AQUEOUS NANOPARTICLE CERAMIC AGGLOMERATE DISPERSION FOR FORMING INK-ABSORBING LAYER OF INK-JET RECORDING MEDIUM

Abstract: An aqueous nanoparticle ceramic agglomerate dispersion, for forming an ink-absorbing layer of an ink-jet recording medium, comprises a nanoparticle ceramic agglomerate dispersed in deionized water. The nanoparticle ceramic agglomerate has an average diameter of 0.05 to 0.3 mm at a viscosity suitable for coating of 10 to 200 mPa.s as measured by a laser diffraction particle size distribution measurement apparatus, and the ratio of the peak width (half width) at a height which is half the maximum height in a size distribution curve of the nanoparticle ceramic agglomerate, determined according to the results of the measurement, to the maximum height is 0.7 or less. This aqueous ceramic dispersion provides an ink-jet recording medium which enables the printing of sharp and clear images.

Description: Aqueous nanoparticle ceramic agglomerate dispersion for forming ink-absorbing layer of ink-jet recording medium BACKGROUND OF THE INVENTION Field of the Invention 1. The present invention relates to an aqueous nanoparticle ceramic agglomerate dispersion which is suitable for ink-absorbing layers on ink-jet recording media and which facilitates printing of sharp and clear images on the ink-jet recording media. 2. Description of the Related Art A typical conventional ink-jet recording medium includes a substrate having a thickness of 100 to 300 μm, such as paper or a polyethylene film, an ink-absorbing layer having a thickness of 30 to 200 μm formed thereon by coating, and a protective layer having a thickness of 1 to 10 μm composed of a water-soluble resin or the like, which is formed on the ink-absorbing layer by spraying. In general, the ink-absorbing layer of the ink-jet recording medium is formed as follows. Nanoparticle ceramic agglomerates, such as a powdered silicon oxide (hereinafter referred to as Si0 2 ) agglomerate and a powdered aluminum oxide (hereinafter referred to as A1 2 0 3 ) agglomerate are added to deionized water to form an aqueous nanoparticle ceramic agglomerate dispersion so that the dispersion has a viscosity suitable for coating of 10 to 200 mPa-s. To the dispersion, for example, a cationic polymer, ethanol, propanol, ethyl acetate, . polyvinyl alcohol, and boric acid are added to prepare a coating. The coating is applied onto the substrate surface and is dried. The above raw materials used for the aqueous nanoparticle ceramic agglomerate dispersion are generally prepared by a vapor phase synthetic method using SiCl4 and AICI3 in the presence of hydrogen and oxygen, for example, from a burner. The resulting nanoparticle ceramic powder has an extremely small average diameter of 7 to 40 nm. Thus, ceramic particles inevitably interact with each other and readily agglomerate. Even when this nanoparticle ceramic powder is added to deionized water after disintegration in a ball mill, the nanoparticle ceramic powder is present as a ceramic powder agglomerate having an average diameter of 1 to 30 μm. In the printing of images onto the ink-jet recording medium, fine ink droplets discharged through dot nozzles of an ink-jet printer are absorbed into the ink-absorbing layer. In color printing, such a process is repeated several times using inks of different colors. With trends toward higher performance in ink-jet printers, the size of the ink droplets discharged from the ink-jet printers has been reduced to 20 μm or less. When this ink is discharged onto the above conventional ink-jet recording medium, the ink droplets flow locally in the ink-absorbing layer and result in bleeding. As a result, printed images are not clear, regardless of how ultrafine the ink droplets are. SUMMARY OF THE INVENTION It is an object of the present invention to provide an aqueous nanoparticle ceramic agglomerate dispersion which is suitable for ink-absorbing layers on ink-jet recording media and which facilitates printing of sharp and clear images onto the ink-jet recording media. The present inventors have researched aqueous nanoparticle ceramic agglomerate dispersions for ink-absorbing layers so that the ink-absorbing layer can hold ultrafine ink droplets discharged from an ink-jet printer at the discharged positions, and have reached the following conclusions. a) In a conventional aqueous nanoparticle ceramic agglomerate dispersion, the nanoparticle ceramic agglomerate has an average diameter of 1 to 30 μm according to measurements by a laser diffraction particle size distribution measurement apparatus. The size distribution curve determined according to the results of the measurement is shown in Fig. 2. The ratio of the peak width at a position having a height which is half the maximum height of the curve (hereinafter referred to as the half width) to the maximum height is 1 to 1.5. Such a ratio indicates that the nanoparticle ceramic agglomerate is relatively rough and sizes thereof are not uniform. That is, the size uniformity of the agglomerates is inadequate. In an auxiliary insulating layer containing such nanoparticle ceramic agglomerates having a broad size distribution, larger agglomerates on the ink-absorbing layer absorb many ultrafine ink droplets. That is, the ultrafine ink droplets cannot be held at discharged positions, and bleed from the discharged positions. b) The above conventional aqueous nanoparticle ceramic agglomerate dispersion is generally prepared by dispersing 1 to 50% of nanoparticle ceramic agglomerate into deionized water using a conventional mixer. When this dispersion is treated using a conventional ultrasonic homogenizer for a predetermined time, or using a jet-mill apparatus for a predetermined time in which ultrahigh-pressure counter jet streams of the dispersion collide with each other, the nanoparticle ceramic agglomerates are rapidly disintegrated in the aqueous medium. When the nanoparticle ceramic agglomerate satisfies the following conditions by cυ M N> H 1 o Cn O Cn O cn Fig. 1 is a size distribution curve of ceramic agglomerates in an aqueous nanoparticle ceramic agglomerate dispersion in accordance with the present invention; and Fig. 2 is a size distribution curve of ceramic agglomerates in a conventional nanoparticle ceramic agglomerate dispersion. DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the average diameter of the nanoparticle ceramic agglomerate is in a range of 0.05 to 0.3 μm. At an average diameter less than 0.05 μm, there are no longer distinct differences in the quality of printed images. At a diameter exceeding 0.3 μm, some fine ink droplets of different colors having diameters of 20 μm or less are absorbed in the same nanoparticle ceramic agglomerate, resulting in ink bleeding. Thus, the resulting images are not clear. The ratio of the half width in the size distribution curve of the nanoparticle ceramic agglomerate to the maximum height is in a range of 0.7 or less. At a half width exceeding 0.7, many ceramic agglomerates having diameters which significantly deviate from the average diameter are present. When an ink-absorbing layer contains these ceramic agglomerates, each of the relatively large agglomerates will absorb different types of color inks, resulting in ink bleeding. As a result, the printed image exhibits color irregularities . The viscosity suitable for coating of the aqueous nanoparticle ceramic agglomerate dispersion is in a range of 10 to 200 mPa « s. At a viscosity of less than 10 mPa-s, the dispersion is not held on the substrate. At a viscosity exceeding 200 mPa-s, the dispersion cannot be uniformly applied on the substrate. CO CO > > P 1 Cn o Cn o Cπ o Cπ CU TJ CU <! 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Moreover, a size distribution curve was prepared to determine the ratio of the half width (the width at a position having a height which was half the maximum height of the curve) to the maximum height. These results are shown in Table 1. To 1000 ml of each dispersion was added 10 to 40 g of cationic polymer, 50 to 100 ml of ethanol, 15 to 30 ml of propanol, 10 to 20 ml of ethyl acetate, 20 to 50 g of polyvinyl alcohol, and 1 to 10 g of boric acid to prepare a coating for forming an ink-absorbing layer. The coating was applied onto a recording surface of water-absorbing paper having a thickness of 200 μm, was rapidly cooled, and was dried by hot air at 50°C for 3 minutes. An ink-jet recording medium having an 80-μm thick ink-absorbing layer was thereby prepared. Yellow, magenta, and cyan solid images were printed onto the ink-jet recording medium using an ink-jet color printer PM-3300C made by Seiko Epson Corporation, and reflection densities were measured for monochromatic light of red, green, and blue. The results are shown in Table 2. A color image of a person having a size of 250x180 mm was printed on the ink-jet recording medium and the image quality was observed at a magnification of 3000 using a high-precision digital microscope. Table 1 Table 2 p> h-» Cπ o cπ P- TJ a Cfl a rt Hi 3 O a 3 P- rt 3 hi P- Ω P- Φ P- ø 1 P- Ω H. P- o 3 1 ør TJ O CQ Ω iQ rt o Φ 3 Ω O H Φ φ H <! 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Claims: WHAT IS CLAIMED IS: 1. An aqueous nanoparticle ceramic agglomerate dispersion, for forming an ink-absorbing layer of an ink-jet recording medium, comprising: - a nanoparticle ceramic agglomerate dispersed in deionized water; - wherein the nanoparticle ceramic agglomerate has an average diameter of 0.05 to 0.3 μm at a viscosity suitable for coating of 10 to 200 mPa*s as measured by a laser diffraction particle size distribution measurement apparatus, and - the ratio of the peak width at a height which is half the maximum height in a size distribution curve of the nanoparticle ceramic agglomerate, determined according to the results of the measurement, to the maximum height is 0.7 or less.

Inventors: ARAI MASAHIDE, MUROTA MASAMICHI, SHIRONO HIROKUNI, ARAI, MASAHIDE, MUROTA, MASAMICHI, SHIRONO, HIROKUNI
Applicants: DEGUSSA, DEGUSSA AG
Application year: 2001
Main classification: B41M5
IPC codes: B41J2, B41M5, C01B33, C01F7, C09C1