Patent ID: 7754314

Claim:
A security paper comprising: at least two plies of cellulose-type paper each formed of a respective fibrous mat, and at least in one area, at least one interlayer located at the junction of the two plies of cellulose-type paper, wherein the security paper includes an authentication element within a thickness of the security paper, and wherein the interlayer includes at least one element giving the security paper a high double-fold resistance, as defined by the standard NF ISO 5626, said element being at least one of (i) a soluble element or an emulsifiable element, and (ii) an element in the form of particles, and wherein the two plies and said element are intimately joined together in the interlayer, wherein (i) constituents of each of the two plies are interpenetrating with each other in the interlayer, and (ii) constituents of each of the two plies and constituents of the interlayer including said element are interpenetrating with one another in the interlayer, so that the fibrous mats of the two plies of cellulose-type paper form a unitary fibrous mat throughout the area of the interlayer.