Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/40—Agents facilitating proof of genuineness or preventing fraudulent alteration, e.g. for security paper
  • D21H21/44—Latent security elements, i.e. detectable or becoming apparent only by use of special verification or tampering devices or methods
  • D21H21/48—Elements suited for physical verification, e.g. by irradiation

Definitions

• This invention relates to security paper containing vesiculated beads which are not visible when viewed by visible light, but which are easily seen when exposed to nonvisible radiation.
• Special papers have been developed for security purposes to help insure that the document is genuine. These papers are illustrated by the use of colored fibers, planchettes, water marks or special dyes. It is desired to provide papers which will be more difficult for the counterfeiter to duplicate. The special character of some of these papers is easily seen by close inspection under ordinary light, so anyone viewing the paper is alerted to the need for using a paper having a special appearance, and it is not too difficult to provide a duplicate paper. In some instances a special light is needed to see a dye in the paper, but it is still not too difficult to provide a paper containing a comparable concentration of the same dye. It is desired to provide security paper which contains very easily visible identification when viewed by nonvisible light, whereas this identification is not visible when the paper is viewed under normal lighting.
• cross-linked, polymeric vesiculated beads having a volume average particle size of at least about 10 microns, preferably at least 20 microns, up to about 35 microns, and which include pigment or dye which responds to nonvisible radiation, especially to ultraviolet light.
• These polymeric vesiculated beads are small enough so that they are not visible to the unaided eye, even when these beads are colored when so viewed and incorporated into white paper. However, under nonvisible light, these beads glow and provided bright spots (which may have a distinctive coloration or combination of colorations) to identify the paper and distinguish it from ordinary paper as well as other special papers having a different density of bright spots and/or spots of different coloration.
• the security paper will contain from 0.1 to 15 weight percent of such beads, preferably from 0.5 to 5% thereof, based on the total weight of the paper.
• This paper may be calendered or uncalendered.
• the vesiculated beads under consideration contain many cells and are quite different from ordinary hollow polymer beads in being load bearing. As a result, these beads can be present in paper which sustains the pressure of the calendering and engraving processes which are involved in the production of security papers.
• the beads in this invention have transparent walls, and the multiplicity of cells retroreflects the incident light to produce a very bright spot of emitted light when the paper is appropriately irradiated. It is very difficult to duplicate the brightness of the vesiculated beads using plastic beads of different character. Moreover, the most effective way to provide the beads which are used herein is to incorporate the pigment or dye into the cell walls at the time of their production, and it would be very difficult to add a corresponding coloration after the beads have been formed. It is unlikely that one attempting to duplicate a security paper would be able to mimic the beads which are used herein.
• the appearance of invisibility in ordinary light and easy visibility in nonvisible light is an aspect of the fact that the beads are uniformly distributed throughout the body of the paper. This uniform distribution of the beads throughout the body of the paper requires that the vesiculated beads be added to the paper furnish. It is found that when the beads are so added, they are effectively retained in the paper as the water and some of the fines and mineral filler used in papermaking pass through the Fourdrinier wire in conventional papermaking.
• Bead retention can be enhanced when conventional retention aids are employed, though this is not essential. Both anionic and cationic retention aids are useful, but anionic retention aids are more efficient.
• the vesiculated beads are distributed quite uniformly throughout the paper and, while many of them are buried within the paper so as to be invisible on casual inspection, they will nonetheless pick up nonvisible light and glow in the visible range to provide a bright spot which is easily seen.
• the retention aids which have been found to be useful herein are themselves well known, and many are available in commerce. Acrylamide and methacrylamide copolymers with monoethylenic acids or monoethylenic amines are preferred, these generally containing from 5% to 50% of the acid or amine monomer, balance the amide monomer.
• the anionic copolymers which are preferred will usually contain acrylic or methacrylic acid as the acid component, and these are rendered anionic with the aid of an amine, which is preferably ammonia.
• a copolymer of 20% methacrylic acid with 80% acrylamide is illustrative of a preferred anionic retention aid.
• the cationic amide copolymers are illustrated by copolymers of acrylamide with diethyl aminoethyl methacrylamide.
• the preferred vesiculated beads are styrene-cross-linked unsaturated polyester resins. These are made into a vesiculated bead in conventional fashion, as illustrated by U.S. Pat. No. 3,879,314.
• the size of the vesiculated beads under consideration may vary considerably, but is generally larger than a volume average of about 10 microns in diameter. For example, beads having a volume average diameter of from about 10 to about 35 microns are conveniently prepared and fully useful in this invention. As the bead size increases above about 20 microns, they become particularly easy to see when properly exposed, and are thus preferred for use herein.
• the vesiculated beads used herein have a highly cross-linked polymeric body which is preferably constituted by a carboxyl-functional unsaturated polyester resin cross-linked with an ethylenically unsaturated monomer copolymerizable therewith.
• the unsaturation in the polyester is preferably maleate unsaturation, these polyesters being themselves well known and illustrated hereinafter. It is preferred that the polyester have an acid value of 10 to 45 mgm KOH per gm.
• the unsaturated monomers used for cross-linking are also well known and are water insoluble monomers typically illustrated by styrene or vinyl toluene.
• the polyesters and monomers are more fully discussed in U.S. Pat. No. 3,879,314 which shows the production of vesiculated beads using a water-soluble polyamine containing at least three amine groups per molecule and having a dissociation constant in water (pKa value) of 8.5-10.5, typically illustrated by diethylene triamine.
• the polyamine is used in a concentration providing at least 0.3 amine groups per polyester carboxyl group, usually from 0.5 to 1.4 amine groups per polyester carboxyl group. It is preferred to have from 35% to 45% of the unsaturated polyester cross-linked with from 55% to 65% of styrene.
• Suitable pigmented vesiculated beads in accordance with this invention are illustrated in U.S. Patent No. 3,879,314 issued April 22, 1975, see particularly Example II.
• a polyester of 18% phthalic anhydride, 37% maleic anhydride and 45% propylene glycol dissolved in styrene to form a solution containing 41.8% of the polyester
• vesiculated beads pigmented with a pigment which glows when irradiated with ultraviolet light, to contain about 19.0% pigment, by volume are provided.
• These beads have an average size of about 25 microns and contain an average of more than 10 cells per bead.
• beads are typically incorporated into a paper furnish in which 800 pounds per ton of softwood kraft, 1200 pounds per ton of hardwood kraft, 300 pounds per ton of clay, 20 pounds per ton of rosin size, and 30 pounds per ton of alum are mixed into water to a consistency of about 3%.
• the pH is adjusted to a pH in the range of 4.5 to 6.5 by the addition of concentrated sulfuric, and this provides the furnish which is modified by the addition of beads in this invention.
• the above proportions are in pounds per ton of finished paper basis.
• This furnish is modified to include 4% or 6% of the vesiculated beads and 1.5% of titanium dioxide, anatase, based on solids content and is supplied to the head box by passing the mixture through a valve in which the solids concentration is reduced to 1.5%.
• the paper made from this bead-containing furnish had a basis weight in the range of 37 to 40 pounds per ream, and it was passed through a size press in conventional fashion and then calendered at either 150 or 900 pounds per linear inch at a temperature of about 150°F. to provide a printable paper.
• This paper when viewed with ordinary liglit, appeared to be an ordinary paper, but when viewed with ultraviolet light was seen to have glowing spots all over it, like salt scattered on black paper.

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Cited By (7)

Citations (3)

• 1986
  • 1986-10-02 EP EP86113634A patent/EP0219743A1/de not_active Withdrawn
  • 1986-10-03 FI FI864014A patent/FI864014A/fi not_active Application Discontinuation
  • 1986-10-03 CA CA000519706A patent/CA1282913C/en not_active Expired - Fee Related

Patent Citations (3)

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