English to French Tech/Engineering Patents Security devices for security substrates

One way is to selectively demetallise régions using a resist and etch technique such as is described in US4652015.

Alternatively, if the second partially metallised polymeric substrate 15 is formed using a resist and etch technique to selectively
demetallise a metallised polymeric film, the resist forms the opaque coloured layer 34. In this embodiment, as illustrated in Figure 10, the second metallised polymeric film 15 is printed with a resist containing a coloured dye or pigment.

Suitable resists include the dye BASF Neozapon X51 or the pigment (well dispersed) "Carbon Black 7" mixed into a material with both good adhésion to métal and caustic résistance.

The dye loading can be up to 50% (by weight) of the final coat of resist depending on coat thickness and desired blackness.

An example of a class of suitable resist materials is vinyl chlorides/vinyl acétate copolymers such as Union Carbide Ucar resins, Sun VHL 31534, or Wacker Vinnol E 15/45m. The printed second metallised film 15 is then partially demetallised, according to a known demetallisation process using a caustic wash which removes the métal in the régions not printed with the resist.

The remaining métal areas 22 are still coated with resist, which provides a dark opaque layer 34 which is visible when the security device 10 of Figure 10 is viewed from its top surface 27 in reflection.

the opaque coloured material is a resist.