GB2613776A

GB2613776A - Compositions and method and uses relating thereto

Info

Publication number: GB2613776A
Application number: GB2117368.7A
Authority: GB
Inventors: Guhl Dieter; Bedford David; Ward Angus
Original assignee: Keeling and Walker Ltd; Inovink Ltd
Current assignee: Keeling and Walker Ltd; Inovink Ltd
Priority date: 2021-12-01
Filing date: 2021-12-01
Publication date: 2023-06-21
Also published as: GB202117368D0

Abstract

An article is disclosed which comprises a substrate which carries a reduced tungsten oxide-based pigment wherein said reduced tungsten oxide-based pigment is encapsulated. The article may be a banknote, and the encapsulated tungsten oxide pigment may be printed on the substrate in the form of an ink to form a security image with improved laundry durability. The encapsulating agent may be selected from synthetic or natural waxes, alginic acid and salts thereof, polysaccharides, maltodextrines, collagen chitosan, lecithines, gelatine, modified and unmodified starches, cellulose ester and ethers, phenol formaldehyde resins, polyurethanes, polyelectrolyte multilayer agents and mixtures thereof.

Description

Compositions and method and uses relating thereto The present invention relates to articles comprising a security feature and to uses and compositions relating thereto.

The invention relates especially to banknotes and to the use of infra-red absorbing pigments as a security feature on banknotes.

In particular the invention relates to articles such as banknotes comprising reduced tungsten oxide based pigments and to methods of improving the stability of security features provided by such pigments.

Reduced tungsten oxide based pigments are often used for their infrared absorbing properties. For example caesium tungstate, Cs033W03, is a well known infrared absorbing compound.

Modified caesium tungstate compounds in which a proportion of the caesium and/or tungsten and/or oxygen atoms are replaced in the lattice are also known and many have infrared absorbing properties. It is further known to incorporate additional atoms or groups of atoms into the caesium tungstate structure. Many materials of this type are also known to have infrared absorbing properties. For example compounds of formula M1aM2bWoOd(P(0),,R0e, wherein each of MI and M2 is independently ammonium or a metal cation; a is 0.01 to 0.5; b is 0 to 0.5; c is 1; d is 2.5 to 3; e is 0.01 to 0.75; n is 1, 2 or 3; m is 1, 2 or 3; and R is an optionally substituted hydrocarbyl group, described by the applicant in W02020/058700, are highly effective infrared absorbing pigments.

Caesium tungstate derived pigments find utility in a number of applications in view of their infrared absorbing properties. The present invention relates in particular to the use of such materials as security features on articles such as banknotes.

Security features on banknotes need to be durable to heat, light, water, chemicals and mechanical impact, abrasion and wear and tear. They must be durable to laundering and to UV light from sunlight. Many reduced tungsten oxide based pigments can provide most or all of these properties. However it has been found that security images printed with some ink compositions comprising caesium tungstate derived pigments on occasions fail harsh laundry stability tests.

It is therefore an aim of the present invention to provide security articles having improved laundry stability.

According to a first aspect of the present invention there is provided an article comprising a substrate which carries a reduced tungsten oxide based pigment wherein said reduced tungsten oxide based pigment is encapsulated.

The present invention relates to a reduced tungsten oxide based pigment which has been encapsulated. This will be referred to herein as the encapsulated reduced tungsten oxide based pigment.

The present invention relates to an article comprising a substrate which carries a encapsulated reduced tungsten oxide based pigment.

The article may be selected from packaging, for example for pharmaceuticals; a label, for example for expensive or designer goods; an identification document, for example a passport, ID card or driving licence; a credit card or other bank card; a ticket or voucher, for example for events or travel; or a certificate, for example a share certificate or stamp certificate.

Most preferably the article is a banknote.

The article comprises a substrate. Preferably the substrate is a sheet substrate, preferably a planar sheet substrate. The substrate may be made from any suitable material. Suitable materials will be known to the person skilled in the art and include for example paper, cardboard, textiles and plastics materials.

In preferred embodiments in which the article is a banknote the substrate is selected from paper, a polymer or a mixture thereof. A preferred paper is banknote paper and preferred polymers include biaxially oriented polypropylene and extruded polypropylene. Other suitable papers and polymers will be known to the person skilled in the art.

The substrate carries a encapsulated reduced tungsten oxide based pigment. By this we mean that the encapsulated reduced tungsten oxide based pigment is retained within or on the surface of the substrate. In some embodiments the encapsulated reduced tungsten oxide based pigment may be held within the body of the substrate, for example dispersed throughout the substrate. For example it may have been mixed within the raw ingredients used to make the substrate. In some embodiments the encapsulated reduced tungsten oxide based pigment may be incorporated in a thread woven into the substrate. In some embodiments the encapsulated reduced tungsten oxide based pigment may be in a coating on some or all of the substrate, on one or both planar surfaces of the substrate. In some embodiments the encapsulated reduced tungsten oxide based pigment may have been printed onto the substrate, on one or both planar surfaces of the substrate. In some embodiments the encapsulated reduced tungsten oxide based pigment may be incorporated only into one portion of the substrate. For example where a banknote includes a window, for example of a substantially transparent polymer, the encapsulated reduced tungsten oxide based pigment may only be present on the window portion or the non window portion.

Preferably the encapsulated reduced tungsten oxide based pigment is carried on the surface of the substrate. It may be present as a coating or a printed image. Suitably it may be printed in the form of a security image.

In preferred embodiments of the present invention the article is a banknote and the encapsulated reduced tungsten oxide based pigment provides a security image on a surface of the banknote.

The present invention relates to a encapsulated reduced tungsten oxide based pigment. By a reduced tungsten oxide based pigment we mean to include any pigment which comprises and/or is derived from a reduced tungsten oxide material. For the avoidance of doubt reference to a reduced tungsten oxide is to a tungsten (VI) oxide (W03) which has been partially reduced tungsten oxide has the chemical formula W03 wherein x is 0.01 to 1. The material typically shows a cubic, triclinic, tetragonal, orthorhombic or hexagonal crystal structure or mixtures thereof Hexagonal materials are preferred.

By reduced tungsten oxide based pigment we mean to include reduced tungsten oxide and any pigment which is derived therefrom for example by adding, removing and/or replacing one or more atomsand/or or ions in the structure. In some embodiments a proportion of the tungsten atoms in the lattice may be replaced by one or more different metals, for example one or more transition metals or rare earth metals. In some embodiments the reduced tungsten oxide based pigment may be a composite tungsten oxide of formula MA4/0y where M is one or more elements selected from Cs, Rb, K, TI, In, Ba, Li, Ca, Sr, Fe, Sn, Al, Cu, Bi, Zn and Na, 0.1 s x S0.5, and 2.2 S y S3.0. Such compounds are known in the art and are described, for example, in EP3318610.

In some embodiments the reduced tungsten oxide based pigment is a reduced tungsten oxide of formula W03 wherein x is 0.01 to 1. Preferably x is 2.2 to 2.92, preferably from 2.6 to 2.8, more preferably from 2.7 to 2.75, for example about 2.72.

Preferred reduced tungsten oxide based pigments include those exhibiting Magneli phases and materials described in W02012/146749 and W02018/203026.

Preferably the reduced tungsten oxide based pigment is an alkali metal tungstate or a derivative thereof. Preferred compounds of formula MxWOy wherein M is Cs or Rb, x is 0.2 to 0.4 and y is 2.6 to 3.

Preferably the reduced tungsten oxide based pigment is caesium tungstate or a derivative thereof.

One preferred reduced tungsten oxide based pigment is Cs0.33W029.

Most preferably the reduced tungsten oxide based pigment is a compound of formula (I) !Vila M2bWcOd(P (0)n Rrn)e (I) wherein each of MI and M2 is independently ammonium or a metal cation; a is 0.01 to 0.5; b is 0 to 0.5; c is 1; d is 2.5 to 3, e is 0.01 to 0.75; n is 1, 2 or 3; m is 1, 2 or 3, and R is an optionally substituted hydrocarbyl group.

Each of MI and M2 is suitably present as a cationic species. Each of MI and M2 is selected from ammonium or a metal cation.

MI is preferably a metal cation selected from the group consisting of alkali metals, alkaline earth metals, group 13 metals, group 14 metals and first or second row d-block metals.

Preferably MI is selected from ammonium, alkali metals, zinc and tin. More preferably MI is selected from ammonium, potassium, sodium, caesium, rubidium, zinc and fin. Most preferably MI is an alkali metal, especially caesium.

M2 is preferably a metal cation selected from the group consisting of alkali metals, alkaline earth metals, group 13 metals, group 14 metals and first or second row d-block metals.

Preferably M2 is selected from alkali metals, alkaline earth metals, zinc and tin. More preferably M2 is selected from alkali metals, zinc and tin. Most preferably M2 is selected from sodium, potassium, zinc and tin.

M2 may comprise a mixture of two or more metals.

Preferably MI is caesium and M2 is not caesium.

Preferably M1 is caesium and M2 is selected from the group consisting of alkali metals, zinc and tin In one embodiment M1 is caesium and M2 is sodium.

In one embodiment M1 is caesium and M2 is zinc.

In one embodiment M1 is caesium and M2 is tin.

In one especially preferred embodiment M1 is caesium and M2 is potassium.

a is from 0.01 to 0.5. Preferably a is from 0.1 to 0.45. Most preferably a is from 0.22 to 0.4.

b is from 0 to 0.5. Preferably b is from 0.001 to 0.4, or from 0.005 to 0.3. Suitably from 0.0075 to 0.25, for example from 0.01 to 0.2.

The sum of a and b is preferably from 0.1 to 0.6, preferably from 0.2 to 0.4, more preferably from 0.3 to 0.35.

d is from 2.5 to 3. Preferably d is from 2.6 to 3. Most preferably d is from 2.7 to 3.

e is 0.01 to 0.75.

Preferably e is from 0.01 to 5, more preferably from 0.02 to 0.4, suitably from 0.03 to 0.4, for example from 0.05 to 0.25.

In one preferred embodiment e is from 0.06 to 0.1.

n may be 1,2 or 3.

Preferably n is 2 or 3. Most preferably n is 3.

m may be 1, 2 or 3.

Preferably m is 1 or 2. Most preferably m is 1.

When m is more than 1 each R may be the same or different. References herein to R apply independently to each R in such embodiments. However in preferred embodiments each R is the same.

R is an optionally substituted hydrocarbyl group.

Preferably R is an optionally substituted alkyl, alkenyl, aryl, aralkyl, alkaryl group or an alkoxy containing group.

Preferably R is an unsubstituted alkyl, alkenyl, aryl, aralkyl or alkaryl group or an alkoxy containing group. Preferably R is selected from alkyl groups, aryl groups, aralkyl groups and alkoxy or phenoxy containing groups.

Suitable alkoxy containing groups include alkoxylated alkyl groups, polyalkoxylated alkyl groups, alkoxylated alcohols and polyalkoxylated alcohols.

Preferred alkoxy containing groups are polyalkoxylated alcohols especially moieties derived from ethylene oxide and/or propylene oxide. Especially preferred alkoxy containing groups are polyethylene glycol (PEG) or polypropylene glycol (PPG) groups having a number average molecular weight from 50 to 2500, more preferably from 50 to 1000, most preferably from 50 to 400.

In some embodiments R is an aryl group. Suitable aryl groups may comprise one or more aromatic rings. In some embodiments R may be naphthyl.

Suitable aryl groups include heterocyclic aryl groups. Preferred aryl groups have 5 to 7 carbon atoms and optionally contain one or more heteroatoms for example N, S or 0.

Preferred aryl groups are phenyl and substituted phenyl groups.

In some embodiments R may be OAr where Ar is an aryl group. For example R may be phenoxy.

Suitable substituents include one or more alkyl and/or alkoxy containing groups. Preferred substituents include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonayl, and isomers thereof; derivatives of poly(isoprene) and poly(isobutylene) and polyalkoxylated alcohols especially moieties derived from ethylene oxide and/or propylene oxide. Some preferred substituents when R is phenyl are isohexyl, isoheptyl and isononyl.

In some embodiments R may be toluol or xylol.

In some embodiments R is an unsubstituted aryl group. In one preferred embodiment R is phenyl In some embodiments R is an optionally substituted alkyl group.

Suitable substituents include halo, hydroxy, nitro, amino and alkoxy.

Preferred alkyl groups are unsubstituted.

Suitably R is an unsubstituted linear or branched alkyl group.

Suitably R is selected from an alkoxy group, a phenoxy group or an alkyl or aryl group having 1 to 36 carbon atoms.

Preferably R is an alkyl or aryl group having 1 to 36 carbon atoms, preferably 2 to 30 carbon atoms, more preferably 4 to 24 carbon atoms, suitably 6 to 20 carbon atoms.

In some embodiments R is an unsubstituted alkyl or aryl group having 4 to 24 carbon atoms.

In some embodiments R is an unsubstituted alkyl group having 8 to 18 carbon atoms.

In one preferred embodiment R is C8I-117.

In one preferred embodiment R is C18H37.

Most preferably R is selected from octyl, octadecyl and phenyl.

Phosphorus may be present in a +3 or +5 oxidation state. Most preferably phosphorus is present in a +5 oxidation state.

Preferably MI is caesium; M2 is selected from alkali metals, tin or zinc; a is 0.1 to 0.45; b is 0 to 0.3; c is 1; d is 2.7 to 3; e is 0.01 to 0.4; n is 2 or 3; m is 1 or 2 and each R is an unsubstituted alkyl or aryl group or an alkoxy group having 1 to 30 carbon atoms.

In some preferred embodiments, MI is caesium; M2 is selected from sodium, potassium, tin or zinc; a is 0.22 to 0.4; b is 0.01 to 0.2; c is 1; d is 2.7 to 3; e is 0.05 to 0.25; n is 2; m is 1 and R is an unsubstituted alkyl or aryl group having 6 to 20 carbon atoms.

B

In one preferred embodiment, M1 is caesium; M2 is potassium; a is 0.32; b is 0.01; c is 1; d is 2.9; e is 0.08; n is 2; m is 1 and R is C8I-117. Thus the material of formula (I) may be Cso 32K0 01W029(P(02)C8H17)0 08.

In one embodiment, M1 is caesium; M2 is potassium; a is 0.32; b is 0.01; c is 1; d is 2.9; e is 0.16; n is 2; m is 1 and R is phenyl. Thus the material of formula (I) may be Cso 32Ko olW02 0(P(02)C6H5)0.10* In one embodiment, M1 is caesium; M2 is potassium; a is 0.27; b is 0.05; c is 1 d is 2.9; e is 0.2; n is 2; m is 1 and R is C181-137. Thus the material of formula (I) may be Cso 27Ko 05W029(P(02)Ci8H37)0 2.

In one embodiment, MI is caesium; M2 is sodium; a is 0.32; b is 0.01; c is 1; d is 3; e is 0.2; n is 2; m is 1 and R is C18H37. Thus the material of formula (I) may be Cso 32Nao 01W03(P(02)CISH37)0 2.

In one embodiment, MI is caesium; M2 is tin; a is 0.22; b is 0.1; c is 1; d is 2.9; e is 0.16; n is 2; m is 1 and R is C18H37. Thus the material of formula (I) may be Cso 228 no IWO2 s(P (02)C18H340.16.

In one embodiment, MI is caesium; M2 is zinc; a is 0.12; b is 0.2; c is 1; d is 3; e is 0.16; n is 2; m is 1 and R is phenyl. Thus the material of formula (0 may be Cso.12Zno 2W03(P(02)CeHs)o.ie.

In some embodiments, b is 0 such that the material of formula (I) does not comprise M2. In such embodiments MI is caesium, a is 0.22 to 0.4; b is 0; c is 1; d is 2.7 to 3; e is 0.05 to 0.25; n is 2; m is 1 and R is an unsubsfituted alkyl or aryl group having 6 to 20 carbon atoms.

In one embodiment, M1 is caesium; a is 0.32; b is 0; c is 1; d is 2.72; e is 0.08; n is 2; m is 1 and R is C18H37. Thus the material of formula (I) may be Cso 32W02.72(P(02)Col-117)o oa.

In one embodiment, MI is caesium; a is 0.31; b is 0; c is 1; d is 2.9; e is 0.16; n is 2; m is 1 and R is phenyl. Thus the material of formula (I) may be Cso 31W02.9(P(02)CoHs)o.lo.

The present invention relates to a tungsten oxide based material. In preferred embodiments the material includes an organophosphorus moiety of formula W-O-P-OR or W-O-P-R.

By a moiety of formula W-O-P-OR or W-O-P-R, we mean that in the material of formula (I) includes a unit in which an oxygen atom which is coordinated to a tungsten atom in the crystal structure is also coordinated to a phosphorus atom, and this phosphorus atom is bonded either directly or via an oxygen atom to an optionally substituted hydrocarbyl group R. In especially preferred embodiments the reduced tungsten oxide based pigment is selected from Cs0.32Ko culA/02 9(P (02)C8H17)0.08, W02.72 and Cso 33W02 9.

The reduced tungsten oxide based pigment is encapsulated.

The reduced tungsten oxide based pigment may encapsulated with one or more encapsulating agents By encapsulated we mean that the pigment is surrounded by a encapsulating agent which covers the surface of the pigment Preferably the encapsulating agent covers the entire surface of the pigment.

In some embodiments the encapsulating agent may form an interaction with the surface of the pigment. Preferably the encapsulating agent does not change the chemical structure of the surface. Preferably the encapsulating agent does not form an interaction with the surface of the pigment. Suitably the interaction of encapsulating agent not change the infrared absorbing properties of the pigment.

Suitable encapsulating agents include natural and synthetic polymers and waxes.

Preferred encapsulation agents include synthetic or natural waxes, alginic acid and salts thereof, polysaccharides, maltodextrines, collagen chitosan, lecithines, gelantine, modified and unmodified starches, cellulose ester and ethers, phenol formaldehyde resins, polyurethanes, polyelectrolyte multilayer agents and mixtures thereof Suitable cellulose ester and ethers include ethylcellulose, hydroxypropylcellulose and 30 carboxymethylcellulose.

Suitable polyelectrolyte mulfilayer agents include those comprising polyacrylates and/or polyamides.

Mixtures of encapsulating agents can also be used. Particularly useful mixtures include combinations of cellulose a materials and alginate compounds; and mixtures of waxes with maltodextrin and starch.

Some suitable encapsulating agents are well known from the personal care and laundry industry and are used for protecting fragrance materials against the attack of other aggressive laundry components. DE19855347 or US 2008/0277812 show some examples of this technology.

Suitable polymeric encapsulating agents include polyvinylpyrrolidone, polyacrylates, polyvinylbenzylsulfonates polyvinylacetate, polyethyleneimines, polyvinylsulfonates, polyoxazolidone and polyvinylalcohols.

Further suitable polymeric encapsulating agents include polymeric materials comprising one or more oxygenated functional groups, for example a polyester or a derivatised polyester.

In some embodiments the encapsulating agent is a polymer comprising ester functional groups. In some embodiments the encapsulating agent is a polymeric material comprising ester functional groups and amino functional groups.

Suitably the encapsulating agent may be a polyacrylic or methacrylic acid ester or a copolymer of acrylic, methacrylic acid esters, wherein the ester groups are formed from alcohols selected form polyethylene glycols, polypropylene glycols, fatty acid alcohols or fatty acid amines or 20 phosphates.

Some preferred encapsulation agents include waxes spheres, alginate / cellulose combinations or phenol formaldehyde resins and polyurethanes.

Preferably the encapsulation agent is selected from synthetic or natural waxes, alginic acid and salts thereof, cellulose ester and ethers, phenol formaldehyde resins, polyurethanes, polyelectrolyte multilayer agents and mixtures thereof.

Especially preferred are encapsulation agents comprising synthetic or natural waxes and/or alginic acid or salts thereof Most preferably the encapsulation agent comprises an alginate salt, especially calcium alginate.

Encapsulation of the reduced tungsten oxide based pigment may be carried out by standard methods. Such methods will be known to the person skilled in the art.

Typical and preferred procedures for microencapsulation of pigments are based on emulsification, dispersion or coaceivafion procedures. Such procedures are well known to the skilled person.

For example encapsulation of the reduced tungsten oxide based pigment with alginates may be achieved by dissolving the water soluble sodium alginate in deionized water to obtain a transparent solution and then adding the pigment particles slowly to the solution whilst stirring, until a homogeneous dispersion has been obtained. An alginate layer will form on the surface of the reduced tungsten oxide based pigment if it has an acidic surface. A hardening and complete encapsulation of the pigment is achieved upon addition of a dilute solution of calcium salts to the dispersion to provide insoluble calcium alginate covering the surface of the pigment particles. The treated pigment particles are recovered from the dispersion by filtration and dried under mild conditions.

In an another embodiment the powdered pigment and wax powder having a melting point below 80°C may be dispersed with a high speed mixer in water. A homogeneous dispersion of maltodextrin and modified starch in water are suitably formulated in a separate reactor into which the pigment / wax dispersion is fed. The components are mixed for a short period and then spray dried with hot air a temperature above 85°C to provide an encapsulated reduced tungsten oxide based pigment.

In some embodiments the encapsulated reduced tungsten oxide based pigment is present in a coating on the surface of the substrate. The coating may be provided in the form of an ink, varnish or as a polymeric film. For the avoidance of doubt this coating is not the encapsulating agent which is on the pigment. Particles of the reduced tungsten oxide based pigment which are encapsulated are incorporated into a coating composition which is used to coat the substrate.

In preferred embodiments the encapsulated reduced tungsten oxide based pigment forms a printed image or coating on the substrate. Preferably the encapsulated reduced tungsten oxide based pigment is present in a security image which has been printed onto the substrate.

Suitably the encapsulated reduced tungsten oxide based pigment is printed onto the substrate using an ink composition. The ink composition is suitably a solution or suspension comprising the encapsulated reduced tungsten oxide based pigment and one or more further components.

The nature of the other components of the ink composition will depend on the printing process in which it is to be used. The formulation of a suitable ink composition is within the competence of the person skilled in the art.

Preferably the reduced tungsten oxide based pigment is incorporated into a coating composition or an ink composition in the form of a powder which has been encapsulated In some embodiments the reduced tungsten oxide based pigment may be provided as nanoparticles.

Preferably the particles of the reduced tungsten oxide based pigment before being encapsulated have an average diameter of 0.01 to 10 microns, preferably 0.1 to 0.5 microns, for example about 0.2 to 0.3 microns.

Particle size may be measured by any suitable method. For example, any of the methods described in PAS 71:2005 published by British Standards could be used. Preferred methods for the determination of particle size include TEM (Transmission Electron Microscopy, when particles are made of a material that has high contrast with a carbon TEM grid), SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy).

When encapsulated with a single encapsulating agent, the encapsulated reduced tungsten oxide based pigment particles have an average particle size of 0.05 to 500 microns, preferably 0.1 to 100 microns, more preferably 0.2 to 10 microns, for example 1 to 5 microns.

Preferably the encapsulated reduced tungsten oxide based pigment is printed onto the substrate using an ink composition. In some embodiments the ink composition may be an aqueous composition. In some embodiments the ink composition may be an oleophilic composition. In some embodiments the ink composition may be a solvent based composition.

The selection of an aqueous based ink composition or an oleophilic based ink composition depends on how the ink is intended to be applied to the substrate. The choice of a suitable base ink composition will be within the competence of the person skilled in the art.

The base ink composition may be suitable for any type of printing, for example offset printing (including lithographic), gravure, intaglio printing, letterpress printing, ink-jet printing and screen printing.

Aqueous ink compositions are typically used in screen printing and inkjet printing.

Oleophilic compositions are preferred for offset printing (including lithographic), gravure printing, intaglio printing and letterpress printing. They can also be used in inkjet printing.

In inkjet printing the ink composition may have an organic solvent base. Suitable organic solvents include acetone and other ketones, for example methyl ethyl ketone.

For some applications monomer based inks may be used, for example acrylic inks.

Rubber based inks may be used in lithographic, offset, letterpress and screen printing.

In preferred embodiments the ink composition of the present invention is an oleophilic composition.

When the composition is an oleophilic composition the major component of the ink may be an oil, for example linseed oil. Other components typically present in printing inks will be known to the person skilled in the art.

The encapsulated reduced tungsten oxide based pigment is preferably present in the ink composition in an amount of at least 0.1 wt%, preferably at least 1 wt%, more preferably at least 2 wt%.

The encapsulated reduced tungsten oxide based pigment may be present in a composition in an amount of up to 50 wt%, suitably up to 30 wt%, for example up to 20 wt% or up to 15 wt%.

The ink composition may comprise one or more further components for example varnishes, cosolvents, preservatives, drying agents, fragrances, thickeners, waxes and emulsifiers. Other suitable components will be known to the person skilled in the art.

In some embodiments the ink composition may comprise one or more further pigments and/or dyes.

In some embodiments there may be no further pigments or dyes present in the composition.

The ink composition may be coated onto the substrate by dipping, spraying, painting or rolling.

In some embodiments the encapsulated reduced tungsten oxide based pigment may be incorporated into a polymer melt composition or other composition which is painted, dipped or sprayed onto the substrate.

The article of the invention may be prepared by coating, spraying, dipping, painting or printing onto the surface of the substrate a composition comprising a encapsulated reduced tungsten oxide based pigment.

In some embodiments the encapsulated reduced tungsten oxide based pigment may be coated onto one surface of the substrate. In some embodiments it may be coated onto both surfaces of a planar substrate. The ink composition may be applied to some or all of the surface or surfaces of the substrate. In some embodiments an image may be applied to the substrate using a printing technique.

In preferred embodiments a composition comprising a encapsulated reduced tungsten oxide based pigment is printed onto a surface of the substrate.

Any suitable printing technique may be used, for example offset printing (including lithographic), gravure, intaglio printing, letterpress printing, ink-jet printing and screen printing. Preferably the composition is printed by gravure printing or intaglio printing. Intaglio printing is especially preferred.

Suitably the ink composition is coated or printed onto the substrate at a thickness of at least 1 micron. The thickness will depend on the printing technique used. For offset printing a thickness of 1 to 2 microns is typically used; for a varnish coating or gravure printing a thickness of 2 to 4 microns is preferred; and for intaglio printing a thickness of at least 5 microns, suitably about 8 microns and up to 40 or even up to 80 microns may be used.

The ink composition may be coated or printed onto one or both sides of the substrate.

In some embodiments the ink composition may be provided as an overcoat varnish.

The article of the first aspect of the present invention comprises a encapsulated reduced tungsten oxide based pigment incorporated within or, preferably, applied to the surface thereof The reduced tungsten oxide based pigment is suitably an absorber of infra-red radiation and thus the article absorbs infra-red radiation at the locus which carries the reduced tungsten oxide based pigment.

Suitably the inclusion of the reduced tungsten oxide based pigment within or on the surface of the substrate does not substantially alter the colour of the substrate in the visible range.

Suitably the difference in colour between the substrate with and without the reduced tungsten oxide based pigment (dE, also referred to as AE, dE" and AE*) is less than 4, preferably less than 2, more preferably less than 1. The skilled person will appreciate that a dE of less than 1 is generally considered to be imperceptible to the human eye.

Because the presence of the reduced tungsten oxide based pigment does not substantially affect the colour of the substrate it may be used to provide a hidden or covert security feature.

In some embodiments the substrate may be printed with two paired inks. Suitably in such embodiments a first portion of the substrate is printed with a first ink composition and a second portion of the substrate is coated with a second ink composition wherein the second ink composition has all of the same components as the first ink composition except that it further comprises a encapsulated reduced tungsten oxide based pigment.

Thus the paired inks are suitably identical except for the inclusion of the encapsulated reduced tungsten oxide based pigment.

Suitably the colour difference dE between the first portion of the substrate printed with the first ink composition of the paired inks and the second portion of the substrate printed with the second ink composition of the paired inks is less than 4, the dE is less than 2, more preferably less than 1.

The article, especially when a banknote, may include one or more further security features, for example a UV image/phosphor, an NIR-absorbing image, a holographic feature, a watermark, a thread, a magnetic image, windows, a colour shift/colour change image or a microprinting feature. Further features will also be known to the person skilled in the art.

The present invention relates to an article which carries a reduced tungsten oxide based pigment which is encapsulated.

Preferably the article has an improvement in at least one property compared with an equivalent article which carries the same reduced tungsten oxide based pigment but which is not encapsulated Preferably the article has one or more improved properties compared with an equivalent article in which the pigment is not encapsulated selected from: improved chemical resistance; improved water resistance; improved visible light durability; improved heat durability; - improved UV light durability; - reduced wear and tear; - improved abrasion resistance; -improved mechanical impact resistance; and - improved laundry durability.

Most preferably the article of the present invention has improved laundry durability compared with an equivalent article in which the reduced tungsten oxide based pigment is not encapsulated.

Laundry durability may be measured by subjecting the article to standard laundry conditions.

By an improved laundry durability we mean that when subjected to a standard laundry durability test, an image on a substrate formed from an encapsulated pigment according to the invention is less degraded compared with an image formed from the same pigment which is not encapsulated.

It has been advantageously found that the article of the invention shows excellent wash durability even when subjected to very harsh test conditions. For example the article of the invention shows excellent laundry durability when washed with detergents comprising percarbonate and/or perborate compounds.

The article of the invention shows excellent laundry durability when washed at 80°C for 30 minutes.

Thus the present inventors have found that the use of encapsulation techniques can improve the laundry durability of reduced tungsten oxide based pigments. Suitably the ability of the pigment to absorb infrared radiation and thus act as a security feature is not diminished by the encapsulation.

According to a second aspect of the present invention there is provided the use of an encapsulating agent to improve the laundry durability of a reduced tungsten oxide based 30 pigment.

Preferred features of the second aspect are as defined in relation to the first aspect.

In preferred embodiments the second aspect of the invention relates to the use of an encapsulating agent to improve the laundry durability of a security image on a banknote provided by a reduced tungsten oxide based pigment.

In especially preferred embodiments the second aspect of the invention relates to the use of an encapsulating agent selected from phenol formaldehyde resins, alginic acid and salts thereof, and wax spheres to improve the laundry durability of a security image on a banknote provided by a reduced tungsten oxide based pigment.

Preferably the reduced tungsten oxide based pigment is a compound of formula (I).

Most preferably the reduced tungsten oxide based pigment is selected from CS0 32K0 01W02 9(P(02)C8H17)0 08, W02.72 and CS0.33W02 9.

Preferably the laundry durability is improved at temperatures of more than 50°C, preferably more than 70°C, for example 80°C.

According to a third aspect of the present invention there is provided an ink composition comprising encapsulated particles of a reduced tungsten oxide based pigment.

Preferred features of the third aspect are as defined in relation to the first and second aspects.

In particular preferred embodiment the invention composition of the third aspect is an intaglio ink composition comprising particles of Cso.32Ko01W02 9(P(02)C8H17)0.08, W02.72 or CS0.33VV02 9. encapsulated with calcium alginate or a wax.

According to a fourth aspect of the present invention there is provided a method of manufacturing an article, preferably a banknote, the method comprising providing a substrate, preferably a substantially planar substrate, and applying to a surface of the substrate an ink composition comprising encapsulated particles of a reduced tungsten oxide based pigment.

Preferred features of the fourth aspect are as defined in relation to the first, second and third aspects.

Most preferably the reduced tungsten oxide based pigment is selected from Cso 32Ko oiWO2 o(P(02)C8H17)0 08, W02.72 and CS0.33W02 9.

Preferably the ink composition is applied to the surface of the substrate by printing, preferably by intaglio printing.

The invention will now be further described with reference to the following non-limiting examples.

Example 1

g carnauba wax was heated in a beaker to approx 85 °C. Under stirring 200 g of hydrophobic C5032K001W029(P(02)CBH17)008 powder was dispersed until a homogeneous mass as obtained. In a second beaker 1000 mL of deionised water and 200 g of modified corn (maize) starch were dissolved, and then mixed using a high speed stirrer set to 2000 rpm. The carnauba wax / CS° 32K0.0M02 g(P(02)C0F100 08 dispersion was added after 10 minutes. The resulting dispersion was then spray dried with hot air at temperature of at least 85°C to provide 550 g of a fine, soft light blue powder.

Example 2

700 g of Cso.33W029 dispersion having a solids content of 40.3 wt% was stirred in a 3 litre beaker using a high speed stirrer. 18.5 g of a 35 wt% solids non-ionic emulsion of HDPE wax having a melting point of 130°C was added. The mixture was stirred at 4400 rpm for 30 minutes and then dried for 16 hours at 115°C. The resulting 290 g dark-blue powder was crushed and sieved through a 150 pm sieve.

Example 3

300 g Cso.33W02.9 dispersion, with a solids content of 20 wt%, and 40 g poly(allylamine hydrochloride) having a number average molecular weight of 17500 were dispersed in 2 L of a 0.5 M NaCI solution under ultrasonic dispersion for 2 hours. Then the sample was centrifuged and washed with distilled water.

The isolated mass was introduced into 10 L of a 0.08 g/L albumin solution and stirred for 4 at a low temperature of less than 10°C. The suspension was centrifuged, washed with water and dried at elevated temperature to denaturize the albumin. The resulting 96 g powder was a fine dark blue powder.

Example 4

g of beeswax was dryblended with 200 g Csos2K0 01W02 9(P(02)C8H17)0 08 particles, until a homogeneous mass was achieved. In a separate beaker 1000 mL of deionised water was stirred and 30 g gelatine and 3 g of carboxymethylcellulose (CMC) were added and the temperature was raised to 40°C to ensure dissolution. Thereafter the solution was cooled to 30°C and the beeswax / Cso.32K0 oilA/02.9(P(02)C8H0o oa mixture was added and dispersed with a high speed mixer. The mixing was continued until the desired particle size distribution was achieved. The pH value of the dispersion was adjusted to 4.8 and dispersion was cooled to 10°C. Then 40 mL of a 25% glutardialdehyde solution in water was added. Stirring at 10°C and at reduced speed was continued for another 16 hours. Thereafter the stirring was stopped and the resulting dispersion was centrifuged to isolate the particles. The particles were dried in an airflow at 60°C to provide a soft, free flowable very fine and blue coloured particles.

Yield: 340 g.

Example 5

g of beeswax was blended with 400 g Cs0.32K001W029(P(02)C8H17)008 dispersion in a suitable solvent (20% solids), until a homogeneous mass was achieved. In a separate beaker 1000 mL of deionised water was stirred and 30 g gelatine and 3 g of carboxymethylcellulosis (CMC) were are added and the temperature raised to 40°C. Thereafter the solution was cooled to 30°C and the beeswax / Cso 32KaoNV02.9(P(02)C51-11* oa mixture added and dispersed with a high speed mixer. Mixing was continued until the desired particle size distribution was achieved. The pH of the dispersion was adjusted to 4.8 and the dispersion cooled to 10°C.

Then 40 mL of a 25% glutardialdehyde solution in water was added. Stirring at 10°C and at reduced speed was continued for another 16 hours. Thereafter the stirring was stopped and the resulting dispersion centrifuged to isolate the particles. The particles were dried in an airflow at 60°C to provide in a soft, free flowable very fine and blue coloured particles. Yield: 260 g.

Example 6

g of Cs033W029 powder was dispersed in 400 mL absolute ethanol. To the stirred solution 100 mL of a 40% hydrolysed ethylsilicate solution were added. 5 mL of an aminopropylsilane was added. After homogenisation 5 mL of 3.2% HCI, and 10 mL of water were added to initiate condensation. Stirring was continued and the temperature increased to 50°C for 1 hour. After cooling stirring was continued for another 10 hours. The resulting dispersion was filtered under suction and washed with deionised water / ethanol (1:1 mix) until a pH of 5 to 7 was achieved. The filter cake was dried in an airflow oven at 100°C overnight.

Yield: 135 g of blue powder.

Example 7 -Detergent Test A 2 litre beaker with a magnetic stirring bar was filled with 1 litre of deionised water. The water was heated to 80°C with stirring. 25 g of washing powder was added and the mixture stirred until homogeneously dissolved. The pH of the solution was measured and found to be pH = 9. Paper strips coated with 5 pm printing ink were immersed into the hot solution for 30 minutes. Afterwards the printed strips were removed, rinsed with cold water and dried in an oven until all moisture had evaporated. The dried strips were analysed using NIR spectroscopy to measure the absorption level at 1000 nm.

The results are summarized in the table: Example number NIR Absorption at 1000 nm as printed NIR Absorption at 1000 nm after alkalinity test 1 >90% 70% 2 >90% 65% 3 >90% 75% 4 >90% 80% >90% 75% 6 >90% 85% Untreated material >90% 50%

Claims

Claims 1. An article comprising a substrate which carries a reduced tungsten oxide based pigment wherein said reduced tungsten oxide based pigment is encapsulated. 5 2. An article according to claim 1 which is a banknote.3. An article according to claim 1 or claim 2 wherein the reduced tungsten oxide based pigment encapsulated with an encapsulating agent selected from selected synthetic or natural waxes, alginic acid and salts thereof, polysaccharides, maltodextrines, collagen chitosan, lecithines, gelantine, modified and unmodified starches, cellulose ester and ethers, phenol formaldehyde resins, polyurethanes, polyelectrolyte multilayer agents and mixtures thereof 4. An article according to claim 1 or claim 2 wherein the reduced tungsten oxide based pigment is encapsulated with an encapsulating agent selected from synthetic or natural waxes, alginic acid and salts thereof, cellulose ester and ethers, phenol formaldehyde resins, polyurethanes, polyelectrolyte multilayer agents and mixtures thereof 5. An article according to any preceding claim wherein the encapsulated reduced tungsten oxide based pigment is printed in the form of a security image.6. An article according to any preceding claim wherein the encapsulated reduced tungsten oxide based pigment is a compound of formula (I) Mla M2bWcOd(P (0)n Rm)e (I) wherein each of MI and M2 is independently ammonium or a metal cation; a is 0.01 to 0.5; b is 0 to 0.5; c is 1; d is 2.5 to 3; e is 0.01 to 0.75; n is 1, 2 or 3; m is 1, 2 or 3; and R is an optionally substituted hydrocarbyl group.7. An article according to any preceding claim which has one or more improved properties compared with an equivalent article in which the pigment is not encapsulated selected from: improved chemical resistance; improved water resistance; - improved visible light durability; - improved heat durability; - improved UV light durability; reduced wear and tear, improved abrasion resistance; improved mechanical impact resistance; and improved laundry durability.8. The use of an encapsulating agent to improve the laundry durability of a reduced tungsten oxide based pigment 9. The use according to claim 8 to improve the laundry durability of a security image on a banknote provided by a reduced tungsten oxide based pigment.10. The use according to claim 9 wherein the encapsulating agent is selected from phenol formaldehyde resins and wax spheres.11. The use according to any of claims 8 to 10 wherein the laundry durability is improved at temperatures of more than 50°C, preferably more than 70°C, for example 80°C.12. An ink composition comprising encapsulated particles of a reduced tungsten oxide based pigment.13. A method of manufacturing an article, preferably a banknote, the method comprising providing a substrate, preferably a substantially planar substrate, and applying to a surface of the substrate an ink composition comprising encapsulated particles of a reduced tungsten oxide based pigment.14. A method according to claim 13 wherein the ink composition is applied to the surface of the substrate by printing, preferably by intaglio printing.