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
1999-12-14
2002-03-19
Cain, Edward J. (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...
C524S435000, C524S523000, C524S157000
Reexamination Certificate
active
06359051
ABSTRACT:
BACKGROUND OF THE INVENTION
Rubbery or semi-flexible magnetic compositions are used in a wide variety of applications. For instance, such materials are widely used as a combination airtight gasket and magnetic closure for refrigerator and freezer doors. They are also used in decorative magnets that will stick to a wide variety of metal (steel) objects, such as oven or refrigerator doors. In any case, such semiflexible or rubbery magnets are typically comprised of a blend of a rubbery polymer and a magnetic powder that is formed into the desired shape and then cured. Such rubbery magnetic compositions also typically lack heat, ultraviolet light and outdoor weather resistance.
Heat and light stabilizers can be employed to improve the heat and ultraviolet light aging characteristics of conventional blends of rubber with magnetic powder. However, the degree to which the aging characteristics of such blends can be improved by the addition of additives is limited. In fact, there is a demand for performance characteristics in such applications that has not heretofore been realized by the utilization of heat and light stabilizers. For instance, it would be highly desirable for rubbery magnets used in refrigerator and freezer doors to have a higher level of resistance to discoloration and cracking under conditions of heat and exposure to ultraviolet light experienced throughout the life of the refrigerator or freezer. Resistance to ultraviolet light is particularly important in out door applications, such as automotive seals and seals for metal framed doors and windows.
U.S. Pat. No. 5,674,933 and U.S. Pat. No. 5,767,173 disclose a rubbery polymer which can be blended with polyvinyl chloride to make leathery compositions having good heat and ultraviolet light resistance, said rubbery polymer being comprised of repeat units which are comprised of (a) butyl acrylate, or optionally a mixture of butyl acrylate and 2-ethylhexyl acrylate containing up to about 40 percent 2-ethylhexyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a surfactant selected from the group consisting of sulfonates and sulfate derivatives, (f) a dispersant selected from the group consisting of aromatic formaldehyde condensation products and polycarboxylates and (g) a crosslinking agent. U.S. Pat. No. 5,380,785 discloses a similar type of rubbery polymer and U.S. Pat. No. 5,616,651 discloses a technique for making a low odor version of the rubbery polymer by adding an aminoalcohol to the emulsion thereof.
U.S. Pat. No. 5,990,218 discloses a polymeric magnet composition which is comprised of (1) from 5 to 19 parts by weight of a rubbery polymer which is comprised of repeat units which are comprised of (a) butyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a surfactant selected from the group consisting of sulfonates and sulfate derivatives, (f) a dispersant selected from the group consisting of aromatic formaldehyde condensation products and polycarboxylates and (g) a crosslinking agent; (2) from 80 to 90 parts by weight of a magnetic powder; and (3) from 1 to 10 parts by weight of a internal lubricant. These magnetic compositions provide a higher level of resistance to heat and ultraviolet light than those made utilizing conventional blends of rubber and magnet powder. They also offer the advantage of being capable of being injection-molded into the desired form without the need for a curing step.
SUMMARY OF THE INVENTION
The present invention relates to a polymeric composition having ultraviolet light and heat resistance that can be extruded into tubing that can be magnetized. The tubing can optionally be cut or chopped into gaskets or washers that can be magnetized. For instance, the tubing can be cut to the desired length and used as solenoid assemblies in automotive door lock systems. These polymeric magnetic compositions offer the advantage of being thermoplastic materials rather than thermosets. By virtue of being thermoplastics, they can be extruded into the desired form without the need for a curing step. Thus, rubbery magnetic tubing can be manufactured by a simpler, less costly process by utilizing the compositions of this invention. Additionally, because the material is a thermoplastic rather than a thermoset, scrap and defective product can easily recycled.
This invention more specifically discloses a polymeric magnet composition that is particularly useful for extrusion into thermoplastic magnetic tubing, said polymeric magnet composition being comprised of(1) from 2 to 8 parts by weight of a rubbery polymer which is comprised of repeat units which are comprised of (a) butyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a surfactant selected from the group consisting of sulfonates and sulfate derivatives, (o a dispersant selected from the group consisting of aromatic formaldehyde condensation products and polycarboxylates and (g) a crosslinking agent; (2) from 2 to 8 parts by weight of a styrene-butadiene resin; (3) from 80 to 90 parts by weight of a magnetic powder; and (4) from 1 to 8 parts by weight of an internal lubricant. The magnetic compositions of this invention provide a higher level of resistance to heat and ultraviolet light than those made utilizing conventional blends of rubber and magnet powder. They also offer the advantage of being capable of being extruded into tubing of the desired form without the need for a curing step.
The present invention also discloses a process for producing thermoplastic magnetic tubing which comprises extruding a polymeric composition into the said thermoplastic magnetic tubing, wherein said polymeric composition is comprised of (1) from 2 to 8 parts by weight of a rubbery polymer which is comprised of repeat units which are comprised of (a) butyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a surfactant selected from the group consisting of sulfonates and sulfate derivatives, (f) a dispersant selected from the group consisting of aromatic formaldehyde condensation products and polycarboxylates and (g) a crosslinking agent; (2) from 2 to 8 parts by weight of a styrene-butadiene resin; (3) from 80 to 90 parts by weight of a magnetic powder; and (4) from 1 to 8 parts by weight of an internal lubricant.
DETAILED DESCRIPTION OF THE INVENTION
The rubbery polymers of this invention are synthesized utilizing a free radical emulsion polymerization technique, such as the technique described in U.S. Pat. No. 5,380,785, U.S. Pat. No. 5,616,651, U.S. Pat. No. 5,674,933 or U.S. Pat. No. 5,767,173. The teachings of U.S. Pat. No. 5,380,785, U.S. Pat. No. 5,616,651, U.S. Pat. No. 5,674,933 and U.S. Pat. No. 5,767,173 are incorporated herein by reference in their entirety. Rubbery polymers of this type are sold by The Goodyear Tire & Rubber Company as Sunigum® rubber. These rubbery polymers are comprised of repeat units which are derived from (a) butyl acrylate, or optionally a mixture of butyl acrylate and 2-ethylhexyl acrylate containing up to about 40 percent 2-ethylhexyl acrylate, (b) methyl methacrylate, ethyl methacrylate, methyl acrylate or ethyl acrylate, (c) acrylonitrile, (d) styrene, and (e) a crosslinking agent. The crosslinking agent is typically a multi-functional acrylate, a multi-functional methacrylate or divinylbenzene. Some specific examples of crosslinking agents that can be used include ethylene glycol methacrylate, divinylbenzene and 1,4-butanediol dimethacrylate.
Technically, the rubbery polymers used in the magnet compositions of this invention contain repeat units (chain linkages) which are derived from (
Gozdiff Michael
Hill Valerie Anne
Cain Edward J.
Rockhill Alvin T.
The Goodyear Tire & Rubber Company
Wyrozebski Kat
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