EMBOSSED ARTICLES

Abstract: A subtrate, (1) e.g. of thermoplastic or paper material, has embossed thereon first (2a) and second (2b) non-light diffract­ ing relief elements which define first and second patterns, respectively. The patterned area is uniformly reflective. For ex­ ample, the first relief elements (2a) form a background area in which are arranged the second elements (2b) in the shape of a company logo. The first (2a) and second (2b) relief elements are so strutured that when the direction of view thereof is changed from a first to a second direction the relative perceived distinctness of the first and second patterns is changed. The substrate may form part of a security document whose authen­ ticity may be checked by ensuring that the relative distinctness of the two patterns changes with the angle of view.

Description: The present invention relates to a method of forming an article with an embossed surface. US-A-4033059 (Hutton & Merry) discloses forming an article having a surface which comprises an embossed patterned uniformly reflective portion by intaglio printing, which portion includes at least first and second non-light-diffracting pattern-defining relief elements defining at least first and second patterns, the pattern-defining relief elements being so structured that, when the direction of view of the surface is changed, the perceived relative distinctiveness of the pattern is changed (so-called latent or transitory images). An intaglio imprint is obtained by pressing a suitable recording medium, for example, paper, against an engraved and inked plate so as to deform the medium into the ink-bearing engraved recesses of the plate. The resulting impression comprises a pattern formed of spaced and raised inked lines and/or other pattern elements. GB-A-2 129 739 (American Bank Note Company) discloses a process of making a readable light diffracting record which comprises securing a laminated structure of an embossed foil layer and a thermoplastic layer to a substrate such as paper by a hot melt adhesive covering the embossed foil. The paper may bear conventional printing, preferably intaglio, the printing being carried out preferably before but possibly after securing the laminated structure. GB-A-2 129 739 also mentions prior art where the embossing and transfering processes are performed simultaneously. The invention comprises a method of forming an article with an embossed surface comprising using a stamping plate to stamp a material to define an embossed patterned uniformly reflective surface portion, which portion includes at least first and second non-light-diffracting pattern-defining relief elements defining at least first and second patterns, the pattern-defining relief elements being so structured that, when the direction of view of the surface is changed the perceived relative distinctiveness of the pattern is changed, characterised by adhering over at least part of the patterned portion a sheet or foil by using the stamping plate simultaneously to apply the sheet or foil to the material in a hot foil blocking process. The invention thus provides a method in which for example a coloured or metallic sheet or foil is applied to the article at the same time as the surface is embossed. The sheet or foil may be a photograph, or the material may be a photograph, in which case the sheet or foil may comprise light diffracting elements, for example a diffraction grating or hologram. The accompanying drawing shows how a sheet or foil is applied to the surface of an article by hot foil blocking. The drawing shows a laminated structure 1 comprising a carrier sheet 2, usually of clear plastics, which is coated with a release layer 3. On the release layer 3 is a coloured layer 4 (for example a metal foil or coloured plastics sheet) and on this is a layer of heat seal adhesive 5. The laminated structure 1 is placed so that its adhesive 5 is in contact with a substrate 6 to be blocked. A heated die or stamping plate 7, having the shape of the area to be blocked and engraved suitably to form an embossed area, is pressed into the back of the carrier sheet 2 as shown by the arrow P. This causes the adhesive 5 to fuse to the substrate 6 and the release layer 3 permits the carrier sheet 2 to be removed. A good result can be difficult to obtain using stamping because of the difficulty of compressing the material into the recesses. Thus, if the substrate 6 is a thermoplastic, the temperature of the plate and the pressure applied have to be as high as possible because the material is cold and the dwell time typically limited. The stamping plate includes an area having recesses corresponding to the relief elements which it is desired to apply to the surface and conventional engraving techniques may be used to prepare the plate. For example, the techniques used in engraving intaglio printing plates are suitable. Preferably a plate is used which would generally be seen as having relief elements to form a pattern which would generally be seen as recessed, that is the majority of the area of the plate would be recessed with a small area in relief whilst the embossed surface would mainly be in relief with a small area of lines, for example, recessed. Where the blocking foil is metallic, the extra reflectance makes the two patterns more easily distinguishable from each other and viewing is particularly attractive. Metal foil blocked surfaces are thus particularly desirable for novelties and packaging. Alternatively, a magnetic foil may be used, in which case the embossing serves as a security device to prevent tampering with the foil. If the substrate (6) does not emboss well, a foil or sheet (which may be transparent) may be applied thereto by hot foil blocking to form an embossable laminate. Holograms are commonly applied to credit and cheque cards for security reasons as well as to non-secure documents for visual appearance. The holograms are applied using a hot foil blocking technique and are supplied to card manufacturers on a roll. Usually there is considerable amount of waste foil surrounding each hologram image. If a blocking die was manufactured to have a flat area designed to transfer the hologram and adjacent to it an area engraved to form an embossed surface the resulting combination would be relatively tamper-proof and visually attractive. Also an additional security feature for plastics cards can be provided by measuring the distance between a feature in the relief area and a feature in the hologram. The two features may be analogous, that is the one corresponds to the other. The distance between the two images will vary for reasons of manufacturing tolerance and if this distance is measured by an appropriate optical technique and the measure recorded, for example, on the magnetic strip of the card, security against unauthorised duplication of cards can be achieved. Any attempt to produce a duplicate card will almost certainly result in the distance between the two images being different from the original. A cash dispenser incorporating a unit to compare the actual distance between the images with the data recorded on the strip would detect a difference and refuse payment. The hologram could be replaced with a diffraction grating and the reflective embossing need overlap with only part of the hologram or diffraction grating foil or sheet. Alternatively, the reflective embossing may overlap with the hologram or diffraction grating itself. Moreover, as a security technique to prevent tampering with a foil or sheet which has been hot foil blocked onto a permanently embossable surface, or duplication of an article carrying such a sheet or foil, the technique is generally applicable. "Latent images" may be applied to security documents or any other suitable articles on which security markings are required. The permanently embossable surface may be part of the article itself or it may be on a separate sheet or material, for example, which is secured to the article. Thus credit cards or tape cassettes, for example, may be embossed during the course of their manufacture to provide good quality patterns of relief elements. Since no inking or other colouring is necessary the process is relatively straight forward. On the other hand somewhat cruder patterns can be applied to documents using a simple press subsequent to their manufacture, for example, identity cards may be embossed on site by the issuers thereof. In addition the ability of photographic paper to accept embossing permits the securing of a photograph by embossing an appropriate security latent image into the photograph simultaneously with its lamination into an identity card or passport. This provides an effective defence against the total removal of a genuine photograph and its replacement by an unauthorised one. The plates needed to emboss the articles are difficult to counterfeit yet an unskilled person can easily check the authenticity of a document by tilting it to change the angle of view and watching the change in contrast between the two (or more) patterns. The sheet or foil may be coloured if desired so that it contrasts more strongly with the substrate material or is more visually appealing. Such coloured embossing may be used with packaging.

Claims: A method of forming an article with an embossed surface comprising using a stamping plate (7) to stamp a material (6) to define an embossed patterned uniformly reflective surface portion, which portion includes at least first and second non-light-diffracting pattern-defining relief elements defining at least first and second patterns, the pattern-defining relief elements being so structured that, when the direction of view of the surface is changed the perceived relative distinctiveness of the pattern is changed, characterised by adhering over at least part of the patterned portion a sheet or foil (4) by using the stamping plate (7) simultaneously to apply the sheet or foil (4) to the material in a hot foil blocking process. A method as claimed in claim 1, wherein the sheet or foil (4) is a photograph. A method as claimed in claim 1, wherein the material (6) is a photograph. A method as claimed in claim 1 or 3, wherein the sheet or foil (4) comprises light diffracting elements. A method as claimed in claim 4, characterised by recording on the article the distance between a feature defined by the relief elements and a feature defined by the diffracting elements. A method as claimed in claim 5, characterised by recording the said distance on a magnetic recording medium.

Inventors: CHATWIN, CHARLES EDWARD
Applicants: THOMAS DE LA RUE AND COMPANY LTD.
Application year: 1986
Main classification: G06K19
IPC codes: B42D15, G06K19, B44C1, B44F1