WO2008044616A1 - Recording sheet for ink jet printing - Google Patents

Recording sheet for ink jet printing Download PDF

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Publication number
WO2008044616A1
WO2008044616A1 PCT/JP2007/069523 JP2007069523W WO2008044616A1 WO 2008044616 A1 WO2008044616 A1 WO 2008044616A1 JP 2007069523 W JP2007069523 W JP 2007069523W WO 2008044616 A1 WO2008044616 A1 WO 2008044616A1
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WO
WIPO (PCT)
Prior art keywords
unsubstituted
acid
substituted
silicon dioxide
aminoorganosilane
Prior art date
Application number
PCT/JP2007/069523
Other languages
French (fr)
Inventor
Meinrad Schaer
Vincent Ruffieux
Original Assignee
Oji Paper Co., Ltd.
Ilford Imaging Switzerland Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oji Paper Co., Ltd., Ilford Imaging Switzerland Gmbh filed Critical Oji Paper Co., Ltd.
Publication of WO2008044616A1 publication Critical patent/WO2008044616A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/50—Recording sheets characterised by the coating used to improve ink, dye or pigment receptivity, e.g. for ink-jet or thermal dye transfer recording
    • B41M5/52—Macromolecular coatings
    • B41M5/5218—Macromolecular coatings characterised by inorganic additives, e.g. pigments, clays
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3081—Treatment with organo-silicon compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/50—Agglomerated particles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values

Definitions

  • the present invention relates to a method for preparation of surface modified silicon dioxide, wherein the surface of the silicon dioxide is modified by mixing said silicon dioxide with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof. Furthermore, the present invention relates to a coating solution for a recording sheet for ink jet printing comprising the surface modified silicon dioxide particles prepared by the present method together with a binder, as well as a recording sheet for ink jet printing having coated onto a support said coating solution.
  • Ink jet printing processes are mainly of two types: continuous stream and drop-on-demand.
  • a continuous ink stream is emitted under pressure through a nozzle.
  • the stream breaks up into droplets at a certain distance from the nozzle. If a specific location on the recording sheet has to be printed the individual droplets are directed to the recording sheet, otherwise they are directed to a collecting vessel. This is done for example by charging unnecessary droplets in accordance with digital data signals and passing them through an static electric field which adjusts the trajectory of these droplets in order to direct them to the collecting vessel.
  • the inverse procedure may also be used wherein uncharged droplets are collected in the vessel.
  • a droplet is generated and expelled from the nozzle in accordance with digital data signals only if a specific location on the recording sheet has to be printed.
  • recording sheets suitable for these printers therefore need to absorb the inks very quickly.
  • recording sheets containing nanocrystalline, nanoporous inorganic compounds preferably oxides such as aluminium oxides or silicon dioxide, or oxide/hydroxides such as aluminium oxide/hydroxides.
  • Such recording sheets are known as "nanoporous" recording sheets.
  • Japanese unexamined patent publication (Kokai) No. 8-034160 describes the preparation of a media coated with a solution containing a silane coupling agent having a quaternary ammonium salt.
  • the disadvantage of the described method is that a solution containing the silane has to be coated on the media in a second step.
  • Japanese unexamined patent publication (Kokai) No. 2000-233572 describes an ink-receiving layer containing a vapor-phase method silica and a silane coupling agent, on a water-resistent supporting body. Mentioned silanes bear alkoxy or halide groups.
  • Japanese unexamined patent publication (Kokai) No.62-178384 describes the preparation of a dispersion containing a silica which has been surface-treated with a silane coupling agent.
  • the silane coupling agent bears epoxy, glycidoxy, amino, mercapto or methacryl functional groups .
  • European patent EP0983867 describes the surface treatment of colloidal silica with an aminosilane to prepare an ink-jet recording media.
  • US patent application US2005/0147770 describes the preparation of a media sheet obtained by dispersing inorganic porous particulates and an active ligand- containing organosilane in water. Described silanes bear for example UV-absorbers, sterically hindered amines or other functional groups as as substituants . Examples mention the use of a silane bearing amino groups.
  • An objective of the invention is to provide nanoporous recording sheets with improved water fastness, improved diffusion fastness and better resistance to degradation by ozone of recording sheets printed with dye-based inks.
  • a further objective of the invention is an improved manufacturability of the coating solutions for a recording sheet for ink jet printing and an improved coating quality of the recording sheets according to the invention.
  • Such a recording sheet consists of a support having coated thereon at least one ink-receiving layer containing the surface modified silicon dioxide of the present invention.
  • a method for preparation of surface modified silicon dioxide wherein the surface of the silicon dioxide is modified by mixing said silicon dioxide with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof.
  • step (ii) said at least one monovalent acid or salt is added to the aqueous solution of step (i) to form the solution of said at least one aminoorganosilane and at least one monovalent acid or salt thereof; and then
  • said silicon dioxide is added to the solution formed in step (ii) to modify the surface of said silicon dioxide .
  • said solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof comprises the reaction product of said at least one aminoorganosilane and at least one monovalent acid or salt thereof which does not have a hydroxyl group.
  • R represents H, substituted or unsubstituted alkyl
  • M represents H or a monovalent cation.
  • Ri, R 2 and R 3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl with 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and R 4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
  • aminoorganosilane is selected from the group consisting of 3-aminopropyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyl-trimethoxysilane, (3- triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyl- triethoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, (3-trimethoxy-silylpropyl) - diethylenetriamine and mixtures thereof.
  • said aminoorganosilane has the general formula
  • R5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms
  • R 6 represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms
  • R 7 , R 8 and Rg independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
  • Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and
  • aminoorganosilane is selected from the group of N- (n- butyl) -aminopropyl-trimethoxysilane, N- (n-butyl) - aminopropyl-triethoxysilane, N- (cyclohexyl-aminopropyl) - trimethoxysilane, N- (cyclohexyl-aminopropyl) - triethoxysilane, N- (cyclohexyl-aminomethyl) - trimethoxysilane, N- (cyclohexyl-aminomethyl) - triethoxysilane, N-ethylamino-isobutyl-trimethoxysilane and N-ethylamino-isobutyl-triethoxysilane .
  • a recording sheet for ink jet printing having coated onto a support an ink receiving layer comprising at least one aminoorganosilane, at least one monovalent acid or salt thereof, silicon dioxide and a binder.
  • R represents H, substituted or unsubstituted alkyl
  • M represents H or a monovalent cation.
  • Ri, R 2 and R 3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl with 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
  • R 4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
  • said aminoorganosilane is selected from the group consisting of 3-aminopropyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyl-trimethoxysilane, (3- triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyl- trietyhoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, (3-trimethoxy-silylpropyl) - diethylenetriamine and mixtures thereof.
  • R 5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms
  • Re represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms
  • R 7 , Rs and Rg independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
  • aminoorganosilane is selected from the group of N- (n-butyl) -aminopropyl-trimethoxysilane, N- (n- butyl) -aminopropyl-triethoxysilane, N- (cyclohexyl- aminopropyl) -trimethoxysilane, N- (cyclohexyl- aminopropyl) -triethoxysilane, N- (cyclohexyl-aminomethyl) - trimethoxysilane, N- (cyclohexyl-aminomethyl) - triethoxysilane, N-ethylamino-isobutyl-trimethoxysilane and N-ethylamino-isobutyl-triethoxysilane .
  • a nanoporous recording sheet for ink jet printing containing in its in-receiving layer a dispersion of surface modified silicon dioxide, wherein the surface of the silicon dioxide has been modified with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof, shows a considerable improvement of the aforementioned properties, compared to a media in which the silica has been cationically modified using either at least one aminosilane and an inorganic acid.
  • the use of the surface modified silicon dioxide prepared by the method of the present invention improves colour rendition, water fastness and resistance to ozone of images printed with dye-based inks.
  • the treatment of silica with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof leads to a much better migration resistance of ink-jet dyes .
  • the synthetic silicon dioxide used in the recording sheets according to the invention may be prepared either by precipitation in a wet process (precipitated silicon dioxide) or in a gas phase reaction (fumed silicon dioxide) .
  • Precipitated silicon dioxide may be prepared for example in the wet process by metathesis of sodium silicate with an acid or by passing through a layer of ion-exchange resin as silicon dioxide sol, by heating and maturing of this silicon dioxide sol or by gelling of a silicon dioxide sol.
  • the gas phase reaction for the preparation of fumed silicon dioxide by flame pyrolysis is also known as a dry- process in contrast to the wet process.
  • silicon tetrachloride is reacted in the presence of hydrogen and oxygen under formation of silicon dioxide and hydrochloric acid.
  • Silanes such as for example methyltrichlorosilane or trichlorosilane, may be used in this process in place of silicon tetrachloride or in combination with silicon tetrachloride.
  • fumed silicon dioxide is used in the recording sheets according to the invention.
  • Fumed silicon dioxide consists of aggregates of small primary particles. These primary particles themselves are not porous. The aggregates, however, are porous and may absorb quickly big amounts of liquids for this reason.
  • the aggregates of fumed silicon dioxide normally have a size (mean diameter) of more than 100 nm. Particles with a size between 100 nm and 500 nm are preferred, particularly preferred are particles with a size between 150 nm and 250 nm. These sizes refer to the aggregates.
  • the primary particles have a size between 1 nm and 100 nm. A size between 1 nm and 30 nm is preferred, particularly preferred is a size between 5 nm and 15 nm.
  • Fumed silicon dioxide has a specific surface between 20 m 2 /g and 400 m 2 /g.
  • a specific surface between 40 m 2 /g and 400 m 2 /g is preferred.
  • Particularly preferred is a specific surface between 90 m 2 /g and 330 m 2 /g.
  • the specific surface is determined by the BET isotherm method, as described by S. Brunauer, P. H. Emmet and I. Teller in "Adsorption of Gases in Multimolecular Layers", Journal of the American Chemical Society 60_, 309 (1938) .
  • fumed silicon dioxide is for example added at high shear rates to a mainly aqueous solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof. Under suitable conditions, a dispersion of surface modified fumed silicon dioxide is obtained that does not coagulate.
  • Deionised water is preferably used for the preparation of the mainly aqueous solutions. Water- miscible solvents such as lower alcohols (methanol, ethanol, propanol and the like) or ketones such as acetone may be added.
  • the solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof may also be added, for example, to an aqueous dispersion of silicon dioxide.
  • the silicone dioxide can be added to a mixture of at least one aminosilane and water under high shear, and the monovalent acid continuously added to balance the pH.
  • the silicone dioxide may be added in a solution of the monovalent organic acid and water, thus resulting in an anionic dispersion of silica at low pH, and at least one aminoorganosilane added under high shear to reverse the neat charge of the silica surface.
  • the preparation of the surface modified silicon dioxide according to the invention can be carried out by, providing an aqueous solution of at least one aminoorganosilane; adding at least one monovalent acid or salt to the aqueous solution to form a solution comprising said aminoorganosilane and said monovalent acid or salt thereof; and then adding a silicon dioxide to the thus-formed solution to modify the surface of said silicon dioxide.
  • the aminosilane is hydrolysed in water at room temperature for about 10 minutes, then the monovalent acid is added and the mixture is stirred for another 10 minutes at room temperature.
  • the aminosilane is quickly hydrolysed at high pH and the reaction product of the monovalent acid and the aminoorganosilane is formed upon addition of the monovalent acid.
  • the silica powder is transferred portionswise to the solution containing the reaction product of the monovalent acid and the aminoorganosilane .
  • the preparation of the surface modified silicon dioxide according to the invention can be carried out by, providing an aqueous solution of at least one monovalent acid or salt thereof; adding at least one aminoorganosilane to the aqueous solution to form a solution comprising said monovalent acid or salt thereof and said aminoorganosilane; and then adding a silicon dioxide to the thus-formed solution to modify the surface of said silicon dioxide.
  • the aminosilane is added to a solution comprising water and the monovalent organic acid or salt thereof and allowed to hydrolyse during 10 minutes under stirring at room temperature.
  • the silica powder is transferred portionswise to the solution containing the reaction product of the monovalent acid and the aminoorganosilane .
  • the modification of the surface of the silicon dioxide with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof is an almost instantaneous process. For this reason, the conversion time is very short (within minutes) and is completed at room temperature.
  • Fumed silicon dioxide is particularly preferred for the surface modification.
  • a mixture of different silicon dioxide powders having different sizes of the primary particles may be used.
  • the modification step with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof may be carried out individually for each silicon dioxide powder or simultaneously with the mixture of the different silicon dioxide powders.
  • the modification step is done at high shear rates, the reaction products are regularly distributed on the surface of the silicon dioxide. Furthermore, the rheological behaviour of the dispersion is improved.
  • Suitable aminoorganosilanes are aminoorganosilanes of formula (I)
  • Ri' R 2 ' R 3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl and
  • R 4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
  • the substituents are independently selected from the group consisting of thiol, sulfide and polyalkylene oxide.
  • selected substituents facilitate the surface modification of silicon dioxide (improved rheological behaviour of the dispersions and of the coating solutions) and improve properties of the recording sheets such as stability against air pollutants, light fastness and physical properties.
  • Condensation products of the aminoorganosilanes may also be used in place of the monomeric aminoorganosilanes. The condensation reactions may occur between identical or different aminoorganosilanes.
  • Preferred aminoorganosilanes are 3- aminopropyltrimethoxysilane, N- (2-aminoethyl) -3- aminopropyl-trimethoxysilane, (3-triethoxysilylpropyl) - diethylentri amine, 3-aminopropyltriethoxysilane, N- (2- aminoethyl) -3-amino propyltriethoxy silane, (3-triethoxysilylpropyl) -diethylenetriamine and their mixtures.
  • Nanoporous media are prone to react with some components of cardboard packing material, leading to more or less strong yellowing of the media even in dark storage conditions. Packing the media in an inert plastic sheet usually helps circumventing this undesired effect, but at the expense of the overall packaging costs.
  • aminosilanes that show this property exhibit the following generic structure:
  • R 5 In(OR 6 ) 3- m -Si (CH 2 ) x (CHR 7 ) y (CR 8 R 9 ) Z -NH-R 1O wherein, R 5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
  • R 6 represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms
  • R 7 , Rs and Rg independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and
  • aminosilanes only bearing a secondary amino group greatly improve the ease of dispersion of silica, when compared to other types of aminosilanes, especially aminoorganosilanes which are terminated by a primary amino group.
  • Suitable monovalent acids include inorganic acid, e.g.
  • hydrochloric acid or nitric acid organic acid such as carboxylic acid, e.g., formic acid, acetic acid, propionic acid, lactic acid, acrylic acid, glyoxylic acid, methoxyacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid or alpha- hydroxyisobutyric acid, sulfonic acid, e.g., methanesulfonic acid, ethanesulfonic acid.
  • the monovalent acid is formic acid, acetic acid or propionic acid, and most preferably, it is formic acid. This list gives examples of possible acids but does not limit in any way the use of other, not cited, monovalent acids.
  • Salts of the monovalent acid can be formed by any monovalent cation, for example, lithium, sodium, potassium, ammonium, or the like.
  • the dispersion of the surface modified silicon dioxide according to the invention is advantageously used directly for the preparation of the coating solution of an ink-receiving layer of a recording sheet for ink jet printing. Therefore, the dispersion has to be stable for at least 24 hours without sedimentation of the surface modified silicon dioxide and is not allowed to change its viscosity considerably. In particular, it is not allowed to gel or to coagulate.
  • the dispersion contains the surface modified silicon dioxide according to the invention in an amount of from 5 percent by weight to 50 percent by weight. Amounts of from 10 percent by weight to 30 percent by weight are preferred, particularly preferred are amounts of from 15 percent by weight to 25 percent by weight.
  • the surface modification of the silicon dioxide with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof leads to a positive surface charge of the silicon dioxide.
  • the colouring compounds (dyes or pigments) contained in inks for ink jet printing very often contain groups which may be ionized, such as SO 3 H, COOH, PO 3 H 2 and the like, increasing the solubility of ink-jet dyes. After the dissociation of these groups, the dyes are therefore negatively charged in the mainly aqueous ink liquid and are therefore electrostatically attracted and fixed by the positive charge at the surface of the modified silicon dioxide.
  • Dispersion of the silicon dioxide can be accomplished, for example, by means of a conventional dispersion device such as Nanomizer ® , Ulitimizer” , Menton- Gaulin ® , Ystral Conti ® , Dyno-Mill ® , and the like.
  • the aforementioned devices may be used alone or two or more types may be used in combination.
  • the total amount of the ingredients used for the preparation of the solution comprising the aminoorganosilane and the monovalent acid or salt thereof has to be chosen in such a way that most of the aggregates of silicon dioxide have the possibility to react with the solution. The total amount depends on the molecular weight of the aminoorganosilane and the number of amino groups in the molecule.
  • the total quantity of the aminoorganosilane, respectively the mixture of aminoorganosilanes, typically is between 0.1 percent by weight and 15 percent by weight relative to the quantity of silicon dioxide. A value between 5 percent by weight and 10 percent by weight is preferred.
  • the weight ratio between the monovalent acid or salt thereof and the aminoorganosilane is preferably chosen in such a way that the desired value of pH is attained when the. two compounds are mixed.
  • a molar ratio between 0.1 and 2.0 is preferred, depending on the number of amino groups in the molecule. Particularly preferred is a molar ratio of the monovalent acid to amino groups of the aminosilane between 0.3 and 1.0.
  • the value of pH of the solution comprising the aminoorganosilane and the monovalent acid or salt thereof is preferably chosen to be between 4 and 10.
  • the pH of the dispersion containing the silicone dioxide surface- with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof is preferably set between 4 and 10, and most preferably between 5 and 8.
  • the solution comprising the aminoorganosilane and the monovalent acid or salt thereof acts as a buffer, which means that there is no need to add further acid or base to maintain the pH upon addition of the silica powder.
  • the recording sheet may contain, in addition to the surface modified silicon dioxide according to the invention, other, porous or non-porous, inorganic compounds .
  • the recording sheet according to the invention may contain, in addition to the surface modified silicon oxide, salts of monovalent copper such as copper (I) chloride, copper (I) bromide or copper (I) sulphite monohydrate as described in patent application EP 1,231,071.
  • the recording sheet may contain, in addition to the salts of monovalent copper, diketo compounds as described in patent application EP 1197345.
  • the recording sheet may contain in addition organic sulphur compounds such as thiodiethylene glycol.
  • the binders are in most cases water-soluble polymers. Especially preferred are film-forming polymers.
  • the water-soluble polymers include for example natural polymers or modified products thereof such as albumin, gelatine, casein, starch, gum arabicum, sodium or potassium alginate, hydroxyethyl cellulose, carboxymethyl cellulose, ⁇ -, ⁇ - or ⁇ -cyclodextrine and the like.
  • gelatine all known types of gelatine may be used as for example acid pigskin or limed bone gelatine, acid or base hydrolyzed gelatine, but also derivatized gelatines like for instance phthalaoylated, acetylated or carbamoylated gelatin or gelatine derivatised with the anhydride of trimellitic acid.
  • Synthetic binders may also be used and include for example polyvinyl alcohol, polyvinyl pyrrolidone, completely or partially saponified products of copolymers of vinyl acetate and other monomers; homopolymers or copolymers of unsaturated carboxylic acids such as maleic acid, (meth) acrylic acid or crotonic acid and the like; homopolymers or copolymers of sulfonated vinyl monomers such as vinylsulfonic acid, styrene sulfonic acid and the like.
  • Preferred synthetic binders are polyvinyl alcohol and polyvinyl pyrrolidone or mixtures thereof.
  • These polymers may be blended with water insoluble natural or synthetic high molecular weight compounds, particularly with acrylate latices or with styrene acrylate latices.
  • water insoluble polymers are nevertheless considered part of the system.
  • the polymers mentioned above having groups with the possibility to react with a cross-linking agent may be cross-linked or hardened to form essentially water insoluble layers. Such cross-linking bonds may be either covalent or ionic. Cross-linking or hardening of the layers allows for the modification of the physical properties of the layers, like for instance their liquid absorption capacity or their resistance against layer damage .
  • cross-linking agents or hardeners are selected depending on the type of the water-soluble polymers to be cross-linked.
  • Organic cross-linking agents and hardeners include for example aldehydes (such as formaldehyde, glyoxal or glutaraldehyde) , N-methylol compounds (such as dimethylol urea or methylol dimethylhydantoin) , dioxanes (such as 2, 3-dihy-droxydioxane) , reactive vinyl compounds (such as 1, 3, 5-trisacrylolyl hexahydro-s-triazine or bis- (vinylsulfonyl) ethyl ether), reactive halogen compounds (such as 2, 4-dichloro-6-hydroxy-s-triazine) ; epoxides; aziridines; carbamoyl pyridinium com-pounds or mixtures of two or more of the above mentioned cross-linking agents .
  • Inorganic cross-linking agents or hardeners include for example chromium alum, aluminium alum or
  • the layers may also contain reactive substances that cross-link the layers under the influence of ultraviolet light, electron beams, X-rays or heat.
  • the layers may further be modified by the addition of fillers.
  • Fillers are for instance kaolin, Ca- or Ba-carbonates, silicon dioxide, titanium dioxide, bentonites, zeolites, aluminium silicate or calcium silicate.
  • Organic inert particles such as polymer beads may also be used. These beads may consist of polyacrylates, polyacrylamides, polystyrene or different copolymers of acrylates and styrene.
  • the fillers are selected according to the intended use of the printed images. Some of these compounds cannot be used if the printed images are to be used as transparencies. However they are of interest in cases where the printed images are be to used as remission pictures. Very often, the introduction of such fillers causes a wanted matte surface.
  • the recording sheets may also contain water-soluble metal salts, as for example salts of the alkaline earth metals or salts of the metals of the rare earth series.
  • the recording sheets according to the invention comprise a support having coated thereon at least one ink-receiving layer, and, optionally, auxiliary layers.
  • a gloss layer comprising fine pigments with a mean particle size of up to 200 nm such as colloidal silica, colloidal alumina, organic pigments or the like may be formed on the ink receiving layer.
  • the coating amount of the gloss layer can be up to 5 g/m 2 , preferably up to 3 g/m 2 , in terms of the absorbability or glossiness of the ink.
  • the gloss layer may comprise a small amount of pigments with a mean particle size of at least 1 ⁇ m so as to improve the transportability by a printer.
  • the pigments with a mean particle size of at least 1 ⁇ m inorganic or organic pigments may be used, and among them, organic particles, in particular, polystyrene pigments are preferable as they do not deteriorate the glossiness .
  • a wide variety of supports are known and commonly used in the art. They include all those supports used in the manufacture of photographic materials. This includes clear films made from cellulose esters such as cellulose triacetate, cellulose acetate, cellulose propionate or cellulose acetate/butyrate, polyesters such as polyethylene terephthalate or polyethylene naphthalate, polyamides, polycarbonates, polyimides, polyolefins, polyvinyl acetals, polyethers, polyvinyl chloride and polyvinylsulfones . Polyester film supports, and especially polyethylene terephthalate or polyethylene naphthalate are preferred because of their excellent dimensional stability characteristics.
  • the usual opaque supports used in the manufacture of photographic materials may be used including for example baryta paper, polyolefin coated papers or voided polyester as for instance Melinex" manufactured by DuPont. Especially preferred are polyolefin coated papers or voided polyester.
  • a subbing layer is advantageously coated first to improve the bonding of the ink-receiving layers to the support.
  • Useful subbing layers for this purpose are well known in the photographic industry and include for example terpolymers of vinylidene chloride, acrylonitrile and acrylic acid or of vinylidene chloride, methyl acrylate and itaconic acid.
  • the surface of the support may be subjected to a corona-discharge treatment before the coating process.
  • Uncoated papers comprising all different types of papers, varying widely in their composition and in their properties, and pigmented papers and cast-coated papers may also be used, as well as metal foils, such as foils made from aluminium.
  • the layers may also be coated onto textile fibre materials consisting for example of polyamides, polyesters, cotton, viscose and wool.
  • the ink-receiving layers according to the invention are in general coated from aqueous solutions or dispersions containing all necessary ingredients.
  • wetting agents are added to those coating solutions in order to improve the coating behaviour and the evenness of the layers. Besides being necessary for coating purposes, these compounds may have an influence on the image quality and may therefore be selected with this specific objective in mind. Although not specifically claimed in this invention, wetting agents nevertheless form an important part of the invention.
  • recording sheets according to the invention may contain additional compounds aimed at further improving their performance, as for example brightening agents to improve the whiteness, such as stilbenes, coumarines, triazines, oxazoles or others compounds known to someone skilled in the art .
  • UV absorbers such as 2-hydroxybenzotriazoles, 2- hydroxybenzophenones, derivatives of triazine or derivatives of cinnamic acid.
  • the amount of UV absorber may vary from 200 mg/m 2 to 2000 mg/m 2 , preferably from 400 mg/m 2 to 1000 mg/m 2 .
  • the UV absorber may be added to any of the layers of the recording sheet according to the invention. It is preferred that, however, if it is added, it should be added to the topmost layer. It is further known that images produced by ink jet printing may be protected from degradation by the addition of radical scavengers, stabilizers, reducing agents and antioxidants.
  • Examples of such compounds are sterically hindered phenols, sterically hindered amines, chromanols, ascorbic acid, phosphinic acids and their derivatives, sulphur containing compounds such as sulphides, mercaptans, thiocyanates, thioamides or thioureas .
  • the above-mentioned compounds may be added to the coating solutions as aqueous solutions. In the case where these compounds are not sufficiently water-soluble, they may be incorporated into the coating solutions by other common techniques known in the art.
  • the compounds may for example be dissolved in a water miscible solvent such as lower alcohols, glycols, ketones, esters, or amides.
  • the compounds may be added to the coating solutions as fine dispersions, as oil emulsions, as cyclodextrine inclusion compounds or incorporated into latex particles.
  • the recording sheet according to the invention has a thickness in the range of 0.5 ⁇ m to 100 ⁇ m dry thickness, preferably in the range of 5 ⁇ m to 50 ⁇ m dry thickness.
  • the coating solutions may be coated onto the support by any number of suitable procedures. Usual coating methods include for example extrusion coating, air knife coating, doctor blade coating, bead coating, cascade coating and curtain coating.
  • the coating solutions may also be applied using spray techniques. Particularly, curtain coating technique is preferable since the tendency of occurrence of a coating defect is low.
  • the height of the curtain i.e., the distance between the coating lip, where the fluid detaches from the hopper device to fall down by gravity, and the support to be coated
  • the application angle of the coating solution falling down onto the support i.e. the angle between the support and the horizontal line (normal to the gravity) at the impact point, the position where the coating solution drops onto the support, etc.
  • the ink-receiving layers may be built up from several individual layers that can be coated one after the other or simultaneously.
  • the coating process is carried out at a speed of about 20 to 400m/min.
  • the individual ink-receiving layers may be different in respect to the used fumed silicon dioxide (in particular its specific surface) , the modification with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof, the ratio between the binders and the silicon dioxide and the quantity of hardener, in particular boric acid.
  • Inks for ink jet printing consist in essence of a liquid vehicle and a dye or pigment dissolved or suspended therein.
  • the liquid vehicle for ink jet inks consists in general of water or a mixture of water and a water-miscible organic solvent such as ethylene glycol, higher molecular weight glycols, glycerol, dipropylene glycol, polyethylene glycol, amides, polyvinyl pyrrolidone, N-methylpyrrolidone, cyclohexyl pyrrolidone, carboxylic acids and their esters, ethers, alcohols, organic sulfoxides, sulfolane, dimethylformamide, dimethylsulfoxide, cellosolve, polyurethanes, acrylates and the like.
  • the non-aqueous parts of the ink generally serve as humefactants, cosolvents, viscosity regulating agents, ink penetration additives or drying agents.
  • the organic compounds have in most cases a boiling point, which is higher than that of water.
  • aqueous inks used for printers of the continuous stream type may contain inorganic or organic salts to increase their conductivity. Examples of such salts are nitrates, chlorides, phosphates and salts of water-soluble organic acids such as acetates, oxalates and citrates.
  • the dyes and pigments suitable for the preparation of inks useable with the recording sheets according to the invention cover practically all classes of known colouring compounds. Dyes or pigments typically used for this purpose are described in patent application EP O 1 559 '324.
  • the recording sheets according to the invention are meant to be used in conjunction with most of the inks representing the state of the art.
  • the inks may further contain other additives such as surfactants, optical brighteners, UV absorbers, light stabilizers, biocides, precipitating agents such as multivalent metal compounds and polymeric additives.
  • additives such as surfactants, optical brighteners, UV absorbers, light stabilizers, biocides, precipitating agents such as multivalent metal compounds and polymeric additives.
  • Patches of the colours yellow, red, magenta, blue, cyan, green and black at 100% print density were printed onto the recording sheets according to the invention with the ink jet printers HP 5652, Canon I 990 and Epson R 300 using the corresponding original inks.
  • the printed colour patches have an edge length of 118 pixels.
  • Each individual colour patch is divided by 11 horizontal and 11 vertical white lines into 144 individual coloured squares having an edge length of 8 pixels.
  • the white lines have a width of 2 pixels.
  • printer settings were used:
  • the printed recording sheets were dried for 24 hours at a temperature of 23 0 C at relative humidity of 50%.
  • the optical densities of the colour patches were measured. Afterwards, the printed recording sheets were stored for 7 days at a temperature of 40 0 C and relative humidity of 80%. Finally, the optical densities were re- measured.
  • the printed recording sheets were dried for 24 hours at a temperature of 23°C at relative humidity of 50%. Then, their L*a*b* colour coordinates were determined. Afterwards, the printed recording sheets were stored for 7 days at a temperature of 40°C and relative humidity of 80%. Finally, L*a*b* colour coordinates were re- determined. The value for the most diffusing colour is given as a measure of dye diffusion
  • Optical density of each colour patch is measured using the channels R, G, B and compared to the optical density of a reference pattern (stored in a protection sheet without gas flow) .
  • the determining value for the assessment of the resistance to ozone fading is the number of ppmh ozone necessary to lose a given fraction of the initial density for the most sensitive channel.
  • the molar ratio between the aminosilane and silica is 2.4 mol-% and the molar ratio of acetic acid to silica is 2.49 mol-%.
  • Example 6 22.1g of N- (2-aminoethyl) -3-aminopropyl- trimethoxysilane (available from Degussa, D ⁇ sseldorf, Germany) were added to 709g deionised water under stirring. After 10' stirring, 63.3g of a 10% solution of propionic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil" M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates.
  • Cab-O-Sil fumed silicon dioxide
  • Example 12 Same procedure as Example 9, but 607.2g of the dispersion of Example 3 was used instead of the dispersion of Example 1.
  • Example 12
  • Example 13 Same procedure as Example 9, but 607.2g of the dispersion of Example 5 was used instead of the dispersion of Example 1.
  • Example 17 Same procedure as Example 9, but 607.2g of the dispersion of Example 8 was used instead of the dispersion of Example 1.
  • Example 17
  • Example 9 140 g/m 2 of the coating solution of Example 9 were coated at a temperature of 40°C with a bar coater onto a polyethylene terephthalate support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 17.5 of surface-treated silica .
  • Example 10 140 g/m 2 of the coating solution of Example 10 were coated at a temperature of 40°C with a bar coater onto a polyethylene terephthalate support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 17.5 of surface-treated silica .
  • Example 17 Same procedure as Example 17, but the coating solution of Example 11 was used instead of the coating solution of Example 9.
  • Example 12 Same procedure as Example 17, but the coating solution of Example 12 was used instead of the coating solution of Example 9.
  • Example 22 Same procedure as Example 17, but the coating solution of Example 13 was used instead of the coating solution of Example 9.
  • Example 22 Same procedure as Example 17, but the coating solution of Example 13 was used instead of the coating solution of Example 9.
  • Example 17 Same procedure as Example 17, but the coating solution of Example 14 was used instead of the coating solution of Example 9.
  • Example 23 Same procedure as Example 17, but the coating solution of Example 15 was used instead of the coating solution of Example 9.
  • Example 17 Same procedure as Example 17, but the coating solution of Example 16 was used instead of the coating solution of Example 9.
  • Table 1 clearly show that the recording sheet for ink jet printing according to the invention, where the surface of the silicon dioxide has been modified with a solution comprising at least one aminoorganosilane and at least one monovalent organic acid or salt thereof (Examples 17-22), exhibits a strongly reduced dye diffusion in comparison to a recording sheet, where the surface of the silicon dioxide has been modified with a solution comprising an aminoorganosilane and an inorganic acid like nitric acid or hydrochloric acid (Examples 23 and 24).
  • Ozone resistance is indicated as the total amount of ozone (in ppmh) necessary to lose a given percentage of colour density.
  • the most sensitive colour is indicated after each printer's name.
  • Dynasylan AMEO from Degussa, D ⁇ sseldorf, Germany) were added to the solution under vigorous stirring.
  • 23Og of fumed silicon dioxide (Cab-O-Sil H-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates.
  • the dispersion was stirred with a rotor-stator-mixer for 5 minutes.
  • a dispersion containing 23.0% SiO2 and exhibiting a pH value of 6.20.
  • the molar ratio between the aminosilane and silica is 6.0 mol-% and the molar ratio of formic acid to silica is 4.12 mol-%.
  • Mowiol 4088 from Clariant AG, Muttenz, Switzerland were added and afterwards 13.3g of an aqueous solution of the wetting agent Olin 1OG (5.26%, available from Arch Chemicals, Norwalk, USA) .
  • the coating solution was diluted with deionised water to a final weight of 100Og.
  • Example 33 140 g/m 2 of the coating solution of Example 29 were coated at a temperature of 40 0 C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 19.04g of surface-treated silica.
  • Example 30 140 g/m 2 of the coating solution of Example 30 were coated at a temperature of 40 0 C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 19.04g of surface-treated silica .
  • Example 36 140 g/m 2 of the coating solution of Example 31 were coated at a temperature of 40°C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 19.04g of surface-treated silica.
  • Example 36 140 g/m 2 of the coating solution of Example 31 were coated at a temperature of 40°C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 19.04g of surface-treated silica.
  • Example 36 140 g/m 2 of the coating solution of Example 31 were coated at a temperature of 40°C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 19.04g of surface-treated silica.
  • Example 36 140 g/m 2 of the coating
  • Example 32 140 g/m 2 of the coating solution of Example 32 were coated at a temperature of 40°C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m 2 of the coated support contains 19.04g of surface-treated silica .
  • the media to test are cut in pieces of 2 x 10cm and put in a white cardboard box of the size 21.5 x 30.5 x 1.5cm, PrintPac, Ilford Art. Nr. 116'194.
  • An internal reference cut in a standard media is joined to the material to test.
  • the box is placed in a sealable, gas fast polyethylene bag from VTT, Germany, sealed and heated for 5 days at the temperature of 60 0 C in a Salvis drying oven.
  • a good measure for the ease of dispersion is to determine the minimum amount of surface-treating agent needed to get a reasonable addition time. This is achieved by starting with a high amount of surface- treating agent, lowering it in subsequent dispersions so that the silica becomes almost impossible to disperse, and drawing a curve of addition time vs. amount of surface-treating agent (referred to as ratio of amine to silica in mol-%) .
  • the minimal quantity of amine before the addition time begins to rise is the measure of dispersibility.
  • the silica dispersions were prepared as in Ex. 25-28, the amount of formic acid being determined such as maintaining identical pH throughout the series.
  • the ⁇ -potential of the treated silicon dioxide surface is measured with a Quantachrome DT-1200 acoustophoresis device.
  • Table 5 gives the amount in g of water, aminosilane and formic acid (20% solution) that were used.
  • the minimum amount of aminosilane necessary to prepare a dispersion containing 23% of silicon dioxide H5 in less than 20 minutes is 6.0mol-% of silicon dioxide when Dynasylan AMEO is used, 2.7mol-% (5.4mol-% of amine) when Dynasylan DAMO is used, and 2.9mol-% when Dynasylan 1189 or Momentive A-LINK15 are used.
  • Table 7 indicates the ⁇ -potential value of these dispersions at 10% silicon dioxide concentration: mol-% AMEO DAMO 1189 A-LINK15 amine [mV] [raV] [mV] [mV]

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Abstract

A method for preparation of surface modified silicon dioxide, wherein the surface of the silicon dioxide is modified by mixing said silicon dioxide with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof is provided.

Description

DESCRIPTION
RECORDING SHEET FOR INK JET PRINTING TECHNICAL FIELD The present invention relates to a method for preparation of surface modified silicon dioxide, wherein the surface of the silicon dioxide is modified by mixing said silicon dioxide with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof. Furthermore, the present invention relates to a coating solution for a recording sheet for ink jet printing comprising the surface modified silicon dioxide particles prepared by the present method together with a binder, as well as a recording sheet for ink jet printing having coated onto a support said coating solution. BACKGROUND ART
Ink jet printing processes are mainly of two types: continuous stream and drop-on-demand.
In continuous stream ink jet printing, a continuous ink stream is emitted under pressure through a nozzle.
The stream breaks up into droplets at a certain distance from the nozzle. If a specific location on the recording sheet has to be printed the individual droplets are directed to the recording sheet, otherwise they are directed to a collecting vessel. This is done for example by charging unnecessary droplets in accordance with digital data signals and passing them through an static electric field which adjusts the trajectory of these droplets in order to direct them to the collecting vessel. The inverse procedure may also be used wherein uncharged droplets are collected in the vessel.
In the non-continuous process, or the so-called "drop-on-demand" process, a droplet is generated and expelled from the nozzle in accordance with digital data signals only if a specific location on the recording sheet has to be printed.
The printing speed of modern ink jet printers is ever increasing for economical reasons. Recording sheets suitable for these printers therefore need to absorb the inks very quickly. Especially suitable are recording sheets containing nanocrystalline, nanoporous inorganic compounds, preferably oxides such as aluminium oxides or silicon dioxide, or oxide/hydroxides such as aluminium oxide/hydroxides. Such recording sheets are known as "nanoporous" recording sheets.
Such recording sheets available today do not meet all of the required demands. In particular, in the case where dye-based inks are used for recording, the water fastness and the diffusion fastness of images printed on these recording sheets have to be improved. Stability against ozone and other environmental gases are also far from ideal.
Japanese unexamined patent publication (Kokai) No. 8-034160 describes the preparation of a media coated with a solution containing a silane coupling agent having a quaternary ammonium salt. The disadvantage of the described method is that a solution containing the silane has to be coated on the media in a second step.
Japanese unexamined patent publication (Kokai) No. 2000-233572 describes an ink-receiving layer containing a vapor-phase method silica and a silane coupling agent, on a water-resistent supporting body. Mentioned silanes bear alkoxy or halide groups.
Japanese unexamined patent publication (Kokai) No.62-178384 describes the preparation of a dispersion containing a silica which has been surface-treated with a silane coupling agent. The silane coupling agent bears epoxy, glycidoxy, amino, mercapto or methacryl functional groups .
International patent application WO 01/05,599 describes the use of silicon dioxide pigments in recording sheets for ink jet printing, wherein the surface of the silicon dioxide has been modified by a treatment with cationic aminoorganosiloxanes . European patent application EP1344654 describes the preparation of a media coated with a dispersion containing silica surface-modified with an organosilanes .
European patent EP0983867 describes the surface treatment of colloidal silica with an aminosilane to prepare an ink-jet recording media.
US patent application US2005/0147770 describes the preparation of a media sheet obtained by dispersing inorganic porous particulates and an active ligand- containing organosilane in water. Described silanes bear for example UV-absorbers, sterically hindered amines or other functional groups as as substituants . Examples mention the use of a silane bearing amino groups.
All cited patents show the disadvantage that big quantities of acid have to be used to maintain the pH in the desired slightly acidic or neutral range. The amount of salts remaining in the media adversely affects the image performance.
DISCLOSURE OF THE INVENTION An objective of the invention is to provide nanoporous recording sheets with improved water fastness, improved diffusion fastness and better resistance to degradation by ozone of recording sheets printed with dye-based inks. A further objective of the invention is an improved manufacturability of the coating solutions for a recording sheet for ink jet printing and an improved coating quality of the recording sheets according to the invention. Such a recording sheet consists of a support having coated thereon at least one ink-receiving layer containing the surface modified silicon dioxide of the present invention.
We have now surprisingly found that these improvements may be obtained by provision of surface modified silicon dioxide, wherein the surface has been modified with a solution comprising a monovalent organic acid and an aminoorganosilane .
In particular, the following inventions are provided:
(1) A method for preparation of surface modified silicon dioxide, wherein the surface of the silicon dioxide is modified by mixing said silicon dioxide with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof.
(2) The method according to (1), wherein said method comprises the following steps;
(i) an aqueous solution of said at least one aminoorganosilane is provided;
(ii) said at least one monovalent acid or salt is added to the aqueous solution of step (i) to form the solution of said at least one aminoorganosilane and at least one monovalent acid or salt thereof; and then
(iii) said silicon dioxide is added to the solution formed in step (ii) to modify the surface of said silicon dioxide . (3) The method according to (1) or (2), wherein said solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof comprises the reaction product of said at least one aminoorganosilane and at least one monovalent acid or salt thereof which does not have a hydroxyl group.
(4) The method according to any of (1) to (3), wherein said monovalent acid is a monovalent organic acid or salt thereof.
(5) The method according to (4), wherein said monovalent organic acid has the general formula (I) :
Figure imgf000005_0001
wherein, R represents H, substituted or unsubstituted alkyl, and M represents H or a monovalent cation. (6) The method according to (5), wherein said monovalent organic acid or salt thereof is formic acid, acetic acid, propionic acid or salt thereof. (7) The method according to any of (1) to (6), wherein said aminoorganosilane has the general formula
(II) :
Figure imgf000006_0001
wherein, Ri, R2 and R3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl with 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and R4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
(8) The method according to any of (1) to (6), wherein said aminoorganosilane is selected from the group consisting of 3-aminopropyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyl-trimethoxysilane, (3- triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyl- triethoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, (3-trimethoxy-silylpropyl) - diethylenetriamine and mixtures thereof. (9) The method according to any of (1) to (6), wherein said aminoorganosilane has the general formula
(III) :
(R5) m(OR6)3-m-Si (CH2) x (CHR7) y (CR8R9) z-NH-Rio (III) wherein,
R5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R6 represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R7, R8 and Rg independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and
m = 0-2, x+y+z = 1-8.
(10) The method according to (9), wherein the aminoorganosilane is selected from the group of N- (n- butyl) -aminopropyl-trimethoxysilane, N- (n-butyl) - aminopropyl-triethoxysilane, N- (cyclohexyl-aminopropyl) - trimethoxysilane, N- (cyclohexyl-aminopropyl) - triethoxysilane, N- (cyclohexyl-aminomethyl) - trimethoxysilane, N- (cyclohexyl-aminomethyl) - triethoxysilane, N-ethylamino-isobutyl-trimethoxysilane and N-ethylamino-isobutyl-triethoxysilane .
(11) The method according to any of (1) to (10), wherein said silicon dioxide is fumed silica. (12) The method according to any of (1) to
(11), wherein said fumed silica has a specific surface area between 20 m2/g and 400 m2/g.
(13) . The method according to any of (1) to (12), wherein the mixing step is carried out by dispersing said silicon dioxide particles in a powder form into said solution by means of a suction-type dispersing device.
(14) The method according to any of (1) to (13), wherein relative to the amount of said silicon dioxide, the amount of said acid or salt thereof is between 0.5 to 10% by weight and the amount of said aminoorganosilane is between 1 and 30% by weight. (15) A coating solution for a recording sheet for ink jet printing comprising the surface modified silicon dioxide particles prepared by the method according to any of (1) to (14) together with a binder. (16) A recording sheet for ink jet printing having coated onto a support the coating solution according to (15) .
(17) A recording sheet for ink jet printing having coated onto a support an ink receiving layer comprising at least one aminoorganosilane, at least one monovalent acid or salt thereof, silicon dioxide and a binder.
(18) The recording sheet according to (17), wherein said monovalent acid is a monovalent organic acid or salt thereof . (19) The recording sheet according to (18), wherein said monovalent acid has the general formula (I):
Figure imgf000008_0001
wherein, R represents H, substituted or unsubstituted alkyl, and
M represents H or a monovalent cation.
(20) The recording sheet according to (19), wherein said monovalent organic acid or salt thereof is formic acid, acetic acid, propionic acid or salt thereof.
(21) The recording sheet according to (17) to (20), wherein said aminoorganosilane has the general formula
( I I ) :
Figure imgf000008_0002
wherein , Ri, R2 and R3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl with 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
R4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group. (22) The recording sheet according to any of (17) to (20), wherein said aminoorganosilane is selected from the group consisting of 3-aminopropyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyl-trimethoxysilane, (3- triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyl- trietyhoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, (3-trimethoxy-silylpropyl) - diethylenetriamine and mixtures thereof.
(23) The recording sheet according to any of (17) to (20) , wherein said aminoorganosilane has the general formula (III) :
(R5) m(OR6)3-m-Si (CH2) x (CHR7) y (CR8R9) Z-NH-R10 (III) wherein,
R5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, Re represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R7, Rs and Rg independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and m = 0-2 , x+y+z = 1-8 .
(24) The recording sheet according to any of (17) to (20) , wherein the aminoorganosilane is selected from the group of N- (n-butyl) -aminopropyl-trimethoxysilane, N- (n- butyl) -aminopropyl-triethoxysilane, N- (cyclohexyl- aminopropyl) -trimethoxysilane, N- (cyclohexyl- aminopropyl) -triethoxysilane, N- (cyclohexyl-aminomethyl) - trimethoxysilane, N- (cyclohexyl-aminomethyl) - triethoxysilane, N-ethylamino-isobutyl-trimethoxysilane and N-ethylamino-isobutyl-triethoxysilane .
(25) The recording sheet according to any of (17) to (24), wherein said silicon dioxide is fumed silica.
(26) The recording sheet according to any of (17) to (25) , wherein said binder is selected from the group consisting of polyvinyl alcohol, polyvinyl alcohol derivative, gelatin, polyvinylpyrrolidone and mixtures thereof.
(27) The recording sheet according to any of (17) to (26) , wherein said ink receiving layer is hardened with boron compound.
(28) The recording sheet according to any of (17) to (27), wherein said ink receiving layer additionally contains optical brightening agents such as stilbenes, coumarines, triazines and oxazoles.
BEST MODE FOR CARRYING OUT THE INVENTION We have surprisingly found that a nanoporous recording sheet for ink jet printing, containing in its in-receiving layer a dispersion of surface modified silicon dioxide, wherein the surface of the silicon dioxide has been modified with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof, shows a considerable improvement of the aforementioned properties, compared to a media in which the silica has been cationically modified using either at least one aminosilane and an inorganic acid. The use of the surface modified silicon dioxide prepared by the method of the present invention improves colour rendition, water fastness and resistance to ozone of images printed with dye-based inks. Furthermore, the treatment of silica with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof leads to a much better migration resistance of ink-jet dyes .
The synthetic silicon dioxide used in the recording sheets according to the invention may be prepared either by precipitation in a wet process (precipitated silicon dioxide) or in a gas phase reaction (fumed silicon dioxide) .
Precipitated silicon dioxide may be prepared for example in the wet process by metathesis of sodium silicate with an acid or by passing through a layer of ion-exchange resin as silicon dioxide sol, by heating and maturing of this silicon dioxide sol or by gelling of a silicon dioxide sol.
The gas phase reaction for the preparation of fumed silicon dioxide by flame pyrolysis is also known as a dry- process in contrast to the wet process. In this process, for example, silicon tetrachloride is reacted in the presence of hydrogen and oxygen under formation of silicon dioxide and hydrochloric acid. Silanes, such as for example methyltrichlorosilane or trichlorosilane, may be used in this process in place of silicon tetrachloride or in combination with silicon tetrachloride.
Preferably, fumed silicon dioxide is used in the recording sheets according to the invention. Fumed silicon dioxide consists of aggregates of small primary particles. These primary particles themselves are not porous. The aggregates, however, are porous and may absorb quickly big amounts of liquids for this reason. The aggregates of fumed silicon dioxide normally have a size (mean diameter) of more than 100 nm. Particles with a size between 100 nm and 500 nm are preferred, particularly preferred are particles with a size between 150 nm and 250 nm. These sizes refer to the aggregates. The primary particles have a size between 1 nm and 100 nm. A size between 1 nm and 30 nm is preferred, particularly preferred is a size between 5 nm and 15 nm.
Fumed silicon dioxide has a specific surface between 20 m2/g and 400 m2/g. A specific surface between 40 m2/g and 400 m2/g is preferred. Particularly preferred is a specific surface between 90 m2/g and 330 m2/g. The specific surface is determined by the BET isotherm method, as described by S. Brunauer, P. H. Emmet and I. Teller in "Adsorption of Gases in Multimolecular Layers", Journal of the American Chemical Society 60_, 309 (1938) . In a preparation method of the surface modified silicon dioxide according to the invention, which will be incorporated into the recording sheets according to the invention, fumed silicon dioxide is for example added at high shear rates to a mainly aqueous solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof. Under suitable conditions, a dispersion of surface modified fumed silicon dioxide is obtained that does not coagulate. Deionised water is preferably used for the preparation of the mainly aqueous solutions. Water- miscible solvents such as lower alcohols (methanol, ethanol, propanol and the like) or ketones such as acetone may be added.
For the preparation of the surface modified silicon dioxide according to the invention, the solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof may also be added, for example, to an aqueous dispersion of silicon dioxide. Alternatively, the silicone dioxide can be added to a mixture of at least one aminosilane and water under high shear, and the monovalent acid continuously added to balance the pH. Further, the silicone dioxide may be added in a solution of the monovalent organic acid and water, thus resulting in an anionic dispersion of silica at low pH, and at least one aminoorganosilane added under high shear to reverse the neat charge of the silica surface.
However, in a preferable embodiment, the preparation of the surface modified silicon dioxide according to the invention can be carried out by, providing an aqueous solution of at least one aminoorganosilane; adding at least one monovalent acid or salt to the aqueous solution to form a solution comprising said aminoorganosilane and said monovalent acid or salt thereof; and then adding a silicon dioxide to the thus-formed solution to modify the surface of said silicon dioxide.
Preferably, the aminosilane is hydrolysed in water at room temperature for about 10 minutes, then the monovalent acid is added and the mixture is stirred for another 10 minutes at room temperature. In this way, the aminosilane is quickly hydrolysed at high pH and the reaction product of the monovalent acid and the aminoorganosilane is formed upon addition of the monovalent acid. Finally, the silica powder is transferred portionswise to the solution containing the reaction product of the monovalent acid and the aminoorganosilane .
In another preferable embodiment, the preparation of the surface modified silicon dioxide according to the invention can be carried out by, providing an aqueous solution of at least one monovalent acid or salt thereof; adding at least one aminoorganosilane to the aqueous solution to form a solution comprising said monovalent acid or salt thereof and said aminoorganosilane; and then adding a silicon dioxide to the thus-formed solution to modify the surface of said silicon dioxide.
Preferably, the aminosilane is added to a solution comprising water and the monovalent organic acid or salt thereof and allowed to hydrolyse during 10 minutes under stirring at room temperature. Finally, the silica powder is transferred portionswise to the solution containing the reaction product of the monovalent acid and the aminoorganosilane .
The modification of the surface of the silicon dioxide with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof is an almost instantaneous process. For this reason, the conversion time is very short (within minutes) and is completed at room temperature.
Fumed silicon dioxide is particularly preferred for the surface modification.
In place of a single fumed silicon dioxide powder, a mixture of different silicon dioxide powders having different sizes of the primary particles may be used. The modification step with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof may be carried out individually for each silicon dioxide powder or simultaneously with the mixture of the different silicon dioxide powders.
If the modification step is done at high shear rates, the reaction products are regularly distributed on the surface of the silicon dioxide. Furthermore, the rheological behaviour of the dispersion is improved.
Suitable aminoorganosilanes are aminoorganosilanes of formula (I)
Figure imgf000014_0001
,
(D wherein
Ri' R2' R3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl and
R4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
In the case where Ri' R2 and R3 are substituted, the substituents are independently selected from the group consisting of thiol, sulfide and polyalkylene oxide. Suitably selected substituents facilitate the surface modification of silicon dioxide (improved rheological behaviour of the dispersions and of the coating solutions) and improve properties of the recording sheets such as stability against air pollutants, light fastness and physical properties. Condensation products of the aminoorganosilanes may also be used in place of the monomeric aminoorganosilanes. The condensation reactions may occur between identical or different aminoorganosilanes. Preferred aminoorganosilanes are 3- aminopropyltrimethoxysilane, N- (2-aminoethyl) -3- aminopropyl-trimethoxysilane, (3-triethoxysilylpropyl) - diethylentri amine, 3-aminopropyltriethoxysilane, N- (2- aminoethyl) -3-amino propyltriethoxy silane, (3-triethoxysilylpropyl) -diethylenetriamine and their mixtures. Nanoporous media are prone to react with some components of cardboard packing material, leading to more or less strong yellowing of the media even in dark storage conditions. Packing the media in an inert plastic sheet usually helps circumventing this undesired effect, but at the expense of the overall packaging costs.
We surprisingly found that some aminosilane treating agents used for the aforementioned surface treatment of silicone dioxide reduce this undesired effect so that storing the media for a long time in an inexpensive cardboard box has no consequence on the media conservation.
The aminosilanes that show this property exhibit the following generic structure:
R5In(OR6) 3-m-Si (CH2) x (CHR7) y (CR8R9) Z-NH-R1O wherein, R5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R6 represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R7, Rs and Rg independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and
m = 0-2, x+y+z = 1-8.
The manufacturing of dispersion of silica having a electrostatic charge reversed from anionic to cationic is a critical process. The need to reduce the time of the preparation of the cationic silica dispersion is becoming important in a cost oriented process.
We also surprisingly and unexpectedly found that aminosilanes only bearing a secondary amino group greatly improve the ease of dispersion of silica, when compared to other types of aminosilanes, especially aminoorganosilanes which are terminated by a primary amino group.
Hypothesis was made that the hydrophobic group on the amine increases the repulsion between two surface- treated silica particles, and hence, stabilizes the dispersion. It is also likely that the same hydrophobic group helps reducing the attraction between already treated (cationic) surfaces and the untreated, anionic ones, thus limiting the strong viscosity rise usually observed when a portion of anionic silica is added to the mixture of already treated silica and excess of surface- treating agent. The consequences are that the time and shear energy, necessary to prepare the dispersion, are strongly reduced and that the amount of aminosilane needed to reach a given surface charge (ζ-potential) is lower. Suitable monovalent acids include inorganic acid, e.g. hydrochloric acid or nitric acid; organic acid such as carboxylic acid, e.g., formic acid, acetic acid, propionic acid, lactic acid, acrylic acid, glyoxylic acid, methoxyacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid or alpha- hydroxyisobutyric acid, sulfonic acid, e.g., methanesulfonic acid, ethanesulfonic acid. Preferably, the monovalent acid is formic acid, acetic acid or propionic acid, and most preferably, it is formic acid. This list gives examples of possible acids but does not limit in any way the use of other, not cited, monovalent acids.
Salts of the monovalent acid can be formed by any monovalent cation, for example, lithium, sodium, potassium, ammonium, or the like.
The dispersion of the surface modified silicon dioxide according to the invention is advantageously used directly for the preparation of the coating solution of an ink-receiving layer of a recording sheet for ink jet printing. Therefore, the dispersion has to be stable for at least 24 hours without sedimentation of the surface modified silicon dioxide and is not allowed to change its viscosity considerably. In particular, it is not allowed to gel or to coagulate. The dispersion contains the surface modified silicon dioxide according to the invention in an amount of from 5 percent by weight to 50 percent by weight. Amounts of from 10 percent by weight to 30 percent by weight are preferred, particularly preferred are amounts of from 15 percent by weight to 25 percent by weight.
The surface modification of the silicon dioxide with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof leads to a positive surface charge of the silicon dioxide. The colouring compounds (dyes or pigments) contained in inks for ink jet printing very often contain groups which may be ionized, such as SO3H, COOH, PO3H2 and the like, increasing the solubility of ink-jet dyes. After the dissociation of these groups, the dyes are therefore negatively charged in the mainly aqueous ink liquid and are therefore electrostatically attracted and fixed by the positive charge at the surface of the modified silicon dioxide. By hypothesis, it is assumed that the presence of the solution comprising the aminoorganosilane and the monovalent acid or salt thereof, particularly the reaction product of the aminoorganosilane and the monovalent acid on the surface of the silica favours a particularly tight fixation of the dye molecules in the uppermost layer of the coating, thus enhancing the colour saturation, reducing the migration ability of the dye molecules and decreasing their exposure to environmental gases. This hypothesis is supported by the close examination of thin cuts of printed material obtained accordingly to the invention, which shows that the ink penetrates less deeply than on comparison media. Dispersion of the silicon dioxide can be accomplished, for example, by means of a conventional dispersion device such as Nanomizer®, Ulitimizer" , Menton- Gaulin®, Ystral Conti®, Dyno-Mill®, and the like. The aforementioned devices may be used alone or two or more types may be used in combination. The total amount of the ingredients used for the preparation of the solution comprising the aminoorganosilane and the monovalent acid or salt thereof has to be chosen in such a way that most of the aggregates of silicon dioxide have the possibility to react with the solution. The total amount depends on the molecular weight of the aminoorganosilane and the number of amino groups in the molecule.
The total quantity of the aminoorganosilane, respectively the mixture of aminoorganosilanes, typically is between 0.1 percent by weight and 15 percent by weight relative to the quantity of silicon dioxide. A value between 5 percent by weight and 10 percent by weight is preferred.
The weight ratio between the monovalent acid or salt thereof and the aminoorganosilane is preferably chosen in such a way that the desired value of pH is attained when the. two compounds are mixed. A molar ratio between 0.1 and 2.0 is preferred, depending on the number of amino groups in the molecule. Particularly preferred is a molar ratio of the monovalent acid to amino groups of the aminosilane between 0.3 and 1.0. The value of pH of the solution comprising the aminoorganosilane and the monovalent acid or salt thereof is preferably chosen to be between 4 and 10. The pH of the dispersion containing the silicone dioxide surface- with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof is preferably set between 4 and 10, and most preferably between 5 and 8. The solution comprising the aminoorganosilane and the monovalent acid or salt thereof acts as a buffer, which means that there is no need to add further acid or base to maintain the pH upon addition of the silica powder.
The recording sheet may contain, in addition to the surface modified silicon dioxide according to the invention, other, porous or non-porous, inorganic compounds . In order to further improve the stability of images in polluted air, the recording sheet according to the invention may contain, in addition to the surface modified silicon oxide, salts of monovalent copper such as copper (I) chloride, copper (I) bromide or copper (I) sulphite monohydrate as described in patent application EP 1,231,071. In order to further improve the stability of images in polluted air, the recording sheet may contain, in addition to the salts of monovalent copper, diketo compounds as described in patent application EP 1197345. In order to improve still further the stability of images in polluted air, the recording sheet may contain in addition organic sulphur compounds such as thiodiethylene glycol.
The binders are in most cases water-soluble polymers. Especially preferred are film-forming polymers. The water-soluble polymers include for example natural polymers or modified products thereof such as albumin, gelatine, casein, starch, gum arabicum, sodium or potassium alginate, hydroxyethyl cellulose, carboxymethyl cellulose, α-, β- or γ-cyclodextrine and the like. In the case where one of the water-soluble polymers is gelatine, all known types of gelatine may be used as for example acid pigskin or limed bone gelatine, acid or base hydrolyzed gelatine, but also derivatized gelatines like for instance phthalaoylated, acetylated or carbamoylated gelatin or gelatine derivatised with the anhydride of trimellitic acid.
Synthetic binders may also be used and include for example polyvinyl alcohol, polyvinyl pyrrolidone, completely or partially saponified products of copolymers of vinyl acetate and other monomers; homopolymers or copolymers of unsaturated carboxylic acids such as maleic acid, (meth) acrylic acid or crotonic acid and the like; homopolymers or copolymers of sulfonated vinyl monomers such as vinylsulfonic acid, styrene sulfonic acid and the like. Furthermore homopolymers or copolymers of vinyl monomers of (meth) acrylamide; homopolymers or copolymers of other monomers with ethylene oxide; polyurethanes; polyacrylamides; water-soluble nylon type polymers; polyesters; polyvinyl lactams; acrylamide polymers; substituted polyvinyl alcohol; polyvinyl acetals; polymers of alkyl and sulfoalkyl acrylates and methacrylates; hydrolyzed polyvinyl acetates; polyamides; polyvinyl pyridines; polyacrylic acid; copolymers with maleic anhydride; polyalkylene oxides; copolymers with methacrylamide and copolymers with maleic acid may be used. All these polymers may also be used as mixtures. Preferred synthetic binders are polyvinyl alcohol and polyvinyl pyrrolidone or mixtures thereof.
These polymers may be blended with water insoluble natural or synthetic high molecular weight compounds, particularly with acrylate latices or with styrene acrylate latices.
Although not specifically claimed in this invention, water insoluble polymers are nevertheless considered part of the system.
The polymers mentioned above having groups with the possibility to react with a cross-linking agent may be cross-linked or hardened to form essentially water insoluble layers. Such cross-linking bonds may be either covalent or ionic. Cross-linking or hardening of the layers allows for the modification of the physical properties of the layers, like for instance their liquid absorption capacity or their resistance against layer damage .
The cross-linking agents or hardeners are selected depending on the type of the water-soluble polymers to be cross-linked.
Organic cross-linking agents and hardeners include for example aldehydes (such as formaldehyde, glyoxal or glutaraldehyde) , N-methylol compounds (such as dimethylol urea or methylol dimethylhydantoin) , dioxanes (such as 2, 3-dihy-droxydioxane) , reactive vinyl compounds (such as 1, 3, 5-trisacrylolyl hexahydro-s-triazine or bis- (vinylsulfonyl) ethyl ether), reactive halogen compounds (such as 2, 4-dichloro-6-hydroxy-s-triazine) ; epoxides; aziridines; carbamoyl pyridinium com-pounds or mixtures of two or more of the above mentioned cross-linking agents . Inorganic cross-linking agents or hardeners include for example chromium alum, aluminium alum or, preferably, boric acid or borax.
The layers may also contain reactive substances that cross-link the layers under the influence of ultraviolet light, electron beams, X-rays or heat.
The layers may further be modified by the addition of fillers. Possible fillers are for instance kaolin, Ca- or Ba-carbonates, silicon dioxide, titanium dioxide, bentonites, zeolites, aluminium silicate or calcium silicate. Organic inert particles such as polymer beads may also be used. These beads may consist of polyacrylates, polyacrylamides, polystyrene or different copolymers of acrylates and styrene. The fillers are selected according to the intended use of the printed images. Some of these compounds cannot be used if the printed images are to be used as transparencies. However they are of interest in cases where the printed images are be to used as remission pictures. Very often, the introduction of such fillers causes a wanted matte surface.
The recording sheets may also contain water-soluble metal salts, as for example salts of the alkaline earth metals or salts of the metals of the rare earth series. The recording sheets according to the invention comprise a support having coated thereon at least one ink-receiving layer, and, optionally, auxiliary layers. A gloss layer comprising fine pigments with a mean particle size of up to 200 nm such as colloidal silica, colloidal alumina, organic pigments or the like may be formed on the ink receiving layer. The coating amount of the gloss layer can be up to 5 g/m2, preferably up to 3 g/m2, in terms of the absorbability or glossiness of the ink. The gloss layer may comprise a small amount of pigments with a mean particle size of at least 1 μm so as to improve the transportability by a printer. As for the pigments with a mean particle size of at least 1 μm, inorganic or organic pigments may be used, and among them, organic particles, in particular, polystyrene pigments are preferable as they do not deteriorate the glossiness .
A wide variety of supports are known and commonly used in the art. They include all those supports used in the manufacture of photographic materials. This includes clear films made from cellulose esters such as cellulose triacetate, cellulose acetate, cellulose propionate or cellulose acetate/butyrate, polyesters such as polyethylene terephthalate or polyethylene naphthalate, polyamides, polycarbonates, polyimides, polyolefins, polyvinyl acetals, polyethers, polyvinyl chloride and polyvinylsulfones . Polyester film supports, and especially polyethylene terephthalate or polyethylene naphthalate are preferred because of their excellent dimensional stability characteristics. The usual opaque supports used in the manufacture of photographic materials may be used including for example baryta paper, polyolefin coated papers or voided polyester as for instance Melinex" manufactured by DuPont. Especially preferred are polyolefin coated papers or voided polyester.
When such supports, in particular polyester, are used, a subbing layer is advantageously coated first to improve the bonding of the ink-receiving layers to the support. Useful subbing layers for this purpose are well known in the photographic industry and include for example terpolymers of vinylidene chloride, acrylonitrile and acrylic acid or of vinylidene chloride, methyl acrylate and itaconic acid. In place of the use of a subbing layer, the surface of the support may be subjected to a corona-discharge treatment before the coating process.
Uncoated papers, comprising all different types of papers, varying widely in their composition and in their properties, and pigmented papers and cast-coated papers may also be used, as well as metal foils, such as foils made from aluminium.
The layers may also be coated onto textile fibre materials consisting for example of polyamides, polyesters, cotton, viscose and wool.
The ink-receiving layers according to the invention are in general coated from aqueous solutions or dispersions containing all necessary ingredients. In many cases, wetting agents are added to those coating solutions in order to improve the coating behaviour and the evenness of the layers. Besides being necessary for coating purposes, these compounds may have an influence on the image quality and may therefore be selected with this specific objective in mind. Although not specifically claimed in this invention, wetting agents nevertheless form an important part of the invention.
In addition to the above mentioned ingredients, recording sheets according to the invention may contain additional compounds aimed at further improving their performance, as for example brightening agents to improve the whiteness, such as stilbenes, coumarines, triazines, oxazoles or others compounds known to someone skilled in the art .
Light stability may be improved by adding UV absorbers such as 2-hydroxybenzotriazoles, 2- hydroxybenzophenones, derivatives of triazine or derivatives of cinnamic acid. The amount of UV absorber may vary from 200 mg/m2 to 2000 mg/m2, preferably from 400 mg/m2 to 1000 mg/m2. The UV absorber may be added to any of the layers of the recording sheet according to the invention. It is preferred that, however, if it is added, it should be added to the topmost layer. It is further known that images produced by ink jet printing may be protected from degradation by the addition of radical scavengers, stabilizers, reducing agents and antioxidants. Examples of such compounds are sterically hindered phenols, sterically hindered amines, chromanols, ascorbic acid, phosphinic acids and their derivatives, sulphur containing compounds such as sulphides, mercaptans, thiocyanates, thioamides or thioureas . The above-mentioned compounds may be added to the coating solutions as aqueous solutions. In the case where these compounds are not sufficiently water-soluble, they may be incorporated into the coating solutions by other common techniques known in the art. The compounds may for example be dissolved in a water miscible solvent such as lower alcohols, glycols, ketones, esters, or amides. Alternatively, the compounds may be added to the coating solutions as fine dispersions, as oil emulsions, as cyclodextrine inclusion compounds or incorporated into latex particles.
Typically, the recording sheet according to the invention has a thickness in the range of 0.5 μm to 100 μm dry thickness, preferably in the range of 5 μm to 50 μm dry thickness. The coating solutions may be coated onto the support by any number of suitable procedures. Usual coating methods include for example extrusion coating, air knife coating, doctor blade coating, bead coating, cascade coating and curtain coating. The coating solutions may also be applied using spray techniques. Particularly, curtain coating technique is preferable since the tendency of occurrence of a coating defect is low. In the course of carrying out the coating process by curtain coating technique in which the coating solution falls down from the lip of a coating head and drops onto the surface of a moving support, the height of the curtain (i.e., the distance between the coating lip, where the fluid detaches from the hopper device to fall down by gravity, and the support to be coated) , the application angle of the coating solution falling down onto the support (i.e. the angle between the support and the horizontal line (normal to the gravity) at the impact point, the position where the coating solution drops onto the support, etc. may be set arbitrarily. Moreover, the application of an electrical charge onto a coating roll or onto the backing roll before coating is effective. The ink-receiving layers may be built up from several individual layers that can be coated one after the other or simultaneously. Preferably, the coating process is carried out at a speed of about 20 to 400m/min. The individual ink-receiving layers may be different in respect to the used fumed silicon dioxide (in particular its specific surface) , the modification with the solution comprising the aminoorganosilane and the monovalent acid or salt thereof, the ratio between the binders and the silicon dioxide and the quantity of hardener, in particular boric acid.
It is likewise possible to provide a double-side recording sheet by applying ink-receiving layers on both sides of a support. It is also possible to coat an antistatic layer or an anticurl layer on the backside. The selected coating method however is not to be considered limiting for the present invention.
Inks for ink jet printing consist in essence of a liquid vehicle and a dye or pigment dissolved or suspended therein. The liquid vehicle for ink jet inks consists in general of water or a mixture of water and a water-miscible organic solvent such as ethylene glycol, higher molecular weight glycols, glycerol, dipropylene glycol, polyethylene glycol, amides, polyvinyl pyrrolidone, N-methylpyrrolidone, cyclohexyl pyrrolidone, carboxylic acids and their esters, ethers, alcohols, organic sulfoxides, sulfolane, dimethylformamide, dimethylsulfoxide, cellosolve, polyurethanes, acrylates and the like.
The non-aqueous parts of the ink generally serve as humefactants, cosolvents, viscosity regulating agents, ink penetration additives or drying agents. The organic compounds have in most cases a boiling point, which is higher than that of water. In addition, aqueous inks used for printers of the continuous stream type may contain inorganic or organic salts to increase their conductivity. Examples of such salts are nitrates, chlorides, phosphates and salts of water-soluble organic acids such as acetates, oxalates and citrates. The dyes and pigments suitable for the preparation of inks useable with the recording sheets according to the invention cover practically all classes of known colouring compounds. Dyes or pigments typically used for this purpose are described in patent application EP O1559 '324. The recording sheets according to the invention are meant to be used in conjunction with most of the inks representing the state of the art.
The inks may further contain other additives such as surfactants, optical brighteners, UV absorbers, light stabilizers, biocides, precipitating agents such as multivalent metal compounds and polymeric additives. This description of inks is for illustration only and is not to be considered as limiting for the purpose of the invention.
The present invention will be illustrated in more detail by the following examples without limiting the scope of the invention in any way. TEST METHODS 1. Dye diffusion
The method used is described essentially by R. Hofmann, E. Baumann and M. Schar in "Print Performance Evaluation of Ink-jet Media: Gamut, Drying, Permanence", IS&Ts NIP 15: International Conference on Digital Printing Technologies, ISBN 0-89208-222-4, pages 408 - 411 .
Patches of the colours yellow, red, magenta, blue, cyan, green and black at 100% print density were printed onto the recording sheets according to the invention with the ink jet printers HP 5652, Canon I 990 and Epson R 300 using the corresponding original inks. The printed colour patches have an edge length of 118 pixels. Each individual colour patch is divided by 11 horizontal and 11 vertical white lines into 144 individual coloured squares having an edge length of 8 pixels. The white lines have a width of 2 pixels. The following printer settings were used:
- HP 6540: Photo REt, Best, HP Premium High Gloss film, 600dpi - Epson R300: Premium Glossy Photo Paper, Photo, HS on, ICM, no colour adjust
- Canon i990: Photo Paper Pro, High, Graphic, Normal
The printed recording sheets were dried for 24 hours at a temperature of 230C at relative humidity of 50%.
Then, the optical densities of the colour patches were measured. Afterwards, the printed recording sheets were stored for 7 days at a temperature of 400C and relative humidity of 80%. Finally, the optical densities were re- measured.
The largest of the determined dye diffusion values (maximal dye diffusion) is given as the percent difference before and after exposition to high humidity/high temperature. 2. Colour shift in grey patches
Grey patches at 30%, 40% and 60% print density were printed onto the recording sheets according to the invention with the ink jet printers HP 5652, Canon I 990 and Epson R 300 using the corresponding original yellow, magenta and cyan inks. The following printer settings were used:
- HP 6540: Photo REt, Best, HP Premium High Gloss film, 600dpi
- Epson R300: Premium Glossy Photo Paper, Photo, HS on, ICM, no colour adjust
- Canon i990: Photo Paper Pro, High, Graphic, Normal
The printed recording sheets were dried for 24 hours at a temperature of 23°C at relative humidity of 50%. Then, their L*a*b* colour coordinates were determined. Afterwards, the printed recording sheets were stored for 7 days at a temperature of 40°C and relative humidity of 80%. Finally, L*a*b* colour coordinates were re- determined. The value for the most diffusing colour is given as a measure of dye diffusion
The colour change ΔE* of each grey patch occurring during storage was determined from the measured values of L*a*b* by using the following formula:
Figure imgf000029_0001
The highest of the three calculated values of ΔΕ* is given as an indication of colour shift. 3. Resistance to ozone
Patches of the following colours are printed with the aforementioned printers from a CMYK file:
- cyan 100%, magenta 90%, yellow 95%, IK black 90%
- red 100%, green 100% and blue 100% - cyan 30%, magenta 25%, yellow 35%, IK black 50%
- 3K black 25%, 50%, 75%, 85% and 90%
- 4K black 10%, 30%, 45%, 60% and 70% Following printer settings are applied:
- HP 6540: Photo REt, Best, HP Premium High Gloss film, 600dpi
- Epson R300: Premium Glossy Photo Paper, Photo, HS on, ICM, no colour adjust
- Canon i990: Photo Paper Pro, High, Graphic, Normal The test patterns are submitted in a Satra-Hampden
903 ozone chamber to a concentration of lppm ozone during 24hours (corresponding to a total ozone exposure of 24ppmh) at a temperature of 30°C and a relative humidity of 50%. Optical density of each colour patch is measured using the channels R, G, B and compared to the optical density of a reference pattern (stored in a protection sheet without gas flow) . The determining value for the assessment of the resistance to ozone fading is the number of ppmh ozone necessary to lose a given fraction of the initial density for the most sensitive channel. EXAMPLES
Example 1
18.3g of N- (2-aminoethyl) -3-aminopropyl- trimethoxysilane (available from Degussa, Dusseldorf, Germany) were added to 757g deionised water under stirring. After 10' stirring, 18.9g of a 20% solution of formic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil® M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO2 and exhibiting a pH value of 6.30. The molar ratio between the aminosilane and silica is 2.4 mol-% and the molar ratio of formic acid to silica is 2.39 mol-%. Example 2
22.1g of N- (2-aminoethyl) -3-aminopropyl- trimethoxysilane (available from Degussa, Dusseldorf, Germany) were added to 752g deionised water under stirring. After 10' stirring, 19.8g of a 20% solution of formic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil® M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO2 and exhibiting a pH value of 6.69. The molar ratio between the aminosilane and silica is 2.9 mol-% and the molar ratio of formic acid to silica is 2.5 mol-%. Example 3
29.5g of 3-aminopropyltrimethoxysilane (available from Degussa, Dϋsseldorf, Germany) were added to 739.6g deionised water under stirring. After 10' stirring, 24.9g of a 20% solution of formic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O- Sil® M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator- mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO2 and exhibiting a pH value of 6.30. The molar ratio between the aminosilane and silica is 4.8 mol-% and the molar ratio of formic acid to silica is 3.15 mol-%.
Example 4
36.4g of 3-aminopropyltriethoxysilane (available from Degussa, Dϋsseldorf, Germany) were added to 133. Iq deionised water under stirring. After 10' stirring, 23.9g of a 20% solution of formic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O- Sil" M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator- mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO3 and exhibiting a pH value of 6.30. The molar ratio between the aminosilane and silica is 4.8 mol-% and the molar ratio of formic acid to silica is 3.02 mol-%.
Example 5
22.1g of N- (2-aminoethyl) -3-aminopropyltrimethoxysilane (available from Degussa, Dusseldorf, Germany) were added to 746g deionised water under stirring. After 10' stirring, 25.7g of a 20% solution of acetic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil® M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO2 and exhibiting a pH value of 6.27. The molar ratio between the aminosilane and silica is 2.4 mol-% and the molar ratio of acetic acid to silica is 2.49 mol-%. Example 6 22.1g of N- (2-aminoethyl) -3-aminopropyl- trimethoxysilane (available from Degussa, Dϋsseldorf, Germany) were added to 709g deionised water under stirring. After 10' stirring, 63.3g of a 10% solution of propionic acid were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil" M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO2 and exhibiting a pH value of 6.28. The molar ratio between the aminosilane and silica is 2.4 mol-% and the molar ratio of propionic acid to silica is 2.49 mol-%. Example 7 22.1g of N- (2-aminoethyl) -3-aminopropyl- trimethoxysilane (available from Degussa, Dϋsseldorf, Germany) were added to 699g deionised water under stirring. After 10' stirring, 73.1 ml of a 1 mo/L nitric acid solution were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil® M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% SiO2 and exhibiting a pH value of 6.30. The molar ratio between the aminosilane and silica is 2.4 mol-% and the molar ratio of nitric acid to silica is 2.13 mol-%. Example 8
22.1g of N- (2-aminoethyl) -3-aminopropyl- trimethoxysilane (available from Degussa, Dϋsseldorf, Germany) were added to 698g deionised water under stirring. After 10' stirring, 73.4 ml of a 1 mo/L hydrochloric acid solution were added under vigorous stirring. 206g of fumed silicon dioxide (Cab-O-Sil® M-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 15 minutes. We obtain in this way a dispersion containing 20.6% Siθ2 and exhibiting a pH value of 6.30. The molar ratio between the aminosilane and silica is 2.4 mol-% and the molar ratio of nitric acid to silica is 2.12 mol-%. Example 9
3.02g of solid boric acid were added at a temperature of 450C to 612g of the dispersion of Example
1. After the dissolution of the boric acid 315g of an aqueous solution of polyvinyl alcohol (8%, available as Mowiol 4088 from Clariant AG, Muttenz, Switzerland) were added and afterwards 3.4g of an aqueous solution of the wetting agent Olin 1OG (5.23%, available from Arch Chemicals, Norwalk, USA) . At the end, the coating solution was diluted with deionised water to a final weight of 100Og. Example 10
3.02g of solid boric acid were added at a temperature of 45°C to 612g of the dispersion of Example
2. After the dissolution of the boric acid 315g of an aqueous solution of polyvinyl alcohol (8%, available as
Mowiol 4088 from Clariant AG, Muttenz, Switzerland) were added and afterwards 3.4g of an aqueous solution of the wetting agent Olin 1OG (5.23%, available from Arch Chemicals, Norwalk, USA) . At the end, the coating solution was diluted with deionised water to a final weight of 100Og. Example 11
Same procedure as Example 9, but 607.2g of the dispersion of Example 3 was used instead of the dispersion of Example 1. Example 12
Same procedure as Example 9, but 607.2g of the dispersion of Example 4 was used instead of the dispersion of Example 1.
Example 13 Same procedure as Example 9, but 607.2g of the dispersion of Example 5 was used instead of the dispersion of Example 1.
Example 14
Same procedure as Example 9, but 607.2g of the dispersion of Example 6 was used instead of the dispersion of Example 1.
Example 15
Same procedure as Example 9, but 607.2g of the dispersion of Example 7 was used instead of the dispersion of Example 1.
Example 16
Same procedure as Example 9, but 607.2g of the dispersion of Example 8 was used instead of the dispersion of Example 1. Example 17
140 g/m2 of the coating solution of Example 9 were coated at a temperature of 40°C with a bar coater onto a polyethylene terephthalate support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m2 of the coated support contains 17.5 of surface-treated silica .
Example 18
140 g/m2 of the coating solution of Example 10 were coated at a temperature of 40°C with a bar coater onto a polyethylene terephthalate support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m2 of the coated support contains 17.5 of surface-treated silica .
Example 19
Same procedure as Example 17, but the coating solution of Example 11 was used instead of the coating solution of Example 9.
Example 20
Same procedure as Example 17, but the coating solution of Example 12 was used instead of the coating solution of Example 9.
Example 21
Same procedure as Example 17, but the coating solution of Example 13 was used instead of the coating solution of Example 9. Example 22
Same procedure as Example 17, but the coating solution of Example 14 was used instead of the coating solution of Example 9.
Example 23 Same procedure as Example 17, but the coating solution of Example 15 was used instead of the coating solution of Example 9.
Example 24
Same procedure as Example 17, but the coating solution of Example 16 was used instead of the coating solution of Example 9.
RESULTS EXAMPLES 17-24
The results of dye diffusion testing are listed in Table 1 below. Comparison examples are examples 23 and 24.
Figure imgf000036_0001
Table 1
The results in Table 1 clearly show that the recording sheet for ink jet printing according to the invention, where the surface of the silicon dioxide has been modified with a solution comprising at least one aminoorganosilane and at least one monovalent organic acid or salt thereof (Examples 17-22), exhibits a strongly reduced dye diffusion in comparison to a recording sheet, where the surface of the silicon dioxide has been modified with a solution comprising an aminoorganosilane and an inorganic acid like nitric acid or hydrochloric acid (Examples 23 and 24).
The results of the determination of the colour shift in grey patches are listed in Table 2.
Figure imgf000036_0002
Table 2
The results in Table 2 clearly show that the recording sheet for ink jet printing according to the invention, where the surface of the silicon dioxide has been modified with a solution comprising at least one aminoorganosilane and at least one monovalent organic acid or salt thereof (Examples 17-22), shows a reduced colour shift in grey patches in comparison to a recording sheet, where the surface of the silicon dioxide has been modified with a solution comprising an aminoorganosilane and an inorganic acid like nitric acid or hydrochloric acid (Examples 23 and 24).
The results of the determination of the resistance to ozone are listed in Table 3. Ozone resistance is indicated as the total amount of ozone (in ppmh) necessary to lose a given percentage of colour density. The most sensitive colour (relevant for the assessment of the resistance to ozone) is indicated after each printer's name.
Figure imgf000037_0001
Table 3
The results in Table 3 clearly show that the recording sheet for ink jet printing according to the invention, where the surface of the silicon dioxide has been modified with a solution comprising at least one aminoorganosilane and at least one monovalent organic acid or salt thereof (Examples 17-22), shows a markedly enhanced resistance to ozone in comparison to a recording sheet, where the surface of the silicon dioxide has been modified with a solution comprising an aminoorganosilane and an inorganic acid like nitric acid or hydrochloric acid (Examples 23 and 24) .
Example 25
36.3g of a 20% solution of formic acid were added to 682.8g deionised water under stirring. After 10', 50.9g of 3-aminopropyltrimethoxysilane (available as
Dynasylan AMEO from Degussa, Dϋsseldorf, Germany) were added to the solution under vigorous stirring. 23Og of fumed silicon dioxide (Cab-O-Sil H-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 5 minutes. We obtain in this way a dispersion containing 23.0% SiO2 and exhibiting a pH value of 6.20. The molar ratio between the aminosilane and silica is 6.0 mol-% and the molar ratio of formic acid to silica is 4.12 mol-%.
Example 26
17.8g of a 20% solution of formic acid were added to 720.9g deionised water under stirring. After 10', 23.Og of N- (2-aminoethyl) -3-aminopropyl-trimethoxysilane (available as Dynasylan DAMO from Degussa, Dϋsseldorf, Germany) were added to the solution under vigorous stirring. 23Og of fumed silicon dioxide (Cab-O-Sil H-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 5 minutes. We obtain in this way a dispersion containing 23.0% SiO2 and exhibiting a pH value of 6.20. The molar ratio between the aminosilane and silica is 2.7 mol-% and the molar ratio of formic acid to silica is 2.02 mol-%.
Example 27
13.2g of a 20% solution of formic acid were added to 730.3g deionised water under stirring. After 10', 26.5g of N- (n-butyl) -aminopropyl-trimethoxysilane (available as Dynasylan 1189 from Degussa, Dϋsseldorf, Germany) were added to the solution under vigorous stirring. 23Og of fumed silicon dioxide (Cab-O-Sil H-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 5 minutes. We obtain in this way a dispersion containing 23.0% SiO2 and exhibiting a pH value of 6.20. The molar ratio between the aminosilane and silica is 2.94 mol-% and the molar ratio of formic acid to silica is 1.49 mol- %.
Example 28
14. Ig of a 20% solution of formic acid were added to 731.Og deionised water under stirring. After 10', 24.9g of N-ethyl-amino-isobutyl-trimethoxysilane (available as Silquest A-Link 15 from Momentive Performance Materials, Wilton, USA) were added to the solution under vigorous stirring. 23Og of fumed silicon dioxide (Cab-O-Sil H-5, available from Cabot Corporation, Billerica, USA) were added in small amounts at high shear rates. Then, the dispersion was stirred with a rotor-stator-mixer for 5 minutes. We obtain in this way a dispersion containing 23.0% SiO2 and exhibiting a pH value of 6.20. The molar ratio between the aminosilane and silica is 2.94 mol-% and the molar ratio of formic acid to silica is 1.60 mol- Example 29
3.84g of solid boric acid were added at a temperature of 45°C to 591.3g of the dispersion of Example
25. After the dissolution of the boric acid 34Og of an aqueous solution of polyvinyl alcohol (8%, available as
Mowiol 4088 from Clariant AG, Muttenz, Switzerland) were added and afterwards 13.3g of an aqueous solution of the wetting agent Olin 1OG (5.26%, available from Arch Chemicals, Norwalk, USA) . At the end, the coating solution was diluted with deionised water to a final weight of 100Og.
Example 30
3.84g of solid boric acid were added at a temperature of 45°C to 591.3g of the dispersion of Example
26. After the dissolution of the boric acid 34Og of an aqueous solution of polyvinyl alcohol (8%, available as Mowiol 4088 from Clariant AG, Muttenz, Switzerland) were added and afterwards 13.3g of an aqueous solution of the wetting agent Olin 1OG (5.26%, available from Arch Chemicals, Norwalk, USA) . At the end, the coating solution was diluted with deionised water to a final weight of 100Og.
Example 31
3.84g of solid boric acid were added at a temperature of 45°C to 591.3g of the dispersion of Example
27. After the dissolution of the boric acid 34Og of an aqueous solution of polyvinyl alcohol (8%, available as Mowiol 4088 from Clariant AG, Muttenz, Switzerland) were added and afterwards 13.3g of an aqueous solution of the wetting agent Olin 1OG (5.26%, available from Arch Chemicals, Norwalk, USA) . At the end, the coating solution was diluted with deionised water to a final weight of 100Og. Example 32
3.84g of solid boric acid were added at a temperature of 45°C to 591.3g of the dispersion of Example 28. After the dissolution of the boric acid 34Og of an aqueous solution of polyvinyl alcohol (8%, available as Mowiol 4088 from Clariant AG, Muttenz, Switzerland) were added and afterwards 13.3g of an aqueous solution of the wetting agent Olin 1OG (5.26%, available from Arch Chemicals, Norwalk, USA) . At the end, the coating solution was diluted with deionised water to a final weight of 100Og.
Example 33 140 g/m2 of the coating solution of Example 29 were coated at a temperature of 400C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m2 of the coated support contains 19.04g of surface-treated silica.
Example 34
140 g/m2 of the coating solution of Example 30 were coated at a temperature of 400C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m2 of the coated support contains 19.04g of surface-treated silica .
Example 35
140 g/m2 of the coating solution of Example 31 were coated at a temperature of 40°C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m2 of the coated support contains 19.04g of surface-treated silica. Example 36
140 g/m2 of the coating solution of Example 32 were coated at a temperature of 40°C with a bar coater onto a white resin-coated support. The coated support was then dried for 60 minutes at a temperature of 35° C. 1 m2 of the coated support contains 19.04g of surface-treated silica .
Method to assess box yellowing
Since yellowing of the media stored in a cardboard box is only noticeable after a long period of time, an accelerated test is done in order to get reliable results in a reasonable time frame. The accelerated test is performed as follows:
The media to test are cut in pieces of 2 x 10cm and put in a white cardboard box of the size 21.5 x 30.5 x 1.5cm, PrintPac, Ilford Art. Nr. 116'194. An internal reference cut in a standard media is joined to the material to test.
On the top of the media are placed two 1.3cm-stacks of densely packed layers of cardboard working as a source of yellowing components, that are made of the same cardboard as the box. These stacks are placed at the long edge of the box, to ensure homogeneous concentration of damaging components in the atmosphere of the box.
Once closed, the box is placed in a sealable, gas fast polyethylene bag from VTT, Germany, sealed and heated for 5 days at the temperature of 600C in a Salvis drying oven.
At the end of the reaction period, the L*a*b* values of the tested media are recorded with a Spectrolino ANSI A spectrometer and compared with the original values. Yellowing of the media is indicated as ΔE*, where:
AE* = ^(AL*)2+(Aa*)2+(Ab*)2 For direct comparisons between two different boxes, the ΔE*-value is corrected accordingly to the ΔE*-value of the internal references:
AE * _ AE - re/2 AE ' actual
AE ' ref\
Method to assess improved dispersibility
A good measure for the ease of dispersion is to determine the minimum amount of surface-treating agent needed to get a reasonable addition time. This is achieved by starting with a high amount of surface- treating agent, lowering it in subsequent dispersions so that the silica becomes almost impossible to disperse, and drawing a curve of addition time vs. amount of surface-treating agent (referred to as ratio of amine to silica in mol-%) . The minimal quantity of amine before the addition time begins to rise is the measure of dispersibility. The silica dispersions were prepared as in Ex. 25-28, the amount of formic acid being determined such as maintaining identical pH throughout the series.
Results of box yellowing
RESULTS EXAMPLES
The results of accelerated box yellowing are listed in Table 4 shown below.
Figure imgf000043_0001
Table 4
The results in Table 4 clearly show that a recording sheet for ink jet printing, where the surface of the silicon dioxide has been modified with a solution comprising an aminosilane bearing only a secondary amino group, exhibits a strongly improved resistance to yellowing by cardboard components in comparison to a recording sheet, where the surface of the fumed silicon dioxide has been modified with a solution comprising an aminosilane bearing a primary amino group.
Results of dispersibility assessment
RESULTS EXAMPLES
For all subsequent dispersions, the same procedure was used: water and formic acid were put in a IL- stainless steel beaker equipped with a 60xl5mm Cowles- type dissolver. Aminosilane was added and allowed to hydrolyse for 5 minutes. Then 138.Og silicon dioxide H5
(Cabot, Billerica USA) was added portions wise to prepare 600ml of a 23% silica dispersion. During the addition, the dissolver rotated at 1550rpm.
For each dispersion the time necessary to add the silicon dioxide is recorded. The minimal necessary amount of aminosilane is obtained when the addition time is below 20 minutes.
The ζ-potential of the treated silicon dioxide surface is measured with a Quantachrome DT-1200 acoustophoresis device.
Table 5 gives the amount in g of water, aminosilane and formic acid (20% solution) that were used.
Figure imgf000045_0001
Table 5
The time necessary to add the silicon dioxide is listed in Table 6 shown below.
mol-% DAMO AMEO 1189 A-LINK15 amine [min] [min] [min] [min]
2.3 43 18
2.9 10 .5
3.6 7.5 6.0
4.2 81 66 6.5 5.0
4.8 37 51
5.4 13.5 34.5
6.0 11.5 18
6.6 14.5 4.5 4.5
Table 6
The minimum amount of aminosilane necessary to prepare a dispersion containing 23% of silicon dioxide H5 in less than 20 minutes is 6.0mol-% of silicon dioxide when Dynasylan AMEO is used, 2.7mol-% (5.4mol-% of amine) when Dynasylan DAMO is used, and 2.9mol-% when Dynasylan 1189 or Momentive A-LINK15 are used.
These results show that surface treatment of silicon dioxide made with an aminosilane bearing a secondary amino group is much easier and faster than a surface treatment made with an aminosilane bearing a primary amino group.
Table 7 indicates the ζ-potential value of these dispersions at 10% silicon dioxide concentration: mol-% AMEO DAMO 1189 A-LINK15 amine [mV] [raV] [mV] [mV]
2.9 30.1 31.3
5.4 32.2
6.0 29.7
Table 7
It makes clear that the quantity needed to treat the surface of the silicon dioxide and to get high positive surface charge is strongly reduced when the aminosilane used as surface-treating agent bears a secondary amino group.

Claims

1. A method for preparation of surface modified silicon dioxide, wherein the surface of the silicon dioxide is modified by mixing said silicon dioxide with a solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof.
2. The method according to claim 1, wherein said method comprises the following steps;
(i) an aqueous solution of said at least one aminoorganosilane is provided;
(ii) said at least one monovalent acid or salt is added to the aqueous solution of step (i) to form the solution of said at least one aminoorganosilane and at least one monovalent acid or salt thereof; and then (iii) said silicon dioxide is added to the solution formed in step (ii) to modify the surface of said silicon dioxide.
3. The method according to claim 1 or 2, wherein said solution comprising at least one aminoorganosilane and at least one monovalent acid or salt thereof comprises the reaction product of said at least one aminoorganosilane and at least one monovalent acid or salt thereof which does not have a hydroxyl group.
4. The method according to any of claims 1 to 3, wherein said monovalent acid is a monovalent organic acid or salt thereof.
5. The method according to claim 4, wherein said monovalent organic acid has the general formula (I):
Figure imgf000047_0001
wherein, R represents H, substituted or unsubstituted alkyl, and
M represents H or a monovalent cation.
6. The method according to claim 5, wherein said monovalent organic acid or salt thereof is formic acid, acetic acid, propionic acid or salt thereof.
7. The method according to any of claims 1 to 6, wherein said aminoorganosilane has the general formula ( I I ) :
Figure imgf000048_0001
wherein ,
Ri, R2 and R3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl with 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
R4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
8. The method according to any of claims 1 to 6, wherein said aminoorganosilane is selected from the group consisting of 3-aminopropyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyl-trimethoxysilane, (3- triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyl- triethoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, (3-trimethoxy-silylpropyl) - diethylenetriamine and mixtures thereof.
9. The method according to any of claims 1 to 6, wherein said aminoorganosilane has the general formula (III) :
(R5) m(OR6)3-m-Si (CH2) x (CHR7)y(CR8R9) Z-NH-Ri0 (III) wherein,
R5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R6 represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R7, Rs and R9 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and
m = 0-2, x+y+z = 1-8.
10. The method according to claim 9, wherein the aminoorganosilane is selected from the group of N- (n- butyl) -aminopropyl-trimethoxysilane, N- (n-butyl) - aminopropyl-triethoxysilane, N- (cyclohexyl-aminopropyl) - trimethoxysilane, N- (cyclohexyl-aminopropyl) - triethoxysilane, N- (cyclohexyl-aminomethyl) - trimethoxysilane, N- (cyclohexyl-aminomethyl) - triethoxysilane, N-ethylamino-isobutyl-trimethoxysilane and N-ethylamino-isobutyl-triethoxysilane .
11. The method according to any of claims 1 to 10, wherein said silicon dioxide is fumed silica.
12. The method according to any of claims 1 to 11, wherein said fumed silica has a specific surface area between 20 m2/g and 400 m2/g.
13. The method according to any of claims 1 to 12, wherein the mixing step is carried out by dispersing said silicon dioxide particles in a powder form into said solution by means of a suction-type dispersing device.
14. The method according to any of claims 1 to 13, wherein relative to the amount of said silicon dioxide, the amount of said acid or salt thereof is between 0.5 to 10% by weight and the amount of said aminoorganosilane is between 1 and 30% by weight.
15. A coating solution for a recording sheet for ink jet printing comprising the surface modified silicon dioxide particles prepared by the method according to any of claims 1 to 14 together with a binder.
16. A recording sheet for ink jet printing having coated onto a support the coating solution according to claim 15.
17. A recording sheet for ink jet printing having coated onto a support an ink receiving layer comprising at least one aminoorganosilane, at least one monovalent acid or salt thereof, silicon dioxide and a binder.
18. The recording sheet according to claim 17, wherein said monovalent acid is a monovalent organic acid or salt thereof.
19. The recording sheet according to claim 18, wherein said monovalent acid has the general formula (I) :
Figure imgf000050_0001
wherein, R represents H, substituted or unsubstituted alkyl, and
M represents H or a monovalent cation.
20. The recording sheet according to claim 19, wherein said monovalent organic acid or salt thereof is formic acid, acetic acid, propionic acid or salt thereof,
21. The recording sheet according to any of claims 17 to 20, wherein said aminoorganosilane has the general formula ( II ) :
Figure imgf000050_0002
wherein,
Ri, R2 and R3 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl with 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
R4 represents an organic moiety substituted by at least one primary, secondary or tertiary amino group.
22. The recording sheet according to any of claims 17 to 20, wherein said aminoorganosilane is selected from the group consisting of 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyl-trimethoxysilane, (3- triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyl- trietyhoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, (3-trimethoxy-silylpropyl) - diethylenetriamine and mixtures thereof.
23. The recording sheet according to any of claims 17 to 20, wherein said aminoorganosilane has the general formula (III) : (R5) m (OR6) 3-m-Si (CH2) x (CHR7) y (CR8R9) Z-NH-R10 (III) wherein,
R5 represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R6 represents hydrogen, unsubstituted or substituted alkyl with 1 to 6 carbon atoms,
R7, R8 and R9 independently represent hydrogen, hydroxyl, unsubstituted or substituted alkyl having from 1 to 6 carbon atoms, unsubstituted or substituted aryl, unsubstituted or substituted alkoxyl having from 1 to 6 carbon atoms or unsubstituted or substituted aryloxyl, and
Rio represents an unsubstituted or substituted alkyl with 1 to 6 carbon atoms, unsubstituted or substituted cycloalkyl with 1 to 6 carbon atoms, unsubstituted or substituted aryl, and
m = 0-2, x+y+z = 1-8.
24. The recording sheet according to any of claims 17 to 20, wherein the aminoorganosilane is selected from the group of N- (n-butyl) -aminopropyl-trimethoxysilane, N- (n-butyl ) -aminopropyl-triethoxysilane, N- (cyclohexyl- aminopropyl) -trimethoxysilane, N- (cyclohexyl- aminopropyl) -triethoxysilane, N- (cyclohexyl-aminomethyl) - trimethoxysilane, N- (cyclohexyl-aminomethyl) - triethoxysilane, N-ethylamino-isobutyl-trimethoxysilane and N-ethylamino-isobutyl-triethoxysilane .
25. The recording sheet according to any of claims 17 to 24, wherein said silicon dioxide is fumed silica.
26. The recording sheet according to any of claims 17 to 25, wherein said binder is selected from the group consisting of polyvinyl alcohol, polyvinyl alcohol derivative, gelatin, polyvinylpyrrolidone and mixtures thereof.
27. The recording sheet according to any of claims 17 to 26, wherein said ink receiving layer is hardened with boron compound.
28. The recording sheet according to any of claims 17 to 27, wherein said ink receiving layer additionally contains optical brightening agents such as stilbenes, coumarines, triazines and oxazoles.
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