Backed adhesive sheets from which labels are cut are printed in either a continuos roll or in sheet form. They are then passed through a cutter to die cut, kiss cut, crease or perforate the backed adhesive sheet. The term"cutter" as used herein is not intended to be restricted to apparatus which cuts through a sheet, that is to die cut the sheet. The term cutter refers herein to other similar processes carried out on the sheet which may not cut through the entire sheet or may not involve a true cutting action, for example, kiss cutting, perforating, creasing or embossing or blocking. A die cut will penetrate the adhesive sheet and release the cut area from the sheet whereas a kiss cut will penetrate only the adhesive sheet, leaving the release sheet uncut. Perforating will form discontinous cut lines through part of or the entire sheet; creasing will emboss a line in the sheet with no cutting; embossing will emboss an area of the sheet and blocking will apply by the application of pressure a coating, for example a foil, to an area of the surface of the sheet, for simplicity the components of the apparatus performing cutting, perforating, creasing, embossing and blocking operations will be referred to herein, for simplicity, as "cutting formes"'.

According to the present invention there is provided a sheet cutter including feed means for sequentially feeding sheet from a supply of sheets to a positioning arrangement, positioners for precisely positioning each sheet in the positioning arrangement, transfer means for presenting the positioned sheet to the nip formed between a pair of cylinders one of which incorporates magnetic means for releasably carrying cutting formes thereon and the other of which forms an anvil for reacting with the said one cylinder, and control means for controlling and synchronising the operations of the feed means, positioners, transfer means and cylinders.

Preferably the anvil is a plain hardened steel cylinder. It may be another magnetic cylinder carrying cutting formes.

Preferably the distance between the axes of rotation of the cylinder and anvil cylinder is adjustable by adjusting means.

Preferably the feed means includes a pneumatic feed system for separating the top sheet from a bundle of sheets and passing it to the positioning arrangement.

Preferably the positioning arrangement includes pneumatic means for retaining a positioned sheet in its precise position until it is moved by the transfer means.

Preferably the transfer means are pneumatic.

Preferably the means for controlling and synchronising the feed means, the positioners, the transfer means and the rotation of the cylinders are computer controlled.

Preferably the said anvil cylinder is provided with pneumatically operated grippers to secure a sheet in position thereon.

Preferably delivery means are provided at the outlet from the nip between the cylinders.

Preferably the cutting formes are manufactured from high tensile etched steel. Preferably they are photo etched from a positive film.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing which shows diagrammatically a side elevation of a sheet cutter.

The cutter comprises a framework 10 which supports a table 12 to which is supplied a bundle of backed adhesive sheets to be cut by the cutter, each sheet comprising a printed top sheet having an adhesive layer on its back, the adhesive being protected by a release sheet.

A feed means in the form of a timed, integrated, single sheet suction separating and feeding arrangement, the construction and operation of which does not form part of the present invention and consequently will not be described in detail, is referenced in the drawing by the general reference numeral 14. In operation the feed means 14 by pneumatic and mechanical means separates the top sheet from the bundle of sheets on the table 12 and advances it into a positioning arrangement 16 which, once again, does not form part of the present invention and will only be described briefly herein. The positioning arrangement comprises a plurality of rollers, cylinders and suction holes which accept a sheet from suction feet 18 of the feed means 14 and, by means of two timed feed rollers 20 positions the sheet on a registration plate 22 which is provided with suction holes (not shown) to hold the sheet in place.

The positioning arrangement 16 has front and side lay stops 24,26 which ensure precise positioning of the sheet and the transfer means release the sheet at a precise point in time which coincides with the precise time that pneumatically operated gripper arms 32 on a cylindrical anvil 34 pick up the sheet and carry it, precisely positioned on the surface of the anvil cylinder 34 into the nip 36 defined between the anvil cylinder 34 and a cylinder 28 which incorporates a plurality of magnetic means (not shown) for holding cutting formes in a precisely located but removable position on the surface thereof.

The surface of the anvil cylinder 34 is of hardened steel, and is plain. Means are provided for adjusting the distance between these axes of rotation of the cylinders 34,28 such that the width of the nip therebetween is adjustable. The cylinders 34,28 are rotated synchronously by an electric motor and transmission assembly (not shown).

It will be appreciated that if the cutting formes have been accurately positioned during set up of the cutter they will register exactly with positions on the sheet held by the grippers 32 of the cylinder 34 to die cut, kiss cut, perforate or crease the backed sheet held on the anvil 24 depending upon the depth and configuration of the die lines on the cutting forme.

Processed sheets exiting from the nip 36 between the cylinders 34,28 are directed to a collecting tray 30 by delivery rollers 40.

The electrical and pneumatic operating means for the components of the cutter are coordinated in their mode and time of operation and coordination is achieved by a computer controlled arrangement. This ensures not only the positionally precise movement of sheets through the cutting nip but also a much improved production speed, sometimes by a factor of two, than normally experienced with existing sheet fed cutters operating according to a conventional letter-press platen technique.

The cutting formes carried by the cylinder 28 are of high precision and are formed from high tensile steel by an etching process. They are photo etched from positive film and leave a cutting profile of a depth varying between 0.44 and 1 mm capable of ten million cuts per forme on materials up to 450 microns thick. The machine is capable of treating up to ten thousand sheets per hour. The formes can be lifted and moved easily by hand to correct the cutting position to mirror the printed sheet. A fully printed B3 plus sheet can be processed by the cutter and the cutter can process sheets having thicknesses within the range 60 microns to 450 microns.

In a modification the anvil cylinder 34 may also be a magnet cylinder similar to the first cylinder 28 but having different magnetic characteristics. It may removably carry formes, complementary to the formes on the cylinder 28 to provide areas on the sheet (which need not be an adhesive backed sheet) which are embossed or blocked by coating a foil, for example gold foil, thereto under the action of pressure exerted by the cylinders.