PROCESS FOR THE PREPARATION OF COATED CONTINUOUS SHEETS TO BE PRINTED BY IMPACT-FREE HEAT PRINTERS, AND SHEET THUS OBTAINED

Abstract: A procedure for the preparation of endless sheets coated for printing using non-impact, thermal transfer printers, and the sheet so constituted. It is characterized in that the product is composed of a base sheet made of a fibrous paper or synthetic material covered by a layer composed of lactone or spiropyrane type colorings or iron metallic complexes that react with weak organic acids, as well as of an inorganic phosphorescent pigment of the ZnS:Cu type of the appropriate particle size to produce phosphorescence in the predetermined time and wave-length, thus providing it printability and phosphorescence properties at the same time.

Description: 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. Such methods are described, e.g., in documents EP-A-0 784 698 and US-A-4,590,499. 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, such as that described in document US-A-5,149,139, which discloses a method of automatically detecting with a machine the presence of a previously-used postage-type stamp attached to a substrate (envelope) involving a marking substance, that can be a fluorescent substance, contained in an adhesive layer. 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. Document US-A-5,308,824 provides a recording material which can be inhibited from alteration of record, comprising a substrate, a first, undercoat layer containing an inorganic fluorescent pigment (that can be ZnS/Cu) and a second, recording layer. According to an embodiment thereof, the recording layer can be a heat sensitive recording layer. The recording layer cam also contain a dye precursor (lactone or spiropyrane or iron metallic complex), a developer, an activator and an absorbent material. This recording material is intended for providing a material which can be inhibited from alteration of record, thus having two layers superimposed on the support and is devised for being applied to monetary exchange documents, such as tickets, bank notes, prepaid cards and like documents. In this manner, according to US-A-5,308,824, if such a document is violated by erasing its outer, recording layer, the undercoat, fluorescent layer becomes visible, emitting light which is an evidence of its manipulation. Summary of the Invention. With the aim of solving the problems of franking and automatically locating and obliterating stamps and seals performed on sheets prepared for non-impact, thermal transfer printing, the present invention provides a procedure for the preparation of endless sheets coated for printing using non-impact, thermal transfer printers, as defined in claim 1. The present invention also provides a sheet that allows printing using non-impact, thermal transfer printers, as defined in claim 2. 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 automatically. 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 stamp. 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 prespecified 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: Dispersion A: 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 is reached. Dispersion B: 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. Dispersion D: 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/m 2 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 640 nanometers.

Claims: A procedure for the preparation of endless sheets coated for printing using non-impact, thermal transfer printers, characterized in that it includes applying by deposition, on sheets of a fibrous paper or synthetic composition, a single special coating containing some lactone or spiropyrane type colorings or iron metallic complexes that react with weak organic acids to produce coloring when heated via a thermal head, as well as activators to accelerate the said reaction, being present, moreover, absorbent materials and charges to absorb the resulting fusion products, and the deposited single special coating also containing an inorganic phosphorescent pigment of the ZnS:Cu type of the appropriate particle size to produce phosphorescence in a predetermined time and wave-length. A sheet that allows printing using non-impact, thermal transfer printers, characterized in that it is composed of a fibrous paper or synthetic material, with or without security devices, coated with a deposited single special coating according to Claim 1, the said deposited single special coating making the sheet able to be printed using thermal transfer printing heads and to produce phosphorescence when activated by ultraviolet light containing wavelengths of between 440 and 640 nanometers.

Inventors: MARGARIT DAROCA PEDRO, MARGARIT DAROCA, PEDRO
Applicants: KEYLINK GESTAO E INVESTIMENTOS, KEYLINK GESTAO E INVESTIMENTOS LDA
Application year: 1998
Main classification: B41M5
IPC codes: B41M3, B41M5, G07D7, B42D15