Formulation suitable for ink receptive coatings

#This invention relates to formulations comprising inorganic oxide particles. In particular, this invention relates to ink receptive coating formulations for paper comprising a novel porous, fine inorganic oxide which provides excellent ink absorption properties, and if desired, glossy finishes.

#Ink receptive coatings typically contain various proportions of inorganic pigments and binder(s). The proportions of these components affect the properties of these coatings, e.g., ink absorption properties. One means of characterizing the proportion of inorganic pigment relative to the proportion of binder is by the pigment volume concentration, or PVC. The definition of pigment volume concentration (PVC) is: 100*Vp/(Vp+Vb), where Vp is the volume of the pigment and Vb is the volume of the binder.

#When a coating is formulated at low PVC, the binder constitutes the continuous phase of the coating within which pigment particles are dispersed. When a coating is formulated at high PVC, the binder phase is no longer a continuous phase, that is, there is not enough binder to fill the voids between packed and semi-rigid or rigid pigment particles. The proportion at which the binder is no longer considered the continuous phase is referred to in the art as the critical pigment volume concentration (CPVC). At proportions above CPVC, a network of interparticle pores form between the close packed particles, and these interparticle pores become reservoirs for ink that is subsequently applied to the dried coating.

#FIG. 1 shows a graph of 1 η 0 η

#versus mass fraction solids for dispersions of particles used in several embodiments of the invention and prior art colloidal silica, wherein η is the viscosity of the dispersions illustrated and η0 is the viscosity of water. Mass fraction solids include undissolved particles and does not include dissolved salts.

#FIG. 2A shows a graph of 2 η 0 η

#(1) Preparation of Inorganic Oxide Particles

#The inorganic oxide particles used in this invention can be prepared from conventional inorganic oxide materials. Suitable inorganic oxides include precipitated inorganic oxides and inorganic oxide gels. These inorganic oxides are referred to herein as “parent inorganic oxides,” “parent particles” or “parent dispersions”. Amorphous precipitated silica and silica gels are particularly suitable parent inorganic oxides. The particles can also be prepared from mixed inorganic oxides including SiO2·Al2O3, MgO.SiO2·Al2O3. The mixed inorganic oxides can be prepared by conventional blending or cogelling procedures.

#Suitable inorganic oxide gels include, but are not limited to, gels comprising SiO2, Al2O3, AlPO4, MgO, TiO2, and ZrO2,. The gels can be hydrogels, aerogels, or xerogels. A hydrogel is also known as an aquagel which is formed in water and as a result its pores are filled with water. A xerogel is a hydrogel with the water removed. An aerogel is a type of xerogel from which the liquid has been removed in such a way as to minimize collapse or change in the gel's structure as the water is removed. Silica gels commercially available as Syloid® grade gels, e.g., grades 74, 221, 234, 244, W300, W500, and Genesis™ silica gels are suitable parent inorganic oxides.