GB2034169A - Improved articles of footwear - Google Patents

Abstract

A shoe embodies a pneumatically inflated insert (10) having a multiplicity of chambers (13) encapsulated in a yieldable foam mass (14). The inflated insert has surface irregularities (peaks and valleys) and the foam mass (14) fills in the valleys. The encapsulated insert can be an integral composite sole having an outsole (16) secured thereto. The insert (10) is initially filled with a gas which is effectively unable to escape therefrom, but is permeable to air which enters the insert and accomplishes a self-pressurizing function. <IMAGE>

Description

1 GB 2 034 169 A 1

SPECIFICATION Improved articles of footwear

The present application is divided out of my copending Patent Application No. 7912998.

This invention relates to improved articles of footwear, and in particular to such articles which are inflatable. Preferred footwear articles embodying the present invention are self inflating devices which, when disposed in surrounding air at atmospheric pressure of e.g. 14.7 psia, exhibit the ability of extracting energy from the ambient air to raise the level of pressure within the device.

Thus, the present invention provides a structure to form part of a shoe, comprising a sealed sole member of elastomeric material providing a plurality of chambers inflatable with a gaseous medium under pressure to a desired initial value, and an elastomeric yieldable outer member encapsulating the said sole member, the latter having peaks and valleys in its upper and lower surfaces, and the outer member filling the valleys in the said upper surface.

Preferably, the sole member exhibits the phenomenon of "diffusion pumpingor-self pressurization when exposed to the atmosphere.

This phenomenon can be described in simple terms in the following way. With the present invention, the gas used for initially inflating the sole member is different from ambient air surrounding the device, or, it is at least partly different from the ambient air surrounding the device. The inflating gas (herein called 11 supergas") is selected from a group of gases having large molecules and low solubility coefficients, such gas exhibiting very low 100 permabilitles and an inability to diffuse readily through the elastomeric material forming the sole member. With the elastomeric material exposed to ambient air, it is noted that the pressure within the chambers rises comparatively rapidly after initial inflation. The rise in pressure is believed to be due to the nitrogren, oxygen and argon in the ambient air diffusing through the elastomeric material to its interior, until the partial pressure of air in the chambers equals the atmospheric pressure 110 outside the chambers. Since the initial inflating gas can diffuse out through the elastomeric material only very slowly, losing essentially no pressure, while the ambient air is diffusing inwardly, the total pressure within the chambers thus rises appreciably. Such total pressure is therefore the sum of the partial pressures of the air within the chambers and the pressure of the initial inflating gas within the chambers.

In some instances, the pressure rises above the 120 initial inflation pressure during the first two to four months of the diffusion pumping action, and then slowly starts to decline. When the total pressure rise reaches its peak level, diffusion pumping has progressed to the point that the partial pressure of 125 air within the device has reached its maximum possible value of 14.7 psia. At this point in the process, two important things have occurred. First, the device is now filled with a maximum amount of pressurizing medium (air) which cannot diffuse out of the device, because the pressure of the inside air is in equilibrium with the outside ambient air, i.e., both are at 14.7 psia. Second, the supergas pressure is now less than it was at initial inflation, primarily because of the increase in volume of the device due to stretching of the elastomeric film. At the lower pressure, the normally very low diffusion rate of the supergas is reduced to even lower values. Both of these two factors, i.e., maximum air at equilibrium pressure and minimum supergas, contribute to long term pressurization at essentially constant pressure.

This pressurization approach is referred to herein as the "Permanent Inflation Technique".

After the pressure reaches a peak, the rate of decline is very low, the total pressure in the device remaining above the initial pressure for about two years or longer thereafter, depending upon the particular inflation gas used, the elastomeric material and the inflation pressure. As noted above, the decline in pressure may continue, but in view of the slow rate of diffusion of the gas from the chambers, the pressure in the chambers, remains sufficiently high as to enable the sole member to continue to be used effectively for several additional years. The sole member is therefore essentially permanently inflated.

Prior elastomeric pneumatic devices for footwear are usually inflated. by air to a desired initial pressure above ambient pressure. In these devices the air can diffuse out quite rapidly with or without use, and the device quickly goes "flat" and becomes useless. In addition, in many cases the elastomeric material stretches under pressure thereby enlarging the internal volume and increasing the rate at which the device becomes unserviceable. Also, load applied to the devices further increases the air pressure there-within thereby accelerating the outward diffusion of a portion of the air through the elastomeric device and producing an even more rapid decrease in the pressure below its initial pressure when the load is removed. Repeated application and removal of the load results in a progressive decrease of the internal air pressure, the inflated device very quickly losing its utility. Most gases (other than supergases) behave in a similar manner, the pressure in a pneumatic device progressively decreasing to a very low value over relatively short time periods.

With a device of the present invention, not only are the chambers eventually permanently inflated, as described above, but diffusion pumping helps maintain substantially constant pressure therein even though the internal volume may increase due to stretching of the elastomeric material. When such a volume increase occurs, additional ambient air diffuses into the chambers and maintains the air pressure irrespective of volume increases. Further, diffusion pumping can maintain the internal pressure at a relatively constant level when the device is subjected to repeated application and removal of external loads, as described in more detail below.

2 GB 2 034 169 A 2 As may be seen, therefore, the present invention more specifically provides a self inflating footwear device which device is partially or entirely filled to less than fully distended volume with one or more of the special supergases, and in 70 which the pressure within the device increases above the pressure to which the device was initially inflated, without resorting to decreasing the volume of the device or mechanically injecting any additional gaseous medium into the device.

The present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a top plan view of a self-inflating insole embodying the invention; Figure 2 is a section taken along the line 2-2 of Figure 1. the insole being made of thin elastomeric film or sheet material and disclosing tubular chambers of the insole inflated and encapsulated in a shoe midsole; Figure 3 is a graph representing pressures within intercommunicating chambers of Figures 1 and 2 over a period of time, in which different gases are used to initially inflate the chambers; Figure 4 is a graph, on an enlarged scale, of part 90 of the left-hand portion of Figure 3; Figure 5 is a graph representing the pressure within the intercommunicating chambers of Figures 1 and 2 over a period of time, the insole being made of different elastomeric materials and inflated initially with the same gas (C2F.); Figure 6 is a graph similar to Figure 5 illustrating the relatively faster rate at which nitrogen diffuses through representative polymer films; Figure 7 is a graph showing the diffusion pumping of the. elastomeric chambers due to reverse diffusion of air into the chambers; and Figure 8 is a bar chart showing percent pressure rise due to diffusion pumping inconstant 105 volume enclosures initially filled with a special gas at several different pressures.

Referring now to the accompanying. drawings, in Figures 1 and 2, an insole construction useful in footwear is illustrated. A pair of elastomeric, 110 permeable sheets 10, 11 are sealed together at desired intervals along weld lines 12 to form intercommunicating chambers 13 which are later inflated with a gas, or a mixture of gases, to a prescribed pressure above atmospheric. When the 115 chambers 13 are inflated, the insole exhibits peaks and valleys in its upper and lower surfaces, as will be clearly apparent from Figure 2. The gas or gases selected have very low diffusion rates through the permeable sheets to the exterior of the chambers, the nitrogen, oxygen, and argon of the surrounding air having relatively high diffusion rates through the sheets into the chambers, producing an increase in the total pressure (potential energy level) in the chambers, resulting 125 from diffusion pumping or self-pressurization, which is the addition of the partial pressures of the nitrogen, oxygen, and argon of the air to the partial pressure of the gas or gases in the chambers.

By means of the concurrent processes of 130 diffusion pumping and permanent inflation technique, the insole has a useful life of over five years.

The insole is embedded within compressible encapsulating material 14, such as a compressible polyurethane foam, to form a midsole 15, said foam depending into and filling the valleys in the upper surface of the insole, as shown in Figure 2.

An outsole 16 is secured to the midsole as shown.

Inflation tests conducted over a five year period on chambered insole constructions, such as illustrated in Figures 1 and 2, in which the chambers 13 were pressurized with various large molecule low solubility coefficient gases, are shown in the graphs of Figures 3 and 4. The curves were arrived at by plotting pneumatic pressure above atmospheric against time, the sheets 10, 11 used in making the insole being polyurethane. In curve A, the inflation gaseous medium was hexafluoroethane (CJ,), in which the initial inflation pressure was 20 psig. It should be noted that the pressure within the chambers first dropped slightly over a period of about one week and then began rising, reaching a maximum pressure in a little over three months of about 23.6 psig. The initial fall in pressure is believed to be due to the initial incrase in volume of the chambers 13 as a result of tensile relaxation of the elastomeric material. After reaching a peak, the pressure then declines very gradually, having a value of about 21 psig after a total elapsed time of two years. The maintenance of the pressure over such an extended period is believed to have been due to the inward diffusion of nitrogen, oxygen, and argon into the chamber of the insole made of polyurethane.

The results of inflation tests using other large molecule inflation gases are shown in curves B, C, D, E, F, G and H, the specified gases being indentified on each curve. In each case, the pressure at first increased and then declined at a very low rate. In curve B, depicting inflation with sulfur hexafluaride (SF,), the pressure within the chambers dropped to about 20 psig after two years. Octafluorocyclobutane (C3F.), curve C, had declined in total pressure to 20 psig after one year and to about 16. 5 psig after two years. The gas of curve D declined to 14 psig after two years. Where the decline in a period of two years drops below 20 psig, as in curves C and D, the total pressure remaining in the enclosures was still adequate to properly support the foot of the wearer.

As contrasted with the gases shown in curves A to H, inclusive, the gases shown at the left portion of Fig. 3 lost pressure relatively rapidly. The lower left end portion of Fig. 3 is shown on a greatly enlarged scale on the graph, Fig. 4. In each case, the polyurethane enclosures were inflated to 20 psig. Chambers inflated with hydrogen, nitrous oxide, carbon dioxide or oxygen lost all of their pressure within 10 to 40 hours, the chambers becoming "flat" or fully deflated. The chambers inflated with Freon 22 (CI-ICIFJ lost all of their pressure within about three days, xenon, argon -t 3 GB 2 034 169 A 3 and crypton within less than six days, Freon 12 (CCI,F2) within 18 days, and methane (CH4) within 22 days. The chamber initially inflated to 20 psig with nitrogen lost pressure, which declined to a little more than 2 psig after 40 days. In all 70 these cases, the initially inflated chambers became ineffective over relatively short periods of time, when compared with the pressure retentions in the chambers when inflated with the gases shown in curves Ato H, inclusive, of Fig. 3.

The gases used for initially inflating the elastomeric insole are incapable of diffusing outwardly from the chambers except at an exceedingly slow rate. These gases are hereinafter sometimes referred to as "supergases". They include the following: hexafluoroethane, sulfur hexafluoride, perfluoropropane, perfluorobutane, perfluoropentane, perfluorohexane, perfluoroheptane, octafluorocyclobutane, perfluorocyclobutane, hexafluoropropylene, tetrafluoromethane, monochloropentafluoroethane, 1,2-di-hforo-tetrafluoroethane; 1,1,2-trichloro-1 2,2 trifluoroethane, chlorotrifluoroethylene, bromotrifluoromethane, and monochlorotrifluoromethane.

The supergases have the following common characteristics: unusually large macromolecules, very low solubility coefficients, inert, non-polar, uniform/sym metric, spherical, speroidal (oblate or prolate) or symmetrically branched molecular shape, non-toxic, non-flammable, non-corrosive to metals, excellent dielectric gases and liquids, high level of electron attachments and capture capability, man-made, exhibit remarkably reduced rates of diffusion through all polymers, elastomers 100 and plastics (solid film). Normally, as gas, liquids, or vapor molecules become larger, they also become more polar. The opposite is true with the supergases. They are among the least polar and most inert of all gases.

Typical sheets or films for producing the insoles and which function properly with respect to the supergaseS, Gan be selected from the group of elastomeric materials consisting of: polyurethane, polyester elastomer, fluoroelastomer, chlorinated polyethylene, polyvinyl chloride, chlorosulforiated polyethylene, polyethylene/ethylene vinyl acetate copolymer, neoprene, butadiene acrylonitirile rubber, butacliene styrene rubber, ethylene propylene polymer, natural rubber, high strength ' silicone rubber, low density polyethylene, adduct rubber, sulfide rubber, methyl rubber, and thermoplastic rubber.

In the curves shown in Figs. 3 and 4 diffusion rates of supergases are set forth through polyurethane. In Fig. 5 a graph is presented showing the diffusion rates of hexafluoroethane through a variety of representative polymer films.

To obtain the data for each curve, each chamber was pressurized to 20 psig. As shown in curve A, a 125 pressure increase of 8 psig was obtained in about five months, where the material forming the chambers was urethane coated nylon cloth, the pressure dropping to a total pressure of about 27.4 psig in about two years. Pressure increases 130 to maximum values about 20 psig and subsequent pressure decreases are also depicted in curves B, C, D, E and F for the materials identified thereon. Within two years the total internal pressure was still in excess of the initial pressure of 20 psig. The pressure inside chambers made from polymer films identified against curves G, H, 1, J, K and L all increased to some extent above the initial pressure of 20 psig, but then declined from the greater pressure to below 20 psig as indicated in the graph.

Fig. 6 is a graph on an expanded scale showing the diffusion rate of nitrogen, initially under a pressure of 20 psig, through representative polymer films identified in the graph. The comparatively high rate of diffusion of nitrogen through the films results in the pressure of the remaining nitrogen gas in the chamber being substantially at zero gage within a maximum period of two months, except for the PVDC and Butyl, shown in curve M of Fig. 6.

The diffusion pumping phenomenon is strikingly clemonstratec( in elastomeric enclosures which are initially inflated to low pressure levels. For example, the pressure rise in an insole initially inflated to 1.0 psig with a supergas, such as hexafluoroethane, is shown in Fig. 7 curve 1. This particular insole was made from a relatively elastic material which caused the insole to grow 40% to 50% in volume as the internal pressure increased, the pressure rising about 550% during a six to eight week period. If the diffusion pumping had occurred in a constant volume enclosure made from one of the special elastomeric materials shown in the upper curves of Fig. 5, the pressure rise would have been even greater, i.e., 1420% (curve 2 of Fig. 7).

The bar charts of Fig. 8 illustrate the percent pressure increases which are possible in constant volume enclosures made from the special elastomeric materials and filled initially with 100% supergas at the gage pressures indicated. As the bar charts shown, a large percentage increase in gage pressure occurs due to diffusing pumping. The maximum increment in pressure rise is 14.7 psi, which occurs at the conclusion of the diffusion pumping action when a maximum amount of air has diffused into the enclosure. Because this increment is constant irrespective of the initial gage pressure when the initial gage pressure is low, the percentage rise in pressure is high. For instance, a percentage rise of 1420% occurs when the initial inflation pressure is 1.0 psig. The rise is 2940% when the initial pressure is 0.5 psig. The corresponding increase is 147% for an initial pressure of 10.0 psig.

The diffusion of the ambient air into an insole inflated initially with a supergas is well supported by an anlaysis of the gases in an insole of the type illustrated in Fig. 1, and which was initially inflated December 10, 1975, to a pressure of 22 psig with pure suffur hexafluoride gas. On January 24, 1978, or slightly more than two years after the initial inflation, the pressure in the insole was checked and was found to be 19. 5 psig. In the 4 GB 2 034 169 A 4 approximate elapsed time of two years, the insole increased in thickness by about 15.3%, indicating that the volume of the chambers in the insole had increased. Had the volume remained constant, the pressure in the insole after approximately two years would have been greater than the measured pressure of 19.5 psig.

The gases in the above insole were analyzed by mass spectroscopy in the latter part of January, 1978. The analysis showed that the insole contained 52% air by volume (nitrogen, oxygen, and argon in the same ratio as - thse elements appear in ambient air), 47% sulfur hexafluoride by volume, and 0.6% carbon dioxide by volume.

Whereas, the gas initially introduced into the insole chambers was 100% sulfur hexafluoride, the analysis demonstrated that in a period of two years, air had been diffusion pumped through the elastomeric enclosure to its interior, while a small portion of the original sulfur hexafluoride had diffused through the elastomeric material of the insole at the atmosphere.

The 0.6% carbon dioxide found to be present in the insole chambers is approximately twenty times-the amount normally found in ambient air. 90 The relatively large amount of carbon dioxide is typical of urethanes and is due to outgasing from the urethane film from the basic reagent theof.

The inward diffusion of ambient air into the insole containing supergas initially results in the maintenance of the total gage pressure in the insole ator near the initial inflation pressure, which, for example, is-about 20 psig. However, a large difference in the makeup of the gas pressure contributing to the total gage pressure has taken 100 place after the insole has been inflated. Initially, 100% of the gage pressure (and also the absolute pressure) within the insole comes from the supergas (SF.). After two years the volume of the insole has increased 25-40%"due to stretching of 105 the highly stressed envelope forming the insole chambers. There has also been a small amount of pressure loss caused by the outward diffusion of the supergas from the chambers. Yet, the useful gage pressure is essentially unchanged, except for 110 an intervening modest pressure rise during about the first two months following initial inflation (see Fig. 3). As the above mass spectroscopy analysis shows, 50% or more of the useful total pressure in the insole comes from the pressure of the ambient 115 air that has diffused into the system. Thus, it is conclusively demonstrated that the diffusion pumping phenomenon is taking place, and the pressure rise shown is not the result of other mechanisms, such as chemical reaction of the gas 120 with the film or outgasing of the film.

The inward diffusion pumping action of the ambient air entering the enclosure, which contains at least a small amount of supergas, automatically extracts work energy from the surrounding atmosphere on a continuous basis during the life of the insole, and adds to the initial stored potential pressure energy within the insole in timed sequence so as to almost completely offset the negative factors of volume growth due to tensile relaxation of the highly stressed film or sheet, absorption and saturation of the supergas into the barrier film, small pressure loss from outward diffusion of the supergas, external air pressure changes due to altitude, and internal air pressure loss due to cyclic load applications.

In the example of the insole, were it not for the diffusion pumping action of the air in combination with the supergas, the useful gage pressure of 20 psig would drop to less than one-half of its value in 2 to 3 months, primarily because of the volume increase of the enclosure. In lower pressure applications, the importance of the diffusion pumping of air is of even greater significance.

It is important to note that the partial pressure of the supergas is like a building block in combination with air. It is always additive to the partial pressure of air in the system. The contribution of the total useful gage pressure made by the air at 14.7 psia is a fixed and stable foundation for the supergas pressure. The 14.7 psia air pressure will never leak out since it is in complete equilibrium with the pressure of the outside air.

This situation further contributes to the long -term inflation of the insole because the pressure components from the supergas is now much less than the initial full total pressura. At lower differential pressures, the normally very low diffusion rates of the supergas is reduced to a fraction of the higher pressure values creating a condition of virtual permanent inflation. As described earlier, this approach to long-term pressurization of enclosures at relatively constant pressure level, using as the inflating media a maximum amount of air at equilibrium pressure with outside ambient air plus a minimum amount of one or more of the supergases, is called the "Permanent Inflation Technique."

When long term cyclic loading and/or pressure changes take place so as to create an unbalance between the inside and ambient air pressure, the diffusion pumping action of the air works in a similar and beneficial way to extend the useful life of the product. As an example, if an insole that has reached stable air equilibrium at sea level is taken to a higher elevation'where the ambient air pressure is lower (such as in an airplane or in the mountains) the firmness of the device would be greater than the optimum value when the insole is manufactured at sea level. The air performs a selfcompensating function, since the air pressure within the insole is greater than outside, outward diffusion takes place, thus reducing the overpressurization in restoring the device to approximately its original condition, having the desired load supporting characteristics.

If the same insole is now returned to sea level, it will be slightly softer than desired, because the partial pressure of air inside the insole will be less than the ambient air pressure. However, in a few hours the diffusion pumping action of the air will build up the internal air pressure to restore equilibrium. The total pressure in the insole will have again been automatically restored to the 1 X approximate desired useful gage pressure level.

This same action takes place when a person stands on the insoles continuously for a full day. During the day some air pressure loss occurs due to the load applied by the person. At night, the load is removed, the supergas expanding the device to its full volume, thus lowering the internal air pressure, diffusion pumping adding air pressure 50 until the 14.7 psia balance is reached. Thus, in the morning when the insole is again worn by the person, the pressure lost the preceding day is restored for the following days use.

Claims (10)

1. A structure to form part of a shoe, comprising a sealed sole member of elastomeric material providing a plurality of chambers inflatable with a gaseous medium under pressure to a desired initial value, and an elastomeric yieldable outer member encapsulating the said sole member, the latter having peaks and valleys in its upper and lower surfaces, and the outer member filling the valleys in the said upper surface.

2. A structure as defined in claim 1, in which the outer member is compressible polyurethane foam.

3. A structure as defined in claim 1 or claim 2, in which the sole member is inflated with the said gaseous medium under pressure, the gaseous medium including one or more gases other than air, oxygen, nitrogen, and the said elastomeric material has characteristics of relatively low permeability with respect to the said gaseous medium to resist diffusion of the said gaseous medium out from the chambers, and of relatively high permeability with respect to the ambient air surrounding said sole member, to permit diffusion of said ambient air through the elastomeric material and into the chambers, thereby to provide a total pressure inside the sole member which is the sum of the partial pressures of the gaseous medium and the air therein, the diffusion rate of GB 2 034 169 A 5 the gaseous medium through the elastomeric material being substantially lower than the diffusion rate of air, oxygen, nitrogen therethrough.

4. A structure as defined in any of claims 1 to 3, wherein the chambers intercommunicate with one another.

5. A structure as defined in any of claims 1 to 4, in which the gaseous medium includes hexafluoroethane; sulfur hexafluoride; perfluoropropane; perfluorobutane; perfluoropentane; perfluorohexane; perfluoroheptane; octafluorocyclobutane; perfluorocyclobutane; hexafluoropropylene; tetrafl uo rom ethane; monochloropentafluor - ethane; 1,2-dichlorotetrafluoroethane; 1,1,2-trichloro-1 2 trifluoroethane; chlorotrifluoroethylene, bromotrifluoromethane; or monochlorotrifluoromethane, or mixtures thereof.

6. A structure as defined in any of claims 1 to 5, in which the said elastomeric material is selected from polyurethone; polyester elastomer; fluoroelastomer; chlorinated polyethylene; polyvinyl chloride; chlorosulfonated polyethylene; polyethylene/ethylene vinyl acetate copolymer; neoprene; butadiene acrylonitrile rubber; butadiene styrene rubber; ethylene propylene polymer; natural rubber; high strength silicone rubber, low density polyethylene; adduct-rubber; sulfide rubber; methyl rubber, and thermoplastic rubber.

7. A structure as defined in any of the preceding claims the shape of which when viewed in plan corresponds generally to the shape of the human foot.

8. Footwear including the structure as defined in any one of the preceding claims.

9. Footwear as defined in claim 8, wherein the sole member and outer encapsulating member together form a midsole, and an outsole is secured to the underside of the said outer member.

10. A structure to form part of an article of footwear substantially as herein described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980. Published by the Patent Office. 25 Southampton Buildings, London, WC2A lAY. from which copies maybe obtained.