Rolls of pressure sensitive adhesive tape are commonplace articles of commerce. Typically, they consist of a central cylindrical core or former, usually made of thick stiff cellulosiσ material, over which is wound a tape of flexible polymeric substrate coated on the one side with a pressure-sensitive adhesive and treated on the other side with some form of anti-adhesion treatment or coating so that the adhesive does not adhere irremovably to the outer surface of the coil to prevent subsequent unwinding.

Such as coil in itself is not a particularly prominent or decorative article, and when packaged for sale is therefore usually mounted upon a more or less decorative or informative card.

In recent years, advances in technology have permitted the production of very clear grades of tape, so that effectively the roll of tape built up on the core is transparent and free from any colouration.

We have realised that this form of tape can be combined with, and optically interact with, an eye

catching visual feature whereby the roll is rendered visually prominent at point of sale and during use.

In one aspect the invention consists in a transparent roll of pressure-sensitive adhesive tape around a central core or former, in which the outer surface of the core or former is visible through the accumulated wound layers of tape, and is provided with a holographically applied pattern.

Preferably the holographically applied pattern consists of a random or regularly repeated array of separate small decorative areas, each area preferably extending for less than 20% across the width of the tape. Preferably moreover the characteristics of the holographically applied pattern are such that it gives, viewed from the appropriate angle, good spectral resolution and reflectance of spectral colours from ordinary levels of daylight, either in the open or more especially in indoor use.

The holographic pattern is preferably applied to a separate treated sheet which is thereafter wrapped round and adhered to the core. Such a sheet can be a metallised polymer sheet, treated by processes known per se. As indicated above, it is preferable if such a sheet is holographically printed in a manner responsive to ordinary levels of daylight.

The holographic pattern may moreover be so applied as to extend only part-way round the core, or otherwise cover only part of the surface.

One category of pattern can consist of a regular or random print of small disc shapes or annular shapes. Another useful array consists of trangular patterns reminiscent of the faceted cuts of a diamond, that is to say with bands of longitudinally extending thin isosceles triangles separated by like bands but of smaller triangles, the bands extending transversely across ^' the tape direction. Brand names or advertising logos (for example those of the tape manufacturer, or those of a large end-user of the tape) can also be incorporated into the holographic surface.

We have found unexpectedly that the provision of such a holographic pattern beneath the transparent tape sets up an optical interaction of a particularly attractive type. Firstly, the curvature of the former or core - normally cylindrical - is such that when it is viewed from a single source of light, a number of bands of different colour are visible. Since the core is covered in a holographically applied array of small units, spaced apart by small distances, the tendency is for some of the units to show blue, .others red, others yellow, and so on. Thus there is one optical effect obtainable by the curvature of the core. Additionally

to this, the successive layers of tape wound upon the core constitute a form of cylindrical lens. There is provided by this an optical effect which extends the holographically applied pattern diametrically across the visible tape. Thus, the view of the hologram is not that of a uniform hologram tilted into different angles, and extending only into a central part of the wound roll, but is instead a hologram defining a generalised band of colours, and extending from one outer curved surface to the other, diametrically. opposed, curved surface.

In practice, when the roll is set up for display in a store, there will be more than one source of light coming from different directions and accordingly more than one set of coloured reflective bands. Indeed, the general appearance is more or less like that of a kaleidoscopic set of bright internal lights extending behind the whole of the roll of tape.

The invention will be further described with reference to the accompanying drawings, in which: -

Figure 1 shows in perspective the component parts of a roll of tape in accordance with the invention.

Figure 2 shown the appearance of that roll of tape viewed at right angles to the axis of the roll.

Figure 3 shows one form of imparted holographic pattern and

Fig 4 shows another possible form of such pattern useful in the practice of the invention.

The roll shown in Figure 1 consists of a core 1 around which is adhered a metal foil 2 having on its outer surface 3 a holographically produced pattern 4 of relatively small elements 5. On this core successive turns of a pressure-sensitive adhesive tape 6 are wound. The substrate and adhesive layer of this tape • are chosen so that the tape is of a completely transparent or "water white" nature. Such tapes are known per se.

Figure 2 shows the general visual appearance of such a roll of tape seen at right angles to the roll. If such a tape is viewed with a single source of multi-wavelength light, e. g. light coming in through a window, the curvature of the core 1 will ensure that the different holographically printed units 5 of the pattern 4 reflect different spectral colours, probably with a general band of reflectance. This feature is not a common feature in holographic technology, since it is usually desired to have a flat hologram which can be

viewed from different directions to achieve the necessary optical effects over essentially its whole surface. In accordance with this embodiment of the present invention the hologram foil 2 is applied specifically over a cylindrically curved surface of core 1 so that there is a band or bands (depending on the number of light sources) of colours corresponding to the spectral composition of the light being reflected.

It is a particularly noticeable moreover that this multi-coloured visual effect, which changes as the roll is handled, extends over the whole visible outer surface of the ^' roll, from one diametrical extreme to the other. This is clearly an optical effect based on refraction and given by the build up of transparent tape into a usable thickness of roll. A consequence is that the roll remains of a decorative nature, i. e. not only at the point of sale but also during use, even when the roll is terminated and the bare hologram surface is exposed.

Figure 3 shows a typical form of holographically printed surface for the metal foil 2. It will be seen that small annular units 5 of diameter typically about 10% of the width of the roll, are located so as to give a multiplicity of colour reflection from the surface. Of course, the annuli, or the central spaces, or the spaces between the annuli pattern can be differently

holographically treated so as to reflect different colours. In practice, the different small components 5 of the pattern each appear to reflect more or less a single colour. This is typically noticeable if the roll is exposed at point of sale, say from 50 to 100cm from the eye of the purchaser. It is also noticeable as the roll is used.

Figure.4 shows an alternative pattern which can be used as a hologram. The pattern consists of alternate stripes 7, extending across the core, one set of stripes 7a being composed of longitudinally oriented long and thin triangles 8 and the other set 7b being composed of shorter triangles 9 so as to give a general impression of a faceted diamond. Once again, the unit triangles 8, 9 are of the order of 10% of the width of the tape so as to give a multiplicity of coloured portions. Different holographic treatments can be given to different triangles so that a complex pattern of colours may be obtained as the roll of tape is used.