Printed bias magnet for electronic article surveillance marker

Details Printed bias magnet for electronic article surveillance marker Printed bias magnet for electronic article surveillance marker

2001-07-30

2003-03-25

Mullen, Thomas (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C148S100000, C340S572200, C340S572800, C428S611000

Reexamination Certificate

active

06538572

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to magnetomechanical electronic article surveillance (EAS) markers, and more particularly to a printed bias used in a magnetomechanical EAS marker.
2. Description of the Related Art
EAS markers are typically attached to articles of merchandise and respond to an electromagnetic field transmitted into an interrogation zone located at the exits of a controlled area. The response of the EAS markers to the electromagnetic field is detected and indicates that the article is being removed from the controlled area without authorization. An alarm can be sounded upon receiving the EAS marker response to alert relevant personnel of an attempt to remove the article.
Conventional magnetomechanical EAS markers that have a magnetostrictive resonator typically use a magnet as a control element either for biasing or deactivation or both. For deactivatable labels, the bias magnet is usually a semi-hard rolled product magnet material. For hard tags that are nondeactivatable, the bias magnet is usually an injection molded ferrite magnet material. The term “marker” refers to both “tags” and “labels”.
Nondeactivatable EAS hard tags are primarily used in the tagging of soft goods, such as clothing in retail stores. The tags, such as that disclosed in U.S. Pat. No. 5,426,419, consist of a plastic housing that contains a magnetoacoustic resonator element and a clutching mechanism. The hard tag assembly process starts with two halves of the plastic housing that are formed using injection molding. The internal parts (resonator, spacer, bias magnet, and clutch/clamp assembly) are placed within the housing, and the two halves of the housing are sealed together, typically using ultrasound energy. The tag can then be attached to articles to be protected by insertion of the pin body through a portion of the article and into the clutching mechanism. The pin cannot be released to detach the tag from the merchandise unless the clutch is opened by a mechanical or magnetic detacher mechanism designed for the particular tag.
Referring to
FIG. 1
, a flow chart of the present manufacturing process for hard tags is illustrated. The bias magnets are produced using an extrusion or injection molding process at step
2
. Magnetic particles with coercivity higher than 3000 Oe are used to make reusable or nondeactivatable markers. These particles are mixed with plastic binder/resin, and are heated to a molten state. They are then molded into individual pieces with injection molding. The extrusion process can also be used to produce a continuous roll having a strip of magnetic material with a thickness of about 30 to 50 mils. The roll can then be slit and cut into individual pieces with desired dimensions at step
6
. Magnetization of the material at step
4
can be performed before or after the cutting process. A batch of resonator strips is also properly cut at step
8
to match with the strength of the magnetic bias strips. The two halves of the plastic housing are formed using injection molding at step
10
. The resonator is placed into the cavity formed in the plastic housing halves at step
12
. A spacer is placed at step
14
prior to placing the bias magnet at step
16
. The clutch assembly is placed into the plastic housing at step
18
. The two plastic housing halves are ultrasonically sealed together at step
19
to complete the tag at step
20
. Due to the thickness of the magnetic bias, a thin reusable marker is not available.
Referring to
FIG. 2
, the manufacturing process of deactivatable labels, such as disclosed in U.S. Pat. No. 6,067,015, is similar to hard tags with some significant differences. The bias magnets are not extruded but made of a semi-hard magnetic metal. The housing is made of a vacuum thermal formed polystyrene. There is no clutch assembly used in a deactivatable label, and the spacer and cover are heat sealed to the housing. Referring to
FIG. 2
, steps that are identical to the steps performed in
FIG. 1
are given the same reference numerals. The vacuum-formed housing is produced at
22
, after the resonator is cut
8
and placed into the cavity
12
, a spacer lid is placed over the resonator and the cavity at
24
, and may be heat-sealed in place. The semi-hard bias magnet material is heat treated and annealed to form a roll having desired bias magnetic properties at
26
, and after cutting at
6
, the bias magnet is placed onto the spacer at
17
, and may be adhesively attached. If the bias is not adhesively attached, a cover lidstock material is placed over the bias at
28
and heat sealed to the housing at
30
. The bias magnet is magnetized at step
4
to complete the process.
Disclosed in the '015 patent are bias magnets formed in various shapes to improve the performance of the EAS label. However, all of these deactivatable bias magnets must be cut from a batch of magnetic material, which is normally formed into a roll after the material is properly heat treated and annealed to obtain desired properties. It should be apparent that shapes other than rectangular each present varying degrees of cutting and forming difficulty, which increase the cost to make EAS markers having shaped bias magnets.
There presently exists a need for an EAS tag that is thinner than those made by conventional methods, and for a bias magnet material this is easier to form into various bias shapes such as, but not limited to, those disclosed in the '015 patent.
BRIEF SUMMARY OF THE INVENTION
The present invention replaces the conventional bias magnets for EAS markers with a paintable or printable bias magnet material, which is either directly painted onto the EAS marker or first placed onto a substrate material, which is then placed into the EAS marker. The material includes a magnetic powder mixed with solvent and resin. This “bias paint” is then applied onto the EAS marker. The magnetic powder and solvent provide a very dense layer after drying, which has a magnetic material density that is usually lower than a rolled product, but is higher than that of the injection-molded magnet material.
A first aspect of the invention is a mapetomechanical electronic article surveillance marker having a housing with a cavity formed therein. A magnetostrictive resonator member is disposed within the cavity. A cover is connected to the housing over the cavity capturing the resonator member therein. A bias magnet is disposed adjacent the resonator member, where the bias magnet is a magnetic powder mixed with at least one material to form a paint that is disposed adjacent the resonator by being painted onto the housing or onto the cover. The bias magnet can be painted onto a substrate, and the substrate can be connected to the housing or to the cover wherein the bias magnet is disposed adjacent the resonator. The bias magnet can be formed of a plurality of layers.
A second aspect of the invention is a method of making a magnetomechanical electronic article surveillance marker by the steps of preparing magnetic ink by mixing magnetic particles with a resin and solvent material. Printing the magnetic ink onto a substrate and curing by heating. Providing a housing having a cavity formed therein, cutting and placing at least one resonator into the cavity. Placing the substrate over the cavity wherein the magnetic ink is aligned adjacent the resonator, and connecting the substrate to the housing, capturing the resonator within the cavity wherein the magnetic ink is disposed adjacent the resonator. The method can include printing and curing in a plurality of passes to form multiple layers of magnetic ink on the substrate. The cavity can be formed by printing nonmagnetic ink onto a flat housing material. A cover can be sealed to the housing capturing the resonator within the cavity prior to connecting the substrate to the housing.
A third aspect of the invention is similar to the second except the ink is pri

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