In recent years, as digital cameras and other devices having color output have advanced, the technology has attempted to keep pace in order to record images on paper sheets or the like. The ultimate goal of such recorded images (“hard copy”) is silver halide photography, and it is desired to provide recorded images from such devices that have the color reproduction, image density, gloss, etc. as close to those of silver halide photography as possible.
The technology of inkjet color printing has attempted to keep pace with the development of digital cameras and other color output devices, but improvements are continually sought in order to be competitive with silver halide images.
Recording sheets for the inkjet printing process available today do not have all the properties required. In particular, there is a need to improve ink absorptiveness, ink absorption rate, image quality, water fastness and light stability. Specifically, ink-receiving materials are sought where the images recorded thereon are resistant to rubbing on the surface and remain intact when in contact with water and should not fade when exposed to light.
It is known that recording sheets for inkjet printing must meet a number of stringent demands. The printed image has to fulfill the following properties: high resolution; high color density; good color reproduction; high resistance to rubbing; good water fastness; and high light stability.
The following conditions have to be met to fulfill these goals:                1. The ink needs to be absorbed quickly into the recording material;        2. The jetted ink droplets have to spread circularly on the recording material and have to form well-defined edges;        3. Dye diffusion in the recording material has to be low so that the diameter of the color points is not increased more than necessary;        4. An ink droplet is not allowed to interfere with a droplet deposited earlier nor should it blur it;        5. The recording material needs to have a surface that gives high color density and brilliance; and        6. The recording material has to show excellent physical properties before and after printing.        
These requirements are partially contradictory; for example, a fast ink absorption rate often results in poor resistance to rubbing of the surface.
Starting from these requirements for a recording material, the best recording material comprises an ink-receiving coating on a support. Examples of such recording materials are disclosed, for example, in patents EP 0 298 424 and EP 0 407 720, and patent applications EP 0 622 244 and JP 60-245,588. These references disclose ink-receiving layers that include as pigment aluminum oxide/hydroxide with a pseudo-boehmite structure. Pseudo-boehmite is an agglomerate of aluminum oxide/hydroxide Al2O3.n H2O where n is from 1 to 1.5. Preferably, this aluminum oxide/hydroxide with a pseudo-boehmite structure is used in the form of its colloidal solution, which provides recording materials with superior image quality. It is well known that such colloidal solutions are only stable at low concentrations of the active ingredient. The storage stability of such colloidal solutions is low and storage conditions have to be tightly controlled.
However, ink receiving layers prepared with aluminum oxide/hydroxide isolated in its solid form from its colloidal solution give images after inkjet printing with a reduced image quality compared with ink receiving layers prepared with the same aluminum oxide/hydroxide in the form of its colloidal solution.
EP 1 000 767 and U.S. Pat. No. 6,156,419 disclose a plurality of layers on a support, wherein one coated layer comprises a porous aluminum oxide/hydroxide containing at least one element of the rare earth metal series of the Periodic Table of the elements with atomic numbers 57 to 71. However, there is no topcoat on the pseudo-boehmite. The rare-earth modified alumina layer is said to have improved lightfastness and image homogeneity, compared to an alumina layer without the rare earth. However, gloss, color gamut, and scratch resistance are poor without a topcoat.
U.S. Pat. No. 5,463,178 describes a silica topcoat on alumina; however, a binder is used which decreases ink adsorption and the silica is anionic, which decreases ink holdout.
An inkjet recording sheet is required that avoids most, if not all, of the foregoing problems, while addressing the needs of photographic-quality prints.