[19]
`United States Patent
`4,941,236
`[11] Patent Number:
`JIll; 17, 1990
`Sherman et a1.
`[45] Date of Patent:
`
`[54] MAGNETIC CLASP FOR WRISTWATCH
`STRAP
`
`[75]
`
`Inventors: Norman Sherman, Woodbury; Victor
`Shiff, Waterbury, both of Conn.
`
`[73] Assignee:
`
`Timex Corporation, Waterbury,
`Conn.
`
`4,615,185 10/1986 Bollinger .............................. 63/5 R
`
`4,620,725 11/1986 Maehashi .
`..... 281/45
`8/1938 Mock ........................................ 63/3
`4,760,714
`
`FOREIGN PATENT DOCUMENTS
`
`1155824 10/ 1963 Fed. Rep. of Germany ........ 24/303
`074871
`1/1961 France .................................. 24/303
`
`[21] App]. No.: 375,990
`
`[22] Filed:
`
`Jul. 6, 1989
`
`Int. Cl.5 ......................... A443 21/00; A44C 5/18
`[51]
`[52] US. Cl.
`...................................... 24/303; 24/71 J;
`24/265 WS
`[58] Field of Search ............... 24/303, 49 M, 265 WS,
`24/71 J, 688; 292/2515
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`7/1926 Donaldson .................... 24/265 WS
`1,591,295
`..... 24/71 J
`2,499,102 2/ 1950 Levine .......
`
`24/230
`2,615,227 10/1952 Hornik
`
`.. 24/201
`2,648,884
`8/1953 Loofboro
`....... 24/303
`2,959,832 11/1960 Baerrnann
`
`6/1971 Krebs ........................ 24/303
`3,589,341
`
`3,747,171 7/ 1973 Montague, Jr.
`24/265 WS
`
`
`........... 24/303
`4,197,618 4/ 1980 Bourguignon .
`3/1981 Holtz ................................ 24/243 R
`4,255,837
`
`Primary Examiner—Victor N. Sakran
`Attorney, Agent, or Firm—-William C. Crutcher
`
`[57]
`
`ABSTRACT
`
`A strap for holding a wristwatch has a pair of separable
`flexible strap ends adapted to curve around the wrist
`and to overlap one another to provide an overlapped
`section. At least one strap end of thermoplastic material
`has particles of permanently magnetizable material em—
`bedded in the thermoplastic material and magnetized to
`provide rows of alternating magnetic poles. The strap
`ends have surfaces contacting one another throughout
`the overlapped section and mutually nesting uniformly
`spaced interlocking teeth, whereby the magnetized
`particles provide a holding force resisting separation of
`the strap ends, while the nested teeth prevent sliding
`disengagement movement between strap ends.
`
`10 Claims, 3 Drawing Sheets
`
`
`
`APPLE 1047
`
`1
`
`APPLE 1047
`
`

`

`US. Patent
`
`J11].17,1990
`
`Sheet 1 013
`
`4,941,236
`
`55
`
`MN
`55
`MN
`55
`MN
`55
`IVA!
`55
`MN
`
`2
`
`

`

`US. Patent
`
`Jul. 17,1990
`
`Sheet 2 of3
`
`4,941,236
`
`
`
`3
`
`

`

`US. Patent
`
`Jul.17, 1990
`
`Sheet 3 of3
`
`4,941,236
`
`
`
`
`
`
`o
` A‘“‘\VA‘I‘“““““‘
`’l""'.."‘'.."I."n".”'."‘l.”'””l.ll.:
`a
`_
`a
`
`.
`¢
`0
`.,
`”so.“
`I °~°°as"
`.” oSaNas- V”.
`
`-
`5"
`'
`r.°::°
`.
`°
`n
`6'
`q
`a
`v
`on
`V
`o
`BB
`0
`D
`
`
`
`9
`
`
`
`4
`
`

`

`1
`
`4,941,236
`
`MAGNETIC CLASP FOR WRISTWATCH STRAP
`
`BACKGROUND OF THE INVENTION
`
`This invention relates generally to straps for wrist
`instruments, especially wristwatches and relates to im-
`proved clasps for attaching the strap ends around the
`wrist of the wearer. More particularly, the invention
`relates to an improved wristwatch flexible strap and
`clasp attachment.
`Conventional wristwatches are held on the wrist by
`leather, metal or plastic straps, bands or bracelets,
`which may be expanded to go over the wrist or at-
`tached around the wrist by attaching strap ends with
`buckle, clasp or other type of detachable fasteners. This
`invention relates to wristwatch attachments employing
`a flexible strap with a pair of strap ends. Typically, the
`strap ends are connected with a buckle which provides
`for adjustment of the strap length. The buckle adds to
`the thickness of the strap, requires a “keeper” to keep
`the tongue of the strap in place, and sometimes is un-
`sightly or has comers which catch upon sleeves or
`clothing.
`Other types of Clasps have been suggested for jew-
`elry, wrist instruments and wristwatches for straps with
`overlapping strap ends. One design has opposing mem-
`bers coated with fibrous material on one strap end and
`a layer of material having resilient hook-like members
`on the other strap end (sold under the registered trade-
`mark Velcro ®), such a construction being shown in
`Montague U.S. Pat. No. 3,747,171, issued July 24, 1973.
`Another type of bracelet clasp suitable for a strap of
`flexible thermoplastic material such as polyurethane
`comprises a sleeve on one strap end with transverse
`internal teeth and a tongue on the other strap end with
`complementary nesting teeth, such a construction being
`shown in Bollinger U.S. Pat. No. 4,615,185, issued Oct.
`7, 1986. Such construction requires a sleeve to provide
`a transverse holding force to maintain the complemen-
`tary teeth engaged.
`Permanent magnets have been suggested in the past
`for providing a separable clasp for jewelry, animals’
`collars or the like. For example, Loofboro U.S. Pat. No.
`2,648,884, issued Aug. 18, 1953 describes a magnetic
`clasp of two rigid, two-pole, permanent magnets with
`an interlocking tongue and groove connection to me-
`chanically lock the sections against relative sliding
`movement tending to separate the clasp. Another mag-
`netic clasp which is intended to disengage without
`catching is provided for animal collars as shown in
`Krebs U.S. Pat. No. 3,589,341, issued June 29, 1971.
`Still another magnetic clasp for jewelry having two
`rigid co-acting magnets encased in plastic sheaths dis-
`closes a variety of mechanical interlocking protuber-
`ances and indentations to prevent sliding separation of
`the magnetically attracted members.
`Holtz U.S. Pat. No. 4,255,837 issued Mar. 17, 1981
`and Maehaski U.S. Pat. No. 4,620,725 issued Nov. 4,
`1986 each show a pair of sheets of flexible synthetic
`resin having magnetizable powder therein, permanently
`magnetized into rows of alternating magnetic polarity
`providing a holding force between sheets. However,
`there are no provisions for ridges, protuberances or
`teeth preventing sliding movement between the mag-
`netically attracted surfaces.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`Accordingly, one object of the present invention is to
`provide an improved flexible strap and clasp attachment
`for a wristwatch.
`
`Another object of the invention is to provide an im-
`proved clasp for a flexible strap which eliminates buck-
`les or other types of protruding members thereby per-
`mitting a thinner, more comfortable flexible strap at-
`tachment.
`Another object is to provide an improved clasp for a
`wristwatch which is secured, yet easy to engage when
`desired.
`
`DRAWINGS
`
`The invention, both as to organization and method of
`practice, together with further objects and advantages
`thereof, will best be understood with reference to the
`following description,
`taken in connection with the
`accompanying drawings, in which:
`FIG. 1 is a plan view of a wristwatch and strap as
`worn on the wrist;
`FIG. 2 is an end elevational view of the wristwatch
`and strap shown in FIG. 1;
`FIG. 3 is a side elevational view of one of the flexible
`strap ends before it is attached to the wristwatch;
`FIG. 4 is a plan view of the strap end shown in FIG.
`
`3;
`
`FIGS. 5, 6 and 7 enlarged schematic perspective
`views of three alternate forms of the improved strap and
`clasp;
`FIG. 8 is an enlarged cross-sectional, elevational
`view of a strap portion showing an alternate form of the
`invention;
`FIG. 9 is an enlarged cross-sectional elevational view
`of a strap portion showing yet another form of the in-
`vention;
`FIG. 10 is an enlarged plan view of another alternate
`form of the invention showing overlapped strap ends
`before connection; and
`FIG. 11 is a cross-sectional, elevational view taken
`along lines XI—XI of FIG. 10.
`SUMMARY OF THE INVENTION
`
`Briefly stated, the invention is practiced by providing
`a strap having a pair of separable flexible strap ends
`adapted to curve around the wrist of a wearer and to
`overlap one another to provide an overlapped section,
`at least one strap end including at least one ply of ther—
`moplastic material having particles of permanently
`magnetizable material embedded in the thermoplastic
`material and magnetized to provide a plurality of rows
`of alternating magnetic poles,
`the strap ends having
`surfaces contacting one another throughout the over-
`lapped section and defining mutually nesting uniformly
`spaced protuberances and indentations, such as inter-
`locking teeth, whereby the magnetized particles pro-
`vide a holding force resisting separation of the strap
`ends, while the nested protuberances and indentations
`prevent sliding disengaging movement between strap
`ends. Preferably,
`the magnetic field is oriented in a
`longitudinal direction so that when the strap is attached
`around the wrist, the. toroidal path of the magnetic field
`will reduce stray magnetic flux.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`Referring now to FIG. 1 of the drawing, a wrist-
`watch shown in FIGS. 1 and 2 of the drawing, includes
`a watch case 1 with strap attachment lugs 2 and flexible
`
`5
`
`

`

`4,941,236
`
`3
`strap 3 of thermoplastic material. The strap is arranged
`to flex and curve around the wrist of the wearer. The
`strap 3 consists of two separate strap ends 4, 5, respec-
`tively, attached to lugs 2 by conventional spring bars,
`although the invention also contemplates a single strap
`member passing through loops on the bezel and termi-
`mating in two strap ends. The strap ends 4, 5 mutually
`cooperate and overlap to provide an overlapped section
`6 by means of uniformly spaced transverse ribs 4a on
`strap end 4 facing outward mutually nesting with simi-
`lar uniformly spaced transverse ribs 5a on strap end 5
`facing inwardly.
`Referring to FIGS. 3 and 4 of the drawing, one of the
`strap ends 4 is illustrated before it has been attached to
`the timepiece. In this case, strap end 4 is shown, but it
`will be appreciated that strap end 5 is similarly con-
`structed, except that the transverse teeth or ridges are
`on the outside of the strap and in some arrangements,
`the type of magnetic material and magnetization pattern
`will be different as will be explained in detail in connec-
`tion with the'specific examples.
`The transverse ridges 4a are molded into the surface
`of the strap and may comprise a simple undulating or
`sinusoidal
`type pattern. Altemately,
`they may be
`formed in a rectangular or saw tooth configuration or
`protuberances of various shape and size as will be illus-
`trated in connection with the accompanying descrip-
`tions of modified forms of the invention.
`_
`In accordance with the invention, the strap material is
`preferably of flexible thermoplastic material of the type
`normally used in watchstraps. Examples of such materi-
`als are polyurethane, plasticized polyvinyl chloride
`(PVC), acrylonitrile-butadiene-styrene (ABS) or poly-
`propylene. Embedded within the thermoplastic strap
`material are finely divided particles of magnetizable
`material, selected to have substantial magnetic rema-
`nance for permanent magnetization and having a high
`maximum energy product BH where B is flux density
`expressed in Gauss (Teslas in SI units) and where H is
`applied magnetic field expressed in Oersteds (Ampere-
`Turns per centimeter in Si units). The maximum energy
`product is the largest rectangle which will fit within the
`hysteresis curve with one corner in the origin and is
`sometimes expressed in s of BH><106 or Mega-Gauss-
`Oersted.
`
`Suitable materials are those permanent or “hard”
`magnetic materials which have substantial residual in-
`duction (remanance), suitable permanent magnet mate-
`rials being alnicos, ferrites or rare-earth magnets. Satis-
`factory results have been obtained using barium ferrite
`which has a maximum energy product (BH) of 3.4
`Mega Gauss-Oersted. Also suitable are cesium cobalt
`(l6 MGOe) and samarium cobalt (22 MGOe). Much
`higher energy products are obtainable with special ma-
`terials such as Neodymium-Iron-Boron having a maxi-
`mum energy product as high as 35 MGOe. Particles of
`permanently magnetizable material preferably of parti-
`cle size between 0.1 and 100 microns 0.0001 mm and 0.1
`mm in SI units) are incorporated and mixed within the
`liquid prepolymers and molded into the strap ends dur-
`ing the normal polymerization process.
`Subsequently, the magnetizable particles are perma-
`nently magnetized by subjecting the strap ends to a
`magnetizing field to provide magnetized pole regions of
`alternating polarity, known as a “multiple pole” struc-
`ture within at least the terminating end of the strap end.
`One such pattern, as see in FIG. 4, has alternating longi-
`tudinal strips of north poles 4b and south poles 4c. A
`
`4
`number of magnetizing patterns are possible, depending
`upon the desired application. The north and south poles
`may be oriented with poles that run longitudinally and
`parallel along one face of the strap, or they may be
`arranged with multiple poles that run laterally and par-
`allel along one or both faces of the strap. The preferred
`arrangement is to provide a pattern of magnetization
`which provides maximum holding force with respect to
`the other overlapped strap end, while minimizing exter-
`nal leakage of magnetic flux outside the strap. A variety
`of arrangements are shown in the remaining FIGS. 5—11
`to illustrate the invention.
`Referring now to FIG. 5 of the drawing, an enlarged,
`perspective view is shown of an overlapped section of a
`strap end 6 and a strap end 7, the curvature around the
`wrist being omitted from the drawing for purpose of
`simplification. Strap end 6 defines a plurality of trans-
`verse ridges 6a and strap end 7 defines a plurality of
`mating ridges 7a. Both strap ends 6 and 7 have embed-
`ded therein permanently magnetizable particles of high
`magnetic remanance, such as the materials described
`previously. Both strap ends 6 and 7 have been subjected
`to magnetizing fields to provide rows of alternating
`north and south poles, such as 6b, 6c, which are aligned
`with similar rows of alternating poles 7b, 7c on strap 7.
`The flux patterns are perpendicular to the strap ends,
`and the polarity of poles is selected such that a holding
`force is developed between strap ends 6, 7 when placed
`in any of the various longitudinal positions provided by
`the interlocking teeth or ridges. The magnetic holding
`force is primarily directed perpendicular to the surface
`of the strap ends, so as to strongly resist separation. The
`nested ridges primarily function to resist sliding move-
`ment between strap ends.
`Referring to FIG. 6 of the drawing, a modification is
`shown wherein one strap end 6 is identical to the one
`previously described. The other strap end, designated 8,
`is formed of flexible thermoplastic material as before,
`but the particles embedded therein are of soft magnetic
`material, such as soft ferrites or high purity iron parti—
`cles. Such particles are magnetizable in the presence of
`a field, but may not be permanently magnetized. How-
`ever, they are selected and arranged to provide a path
`of high magnetic permeability and therefore provide a
`holding force by the permanent magnets in strap end 6
`while reducing external magnetic flux.
`Referring to FIG. 7 of the drawing, a strap end 9 and
`an overlappped strap end 10 are provided with longitu-
`dinally extending ribs 90 and 10a. The permanently
`magnetizable particles embedded in the flexible thermo-
`plastic material of strap ends 9 and 10 are magnetized in
`a pattern as shown providing a plurality of transverse
`rows of alternating magnetic poles 9b, 9c in strap end 9
`and similar alternating rows 10b, 10c in strap end 10.
`Contrary to the arrangements shown in FIGS. 5 and 6,
`the poles alternate in a longitudinal direction and extend
`transversely across the strap. The interlocking ridges
`9a, 10a in this case provide transverse alignment of the
`overlapped ends, preventing sidewise or lateral slipping
`while the magnetic poles serve to provide holding force
`and longitudinal adjustment. It will be seen that separa-
`tion and replacement of strap end 9 with respect to strap
`end 10 will only provide a number of uniformly spaced
`locations in which the poles are properly aligned to
`provide a holding force by mutual attraction between
`north and south poles. One such position longitudinally
`spaced is indicated by the phantom lines shown at 9’.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`6
`
`

`

`5
`FIG. 8 of the drawing illustrates another modifica-
`tion, Wherein a strap end 11 and a strap end 12 each
`define on their contacting surfaces a set of transversely
`extending slanted teeth 11a, 12a, respectively. The teeth
`mutually engage and are slanted away from the respec-
`tive terminating ends of the strap ends (toward the wrist
`instrument-not shown) so that they positively prevent
`longitudinal displacement or sliding disengagement of
`the strap ends. However, the teeth 12a, 11a are uni-
`formly spaced so that the strap ends may be separated
`and re-positioned in another longitudinally displaced
`position for adjustment of the strap length. Both strap
`ends 11, 12 contain magnetizable particles dispersed
`therein, which are magnetized to provide sets of north
`poles 13 and sets of south poles 14 oriented to produce
`lines of magnetic flux in a longitudinal direction along
`the strap, as well as to provide mutually attracting poles
`along the contacting surfaces of each of the slanted
`teeth. Directing the magnetic flux in the longitudinal
`direction through the strap will reduce stray magnetic
`field which might affect Surrounding objects.
`FIG. 9 illustrates another modification. A strap end
`shown generally at 15 comprises three plies in a lami-
`nated construction. One ply, 15a, is of flexible thermo-
`plastic material without magnetizable particles. An in-
`termediate ply 15b is a metallic foil and an inner ply 15c
`is molded of thermoplastic material containing perma-
`nently magnetizable particles as before. Uniformly
`spaced transverse teeth 15d are indicated as having a
`rectangular cross section, but they may be any of the
`other shapes previously discussed. An overlapped strap
`end 16 is also provided with nesting transverse teeth 16a
`of rectangular cross section. Strap end 16 is a thermo-
`plastic material having dispersed therein magnetizable
`particles of soft magnetic iron material of high permea-
`bility as previous discussed in connection with FIG. 6.
`The particles in strap ply 16 are not permanently mag-
`netized, but serve as a path for magnetic flux for perma-
`nently magnetized poles such as 15e, 15fin strap end 15.
`The foil 15b serves as a pole piece to intensify and direct
`magnetic flux lines from the permanently magnetized
`particles and also serves as a shield against stray flux.
`For a stronger holding force between strap ends, the
`lower strap end 16 may be constructed exactly like strap
`end 15 in a multi-ply laminated construction.
`Lastly, FIGS. 10 and 11 illustrate a strap end 17 and
`a strap end 18, both of flexible thermoplastic material
`and having poles magnetized in a three pole arrange-
`ment. Rather than employing identical tooth shapes in
`both members to resist sliding separation, one of the
`members defines protuberances 17a and the other mem-
`ber 18 defines mating indentations 18a which may either
`be indented only sufficiently to accept protuberances
`1712 or may be holes simply punched all of the way
`through the strap end. Obviously, the protuberances
`17a and receiving indentations 18a may be of any se-
`lected shape and arrangement so long as they are uni-
`formly spaced along the strap ends so that adjustment
`can be made by separating the strap ends and replacing
`the strap ends in a longitudinally displaced position. In
`a more specific sense, therefore, term protruberances
`includes the transverse rows of teeth previously de-
`scribed and the term indentations includes the valleys
`between rows of teeth.
`The improved clasp is easy to intentionally disengage
`by pulling one strap end up from the other against the
`magnetic holding force, which nevertheless is very
`strong in the case of high energy product magnetic
`particles. While the watch is being worn, protuberances
`(or ridges) and identations (valleys) strongly resist unin-
`tentional or sliding disengagement of the strap ends,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`_ 4,941,236
`
`6
`especially where they are shaped as slanted teeth (FIG.
`8). The magnetic poles cooperate to hold the strap ends
`in a nested position, yet are releasable to allow the strap
`ends to be adjustable by positioning in another nested
`position.
`While there has been described herein what is consid-
`ered to be the preferred embodiment of the invention,
`other modifications will occur to those skilled in the art
`and it is desired to secure in the appended claims all
`such modifications as fall within the true spirit and
`scope of the invention.
`We claim:
`
`1. An improved strap and clasp assembly comprising
`a strap having a pair of separable flexible strap ends
`adapted to curve around the wrist of a wearer and to
`overlap one another to provide an overlapped section,
`at least one of said strap ends including at least one ply
`of flexible thermoplastic material having embedded
`particles of permanently magnetizable material, said
`particles being magnetized to provide a first plurality of
`rows of alternating magnetic poles, the other of said
`strap ends including embedded particles of magnetiz-
`able material, said strap ends having surfaces contacting
`one another within said overlapped section, said con-
`tacting surfaces defining mutually nesting, uniformly
`spaced, protuberances and indentations, whereby said
`magnetized particles provide a holding force resisting
`separation of the strap ends, while said nesting protu-
`berances and identations prevent sliding movement
`between strap ends.
`2. The combination according to claim 1, wherein
`said other strap end embedded particles are of perma-
`nently magnetizable material magnetized to provide a
`second plurality of rows of alternating magnetic poles.
`3. The combination according to claim 1, wherein
`said other strap end embedded particles are of high
`permeability soft magnetic material.
`4. The combination according to claim 1, wherein
`said mutually nesting, uniformly spaced protuberances
`and identations comprise parallel ridges and valleys,
`respectively.
`5. The combination according to claim 4, wherein
`said ridges and valleys extend transversely across the
`strap ends and wherein said first plurality of rows of
`alternating magnetic polarity extend longitudinally of
`said strap ends.
`6. The combination according to claim 4, wherein
`said ridges and valleys extend longitudinally of said
`strap ends and wherein said first plurality of rows of
`alternating magnetic polarity extend transversely across
`the strap ends.
`7. The combination according to claim 1, wherein
`said protuberances comprise transversely extending
`teeth slanted away from the respective terminating ends
`of said strap ends and wherein said teeth of at least said
`one strap end have their opposite sides permanently
`magnetized with poles of alternating polarity.
`8. The combination according to claim 1, wherein
`said one strap end includes an additional ply of mag-
`netic foil material arranged to serve as a pole piece.
`9. The combination according to claim 1, wherein
`said thermoplastic material is selected from the group
`consisting of polyurethane, plasticised polyvinyl chlo-
`ride, acrylonitrile-butadiene-styrene, polypropylene, or
`combinations thereof.
`10. The combination according to claim 1, wherein
`said permanently magnetizable particles are selected
`from the group consisting of alnico, ferrites, rare—earth
`materials, transition metals or combinations thereof.
`it
`*
`*
`III
`*
`
`7
`
`