A coating composition and a method of preparing the same

Abstract

There is provided a coating composition and a method of preparing the same. The coating composition comprises mixture of an ethylene vinyl alcohol (EVOH), an acid, water and an organic solvent, wherein the EVOH has an ethylen content of 29 mol% to 65 mol%, and wherein the acid comprises at least 2 acidic hydrogen atoms. There is also provided a coated substrate coated with the coating composition. There is also provided a method of reducing transmission rat of a substrate and of an ethylene vinyl alcohol coating composition

Description

[0001] A Coating Composition and A Method of Preparing the Same

[0002] References to Related Application

[0003] This application claims priority to Singapore application number 10202403253T filed with the Intellectual Property Office of Singapore on 18 October 2024, the contents of which is hereby incorporated by reference in its entirety for all purposes.

[0004] Technical Field

[0005] The present invention relates generally to a coating composition and a method of preparing the same. The present invention further relates to a coated substrate coated with the coating composition. The present invention also relates to a method of reducing transmission rate of a substrate and of an ethylene vinyl alcohol coating composition.

[0006] Background Art

[0007] Ethylene vinyl alcohol (EVOH) with good gas barrier has been widely co-extruded with other plastics such as nylon, polyolefin and polyethylene terephthalate (PET) to produce flexible high barrier film for food packaging applications. A plastic barrier film with EVOH as the barrier layer, which is produced through co-extrusion has been previously provided.

[0008] Polyolefin has been heavily applied in food packaging because of its unique mechanical property, chemical resistance, light transparency and process ability. While polyolefin has good moisture barrier, its oxygen barrier is very poor. The oxygen transmission rate of polyolefin film available in the market is around 2000 cc / m2.day. Therefore, the application of mono-polyolefin food packaging film is hindered by its poor gas barrier.

[0009] Co-extruded polyolefin / EVOH food packaging film with high oxygen barrier is then developed. However, such co-extruded flexible film always comprises 2 tier layers with EVOH layer sandwiched between the 2 tier layers for high interfacial bonding between the EVOH layer and the neighbouring layers. A method to produce melt co-extrusion multilayer composite high barrier film with EVOH as the inner barrier layer has been previously provided. The tier layers have been co-extruded between the EVOH layer and substrate layer for improving the adhesion between the EVOH layer and substrate layer. In general, the thickness of the tier layer is 3 pm or higher for producing high quality films. On the other hand, the minimum thickness of the EVOH layer in co-extruded flexible films with good barrier property and productivity in the current market is 12 pm. This is mainly due to the limited extrusion capability of the co-extruder available in the market. As a result, the total thickness of the EVOH layer plus 2 tier layers in a coextruded flexible film would be 18 pm or higher. In order to meet the requirement of less than 10% of non-polyolefin in a polyolefin-based packaging film to produce recyclable polyolefin film, the total thickness of polyolefin film co-extruded with EVOH would be of 180 pm or higher, which is much thicker than that of conventional flexible multimaterials film with a thickness of around 100 pm. This will incur high cost and high negative impact on the environment. In other words, if the acceptable thickness of the polyolefin film is kept at around 100 pm, the co-extruded EVOH layer plus its tier layers will compromise the recyclability of the mono-polyolefin packaging film.

[0010] Furthermore, purging co-extruder with plain plastic resin before and after co-extruding the film containing EVOH layer will generate a lot of plastic waste, which will incur production cost and generate high negative environment impact

[0011] Therefore, there is a high market demand in the flexible packaging industry to produce a EVOH coating solution, which can be applied onto flexible substrates in a straight forward manner by using existing infrastructure.

[0012] There is thus a need to provide a coating composition that meets the demand and overcomes, or at least ameliorates, one or more of the disadvantages described above.

[0013] Summary

[0014] In one aspect, the present disclosure relates to a coating composition comprising a mixture of an ethylene vinyl alcohol (EVOH), an acid, water and an organic solvent, wherein the EVOH has an ethylene content of about 29 mol% to about 65 mol%, and wherein the acid comprises at least 2 acidic hydrogen atoms. Advantageously, the coating composition may provide improved gas and moisture barrier when coated on a substrate due to the presence of the acid. The coating composition may also provide improved cohesion due to the presence of the acid. Further advantageously, the coating composition may provide improved bond strength and adhesion to the substrate due to the presence of the acid. Still further advantageously, the EVOH may be highly stable in the coating composition due to the presence of the acid.

[0015] In another aspect, the present disclosure relates to a coated substrate, wherein the substrate is coated with the coating composition as described herein.

[0016] In another aspect, the present disclosure relates to a method of preparing a coating composition comprising the steps of: a) forming a solution of ethylene vinyl alcohol (EVOH) in a mixture of a first organic solvent and water, wherein the EVOH has an ethylene content of about 29 mol% to about 65 mol%; and b) adding an acid to the solution, wherein the acid comprises at least 2 acidic hydrogen atoms.

[0017] Advantageously, the addition of the acid after the formation of the solution facilitates the formation of a layer of acid that is entangled with the vinyl alcohol repeating unit of the EVOH that at least partially encapsulates the EVOH, compared to adding the acid together with the EVOH into the organic solvent and water. This entanglement stabilises the EVOH, which contains a high ethylene content of at least about 29 mol%.

[0018] In another aspect, the present disclosure relates to a method of reducing transmission rate of a substrate, comprising the step of coating a substrate with the coating composition as described herein.

[0019] In another aspect, the present disclosure relates to a method of reducing transmission rate of an ethylene vinyl alcohol (EVOH) coating composition, comprising adding an acid to an EVOH coating composition, wherein the acid comprises at least 2 acidic hydrogen atoms, and wherein the EVOH coating composition comprises a mixture of EVOH having an ethylene content of about 29 mol% to about 65 mol%, water and an organic solvent.

[0020] Definitions

[0021] The following words and terms used herein shall have the meaning indicated:

[0022] Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also pennit inclusion of additional, unrecited elements

[0023] As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically, + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0024] Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0025] Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. Detailed Disclosure of Embodiments

[0026] Exemplary, non-limiting embodiments of a coating composition will now be disclosed.

[0027] The coating composition comprises a mixture of an ethylene vinyl alcohol (EVOH), an acid, water and an organic solvent, wherein the EVOH has an ethylene content of about 29 mol% to about 65 mol%, and wherein the acid comprises at least 2 acidic hydrogen atoms.

[0028] Advantageously, the coating composition may provide improved gas and moisture barrier when coated on a substrate due to the presence of the acid. The acid may reduce the EVOH particle size and provide a more uniform particle size distribution, resulting in an increase in the smoothness of the coated surface. The EVOH particle size varying in the range of about 0.3 pm to 2.5 pm without the acid, may be reduced to a more uniform distribution of about 0.3 pm to 0.9 pm with the acid. Without the acid, the particle size distribution d50 of the EVOH may be about 1.13±0.74 pm while it is about 0.50±0.16 pm with the acid. This increased smoothness is beneficial to the gas barrier improvement. The acid may also result in the EVOH particles having no holes on their surfaces leading to the EVOH particles to be considered as less porous.

[0029] Further advantageously, the coating composition may provide improved cohesion due to the presence of the acid. The coating composition may also provide improved bond strength and adhesion to the substrate due to the presence of the acid. The acid may enhance the internal cohesion of the coating composition and the interfacial adhesion between the coating composition and the substrate.

[0030] Still further advantageously, the EVOH may be highly stable in the coating composition. EVOH with high ethylene content such as at least about 29 mol% is generally unstable in solution in that it precipitates out of the solution, resulting in an uneven coating with poor gas barrier. In contrast, the EVOH with high ethylene content is able to form a stable dispersion in the present coating composition due to the presence of the acid. Still further advantageously, the coating composition can be applied onto metalized substrate to achieve superior gas and moisture barrier properties.

[0031] Still further advantageously, the coating composition can be applied onto polyolefin film, metalized polyolefin film, paper and metalized paper to produce recyclable mono- polyolefin packaging and re-pulpable paper packaging with high gas barrier.

[0032] The ethylene content of the EVOH may be in the range of about 29 mol% to about 60 mol%, about 29 mol% to about 45 mol% or about 29 mol% to about 35 mol%.

[0033] Advantageously, the ethylene content of at least about 29 mol% may impart high oxygen barrier with strong moisture resistance properties. With ethylene content lower than 29 mol%, the gas barrier of the coating composition at high humid environment is compromised.

[0034] The degree of polymerisation of the EVOH may be in the range of about 400 to about 5000, about 700 to about 2500, or about 700 to about 1500.

[0035] The total solid content of the EVOH in the coating composition, based on the total weight of the coating composition, may be in the range of about 1 wt% to about 60 wt%, about 3 wt% to about 30 wt%, about 5 wt% to about 20 wt% or about 5 wt% to about 10 wt%.

[0036] The acid may be a polyacid, a polymeric acid or a mixture thereof. Without being bound by theory, it is believed that the acid is entangled with the vinyl alcohol repeating unit of the EVOH through hydrogen bonding and forms a layer that at least partially encapsulates the EVOH. Advantageously, this stabilises the EVOH as described herein, which contains a high ethylene content of at least about 29 mol%, in the coating composition. No crosslinking is formed between the acid and the EVOH.

[0037] The polyacid may be an acid that comprises more than 2 acidic hydrogen atoms and which is not a polymeric acid. The polyacid may be selected from the group consisting of phosphoric acid, citric acid, agaric acid, propane- 1,2, 3 -tricarboxylic acid, trimesic acid, nitrilotriacetic acid, boric acid and combinations thereof.

[0038] The polymeric acid may be a polymer free of polymerizable group and comprises repeating units comprising an acid functional group. The acid functional group may be a carboxylic acid, phosphoric acid, sulfonic acid or a combination thereof. The polymeric acid may be a homopolymer or copolymer of (meth)acrylic acid, methyl methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, cinnamic acid, 2-methylmaleic acid, fumaric acid, itaconic acid, 2-methyl itaconic acid, a, P-methylene glutaric acid, vinyl phosphonic acid and styrene sulfonic acid. The polymeric acid may be a polyacrylic acid, polymethacrylic acid or a combination thereof

[0039] The polymeric acid may have a number average molecular weight (Mn) in the range of about 500 g / mol to about 1,000,000 g / mol, about 5,000 g / mol to about 1,000,000, about 50,000 g / mol to about 1,000,000, about 100,000 g / mol to about 1,000,000, about 200,000 g / mol to about 1,000,000, about 300,000 g / mol to about 1,000,000, about 400,000 g / mol to about 1,000,000 g / mol, about 450,000 g / mol to about 1,000,000 g / mol or about 450,000 g / mol to about 800,000 g / mol. The number average molecular weight may be about 450,000 g / mol, about 550,000 g / mol, about 650,000 g / mol or about 800,000 g / mol.

[0040] Advantageously, the number average molecular weight of the polymeric acid is high such that it stabilizes the EVOH.

[0041] The weight percentage of the acid to the EVOH may be in the range of about 1 wt% to about 50 wt%, about 4 wt% to about 30 wt%, about 5 wt% to about 20 wt%, about 10 wt% to about 20 wt%, about 10 wt% to about 15 wt%, about 15 wt% to 20 wt%, or about 5 wt% to about 10%.

[0042] The organic solvent may be selected from the group consisting of a lower alcohol, tetrahydrofuran, 1,3 -di oxane, acetonitrile, ethyl acetate, propyl acetate, acetone and combinations thereof. The lower alcohol may be a C2 to C4 alcohol. The C2 to C4 alcohol may be selected from the group consisting of ethanol, propanol (including isomers thereof), butanol (including isomers thereof) and combinations thereof. The lower alcohol may be ethanol or n-propanol.

[0043] The coating composition may comprise at least 10 wt% of the organic solvent based on the total weight of the coating composition. The organic solvent may be present in the range of about 30 wt% to about 60 wt%, about 30wt% to about 50 wt%, or about 40 wt% to about 50 wt%. The amount of the organic solvent may be suitably selected based on the ethylene content of the EVOH, with a higher amount of organic solvent used with higher ethylene content.

[0044] The coating composition may comprise at least 30 wt% of the water based on the total weight of the coating composition. The water may be present in the range of about 30 wt% to about 85 wt%, about 30wt% to about 50 wt%, or about 40 wt% to about 50 wt%.

[0045] The coating composition may not comprise an inorganic filler, such as clay. Therefore, the coating composition may consist essentially of or consist of a mixture of the EVOH, the acid, the water and the organic solvent.

[0046] Exemplary, non-limiting embodiments of a coated substrate will now be disclosed.

[0047] The substrate may be coated with the coating composition as described herein.

[0048] The substrate may be any film that is used in food packaging. The substrate may be a flexible film used to produce flexible food packaging. The substrate may be a plastic, polyamide, cellulosic or a multilayer composite thereof. The plastic may be a polyolefin, polyester or polycarbonate. The polyester may be a polyethylene terephthalate. The polyamide may be nylon 66, nylon 11 or nylon 12. The cellulosic may be cellulosic film or paper. The multilayer composite may include a metal or an inorganic chemical coating, such as a metalized substrate. The multilayer composite may be a metalized substrate such as metalized polyolefin film, metalized paper or aluminium oxide (Alox) coated polyolefin film or silicon dioxide (Silox) coated polyolefin film. Advantageously, the substrate may be a polyolefin film, metalized polyolefin film, paper or metalized paper, such that a recyclable mono-polyolefin packaging and re-pulpable paper packaging with high gas barrier is produced.

[0049] The oxygen transmission rate (OTR) of the coated substrate may be from about 0.01 cm3 / (m2.day) to about 100 cm3 / (m2.day), from about 0.07 cm3 / (m2.day) to about 0.74 cm7(m2.day), from about 0.44 cm7(m2.day) to about 1.40 cm3 / (m2.day), about 0.04 cm3 / (m2.day), about 1.10 cm3 / (m2.day), or about 2.80 cm3 / (m2.day), when measured at 23°C and 0% relative humidity. The OTR may be measured using Mocon OX-TRAN Model 2 / 2. The OTR may be measured in accordance with ASTM D3985 using a sample testing area of 50 cm2and sample thickness of 0.0254 mm (1 mil).

[0050] The water moisture transmission rate (W VTR) of the coated substrate may be from about <0.01 g / (m2.day) to about 120.00 g / (m2.day), from about 0.11 g / (m2.day) to about 0.15 g / (m2.day), from about 21.43 g / (m2.day) to about 27.96 g / (m2.day), about <0.01 g / (m2.day), about 5.30 g / (m2.day) or about 41.23 g / (m2.day) when measured at 37.8°C and 90% relative humidity. The WVTR may be measured using Mocon Permatran W 3 / 33. The WVTR may be measured in accordance with ASTM F-1249 using a sample testing area of 50 cm2and sample thickness of 0.0254 mm (1 mil).

[0051] Advantageously, when the substrate is a metalized substrate, the EVOH and the acid may work synergistically with the metal of the metalized substrate to result in superior gas and moisture barrier properties. This coated substrate can be used to produce packaging films with superior gas and moisture barrier properties to replace laminated aluminium (Alu) film to preserve dried foods, where there is a high requirement for moisture barrier. As mentioned above, the addition of the acid results in EVOH particles with smaller particle size, more uniform particle size distribution and without holes (or less porous), which when coated on the metalized substrate, the smaller less porous EVOH particles fill up the pinholes in the metal layer to achieve superior barrier against oxygen. In addition, the superior moisture barrier is due to the reaction between the acid group of the acid and metal atom on the metalized substrate. The acid group reacts with the metal to form metal oxide, which also fills up the pinholes in the metal layer, resulting in an increase in the integrity of the metal layer.

[0052] The coating composition may be applied onto the substrate to form the coated substrate by suitable coating techniques, such as slot die coating, doctor blading, bar coating or rotogravure coating. The coating composition may be blade coated onto the substrate using a bird applicator.

[0053] An anchor coat agent may be applied on the substrate prior to applying the coating composition for improving the bond between the substrate and the coating composition.

[0054] Exemplary, non-limiting embodiments of a method of preparing a coating composition will now be disclosed.

[0055] The method of preparing a coating composition comprises the steps of: a) forming a solution of ethylene vinyl alcohol (EVOH) in a mixture of a first organic solvent and water, wherein the EVOH has an ethylene content of about 29 mol% to about 65 mol% as described herein; and b) adding an acid to the solution, wherein the acid comprises at least 2 acidic hydrogen atoms as described herein.

[0056] The first organic solvent may be selected from the group consisting of a lower alcohol, tetrahydrofuran, 1,3 -di oxane, acetonitrile, ethyl acetate, propyl acetate, acetone and combinations thereof. The lower alcohol may be a C2 to C4 alcohol. The C2 to C4 alcohol may be selected from the group consisting of ethanol, propanol (including isomers thereof), butanol (including isomers thereof) and combinations thereof. The lower alcohol may be ethanol or n-propanol.

[0057] Advantageously, the addition of the acid after the formation of the solution facilitates the formation of a layer of acid that is entangled with the vinyl alcohol repeating unit of the EVOH through hydrogen bonding that at least partially encapsulates the EVOH, compared to adding the acid together with the EVOH into the organic solvent and water. As previously described, this entanglement stabilises the EVOH, which contains a high ethylene content of at least about 29 mol%.

[0058] Step a) may comprise dissolving the EVOH into the mixture at an elevated temperature under stirring to produce a clear EVOH solution. The elevated temperature may be a temperature in the range of about 40 °C to about 100 °C, about 50 °C to about 90 °C, or about 50 °C to about 70 °C.

[0059] After the EVOH is completely dissolved, the solution may be kept as a stock solution.

[0060] Step b) may comprise adding the acid to the solution at an elevated temperature The elevated temperature may be a temperature in the range of about 40 °C to about 100 °C, about 50 °C to about 90 °C, or about 50 °C to about 70 °C.

[0061] The acid may be added to the solution under vigorous stirring.

[0062] The method may further comprise prior to step b), dissolving the acid into a mixture of a second organic solvent and water.

[0063] The second organic solvent may be an organic solvent that is miscible with water. The second organic solvent may be the same as the first organic solvent used in step a).

[0064] The method may further comprise a step c) of stirring the acid and EVOH under the elevated temperature for a period of time to produce a clear solution. The period of time may be in the range of about 0.5 hour to about 5 hours, or about 2 to about 4 hours. The time may be about 2 hours.

[0065] The method may further comprise after the step c), a step d) of cooling the clear solution of step c) down to room temperature under stirring. The room temperature may be in the range of about 15°C to 35°C. Exemplary, non-limiting embodiments of a method of reducing transmission rate of a substrate will now be disclosed.

[0066] The method of reducing transmission rate of a substrate comprises the step of coating a substrate with the coating composition as described herein.

[0067] The transmission that can be reduced may be gas, moisture or a combination thereof. When the transmission to be reduced is oxygen, the transmission may be reduced by at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 97%, at least 98% or at least 99%. When the transmission to be reduced is water vapour, the transmission may be reduced by at least 20%, at least 40%, at least 50%, about 20% to 90%, about 40% to 99%, about 50% to 70% or about 50% to 60%.

[0068] Exemplary, non-limiting embodiments of a method of reducing transmission rate of an EVOH coating composition will now be disclosed.

[0069] The method of reducing transmission rate of an ethylene vinyl alcohol (EVOH) coating composition comprises adding an acid to an EVOH coating composition, wherein the acid comprises at least 2 acidic hydrogen atoms as described herein, and wherein the EVOH coating composition comprises a mixture of EVOH having an ethylene content of about 29 mol% to about 65 mol% as described herein, water and an organic solvent as described herein.

[0070] The transmission that can be reduced may be gas, moisture or a combination thereof. When the transmission to be reduced is oxygen, the transmission may be reduced by at least 20%, at least 50%, at least 60%, at least 70%, at least 80%, about 70% to 95% or about 90% to 95%. When the transmission to be reduced is water vapour, the transmission may be reduced by at least 20%, at least 30%, at least 40%, at least 50%, about 20% to 90%, about 30% to 99%, about 40% to 90%, about 50% to 90% or about 40% to 60%. Brief Description of Drawings

[0071] The accompanying drawings illustrate a disclosed embodiment and serve to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0072] Fig. la

[0073] Fig. la shows a SEM image (top view) of a BY-Paper without coating. Scale bar is at 1pm.

[0074] Fig. lb

[0075] Fig. 1b shows a SEM image of (top view) of a BY-Paper with EVOH-PAA coating (after

[0076] 4 times coating). Scale bar is at 1pm.

[0077] Fig. 2a

[0078] Fig. 2a shows a SEM image of EVOH with bigger particle size and with holes as compared to the EVOH with polyacrylic acid (Fig. 2b). Scale bar is at 1pm.

[0079] Fig. 2b

[0080] Fig. 2b shows a SEM image of EVOH with polyacrylic acid, with smaller particle size, more uniform particle size distribution and without holes as compared to EVOH without acid (Fig. 2a). Scale bar is at 1pm.

[0081] Examples

[0082] Non-limiting examples of the invention will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

[0083] Example 1 - Preparation of EVOH / PAA coating solution (EVOH-PAA)

[0084] Preparation of ethylene vinyl alcohol (EVOH) stock solution

[0085] 10 g of ethylene vinyl alcohol (EVOH, D2908 (ethylene content: 29 mol%, obtained from Mitsubishi Chemical, Singapore)) was added into 90 g of n-propanol (obtained from Merck KGaA, Darmstadt, Germany ) / deionised (DI) water mixture (n-propanol / DI water: 50 / 50) under stirring. The dispersion was heated up to 90 °C and kept stirring at 90 °C until the EVOH is dissolved. This solution (10 wt%) was kept as a stock solution Preparation of polyacrylic acid (PAA) solution

[0086] A polyacrylic acid (PAA, Mn450k or 800k, (obtained from Nippon Shokubai (Asia) Pte. Ltd., Singapore)) solution with concentration of 7.7 wt% was prepared by first dispersing 1 .5 g of PAA into 9 g of DI water and kept stirring till the PAA was dissolved. This was followed by adding 9 g of n-propanol into the PAA solution.

[0087] Preparation of EVOH / PAA coating solution (EVOH-PAA)

[0088] 5.4 g of the PAA solution was added slowly into 30 g of EVOH solution under stirring at 90 °C. The mixture (where concentration of PAA and EVOH is 1.2 wt% and 8.5 wt % respectively) was kept stirring at 90 °C for 2 hours and then allowed to cool down to room temperature to produce EVOH-PAA coating solution.

[0089] Example 2 - Preparation of EVOH / phosphoric acid coating solution (EVOH-PPA) 0.34 g of 85 wt% phosphoric acid (PPA, from Sigma Aldrich, Massachusetts, USA) was added slowly into 15 g of the EVOH solution prepared in Example 1 under stirring at 90 °C. The mixture (where concentration of PPA and EVOH is 1.9 wt% and 9.9 wt %, respectively; PPA percentage to EVOH: 19.3 wt%) was kept stirring at 90 °C for 2 hours and then allowed to cool down to room temperature to produce EVOH-PPA coating solution.

[0090] Example 3 - Preparation of EVOH coating solution

[0091] 10 g of ethylene vinyl alcohol (EVOH, D2908 (ethylene content: 29 mol%, obtained from Mitsubishi Chemical, Singapore)) was added into 90 g of n-propanol (obtained from Merck KGaA, Darmstadt, Germany ) / deionised (DI) water mixture (n-propanol / DI water: 50 / 50) under stirring. The dispersion was heated up to 90 °C and kept stirring at 90 °C until the EVOH is dissolved to produce the EVOH coating solution.

[0092] Example 4 - Application of EVOH-PAA and EVOH-PPA coating solutions

[0093] EVOH-PAA coating solution obtained from Example 1 was blade coated onto substrates at a wet thickness of 15 pm by using a bird applicator at a coating speed of 50 mm / second followed by air drying at room temperature and vacuum drying at 60°C. EVOH-PPA coating solution obtained from Example 2 was blade coated onto substrates at a wet thickness of 15 pm by using a bird applicator at a coating speed of 50 mm / second followed by air drying at room temperature and vacuum drying at 60°C.

[0094] EVOH coating solution obtained from Example 3 was blade coated onto substrates at a wet thickness of 15 pm by using a bird applicator at a coating speed of 50 mm / second followed by air drying at room temperature and vacuum drying at 60°C.

[0095] The different substrates that the coating solutions were coated onto are shown in Table 1 below. The “(EVOH-PAA)X4” coating composition refers to the EVOH-PAA coating solution obtained from Example 1 coated onto the substrate 4 times sequentially

[0096] Oxygen / water vapour transmission rate

[0097] After coating, the oxygen and water vapour permeability of the coated substrates were measured using Mocon OX-TRAN Model 2 / 21 and Mocon Permatran W 3 / 33 respectively. Oxygen permeability measurements were conducted at 23°C and 0% relative humidity in accordance with ASTM D3985 using sample testing area of 50cm2and sample thickness of 0.0254 mm (1 mil). Water vapour permeability measurements were conducted at 37.8°C and 90% relative humidity in accordance with ASTM F-1249 using sample testing area of 50cm2and sample thickness of 0.0254 mm (1 mil).

[0098] Table 1 shows typical oxygen transmission rate (OTR) and moisture transmission rate (WVTR) of various packaging control films with and without EVOEI based coating solution. EVOH coating without addition of acid (EVOH) was prepared as a control to show the contribution of adding polyacid and polymeric acid for enhancing the barrier of EVOH coating.

[0099] Table 1. OTR and WVTR of substrate films with and without EVOH or EVOH-PAA (or PPA) coating.

[0100]

[0101] In Table 1, MBOPP, PET, MCPE, CSPE and BY-Paper refer to metalized biaxially oriented polypropylene (obtained from Aegis Packaging Pte Ltd, Singapore), polyethylene terephthalate (obtained from Don Yee Enterprises (S) Pte Ltd, Singapore), metalized cast polyethylene (obtained from Aegis Packaging Pte Ltd, Singapore), cast polyethylene (obtained from Aegis Packaging Pte Ltd, Singapore) and plain paper (obtained from Yantai Boyuan Technology Materials Co., Ltd, China), respectively. As shown in Table 1, both OTR and WVTR of the substrate fdms decreased with EVOH coating and much more reduction was observed with EVOH based coating with addition of PAA or H3PO4 (EVOH-PAA or EVOH-PPA) Lowest WVTR was observed with MBOPP and MCPE coated with EVOH-PAA or EVOH-PPA. The MBOPP and MCPE coated with EVOH-PAA or EVOH-PP have the potential to replace laminated aluminium (Alu) film to preserve dried foods, where there is a high requirement for moisture barrier. Surface smoothness

[0102] SEM images of the top view of a BY-Paper without coating (Fig. la) and the BY-Paper with EVOH-PAA coating according to Table 1 (Fig. lb) were obtained. As shown in Fig. lb, the SEM image of the BY-Paper with the EVOH-PAA has enhanced smoothness compared to the BY-Paper without coating (Fig. la). The increased smoothness is beneficial to the gas barrier improvement.

[0103] Particle size

[0104] Fig. 2a is a SEM image of EVOH particles in EVOH coating solution of Example 3 and casted on a silicon wafer and Fig. 2b is a SEM image of EVOH-PAA particles in EVOH- PAA coating solution of Example 1 (PAA: Mn450k) and casted on a silicon wafer, where the silicon wafers were used to prepare the samples for SEM imaging. As shown in Fig. 2b, the addition of the PAA results in EVOH with smaller particle size, more uniform particle size distribution and without holes as compared to EVOH without the PAA (Fig. 2a).

[0105] Bond strength

[0106] Linear low-density polyethylene (LLDPE) film (obtained from Tobe Packaging Industries Pte Ltd, Singapore) was blade coated with a layer of adhesive (mixture of NC- 7109 and C A-27, obtained from COIM Asia Pacific Pte Ltd, Singapore) at a wet thickness of 15 pm by using a bird applicator at a coating speed of 50 mm / second and allowed to dry in an oven at 55°C for 5 mins. The LLDPE film was then laminated together with previously prepared coated substrates (indicated in Table 2 below) using a table-top laminator at room temperature.

[0107] Six pieces of uniformly cut laminated film samples with dimensions of 25mm wide and 250mm long for each of the coated substrate were preconditioned in a dry cabinet at 23°C and 50% RH (relative humidity) for at least 40 hours. The cut laminated film samples were then measured for their bond strength using Labthink XLW (PC) Auto tensile Tester at a pull speed of 300mm / min. Table 2. Average bond strength of laminated MBOPP / / LLDPE or PET / / LLDPE film with EVOH or EVOH-PAA coating (PAA: „ 800k).

[0108] As shown in Table 2, the bonding strength of laminated films with EVOH-PAA is higher than that of laminated film with EVOEI, demonstrating the contribution of addition of

[0109] PAA for enhancing the bonding strength of laminated films.

[0110] Industrial Applicability

[0111] The coating composition of the disclosure may be used to enhance gas or moisture barrier in a variety of applications such as food and beverage packaging, electronic packaging, cosmetic packaging and pharmaceutical packaging.

[0112] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

Claims1. A coating composition comprising a mixture of an ethylene vinyl alcohol (EVOH), an acid, water and an organic solvent, wherein the EVOH has an ethylene content of about 29 mol% to about 65 mol%, and wherein the acid comprises at least 2 acidic hydrogen atoms.

2. The coating composition of claim 1, wherein the acid is a polyacid, a polymeric acid or a mixture thereof, wherein the polymeric acid comprises repeating units comprising an acid functional group, wherein the acid functional group is carboxylic acid, phosphoric acid, sulfonic acid or a combination thereof.

3. The coating composition of claim 2, wherein the polymeric acid may be a homopolymer or copolymer of (meth)acrylic acid, methyl methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, cinnamic acid, 2 -methylmaleic acid, fumaric acid, itaconic acid, 2-methyl itaconic acid, a, P-methylene glutaric acid, vinyl phosphonic acid and styrene sulfonic acid.

4. The coating composition of claim 2 or 3, wherein the polymeric acid has a number average molecular weight in the range of about 500 g / mol to about 1,000,000 g / mol.

5. The coating composition of claim 2, wherein the polyacid is selected from the group consisting of phosphoric acid, citric acid, agaric acid, propane-1, 2, 3 -tricarboxylic acid, trimesic acid, nitrilotriacetic acid, boric acid and combinations thereof.

6. The coating composition of any one of claims 1-5, wherein the organic solvent is selected from the group consisting of a lower alcohol, tetrahydrofuran, 1,3-dioxane, acetonitrile, ethyl acetate, propyl acetate, acetone and combinations thereof.

7. A coated substrate, wherein the substrate is coated with the coating composition of any one of claims 1-6.

8. The coated substrate of claim 7, wherein the substrate is a polyolefin, polyester, polycarbonate, polyamide, cellulosic or a multilayer composite thereof.

9. The coated substate of claim 7 or 8, wherein the substrate is a metalized substrate.

10. A method of preparing a coating composition comprising the steps of: a) forming a solution of ethylene vinyl alcohol (EVOH) in a mixture of a first organic solvent and water, wherein the EVOH has an ethylene content of about 29 mol% to about 65 mol%; and b) adding an acid to the solution, wherein the acid comprises at least 2 acidic hydrogen atoms.

11. The method of claim 10, further comprising prior to step b), dissolving the acid into a mixture of a second organic solvent and water.

12. A method of reducing transmission rate of a substrate, comprising the step of coating a substrate with the coating composition of any one of claims 1-6.

13. A method of reducing transmission rate of an ethylene vinyl alcohol (EVOH) coating composition, comprising adding an acid to an EVOH coating composition, wherein the acid comprises at least 2 acidic hydrogen atoms, and wherein the EVOH coating composition comprises a mixture of EVOH having an ethylene content of about 29 mol% to about 65 mol%, water and an organic solvent.14 The method of claim 1 or 13, wherein the transmission of gas, moisture of a combination thereof is reduced.

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