Storage stable coating compositions

Abstract

The present invention relates to a hydroalcoholic coating composition comprising, based on the total composition, between 12 wt% and 35 wt% zein proteins, said zein proteins comprising more than 92 wt% α-zein, between 65 wt% and 88 wt% of a solvent system, and up to 5 wt% of one or more additives, wherein the solvent system consists of one or more alcohols, water and one or more fatty acids, wherein the one or more alcohols comprise ethanol in an amount of more than 70 wt% of the one or more alcohols, wherein the one or more fatty acids comprise one or more C16-C18 unsaturated fatty acids, and wherein the amount of the one or more alcohols in the solvent system is greater than or equal to [61 – 0.58 x the amount of the one or more fatty acids in wt% in the solvent system] and less than or equal to [93 – 0.84 x the amount of the one or more fatty acids in wt% in the solvent system].

Description

[0001] STORAGE STABLE COATING COMPOSITIONS

[0002] FILED OF THE INVENTION

[0003] The present invention relates to a storage stable coating composition for coating cardboard and other substrates. More specifically, the present invention relates to a hydroalcoholic coating composition comprising, based on the total composition, between 12 wt.% and 35 wt.% zein proteins, said zein proteins comprising more than 92 wt.% a-zein, between 65 wt.% and 88 wt.% of a solvent system, and up to 5 wt.% of one or more additives, wherein the solvent system consists of one or more alcohols, water and one or more fatty acids, wherein the one or more alcohols comprise ethanol in an amount of more than 70 wt.% of the one or more alcohols, wherein the one or more fatty acids comprise one or more CIGCIS unsaturated fatty acids, and wherein the amount of the one or more alcohols in the solvent system is greater than or equal to [61 - 0.58 x the amount of the one or more fatty acids in wt.% in the solvent system] and less than or equal to [93 - 0.84 x the amount of the one or more fatty acids in wt.% in the solvent system],

[0004] BACKGROUND OF THE INVENTION

[0005] The use of zein and other prolamin proteins as coating agents is very 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.

[0006] Zein is insoluble in water. It is commonly dissolved in aqueous ethanol at ethanol concentrations of between 60% and 95%. The concentration of ethanol depends on the type of zein used - whether alpha, beta or gamma. The presence of some water is essential for zein to dissolve in ethanol. Zein can also be dissolved in aqueous acetone, alcohols such as propan-1 -ol and other organic solvents.

[0007] Pure zein is not commonly used by itself as a film-former or coating due to its brittle nature, hence materials are added as plasticisers. A range of plasticisers can be used, such as glycerol, but the choice of plasticiser will affect the properties of the resulting film. Oleic acid is used as a plasticiser or additive for prolamin films to improve their flexibility whilst maintaining the hydrophobic nature of the film. Oleic acid is soluble in ethanol and oleic acid has been mixed into ethanolic solutions of zein and sprayed onto surfaces, such as fruits, to form a coating. 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. A particularly good packaging material is cardboard and other packaging materials based on cellulose fibres due to its ability to be recycled and re-used.

[0008] However, such materials have no barrier properties to liquids or vapours and 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 the packaging material cannot be recycled.

[0009] One particular application that would benefit from improved recyclability or biodegradability is the packaging used for prepared meals. Such packaging is widely used - for example in takeaway foods. As such, it generates large 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 associated issues.

[0010] Biomaterials such as starches are used to provide barrier properties to cardboard and paper or as sizing to help the properties of the paper / cardboard. Starch coatings can provide resistance to oils and other hydrophobic liquids but do not have good barrier properties for aqueous materials. Food packaging needs to have barrier properties to both water and oils.

[0011] There is therefore a benefit in the development of a coating based on natural, biodegradable or recyclable biomaterials that can be used to provide barrier properties to a cardboard or similar material. One approach is to have a dual layer coating on a cardboard using two biomaterials that have different properties and can - in combination - provide the overall barrier properties required.

[0012] The hydrophobic properties of zein make it highly attractive as a coating material providing some level of water barrier properties. Zein coatings have been applied with the zein dissolved in aqueous ethanol. The zein solution is sprayed onto a surface and the evaporation of the ethanol leaves a film of zein. As previously mentioned, pure zein is very brittle and plasticisers are used to make zein films more flexible. Hydrophilic plasticisers are effective at making zein more flexible, but the hydrophilic nature of such plasticisers reduces the moisture barrier properties of the zein. This rather negates the purpose of using hydrophobic zein in the first place. Fatty acids can be used to provide zein films with flexibility whilst still maintaining hydrophobic properties. Oleic acid is one fatty acid that is used as a plasticiser for zein. Oleic acid is soluble in ethanol and zein and oleic acid can be dissolved in dilute aqueous ethanol solutions and provide a solution that can be sprayed onto substrates. Typically, such solutions only contain low levels of zein and lower levels of oleic acid.

[0013] Such solutions, whilst quite practical in a lab environment, can be difficult and expensive to implement in an industrial environment due to issues with evaporating large amounts of volatile solvents such as ethanol. There is always a benefit in industrial conditions from increasing the level of solids in a coating material and lowering the amount of alcohol required. Increasing the solids content of a liquid coating means that less coating will typically be required to create a film of the required thickness. This typically simplifies coating by reducing the degree of drying required. This can have production rate and energy use benefits. Reducing the amounts of alcohol will simplify handling and improve safety. In addition, coating a fibrous substrate such as paper or cardboard is often better done with a more viscous coating composition so as to better form a layer on the surface. Low viscosity coating compositions will typically penetrate into the substrate and may be worse at leaving a coherent surface coating.

[0014] Any coating of a paper or cardboard material will need to handleable and spreadable in use. It also needs to be sufficiently stable that the material can be shipped and stored prior to use whilst maintaining acceptable rheological properties.

[0015] Hence it can be seen that any coating composition needs to fulfil multiple requirements simultaneously to be industrially viable. 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 and processable. It should have as high a solids level as practical to minimise the amount of material needing to be applied to a substrate. This can increase production rate by limiting the amount of drying needed. It should limit the amounts of volatile solvents being dried off. The coating film needs to be sufficiently flexible that any coated paper or cardboard can be bent and folded without the coating cracking or falling off. Such cracks can provide leak points. Ideally the dried coating should be heat sealable. Finally, the coating composition must be sufficiently storage stable, i.e. , it does not gel or phase separate, to be handled in conventional supply chains with the various delays and ranges of conditions that can be encountered.

[0016] US6635206 describes a process for making a mouldable zein : oleic acid mixture by dissolving zein in aqueous ethanol, adding a fatty acid such as oleic acid, adding the solution to cold water to precipitate a zein : oleic acid material and heating and kneading the resulting solid mass to remove the water and ethanol. Oleic acid is added at a level of 0.1 - 1 g / g zein but no details are given about the level and concentration of aqueous ethanol used. Formation of a zein : oleic acid mixture is described widely elsewhere.

[0017] CN101024725A describes a similar process for precipitating a zein : oleic acid material.

[0018] CN 112898612 mentions oleic acid as a ratio of 0.5 oleic acid to 1 part zein in ethanol.

[0019] Rakontoni rainy et al (Rakotonirainy, A.M., Wang, Q. and Padua, G.W, Evaluation of Zein Films as Modified Atmosphere Packaging for Fresh Broccoli, Journal of food science 2001 , 66(8), pp.1108-1111) disclose a composition of 13.8% zein, 13.8% oleic, 54.3 % ethanol and 18.1% water. It is described as an emulsion. This composition is then heated and then dispersed in cold water to precipitate the zein : oleic mixture as in US6635206. The composition is in the area that we would expect a solution at room temperature but it is expected that the heating step to 75 to 80°C after mixing the materials causes the material to be inhomogeneous.

[0020] Lai et al (Lai, H.M. and Padua, G.W, Water vapor barrier properties of zein films plasticized with oleic acid, Cereal Chemistry 1998, 75(2), pp.194-199) disclose a mixture of 0.5g oleic acid per 1 g of zein. This is dissolved in 75% ethanol but the amounts of ethanol are not given so this composition cannot be worked out.

[0021] Wang et al (Wang, Y. and Padua, G.W, Water barrier properties of zein-oleic acid films, Cereal Chemistry 2006, 83(4), pp.331-334.) disclose mixtures with a total zein : oleic level of 33% and varying ratios of zein to oleic with ethanol always at 63.8% and water at 3.4%. The mixtures are used to make films.

[0022] Lawton (Lawton, Plasticizers for Zein: Their Effect on Tensile Properties and Water Absorption of Zein Films, Cereal Chemistry 2004, 81(1), pp.1-5) tests the properties of zein films with various plasticisers including oleic. Plasticiser levels are 30% of the zein. The zein and oleic acid were dissolved in 95% ethanol.

[0023] Arcan et al (Arcan, I. and Yemenicioglu, A., Development of flexible zein-wax composite and zein-fatty acid blend films for controlled release of lysozyme, Food Research International 2013, 51(1), pp.208-216.) describe using zein films with 5% oleic acid added. EP4194485 describes a process for making a thermoplastic material by extracting prolamins (typically zein) and lipids from a grain source by solvent extraction of hydroalcoholic soluble prolamins and lipids. The prolamin and lipid containing alcohol solution is then chilled to precipitate and separate the less soluble (typically higher molecular weight) prolamin and lipid materials. The residual, more soluble and more processable fractions of the material are then collected by drying and can be used as a thermoplastic material to form products including flexible films.

[0024] WO2021249621 has an example 2 in which zein is dissolved in 70% ethanol and oleic added at 12% of the zein. No details about the amounts of ethanol are given so no composition information is available apart from the low level of oleic acid.

[0025] US5585060 teaches that dissolving zein in acetone rather than in ethanol gives better quality films. There is no mention of oleic acid being added.

[0026] Zein Corporation filed multiple applications relating to zein and various non-ethanol solvent systems, such as US 2185122 that can include various plasticiser but are focussed on non- ethanol solvent systems.

[0027] US6635206B1 describes a process of mixing oleic acid into a precipitated zein material. The zein is precipitated from an ethanol solution and mixed with oleic. Compositions are not given but the levels of zein to ethanol will be high.

[0028] SUMMARY OF THE INVENTION

[0029] Viewed from a first aspect, the present invention relates to a hydroalcoholic coating composition comprising, based on the total composition, between 12 wt.% and 35 wt.% zein proteins, said zein proteins comprising more than 92 wt.% a-zein, between 65 wt.% and 88 wt.% of a solvent system, and up to 5 wt.% of one or more additives, wherein the solvent system consists of one or more alcohols, water and one or more fatty acids, wherein the one or more alcohols comprise ethanol in an amount of more than 70 wt.% of the one or more alcohols, wherein the one or more fatty acids comprise one or more C16-C18 unsaturated fatty acids, and wherein the amount of the one or more alcohols in the solvent system is greater than or equal to [61 - 0.58 x the amount of the one or more fatty acids in wt.% in the solvent system] and less than or equal to [93 - 0.84 x the amount of the one or more fatty acids in wt.% in the solvent system]. Viewed from another aspect, the present invention relates to a method for producing the inventive hydroalcoholic coating composition as described herein comprising mixing the zein into either the solvent system or mixing the zein into the alcohol-water mixture followed by mixing of the water-alcohol mixture with the one or more fatty acids, wherein the mixing is carried out at a temperature between 4 °C and 40 °C.

[0030] Viewed from a further aspect, the present invention relates to the use of the inventive hydroalcoholic coating composition described herein for coating a cellulose-based substrate, in particular for coating paper, card or cardboard. The inventive hydroalcoholic coating composition described herein is beneficially used in the preparation of biodegradable, natural and / or food safe coatings.

[0031] DETAILED DESCRIPTION OF THE INVENTION

[0032] In a first aspect, the present invention relates to a hydroalcoholic coating composition comprising, based on the total composition, between 12 wt.% and 35 wt.% zein proteins, said zein proteins comprising more than 92 wt.% a-zein, between 65 wt.% and 88 wt.% of a solvent system, and up to 5 wt.% of one or more additives, wherein the solvent system consists of one or more alcohols, water and one or more fatty acids, wherein the one or more alcohols comprise ethanol in an amount of more than 70 wt.% of the one or more alcohols, wherein the one or more fatty acids comprise one or more C16-C18 unsaturated fatty acids, and wherein the amount of the one or more alcohols in the solvent system is greater than or equal to [61 - 0.58 x the amount of the one or more fatty acids in wt.% in the solvent system] and less than or equal to [93 - 0.84 x the amount of the one or more fatty acids in wt.% in the solvent system].

[0033] The inventors have seen that mixtures of zein and fatty acids, with high levels of fatty acids (as a proportion of the zein level), can deliver robust coatings for cellulose-based substrates, including paper, card and cardboard products, such as food packaging with water and oil barrier properties and sufficient film flexibility. The levels of fatty acids are typically higher than much of the art due to the high levels of flexibility required.

[0034] However, blends of zein with fatty acids, alcohol and water show complex phase behaviours, especially at the higher zein and fatty acid levels of interest. Many compositions form unstable inhomogeneous mixtures that phase separate on storage and are unsuitable for use in industrial coating applications. The inventors have realised that the phase behaviour of such mixtures is highly complex due to the fatty acid being able to act as a solvent for zein under some conditions, in addition to the alcohol and water. Instead, the mixture of fatty acid, alcohol and water should be regarded as the solvent system - in its own right - for the zein. Due to the complex interactions within the zein-solvent system it is very hard to predict the nature and behaviour of the resulting compositions.

[0035] The inventors have discovered that certain compositions of the solvent system (of fatty acid, alcohol and water) can be combined with zein to form transparent single-phase solutions that are storage stable whilst still having sufficiently high levels of zein and fatty acid to be of industrial interest. Whether a composition has formed a solution or an emulsion or dispersion is determined by the turbidity of the composition. Solutions are single phase and have low turbidity and this can be observed as a highly transparent solution with high light transmittance. Solutions are more stable than emulsions or dispersions, and the turbidity, or transparency, of a zein-solvent mixture, measured as light transmittance, can be used as a predictive measure of stability for a single-phase composition. Many compositions outside the scope of the invention tested by the inventors were found to phase separate either as soon as made or over time. For these compositions it is not possible to measure transmittance as there is more than one phase. Commercially available grades of corn- derived material comprising zein protein contain naturally occurring colourants. This, coloration can vary from dark orange to pale yellow. This however does not affect the light transmittance as measured herein.

[0036] Within the meaning of the present invention, hydroalcoholic coating compositions with high transmittance, such as at least 20%, preferably at least 40%, more preferably at least 60% measured according to the method described herein, indicate improved storage stability such as reduced tendency to phase separate.

[0037] The inventors have seen that the range of solvent system compositions that can form high transparency solutions with higher levels of zein, form a distinct and definable region of the 3-phase diagram of the solvent system formed by fatty acid, alcohol and water. This region is not easily understood in terms of conventional parameters such as Hansen Solubility Parameters. The inventive region of the solvent system phase diagram can be delineated by upper and lower limits on the wt.% of alcohol in the solvent system as a function of the wt.% of fatty acid in the solvent system. The balance (to 100 wt.%) is the water content. The inventors have seen that the solvent system defined by the inventive parameters can be used to form high transparency solutions over a range of zein concentrations in the coating compositions, such as 12 wt.% zein and 35 wt.% zein. Lower concentrations of zein are less industrially relevant as a minimum solids content is required to minimise the energy required for drying the coatings in a commercially viable process. High concentrations of zein form compositions with higher viscosities which are harder to pump and coat uniformly. Coating compositions of the invention have a viscosity, measured from rest, pre-shearing, less than 5000 mPas at 50s-1, preferably less than 4000 mPas at 50s-1, more preferably less than 3000 mPas at 50s-1, even more preferably less than 2000 mPas at 50s-1. Preferably the coatings of the present invention are shear thinning.

[0038] The inventors have also surprisingly found that controlling the temperature of the mixing of the solvent system and zein and its long-term storage is important for producing a highly transparent and storage stable solution. Traditionally heat is used to increase the solubility of solids in a solvent system. It has been surprisingly found that in the case of the alcohol - water - fatty acid solvent system the zein solubility in fact decreases. In addition the heating of the mixture for more than a few minutes in an open system will also result in a preferential loss of alcohol due to its high volatility. This will inevitably change the composition of the solvent system, reducing the proportion of alcohol and becoming less transparent and less stable.

[0039] Compositions of the present invention can be prepared by simple gentle mixing or optionally with shear. Large inputs of energy are not required to form the transparent solutions.

[0040] Plant-based 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 glutelins (soluble in dilute acid / alkaline solutions or insoluble in water).

[0041] Prolamins and glutelins make up 85% of protein 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 from corn, kafirin from sorghum, avenin 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 from corn are the most widely commercially available.

[0042] 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, and y(gamma)-zein protein. 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.

[0043] P-Zein protein accounts for about 10-20% of the total zein protein content in corn. 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. 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. 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.

[0044] Commercially available grades of zein are generally obtained by extraction from 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. For the avoidance of doubt all references to a-zein protein include both the monomer and dimer forms.

[0045] In a preferred hydroalcoholic coating compositions of the present invention, the zein proteins come from a corn-derived material comprising 90 wt.% or more, more preferably 91 wt.%, most preferably 92.37 wt.% or more of the zein proteins based on total dry solids.

[0046] The inventors have found that to achieve highly transparent and storage stable solutions in a fatty acid - alcohol - water solvent system, the zein proteins must comprise more than 92 wt.% a-zein protein, preferably more than 94 wt.% % a-zein protein, more preferably more than 96 wt.% a-zein protein, even more preferably more than 97 wt.% a-zein protein, and most preferably more than 98 wt.%.

[0047] The inventors have found that to achieve highly transparent and storage stable solutions in a fatty acid - alcohol - water solvent system, the zein proteins must comprise less than 10 wt.% p, y, b-zein proteins, preferably less than 8 wt.% % p, y, 5 -zein proteins, more preferably less than 6 wt.% p, y, 5 -zein proteins, even more preferably less than 4 wt.% p, y, 5 -zein proteins, and most preferably less than 3 wt.% p, y, b-zein proteins.

[0048] The inventors have seen that controlling the level of water in the solvent system is beneficial in enabling the use of a wider range of commercial zein materials without issue. Without wishing to be bound by theory, the inventors believe that zeins from different suppliers may contain different levels of a, p and y-zeins, depending on differences in the extraction processes, without these differences being reported or recognised. Higher (albeit still low on an absolute level) amounts of p and y zeins, particularly y-zeins, are believed to cause reduced solubility and transparency.

[0049] A minimum level of water is necessary for the dissolution of any zein, but limiting the maximum level of water in the solvent system is also believed to decrease the potential for p and Y zein containing compositions to be less transparent on extended storage.

[0050] Commercial grades of corn-derived material comprising zein proteins 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 10wt% of the zein, preferably less than 8wt% of the zein, more preferably less than 6 wt.% of the zein, most preferably less than 4 wt.% of the zein.

[0051] Commercially available grades of corn-derived material comprising zein proteins comprise impurities, many of which are organic impurities, such as carbohydrates, lipids, organic acids etc. Commercial grades of corn-derived material comprising zein proteins also have different colours ranging from pale to bright yellow. These different grades contain different levels of pigments which are also considered as impurities.

[0052] High purity grades of corn-derived material comprising zein proteins typical for this invention contain at least 85 wt.% zein proteins, preferably at least 90 wt.% zein proteins, more preferably at least 91 wt.% zein proteins, more preferably at least 92 wt.% zein proteins, even more preferably at least 93 wt.% zein proteins.

[0053] High purity grades of corn-derived material comprising zein proteins typical for this invention contain less than 10 wt.% of impurities, preferably less than 8 wt.% of impurities, more preferably less than 6 wt.% of impurities, even more preferably less than 5 wt.% of impurities, even more preferably less than 4 wt.% of impurities, even more preferably less than 3 wt.% of impurities, most preferably less than 2 wt.% of impurities.

[0054] Total protein content, either of the corn-derived material or the coating composition, can be measured 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 such as Thermo Fisher Scientific or Sigma-Aldrich.

[0055] Zein proteins content by type of zein protein, either of the zein or the coating composition, can be measured by diluting the zein or coating composition in an aqueous 8M urea / 3M thiourea solution / 1.54 wt.% Dithiotheitol (DTT), heating, vortexing and sonicating to promote protein solubilization. The samples are then loaded into a sodium dodecyl sulphatepolyacrylamide gel (SDS-PAGE) using Mini-PROTEAN Tetra Vertical Electrophoresis Cell (BIO-RAD) with 4-15% Mini- PROTEAN ® TGX™ Precast protein gels with tris / glycine / SDS buffer for gel electrophoresis analysis. Gels can be stained with Page Blue protein stain. As a control reference, a standard 80% ethanol aqueous solution containing an isolated prolamin protein (e.g. a-zein), can be prepared following the method described above, and be loaded into the polyacrylamide gel (SDS-PAGE). The presence of prolamin proteins can be confirmed and then quantified by comparison of the test sample with the control by collecting images of the gels and comparing the intensity of the respective band within a lane to the total intensity of all the protein bands within the same lane. Analysis of the images will require background subtraction, for example rolling ball subtraction. It should be noted that other components of the coating composition, for example fatty acids, and impurities from the zein, will also be present and need to be accounted for within the analysis. Examples of use of such a SDS-PAGE method is given in Effect of pH and ethanol content of solvent on rheology of zein solutions, Nonthanum, P. et al in Journal of Cereal Science 58 (2013) 76-81.

[0056] Similarly the same method can be used to analyse the protein composition of a dry coating once this has been extracted from the substrate it was dried onto and suitably concentrated so as to result in bands of suitable intensity. Alternatively an LC-MS method can be used to quantify the proteins within zein protein as used in WO 2025045380.

[0057] In preferred hydroalcoholic coating compositions of the present invention, based on the total composition, the amount of zein protein is between 13 wt.% and 32 wt.%, more preferably between 14 wt.% and 30 wt.%, even more preferably between 15 wt.% and 28 wt.%, most preferably between 16 wt.% and 25 wt.%.

[0058] The fatty acids of the present invention may be selected from the group consisting of C16 to C18 unsaturated fatty acids, C14 saturated fatty acids (e.g. myristic acid) and C12 saturated fatty acids (e.g. lauric acid), more preferably C16 to C18 unsaturated fatty acids, even more preferably C18 unsaturated fatty acids, most preferably C18 mono- unsaturated fatty acid, oleic acid, and / or C18 di-unsaturated fatty acid, linoleic acid.

[0059] 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.

[0060] In preferred hydroalcoholic coating compositions of the present invention the one or more C16-C18 unsaturated fatty acids comprise oleic acid and / or linoleic acid. Most preferably, the one or more C16-C18 unsaturated fatty acids comprise oleic acid.

[0061] Oleic acid is a monounsaturated 18 carbon chain fatty acid. It can be used in the inventive mixtures as a pure compound or as part of a natural oil. Commercially available oleic acid is often a mixture of unsaturated carbon chain fatty acids. Such unsaturated 18 carbon chain fatty acids include di-unsaturated 18 carbon chain fatty acid, linoleic acid, and tri-unsaturated 18 carbon chain fatty acid, linolenic acid.

[0062] Tall oil fatty acid is a commercially available mixture of oleic acid and linoleic acid with typically 40 to 60% oleic acid and 30-40% linoleic acid.

[0063] In preferred hydroalcoholic coating compositions of the present invention the fatty acid has a melting point below 60°C as adding materials at a temperature higher than this to an ethanol mixture is highly undesirable due to health and safety concerns. Examples of such fatty acids include C12 to C18 unsaturated fatty acids and C12 to C14 saturated fatty acids. Preferably the fatty acid is extracted from plant sources, for example rapeseed oil has a high content of oleic acid.

[0064] In preferred hydroalcoholic coating compositions of the present invention the one or more fatty acids comprises at least 60 wt.% oleic acid and / or linoleic acid by weight of the total fatty acids, more preferably at least 70 wt.% oleic acid and / or linoleic acid, even more preferably at least 80 wt.% oleic acid and / or linoleic acid, even more preferably at least 90 wt.% oleic acid and / or linoleic acid, most preferably at least 95 wt.% oleic acid and / or linoleic acid.

[0065] In alternatively preferred hydroalcoholic coating compositions of the present invention the one or more alcohols consist of 100 wt.% ethanol and the one or more fatty acids comprise greater than 95 wt.% of oleic acid and / or linoleic acid.

[0066] As well as acting as a solubilising agent within the inventive solvent system, when the coating is formed, the alcohol and water evaporate leaving an intimate mixture of zein protein and oleic acid on the substrate being coated.

[0067] Without wishing to be bound by theory it is believed that fatty acid increases the hydrophobicity of the zein protein coating resulting in better barrier properties. It is believed that this is in part due to the reduced surface roughness. There are multiple well-established parameters for measuring the roughness of a surface, that is the variability of a surface profile. Different parameters are used for different applications. The most used parameters are (i) Ra, the arithmetic mean deviation of the profile and (ii) Rz, the maximum height of the profile. Rz measures the maximum distance between a peak and a trough along the surface profile. Ra, which is a commonly used measure for surface roughness (based on profilometry) is an average. Hence similar Ra values can be obtained for a surface with (i) many small peaks / troughs or (ii) a surface with a fewer but larger peaks / troughs. This difference is better shown by the Rz values. The tactile perception is better for surfaces with multiple smaller peaks / troughs as compared to surfaces with fewer, but larger peaks / troughs. Such surfaces can feel rougher or scratchy to the touch. High Rz values mean a “scratchier” surface. Acceptable surfaces can be defined by specifying Ra and Rz values. Suitable equipment for this test is the Surtronic (RTM) range of Roughness Testers from Taylor Hobson (RTM), including the Duo and S-series. This equipment can measure roughness parameters according to ASTM 4287 including Rz (maximum height of the profile) and Ra (the arithmetic mean deviation of the profile). The equipment uses a very fine stylus and the probe is moved across the surface by simply drawing the probe along the length of the surface being tested. Typically, five or so different measurements are taken across the surface so as to get a broader average and ensure all surfaces are measured. The equipment can automatically calculate the various surface roughness measurements including Ra and Rz when correctly following the manufacturer’s instructions.

[0068] It is also believed that the fatty acid also provides flexibility to the coating and allows for the substrate to be bent and folded, such as in the making of cardboard boxes.

[0069] In preferred hydroalcoholic coating compositions of the present invention, the amount of the one or more fatty acids in the solvent system is between 5.0 wt.% and 45.0 wt.% of the solvent system.

[0070] Preferably, in these hydroalcoholic coating compositions, the amount of water in the solvent system is greater than 7 wt.% of the solvent system.

[0071] Preferably, in these hydroalcoholic coating compositions, the amount of water in the solvent system is less than 20 wt.%, or less than 19 wt.%, or less than 17 wt.%, or less than 15 wt.% or even less than 13 wt.% of the solvent system. The lower levels of water are believed to help storage stability when using commercial zeins, in particular for those with higher levels of p- and y-zeins.

[0072] In alternatively preferred hydroalcoholic coating compositions of the present invention, the amount of the one or more fatty acids in the solvent system is between 55.5 wt.% and 70.0 wt.% of the solvent system.

[0073] It may be preferred that the one or more fatty acids comprises more than 1 wt.%, more than 2 wt.%, more than 3 wt.%, or more than 4 wt.% of the coating composition.

[0074] It may be preferred that the weight ratio between zein protein and the one or more fatty acids is between 1.0: 1.4 and 1.0:0.3, more preferably between 1.0: 1.2 and 1.0:0.6, most preferably between 1.0: 1.1 and 1.0:0.9.

[0075] It may also be preferred that the weight ratio between zein protein and the one or more fatty acids is between 1.0: 1.0 and 1.0:5.0, more preferably between 1.0: 1.5 and 1.0:4.0, most preferably between 1.0:2.0 and 1.0:3.0. In preferred hydroalcoholic coating compositions of the present invention the alcohol comprises at least 80 wt.% ethanol, preferably at least 85 wt.% ethanol, more preferably at least 90 wt.% ethanol, even more preferably at least 95 wt.%, most preferably at least 97 wt.% ethanol.

[0076] Alcohols can be selected from the list comprising isopropyl alcohol (propan-2-ol), n-propyl alcohol (propan-1 -ol), n-butanol (1-butanol), isobutyl alcohol (2-methyl 1-propanol), s-butanol (2-butanol), t-butanol (2-methylpropan-2-ol). For the avoidance of doubt alcohols do not include diols, for example those included in this invention as plasticisers.

[0077] In preferred hydroalcoholic coating compositions of the present invention the alcohol comprises ethanol and / or isopropanol. Most preferably, the alcohol comprises ethanol.

[0078] In alternatively preferred hydroalcoholic coating compositions of the present invention the one or more alcohols comprise at least 80 wt.% ethanol, more preferably at least 85 wt.% ethanol, even more preferably at least 90 wt.% ethanol, even more preferably 95 wt.% ethanol, most preferably at least 97 wt.% ethanol.

[0079] Alcohols of the present invention preferably have a boiling point of less than 120°C, more preferably less than 110°C, even more preferably less than 100°C. This enable the alcohol and any water to be removed through conventional large scale drying manufacturing equipment.

[0080] Alcohols can be obtained from both synthetic and natural plant sources., Most preferably alcohols are obtained from natural plant sources and ethanol is widely available from sources such as sugar beet or sugar cane. Ethanol is available in varying grades of purity and concentration in an aqueous ethanol solution. Such aqueous solutions maybe used instead of separate sources of ethanol and water.

[0081] Compositions of the present invention may also comprise up to 5 wt.% of one or more additives, which are preferably selected from the group consisting of preservatives, denaturants, plasticisers, pH adjustment materials, processing aids, and combinations thereof. The level of additives should be such that it does not adversely affect the transparency of the compositions.

[0082] For compositions where the alcohol level is low, typically less than 50 wt.%, it may be necessary to add preservatives to prevent the growth of undesirable microorganisms. Examples of suitable preservatives include sodium benzoate, potassium benzoate, calcium benzoate, 1,2-benzisothiazolin-3-one, potassium sorbate, sodium sulphite, sodium metabisulphite and methyl paraben.

[0083] Denaturants are often added to ethanol make them unpalatable and therefore not for use in human consumption. This is often done for commercial reasons so that such ethanol supplies are not subject to alcoholic drinks taxation. Bitterant materials include denatonium salts such as denatonium benzoate, denatonium saccharide, and denatonium chloride; sucrose octa acetate; quinine; flavonoids such as quercetin and naringen; and quassinoids such as quassin and brucine) and pungents (e.g., capsaicin, piperine, allyl isothiocyanate, and resinferatoxin). These are added for such purposes at very low levels.

[0084] Plasticisers can be added to either the composition in addition to fatty acids to improve coating flexibility and modify performance. Fatty acids are not considered plasticisers in the context of this invention.

[0085] 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.

[0086] Preferably, the one or more hydrophilic plasticisers are independently selected from the group consisting of: 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, 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, c) polyol reaction products having from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms with chain extenders, 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. A hydrophobic plasticiser can be a water insoluble vegetable oil or wax. Preferred waxes are made from natural waxes passing the OECD301 B biodegradation screening test, such as bees wax, rapeseed wax, castor wax, candelilla wax, soy wax, palm oil wax or another natural wax, provided that the temperature of exposure does not exceed the wax melting point. In some cases, some paraffin oil-based waxes may also pass OECD301B.

[0087] More preferably, the one or more plasticisers are independently selected from glycerol, polyethylene glycol, propylene glycol, sorbitol, mannitol, xylitol, triethyl citrate, monoglycerides, diglycerides, triglycerides, glucose, mannose, fructose, sucrose, urea, lecithin, waxes, amino acids, or a mixture thereof, with glycerol being most preferred.

[0088] Preferably, the plasticisers are bio-based and even more preferably plant-derived. 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.

[0089] The pH of the aqueous composition can be adjusted by pH adjustment agents so that it is either acidic, neutral or alkaline.

[0090] In preferred hydroalcoholic coating compositions of the present invention the pH of the hydroalcoholic composition is less than 10, more preferably less than 9, more preferably less than 9, even more preferably less than 8, most preferably less than 7.

[0091] Without wishing to be bound by theory it is believed that limiting the pH to 10 or less will limit any alkaline hydrolysis of the plant protein to an insignificant level. Typically, alkaline hydrolysis of plant protein, which is not a desired feature of the present invention, will only happen at pH values greater than 10, such as around pH 11 or pH 12. Controlling the pH to 10 or less allows for the use of chemistries and additives that may work best under alkaline conditions without risk of unwanted alkaline hydrolysis of the plant protein.

[0092] In preferred hydroalcoholic coating compositions of the present invention the pH of the hydroalcoholic composition is between 2.0 and 7.0, preferably between 2.5 and 6.8, more preferably between 3.0 and 6.6, more preferably between 3.5 and 6.4, more preferably between 4.0 and 6.2 and most preferably between 4.5 and 6.0.

[0093] The aqueous coating composition may include pH-adjusting materials other than fatty acids. pH-adjusting agents of this invention that reduce pH include inorganic acids, including hydrochloric acid, sulphuric acid, nitric acid, phosphoric acid, hydrofluoric acid and carbonic acid. pH-adjusting agents of this invention that reduce pH include organic acids, including acetic acid, lactic acid, citric acid, oleic acid, malic acid, maleic acid, glycolic acid, gluconic acid, tartaric acid, p-hydroxypropionic acid, p-hydroxybutyric acid, p-hydroxy p-methylbutyric acid, 2-hydroxybenzoic acid, carnitine and mixtures thereof. pH-adjusting agents of this invention that increase pH include alkalis, bases that are water soluble, include sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonia.

[0094] In a preferred aspect of the present invention the pH of the aqueous coating composition is more than 0.5 units, more preferably more than 1.0 unit away from the isoelectric point of the zein. Without wishing to be bound by theory it is believed that this can reduce the likelihood of unwanted protein aggregation

[0095] Compositions of the present invention may be further modified by the addition of rheology modifiers and processing aids including e.g. surfactants, dispersants, and defoaming agents.

[0096] Suitable surfactants may include, but are not limited to, the nonionic, cationic, anionic and zwitterionic classes. Suitable surfactants may include, but are not limited to, polyoxyethylenated polyoxypropylene glycols, alcohol ethoxylates, alkylphenol ethoxylates, tertiary acetylenic glycols and alkanolamides (nonionics), polyoxyethylenated amines, quaternary ammonium salts and quaternised polyoxyethylenated amines (cationics), and amine oxides, N-alkylbetaines and sulfobetaines (zwitterionics). Other suitable surfactants may include, but are not limited to, polyglucosides, fatty acid soaps, dioctyl sodium sulfosuccinate, lactylated fatty acid esters of glycerol and propylene glycol, lactylic esters of fatty acids, sodium alkyl sulfates, polysorbate 20, polysorbate 60, polysorbate 65, polysorbate 80, lecithin, acetylated fatty acid esters of glycerol and propylene glycol, and acetylated esters of fatty acids, and combinations thereof. The amount of surfactant in the dry coating may be in a range of from about 0.1 wt.% to about 2.5 wt. %, preferably from 1.0 wt.% to 2.0 wt.% by weight of the dry coating.

[0097] 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, plasticizer compatibilizers, release agents, salts (e.g.: magnesium chloride, calcium chloride) and other functional ingredients, in amounts suitable for their intended purposes.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Silicon-containing compounds can improve the barrier properties of the coating formed by applying the aqueous coating composition to a substrate. 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, methyltriethoxysilane and tetramethyl orthosilicate, or combinations thereof.

[0102] In a second aspect, the present invention relates to a method for producing a hydroalcoholic coating composition according to the invention comprising mixing the corn-derived material comprising zein proteins into either the solvent system or mixing the corn-derived material comprising zein proteins into the alcohol-water mixture followed by mixing of the water- alcohol mixture with the one or more fatty acids, wherein the mixing is carried out at a temperature between 4 °C and 40 °C, preferably between 10 °C and 30 °C, more preferably between 15 °C and 25 °C.

[0103] In preferred methods of the present invention, the zein proteins are added to the composition in the form of a corn-derived material comprising 89 wt% or more, more preferably 90 wt% or more, even more preferably 91 wt% or more, most preferably 92.37 wt% or more of the zein proteins based on total dry solids. Compositions of the present invention can be prepared by simple gentle mixing or optionally with shear. Large inputs of energy are not required to form the transparent solutions.

[0104] In a third aspect, the present invention relates to a hydroalcoholic coating composition obtained or obtainable by the inventive method as described hereinbefore.

[0105] In a fourth aspect, the present invention relates to the use of the hydroalcoholic coating composition according to the present invention for coating a cellulose-based substrate.

[0106] Preferably, said substrate is selected from paper, fine paper, recycled paper, paperboard, corrugated paperboard, card, wallpaper, photo paper, tissue paper and / or cardboard.

[0107] Furthermore, the substrate is not limited to a specific shape or form. The substrate may be die cut and / or cut to a specific geometrical form etc.

[0108] In another preferred embodiment, the paper component has a grammage in the range of from 15 to 400 g / m2, more preferably from 50 to 350 g / m2, and most preferably 100 to 300 g / m2.

[0109] In another preferred embodiment, the paper component is a paper, a card stock or a paperboard having a grammage in the range of from 15 to 400 g / m2, more preferably from 50 to 350 g / m2, and most preferably 100 to 300 g / m2.

[0110] The substrate may be pre-coated or treated using any method known in the art (e.g. calendering) prior to application of the coating of the present invention.

[0111] Said substrate may also be pre-treated or pre-coated with a base layer of other materials, preferably wherein said pre-treatment or pre-coating contain natural and / or biodegradable materials, including globulin, glutelin or non-zein prolamin proteins, (e.g. pea or rapeseed protein), plant polysaccharides (e.g.: starch) and seaweed-derived polysaccharides (e.g.: alginate or carrageenan salts).

[0112] The inventive hydroalcoholic coating composition described herein is beneficially used in the preparation of biodegradable, natural and / or food safe coatings.

[0113] BRIEF DESCRIPTION OF THE FIGURES

[0114] Figure 1 - transparent single phase composition of Example 1b Figure 2 - two-phase composition of Example 2a

[0115] Figure 3 - cloudy composition of Example 2c

[0116] Figure 4 - transparent composition of Example 5a

[0117] Figure 5 - cloudy composition of Comparative Example 5b

[0118] EXAMPLES

[0119] Materials

[0120] FloZein™, F4000C (92.37% based on total dry solids, 2.15% moisture, 97.1% of the zein proteins as a-zein protein) was purchased from FloZein Products, Flo Chemical Corp., USA. The zein protein content as a % of total solids is 90.38%. The dry solids measurement is obtained by first heating the material at 100°C for several hours until there is no change is weight.

[0121] Oleic acid, tech. 90%, (92.9 wt% C18 unsaturated fatty acids) was purchased from Thermo Fisher Scientific.

[0122] Lauric acid (99%) and Myristic acid (99%) were purchased from Thermo Fisher Scientific. Linoleic acid, 70% (71.5% linoleic acid, 17.2% oleic acid, 7.1% palmitic acid, 3.5% stearic acid) was purchased from Thermo Fisher Scientific.

[0123] Absolute ethanol (100wt%) and Isopropyl alcohol (I PA) (99.99 wt%) were purchased from Fisher Scientific.

[0124] Water was purified by reverse osmosis.

[0125] Methods -Transmittance

[0126] Transparency was characterized by measuring transmittance using UV-vis spectrometer (Eppendorf BioSpectrometer basic). The background was measured using an empty cuvette (FisherBrand Acryllic, 4.5ML cuvettes). Approximately 2 mL of sample was transferred to the cuvette and the transmittance ranging from 285 to 830 nm was recorded. The transmittance % at 600 nm was reported. In cases where the sample was very cloudy and formed an emulsion there was no transmittance and a % value could not be reported.

[0127] In the Examples that follow, all references to “ambient temperature” are to a temperature of approximately 20°C.

[0128] Example 1 - Preparation of hydroalcoholic coating compositions Coating compositions were prepared by mixing together, in a falcon tube, absolute ethanol, water and oleic acid (Fisher), according to the levels in Table 1, at ambient temperature. FloZein powder - known to have a high a-zein content and thus believed to be more water tolerant - was then added according to the levels in Table 1 , and vortexed for 5-10 seconds at ambient temperature. The pH of the compositions were all in the range 5 to 5.5, measured with a standard pH meter. The mixtures were left in a falcon tube overnight and observations and transmittance measurements undertaken according to the method herein described.

[0129] Table 1

[0130] All the inventive compositions were single phase and highly transparent with a transmittance of at least 80%. A photo of Example 1 b is given in Figure 1. The stability of the inventive compositions could also be assessed by rheology measurements after extended storage, such as after 1 week.

[0131] Example 2 - Preparation of comparative hydroalcoholic coating compositions

[0132] Coating compositions were prepared by mixing together, in a falcon tube, absolute ethanol, water and oleic acid (Fisher), according to the levels in Table 2, at ambient temperature. FloZein powder was then added according to the levels in Table 2, and vortexed for 5-10 seconds at ambient temperature. The mixtures were left in a falcon tube overnight and observations and transmittance measurements undertaken according to the method herein described.

[0133] Table 2

[0134] Comparative Compositions 2a, 2b and 2e had split into two phases, one of which was cloudy. A photo of Example 2a is given in Figure 2. Comparative Compositions 2c and 2d were completely cloudy. A photo of Example 2c is given in Figure 3. It was not possible to record the transmittance for any of these compositions as they were too cloudy.

[0135] Example 3 - Preparation of further hydroalcoholic coating compositions

[0136] Coating compositions were prepared by mixing together, in a falcon tube, absolute ethanol, water and oleic acid (Fisher), according to the levels in Table 3, at ambient temperature. FloZein powder was then added according to the levels in Table 3, and vortexed for 5-10 seconds at ambient temperature. The pH of the compositions were all in the range 5 to 5.5, measured with a standard pH meter. The mixtures were left in a falcon tube overnight and observations and transmittance measurements undertaken according to the method herein described.

[0137] Table 3

[0138] Both inventive compositions were single phase and transparent with a transmittance of at least 60%.

[0139] Example 4 - Preparation of further comparative hydroalcoholic coating compositions

[0140] Coating compositions were prepared by mixing together in a falcon tube, absolute ethanol, water and oleic acid (Fisher), according to the levels in Table 4, at ambient temperature. FloZein powder was then added according to the levels in Table 4, and vortexed for 5-10 seconds at ambient temperature. The mixtures were left in a falcon tube overnight and observations and transmittance measurements undertaken according to the method herein described.

[0141]

[0142] Table 4

[0143] The comparative compositions were completely cloudy. For some it was possible to measure a very low transmittance value, below 20, but for others it was not possible to record the transmittance.

[0144] Example 5 - Preparation of coating compositions with and without heating

[0145] Coating composition 5a was prepared by mixing together 150 ml of absolute ethanol and 50 ml of water in a beaker. Then 32g of zein (FloZein powder, protein content 92.3%) was added to this solution and mixed for 10 minutes in a food processor at 600 rpm. The 32g of oleic acid (Fisher) was added slowly whilst the contents were mixed at ambient temperature. A clear transparent yellow solution was formed as shown in Figure 4. The transmittance was measured according to method herein to be 91.6%.

[0146] Comparative coating composition 5b was prepared as above and the solution was then heated using a water bath to 75°C whilst stirring at 3500 rpm and once that temperature was reached it was stirred at that temperature for 10 minutes. The mixture was then cooled back to ambient temperature and was observed to be cloudy, as shown in Figure 5 indicating that subjecting the solution to a high temperature does not improve solubility of the zein in the solvents, but in fact reduces, this as shown by the cloudiness of the sample. The sample was too cloudy for transmission to be measured. After 4 days the sample was vortexed and the cloudiness visually increased further indicating that composition was an emulsion and not a solution.

[0147] Example 6 - Preparation of coating compositions with a mixture of fatty acids Coating compositions 6a and 6b and 6c were prepared according to the formulations in Table 5. Oleic acid and either lauric acid, myristic acid or Linoleic acid respectively (Fisher) were mixed in a 1:1 ratio at 50 °C, until any solid fatty acid had melted. The fatty acid mixture was then added to the water and absolute ethanol mixture at ambient temperature. FloZein powder was then added and vortexed for 5-10 seconds at ambient temperature. The mixture was left in a falcon tube overnight and observations and transmittance measurements undertaken according to the method herein described.

[0148] Table 5 All three inventive compositions were single phase and transparent with a transmittance of at least 90%, demonstrating that a mixture of different fatty acids can be used to prepare a transparent composition.

[0149] Example 7 - Preparation of coating compositions with I PA / ethanol mix

[0150] Coating compositions 7a was prepared according to the formulations in Table 6. Oleic acid (Fisher) was added to a water, absolute ethanol and isopropyl alcohol mixture at ambient temperature. FloZein powder was then added and vortexed for 5-10 seconds at ambient temperature. The mixture was left in a falcon tube overnight and observations and transmittance measurements undertaken according to the method herein described.

[0151] Table 6

[0152] The inventive composition was single phase and transparent with a transmittance of at least 90%, demonstrating that the formulation can be transparent with a mixed alcohol solvent system.

Claims

CLAIMS1. A hydroalcoholic coating composition comprising, based on the total composition, between 12 wt.% and 35 wt.% zein proteins, said zein proteins comprising more than 92 wt.% a-zein, between 65 wt.% and 88 wt.% of a solvent system, and up to 5 wt.% of one or more additives, wherein the solvent system consists of one or more alcohols, water and one or more fatty acids, wherein the one or more alcohols comprise ethanol in an amount of more than 70 wt.% of the one or more alcohols, wherein the one or more fatty acids comprise one or more C16-C18 unsaturated fatty acids, and wherein the amount of the one or more alcohols in the solvent system is greater than or equal to [61 - 0.58 x the amount of the one or more fatty acids in wt.% in the solvent system] and less than or equal to [93 - 0.84 x the amount of the one or more fatty acids in wt.% in the solvent system],2. A hydroalcoholic coating composition according to claim 1 , wherein the amount of the one or more fatty acids in the solvent system is between 5.0 wt.% and 45.0 wt.% of the solvent system.

3. A hydroalcoholic coating composition according to claim 1 , wherein the amount of the one or more fatty acids in the solvent system is between 55.5 wt.% and 70.0 wt.% of the solvent system.

4. A hydroalcoholic coating composition according to claim 2, wherein the amount of water in the solvent system is greater than 7 wt.% of the solvent system.

5. A hydroalcoholic coating composition according to any of claims 1 , 2 and 4, wherein the weight ratio between zein proteins and the one or more fatty acids is between 1.0: 1.4 and 1.0:0.3, preferably between 1.0: 1.2 and 1.0:0.6, most preferably between 1.0:1.1 and 1.0:0.9.

6. A hydroalcoholic coating composition according to claim 3, wherein the weight ratio between zein protein and the one or more fatty acids is between 1.0: 1.0 and 1.0:5.0, preferably between 1.0: 1.5 and 1.0:4.0, most preferably between 1.0:2.0 and 1.0:3.0.

7. A hydroalcoholic coating composition according to any of claims 1 to 6, wherein, based on the total composition, the amount of zein proteins is between 13 wt.% and32 wt.%, preferably between 14 wt.% and 30 wt.%, more preferably between 15 wt.% and 28 wt.%, most preferably between 16 weight % and 25 weight %.

8. A hydroalcoholic coating composition according to any of claims 1 to 7, wherein the one or more additives are selected from the group consisting of preservatives, denaturants, plasticisers, pH adjustment materials, processing aids, and combinations thereof.

9. A hydroalcoholic coating composition according to claim 1 or 2 or any of claims 4 to 8, wherein the amount of water in the solvent system is less than 20 wt.% of the solvent system.

10. A hydroalcoholic coating composition according to any of claims 1 to 9, wherein the one or more fatty acids comprise more than 4 wt.% of the coating composition.

11. A hydroalcoholic composition according to any of claims 1 to 10, wherein the one or more C16-C18 unsaturated fatty acids are selected from the group consisting of oleic acid and linoleic acid.

12. A hydroalcoholic composition according to any of claims 1 to 11 , wherein the one or more alcohols comprise at least 80 wt.% ethanol, preferably at least 85 wt.% ethanol, more preferably at least 90 wt.% ethanol, even more preferably 95 wt.% ethanol, most preferably at least 97 wt.% ethanol.

13. A hydroalcoholic composition according to any of claims 1 to 12, wherein the one or more fatty acids comprise at least 60 wt.% oleic acid and / or linoleic acid, preferably at least 70 wt.% oleic acid and / or linoleic acid, more preferably at least 80 wt.% oleic acid and / or linoleic acid, even more preferably at least 90 wt.% oleic acid and / or linoleic acid, most preferably at least 95 wt.% oleic acid and / or linoleic acid.

14. A hydroalcoholic composition according to any of claims 1 to 13, wherein the one or more alcohols consist of 100 wt.% ethanol and the one or more fatty acids comprise greater than 95 wt.% of oleic acid and / or linoleic acid.

15. A method for producing a hydroalcoholic coating composition according to any of claims 1 to 14 comprising mixing the corn-derived material comprising zein proteinsinto either the solvent system or mixing the corn-derived material comprising zein proteins into the alcohol-water mixture followed by mixing of the water-alcohol mixture with the one or more fatty acids, wherein the mixing is carried out at a temperature between 4 °C and 40 °C, preferably between 10 °C and 30 °C, more preferably between 15 °C and 25 °C.

16. A method for producing a hydroalcoholic coating composition according to claim 15, wherein the zein proteins are added to the composition in the form of a corn-derived material comprising 89 wt.% or more, preferably 90 wt.% or more, more preferably 91 wt.% or more, most preferably 92.37 wt.% or more of the zein proteins based on total dry solids.

17. A hydroalcoholic coating composition obtained or obtainable by a method according to claim 15 or claim 16.

18. Use of the hydroalcoholic coating composition according to any of claims 1 to 14 or 17 for coating a cellulose-based substrate.

19. Use according to claim 18, wherein the substrate is selected from paper, card and cardboard.

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