High security paper and process of manufacture

Abstract

The invention relates to high security paper wherein the security feature(s) is/are incorporated into the paper during the manufacturing process using a polymeric film as a carrier for the security feature(s). The invention enables the security feature(s) to be delivered at precise places into security paper used for such diverse applications as bank notes, passport paper, visa paper, security documents, etc. The polymeric film may be a cold water soluble film or hot water soluble film or water insoluble hydrophilic film or a or a non soluble non hydrophilic film or a combination of these films or slit strips of any of these woven or intertwined offline and incorporated into the paper during the paper making process. Alternatively the polymeric film may comprise zone coating or discreet printing or zone extrusion striping or formation of hot water soluble film on preformed cold water soluble film which is then inserted into paper during the paper making process. The combination of polymeric films may be plain or wholly or partially perforated. The security features may be light source readable or machine readable or both.

Description

FIELD OF INVENTION

This invention relates to high security paper and to a process for the manufacture of high security paper.

BACKGROUND OF INVENTION

The technology of machine reading security features needs expensive chemicals, pigments and DNAs. Being machine readable and invisible to the naked eye, the security features need to be positioned discreetly so as to enable the reader to accept or reject the final security documents or bank notes. Precise delivery of these expensive chemicals/security features is needed to identify location and control final costs.

The cost of currency notes includes the cost of the paper plus the cost of ink (60%) and other hidden costs (40%) like vending/distribution costs to the end user. High strength currency paper is necessary and 100% polymer currency, also known as “plastic” currency, has been in circulation in various countries. This “plastic” currency has inherent disadvantages. For example they cannot have a security watermark. Deadfold is not like paper, special inks are needed to adhere to polymer substrate, security threads cannot be inserted/embedded so surface security (like printing, embossing) is the only method of securing these kinds of “plastic” currency notes. This has been perceived by many countries to be a compromise, which many Reserve Banks are ready to accept in line of the phenomenal strength that this “plastic” currency can impart. Banknotes with lower denominations having lower working life are being promoted as targets for these “plastic” currency notes.

Several patents have been filed on delivering security features to the paper but the invention addresses the need for delivering several types of security features at precise location with minimum costs as well as give the combined strength of a paper plus film.

One such patent is U.S. Pat. No. 4,552,617 wherein thin strips soluble in water are printed with security features and these individually printed strips are then acetylated or heat treated prior to locating on the paper web. The thin strips dissolve during the dewatering and drying stage and the microprinted indicia will remain in the paper. Problems arise for accurately locating individual strips on the paper web. Also, it is not possible to deliver security features of high dimension using very thin strips.

Accordingly, it is an object of the present invention to provide an improved method of producing high security paper with security features at precise locations.

According to a first aspect of the invention, there is provided a process of delivering one or more security features at precise places into security paper used for bank notes, passport paper, visa paper, security documents, etc. using polymeric film(s) as a carrier for the security feature(s).

By this invention, the security feature(s) is/are embedded/embossed/printed within/on the polymeric film and this pre-formed polymeric film containing the security feature(s) is incorporated into the security paper during the paper making process.

In preferred embodiments, the security features are printed on a continuous web of polymeric film that is incorporated in the paper during the papermaking process. In this way, the security features can be embedded/embossed/printed at precise locations onto the continuous web of polymeric film so as to accurately position the security features when the paper and polymeric film webs are brought together. This method allows security features having a wide range of to be embedded in the finished paper. Also, multi-coloured multi security features can be incorporated in a reliable manner.

In this way, the invention addresses the need for delivering several types of security features at precise location with minimum costs.

As used hereinafter in the description and claims, the following terms shall have the meaning defined

WSF (water soluble film): By definition shall mean Water Soluble film(s) of all types. WSF can be manufactured by process of direct casting on a conveyor, by casting on a detachable liner, by casting from a T-die casting, by blowing film on extrusion machines, or by extrusion via T-die extrusion. The formulation of the WSF shall determine the temperature of water in which the WSF shall easily dissolve. This range of water temperature varies between 5° C. to 100° C. For the purpose of this invention it is clarified that WSF encompass all types of WSF made from any of the above methods, including direct coating of WSF film forming resins.

For the purpose of this invention it is clarified that CWSF means cold water soluble film, which becomes tacky, break and finally dissolve in temperature ranging from 5° C. to 40° C., preferably from 10° C. to 40° C., more preferably from 20° C. to 40° C. The time of tack, break and dissolution of the CWSF shall range between 1 second to 3 minutes upon contact with water/water pulp slurry. However, this shall depend upon the CWSF formulation.

Similarly, for the purpose of this invention it is clarified that HWSF means hot water soluble film, which shall become tacky, break and finally dissolve in temperature ranging from 40° C. to 100° C., preferably from 45° C. to 90° C., more preferably from 50° C. to 85° C. The time of tack, break and dissolution of the HWSF shall range between 5 seconds to 5 minutes upon contact with hot water/water pulp slurry. However, this shall depend upon the HWSF formulation.

Similarly, for the purpose of this invention it is clarified that NSHF means non soluble hydrophilic film, which shall become tacky and may break/crack at certain places but shall not dissolve on contact with water/water pulp slurry. The tack and break time shall range between 7 seconds to 10 minutes, which can depend upon the formulation of the non soluble hydrophilic film and the temperature of water.

The water soluble films mentioned in this invention are made from materials selected from various film forming resins like polyvinyl alcohol copolymer ionomers, polyvinyl alcohol homopolymer, non-ionomeric poly vinyl alcohol polymer, polymethacrylate, polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyurethane, polyethyleneglycol, polyvinylpyrrolidone, proteinaceous binders such as gelatin, modified gelatins such as phthaloyl gelatin, polysaccharides such as starch, gum Arabic, pullulan and dextrin and water soluble cellulose derivatives or combination thereof. The cellulose derivatives used are methyl cellulose, hydroxy propyl cellulose, hydroxy propyl methyl cellulose, hydroxy propyl ethyl cellulose, hydroxy ethyl cellulose, carboxy methyl cellulose. However, these are by no means limiting.

Addition and inclusion of certain additives like ammonium chloride and other such alkaline chemicals will render the film to be non soluble hydrophilic film.

NSNHF: This is a non soluble non hydrophilic type of film. This type of film is readily available in the market and can be selected from PP (Poly propylene), PE (Poly ethylene), LDPE (Low density poly ethylene), HDPE (high density polyethylene), LLDPE (Linear low density polyethylene), HIPS (High impact polystyrene), HMHDPE (High molecular high density polyethylene), BOPP (Biaxially oriented poly propylene). However, these are by no means limiting.

This non soluble non hydrophilic film can also be made out of biodegradable materials such as PLA (Poly Lactic Acid), PHA (polyhydroxyalkanoic acid) or thermoplastic starch materials or biodegradable polyesters such as ecoflex.

NSNHF is necessarily combined with a layer of CWSF polyme on one or both sides, depending upon its end use.

Film combinations: The films used for increasing the strength of the paper may be a cold or hot water soluble film or non soluble hydrophilic film or non soluble non hydrophilic film or a combination of these films as mentioned below:

• • 1. CWSF+HWSF: This is a combination of cold and hot water soluble films wherein the cold/hot water soluble is cast/coated/laminated onto the hot/cold water soluble film.
  • 2. CWSF+HWSF+CWSF: This is a combination of water soluble films wherein the hot water soluble film will be between two cold water soluble films.
  • 3. CWSF+NSHF: This is a combination of cold water soluble and non soluble hydrophilic films wherein the NSHF/CWSF is cast/coated/laminated on the CWSF/NSHF film.
  • 4. CWSF+NSHF+CWSF: This is a combination of cold water soluble/non soluble hydrophilic/cold water soluble films wherein the NSHF will be between two cold water soluble films.
  • 5. CWSF+NSNHF: This is a combination of cold water soluble and non soluble non hydrophilic film wherein the NSNHF/CWSF is cast/coated/laminated on the CWSF/NSNHF film.
  • 6. CWSF+NSNHF+CWSF: This is a combination of cold water soluble/non soluble non hydrophilic/cold water soluble films wherein the NSNHF will be between two cold water soluble films.
  • 7. Machine direction strips matrix: Strips of polymeric films inserted/cast/coated onto another polymeric film. This combination can be formed by zone coating or discreet printing or zone extrusion striping or formation of a film on another polymeric film which is then inserted into paper during the paper making process.
  • 8. Woven tape matrix: Strips of polymeric films or PVA threads inter-woven by a warp and weft method. Here the polymeric film or its combination as described before, is slit into microtapes having width in the range of 3 mm to 15 mm, preferably 4 mm to 10 mm, more preferably 5 mm to 7 mm. However, this range is by no means limiting. However, this range is by no means limiting. The size of the PVA threads ranges from 50 deniers to 1000 deniers, preferably 150 deniers to 700 deniers, more preferably from 300 deniers to 500 deniers. However, this range is by no means limiting. These tapes or threads are woven offline into a warp and weft, as can be seen in a fabric making machine, and a continuous matrix is made in a roll form. These tapes can be inserted into a pulp-paper web in a combination of MD (machine direction) and CD (cross direction).
  • 9. Films With Perforations: Any of the above mentioned films or combination of films could be perforated at random places, discreet places or all over. These perforations can be done by various methods like hot needles, mechanical/needle covered rollers, pneumatic/mechanical perforation machines etc. However, these methods are by no means limiting.

Paper pulp: The paper pulp used for manufacturing this high strength paper is selected from a mixture of fibers of hardwood and softwood, cotton fibres such as cotton linters and cotton rags, linen, flax, jute, hemp, kozo, mitsumata, gampi, grass fibres such as esparto, bamboo, giant nettle, rice straw and rattan; and wood pulp. However, these are by no means limiting.

Security Features: The security features embedded in the water soluble film may include although not limited to micro-printed text, logos, metallised/demetallised particles/fibres, bar-codes, watermarks, nano-particles which may be machine readable, micro-taggants, DNA (synthetic, natural), UV, PCR, computer, machine readable, RFID devices, etc.

The polymeric film may be a cold water soluble film or hot water soluble film or water insoluble hydrophilic film or water insoluble non hydrophilic film or a combination of cold+hot+cold water soluble films or cold+hot water soluble films or cold+non soluble hydrophilic film or cold+non soluble hydrophilic+cold water soluble films or cold+non soluble non hydrophilic films or cold+non soluble non hydrophilic+cold films or slit strips of one or many of these combinations woven or intertwined offline or strips of polymeric films inserted/cast/coated onto another polymeric film and incorporated into the paper during the paper making process.

The term “polymeric film” is to be construed accordingly to include all of these for the purpose of this invention.

Preferably, perforations are used for HWSF or NSHF or NSNHF types of polymeric films or their combinations, but this shall not be limiting as far as all types of polymeric films and their combinations are concerned.

The polymeric film may be plain or perforated wholly, partially or randomly.

One of the embodiment of the invention provides for strengthening the security paper by incorporating a water soluble film or non soluble hydrophilic film or non soluble non hydrophilic film or a combination of these films during the paper making process.

In another embodiment of the invention, the security feature(s) is/are delivered through a cold water soluble film wherein the security feature(s) is/are embedded/printed within/on the cold water soluble film. The cold water soluble film will solubilise within the pulp fibres and hence deliver the security features at the desired location.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a hot water soluble film, optionally perforated selectively, wherein the security features are embedded/printed within/on the hot water soluble film. The hot water soluble film—carrying the security feature(s)—will remain intact due to the differential temperature of pulp+water slurry and deliver the security features at the desired location, thereby solving the problem of micro-text words or logos floating within the matrix of the paper pulp which may happen when using only a CWSF, or strips of CWSF. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a non soluble hydrophilic film, optionally perforated selectively, wherein the security feature(s) is/are embedded/printed within/on the non soluble hydrophilic film. This film will not dissolve into the pulp fibres but will become tacky due to its hydrophilic nature and shall adhere to the partially formed bed of pulp. Hence the film will remain intact and deliver the security feature(s) at the desired location. It will also give added strength to the final product. This film can be used particularly when the water-pulp slurry temperature is a little higher. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a non soluble non hydrophilic film wherein the security features are embedded/printed within/on the NSNHF. The non soluble non hydrophilic film will not dissolve into the pulp fibres and also will not become tacky but will be sucked inside as it is perforated, hence delivering the security features at precise place and increasing the strength of the paper.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of cold+hot water soluble film, wherein the HWSF is optionally perforated selectively and the security feature(s) is/are embedded/embossed/printed within/on the hot water soluble film. The cold water soluble film will solubilise into the pulp fibres increasing the strength of the paper while the hot water soluble film containing the security feature(s) will remain intact and hence deliver the security features at the desired place. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of cold+hot+cold water soluble films, wherein the HWSF is optionally perforated selectively and security feature(s) is/are embedded/embossed/printed within/on the hot water soluble film. The cold water soluble films will solubilise into the pulp fibres increasing the strength of the paper while the hot water soluble film consisting security features will remain intact due to the differential temperature of the pulp+water slurry, to locate the security feature(s) at the desired place and give added strength to the final produce.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of cold+non soluble hydrophilic films, wherein the NSHF is optionally perforated selectively and the security feature(s) is/are embedded/embossed/printed within/on the non soluble hydrophilic film. The cold water soluble film will solubilise into the pulp fibres increasing the strength of the paper while the non soluble hydrophilic film will not dissolve into the pulp fibres but will become tacky due to its hydrophilic nature and shall adhere to the partially formed bed of pulp. Hence the film will remain intact and deliver the security feature(s) at the desired place. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of cold+non soluble hydrophilic+cold water soluble films, wherein the NSHF is optionally perforated selectively and the security feature(s) is/are embedded/embossed/printed within/on the non soluble hydrophilic film. The cold water soluble films will solubilise into the pulp fibres increasing the strength of the paper while the non soluble hydrophilic film consisting security features will not dissolve into the pulp fibres but will become tacky due to its hydrophilic nature and shall adhere to the partially formed bed of pulp. Hence the film will remain intact and deliver the security feature(s) at the desired place. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of cold+non soluble non hydrophilic films, wherein the NSNHF is optionally perforated selectively and the security feature(s) is/are embedded/embossed/printed within/on the non soluble non hydrophilic film. The cold water soluble film will solubilise into the pulp fibres increasing the strength of the paper while the non soluble non hydrophilic film will not dissolve into the pulp fibres. Hence the film will remain intact and deliver the security feature(s) at the desired place. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of cold+non soluble non hydrophilic+cold water soluble films, wherein the NSNHF is optionally perforated selectively and the security feature(s) is/are embedded/embossed/printed within/on the non soluble non hydrophilic film. The cold water soluble films will solubilise into the pulp fibres increasing the strength of the paper while the non soluble non hydrophilic film consisting security features will not dissolve into the pulp fibres. Hence the film will remain intact and deliver the security feature(s) at the desired place. It will also give added strength to the final product.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a combination of polymeric films including strips of films wherein the strips are inserted/cast/coated onto another film, to deliver security features that are embedded/printed within/on the film strips.

E.g. strips of HWSF consisting security features are inserted/cast/coated on a cold water soluble film. The cold water soluble film will solubilise into the pulp fibres increasing the strength of the paper while the hot water soluble film with security features will remain intact due to the differential temperature of pulp-water slurry, thus solving the problem of micro-text words or logos floating within the matrix of the paper pulp which may happen while only using only CWSF, or strips of CWSF.

In yet another embodiment of the invention, the security feature(s) is/are delivered through a film matrix wherein the security features embedded/printed within/on the polymeric film strips or on the PVA threads are inter-woven by a warp and weft method. E.g. The strips may be a combination of cold+hot water soluble films or only hot water soluble strips or non soluble hydrophilic strips or only cold water soluble strips, to deliver the security features that are embedded/printed within/on the hot water soluble film. The HWSF or NSHF used are optionally perforated selectively The cold water soluble strips will solubilise into the pulp fibres increasing the strength of the paper while the hot water soluble strips containing the security feature(s) will remain intact and hence deliver the security features at the desired place. It will also give added strength to the final product.

According to a second aspect, the present invention provides security paper made by the method according to the first aspect of the invention.

Embodiments of the invention will now be described in more detail, by way of example with reference to the accompanying drawings, wherein:

FIG. 1 shows a first process for the manufacture of high strength paper according to the invention; and

FIG. 2 shows a second process for the manufacture of high strength paper according to the invention.

Referring to FIG. 1, the process of incorporating a polymeric film embedded/embossed/printed with security features into the paper during the paper making process by the cylinder mould method is as follows:

• • 1. Filling the vat (2) with the pulp-water slurry entering at (3), the pulp content ranging from 5 to 7%.
  • 2. Formation of the paper body on the outside of the rotating cylinder (1) covered with a wire cloth. As the cylinder rotates, water is removed from the inside of the cylinder and a layer of fibres is formed on the outside. This is consolidated by couch roll (7), which squeezes more water away. The couch roll also peels the wet paper cleanly off the cylinder mould and transfers it to the continuous moving belt (3).
  • 3. Layering of a preformed polymeric film (8), which is embedded/embossed/printed with security features, onto the pulp fiber bed at the couch roll as shown in the figure.
  • 4. Passing the construction through the vacuum boxes (9) to remove excess water from the pulp bed. The fiber content in the pulp increases to 30 to 40%.
  • 5. Passing the construction through press roll (10) to remove excess water.
  • 6. Sending the construction to dryers for further evaporating the moisture from the paper web.

Similarly, the polymeric film containing security features can also be incorporated during the fourdrinier process of paper making.

During step 3, if the film is a CWSF embedded/embossed/printed with security features, then the film will start dissolving as soon as it comes in contact with the pulp bed and will be sucked into the paper when it passes through vacuum boxes and the security features will remain intact in the pulp bed.

If the film is a HWSF or NSHF or NSNHF or any of the combination having at least one layer or strip of HWSF/NSHF/NSNHF, then the film will not dissolve and will stay on the surface of the pulp bed due to lower capacity of the vacuum suction box. Hence, if a HWSF or NSHF or NSNHF or any other combinations of films consisting HWSF/NSHF/NSNHF have to be incorporated into the pulp bed, a Twin former process may be required, depending upon the needs and ultimate quality of paper required.

As shown in FIG. 2, a first ply of wet paper is formed as the water-pulp slurry coming from the stock approach box (12) is dropped on a continuous moving belt (11) by the first former (13). The temperature of the pulp water slurry in the stock approach box ranges 15° C. to 40° C., more preferably from 25° C. to 30° C. The concentration of the pulp fibres in the pulp-water slurry in the stock approach box is 5% to 7%. The first ply of wet paper formed by the first former constitutes of 80% of wt/thickness of the final paper.

A polymeric film or either a combination of polymeric films embedded/embossed/printed with security features, as unwound from the unwinder (15), is incorporated into the first ply of the wet paper web with the help of a guide roll (16) as shown in the figure.

A second ply of wet paper is formed on the polymeric film side of the first ply of wet paper by the second former (14). The cylinder (14), covered with a wire cloth, rotates in the vat (17) containing pulp-water slurry. As the cylinder rotates, water is removed from the inside of the cylinder, while a layer of pulp fibres is formed on the outside. This is consolidated by the couch roll (18), which squeezes more water away. The couch roll also peels the wet paper cleanly off the cylinder and transfers it to the moving continuous belt, which carries it to the press section. The second ply of wet paper formed by the second former constitutes of 20% of wt/thickness of the final paper.

More water is removed at the press section (19), and the two ply paper is further sent to dryers for further evaporating the moisture from the paper web.

The polymeric film or combination of polymeric films containing the security features may be any of the types previously described where the security features are incorporated during the paper making process at precise locations using the polymeric film as a carrier to position the security features precisely in the final paper.

The following experiments were conducted in the lab to prove that a polymeric film when incorporated into the paper will increase the strength of the paper:

The following experiments were conducted in the lab to prove the invention:

Forming Paper:

• • 1. We got some dehydrated virgin pulp from a paper mill and cut the pulp matrix into small pieces and soaked the pieces in warm water in the large tub overnight.
  • 2. We filled the blender halfway with warm water, then added a handful of the soaked pulp pieces. We blended the pieces until no pieces of pulp sheet were seen. This formed into the pulp-water slurry.
  • 3. We poured the blended mixture into the large tub and then filled the tub with warm water, mixing thoroughly until the ingredients were evenly dispersed.
  • 4. We slide a screen/sieve into the tub and allowed some pulp to settle onto the screen and still holding the screen underwater, gently moved it back and forth to get an even layer of fibers on the screen.
  • 5. We lifted the screen out of the slurry, keeping it flat and allowed it to drip over the tub until most of the water has drained through.
  • 6. We dried the wet paper with the help of a hair dryer and then left it to dry for few hours to remove excess water.
  • 7. When the paper was dry, we gently peeled it off from the screen to form a hand made paper. We weighed the paper which was 110 GSM.
  • 8. We tested the tensile strength of this paper as per standard D 882 on a universal testing machine (UTM).Forming Paper Incorporated with CWSF:
  • 1. We dipped a screen into the tub containing pulp-water slurry as formed in the above process and allowed some pulp to settle onto the screen and still holding the screen underwater, gently moved it back and forth to get an even layer of fibers on the screen.
  • 2. We lifted the screen out of the slurry, keeping it flat and allowed it to drip over the tub until most of the water has drained through and placed the screen on the floor.
  • 3. We layered the top of the wet paper with 30 microns CWSF. As soon as the CWSF came in contact with wet paper, it started dissolving and after some time dissolved completely.
  • 4. We dried the wet paper+CWSF with the help of a hair dryer and then left it to dry for few hours to remove excess water.
  • 5. When the paper+CWSF was dry, we gently peeled it off from the screen to form a high strength paper. The thickness of this construction was 110 GSM.
  • 6. We tested the tensile strength of this paper+CWSF as per standard D 882 on a universal testing machine (UTM).Forming paper Incorporated with HWSF:
  • 1. We dipped a screen into the tub containing pulp-water slurry as formed in the above process and allowed some pulp to settle onto the screen and still holding the screen underwater, gently moved it back and forth to get an even layer of fibers on the screen.
  • 2. We lifted the screen out of the slurry, keeping it flat and allowed it to drip over the tub until most of the water has drained through and placed the screen on the floor.
  • 3. We layered the top of the wet paper with 20 microns HWSF. As soon as the HWSF came in contact with wet paper, it became tacky but did not dissolve.
  • 4. We formed another layer of wet pulp on another screen and let the water drip as explained above and we gently put this screen on top of the HWSF side of the wet paper as formed in step 3.
  • 5. We dried the wet paper+HWSF+paper with the help of a hair dryer and then left it to dry overnight to remove excess water.
  • 6. When the paper+HWSF+paper was dry, we gently peeled it off from the screen to form a high strength paper.
  • 7. We tested the tensile strength of this paper+HWSF+paper as per standard D 882 on a universal testing machine (UTM).

Similarly, a C-H combination of WSF (20 microns) was incorporated into the paper as per the above process.

Care was taken that the thickness of the paper incorporated with polymeric film was kept constant.

The strength comparison of paper, paper incorporated with CWSF, paper incorporated with HWSF and paper incorporated with C-H combination of WSF is shown table 1:

	Mech. Props.
	Tensile
	Strength		Peak Load
	Kg/cm2	% Elongation %	Kg
Paper (110 GSM)	66.53	2.1	1.82
Paper incorporated with	135.05	5.56	4.33
CWSF (110 GSM)
Paper incorporated with	97.67	4.15	2.686
HWSF (110 GSM)
Paper incorporated with C-H	122.07	5.7	3.357
combination (110 GSM)

Experiment were also done to

• 1. We cast a HWSF film and zone coated using CWSF formulation with security elements, like UV light visible security dyes, embedded within the batch mix, forming strips of coated and uncoated CWSF lines.
• 2. We inserted this matrix as formed in 1, into pulp mix by the paper making process as described in the experiments done earlier.
• 3. We inspected the sheet of paper and found that the security elements as mentioned in 1 were deposited at the same desired place and that strength had increased as an advantage to this method.

To prove that we can now embed many visible and invisible security elements and ensure that the same are released at a desired location on the web of paper and therefore, in the final sheet of paper, for example a Bank Note.

Experiment of Security element “Printed” on a zone cast film using combination of CWSF and HWSF methods.

• 4. We cast a HWSF film and zone coated using CWSF formulation with security elements, like UV light visible security dyes, embedded within the batch mix, forming strips of coated and uncoated CWSF lines.
• 5. We printed an indicia, using a secure gravure cylinder and security inks, on top of the CWSF areas, which may be optionally be identified using a UV lamp for facilitating print registration.
• 6. We inserted this matrix as formed in 1, into pulp mix as mentioned earlier.
• 7. We inspected the sheet of paper and found that the security elements as mentioned in 4 and 5 were deposited at the same desired place and that strength had increased as an advantage to this method.

Experiment of Security element “Printed” on a zone cast film using combination of CWSF and HWSF methods.

• 8. We cast a CWSF film, and coated a time delay tie coating, like a water based film forming acrylic coating, and zone coated using HWSF formulation with security elements, like UV light visible security dyes, embedded within the batch mix, forming strips of coated and uncoated HWSF lines.
• 9. We printed an indicia, using a secure another gravure cylinder station and security inks, on top of the HWSF areas, which may be optionally be identified using a UV lamp for facilitating print registration. It can be seen that using multiple station one can embed multiple security elements within paper as desired locations.
• 10. We inserted this matrix as formed in 1, into pulp mix as mentioned above.
• 11. We inspected the sheet of paper and found that the security elements as mentioned in 8 and 9 were registered at the same desired place and that the printed indicia was visible and intact as it was printed. There was noticeable addition to strength of paper, using this method.
  • Similarly, by varying combinations of Cold and Hot water soluble films and “Print Coating”, or “Print Casting” or zone coating, desired areas to identify security elements can be produced. Subsequently, these areas can be identified as per the master art work, for searching the security elements in a particular sheet of paper, even after cutting them into small sheets like bank note paper.
  • This solves certain problems, like precision insertion of small, unmanageable threads into a master web of bed of pulp, or “floating” of indicia, leading to heavier rejections and subsequently paper manufacturing process.

As will be appreciated, the present invention provides a process for making security paper in which one or more security features is accurately positioned in the paper and the paper is optionally strengthened using polymeric film as the carrier for the security feature(s) during the manufacturing process. The polymeric film may be a water soluble film selectively soluble at temperatures above or below the temperature of the water contained in the paper substrate to which it is applied during the process. In this way we can control the manner in which the water soluble film is incorporated and hence the location of the security feature(s) in the finished product. For example the water soluble film may dissolve or remain intact and we may employ combinations of films which may dissolve or remain intact or combinations of any of these with or without other films such as non soluble hydrophilic films.

According to another aspect of the invention we provide a method of making security paper comprising providing a carrier film containing one or more security features at predetermined locations, forming a paper web, applying the carrier film to the web to position the security feature(s) at desired places on the web wherein the carrier film includes water soluble films, non soluble hydrophilic films and non soluble non hydrophilic films.

The water soluble film may solubilise and be absorbed into the web leaving the security feature(s) at desired places on the web. Alternatively, the water soluble film may remain intact to position the security feature(s) at desired places on the web.

The carrier film may comprises two or more films having different solubilities where the differential solubilities of the films can be used to position the security feature(s) at desired locations during the paper making process and optionally to strengthen the paper. For example the carrier film may comprise a combination of any two or more of cold water soluble film, hot water soluble film, non soluble hydrophilic film and non soluble non hydrophilic film. The security feature(s) may be incorporated in any one or more of the films making up the carrier film.

Claims

1. A method of making a security paper having one or more security features at precise locations within the paper by using polymeric film as a carrier for the security feature(s) and incorporating the polymeric film containing the security feature(s) into the paper web during the paper making process.

2. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a cold water soluble film that dissolves and is absorbed into the pulp fibres of the web during the paper making process.

3. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a hot water soluble film that remains intact and adheres to the web during the paper making process.

4. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a non soluble hydrophilic film that remains intact and adheres to the web during the paper making process.

5. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a non soluble non hydrophilic film that remains intact in the web during the paper making process.

6. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a combination of cold and hot water soluble films wherein the cold water soluble film dissolves and is absorbed into the pulp fibres and the hot water soluble film remains intact and adheres to the web.

7. A method according to claim 6 wherein the security feature(s) is/are contained in the hot water soluble film.

8. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a combination of cold and non soluble hydrophilic films wherein the cold water soluble film dissolves and is absorbed into the pulp fibres and the non soluble hydrophilic film remains intact and adheres to the web.

9. A method according to claim 8 wherein the security feature(s) is/are contained in the non soluble hydrophilic film.

10. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a combination of cold and non soluble non hydrophilic films wherein the cold water soluble film dissolves and is absorbed into the pulp fibres and the non soluble non hydrophilic film remains intact in the web.

11. A method according to claim 10 wherein the security feature(s) is/are contained in the non soluble non hydrophilic film.

12. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is a cold water soluble film inserted/cast/coated with hot water soluble film strips or non soluble hydrophilic film strips or vice versa.

13. A method according to claim 1 wherein the security feature(s) is/are provided by a polymeric film which is in the form of a matrix wherein one or more polymeric films or PVA threads are inter-woven into a matrix by warp and weft method.

14. A method according to claim 12 or 13 wherein the width/size of the polymeric film strips range from 3 mm to 15 mm, preferably from 4 mm to 10 mm, more preferably from 5 mm to 7 mm.

15. A method according to claim 13 wherein the size of the PVA thread range from 50 deniers to 1000 deniers, preferably 150 deniers to 700 deniers, more preferably from 300 deniers to 500 deniers.

16. A method according to claim 1, wherein the polymeric film embedded/embossed/printed with security feature(s) is applied to the wet paper pulp web during a cylinder mould process of paper making comprising the following steps: a. filling the vat with the pulp-water slurry entering;b. formation of the paper body on the outside of the rotating cylinder covered with a wire cloth;c. layering of a preformed polymeric film embedded/embossed/printed with security feature(s) onto the pulp fiber bed at the couch roll;d. passing the construction through the vacuum boxes to remove excess water from the pulp bed;e. passing the construction through press roll to remove excess water and then to dryers for further evaporating the moisture from the paper web.

17. A method according to claim 1, wherein the polymeric film embedded/embossed/printed with security feature(s) is applied to the wet paper pulp web during a twin former process of paper making comprising the following steps: a. formation of first ply of wet paper web by the first former on a continuous moving belt;b. incorporation of the polymeric film embedded/embossed/printed with security feature(s) into the first ply of the wet paper web with the help of a guide roll;c. formation of the second ply of wet paper on the polymeric film side of the first ply of wet paper by the second former;d. passing the construction through press section to remove excess water and then to dryers for further evaporating the moisture from the paper web.

18. A method according to claim 16 or 17 wherein the polymeric film includes at least one film containing the security feature(s) that remains intact between first and second paper webs during the paper making process.

19. A method according to claim 16 or 17 wherein the polymeric film includes at least one film that dissolves and is absorbed into the pulp fibres of the first and/or second paper webs.

20. A method according to claim 16 or 17 wherein the polymeric film comprises a combination of at least two films wherein at least one film is soluble at a lower temperature than the other film.

21. A method according to claim 16 or 17 wherein the water soluble film comprises at least one cold water soluble film and at least one hot water soluble film where the security feature(s) is/are provided by the hot water soluble film.

22. A method according to claims 1 to 21 wherein one or more polymeric films are perforated.

23. Security paper made by the method according to any preceding claim.

24. Security paper according to claim 23 wherein the carrier polymeric film is incorporated into the fibres of the paper during the cylinder mould process of paper making.

25. Security paper according to claim 23 wherein the carrier polymeric film is incorporated between two webs of the paper during the twin former process of paper making.

26. Security paper according to any of claims 23 to 25 wherein the polymeric film is a water soluble film made from materials selected from the group comprising polyvinyl alcohol copolymer ionomers, polyvinyl alcohol homopolymer, non-ionomeric poly vinyl alcohol polymer, polymethacrylate, polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyurethane and edible film forming materials like polyethyleneglycol, polyvinylpyrrolidone, proteinaceous binders such as gelatin, modified gelatins such as phthaloyl gelatin, polysaccharides such as starch, gum Arabic, pullulan and dextrin and water+soluble cellulose derivatives or combination thereof. The cellulose derivatives used are methyl cellulose, hydroxy propyl cellulose, hydroxy propyl methyl cellulose, hydroxy propyl ethyl cellulose, hydroxy ethyl cellulose, carboxy methyl cellulose.

27. Security paper according to any of the claims 23 to 25 wherein the polymeric film is a non soluble non hydrophilic film selected from PP (Poly propylene), PE (Poly ethylene), LDPE (Low density poly ethylene), HDPE (high density polyethylene), LLDPE (Linear low density polyethylene), HIPS (High impact polystyrene), HMHDPE (High molecular high density polyethylene), BOPP (Biaxially oriented poly propylene).

28. Security paper according to any of the claims 23 to 25 wherein the polymeric film is a non soluble non hydrophilic film made from biodegradable materials such as PLA (Poly Lactic Acid), PHA (polyhydroxyalkanoic acid), thermoplastic starch materials or biodegradable polyesters such as ecoflex.

29. Security paper according to any of claims 23 to 29 wherein the polymeric film has a thickness ranging from 5 microns to 150 microns, preferably from 10 microns 70 microns, more preferably from 15 microns to 35 microns.

30. Security paper according claim 25 wherein the paper comprises at least two plies.

31. Security paper according to claim 25 having a polymeric film containing the security feature(s) between the plies.

32. Security paper according to any of claims 23 to 31 wherein the security feature(s) are selected from the group comprising micro-printed text, logos, metallised/demetallised particles/fibres, bar-codes, watermarks, nano-particles, micro-taggants, DNA (synthetic, natural), UV, PCR, computer, machine readable, RFID devices.