[0019] As shown in FIG. 1, a wide roll of adhesive tape 1 is unwound and the tape passes under a flexo printer 2 which prints a band of coloured ink 3 across the entire width of the tape. The bands of coloured ink are all of equal width, approximately 25 mm. The interval between successive bands of ink is approximately G5 mm. The coloured ink is of a different colour to the adhesive side of the tape and where the ink is applied it neutralises the adhesive on the tape i.e. the adhesive on the tape is made non-adhesive by the application of the ink onto it. Suitable inks include Flexo vinyl masking (yellow/red/green/blue) CON 043 available from Inktech of Crawford Street, Rochdale, OL16 5NU, UK. Once the ink has been printed on the tape, the tape can be cut into strips of the required width and pancake or spool wound.

[0020] In a typical bag tying machine the adhesive tape is applied to the neck of a filled bag with movement of the gathered together neck of the bag through a bag tying machine. A typical bag tying machine is shown in GB-A1381871 and only the differences from such a conventional machine are shown in FIG. 2 and described subsequently. The neck of the bag 10 contacts the adhesive side of a length of adhesive tape 1 arranged perpendicular to the direction of motion of the neck of the bag. The neck continues on its path pulling the tape with it and passes through a pair of rollers 11. The action of the rollers folds the length of adhesive tape around the neck of the bag and onto itself to form a seal. The sealed bag then moves on out of the tying machine.

[0021] The apparatus for cutting the tape into the desired lengths is shown in FIG. 3. FIG. 3a shows a pair of gripper arms 12 in an open position at a point in the tying cycle just after a seal has been formed around one bag, cut by a pair of cutting blades 13, released by the gripper arms and moved out of the tying machine. The gripper arms 12 are moved up and down and opened and closed by pneumatic piston and cylinder assemblies as described in GB-A1381671. The gripper arms 12 have a pneumatic brake system which consists of a slide bar 15, which moves up and down with the gripper arms 12, and brake pads 16 which are anchored in a fixed position on the tying machine. The brake pads 16 are shown in a released position as the gripper arms 12 are about to move up and grip the free end of the tape 1 in the next step.

[0022] FIG. 3b shows the gripper arms 12 at their uppermost point, where the gripper arms 12 close so gripping the free end of the tape 1. The tape 1 is then pulled as the gripper arms 12 move down, as shown in FIG. 3c, until a detector 14 detects the leading edge 18 of a printed band of tape. A proximity switch 17 detects the tail 19 of the brake slide bar 15, and when both detections are made, as shown in FIG. 3d, the brake pads 16 are applied to brake the movement of the brake bar 15 and hence halt the movement of the gripper arms 12.

[0023] The detector 14 is an optical detector which sends a beam through an optic fibre to the tape and detects the reflected light re-entering the optic fibre. From a change in the reflected light the boundary between inked and noninked sections of the tape can be ascertained. A suitable detector is manufactured by Keyence Corporation of Milton Keynes, UK and designated their CZ-41.

[0024] As the gripper arms 12 are halted the neck of the next bag is pushed into the path of the tape 1 and 6 mm more tape is allowed to be pulled from the reel. This situation is shown in FIG. 3e. A signal is then sent to the pair of cutting blades 13. Upon receipt of the signal the cutting blades 13 move to cut the tape 1 to form the next tie. The tape is cut just prior to the entry of the neck of the bag 10 into the nip between the rollers 11 where the cut length of tape is formed into a tie around the neck of the bag. This position is shown in FIG. 3f. The relative positioning of the blades 13 and the detector 14 is such that the blades cut the tape at the midpoint of the preceding inked band of the tape 3 than that, the position of which has just been detected. The position of the detector 14 relative to the cutting blades 13 is arranged to compensate for the extra 6 mm of tape.

[0025] FIG. 4 shows a length of inked adhesive tape 1 prior to it being cut into lengths. The length of each inked band 3 is 25 mm. The inked bands are eventually cut in the middle, leaving inked, non-adhesive tabs 3 of 12.5 mm in length. Crucially this is sufficient length for a consumer to grip with finger and thumb in order to peel apart the seal. The interval between inked bands must be of sufficient length to encompass the neck of the gathered bag to be sealed, in this example it is 65 mm. This means that the total length of one tape seal is 90 mm. For some applications the total length of each seal is 110 mm.

[0026] FIG. 5 shows the neck of a bag with an adhesive tape seal applied. The inked tabs 3 are free and form gripping portions.