EP0939943A1

EP0939943A1 - Display element for use in a magnetic anti-theft system

Info

Publication number: EP0939943A1
Application number: EP98951172A
Authority: EP
Inventors: Matthias Herget; Ottmar Roth
Original assignee: Vacuumschmelze GmbH and Co KG
Current assignee: Vacuumschmelze GmbH and Co KG
Priority date: 1997-09-17
Filing date: 1998-08-19
Publication date: 1999-09-08
Also published as: DE19740908C1; US6166636A; JP2001505344A; WO1999014718A1

Abstract

The invention relates to a display element for use in a magnetic anti-theft system, said element comprising an elongated alarm strip (2) consisting of an amorphous ferromagnetic alloy and at least one elongated activation strip (1d) consisting of a semi-rigid magnetic alloy and applied to the alarm strip. One or more physically separate regions consisting of a non-magnetic phase are incorporated in the activating strips (1d) by thermal treatment. The semi-rigid magnetic alloy has a coercitive force Hc of between 15 and 100 A/cm and a retentivity of at least 0,8 T. This design allows for a very easy magnetisation of the activation strip (1d) in one direction as a result of the directional homogeneity. This therefore makes it possible to work at a greater distance from the source of the external magnetic field, and to carry out a remote activation. These activation strips (1d) are easy to produce compared to activation strips which are partly segmented or are perforated.

Description

description

Display element for use in a magnetic anti-theft system

The invention relates to a display element for use in a magnetic anti-theft system consisting of:

1. An elongated alarm strip made of an amorphous ferromagnetic alloy and at least

2. an elongated activation strip applied to the alarm strip and made of a semi-hard magnetic alloy.

Such magnetic anti-theft systems and display elements are well known and are described in detail, for example, in EP 0 121 649 B1 and in WO 90/03 652. On the one hand there are so-called magneto-elastic systems in which the activation strip is used to activate the alarm strip by magnetizing, on the other there are so-called harmonic systems in which the activation strip serves to deactivate the alarm strip after it has been magnetized.

Alloys with semi-hard magnetic properties used for the bias strips include Co-Fe-V alloys, e.g. B. are known as Vicalloy, Co-Fe-Ni alloys, which as z. B. Vacozet are known, as well as Fe-Co-Cr alloys, the z. B. are known as Crovac.

These alloys are applied either in individual subsegments or as continuous strips parallel to the alarm strip.

The sub-segments are then magnetized in one direction to activate or deactivate the alarm strip. to Deactivating or activating a continuous activation strip is magnetized in alternating polarity.

When partial segments are magnetized in one direction, because of the homogeneity of the direction, it is possible to work at a considerably greater distance from the source of the external magnetic field than when a continuous activation strip is magnetized. When magnetizing a continuous activation strip, it must be brought very close to the source in order to be able to achieve the alternating magnetization. With a continuous activation strip, only contact activation and no distance activation can be carried out.

However, since people are now moving to incorporate the display elements of the anti-theft systems directly into the product to be secured (source tagging), there is a need to provide the alarm strips with activation strips that can be magnetized from a greater distance or with smaller fields. It has been shown that the coercive force of these activation strips must be limited to values of at most 60 A / cm.

However, this requirement can only be met unsatisfactorily by the continuous activation strips known from the prior art. In terms of process technology, however, the processing of continuous activation strips has considerable advantages over the application of partial segments, since the activation strip is simply applied in parallel and permanently to the alarm strip.

When using sub-segments, on the other hand, they must either be pre-assembled or applied directly in individual parts. Pre-assembly causes higher costs. The application of sub-segments brings considerable benefits problems with the exact geometric assignment of the individual sub-segments on the alarm strip.

From US 3,820,104 it is known to apply continuous activation strips to the alarm strips, which are provided with holes. This perforation simulates a sub-segment structure that enables distance deactivation.

However, the geometrical assignment of the perforated

Activation strips on the alarm strips pose significant problems. An exact assignment of alarm strips and perforated activation strips can only be guaranteed in a spreading range of approx. +/- 0.5 mm in width. As a result, some overlap of the holes with the alarm strip is necessary, i. H. the diameter of the holes must be approximately the bandwidth of the alarm strip plus 1 mm, the bandwidth of the band this diameter plus a web width of at least 1 mm. As a result, an increased use of material and consequently increased material costs are necessary.

The object of the present invention is therefore to develop the display elements mentioned at the outset with regard to their activation strips in such a way that a distance deactivation is satisfactorily possible with continuous activation strips using simple means.

According to the invention, this object is achieved in that a) that one or more spatially separated regions which consist of a non-magnetic phase are introduced into the semi-hard magnetic alloy by means of heat treatment, and b) that the semi-hard magnetic alloy has a coercive force H _c of 15 to 100 A. / cm and has a remanence B _r of at least 0.8 T. Such a heat treatment induces phase transitions from a magnetic crystal structure to a non-magnetic crystal structure in suitable semi-hard magnetic alloys. These phase transitions are spatially limited, ie a permanent, irreversible, non-magnetic state is locally produced by locally limited heat input, which leads to a reduction in the effective magnetically conductive cross section.

As a result, the effective magnetically conductive cross section in this area loses the ability to continue to carry the entire magnetic flux.

The semi-hard magnetic Fe-Co-Cr alloys mentioned above have proven to be particularly suitable.

Activation strips which are composed of 0.1 to 10% by weight of nickel, 0.1 to 15% by weight of chromium, 0.1 to 15% by weight of molybdenum and the remainder iron in a total proportion of iron, nickel and molybdenum of less than are very particularly suitable 95% by weight of the alloy are composed.

Such alloys can also contain 0 to 10% by weight of cobalt and / or at least one of the elements Mn, Ti, Zr, Hf, V, Nb, Ta, W, Cu, Al, Si in individual proportions of less than 0.5% by weight of the Alloy and in a total proportion of less than 1% by weight of the alloy and / or at least one of the elements C, N, S, P, B, H, O in individual proportions of less than 0.2% by weight of the alloy and in a total proportion of less than 1% by weight of the alloy. The alloy is characterized by a coercive force H _c of 30 to 60 A / cm and a remanence B _r of at least 0.8 T.

These alloys are extremely ductile and extremely cold formable. Activation strips with thicknesses of 0.04 to 0.07 mm can be produced with these alloys. Furthermore, these alloys are characterized by cellular magnetic properties and high corrosion resistance.

An advantageous further development of these alloys are semi-hard magnetic alloys which contain 3 to 9% by weight of nickel, 5 to 11% by weight of chromium and 6 to 12% by weight of molybdenum.

Typically, the bias strips are made by melting the alloy under vacuum and casting into a ingot. The casting block is then hot-rolled into a strip at temperatures above approximately 800 ° C., then annealed at a temperature of approximately 1100 ° C. and then rapidly cooled. This is followed by cold working, suitably cold rolling, in accordance with a cross-sectional reduction of at least 75%, preferably 85% or higher. As a last step, the cold-rolled strip is tempered at temperatures of approx. 500 ° C to 800 ° C.

In an embodiment of the present invention, this local heat treatment can be carried out by a laser, the interaction time, the beam focusing of the laser and the power input of the laser being adapted in such a way that the heat affected zone corresponds to the geometric dimensions of the spatially separated non-magnetic regions to be achieved .

In an alternative embodiment of the invention, the activation strips, which have not yet been cut to length, are guided over a heated gearwheel, the gearwheel width of which approximately corresponds to the extent of the non-magnetic areas to be achieved, and the spacing of the individual teeth should correspond to the extent of the magnetic areas. The gear is brought to a temperature that is above the phase transition temperature.

The invention is described in detail below with reference to the drawing. Show 1 shows an alarm strip with a continuous elongated activation strip according to the prior art,

FIG. 2 shows an alarm strip with applied segmentation according to the prior art,

3 shows an alarm strip with applied continuous activation strips with perforations according to the prior art and

Figure 4 shows an alarm strip with a continuous applied activation strip according to the present invention.

Figure 1 shows an alarm strip 2 with a continuous elongated activation strip la according to the prior art. The elongated activation strip la is continuous and magnetized in an alternating polarity. The continuous activation strip la can only be magnetized satisfactorily if it is brought very close to the source of the external magnetic field. With such a continuous activation strip, a distance activation or distance deactivation is therefore only unsatisfactorily possible.

FIG. 2 shows an alarm strip 2 on which a plurality of partially segmented activation strips 1b are applied. This alarm strip 2 is activated or deactivated by magnetizing the sub-segments 1b. The magnetization of the partial segments 1b in one direction can take place at a substantially greater distance from the source of the external magnetic field due to the directional homogeneity. However, as can be imagined from FIG. 2, the application of these relatively small sub-segments 1b to the continuous alarm strips 2 connected with considerable effort.

FIG. 3 shows a continuous alarm strip 2 with an applied continuous activation strip 1c. This activation strip lc is provided with holes 3. The sub-segment structure of FIG. 2 is simulated through these holes 3. Here, however, the geometrical assignment of the holes 3 of the activation strip 1c on the alarm strip 2 is associated with considerable problems.

An exact assignment of the alarm strip 2 and the holes 3 of the activation strip 1c can only be guaranteed in a range of approximately +/- 0.5 mm in width. As a result, a certain overlap of the holes 3 with the alarm strip 2 is necessary. The diameter of the holes 3 must be approximately the width of the alarm strip plus 1 mm, the bandwidth of the activation strip 1c this diameter plus a web width of at least 1 mm. This means that the activation strip 1c must be considerably wider than the alarm strip 2 in order to allow the label to function reliably.

Figure 4 illustrates the present invention. As can be seen from Figure 4, is an elongated

Alarm strip 2 in turn an elongated continuous activation strip lb applied. In the elongated activation strip 1d, two spatially separated areas 4 are introduced, which consist of a non-magnetic phase.

These non-magnetic regions 4 are achieved by heat treatment of the activation strip 1d. Phase transitions from a magnetic crystal structure to a non-magnetic crystal structure are induced in a suitable semi-hard magnetic alloy. These phase transitions are spatially limited so that the areas 4 have no overlap.

A locally limited heat input therefore locally creates a permanent, irreversible, non-magnetic state, which leads to a reduction in the effective magnetically conductive cross section.

As a result, the effective magnetically conductive cross section in these regions 4 loses the ability to carry on the entire magnetic flux.

The semi-hard magnetic activation strip 1b shown in FIG. 4 consists of an Fe-Co-Cr alloy. The activation strips shown in FIGS. 1 to 4 consist of 0.1 to 10% by weight of nickel, 0.1 to 15% by weight of chromium, 0.1 to 15% by weight of molybdenum and the remainder iron in a total proportion of iron, nickel and molybdenum less than 95% by weight of the alloy. The activation strip 1d shown was produced by the following method:

1. casting the alloy at 1600 ° C,

2. hot rolling of the casting block at temperatures above 800 ° C., 3. intermediate annealing at approx. 1100 ° C.,

4. rapid cooling in water,

5. cold rolling,

6. interim annealing at approx. 1100 ° C,

7. rapid cooling in water, 8. cold working corresponding to a reduction in cross-section of 90%, 9. tempering for several hours at approx. 650 ° C and

The activation strips are then heat treated with a laser to achieve the non-magnetic areas. In an alternative embodiment of the present invention, the activation strips are heat-treated in a continuous process before being cut to length. The activation strips are passed through a heated gearwheel whose gearwheel width corresponds approximately to the extent of the non-magnetic areas to be achieved. The distances between the individual teeth of the gear correspond to the dimensions of the magnetic areas. The gear is brought to a temperature that is above the phase transition temperature

Claims

claims

1. display element for use in a magnetic anti-theft system consisting of: 1) an elongated alarm strip (2) consisting of an amorphous ferromagnetic alloy and at least 2) an elongated activation strip (ld) applied to the alarm strip and consisting of a semi-hard magnetic alloy, characterized gekennzeic net, a) that one or more spatially separated areas (4) are introduced into the semi-hard magnetic alloy by means of a heat treatment, which consist of a non-magnetic phase, and b) that the semi-hard magnetic alloy has a coercive force H _c of 15 to 100 A. / cm and has a remanence B _r of at least 0.8 T.

2. Display element according to claim 1, characterized in that a) that the semi-hard magnetic alloy

0.1 - 10% by weight Ni 0.1 - 15% by weight Cr

0.1 - 15% by weight Mo rest Fe and in a total proportion of Fe, Ni and Mo of less than 95% by weight of the alloy,

b) that the alloy may further contain

- 0 - 10 wt% Co and / or

- at least one of the elements Mn, Ti, Zr, Hf V. Nb, Ta, W, Cu, Al, Si in individual proportions of less than

0.5% by weight of the alloy and in a total proportion of less than 1% by weight of the alloy and / or

- at least one of the elements C, N, S, P, B, H, O in individual proportions of less than 0.2% by weight of the alloy and in a total proportion of less than 1% by weight of the alloy, and c) that the semi-hard magnetic alloy has a coercive force H _c of 30-60 A / cm and a remanence B _r of at least 0.8 T (10,000 Gauss).

3. Display element according to one of claims 1 or 2, characterized in that the semi-hard magnetic alloy

3 - 9% by weight Ni and / or Co 5 - 15% by weight Cr

3 - 12 wt% Mo rest Fe exists.

4. A process for producing the activation strip according to claims 1 or 2, characterized by the following process steps:

1) melting the alloy under vacuum or protective gas and then casting it into a casting block;

2) thermoformed the ingot into a strip at temperatures above approx. 800 ° C;

3) hissing annealing of the strip at a temperature of about 1100 ° C; 4) rapid cooling;

5) cold forming corresponding to a cross-sectional reduction of at least 85%;

6) tempering at temperatures between 500 ° C and 800 ° C;

7) Penetration of one or more spatially separated non-magnetic areas by local heat treatment.

5. The method according to claim 4, characterized in that the activation strips are locally heat-treated continuously with a laser.

6. The method according to claim 4, characterized in that the activation strips are guided in a pass through a gear and that the local heat treatment is carried out by the teeth of the gear.