WO1997006959A1

WO1997006959A1 - Producing a raised fine-line printed image

Info

Publication number: WO1997006959A1
Application number: PCT/GB1995/001904
Authority: WO
Inventors: Kenneth Arnold Lavender; Adrian Aspinall
Original assignee: Walsall Security Printers Limited
Priority date: 1995-08-11
Filing date: 1995-08-11
Publication date: 1997-02-27
Also published as: AU3187795A

Abstract

After printing a flat multi-colour image by offset-litho, or other suitable process, the image is raised by embossing to produce a fine-line image having the appearance and feel of an intaglioprinted image.

Description

PRODUCING A RAISED FINE-LINE PRINTED IMAGE

Producing a raised fine-line printed image, in which lines of the image are discernibly raised in the finished document or article to give a tactile effect, is ordinarily achieved by intaglio printing using an engraved plate; the design to be printed is engraved or etched into a plain face of a copper plate, the plate is inked (and doctored to remove ink from the face itself), and a substrate pressed against the plate to take up the ink from the engraved design and create the image on the substrate.

Intaglio printing,and especially multi-colour intaglio printing, is a very expensive process commercially. It is accordingly used mainly for speciality printing, such as printing currency notes and security documents, often in combination with offset litho printing to produce areas of flat image in the same document.

It is an object of the present invention to enable a raised fine-line printed image to be created in a relatively inexpensive manner.

The invention provides, in one of its aspects, a method of producing an intaglio-like fine-line printed image in which the image is printed substantially flat and subsequently raised by embossing. Such method can be used equally with multi¬ colour as with single colour printing. Embossing can be effected in a single pass, and areas of full (convential) embossing can be achieved simultaneously. Embossing depth can be varied infinitely within the limits of the structural integrity of the paper or the substrate employed.

There now follows a description, to be read with reference to the accompanying drawings, of a method of creating a document, having a raised multi-colour printed image, which illustrates the invention by way of example.

The accompanying drawings illustrate successive steps in producing an embossing set comprising a female embossing plate and a male force which correspond in their pattern to a preselected multi¬ colour image to be printed.

In preparation for colour printing of a paper security document, colour-separated photographic representations of a multi-colour fine-line image which is required to be raised are produced in a customary manner. These colour-separated representations are then combined into a single representation on photographic film to show all elements of the multi-colour image which are to be raised (hereinafter referred to as the raised image elements) .

A plain face of a quarter inch (6.35mm) thick copper plate 10 (Figure 1 ) is coated with a photo resist material 12. The prepared film 14 is placed in vacuum contact with the resist-coated face and exposed to strong light from a suitable source 16, so causing hardening of the areas of resist not coinciding with the raised image elements as presented by the film.

After exposure (Figure 2) the unhardened areas of the resist, which had been protected from the light by the film, are acid etched to a predetermined depth which is related to the minimum height to which any part of the raised image is to be raised.

A low relief etch 18, corresponding to the raised image elements, is so created in the face of the copper plate, the depth of the etch depending upon the fineness of the detail and the type of paper to be used. A vacuum formed male plastics matrix is now cast from the etched copper plate, so creating a first embossing set comprising the matrix

(male die) and copper plate (female die) . A sample of the paper to be used is pressed between the matrix and the plate to check that the etch depth is correct for the embossing effect to give the minimum raising required.

If satisfied with the low relief depth of the copper plate, engraving tools are next employed to create higher relief depths 20 (Figure 3) where required for such parts of the raised image elements as are to be more greatly raised than the minimum. Careful attention is given to the profile of the higher relief engraving, since a correct profile is important in ensuring that the paper can be embossed into the higher relief regions without bursting of the fibres of the paper. A second plastics matrix 22 (Figure 4) is now cast from the copper plate and a further sample of the paper embossed in the second embossing set so created, in order to assess the final quality of the copper embossing plate 10.

If satisfied with the performance of the embossing plate, a single vacuum formed plastics plate 24 is created from the second matrix, so making an exact duplicate of the copper embossing plate 10.

A complete multi-colour proof is now produced and embossed in register with the colour print by means of a final embossing set comprising the female plate 24 (placed above the print) and a force 26

(placed below the paper) . A multi-colour printed document is so produced in which the image is selectively raised, to a variety of heights in the same document, in a manner giving the appearance and feel of having been created by intaglio printing.

The force can be formed at the same time as the plastic plate 24, the assembly incorporating matching pins and holes to guarantee registration between the plate and the force. A force can be produced on an embossing machine using powder, liquid and heat, the choice of production method being dependent upon the material to be embossed and the length of printing run intended.

On acceptance of the embossed proof, duplicates of the plastic plate 24 are formed from the second (final) matrix 22 to provide the total number of printing images which there will be on a production sheet. Pin registered forces are produced at the same time.

A production run of security documents are printed by offset-litho (or other suitable printing process) using such inks as will give the appearance of intaglio printing when embossed. A sheet of heavy gauge stable polyester film is printed at the same time to act as an overlay when positioning multiple dies and forces to register with the completed multiple sheets of security documents.

Claims

CLAIM

1. A method of producing an intaglio-like fine- line printed image in which the image is printed substantially flat and subsequently raised by embossing.