Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M3/00—Printing processes to produce particular kinds of printed work, e.g. patterns
  • B41M3/14—Security printing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
  • B41M7/0027—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock using protective coatings or layers by lamination or by fusion of the coatings or layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/50—Recording sheets characterised by the coating used to improve ink, dye or pigment receptivity, e.g. for ink-jet or thermal dye transfer recording
  • B41M5/52—Macromolecular coatings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/50—Recording sheets characterised by the coating used to improve ink, dye or pigment receptivity, e.g. for ink-jet or thermal dye transfer recording
  • B41M5/52—Macromolecular coatings
  • B41M5/5254—Macromolecular coatings characterised by the use of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds, e.g. vinyl polymers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/50—Recording sheets characterised by the coating used to improve ink, dye or pigment receptivity, e.g. for ink-jet or thermal dye transfer recording
  • B41M5/52—Macromolecular coatings
  • B41M5/5263—Macromolecular coatings characterised by the use of polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • B41M5/5281—Polyurethanes or polyureas

Definitions

• the present invention relates to a method for preparing a security document, and more particularly to those documents which are subject to considerable amounts of handling such as banknotes and driving licences.
• security documents should be durable; in other words they should be resistant to tearing, fold damage and soiling. Moisture and chemicals absorbed by such security documents during handling can lead to physical degradation. It is desirable that the substrate for such security documents is resistant to absorption. It is, of course, a prime requirement for such security documents that the print which is applied to the substrate should adhere well, especially under severe conditions involving mechanical abrasion or accidental laundering.
• Security documents of the kind with which this invention is concerned incorporate one or more security features, especially visible security features, to prevent or deter counterfeiting.
• security features which may be used include, for example, watermarks and security threads present in the paper.
• Security threads may be disposed entirely within the paper or may appear in so-called windows located between regions where the thread is positioned between the surfaces of the paper for example as present in the Bank of England Series E banknotes.
• the substrate It is normal in security documents for the substrate to be of sufficiently good quality such as to enable satisfactory embossing to be achieved, such as embossing produced by the known Intaglio printing and to ensure good wear properties.
• a coating composition involving a pigment is used for the production of security paper, e.g. as in WO-A-91/12372
• such pigment usually has a benefit in providing microporosity or roughness which enables satisfactory ink keying to be achieved.
• a security feature such as a watermark or windowed thread present in the substrate is to some extent obscured.
• Pigmented coatings are inherently weak resulting from the presence of the pigment which causes the binder to be less firmly attached to the substrate in specific locations.
• EP-A-813,321 describes a method of preparing a security document in which a substantially transparent coating composition comprising an unpigmented polyurethane which meets certain requirements is applied after a sizing agent on paper to prepare a security paper.
• This security paper may be printed on to form a security document.
• Such a method produces security paper which has performed well in the market. It is possible to further improve the soil resistance of the paper by having a thicker coating. However, it has been found that the thicker the coating, the more problems there are with ink adhesion of the printing on top of the coating. In particular the adhesion becomes poorer after the security document has been in circulation for some time, particularly with relatively thick printing such as Intaglio printing.
• the present invention provides a method of preparing a security document which comprises printing on at least one side of a security paper and thereafter applying to at least one side of the printed security paper over the printing a substantially transparent coating composition comprising an unpigmented polyurethane and/or polyacrylate, said coating composition being such as to provide a film, when cast on a glass surface, that has a König hardness of from 15 to 130 seconds, and also passes the water resistance test as defined by the following steps:
• the present invention also provides a security document comprising a security paper having printing on at least one side thereof and a coating composition as defined above applied over said printing.
• the polyurethane used in the coating in the present invention is the same as defined in EP-A-815,321 which is herein incorporated by reference.
• the aqueous polyurethane and/or polyacrylate may be in the form of an aqueous dispersion, for example having a polyurethane and/or polyacrylate content of 2 to 70 wt.%, especially 5 to 40 wt.%, more especially 5 to 30 wt.% with respect to the total weight of the dispersion.
• the coating may incorporate an extender such as a polyacrylate and hence be in the form of, for example, a urethane-acrylic blend; such a blend provides good water and chemical resistant coatings. Also, the low cost of an extender relative to that of the polyurethane results in the blend being considerably less costly than the polyurethane alone.
• the coating may be a polyurethane and/or polyacrylate dispersion with a one component pre-crosslinked polyurethane and/or polyacrylate or with a one component, blocked polyurethane which has isocyanate groups chemically bound to the polymer chains but which isocyanate groups are regenerated at those elevated temperatures which are generally used in the final stages of a security printing process, for example using heat from the printer driers.
• the coating may be a polyurethane and/or polyacrylate dispersion of a two-component product which can be crosslinked by using multi-functional reagents such as melamine/formaldehyde precondensate. Crosslinking agents which may be used are described later.
• the polyurethane may be, for example of the aliphatic polyester and/or aliphatic polyether type. It may also, for example, be an aliphatic polycarbonate polyurethane.
• the polyacrylate may be, for example, of the aromatic type, particularly a styrene/acrylic copolymer such as Neocryl 1092 obtainable from Neoresins.
• the polyacrylate may be the same or different as the polyacrylate extender.
• a mixture of a polyurethane and a polyacrylate are used, they can be used in any proportion, for example in a ratio of 90:10 to 10:90 solids content by weight, preferably 75:25 to 25:75.
• a polyurethane and/or polyacrylate composition for use in the method of this invention may include ingredients known to those skilled in the art such as catalysts, cosolvents and emulsifying agents and/or surfactants. Care has to be taken, however, because an emulsifying agent can detract from the performance of the coating under wet or humid conditions. Additionally, other known additives may be used such as defoamants, flow additives, thickeners and/or viscosity modifiers. In general an additive included in the coating composition should be kept to a minimum as important properties such as adhesion to the substrate may be adversely affected.
• various functional additives may be used in order to provide specific effects which enhance the security of a security document produced from the paper of this invention without significantly interfering with the general benefits provided by the unpigmented polyurethane and/or polyacrylate coating.
• pigments are added to coatings, especially to paper coatings to provide colour or opacity.
• the functional security additives which may be used in accordance with this invention are particulate materials which satisfy the following criteria:
• the functional additive is preferably a fluorescent or iridescent pigment.
• a security functional additive will provide some specific effect to enhance the security or recognisability of a security document produced in accordance with this invention and hence constitutes an additional security feature when such additive is present in the polyurethane and/or polyacrylate coating.
• security functional additives fall into three classes:
• the coating comprising the polyurethane and/or polyacrylate must be substantially transparent as explained herein, and preferably have a 100% modulus of greater than 4.0 mPa. It is desirable that the polyurethane and/or polyacrylate coating has an ultimate tensile strength of greater than 40 mPa, for example from 40 to 80 mPa, as well as having a König hardness of greater than 20 seconds, for example from 20 to 40 seconds.
• Extenders can be used in the formulation of the coating in order to reduce the cost; they may also impart useful properties such as improved adhesion of surface applied security features, such as holograms.
• Extenders which may be used in accordance with this invention are typically dispersions of water insoluble binders such as styrene/acrylic copolymers, acrylated vinyl acetate, vinyl chloride/ethylene copolymers, or vinyl acetate copolymers. They are generally unable to withstand both the water-resistance and hardness tests.
• An alternative extender is a VA/VEOVA copolymer, for example that sold under the trade name Vinamul 6975.
• the extenders function satisfactorily in terms of the criteria previously set out, provided that the composition comprising the polyurethane and/or polyacrylate and the extender possess the specified König Hardness and pass the water-resistance test.
• the extenders may be added at levels up to 70, preferably from 15 to 50, parts per 100 parts of the coating formulation. The strongest and most water-resistant extenders can be added at this level. Weaker and less water-resistant extenders clearly cannot be added at such high levels bearing in mind the properties specified for the coating composition.
• Crosslinking agents can be used to increase the water-resistance, including laundry resistance, and hardness of the polyurethane and/or polyacrylate and/or polyacrylates coating. They can be used to obtain the required properties from polyurethanes and/or polyacrylates which would otherwise be unsuitable. They can also improve the properties of the polyurethane and/or polyacrylate component thereby enabling greater quantities of extender to be used.
• Suitable crosslinking agents include polyaziridine, carbodiimide, isocyanate and zirconium salts. Other crosslinkers such as an epoxy resin may be used but are less practical due to their high cure temperatures or longer cure times.
• the dry coat weight of the coating applied over the printing is, for example, from 0.05 to 20g per square metre, preferably 0.5 to 10g per square metre, more preferably 1 to 7g per square metre and especially 2 to 6g per square metre. It is also possible for the security paper to be coated with a coating composition before it is printed. Any coating composition may be used, although desirably a coating composition meeting the same requirements as the coating composition defined above applied over the printing is used. In this case the coating composition applied under the printing may be the same or different as the coating composition applied over the printing.
• the dry coat weight of the coating composition applied under the printing is generally from 0.5 to 5g per square metre, preferably 1 to 2.5g per square metre.
• the total dry coat weight of the coating compositions applied before and after the printing is preferably 0.05 to 20g per square metre, more preferably from 0.5 to 10g per square metre, even more preferably from 3 to 10g per square metre, most preferably from 3 to 7g per square metre, especially 4 to 5g per square metre.
• Such further printing may, for example, be part of the design of the security document or may simply be a unique identifier for a particular security document, such as a number.
• the printing on the security document may be any type of printing, for example litho or intaglio or a combination thereof.
• the coating may be applied at any time after the first printing, but preferably after substantially all of the printing except optionally for minor additional printing such as unique identifiers. It has surprisingly been found that the coatings used in the present invention can be used over intaglio printing even though the intaglio printing has a thickness which is typically 40 ⁇ m but which can be significantly greater, e.g. about 85 ⁇ m, creating large peaks and valleys on the printed paper.
• the coating can be applied over all of the surface of the document, or only over parts of a surface. Thus same areas may be left uncoated.
• the method of the present invention can be used by a single security document manufacturer on paper provided by different paper manufacturers. There may also be a cost saving since it is only the final security document which needs to be coated and not large paper rolls, some of which paper may be wasted.
• the security paper may be prepared by any known method such as the method described in EP-A-815,321.
• paper-making fibres may be supplied to a papermachine, at least one security feature incorporated into the paper during its manufacture to produce the paper, and a sizing agent applied to the resulting paper to size the paper.
• Suitable security features are, for example, a watermark and/or an embedded thread or windowed thread which may itself optionally incorporate visual or a coverture security elements.
• a paper coating composition was prepared by adding the following components to water to provide a composition containing about 35% solids: Polyurethane - Witcobond WB785 40kg CX 100 Cross Linker 150g Antifoam 40g
• composition was then diluted before use to a suitable coating viscosity and to achieve the coat weights defined below.
• the first was uncoated paper having printing thereon to act as a comparison.
• the second had the above coating under the printing at a coat weight of 2.5 g/m 2 .
• the third and fourth were in accordance with the present invention.
• the third sample consisted of the same printed paper but with a coating only over the printing in accordance with the present invention. This coating had a coat weight of 2.5 g/m 2 .
• the fourth sample also consisted of the same printed paper but with the same coating being applied both under the printing at a coat weight of 2 g/m 2 and over the printing in a coat weight of 2.5 g/m 2 .
• a paper coating composition was prepared by adding 90 parts of Neocryl 1092, a polyacrylate obtainable from Neoresins, to 10 parts of water. The same tests set out in Example 1 were carried out and similar results were obtained showing the superiority of the present invention.
• a paper coating composition was prepared by mixing together the following components:
• Example 1 The same tests set out in Example 1 were carried out and similar results were obtained showing the superiority of the present invention.

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• Paper (AREA)
• Paints Or Removers (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (9)

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Citations (3)

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• 2002
  • 2002-02-19 GB GB0203916A patent/GB2385298B/en not_active Expired - Fee Related
• 2003
  • 2003-02-18 EP EP03250978A patent/EP1338430A1/de not_active Withdrawn
  • 2003-02-18 CA CA 2419190 patent/CA2419190A1/en not_active Abandoned

Patent Citations (3)

Non-Patent Citations (2)

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