FORM 2
THE PATENTS ACT-1970
(39 of 1970)
and
The Patent Rules, 2006
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1. TITLE OF THE INVENTION
A Biaxially-Oriented Transparent High Barrier PET Packaging Film and Manufacturing Method thereof
2. APPLICANT

a) Same SRF Ltd.
b) Nationality Indian
c) Address SRF Ltd.
Packaging Film Business
Sec-3, Pithampur
Madhya Pradesh
India
Email id-akshav.naravanfSisrf.com
Mobile no. - +917389944543
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a biaxially-oriented, transparent, high barrier PET packaging film. More particularly, it relates to a biaxially-oriented, transparent PET packaging film coated with PVOH and nanoclay solution, which forms an excellent barrier to oxygen, water vapour and aroma. Still more particularly, it relates to a biaxially-oriented, transparent high barrier PET packaging film coated with fully or partially hydrolyzed PVOH and nanoclay dispersion, and which does not release hazardous chlorine into the environment. The invention further relates to the method of manufacturing the said biaxially-oriented, transparent, chlorine-free, high barrier PET packaging film.
BACKGROUND OF THE INVENTION
The increasing pressures of modern fast-paced life style leave less time and inclination to prepare proper meals. This places a lot of importance on storage of food for longer times. To ensure long shelf lives of these packaged foods, packaging films with excellent barrier against moisture and atmospheric gases (mainly oxygen) were developed.
Several such packaging films have been discussed in the prior art. Biaxially-oriented polyteraphthalate (BOPET) films are commonly employed in flexible packaging of food products. Although BOPET films are known for their high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation, the use of BOPET in dry and wet food packaging application is fraught with challenges like high oxygen (gas) barrier, air and liquid sealability, flex resistance, pin-hole resistance, absence of harmful leaching chemicals etc., to ensure long shelf life and stability of the packaged food product.
One of the much practiced approaches to achieve the above goals has been the use of aluminium-metallized films. Prepared in high-vacuum by physical vapor deposition technique, these films commonly use evaporated aluminium, but silver, nickel and chromium may also be used. These metallized films demonstrate good

barrier properties (OTR - 0.5-1.5 cc/m2/day; WVTR - 0.5-1.5 gm/ m2/day) but are susceptible to pin-hole formations, which destroy the barrier, thereby unfavourably skewing the OTR and WVTR. Also, these films are not transparent, which may not be desirable for several food packaging purposes. Thus, their low flex resistance and lack of transparency make them inappropriate choices for see through packaging. Also, manufacturing costs are high for metallized films, as a secondary process needs to be established for vacuum evaporation and vapour deposition of the metal over the film. These challenges have been overcome by the present invention as it is transparent, has good flex resistance and excellent barrier properties, and is manufactured cost-effectively without the need of separate elaborate set-up.
Another commonly employed technique in the prior art is that of coating the packaging films with ceramic materials such as SiOx, A1Ox or MgOx. The patent documents US6194054 and US6376042 show examples of both metallized and ceramically coated films, while US6764752 discusses a metallized laminated biaxially oriented polypropylene film. The patent document US5674618 mentions even zinc oxide as the chosen coating material. Although this type of coating provides transparency and good barrier properties to the film, they suffer from low flex resistance, as pin-holes are formed easily on such films, thereby making them irregular and depleting their barrier properties.
The preferred material today for coating of a BOPET film in order to improve its barrier properties is polyvinylidene chloride or PVDC. Some of the patent documents mentioning PVDC coating over PET to enhance barrier protection are CN202923067, CN202412847 and CN102964937. PVDC coating provides high barrier against moisture and oxygen, while maintaining its transparency. However, PVDC coatings suffer from a major "disadvantage of chlorine being released into the environment while manufacturing from the film, and from the prepared packaging film, over time. This chlorine release can prove to be hazardous for both the environment and for human health. Also, PVDC coated films are sticky and are known to deteriorate or turn yellow with time. Such films

are expensive to manufacture and consume high amounts of energy, as PVDC needs to be cured at high temperatures. The present invention uses polyvinyl alcohol (PVOH) solution in combination with nanoclay dispersion and binding agent for coating, thereby addressing the issues of chlorine-leaching and yellowing.
The patent document US5506014 describes a copolyester made from terephthalic acid, naphthalene dicarboxylic acid and ethylene glycol. Although, this polyester gave good barrier properties, it used expensive raw materials. The present invention uses biaxially-oriented polyterephthalate (PET) instead of other high barrier providing materials like polyethylene naphthalate (PEN) or copolyesters, mainly because they are significantly more expensive than PET. Also, the present invention is more cost-effective as it involves offline coating of the PVOH solution.
To address the above mentioned concerns in the field of dry and wet food packaging, especially for see through packages, there was a need to develop a high barrier, cost-effective, chlorine-free packaging film which is transparent and has good flex crack resistance. The present invention eliminates all of the drawbacks of the currently used packaging films, and provides an economic and innovative solution to the problem of high-barrier food packaging.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a biaxially-oriented high barrier transparent PET packaging film used mainly for packaging dry ready-to-eat food products.
Another object of the present invention is to provide a biaxially-oriented high barrier transparent PET packaging film which is free from the problem of chlorine release into the environment.

Still another object of the present invention is to provide a biaxial ly-oriented high - barrier transparent PET packaging film which has excellent flex crack resistance, and does not form pin holes even after 100 gelbo flex.
Yet another object of the present invention is to provide a biaxially-oriented high barrier transparent PET packaging film having excellent abrasion resistance and scratch resistance.
Further object of the present invention is to provide a biaxially-oriented high barrier transparent PET packaging film which is excellent for printing and lamination and remains optical clear and thermally stable during and after the manufacturing process.
Still further object of the present invention is to provide a simple and cost-effective method for manufacturing a biaxially-oriented high barrier transparent PET packaging film.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a biaxially-oriented high barrier PET packaging film has been developed wherein the said film, when laminated with low-density polyethylene or LDPE (60 microns), demonstrates an OTR in the range of (0.26 to 1.08 cc/m2/day) and a WVTR in the range of (1.8 to 2.28 gm/m2/day). The laminated film is especially suited for-packaging food products and enhancing their shelf life. Examples of the food packaging applications include fresh meat, prepared dry ready-to-eat food, processed meat and cheese, confection and snacks, pet food, medicines, dairy products, fruits, vegetables and convenience food.
According to another aspect of the invention, the biaxially-oriented high barrier PET packaging film is coated with a solution of fully or partially hydrolyzed PVOH along with nanoclay dispersion. Into this solution, a cross-linking solution made of polyurethane or polyethyleneimine is mixed for improving its barrier

properties. The PVOH solution coating is advantageous to the present invention as while it ensures high oxygen and water vapour barrier, it does not contain chlorine and is free from the problem of chlorine release into the environment, which is commonly encountered with PVDC coatings"
In another aspect of the present invention, the biaxially-oriented high barrier transparent PET packaging film is composed of several layers. The main layer of PET resin is flanked on both sides by co-extruded PET layers. Primer is coated online over the coextruded layer 1 using online coating method, over which the PVOH solution is coated offline. Primer coating is done on BOPET film substrate to give enhanced adhesion between BOPET and PVOH material.
In still another aspect of the present invention, the manufacturing system o.f the biaxially-oriented high barrier transparent PET packaging film consists of a feeding section, extrusion system which is followed by a casting unit, machine direction orienter (MDO) to stretch the film in the direction of the machine, transverse direction orienter (TDO) to stretch the film transversely, take-up and transfer section (TUT) and a winder.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of processing and to the arrangements of the components set forth in 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 and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
STATEMENT OF THE INVENTION
Accordingly the present invention provides a high barrier biaxially-oriented PET packaging film which is coated with a solution of PVOH, nanoclay and a cross-

linker with polyurethane dispersion wherein the said film is suitable for packaging food products and for "enhancing their shelf lives. There is also'provided a method for manufacturing of the mentioned biaxially-oriented high barrier PET packaging film.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and/or other objects, features and advantages, of the invention will become more apparent from the following description of the preferred embodiment with reference to the accompanying drawings in which reference numerals designate the elements of the invention and wherein -
Fig. 1 shows the basic layer structure of the co-extruded BOPET film according to' one of the preferred embodiments of the present invention.
Fig. 2 shows the cross-section of the laminated structure of the developed PVOH-coated BOPET film according to one of the preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention describes a biaxially-oriented high barrier PET packaging film "which is produced by coating a PVOH and nanoclay solution for improving its barrier properties.
Referring to Fig. 1, the layer structure for the BOPET film is shown, wherein the main layer of BOPET film (1) which is 9-10 microns thick, is flanked on both sides by coextruded layer-1 (2) and co-extruded layer-2 (3), both having thickness of 1-1.5 microns. Together the three layers, main layer (1), co-extruded layer 1 (2) and co-extruded layer-2 (3) make the BOPET film substrate over which the

primer and PVOH are coated. The polyester resin used for the invention was synthesized in-house by using purified terephthalic acid (PTA) and monoethylene glycol (MEG). Polymerization of PTA and MEG was carried out through esterification and polycondensation reaction in the temperature range of 260 to 280 °C, in the presence of a catalyst.
The three layers of BOPET film substrate are manufactured using the PET resin, wherein each layer consists of varying concentrations of three different kinds of polyester resin, namely - bright PET, recycled PET and additive PET. Additive PET resin contains 0.4% wt% of silica additive which provide anti-blocking characteristics to the PET film. Additive PET resin is fed only in the coextruded layer 1 (2) and co-extruded layer 2 (3). Recycled PET resin is synthesized from recycling of in-house trimming waste of PET film, and is fed in optimized concentration in the main layer (1) of BOPET film. Bright PET resin is virgin PET resin, without any recycled or additive contents, and forms the major component of all the three layers of the BOPET film. In one of the preferred embodiments of the present invention, the concentrations of the three kinds of PET resins is in the ranges as mentioned in Table 1.
Table 1

Extrusion system Weight %
Main extrusion system
Bright PET resin 65-75
Recycled PET resin 25-35
Co-extrusion system 1
Bright PET resin 50-60
Additive PET resin 40-50
Co-extrusion system 2
Bright PET resin 50-60
Additive PET resin 40-50

Another type of BOPET substrate film may be employed for the present invention. This film is a heat-sealable BOPET film which uses a different resin — composition for the co-extruded layer-2 (3). This resin isxomposed of PTA, mono MEG and isophthalic acid. The heat-seal resin has a lower melting point (200 °C) than bright PET resin (253 °C) due to addition of isophthalic acid. It also exhibits higher intrinsic viscosity and lamination bond strength than bright PET resin, and displays unique heat-sealing properties.
The concentrations of the different PET resins in heat-sealable film are mentioned in table 2.
Table 2

Extrusion system Weight %
Main extrusion system
Bright PET resin 65-75
Recycled PET resin 25-35
Co-extrusion system 1
Bright PET resin 50-60
Additive PET resin 40-50
Co-extrusion system 2
Heat-seal resin 100
According to another preferred embodiment of the present invention, the manufacturing system for BOPET film comprises of a feeding section, an extrusion system followed by a casting unit, a machine direction orienter (MDO), an inline coater, transverse direction orienter (TDO), take-up and transfer section (TUT) and winder. The manufacturing process begins when PET resins (bright, recycled and additive) in the form of chips are fed to the main and co-extruders. The resin chips form a melt in the extruders and are transferred to a three-layered extrusion die, the output of which is a three-layered film. The middle layer or the main layer (1) is formed by the throughput of the main extruder while the throughput of the co-extruder forms the two coextruded layers. The purpose of the

additive PET resin (silica containing PET resin) is to provide haze to film as well as antiblocking characteristics to the film. The film coming out from the die falls in chill roll, which is maintained at 25-30 °C. The film coming out of the chill roll is called cast film. This cast film is stretched in two stage processes (two gaps) to provide excellent mechanical properties and thermal stability. In first stage, the cast film enters the MDO where the film is stretched in the machine direction (stretching being 3.2-3.5 times). The MDO rolls are heated using hot water which bring the film to its glass transition temperature so that it can be stretched. The heating temperature in MDO ranges from 78 to 96 °C. The film coming out of MDO is called mono film. Thereafter, the mono film is surface-treated via inline primer coating to improve the adhesion/anchorage between the PVOH coating and BOPET film substrate. The primer coating (4) is usually of 0.02-0.08 gm/cm2. The online primer coating (4) is advantageous to the present invention as it results in reducing a process step, thereby minimizing the energy consumption and minimizing the process time for film development which is critical for the industries. The reduction of one process step also reduces the process cost by 25 to 30%. Different types of primers may be coated on the BOPET film substrate in the present invention, like aqueous solutions of copolyester resins or polyurethane (PU) dispersions. Coating of primer on BOPET film substrate (4) results in excellent printability characteristics of the BOPET film, particularly to vinyl based inks, nitrocellulose based inks and polyurethane based inks. Also, these primers are suitable for solvent free as well as solvent based adhesives used in lamination process. The coated mono film is then sent to the transverse direction orienter (TDO) where it is stretched in transverse direction at the stretching ration of 4.0 to 4.3. The TDO has twelve zones wherein first three zones are preheating zones, followed by five stretching zones and a neutral zone. Machine speed during TDO is about 400 m/min. The temperature of the BOPET film ranges from 94 to 235 °C during the TDO process. After stretching zones, the BOPET film is subjected to three crystallizing zones followed by a neutral zone and a cooling . zone. The film at this stage is called the final film. The final film then passes on to take-up and transfer section (TUT), where it is trimmed from both sides and its

thickness is measured. Another optional step in the manufacturing process of the present invention is!corona treatment of the BOPET. film substrate, wherein the film surface is exposed to ozone produced by electric discharge of the electrodes. This optional corona treatment on other side provides excellent adhesion of various adhesive during further process of making laminates. The film is then passed on to the winder for winding on to steel rolls called core.
The BOPET film thus prepared is then coated with the fully or partially hydrolyzed PVOH solution which renders the film highly resistant against gas, aroma and moisture (water vapour). Referring to Fig. 1, the PVOH solution coating layer (5) is shown. The coating solution is preferably aqueous and is prepared by adding PVOH powder into cold water. The water-based PVOH solution is then heated in the temperature range of 80 to 100 °C in order to dissolve the PVOH. Ford cup viscosity of the PVOH solution is adjusted to 16-17 sees, and the total solid content of PVOH dispersion falls in the range of 3-12%, more preferably 5-10%, and most preferably 6-8%. Aqueous PVOH solution is cross-linked further by addition of cross-linking agents chosen from polyurethane dispersion and hexamethylenediisocynate (HDI), polyethylene amine), melamine, urea formaldehyde, modified polyethylenimine and glyoxal. The cross-linking . process may be catalyzed by sulphuric acid catalyst or aluminium chloride. The resulting solution is further agitated at a speed of 30 rpm, after which nanoclay suspension is mixed into the solution and agitated for 60 minutes at room temperature.
Various kinds of layered nanoclay and nanosilica dispersion may be employed for the present invention to provide high oxygen and water vapour barrier to the BOPET film including phyllosilicates, e.g. montmorillonite, particularly sodium montmorillonite, magnesium montmorillonite, and/or calcium montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite, sobockite, stevensite, svinfordite, vermiculite, magadiite, kenyaite, talc, mica, kaolinite, and mixtures thereof. Other useful layered materials may be the layered double hydroxide clays or hydrotalcites, such as Mg6Al34(OH)188(C03)1.7H2O, which

have positively charged layers and exchangeable anions in the interlayer spaces. Organically.modified nanoclays by primary, secondary and tertiary "ammonium cations may also be used for the present invention. Preferred layered materials may be swellable so that other agents, usually organic tons or molecules, can intercalate and/or exfoliate the layered material resulting in a desirable dispersion of the inorganic phase. These swellable layered materials include phyllosilicates of the 2:1 type. For this invention, the clay particles should have a lateral dimension of from 1.0 μm to 8 urn, and preferably from 2 μm to 6 μm, and more preferably from 3 μm to 5 μm. The thickness or the vertical dimension of the clay particles can preferably vary from 0.5 nm to 10 nm, and more preferably from 1 nm to 5nm. This dimensional disparity results in large aspect ratio which is a property conducive to barrier enhancement based on the principle of tortuous path migration.
The above mentioned high barrier PVOH and nanoclay coating (5) is done using offline reverse gravure coating process. This coating method relies on an engraved roller running in a coating bath, which fills the engraved dots or lines of the roller with the coating material. The excess coating on the roller is wiped off by the doctor blade and the coating is then deposited onto the substrate as it passes between.the engraved roller and a pressure roller. In this method, the BOPET film is first loaded onto an unwinder where it travels through various path rollers, bow rollers, gravure rollers and nip rollers. The resulting PVOH solution coating (5) is of 0.3-0.5 gsm. The offline coating process parameters are listed in the Table 3 below.
Table 3

Process parameter Value
Oven temperature 130-140 °C
Gravure roll chiller temperature 10-20 °C
Machine speed 40 meters/min
Cooling temperature 22 °C

Gravure type (mesh size) 120, 150,225
Coating type Forward coating
The distinct advantages of this offline PVOH coating system are -
1) It ensures uniform coating thickness
2) Coating at low speed is possible with high solution pick-up capacity
3) Gravure roll is available in various cell sizes and types, for example helical, pyramidal, quadrangular and hexagonal. For the present invention, the hexagonal cell is preferred for its optimal results.
The developed high barrier transparent BOPET film after PVOH solution offline coating are printed with various ink and laminated with polyolefin films and subjected to pouch making for end use food packaging applications. Referring to Fig. 2, the cross-section of the laminated PVOH and nanoclay coated high barrier transparent BOPET film is shown. The developed BOPET layer comprising of main layer (1), co-extruded layer 1 (2), co-extruded layer 2 (3), chemical/primer treated layer (4). The high barrier coating (5) of PVOH and nanoclay solution can be seen above the BOPET layer in Fig. 2. Before lamination, reverse printing on high barrier BOPET film is done using vinyl ester ink in four different colours. The thin layer of printing (6) is followed by a layer of PU based or acrylic based high bond strength adhesive (7). The printed films are further laminated with low density polyethylene films (LDPE) of 50-60 micron thickness. The transparent lamination (8) is also illustrated in Fig. 2.
Several characterization techniques were employed to validate the quality of the high barrier BOPET packaging film. Some of the properties characterized are elaborated below.
• Barrier properties
Oxygen transmission rate (OTR) of PVOH coated BOPET film was evaluated according to ASTM D3985 method by using MOCON OX-TRAN 2/21 at the test condition of 23 °C and 0% relative humidity (RH).

Water vapour transmission rate (WVTR) was evaluated according to ASTM F372 method by using MOCON PERMATRAN-W 3/33" at the test condition of 37 °C and 90% RH. • Coating thickness
Coating thickness is measured in gm/m2or gsm. In order to determine the coating thickness, samples were cut in the size of 100 mm xlOO mm template and their weight was measured using weighing balance having accuracy of 0.001 gms. Thereafter, the coating of the film was removed by using ethyl acetate and the sample was weighed again. The difference in the weight of the sample was used to measure coating thickness using the following equation -

• Tensile properties
The tensile properties namely tensile strength, tensile modulus and % elongation of the PVOH coated film was measured by using Tinius Olsen tensile tester machine according to ASTM D882 method.
• Ink-tape test
Ink test was used to analyze the printability of the PVOH coated film with ' . • . various types of printing ink. 3M scotch tape test method was used for this study. A film sample of 30 cm X 30 cm was cut from the PVOH coated BOPET film. Vinyl based ink was drawn down on the coated side with the help of a bar coater and dried. The scotch tape was used to check for transferability on the coated side. If there is no ink transfer from the film to the tape, the film is considered to pass the ink test.
• Boiling water ink-tape test
The ink-test as described above was conducted again after immersing the film in boiling water for 10 minutes. If there is no ink transfer from the film to the tape, the film is considered to pass the ink test.

• Haze and transmittance
Haze (%) and transmittance (%) of the PVOH coated BOPET film was • measured - by the use of a hazemeter or a by a spectrophotometer, according to ASTM D1003 method.
• Thermal stability (heat shrinkage) of the film
Thermal shrinkage of the PVOH coated BOPET film was measured according to ASTM D2838 test method, wherein samples were cut in the required sizes (254 mm X 254 mm) from different areas of the film. Initial dimensions were measured and marked as machine direction (MD) and transverse direction (TD) on the film sample, which was then placed in an oven at 150 °C for 30 minutes. The sample was taken out after the prescribed time and allowed to cool at room temperature. The final dimensions of the sample are measured again to check for shrinkage due to the heat.
• Laminate bond strength
Laminate bond strength of the laminated high barrier transparent BOPET film was measured by using Tinius Olsen machine according to ASTM F904.
• Gelbo flexing
The flex resistance or flex durability of a plastic film is a measure of its toughness, specifically its resistance to pin-holing when subjected to flexing abuse. A cylinder of the film is repeatedly flexed under specified conditions using a Gelbo flex tester and the sample inspected for pinholes after a set number of full or partial flex cycles according to ASTM F392. Alternatively, in the case of barrier films, the oxygen or water vapour transmission rates can be tested after flexing. A breakdown in the metallization, oxide coating or foil layer will often compromise the barrier performance of a plastic film laminate long before a pinhole through the structure is seen.

EXAMPLES
The following examples illustrate the improved properties associated with the coating solution of the present invention. All of the examples use BOPET substrates for coating with PVOH solutions, the composition of which varies.
Example 1
The BOPET substrate film was coated with a solution containing 5.71% w/v polyvinyl alcohol (PVOH), 0.93% w/v polyurethane cross-linking solution, 0.39% w/v montmorillonite nanoclay and 37.18% v/v IPA in DM water. The BOPET substrate in this trial was corona surface treated to ensure good adhesion of the coating film. The resulting film when tested for barrier properties, exhibited an OTR of 0.72 cc/m2/day and a WVTR of 13.3 gm/m2/day. The coating thickness was 0.29 g/cm2 and the surface energy value was 66 dyne/cm on the coated side. While testing the optical properties of the film, a haze value of 3.5% was obtained. It also passed the ink-tape test and partially passed the boiling water test. Thereafter, this trial film was printed with vinyl based ink and further laminated with low density polyethylene (LDPE of 60 micron thickness with adhesive). Prepared laminate was tested for barrier properties. The OTR was found to be 0.69 cc/m2/day. The laminate enhanced the moisture resistance properties of the film by significantly reducing the WVTR to .-- 2.3 gm/m /day. The laminate bond strength was found to be 100-145 gm/25mm.
Example 2
This trial involved coating an acrylic primer coated BOPET substrate with a coating solution containing 5.71% w/v polyvinyl alcohol (PVOH), _ 0.93% w/v polyurethane cross-linking solution, 0.39% w/v montmorillonite nanoclay and 37.18% v/v IPA in DM water. The resulting

film showed good barrier characteristics by giving OTR of 0.6 cc/m2/day
and WVTR of 14.2 gm/m2/day. It also passed the ink-tape test but failed
the boiling water test. When tested for optical properties, the haze value obtained for this film was 3.6%.The coating thickness for this film was found to be 0.27 gm/cm2, and the surface energy on the coated side is 54 dyne/cm.
Example 3
In this trial, the BO PET substrate was coated using a terephthalic acid based water-soluble co-polyester primer, which also comprises of MEG, isophthalic acid and other aliphatic dicarboxylic acids containing sulpho groups. This primer coated substrate was then coated with a solution containing 5.71% w/v polyvinyl alcohol (PVOH), 0.93% w/v polyurethane cross-linking solution, 0.39% w/v montmorillonite nanoclay and 37.18% v/v IPA in DM water. The trial showed an OTR of 0.82 cc/m2/day and a WVTR of 17.6 gm/m2/day. It passed the ink-tape test but failed the boiling water test. The film showed a haze value of 5.2% and the surface energy on the coated side was 56 dyne/cm. The thickness of the coating was 0.3 gm/cm2.
Example 4
For this example, a BOPET substrate coated with a co-polyester primer was used. This water-soluble co-polyester was based on terephthalic acid . and contained MEG and other diols containing ammonia group. Over this substrate, was applied a coating solution containing 5.71% w/v polyvinyl alcohol (PVOH), 0.93% w/v polyurethane cross-linking solution, 0.39% w/v montmorillonite nanoclay and 37.18% v/v IPA in DM water. This film when tested for barrier properties exhibited OTR of 0.41 cc/m2/day and WVTR of 11.4 gm/m2/day. This film passed the ink-tape test and partially, passed the boiling water test. The coating thickness of the film was 0.28 gm/cm2 and the surface energy on the coated side was 66

dyne/cm. Haze value for this film was found to be 4.8%. The film resulting from this trial was then printed with vinyl based ink and also laminated using LDPE (60 microns). The laminate showed bond strength of 200-235. gm/25 mm signifying good adhesion of printing ink and BOPET film; The lamination by LDPE also enhanced the moisture barrier properties by significantly reducing the WVTR to 2.1 gm/m2/day.
Example 5
The BOPET substrate for this trial was coated with a polyurethane based primer, and coated with a solution containing 5.71% w/v polyvinyl alcohol (PVOH), 0.93% w/v polyurethane cross-linking solution, 0.39% w/v montmorillonite nanoclay and 37.18% v/v IPA in DM water. The film thus prepared exhibited OTR of 0.38 cc/m2/day and WVTR of 8.3 gm/m2/day. It also passed the ink-tape test and the boiling water test. The coating thickness was found to be 0.33 gm/cm2 and haze value was 4.2%. The surface energy on the coated side was 66 dyne/cm. This film was further laminated using LDPE (60 microns) after printing with vinyl based ink. This laminated film displayed excellent bond strength of 360-380 gm/25 mm. It also passed the boiling water test, as there was no ink transferred on to the polyethylene side from PET side. The main advantage of this laminate was to bring down the WVTR value to 1.8 gm/m2/day. This laminated film was also tested for Gelbo flex cracking, and it was observed (asmentioned in Table 6) that even at a flex of 100 Gelbo, the OTR and WVTR did not change significantly.
Example 6
For this trial, the heat-sealable PET film was used as the substrate. It was then coated using the solution containing 5.71% w/v polyvinyl alcohol (PVOH), 0.93% w/v polyurethane cross-linking solution, 0.39% w/v montmorillonite nanoclay and 37.18% v/v IPA in DM water. The resulting

film gave OTR of 0.58 cc/m2/day and WVTR of 10.6 gm/m2/day. The haze, value obtained for the film was 6.1% and surface energy on the PET side was 66 dyne/cm. Coating thickness was found to be 0.31 gm/cm2.
Example 7
The coating composition for this example was different from the earlier trials, as it employed polyethyleneimine as cross-linking agent instead of polyurethane. On a corona surface treated BOPET film, was applied a coating solution containing 5.71% w/v PVOH, 0.39 % w/v montmorillonite nanoclay, 0.32% w/v polyethyleneimine cross-linking solution and 37.18% v/v IPA in DM water. On testing, the film revealed OTR of 0.5 cc/m2/day and WVTR of 17.2 gm/m2/day. The coating thickness was found to 0.28 gm/cm2 and haze value was calculated as 4.5%. This film passed the ink-tape test but failed the boiling water test. The surface energy on the coated side for this film was 66 dyne/cm. This film was printed with vinyl based ink, over which lamination with LDPE (60 microns) was carried out. This laminate gave bond strength of 120-160 gm/25mm. After lamination, the WVTR of the film came down to 2.28 gm/m2/day.
Example 8
For this trial, the BOPET substrate was coated with an acrylic based
polymer. The substrate was then coated..with absolution containing 5.71%.
w/v PVOH, 0.39 % w/v montmorillonite nanoclay, 0.32% w/v polyethyleneimine cross-linking solution and 37.18% v/v IPA in DIV1 . -water. The barrier property tests on this coated film revealed OTR of 0.5 cc/m2/day and WVTR of 12.2 gm/m2/day, while the optical property test gave haze value of 4.2%.The coating thickness was found to be 0.27 gm/cm2 and the surface energy on the coated side was 66 dyne/cm. ..

Example 9
In this example, the BOPET substrate .was coated using a terephthalic acid based water-soluble co-polyester primer, which also comprises of MEG, isophthalic acid and other aliphatic dicarboxylic acids containing sulpho groups with a copolyester based primer, and the resulting substrate was further coated with a solution containing 5.71% w/v PVOH, 0.39 % w/v montmorillonite nanoclay, 0.32% w/v polyethyleneimine cross-linking solution and 37.18% v/v IPA in DM water. This film when tested for barrier properties showed OTR of 0.8 cc/m2/day and WVTR of 14.5 gm/m2/day. This film partially passed the ink-tape test but failed the boiling water test. Optical property evaluation showed haze value of 4.4%. The coating thickness was 0.32 gm/cm2 and the surface energy on the coated side was 66 dyne/cm.
Example 10
Copolyester based primer coating was done on a BOPET substrate to ensure better adhesion properties. This water-soluble co-polyester was based on terephthalic acid and contained MEG and other diols containing ammonia group. This primer coated film was then coated with a solution containing 5.71% w/v PVOH, 0.39 % w/v montmorillonite nanoclay, 0.32% w/v polyethyleneimine cross-linking solution and 37.18% v/v IPA in DM water. The film was then tested for its barrier properties and optical properties. It showed an OTR value ofJ3.47„cc/m2/day„and a.WVXR value of 9.6 gm/m7day. This film passes both the ink-tape test and the boiling water test. Haze value was found to be 3.6%. The coating thickness was 0.27 gm/cm2 and surface energy value on the coated side was 66 dyne/cm. This film was printed with vinyl based ink and laminated with LDPE (60 microns). Bond strength of the laminate was found to be 180-190 gm/25 mm. The. lamination caused a great reduction in.the WVTR value of the film (1.92,gm/m2/day) and improved its moisture barrier This laminated film was also tested for Gelbo flex cracking, and it was observed (as

mentioned in Table 6) that even at a flex of 100 Gelbo, the OTR and WVTR did not change significantly.
Example 11
In this trial, the BOPET substrate was coated with polyurethane based primer. This substrate was coated with a solution containing 5.71% w/v PVOH, 0.39 % w/v montmorillonite nanoclay, 0.32%- w/v polyethyleneimine cross-linking solution and 37.18% v/v IPA in DM water. The resulting film showed OTR of 0.32 cc/m2/day and WVTR of 7.1. It passed both the ink-test and the boiling water test. The haze value was calculated to be 3.97%. The coating thickness for this film was 0.33 gm/cm2 and the surface energy on the coated side was 66 dyne/cm. This film was further printed with vinyl based ink and laminated using LDPE (60 microns). The bond strength of this laminate was in the range of 250-260 gm/25mm. The laminate passed the boiling water test and brought down the WVTR value to 1.92, thereby further enhancing the moisture barrier. This laminated film was also tested for Gelbo flex cracking, and it was observed (as mentioned in Table 6) that even at a flex of 100 Gelbo, the OTR and WVTR did not change significantly.
Example 12
This trial was conducted on a heat-sealable PET substrate. This substrate was coated using the solution containing 5.71% w/v PV.OH, 0.39 % w/v montmorillonite nanoclay, 0.32% w/v polyethyleneimine cross-linking solution:and-37.18% v/v IPA in DM.water. This film demonstrated OTR-. of 0.62 cc/m2/day and WVTR of 11.4 gm/m2/day. When tested for optical properties, it gave a haze value of 5.2%. This film partially passed the ink-tape test but failed the boiling water test. The coating thickness was 0.28 gm/cm and the surface energy on the coated side was 66 dyne/cm. ,.
The properties for all the above trials are listed in Table 4 below.

Table 4

S.No OTR
(cc/m2/day ) WVTR
(gm/m2/ day) Coating
thickness
(gm/m2) Haze
(%) "Surface energy (dyne/cm) Ink test boil water test (at 90 °C for 10 min)
Example 1 0.72 13.3 0.29 3.5 66 Pass Partial pass
Example 2 0.6 14.2 0.27 3.6 54 Partial pass Fail
Example 3 0.82 17.6 0.3 5.2 56 Pass Fail
Example 4 0.41 11.4 0.28 4.8 66 Pass Partial pass
Example 5 0.38 8.3 0.33 4.2 66 Pass Pass
Example 6 0.58 10.6 0.31 6.1 66 Fail Fail
Example 7 0.5 17.2 0.28 4.5 66 . Pass Fail
Example 8 0.5 12.2 0.27 4.2 66 Fail Fail
Example 9 0.8 14.5 0.32 4.4 66 Partial
pass Fail
Example 10 0.47 9.6 0.27 3.6 66 Pass Pass
Example 11 0.32 7.1 0.33 3.97 66 Pass Pass
Example 12 0.62 11.4 0.28 5.2 66 Partial pass Fail
Amongst the above 12 examples, lamination was done for 6, namely Example No. 1, 4, 5, 7, 10, 11. The barrier properties, bond strength and capacity of retaining printed ink was checked for these 6 examples, the results of which are given in Table 5.
Table 5

Example no OTR
(cc/m2/day) WVTR
(gm/m2/day) Average Laminate Bond strength (gm/25 mm) Boiling water
test at 90 °C for 10 min
Plain Laminate Plain Laminate

1 0.72 0.69 13.3 2.3 100-145 Fail
4 1.2 1.08 16.2 2.1 220-235 Fail
5 0.38 0.36 8.3 1.8 360-380 Pass
7 0.5 0.47 17.2 2.28 120-160 Fail
10 0.47 0.48 9.6 1.78 180-190 Fail
11 : 0.32 0.26 7.1 1.92 250-260 pass

Gelbo Flex cracking test was conducted for 3 of the above examples - Example 5, Example 10 and Example 11. As is clear from Table.6, the. barrier properties (OTR and WVTR) remained unaffected even after flexing 100 times.
Table 6

Properties Gelbo
flexing
(number) Example
5 Example 10 Example 11
OTR(cc/m2/day) 0 0.3 0.47 0.26

20 0.33 0.47 0.27

50 0.33 0.48 0.28

100 0.35 0.48 0.28
WVTR
(gm/m2/day) 0 1.2 1.8 1.6

20 1.5 1.8 1.6

50 1.6 2.0 1.7

100 1.6 2.2 1.7
Advantages of the present invention
The present invention serves to solve several of the problems of the prior art. Some of the mentionable advantages of the present invention are -
• The PVOH and nanoclay coated BOPET film demonstrates excellent
barrier properties against oxygen, water vapour and aroma, resulting in extended shelf-lives for the packaged food.
• The PVOH and nanoclay coated BOPET film ensures similar or superior
barrier properties in comparison to metallized films, and also allows see-
through packaging owing to its transparency, which is not possible with
the metallized films.
• The present invention overcomes the drawback of easy pin-hole formation
as-seen in metal oxide coated films, which leads to.an increase in the OTR
and WVTR values. This film possesses excellent flex resistance, abrasion and scratch resistance, and does not form pin-holes even at 100 gelbo flex.
• The present invention can be used in microwave ovens, and remains stable
even when the packaged food is subjected to pasteurization.

• The present invention is a welcome alternative to PVDC coatings which have high chlorine content which leaches out into the packaged food with time, resulting in hazardous consequences for the consumer's health. The PVOH coating used in the present invention is chlorine-free, while offering similar or superior barrier properties when compared to PVDC coatings.
• The present invention is excellent for further processes like printing and lamination, and is suitable for high graphic printing as well.

CLAIMS We ctaim,
1) A transparent high-barrier biaxially-oriented PET film structure produced by a
process comprising,
coating the biaxially-oriented PET film substrate online with a primer, followed by coating at least one side of the said substrates with a solution of polyvinyl alcohol (PVOH)containing a nanoclay and a cross-linking agent.
2) The transparent high-barrier biaxially-oriented PET film structure as mentioned
in Claim 1, wherein the said primer is coated online, and is preferably selected from polyurethane, polyethyleneimine and terephthalic acid based water-soluble
co-polyesters.
3) The transparent high-barrier biaxially-oriented PET film structure according to Claim 1, wherein the said nanoclayparticles have lateral dimensionsfrom 1.0 urn to 8 μm, preferably from 2μm to 6μm, and more preferably from 3 μm to 5 μm, and the thickness or the vertical dimension of the clay particles is in the range of 0.5 nm to 10 nm, and more preferably in the range of 1 nm to 5nm.
4) The transparent high-barrier biaxially-oriented PET film structure according to Claim 1, wherein the said cross-linking agent may be selected from, but is not restricted to hexamethylenediisocynate (HDI), epomine, glyoxal, polyurethane (PU) dispersion, polyethylenimine resin dispersion and polyethylene amine.
5) The transparent high-barrier biaxially-oriented PET film structure according to Claim 1 wherein the said coated film is laminated with low density polyethylene films having thickness of 35-100 microns, using high bond strength adhesives.

6) The transparent high-barrier biaxially-oriented PET film structure according to
Claim 1 wherein the bond strength of the laminate is in the range of 220-380
gm/25 mm.
7) The transparent high-barrier biaxially-oriented PET film structure according to Claim 1, wherein the oxygen transmission rate (OTR) of the said coated film after lamination is in the range of 0.26 to 1.08 cc/m2/day.
8) The transparent high-barrier biaxially-oriented PET film structure according to Claim 1 wherein the water vapour transmission rate (WVTR) of the said coated film after lamination is in the range of 1.8 to 2.28gm/m2/day.
9) The transparent high-barrier biaxially-oriented PET film structure according to Claim 1 wherein the said coated film demonstrates high flex crack resistance, i.e. at gelbo flex upto 100, the OTR values were in the range of 0.2 to 0.5 cc/m2/day and WVTR values were in the range of 1.2 to 2.2 gm/m2/day