PRINTING METHOD AND APPARATUS

Abstract: In security printing apparatus for attaching a foil imprint of predetermined shape to stock (10) such as bank note sheets, a tape (8; 108) carrying foil to be printed and a layer of hot-melt adhesive is conveyed with the stock past a heated printing roll (2; 102). In order to allow high printing speeds the adhesive is at least partially activated by pre-heating just prior to printing. The pre-heating means may comprise hot air, radiation or heated guide means for the foil carrier web. Details of pattern or shape may be etched on the foil, either before or after printing, by means of laser beam, the details being defined by a mask moving with the foil.

Description: l Printing Method and Apparatus 2 3 This invention relates to printing apparatus, and in particular to « such apparatus for carrying out a process commonly known as hot foil 5 stamping. e In security printing apparatus it is known to apply a thin layer of 7 metal foil of predetermined shape and/or pattern to a stock, e.g. a sheet β of bank notes, usually as a feature intended to make counterfeiting more 9 difficult. In a typical application the foil is carried as a continuous 10 lamination between a carrier substrate and a layer of hot melt adhesive, π the shape or pattern to be applied being determined by a stamp or i2 press. In prior art arrangements the carrier substrate and the stock (e.g. i3 a sheet of bank notes) are placed together beneath a platen-type press i4 carrying an array of stamps which are simultaneously applied to cause is an array of hot foil imprints to be applied to the stock. Heat for activating i6 the hot melt adhesive is generally applied from the press, and an inability i7 to transfer heat sufficiently quickly is a factor in limiting the speed of such is prior art arrangements. i9 According to a first aspect of the invention printing apparatus for 20 applying foil to a stock comprises means for conveying a carrier for the 2i foil together with an adhesive which is activated by heat towards a 22 printing position, means for conveying a stock towards said printing 23 position, printing means at which the carrier and stock are moved 24 together past said printing position at which pressure is applied to 25 transfer a predetermined pattern and/or shape of foil from the carrier to 25 the stock, and pre-heating means for transferring heat to the carrier 27 before it reaches the printing position and/or before it contacts the stock. 28 Preferably the pre-heating means is effective to transfer heat to the 29 carrier immediately upstream of the printing position. For example, 30 where the printing means comprises a nip between a print wheel and a 3i counter wheel the pre-heating means may be located to be effective as 3 2 close as possible to said nip. Preferably the pre-heating means 33 comprises means directed particularly at the adhesive layer, e.g . 3 comprising radiation or hot air directed at said layer. 35 In a preferred arrangement the printing means comprises means 36 for applying both pressure and heat at said printing position. For 3 example, the printing means may comprise a print wheel carrying one or 38 more stamps defining said predetermined pattern and/or shape, the 1 wheel carrying heating means in the vicinity of said stamp or stamps. 2 The printing apparatus may form part of security printing 3 apparatus of the type disclosed in EP 0441596A, the disclosure of which 4 is hereby incorporated herein in its entirety. This apparatus discloses a 5 security printing process in which thin film security material is 6 transported on a carrier ribbon past a printing position together with a 7 moving stock. s According to another aspect of the invention a method of applying 9 foil to a substrate by means of pressure and heat to secure the foil to the ιo substrate by means of a hot melt adhesive in which the foil and substrate a are moved together past a printing position so that successive foil i2 imprints are made at said position, includes a process step in which the i3 adhesive carried with the foil is pre-heated before it reaches said i4 position. is According to a further aspect of the invention a method of i6 applying foil to a substrate by means of pressure and heat to secure the i7 foil to the substrate by means of a hot melt adhesive in which the foil and is substrate are moved together past a printing position so that successive i9 foil imprints are made at said position includes the step of laser etching 20 the shape or pattern of the foil either upstream or downstream of the 2i printing position. Preferably said laser etching is carried out using a 22 suitably shaped or patterned mask which is moved together with the foil. 23 The invention will be further described, by way of example only, 2 with reference to the accompanying diagrammatic drawings, in which: 25 Figure 1 is a side view of part of a foil printing apparatus, 26 Figure 2 is a sectional view, not to scale, of a carrier tape 27 including a layer of foil to be printed, 28 Figure 3 is a cross-sectional view, not to scale, of a printing stamp 29 usable with the apparatus of Figure 1 , 30 Figure 4 is a side view of a security printing machine incorporating 3i foil printing apparatus, and 32 Figure 5 is a perspective view of the foil printing apparatus in the 33 machine of Figure 4. 34 Figure 1 shows a driven printing wheel 2 carrying one or more 35 heated dies or stamps 4 which cooperate with a substrate wheel 6. The 36 wheel 6 has a sleeve comprising a flexible polymer printers' makeready. A tape 8 carrying foil to be printed is delivered to the nip of the wheels 2 38 and 6 along with a web or sheet 10 on which a foil pattern corresponding 1 to that on the stamp 4 is to be printed. 2 The apparatus shown in Figure 1 forms part of a security printing 3 machine such as that disclosed in EP 0441596A. In particular, the 4 wheels 2 and 6 correspond to the cylinders 46 and 48 in that machine. 5 The tape 8 is driven in the same manner as the tape 34 in EP 0441596A, 6 that is to say for each printing cycle it is accelerated up to the speed of 7 the web 10 (normally corresponding to the peripheral speed of the β wheels 2 and 6), maintained at that speed through the nip between the 9 wheels 2 and 6 while the stamp 4 passes through the nip , and ιo subsequently decelerated to rest and reversed so that the net advance u of the tape for each printing cycle only slightly exceeds the length of the i2 image to be imprinted by the stamp 4. i3 Figure 2 is a cross-sectional view (not to scale) showing the tape i 8, which comprises four layers: a polyester carrier layer 12, a layer 14 of is release wax, a layer 16 of foil, typically aluminium, and a layer 18 of a hot i6 melt adhesive. Typical thickness (in mm) for each of the layers of the i7 tape 8 are: i8 Carrier (12): 0.012-0.030 i9 Release Wax (14) : 0.0001 20 Foil (16): 0.001-0.002 2i Adhesive (18) 0.001-0.003. 22 Figure 3 is a sectional view of a typical stamp 4, indicating that it 23 comprises areas 4A intended for printing and areas 4B which are 24 relieved, by up to 2mm as indicated at X, and hence not to be printed. 25 Within some of the areas 4A there are micro-engravings 4C, which are 26 raised by typically 0.02-0.03mm above the general level of the area (as 27 indicated at Y) and are intended to produce fine detail in the imprint. 28 In operation, the tape 8 and web 10 travel through the nip which is 29 subject to a high pressure (typically 350-1 OOObar) so that the stamp 4 30 causes a pattern of foil corresponding to that determined by the raised 3i area of the stamp to be released from the carrier layer 12 and to be 32 adhesively secured to the web 10 by means of the hot melt adhesive 33 layer 18 activated by the heated stamp 4. Pressure at the nip is much 34 lower during periods when a stamp 4 is not passing through, so that the 35 tape 8 may be decelerated and reversed as previously explained. 36 At higher speeds (up to 2m per second or more) and for detailed 37 patterns to be transferred by the stamp 4 it is important that sufficient 38 heat is transferred to the tape 8 to activate the hot melt adhesive layer 1 18. Although the stamp 4 is heated, typically to a temperature in the 2 range 120-170°C by a cartridge heater 20 carried by the wheel 2, there 3 may be insufficient time for adequate heat to penetrate the tape 8 to the layer 18. Increasing further the temperature of the stamp 4 may cause 5 physical damage to the tape 8. In order to provide adequate heat at the 6 layer 18, therefore, pre-heating of the tape 8 is effected by passing it 7 around a heated bar (or rolle r) 22, whi ch m ay be heated to a a temperature in the range 60-120°C. 9 Although passing the tape 8 around the bar 22 is effective in ιo providing additional heat just upstream of the position at which printing π takes place, this heat is still applied from the side of the tape remote from i2 the adhesive layer 18. Although it is not possible to pass the layer 18 i3 over a heated surface as this would release adhesive on to the surface, i additional or alternative pre-heating can be provided on the side of the is layer 18 by directing hot air at it just upstream of the nip between wheels i6 2 and 6, as indicated at 24 in Figure 1 where hot air is supplied by a i7 blower unit 25. Additionally, or as a further alternative, heat may be is supplied by directing infra-red radiation at the layer 18 just upstream of i9 the nip (i.e. the unit 25 could include or consist of an infra-red radiator). 20 The frequency of the radiation may be selected so as to be appropriate 2i to the material of the hot-melt adhesive, i.e. so as to be readily absorbed 22 by it. A further possibility would be to use microwave radiation: this 23 might also be directed from the side of the adhesive layer 18, but could 2 be directed from the other side of the tape 8 and still cause effective 25 activation of the hot melt adhesive. 26 Any of the means of pre-heating could be used in combination: in 27 all cases the pre-heating is preferably carried out closely adjacent to the 28 printing position, as the thermal mass of the tape 8 is small and its 29 surface area relatively large so that it loses heat and returns to ambient 30 temperature rapidly. 3i The security printing machine shown in Figure 4 comprises a 32 sheet feeding unit 130 for feeding sheets 110 from successive stacks 33 132 delivered to the unit. Each successive sheet 110 is fed down a ramp 3 134 to a lay device 136 which transfers the sheet onto a substrate wheel 35 106. The wheel 106 cooperates with a print wheel 102 carrying heated 36 stamps (not shown) which are similar to the stamps 4 so as to cause a 37 foil imprint to be applied to the sheet 1 10 in predetermined positions. 38 Printed sheets 110 are conveyed by suction around the wheel 106 and 1 transferred to a belt conveyor 138 provided with individual sheet grippers 2 140. The conveyor 138 delivers printed sheets 1 10 to a stacking unit 3 142 having two stacking positions. 4 A carrier tape 108, similar to the tape 8, is delivered from a reel 5 144 through a suction reservoir 146, which provides tension for the tape, β to the nip between the print wheel 102 and the substrate wheel 106. 7 Just upstream of this nip the tape 108 passes a pre-heating unit 148, a which comprises infra-red heating elements directing radiation at the 9 adhesive layer of the tape but which could comprise alternatively or ιo additionally any of the other pre-heating means described with reference a to Figure 1 or any other convenient pre-heating means. Downstream of i2 the wheels 102 and 106 the tape 108 passes between drive rolls 150 and i3 is subsequently collected in a waste unit 152. i4 As is apparent from Figure 5, the reel 1 44 carries multiple is laterally-spaced tapes 108 (although only one tape run is shown in i6 Figure 5) so that foil imprints can be simultaneously placed at i7 laterally-spaced predetermined positions on the sheets 110 which, as is indicated, may comprise several images (e.g. for bank notes) across i9 their widths. The arrangement is similar to that disclosed in 2o EP 0441596A, where each of the sheets to be printed consisted of 10 2i bank notes across the width and there were correspondingly ten ribbons 22 corresponding to the tape 108. 23 It is possible to etch details of shape or pattern on the foil by 2 means of a suitable laser beam (e.g. a C0 2 laser). The etching may take 25 place on the tape, i.e. before printing, or on the foil applied to the sheet, 2 6 i.e. after printing, or possibly both before and after printing. The pattern 2 7 or detail to be etched may be defined by means of a mask moving at the 28 same speed as the tape or sheet: in addition the beam itself may be 29 scanned relative to the tape or sheet. Laser etching may avoid the need 30 for stamps with particularly detailed shapes or patterns, these being 3i provided by the laser in combination with a basic stamp pattern. Clearly 32 the power intensity of the laser beam needs to be closely controlled so 33 as to remove only foil (or foil and adhesive in the case of etching of the 34 tape) without causing damage to the underlying material. 35 36 37 38

Claims: i Claims: 2 3 1. A method of applying foil to a substrate by means of pressure and heat to secure the foil to the substrate by means of a hot 5 melt adhesive in which the foil and substrate are moved together past a 6 printing position so that successive foil imprints are made at said 7 position, including a process step in which the adhesive carried with the β foil is pre-heated before it reaches said position. 9 lo 2. Apparatus for applying foil to a stock, comprising means a (1 50) for conveying a carrier (8; 108) for the foil together with an i2 adhesive which is activated by heat towards a printing position, means i3 (6; 106) for conveying a stock towards said printing position, printing .4 means (2; 102) at which the carrier and stock are moved together past is said printing position at which pressure is applied to transfer a i6 predetermined pattern and/or shape of foil from the carrier to the stock, i7 and pre-heating means (22,25; 148) for transferring heat to the carrier is before it reaches the printing position and/or before it contacts the stock. 19 20 3. Apparatus as claimed in claim 2, wherein the pre-heating 2i means (22,25; 148) is arranged to transfer heat to the carrier immediately 22 upstream of the printing position. 23 24 4. Apparatus as claimed in claim 2 or claim 3, wherein the 25 printing position includes a nip between a printer wheel (2; 102) and a 26 counter wheel (6; 106) and the preheating means (22,25; 148) is 27 arranged to supply heat to the carrier and it is delivered into said nip. 28 29 5. Apparatus as claimed in any of claims 2 to 4, wherein the 30 pre-heating means includes means (25) for directing radiation at said i adhesive layer. 32 33 6. Apparatus as claimed in any of claims 2 to 5, wherein the 34 preheating means includes means (25) for directing hot gas at said 35 adhesive layer. 36 37 7. Apparatus as claimed in any of claims 2 to 6, wherein the 38 printing means (2; 102) includes means (4) for applying both pressure l and heat at said printing position. 2 3 8. Apparatus as claimed in claim 7, wherein the printing means comprises a print wheel (2; 102) carrying one or more stamps (4) 5 defining said predetermined pattern and/or shape. 6 7 9. A method of applying foil to a substrate by means of β pressure and heat to secure the foil to the substrate by means of a hot 9 melt adhesive in which the foil and substrate are moved together past a ιo printing position. so that successive foil imprints are made at said a position, including the step of laser etching the shape or pattern of the i2 foil either upstream or downstream of the printing position. 13 i4 10. A method as claimed in claim 9, wherein said laser etching is is carried out using a mask which is moved together with the foil. 16 i7 11. A method as claimed in claim 1 and either claim 9 or claim 18 10. 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Inventors: AINDOW ALAN MICHAEL, CAHILL MICHAEL JOHN, SANTON DAVID, AINDOW, ALAN, MICHAEL, CAHILL, MICHAEL, JOHN, SANTON, DAVID
Applicants: AINDOW ALAN MICHAEL, CAHILL MICHAEL JOHN, MOLINS PLC, SANTON DAVID, AINDOW, ALAN, MICHAEL, CAHILL, MICHAEL, JOHN, SANTON, DAVID
Application year: 1996
Main classification: B41F19
IPC codes: B41F16, B41F19, B42D15, B44C1, B44F1