Load carrying cushioning device with improved barrier material for control of diffusion pumping

A product in the form of a cushioning device made from thermoplastic film containing crystalline material inflated to a relatively high pressure and sealed at the time of manufacture. The product maintains the internal inflatant pressure for long periods of time by employing a form of the diffusion pumping phenomenom of self-inflation in which the mobile gas is the gas components of air other than nitrogen. Improved and novel cushioning devices use new material, for the film of the enclosure nevelope which can selectively control the rate of diffusion pumping, thereby permitting a wider latitude flexibility and greater accuracy in the design of such new cushioning device, thus improving the performance and reducing cost of such devices while elminating some of the disadvantages of the earlier products. It is possible to permanently inflate certain types of new devices using readily available gases such as nitrogen, or air in which case nitrogen forms the captive gas.

FIELD OF INVENTION 
The present invention relates to load bearing cushioning devices and more 
particularly to an improved inflated cushioning device which utilizes an 
improved barrier material which selectively controls diffusion of nitrogen 
and which precludes the diffusion of supergases while permitting 
controlled diffusion of other gases contained in air. 
Related Applications 
This application is related to U.S. application Ser. No. 07/147,131, filed 
on Feb. 5, 1988 for "Pressurizable Envelope and Method", whose disclosure 
is incorporated herein as though fully set forth. 
BACKGROUND OF THE INVENTION 
This application is an improvement of my earlier U.S. patents, including 
U.S. Pat. No. 4,183,156, entitled "Insole Construction for Articles of 
Footwear", issued Jan. 15, 1983, and U.S. Pat. No. 4,287,250, entitled 
"Elastomeric Cushioning Devices for Products and Objects," issued on Sept. 
1, 1981, and U.S. Pat. No. 4,340,626, entitled "Diffusion Pumping 
Apparatus Self-Inflating Device," issued July 20, 1982. 
U.S. Pat. No. '156 describes a cushioning device for articles of footwear 
comprising a elastomeric film envelope enclosure, preferably heat-sealed, 
and which is permanently inflated and pressurized during manufacture. U.S. 
Pat. No. '250 is more general and applies to other types of cushioning 
products, i.e., shock absorbers, packaging liners, helmets, door and 
window seals, athletic mats, mattresses, personal protective padding, etc. 
These earlier products utilize thermoplastic elastomeric films with the 
described physical properties and are inflated with novel inflatant gases, 
i.e. "supergases" as therein described, to achieve long-term 
pressurization at relatively high pressures. The method of achieving this 
essentially permanent inflation for the useful life of the products makes 
use of the novel process of diffusion pumping as described in detail in my 
prior U.S. Pat. No. '626. 
Some form of permanent inflation and the technique therefor are important 
with respect to commercial acceptance of inflated product or air cushion 
elements to be used in footwear. For example: 
(1) All valving systems leak to some degree even when new and to a much 
greater degree when dirty. Due to the small volume of the inflated part, 
even minute leaks cause an unacceptable loss in pressure and a concurrent 
loss of cushioning, resiliency and support. 
(2) Proper cushioning requires that the air cushion or inflated product 
maintain a fairly precisely controlled level of pressurization, i.e., 
within a few pounds of the desired pressure. 
(3) The user is generally impatient and will not take the necessary time or 
trouble to maintain the proper inflation pressure within the device. 
(4) The cost of the air cushion or the product with system tends to be 
expensive. Not only is there the cost of the valve, but the user must be 
provided with a pump and a pressure gage, both of which may be costly. 
(5) The air cushion or inflated device may be easily over pressurized and 
damaged or destroyed by the user. 
(6) Improper pressurization or under pressurization may result in injury to 
the user. 
(7) The pump and pressure gage may not be available to the user when 
needed. 
(8) In cushion devices having small volumes, such as cushioning elements 
for footwear, the volume is so small and the pressure is so high that the 
process of taking a pressure reading with a typical Bourden tube pressure 
gage will drop the pressure between 2 and 5 pounds. Thus, the user must 
learn to over inflate by 2 to 5 pounds before taking a reading. This can 
be a tricky procedure, especially for younger children. 
(9) Efforts to make a gas barrier envelope comprised of a multi-layered 
film sandwich comprising some sort of barrier layer within the sandwich 
invariably fail because of delamination adjacent to the weldments or in a 
region of high flexural stress. 
With these devices, it is important to use diffusion pumping because to 
make a practical long-term pressurized cushion, it was necessary to 
utilize a thermoplastic elastomeric envelope film possessing certain 
specified physical characteristics, i.e., good processability, good 
heat-sealing properties, superior fatigue resistance under repeated 
application of comparatively high cyclical loads, as well as appropriate 
properties of tensile strength, puncture resistance, tear-strength, and 
elasticity. Because these practical considerations took precedence over 
the barrier properties (resistance to outward diffusion of inflation 
gases) of the film, it was necessary to inflate with supergas(es) and use 
diffusion pumping by air to help maintain the internal pressure within 
design limits. Good barrier materials would have been desirable for 
maintaining inflatant pressure, but they are necessarily crystalline in 
structure and thus have very poor and unacceptable physical properties, 
especially as regards heat-sealability, fatigue resistance and elasticity. 
Therefore, they could not be used for these applications. In other words, 
one of the considerations in the selection of barrier film materials was 
the fact that relatively large molecular diameter inflatant gases such as 
the supergases mentioned were used as the inflatant and the film materials 
were those which would retain the supergases but permit diffusion of 
smaller molecular diameter gases such as those present in air whose 
composition is nitrogen (78%), oxygen (20.9%), carbon dioxide (0.033%), 
argon (0.934%) and the other gases (neon, helium, krypton, xenon, 
hydrogen, methane and nitrous oxide) which collectively make up about 30 
parts per million of environmental air. 
Diffusion pumping is described in my earlier U.S. Pat. No. '626 as follows. 
A pair of elastomeric, selectively permeable sheets are sealed together at 
desired intervals along weld lines to form one or more chambers which are 
later inflated with a gas, or a mixture of gases, to a prescribed pressure 
above atmospheric. The gas or gases selected have very low diffusion rates 
through the permeable sheets to the exterior of the chamber(s), 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 from diffusion pumping, 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. 
Since diffusion pumping with supergas as the inflatant relies on the 
diffusion of the gas components of air into the envelope, there is a 
period of time involved before a steady state internal pressure is 
achieved. For example, oxygen gas diffuses into the envelope rather 
quickly, usually in a matter of weeks. The effect is to increase the 
internal pressure by about 2.5 psi. Over the next months, nitrogen gas 
will diffuse into the envelope and the effect is gradually to increase the 
pressure by an increment of about 12 psi. 
There is a second effect which takes place due to the elastomeric nature of 
the film and that is tensile relaxation or what is sometimes called creep. 
The gradual increase in pressure causes about a 20% increase in the volume 
of the envelope over its original configuration before a steady state 
configuration is achieved. The net effect is that over a period of time, 
the internal pressure increases by about 14 psi and the volume of the 
envelope geometry changes by expanding. As a practical matter, these 
changes in geometry have been compensated for by controlled manufacturing 
techniques to provide an effective product. Nonetheless, the change in 
geometry has handicapped the design of inflated products whose geometry 
must be closely controlled. 
Having in mind that the object was to provide an inflated product which 
provided a cushion feel, in addition to the other advantages mentioned in 
the earlier identified patents, over inflation tended to produce a hard 
product rather than a cushion. Under inflation to compensate for later 
increase in internal pressure resulted in product which would "bottom out" 
rather than act as a cushion. The increase in pressure over a period of 
months was a consideration which resulted in initially filling the 
envelope with a mixture of supergas and air in order to provide a product 
which was not over inflated, thus initially providing the desired cushion 
feel. This did not, however, eliminate the volume growth due to tensile 
relaxation. The need to mix predetermined quantities of supergas and air 
in order to provide the cushion feel tended to complicate the 
manufacturing process. 
The accomplished objectives of my prior diffusion pumping technology was to 
develop and perfect an exceptionally durable, reliable, fatigue resistant 
and long life means of extracting the partial pressure energy of the 
inflatant gases comprising the ambient air, and to use or convert this 
potential energy to perform useful work in various products. 
While diffusion pumping using supergases and elastomeric 
non-crystallographic film material has operated satisfactorily, an 
improved product is desirable. For example, many millions of pairs of 
footwear have been sold in the United States and throughout the world over 
the past ten years under the trademark "AIR SOLE" and other trademarks by 
Nike Shoe Company. These products of Nike Shoe Company are made in 
accordance with one or more of the previously identified patents and are 
generally regarded as premium quality footwear having the benefits of a 
gas filled, long service life component which offers practical advantages 
over competitive footwear products. The failure rate from all causes, 
including accidental puncture, is believed to be less than 0.001 percent. 
Even so, there is room for improvement in the currently commercial 
versions of the inventions of the above patents, as will be discussed. 
It is also known in the art to use certain types of plastics which are 
essentially impermeable to diffusion of oxygen or carbon dioxide. 
Typically these plastics are polycarbonate materials used in the plastic 
bottles of the beverage industry or SARAN or PVDC or 
polyethyleneterephthalate (PET). The difficulty with polycarbonate and 
similar totally impermeable plastics is the relatively low fatigue 
resistance and the difficulty in forming R-F welds. For example, when an 
inflated and pressurized product of these materials is subjected to severe 
flexural fatigue, the part would fail after a few minutes or hours of use. 
In order to seal such materials, it is generally necessary to heat the 
facing plastics to the melting point to bring about some flow. The result 
is that it is difficult, if not impossible with these materials, to hold a 
predetermined geometry and to obtain tight and good welds by heat fusion. 
These materials are not polar in nature and they generally cannot be R-F 
welded successfully. 
If highly fatigue resistant and readily weldable and heat sealable and 
vulcanizable elastomeric materials are used, and the pressurizing gas is 
air or other gases such as nitrogen or carbon dioxide or argon or xenon or 
conventional Freon refrigerant gases, the latter would diffuse rapidly 
through these materials. This problem was solved by the prior diffusion 
pumping technique and the use of "supergas(es)" with elastomeric barrier 
materials with the benefits of reverse diffusion of oxygen and nitrogen 
gas from ambient air into the part. Over a period of time, there was 
almost perfect compensation for the volume growth of the part that 
resulted from the tensile relaxation properties of the elastomeric barrier 
material. However, if the part was to be pressurized to a relatively low 
inflation pressure, as is the case with "fashion footwear" as contrasted 
to "service footwear" the diffusion pumping of ambient air resulted in an 
unacceptably large pressure variation (increase) during the beginning life 
of the product. This and other problems are solved by the present 
invention. 
Therefore, it is an object of this invention to provide an inflated 
cushioning device having longer service life at the designed internal 
pressure and which can be accurately controlled both in terms of steady 
state internal pressure and geometry. 
It is a further object of this invention to match more closely the tensile 
relaxation properties of the enclosure film with the outward flow of 
gases, thereby helping to maintain more constant inflatant pressure over 
the service life of the product. 
Another object is to slow down the inward flow of ambient air during early 
stages (6 to 24 months) of diffusion pumping, thereby reducing the 
tendency of over pressurizing certain types of the devices or bringing 
about gradual and undesired changes in geometry. 
A further object of the invention is to use more readily available, lower 
weight, less expensive gases that function as the captive gas. 
A further object is to permit use of selected envelope films which are 
superior and/or less costly for some applications. 
Still another object is to provide a practical inflated cushioning device 
which can be pressurized with air or nitrogen, or combination thereof, and 
maintain inflated characteristics over its service life while exposed to 
the duty cycle experienced by such cushioning products. 
BRIEF DESCRIPTION OF THE INVENTION 
Therefore, this present invention relates to load carrying cushioning 
devices (pneumatic enclosures) with novel envelope film having the needed 
physical properties of thermoplastic elastomeric film with the added 
feature of improved barrier properties with respect to nitrogen gas and 
the supergases. These films are formulated so as to selectively control 
the rate of outward diffusion of certain captive gases such as nitrogen 
and the supergases through the envelope as well as the diffusion pumping 
of other gases, i.e., mobile gases such as oxygen, carbon dioxide and the 
other gases mentioned and which are present in ambient air, inwardly into 
the pressurized devices. 
Typically, the barrier materials usable in accordance with this invention 
are preferably thermoplastic, elastomeric and polar in nature and 
processable to form products of the various geometries to be discussed. 
The barrier materials of the present invention should contain the captive 
gas within the envelope for a relatively long period of useful life, e.g. 
two years or more. For example over a period of two years, the envelope 
should not lose more than about 20% of the initial inflated gas pressure. 
Effectively this means that products inflated initially to a steady state 
pressure of 20 to 22 psig should retain pressure in the range of about 16 
to 18 psig. 
Additionally, the barrier material should be flexible, relatively soft and 
compliant and should be fatigue resistant and be capable of being welded 
to form effective seals by essentially a molecular cross-linking, 
typically achieved by radio frequency (R-F) welding. Especially important 
is the ability of the barrier film material to withstand high cyclical 
loading without failure, especially in the range of film thickness of 
between about 5 mils to about 50 mils. Film materials which are 
crystallographic in nature tend not to possess fatigue resistance, 
although the barrier qualities are generally quite good. Another important 
quality of the barrier film material is that it must be processable into 
various shapes by techniques used in high volume production. Among these 
techniques known in the art are blow molding, injection molding, slush 
casting, vacuum molding, rotary molding, transfer molding and pressure 
forming to mention only a few. These processes result in a product whose 
walls have essentially film properties and whose cross-sectional 
dimensions can be varied in various portions of the product but which are 
overall essentially film like in character. 
In addition to the above qualities which are important in the effective use 
of the barrier material which forms an envelope, there is the all 
important quality of controlled diffusion of mobile gases through the film 
and retention of captive gases within the envelope. By the present 
invention, not only are the supergases usable as captive gases, but 
nitrogen gas is also a captive gas due to the improved nature of the 
barrier. The primary mobile gas is oxygen, which diffuses relatively 
quickly through the barrier, and the other gases present in air except 
nitrogen. The practical effect of providing a barrier material for which 
nitrogen gas is a captive gas is significant. 
For example, the envelope may be initially inflated with nitrogen gas or a 
mixture of nitrogen gas and one or more supergases or with air. If filled 
with nitrogen or a mixture of nitrogen and one or more supergases, the 
increment of pressure increase is that due to the relatively rapid 
diffusion of principally oxygen gas into the envelope since the captive 
gas is essentially retained in the envelope. This effectively amounts to 
an increase in pressure of not greater than about 2.5 psi over the initial 
inflation pressure and results in a relatively modest volume growth of the 
envelope of between 1 to 5%, depending on the initial pressure. 
If air is used as the inflatant gas, oxygen tends to diffuse out of the 
envelope while the nitrogen is retained as the captive gas. In this 
instance, the diffusion of oxygen out of the envelope and the retention of 
the captive gas results in a decrease of the steady state pressure over 
the initial inflation pressure. For example, if inflated initially with 
air to a pressure of 26 psig, the pressure drop will be about 4 psig in 
order to balance the partial pressure of oxygen gas on each side of the 
barrier envelope wall. The drop in pressure also tends to achieve an early 
steady state condition with respect to tensile relaxation or creep in that 
creep is reduced or eliminated because there is no further increase in 
internal pressure. 
It is thus important in the practice of the present invention to provide a 
barrier material which has effectively the same desirable qualities as 
previously described, but which has the added quality of being a barrier 
to nitrogen gas. As already noted, plastic materials or laminated or 
co-extruded combinations of plastic materials which also operate as 
barriers to oxygen tend to be essentially crystalline in nature and tend 
to lack the fatigue resistance needed for products contemplated by this 
invention and which are subject to relatively high cyclic loads for 
comparatively long periods of time. 
Barrier materials having the desired barrier properties and the other 
needed qualities in accordance with this invention are those which are 
basically elastomeric and polar in nature and which have the properties of 
being comparatively flexible and have high fatigue resistance while also 
having sufficient crystalline qualities to prevent diffusion of nitrogen 
gas and the supergases through the envelope. These crystalline qualities 
may be imparted any one of several ways, including a mechanical 
crystalline barrier or a molecular crystalline barrier to inhibit the 
diffusion of the captive gases and several such film and other types of 
materials will be described in detail. 
It is thus apparent that the present invention has several advantages over 
the prior art and prior patents referred to previously. 
It is thus apparent that the present invention has several advantages over 
the prior art and prior patents referred to previously. 
This invention has many other advantages, and other objectives, which may 
be more clearly apparent from consideration of the various forms in which 
it may be embodied. Such forms are shown in the drawings accompanying and 
form a part of the present specification. These forms will now be 
described in detail for the purpose of illustrating the general principles 
of the invention; but is understood that such detailed description is not 
to be taken in the limiting sense.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings which illustrate preferred forms of the present 
invention, except as noted, FIG. 1 illustrates an inflated heel ped 10 in 
accordance with this invention. The term "ped" for the purposes of this 
invention is defined as a load carrying cushioning device positioned in 
the heel or forefoot regions of footwear. As shown, the heel ped is in the 
form of an sealed envelope containing an inflatant captive gas. The 
envelope wall is formed of a barrier film material which permits diffusion 
through the film of the mobile gas(es) but which effectively prevents 
diffusion of the captive gas(es). In this form, the enhanced barrier 
qualities are provided by a crystalline barrier material imbedded in the 
parent polar, elastomeric and thermoplastic film material forming the 
pressure containing envelope. The internal pressure may vary widely from a 
few psig to as much as 30 or more psig. This heel ped may either be fully 
or partly encapsulated into a foamed sockliner of an article of footwear, 
or cemented into place within a preformed cavity within a sockliner or be 
fully or partly encapsulated into the midsole or outsole of an article of 
footwear. Of course, as is known in the footwear art, other locations and 
disposition of the ped and other cushion elements of footwear may be used. 
A substantial number of heel peds, virtually millions of pairs, having the 
geometry illustrated in FIG. 1 have been used commercially and have been 
made in accordance with the prior patents identified. These prior peds, 
however, were fabricated with a 100% elastomeric material which did not 
act as a barrier for air gases, and the captive gas was one or more 
supergases. Typically the materials which may be used for the envelope of 
the prior devices, supergas inflated products, included polyurethane 
elastomer materials, polyester elastomers, fluoroelastomers, polyvinyl 
chloride elastomers, and the like. Polyurethane elastomer materials were 
preferred as the commercial material because of the superior heat sealing 
properties, good flexural fatigue strength, a suitable modulus of 
elasticity, good tensile and tear strength, and good abrasion resistance. 
Of course these properties are also present in the improved barrier 
materials of the present invention. Other materials include polyethylene 
terephthalate glycol (PET 9), Dacron 56 and the like. 
In contrast to the envelope material of the supergas inflated products of 
the prior art, the envelope material of the present invention includes a 
considerable amount of crystalline material and has considerable lower 
permeability to fluids and gases as compared to the prior art envelope 
materials. The crystalline material, regardless of type and manner of 
incorporation, effectively blocks a large portion of the flow passages 
through which the inflatant gas must diffuse as it migrates outwardly 
through the film. Typical highly crystalline material which may be used 
are polyester materials, nylon materials, polypropylene materials, 
graphite, glass, Kevlar, metals and virtually any crystalline material. 
Materials of these types come in many forms which can be utilized in the 
products of this invention: thread-like fibers, filaments, chopped fibers, 
scrims and meshes, or uniformly distributed particulate or platelet 
crystalline materials, various types of knitted, woven, and non-woven 
cloth, expandable fabrics, whiskers, etc. Other material which may be used 
are: amorphous graphite cloth, filament or whiskers; mica; Aramid or 
Kevlar cloth, filaments or whiskers; metallic cloth, filaments or 
whiskers, for example steel or aluminum; nylon or polyester or glass or 
PET cloth, filaments or whiskers. Various metals and metal alloys may be 
used in the form of filaments, powder, platelets, cloth, beads and 
micro-spheres and the like. Such materials are well-known to the 
reinforced-plastics industry for other applications. It is to be noted, 
however, that the use of the crystalline materials is not for the primary 
purpose of reinforcement in accordance with the present invention since 
many of the useable materials and the form of the materials do not 
appreciably contribute to film strength. 
The heel peds 12 and 14 of FIGS. 2 and 3 are similar to the heel ped of 
FIG. 1 except that each contains successively more barrier crystalline 
material. The effect of spacing of the barrier materials is shown more 
clearly in FIGS. 4, 4A and 5 and 5A where a thread-like barrier 15 is 
diagrammatically shown imbedded within the parent thermoplastic 
elastomeric film 17. As shown, the material 15 is disposed between the 
opposing surfaces 19 and 20 of the film. By this arrangement, the surfaces 
are principally and entirely parent elastomer material and may thus be 
readily heat sealed by R-F welding and the like to form a sealed envelope. 
If the thread-like barrier material was present on the surface, there 
would be some difficulty in sealing the envelope if formed of preformed 
sheet. 
The barrier material of FIG. 5 has closer spacing of the fibers 15 in the 
film 17 and thus more flow-blockage (70 percent crystalline) as compared 
to barrier material of FIG. 4 (55 percent crystalline fibers). Therefore 
the rate of diffusion and diffusion pumping of the mobile gas would be 
lower in the FIG. 5 embodiment than in the FIG. 4 form. The diameter of 
the fibers and the cross-section geometry can also be changed to adjust 
the rate of diffusion. In addition, the type of barrier material chosen 
for the design can effect the rate of diffusion pumping. For instance, 
diffusion would be lower with graphite scrims than polyester scrims. As 
can be seen in the cross-sections of FIGS. 4, 4A, 5 and 5A, it is 
beneficial to have the crystalline material close to the outside surface 
of the film, but located beneath the film surfaces so as to have as large 
a portion as possible of elastomeric material on the surface so as to 
achieve the best possible heat-seal joint or weld between the sheets of 
film. It is understood that the crystalline fibers may protrude partially 
from only one surface thus providing essentially a two-sided film. In that 
case, sealing must be between the one side of the surfaces from which the 
fibers do not extent. It is preferred in accordance with this invention 
that the barrier material be one-sided, i.e., the crystalline material 
should be completely imbedded in the film. This eliminates the need to 
assure that the proper surface of the film materials are in facing contact 
when forming envelopes initially from sheet materials. 
It is also important to have the elastomeric material surround the 
crystalline material sufficiently in order that the two be intimately 
connected thereby avoiding the separation of the two types of material in 
service. Such separation did occur early in the development program for 
this invention. In that case, an attempt was made to incorporate 
crystalline barrier materials with the elastomeric material using 
co-extrusions or co-lamination of the two types of plastics. FIGS. 6A and 
6B, which do not represent forms of this invention, illustrate the 
unfortunate result of such an approach. A portion of the pressurizing 
gases diffused outwardly through the inner layer of elastomeric film 25 
and were blocked by the outer layer 26 of barrier film. Pressure against 
the outer layer 26 caused the two layers to separate as seen in FIG. 6B 
with the result that the barrier layer ballooned, as seen at 28, outwardly 
thereby failing either by bursting or by forming a large aneurysm. 
Therefore, it became necessary to improve the approach by submerging or 
imbedding the crystalline material intimately into the parent elastomeric 
layer. Initially a scrim was imbedded in urethane material known 
commercially as MP-1790 AE urethane (XPR-396 of Uniroyal, Inc.) by 
extruding the thermoplastic material onto a 10.times.10 course woven (10 
strands per inch in each direction) nylon mesh, basically an open type of 
mesh. The results were quite good. However, the modulus of elasticity of 
the scrim was too high relative to that of the parent material, i.e., the 
plastic film stretched more than the scrim. This resulted in some 
wrinkling and distorting of the composite film during heat-sealing and 
inflation. Such distortions resulted in stress concentrations within the 
inflated envelope and reduced the flexural fatigue life of the part. 
Fatigue ruptures occurred in the most highly stressed areas, i.e., near 
the heat-sealed weldments. 
For inflated cushion products using cloth, scrims or meshes in accordance 
with the present invention, it is important that 1) the physical 
properties of the crystalline fibers (especially modulus of elasticity, 
slope of the stress-strain relationship and yield stress), 2) the geometry 
and density of the crystalline elements themselves, 3) the arrangement 
(spacing and orientation) of the fibers within the elastomeric material, 
be such that at the design internal pressure levels (stress levels) the 
crystalline elements at the highest stress regions will have been stressed 
beyond their yield point. Such yielding (beyond the elastic range) 
redistributes and evens out the loads throughout the enclosing envelope of 
the inflated product. Approximately 20% of the fibers should be stressed 
beyond the yield point. None of the elastomeric material operates beyond 
the yield point. 
After the early test previously referred to, a cushion product was 
developed and successfully tested and incorporated some of the design 
features mentioned. In this instance, the crystalline mesh was a tighter 
weave of smaller diameter and low denier fibers. When inflated to design 
pressure some of the mesh (adjacent to highly stressed regions around the 
weldments) yielded and some permanent set resulted. This particular 
product retained the desired air pressure for an extremely long period of 
time (more than about ten years) and has not lost any measurable pressure. 
The fatigue resistance was good and the inflated shape of the cushion was 
excellent and without objectionable distortions of the envelope. 
FIG. 7 shows another form of the present invention in which the elastomeric 
material 30 includes a multiplicity of individual crystalline elements 32 
in the form of platelets essentially uniformly dispersed throughout the 
host elastomer. In this embodiment the small planer platelets are mixed 
with the elastomeric polymer and extruded or blown with the polymer into 
sheets of film. These sheets are in the thickness range 0.005 to 0.050 
inches. During this process the platelets 32 align parallel with the 
surface of film as seen in FIG. 7B, thereby more effectively forming a 
barrier arrangement. 
The various techniques for imbedding a crystalline element into the parent 
film include: 1) extruding the parent material onto a scrim or mesh, 2) 
coating cloth made from crystalline fibers with the parent material 
(normally both sides are coated), 3) mixing the polymer of the parent film 
with various forms of barrier material (i.e. flakes, thread-like fibers, 
chopped fibers, whiskers, platelets, etc.) and extruding or blowing the 
mixture into a film or sheet and 4) either intimately blending or 
co-polymerizing the elastomeric polymer with the crystalline material. 
Some of these procedures have already been discussed, others will be 
discussed below. 
It is important at this point to explore the practical limits for the 
applications of controlled diffusion for inflated devices in accordance 
with the present invention. With products of this type and for practical 
commercial utility it is important and essential to have an appropriate 
and optimized balance between: 1) The minimum rate of activated diffusion 
on the one hand and 2) such physical properties as fatigue resistance, 
manufacturing processability, and heat-sealability on the other hand. 
Because of the necessity for achieving such a compromise, it is probably 
not practical to have such a high concentration of crystalline materials 
so as to form a 100% barrier against diffusion of all gases. The major 
exception is oxygen. Other gases, including nitrogen and the supergases, 
can be effectively prevented from diffusing through the enclosure envelope 
of the inflated devices, and still maintain the essential elastic fatigue 
resistant characteristics of the barrier envelope material. 
The fact that oxygen can diffuse through the envelope is not a problem, and 
is, in fact, a desirable and unique benefit. This is an important, novel 
concept for this invention. For example, the product can be inflated with 
a mixture of nitrogen and/or supergas or air. After inflation with 
nitrogen and/or supergas, the oxygen of the ambient environment can 
diffuse into the envelope through the mechanism of diffusion pumping. 
Thus, the partial pressure of oxygen is added to the partial pressures of 
nitrogen and/or supergas already contained within the envelope, with the 
result that the total pressure of the product rises. The partial pressure 
of oxygen in the ambient atmosphere is about 2.5 psia (out of a total 
pressure at sea level of 14.7 psia). Thus, the reverse diffusion of oxygen 
gas into the envelope will cause a maximum rise in pressure about of 2.5 
psia. Such a rise in pressure is useful in offsetting the substantial 
tensile relaxation of the envelope (with resultant increase in the 
internal volume of the enclosure) where all of the gas components of air 
diffuse into the envelope. Thus, a novel feature of this invention is that 
the composite material of the envelope is a semi-permeable membrane to the 
gases in air other than nitrogen and is therefore not a complete gas 
barrier. The practical advantage is that the maximum volumetric and 
dimensional change in the product is between 3% and 5% because the maximum 
increase or change in pressure with respect to the initial inflation 
pressure is the partial pressure of oxygen. 
If cost is of paramount importance, the inflatant gas can be 100% nitrogen 
and the same phenomenon of reverse diffusion of oxygen gas into the 
envelope will occur. Also a mixture of nitrogen plus 2.5 psia of oxygen 
can be useful in some applications. In addition, 100% of air can be used. 
In this case it is necessary to initially over-inflate the device if the 
partial pressure of oxygen in the device exceeds 2.5 psia to offset the 
increment of the difference, a pressure loss of between the actual partial 
pressure of oxygen within the enclosure and 2.5 psia. 
There are many advantages in controlling the rate of diffusion pumping in 
inflated elastomeric devices such as components for footwear, 
shock-absorbers, cushioning elements for packaging and shipping purposes, 
helmets, athletic protective gear/padding, military boot, etc. One 
advantage is the ability to maintain the product at design inflated 
pressure for longer periods of time than would otherwise be possible. As 
an example, most presently made inflated footwear components, which are 
sold throughout the world, are made from ester-base polyurethane film 
because it has lower permeability with respect to supergas than 
ether-based polyurethane film, and thus has a acceptably long service life 
in footwear, However, ester-based film has the disadvantage that it may be 
much more adversely affected by moisture (hydrolysis instability) than the 
ether-based counterpart. In the current commercial form of footwear, 
protection against moisture is achieved by encapsulating the inflated 
component in a foamed midsole. This operation is costly and the foam of 
the midsole, while it increases fatigue life of the composite product, 
tends to detract from the beneficial cushioning and energy return 
properties of the inflated product and greatly adds to the weight of the 
shoe. By imparting a crystalline property to the barrier film, e.g., the 
ether-based film, the latter may be used in footwear having long service 
life and the moisture degradation problem is largely eliminated. 
Another example of the advantages of the improved barrier film material of 
this invention is the "cold-cracking" problem. The prior art supergas 
inflated products when exposed to low environmental temperatures of below 
about 10 degrees F. tend to develop fatigue cracks in the elastomeric film 
and become flat. Special film materials may be developed to reduce the 
cold-cracking problem. However, these film materials more suitable for 
cold temperature tend to become more permeable to the pressurized gas at 
room temperature. The permeability may be reduced, in accordance with this 
invention, by incorporating crystalline components or molecular segments 
to the elastomeric film to restore the loss of permeability caused by 
attempting to reduce the effects of cold-cracking and which may also 
result in greater gas permeability. 
One of the practical advantages of controlling permeability and diffusion 
pumping relates to matching the tensile relaxation properties of the 
product with the changes in pressure due to retention of the captive gas 
and diffusion of the mobile gas. For example, in some products it is 
desirable to use a film either with a lower modulus of elasticity or 
thinner gage to provide a softer feel to the cushioning device. With lower 
gage or lower modulus, there is a greater tendency for the captive gas to 
diffuse through the film. To compensate for such loss, the device may be 
over-inflated slightly. However, due to the thinness or modulus of the 
film, the envelope tends to enlarge to a greater extent than would be the 
case with thicker films or those of higher modulus. This increased growth, 
tensile relaxation or creep, provides a product whose geometry is not 
quite that desired or which changes over time. By adding a crystalline 
material to the film material, the modulus of elasticity is increased and 
also the flow of the captive gas is reduced and the product is able to 
maintain inflatant pressure with a comparatively small change in 
configuration without the need to over inflate the product. 
On the other hand, there are certain types of products, such a tensile-type 
units, see FIGS. 11, 11A and 11B of the application previously identified, 
which tend to over inflate in the first 3 to 6 months of inflation since 
the nature of the part is such that there is very little enlargement of 
the envelope. Since the internal volume of the product cannot change as 
other products do, the diffusion of air into the elastomeric and non 
crystalline envelope causes over pressurization. While one could store 
these products for 3 to 12 months to achieve a steady state inflation 
pressure, this is not practical from a commercial view point. If 
crystalline molecular segments are included in or added to the material 
used to form the tensile type products, less expensive captive gases may 
be used and light weight and less expensive envelope materials may be 
used. The following table compares two supergases with less expensive 
captive gases that effectively act as supergases in accordance with this 
invention. 
One cubic foot of gas or vapor at 25 psig and 70 degrees F. 
______________________________________ 
LBS/FT.sup.3 
OF VAPOR 
OR GAS DOLLARS 
AT 25 PSIG PER 
AND 70 DEGREES F. 
LB. 
______________________________________ 
Hexafluoroethane 
1.00 $7.19 
(Supergas) 
Sulfurhexafluoride 
1.05 $5.90 
(Supergas) 
Nitrogen 0.19 $0.09 
Air 0.20 zero 
______________________________________ 
Although not classed as supergases, air and nitrogen have been added to the 
table above because, from the standpoints of availability, cost and weight 
they are excellent inflatant candidates. In order fully to utilize these 
gases, upwards of 70 percent by weight of the envelope film may be 
crystalline. Thus, the weight of parent thermoplastic material would be 
reduced proportionally. However, it is understood that the use of very 
small percentages of crystallographic material are included within the 
scope of this invention, so as to control the diffusion of both oxygen and 
nitrogen gas as both are mobile gases. Addition of crystalline materials 
to the costly elastomeric materials can produce a composite material with 
substantial cost savings over using 100% elastomeric polyurethane, for 
example. 
A good way to visualize some of the above concepts of using a composite 
material comprising both elastomeric and crystalline components or 
segments is to think of the elastomeric material as the matrix which binds 
together the crystalline elements. The elastomeric material provides good 
fatigue resistance and the desired physical properties of modulus of 
elasticity, elongation, manufacturing processability and heat-sealability. 
The crystalline components provide the enhanced gas diffusion barrier. In 
this way, the elastomeric properties of the composite structure exist up 
to the boundaries between elastomeric and crystalline elements of the 
structure. Thus, the crystalline materials do not have to bend and flex to 
any significant degree and are not subject to fatigue stresses. 
Heat-sealability is accomplished within the elastomeric portion of the 
composite. 
Next, attention should be directed to FIGS. 8 through 16F which illustrate 
various inflated products in accordance with this invention. FIGS. 8 to 8E 
illustrate a heel wedge 50 as the latter is removed from a mold in which 
the envelope 53 is initially formed. The wedge 50 includes a curved rear 
wall 54 integrally formed with top and bottom walls 56 and 57, the latter 
being thinner than the rear wall for added cushioning and flexibility. 
Integrally formed with the top, bottom and rear walls are side walls 58 
and 59, the latter including portions 58a and 59a which are thicker than 
the top and bottom walls. As illustrated, the thicker portions of the 
envelope are joined to the thinner portions by transition sections. 
Portions 58b and 59b of the side walls are thinner than portions 58a and 
59a. As shown, the rear wall 54 is slightly angled along its outer 
peripheral surface 54a for strength and rear foot support and stability. 
Visibility of the cushioning product is also an important marketing 
consideration. As removed from the mold, the front end 62 of the wedge is 
open. It is understood that the material of envelope contains both 
elastomeric and crystalline materials, as described. 
In the next operation, illustrated in FIGS. 9 to 9D, the envelope 50 is 
processed to form multiple chambers, filled with a captive gas and sealed. 
As seen in FIGS. 9 and 9A, the chambers 61-66 extend between the side 
walls and are joined to chambers 67 and 68 (see FIG. 9C) which extend 
along the side walls. The various chambers are formed by R-F welding to 
provide webs 70 between the adjacent chambers. It is understood, however, 
that other form of heat sealing may be used, as is known in the art. R-F 
welding is preferred. 
Also, in some cases, it is desirable (as with "blow molding") to eliminate 
the separate R.F.welding step. This is accomplished by having the side 
sections of the mold move inwardly during the molding procedure to form 
the webs 70. Thus, the envelope material from opposite sides of the 
cushioning device is shaped and pressed together while the envelope 
material is semi-molten, viscous or sticky. The clean, semi-molten, sticky 
or tacky inner elastomeric surfaces are held in contact, under pressure, 
until the materials fuse and cool. This procedure therefore replaces the 
previously described R.F. welding step. It has been found that the 
reliability of these welds can be substantially improved if the surfaces 
to be joined are primedas by injecting a "coupling agent" such as Dow 
Silane X 16106 as a vapor, into the pressurizing gas used in the blow 
molding procedure. Further, for certain very severe fatigue applications, 
a secondary R.F. welding step can be added to the manufacturing procedure 
to create a weldment that exceeds the durability of the adjacent parent 
film. 
The front end is also R-F welded to form a sealed front end 72 and portions 
72a and 72b are trimmed. An inflation tube, not shown, may be attached to 
chamber 66 for inflation with a captive gas, as described, and then sealed 
off, as is known in the art. The chambers may all be in fluid 
communication with each other to provide an inflated cushioned heel wedge 
for use in footwear. However, the chambers may also be independent 
chambers, pressurized at different pressure levels. In the next few months 
after initial inflation, oxygen gas will diffuse from environmental air 
into the sealed envelope to increase the pressure(s) by about 2.5 psi. The 
initial pressure level will be largely determined by the cushioning level 
desired. Typically a final steady state pressure of between 20 and 30 psig 
is satisfactory. In some instances, it may be desirable to inflate 
initially to a greater or lesser pressure, the final steady state pressure 
being about 2.5 psi over the initial pressure. 
One of the important advantages of this invention is apparent from the 
device of FIG. 9. As noted, there is no substantial expansion of the 
envelope over the period of diffusion pumping. The overall dimensions of 
the envelope remain within about 3 to 5% of the original dimensions. Thus, 
the shape and geometry of the part remain fairly constant over the period 
of from initial inflation, through diffusion pumping and through the 
useful life of the product. 
FIGS. 10 and 10A illustrate a variation of the heel wedges described in 
that the wedge 75 is formed essentially of three parts, the third part 78 
being a film material of the type described and which is heat sealed to 
portions of the sheets 79 and 80. The third or intermediate sheet 78 of 
elastomeric material is positioned between barrier members 79 and 80 of 
the previously formed part prior to welding. In this form, some of the 
welds 81, 81a, 82, 83, 84 and 85 are on the upper portion, while other 
welds 81, 86, 87, 88 are on the lower part. There is also a peripheral 
chamber and all the chambers are interconnected. This particular form of 
the invention also indicates the relatively complex parts and products 
that may be fabricated in accordance with this invention. In making the 
part just described, it is necessary either to preform the welds 81a, 82, 
83, 84 and 85 in a sequential fashion, or to introduce a release agent in 
the appropriate locations so that only two of the three sheets will join 
together. 
FIGS. 11 through 11D illustrate a tensile type of heel wedge 90 which 
contains a single chamber but which incorporates a tensile element 92. The 
advantages of this type of product are described in detail in the prior 
application referred to above. In addition to those advantages, the 
tensile type product of this invention offers advantages over and above 
the prior tensile type product. The tensile element 92 may be of nylon or 
polyester having a first and second surface portion 94, 95 with tensile 
filaments 96 extending between the two. Representative fabrics that may be 
used are three dimensional, lock stitch or woven, or double needle-bar 
Raschel knit products. The outer envelope 98 may be of any of the improved 
barrier materials herein described and the spaced surface portions 94 and 
95 are affixed to the top and bottom wall of the envelope. The front end 
99 is sealed and the envelope is initially inflated with a captive gas 
which may be any of those mentioned. The tensile elements 92 maintain the 
top and bottom walls of the inflated product in essentially parallel or 
contoured relation. During diffusion pumping, oxygen gas diffuses through 
the envelope to increase the internal pressure by about 2.5 psi, but the 
top and bottom walls remain parallel or contoured. The advantage which the 
tensile product of this invention has over that previously described is 
that the effect of tensile relaxation is largely controlled. The 
dimensional tolerances of the part are very stable and the product is not 
over inflated. 
This product is unique from the other products described in that it 
achieves 100% pneumatic support without detraction of non-supporting 
weldments joining together the upper and lower barrier surfaces in the 
load supporting areas. 
The inflated size, shape, and geometry of this tensile product is very 
precisely controlled, and it cannot grow or enlarge significantly even 
when pressurized to unusually high pressures, i.e., 100 to 200 psig. 
Likewise, the diffusion pumping is precisely controlled. The finished 
product is therefore able to be adapted easily into high speed "turn key" 
automated manufacturing procedures. The product is also able to withstand 
extreme manufacturing environments much better than was possible with the 
prior art products. Furthermore, this tensile product retains the precise 
and desired level and degree of cushioning, compliance and resiliency 
throughout its significantly extended lifetime, as compared with the prior 
art products. 
Steady state internal pressure is reached within a few months and at a 
level which is about 2.5 psi over the initial pressure, assuming supergas 
or nitrogen is used as the initial inflatant captive gas. If air is used 
as the initial inflatant gas, the pressure tends to drop, as earlier 
discussed. The important fact is that the product does not significantly 
change configuration or dimension and reaches the desired steady state 
inflation pressure in a relatively short time. The latter is important in 
the manufacture of footwear on a commercial basis and through the use of 
automated equipment. 
FIGS. 12 through 12E illustrate a full length and inflated sole element 100 
in accordance with this invention as the latter is removed from the mold. 
The rear wall 102 is curved and slanted, as already described and somewhat 
thicker than the top and bottom walls 103 and 105. Portions of the side 
walls 106 and 107 along the mid-section are thicker than the forward 
portion, as seen in FIG. 12D. Moreover, the side wall portion 109 on the 
inside of the foot is thicker than the side wall portion 110 on the outer 
side of the foot, as seen in FIG. 12C. The front end 112 is open and the 
entire structure is essentially planer, as contrasted to being tapered. 
The open end 112 as shown in FIG. 12E is bell-mouthed in shape to allow 
withdrawal of a mandrel if injection molding is used. However, if the part 
is blow molded, this would not be required. 
FIGS. 13 and 13A illustrate the finishing operations which include heat 
sealing to form a plurality of spaced chambers 113 separated by a 
plurality of webs 114. The front end is also peripherally sealed and parts 
115a and 115b are trimmed away to provide a rounded front end. The 
envelope is then initially inflated with a captive gas, as described and 
the fill section is sealed. When assembled to footwear, the full sole 
element may permit the chambers to be seen through the side wall, i.e., a 
visible inflated cushion. 
It is understood that these devices may be compartmentilized in any desired 
arrangement, with each separate chamber pressurized at the same or at any 
different desired pressurized pressure level. Conversely, some or all of 
the chambers may be joined by narrow sonic venturi or similar flow 
restricting passages. 
FIGS. 14 through 14D illustrate a full sole product 125 which may initially 
be formed by injection or blow molding. In general the product is similar 
to that of FIG. 13 except that there is a sag portion 127 between the side 
walls (see FIG. 14A) and the sole has a tapered configuration. The sag 
portion moves out of the way to permit extraction of the mandrel. The 
product, after initial formation, is then processed to provide a a 
cushioning device as illustrated in FIGS. 15 through 15D. 
The finished product is inflated and includes a variable thickness profile, 
the thickest portion 130 being in the heel section, the thinnest being the 
forefoot portion 135, the latter being interconnect by a sloping 
transition section 137. The various drawings also illustrate a plurality 
of chambers 138 with the webs 139 which extend transversely and 
communicate which peripheral chambers 140 and 141. 
FIGS. 16 through 16F illustrate a product in accordance with this invention 
which may be formed by blow molding or by vacuum forming techniques or 
from separately formed sheet materials. Blow molding, however, is the 
preferred technique. The film thickness of this form of the invention 
regardless of how formed, like the thinnest film thickness of the other 
forms, may be from 5 mils to 50 mils, but film thicknesses in the range of 
20 to 25 mils are preferred. 
The full length inflated sole 150 includes both generally transverse 
chambers 151 and generally longitudinal chambers 153 in the heel portion 
155. The heel portion is thicker than the forefoot portion 156, the two 
portions being joined by a tapered transition section 158. As already 
described the various chambers are separated by weld bands 160. In some 
cases, the weld sections are relatively short sections 162, see FIG. 16D. 
The general transverse orientation of the welds and chambers in the 
forefoot region tends to promote flexibility whereas the heel portion does 
not require the same type of flexibility. To promote forefoot and lateral 
flexibility, there are sidewall flex notches 165 provided in the form of 
truncated apertures with the small diameter ends adjacent to each other as 
shown. Both of the above measures decrease the cross-section moment of 
inertia of the mid-sole to cause the shoe to flex easily during the 
toe-off phase of running. 
Like the other forms of this invention, the inflated product is made of an 
envelope which is an improved barrier for captive gases and a permeable 
barrier for the mobile gases mentioned. As in the other forms, there is a 
peripheral chamber on the medial and lateral side and the various chambers 
are all interconnected. 
While the various forms illustrated show intercommunicating chambers with 
essentially free flow of the captive gas and the mobile gas between the 
chambers, it is understood that the various compartments may be partially 
connected with flow-restricted passages, or the product may be formed of 
chambers which are fully independent of other chambers, inflated to 
different pressure levels and inflated cushions that have only a single 
chamber as in the tensile product of FIG. 11. 
The various products described in these figures are designed to be used as 
midsoles of articles of footwear, primarily athletic and leisure shoes. In 
such an application these inflated products may be used in any one of 
several different embodiments: 1) completely encapsulated in a suitable 
midsole foam, 2) encapsulated only on the top portion of the unit to 
fill-in and smooth-out the uneven surfaces for added comfort under the 
foot, 3) encapsulated on the bottom portion to assist attachment of the 
outsole, 4) encapsulated on the top and bottom portions but exposing the 
perimeter sides for cosmetic and marketing reasons, 5) same as item (4) 
but exposing only selected portions of the sides of the unit, 6) 
encapsulated on the top portion by a molded "Footbed", 7) used with no 
encapsulation foam whatsoever. 
In addition to the addition of crystalline materials to a host elastomer, 
crystalline properties may be imparted by other techniques. One is to 
laminate different materials together, but this must be done carefully to 
prevent delamination of the components. For example, laminated products 
have been used in the packaging industry to prevent passage of oxygen gas 
into a sealed package. These packaging laminates are generally not 
satisfactory for the present invention since the composites have poor heat 
seal qualities or rapidly fail due to cracking caused by fatigue loading. 
One process which has operated satisfactorily was the co-lamination of 
polyvinyl vinylidene chloride copolymer and a urethane elastomer film. The 
inflated cushions fabricated from such material had acceptable barrier 
properties, but the composite delaminated under pressure. It was 
discovered that if an intermediate bonding agent such as silane X-b 1-6106 
or PAPI 50 is used, the proper time-temperature relationship was observed 
during the lamination process, results could be improved. Such time and 
temperature control involved the use of a heated platen press, coupled 
with a cold press which can freeze the different materials together under 
pressure. 
In addition to the methods described for increasing the crystalline content 
of the parent elastomeric film by mixing in discrete pieces of particulate 
crystalline material or by joining the elastomeric material to structural 
elements of crystalline material, there are other approaches. One 
approach, mentioned above, is on the molecular scale. This approach 
involves blending or co-polymerizing the parent elastomeric polymer with 
highly crystalline polymers as polyethylene terephthalate (PET), acrylic 
copolymers, polyvinylidene chloride copolymers, polyester copolymer 
elastomers, ultra thin liquid crystal densely packed fibrous molecular 
chains, polyurethane-nylon blends and other polyurethane blends, for 
example. 
Other approaches involve the use of: vacuum deposited glass, less than 500 
Angstroms thick, on to an ultra-thin flexible layer of polyethylene 
terephthalate (PET), in combination with a polyurethane elastomer film 
material; ultra-thin liquid crystal polymer layer(s) within the 
elastomeric matrix, consisting of densely packed fibrous molecular chains; 
acrylic polymers with urethanes; elastomeric and crystalline alloys; glass 
filled thermoplastic urethanes such as "Elastollon" from BASF Corp.; 
fiberglass filled or reinforced thermoplastic urethanes; copolyesters of 
the hard crystalline segments of thermoplastic polyurethanes and 
thermoplastic elastomers; thermoplastic elastomers having appropriate 
proportions of soft rubbery components in combination with hard glassy 
crystallographic materials such as (1) thermoplastic copolymers of 
polyethers and esters such as alternating block polymers of soft rubbery 
polymer segments with hard glassy crystalline PET polymer segments, (2) 
styrene (crystalline)/butadiene (rubbery)/styrene (crystalline) block 
polymers; thermoplastic polyolefin elastomers, including blends of 
ethylene-propylene rubber with crystalline polypropoxylene; chlorinated 
polyethylene (crystalline) and ethylene vinyl acetate copolymer (EVA) 
(rubbery); chlorobutyl rubber (rubbery) and polypropylene (crystalline); 
copolymers of polyethers and amines; polyurethane hyper blends such as 
polyurethanes and nylons; styrene block copolymers in combination with 
different elastomeric mid-segments, such as (1) polybutadienes, (2) 
polyisopropenes, (3) ethylene butadienes, (4) ethylene propylenes such as 
Kraton D and Kraton G. Other materials include polyesters, rayon, Kevlar, 
acrylic materials, nylons of the various types, polypropylene, polyesters 
of all types, cotton, wool and mixtures thereof. 
In addition, another approach for achieving an improved barrier enclosure 
for control of diffusion pumping is the use of vacuum metallizing or 
vacuum deposition of a thin metallic layer on one or both surfaces of the 
elastomeric element. Such a metallic layer needs to be only a few 
millionths of an inch in thickness in order to be effective. The metal 
deposit may be on either the outer or inner surface of the film, with the 
inner surface being preferred. Also, it can be used as a laminate between 
two elastomeric sheets. Good bonds may be achieved between mating 
elastomeric layers using conventional bonding processes, other than R.F. 
bonding techniques. 
Early in the development of this invention, blends were compounded of 
crystalline and elastomeric materials for controlling diffusion of an 
inflated product. These attempts to impart crystallinity by molecular 
blending were not entirely successful in that the resultant products did 
not possess some of the properties deemed important to the practice of the 
invention, For example, blends of polyvinyl chloride and elastomeric 
urethane produced fils that had good dielectric properties for R-F welding 
and good fatigue resistance. The diffusion rates of the gases was lower 
than that of urethane alone. The difficulty was tensile relaxation or 
creep in that the inflated products would gradually grow in size under 
pressure and eventually explode. This was especially true in warm 
climates. 
Polyethylene was considered to be a good barrier material but it acted as a 
lubricant when blended with polyurethane. Slip planes existed between the 
polyethylene and the elastomeric urethane. Apparently there was 
insufficient cross-linking between the crystalline and elastomeric 
components. The result, again, was uncontrolled and excessive elongation 
due to tensile relaxation. Later tests indicated that at least 10% 
cross-linking was necessary to prevent these problems and to provide 
materials useable in inflated cushions where diffusion pumping is 
important to maintain pressure. Thus, new materials are now available 
which may be used in accordance with this invention. 
Polyurethane has proved to be an excellent thermoplastic elastomeric film 
for use in hundreds of millions of inflated products manufactured and sold 
world-wide by Nike Shoe Company during the last ten years. Therefore, it 
is an excellent choice for blending or copolymerizing with a crystalline 
polymer as PET. The physical properties of this polyurethane are as 
follows: 
______________________________________ 
Durometer 80A to 100A 
Tensile Strength, psi 7000 to 10,000 
Elongation at break 350 
Modulus of Elasticity at 100% 
2000 to 3000 
elongation (psi) 
Tear strength (lbs per inch).sup.2 
500 
Taber abrasion.sup.1 4 
Dielectric heat seal Excellent 
Flexural fatigue resistance 
Excellent 
______________________________________ 
.sup.1 Taber ASTM D1044 CS17 Wheel, 1000 grams load, 5000 cycles. 
.sup.2 ASTM D1044 
Polyurethane is a thermoplastic elastomer with alternating block copolymers 
having segments (20%) of a hard, highly polar or crystalline material 
linked by segments (80%) of amorphous elastomeric materials (polyesters or 
polyethers) which are rubber-like at normal service temperatures. The hard 
and soft segments alternate along the polymer chain. The hard blocks 
typically consist of a mixture of 2, 4- and 2, 6-toluene diisocyanate, 
chain-extended with butane diol. When heated, the hard segments melt and 
the material becomes fluid. When cooled, the segments reharden and link 
the soft segments to give a solid-state structure similar to thermoplastic 
rubber. Because these polymers do not retain phase separation or structure 
in the melt, they are easily processed. Because the soft elastomer 
segments are polar, they are quite readily heat-sealable, especially with 
R-F dielectric heat-sealing. Their superior flexural fatigue properties 
have been demonstrated in tens of thousands of severe tests with 
laboratory endurance fatigue machines as well as in tens of millions of 
pairs of athletic and leisure shoes. 
In order to retain the above stated essential mechanical properties and 
manufacturing advantages, while reducing the permeability of the film to 
supergas and nitrogen, it is necessary to blend the polymers with other 
polar polymers. Of particular interest are blends with polyethylene 
terephthalate (PET) polyester. It is a condensation polymer made by 
reacting dimethyl terephthalate with ethylene glycol. Biaxially oriented 
PET film finds wide application. Owing to extremely low moisture 
absorption of PET, mechanical properties are virtually unaffected by 
humidity. Greater impact resistance is available with new toughened grades 
of PET. These materials are based on PET/elastomer alloys. Reinforced PET 
polymers are also available and useful. 
Another thermoplastic elastomer parent material that can be blended or 
copolymerized with crystalline elements is "HYTREL" (trade name of the Du 
Pont Company). Hytrel can also be processed by conventional thermoplastic 
techniques. Several formulations possess the requisite physical properties 
of melt-point, tensile strength, elongation, flexural modulus, fatigue 
resistance and tear strength. Hytrel has 40 to 80 percent hard segments 
and 60 to 20 percent soft segments. Although hydrolytic instability can be 
a problem it can be reduced to acceptable levels through the addition of 
Stiboxol. The harder Hytrel formulations have excellent low gas diffusion 
rates but are too stiff for air-cushion applications. The softer 
formulations (40D shore durometer, Hytrel 4056 for example) have good 
flexural properties but lack low-permeability properties. Using the 
approaches outlined in this application, this can be rectified by blending 
or copolymerizing with crystalline polymers. 
Still another good thermoplastic parent material is "RITEFLEX" (trade name 
of the Cellanese Corp.). Riteflex 540 and Tieflex 547, with durometers of 
40D and 47D are typical candidates which can be processed in conventional 
injection molding and extrusion equipment. The materials are 30 to 40 
percent crystalline. Melt temperatures are somewhat lower than the 
Hytrels, and are in the 380-420 degrees F. range. 
It should be understood that this invention is not limited to the 
thermoplastic elastomer formulations discussed in this application as 
parent envelope materials, but includes such materials in the general 
sense. The thermoplastic materials can be either thermoplastic or 
thermoset. The same generalization applies to the more highly crystalline 
elements which are blended or copolymerized with the parent polymer to 
achieve desired control of rates of diffusion pumping and permeability. 
To understand better the differences between the present invention and the 
prior diffusion pumping technique and the advantages of the present 
invention, reference is made to FIGS. 17-19. Curve A of FIG. 17 
illustrates the pressure trend with time that would take place in an 
idealized limiting case, i.e., a sealed envelope which has a constant 
volume (the envelope material does not stretch) and which is inflated at 
20 psi with a supergas (Freon 116) which has a constant partial pressure 
within the envelope. As seen, the internal pressure continues to rise 
until stabilized at a pressure level of 34.7 psig. This pressure rise is 
due to the diffusion pumping of nitrogen gas, curve C of FIG. 17 and of 
oxygen gas, curve D of that figure, from ambient environmental air. Curve 
A is the sum of curves C and D added to the initial 20 psi inflation as 
represented by curve A. For example, after 6 months, enough nitrogen gas 
will have diffused into the envelope to create a partial pressure of 
nitrogen gas of 10.8 psi. Likewise, the partial pressure of oxygen gas 
will be 3.1 psi. The sum of these two pressures added to the initial 
pressurization gives the 33.9 psig value of curve A after 6 months. 
Curve A of FIG. 17 is, however, an idealized case which provides a 
convenient manner of describing the prior diffusion pumping technique when 
related to curves C and D. An actual case of diffusion pumping of an 
inflated load carrying device is illustrated in curve B of FIG. 17. The 
latter curve is identical to curve A of FIG. 9 of the U.S. Pat. No. '626 
and FIG. 13 of the U.S. Pat. No. '250 which is the case of an actual AIR 
SOLE using polyurethane film and pressurized with F 116 supergas. In 
comparing the idealized curve A with the actual device, curve B, it is 
seen that the pressure in curve B is considerably lower than the idealized 
case. The pressure difference is due to tensile relaxation of the film, or 
stretching thereof, and the outward diffusion loss of some of the 
supergas. As seen, curve B rises quite quickly as the oxygen and nitrogen 
gas are diffusion pumped inwardly during the first 4 to 6 months of 
inflation. 
FIG. 18 presents data, again as pressure trend versus time for products in 
accordance with this invention. Curves E, F, G, and H correspond 
respectively to curves A, B, C, and D of FIG. 17. Curve E is an idealized 
case in accordance with this invention (constant volume and constant 
supergas internal partial pressure). Curve G is nitrogen gas partial 
pressure which has diffusion pumped into the device while curve H is the 
oxygen gas partial pressure which has been diffusion pumped into the 
device. In comparing curves G and H with curves C and D, it is seen that 
with the improved barrier film in accordance with this invention, inward 
diffusion of oxygen and nitrogen gas occurs more slowly. For example, 
after 6 months the partial pressure of nitrogen gas is only 3.1 psi while 
that of oxygen is 2.9 psi. Oxygen diffusion pumps more rapidly than 
nitrogen. These partial pressures when added to the 20 psi initial 
inflation pressure give the total pressure of 26 psi of curve E. 
Again, it is seen that curve F which is the actual data for a load carrying 
device of the present invention is lower in pressure than the idealized 
curve E. However, the difference between the actual and idealized curves 
in accordance with this invention is less than data of FIG. 17. This is 
because the improved barrier film material of this invention reduces 
further the normally slow outward diffusion of supergas and the improved 
film material of this invention has reduced tensile relaxation. The result 
is that the inflated volume of products in accordance with this invention 
remains relatively constant over time. The differences between curves E 
and F is primarily due to tensile relaxation of the film because loss of 
supergas pressure is very slight over the long term. 
FIG. 19 superimposes the data from FIGS. 17 and 18 and expands the scale 
from 21/2 years to 14 years to illustrate the improved pressure 
maintenance in accordance with this invention. In comparing curve B and F, 
it is seen that the pressure of curve B starts to fall rather drastically 
after the first 4 months, during which time the pressure had actually 
risen quite rapidly due to the rapid diffusion pumping of oxygen and 
nitrogen gases (curves C and D) into the enclosure. As time passes, the 
pressure continues to fall, so that after 21/2 years, the pressure has 
decreased back to the 20 psi initial inflation pressure. After 4 years, 
the pressure has dropped to 17 psig and continues to fall. 
By contrast, curve F, representing the present invention, never experiences 
a drop in pressure, but in fact exhibits a continued gradual rise in 
pressure until the pressure levels out to a steady state constant value of 
28 psig after about 7 years. Data from curves B and F for the actual two 
load carrying devices can be tabulated to show more effectively the 
advantages of the present invention, as follows: 
______________________________________ 
Curve B Curve F Percent 
Time (psi) (psi) Improvement 
______________________________________ 
1 year 22.8 26.2 15% 
2 years 21.0 27.1 29% 
3 years 18.2 27.3 50% 
5 years 14.5 27.5 90% 
7 years 12.0 27.7 130% 
______________________________________ 
These data indicate the improvement in long term pressurization that can be 
obtained in accordance with this invention. Long term tests confirm the 
new and unique long term results using F 116, air and nitrogen gas, as 
shown in the graphs. Acceptable pressurization therefore can be achieved 
with lesser, less expensive supergases, or in the limiting case, inflation 
with air or nitrogen. 
Curve F of FIG. 19 represents the case of the improved barrier material of 
this invention where oxygen gas is the mobile gas, reaching a full partial 
pressure of 3.1 psi in one year, and nitrogen is the semi-mobile gas, 
reaching a full 11.6 psi partial pressure in 12 years. As indicated from 
curve F, it is possible to obtain very long term permanent inflation 
within an envelope in accordance with this invention. However, one 
possible disadvantage is that the pressure rises to 27 psi after a couple 
of years, which is 7 psi higher (about 1/3 higher) than the initial 
inflation pressure. This can be mitigated by initial inflation with a 
mixture of air and supergas, or by inflating with one of the lesser 
supergases, i.e., one that diffuses more rapidly. 
A better and preferred solution in accordance with this invention, is 
initially to inflate with 100% nitrogen gas. Curve K of FIG. 20 represents 
the pressure-time relationship for a product in accordance with this 
invention initially pressurized with 100% nitrogen gas. Curve I shows the 
reverse diffusion of the partial pressure of the mobile oxygen gas into 
the enclosure while curve J is the partial pressure of nitrogen gas within 
the enclosure. Curve K is the sum of curves I and J. As is seen, the 
pressure "overshot" of curve K is only 10% of the initial inflation 
pressure, which is quite acceptable. Also, the initial pressure does not 
start dropping below the 20 psi initial inflation pressure until about 
51/2 years have elapsed. This is considered excellent long-term permanent 
inflation and is achieved by inflating with an available, inexpensive and 
harmless gas, nitrogen gas. 
FIG. 21 is a composite of the three types of diffusion pumping already 
described in the prior graphs. Curve B is the prior diffusion pumping with 
a supergas. Curve F is diffusion pumping in accordance with this 
invention, using supergas and mobile oxygen and captive nitrogen gases. 
Curve K is the same as curve F, but initial inflation is at 20 psig using 
pure nitrogen gas in place of supergas. 
FIGS. 22 through 24 illustrate various structures in accordance with this 
invention in order to understand better the diffusion phenomena described. 
In FIG. 22, the crystalline elements are shown enlarged about 1000 times 
and are securely bonded to the elastomeric material of the improve barrier 
layer. In the form illustrated, the crystalline material may be 
crystalline mesh or fibrous fabric material bonded securely to the 
elastomeric material as by adhesive, mechanical or molecular attachment. 
The small arrows illustrate the flow (activated diffusion) of the 
inflatant medium or reverse diffusion of ambient air through the barrier 
material. In activated diffusion, the inflatant gases first condense on 
the outer surfaces of the barrier film, then migrate through the film in 
the liquid state, to emerge on the opposite side of the film and then 
re-evaporate as a gas. As indicated in FIG. 22, the crystalline elements 
effectively form a blockage or flow restriction to the movement of the 
inflatant medium through the barrier envelope and the inward reverse 
diffusion of air. This is illustrated diagrammatically by the bent arrows 
impinging on the surfaces of the crystalline material, thereby deflecting 
the flow around the crystalline elements, and subsequently crowding or 
squeezing the flow within the narrow passages between adjacent portions of 
the crystalline elements, as the inflatant medium continues to move 
through the elastomeric material encompassing the crystalline material. 
In the form illustrated in FIG. 22, a large portion of the barrier film 
cross-section is occupied by the crystalline material, which permits 
essentially zero flow of inflatant medium. This, combined with the fact 
that the elastomeric material basically is a reasonably good barrier to 
supergas diffusion, results in a very effective mechanism for control of 
diffusion pumping, so as to achieve much more precise and stable inflation 
pressures, over a substantially greater time period thereby providing a 
much improved and superior product. 
The form illustrated in FIG. 23 is similar to that of FIG. 22 except that 
the crystalline elements are merely imbedded in the elastomeric material, 
rather than being securely attached thereto, as in FIG. 22, through the 
use of appropriate bonding or coupling procedures including temperature, 
pressure and time which is needed to achieve a good mechanical or chemical 
bond. If a good bond is not achieved, as illustrated in FIG. 23, voids 
exist around the crystalline elements or structure. These voids are 
illustrated in FIG. 23 as concentric rings or spaces around the idealized 
crystalline elements illustrated for purposes of explanation. The arrows, 
which indicate the movement of the inflatant medium, are shown to move 
into the voids and selectively transport very easily and quickly through 
the path of least resistance created by the voids. The longer length of 
the arrows, as compared to FIG. 22, are meant to indicate comparative ease 
of transport of the inflatant medium with reduced crowding and 
constricting flow at the narrow passages between adjacent portions of the 
crystalline material. Thus, it is important in producing an effective 
composite structure for control of diffusion pumping to achieve a good 
bond between the elastomer material and the crystalline material or 
elements. This is also important in achieving acceptable, long term 
flexural fatigue strength and life. 
The form illustrated in FIG. 24 includes crystalline elements in the form 
of thin walled, hollow glass spherical micro-beads with random diameters 
ranging from 50 to 200 microns or more. Beads with such various diameters 
are more cost effective than those with uniform diameters, although the 
latter may be used. As in FIGS. 22 and 23, the transport of inflatant 
medium through the composite improved barrier material is shown by arrows. 
The enlargement of this view is about 100,000 times. The blunted and 
distorted arrows indicate the flow impinging on the surface of the beads 
and thus being deflected around the beads into the flow restricting 
passages between adjacent beads. It is understood that the crystalline 
beads can also be of a larger size, solid rather than hollow, and made 
from crystalline material other than glass. 
Referring to FIG. 25, the latter illustrates one form of the invention in 
which an improved barrier film 200 is used to form the envelope to be 
pressurized. In this form, the barrier film is in the form of a composite 
crystallographic-amorphous-elastomeric barrier material in which the host 
material 202 is an amorphous elastomeric material whose crystallinity 
increased by the presence of hard crystalline segments or elements 203 
which may be highly distorted, elongated or flattened out. These hard 
crystalline segments or elements are preferably uniformly distributed 
throughout the host material. This may be achieved by appropriate 
cross-linking and grafting or other polymerization techniques. The 
distortion may be achieved by stretching or compressing the material while 
the crystals are in formation. The distortion effectively stresses the 
crystal structure of the elements 203 in the host material with the result 
that there is an increase in the cohesive energy density and the 
crystalline elements are far more effective as crystalline diffusion 
barrier elements than those which have not been distorted. Side 204 is the 
interior wall of the envelope and side 205 is the exterior side or ambient 
air side of the envelope. 
In this form, the barrier material is permeable to mobile gases, 
semi-permeable to select captive gases and essentially impermeable to 
supergases. The scale illustrated is that which would be seen under an 
electron microscope. Again, the arrows indicate the flow of the mobile gas 
through the barrier film. In this form the host material comprised of soft 
elastomeric segments or regions while the crystalline segements or regions 
are of a hard crystalline material. 
As should now be apparent to those skilled in the art, the products of this 
invention may be used in a wide variety of products, although the 
description has focused on foot wear. For example, the products in 
accordance with this invention may be used in helmets for athletic, 
military, construction, industrial, motorcycle, bicycle, or other helmets; 
in saddles and seat cushions; in gloves or protective gear; in seals for 
doors, windows, aircraft, space vehicles, industrial and oil field seals; 
mattresses and pillows; packaging products; flotation devices of various 
types; handles and handle grips for tennis racquets, jack hammers, power 
saws; shock mounted or shock producing devices of various types; and any 
of the various devices or uses which are apparent to those skilled in the 
art who are familiar with energy absorbing and energy return devices and 
cushioning and resilient devices, as will be apparent from the above 
detailed disclosure.