LAMINATES

FIELD OF INVENTION

The present disclosure generally relates to the field of flexible packaging. More specifically, the present disclosure relates to a polyester-based mono-material heat sealable packaging film.

BACKGROUND OF THE INVENTION

BoPET is a polyester-based film made from stretching Polyethylene terephthalate (PET) in two directions. Such a film is preferred for flexible packaging due to its special properties such as high tensile strength, excellent heat resistance, chemical resistance, dimensional stability, transparency, barrier properties (low permeability), and excellent printability, and so on. The BoPET film can be made through melt extrusion and casting. It can be monolayer extrusion or multilayered extrusion. In the multilayered extrusion, more than two layers make the layers of polyester polymers which may be same or different. For example- ABB, BBA, ABC, CBA, and AAA are the different types of layer configuration where A, B, and C refer to layers of polyester polymers. Such layers can either be Polyethylene terephthallate polyester based or may be combined with co-polyesters of Polyetheylene terephthallate polyester. The skin layers A or C i may also contain anti-blocking agent such as silica to prevent blocking of the layers when wound in roll form.

Such a casted film undergoes biaxially stretching- sequentially or simultaneously. The sequential stretching involves two steps. The first step involves using a machine direction orienter (MDO) to stretch the material in the direction of the machine over a series of rollers, effectively increasing the length and decreasing the thickness of the web. In the second step, a transverse direction orienter (TDO) stretches the film or sheet perpendicular to the MDO in the transverse (cross) direction on a tenter, increasing the width of the web and further decreasing its thickness. Such steps are usually undertaken in-line one after the other following extrusion and casting of the web.

Sequential stretching is most often used in the production of material such as BOPS, BOPP, BOPET, BOPLA, and BOPTFE. The primary advantage of such a method is that it provides immense flexibility in process conditions (e.g. MD andTD stretch ratios) and a high production rate. It is also relatively cost effective. During simultaneous stretching, the web is restrained in the tenter clips and suspended in air while being stretched in both the machine and transverse directions at the same time. Such an orientation allows for improved optical and mechanical properties.

BoPET films having thickness in the range of 50 to 350 microns is suitable for various applications such as electronic displays, PV, and other electrical applications, while thin BoPET film (6-50 microns) is suitable for flexible packaging of a variety of materials such as food, non- food materials. Food materials are safe materials for human consumption such as medicines, fruits, vegetables, dry snacks, various processed food items, and so on. Non-food materials may include materials detrimental for human consumption, for example colors, dyes, articles, and so on.

Packaging is of utmost importance in the food processing, preservation, supply, and distribution chain. The primary function of any packaging system is to contain and protect the food material. There is an increasing demand for natural and “fresh-like” foods that are minimally processed with acceptable shelf life. Hence, the packaging film must bear necessary properties such as heat resistance, good thermal stability, good machinability, good printability, good transparency, good barrier to oxygen and water vapor, good impact resistance, good puncture resistance, good sealability and good seal integrity.

However, it is not possible to get all the properties from one type of film or polymer. Therefore, multilayer packaging is a common technique that amalgamates the unique functionalities of various polymers with the aim of developing a package with improved performance in terms of improved protection and durability. In most cases, it is impossible for a single monolayer of polymer to meet all requirements of food packaging, including containment (strength and sealability), protection/preservation (moisture, gas, light, flavor/ odor barrier), machinability (tensile strength, softening, slip, rigidity, pliability, and heat resistance), promotion, and convenience, while ensuring cost-effectiveness and adhering to all aspects of food safety. Thus, the rationale behind the manufacturing of multilayer packaging is to develop a packaging structure that possesses multiple functional properties in order to meet all the complex functional requirements of packaging. In general, the multilayer packages may consist of two to seven layers. Over the years, compared to conventional packaging materials such as metal, glass, and paper, the use of synthetic polymer- based packaging materials has found widespread applications in the food industry owing to merits in terms of affordability, versatility, functionality, and convenience to scale-up. Multilayer polymeric packages offer additional functionalities such as the combined advantage of functional and barrier properties of individual polymers and reduction in the total amount of material being used, while producing thinner, lighter, and compact packages.

Such multilayered laminate structures which include different layers of polymeric films such as BOPET, BOPP, Nylon, EVOH, BOPP, PE, CPP films, bond to each other with the help of adhesives. One or more of such films are included in the laminates because of their different unique and good properties. For example, CPP & PE provides excellent heat sealability, nylon provides good impact and puncture resistance. The BOPET film alone provides all the properties except good puncture resistance, good heat sealability, and good impact resistance. Hence, an ideal packaging film laminate is made by laminating different substrates or films to achieve all the desired properties. However, since all of the such materials, (such as PE film, Aluminum foil, Nylon, EVOH, Polyester film) are not compatible to each other due to their different solubility parameters or belonging to different polymer family, so it becomes nearly impossible to recycle and reuse all such kind of heterogeneous laminates. It is not economically feasible to separate and segregate each layer to recycle individually. There are methods for chemical recycling such as pyrolysis, however such a method does not yield economic benefits.

There have been some conventional arts which led to improvement in properties like puncture and impact resistances in BOPET films by incorporating co-polyesters and co-polyamides into the PET however such an improvement is insufficient to replace the Nylons/PE/CPP from the laminate.

Similarly, in order to improve heat scalability in BOPET- films, conventionally the copolymers of PET such as Polyethylene isophthalate are used. These are called Co-Polyesters. The Copolyesters are formed when modifications are made to polyesters, which are combinations of diacids and diols. For example, by introducing other diacids, such as isophthalic acid (IPA), or other diols, such as cyclohexane dimethanol (CHDM) to the polyester polyethylene terephthalate (PET), the material becomes a copolyester due to its comonomer content. The Copolyesters made by IPA and CHDM are generally amorphous in nature. They have a lower T _g as compared to PET and their molecules are randomly arranged because of their metamorphic structure. This leads to better heat scalability. Hence, some conventional arts pertain to improvement in heat sealable properties of BOPET films by incorporating amorphous copolyesters in the skin layer (A or C) in ABC or ABB, ABA type of layer configuration as shown in Figure 1 (Prior Art). However, the seal strength thereof is either very low or lack seal integrity, which is insufficient to replace PE or CPP from multilayer packaging structure.

Hence, all of the conventional techniques have one or more draw backs. Therefore, in light of the foregoing discussion, there exists an immediate need for providing alternatives for multilayer laminates, and develop a mono-material packaging film.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a monomaterial heat sealable polyester film is disclosed. The monomaterial heat sealable polyester film provides a sustainable alternative to multilayered laminates. The monomaterial polyester film includes a skin layer modified with amorphous co-polyester, and semi-crystalline elastomeric co-polyester. The amorphous, and semi-crystalline elastomeric co- polyesters have broad melting temperature range with a wide distribution of crystallites. The melting temperature is in the range of 80 deg C to 200 deg C. In this respect, before explaining at least one embodiment of the present invention in detail, it is to be understood that the invention is not limited to in its application to the details of processing and to the arrangements of the components set forth m the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the embodiment will be apparent from the following description when read with reference to the accompanying drawings. In the drawings, wherein like reference numerals denote corresponding parts throughout the several views:

Other objects, features, and advantages of the embodiment will be apparent from the following description when read with reference to the accompanying drawings. In the drawings, wherein like reference numerals denote corresponding parts throughout the several views:

Referring to Figure 1, illustrates an exemplary prior art of PET film;

Referring to Figure 2, shows a schematic view of a monomaterial heat- sealable BOPET film (100), in accordance with an illustrative embodiment of a present invention;

Referring to Figure 3, shows a graph depicting thermal characterization of alloy, in accordance with the illustrative embodiment of the present invention; and Refemng to Figure 4, shows a graph depicting measurement of sealing strength at different temperatures, in accordance with the illustrative embodiment of the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of way sin which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention as hereinbefore described with reference to the accompanying drawings.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

As used herein, the singular forms “a”, “an”, “the” include plural referents unless the context clearly dictates otherwise. Further, the terms “like”, “as such”, “for example”, “including” are meant to introduce examples which further clarify more general subject matter, and should be contemplated for the persons skilled in the art to understand the subject matter.

The reference in this specification to any prior art publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates.

The term “Flexible packaging” herein relates to any packaging or a part thereof whose shape can be changed readily. For example, bags, pouches, tubes, and so on.

The term “Polyethylene terephthalate (PET)” herein defines a form of polyester, which can be extruded, casted, and stretched bidirectional to form a thin film for packaging for the purposes of packaging foods, beverages, pharmaceutical products like tablets, and so on.

The term “Biaxially-oriented polyethylene terephthalate (BOPET)” herein defines a polyester film which is obtained by stretching the PET film in two perpendicular directions thereof, achieving the BOPET film. The film is well preferred for flexible packaging due to its special properties such as high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties (low gas permeability), and electrical insulation (good insulation performance), good deflection, good optical property, and so on.

For packaging purposes, the packaging film must bear properties of good heat resistance, low thermal shrinkage, good machinability, good printability, good transparency, good barrier to oxygen and water vapour, good impact resistance; good puncture resistance. The BOPET film is considered as the most preferred flexible film for packaging food and non-food products.

The term “Co-extruded” is a well-known term used in the industry of polymers and flexible packaging. The “co-extruded” or “coextrusion” defines a process of forming a single film through two or more extruders, from more than one type ofthermoplastic resin layers.

In flexible packing, the polyester films involve incorporation of other dissimilar polymeric layers such as Polyethylene or polypropylene having a good heat sealability to fulfil poor heat sealability characteristics of the original polyester films. Such dissimilar layers are generally called a laminate. Such a usage of multi-layered heterogeneous laminates may pose serious environmental concerns because such layers cannot be recycled in effective manner. The entire industry globally is looking forward to avoid usage of such multilayered heterogeneous laminates. Therefore, objective of the present invention is to develop a polyester film having all the basic properties of multilayered heterogeneous laminates such as excellent heat scalability, improved impact and puncture resistance without compromising on other intrinsic properties of polyester film, which can avoid usage of PE, PP foils etc. in the flexible packs. Such an objective not only will have a large positive impact on environment by eliminating the problem of recycling, but also additionally reduces the processing steps and cost significantly.

The present invention discloses a monomaterial heat sealable polyester film. The monomaterial heat sealable polyester film provides a sustainable alternative to conventional multilayered laminates in a wide variety of applications.

The “monomaterial heat sealable polyester film” is referred to as “monomaterial film” hereinafter.

Figure 2 shows a schematic view of a monomaterial BoPET film (100). The monomaterial film (100) has a skin layer (102) modified with co-polyester alloys. The co-polyester alloys contain amorphous and semi-crystalline elastomeric co-polyesters coextruded thereinto. The co-polyesters alloy improves the heat seal strength up to 3500 gf/in. The semi-crystalline elastomeric co- polyesters have broad crystallites melting temperature range with a wide distribution. The crystallites have melting temperature is in the range of 80 deg C to 200 deg C. The alloy contains amorphous co-polyester in the range of 20-40 wt%, while the semicrystalline elastomeric co-polyester may be the range of 40-80 wt%. The film (100) has haze of less than 10 in 23 -micron thick film. Thickness of the film can be in the range of 10 micro meters to 100 micro meters.

The amorphous co-polyesters tend to improve the sealability and also reduce the crystallinity of the film (100). Infact, such copolyesters adjust the crystalline content and the heat seal temperature, contributing to overall seal strength of the film in which they are introduced along with the other co- polyesters. The amorphous co-polyester is a random copolymer based on a mixture of 1,4/1, 3- aromatic dicarboxylic acids and ethylene glycol. The mixture has 1,4 and 1,3- aromatic dicarboxy lie acids in the range of 90/10 and 60/40. The semi-crystalline elastomeric copolyesters further include soft and hard blocks arranged randomly. The dicarboxylic acids may include such as but not limited to terephthalic/isophthalic acids, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid. In some aspects, the dicarboxylic acids may include atleast 5- 30% by weight of isophthalic acid component.

The diols may include such as but not limited to ethylene glycol/butane diol/propane diol/polyether polyol /cyclohexane dimethanol, 1,3-propylene glycol, 1 ,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1 ,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, and polycarbonate diol.

The semi-crystalline elastomeric copolyesters include soft and hard blocks in a random arrangement. Crystallinity decreases with increasing random character or by changing the symmetry packing ability, the soft block includes an aliphatic polyether and polyester and the hard segment includes a dicarboxylic acid component, and a diol component. The dicarboxylic acid other than terephthalic acid is isophthalic acid in 10-20% by weight and 10-20% by weight of butanediol as diol component and 2-20% polyether component as a soft component. In block copolymers, the soft segment provides flexibility which helps in increasing the puncture resistance and impact strength and hard segments provide the toughness. The semi-crystalline elastomeric polyester film has the degree of crystallinity in the range of 10%-30%.

As shown in Figure 2, the film (100) has a core layer (104) and a second skin layer (106). The core layer (104) may include 0-100% by weight of either Poly ethylene terephalate resin (PET) or Post- Consumer recycled (PCR) PET. The second skin layer (106) further may include PET with anti-block. The anti-block is configured to prevent blocking during formation of the film (100) as aforementioned hereinabove.

The second skin layer (106) is a non-sealing side of the film (100), which can be surface (108) treated for better printability, for better metal adhesion or for better barrier properties of the film (100). The surface (108) treatment can be corona treatment or the in-line coating with water based acrylic coatings, copolyester coating or polyurethane based coatings for ink or metal adhesion, and ALOX, PVOH, EVOH, PVDC or Organo-metallic hybrid coatings for better barrier properties. The mono-material co-polyesters may be introduced m either A- layer or C-layer where B is the core layer. In some embodiments, recycled PET (PCR PET) in the core layer (B layer) in the range of 0-100 wt%. This further reduces the carbon foot print of the environment by re-using the waste polyester resin.

In another embodiment, the present disclosure discloses a method for preparing the monomaterial heat sealable polyester film. The method involves co-extruding the amorphous co-polyester and semi-crystalline elastomeric co-polyester into the skin layer of the film.

Experimental data:

The random incorporation of co-monomers and concentration thereof in polyester chains reduces the formation of crystallites, decreases lamellae thickness and increases the amorphous phase. Such a change in morphology is expected to decrease the melting point as well as modulus.

Thus, various co-polyesters were made in combination of different co-monomers, and underwent thermal studies.

DSC is the most common thermal technique used to evaluate crystallinity level of polymers. Successive self -nucleation and annealing thermal analysis [SSA-DSC] have been used for thermal fractionation by crystallization after annealing at different temperatures. This technique allows segregation of molten and solid fractions during thermal cycling, promoting nucleation at different temperatures and growth of crystals during annealing. Out of several polyesters vital few were chosen based on the DSC scans and SSA analysis at varying temperature difference of 10 deg Celsius. The polyesters named as: Polymer-X, Polymer-Y and Polymer-Z and prepared as following:

1. Polymer-X: A Co-Polyester containing atleast 15 wt% of Isophthalic acid content along with anti-block agent to prevent blocking during film formation.

2. Polymer-Y : An Ester elastomer containing 10 wt% of isophthalic acid component, 20 wt% Butanediol component and 5% polyether component as the co-monomers. 3. Polymer Z: An Amorphous Copolyester made by 20 wt % of Isophthalic acid with anti-block agents such as SiO2.

Target Total film thickness = 23 micron

Experiment no 5 yielded the best results with the minimum haze and highest heat seal strength. Polymer Z also acted as a compatibilizer to PET and Ester Elastomer when it is wet blended. It forms homogeneous alloy and the resultant alloy showed broad sealing temperature.

On thermal characterization of Alloy, it showed a very broad melting range from 80 to 200 deg C as shown in Figure 3. The sealing strength was measured at different temperatures as shown in Figure 4 and data as tabulated as below:

Hence, the present invention provides a greener, sustainable, and recyclable monomaterial packaging film based on polyester. The present invention does not require additional poly ethyl ene/CPP and adhesives for heat sealing. The film achieves the sealing strength in the range of 1000 to 3500 g/inch.

The foregoing descriptions of exemplary embodiments of the present disclosure have been presented for purposes of illustration and description. They are notintended to be exhaustive or to limit the disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to best explain the principles of the disclosure and its practical application, to thereby enable others skilled in the art to best utilize the disclosure and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions, substitutions of equivalents are contemplated as circumstance may suggest or render expedient but is intended to cover the application or implementation without departing from the spirit or scope of the claims of the present disclosure.