WO2018065259A1

WO2018065259A1 - Polyester sheet

Info

Publication number: WO2018065259A1
Application number: PCT/EP2017/074362
Authority: WO
Inventors: Zahir BASHEER; Rajiva JOSHI
Original assignee: Sabic Global Technologies B.V.
Priority date: 2016-10-07
Filing date: 2017-09-26
Publication date: 2018-04-12

Abstract

The present invention relates to a 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 pm 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.

Description

Polyester sheet.

The present invention relates to a sheet comprising polyester. Furthermore, the invention relates to an arrangement comprising such sheet. The invention also relates to a packaging comprising such arrangement.

In certain packaging applications, such as for example in packaging of dairy products, there is a desire to package multiple quantities of the dairy products together in one packaging. In such way, several individual portions of the products may be sold in a single packaging. For example, such package may comprise 4, 6 or 8 of such individual portions.

Particularly, it is preferred the individual portions are combined into one packaging in such way that the segments of the packaging are connected, and may be separated by the consumer on his desire to retrieve a single portion from the packaging. A particularly desirable way by means of which this is done is by providing a sheet of a thermoplastic material, in which cavities are introduced by for example thermoforming. During the packaging process, these cavities are filled with the product, and covered with for example an adhesive sheet to close the segments comprising the individual cavities.

In order for the consumer to be able to retrieve an individual portion from the package, the segments comprising the portions need to be easily separable. To achieve this, the area where the segments are to be separated may for example an area that is able to snap; that is, an area where the sheet may be broken into the individual segments along a pre-defined path. Such pre-defined path may be introduced into the sheet by the provision of one or more grooves in the sheet, allowing the consumer to break the packaging along the grooves. Such grooves are also referred to as pre-cuts. In the context of the present invention, a segment may be understood as identifying an area of the sheet demarcated by the outer edge(s) of the sheet and one or more of the groove(s).

In order for the package to break along the grooves in a predictable way, the material in the area of the groove needs to be such that it snaps when the consumer bends the packaging along the groove. It is more preferred that snapping occurs on bending along the groove.

Snapping by twisting or tearing is not desirable as the package separation becomes difficult for the consumer. However, it is also desirable that the packaging is sufficiently rigid that it does not bend along the grooves under the influence of its own weight.

A further requirement is related to the transparent appearance of the packaging. It is particularly desired that the packaging is transparent in the area containing the product. One material that is particularly suitable for use in the production of such sheets is polyester. More particularly, such polyester may be a polyethylene terephthalate), even more particularly a polyethylene terephthalate) homopolymer.

Such polyester may be provided as a transparent sheet. For example, such transparent sheet may comprise an amorphous polyester. However, such transparent polyester sheets do not provide sufficient ability to snap.

Therefore, there is a desire to provide a sheet comprising polyester that is able to be snapped along a pre-defined path, whilst still providing such rigidity to avoid undesired bending under the influence of the weight of the package.

This has now been achieved according to the present invention by a 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 pm in the area (a).

The depth may be understood to be determined as the distance between the top surface on the sheet on the side comprising the groove and the deepest part of the groove.

The sheet according to the invention 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. In particular, the sheet provides the ability to snap along the grooves in a predictable manner whilst providing sufficient rigidity to avoid bending under the influence of its own weight where the sheet is used in a packaging comprising up to 8 individual segments, each segment containing up to 200 g of product. More particularly, the sheet provides the ability to snap along the grooves in a predictable manner, such as along a linear line, whilst providing sufficient rigidity to avoid bending under the influence of its own weight where the sheet is used in a packaging comprising up to 8 individual segments, each segment containing up to 150 g of product.

An indicator for the presence of sufficient rigidity may for example be determined as the degree of bending of a sheet when subjected to a certain weight positioned at one end where the sheet is clamped on the other end.

It is particularly desired that the groove(s) have a depth of 35-45 % with regard to the thickness of the sheet in the area (a). It is also particularly desirable that the polyester in area (a) has a degree of crystallinity of ≥ 10% and <50%. More particularly, the polyester in area (a) has a degree of crystallinity of 15- 30%. The degree of crystallinity may for example be determined based on the density according to the formula:

Pc (Ps ^— Pa )

Ps (Pc - Pa)

Wherein:

• Xc is the degree of crystallinity in %;

• pc is the density of the polyester in 100% crystalline form

• p₃ is the density of the sample in the location where the degree of crystallinity is to be determined; and

• p_a is the density of the polyester in fully amorphous form, i.e. 0% crystallinity.

For poly(ethylene terephthalate) homopolymers, the value for p_c is 1.455 g/cm³ and for p_a is 1 .333 g/cm³. The density of the sample may for example be determined in accordance with ISO 1 183-1 (2004).

The area (a) may be in the form of one or more strip(s). The strip(s) may be extending from one side of the sheet to another side of the sheet, thus dividing the sheet into segments divided by the strip(s). The strip(s) may be straight line or curved. The sheet may comprise a plurality of strips arranged such as to provide the sheet in a number of segments. The sheet may comprise a plurality of strips some of which are positioned perpendicular to each other, for example such as to form a grid.

It is preferred that the groove(s) are positioned in the same direction of and centrally in the strip(s). Preferably, the groove(s) are positioned to allow dividing the sheet into segments. Particularly preferably, the groove(s) are positioned to allow breaking the sheet along the groove(s).

The sheet according to the present invention may be subjected to thermoforming to form a cavities in the sheet that are suitable to be filled with for example dairy products. Preferably, a plurality of cavities are formed during the thermoforming step. The thermoforming of the sheet preferably takes place in the area that has a degree of crystallinity of < 5%. Preferably, the thermoforming takes place by thermoforming of one or more area(s) (b). Preferably, each segment comprises an area (b) where the polyester has a degree of crystallinity of < 5 %. Each segment may individually be selected to be subjected to thermoforming. The sheet may for example be prepared by subjecting a polyester sheet having a degree of crystallinity of < 5% to a treatment for increasing the crystallinity selectively to a degree of crystallinity of > 10% in selected areas of the sheet.

The sheet may be subjected to thermoforming prior to the treatment for increasing the crystallinity selectively. Alternatively, the sheet may be subjected to thermoforming after the treatment for increasing the crystallinity selectively.

In the case where the polyester is a poly(ethylene terephthalate), the thermoforming is preferably performed at a temperature above 78 C. Such temperature is required to ensure the polyester is able to deform as a result of softening of the material. The temperature of thermoforming of poly(ethylene terephthalate) is preferably < 100 C. Thermoforming at such temperatures prevents crystallisation to occur, particularly in area (b).

The treatment for increasing the degree of crystallinity selectively may for example be a thermal treatment or a treatment involving exposure to laser irradiation. Preferably, it is a local thermal treatment. For example, the treatment for increasing the degree of crystallinity selectively may for example be a thermal treatment performed at a temperature of 125— 240 C, preferably 140-200 C, more preferably 140-180 C, even more preferably 160-180 C. It is preferred that the temperature of the thermal treatment for increasing the crystallinity selectively is above the glass transition temperature of the polyester.

The treatment for increasing the degree of crystallinity selectively may be performed prior to the introduction of the groove(s) into the sheet. Alternatively, the treatment for increasing the degree of crystallinity selectively may be performed after the introduction of the groove(s) into the sheet.

The sheet, in the case where the polyester is a polyethylene terephthalate) may for example be subjected to the thermal treatment for a period of 40-100 s when the treatment temperature is 125-155 C; alternatively, the sheet, in the case where the polyester is a poly(ethylene terephthalate) may for example be subjected to the thermal treatment for a period of 25-50 s when the treatment temperature is 156-175 C; alternatively, the sheet, in the case where the polyester is a poly(ethylene terephthalate) may for example be subjected to the thermal treatment for a period of 15-50 s when the treatment temperature is >175 C.

The thermal treatment may for example be performed by contact heating or non-contact heating. For example, the thermal treatment may be performed using laser irradiation. It is preferred that 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%. The polyester according to the present invention may be a crystallisable polyester derived from at least one alcohol-based compound and at least one carboxylic acid-based compound.

The carboxylic acid-based compound may for example be a carboxylic acid or and ester- forming derivative thereof, such as an ester, especially an alky- or hydroalkyl-ester, or acid chloride. Preferably, the carboxylic acid-based compound is a dicarboxylic acid or the formula HOOC-R-COOH, wherein R is a linear group or a branched group, and wherein R is an alkylene group, an arylene group, an alkenylene group, or a combination thereof. Preferably, R comprises 2-30, more preferably 4-15 carbon atoms. Suitable examples of carboxylic acid- based compounds may include saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid, 3-cyclobutanedicarboxylic acid, 1 .3-cyclopentanedicarboxylic acid, 1 ,2-cyclohexanedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid, 1 ,4- cyclohexanedicarboxylic acid, 2.5-norbonanedicarboxylic acid, and dimeric acid; unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid and itaconic acid; and aromatic dicarboxylic acid such as orthophthalic acid, isophthalic acid, terephthalic acid, 5-(alkali metal)sulfoisophthalic acid, diphenic acid, 1 ,3-naphthalenedicarboxylic acid, 1 ,4- naphthalenedicarboxylic acid, 1 .5-napthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4.4^'-biphenyldicarboxylic acid, 4,4^'- biphenylsulfonedicarboxylic acid, 4,4 -biphenyl ether dicarboxylic acid, 1 ,2-bis(phenoxy)ethane- p.p^'-dicarboxylic acid, pamoic acid, and anthracenedicarboxylic acid. Other dicarboxylic acids and minor amounts of polycarboxylic acids may also be used as constituent components.

More preferable, the carboxylic acid-based compound is at least one compound selected from the group comprising terephthalic acid, isophthalic acid, succinic acid, adipic acid, glutaric acid, oxalic acid, and maleic acid. Most preferably, the carboxylic acid-based compound is terephthalic acid.

The alcohol-based compound may be a hydroxyl-functional compound. Preferably, the alcohol-based compound is a bifunctional alcohol, such as an alkylene glycol of the formula HO- R'-OH, a polyalkylene glycol having the formula HO-[R"-0]_n-H or combinations thereof, wherein R' is an alkylene group, linear or branched, comprising 2 to 10, preferably 2 to 4 carbon atoms, and wherein R", being the same or different, is an alkylene group comprising 1 to 10, preferably 1 to 5 carbon atoms.

Suitable examples of such alcohol-based compound include aliphatic glycols such as ethylene glycol, 1 ,2-propylene glycol, 1 .3-propylene glycol, diethylene glycol, triethylene glycol, 1 ,2-butylene glycol, 1.3-butylene glycol, 2,3-butylene glycol, 1 ,4-butylene glycol, 1 ,5- pentanediol, neopentyl glycol, 1 ,6-hexanediol, 1 ,2-cyclohexanediol, 1.3-cyclohexanediol, 1 ,4- cyclohexanediol, 1 .2-cyclohexanedimethanol, 1 .3-cyclohexanedimethanol, 1 ,4- cyclohexanedimethanol, 1 ,4-cyclohexanediethanol, 1 ,10-decamethylene glycol, 1 ,12- dodecanediol, polyethylene glycol, polytrimethylene glycol, and polytetramethylene glycol; and aromatic glycols such as hydroquinone, 4,4^'-dihydroxybisphenol, 1 .4-bis(p- hydroxyethoxy)benzene, 1 ,4-bis(hydroxyethoxyphenyl)sulfone, bis(p-hydroxyphenyl)methane, 1 .2-bis(p-hydroxyphenyl)ethane, bisphenol A, bisphenol C, 2,5-naphthalenediol, and glycols obtained by adding ethylene oxide to the glycols. Preferably, the alcohol-based compound is at least one compound selected from the group consisting of ethylene glycol, 1 ,3-propylene glycol, 1 ,4-butylene glycol, and 1 ,4-cyclohexanedimethanol. More preferably, the alcohol-based compound is ethylene glycol.

It is particularly preferred that the polyester is derived from ethylene glycol and

terephthalic acid. The polyester may for example be a poly(ethylene terephthalate).

The polyester may comprise up to 20.0 wt% of moieties derived from a comonomer.

Preferably, the polyester comprises up to 10.0 wt% of moieties derived from a comonomer. More preferably, the polyester comprises up to 5.0 wt% of moieties derived from a comonomer, such as 1 .0-5.0 wt%. Such comonomer may for example be one or more selected from isophthalic acid, 1.4-cyclohexanedimethanol, pentaerythritol, pyromellitic anhydride, or combinations thereof. Preferably, the comonomer is isophthalic acid. For example, the polyester may comprise 1.0-5.0 wt% of moieties derived from isophthalic acid. For example, the polyester may be derived from ethylene glycol and terephthalic acid, and may comprise 1.0-5.0 wt% of moieties derived from isophthalic acid, with regard to the total weight of the polyester. A suitable polyester preferably has a molar mass that results in a melt viscosity that allows easy and stable extrusion, and which results in a desired level of mechanical properties of the products. A typical indication of the molar mass is provided by the intrinsic viscosity of the polyester. The intrinsic viscosity may for example be determined in accordance with ASTM D2857-95 (2007). Suitable polyesters to be used in the production of the sheet according to the present invention have an intrinsic viscosity of 0.50 - 2.50 dl/g. A lower intrinsic viscosity allows for quick selective crystallisation; however if the intrinsic viscosity is too low, the sheet may sag during the heating before the thermoforming. It is preferred that the polyester has an intrinsic viscosity of 0.6 - 1.5 dl/g, more preferably 0.7 - 1.0 dl/g.

In a particular embodiment, the present invention relates to a sheet comprising polyester, the sheet comprising at least one area (a) where the polyester has a degree of crystallinity of 15-30%, 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); and wherein the polyester is poly(ethylene terephthalate) having an intrinsic viscosity of 0.7 - 1 .0 dl/g.

In a further particular embodiment, the present invention relates to a sheet comprising polyester, the sheet comprising at least one area (a) where the polyester has a degree of crystallinity of 15-30%, 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 pm in the area (a); wherein the polyester is poly(ethylene terephthalate) having an intrinsic viscosity of 0.7 - 1.0 dl/g; and wherein the area(s) forms a grid across the sheet allowing for the division of the sheet into several segments by snapping along the grooves.

In a preferred embodiment, where the sheet comprises multiple grooves, and where these grooves intersect, the sheet comprises an aperture in the area of each intersection. Such aperture may for example be a diamond-shaped or rhombus-shaped aperture. Such apertures allow detaching of a single segment by snapping on bending.

The present invention, in one of its embodiments, also relates to an arrangement comprising a sheet according to the invention comprising multiple cavities for containing foodstuff formed by thermoforming.

The invention further also relates to the use of such arrangement for production of a foodstuff packaging comprising multiple cavities that can be separated by breaking along the groove(s). The invention also relates to a packaging comprising such arrangement. Such packaging may for example be used to pack dairy products such as yoghurts, Alternatively, such packaging may be used to pack of other foodstuffs such as coffee or tea portions. Further use of the packaging of the invention to pack other sorts of foodstuffs is also envisioned. The packaging may also be used to pack medicines in the form of tablets or pills such that individual portions may be separated from the strip. The transparency of the thermoformed cavity is such application may have a further desirable effect in that the contents of the package can be more easily identified.

A further use of the packaging of the present invention is in packing electronic

components, such as batteries. In such application, the individual battery may be withheld from exposure to atmospheric conditions, which may be beneficial for the durability of the battery.

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

• (1 ) indicates the polyester sheet;

• (2) indicates the grooves;

• (3) indicates area (a) having a degree of crystallinity of > 10%;

• (4) indicates area (b) having a degree of crystallinity of≤ 5%; and

• (5) indicates a diamond-shapes aperture.

The present invention also in one of its embodiments relates to a process for the preparation of the snappable sheets, wherein the process comprises the steps in this order of:

a) providing a polyester sheet having a degree of crystallinity of < 5%;

b) introducing one or more groove(s) into the sheet in the area (a); and c) subjecting the sheet to a treatment inducing crystallisation in area (a).

The production of sheets according to such process allows for the introduction of the groove(s) with high degree of dimensional accuracy without chipping of polymer or sharp groove edges occurring, which may occur when the area (a) is subjected to crystallisation prior to introduction of the desired groove(s).

In a further embodiment, the invention provides for a process for forming an arrangement comprising cavities for containing foodstuff, the process comprising the steps in this order of:

a) providing a polyester sheet having a degree of crystallinity of < 5%, comprising one or more area(s) (a) and one or more area(s) (b);

b) introducing one or more groove(s) into the sheet in the area(s) (a);

c) subjecting the sheet to a treatment inducing crystallisation in area(s) (a); and d) introduction of one or more cavities in the area(s) (b) by thermoforming. The invention will now be illustrated by the following non-limiting examples.

Specimen preparation.

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 15 cm width, 800 pm thickness and a crystallinity of < 1 %. The obtained sheet was cut into rectangular specimen sheets of 10 cm by 15 cm. Introduction of grooves.

Grooves were introduced in the snapping area of certain of the specimens, i.e. in the middle of the specimen sheets, the grooves being introduced perpendicular to the long edges of the sheet. Selective crystallinity increase treatment.

The crystallinity in the snapping area of certain of the specimens was increased to > 10% by subjecting the specimens to a selective heat treatment in the snapping area, i.e. a strip of ca.

5 mm in the middle of the specimen sheets perpendicular to the long edges of the sheet.

Specimens containing a groove that were subjected to crystallinity increase in the snapping area, the strip that was subjected to crystallinity increase was positioned such as to have the groove positioned in the centre of the strip.

Determination of rigidity.

A specimen sheet prepared as described above was positioned in a clamp at one of the short sides. The other short side was subjected to a weight of 800 g. The degree of bending was determined. Determination of snapability.

A specimen sheet prepared as described above was positioned in a clamp at one of the short sides. The other short side was subjected to a weight of 2 kg. Examples.

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 desired for the packaging applications such as packaging of individual portions of dairy products.

Claims

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 pm in the area (a).

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

3. Sheet according to any one of claims 1 -2, wherein the groove(s) are positioned to allow dividing the sheet into segments.

4. Sheet according to any one of claims 1 -3, wherein the groove(s) are positioned to allow breaking the sheet along the groove(s).

5. Sheet according to any one of claims 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%.

6. Sheet according to claim 5, wherein the treatment for increasing the degree of crystallinity selectively is a thermal treatment or a treatment involving exposure to laser irradiation.

7. Sheet according to any one of claims 5-6, wherein the groove(s) are introduced prior to the treatment for increasing the crystallinity selectively.

8. Sheet according to any one of claims 5-6, wherein the grooves are introduced after the treatment for increasing the crystallinity selectively.

9. Sheet according to any one of claims 5-8, wherein each segment comprises an area (b) where the polyester has a degree of crystallinity of < 5 %.

10. Sheet according to claim 9 wherein the area (b) is subjected to thermoforming prior to the treatment for increasing the crystallinity selectively.

1 1. Sheet according to claim 9 wherein the area (b) is subjected to thermoforming subsequent to the treatment for increasing the crystallinity selectively.

12. Arrangement comprising a sheet according to any one of claims 10-1 1 comprising multiple cavities for containing foodstuff formed by thermoforming.

13. Use of the arrangement according to claim 12 for production of a foodstuff packaging comprising multiple cavities that can be separated by breaking along the groove(s).

14. Packaging comprising the arrangement according to claim 12.

15. Process for the preparation of the sheet according to any one of claims 1 -1 1 , wherein the process comprises the steps in this order of:

a) providing a polyester sheet;