CA2181960A1 - A deactivatable security strip and a process and a facility for manufacture of a deactivatable security strip - Google Patents

Abstract

The invention relates to a deactivatable security strip, as well as to a process and a facility for manufacture of a deactivatable security strip (1), particularly suitable for article surveillance in retail stores.
The invention is based on the problem of proposing a security strip (1), which can be manufactured cost-effectively.
The invention solves the problem by treating the semi-hard or hard magnetic strip (3), applying current to periodic consecutive sections (4b) of a specified length (b) a specified distance apart (a), in such a way that the remanent magnetisation component (M1r) parallel to the longitudinal axis (: = easy axis) of the semi-hard or hard magnetic strip (3) in the sections (4b) is less than the remanent magnetisation component (M0r) in the intervening, untreated sections (4a).

Description

A deactivatable security strip and a process and a facility for manufacture of a deactivatable sQcurity strip The invention relates to a deactivatable security strip, particularly suitable for article surveillance in retail stores, comprising a soft magnetic strip of a specified length, which is induced to output a characteristic signal when an alternating magnetic iield is applied, and sections of a semi-hard or hard magnetic material of a defined length, which are arranged relative to the soft magnetic strip in such a way that they suppress the characteristic signal output by the soft magnetic strip in their saturation state. The invention also relates to a process and a facility for manufacture of a security strip of this nature.
Activatable magnetically soft material (e . g . permalloy) is characterised by high permeability and low coercivity and is induced to radiate a characteristic signal by an alternating magnetic field within the surveillance zor,e in the entrance/exit area of a retail store. A detector device, sensitive in the signal ' s frequency range, subsequently detects this signal and evaluates it as the identification signal for an article passing through the surveillance zone in an illegal .. .. . . _ _ .

manner; an alarm is triggered.
It goes without saying that the detector device should no longer respond as soon as the article has been paid for in the proper manner. The semi-hard or hard magnetic strip sections are used for this purpose. The properties of magnetically semi-hard or hard material are opposite to those of magnetically soft material; it is characterised by low permeability and high coercivity. The high coercive intensity of the deactivation material causes it to remain unaffected by the alternating magnetic field in the surveillance zone in its non-deactivated state. As soon as the deactivation material is saturated by an appropriately high magnetic field - which is what happens when the article is paid for in the due manner - its magnetisation prevents the magnetically soft material from responding to the alternating magnetic field in the surveillance zone.
Large quantities of deactivatable security elements are used.
Each security element is only usually used for article surveillance once, which means that particular attention is paid to cost-effecti~e manufacture.
A process for the manufacture of security tags is already known from DE 42 23 394 A1, which consists of the following manufacturing steps: a hard magnetic metal strip is bonded onto a non-metallic band and an elastic carrier foil is then bonded onto the metal strip. The carrier foil is so thick and flexible that the deformation of the metal strip caused by a rotating punching tool is adequate to cut the metal strip into individual sections. The cut-away sections of the metal strip and the non-metallic band are drawn off by the carrier foil and a soft magnetic band is subsequently applied to the remaining parts of the metal strip. Label paper is bonded onto one side of the band and backing tape is bonded onto the other side, -in the usual manner - in order to produce a finished band of labels or tags.

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~ 3 - 2181960 This known process is no doubt ideal for the production of high quantities of security elements. The relatively high costs and ef fort involved in production and applying the semi-hard or hard magnetic sections onto the soft magnetic strip are less satisfactory, however.
The invention is based on the problem of proposing a cost-effective, easily realised deactivatable security strip, as well as a process and a facility, which enable cost-effective and simple manufacture of a deactivatable security strip.
As far as the security strip is concerned, the problem is solved by treating the semi-hard or hard magnetic strip, applying current to periodic consecutive sections of specified length b, which are a specified distance apart, given by a, in such a way that in the treated sections, the remanent magnetisation component M1, parallel to the longitudinal axis (:
= easy axis) of the semi-hard or hard magnetic strip is lower than the remanent magnetisation component Mr in the intervening, untreated sections. This can be expressed in the mathematical inequation: Mr Mlr or Mr/MIr 1.
An expedient e_bodiment of the security strip in accordance with the invention provides for the saturation magnetisation M"
in the sections parallel to the easy axis of the semi-hard or hard magnetic stri,o tending to zero.
An alternative way of carrying out the invention, which can certainly be used in conjunction with the embodiment mentioned initially, provides for the i n~ m~nt of a mono-axial anisotropy K'u across the easy axis of the semi-hard or hard magnetic strip in the treated sections.

As far as the process for manufacture of a security strip in accordance with the invention is l-17n~ ~rnf~1, the problem is solved by applying current to periodic consecutive sections of length b of the semi-hard or hard magnetic strip, a specified distance apart, given by a, whereby the power supply is dimensioned in such a way that the treated sections of the strip demonstrate a remanent magnetisation component Ml,~ along the easy axis of the semi-hard or hard magnetic strip, which is less than the remanent magnetisation component M~ in the intervening untreated sections.
An expedient further embodiment of the process in accordance with the invention provides for the electrical heating of the periodic consecutive sections, a specified distance apart, by applying current. ~his embodiment of the process can be realised extremely easily and also enables a high operating speed .
A cost-effective and reliable embodiment of the process in accordance with the invention proposes that the temperature is monitored in the treated sections and that the circuit is interrupted as soon as the temperature in the treated sections reaches a specified limit. Apart from the fact that non-contact temperature measurement can be realised very easily and with a high degree of accuracy using a radiation detector, temperature :
measurement also offers an ideal means of indicating when the physical properties of the originally semi-hard or hard magnetic material have changed.
The process is terminated in a simple manner when the circuit opens. This can be achieved by lifting the strip away from the contact heads and/or by the current source being switched of f by the control device.

A particular advantage offered by a further embodiment of the process in accordance with the invention is that the strip with the semi-hard or hard magnetic sections and the treated sections is subsequently directly applied to the magnetically soft strip. The direct bonding of semi-hard or hard magnetic strip stock and magnetically soft strip stock enables the manufacture of very fine security strips, which is particularly important for so-called source integration, i . e. when the security strip is implemented into the article to be protected.
Apart from the application of electrical current, an expedient further embodiment of the process in accordance with the invention also enables the application of laser energy to the sections of length b.
The application of a magnetic field with an anisotropic field strength of at least Hk, where Hk = 2 Ku/M,, while applying current to the sections of length b, has proven to be particularly expedient, whereby the axis of the magnetic field is approximately perpendicular to the easy axis of the semi-hard or hard magnetic strip. The anisotropic field strength Hk is the field strength required to saturate the material across the easy axis.
The same effect can also be achieved by subjecting the sections of length b to mechanical stress (tensile stress or compressive strain) while the current is being applied. The stress is again dimensioned in such a way that a stress-induced anisotropy is generated perpendicular to the easy axis of the semi-hard or hard magnetic strip in the treated sections.
As far as the facility is concerned, the problem is solved by arranging several h~n~l ing stations, separated by a distance of a, which supply current to the sections of the semi-hard or hard magnetic strip stock of length b, with at least one open-loop control device which controls the supply of current to the treated sections and the forward feed of the strip stock.
Each handling station expediently comprises two contact heads, arranged at a distance of b, which are connected to a current source, whereby the section to be treated constitutes a part of the ci rcui t .
An expedient embodiment of the facility in accordance with the invention provides for press-on elements arranged on the opposite side of the strip stock to the contact heads, and corresponding to the contact heads, which press the strip stock against the contact heads during the period of treatment.
As mentioned above, a radiation detector ~photodetector) is used as a temperature sensor, measuring the temperature by optical transmission.
An expedient further embodiment of the facility in accordance with the invention provides for a pair of rollers, driven intermittently, moving the strip stock between the contact heads and the press-on elements.
The invention is described in detail below with reference to drawings, in which:
Figure 1 is a perspective view of a deactivatable security strip in accordance with the invention, Figure 2a is a perspective view of a conventional semi-hard or hard magnetic strip, Figure 2b shows a typical hysteresis curve of the semi-hard or hard magnetic strip shown in Figure 2a, '~ ~ 7 ~ 2181960 Figure 3a is a perspective view of a security element in accordance with the invention, in conformity with its initial embodiment, Figure 3b shows a typical hysteresis curve along the easy axis of the treated sections of the strip shown in Figure 3a, Figure 3c is a schematic representation of the distribution of stray field H, for the strip shown in Figure 3a (longitudinal section through strip 1), Figure 4a is a perspective view of a security element in accordance with the invention in conformity with a second el[ bodiment, Figure 4b shows a typical hysteresis curve along the easy axis of the treated sections of the strip shown in Figure 4a, Figure 4c is a schematic representation of the distribution of stray field Hs for the strip shown in Figure 4a (longitudinal section through the strip), Figure 5 is a schematic representation of a manufacturing process for security strips, with the facility and process in accordance with the invention integrated into the system, Figure 6 shows one way of carrying out the facility in accordance with the invention and Figure 7 is a flow chart to control open-loop control device 19 for the facility shown in Figure 5.
Figure 1 shows a perspective view of a deactivatable security strip. Deactivatable security strip 1 comprises a soft magnetic strip 2 with a semi-hard or hard magnetic strip 3 laminated onto it. The structure and the properties of the semi-hard or _ _ _ _ . . _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - 8 - 2t81960 hard magnetic strip 3 are changed by applying current to periodic consecutive sections 4b, separated by a distance of a.
In accordance with the invention, the application of current causes a change in the original physical properties of the treated sections 4b of the semi-hard or hard magnetic strip This means that the original physical properties of the semi-hard or hard magnetic strip 3 only apply in the untreated sections 4a.
Figure 2a shows a perspective view of a conventional semi-hard or hard magnetic strip 3 with remanent magnetisation M~. As a consequence of the manufacturing process, strip 3 demonstrates a remanent magnetisation M~ and an anisotropy Ku along a preferred axis. The preferred or easy axis is the x axis in the example shown.
Figure 2b shows the hysteresis curve of the semi-hard or hard magnetic strip 3 shown in Figure 2a, i . e . the change in magnetisation M as a function of field strength H of the external magnetic field. SEMIVAC, available from Vakuumschmelze, is an example of a magnetically semi-hard material .
Figure 3a shows a perspective view of an initial embodiment of the semi-hard or hard magnetic strip 3 in accordance with the invention. The semi-hard or hard magnetic strip 3 demonstrate sections 4b of length b, separated from one another by distance a . Sections 4b have been subj ected to heat treatment and their magnetic properties have changed as a result of this heat treatment .
As is clearly evident from a comparison of the two figures 2b and 3b, the remanent magnetisation M~ in the treated sections 4b has decreased compared with the corresponding sections before treatment. The desired result, pursued and realised by the invention, has been achieved when the following condition is fulfilled in mathematical terms: Mr Mlr, Mr/MIr 1. The magnetisation M is therefore the only factor that has changed in the treated sections 4b in this embodiment. Like the untreated sections 4a, the treated sections 4b still demonstrate a mono-axial anisotropy Ku parallel to the easy axis (in this case: x axis).
Figure 3c shows a longitudinal section through strip 3 in accordance with the invention shown in Figure 3a. This drawing shows the magnetic field distribution particularly clearly.
Stray fields occur as a result of the different remanent magnetisation Mr and M1r in the treated sections 4b and the untreated sections 4a respectively. In an ideal situation, the untreated sections 4a demonstrate a similar physical response to that for a strip where there is no material (or air) between the treated sections 4b. This means that the effect demonstrated by the previously known security strips, which have deactivation sections with spaces between them, is also achieved here.
Figure 4a shows a perspective view of a second way of carrying out strip 3 in accordance with the invention. ~hile the remanent magnetisation Mr is the only factor affected as a result of the current applied to sections 4b of the embodiment shown in Figures 3a, 3b and 3c, a mono-axial anisotropy KlU is also generated across the easy axis (in this case, x axis) in the treated sections 4b. The original anisotropy Ku of the semi-hard or hard magnetic strip 3 is still demonstrated in the untreated sections 4a. This can be achieved by applying a magnetic field H while current is being applied to sections 4b.
The applied magnetic field H should demonstrate an anisotropic field strength Hk= 2KU/,Mr at least. As mentioned above, the anisotropic field strength Hk is the field strength required to overcome the anisotropy along the easy axis in the treated - lO - 2 1 8 1 9 60 sections 4b and to impress a mono-axial anisotropy K1~ across the easy axis of the semi-hard or hard magnetic strip 3 in the treated sections 4b.
As shown in Figures 4b and 4c, the effect of this embodiment Df the security strip 1 in accordance with the invention on the remanence (remanent magnetisation component) along the easy axis and on the distribution of stray field ~ is equivalent to that of the embodiment shown in Figures 3a, i3b and 3c.
Figure 5 shows a schematic representation of a manufacturing process for a security strip. The facility in accordance with the invention and the process in accordance with the invention are integrated into this manufacturing process.
The magnetically soft strip stock 2 is wound off roller 5 into loop buffer 7. The magnetically soft strip stock 2 is fed round guide roller 9 into the facility 10. In facility 10, adhesive is applied to one side of the magnetically soft strip stock 2.
The semi-hard or hard magnetic strip stock 3 is also wound off a roller 6 into a loop buffer 8. In the facility 11 in accordance with the invention, the semi-hard or hard magnetic strip stock 3 is divided into individual sections 4 and is subsequently bonded onto the magnetically soft strip stock 2 with spacing b. Security strip 1 is dried in drier 12. The dried security strip 1 is finally wound onto roller 14, whereby another loop buffer is connected downstream of the roller to compensate any fluctuations in the tensile stress acting on security strip 1.
Figure 6 shows a way of carrying out the facility 11 in accordance with the invention. The roller pair 19 feeds the semi-hard or hard magnetic strip stock 3 between contact heads 15, 16 and the opposite press-on elements 22 step by step. The distance between the right-hand contact head 16 of a pair, or the corresponding press-on element 22, and the left-hand contact head 15, or the corresponding press-on element 23 of the following pair is given by a.
When strip stock 3 reaches the required position, open-loop control device 20 moves the press-on elements 22 and contact heads 15, 16 together until contact heads 15, 16 make intimate contact with the strip stock. Power supplies 17 are then activated. The current flowing between contact heads 15, 16 heats sections 4b of strip stock 3 until its original semi-hard or hard magnetic properties have changed in accordance with the invention. A certain temperature must prevail in sections 4b for this physical change to take place, which means that the acquisition of a predetermined temperature is used to indicate that the conversion process has been completed. The temperature in the treated sections 4b is measured expediently by optical transmission using radiation sensors 18 ~photosensors). The temperature values are passed on to the open-loop control device .
As soon as the temperature has reached the speci f ied value, the open-loop control device 20 causes the contact heads 15, 16 and press-on elements 22 and 23 to move apart. Open-loop control device 20 subsequently advances roller pair 19 by and angle of x, corresponding to a distance of n- (a+b) and the process stages described above are repeated. The information concerning the angle setting is supplied by phase-angle sensor 21, which is attached to the shaft of one of the two rollers l9a, l9b.
The rotary movement of the two rollers l9a, l9b of roller pair l9 is preferably coupled via gear wheels, not shown in detail in the drawing. Strip stock 3 with the semi-hard or hard magnetic sections 4a and treated sections 4b is then directly - 12 - 2181q60 laminated onto the magnetically soft strip stock 2, supplied via roller l9b.
Figure 7 shows a flow chart to control open-loop control device 19 for the facility shown in Figure 5. Once the programme has started at 24, contact heads 15, 16 and the corresponding press-on elements 22, 23 are moved together in accordance with programme items 25 and 26 until contact heads 15, 16 make intimate contact with strip stock 3 - which is the case after travelling a distance x. Current sources 17 are activated at 27 and 28 until the specified reference temperature T~ef has been reached in treated sections 4b. The contact heads 15, 16 and the press-on elements 22, 23 are subsequently moved apart by distance ~ at 29 and 30. Strip stock 3 is then advanced by distance 3- (a+b) in accordance with programme items 31 and 32;
this distance corresponds to a rotation of angle of rollers l9a, l9b of roller pair 19. As soon as the roller pair has rotated by angle , the programme returns to item 25 and the cycle is repeated.

-13- 218Iq6~
~eference list Deactivatable security strip 2 Soft magnetic strip 3 Semi-hard or hard magnetic strip 4a Semi-hard or hard magnetic section 4b Treated section 5 Roller 6 Roller 7 Loop buf f er 8 Loop buffer 9 Guide roller 10 Adhesive feed device 11 Facility for the manufacture of security strip 12 Drier 13 Loop buffer 14 Roller 15 Contact head 16 Contact head 17 Power supply 18 Radiation sensor 19 Roller pair l9a Roller l9b Roller 20 Open-loop control device 21 Phase-angle sensor 22 Press-on element 23 Press-on element

Claims (14)

1. Deactivatable security strip, particularly suitable for article surveillance in retail stores, comprising a soft magnetic strip of a specified length, which is induced to output a characteristic signal when an alternating magnetic field is applied, and sections of a semi-hard or hard magnetic material of a defined length, which are arranged relative to the soft magnetic strip in such a way that they suppress the characteristic signal of the soft magnetic strip in their saturation state, characterised in that the semi-hard or hard magnetic strip (3) is treated in such a way, applying current to periodic consecutive sections (4b) of a specified length (b) at specified intervals (a), that in the treated sections (4b) the remanent magnetisation component (M1r) parallel to the longitudinal axis (: = easy axis) of the semi-hard or hard magnetic strip (3) is less than the remanent magnetisation component (M0r) in the intervening untreated sections (4a).

2. Security strip in accordance with claim 1, characterised in that the saturation magnetisation (Ms) in the treated sections (4b) parallel to the easy axis of the semi-hard or hard magnetic strip (3) tends towards zero.

3. Security strip in accordance with claim 1, characterised in that a mono-axial anisotropy (K1u) is induced across the easy axis of the semi-hard or hard magnetic strip (3) in the treated sections (4b).

4. Process for the manufacture of deactivatable security strips, particularly suitable for article surveillance in retail stores, whereby a deactivatable security strip comprises a soft magnetic strip, carrying sections of a semi-hard or hard magnetic material of a specific length at defined intervals, characterised in that current is applied to periodic consecutive sections (4b) of the semi-hard or hard magnetic strip (3) of length (b) at intervals (a), whereby the power supply is dimensioned in such a way that the treated sections (4b) of the strip demonstrate a remanent magnetisation component (M1r) along the easy axis of the semi-hard or hard magnetic strip (3) which is less than the remanent magnetisation component (M0r) in the intervening, untreated sections (4a).

5. Process in accordance with claim 4, characterised in that the periodic consecutive sections (4b) at specified intervals (a) are heated electrically by applying current.

6. Process in accordance with claim 4 or 5, characterised in that the supply of current to the periodic consecutive sections (4b) of the semi-hard or hard magnetic strip (3) at intervals (a) is cut off as soon as the temperature in the treated sections (4b) reaches a specific value.

7. Process in accordance with claim 4, characterised in that laser energy is applied to the sections (4b).

8. Process in accordance with claim 4, 5, 6 or 7 characterised in that a magnetic field with an anisotropic field strength (Hk) of at least Hk = 2K0u/M0s is applied to the sections (4b) while current is being applied, whereby the axis of the magnetic field is approximately perpendicular to the easy access of the semi-hard or hard magnetic strip (3).

9. Process in accordance with claim 4, 5, 6 or 7 characterised in that while current is being applied, the sections (4b) are subjected to a mechanical stress, dimensioned in such a way that the stress-induced anisotropy is perpendicular to the easy axis of the original, untreated semi-hard or hard magnetic strip (3).

10. Facility for manufacture of a deactivatable security strip, particularly suitable for article surveillance in retail stores, whereby the deactivatable security strip comprises a soft magnetic strip; carrying sections of a semi-hard or hard magnetic material of a specified length at defined intervals, characterised in that provision is made for several handling stations (15, 16, 17) arranged at a distance (a) apart, which apply the current to the sections (4b) of the semi-hard or hard magnetic strip (3) of length (b), and provision is made for at least one open-loop control device (20), which controls the supply of power to the sections (4b) of the semi-hard or hard magnetic strip (3).

11. Facility in accordance with claim 10, characterised in that a handling station (15, 16, 17) comprises two contact heads (15, 16) arranged at a distance of (b), connected to a current source (17), whereby the circuit is closed by making contact with the semi-hard or hard magnetic strip (3).

12. Facility in accordance with claim 10 or 11, characterised in that provision is made for press-on elements 22, 23 which are positioned opposite to contact heads 15, 16.

13. Facility in accordance with claim 10, characterised in that provision is made for a radiation detector (18), acting as a temperature sensor, which measures the temperature of the sections (4b).

14. Facility in accordance with claims 11 and 12, characterised in that provision is made for a roller pair (19), comprising rollers (19a, 19b), driven intermittently, moving the strip (3) between the contact heads (15, 16) and the press-on elements (22, 23).