Ferromagnetic fiber having uses in monitoring electrical appliances and manufacture thereof

(42) Date of commencement of the patent: 15. 2. 1994 (45) Date of issue: 25.11.1994

<td>(30) Priority:</td><td>(73) Patent owner:</td>

<td>27.12.1988 US 290547 claims.</td><td>PITNEY BOWES INC. CT 06926-0700 STAMFORD (US).</td>

(54) BRAND FOR USE IN ELECTRONIC ARTICLE MONITORING, FERROMAGNETIC FIBERS AND METHOD OF MANUFACTURING THE SAME (57) A ferromagnetic fiber has been produced which has particular use in the field of electronic article surveillance (EAS). The ferromagnetic fiber is produced by using a spinneret (12) device which engages a bath of molten alloy (20) having the desired composition for the fiber. The use of ferromagnetic fibers has made the ability to produce electronic article surveillance tags so small that they can be dispensed using a commercial labeller.

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AT 398 253

<img file="AT398253B_D0001.tif" />

BOR 6ΕΓ73313

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The unauthorized entrainment of merchandise articles has long been a problem for one-trade businesses. Various efforts have been made to prevent such unauthorized take-off, commonly referred to as shoplifting. Picard designed an electronic article surveillance system of electromagnetic design, as described in its French patent application no. 763 681, which was published in 1934. The Picard system includes a transmitter, a receiver and a ferromagnetic tag. Attempts have been made to reduce the size and cost of the article surveillance marks as proposed in US Pat. February 1986 for Pokalsky was granted. In accordance with the disclosure of the Pokalsky patent, the drawn wire tag member has a diameter of about 0.127 mm (127 micrometers), which is significant, the tag itself has a length of about 76.2 mm. The US new edition patent 32 427, which was released on 26. It was issued May 5, 1987 to Gregor, and relates to a tag member consisting of an elongated, stretchable strip of amorphous ferromagnetic material that retains its signal identity after being bent over.

The invention has embraced a method of forming ferromagnetic fibers for use in tags. By brand is meant any article that can be detected by a sensor system after the tag has been placed in a magnetic field of appropriate characteristics. The invention includes a magnetic fiber or fibers which are held in any suitable manner. The fibers can be detected in an interrogation zone and have a length of less than 15 mm. It has been found that one of the important parameters of the ferromagnetic fibers is the aspect ratio. Fibers having a diameter of approximately 100 micrometers or less have been found to be suitable for making a mark, such as a label having a length of approximately 15 mm or less. It is understood that the length may be longer if desired.

Another important parameter is the method by which the ferromagnetic fiber is made. Rapid solidification processes are used in which the fibers are cast directly into their final physical dimensions and which do not require subsequent mechanical or thermal treatment in the practice of the invention. Fibers produced by rapid solidification processes are in a stress state and molecular orientation that are favorable in terms of their as-cast magnetic properties.

The invention has for its object to provide an improved brand for an electronic article surveillance system having a ferromagnetic marker element which is substantially shorter than known brands and which has a low cost and yet provides effective electromagnetic response in the system.

It is another object of the present invention to provide an improved mark for use in an electronic article surveillance system in which the marker element is either a crystalline or amorphous fiber made by rapid solidification processes.

Finally, it is an object of the invention to provide an improved method of making an electromagnetic tag for use in an electronic article surveillance system in which the tag member is manufactured by rapid solidification techniques.

Finally, it is an object of the present invention to provide an improved mark for use in an electronic surveillance system in which a ferromagnetic marker element or more thereof, in random orientation on a respective carrier, for example on a recording element, such as a piece of paper, a sign or a label , are attached.

It is another object of the invention to provide an improved mark for use in an electronic article surveillance system which utilizes a crystalline ferromagnetic material such as a permalloy and in which the marker element is sufficiently stretchable to handle without loss of its signal identity to be able to.

It is another object of the invention to provide an improved mark for an electronic article surveillance system in which a marker element comprises a fiber laid in a fabric.

It is another object of the invention to provide an improved tag for use in an electronic article surveillance system in which a tag member is received directly in paper.

Finally, the invention has the object, an improved method for producing a

To create a brand for use in an electronic article surveillance system in which a

Brand element or more thereof are contained in a papermaking slurry, which is then gewaizt to paper, whereby the paper obtained by the system is detectable.

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Another object of the invention is to provide an improved tag for use in an electronic article surveillance system in which the tag comprises a tag member having a design and tension which provides favorable ferromagnetic properties.

Another object of the invention is to provide an improved tag for use in an electronic article surveillance system in which the tag comprises a tag member having a ferromagnetic fiber no longer than 15 mm.

Another object of the invention is to provide a tag having at least one film comprising one or more ferromagnetic fibers.

Further, it is an object of the invention to provide an improved, inexpensive ferromagnetic tag member.

Another object of the invention is to provide a ferromagnetic marker element in a process step that provides a ready-to-use product.

Further, it is an object of the invention to provide a ferromagnetic material useful for shielding magnetic fields.

Another object of the invention is to provide an improved tag for use in an electronic article surveillance system in which the tag comprises a ferromagnetic tag member having a cross-sectional area smaller than 6x10^-3 mm² is.

Finally, it is an object of the invention to provide an improved tag for use in an electronic article surveillance system in which the tag member comprises a ferromagnetic fiber having a maximum transverse dimension of less than 80 micrometers.

Finally, it is a further object of the invention to provide an improved tag for use in an electronic article surveillance system in which the tag member comprises a ferromagnetic fiber having a weight of less than 20 mg. Another object of the invention is to provide a ferromagnetic tag which can be used in the currently used commercial labeling machines.

The above-mentioned object is achieved by a trade mark for use in an electrical article surveillance system comprising a ferromagnetic fiber made by rapid solidification from a molten ferromagnetic alloy and a carrier for the ferromagnetic fiber.

In the drawings show:

1 is a sectional view of a Schmelzextraktiongsvorrichtung for producing ferromagnetic fibers,

2 is an enlarged sectional view taken along the line 2-2 of FIG. 1 of the circumference of the spinning disk shown in Fig. 1,

Fig. 3 is a sectional view taken along line 3-3 of Fig. 1, indicating a cross section of a fiber made by the apparatus of Fig. 1;

FIG. 4 is a plan view of a composite web containing fibers made by the apparatus of FIG. 1. FIG.

Fig. 5 is a sectional view taken along line 5-5 of Fig. 4, showing a side view of the composite web, and

Fig. 6 is a plan view indicating an alternative fiber distribution within a label.

Reference is made to the detailed description of the preferred embodiment. Initially, Figs. 1 3, wherein at 10 is shown a rotating wheel assembly capable of producing a rapid solidification that produces ferromagnetic fibers in accordance with the principles of the present invention. Shown and described is a melt extraction process, however, it is to be understood that other methods of practicing the invention can be used including melt spinning, melt drawing and hanging drop processes. The correct requirement is that "the material has a shape as explained below and solidifies rapidly. The device 10 comprises a disc 12 or a wheel which is fixedly supported by a rotatable shaft 13 and which has a reduced portion 14 at its periphery. The reduced portion 14 has an edge 16. The disk 12 used in the practice of the invention has a diameter of 15 cm and the wheel 16 has a radius of curvature of approximately 30 microns, but 5 to 50 microns would be acceptable. The shaft 13 is engaged by any suitable device with a motor 17 so that the shaft and the disc 12 mounted thereon can be rotated.

A cup-shaped funnel 18 is disposed under the disc 12 and can receive a metal alloy composition 20. Induction coils 22 are arranged around the funnel 18 and connected to a power supply 23. If sufficient power is supplied to the induction coils 22, the metal alloy composition 20 within the funnel 18 melts

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Arrow 1 is rotated, and upon rotation of the disk within the molten alloy composition, a fiber 24 is produced. Optionally, the flange 18 is in contact with a scraper 26 made of a material, such as cloth, to keep the reduced portion 14 clean.

It is now on the Fig. 4 5, the fibers 24 are oriented relative to one another and are each disposed between upper and lower foils 30 and 32, which are joined by an adhesive 34 to form a mark, which is shown in the form of a label 28. The labels 28 are carried by a web 36 and may be applied to the surface of an article by use of a labeller in a known manner. In this context, the term label should also include bills and signs. For details of a carrier web described herein, reference may be made to U.S. Patent No. 4,207,131. Preferably, the mark 28 has a length of less than 2.5 cm, and preferably about 15 mm. With such a size, the composite web 38 can be used in a commercial labeler, such as in a labeller 1110, available from Monarch Marking Systems Inc. of Dayton, Ohio. Although the mark 28 is shown with upper and lower sheets 30, 32, it will be understood that the fibers 24 can only adhere to the lower sheet 32 ​​and the upper sheet can be omitted.

The power supply 23 is turned on to cause the induction coils 22 to heat the metal alloy 20 above its melting point, thereby producing a molten metal alloy bath. As can be seen, the reduced portion 14 of the disc 12 extends into the metal alloy 20. Although the metal is shown here with a dome-like appearance, this is slightly exaggerated to show the reduced portion 14 within the melt. In any event, a portion of the diameter of the disc 12 extends into the uppermost portions of the funnel to capture the metal alloy 20 after it reaches its corresponding temperature. Depending on the temperature of the alloy, the arm 19 is lowered so as to introduce the reduced portion 14 into the metal alloy, and the motor 17 is turned on to rotate the disk 12. The disk 12 is in the In Fig. 1 rotated arrow direction and thereby a fiber of ferromagnetic metal 24 is formed. This fiber can be as long as necessary.

It is understood that the described rapid solidification process provides a fiber which is in a working condition, ie which goes from the molten state immediately to the solid state in a state for immediate use. No subsequent treatment is required to achieve the desired properties. This is in contrast to known ferromagnetic materials, such as wires and permalloy films, where mechanical and / or heat treatment is necessary to obtain the required properties.

In accordance with the invention, a ferromagnetic fiber is defined as a substantially elongated article consisting of either an amorphous or crystalline ferromagnetic material and having a diameter of 3 to 80 microns, an aspect ratio, ie has a length / diameter ratio of at least 150 and a magnetic switching time at the half-amplitude points (t1 / 2) of less than 10 microseconds at a sinusoidal control frequency of 6 kHz and an amplitude of the order of 1 oersted. The fiber produced in the apparatus described above has a cross-section which is shown in FIG. 3 is shown and which is substantially kidney-shaped. One embodiment of the fiber was kidney-shaped with a dimension of 30-80 microns in one direction and 20-30 microns in the other direction. When the speed of the disk 12 was increased, the fiber 24 took a more oval shape than a kidney shape, and finally obtained a circular cross-section with a narrow groove if the diameter of the fibers was 15 microns or less. The best results were obtained with a fiber 24 which had a substantially circular cross-section. Under optimal conditions, the fiber 24 could not have a certain length, but it has been found that certain conditions affect the length of the fiber. The conditions that cause a change in the length of the fiber are the orbital speed of the pulley 12, the vibrations in the system, and the shape and design of the pulley.

The fiber 24 was cut into lengths of approximately 1.9 cm and applied to a first layer 32 of a label. A second ply 30 was placed over the fibers 24 aligned with the first ply, with adhesive applied between the plies to form a label. The fibers 24 can according to FIG. 4 spaced approximately 1 mm apart or they may be as shown in FIG. 6 distributed indiscriminately within the label. It has been found that three or more fibers arranged in alignment are sufficient for the mark to be detected in an interrogation zone; if, on the other hand, the fibers are randomly arranged, then five or more fibers were sufficient. The arrangement of the fibers 24 randomly with mutual overlap is unique in this field. Known brands demanded that the multiple elements align and / or follow one another.

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Other orientations are possible. A fiber or multiple fibers that are helical, bent, or curved may also provide a sufficient response for detection. It has been found that the minimum total weight of the fibers 24 that are detectable was approximately 0.2 mg.

A large number of compositions have been reported for the manufacture of the fibers. The following is a table of some of the compositions tested, with the physical form and test results of the system:

<td>COMPOSITION</td><td>SHAPE</td><td>t1 / 2 (lO^-Gs)</td>

<td>FezoAlasCrs</td><td>C</td><td>5</td>

<td>Fe7oAI₂4.8CrsCo, iPo.i</td><td>C</td><td>10</td>

<td>Fe₃₃ AtaCrs</td><td>C</td><td>3 and 5</td>

<td>Fe72AI₂5Cr3</td><td>C</td><td>7 and 8</td>

<td>Fe72AI28</td><td>C</td><td>6</td>

<td>Fe7₂Al25Cr3</td><td>C</td><td>7</td>

<td>Fe7oAl25Crs</td><td>C</td><td>5</td>

<td>Ni72Cui4Mo₃Fei i</td><td>C</td><td>2</td>

<td>Ni7₂Cui4Cr₃Fei 1</td><td>C</td><td>3</td>

<td>Ni72Cui₃M02Mn2Fei 1</td><td>C</td><td>4</td>

<td>N171 Cu-1 ₃ Mo₂ Mn₃ Fei 1</td><td>C</td><td>2.4</td>

<td>Ni7₃Cui ₃ Mo₂Mm F © i 1</td><td>C</td><td>1.8</td>

<td>Ni7gFeisM05 mm</td><td>C</td><td>1.5</td>

<td>Ni8₂Fei2Cui Mo₃Mn₂</td><td>C</td><td>2.5</td>

<td>Co7oFe4.SiisBw</td><td>A</td><td>2.4</td>

<td>Co69.6Fe4.i Moo.gSi 17.5 B7.75</td><td>A</td><td>2.8</td>

<td>Fo78Sig Bi ₃</td><td>A</td><td>5.2</td>

<td>Fe74.Nb8Sis B12</td><td>A</td><td>2.7</td>

in which

C = crystalline

A = amorphous t1 / 2 = pulse measurement in microseconds

In determining the performance of a ferromagnetic tag, perhaps the most critical parameter is the fl / 2 value, which is a measure of how steep the pulse induced by such a tag in an interrogation zone is, in particular t1 / 2 in microseconds Time span between the rising and falling edge at half the peak value of the induced signal. A value of t1 / 2 = 10 microseconds or less is considered acceptable. A lower value is desirable because it indicates a steep, easy to detect vertex and thus a high proportion of harmonics.

Although efforts have been made in the past to use a crystalline ferromagnetic material, commonly known as permalloy, as an element in a trademark, two factors have prevented its use. First, in the known forms of permalloy elements, the t 1/2 was too large for practical use in the electronic article surveillance field. Second, bending, since permalloy is crystalline, tended to change its magnetic properties. According to the invention, it has been found that these adverse properties are sufficiently reduced to allow the use of permalloy. As previously stated, small amounts of ferromagnetic material in fiber form are detectable in an interrogation zone.

Furthermore, it can be said that all ferromagnetic materials which are useful in the electronic article surveillance as a brand element in the form of a band can be used in the form of a fiber. For embodiments of such composition, reference may be had to US Reissue Patent 32,427.

In general, the fiber may be formed of ferromagnetic material which substantially conforms to one of the following formulas:

Fa Lb Oc, where

F stands for iron,

L is at least one element of silicon and aluminum,

AT 398 253 B is at least one of chromium, molybdenum, vanadium, copper and manganese, and a ranges from about 60 to 90 atomic%, b ranges from about 10 to 50 atomic%, and c ranges from about 0 to 10 atomic%

OR

Na Fb Mc, being

N stands for nickel,

F for iron, and

M is at least one of copper, molybdenum, vanadium, chromium, manganese, or other non-magnetic elements, and a ranges from about 60 to 84 atomic%, b ranges from about 0 to 40 atomic%, and c ranges from about 0 to 50 atomic%

OR

Ma Nb Xd Yc, where

M is at least one element of iron and cobalt,

N is nickel,

O is at least one element of chromium and molybdenum,

X is at least one element of boron and phosphorus,

Y is silicon,

Z is carbon, and a ranges from about 35 to 85 atomic%, b ranges from about 0 to 45 atomic%, c ranges from about 0 to 7 atomic%, and from about 5 to 22 atomic% %, extending from about 0 to 15 atomic%, ranging from about 0 to 2 atomic%, and the sum of d + e + f ranging from about 15 to 25 atomic%.

It should be noted that substantially those fibers that are amorphous may be made in an ambient atmosphere while those fibers formed from crystalline compositions must be formed in a vacuum or inert atmosphere such as argon. It has been found that all devices which emphasize rapid magnetic flux change resulting from the change in the magnetization of a soft magnetic material are improved by using the material in fiber form. Although the reasons that an electromagnetic fiber produced by rapid cooling provides superior performance in an electronic article surveillance field are not well known, calculations have been made which show that a cylindrically shaped electromagnetic material is the same material in tape form is superior.

Signal comparison for a strip and a fiber B = 0.6 Tesla saturation magnetization of the material Im = Io 100,000 magnetic permeability of the material W = 2 p 6000 sec^-1 Frequency of applied field Hm = 1.5 Oersted applied field

G: = -0.3 d

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Coupling factor to the pickup coil

Dimensions of a fiber (F) and a strip (S)

Length (In) = 20 mm Width (w) = .8 mm

Diameter (d) = 25 μm thickness (t) = 25 μm

N = 10 number of turns of pickup coil n_f = 1 number of fibers

Effective magnetic permeability for a fiber 1 DF compared to a strip 1 DS taking into account the demagnetization effect (ln, d) DF

<img file="AT398253B_D0002.tif" />

p 1 (ln, w, t) = -

DS 14.25 twu (ln, d) «67.31 x 10 1 (ln, v, t)

DF DS

3,279 X 10

As shown, the effective magnetic permeability for a ferromagnetic fiber is significantly greater than that for a band.

Volume of the magnetic material:

d

V (1, d) = p - 1 V (ln, w, t,) = wt 1

F 4 S

Ratio of Applied Field to Critical Field for a Fiber (BF) and a Stripe (BS):

BF (ln, d) = BS (ln, w, t): = in

-ι1 1 (ln, d)

DF

Ι 1 (ln, w, t) 0 DS

Reduce or roll the signal from one harmonic to the next:

AF (ln, d) =

BF (ln, d) - ln

AS (ln, w, t) ln + BS (ln, w, t) -1

BF (ln, d)

AF (ln, d) = 0.821

AS (ln, w, T) - 0.191

Signal at the ninth harmonic for a fiber (SF) and a stripe (SS):

BS (ln, w, t)

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SF (ln, d) = -BwV (ln, d) AF (ln, d) n_NGp SS ^e

SS (ln, w, t) = 4 Bs w Vg (ln, w, t). AS (ln, v, t)⁹ Nf NG

SF (ln, d) = 3,674 x 10 volts SS (ln, W, t) = 2,783 x 10 volts

SF (ln, d) = 132,017

Signal ratio = 0.025

Ratio of material volumes.

As can be seen from the above calculations, the signal generated by a fiber is 132 times larger than the signal generated by a strip of equal length 20 mm. It will be appreciated that the other dimensions of the strip may be changed to change the response of the strip, but the ratio of the selected dimensions has been found to be typical. Although the novel fiber of the present invention has been illustrated in its use in labels, it will be appreciated that other applications for such fibers exist. The fibers, if sufficiently small, can be woven as part of a paper from which documents are made. In this way an article with non-obvious sensor properties would be obtained. Another use for which these fibers can be used is the localization and identification of devices such as underground cables or other inaccessible structures. The filaments could be formed as part of the cable laid underground, and by means of suitable detection devices the cables could be located even if they are not exposed. Another application is In a shield. For example, in shielding, an electrical cable would tend to insulate the cables from the field when coated over the cables that contain ferromagnetic fibers. In another application, the electromagnetic fibers can be added to a paper slurry from which paper with the fibers contained therein can be made. Such papers would be detectable and have a wide application area where security is required, for example in the production of paper money.