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
2000-05-31
2002-09-24
Michl, Paul R. (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...
C002S024000, C036S03500R, C036S037000, C036S071000, C524S481000, C524S485000
Reexamination Certificate
active
06455623
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to freeze-resistant fluid compositions, and in particular to freeze-resistant fluid compositions suitable for use in deformable, pressure-compensating padding devices.
A wide variety of deformable, pressure-compensating fluid compositions have been developed for use in seats, cushions, boot liners, mattresses, fitting pads, athletic equipment, prosthetic devices and other padding devices which are placed in prolonged contact with the human body. The compositions have the capacity to deform in response to continuously applied pressure and thereby adapt to the contour of a particular part of the human body. Some of the compositions maintain their shape and position in the absence of continuously applied pressure.
One such fluid composition is described in U.S. Pat. No. 5,869,164 to Nickerson et al. The composition is a viscous, grease-like thixotropic fluid comprising an oil thickened with a diblock polymer. The diblock polymer includes a first block that is compatible with the oil and a second block that is incompatible with the oil. The patent states that the composition does not stiffen to unacceptably high viscosities when chilled to a temperature of 40° F. (4° C.). However, it has now been found that the composition stiffens considerably when exposed to lower temperatures, e.g., 25° F. (−4° C.) or below. This can cause problems because padding devices are sometimes exposed to low ambient temperatures. A fluid that is stiff and incapable of deforming in response to pressure is unacceptable for use in a padding device. Other deformable, pressure-compensating fluid compositions also suffer from this drawback. Accordingly, there is a need for a deformable, pressure-compensating fluid composition suitable for use in padding devices that is resistant to freezing at low temperatures.
SUMMARY OF THE INVENTION
The present invention provides a freeze-resistant fluid composition. In a first embodiment, the composition comprises a fluid composition having the capacity to deform in response to continuously applied pressure and having the ability to maintain its shape and position in the absence of continuously applied pressure. The composition contains a freeze point depressant effective to make the composition resistant to freezing as measured by a penetrometer measurement of at least 13 millimeters at 25° F. (−4° C.). In a second embodiment, the composition comprises a fluid mixture of a relatively saturated oil, a relatively unsaturated oil, a block copolymer, and a freeze point depressant. In a third embodiment, the composition comprises a fluid mixture of a relatively saturated oil in an amount within the range of from about 20% to about 70% by weight, a relatively unsaturated oil in an amount within the range of from about 20% to about 70% by weight, and a block copolymer in an amount within the range of from about 0.3% to about 10% by weight. Preferably, the oils are vegetable oils. The invention also provides a pressure compensating padding device comprising a flexible envelope and the freeze-resistant fluid composition within the envelope.
Various advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The freeze-resistant fluid composition can be any composition which is resistant to freezing and which is suitable for use in its intended application. Typically, the fluid composition is used in a deformable, pressure-compensating padding device. The fluid composition usually has a viscosity within a range of from about 100,000 to about 1,000,000 centipoise, and typically from about 100,000 to about 280,000 centipoise. When used in a padding device, the fluid composition should have the capacity to deform in response to continuously applied pressure and the ability to maintain its shape and position in the absence of continuously applied pressure.
One such fluid composition is disclosed in U.S. Pat. No. 5,549,743 to Pearce, issued Aug. 27, 1996 (incorporated by reference herein). The fluid composition is a mixture of spherical objects and lubricant suitable for providing cushioning properties. Typically, the spherical objects are microspheres having a diameter less than 2000 microns. Any of a variety of lubricants facilitating sliding and rolling between the microspheres can be used.
The above-described U.S. Pat. No. 5,869,164 to Nickerson et al., issued Feb. 9, 1999 (incorporated by reference herein), discloses a viscous thixotropic fluid suitable for use in a deformable, pressure-compensating padding device. The fluid composition comprises an oil thickened with a block copolymer. Various oils and block polymers suitable for use in the fluid composition are described in more detail below.
The Oil
The oil suitable for use in the fluid composition can be any type of oil suitable for forming a composition having the intended properties. Certain types of oils are particularly suited for combining with block copolymers to make viscous, thixotropic fluid compositions. Such oils include, for example, vegetable oils, polyalphaolefin oils, polybutene oils, dialkyl carbonate oils, and paraffinic mineral oils.
Some examples of suitable vegetable oils include canola, cottonseed, corn, olive, soy, peanut, coconut, linseed, safflower, sunflower, and other triglyceride oils. Mixtures of different vegetable oils can also be used. To reduce the potential for oxidation of the vegetable oil over time, preferably an oxidation-resistant vegetable oil is used in the composition, and/or the vegetable oil is processed to resist oxidation. Canola oil is an example of a vegetable oil that is less susceptible to oxidation than most other vegetable oils. The vegetable oil can be hydrogenated and/or fractionated to provide a lower degree of unsaturation for greater resistance to oxidation. A preferred vegetable oil for use in the composition of the invention is a partially hydrogenated, fractionated canola oil, such as Solo 1000 produced by C&T in Charlotte, N.C. Genetically engineered versions of regular and hydrogenated canola oil, which are particularly robust, are sold by Cargill Foods as Clear Valley 65, Clear Valley 75 and Odyssey 500.
Fluid compositions formed with vegetable oils according to the invention are usually more biodegradable than conventional materials used in padding devices. The compositions can be broken down by microorganisms so that they cause fewer problems in the environment. Preferably, the compositions are substantially completely broken down in less than 100 years under optimal biodegradation conditions (e.g., suitable moisture, heat, oxygen, and presence of microorganisms). Biodegradable compositions are in great demand in the marketplace.
Polyalphaolefin (PAO) oils are synthetic, saturated aliphatic oils, which are polymerized from a variety of feedstocks. The “Durasyn” brand of PAO oils are produced from a 1-decene (10 carbon chain) feedstock from Amoco Corporation. The Durasyn PAO oils are available in a wide variety of molecular weights depending on the number of 1-decene units that are incorporated into the final molecule. A preferred PAO oil is Durasyn 168, which is a hydrogenated homopolymer of 1-decene with a molecular weight of about 1120.
Polybutene oils suitable for use in the fluid composition include the “Indopol” brand of polybutene oils sold by Amoco. These low molecular weight polybutene oils create a very thick, very viscous, highly thixotropic composition. Suitable dialkyl carbonate oils include the “Mix Oil” dialkyl carbonate oils sold by Agip Petroli. Suitable paraffinic mineral oils include the Shell “Carnea” paraffinic mineral oils.
In some preferred embodiments, the freeze-resistant fluid composition includes a blend of a relatively saturated oil and a relatively unsaturated oil. In these embodiments, the relatively unsaturated oil is important for providing a fluid composition that does not easily freeze; a composition containing a relative
MacMillan Sobanski & Todd LLC
Michl Paul R.
Sunrise Medical HHG Inc.
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