GB2053497A - Photosensitive Materials for Making Signs and Labels - Google Patents

Abstract

Sign-making materials are described which consist of two sheets held together via intermediate layers and peelable apart. Adjacent a transparent or translucent one of the sheets is a layer of adhesive, and between this layer and the other sheet is an imaging layer which after imagewise exposure, shears along the edges of the images when the sheets are peeled apart. The image-forming layer may be made of a pigmented non-photosensitive layer and an unpigmented photosensitive layer. The adhesive layer may be of permanently tacky pressure-sensitive adhesive.

Description

SPECIFICATION The Manufacture of Signs and Labels This invention relates to the manufacture of signs and labels.

In recent years many signs and labels have been produced in the form of so-called self adhesive materials. These consist of a flexible carrier on which the legend of the sign or label is applied and which bear on the side opposite the legend a coating of a highly tacky pressure sensitive adhesive. The sign or label is protected until required to be used by the adherence to that adhesive of a sheet of so called release paper which is peeled away prior to application of the sign or label to the desired location.

The disadvantage of such labels and signs is that the legend is liable to become abraded or otherwise damaged. This may be avoided by coating the sign after application with a suitable protective layer or applying a self adhesive film over the sign but such methods increase expense and, are generally cumbersome.

According to a first feature of the present invention there is provided a sign making material which consists of a pair of sheets which can be peeled apart and which are held together via at least one layer of adhesive, and at least one image forming layer which, after imagewise exposure of the material to actinic radiation and peeling apart of the sheets shears around the area of the images and wherein the image forming layer or at least one further layer is photosensitive, the layer of adhesive and the adjacent sheet being transparent or translucent.

On imagewise exposure of such a material and peeling apart of the carrier sheets, the transparent or translucent carrier sheet bearing the coating of adhesive will remove with it part of the image forming layer and will accordingly constitute an adhesive sign or label bearing on its adhesive side a desired legend. The desired legend will normally be in the form of a plurality of indicia such as signs, symbols, letters and figures each surrounded by adhesive which serves to adhere the whole sheet to a desired location.

The adhesive may be a permanently tacky pressure-sensitive adhesive, or it may be a pressure-, heat- or light-activated adhesive or one activated by any other appropriate means such as solvent or exposure to atmospheric oxygen.

The photosensitive material of the present invention may be constructed to be positive or negative working. Specific materials for various components of the photo-sensitive material are as follows: The carrier sheets in the sign making material may be made of any convenient sheet material for the purpose. At least one of the sheets must be translucent or transparent in order to allow imagewise exposure of the intermediate layers but both sheets may be transparent or translucent if desired. A wide variety of suitable plastics films is available in commerce and particularly suitable for use are carrier sheets of polyethylene, styrenebutadiene copolymers, polyethylene terephthalate and various cellulose derivatives such as cellulose triacetate sheet.The pressure sensitive adhesive may be selected from a wide variety of such adhesive compositions and should preferably be one which is not aggressively tacky. The tack of such pressure sensitive adhesives may be controlled by formulation techniques common in the art, for example the incorporation into an adhesive composition based on a highly tacky polymer such as a polyvinyl ethylether or polyisobutylene of detackifying materials such as waxes or finely divided mineral materials e.g. silica.

The photosensitive layer may be made of a variety of polymeric materials and embody one of a variety of photopolymerisable systems. For example, the photopolymerisable systems may be of the types set out in United States Patent Specification 3,353,955 and other United States Patents referred to therein.

The photosensitive layer may vary in consistency from a thin liquid layer through a thick liquid or gelled or semi-solid layer to a relatively solid layer, and should be one in which the action of actinic radiation produces major changes in the bulk mechanical properties of the layer by means of polymerisation and/or cross-linking. Typically the layer can comprise a photoinitiator and an unsaturated monomer. The action of light on the photoinitiator produces free radicals which initiate the polymerisation and cross-linking of the monomer. The photoinitiator can be selected from a very wide range of compounds known to produce free radicals on irradiation with electromagnetic radiation of the appropriate wavelength.Particularly suitable are aromatic carbonyl compounds such as benzil and its derivatives, acetophenone and its derivatives, benzophenone, benzoin, benzoin ethers, chlorothioxanthones and anthraquinones. Another system of value is to generate a Lewis acid induced polymerisation: aryl diazonium salts can be used as initiators in epoxy resin based layers. The advantage of this system is that the wholly ionic mechanism is not oxygen-inhibited and polymerisation continues somewhat after the initial exposure giving good contrast.

Further compounds can be incorporated to enhance the speed of the photosensitive layer: amines and perhalogenated alkanes are two major classes of reaction enhancer. Small amounts of polymerisation inhibitor can be included. The photoinitiator can also contain groups which will themselves cross-link unsaturated molecules; molecules containing the azido group are known to do this.

Unsaturated monomers for use in the photosensitive layer can be chosen from the numerous unsaturated polyfunctional acrylates known. Their properties can be modified by the addition of monomers containing only one site of unsaturation.

Further compounds such as pre-polymers and oligomers can be incorporated in the photosensitive layers. A wide range of such compounds is well known from their use in U.V. curing inks. The photosensitive layer can be quite fluid and need have little cohesive strength. If it is a solid, semi-solid or gel then it should have a minimum of cohesive strength. It is preferred that the difference between the cohesive strength of the exposed and unexposed areas should be maximised to enable the image to obtain maximum definition.

Image or image forming layers can be constructed from numerous solids. Pigments can form a major component of the layer and may be held together to form a layer with a resinous, polymeric or gum base. Inert mineral solids such as glass, silica, alumina and asbestos may be incorporated in the image or image forming layer(s) and polymers and/or polymer beads can be incorporated which a posttreatment can fuse or cure for specific purposes. The image forming layer may also be a vacuum deposited layer of metal.

Preferably the shearable image forming layer is made of a photosensitive but otherwise non-light absorptive layer and an adjacent shearable pigmented layer, both as set out above.

The following example will serve to illustrate the invention: Example A homogeneous adhesive solution was made by dissolving in xylene its own weight of an equal weight mixture of two commercially available silicone adhesives (silicone adhesive 282 ex Dow Corning and Silgrip 573 ex General Electric).

A photosensitive coating composition was then made by mixing together the following materials in the proportions given by weight; parts oligotriacrylate (OTA 480 ex U.C.B.) 25.0 surfactant (Span 80 ex Honeywell 8 Atlas) 0.1 surfactant (Tween 80 ex Honeywell s Atlas) 0.2 photoinitiator (Quantacure 659 ex Ward Blenkinsop Ltd.) 3.2 crosslinkable polymer emulsion (Bevaloid 6464 ex Bevaloid Ltd.) 70 water 20 surfactant (Superonic NX ex I.C.l.) 1 carbon black dispersion 4.5 The carbon black dispersion was made by mixing 35 parts by weight of carbon black (Elftex 150 ex Cabot Carbon Ltd.) into 65 parts by weight of a 10% by weight solution of polyvinyl alcohol in water (Gelvatol 40-10 ex Monsanto).

The carbon black mixture was ballmilled for 48 hours to homogeneity.

Sheets of polyethylene terephthalate were then taken (542 Melinex ex l.C.l.). Some sheets were coated with a commercially available acrylic pressure sensitive adhesive'(Gelva RA1753 ex Monsanto) using a wire-wound bar of wire diameter 0.25 mm and, after drying that adhesive coating, those sheets were overcoated with the photosensitive coating composition noted above, likewise using a wirewound bar of wire diameter 0.25 mm. The so coated material was then dried.

Other polyethylene terephthalate sheets were coated using a wire-wound bar of wire diameter 0.75 mm with the silicone adhesive composition given above and after that coating had been dried and two types of coated polyethylene terephthalate sheet were laminated together by passing them through a nip between two rollers each of which had its surface heated to 1200 C. The roller diameter was 110 mm and the nip gap was adjusted to give a firm pressure on the laminate. The lamination was effected at a lamination speed of about 10 mm per second.

The laminate so obtained was imagewise exposed through a transparency to light from a 2 kw mercury-metal halide lamp located at a distance of 1 m. The polyethylene terephthalate sheet bearing the coating of acrylic adhesive composition was closest to the lamp. Exposure time was 20 seconds.

Following exposure, the two polyethylene terephthalate sheets were peeled apart and that coated with silicone adhesive pulled off areas of the black photo-sensitive coating from the other polyethylene terephthalate sheet in the unexposed areas. In the exposed areas, a complementary image adhered to the layer of commercial acrylic polymeric adhesive. Both sheets were accordingly self-adhesive signs.

Claims (6)

Claims

1. A sign-making material which consists of a pair of sheets which can be peeled apart and which are held together via at least one layer of adhesive, and at least one image forming layer which, after imagewise exposure of the material to actinic radiation and peeling apart of the sheets shears around the area of the images and wherein the image-forming layer or at least one further layer is photosensitive, the layer of adhesive and the adjacent sheet being transparent or translucent.

2. A sign-making material according to claim 1 wherein the shearable image forming layer consists of a photo-sensitive but otherwise non-light-absorptive layer and an adjacent shearable pigmented layer.

3. A sign-making material according to claim 1 or 2 wherein the adhesive is a permanently tacky pressure-sensitive adhesive.

4. A sign-making material according to any one of claims 1 to 3 wherein between the two sheets are located two adhesive layers, one each side of the shearable image forming layer.

5. A sign-making material substantially as hereinbefore described with reference to the foregoing specific Example.

6. An adhesive sign made by imagewise exposure of a sheet of sign making material according to any one of claims 1 to 5 followed by peeling apart of the sheets.