Patent of the month: Golf balls that age better

Materials World magazine
1 May 2018

A new golf ball that is more resilient to wear and tear is this month’s patent of the month. Dr Jennifer Unsworth, Patent Attorney at intellectual property law firm
Withers and Rogers, reports.

Injection moulding is a favoured means of production in the polymer and composite industries (see more on this in Spotlight) as it enables large volumes of product to be made in complex shapes at relatively low cost. One common application of the technology is the manufacture of sporting goods, more specifically, golf balls.

It is important that the methods by which golf balls are manufactured can meet the high demands of the global golf industry. The balls are typically produced from a polybutadiene core, which is compressed into a sphere. The core is then placed within a mould before being applied with a polyurethane cover via injection or compression moulding. 

There are, however, a number of drawbacks with current designs. Firstly, the core is susceptible to failure over time due to cracking from the repeated, high-velocity impacts that are encountered during use. This means golf balls have to be replaced regularly, as cost-conscious amateur golfers will know. 

Over time, golf balls also tend to become less resilient and more prone to wear and tear. This means that the amount of force required to hit the ball a specific distance will tend to increase with age, leading to a decrease in driving distance. Again, this is not ideal for amateur golfers wishing to squeeze every last metre out of their golf swings.

The improved ball

To address these problems, Callaway Golf Company, based in Carlsbad, California, USA, has developed a novel golf ball designed with these issues in mind. The patented technology features in US 9,789,336 B1, which was granted on 17 October 2017. 

This ball comprises a core (12), a mantle layer (14), consisting of an Ionomer material blend, such as SURLYN (manufactured by DuPont), and a polyurethane cover (16).

While these features are well known among golf ball manufacturers, Callaway’s invention resides in the make-up of the core, which, in addition to featuring polybutadiene, also contains between 0.4–2.5wt% graphene.

During manufacture, 40–90wt% polybutadiene is mixed with 0.4–2.5wt% graphene in addition to varying amounts of polyisoprene, zinc diacrylate, zinc oxide, and zinc stearate along with a peroxide initiator. The mixture is then compression moulded to form a spherical core, with a diameter of between 2–4cm. The core is also formed with the mantle layer and the cover, which are applied using compression or injection-moulding methods.

Callaway has found that incorporating graphene into the golf balls’ core makes them more durable and resistant to cracking thanks to the high-tensile and flexural properties of graphene. This enables their balls to endure more hits with a golf club, compared with those without a graphene core. It also reduces the number of times the golfer has to replace their ball.

By incorporating graphene into their golf balls, Callaway has also found that its balls age better than their counterparts. They are more resilient, meaning that they better retain their co-efficient of restitution over time. While this innovation will not necessarily allow golfers to add distance to their shots, it does mean they can maintain their optimal driving distances for longer. 

This patent demonstrates the application potential of graphene, where it can be shown to deliver a real benefit for the end user. 

Needless to say, it is likely that many competitors will be attempting to move into this area in the coming months. By obtaining a granted patent for its innovation, Callaway Golf Company is in a position to better protect its design, which seems set to become a unique selling point for the product for years to come.

Read the full patent here: