Ink-jet recording material containing alumina-doped silica

Abstract: An ink jet recording material excellent in all of the characteristics such as drying property, ink absorbency, water resistance and the like is provided in accordance with the present invention. The ink jet recording material has an ink-receiving layer comprising a hydrophilic resin and inorganic pigments, the ink-receiving layer containing silica particles with a surface doped with alumina as the inorganic pigments. The alumina-doped silica is prepared by a process employing flame hydrolysis techniques combined with a pyrolysis. The ink-receiving layer preferably contains the alumina-doped silica in an amount ranging from 5 to 200 weight parts based on 100 weight parts of the hydrophilic resin.

Description: BACKGROUND OF THE PRESENT INVENTION The present invention relates to ink jet recording materials (recording materials for ink jet printing), particularly to ink jet recording materials excellent in an ink drying property and glossiness. Ink-jet printing is one of the most popular recording processes along with electrophotography (PPC). Various kinds of top-coated materials for the ink-jet printing have been proposed to obtain an image of a high quality. As the topcoating for the image receiving, a resin having both a good water resistance and an ink absorbency is generally used for coating on a substrate such as a paper sheet or a film. There have been proposed materials using a graft-polymer or a block polymer (Japanese Patent Application laid-open Publication No.61-21780), materials using a polyvinyl pyrrolidone and an acrylic acid polymer (Japanese Patent Application laid-open Publication No.62-218181) or materials used for both ink-jet printing and PPC (Japanese Patent Application laid-open Publication No.5-177921). Document D1 (WO-A 9822388 / EP 0 963 947 A1) describes a composite inorganic fine powder which has abilities in ink adsorption and ink fixation. The composite inorganic powder consists of particles as a core having hydroxyl groups and a shell being formed from an aluminium compound selected from aluminium oxide and aluminium hydroxide. Document D2 (JP-A-06 297 830) describes a recording sheet for an ink-jet recording system which contains an ink accepting layer consisting of a cationic colloidal silica, an alumina hydrate and a hydrophilic resin. Document D3 (EP-A-0 218 956) describes a recording sheet of paper and porous particles provided on the paper surface, whereby the porous particles consist of silica, silica-alumina or alumina. In most of the conventional ink jet recording materials, inorganic pigments such as clay, talc, silica, alumina (aluminum oxide), titanium oxide are added to the coating in order to improve ink absorbency of the material. The inorganic pigments are selected considering their transparency or color (transparent or white). For example, when transparency of the ink jet recording material is required for the application to OHP etc., a transparent crystalline pigment such as alumina or the like is selected. When the ink jet printing material should be white, a white pigment such as talc, titanium oxide or the like is selected. In addition to the color of the inorganic pigment, the dispersability in a coating solution, fluidity of the coating solution, effects on ink absorbency or drying property of the ink-receiving layer should be also considered when the inorganic pigment is selected. However, each of the aforementioned inorganic pigments has different characteristics and does not satisfy all of the requirements. Therefore, an object of the present invention is to provide an ink jet recording material excellent in all of the characteristics such as drying property, ink absorbency, water resistance and the like. Another object of the present invention is to provide an ink jet recording material capable of providing an image of a high quality. SUMMARY OF THE PRESENT INVENTION In order to attain the aforementioned objects, the inventors have conducted a research on inorganic pigments used for the ink-receiving layer of the ink jet recording material and, as the result, found that pyrogenically prepared silica particles with a surface doped with alumina (alumina-doped silica) had both characteristics of silica and those of alumina and that their properties were superior to each or mixture of the two inorganic pigments. The ink jet recording material according to the present invention has an ink-receiving layer comprising a hydrophilic resin and an inorganic pigment, wherein the ink-receiving layer contains pyrogenically prepared silica particles with a surface doped with alumina as the inorganic pigment. The amount of the alumina is preferably 0.00001 to 20 wt %. The alumina-doped silica exhibits a good fluidity and a good dispersability when it is dispersed in a coating solution, and enables to form a strong coating layer. The ink-receiving layer containing the pyrogenically prepared alumina-doped silica has a high water resistance, an excellent ink absorbency and is capable of producing an image of a high quality. An amount of the pyrogenically prepared alumina-doped silica is, not particularly limited to this, but preferably 5-200 parts by weight based on 100 parts by weight of the hydrophilic resin. According to one preferable embodiment of the present invention, the ink receiving layer is formed on a substrate. As the substrate, a plastic film and a paper sheet are exemplified. When the paper sheet is employed, the ink receiving layer may be formed thereon by coating. Alternatively, the paper itself can be the ink receiving layer. In the latter case; the pyrogenically prepared alumina-doped silica can be added to pulps as a loading material for inner sizing or added to a sizing coating as a pigment thereof in a paper manufacturing process. PREFERRED EMBODIMENT OF THE PRESENT INVENTION The ink jet recording material of the present invention will be explained in more detail hereinafter. Fig.1 (a) is a cross-sectional view of the one embodiment of the ink jet recording material according to the present invention. The ink jet recording material has a structure shown in Fig. (a) in which an ink-receiving layer 2 is formed on a substrate 1. As the substrate 1, a transparent or opaque film, for example, a synthetic resin film such as a polyester, polycarbonate, polyethylene, polypropylene, tri-acetyl cellulose, polyvinyl chloride, acrylic resin, polystyrene, polyamide, polyimide, vinylidene chloride-vinyl chloride copolymer or the like, a paper sheet, synthetic paper, cloth, tarpaulin, or a composite of a plastic film and paper or the like can be employed. The surface of the substrate may be subjected to a treatment for improving adhesiveness so that the ink-receiving layer is easily formed thereon. An anchor coating may be applied to the surface. As the anchor coating, a resing having a good adhesiveness to both of the resin of the ink receiving layer and the substrate can be employed. The substrate may be a multiple-layer substrate provided with an adhesion layer, a matte layer or the like on the opposite side to the ink receiving layer for adding writing property, adhesiveness to the other materials and the like. The thickness may be selected taking account of feeding or supplying to the ink jet printer and is, for example, in the range of 20 to 200 µm. The ink-receiving layer 2 comprises a hydrophilic resin and an inorganic pigment. As the inorganic pigment, pyrogenically prepared alumina-doped silica particles are used. The pyrogenically prepared alumina-doped silica particles, especially pyrogenically prepared silica particles with a surface doped with alumina, have both characteristics of pyrogenically prepared silica and those of alumina and show specific properties, for example, an excellent fluidity or dispersability, which each or mixture of pyrogenically prepared silica and alumina does not exhibit. The amount of a dopant (alumina) is in the range from 0.00001 to 20 wt %, preferably in the range from 0.0001 to 1.0 wt %, more preferably in the range from 0.01 to 0.5 wt %. In this range, the aforementioned properties can be obtained. The particle size (average size) of pyrogenically prepared silica may be 1-300 nm, preferably 10-100 nm, more preferably 60-80 nm. As a process for preparing the pyrogenically prepared alumina-doped silica, the following processed may be exemplified: 1) coating pyrogenically prepared silica particles with a solution including an aluminum compound such as AlCl 3 and drying and sintering the particles, 2)flame hydrolysis techniques (feeding a gas mixture of an Al compound and a Si compound into a flame and allowing them to react to form oxides). However, the alumina-doped silica used in the present invention can be made by the following process employing flame hydrolysis techniques combined with a pyrolysis. The surface of silica particles can be doped with alumina by this process and homogeneously even at very small amounts. In this process, a gaseous silicon compound (typically halogenated silicon, e.g., SiCl 4 ) is fed into a flame and is homogeneously mixed with an aerosol containing aluminum compound such as AlCl 3 . The aerosol containing the aluminum compound is prepared by ultrasonic nebulization using an aerosol generator, which contains a dopant solution or suspension. After the aerosol is mixed homogeneously with the gaseous silicon compound, the mixture is allowed to react in the flame and the resulting pyrogenically prepared alumina-doped silica is separated from the gas stream in a known manner. This process can prevent formation of alumina particles and silica particles separately. Resulting pyrogenically prepared alumina-doped silica consists of particles with a surface doped with alumina and the BET surface area thereof is between 5 and 600 m 2 /g. By using thus pyrogenically prepared alumina-doped silica for the ink receiving layer, an ink jet printing material having excellent properties can be obtained. The amount of the pyrogenically prepared alumina-doped silica is, not particularly limited to this, in the range of from 5 to 200 parts by weight, preferably 10 to 70 parts by weight based on 100 weight parts of the hydrophilic resin. When the pyrogenically prepared alumina-doped silica is added to a coating solution in this range, fluidity and dispersability of the coating solution and an ink drying property of the coated layer (ink-receiving layer) can be improved. While it is difficult to form a film for a coating solution including 100 parts by weight of ordinary silica particles, the pyrogenically prepared alumina-doped silica is capable of forming a homogeneous film even if 100 parts by weight or more are added to the coating solution because of the low viscosity and good dispersability. As the hydrophilic resin, resins generally used for an ink-receiving layer of the conventional ink jet printing materials can be used. A water resistant resin with a good absorbency of aqueous ink is preferably employed. As such a resin, synthetic resins such as polyvinyl alcohols, polyvinyl pyrrolidones, water soluble cellulose resins, water soluble polyester resins, polyvinyl acetal, acrylic acids-acrylic amide copolymer, melamine resins, polyetherpolyol resins and its cross-linked compounds and the like, natural resins such as gelatin, casein, starch, chitin, chitosan and the like, and water soluble high-molecular compounds imparted with water resistance to some extent are exemplified. Hardened polyvinyl alcohols or polyvinyl pyrrolidones by a know process, water soluble resins having a cinnamoyl group, a stilbazolium group, a styrylquinolium group or a diazo group and the like may be employed. These resins are used solely or as any mixture thereof. Combination of polyvinyl pyrrolidones and polyvinyl alcohols or acrylic acids copolymer is preferable in view of high water resistance. The ink-receiving layer may contain, in addition to the pyrogenically prepared alumina-doped silica, other inorganic pigments such as clay, talc, diatom earth, calcium carbonate, calcium sulfate, barium sulfate, aluminum silicate, titanium oxide, zinc oxide, synthetic zeolite, alumina, smectite or the like, to the extent that they do not hamper the property of the pyrogenically preperad alumina-doped silica. The total amount of the inorganic pigments, including the pyrogenically prepared alumina-doped silica, is in the range of 5 to 200 parts by weight based on 100 parts of the resins. The ink-receiving layer may further contain optional additives such as anti-foam agents, leveling agents, UV absorbers, light stabilizers, pigments and the like. The ink jet recording material can be prepared by applying a coating solution for the ink-receiving layer comprising the pyrogenically prepared alumina-doped silica, the hydrophilic resins and other additives, if necessary, dissolved or dispersed in a solvent through a known coating method such as bar coating, spray coating, roll coating on a substrate, and drying the coated layer. When a paper sheet is used as the substrate, it may be impregnated with the coating solution by immersing in the solution. When the paper sheet is employed as the substrate, the pyrogenically prepared alumina-doped silica can be added to pulps as a loading material for inner sizing or added to a sizing coating as a pigment thereof in a manufacturing process of paper of fine or middle class. Using a paper sheet as the substrate can reduce the amount of coating required for imparting the ink jet recording properties, since capillarity of pulps aids ink to wick. On the other hand, for the purpose of obtaining a texture similar to photograph, a plastic film is preferred because it provides a high glossiness to the ink-receiving layer. A thickness of the ink-receiving layer is not particularly limited but it may be 1-50 µm, preferably 3-40 µm. Although the ink-jet recording material having a basic structure in which the ink-receiving layer 2 is formed on the substrate 1 has been explained, the ink-jet recording material of the present invention is not limited to this and various structures can be realized. Fig.1(b) shows a multiple-layer ink-jet recording material as another embodiment of the present invention. This ink-jet recording material has a two layer structure where an ink-receiving layer 2 and an ink-permeable layer 3 are formed on a substrate 1 in this order. The ink-receiving layer 2 is the same as the above-mentioned ink-receiving layer 2 (Fig.1(a)) and includes a hydrophilic resin and an inorganic pigment as main components. The ink-permeable layer 3 is a porous layer. Dyes or pigments of ink printed on this ink jet recording material are adsorbed partly in the pores of the ink-permeable layer 3 and the ink which permeates through the ink-permeable layer 3 is absorbed in the ink-receiving layer 2. Thus, a high ink drying speed and an excellent ink absorbency can be obtained in this ink jet recording material. In addition, the printed surface exhibits a high glossiness and a clear image. EXAMPLES The present invention will be explained more in detail with reference to the following examples. In the examples, "parts by weight" will be abbreviated to "parts". Example 1 1. Preparation of pyrogenically prepared Alumina-doped Silica Pyrogenically prepared Silica particles having a surface doped with alumina were prepared in the following manner by using an apparatus shown in Fig.2. 5.25 kg/h of SiCl 4 were evaporated at about 130 °C and introduced in the central tube 22 of the burner 21. 3.4 Nm 3 /h of primary hydrogen and 3.76 Nm 3 /h of air were also fed to the central tube 22. The gas mixture flew out of the inner nozzle 23 of the burner 21 and burned in the combustion chamber 28 and the water-cooled flame tube 30 connected in series therewith. 0.5 Nm 3 /h of secondary hydrogen were fed to the mantle nozzle 24 surrounding the central nozzle 23 in order to prevent caking of the nozzle. An additional 20 Nm 3 /h of secondary air were fed to the combustion chamber 28. On the other hand, an aluminum salt aerosol was produced in an amount of 460 g/h by ultrasonic nebulization of a 2.2 % aqueous aluminum chloride solution in the aerosol generator 26. The aerosol was passed through a heated pipe 27 with the assistance of 0.5 Nm 3 /h of air as carrier gas, where the aerosol was converted into a gas and a salt crystal aerosol at temperatures around 180 °C. The aerosol flew out of an axial tube 25 into the central tube 22. At the mouth of the burner 21, the temperature of the gas mixture (SiCl 4 /air/hydrogen, aerosol) was 156 °C. The reaction gases and the resulting pyrogenically prepared silica, doped with alumina, were removed under suction via a cooling system 31 by applying a reduced pressure and thus cooled to about 100 to 160 °C. The solid was separated from the gas stream in a filter or cyclone. In a further step, adhering hydrochloric acid residues were removed from the pyrogenically prepared alumina-doped silica by treatment with water vapor-containing air at elevated temperatures. The particle size of thus pyrogenically prepared prepared Al-doped silica was 80 nm and the amount of alumina was approximately 0.25 % by weight. 2. Preparation of an ink jet recording material A coating solution for an ink-receiving layer having the following composition was applied to a polyethylene terephthalate film (Melinex: Du Pont) of a thickness of 100 µm in amount of 5-5.5 g/m 2 by a bar coater and dried to form an ink-receiving layer. Composition of the coating solution for ink-receiving layer polyvinyl alcohol 30 parts polyvinyl pyrrolidone 50 parts pyrogenically prepared alumina-doped silica 50 parts (average particle size:80 nm, amount of alumina:0.25%) water 520 parts Fluidity(viscosity) and dispersability of the coating solution, drying time, transparency and wicking of the ink-receiving layer and print quality after ink-jet printing were evaluated. The results are shown in Table 1. In Table 1, o ○, ○, Δ and × represent excellent, good, practical but not so good and bad respectively. Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Inorganic Pigment pyrogenically-prepared Alumina-doped Silica Alumina-Silica Mixed Oxide Silica Alumina Viscosity (mPa.S) 210 420 1200 330 Dispersability o ○ ○ ○ ○ wicking(mm) 27 31 26 22 Drying time (sec) 160 189 165 209 Transparency o ○ ○ Δ ○ Print Quality ○ o ○ ○ ○ Comparative Example 1 A coating solution for an ink-receiving layer having the following composition was applied to a polyethylene terephthalate film same as that of Example 1 in amount of 5-5.5 g/m 2 by a bar coater and dried to form an ink-receiving layer. The silica-alumina mixed oxide used in this example is available on the market (Aerosil MOX 170: Degussa A. G.) and the particle thereof consists of homogeneous mixture of silica and alumina. Composition of the coating solution for ink-receiving layer polyvinyl alcohol 30 parts polyvinyl pyrrolidone 50 parts silica-alumina mixed oxide 50 parts (average particle size:15 nm, amount of alumina:1%) water 520 parts The properties of coating solutions and the properties of each ink-receiving layers of these ink-jet recording materials were also evaluated in a manner same as that of Example 1 and the results are shown in Table 1. Comparative Examples 2,3 An ink-receiving layer was formed on the same polyethylene terephthalate film as Example 1 in a manner similar to that of Example 1 to produce an ink jet recording material, except that silica (Aerosil 200:Nippon Aerosil Co., Ltd.) or alumina (Aluminium Oxide C: Degussa AG) was used in Comparative Examples 2 and 3 respectively instead of the pyrogenically prepared alumina-doped silica. The properties of coating solutions and the properties of each ink-receiving layers of these ink-jet recording materials were also evaluated in a manner same as that of Example 1 and the results are shown in Table 1. As shown in Table 1, the coating solution of Example 1 exhibited an excellent dispersability and a good fluidity. A coating film of a desired thickness could be easily formed by using this solution. Its properties were superior to those obtained by Comparative examples using silica or alumina. The ink jet recording material of the Example 1 also showed a superior drying property to any of Comparative examples. These results indicate that the pyrogenically prepared alumina-doped silica has specific properties. It was also shown that the ink-receiving layer of the Example 1 had a transparency similar to that of the ink jet recording material using alumina or silica and a good image quality was obtained similarly to the ink-jet recording material using alumina or silica. Examples 2-4 Coating solutions for an ink-receiving layer having the following composition were prepared by using the same pyrogenically prepared alumina-doped silica as Example 1 and various kinds of hydrophilic synthetic resins. Composition of the coating solution for ink-receiving layer hydrophilic synthetic resin 10 parts inorganic pigment (pyrogenically prepared alumina-doped silica) 10 parts dispersing medium 80 parts As the hydrophilic synthetic resin, polyvinyl alcohol (GOHSENOL: Nippon Synthetic Chemical Industry Co., Ltd.), cation-modified polyvinyl alcohol (C-318-A: Nippon Synthetic Chemical Industry Co., Ltd.) and a mixture of acrylate copolymer and polyvinyl pyrrolidone in a ratio of 3:2 by weight were used in Example 2, 3 and 4 respectively. The dispersion medium was water in Examples 2 and 3, and meta-denatured alcohol in Example 4. Monomers of the acrylate copolymer used in Example 4 were methylmethacrylate 45 mol%, butylmethacrylate 10 mol%, hydroxy-ethylmethacrylate 30 mol% and dimethylaminoethylmethacrylate 15 mol%. Each of the coating solution was applied to a polyethylene terephthalate film (Melinex 535: Du Pont) and dried to form an ink jet recording material having an ink-receiving layer of a thickness of 25 µm. Comparative Examples 4-7 Coating solutions for an ink-receiving layer having the following composition were prepared in a manner similar to that of Example 2 by using the same polyvinyl alcohol (GOHSENOL: Nippon Synthetic Chemical Industry Co., Ltd.) as Example 2 and various kinds of inorganic pigments. Composition of the coating solution for ink-receiving layer hydrophilic synthetic resin (polyvinyl alcohol) 10 parts inorganic pigment 10 parts water 80 parts As the inorganic pigment, silica (Aerosil 200:Nippon Aerosil Co., Ltd.), alumina (Degussa AG) and silica (MIZUKASIL: Mizusawa Industrial Chemicals) were used in Comparative Example 4, 5, 6 respectively. As Comparative Example 7, a coating solution including no inorganic pigment was prepared by using 10 parts or polyvinyl alcohol (GOHSENOL: Nippon Synthetic Chemical Industry Co., Ltd.) and 90 parts of water. Ink jet recording materials were prepared by using these coating solutions in a manner similar to that of Example 2. Fluidity(viscosity) and dispersability of the coating solution were evaluated. Film strength, transparency, water-resistance and ink-absorbing speed of the ink-receiving layer, and print quality after ink-jet printing were also evaluated. The results are shown in Table 2. Coating solution Coating layer Fluidity Dispersability Film strength Transparency Water resistance Ink absobing speed Print quarity Example 2 ○ ○ ○ ○ × ○ ○ Example 3 ○ ○ ○ ○ × ○ ○ Example 4 ○ ○ ○ ○ ○ ○ ○ Comp. Exam. 4 × ○ × × × ○ Δ Comp. Exam. 5 ○ × ○ ○ × ○ ○ Comp. Exam. 6 × ○ × × × ○ Δ Comp. Exam. 7 ○ - ○ ○ × × × In evaluation of the fluidity, ○ represents that the coating was easily applied to the film by Mayer bar coating, and × represents that it was difficult to apply the coating to the film. As for the dispersability, ○ represents that the pigment was homogeneously dispersed in the medium (water) and × represents that the dispersion was not stable. As for the film strength, ○ represents that cohesive failure did not occur by peel test using an adhesive-backed tape and × represents that cohesive failure occurred. As for the transparency of the layer, ○ represents that the substrate film could be seen through the layer and × represents that the substrate was hidden by the layer. The water-resistance of the layer was evaluated by immersing the ink jet material in distilled water of 25 °C for 5 minutes. In the evaluation, ○ represents that the layer was kept as it was after 5 minutes and × represents that the layer was dissolved in water. For evaluating the ink absorbing speed and the print quality, ink image was printed on each of the ink jet recording materials by an ink jet printer (PM700C: Seiko Epson Corporation). In evaluation of the ink absorbing speed, ○ represents that the ink image was dried within 5 minutes after printing and × represents that the ink image was not dried within 5 minutes. As for the print quality, ○ represents good, Δ represents that the image was blurred, and × represents that the image could not be formed on the material. As apparent from the result shown in Table 2, when silica was used as the inorganic pigment (Comparative Examples 4, 6), the coating layer with a sufficient film strength could not formed because of their bad fluidity and the ink image printed on the material was blurred. When alumina was used as the inorganic pigment(Comparative Example 5), the dispersability was bad. In contrast with these Comparative Examples, the coating solutions of Example 2-4 were excellent in both fluidity and dispersability, no matter which hydrophilic resin was used. A homogeneous ink-receiving layer could be formed easily by using the coating solutions. In addition, all of the ink jet recording materials of Example 2-4 was excellent in film strength, transparency and ink drying speed and a good printing quality was obtained in all of the materials. Particularly, the ink jet material of Example 4, which employed a combination of acrylate copolymer and polyvinyl pyrrolidone as a hydrophilic resin, showed an excellent water resistance in addition to the above-mentioned properties. ADVANTAGE OF THE PRESENT INVENTION The ink-jet recording material of the present invention, by using pyrogenically prepared alumina-doped silica as inorganic pigments for the ink-receiving layer comprising a hydrophilic resin and inorganic pigments, is excellent in all of the properties such as an ink-drying property, ink-absorbency, water resistance and the like and is capable of producing an image of a high quality. BRIEF EXPLANATION OF DRAWINGS Fig.1 (a) and (b) are cross-sectional views of the ink jet recording material of the present invention respectively, where 1 represents a substrate, 2 represents an ink-receiving layer and 3 represents an ink-permeable layer. Fig. 2 is a diagram of an apparatus for preparing an alumina-doped silica used for the ink jet recording material of the present invention.

Claims: An ink jet recording material having an ink-receiving layer comprising a hydrophilic resin and inorganic pigments, wherein the ink-receiving layer contains pyrogenically prepared silica particles with a surface doped with alumina as the inorganic pigments. The ink jet recording material of claim 1, wherein the pyrogenically prepared silica particles are doped with alumina at 0.00001 to 20 wt %. The ink jet recording material of claim 1, wherein the amount of the pyrogenically prepared silica particles doped with alumina is in the range of from 5 to 200 weight parts based on 100 weight parts of the hydrophilic resin. The ink jet recording material of claim 1, wherein the ink receiving layer is formed on a substrate. The ink jet recording material of claim 4, wherein the substrate is a paper sheet. The ink jet recording material of claim 4, wherein the substrate is a plastic film.

Inventors: MANGOLD HELMUT, OCHIAI MITSURU, OHTA TETSUJI, MANGOLD, HELMUT, OCHIAI, MITSURU, OHTA, TETSUJI
Applicants: DEGUSSA, KIMOTO KK, NIPPON AEROSIL CO LTD, DEGUSSA AG, KIMOTO CO., LTD., NIPPON AEROSIL CO., LTD.
Application year: 1999
Main classification: B41M5
IPC codes: B41M5, B32B9, B41J2, D21H27, D21H19