Fastener means

Abstract: A fastener means for releasably fastening first and second elements, for example a handbag and flap for closure has first and second members which in use are attached to the first and second elements respectively. The first member includes a permanent magnet (1) having a hole (4) therethrough between the opposite end surfaces (1a,1b). Respective poles of the magnet are located adjacent the respective opposite end surfaces (1a,1b), one such end surface (1b) being oriented so as to extend in a direction away from the first element when the first member is attached thereto. At least part of the surface of the magnet are covered by a covering (5). The second member comprises a ferromagnetic member (2) attracted in use to the pole adjacent this one end surface (1a). The covering (5) is formed of a ferromagnetic material having a thickness of between 0.03 mm and 0.20 mm.

Description: The present invention relates to fastener means. Fastener means which operate by magnetic attraction have been long known in a variety of industries including in particular for use as handbag clasps. In a typical arrangement the fastener means comprises a first member which in use is attached to, say, the body of the handbag and a second member which is attached to, say, the handbag flap. When the two members are brought into confronting relation, the magnetic force between them provided by a permanent magnet which forms part of one such member serves to hold them together and maintain the flap fastened to the body of the handbag. However, the magnetic attraction force is sufficiently small that the handbag may be opened by the user at will. In a typical such prior arrangement as disclosed in GB-A- 2 114 208, the permanent magnet has a through hole and there are a pair of ferromagnetic plates. One of these together with the permanent magnet effectively forms the first member of the fastener means and the other plate by itself serves as the second member of the fastener means. One or both of the plates is provided with a post so that when the first and second members are in facial contact with each other, the post of one such ferromagnetic plate extends along the axis of the through hole to make contact with the other ferromagnetic plate. In an exactly equivalent construction, each plate may in effect have a half post, the two half posts meeting in the through hole, thereby completing a magnetic circuit. The permanent magnet is commonly made of a sintered material such as ferrite. Such magnets have a generally unpleasing appearance and thus, for entirely aesthetic reasons such as fashion, it has been the practice to cover the surface of the permanent magnet with a casing or coating or plating. The sintered ferrite material is also subject to impact, particularly in the case of a handbag and can easily become broken or cracked. The coating serves in effect as a physical protection, usually with an intervening ferromagnetic plate, as well as providing an aesthetically pleasing appearance. The preferred material for the casing has been brass though other nonmagnetic materials have also been employed. This has resulted in serious problems for the designer of such fastener means since if the brass or other nonmagnetic material casing is fairly thick, then the attractive forces between first and second members can be substantially reduced by the intervening nonmagnetic material. Conversely, if the material is made relatively thin so as to allow ready penetration by the magnetic lines of force, then two effects result. Firstly, the thin material may result in the underlying ferrite sintered material, which often has an uneven surface, gradually showing through the thin brass or other nonmagnetic material layer. This may result in scratching or wearing and leads to an aesthetically unpleasing appearance. One attempt to overcome this problem was the provision of the ferromagnetic plate between the magnet and the thin brass casing, as mentioned above. The second deleterious effect resulting from the adoption of thin brass or other nonmagnetic casings is the substantial leakage of magnetic flux. Such leakage flux can commonly exceed 300 gauss and may cause destruction of magnetically recorded information on various means such as magnetic tickets or tokens, credit cards, magnetic tapes, floppy discs and the like. This is plainly a serious disadvantage and one for which no satisfactory solution has been available heretofore. One proposal which has been considered but rejected by us is to make the casing not of brass or other nonmagnetic material but of ferromagnetic material. While this may substantially reduce or eliminate the leakage flux, such ferromagnetic casings will also substantially reduce the attractive force between the first and second members of the fastener. The only way we could see to overcome that was to increase the strength of the permanent magnet which may simply lead to the same problem as previously, namely a problem with leakage of magnetic flux. As a consequence of this, the potential solution of a ferromagnetic casing has heretofore been rejected. We have now found that a satisfactory result can after all be achieved by the use of a ferromagnetic casing provided, however, the ferromagnetic casing has a thickness which lies in a particular range, and provided that the casing is contiguous with the end surface of the permanent magnet without any intervening ferromagnetic plate. The casing needs to be sufficiently thick that surface irregularities in the underlying sintered magnet material do not show through in the same way as with the prior art brass casings, but not so thick that the attractive force between the first and second members is reduced too much. Since ferromagnetic materials tend to be not as soft as brass, we have found that satisfactory results can be obtained with a casing with a thickness as low as 0.03 mm. At the upper range, we have found that an adequate magnetic attraction force is still retained when the thickness is as great as 0.20 mm. Accordingly, there is provided in accordance with the present invention a fastener means adapted for releasably fastening first and second elements, for example a handbag and a flap for closure of the same, the fastener means comprising a first member adapted to be attached to said first element and a second member adapted to be attached to said second element; said first member comprising a permanent magnet having a hole therethrough extending between opposite end surfaces thereof, the magnet having a pole of first magnetic polarity adjacent one said end surface oriented to extend in the direction away from said first element when said first member is attached thereto and a pole of opposite magnetic polarity adjacent the opposite said end surface, and a covering at least partially encasing the permanent magnet; and said second member comprising a ferromagnetic member detachably attracted to said first pole; the fastener means being characterised in that said covering is formed of a ferromagnetic material having a thickness of between 0.03 mm and 0.20 mm and directly covers at least said one end surface, being contiguous therewith, without an intervening ferromagnetic plate. In preferred embodiments, the first member includes a ferromagnetic member attached to the end surface of said magnet adjacent to said second pole. One and/or the other of the ferromagnetic members is in the form of a plate having a post extending into said through hole such that the ferromagnetic members abut against and are attracted to each other via said through hole. The covering may be a casing which may attach the ferromagnetic member to the permanent magnet. Alternatively the covering may be a plating. The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings in which:- Fig. 1 is a perspective view of a first embodiment of fastener means constructed in accordance with the present invention, in an exploded view; Fig. 2 is a sectional view of the embodiment of Fig. 1; Fig. 3 is a similar sectional view of a modified embodiment; Fig. 4 is a sectional view of yet an alternative embodiment also constructed in accordance with the present invention; Fig. 5 shows the permanent magnet of the embodiments of Figs. 1-4 in a sectional view; Fig. 6 illustrates in a sectional view measurement of the magnetic flux when no casing is present; Fig. 7 shows a similar view measuring the magnetic flux in a modified version of the Figs. 1 and 2 embodiment in which it will be noted that the post is not integrally formed with the associated ferromagnetic plate; Fig. 8 shows the measurement of magnetic flux in a similar view in relation to the embodiment of Fig. 3; Fig. 9 again illustrates in sectional view measurement of the magnetic flux in a modified version of the Fig. 4 embodiment, again with a post which is not integral with the associated ferromagnetic plate; Figs. 10-13 correspond generally to Figs. 6-9 respectively illustrating the arrangement of the two members when measuring attraction force between them; Figs. 14, 15 and 16 are graphs illustrating the magnetic flux in gauss and the attraction force in kilograms respectively for embodiments of different configuration and with different casing thicknesses; Fig. 17 is a sectional view showing the apparatus for measuring attraction force; Fig. 18 shows an exploded view in perspective of a typical practical embodiment of fastener means constructed in accordance with the present invention including the means by which the members of the fastener are attached to the underlying element such as a handbag and its flap; Fig. 19 is a sectional view showing a further embodiment of fastener means constructed in accordance with the present invention; Fig. 20 is a further embodiment of fastener means constructed in accordance with the present invention illustrating alternative means for attaching the first and second member to the elements to which they are to be attached in use; Fig. 21 illustrates yet another alternative arrangement involving the use of double-sided tape for attaching the two members of the fastener means to underlying surfaces; and Fig. 22 shows yet another embodiment of fastener means in accordance with the present invention, in this case for use in jewelry or the like as a clasp. The fastener means shown in FIGs. 1 through 4 will now be described. The fastener means shown in FIGs. 1 and 2 comprises an annular permanent magnet 1 having a through-hole 4 extending between the magnetic poles, a plate-like ferromagnetic member 2 which is to be abutted against one of the magnetic pole surfaces 1a of the permanent magnet 1 and is integrally held together therewith by a casing 5 made of a ferromagnetic material, and a plate-like ferromagnetic member 3 which is to be attracted to the other magnetic pole surface 1b via said ferromagnetic member 5. There are provided a projection 2a on the ferromagnetic member 2 which extends into said through-hole 4 of the permanent magnet 1, and a projection 3a on the ferromagnetic member 3 which will contact said projection 2a. The construction is such that when the plate member 3b of the ferromagnetic member 3 attracted to the permanent magnet 1 is in contact with the surface of said ferromagnetic member 5, the projection 3a of said ferromagnetic member 3 comes in contact with the projection 2a of the member 2. The ferromagnetic member 5 is made of a material that will be attracted to the permanent magnet such as iron, cobalt, nickel and alloys thereof, and is shaped like a dish placed upside down. There is a hole 5a made at the bottom of the inverted dish which communicates with the through-hole 4a of the magnet 1. The permanent magnet 1 is housed inside the casing made of this ferromagnetic member 5. The ferromagnetic member 2 is also housed inside the casing made of the ferromagnetic member 5 in such a way that the projection 2a projects into the through-hole 4 of the magnet 1. The ferromagnetic casing 5 integrally retains the component parts together. Ferromagnetic material for the member 5 includes any material which is attracted to a permanent magnet such as iron, cobalt, nickel and alloys thereof. Therefore, those stainless steel materials that are attracted to a permanent magnet are also included. The ferromagnetic member 5 is designed to have the thickness in the range of from 0.03 to 0.20 mm in view of the magnitude of leakage flux to be described hereinafter as relative to the attraction force of the fastener means. The fastener means shown in FIG. 3 will now be described. In this embodiment, the ferromagnetic member 2 has no projection 2a but comprises a plate member 2b alone. The projection 3a of the ferromagnetic member 3 to be attracted to the magnet 1 fits into the through-hole 4 of the magnet 1 and is attracted to the plate member 2b of the ferromagnetic member 2. The fastener means shown in FIG. 4 will now be described. In this embodiment, the projection 2a of the ferromagnetic member 2 protrudes slightly outside the through-hole 4 of the magnet 1, or is flush with or slightly below the open edge of the through-hole 4. The top surface of the projection 2a directly contacts the ferromagnetic member 3. Preferably, a ridge which abuts the peripheral side face of the magnet 1 is provided along the peripheral edge of the ferromagnetic member 3 to prevent the ferromagnetic member 3 from laterally sliding on the contact face with the magnet 1 when the member 3 is attracted to the magnet 1. The term "ferromagnetic member 5" used herein means a member which is made of a material that can be attracted to a permanent magnet, as mentioned with respect to the embodiment shown in FIGs. 1 and 2, and has the thickness in the range of from 0.03 to 0.20 mm. Although the ferromagnetic member 5 is shown as an inverted dish in the embodiment, it may be a plated ferromagnetic film. The ferromagnetic member may be covered with non-ferromagnetic plating so long as the ferromagnetic member has the thickness of from 0.03 to 0.20 mm. Leakage of magnetism from and the attraction force of the fastener means can be controlled in the manner to be described below as the surfaces of the magnet 1, particularly the surfaces other than the magnetic pole surface 1a where the ferromagnetic member 2 is attached are covered with the ferromagnetic member 5 having the thickness of from 0.03 to 0.20 mm. The permanent magnet 1 used in the embodiment is an annular magnet shaped like a doughnut, as shown in FIG. 5 and measures 17.5 mm in diameter L, 3 mm in thickness H, and 7.5 mm in hole diameter L′. FIGs. 6 through 9 show the embodiment of attraction means A which is one of the component parts of the fastener means subjected to measurement. A non-magnetic material T is attached to the top face of the attraction means A, to which the sensor G of a gauss meter is contacted for measurement. The attraction means used A herein comprises the permanent magnet 1 shown in FIG. 5, a ferromagnetic member 2 having the thickness of 1 mm with a plate member 2b, a ferromagnetic projection 2a of 6 mm diameter and 1.67 mm height, and a bent leg member 6, the projection and the leg member being integrally caulked together. The counterpart members in Comparative Embodiment shown in FIG. 6 are integrally held together by means of adhesive, and those in the Embodiment shown in FIG. 7 are integrally held together by means of a ferromagnetic casing 5. The ferromagnetic member 2 shown in FIG. 8 comprises the plate member 2b alone and has no projection 2a and is integrally held together with the permanent magnet by means of the ferromagnetic member 5, to form the attraction means A. In the embodiment shown in FIG. 9, the projection 2a extends in the through-hole 4 of the magnet 1 and its top is substantially flush with the attraction surface of the attraction means A. Similarly as mentioned above, the ferromagnetic member 5 retains the permanent magnet 1 integrally with the ferromagnetic member 2 and other parts to form the attraction means A to be subjected to measurement. The leg member 6 comprises a seat 6b having a hole 6c through which the portion of the projection 2a with a smaller diameter passes, and two opposing leg strips 6a, 6a at both ends of the seat 6b. In the attraction means A shown in FIGs. 6, 7 and 9, the portion of the projection 2a with a smaller diameter is fitted in the hole 2c in the ferromagnetic member 2 and caulked with the plate member 2b. In the attraction means A shown in FIG. 8, the seat 6b of the leg member 6 is not provided with the hole 6c; instead, the leg member 6 is welded to the plate member 2b of the ferromagnetic member 2. A gauss meter of galvanomagnetic effect type with a gallium arsenide sensor is used for measurement. (Model GT-3B by Nippon Denji Sokutei Kiki K.K.) Standard steel SK-2 used in JIS measurements is used as the ferromagnetic member 5 for the attraction means A. In the following measurements, the Embodiments used are those provided at the back of the permanent magnet with a ferromagnetic member 5 having a thickness ranging from 0.03 to 0.20 mm. A fastener means in which the permanent magnet is not provided at its back with a ferromagnetic member 5, and the one provided with a ferromagnetic member 5 which is 0.30 mm in thickness are used as the Comparative Embodiments. Attraction force of the fastener means was measured using the attracted means shown in FIGs. 10 through 13 attracted to the attraction means shown in FIGs. 6 through 9 respectively. The attracted means B according to the Embodiments and Comparative Embodiments shown respectively in FIGs. 10 through 13 each comprise a ferromagnetic member 3 and a leg member 6 such as shown in FIGs. 6 through 9 respectively. In the attracted means B shown in FIGs. 10 through 12, the portion of the projection 3b with a smaller diameter is fitted in the hole 3c of the plate member 3b and through the hole 6c of the leg member 6 and integrally caulked with the leg member 6. The projection 3a is so formed that when it comes in contact with the projection 2a or the plate member 2b of the ferromagnetic member 2 within the through-hole 4 of the magnet 1, the plate member 3b of the ferromagnetic member 3 comes in contact with the attraction face of the attraction means A. The attracted means B of the Embodiment shown in FIG. 13 has no projection 3b; instead, the plate member 3b thereof is directly contacted with the attraction face and the projection 2a of the attraction means A. The seat 6b of the leg member 6 is welded to the plate member 3b. The plate member 3b of the ferromagnetic member 3 in the attracted means B has a thickness of 1.0 mm, and the projection 3a has a diameter of 6 mm. FIG. 17 shows the device used to measure the attraction force of the fastener means. The attraction means A is attached to a table 7 of an instrument K. The attracted means B is attached to the tip end of a tension rod 9 which in turn is attached to a movable arm 8 of the instrument K. The movable arm 8 is pulled up, and the pulling force (Kp=9,81 N) which pulls the attraction means A and the attracted means B apart is measured. (A cylindrical standard tension gage by Oba Keiki Seisakusho was used. A sleeve 10 each was interposed between the leg strips 6a, 6a of the leg member 6 both in the attraction means A and attracted means B. The tip of a fixing screw 11 was screwed to the sleeve, and a hole each was made in the leg strips 6a, 6a. A pin 12 was inserted in each of the holes to reach the sleeve 10 to attach the means A and B respectively to the device.) Amount of magnetic flux in the attraction means A both according to the Embodiments and Comparative Embodiments was measured. First, leakage flux from the attraction surface of the attraction means A of the Embodiments as shown in FIG. 7 and of the Comparative Embodiments was measured. The sensor G of the gauss meter was disposed 2.5 mm away from and parallel to the attraction surface by interposing a non-magnetic material T having the thickness of 2.5 mm and the leakage flux from the attraction surface was measured at this distance. (Magnetic flux mentioned hereinafter is measured in the same manner). Table 1 shows the result of the measurement. The graph I shown in FIG. 14 indicates the trend of the change in the magnetic flux. Surface Leakage Flux (1) Ferromagnetic member 5 Leakage flux None 340 gauss 0.03 mm thick 283 gauss 0.05 mm thick 272 gauss 0.08 mm thick 262 gauss 0.10 mm thick 243 gauss 0.15 mm thick 215 gauss 0.20 mm thick 172 gauss 0.30 mm thick 143 gauss The abscissa in the graphs shown in FIGs. 14 through 16 respectively represents the thickness of the attraction means without the ferromagnetic member 5 (0.00 mm) and the thickness of the attraction means with the ferromagnetic members (0.03 - 0.30 mm), and the ordinate represents the surface leakage flux (in the unit of gauss) and the attraction force (in the unit of Kp = 9,81 N). Surface leakage flux in the attraction means of the Embodiments as shown in FIG. 8, and of the Comparative Embodiments was measured according to the same method as mentioned above. The result of measurement is shown in Table 2. The trend of the changes in the magnetic flux is shown in the graph II of FIG. 15. Surface Leakage Flux (2) Ferromagnetic member 5 Leakage flux None 361 gauss 0.03 mm thick 288 gauss 0.05 mm thick 273 gauss 0.08 mm thick 267 gauss 0.10 mm thick 248 gauss 0.15 mm thick 222 gauss 0.20 mm thick 181 gauss 0.30 mm thick 151 gauss Further, surface leakage flux in the attraction means of the Embodiments as shown in FIG. 9, and of the Comparative Embodiments was measured according to the same method as mentioned above. The result of measurement is shown in Table 3. The trend of the changes in the magnetic flux is shown in the graph III of FIG. 15. Surface Leakage Flux (3) Ferromagnetic member 5 Leakage flux None 310 gauss 0.03 mm thick 221 gauss 0.05 mm thick 210 gauss 0.08 mm thick 190 gauss 0.10 mm thick 177 gauss 0.15 mm thick 137 gauss 0.20 mm thick 96 gauss 0.30 mm thick 76 gauss Attraction force of the fastener means according to the Embodiments and Comparative Embodiments was then measured. The Comparative Embodiments and the Embodiments as shown in FIG. 11 were subjected to measurement using the device for measuring the pulling force as shown in FIG. 17. The result is shown in Table 4. Simple averages of the measured attraction force were ∼37,8 N (3,85 Kp) in the fastener means without the ferromagnetic member 5, ∼37,3 N (3,8 Kp) in the fastener means with 0.03 mm thick ferromagnetic member 5, ∼37,3 N (3,8 Kp) in the fastener means with 0.05 mm thick member, ∼34,2 N (3,49 Kp) in the means with 0.08 mm thick member, ∼31,9 N (3,25 Kp) in the means with 0.10 mm thick member, ∼30,1 N 3,07 Kp) in the means with 0.15 mm thick member, ∼28,35 N (2,89 Kp) in the means with 0.20 mm thick member, and ∼21,97 N (2,24 Kp)in the means with 0.30 mm thick member. These averages are plotted in the graph IV in FIG. 14. Attraction Force Measurement (1) Kp ≙ 9,81 N Ferromagnetic member 5 (thickness) I II III IV V None 3.90 3.80 3.90 3.80 3.85 0.03 mm 3.75 3.85 3.75 3.75 3.90 0.05 mm 3.80 3.80 3.75 3.90 3.75 0.08 mm 3.45 3.65 3.35 3.35 3.65 0.10 mm 3.35 3.20 3.30 3.15 3.25 0.15 mm 3.00 3.05 3.00 3.25 3.05 0.20 mm 2.85 3.05 2.90 2.85 2.80 0.30 mm 2.20 2.20 2.25 2.35 2.20 Attraction force of the Embodiment fastener means as shown in FIG. 12 and Comparative Embodiments was measured in the same manner as mentioned above. The result is shown in Table 5. Simple averages of the measured attraction force were ∼36,78 N (3,75 Kp) in the fastener means without the ferromagnetic member 5, ∼35,90 N (3,66 Kp) in the fastener means with 0.03 mm thick ferromagnetic member 5, ∼35,80 N (3,65 Kp) in the fastener means with 0.05 mm thick member, ∼33,35 N (3,4 Kp) in the means with 0.08 mm thick member, ∼31,29 N (3,19 Kp) in the means with 0.10 mm thick member, ∼29,23 N (2,98 Kp) in the means with 0.15 mm thick member, ∼27,27 N (2,78 Kp) in the means with 0.20 mm thick member, and ∼20,99 N (2,14 Kp) in the means with 0.30 mm thick member. These averages are plotted in the graph V in FIG. 15. Attraction Force Measurement (2) Kp ≙ 9,81 N Ferromagnetic member 5 (thickness) I II III IV V None 3.75 3.70 3.80 3.70 3.80 0.03 mm 3.70 3.65 3.60 3.70 3.65 0.05 mm 3.65 3.60 3.70 3.70 3.60 0.08 mm 3.40 3.35 3.50 3.35 3.40 0.10 mm 3.10 3.20 3.20 3.30 3.15 0.15 mm 3.00 2.95 2.90 3.05 3.00 0.20 mm 2.80 2.75 2.80 2.85 2.70 0.30 mm 2.15 2.10 2.10 2.20 2.15 Attraction force of the Embodiment fastener means as shown in FIG. 13 the Comparative Embodiments was measured in the same manner as mentioned above. The result of measurement is shown in Table 6. Simple averages of the measured attraction force were ∼36,89 N (3,76 Kp) in the fastener means without the ferromagnetic member 5, ∼36,1 N (3,68 Kp) in the fastener means with 0.03 mm thick ferromagnetic member 5, ∼35,81 N (3,65 Kp) in the fastener means with 0.05 mm thick member, 33,65 N (3,43 Kp) in the means with 0.08 mm thick member, ∼30,61 N (3,12 Kp) in the means with 0.10 mm thick member ∼29,33 N (2,99 Kp) in the means with 0.15 mm thick member, ∼26,39 N (2,69 Kp) in the means with 0.20 mm thick member, and ∼20,40 N (2,08 Kp) in the means with 0.30 mm thick member. These averages are plotted in the graph VI in FIG. 16. Attraction Force Measurement (3) Kp ≙ 9,81 N Ferromagnetic member 5 (thickness) I II III IV V None 3.70 3.75 3.75 3.80 3.80 0.03 mm 3.65 3.70 3.60 3.70 3.75 0.05 mm 3.60 3.60 3.65 3.70 3.70 0.08 mm 3.50 3.35 3.35 3.50 3.45 0.10 mm 3.00 3.10 3.15 3.15 3.20 0.15 mm 2.90 2.95 3.00 3.00 3.10 0.20 mm 2.75 2.70 2.65 2.70 2.65 0.30 mm 2.10 2.00 2.00 2.15 2.15 These measurements on leakage flux and attraction force indicate that the attraction means of the fastener means becomes more effective when it is covered with a ferromagnetic member 5; more particularly, the permanent magnet constituting the attraction means is preferably covered with a ferromagnetic member 5 of the thickness in the range of from 0.03 to 0.20 mm. In other words, the Comparative Embodiments comprising the attraction means that is not covered with the ferromagnetic member 5 on the surface of the permanent magnet exhibited leakage flux which was more than 300 gauss. Magnetically recorded information on magnetic tapes and tickets are likely to be destroyed when the tapes or the tickets come in close contact with the attraction means. However, by covering the surface of the permanent magnet with a ferromagnetic member 5 having the thickness of more than 0.03 mm, surface leakage flux from the attraction means can be reduced to 300 gauss or less without a significant loss of attraction force. Surface leakage flux from the attraction means can be suppressed by providing the surface of the permanent magnet with a plating of ferromagnetic material 5. No inconveniences will arise even if the ferromagnetic member 5 is coated with a non-magnetic plating, so long as the ferromagnetic member 5 has the thickness of from 0.03 to 0.20 mm. When the ferromagnetic member 5 is thinner than 0.03 mm, surface leakage flux from the attraction means shows an abrupt increase, and the ferromagnetic member 5 itself becomes too brittle to give sufficient protection for the outer surface of the attraction means. On the other hand, if the thickness of the ferromagnetic member 5 exceeds 0.20 mm and reaches 0.3 mm, attraction force of the fastener means decreases significantly, making it unsuitable for use. FIG. 18 shows a typical embodiment of the present invention, more specifically the fastener means shown in FIG. 11 in an exploded view. The fastener means comprises a ferromagnetic member 5 which is shaped like an upside-down dish and is provided with a hole 5a, a bent collar 5a′ inside the hole 5a, and claws 5b provided at the open edge of the dish-like member 5. Thus the collar 5a′ of the member 5 will abut against the peripheral edge of the through-hole 4 of the permanent magnet 1 and the claws 5b will be bent on the surface of the ferromagnetic member 2 when the member 5 and the magnet 1 are integrally held inside a casing to form the attraction means. The component parts identical with those in the embodiments described in the foregoing are given the same reference numbers and the description is omitted. FIG. 19 shows a fastener means wherein the ferromagnetic member 5 is formed as a casing and has a peripheral side wall 5c which is erected along the peripheral edge of the ferromagnetic member 5 at its attraction face. This construction prevents lateral movement of the attracted means attracted to the attraction face of the attraction means, and is also advantageous in that said peripheral side wall 5c protects magnetic tapes or magnetically operable tickets from directly contacting the attraction means. The component parts identical with those in the embodiments described in the foregoing are given the same reference numbers and the description is omitted. FIG. 20 shows a fastener means wherein the leg member 6 is omitted; instead, cylindrical caulking members 13 are attached to the ferromagnetic members 2 and 3 respectively by means of the projections 2a and 3a. Each caulking member 13 comprises a cylinder portion with a horizontal outer collar 13a′ on one side, and a seat 13b which is attached to the outer collar 13a′. The component parts identical with those in the embodiments described in the foregoing are given the same reference numbers and the description is omitted. The fastener means shown in FIG. 21 uses a double coated tape 14 as the means to attach the fastener means; the double coated adhesive tape 14 are adhered to the ferromagnetic members 2 and 3 respectively to form the fastener means. The component parts identical with those in the foregoing embodiments are given the same reference numbers and the description is omitted. The fastener means shown in FIG. 22 is used as a clasping means for chains and strings such as necklaces; the ferromagnetic members 2 and 3 are respectively provided with fixing holes 2d and 3d for the chain 15 and the like. The component parts identical with those in the foregoing embodiments are given the same reference numbers and the description is omitted. The foregoing embodiments are the typical ones, and other constructions are possible for both the attraction and attracted means as well as for the fixing means to suit the requirements of each individual use of the fastener means. As has been described in the foregoing, because the permanent magnet 1 which constitutes the fastener means according to the present invention has a ferromagnetic member 2 on one of the magnetic pole surfaces and is covered with a ferromagnetic member 5 on the other magnetic pole surface 1b as well as on the surface extending between the magnetic pole surfaces 1a and 1b, a magnetic path is formed between the magnetic pole surfaces 1a and 1b via the ferromagnetic member 5. When the thickness of the ferromagnetic member 5 is in the range of from 0.03 to 0.20 mm, the total magnetic flux passing through said ferromagnetic member 5 can be maintained within a given range. In the fastener means according to the present invention, the attraction means is provided with a through-hole 4 extending between the two magnetic pole surfaces and a ferromagnetic member 2 is attached to one of the magnetic poles. By covering the surfaces of the permanent magnet where this ferromagnetic member 2 is not attached (including or excluding the through-hole 4) with the ferromagnetic member 5 in the form of casing or plating, surface leakage flux from the attraction means can be reduced significantly. To reduce the leakage flux to 300 gauss or less while maintaining the attraction force of the fastener means not less than ∼24,52 N (2,50 Kp), the thickness of the ferromagnetic member 5 is set within the range of from 0.03 to 0.20 mm. The present invention therefore provides a fastener means which has sufficient attraction force but low leakage flux from the attraction face.

Claims: A fastener means adapted for releasably fastening first and second elements, for example a handbag and a flap for closure of the same, the fastener means comprising a first member ( 2 ) adapted to be attached to said first element and a second member ( 3 ) adapted to be attached to said second element; said first member ( 2 ) comprising a permanent magnet (1) having a hole (4) therethrough extending between opposite end surfaces (1a,1b) thereof, the magnet (1) having a pole of first magnetic polarity adjacent one said end surface (1b) oriented to extend in the direction away from said first element when said first member ( 2 ) is attached thereto and a pole of opposite magnetic polarity adjacent the opposite said end surface (1a), and a covering (5) at least partially encasing the permanent magnet (1); and said second member ( 3 ) comprising a ferromagnetic member detachably attracted to said first pole; the fastener means being characterised in that said covering (5) is formed of a ferromagnetic material having a thickness of between 0.03 mm and 0.20 mm and directly covers at least said one end surface (1b), being contiguous therewith, without an intervening ferromagnetic plate. A fastener means according to Claim 1, further characterised in that said first member ( 2 ) further comprises a ferromagnetic member attached to said end surface (1a) of said magnet (1) adjacent to said second pole, said first member ( 2 ) being adapted to be attached to said first element via said first ferromagnetic member. A fastener means according to Claim 2, further characterised in that one and/or the other of said ferromagnetic members is in the form of a plate having a post (2a,3a) adapted for extending into said through hole (4), such that said ferromagnetic members are abutted against and attracted to each other via said through hole (4) when said first ( 2 ) and second members ( 3 ) are in facial contact with each other. A fastener means according to any preceding claim, further characterised in that said covering (5) is in the form of a casing. A fastener means according to Claim 4 and either of Claims 2 or 3, further characterised in that said ferromagnetic member is attached to said end surface of said magnet (1) by means of said casing. A fastener means according to any of Claims 1, 2 or 3 further characterised in that said covering (5) is in the form of a plating. A fastener means according to any preceding Claim, further characterised in that said covering (5) extends to cover a portion of the surface of said through hole (4) adjacent said first pole.

Inventors: MORITA TAMAO, MORITA, TAMAO
Applicants: TARMO CO LTD, TARMO CO. LTD.
Application year: 1991
Main classification: A41F1
IPC codes: A45C13, A41F1, H01F7