Alloy blends of polyurethane and rubber

Abstract

The present invention relates to a rubber formulation suitable for making barrier articles, such as inflatable sports balls or bicycle tubes, that resist the passage of gases, such as air, particularly as applicable to tennis balls, and more particularly to the rubber formulation which contains substantially amorphous, millable polyurethane alloyed with natural and / or synthetic rubbers.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims benefit of the priority of Provisional Application No. 60 / 455,674 filed Mar. 18, 2003 and U.S. application Ser. No. 10 / 802,137 filed Mar. 17, 2004, now abandoned.FIELD OF THE INVENTION [0002] The present invention relates to a rubber formulation suitable for making barrier articles, such as inflatable sports balls or bicycle tubes that resist the passage of gases, such as air, particularly as applicable to tennis balls and more particularly to the rubber formulation which contains substantially amorphous, millable polyurethane alloyed with natural and / or synthetic rubbers. BACKGROUND OF THE INVENTION [0003] In rubber barrier articles for producing pressurized sports articles, such as hollow core tennis balls or bladders for soccer balls, volleyballs, basketballs or bicycle innertubes, vulcanizable natural or synthetic butyl rubbers and combinations thereof are commonly employed. These cured rubber components are f...

AI Technical Summary

Benefits of technology

[0015] An aspect of the present invention provides barrier articles with novel formulations for use in hollow or inflatable articles, such as tennis balls, basketballs, volleyballs, soccer balls, inner tubes, and tires having substantially improved barrier properties.

[0016] An aspect of the present invention provides barrier articles with novel millable polyurethane (MPU) / rubber alloys providing enhanced barrier properties along with good balance of other mechanical properties, such as resiliency, strength etc.

[0017] A further aspect of the present invention provides a barrier article with novel MPU / rubber formulations which can be used to make barrier articles without requiring new manufacturing equipment or process lines.

Problems solved by technology

These cured rubber components are fabricated with conventional rubber milling and molding methods and form products that are sufficient in some properties but are typically deficient in either air retention or elastic properties.

Bladders, or “cores,” made from natural rubber can suffer from deficient gas barrier performance, undesirably high rubber aging, and undesirable rubber hysteresis attributes.

Natural rubber is known to age harden over time and suffers from high hysteresis in that the rubber does not readily recover its pre-stretched elastic properties.

Moreover, because of the deficient gas barrier performance of natural rubber, the pressure gradient between the pressurized inside and ambient outside, causes air to gradually diffuse from balls made from natural rubber.

Loss of air ultimately renders these balls unsuitable for play.

As a result of undesirable rubber aging and poor rubber hysteresis properties, the bounce and feel of these balls tends to decay substantially within the normal use timeframe.

However, they are significantly deficient in resilience which negatively affects their bounce, control, and feel.

Deficiencies in resilience exacerbates vulnerability of articles such as innertubes to puncture damage.

However, because of pressure differential between inside the core and outside, the air gradually diffuses to the outside, causing “softening” of the ball which results in loss of good bounce and playability.

However, once a tennis ball is removed from its pressurized can, air pressure loss starts and softening of the ball resumes and play consistency continues to deteriorate.

On the other hand, in the premium performance soccer balls, natural latex rubber bladders are employed for superior foot-speed and control, but at a significant air retention penalty.

The poor air retention of natural rubber soccer balls becomes an even bigger problem on a long hot summer day.

However, these airless tennis balls do not have the same “feel” and bounce as the pressurized balls, consequently pressureless balls have not been adopted by tennis professionals.

Another difficult approach is to employ a flexible barrier spray-coated inside the bladder or core halves.

However, each of these is expensive and cumbersome to employ.

In the case of sulfur hexafluoride, internal pressure actually increases with time due to pneumatic pumping of air molecules from the outside the ball into the inside of the ball driven by the partial pressure gradient and limited by the relatively slow permeability of the sulfur hexafluoride.

Moreover, these tennis balls, which are made of a molded spherical shell of elastomeric material, such as natural rubber or artificial rubber suffer from the same softening due to air leakage in between the pumping events.

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