[0001] This invention relates to cushioning articles.
[0002] 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.
[0003] According to the present invention, light-weight cushioning can be made from gas-filled
plastics or mineral enclosures, or mixtures of both, dispersed in a lubricant so that
movement of gas-filled enclosures within the lubricant is possible. This dispersion
of gas-filled enclosures is contained within a covering which is impermeable to the
lubricant, and which in turn may be covered by conventional upholstery materials.
[0004] Thus, the present invention 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.
[0005] The cushioning so produced will follow the body contours of a user, thus distributing
pressure evenly and providing greater comfort. The possibility of the development
of ischaemia (local deficiency of blood supply due to spasm 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.
[0006] 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.
[0007] The gas-filled enclosures may be made of any one or more of the following films,
foils or coatings:-
polyethylene, polypropylene, polyurethane, polyvinylidene chloride, plasticised polyvinyl
chloride, butyl rubber, polyester, polyamide, aluminium, chlorinated rubber or fluorinated
polymers.
[0008] It is preferred that it should be rubber-like/flexible. 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.
[0009] 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(9), 1052-8).
[0010] 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.
[0011] 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, alkali-soluble acrylics, gelatine, alginates, polyacrylamide, finely divided
'fillers', glass cenospheres or mineral cenospheres.
[0012] 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.
[0013] The impermeable covering constituting the envelope 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.
[0014] 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.
[0015] The impermeable covering may be reinforced e.g. by woven or non-woven fabrics of
artificial, or natural materials, or of glass.
[0016] 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 envelope 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 Standard for flammability.
[0017] 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.
[0018] Preferred embodiments of the present invention will be illustrated by way of the
following Examples:
EXAMPLE 1
[0019] Air-filled enclosures of 30 mm diameter were dispersed in a gel made to the following
formulation:-
20% by mass aqueous salt solution 100 p.b.w.
Hydrated magnesium silicate (i) 12 p.b.w.
Fumed silica (ii) 5 p:b.w.
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.
[0020] The viscosity of the gel, determined on a Brookfield viscometer model R.V.F, spindle
7 at 20°C. was:-
920 poise at speed 10
360 poise at speed 20
136 poise at speed 50
l14 poise at speed 100
[0021] This gel is strongly pseudoplastic.
[0022] The air-filled enclosures and gel were contained in a cover fabricated from a polyurethane/polyvinylidene
chloride/polyurethane laminate. The whole was encased in an outer cover comprising
polyester wadding and a flame-retardant fabric.
EXAMPLE 2
[0023] Air-filled enclosures of 25 mm diameter were dispersed in a gel made to the following
formation:-
Glycerol B.P. 100 . p.b.w.
Hydrated magnesium silicate (i) 5.25 p.b.w..
Fumed silica (ii) 3.75 p.b.w.
[0024] A suitable bactericide/fungicide was incorporated.
(i) and (ii): See EXAMPLE 1.
[0025] The viscosity of the gel, determined on a Brookfield viscometer model R V F spindle
7 at 20°C. was:-
1560 poise at speed 10
960 poise at speed 20
528 poise at speed 50
360 poise at speed 100
[0026] This gel is also strongly pseudoplastic.
[0027] 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
[0028] 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.
1. A cushioning article comprising a totally sealed, gas-impermeable flexible envelope
characterised in that the envelope contains:
(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 said gas-filled enclosures
(a) within the envelope.
2. An article according to Claim 1, characterised in that the lubricant (b) is a liquid.
3. An article according to Claim 1 or 2, characterised in that the lubricant (b) is
a liquid including one or more thickeners.
4. An article according to Claim 1, 2 or 3, characterised in that the lubricant (b)
is water containing one or more thickeners and sodium chloride.
5. An article according to Claim 1, 2 or 3, characterised in that the lubricant (b)
is a gel.
6. An article according to Claim 1, characterised in that the lubricant (b) is a powdered
solid material.
7. An article according to any one of the preceding claims, characterised in that
the gas-filled enclosures (a) consist essentially of discrete undivided bubbles.
8. An article according to any one of Claims 1 to 6, characterised in that the gas-filled
enclosures (a) consist essentially of discrete spheres of a cellular material.
9. An article according to any one of the preceding claims, characterised in that
the enclosures are air-filled.