	US 11,788,231 B2
	Paper substrates incorporating covert marking pigments, and processes for obtaining and using same
David Verd Reed, Blue Ash, OH (US); Matthew James Bovee, Morrow, OH (US); James D. Regel, Loveland, OH (US); Benny Joe Skaggs, Maineville, OH (US); and Maria A. Dannemiller, Memphis, TN (US)
Assigned to International Paper Company, Memphis, TN (US)
Filed by INTERNATIONAL PAPER COMPANY, Memphis, TN (US)
Filed on Jun. 24, 2019, as Appl. No. 16/450,320.
Prior Publication US 2020/0399834 A1, Dec. 24, 2020
Int. Cl. D21H 21/48 (2006.01); B42D 25/382 (2014.01); D21H 19/38 (2006.01); G01N 21/64 (2006.01); D21H 21/16 (2006.01); D21H 23/78 (2006.01)

CPC D21H 21/48 (2013.01) [B42D 25/382 (2014.10); D21H 19/38 (2013.01); D21H 19/385 (2013.01); D21H 21/16 (2013.01); D21H 23/78 (2013.01); G01N 21/64 (2013.01)]

18 Claims

1. A covertly marked paper substrate article comprising:

a paper substrate; and

a covert marking pigment having a particle size in the range of from about 0.1 to about 5 microns and being incorporated into the paper substrate in an infrared (IR) detectable amount of from about 0.1 to about 1,000 mg/m², wherein the covert marking pigment is incorporated into the paper substrate at a wet end of the paper making process such that the covert marking pigment is distributed within the paper substrate,

the covert marking pigment being one or more IR anti-Stokes shift pigments selected from one or more of: yttrium oxide; sodium yttrium fluoride; lanthanum oxide; lanthanum fluoride; lanthanum oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb); or mixtures thereof.