, Description:FIELD OF THE INVENTION:
The present invention relates to water vapour barrier coating compositions, and packaging laminates containing polyester substrate layers, the polyester substrate layers are coated with water vapour barrier coating compositions. The water vapour barrier coating compositions of the present invention impart excellent water vapour barrier properties to the polyester substrates they are coated onto.

BACKGROUND OF THE INVENTION:
Barrier to moisture or water vapour is generally required for packaging goods such as food, confectionary, pharmaceutical and cosmetic products that are sensitive to atmospheric vapour or moisture, and where water vapour or moisture admission into the packaging articles can degrade the quality and properties of the substance within the packaging article. The currently existing technologies provide numerous solutions to impart water vapour barrier properties to the packages; however, there are limitations to the currently existing technologies, including insufficient barrier performance, and inadequate protection from varying environmental factors as high temperature and high humidity conditions, and high cost.

In the absence of a suitable water vapour barrier layer, it necessitates the industry to use four layer laminates to control the water vapour transmission rate (WVTR) through the packaging laminate layers. Conventional four-layer laminate structures are based on biaxially-oriented polypropylene (BOPP) / /polyethylene extrusion layer/ metallized polyethylene terephthalate (MET PET) /POLYETHYLENE (PE). This substantially increases the cost of production, and yet not effectively controls the WVTR.

Various water vapour barrier coatings have been developed using polymer compositions to form a water vapour barrier layer on a substrate used in packaging. The use of polyurethanes for barrier applications has been around in the last 15 years with various companies such as Mitsubishi, Mitsui, and PPG reported to have developed polyurethanes to be used as barrier coatings. However, these systems, for example WPB 341 from Mitsui fails to exhibit good water vapour barrier properties under high humidity conditions in packaging laminate structures. In order to achieve good water vapour barrier properties using polyurethane resin coatings, several efforts have been made including addition of inorganic filler in the coating composition, treating the surface of the base film with a metal oxide layer, or using a metallised film.

Chinese patent application 107699068 discloses a water vapour barrier aqueous based coating composition that includes any combination of polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinylidene chloride, polyether polyol, polyethylene glycol, polyamide or polyether polyurethane, where the water vapour transmission rate of up to 1.6 g / m2.day.

PCT patent application 2016/007157 discloses an adhesive composition that includes polyurethane polyisobutylene hybrid polymer comprising residual isocyanate moieties to impart a water vapour transmission rate at 37 .8°C and 100%RH: 1 .4 g/ (100 inch2.day), which is equivalent to 2.1 g/m2.day.

PCT patent application 2016/038350 discloses a laminated structure for use in barrier packaging comprising a first layer providing oxygen barrier properties and a second layer providing moisture barrier properties, where the second layer has a water vapour transmission rate of 10 g/m2/day.

However none of these are able to impart effective water vapour barrier properties to the packaging laminates used for packaging food, confectionery, pharmaceutical and cosmetic products. Also they are not able to reduce the cost of packaging.

Hence, there is a need to prepare a three layer laminate structure which reduces the cost of production of the laminate packaging materials, and the water vapour barrier coating of the present invention applied onto the three layer laminate.

OBJECTS OF THE INVENTION:
The principal objective of the present invention is to provide organic solvent based water vapour barrier coating compositions applied to the surface of a polyester substrate layer in a packaging laminate to impart excellent barrier to moisture or water vapour.

Another objective of the present invention is to provide a three layer packaging article with the top of the three layers being a polyester substrate layer, and a middle metallized polyester layer, where improved organic solvent based water vapour barrier coating compositions applied to the surface of a polyester substrate layer in the three layer laminate. The packaging articles that use the coated three layer laminate structure of the present invention are for packaging food, confectionary, pharmaceutical and cosmetic products, where water vapour or moisture admission into the packaging articles can substantially impair the quality and properties of the substance within the packaging article.

A further objective of the present invention is to provide organic solvent based water vapour barrier coating compositions applied to the surface of a polyester substrate layer in a three layer packaging laminate, which reduces the cost of production by reducing one sheet layer from conventionally used four layer packaging laminates, and applying a vapour barrier coating layer to the three layer laminate structure for improved vapour barrier performance.

Other objectives, features and advantages will become apparent to those skilled in the art from the detailed description and the appended claims.

SUMMARY OF THE INVENTION:
The present invention relates to water vapour barrier coating compositions applied to a polyester substrate layer in a three layer laminate structure used for packaging food, confectionery, pharmaceutical and cosmetic products.

In one embodiment, the present invention provides polyester substrate layers in a three layer packaging laminate comprising the water vapour barrier coating composition of the present invention.

In another embodiment, the present invention provides an article, such as a packaging article, where the water vapour barrier coatings of the present invention impart improved (reduced) water vapour transmission rate (WVTR) to the polyester substrate layers.

In a further embodiment, the present invention provides a packaging article, where the water vapour barrier coatings of the present invention impart reduced water vapour transmission rate (WVTR) to the polyester substrate layers present in laminates for packaging food, confectionary, pharmaceutical and cosmetic products, where penetration of water vapour or moisture into the article can substantially impair the substance within the package.

In a specific aspect, the present invention provides water vapour barrier coating compositions comprises a two-part formulation.

Part A.
A1. Polyurethane Resin (solid fraction): 8 - 15 % by weight,
A2. Terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol (solid fraction): 2 - 6 % by weight,
A3. Additives (solid fraction) 0 – 5 % by weight; and
A4. Organic solvents (Q.S. 100% by weight).

Part B.
B1. Aliphatic isocyanate biurets (solid fraction) 15 – 20 % by weight,
B2. Aliphatic isocyanate trimers (solid fraction) 15 – 20 % by weight; and
B3. Organic solvents (Q.S. 100 % by weight).

The two parts i.e. Part A and Part B are mixed to form the barrier coating composition in a ratio ranging from 100:0.5 to 100:5 w/w.

The water vapour barrier coating compositions advantageously maintain water vapour barrier properties even after repeated flexing and twisting of the coated substrate, for example flexible substrates that require to endure the varying impacts during bulk storage, transportation and multiple handlings.

The water vapour barrier coating compositions show improved water vapour barrier properties even in high humidity conditions, and at high temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1 illustrates a three layer laminate incorporating the water vapour barrier coating composition applied to the top polyester sheet.
Fig. 2 illustrates a three layer laminate incorporating the water vapour barrier coating applied to the middle metallised polyester layer.
DETAILED DESCRIPTION OF THE INVENTION:
The preferred embodiments of the present invention will be described in detail with the accompanying drawings and examples. The foregoing general description and the following detailed description are provided to illustrate only some embodiments of the present invention and not to limit the scope of the present invention. The invention is capable of other embodiments and can be carried out or practiced in various other ways.

Unless otherwise specified, all the technical and scientific terms used herein have the same meaning as is generally understood by a person skilled in the art pertaining to the present invention. All the patents, published patent applications referred to throughout the entire disclosure herein, unless specified otherwise, are incorporated by reference in their entirety.

Definitions of terms used in this application:
Substrate: "Substrate" or “substrates” means any physical layer or physical surface to which a coating can be applied. Substrates include, but are not limited to a polyester layer alone, or a polyester layer in combination with other layers of materials to form a laminate, where the polyester layer is coated.

Article: "Article" or "articles" means a substrate or product of manufacture including the substrate alone or in combination with other layers of materials to form a laminate. Examples of articles include, but are not limited to substrates like packaging materials, laminated sheets, containers formed from layered substrates, polyester materials for example polyethylene terephthalate (PET), and physically (not chemically) modified polyesters.

Polyurethane: "Polyurethane," “polyurethanes,” "urethane polymers," refer to polyurethane polymers irrespective of the monomers from which an urethane polymer is derived from. "Polyurethane" refers to a polymer comprising multiple urethane (-NH- C(O)-O-) linkages and, optionally, urea linkages (NH-C(O)-NH-) in the backbone.

"Polyester" refers to linear or branched polymer chains that contain multiple ester links.
Terpolymer refers to a polymer synthesized from three different monomers.

Composition: “Composition” or “compositions” or “formulation” or “formulations” means the water vapour barrier coating preparation made according to the present invention by mixing or combining the ingredients or constituents according to this invention in different ratios.

Water vapour barrier coating composition: "water vapour barrier coating composition," "vapour barrier coating composition," "barrier coating composition," "moisture vapour barrier coating composition," "moisture vapour barrier coating," "moisture barrier coating," "barrier coating" in general refer to the water vapour barrier coating composition of the present invention as they are formulated in the ready to apply state prior to application to the substrate, or the coating formed after applying to a substrate, and the layer or film formed after drying and / or curing on the substrate.

Ratios, ranges, amounts: The ratios, ranges and amounts in this application often expressed as "about" a certain number, value or range. "About" means the exact amount or an amount within the limit of experimental error for the intended purpose.

One embodiment of the present invention relates to water vapour barrier coating compositions applied to polyester substrate layers in a three layer packaging laminate comprising the water vapour barrier coating composition, where the water vapour barrier coating compositions comprises a two-part formulation.

Part A.
A1. Polyurethane Resin (solid fraction): 8 - 15 % by weight,
A2. Terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol (solid fraction): 2 - 6 % by weight,
A3. Additives (solid fraction) 0 – 5 % by weight; and
A4. Organic solvents (Q.S. 100% by weight).

Part B.
B1. Aliphatic isocyanate biurets (solid fraction) 15 – 20 % by weight,
B2. Aliphatic isocyanate trimers (solid fraction) 15 – 20 % by weight; and
B3. Organic solvents (Q.S. 100 % by weight).

The two parts i.e. Part A and Part B are mixed with an appropriate amount to form the barrier coating composition with a ratio ranging from 100:0.5 to 100:5 w/w.

The water vapour barrier coatings of the present invention impart improved (reduced) water vapour transmission rate (WVTR) to the polyester substrate layers present in three layer laminates for packaging food, confectionary, pharmaceutical and cosmetic products, where penetration of water vapour or moisture into the article can substantially impair the properties and quality of the substance within the package. The water vapour barrier coatings of the present invention are clear, flexible coatings.

The improved water vapour barrier coating compositions of the present invention have the ability to inhibit the admission of moisture and water vapour present in the surrounding atmosphere of the packaged articles that use the polyester substrates coated with the water vapour barrier coatings of the present invention as one of the layers of the three layered laminate structures. The water vapour barrier coating compositions of the present invention can be used to coat, and impart water vapour barrier properties to a variety of packaging needs for food, confectionery, pharmaceuticals and cosmetics where water vapour or moisture admission into the packaging articles can substantially impair the quality and properties of the substance within the packaging article.

Ingredients of the water vapour barrier coating compositions of the present invention:

Part A:
A1. Polyurethane Resin:
Polyurethane Resin (solid fraction): 8-15% by weight (can be of low molecular weight plasticizing, semi-film forming or film forming grades. Particularly suitable are film-forming grades. The film forming polyurethanes can be based on polyesters, polyethers or both as polyol component, and aliphatic, cycloaliphatic and/or aromatic type isocyanates. Particularly suitable polyurethanes are polyester types, yet further suitable types are those based on polyesters of adipates, phthalates, isopthalates and/or terephthalates or a combination thereof using diols such as methyl propane diol, methyl pentane diol, neo pentyl glycol, hexane diol, butane diol, 1,2 propane diol, mono-ethylene glycol, diethylene glycol etc. The polyurethane may use chain extenders such as amines and/or short-chain diols such as methyl propane diol, methyl pentane diol, neo pentyl glycol, hexane diol, 1,2 propane diol, mono-ethylene glycol, diethylene glycol, butane diol etc. The polyurethane polymers may incorporate acid groups onto the backbone of the polymer. Any polyurethane with a backbone bearing acid functionality, such as a pendant carboxylate, sulphonate and phosphonate groups, with innate gas and moisture vapor barrier properties can be utilized. The pendant acidic groups present in the polyurethane resins of the invention may, for example, be selected from carboxylic acid groups, sulfonic acid groups and phosphonic acid groups, especially carboxyl groups, either as the free acids or in salt form. The acid groups can, advantageously, be utilized as functional groups for reaction with crosslinking agents, especially polyvalent metal cations.

An organic solvent-soluble polyurethane resin is a resin that dissolves in an organic solvent or a blend of organic solvents, such as esters, alcohols, hydrocarbons, ketones and mixtures thereof. Preferably the polyurethane resin is soluble in isopropanol; 1-Methoxy, 2-Propanol; n-propyl acetate; ethyl acetate and butyl acetate.
The polyurethane resin in the Part A of the two part water vapour barrier coating composition is present in an amount of solid fraction of 7 to15% by weight, more preferably in an amount of solid fraction of 10 to 13% by weight, and most preferably in an amount of solid fraction of 11 to12% by weight.

A2. Terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol:
The vinyl resins of the present invention are derivatives of polyvinyl chloride-vinyl acetate having functional groups which can react with isocyanate groups.

The terpolymers of vinyl resin can be of various types according to their solubility with various solvent systems. Sometimes the terpolymers can be used along with other co-resin systems such as polyvinyl butyral, cellulose acetate butyrate, nitrocellulose etc.
The particularly suitable terpolymers for the water vapour barrier composition of the present invention are vinyl chloride-vinyl acetate-vinyl alcohol terpolymers.

A terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol is represented in the following structure.

Wherein, the transition temperature (Tg) of the terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol (A1) is about 77 °C., an intrinsic viscosity of about 0.2 to about 0.5 dL/g, average molecular weight (Mn) of about 26,000 to 28,000. The fraction of the three monomers in the final terpolymer may range from vinyl acetate from 3% to 10%, vinyl alcohol from 5% to 10% and vinyl chloride from 80% to 92%, more preferably the fraction of the three monomers in the final terpolymer may range from vinyl acetate from 4% to 6%, vinyl alcohol from 6% to 8% and vinyl chloride from 86% to 90%, and most preferably the fraction of the three monomers in the final terpolymer may range from vinyl acetate from 4% to 5%, vinyl alcohol 6% to 7% and vinyl chloride from 88% to 90%.

The terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol (A1) is prepared, as is known by those skilled in the art, by copolymerizing from about 80 to about 95% vinyl chloride with about 20% vinyl acetate in suspension, emulsion or solution systems with a free-radical generating catalyst. Thereafter the resulting copolymers are treated to hydrolysis conditions to partially hydrolyse the acetate portion of the copolymer. The hydrolysis is readily accomplished in solution or dispersion with alkali metal hydroxides, alkali metal alcoholates and the like, for example, with potassium hydroxide in methanol. Another method for providing such materials is described in US2852499. Normally, greater than 60% and usually, about 70 to 90% of the acetate groups are hydrolysed to hydroxyl groups. The copolymers preferably contain about to 7% hydroxyl groups calculated as vinyl alcohol. Such copolymers preferably have an intrinsic viscosity in the range of about 0.2 to- 0.3 dl/g.

The vinyl terpolymer in the Part A of the two part water vapour barrier coating composition is present in an amount of solid fraction of 2 - 6% by weight, more preferably in an amount of solid fraction of 3 - 5% by weight, and most preferably in an amount of solid fraction of 4.2 to 4.5% by weight.

A3. Additives
The water vapour barrier composition of the present invention also includes additives to enhance the coating and post-coating performances such as anti-blocking, better adhesion to various substrates.
The additives for the present invention can be selected from antioxidants, leveling agents, antistatic agents, resolubility additive, defoamer, adhesion promoter, anti-blocking agent, plasticizers, stabilizers or any combinations thereof.

The additives in the Part A of the two part water vapour barrier coating composition is present in an amount of solid fraction of 0 - 5% by weight, more preferably in an amount of solid fraction of 0.2 - 1% by weight, and most preferably in an amount of solid fraction of 0.3 – 0.7% by weight.

A4. Organic solvents
For the selection of organic solvents it is essential to avoid alcohols as they may react with the isocyanate groups. The non-limiting organic solvents are selected from aromatic hydrocarbons, aliphatic alcohols, organic acid esters, aliphatic ketones, glycol ethers, aliphatic hydrocarbons or cycloaliphatic hydrocarbons. Suitable aromatic hydrocarbons include but not limited to toluene, xylene, ethylbenzene. Suitable aliphatic alcohols include but not limited to isobutanol and 1-Methoxy, 2-Propanol and mixtures thereof. Suitable organic acid esters include but not limited to methyl acetate, ethyl acetate, propyl acetate, butyl acetate and mixtures thereof. Suitable aliphatic ketones include but not limited to methyl ethyl ketone. Suitable aliphatic hydrocarbons include but not limited to pentane, hexane, heptane, octane, nonane, decane, isopentane, isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, kerosene, petroleum spirits, petroleum ether and mixtures thereof; and suitable cycloaliphatic hydrocarbons include but not limited to cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane and mixtures thereof. Mixtures of any of these aromatic hydrocarbons, aliphatic alcohols, organic acid esters, aliphatic ketones, glycol ethers, aliphatic hydrocarbons and cycloaliphatic hydrocarbons may also be used.

In a preferred embodiment, the organic solvents are selected from non-hydrocarbon and non-ketone solvents.

One of the above organic solvent or mixture of organic solvents is added to the other given ingredients of Part A in order to balance the Part A to 100 % by weight.

Part B
The part B of the water vapour barrier coating composition of the present invention includes biurets and trimers of aliphatic polyisocyanates.

The aliphatic polyisocyanate compound of the present invention can be a compound having at least two isocyanate groups per molecule. Non-limiting examples of aliphatic diisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, 1,10-decamethylene diisocyanate, Tetramethylxylylene Diisocyanate (TMXDI) and 1,3,6-hexamethylene triisocyanate.

B1. Aliphatic isocyanate biurets:
The preparation of biuret group-containing polyisocyanate of the present invention having a functionality of at least 4 and a number average molecular weight of about 500 to 3,000, comprises reacting a polyisocyanate adduct which is prepared from an aliphatic diisocyanate, preferably 1,6-hexamethylene diisocyanate, with 0.01 to 0.15 moles of water or a mixture of up to 50 mole percent, based on the total moles of biuretizing agent, of biuretizing agents other than tertiary alcohols for each equivalent of isocyanate groups in the polyisocyanate adducts at a temperature of 50 to 180° C. to incorporate biuret groups into the polyisocyanate adduct. Suitable processes are disclosed in US2008064829A1, US3124605 and US3903127 the disclosures of which are herein incorporated by reference.

The aliphatic isocyanate biurets in the Part B of the two part water vapour barrier coating composition is present in an amount of solid fraction of 15 - 20% by weight, more preferably in an amount of solid fraction of 16 - 19% by weight, and most preferably in an amount of solid fraction of 18 -19% by weight.

B2: Aliphatic isocyanate trimers:
The aliphatic trimers can be selected from Hexamethylene diisocyanate trimers, methylene dicyclohexyl diisocyanate trimers or isophorone diisocyanate trimers. The preferred trimers of the present invention are isophorone diisocyanate trimers (IPDI trimer).

The isophorone diisocyanate trimers in the Part B of the two part water vapour barrier coating composition is present in an amount of solid fraction of 15 - 20% by weight, more preferably in an amount of solid fraction of 17 – 19.5% by weight, and most preferably in an amount of solid fraction of 18.5 - 19% by weight.

B3. Organic solvents
The organic solvents discussed in A4 of part A can be used as the organic solvent for Part B. The organic solvent or mixture of organic solvents is added to the other given ingredients of Part B in order to balance the Part B to 100 % by weight.

In a preferred embodiment, the organic solvents in Part A or Part B of the barrier coating composition are selected from non-hydrocarbon and non-ketone solvents.

In a preferred embodiment of the invention, the organic solvent fractions present in the barrier coating composition are in the range of 82 to 84 % by weight of the total composition of Part-A and 62 to 64% by weight of the total composition of part-B, more preferably the organic solvent fractions are present in the range of 83 to 83.5 % by weight of the total composition of Part-A and 62.5 to 63% by weight of the total composition of part-B, most preferably the organic solvent fractions are 83 to 83.5 % by weight of the total composition of Part-A and 62.5 to 63% by weight of the total composition of part-B.

Method of coating:
A layer of a coating of the water vapour barrier compositions is applied contiguously upon at least one of the surfaces of the polyester substrate layer. The method of applying this coating layer to the substrate layer can be of various means well known in the art, such as a coating roll (e.g. gravure roll or Meyer rod) or other coating means, and drying of the coating.

Method of applying the water vapour barrier compositions to the polyester substrate of the present invention is not particularly limited. The coating methods that are industrially known can be used for the coating purpose of the present invention, the non-limiting examples of various industrially known coating methods include screen printing, gravure printing, offset printing, flexographic printing, ink-jet method, reverse gravure method, or the like is generally used. Other methods of coating, dipping, brushing, die coating method, roll coating method, slit coating method, spin coating method, spray coating method or the like.

Drying:
The barrier coating on the coated polyester substrate is further subjected to drying by any of the drying methods known in the industry, including convection drying, vacuum drying, drying in hot air stream, radiant heat (IR) drying and induction drying.

In an embodiment of the present invention, Fig. 1 illustrates a three layered laminate 100 incorporating the water vapour barrier coating composition of the present invention. The three layer laminate includes a top polyester layer 101, a middle layer 102 of metallised polyester, and a bottom layer 103 made of polyethylene, or polypropylene, where the water vapour barrier coating is applied to the top polyester layer 101.

In another embodiment of the present invention, Fig. 2 illustrates a three layer laminate 200 incorporating the water vapour barrier coating composition. The three layer laminate includes a top polyester layer 201, a middle layer 202 of metallised polyester, and a bottom layer 203 made of polyethylene, or polypropylene, where the water vapour barrier coating is applied to the middle metallised polyester layer 202.

The polyester in the top polyester layer or the polyester in the middle metallised polyester layer in the three layer laminate of the present invention can be the same polyester or dissimilar polyesters.

The polyester in the top polyester layer or the polyester in the middle metallised polyester layer in the three layer laminate of the present invention preferably is from poly(ethylene terephthalate) (PET).

In a preferred embodiment of the invention, the water vapour barrier composition includes the ingredients as given in Table 1.

Table 1
PART-A PART-B
Ingredient Amount
(Weight %) Ingredient Amount
(Weight %)
Polyurethane (100% solid) 11.40 Biuret- aliphatic polyisocyanate resin based on hexamethylene diisocyanate (HDI). (100% Solid) 18.50
Vinyl Chloride vinyl acetate Vinyl alcohol terpolymer (100% Solid) 4.40 Trimer - Isophorone diisocyanate trimer (IPDI trimer) (100% Solid) 18.90
Additive (antiblocking agent) 0.50 Organic Solvents 62.60
Additive - Resolubility/Printability improvement 0.50
Organic Solvents 83.20
Total 100.00 100.00

Example 1
The water vapour barrier composition of the present invention is prepared by mixing the two parts Part-A and Part-B (as given in Table 1) in the ratio of 100:3 w/w. The barrier coating composition was then applied to the top polyester layer of the three layer laminate. The laminate includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer.

Sample test result:
Water vapour transmission rate (WVTR) of the three layer laminate coated with the coating composition:

The water vapour transmission rate (WVTR) of the laminate was measured by ASTM F 1249-13. The test was performed using HS/MT/SOP/34 method with the instrument MOCON WVTR SG-3/33 at maintained test temperature of 38±0.5 °C and maintained test relative humidity (RH) at 90±3%. The water vapour transmission rate (WVTR) of the laminate was found to be 0.506 g/(m2.day).

Example 2
In a further embodiment, the water vapour barrier composition of the present invention is prepared by mixing the two parts Part-A and Part-B (as given in Table 1) in the ratio of 100:0.5 w/w. The barrier coating composition was then applied to the top polyester layer of the three layer laminate that includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer.

Sample test result:
WVTR of the three layer laminate coated with the coating composition:

The water vapour transmission rate (WVTR) of the laminate was measured with the same method and same parameters as given in example 1, where the water vapour transmission rate (WVTR) of the laminate was found to be 0.574 g/(m2.day) at 38±0.5 °C and relative humidity (RH) at 90±3%.

Example 3
In another embodiment, the water vapour barrier composition of the present invention is prepared by mixing the two parts Part-A and Part-B (as given in Table 1) in the ratio of 100:1.0 w/w. The barrier coating composition was then applied to the top polyester layer of the three layer laminate that includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer.

Sample test result:
The WVTR of the laminate was measured with the same method and same parameters as given in example 1 was found to be 0.547 g/(m2.day) at 38±0.5 °C and relative humidity (RH) at 90±3%.

Example 4
In a further embodiment, the water vapour barrier composition of the present invention is prepared by mixing the two parts Part-A and Part-B (as given in Table 1) in the ratio of 100:2.0 w/w. The barrier coating composition was then applied to the top polyester layer of the three layer laminate that includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer.

Sample test result:
The WVTR of the laminate was measured with the same method and same parameters as given in example 1 was found to be 0.523 g/(m2.day) at 38±0.5 °C and relative humidity (RH) at 90±3%.

Example 5
In yet another embodiment, the water vapour barrier composition of the present invention is prepared by mixing the two parts Part-A and Part-B (as given in Table 1) in the ratio of 100:4.0 w/w. The barrier coating composition was then applied to the top polyester layer of the three layer laminate that includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer.

Sample test result:
The WVTR of the laminate was measured with the same method and same parameters as given in example 1 was found to be 0.565 g/(m2.day) at 38±0.5 °C and relative humidity (RH) at 90±3%.

Example 6
In a further embodiment, the water vapour barrier composition of the present invention is prepared by mixing the two parts Part-A and Part-B (as given in Table 1) in the ratio of 100:5.0 w/w. The barrier coating composition was then applied to the top polyester layer of the three layer laminate that includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer.

Sample test result:
The WVTR of the laminate was measured with the same method and same parameters as given in example 1 was found to be 0.593 g/(m2.day) at 38±0.5 °C and relative humidity (RH) at 90±3%.

Example 7
In another embodiment, the three layer laminate that includes a top polyester layer, a middle metallised polyester layer; and a bottom polyolefin layer, where the top polyester layer is polyethylene terephthalate (PET).

The laminates formed with the coated polyester layers with the water vapour barrier coatings of the present invention can be safely used as packaging materials for food, confectionery, pharmaceutical and cosmetic products.

The use of three layered laminate structure effectively reduces the packaging cost for the industry while providing better water vapour barrier properties.

The water vapour barrier coating compositions maintain high water vapour barrier properties even after repeated flexing and twisting of the coated substrate, for example flexible substrates that require to endure the varying impacts during bulk storage, transportation and multiple handlings.

The water vapour barrier coating compositions show improved water vapour barrier properties even in high humidity conditions, and at high temperatures.

Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims:CLAIMS
We claim
1. A water vapour barrier coating composition comprising:
a. a first part comprising a polyurethane resin, a terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol, additives, and organic solvents; and
b. a second part comprising isocyanate biurets, isocyanate trimers, and organic solvents,

wherein, the first part and the second part are mixed together in a ratio of first part to the second part 100:0.5 w/w to 100:5 w/w.

2. The water vapour barrier coating composition according to claim 1, wherein the solid fraction of polyurethane resin is about 8% to 15% by weight.

3. The water vapour barrier coating composition according to claim 1, wherein the solid fraction of terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol is about 2% to 6% by weight.

4. The water vapour barrier coating composition according to claim 1, optionally consists of additives selected from antioxidants, leveling agents, antistatic agents, resolubility additive, defoamer, adhesion promoter, anti-blocking agent, plasticizers, stabilizers or any combinations thereof, wherein the solid fraction of the additives is about up to 5% by weight.

5. The water vapour barrier coating composition according to claim 1, wherein the isocyanate biurets are aliphatic isocyanate biurets; and the isocyanate trimers are aliphatic isocyanate trimers.

6. The water vapour barrier coating composition according to claim 5, wherein, the solid fraction of aliphatic isocyanate biurets is about 15% to 20% by weight; and the solid fraction of aliphatic isocyanate trimers is about 15% to 20% by weight.

7. The water vapour barrier coating composition according to claim 1, wherein, the balance in each of the first part and the second part is an organic solvent selected from aromatic hydrocarbons such as toluene, xylene, ethylbenzene; aliphatic alcohols such as isobutanol and 1-Methoxy, 2-Propanol and mixtures thereof; organic acid esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate and mixtures thereof; aliphatic ketones such as methyl ethyl ketone; glycol ethers; aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, isopentane, isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, kerosene, petroleum spirits, petroleum ether and mixtures thereof; and cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane and mixtures thereof; or mixtures of any of these aromatic hydrocarbons, aliphatic alcohols, organic acid esters, aliphatic ketones, glycol ethers, aliphatic hydrocarbons and cycloaliphatic hydrocarbons.

8. The water vapour barrier coating composition according to claim 1, wherein, the balance in each of the first part and the second part is an organic solvent selected from aliphatic alcohols such as isobutanol and 1-Methoxy, 2-Propanol and mixtures thereof; organic acid esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate and mixtures thereof; glycol ethers; or mixtures of any of these aliphatic alcohols, organic acid esters, glycol ethers.

9. A three-layer laminate structure comprising:
a top polyester layer,
a middle metallised polyester layer; and
a bottom polyolefin layer,

wherein, the bottom polyolefin layer is selected from a polyethylene layer, and a polypropylene layer,

wherein at least one of the top polyester layer and the middle metallised polyester layer are coated with a water vapour barrier composition, the water vapour barrier coating composition comprising:

a. a first part comprising a polyurethane resin, a terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol, additives, and organic solvents; and
b. a second part comprising aliphatic isocyanate biurets, aliphatic isocyanate trimers, and organic solvents,

wherein, the first part and the second part are mixed together at a ratio of first part to the second part 100:0.5 w/w to 100:5 w/w,

wherein, the polyester in the top polyester layer and the polyester in the middle metallised polyester layer is the same polyester or are dissimilar polyesters, wherein the polyester for any of the top polyester layer and the middle metallised polyester layer is poly(ethylene terephthalate) (PET).

10. The water vapour barrier coating composition according to claim 9, wherein, the balance in each of the first part and the second part is an organic solvent selected from aliphatic alcohols such as isobutanol and 1-Methoxy, 2-Propanol and mixtures thereof; organic acid esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate and mixtures thereof; glycol ethers; or mixtures of any of these aliphatic alcohols, organic acid esters, glycol ethers.