POLYESTER SHEET

Abstract

The present invention relates to a sheet comprising polyester, the sheet comprising at least one area (a) wherein the area (a) comprises at least one groove having a depth of >50% with regard to the thickness of the sheet in the area (a), wherein the sheet has a thickness of 200-1000 m in the area (a). Such sheet provides the ability to snap along the grooves in a predictable manner, whilst providing sufficient rigidity to avoid undesired bending under the influence of its own weight.

Claims

1. A sheet comprising: polyester, the sheet comprising an area (a) wherein the area (a) comprises a groove having a depth of >50% with regard to the thickness of the sheet in the area (a), wherein the sheet has a thickness of 200-1000 m in the area (a).

2. The sheet according to claim 1, wherein the polyester is poly(ethylene terephthalate).

3. The sheet according to claim 1, wherein the polyester has an intrinsic viscosity determined in accordance with ASTM D2857-95 (2007) of 0.6-1.5 dl/g.

4. The sheet according to claim 2, wherein the poly(ethylene terephthalate) comprises up to 20.0 wt % of moieties derived from a comonomer wherein the comonomer is one or more selected from isophthalic acid, 1,4-cyclohexanedimethanol, pentaerythritol, pyromellitic anhydride, or combinations thereof.

5. The sheet according to claim 1, wherein the depth of the groove is >60% with regard to the thickness of the sheet in area (a).

6. The sheet according to claim 1, wherein the depth of the groove is >60% with regard to the thickness of the sheet in area (a) and the sheet has a thickness of 700-1000 m.

7. The sheet according to claim 1, wherein the polyester is amorphous poly(ethylene terephthalate),

8. The sheet according to claim 1, comprising at least one area (a) wherein the area (a) comprises at least one groove having a depth of >60% with regard to the thickness of the sheet in area (a), wherein the groove(s) divide the sheet in multiple segments, wherein the sheet has a thickness in area (a) of 700-1000 m.

9. The sheet according to claim 1, wherein the area (a) comprises a groove having a depth of >70% with regard to the thickness of the sheet in area (a), wherein the groove divides the sheet in multiple segments, wherein the sheet has a thickness in area (a) of 700-1000 m, wherein each of the groove has a length of 40-55 mm.

10. The sheet according to claim 1, wherein the sheet has a thickness of 700-850 m.

11. A package comprising the sheet according to claim 9, wherein each segment comprises a cavity formed by thermoforming.

12. The package according to claim 11, wherein the volume of each of the cavities is 75-125 ml.

13. The package according to claim 11, wherein the package comprises an arrangement of 4, 6 or 8 segments each comprising a cavity.

14. The package according to claim 13, wherein the arrangement is formed by 2 rows of 2 segments, 1 row of 4 segments, 2 rows of 3 segments, or 2 rows of 4 segments.

15. A sheet comprising: polyester; wherein the sheet comprises an area (a) wherein the area (a) comprises a groove having a depth of >70% with regard to the thickness of the sheet in the area (a); wherein the sheet has a thickness of 700-1000 m in the area (a); wherein each of the groove has a length of 40-55 mm; wherein the polyester has an intrinsic viscosity determined in accordance with ASTM D2857-95 (2007) of 0.6-1.5 dl/g.

16. The sheet according to claim 15, wherein the polyester is poly(ethylene terephthalate), and wherein the poly(ethylene terephthalate) comprises up to 20.0 wt % of moieties derived from a comonomer wherein the comonomer is one or more selected from isophthalic acid, 1,4-cyclohexanedimethanol, pentaerythritol, pyromellitic anhydride, or combinations thereof.

Description

[0056] An exemplary sheet according to the present invention is presented in FIG. 1. In this figure:

[0057] (1) indicates the polyester sheet;

[0058] (2) indicates the grooves;

[0059] (3) indicates area (a) having a degree of crystallinity of 10%;

[0060] (4) indicates area (b) having a degree of crystallinity of 5%; and

[0061] (5) indicates a diamond-shapes aperture.

[0062] The invention in certain of its embodiments relates to the following aspects: [0063] Aspect 1: Sheet comprising polyester, the sheet comprising at least one area (a) where the polyester has a degree of crystallinity of 10%, and at least one area (b) where the polyester has a degree of crystallinity of 5%, wherein the area (a) comprises at least one groove having a depth of 30-50% with regard to the thickness of the sheet in the area (a), wherein the sheet has a thickness of 200-1000 m in the area (a). [0064] Aspect 2: Sheet according to aspect 1, wherein the polyester is a poly(ethylene terephthalate). [0065] Aspect 3: Sheet according to any one of aspects 1-2, wherein the groove(s) are positioned to allow dividing the sheet into segments. [0066] Aspect 4: Sheet according to any one of aspects 1-3, wherein the groove(s) are positioned to allow breaking the sheet along the groove(s). [0067] Aspects 5: Sheet according to an one of aspects 1-4, wherein the sheet is produced by subjecting a sheet comprising a polyester having a degree of crystallinity of 5% to a treatment for increasing the degree of crystallinity selectively to 10%. [0068] Aspect 6: Sheet according to aspect 5, wherein the treatment for increasing the degree of crystallinity selectively is a thermal treatment or a treatment involving exposure to laser irradiation. [0069] Aspect 7: Sheet according to any one of aspects 5-6, wherein the groove(s) are introduced prior to the treatment for increasing the crystallinity selectively. [0070] Aspect 8: Sheet according to any one of aspects 5-6, wherein the grooves are introduced after the treatment for increasing the crystallinity selectively. [0071] Aspect 9: Sheet according to any one of aspects 5-8, wherein each segment comprises an area (b) where the polyester has a degree of crystallinity of 5%. [0072] Aspect 10: Sheet according to aspect 9 wherein the area (b) is subjected to thermoforming prior to the treatment for increasing the crystallinity selectively. [0073] Aspect 11: Sheet according to aspect 9 wherein the area (b) is subjected to thermoforming subsequent to the treatment for increasing the crystallinity selectively. [0074] Aspect 12: Arrangement comprising a sheet according to any one of aspects 10-11 comprising multiple cavities for containing foodstuff formed by thermoforming. [0075] Aspect 13: Use of the arrangement according to aspect 12 for production of a foodstuff packaging comprising multiple cavities that can be separated by breaking along the groove(s). [0076] Aspect 14: Packaging comprising the arrangement according to aspect 12.

[0077] The invention will now be illustrated by the following non-limiting examples.

[0078] Specimen Preparation.

[0079] For the experimental part, polyester sheets having a thickness of 800 m and were used. The sheets were produced using as polyester a PET homopolymer having an intrinsic viscosity of 0.84 dl/g. The sheets were produced from the PET by drying PET pellets at 170 C. for 5 hrs, and extruding at 280 C. using an extruder equipped with a sheet casting die to obtain a sheet of 13 cm width, 800 m thickness and a crystallinity of 1%. The obtained sheet was cut into specimen sheets of 13 cm by 13 cm.

[0080] Introduction of Grooves.

[0081] Grooves were introduced in the snapping area of certain of the specimens, i.e. in the middle of the specimen sheets, over the full length of the sheet, the grooves being introduced using a knife to a predetermined depth, determined by microscopy. Grooves were made in the upper surface of the sheets.

[0082] Determination of Snapability.

[0083] Specimen sheets prepared as described above was provided with a groove with a depth of 70% of the thickness (example A) or 50% (example B). The sheets were each bent upwards (the groove being positioned in the upper surface) manually in a rapid movement. The sheet of example A demonstrated a clean snap over the entire length of the groove, whereas the sheet of example B did not snap but only bend.

[0084] Determination of Resistance to Load.

[0085] A specimen sheet prepared as described above was provided with a groove with a depth of 70% of the thickness of the sheet to obtain a sheet with 2 segments divided by the groove. A vertical 11 cm square was punched out from the centre of the sheet, resulting in a 1313 cm sheet with two groove segments on either side of the central aperture. The sheet was positioned in a clamp with one of its sides parallel to the grooves, the grooves facing upwards. A load of 700 g was positioned onto the segment of the sheet that was not held by the clamp. The segment comprising the load did show a minor bending but did not snap.

[0086] The above examples demonstrate that the sheet according to the invention, as demonstrated under example 1, provide the desired balance of rigidity and snapability that is desired for the packaging applications such as packaging of individual portions of dairy products.