AU674740B2 - Postage stamp - Google Patents

Description

e- I 1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION S P C F C T 0 FOR A STANDARD PATENT

ORIGINAL

s s o o o o Name of Applicant: LEIGH-MARDON PTY. LIMITED, A.C.N. 004 432 633 e o r r r o s s o a Actual Inventor: Address for Service: Invention Title: Details of Associated Syd Gilding SHELSTON WATERS 55 Clarence Street SYDNEY NSW 2000 "POSTAGE STAMP" Provisional Application No: PL9377 dated 11th June, 1993 The following statement is a full description of this invention, including the best method of performing it known to us:- -2- This invention relates to a method of printing a luminescent coating on a postage stamp, to an ink suitable for use in the method, and to a stamp when manufactured by the method.

Postage stamps are well-known and have been sold in great variety. Most stamps nowadays bear images on the face side printed in a plurality of colours by means of any one of a variety of printing processes and usually have gummed or selfadhesive backings. The stamps are sold in sheets, rolls, booklets, and individually.

When self-adhesive backings are used, a water-soluble layer may be interposed between the adhesive and the backing to assist philatelists to recover used stamps.

In many countries a stamp is required to be luminescent so as to be detectable by apparatus at a mail centre. By luminescent is meant light emission, not due to incandescence, for example phosphorescent, fluorescent and the like. Luminescence may be achieved by employing a luminescent coated paper as the printing stock or by overprinting the preprinted stamp with a luminescent coating. In the latter case, the luminescent coating may cover the whole surface or may be in a striped, stippled or Sother pattern.

The luminescent coating is required to meet stringent requirements. As well as being suitable for detection, the coating must be colour and rub fast, not adversely 20 affect the underlying colours, permit penetration and drying of cancelling inks, and so on1.

In the manufacture of such stamps, the paper stock is printed by a conventional means lithography, letterpress, etc.) in the normal manner with for example four colours (black, yellow, magenta and cyan) "wet on wet".

:25 It is then necessary to allow the printing ink to dry before applying the overlying phosphor varnish.

It is an object of the present invention to provide an improved method for the manufacture of such stamps.

According to one aspect, the invention consists in a method of manufacture of a postage stamp comprising the steps of: printing with ink of at least one colour on the face side of the stamp, -3applying a UV curable luminescent varnish to the face side of the stamp and curing the luminescent varnish by UV radiation. Preferably the T TV curable luminescent varnish applied in step is a phosphor varnish and is applied while the ink applied in step is still wet over the wet ink. In a highly preferred method according to the invention steps and are conducted by means of offset lithography or letterpress printing.

Previously used phosphor varnishes were difficult to apply successfully because where high concentrations of the phosphor pigment were used this often separated from the varnish and resulted in varying levels of luminescence on the printed stamp. If the proportion of phosphor pigment is reduced, the amount of varnish that has to be applied is such that the printed matter remains wet and the printed sheets stick together when piled up in the delivery of a press. The process of the invention overcomes this problem by instantly drying the varnish so that there is no adhesion between printed sheet stamps.

Although varnishes which are UV curable are known and have been used in the past to produce high-gloss finishes on printed material, those varnishes have not contained phosphors. It has been thought that phosphorescent dyes such as have been used in stamp detection varnishes would be adversely affected ("blinded") by UV radiation of the intensity used during normal UV curing.

It has now been found that a varnish composition can be selected for use on stamps which is luminescent and which is both radiation curable and nLains adequate phosphorescence for detection. Moreover the selected composition can be applied "wet on wet" and thus yields significant improvements in efficacy of stamp 25 manufacture.

According to a secr.ad aspect, the invention consists in a stamp when manufactured according to the first aspect.

The invention will now be more particularly described by way of example only: For use in the invention a UV curable phosphor varnish was prepared by combining:

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3 parts of a low viscosity, UV curable, gloss varnish supplied by Sicpa Security Inks Pty. Ltd. of 3 Millers Road, Brooklyn, Victoria, and 1 part of Helecon 3336 phosphor supplied by Chemical and Petroleum Industries of 20 Ponting Street, Williamstown, Victoria.

A conventionally colour separated stamp design was printed on an offset lithographic press fitted with UV drying facilities. Four colours were printed with conventional inks followed immediately by a phosphor varnish as described above.

This is known as printing wet-on-wet. The paper stock was a self adhesive grade supplied by Fasson Pty. Ltd. of Hewittson Road, Elizabeth, South Australia and comprised a face stock of "Redan label paper", 80 gsm from APPM, Burnie, Tasmania, a water soluble layer and a conventional pressure sensitive adhesive with a siliconised paper backing. Other papers could be used, for example, a PVA gummed, clay coated paper such as supplied by CPL of Macclesfield, Cheshire, UK. The conventional inks used were from Colortron, 30 Crown Avenue, Mordialloc, Victoria but could also be UV curable inks supplied, for example, by Sicpa.

The printing plate can, for example, be a lithographic plate or a dry offset plate with a suitable pattern imposed upon it. This pattern may be comprised of a solid area, or bars or a line ruling or screen suitably arranged to suit the stamp design being .printed or may be a frame surrounding the printed area or the like.

20 The printed sheets may then be finished by die cutting to simulate a perforation if a self adhesive paper is used or by pin perforation if a PVA glued paper is used. The final article is then obtained by guillotining the sheets to final size. If I desired, the final article may be produced as rolls, booklets or in other forms.

It will be understood that although the invention is herein described with 25 reference to UV cure, similar results could be obtained by electron beam or other forms of irradiation and such methods are comprehended within the scope of the invention.

Claims (6)

1. 2. A method according to claim 1 wherein the UV curable luminescent varnish is a phosphor varnish.
2. 3. A method according to claim 1 or 2 further comprising the step of applying the UV curable luminescent varnish of step to the ink of step while the ink of step is wet.
3. 4. A method according to any one of the preceding claims wherein steps and are conducted by means of offset lithography or letterpress printing. A method according to any one of the preceding claims wherein the ink of step is UV curable.
4. 6. A method according to any one of the preceding claims wherein the stamp comprises a pressure sensitive adhesive on the opposite side to the face side of the stamp.
5. 7. A postage stamp manufactured by a method according to any one of claims 1 20 to
6. 8. A method of manufacturing a postage stamp according to claim 1 and substantially as herein described with reference to the Example. DATED this 17th Day of October, 1996 "LEIGH-MARDON PTY. LIMITED :25 Attorney: IAN T. ERNST Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS ABSTRACT The present invention relates to a method of manufacture of a postage stamp comprising the steps of: printing with ink of at least one colour on the face side of the stamp, applying a UV curable luminescent varnish to the face side of the stamp and curing the luminescent varnish by UV radiation. o a a o *e 6