WO2019092454A1

WO2019092454A1 - Coating method and product thereof

Info

Publication number: WO2019092454A1
Application number: PCT/GB2018/053282
Authority: WO
Inventors: Dermot O'hare; Kanittika RUENGKAJORN
Original assignee: Scg Chemicals Co., Ltd.; Scg Packaging Public Company Limited
Priority date: 2017-11-13
Filing date: 2018-11-13
Publication date: 2019-05-16
Also published as: GB201718722D0

Abstract

A process for the preparation of a coated substrate is described, in which a substrate is coated with a coating mixture containing a polymer and a layered double hydroxide, the layered double hydroxide having been derived from a layered double oxide. The process of the invention is markedly simpler than conventional techniques for affording coated substrates having reduced permeability to degradative gases. The coated substrates obtainable by the process are particularly useful in packaging applications, notably in the food industry.

Description

COATING METHOD AND PRODUCT THEREOF

INTRODUCTION

[0001] The present invention relates to a process for the preparation of a coated substrate, as well as to coated substrates obtainable by the process and their uses in packaging applications. The present invention also relates to a process for the preparation of a coating mixture suitable for use in coating applications, as well as to coating mixtures obtainable by such a process. More specifically, the present invention relates to a process for the preparation of a coated substrate comprising an LDH-containing coating.

BACKGROUND OF THE INVENTION

[0002] Polymer films have been widely applied as packaging materials (e.g. in the food industry) due to their light weight, low cost and good processability (T. Pan, S. Xu, Y. Dou, X. Liu, Z. Li, J. Han, H. Yan and M. Wei, J. Mater. Chem. A, 2015, 3, 12350-12356). However, the effectiveness of polymer packaging materials in preventing product degradation depends on their impermeability to degradative gases such as oxygen (Y. Dou, S. Xu, X. Liu, J. Han, H. Yan, M. Wei, D. G. Evans and X. Duan, Adv. Fund. Mater, 2014, 24, 514-521) and water vapour.

[0003] In an endeavour to reduce the gas permeability of polymeric films used in packaging applications, inorganic materials have been incorporated directly into the polymeric films themselves (e.g. as fillers), or have been applied to the surface of such polymeric films (e.g. as a coating). Clays (such as montmorillonite) have been considered promising candidate materials for reducing the gas permeability of polymeric films. However, these materials suffer from the fact that they are naturally-occurring, and as such may be heavily contaminated with potentially harmful substances (e.g. heavy metals), thereby hampering their use in food packaging.

[0004] Aside from clays, layered-double hydroxides (LDHs) have been recognised as potentially useful materials for reducing the gas permeability of polymeric films. However, to date, research in the area of LDH coatings on polymeric films has focussed on the preparation of a complex "brick-mortar" structure obtained via layer-by-layer (LbL) assembly of LDH nanoplatelets and polymer on the film, in which a highly-ordered stack of alternating layers of LDH (brick) and polymer (mortar) is prepared by a series of alternating spin or dip coating steps using i) an LDH dispersion, and ii) a polymer solution. These assemblies have been rendered even more complex by infilling voids with CO2 (to give a "brick-mortar-sand" structure) in an endeavour to further reduce the oxygen transmission rate (OTR) of the polymeric film. However, the elaborate and complex nature of such LbL techniques restricts their implementation on an industrial scale.

[0005] In spite of the advances made by the prior art, there remains a need for improved means for reducing the gas permeability of polymeric films. In particular, there remains a need for an overall simpler coating technique allowing for the preparation of coated polymeric films having acceptable OTR and/or water-vapour transmission rate (WVTR) properties.

[0006] The present invention was devised with the foregoing in mind.

SUMMARY OF THE INVENTION

[0007] According to a first aspect of the present invention there is provided a process for the preparation of a coated substrate, the process comprising the steps of:

a) providing a coating mixture comprising a layered double hydroxide, a polymer and a solvent, the coating mixture obtainable by mixing at least the following: i. a layered double oxide,

ii. a polymer, and

iii. a solvent for the polymer;

b) applying a layer of the coating mixture to a first substrate to provide a coated first substrate; and

c) drying the coated first substrate.

[0008] According to a second aspect of the present invention there is provided a coated substrate obtainable, obtained or directly obtained by the process according to the first aspect.

[0009] According to a third aspect of the present invention there is provided a coated substrate comprising:

a) a first substrate; and

b) a coating layer provided on a least one surface of the first substrate, wherein the coating layer comprises 1-70 wt% of layered double hydroxide dispersed throughout a polymeric matrix.

[0010] According to a fourth aspect of the present invention there is provided a process for the preparation of a coating mixture suitable for use in a coating application, the coating mixture comprising a layered double hydroxide, a polymer and a solvent for the polymer, the process comprising the step of:

a) mixing at least the following: i. a layered double oxide,

ii. a polymer, and

iii. a solvent for the polymer.

Suitably, the coating mixture is suitable for use in food packaging.

[0011] According to a fifth aspect of the present invention there is provided a coating mixture obtainable, obtained or directly obtained by the process according to the fourth aspect.

According to a sixth aspect of the present invention there is provided a coating mixture comprising a layered double hydroxide, a polymer and a solvent for the polymer. Suitably, the coating mixture is suitable for use in food packaging.

[0012] According to a seventh aspect of the present invention there is provided a use of a coating mixture according to the fifth or sixth aspect in the formation of a coating on a substrate.

[0013] According to an eighth aspect of the present invention there is provided a use of a coated substrate according to the second or third aspect in packaging.

[0014] According to a ninth aspect of the present invention there is provided packaging comprising a coated substrate according to the second or third aspect.

DETAILED DESCRIPTION OF THE INVENTION

Preparation of coated substrates

[0015] According to a first aspect of the present invention there is provided a process for the preparation of a coated substrate, the process comprising the steps of:

a) providing a coating mixture comprising a layered double hydroxide, a polymer and a solvent, the coating mixture obtainable by mixing at least the following:

i. a layered double oxide,

ii. a polymer, and

iii. a solvent for the polymer;

c) drying the coated first substrate.

[0016] The process of the invention provides a number of advantages over conventional techniques for reducing the gas permeability characteristics of polymeric films. When compared with techniques employing the use of an inorganic filler in the film itself, the present invention is advantageous in that it allows various different substrates to be coated with the same coating mixture. Hence, it not necessary for each substrate (e.g. PET, PU, PE) to be purpose-made with the inclusion of an inorganic filler.

[0017] The use of LDH in the process of the invention also presents numerous advantages over prior art techniques employing clays. In contrast to clays (e.g. montmorillonite), LDHs are entirely synthetic materials, the composition, structure and morphology of which is wholly governed by the manner in which they are prepared. As a consequence, the replacement of clays with LDHs in coated substrates for packaging applications considerably reduces - if not eliminates - the risk posed by potentially harmful contaminants (such as heavy metals), which present clear advantages for the food industry.

[0018] The process of the invention also presents a number of advantages over conventional LbL assembly techniques. As discussed hereinbefore, LbL techniques have been used to prepare complex "brick-mortar" structures, containing a highly-ordered stack of alternating layers of LDH (brick) and polymer (mortar) which is grown directly on a substrate by a series of alternating spin or dip coating steps using i) an LDH dispersion, and ii) a polymer solution, or is assembled separate from the substrate prior to being transferred onto it. In contrast to this approach, the present invention provides a considerably simpler technique for achieving coated polymeric substrates having acceptable OTR and/or WVTR properties. In particular, in the present process, both the LDH and the polymer are simultaneously applied to the substrate in a single step, whereas LbL processes require successive alternating separate steps for applying the LDH and polymer. This necessarily facilitates up-scaling of the present process, the coating mixture of which can be applied to the substrate from a single vessel in a production line in a single application step. Moreover, the present process provides a greater degree of flexibility in the manner in which the coating mixture may be applied to the substrate on an industrial scale. As a non-limiting example, the present process may be implemented using a roller-and-bath apparatus, in which the coating mixture is licked onto a roller being in contact with a bath, and is then transferred onto a substrate also being in contact with the roller, thereby allowing vast quantities of substrate to be continuously coated in a short period of time. Such cost-effective techniques are entirely incompatible with LbL techniques, the complex structures of which can only be achieved by sequential alternating dip or spray coating techniques.

[0019] Yet a further advantage of the present process is that the LDH contained within the coating mixture has improved morphological properties when compared with LDHs employed in prior art techniques. In particular, the coating mixtures used in the present process are those that are obtainable by a process in which a layered double oxide (LDO) is mixed with the other components of the coating mixture (e.g. a polymer and a solvent for the polymer). Upon contacting the solvent (e.g. water) of the coating mixture with the LDO in air, the LDO is converted (e.g. reconstructed) into an LDH. Without wishing to be bound by theory, it is believed that the presence of the other components of the coating mixture (e.g. the polymer) during the reconstruction of the LDH from the LDO gives rise to an LDH having advantageous morphological properties. In particular, when compared with the LDH contained in coating mixtures that are formed by mixing LDH directly with the other components of the mixture, coating mixtures derived from LDO may contain LDH platelets having an improved aspect ratio. The aspect ratio of the LDH platelets is seen as an important factor in the formation of coatings having a sufficiently tortuous pathway to reduce the transmission of gases and vapours (e.g. O2 and H₂0).

[0020] Yet a further advantage of the presence process is that the use of an LDO-derived LDH considerably reduces the possibility of the LDH being contaminated with harmful organic products. For example, urea, which is commonly used in LDH manufacturing processes to improve the aspect ratio of LDH platelets, is known to be toxic, thus presenting considerations for manufacturers of food packaging. However, the present inventors have now surprisingly found that high aspect ratio LDH platelets can be prepared by reforming (e.g. reconstructing) an LDH from the corresponding LDO, even when the precursor LDH was of a low aspect ratio prepared by a non-urea containing synthesis (e.g. simple coprecipitation). Even if the precursor LDH is prepared by a urea-containing synthesis, thermally treating the LDH (e.g. at 260-550°C) to yield the corresponding LDO will mean that any residual urea present within the LDH is removed, meaning that the LDH that is subsequently reformed from the LDO (e.g. by reconstruction) is free from urea.

[0021] The actual manufacturing steps for preparing the coating mixture need not necessarily be performed as part of the overall process for the preparation of a coated substrate, provided that the coating mixture is obtainable by mixing at least the LDO, the polymer and the solvent for the polymer.

[0022] In an embodiment, the coating mixture may be prepared as part of the overall process for the preparation of a coated substrate, in which case step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) providing a mixture of the solvent and the polymer; and

a-iii) mixing the layered double oxide and the mixture of the solvent and the polymer to form the coating mixture.

[0023] Alternatively, step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) mixing the layered double oxide with the solvent; and a-iii) mixing the mixture formed in step a-ii) with a mixture of the polymer and solvent to form the coating mixture.

[0024] Suitably, where the coating mixture is prepared as part of the overall process for the preparation of a coated substrate, step a-iii) is conducted at a temperature of 15-90°C.

[0025] In an embodiment, the combined quantity of the LDH and polymer in the coating mixture is 2.5-12.0% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 2.5-10% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 2.5-7.5% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 3-7% by weight relative to the total weight of the coating mixture. More suitably, the combined quantity of the LDH and polymer in the coating mixture is 3.5-6.5% by weight relative to the total weight of the coating mixture. Yet more suitably, the combined quantity of the LDH and polymer in the coating mixture is 4-6% by weight relative to the total weight of the coating mixture.

[0026] In an embodiment, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :6 to 2: 1. Suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :5 to 1.5: 1. More suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :5 to 1.2: 1. Most suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :4 to 1.1 : 1.

[0027] In an embodiment, the layered double hydroxide present within the coating mixture is substantially free from organic compounds used in the preparation of layered double hydroxides.

[0028] In an embodiment, the layered double hydroxide present within the coating mixture is substantially free from toxic organic compounds (e.g. urea).

[0029] In an embodiment, the layered double hydroxide present within the coating mixture is free from urea. Hence, the coated substrate is free from urea.

[0030] In an embodiment, the polymer is a water-soluble polymer. Suitably, the water-soluble polymer is one or more polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA). More suitably, the water-soluble polymer is polyvinyl alcohol) (PVOH). Alternatively, the polymer is a water-based polymer. The term water-based polymer will be familiar to one of ordinary skill in the art, and is used to denote a polymer that may not be water-soluble, but which has been functionalised to render it readily dispersible in water. Water-based polymers include water-based polyurethane and water-based polyacrylate.

[0031] In a particularly suitable embodiment, the polymer is crosslinked PVOH

[0032] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 150,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 60,000 Da. More suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 27,000 to 40,000 Da.

[0033] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 40,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 170,000 to 210,000 Da.

[0034] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 70 to 100 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 99 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 95 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 83 to 92 mol%. More suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 85 to 90 mol%.

[0035] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 60,000 Da and a degree of hydrolysis of 83 to 92 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 27,000 to 40,000 Da and a degree of hydrolysis of 85 to 90 mol%.

[0036] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 40,000 to 220,000 Da and a degree of hydrolysis of 80 to 99 mol%.

[0037] In an embodiment, the solvent is water. Additional solvents may or may not be present. Suitably, >95 vol.% of the solvent is water

[0038] In an embodiment, the coating mixture has a viscosity at 25°C of 1 to 1000 cP.

[0039] In an embodiment, the coating mixture is obtainable by mixing at least the following:

i. the layered double oxide,

ii. the polymer,

iii. the solvent for the polymer, and either or both of

a. a source of an inorganic oxyanion (e.g. a salt), and b. a polymer crosslinking agent (e.g. a crosslinking agent suitable for crosslinking PVOH, such as trisodium trimetaphosphate)

[0040] Suitable inorganic oxyanions include carbonates, bicarbonates, hydrogenphosphates, dihydrogenphosphates, nitrites, borates, nitrates, phosphates and sulphates.

[0041] Coating mixtures prepared in accordance with the present invention allows for a greater degree of control over the composition of the coating mixture. Coating mixtures used in the prior art have been prepared by blending together polymerisable acrylic monomers, other polymers and inorganic materials (e.g. clays) in the presence of a solvent and then conducting radical polymerisation of the resulting blend under elevated temperature to yield the polymeric coating mixture. As a consequence, coating mixtures prepared by such in-situ polymerisation techniques are likely to contain a variety of polymeric products, each having different properties (e.g. molecular weight). This necessarily makes it different to prepare multiple batches of coating mixture to the exact same specification. In contrast to this approach, the coating mixtures of the present process can be prepared by mixing together predetermined quantities of i) an LDO, ii) a polymer, and iii) a solvent for the polymer. The resulting polymeric solution therefore has pre-determined properties (e.g. viscosity). The present process also eliminates the risk of generating potentially unwanted (or harmful) side products by uncontrolled radical polymerisation of a complex blend of ingredients.

[0042] The first substrate is suitably sheet-like. Suitably, the first substrate has a thickness of 1 - 30 μηι. More suitably, the first substrate has a thickness of 5 - 20 μηι.

[0043] In an embodiment, the first substrate is selected from polyethylene terephthalate (PET), polyethylene (PE), biaxiaily oriented polypropylene film (BOPP), polypropylene (PP), polyvinyl dichloride (PVDC), polyamide, nylon, and polylactic acid (PLA). Suitably, the first substrate is PET. In a particularly suitably embodiment, the first substrate is PET having a thickness of 5 - 20 μι ι.

[0044] In an embodiment, the LDH contained within the coating mixture is a Zn/AI, Mg/AI, Ca/AI or Zn, Mg/AI LDH. Suitably, the LDH contained within the coating mixture is a carbonate- containing LDH.

[0045] In an embodiment, the LDH contained within the coating mixture is a Mg/AI LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): 1.

[0046] In an embodiment, the LDH contained within the coating mixture is a carbonate- containing LDH. [0047] In an embodiment, the LDH contained within the coating mixture is a nitrate-containing LDH.

[0048] In an embodiment, the LDH contained within the coating mixture is a magnesium aluminium carbonate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5):1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): !

[0049] In an embodiment, the LDH contained within the coating mixture is a magnesium aluminium nitrate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): 1.

[0050] In an embodiment, the aspect ratio of the layered double hydroxide contained within the coating mixture is 10-500, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet. Suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is greater than 85. More suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is 90-400. More suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is 100-300.

[0051] In an embodiment, the layered double oxide has BET surface area of > 10 m²/g. Suitably, the layered double oxide has BET surface area of > 100 m²/g. More suitably, the layered double oxide has BET surface area of 100-500 m²/g.

[0052] In an embodiment, the layered double oxide has total pore volume of > 0.4 cm³/g. Suitably, the layered double oxide has total pore volume of 0.4-2.0 cm³/g.

[0053] Step b) of the present process may be performed by various different techniques.

[0054] In one embodiment, the coating mixture may be applied to the substrate in step b) by spraying, dip coating or spin coating.

[0055] Alternatively, the coating mixture may be applied to the substrate in step b) using a bath-and-roller assembly. Such assemblies will be understood to comprise a rotating roller being in partial contact with a bath containing a coating mixture. As the roller rotates, the coating mixture coats the surface of the roller, and is transferred onto a substrate passing over the surface of the roller. Additional rollers may be present to meter the quantity of coating mixture applied to the substrate, or to remove excess coating mixture. Such assemblies may additionally comprise a Mayer rod, or other means, to ensure uniform distribution of the coating mixture across the surface of the substrate.

[0056] In an embodiment, the coating mixture is applied to the substrate in step b) at a thickness of 50 nm - 2.5 μηι. Suitably, the coating mixture is applied to the substrate in step b) at a thickness of 100 nm - 1.8 μηι. [0057] The coated substrate prepared by the process of the invention may have a laminated structure. In such cases, after step b) and prior to step c), the coated first substrate is contacted with a second substrate, such that the layer of coating mixture is provided between the first and second substrates. In such an embodiment, the wet coating mixture serves as an adhesive to adhere the second substrate to the first substrate.

[0058] Alternatively, a laminated structure may be achieved by using a separate, dedicated adhesive layer. Hence, the process may further comprise the steps of:

d) applying a layer of adhesive to the dried coated first substrate resulting from step c), such that the layer of adhesive is provided on top of the layer applied during step b); and

e) contacting the layer of adhesive applied in step d) with a second substrate.

[0059] The second substrate is suitably sheet-like. The second substrate may be selected from polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyamide, nylon, polylactic acid (PLA) and polyvinyl dichloride (PVDC). The second substrate and the first substrate may be the same or different.

[0060] The adhesive may be selected from cellulose acetate, polyvinyl alcohol) (PVOH), polyvinyl acetate, polyvinyl dichloride (PVDC), polyurethane, an acrylic-based adhesive, an epoxy resin and mixtures thereof. Alternatively, the adhesive may be a copolymer based on one or the aforementioned polymers and one or more additional comonomers, such as ethylene (e.g. polyethylene vinyl alcohol). Suitably, the adhesive is food-grade. Suitably, the adhesive may also comprise a curing agent.

[0061] In an embodiment, the adhesive may be a polyurethane and/or acrylic-based adhesive.

[0062] In an embodiment, the process comprises a step d') of coating the dried layer of coating mixture resulting from step c) with a further layer of coating mixture, and then drying the further layer of coating mixture. Step d') may be repeated multiple times to afford a substrate containing a plurality of individually coated layers. It will be appreciated that each coating layer may be the same or different.

[0063] As used herein, the term "layered double oxide" will be understood to denote a semi- amorphous mixed metal oxide obtainable by thermally treating a precursor layered double hydroxide at a temperature of 260-550°C. Due to the "memory effect", LDOs obtainable by thermally treating a precursor layered double hydroxide at such a temperature will reform the layered double hydroxide structure upon addition of water and an anion. The precursor LDH will be understood as being that which is, once thermally treated at the specific temperature, yields a LDO. Suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 290-525°C. More suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 310-500°C. Most suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 325-475°C.

[0064] In an embodiment, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 1-48 hours. Suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 4-24 hours. More suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 6-18 hours.

[0065] In an embodiment, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide in air.

[0066] In an embodiment, the precursor layered double hydroxide and/or the layered double hydroxide contained within the coating mixture has a structure according to formula (I) shown below:

[M^z+ ₁.xM'y⁺x(OH)₂]^a+(X'¹-)_m 0H20 c(solv)

(I)

wherein

M is a charged metal cation;

M' is a charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<6≤10;

0≤c≤10;

X is an anion;

n is the charge on anion X;

a is equal to z(1-x)+xy-2;

m≥ a/n; and

solv denotes an organic solvent capable of hydrogen-bonding to water.

[0067] In an embodiment, when z is 2, M is Mg, Zn, Fe, Ca, or a mixture of two or more of these, or when z is 1 , M is Li. Suitably, z is 2 and M is Ca, Mg, Zn or Fe. More suitably, z is 2 and M is Ca, Mg or Zn.

[0068] In an embodiment, when y is 3, M' is Al, Fe, Ti, or a mixture thereof, or when y is 4, M' is Ti. Suitably, y is 3. More suitably, y is 3 and M' is Al. [0069] In an embodiment, I is Al.

[0070] In an embodiment, 0<c≤10.

[0071] In an embodiment, X is at least one anion selected from the group consisting of a halide (e.g., chloride) and an inorganic oxyanion (e.g. X'_mOn(OH)p^"i?, in which m = 1-5; n = 2-10; p = 0-4, q = 1-5; X' = B, C, N, S, P; such as carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate, hydroxide, silicate). Suitably, X is at least one anion selected from the group consisting of carbonate, bicarbonate, nitrate and nitrite. Most suitably, X is carbonate.

[0072] In an embodiment, x has a value according to the expression 0.18<x<0.9. Suitably, x has a value according to the expression 0.18<x<0.5. More suitably, x has a value according to the expression 0.18<x<0.4.

[0073] In an embodiment, the precursor LDH and/or the LDH contained within the coating mixture is a flower-like layered double hydroxide or a platelet-like layered double hydroxide. The term flower-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a co-precipitation technique. The term platelet-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a urea-hydrothermal technique.

[0074] In an embodiment, the precursor LDH is a Zn/AI, Mg/AI, Ca/AI or Zn,Mg/AI LDH. Suitably, the precursor LDH is a Mg/AI LDH.

Coated substrates

[0075] According to a second aspect of the present invention, there is provided a coated substrate obtainable by a process according to the first aspect.

[0076] According to a third aspect of the present invention, there is provided a coated substrate comprising:

a) a first substrate; and

[0077] The coated substrates of the invention have improved oxygen transmission rate (OTR) properties with respect to prior art films. In an embodiment, the OTR of the coated substrate is less than 15 cc/m²/day/atm. Suitably, the OTR of the coated substrate is less than 10 cc/m²/day/atm, such as less than 5 cc/m²/day/atm. More suitably, the OTR of the coated substrate is less than 1 cc/m2/day/atm, such as less than 0.5 cc/m²/day/atm. [0078] It will be understood that the coated substrates of the invention are distinguished from LbL-prepared films by virtue of the fact that they do not contain a plurality of alternating layers of polymer and LDH. Rather, the coated substrates of the invention contain a single layer of LDH dispersed throughout a polymeric matrix. The LDH may be randomly dispersed throughout the polymeric matrix.

[0079] In an embodiment, the layered double hydroxide is substantially free from organic compounds used in the preparation of layered double hydroxides.

[0080] In an embodiment, the layered double hydroxide is substantially free from toxic organic compounds (e.g. urea). Hence, the coated substrate is substantially free from toxic organic compounds (e.g. urea).

[0081] In an embodiment, the layered double hydroxide is free from urea. Hence, the coated substrate is free from urea.

[0082] In an embodiment, the layered double hydroxide is randomly dispersed throughout the polymeric matrix.

[0083] In an embodiment, the weight ratio of layered double hydroxide to polymer in the coating layer ranges from 1 :6 to 2: 1. Suitably, the weight ratio of layered double hydroxide to polymer in the coating layer ranges from 1 :5 to 1.5: 1. More suitably, the weight ratio of layered double hydroxide to polymer in the coating layer ranges from 1 :5 to 1.2: 1. Most suitably, the weight ratio of layered double hydroxide to polymer in the coating layer ranges from 1 :4 to 1.1 : 1.

[0084] In an embodiment, the polymeric matrix comprises a water-soluble polymer. Suitably, the water-soluble polymer is one or more polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA). More suitably, the water-soluble polymer is polyvinyl alcohol) (PVOH). Alternatively, the polymeric matrix comprises a water-based polymer. The term water-based polymer will be familiar to one of ordinary skill in the art, and is used to denote a polymer that may not be water-soluble, but which has been functionalised to render it readily dispersible in water. Water- based polymers include water-based polyurethane and water-based polyacrylate.

[0085] In a particularly suitable embodiment, the polymer is crosslinked PVOH.

[0086] In an embodiment, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 150,000 Da. Suitably, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 60,000 Da. More suitably, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 27,000 to 40,000 Da.

[0087] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 40,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 170,000 to 210,000 Da.

[0088] In an embodiment, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 70 to 100 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 99 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 95 mol%. Suitably, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 83 to 92 mol%. More suitably, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 85 to 90 mol%.

[0089] In an embodiment, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 60,000 Da and a degree of hydrolysis of 83 to 92 mol%. Suitably, the polymeric matrix comprises polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 27,000 to 40,000 Da and a degree of hydrolysis of 85 to 90 mol%.

[0090] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 40,000 to 220,000 Da and a degree of hydrolysis of 80 to 99 mol%.

[0091] In an embodiment, the coating layer comprises 5-70 wt% of layered double hydroxide. Suitably, the coating layer comprises 10-70 wt% of layered double hydroxide. More suitably, the coating layer comprises 10-60 wt% of layered double hydroxide Suitably, the coating layer comprises 20-50 wt% of layered double hydroxide. Alternatively, the coating layer comprises 50-70 wt% of layered double hydroxide.

[0092] The first substrate is suitably sheet-like. Suitably, the first substrate has a thickness of 1 - 30 μηι. More suitably, the first substrate has a thickness of 5 - 20 μηι.

[0093] In an embodiment, the first substrate is selected from polyethylene terephthalate (PET), polyethylene (PE), biaxiaily oriented polypropylene film (BOPP), polypropylene (PP), polyvinyl dichloride (PVDC), polyamide, nylon, and polylactic acid (PLA). Suitably, the first substrate is PET.

[0094] In a particularly suitably embodiment, the first substrate is PET having a thickness of 5 - 20 μηι.

[0095] In an embodiment, the LDH is a Zn/AI, Mg/AI, Ca/AI or Zn,Mg/AI LDH. Suitably, the LDH is a carbonate-containing LDH. [0096] In an embodiment, the LDH is a Mg/AI LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): 1.

[0097] In an embodiment, the LDH is a carbonate-containing LDH.

[0098] In an embodiment, the LDH is a nitrate-containing LDH.

[0099] In an embodiment, LDH contained within the coating layer is a magnesium aluminium carbonate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25):1.

[00100] In an embodiment, the LDH contained within the coating layer is a magnesium aluminium nitrate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): 1.

[00101] In an embodiment, the aspect ratio of the layered double hydroxide is 10-500, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet. Suitably, the aspect ratio of the layered double hydroxide is greater than 85. More suitably, the aspect ratio of the layered double hydroxide is 90-400. More suitably, the aspect ratio of the layered double hydroxide is 100-300.

[00102] In an embodiment, the coating layer comprises a magnesium aluminium carbonate layered double hydroxide dispersed throughout a polymeric matrix comprising polyvinyl alcohol) (PVOH). Suitably, the aspect ratio of the layered double hydroxide is greater than 85 and the OTR of the coating layer is less than 10 cc/m²/day/atm. More suitably, the aspect ratio of the layered double hydroxide is greater than 100 and the OTR of the coating layer is less than 1 cc/m²/day/atm, such as less than 0.5 cc/m²/day/atm.

[00103] In an embodiment, the layered double hydroxide has a structure according to formula (I) shown below:

[M^z+ ₁.xM'y⁺x(OH)₂]^a+(X'¹-)_m 0H20 c(solv)

(I) wherein

M is a charged metal cation;

M' is a charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<6≤10; 0≤c≤10;

X is an anion;

n is the charge on anion X;

a is equal to z(1-x)+xy-2;

m≥ a/n; and

solv denotes an organic solvent capable of hydrogen-bonding to water.

[00104] In an embodiment, when z is 2, M is Mg, Zn, Fe, Ca, or a mixture of two or more of these, or when z is 1 , M is Li. Suitably, z is 2 and M is Ca, Mg, Zn or Fe. More suitably, z is 2 and M is Ca, Mg or Zn.

[00105] In an embodiment, when y is 3, M' is Al, Fe, Ti, or a mixture thereof, or when y is 4, M' is Ti. Suitably, y is 3. More suitably, y is 3 and M' is Al.

[00106] In an embodiment, M' is Al.

[00107] In an embodiment, 0<c≤10.

[00108] In an embodiment, X is at least one anion selected from the group consisting of a halide (e.g., chloride) and an inorganic oxyanion (e.g. X'_mO_n(O )p~^q, in which m = 1-5; n = 2- 10; p = 0-4, q = 1-5; X' = B, C, N, S, P; such as carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate, hydroxide, silicate). Suitably, X is at least one anion selected from the group consisting of carbonate, bicarbonate, nitrate and nitrite. Most suitably, X is carbonate.

[00109] In an embodiment, x has a value according to the expression 0.18<x<0.9. Suitably, x has a value according to the expression 0.18<x<0.5. More suitably, x has a value according to the expression 0.18<x<0.4.

[00110] In an embodiment, the layered double hydroxide is a flower-like layered double hydroxide or a platelet-like layered double hydroxide. The term flower-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a co- precipitation technique. The term platelet-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a urea-hydrothermal technique.

[00111] In another embodiment, the coating layer has a thickness of 0.1 -10 μηι (e.g. 1-10 μηι).

[00112] In an embodiment, the coating layer has a thickness of 50 nm - 2.5 μηι. Suitably, the coating layer has a thickness of 100 nm - 1.8 μηι. [00113] In an embodiment, the coated substrate comprises multiple coating layers. Suitably, the coated substrate comprises 1-10 individually coated layers. Suitably, the coated substrate comprises 1-4 individually coated layers.

[00114] In another embodiment, the coating layer comprises:

a) 5-70 wt% of layered double hydroxide;

b) 30-95 wt% of polymeric matrix; and

c) 0-2 wt% of solvent (e.g. water).

[00115] In another embodiment, the coating layer comprises:

a) 10-60 wt% of layered double hydroxide;

b) 40-90 wt% of polyvinyl alcohol); and

c) 0-2 wt% of water.

[00116] The coated substrate may have a laminated structure. Hence, in one embodiment, the substrate is a first substrate, and the coated substrate comprises a second substrate disposed on top of the coating layer, such that the coating layer is located between the first and second substrates. In such embodiments, the coating layer serves as an adhesive to adhere the second substrate to the first substrate.

[00117] Alternatively, the coated substrate comprises a layer of adhesive provided between the coating layer and the second substrate. In such embodiments, a dedicated adhesive layer adheres the second substrate to the coated first substrate. The adhesive may be a polyurethane and/or acrylic-based adhesive.

Preparation of coating mixtures

[00118] According to a fourth aspect of the present invention, there is provided a process for the preparation of a coating mixture suitable for use in a coating application, the coating mixture comprising a layered double hydroxide, a polymer and a solvent for the polymer, the process comprising the step of:

a) mixing at least the following:

a layered double oxide,

a polymer, and

a solvent for the polymer.

[00119] The coating mixtures prepared in accordance with the fourth aspect of the invention are useable in accordance with the first aspect of the invention. The numerous advantages discussed hereinbefore in connection with the first aspect of the invention are thereby equally applicable to the fourth aspect of the invention.

[00120] Of particular note is that the LDH contained within the coating mixture has improved morphological properties when compared with LDHs employed in prior art techniques. The coating mixtures are those that are obtainable by a process in which a layered double oxide (LDO) is mixed with the other components of the coating mixture (e.g. a polymer and a solvent for the polymer). Upon contacting the solvent (e.g. water) of the coating mixture with the LDO in air, the LDO is converted (e.g. reconstructed) into an LDH. Without wishing to be bound by theory, it is believed that the presence of the other components of the coating mixture (e.g. the polymer) during the reformation of the LDH from the LDO gives rise to an LDH having advantageous morphological properties. In particular, when compared with the LDH contained in coating mixtures that have been formed by mixing LDH directly with the other components of the mixture, coating mixtures derived from LDO may contain LDH platelets having an improved aspect ratio. The aspect ratio of the LDH platelets is seen as an important factor in the formation of coatings having a sufficiently tortuous pathway to reduce the transmission of gases and vapours (e.g. O2 and H2O).

[00121] In an embodiment, step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) providing a mixture of the solvent and the polymer; and

[00122] Alternatively, step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) mixing the layered double oxide with the solvent; and

a-iii) mixing the mixture formed in step a-ii) with a mixture of the polymer and solvent to form the coating mixture.

[00123] Suitably, step a-iii) is conducted at a temperature of 15-90°C.

[00124] In an embodiment, the combined quantity of the LDH and polymer in the coating mixture is 2.5-10.0% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 2.5-7.5% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 3-7% by weight relative to the total weight of the coating mixture. More suitably, the combined quantity of the LDH and polymer in the coating mixture is 3.5-6.5% by weight relative to the total weight of the coating mixture. Yet more suitably, the combined quantity of the LDH and polymer in the coating mixture is 4-6% by weight relative to the total weight of the coating mixture.

[00125] In an embodiment, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :6 to 2: 1. Suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :5 to 1.5: 1. More suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :5 to 1.2: 1. Most suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :4 to 1.1 : 1.

[00126] In an embodiment, the layered double hydroxide present within the coating mixture is substantially free from organic compounds used in the preparation of layered double hydroxides.

[00127] In an embodiment, the layered double hydroxide present within the coating mixture is substantially free from toxic organic compounds (e.g. urea).

[00128] In an embodiment, the layered double hydroxide present within the coating mixture is free from urea. Hence, the coated substrate is free from urea.

[00129] In an embodiment, the polymer is a water-soluble polymer. Suitably, the water-soluble polymer is one or more polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA). More suitably, the water-soluble polymer is polyvinyl alcohol) (PVOH). Alternatively, the polymer is a water-based polymer. The term water-based polymer will be familiar to one of ordinary skill in the art, and is used to denote a polymer that may not be water-soluble, but which has been functionalised to render it readily dispersible in water. Water-based polymers include water-based polyurethane and water-based polyacrylate.

[00130] In a particularly suitable embodiment, the polymer is crosslinked PVOH.

[00131] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 150,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 60,000 Da. More suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 27,000 to 40,000 Da.

[00132] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 40,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 170,000 to 210,000 Da. [00133] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 70 to 100 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 99 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 95 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 83 to 92 mol%. More suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 85 to 90 mol%.

[00134] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 60,000 Da and a degree of hydrolysis of 83 to 92 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 27,000 to 40,000 Da and a degree of hydrolysis of 85 to 90 mol%.

[00135] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 40,000 to 220,000 Da and a degree of hydrolysis of 80 to 99 mol%.

[00136] In an embodiment, the solvent is water. Additional solvents may or may not be present. Suitably, >95 vol.% of the solvent is water.

[00137] In an embodiment, the coating mixture has a viscosity at 25°C of 1 to 1000 cP.

[00138] In an embodiment, step a) comprises mixing at least the following:

i. the layered double oxide,

ii. the polymer,

iii. the solvent for the polymer, and either or both of

a. a source of an inorganic oxyanion (e.g. a salt), and

b. a polymer crosslinking agent (e.g. a crosslinking agent suitable for crosslinking PVOH, such as trisodium trimetaphosphate).

[00139] Suitable inorganic oxyanions include carbonates, bicarbonates, hydrogenphosphates, dihydrogenphosphates, nitrites, borates, nitrates, phosphates and sulphates.

[00140] Coating mixtures prepared in accordance with the present invention allows for a greater degree of control over the composition of the coating mixture. Coating mixtures used in the prior art have been prepared by blending together polymerisable acrylic monomers, other polymers and inorganic materials (e.g. clays) in the presence of a solvent and then conducting radical polymerisation of the resulting blend under elevated temperature to yield the polymeric coating mixture. As a consequence, coating mixtures prepared by such in-situ polymerisation techniques are likely to contain a variety of polymeric products, each having different properties (e.g. molecular weight). This necessarily makes it different to prepare multiple batches of coating mixture to the exact same specification. In contrast to this approach, the coating mixtures of the present process can be prepared by mixing together predetermined quantities of i) an LDO, ii) a polymer, and iii) a solvent for the polymer. The resulting polymeric solution therefore has pre-determined properties (e.g. viscosity). The present process also eliminates the risk of generating potentially unwanted (or harmful) side products by uncontrolled radical polymerisation of a complex blend of ingredients.

[00141] In an embodiment, the LDH contained within the coating mixture is a Zn/AI, Mg/AI, Ca/AI or Zn, Mg/AI LDH. Suitably, the LDH contained within the coating mixture is a carbonate- containing LDH.

[00142] In an embodiment, the LDH contained within the coating mixture is a Mg/AI LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): 1.

[00143] In an embodiment, the LDH contained within the coating mixture is a carbonate- containing LDH.

[00144] In an embodiment, the LDH contained within the coating mixture is a nitrate-containing LDH.

[00145] In an embodiment, the LDH contained within the coating mixture is a magnesium aluminium carbonate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5):1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): !

[00146] In an embodiment, the LDH contained within the coating mixture is a magnesium aluminium nitrate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): ! More suitably, the molar ratio of Mg:AI is (2.0-2.25): !

[00147] In an embodiment, the aspect ratio of the layered double hydroxide contained within the coating mixture is 10-500, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet. Suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is greater than 85. More suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is 90-400. More suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is 100-300.

[00148] In an embodiment, the layered double oxide has BET surface area of > 10 m²/g. Suitably, the layered double oxide has BET surface area of > 100 m²/g. More suitably, the layered double oxide has BET surface area of 100-500 m²/g.

[00149] In an embodiment, the layered double oxide has total pore volume of > 0.4 cm³/g. Suitably, the layered double oxide has total pore volume of 0.4-2.0 cm³/g. [00150] In an embodiment, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 260-550°C. The precursor LDH will be understood as being that which is, once thermally treated at the specific temperature, yields a LDO. Suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 290-525°C. More suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 310-500°C. Most suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 325-475°C.

[00151] In an embodiment, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 1-48 hours. Suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 4-24 hours. More suitably, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 6-18 hours.

[00152] In an embodiment, the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide in air.

[00153] In an embodiment, the precursor layered double hydroxide and/or the layered double hydroxide contained within the coating mixture has a structure according to formula (I) shown below:

[M^z+ ₁.xM'y⁺x(OH)₂]^a+(X'¹-)_m 0H20 c(solv)

(I) wherein

M is a charged metal cation;

M' is a charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<6≤10;

0≤c≤10;

X is an anion;

n is the charge on anion X;

a is equal to z(1-x)+xy-2;

m≥ a/n; and

solv denotes an organic solvent capable of hydrogen-bonding to water. [00154] In an embodiment, when z is 2, M is Mg, Zn, Fe, Ca, or a mixture of two or more of these, or when z is 1 , M is Li. Suitably, z is 2 and M is Ca, Mg, Zn or Fe. More suitably, z is 2 and M is Ca, Mg or Zn.

[00155] In an embodiment, when y is 3, M' is Al, Fe, Ti, or a mixture thereof, or when y is 4, M' is Ti. Suitably, y is 3. More suitably, y is 3 and M' is Al.

[00156] In an embodiment, M' is Al.

[00157] In an embodiment, 0<c≤10.

[00158] In an embodiment, X is at least one anion selected from the group consisting of a halide (e.g., chloride) and an inorganic oxyanion (e.g. X'_mOn(OH)p^"i?, in which m = 1-5; n = 2-10; p = 0-4, q = 1-5; X' = B, C, N, S, P; such as carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate, hydroxide, silicate). Suitably, X is at least one anion selected from the group consisting of carbonate, bicarbonate, nitrate and nitrite. Most suitably, X is carbonate.

[00159] In an embodiment, x has a value according to the expression 0.18<x<0.9. Suitably, x has a value according to the expression 0.18<x<0.5. More suitably, x has a value according to the expression 0.18<x<0.4.

[00160] In an embodiment, the precursor layered double hydroxide and/or the layered double hydroxide contained within the coating mixture is a flower-like layered double hydroxide or a platelet-like layered double hydroxide. The term flower-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a co-precipitation technique. The term platelet-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a urea-hydrothermal technique.

[00161] In an embodiment, the precursor LDH is a Zn/AI, Mg/AI, Ca/AI or Zn,Mg/AI LDH. Suitably, the precursor LDH is a Mg/AI LDH.

Coating mixtures

[00162] According to a fifth aspect of the present invention, there is provided a coating mixture obtainable by a process according to the fourth aspect of the invention.

[00163] According to a sixth aspect of the present invention, there is provided a coating mixture comprising a layered double hydroxide, a polymer and a solvent for the polymer.

[00164] The coating mixtures of the fifth and sixth aspects of the invention are useable in accordance with the first aspect of the invention. The numerous advantages discussed hereinbefore in connection with the first aspect of the invention are thereby equally applicable to the fifth and sixth aspects of the invention. [00165] It will be understood that the LDH contained within the coating mixture is an LDO- derived LDH.

[00166] In an embodiment, the combined quantity of the LDH and polymer in the coating mixture is 2.5-10.0% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 2.5-7.5% by weight relative to the total weight of the coating mixture. Suitably, the combined quantity of the LDH and polymer in the coating mixture is 3-7% by weight relative to the total weight of the coating mixture. More suitably, the combined quantity of the LDH and polymer in the coating mixture is 3.5-6.5% by weight relative to the total weight of the coating mixture. Yet more suitably, the combined quantity of the LDH and polymer in the coating mixture is 4-6% by weight relative to the total weight of the coating mixture.

[00167] In an embodiment, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :6 to 2: 1. Suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :5 to 1.5: 1. More suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :5 to 1.2: 1. Most suitably, the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :4 to 1.1 : 1.

[00168] In an embodiment, the layered double hydroxide present within the coating mixture is substantially free from organic compounds used in the preparation of layered double hydroxides.

[00169] In an embodiment, the layered double hydroxide present within the coating mixture is substantially free from toxic organic compounds (e.g. urea).

[00170] In an embodiment, the layered double hydroxide present within the coating mixture is free from urea. Hence, the coated substrate is free from urea.

[00171] In an embodiment, the polymer is a water-soluble polymer. Suitably, the water-soluble polymer is one or more polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA). More suitably, the water-soluble polymer is polyvinyl alcohol) (PVOH). Alternatively, the polymer is a water-based polymer. The term water-based polymer will be familiar to one of ordinary skill in the art, and is used to denote a polymer that may not be water-soluble, but which has been functionalised to render it readily dispersible in water. Water-based polymers include water-based polyurethane and water-based polyacrylate. In a particularly suitable embodiment, the polymer is crosslinked PVOH. [00172] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 20,000 to 150,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 60,000 Da. More suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 27,000 to 40,000 Da.

[00173] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 40,000 to 220,000 Da. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 170,000 to 210,000 Da.

[00174] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 70 to 100 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 99 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 80 to 95 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 83 to 92 mol%. More suitably, the polymer is polyvinyl alcohol) (PVOH) having a degree of hydrolysis of 85 to 90 mol%.

[00175] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 20,000 to 60,000 Da and a degree of hydrolysis of 83 to 92 mol%. Suitably, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (Mw) of 27,000 to 40,000 Da and a degree of hydrolysis of 85 to 90 mol%.

[00176] In an embodiment, the polymer is polyvinyl alcohol) (PVOH) having a molecular weight (M_w) of 40,000 to 220,000 Da and a degree of hydrolysis of 80 to 99 mol%

[00177] In an embodiment, the solvent is water. Additional solvents may or may not be present. Suitably, >95 vol.% of the solvent is water.

[00178] In an embodiment, the coating mixture has a viscosity at 25°C of 1 to 1000 cP.

[00179] In an embodiment, the LDH contained within the coating mixture is a Zn/AI, Mg/AI, Ca/AI or Zn, Mg/AI LDH. Suitably, the LDH contained within the coating mixture is a carbonate- containing LDH.

[00180] In an embodiment, the LDH contained within the coating mixture is a Mg/AI LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): !

[00181] In an embodiment, the LDH contained within the coating mixture is a carbonate- containing LDH.

[00182] In an embodiment, the LDH contained within the coating mixture is a nitrate-containing LDH. [00183] In an embodiment, the LDH contained within the coating mixture is a magnesium aluminium carbonate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5):1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): 1.

[00184] In an embodiment, the LDH contained within the coating mixture is a magnesium aluminium nitrate LDH. Suitably, the molar ratio of Mg:AI is (1.9-2.5): 1. More suitably, the molar ratio of Mg:AI is (2.0-2.25): !

[00185] In an embodiment, the aspect ratio of the layered double hydroxide contained within the coating mixture is 10-500, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet. Suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is greater than 85. More suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is 90-400. More suitably, the aspect ratio of the layered double hydroxide contained within the coating mixture is 100-300.

[00186] In an embodiment, the layered double hydroxide has a structure according to formula (I) shown below:

[M^z+ ₁.xM'y⁺x(OH)₂]^a+(X'¹-)_m 0H20 c(solv)

(I) wherein

M is a charged metal cation;

M' is a charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<6≤10;

0≤c≤10;

X is an anion;

n is the charge on anion X;

a is equal to z(1-x)+xy-2;

m≥ a/n; and

solv denotes an organic solvent capable of hydrogen-bonding to water.

[00187] In an embodiment, when z is 2, M is Mg, Zn, Fe, Ca, or a mixture of two or more of these, or when z is 1 , M is Li. Suitably, z is 2 and M is Ca, Mg, Zn or Fe. More suitably, z is 2 and M is Ca, Mg or Zn. [00188] In an embodiment, when y is 3, M' is Al, Fe, Ti, or a mixture thereof, or when y is 4, M' is Ti. Suitably, y is 3. More suitably, y is 3 and M' is Al.

[00189] In an embodiment, I is Al.

[00190] In an embodiment, 0<c≤10.

[00191] In an embodiment, X is at least one anion selected from the group consisting of a halide (e.g., chloride) and an inorganic oxyanion (e.g. X'_mOn(OH)p^"i?, in which m = 1-5; n = 2-10; p = 0-4, q = 1-5; X' = B, C, N, S, P; such as carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate, hydroxide, silicate). Suitably, X is at least one anion selected from the group consisting of carbonate, bicarbonate, nitrate and nitrite. Most suitably, X is carbonate.

[00192] In an embodiment, x has a value according to the expression 0.18<x<0.9. Suitably, x has a value according to the expression 0.18<x<0.5. More suitably, x has a value according to the expression 0.18<x<0.4.

[00193] In an embodiment, the layered double hydroxide is a flower-like layered double hydroxide or a platelet-like layered double hydroxide. The term flower-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a co- precipitation technique. The term platelet-like LDH will be understood by one of skill in the art to denote one which has been prepared according to a urea-hydrothermal technique.

Applications

[00194] According to a seventh aspect of the present invention there is provided a use of a coating mixture according to the fifth or sixth aspect in the formation of a coating on a substrate.

[00195] The substrate may have any of the definitions discussed hereinbefore in respect of any other aspect of the invention.

[00196] According to an eighth aspect of the present invention there is provided a use of a coated substrate according to the second or third aspect in packaging.

[00197] According to a ninth aspect of the present invention there is provided packaging comprising a coated substrate according to the second or third aspect.

[00198] The advantageous OTR properties of the coated substrates of the invention render them useful in the field of packaging, particularly in the food industry. Accordingly, the coated substrates of the invention may be used in packaging or in a container that is intended to package or contain a foodstuff. [00199] Suitably, the coated substrates have acceptable optical properties (e.g. transparency, clarity and/or haze).

[00200] The following numbered statements 1 to 82, are not claims, but instead describe particular aspects and embodiments of the invention:

1. A process for the preparation of a coated substrate, the process comprising the steps of:

ii. a polymer, and

iii. a solvent for the polymer;

c) drying the coated first substrate.

2. The process of statement 1 , wherein step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) providing a mixture of the solvent and the polymer; and

3. The process of statement 1 , wherein step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) mixing the layered double oxide with the solvent; and

4. The process of statement 2 or 3, wherein step a-iii) is conducted at a temperature of

15-90°C.

5. The process of any preceding statement, wherein the combined quantity of the LDH and polymer in the coating mixture is 2.5-7.5% by weight relative to the total weight of the coating mixture.

6. The process of any preceding statement, wherein the combined quantity of the LDH and polymer in the coating mixture is 3-7% by weight relative to the total weight of the coating mixture.

7. The process of any preceding statement, wherein the combined quantity of the LDH and polymer in the coating mixture is 4-6% by weight relative to the total weight of the coating mixture. The process of any preceding statement, wherein the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :6 to 2: 1.

The process of any preceding statement, wherein the weight ratio of layered double hydroxide to polymer in the coating mixture ranges from 1 :4 to 1.5: 1.

The process of any preceding statement, wherein the polymer is a water-soluble polymer or a water-based polymer.

The process of any preceding statement, wherein the polymer is one or more water-soluble polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA), or one or more water-based polymers selected from the group consisting of water-based polyurethane and water-based polyacrylate.

The process of statement 10 or 1 1 , wherein the polymer is polyvinyl alcohol) (PVOH). The process of any preceding statement, wherein the coating mixture is aqueous and the solvent is water.

The process of any preceding statement, wherein the coating mixture has a viscosity at 25°C of 1 to 1000 cP.

The process of any preceding statement, wherein the coating mixture is obtainable by mixing at least the following:

i. the layered double oxide,

ii. the polymer,

iii. the solvent for the polymer, and either or both of

a. a source of an inorganic oxyanion (e.g. a salt), and

b. a polymer crosslinking agent.

The process of any preceding statement, wherein the first substrate is selected from the group consisting of polyethylene terephthalate (PET), polyethylene (PE), biaxialiy oriented polypropylene film (BOPP), polypropylene (PP), and polyvinyl dichloride (PVDC).

The process of any preceding statement, wherein the first substrate is polyethylene terephthalate (PET).

The process of any preceding statement, wherein the aspect ratio of the layered double hydroxide contained within the coating mixture is 10-500, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet. The process of statement 18, wherein the aspect ratio of the layered double hydroxide contained within the coating mixture is greater than 85.

The process of any preceding statement, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 260-550°C. The process of any preceding statement, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 325-475°C. The process of statement 20 or 21 , wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 1 -48 hours.

The process of statement 20, 21 or 22, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 6-18 hours.

The process of any one of statements 20 to 23, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide in air.

The process of any preceding statement, wherein either or both of the precursor layered double hydroxide and the layered double hydroxide contained within the coating mixture has a structure according to formula (I) shown below:

[M^z+ ₁.xM'y⁺x(OH)₂]^a+(X'¹-)_m 0H20 c(solv)

(I)

wherein

M is a charged metal cation;

M' is a charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<6≤10;

0≤c≤10

X is an anion;

n is the charge on anion X;

a is equal to z(1-x)+xy-2;

m≥ a/n; and

solv denotes an organic solvent capable of hydrogen-bonding to water.

The process of statement 25, wherein when z is 2, M is Mg, Zn, Fe, Ca, or a mixture of two or more of these, or when z is 1 , M is Li.

The process of statement 25 or 26, wherein when y is 3, M' is Al, Fe, Ti, or a mixture thereof, or when y is 4, M' is Ti. The process of any one of statements 25, 26 and 27, wherein M' is Al.

The process of any one of statements 25 to 28, wherein the layered double hydroxide of formula (I) is a Zn/AI, Mg/AI, Ca/AI or Zn,Mg/AI layered double hydroxide.

The process of any one of statements 25 to 29, wherein X is at least one anion selected from the group consisting of a halide (e.g., chloride) and an inorganic oxyanion (e.g.

X'_mOn(OH)p-^(?, in which m = 1-5; n = 2-10; p = 0-4, q = 1-5; X' = B, C, N, S, P; such as carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate, hydroxide, silicate).

The process of any one of statements 25 to 30, wherein X is at least one anion selected from the group consisting of carbonate, bicarbonate, nitrate and nitrite.

The process of any one of statements 25 to 31 , wherein X is carbonate.

The process of any preceding statement, wherein either or both of the precursor layered double hydroxide and the layered double hydroxide contained within the coating mixture is a flower-like layered double hydroxide or a platelet-like layered double hydroxide.

The process of any preceding statement, wherein either or both of the precursor layered double hydroxide and the layered double hydroxide contained within the coating mixture is a Zn/AI, Mg/AI, ZnMg/AI or Ca/AI layered double hydroxide.

The process of any preceding statement, wherein either or both of the precursor layered double hydroxide and the layered double hydroxide contained within the coating mixture is a carbonate-containing layered double hydroxide.

The process of any preceding statement, wherein the layered double oxide has BET surface area of > 10 m²/g.

The process of any preceding statement, wherein the layered double oxide has BET surface area of > 100 m²/g.

The process of any preceding statement, wherein the layered double oxide has BET surface area of 100-500 m²/g.

The process of any preceding statement, wherein the layered double oxide has total pore volume of > 0.4 cm³/g.

The process of any preceding statement, wherein the layered double oxide has total pore volume of 0.4-2.0 cm³/g. The process of any preceding statement, wherein after step b) and prior to step c), the coated first substrate is contacted with a second substrate, such that the layer of coating mixture is provided between the first and second substrates.

The process of any preceding statement, further comprising the steps of:

e) contacting the layer of adhesive applied in step d) with a second substrate.

The process of statement 41 or 42, wherein the second substrate is selected from polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polyvinyl dichloride (PVDC).

The process of statement 42 or 43, wherein the adhesive is selected from polyvinyl alcohol) (PVOH) and poly(lactic acid) (PLA).

A coated substrate obtainable by the process of any preceding statement.

A coated substrate comprising:

a) a first substrate; and

b) a coating layer provided on a least one surface of the first substrate,

wherein the coating layer comprises 1 -70 wt% of layered double hydroxide dispersed throughout a polymeric matrix.

The coated substrate of statement 46, wherein the layered double hydroxide is randomly dispersed throughout the polymeric matrix.

The coated substrate of statement 46 or 47, wherein the coating layer comprises 10-60 wt% of layered double hydroxide.

The coated substrate of any one of statements 46, 47 and 48, wherein the coated substrate is free from urea.

The coated substrate of one of statements 46 to 49, wherein the layered double hydroxide is as defined in any one or more of statements 18, 19 and 25 to 35.

The coated substrate of any one of statements 46 to 50, wherein the polymeric matrix comprises a polymer as defined in statement 10, 1 1 or 12.

The coated substrate of any one of statements 46 to 51 , wherein the first substrate is as defined in statement 16 or 17.

The coated substrate of any one of statements 46 to 52, wherein the coating layer comprises: a) 5-70 wt% of layered double hydroxide;

b) 30-95 wt% of polymeric matrix; and

c) 0-2 wt% of solvent (e.g. water).

The coated substrate of any one of statements 46 to 53, wherein the coating layer has a thickness of 0.1 -10 μηι (e.g. 1-10 μηι).

The coated substrate of any one of statements 46 to 53, wherein coated substrate comprises a second substrate disposed on top of the coating layer, such that the coating layer is located between the first and second substrates.

The coated substrate of statement 55, wherein the coated substrate comprises a layer of adhesive provided between the coating layer and the second substrate.

The coated substrate of statement 56, wherein the adhesive is as defined in statement 44. Use of a coated substrate as claimed in any one of statements 46 to 57 in packaging. The use of statement 58, wherein the packaging is food packaging.

Packaging comprising a coated substrate as claimed in any one of statements 46 to 57. The packaging of statement 60, wherein the packaging is food packaging.

A process for the preparation of a coating mixture suitable for use in a coating application, the coating mixture comprising a layered double hydroxide, a polymer and a solvent for the polymer, the process comprising the step of:

a) mixing at least the following:

i. a layered double oxide,

ii. a polymer, and

iii. a solvent for the polymer.

The process of statement 62, wherein step a) comprises the steps:

a-i) providing a layered double oxide;

a-ii) providing a mixture of the solvent and the polymer; and

The mixture of statement 62, wherein step a) comprises the steps:

a-i) providing a layered double oxide;

a-ii) mixing the layered double oxide with the solvent; and

a-iii) mixing the mixture formed in step a-ii) with a mixture of the polymer and solvent to form the coating mixture. 65. The process of statement 63 or 64, wherein step a-iii) is conducted at a temperature of 15-90°C.

66. The process of any one of statements 62 to 65, wherein coating mixture is as defined in any one or more of statements 5 to 9.

67. The process of any one of statements 62 to 66, wherein the polymer is as defined in any one or more of statements 10, 11 and 12.

68. The process of any one of statements 62 to 67, wherein the coating mixture is aqueous and the solvent is water.

69. The process of any one of statements 62 to 68, wherein the coating mixture has a viscosity at 25°C of 1 to 1000 cP.

70. The process of any one of statements 62 to 69, wherein the coating mixture is obtainable by mixing at least the following:

i. the layered double oxide,

ii. the polymer,

iii. the solvent for the polymer, and either or both of

a. a source of an inorganic oxyanion (e.g. a salt), and

b. a polymer crosslinking agent.

71. The process of any one of statements 62 to 70, wherein the aspect ratio of the layered double hydroxide contained within the coating mixture is 10-500, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet.

72. The process of statement 71 , wherein the aspect ratio of the layered double hydroxide contained within the coating mixture is 100-500.

73. The process of any one of statements 62 to 72, wherein the layered double oxide is

obtainable by thermally treating a precursor layered double hydroxide at a temperature of 260-550°C.

74. The process of any one of statements 62 to 73, wherein the layered double oxide is

obtainable by thermally treating a precursor layered double hydroxide at a temperature of 325-475°C.

75. The process of statement 73 or 74, wherein the layered double oxide is obtainable by

thermally treating a precursor layered double hydroxide for a period of 1 -48 hours.

76. The process of statement 73, 74 or 75, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 6-18 hours. 77. The process of any one of statements 73 to 76, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide in air.

78. The process of any one of statements 73 to 77, wherein either or both of the precursor layered double hydroxide and the layered double hydroxide contained within the coating mixture is as defined in any one or more of statements 25 to 35.

79. The process of any one of statements 62 to 78, wherein the layered double oxide is as

defined in any one or more of statements 36 to 40.

80. A coating mixture obtainable by the process of any one of statements 62 to 79.

81. Use of a coating mixture as stated in statement 80 in the formation of a coating on a

substrate.

82. The use of statement 81 , wherein the substrate is intended for use in packaging (e.g. food packaging).

EXAMPLES

[00201] One or more examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:

Fig. 1 shows TEM images of LDHs used this study: (a) Mg₄AI-C03-AMO LDH from co- precipitation (Cop-AMO LDH) and (b) Mg₄AI-C03-AMO LDH from urea-hydrothermal method (UHT-AMO LDH).

Fig. 2 shows TEM of reconstructed LDH in water (AMO-LDO in water calcined at 450°C) at room temperature and 80°C. (a), (b) Cop-AMO-LDO reconstructed at room temperature and 80°C. (c), (d) UHT-AMO-LDO at room temperature and 80°C

Fig. 3 shows TEM of reconstructed LDH from Cop-AMO-LDO calcined at 450°C in PVA aqueous solution (at ratio of 50/50) at room temperature and 80°C.

Fig. 4 shows TEM of reconstructed LDH from UHT-AMO-LDO calcined at 450°C in PVA aqueous solution (at ratio of 50/50) at room temperature, (a) Low magnification and (b) high magnification.

Fig. 5 shows TEM images of reconstructed LDH in water from LDO calcined at different calcination temperature: Cop-AMO-LDO calcined at (a) 250°c, (b) 350°C, (c) 450°C, and (d) 550°C and Cop-Water-LDO calcined at (e) 250°C, (f) 350°C, (g) 450°C, and (h) 550°C.

Fig. 6 shows TEM of reconstructed LDH from Cop-LDO from different calcination temperature in PVA aqueous solution (at ratio of 50/50): Cop-AMO-LDO calcined at (a) 250°c, (b) 350°C, (c) 450°C, and (d) 550°C and Cop-Water-LDO calcined at (e) 250°C, (f) 350°C, (g) 450°C, and (h) 550°C.

Fig. 7 shows TEM of commercial LDH, calcined LDO at 450°C and reconstructed LDH in water, and reconstructed in PVA aqueous solution (at ratio of 50/50): (a) Plural MG 70 HT LDH, (b) Plural MG 70 HT LDO in water, (c) Plural MG 70 HT LDO in PVA aqueous solution, (d) Aldrich hydrotalcite, (e) Aldrich hydrotalcite LDO in water, and (f) Aldrich hydrotalcite LDO in PVA aqueous solution.

Fig. 8 shows TEM of reconstructed LDH from Cop-AMO-LDO calcined at 450°C in water at different stirring speed for 1 hour at (a) 750 rpm and (b) 8000 rpm.

Fig. 9 shows TEM of reconstructed LDH from Cop-AMO LDO from different calcination temperature in PVA aqueous solution (at ratio of 50/50) with different adding sequence: (a) 350°C with sequenced , (b) 450°C with sequenced , (c) 350°C with sequence#2, and (d) 450°C with sequence#2.

Fig. 10 shows TEM of reconstructed LDH from Cop-AMO LDO calcined at 450°C in different PVA aqueous solution (at ratio of 50/50) with adding sequence#1 : (a) Mowiol 4-88, (b) Mowiol 8-88, (c) Mowiol 18-88, (d) Mowiol 4-98, (e) Mowiol 10-98, and (f) Mowiol 20-98.

Fig. 1 1 shows TEM of reconstructed LDH from Cop-AMO LDO calcined at 450°C in different PVA aqueous solution (at ratio of 50/50) with adding sequence#2: (a) Mowiol 4-88, (b) Mowiol 8-88, (c) Mowiol 18-88, (d) Mowiol 4-98, (e) Mowiol 10-98, and (f) Mowiol 20-98.

Fig. 12 shows XRD pattern of co-precipitated LDO/LDH at different calcination temperature: (a) AMO-washed series and (b) Water-washed series.

Fig. 13 shows BET isotherm of co-precipitated LDO/LDH at different calcination temperature: (a) AMO-washed series and (b) Water-washed series.

Fig. 14 shows Pore size distribution of co-precipitated LDO/LDH at different calcination temperature: (a) AMO-washed series and (b) Water-washed series.

Fig. 15 shows BET surface area (a) and total pore volume (b) of co-precipitated LDO/LDH at different calcination temperature.

Fig. 16 shows XRD pattern of Cop-AMO-LDO reconstructed in water.

Fig. 17 shows XRD pattern of LDO/PVA coating mixture, LDH and PVA (LDO from co- precipitation vs. urea-hydrothermal).

Fig. 18 shows XRD pattern and FTIR spectra of cop-LDO/PVA (at ratio of 50/50) coating mixture from water washed and AMO treated LDHs calcined at different temperature. Fig. 19 shows XRD pattern of commercial LDHs, LDO calcined at 450°C, LDO reconstructed in water and in PVA aqueous solution at ratio of 20/80 and 50/50. (a) Plural MG70HT and (b) Aldrich hydrotalcite.

Fig. 20 shows (a) TGA and (b) DTG of LDO from co-precipitation (AMO and water washed) at different calcination temperature.

Fig. 21 shows FTIR of various coated and uncoated PET substrates.

Fig. 22 shows oxygen transmission rate of coated film with LDO/PVA coating mixture prepared at room temperature vs. 80°C. Cop-LDO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique.

Fig. 23 shows oxygen transmission rate of coated film with LDO/PVA coating mixture: Cop- LDO vs UHT-LDO. Cop-LDO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique. UHT-LDO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a urea-hydrothermal technique.

Fig. 24 shows oxygen transmission rate of coated film with LDO/PVA: AMO vs water washed. Cop-LDO-AMO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique and subjected to acetone washing. Cop-LDO-W/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique and subjected to water washing.

Fig. 25 shows oxygen transmission rate of coated film with AMO LDO/PVA with different adding sequence.

Fig. 26 shows optical properties of coated film with LDO/PVA coating mixture: Cop-LDO vs UHT-LDO. (a) transparency; (b) haze; and (c) clarity.

Fig. 27 shows optical properties of coated film with Cop AMO LDO/PVA at different calcination temperature, (a) transparency; (b) haze; and (c) clarity.

Fig. 28 shows optical properties of coated film with Cop W LDO/PVA at different calcination temperature, (a) transparency; (b) haze; and (c) clarity.

Fig. 29 shows optical properties of coated film with Cop AMO LDO/PVA at different calcination temperature and adding sequence, (a) transparency; (b) haze; and (c) clarity. Fig. 30 shows optical properties of coated film with Cop AMO LDO/PVA with different PVA and adding sequence, (a) transparency; (b) haze; and (c) clarity.

Fig. 31 shows TEM images of commercial LDHs, calcined LDOs at 450°C and reconstructed LDH in water, or reconstructed in PVA aqueous solution at ratio (LDO: PVA) of 50:50: (a) Plural MG 70 HT LDH, (b) Plural MG 70 HT LDO in water, (c) Plural MG 70 HT LDO in PVA aqueous solution, (d) Aldrich hydrotalcite, (e) Aldrich hydrotalcite LDO in water, and (f) Aldrich hydrotalcite LDO in PVA aqueous solution.

Fig. 32 shows XRD patterns of commercial LDHs, LDOs calcined at 450°C, LDOs reconstructed in water and in PVA aqueous solution at ratio (LDO: PVA) of 20:80 and 50:50 (a) Plural MG70HT and (b) Aldrich hydrotalcite.

Fig. 33 shows TEM images of (a) F1 (Mg2AI-C03 LDH from Atomic Economic Process) and (b) D2 (Mg2AI-C03 LDH from colloidal mill process) commercially available LDHs.

Fig. 34 shows TEM images of LDHs from (a) F1 and (b) D2 calcined at 450°C and reconstructed in water.

Fig. 35 shows TEM images of LDHs calcined at 450°C and reconstructed in PVA aqueous solution at ratio (LDO: PVA) of 50:50 using Sequenced (a) F1 and (b) D2, and Sequence#2 (c) F1 and (d) D2.

Fig. 36 shows XRD patterns of (a) F1 and (b) D2 LDHs, LDOs calcined at 450°C, and LDOs reconstructed in water.

Fig. 37 shows FTIR spectra of (a) F1 and (b) D2 LDHs, LDOs calcined at 450°C, and LDOs reconstructed in water.

Fig. 38 shows XRD pattern of LDO/PVA (at ratio of 50:50 with Sequence#2) coating mixture of (a) D2 LDO/PVA, (b) F1 LDO/PVA and (c) PVA.

Fig. 39 shows TEM images of (a) M2 (Mg₂AI-C0₃ LDH), (b) M3 (Mg₃AI-C0₃ LDH), and (c) M4 (Mg₄AI-C0₃ LDH) commercially available LDHs prepared by colloidal mill process.

Fig. 40 shows TEM images of LDHs calcined at 450°C and reconstructed in water: (a) M2 (Mg₂AI-C0₃ LDH), (b) M3 (Mg₃AI-C0₃ LDH), and (c) M4 (Mg₄AI-C0₃ LDH).

Fig. 41 shows TEM images of LDHs calcined at 450°C and reconstructed in PVA aqueous solution at ratio (LDO:PVA) of 50:50 using Sequence#2: (a) M2 (Mg₂AI-C0₃ LDH), (b) M3 (Mg₃AI-C0₃ LDH), and (c) M4 (Mg₄AI-C0₃ LDH).

Fig. 42 shows XRD patterns of M2, M3 and M4 commercially-available LDHs from a colloidal mill process, LDOs calcined at 450°C, and LDOs reconstructed in water: (a) M2 (Mg₂AI-C0₃ LDH), (b) M3 (Mg₃AI-C0₃ LDH), and (c) M4 (Mg₄AI-C0₃ LDH). Fig. 43 shows FTIR spectra of M2, M3 and M4 LDHs commercially-available LDHs from a colloidal mill process, LDOs calcined at 450°C, and LDOs reconstructed in water: (a) M2 (Mg₂AI-C0₃ LDH), (b) M3 (Mg₃AI-C0₃ LDH), and (c) M4 (Mg₄AI-C0₃ LDH).

Example 1 - Formation of coated substrates

[00202] Scheme 1 below is a flow diagram illustrating the various steps involved in the formation of the coated substrates of the invention.

Scheme 1 - Formation of the coated substrates of the invention

Example 1a - Preparation of precursor LDHs

[00203] The precursor Mg₃AI-C0₃ LDHs used in the preparation of coated substrates were prepared either by a co-precipitation (Cop) technique (to yield flower-like LDHs) or a urea- hydrothermal (UHT) technique (to yield platelet-like LDHs). The general synthetic approach for each technique is outlined below. [00204] General co-precipitation technique: Aqueous solution (50 ml_) of 0.80 M Mg(N0₃)2-6H₂0 and 0.20 M of AI(N0₃)3-9H₂0 was added drop-wise into the 50 ml_ of 0.5 M Na2CC>3 solution with stirring and the pH was controlled at 10 using 4.0 M NaOH solution. After stirring at room temperature for 24 hours, the product was filtered and washed with Dl water until the pH was close to 7.

[00205] General urea-hydrothermal technique: An aqueous solution (100 ml_) of 0.40 M Mg(N0₃)₂-6H₂0, 0.10 M of AI(N0₃)₃-9H₂0, and 0.80 M urea was prepared. The mixed solution were transferred to a Teflon-lined autoclave and heated in an oven at the 100 oC for 24 hours. After the reactions were cooled to room temperature, the precipitate products were washed several times with deionised water by filtration.

[00206] Prior to drying, the as-prepared LDHs were subjected to one of two washing techniques. LDHs denoted "water" or "W" were washed with Dl water and then subsequently dried. LDHs denoted "AMO" or "A" were washed with acetone (an Aqueous Miscible Organic solvent) and then subsequently dried.

[00207] Figure 1 shows TEM images of (a) Mg₄AI-C03-AMO LDH from co-precipitation (Cop- AMO LDH) and (b) Mg₄AI-C0₃-AMO LDH from urea-hydrothermal method (UHT-AMO LDH). The difference in morphology (flower vs platelet) arising from the different preparation techniques is readily apparent.

Example 1 b - Formation of LDO and reconstruction of LDH

[00208] LDHs prepared in Example 1a were then calcined in air at 250, 350, 450 or 550°C for 12 hours to yield the corresponding LDOs.

[00209] The LDOs were then used in the preparation of various coating mixtures containing polyvinyl alcohol) (PVA) and water. The coating mixtures were prepared at room temperature (RT) or at 80°C. During preparation of the coating mixtures, the adding sequence of LDO, PVA and water was varied.

[00210] According to Sequence#1 , LDO was added to a 10 wt% solution of PVA in water and the resulting mixture was then stirred for 24 hours.

[00211] According to Sequence#2, LDO was added to water. The resulting mixture which was then stirred for 24 hours before being added to a 10 wt% solution of PVA in water. The resulting mixture was then stirred for a further 24 hours.

[00212] Irrespective of the addition sequence, the total solids content (LDO and PVA) used in the coating mixture was controlled at 5 wt% and the weight ratio of LDO to PVA used in the coating mixture was either 20:80 or 50:50. [00213] Upon adding the LDO to the water or aqueous PVA solution, the LDO was reconstructed to LDH. Figures 2-9 show TEM images of various LDHs that have been reconstructed from their corresponding LDOs during preparation of the coating mixture.

[00214] Figures 10 and 1 1 show the effect that varying the molecular weight (Mw) and degree of hydrolysis (DH) of the PVA has on the morphology of the reconstructed LDH. Figure 10 shows that for Sequence#1 , using partially hydrolysed PVA (DH - 86.7 to 88.7 mol%) resulted in increased particle uniformity, with less aggregation. Figure 1 1 shows that using Sequence#2 gives rise to even better particle uniformity, irrespective of the molecular weight (Mw) and degree of hydrolysis (DH) of the PVA.

[00215] Figures 12 to 20 provide further characterisation of the LDOs used in the coating mixtures, and the reconstructed LDHs resulting therefrom.

[00216] The XRD data shown in figure 12 illustrate differences in the structures of LDOs calcined at different temperatures.

[00217] The BET results (isotherm and pore size distribution) shows in figures 13-15 highlight that the acetone-washed AMO-LDOs/AMO-LDHs exhibited higher surface area and larger pores than the water-washed W-LDOs/W-LDHs.

[00218] Figures 16-19 show XRD and FTIR data for various LDOs, precursor LDHs, reconstructed LDHs and coating mixtures.

[00219] The TGA and DTG curves of Figure 20 show mass loss from various AMO-LDOs, water-LDOs, AMO-LDHs and water-LDHs.

Example 1c - Coating onto substrate

[00220] The various coating mixtures prepared in Example 1 b were coated onto a 23 μηι thick PET substrate using an automated coater (K101 Control Coater). The coated substrates were then dried at room temperature for 5-30 minutes.

[00221] The FTIR data presented in figure 21 demonstrate characteristic peaks of PET and PVA.

[00222] The OTR properties of the coated and uncoated substrates were assessed. Figure 22 demonstrates the OTR properties of various coated and uncoated PET substrates. Cop- LDO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co- precipitation technique. It is clear that the substrates coated with LDH-containing coatings gave markedly reduced OTR properties when compared with the uncoated PET substrate and the PVA-coated PET substrate. [00223] Figure 23 demonstrates the OTR properties of various coated and uncoated PET substrates. Cop-LDO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique. UHT-LDO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a urea-hydrothermal technique. It is clear that the substrates coated with LDH-containing coatings gave markedly reduced OTR properties when compared with the uncoated PET substrate and the PVA-coated PET substrate.

[00224] Figure 24 demonstrates the OTR properties of various coated and uncoated PET substrates. Cop-LDO-AMO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique and subjected to acetone washing. Cop-LDO-W/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique and subjected to water washing. With the exception of samples calcined at 250°C, it is clear that the substrates coated with LDH-containing coatings gave markedly reduced OTR properties when compared with the uncoated PET substrate and the PVA-coated PET substrate.

[00225] Figure 25 demonstrates the OTR properties of various coated and uncoated PET substrates. Cop-LDO-AMO/PVA denotes a coating mixture containing LDH that has been reconstructed from LDO, wherein the LDO originates from a precursor LDH that was prepared according to a co-precipitation technique and subjected to acetone washing. It is clear that all samples exhibited remarkably low OTR properties. The results show that coating mixtures prepared according to Sequence#1 give rise to lower OTR values when the LDO has been calcined at lower temperatures, whereas coating mixtures prepared according to Sequence#2 give rise to lower OTR values when the LDO has been calcined at higher temperatures.

[00226] The optical properties of the coated and uncoated substrates were also assessed.

[00227] The transmittance of the coated and uncoated substrates was assessed by a haze meter (The haze-gard I, BYK-Gardner GmbH Inc) according to ASTM D 1003. It is the ratio of transmitted light to the incident light, which is influenced by the absorption and reflection properties of the materials. The specimen is placed at the film holder at the entrance port of the haze meter in order to measure the transmittance. Average of ten measurements is reported in units of percent.

[00228] The haze of the coated and uncoated substrates was assessed by a haze meter (The haze-gard I, BYK-Gardner GmbH Inc) according to ASTM D 1003. It is the percent of transmitted light which, in passing through the sample, deviates from the incident beam greater than 2.5 degrees in the average. The specimen is placed at the film holder at the entrance port of the haze meter in order to measure the haze. Average of ten measurements is reported in units of percent.

[00229] The clarity of the coated and uncoated substrates was assessed by a haze meter (The haze-gard I, BYK-Gardner GmbH Inc). This measurement describes how well very fine details can be seen through the specimen. It needs to be determined in an angle range smaller than 2.5 degrees. The specimen is placed at the film holder at the entrance port of the haze meter in order to measure the clarity. Average of ten measurements is reported in units of percent.

[00230] Figures 26-30 demonstrate the optical properties of various uncoated and coated substrates. The results show that, when compared with uncoated PET substrates, the coated substrates of the invention exhibited comparable - and in some cases better - optical properties.

Example 2 - Direct reconstruction of commercial LDHs

[00231] The effect of calcination, followed by direct reconstruction of the LDH structure, on the morphology of various commercially-available LDH samples was assessed. For all samples, direct reconstructions of the LDH structure from the corresponding LDO was carried out in either water and/or an aqueous PVA solution.

[00232] Figure 31 (a) shows a TEM of the commercially available Plural MG 70 HT LDH. The effect on morphology of calcining the LDH at 450°C and adding the resulting LDO to water and an aqueous PVA solution is shown in figures 31 (b) and (c) respectively. Figure 31 (d) provides a TEM of the commercially available Aldrich hydrotalcite. The effect on morphology of calcining the hydrotalcite at 450°C and adding the resulting LDO to water and an aqueous PVA solution is shown in figures 31 (e) and (f) respectively. Figure 31 clearly shows an improvement in particle morphology and uniformity can be achieved by calcination followed by direct reconstruction of the LDH structure in water or an aqueous PVA solution. Figure 32 shows the XRD patterns of the various commercial LDHs, their corresponding LDOs and the LDHs resulting from direct reconstruction in water or an aqueous PVA solution.

[00233] Figure 33 shows TEMs of two commercially-available LDHs, namely (a) F1 , a Mg2AI- CO3 LDH obtained by an Atomic Economic Process, and (b) D2, a Mg2AI-C03 LDH obtained by a colloidal mill process. Figure 34 shows the effect on the morphology of F1 (a) and D2 (b) of calcining the LDHs at 450°C and adding the resulting LDO to water. Figure 35 shows the effect on the morphology of F1 (a,c) and D2 (b,d) of calcining the LDHs at 450°C and adding the resulting LDO to an aqueous PVA solution (50:50 LDO: PVA solution) using Sequence#1 (a,b) and Sequence #2 (c,d). Figures 33 to 35 clearly shows an improvement in particle morphology and uniformity can be achieved by calcination followed by direct reconstruction of the LDH structure in water or an aqueous PVA solution. Figure 36 shows the XRD patterns of the various commercial LDHs, their corresponding LDOs and the LDHs resulting from direct reconstruction in water or an aqueous PVA solution. Figure 37 shows the FTIR spectra of the various commercial LDHs, their corresponding LDOs and the LDHs resulting from direct reconstruction in water. Figure 38 shows the XRD pattern of (c) PVA, as well as the XRD patterns of coating mixtures formed by adding (using Sequence#2) either (a) the LDO formed by calcining commercially-available D2, or (b) the LDO formed by calcining commercially- available F1 , to an aqueous solution of PVA (50:50 LDO:PVA solution).

[00234] Figure 39 shows TEMs of three commercially-available LDHs, namely (a) M2, a Mg2AI- C0₃ LDH, (b) M3, a Mg₃AI-C0₃ LDH, and (c) M4, a Mg₄AI-C0₃ LDH, all of which are obtained by a colloidal mill process. Figure 40 shows the effect on the morphology of M2 (a), M3 (b) and M4 (c) of calcining the LDHs at 450°C and adding the resulting LDOs to water. Figure 41 shows the effect on the morphology of M2 (a), M3 (b) and M4 (c) of calcining the LDHs at 450°C and adding the resulting LDOs to an aqueous PVA solution (50:50 LDO: PVA solution) using Sequence#2. Figures 39 to 41 clearly show an improvement in particle morphology and uniformity can be achieved by calcination followed by direct reconstruction of the LDH structure in water or an aqueous PVA solution. Figure 42 shows the XRD patterns of the various commercial LDHs, their corresponding LDOs and the LDHs resulting from direct reconstruction in water. Figure 43 shows the FTIR spectra of the various commercial LDHs, their corresponding LDOs and the LDHs resulting from direct reconstruction in water.

[00235] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims

ii. a polymer, and

iii. a solvent for the polymer;

c) drying the coated first substrate

2. The process of claim 1 , wherein step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) providing a mixture of the solvent and the polymer; and

3. The process of claim 1 , wherein step a) comprises the steps of:

a-i) providing a layered double oxide;

a-ii) mixing the layered double oxide with the solvent; and

4. The process of claim any preceding claim, wherein the combined quantity of the LDH and polymer in the coating mixture is 2.5-7.5% by weight relative to the total weight of the coating mixture.

5. The process of any preceding claim, wherein the weight ratio of layered double

hydroxide to polymer in the coating mixture ranges from 1 :6 to 2: 1.

6. The process of any preceding claim, wherein the polymer is one or more water-soluble polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA), or one or more water-based polymers selected from the group consisting of water-based polyurethane and water- based polyacrylate.

7. The process of any preceding claim, wherein the coating mixture is aqueous and the solvent is water.

8. The process of any preceding claim, wherein the first substrate is selected from the group consisting of polyethylene terephthalate (PET), polyethylene (PE), biaxiaiiy oriented polypropylene film (BOPP), polypropylene (PP), and polyvinyl dichloride (PVDC).

9. The process of any preceding claim, wherein the first substrate is polyethylene

terephthalate (PET) and the polymer is polyvinyl alcohol) (PVOH).

10. The process of any preceding claim, wherein the aspect ratio of the layered double hydroxide contained within the coating mixture is greater than 85, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet.

1 1. The process of any preceding claim, wherein the layered double oxide is obtained by thermally treating a precursor layered double hydroxide at a temperature of

260-550°C.

12. The process of claim 1 1 , wherein either or both of the precursor layered double

hydroxide and the layered double hydroxide contained within the coating mixture has a structure according to formula (I) shown below:

[M^z+ ₁.xM'y⁺x(OH)₂]^a+(X'¹-)_m 0H20 c(solv)

(I)

wherein

M is a charged metal cation;

M' is a charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<6≤10;

0≤c≤10 X is an anion;

n is the charge on anion X;

a is equal to z(1-x)+xy-2;

m≥ a/n; and

solv denotes an organic solvent capable of hydrogen-bonding to water.

13. The process of claim 12, wherein the layered double hydroxide of formula (I) is a Zn/AI, Mg/AI, Ca/AI or Zn,Mg/AI layered double hydroxide.

14. The process of claim 12 or claim 13, wherein X is at least one anion selected from the group consisting of carbonate, bicarbonate, nitrate and nitrite.

15. The process of any one of claims 12 to 14, wherein the layered double hydroxide of formula (I) is a magnesium aluminium carbonate layered double hydroxide.

16. The process of any one of claims 1 1 to 15, wherein either or both of the precursor layered double hydroxide and the layered double hydroxide contained within the coating mixture is a flower-like layered double hydroxide or a platelet-like layered double hydroxide.

17. The process of any preceding claim, wherein after step b) and prior to step c), the

coated first substrate is contacted with a second substrate, such that the layer of coating mixture is provided between the first and second substrates.

18. The process of any preceding claim, further comprising the steps of:

e) contacting the layer of adhesive applied in step d) with a second substrate.

19. A coated substrate comprising:

a) a first substrate; and

20. The coated substrate of claim 19, wherein the coated substrate is free from urea.

21. The coated substrate of claim 19 or claim 20, wherein the layered double hydroxide is a magnesium aluminium carbonate layered double hydroxide.

22. The coated substrate of one of claims 19 to 21 , wherein the aspect ratio of the layered double hydroxide is greater than 85, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet.

23. The coated substrate of any one of claims 19 to 22, wherein the polymeric matrix

comprises one or more water-soluble polymers selected from the group consisting of polyvinyl alcohol) (PVOH), polyvinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA).

24. The coated substrate of any one of claims 19 to 23, wherein the first substrate is

selected from the group consisting of polyethylene terephthalate (PET), polyethylene (PE), biaxia!iy oriented polypropylene film (BOPP), polypropylene (PP), and polyvinyl dichloride (PVDC).

25. The coated substrate of any one of claims 19 to 24, wherein the first substrate is PET and the polymeric matrix comprises polyvinyl alcohol) (PVOH).

26. The coated substrate of any one of claims 19 to 25, wherein the oxygen transmission rate of the coated substrate is less than 10 cc/m²/day/atm.

27. Use of a coated substrate as claimed in any one of claims 19 to 26 in packaging, such as food packaging.

28. Packaging comprising a coated substrate as claimed in any one of claims 19 to 26.

29. The packaging of claim 28, wherein the packaging is food packaging.