Sodium silicate treatment for printing papers

Abstract

Integrating sodium silicate during the paper-making process, or after paper manufacture at any time prior to final image formation. Intimately associating or bonding the fiber and the silicate provides significant benefits, for example, adding additional stiffness to papers that otherwise would not be stiff enough for use in high-speed digital laser printers, and improving the quality of colored image reproduction on high speed digital laser printers. Two specific examples are transfers of financial printing on electronic digital printers to lighter weight papers, and colored image formation in advertising material where the reproductive quality of the image must be of high quality.

What is claimed is:  
     
         1 . Printing paper comprising sodium silicate applied at or near at least one paper surface, said sodium silicate optionally saturating the paper.  
     
     
         2 . The printing paper of  claim 1  in which the paper is characterized by a gurly stiffness, TAPPI specification T-543 bending resistance of paper, at least 5% greater than the gurly stiffness of a reference paper that lacks sodium silicate and is otherwise similar in composition and physical properties to the paper containing sodium silicate.  
     
     
         3 . The printing paper of  claim 1  in which the sodium silicate is present in a higher concentration at or near one of the paper surfaces.  
     
     
         4 . The printing paper of  claim 1  in which the sodium silicate is present in a higher concentration at or near both surfaces of the paper.  
     
     
         5 . The printing paper of  claim 1  in which the printing paper comprises a film-forming compound that assists in concentrating the sodium silicate at or near one or both surfaces of the paper.  
     
     
         6 . The printing paper of  claim 1  and  4  in which the paper comprises sodium silicate in an amount>0.03 lbs/1000 square feet of paper.  
     
     
         7 . The printing paper of  claim 3  in which the paper comprises sodium silicate in an amount>0.015 lbs/1000 square feet of paper.  
     
     
         8 . The printing paper of  claim 1  in which the paper has a basis weight less than 50 lbs. for 500 25″×38″ sheets.  
     
     
         9 . The printing paper of  claim 1  in which the paper has a basis weight greater than 50 lbs. for 500 25″×38″ sheets.  
     
     
         10 . The printing paper of  claim 1  in which the paper has a gurly stiffness of ≧80 grams.  
     
     
         11 . The paper of  claim 1  in which the paper has a grade stiffness less than 80 grams  
     
     
         12 . The printing paper of  claim 1  in which the sodium silicate is intimately entwined with or bound to cellulose fibers in the paper.  
     
     
         13 . The printing paper of  claim 1  in which the paper contains cotton fibers.  
     
     
         14 . The printing paper of  claim 1  in which the paper meets both the U.S. Postal Service requirements for business reply postal cards and the requirements of digital laser color printers.  
     
     
         15 . The printed paper of  claim 1  in which the paper meets specifications for direct mail advertising or magazine covers.  
     
     
         16 . A method of forming an image on the paper comprising, 
 providing a paper according to any of claims  1 - 15 ; and    producing an image on the paper.    
     
     
         17 . The method of  claim 16  in which the image is produced by a laser or laser-like printing process.  
     
     
         18 . A method of producing a bleached printing paper comprising 
 producing a bleached printing paper in a process that converts a fiber slurry into a bleached printing paper;    adding sodium silicate at any point during the paper-production process or at any point after the paper production process and prior to final image production on the paper.    
     
     
         19 . The method of  claim 18  in which sodium silicate is added in an aqueous mixture.  
     
     
         20 . The method of  claim 19  in which the aqueous mixture further comprises a film-forming compound.  
     
     
         21 . The method of  claim 19  or  claim 20  in which the aqueous mixture has a pH high enough to maintain sodium silicate in solution, and low enough to substantially avoid detrimental yellowing of the bleached paper.  
     
     
         22 . The method of  claim 19  and 20 in which the aqueous mixture has a pH>7.0 and <11.0.  
     
     
         23 . The method of  claim 18  in which the sodium silicate is added by wet end addition, by size press, by spraying or by coating on or off of a paper-making machine.  
     
     
         24 . Printing paper comprising sodium silicate applied at least at or near one paper surface or saturated with sodium silicate said paper being a bleached printing paper or unbleached sulfite printing paper, with or without groundwood fiber.  
     
     
         25 . A method of laser printing on a bleached paper comprising, 
 providing a paper comprising sodium silicate; and    using a laser to produce an image on the paper, whereby the image exhibits a superior image quality.    
     
     
         26 . A method of laser printing an image according to  claim 25 , in which the only image on the paper is black.  
     
     
         27 . A method of laser printing an image according to  claim 25 , in which the only image on the paper is single-colored or multicolored.  
     
     
         28 . A method of laser printing an image according to claims  25 - 27  in which solid printed areas exhibit a greater degree of gloss than do identical solid areas on a reference paper which has been printed in the same way, said reference paper lacking sodium silicate and being otherwise similar in composition and physical properties to the paper containing sodium silicate.  
     
     
         29 . A method of laser printing an image according to claims  25 - 27  in which the appearance of gloss in the solid and half-tone areas of the image derives from the ink/toner in combination with the sodium silicate and not from the surface reflective characteristics of the unprinted paper.  
     
     
         30 . A method of laser printing an image according to claims  25 - 27  in which there is greater fidelity of reproduction than does an identical image produced in the same manner of a reference paper lacking sodium silicate and being otherwise similar in composition and physical properties to the paper containing sodium silicate.  
     
     
         31 . A method of laser printing an image according to claims  25 - 27  which more closely approaches photographic quality than does an identical image produced in the same manner of a reference paper lacking sodium silicate and being otherwise identical in composition and physical properties to the paper containing sodium silicate.  
     
     
         32 . The invention when produced as described herein has clear application as a coating base for coatings developed for digital laser printers, as the sodium silicate will further enhance the coating's surface characteristics to react with the ink toners thereby enhancing the image quality as well as improving stiffness.