Aqueous coating compositions

Abstract

The present invention relates to aqueous coating compositions suitable for coating substrates, such as cardboard and paper used in food packaging. The coating compositions are made from plant-derived materials, are storage stable and can be made at high solids contents. The coating compositions can be made from materials that are commonly available in food-grade specifications. This combination of properties makes the coating compositions particularly relevant for food packaging applications, though other applications are also possible.

Description

[0001] AQUEOUS COATING COMPOSITIONS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to aqueous coating compositions suitable for coating substrates, such as cardboard and paper used in food packaging. The coating compositions are made from plant-derived materials, are stable and can be made at high solids contents. The coating compositions can be made from materials that are commonly available in foodgrade specifications. This combination of properties makes the coating compositions particularly relevant for food packaging applications, though other applications are also possible.

[0004] BACKGROUND OF THE INVENTION

[0005] There is a current need to develop packaging materials which have an improved environmental profile, such as not requiring the use of petrochemicals and having good recyclability or biodegradability. Particularly good packaging materials are cardboard and paper and other packaging materials based on cellulose fibres due to their ability to be recycled and re-used. However, such materials have no barrier properties to liquids or vapours. Typically, a thin layer of a plastic material is used to form a composite material that combines physical robustness and barrier properties. However, the use of such plastic liners or coatings means that such composite packaging material is not really biodegradable and cannot be recycled.

[0006] One particular application that would benefit from improved recyclability or biodegradability is the packaging used for prepared or take-away meals. Such packaging is increasingly widely used, for example to store take-away food during delivery. As such, it generates large - and increasing - amounts of waste. Such packaging is required to have barrier properties for both water and oils for a period of time of some hours. Currently, such packaging typically uses a thin plastic layer to provide general barrier properties, with the biodegradability and recyclability issues highlighted above.

[0007] There is therefore a specific need to develop coated cardboard and paper packaging that has barrier properties to water and oils and that can be recycled or biodegraded. Any solution needs to be applicable on a large-scale. Issues such as handling high levels of volatile solvents, or applying coating mixtures with low solids content (meaning more has tobe applied to get a sufficiently thick coating layer), may be manageable in a lab environment but become major issues in a large-scale industrial context.

[0008] A further issue relating to industrial applicability is the storage stability of any coating compositions. Any coating composition used on an industrial scale needs to have sufficient storage stability that it can be stored and handled over extended periods of time. It would be highly impractical if - for example - a coating composition had to be manufactured in close proximity to a paper mill and then immediately used just because its storage stability was too limited to enable a more conventional and practical supply chain.

[0009] A further, preferred application is for a food package coating where the coating could be ingested or eaten without issue. Consumer acceptance of such coated cardboard and paper food packaging is typically much higher if the coating materials can be described as edible. Therefore, there is a benefit to have coating compositions that give a coating consisting of materials that are available (when required) in food-contact or food grade specifications.

[0010] The use of polysaccharide-based biomaterials, such as starches and alginates, in coating compositions is known in the art. Starch-based coatings are currently used in some applications to provide barrier properties to cardboard and paper or as sizing. Starch coatings can provide resistance to oils and other hydrophobic liquids but do not have good barrier properties for aqueous materials, for example wet foods. Alginate-based coatings are similar in providing oil, but not water, barrier properties. Food packaging for take-away foods such as curries or pastas really needs to have barrier properties to both water and oils.

[0011] Another class of plant-based biomaterials that are well-known in the literature and available commercially are plant proteins, for example corn zein protein. The use of zein and other plant prolamin proteins as coating agents is well known due to their hydrophobic nature and good film-forming properties. Zein has been used for coatings from the 1930s onwards and there is much art in this space. Zein / prolamin coatings have many advantages including good general barrier properties and the ability to be heat sealed. However, they have issues which limit their industrial uses.

[0012] Prolamins such as zein are insoluble in water - like other plant proteins. However, zein does dissolve in aqueous solutions of alcohols such as ethanol, propan-1-diol, propan-2-diol as well as some other organic solvents. Consequently, zein has often been dissolved in aqueous ethanol (usually between 60% and 95% ethanol) or other solvent systems to prepare compositions that can be used as a coating or for film-forming. The presence ofsome low level of water is essential for zein to dissolve in many alcohols. Zein is also soluble in more concentrated aqueous solutions of acetic acid and in other aqueous low pH solutions.

[0013] Zein, like other prolamins, is not commonly used by itself as a film-former or coating due to its brittle nature. Hence plasticisers are typically added. A range of plasticisers can be used, such as glycerol, but the choice of plasticiser will affect the properties of the resulting coating. For example, the addition of a hydrophilic plasticiser like glycerol will reduce the hydrophobicity of the coating. Fatty acids, such as oleic acid, can be used as a plasticiser to improve their flexibility whilst maintaining or even increase the hydrophobic nature of the coating. Longer-chain fatty acids, such as oleic acid, are insoluble in water but soluble in many organic solvents. Oleic acid has been mixed into ethanolic solutions of zein and used to form a coating.

[0014] The use of high levels of ethanol - or other organic solvents such as acetic acid - is highly problematic at an industrial scale for safety, handling and cost reasons. There has therefore been ongoing work to provide coating compositions with reduced, or even no, organic solvent. Reducing, or eliminating the amounts of ethanol or other organic solvent in coating compositions will simplify handling and improve safety. It is highly preferred to use aqueous compositions comprising low levels of ethanol or other organic solvent, such as less than 20% or less than 10% or even less than 5% organic solvent. In preferred embodiments, the aqueous coating composition does not comprise any ethanol or other organic solvent.

[0015] There is always a benefit in industrial conditions to increase the level of solids in a coating composition and reduce the amount of solvent(s) required. Increasing the solids content of a coating composition means that less coating will typically be required to leave a coating of the required thickness. This typically simplifies coating by reducing the degree of drying required which can have increased production rate, lower energy use benefits and lower environmental footprint. In addition, coating a fibrous substrate such as paper or cardboard is often better done with a higher viscosity coating composition to form a better layer on the surface. Very low viscosity coating compositions, typical of solutions of zein in ethanol, will typically penetrate a fibrous substrate and will result in a poorer and less coherent substrate coating.

[0016] Hence it can be seen that any coating composition needs to fulfil multiple requirements simultaneously to be industrially and commercially successful, especially for food packaging applications. It needs to be capable of delivering the required coating performance in terms of barrier properties. It needs to have the rheological properties to be handleable andprocessable and spreadable on a substrate, including after storage. Storage stability needs to be sufficient for the coating compositions to be handled in conventional supply chains with the various delays and ranges of conditions that can be encountered. It should have as high a solids level as practical to minimise the volume of composition to be applied to a substrate. This can increase production rate by reducing the amount of drying needed. It should limit the levels of volatile solvents that need to be dried off as this will reduce emissions and improve the coatings environmental footprint and safe handling. The coating layer formed by the coating composition needs to be sufficiently coherent to act as a barrier - i.e., it must be able to form a continuous and defect-free layer on the substrate. Preferably, the coating should also be sufficiently flexible that coated paper or cardboard can be bent and folded without the coating layer immediately cracking or falling off. Such cracks can provide failure points. Ideally the dried coating should be heat sealable. Finally, the coating material should be capable of being made from food-grade ingredients. Success means achieving all of these requirements at the same time. A coating composition is not successful if it can form a high-quality coating immediately after manufacture but then gels or phase separates on storage. Likewise, a coating composition cannot be described as successful if it is storage stable but does not make a good quality coating.

[0017] The prior art does not address these issues sufficiently simultaneously to provide viable coating compositions based on readily available plant materials that can (i) be handled and processed on an industrial scale and (ii) give good barrier coatings which are flexible enough for food and other packaging and (iii) be made from food-grade components if needed. Much of the earlier work on zein / prolamin coatings is for general use as a varnish-type material and modern applications such as recyclable disposable food packaging using food-grade materials simply did not exist at the time and could not be taken into account.

[0018] Many papers and patents describe the preparation of coatings and films made from prolamins like zein and oily materials such as oleic (or other fatty acids) wherein the zein and oily material are dissolved in an ethanol solution. Either the solution is used as is and the evaporation of the ethanol and water leaves a coating or film, or the zein-oleic mixture is precipitated out to form a dough which can be moulded to form a film.

[0019] BR102022018776 describes a coating composition of zein and macauba oil wherein zein, macauba oil and glycerol are dissolved in aqueous ethanol and the mix sprayed onto fruit.

[0020] Kleen etal. (Kleen, D., Padua, G. and Engeseth, N., ..Stabilization of Lipids in a Biodegradable Zein-Oleate Film by Incorporation of Antioxidants”, Cereal chemistry2002, 79(5), 687-694) precipitate a dough of zein and oleic acid from ethanol solution. The dough is too viscous to be sprayed or spread and the ethanol still has to be dealt with.

[0021] WO2021211995 describes making edible films by a process of dissolving zein in an organic solvent that is not ethanol, preferably propan-1, 3-diol and then mixing with water. The use of oleic acid as a possible plasticiser is mentioned. The pHs of the final compositions are described as neutral and it describes the use of ammonia solutions as being undesirable due to their “corrosiveness”.

[0022] US5324351 describes coating compositions comprising aqueous suspensions of zein precipitated from ethanol solutions and having a pH of < 7. This produces aqueous suspensions of zein after the ethanol is removed and the mixture is concentrated. This just moves the problems of ethanol extraction and handling to elsewhere in the process and the lack of plasticiser like oleic will result in coatings having low flexibility.

[0023] WO 2025 / 003490 describes a mixture that comprises a plant-based protein that is an alkali-treated plant-based protein, wherein the plant-based protein has been mixed with a base or alkali, so that when the resulting plant-based protein is mixed into water the pH of the dispersion is greater than 7.5. The mixture may also contain a plasticiser which can be selected from a list including oleic acid. There is no detail as to the selection of the base or alkali, no mention of ammonium hydroxide or the need to form ammonium oleate. Moreover linoleic acid is not included in the mixture and therefore likewise there will also be no ammonium linoleate present.

[0024] US2377237 describes the preparation of aqueous coating compositions of zein dispersed in various soap / surfactant compositions including ammonium soaps (fatty acid salts) of tall oil, such as in Example 3. Tall oil contains around 50% fatty acids, mainly oleic and linoleic acids, but importantly also around 50% rosins, sterols and other materials with very poor coating behaviours and properties, especially relating to the flexibility of the coating. The inherently greater crystallinity of many saturated fatty acids and the longer chain sterols and rosins means that the use of tall oil would not produce the stable and good quality flexible coatings of this invention. In addition tall oil is not available as a food-grade or food-contact material suitable for food packaging applications.

[0025] US2377237 further teaches compositions having a very high solids contents which are described as “pastes”. There is no teaching about the storage stability of such high solids compositions and especially regarding their tendency to gel. US2377237 is focussed onstability in the context of zein not precipitating and phase separate out. Success in the context of the present invention means a product that can be stored, handled and coated onto a substrate whilst giving a coating having suitable barrier properties and preferably sufficient flexibility.

[0026] US2377237 also discloses the use of a pre-formed ammonium soap of linseed oil fatty acids (comprising mainly linolenic and linoleic acid and much smaller amounts of oleic acid) dissolved in water and mixed with zein to form a coating composition in Example 12. There is no information about the pH of the resulting mixture. The use of a soap, wherein the fatty acid present is inherently in the form of the ammonium salt, is fundamentally different to the present invention by the absence of free fatty acids. The pH of an ammonium soap, as used in US 2377237, will inherently have to be quite high, typically above 10. The pKa of fatty acids in these situations is shifted to the alkaline region due to stabilising effects, such as those of the fatty acid micelles. Typically, high levels of ammonium hydroxide are used to ensure complete neutralization of the fatty acids to form the fatty acid salt. In US2377237 there is no teaching about the benefit of alkaline pHs and optimal pHs are described as being “close to the neutral point”. In fact US2377237 also describes examples where acidic pHs are desirable.

[0027] The inventors have seen that a high proportion and level of ammonium oleate and ammonium linoleate present in coating composition can cause stability problems in the liquid coating composition and aesthetic problems on substrates coated with the composition. This is due the formation of the fatty acid amides, such as oleamides or linolamides, during the coating drying and heat-sealing steps. Fatty acid amides are formed by the chemical reaction of ammonium soaps to form an amide group by a dehydration reaction. This can happen during the storage and drying of the coating composition and especially with the application of heat, as will happen during drying in an industrial oven and / or during heat-sealing of the coated substrate. These fatty acid amides typically appear as an undesirable whitening effect on the surfaces the compositions are coated onto. The level of whitening is related to the level of ammonium soaps present in the coating composition. The lower the proportion and level of oleate and linoleate, the less the whitening problem. The present invention uses lower levels of ammonium oleate and linoleate to emulsify higher levels of plant protein in the coating composition. This is very different to having all the fatty acids present only as the ammonium soap, as in US2377237.

[0028] The balance of fatty acid / fatty acid ammonium soap is determined by the pH of the composition. By controlling the pH range of the composition to above 7.5, such as above 7.75, it is possible to ensure that there is sufficient ammonium oleate to emulsify the oleic acid present and thus ensure the stability and performance of the coating composition. Limiting thepH of the coating composition to values below 11, such as 10.5 or 10.0 or 9.5 or 9.0, ensures that the oleate and linoleate levels are not too high to avoid the possible formation of oleamides or linolamides.

[0029] KR 102405733 describes coating compositions made by mixing chemically modified protein (by covalent reaction of amine groups in the protein) with ammonium oleate and crosslinkers, especially ZnO. This type of chemical modification of the protein has major detrimental impacts on the suitability of the compositions for food use and on biodegradability and is not part of the present invention.

[0030] US20220312784 describes low solids, low viscosity coating compositions comprising monoglyceride and which can contain proteins, including zein, and fatty acids including oleic acid. In such compositions the monoglyceride is the predominant component and they are intended for coating fruit products to reduce water loss only.

[0031] SUMMARY OF THE INVENTION

[0032] In a first aspect, the present invention relates to an aqueous coating composition comprising a solids component and water, wherein the solids component comprises a film-forming component, wherein the film-forming component comprises

[0033] a. one or more plant proteins;

[0034] b. ammonium salt of oleic acid;

[0035] c. oleic acid;

[0036] d. ammonium salt of linoleic acid; and

[0037] e. linoleic acid;

[0038] wherein the amount of water in the aqueous coating composition is between 30 wt.% and 80 wt.% of the aqueous coating composition, and wherein the pH of the aqueous coating composition is above 7.5.

[0039] In another aspect, the present invention relates to a method of producing an aqueous coating composition according to any preceding claim comprising:

[0040] a) mixing one or more plant proteins, water, ammonium hydroxide, oleic acid and linoleic acid; and / or

[0041] b) mixing one or more plant proteins, water, and ammonium salts of oleic acid and ammonium salts of linoleic acid; and

[0042] c) optionally adjusting the pH of the mixture obtained in step a) or in step b).In a further aspect, the present invention relates to the use of an aqueous coating composition as herein defined for coating a substrate.

[0043] In an even further aspect, the present invention relates to a method of applying an aqueous coating composition as herein defined to a substrate.

[0044] In an even further aspect, the present invention relates to a coated substrate obtained by a method as herein defined.

[0045] DETAILED DESCRIPTION OF THE INVENTION

[0046] In a first aspect, the present invention relates to an aqueous coating composition comprising a solids component and water, wherein the solids component comprises a film-forming component, wherein the film-forming component comprises

[0047] a. one or more plant proteins;

[0048] b. ammonium salt of oleic acid;

[0049] c. oleic acid;

[0050] d. ammonium salt of linoleic acid; and

[0051] e. linoleic acid;

[0052] wherein the amount of water in the aqueous coating composition is between 30 wt.% and 80 wt.% of the aqueous coating composition, and wherein the pH of the aqueous coating composition is above 7.5.

[0053] In preferred aqueous coating compositions of the present invention, the amount of water in the aqueous coating composition is between 40 wt.% and 80 wt.% of the aqueous coating composition, more preferably between 50 wt.% and 80 wt.% of the aqueous coating composition, most preferred between 55 wt.% and 80 wt.% of the aqueous coating composition.

[0054] Plant proteins are mainly comprised of globular proteins which are storage proteins and can be classified as albumins (soluble in water), globulins (soluble in dilute salt solutions), prolamins (soluble in aqueous ethanol solutions), and glutelin’s (soluble in dilute acid / alkaline solutions or insoluble in water).

[0055] Albumins and globulins are predominately present in all pulses (at greater than 50%) and some pseudo cereals (such as quinoa and amaranth). Globulins represent between about 70 and 78 wt.% of the protein found in legume seeds, whereas albumins constitute betweenabout 10 and 20 wt.% of the protein. Globulins are the storage proteins of most legume seeds. Globulins have higher molecular weights than albumins and are insoluble in pure water but dissolve in dilute salt solutions. Globulins are typically more water soluble than prolamins.

[0056] The storage proteins from different plants can be classified by their sedimentation coefficient in Svedberg units (S). This coefficient indicates the speed of sedimentation of a macromolecule in a centrifugal field. It should be noted however that some small variations of sedimentations are expected depending on the type of plant and / or the extraction protocol employed. Therefore, the sedimentation coefficient is not intended to be restrictive, but rather serve as a useful guide for the classification of the storage proteins.

[0057] The major globulins found in pulses are vicilin (7S) and legumin (11 S). The vicilin (7S) has a trimeric structure with molecular mass (MM) of -175-180 kDa and lacks disulfide bridging. In contrast, the legumin (11 S) has a hexameric (MM of -340-360 kDa) quaternary structure composed of 6 subunits (MM of ~60kDa) linked by non-covalent interactions. Each subunit pair is comprised of an acidic (MM -40 kDa) and basic (MM -20 kDa) chain joined by a disulfide bond. The ratio of the legumimvicilin (L / V) is not fixed and may vary among different pulse varieties and species. A third globulin pulse protein is convicilin with 3 or 4 subunits each having a MM of -70 kDa and a sedimentation coefficient of -8S. Convicilin is present in lesser amounts as compared to other globulins. Other globulins include for example 2S globulins, conglutin, sfa, edestin, amandin, concanvalin, cruciferin, helianthinin.

[0058] The albumins found in pulse proteins are soluble proteins with a variable molecular mass (-12-28 kDa). Albumin proteins include for example 2S albumins, napins, barley trypsin inhibitor and wheat a-amylase inhibitor. In typical commercial protein isolates, there are generally only residual amounts of albumins present as they are generally removed during the protein extraction process.

[0059] Globulins are typically obtained from soybean, pea, rice, potato, rapeseed, sunflower, lentil, bean, fava bean, mung bean, sunflower seed, pumpkin seed, flax, chia, canola, lupine, alfalfa, moringa, borage, hemp seed, and cotton seed; preferably obtained from pea protein, potato protein, rapeseed protein, and / or sunflower protein.

[0060] Prolamins and glutelins make up 85% of proteins in the cereal and pseudo cereal families. Prolamins are typically found in wheat, corn, barley and rye. They include gliadin from wheat, hordein from barley, secalin from rye, zein protein from corn, kafirin from sorghum, andavenin from oats. Prolamins are high in proline and glutamine amino acid content. They have a relatively high fraction of non-polar functionalities. Of all the prolamins, zein protein from corn is the most widely commercially available.

[0061] Zein proteins can be classified into different types based on their solubility, amino acid composition and molecular weight. The primary types of zein protein are a-(alpha) zein protein, p-(beta) zein protein, and y(gamma)-zein protein. Commercially available zein protein is a combination of all three protein types but primarily composed of a-Zein protein. In this invention the term zein protein includes a-(alpha) zein protein, p-(beta) zein protein, y-(gamma) zein protein and b-(delta) zein protein.

[0062] a-Zein protein is the most abundant form of zein protein, comprising greater than 70 of the total zein protein content in corn. It is soluble in 70-90% aqueous ethanol solution and typically exists as a monomer in solution. It has a high content of nonpolar amino acids like leucine, proline, and alanine, which contribute to its hydrophobic nature. a-Zein protein consists of two polypeptides with molecular weights of about 19 and 22 kDa. a-Zein protein can also exist as a dimer. For the avoidance of doubt all references to a-zein protein include both the monomer and dimer forms

[0063] P-Zein protein accounts for about 10-20% of the total zein protein content. It is soluble in more polar solvents compared to a-zein protein and tends to form aggregates more readily than a-zein protein. It has a higher content of sulphur-containing amino acids like cysteine and methionine. p-Zein protein has a molecular weight of about 14-17 kDa.

[0064] y-Zein protein makes up about 5-20% of the total zein protein content in corn. It is soluble in aqueous alcohol solutions and in reducing agents that break disulfide bonds. It is known for forming more stable aggregates due to the presence of disulfide bonds from the significant presence of amino acids like cysteine. It also has a relatively higher proportion of polar amino acids compared to a-zein. y-Zein protein has a molecular weight of about 27 kDa.

[0065] b-zein protein makes up a very small proportion, typically less than 1wt.%, of the zein protein in corn. It has a molecular weight of about 10 kDa.

[0066] Preferably, the one or more plant proteins are selected from prolamins, glutelins, albumins, globulins and combinations thereof. More preferably, the one or more plant proteins comprise one or more prolamin proteins. Even more preferably, the one or more prolamin proteins comprise zein proteins. Most preferred, the one or more prolamin proteins comprise zeinproteins in combination with one or more globulin proteins and / or one or more glutelin proteins.

[0067] Even more preferably, the one or more plant proteins are selected from the group consisting of soybean protein, pea protein, rice protein, potato protein, rapeseed protein, sunflower protein, lentil protein, bean protein, fava bean protein, mung bean protein, sunflower seed protein, pumpkin seed protein, flax protein, chia protein, canola protein, lupine protein, alfalfa protein, moringa protein, borage protein, hemp seed protein, cotton seed protein, wheat protein, barley protein, rye protein, corn protein, sorghum protein, and avenin protein.

[0068] Even more preferably, the one or more plant proteins are selected from the group consisting of pea protein, potato protein, rapeseed protein, sunflower protein and corn protein.

[0069] Most preferably, the one or more plant proteins comprise corn protein in combination with any other plant protein.

[0070] In a preferred aspect of the present invention, the plant protein is within of a plant proteincontaining material selected from protein isolates, protein concentrates, flours and meal. Plant protein isolates have a higher concentration of protein, typically 80%. Plant protein concentrates have a lower concentration of protein, typically 65%, and plant protein flours have the lowest concentration of protein, typically 55%. Meals such as rapeseed meal or corn gluten meal have a lower concentration of protein, typically greater than 30%. The amount of plant protein in the plant protein-containing material is preferably greater than 25%. Such plant protein-containing materials may comprise more than one plant protein type, for example globulins and prolamins.

[0071] The majority of the remaining plant material in a plant protein-containing material is composed of carbohydrates. The level of carbohydrate can be analysed by readily available methods, such as the phenol-sulfuric acid method, in which polysaccharides are hydrolysed and then converted to furfural or 5-hydroxymethyllfurfural. These compounds react with a developer to generate a chromogen, which can be detected spectrophotometrically.

[0072] All commercially available grades of corn protein are suitable for use in this invention. These are mainly obtained by extraction from corn protein-containing material such as corn kernel material and / or corn gluten meal and mainly comprise a-Zein protein, typically greater than 70% a-zein protein, with other zein proteins also present, typically at lower levels. Some commercial grades of zein may comprise very high levels of a-Zein protein, preferablygreater than 80% a-zein protein, more preferably greater than 85% a-zein protein, more preferably greater than 90% a-zein protein, more preferably greater than 95% a-zein protein, even more preferably more than 97 wt.% a-zein protein, and most preferably more than 98 wt.% a-zein protein.

[0073] Commercial grades of corn protein are available as a powder of varying particle size or flakes depending on the process used to dry the protein. The dry powder still contains some bound water, which is less than 10 wt.% of the corn protein, preferably less than 8wt.% of the corn protein, more preferably less than 6 wt.% of the corn protein, most preferably less than 4 wt.% of the corn protein. Commercially available grades of corn protein usually comprise organic impurities, such as carbohydrates, lipids, organic acids etc. As such, small amounts of oleic acid may already be present in the commercially available grades of corn protein.

[0074] Corn gluten meal is a suitable protein-containing material source of zein protein but also contains significant levels of carbohydrates. De-starched corn gluten meal is also a suitable source of zein protein with a lower level of carbohydrates. Both corn gluten meals typically have concentrations of between 25 and 40 wt.% zein protein but also contain significant levels of glutelins and globulins. Different protein extraction processes of these sources can result in varying levels of zein protein and varying levels of other proteins, typically corn glutelins and globulins. Corn Glutelins, sometimes referred to as zeanins, can be isolated as the major component of the solid protein cake left after extraction of zein from corn gluten meal, with 80% ethanol.

[0075] Commercial grades of corn proteins also have different colours ranging from pale yellow to dark orange. These different grades contain different levels of naturally occurring colourants and pigments which are also considered as impurities.

[0076] In aqueous coating compositions of the present invention, the one or more plant proteins may be native or enzymatically modified or hydrolysed.

[0077] In preferred aqueous coating compositions of the present invention, the one or more plant proteins are not covalently modified.

[0078] The plant protein content of a plant protein-containing material or raw material, or protein content of a coating, can be determined by the colorimetric Bradford Assay, which uses Bovine Serum Albumin as the standard and the colour change from brown to bule as the dye binds to the protein. It is commonly available as a Kit from chemical laboratory suppliers suchas Thermo Fisher Scientific or Sigma-Aldrich. The plant protein can be extracted from the aqueous coating composition by precipitation. For example, prolamins can be extracted with 80% ethanol then precipitated by adding water, whilst globulins can be extracted by addition of alkali or salt.

[0079] Globulin protein content, for example, pea protein can be measured by SDS-PAGE, Enzyme Linked Immunosorbent Assay (ELISA), or by a selective extraction (e.g. with salt solution or alkali) followed by quantification of extraction yield.

[0080] Glutelin protein content can be similarly measured by SDS-PAGE, ELISA, or by a selective extraction followed by quantification of extraction yield.

[0081] In preferred aqueous coating compositions of the present invention, the amount of plant protein in the aqueous coating composition is at least 5 wt.%, preferably at least 10 wt.%, more preferably at least 15 wt.% and even more preferably at least 20 wt.% of the aqueous coating composition.

[0082] Ammonium oleate is an emulsifier commonly used in cosmetic cleansing compositions. It is the ammonium salt of oleic acid. It is also referred to as ammonia soap. Ammonium linoleate is a speciality chemical with less common usage. It is the ammonium salt of linoleic acid.

[0083] In a preferred embodiment of the present invention the ammonium oleate and ammonium linoleate are formed in-situ by the mixing of oleic acid and linoleic acid with ammonium hydroxide. This may be done in the presence of the plant protein or maybe done in the absence of the plant protein, which is then added in another step.

[0084] In an alternative embodiment of the present invention ammonium oleate and ammonium linoleate are prepared prior to being added to the plant protein and water mixture in the manufacturing process of the aqueous coating compositions.

[0085] In preferred embodiments only a proportion of the fatty acids are converted to the ammonium salts.

[0086] Without wishing to be bound by theory it is believed that at pHs close to the pKa of the fatty acids, the equilibrium is such that the formation of the ammonium fatty acid salts occurs sufficiently to increase solubility of the protein. However the degree to which this occurs is also balanced by the formation of micelles by the fatty acids and their salts, and theequilibrium is therefore affected by their critical micelle concentrations. The pKa of fatty acids in these situations is shifted from the acid region (typically pH 4-5) to the alkaline region, due to stabilising effects such as the formation of micelles. The presence of plant proteins is also believed to affect the equilibrium between the fatty acids and ammonium salts. The pKa of the coating compositions can be determined experimentally through commonly used titration methods whilst taking into account the complex mixtures by measurement of appropriate controls. It is believed that controlling the pH of the aqueous coating composition is key to controlling the level of fatty acid salts and hence protein solubility. Excessive levels of fatty acid salts are however undesirable as they can lead to unwanted formation of insoluble visible residues.

[0087] Ammonium salts of fatty acids are much less crystalline, more soluble and less prone to precipitation than sodium salts of fatty acids, due to the larger size of the ammonium ion, which means the salts of the fatty acids do not pack as tightly as it would with the sodium ion. It has been found that this produces coating compositions that are more stable. Sodium oleate tends to form middle phases which are hard to disperse, unlike ammonium oleate. Ammonium salts of the fatty acids have a distinct advantage over sodium salts of fatty acids in forming stable coating compositions. The presence of ammonium salts in the coating composition can be verified by isolating and extracting the salt using organic solvents, for example acetone.

[0088] It has also been found that ammonium oleate and ammonium linoleate in the liquid coating composition will revert to oleic acid and linoleic acid respectively when drying to form a coating, due to the loss of ammonia through evaporation shifting the equilibrium of the system towards the fatty acids. If the liquid coating composition contained sodium oleate and sodium linoleate, rather than ammonium oleate and ammonium linoleate, then on drying there would be no loss of sodium, and therefore no shift in the equilibrium towards the free fatty acids. The fatty acids are fundamentally more compatible with zein protein than the corresponding fatty acid salts (soaps). Just enough ammonia or ammonium salts needs to be added to the coating composition to have the desired solubility effect without an excess of ammonia causing issues of a strong malodour associated with the coating or producing emissions during industrial drying that are costly to handle appropriately from a safety and environmental perspective.

[0089] In addition fatty acid salts (soaps) formed from inorganic bases, such as sodium or potassium hydroxides or carbonates, will be left in the dry coating and can have a detrimental effect on the water barrier properties of the coating and should therefore beminimised. This is best achieved by only using ammonium fatty acid salts. These are formed from ammonium hydroxide, NH4OH, a basic solution of ammonia in water, also known as ammonia solution. It is commonly used in household cleaners and manufacturing of fertilizers and textiles. At high concentrations it can have a strong odour but at the low levels used in this invention it is less noticeable

[0090] The combination of the fatty acids and ammonium hydroxide in water in varying ratios results in aqueous coating compositions of the present invention of varying pH, but which are above 7.5. Preferably the pH of the coating composition is between 7.75 and 11.0, more preferably between 8.0 and 10.5, even more preferably between 8.0 and 10.25, even more preferably between 8.0 and 10.0, even more preferably between 8.25 and 9.75, even more preferably between 8.25 and 9.5, even more preferably between 8.5 and 9.25, most preferably between 8.5 and 9.0.

[0091] Controlling the pH of the aqueous composition to above pH 7.5 ensures that some ammonium oleate and ammonium linoleate are present which is essential for creating a stable aqueous coating composition comprising plant proteins that are otherwise unstable in water. If an excess of ammonium hydroxide is present the pH will be very much higher, for example greater than 11. At such high pHs there is a significant risk of undesirable hydrolysis of the plant proteins resulting in poor quality coatings. At such high pHs there will also be greater formation of ammonia on drying which will results in an undesirable odour and, in industrial processing, the need for dedicated equipment to handle the hazardous vapours and dispose of them in an environmentally sound manner.

[0092] Oleic acid and linoleic acids are monounsaturated 18-carbon chain fatty acids. Oleic acid is mono-unsaturated whilst linoleic acid is di-unsaturated. Oleic acid can be used in the inventive mixtures as a pure compound, or as an mixture with linoleic acid or as part of a complex oil with other fatty acids and materials. Commercially available oleic acid is often a mixture with unsaturated 18 carbon chain fatty acids including linoleic acid, and minor levels of tri-unsaturated 18 carbon chain fatty acid, linolenic acid. Linolenic acid is a drying acid, so only minor levels are tolerated in the aqueous coating composition of this invention.

[0093] Commercially available oleic acid may also include 16-carbon chain fatty acids.

[0094] Tall oil, an unrefined by-product of wood pulp manufacture, importantly in addition to oleic acid and linoleic acid, contains typically around 50 wt.% resin acids, such as abietic acid and pimaric acid, as well as rosins, sterols and other materials with very poor coating behaviours and properties. It is therefore not a suitable material for this invention. Tall oil can be furtherprocessed to extract only the tall oil fatty acids. This highly refined by-product of wood pulp manufacture is a mixture of typically 40 to 60 wt.% oleic acid and most of the remainder being linoleic acid, making it a suitable material for this invention.

[0095] Oleic acid and linoleic acid behave as plasticisers when the aqueous coating composition is dried onto a substrate. The low melting points of oleic acid and linolenic acid, 13°C and -5°C respectively, are key for their plasticising effect and these two unsaturated fatty acids do not form crystalline structures, which would otherwise be detrimental to forming flexible coatings. They also make the dried coating more hydrophobic and therefore a better moisture barrier.

[0096] Oleic acid and linoleic acid therefore have multiple functions within the coating composition. Firstly, they transform into their respective salts in the liquid aqueous coating composition in the presence of ammonium hydroxide to stabilise the plant protein, secondly they affect the pH of the coating composition and thirdly they add flexibility and hydrophobic characteristics to the dry coating. These two fatty acids are key to preparing stable and processable coating compositions as well as forming good quality coatings upon drying.

[0097] In a further aspect the coating compositions of the present invention may additionally comprise one or more other C12 to C18 saturated or unsaturated fatty acids and / or salts, in an amount of less than 50 wt.% of the oleic and / or linoleic acids and / or salts. The higher proportion of oleic and linoleic acid and / or salts relative to other fatty acids and / or salts is required to ensure that the dry coating has good flexibility. Fatty acids with a higher melting point than oleic acid tend to form crystalline structures reducing the coating flexibility. The additional fatty acids of the present invention may be selected from the group consisting of C16 unsaturated fatty acids, C14 saturated fatty acids (e.g. myristic acid) and C12 saturated fatty acids (e.g. lauric acid). For the avoidance of doubt triglycerides or esters formed from fatty acids and are not themselves fatty acids, having very different physical and chemical properties. In preferred coating compositions of the present invention the additional fatty acid has a melting point below 60°C as adding materials at a temperature higher than this to an ammonia containing mixture is undesirable due to the potential loss of ammonia through premature evaporation, as well as health and safety concerns. Preferably the fatty acids are extracted from plant sources, for example rapeseed oil has a high content of oleic acid.

[0098] Suitable pH adjusters can be selected from the group including, ammonium hydroxide, sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, glucono-b-lactone, acetic acid or lactic acid. pH adjusters are used at low levels to trim the pH of the coatingcomposition above pH 7.5 and only in addition to, and not as an alternative to, ammonium hydroxide and oleic acid and linoleic acid.

[0099] The viscosity of the coating composition should preferably be suitable for coating substrates using a variety of application, spreading and drying techniques. In one embodiment the viscosity is reduced by diluting the aqueous coating composition with water. The level of water in the aqueous composition can be measured by Karl Fisher titration and can be easily completed using commercially available equipment. In another embodiment the viscosity is reduced by adjusting the pH to be acidic resulting in the formation of a colloidal suspension prior to coating.

[0100] The aqueous coating compositions may be shear thinning and this is measured as a lower viscosity at a higher shear rate. Shear thinning behaviour can be advantageous as higher viscosity compositions can be physically stable for longer periods but with a low level of shear they are thin enough to be compatible with existing coating equipment. The viscosity of the aqueous coating composition varies according to the solids content, but typically is greater than 100 mPa.s. The viscosity at 1 s’1shear rate is used as an indication of viscosity at low shear and the viscosity at 55 s’1shear rate is used as an indication of viscosity at high shear. Preferably the viscosity of the coating compositions is less than 50,000 mPa.s at 55 s’1shear rate, more preferably less than 20,000 mPa.s at 55 s’1shear rate, even more preferably less than 10,000 mPa.s at 55 s’1shear rate, even more preferably less than 5000 mPa.s at 55 s’1shear rate, even more preferably less than 2000 mPa.s at 55 s’1shear rate, even more preferably less than 1000 mPa.s at 55 s’1shear rate and most preferably less than 500 mPa.s at 55 s’1shear rate. The viscosity of the aqueous coating composition is measured by methods well known in the art, such as an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry.

[0101] In preferred aqueous coating compositions of the present invention, the solids content is between 15 wt.% and 55 wt.%. In preferred aqueous coating compositions of the present invention the solids content is between 15 wt.% and 52 wt.%, more preferably between 16 wt.% and 49 wt.%, more preferably between 17 wt.% and 46 wt.%, even more preferably between 18 wt.% and 43 wt.%. The solids content is defined as the part of the composition that remains as a solid on a substrate when then volatile components of the composition are removed or lost through evaporation. The solids content can be measured by placing a small sample, preferably as a thin film on glass, of the aqueous composition in an oven at between 80° and 150°C for several hours, preferably overnight, and left until a constant weight is reached.In preferred aqueous coating compositions of the present invention, the ratio of oleic acid and ammonium salts of oleic acid to plant protein in the solids content is between 1 :4 and 2:1, more preferably 1:2 and 1:1.

[0102] In alternatively preferred aqueous coating compositions of the present invention, the combined amount of one or more plant proteins, ammonium salt of oleic acid, oleic acid, ammonium salt of linoleic acid, and linoleic acid is greater than 75 wt.% of the film-forming component.

[0103] In a preferred aspect of the present invention, the solids component further comprises one or more preservatives. Preferably, the one or more preservatives are selected from preservatives that perform their antimicrobial function in alkali aqueous compositions. More preferably, the one or more preservatives are selected from the group consisting of methyl paraben, propyl paraben, benzyl alcohol, phenoxyethanol, isothiazolinones (such as methylisothiazolinone (MIT) chloromethylisothiazolinone (CMIT) and benzisothiazolinone (BIT)), formaldehyde releasers (such as DMDM hydantoin, imidazolidinyl urea, diazolidinyl urea), antimicrobial essential oils, which are mixtures of volatile compounds extracted from plants and possessing antimicrobial activity (such as essential oils extracted from thyme, oregano, clove, lavender, clary sage, or cedar and those described in Baser, K.H.C.;

[0104] Buchbauer, G.’s Handbook of Essential Oils, 3rd ed.; CRC Press: Boca Raton, FL, USA, 2020), antimicrobial fragrance and flavour compounds (such as thymol, carvacrol, eugenol, cr-cedrol, cinnamaldehyde, geraniol), and combinations thereof.

[0105] Preservatives are present in the aqueous composition at less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 1 wt.%, even more preferably less than 0.5 wt.%, most preferably less than 0.1 wt.%. Preservatives are typically added at such a low level that it does not typically have any noticeable or significant impact on the physical and chemical properties and behaviours of the coating compositions or on the resultant coatings. In this regard the specific preservative is not limiting, and the selection of the one or more preservatives can be made on other applicable factors such as cost, convenience, and whether the coated packaging is for food contact or not.

[0106] In an alternatively preferred aspect of the present invention, the solids component further comprises a film-modifying component, wherein the film-modifying component comprises one or more of plasticisers, spreading agents and fillers.Spreading agents are materials that are added at low levels in coating compositions to alter the rheological properties of the composition to make it easier to apply to a surface, for example by a painting mechanism. Suitable materials include alcohols and polyols with a chain carbon length greater than 2, such as butanol, and glycols, such as propylene glycol. Preferably the spreading agent is propylene glycol.

[0107] Plasticisers can be added to aid processing and to increase coating flexibility. When the substrates that are to be coated are flexible it is important to avoid them cracking when handled, for example when card is folded into boxes, so as not to expose the underlying original uncoated substrate. Plasticisers maybe hydrophobic or hydrophilic. Hydrophilic plasticisers can negatively affect the coatings moisture resistance whilst hydrophobic plasticisers can negatively affect the coatings oil resistance, so the level needs to be controlled to balance these features.

[0108] Preferably, the one or more hydrophilic plasticisers are independently selected from the group consisting of:

[0109] a) polyols formed by from 1 to 20 repeating hydroxylated units each unit including from 2 to 6 carbon atoms, provided that when the polyol is formed by only one repeating unit it has at least 4 carbon atoms, with the exclusion of sorbitol,

[0110] b) ethers, thioethers, inorganic and organic esters, acetals and amino-derivatives of polyols formed by from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms with the exclusion of acetic esters of glycerine, triethyl citrate and tributyl citrate,

[0111] c) polyol reaction products having from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms with chain extenders,

[0112] d) polyol oxidation products having from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms including at least one aldehydic or carboxylic functional group or mixtures thereof.

[0113] A hydrophobic plasticiser can be a water insoluble vegetable oil or wax.

[0114] In accordance with the present invention, the one or more plasticisers are preferably selected from the group consisting of urea, glycerol, sorbitol, mannitol, xylitol, propane-1 ,2-diol, propane-1, 3-diol, 2-methyl-1,3-propanediol, ethylene glycol, polyethylene glycol, monoglycerides, diglycerides, triglycerides, glucose, mannose, fructose, sucrose, lecithin, waxes, amino acids, glycerol formal, glycerol triacetate, acetyltributyl citrate, epoxidized soybean oil, sucrose esters of fatty acids, glyceryl esters of fatty acids, glycol esters of fatty acids, sugar surfactants and combinations thereof.Sugar surfactants are preferably composed of at least one, preferably more than two, monosaccharide units linked glycosidically and may include what are termed ‘sugar’ moieties (two 10 monosaccharide units) or from three monosaccharides. The monosaccharides of the sugar moiety may be of the same type (homopolysaccharide) or different (heterosaccharide). Preferably, the sugar surfactant is ionic, more preferably it is anionic, cationic, or amphoteric. More preferably, the sugar surfactant is anionic. The sugar surfactant is preferably selected from functionalised alkyl polyglycosides, fatty acid 15 glucamides, glycinates, glycolipid biosurfactants, such as rhamno-based surfactants (e.g. rhamnolipids) or sophorolipids, or mixtures thereof.

[0115] Preferably, the plasticisers are bio-based and even more preferably plant-derived.

[0116] Plasticisers can also be added in the form of a mixture with other components, preferably a bio-based and even more preferably a plant-derived mixture.

[0117] Preferably, the one or more fillers are selected from inorganic and organic fillers.

[0118] More preferably, the organic fillers are selected from the group consisting of wood powder, rice husk, cellulose, microfibrillated cellulose, cellulose nanofibrils, cellulose nanocrystals, starch, plant fibres, olive pit powder, lignin particles, organic pigments, organic dyes and combinations thereof.

[0119] Even more preferably, the one or more fillers are inorganic fillers. Most preferably, the inorganic fillers are selected from the group consisting of clays, silica, calcium carbonate, talc, gypsum, mica, calcium silicate, inorganic pigments, inorganic dyes and combinations thereof.

[0120] Coating compositions of the present invention may also include processing aids that do not interfere with the integrity of the coating composition or the dried coating. Processing aids if used are present in the aqueous composition at less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 1 wt.%, even more preferably less than 0.5 wt.%, most preferably less than 0.1 wt.%.

[0121] Processing aids can be selected from a list including, but not exclusively anti-blocking agents, antifoams, antioxidants, bleaching agents (e.g., sodium metabisulfite, sodium bisulfite or others), detackifying agents, extenders, wetting agents, levelling agents, colloidal stabilisers, rheology modifiers, adhesion promoters, light stabilisers, lubricants, plasticizercompatibilizers, release agents, salts (e.g.: magnesium chloride, calcium chloride) and other functional ingredients, in amounts suitable for their intended purposes.

[0122] Colourants can be added to the coating composition to provide a different aesthetic experience to the final coated product. Colourants can be liquids or particulates. Examples include curcumin, quinoline yellow, cochineal, indigo carmine, carotenes, annatto and anthocyanins. Examples of colourant pigments include iron oxide pigments. Colourants may be of natural or synthetic origin. In preferred embodiments the colourants are of natural origin and are classed as food safe materials.

[0123] Pigments can also comprise whitening and opacifying pigments including titanium dioxide and extenders such as amorphous silica. This can provide both a whitening effect for paper substrates but also can act as a processing aid by reducing the viscosity of the protein mixture.

[0124] Phyllosilicates can be added to the coating composition to provide a different aesthetic experience to the final coated product. Phyllosilicates include a serpentine mineral, a clay mineral, a chlorite mineral or a mica mineral, or mixtures thereof. Preferably, said clay mineral is selected from bentonite, kaolinite, pyrophyllite, vermiculite and a smectite (e.g. montmorillonite, cloisite, laponite, hectorite etc.), or mixtures thereof. Silicon-containing compounds can improve the barrier properties of the coating formed by applying the aqueous coating composition to a substrate.

[0125] Silicon-containing compound include silica sol, silica powders, hydrolysable silanes, sodium silicates such as sodium metasilicate, sodium orthosilicate and sodium pyrosilicate, tetra ethoxy silane (commonly known as tetraethyl orthosilicate, TEOS), tetrapropyl orthosilicate, dimethyl diethoxysilane, methyl triethoxysilane and tetramethyl orthosilicate, or combinations thereof.

[0126] In another aspect, the present invention relates to a method of producing an aqueous coating composition according to any preceding claim comprising

[0127] a) mixing one or more plant proteins, water, ammonium hydroxide, oleic acid and linoleic acid; and / or

[0128] b) mixing one or more plant proteins, water, and ammonium salts of oleic acid and ammonium salts of linoleic acid; and

[0129] c) optionally adjusting the pH of the mixture obtained in step a) or in step b).Preferably, in step a) the oleic acid and the linoleic acid are added to a solution of ammonium hydroxide in water comprising the one or more plant protein. Alternatively, the ammonium hydroxide solution and the oleic and linoleic acids can be combined prior to the mixing with the one or more plant protein. This however can result in a solid paste that is much harder to process and requires dilution before addition the one or more plant protein.

[0130] In a further aspect, the present invention relates to the use of an aqueous coating composition according to the invention for coating a substrate.

[0131] The substrate suitable for coating may be any substrate that requires protection. The substrate material may be a crystalline material, an amorphous material or a fibre-based material. The material may be natural or synthetic; alternatively, it may be plant-based, animal-based or inorganic. Typical crystalline materials include metals, typical amorphous materials include glass, fibre optics and synthetic or bio-based polymers and typical fibrebased materials include paper, textiles, seeds, fruits and vegetables.

[0132] Preferably, the substrate is a cellulose-based substrate, more preferably the cellulose-base substrate is selected from paper, card and cardboard.

[0133] In a preferred aspect of the present invention, if the substrate is an uncoated substrate, then the aqueous coating composition is applied as base coating, and if the substrate is a coated substrate, then the aqueous coating composition is applied either as a top coating or as an intermediate coating where it is itself overcoated.

[0134] In an even further aspect, the present invention relates to a method of applying an aqueous coating composition according to the invention to a substrate.

[0135] Preferably, after the aqueous coating composition has been produced according to the invention and before the coating composition is applied to the substrate, the coating composition is stored for at least 12 hours, more preferably for at least 24 hours, even more preferably for at least 48 hours, most preferably for at least 3 days.

[0136] The coating composition is best stored at a modest temperature, preferably below 40°C, more preferably below 30°C, even more preferably at room temperature. Preferably the coating composition is not allowed to freeze, preferably being stored above 5°C.After application of the aqueous coating composition to the substrate the coating may be dried. Preferably, the coating may be dried by the application of heat.

[0137] In a further aspect, the present invention relates to a coated substrate obtained by the inventive method described herein.

[0138] In one aspect of the present invention, plant protein coatings for fibres are preferred due to the opposite charge between the positively charged plant protein and the negatively charged fibre material, for example cellulose, resulting in the formation of a strongly bonded coating. These strong electrostatic interactions, typically result in enhanced properties, including mechanical properties such as strength, stiffness, wear resistance, water resistance, and elasticity. Polycations normally used for electrostatically binding to negatively charged cellulose fibres are animal derived (for example chitosan) or are non-biodegradable (i.e. polyvinyl amines).

[0139] Fibre-based materials maybe be cellulosic in origin and can be selected from paper (bleached, unbleached, coated in which pores still remain, uncoated, super-calandered), cardboard, wood, fabric or textile, seeds, fruits and vegetables.

[0140] Examples of paper materials can include generally thinner, flexible papers, for example useful as wrapping materials, or in making sachets, as well as generally thicker, rigid papers or cardboard (e.g., corrugated cardboard, paperboards, moulded fibreboard), for example useful as boxes, containers, plates, cups, or other storage or food-service items. In this case it is essential that items used for food service are coated with materials that are food-grade. In this case it is highly desirable that the coating is biodegradable and / or does not affect the recyclability of the paper or cardboard. Test methods commonly used to assess the effect of materials on recyclability include PTS-RH 021:2012 Cat 1 and Cat 2. Additionally in this case, where consumers are handling the packaging material, it is also highly desirable that the coating does not disturb the aesthetics of the packaging material. Much of this is brown or beige coloured craft paper or cardboard and a clear consistent coating with no oleamide or linolamide white residues is highly desirable, or consumers may question whether the surfaces are contaminated in some way

[0141] It can also be advantageous that the coating can be heat sealed to enable sachets and boxes to be closed and sealed.Natural fibres include non-woody fibres, such as cotton, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute, hemp, bagasse, milkweed floss fibres, and pineapple leaf fibres; and woody fibres, such as wood or pulp fibres such as those obtained from deciduous and coniferous trees, including softwood fibres, such as northern and southern softwood kraft fibres, hardwood fibres, such as eucalyptus, maple, birch, and aspen. Pulp fibres may be prepared in high-yield or low-yield forms and may be pulped in any known method, including kraft, sulphite, high-yield pulping methods and other known pulping methods.

[0142] The natural fibres to be used in accordance with the present invention may be recycled natural fibres, virgin natural fibres or mixes thereof. Additionally, for good mechanical properties, it may be desirable that the natural fibres be relatively undamaged and largely unrefined or only lightly refined.

[0143] Suitable wood materials can be any type of wood commonly used in home, office, and outdoor settings and the material can include furnishings and construction materials. In such cases it is desirable that the coating does not alter negatively the aesthetics and physical properties of the items.

[0144] In a particular aspect, the material comprises a porous cellulosic material. A cellulosic material generally includes at least one of cellulose and hemicellulose, and it can further include lignin (e.g., as a lignocellulosic material).

[0145] Cellulose-based fibres may include regenerated cellulose fibre such rayon or Cuprammonium rayon, and high pulping yield fibres, unless specified differently. The term “cellulose-based fibres” also includes chemically treated natural fibres, such as mercerized pulps, chemically stiffened or cross-linked fibres, or sulfonated fibres. Also included are mercerized natural fibres, regenerated natural cellulosic fibres, cellulose produced by microbes, the rayon process, cellulose dissolution and coagulation spinning processes, and other cellulosic material or cellulosic derivatives. Other cellulose-based fibres included are paper broke or recycled fibres and high yield pulp fibres including bleached chemo-thermomechanical pulp (BCTMP), chemo-thermomechanical pulp (CTMP), pressure / pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), high yield sulphite pulps, and high yield Kraft pulps, all of which leave the resulting fibres with high levels of lignin but are still considered to be natural fibres. High yield fibres are well known for their stiffness in both dry and wet states relative to typical chemically pulped fibres.Suitable fabric or textile substrates can include any cellulosic materials commonly used in garments or upholstery or otherwise, such as cotton, jute, flax, sisal, hemp, etc.

[0146] Suitable seed substrates include those which can be used in domestic, horticultural, or agricultural settings. In this case it is highly desirable that the coating is biodegradable so as not to pollute the environment.

[0147] Fruit and vegetable substrates may be fresh or dried or frozen and will benefit from a coating to provide protection during storage and transports to increase their shelf life and reduce spoilage. Fruit and vegetables also benefit from the coating providing a gas barrier to reduce the ripening effects of ethanol produced by other produce stored in close proximity. In this case it is necessary that the coating is edible and highly desirable that it is digestible.

[0148] Inorganic fibres are often fragile and require protection from the environment. Common examples of such fibres are silica-based fibres such as fibre optics which is very pure and has a very low index of refraction, however they are fragile. Alternatively, plastic fibre optic cables are made from acrylate and polyimides, can be used but these eventually breakup in the environment into harmful micro plastic. Glass fibres also include those used in Fibreglass or mineral wool and Rockwool.

[0149] In a preferred aspect of the invention, the substrate material is a fibre-based material. In another preferred aspect of the invention, the substrate material is a cellulosic material.

[0150] More preferably, the substrate material is selected from the group consisting of wood, wood pulp, cotton fibres, hemp fibres, jute fibres, sisal fibres, flax fibres, cellulose-based fibres, silica-based fibres, fruits, vegetables, and seeds.

[0151] More preferably, the substrate material is selected from the group consisting of paper, card, cardboard, corrugated board.

[0152] A variety of coating methods can be employed depending on the substrate to be coated.

[0153] For physically fragile and / or heat-sensitive substrates, such as fruits and vegetables, coating is typically achieved by dip coating or spray coating, with drying at temperatures between 4°C and 50°C, preferably between ambient and 30°C, more preferably at ambient. For drying at lower temperatures this may need to take place over several hours.For seeds the coating is typically applied in a drum coater, spray coater, rotary coater, fluid bed or extruder. Drying typically is carried out at ambient temperature.

[0154] In a preferred aspect of the invention, applying the aqueous coating composition to the substrate is achieved by roller coating, dip coating, slot dies, air knives, or spray coating.

[0155] For materials that are not sensitive to heat, pressure or shear, for example paper or fabrics, coating can be undertaken using a variety of equipment including reverse rollers, direct rollers, gravure rollers (direct and reverse), blade over rollers, flexographic equipment, lithographic equipment, slot dies, air knives, spray coating or dip coating.

[0156] The viscosity of the coating composition is an important factor in its ability to successfully for a dried coating on a substrate. If the coating composition is too viscous the coating does not spread evenly or cannot be handled by existing coating equipment and forms an inconsistent coating with poor barrier and heat-sealing properties. If the coating composition is too thin the coating spreads too thinly or cannot be handled by existing coating equipment and does not form a thick enough coating with poor barrier and heat-sealing properties.

[0157] Once the coating has been applied, the wet coated sample is exposed to temperatures between 50°C and 200°C, preferably 70°C and 150°C, more preferably 80°C and 130°C in order to dry it including equipment such as steam cylinders, Yankee Dryers, Flakt Dryers, Infra-red dryers, non-contact dryers (fans) or air flotation dryers.

[0158] In a further preferred aspect of the invention, drying of the aqueous coating composition is achieved by exposure to air at temperature between 50°C and 250°C for between 0.1 seconds and 10 minutes, more preferably 60°C and 200°C for between 2 seconds and 5 minutes, most preferably between 80 °C and 150°C for between of 6 seconds and 3 minutes. Preferably, drying of the aqueous coating composition is achieved by non-contact drying, preferably by using a fan. If drying in an open system sufficient ventilation is needed to ensure any ammonia vapour is removed.

[0159] In a further preferred aspect of the invention, drying of the aqueous coating composition on a substrate is carried out in a closed environment, so that any ammonia that is evaporated is captured in order to be either recycled or disposed of in a responsible manner. Drying may also be carried out under reduced pressure, including under vacuum, enabling lower drying temperatures to be used.When the substrate is paper or cardboard, drying of the aqueous coating composition is preferably achieved by exposure to elevated temperatures for a period of time of 10 seconds or less, more preferably 5 seconds or less, most preferably 2 seconds or less.

[0160] Many substrates such as paper, cardboard, fabrics or textiles have print applied for background colour, branding or packaging information. For examples industrially Offset Printing, Lithography, Digital Printing, Gravure, Screen Printing or Flexography can be used to apply print to paper. All of these methods use roller technology to apply single-colour inks or pigments to the substrate one at a time. Therefore, there needs to be minimal bleed between the layers of colour to prevent smudging and warping of the printed image. The inventive coatings can prevent bleeding of inks or pigments, particularly when used on low density substrate materials such as tissue, blotting or porous paper by providing a less permeable printing surface. The inventive coatings can be used in conjunction with overprint varnishes (OPVs) to give a gloss, satin or matt finish to printing.

[0161] In a preferred aspect of the invention, the average thickness of the dried coating is between 1 and 20 microns, more preferably between 2 and 15 microns.

[0162] In an alternatively preferred aspect of the invention, the average coverage of the dried coating is between 1 and 20 g / m2(often referred to as gsm).

[0163] A recyclable item prepared with the coated substrate can easily be recycled as the coating can be easily removed or partly removed from the substrate. This is because the coating is not covalently bonded to the substrate, for example paper. In addition, the ease of removing the coating may encourage recycling of the coated substrate within a single recycling stream, such as a paper recycling stream.

[0164] The methods of recycling the coated substrates include extracting the coating in one or more aqueous extraction medium having pH value sufficient to separate the coating from the substrate.

[0165] The recycling method can further include performing a size reduction process on the coated substrate prior to extracting the coated substrate in the aqueous extraction medium. Size reduction can include pulping, grinding, or any other type of destructive mechanical process to fragment the coated substrate into smaller fragments, in particular to increase surface area exposure at interfacial regions between the substrate and the coating, therebyenhancing contact between the aqueous extraction medium and coating. In general, smaller fragment sizes can promote extraction efficiency.

[0166] The coating can be washed off from coated substrates, for example from paper pulp during re pulping. For example, the coating can be removed from the coated paper using an acidic solution, for example 40% v / v acetic acid solution. Alternatively, a rinse of pulp with a 70-90 vol% ethanol aqueous solution can be used to remove the coating from the coated paper.

[0167] The recycling method can further include separating the substrate from the aqueous extraction medium and recovering and / or reforming the substrate. Separating the substrate from the aqueous extraction medium can be performed by any suitable solid / liquid separation process, for example filtration or decantation to retain the substrate and remove the extraction medium with the coating components therein. Optionally, the separation can be followed by one or more washing steps to remove any residual coating material remaining in and / or on the substrate. If the coated material is pulped, ground, or otherwise size-reduced prior to extraction, the resulting substrate fragments can be recovered after separation from the aqueous extraction medium and then re-formed into a new, recycled substrate, for example recycled paper or other cellulosic substrate. In embodiments, the recovered or reformed porous substrate is substantially free from the coating, for example having 5 wt.% or less coating material remaining relative to the initial coating material prior to extraction. For example, the recovered or reformed substrate can have up to 1 , 2, or 5 wt.% less coating material relative to the initial coating material prior to extraction. Alternatively, or additionally, the recovered or reformed substrate can have 0.1 wt.% or less coating material relative to the substrate material. For example, the recovered or reformed substrate material can have at least up to 0.001, 0.01, or 0.1 wt.% less coating material, relative to the material.

[0168] Extraction can remove substantially all of the coating from the substrate, for example at least 95, 98, or 99 wt.% and / or up to 90, 95, 98, 99, or 100 wt.% of the coating initially present on the coated substrate.

[0169] Alternatively, or additionally, if the pulp is not washed or extracted or partially washed / extracted, the remaining coating materials can become part of the recycled paper.

[0170] An adhesive is a substance that is capable of holding materials together in a functional manner by surface attachment that resists separation. Adhesives are routinely used in the manufacture of items for example boxes from cardboard, sachets from paper. The coatings of the invention can heat seal and therefore act as an adhesive in the preparation of itemsfrom coated materials. This negates the need for a separate adhesive which is often non-biodegradable.

[0171] Alternatively, if additional sealing is required the coatings of the present invention are compatible with typical adhesives such as starch-based adhesives, polyvinyl acetate-based adhesives, and polyethylene oxide-based adhesives or water dispersible adhesives including thermoplastic elastomer-based adhesives and polyvinyl acetate-based adhesives.

[0172] Additionally, adhesives that can dissolve in water during the re-pulping step or the disintegration step of the paper recycling process may be particularly suitable for the items of the present invention.

[0173] For items of the present invention that are intentionally left in the environment, for example seeds, or inadvertently are disposed of in the environment, for example paper packaging, it is important they are biodegradable and do not add to the growing micro plastic pollution crisis. Preferred coatings of the present invention are highly biodegradable leaving little trace of their previous existence. Coatings can be prepared for biodegradation assessment by drying aqueous coating composition according to the methods described herein onto a substrate where it can be scraped off mechanically or peeled off, such as mylar or glass.

[0174] In preferred coatings of the present invention, the biodegradation percentage based upon 02 consumption of the coating as measured according to ISO-14851 after 28 days is 70 to 100%, more preferably 80 to 100%, most preferably 85 to 100%.

[0175] In preferred coatings of the present invention, the biodegradation percentage based upon CO2 production of the coating as measured according to ISO-14851 after 28 days is 70 to 100%, more preferably 75 to 100%, most preferably 80 to 100%.

[0176] The invention also relates to the use of the coated substrate described herein for making an item selected from the group consisting of plates, cups, containers, boxes, cartons, corrugated boxes, wrappers and sachets.

[0177] In another aspect an item intended for wrapping or enclosing a product, for example a food box or sachet, may be sealed by heat-sealing, wherein the coating itself behaves as an adhesive. Aqueous compositions of the present invention were observed to form very strong seals prepared by heat-sealing the dry coating. For heat-sealing to occur, the coatings at the interface must be at or above the thermal onset temperature. Controlling thethicknesses of the coating and substrate allows sufficient heat to be transferred to the interface in the time available. A coating with an external surface comprising prolamin proteins can produce a seal when heated, therefore not requiring additional adhesive material - a self-sealing coating. In preferred embodiments of the coating when heat-sealed it may be present on one or both sides of the seal prior to applying heat and / or pressure. Therefore, it is possible to seal a coated surface to an uncoated surface or a coated surface to another coated surface. Preferably the coated substrate surface is sealed to another similarly coated surface.

[0178] Preferably, the coating of the present invention has a maximum heat-sealing strength of at least 20 N / m, more preferably at least 40 N / m, more preferably at least 60 N / m, even more preferably at least 80 N / m, even more preferably at least 100 N / m, most preferably at least 120 N / m, as measured by ASTM F88 / F88M-15 at 55% relative humidity and 20 °C after the coated item has been conditioned at 55 % relative humidity and at 20 °C for at least one hour and then sealed at a temperature of 130 °C and a pressure of 3 bar applied for a time of 1 second.

[0179] In a further aspect the coating composition can be dried onto a temporary substrate, one from which the coating can then be removed to form a self-supporting film. Suitable substrates include glass, mylar and surfaces pre-coated with non-stick or quick release agents. It is necessary for the films to have sufficient tensile strength for their intended application. Such films can be used for wrapping or enclosing a variety of products.

[0180] BRIEF DESCRIPTION OF THE FIGURES

[0181] Figure 1 - Photograph of the single-phase stable composition of Example 1b

[0182] Figure 2 - Photograph of the two-phase unstable composition of Comparative Example 2b

[0183] EXAMPLES

[0184] Materials

[0185] FloZein™, F4400C (94.78 wt.% zein based on total dry solids, 2.15% moisture) was purchased from FloZein Products, Flo Chemical Corp., USA. [The dry solids measurement is obtained by first heating the material at 100°C for several hours until there is no change is weight].BioZein™ BZ (89.19 wt. % zein protein based on total dry solids, 6.15 wt.% moisture, 0.76 wt.% fat, 0.15 wt.% ash, 9.24 wt.% unassigned impurities) was obtained from BioZein Technology Corp. Ltd, Hong Kong, China. [The dry solids measurement is obtained by first heating the material at 100°C for several hours until there is no change is weight.]

[0186] Pea Protein Isolate (PPI) (81.5 wt.% protein) (ProEarth P16109) was purchased from Cambridge Commodities Ltd.

[0187] Commercial Oleic acid, 76.5 wt.% oleic acid, 13.3% Linoleic acid, was obtained from White Sea & Baltic Co Ltd, UK.

[0188] Tall oil fatty acid, 98 wt.% oleic and linoleic acid, with 45-55 wt.% oleic acid and 30-40 wt.% linoleic acid, was purchased from Mistral Industrial Chemicals Ltd, Ireland

[0189] Lauric acid (99 wt.%) and Myristic acid (99 wt.%) were purchased from Thermo Fisher Scientific.

[0190] Methyl paraben. 99.7 wt.% purity was purchased from Alfa Aesar (UK)

[0191] Ammonium Hydroxide, 25 wt.% aqueous solution was purchased from Thermo Fisher Scientific Inc, UK

[0192] Water was purified by reverse osmosis

[0193] Methods

[0194] £H

[0195] Measurements of pH were taken after between 48 hours and 60 hours of making, at room temperature, using a Mettler Toledo Five Easy Standard benchtop meter equipped with a Mettler Toledo Economy Series pH and pH / ATC Combination Electrode.

[0196] Viscosity

[0197] Viscosity measurements were made using an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50mm plate and 1 degree angle. The sample was tested on a shear sweep from 0.1 s-1to 1000 s-1at 20°C. The viscosity at 1.13 s-1shear rate and 54.6 s-1shear rate at 20 °C can be reported, for simplicity in the data tables and text they are referred to as 1 s-1and 55 s-1respectively. It is important that the sample is left for a suitable rest period, such as 2 minutes, prior to testing so that the viscosity is not disturbed by shear introduced by pipetting or spooning the sample into the measurement equipment

[0198] Mixture stability method

[0199] The stability of the mixture was assessed visually after the sample was left for between 48 and 60 hours after making. A mixture was judged as stable (Pass) if it was a homogeneous single-phase solution, suspension or emulsion. A mixture was judged as unstable (Fail) if more than one phase was observed, such as oil floating on top, or some sedimented solid was observed.

[0200] Coating coherence test method

[0201] The ability to form a coating on glass was assessed visually after the sample was left for between 48 and 60 hours after making. 10-20 ml of the mixture was placed on a large glass pane (approximately 45 by 45 cm) and coated using a Blue K-Bar (wet thickness 100pm). The wet pane was placed in a vented oven at 120°C for 5 minutes to dry. The pane was taken out of the oven and left too cool for a minimum of 45 mins. The ability of a coating composition to form a coating was empirically characterised by the scale of Table 1. The robustness and integrity of the coating was then determined by trying to peel the coating layer off the glass. For a coating to be considered a successful dry coating, it needs to be able to form a coherent coating layer which is indicated by a score of “2” or more. Coatings do not necessarily need to be robust and flexible but, as a minimum, they need to be coherent. Higher scores than 2 on the scale indicate that the composition can form more robust and flexible coatings. Such higher values may be preferred for specific applications, such as where the coated substrate needs to be folded or bent.

[0202]

[0203] Table 1

[0204] Heating-sealing method

[0205] An agueous coating composition was coated onto paper board and tested for its heat-sealing strength according to the method given in ASTM F88 / F88M-15. The rough side of 230 gsm board (Stora Enso CKB NUDE) was coated using a black K-bar (RK print, 40 pm wet thickness) and dried at 120 °C in an oven for 5 minutes. Test samples of width 25 mm were cut to the dimensions given in ASTM F88 / F88M-15 and conditioned for 1 hour at 55% relative humidity and 20°C. Test strip samples were then sealed using an RDM heat sealer to give a fin seal. Sealed test specimens were tested using technigue A (unsupported) in aTinnius Olsen tensile tester. A sealing temperature of 130 °C and a dwell time of 1 second and pressure of 3 bar were employed. The maximum force encountered as each specimen was stressed to failure is recorded in Newtons / meter (N / m).

[0206] Example 1 - Preparation of coating compositions

[0207] Aqueous coating compositions were prepared by adding water and ammonium hydroxide (25 wt.% aqueous solution) into a 250 ml beaker at room temperature and then adding plant protein according to the levels in Tables 2-5 and mixing with an overhead stirrer (anchor blade at 333 rpm) for 5 minutes. The fatty acid was then added, and lastly the preservative, all according to the levels in Tables 2-5 and mixed for a further 40 minutes at room temperature.

[0208] The mixtures were transferred to 100ml glass bottles and left for between 48 and 60 hours at room temperature before stability assessments, pH and viscosity measurements and coating tests were undertaken according to the methods herein described, with the results in Tables 2-5. In this time frame any foam formed during the mixing had collapsed.

[0209]

[0210] Table 2

[0211]

[0212]

[0213] Table 3

[0214] The aqueous coating compositions of Tables 2 and 3 comprised a high purity grade of a prolamin protein, zein protein, and a mix of oleic and linoleic fatty acids and their respective salts.

[0215] The aqueous coating compositions of Tables 2 and 3 formed a single-phase mixture which were evaluated as stable according to the method herein. Figure 1 shows the stable mixture of Example 1b. They also all formed suitable dry coatings according to the method herein with a grade of at least 4.

[0216] The aqueous coating compositions of Tables 2 and 3 all had measured pHs greater than 7.5. This demonstrates that there was sufficient ammonium hydroxide to deprotonate at least a significant portion of the fatty acids and the ammonium salts were formed. All the pHs were less than 11 which reduced the risk of forming white residues of oleamides and linolamides, none of which were observed.

[0217]

[0218]

[0219] Table 4

[0220] The aqueous coating compositions of Table 4 comprised either lower grade purity of a prolamin protein, zein protein, and / or an alternative source of oleic and linoleic fatty acids / salts than the compositions of Table 2 and 3.

[0221] The aqueous coating compositions of Table 4 all formed a single-phase mixture which were evaluated as stable according to the method herein. They also formed a suitable coating according to the method herein with a grade of at least 4.

[0222] The aqueous coating compositions of Table 4 all had measured pHs greater than 7.5. This indicated that there was sufficient ammonium hydroxide to deprotonate at least a significant portion of the fatty acids and the ammonium salts were formed. All the pHs were less than 11 which reduced the risk of forming white residues of oleamides and linolamides, none of which were observed.

[0223] The aqueous coating compositions of Example 1h and 1i were both suitable for use in standard coating equipment and slightly shear thinning, both greater than 100 mPa.s.

[0224] Example 1h had higher viscosities than Example 1i due to its higher solids content but still acceptable for use as a coating composition.

[0225] The aqueous coating composition of Example 1h was also coated onto paper board and tested for its heat-sealing strength according to the method herein. The mean of four replicates was calculated as a maximum force to failure of 575 N / m. This is a very high seal strength and indicates that the coating would be very suitable for heat-sealing of paper packaging.

[0226]

[0227] Table 5

[0228] The aqueous coating compositions 1j and 1k of Table 5 comprised additional fatty acids and salts as well as oleic and linoleic fatty acids and salts and zein protein. The aqueous coating composition 11 of Table 5 comprised a globulin protein, pea protein, with oleic and linoleic fatty acids and salts.

[0229] The aqueous coating compositions of Table 5 all formed a single-phase mixture which were evaluated as stable according to the method herein. They also formed a suitable coating according to the method herein with a grade of at least 4.

[0230] The aqueous coating compositions of Table 5 all had measured pHs greater than 7.5. This indicated that there was sufficient ammonium hydroxide to deprotonate at least a significant portion of the fatty acids and the ammonium salts were formed. All the pHs were less than11 which reduced the risk of forming white residues of oleamides and linolamides, none of which were observed.

[0231] The aqueous coating compositions of Example 1j and 1k were both suitable for use in standard coating equipment, both greater than 100 mPa.s. They were slightly less viscous than Example 1 i of comparable composition but without the substitution of some of the oleic and linoleic acids.

[0232] Comparative Example 2 - Preparation of comparative coating compositions

[0233] Aqueous coating compositions were prepared according to the method of Example 1 and the formulations in Table 6. The mixtures were similarly assessed according to the methods herein described with the results in Table 6

[0234]

[0235] Table 6

[0236] The aqueous coating compositions of Comparative Examples 2a to 2c were all neutral or slightly acidic with measured pHs less than 7.5. This indicated that there was insufficient ammonium hydroxide to deprotonate the fatty acids.

[0237] The aqueous coating compositions of Comparative Examples 2a to 2c were all mixtures with more than one phase and evaluated as unstable according to the method herein. Figure 2 shows the unstable mixture of Example 2b.The aqueous coating compositions of Comparative Examples 2b and 2c were unable to form a suitable coating according to the method herein with a grade of 1. Although Comparative Example 2a formed a suitable, but poor-quality coating, it was not sufficiently stable to be of industrial applicability.

[0238] Inventive Example 3 - Preparation of composition with alternative order of addition

[0239] Aqueous coating compositions of Table 7 were prepared according to 2 different orders of addition of the materials.

[0240] Coating composition 3a was prepared according to the method of Example 1 wherein the ammonium hydroxide and plant protein were combined prior to the mixing in of the oleic / linoleic acids.

[0241] Coating composition 3b was prepared according to the method below wherein the ammonium hydroxide (25 wt.% aqueous solution) and oleic / linoleic acids were combined prior to the mixing in of the plant protein. Firstly oleic / linoleic acid and ammonium hydroxide were mixed in a 250 ml beaker at room temperature to create a solid paste. Then water was added according to the quantities in Table 7 and mixed with an overhead stirrer (anchor blade at 333 rpm) for 5 minutes. Zein was then added, and lastly the preservative, according to Table 7 and mixed for a further 40 minutes at room temperature.

[0242]

[0243] Table 7The aqueous coating compositions of Table 7 both formed single-phase mixtures which were evaluated as stable according to the method herein. They also formed a suitable coating according to the method herein with a grade of 4.

[0244] The aqueous coating compositions of Table 7 both had measured pHs greater than 7.5. This indicated that there was sufficient ammonium hydroxide to deprotonate at least a significant portion of the fatty acids and the ammonium salts were formed. All the pHs were less than 11 which reduced the risk of forming white residues of oleamides and linolamides, which were not observed.

[0245] The aqueous coating compositions of Table 7 were both suitable for use in standard coating equipment, both greater than 100 mPa.s. The relatively high viscosity was due to their high solids content. Example 3b which began with forming a solid paste had the highest viscosity. Both compositions were shear thinning and resulted in very similar sheared viscosities which are suitable for coating onto a substrate.

Claims

CLAIMS1. An aqueous coating composition comprising a solids component and water, wherein the solids component comprises a film-forming component, wherein the film-forming component comprisesa. one or more plant proteins;b. ammonium salt of oleic acid;c. oleic acid;d. ammonium salt of linoleic acid; ande. linoleic acid;wherein the amount of water in the aqueous coating composition is between 30 wt.% and 80 wt.% of the aqueous coating composition, and wherein the pH of the aqueous coating composition is above 7.5.

2. An aqueous coating composition according to claim 1 , wherein the solids content is between 15 wt.% and 55 wt.%.

3. An aqueous coating composition according to claim 2, wherein the ratio of oleic acid and ammonium salt of oleic acid to plant protein in the solids content is between 1:4 and 2:1, preferably between 1:2 and 1:1.

4. An aqueous coating composition according to any of claims 1 to 3, wherein the one or more plant proteins are selected from prolamins, glutelins, albumins, globulins and combinations thereof, preferably wherein the one or more plant proteins comprise one or more prolamin proteins, more preferably wherein the one or more prolamin proteins comprise zein proteins, most preferably wherein the one or more prolamin proteins comprise zein proteins in combination with one or more globulin proteins and / or one or more glutelin proteins.

5. An aqueous coating composition according to any of claims 1 to 4, wherein the solids component further comprises one or more preservatives.

6. An aqueous coating composition according to claim 5, wherein the one or more preservatives are selected from the group consisting of methyl paraben, propyl paraben, benzyl alcohol, phenoxyethanol, isothiazolinones, formaldehyde releasers, antimicrobial essential oils, antimicrobial fragrance and flavour compounds, and combinations thereof.

7. An aqueous coating composition according to any of claims 1 to 6, wherein the combined amount of the one or more plant proteins, the ammonium salt of oleic acid, the oleic acid, the ammonium salt of linoleic acid, and the linoleic acid is greater than 75 wt.% of the film-forming component.

8. An aqueous coating composition according to any of claims 1 to 7, wherein the solids component further comprises a film-modifying component, wherein the film-modifying component comprises one or more of plasticisers, spreading agents and fillers.

9. An aqueous coating composition according to claim 7, wherein the one or more plasticisers are selected from the group consisting of urea, glycerol, sorbitol, mannitol, xylitol, propane-1, 2-diol, propane-1, 3-diol, 2-methyl-1,3-propanediol, ethylene glycol, polyethylene glycol, monoglycerides, diglycerides, triglycerides, glucose, mannose, fructose, sucrose, lecithin, waxes, amino acids, glycerol formal, glycerol triacetate, acetyltri butyl citrate, epoxidized soybean oil, sucrose esters of fatty acids, sugar surfactants, and combinations thereof.

10. An aqueous coating composition according to claim 7 or claim 8, wherein the one or more fillers are selected from inorganic and organic fillers, preferably wherein the one or more fillers are inorganic fillers, more preferably wherein the inorganic fillers are selected from the group consisting of clays, silica, calcium carbonate, talc, gypsum, mica, calcium silicate, inorganic pigments and inorganic dyes and combinations thereof.

11. An aqueous coating composition according to any of claims 1 to 10, wherein the pH of the coating composition is between 7.75 and 11.0, preferably between 8.0 and 10.5, more preferably between 8.0 and 10.25, even more preferably between 8.0 and 10.0, even more preferably between 8.25 and 9.75, even more preferably between 8.25 and 9.5, even more preferably between 8.5 and 9.25, most preferably between 8.5 and 9.0.

12. A method of producing an aqueous coating composition according to any preceding claim comprising:a) mixing one or more plant proteins, water, ammonium hydroxide, oleic acid and linoleic acid; and / orb) mixing one or more plant proteins, water, and ammonium salts of oleic acid and ammonium salts of linoleic acid; andc) optionally adjusting the pH of the mixture obtained in step a) or in step b).

13. A method according to claim 12, wherein in step a) the oleic acid and the linoleic acid are added to a solution of ammonium hydroxide in water comprising the one or more plant proteins.

14. Use of an aqueous coating composition according to any of claims 1 to 11 for coating a substrate.

15. Use according to claim 14, wherein the substrate is a cellulose-based substrate, preferably wherein the cellulose-base substrate is selected from paper, card and cardboard.

16. Use according to claim 14 or claim 15, wherein if the substrate is an uncoated substrate, then the aqueous coating composition is applied as a base coating, and if the substrate is a coated substrate, then the aqueous coating composition is applied either as a top coating or as an intermediate coating.

17. A method of applying an aqueous coating composition according to any of claims 1 to 11 to a substrate.

18. A method according to claim 17, wherein after the aqueous coating composition has been produced according to claim 12 or claim 13 and before the coating composition is applied to the substrate, the coating composition is stored for at least 12 hours, more preferably for at least 24 hours, even more preferably for at least 48 hours, most preferably for at least 3 days.

19. A method according to claim 17 or claim 18, wherein after application of the aqueous coating composition to the substrate the coating is dried, preferably wherein the coating is dried by the application of heat.

20. A coated substrate obtained by the method of any of claims 17 to 19.

Images