GB1594111A - Floatation cushions - Google Patents

Description

(54) IMPROVEMENTS IN FLOTATION CUSHIONS (71) We, OLIVELARK LIMITED, a British Company of Windjammer Works, Ferndale Road, Silverton, Exeter, in the County of Devon, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to upholstery cushions of the flotation type (referred to herein as flotation cushions) in which the filling includes an elastically compressible mess and a separate layer of a liquid, preferably in the form of a gel.The elastically compressible mass may be in the form of an air bag or any other resilient medium, or a combination of both, the principal function of which is to resist "bottoming" - a condition in which a localised zone of the composite filling is compressed onto a rigid base of foundation by the supported body beyond the limit of resilience so that any further increase in load over that zone results in no further compression of the filling. The principal function of the liquid layer is to minimise friction between adjacent surfaces within the cushion so as to reduce resistance to small lateral movements such as occur naturally with changes of posture of a sitter.Each component of the filling will, of course, also contribute towards the performace of the main function of the other, especially in the case of the liquid component which acts as a distributor of local pressures over a larger area.

Our patent No. 1,463,672 describes an upholstery cushion having a flexible but substantially inextensible material snugly embracing a main filling consisting of a highly compressible pad of a resiliently deformable solid substance and a secondary filling consisting of a layer or body of a lubricant fluid interposed between one loadsupporting face of the pad and the adjacent wall of the cover and of such volume or thickness as to prevent bottoming of the pad under its designed maximum loading.

Our patent No. 1,508,830 discloses a flotation cushion in which the cover has upper and lower panels united by an upstanding girdle and encloses three substantially coextensive (in plan) compartments filled, respectively, with a flexible thermally insulating material; a liquid medium; and air under sufficient pressure to prevent bottoming, the air compartment having its upper and lower walls sealed around their peripheral edges to the upper and lower edges, respectively, of the girdle and also to each other at one or more intermediate points over their surfaces.

The patented construction of cushion has a fixed bulk for a designed load. The construction of flotation cushion according to our above-numbered patent allows the bulk of the cushion to be reduced, for transport or storage purposes, by deflation of the air compartment, but the use of the girdle necessarily adds to the bulk of the material present.

Experience gained with both the preceding designs of cushion has confirmed the value of their composite fillings when in use, especially by long-term invalids or permanently disabled patients who find the comfort of the uniform and stable support they afford a major contribution to the absence of sores.

In this connection, the use of a highly thermal absorptive gel such as an aqueous solution of S.C.M.C. (sodium carboxy-methyl cellulose) is a mjaor factor in preventing an undue increase in skin temperature. This is more apparent to sitting patients than to the bedridden, the former being in general more prone tò bed sores than the latter due to the higher pressure engendered by the support of the same body weight over a small area when sitting.

Able-bodied and less seriously disabled persons find themselves, from time to time, liable to the same inconvenience as the permanently disabled or geriatrics when compelled to remain seated for prolonged periods of time. A more portable version of the previous designs of cushion would be considerable advantage on such occasions, and it is an object of the present invention to meet this need. Specifically, it is an object of the present invention to provide a construction of flotation cushion which can be col lapsed - as by folding or rolling - into a more readily portable form by reason of a reduction in bulk without sacrifice of the advantages of the composite fillings of the above designs.

According to the present invention a flotation cushion has a cover of flexible and relatively in extensible impervious material subdivided by a transverse impermeable membrane into three superposed coextensive compartments, the centre compartment being formed as a sac within the thickness of the transverse membrane and filled with gel.

The upper compartment contains a flexible, and preferably resilient, pad of a thermally insulating material, such as foamed plastics, coextensive in area with that of the gel compartment or sac. The lower compartment embraces an inflatable annular cell which is coextensive with a marginal zone of the gel sac, the term "annular" being deemed to cover shapes in plan other than circular.

Thus, a cell which underlies a continuous zone around the periphery of a rentangular gel sac is deemed to be "annular".

Preferably, the cell is provided with a suitable form of inflation/deflation valve.

Advantageously, the area of the cover lying within the ambit of the annular cell is permantly vented to atmosphere.

Conveniently, the annular cell is formed by welding two sheets of heat-sealable plastics laminate along two parallel or concentric lines spaced apart according to the predetermined width of the marginal zone of the gel compartment to be underlaid by the annular air cell. At least one of the weld lines is made by an electrode having a dimpled operative surface in which non-contiguous shallow circular pockets or "dimples" of less diameter than the width of the weld zone are closely spaced at preferably regular intervals along the length of the operative surface of the electrode.This configuration of welding electrode has the advantage that any material extruded under the welding pressure from the mating zones of the electrodes can be displaced into adjacent shallow circular recesses or "dimples" instead of being displaced laterally from the weld zone so that a stronger and more continuous weld results.

A practical embodiment of the present invention will now be described, by way of illustration only thereof, with reference to the accompanying drawings in which: Figure 1 is an exploded section through a flotation cushion on the line I-I of Figure 2, and Figure 2 is an underplan view of Figure 1.

The cushion 10 consists of two cover panels 12, 14 of flexible and relatively inextensible thermo-plastic laminate sheets, the panel 12 being the normal top face of the cushion. The bottom panel 14 is of double thickness, and both panels are seam welded together around their peripheries in sandwich with a central membrane 16, also of double thickness, the majority of which is distended to form a central compartment or sac 18 containing an aqueous solution of S.C.M.C. (sodium carboxy-methyl cellulose) gel. This compartment is defined by a separate inner weld 20. Above the central compartment or sac 18 is an upper compartment 22 defined by the top panel 12 and the membrane 16 which is filled with a resilient pad 24 of polyurethane foam or like thermally insulating material.

Below the central membrane 16 is a lower compartment 26 defined by the bottom double thickness panel 14 and the central membrane 16. The bottom panel 14 is also distended over an annular zone 28 to form an air compartment or cell 30 having an inflation/deflation valve 32. This cell is formed between outer and inner seam welds at 34, 36 uniting the two laminates which constitute the bottom panel 14. The inner seam weld 36 is formed by an appropriately shaped electrode having a continuous series of uniformly distributed non-contiguous dimples or shallow circular pockets which cause corresponding bulges 38 to form on the surface of the laminate from material which would normally have been extruded by a conventional flat-faced electrode beyond the boundary of the seam. Thus a stronger leak-resistant weld results.If necessary, a third sheet can be inserted between the two laminates to add more bulk to the inner weld 36.

The membrane portion of the panel 14 surrounded by the annular air compartment or cell 30 is permanently vented to atmosphere at 40.

In use, the air cell 30 is inflated to a pressure which will avoid bottoming of the cushion when the person concerned sits on it. This value is found by trial and error. At the critical pressure, the gel compartment or sac 18 is supported around its periphery by the annular air compartment or cell 30 and its centre sags into contact with the base surfaces on which the cushion is placed. This gives the cushion good lateral stability while the interposition of the gel 18 between the top cover 12 and the annular air cell 30 ensures substantially zero friction against the wall of the cell every time the sitter changes position.

When the cushion is no longer required, the valve 32 is opened to deflate the annular air cell 30. The whole cushion can now be rolled or folded into a small compass for transport or storage. The folded cushion can be carried in a shopping bag or carrier so as to be ready for use when required.

At least the bottom panel 14 is preferably a multi-layer assembly of separate sheets of PVC which are superimposed flat and bonded together around their peripheries only before being seam welded at 34, 36 to form the annular air cell 30. The valve 32 is secured in position before the peripheral bond is made. Each wall of the air cell 30 is composed of at least two sheets of PVC which are unconnected save at the peripheral bond and the local seam welds 34, 36 which define the annular cell 30. This loose ply structure has been found in practice to be more airtight than either a single sheet of the same thickness or a laminate of two sheets bonded together over their whole surface areas. The problem of airtightness arises initially because thin PVC sheet almost always has pinholes through which air can escape.

By overlaying two sheets, the risk that two pinholes will coincide is very remote, so that an airtight seal can more reliably be formed by a two-ply sheet. However, surface bonding has been found to be an unreliable solution of the problem inasmuch as the plies or laminae can separate at random zones, and any one zone may span individual pinholes in the separate plies or laminae, thereby reestablishing the perviousness of the laminate.

Another problem is also introduced by the surface-bonded laminate. This arises when a random zone of separation embraces a pinhole in the ply or laminae on the high pressure side. Air can seep into the zone of separation and, on the collapse of the cell or compartment bounded by the laminate, can become trapped. When the cell or compartment is repeatedly inflated and deflated, inexhaustible bubbles can be formed between the plies which become permanent deformations of the cell or compartment wall, disturbing both its shape and performance. By leaving the plies loose or separate, the pinholes in the outer or low pressure ply ensure that air can never be trapped between the plies so that each is free to act as a flap valve which seals the pinholes in the other, and airtight, bubble-free performance is obtained.

In the particular construction of cushion illustrated in the drawings, air bubble problems have been encountered when using surface-bonded laminates for the walls of the air cell 30 in the zones of the lower compartment 26 outside the central zone exhausted by the permanent air vent 40. Bubbles have been found to form between the air cell 30 and the gel compartment 18 which have proved substantially impossible to exhaust and which have rendered the cushion unstable in use.

A fairly average weight of S.C.M.C. gel in the sac 18 is 5 lb. The pad 24 can be 1/4-inch thick polyurethane or polyether foam, and the whole cushion can weight about 6 lb.

By comparison with the construction described in the specification or our patent No. 1,508,830, the construction described above is cheaper to manufacture owing to the much reduced time involved by elimination of the girdle. It may, however, not prove to be so comfortable for those who are chairbound permanently or for long periods. The deeper and full-area air compartment in the girdled cushion of our above-numbered patent is specifically designed for such chronic cases, but its bulk when deflated and its cost are both significantly greater than those of a cushion according to the present invention.

Although in the foregoing description of the design illustrated only the lower "pneumatic" compartment 26 is vented to atmosphere at 40, a similar vent can be provided for the upper insulation compartment 22. The edges of the sheets bounding the vent 40 may be sealed by radio frequency heating.

The thickness of the thermally insulating pad 24 is determined primarily by the required rate of heat absorption by the gel in the sac 18 from the body of the sitter. Ideally, therefore, this thickness would be adjustable, but since a foamed plastics is the most suitable material for the purpose such adjustment at will is impracticable. In general, the thickness of the pad is chosen empirically, and is found to vary approximately directly as the volume of gel in the sac 18.

The object is to remove excess body heat generated by a person sitting in the same position for long periods.

The outer seam weld 34 of the annular air cell 30 can also be of the "multi-pocket" kind described and illustrated in respect of the inner weld 36. This method minimise the risk which is inherent in the conventional "tearseal" seam welding technique that the thinning of the sheets may become excessive, either locally or generally, leading to failure and bursting of the air cell.

WHAT WE CLAIM IS: 1. A flotation cushion comprising a cover of flexible and relatively inextensible material enclosing a sealed flexible sac filled with a gel; a superposed layer of a foamed plastics material on one side of the sac, and an annular inflatable compartment registering with the boundaries of the gel sac on the side opposite the foamed plastics layer.

2. A flotation cushion according to claim 1 wherein the cover is constftuted y upper and lower panels sealed together around their peripheries; and the sealed flexible sac is sandwiched between them at the peripheral seal to constitute a transverse membrane.

3. A cushion according to claim 1 or 2 wherein the sealed flexible sac is formed by two similar transverse laminae both sandwiched around their peripheries within the peripheral seal of the outer cover panels and defining between them a central compartment.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. form the annular air cell 30. The valve 32 is secured in position before the peripheral bond is made. Each wall of the air cell 30 is composed of at least two sheets of PVC which are unconnected save at the peripheral bond and the local seam welds 34, 36 which define the annular cell 30. This loose ply structure has been found in practice to be more airtight than either a single sheet of the same thickness or a laminate of two sheets bonded together over their whole surface areas. The problem of airtightness arises initially because thin PVC sheet almost always has pinholes through which air can escape. By overlaying two sheets, the risk that two pinholes will coincide is very remote, so that an airtight seal can more reliably be formed by a two-ply sheet. However, surface bonding has been found to be an unreliable solution of the problem inasmuch as the plies or laminae can separate at random zones, and any one zone may span individual pinholes in the separate plies or laminae, thereby reestablishing the perviousness of the laminate. Another problem is also introduced by the surface-bonded laminate. This arises when a random zone of separation embraces a pinhole in the ply or laminae on the high pressure side. Air can seep into the zone of separation and, on the collapse of the cell or compartment bounded by the laminate, can become trapped. When the cell or compartment is repeatedly inflated and deflated, inexhaustible bubbles can be formed between the plies which become permanent deformations of the cell or compartment wall, disturbing both its shape and performance. By leaving the plies loose or separate, the pinholes in the outer or low pressure ply ensure that air can never be trapped between the plies so that each is free to act as a flap valve which seals the pinholes in the other, and airtight, bubble-free performance is obtained. In the particular construction of cushion illustrated in the drawings, air bubble problems have been encountered when using surface-bonded laminates for the walls of the air cell 30 in the zones of the lower compartment 26 outside the central zone exhausted by the permanent air vent 40. Bubbles have been found to form between the air cell 30 and the gel compartment 18 which have proved substantially impossible to exhaust and which have rendered the cushion unstable in use. A fairly average weight of S.C.M.C. gel in the sac 18 is 5 lb. The pad 24 can be 1/4-inch thick polyurethane or polyether foam, and the whole cushion can weight about 6 lb. By comparison with the construction described in the specification or our patent No. 1,508,830, the construction described above is cheaper to manufacture owing to the much reduced time involved by elimination of the girdle. It may, however, not prove to be so comfortable for those who are chairbound permanently or for long periods. The deeper and full-area air compartment in the girdled cushion of our above-numbered patent is specifically designed for such chronic cases, but its bulk when deflated and its cost are both significantly greater than those of a cushion according to the present invention. Although in the foregoing description of the design illustrated only the lower "pneumatic" compartment 26 is vented to atmosphere at 40, a similar vent can be provided for the upper insulation compartment 22. The edges of the sheets bounding the vent 40 may be sealed by radio frequency heating. The thickness of the thermally insulating pad 24 is determined primarily by the required rate of heat absorption by the gel in the sac 18 from the body of the sitter. Ideally, therefore, this thickness would be adjustable, but since a foamed plastics is the most suitable material for the purpose such adjustment at will is impracticable. In general, the thickness of the pad is chosen empirically, and is found to vary approximately directly as the volume of gel in the sac 18. The object is to remove excess body heat generated by a person sitting in the same position for long periods. The outer seam weld 34 of the annular air cell 30 can also be of the "multi-pocket" kind described and illustrated in respect of the inner weld 36. This method minimise the risk which is inherent in the conventional "tearseal" seam welding technique that the thinning of the sheets may become excessive, either locally or generally, leading to failure and bursting of the air cell. WHAT WE CLAIM IS:

1. A flotation cushion comprising a cover of flexible and relatively inextensible material enclosing a sealed flexible sac filled with a gel; a superposed layer of a foamed plastics material on one side of the sac, and an annular inflatable compartment registering with the boundaries of the gel sac on the side opposite the foamed plastics layer.

2. A flotation cushion according to claim 1 wherein the cover is constftuted y upper and lower panels sealed together around their peripheries; and the sealed flexible sac is sandwiched between them at the peripheral seal to constitute a transverse membrane.

3. A cushion according to claim 1 or 2 wherein the sealed flexible sac is formed by two similar transverse laminae both sandwiched around their peripheries within the peripheral seal of the outer cover panels and defining between them a central compartment.

4. A cushion according to claim 1, 2 or 3

wherein the inflatable compartment is constituted by a cell formed within the thickness of the outer bottom panel which underlies the gel sac.

5. A cushion according to claim 4 wherein the outer cover bottom panel is of multi-ply construction such that the plies are separate except where bonded around their peripheries or at local seams, and the inflatable annular cell is formed between walls each of which consists of two separate plies.

6. A cushion according to claim 4 or 5 wherein the plies forming the inflatable annular cell are intermittently bonded to each other to increase the lateral stability of the cell.

7. A cushion according to any preceding claim wherein the outer bottom panel is permanently vented to atmosphere in the zone surrounded by the inflatable annular compartment.

8. A cushion according to any preceding claim wherein the inflatable compartment has a pressure control valve for regulating the inflation pressure to suit the sitter's comfort.

9. A cushion according to any preceding claim wherein the laminae forming the transverse membrane are sealed together along a continuous line spaced inwards from the peripheral seal.

10. A cushion according to any of claims 4 to 8 wherein at least one seal defining the inflatable cell is formed under heat and pressure by an electrode having non-contiguous shallow dimples or pockets on its operative surface to accommodate material displaced by the other areas of the surface.

11. The method of seam-welding heatsealable plastics laminae for a flotation cushion according to any preceding claim wherein an area to be welded is compressed by an electrode having the desired contour of the weld and whose operative surface has noncontiguous dimples or shallow pockets formed wholly within the boundaries thereof.

12. A flotation cushion substantially as hereinbefore described with reference to the accompanying drawings.