Patent Application
20080053621
As seen in
Both the inner fabric layer 22 and the embedded fabric layer 18 are made from an extensible fabric, such as a tricot knitted elastic weave. A fabric designated as Milliken 2700-D022, commercially available from Milliken Europe n.v., Ghent, Belgium is suitable. In an important aspect, the fabric is at least two way stretchable, preferably four way stretchable, to at least about 200% of the fabric not under tension with the fabric having the ability to return to its original size and shape when the tension is released. While the inner fabric layer forms an inner liner for the inner surface of the bladder, the embedded outer fabric layer is embedded in the elastomer between the outer elastomer layer 16 and the inner elastomer layers 20. The elastic fabric reinforcement plies may be polyurethane or blends of polyurethane and polyamides, such as Nylon. The fabric may be a Lycra type fabric. The fabric has a weight of at least about 200 g/m2 and preferably from about 235 g/m2 to about 270 g/m2, and an average gauge of at least about 0.55 mm, and preferably 0.6 mm to 0.8 mm. The fabric ply stretches in at least two directions, and preferably four, up to at least about 200%, and preferably 300%, and most preferably 500% to 600% of its size at rest with a recovery to its original size and shape. The yam structure or linear mass density of the fibers of the fabric may run from 5 to 50 Dtex (Milliken's 2700-D022 runs from 6 to 44 Dtex). The fabric for both the fabric embedded in the elastomer of the bladder and the fabric at the inner surface of the bladder should be coated or dipped with a material which facilitates adhesion and compatability of the fabric ply with the elastomer rubber. These fabric coatings are known. The amount and type of coating material for the fabric will vary depending upon the fabric and elastomer you are attaching the fabric to. For a polyurethane fabric a resorcinol formaldehyde latex coating is particularly appropriate. The latex can be a terpolymer based on styrene, butadiene and vinyl pyridine. The fabric is coated such as by dipping with the resorcinol formaldehyde latex fabric coating (85% fabric and 15% coating). Other coating materials, such as if the rubber is a EPDM (ethylene-propylene-diene) rubber, can include latexes which include hydrogenated styrene-butadiene rubber, carboxylated hydrogenated styrene-butadiene rubber, hydrogenated nitrile butadiene rubber and others as generally described in U.S. Pat. No. 6,860,962 to Pelton which is incorporated herein by reference. The amount and type of coating should be effective for permitting the fabric to be compatible with and adhere to the elastomer used to construct the bladder.
The elastomer used to make the outer elastomer layer 16 and the inner elastomer layers 20 of the bladder includes black rubber compound (a natural rubber filled with from about 20 to about 25 weight percent carbon black having an average particle size in the range of from 20 to 25 microns. Typical elastomers include those made from conjugated dienes, such dienes generally having 4 to 8, and preferably from 4 to 6, carbon atoms, with specific examples including butadiene and isoprene. Both natural rubber and synthetic rubber may be used. Elastomeric substrates can be various copolymers made from a conjugated diene monomer such as those mentioned above and a vinyl substituted aromatic having from 8 to 12, and preferably from 8 to 10 carbon atoms, such as styrene and alpha-methyl styrene. Natural rubber is a preferred elastomer.
The former bladder is made by the application of elastomeric and fabric plies over an appropriately sized mandrel or drum. After the layers of elastomer and fabric have been wrapped around the drum and the bladder has formed the layered components, the fabric and rubber components are prepared for curing which can be while the components are on the drum. Alternatively the components may be put into a mold. Either way the components are cured in an autoclave at times and temperatures which are known. Thereafter the cured components are removed from the autoclave and cooled. Excess material then is trimmed from the cured part.
The outer surface of the bladder has to readily release from the inner surface of the green tire. To accomplish this a release agent is applied to applied to a primed layer on the outer surface of the bladder. The surface of the elastomer is first subjected to buffing with a sander, then washed with a solvent such as acetone. Then the washed outer surface of the bladder is subjected to a treating agent such as halo cyclic amide in ethyl acetate, such as Chemlok 7701 commercially available from from Lord Chemical, Lord Corporation, 111 Lord Drive, Cary, N.C., USA. Thereafter the primer is applied to the treated surface of the elastomer. Primers which may be used include silicone rubber elastomer adhesives which may be one or more organic silane in an solvent such as methanol (such as Chemlok 607 also available from Lord Chemical, Lord Corporation, 111 Lord Drive, Cary, N.C., USA). The silicone release agent then is applied, such as by spraying, brush coating or roller painting, to the primed surface of the bladder. In an important aspect the release agent is air dried. This saves time and energy in producing the bladders. In this connection the air dried release coating may be a mixture of materials such as vinyl tri(methyl-ethyl ketoxime) silicone (commercially available as PRX 306 from Dow Corning Toray Silicone Co., Ltd., Tokyo, Japan) and a silicone with a catalyst (commercially available as SE 9500 WV83VB from Dow Corning Toray Silicone Co., Ltd., Tokyo, Japan). Other release coatings which may be used include Silastic Liquid Silicon (SLR) from Dow Corning and Silquest from GE Advanced Materials. After the release coating is applied, the release coated bladder is air dried for at least one day, preferably for about three days.
