U.S. patent number 3,755,730 [Application Number 05/165,892] was granted by the patent office on 1973-08-28 for a steel object having hidden magnetically readable identification and the method for applying the identification.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Peter J. Vogelgesang.
United States Patent |
3,755,730 |
Vogelgesang |
August 28, 1973 |
A STEEL OBJECT HAVING HIDDEN MAGNETICALLY READABLE IDENTIFICATION
AND THE METHOD FOR APPLYING THE IDENTIFICATION
Abstract
A vehicle, appliance or tool having a multiplicity of
magnetizable identifying indicia hidden by an opaque, protective
layer such as paint. The indicia may be read by the use of a
magnetic reader.
Inventors: |
Vogelgesang; Peter J.
(Roseville, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
22600904 |
Appl.
No.: |
05/165,892 |
Filed: |
July 26, 1971 |
Current U.S.
Class: |
382/104; 235/493;
324/262; 427/132; 340/5.8; 382/320; 101/389.1; 324/214; 360/1 |
Current CPC
Class: |
G09F
3/00 (20130101); G06K 7/082 (20130101); G06K
19/12 (20130101) |
Current International
Class: |
G06K
7/08 (20060101); G06K 19/12 (20060101); G09F
3/00 (20060101); G01r 033/00 () |
Field of
Search: |
;324/34R,41 ;117/235,237
;340/149A,146.3K,146.3C ;346/74M,74MP ;235/61.12M,61.11D |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
626,756 |
|
Sep 1961 |
|
CA |
|
880,661 |
|
Oct 1961 |
|
GB |
|
Other References
Benson et al.; Machine Readable Credit Card; IBM Tech. Bull.; Vol.
12; No. 5; Oct. 1969; pp. 715..
|
Primary Examiner: Corcoran; Robert J.
Claims
What is claimed is:
1. A vehicle, appliance or tool having a steel body part; a
multiplicity of discontinuous alphanumeric indicia scattered over
the body part, each of said indicia providing complete
identification of the vehicle, appliance or tool, said indicia
having line widths of at least 0.005 inch and comprising
magnetizable particles dispersed in a nonmagnetizable binder, the
particles having a coercivity at least twice that of said part and
having a remanent magnetism exceeding 5 emu per gram; and a thin,
opaque permanent protective layer of paint over the part and
indicia providing a uniform surface hiding the identifying indicia;
said magnetizable particles being present in sufficient amount to
provide, when magnetized, a remanent magnetic moment exceeding 50
gauss at the surface of the paint to permit the identifying indicia
to be readily inspected using a magnetic reader; the combination of
paint and indicia providing a theft deterrent in that the vehicle,
appliance or tool cannot be provided with counterfeit
identification without removal of the paint and indicia,
application of a multiplicity of false magnetizable indicia, and
repainting.
2. A method of applying to at least one painted steel body part of
a vehicle, appliance, or tool identification which is a theft
deterrent in that the vehicle, appliance or tool cannot be provided
with counterfeit identification without removal and replacement of
a significant portion of the paint, the method comprising the steps
of:
preparing a dispersion of nonmagnetizable binder and magnetizable
particles having a remanent magnetism above 5 emu per gram and
coercivity at least twice that of said part;
applying the dispersion to the part to provide a multiplicity of
discontinuous alphanumeric identifying indicia scattered over the
part, each of said indicia providing complete identification of the
vehicle, appliance or tool, and having line widths of at least
0.005 inch; and
applying over the identifying indicia a thin, opaque permanent
protective layer of paint having sufficient thickness to provide a
uniform exterior surface hiding the identifying indicia, the amount
of magnetizable particles at all points of the indicia being
selected to provide when magnetized, a remanent magnetic moment
exceeding 50 gauss at the surface of the paint to permit convenient
inspection of the identifying indicia using a magnetic reader.
3. A vehicle, appliance or tool according to claim 1 wherein said
magnetizable particles have a coercivity of at least seven times
that of said part and have a remanent magnetism above 50 emu per
gram, and said indicia have a thickness less than one quarter the
thickness of said protective layer of paint.
4. A method of providing hidden magnetically readable
identification on at least one painted steel body part of a
vehicle, appliance or tool, which identification is a theft
deterrent in that the vehicle, appliance or tool cannot be provided
with counterfeit identification without removal and replacement of
a significant portion of the paint, the method comprising the steps
of:
preparing a dispersion of nonmagnetizable binder and magnetizable
particles having a remanent magnetism above 5 emu per gram and
coercivity at least twice that of said part;
applying the dispersion to the part to provide a multiplicity of
discontinuous identifying indicia scattered over the part, each of
said indicia providing complete identification of the vehicle,
appliance, or tool, and having line widths of at least 0.005
inch;
applying over the identifying indicia a thin, opaque permanent
protective layer of paint having sufficient thickness to provide a
uniform exterior surface hiding the identifying indicia, the amount
of magnetizable particles at all points of the indicia being
selected to provide, when magnetized, a remanent magnetic moment
exceeding 50 gauss at the surface of the paint;
magnetizing the particles in the indicia; and
positioning adjacent the paint means for providing a visible image
corresponding to the outline of the hidden indicia.
5. A system for hidden magnetically readable identification on at
least one painted steel body part of a vehicle, appliance or tool
which identification is a theft deterrent in that the vehicle,
appliance or tool cannot be provided with counterfeit
identification without removal and replacement of a significant
portion of the paint, the system comprising:
a dispersion of nonmagnetizable binder and magnetizable particles
having a remanent magnetism above 5 emu per gram and coercivity at
least twice that of said part;
means for applying the dispersion to the part to provide a
multiplicity of discontinuous identifying indicia scattered over
the part, each of said indicia providing complete identification of
the vehicle, appliance, or tool, and having line widths of at least
0.005 inch;
means for applying over the identifying indicia a thin, opaque
permanent protective layer of paint having sufficient thickness to
provide a uniform exterior surface hiding the identifying indicia,
the amount of magnetizable particles at all points of the indicia
being selected to provide, when magnetized, a remanent magnetic
moment exceeding 50 gauss at the surface of the paint;
means for magnetizing the particles in the indicia; and
means positionable adjacent the opaque protective layer for
providing a visible image corresponding to the outline of the
hidden indicia.
6. A system according to claim 5 wherein said magnetizable
particles have a coercivity of at least seven times that of said
steel body part, and have a remanent magnetism above 50 emu per
gram.
7. An automobile having:
a steel body;
a multiplicity of discontinuous alphanumeric magnetizable indicia
scattered over the body, each of said indicia providing complete
identification of the automobile; and
a thin opaque permanent protective layer of paint over the body and
indicia providing a uniform surface hiding the identifying
indicia;
the combination of indicia and paint providing a theft deterrent in
that the automobile cannot be provided with counterfeit
identification without removal of the paint and indicia,
application of a multiplicity of false magnetizable indicia, and
repainting;
said indicia having a thickness less than one quarter the thickness
of the layer of paint, having line widths of at least 0.005 inch
and comprising magnetizable particles dispersed in a
nonmagnetizable binder; and
said particles having a coercivity at least seven times that of
said body, a remanent magnetism exceeding 50 emu per gram, and
being present in sufficient amount to provide, when magnetized, a
remanent magnetic movement exceeding 50 gauss at the surface of the
paint to permit the identifying indicia to be readily inspected
using a magnetic reader.
Description
FIELD OF THE INVENTION
This invention relates to providing identification for a commercial
article, especially a vehicle, appliance or tool.
DESCRIPTION OF THE PRIOR ART
Articles of commerce are commonly identified by serial numbers,
conventionally by attaching a printed plate or imprinting the
article. When an article is stolen, its serial number often is
altered or replaced with a different number to prevent subsequent
identification.
On some automobiles the serial number is attached at several
locations not easily located or accessible in an effort to
frustrate attempts to alter or replace them. These inaccessible
serial numbers do not provide a means for easily identifying an
automobile on the street or at traffic checks.
SUMMARY OF THE INVENTION
Commercial articles are provided with identification which cannot
reasonably be altered or removed but which can be conveniently
inspected. This novel identification is provided by a multiplicity
of magnetizable identifying indicia which are hidden by an opaque,
permanent protective layer of the article. The identifying indicia
may include alphanumeric or other characters formed of magnetizable
particles dispersed in a nonmagnetizable binder. As the indicia are
not visible beneath the protective layer, they may have easily
accessible locations such as on the exterior of several body parts
of an automobile without visually revealing their location or
detracting from the appearance.
According to the present invention there is provided a vehicle,
appliance or tool having on at least one part identification which
cannot reasonably be altered or removed. The identification is
provided by a multiplicity of identifying indicia having line
widths of at least 0.005 inch and comprising magnetizable particles
dispersed in a nonmagnetizable binder. The particles have a
coercivity at least twice that of said part and have a remanent
magnetism exceeding 5 emu per gram. A thin, opaque permanent
protective layer is applied over the part and indicia providing a
uniform surface hiding the identifying indicia. The magnetizable
particles are present in sufficient amount to provide, when
magnetized, a remanent magnetic moment exceeding 50 gauss at the
surface of the protective layer.
Although not visible, the magnetized indicia may be read by placing
a magnetic reader over the indicia. A convenient magnetic reader
for this purpose is described in U.S. Pat. No. 3,013,206. This
magnetic reader includes a visible suspension in a transparent
liquid vehicle of flat, weakly ferromagnetic crystals which will
visibly orient in the liquid in accordance with an adjacent
magnetic field. When the magnetic reader is placed on the
protective layer over the identifying indicia, the ferromagnetic
crystals in the reader will visibly outline the magnetic indicia by
aligning in response to the field gradients about the periphery of
the indicia. Alternatively, the indica could be revealed by
distributing ferromagnetic particles (e.g. carbonyl iron or
magnetite, either as a powder or in liquid suspension) on the
protective coating above the indicia and allowing these particles
to migrate to outline the magnetized indicia.
A multiplicity of the magnetizable identifying indicia may be
applied to an article, thus requiring extensive removal of the
protective layer on an article to remove all of the indicia. The
requirement to remove the paint for removal of the indicia and to
apply different indicia and new paint for falsifying serial number
identification thereon will be a strong deterent to removing or
changing identifying indicia applied to automobiles according to
the present invention.
A variety of magnetizable particles are useful, such as gamma
Fe.sub.2 O.sub.3, chromium dioxide, barium ferrite or powdered
magnetizable metal. The magnetizable particles should have a
coercivity of at least twice the coercivity of the part of the
article to which the indicia are applied so that the particles may
be selectively magnetized, either for initial magnetization of the
indicia, or to afford remagnetization if the indicia should become
demagnetized. Selective magnetization of the indicia may be
accomplished by passing a permanent magnet adjacent the indicia,
and then (if the part is magnetizable) demagnetizing the part with
an A.C. magnetic field adjusted in intensity to exceed the
coercivity of the part but to be less than the coercivity of the
magnetized particles in the indicia.
Magnetizable particles in indicia applied to a part of structural
sheet steel (such as a body part of an automobile having typically
a coercivity of 40 oersteds) preferably are selected to have a
coercivity of more than seven times the coercivity of the body
part. This greater difference in coercivities affords selective
demagnetization of the part with less accurately regulated sources
of A.C. magnetic fields.
The identifying indicia when magnetized must provide a remanent
magnetic moment at the surface of a protective layer which will
afford a clear outline of the magnetized indicia. A remanent
magnetic moment at the surface of the protective layer of 50 gauss
has been found acceptable to provide a clear outline of the indicia
in the magnetic reader previously described.
The remanent magnetism of the magnetizable particles should be
above 5 emu per gram and preferably above 50 emu per gram so that
the volume of the dispersion of magnetizable particles and binder
or marking material used to form the indicia may be minimized while
still producing the required remanent magnetic moment for
activating a magnetic reader. The remanent magnetic moment of a
given volume of marking material is directly dependent on the
remanent magnetism of the magnetizable particles and the percentage
of the magnetizable particles dispersed in the binder. The
percentage of the magnetizable particles, however, should not be
increased beyond the point at which the binder can contact
essentially the entire surface area of the magnetizable particles
to bond the marking material into an integral mass which will
adhere to a part to which it is applied and will retain a desired
shape of the indicia until the protective coating has been affixed.
This maximum percentage by volume of the magnetizable particles is
generally about 85 percent.
Each line of each character in the identifying indicia must be
formed of a volume of marking material which will produce a
sufficient remanent magnetic moment when magnetized to provide the
required remanent magnetic moment at the surface of the protective
layer to clearly outline the indicia in the magnetic reader. The
maximum thickness of each line of a character (measured normal to
the surface on which the character is applied) and the width of
each line may be limited, however. The thickness of the line should
not cause a visible impression of the identifying indicia on the
surface of a protective layer. Line thickness up to about
one-fourth the thickness of the protective layer is generally
acceptable. Line widths above 0.005 inch afford clear definition in
the magnetic reader. The maximum width of the line is limited only
by practical considerations, e.g., to permit inspection by a
reasonably compact magnetic reader. Line widths below 0.1 inch are
considered practical.
Thus, the remanent magnetism of the magnetizable particles, the
percentage of magnetizable particles in the marking material, and
cross sectional dimensions of the lines should be selected from
within the indicated ranges to produce the required magnetic moment
at the surface of the protective layer.
The identifying indicia may be applied with a rubber stamp or by
spraying the magnetizable indicia onto the part with the use of a
stencil. Other means of applying the indicia include forming
indicia on a releasable liner as by stenciling or vapor coating and
including, as at least a portion of the binder, a thin adhesive
coating over the surface of the indicia opposite the liner. The
indicia can then be transferred from the liner to a part by
pressure or heat.
The protective layer which is applied to the part over the indicia
should be opaque and should afford permanent protection for the
part and the indicia. The protective layer may be one or several
layers of paint, or may comprise an overlay of vinyl or the like.
The protective layer should have sufficient thickness to provide a
uniform exterior surface which may be smooth, rippled or crinkled,
as long as it does not visibly reveal the indicia. If the
protective layer is applied in liquid form, the binder of the
indicia should be sufficiently resistant to the protective layer
that the indicia are not substantially deformed on the part.
The identifying indicia may be magnetized after application to the
part in the aforementioned manner, or prior to application of the
marking material to the part if the particulate material has been
bonded together in a fixed relationship as by forming the indicia
on a releasable liner. Magnetization of the indicia in a direction
perpendicular to the surface on which it is applied is preferred to
provide uniformity of indicia outline in the magnetic reader.
Magnetization across the indicia tends to stress character lines
running at right angles to the direction of magnetization. Also,
when the indicia is applied to a magnetically conductive part and
the indicia is magnetized in a direction parallel with the surface
of the part, the part will tend to short circuit the field lines
emanating from the indicia, thereby reducing the remanent magnetic
moment at the surface of a protective layer. When the indicia is
magnetized in a direction perpendicular to the surface, however,
the part will serve as a keeper for the magnetized indicia, and the
remanent magnetic moment at the surface of the protective layer
will not be reduced.
The present invention is useful for many types of vehicles such as
automobiles, trucks, motorcycles, bicycles, snowmobiles, trailers,
marine craft and railroad cars; many types of appliances including
washers, dryers, refrigerators, television sets, and vending
machines; and many types of tools including generators, saws,
drills, and thread cutters.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is a fragmentary view illustrating a part of an article
according to the present invention having the protective layer
broken away in part to reveal magnetizable indicia applied thereto;
and
FIG. 2 is a fragmentary view of the part in FIG. 1 which
illustrates the use of a magnetic reader to read the indicia.
DESCRIPTION OF THE INVENTION
FIG. 1 shows a fragmentary part 10 of an article according to the
present invention, which article may be a vehicle, appliance or
tool having a multiplicity of magnetizable identifying indicia 11
in the form of letters and numbers applied thereto. The fragmentary
part 10 may be of metal or fiberglass. A protective layer,
illustrated as a prime coat 14 and a finish coat 16 of paint, in
part broken away, has been applied over the part 10 and the indicia
11.
The magnetizable identifying indicia 11 are formed of a thin layer
of marking material applied to the part 10 as by the use of a
rubber stamp. The marking material comprises magnetizable particles
dispersed in a nonmagnetizable binder as previously described.
FIG. 2 illustrates the same part 10 as FIG. 1. A magnetic reader 20
according to U.S. Pat. No. 3,013,206 has been placed on the finish
coat 16 to inspect the magnetized indicia 11. The indicia 11 are
shown by outlines 11A by the ferromagnetic crystal in the magnetic
reader 20.
EXAMPLE I
A marking material was prepared by dispersing 100 grams of Fe.sub.2
O.sub.3 having a coercivity of 300 oersteds and a remanent
magnetism of 70 emu per gram in a binder comprising 2 grams of
potassium tripolyphosphate, 2 grams of lecithin, one-half gram
acetylenic glycol wetting agent dissolved in 2-ethyl-hexyl alcohol
(Surfynol 104A), 35 grams acrylic thickening agent (Rhoplex
ASE-95), 115 grams of a solution comprising 3 parts concentrated
ammonium hydroxide in 200 parts water, and 165 grams alkaline,
water-soluble acrylic ester (Carboset 525).
The marking material was applied with a rubber stamp to a sheet of
18-gauge steel having a coercivity of 40 oersteds. The characters
on the stamp were sized to produce magnetizable indicia 11 in the
form of letters and numbers, one-fourth inch in height, having line
widths of one-sixteenth inch. The thickness of the characters was
measured to be 0.0005 inch. A thin, opaque, permanent, protective
coating was then applied over the surface of the steel sheet and
magnetic indicia 11 by spraying on a 0.001 inch primer coat 14 of
paint comprising titanium dioxide pigment in a cellulose nitrate
and ketone vehicle (Spar-Var), and a 0.003 inch finish coat 16 of
an acrylic automobile lacquer (DuPont Lucite Acrylic Lacquer). The
indicia did not form a visible impression on the surface of the
protective coating. The indicia were selectively magnetized after
application, in the direction vertical to the surface, and the
remanent magnetic moment at the surface of the protective coating
was measured to be 400 gauss. When a magnetic reader of the type
described in U.S. Pat. No. 3,013,206 was positioned adjacent the
surface of the protective coating over the indicia, the outlines of
the letters and numbers were clearly distinguishable.
EXAMPLE 2
A sheet of 18-gauge steel having indicia applied thereto was
prepared which was essentially identical to that of Example 1. An
exterior coating comprising a 0.008 inch thick sheet of
adhesive-backed vinyl material imprinted with a wood grain finish
(Di-Noc) was applied to the frame over the magnetic indicia. The
indicia did not form a visible impression on the surface of the
vinyl material. When the magnetic reader was held adjacent the
vinyl material over the magnetic indicia, the outline of the
characters was clearly visible with the magnetic reader 20. The
remanent magnetic moment of the indicia at the surface of the vinyl
material over the indicia was measured to be 300 gauss.
* * * * *