GB2248800A - Production of coloured legends - Google Patents

Abstract

Coloured legends are formed by assembling a legend using a dry transfer material for individual indicia, e.g. on a paper or other substrate and subsequently transferring to the exposed surfaces of the indicia a colouring layer from a blocking foil. In accordance with the invention, transfer of the colour layer from the blocking foil is enhanced by a suitable treatment of the exposed indicia surfaces following assembly of the legend prior to the application of the blocking foil. Solvent treatment, preferably by spraying, is preferred, using one or more of a solvent for the polymeric material of the indicia or a solvent plasticiser for such polymeric material.

Description

PRODUCTION OF COLOURED LEGENDS This invention relates to the production of coloured legends.

International Patent Publication WO 83/02089 describes a process for the production of coloured legends consisting of two stages. In the first stage a legend is assembled on a substrate using conventional dry transfer lettering, symbols or the like. In the second stage, the assembled legend is covered with a so-called blocking foil, colour layer side towards the legend, and the assembly of legend on its substrate and blocking foil passed through, e.g. a heated nip. The colour layer on the blocking foil transfers selectively to the indicia making up the legend, and when the foil is pulled away after the heat and pressure treatment, the coloured legend is left adherent to the substrate on which it was built up, usually paper.

This system does not work well. In particular, many commercially available blocking foils simply do not work adequately with commercially available dry transfer materials as these are usually made with inks designed to be heat resistant. Although specially formulated dry transfer materials and blocking foils can be used to provide satisfactory systems, they are not normally available in commerce.

According to the present invention, between the formation of the legend and the application of the blocking foil, the surface of the legend is treated to render it more receptive to the coloured coating on the blocking foil.

Preferably the treatment is by the application of a material to the legend which is a solvent for the polymeric component of the indicia making up the legend.

The substance may be applied in liquid or vapour form, liquid form being usually quicker to effect but requiring more skill on the part of the user.

Many commercially available dry transfer materials have indicia made of black ink on a nitrocellulose basis.

While many solvents for nitrocellulose are known, it is naturally preferred to use a solvent with low toxicity and low flammability. The solvent of choice is N-methyl pyrrolidone. This is an excellent solvent for nitrocellulose. In order to provide easily workable systems, it is preferred to mix N-methyl pyrrolidone with diluents, for example ethanol, isopropanol and/or water.

Alternatively, the solvent for the polymeric material of the indicia forming the legend may be a solvent plasticiser for such polymeric material. Solvent plasticisers, for example dibutyl sebacate and diisobutyl adipate may be used to good effect.

It is found that results may also be improved, particularly with respect to the reliability of blocking foil transfer, by incorporating in the solvent or solvent mix a small proportion, e.g. up to 5% by weight, of a resin compatible with the polymeric basis of the indicia.

For nitrocellulose based indicia, suitable resins are ester gums or hydrogenated rosins, for example that sold under the Registered Trade Mark DYMEREX by Hercules Chemical.

Liquid application methods requiring the user to contact the indicia, e.g. using wipes, pads or the like, may be employed, but are sensitive to operator variation. It is all too easy to use more solvent than is necessary and even with a skilled operator the solvent can sometimes be applied somewhat unevenly. Improvements can sometimes be achieved by incorporating wetting agents in the liquid applied, to promote even treatment of all the indicia surfaces in the legend.

An alternative and preferred approach is to treat the legend using a non-contact application method, e.g. by exposing its surface to solvent vapour, either of a single solvent or mixed solvents, or by spraying. The first of these may be easily achieved by preparing an appropriate chamber with a source of solvent inside it, for example a swab or pad moistened with solvent, and leaving the atmosphere inside the chamber to saturate with vapour.

This may take up to 30 minutes. Thereafter, the legend may be slid in (avoiding vapour loss as much as possible) and left there for five to ten minutes. Although this approach takes time to effect, it generally provides a very evenly treated surface.

The alternative approach to applying a small quantity of activated liquid to the surface of the legend by spraying a solvent or solvent mix on to the surface of the indicia making up the legend is quicker. Mixtures of N-methyl pyrrolidone and isopropanol at a weight ratio of 1:3 to 1:1 respectively can be sprayed satisfactorily. Mixtures of ethanol and N-methyl pyrrolidone containing 5 to 50%, preferably 5 to 20% by weight of N-methyl pyrrolidone can also be used and have the additional advantage of less tendency to swell the substrate. With a little practice both the amount of spray and the timing can be adjusted to give excellent results.

The apparatus used to provide the spray may be any convenient apparatus, but care needs to be taken to ensure that it is one which provides an adequately fine mist and even spray. Pump spray applicators operated by hand tend to give a spray of rather coarse droplets leading to uneven coverage and unsatisfactory results. Aerosol sprays may be used but these are bulky and require propellant. Most preferred is to apply a fine spray or mist using an air operated system such as an airbrush or a system in which a stream of air is passed over a capillary fed tip such as used in felt tip marker pens, the air flow geometry being arranged to detach tiny drops of liquid on the tip. Apparatus of this sort for use with coloured felt tip marker pens is commercially available under the Trade Mark LETRAJET.In place of a conventional marker pen, a unit is used in which, instead of a coloured ink, the desired solvent mix is contained within the usual ink reservoir.

Following the treatment of the exposed surface of the legend, blocking foil is laid over the legend and pressure, preferably accompanied by heating, is applied.

This may be effected by passing the assembly of the substrate bearing the legend and the blocking foil through a heated nip. Alternatively a heated pad may be passed over the assembly, with the foil being held in position during such passage. In such a case, the assembly is preferably located on a relatively soft yielding base, for example a thin sheet of silicone rubber, to ensure the even application of pressure and accordingly to ensure even heat and pressure treatment. Thereafter, optionally after a suitable cooling period, the blocking foil is peeled away to leave the now coloured legend visible.

The timing of the various aspects of the process according to the invention for making a coloured legend may be relatively critical. In order to assist the user in determining the appropriate timing, and in particular to enable the user to tell when the exposed surface of the indicia making up the legend has been adequately treated, liquid formulations may include components which, after an appropriate period of exposure to ambient atmosphere, show a colour change. For example, liquid formulations may include an indicator dye and a material which will evaporate at room temperature, the quantity of evaporatable material serving to promote a change in the colour of the indicator dye. For example a liquid formulation may contain phenolphthalein dye and ammonia.

This, when applied, is pink, but as the ammonia evaporates the pink colour disappears. By the time the colour has disappeared, other components in the liquid formulation have had time adequately to activate the surface of the indicia making up the legend to enable satisfactory colouring using a blocking foil.

Alternatively, reliance may merely be placed on the change in the visual appearance of the dry transfer lettering.

Most dry transfer lettering as laid down from standard commercially available sheets has a relatively matt surface. Once solvent is applied, the surface takes on a slight gloss, and if too much solvent is applied, the surface takes on a wet shiny appearance. If that happens, it is not generally disastrous: the legend can merely be allowed to dry out a little until the surface has a slight gloss and then the blocking foil may be applied.

We have found that using the techniques in accordance with the invention, satisfactory results can be obtained using a wide variety of blocking foils and a wide variety of commercially available dry transfer materials. Because of the wide variation of commercially available materials, however, there will be some variations in practice between different materials. We have found that the system works particularly well with dry transfer lettering which is based on a nitrocellulose based ink especially where, in addition, the ink formulation includes a small proportion of an acrylic resin or a rosin derivative.

We have also found that it is very desirable to burnish down the transferred letters after application to form the legend. Close contact between the letters and substrate ensures that the activation is evenly distributed. In addition, when the foil is peeled away, there is a tendency for the foil to lift the letters off the substrate; burnishing eliminates this by increasing the adhesion of the letters to the substrate.

The following Examples will serve to illustrate the invention.

Example 1 A legend was built up from black dry transfer lettering (Instant Lettering ex Esselte Letraset Limited) on a bristol board substrate.

This legend was wiped over with an activator solution consisting of the following ingredients in the following proportions by weight N-methyl pyrrolidone 30 percent Isopropanol 40 percent Water 20 percent Polyvinyl alcohol solution (10% by weight solution in water, AIRVOL 540 (ex Air Products and Chemicals Inc.) 10 percent After wiping over, a strip of coloured hot blocking foil (ColorTAG ex Esselte Letraset Limited) was laid over the legend and ironed down on to the legend using a small hand held heated iron. The foil was then peeled away to leave the coloured legend on the bristol board.

Example 2 A legend was assembled on bristol board as in Example 1.

A picture frame of size larger than the legend was taken and a small absorbent pad secured in each corner behinnd the glass. On to the pad was then applied a few ml of N-methyl pyrrolidone and the frame laid down, glass upwards, on the board thus forming a relatively sealed chamber. The air in the chamber is then allowed to saturate with solvent vapour. At this stage, the legend on the Bristol board is introduced into the chamber.

After ten minutes the frame was removed and the legend coloured by the application of a coloured foil as in Example 1. Similar satisfactory results were obtained.

Example 3 Example 2 was repeated but in place of N-methyl pyrrolidone the pads at the corners of thhe frame were moistened with methyl ethyl ketone. Vaporisation of the solvent within the frame was accelerated and the equilibrium vapour concentration increased, by placing the frame on a heating pad, which maintained the temperature of the chamber at 45"C. The legend bearing Bristol board was then placed in the frame for five minutes. Following removal from the frame, the foil could be immediately applied, and similar satisfactory results obtained by placing the assembly of the frame and legend bearing Bristol board in a drying cupboard at a temperature of 45"C for five minutes. Following removal from the drying cupboard the foil could be immediately applied and similar satisfactory results obtained.

Claims (10)

1. A process for the production of coloured legends which comprises, in a first stage, assembling a legend on a substrate using dry transfer lettering symbols or other indicia and, in a second stage, covering the assembled legend with a blocking foil, the blocking foil having a coloured layer towards the legend, and subsequently subjecting the assembly of legend, substrate and blocking foil to heat and pressure to transfer the colour layer from the blocking foil selectively on to the indicia making up the legend, whereafter the blocking foil is pulled away to leave the now coloured legend adherent to the substrate, characterised in that, subsequent to the formation of the legend and prior to the application of the blocking foil thereto, the surface of the legend is treated to render it more receptive to the coloured coating of the blocking foil.

2. A process according to Claim 1, wherein the treatment to render the surface of the legend more receptive to the coloured coating of the blocking foil comprises applying to the surface of the indicia a solvent material for the polymeric component thereof.

3. A process according to Claim 2, wherein a liquid solvent is applied to the surface of the indicia.

4. A process according to Claim 2 or 3, wherein a solvent plasticiser is applied to the surface of the indicia.

5. A process according to Claim 3 or 4, wherein, in addition, a small quantity of a resin compatible with the polymeric component of the indicia is applied to the surface thereof.

6. A process according to any one of Claims 2 to 5, wherein N-methyl pyrrolidone, optionally in admixture with an alcohol and/or water, is applied to the surface of the indicia.

7. A process according to any one of Claims 2 to 6, wherein the solvent material is applied to the surface of the indicia by spraying.

8. A process according to any one of Claims 2 to 6, wherein the solvent material is applied to the surface of the indicia by vapour absorption.

9. A process for forming a coloured legend substantially as hereinbefore described wiith reference to any one of the foregoing specific Examples.

10. A coloured legend on a substrate formed by the process of any one of the preceding Claims.