis Copolyester Crystallized Resin, having the trade dame Bondz BO 035, as mentioned in the above.

[0132] Before the (co-)extrusion coating step, the heat seal layer material can be heated in an oven to about 140° C. before providing the material to a feed zone of an extrusion coating or coextrusion coating apparatus or machine.

[0133] The tie layers 4, 5 tie or bond the heat seal layer 3 to the base film 2.

[0134] In the packaging film 1d of FIG. 4, the base film 2 is aluminized so as to include a metallization coating 6 on a surface facing the heat seal layer 3.

[0135] The base film 2 can have a thickness of 36 .Math.m. The (co-)extrusion coated layer(s) can be (co-)extrusion coated in a total grammage of, for example, 17 g/m.sup.2.

[0136] The copolyester of the heat seal layer 3 can be dried for 4 to 6 hours before the (co-)extrusion coating.

[0137] Each of the packaging films 1a to 1d forms one coherent film in which the base film 2 and (co-)extrusion coated layers 3 and potentially 4, 5, adhere to each other in sequence. This adherence is established by the (co-)extrusion coating.

[0138] Each of the packaging films and their associated base film 2, tie layer(s) 4, 5, and heat seal layer 3 are distributed to have substantially uniform thickness and grammage across substantially an entire planar extent of the packaging film 1a to 1d.

[0139] The base film 2 can be opaque, translucent, or transparent. The base film 2 can comprise a colouring agent and may be white or another colour.

[0140] The packaging films 1a to 1d include no further layers, films, or materials. Each of the layers only comprises a single layer, i.e. no sub-layers. In other examples, the packaging sheets 1a to 1d may comprise a print layer on either side of the base film 2. If on an exterior surface of the base film 2, a protective lacquer may be provided to protect the print layer.

[0141] The material of the tie layers 4 and/or 5 can be Lotader 4503 or another of the extrusion coating tie layer materials suggested in the above.

[0142] The (co-)extrusion coating is generally performed in an extruder as explained in the above.

[0143] FIG. 5 shows an example of the packages of the present disclosure, in the form of a cup 7 of APET, and a film lid or sheet lid 8 pre-punched from the packaging film 1b of FIG. 2. The cup 7 comprises a seal rim 9 surrounding an opening 10 of the cup 7. A corresponding circumferential rim 11 of the lid 8 is heat-sealed to the rim 9 in a suitable heat-sealing tool with the heat heal layer 3 facing an upper seal surface of the rim 9. The cup can be filled with, for example, yogurt (not shown) before the cup 9 is closed and sealed in this manner. The lid 8 can then be torn off by a consumer to gain access to the packaging contents.

[0144] When a consumer later tears off the lid 8, the torn-off lid 8 can be disposed off as recyclable polyester, potentially together with the cup 7. According to an example of a method of recycling the lid 8, the lid 8 waste is separated and extracted, potentially together with further waste, such as the cup 7 waste, in a process where the waste is dried at, for example, about 140° C.

[0145] According to known processes of extraction of polyester from waste for waste recycling, polyester waste including waste from the packaging films according to the present disclosure, such as the torn-off lid 8, and/or an object to which the film was heat-sealed, such as the cup 7, can first be collected. The collected waste is then transported, potentially in bales, to a sorting facility where a polyester fraction of the waste can be separated, such as by means of infra red (IR) or near infra red (NIR) and/or a visual (VIS) spectrometry sensor. The polyester waste can then be subjected to an alcalic hotwash. Then, the waste can be shredded or ground into flakes after which the flakes can be washed, e.g. to remove contaminants, such as yogurt remains. A further alcalic hotwash can then be performed. The flakes can then be dried, potentially by means of dry air blowing, potentially in an oven, potentially at a hot air temperature of 140 to 160° C. The waste from the packaging films according to the present disclosure may here at least partly recrystallize, which may at least partly prevent the flakes from agglomerating. The flakes can then be extruded, potentially to form an extruded granulate. The extruded recycled polyester granules can then be (re-)crystallized to be ready for reuse. Before being reused, the granules may again be dried at a similar temperature.

Experiments

[0146] Five different samples, Samples 1, 1a, 2, 3, and 4, of the packaging film 1b of FIG. 2 were manufactured by the method as explained above. The samples were provided with varying grammages of the coextrusion coated layers.

[0147] The base film 2 was a one-side corona-treated, 36 .Math.m BOPET film, FLEX FF-PAP-36-N. The extrusion coating was performed on the corona-treated surface of the base film 2.

[0148] The tie layer material for the tie layer 4 was Lotader 4503 as described in the above.

[0149] The heat seal layer material for the heat seal layer 3 was Bondz BO 035 as described in the above. Before the coextrusion coating, the heat seal layer material was dried for 4-6 hours at 140° C.

[0150] Before the coextrusion coating, an extrusion coating primer was applied to the surface of the base film 2 for facing the heat seal layer 3. The primer was MICA A-131-X, a water based, modified polyethyleneimine, single component resin dispersion extrusion primer.

[0151] The cooling roller was a Teflon/metal roller, and the counter-roller was a silicone rubber roller. Other types of rollers, such as metal rollers, can alternatively be applied.

[0152] When coated, the tie layer melt was set to a temperature of 275° C., and the heat seal layer melt was set to a temperature of 290° C. The temperature in the feedblock and in the die was set to 275° C.

[0153] The manufactured packaging films were each heat sealed at 210° C. to a, APET cup in a manner similar to as disclosed above in connection with FIG. 5. The heat sealed packaging films were then subjected to two tests of heat seal strength. In the first test, the films were peeled off the cup, and the peel in the heat seal zone was manually evaluated and given a score from 1 to 5 out of 5 where 5 indicated an a highest score, uniform peel with suitable peel strength and without strings of material, and 1 indicated an unsatisfactory peel. The second test was a vacuum test in which the sealed cups (sealed at atmospheric pressure) were subjected to an atmospheric pressure of minus 200 hPa. The, it was manually observed whether the sealed cups remained sealed, i.e. whether the seal survived the sub-pressure, and the Samples were provided with a pass/fail score.

[0154] Theoretical applied grammages of the coextrusion coated tie layer material and heat seal material are shown in Table 1 below. A grammage of the resultant coextruded layers was measured after manufacture. The measured grammage was somewhat different from the theoretical grammages, which is expected to be due to a varying width of the coextrusion coating; the width was set to 0.54 m but varied somewhat and was not measured for the Samples.

TABLE-US-00001 Sample Tie layer, theoretic grammage [g/m.sup.2] Heat seal layer, theoretic grammage [g/m.sup.2] Total theoretic grammage [g/m.sup.2] Total measured grammage [g/m.sup.2] 1 10.8 4.0 14.8 12.0 1a 14.6 5.3 19.9 15.8 2 10.6 5.3 15.9 12.5 3 8.1 4.5 12.6 11.0 4 6.6 7.5 14.2 12.3

[0155] Table 2 below shows the results from the peel test and the vacuum test.

TABLE-US-00002 Sample Peel test Vacuum test 1 4/5 Fail 1a 5/5 Pass 2 4/5 Fail 3 5/5 Fail 4 5/5 Pass

[0156] All Samples could be heat sealed and subsequently peeled off. It was also observed that Samples 1, 1a, and 2 ran very well with a homogeneous coating, whereas there was a tendency of die swelling and a more heterogeneous coating in the manufacture of Samples 3 and 4. The Samples generally peeled (as intended) between the tie layer and the heat seal layer; however, Sample 1 peeled in the heat seal layer.

[0157] A differential scanning calorimetry (DSC) was performed on a Perkin-Elmer DSC-7 on the copolyester “waste” of a heat seal layer of one of the packaging films of the above experiments. The analysis indicated that the amorphous heat seal layer material started to recrystallize at about 120 to 140° C. At e.g. hot air drying at air temperatures at or above the recrystallization temperature, the waste can, therefore, be foreseen to agglomerate less upon heating than e.g. PETG based heat seal layers.

[0158] The packaging films of the Samples can be recycled according to any one of the methods of recycling as disclosed herein.