Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2002-09-26
2004-09-21
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031080, C106S031610, C106S031620, C106S031630, C106S031640, C106S420000, C106S442000, C106S449000, C106S450000, C106S461000, C106S466000, C106S482000, C106S452000, C106S419000
Reexamination Certificate
active
06793720
ABSTRACT:
The present invention relates to a solid marking composition as writing means in a writing instrument, to a writing instrument comprising the solid marking composition, to an optically variable marking layer and to the use of a plurality of optically variable pigments according to the preamble of the independent claims. The solid marking composition of the present invention is particularly adapted for the application of hand-written markings to articles or documents which must be copy-protected or unambiguously marked as originals.
The fight against forgery of high value branded articles and against counterfeiting of currency or cheques has brought forward a large diversity of different security systems in the recent years. One of the most effective means especially for preventing unauthorized photocopying of documents is the application or incorporation of certain sections onto or in the document or article which exhibit a viewing angle dependent shift of color. This effect is producible by interference pigments. The pigments are either incorporated in the documents' bulk material or blended in a coating composition or printing ink which afterwards is applied on the document.
Optically variable pigments are principally based on an interference effect which takes place when light is reflected at a first and a second surface of a thin layer of a suitable dielectric material. The interference of the two reflected waves enhances the reflected intensity in certain domains of the visible spectrum and extinguishes it in others. As a consequence, said thin layer appears colored; the colors depend upon the difference in optical paths between the two reflected waves. As the optical path in said thin layer is viewing-angle dependent, the color appearance is viewing-angle dependent, too.
Pigments showing a viewing-angle dependent variation of color are usually of a flake like shape and can be of inorganic or organic or mixed nature. The pigment flakes can be produced in various well known ways, e.g.:
i) by physical vapour deposition techniques, thereby creating a sheet of superposed layers which are plane and parallel to each other. This is done on a suitable carrier which is detached or dissolved afterwards to leave the unsupported film. The film is reduced to pigment size;
ii) by wet or dry chemical deposition techniques, thereby depositing layers of materials having the desired physical parameters onto the surfaces of already existing particles (such as aluminum flakes, mica, etc.);
iii) by chemical polymerization processes where an extended sheet of helically arranged or similar liquid crystal material is hardened by UV irradiation and the resulting sheet is subsequently comminuted to pigment flakes. In this case the interference effect results from the periodic modulation of the refractive index in the arranged liquid crystal stack;
iv) by providing an all-polymer multi-layer sheet as described in U.S. Pat. No. 3,711,176, and comminuting it to pigment.
In the case of i) and ii) two basic design configurations are possible for the multi-layer interference stack. The first of the two designs can be characterized as an all-dielectric stack consisting of a periodic structure of alternating high and low index dielectric films. The other design type can be characterized as a metal-dielectric system and consists of a periodic structure of alternating partially transmitting, partially reflecting metal and dielectric layers on an almost totally reflecting opaque metal layer. This definition includes all designs based on the Fabry-Perot resonator principle. Whereas in all-dielectric designs the reflectance in a given high reflectance band increases with the number of periods, the highest reflectance of the metal-dielectric design is achieved already by a three layer stack: an opaque totally reflecting metal layer, a layer of a dielectric material arranged on top of the totally reflecting layer having an index of refraction preferably not exceeding 1.65 and, arranged on top the dielectric layer, a semi-transparent partially reflecting layer of a metal or metal oxide. For printing pigments, a symmetric structure having the sequence of dielectric and partially reflecting layer arranged on both of the surfaces of the opaque totally reflecting layer is preferred. Pigment flakes consisting of multi-layer structure of more than three (asymmetric design) respectively more than five superposed layers (symmetric design) have also been described in the state of the art and are applicable as well.
Coating compositions for producing a viewing-angle dependent variation of color by means of interference pigment flakes have been extensively described. However, they are all of a liquid and/or pasty consistency before application.
U.S. Pat. No. 5,059,245 and U.S. Pat. No. 5,171,363 disclose liquid printing inks comprising optically variable pigments of type i). U.S. Pat. No. 5,059,245 mentions as another alternative to incorporate the optically variable paint flakes in a plastic material which may then be cast, molded or extruded into a final article. In the context of the patent specification it is evident that said plastic material having incorporated optically variable pigment flakes is not meant as a means for coating other articles, but is itself considered the final article, which is colored by the incorporation of optically variable pigment flakes.
The same patent, U.S. Pat. No. 5,059,245, teaches that the aspect ratio of the optically variable pigment flakes is “important in that it helps to ensure that the flakes will land either on their top and bottom sides and not on their ends” and that “the ink should have good flow characteristics” in order to develop the required effect. From this, it is evident that the authors of U.S. Pat. No. 5,059,245 did not consider the possibility of creating an optically variable effect by the mere abrasion of a solid composition containing optically variable pigment. The aspect ratio is defined as the largeness-to-thickness ratio of the flakes.
Plastic sheets having incorporated optically variable pigment flakes of type i) have been described in U.S. Pat. No. 5,424,119. Those plastic sheets are produced by casting or extrusion of a bulk material in its thermoplastic state.
The fabrication and use of optically variable pigment of type ii) is described in EP 571 836, EP 668 329, EP 741 170 and EP 353 544. No application in solid-abrasion writing compositions is claimed.
Solid marking compositions comprising aluminum glitter pigments are known from U.S. Pat. No. 4,990,013. The aluminum pigments provide the layer produced therewith with a glitter effect. The glitter effect is the better pronounced, the more disordered the pigments are arranged in the layer. A disorderly arrangement provides a variety of planes and edges which reflect the incident light in a variety of different directions thereby producing the glitter effect. No optically variable appearance is produced.
The incorporation of pearlescent pigments, i.e. mica flakes coated with titanium dioxide, into solid-abrasion writing compositions, i.e. crayons, has been disclosed in JP 59174668 and JP 09078019. The aim of these patents was a marking material which develops a high reflective brightness and a lustrous color tone in particular on dark areas, remaining transparent on white areas. No substantial color shift is observed.
Pearlescent, or luster pigments, although they belong to the class of interference pigments, do not exhibit the strong angle-dependent color shifts which are observed with optically variable pigments. This is a direct consequence of their structure and of the impossibility to control their optical parameters: To obtain iridescent pigment, low-refractive-index (n=1.6) mica platelets having diameters of about 50 &mgr;m and thickness of about 1 &mgr;m are coated on both sides with a thin layer of high-refractive-index (n=2.0) titanium dioxide or similar materials. This results in a transparent, 3-layer interference stack, where part of the incident light is reflected at the t
Müller Edgar
Rozumek Olivier
Shoemaker and Mattare
SICPA Holding S.A.
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