Security element in the form of a thread or be embedded in...

Details Security element in the form of a thread or be embedded in... Security element in the form of a thread or be embedded in...

2000-01-20

2002-11-05

Wellington, A. L. (Department: 3722)

Printed matter

Having revealable concealed information, fraud preventer or...

C283S082000, C283S083000, C283S091000, C283S092000, C235S379000, C235S380000, C235S382000, C235S382500

Reexamination Certificate

active

06474695

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a security element in the form of a thread or strip to be embedded in security documents such as bank notes, checks, bonds or the like, having characters, patterns, etc . . . that are readable by transmitted light to the naked eye and/or by machine, and to methods of producing such security documents.
2. Description of the Related Technology
It has been known for some time to protect bank notes and other money-value papers such as cheeks, shares, travelers checks, check cards and credit cards, but also passports and identity cards, by adding socalled security threads. Papers of this kind shall be referred to in the following as security papers. The security threads used for this purpose are made of a great variety of materials in the form of fine strips which are added in widths of 0.4 to 2 mm to the paper sheet during its manufacture. They are primarily produced from plastic films coated with metal foils, printed, colored or provided e.g. with pigmentlike substances. Furthermore, it is also known to give these security threads magnetic, fluorescent, X-ray absorbent and other properties by applying appropriate substances.
It has proven particularly advantageous to use security threads with microprints, whereby this microprint may contain information that is readable by the naked eye or else only by machine.
With respect to protection from forgery, security threads with metallically reflecting surfaces have proven particularly useful, since such threads introduced inside the paper are almost invisible by incident light, as the light rays passing through the upper layer of paper are completely reflected by the, metallic surface and leave the paper diffusely scattered. By transmitted light, however, such threads appear as black strips which are clearly distinct from their surroundings. Threads of this kind cannot be imitated by printing on the paper. On the other hand, they show the disadvantage that a corresponding impression can be incorrectly aroused by introducing thin aluminum foils between two layers of paper. It has therefore been proposed to provide such aluminized security threads with microwriting (German laid open print no. 14 46 851). However, this has proven to be of little use in practice since this writing cannot be detected on the otherwise opaque security thread by transmitted light, and can only be detected with great difficulty by incident light. It is usually necessary to make the paper transparent with chemical means at least for the time of testing. The execution of such microwriting in special, e.g. fluorescent, colors has proven to be of little advantage in the same way and for the same reasons.
German “Auslegeschrift” no. 22 05 428 discloses a security thread designed as a metal strip and having a machine readable and/or visually readable coding applied by laser. The writing on this thread, that may possibly contain alphanumeric characters, consists of perforations, whereby the diameter of the holes or “line width” is to be small compared to the thickness of the metal strip in order to impede imitation.
Due to their extremely small line width, the characters of this security thread are detectable as poorly visible lighter areas on the dark background. Furthermore, such writing is relatively troublesome to produce, since very powerful lasers are required to provide the perforations in the metal thread. The perforation of the security thread material is so time-consuming that this method cannot be used for producing large amounts (thousands of kilometers) simply for reasons of time and thus of costs.
U.S. Pat. No. 4,652,015 also discloses a security thread to be used for bank notes and the like, on which metallically shining microcharacters are provided on clear transparent film material. The security thread and microcharacters located thereon as described in this patent are not detectable by incident light. However, by transmitted light solely the characters are detectable as sharp contours since the security thread itself is of transparent design. This security thread is produced by metalizing a transparent film over a large surface with a thin aluminum layer, printing the microcharacters on this layer using an acidproof ink and then etching away the unprinted areas, whereupon the characters are left on a transparent base.
By transmitted light an observer thus sees only writing that runs through the bank note. However, a disadvantage is that this writing is difficult to find due to the small size of the characters, its embedding in the paper pulp and a printed pattern that may be superimposed. The thread as such cannot be detected by the naked eye and cannot be felt as an uneven formation on the surface of the paper due to the extremely thin design required here. These detection features that normally characterize a security thread are thus no longer present in the known thread.
SUMMARY OF THE INVENTION
The invention is based on the problem of providing a security thread with characters and patterns that are readable to the naked eye and/or machine, whereby both the thread structure and the characters and patterns are clearly recognizable when the thread is embedded in a document, and whose visual impression and protection from forgery are improved.
This problem is solved by the features stated in the characterizing part of the main claim. Developments of the invention and methods for producing such security elements are the subject of subclaims and independent claims.
In a preferred embodiment, the security thread consists of a transparent plastic film provided on one side with a metal coating. Characters are introduced into this reflecting metal coating, that is opaque by transmitted light, by locally removing the coating material. In addition to this metal coating, the thread is provided with a coat of color which may extend over the entire thread surface. The coloring agents used have no opaque effect and are preferably glazing printing inks in various colors and tones. However, the plastic film may also be colored with appropriate coloring agents in such a way that its transparency is retained in a partial region of the visible spectrum.
When such a thread is regarded by transmitted light after it is embedded in paper or only white translucent plastic material, as is sometimes used for producing identity cards or credit cards, the thread is detectable quite readily as a dark strip in the document and the characters and patterns are distinct as light, colored areas compared to their direct surroundings, the opaque thread coating, and additionally compared to the wider surroundings, the white paper or plastic material. The thread is thus very easy to find in the document, and the characters are clearly recognizable due to their contrasting effect with the surroundings and can be read at any time without aids if their size is appropriate.
While the characters thus appear by transmitted light as colored characters compared to the dark or white background, the thread is invisible or only barely visible by incident light due to the greatly reflecting metal coating and the use of glazing or nonopaque coloring agents. It can therefore not be imitated by an external print, which is inevitably clearly visible both by incident light and by transmitted light.
Suitable opaque coating materials are not only metal layers but also nonmetallic layers that contrast with their surroundings in terms of color and/or gray tones when viewed by transmitted light, such as opaque, preferably white, layers of color, metallically shining layers such as titanium nitride, interference layers such as those disclosed e.g. in U.S. Pat. No. 3,858,977.
By using luminescent colors, one can further improve the visual impression of this thread and make it more effective. The luminescent colors can either be colorless in the unexcited state or have a body color that preferably differs from the color of the emission light. The characters or patterns then appear in color or change their color only in the

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