GB2264672A - A method of making paper with a simulated watermark. - Google Patents

Abstract

Paper is provided with a simulated watermark by using a relief plate having an elevated part corresponding to the watermark which is mounted on a roll of a printing machine. Transparent ink is applied to the elevated part of the relief plate and is transferred to the rear face of sheets of paper. The transparent ink dries to form the simulated watermark. <IMAGE>

Description

Description of Invention "Improvements in or relating to paper and a method of making paper" THE PRESENT INVENTION relates to paper and a method of making paper.

High quality paper is frequently provided with a so-called "watermark". Conventionally such a mark is impressed into the paper during manufacture by means of a dandy roll or a projecting wire on a mould. A watermark is most visible when a sheet of paper is held up to the light, since in the region of the watermark the paper appears to be more translucent.

A watermark has to be incorporated into paper during the actual manufacture of the paper. This is usually done by using a dandy roll. Paper is manufactured as very large sheets, and is then cut to size. Because of inevitable errors in the cutting process it is extremely difficult to manufacture paper having a watermark present at exactly the same position on each sheet of the paper.

The cost of a dandy roll is significant, making it commercially necessary to make a large quantity of paper with any particular watermark.

The present invention seeks to provide an alternative improved method of relating paper with a "watermark", and paper made by the method.

According to this invention there is provided a method of producing paper with a simulated watermark comprising the steps of providing a relief plate having an elevated part corresponding to the watermark, mounting the relief plate on a roll of a printing machine, applying transparent ink to the elevated part of the relief plate, and transferring the ink to the rear face of sheets of paper, and permitting the transparent ink to dry to form the simulated watermark.

Conveniently, the said relief plate is mounted on the blanket roll of an offset printing machine, the ink being applied-to the plate via the inking rolls and a substantially smooth roll in the place of the plate cylinder of the machine.

Advantageously, the method includes the step of creating the relief plate from a laminate comprising a base layer and a layer of light sensitive material, areas of the layer of light sensitive material being selectively exposed to light, and the remaining areas of the layer of light sensitive material being removed by means of an appropriate solvent, to provide the desired relief plate.

Conveniently, the ink comprises a water-based ink.

Advantageously, the method may include the step of printing, in visible ink, on the front of the sheet of paper.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of part of an offset printing machine for use in producing paper with a "watermark" in accordance with the invention; and Figure 2 is an enlarged view of part of a plate used on the machine of Figure 1.

The present invention relates to a method of producing a "watermark" or, to be more precise, a simulated watermark, on paper after the paper has been manufactured. It has been realised that if a transparent ink is printed onto the back or reverse side of a sheet of paper, and the ink is then dried, the end result is a sheet of paper which, when held up to the light, appears to possess a greater degree of translucence in the areas where the ink has been printed on the paper. Transparent ink is ink which, when it has dried on the paper, does not present any significant colour, but which is still visible. The ink when dry, thus resembles a transparent varnish, in appearance. It is believed that if the ink is printed on the back or reverse side of the paper, part of the ink is absorbed into the paper, thus providing the described "translucence" effect.The paper thus presents the appearance of paper with a watermark, as the transparent ink, when dry, comprises a simulated watermark.

Referring now to Figure 1, the operative parts of a conventional offset printing machine are shown diagrammatically. The machine comprises the conventional inking rolls 1, only some of which are shown. The inking rolls are adapted to apply ink to a roll 2 corresponding to the plate cylinder which, in a conventional offset printing apparatus carries the plate. However, the roll 2 is a roll which is larger than a conventional plate cylinder. In the present arrangement the roll 2 does not carry a plate but has a smooth outer surface. The roll 2 contacts a blanket roll 3, the blanket roll 3 carrying an etched relief plate 4. Ink is thus transferred to the elevated parts of the relief plate 4. A sheet of paper 5 is pressed against the relief plate 4 carried by the blanket roll 3 by means of a pressure roll 6.The ink is transferred to the paper from the elevated parts of the relief plate 4.

Figure 2 illustrates part of the etched relief plate 4 in greater detail. The relief plate 4 consists of a substantially planar substrate or support 7 carrying elevated (or "relief") areas 8, 9 which together correspond to a desired "watermark". The elevated areas have planar upper surfaces which are slightly roughened.

A plate, such as the plate 4 illustrated in Figures 1 and 2 may be formed from a laminate of two sheets. The first sheet comprises a flexible base, which is preferably transparent and the second sheet comprises a material which is responsive to light, such as ultraviolet light. The laminate may be exposed to light through an appropriate mask, so that the second layer responds to the light, in the areas where the sheet is exposed to the light. Subsequently, using an appropriate solvent, the portions of the second layer of the laminate which were not exposed to the light are washed away. The exposed portions of the second layer remain as elevated "relief" areas which have substantially planar ink receptor surfaces.

It is preferred that the plate making process should involve an initial step of exposing the plate to light through the first sheet of the plate for a brief period of time, typically between 10 and 12 seconds, to maximise sensitivity of the second layer and to ensure that the two layers of the laminate are bonded together.

Subsequently the second layer of the plate is exposed to light through a film negative to form the image. The exposure time may be between 7 and 12 minutes. The plate is mounted in a processor where the plate is treated in a solvent to remove the unexposed area of the second layer.

The plate is then dried in an appropriate dryer and finished in a light finishing unit to eliminate surface tack. The dried plate is then further exposed to ensure that the remaining areas of light sensitive material of the second layer are fully exposed.

Various plates of this type are available commercially, but one particular plate which has been found to be especially satisfactory is a plate manufactured by Du Pont and sold under the Trade Designation CYREL CL (CYREL is a registered Trade Mark).

A relief plate of this type is mounted on the blanket roll by means of conventional blanket bars.

The transparent ink that is utilised is preferably a water-based transparent ink which can be dried by oxidation or absorption. Thus no special process steps are necessary to effect drying of the ink.

One ink which has been found to be particularly suitable is an ink sold by Zeller and Gmelin GmbH of D-7332 Eislingen of Germany under their Trade Designation A44346.

Turning again to Figure 1 of the drawings it is to be appreciated that in carrying out a method in accordance with the invention transparent ink as described above is applied to the inking rollers 1 and is then transferred onto the roll 2. Ink from the roll 2 passes to the planar upper surfaces of the raised relief areas 8, 9 on the plate 4, which is carried on the blanket roll 3. These raised areas 8, 9 correspond to a desired "watermark". The ink is then transferred to the back or reverse surface of a sheet of paper 5, forming a marking 10, as can be seen in Figure 1. This marking is a "reverse" of the desired watermark. The marking can, however, be placed at any desired accurately predetermined location on the sheet of paper, and many sheets of paper can be produced with the marking at the required position.Printing may then be applied in any conventional manner to the front of the sheet of paper, using ordinary visible ink.

By using a conventional offset printing machine, as described, when successive sheets of paper are fed through the machine, the printing effected by the machine is at precisely the same position on each sheet. Thus, the resultant "watermark" is at the same position on every sheet.

It is to be appreciated that when the sheet of paper 5 is held up to the light the marking 10 on the reverse side of the sheet of paper will provide the appearance of a simulated watermark, and because it is viewed through the paper, from the front side, it will appear te be the right way round, and not in "reverse".

It is to be appreciated that a single printing apparatus may be utilised to produce-any desired number of sheets of paper carrying any specific 1,watermark". If a new "watermark" is to be produced it is only necessary to provide a new plate, such as the plate 4, carrying the appropriate new "watermark". Since the plate can be produced quite cheaply it is commercially possible to produce paper in a modest quantity that carries a simulated watermark. The relief plate 4 may, in such a case, be mounted on a roll of any conventional printing machine, since the advantages of using the offset machine described above are more apparent with a long "run".

Claims (8)

CLAIMS:

1. A method of producing paper with a simulated watermark comprising the steps of providing a relief plate having an elevated part corresponding to the watermark, mounting the relief plate on a roll of a printing machine, applying transparent ink to the elevated part of the relief plate, and transferring the ink to the rear face of sheets of paper, and permitting the transparent ink to dry to form the simulated watermark.

2 A method according to Claim 1, wherein the said relief plate is mounted on the blanket roll of an offset printing machine, the ink being applied to the plate via the inking rolls and a substantially smooth roll in the place of the plate cylinder of the machine.

3. A method according to Claim S or 2 including the step of creating the relief plate from a laminate comprising a base layer and a layer of light sensitive material, areas of the layer of light sensitive material being selectively exposed to light, and the remaining areas of the layer of light sensitive material being removed by means of an appropriate solvent, to provide the desired relief plate.

4. A method according to any one of the preceding claims wherein the ink comprises a water-based ink.

5. A method according to any one of the preceding claims including the step of printing, in visible ink, on the front of the sheet of paper.

6. A method of producing paper with a simulated watermark substantially as herein described with reference to the accompanying drawings.

7. A sheet of paper provided with a simulated watermark by a method according to any one of the preceding Claims.

8. Any novel feature or combination of features disclosed herein.