WO2006011800A1

WO2006011800A1 - Recording medium

Info

Publication number: WO2006011800A1
Application number: PCT/NL2005/000556
Authority: WO
Inventors: Jacko Hessing; Willem Johannes Van Baak; Akira Kase
Original assignee: Fuji Photo Film B.V.
Priority date: 2004-07-30
Filing date: 2005-07-29
Publication date: 2006-02-02

Abstract

The invention is directed to recording media, in particular swellable inkjet recording media of photographic quality that have excellent image printing quality, outstanding absorption speed, as well as good lightfastness. According to the present invention a recording medium is provided comprising a support and an ink receiving layer adhered to said support, wherein the ink-receiving layer is a multilayer comprising an overlayer and an underlayer, wherein the overlayer comprises a specific water soluble polymer and an optical brightening agent. The present invention is further directed to methods for preparing and using such a medium

Description

Title: Recording media

Field of invention

The invention is directed to recording media, in particular swellable inkjet recording media of photographic quality that have excellent image printing quality, outstanding absorption speed, as well as good lightfastness. The present invention is further directed to methods for preparing and using such media.

Background of the invention

In a typical ink-jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye, and a relatively large amount of solvent in order to prevent clogging of the nozzle. The solvent, or carrier liquid, typically is made up of water and organic material such as monohydric alcohols. An image recorded as liquid droplets requires a receptor on which the recording liquid dries quickly without running or spreading. High quality image reproduction using ink -jet printing techniques requires receptor supports, typically sheets of paper or opaque or transparent film, that readily absorb ink droplets while preventing droplet diffusion or migration. Good absorption of ink encourages image drying while minimizing dye migration by which good sharpness of the recorded image is obtained.

These recording media should provide good image quality, in particular beading behaviour, over a wide range of ink loads. Beading or puddling is the phenomenon of coalescence of adjacent ink dots before the ink is absorbed by the ink receiving layer. A good beading behaviour means that these recording media should provide a correspondingly good absorption capacity, while at the same time the image quality should also be good. To improve beading several approaches have been proposed. EP-A-O 272 125 and EP-A-O 350 257 apply highly water-absorptive particles in the ink receiving layer while EP-A-I 285 774 describes specific organic particles in a porous layer in order to make the inkjet paper resistive against beading. Alternatively EP-A-I 127 706 applies a silanol modified polyvinyl alcohol in combination with a film forming polymer in a pigment containing layer. EP-A-I 288 013, JP-A-2003/011490 and JP-B-3112642 describe specific combinations of polymeric binders to improve beading.

Optical brightening agents, also referred to as fluorescent whitening agents, are added to improve optical properties especially whiteness. The use of optical brightening agents in inkjet media is known for over 20 years, see e.g. Research Disclosure RD231036, published by Kenneth Mason Inc. The way these compounds are applied varies widely. EP-A-I 086 825 teaches a combination of a fluorescent brightening agent and a cationic polymer in a certain ratio coated on a neutral base paper. WO-A-2004/014659 describes a fluorescent brightening agent in the outermost pigment containing ink receiving layer, while EP-A-O 956 970 teaches to add the optical brightener in a layer lower than the toplayer. Also in EP-A-O 699 452 the whiteness improving layer is located in between the support and the receptive layer. WO-A-02/40288 discloses a single ink-receiving layer comprising an optical brightener. In order to achieve significant effects, quantities of optical brightener are usually in the range of 1 to 5 weight percent as in US-A-6 238 804 or 1 to 3 g/m² as in EP-A-I 086 825.

Although these recording media provide for considerable improvements, there is a need for other approaches for improving the properties of inkjet media with respect to absorption and image quality, including beading properties, in particular when these recording materials are of the swellable type based on water soluble polymers. Summary of the invention

The object of the present invention is to provide a recording medium having good overall properties, said recording medium more in particular being suited to produce images of photographic quality, wherein said medium has an improved beading behaviour at high ink loads and a superior gloss.

At the same time it is desirable that the media of the present invention maintain other favourable properties with respect to lightfastness and whiteness, good behaviour on the appearance at high densities and bleeding properties. It is another objective of the present invention to provide a recording medium with reduced brittleness at low humidities and excellent curl behaviour.

It has been found that these objectives can be met by providing a recording medium comprising a support and an ink-receiving layer adhered to said support, wherein the ink-receiving layer is a multilayer comprising an overlayer and an underlayer (viz. a layer that is situated closer to the support than said overlayer), wherein the overlayer comprises a specific water soluble polymer and an optical brightening agent.

Detailed description

The invention is directed to a recording medium comprising a support and an ink-receiving layer adhered to said support, wherein the ink- receiving layer is a multilayer comprising an overlayer and an underlayer, wherein the overlayer comprises a specific water soluble polymer and an optical brightening agent.

Although the invention is described herein with particular reference to inkjet printing, it will be apparent to the skilled person that the high quality recording media of the present invention are not limited to inkjet recording media (viz. media suitable to be printed on using inkjet printers), but that it is within the scope of the present invention to provide recording media that are suitable for creating high quality images by using other techniques as well, such as Giclee printing, colour copying, screen printing, gravure, dye- sublimation, flexography, and the like.

The overlayer of this invention may be a single layer, or it may be a multilayer of sublayers. Also the underlayer may be a single layer or a multilayer of sublayers. The total number of sublayers is not specifically limited and depends largely on the available technique for application of layers and the required ink receiving properties of the ink receiving layer. The total number of sublayers may be from 2 to 25, more preferably from 3 to 17. Surprisingly our research team has found that applying optical brightening agents in combination with certain water soluble polymers the beading improves strikingly. At the same time the product benefits from the fluorescent properties of these brightening agents, which leads to a better whiteness. In order to obtain the maximum effect on the beading behaviour, it is preferred that both the brightening agent and the specific water soluble polymer are present in the overlayer. The obtained effect is in principle independent of the layer wherein the optical brightening agent is originally present at the time of coating.

Another aspect of the present invention is the process for producing the recording media of the present invention, which comprise at least one layer in which the optical brightening agent is present in combination with certain specific water soluble polymers. Rather than directly applying (a solution of) the optical brightener to the solution for the layer comprising the water soluble polymers (which approach frequently has been found to result in a matte appearance instead of a glossy surface, which matte appearance is believed to be associated with phase separation that is triggered by the addition of the optical brightener), the present inventors found that the optical brightener, optionally in the form of a solution, should be applied in one of the other layers. Before drying the optical brightening agent is believed to diffuse through the layer structure towards the layer comprising the specific water soluble polymer where an interaction takes place between the optical brightening agent and the water soluble polymer. Thus phase separation is prevented and a high gloss may be obtained.

In one embodiment a protective toplayer is coated as the outermost layer. For a maximum effect on beading it is important that this toplayer is not a thick layer, preferably having a dry thickness of less than 2 μm, preferably less than 1 μm. In case the number of layers farther away from the support than the layer comprising the specific water soluble polymer is higher than one it is preferred that the total thickness of the layers coated on top of the layer comprising the water soluble polymer is less than 2 μm.

As was mentioned, one drawback of some combinations of optical brightening agent and water soluble polymer that occurs especially when also gelatin is present in the overlayer, is a lower gloss. This phenomenon frequently occurs when both components are added to the same solution. This problem can be prevented by adding the optical brightening agent into the solution for another layer. This other layer preferably is free from water soluble polymers that have a strong interaction with the optical brightening agent. In a preferred embodiment the optical brightening agent is added to the solution for the outermost layer of the overlayer while the water soluble polymer is an ingredient of the solution for another sublayer of the overlayer. When a matte surface is desired the optical brightening agent can be added to the same solution of the layer comprising the water soluble polymer. In another embodiment besides the overlayer also the underlayer comprises a water soluble polymer that has a strong interaction with the optical brightening agent. In this case preferably the optical brightening agent is added in one of the layers adjacent to the overlayer comprising the water soluble polymer in order to concentrate the optical brightening agent as much as possible in the layer close to the outer surface of the recording medium where the effect on beading is large. Preferably the optical brightening agent is then added to a sublayer farther away form the support than the sublayer comprising the water soluble polymer e.g. to the toplayer.

Preferably the ink receiving layer does not comprise inorganic porous particles since these generally have a negative influence on the gloss of the medium. The best gloss is obtained with media of the swellable type. This type of media is also preferred because of its superior lightfastness property.

Suitable optical brighteners are disclosed in e.g. RD11125, RD9310, RD8727, RD8407, RD36544 or Ullmann's Encyclopedia of industrial chemistry (Vol. A18 pl53-167), and comprise thiophenes, stilbenes, triazines, imidazolones, pyrazolines, triazoles, bis(benzoxazoles), coumarins and acetylenes. Preferred optical brightening agents to be used in the invention are preferably water-soluble and comprise distyrylbenzenes, distyrylbiphenyls, divinylstilbenes, diaminostilbenes, stilbenyl-2H-triazoles, diphenylpyrazolines, benzimidazoles and benzofurans. Most preferred are triazinylaminostilbenes such as derivatives of bis(4,4'-triazinylamino)-stilbene-2,2'-disulfonic acid.

The amount of optical brightening agent needed to achieve the found effect is significantly lower than the amounts described in the prior art. Optimum amounts are lower than 1 g/m²; preferably between 0.005 and 0.5 g/m²; more preferably 0.005 or more, but less than 0.2 g/m²; e.g. less than 0.1 g/m².

Suitable water soluble polymers are those that have a strong interaction with the optical brightening agent. Preferred polymers are polyvinyl alcohol (PVA), modified PVA's such as such as fully hydrolysed or partially hydrolysed PVA, carboxylated PVA, acetoacetylated PVA, quaternary ammonium modified PVA, polyvinyl pyrrolidone (PVP), modified PVP's such as polymers based on N-(2-hydroxyethyl)-2-pyrrolidone or N-cyclohexyl-2- pyrrolidone, copolymers and terpolymers based on PVA and/or PVP, e.g. copolymers of PVA and polyethyleneoxide, copolymers of PVA and PVP, copolymers or terpolyrαers containing polymethylacrylic acid, polyacrylamide or urea derivatives.

In general a large variety of PVA- or PVP -based polymers can be used, but the preferred (co- or ter-)polymers are those which have been modified to give a good miscibility with aqueous gelatin solutions. These modifications are such, that in the polymer back bone groups are introduced which provide a hydrogen bonding site, an ionic bonding site, carboxylic groups, sulphonyl groups, amide groups and the like, thus providing a modified polymer. A modified PVA-based polymer giving very good results is a poly(vinyl alcohol) -co-poly (n-vinyl formamide) copolymer (PVA-NVF). Very suitable PVA-NVF copolymers for use with the present invention are the copolymers described in WO-A-03/054029, which have the general formula I:

wherein n is between 0 and about 20 mole percent; m is between about 50 and about 97 mole percent; x is between 0 and about 20 mole percent; y is between 0 and about 20 mole percent; z is between 0 and about 2 mole percent and x+y is between about 3 and about 20 mole percent;

Ri, and R3 are independently H, 3-propionic acid or Ci-Cβ alkyl ester thereof, or is 2-methyl-3-propionic acid or Ci-Cβ alkyl ester thereof; and

R2 and R₄ are independently H or Ci-Ce alkyl.

The PVA- or PVP -based polymer is applied in an amount ranging from 0.5 until 15 g/m² and more preferably from 1.0 until 10 g/m². Preferably the overlayer contains at least 50% of the water soluble polymer that has a strong affinity for the optical brightening agent. When the overlayer is a multilayer for the invention it is sufficient that only one sublayer comprises the specific water soluble polymer but also more or all sublayers may comprise this water soluble polymer. Preferably the sublayer of the overlayer with the highest concentration of this water soluble polymer is the outermost layer of this multilayer or in case a thin toplayer is present the layer adjacent to this toplayer. The overlayer may contain other water soluble polymers and gelatin. The gelatin used in the overlayer can be any gelatin whether lime- processed or acid processed, hydrolysed or modified, made from animal collagen, preferably gelatin made from pig skin, pig bone, cow skin, cow bone or fish gelatin. Examples of modified gelatins are amino group deactivated gelatin such as acetylated gelatin, phthalated gelatin, succinated gelatin, quaternary ammonium modified gelatin, et cetera.

In a specific embodiment a toplayer e.g. the layer farthest away from the support, is applied. This protective toplayer preferably comprises a modified gelatin and optionally a fluorosurfactant. By using a modified gelatin a high gloss is obtained. Besides the toplayer also other sublayers of the overlayer may comprise a modified gelatin.

Good results are obtained with a modified gelatin, of which at least 30% of the NH2 groups is modified by a condensation reaction with a compound having at least one carboxylic group as described among others in DE-A-19721238. The compound having at least one carboxylic group can have an other functional group like a second carboxylic group and a long aliphatic tail, which in principle is not modified. Long tail in this context means from at least 5 to as much as 25 C atoms, e.g. 6 - 20 C atoms. This aliphatic chain can be modified still to adjust the properties like water solubility and ink receptivity. Specially preferred gelatins of this type are succinic acid modified gelatins in which the succinic acid moiety contains an aliphatic chain from 5 to 25 carbon-atoms, e.g. 6 to 20 C atoms, where the chain can still be modified to a certain extend to adjust the water soluble properties or ink receptive properties. Preferably the succinic acid moiety contains an aliphatic chain from 7 to 18 carbon-atoms. Most preferred is the use of dodecenylsuccinic acid modified gelatin, in which at least 30% of the NH2 groups of the gelatin have been modified with said dodecenylsuccinic acid.

Another method for obtaining modified gelatin is described in EP-A-0576911, where said gelatin is formed from gelatin containing pendant amine groups and pendant carboxylic groups wherein at least one amine group of said gelatin is modified to form an amide of the formula -NHCOR. The process typically involves reaction of an amine group with an activated carboxyl, i.e. a reaction product of a carboxyl activating agent and carboxylic acid, i.e., RCOOH wherein R represents substituted or unsubstituted alkyl of 1-10 carbons, substituted or unsubstituted aryl of 6-14 carbons, or substituted or unsubstituted arylalkyl of 7-20 carbons.

Other suitable methods are described by V.N. Izmailova, et al. (Colloid Journal, vol. 64, No. 5, 2002, page 640-642), and by O. Toledano, et al. (Journal of Colloid and Interface Science 200, page 235-240) wherein hydrophobic groups are attached to gelatin molecules by reacting gelatin with respectively N-hydroxysuccinimide ester of caprylic acid and N- hydroxysuccinimide ester of various fatty acids (CVCiβ).

Other modified gelatins giving good results are gelatins modified to have quaternary ammonium groups. Examples of such a gelatin are the "Croquat™" gelatins produced by Croda Colloids Ltd. The (modified) gelatin in the overlayer is preferably applied in an amount ranging from 0.1 to 10 g/m², more preferably from 0.2 to 8 g/m².

The overlayer may include one or more fluorosurfactants, preferably in the amount between 2.5 mg/m² and 250 mg/m². It was found that this kind of surfactants improves amongst others the gloss and beading. The term "fluorosurfactant" as used herein, refers to surfactants (viz. molecules having a hydrophilic and a hydrophobic part) that contain fluorocarbon or a combination between fluorocarbon and hydrocarbon as the hydrophobic part. Suitable fluorosurfactants may be anionic, non-ionic or cationic. Examples of suitable fluorosurfactants are: fluoro C2-C20 alkylcarboxylic acids and salts thereof, disodium N-perfluorooctanesulfonyl glutamate, sodium 3-(fluoro-C6-Cii alkyloxy)-l-C3-C4 alkyl sulfonates, sodium 3-(omega -fhioro-Cβ-Cs alkanoyl-N-ethylamino)-l-propane sulfonates, N-[3- (perfluorooctanesulfonamide)-propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine, perfluoro alkyl carboxylic acids (e.g. C₇-Ci3-alkyl carboxylic acids) and salts thereof, perfluorooctane sulfonic acid diethanolamide, Li, K and Na perfluoro C₄-C₁₂ alkyl sulfonates, Li, K and Na N-perfluoro C4-C13 alkane sulfonyl— N-alkyl glycine, fluorosurfactants commercially available under the name Zonyl® (produced by E.I. Du Pont) that have the chemical structure of RfCH₂CH₂SCH₂CH₂CO₂Li or

RfCH₂CH₂O(CH₂CH₂O)_x H wherein Rf = F(CF₂CF₂)₃-8 and x = 0 to 25, N- propyl-N-(2-hydroxyethyl)perfluorooctane sulfonamide, 2-sulfo-l,4- bis(fluoroalkyl)butanedioate, 1,4-bis (fluoroalkyl)-2-[2-N,N,N- trialkylammonium) alkyl amino] butanedioate, perfluoro Ce-C₁O alkylsulfonamide propyl sulfonyl glycinates, bis-(N-perfluorooctylsulfonyl-N- ethanolaminoethyl)phosphonate, mono-perfluoro Cβ-Ciβ alkyl-ethyl phosphonates, and perfluoroalkylbetaine. Also useful are the fluorocarbon surfactants described e.g. in US-A-4 781 985 and in US-A-5 084 340.

Preferably the fluorosurfactant is chosen from Li, K and Na N- perfluoro C4-C13 alkane sulfonyl-N- alkyl glycine, 2-sulfo-l,4- bis(fluoroalkyl)butanedioate, 1,4-bis (fluoroalkyl)-2-[2-(N,N,N- trialkylammonium alkyl amino] butanedioate, perfluoroalkyl subsitituted carboxylic acids commercially available under the name Lodyne® (produced by Ciba Specialty Chemicals Corp.) and fluorosurfactants commercially available under the name Zonyl® (produced by E.I. Du Pont) that have the chemical structure Of RfCH₂CH₂SCH₂CH₂CO₂Li or RfCH₂CH₂O(CH₂CH₂O)_x H wherein Rf = F(CF₂CF₂)S-S and x = 0 to 25.

The overlayer may further comprise an UV absorbing agent. Any UV agent known in the art can be added. Suitable UV agents are selected from the group consisting of purine compounds, pyrimidine compounds, benzimidazole compounds, imidazolidine compounds, urazole compounds, pyrazole compounds, triazole compounds, benzotriazole compounds, tetrazole compounds, pyrazine compounds, cinnamate compounds, aminobutadien compounds and mixtures thereof. Examples of UV agent are those described in Research Disclosure

RD24239, RD290119, RD30326, EP-A 0 673 783, GB-A 2088 777, EP-A-O 955 180, EP-A-O 738 718, US-A-4926190 and in Ullmann's Encyclopedia of Industrial Chemistry, 5th completely revised edition 1992, volume 20, page 468-471. Suitable UV agents are also compounds containing a triazine skeleton. These compounds are described, for example, in JP-A-46-

3335, JP-A-55- 152776, JP-A-5-197074, JP-A-5-232630, JP-A-5-307232, JP-A-6- 211813, JP-A-8-53427, JP-A-8-234364, JP-A-8-239368, JP-A-9-31067, JP-A-IO- 147577, JP-10-182621, JP-T-8-501291 ("JP-T" means published searched patent publication). EP-A-0711804 and DE-A-19739797 are preferable. Preferred UV agents are benzotriazole compounds, such as 2-(2- hydroxy-5'methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t- butylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'~di-t-butylphenyl)-5- chlorobenzotriazole, 2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole, 2-(2'- hydroxy-5'-t-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-sec-butyl-5'-t- butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-sec-butyl-5'-t-butylphenyl)-5- chlorobenzotriazole, 2-(2'-hydroxy-4'-n-hexyloxyphenyl)benzotriazole, 2-(2'- hydroxy-5'-isoocytlphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t- amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-isooctylphenyl)-5'-methyl- benzotriazole, 2-(2'-hydroxy-3',5'-di-t-amylphenyl) benzotriazole, 2-(2'-hydroxy- 3'-t-butyl-5'mehtylphenyl)benzotriazole, 2-(2'-hydroxy-3'-sec-dodecyl- 5'mehtylρhenyl) benzotriazole, as well as the benzotriazole compounds described in EP-A-O 738 718, the benzotriazole compounds described in US-A- 4926190, and mixtures thereof. The UV agent can be added in a suitable solvent or as a component of an oil in water emulsion. Also UV agents linked to gelatin can be used. The UV agent may be added in the amount from 0.03 g/m² to 10 g/m². Preferable between 0.03 g/m² and 5 g/m².

The overlayer may optionally include matting agents, thickener agents, biocides, crosslinking agents and further various conventional additives such as colorants, mold lubricants, permeating agents, fixing agents for ink dyes, anti-oxidants, dispersing agents/non-fluorosurfactants, anti- foaming agents, leveling agents, fluidity improving agents, antiseptic agents, viscosity stabilizing and/or enhancing agents, pH adjusting agents, anti- mildew agents, anti-fungal agents, agents for moisture -proofing, agents for increasing the stiffness of wet paper, agents for increasing the stiffness of dry paper and anti-static agents. The above-mentioned various additives can be added ordinarily in a range of 0 to 10 weight % based on the solid content of the ink receiving layer composition.

Also the underlayer may be a multilayer of sublayers. The underlayer typically comprises gelatin and at least one other water soluble polymer and optionally additives to adjust the physical properties. This swellable underlayer determines mainly the physical properties like water uptake, drying speed, brittleness and curl.

There is a variety of gelatins, both non-modified as well as modified gelatins which can be used in the underlayer. Examples of non-modified gelatins are alkali-treated gelatin (cattle bone or hide gelatin), acid-treated gelatin (pigskin, cattle/pig bone gelatin), hydrolyzed gelatin and fish gelatin. Examples of modified gelatins are amino group deactivated gelatin such as acetylated gelatin, phthalated gelatin, succinated gelatin, quaternary ammonium modified gelatin, et cetera. These gelatins can be used singly or in combination for forming the underlayer. Acid and alkali treated gelatins are preferred.

Water soluble polymers suitable to be mixed with the (modified) gelatin include PVA-based polymers, such as fully hydrolysed or partially hydrolysed polyvinyl alcohol (PVA), carboxylated PVA, acetoacetylated PVA, quaternary ammonium modified PVA, copolymers and terpolymers of PVA with other polymers, watersoluble cellulose derivatives such as alkyl cellulose (e.g. methyl cellulose), hydroxyalkyl cellulose (e.g. hydroxyethyl cellulose or hydroxypropyl cellulose), carboxy alkyl cellulose (e.g. carboxymethyl cellulose), dextrin, casein, gum arabic, dextran, polyacrylic acid and its copolymers or terpolymers, polymethylacrylic acid and its copolymers or terpolymers, and any other polymer, which contain monomers of carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and crotonic acid, polyvinylpyrrolidone (PVP), polyethylene oxide, polyacrylamide, polymers of 2-pyrrolidone and its derivatives such as N-(2-hydroxyethyl)-2-pyrrolidone and N-cyclohexyl-2- pyrrolidone, urea and its derivatives such as imidazolidinyl urea, diazolidinyl urea, 2-hydroxyethylethylene urea, and ethylene urea.

The gelatin of the underlayer is preferably used in a total amount of from 0.2 to 12 g/m², and more preferably from 0.4 to 9 g/m². The amount of water soluble polymer used in a certain formulation is typically in the range from 0.5 g/m² to 15 g/m² and more preferably between 1 g/m² and 8 g/m².

It was found that in case the underlayer is a multilayer it is beneficial to apply different concentrations of gelatin and water soluble polymer in the sublayers of the underlayer. A lower concentration of gelatin and water soluble polymer in the sublayer closest to the support enables a lower viscosity of the mixture which improves the coatability and allows higher coating speeds.

In a specific embodiment closest to the support an adhesion promoting layer is applied to enhance the adhesion of the coated layers onto the support. This adhesion promoting layer may be coated in a separate step or simultaneously with the receiving layers. The adhesion promoting layer is a thin layer, preferably has a dry thickness of less than 3 μm, more preferably less than 1 μm.

If desired, the gelatin and/or the water soluble polymer can be cross- linked in the image -recording elements of the present invention in order to impart mechanical strength to the layer. This can be done by any cross-Linking agent known in the art.

For gelatin, there is a large number of known cross-linking agents- also known as hardening agents. Examples of the hardener include aldehyde compounds such as formaldehyde and glutar aldehyde, ketone compounds such as diacetyl and chloropentanedion, bis (2-chloroethylurea), 2-hydroxy-4, 6- dichloro-l,3,5-triazine, reactive halogen-containing compounds disclosed in US-A-3 288 775, carbamoyl pyridinium compounds in which the pyridine ring carries a sulphate or an alkyl sulphate group disclosed in US-A-4 063 952 and US-A-5 529 892, divinylsulfones, and the like. These hardeners can be used singly or in combination. The amount of hardener used, preferably ranges from 0.1 to 10 g, and more preferably from 0.1 to 7 g based on 100 g of gelatin contained in the ink-receiving layer. For PVA it is preferable to choose a cross- linking agent selected from borax, glyoxal, dicarboxylic acids and the like. The ink-receiving layer may further contain the following ingredients in order to improve the ink receiving layer properties with respect to ink receptivity and strength:

- One or more plasticizers, such as ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, glycerol monomethylether, glycerol monochlorohydrin, ethylene carbonate, propylene carbonate, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, urea phosphate, triphenylphosphate, glycerolmonostearate, propylene glycol monostearate, tetramethylene sulfone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, and polymer lattices with low Tg-value such as polyethylacrylate, polymethylacrylate and the like. - One or more mordants. Mordants may be incorporated in the underlayer of the present invention. Such mordants are represented by cationic compounds, monomeric or polymeric, capable of complexing with the dyes used in the ink compositions. Useful examples of such mordants include quaternary ammonium block copolymers. Other suitable mordants comprise diamino alkanes, ammonium quaternary salts and quaternary acrylic copolymer latexes. Other suitable mordants are fluoro compounds, such as tetra ammonium fluoride hydrate, 2,2,2-trifl.uoroethylamine hydrochloride, 1- (alpha, alpha, alpha -trifluoro-m-tolyl) piperazine hydrochloride, 4-bromo- alpha, alpha, alpha -trifluoro-o-toluidine hydrochloride, difluorophenylhydrazine hydrochloride, 4-fluorobenzylamine hydrochloride, 4- fluoro- alpha, alpha -dimethylphenethylamine hydrochloride, 2- fluoroethylaminehydrochloride, 2-fluoro-l-methyl pyridinium-toluene sulfonate, 4-fluorophenethylamine hydrochloride, fluorophenylhydrazine hydrochloride, l-(2-fluorophenyl) piperazine monohydrochloride, 1 -fluoro pyridinium trifluoromethane sulfonate.

- One ore more conventional additives, such as:

• UV-absorbers

• biocides; • pH controllers;

• preservatives;

• viscosity modifiers;

• dispersing agents;

• anti-oxidants; • antistatic agents; and/or

• anionic, cationic, non-ionic, and/or amphoteric surfactants, typically used in amounts ranging from 0.1 to 1000 mg/m², preferably from 0.5 to 100 mg/m².

These additives may be selected from known compounds and materials in accordance with the objects to be achieved. The above-mentioned additives (plasticizers, mordants, conventional additives) may be added in a range of 0 to 30% by weight, based on the solid content of the water soluble polymers and/or gelatin in the ink-receiving layer.

A suitable process for preparing a recording medium according the present invention comprises the following steps.

Preparation of the following set of solutions:

- a first coating solution comprising a water soluble polymer that is selected from the group consisting of polyvinyl alcohol (PVA) based polymers; polyvinyl pyrrolidone (PVP) based polymers; combinations thereof; and mixtures thereof;

- a second coating solution which is essentially free of PVA based or PVP based polymer;

- a third coating solution;

- optionally additional coating solutions; and - an aqueous solution of an optical brightener which is added to at least one of the coating solutions essentially free of any PVA based or a PVP based polymer.

These solutions are applied in accordance with the process of the present invention as follows: - the first solution comprising a PVA- or PVP -based polymer for the overlayer;

- the second solution essentially free of PVA- or PVP -based polymer for a second sublayer of the overlayer;

- a third solution for the underlayer; - optionally a fourth solution not comprising a PVA-based or a PVP- based polymer for a second sublayer of the underlayer;

The solutions that are essentially free of the water soluble polymers preferably contain less than 1 wt.% of each of these polymers,, more preferably less than 0.5 wt.%, even more preferably no detectable amounts of these polymers, viz. about zero wt.%.

An aqueous solution of an optical brightener is added to the second, the third and/or the fourth solution depending on the chosen layer structure of the medium and on the other ingredients of the layers. The resulting formulations for the (sub)layers of the overlayer and the underlayer can be coated consecutively or simultaneously to a support by any method known in the art. The coating methods are for example, a curtain coating, an extrusion coating, an air-knife coating, a slide coating, a roll coating method, reverse roll coating, dip coating processes and a rod bar coating. After coating but presumably before drying the optical brightener diffuses to the layer comprising the PVA-based or PVP -based polymer. Because the optical brightener has a strong affinity with those polymers essentially all (e.g. 90 wt.% or more) of the optical brightener is thought to diffuse to the layer comprising the PVA-based or PVP -based polymer. An important advantage that can be obtained in accordance with the present invention is that the optical brightener (solution) does not interfere with the solution of the water soluble polymer (the PVA-based polymer or the PVP -based polymer). Normally this would result in phase separation of polymer solution, which is phase separation believed to be responsible for the matte appearance, referred to above. Thus the process described above allows for providing a recording medium which has the optical brightener in the water soluble polymer layer, but while maintaining a high gloss.

Preferably the layers are coated simultaneously, but part or all of the layers can be coated consecutively since an already dried layer will start to swell allowing diffusion when another layer is coated on top of that layer.

An important characteristic of the inkjet recording medium is the gloss. Surprisingly it has been found that the gloss of the medium can be further improved by selecting the appropriate surface roughness of the used support. It was found, that providing a support having a surface roughness characterised by the value Ra being less than 1.0 μm, preferably below 0.8 μm a very glossy medium can be obtained. A low value of the R_a indicates a smooth surface. The Ra is measured according to DIN 4776 using a UBM equipment, software package version 1.62, with the following settings: (1) Point density 500 P/mm (2) Area 5.6 x 4.0 mm² (3) Cut-off wavelength 0.80 mm (4) Speed 0.5 mm/sec.

The base paper to be used as the support for the present invention is selected from materials conventionally used in high quality printing paper. Generally it is based on natural wood pulp and if desired, a filler such as talc, calcium carbonate, Tiθ2, BaSO₄, and the like can be added. Generally the paper also contains internal sizing agents, such as alkyl ketene dimer, higher fatty acids, paraffin wax, alkenylsuccinic acid, epichlorhydrin fatty acid amid and the like. Further the paper may contain wet and dry strength agents such as a polyamine, a poly-amide, poly aery lamide, poly-epichlorohydrin or starch and the like. Further additives in the paper can be fixing agents, such as aluminium sulphate, starch, cationic polymers and the like. The Ra value for a normal grade base paper is well above 1.0 μm typically above 1.3 μm. In order to obtain a base paper with a Ra value below 1.0 μm such a normal grade base paper can be coated with a pigment. Any pigment can be used. Examples of pigments are calcium-carbonate, TiO2, BaSO₄, clay, such as kaolin, styrene- acrylic copolymer, Mg-Al-silicate, and the like or combinations thereof. The amount being between 0.5 and 35.0 g/m² more preferably between 0.5 and 20.0 g/m². This pigmented coating can be applied as a pigment slurry in water together with a suitable binders like styrene-butadiene latex, methyl methacrylate-butadiene latex, polyvinyl alcohol, modified starch, polyacrylate latex or combinations thereof, by any technique known in the art, like dip coating, roll coating, blade coating or bar coating. The pigment coated base paper may optionally be calendered. The surface roughness can be influenced by the kind of pigment used and by a combination of pigment and calendering. The base pigment coated paper substrate has preferably a surface roughness between 0.4 and 0.8 μm. If the surface roughness is further reduced by super calendering to values below 0.4 μm the thickness and stiffness values will generally become below an acceptable level.

The ink receiving multilayer of the present invention can be directly applied to the pigment coated base paper. In another embodiment, the pigment coated base paper having a pigmented top side and a back-side is provided on both sides with a polymer resin through high temperature co-extrusion giving a laminated pigment coated base paper. Typically temperatures in this (co-) extrusion are above 280 ⁰C but below 350 ⁰C. The preferred polymers used are poly olefins, particularly polyethylene. In a preferred embodiment the polymer resin of the top side comprises compounds such as an opacifying white pigment e.g. Tiθ2 (anatase or rutile), ZnO, ZnS, dyes, coloured pigments, including blueing agents e.g. ultramarine and cobalt blue, adhesion promoters, optical brighteners, antioxidant and the like to improve the whiteness of the laminated pigment coated base paper. By using other than white pigments a variety of colors of the laminated pigment coated base paper can be obtained. The total weight of the laminated pigment coated base paper is preferably between 80 and 350 g/m². The laminated pigment coated base paper shows a very good smoothness, which after applying the ink receiving layer of the present invention results in a recording medium with excellent gloss.

Other supports used in this invention may suitably be selected from a synthetic paper or a plastic film in which the top and back coatings are balanced in order to minimise the curl behaviour.

Examples of the material of the plastic film are polyolefins such as polyethylene and polypropylene, vinyl copolymers such as polyvinyl acetate, polyvinyl chloride and polystyrene, polyamide such as 6,6-nylon and 6-nylon, polyesters such as polyethylene terephthalate, polyethylene-2 and 6- naphthalate and polycarbonate, and cellulose acetates such as cellulose triacetate and cellulose diacetate. The support may have a gelatin subbing layer to improve coatability of the support. The support may be subjected to a corona treatment in order to improve the adhesion between the support and the ink receiving layer. Also other techniques, like plasma treatment can be used to improve the adhesion.

The swellable ink-receiving layer preferably has a dry thickness from 1 to 50 micrometers, preferably from 5 to 25 and more preferably between

8 and 20 micrometers. If the thickness of said ink receiving layer is less than 1 micrometer, adequate absorption of the solvent will not be obtained. If, on the other hand, the thickness of said ink receiving layer exceeds 50 micrometers, no further increase in solvent absorptivity will be gained. The recording medium of the invention can be used for forming a permanent, precise inkjet image by bringing ink into contact with the medium in the pattern of a desired image.

The present invention will be illustrated in more detail by the following non-limiting examples. Unless stated otherwise, all ratios given are ^" based on weight.

Examples

A. Preparation of composition 'A' of the ink receiving layer for sublayer 1 of the underlaver (adhesion promoting layer). A solution containing 100 weight parts of lime bone gelatin with an IEP of 5.0 and an average MW of 250 kD (determined by the method described in the Journal of Colloid and Interface Science 243, 476-482, 2001), 1911 weight parts of water and 136 weight parts of a solution of optical brightener blankophor PPW (10% aqueous solution from Bayer AG, Germany) was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 8.5 by adding NaOH.

B. Preparation of composition 'B' of the ink receiving layer for sublayer 1 of the underlaver (adhesion promoting layer). A solution containing 100 weight parts of lime bone gelatin with an IEP of 5.0 and an average MW of 250 kD and 2047 weight parts of water was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 8.5 by adding NaOH.

C. Preparation of composition 'C of the ink receiving layer for sublayer 2 of the underlaver. A solution containing 100 weight parts of lime bone gelatin with an IEP of 5.0 and an average MW of 250 kD, 25 weight parts of polyvinyl alcohol (PVA Mowiol 4-88 from Kuraray Specialties Europe) and 782 weight parts of water was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 9.0 by adding NaOH.

D. Preparation of composition O' of the ink receiving layer for sublayer 1 of the overlayer. A solution containing 27 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany; modification grade 40%) having an IEP of 5.4, 54 weight parts of PVA-NVF co polymer (CGPS-910, melting range 210-230 ⁰C, CIBA Specialty Chemicals) and 919 weight parts of water was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 9.5 by adding NaOH.

E. Preparation of composition Ε' of the ink receiving layer for sublayer 1 of the overlayer. A solution containing 27 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany; modification grade 40%) having an IEP of 5.4, 54 weight parts of polyvinyl alcohol (PVA Mowiol 4-88 from Kuraray Specialties Europe) and 919 weight parts of water was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 9.5 by adding NaOH. F. Preparation of composition 'F of the ink receiving layer for sublayer 1 of the overlayer. A solution containing 40.5 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany; modification grade 40%) having an IEP of 5.4, 40.5 weight parts of PVA-NVF co polymer (CGPS-910, melting range 210-230 ⁰C, CIBA Specialty Chemicals) and 919 weight parts of water was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 9.5 by adding NaOH.

G. Preparation of composition 'G' of the ink receiving layer for sublayer 1 of the overlayer. A solution containing 40.5 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany; modification grade 40%) having an IEP of 5.4, 40.5 weight parts of polyvinylpyrrolidone (PVP from ICN Biochemicals) and 919 weight parts of water was prepared at 40 ⁰C. Additional binder was added for bringing the viscosity to a suitable level for coating. The pH of the solution was adjusted to 9.5 by adding NaOH.

H. Preparation of composition ⁽H' of the ink receiving layer for sublayer 2 of the overlayer (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl® surfactant (a fluoro-carbon type of surfactant) and 5865 weight parts of water was prepared at 40 ⁰C. The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating.

I. Preparation of composition T of the ink receiving layer for sublayer 2 of the overlaver (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 5833 weight parts of water was prepared at 40 ⁰C, 32 weight parts of a solution of optical brightener blankophor PPW (10% aqueous solution from Bayer AG). The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating.

J. Preparation of composition 'J' of the ink receiving layer for sublayer 2 of the overlayer (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 5822 weight parts of water was prepared at 40 ⁰C, 43 weight parts of a solution of optical brightener blankophor PPW (10% aqueous solution from Bayer AG). The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating.

K. Preparation of composition 'K' of the ink receiving layer for sublayer 2 of the overlaver (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 5812 weight parts of water was prepared at 40 °C, 53 weight parts of a solution of optical brightener blankophor PPW (10% aqueous solution from Bayer AG). The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating. L. Preparation of composition 'L' of the ink receiving layer for sublayer 2 of the overlaver (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 5833 weight parts of water was prepared at 40 ⁰C, 32 weight parts of a solution of optical brightener Tinopal FSP (10% aqueous solution, CIBA Specialty Chemicals). The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating.

M. Preparation of composition 'M' of the ink receiving layer for sublayer 2 of the overlaver (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from

Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 5833 weight parts of water was prepared at 40 ⁰C, 32 weight parts of a solution of optical brightener CWT- 181 (10% aqueous solution, AGFA). The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating.

N. Preparation of composition 'N' of the ink receiving layer for sublayer 2 of the overlayer (top layer). A solution containing 100 weight parts of modified gelatin (dodecenyl-succinic modified acid treated gelatin from

Stoess GmbH, Germany with a modification degree of 40% and an IEP of 5.4), 5.5 weight parts of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 5776 weight parts of water was prepared at 40 °C, 89 weight parts of a solution of optical brightener blankophor PPW (Bayer). The pH of the solution was adjusted to 8.5 by adding NaOH and additional binder was added for bringing the viscosity to a suitable level for coating.

The compositions for sublayer 1 and 2 of the underlayer and sublayer 1 and 2 of the overlayer mentioned above were fed into a slide coating machine, commonly known in the photographic industry, and coated on a photographic grade paper having polyethylene laminated at both sides. After coating, the medium was chilled at a temperature of ca. 15 ⁰C to set the gelatin and then dried with dry air at a maximum temperature of 40 ⁰C. These examples describe one way of applying the invention. An overview of the layer structures of these examples is given below.

Layer structure

Various recording media were produced by applying on a substrate four layers: sublayer 1 of the underlayer (an adhesion promoting layer), sublayer 2 of the underlayer, sublayer 1 of the overlayer and sublayer 2 of the overlayer (a top layer) as shown in the scheme below. In the examples each layer is applied in the indicated amount, by the applied flow rate of the coated compositions.

Overlayer, sublayer 2 (toplayer)

Overlayer, sublayer 1

Underlayer, sublayer 2

Underlayer, sublayer 1 (adhesion promoting layer)

Photographic grade paper with polyethylene laminated on both sides

(Laminated Substrate) Example 1

In the order recited, the following layers were coated on a laminated substrate:

Sublayer 1 of the underlayer: 10 cc/m² of composition 'A' Sublayer 2 of the underlayer: 55 cc/m² of composition 'C

Sublayer 1 of the overlayer: 82 cc/m² of composition 'D'

Sublayer 2 of the overlayer: 17 cc/m² of composition 'H'

This gives a inkjet recording material with good general properties that has a good whiteness.

Example 2

Example 2 is prepared according to the method described in Example 1, except that instead of composition A, composition B is used for sublayer 1 of the underlayer ; and instead of composition H, composition I is used for sublayer 2 of the overlayer.

Example 3

Example 3 is prepared according to the method described in Example 2, except that instead of composition I, composition J is used for sublayer 2 of the overlayer.

Example 4

Example 4 is prepared according to the method described in Example 2, except that instead of composition I, composition K is used for sublayer 2 of the overlayer.

Example 5

Example 5 is prepared according to the method described in Example 2, except that instead of composition I, composition L is used for sublayer 2 of the overlayer. Example 6

Example 6 is prepared according to the method described in Example 2, except that instead of composition I, composition M is used for sublayer 2 of the overlayer.

Example 7

Example 7 is prepared according to the method described in Example 2, except that instead of composition D, composition E is used for sublayer 1 of the overlayer.

Example 8

Example 8 is prepared according to the method described in Example 2, except that instead of composition D, composition F is used for sublayer 1 of the overlayer.

Example 9

Example 9 is prepared according to the method described in Example 2, except that instead of composition D, composition G is used for sublayer 1 of the overlayer.

Example 10

Example 10 is prepared according to the method described in Example 2, except that instead of composition I, composition N is used for sublayer 2 of the overlayer.

Example 11

Example 11 is prepared according to the method described in Example 1, except that instead of composition A, composition B is used for sublayer 1 of the underlayer. Example 11 is a reference example, in which no optical brightener is present.

Evaluation The ink jet media prepared by the above mentioned formulation and coating process, were printed with a standard image comprising black, cyan, magenta and yellow bars. The image contained also two pictures; including a portrait picture and a composition picture. The image was printed at a room conditions (23 ⁰C and 48% Relative Humidity RH) and the printed materials were kept at this condition for at least 1 hour to dry.

An EPSON 950 was used to print the images by using the following settings:

• Print quality: quality mode

• Selected Paper type: EPSON premium photopaper • Other parameters were according to the factory setting.

The quality of the printed images is analysed visually by analysing the beading behaviour as depicted in the table below.

Table 1

Furthermore whiteness was measured with the Minolta CMlOOO colour measurement equipment. Results are noted as L*a*b*, in which L* indicates the amount of reflected light, a* and b* are colour directions. For a good whiteness L* should be as high as possible and theoretically a* and b* should be zero to give no additional colour. But practically a somewhat more bluish white is preferable above a pure neutral white. The application of an optical brightener will reduce the b*-value resulting in a negative b*-value indicating a more bluish white. The optimum b*-value is depending on the application and on personal preference. The range of the b*-value giving a bright white inkjet paper is from -4 to —8. Values higher than -4 are considered slightly yellowish, values lower than —8 are bluish and are not preferred.

Results Comparative Example 1 has been taken as reference to judge the effects of the compounds on beading. The results are summarized in Table 2.

Table 2

optical brightener is added to the composition for sublayer 1 of the underlayer, for all other examples, except comparative Example 11, the optical brightener is added to sublayer 2 of the overlayer. The reference Example 1 contains a certain level of optical brightener sufficient to achieve a preferred whiteness which is added to the layer near the support according to the state of the art as is described in e.g. EP-A-O 956 970. For this Example the beading is not optimal; it is comparable to Example 11 that does not contain optical brightener as is visible from the relative high b*- value. It is the objective of this invention to improve the performance on beading as well as maintaining a good whiteness. All inventive examples have a good whiteness corresponding with b*-values between -5 and -8. However the amount of optical brightener needed to obtain this good whiteness is significantly lower when added in the toplayer (sublayer 2 of the overlayer). Example 4 with 25% of the amount used in Example 1 has a whiteness comparable to that of Example 1. Even the examples with only 15% of the amount used in Example 1 show a good whiteness. Examples 5 and 6 with another type of optical brightener show slightly different values but are still performing well. Example 10 containing 42% of the amount used in

Example 1 clearly has a lower b*-value indicating a more bluish whiteness. The most surprising effect of adding the optical brightener to the toplayer is the effect on beading. Quantities as low as 0.009 g/m² of blankophor PPW (based on the dry content) lead to a much improved beading behaviour. Higher amounts do not improve beading further but do have an influence on whiteness. It may be beneficial to add the optical brightener in more than one layer. To optimize beading a certain amount may be added in one of the sublayers of the overlayer. The whiteness can be further optimized by adding an additional amount to another layer e.g. to a sublayer of the underlay er. The water soluble polymer in the overlayer has an important role. With the PVA- based polymer (PVA-NVF, Examples 2-6, 10) and with PVA (Example 7) very good results are obtained. In Example 8 the quantity of polymer is reduced while the quantity of gelatin is increased resulting in a less improved beading. This result shows that the content of the water soluble polymer should not be too low. In Example 9 as water soluble polymer PVP was used in stead of the PVA-based polymer. With this polymer only a slight improvement was obtained. This result indicates that PVA and PVA based polymers are more preferred.

Claims

1. Recording medium comprising a support and a receiving layer adhered to said support, which receiving layer is a multilayer comprising an overlayer and an underlayer, which overlayer and underlayer both comprise one or more sublayer(s), wherein at least one of said sublayers of the overlayer comprises a watersoluble polymer selected from the group of polyvinyl alcohol (PVA)-based polymer, polyvinyl pyrrolidone (PVP)-based polymer, and combinations thereof, and an optical brightening agent.

2. Medium according to claim 1, wherein said PVA-based polymer is selected from the group consisting of fully hydrolysed or partially hydrolysed polyvinyl alcohol, carboxylated PVA, acetoacetylated PVA, quaternary ammonium modified PVA, copolymers and terpolymers of PVA with other polymers, and combinations thereof. 3. Medium according to claim 1, wherein said PVA-based polymer is a PVA-NVF polymer according to formula I:

wherein n is between 0 and about 20 mole percent; m is between about 50 and about 97 mole percent; x is between 0 and about 20 mole percent; y is between 0 and about 20 mole percent; z is between 0 and about 2 mole percent and xΛ-y is between about 3 and about 20 mole percent; Ri, and R3 are independently H,

3-prop ionic acid or Ci-Cβ alkyl ester thereof, or is 2-methyl-3-propionic acid or Ci-Cβ alkyl ester thereof; and R2 and R4 are independently H or Ci-Cβ alkyl.

4. Medium according to any of the previous claims, wherein said optical brightener is selected from the group consisting of thiophenes, stilbenes, triazines, imidazolones, pyrazolines, triazoles, bis(benzoxazoles), coumarins, acetylenes and mixtures thereof.

5. Medium according to any of the previous claims, wherein said optical brightener is a diaminostilbene derivative, preferably a bis(4,4'- triazinylamino)-stilbene-2,2'-disulfonic acid derivative.

6. Medium according to any of the previous claims, wherein the ink receiving layer is substantially free from inorganic porous particles.

7. Medium according to any of the previous claims, wherein said overlayer further comprises a gelatin, preferably a modified gelatin selected from the group consisting of acetylated gelatin, phthalated gelatin, alkyl quaternary ammonium modified gelatin, succinated gelatin, alkylsuccinated gelatin, gelatin chemically modified with N- hydroxy succinimide ester of fatty acid, and combinations thereof.

8. Medium according to any of the previous claims, wherein said modified gelatin is succinic acid modified gelatin, wherein the succinic acid moiety contains an aliphatic chain from 5 to 20 carbon-atoms; preferably dodecenylsuccinic acid modified gelatin, in which at least 30% of the NH2 groups of the gelatin has been modified with said dodecenylsuccinic acid.

9. Medium according to any of the previous claims wherein said optical brightening agent is applied to the sublayer of said overlayer that is farthest away from said support.

10. Medium according to any of the previous claims, wherein said PVA- or PVP-based polymer is used in an amount of 0.5 to 15.0 g/m², preferably from 1.0 to 10.0 g/m².

11. Medium according to any of the previous claims, wherein said optical brightener is used in an amount of 5 to 500 mg/m², preferably from 5 to 100 mg/m².

12. Medium according to any of the previous claims where the multilayer further comprises an UV agent, an anti-oxidant, a light stabilizer, a radical scavenger, a surfactant, a fluoro surfactant or combinations thereof.

13. Medium according to the previous claims, where the support is selected from a paper, a base paper, a pigment coated base paper, a laminated pigment coated base paper, a laminated paper, a synthetic paper or a film substrate.

14. Medium according to any one of the previous claims, wherein the support has a surface roughness Ra smaller than 1.0 μm, preferably smaller than 0.8 μm.

15. A set of coating solutions for producing a recording medium comprising a first coating solution comprising a water soluble polymer selected from polyvinyl alcohol (PVA) based polymer, polyvinyl pyrrolidone (PVP) based polymer, and combinations thereof, a second coating solution essentially free of PVA based or PVP based polymers, a third coating solution, optionally additional coating solutions and an aqueous solution of an optical brightener which is added to at least one of the coating solutions that is essentially free of PVA based and PVP based polymers.

16. Process for preparing a recording medium, in particular a recording medium according to any of the claims 1-14, comprising the steps of: providing a first solution comprising a watersoluble polymer selected from the group of polyvinyl alcohol (PVA)-based polymer, polyvinyl pyrrolidone (PVP)-based polymer, and combinations thereof for the overlayer; - providing a second solution, which is essentially free of a PVA- or PVP -based polymer for a second sublayer of the overlayer; providing a third solution for the underlayer; optionally providing a fourth solution essentially free of a PVA- based or a PVP -based polymer for a second sublayer of the underlayer; - adding an aqueous solution of an optical brightener to the second, the third and/or the fourth solution; coating said, mixtures consecutively or simultaneously on a support, whereby the optical brightener diffuses to the layer comprising said water soluble polymer, followed by drying the coated support.

17. Process according to claim 16, wherein said coating step is carried out using curtain coating, extrusion coating, air-knife coating, slide coating, a roll coating method, reverse roll coating, dip coating processes and/or a rod bar coating.

18. A method of forming a permanent, precise inkjet image comprising the step of: a. providing a recording medium as defined in any of the claims 1-

14 or made by the process according to claim 16; and b. bringing ink into contact with the medium in the pattern of a desired image.