PAPER PRODUCTS AND CHEMICAL FORMULATIONS FOR THEIR MANUFACTURE

Abstract: There is described a process for the manufacture or treatment of paper or a paper product. The method comprises applying to the paper product, either during manufacture or subsequently, a solution or dispersion of a rubber in an organic solvent or mixture of solvents, the solution or dispersion being at least substantially free of polymers containing perfluorinated alkyl groups. Synthetic rubbers such as neoprene are preferred. Papers prepared in accordance with the process are particularly suitable for use as security papers and banknotes.

Description: Title - Paper Products and Chemical Formulations For Their Manufacture This invention relates to novel paper products, a process for the manufacture of such products by chemical treatment of paper, and a chemical formulation utilized in that process. In particular, the invention relates security paper products, eg banknotes. Paper has been used for centuries, mainly for three purposes. First, paper is used to record thoughts or ideas by way of printing and writing. Secondly, paper is used as packaging or as packaging articles such as labels or cartons and bags of paper. Thirdly, paper is also used as a medium of exchange in the form of printed currency, banknotes, cheques etc. For many paper products it is desirable that the lifetime of the paper should be as long as possible. One example is items such as banknotes which are frequently handled and folded or rolled. Such items come into contact with moisture (eg as perspiration) during normal usage. Another example is paper used in documents such as passports or share certificates which are valuable and contain information which must be preserved over lengthy periods of time. There is therefore a need for long-lasting paper which will maintain its integrity over a long period of storage and/or after repeated handling. To date, however, this requirement has not been fully satisfied. Conventional papers normally absorb water or moisture to a considerable extent, with the result that the paper becomes soft and easy to tear, and also may spoil the contents of packaging in which it is used. The absorption of moisture also has an adverse effect on the other properties of the paper. For instance, it may be difficult or impossible to print or write on the paper and/or existing printed or written material may fade or become illegible. Paper used as packaging may fall apart or become torn; paper used in currency may have a short lifetime. One approach to this problem which is used is to coat paper with a varnish. This gives the paper a shiny appearance but is not waterproof and also gives no additional strength to the papers. More recently, processes have been developed to wax papers. The quality of printing and writing on a waxed paper is of reduced quality, and bonding of such papers is also not good. Another coating process comprises laminating the paper with plastic films such as PNC, polyester, HDP etc. However, these processes suffer from similar disadvantages to waxing. Lastly, plastic alternatives to papers are known which, whilst they are sturdy and waterproof and give good printing, are expensive and therefore not popular. Plastic alternatives to paper are costly and writing on them is not feasible. British Patent No 1095728 discloses surface treatment of materials with mixtures of polymers containing perfluorinated alkyl groups and any of a wide range of other polymers. Paper is one of the materials mentioned. International Patent Application WO98/14661 discloses a process for improving the water- repellency of papers and in particular to papers for use in banknotes. The process comprises the application of a formulation to the paper, the formulation being described only as a dispersion of a polymer or polymer precursor in organic solvents. The preferred polymers are graft copolymers, the precise nature of the copolymers not being specified. There have now been devised novel paper products, a process for the manufacture or treatment of such paper or paper products, and a chemical formulation for use in that process, which overcome or substantially mitigate the above disadvantages. According to a first aspect of the present invention, there is provided a water-repellent and washable paper. The paper may be in the form of a security paper or banknote. By the term "a washable and water-repellent paper" is meant a paper which is sufficiently water-repellent to survive exposure to moisture in normal usage and even a washing process. Such a paper is characterized by a very low degree of water absorption. This can be expressed in terms of the parameter known as the Cobb value. Papers in accordance with the invention may have Cobb values of between 0.01 and 20, more preferably of between 0.01 and 15, and particularly between 0.01 and 10. This is in contrast with papers conventionally used for security papers such as banknotes, for which the Cobb value is typically 50 or more. Despite the very low water absorption and Cobb value of the paper according to the invention, the paper is nonetheless printable, as well as having other advantageous properties such as improved tensile strength, wet strength and "burst factor". Consequently, the products may be more durable than conventional papers and increased lifetime. According to another aspect of the invention, there is provided a process for the manufacture or treatment of paper or a paper product, which method comprises applying to the paper or paper product, either during manufacture or subsequently, a solution or dispersion of a rubber in an organic solvent or mixture of solvents, the solution or dispersion being at least substantially free of polymers containing perfluorinated alkyl groups. The process according to the invention is advantageous in that the paper produced by the process has the improved properties referred to above, notably reduced, water-absorbing characteristics compared with conventional papers. In another aspect the invention provides a paper or paper product prepared by the process described above. The product may be a security paper or banknote. According to another aspect of the invention, there is provided a chemical formulation for use in the manufacture or treatment of paper or paper products, the formulation comprising a solution or dispersion of a rubber in an organic solvent or mixture of solvents, the solution or dispersion being at least substantially free of polymers containing perfluorinated alkyl groups. By "substantially free of polymers containing perfluorinated alkyl groups" is meant that the solution or dispersion contains no such polymers or contains very little of such polymers, eg less than 1 % w/w, or more preferably less than 0.1% w/w. Preferably, the formulation is free of such polymers. The rubber may be a natural rubber, but is preferably a synthetic rubber. The synthetic rubber is preferably a polymer of butadiene or a substituted derivative thereof. The synthetic rubber may be a homopolymer or may be a block or random copolymer of the butadiene or derivative thereof with another monomer. A particularly preferred synthetic rubber is that known as neoprene, ie polychloroprene (2-chlorobutadiene). The synthetic rubber is preferably present in the formulation at a level of from about 1% to 20% w/w, more preferably from 1% to 10% w/w, and most preferably about 5% w/w. The synthetic rubber is preferably dispersed or dissolved in a mixture of solvents. A wide variety of solvents may be used, including aromatic solvents such as xylene and toluene. Another example of a suitable solvent is methyl isobutyl ketone. Further components of the solvent system may be incorporated for reasons of economy, or to reduce the flash point of the formulation or to minimise noxious properties of the formulation. Such solvent components are mineral turpentine oil, turpentine substitute or white spirit, ie petroleum- derived solvents. A particularly preferred solvent is xylene. The xylene may be mixed with mineral turpentine oil or turpentine substitute, most preferably in approximately equal proportions. The formulation may also include further components which enhance the properties of the finished paper product or have other beneficial properties. Examples include preservatives or antioxidants (or optical whiteners) which prolong the life of the formulation. Such additives are generally present only at relatively low levels, typically less than 1%. Another example of additives which may be incorporated are plasticizers. Particularly preferred plasticizers are dioctyl maleate and dioctyl phthalate. Such compounds are typically present at the level of a few %, most commonly between 1% and 10% w/w, typically around 5% w/w. The formulation may also include one or more components to increase the hydrophobicity of the paper surface and/or reduce aging. An example of such a material is paraffin wax, again typically at the level of a few %, most commonly between 1% and 10% w/w, typically around 5% w/w. Other additives which may be present in the formulation include polyvinyl acetate (typically 1 to 10% w/w), ethylene thiourea (typically 0.2 to 0.5%), sulfur (typically 0.1 to 2%), magnesium oxide (typically 1 to 4%), zinc oxide (typically 1 to 10%) and titanium dioxide (typically 1 to 10%). Numerous other additives, such as activators, catalysts, accelerators, cross-linking agents etc, may also be included in the formulation where appropriate. The formulation of the invention may be prepared by dissolving or dispersing all of the components directly in the solvent. Alternatively, the rubber may first be mixed or compounded with components such as the inorganic oxides, antioxidants etc and the mixture then dissolved or dispersed in the solvent. Components such as paraffin wax and polyvinyl acetate may be added to the solvent either before or after mixing of the solvent with the rubber mixture. Typically, the formulation according to the invention has the following characteristics: Solid content 10-20% w/w pH 4-8 The process of the invention may be applied to any and all types of paper. The process may be applied during manufacture of the paper or paper product at any suitable stage. Alternatively, the process may be applied to a conventional paper at the end of the normal manufacturing process, or subsequently. The process may also be applied to completed paper products, eg assembled paper packaging units such as envelopes, boxes or cartons. Depending on the application, the external and/or internal surfaces of such packaging may be treated in accordance with the invention. Where the packaging is made of laminated papers, the external and/or internal layers may be produced from papers treated in accordance with the invention. The process of the invention is of particular utility in relation to security papers for use in, for instance, banknotes. Particularly in less developed countries the lifetime of banknotes may be very short (eg no more than a few months) and the regular replacement of banknotes in circulation represents a very costly matter. By extending the lifetime of banknotes by treatment in accordance with the process of the invention very considerable savings may be made. Security papers subjected to the process of the invention may also incorporate other security features, eg watermarking, security threads etc. The water repellency of the paper in itself represents a security feature, being readily demonstrable and distinguishing banknotes made from paper in accordance with the invention from counterfeit notes. Waterproof or water-repellent security papers and items, eg banknotes, produced from them represent a further novel aspect of the present invention. The process of the invention may be applied to any kind of paper made of any kind of pulp, cotton comber or rag, before calendering, before or after polyvinyl alcohol / gelatine bath or final processing. In the case of security papers, the process may be applied before or after application of a watermark, eg by cylinder mould, four dinier or other process. Similarly, the process may be applied before or after full or alternate embedding or window threading of any type of security thread, eg comet, continuous printed or unprinted, metallised or demetallised, positive text or negative text, magnetic or machine-readable threads etc. Coating by the process of the invention may also take place before or after incorporation of UN- detectable fibres. The process may also be applied after the paper is calendered and ready for use or printing. The process may be applied to all types of plain or printed papers, including currency, posters or packaging, before or after printing by any type of printing ink, including intaglio, magnetic, short-wave, UN, etc. Treated papers produced by the process of the invention may be used for any purpose, eg as currency (banknotes) of all denominations, secured documents, security papers, cheques, packaging papers. Papers for use in packaging may be converted into corrugated boxes, cartons, bags, or special purpose moisture-controlling packaging for soaps, detergents, medicines, processed and unprocessed food articles, fruit and vegetables, etc. The chemical formulation of the invention may be applied by various means, eg using a conventional varnishing machine, gravure machine, brush coating, dip coating or any other method of coating, or on-line during manufacture of the paper. The formulation may be applied either before or after printing, to paper sheets, paper web or any other paper article. Despite the reduced water absorptivity of the paper, it is nonetheless receptive to the printing process, eg by intaglio or dry offset printing. The process may be applied to any and all types of papers including banknote paper, security papers, craft papers, chromo-art, maplitho, yugoart, currency papers with or without security features. Plain or printed papers may be treated in the required quantity depending upon the requirements, in roll, sheet, container or any other desired form. The application of the process of the invention will now be illustrated by means of the following examples and accompanying drawing which shows schematically the stages in the production of a security paper containing a watermark and security thread. Example 1 polychloroprene 5 % w/w paraffin wax 5 % optical whitener 0.02 % dioctyl maleate 5 % xylene / mineral turpentine oil (50:50 mixture) to 100% The formulation is prepared by dissolving or dispersing the polychloroprene, paraffin wax, optical whitener (antioxidant) and dioctyl maleate (plasticizer) in the solvent mixture. Example 2 polychloroprene 5 % w/w paraffin wax 5 % optical whitener 0.02 % sulfur 0.2 % ethylene thiourea 0.3 % dioctyl maleate 5 % xylene / mineral turpentine oil (50:50 mixture) to 100% Prepared by the same method as Example 1. Example 3 polychloroprene 5 % w/w paraffin wax 5 % optical whitener 0.02 % sulfur 0.2 % ethylene thiourea 0.3 % dioctyl phthalate 5 % xylene / mineral turpentine oil (50:50 mixture) to 100% Prepared by the same method as Example 1. Example 4 polychloroprene 5 % w/w paraffin wax 5 % optical whitener 0.02 % sulfur 0.2 % ethylene thiourea 0.3 % dibutyl phthalate 5 % xylene / mineral turpentine oil (50: 50 mixture) to 100% Prepared by the same method as Example 1. Example 5 polychloroprene 5 % w/w paraffin wax 5 % optical whitener 0.1 % dioctyl maleate 5 % ethylene thiourea 0.3 % magnesium oxide 4 % polyvinyl acetate 5 % titanium dioxide 2 % zinc oxide 5 % xylene / mineral turpentine oil (50:50 mixture) to 100% The formulation is prepared by mixing the polychloroprene, titanium dioxide, zinc oxide, ethylene thiourea and optical whitener, and then dissolving or dispersing the mixture in the solvent, either after or before addition to the solvent of the paraffin wax, polyvinyl acetate and dioctyl maleate. Example 6 polychloroprene 5 % w/w paraffin wax 5 % optical whitener 0.1 % dioctyl maleate 5 % ethylene thiourea 0.3 % magnesium oxide 4 % titanium dioxide 2 % zinc oxide 5 % xylene / mineral turpentine oil (50:50 mixture) to 100% Prepared by the same method as Example 5, but omitting the polyvinyl acetate. Example 7 natural rubber 5 % w/w paraffin wax 5 % optical whitener 0.02 % sulfur 0.2 % xylene / mineral turpentine oil (50:50 mixture) to 100% The formulation is prepared by mixing the rubber, sulfur and optical whitener, and then dissolving or dispersing the mixture in the solvent, either after or before addition to the solvent of the paraffin wax. Referring to the drawing, a manufacturing line and process for a security paper incorporating a watermark and security thread (eg suitable for the printing of banknotes) contains the following stages: 1 roll of security thread 2 cylinder mould, dandee roll or the like for watermarking 3 vat 4 sizing 5 drying 6 sizing 7 PN A/Gelatin bath 8 drying 9 steaming 10 on-line coating machine for application of waterproofing formulation 11 calendering 12 calendering 13 finishing 14 finished roll sheet In the arrangement illustrated, the formulation of the invention is applied at the point 10, using an on-line coating machine. Alternatively, the process may be applied at other stages. For example, the treatment may be applied between stages 4 and 5, between stages 5 and 6, stages 8 and 9, stages 11 and 12, stages 12 and 13, stages 13 and 14, or subsequent to stage 14. The process of the invention, comprising treatment of the paper with the chemical formulation of the invention, may also replace the PV A gelatin bath at stage 7. It will be understood that the process of the invention may be applied at any suitable stage of the paper manufacturing process. In other paper manufacturing processes the sequence and methods of operations may be different to that illustrated, and the precise point at which the treatment according to the invention is carried out will generally not be important.

Claims: Claims 1. A process for the manufacture or treatment of paper or a paper product, which method comprises applying to the paper or paper product, either during manufacture or subsequently, a solution or dispersion of a rubber in an organic solvent or mixture of solvents, the solution or dispersion being at least substantially free of polymers containing perfluorinated alkyl groups. 2. A process as claimed in Claim 1 , wherein the formulation contains less than 1 % w/w of polymers containing perfluorinated alkyl groups. 3. A process as claimed in Claim 1, wherein the formulation is free of polymers containing perfluorinated alkyl groups. 4. A process as claimed in any preceding claim, wherein the rubber is a synthetic rubber. 5. A process as claimed in any preceding claim, wherein the rubber is a polymer of butadiene or a substituted derivative thereof. 6. A process as claimed in Claim 5, wherein the rubber is 2-chlorobutadiene. 7. A process as claimed in any preceding claim, wherein the synthetic rubber is present in the formulation at a level of from about 1% to 20% w/w. 8. A process as claimed in any preceding claim, wherein the solvent comprises one or more solvents selected from the group consisting of xylene, toluene, methyl isobutyl ketone, mineral turpentine oil, turpentine substitute and white spirit. 9. A process as claimed in any preceding claim, wherein the solvent comprises xylene. 10. A process as claimed in any preceding claim, wherein the rubber is dispersed or dissolved in a mixture of solvents. 11. A process as claimed in Claim 10, wherein the mixture of solvents includes xylene. 12. A process as claimed in Claim 11 , wherein the mixture of solvents comprises xylene and a petroleum-derived solvent selected from the group consisting of mineral turpentine oil, turpentine substitute and white spirit. 13. A process as claimed in any preceding claim, wherein the formulation further comprises one or more additional components selected from the group consisting of preservatives, antioxidants, plasticizers, paraffin wax, polyvinyl acetate, ethylene thiourea, sulfur, magnesium oxide, zinc oxide and titanium dioxide activators. 14. A chemical formulation for use in the manufacture or treatment of paper or paper products, the formulation comprising a solution or dispersion of a rubber in an organic solvent or mixture of solvents, the solution or dispersion being at least substantially free of polymers containing perfluorinated alkyl groups. 15. A formulation as claimed in Claim 14, which contains less than 1 % w/w of polymers containing perfluorinated alkyl groups. 16. A formulation as claimed in Claim 14, which is free of polymers containing perfluorinated alkyl groups. 17. A formulation as claimed in any one of Claims 14 to 16, wherein the rubber is a synthetic rubber. 18. A formulation as claimed in any one of Claims 14 to 17, wherein the rubber is a polymer of butadiene or a substituted derivative thereof. 19. A formulation as claimed in Claim 18, wherein the rubber 2-chlorobutadiene. 20. A process as claimed in any one of Claims 14 to 19, wherein the rubber is present in the formulation at a level of from about 1% to 20% w/w. 21. A formulation as claimed in any one of Claims 14 to 20, wherein the solvent comprises one or more solvents selected from the group consisting of xylene, toluene, methyl isobutyl ketone, mineral turpentine oil, turpentine substitute and white spirit. 22. A formulation as claimed in any one of Claims 14 to 21, wherein the solvent comprises xylene. 23. A formulation as claimed in any one of Claims 14 to 22, wherein the rubber is dispersed or dissolved in a mixture of solvents. 24. A formulation as claimed in Claim 23, wherein the mixture of solvents includes xylene. 25. A formulation as claimed in Claim 24, wherein the mixture of solvents comprises xylene and a petroleum-derived solvent selected from the group consisting of mineral turpentine oil, turpentine substitute and white spirit. 26. A formulation as claimed in any one of Claims 14 to 25, wherein the formulation further comprises one or more additional components selected from the group consisting of preservatives, antioxidants, plasticizers, paraffin wax, polyvinyl acetate, ethylene thiourea, sulfur, magnesium oxide, zinc oxide and titanium dioxide activators. 27. A paper or paper product prepared by the process of any one of Claims 1 to 13. 28. A paper or paper product as claimed in Claim 27, which is a security paper or banknote. 29. A water-repellent and washable paper. 30. A paper as claimed in Claim 29, in the form of a security paper or banknote. 31. A paper as claimed in Claim 29 or Claim 30, which has a Cobb value of between 0.01 and 20.

Inventors: KAPADIA SURESH BABUBHAI, KAPADIA, SURESH, BABUBHAI
Applicants: GHELANI MEENA PARESH, KAPADIA SURESH BABUBHAI, GHELANI, MEENA, PARESH, KAPADIA, SURESH, BABUBHAI
Application year: 1999
Main classification: D21H21
IPC codes: D21H17, D21H21