GB2201589A - Cushioning structure - Google Patents

Abstract

A cushioning structure, e.g. for seat cushions, mattresses, carpet underlay, etc., has an air-filled envelope (1) of gas permeable plastics film enclosing a spring formed by a block of plastics foam (4). Gas escapes gradually from the envelope when it is subject to a load, and after the load is removed the spring which itself serves no load supporting function, expands the envelope to restore its initial shape and to cause gas to enter to replace that which had escaped. <IMAGE>

Description

Cushioning Structure This invention relates to cushioning structures.

A wide variety of manufactured products incorporate some form of cushioning and as examples there may be mentioned seat cushions, mattresses, cushion linings for shoes, carpet underlay and backing for floor coverings.

There are known cushion and mattress supports consisting of an outer cover or enclosure filled with a large number of substantially elastic spheres which may or may not be capable of moving freely relative to each other within the enclosure. According to some specific proposals the spheres may take the form of hollow spheres of plastics film, or solid foam spheres, and a liquid or solid lubricant can be employed to facilitate relative movement between the spheres if that is required. Thus, US-A-4027888 describes a seating unit consisting of a flexible covering, such as an upholstery fabric, loosely filled with a freely flowable filler consisting of spherical beads of expanded polystyrene, possibly coated or impregnated with a lubricant.

Disclosed in GB-A-2150431 is a cushioning article in which a flexible enclosure contains a plurality of gasfilled, flexible-walled spheres dispersed within a lubricant. These forms of cushion have the ability to conform to the shape of a person sitting or lying on them so that the pressure exerted against the body is more evenly distributed and localised areas of increased pressure are averted. Consequently, comfort to the user is enhanced. However, there is a tendency for the spheres filling the cushions to collapse over long term use. In the case of solid spheres, e.g. of polystyrene foam they may become permanently deformed. If this is countered by giving them a closed cell structure or greater rigidity less comfortable support is achieved, especially for spheres having a diameter greater than about 5 mm.

With gas-filled spheres of plastics film collapse is due to a loss of gas from within them. When a load is applied the spheres deform and the enclosed gas is compressed to support the load. Because plastics films are generally gas permeable to some degree, gas permeates through the sphere membrane under the positive internal pressure. When the load is subseqlsently removed there is limited elastic recovery of the sphere to its initial shape and the escaped gas is not replaced.

Eventually, whether due to continuous or repeated compressive loading, all the gas will become expelled and the sphere will be flattened with the result that it is no longer capable of providing cushioned support. The loss of gas from the spheres is an irreversible process suffered by all spheres made of Fas permeable plastics films. It may be very slow in the case of films having relatively low gas permeability, such as PVdC coated polypropylene or nylon/polyethylenelaminates, but it is nevertheless significant having regard to the expected useful lifetime of a cushioning article.

As a solution to the above drawbacks, the present invention proposes a cushioning structure comprising at least one gas-filled envelope, at least a portion of the envelope being of flexible material whereby the envelope is adapted to deform under an applied load to compress the gas within the envelope, the envelope material having some permeabrlity to gas so that gas escapes gradually when the envelope is compressed, and resilient means within the envelope for acting thereon to expand the envelope after an applied load has been removed, thereby to cause gas to enter the envelope from the ambient atmosphere to replace the escaped gas, the resilient means exerting such a light force on the envelope that the support given by the envelope to an applied load is substantially wholly due to the gas pressure within the envelope.

The inclusion of the resilient means ensures that the gas filled enclosure will not become irreversibly deflated when a load is applied, and the performance of the cushioning structure during the course of time will be substantially independent of the degree of gas permeability of the envelope.

It is an important feature of the invention that the resilient means exerts only a light restoring force against the walls of the enclosure and does not make any substantial contribution to the support given to an anplied load. This ensures that the characteristic cushioning support of the gas-filled envelope will not he deleteriously affected. However, the resilient means which deforms resiliently to accommodate the viscoelastic deformation of the gas-filled envelope under an applied load, will upon removal of that load, act on the envelope internally so that, in due course, it will resume its original state of shape, volume and gas content. The expansion of the envelope causes gas from the ambient atmosphere to enter through the gas permeable envelope for replacing the gas which had previously escaped.

The resilient means could be a conventional metal coil spring or any other known spring. Especially convenient is a spring of plastics foam, either as loose crumbs or chopped pieces, or as a single block of foam which is shaped to fill the envelope. Alternatively, a foam spring could be integral with the envelope and be formed in situ.

The envelope preferably consists entirely of plastics film, and it can conveniently be made by sealing together two films or sheets of plastics material with the resilient means interposed therebetween. At least one of the sheets may be subject to a shaping process, such as by vacuum forming before the sheets are sealed together. The normal or undeformed shape of the envelope is unimportant and may be chosen according to convenience and ease of manufacture. The envelope can for example take the form of a sphere, hemisphere, cylinder or sachet. Furthermore, the size of the envelope can be varied within wide limits to suit the particular use of the cushioning structure. Thus, the envelope diameter may range from about 5 mm to several metres or more.

The cushioning structure may include a large number of separate,relatively movable gas-filled enclosures contained within a cover, which may be appropriate for a cushioning article such as a seating cushion or mattress. Alternatively, a large number of the gasfilled enclosures may be connected together in a fixed array to provide a cushioning sheet.

In any practical embodiment the properties of the enclosure materials will be selected so that in normal use of the product the periods during which it is subject to loading and free from loading are such that the enclosure should recover its shape and volume fully after each use. Also, for some products, such as a mattress, it is desirable that not more than about 1o' of the gas in the enclosure be expelled during a normal period of use. The rate of expulsion of gas depends on several factors such as the gas permeability of the envelope, the load applied, the temperature and the viscoelastic nature of the envelope material. Similarly, the time required for the original condition of the envelope to be restored after deformation will depend on, inter alia, the resilience of the resilient means1 the gas permeability of the envelope and the temperature.

Under normal conditions of use the time taken for a substantial part of the gas within the envelope to become expelled should he considerable. Typically it might be in the order of 1 day for enclosures made of some grades of low density polyethylene films, but even this relatively short time would be satisfactory for some cushioning structures which in normal use are subject only to comparatively short term loading. At the other end of the range, a year or more would be required for enclosures made of barrier films such as those made from nylon, although in general the time will be substantially less than the expected useful lifetime of the product incorporating the cushioning structure, which for cushions and mattresses would be in the order of 5 to 15 years.

Nost conveniently the gas filling the enclosures is air. Other gasses could, however, be used if required.

However, since gas is repeatedly expelled and drawn in from the surrounding atmosphere special steps would need to be taken to ensure that a particular filling gas other than air does not become gradually replaced by air.

The cushioning structure of the invention may be plied to many different manufactured products, examples of which are seating, cushions and mattresses for medical and non-medical uses, cushion linings and pads for use in footwear, and underlay or hacking for carpets and other floor coverings.

Further description and explanation of the invention will now be given with reference to the accompanying drawing, in which: Figure la shows in cross-section a gas-filled enclosure of a cushioning structure embodying the invention; Figure 2a shows the gas-filled enclosure subject to an applied load; Figure 3a shows the gas-filled structure after removal of the load; and Figures Ib, 2b and 3b are corresponding views of a gas-filled enclosure not having any resilient means.

Illustrated in Figure Ia is an air-filled plastic film enclosure 1 shaped as a hemisphere. The enclosure is made from two sheets of low density polyethylene, one of which is vacuum formed to provide a dome 2 with a peripheral flange 3. A light spring in the form of a rectangular block of plastics foam 4 is inserted into the dome and the flange 3 is heat sealed to the second sheet of film 5 to complete the hemispherical enclosure.

The gas-filled hemisphere shown in Figure 1b is made in the same way except the foam spring is omitted.

When the hemispheres are subject to a load, applied by a weight W as shown in Figure 2, their domes become flattened. The internal volume of the enclosures is reduced and hence the pressure of the gas within them is increased above that of the surrounding atmosphere.

The gas pressure supports and cushions the load. Under this loaded condition air passes very gradually but continuously out through the gas permeable film walls of the hemispheres, and the hemispheres gradually collapse as the air escapes, to maintain the internal pressure.

If the load were applied for long enough the hemispheres would become completely flattened and would no longer support the load. In this load supporting respect the two illustrated hemispheres perform essentially the same as the foam spring 4 does not make any significant contribution to the support of the load obtained by the gas pressure.

When the load is removed, the hemisphere of Figure 1b will expand only by the amount necessary to equalise the pressures inside and outside of the flex ib]e walled enclosure and it will retain partly its deformed configuration, as illustrated in Figure 3b.

In the case of the hemisphere embodying the invention However, the foam spring 4 acts on the inside wall of the enclosure 1 causing it to expand and hence the pressure within it to fall below that of the surrounding atmosphere so that air passes through the gas-permeable film wall into the enclosure, thereby replacing the air which had previously escaped. After a certain time the enclosure is restored to its original shape, volume and air content, as illustrated in Figure 3.

From the foregoing it will be apparent that the gas-filled enclosures including resilient means according to the invention have the same load supporting and cushioning properties of solely gas-filled enclosures, hut will retain those properties over greater time periods.

Some specific examples of structures according to the invention will now be described.

Example 1.

Two hemispheres as shown in Figures la and lb were made from 80,u thick low density polyethylene films.

The vacuum formed dome had a diameter of 2.5 cm and a 3 mm flange which was heat sealed to the flat sheet. A 1.5 cm cube of polyether foam was included in one hemisphere.

Each hemisphere was loaded intermittently in compression with a 2 kg weight. The load cycle in each case was 24 hours on and 24 hours off. After 10 davs the hemisphere without the foam spring had completely lost its air cusion support but the hemisphere containing the spring continued to provide air cushion support even after 100 days.

Example 2.

Two 2.5 cm diameter hemispheres were vacuum formed from a laminate of 30/u nylon 6 and 40/u high density polyethylene with the polyethylene inside. A 2.5 cm cube of polyether foam was inserted hetween the two hemispheres, which were then heat sealed together to form a sphere. An identical sphere was made without a foam spring. The spheres were repeatedly loaded with 2 kg weights for 48 hours with similar unloaded intervals. After 100 days, the sphere without a foam spring had lost much of its air and no longer performed satisfactorily as a cushion, whereas the sphere containing the foam spring showed no significant loss of cushioning properties.

Example 3.

A regular array of 2.5 cm diameter hemispherical formings made from 30/u nylon high density polyethylene laminate film were filled with a light spring foam and sealed with a similar laminate film to produce a 1 sq metre regularly spaced array of hemispheres with the properties described in Example 2. The material was shown to be useful, for example, as a floor covering.

Claims (9)

CLAI'!S:

1. A cushioning structure comprising at least one gas-filled envelcpe, at least a portion of the envelope being of flexible material whereby the envelope is adapted to deform under an applied load to compress the gas within the envelope, the envelope material having some permeability to gas so that gas escapes gradually when the envelope is compressed, and resilient means within the envelope for acting thereon to expand the envelope after an applied load has been removed, thereby to cause gas to enter the envelope from the ambient atmosphere to replace the escaped gas, the resilient means exerting such a light force on the envelope that the support given by the envelope to an applied load is substantially wholly due to the gas pressure within the envelope.

2. A cushioning structure according to claim 1, wherein the resilient means comprises a plastics foam.

3. A cushioning structure according to claim 2, wherein the resilient means comprises a single block of plastics foam.

4. A cushioning structure according to claim 1, 2 or 3, wherein the envelope is formed of plastics film material.

5. A cushioning structure according to claim 4, wherein the envelope is formed by sealing together two plastics films.

6. A cushioning structure according to claim 5, wherein at least one of the plastics films is subject to a shaping process before the films are sealed together.

7. A cushioning structure according to claim 6, wherein the shaping process is vacuum forming.

8. A cushioning structure according to claim 5, 6 or 7, wherein the films are heat sealed together.

9. A cushioning structure according to claim 1 and substantially as herein described.