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AssigneeSparxell UK Limited
InventorsSilvia VIGNOLINI, Benjamin E. DROGUET, Hsin-Ling LIANG, Bruno FRKA-PETESIC, Michael DE VOLDER, Jeremy J. BAUMBERG, Richard PARKER
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The invention relates to a method for producing structurally coloured films, particles and interference pigments comprising cellulose nanocrystals, such as neutralised cellulose nanocrystals. The films and particles can be used as interference pigments or coloured particles such as glitters for various applications. The method comprises steps of depositing a nanocrystal suspension comprising cellulose nanocrystals onto a substrate: spreading the nanocrystal suspension across the substrate using a spreader: ageing the nanocrystal suspension to partially or completely recover the cholesteric structures lost during deposition and spreading: drying the deposited nanocrystal suspension so that the nanocrystals self-assemble to form a structurally coloured film: and annealing the structurally coloured film to increase the water resistance of the film. The structurally coloured film comprises nanocrystals which are organized into chiral nematic structures to provide the structural colour.
A process for producing structurally coloured films, the process comprising the steps of:
The method of any one of the preceding claims, wherein the coating process is a roll-to-roll printing process.
The method of any one of the preceding claims, wherein the drying step is carried out at 10 to 250° C., preferably at 10 to 70° C.
The method of any one of the preceding claims further comprising a treating step wherein at least a portion of the substrate is modified to increase its surface energy prior to the depositing step.
The method of any one of the preceding claims further comprising the step of sonicating the nanocrystal suspension before the depositing step, optionally wherein the treatment is from 0.1 to 45 s/mL, such as around 2.2 s/mL.
The method of any one of the preceding claims where the cellulose nanocrystal suspension comprises at least one additive, such as an acid or a base, a filler, a polymer, a salt or a functional molecule.
The method of any one of the preceding claims further comprising the step of peeling the structurally coloured film from the substrate.
The method of any preceding claim, wherein the temperature of the annealing step is from 100 to 250° C.
The method of any preceding claim, wherein the annealing step is carried out for from 1 minute to 120 minutes.
The method of any one of the preceding claims further comprising the step of dividing the structurally coloured film to produce structurally coloured particles.
A structurally coloured film comprising cellulose nanocrystals, preferably neutralised cellulose nanocrystals, wherein the nanocrystals are organized into chiral nematic structures, preferably wherein the film has a thickness such that the director of a chiral nematic structure performs at least one revolution within the film, wherein the film as a thickness of 20 μm or less.
A structurally coloured particle comprising cellulose nanocrystals, preferably neutralised cellulose nanocrystals, wherein the nanocrystals are organized into chiral nematic structure, preferably wherein the particles have a facetted geometry corresponding to at least one chiral nematic domain.
The structurally coloured particle of claim 20 or 21, wherein the median average particle diameter is from 2 μm or more. 23 The structurally coloured particle of any one of claims 20 to 22, wherein the particle reflects 5% or more of the incoming light at a wavelength in the range 200 to 1300 nm.
Dependencies are inferred from the claim text.