A multi-layer bladder construct consisting of a non-stretchable outer covering and a stretchable inner bladder. The outer covering has an inner surface and is made from woven polymer fibers having a warp direction and a weft direction. The inner bladder is made from a bi-axially oriented polymer film. The inner bladder has an outer surface area that is smaller than the inner surface area of the outer covering. Upon inflation, the inner bladder stretches and expands until the outer surface of the inner bladder engages the inner surface of the outer covering, whereby a portion of tensile force loading on the outer covering is shared with the inner bladder. The multi-layer bladder was developed for use in air-inflated kites used in the sport of kiteboarding, but has broader potential application.

FIELD

There is described a multi-layer bladder construct that was developed for an air-inflated kite used in the sport of kite boarding. It is now realized that this multi-layer bladder construct has wider application.

BACKGROUND

For the extreme sport of kite boarding, the weight and integrity of the bladder is of paramount importance for performance and safety. In kite boarding, sometimes referred to as kite surfing, a person uses a kite, generally having a “C” shape. Such kite shape, also termed “a leading edge (LE) inflatable kite”, has a tube that tappers from the leading edge portion to the tips. An oversized elastomeric bladder is contained within the protective tube cover material forming the kite's leading edge tube. The kite's (pressurized) leading edge tube forms a rigid C-shape that is 10 cm-25 cm in diameter in the central portion, reducing in diameter at each tip end. The kite also has with one or more orthogonally aligned abutting struts, each containing a separate bladder, which structure supports the fabric material forming the kite's canopy.

Kites are deflated for packaging and transport. During use, the kite's leading edge tube and strut bladders are inflated to about 13-36 Newtons (3-8 lbs.) above ambient atmospheric pressure. The leading edge bladder and struts can be inflated simultaneously, or separately. Without inflation, or low inflation, a kite becomes floppy in the water, or in the air, with some wind drag, but cannot create a proper aerodynamic shape.

U.S. Pat. No. 4,708,078 by Legaignoux, et. al. teaches the first use of a kite design that can be re-launched from the water surface, which key innovation spurred the sport of kite boarding. Subsequent innovations seek to improve on re-launching the kite from the water surface, such as, for example, U.S. Pat. No. 7,104,504 B2 by Peterson et al. which describes a system whereby the kite rider can use a dedicated line (or piggybacking onto one of the existing lines) to adjust the kite canopy profile to exhibit different aerodynamic characteristics to facilitate re-launching the kite. However, a key aspect of all kites is weight, as the overall kite weight will determine the ease of re-launch, responsiveness of the kite during riding, and the ability of the kite to fly in light winds.

SUMMARY

There is provided a multi-layer bladder construct consisting of a non-stretchable outer covering and a stretchable inner bladder. The outer covering has an inner surface and is made from woven polymer fibers having a warp direction and a weft direction. The inner bladder is made from a bi-axially oriented polymer film. The inner bladder has an outer surface area that is smaller than the inner surface area of the outer covering. Upon inflation, the inner bladder stretches and expands until the outer surface of the inner bladder engages the inner surface of the outer covering, whereby a portion of the tensile force loading on the outer covering is shared with the inner bladder.

In developing the above described multi-layer bladder construct, a problem had to be addressed as to how to make the bladder construct lighter in weight, without sacrificing integrity when the bladder construct was placed under load. The use of an inner bladder with an outer surface area that is smaller than the inner surface area of the outer covering, makes the multi-layer bladder construct lighter. A smaller bladder can be used, as expansion of the inner bladder is limited by the inner surface of the outer covering. This also serves to share a portion of the tensile force load from the outer covering to the inner bladder, so that the multi-layer bladder construct is able to handle greater tensile force load than the outer covering alone can bear. The expanded bladder essentially acts as a tensile-bearing component, allowing for the use of a lighter outer covering, and thus a lighter kite.

DETAILED DESCRIPTION

A multi-layer bladder construct will now be described with reference toFIG. 1throughFIG. 5. The description will use as an example the multi-layer bladder construct in use with respect to an air-inflatable kite used in the sport of kite boarding.

Structure and Relationship of Parts:

FIG. 1illustrates a kilter10engaged in the sport of kite boarding or kite surfing. The kiter stands on a kite board12on the water surface13holding a control bar14. Outside (steering) lines15are connected near the wingtips17, and inside lines16are also attached to the kite18at the distil end. The leading edge tube19is inflated, thereby creating a curved rigid structure, with struts21supporting the canopy20to create aerodynamic lift. Outside lines15are connected to control bar14to provide for steering the kite. Inside lines16are connected at the proximal end to a hook mechanism on the kiter's harness. A safety leash line11connects the kiter to one or two of the inside lines to remain tethered to the kite in the event the kiter lets of the control bar and also detaches from the hook connecting the inside lines. The kite18is not attached to the board12. The kiter10manoeuvers kite18so as to pull the kiter and the board12across the surface of the water13.

FIG. 2shows an expanded view of an inflated leading edge tube19(without struts or canopy). For clarity, the tip sections, which sections are generally tapered, are shown as26. The rest of the leading edge tube19, which tube has a larger diameter, is defined as the “main tube section”. To create a curved shape, a non-stretchable outer covering32is formed into panels55are sewn together at various locations22, where the length of the inner curved surface24is shorter than the outer curved surface25, thereby causing the leading edge tube19to form a curved shape when inflated.

Referring toFIG. 3, leading edge tube19is made from a multi-layer bladder construct30consisting of the non-stretchable outer covering32and a stretchable inner bladder34. Outer covering32has an inner surface36. Inner bladder34has an outer surface area38that is smaller than inner surface36of outer covering32. A valve33is provided for the purpose of inflating and deflating inner bladder34.

Referring toFIG. 4bladder34is shown as inflated, with the outer surface contacting the non-stretchable outer covering32. Outer covering32is made from a woven polymer fabric which fibres are oriented in a warp direction61and a weft directions60(seeFIG. 5). A suitable material for the outer covering32is a woven Dacron fabric that is coated with a sealant polymer, and as such, does not significantly stretch in the warp, weft or bias directions.

Referring toFIG. 5, inner bladder34is made from a bi-axially oriented polymer film46having molecular orientation in both a first direction63referred to as “Machine Direction (MD)”, and a second direction62, referred to as “Transverse Direction (TD)”. Although any biaxially-oriented polymer film, such as, for example, BOPP, BOPE, BOPET, BOPA, PEN or PPS could be used for fabricating the bladder construct, it is preferred to use a biaxially-oriented BOPET film that will result in a bladder construct weighting about 10-70 gsm (grams per square meter), preferably about 20-45 gsm where both sides of such a BOPET film are fused to a (thermoplastic) heat-sealable or fusible layer, shown as50and51, comprised of, for example, a polyethylene, or a polyolefin, a polyurethane, or a co-polymer thereof, or a co-polymer polyamide, with a melting temperature that is 10 C or more below the melting point of the BOPET film. Such biaxially-oriented films are much stronger and resilient in the MD63and TD62directions than prior art TPU bladder films, allowing for the use of much lighter bladders.FIG. 5also illustrates the woven polymer fabric40forming outer covering32, with warp fibers42shown in the warp direction61and weft fibers44in weft direction60.

Referring toFIG. 5, it is preferred one of the MD63or TD62direction of the bi-axially oriented polymer film46forming inner bladder34is aligned with one of fibres42in the warp direction61or fibres44the weft direction60of woven polymer fabric40forming outer covering32. This co-alignment of outer covering fibers and oriented polymer bladder serves to increase both the radial and longitudinal tensile strength of the multi-layer bladder construct, as will hereinafter be further explained.

Referring toFIG. 3, there is illustrated inner bladder34undersized by approximately 1%-5% when the surface area of the bladder is compared to the surface area of the non-stretchable outer covering, When inflated, inner bladder34expands within or near its elastic limit with inner bladder34thickness thinning during inflation until outer surface38of inner bladder32engages inner surface36of outer covering32. When this occurs a portion of the tensile force loading on outer covering32is shared with inner bladder34. It is preferred that inner bladder34, when inflated, shares at least 5% of the tensile force loading on outer covering32.

The structure of multi-layer bladder construct30, shown inFIG. 4, greatly reduces the probability of herniation, or material aneurysm, tear or rupture, and when installed undersized, provides part of the tensile force loading of the inflated Dacron fabric leading edge.

By co-aligning, for example, the Dacron fabric warp with the oriented film MD (Machine Direction), and the fabric weft with the film TD (Transverse Direction) such oriented layering adds the tensile strength of both materials add to provide an exceptionally high combined tensile strength construct.

Since the tensile loading of the inflated leading edge is predominately in the radial direction, it is advantageous to orient the layers such that maximum combined tensile strength is in the radial direction.

Such combined tensile strength of the Dacron fabric and the orientated film also provides for the use of a lighter Dacron weave weight in the radial direction, as the loading of the Dacron weave is partially shared with the oriented film, thus allowing for the design of a lighter kite.

It has been found that heat sealing a mono-layer of biaxially-oriented polymer film to itself for use as an air-tight bladder is either not possible, depending on the polymer, or, for thermoplastic materials, causes buckling of the film at the seal area, which leads to an imperfect seal and air leakage. Better results have been obtained by applying a heat fusible adhesive layer to one or both sides of the biaxially-oriented polymer film. Such heat fusible films need to have a melting point about 10 C or more below the melting point of the biaxially-oriented polymer.

The prior art uses a highly stretchable TPU film. Under-sizing such a elastomeric film is problematic, as this would thin out the film, and be prone to create areas of herniation, pinhole leaks and greatly increase the probability of rupturing the delicate TPU film.

Referring toFIG. 2, it should be noted that leading edge tube19has tip sections26that are generally tapered. This is a vulnerable area. It is recommended that inner bladder not be undersized at tip section26and instead be tapered to conform to tip sections26without any, or with minimal, stretch. It is also preferred that the thickness of the inner bladder in the tip area be at least 25% thicker than the inner bladder in the leading edge area.

The scope of the claims should not be limited by the illustrated embodiments set forth as examples, but should be given the broadest interpretation consistent with a purposive construction of the claims in view of the description as a whole.