GB2220386A - Making a diffractive composition - Google Patents

Abstract

A diffractive composition in at least two contrasting diffractive colours is made by hot stamping a diffractive hot stamping transfer foil with a hot stamping plattern to apply at least parts of said foil to a substrate and hot stamping a second diffractive hot transfer foil with a second hot stamping plattern having a surface relief pattern thereon to apply said pattern to said second foil to thereby transfer selected parts of said second foil to the substrate or to the first foil. By sequentially hot stamping a plurality of hot stamping different hot transfer foils so a graphic design or composition may be produced. One of the hot stamping platterns may bear a holographic image.

Description

METHOD OF MAKING A DIFFRACTIVE COMPOSITION This invention relates to a method of making a diffractive composition in at least two contrasting diffractive colours.

The invention is generally concerned with the field of light diffraction patterns, such as diffraction gratings and holograms.

An existing method of using diffraction gratings to compose patterns and coloured designs without the use of paints or pigments has been described, for example, Ralph Douglas Doner in U.S. Patent No.

1,354,471 wherein jewellery, signs and other articles are decorated by colours derived from the diffraction of light and are therefore of a luminous and irridescent quality which cannot be achieved by the use of inks or pigments.

Light diffracting patterns as described in the U.S. Patent No.

1,354,471 are formed by mechanically ruling fine parallel lines into a suitable substrate, the different combinations of shades or colours being attained by varying the number and direction of lines which are ruled on the surface upon which the design is to appear.

A method for originating diffraction gratings is disclosed by R.

E. Brooks in U.S. Patent No. 3,578,845 by exposing a photographic plate to beams of coherent light from a laser to form a holographic diffraction grating.

The use of holographically formed diffraction gratings to produce decorative patterns which may be embossed into plastic is described by M.

C. Hutley in the Spring 1979 issue of the National Physical Laboratory Newsletter pages 6-7. By this method, a plurality of complimentary photographic masks are used in conjunction with the surfacerelief holographic gratings formed in a photo-resist, to produce the desired decorative pattern, a method developed by the Bank of England for security purposes.

A similar, though more elaborate, method is described by S. P.

McGrew in P.C.T. Application US/81/01439 utilising a hologram of a sheet of ground glass to produce diffractive colour effects. In the prior art a diffraction grating or hologram in the form of a fine surface relief pattern is first formed in photo-resist, using a laser. The hologram or diffraction grating is comprised of several exposures each made with slightly different optical configurations, so as to create a design or graphic composition or pattern made up of different diffractive colours, each of which diffracts incident white light into spectral hues, but is contrived so as to produce a different colour, relative to the other areas of the design or pattern, at any one time, as seen from a predetermined viewing position.

Also, in the prior art the areas of diffractive colour may incorporate three dimensional images and textural effects, a plurality of which may be combined by means of complimentary photomasks onto one holographic master plate.

In the prior art, the holographic master plate formed with several holographic exposures to create the many different and various diffractive effects is then used to form a metallic stamping master by means of electroforming, and this metallic stamping master is in turn used to emboss the hologram or diffraction grating design or composition into an embossable material such as P.V.C.

Fine line surface relief structures such as the holograms and diffraction gratings described above may also be embossed into the lacquer of hot stamping foil, also called hot transfer foil, as disclosed in GB-A-1,568,563 and GB-B-2,129,739.

The origination of the master embossing plates described in the prior art is a complex procedure requiring specialised equipment and expertise. The skills required to make suitable masters for embossing plates is known only to a very few practitioners in the art, and the process is expensive and time consuming. This places a severe limitation on the number of new patterns and designs which can be fabricated.

It is an object of this invention to provide a method of making a diffractive composition in at least two contrasting diffractive colours which is less expensive and quicker to produce than the compositions described above.

According to this invention there is provided a method of making a diffractive composition in at least two contrasting colours including the steps of providing a first foil having a first predetermined diffraction colour at a predetermined viewing position, hot stamping said first foil with a first hot stamping plattern to transfer said foil to a substrate, providing a second foil having a second predetermined diffraction colour at said predetermined viewing position, hot stamping said second foil with a second hot stamping plattern having a surface relief pattern thereon for selectively transferring areas of the second foil on to the first foil or the substrate.

Advantageously further foils each with different diffraction colours thereon at said predetermined viewing position are provided and a like number of hot stamping platterns are provided to build up a composition.

In some embodiments of this invention the first hot stamping plattern may have a surface relief pattern thereon which is different to the surface relief pattern on said second hot stamping plattern.

In a preferred embodiment a first stamping plattern has a substantially planar surface to transfer the first foil as a background diffractive colour onto the substrate, a second hot stamping plattern has one surface relief pattern thereon which is applied to selectively transfer areas of the second foil onto said first foil, and a third foil is provided having a third predetermined diffractive colour at said predetermined viewing position, said third foil being hot stamped with a third hot stamping plattern having a surface relief pattern thereon for selectively transferring areas of the third foil onto either the first foil or the second foil.

In another preferred embodiment the first and second hot stamping platterns provide complimentary patterns on the substrate.

In a further embodiment of the invention one or more of the hot stamping platterns has a general and repetitive pattern thereon which is used to transfer a respective foil. The general and repetitive pattern may be a holographic image.

Conveniently each foil has a heat sensitive release layer to permit transfer of said foil and advantageously the heat sensitive release layer of each foil is different from another foil such that the foil with the highest release temperature is transferred first and so on to the foil with the lowest release temperature.

Preferably the required surface relief pattern is provided on a desired plattern by chemical action or manual profiling or electron beam milling or CO2 laser cutting.

Advantageously at one of the hot stamping steps the associated plattern is arranged to have a surface relief pattern bearing a number particular to each composition so that the number for each composition sequentially vary to provide security to a holographic composition.

In such an embodiment the foil bearing the number is covered with another foil which is partially light transmissive.

The present invention thus provides a technique for swift and inexpensive manufacture of new light diffracting patterns and designs composed of a plurality of diffractive colours or gratings incorporating hologram images, without the need for a new holographic origination for each new pattern or design.

The invention also provides a means by which the light diffracting patterns or designs may be composed from a range of light diffracting surface-relief gratings or gratings forming holograms without the need for any specialist skills or expensive equipment, such as that required for holography.

In this invention the graphical design or pattern is not composed in the master hologram step as in the prior art, but at the hot stamping transfer step. Thus in the prior art the completed graphical design is embossed into hot stamping foil and later the entire pattern is transferred in a single pass by a plain hot stamping plattern onto a substrate whereas, in this invention, a plurality of different hot stamping foils are manufactured, each preferably being embossed with a different diffraction grating of a uniform type. Each foil is then hotstamped using a different hot stamping plattern, each of which has been etched or shaped to transfer an area of a graphic design or pattern onto the substrate.By means of consecutive passes of different hot stamping foils, each yielding a different diffraction grating, using a series of complimentary hot-trasfer platterns, the full graphic design or pattern is built up.

Although several passes of several foils using several different platterns are required in this invention, rather than a single pass with a single plain plattern as in the prior art, this apparent disadvantage is outweighed by the great versatility of the present method and the simplicity and speed with which new and original patterns may be achieved using inexpensive materials.

A further advantage of the present invention is the almost unlimited range of designs which may be built up from a set of two or more basic foils. By registration of the substrate along the x-y coordinates below the plattern, precise registration of designs is possible, as the graphic design is formed by the plattern rather than the foil, the foil being of a uniform field of diffraction colour or a generated repeated image or pattern.In this way, using four primary colours of foil - red, green, blue and yellow -pseudocolour diffraction photographs may be built up using complimentary platterns which have been photo-etched with photographic separations generated from filtered colour photographs, screened through complimentary half tone screens, The invention will now be described by way of example with reference to the accompanying drawings in which:: Figure l(a) shows a diagrammatic representation of a foil carrying a diffraction grating and shows the colours that may be seen on the foil at different viewpoints, Figures l(b), l(c) and l(d) each schematically show a respective diffraction grating producing different colours at the same predetermined viewpoint, Figure 2 shows a diagrammatic cross-sectional view of a hot stamping foil embossed with a diffraction grating, Figure 3 shows the hot stamping transfer step using a planar plattern, Figure 4 shows the heated plattern and foil after the transfer step of Figure 3, Figure 5 shows a further embodiment similar to the step of Figure 3 but in which the plattern has a surface image profile thereon, Figure 6 shows the result of the hot stamping process with the profiled plattern of Figure 5 and is a view similar to that of Figure 4, Figure 7 shows a cross-section of a diffractive composition composed of three different diffractive colours. in which two colours are provided on a common background of a different colour, Figure 8 shows a cross-section of a diffractive composition in which three different colours are transferred complimentarily to one another, Figure 9 shows in schematic form an arrangement for registering foils at the hot transfer step, Figures 10, 11, and 12 show the steps in forming a profile on a plattern, Figure 13 shows a diffractive composition using four contrasting diffractive colours, and Figure 14(a)-14(c) show each of the faces of four complimentary hot stamping platterns used to compose the composition of Figure 13.

In the drawings like references denote like parts.

In this invention a range of diffractive hot stamping foils are produced using the methods known from the prior art, for example a range of foils each of which generates a slightly different diffractive colour from a predetermined viewing position. Thus for example, a range of similar foils are produced which show a different diffractive colour when viewed from an exactly central position, the range of colours including primary red, yellow, green and blue diffractive colours and which may also include orange, lemon and lime hues which lie in between the four primary colours.

To a casual observer handling the foils, the diffraction gratings might appear to be identical to one another because each of the foils will produce the whole visable spectrum of colour depending on the observer's viewpoint and the definition green or red, for example, is determined only by the exact fixed position of the observer when viewing the foils.

This effect is shown in Figure l(a) which shows a foil 1 which has been produced, for example, by the method described by M. C. Hutley noted above in which an observer viewing along the axis views colour green G, above the axis colour red R and below the axis colour blue B.

It will be appreciated that only one diffractive foil need be manufactured to produce the whole range of colours, each different colour being determined by cutting a small amount, for example about 0.5 inches (1.27cm) off the edge of the foil. Thus a diffraction foil 6 inches (15.24cm) wide which gives colour red at a central viewing position might be trimmed to a 5.5 inches (13.97cm) wide foil, which when laid next to the first foil, so that the trimmed edge is flush with the original edge, the perceived colour at the predetermined viewing position is no longer colour red but orange or yellow.

For the purposes of this description it will be assumed that a full width, e.g. 6 inches (15.24cm) foil is prepared for each colour.

Because the foils appear very similar to one another it is advisable that one edge of each foil be marked to in#dicate the lower "edge" so that it does not become inverted or used in the wrong direction at the hot transfer stage. This is important because the colour difference between the foils is dependent upon their orientation and positioning at the hot transfer stage. For this reason the foils should also be marked on one edge with notation which indicates the diffractive colours are yield at a given, e.g. central, viewing position.

Figures l(b)-l(d) show in pictorial form differing colours. Thus the part circular beads of Figure l(b) represent colour red R, the sawo tooth representation of Figure l(c)represents colour green G and the rectangular formation of Figure l(d) represents colour blue B. In this respect the colours are representative of different diffractive colours when each is viewed in turn from the same viewpoint, for example directly in line with the centre of the foil. Each of the representations in Figures l(b), l(c), l(d) represents a uniform field of colour.

Figure 2 shows a diagrammatic cross-section of a hot stamping foil which has been embossed with the colour green diffraction grating of Figure l(c). In Figure 2 a transparent carrier of polyester 1 such as P.V.C. supports a thin release layer 2 (which is optionally provided), a thermoplastic lacquer 3 into which a grating 4 representative of colour green is embossed. A vacuum deposited metal, for example aluminium, coating 5 is provided to sustain the embossed grating and a heat activated adhesive layer 6 supports the assembly on a substrate 7 of, for example, plastics or paper. Such a diffraction grating is known in the art as described by Bartolini et al in Applied Optics Vol.9, No.10, October 1970, pages 2283-2290.

In the particular embodiment of Figure 3 of this invention, a hot stamping foil uniformly embossed with a green diffraction grating is to be applied to a substrate 7. A heated plattern 10 having a planar surface is brought into contact with the carrier 1 to deform the grating onto the substrate 7 and the heat of the plattern 10 warms the heat activated adhesive 6 so that it- bonds the lacquer embodying the grating 4, 5 to the substrate 7. In Figure 4, the plattern 10 is raised and the diffraction grating 4, 5 is pulled away from the carrier web 1 leaving only the part of the diffraction grating that was directly under the plattern 10 adhering to the substrate 7.Thus the combination of heat and pressure applied by the transfer plattern 10 warms the hot transfer foil to release at the release layer 2 and at the same time causes the heat activated adhesive layer 6 to bond the thermo-plastic lacquer layer 3 3 containing the diffractive colour to the substrate 7.

Referring now to Figure 5, a plattern 20 has surface relieved portions 21, 22 and 23 so that projecting surfaces 24, 25, 26, 27 remain.

Thus when the plattern 20 is brought into contact with the hot transfer foil as shown in Figure 5 and pressure and heat applied to the foil only those areas which are contacted by the plattern are bonded to the substrate and those areas not in contact with the plattern projecting surfaces 24-27 remain attached to the polyester carrier web 1. The preferred method of profiling the plattern 20 will be described later herein with reference to Figures 10-14.

A sequence of selected diffractive foils each presenting a different desired diffractive colour at the same predetermined viewing point may be built up as shown in Figure 7 to produce a desired graphic composition element by element until a finished design is achieved in the full range of required diffractive colours. Referring to Figure 7, there is there shown a composition composed of three different diffractive colours, red R, green G and blue B. Thus substrate 7 is shown supporting a green background colour or pattern G with foreground colours blue B and red R transferred onto the green foil G. In such an arrangement the foils used for the subsequent colours blue and red may have release characteristics which differ from the primary foil G.It may be desirable that the temperature of the hot transfer of the blue and red colours be less than that of the primary foil G to ensure that the subsequent hot transfer steps of foils R and B do not melt or damage the adhesive or lacquer layers of foil G.

In Figure 8 there is shown a cross-section of a diffractive composition in which three foils each of a different colour R, G, B have been transferred with respective hot transfer platterns, each plattern having a different surface relief pattern on the face thereof and where each of the three patterns is complimentary to the other.

Referring now to Figure 9, there is shown an arrangement for registration of a substrate and for each of the hot foils. Orthogonally disposed stops 41, 42 are provided and substrate 7, for example, is biased against the inner surfaces of stops 41, 42 by spring loaded rams 43, 44 respectively. Thus precise positioning of the substrate 7 and foils is maintained.

An apparatus for forming the profiled surface of the plattern 10 will now be described with reference to Figures 10-14. In Figure 10 an L-shaped bed 50 having at least two spaced registration pins 51 supports a polished metal plattern 60. The upper surface of the plattern 60 is coated with photo-resist 61 and a photographic high contrast transparency 62 of, for example, KODALITH film having an image thereon for one of the colours to be hot stamped is mounted over the photo-resist. The transparency 62 has opaque areas 64 through which the ultra-violet illumination may project and dark areas 65 which prevent passage of ultra-violet radiation. The transparency 62 has an edge in which are at least two holes for closely fitting over the pins 51. In use, the photo-resist 61 is exposed through transparency 62 by an-ultra-violet lamp 63.The exposed areas of photo-resist are then removed to leave only the unexposed areas of photo-resist 66 as a negative of the desired image element as exposed metal on the plattern face.

The plattern 1 is then etched to remove areas where photo-resist is not present so that areas protected by the photo-resist remain unetched and present a smooth polished raised surface 67.

The composite diffractive image shown in Figure 13 is made from a sequence of hot foils of colours green, yellow, blue and red. The faces of each of the four complimentary hot stamping platterns to be used for the composite design of Figure 13 are shown in Figures 14(a)-(d). Figure 14(a) shows the plattern used to hot stamp a diffractive foil yielding colour green at a given viewing position, Figure 14(b) shows a plattern used to hot stamp a diffractive foil providing colour yellow at said given viewing position, Figure 14(c) shows a plattern used to hot stamp a diffractive foil giving colour blue at said gIven viewing position, and Figure 14(d) shows a plattern used to hot stamp a diffractive foil which yields colour red at said given viewing position.

It is to be appreciated that the scope of this invention is not to be limited to the colours described herein and any desired number of foils may be used to build up a composite image. Moreover the arrangements for registering the substrates and foils and of the photographic transparencies are not intended to be imitative and other forms of registration will be apparent to those skilled in the art.

Although it is usual to etch the plattern with acid to form the relief pattern that is required, more direct methods such as hand engraving can also be employed although it will be realised that such a manual method gives some restriction to the elaborate nature of the design. Also although it has been described that the plattern is metallic, this is not intended to be limiting since the plattern can be made of any other suitable material provided that it has a smooth surface in the areas arranged to contact with the foil and which can be recessed in other areas.

Although the invention has been described in relation to different diffractive colours, it is intended that the invention should not be so limited. In this respect shallow hologram images of small objects, for example coins, may serve as general backgrounds and a range of such images could be used in the same way as the pure diffractive colours.

Similarly, foils of a uniform nature may include patterns incorporating more than one diffractive colour arranged in repetitive patterns, for example alternately coloured straight lines, or zig-zag lines, or polkadots etc. which might also be used as backgrounds of a general nature.

In composing a particular graphic composition, a printer will first prepare artwork, dividing a multi-colour graphic composition into separate components and ascribing a different colour to each component.

In addition to having what amounts to a pallet of different diffracting coloured foils, i.e. different colours at a predetermined viewing point, or one or more background images or patterns may be selected which could be a hologram image with apparent three-dimensional depth giving a spatial contrast to the flat surface of the diffractive colours.

The plattern is fitted in a press and means are required to position the plattern with accuracy so that differing platterns are sequentially located in the same position. Simple graphic designs such as a silloette in one diffractive colour placed upon a plain diffractive background will clearly require less accuracy in positioning of the plattern whereas complex images and in particular photographic images of a line resolution of 80-200 lines per inch (31-79 lines per cm) will require micrometer adjustment of either the plattern mounting block or of the jig holding the substrate.

Claims (13)

CLAIMS:

1. A method of making a diffractive composition in at least two contrasting colours including the steps of providing a first foil having a first predetermined diffraction colour at a predetermined viewing position, hot stamping said first foil with a first hot stamping plattern to transfer said foil to a substrate, providing a second foil having a second predetermined diffraction colour at said predetermined viewing position, hot stamping said second foil with a second hot stamping plattern having a surface relief pattern thereon for selectively transferring areas of the second foil on to the first foil or the substrate.

2. A method as claimed in claim 1 wherein further foils each with different diffraction colours thereon at said predetermined viewing position are provided and a like number of hot stamping platterns are provided to build up acomposition.

3. A method as claimed in claim 1 or 2 wherein the first hot stamping plattern has a surface relief pattern thereon which is different to the surface relief pattern on said second hot stamping plattern.

4. A method as claimed in claim 1 wherein a first stamping plattern has a substantially planar surface to transfer the first foil as a background diffractive colour onto the substrate, a second hot stamping plattern has one surface relief pattern thereon which is applied to selectively transfer areas of the second foil onto said first foil, and a third foil is provided having a third predetermined diffractive colour at said predetermined viewing position, said third foil being hot stamped with a third hot stamping plattern having a surface relief pattern thereon for selectively transferring areas of the third foil onto either the first foil or the second foil.

5. A method as claimed in claim 1 wherein the first and second hot stamping platterns provide complimentary patterns on the substrate.

6. A method as claimed in claim 1 wherein one or more of the hot stamping platterns has a general and repetitive pattern thereon which is used to transfer a respective foil.

7. A method as claimed in claim 6 wherein the general and repetitive pattern is a holographic image.

8. A method as claimed in any preceding claim wherein each foil has a heat sensitive release layer to permit transfer of said foil and advantageously the heat sensitive release layer of each foil is different from another foil such that the foil with the highest release temperature is transferred first and so on to the foil with the lowest release temperature.

9. A method as claimed in any preceding claim wherein the required surface relief pattern is provided on a desired plattern by chemical action or manual profiling or electron beam milling or C02 laser cutting.

10. A method as claimed in any preceding claim wherein at one of the hot stamping steps the associated plattern is arranged to have a surface relief pattern bearing a number particular to each composition so that the number for each composition sequentially vary to provide security to a holographic composition.

11. A method as claimed in claim 10 wherein the foil bearing the number is covered with another foil which is partially light transmissive.

12. A method substantially as herein described with reference to and as shown in the accompanying drawings.

13. A diffractive composition when made according to the method of claim 1.