Stock material or miscellaneous articles – Structurally defined web or sheet – Nonplanar uniform thickness material
Reexamination Certificate
2001-02-20
2004-01-06
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Nonplanar uniform thickness material
C428S195100, C428S209000, C428S212000, C156S153000, C156S272800, C283S072000, C106S031130, C106S031650
Reexamination Certificate
active
06673420
ABSTRACT:
The invention relates to an inorganic sheet carrying at least one symbol for making pigments of a predetermined size for the marking of articles and to a method for forming such inorganic pigments and a pigment according to the preamble of the independent claims.
The incorporation of microscopically small aluminum platelets carrying information in the form of symbols in coating compositions has already been described in U.S. Pat. No. 5,744,223. The aluminum platelets are formed as embossed sections in a thin aluminum foil which thereafter is cut to platelet size. The embossed platelets serve as information carriers to hinder the unauthorised sale or theft of vehicles.
Since the aluminum platelets are silvery opaque, one disadvantage is their visible, eye-catching appearance in coating composition, particularly in printing inks having either no colour or different colours than the platelets. This makes the fact that an article has been tagged immediately obvious to any counterfeiter. On the other hand, in coating compositions which are of the same colour as the aluminum platelets the detection of embossed aluminum platelets is extremely difficult.
Applying symbols to foils by means of embossing is limited to those materials which are ductile (aluminum, plastic, etc.). It is therefore not possible to apply symbols to brittle and non-ductile materials by means of a direct embossing.
Another disadvantage of the embossing procedure is the risk to damage the passivating layer of the aluminum particle which protects the particles from detrimental influences such as water.
Object of the invention is to avoid the disadvantages of the prior art, particularly to provide pigments and improved means and ways to make pigments carrying improved safety features for a broad variety of applications.
It is a particular object of the present invention to provide symbol carrying pigments with matching colours with respect to the colour of the coating composition or printing ink.
It is another object to provide pigments carrying a symbol which can be easily detected within coating compositions having dark or strong colours.
It is still object to provide pigments having both overt and covert anti-counterfeiting properties.
It is a further object to provide a method for applying symbols on materials which do not have the ductility of aluminum or plastic.
It is a further object to protect any metal layer against corrosion the surface of which may have been damaged during a direct embossing process.
These objects are solved by the features of the independent claims.
In particular they are solved by providing an inorganic sheet for making pigments of a predetermined size, carrying at least one symbol, wherein the sheet comprises at least two superposed layers which are different in their physical and/or chemical composition.
Pigments made from inorganic sheets are usually of a flake like shape. In the context of this invention all types of lustre or effect pigment flakes which consist of at least two superposed layers and which are made from inorganic sheets are suitable. Particularly good results are achieved with pearl lustre pigments according to the definition of DIN 55943: 1993-M and interference pigments according to the definition of DIN 55944: 1990-04. Pigments having at least two layers of different colours are well suited, too.
This inorganic sheet of at least two superposed layers may be produced, for instance, by any of the known techniques for applying thin films, such as vacuum evaporation, physical vapour deposition, chemical vapour deposition, sputtering or wet processes, as described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, fifth edition, volume A6, page 67, Verlag Chemie, Weinheim, Germany.
A preferred embodiment of the present invention is an inorganic sheet having a viewing angle dependent variation of colour and carrying symbols for making pigments.
Pigment flakes having viewing angle dependent variation of colour are wellknown. They are of particular interest for the incorporation into printing inks for security documents. Since the angle-dependent colour variation is not reproducible by photocopying machines, these pigment flakes provide the document with a strong security feature. The pigment flakes, their production and various applications have been already described in numerous patents, e.g. U.S. Pat. No. 4,434,010, U.S. Pat. No. 5,059,245, U.S. Pat. No. 5,084,351, U.S. Pat. No. 5,135,812, U.S. Pat. No. 5,171,363, U.S. Pat. No. 5,279,657.
The working principle of these optically variable pigment flakes is based on a sequence of planar thin layers which are parallel to each other with different optical characteristics. The hue, the colour shift and chroma of the pigment flakes depend on the materials constituting the layers, the sequence of the layers, the number of layers and the layer thickness.
A simple inorganic sheet having a viewing angle dependent variation of colour to which symbols can be applied and which can be comminuted to pigment flakes of a predeterminable size, consists of two planar, partially reflecting, i.e. semi-transparent, metal layers which are substantially parallel to each other and which are separated by a layer of a low refractive index material e.g. SiO
2
or MgF
2
. The low refractive index material often is described as dielectric material. This type of pigment flake which is based on the Fabry-Perot principle was first patented by Du Pont in U.S. Pat. No. 3,438,796.
The terms semi-transparent, transparent, opaque, totally and partially reflecting all relate to the light in the visible range of the electromagnetic spectrum, i.e. from about 400 nm to about 700 nm.
A significant improvement with respect to the colour saturation (chroma) and the angle dependent colour variation was achieved by an incorporation of an opaque totally reflecting thin layer into the stack of dielectric and partially reflecting layers. This can result in a symmetric structure, having the opaque totally reflecting layer with first and second surfaces as a central layer. To achieve a symmetric multilayer stack on the first and second surface of the opaque totally reflecting layer a thin layer of a dielectric material is deposited; subsequently, semi-transparent, partially reflecting thin layers are applied on top of both of the dielectric layers. The minimum for a symmetric structure are thus five layers. However, an asymmetric stack can be produced as well, with a minimum of three layers consisting of one opaque totally reflecting layer, one dielectric layer and one partially reflecting partially transmitting layer.
The opaque totally reflecting layer is usually made of a metal and preferably consists of aluminum in a thickness of up to 300 nm, but preferably in the range of 50-150 nm. Gold, copper and silver are applicable as alternative metals.
The dielectric material must be transparent, with a refractive index not higher than 1.65. Usually SiO
2
or MgF
2
are deposited as a dielectric, in a thickness between 300 and 500 nm.
The partially reflecting semi-transparent layer or layers may consist of a metal, a metal-oxide or a metal-sulphide. This can be aluminum, nickel, Inocel, chromium, MoS
2
, Fe
2
O
3
, etc. Semi-transparency of metal layers is a function of the layer thickness. Usually the thickness of the semi-transparent layer is between 5 and 20 nm.
The inorganic sheet having viewing angle dependent variation of colour is preferably produced on a supporting material, such as a flexible web of e.g. PET. In the majority of the cases a first semi-transparent layer is deposited on the flexible web. After having deposited all subsequent layers, the multi-layered coating is detached from the flexible web whereby it typically breaks into small pieces of irregular shape and size. These pieces require further grinding to achieve the desired pigment flake size, suitable for coating compositions and particularly printing inks or for incorporation into bulk material.
As already described, pigments which have a viewing angle dependent shift of colo
Bleikolm Anton
Müller Edgar
Rozumek Olivier
Loney Donald J.
Shoemaker and Mattare
SICPA Holding S.A.
LandOfFree
Inorganic sheet carrying symbols for making pigments does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inorganic sheet carrying symbols for making pigments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inorganic sheet carrying symbols for making pigments will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3208078