GB2180564A - Method of providing security features in paper - Google Patents

Abstract

Security features for authentification of currency paper are incorporated within a paper web during the paper making process. Various codes (11, 12 and 13) may be incorporated within the paper for viewing by means of transmitted light. In one embodiment identifying indicia (23) is microprinted on thin strips (10) of a carrier material which dissolves or is dissolved during the dewatering and drying stage of a paper making process carried out on a Fourdrinier or a cylinder-type paper making machine acting on a fibrous slurry (24). The microprinted indicia (23) remains intact and is readable by means of transmitted light yet is neither legible nor reproducible with reflected light. <IMAGE>

Description

SPECIFICATION Method of providing security features in paper This invention concerns methods of providing security features in paper.

Methods are currently available for providing non-removable and optically readable security devices in paper during the paper making process. U.S. Patent Specification No. 4,437,935 discloses a method for incorporating one such security device by using a carrier paper which becomes dispersed upon contact with the wet paper stock during the paper making process.

Another method suggests introducing a security device within the paper stock during the paper making process by employing a carrier paper to which the device is adhered. The carrier paper intermeshes with the base paper fibres forming a composite paper facilitating permanent attachment of the device.

In both the aforementioned methods the carrier paper used to transport the security device remains an integral part of the finished paper and can be discerned from the base paper only by close examination. When it is desired to provide a micro-code integrally formed within the substance of the paper for optical reading by means of transmitted light, the carrier paper is an inappropriate substrate for fine line codes or microprint.

U.S. Patent Specification No. 3,880,706 describes a method for imparting security fibres manufactured from a thermoplastic material which is fused within the paper fibres during the paper making process. One such material is a thermoplastic material which becomes fused at the final stages of the paper making process by subjecting the paper to a predetermined temperature. Once the thermoplastic material has become fused within the paper, its presence may be detected by transmitted light.

When micro-coded information is to be deployed within paper, it is first microprinted on a thin strip of transparent material such as a polyester plastic film. The polyester film is then introduced from a continuous spool to the paper stock on a Fourdrinier or a cylinder mould machine during the sheet forming process. Once the paper fibres are pressed and dried to form the finished paper, the polyester film remains intact and the microprinted material can be viewed by transmitted light. Such a film is removable from the paper by tearing the paper to expose the film and then lifting the film from the paper as a continuous strip.

The authenticity of a banknote or security document can be brought into question if part or all of the encoded thin film strip has been removed. If the micro-code contains machinereadable information for both verifying the authenticity of currency, for example, as well as identifying the denomination of the currency, this could present a serious problem.

The identifying micro-code for a higher denomination currency could be reinserted.

This invention seeks to provide a method for incorporating micro-coded information within security paper without leaving any indication of a carrier paper or of a carrier film.

According to the present invention then, a method of providing security features within paper comprises the steps of imparting indicia to the surface of a substrate material which can be selectively dissolved during a paper making process, inserting the indiciabearing substrate within a water slurry containing paper fibres, and dissolving the substrate at least in part to leave the indicia within the paper fibres during dewatering and drying of the paper fibres to form the paper embodying the indicia as security features.

A further such method comprises the steps of providing indicia material on the surface of a substrate material, both the indicia material and the substrate material being insoluble during dewatering and heating of paper fibres, incorporating the indicia-bearing substrate material in a slurry of paper fibres, dewatering and heating the paper fibres to form a finished paper, and submitting the finished paper to a solvent material for dissolving the substrate material without dissolving the indicia material.

The invention discloses the incorporation of micro-coded information on a substrate which is later dissolved during the stages of the paper making process to leave the micro-coded information within the paper web. The microcoded information may be machine-read by transmitted light or detected by the emittance of unique radiation when exposed either in reflectance or transmittance to a specific source of excitation energy. This information cannot be removed from the paper without destroying both the paper and the microcoded information. In one embodiment, the micro-coded information is provided by microprinting on a thin strip of polyvinyl alcohol film. The polyvinyl alcohol polymer may be modified by acetylation or heat treatment to produce a film strip with specifically controlled solubility properties.

The invention will now be further described by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a top perspective view of the substrate of the invention microprinted with various security codes, Fig.2 is a schematic side view in partial section of a Fourdrinier paper making machine with a funnel tube for introducing the soluble substrate strip into the paper fibres being deposited on the wire; Fig.3 is a schematic side view in partial section of a cylinder-type paper making machine with a tube for inserting the soluble substrate film within the paper fibres; Fig.4 is an enlarged cross-section of the PVA substrate with printed indicia applied to the surface; Fig.5 is a similar sectional view of the PVA strip after it is formed within the wet paper web prior to dissolution;; Fig.6 is another sectional view of the PVA strip while the film is dissolving and the paper web is becoming more dense; Fig.7 is a sectional view of the finished paper with only indicia embedded therein; Fig.8 is a plan view of a currency note containing the micro-code inserted therein by the soluble substrate strip according to the invention; and Fig.9 is an end view of a PVA strip with the micro-code impressed directly on the strip.

Fig. 1 illustrates a soluble carrier substrate which consists of a film or strip 10 of a polyvinyl alcohol (PVA) such as is manufactured by Meno-sol Co. of Gary, Indiana, U-S-A. The micro-code consists of microprint indicia 11, bar graph code indicia 12 as well as phosphorescent indicia 13 which is applied to the film or strip by means of a microprinting or coating process. The PVA strip 10 may have a thickness of 1.5 thousandths of an inch and a width of approximately 1/32 of an inch. The PVA is treated by heating the polymer in air in order to render the polymer insoluble in water up to a temperature of 1600F. This allows the PVA strip 10 to be inserted within the slice 15 of a Fourdrinier paper making machine 16 by introducing it within the fibre slurry 17 through a tube 14.The slurry 17 contains a mixture of cellulosic fibres 24 which are dewatered along the Fourdrinier wire 18 to form the finished paper in known manner. The slurry temperature is maintained less than 160"F allowing the soluble PVA strip 10 to become incorporated within the nascent web which is later formed during dewatering of the fibrous slurry and then the web is pressed and dried to completely remove all the water. During the drying process the web temperature exceeds 160 F, the PVA strip dissolves and leaves the micro-code indicia intact within the web.PVA is selected as the soluble carrier substrate for the obvious reason that the PVA polymer is soluble in water and the stage at which the PVA dissolves can be controlled by the temperature usually between 100"F and 200"F. When other water soluble materials such as gelatin, for example, are employed, the water temperature is adjusted in accordance with the preferred solu bility of gelatin in water. When non-water sol uble carrier substrates are used, a post pro cessing exposure to the solvent can be made by immersing the paper in a solvent bath.

Should aqueous insoluble resins be employed, the wet paper fibre containing these resin sub strates can be exposed to alcohols, ketones, esters as well as specific hydrocarbons de pending upon the composition of the particular resin.

Fig.3 shows a cylinder machine 20 wherein the PVA strip 10 is introduced through a tube 14 inserted within the slurry 17 consisting of a plurality of mixed cellulosic fibres 24 in water. A paper cylinder mould 21 in combination with a couch roll 22 is employed for forming the fibres into the finished paper.

The method in which the microprinted indicia is retained intact within the paper web is not clearly understood at this time, one explanation being that the microprinted ink material 23, best seen in Fig.4, being non-water soluble retains its integrity after the water soluble PVA strip 10 dissolves and migrates under capillary forces within the pores and interstices of the paper web. Other materials that have been applied to the surface of PVA strip 10 include fluorescent pigments and dyes, and metallized and metal oxide coated films. All these materials remain intact and in position upon the dissolving of the PVA strip.

An enlarged cross-section of a portion of the strip 10 shown in Fig. 1 is depicted in Fig.4 to show the relative thickness of the ink 23 to the strip 10.

The enlarged strip 10 is shown in Fig.5 submerged within the slurry 17 with the individual paper fibres 24 on both sides of the strip and before the strip becomes dissolved by the water contained within the slurry.

The partial dissolution of the strip 10 is shown in Fig.6 with the strip material being displaced by the paper fibres during the dissolution process.

In Fig.7 the strip material has completely dissolved and the individual fibres 24 have set the ink 23 within a predetermined position within the slurry as determined by the original placement of the strip carrying it.

Fig.8 shows a currency note 25 manufactured containing the dissolving strip according to the invention and detailing the placement of the indicia 11 at a particular position as viewed by high-intensity transmitted light projected from the back surface.

In lieu of providing non-water soluble indicia on the strip surface as depicted in Fig.1, an alternative method for providing authentication features within the paper involves the properties of the strip material itself.

Fig.9 depicts an end view of an alternative strip 10 as viewed by means of polarized light within a pair of crossed polarizers. The infor mation is impressed upon the surface of the strip 10 by an instrument similar to a type writer with the ribbon removed. The bar code or symbols are pressed onto the surface of the strip to form indentations 27 below the surface 26. When PVA material is used for the dissolving or "disappearing" strip 10 it was determined that the stress imposed upon the PVA material drastically changed its solu bility characteristics. The polarized strain lines 28 which represent the densification of PVA material comprising strip 10 indicates that the material under the depressions 27 is much denser than that under the un-stressed surface 26.When the water temperature is adjusted such that the unstressed PVA material dissolves during the dewatering and drying stage the stressed PVA remains within the interstices of the paper fibres. The result is strikingly similar to a high quality water mark wherein the paper fibres are displaced from the region occupied by the undissolved PVA material and the indicia comprising the undissolved PVA material is readily readable by transmitted light. Other methods for selectively stressing the PVA material include treatment by ultraviolet light or high energy electrons wherein the material to be dissolved is masked. This is similar to the photoresist process used in making semiconductor devices where acids are used to dissolve the undesired material. Besides its use as a means for authentification purposes, the impressment of indicia on the dissolving PVA strip 10 can also be used for other purposes for which watermarks are employed. The size of the watermark would determine the thickness as well as the width of the dissolving strip to be employed in the process.

This invention describes methods and materials for imparting authentification indicia within paper during the paper making process such that the substrate for such indicia is dissolved in the process and is not removable from the paper material. It also describes a method for providing high quality simulated watermarks having detailed features within the paper that are not otherwise attainable by standard wet screen watermark techniques.

Claims (14)

1. A method of providing security features within paper comprises the steps of imparting indicia to the surface of a substrate material which can be selectively dissolved during a paper making process, inserting the indiciabearing substrate within a water slurry containing paper fiores, and dissolving the substrate at least in part to leave the indicia within the paper fibres during dewatering and drying of the paper fibres to form the paper embodying the indicia as security features.

2. A method as claimed in claim 1, wherein the substrate material is water soluble at a temperature higher than that of the fibre slurry.

3. A method as claimed in claim 1 or 2, wherein the drying temperature is in excess of 100 F.

4. A method as claimed in claim 1, 2 or 3, wherein the slurry includes water, alcohols, ketones, and esters.

5. A method as claimed in any one of claims 1 to 4, wherein the substrate material comprises a water soluble ester.

6. A method as claimed in any one of claims 1 to 5, wherein the indicia comprises a non-water soluble material.

7. A method as claimed in claim 6, wherein the indicia material comprises fluorescent pigments and dyes, metallized and metal oxide films and printer's ink.

8. A method as claimed in claim 1, comprising impressing the substrate material to stress harden the material and to impart indicia at specific locations thereon, the substrate being subsequently dissolved other than in said specific locations.

9. A method as claimed in claim 1, comprising the steps of impressing indicia at a specific location on the surface of a substrate material, treating the substrate material at the specific locations to render the specific locations less soluble than the substrate material at other locations, inserting the substrate material within a slurry containing paper making fibres, and dewatering and heating the paper fibres to dissolve the substrate material except for the treated locations thereby providing means for determining the specific locations within the paper by means of transmitted light.

10. A method of providing security features in paper comprising the steps of providing indicia material on the surface of a substrate material, both the indicia material and the substrate material being insoluble during dewatering and heating of paper fibres incorporating the indicia-bearing subsrate material in a slurry of paper fibres, dewatering and heating the paper fibres to form a finished paper, and submitting the finished paper to a solvent material for dissolving the substrate material without dissolving the indicia material.

11. A method as claimed in claim 1, wherein the substrate material is one which can be selectively dissolved at a predetermined temperature during the paper making process, the indicia-bearing substrate is inserted within a water slurry containing paper fibres during dewatering thereof, maintaining the slurry at a first temperature less than said predetermined temperature to incorporate the substrate within said paper fibres while dewatering the slurry to consolidate the paper fibres into a wet paper sheet without dissolving the substrate, and subsequently dissolving the substrate at said predetermined temperature to incorporate it within the paper sheet and to leave the indicia within the paper sheet without dissolving the paper fibres during drying of the wet paper sheet.

12. A method as claimed in claim 1, wherein the indicia is impressed onto a surface of a substrate material, which is water soluble at a first predetermined temperature, to stress harden the material, to impart indicia at specific locations on the material and to selectively increase the temperature at which the stress-hardened material will dissolve up to a second predetermined temperature, the substrate is inserted within a water slurry con taining paper fibres during a paper making process to surround the substrate within the paper fibres, and thereafter the paper fibres are dewatered to a drying temperature intermediate the first and second predetermined temperature to dry the paper fibres and to dissolve the substrate other than at the specific locations.

13. A method as claimed in claim 1, wherein the substrate material is water soluble at a first predetermined temperature, the indicia material being non-soluble during dewatering and heating of paper fibres at the first predetermined temperature, and the substrate material being non-soluble during such dewatering of paper fibres, and the paper fibres are heated to a drying temperature higher than the first predetermined temperature after such dewatering to dry the paper fibres and to dissolve the substrate material without dissolving the indicia material.

14. Methods of providng security features within paper, substantially as herein described with reference to the accompanying drawings.