Paper substrate having enhanced print density

Abstract

The present invention relates to a sizing composition that, when applied to paper substrate, creates a substrate, preferably suitable for inkjet printing, having increased print density, print sharpness, low HST, and/or image dry time, the substrate preferably having high brightness and reduced color-to-color bleed as well. In addition, the present invention relates to a method of reducing the HST of a paper substrate by applying the sizing composition to at least one surface thereof. Further the application relates to methods of making and using the sizing composition, as well as methods of making and using the paper containing the sizing composition.

What is claimed is: 
     
         1 . A sizing composition, comprising at least one pigment; at least one binder; at least one cationic optical brightening agent; and at least one inorganic salt. 
     
     
         2 . The sizing composition of  claim 1 , wherein the at least one binder is starch. 
     
     
         3 . The sizing composition according to  claim 1 , wherein the total binder is present at an amount of at least 20 wt %, based upon the total weight of the solids in the composition. 
     
     
         4 . The sizing composition according to  claim 3 , wherein the total cationic optical brightening agent is present at an amount ranging from 10 to 75 wt % based on the total weight of the solids in the composition. 
     
     
         5 . The sizing composition according to  claim 1 , comprising at least one pigment at an amount of at least 30 wt % based upon the total weight of the solids in the composition; at least one binder at an amount of at least 20 wt % based upon the total weight of the solids in the composition; and at least one inorganic salt at an amount of at least 0.25 wt % based upon the total weight of the solids in the composition. 
     
     
         6 . The sizing composition according to  claim 1 , comprising at least two binders. 
     
     
         7 . The sizing composition according to  claim 6 , wherein the at least two binders are polyvinyl alcohol and starch. 
     
     
         8 . The sizing composition according to  claim 7 , wherein the polyvinyl alcohol and starch are present at a starch/polyvinyl alcohol weight ratio of from 10/1 to 1/5. 
     
     
         9 . The sizing composition according to  claim 8 , wherein the total binder is present at an amount ranging at least 20 wt %, based upon the total weight of the solids in the composition. 
     
     
         10 . The sizing composition according to  claim 8 , wherein the total cationic optical brightening agent is present at an amount ranging from 10 to 75 wt % based on the total weight of the solids in the composition. 
     
     
         11 . The sizing composition according to  claim 6 , comprising at least one pigment at an amount of at least 30 wt % based upon the total weight of the solids in the composition; at least one binder at an amount of at least 20 wt % based upon the total weight of the solids in the composition; and at least one inorganic salt at an amount ranging from 0.25 to 25 wt % based upon the total weight of the solids in the composition. 
     
     
         12 . The sizing composition according to  claim 11 , comprising at least two binders wherein the at least two binders are starch and polyvinyl alcohol at a weight ratio of from  10 / 1  to  1 / 5  starch/polyvinyl alcohol. 
     
     
         13 . A paper substrate, comprising the sizing composition according to  claim 1 . 
     
     
         14 . The paper substrate according to  claim 13 , wherein the substrate has a print density of at least 1.0. 
     
     
         15 . The paper substrate according to  claim 13 , wherein the substrate has a waterfastness of at least 95%. 
     
     
         16 . The paper substrate according to  claim 13 , wherein the substrate has an HST of not more than 10 seconds. 
     
     
         17 . The paper substrate according to  claim 13 , which comprises a web of cellulosic fibers, wherein the sizing composition is coated on the web. 
     
     
         18 . The paper substrate according to  claim 13 , which comprises a web of cellulosic fibers, wherein the sizing composition interpenetrates the web. 
     
     
         19 . A method of making a paper substrate for ink jet printing, comprising contacting a web of cellulosic fibers with the sizing composition of  claim 1 . 
     
     
         20 . A method of making the sizing composition according to  claim 1 , comprising simultaneously or consecutively contacting at least one pigment at least one binder, at least one cationic optical brightening agent, and at least one inorganic salt. 
     
     
         21 . A method of increasing the print density of a paper substrate, comprising contacting a web of cellulosic fibers with the composition according to  claim 1  to form the substrate.