EP0200822B1

EP0200822B1 - Cushioning articles

Info

Publication number: EP0200822B1
Application number: EP19850302540
Authority: EP
Inventors: Janet Parker
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-11-28
Filing date: 1985-04-11
Publication date: 1990-04-11
Also published as: GB2150431B; GB8429384D0; GB2150431A; EP0200822A1

Description

This invention relates to cushioning articles.
Until now, cushioning has been made of springs, foam rubbers, polyurethane foam, rubber straps, horse-hair, artificial fibres, wadding, felt, air inflated bags, silicone fluid/rubber filled bags etc. or combinations of these. There are also waterbeds. Cushions are available, made from plastics containers filled with a high viscosity liquid/gel, which may contain mineral cenospheres, or foamed polystyrene beads, but these cushions are heavy, not always low in flammability, and relatively expensive.
According to the present invention, light-weight cushioning article can be made from flexible gas-filled plastics or mineral enclosures, or mixtures of both in an envelope. Being flexible, the enclosures distort under load to transmit load across the article.
A cushion of this nature has been seen in GB-A-1465817 where individual enclosures contained within a permeable envelope have flexible walls. If this cushion was to retain its shape under load, the enclosures were to be adhered or cohered together; however, they might try to escape sideways away from the point of compression.
According to the invention, relative movement of the enclosures within the envelope is assisted, so they can redistribute themselves under load, by the presence in the gaps between the enclosures of a lubricant. This dispersion of gas-filled enclosures is contained within an envelope which is impermeable to the lubricant, and which in turn may be covered by conventional upholstery materials.
In US-A-3407406 the redistribution of essentially rigid microscopic spherical particles is assisted by the presence of a lubricant.
The present invention is defined in claim 1. It provides a cushioning article comprising a totally sealed gas-impermeable flexible envelope containing

(a) a plurality of discrete, relatively movable gas-filled enclosures bounded by respective permanent flexible walls; and
(b) a lubricant to facilitate the relative movement of the gas-filled enclosures within the envelope.

The cushioning so produced will follow the body contours of a user but will also be resilient due to the distortion of the individual enclosures, thus distributing pressure evenly and providing greater comfort. The possibility of the development of ischaemia (local deficiency of blood supply due to sperm or obstruction of an artery), and decubitus ulcers (pressure sores or ulcers relating from pressure on parts of the body in persons confined to bed for a long time, or needing to sit, for example, in wheelchairs, for long periods), is reduced.
The gas-filled enclosures (which may, for example consist essentially of discrete undivided bubbles or discrete spheres of a cellular material) may contain a non-flammable gas such as nitrogen, carbon dioxide or helium. Alternatively, they may contain air.
The gas-filled enclosures may be made of film foils or coatings of any one or more of the following:-

polyethylene, polypropylene, polyurethane, polyvinylidene chloride, plasticised polyvinyl chloride, butyl rubber, polyester, polyamide, aluminium, chlorinated rubber or fluorinated polymers.

The gas-filled enclosures may consist wholly of any one of the aforementioned materials. Alternatively, the gas-filled enclosures may comprise a laminate of two or more of the materials or a coating of one on another.
The diameter of the gas-filled enclosures is preferably between 5 microns and 50 mm. The enclosures may be spherical, but can be other shapes, e.g. ellipsoidal. It has been found that a mixture of various sizes of gas-filled enclosures will minimise the mass of lubricant needed, and save weight in the cushion. For example, if spherical enclosures of 30 mm diameter are used, they will only occupy about 50% of the total envelope volume, and proportions of smaller-diameter spherical enclosures can be incorporated in the spaces, thus reducing the volume of lubricant needed (see Furnas, Ind. Eng. Chem. 1931, 23(9J, (1052-8).
The lubricant in which the gas-filled enclosures are dispersed must have a low coefficient of friction and must flow. The lubricant may be a liquid, e.g. water, aqueous salt solution, polyhydric alcohols, natural or synthetic mineral or silicone oils or greases, the liquid optionally being thickened to give a pseudoplastic gel. Alternatively, the lubricant can be a finely-divided solid (e.g. natural silicates of plate-like structure such as talc), graphite, molybdenum disulphide or derivatives of long-chain organic materials having a plate-like structure (e.g. stearic acid and calcium stearate), soft waxes, fluorinated polymers (e.g. polytetrafluoroethylene) or mixtures of these materials. Regard should be had to the fact that some of the above-mentioned lubricants are less desirable than others because of inherent flammability and/or the possibility of the evolution of toxic gases when burning.
The rheology of the liquid lubricant may be altered by using thickeners or thixotropic agents known to those skilled in the art, e.g. clays, gaseous-produced silicas, cellulose ethers, alkalisoluble acrylics, gelatine, alginates, polyacrylamide, finely divided 'fillers', glass cenospheres or mineral cenospheres.
A preferred lubricant for use in this invention is a 20% by weight aqueous sodium chloride solution, thickened by means of clays, gaseous-produced silicas or cellulose ethers. At -20°C a 25% by weight saline solution is still fluid, but a 20% by weight saline solution forms a slush at this temperature. Any lower proportion of salt in the solution produces a solid at this temperature. We have found that this lubricant gives good low- temperature properties, low flammability, low order of toxicity and low cost.
The impermeable covering constituting the enyelope may be made of any one or more of the materials mentioned hereinbefore. It is preferred that the envelope should be rubber-like/flexible, without being so brittle as to be noisy in use.
The envelope may be sealed by means of radiofrequency, heat-sealing or thermoforming in the configuration most suitable for the intended use of the cushioning article and/or to reduce volume and weight. Alternatively, the envelope can, in appropriate cases, be formed by rotational casting or blow-moulding.
The impermeable covering may be reinforced e.g. by woven or non-woven fabrics of artificial, or natural materials, or of glass.
Suitable laminates/coatings for the envelope include the following:

polypropylene to polyester to polypropylene
polyethylene to polyester to polyethylene
polypropylene to aluminium to polypropylene
polyethylene to aluminium to polyethylene
polyurethane to aluminium to polyurethane
polyester to aluminium to polyester

polyurethane to polyvinylidene chloride to polyurethane
polyester to polyvinylidene chloride to polyethylene
The outermost covering of the envlope may be of any standard upholstery fabric or sheepskin, or leather or leathercloth and may be wholly or partly lined with materials such as polyester wadding or polyurethane foam. The outermost covering may be made to conform to the appropriate British Standrd for flammability.
Amongst the applications for cushioning articles according to the present invention are:
wheelchair cushions, orthopaedic seating, invalid car seats, pressure support products such as rings, heel and elbow pads, hospital mattresses, aircraft seats, helicopter seats, seats for buses, cars, fork-lift trucks, lorries and vans, for agricultural vehicles and heavy plant, in domestic and office furniture, kneeling pads, and in shock absorbing pads for equipment.
Preferred embodiments of the present invention will be illustrated by way of the following Examples:

Example 1

Air-filled enclosures of 30 mm diameter were dispersed in a gel made to the following formulation:-
A suitable bactericide/fungicide was incorporated.

(i) Available under the Registered Trade Mark PANGEL S.
(ii) Available under the Registered Trade Mark CAB-O-SIL M-5.

The viscosity of the gel, determined on a Brookfield viscometer model R.V.F. spindle 7 at 20°C, was:-
This gel is strongly pseudoplastic.
The air-filled enclosures and gel were contained in a cover fabricated from a polyurethane/poly- vinylidene chloride/polyurethane laminate. The whole was encased in an outer cover comprising polyester wadding and a flame-retardant fabric.

Example 2

Air-filled enclosures of 25 mm diameter were dispersed in a gel made to the following formation:-
A suitable bactericide/fungicide was incorporated. (i) and (ii): See Example 1.
The viscosity of the gel, determined on a Brookfield viscometer model R.V.F. spindle 7 at 20°C, was:-

This gel is also strongly pseudoplastic.

The air-filled enclosures and gel were contained in a cover fabricated from polyvinylidene chloride/polyester/polyethylene laminate. The whole was encased in an outer cover comprising polyester wadding and a flame-retardant fabric.

Example 3

Air-filled plastics enclosures of 30 mm diameter were dispersed in powdered graphite, and contained in a cover fabricated from a polyurethane film. The whole was encased in an outer cover comprising polyester wadding and a flame retardant fabric.

Claims

1. A cushioning article comprising a closed volume defined by a flexible envelope within which is a plurality of separate, individually- relatively-movable gas-filled enclosures bounded by respective permanent flexible walls; the enclosures being elastically compressible to transfer load across the article characterized in that there is a lubricant in the volume between the enclosures whereby to assist redistribution of the enclosures by relative movement within the envelope in response to a load, and the envelope is totally sealed and impermeable to the lubricant.

2. A cushioning article according to claim 1 wherein the permanent flexible walls of the enclosures are a film foil or coating.

3. A cushioning article according to claim 2 wherein the film foil or coating is of one or more of the following materials:

4. An article according to any one of the preceding claims in which the lubricant is a pseudoplastic gel.

5. An article according to claim 4 wherein the viscosity of the gel is between 920 and 1560 poise at speed 10, and 114 and 360 poise at speed 100, all as measured on a Brookfield viscometer model R.F.V. spindle 7 at 20°C.

6. An article according to any one of the preceding claims in which the lubricant is water containing one or more thickeners or thixotropic agents and sodium chloride.

7. An article according to claim 6 wherein the lubricant is a 20% wt. sodium chloride solution containing one or more clays, gaseous-produced silicas or cellulose ethers.

8. An article according to claim 1 in which the lubricant is a powdered solid material.

9. An article according to any one of the preceding claims, in which each gas-filled enclosure is discrete and encloses a discrete undivided volume of gas.