Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-06-08
2001-05-08
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S430000, C524S431000, C524S435000, C524S436000, C524S437000, C524S439000, C524S440000, C524S441000, C524S589000
Reexamination Certificate
active
06228933
ABSTRACT:
TECHNICAL FIELD
This invention relates to physically soft magnets, that is with a surface hardness of less than about 70 on the Shore 00 scale, that are capable of visco-elastic deformation without distorting the associated magnetic fields and methods for manufacture thereof. Drawing #1 shows a simplified comparison of the several Shore scales of hardness.
BACKGROUND TO THE INVENTION
It is well known that pieces of certain pure metals, namely iron, cobalt and nickel can be treated in such a way that their magnetic moments or domains become aligned and said pieces then behave as magnets, that is they acquire a magnetic field within which magnetic materials may be influenced as to their energy content and potential. The strength of the field increases according to the percentage of the domains present and those aligned. The field can be further increased by the addition of other metals or their oxides to form magnetic alloys, for example barium, boron, copper, neodymium, promethium and samarium. Tri-alloys can also be formed further increasing the field strength, for example, neodymium-iron-boron. Another group of suitable magnetic materials is called ferrites. These consist of the oxides of iron to which small quantities of transition metal oxides; for example, cobalt or nickel have been added. These are known as spinel ferrites and have the general formula M(OFe
2
O
3
) where M is a divalent transition ion. Another form of ferrite is iron oxide to which the oxides of the reactive metals strontium or barium have been alloyed. Ferrites are particularly useful because they are easily reduced to a powder and can be reformed to suitable shapes by compaction or as a component of a plastic or ceramic compound. Such reconstituted ferrite particles when part of a ceramic compound produce a magnet with a surface hardness as high as 70 on the Shore D scale. When incorporated in a plastic the hardness is reduced generally to around 90 on the Shore A scale and as a rubber component the reading is about 60 on the Shore A scale. Plastic and rubber based magnets can be made flexible if cast in very thin section in which case, however, the field strength is usually impracticably low. To overcome this the magnetic sheet is often rolled to form a round or square section tube. The result is almost a total loss of cross-sectional flexibility but retaining such longitudinal flexibility as to make them useful for gaskets including domestic appliances such as refrigerators where curvature is gentle and sharp bends are catered for by miter jointing. Thin flat magnets of low field strength find a use as markers on a magnetic indicator board, in children's toys and as decorative refrigerator magnets which sometimes double as note-holders. It has been found that magnets of higher strength that is of thicker cross section are capable of attracting the hemoglobin content of erythrocytes present in blood plasma. Such magnets have been strategically placed in medical devices to attract erythrocytes to various parts of the body to increase the oxygen supply to that point. These points are often nerve endings and are sometimes described in Oriental medicine as pressure or acupuncture points. Magnets are embedded in or attached to rubber, plastic, cloth or other materials to hold them in place. It will be seen that these magnets are necessarily small in diameter, comparatively large in cross section and of hardness at least measurable as 50 on the Shore A scale. Such magnets must be cushioned if they are placed near to soft tissue. Any barrier will reduce the field strength of a magnetic source. The magnets are always discernable and often uncomfortable especially when used in footwear and more especially on the upper regions of footwear insoles where loads are heavy and vertically applied. Furthermore, it will be seen that these discreet magnet areas of high compression combined with the magnetic attraction directed towards the hemoglobin can slow the blood to such an extent as to encourage vascular restriction or clotting. When the hemoglobin becomes met-hemoglobin, that is the oxide has degenerated from ferrous (
) to ferric (
) a localized area of cyanosis may be caused due to lack of oxygen. Clotting in this region could prove fatal. Such quasi (or alternative) medical devices include shoe insoles, elbow, knee, spinal and neck pads.
SUMMARY OF THE INVENTION
It will be seen that there is a need for a magnet that, for quasi medical purposes, can be worn next to soft tissue without interfering with the comfort or well being of the wearer and for other purposes such as washers, isolators, energy dissipating pads and gaskets, for example those used in manhole cover systems, capable of deflecting easily but with a limited degree of permanent compression and a pre-determined recovery rate. For quasi-medical purposes this recovery rate should be similar to that of the soft tissue with which it is going to closely function. For example, the recovery rate of the calcaneal fat pad is between 10 and 100 milliseconds and on very rare occasions this delay may be extended to 200 milliseconds.
The ideal compound will be based on a flexible plastic or rubber containing suitable quantities of a magnetic powder or finely divided crystal which may be a ferrite or other magnetic mixtures as previously described. Such a compound could be cast, injection molded, rotationally molded, transfer molded, compression molded or a combination of these practices. The preferred method of manufacture is by thermo-setting casting.
It has been discovered that a filled polyurethane elastomer composition having a density of from about 1 to 3.5 gms. per cc., a compression set of less than about 5% and a recovery time from about 10 to 200 milliseconds having particular utility as an energy dissipating medium and having the appropriate magnetic field strength when cast can be prepared. Such polyurethane elastomer compositions contain a ferro-magnetic or similar compound in quantities to command a suitable magnetic field strength and, where necessary when weight is critical, a light weight filler material may be combined, for example, hollow glass or ceramic spheres can be coated with a metal such as nickel or iron (steel). Such a compound will contain at least four urethane-forming reactive sites, which are capable of forming stable complexes.
The invention is directed to a process for forming a polyurethane elastomer composition wherein a compound is mixed having at least four urethane-forming reactive sites and capable of forming stable complexes through free radicle reactive sites with an elasticizing diol or triol, a plasticizer if preferred, a light-weight reinforcing filler material if necessary and a magnetic component capable of supporting a suitable magnetic field and adding a diisocyanate in less than stoichiometric amounts allowing the formation of urethane linkages involving less then about 85% of the urethane-forming reactive sites of the quadra-functional forming a coordinately bonded or chelated complex to provide a stable solid having a density between 1.2 and 3.8 grams per cc. and a compression set of less than about 5% and a recovery time of about 10 to about 200 milliseconds. A diisocyanate, such as 4′4′ dimethyl diisocyanate is added to the polyol mixture to form the cross linking sites at a ratio of between (parts by weight) of polyol to 1 pbw of diisocyanate and 15 pbw of polyol to 1 pbw of diisocyanate. The magnetic powder is added at a level of between 5% and 100% of the polymer prior to reaction. In cases where weight is a critical factor some or most of the magnetic powder can be replaced by a light weight filler such as glass or ceramic micro-balloons (coated or uncoated), fly ash or fumed silica. Thus the density of the cured compound can be between 0.4 and 2.5 grams per cc.
During and after the reaction, the unreacted urethane forming reactive sites are stabilized by the formation of complexes, preferably by chelation with ionic species introduced as part of the complete formulation. Preferably a
Niland Patrick D.
Remington Products Company
Renner Kenner Greive Bobak Taylor & Weber
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