Stock material or miscellaneous articles – Ink jet stock for printing – Particles present in ink receptive layer
Reexamination Certificate
2000-02-11
2003-09-23
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Ink jet stock for printing
Particles present in ink receptive layer
C106S286800
Reexamination Certificate
active
06623820
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a silica-alumina composite sol and a method for producing it. Particularly, it relates to a silica-alumina composite sol suitable for forming an ink-receiving layer of a recording medium for an ink jet printer, a method for producing it and a recording medium.
BACKGROUND ART
In recent years, reflecting wide use of digital cameras and computers, the hard copy technology to record images thereof on e.g. paper sheets has been rapidly developed. As hard copy recording systems, various systems have been known including not only a system wherein a display indicating an image is directly photographed by silver halide photography, but also a sublimation type thermal transfer system and an ink jet system.
Among these, an ink jet system is a system wherein ink droplets comprising dyes and a large amount of a solvent are ejected at a high speed from nozzles to a recording medium. An ink jet printer has been widely used in recent years, since full coloring and high-speed printing are easy, and the printing noise is low.
As the recording medium for an ink jet printer, in order to quickly absorb inks and to present a clear image, one having a substrate such as a paper sheet or a film, and a porous ink-receiving layer comprising inorganic fine particles of e.g. silica or alumina and a binder such as a polyvinyl alcohol, formed on the substrate has been known. The recording medium for an ink jet printer is required to absorb a large amount of the solvent contained in the ink, in the pores in the ink-receiving layer. Accordingly, the ink-receiving layer is required to have an appropriate pore size and a large pore volume. Further, the more transparent the ink-receiving layer is, the higher the color density will be, whereby a clearer image will be formed. Accordingly, one having a high transparency is preferred as the ink-receiving layer.
Further, since aqueous inks are employed for the ink jet recording system, it becomes important that even if exposed to water after formation of the image, the ink-receiving layer will have no defect in appearance, or the inks will not bleed due to flow of the dyes in the inks (hereinafter referred to as water resistance), quality of the recorded product will not deteriorate by scuffs generated when the surface of the recording medium is in contact with some sharp-edged stuff (hereinafter referred to as scuffing resistance), and the degree of glossiness on the surface is high (hereinafter referred to as glossiness), in addition to the above-mentioned ink absorptivity and transparency.
A silica type material such as a silica gel has pores in moderation. However, the surface of the particles of silica is usually negatively charged, and silica does not absorb an acid dye or a direct dye having anionic dissociative groups, to be used for ink jet, and silica has a low water resistance.
Accordingly, a method as disclosed in JP-A-60-257286, wherein polyaluminum chloride is contained in the ink-receiving layer, is mentioned. However, since the polyaluminum chloride is a water-soluble salt, the polyaluminum chloride in the ink-receiving layer itself dissolves in water, thus generating defects in appearance in a form of pits on the surface of the ink-receiving layer, and the water resistance is not necessarily adequate. Further, in a case of a long-term preservation, the polyaluminum chloride undergoes migration to clog the pores of the ink-receiving layer, thus decreasing the ink absorptivity.
Further, a method for producing a colloidal silica sol charged positively, by coating the surface of silica with alumina, is disclosed in JP-B-47-26959. The method comprises gradually adding a silica sol having particles sizes of from 2 to 150 nm to an aqueous solution of polyaluminum chloride, aging the mixture until the pH becomes constant, i.e. usually it becomes 4 or less, and then adding an alkali to increase the pH of the mixture to a level of from 4.5 to 7.0. By this method, a silica sol having its surface coated with alumina, having excellent transparency and stability, can be obtained. However, since secondary aggregate particles are not formed, a xerogel obtainable by drying the silica sol has a small pore volume and pore radius, whereby the ink-receiving layer formed by employing the silica sol may have an inadequate ink absorptivity, in some cases.
An ink-receiving layer formed by using an alumina hydrate such as pseudo-boehmite, is excellent from the viewpoints of ink absorptivity, transparency, water resistance and glossiness, but has a problem in view of scuffing resistance. This is estimated to be because the alumina hydrate is not spherical. To overcome the problem, a method as disclosed in JP-A-7-76162, wherein a silica gel layer having a thickness of from 0.1 to 30 &mgr;m is provided on a porous layer made of pseudo-boehmite, is mentioned. However, this method has such a drawback that the silica gel layer inhibits the ink absorptivity, and is disadvantageous in view of industrial production because of the two-layer structure.
DISCLOSURE OF THE INVENTION
The present invention provides a silica-alumina composite sol which is a colloidal solution having aggregate particles containing silica and alumina dispersed in an aqueous medium, wherein the silica is such that the primary particles are spherical and the average particle size of the primary particles is from 2 to 200 nm, the average particle size of the aggregate particles is at least twice the average particle size of the silica primary particles and at most 1,000 nm, the &zgr;-potential of the aggregate particles is at least +10 mV, and the pH of the solution is from 3 to 9.
The present invention provides, as a preferred method for producing the above-mentioned silica-alumina composite sol, the following first production method and second production method.
The first production method is a method for producing a silica-alumina composite sol, which comprises gradually adding an aluminum salt of which the liquid exhibits acidity when dissolved in water, to a silica sol containing such silica particles that the primary particles are spherical and the average particle size of the primary particles is from 2 to 200 nm.
The second production method is a method for producing a silica-alumina composite sol, which comprises mixing a silica sol with an alumina sol having a specific surface area of a xerogel obtainable by drying of at least 150 m
2
/g, to form aggregate particles containing silica and alumina, and adjusting the aggregate particles to have an average particle size of from 30 to 1,000 nm, by peptization treatment.
The present invention further provides a recording medium having a porous layer formed by coating and drying on a substrate a silica-alumina composite sol which is a colloidal solution having aggregate particles containing silica and alumina dispersed in an aqueous medium, wherein the silica is such that the primary particles are spherical and the average particle size of the primary particles is from 2 to 200 nm, the average particle size of the aggregate particles is at least twice the average particle size of the silica primary particles and at most 1,000 nm, the &zgr;-potential of the aggregate particles is at least +10 mV, and the pH of the solution is from 3 to 9.
BEST MODE FOR CARRYING OUT THE INVENTION
The silica-alumina composite sol of the present invention comprises aggregate particles containing silica and alumina, as colloidal particles, dispersed in an aqueous medium.
The silica in the aggregate particles are such that the primary particles are spherical and the average particle size of the primary particles is from 2 to 200 nm.
The silica-alumina composite sol of the present invention has silica primary particles being spherical, whereby a high scuffing resistance can be obtained when the coating layer is formed on the substrate.
If the average particle size of the silica primary particles is smaller than 2 nm, when the composite sol is dried, a xerogel having a large average pore radius and pore volume can not obtainab
Hirano Hachiro
Inokuma Hisao
Matsubara Toshiya
Nakahara Katsumasa
Suzuki Shin'ichi
Asahi Glass Company Ltd.
Grendzynski Michael
Hess Bruce H.
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