Dispensing of labels
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the dispensing of labels from a strip incorporating a supply of labels. 
     2. Description of the Prior Art 
     It is well known that strips of silicone-treated backing paper are used to carry a continuous series of discrete self-adhesive labels, and that such labels are detached adjacent the point of application by passage over a dispense edge member at which the backing paper is drawn sharply away from a label as the label is about to be dispensed. The label is then applied to an article to be labelled by a roller or a pad, or, in certain instances, by the application of suction to the label followed by a blowing action impelling the label on to an article to be labelled. 
     Hitherto, such dispense edge members have included a rectilinear edge extending transversely to the path of the backing strip and, at the instant when a label becomes completely detached from the backing strip, the label is, ideally, plane. 
     The facility of detaching a label from the backing strip depends to a large extent on the comparatively higher stiffness of the label in comparison with the stiffness of the silicone-treated paper backing strip but nevertheless there is a risk, in practice, that the label will &#34;droop&#34; once it has become partially detached and such droop can result in the label becoming bent about a transverse band line and then mis-applied by the application member. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a method of dispensing a pressure-sensitive label carried by a backing strip such that the label can be peeled from the strip, wherein the strip is passed over a dispense edge to remove the strip from said label, and the label is curved transversely to the direction of dispense during removal of the strip. 
     According to another aspect of the invention, there is provided a device for detaching a pressure-sensitive label from a backing strip, said device comprising means locatable in the path of the strip to deflect the strip whereby to cause the strip to be drawn away from the label, said means being so shaped as to impart a curvature to the label transversely to the direction of detachment, and the shape of said means being such that the path length of the strip in the direction of passage over said means is substantially the same across the whole width of the strip. 
     According to yet another aspect of the invention, there is provided a method of forming a dispense edge member, wherein a sheet metal blank is folded into two parts interconnected by a curved fold which forms the leading edge portion of the member, and one of said parts and the adjacent portion of the fold are shaped, by a pressing operation, to define a concave depression having its axis directed transversely of the leading edge portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: 
     FIG. 1 is a schematic side elevation of a label applicator including a dispense edge member in accordance with the invention; 
     FIG. 2 is a perspective view of a dispense edge member in accordance with the invention; 
     FIGS. 3 to 7 are perspective views of further forms of the dispense edge member; 
     FIG. 8 is a schematic plan view of a dispense edge member in accordance with the invention with the shape of the member being exaggerated for explanatory purposes; 
     FIG. 9 is a side elevation of the member shown in FIG. 8 and indicating the curvature of the member at two different locations; 
     FIG. 10 is a transverse cross-section of the member shown in FIGS. 8 and 9; 
     FIG. 11 is a perspective view showing a first stage in the manufacture of a dispense edge member from a sheet metal blank; 
     FIG. 12 is a transverse section showing a second stage in the manufacture of the member from the blank; and 
     FIG. 13 is a perspective view showing the finished member. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The label applicator shown in FIG. 1 comprises a reel 2 containing a roll of backing strip 4 carrying a series of self-adhesive labels 6 which have a greater rigidity than that of the strip 4. The backing strip 4 is silicone-treated or is otherwise such as to permit the labels to be peeled from the strip 4. The strip 4 passes around a dispense edge member 8 the leading edge portion 8a of which defines a dispense edge located in the path of the strip and which causes the individual labels 6 to be detached from the strip 4 by abruptly deflecting the strip 4 away from the labels 6. The labels 6, when detached, are applied to an article by a roller 10 or any other suitable means, and the strip 4 free of labels is wound on a reel 12. 
     Referring to FIG. 2, the leading edge portion 8a of the dispense edge member 8 is convex as viewed in plan, and the upper surface 8b of the member 8 is concave. For convenience the lower surface of the member 8 is plane. With this arrangement the label will be given a curved or bowed form in cross-section transversely to the direction of dispensing movement with the concavity facing upwardly so that any tendency to droop is resisted because the rigidity is increased longitudinally of the label by virtue of its curved or bowed form. The convex form of the leading edge portion 8a of the member 8 causes stripping or peeling of each label 6 to commence at the center of the edge portion 8a and to progress outwardly in both senses. It will be noted from FIG. 2, that due to the concave form of the upper surface 8b, the thickness of the member 8 increases progressively from its longitudinal central portion towards each of its lateral edges. This increasing thickness is compensated for by the curvature of the leading edge portion 8a so that the overall path length of the backing strip 4 along the member 8 is substantially constant across the whole width of the strip 4, thus obviating the formation of differential stresses across the width of the strip 4. 
     As the detachment of the label 6 from the backing strip 4, progresses along the length of the label only a decreasing portion will be progressively held on the backing strip and ultimately the applying roller 10 or other applying means will take over control of the partially detached label 6 before the detachment is completed. 
     As will be apparent, by means of the dispense edge member described, it will be possible to improve, substantially, the accuracy with which a label can be applied to an article whether by hand or by a machine. Stray air currents will have less effect and, as in the case of a belt pulley which is cambered, the path of the strip will be more exactly defined along the center-line. 
     In the embodiment of FIG. 3 the dispense edge member 18 is defined by a plane support member 20 having a leading edge portion 20a which is convex when viewed in plan, with upstanding longitudinal ribs 22. To assist in bowing the labels about to be dispensed, pressing means in the form of rollers 24 of varying sizes are arranged so that each one lies opposite one of the grooves defined by adjacent ribs but the rollers do not extend into the grooves. All the rollers 24 rotate about the same axis 26. As will be apparent, the ribs 22 are of different heights with the shallowest ribs nearest the center-line of the member 20; the terminal curvatures of the ribs 22 differ correspondingly. The ribs 22 define a concave surface having a similar effect to that provided by the surface 8b of FIG. 2. The rollers 24 may be replaced by corresponding downwardly extending ribs. 
     The dispense edge member 28 of FIG. 4 is generally similar to that of FIG. 2, but a single transverse pressing roller 30 is provided having a curvature complementary to the upper surface of the dispense edge member 28. As in the previous embodiments this roller assists in imposing a bowed form on the labels. 
     The dispense edge member 38 of FIG. 5 has a leading edge portion defined by a series of beads or small rollers 40. The upper surface is plane, but the lower surface of the member has a form similar to the upper surfaces of the previous embodiments. In this embodiment, the dispense edge member is used in a label applicator in which a backing strip having labels on its under-surface passes along the lower surface of the member and then along the upper surface, whereby the labels will be dispensed with their adhesive surfaces uppermost. 
     In FIG. 6, the small rollers 40 of FIG. 5 are replaced by three longer rollers 42 and two circular beads 44 nested in adjacent end cavities of the longer rollers. The beads 42 may be retained by wire. The edge member is thickened below to ensure a constant length path over the whole width of the backing strip. 
     The dispense edge member 45 shown in FIG. 7 comprises a central roller 46 and two outer rollers 47 of frusto-conical form or of generally frusto-conical form but with a convex curvature. The roller 46 acts in conjunction with the rollers 47 to impart a bowed form to the labels being dispensed, and the shape of the rollers 47 ensures that the strip follows substantially the same path length around the rollers 47 at all positions across its width. 
     The calculations involved in constructing a dispense edge member in accordance with the invention will now be set out with particular reference to FIGS. 8 to 10 which relate to the dispense edge member of FIG. 2 and schematically show the member in plan, in longitudinal section at two positions across the width of the member, and in transverse section. 
     Assuming a circular curvature of radius r for the upper surface 8b of the dispense edge member, and that the thickness of the member at its longitudinal central plane is t C , then the thickness t Y  at any point Y on the curved surface 8b at a distance l from the longitudinal central plane C--C of the member is determined by the following equation: 
     
         t.sub.Y = r + t.sub.C - √r.sup.2 - l.sup.2          EQN.I 
    
     the leading edge portion 8a of the member is assumed to be of semi-circular section (as viewed in FIG. 9) at the centerline and at any point on either side of the centerline. In order to avoid differential stresses arising across the width of the backing strip as it passes over the member, it is required that any path traced along the surface of the member parallel to the central plane C--C, and starting from a transverse line on the upper surface of the member, and passing around the leading edge portion of the member and along the lower surface of the member to a transverse line vertically beneath the starting line, shall be of the same length irrespective of its distance from the plane C--C. 
     Taking a section (FIG. 9) through point Y a path can be traced from a point A on a transverse line X--X on the upper surface of the member, around the semi-circular leading edge portion and along the lower surface of the member to a point B on a transverse line aligned with the line X--X. 
     This path length (AB) is given by the following equation: 
     
         AB = 2M + π/2 t.sub.Y                                   EQN.II 
    
     where M is the distance between the line X--X and the center of curvature O Y  of the semi-circular section of the leading edge portion 8a at the point Y. 
     Similarly, taking a section through the plane C--C we have a path 
     
         C&#39;B&#39; = 2M + 2P + π/2 t.sub.C                            EQN.III 
    
     where P is the distance between a transverse line passing through the center of curvature O Y  at the point Y, and the center of curvature Oc of the semi-circular section of the leading edge portion at the plane C--C. 
     Since it is required that 
     AB = C&#39;B&#39;, by combining equations I, II and III it follows that 
     
         P = π/4 (r - √r.sup.2 - l.sup.2)                 EQN.IV 
    
     the distance by which the leading edge portion 8a of the member 8 at the center is in advance of that at any point Y determines the curvature of the leading edge portion in plan and is designed Q in FIGS. 8 and 9. 
     
         Q = P + (t.sub.C /2) - (t.sub.Y /2)                        EQN.V 
    
     substituting EQN.IV in EQN.V. 
     
         q = (π/4 - 1/2) (r - √r.sup.2 - l.sup.2)         EQN. VI 
    
     taking a pratical example of a 65 mm. wide dispense edge member with a minimum central thickness (t C ) of 1.5 mm. and a maximum depth of 10 mm. at each side, the radius r will equal 66.382 mm. From EQN.VI we can plot Q for r = 66.382 and various values of l between 0 and 65/2 mm. as shown in Table I below: 
     
                       TABLE I                                                     
______________________________________                                    
l (mm)             Q (mm)                                                 
______________________________________                                    
 1                 0.002                                                  
 5                 0.054                                                  
10                 0.216                                                  
15                 0.490                                                  
20                 0.880                                                  
25                 1.395                                                  
30                 2.045                                                  
32.5               2.426                                                  
______________________________________                                    
 
    
     In the above equations I and VI, the shape of the leading edge portion of the member is calculated from the criterion that the concave surface of the member is of circular cross-section. 
     Alternatively, the leading edge portion of the member can be of part-circular form when viewed in a direction normal to the direction of movement of the strip, and the curvature of the concave surface of the member can be calculated from this criterion so that the path length of the backing strip is substantially constant across the entire width of the strip. 
     There is shown schematically in FIGS. 11 to 13 a method of manufacturing from sheet metal, a dispense edge member 48 dimensioned according to the criteria discussed in relation to FIGS. 8 to 10. As shown in FIG. 11 a sheet of metal is folded in two with a curved fold 48a which forms the leading edge portion of the member, the radius of curvature of the fold 48a being substantially equal to the required radius at the lateral edges of the leading edge portion of the member. 
     The folded metal sheet is then located in a press tool comprising a female die 50 (FIG. 12) located between the two layers of the sheet and having a part-cylindrical surface 50a with a radius of curvature corresponding to the required radius r of the upper surface of the member, with appropriate allowance being made for the thickness of the sheet. The upper surface of the sheet is then pressed into the die 50 by a male press member 52 having a part-cylindrical surface 52a with a radius of curvature corresponding to the required radius r. The folded sheet is confined laterally during pressing by lateral blocks 54; the curved fold 48a is, however, unconfined during pressing to enable it to bulge and adopt the correct curvature. The completed dispense edge member is shown in FIG. 13. The outer surface of the member preferably has a P.T.F.E. layer which is applied, prior to shaping the metal sheet, either in the form of a self-adhesive layer, or as a coating. The P.T.F.E. layer acts as a lubricant during shaping of the metal sheet, and also provides a low-friction surface for the backing strip 4 when the member is in use. 
     In each of the dispense edge members described above, peeling is progressive from a point and a curvature is imparted to a label being dispensed to stiffen the label whereby droop of the label is obviated. The absence of such droop allows the trailing edge of a label being dispensed to be detected at a point very close to the dispense edge so that a substantial proportion of the label will have been dispensed, but retained rigidly at the instant of detection. This enables far more accurate positioning of labels than is possible if the label is sensed well upstream of the dispense edge.