Compositions: coating or plastic – Coating or plastic compositions – Pore forming
Reexamination Certificate
1997-04-09
2001-03-06
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Pore forming
C501S032000, C501S105000, C501S065000, C501S065000, C523S223000, C005S644000, C005S909000
Reexamination Certificate
active
06197099
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates to the field of lightweight flowable and shearable materials including materials for cushions and padding, such as seat cushions or bed pads, where skin comfort and skin preservation are important. More particularly, this invention relates to a composite mixture of a lubricant and spherical objects which may be encased within a flexible container or sack and used as a cushion or padding. The exterior surfaces of the spherical objects are lightly lubricated to accommodate flow and shear, but lubricant is not used in an amount sufficient to cause dispersion of the spherical objects in the lubricant. Additionally, the mixture is adapted to minimize memory which would cause it to move, flow or change shape when a deforming force is removed. The composite mixture has a very low specific gravity, making it excellent for use with lightweight vehicles such as wheelchairs and bicycles, and which makes it an excellent flotation material.
B. The Background Art
In the prior art there has been substantial difficulty in designing padding or cushioning for contact with a patient's skin that has some or all of the following characteristics: (i) equalization of pressure across the entire area of skin contacted in order to prevent skin damage, (ii) readily flowable, (iii) low shearing force threshold, (iv) no or minimal memory, (v) low specific gravity, (vi) lightweight, and (vii) comprising a flowable material which has some or all of the following characteristics: (a) capable of being contained in a flexible, elastic bladder without leakage, (b) does not substantially vary in performance with temperature, (c) does not break down or separate into its constituent components over time, (d) does not feel overly cold to the touch, and (e) quickly warms to body temperature. The prior art has also been unable to design a flotation material which has a low specific gravity for buoyancy but is not stiff or semi-rigid and, therefore, somewhat uncomfortable for the wearer of a life vest containing such material.
For example, the typical prior art wheelchair seat consists of a fabric sling stretched between two metal bars on which the patient sits. Frequently the sling has a plastic or rubber coating for durability. Sling seats such as these are unable to conform to the shape of the human body, resulting in greater force being applied to some portions of the patient's anatomy than to others. Over time, high spots or bony areas on the patient's body often develop decubitus ulcers (pressure sores) or other tissue damage. Sling seats typically also have a high shearing force threshold, being resistent to movement or turning in response to movement by the patient. As the patient turns or moves within the seat, friction with the patient's body would tend to move the portion of the seat in direct contact with the patient's body. All portions of the typical seat, however, are typically held fast together, whether by monolithic construction, such as in foam seats, with stitching as in sling seats, or otherwise. The resulting high shearing force threshold causes tissue damage during turning or movement. Tissue damage from shear-resistant seats can be cumulative and debilitating over time. Foams and other traditional types of cushions and padding have provided little relief from the disadvantages of sling seats. For example, patients confined to bed typically experience the same skin damage as those using a sling seat even though mattresses usually include a combination of metal springs, foam padding and cotton or synthetic batting.
The previous solution to the problems of typical cushions and padding has been the use of gels or viscous and slimy liquids (hereinafter “fluid”) contained within a flexible bag or bladder. The use of fluid within a flexible bladder for contact with a patient's body achieves much more uniform force or pressure on irregular body surfaces than traditional cushions and padding. The shearing force threshold of fluid within a bladder may be lower than in other cushions or pads because the bladder surface closest to the patient's body is free, within certain limits, to move with the patient's body as the patient moves. The bladder walls are not anchored to the gel so that as the patient moves, the bladder may move with respect to the gel. The fluid also has some ability to shear with respect to itself. The result is a seat which-is less damaging to human skin than a typical sling seat. Unfortunately, most viscous fluids are very slow to respond to body movement, giving an undesirably high shearing force during quick body movement and failing to fully preserve the integrity of the patient's skin. Fluid within a bladder is currently used as padding in some wheelchair and bicycle seats. Such fluids are also very heavy, even when hollow microbeads are dispersed in the fluid. Further, prior art fluids flow under their own weight, causing them to exert a “head pressure” on bony protuberances of the body, causing skin damage and discomfort. Some prior art fluids also have memory, thereby exerting a force on bony protuberances of the body as the fluids try to return to shape; memory increases the likelihood of tissue damage.
Fluid has the disadvantage of being much heavier than the flexible foam used in typical cushions. Fluids commonly used in cushioning have specific gravities of 0.6 to 1.2, whereas a typical cushion foam may have a specific gravity of only 0.05 to 0.10. Thus, in order to achieve a lightweight seat, fluid must be used sparingly. When fluid is used sparingly, its positive characteristics are minimized. Use of gels in sufficient quantity to achieve the desired effect results in a seat weight unacceptable for many applications. For example, patients using wheelchairs commonly suffer from a weakened physical condition, and an increase in the weight of a wheelchair by only a few pounds can make it excessively burdensome for the patient to use. As another example, total bicycle weight is typically a primary consideration in the design of both road bikes and mountain bikes. The additional weight of a fluid seat is often unacceptable to all but the most casual of riders.
Another disadvantage of such gels is that they have a high thermal mass and a high coefficient of heat transfer. As a result, fluid seats typically feel cold to the touch, providing initial discomfort to the user and remain cold for long periods of time before warming. Fluids used in cushioning also exhibit substantial viscosity changes with temperature, causing them to become more viscous and lose their functional characteristics in cold temperatures. Similarly, in very warm temperatures, such fluids will exhibit excessive flow characteristics and again will not function as desired. Finally, fluids used in cushioning which have hollow microspheres dispersed therein will tend to break down and separate into their constituent components over time, causing a loss of functional characteristics. The user of such a fluid cushion must, therefore, periodically knead the cushion to re-mix the components of the fluid and keep it functioning. Kneading a fluid cushion can be difficult or impossible for many wheelchair users because of the hand strength required, which makes a fluid cushion very undesirable.
U.S. Patents to Terrence M. Drew et al. issued Mar. 3, 1992 (U.S. Pat. No. 5,093,138) and Mar. 31, 1992 (U.S. Pat. No. 5,100,712) describe a flowable, pressure compensating composition including water, a material for increasing the viscosity of water, and spherical particles dispersed throughout the volume of the water. Both of these patents are hereby incorporated by reference in their entirety. The composition disclosed in these patents is a deformable fluid which has the disadvantages of substantial weight, memory, and being slow to flow or shear in response to a deforming pressure and, thus, being prone to cause skin damage.
U.S. Patents to Chris A. Hanson issued Oct. 22, 1991 (U.S. Pat. No. 5,058,291) an
Brunsman David
Millarthy Daniel
Power Brick
Sandbaken Mark
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