The present invention relates to a procedure for the preparation
of endless sheets coated with a prepared coating for printing using non-impact,
thermal transfer printers, and which are also phosphorescent when activated by
light containing wave lengths of between 440 and 640 nanometers, as well as to
the sheet so constituted.
These sheets are designed for use in the manufacture of adhesive
postage stamps and seals which must be obliterated (rubber-stamped) by automatic
obliteration machines. The said sheets may then be bonded on their reverse side
with damp-reacting adhesives or self-adhesive materials so that they can be applied
after printing and punching onto the letters or objects to be sent, according
to postal or other requirements, in a manner customary up until the present in
the sending of correspondence and bulk franking.
Current State of the Art.
Currently, postage stamps are manufactured by two different methods:
- 1) Via thematic motif printing according to the series, together with the face
value of the same.
- 2) Via printing of the thematic motif, on paper prepared for non-impact, thermal
transfer printing which allows the possibility for the franking value to be post-printed
using non-impact, thermal transfer printers at the moment of franking when the
weight and destination of the correspondence to be franked is known.
On the other hand, in both cases, to invalidate the stamp once the
letter or similar has been franked and to ensure in this manner that the stamp
may not be used again for the same object, it is stamped with inks via a rubber
stamp. This process receives the name of obliteration.
The obliteration process may be manual or automatic.
The manual obliteration process demands that an employee from the
Post Office or similar entity manually stamps by rubber stamp all and each one
of the stamps that have been affixed to the corresponding envelopes.
The automatic process necessitates automatic stamp detection, in
such a manner that the stamp's position on the envelope is known in order to be
able to obliterate or stamp it automatically. For this purpose there currently
exist machines capable of fulfilling this function based on the stamp emitting
phosphorescent light so that its exact position may be detected.
It has been demonstrated that non-impact thermal transfer printing
greatly facilitates the franking of correspondence, and allows the use of self-adhesive
stamps with a face value printed in the act of franking, this entire process fusing
with the possibility of automatic obliteration with the object of invalidating
the stamp once it has been used.
The technique of the invention claimed in this patent solves the
problems of franking and the automatic obliteration of stamps and seals performed
on sheets prepared for non-impact, thermal transfer printing, used in the sending
of correspondence or parcels. The present invention unites in a single paper or
synthetic sheet the following properties:
- 1. That the said sheet is printable by non-impact, thermal transfer printers
so that the franking value or other logotypes may be printed on it.
- 2. That at the same time it is phosphorescent so that it may be obliterated
Also, at the same time, this processed, paper or synthetic sheet
may be printed using any of the traditional printing methods: Offset, Gravure-printing,
Flexography, Transfer, etc. to create the non-variable motifs on the adhesive
Description of the obtention procedure and of the product so obtained.
The coat to be applied on the sheet consists of some lactone or spiropyrane
type colorings or iron metallic complexes that react with weak organic acids to
produce the coloring when heated via a thermal head, as well as activators to
accelerate the said reaction. Also absorbent materials and charges to absorb the
resulting fusion products. Moreover, it contains an inorganic phosphorescent pigment
of the ZnS:Cu type of the appropriate particle size to produce phosphorescence
in a pre-specified time and wave-length.
Example of preparation
A practical preparation example of the sheets, object of the invention,
is that described below:
The following dispersions are prepared separately:
10 parts by weight of a coloring derived from spiropyrane (e.g.:
3-diethylamino, 6-methyl, 7-anilino flourane) are dispersed over 100 parts by weight
of a base containing 10% polyvinyl alcohol dissolved in water. After a good dispersion,
it is processed in a colloidal mill until an average particle size of 1 micron
25 parts by weight of Bisphenol-A and 30 parts by weight of Parabenzylbiphenile
are dispersed over 100 parts by weight of a base containing 10% polyvinyl alcohol
dissolved in water.
After a good dispersion, it is processed in a colloidal mill until
an average particle size of 2.5 microns is reached.
Dispersion C: 30 parts by weight of calcium carbonate precipitate are
dispersed over 100 parts by weight of water. After a good dispersion, it is processed
in a colloidal mill until an average particle size of 3 microns is reached.
20 to 80 parts by weight of SZn:Cu phosphorescent pigment are dispersed
over 100 parts by weight of water. Once these dispersions have been performed,
they are mixed together to obtain the preparation to apply on the cellulose or
synthetic supports (that is, the sheets), by preparing:
- 80 parts by weight of dispersion A.
- 155 parts by weight of dispersion B.
- 185 parts by weight of dispersion C.
- 100 parts by weight of dispersion D.
The viscosity and solids in the preparation are adjusted to obtain
the correct application characteristics according to the machinery used with the
object of obtaining a deposition of about 10 gr/m2 in a dry state.
The deposited coat has the properties of:
- 1. Being able to be printed using thermal transfer printing heads.
- 2. Producing phosphorescence when activated by ultraviolet light.
The sheets so obtained are therefore, base sheets that may be of
a fibrous paper or synthetic composition, with or without security devices, covered
with the special coating earlier described, that gives them the property of being
able to be printed using thermal transfer printing heads and producing phosphorescence
when activated by ultraviolet light containing wavelengths of between 440 and