WO2009065782A1

WO2009065782A1 - Mulitlayered colouring composition and process for making the same

Info

Publication number: WO2009065782A1
Application number: PCT/EP2008/065597
Authority: WO
Inventors: Konstantia Asteriadou; John William Davison; Ramin Djalali; Philip Michael Parkins
Original assignee: Unilever Plc; Unilever N.V.; Hindustan Unilever Limited
Priority date: 2007-11-23
Filing date: 2008-11-14
Publication date: 2009-05-28

Abstract

A multilayered colouring composition comprising an ink formulation on a substrate, the ink formulation comprising monodisperse particles wherein an adhesive layer is located between the ink formulation and the substrate.

Description

Mu I ti layered Colouring Composition and Process for Making the Same-

Technical field of the invention

The present invention relates to multilayered colouring composition based on structured colour and a process for making the same

Background of the invention

Monodisperse particles capable of forming colloidal crystals have been known for some time and are for example described in WO2007057146.

EP01459112 describes a coating composition comprising a colloidal crystal array in a polymeric resinous binder, where the refractive index contrast between the polymer and the particles is at least 0.01.

WO2004104115 discloses a multi-layer coating composition and process which comprises a colour-imparting layer of colloidal crystals containing polymeric particles(in particular PMMA related polymers).

WO20061 16640 describes a process for the preparation of opalescent effect coatings, comprising the application of a suspension of monodisperse spheres onto an absorbent substrate (selected from paper, textiles and wood) and removing the liquid from the dispersion to produce colloidal crystals. The use of the material in coating and ink compositions is mentioned.

When attempting to print on various substrates with ink based on colloidal crystal coatings, the adhesion to substrate has been found to be problematic, leading to adhesion failures. The present invention provides a way to overcome adhesion failures of colloidal crystal coatings on various substrates and provides protection via a top coat.

Definitions:

PRESSURE-SENSITIVE SUBSTRATES (PS): Adhesive products that provide permanent adhesion on a variety of dissimilar materials with the use of minimal pressure and without the need for solvents, water or heat for activation. Adhesives may be cast as free transfer films on paper release liners or on various film backings for laminating to paper, plastic, metal, glass, wood, low-energy surfaces and other substrates in industrial applications. Good cohesive strength allows clean removal of these high-tack materials without adhesive residue.

ADHESIVE BONDING PRIMERS: Priming is a method of surface preparation often used to increase the surface energy of polymers and other substrates to enhance adhesion. In priming, a coating is applied, usually one with a higher surface energy and compatible with the substrate to be primed. (See also Adhesion Promoters).

ADHESION PROMOTERS: Adhesion promoters are usually acid-modified or hydroxyl monomers. Their dual functionality helps formulators increase adhesion and lower viscosity. Depending on the application, polyester oligomers and specialty resins may also function as adhesion promoters.

General description of the invention

It is a first object of the present invention to provide a multilayered colouring composition comprising an ink formulation on a substrate, the ink formulation comprising: . monodisperse particles wherein an adhesive layer is located between the ink formulation and the substrate.

Preferably the adhesive layer is a pressure sensitive substrate, or an adhesive bonding primer or an adhesion promoter. More preferably, the adhesive layer is a pressure sensitive substrate or an adhesive bonding primers.

Depositing colloidal ink on adhesive (pressure sensitive substrate) or supportive film (adhesive bonding primers) substrate provides colloidal assemblies stability after deposition. The adhesive film contains (optionally) an agent, which has high affinity to the resin and/or colloids in the colloidal ink formulation. After applying the colloidal ink formulation on the adhesive-substrate, UV irradiation initialises curing and connecting the adhesive material with the formulation through real chemical bonds.

In a preferred embodiment of the invention, a top coat is located on top of the ink formulation, preferably, the top coat is transparent In an even preferred embodiment of the invention, printings are located on at least one of the top coat sides.

In one embodiment the printing on the top caot side opposite to the ink formulation, In another embodiment, the printing is on the top coat side in contact with the ink formulation.

It is a second object of the present invention to provide a process for manufacturing a multilayered colouring composition comprising the steps of:

1 ) providing a substrate with an adhesive layer

2) depositing onto the adhesive layer colloidal ink comprising monodisperse particles, at least one curing material, at least one initiator and at least one solvent.

Preferably, a top coat is applied onto the ink formulation

In a preferred embodiment, the top coat is a applied as a film. In another preferred embodiment, the top coat is applied is printed or sprayed.

Monodisperse particles and their manufacturing process

Monodisperse particles used in the present invention preferably comprise a low amount of at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent, which is encapsulated in the monodisperse particle. Such encapsulated monodisperse particles result in colourant compositions that produce enhanced structural colour effects, for example compared to the prior art compositions discussed above. In a less preferred embodiment of the invention, monodisperse particles do not comprise a broad spectrum absorber contrast agent or any precursor of it.

The monodisperse particles used in the present invention are easy to produce. Additionally, there are easy to handle and even with less ordered crystals formed from monodisperse particles the colour effect is brilliant. - A -

The monodisperse particles capable of forming a colloidal crystal, wherein at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is encapsulated in the particles, comprise

(i) 97 - 99.999 wt-%, based on the total weight of the monodisperse particles, of the monodisperse particle material, and

(ii) 0.0001 - 3 wt-%, based on the total weight of the monodisperse particles, of at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent, which is encapsulated.

The amount of at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent encapsulated in such monodisperse particles must not be too high (less than 3 wt-%, based on the total weight of the monodisperse particles). The amount varies depending on the absorption coefficient of the broad spectrum absorber contrast agent and/or the precursor of a broad spectrum absorber contrast agent.

The weight percentages are based on the total weight of the monodisperse particles which comprise the broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent. Therefore it is obvious that the addition of the wt-% of (i) and of (ia) is 100%.

Preferably, monodisperse particles capable of forming a colloidal crystal, wherein at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is encapsulated in the particles, comprise (i) 99 - 99.999 wt-%, preferably 99.5 - 99.9999, based on the total weight of the monodisperse particles, of the monodisperse particle material, and (ii) 0.0001 - 1 wt-%, preferably 0.0001 - 0.5 wt-%, based on the total weight of the monodisperse particles, of at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent, which is encapsulated.

By the term "monodisperse particle material" it is meant the material which encapsulates the broad spectrum absorber contrast agent and/or the precursor of a broad spectrum absorber contrast agent and forms the monodisperse particles. The monodisperse particles may be formed from the same material or they may also be formed from different materials.

By the term "monodisperse particles" we mean particles wherein at least 60% of the particles fall within a specified particle size range. For example, the monodisperse particles preferably have a diameter that deviates less than 10% in root mean square (rms), more preferably that deviates less than 5% in rms diameter.

By the term "encapsulated" we mean that the broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is enclosed or embedded within the monodisperse particles. The broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is (more or less) evenly distributed in the monodisperse particles. That means that it is not concentrated mainly in one part of the monodisperse particle.

Typically, the monodisperse particles are capable of forming a colloidal crystal that reflects and/or diffracts light having a wavelength in a range that corresponds to the wavelength of visible light.

Suitable monodisperse particles typically have a rms diameter of less than about 1 μm and greater than about 1 nm, and are, therefore, classed as "nanoparticles". In particular, the monodisperse particles may have a rms diameter of greater than 100, preferably greater than 120 nm. Preferably the monodisperse particles may have a rms diameter of less than 900 nm, preferably less than 800 nm. More preferably, the rms diameter of the monodisperse particles is in the range of from 120 nm to 800 nm.

Monodisperse particles suitable for use in the present invention may be of varying geometry. They can have any geometrical forms. For example, the monodisperse particles may be shaped as needles, plates and/or rods and/or may be substantially spherical. The shape of the monodisperse particles does not significantly influence their effectiveness in the colourant compositions of the present invention.

The monodisperse particles used in the present invention can be core/shell particles. A core/shell particle consists of (at least) two layers, the core and the shell. In such core- shell particles, there is a difference Δn of at least 0.001 (preferably 0.01 , more preferably 0.1 ) between the refractive indices of the core material and of the shell material, at least one broad spectrum absorber contrast agent and/or at least one precursor material of a broad spectrum absorber contrast agent being encapsulated in the core-shell particle.

Non core-shell particles, which preferably used in the present invention, only consist of one layer. The broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is not concentrated in the centre of the monodisperse particle (or in another part of the monodisperse particle). It is distributed in the whole monodisperse particle. Usually it is evenly distributed therein.

Therefore preferably monodisperse particles have at least one broad spectrum absorber encapsulated and where the broad spectrum absorber contrast is distributed over the whole monodisperse particle

The monodisperse particles suitable for use in the present invention may be made from any suitable material, including organic and inorganic materials. For example, suitable organic materials include organic polymer particles such as latex, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co-butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles, hydrogel colloids and copolymerisate thereof: poly (N-isopropylacrylamide), poly(acrylic acid), poly(acrylic acid)lhydroxypropylcellulose, dextranlpoly(N-isopropylacrylamide), and dextranlhydroxylpropylcellulose. Also copolymers comprising monomer units of the polymers mentioned before can be used for the invention as well.

Suitable inorganic materials include metal chalcogenide, metal pnictide, silica, metal and metal oxide particles. Examples of suitable metal oxides include, for example, AI₂O₃, TiO₂, SnO₂, Sb₂O ₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃. Examples of suitable metals include, for example, gold, copper and silver.

By the term "metal chalcogenide" we mean metal compounds formed with anions from group 16 of the Periodic Table of Elements (according to established IUPAC nomenclature), i.e. oxygen, sulphur, selenium, tellurium and polonium.

By the term "metal pnictide" we mean metal compounds formed with anions from group 15 of the Periodic Table of Elements (according to established IUPAC nomenclature), i.e. nitrogen, phosphorus, arsenic, antimony and bismuth. In one embodiment the monodisperse particles comprise organic polymer particles, such as those listed above. In particular, the monodisperse particles may comprise organic polymers selected from polystyrene and poly(methylmethacrylate). Such organic polymer particles are advantageous because they are easy to prepare and can easily be doped with the broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent (for example by surfactant free emulsion polymerisation), i.e. so as to encapsulate the contrast agent. This enables effective control of the concentration of the contrast agent.

Monodisperse particles are commercially available or can be prepared by methods known in the art. Monodisperse particles made from organic polymer particles may be prepared as dispersions using emulsion, dispersion or suspension polymerisation

For example, US 6,800,709 describes the preparation of monodisperse particles with a narrow size distribution by free radical polymerization or copolymerization of hydrophobic monomers in a water-based system in the presence of cyclodextrin. Suitable hydrophobic monomers include styrenics, acrylonitrile, methacrylonitrile, acrylates, methacrylates, methacryl amides, acrylamides, maleimides, vinyl ethers, vinyl esters, monoalkylmaleates, dialkyl maleates, fluorinated acrylates and fluorinated methacrylates.

Monodispersed poly(methylmethacrylate) composites may be prepared following the process described by M. Egen, R. Zentel (Macromol. Chem. Phys. 2004, 205, 1479- 1488) or are commercially available from Duke Scientific Corporation.

When the broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is encapsulated in the monodisperse particles, the monodisperse particles typically are formed in the presence of the broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent. For example, monodisperse organic polymer particles (such as polystyrene or poly(methylmethacrylate) particles) that encapsulate at least one broad spectrum absorber contrast agent (such as a dye) and/or at least one precursor of a broad spectrum absorber contrast agent may be prepared using surfactant free emulsion polymerisation, as discussed in more detail below. Monodisperse particles made from inorganic materials, such as silica particles, may be prepared as dispersions using sol-gel processes.

For example, monodisperse silica spheres can be prepared following the well-known process by Stober, Fink and Bohn (J. Colloid Interface Sci. 1968, 26,62). The process was later refined by Bogush et al. (J. Non-Crys. Solids 1988, 104, 95). Alternatively, silica particles can be purchased from Blue Helix, Limited or they can be freshly prepared by the process described in US 4,775,520 and US 4,911 ,903.

Monodisperse silica spheres may also be produced by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous-ammoniacal medium, a sol of primary particles being produced first of all and then the silica particles obtained being brought to the desired particle size by continuous, controlled addition of tetraalkoxysilane. With this process it is possible to produce monodisperse silica spheres having average particle diameters of between 0.05 and 10 μm with a standard deviation of less than 7%.

The surface of the monodisperse particles may be modified so as to implement a variety of effects. The surface groups on the monodisperse particles may be modified and/or changed by performing a chemical reaction. For example, the monodisperse particles may be modified so as to carry charged functional groups, such as carboxylate, sulfate or amine groups. Such modifications would be well known to a person skilled in the art.

By the term "broad spectrum absorber contrast agent" we mean a compound that

(a) absorbs substantially all light having a wavelength in a range that corresponds to the wavelength of visible light, and

(b) eliminates diffuse light.

In the light of the present invention the term "broad spectrum absorber contrast agent" also comprises a mixture of compounds wherein that mixture has the same absorption property as a single broad spectrum absorber contrast agent. Such a mixture still must eliminate diffuse light. That means that each single compound of such a mixture only absorbs the light in a well defined area and only the combination of these compounds provide a broad spectrum absorber. Therefore in a further embodiment of the present invention, it can also be used monodisperse particles capable of forming a colloidal crystal, wherein a broad spectrum absorber contrast agent, which is a mixture of compounds and wherein that mixture has the same absorption property as single broad spectrum absorber contrast agent and wherein the mixture is encapsulated in the particles.

In the following the term "broad spectrum absorber contrast agent" always stands for either a single compound or a mixture of compounds.

It is also possible to encapsulate a precursor material of a broad spectrum absorber contrast agent. That precursor is converted into the broad spectrum absorber contrast agent by using a form of energy (such as light (UV), heat, etc). This conversion usually happens after the encapsulation process.

Suitable precursors for the present invention are metal salts, preferably hydrophilic metal salts, such as nitrates or halogenides. Preferred halogenides are F, Cl or I, whereas Cl is the most preferred halogenide.

The metals are for example alkaline metals, alkaline earth metals, noble metals, rare earth metals or transition metals. Suitable metals are for example K, Ca, Sr, Ba, Zn, Pb, Fe, Ni, Ce, Co, Cr, Cu, Mn, Sn, Al, Ag, Mg, Au, and Cd. Preferred are Ca. Mg, Al, Ag and Zn.

Very suitable metal salts are Ag nitrate, Ag halogenide, Fe nitrate and Fe halogenide (especially FeCI₂ and FeCI₃).

As an example AgNO₃ is converted into colloidal silver. It is also possible to use more than one precursor.

As a further example FeCI₂ as well as FeCI₃ are converted into Fe₃O₄ and/or iron hydroxide.

Additionally it is also possible to use one or more precursor and another compound which form then a mixture, which has the required broad spectrum absorber contrast agent property. In the following the term "precursor of a broad spectrum absorber contrast agent" always stands for either a single compound or a mixture of compounds. By this we mean that, as a pure material, the broad spectrum absorber contrast agent absorbs sufficient light so as to appear black or darkly coloured (for example dark blue or dark purple) to the human eye. For example, a broad spectrum absorber contrast agent absorbs most (particularly all) light having a wavelength in a range of from 380 to 780 nm. More specifically, the broad spectrum absorber contrast agent absorbs at least 90% (preferably at least 95%, more preferably 100%) of light having a wavelength in a range of from 380 to 780 nm.

The term "broad spectrum absorber contrast agent" is not intended to encompass those agents that do not absorb substantially all light having a wavelength in a range that corresponds to the wavelength of visible light (and, therefore, that, as a pure material, do not appear black or darkly coloured to the human eye). This term also is not intended to encompass single fluorescent agents, such as single fluorescent dyes or single pigments. But it is possible to encapsulate for example a mixture of various pigments, which have different absorption maxima and wherein the addition of these maxima has a broad spectrum absorber property.

By the term "organic broad spectrum absorber contrast agent" we mean a contrast agent that contains atoms selected from carbon, hydrogen, oxygen, nitrogen and/or sulfur only. By the term "inorganic broad spectrum absorber contrast agent" we mean a contrast agent that contains metal atoms.

In the compositions used in present invention, the broad spectrum absorber contrast agent typically absorbs substantially all of the light that is diffused by the colloidal crystal and that has a wavelength in a range that corresponds to the wavelength of visible light.

Contrast agents that are not broad spectrum absorbers as defined herein do not absorb substantially all of the diffused light. The unabsorbed, diffused light dilutes the structural colour effect caused by the direct reflection and/or diffraction of visible light by the colloidal crystal.

The broad spectrum absorber contrast agent may, for example, be a dye or a pigment or a mixture of dyes or a mixture of pigments and dyes as well as a mixture of pigments and dyes, which fulfils the requirements for the broad spectrum absorber contrast agent as defined in the present patent application. A "dye" generally has an affinity to the substrate to which it is applied and generally is in the form of a solution or oil. A "pigment" generally does not have an affinity to the substrate to which it is applied and is in the form of a solid. As the skilled person would appreciate, the exact physical form of the contrast agent is not essential to the present invention and the physical form may change upon application of the colourant composition to a suitable substrate.

The broad spectrum absorber contrast agent is encapsulated in the monodisperse particles. The broad spectrum absorber contrast agent typically is encapsulated in the monodisperse particles before the colloidal crystals are formed.

The broad spectrum absorber contrast agent may be encapsulated in the monodisperse particles in any suitable way. For example, discrete particles of the broad spectrum absorber contrast agent may be embedded inside the monodisperse particles. References herein to the encapsulation of the contrast agent in the monodisperse particles are intended to refer to encapsulation by only one or by two or more of the aforementioned ways of encapsulation.

When the broad spectrum absorber contrast agent is encapsulated in the monodisperse particles, then the colour produced is long lasting. Additionally, the encapsulation of the contrast agent provides environmental advantages, for example because any toxic or undesirable broad spectrum absorber contrast agent material is enclosed in the monodisperse particles and, therefore, is not released into the environment upon application of the colourant composition to a substrate.

Methods for encapsulating a broad spectrum absorber contrast agent or a mixture of compounds with the same property as a broad spectrum absorber contrast agent into monodisperse particles are known and any such suitable method may be used to prepare the colourant compositions of the present invention.

A broad spectrum absorber contrast agent may be encapsulated into monodisperse particles using Surfactant Free Emulsion Polymerisation (SFEP) processes, in which the polymerisation is conducted in the presence of an appropriate contrast agent. For example, Zentel et al. (Chemistry of Materials, 12 (8): 2508) describes a process in which monodisperse organic polymer particles are produced in a Surfactant Free

Emulsion Polymerisation (SFEP) in the presence of a water soluble dye. The SFEP process typically produces substantially spherical polymer particles of a narrow size distribution and having surface charges that produce electrostatic repulsion so as to prevent aggregation. The SFEP process also is typically conducted in the absence of emulsifiers which, if present, could bond the particles together so as to make the formation of the colloidal crystals (for example by sedimentation or self-assembly methods) difficult.

A water-insoluble broad spectrum absorber contrast agent may be encapsulated into the monodisperse particles by emulsifying the monodisperse particles in a suitable oil. In this case, the monodisperse particles may additionally encapsulate an oil.

As the person skilled in this art would appreciate, the monodisperse particles may comprise any suitable broad spectrum absorber contrast agent. In one aspect of the invention, the monodisperse particles comprise a broad spectrum absorber contrast agent that is organic.

Another aspect of the present invention relates to the use of

(i) monodisperse particles capable of forming a colloidal crystal as defined above and

(ia) at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent, which is encapsulated in the monodisperse particles.

In another aspect of the invention, the monodisperse particles comprise a broad spectrum absorber contrast agent that is inorganic.

Suitable broad spectrum absorber contrast agents include absorbing elements such as silver, dyes such as Alizarin Blue Black and Brilliant Blue Black, as well as pigments such as carbon black (for example the carbon black product line from Degussa, such as Purex^® LS 35 and Corax^® N 115), iron hydroxide and iron oxide black.

Another aspect of the present invention relates to the use of monodisperse particles comprising

(i) monodisperse particles capable of forming a colloidal crystal as defined above and (ia) at least one broad spectrum absorber contrast agents chosen from the group consisting of Alizarin Blue Black and Brilliant Blue Black, as well as pigments such as carbon black (for example the carbon black product line from Degussa, such as

Purex^® LS 35 and Corax^® N 1 15), iron hydroxide and iron oxide black., which is encapsulated in the monodisperse particles.

The monodisperse particles of the present invention are capable of forming a colloidal crystal, for example upon application of the colourant composition to a substrate. In another related aspect of the present invention, the colourant compositions can comprise colloidal crystals formed from monodisperse particles. Typically, the colloidal crystals reflect and/or diffract light having a wavelength in a range that corresponds to the wavelength of visible light. There typically is also some diffusion of the light by the colloidal crystal.

For the avoidance of doubt, the wavelength of visible light is, for example, in the range of from 380 to 780 nm. Thus, the colloidal crystals appear coloured to the human eye.

For the avoidance of doubt, references herein to "a colloidal crystal" are intended to relate to one or more colloidal crystals.

By the term "colloidal crystal" we mean a regular array of monodisperse particles having a substantially regular or constant spacing there between. Thus, the array of monodisperse particles forms a dispersed phase arranged in a continuous phase (or matrix). The continuous phase (or matrix) may comprise a gas, a liquid or a solid of a different refractive index to the dispersed phase.

As the skilled person would appreciate, a colloidal crystal may, however, contain some impurities and/or defects. The levels of impurities and/or defects typically will depend on the materials and methods of preparation used.

The term "colloidal crystal" has the same meaning as the term "super-lattice". A colloidal crystal or super-lattice is a type of photonic crystal, which is an optical, artificial structure characterised by 2D or 3D periodic arrangements of dielectric material which lead to the formation of energy band structures for electromagnetic waves propagating in them. As discussed above, the colloidal crystals appear coloured to the human eye. In other words, the colloidal crystals reflect and/or diffract light in the visible spectrum.

The crystal colour or colours observed by the human eye depend principally on two factors. These factors are the lattice spacing within the colloidal crystal and the refractive index of the disperse and continuous phases. Both of these factors affect the wavelength of light reflected and/or diffracted by the colloidal crystal.

The lattice spacing is determined by factors such as the size of the monodisperse particles. For example, monodisperse particles having a rms diameter in the range of from 250 to 510 nm can be used to form colloidal crystals that have colours ranging from blue and red to green and yellow. Colloidal crystals can have different colours when viewed from different angles because the lattice spacing can be different in different axes of the crystal. Provided that the lattice spacing in at least one axis results in the reflection and/or diffraction of light with a wavelength in the visible spectrum then the colloidal crystal will appear to the human eye to be coloured.

The colloidal crystal (once formed) may have a lattice spacing in at least one axis in a range that corresponds to the wavelength of visible light. Preferably, the lattice spacing in at least one axis is in a range of from 380 to 700 nm.

References above to the refractive index of the disperse and continuous phases are especially intended to relate to the difference in refractive index between the disperse and continuous phases. This is known as the "refractive index contrast", which is the ratio of the refractive index of the two phases.

Methods of forming colloidal crystals from monodisperse particles are known in the art. For example, sedimentation or self-assembly methods may be used.

The sedimentation method of forming colloidal crystals comprises the steps of placing a solution or suspension of monodisperse particles in a suitable carrier or solvent in an appropriate container or vessel and then simply allowing the monodisperse particles to form the colloidal crystals as they settle in the container or vessel.

The sedimentation process is driven by gravitational forces. The gravitational force counteracts the Brownian motion of the monodisperse particles in the dispersion. Above a critical volume content (for example greater than about 50% by volume), an equilibrium- state between a disorganised liquid phase and a denser colloidal crystalline phase is developed. This process is, however, typically very slow. For example, polystyrene particles with a rms diameter of 1 μm take approximately one month to reach the aforementioned equilibrium state. This period of time can be reduced by using centrifugal forces, for example by using a centrifuge.

Thus, the monodisperse particles may be formed into colloidal crystals by placing the solution or suspension of monodisperse particles in a suitable carrier or solvent in an appropriate container or vessel and the centrifuging the solution or suspension. The carrier or solvent may then be removed from the colloidal crystals that are formed by any suitable method. For example, the carrier or solvent may be removed by evaporation or by decanting the carrier or solvent. Once the carrier or solvent has been removed, the colloidal crystals may be analysed by any suitable method, such as by Transmission Electron Microscopy and Scanning Electron Microscopy methods.

Typically, the sedimentation process provides colloidal crystals of a face-centred-cubic structure. However, as the skilled person would appreciate, some defects are unavoidable, such as the formation of some colloidal crystals of a body-centred-cubic structure.

The self-assembly method of forming colloidal crystals comprises the step of providing a suspension or solution of monodisperse particles in a suitable carrier or solvent and contacting a suitable substrate with the suspension or solution, for example by placing the suitable substrate in the suspension or solution. Slow evaporation of the carrier or solvent under the appropriate conditions leaves a deposit of colloidal crystals on the substrate. Typically, a carrier or solvent (such as an alcohol) is selected which will evaporate within a convenient time scale.

The self-assembly method is driven by capillary forces. This method provides a template form, referred to in the art as a "planar opal". The capillary forces act to uniformly deposit a specific number of layers (for example 25) of close-packed monodisperse particles onto the substrate. This method was used by Denkov et al. to make two-dimensionally periodic monolayers of monodisperse particles (see "Two-Dimensional Crystallization", Nature, Vol. 361 , p. 26 (1993) and US 5,540,951 ) and was extended by Jiang et al. to make three-dimensional opaline structures (see "Template-Directed Preparation of Macroporous Polymers with Oriented and Crystalline Arrays of Voids", Journal of the American Chemical Society, Vol. 121 , pp. 1 1630-1 1637 (1999)). In the method of Jiang et al., a glass substrate was placed vertically in a solution of monodisperse particles. Slow evaporation of the solvent under the appropriate conditions leaves a deposit of three-dimensionally ordered particles in a face-centred cubic lattice, i.e. colloidal crystals.

Whilst the self-assembly method typically forms colloidal crystals in which point defects may remain, the crystals formed by this method have the potential of being single crystals. Thus, the colloidal crystals formed by the self-assembly method are often superior to those formed by the sedimentation method because they are not polycrystalline, they are of a well-defined thickness, and they have a known crystal orientation.

Apparatus for forming colloidal crystals by the self-assembly method are known. For example, Nagayama et al. (J. Phys.: Condens. Matter; 1994 (6), A395) describes a mechanical apparatus, which acts to pull a glass slide out of a highly diluted dispersion of monodisperse particles. The monodisperse particles are pulled onto the glass slide and ordered so as to form colloidal crystals. This ordering of the monodisperse particles occurs because the surface of the liquid on the glass slide obtains a curvature through dewetting. Thus, a thin liquid film is observed on the glass slide, which has a decreasing thickness towards the edges. In the position where the film is thinner than the diameter of the colloidal crystals, the monodisperse particles are pulled out together, due to capillary forces, into a dense packet. During evaporation of the solvent, a convection effect is created in the liquid, through which further monodisperse particles are transported along. The glass slide is pulled out of the dispersion at a speed that corresponds to the growth rate of the colloidal crystals. The crystalline order is consequently gained by capillary forces. The direction of the crystal growth is determined by the movement of the glass slide, which counteracts to the effective diffuse mobility of the particles. Very thin layers of colloidal crystal are generated, for example packed in from one to three hexagonal sorted layers.

This procedure was further developed by Colvin et al. (Phys. Rev. B; 2001 (64), 205103) using dispersions of silica particles in ethanol. The mechanical extraction of the glass slide was replaced by a slow evaporation process of the solvent from a sample holder, which was positioned vertically in a narrow vial. The colloidal crystals grow continuously on the glass surface of the sample holder, as the liquid level decreases by evaporation. The samples are allowed to stand for a few hours. This method forms layers of colloidal crystals of controlled thickness, as observed by Scanning Electron Microscopy methods.

According to an aspect of the present invention, it can be used a colloidal crystal formed from monodisperse particles and that reflects and/or diffracts light having a wavelength in a range that corresponds to the wavelength of visible light, wherein the colloidal crystal comprises at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent, which is encapsulated in the monodisperse particles. According to another related aspect of the present invention, it can be used a colloidal crystal formed from monodisperse particles and that reflects and/or diffracts light having a wavelength in a range that corresponds to the wavelength of visible light, wherein the colloidal crystal comprises at least broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent which is encapsulated in the monodisperse particles. The broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is encapsulated in the monodisperse particles and may additionally be positioned in interstices between the monodisperse particles and/or may be additionally located on the surface of the monodisperse particles. The colloidal crystal may be formed by any suitable method, for example by a method as discussed above.

Therefore the present invention also relates to the use of a colloidal crystal formed from monodisperse particles as defined above.

The monodisperse particles, wherein at least one broad spectrum absorber contrast agent and/or at least one precursor of a broad spectrum absorber contrast agent is encapsulated as described above as well as the colloidal crystal as described above can be used in a colourant composition.

Example A - Synthesis of Monodisperse Polv(methylmethacrylate) Particles encapsulating a Dye

A three necked flask (250 ml) was charged with 150 ml of double deionised water and 4 to 40 mg of a dye (for example Brilliant Black BN). The flask was sealed with a septum.

The flask was heated up to 9O⁰C and flushed with nitrogen for 45 minutes. After the nitrogen flow had stopped, 15 ml (141 mmol) of methylmethacrylate was added through the septum. The polymerisation was initiated with potassium peroxodisulfate after another 30 minutes at 9O⁰C by adding 5 ml (1.8 mmol, 500 mg) of a 10% by weight solution. The solution was flushed for 10 minutes at 9O⁰C with nitrogen. The reaction solution was stirred with a mechanical quirler at 400 revolutions per minute (rpm). After 2.5 hours reaction time, the flask was opened and the resulting warm solution was filtered through a standard paper filter to remove large agglomerations. The solution was then washed twice for 5 to 10 minutes in the centrifuge at 4000 rpm to separate the transparent pellet. Afterwards it was centrifuged for 30 to 90 minutes, until a clear liquid was formed above the iridescent pellet. The liquid was then poured out and the pellet was re-dispersed in 60 ml of double deionised water. This was repeated for another 4 times in order to separate the polymer from oligomers. The solution were then stored as a 10 to 20% by weight suspension. The yield depended on the separated polymer/oligomer ratio and was typically in a range of from about 50 to 90%.

The polymer spheres grown by this method showed surface charges, which give rise to electrostatic repulsion that prevent aggregation.

The monodisperse dye encapsulated polymer spheres produced had average particle diameters of between about 0.05 and 0.7 μm, with a standard deviation of less than 4%.

The samples were then purified by centrifuging the dispersion at 5000 rpm for 20 minutes to separate the solid from the liquid. The solid was re-dispersed in distilled water to the original volume by mechanical stirring and ultrasonic treatment. This procedure was repeated three or four times.

The samples produced by this method exhibited a brilliant colour due to Bragg diffraction of visible light.

Example B - Fabrication of colloidal crystals in a test-tube

A suspension of 10% of uniform-sized poly(methylmethacrylate) spheres (prepared as Example 1 ) in water (particle volume fraction: 10%; diameter: 210 nm; standard deviation: 3%) containing volume fraction of 0.3 % Brilliant Black BN was poured in a 2 ml plastic vial (8 mm wide and 30 mm long) and then centrifuged at 10000 rpm (about 3500 G) for 10 minutes. After centrifugation, an iridescent crystalline region formed at the bottom of the cell, a turbid noncrystalline region in the middle, and a transparent region on the top. The same method was also performed on a solution containing bare poly(methylmethacrylate) particles (particle volume fraction: 10%; diameter: 210 nm; standard deviation: 3%) in distilled water (with no dye, pigment and/or chromophore). The colloidal crystal formation was performed under the same conditions as those described above. After centrifugation, an iridescent crystalline region formed at the bottom of the cell, a turbid noncrystalline region in the middle, and a transparent region on the top.

Printing formulation The printing formulation used in the present invention comprises

(i) monodisperse particles,

(ii) at least one curing material,

(iii) at least one initiator, and

(iv) at least one solvent.

Monodisperse particles can be of the type described under "Monodisperse particles and their manufacturing process", herein above.

The advantage of adding a separate curing agent and initiator (instead of a core/shell particle, wherein the shell forms a matrix system) is that any kind of curing agents and initiators can be used. Such a curing agent/initiator-system covers the gaps between each sphere in the layer arrangement in an excellent manner, so that even core/shell particles with a matrix forming shell get a better stabilisation and therefore a better printing quality is obtained.

Because of using an initiator the curing reaction takes place immediately and the printing is made stable in a fast manner.

The initiation process is started by an input of energy. Such energy can be in the form of heat, radiation (e.g. normal light, UV light), pressure etc.

Preferably the curing of the printing is done by (UV) light. In such a case the term "initiator" is equivalent to the term "photoinitiator", which is a chemical that decompose with energy from UV or visible light. Curing is a term in polymer chemistry and Process Engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains.

Processes for applying the formulation are commonly known process and they will be discussed below.

In a formulation used in the present invention the amount of monodisperse particles capable of forming a colloidal crystal that diffracts light having a wavelength in a range that corresponds to the wavelength of visible light can vary a lot, particularly depending whether the formulation is used as a concentrate which is to be diluted (with water and/or other solvents) or as a ready-to-use formulation. In the first case the amount of monodisperse particles is large, up to 70 weight-% (wt-%), based on the total weight of the printing formulation.

In the latter case the amount of the monodisperse particles can vary from 0.01 up to 30 wt-%, based on the total weight of the printing formulation.

It is obvious that the amount of the monodisperse particles also depend on the substrate which is to be printed as well as on the hue which needs to be obtained.

In a printing formulation used in the present invention, the amount of monodisperse particles lies between 30 wt-% and 70 wt-%, preferably between 30 wt-% and 60 wt-%, more preferably between 30 wt-% and 55 wt-%, based on the total weight of the printing formulation.

In another printing formulation used in the present invention, the amount of monodisperse particles lies between 0.01 wt-% and 30 wt-%, between 0.1 and 30 wt-%, more preferably between 0.1 and 20 wt-%, based on the total weight of the printing formulation.

It also to be stated that the amount of monodisperse particles can vary depending of the physical form of the formulation, that means the concentration can vary in case that the formulation is in liquid, gel, wax or paste form.

Monodisperse particles are defined as having at least 60% of the particles falling within a specified particle size range. Monodispersed particles deviate less than 10% in root mean square (rms) diameter. Highly monodisperse particles deviate less than 5% in rms diameter. Monodisperse particles for use in the invention typically have an rms diameter of less than about 1 μm and greater than about 1 nm, and are therefore classed as nanoparticles. Preferably the monodisperse particles have an rms diameter of greater than about 150 or about 200 nm. Preferably the monodisperse particles have an rms diameter of less than about 900 nm or about 800nm. That means a usual diameter goes from 150 nm to 900nm, preferably from 150 nm to 800 nm. More preferably the diameter of the monodisperse particles is from about 200 nm to about 550nm.

The monodisperse particles are chosen such that they can form a colloidal crystal which appears coloured to the human eye, i.e. in the visible spectrum. The crystal colour or colours observed depend principally on two factors, namely the lattice spacing within the colloidal crystal and the refractive index of the particles and matrix, which affects the wavelength of light diffracted. The lattice spacing is determined by factors such as the size of the monodisperse particle. For example, we have used particles having a diameter of from 250 to 510 nm to generate coloured colloidal crystals having colours ranging from blue and red to green and yellow. Colloidal crystals can have different colours when viewed from different angles because the lattice spacing can be different in different axes of the crystal. Provided that the lattice spacing in at least one axis results in diffraction of light with a wavelength in the visible spectrum then the crystal will appear to be coloured.

Monodisperse particles can be of varying geometry. In a preferred embodiment, the monodisperse particles are substantially spherical.

In another preferred embodiment of the present invention the monodisperse particles are spherical.

In another preferred embodiment of the present invention the monodisperse particles are inorganic.

In another preferred embodiment of the present invention the monodisperse particles are organic polymers.

Preferably, the lattice spacing in at least one axis is from about 350 to about 780 nm, preferably from 380 to 770 nm. The monodisperse particles suitable for use in the printing formulations used in the present invention may be made from any suitable material, including one or more selected from organic and/or inorganic materials. For example, suitable organic materials include organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co-butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles. Suitable inorganic materials include metal chalcogenide, metal pnictide, silica, metal and metal oxide particles. Examples of suitable metal oxides include, for example, AI₂O3, TiC>₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃. Examples of suitable metals include, for example, gold, copper and silver.

By the term "metal pnictide" we mean metal compounds formed with anions from group 15 of the Periodic Table of Elements (according to established IUPAC nomenclature), i.e. nitrogen, phosphorus, arsenic, antimony and bismuth.

Methods for preparing monodisperse particles are known in the art. Dispersions may be prepared using emulsion, dispersion, suspension polymerization if particles are polymeric, or if particles are inorganic (e,g,. silica particles) the dispersion may be prepared using sol-gel processes.

Monodispersed silica spheres can be prepared following the well-known process by Stober, Fink and Bohn (J. Colloid Interface Sci. 1968, 26,62). The process was later refined by Bogush, et. al. (J. Non-Crys. Solids 1988, 104, 95). Alternatively, silica particles can be purchased from Blue Helix, Limited or they can be freshly prepared by the process described in US 4,775,520 and US 4,91 1 ,903. For example, monodisperse silica spheres can be produced by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous-ammoniacal medium, a sol of primary particles being produced first of all and then the silica particles obtained being brought to the desired particle size by continuous, controlled addition of tetraalkoxysilane. With this process it is possible to produce monodisperse SiO₂ spheres having average particle diameters of between 0.05 and 10 μm with a standard deviation of less than 7%.

The formulations according to the present invention comprise monodisperse particles capable of forming a colloidal crystal, for example upon application of the colorant composition to a substrate.

The term "colloidal crystal" has the same meaning as the term "super-lattice". A colloidal crystal or super-lattice is a type of photonic crystal, which is an optical, artificial structure characterised by 2D or 3D periodic arrangements of dielectric material which lead to the formation of energy band structures for electromagnetic waves propagating them. Preferably the colloidal crystal has a lattice spacing in a range that corresponds to the wavelength of visible light.

In a preferred embodiment the colloidal crystal has a lattice spacing in a range that corresponds to the wavelength of visible light.

A printing formulation (PF Ia) used in the present invention comprises (i) monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co-butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and

(ii) at least one curing material, and

(iii) at least one initiator, and (iv) at least one solvent.

Preferred are printing formulations wherein inorganic materials are used. Such materials are not only (UV) light resistant but they are also more stable to elevated temperature. Elevated temperature can be used (depending on the solvent of the formulation) to get rid of the solvent during or after the printing process.

Another printing formulation (PF Ib) used in the present invention comprises

(i) monodisperse particles, chosen from the group consisting inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂,

Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and (ii) at least one curing material, and (iii) at least one initiator, and (iv) at least one solvent.

The monodisperse particles of printing formulations (PFIa) and (PFIb) deviate less than 10% in root mean square (rms) diameter, preferably less than 5% in rms diameter and they have a diameter from 150nm to 900nm, preferably from 150nm to 800nm, more preferably the diameter of the monodisperse particles is from about 200nm to about 550nm.

The printing formulation comprises at least one solvent.

Preferably the solvent is an organic solvent, which can be polar or nonpolar. Examples of polar solvents include water, alcohols (mono or poly), esters, ketones and ethers, particularly mono- and di-alkyl ethers of glycols and polyglycols such as monomethyl ethers of mono-, di- and tri-propylene glycols and the mono-n-butyl ethers of ethylene, diethylene and triethylene glycols.

Examples of nonpolar solvents include aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and byproducts.

The printing formulation can be prepared as an aqueous or as a non-aqueous solution.

Therefore, a printing formulation as described above, can be aqueous or nonaqueous. Therefore, a printing formulation (PF II) used in the present invention comprisies

(i) monodisperse particles, and (ii) at least one curing material, and (iii) at least one initiator, and (iva) water, and

(iva) optionally at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products.

Another printing formulation (PF Na) used in the present invention comprises

(i) monodisperse particles, and

(ii) at least one curing material, and

(iii) at least one initiator, and (iv) at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products.

The monodisperse particles of printing formulations (PFII) and (PFIIa) deviate less than 10% in root mean square (rms) diameter, preferably less than 5% in rms diameter and they have a diameter from 150nm to 900nm, preferably from 150nm to 800nm, more preferably the diameter of the monodisperse particles is from about 200nm to about 550nm. In a preferred embodiment, the solvent can be chosen from water; alcohols, such as ethanol, methanol, propanol, butanol; esters; ketones; and ethers, particularly mono- and di-alkyl ethers of glycols and polyglycols such as monomethyl ethers of mono-, di- and tri- propylene glycols and the mono-n-butyl ethers of ethylene, diethylene and triethylene glycols.

But, even when no water is deliberately added to the nonaqueous vehicle, some adventitious water may be carried into the formulation, but generally this will be no more than about 2 - 4 wt-%, based on the total weight of the printing formulation. By definition, a nonaqueous printing formulation used in this invention will have no more than about 10%, and preferably no more than about 5 wt-% water, based on the total weight of the printing formulation.

The amount of solvent in the printing formulation is typically in the range of about 10 to about 99.99 wt-%, preferably from about 20 to about 99.9-wt %, and more preferably from about 30 to about 99.9 wt-%, based on the total weight of the printing formulation.

The amount of solvent which is part of the printing formulation can very a lot. The reasons for that are the same as explained for the monodisperse particles above.

When the formulation is used as a concentrate then the amount of solvents is low, usually between 30 and 70 wt-%, based on the total weight of the printing formulation. In certain cases the printing formulation can comprise even less that 30 wt-%.

When the formulation is in a ready-to-use form then the solvent content can be up to 99.99 wt-%, based on the total weight of the printing formulation.

It is obvious that the amount solvent also depend on the substrate which is to be printed as well as on the hue which needs to be obtained.

Therefore, the present invention also relates to the use of a concentrated printing formulation, wherein the amount of solvent lies between 30 wt-% and 70 wt-%, preferably between 35 wt-% and 70 wt-%, more preferably between 35 wt-% and 65 wt-%, based on the total weight of the printing formulation. The present invention also relates to the use of a printing formulation, wherein the amount of water lies between 70 wt-% and 99.99 wt-%, -%, preferably between 70 wt-% and 99.9wt-%, more preferably between 80 wt-% and 99.9 wt-%, based on the total weight of the printing formulation.

The formulations which comprise water (pure aqueous as well as water/solvent-mixtures) are preferred.

It also to be stated that the amount of monodisperse particles as well as of the solvent can vary depending of the physical form of the formulation, that means the concentration can vary in case the printing formulation is a liquid, gel or a paste.

The printing formulation also comprises at least one curing agent. A curing agent has good mechanical, adhesive and thoughness properties as well as good resistance to environmental degradation. The curing agents can be classified into two main groups the "thermoplastic" and "thermosetting" types. Any kind of commonly know curing agent can be used. Usually curing agent are resins which are crosslinkable. These are low molecular or oligomeric polyfunctional compounds with a molecular mass <1000 g/mol. The functional groups which are often terminal groups (for example epoxy-, isocyanate-, amine- or hydroxy-groups) are chose that way (amount of groups as well as kind of the groups) that the react according to the polyaddition or polycondensation mechanism.

Suitable curing agents are polyester, vinylester and epoxy compounds. Furthermore phenolic, cyanate ester, polyurethane, bismaleimide, polyimide, epoxy acrylate, polyurethane acrylate, polyester acrylate, acrylated polyol and acrylated polyether compounds can be used as well.

Curing agents are well known and can be bought commercially for examples from BASF, from Jenton International UK, or from ALBERDINGK.

Therefore in a preferred printing formulation, the curing agent is chosen from the group consisting of polyester, vinylester, epoxy, phenolic, cyanate esters, polyurethanes, bismaleimides, polyimides, epoxy acrylates, polyurethane acrylates, polyester acrylates, acrylated polyols and acrylated polyether compounds. Such curing agents are used in an amount of 0.01wt-% - 15wt-%, based on the total weight of the printing formulation. Preferably, curing agents are present in an amount of 0.1 - 10 wt-%, based on the total weight of the printing formulation.

In combination with the curing agent(s) at least one initiator is used. This initiator is which starts the polymerisation of the curing agent.

When the initiation takes place with radiation, it is usually done by exposition to light (400 nm - 800nm) and/or UV-light (100 nm - 400 nm) and/or IR (800nm -1400nm).

Such an initiator can be peroxide or peroxide containing compounds, benzophenone and benzophenone derivatives, acetophenone and acetophenone derivatives, benzoin ether derivatives and thioxanthones derivatives.

Therefore in a further preferred a printing formulation, the initiator is chosen from the group consisting of peroxide or peroxide containing compounds, benzophenone and benzophenone derivatives, acetophenone and acetophenone derivatives, benzoin ether derivatives and thioxanthones derivatives.

Further suitable initiators are α-hydroxyketone, phenylglyoxylate, benzyldimethyl-ketal, α- aminoketone, mono acyl phospine, bis acyl phosphine, phosphine oxide, metallocene, iodinum salts.

Such initiators are well known and are available for examples from BASF (Lucricin^®) or Ciba Specialty Chemicals (IRGACURE^® range: IRGACURE^® 184, IRGACURE^® 500, IRGACURE^® 2959, IRGACURE^® 754, IRGACURE^® 651 , IRGACURE^® 369, IRGACURE^® 907, IRGACURE^® 1300, IRGACURE^® 819, IRGACURE^® 819DW, IRGACURE^® 2022, IRGACURE^® 2100, IRGACURE^® 784, IRGACURE^® 250 as well as the DAROCUR^® range: DAROCUR^® 1173, DAROCUR^® MBF, DAROCUR^® TPO and DAROCUR^® 4265).

Such initiators are used in an amount of 0.005wt-% - 10wt-%, based on the total weight of the printing formulation. Preferably, initiators are present in an amount of 0.01 - 8 wt-%, based on the total weight of the printing formulation.

Therefore a printing formulation (PF III) used in the present invention comprises (i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, and (ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and (iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent.

Therefore, a printing formulation (PF Ilia) used in the present invention comprises

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and

(ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and

(iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and

(iva) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation of water, and

(ivb) optionally 0.1 wt-% and 89.99 wt-%, based on the total weight of the formulation of at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products.

Therefore, another printing formulation (PF Ilia') used in the present invention comprises (i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and

(ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material chosen from the group consisting of polyester, vinylester, epoxy, phenolic, cyanate ester, polyurethane, bismaleimide, polyimide, epoxy acrylate, polyurethane acrylate, polyester acrylate, acrylated polyol and acrylated polyether compounds, and

(iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator chosen from the group consisting of peroxide or peroxide containing compounds, benzophenone and benzophenone derivatives, acetophenone and acetophenone derivatives, benzoin ether derivatives, thioxanthones derivatives α- hydroxyketone, phenylglyoxylate, benzyldimethyl-ketal, α-aminoketone, mono acyl phospine. bis acyl phosphine, phosphine oxide, metallocene, iodinum salts, and (iva) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of water, and

Therefore, yet another printing formulation (PF INb) used in the present invention comprises.

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and

(ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and (iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products.

Therefore, yet another printing formulation (PF INb') used in the present invention comprises

(iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator chosen from the group consisting of peroxide or peroxide containing compounds, benzophenone and benzophenone derivatives, acetophenone and acetophenone derivatives, benzoin ether derivatives, thioxanthones derivatives α- hydroxyketone, phenylglyoxylate, benzyldimethyl-ketal, α-aminoketone, mono acyl phospine. bis acyl phosphine, phosphine oxide, metallocene, iodinum salts, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products.

Most preferred are formulations which comprise water (pure aqueous as well as water/solvent-mixtures), at least one curing agent and at least one photoinitiator (for light, UV or IR). The monodisperse particles of printing formulations (PF III), (PF Ilia), (PF Ilia'), (PF 1Mb) and (PF 1Mb') deviate less than 10% in root mean square (rms) diameter, preferably less than 5% in rms diameter and they have a diameter from 150nm to 900nm, preferably from 150nm to 800nm, more preferably the diameter of the monodisperse particles is from about 200nm to about 550nm.

All the preferences for the components (i), (ii), (iii), (iv), (iva) and (ivb) regarding the compounds and the amount which are disclosed above can all be applied to these formulations (PF III), (PF Ilia). (PF Ilia'). (PF INb) and (PF INb').

Additionally a printing formulation can comprise further auxiliaries. Such auxiliaries are these commonly used in the field of printing.

Auxiliaries are those additional chemicals which are used along with the dyes, to fix the dyes to the fabric or otherwise improve our results of the printing process. Furthermore, under the term auxiliaries is to be understood the chemicals, which help to improve the property of the formulation itself, such as storage, better manipulability of the formulation, etc.

Examples of auxiliaries are for examples pigments (such as titanium dioxide or carbon black), fillers (such as barytes, calcite, mica, talc, whiting, and wollastonite), extenders, (such as aluminum silicate), degassing agents, dry flow agents, flow agents (such as polyacrylates, silicones, surfactants, and fluorinated alkyl esters), matting agents, texturing agents, rheological additives, coalescence agents and waxes.

Such auxiliaries are usually present in a smaller amount, which can go up to about 10 wt- %, based on the total weight of the printing formulation.

If one or more auxiliaries are present the amount goes usually from 0.1 wt-% to 10 wt-%.

Therefore a further embodiment of the present invention relates to a printing formulation as described above comprising additionally at least one auxiliary.

Therefore another printing formulation (PF IV) used in the present invention comprises (i) monodisperse particles, and (ii) at least one curing material, and (iii) at least one initiator, and (iv) at least one solvent, and (v) at least one auxiliary.

Therefore another a printing formulation (PF V) used in the present invention comprises

(i) monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co-butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and

(ii) at least one curing material, and (iii) at least one initiator, and

(iv) at least one solvent, and

(v) at least one auxiliary.

Therefore another printing formulation (PF Vl) used in the present invention comprises (i) monodisperse particles, and

(ii) at least one curing material, and (iii) at least one initiator, and (iv) at least one further solvent, and

(v) at least one auxiliary chosen from the group consisting of pigments (such as titanium dioxide or carbon black), fillers (such as barytes, calcite, mica, talc, whiting, and wollastonite), extenders, (such as aluminum silicate), degassing agents, dry flow agents, flow agents (such as polyacrylates, silicones, surfactants, and fluorinated alkyl esters), matting agents, texturing agents, rheological additives, coalescence agents and waxes.

Therefore another printing formulation (PF VII) used in the present invention comprises

(i) monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co-butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂,

Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and (ii) at least one curing material, and (iii) at least one initiator, and

(iv) at least one further solvent, and

Another printing formulation (PF VIII) used in the present invention comprises

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, and (ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and (iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent, and

(v) 0.1 wt-% to 10 wt-%, based on the total weight of the formulation, of at least one auxiliary.

Another printing formulation (PF IX) used in the present invention comprises

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and (ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and (iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent, and (v) 0.1 wt-% to 10 wt-%, based on the total weight of the formulation, of at least one auxiliary.

Another printing formulation (PFX) used in the present invention comprises

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, and (ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and (iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one further solvent, and

(vi) 0.1 wt-% to 10 wt-%, based on the total weight of the formulation, at least one auxiliary chosen from the group consisting of pigments (such as titanium dioxide or carbon black), fillers (such as barytes, calcite, mica, talc, whiting, and wollastonite), extenders, (such as aluminum silicate), degassing agents, dry flow agents, flow agents (such as polyacrylates, silicones, surfactants, and fluorinated alkyl esters), matting agents, texturing agents, rheological additives, coalescence agents and waxes.

Another printing formulation (PF Xl) used in the present invention comprises

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and (ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material, and (iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator, and (iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent, and (v) 0.1 wt-% to 10 wt-%, based on the total weight of the formulation, of at least one auxiliary chosen from the group consisting of pigments (such as titanium dioxide or carbon black), fillers (such as barytes, calcite, mica, talc, whiting, and wollastonite), extenders, (such as aluminum silicate), degassing agents, dry flow agents, flow agents (such as polyacrylates, silicones, surfactants, and fluorinated alkyl esters), matting agents, texturing agents, rheological additives, coalescence agents and waxes.

Another printing formulation (PF XIa) used in the present invention comprises

(i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂, Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and (ii) 0.01 wt-% to 15wt-%, based on the total weight of the formulation, of at least one curing material chosen from the group consisting of polyester, vinylester, epoxy, phenolic, cyanate ester, polyurethane, bismaleimide, polyimide, epoxy acrylate, polyurethane acrylate, polyester acrylate, acrylated polyol and acrylated polyether compounds, and

(iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator chosen from the group consisting of peroxide or peroxide containing compounds, benzophenone and benzophenone derivatives, acetophenone and acetophenone derivatives, benzoin ether derivatives, thioxanthones derivatives α- hydroxyketone, phenylglyoxylate, benzyldimethyl-ketal, α-aminoketone, mono acyl phospine. bis acyl phosphine, phosphine oxide, metallocene, iodinum salts, and (iva) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of water, and (ivb) optionally 0.1 wt-% and 89.99 wt-%, based on the total weight of the formulation of at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products, and (v) 0.1 wt-% to 10 wt-%, based on the total weight of the formulation, of at least one auxiliary chosen from the group consisting of pigments (such as titanium dioxide or carbon black), fillers (such as barytes, calcite, mica, talc, whiting, and wollastonite), extenders, (such as aluminum silicate), degassing agents, dry flow agents, flow agents (such as polyacrylates, silicones, surfactants, and fluorinated alkyl esters), matting agents, texturing agents, rheological additives, coalescence agents and waxes.

Another printing formulation (PF XIb) used in the present invention comprises (i) 0.01 wt-% to 70 wt-%, based on the total weight of the formulation, of monodisperse particles, chosen from the group consisting of organic polymer particles such as latex, acrylic, polystyrene, polyvinyl acetate), polyacrylonitrile, poly(styrene-co- butadiene), polyester, polyamides, polyurethane, poly(methylmethacrylate) and poly(fluoromethylmethacrylate) particles; inorganic materials such as metal chalcogenide, metal pnictide, silica, metal (such as gold, copper and silver) and metal oxide particles (such as AI₂O₃, TiO₂, SnO₂,

Sb₂O₅, Fe₂O₃, ZrO₂, CeO₂ and Y₂O₃), and

(iii) 0.005wt-% to 10wt-%, based on the total weight of the formulation, of at least one initiator chosen from the group consisting of peroxide or peroxide containing compounds, benzophenone and benzophenone derivatives, acetophenone and acetophenone derivatives, benzoin ether derivatives, thioxanthones derivatives α- hydroxyketone, phenylglyoxylate, benzyldimethyl-ketal, α-aminoketone, mono acyl phospine. bis acyl phosphine, phosphine oxide, metallocene, iodinum salts, and

(iv) 10 wt-% and 99.99 wt-%, based on the total weight of the formulation, of at least one solvent, chosen from the group consisting of alcohols, esters, ketones, ethers and aliphatic and aromatic hydrocarbons having at least six carton atoms and mixtures thereof including refinery distillation products and by-products, and (v) 0.1 wt-% to 10 wt-%, based on the total weight of the formulation, of at least one auxiliary chosen from the group consisting of pigments (such as titanium dioxide or carbon black), fillers (such as barytes, calcite, mica, talc, whiting, and wollastonite), extenders, (such as aluminum silicate), degassing agents, dry flow agents, flow agents (such as polyacrylates, silicones, surfactants, and fluorinated alkyl esters), matting agents, texturing agents, rheological additives, coalescence agents and waxes.

The monodisperse particles of printing formulations (PF IV), (PF V), (PF Vl), (PF VII), (PF VIII), (PF IX), (PF X), (PF Xl), (PF XIa) and/or (PF XIb) deviate less than 10% in root mean square (rms) diameter, preferably less than 5% in rms diameter and they have a diameter from 150nm to 900nm, preferably from 150nm to 800nm, more preferably the diameter of the monodisperse particles is from about 200nm to about 550nm.

As already mentioned the printing formulation can be in any suitable physical form. Usually it is in the form of a liquid, a gel or a paste.

It is to be said as well once again that the water content and the content of the monodisperse particles can vary dependent whether a concentrated formulation or a ready to use (diluted) formulation is provided.

The invention also relates to the use of a formulation (PF I), (PF Ia), (PF Ib), (PF II), (PF Na), (PF III), (PF Ilia), (PF Ilia'), (PF INb), (PF INb'), (PF IV), (PF V), (PF Vl), (PF VII), (PF

VIII), (PF IX), (PF X). (PF Xl), (PF XIa) and/or (PF XIb) for printing a substrate, which method comprises contacting the substrate with a composition comprising monodisperse particles capable of forming a colloidal crystal that diffracts light having a wavelength in a range that corresponds to the wavelength of visible light, such that colloidal crystals comprising the monodisperse particles form on the substrate.

The substrate is preferably exposed to light (400 nm - 800nm) and/or UV-light (100 nm - 400 nm) and/or IR (800nm -1400nm) during the application of the printing formulations as described above and/or afterwards. In the above applications, it is sufficient for a single layer of colloidal crystals to form on the substrate. However, it is preferred that at least two or three layers of colloidal crystals are formed. The coverage of colloidal crystalline layers need not be complete i.e. it can be a discontinuous layer. Depending on the substrate, which may be porous, colloidal crystals may form on the surface of, and/or within, the substrate. Further, the crystalline layer or layers need not be entirely regular, provided that the desired colour effects are achieved. In other words some crystal disorder is permitted.

Examples of printing formulations

Preparation of ink compositions

Several Ink compositions were prepared, comprised of silica-particles dispersed in ready to use base materials, which are commercial available.

Synthesis of silica-particles

Monodispersed silica spheres were prepared following the well-known process by Stober, Fink and Bohn (J. Colloid Interface Sci. 1968, 26,62), as refined by Bogush, et. al. (J. Non-Crys. Solids 1988, 104, 95).

Briefly, the spheres were produced by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous-ammoniacal medium, a sol of primary particles being produced first of all and then the SiC>₂ particles obtained being brought to the desired particle size by continuous, controlled addition of tetraalkoxysilane (see US Patent No. 4,775,520). The final particle size obtained depends on the quantity of tetraalkoxysilane added in total. With this process it is possible to produce monodisperse SiC>₂ spheres having average particle diameters of between 0.05 and 10 μm with a standard deviation of less than 7%. This procedure was used to prepare monodisperse silica spheres have average particle diameters of 250 nm, 330 nm, 410 nm or 500 nm.

The samples were then purified using the following method: The dispersion was centrifuged at 3000 rpm for 20 minutes to separate the solid from the liquid. The solid was redispersed in anhydrous ethanol to the original volume by mechanical stirring and ultrasonic treatment. This procedure was repeated several times. The dispersion so prepared was then centrifuged and dried out, resulting a white powder, comprised of silica spheres and was used from now on as the solid component for following ink compositions.

Example C

Silica colloids in Clear Size base solution (Vitalac 710^®; ICI Packaging Coatings)

This solvent-base ink composition, when applied to a substrate, especially black substrate forms a writing of iridescent metallic blue, which changes to green at a far viewing angle when using colloids of 250nm.

Example D

Silica colloids in Overprint Varnish solution (Aquabase 105^®; ICI Packaging Coatings)

This water-base ink composition, when applied to a substrate, especially black substrate forms a writing of iridescent metallic blue, which changes to metallic green at a far viewing angle when using colloids of 250nm. The films are stable, when applying mechanical force compared to systems of the prior art (e.g. US20050137283 A1 ) without having epoxy resin incorporated.

Both experiments show that colourless colloids can be dispersed into both, solvent base and water base systems and show colour without the presence of carbon black when applied onto a substrate and in addition providing stability when curing agents are present in the liquid phase.

Example E

Silica colloids in Overprint Varnish in waterborne UV resin LUX 3381 (Solvent-free UV- curable polyurethane-acrylic dispersion from ALBERDI NGK^®).

This water-based UV-curable polyurethane-acrylic ink composition, when applied to a substrate, especially black substrate forms a writing of iridescent metallic blue, which changes to metallic green at a far viewing angle when using colloids of 250nm. The films are stable, after pre-drying of 5-10 min at 5OC under normal light, but more stable after exposure to efficient UV lamps, usually medium pressure mercury lamps of at least 80 W/cm. (Hg 80 W/cm), is required. When applying mechanical force the printing obtained by using formulation according to the present patent application are better than those of the prior art (e.g. US20050137283 A1 ) without waterborne UV activated resin incorporated.

Example F

Silica colloids in Overprint Varnish in waterborne UV resin LUX 285 (Solvent-free UV- curable polyurethane-acrylic dispersion from ALBERDI NGK^®).

This water-based UV-curable polyurethane-acrylic ink composition, when applied to a substrate, especially black substrate forms a writing of iridescent metallic blue, which changes to metallic green at a far viewing angle when using colloids of 250nm. The films are stable, after pre-drying of 5-10 min. at 5OC, but more stable after exposure to efficient UV lamps, usually medium pressure mercury lamps of at least 80 W/cm. (Hg 80 W/cm), is required.

When applying mechanical force the printing obtained by using formulation according to the present patent application are better than those of the prior art (e.g. US20050137283 A1 ) without waterborne UV activated resin incorporated.

The following examples described the present invention Example 1 Multilayer Colourant Composition:

In this example a layered structure was produced consisting of:

. Top transparent layer . Intermediate colloidal ink layer . PVC substrate with Pressure sensitive adhesive obtainable form 3M

0.5 g of this water-based UV-curable polyurethane-acrylic ink composition was applied to a clear, white or coloured PVC Pressure sensitive (PS) Adhesive from 3M Block out film by a k-bar coater (bar no.2) and was drawn down over the substrate at a constant speed in order to produce a thin film.

The Intermediate colloidal ink layer had the following composition

The produced layers, especially on black substrate forms a writing of iridescent metallic blue, which changes to metallic green at a far viewing angle when using colloids of 250nm. The films are stable, after pre-drying of 5-10 min. at room temperature and further 5-10min @ 50⁰C, but more stable after exposure to efficient UV lamps, usually medium pressure mercury lamps of at least 80 W/cm. (Hg 80 W/cm), is required.

A protected Top-coat was applied by a subsequent bar coating, spraying or laminating step. Example 2 Multilayer Colourant Composition with an artwork printed Top-Coat

Similar to example 1 , but the top layer has a print. The print can be on top of the layer or on the side facing the colloidal ink layer.

Example 3 a)

Multilayer Colourant Composition with controlled adhesion

In the is example an adhesive film was applied on a substrate.

An adhesive film of following composition was applied on a wide range of plastics white, clear or coloured materials, including PE, PET or PVC and left to dry for min. 10min at 50⁰C. The adhesive is comprised of following composition:

Colloidal layers were prepared according to example 1. The final structure can be visualised in the SEM and shows clearly the adhesion of colloidal layers on the adhesive film.

The produced layers, especially on black substrate forms a writing of iridescent metallic blue, which changes to metallic green at a far viewing angle when using colloids of 250nm. The visual perception is influenced by the tackiness of the adhesive and drying speed of the colloidal ink formulation. SEM characterisation reveals mud cracks of dimensions of about 30-50μm.

Example 3b

An adhesive film was prepared similar to example 3a with following composition:

The optical appearance was improved compared to sample from example 3a. In the SEM less cracks can be observed with larger dimensions ca. 100-150μm.

Smoother film (less defects) leads to better visual perception. Larger Cracks leads to black contrast agent from substrate shows through

Claims

1. Multilayered colouring composition comprising an ink formulation on a substrate, the ink formulation comprising monodisperse particles wherein an adhesive layer is located between the ink formulation and the substrate.

2. Multilayered colouring composition wherein the adhesive layer is is a pressure sensitive substrate, or an adhesive bonding primer or an adhesion promoter.

3. Multilayered colouring composition according to claim 1 or 2 wherein a top coat is located on top of the ink formulation.

4. Multilayered colouring composition according to claim 3 wherein printings are located on at least one of the top coat sides.

5. Process for manufacturing a multilayered colouring composition comprising the steps of:

1 ) providing a substrate with an adhesive layer

2) depositing colloidal ink onto the adhesive layer

6 Process according to claim 5 wherein a top coat is applied onto the colloidal ink.