Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SECURITY VAPER CONTAINING
~ES I CULATED BEADS
DESCRIPTION
Technical rield
This inven-tion 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.
Background Art
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. I-t is desired to provide papers which will be
15 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
20 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
25 provide security paper which contains very easily
visible identification when viewed by nonvisible
light, whereas this identification is not visible
when the paper is vlewed under normaL lighting. In
this way, one attcmpting to mimic the document may
30 not be alert to the fact that ordinary papcr cannot
be usecl~ Moreover, it is clesired to provide paper
which is not easily duplicated even when the party
attempting to mimic the document is alert to the fact
that the paper has a peculiar appearance under
35 nonvisible light.
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It is also important to provide a paper which is
economically producible, which is printable, as by enyraving
procèsses, without damage, and which can be viewed to insure its
genuine nature from either side of the paper.
_sclosure of Invention
In accordance with this invention, there is incorporated
into the paper furnish, cross-linked, polymeric vesiculated beads
havlng transparen-t walls and 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. ~Iowever, under
nonvisible light, these beads glow and provided bright spots
(which may have a distinctive coloration or combination of colora-
tions) 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.
In preferred practice, the security paper will contain
from 0.1 to 15 weight percent of such beads, preferably from 0.5
to 596 thereof, based on the total weight of the paper. This
paper may be calendered or uncalendered.
It is desired to point out that prior security papers
are frequently single sided in that the fibers or other identify-
ing devices concentrate at the wire side of the paper. In this
invention, the beads which are incorporated in the paper become
visible under nonvisible liyht at both sides of the
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paper, and this eases the burden of examination.
It is stressed that the vesiculated beads
under consideration contain many cells and are quite
different from ordinary hollow polymer beads in being
S 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 procduction of security papers.
The beads under consideration normally
10 contain an average of at leas-t about 5 cells per
bead, preferably at least about 10 cells per bead.
It appears that the presence of a large number of
cells in each bead is what allows the bead to avoid
collapse when paper containing the same is compressed
15 under the considerable force imposed in the
calendering operation.
It is stressed that the beads in this
invention have transparent walls, and the
multiplicity of cells retroreflects the incident
20 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
25 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 Eormed. I-t is unlikely that one
30 attempting to duplicate a security paper woul(l he
able to mimic the beads which are used herein.
It is also stressecl tha-t the appearance of
invisibility in ordinary light and easy visibility in
nonvisible light is an aspect of the fact that the
35 beads are ulliformly distributed throughou-t the body
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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 th0 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
10 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,
15 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
25 containing from 5% to 50~ of the acid or amine
monorner, balance the amide monomer. Ihe 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
30 amine, which is preferably ammonia. Thus, a
copolymer of 20% methacrylic acid with 80% acrylami(le
is illustrative of a preferred anionic retention aid.
The cationic amide copolymers are
illustrated by copolymers of acrylamide Wit}l diethyl
35 aminoethyl methacrylamide.
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Various other anionic and cationic resins
which may be used as the retention aid are discussed
in the Kirk Othmer "Encyclopedia of Chemical
Technology, third edition" Volume 16, at page 804
which points out that the usual fillers having a size
up to 5 microns are not effectively retained because
they are so small, thus provoking the use of
retention aids in the paper furnish. The beads used
herein are generally much larger, but their retention
10 on the Fourdrinier wire is enhanced by the
conventional retention agents nonetheless.
The preferred vesiculated beads are
styrene-cross-linked unsaturated polyester resins.
These are made into a vesiculated bead in
15 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 ~han a volume average oE about 10 microns in
diameter. For example, beads having a volume average
20 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
25 herein.
Various other patents are of interest to the
formation of vesiculated beads useEul in this
invention, particular attention being directed to
U.S. patents Nos. 3,8Z2,22~, 3,923,70~ and
30 3,933,579. This last~namecl patent clescribes the
vesiculatecl beads which are preferred herein, namely,
those having a ratio of granular diameter to mean
vesicle diameter of at least 5:1, a vesicle volulne of
Erom 5% to 95% of the volurne oE the granule, and not
35 more than about G0% pigment, by volume.
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The vesiculated beads used herein have a
highly cross-linked polymeric body which is
preEerably 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
10 an acid value of 10 to ~5 mgm K0~l 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
15 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
20 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% o~ the
25 unsaturated polyester cross-linked with from 55% to
65% of styrene.
The invention is illustrated as follows, it
being understood that all parts and proportions are
by weight, unless otherwise specified.
30 Example
Suitable pigmented vesiculated beads in
accordance with this invention are illllstrated in
ll.S. Patent No. 3,879,314 issued ~pril 22, 1975, see
particularly ~xample II. By proceeding in accordance
35 with said Example II and Usillg a polyester of 18%
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phthalic anhydride, 37~ maleic anhydride and 45%
propylene glycol dissolved in styrene to form a
solution containing ~1.8% 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 haYe an average size of about 25 microns and
contain an average of more than 10 cells per bead.
These beads are typically incorporated into a
10 paper furnish in wllich 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
15 adjusted to a pH in the range of ~.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
20 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 ~0
pounds per ream, and it was passed through a size
press in conventional Eashion and then calendered at
either 150 or 900 pounds per llnear inch at a
30 temperature of about 150~. to provide a printable
paper. This paper, when viewed with ordinary light,
appeared to be an ordinary paper, but when viewed with
ultraviole-t light was seen to have glowing spots all
over it, like salt scattered on black paper.
