WO2006011798A1

WO2006011798A1 - Inj jet recording medium

Info

Publication number: WO2006011798A1
Application number: PCT/NL2005/000554
Authority: WO
Inventors: Willem Johannes Van Baak; Jacko Hessing; 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 present invention relates to a recording medium, in particular an ink-jet recording medium of photographic quality that has excellent lightfastness. According to the present invention a recording medium is provided, comprising a support and a receiving layer adhered to said support, wherein the receiving layer comprises an overlayer and an underlayer, wherein said overlayer comprises a combination of a PVA-based polymer and a hindered amine. The present invention is further directed to methods for obtaining and using such a medium.

Description

Title: INK JET RECORDING MEDIUM

Field of invention

The present invention relates generally to a recording medium, in particular an ink -jet recording medium of photographic quality that has excellent ink absorption speed, good drying characteristics and a good image printing quality, in particular an improved lightfastness, as well as 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.

A further important property of inkjet media is that they should provide for a good lightfastness, viz. the printed images must not fade over longer periods of time. In order to improve the lightfastness of inkjet media, several approaches have been suggested in the prior art. JP-A-4 201 594, for instance, suggests to include hyperfine powder of specific transition metal oxides into one or more layers and GB-A-2 147 003, for instance, suggest to combine metal salts with cationic polymeric substances to improve lightfastness of the produced images. Furthermore, JP-A-2002/220 559 and EP-A-O 869 010 describe a specific copolymer, which is to be included in one or more of the layers of the inkjet media, to improve lightfastness.

JP-A-2000/280 601 discloses inkjet recording media wherein the lightfastness is improved by incorporating a UV absorbent in a protective layer of the media.

WO-A-03/054029 describes polyvinyl alcohol)-co-poly(N-vinyl formamide) copolymers (PVA-NVF) for use in inkjet recording media. The inkjet recording media of this document are said to have improved image permanence against the harmful effects of light and/or atmospheric pollutants. The application of sterically hindered amine light stabilisers (HALS) in inkjet media to protect the image against fading upon exposure to light is known since 1989 (Research Disclosure 1989-303062, Kenneth Mason publ.). Specific HALS compounds have been suggested in Research Disclosure 1990- 319080, in EP-A-I 205 312 and in WO-A-02/055618. EP-A-I 329 331 discloses an ink-jet recording sheet comprising a hindered amine compound and claims a good ozone resistance and a good light stability but is silent about the whiteness after prolonged aging.

Whiteness is an important aspect of recording materials. When the lightfastness is to some extend solved, it is still a problem to have a good whiteness maintaining at the same time good drying properties together with good gloss, good image printing quality, good curl and brittleness, having good behavior on bleed, beading and matte appearance at high density parts and also be available at low cost. Thus there remains a need for ink-jet materials having good lightfastness and whiteness keeping at the same time good physical properties as mentioned above. It is towards fulfilling these needs that the present invention is directed. Summary of the invention

Object of the present invention is to provide a recording medium, in particular an ink-jet 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 lightfastness.

It is a further objective of this invention to provide an ink -jet recording medium where the medium has an improved lightfastness as well as a good whiteness.

At the same time it is desirable that the media of the present invention maintain other favourable properties with respect to good drying properties, good gloss, good image printing quality, good curl and brittleness, having at the same time good behavior on bleed, beading and matte appearance at high density parts.

It was 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 comprises an overlayer and an underlayer (viz. a layer that is situated closer to the support than said overlayer), wherein said overlayer comprises the combination of a polyvinyl alcohol (PVA)-based polymer and a hindered amine, wherein the ratio of said PVA-based polymer and hindered amine is larger than 5 kg polymer/mol of hindered amine moiety, preferably larger than 6 kg/mol.The obtained medium is stable with respect to yellowing.

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 comprises an overlayer and an underlayer, wherein said overlayer comprises the combination of a polyvinyl alcohol (PVA)-based polymer and a hindered amine, wherein the ratio of said PVA-based polymer and hindered amine is larger than 5 kg polymer/mol of hindered amine moiety, preferably larger than 6 kg/mol. This invention is also related to the manufacturing of such a recording medium and the use of this medium.

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.

Both the overlayer and the underlayer of this invention may be 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 2 to 17.

The use of a hindered amine in an ink-receiving layer has been described in the literature as effective to improve the light fading properties of the image after producing such an image by inkjet printing. It is thought that the hindered amine acts as a radical scavenger. However investigations showed that especially unprinted areas slowly become yellow as a result of decomposition of the hindered amine compound. Also unused sheets of inkjet paper upon natural aging suffer from this phenomenon of yellowing.

By our research it was surprisingly found that this adverse property of yellowing can be prevented while maintaining the beneficial effects of the hindered amine by combining the hindered amine compound with a PVA based polymer.

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 gelatin solutions. 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 polyvinyl 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:

O OH N-Ri N-R₃ NH₂

C=O C=O C=O

I I I

CH₃ R₂ R4 ,-p.

wherein n is between O 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 χ-Hy 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-Ce alkyl ester thereof; and

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

The PVA-based polymer 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 hindered amine is preferably water-soluble and can be selected from a large number of compounds that contain one or more sterically hindered N-atoms. Preferably the hindered amine compound can be described according the general formula (II):

wherein each Of R₁-Re are independently H, C₁, C2, C3 θr C4-alkyl, X"- is a inorganic or organic anion, such as phosphate, phosphonate, carbonate, bicarbonate, nitrate, chloride, bromide, bisulfite, sulfite, bisulfate, sulfate, borate, formiate, acetate, benzoate, citrate, oxalate, tartrate, acrylate, fumarate, maleate, itaconate, glycolate, gluconate, malate, mandelate, tiglate, ascorbate, a carboxylate of nitrilo triacetic acid, hydroxyethylethylenediamine triacetic acid, ethylenediamine tetra-acetic acid or of diethylenetriamine penta-acetic acid, a diethylenetriaminepentamethylenephosphonate, an alkylsulfonate or an arylsulfonate, n is 1-4. Examples of hindered amines of this type are those of the CGP-serie commercially available from Ciba Specialty Chemicals.

Although the combination of PVA based polymer and hindered amine shows an improved behaviour related to the resistance to dye fading and discolouration of the recording medium it was found that a too high quantity of hindered amine compound leads to yellowing of the medium. Thus the hindered amine is preferably present in an amount that is effective to avoid excessive yellowing. In order to quantify the extent of yellowing the Lab color model is used. CIE L*a*b (CIELAB) is the most complete color model used conventionally to describe all the colors visible to the human eye. It was developed for this specific purpose by the International Commission on Illumination (Commission Internationale d'Eclairage, hence the CIE acronym in its name). The three parameters in the model represent the luminance of the color (L, the smallest L represents black), its position between red and green (a, the smallest a represents green) and its position between yellow and blue (b, the smallest b represents blue). Excessive yellowing may suitably be defined by the change of the b- value upon natural aging, which can be measured as set out in the examples hereinbelow. In accordance with the present invention the change of the b- value is preferably not larger than 2, more preferably not larger than 1. Natural aging is the aging behaviour under temperature and humidity conditions that are taken as average. For temperature a value of 21 ⁰C and for relative humidity a value of 47 % is taken as standard.

Good results were obtained when the ratio of PVA-based polymer and hindered amine is above a certain value. It seems that the polymer has a stabilising effect on the hindered amine and that it should be prevented that an excess of hindered amine is present. Since for polymers it is impossible to determine an exact molecular weight, it has been found convenient to express the amount of hindered amine used as unit weight of polymer per mol of nitrogen atoms that are present in the form of hindered amine (mol of hindered amine moiety). The ratio of PVA-based polymer and hindered amine (HALS) preferably is larger than 5 kg polymer/mol of hindered amine moiety, more preferably larger than 6 kg/mol, most preferably larger than 8 kg/mol. Since the main purpose of adding the hindered amine compound is to prevent or reduce the light fading of the dyes, a balance must be found between the light stabilising function and the adverse effect of yellowing. In general at a quantity of less than 0.1 mmol/m² the hindered amine compound does not have a significant effect on light stability.

In one embodiment the overlayer is a single layer and comprises the combination of a PVA based polymer and a hindered amine and may contain a gelatin and a fluorosurfactant. In another embodiment the overlayer is a multilayer of sublayers wherein at least one sublayer comprises the combination of a PVA based polymer and a hindered amine. In a specific embodiment a toplayer is coated on top of the overlayer, which toplayer is for instance the layer that is farthest away from the support and may comprise a (fluoro) surfactant and a gelatin while the combination of the PVA based polymer and the hindered amine may be in a sublayer located between said toplayer and the underlayer.

The overlayer and/or the toplayer may comprise a gelatin, preferably a modified gelatin which has a positive effect on the gloss of the recording medium. The gelatin used in the overlayer and/or the toplayer can be any gelatin whether lime-processed or acid processed made from animal collagen, preferably gelatin made from pig skin, pig bone, cow skin or cow bone or modified gelatin.

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 such as acetylated gelatin, phthalated gelatin, alkyl quaternary ammonium modified gelatin, succinated gelatin, alkylsuccinated gelatin, gelatin chemically modified with N-hydroxysuccinimide ester of fatty acid, and combinations thereof. 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-197 21 238. 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-O 576 911, 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 (C4-C16). Other 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. Still other modified gelatins known in the common gelatin technology, such as phtalated gelatin and ace ty late d gelatins are also suitable. The gelatin is preferably applied to the solution for the overlayer and/or the top layer in an amount ranging from 0.1 to 10 g/m² and more preferably from 0.2 to 8 g/m².

A further improvement can be obtained by including in the overlayer and/or the toplayer 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. Beading is defined as the phenomenon that large ink dots become visible on the printed image. The mechanism of "beading" is not clear yet. One hypothesis is that several small ink drops coalesce with each other on the surface of the ink jet media and form large ink droplets.

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-(fluoro-C6-Cπ alkyloxy)-l-C3-C4 alkyl sulfonates, sodium 3-(omega -fluoro-Cβ-Cs alkanoyl-N-ethylamino)-l-propane sulfonates, N-[3- (perfluorooctanesulfonamide)-propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine, perfluoro alkyl earboxylic 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-perfiuoro 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)_xH 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 Cβ-Cio alkylsulfonamide propyl sulfonyl glycinates, bis-(N-perfluoro-octylsulfonyl-N- ethanolaminoethyl)phosphonate, mono-perfluoro Ce-C₁G 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 (fluoroaIkyl)-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)_xH wherein Rf = F(CF₂CF₂)_3-8 and x = 0 to 25.

The overlayer and/or the toplayer may further comprise water insoluble particles inter alia to regulate the slip behaviour and other additives to optimise the surface properties. The overlayer and/or the toplayer may include other water-soluble polymers, matting agents, brightening agents, thickener agents, biocides, crosslinking agents and further various conventional additives such as colorants, colored pigments, pigment dispersants, mold lubricants, permeating agents, fixing agents for ink dyes, anti-oxidants, dispersing agents/non-fluorosurfactants, anti-foaming agents, levelling 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 can be a multilayer of sublayers. The underlayer typically comprises gelatin and at least one 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), hydroxy alkyl cellulose (e.g. hydroxyethyl cellulose or hydroxypropyl cellulose), carboxyalkyl cellulose (e.g. carboxymethyl cellulose), dextrin, casein, gum arabic, dextran, poly aery lie 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 1 to 30 g/m², and more preferably from 2 to 20 g/m². The amount of water soluble polymer used in a certain formulation is typically in the range from 200 mg/m² to 30 g/m² and more preferably between 400 mg/m² and 20 g/m². When preparing the ink -jet-receiving sheet by coating a plurality of ink receiving layers, each ink-receiving layer preferably comprises an amount of gelatin ranging from 0.2 to 10 g/m².

Preferably the ratio of gelatin and water soluble polymer in the underlayer is chosen in such a way that the miscibility remains good and that properties such as curling and cockling are at an optimum level. It was found that a ratio of gelatin and water soluble polymer between 0.2 and 5 gives satisfactory results. In case acid or alkali treated gelatin is used in combination with PVP or PVA, the optimum ratio lies between 0.25 and 1. Good curling behaviour is achieved together with excellent gloss and fast drying.

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, preferably having 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 chloropentanedione, 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 (i.e. overlay er and/or the toplayer and/or the underlayer) 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, aminobutadiene compounds and mixtures thereof.

Examples of UV agents are those described in Research Disclosure RD24239, RD290119, RD30326, EP-A-O 673 783, GB-A-2 088 777, EP-A-O 955 180, EP-A-O 738 718, US-A-4 926 190 and in Ullmann's Encyclopedia of Industrial Chemistry, 5^th 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-10-147577, JP -10-182621, JP-T-8-501291 ("JP-T" means published searched patent publication). EP-A-O 711 804 and DE-A-197 39 797 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'methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-sec-dodecyl- 5'mehtylphenyl) benzotriazole, as well as the benzotriazole compounds described in EP-A-O 738 718, the benzotriazole compounds described in US-A-4 926 190, 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 ink-receiving layer may further comprise an optical brightener.

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, irαidazolones, pyrazolines, triazoles, bis(benzoxazoles), coumarins and acetylenes. The optical brightener can be added in a suitable solvent or as a component of an oil in water emulsion. Also optical brighteners linked to gelatin can be used.

The optical brightener is present in the ink receiving layer in an amount lower than 1 gram/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. 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 fillers; both organic and inorganic particles can be used as fillers. Useful filler examples are represented by silica (colloidal silica), alumina or alumina hydrate (aluminazol, colloidal alumina, a cat ion aluminum oxide or its hydrate and pseudo-boehmite), a surface-processed cat ion colloidal silica, aluminum silicate, magnesium silicate, magnesium carbonate, titanium dioxide, zinc oxide, calcium carbonate, kaolin, talc, clay, zinc carbonate, satin white, diatomaceous earth, synthetic amorphous silica, aluminum hydroxide, lithopone, zeolite, magnesium hydroxide and synthetic mica. Useful examples of organic fillers are represented by polystyrene, polymethacrylate, polymethylmethacrylate, elastomers, ethylene-vinyl acetate copolymers, polyesters, polyester-copolymers, polyacrylates, polyvinylethers, polyamides, polyolefins, polysilicones, guanamine resins, polytetrafluoroethylene, elastomeric styrene-butadiene rubber (SBR), urea resins, urea-formalin resins. Such organic and inorganic fillers may be used alone or in combination.

- 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-fhiorophenyl) piperazine rαonohydrochloride, 1-fluoro pyridinium triϋuorom ethane sulfonate.

- One ore more conventional additives, such as:

• pigments: white pigments such as titanium oxide, zinc oxide, talc, calcium carbonate and the like; blue pigments or dyes such as cobalt blue, ultramarine or phthalocyanine blue; magenta pigments or dyes such as cobalt violet, fast violet or manganese violet; • • 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, fillers/pigments, 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.

The particle sizes of the non water-soluble particulate additives should not be too high, since otherwise a negative influence on the resulting surface will be obtained. The used particle size should therefore preferably be less than 10 μm, more preferably 7 μm or less. The particle size is preferably above 0.1 μm, more preferably about 1 μm or more for handling purposes. The process for producing a recording medium according to the invention can be described by the following steps:

- preparation of at least one mixture comprising a PVA-based polymer and a hindered amine for the overlayer; - preparation of at least one mixture for the underlayer; in case a toplayer is applied, preparing a mixture for the toplayer; providing a support for receiving said mixtures; and

- coating the resulting formulations for the overlayer and the underlayer 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.

An important characteristic of the inkjet recording medium is the gloss. Surprisingly 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, 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, Tiθ2, 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 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 like 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.

The swellable ink-receiving layer 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 underlaver composition 'A' of the ink receiving layer.

A solution containing 105 weight parts of 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), 26 weight parts of polyvinyl alcohol (PVA Mowiol™ 4-88, from Kuraray Specialties Europe) and 869 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.

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

A solution containing 60 weight parts of lime bone gelatin with an IEP of 5.0 and average MW of 250 kD, 15 weight parts of polyethylene oxide (PEO with a MW of about 100 kD from Sigma Aldrich Chemicals, Netherlands), 5 weight parts of polyvinylpyrrolidone (PVP with a MW of about 30 kD from ICN Biochemicals) and 920 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 toplaver composition '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 overlayer composition 'D' of the ink receiving layer.

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.

The underlayer, overlayer and toplayer compositions 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 °C 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 most examples each layer is applied in the indicated amount, by the applied flow rate of the coated compositions. Toplayer

Overlayer

Underlayer

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:

Underlayer 1: 57 cc/m² of underlayer solution 'A' Overlayer 1: 80 cc/m² of overlayer solution 'B' Toplayer 1: 17 cc/m² of toplayer solution 'C

This gives a inkjet recording material with good general properties that has reasonable light fading properties.

Example 2

Example 2 is prepared according to the method as described in Example 1 except that in stead of composition B for the overlayer is used composition D.

Example 3

To composition B for the overlayer is added a solution of CGP-520, a hindered amine compound commercially available from Ciba Specialty Chemicals, in an amount of 0.25 g/m², corresponding to a ratio of PVA-NVF co¬ polymer and CGP-520 of 4.1 kg/mol of hindered amine moiety. The recording medium is prepared according the method as described in Example 1. Example 4

Example 4 is prepared according to the method as described in Example 3 except that in stead of composition B for the overlayer is used composition D.

Example 5

Example 5 is prepared as in Example 4, except that to the composition for the overlayer is added a solution of CGP-520 in an amount of 0.125 g/m², corresponding to a ratio of PVA-NVF co-polymer and CGP-520 of 8.2 kg/mol of hindered amine moiety.

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 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.

A HP Deskjet^® 5650 was used to print the images using the following settings:

- Print quality : best

- Selected Paper type: HP premium plus photo paper, glossy

- Other parameters were according to the factory setting.

The whiteness of the samples is measured as follows. The CIE Lab parameters are measured by the Minolta CMlOOO with the following settings:

Light source: D65

Observer angle: 10°

The b-value is taken as a measure for whiteness and is determined for an unprinted fresh sample just after coating and after storage of the medium for a prolonged period of time at room temperature conditions (natural aging).

Lightfastness is a measure for the dye stability during the display or storage at (ambient) light conditions. In order to evaluate this behavior a sample was exposed for 504 hrs using a xenon light (85 000 Ix) in an Atlas Wether-O-Meter C I 4000, manufactured by Atlas, Illinois, USA. Using a cycle of 228 minutes light on with a temperature of 31 ⁰C and a relative humidity (RH) of 50 % and a period of 60 minutes light off at a temperature of 19 ⁰C and a RH of 90 %. The image density of the color on the printed area is measured before and after the xenon exposure and was measured by a reflection densitometer (X- Rite color model DTP41) and evaluated as the dye residual percentage. The following classification has been defined:

O: 90 % or more residual percentage Δ: 85-90 % residual density

X: less than 85 % of residual density

Results

* natural aging time has been 4 months. The examples show a large effect of the composition of the overlayer on the whiteness after natural aging. Low b-values are preferred, values between -6 and -7 indicate a very bright inkjet paper providing images with vibrant colors. Higher values (-4 and higher) indicate inkjet media that are yellowish and are not preferred. Media with lower values (-8 and lower) tend to be bluish and are less preferred.

For a good light stability the presence of a hindered amine compound is desired. As shown in Example 5 an amount of 0.125 g/m² in combination with the PVA based polymer is sufficient to achieve an excellent light fastness while the whiteness is maintained at a good level. Using another water soluble polymer e.g. a mixture of PEO and PVP has a negative effect on the whiteness.

Claims

1. Recording medium comprising a support and a receiving layer adhered to said support, which receiving layer is a multilayer comprising an underlayer and an overlayer, which overlayer comprises one or more (sub-)layer(s), wherein at least one of said (sub-)layers comprises the combination of a polyvinyl alcohol (PVA)-based polymer and a hindered amine, wherein the ratio of said PVA-based polymer and hindered amine is larger than 5 kg polymer/mol of hindered amine moiety, preferably larger than 6 kg/mol.

2. Medium according to any one of the previous claims, wherein said PVA-based polymer is selected from the group of poly(vinyl alcohol)-co-poly(N- vinyl formamide) (PVA-NVF) co-polymers 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 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.

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

4. Medium according to any of the previous claims, wherein said hindered amine can be described according the general formula (II):

wherein each of R₁-Re are independently H, C₁, C2, Cs or C₄ alkyl, X^n~ is a inorganic or organic anion, n is 1-4.

5. Medium according to any of the previous claims, wherein the overlayer further comprises a modified gelatin.

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

7. Medium according to any one of the previous claims, wherein said modified gelatin is selected from the group consisting of acetylated gelatin, phthalated gelatin, alkyl quaternary ammonium modified gelatin, succinated gelatin, alkylsuccinated gelatin, gelatin chemically modified with N- hydroxysuccinimide ester of fatty acid, and combinations thereof.

8. Medium according to any of the previous claims wherein said modified gelatin is a succinated gelatin comprising a C5-C25 alkyl group, a C5- C25 fatty acid group, or both; more preferably a C₇-C₁S alkyl group, a Cγ-Ciβ fatty acid group, or both.

9. Medium according to any of the previous claims, wherein the modified gelatin is dodecenylsuccinic acid modified gelatin in which at least 30% of the NH2 groups of the gelatin have been modified with said dodecenylsuccinic acid.

10. Medium according to any of the previous claims, wherein the modified gelatin is used in an amount of 0.1 to 10.0 g/m², more preferably from 0.2 to 8.0 g/m².

11. Medium according to any of the previous claims, wherein the toplayer comprises a fluorosurfactant.

12. Medium according to any one 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.

13. 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.

14. Process for producing a recording medium, comprising the steps of: a) preparation of at leas t one mixture comprising a PVA-based polymer and a hindered amine for the overlayer; b) preparation of at leas t one mixture for the underlayer; c) providing a support for receiving said mixtures; 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.

15. A method of forming a permanent, precise inkjet image comprising the step of: providing a recording medium as defined in any of the claims 1-13 or made by the process according to claim 14; and bringing ink into contact with the medium in the pattern of a desired image.