WO2006011797A1

WO2006011797A1 - Recording media

Info

Publication number: WO2006011797A1
Application number: PCT/NL2005/000553
Authority: WO
Inventors: Willem Johannes Van Baak; Jacko Hessing; Akira Kase
Original assignee: Fujifilm Manufacturing Europe BV
Current assignee: Fujifilm Manufacturing Europe BV
Priority date: 2004-07-30
Filing date: 2005-07-29
Publication date: 2006-02-02
Anticipated expiration: 2007-01-30

Abstract

The invention is directed to recording media, in particular swellable inkjet recording media. The inkjet recording media of the present invention comprise a support and an ink receiving layer adhered to said support, wherein the ink receiving layer is a multilayer having at least one layer comprising a water soluble polymer and at least one compound according to general formula (I): wherein: at least one of X1, X2 and X3 is C and the other(s) is (are) N, wherein X1-X3 and the two N atoms in the 1 and 3 position form a five ring; and R1 is cyclic C6, R2 and R3 are each independently selected from H, C1-C6 alkyl, hydroxyl, C1-C2 alkoxy, mercapto, C1 C6 alkylthio, amino, alkylamino, dialkylamino, halogen, sulfonyl, and carboxyl, wherein R1 may be absent if X2 is N, R2 may be absent if X3 is N and R3 may be absent if X1 is N, or R1 and R2 combined form a 6-membered ring fused to the five ring, which 6-membered ring may be heterocyclic and is optionally substituted, wherein each of the bonds may be single or double. The media of the present invention have improved properties, in particular with respect to beading behaviour.

Description

Title : Recording me dia

The invention is directed to recording media, in particular swellable inkjet recording media.

InkJet printers may usually be classified as either thermal inkjet printers that use heat to transfer the ink from the ink cartridge to the recording medium or inkjet printers which are based on Piezo technology, wherein instead of a heating element, each nozzle's ink chamber contains a Piezo crystal, which upon application of an electric current vibrates and thus forces the ink out of the nozzle to the recording medium.

These recording media should provide good image quality, in particular beading behaviour, over a wide range of ink loads. This means that these media should provide a correspondingly good absorption capacity, while at the same time the image quality should also be good. One approach that leads to recording media having these improved absorption characteristics combined with good image properties is disclosed in international patent application WO-A-2004/050379, which describes a recording medium comprising a porous water-swellable layer adhered to a support.

Although these (micro-)porous swellable 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.

It has been found that a certain class of heterocyclic compounds can effectively be used as an additive in inkjet recording media to improve beading behaviour. Thus the present invention relates to a recording medium which comprises a support and an ink receiving layer adhered to said support, wherein the ink receiving layer is a multilayer having at least one layer comprising a water soluble polymer and at least one compound according to general formula I: 1

wherein: at least one of X₁, X2 and X3 is C and the other(s) is(are) N, wherein Xi, X2, X3 and the two N atoms in the 1 and 3 position form a five ring; Ri is cyclic Cβ; and

R2 and R3 are substituents each independently selected from H, Ci- Ce alkyl, hydroxyl, C₁- C2 alkoxy, mercapto, Ci-Ce alkylthio, amino, alkylamino, dialkylamino, halogen, sulfonyl, and carboxyl; wherein Ri may be absent if X2 is N, R2 may be absent if X3 is N and R3 may be absent if Xi is N; or Ri and R2 combined form a 6-membered ring fused to the five ring, which 6-membered ring may be heterocyclic and is optionally substituted, wherein each of the bonds may be single or double.

Preferred compounds to be used according to the present invention are those of formula II:

wherein Xi, X2 and X4 are each independently selected from C and N; and R3, R4, R5, Re and R7 are substituents each selected independently from H, Ci-Ce alkyl (methyl, ethyl, propyl, butyl, pentyl, hexyl), hydroxyl, C1-C2 alkoxy (methoxy, ethoxy), mercapto, Ci-Cβ alkylthio (methylthio, ethylthio, propylthio, butylthio, pentylthio, hexylthio), amino, Ci- Cβ alkylamino, Ci-Cβ dialkylamino, halogen (chloro, bromo, iodo), sulfonyl, and carboxyl, wherein R3 may be absent if Xi is N and R₇ may be absent if X4 is N.

Preferred compounds in accordance with formula II are triazaindolizine compounds (also referred to as tetra-azaindene compounds), in particular compounds having a structure of formula III:

wherein R3, R4 and Re have the same meaning as defined with formula II above. The numbering indicated in formula IV is used for these indene compounds:

Preferred indene compounds are 4-hydroxy-6-methyl-l,3,3a,7-tetra- aza indene (formula Va; also described in EP-A-I 340 621) and 4-hydroxy-2- methylthio-6-methyl-l,3,3a,7-tetra-aza indene (formula Vb; also described in EP-A-I 340 621):

Other suitable compounds in accordance with formula (II) are compounds containing a triazole ring, in particular lH-benzotriazole (formula VI):

wherein R₄, Rs, Re and R₇ have the same meaning as defined with formula II above.

Other suitable compounds in accordance with formula (I) are tetrazole compounds, in particular l-phenyltetrazole-5-thiol (formula VII):

wherein Rs, R9 and R₁₀ are substituents each selected independently from hydroxyl, alkoxy, carboxyl, alkylcarbamido, amino, acetamino, chloro, sulfon and carbamoyl. These tetrazole compounds are usually less preferred because of their price.

Another suitable compound in accordance with formula II is benzimidazole or derivatives thereof (formula VIII):

wherein R3, R4, R5, Re and R7 have the same meaning as defined with formula II above.

Examples of benzimidazole derivatives are sodium-2- mercaptobenzimidazole-5-sulfonate, hydroxybenzimidazoles, mercapto- benzinaidazoles and methylbenzimidazoles (all available from Merck KgaA, Germany). 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.

It was found that by using the above-mentioned compounds in inkjet recording media a considerable improvement with respect to beading behaviour is obtained. In addition, an improvement on curling, in particular curling as a result of low humidity may be obtained according to the present invention. Furthermore the phenomenon called cracking which sometimes occurs at very low humidities also showed an improvement upon adding the above-mentioned compounds.

Preferably the compounds mentioned above are applied as an aqueous solution. If necessary to increase the solubility in water a high pH can be applied e.g. a pH of 9 or 10.

The compounds mentioned above are preferably used in an amount up to 10 mmol/m², more preferably in an amount between 0.5 and 5 mmol/m², most preferably in an amount between 0.5 and 4 mmol/m², depending on the total layer thickness.

The compounds mentioned above are used in the ink receiving layer. The ink receiving layer is a multilayer comprising an underlayer and an overlayer which both can be a multilayer of sublayers. In a specific embodiment a toplayer is provided on top of the overlayer. The compounds mentioned above are preferably applied in the outermost layer or layers of the multilayer (viz. furthest away from the support). In case a toplayer is provided it is preferable to add above mentioned compounds in a layer under the toplayer, in order to achieve an optimal effect on beading. It was found that the physical environment in which these compounds are active has an important influence on the effectiveness of the mentioned compounds. In an environment of gelatin no effect on beading is observed. The presence of water soluble polymers other than gelatin appeared necessary to provide a stabilising matrix. Without the presence of water soluble polymers, no improvement of beading is observed. In case gelatin is present preferably the weight ratio of water soluble polymer/gelatin in the overlayer is at least 1. More preferably this the weight ratio is at least 2. A high ratio is beneficial for an optimal effect. Water soluble polymers that are suitable for using in combination with the compounds of the invention include polyvinyl alcohol (PVA)-based polymers, such as fully hydrolysed or partially hydrolysed 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), carboxyalkyl 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, polyvinylpyrolidone (PVP), polyethyleneoxide (PEO), 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.

Most preferred are PVA-based polymers. Not only do these polymers contribute to the improvement of beading, they also appeared very effective for improving lightfastness properties. In general a large variety of PVA-based polymers can be used, but the preferred PVA-based polymers are those which have been modified to give a good miscibility with aqueous solutions of gelatin. These modifications are such, that in the PVA-based 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 PVA-based 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 X:

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-me thy 1- 3-propionic acid or Ci-Ce alkyl ester thereof; and

R2 and R₄ are independently H or Ci-Cβ alkyl. The water soluble polymer in the overlayer is preferably applied in an amount ranging from 0.5 to 15 g/m² and more preferably from 1.0 to 10 g/m².

The overlayer may further comprise a 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 or cow bone is used. In case a top layer is provided this toplayer preferably comprises a modified gelatin and optionally a fluorosurfactant. By using a modified gelatin a high gloss is obtained.

The term "modified gelatin" as used herein, refers to gelatin compounds in which at least part of the NH2 groups is chemically modified. A variety of modified gelatins can be used in the overlayer and/or in the toplayer. Good results are obtained, when at least 30% of the NH2 groups of the gelatin 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 20 C atoms. This aliphatic chain can be modified further to adjust the properties like water solubility and ink receptivity. Particularly preferred gelatins of this type are succinic acid modified gelatins in which the succinic acid moiety contains an aliphatic chain from 5 to 20 carbon-atoms, where the chain can be further modified to a certain extend to adjust the water soluble properties or ink receptive properties. Most preferred is dodecenylsuccinic acid modified gelatin, in which at least 30% of the NH2 groups of the gelatin have been modified with said dodecenylsuccinic acid.

Suitable methods for obtaining modified gelatins for use with the present invention are described e.g. in EP-A-O 56 911, 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). Other suitable modified gelatins giving good results are gelatins modified to have quaternary ammonium groups. An example of such a gelatin is the "Croquat™" gelatin produced by Croda Colloids Ltd. Yet other modified gelatins known in the common gelatin technology, such as phtalated gelatins and acetylated gelatins are also suitable to be used in the toplayer and/or the overlayer. Particularly suitable modified gelatins are available under the trade name Imagel™. The (modified) gelatin in the overlayer and/or toplayer is preferably applied in an amount ranging from 0.1 to 10 g/m², more preferably from 0.2 to 8 g/m².

The modified gelatin in the toplayer can be used alone or in combination with another water soluble polymer. Suitable water soluble polymers are the same as mentioned above for use in the overlayer.

The toplayer and/or the overlayer may further comprise one or more fluorosurfactants, preferably in an amount of 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 alky lcarboxy lie acids and salts thereof, disodium N-perfluorooctanesulfonyl glutamate, sodium 3-(SuOrO-Ce-C₁₁ alkyloxy)-l-C3-C4 alkyl sulfonates, sodium 3-(omega -fluoro-Cβ-Cβ alkanoyl-N-ethylamino)-l-propane sulfonates, N-[3- (perfluorooctanesuh^conamide)-propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine, perfluoro alkyl carboxylic acids (e.g. C^Cis-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-C₁S 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)S-S and x = 0 to 25, N-propyl- N-(2-hydroxyethyl)perfl.uorooctane sulfonamide, 2-sulfo-l,4- bis(fluoroalkyl)butanedioate, 1,4-bis (fluoroalkyl)-2-[2-N,N,N- trialkylammonium) alkyl amino] butanedioate, perfluoro Cβ-Cio alkylsulfonamide propyl sulfonyl glycinates, bis-(N-perfluorooctylsulfonyl-N- ethanolaminoethyl)phosphonate, mono-perfluoro Cβ-Ciβ alkyl-ethyl phosphonates, and perfluoroalkylbetaine. Also useful are the fhiorocarbon 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 fluoro surfactants 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.

Beside the (modified) gelatin or (modified) gelatin/water soluble polymer mixture and fluorosurfactant(s) it may be desirable to add in the overlayer and/or the toplayer an anti-blocking agent to prevent image transfer when several printed inkjet mediums are piled up. Very suitable anti-blocking agents (also known as matting agents) have a particle size from 1 to 20 μm, preferably between 2 and 10 μm. The amount of matting agent is from 0.01 to 1 g/m², preferably from 0.02 to 0.5 g/m². The matting agent can be defined as particles of inorganic or organic materials capable of being dispersed in a hydrophilic organic colloid. The overlayer and/or the toplayer may optionally include thickener agents, biocides, crosslinking agents, brightening agents and further various conventional additives such as colorants, colored pigments, pigment dispersants, mold lubricants, permeating agents, fixing agents for ink dyes, UV absorbers, light stabilising agents, anti-oxidants, dispersing agents, non-fluorosurfactants, anti-foaming agents, leveling agents, fluidity improving agents, antiseptic agents, brightening 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 water soluble polymers and/or gelatin in the ink receiving layer composition.

The multilayer of the recording medium comprises an overlayer and an underlay er. The overlayer may be a multilayer of sublayers. Also the underlayer may be a multilayer of sublayers. In a specific embodiment all layers are coated in a single step and the compounds of the invention are added to the mixture or mixtures of the underlayer. Before drying the compounds diffuse through the layers and are thought to be trapped by binding sites at the water soluble polymer present in the overlayer of the recording medium. Surprisingly by applying this method an even higher gloss level is achieved than when the compounds are added in the mixture for the overlayer. The mechanism for this enhanced gloss is not yet clear.

The underlayer typically comprises gelatin and at least one water soluble polymer. 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), carboxyalkyl cellulose {e.g. carboxymethylalkyl 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, polyvinylpyrolidone (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 quantity of gelatin used in the underlayer is preferably from 0.2 to 12.0 g/m², more preferably from 0.4 to 9.0 g/m². The quantity of water soluble polymer used in the underlayer is preferably from 0.5 to 15.0 g/m², more preferably from 1.0 to 8.0 g/m².

The homogeneous aqueous solutions for the underlayer may further contain the following ingredients: - crosslinking agents such as aldehyde compounds, such as formaldehyde and glutaraldehyde, ketone compounds such as diacetyl and chloropentanedion, bis (2-chloroethylurea), triazine compounds such as 2- hydroxy-4, 6-dichloro-l,3,5-triazine, reactive halogen-containing compounds, carbamoyl pyridinium compounds, divinylsulfones, and the like. - One or more plasticizers, such as (poly)alkylene glycol, glycerol ethers and polymer lattices with low Tg-value such as polyethylacrylate, polymethylacrylate and the like.

One or more mordants such as quaternary ammonium block copolymers, diaminoalkanes, ammonium quaternary salts and quaternary acrylic copolymer latexes, fluoro compounds, such as tetra ammonium fluoride hydrate, 2,2,2-trifluoroethylamine hydrochloride, l-(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-1-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 pigments, biocides, pH controllers, preservatives, viscosity modifiers, dispersing agents, UV absorbing agents, brightening agents, anti-oxidants, light stabilising agents, antistatic agents and/or anionic, cationic, non-ionic, and/or amphoteric surfactants 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 20% by weight, based on the solid content of the water soluble polymers and/or gelatin in the ink receiving layer.

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 an adhesion promoting layer is applied between the support and the underlayer 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, and preferably has a dry thickness of less than 3 μm, more preferably less than 1 μm. The adhesion promoting layer comprises a gelatin or another water soluble polymer that promotes the adhesion of the underlayer.

As stated above an important characteristic of the inkjet recording medium is the gloss. It has been found that the gloss of the medium can be 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 Ra 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, T-.O2, 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, such as epichlorhydrin fatty acid amid and the like. Further the paper may contain wet an 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 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 calendaring 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 or ZnS, dyes, coloured pigments, including blueing agents, e.g. ultramarine or 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. A process for producing a recording medium of the present invention typically comprises the steps of: a. preparing at least one aqueous mixture for the underlayer; b. preparing at least one aqueous mixture of at least a water soluble polymer for the overlayer; c. in case a toplayer is applied, preparing an aqueous mixture for the top layer; d. adding one or more additives according to general Formula I as defined above, to at least one of the mixtures for the overlayer or the underlayer; and e. coating said mixtures consecutively or simultaneously on said support using curtain coating, extrusion coating, air-knife coating, slide coating, a roll coating method, reverse roll coating, dip coating processes or a rod bar coating, followed by drying the coated support. Without wishing to be bound by theory, the present inventors surmise that two mechanisms may be present when the recording media of the present invention are put to use. According to the first mechanism the compounds of formula (I) described above interact with the positive charges that remain in the recording media after printing. By this physical interaction between the molecules of the water soluble polymers and/or the gelatin is reduced and as a consequence faster swelling and thus faster ink absorption is obtained. By the same reasoning the lower tendency of cracking of the layers at low humidities can be explained. According to the second hypothetical mechanism the above-mentioned compounds create binding sites by interacting with the water soluble polymer which can be occupied by the colorants of the ink.

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 underlaver solution 'A' of the ink receiving layer.

A 17 wt.% aqueous solution of a lime bone gelatin with an IEP of 5.0 and average MW of 250 kD (determined by the method described in the

Journal of Colloid and Interface Science 243, 476-482, 2001) was adjusted to pH 8.5 with NaOH. An aqueous solution of 30 wt % polyvinyl pyrollidone (PVP) having a molecular weight of 30 000 Daltons (ICN Biochemicals), was also prepared at pH 8.5. A homogeneous mixture (viz. no phase separation occurred), of gelatin and PVP having a weight ratio of 6:1 was made by adding 96 weight parts of said PVP solution and 161 weight parts of water into 1000 weight parts of said gelatin solution at a temperature of 40⁰C; the pH is kept at 8.5. This mixture was agitated for about 30 minutes.

B. Preparation of the overlaver solution 'B' of the ink receiving layer.

An aqueous 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 copolymer (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.

C. Preparation of the toplayer solution 'C of the ink receiving layer. A. solution containing 32 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), 1 weight part of Zonyl^® surfactant (a fluoro-carbon type of surfactant) and 967 weight parts of water was prepared at 40 ⁰C. The pH of the solution was adjusted to 8.5 by adding NaOH. D. Preparation of the overlaver solution 'D' of the ink receiving layer.

The solution was prepared in the same way as overlayer solution 'B' except that 27 weight parts of PVA-NVF co polymer and 946 parts of water were added.

The underlayer, overlayer and toplayer solutions 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 solution 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 three layers: an underlayer, an overlayer and 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 solution.

Toplayer

Overlayer

Underlayer

Photographic grade paper with polyethylene laminated on both sides (Laminated Substrate) Example 1 - comparative example

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

Underlayer 1: 57 cc/m² of underlayer solution 'A'

Overlayer 1: 80 cc/m² of overlayer solution 'B'

Top layer 1: 17 cc/m² of top layer solution 'C

This gives a inkjet recording material with good general properties that has reasonable beading properties. This examples forms the reference for the inventive examples.

Examples 2~12 - inventive:

The samples were prepared as in Example 1, except that to the composition of the underlayer is added one of the compounds of table 1 in an amount of 1.8 mmol/m².

Table 1.

Examples 13~16 — comparative:

The samples were prepared as in Example 1, except that to the composition of the underlayer is added one of the compounds of table 2 in an amount of 1.8 mmol/m².

Table 2.

Examples 17~19 - inventive:

The samples were prepared as in Example 1, except that in stead of overlayer solution 'B' composition 'D' was used to make the recording media. The compounds of table 3 are added to the underlayer.

Table 3.

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 (23⁰C 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 4

Results

Comparative example 1 has been taken as reference to judge the effects of the compounds on beading.

Table 5

Example Beading

15 X 16 X 17 Δ 18 Δ 19 Δ

Compounds 2~9 all showed a clear and significant improvement, compounds 13~16 showed no improvement. The best results were obtained with compounds 10~12. This result indicates that the compounds diffuse through the layers after coating and become effective at the surface. The influence of the PVA-NVF polymer used in the overlayer is demonstrated by examples 17-19. For those examples the coated quantity of polymer is reduced by 50% resulting in a less improved beading behaviour. When reducing the content of polymer even further at a certain point no improvement of the inventive compounds is observed.

Claims

1. Recording medium, which comprises a support and an ink receiving layer adhered to said support, which ink receiving layer is a multilayer comprising an underlayer and an overlayer which underlayer and overlayer both comprise one or more (sub-)layer(s), having at least one layer comprising a water soluble polymer and at least one compound according to general

Formula I:

1

^R2\ ___M

X₃ \ I _/Xi-R₃ 2

3 (D wherein: at least one of X₁, X2 and X3 is C and the other(s) is (are) N, wherein Xi₁ X2, X3 and the two N atoms in the 1 and 3 position form a five ring; R₁ is cyclic Cβ; and

R2 and R3 are each independently selected from H, Ci- Cβ alkyl, hydroxyl, C1-C2 alkoxy, mercapto, Ci-Cβ alkylthio, amino, alkylamino, dialkylamino, halogen, sulfonyl, and carboxyl, wherein R₁ may be absent if X2 is N, R2 may be absent if X3 is N and R3 may be absent if X₁ is N; or Ri and R2 combined form a 6-membered ring fused to the five ring, which 6-membered ring may be heterocyclic and is optionally substituted, wherein each of the bonds in Formula (I) may be single or double.

2. Medium according to claim 1, wherein said water soluble polymer is selected from the group consisting of polyvinyl alcohol (PVA)-based polymers, watersoluble cellulose derivatives, polyvinylpyrolidone (PVP), polyethyleneoxide (PEO), poly aery lamide, dextrin, dextran, polyacrylic acid and its copolymers or terpolymers, polymethylacrylic acid and its copolymers or terpolymers, and combinations thereof.

3. Medium according to any one of the previous claims, wherein said polyvinyl alcohol (PVA)-based polymer is selected from the group of fully hydrolysed or partially hydrolysed PVA, carboxylated PVA, acetoacetylated PVA, quaternary ammonium modified PVA, copolymers and terpolymers of PVA with other polymers, such as polyvinyl alcohol - N-vinylformamide (PVA-NVF) co-polymers according to formula X:

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.

4. Medium according to any of the previous claims, wherein the overlayer further comprises a gelatin, preferably a gelatin selected from lime- processed gelatin or acid processed gelatin, which is preferably pig skin, pig bone, cow skin or cow bone, hydrolysed or modified gelatin.

5. Medium according to claim 4, wherein the ratio of said water soluble polymer/gelatin in the overlayer is at least 1.

6. Medium according to any of the previous claims, wherein said compound of formula I and said water soluble polymer are present in at least one sublayer of the overlayer, which is situated furthest away from the support of the recording medium, optionally covered by a protective toplayer.

7. Medium according to any of the previous claims, wherein said compound of formula I is a compound of formula II:

wherein X₁, X2 and X4 are each independently selected from C and N; and R3, R4, R5, Re and R7 are substituents each selected independently from H, Ci- GQ alkyl, hydroxyl, Ci- C2 alkoxy, mercapto, Ci-Ce alkylthio, amino, alkylamino, dialkylamino, halogen, sulfonyl, and carboxyl, wherein R3 may be absent if Xi is N and R7 may be absent if X4 is N.

8. Medium according to any of the previous claims, wherein said compound of formula I is a triazaindolizine compound of formula III:

wherein R3, R4 and Re have the same meaning as defined in claim 7.

9. Medium according to any of the previous claims, wherein said compound of formula I is 4-hydroxy-6-methyl-l_J3,3a,7-tetra-aza indene, or 4- hydroxy-2-methylthio-6-methyl-l,3,3a,7-tetra-aza indene.

10. Medium according to claim 1-4, wherein said compound of formula I comprises a triazole ring (formula VI), and is preferably lH-benzotriazole:

wherein R4, R5, Ke and R7 have the same meaning as defined in claim 7.

11. Medium according to claim 1-4, wherein said compound in accordance with formula (I) is a tetrazole compound, preferably 1- phenyltetrazole-5-thiol (formula VTI):

wherein Re, R9 and R₁₀ are substituents each selected independently from hydroxyl, alkoxy, carboxyl, alkylcarbamido, amino, acetamino, chloro, sulfon and carbamoyl.

12. Medium according to claim 1-4, wherein said compound in accordance with formula (I) is a compound in accordance with formula II being benzimidazole or derivatives thereof (formula VTII):

wherein R3, R4, Rs, Re and R₇ have the same meaning as defined in claim 7, preferably sodium-2-mercaptobenzimidazole-5-suhOnate, hydroxybenzimidazoles, mercaptobenzimidazoles, or methylbenzimidazoles.

13. Medium according to any of the previous claims, wherein said at least one layer comprises a water soluble polymer being applied in an amount ranging from 0.5 tolδ g/m² and at least one compound according to general formula I being applied in an amount of up to 10 mmol/m².

14. Medium according to any of the previous claims, wherein a toplayer comprising a modified gelatin is provided on top of the overlayer.

15. Medium according to any of the previous claims, wherein the outermost layer comprises a fluorosurfactant.

16. Medium according to any of the previous claims, wherein 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 support.

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

18. Process for producing a recording medium, comprising the steps of: a. preparing at least one aqueous mixture for the underlayer; b. preparing at least one aqueous mixture of at least a water soluble polymer for the overlayer; c. adding one or more additives according to general Formula I as defined in claim 1, to at least one of the mixtures for the overlayer or the underlayer; and d. coating said mixtures consecutively or simultaneously on said support using curtain coating, extrusion coating, air-knife coating, slide coating, a roll coating method, reverse roll coating, dip coating processes or a rod bar coating, followed by drying the coated support.

19. A method of forming a permanent, precise inkjet image comprising the steps of: a. providing a recording medium as defined in any of the claims 1-17 or made by the process according to claim 18; and b. bringing ink into contact with the medium in the pattern of a desired image.