Structurally coloured cellulose inks

Abstract

The present invention relates to an ink composition comprising a structurally coloured pigment, a polymer binder and a liquid carrier; a method of printing the ink composition; an ink deposit obtained from the ink composition and a printed article comprising the ink deposit. The ink composition includes the polymer binder present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment present at 50 wt.% or less based on the total mass of the ink composition. The ink composition may be used to apply a range of colours and visual effects to a substrate.

Description

[0001] Structurally Coloured Cellulose Inks

[0002] Related Application

[0003] The present application claims priority to, and the benefit of, GB 2502797.0 filed 26 February 2026 (26.02.2026), the content of which is incorporated herein by reference in its entirety.

[0004] Field of the Invention

[0005] The present invention relates to an ink composition comprising a structurally coloured pigment and a polymer binder, a method of printing the ink composition, an ink deposit obtained from the ink composition and a printed article comprising the ink deposit.

[0006] Background

[0007] Cellulose nanocrystals (CNCs) extracted from natural sources are abundant, sustainable, biocompatible, biodegradable, and multifunctional (Frka-Petesic etal.). The self-assembly of CNCs into cholesteric formations generating vibrant structural colour has attracted significant attention (Parker et al.), and the large-scale fabrication of coloured CNC films based on blade coating and roll-to-roll deposition techniques and the fabrication of sustainable CNC structurally coloured pigments has recently been demonstrated (Droguet et al.). For example, the inventors have previously descried in WO 2023 / 025863 and WO 2024 / 175776 the deposition of structurally coloured films on substrates.

[0008] In this earlier work, structurally coloured films and pigments are applied directly to substrates. This provides excellent visual results; however, it also requires precise formulation of the cellulose suspension, and for the film to be cast, relaxed and dried under carefully controlled conditions. This is needed to ensure the self-assembly of the cholesteric structures which provide the vibrant structural colouration. These specialized conditions are not easily transferable to a commercial scale. They are time intensive and require skilled labor to reproduce. Moreover, structural coloured films formed directly on substrate can be fragile and have poor abrasion or washing resistance.

[0009] There is need for improved ways to apply cellulose based structurally coloured materials to substrates.

[0010] The present invention is devised with these considerations in mind.

[0011] Summary of the Invention

[0012] The inventors have identified that by formulating an ink including a structurally coloured pigment with a polymer binder, it is possible to provide a composition which can be easily applied to a variety of substrates using standard printing techniques and equipment. The ink

[0013] 008928681deposit produced from the ink has the excellent optical properties of the cellulose based structurally coloured pigments, but can be applied more easily and have improved durability.

[0014] The cellulose based structurally coloured pigment described herein has formulation properties unlike typical pigments or glitters. Traditional coloured pigments typically consist of metalorganic complexes or molecules bearing chromophores interacting with one another. They are often formulated as fine powders with very small particle sizes to aid their suspension. The traditional coloured pigments are often insoluble and hydrophobic. In contrast, cellulose based structurally coloured pigments are relatively hydrophilic and hygroscopic, as a result of the cellulose content. The particle size is also considerably larger, as the colour is derived from the pigment’s internal chiral nematic structure, which needs to be retained to provide a strong colour. This is not a consideration for traditional pigments, where colour arises from electronic absorption.

[0015] It follows that the formulation of inks including cellulose based structurally coloured pigments includes unique considerations.

[0016] The inventors have identified that by formulating an ink with 5 wt.% or more of polymer binder and 50 wt.% or less of structurally coloured pigment, the ink deposit formed from the ink is able to effectively encapsulate the structurally coloured pigment. The polymer binder is able to fully or partially encapsulate the pigment. When the pigment is fully encapsulated the ink deposit tends to have has a strong and uniform colour, as the pigment particles are aligned in a similar orientation. The structurally coloured pigment is provided in a uniform environment which provides predictable and uniform optical properties. Where the pigment is partially encapsulated, some of the pigment particles on the surface have a more varied orientation, giving a characteristic white or silver appearance.

[0017] By fully encapsulating the structurally coloured pigment, the durability of the ink deposit is also enhanced, such as abrasion resistance or wash fastness. This is particularly important for printing on fabric, such as garments.

[0018] The use of structurally coloured pigments in the inks of the invention allows the ink deposit and resulting article to have a tuneable visual appearance. The pigments have a variable internal structure which allows for the full gamut of colours to be produced. However, the external structure of different coloured pigments is very chemically and physically similar. Thus, a similar (or identical) ink formulation may be used to achieve a range of colours and visual effects, ranging from metallic to matte appearances. This also allows for the formulation of multiple different coloured pigments into a single ink formulation, allowing access to a more complex and diverse range of colours.

[0019] This contrasts to traditional pigments - where the chemistry and external properties of the pigment typically differ between colours, meaning each ink colour needs to be formulated especially to suit the pigment. This can result in incompatibility between inks and printing

[0020] 008928681processes. It also makes the production of complex colours more difficult, as multiple layers of printing using different inks may be needed to access the complex colours.

[0021] The present invention addresses these variabilities by providing an ink composition capable of delivering a variety of structurally coloured pigments and complex colours, using a single versatile ink formulation.

[0022] At its most general, the present invention provides an ink composition comprising a structurally coloured pigment and a polymer binder, wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the ink composition.

[0023] In a general aspect, the present invention provides an ink composition comprising:

[0024] a structurally coloured pigment,

[0025] a polymer binder; and

[0026] a liquid carrier,

[0027] wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the ink composition.

[0028] In a first aspect of the invention there is provided an ink composition comprising:

[0029] a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures;

[0030] a polymer binder; and

[0031] a liquid carrier,

[0032] wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the ink composition.

[0033] In some embodiments, the polymer binder is present at 10 wt.% or more based on the total mass of the ink composition, preferably 20wt.% or more, more preferably 30 wt.% or more. In some embodiments, the polymer binder is present at from 20 to 75 wt.% based on the total mass of the ink composition, preferably from 30 to 65 wt.%, more preferably from 35 to 60 wt.%, even more preferably from 40 to 55 wt.%, yet more preferably from 45 to 50 wt.%.

[0034] In some embodiments, the liquid carrier is present at 90 wt.% or less based on the total mass of the ink composition, preferably 80 wt.% or less, more preferably 70 wt.% or less. In some embodiments, the liquid carrier is present at from 35 to 90 wt.% based on the total mass of the ink composition, preferably from 40 to 70 wt.%, more preferably from 45 to 60 wt.%, yet more preferably from 45 to 50 wt.%.

[0035] 008928681In some embodiments the structurally coloured pigment is present at from 1 to 50 wt.% based on the total mass of the ink composition, preferably from 3 to 30 wt.%, more preferably from 5 to 20 wt.%, yet more preferably from 8 to 12 wt.%.

[0036] In some embodiments, the mass ratio of polymer binder to structurally coloured pigment is 1 or more, preferably 2 or more, more preferably 3 or more, yet more preferably 4 or more.

[0037] By providing an ink having these relative amounts of polymer binder and pigment, the ink deposit formed from the ink is able to effectively encapsulate the structurally coloured pigment. This improves the durability of the ink deposit as well as the optical properties, as described herein.

[0038] The inks of the present invention may be applied using any suitable printing process.

[0039] In a second aspect of the invention there is provided a use of the ink composition of the first aspect, for screen printing, spray coating, dip coating or transfer printing. Preferably, the use of the ink composition is for screen printing or transfer printing.

[0040] In an aspect of the invention there is provided a use of the ink composition of the first aspect, for screen printing, spray coating or dip coating. Preferably, the use of the ink composition is for screen printing.

[0041] In a third aspect of the invention there is provided a method of printing an ink composition onto a substrate, wherein the ink composition is the ink composition of the first aspect, the method comprising:

[0042] applying the ink composition onto a substrate;

[0043] drying the ink composition to remove at least a portion of the liquid carrier, to provide an ink deposit.

[0044] The method of printing the inks results in an ink deposit formed from the dried ink. The ink deposit typically includes the non-volatile components of the ink. By using the mass ratio of the polymer binder to structurally coloured pigment described above, an ink deposit can be formed from the ink where the pigment is effectively encapsulated by the binder.

[0045] In some embodiments the method comprises shearing the ink composition. The shearing may align the orientation of the structurally coloured pigment.

[0046] In a fourth aspect of the invention there is provided an ink deposit obtained or obtainable by the method of the third aspect.

[0047] In some embodiments, the structurally coloured pigment is fully and / or partially encapsulated by the polymer binder. Some of the pigment may be fully encapsulated and some of the

[0048] 008928681pigment may be partially encapsulated. The partially encapsulated pigment is typically present on the surface of the ink deposit.

[0049] In some embodiments the structurally coloured pigment is fully or partially encapsulated by the polymer binder. The pigment may be fully encapsulated. That is, all the pigment present in the deposit is fully encapsulated. If the pigment is fully encapsulated the ink deposit tends to have has a strong and uniform colour.

[0050] The pigment may be partially encapsulated. That is, all the pigment present in the deposit is partially encapsulated. If the pigment is partially encapsulated, the ink deposit tends to have an iridescent and shiny appearance.

[0051] In a fifth aspect of the invention there is provided an ink deposit comprising:

[0052] a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures; and

[0053] a polymer binder,

[0054] wherein the polymer binder encapsulates the structurally coloured pigment.

[0055] In some embodiment, the structurally coloured pigments are aligned in substantially the same direction in the ink deposit. The alignment may be achieved by shearing the ink composition during the printing process.

[0056] In some embodiments, the structurally coloured pigments lay substantially flat. That is, a facet of the structurally coloured pigments is aligned parallel to the substrate.

[0057] The ink deposit typically exhibits photonic colour. The colour of the ink deposit may appear matt, lustrous, iridescent or metallic.

[0058] In a sixth aspect of the invention there is provided a printed article, the article comprising an ink deposit of the fourth or fifth aspects deposited on the substrate.

[0059] The ink deposit and / or article are preferably recyclable. By providing an ink composition of the invention, including a cellulose based pigment, the ink does not hinder the recyclability of the article. In particular, where a bio-based binder is used with the structurally coloured cellulose pigment, the article may be recyclable.

[0060] As a result of the ink deposit on the article, the article exhibits photonic colour. The colour of the ink deposit may appear matt, lustrous, iridescent or metallic.

[0061] In another aspect of the invention there is provided an ink container comprising the ink of the first aspect.

[0062] 008928681In another aspect of the invention there is provided a kit comprising the components of the ink composition. The kit may comprise:

[0063] a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures;

[0064] a polymer binder; and

[0065] a liquid carrier,

[0066] wherein the polymer binder is present in the kit at 5 wt.% or more based on the total mass of the kit, and the structurally coloured pigment is present in the kit at 50 wt.% or less based on the total mass of the kit.

[0067] In some embodiments the kit comprises a solid part, including the structurally coloured pigment, and a liquid part, including the polymer binder and liquid carrier.

[0068] The kit may allow for the ink composition to be prepared. The kit may be used to prepare the ink composition at the time of printing.

[0069] The kit may also allow the ink composition to be applied using flocking. For example, the polymer binder and liquid carrier (liquid part) may be applied to a substrate, and the structurally coloured pigment (solid part) may then be applied to the surface of the polymer binder and liquid carrier on the substrate.

[0070] In a related aspect of the invention, there is provided a method of preparing the ink composition. The method of preparing the ink composition comprises combining a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures, a polymer binder, and a liquid carrier to provide the ink composition;

[0071] wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present in the ink composition at 50 wt.% or less based on the total mass of the ink composition.

[0072] Combining the components of the ink composition may include a step of mixing the ink composition and a step of dispersing the pigment. The dispersing step is intended to homogenise the mixture, and suspend the pigment and / or binder in the liquid carrier.

[0073] The components of the ink composition may be combined using any suitable means. The components of the ink may be mixed until the ink appeared uniform.

[0074] At a small scale, a spatula may be used to mix the components. A vortex mixer may then be used to disperse the pigments in the liquid components.

[0075] At a larger scale, an overhead stirrer or mixer may be used to mix the components. A homogeniser or ultraturrax disperser may be used to disperse the pigment.

[0076] 008928681The amount of mixing is preferably minimised, to prevent disintegration of the pigment particles.

[0077] Summary of the Figures

[0078] The present invention is described with reference to the figures listed below.

[0079] Figure 1 shows images of cellulose based structurally coloured pigments of different size ranges on different backgrounds and at different magnification. The top row shows macroscopic images of pigments embedded in UV resin on a black background. The bottom row shows microscopic images of pigments on a glass slide.

[0080] Figure 2 shows photographs of Screenprints with 10 wt%, 75-106pm pigments and a 15T mesh with varying binders. Figure 2(a) is Ink 6; Figure 2(b) is Ink 4; Figure 2(c) is Ink 5; Figure 2(d) is Ink 3; Figure 2(e) is Ink 1 ; and Figure 2(f) is Ink 2.

[0081] Figure 3 shows graphs of the variation of viscosity with shear rate for pigments with 0, 2 and 8 hours heat-treatment in 3 different binders: (a) Ink 5 (CSFXC Glitter Printing Binder), (b) Ink 1 (Bondoglit DP2720) (c) Ink 2 (Tubiscreen GD200). Figure 3(d) compares results for Inks 1, 2 and 5.

[0082] Figure 4 shows a graph comparing the rheology behaviour for different of the polymer binders and carrier liquid combinations for 0% pigment and 10% pigment (Ink 1-6).

[0083] Figure 5 shows a comparison of pigments size and concentration on viscosity. Figure 5(a) shows the dependence of pigments size and concentration on the viscosity. Figure 5(b) shows the dependence of pigment particle diameter and concentration on the viscosity.

[0084] Figure 6 shows images of ink deposits formed by screen printing Inks 6-10 on lyocell using a 15T mesh.

[0085] Figure 7 shows images of ink deposits formed by screen printing Inks 9XS to 9XL using different mesh sizes for the screen printing process.

[0086] Figure 8 shows images of screen-printed sample of Ink 9XL printed onto a knit cotton jersey without (left) and with (right) a base layer.

[0087] Figure 9 shows images of screenprints prepared using (a) red, (b) orange, (c) green, (d) turquoise, (e) blue pigments in example ink formulations of the invention.

[0088] 008928681Figure 10 shows images of screenprints prepared using (a) red pigments, (b) green pigments, (c) blue pigments, (d) red and green pigments; (e) green and blue pigments; and (f) blue and red pigments in example ink formulations of the invention.

[0089] Figure 11 shows images of ink deposits of red, green and blue example inks on substrates with red, green, blue, black colours.

[0090] Figure 12 shows a schematic of a red base layer and a green ink deposit, and the colours which are absorbed, reflected or transmitted by each layer.

[0091] Figure 13 shows images of ink deposits formed from examples inks of the invention on different substrates: (a) plain weave lyocell, (b) plain weave cotton, (c) cotton twill, (d) cotton indigo dyed denim, (e) knit cotton jersey, (f) knit diagonal cotton fleece, (g) recycled polyester satin, (h) recycled polyester twill, (i) leather and (j) paper.

[0092] Figure 14 shows images of ink deposits of Inks 10XL and 10M with a circle design.

[0093] Figure 15 shows images of ink deposits before (left) and after (right) wet crocking test with 100 revolutions.

[0094] Figure 16 shows the different possible microscopic arrangement of pigments that dominates the different macroscopic visual appearances: (a) large particles with preferred aligned orientations, (b) large particles with random orientations, (c) large particles without insufficient binder coverage, (d) small particles with aligned orientations, (e) small particles with random orientations and (f) small particles with insufficient binder coverage.

[0095] Figure 17 shows schematic illustrations of some example printing methods.

[0096] Detailed Description of the Invention

[0097] The present invention provides an ink composition comprising a structurally coloured pigment and a polymer binder, wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the ink composition.

[0098] The concept of embedding structurally coloured pigments into a polymer matrix has been described before, for example, in WO 2023 / 025863. This document describes how particles of structurally coloured cellulose may be embedded in an epoxy binder. However, epoxy is not a suitable binder for a printable ink composition because of undesirable rheological properties and curing times. The epoxy composition does not include a carrier liquid and a polymer binder, and thus is not an ink composition.

[0099] 008928681WO 2018 / 033584 describes the preparation of structurally coloured particles using fluidics. The document mentions that structurally coloured particles may be used in ink compositions. However, WO 2018 / 033584 does not describe the amount of polymer binder and structurally coloured pigment described in the present case.

[0100] ON 118388995 describes a process for preparing 3D printing inks, and appears to describe adding coloured particles to a polymer. The document does not describe a polymer binder together with liquid carrier, or give information about the relative amounts of the coloured particles and polymer binder.

[0101] Ink Composition

[0102] In a first aspect of the invention there is provided an ink composition comprising:

[0103] a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures;

[0104] a polymer binder; and

[0105] a liquid carrier,

[0106] wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the ink composition.

[0107] The ink composition comprises a structurally coloured pigment, a polymer binder and a liquid carrier. In some embodiments, the ink composition consists of a structurally coloured pigment, a polymer binder and a liquid carrier.

[0108] The ink composition may be for printing, by any suitable means. The ink composition may be for screen printing, spray coating, dip coating, flocking or transfer printing. The ink composition may be for screen printing or spray coating. The ink composition may be for screen printing or transfer printing.

[0109] The ink composition may be for printing, by any suitable means. The ink composition may be for screen printing, spray coating, dip coating or flocking. The ink composition may be for screen printing or spray coating. The ink composition may be for screen printing.

[0110] The ink composition may be a screen printing ink, a spray coating ink, a dip coating ink or a transfer printing ink. The ink composition may be a screen printing inks or a spray coating ink. The ink composition may be a screen printing ink or a transfer printing ink.

[0111] The ink composition may be a screen printing ink, a spray coating ink, or a dip coating ink. The ink composition may be a screen printing inks or a spray coating ink. The ink composition may be a screen printing ink.

[0112] 008928681Polymer Binder

[0113] The ink composition comprises a polymer binder. A binder is typically a material which holds together other components and / or adheres components to a substrate. In an ink, the binder holds together the pigment to form a solid ink deposit, and adheres the ink deposit to a substrate.

[0114] The polymer binder is present at 5 wt.% or more based on the total mass of the ink composition. In some embodiments, the polymer binder is present at 10 wt.% or more based on the total mass of the ink composition, preferably 20wt.% or more, more preferably 30 wt.% or more.

[0115] In some embodiments, the polymer binder is present at 75 wt.% or less based on the total mass of the ink composition, preferably 65 wt.% or less, more preferably 60 wt.% or less, even more preferably 55 wt.% or less, yet more preferably 50 wt.% or less.

[0116] In some embodiments, the polymer binder is present at from 20 to 75 wt.% based on the total mass of the ink composition, preferably from 30 to 65 wt.%, more preferably from 35 to 60 wt.%, even more preferably from 40 to 55 wt.%, yet more preferably from 45 to 50 wt.%;

[0117] In some embodiments the polymer binder is present at from 20 to 75 wt.% based on the total mass of the polymer binder and the liquid carrier, preferably from 30 to 65 wt.%, more preferably 35 to 60 wt.%, even more preferably from 40 to 55 wt.%, yet more preferably from 48 to 52 wt.%.

[0118] The amount of polymer binder present in an ink composition may be determined by calculating the solid components present in a polymer binder solution. The polymer binder solution typically includes a polymer binder and a liquid carrier. Evaporation of the liquid carrier and comparison of the mass before / after evaporation can reveal the mass of the solid content. This may be used to infer the content of polymer binder present in the binder solution.

[0119] In some embodiments the solid content of the ink composition is from 30 to 85 wt.% based on the total mass of the polymer binder and the liquid carrier, preferably from 40 to 75 wt.%, more preferably 45 to 70 wt.%, even more preferably from 50 to 65 wt.%.

[0120] In the ink composition, the polymer binder may be present as a monomeric or pre-polymeric form. During curing, the monomer or pre-polymer may polymerise and / or cross-link to form a polymer binder matrix. The polymer binder may be referred to as a polymer binder even when in a monomeric or pre-polymeric state, provided the binder is capable of forming a polymer during curing.

[0121] 008928681During curing, polymerisation may occur between all species of the polymer binder. For example, polymerisation and / or cross-linking may occur between monomeric and prepolymeric species.

[0122] The polymer binder may bind to the pigments. The binding may use intermolecular or intramolecular bonds. Where intramolecular bonds are present, during curing, polymerisation may occur between the polymer binder and the pigment. For example, polymerisation and / or cross-linking may occur between polymer binder and the pigment.

[0123] The polymer binder may bind to the substrate. The binding may use intermolecular or intramolecular bonds. Where intramolecular bonds are present, during curing, polymerisation may occur between the polymer binder and the substrate. For example, polymerisation and / or cross-linking may occur between polymer binder and the substrate.

[0124] The polymer binder may be selected based on the substrate. For example, a rigid substrate (e.g., wood) may be suited to a rigid polymer binder. On the other hand, a flexible substrate (e.g., a stretch fabric) may be suited to an elastomeric polymer binder.

[0125] In some embodiments, the mass ratio of polymer binder to structurally coloured pigment is 1 or more, preferably 2 or more, more preferably 3 or more, yet more preferably 4 or more.

[0126] In some embodiments, the mass ratio of polymer binder to structurally coloured pigment is 10 or less, preferably 8 or less, more preferably 6 or less, yet more preferably 4 or less.

[0127] In some embodiments, the mass ratio of polymer binder to structurally coloured pigment is from 1 to 10, preferably from 2 to 8, more preferably from 3 to 6, yet more preferably from 4 to 5.

[0128] The polymer binder may be selected because of its refractive index. The polymer binder may have a refractive index which is similar to the cellulose structurally coloured pigment. The cellulose structurally coloured pigment typically has a refractive index of about 1.55.

[0129] The refractive index of the polymer binder refers to the cured polymer binder, as present in the ink deposit. The refractive index is the refractive index of the polymer binder in cured form. The refractive index of the polymer binder may be measured using any suitable means, such as a refractometer. The values of refractive index given are the absolute refractive index.

[0130] In some embodiments the polymer binder has a refractive index of from 1.40 to 1.70, preferably from 1.45 to 1.65, more preferably from 1.50 to 1.60. In some embodiments the polymer binder has a refractive index of about 1.55.

[0131] 008928681In some embodiments the difference between the refractive index of the polymer binder and the structurally coloured pigment is 0.25 or less, preferably 0.10 or less, more preferably 0.08 or less, yet more preferably 0.05 or less, even more preferably 0.02 or less.

[0132] In some embodiments the difference between the refractive index of the polymer binder and the structurally coloured pigment is from 0 to 0.25, preferably from 0.05 to 0.10, more preferably from 0.1 to 0.08, yet more preferably 0.2 to 0.06, even more preferably from 0.3 to 0.5.

[0133] Alternatively, the refractive index of the polymer binder refers to the polymer binder present in the ink composition. In other words, the refractive index may refer to the polymer binder formulated in a liquid carrier. The refractive index may be measured using any suitable means, such as a refractometer. The values of refractive index given are the absolute refractive index. In some embodiments the polymer binder has a refractive index of from 1.40 to 1.70, preferably from 1.45 to 1.65, more preferably from 1.50 to 1.60. In some embodiments the polymer binder has a refractive index of about 1.55. In some embodiments the difference between the refractive index of the polymer binder and the structurally coloured pigment is 0.25 or less, preferably 0.10 or less, more preferably 0.08 or less, yet more preferably 0.05 or less, even more preferably 0.02 or less.

[0134] Any suitable polymer binder for an ink composition may be used. For example, the polymer binder may be acrylates / steareth-20methacrylatecopolymer, aromatic polymer (such as polycarbonate, polyester, polystyrene), Carbopol®, dimethylhydantoin-formaldehyde, halogenated polymer, hydrogenatedpolydecene, keratin, para-aramid, poloxamer, polyacrylamide, polyacrylonitrile, polyaminoacid, polyamide (such as Nylon 6, Nylon 6,6, Nylon 12), polyether, polyolefin (such as but are not limited to polyethylene, polyisoprene, polypropylene, polybutadiene, polyethylene glycol), polypeptide, polymethacrylate, polymethylmethacrylate cross-polymer, polymethylsilsesquioxanes, polyquaternium, silicones, silk fibroin, silk sericin, ulvan, vinyl acetate, vinyl acetate / crotonic acid copolymer, methyl vinyl ether and maleic semester copolymer, vinylpyrrolidone. The polymer can be a cellulose- or a lignin-derivative, such as cellulose acetate, cellulose nitrate, cellophane, nitrocellulose and celluloid. The polymer can be a starch-derivative. The polymer can be a chitin-, a chitosan- or a sericin derivative. The polymer can be an alignate-, a carrageenan -, a collagen-, gelatin-, hyaluronic acid- or pectin-derivative. Preferentially the polymer is synthetised from natural feedstock and / or biobased and / or renewable monomers, and the resulting polymer is preferably biodegradable such as aliphatic polyesters, for instance poly(lactic acid), poly (e-caprolactone), and poly(3-hydroxybutyrate-co-3 hydroxy valerate).

[0135] In some embodiments, the polymer binder is bio-based. The polymer binder may have a modern carbon content of 70wt.% or more, such as 80wt.% or more, such as 90 wt.% or more.

[0136] 008928681In some embodiments, the polymer binder is biodegradable. The polymer binder may be biodegradable on a timescale similar to the cellulose structurally coloured pigments.

[0137] The polymer binder may be a bio-based biodegradable polymer or a synthetic biodegradable polymer.

[0138] Suitable bio-based biodegradable polymers include polysaccharide polymers, such as starch based polymers, cellulose based polymers, lignin based polymers, chitin or chitosan based polymers; polypeptide polymers, such as gluten, collagen, gelatine, casein; poly hydroxy alcanoates; or poly-3-hydroxybutyrates.

[0139] Suitable synthetic biodegradable polymers include polyesters, such as polylactic acid, polyglycolic acid, polycaprolactone, polybutylene succinate or polybutylene succinate adipate; polyvinyl alcohol; or poly vinyl acetate.

[0140] In some embodiments the polymer binder is a polyurethane, a poly(meth)acrylate, a polyvinyl acetate or a combination thereof, preferably wherein the polymer binder is a polyurethane.

[0141] The refractive index of polyurethane is about 1.67. The refractive index of poly vinyl acetate is about 1.47. The refractive index of a poly(meth)acrylate is about 1.49. These binders have a similar refractive index to cellulose structurally coloured pigments, and so provdie a good level of index matching and excellent optical properties for the ink deposit.

[0142] In some embodiments the polymer binder is cross-linkable. The polymer binder may be self-cross-linkable or be cross-linked using an additional cross-linker.

[0143] Additionally, in some embodiments the polymer binder is an elastomeric polymer binder. An elastomer may refer to any polymer binder having viscoelasticity. Viscoelasticity may be characterised by a low stress / strain ratio.

[0144] Any suitable elastomeric polymer binder may be used, such as a polyurethane, a poly(meth)acrylate, or a polysiloxane binder (e.g., polydimethylsiloxane).

[0145] A copolymer binder may be used, such as copolymer of polyurethane, poly(meth)acrylate and / or polystyrene. The copolymer elastomeric binder may be a copolymer of poly(meth)acrylate and polyurethane, or a copolymer of poly(meth)acrylate and polystyrene. Liquid Carrier

[0146] The ink composition comprises a liquid carrier. Any suitable liquid carrier may be used, which is able to suspend the structurally coloured pigment and polymer binder. The liquid carrier may be able to dissolve the polymer binder.

[0147] 008928681The liquid carrier is preferably vapourisable under printing conditions. That is, the liquid carrier can be removed by drying the ink composition to leave an ink deposit comprising the pigment and polymer binder. The ink deposit may be substantially free of liquid carrier.

[0148] Any suitable liquid carrier may be used. In some embodiments the liquid carrier is an organic solvent, water or a combination thereof. Preferably the liquid carrier is water.

[0149] The organic solvent may be 2-propanol, 1,2-dichloroethane, 1,4-dioxane, 18-crown-6, 2-propanol, 2-ethoxyethanol, acetic acid, acetone, acetonitrile, ammonia, benzene, n-butanol, n-butyl acetate, chloroform, cyclohexane, dichloromethane, diethyl ether, diglyme, dimethyl formamide, dimethyl sulfoxide, DME, ethane, ethanol, ethyl acetate, ethylene, ethylene glycol, formic acid, glycerine, heptane, hexane, hexamethylbenzene, HMDSO, HMPA, Hydrogen, Imidazole, isobutanol, isopropyl alcohol, methane, methanol, n-hexane, nitromethane n-pentane, propane, propylene, propylene carvonate, pyridine, pyrrole, pyrrolidine, silicone grease, tert-butyl alcohol, tetra hydrofuran, toluene, triethylamine, white spirit and xylene or a mixture thereof.

[0150] The liquid carrier may be present at a relatively low amount. The amount of liquid carrier may be adjusted to suit the polymer binder type and amount. The amount of liquid carrier may be adjusted to suit the ink type, such as the type of printing which the ink is intended to be used for.

[0151] In some embodiments the liquid carrier is present at 90 wt.% or less based on the total mass of the ink composition, preferably 50wt.% or less, more preferably 10 wt.% or less.

[0152] In some embodiments the liquid carrier is present at from 1 to 90 wt.% based on the total mass of the ink composition, preferably from 2 to 70 wt.%, more preferably from 5 to 50 wt.%, yet more preferably from 10 to 30 wt.%.

[0153] In some embodiments the liquid carrier is present at from 1 to 90 wt.% based on the total mass of the ink composition, preferably from 2 to 70 wt.%, more preferably from 5 to 50 wt.%, yet more preferably from 10 to 30 wt.%.

[0154] In some embodiments the liquid carrier is present at 90 wt.% or less based on the total mass of the ink composition, preferably 80wt.% or less, more preferably 70 wt.% or less.

[0155] In some embodiments the liquid carrier is present at from 35 to 90 wt.% based on the total mass of the ink composition, preferably from 40 to 70 wt.%, more preferably from 45 to 60 wt.%, yet more preferably from 45 to 50 wt.%.

[0156] In some embodiments the liquid carrier is present at from 20 to 75 wt.% based on the total mass of the polymer binder and the liquid carrier, preferably from 30 to 70 wt.%, more

[0157] 008928681preferably 40 to 65 wt.%, even more preferably from 45 to 55 wt.%, yet more preferably from 48 to 52 wt.%.

[0158] The amount of liquid carrier present in an ink composition may be determined by calculating the liquid components present in a polymer binder solution. The polymer binder solution typically includes a polymer binder and a liquid carrier. Evaporation of the liquid carrier and comparison of the mass before / after evaporation can reveal the mass of the liquid components.

[0159] In some embodiments the liquid content of the ink composition is from 20 to 75 wt.% based on the total mass of the polymer binder and the liquid carrier, preferably from 30 to 70 wt.%, more preferably 40 to 65 wt.%, even more preferably from 45 to 55 wt.%, yet more preferably from 48 to 52 wt.%.

[0160] In some embodiments, the liquid carrier is bio-based. In particular, where the liquid carrier is an organic solvent, the organic solvent may be bio-based. The organic solvent may have a modern carbon content of 70wt.% or more, such as 80wt.% or more, such as 90 wt.% or more.

[0161] Structurally Coloured Pigment

[0162] The ink composition comprises a structurally coloured pigment. The structurally coloured pigment comprises cellulose nanocrystals. The cellulose nanocrystals are organised into chiral nematic structures.

[0163] Additionally, structurally coloured pigment may refer to pigment particles that reflect light from one or more bands of light in the visible, ultraviolet (UV) and infrared (IR) regions, such as one band of light in the visible, UV and IR regions. Structurally coloured pigment particles typically refer to pigment particles that reflect one or more bands of light in the visible region, such as one band of light in the visible region. In this way, the pigments appear coloured.

[0164] The structurally coloured pigments are present at 50 wt.% or less of the ink composition.

[0165] In some embodiments the structurally coloured pigment is present at from 40 wt.% or less based on the total mass of the ink composition, preferably 30 wt.% or less, more preferably 20 wt.% or less.

[0166] In some embodiments the structurally coloured pigment is present at from 1 wt.% or more based on the total mass of the ink composition, preferably 5 wt.% or more, more preferably 10 wt.% or more.

[0167] In some embodiments the structurally coloured pigment is present at from 1 to 50 wt.% based on the total mass of the ink composition, preferably from 3 to 30 wt.%, more preferably from 5 to 20 wt.%, yet more preferably from 8 to 12 wt.%.

[0168] 008928681In some embodiments the structurally coloured pigments have an average particle diameter of from 2 to 5000 pm, preferably 10 to 1000 pm, more preferably from 15 to 500 pm, yet more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0169] In some embodiments the structurally coloured pigments have an average particle diameter of from 2 to 500 pm, preferably 10 to 300 pm, more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0170] In some embodiments 80 wt.% or more of the structurally coloured pigments have a particle diameter of from 2 to 5000 pm, preferably 10 to 1000 pm, more preferably from 15 to 500 pm, yet more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0171] In some embodiments 80 wt.% or more of the structurally coloured pigments have a particle diameter of from 2 to 500 pm, preferably 15 to 300 pm, more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0172] The size of the structurally coloured pigment may be determined using standard techniques. For example, the median average particle diameter of the structurally coloured particles may be measured by SEM or optical microscopy. Preferably, the surface area of each particle is measured and then the diameters of a spherical particle having the same surface area is calculated to retrieve the diameter. This diameter is recorded as the diameter of the particle and the median average of all particles measured is calculated from the individual particle diameters.

[0173] The ink composition of any preceding claim, wherein the structurally coloured pigments have a median average particle diameter of from 2 to 5000 pm, preferably 10 to 1000 pm, more preferably from 15 to 500 pm, yet more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0174] The ink composition of any preceding claim, wherein the structurally coloured pigments have a D50 particle diameter of from 2 to 5000 pm, preferably 10 to 1000 pm, more preferably from 15 to 500 pm, yet more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0175] The ink composition of any preceding claim, wherein the structurally coloured pigments have a median average particle diameter of from 2 to 500 pm, preferably 10 to 300 pm, more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0176] The ink composition of any preceding claim, wherein the structurally coloured pigments have a D50 particle diameter of from 2 to 500 pm, preferably 15 to 300 pm, more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

[0177] 008928681The ink composition of any preceding claim, wherein the structurally coloured pigments have a D90 particle diameter of 500 pm or less, preferably 300 pm or less, more preferably 150 pm or less, even more preferably from 110 pm or less.

[0178] The ink composition of any preceding claim, wherein the structurally coloured pigments have a D10 particle diameter of 2 pm or more, preferably 15 pm or more, more preferably from 20 pm or more, even more preferably 70 pm or more.

[0179] In some embodiments, the structurally coloured pigments have a narrow particle size distribution. The narrow particle size distribution may be achieved by, for example, by differential sieving.

[0180] In some embodiments, the structurally coloured pigments have a difference between the D90 and D10 values of 100 pm or less, preferably 50 pm or less, more preferably 40 pm or less, even more preferably 30 pm or less.

[0181] In some embodiments, the structurally coloured pigments have a particle diameter spread, defined as (D90 - D10) / D50 of 1 or less, preferably 0.9 or less, more preferably 0.8 or less. In some embodiments, the structurally coloured pigments have a particle diameter spread, defined as (D90 - D10) / D50 of from 0.2 to 1, preferably from 0.3 to 0.9. In one embodiment, the particle diameter spread may be from 0.2 to 0.5, such as from 0.3 to 0.4. In another embodiment, the particle diameter spread may be from 0.5 to 1, such as from 0.7 to 0.8

[0182] The D10, D50 and D90 particle diameters of some example pigments are provided in the Table below, along with an example calculation of particle diameter spread.

[0183]

[0184] Typically, the pigment is substantially insoluble in the carrier liquid and / or polymer binder. Typically, the pigment is substantially unreactive with the carrier liquid and / or polymer binder. The pigment differs from a dye, which is soluble with the carrier liquid.

[0185] In some embodiments the structurally coloured pigments consist of cellulose nanocrystals. In some embodiments the structurally coloured pigments comprise neutralised cellulose nanocrystals. In some embodiments, the structurally coloured pigments consist of neutralised cellulose nanocrystals.

[0186] 008928681In some embodiments the ink composition includes a single colour of structurally coloured pigment.

[0187] In some embodiments the ink composition comprises two or more different coloured structurally coloured pigments.

[0188] In some embodiments each particle of the structurally coloured pigment has a chiral nematic structure having a single cholesteric pitch.

[0189] In some embodiments each particle of the structurally coloured pigment has a chiral nematic structure having a two or more different cholesteric pitches.

[0190] In some embodiments each particle of the structurally coloured pigment has two more layers, and optionally each layer of the particle has a chiral nematic structure having a different cholesteric pitch.

[0191] In some embodiments each particle of the structurally coloured pigment further comprises a cholesteric layer, preferably wherein the cholesteric layer is sandwiched between two layers of chiral nematic structure.

[0192] In some embodiments the ratio of the average particle diameter to the amount of structurally coloured pigment present in the ink is from 2 to 20, preferably from 3 to 15, more preferably from 4 to 10, even more preferably about 6;

[0193] wherein the average particle diameter is measured in pm; and

[0194] the amount of structurally coloured pigment is measured in wt.% and is based on the mass of the total ink composition.

[0195] In some embodiments the structural coloured pigment is an annealed pigment. An annealed pigment refers to a pigment which has undergone heat treatment. An annealed pigment may have undergone heat treatment such that it does not absorb water.

[0196] The pigment may undergo heat treatment for 15 minutes or more, such as 30 minutes or more, such as 1 hour or more, such as 2 hours or more, such as 8 hours or more. The pigment may undergo heat treatment for from 2 to 8 hours.

[0197] The annealing process reduces the hygroscopicity of the pigment, and improves the pigments stability. The resulting pigments showed a much lower viscosity increases with increased pigment loading when formulated into ink compositions.

[0198] The annealing process is also thought to improve durability, such as abrasions resistance and colour fastness, of the ink deposit. The annealing process may decrease the water absorbance of the pigment by 10% or more, such as 20% of more, such as 50% or more.

[0199] 008928681The water absorbance may be measured by comparing the mass of the material before and after exposure to water.

[0200] The pigment may be treated to decrease its light absorbance, such as visible light absorbance. The pigment may be treated to increase the light reflectance, such as the visible light reflectance.

[0201] The structurally coloured pigment may be a particle as described in WO 2023 / 025863, the contents of which is incorporated by reference in its entirety.

[0202] The structurally coloured pigment may be produced by the methods described herein, such as dividing the structurally coloured films described herein. The steps of processing the film into pigment particles preserves the chiral nematic structures of the nanocrystals without significantly altering them. The particles produced by the methods above have exceptional optical quality such as high intensity and saturation.

[0203] In some cases, the structurally coloured pigment has a rock-like shape. In some cases, the structurally coloured pigment may have facets where the chiral nematic phase is revealed.

[0204] Typically, the pigments have at least 4 distinguishable facets, originating from the nucleation and growth of the self-assembled cholesteric domains. The pigments may comprise one or more cholesteric domains, preferably one cholesteric domain.

[0205] The highly ordered chiral nematic structures in the particles result in high reflectivity.

[0206] The structurally coloured pigments reflect 25% or more of the incident light at a given wavelength in the visible range (300 nm to 700 nm) Preferably, the pigments reflect 30% or more of the incident light, more preferably 35% or more, and even more preferably 40% or more.

[0207] The reflectance of the particles can be measured using standard techniques, such as using an optical microscope coupled with a spectrometer, used in bright field imaging configuration with or without polariser. The reflectance values are measured relative to the reflectance of a mirror, typically a silver mirror (maximal reflectance) used to obtain the normalized reflectance of the sample. The background noise is subtracted. The reflectance values are measured in the visible range (300 nm to 800 nm). Typically, the samples are mounted flat on the stage of the microscope such that the light rays can be considered to travel perpendicular to the sample’s surface to measure reflection at normal incidence, with the light being collected within the cone (numerical aperture) of the objective (maximal reflectance). Typically, the reflectance values are measured in air.

[0208] The pigments may reflect light of different wavelengths with different reflectance.

[0209] 008928681At 500 nm, the particles typically exhibit a reflectance 30% or more of the incident light, more preferably 35% or more, and even more preferably 40% or more.

[0210] The full width at half maximum of the reflected light is typically 150 nm or less, and preferably 125 nm or less.

[0211] In the range 400 nm to 650 nm, the films typically exhibit a full width at half maximum of 150 nm or less, and preferably 125 nm or less.

[0212] The reflected structural colour may be iridescent, and so it is angle-dependent. The level of iridescence can be controlled through the extent of disorder of the chiral nematic structures within the particle.

[0213] The structurally coloured pigment may be a pigment as described in WO 2024 / 175776, the contents of which is incorporated by reference in its entirety.

[0214] The pigment may be a multi-layered particle, comprising two or more cholesteric layers which are in direct contact with another cellulose containing layer.

[0215] In some embodiments, the multi-layered pigment comprises a cholesteric layer and a nematic layer, wherein the cholesteric layer in direct contact with a nematic layer. Preferably, the nematic layer is in direct contact with two cholesteric layers.

[0216] In some embodiments, the multi-layered pigments comprise two or more cholesteric layers, wherein

[0217] each cholesteric layer comprises cellulose nanocrystals and the nanocrystals are organized into chiral nematic structures,

[0218] each cholesteric layer has a thickness such that the director of a chiral nematic structure performs at least one revolution within the layer, the layer having a thickness of 50 pm or less, preferably 20 pm or less, and

[0219] the multi-layered pigment comprises the cholesteric layer in direct contact with another cellulose containing layer.

[0220] In some embodiments, the multi-layered pigment comprises two or more cholesteric layers and a nematic layer, wherein

[0221] each cholesteric layer comprises cellulose nanocrystals and the nanocrystals are organized into chiral nematic structures,

[0222] each cholesteric layer has a thickness such that the director of a chiral nematic structure performs at least one revolution within the layer, the layer having a thickness of 50 pm or less, preferably 20 pm or less,

[0223] the nematic layer comprises cellulose nanocrystals and the nanocrystals are aligned in a non-chiral nematic structure; and

[0224] 008928681wherein the multi-layered pigment comprises the cholesteric layer in direct contact with another cellulose containing layer, and the nematic layer in direct contact with the cholesteric layer.

[0225] Preferably, the nematic layer acts as a half-wave retardation plate for circularly polarised light for a wavelength within 400nm of the maximum reflectance wavelength of one or more of the cholesteric layers, such as within 300nm, within 200nm, within 100nm, or within 50nm.

[0226] The pigment may be prepared according to the methods described herein.

[0227] By dividing the multi-layered film, a population of pigment particles is produced. The population of particles comprises particles having different numbers of layers. Typically, if the multi-layered film has N layers, then the population of particles comprises particles having a range of layers from 1 to N (e.g. N, N-1, N-2, ...1 layers).

[0228] Preferably, the population of pigment particles has a high proportion of particles having more than 1 layers (e.g., from 2 to N layers), as this imparts improved optical properties to the population of pigment particles. In some embodiments, the amount of pigment particles having more than 1 layers relative to the total population of particles is 10 wt.% or more, preferably 20 wt.% or more, more preferably 30 wt.% or more, yet more preferably 40 wt.% or more, even more preferably 50 wt.% or more

[0229] Preferably, the population of pigment particles has a higher proportion of N layered pigment particles, as this imparts improved optical properties to the population of pigment particles. In some embodiments, the amount of N layered pigment particles relative to the total population of particles is 10 wt.% or more, preferably 20 wt.% or more, more preferably 30 wt.% or more, yet more preferably 40 wt.% or more, even more preferably 50 wt.% or more.

[0230] The multi-layer pigment particles may have facets where the nematic phase of the pigment particle is revealed. This may be referred to as a facetted geometry.

[0231] The facetted geometry is revealed when the pigment particles are formed by dividing the film, and the film is divided in-between adjacent chiral nematic domains. The presence of the facetted geometry is indicative that the film has split between chiral nematic domains, rather than through the domains. Importantly, this means that the chiral nematic domains are retained in the particles which allows for the high reflectivity and colour saturation observed.

[0232] The pigment particles may have a facetted geometry, corresponding to at least one chiral nematic domain of the cholesteric layer. The pigment particles may also have a facetted geometry, corresponding to at least one non-chiral nematic domain of the nematic layer.

[0233] Typically, the pigment particles have at least 4 distinguishable facets, originating from the nucleation and growth of the self-assembled chiral nematic domains in the cholesteric layers.

[0234] 008928681The cholesteric layers may comprise one or more chiral nematic domains, preferably one chiral nematic domain.

[0235] The highly ordered chiral nematic structures in the pigment particles result in high reflectivity.

[0236] The multi-layer pigment particles may reflect 25% or more of the incident light at a given wavelength in the visible range (e.g., 100 nm to 1000 nm, such as 400 to 800 nm).

[0237] Preferably, the particles reflect 30% or more of the incident light, more preferably 35% or more, and even more preferably 40% or more.

[0238] The pigment particles may reflect incident light wherein the reflected light has a maximum reflectance at a wavelength of from 100 nm to 1000 nm, such as 400 to 800 nm, of 50% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more.

[0239] The pigment particles may reflect right circularly polarised light, wherein the reflected right circularly polarised light has a maximum reflectance at a wavelength of from 100 nm to 1000 nm, such as 400 to 800 nm, of 40% or more, preferably 50% or more, more preferably 60% or more, even more preferably 70% or more.

[0240] Preferably, the pigment particles reflect right circularly polarised light and left circularly polarised light, and the difference between the average reflectance of right circularly polarised light and left circularly polarised light at a given wavelength (e.g., 100 nm to 1000 nm, such as 400 to 800 nm) is 50% or less, preferably 40% or less, more preferably 30% or less, even more preferably 20% or less.

[0241] The pigment particles may reflect light of different wavelengths with different reflectance. As a result, the particles may have a coloured appearance. The full width at half maximum of the reflected light is typically 150 nm or less, and preferably 125 nm or less.

[0242] Preparation of Structurally Coloured Pigments

[0243] The structurally coloured pigment may be prepared using the methods described in

[0244] WO 2023 / 025863 and WO 2024 / 175776, the content of which are incorporated by reference in their entirety.

[0245] Briefly, the pigment may be prepared by forming a structurally coloured film and dividing the film to form pigment particles.

[0246] The film is prepared by:

[0247] a) depositing a nanocrystal suspension comprising cellulose nanocrystals onto a substrate;

[0248] b) spreading the nanocrystal suspension across the substrate using a spreader;

[0249] 008928681c) ageing the nanocrystal suspension to partially or completely recover the cholesteric structures lost during deposition and spreading; and

[0250] d) drying the deposited nanocrystal suspension so that the nanocrystals selfassemble to form a cholesteric layer.

[0251] The final colour of the layer can be tuned by, for example, adjusting the properties of the nanocrystal suspension, adjusting the deposition rate, adjusting the spreading (coating) conditions, and by adjusting the drying conditions.

[0252] In the coating process, the nanocrystal suspension may be spread across the substrate using a coating applicator or a spreader. The gap between the coating applicator / spreader and the substrate is fixed and is from 5 pm to 5 mm, preferably from 300 to 1500 pm, more preferably 300 to 1100 pm. The term “fixed” here is used to mean that the gap does not change during coating except by interference of the user. That is, the gap does not vary independently in an uncontrolled manner.

[0253] In the coating process, the coating speed is at least 0.6 mm / s. Coating speed refers to the speed at which the substrate moves relative to the spreader during at least the spreading step.

[0254] In the coating process the substrate is kept level during the depositing, spreading and drying steps. The term kept level is used here to refer to substantially the entire surface of the substrate remaining in a substantially horizontal plane during the depositing, spreading and drying steps.

[0255] In this way, unwanted flow of the nanocrystal suspension during deposition, spreading and drying is prevented. Unwanted flow of the nanocrystal suspension can result in disturbance of the self-assembly process and therefore reduced ability of the nanocrystals to form the chiral nematic order required for optimal structural colouration.

[0256] The substrate may be kept level by using a rigid substrate, by tensioning the substrate, by supporting the substrate or by any combination thereof.

[0257] For example, the rigid substrate may be thick enough not to warp during deposition and spreading. Preferably the rigid substrate is also flexible enough to be carried on the drums of a roll-to-roll printing machine. For example, the substrate may have a tension of from 10 to 250 N, more preferably from 25 to 125 N and even more preferably from 40 to 90 N. The tension difference between the ends of the web was such so that it exceeds 20 N, more preferably 40 N and even more preferably 60 N. The film tension may be determined by a load cell sensor.

[0258] In this way, cholesteric layers may be reliably and reproducibly prepared on large scale using industrially viable methods.

[0259] 008928681The cholesteric layer formation includes the steps of depositing and spreading a nanocrystal suspension across a substrate. These may be known as the depositing step and spreading step. Preferably, the nanocrystal suspension comprises neutralised cellulose nanocrystals.

[0260] The nanocrystal suspension may be deposited onto the substrate using a coating applicator. Any suitable coating applicator may be used. Suitable deposition methods include using a printing nozzle, spray head or slot die through which the cellulose suspension can flow in a controllable manner.

[0261] The nanocrystal suspension may be spread over the substrate using a spreader. Any suitable spreader may be used. Suitable spreaders include a knife, doctor blade, or a slot die.

[0262] The coating applicator and spreader can refer to the same apparatus. For example, when the coating applicator is a slot-die used with a moving belt, the steps of depositing and spreading are both achieved by the slot die. Slot die coating is well known, in particular slot die coating is well known in roll-to-roll printing processes. Preferably, a slot die is used as the coating applicator and spreader.

[0263] During spreading, the nanocrystal suspension experiences shear. The spreading step is an active spreading step. That is, the suspension is typically actively spread by applying an external mechanical force. This differs from passive spreading, where the suspension is allowed to spread passively (e.g., under gravity). During passive spreading the suspension does not typically experience shear.

[0264] The shear rate is calculated according to the following equation:

[0265] Shear rate = coating speed I coating gap

[0266] In some cases, the shear rate during the spreading step is 30.0 s'1or less, 20.0 s'1or less, 10.0 s'1or less, 8.0 s-1or less, 4.0 s-1or less, 3.0 s-1or less, preferably 2.8 s-1or less and more preferably 2.5 s'1or less. In some cases, the shear rate during the spreading step is 0.5 s'1or more, preferably 1.0 s-1or more, and more preferably 2.0 s-1or more.

[0267] The shear rate during the spreading step may be selected from a range with the upper and lower limits selected from the values given above. For example, the shear rate during the spreading step may be from 2.0 s-1to 20.0 s-1, preferably 2.0 s-1to 2.5 s-1, such as around 2.2 S'1.

[0268] The nanocrystal suspension may be deposited in discrete batches. In this case, each discrete batch is spread across the substrate during the spreading step.

[0269] 008928681Alternatively, the nanocrystal suspension may be deposited continuously. In this case, the nanocrystal suspension is continuously spread across the substrate.

[0270] The quantity of nanocrystal suspension deposited per unit area of the substrate (the areal loading) may be of 100 pL / cm2or less, 90 pL / cm2or less, preferably 80 pL / cm2or less and more preferably 60 pL / cm2or less.

[0271] The areal loading may be 10 pL / cm2or more, 20 pL / cm2or more, preferably 30 pL / cm2or more, and even more preferably 40 pL / cm2or more.

[0272] The areal loading may be selected from a range with the upper and lower limits selected from the values given above. For example, the deposition may be at a rate of from 40 pL / cm2to 60 pL / cm2such as around 50 pL / cm2.

[0273] The quantity of material deposited per unit time (the deposition rate) may be 12,000 pL / min or less, 10,000 pL / min or less, preferably 8,000 pL / min or less and more preferably 6,000 pL / min or less.

[0274] The deposition rate may be 800 pL / min or more, 1,200 pL / min or more, 1,600 pL / min or more, preferably 2,000 pL / min or more, and even more preferably 2,400 pL / min or more.

[0275] The deposition rate may be selected from a range with the upper and lower limits selected from the values given above. For example, the deposition may be at a rate of from 2,000 pL / min to 8,000 pL / min such as around 6,000 pL / min.

[0276] Typically, the substrate is moved relative to the coating applicator and the spreader. In this way, the nanocrystal suspension can be spread along the substrate by a combination of the spreader and the movement of the substrate.

[0277] Coating speed refers to the speed at which the substrate moves relative to the coating applicator or spreader during at least the spreading step.

[0278] The coating speed may be at least 1.0 mm / s, at least 1.5 mm / s at least 2.0 mm / s at least 4.0 mm / s preferably at least 1.0 mm / s and more preferably at least 1.5 mm / s.

[0279] The coating speed may be 60.0 mm / s or less, 30.0 mm / s or less, 15.0 mm / s or less, 3.0 mm / s or less, preferably 2.7 mm / s or less and more preferably 2.4 mm / s or less.

[0280] The coating speed may be selected from a range with the upper and lower limits selected from the values given above. For example, the coating speed may be from 1.0 mm / s to 2.4 mm / s, such as around 1.5 mm / s.

[0281] 008928681Preferably the coating process is a roll-to-roll printing process. Roll-to-roll printing is a well-known printing technique. Roll-to-roll printing involves the deposition of a substance from a fixed print head onto a moving substrate. Typically, the moving substrate is provided in the form of a roll and is often referred to as a web. The term web refers to a flat, elongated (sometimes continuous) substrate that can be wound and rewound. During printing, the substrate or web is unwound from the roll, a substance is deposited on the unwound portion of the web, and the deposited substance is carried on the surface of the substrate or web for further processing, such as drying. The web or substrate may be re-wound to form a second roll, either with or without the deposited substance on the surface of the web. Alternatively, the deposited substance may be removed and the web or substrate continuously recycled in further processing steps (Here, the web or substrate is in the form of a closed loop).

[0282] In some cases, the deposition can be performed over one or more discrete areas of the substrate or web.

[0283] In the present case, after deposition of the nanocrystal suspension on the web or substrate, the further processing steps include spreading, drying, and optionally removal of the cholesteric film from the surface of the web or substrate (peeling). Additional pre-treatment steps may also be carried out on the web or substrate prior to deposition of the nanocrystal suspension. The additional pre-treatment and later processing steps are discussed in more detail below.

[0284] The substrate is a suitable surface on which the nanocrystal suspension may be deposited, spread and dried.

[0285] For the initial layer of the multi-layer film, the substrate is typically a non-cellulosic material as described below. This may be known as the base substrate. For second and subsequent layers of the multi-layer film, the layers are applied directly to the previous cellulose containing layers. Accordingly, the previous layers are acting as the substrate.

[0286] In some cases, the base substrate has a thickness of 10,000 pm or less, 1,000 pm or less, preferably 800 pm or less, and even more preferably 500 pm or less.

[0287] In some cases, the base substrate has a thickness of 50 pm or more, 100 pm or more, preferably 300 pm or more, and even more preferably 400 pm or more.

[0288] The base substrate thickness may be selected from a range with the upper and lower limits selected from the values given above. For example, the substrate thickness may be from 300 to 500 pm such as around 400 pm.

[0289] In this way, the base substrate is relatively rigid and assists in keeping the substrate uniform and level during deposition and drying.

[0290] 008928681The base substrate may be or comprise any suitable material. Suitable substrate materials include polyvinyl alcohol, cellophane, polystyrene, acetal, ethylene-vinyl acetate, polyethylenes such as polyethylene terephthalate, polypropylene, fluoropolymer; polyimide, nylon, polyester, epoxy resin, acrylic resin, phenolic resin, polycarbonate, polyurethane, polyvinylchloride, and polyester. Preferably the web is polyethylene terephthalate (PET).

[0291] The base substrate may comprise substantially one suitable material. Alternatively, the base substrate may comprise two or more suitable materials. In such case, the materials may be mixed (blended) together, or they may be combined to form separate domains of each material.

[0292] The base substrate may be pre-structured, such as micro or nano-structured. In such cases, the substrate may be referred to as “patterned”. This pre-existing patterning can influence the interaction of the deposited substance with the substrate. For example, the substrate may exhibit areas where the deposited nanocrystal suspension can more favorably interact with, or have greater wetting of, the substrate. Similarly, the patterning may provide areas in which the deposited nanocrystal suspension interacts less favorably with, or has poorer wetting or, the substrate such that it preferentially avoids such areas.

[0293] The orientation of the cholesteric domains may be altered as a result of the patterning. For example, the orientation may follow the topography of the substrate such that the reflection from the cholesteric domains occurs over a wider range of angles. This can create a more complex visual effect than when a planar substrate with no such pre-existing pattern is used.

[0294] After formation of the multi-layer film, the base substrate may be separated from the film. This step may be referred to as peeling, and is discussed in further detail herein.

[0295] In some cases, the substrate can be reused several times in a closed-loop fashion.

[0296] Additionally, in some cases, the substrate is in the form of a moving belt such as a heat-resistant moving belt, such as made of metal.

[0297] The cholesteric layer formation includes the step of depositing a nanocrystal suspension, such as a cellulose nanocrystal suspension, onto a substrate.

[0298] Cellulose nanocrystals (CNCs) are well known in the art. Methods for the preparation of cellulose nanocrystals are also well known in the art. Many types of cellulose nanocrystals are known, and examples includes those cellulose nanocrystals obtained from different biological sources as well as those nanocrystals prepared in different ways from the same source.

[0299] 008928681The cellulose nanocrystals used in this invention can be any suitable cellulose nanocrystal. The cellulose nanocrystals can be any cellulose nanocrystal able to self-assembled into cholesteric structures.

[0300] Cellulose nanocrystals may be prepared from bacterial, vegetal or animal sources (e.g. chitin), including plant-based and biomass source such as cotton and wood and any subsequent processed element coming from such, such as paper, filter-paper cotton linters, and wood pulp.

[0301] The processing procedures carried out on the source material in order to produce cellulose nanocrystals typically involve hydrolysis, separation of the hydrolysed compounds and purification. Separation can be performed through centrifugation. Purification can be carried out by dialysis and membrane ultrafiltration. Known methods for producing cellulose nanocrystals are described by Lagerwall et al, the contents of which are hereby incorporate by reference.

[0302] Typically, the cellulose source is hydrolyzed, such as with sulfuric or hydrochloric acid or other acids, or alkaline medium in the preparation process, or the cellulose source is oxidized, such as in the case of the preparation of TEMPO-oxidized cellulose nanocrystals.

[0303] Preferably, the nanocrystal solution comprises pH-neutralized cellulose nanocrystals. More preferably, the nanocrystal solution comprises the sodium form of cellulose nanocrystals.

[0304] During hydrolysis, it is proposed that the cellulose chain backbone of the cellulose nanocrystals are modified at the molecular level to provide colloidal stability to the nanocrystals. For example, sulfuric acid hydrolysis is thought to modify the cellulose chains with sulfate half ester groups. Another example of alteration occurs during extraction with hydrogen peroxide, in which the cellulose chains are thought to be modified with carboxylic groups, providing carboxylate cellulose nanocrystals. As a result of the modification of the cellulose chains with charged groups, several counter ions can be used to balance the charges. Most commonly, H+ (to give acidic-form cellulose nanocrystals) and Na+(to give neutralized (e.g. sodium form) cellulose nanocrystals. Counter ions (e.g. H+) may be exchanged in suspension, for example by using concentrated NaOH or NaCI solution to give fully or partially neutralized cellulose nanocrystals. Na+ can be exchanged in suspension similarly, for example by using concentrated HCI or H2SO4.

[0305] Preferably, the nanocrystal suspension comprises pH-neutralized cellulose nanocrystals, partially pH-neutralized cellulose nanocrystals or acidic-form cellulose nanocrystals. More preferably, the nanocrystal suspension comprises the sodium form of cellulose nanocrystals.

[0306] In the present case, the preparation of the cellulose nanocrystal suspension may include sonication of the cellulose nanocrystal suspension.

[0307] 008928681A cellulose nanocrystal is typically rod-shaped. Thus, the crystal may be elongate with a length dimension considerably greater than the width dimension.

[0308] A cellulose nanocrystal for use in the present case may have a length that is at most 200, at most 500, at most 1 ,000, or at most 1 ,500 nm.

[0309] The cellulose nanocrystal for use in the present case may have a length that is at least 50, at least 70, or at least 100 nm.

[0310] The cellulose nanocrystal for use in the present case may have a width that is at most 20, at most 30, at most 50 nm.

[0311] The cellulose nanocrystal for use in the present case may have a width that is at least 1, at least 3, at least 5, or at least 10 nm.

[0312] The aspect ratio for the cellulose nanocrystal may be at least 5, 7, 10, 15 or 20.

[0313] The aspect ratio for the cellulose nanocrystal may be at most 40, 50, 100, 150 or 200.

[0314] The cellulose nanocrystals can be provided as a suspension, e.g. in a solvent, or as a powder, such as a spray-dried or freeze-dried powder. Such powders are redispersed to provide the cellulose nanocrystal suspension used in the present invention.

[0315] Any suitable solvent may be used, such as any solvent in which the cellulose nanocrystals can form a colloidally stable suspension, with or without the use of additive such as a surfactant. Suitable solvents includes: water, acetic acid, acetone, acetonitrile, benzene, 1-butanol, 2-butanol, 2-butanone, t-butyl alcohol, carbon tetrachloride, chlorobenzene, chloroform, cyclohexane, 1,2-dichloroethane, diethylene glycol, diethyl ether, diglyme (diethylene glycol, dimethyl ether), 1,2-dimethoxy-, ethane (glyme, DME), dimethyl-, formamide (DMF), dimethyl sulfoxide (DMSO), 1,4-dioxane, ethanol, ethyl acetate, ethylene glycol, glycerin, heptane, hexamethylphosphoramide, (HMPA), hexamethylphosphorous, triamide (HMPT), hexane, methanol, methyl t-butyl, ether (MTBE), methylene chloride, N-methyl-2-pyrrolidinone, (NMP), nitromethane, pentane, petroleum ether, 1-propanol, 2-propanol, pyridine, tetrahydrofuran (THF), toluene, triethyl amine, o-xylene, m-xylene, p-xylene or ionic liquids.

[0316] Preferably the solvent is water.

[0317] An increase in the concentration of the cellulose nanocrystals in the suspension may be associated with an increase in anisotropy of the suspension. Conversely, a decrease in the concentration of the cellulose nanocrystals in the solvent may be associated with a decrease in anisotropy in the suspension. For example, the cellulose nanocrystal suspension used in

[0318] 008928681the worked examples show complete anisotropy in water at around 7 wt % and above (Figure 6). Complete loss of anisotropy is seen at around 3.5 wt % and below.

[0319] Preferably, the concentration of the cellulose nanocrystals in the suspension is chosen to provide a mixture which has at least some anisotropy, for example in the form of chiral nematic structure. The present inventors have found that the use of nanocrystal mixtures, such as aqueous suspensions, where the suspension is in a liquid crystalline state with no, very low or partial anisotropy (e.g. a biphasic state) does not provide films having optimal colouration of high quality. It is proposed that such films have inhomogeneities which provide the poorer colouration properties observed.

[0320] Typically, the nanocrystal suspension comprises cellulose nanocrystals (such as neutralised cellulose nanocrystals) at a concentration of at most 12 wt%, preferably at most 11 wt%, more preferably at most 10 wt%, even more preferably at most 9 wt%, and most preferably at most 8 wt%.

[0321] Typically, the nanocrystal suspension comprises cellulose nanocrystals (such as neutralised cellulose nanocrystals) at a concentration of at least 1.5 wt%, preferably at least 2 wt%, more preferably at least 3 wt%, even more preferably at least 4 wt%, and most preferably at least 5 wt%.

[0322] The nanocrystal suspension may comprise cellulose nanocrystals in a range with upper and lower limits selected from the values given above. Typically, the nanocrystal is present in the mixture in an amount selected from 4 to 12 wt %, preferably from 4 to 8 wt%, more preferably from 6 to 8 wt%.

[0323] Preferably, for the cholesteric layer formation step the concentration of the nanocrystal suspension is 3.5 to 7 wt.%, preferably 5 to 6.5 wt.%, more preferably about 6 wt.%.

[0324] The wt % values that are chosen will depend upon the level of anisotropy that results from the use of a given cellulose nanocrystal and can be appropriately chosen.

[0325] Additionally or alternatively, the amount of nanocrystal used may be expressed in terms of the level of anisotropy within the nanocrystal suspension.

[0326] The nanocrystal may be present in a mixture where the level of anisotropy is at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or 70 %. Additionally, or alternatively, the nanocrystal may be present in a mixture where the level of anisotropy is at most 65, 70, 75, 80, 85, 90 or 95%. The nanocrystal may be present where the mixture is substantially all anisotropic (substantially 100% anisotropy).

[0327] The nanocrystal may be present in the mixture where the level of anisotropy selected from a range with the upper and lower limits selected from the values given above. For example,

[0328] 008928681nanocrystal may be present in the mixture where the level of anisotropy is selected from 25 to 100 %.

[0329] In the case where a sonication step is performed before the deposition step, the anisotropy refers to the anisotropy of the cellulose nanocrystal suspension before the sonication.

[0330] Sonication can alter the level of anisotropy in the suspension. In some cases, it may be preferable to discard the non-anisotropic portions of the suspension.

[0331] Other components may be present with the cellulose nanocrystal or added to the cellulose nanocrystal suspension to alter the self-assembly properties of the cellulose nanocrystals, and / or the physical and chemical properties of the cellulose nanocrystals, the nanocrystal suspension, and / or cholesteric film. For instance, additives, particularly polymers, functional molecules, and filler may be included, which can act as rheology modifiers, plasticizers, thickeners or reinforcing agents to provide additional functionality such as increased flexibility or strength to the cholesteric films as required. Examples of suitable additives are listed below.

[0332] Suitable acids include both organic and mineral acids, and their corresponding salt forms. Suitable organic acids include carboxylic acids their corresponding acid anhydrides, such as the non-phenolic organic acids 2,5-furandicarboxylic acid, acetic acid, adipic acid, ascorbic acid, benzoic acid, boric acid, carbonic acid, citric acid, formic acid, fumaric acid, lactic acid, itaconic acid, levulinic acid, malic acid, oxalic acid, propionic acid, succinic acid; and the phenolic organic acids benzoic acid, ferulic acid, gallic acid, gentisic acid, parahydroxybenzoic acid, paracoumaric acid, protocatechic acid, vanillic acid, salicylic acid, sinapic acid, syringic acid, phenol acid. Additionally, uric acid may also be used. Suitable mineral acids include hydrochloric acid, chloroacetic acid, hydrobromic acid, bromoacetic acid, hydrochloric acid, hydrofluoric acid, hypobromous acid, hypochlorous acid, hypoiodous acid, iodic acid, iodoacetic acid, nitric acid, perchloric acid, phosphoric acid, phosphorous acid, selenic acid, sulfurous acid, sulfuric acid, telluric acid, tribromoacetic acid, trichloroacetic acid, trifluoroacetic acid. The acid forms corresponding to the bases listed below may also be used. Mixtures of acids may also be used.

[0333] Suitable bases include amines, amides, alkaline salts such as sodium acetate, sodium amide, 3-amino-3-methylpentane, ammoniac, aniline, azetidine, bromopyridine, butyl lithium, cadaverine, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, choline, cyclohexylamine, lithium diethylamide, diethylamine, diisopropylamine, dimethylamine, 2,4-dimethylimidazole, 1,2-dimethylaminoethane, 1 ,2-dimethylpyrrolidine, ethylamine, ethanediamine, ethanolamine, sodium ethanoate, potassium ethanoate, ferrous and ferric hydroxide, examethylenediamine, hexylamine, hydrazine, sodium hydride, barium hydroxide, calcium hydroxide, iron hydroxide, lithium hydroxide, magnesium hydroxide, potassium hydroxide, sodium hydroxide, hydroxylamine, methylamine, 2-methyl-2-butanamine, 3-methyl-1-butanamine, methylglycine, 1-methylpiperidine, monoethanolamine, n-butylamine, nitrophenols, N-methylpyrrolidine, N-

[0334] 008928681methylpyridinamine, 3-pentanamine, pentylamine, piperidine, propylamine, 1,3-propanediamine, 4-pyridinamine, pyridine, pyrrolidine, sec-butylamine and tert-butylamine, and triethylamine. The alkanaline forms corresponding to the acid previously listed may also be used. Mixtures of bases may also be used.

[0335] Suitable salts include neutral salt such as sodium chloride, potassium chloride, ferrous and ferric chloride. Ionic liquids, in which the nanocrystals can be suspended, may also be used. Mixtures of salts may be used.

[0336] Suitable polymers include polyethylene glycol, polyethylene imine, polyethylene oxide, polyvinyl alcohol, quaternary polyamines, polyacrylamides, polyacrylic acid and its copolymers, polyacrylates including sodium polyacrylate, dicyandiamide resins, polyvinylpyrrolidone, sodium polystyrene sulphonate, sodium polyvinyl-sulphonate, polyamidoamines, carboxypolymethylene, polyvinyl methyl ether-maleic anhydride; polyols such as polyether polyol and polyester polyol; cellulose derivative such as cellulose nanofibers, microfibrillated cellulose, calcium carboxymethyl cellulose, carboxymethyl cellulose acetate butyrate, carboxymethyl hydroxyethylcellulose, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose gum, cellulose acetate propionate, cellulose acetate propionate carboxylate, cellulose succinate, cetyl hydroxyethylcellulose, ethylcellulose, hydrolyzed cellulose gum, hydroxybutyl methylcellulose, hydroxyethylcellulose, hydroxyethyl ethylcellulose, hydroxypropylcellulose, hydroxypropyl methylcellulose, hydroxypropylmethylcellulose acetate / succinate, hydroxypropyl methylcellulose phthalate, methylcellulose, methyl ethylcellulose, methyl hydroxyethylcellulose, microcrystalline cellulose, potassium cellulose succinate, sodium cellulose sulfate, nitrocellulose, cellulose acetate, rayon, regenerated cellulose, cellulose acetate-propionate, cellulose acetatebutyrate, cellulose triacetate, viscose; other polysaccharides, glucose and polysaccharide derivatives such as arabinoxylans, carrageenan, chitin, chitosan, fucoidan, galactogen, galactomannan, glucans, glycans, glycogen, inulin, lignin, mannan, pectins, starch and xylans. In addition to the polysaccharides listed above, sulfated and oxidized polysaccharides may also be used. In addition to the cellulose derivatives listed above, hemicelluloses may also be used. Mixtures of polymers may be used.

[0337] Suitable functional molecules include monosaccharides such as arabinose, deoxyribose, erythrose, fructose, galactose, glucose, and sorbose; sugar alcohol and polyols such as arabitol, cyclitols such as pinitol, ethylene glycol, erythritol, galactitol, glycerol, isomalt, lactitol, maltitol, mannitol, pentaerythritol sorbitol and xylitol; proteins such as collaged, gelatin and sericin; and aminoacids. Small molecules also include dyestuff such as acid dyes, basic dyes, direct dyes, sulphur dyes, vat dyes, reactive dyes and azoic colorants. Additionally, the dye stuff may be a black dye, or may result in a black appearance. Mixtures of functional molecules may be used.

[0338] Suitable fillers include water-soluble inorganic material and nano-objects such as clays, including hectorite, kaolin, mica, montmorrilonite, laponite, cloisite; carbon materials, such as

[0339] 008928681carbon nanotubes, graphite, graphene, carbon black; and water-soluble proteins such as albumins, whey, plant-derived proteins and zein. Mixtures of functional fillers may be used.

[0340] Additionally, typical fillers include water-soluble inorganic material, micro-materials and nanoobjects such as clays, including hectorite, kaolin, mica, minerals, oxides, montmorrilonite, laponite, cloisite; carbon materials, such as carbon nanotubes, graphite, graphene, carbon black; and water-soluble proteins such as albumins, whey, plant-derived proteins, and zein. In addition, typical fillers include organic and inorganic pigments such as aluminum, copper, cobalt, gold, iron, manganese, cadmium, chromium, arsenic, bismuth, chromium, lead, titanium, barium, tin, zinc, cerium, mercury, carbonaceous, antimony based pigments; fluorescent pigments.

[0341] Further modifications to the cellulose nanocrystals, and to the compounds used in the preparation of the cellulose nanocrystals, are described in the art. Such modification is typically made with a view to maintaining the ability of the cellulose nanocrystal to form a chiral nematic phase.

[0342] The cholesteric layer formation includes an ageing step. During the ageing step, the nanocrystal suspension partially or completely recovers any cholesteric structures lost during deposition and spreading.

[0343] In this way, the optical properties of the resulting layer can be optimised. Without wishing to be bound by theory, it is proposed that high shear during spreading can disrupt pre-existing chiral nematic ordering and result in poorer optical properties. If any disruption of any anisotropy in the nanocrystal suspension resulting from excessive shear rate occurs, any pre-existing chiral nematic ordering can be recovered, partially or fully, by lengthening the ageing time, as the dissipation of the alignment is a thermodynamically favoured process. In addition, nanocrystal suspensions having a lower viscosity permit a return to equilibrium with a short relaxation time. As such, nanocrystal suspension having a relaxation time of 30 minutes or less are preferred.

[0344] Typically, the deposited nanocrystal suspension is aged for 360 minutes or less. Preferably, the nanocrystal suspension is aged for 120 minutes or less, more preferably 60 minutes or less, even more preferably 45 minutes or less, and most preferably 30 minutes or less.

[0345] Typically, the deposited nanocrystal suspension is aged for 1 minute or more, 5 minutes or more. Preferably, the nanocrystal suspension is aged for 10 minutes or more, more preferably 15 minutes or more, and even more preferably 20 minutes or more.

[0346] The time for the ageing step may be selected from a range with upper and lower limits selected from the values given above. For example, the deposited nanocrystal suspension may be aged for from 5 to 120 minutes, preferably 5 to 30 minutes.

[0347] 008928681The ageing step may be carried out as a pause before any further processing steps.

[0348] Alternatively, the ageing step may be carried out simultaneously with the drying step, for example, by extending the drying time.

[0349] During the ageing step, the partial or total recovery of the chiral nematic ordering in the applied nanocrystal suspension can be facilitated throughout the deposited nanocrystal suspension or locally, by an external electromagnetic field.

[0350] The cholesteric layer formation includes a drying step for drying the deposited nanocrystal suspension to form a cholesteric film. This may be known as the drying step.

[0351] Drying may be concurrent with the previously described ageing step.

[0352] The drying step may be carried out at room temperature without external heating.

[0353] Typically, however, the drying step is carried out at elevated temperature.

[0354] The drying step may be carried out at a temperature of 250 °C or less, 150 °C or less, 100 °C or less, preferably 80 °C or less, and even more preferably 70 °C or less.

[0355] The drying step may be carried out at a temperature of 10 °C or more, 20 °C or more, 30 °C or more, preferably 40 °C or more, and even more preferably 50 °C or more.

[0356] The temperature of the drying step may be selected from a range with the upper and lower limits selected from the values given above. For example, the temperature of the drying step may be from 10 to 70 °C such as around 60 °C.

[0357] The temperatures of the drying step may be selected based on the solvent mixture used in the nanocrystal suspension. Preferably, a temperature is used at which the solvent mixture is not boiling or near boiling.

[0358] In this way, the cholesteric layer produced may have the desirable coloration properties. It is proposed that, when the solvent mixture is boiling or near boiling the increased movement of the solvent and gas bubble formation may disturb the chiral nematic structures and create inhomogeneities in the final dry film.

[0359] The drying step may be carried out such that the dried film is formed in 720 minutes or less, 360 minutes or less, 120 minutes or less, 60 minutes or less, preferably 45 minutes or less, and even more preferably 30 minutes or less.

[0360] 008928681The drying step may be carried out such that the dried cholesteric layer is formed in 10 minutes or more, preferably 15 minutes or more, and even more preferably 20 minutes or more.

[0361] The time for the drying step may be selected from a range with the upper and lower limits selected from the values given above. For example, the drying step may be carried out such that the dried film is formed in 10 to 60 minutes such as around 30 minutes.

[0362] The combination of drying time and temperature will depend on the coating gap, coating speed and width, and thickness of the deposited suspension. For thicker deposited suspensions (i.e. larger gaps), longer drying times will be observed at the same temperature than for a thinner deposited suspension (i.e. smaller gaps).

[0363] Time constrained drying, for example short drying times with respect to the amount of cellulose nanocrystal suspension deposited, affects the colouration of the resulting film, in particular the reflectance of the film. Without wishing to be bound by theory it is proposed that time-constrained evaporation such as during heating induces less homogeneous and more disordered films. Disorder can result from chiral nematic domains that became kinetically arrested in random orientation and non-optimal compression of the domains upon drying as it has been described in the literature (see for instance Parker et al.). It is also proposed that heating results in more significant flow of solvent and compounds within the cellulose nanocrystal suspension due to, for example, temperature or concentration gradient that disturb the cellulose nanocrystal suspension. Overall, such effect means that the reflectance peak decreases and a redshift of the peak can be observed.

[0364] In some cases, the dried cholesteric layer has a thickness of at least 1.0 pm, 2.0 pm, at least 3.0 pm, at least 4.0 pm, at least 5.0 pm, at least 6.0 pm, at least 7.0 pm, at least 8.0 pm , or at least 9.0 pm.

[0365] In some cases, the dried cholesteric layer has a thickness of 50.0 pm or less, 30.0 or less, 20.0 or less, 17.0 or less, 15.0 or less, 12.0 pm or less, 10.0 pm or less.

[0366] The layer thickness may be selected from a range with the upper and lower limits selected from the values given above. For example, the film thickness may be from 1.0 to 50.0 pm, such as from 6.0 pm to 12.0 pm, such as around 9.0 pm.

[0367] The drying step may be carried out uniformly across the width of the cholesteric layer.

[0368] Alternatively, the drying conditions may be locally varied.

[0369] The drying is carried out with any suitable drying apparatus. Suitable drying apparatus includes an I R or UV radiation lamp, a hot air drier, an oven, a convection oven, a furnace, a vacuum oven and a hot plate. Combinations of drying steps using different apparatus may be used, either successively or simultaneously.

[0370] 008928681The cholesteric layer formation may further comprise the step of sonicating the nanocrystal suspension before the depositing step.

[0371] Sonication, such as tip-sonication, of the nanocrystal suspension before deposition may be used to alter, such as red shift, the final colour of the dry nanocrystal film. It is proposed that sonication acts to expand the pitch of the chiral nematic phase resulting in a redshift, although the exact mechanism for this is not clearly identified and may involve a reduction of the size of the nanocrystal, a reduction of the size of the nanocrystal bundle, and possible release of trapped ions.

[0372] The sonication energy delivered may depend on the device used, the power and amplitude delivered, and the volume of cellulose nanocrystal suspension as well as the concentration nanocrystals in the suspension. Suitable sonication devices are known in the art, and the power, amplitude and time can be appropriately adjusted.

[0373] The length of time over which sonication is performed may be altered, and longer times may be used for the sonication of larger quantities of material or particular CNC particles.

[0374] Sonication results in a colour shift of the cholesteric layer prepared from the sonicated nanocrystal suspension. Increasing the sonication energy increases the red shift in the cholesteric layer.

[0375] Sonication in the prior art is usually performed on isotropic suspension at around 2 wt% nanocrystals. In the present case, the preferred nanocrystal suspensions contain at least 4 wt% nanocrystals and have some anisotropy.

[0376] For the purpose of comparing sonication treatment between samples regardless of the quantity of material being sonicated, the sonication treatment is commonly expressed in Joules per mass (J / g), for example Joules per mass of cellulose nanocrystals in the cellulose nanocrystal suspension (J / gcNc). The sonication treatment can also be expressed in second of treatment per millilitre of cellulose nanocrystal suspension (s / mL). While both units are used, the second unit may be preferred as it can be directly calculated from the input parameters.

[0377] The sonication step may be performed for 45 s / mL or less, such as 22.5 s / mL or less, preferably 11.2 s / mL or less, or more preferably 6.7 s / mL or less.

[0378] The sonication step may be performed for at least 0.1 s / mL, at least 0.5 s / mL, at least 1 s / mL, at least 2.2 s / mL, at least 22.5 s / mL preferably at least 0.2 s / mL or more preferably of at least 1 s / mL.

[0379] 008928681The sonication step may be performed for a time per millilitre of suspension selected from a range with the upper and lower limits selected from the values given above. For example, the sonication step may be performed for from 0.1 to 45 s / mL, such as around 2.2 s / mL.

[0380] The sonication step may deliver to the nanocrystal suspension an energy of 200 kJ / g or less, 100 kJ / g or less, preferably 50 kJ / g or less, or more preferably 30 kJ / g or less.

[0381] The sonication step may deliver to the nanocrystal suspension an energy of at least 3 J / g, at least 5 kJ / g, at least 10 kJ / g, at least 100 kJ / g preferably at least 3 kJ / g or more preferably of at least 5 kJ / g.

[0382] The sonication step may deliver to the nanocrystal suspension an energy selected from a range with the upper and lower limits selected from the values given above. For example, the sonication step may deliver to the nanocrystal suspension an energy may be from 1 to 100 kJ / g, such as around 10 kJ / g.

[0383] In one embodiment, the energy delivered by the sonicating step is from 1 to 100 kJ g-1, preferably from 3 to 50 kJ g-1, more preferably from 6 to 30 kJ g-1, even more preferably from 7 to 22 kJ g-1.

[0384] The sonication step may be performed for 2,000 seconds or less, 1,000 seconds or less, 500 seconds or less, 400 seconds or less, preferably 300 seconds or less and more preferably 200 seconds or less.

[0385] The sonication step may be performed for 20 seconds or more, 30 seconds or more, preferably 40 seconds or more and more preferably 50 seconds or more.

[0386] The sonication step may be performed for a duration from a range with the upper and lower limits selected from the values given above. For example, the sonication step may be performed for from 20 to 2,000 seconds, such as around 200 seconds.

[0387] The film needs to be separated from the substrate. This involves a step of peeling the multilayered film from the substrate. The peeling step typically occurs after the drying step has occurred for the final layer. Preferably the peeling step is carried out on a dry substrate. The peeled film may be transferred to a different substrate, or can be used as a standalone film.

[0388] In this way, after peeling, the substrate can be re-used, for instance in a close loop fashion instead of being rewound, to allow for continuous printing.

[0389] In some cases, the substrate may be in the form of a moving belt such as a heat-resistant moving belt, such as made of metal. The term belt here refers to a closed loop form of the substrate.

[0390] 008928681In some cases, the edges of the multi-layered film are removed after the peeling step.

[0391] The film may be annealed. Typically, the annealing step is carried out on the multi-layered film, although it may also be carried out the multi-layer particles, as described below. In such case, the annealing step is carried out after the drying step and before the dividing step, if present.

[0392] Furthermore, the annealing step may be carried out on one or more cholesteric layers, or one or more nematic layers during formation of the multi-layered film. That is, the annealing step may be carried out on a partially constructed film between application of layers. For example, the annealing step may be carried out between cholesteric film preparation steps, or between a cholesteric film preparation step and a nematic layer preparation step.

[0393] The annealing step refers to a step of heating the multi-layered film or layers thereof. Without wishing to be bound by theory, it is proposed that annealing removes tightly-bound water molecules and promotes destabilization of the sulphate half ester groups covering the surface of the cellulose nanocrystals, therefore becoming reactive. It is proposed that the removal of water and desulfation promotes the formation of new molecular bonds between adjacent nanocrystals. As a result, water molecules are less prone to interact with the chains and to penetrate the nanostructure, preventing the swelling and disintegration of the particles in water from occurring.

[0394] The annealing step may lead to oxidation, polymerisation and crosslinking between the cellulose nanocrystals and any additional compounds or additives that remain in the film after the drying step.

[0395] The annealing is carried out with any suitable apparatus able to heat, oxidize, polymerise, crosslink the cellulose nanocrystals and any additional compounds or additives that remain in the film as well as removing tightly-bound water molecules and destabilizing the sulphate half ester groups covering the surface of the cellulose nanocrystals. Suitable drying apparatus includes an I R or UV radiation lamp, a furnace, a hot air drier, an oven, a convection oven, a vacuum oven and a hot plate. Combinations of drying steps using different apparatus may be used, either successively or simultaneously.

[0396] The temperature of the annealing step may be 250 °C or less, 230 °C or less, preferably 220 °C or less, and more preferably 190 °C or less.

[0397] The temperature of the annealing step may be 100 °C or more, 110 °C or more, preferably 140 °C or more, and more preferably 170 °C or more.

[0398] The temperature of the annealing step may be selected from a range with the upper and lower limits selected from the values given above. For example, the temperature of the annealing step may be from 100 to 250 °C, preferably from 140 to 220 °C.

[0399] 008928681The annealing step may be carried out for 120 minutes or less, 60 minutes or less preferably 40 minutes or less, and more preferably 30 minutes or less.

[0400] The annealing step may be carried out for 2 minutes or more, 5 minutes or more, 10 minutes or more, preferably 15 minutes or more, and more preferably 20 minutes or more.

[0401] The film is divided into pigment particles. This may be known as the dividing step.

[0402] In the dividing step, the dimensions of the film are reduced to provide particles that can be used as pigment.

[0403] Dividing can be performed using any suitable fracturing or chopping apparatus, such as a device using rotating blades, as well as any suitable grinding apparatus, such as a device using grinding elements and high intensity shocks (for instance a mill such as a ball mill, a crusher, a pulveriser, or a cryogrinder). A die- or laser-cutter may also be used to reduce the dimensions of the film and yield particles with a defined shape.

[0404] Preferably, a fracturing apparatus is used. In such cases, the dividing step may be referred to as a fracturing step.

[0405] Alternatively, a grinding apparatus is used. In such cases, the dividing step may be referred to as a grinding step.

[0406] In some case, a fracturing and a grinding apparatus are successively used. In such cases, fracturing provides larger particles which can be broken down into smaller particles through separate grinding for production of particles with specific sizes in specific yield.

[0407] The dividing step preferably occurs after a peeling step. In this way, the substrate is not damaged during the dividing and is not incorporated into the coloured particles, and so does not contribute to the thickness of the particles.

[0408] The pigment particles may be sorted by size to obtain particles of the desired diameter or surface area. The size sorting can be carried out during fracturing and / or grinding for example when dividing is carried out with an ultracentrifugal mill. The size sorting can be carried out after fracturing and / or grinding, for example, by sieving. Particles with larger sizes (e.g. larger median average diameter or average surface areas) have improved optical properties compared to particles with smaller sizes. That is, they have a narrower and / or taller reflection peak. Hence particles with larger sizes may appear more lustrous or metallic than matte.

[0409] Rheology

[0410] The ink composition has a rheology suitable for printing, such as screen printing.

[0411] 008928681In some embodiments the ink composition is shear thinning.

[0412] The viscosity of the ink compositions may depend on the particle size and the content of pigment in the ink composition.

[0413] In some embodiments, a higher content of the pigment will increase the viscosity. In some embodiments, a smaller particle size will typically increase the viscosity.

[0414] In some embodiments, the viscosity of the formulations with differently sized particles are relatively similar. However, the viscosity at different contents of pigment in the ink composition may be different.

[0415] In some embodiments, viscosity measured at a shear rate of 100s-1is 1.1 to 1.3 Pa.s, when the pigment is present at 5 wt.% based on the total mass of the ink composition.

[0416] In some embodiments, viscosity measured at a shear rate of 100s-1is 1.3 to 1.5 Pa.s, when the pigment is present at 10 wt.% based on the total mass of the ink composition.

[0417] In some embodiments, viscosity measured at a shear rate of 100s-1is 2.3 to 2.6 Pa.s, when the pigment is present at 20 wt.% based on the total mass of the ink composition.

[0418] The viscosity may be within the above ranges for structurally coloured pigments with a particle size of 2 to 150 pm.

[0419] In some embodiments, structurally coloured pigment content has an exponential / power relationship with the resulted viscosity. The relationship of viscosity and pigment content may be represented by Formula (I):

[0420] q = a*e(b*C)(I)

[0421] wherein

[0422] is viscoisty measured at a shear rate of 100s-1

[0423] a is a constant from 0.5 to 1.5. preferably 0.9 to 1.1

[0424] b is a constant from 0.04 to 0.05. preferably 0.044 to 0.045

[0425] C is concentration of the pigment, in wt.% based on the total mass of the ink composition.

[0426] Due to the relatively high visoscity of the structurally coloured pigment, it is preferable to have a relatively low binder viscosity to allow for higher loadings of the cellulose pigment.

[0427] The viscosity of the polymer binder and carrier liquid measured at a shear rate of 100s-1is typically from 0.1 to 10 Pa.s, preferably from 0.2 to 2 Pa.s, more preferably from 0.3 to 1.5 Pa.s, yet more preferably from 0.4 to 1 m Pa.s.

[0428] 008928681The viscosity of the ink composition may be measured using any suitable means. The viscosity of the ink composition may be measured by under ambient conditions, such as a temperature of 20 °C and a pressure of 1 atm. The viscosity of the ink composition refers to the viscosity of the ink prior to application or curing. Typically, as the ink is cured (e.g., due to polymerisation of the binder and / or removal of the carrier liquid) the viscosity of the ink increases).

[0429] Additives

[0430] The ink composition may comprise additives, present in addition to the pigment, polymer binder and carrier liquid.

[0431] Any suitable ink additives may be used. Suitable additives may include a rheology modifier, a plasticizer, a crosslinker, a surfactant, a dispersing agent, a preservative, a conductivity agent, a wetting agent, an adhesion promoter, a biocide or a combination thereof. Suitable additives may include a rheology modifier, a plasticizer, a crosslinker, a surfactant, a dispersing agent or a combination thereof.

[0432] The ink composition may be free from additional colourants, such as additional dyes or pigments. That is, the ink composition may only include the structurally coloured pigment as the colourant. In particular, the ink composition is free from non-bio-based and / or non-biodegradable dye or pigments.

[0433] Additionally, the structurally coloured pigment may be free from additional colourants, such as additional dyes or pigments. That is, the structurally coloured pigment may rely exclusively on structural colour and not on additional dyes or pigments.

[0434] Alternatively, the ink composition may include additional colourants, such as additional dyes or pigments. The ink composition may include the structurally coloured pigment and an additional dye and / or pigment. The additional dye and / or pigment is preferably bio-based and / or biodegradable. The structurally coloured pigment may include additional colourants, such as additional dyes or pigments.

[0435] Printing Methods and Use

[0436] In a second aspect of the invention there is provided a use of the ink composition of the first aspect for screen printing, spray coating, dip coating or transfer printing. Preferably the use is for screen printing or transfer printing.

[0437] In an aspect of the invention there is provided a use of the ink composition of the first aspect for screen printing, spray coating or dip coating. Preferably the use is for screen printing.

[0438] 008928681The inks of the invention may be used for changing the appearance of a substrate. For example, the inks of the invention may be used for changing the colour of a substrate. The inks of the invention may be used for applying colour to a substrate.

[0439] In a third aspect of the invention there is provided a method of printing an ink composition onto a substrate, wherein the ink composition is the ink composition of the first aspect, the method comprising:

[0440] applying the ink composition onto a substrate;

[0441] drying the ink composition to remove at least a portion of the liquid carrier, to provide an ink deposit.

[0442] The ink composition may be applied to a substrate using any suitable means. The ink composition may be deposited onto a substrate using any suitable means.

[0443] Figure 17 illustrates a selection of application methods that have been successful in applying the ink compositions onto substrates.

[0444] The ink composition may be applied using screen printing, spray coating, dip coating, flocking or transfer printing. The ink composition may be applied using screen printing, spray coating, dip coating or flocking. Preferably, the ink composition is applied using screen printing or spray coating. More preferably, the ink composition is applied by screen printing.

[0445] Screen printing is achieved using a squeegee to push the formulation containing pigments through the patterned mesh. Screen printing is studied preferred as it provides versatility in mesh size, patterning, multiple passes, etc, and it is also relevant at lab scale and industrial scale.

[0446] Spray coating uses pressurised gas to push and atomise the formulation through the nozzle. Notably, the chosen pigment sizes need to be compatible with mesh and nozzle size. Large particle size in relation to the mesh and nozzle size may end up clogging the tool. The shear thinning properties of the formulation is critical to allow liquid through the small mesh and nozzle.

[0447] Dip coating starts by immersing the fabric in a bath of formulation and followed by removing the excessive paint. At the lab scale, the shear is relatively low making the application process challenging, while the industrial process will induce higher shear as the fabric is fed through the tank and drained under high speed and tension.

[0448] The flocking method applies the base binder / adhesives and powder in separate steps. It starts by applying a layer of adhesives on the fabric, then pigments are sprinkled on the surfaces, finally the pigments are covered by a topcoat.

[0449] 008928681Additionally, transfer printing typically involves applying ink onto a temporary substrate and then transferring the ink on the temporary substrate to a final substrate via direct contact of the ink with the final substrate. Additional adhesive may be applied to the temporary substrate or the final substrate, to improve adhesion between the ink and the final substrate. Heat and / or pressure may be applied to the temporary substrate, to improve the transfer and / or adhesion of the ink to the final substrate. The temporary substrate may be heat-pressed onto the final substrate.

[0450] Transfer printing is particular suitable for printing onto fabrics, such as stretch fabrics.

[0451] All the application methods result in the structurally coloured pigment being partially or fully (preferably fully) embedded in a polymer binder matrix. This provides good index matching and structural integrity.

[0452] In some embodiments, the printing process further comprises shearing the ink composition. Shearing the ink composition may be achieved by spreading the ink composition. The shearing is an active shearing step, that is the ink is actively spread by applying an external mechanical force. This differs from passive shearing, where the suspension is allowed to spread passively (e.g., under gravity). During passive spreading the suspension does not typically experience the same intensity of shearing or deformation.

[0453] In some embodiments, shearing the ink composition includes an alignment of the orientation of the structurally coloured pigment. In this way, the ink deposit has pigments which have their orientation aligned. Alignment typically refers to the external structure of the pigment. A pigment may be considered aligned when the direction defining its length (i.e. , the longest dimension of the pigment particle) is substantially in the same direction as other particles. The pigment may have its external structure aligned (e.g., the direction defining the length aligned), but have its internal structure non-aligned (e.g., the director of the chiral nematic structure non-aligned). The internal structure of different particles is typically randomly orientated.

[0454] The structurally coloured pigments may be aligned in substantially the same direction.

[0455] Two particles may be considered aligned where the longest dimension of the pigment particles are within 30° or parallel, such as within 20° of parallel, such as within 10° of parallel.

[0456] In some embodiments, 50 wt.% of the pigments are aligned, such as 70 wt.% aligned, such as 90 wt.% aligned. In some embodiments, 50 wt.% of the pigments have the longest dimension of the pigment particles within 30° of parallel, such as within 20° of parallel, such as within 10° of parallel. In some embodiments, 70 wt.% of the pigments have the longest dimension of the pigment particle within 30° of parallel, such as within 20° of parallel, such as within 10° of parallel. In some embodiments, 90 wt.% of the pigments have the longest

[0457] 008928681dimension of the pigment particles within 30° of parallel, such as within 20° of parallel, such as within 10° of parallel.

[0458] In some embodiments, the structurally coloured pigments lay substantially flat. That is, a facet of the structurally coloured pigments are aligned parallel to the substrate. The facet may be the main facet of the pigment, such as the largest (by area) facet of the pigment. A particle may be considered flat where the line normal to the facet is parallel to a line normal to the substrate surface.

[0459] In some embodiments, the substrate is bio-based. In particular, where the substrate is a fabric, the fabric may be bio-based. The substrate, such as the fabric, may have a modern carbon content of 70 wt.% or more, such as 80 wt.% or more, such as 90 wt.% or more.

[0460] In some embodiments the ink composition is applied onto a base layer. The base layer may be formed from a traditional ink composition or an ink composition of the invention.

[0461] The base layer is preferably formed from an ink deposit formed from an ink composition of the invention. In this way, the ink composition may layer colours on top of each other to provide complex colours.

[0462] In some embodiments the ink composition is applied onto a non-coloured base layer. The base layer may be a layer of polymer binder without any colourant. The polymer binder may be the same as the binder of the ink composition.

[0463] In some embodiments a top layer is applied over the ink deposit. The top layer may be noncoloured. The top layer may be a layer of polymer binder without any colourant. The top layer may be the same as the binder of the ink composition. The top layer may serve to protect the ink deposit, and improve the durability of the ink deposit. In addition, the top layer may serve to fully encapsulate any partially encapsulated pigment particles, thereby changing the optical properties of the ink deposit.

[0464] Ink Deposits and Article

[0465] The printing method described above may be used to form an ink deposit.

[0466] In a fourth aspect of the invention there is provided an ink deposit obtained or obtainable by the method of the third aspect.

[0467] In a fifth aspect of the invention there is provided an ink deposit, wherein the ink deposit is deposited on a substrate, the ink deposit comprising:

[0468] a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures; and

[0469] a polymer binder, wherein the polymer binder encapsulates the structurally coloured pigment.

[0470] 008928681The polymer binder may fully or partially encapsulate the structurally coloured pigment.

[0471] The ink deposit may be used as decorative or functional features on textiles, clothes, interior fabrics, outdoor fabrics, bobbins, and packaging materials.

[0472] The ink deposit may be recyclable, biodegradable or compostable. By providing an ink deposit of invention, including a cellulose based pigment, the ink deposit can be recycled, biodegraded or composted. In particular, where a bio-based binder is used with the structurally coloured cellulose pigment, the ink deposit may contain only bio-based elements and be fully recyclable, biodegradable or compostable.

[0473] The ink deposit is typically provided on a substrate. Together the deposit and the substrate form a printed article. The ink deposit may be provided on a base layer as described above. The ink deposit may be provided with a top layer as described above.

[0474] In a sixth aspect of the invention there is provided a printed article, the article comprising an ink deposit of the fourth or fifth aspects deposited on the substrate.

[0475] The substrate may be a fabric, leather, vegan leather, a yarn, paper or cardboard The substrate may be a synthetic fabric. The substrate may be a stretch fabric, such as 2-way or 4-way stretch fabric.

[0476] The article may be a garment, handbag or luggage. The garment may be sportswear. The article may be a packing element or packaging material.

[0477] The article is preferably recyclable, biodegradable or compostable. By providing an ink composition of the invention, including a cellulose based pigment, the ink does not hinder the recyclability, biodegradability or compostability of the article. In particular, where a bio-based binder is used with the structurally coloured cellulose pigment, the article may contain only bio-based elements and be fully recyclable, biodegradable or compostable. The printed deposit may be easier to recycle and decolorise than a traditional bath-dyed substrate or printed substrate with traditional pigments or dyes.

[0478] The ink deposit may be deposited on the substrate uniformly. The ink deposit may be deposited on the substrate continuously. The ink deposit may be deposited on the substrate non-continuously, such as in a pattern. The pattern may follow a design or motif. The pattern may be achieved using any suitable means, such as masking areas of the article or using standard screen-printing techniques.

[0479] 008928681Other Preferences

[0480] Each and every compatible combination of the embodiments described above is explicitly disclosed herein, as if each and every combination was individually and explicitly recited.

[0481] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0482] “and / or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, “A and / or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0483] Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

[0484] Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described above.

[0485] Examples

[0486] The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

[0487] Preparation of Structurally Coloured Pigments

[0488] A selection of base cellulose nanocrystal pigments were prepared according to the methods described in WO 2023 / 025863.

[0489] An aqueous CNC suspension was diluted with ultrapure water to 6 wt % in an ice bath and sonicated using an ultrasonic disintegrator. The tip sonication was applied at different intensities (7.5, 14.5 and 21.5 kJ / g). After equilibrating the suspension for 1-3 days at ambient temperature, the denser anisotropic phase was separated and collected for further use. The colour of the dried CNC film could be red-shifted by increasing the duration of the tip sonication process, allowing for red, green and blue films to be produced from tip sonication at 21.5, 14.5 and 7.5 kJ / g.

[0490] Roll-to-roll coating was used to achieve continuous deposition of the CNC suspension and demonstrate the scalability of the process. Roll-to-roll printing was achieved using a modified roll-to-roll coating system (Coatema Coating Machinery, Smartcoater 28) equipped with a custom-made slot-die (coating width = 10 cm, internal reservoir 22 mL). The slot die was made of two screw-joined aluminium plates separated by a 125 pm-thick spacer shim

[0491] 008928681- M -

[0492] configured for a 100 mm slot clearance positioned perpendicular to the web. A syringe pump (New Era) was used to continuously dispense the CNC suspension to the slot-die, with the dispensing rate (ca. 6000 pL / min) adjusted depending on the desired film thickness and coverage width. The distance between the slot lips and the substrate was controlled with a thickness feeler gauge. Web-holders were placed so that the average distance between each holder was reduced to 30 cm. The substrate was levelled before coating using a bullseye spirit level (Thorlabs LVL01) at several positions along the web path and at the middle of the width. The web was translated through the roll-to-roll system at the lowest accessible speed (speed = 0.1 mm.s-1= 1.7 mm.s’1). Shear rates were calculated from the translational speed of the web and the coating-gap thickness.

[0493] The CNC suspension was allowed to dry at ambient conditions without motion until completion of the film formation (for a few hours and typically less than a day which duration depends on the amount of material deposited, length and thickness of covered areas).

[0494] The R2R CNC film was detached from the substrate placing a thin plastic blade attached to the upper collection web at an angle between the substrate and the CNC film, manually peeled over few centimetres beforehand and by moving the web at a constant speed.

[0495] The CNC film was chopped using a coffee grinder. The CNC pigment particles were size sorted sequentially using sieves with decreasing mesh sizes.

[0496] The median size of the particles for each size category was retrieved from SEM images by highlighting the contours of individual particles and fitted with the Ferret area function in imaged.

[0497] Images of the resulting pigments are shown in Figure 1. The top row shows macroscopic image of pigments on a bright background. The middle row macroscopic images of pigments embedded in UV resin on a black background. The bottom row shows microscopic images of pigments at 200x magnification on a glass slide.

[0498] The colours of the pigments are produced by light interference with the internal chiral nematic structure, obtained through the self-assembly process during the drying of the cellulose nanocrystal suspension. The pigments have a white appearance on their own. This is thought to be caused by optical scattering from the small particle sizes and rough edges. When the pigments are dispersed in a matrix, such as UV resin having a similar refractive index to the cellulose pigments (e.g., n = ~1.6), the scattering is reduced by index matching and thus increases the colour contrasts of the pigments.

[0499] Polymer Binder Testing

[0500] A range of different binders were tested to evaluate their performance with cellulose structurally coloured pigments.

[0501] 008928681Preparation of Ink Compositions

[0502] Ink compositions were prepared using the cellulose structurally coloured pigments. A series of formulations were prepared to explore the impact of binder type on formulation properties and final print quality.

[0503] For easier comparison, all of the inks were prepared using a blue pigment. As the colour of the pigment is obtained by adjusting the internal hierarchical structure instead of altering the chemical composition of the pigment, it is believed that the pigment colour does not impact on the properties and quality of the ink formulation and printed. For this reason, blue is chosen as a representative colour for pigments.

[0504] The inks were formulated by mixing the blue cellulose structural coloured pigments with a particle diameter of 75-106pm with six different binder composition.

[0505] The components of the ink were mixed until the ink appeared uniform. A spatula was used to initially mix the components, and a vortex mixer was then used to disperse the pigments in the liquid.

[0506] The details of the binders are provided in Table 1.

[0507] The moisture content of the different binders were evaluated. The mass of the binders was measured. The binders were heated to 120 °C to evaporate the carrier solvent from the binder. The mass of the binders after evaporation was measured, and the difference in the mass compared to the original mass was recorded. The solvent content was calculated as the difference in mass before and after evaporation. The solid content of the binder was calculated as the mass remaining after evaporation. The results are shown in Table 1.

[0508] Table 1 - Formulation of Inks 1-6

[0509]

[0510] 008928681

[0511]

[0512] Bondoglit DP2720 includes a polyurethane polymer binder and a diethylene glycol carrier liquid.

[0513] Tubiscreen GD200 includes a polyurethane polymer binder.

[0514] Selectasine SF20 solvent free includes an acrylic binder and water as the carrier liquid.

[0515] Printing and Optical Performance

[0516] The optical performance of the inks was evaluated by printing the inks onto a substrate. Inks 1 to 6 were screen printed using a 15T mesh onto a black lyocell substrate to form an ink deposit.

[0517] Images of the resulting ink deposit are provided in Figure 2. Figure 2(a) is Ink 6; Figure 2(b) is Ink 4; Figure 2(c) is Ink 5; Figure 2(d) is Ink 3; Figure 2(e) is Ink 1 ; and Figure 2(f) is Ink 2.

[0518] The images illustrate the different optical performance and appearance achieved by printing the cellulose structurally coloured pigments using binders having different polymer binder concentrations and different liquid carrier concentrations.

[0519] Ink 1-3 produce prints that have a very strong blue appearance. Ink 4-6 produce prints that have a whiter appearance on top of the blue hue.

[0520] Without wishing to be bound by theory, it is thought that the white appearance arises from the scattering of the light due to the small particles sizes and the surface roughness arising from the milling process, as observed in Figure 2. The broadband, white scattered light thus reduces the contrast of the pigments, which reflects more narrowly in the specific wavelength range (blue in this example).

[0521] To inhibit the scattering for better colour contrast, it is thought that dried polymer binders need to have sufficient thickness to encapsulate or envelop the pigments. It is thought that one factor in changing the final dried binder thickness is the dry mass content of the binder, which is indicative of the polymer binder content of the binder. Inks 4-6 have a relatively low solid content (<20%), which contributes to a low binder thickness and only partial encapsulation of the pigment. In contrast, Inks 1-3 have a relatively high solid content (>30%), which contributes to a high binder thickness and full encapsulation of the pigment. This in turn leads to a stronger blue colour in the ink deposit.

[0522] Another factor which may be relevant for the visual appearance of the ink deposit is the refractive index of the cured biner. The structurally coloured cellulose pigments have a

[0523] 008928681refractive index of around 1.55. For efficient index matching, it is thought to be desirable to have a similar refractive index for the binder and pigment. Certain polymer binders, such as polyurethane (n=1.67), poly vinyl acetate (n=1.47) and acrylics (1.49) all have a similar refractive index to the cellulose pigment. It is thought that this improves the index matching when the pigment is embedded in the cured binder, and results in a stronger colour contrast. Rheology

[0524] Ink rheology is an important consideration for different printing applications. For example, the ink viscosity may play an important role in how the ink spreads and the wet thickness formed during screen printing. A higher viscosity allows for a greater wet thickness, and thus a greater dry thickness of the ink deposit, even with the same solid content. A thicker ink deposit may have greater colour intensity.

[0525] The rheology properties of Inks 1, 2 and 5 were tested. The inks were re-formulated with pigments which had undergone different amounts of heat treatment. Pigments were prepared as described above, with some pigments having no heat treatment, some having 2 hours of heat treatment and some having 8 hours of heat treatment. The viscosity was measured at a variety of different shear rates. The results are shown in Figure 3.

[0526] The rheology properties were measured using a rotation rheometer (TA Instruments DHR-2) using a 20mm parallel steel plate, at shear rates from 1 to 1000 s-1(flow sweep), using a 1000 pm geometry gap, 50 pm trim gap offset and at a temperature of 25 °C.

[0527] Figure 3 shows a graph of the variation of viscosity with shear rate for pigments with 0, 2 and 8 hours heat-treatment in 3 different binders: (a) Ink 5 (CSFXC Glitter Printing Binder), (b) Ink 1 (Bondoglit DP2720) (c) Ink 2 (Tubiscreen GD200). Figure 3(d) compares results for Inks 1, 2 and 5.

[0528] As the cellulose pigments are highly hygroscopic and the carrier liquid present in the ink is water, it was observed that pigments which had not undergone some heat treatment (annealing) would tend to absorb water and consequently increase the viscosity of the ink formulation. It can be seen that it is possible to increase pigment stability by employing postprocessing steps to the pigments, such as long duration heat treatment. The resulted pigments showed a much lower viscosity increment with increasing degree of treatment and water stability. It can be seen that the viscosity of inks where the particles have undergone less heat treatment have a greater viscosity across all shear rates.

[0529] The effect of the cellulose structurally coloured pigment on viscosity was also investigated. Inks 1-6 had their viscosity measured at various shear rates. Inks 1-6 were then prepared with no pigment, to provide a comparative set of compositions including the same polymer binder and liquid carrier as Inks 1-6, but without any pigment present. These comparative compositions had their viscosity measured at various shear rates. The results are shown in Figure 4.

[0530] 008928681Figure 4 shows that the rheology behaviour for each of the polymer binder and carrier liquid combinations for 0% pigment and 10% pigment. It can be seen that the inks have very similar rheology behaviours to the binder without pigment. It was observed that Ink 3 has a higher viscosity than the other inks. It is thought that the higher viscosity is due to the higher binder content of the ink.

[0531] Pigment Size and Concentration Testing

[0532] Further tests were carried out to test the effect of pigment particle size and pigment loading. Preparation of Ink Compositions

[0533] Ink compositions were prepared using the cellulose structurally coloured pigments. As explained above, for easier comparison, all of the inks were prepared using a blue pigment. Inks were prepared with Extra Small (XS - 2-20pm), Small (S - 20-45pm), Medium (M - 45-75pm), Large (L - 75-106pm) or Extra Large (XL - 106-150pm) particle sizes of pigment, and with different amounts of pigment, at 1 wt.%, 5 wt.%, 10 wt.% and 20 wt.%. All the inks were prepared with the Tubiscreen GD 200 binder used for Ink 2 (above).

[0534] The inks were prepared as described above. The different ink compositions are shown in Table 2 below.

[0535] Table 2 - Formulation of Inks 7-10

[0536]

[0537] 008928681

[0538]

[0539] Rheology

[0540] Further rheology testing was carried out to test the effect of pigment particle size and pigment loading on viscosity. The viscosity of Inks 8, 9 and 10 were measured in the S, M and L guises. The results are shown in Figure 5.

[0541] The rheology properties were measured using a rotation rheometer (TA Instruments DHR-2) using a 20mm parallel steel plate, at shear rates from 1 to 1000 s-1(flow sweep), using a 1000 pm geometry gap, 50 pm trim gap offset and at a temperature of 25 °C.

[0542] Figure 5(a) shows the dependence of pigments size and concentration on the viscosity. For concentrations range from 5% - 10% (Inks 8 and 9) the viscosity dependency on particle size is not apparent. However, at higher concentrations of 20% (Ink 10), there is a sudden increase in viscosity when larger particle sizes (75-106 pm) are used. This is surprising, as decreasing particle size is usually associated with higher viscosity.

[0543] Nonetheless, matching polymer binder concentration, pigment loading and pigment particle size allows the viscosity to be controlled, to allow for excellent printing properties.

[0544] Printing and Optical Performance

[0545] Inks 7, 8, 9 and 10 in S, M, L and XL guises were screen printed onto a lyocell substrate using a 15T mesh. The prints were dried to provide an ink deposit.

[0546] Images of the ink deposits were taken, and these are shown in Figure 6.

[0547] Figure 6 demonstrates the effect of pigment loading and particle size on the visual appearance of the ink deposits. Increasing weight percentage leads to better coverage and brighter prints. The smaller pigments can achieve 100% coverage at lower weight loading than the bigger pigments. This is thought to be related to the geometry and aspect ratio of the pigments. Smaller particles are expected to be thinner from the milling and sieving process, making them more efficient in covering the entire area at the same weight loading. Printing with larger particles, however, can produce brighter prints due to reduced scattering (bigger sizes and less rough edges) and higher reflectance from individual particles due to increased thickness and thus a more substantial internal chiral nematic structure present in each particle. In contrast, prints using smaller pigments produce a more matte overall appearance, due to the stronger scattering and less reflecting individual pigments.

[0548] Inks 7-10 demonstrate the differences in appearance which can be achieved using inks composition of the invention by varying pigment particle size and concentration.

[0549] 008928681Printing Conditions

[0550] The effect of different printing techniques and conditions were investigated.

[0551] Inks 9XS, 9S, 9M, 9L and 9XL were printed using a variety of screen printing mesh sizes. Inks 9XL and 9L were printed with a 15T size only, Ink 9M was printed with a 15T and 32T mesh size, Ink 9S was printed with a 15T, 32T and 43T mesh size, and Ink 9XS was printed with a 15T, 32T, 43T and 80T mesh size. The different sizes of mesh are dictated by the pigment size - as the pigment size needs to be smaller than the opening in the mesh. The prints were dried to form an ink deposit. Images of the ink deposits were taken and are shown in Figure 7.

[0552] Figure 7 shows the difference in final print appearance when using different mesh sizes during the screen printing. A decreasing mesh size can turn the print appearance from more brightly coloured to a more matte appearance. This is thought to be attributable to the reduced wet thickness being applied during the screen-printing process, and hence less dried thickness of the ink deposit. In addition, it was observed that the best print quality was achieved when the screen print mesh was at least three times greater than the pigment particle diameter.

[0553] The effect of different substrates was also tested. Ink 9XL was printed directly onto a cotton substrate, and dried to provide an ink deposit. The cotton substrate was a knit cotton jersey. The printing was achieved by screen printing through a 15T mesh.

[0554] On a second cotton substrate, a base layer of binder and carrier liquid (with 0 wt.% pigment) was printed onto a cotton substrate and dried to provide a base layer. Subsequently, Ink 9XL was printed onto the dried base layer, and dried to provide an ink deposit.

[0555] Images of the two ink deposits were taken and are shown in Figure 8.

[0556] Figure 8 demonstrates that the ink compositions of the invention can be effectively printed onto porous substrates, such as cotton.

[0557] This also shows the benefits of applying a base layer before printing with the ink compositions when a porous fabric substrate is used. With the porous fabric, such as knitted cotton, large portion of the binders are infused into the fabric, producing a thinner final dry coat above the fabric. This can lead to lower coverage of the binder on the pigments and thus produces more highly scattered, white appearance of the prints. Additionally, some pigments will also be hidden within the fabric matrix instead of staying on the surface. With an extra initial base layer, the binder formulation with pigments tend to stay on top of the base coat, allowing better binder coverage of the pigments and hence greater index matching, producing brighter prints.

[0558] 008928681Coloured Pigment Testing

[0559] Further testing was carried out on a range of differently coloured inks. The ink composition was based on Ink 9L, but with different coloured pigments. Inks including red (ink 9LR), orange (Ink 9LO), green (Ink 9LG), turquoise (Ink 9LT) and blue (Ink 9L) structurally coloured cellulose pigments were prepared with the Tubiscreen GD200 binder. The inks included 10 wt.% of pigments having a pigment particle size of 75-106pm.

[0560] The inks were screen printed onto a black woven lyocell substrate using a 15T mesh. The prints were dried to form an ink deposit. Images of the ink deposits were taken and are shown in Figure 9.

[0561] Figure 9 shows how a selection of colours can be produced using a similar ink composition and different cellulose based pigments. As the pigments’ structural colours arise from constructive interference of the light in the internal structure of the pigment, instead of absorption mechanisms used by traditional pigments. The internal structure can be adjusted without altering the chemistry of the system, allowing the pigments to display full range of colours from UV, visible (red to blue) to IR using the single biopolymer. This allows for effective printing of a range of colours using a single ink formulation. No adjustment to the formulation for pigment compatibility or viscosity are required when printing different colours, unlike traditional pigments and dyes.

[0562] Complex coloured inks were also prepared, by including multiple different colours of pigments in a single ink composition. These were compared to single colour inks. Inks were prepared including, red pigments, green pigments, blue pigments, red and green pigments; green and blue pigments; and blue and red pigments. The inks were prepared using a Tubiscreen GD200 binder. The inks included 10 wt.% of pigments having a pigment particle size of 45-75pm. The inks were based on Ink 9M, but with a mixture of pigments.

[0563] The inks were screen printed onto a black woven lyocell substrate using a 15T mesh. The prints were dried to form an ink deposit. Images of the ink deposits were taken and are shown in Figure 10.

[0564] Figure 10 shows the expected behaviour when mixing cellulose structurally coloured pigments with two distinct colours in one formulation. For example, when mixing red and blue pigments together, the red and blue light is reflected by the red and blue pigments respectively, while the green light will passthrough and reach the black substrate and be absorbed. If the pigments are small and viewed from distance, the pigments will not be individually resolved, giving rise to a purple / magenta appearance. This allows for a wider gamut of colours to be prepared using a single ink composition.

[0565] The effect of different coloured backgrounds was also investigated.

[0566] 008928681The green, red and blue inks (prepared as discussed above) were printed onto red, green, blue and black substrates. The inks were dried to form an ink deposit. Images of the resulting ink deposits are shown in Figure 11.

[0567] It can be seen that printing on a substrate with the same colour as the pigments tends to provide a solid colour while the cellulose pigments contribute to the shine and metallic effect to the print. Printing on a substrate which a different colour to the pigment results in scattered light from the substrate which mixes with the reflected light from the pigments, giving rise to complex colours. The substrate colour is produced by scattering while the cellulose pigments produce colour by reflection. Where only strong direct light exists without diffused illumination, the substrate colour will be visible at any viewing angles while the cellulose pigment colour is visible only at specular angle, which produces a “on / off” visual effects of the colour.

[0568] Figure 12 illustrates how the viewed colour of the sample may change depending on the colour of the base layer underneath structurally coloured pigment in an ink deposit. The selective wavelength of light will be reflected by the cellulose pigments while the rest of the wavelength range will arrive at the substrate. The wavelength range of light that matches the colour of the substrate will be scattered back, while others will be absorbed. The scattered light and reflected light give rise to the final overall appearance of the print.

[0569] Different Substrate Testing

[0570] Ink 9L was printed onto a range of different deposits, using screen printing with a 15T mesh. The substrates included: (a) plain weave lyocell, (b) plain weave cotton, (c) cotton twill, (d) cotton indigo dyed denim, (e) knit cotton jersey, (f) knit diagonal cotton fleece, (g) recycled polyester satin, (h) recyceled polyester twill, (i) leather and (j) paper.

[0571] Images of the ink deposits were obtained, and the images are shown in Figure 13.

[0572] Figure 13 demonstrates the versatility of the ink compositions of the invention to apply to a number of substrates. This includes common fabrics and other substrates. These structures vary in structure (e.g. woven vs knitted), vary in origin and composition (e.g., synthetic and natural materials, such as polyester, cotton, lyocell, leather), vary in porosity and texture (e.g., fabric, leather, paper). This example shows that these different substrates all compatible with the ink formulations of the invention.

[0573] Different visual effects on different substrates may be attributed to the surface structure of the substrate, absorption and refractive indices.

[0574] Patterned designs were also tested. Ink 10XL was screen printed onto a black lyocell with a circle design. The print was dried to provide an ink deposit. Images were obtained of the ink deposit and are shown in Figure 14.

[0575] 008928681Figure 14 illustrates how complex designs with sharp edges can be achieved using inks of the invention. The resulting ink deposits are high resolution and have sharp contrast and appearance.

[0576] Durability and Colour Fastness

[0577] Inks 1, 2 and 5 were prepared as described above. The inks were re-formulated with pigments which had undergone different amounts of heat treatment. Pigments were prepared as described above, with some pigments having no heat treatment, some having 2 hours of heat treatment and some having 8 hours of heat treatment.

[0578] The inks were screen printed onto a black woven lyocell substrate, using a 15T mesh. The inks were cured at a temperature of 120 °C for 5 minutes and 150 °C for 10 minutes.

[0579] The durability of the ink deposits was tested by wet crocking. Wash and abrasion fastness of prints with different formulations were tested using 100 cycles of wet crocking (10x more than the ISO standard for wet crocking). The images of the ink deposits before and after wet crocking are shown in Figure 15.

[0580] Ink 2 appears to show the best durability to wet crocking, with little difference in appearance before / after crocking. It is thought that this is due to stronger adhesion of the binder of Ink 2 to the fabric, better compatibility of binder to the pigments and stronger mechanical properties of the binder due to crosslinking density and binder material performance.

[0581] The print stability is also seen to improve with the increasing annealing time (and thus water stability) of the pigments.

[0582] References

[0583] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0584] Droguet et al. Nature Materials, 21, 352-358 (2022).

[0585] Frka-Petesic, B. & Vignolini, S. Nature Photonics 13, 365-367 (2019)

[0586] Parker, R. M. etal. Advanced Materials, 30, 1704477 (2018)

[0587] WO 2023 / 025863

[0588] WO 2024 / 175776

[0589] 008928681

Claims

Claims1. An ink composition comprising:a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures;a polymer binder; anda liquid carrier,wherein the polymer binder is present at 5 wt.% or more based on the total mass of the ink composition, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the ink composition.

2. The ink composition of claim 1, wherein:(i) the polymer binder is present at 10 wt.% or more based on the total mass of the ink composition, preferably 20wt.% or more, more preferably 30 wt.% or more, and / or(ii) the liquid carrier is present at 90 wt.% or less based on the total mass of the ink composition, preferably 80wt.% or less, more preferably 70 wt.% or less.

3. The ink composition of any preceding claim, wherein:(i) the polymer binder is present at from 20 to 75 wt.% based on the total mass of the ink composition, preferably from 30 to 65 wt.%, more preferably from 35 to 60 wt.%, even more preferably from 40 to 55 wt.%, and / or(ii) the liquid carrier is present at from 35 to 90 wt.% based on the total mass of the ink composition, preferably from 40 to 70 wt.%, more preferably from 45 to 60 wt.%.

4. The ink composition of any preceding claim, wherein the structurally coloured pigment is present at from 1 to 50 wt.% based on the total mass of the ink composition, preferably from 3 to 30 wt.%, more preferably from 5 to 20 wt.%, yet more preferably from 8 to 12 wt.%.

5. The ink composition of any preceding claim, wherein the mass ratio of polymer binder to structurally coloured pigment is 1 or more, preferably 2 or more, more preferably 3 or more, yet more preferably 4 or more.

6. The ink composition of any preceding claim, wherein the polymer binder has a refractive index of from 1.40 to 1.70, preferably from 1.45 to 1.65, more preferably from 1.50 to 1.60.

7. The ink composition of any preceding claim, wherein the difference between the refractive index of the polymer binder and the structurally coloured pigment is 0.25 or less, preferably 0.10 or less, more preferably 0.08 or less, yet more preferably 0.05 or less, even more preferably 0.02 or less.0089286818. The ink composition of any preceding claim, wherein the polymer binder is a polyurethane, a poly(meth)acrylate, a polyvinyl acetate or a combination thereof, preferably wherein the polymer binder is a polyurethane.

9. The ink composition of any preceding claim, wherein the liquid carrier is an organic solvent, water or a combination thereof, preferably wherein the liquid carrier is water.

10. The ink composition of any preceding claim, wherein the structurally coloured pigments have an average particle diameter of from 2 to 5000 pm, preferably 10 to 1000 pm, more preferably from 15 to 500 pm, yet more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

11. The ink composition of any preceding claim, wherein 80 wt.% or more of the structurally coloured pigments have a particle diameter of from 2 to 5000 pm, preferably 10 to 1000 pm, more preferably from 15 to 500 pm, yet more preferably from 20 to 150 pm, even more preferably from 70 to 110 pm.

12. The ink composition of any preceding claim, wherein the ratio of the average particle diameter to the amount of structurally coloured pigment present in the ink composition is from 2 to 20, preferably from 3 to 15, more preferably from 4 to 10, even more preferably about 6;wherein the average particle diameter is measured in pm; andthe amount of structurally coloured pigment is measured in wt.% and is based on the total mass of the ink composition.

13. The ink composition of any preceding claim, wherein the structurally coloured pigment is a single layer particle, preferably wherein the single layer comprises cellulose nanocrystals organized into a chiral nematic structure.

14. The ink composition of claim 13, wherein the structurally coloured pigment is a multilayer particle, preferably wherein particle comprises two or more cholesteric layers comprising cellulose nanocrystals organized into chiral nematic structures, and the two or more cholesteric layers are in direct contact with another cellulose containing layer.

15. The ink composition of any preceding claim, wherein the ink composition is shear thinning.

16. The ink composition of any preceding claim, further comprising a rheology modifier, a plasticizer, a crosslinker, a surfactant, a dispersing agent or a combination thereof.

17. The ink composition of any preceding claim, wherein the ink is a screen printing ink, a spray coating ink, a dip coating ink or a transfer printing ink preferably wherein the ink is a screen printing ink or a transfer printing ink.00892868118. Use of the ink composition of any of the preceding claims, for screen printing, spray coating, dip coating or transfer printing, preferably for screen printing or transfer printing.

19. A method of printing an ink composition onto a substrate, wherein the ink composition is the ink composition of any one of claims 1 to 17, the method comprising:applying the ink composition onto a substrate;drying the ink composition to remove at least a portion of the liquid carrier, to provide an ink deposit.

20. The method of claim 19, wherein applying the ink composition onto the substrate further comprises shearing the ink composition, optionally wherein shearing the ink composition substantially aligns the orientation of the structurally coloured pigment.

21. An ink deposit obtained or obtainable by the method of claim 19 or 20.

22. An ink deposit comprising:a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures; anda polymer binder,wherein the polymer binder encapsulates, fully or partially, the structurally coloured pigment.

23. The ink deposit of claim 21 or 22, wherein the structurally coloured pigments are aligned in substantially the same direction.

24. An article comprising an ink deposit of claims 21 to 23 applied onto a substrate.

25. A kit comprising a structurally coloured pigment, wherein the structurally coloured pigment comprises cellulose nanocrystals and the cellulose nanocrystals are organised into chiral nematic structures,a polymer binder, anda liquid carrier;wherein the polymer binder is present at 5 wt.% or more based on the total mass of the kit, and the structurally coloured pigment is present at 50 wt.% or less based on the total mass of the kit.008928681

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