US 11,987,066 B2
Optical security elements, marked object, method of authenticating an object and use of optical security elements for authenticating or securing against counterfeiting
Andrea Callegari, Chavannes-près-Renens (CH); Pierre Degott, Mollie-Margot (CH); Todor Dinoev, Chavannes-près-Renens (CH); and Philipp Egger, Crissier (CH)
Assigned to SICPA HOLDING SA, Prilly (CH)
Appl. No. 17/282,959
Filed by SICPA HOLDING SA, Prilly (CH)
PCT Filed Oct. 4, 2019, PCT No. PCT/EP2019/076943
§ 371(c)(1), (2) Date Apr. 5, 2021,
PCT Pub. No. WO2020/070299, PCT Pub. Date Apr. 9, 2020.
Claims priority of application No. 18198945 (EP), filed on Oct. 5, 2018.
Prior Publication US 2021/0370703 A1, Dec. 2, 2021
Int. Cl. B42D 25/00 (2014.01); B42D 25/21 (2014.01); B42D 25/324 (2014.01); B42D 25/29 (2014.01); G07D 7/12 (2016.01)
CPC B42D 25/324 (2014.10) [B42D 25/21 (2014.10); B42D 25/29 (2014.10); G07D 7/12 (2013.01); G07D 2207/00 (2013.01)] 9 Claims
OG exemplary drawing
 
1. An optical security element made of a refractive transparent or partially transparent optical material and comprising an optical assembly of a caustic layer having a light-redirecting surface with a relief pattern of given depth and a focal length fc and an adjacent lens element of focal length fL configured to redirect incident light received from a point-like light source through it and form a projected image containing a caustic pattern directly on a retina of an observer looking at the point-like source through the optical security element; wherein
the optical security element comprises one of the following:
a) the caustic layer has a positive focal length (fC>0) and the lens element has a negative focal length (fL<0), or
b) the caustic layer has a negative focal length (fC<0) and the lens element has a positive focal length (fL>0); and
wherein a relationship between the focal length of the lens element and the focal length of the caustic layer satisfies following equation:

OG Complex Work Unit Math
where:
R is distance between the caustic layer and an eye of the observer;
ds is a distance between the point-like light source and the optical security element; and
dR is a comfortable reading distance from the eye, which is at least 25 cm.