NO803132L - SHEET MATERIALS WITH PICTURES AND PROCEDURES FOR THEIR PREPARATION. - Google Patents

Abstract

An unobtrusive image is applied to paper or other sheet material by means of a charged droplet printer, for example an ink jet printer. The unobtrusive image applied may perform the function usually associated with a watermark in paper, but in contrast to a watermark, may be applied to papers during their production on high speed wide deckle machines or to coated papers. The method is particularly suitable for unobtrusively imaging pressure sensitive copying material.

Description

The present invention relates to sheet material which carries an inconspicuous image and a method for its production. The inconspicuous image can e.g. given the paper to give an invention indication. The invention applies in particular, but not exclusively, to paper-sheet materials.

Watermarking using a dandy roller and rubber marking using a raised image on a press roller are well-known means of applying a discreet or inconspicuous image to paper to indicate its origin.

However, watermarking and rubber marking contribute significantly to the price of the paper and have therefore mainly been used for high-quality and high-priced paper, such as e.g. "representative" paper. Watermarking and rubber marking are usually uneconomical for papers produced at high speed and/or on wide paper machines. A further problem is that in the area of the watermark or rubber stamp, certain of the paper's properties will be affected, e.g. density, absorbency, porosity and smoothness. This can be disadvantageous under certain circumstances, e.g. if the paper is to be coated at a later stage and you want a uniform surface to receive the coating. In any case, watermarking and rubber marking are of limited value in the case of coated papers because the watermark or rubber mark will. covered by the coating.

It has now been found that printing techniques in which electrically charged droplets of the marking material are passed through an electric or magnetic field which directs their path towards a material to be printed provide a means of applying

a discreet or unobtrusive image on coated or uncoated papers or other sheet materials, even where high production speeds or wide webs are used. Such printing techniques that include ink jet printing and printing with electrostatic cloth are hereafter called charged drop printing techniques. They are in themselves well known. Such printing is e.g. described in an article entitled "Jet Set" in the British Printer, June 1980, and in the British Patents no.

1,354,890, 1,432,366, 1,461,385, 1,462,193, 1,464,370, 1,479,963, 1,491,234, 1,500,908 and 1,533,659.

According to a first aspect of the invention, a sheet material is produced which carries an inconspicuous image applied by printing with charged droplets, preferably black-jet printing.

According to another aspect of the invention, a method is provided for producing a sheet material with an inconspicuous image comprising applying the image to the sheet material by means of a printer with charged droplets, preferably an ink jet printer.

The sheet material can e.g. be paper or coated paper. In a preferred method according to the invention, the printer is mounted on the paper-making or paper-coating machine on which the paper or the coated paper is produced, whereby the path speed through the printer is the same as the path speed through the machine. Usually, a number of printers will be arranged across the width of the web.

Marking material used to provide a discreet or inconspicuous image can be an ink or any other material that provides a contrast to the sheet material, e.g. a resin or other substance which has the effect of rendering the paper sheet material to which it is applied transparent.

The invention is particularly suitable for use with pressure-sensitive copying materials because copying materials are not subjected to pressure during printing (any change in the local properties of the base material caused by water or rubber marking can be particularly unfavorable to the functional performance of a pressure-sensitive copying material). The copying material is preferably of the type where the image formation occurs as a result of a reaction between two individually colorless reactants which are brought into contact with each other under the influence of image printing to form a colored product. In most commonly used systems of the type just described, one of the reactants is contained

(the color former) in solution in microcapsules that can be crushed under the application of pressure to release the contents for contact with the second reactant (the color developer).

Pressure-sensitive copying systems employing microcapsules in the manner just described may be "self-supporting" or of the transfer type. In the transfer type, an upper sheet is coated on the lower surface with a coating of microcapsules containing color former solution and a lower sheet is coated on the upper surface with a color developer. Intermediate sheets coated with color developer on the upper surface and microcapsules containing color former on the lower surface can be provided if more than one copy is desired. In the "self-supporting" type, one surface of the sheet carries a coating preparation containing both microcapsules and color developer. Alternatively, both microcapsules and color developer can be present in the thickness of the sheet. As an alternative to the use of microcapsules (apart from the latter embodiment), the color former solution can be present as "bubbles" in a pressure-breakable coated matrix, e.g. of gelatin or wax.

The present method can be used to apply a discrete or inconspicuous image to any surface of the upper, lower or intermediate sheets of a transfer system as just described, or to any surface of a self-supported sheet as just described.

The reactants used in pressure-sensitive copying materials for discrete or inconspicuous images according to the invention may be conventional, e.g. the color former can be fluorans, phthalides or spirobipyrans. and the color developers can e.g. be acid clays, phenolic resins or salts of certain aromatic acids. Alternatively, one reactant may be an aromatic solvent of N,N<1->dibenzyl dithiooxamide and the other reactant may be a nickel rosin derivative. Because the nature of pressure-sensitive copying materials is now very well known and is described extensively in the patent literature, no further

more details.

Care must be taken that the ink or other marking material used for the image in a pressure-sensitive copying system does not desensitize the reactants or otherwise reduce the functional performance of the copying system. Similar considerations apply, of course, to other sheet materials with functional coatings.

Although the application of the invention to the pressure-sensitive material is emphasized, it should also be pointed out that the invention finds application in other areas when it is desirable that the origin or brand of a particular material be acknowledged not only to the manufacturer's immediate customer, but also to a subsequent buyer (e.g. to

to increase the effectiveness of the manufacturer's advertising and to capitalize on the goodwill gained through previous satisfactory use of the same manufacturer's product). It should be pointed out in this regard that because paper and similar products often reach the end user through a printer or the like, rather than directly from the manufacturer, the end user may receive the product in a different package and with different labels than that used by the manufacturer.

Examples of other products where the present invention can be used are heat-sensitive registration materials and numerous printing and writing papers, photographic printing bases, air and oil filter base papers for pictures etc., and compressible sealing and jointing materials.

The invention shall be illustrated by means of the following examples.

Example 1

This example illustrates the use of a static test rig for ink jet printing (shown in the attached drawing) for the production of sheets with unobtrusive images for use in a pressure sensitive copying system.

The rig comprises an ink gun 1 with a single nozzle 2 adapted to emit a stream of ink droplets 5 in a conventional manner. The nozzle 2 was placed generally above a 5

paper support platform 3 which was movable in two directions. are x, y at right angles to each other, and in the direction Z for the ink droplet discharge. Movement of the paper carrier platform 3 was controlled by a punch card so that the ink drops could hit the paper in a predetermined pattern. The nozzle had a diameter of approx. 75 ym and was arranged for pulsing to emit ink droplets. Deflector plates 4 were placed near the nozzle to deflect certain of the ink droplets 5 towards the paper (only one such deflected droplet 7 is shown). A drain 6 was placed below the nozzle to collect non-deflected ink droplets.

A sheet of clay-coated color development paper ('Idem" CF57) was placed clay-coated side up and the paper-carrying platform and rig were operated to produce an inconspicuous image on the sheet. The ink used was conventional inkjet ink, except that it was much lighter intensity than those used for standard printing. The pulse frequency was 64 KHz, which produced ink droplets with a diameter of about 140 ym and the deflection voltage was adjusted until the desired deflection angle was achieved. The deflection voltage was held constant so that each deflected droplet was deflected to the same extent. This arrangement was such that only 1 drop per 1,000 from the drop emitter was actually deflected. The path of travel of each drop before hitting the paper was about 70 mm. The resulting spot diameter on the paper was found to be approx. 400 etc.

The whole thing was then repeated first with two microcapsule coated sheets "Idem" CB56, in one case with the uncoated surface at the top and in the other with the coated surface at the top, and then with two sheets each coated on one surface with color developer oq on the other with microcapsules "Idem" CFB53. In one case the clay coated surface was on top and in the other the microcapsule coated surface was on top. The desired unobtrusive image was achieved in each case.

By assembling the sheets to form a pressure-sensitive copy set and then subjecting this to normal use, it was found that the inconspicuous images did not affect the formation of qode and legible copies.

Example 2

This illustrates the use of an ink jet printer on a paper coating machine. The printer as described in example 1 was arranged near the track downstream of the drying station in the coater and near a steam jet station. Carrier platform 3 was of course omitted. A variable deflection voltage was used to deflect the ink droplets to varying degrees to form the desired image. The voltage variations were regulated using a punched card. A range of coated and uncoated papers were fed through the machine at speeds up to 750 m/min. and in each case unobtrusive images were successfully obtained. It was found that even at web speeds of 750 m/min. air that had been carried by the web did not affect the path of movement of the droplets, thereby causing disturbance of the image, and that during stacking there was no contamination of ink on the nearby sheet. The presence of steam was not found to affect the image due to the ink being water based.

The papers that were printed in this way were as follows: a) standard 49 g/m2 base paper of the type that is used commercially in the production of "Idem" pressure-sensitive copying papers, b) clay-coated development paper "Idem" CF 46, in some trials was the coated surface given an image and i

second the non-coated surface,

c) "Idem" CF 46 coated on its surface which did not bear the clay coating with pigments containing microcapsules and

particulate "stilled" material (ground cellulose fiber flocculate) which serves to protect the microcapsules from premature crushing due to treatment and storage of the paper (the microcapsule coating was applied by the coating machine on which the printer was mounted), in some experiments the clay-coated surface was given an image and in others the microcapsule-coated surface,

d) standard 49 g/m 2 base paper as described under (a), but coated on one surface with a microcapsule coating

as described under (c), in some experiments the coated surface was imaged and in others the uncoated surface.

When printed coated papers of the type described above were assembled together into pressure-sensitive copying sets, these worked satisfactorily.

Claims (8)

1. Sheet material with an unobtrusive image, characterized in that it has been applied by printing with charged droplets. 2. Sheet material according to claim 1, characterized in that the image is applied by ink jet printing. 3. Sheet material according to claim 1 or 2, characterized in that the sheet material is paper. 4. Sheet material according to any one of the preceding claims, characterized in that the sheet material is a pressure-sensitive copying material. 5. Method for producing sheet material with an unobtrusive image, characterized in that the image is applied to the sheet material using a printer with charged droplets. 6. Method according to claim 5, characterized in that the image is applied to the sheet material using an ink jet printer. 7. Method according to claim 5 or 6, characterized in that the sheet material is a web of paper or coated paper and that the printer is mounted on the machine for producing paper or coated paper on which the web is produced, whereby the web speed through the printer is the same as the web speed through the machine. 8. Sheet material with an inconspicuous image, characterized in that it is produced by a method according to any one of claims 5 - 7.