Patent ID: 8673114
Filing Date: 2014-03-18
Classification: D21F,Y10T

Abstract:
1. Method for producing a watermark element for forming a shadow watermark image in a substrate by means of dewatering of a fibrous suspension, wherein the watermark element comprises a body with a relief side having a relief and a dewatering side positioned opposite the relief side, perforations being provided at least in the relief, a perforation comprising a channel extending a channel height (h) from a channel inlet on an exterior surface of the relief side to a channel outlet on an exterior surface of the dewatering side, the channel inlet and outlet having an open surface area defined as the cross sectional area of the channel inlet and outlet, respectively, at the surfaces of the relief and dewatering sides, the method comprising: forming perforations in the body in a mechanical manner by a mechanical machining process; and introducing the relief in the intended relief side; wherein the dewatering capacity of a perforation is expressed as the open surface area of the channel inlet of the perforation per unit of surface area of the relief; wherein the dewatering capacity of a portion of the relief is the total open surface area of the channel inlets in that portion of the relief per the total surface cross sectional area of that portion of the surface of the relief side, and is dependent on the channel height (h) of each perforation in that portion of the relief; wherein the higher the channel height of the perforation, the lower the dewatering capacity of that perforation; and wherein the perforations comprise channels having a uniform cross section along the channel height (h), the size of the area of the uniform cross section for each perforation dependent on the channel height (h) of each perforation.