The present invention relates to a method of and an apparatus for producing a succession of self-adhesive labels carried on a backing of release material.
It is known, for example from EP-A-0275670, to produce a succession of self-adhesive labels which are carried directly on a backing of release material.
The present invention aims to provide an improved method of and apparatus for producing labels.
Accordingly, the present invention provides a method of producing a succession of self-adhesive labels carried on a backing of release material, the method comprising the steps of:- (a) providing a plurality of printed sheets; (b) feeding the sheets in succession through an adhesive spraying station at which adhesive is sprayed from a spray nozzle onto an exposed surface of each sheet; and (c) adhering the adhesive-coated exposed surface of each of the succession of sheets to a backing of release material, characterised in that prior to feeding step (b) the sheets are electrostatically charged thereby to enhance the coating of adhesive onto the exposed surfaces.
The present invention also provides an apparatus for producing a succssion of self-adhesive labels carried on a backing of release material, the apparatus comprising an adhesive spraying station comprising a spray nozzle for spraying adhesive, means for feeding a succession of printed sheets through the adhesive spraying station so that an exposed surface of each sheet is coated with adhesive and means for adhering the adhesive-coated surface of the sheets to a backing for release material, characterised by means for electrostatically charging the sheets before the sheets are fed through the adhesive spraying station.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:-
Referring to Figures 1 and 2, an apparatus, designated generally as 2, for producing a succession of self-adhesive labels carried on a release backing material includes a magazine 4 for holding a stack of printed sheets 6. The sheets 6 may be single layer or multi-layer sheets and are printed by any suitable printing method, such as lithographic, screen or laser printing. A sheet feeding mechanism 8 is located above the stack of sheets 6 and is adapted to feed from the magazine 4 a succession of sheets 6 from the top of the stack. The sheet feeding mechanism 8 is represented as a rotatable drive cylinder but may alternatively comprise any suitable known sheet feeding mechanism. The sheets are fed in succession past an electrostatic charging device 10 which is adapted to apply an electrostatic charge of a given polarity across the upper surface of the sheets 6. When the sheets 6 are made of paper, this charge is retained evenly over the sheets 6. If desired, the electrostatic charging device 10 may be omitted when the sheet feeding mechanism 8 is adapted to feed sheets from the stack in such a way that the fed sheets have an electrostatic charge. The sheets are fed by the sheet feeding mechanism 8 onto a vacuum drive means incorporating a vacuum conveyor 12 which comprises an endless belt 14 mounted between a pair of drive rollers 16. The surface of the endless belt 14 is provided with a series of holes 18 and the space 20 between the opposed inner surfaces of the endless belt 14 is connected to a source of suction. As the sheets 6 are deposited onto the vacuum conveyor 12 the bottom surface 22 of each sheet is sucked through the holes 18 against the upper surface 24 of the endless belt 14. This ensures that each sheet 6 is firmly located on the vacuum conveyor 12.
The vacuum conveyor 12 conveys the succession of sheets 6 through an adhesive spraying station 26 comprising a spray nozzle 28 for spraying a coating of adhesive 30 onto the exposed upper surface 32 of each sheet 6 passing through the adhesive spraying station 26. In the preferred embodiment, the spray nozzle 28 is adapted to spray electrostatically charged droplets of adhesive onto the exposed surfaces 32. This may be effected by feeding electrostatic charge from a source of electric power to the spray nozzle 28, the charge being of opposite polarity to that which is applied by the electrostatic charging device 10. The adhesive may be a water-or solvent-based pressure-sensitive adhesive or alternatively a heat-sealable pressure-sensitive adhesive.
The succession of sheets 6 coated with adhesive 30 is then fed by the vacuum conveyor 12 to a laminating station 34 comprising a pair of opposed rollers 36, 38 between which the succession of sheets 6 is laminated to a backing 40 of release material, the laminating being achieved by adhering the adhesive-coated surface 32 of each sheet 6 to the backing 40 of release material. The backing 40 of release material is fed out from a reel 42 thereof and typically comprises a wax-or silicone-coated paper. The adhesive coating 30 is urged against the backing 40 of release material and then the combined assembly passes over an idle roller 44 and is then wound up on a take-up reel 46 of the succession of self-adhesive labels 6 on the backing 40 of release material.
In the illustrated arrangement, the sheets 6 are conveyed through the adhesive spraying station 26 in spaced relation. The spraying nozzle 28 may be operated either continuously or intermittently in synchronism with the disposition thereunder of a sheet 6 to be sprayed with adhesive. A washing and cleaning mechanism 48 is disposed in contact with the endless belt 14 for cleaning excess adhesive 30 off the outer surface of the endless belt 14.
If desired, the apparatus may also comprise a slitting mechanism at, or downstream of, the laminating station 34 at which the backing 40 of release material and the succession of sheets 6 adhered thereto are longitudinally slit so as to provide two adjacent reels 46 of the self-adhesive labels carried on the backing of release material. With this arrangement, each printed sheet 6 would have a pair of identical images printed thereof transversely adjacent to each other.
As shown in Figure 3, the endless belt 14 may be modified by the provision thereon of a succession of raised pads 58. In use the sheet feeding mechanism 8 feeds the sheets 6 so that each sheet lies on a respective pad 58 above the surface 60 of the endless belt 14. This assists the application of adhesive to the sheets 6 and ensures that those parts of the endless belt 14 which receive extraneous adhesive do not actually contact the edges of the sheets 6.
A second embodiment of an apparatus for producing labels in accordance with the present invention is shown in Figure 4. This embodiment is a modification of that shown in Figures 1 and 2 and like parts are identified by like reference numerals. In this embodiment, the vacuum conveyor 50 comprises a vacuum cylinder 52 which is hollow and the cylindrical surface of which is provided with an array of holes (not shown). The cylindrical void in the centre of the vacuum cylinder is connected to a source of suction. The sheets 6 are fed out from the stack thereof by the sheet feeding mechanism 8. The bottom surface 22 of each sheet 6 engages the upper surface of the printing cylinder 52 which is rotatably driven and conveys the sheet 6 through the adhesive spraying station 26 to the laminating station 34. The adhesive spraying station 26 is additionally provided with a pair of shields 54, 56 which are located on upstream and downstream sides, in relation to the direction of feeding of the sheets 6, of the spray nozzle 28. The shields 54, 56 are arranged so as to control the application of the spray of adhesive 30 to within defined boundaries. If desired, the operation of the spray nozzle 28 is controlled so as to be intermittently synchronized with the location of a sheet 6 between the shields 54, 56.
As with the first illustrated embodiment, the apparatus may be modifed by the addition thereto of a slitter for longitunally slitting the assembly of self-adhesive labels carried on the release material. The apparatus may additionally be provided with a downstream inspection station at which the assembly of self-adhesive labels on the reel of release backing material can be inspected.
In each of the two illustrated embodiments, the electrostatic charge initially on the sheets as they enter the adhesive spraying station is either neutralised by the application of the adhesive or dissipated at, or downstream of, the adhesive spraying station as a result of contact of the sheets with other parts of the apparatus. In the resultant reel of self-adhesive labels, there is no substantial electrostatic charge.