A method for forming a golf ball core with a nanofiller masterbatch is disclosed herein. The method includes mixing the nanofiller masterbatch, a graphene masterbatch material with other materials to form a core mixture, wherein the masterbatch preferably comprises 1-80% by weight of nanofillers and 20-99% by weight of a carrier polymer.

In a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer and a cover, the core is formed of a rubber composition, the envelope layer, intermediate layer and cover are each formed of a single layer of resin material; the hardness relationship among the layers, in terms of Shore C hardness values, satisfies the following two conditions:

material hardness of cover>material hardness of intermediate layer, and

material hardness of envelope layer≥surface hardness of core; and

the thickness relationship among the layers satisfies the following condition:

(cover thickness intermediate layer thickness)<envelope layer thickness.

This ball serves as a distance ball which enables a superior distance to be achieved on full shots with a driver and with irons.

In a golf ball having a core, envelope layer, intermediate layer and cover, the (core diameter)/(ball diameter) value falls within a particular range, the core has a specific hardness profile, and the Shore C hardness relationships among the core center and surface hardnesses and the surface hardnesses of the envelope layer-encased sphere, intermediate layer-encased sphere and ball satisfy the following conditions:
core surface hardness<surface hardness of envelope layer-encased sphere<surface hardness of intermediate layer-encased sphere>ball surface hardness,  (1)
(surface hardness of envelope layer-encased sphere)−(core center hardness)≥28.  (2)
Also, the envelope layer, intermediate layer and cover have respective thicknesses which satisfy the condition:
cover thickness<intermediate layer thickness  (3)
cover thickness<envelope layer thickness  (4)
envelope layer thickness≥0.8 mm.  (5)
This ball enables mid-level and skilled amateur golfers to achieve superior distances on driver shots and on iron shots, and moreover has a soft yet good feel at impact.

In a golf ball having a core, an envelope layer, an intermediate layer and a cover, the core, the envelope layer-encased sphere obtained by encasing the core with the envelope layer, the intermediate layer-encased sphere obtained by encasing the envelope layer-encased sphere with the intermediate layer and the ball obtained by encasing the intermediate layer-encased sphere with the cover have respective deflections when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which satisfy specific conditions. This ball achieves a good distance on shots with a utility club and with irons, is receptive to spin in the short game and has a soft feel at impact on all shots, making it useful to amateur golfers.

In a golf ball having a core and a cover, the cover is formed primarily of polyurethane, the ball has a diameter of at least 43.0 mm and, in an impact test carried out by hitting the ball with a driver at a head speed of 40 m/s, the sum t1+t2 of the time t1 required from initial contact by the driver with the ball for deformation of the ball to reach a maximum and the time t2 required from the state of maximum ball deformation for the ball and driver to separate is 650 μsec or less. This golf ball makes it possible for golfers who have a high head speed and ordinary golfers who do not to compete without relying excessively on superiority in terms of distance.

In a golf ball having a core and a cover, the cover is formed primarily of polyurethane, the ball has a weight of 44.8 g or less and, in an impact test carried out by hitting the ball with a driver at a head speed of 40 m/s, the sum t1+t2 of the time t1 required from initial contact by the driver with the ball for deformation of the ball to reach a maximum and the time t2 required from the state of maximum ball deformation for the ball and driver to separate is 650 μsec or less. This golf ball makes it possible for golfers who have a high head speed and ordinary golfers who do not to compete without relying excessively on superiority in terms of distance.

Multi-layered golf balls having at least one layer made of a foamed silicone composition are provided. Multi-layered golf balls having at least one layer made of non-foamed silicone elastomer composition also are provided. For example, three-piece, four-piece, and five-piece golf balls containing different core and cover structures can be made. The foamed silicones have good thermal stability and durability without sacrificing resiliency. The non-foamed silicone elastomers have high elongation, tensile strength, chemical/fluid-resistance, and weatherability properties. These compositions can be used to form any layer, for example, core, intermediate, or cover, in the golf ball.

Multi-piece golf balls having a multi-layered solid core and multi-layered cover are provided.

A golf ball includes a core having an outer surface and a geometric center; an inner cover layer, and an outer cover layer. The inner cover layer includes an ionomeric material and has a material hardness of about 60 Shore D or greater. The outer cover layer is formed from a polyurea or polyurethane and has a material hardness of about 60 Shore M or greater. The outer surface of the core has a hardness of about 68 to 92 Shore C. The geometric center of the core has a hardness of about 45 to 85 Shore C. The core outer surface hardness is greater than the geometric center hardness by about 5 to 21 Shore C to define a positive hardness gradient. The core also has a volume weighted average hardness, H.sub.V, of about 70 to 80, where

[00001]${\stackrel{\_}{H}}_V=\frac{I_V}{V_c}.$

Provided is a golf ball is excellent in flight distance performance, approach performance, and feel at impact. A ball 2 includes a core 4, a mid layer 6, and a cover 8. The core 4 includes an inner core 10 and an outer core 12. The cover 8 includes an inner layer cover 10 and an outer layer cover 12. An inner core volume Vc, a mid layer volume Vm, a mid layer hardness Hm, an inner layer cover volume Vinc, an inner layer cover hardness Hinc, an outer layer cover volume Vouc, an outer layer cover hardness Houc, and a ball volume V meet the following relational expressions (a) to (g): (a) Vc/V<0.07, (b) Hm>Hinc>Houc, (c) Hm−Houc>25, (d) Vm>Vinc>Vouc, (e) (Vm+Vinc+Vouc)/V<0.30, (f) Vm/Vouc>1.50, and (g) (Vm*Hm)/(Vouc*Houc)>3.0.