Label imaging and cutting

Abstract

The present invention discloses a method and apparatus for imaging and cutting a label from a linerless label substrate 6, the substrate 6 comprising: a paper or polymeric film base layer; a colour change layer, incorporating a colour change compound operable to change colour in response to illumination by a laser 1; an adhesive layer; and a release layer adapted to have low adherence to the adhesive layer. The label substrate 6 is transported from a storage reel to an imaging area. At the imaging area, the label substrate 6 is selectively illuminated by laser 1 to form an image in the colour change layer. Subsequently, further laser illumination is used to cut the label substrate 6 thereby providing a single label for application to an object. The invention is characterised in that the laser spot size is varied for imaging and cutting.

Claims

1. A label printing and cutting apparatus suitable for use with a strip of label substrate, the strip of label substrate comprising a colour change layer in which a printed image may be formed, the label printing and cutting apparatus comprising: the strip of label substrate; an imaging area; and laser illumination means operable to selectively illuminate the strip of label substrate in the imaging area so as to induce colour change in the colour change layer thereby forming the printed image, the laser illumination means further operable to cut the label substrate and characterised in that the laser illumination means comprises laser spot size adjustment means operable to vary the spot size of the laser for imaging and for cutting, wherein the laser spot adjustment means comprises an image focusing means and at least one anamorphic lens, the at least anamorphic lens being placed between the image focusing means and the label substrate and the laser spot size adjustment means comprise a cutting beam deflector operable to deflect the beam from a scanning unit through a cut focussing means.

2. An apparatus as claimed in claim 1 wherein the apparatus comprises a label applicator operable to apply a cut and printed label to an object.

3. An apparatus as claimed in claim 1 wherein the spot size adjustment means comprise a high speed beam deflector provided between the laser illumination means and the scanning unit.

4. An apparatus as claimed in claim 1 wherein the spot size adjustment means comprises one or more indexable beam deflectors operable to deflect the beam emitted from the laser illumination means into a selected one of multiple optical pathways, each pathway comprising one or more optical elements operable to vary the beam diameter and/or divergence.

5. An apparatus as claimed in claim 1 wherein the laser illumination means has an operating wavelength in the range 200 nm to 20 m.

6. An apparatus as claimed in claim 1 wherein the substrate comprises a base layer having an adhesive layer provided on one side and the colour change layer covered by a release layer on the other side; or wherein the substrate comprises a base layer having a release layer provided on one side and the colour change layer covered by an adhesive layer on the other side.

7. An apparatus as claimed in claim 1 wherein the spot size adjustment means comprise a variable beam expander operable to controllably vary the diameter and/or divergence of the beam provided to the scanning unit.

8. An apparatus as claimed in claim 1 wherein the apparatus is provided with a cut focusing means operable to reduce the spot size in one dimension only.

9. An apparatus as claimed in claim 8 wherein the cut focusing means comprise cylindrical lenses.

10. An apparatus as claimed in claim 1 wherein the laser illumination means is provided with a scanning unit operable to direct the generated laser beam onto selected areas of the substrate for printing and/or cutting.

11. An apparatus as claimed in claim 1 wherein the apparatus is provided with a beam expander positioned between the laser illumination means and the scanning unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

(2) FIG. 1a is a schematic illustration of a first embodiment of an apparatus for imaging and cutting a label according to the present invention;

(3) FIG. 1b is a schematic illustration of a variant of the first embodiment of an apparatus for imaging and cutting a label according to the present invention;

(4) FIG. 2a is a schematic illustration of a second embodiment of an apparatus for imaging and cutting a label according to the present invention;

(5) FIG. 2b is a schematic illustration of a variant of the second embodiment of an apparatus for imaging and cutting a label according to the present invention;

(6) FIG. 3a is a schematic illustration of a third embodiment of an apparatus for imaging and cutting a label according to the present invention;

(7) FIG. 3b is a schematic illustration of a variant of the third embodiment of an apparatus for imaging and cutting a label according to the present invention;

(8) FIG. 4 is a schematic illustration of a variant of the third embodiment of an apparatus for imaging and cutting a label according to the present invention, including a schematic illustration of the optical elements of a variable beam expander; and

(9) FIG. 5 is a schematic illustration of a fourth embodiment of an apparatus for imaging and cutting a label according to the present invention.

(10) The present invention discloses a method and apparatus for imaging and cutting a label from a label substrate. In particular the present invention might be applied to imaging and cutting a label from a linerless label substrate. Such a substrate is disclosed in our co-pending UK patent application No. 1506312.6 (and family) and might comprise: a paper or polymeric film base layer; a colour change layer, incorporating a colour change compound operable to change colour in response to illumination by a laser; an adhesive layer; and a release layer adapted to have low adherence to the adhesive layer. The release layer thereby enables the label substrate to be wound on and dispensed from a storage reel.

(11) In operation, the label substrate is transported from a storage reel to an imaging area. At the imaging area, the label substrate is selectively illuminated by a laser to form an image in the colour change layer. Subsequently, further laser illumination is used to cut the label substrate thereby providing a single label for application to an object.

(12) Turning now to FIGS. 1a and 1b, two variants on an embodiment of an apparatus for carrying out imaging and cutting of the label substrate 6 according to the present invention are illustrated schematically. In particular, the apparatus comprises a laser 1, beam expander 3, scanning unit 4, and image focussing means 5. The beam expander 3 is optional and would typically be included to ensure a sufficiently small spot is achieved. The scanning unit 4 is operable to direct the laser beam as required for imaging. The image focussing means 5 is an imaging lens selected so as to focus the directed beam from the scanning unit 4 onto the substrate 6 for imaging. Operation of the laser 1 and the scanning unit 4 is carried out in response to signals from the controller 7.

(13) In addition to the above, the apparatus is also provided with laser spot size adjustment means. In this embodiment, the spot size adjustment means comprise cutting beam deflector 8, and cut focussing means 9, 10. The cutting beam deflector 8 may comprise an optical element such as a mirror, prism, standard grating or holographic grating. Indeed, it is also possible for the cutting beam deflector to comprise a combination of such elements. The cut focussing means 9, 10 shown in FIGS. 1a & 1b comprise a diverging lens 9 and a converging lens 10. The purpose of lens 9 is to modify the convergence of the beam from the imaging lens 5 in the plane perpendicular to the direction of cut such that the diameter at the cutting lens 10 is increased. As a result, the cutting lens 10 produces a smaller focussed spot in this plane at the substrate. In particular, lens 9 may be an anamorphic lens or a cylindrical diverging lens and lens 10 may be an anamorphic lens or a cylindrical converging lens. This can enable the spot width to be reduced in a direction perpendicular to the cut direction enabling a narrower cut to be produced. Cylindrical lenses are particularly advantageous for this as they do not impact on the scan length as determined by the imaging lens 5.

(14) In the variant of FIG. 1a, during cutting operation the laser beam is directed into the beam deflector 8 by using the scanning unit 4 to direct the beam beyond the normal imaging range. Alternatively, as is shown in the variant of FIG. 1b, the beam deflector 8 may be moved during cutting operation so as to intercept the laser beam. Typically, this movement may comprise tilting or translating the cutting beam deflector 8.

(15) The location of the cutting beam deflector 8 and cut focussing means 9, 10 could be either side of the centre of the field of view and depends on the direction of motion of the substrate. The aperture of the cutting beam deflector 8 and cut focussing means 9, 10 is selected such that they can accommodate the scan required to cut the full width of the substrate 6. Whilst in the above example the cut focussing means 9, 10 are described as lenses the skilled man will appreciate that it is alternatively possible to construct an equivalent arrangement using mirrors which may be cylindrical, parabolic or elliptical in one axis.

(16) In addition to the above, whilst FIGS. 1a & 1b show the scanning unit provided before the imaging lens, it is alternatively possible to provide the imaging lens before the scanning unit. In such circumstances, the cutting beam deflector 8 and cut focussing means 9, 10 are now located after the scanning unit 4.

(17) Turning now to FIGS. 2a and 2b, two variants on a further embodiment of an apparatus for carrying out imaging and cutting of the label substrate 6 according to the present invention are illustrated schematically. As with the apparatus of FIGS. 1a & 1b, each apparatus comprises a laser 1, beam expander 3, scanning unit 4, and image focussing means 5 and the spot size adjustment means comprise cutting beam deflector 8, and cut focussing means 9, 10. For further control of the beam spot size, the spot size adjustment means in the apparatus of FIGS. 2a & 2b further comprises a high speed deflector 2, typically an acousto-optic (A/O) or electro-optic (E/O) deflector. The high speed deflector may be provided either before (FIG. 2a) or after (FIG. 2b) the optional beam expander 3.

(18) The provision of the high speed deflector 2, provides for improvements in the imaging time for barcodes, bold text, graphics or the like. This is achieved by using the high speed deflector 2 to deflect the beam in a direction substantially perpendicular to the scan direction. Such deflection can increase the effective beam width and thereby reduce the number of scans and hence the time required to image blocks within barcodes, bold text or graphics.

(19) In one implementation, the high speed deflector 2 may be operable to rapidly deflect the beam so as to generate the width of the line required for the bar code or text. In an alternative implementation, the high speed deflector 2 may be operable to rapidly deflect the beam by a preset multiple of the spot diameter. The preset multiple may be determined by the available power and fluence requirements. Typically, the range of deflection may be in the region of 2-4 time the normal spot diameter. In these implementations, the deflection of the laser beam by the high speed deflector may be continuous or it may involve a plurality of indexed steps.

(20) As with the embodiment of FIGS. 1a & 1b, the differing variants of the cutting beam deflector 8 and cut focussing means 9, 10 may be used in relation to the apparatus of FIGS. 2a & 2b. Similarly, as discussed in relation to FIGS. 1a & 1b the order of the scanning unit 4 and imaging lens 5 can be interchanged as required or desired.

(21) Turning now to FIGS. 3a and 3b, two variants on a further embodiment of an apparatus for carrying out imaging and cutting of the label substrate 6 according to the present invention are illustrated schematically. As with the apparatus of FIGS. 1a & 1b, each apparatus comprises a laser 1, scanning unit 4, and image focussing means 5. As with the apparatus of FIGS. 1a & 1b, the variant of FIG. 3a is provided with a cutting beam deflector 8, and cut focussing means 9, 10 of the type provided in FIG. 1a whilst the variant of FIG. 3b is provided with a cutting beam deflector 8, and cut focussing means 9, 10 of the type provided in FIG. 1b. The spot size adjustment means in the apparatus of FIGS. 3a & 3b further comprises a variable beam expander 13 in place of the beam expander 3. The variable beam expander 13 is operable to adjust both the diameter and divergence of the laser beam at the imaging lens 5. The adjustment is made under the control of the controller 7 in response to the action required i.e. imaging a bar code, imaging text or cutting the label. Where the variable beam expander 13 provides a sufficient range of adjustment, it is possible to omit the cutting beam deflector 8 and cut focussing means 9, 10.

(22) The spot size, d.sub.0, of the beam focussed by imaging lens 5 may be determined from the equation

(23) ##STR00001##

(24) Where f is the focal length of lens 5; is the laser wavelength; M.sup.2 is the beam quality parameter; and D.sub.0 is the diameter of the laser beam incident upon the lens 5. As such, it is evident that the focussed spot size do is inversely proportional to the laser beam diameter entering imaging lens 5. Accordingly, using the variable beam expander 13 to adjust the diameter of the beam entering the imaging lens 5 can change the focussed spot size. In this context, whilst the major influence on spot size is the beam diameter, beam divergence can have a secondary effect, particularly as the location of the focal position in relation to the imaging lens 5 will depend on the divergence of the incident beam.

(25) In typical text imaging operation the beam may have a standard spot size. For cutting operation the beam should have a reduced spot size. Accordingly, the variable beam expander 13 is adjusted to increase the beam diameter at the imaging lens 5. The variable beam expander is operable to expand the beam diameter by a factor of, say, 1.3 to 2 or preferably by a factor of, say, 2 to 3; or most preferably by a factor in the range 4 to 9. This results in reduction of the spot size at the substrate 6 by an equivalent factor. For imaging barcodes or the like, the beam should have an increased spot size. Accordingly, the variable beam expander 13 is adjusted to reduce the beam diameter at the imaging lens 5. The variable beam expander is operable to reduce the beam diameter by a factor of, say, 1.3 to 2 or preferably by a factor of, say, 2 to 3; or most preferably by a factor in the range 4 to 9. This results in an increase in the spot size at the substrate 6 by an equivalent factor.

(26) In some implementations, the variable beam expander 13 may be operable to adjust the beam dimensions on a single axis only. Preferably, this axis is perpendicular to the scanning direction thereby varying the spot size in this direction for more effective cutting/block imaging as appropriate.

(27) As with the embodiment of FIGS. 1a & 1b, the differing variants of the cutting beam deflector 8 and cut focussing means 9, 10 may be used in relation to the apparatus of FIGS. 3a & 3b. Similarly, as discussed in relation to FIGS. 1a & 1b the order of the scanning unit 4 and imaging lens 5 can be interchanged as required or desired.

(28) Turning now to FIG. 4, a schematic illustration of a variable beam expander 13 in use in an apparatus according to the present invention is shown. In this example, the variable beam expander 13 comprises a pair of lenses 28, 29 operable to increase the divergence of the incoming laser beam and a pair of lenses 26, 27 operable to reduce the divergence and substantially re-collimate the beam. Adjustment of the separation between the lenses 28, 29 allows for variation in the divergence provided by the first lens pair. Adjustment of the separation between the lenses 26, 27 provides variable control over the divergence of the beam entering the imaging lens 5. Therefore the effective focal length of lens pair 28, 29 set the magnification and lens pair 26, 27 control the divergence and hence location of the focal plane. It is also possible to adjust the separation between the lens pair 28, 29 and the lens pair 26, 27 to provide further control.

(29) Whilst the above configuration of the variable beam expander 13 includes two lens pairs 28, 29 and 26, 27 the skilled man will appreciate that other combinations of multiple lenses (including two pairs of converging lenses), deformable lenses or mirrors could achieve the same result.

(30) As with the embodiment of FIGS. 1a & 1b, the differing variants of the cutting beam deflector 8 and cut focussing means 9, 10 may be used in relation to the apparatus of FIG. 4. Similarly, as discussed in relation to FIGS. 1a & 1b the order of the scanning unit 4 and imaging lens 5 can be interchanged as required or desired.

(31) Turning now to FIG. 5, a further embodiment is illustrated. In this embodiment, the apparatus is provided with indexable beam deflectors 20, 21 operable to deflect the laser beam into multiple different optical pathways 22, 30, 31. Typically, the indexable deflectors 20, 21 may comprise galvanometer scanning mirrors, electro optical or acousto-optical means, or microelectromechanical (MEMS) means as desired or as appropriate.

(32) Each pathway 22, 30, 31 comprises one or more optical elements operable to vary the beam diameter and/or divergence. For instance, optical pathway 22 comprises no additional optical elements and does not vary the beam diameter. Accordingly, this provides a standard size spot for imaging operation. If necessary, the skilled man will appreciate that an optional beam expander 3 may be provided as part of optical pathway 22 to achieve a desired spot size.

(33) Optical pathway 30 comprises mirror 33 operable to direct the beam from deflector 20 into beam expanding lens pair 38, 39 and a mirror 34 operable to direct the beam from the lens pair 38, 39 back to deflector 21. As such, the beam incident on scanning unit 4 and imaging lens 5 is of greater diameter and hence can be focussed to a reduced spot size for cutting operation.

(34) Optical pathway 31 comprises mirror 32 operable to direct the beam from deflector 20 into beam expanding lens pair 36, 37 and a mirror 35 operable to direct the beam from the lens pair 36, 37 back to deflector 21. As such, the beam incident on scanning unit 4 and imaging lens 5 is of reduced diameter and hence can be focussed to a larger spot size spot size for imaging barcodes or the like.

(35) In alternative embodiments, the skilled man will appreciate that the indexable deflectors 20, 21 need not be external to the beam expanders as shown in FIG. 5 but could be integrated with a variable beam expander.

(36) In some implementations, the alternative optical pathways 30, 31 may comprise optical elements operable to adjust the beam dimensions on a single axis only. Preferably, this axis is perpendicular to the scanning direction thereby varying the spot size in this direction for more effective cutting/block imaging as appropriate.

(37) As with the embodiment of FIGS. 1a & 1b, the differing variants of the cutting beam deflector 8 and cut focussing means 9, 10 may be used in relation to the apparatus of FIG. 5. Similarly, as discussed in relation to FIGS. 1a & 1b the order of the scanning unit 4 and imaging lens 5 can be interchanged as required or desired.

(38) In a preferred implementation, the laser 1 is a CO2 laser which has been surprisingly found to enables the formation of clear printed images through release layer. Furthermore, the output of a CO2 laser is readily absorbed by the base layer of the substrate 6. As such, the same laser 1 may be used for both imaging and cutting. Surprisingly, it has been found that use of the same laser to print an image and cut the substrate 6 does not result in significant discolouration at the cut edge of the substrate 6.

(39) Typically, the normal CO2 laser wavelength is around 10.6 m and this is absorbed by many polymeric films and is adequate for cutting. However, this operating wavelength may be tuned for optimum absorption in the base layer as this can reduce the laser fluence required for cutting. In the case of a polypropylene base layer, the absorption of polypropylene is significantly higher at 9.3 m and 10.3 m than it is at the usual operating wavelength for a CO2 laser (10.6 m). Accordingly, it is desirable, but not essential, to select an operating wavelength from the so called P and R vibrational bands of the CO2 molecule at 9.4 m and 10.4 m respectively.

(40) The skilled man will note that whilst Galilean configurations of lens pairs/beam expanders are used in the examples shown in the figures, it is alternatively possible to use Keplerian or other configurations, where appropriate.

(41) The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.