Manufacture of silicate-coated papers

Claim 1

IN THE MANUFACTURE OF GREASEPROOF PAPER FROM LOW-COST PAPER STOCKS CONTAINING LIGNIN AND TANNIN COMPONENTS SUBJECT TO STAINING BY ALKALI, THE PROCESS WHICH COMPRISES APPLYING TO A WEB OF SUCH A PAPER STOCK WHILE IT IS IN THE PROCESS OF BEING MADE ON A PAPER MAKING MACHINE, FROM A BOX MOUNTED ON SAID PAPER MAKING MACHINE AND AT A POINT WHERE SAID WEB CONTAINS NO MORE THAN ABOUT 20% OF WATER BY WEIGHT, A SODIUM SILICATE SOLUTION, HAVING VISCOSITY WITHIN THE RANGE OF FROM ABOUT 1 TO 50 CENTIPOISES, SUFFICIENTLY LOW TO CAUSE THE SOLUTION TO PENETRATE THE WEB, TO INCREASE ITS STIFFNESS, TO DECREASE ITS POROSITY AND TO RENDER IT OIL AND GREASE RESISTANT; SAID SILICATE SOLUTION HAVING A GRAVITY BETWEEN ABOUT 10* AND 55* BE., CONTAINING A WEIGHT RATIO OF NA2O TO SIO2 WITHIN THE RANGE OF FROM ABOUT 1:1.6 TO 1:4 AND CONTAINING FROM ABOUT 0.25 TO 50% OF HYDROGEN PEROXIDE AND AS A STABILIZING AGENT A MIXTURE OF A WATER SOLUBLE PYROPHOSPHATE AND A WATER SOLUBLE MAGNESIUM SALT, WHEREBY THE BRIGHTNESS OF THE COATED SURFACE OF THE WEB IS AT LEAST AS HIGH AS THAT OF A WEB MADE FROM THE SAME PAPER STOCK WITHOUT APPLICATION OF SAID SILICATE SOLUTION; THE SILICATE SOLUTION BEING APPLIED SO THAT NO EXCESS IS LEFT ON THE SURFACE AND WITH A SPREAD RANGING FROM ABOUT 2 TO 30 POUNDS PER 1000 SQUARE FEET OF WEB SURFACE; AND DRYING THE SO-APPLIED COATING WITHOUT REMOVING THE COATING OR WASHING OUT THE RESIDUES OF THE BLEACHING REACTION.