GB2182888A

GB2182888A - Method of making transfers

Info

Publication number: GB2182888A
Application number: GB08527957A
Authority: GB
Inventors: Colin George Thompson
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-11-13
Filing date: 1985-11-13
Publication date: 1987-05-28
Also published as: GB8527957D0

Abstract

A pigmented water soluble photoresist is applied to a backing and developed in a water based solvent after imagewise exposure to actinic radiation. The adhesive for the transfer may be incorporated as a micro-encapsulated adhesive in the photoresist to be removed from non-image areas at the same time as the unexposed photoresist.

Description

SPECIFICATION Transfers The present invention relates to transfers.

It is known to form a transfer by a process which comprises the steps of: 1. applying a release coating to a sheet of transparent material, 2. coating the entire surface ofthe release coating with an ink, 3. coating the ink with a photopolymerisable material, hereinaftertermed a photoresist, 4. imagewise exposing the photoresistto actinic radiation to harden selectively the parts ofthe photoresist where the image isto remain, 5. developing the photoresistto remove the unexposed portions, 6. removing the inkfrom the parts not protected by any onerlying hardened photoresist, and 7. applying a layer of adhesive over the sheet.

The photoresist is water soluble but the ink is not soluble in water. Thus the photoresist may be developed without affecting the underlying layer of ink and following the development of the photoresist the ink layer may be removed bythe use of a suitable solvent which does not affect the photoresist.

The above process can be seen to comprise several steps and is therefore slow. Furthermore, the resolutionthatcan be achieved in the image lefton the transfer is limited by the factthatthe ink layer is developed through an overlying mask of hardened photoresist and there is a tendencyfor undercutting to occur. Theterm "undercutting" will be clearfrom analogy to the manufacture of silicon semiconductor components, where it is used to indicate the etching that occurs below areas protected by a masknearthe edges ofthe mask.

The present invention seeks to provide a method of making a transfer which mitigates the foregoing disadvantages.

According to the present invention, there is provided a method of making a transfer comprising the steps of: 1. addingtoawater-soluble photoresista colouring pigment, 2. applying a layer ofthe pigmented photoresistto a sheet previously coated with a release coating, 3. imagewise exposing the pigmented photoresistto actinic radiation to harden selected ares ofthe photoresist, 4. removing the unexposed areas ofthe photoresist by the use of a water based solvent, and 5. applying a layer adhesive at least to the areas of the sheet in which the hardened photoresit remains.

The advantages of the invention stem from the fact thatthephotoresistlayerandthepigmentlayerare one and the same. Thus they are developed atthe same reduced, thereby reducing the number of process steps and as the pigment layer is no longer developed through an overlying mask, the risk of undercutting, which limits image resolution, is obviated.

In a preferred embodiment of the invention, the adhesive is applied to the sheet by incorporating in the photoresist a micro-encapsulated adhesive.

This method of applying the adhesive has several advantages both when making and when using the transfer. The advantage when making the transfer is that there is then no need for a separate processing step, thus simplifying and speeding up the process.

Because the adhesive is incorporated in the photoresist, it is developed at the same time and is thereby removed from the area surrounding the image. This is preferred as the adhesive is visible if the transfer is applied to a gloss surface.

Lastly, because ofthe encapsulation, the surface of the transfer is not tacky to the touch and no special steps are required to protect the surface.

To usethetransfer, itis placed overtheobjectto which it is to be transferred and the surface is rubbed with the end of a blunt instrument. The adhesive is then released by rupture of the encapsulation and acts to adhere the image to the surface to which it is to be applied. The release coating on the transparent sheet ensures that the image does not adhere stronglytothetransparent sheet and the backing of the transfer can readily be removed to leave the image behind.

While the use of a micro-encapsulated adhesive is preferred, it is alternatively possible to use a conventional adhesive layer overlying the entire surface ofthe sheet supporting the transfer images.

The photoresist is slightly coloured and tends to change colour as it dries. This can makethe matching of a particular shade rather difficult if an attempt is made to blend photoresistspigmented with different colours. It is instead preferred that the pigments and the photoresist be supplied to the user separately so that the pigments may be mixed and their colours matched to a desired shade before the pigments are added to the photoresist.

The invention will now be described further by reference to a preferred embodiment, given only by way of non-limiting example.

A sheet of transparent acetate paper is coated with a silicone release coating. This step is not carried out by the end user as precoated sheets for use in making transfers are already commercially available.

This means that fewer processing steps have to be carried out be the user.

The sheet which will now be referred to as the backing is laid down on a conventional processing base which comprises a foam rubber or other resilient pad covered with a sheet of replaceable absorbent paper.

A coating of a sealant is applied to the backing by laying excess sealant along one edge of the backing and spreading the sealant using a so-called Meyers bar. The latter is a rod with afinewire coiled around, the diameter of the wire being selected to varythe thickness of the layer laid down in this manner. After spreading of the sealant coating, the latter is dried by blowing over the surface of the sealant with a conventional hairdrierfora few seconds.

The sealant is conveniently formed from a nitro-cellulose lacquer mixed with a suitable solvent such as ethyl acetate or acetone. Such a sealant coating has the desirable properties of being water resistant, quick drying and forms a smooth surface over which the pigmented photoresist may be applied. To provide as smooth a surface as possible, the sealant is required to have a low content of plasticizer, high surface tension and low viscosity.

The photoresist comprises a phosphate salt of a reduction product of diazodiphenylamine and formaldehyde dissolved in water. This is a photopolymerisable material which hardens when exposed to ultraviolet light. An organic pigment of the desired colour is mixed from suitable known pigments which do not react with the photoresist.

The pigments are dissolved in a solution of polyvinyl alcohol in water and are added to the photoresist in an appropriate ratio. The pigments are first matched to the desired shade and only then are the added to the photoresist. This gives the advantage of easier colour matching and also reduced the problem that stock solution become unusabling through being stored for long periods.

Amicro-encapsulatedadhesive is added tothe pigmented photoresistandthethereafterthe photoresist is laid down in the same manner as the sealant coated and dried.

The backing sheet is now removed from the base and placed in a light box. A previously prepared photographic negative is placed over the backing andthelidoftheboxisthen broughtdown to clamp the negative to the backing. The photoresist is now exposed imagewiseto radiation forsufficienttimeto polymerise the exposed parts of the photoresist. The exposure will naturally depend on the powerofthe light source but may typically lastthirty seconds.

The backing is now returned processing base and the unexposed photoresist is removed by drawings across the surface a wipe previously immersed in waterto which wetting solution may if desired be added.

After drying, the transfer is ready for use and any image may be rubber down under any desired surface in the usual manner. The micro-encapsulation is ruptured when the transfer is rubbed down and acts to adhere the image and the sealan coating to the surface. The resulting bond between the sealant coating and the surface to which the image is to be transferred is stronger than the bond to the release coating so that the image remains adhering to the surface as the backing is removed.

Claims

CLAIMS 1. A method of making a transfer which comprises the steps of:

1. adding to a water-soluble photoresist a colouring pigment,

2. applying a layer of the pigmented photoresistto a sheet previouslycoated with a release coating,

3. imagewise exposing the pigmented photoresistto actinic radiation to harden selected ares of the photoresist,

4. A method as claimed in any preceding claim, wherein pigments are blended with one another to achieve a desired shade priortothe pigment being added to the photoresist.

4. removing the unexposed areas ofthe photoresist by the use of a water based solvent, and

5. applying a layer of adhesive at least to the areas of the sheet in which the hardened photoresit remains.

2. A method as claimed in claim 1, wherein the adhesive is applied to the sheet by incorporating in the photo resist a micro-encapsulated adhesive.

3. A method as claimed in claim 1,wherein adhesive is applied to the entire surface after development of the pigmented photoresist.