Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-27
2001-10-23
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S161000, C522S090000, C522S100000
Reexamination Certificate
active
06306929
ABSTRACT:
The present invention belongs to the field of the art of printing and describes a new and useful ink, a method of manufacturing an ink and the use of a composition as an ink which can be printed particularly by dry or wet offset by screen-, flexo- and gravure-printing as well as letterpress printing methods such as those used mainly on security documents. Such inks are also named “fugitive inks”.
A great number of security documents are presently known; examples of such documents are bank checks, money transfer orders, identity cards, other identity documents such as passports and driver's licences, postal stamps, lottery tickets, airline transportation tickets, shares, certificates, affidavits and others.
All security documents should be protected against forgery or counterfeiting. The main threats are:
Total counterfeit where a document is reproduced in its entirety; or
Forgery where a document is altered by deleting and/or replacing information, for example the amount of money on a check, a signature on a driver's licence, or information on a passport.
In each case, a well selected security printing ink can contribute considerably to the security of the document.
Solvent bleeding printing inks are already known and have been used for a rather long time in the field of security inks. The protection conferred to the security document is established by a fading or even disappearance of the color, by a change in colour or by a bleeding off when the document is contacted with an organic solvent or any other chemical substance used as a falsifying reagent.
The application methods and the principles of the function of the bleeding or fugitive printing inks in contact with solvents and other chemical agents, are the following:
The inks can be printed specifically by dry or wet offset by screen-, flexo- and gravure-printing or by letterpress. They are composed of a vehicle or binder whose components are mineral oils and alkyd resins, one or more dyestuffs that are soluble in organic solvents and are the substances sensitive to said chemical agents, and different additives. The dyestuffs are mostly chromium complexes, cobalt complexes or copper phthalocyanine blue. The drying mechanism is a purely physical one and acts principally by penetration into an absorbing solid fibrous substrate. In fact, if drying is defined as a conversion of the liquid printing ink into a solid and stationary film on the substrate, these printing inks do not dry but remain “liquid”; however, they are sufficiently permanently entrapped within the interstices of the fibres of the substrate for their mobility to be drastically reduced. The absorption of such printing inks is partial and progressive, and several days after the printing are necessary for the printed document to show an apparently dry condition, typically 5 to 7 days. Only after that time can the printed substrate be further processed, for example in order to apply personalised information, i.e. by laser printer or ion deposition printer. Furthermore, the absorption capacity of the substrate determines the quality and the drying time.
Thus, the working principle of bleeding printing inks known to date is based on the fact that the matrix of the ink remains soluble in organic solvents and other chemical agents.
Now, the objective of the present invention is to provide printing inks for the above-mentioned printing processes that can be effectively dried to form a solid matrix but which also form a print that remains sensitive to solvents and other chemical reagents. Another objective of this invention is to provide bleeding security documents that will be at least in part printed with such inks.
The bleeding printing inks, printed layers, printed substrates, methods of making an ink composition of this invention which meet the objectives mentioned above are defined in the independent claims. The new use of an ink composition is also the subject matter of this invention. Special embodiments of the ink and the security documents are defined in the dependent claims.
The invention is based on the highly unexpected finding that it is possible to obtain a printing ink which bleeds in contact with organic solvents and other chemical reagents, this even if the formulation of the ink is based on a solid matrix which is formed when the liquid ink is transformed into a solid film on the substrate and wherein this solid film itself is resistant to said solvents and chemical reagents after drying. The condition necessary to obtain the required sensitivity to bleeding is the use of dyestuffs and colouring agents which are sensitive to said solvents and chemical reagents. That is, the soluble dyestuff is attacked by the said solvents and/or reagents whereas the said matrix remains unaltered.
Manufacturing of the inks of the present invention rely on the dispersion of the dyestuffs in the binder matrix which results in an ink product wherein substantially homogeneously distributed dye molecules, dye molecule aggregates and substantially undissolved and also substantially homogeneously distributed dye particles may coexist. The extent to which the dye particles are dissolved depends mainly on the dye/binder system. Complete dye solution will strongly and positively impact on colour development and therefore on the tinctorial strength of the prints whereas undissolved dye particles will adversely affect these characteristics.
When brought into contact with a dried print performed with an ink of the invention, solvents and/or reagents will diffuse through the binder matrix and reach dye molecules and particles causing them respectively to be washed-off or dissolved, leading to the so-called “bleeding effect”. It is the surprising experience of the inventors that, provided the dyestuff is sensitive to the solvent or reagent, bleeding is necessarily observed.
The presence of porosities and defects in the dried ink film accounts probably much more for the penetration of the solvents or reagents than pure diffusion of molecules of the bleeding agent through the polymeric network formed upon curing of the binder matrix. A dried ink film whatever the printing technique used inevitably presents micro-defects and porosities of all kinds such as micro-voids, micro-cracks, bubbles and others wich are so many penetration paths for the bleeding agent.
Moreover, the roughness of the substrate may indirectly impact on the bleeding effect by disturbing the ink film structure and in situations where the ink film is very thin it will actually consist of discontinuous and unconnected areas more easily accessible to the solvents and the reagents than large and solid ink spots. This undoubtedly applies to an offset print on a standard cheque or bond paper where the 1 to 4 &mgr;m thick offset ink film is unable to compensate for the roughness of the substrate, the amplitude of which is at least 10 &mgr;m.
The binder matrix may also be made specifically porous. Porosity may be achieved by a variety of known techniques, such as using a solvent which evaporates and leaves micropores, by mixing incompatible compounds, by adding additives creating micropores and by other techniques.
The substantially homogeneous distribution of the dyestuff (molecules and/or aggregates and/or particles) in the binder matrix results in an ink layer containing substantially homogeneously distributed dyestuff. This results in dye molecules and/or aggregates and/or particles being distributed also on the surface or with very little coverage by the binder matrix which allows solvent to diffuse/reach the dye rather easily.
It is worthwhile to note that a poor colour development may favour a strong bleeding effect by reinforcing the contrast between untouched areas and those tested for bleeding.
Also of interest are all combinations between dyestuffs exhibiting a sensitivity toward different solvents or reagents. This will provide tamper evidence against attempts made by using various chemicals and therefore reinforce the protection of the document against falsification.
Combinations of such dyestuffs a
Amon Philippe
Bleikolm Anton
Papadimitriou Pandelis
Rozumek Olivier
Jagannathan Vasu
Shoemaker & Mattare
Shosho Callie E.
SICPA Holding S.A.
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