Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-11-14
2003-05-13
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S323000, C428S329000, C428S331000, C428S422000
Reexamination Certificate
active
06562441
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording medium having an ink-receiving layer mainly comprising a pigment. In particular, the present invention relates to a high-performance ink jet recording medium excellent in gloss, transparency and water resistance and capable of providing a high image quality and ink drying property.
Various output systems of computers, such as wire-dot printing system, thermal recording system, ink melting heat transfer printing system, sublimation heat transfer printing system, electrophotographic system and ink jet printing system, were developed. Among them, the ink jet printing system is recognized to be suitable for personal use because plain paper is usable as the printing sheet, the running cost is low and the hardware is compact and inexpensive. Further, since full color system and high resolution were attained recently, the ink jet printing system attracts attention as an easy means of the output of color images, and printers of this system are rapidly increasing in number on the market.
The basic properties required of the ink jet recording medium used for the output of the ink jet printers are as follows: It rapidly absorbs an ink comprising water, a dye, an organic solvent, additives, etc. to reproduce fine letters or image; the color density of the image is high; and the tone is uniform. To satisfy these requirements, many high-performance ink jet printing media comprise a special ink-receiving layer on a base material. Such ink-receiving layers are roughly divided into two groups, i.e., a resin receiving layer and a pigment receiving layer. The ink-receiving resin layer is usually prepared by applying an aqueous solution of a water-soluble resin such as polyvinyl alcohol, polyvinylpyrrolidone, a water-soluble cellulose derivative or gelatin to a base material sheet and drying it. The preparation cost is relatively low, and the preparation is relatively easy. The resin ink-receiving layer is often used also for ink jet recording medium for over-head projectors (hereinafter referred to as “OHP”) which medium necessitates a high transmittance, taking advantage of a high transparency thereof. Another advantage of the resin ink-receiving layer is that the ink absorption per a unit weight thereof is higher than that of the pigment ink-receiving layer.
However, various properties are required of the ink jet recording media such as ink-drying properties, water resistance of the printed matter, resistance of the image to the deterioration even after leaving it indoors or outdoors for a long period of time and freeness from blocking even after the storage of them piled up, in addition of the above-described high image quality. The resin ink-receiving layer was inferior to the pigment ink-receiving layer particularly in the ink-drying property and water resistance. Therefore, it has been said that the improvement in these properties of the former is necessary. An ordinary method tried for improving the quality was to cross-link a water-soluble resin in the ink-receiving layer with a crosslinking agent or to mix a hydrophobic resin therein to impart the water resistance to the layer. However, when a sufficient water resistance was tried to be imparted to the layer by using any possible crosslinking agent or hydrophobic resin, the ink-absorption of the ink-receiving layer was seriously reduced. Thus, both image quality and water resistance could not be improved at the same time.
Under these circumstances, the inventors proposed a resin ink-receiving layer prepared by applying an aqueous composition containing, as the main ingredient, a water-soluble resin free of radical-polymerizable unsaturated bond and capable of forming a hydro-gel by electron beam irradiation to a base material sheet and irradiating electron beam to form a hydrogel and then drying the sheet [Japanese Patent Unexamined Published Application (hereinafter referred to as “J. P. KOKAI”) No. Hei 11-157202 corresponding to EP919395A]. Water resistance could be thus imparted to the above-described resin ink-receiving layer without seriously deteriorating the image quality unlike the non-crosslinked ink-receiving layer which was not irradiated with electron beam. However, the ink-absorption velocity of the ink-receiving resin layer is limited because it is not porous and as for the ink-absorption mechanism, it absorbs the ink by swelling. Thus, a further improvement is necessitated for obtaining both satisfactory image quality and ink-drying time with the latest ink jet printer which jets a large quantity of inks. Although the water resistance of the ink-receiving resin layer is on a very high level as compared with other similar products, it is yet lower than that of the high-performance pigment ink-receiving layer.
J. P. KOKAI Nos. Hei 8-207423 and Hei 8-267905 disclose ink jet printing sheets having a surface layer cured by the irradiation with electron beam and containing a water-soluble polyalkylene oxide and colloidal silica. However, in this ink-receiving layer, a pigment is only dispersed in the resin but it is not porous. Therefore, the ink is absorbed only by the swelling of the layer like ink-receiving layers comprising only a resin.
On the other hand, a pigment ink-receiving layer prepared by fixing a pigment with a binder resin is capable of rapidly receiving an ink by the capillarity in the pores formed within and outside the pigment particles. Thus, the image quality and ink-drying property of this layer more excellent than those of the resin ink-receiving layer, which absorbs the ink by the dissolution and swelling, can be easily obtained. Further, a very high water resistance of the pigment ink-receiving layer can be obtained when the binder resin is resistant to water. However, for obtaining an image of a high quality, it is necessary to secure a pore volume sufficient for the jetted ink in the layer. Thus, a very large amount of the coating must be applied in order to correspond to the high-performance ink jet printer which jets a large amount of inks.
A pigment ink-receiving layer is prepared at present by dispersing a synthetic, amorphous silica in the form of a powder having an average particle diameter of 1 to 20 &mgr;m in water, mixing a water-resistant binder resin and additives in the resultant dispersion, and applying the resultant mixture to a base material. Although such a pigment ink-receiving layer has a high water resistance and ink absorption, the transparency of the ink-receiving layer is low because the average particle diameter of the pigment is large. Such a low transparency of the ink-receiving layer is unsuitable for the preparation of a transmittant recording medium with a transparent base material and, in addition, the printing density of the image is low even when an opaque base material is used. In addition, because the synthetic amorphous silica used therein has a large and ununiform particle diameter, the gloss of the ink-receiving layer is low and such a layer is unsuitable for the preparation of a gloss ink jet recording medium.
Taking the above-described points into consideration, it is necessary, for obtaining a high gloss and ink absorption of the ink-receiving layer, that a fine pigment having a large pore volume and a small and uniform average particle diameter is used for the preparation of a high-quality ink jet recording medium. Pigments in the form of fine particles such as silica, aluminum hydroxide, boehmite, pseudo-boehmite and alumina are suitably used. However, because such a fine pigment has a large pore volume and small pore diameter, the shrinkage by the capillary power, which is caused in the course of the drying after the application, is serious, and the resultant coating layer is very easily cracked. After the investigations, the inventors found that the cracking of the ink-receiving layer and the lowering of the gloss and transparency caused by the cracking can be prevented by mixing a completely saponified polyvinyl alcohol having a high degree of polymerization and a hig
Maeda Masayo
Tajiri Kozo
Grendzynski Michael
Hess Bruce H.
Oji Paper Co. Ltd.
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