Golf balls having cores with increased hardness gradient

Abstract

To provide golf balls having cores with an increased hardness gradient.SOLUTION: The cores have a "positive" hardness gradient (or a "hard-to-soft" hardness) where the outer surface of the core is harder than the center. The increased positive hardness gradient can be achieved by introducing a water-releasing agent into a core rubber formulation during a curing process. Resulting golf balls have reduced spin and sufficient impact durability.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to golf balls. More specifically, the present disclosure relates to golf balls having a core with an increased hardness gradient. The resulting golf ball has reduced spin rates and sufficient impact durability. [Background technology]

[0002] Solid golf balls are typically made with a solid core surrounded by a cover, both of which may have multiple layers, such as a dual core having a solid center (or inner core) and an outer core layer, or a multi-layer cover having an inner cover layer and an outer cover layer. Generally, the golf ball core and / or center are composed of a thermoset rubber, such as a polybutadiene-based composition.

[0003] Thermoset rubbers are heated and crosslinked in various processing steps to create golf ball cores with certain desired properties, such as higher or lower compression or hardness, which can affect the ball's spin rate and / or provide a better "feel". These and other properties can be tailored to the needs of golfers of different abilities. For example, professional and highly accomplished amateur golfers can more easily apply backspin on balls with relatively high spin rates, which helps them to control the ball better and improves shot accuracy and placement. On the other hand, recreational players who cannot intentionally control the spin rate when hitting the ball with a club are less likely to use high spin rate balls. Due to the nature of the thermoset material and the heating / curing cycles used to form the material into the core, manufacturers can achieve a variety of properties throughout the core (i.e., from the core surface to the center of the core).

[0004] In conventional polybutadiene-based cores, the physical properties of the molded core are highly dependent on the cure cycle (i.e., the time and temperature the core is subjected to during molding). This time and temperature history is inherently variable throughout the core, with the center of the core being exposed to a different time / temperature (i.e., shorter time at a different temperature) than the surface (because it takes longer to get heat to the center of the core), allowing a property gradient to exist at points between the center and the core surface. This physical property gradient is easily measured as a hardness gradient.

[0005] The prior art contains multiple references that describe "hard to soft" hardness gradients across thermoset golf ball cores. The "hard to soft" hardness gradients are typically in the range of 5 Shore C to 30 Shore C. While these hardness gradients are helpful in reducing the spin rate of a golf ball, it would be advantageous to design a core that has a greater hardness gradient between the center and the core surface than currently used in the art, so that the spin rate of a golf ball can be further reduced while maintaining sufficient impact durability and resilience. Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned problems, as well as other problems, are addressed by the following invention, although it should be understood that not every embodiment of the invention described herein addresses each and every problem discussed above. [Means for solving the problem]

[0007] In one embodiment, a golf ball is provided, the golf ball including a dual core and a cover layer surrounding the dual core, the dual core including an outer core layer disposed on an inner core layer, at least one of the outer core layer or the inner core layer being formed from a rubber composition cured under heat, the rubber composition including a base rubber including a polybutadiene rubber, a crosslinking coagent including an organic peroxide, an acrylate, a diacrylate, a methacrylate, or a zinc salt of a dimethacrylate, a water releasing agent including a metal sulfate hydrate having 1 to 4 waters of hydration, the water release agent is present in the rubber composition in an amount of from about 1 phr to about 3.9 phr; the layers formed from the rubber composition have an outer surface and a geometric center, each having a hardness, the hardness of the geometric center being in a range of from about 45 Shore C to about 65 Shore C, the hardness of the outer surface being in a range of from about 80 Shore C to about 100 Shore C, the hardness of the outer surface being greater than the hardness of the geometric center and defining a positive hardness gradient of at least 30 Shore C units; and the cover layer comprises an ionomer, a polyurethane, a polyurea, a polyurethane-urea hybrid, or copolymers and mixtures thereof.

[0008] In one embodiment, the metal may be an alkaline earth metal. In a further embodiment, the inner core layer has a diameter ranging from about 6.35 millimeters to about 38.35 millimeters. In yet a further embodiment, the dual core has a diameter ranging from about 35.31 millimeters to about 41.15 millimeters. In yet a further embodiment, the outer core layer and the inner core layer are formed from a rubber composition. In another embodiment, the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr. In a further embodiment, the water synergist is calcium sulfate dihydrate.

[0009] In another embodiment, a golf ball is provided, the golf ball including a dual core including an outer core layer disposed on an inner core layer, an inner cover layer surrounding the dual core, and an outer cover layer disposed about the inner core layer, the outer core layer being formed of a first rubber composition cured under heat, the first rubber composition including a base rubber including a mixture of polybutadiene rubber and styrene butadiene rubber, an organic peroxide, and zinc diacrylate, the inner core layer being formed of a second rubber composition cured under heat, the second rubber composition including The rubber composition includes a base rubber including polybutadiene rubber, an organic peroxide, zinc diacrylate, and a water-releasing agent including a metal sulfate hydrate having one to four waters of hydration, the water-releasing agent being present in the rubber composition in an amount of about 1 phr to about 3 phr, the inner core layer having a geometric center and an outer surface, each having a hardness, the hardness of the outer surface being greater than the hardness of the geometric center, defining a positive hardness gradient of 30 Shore C units to 50 Shore C units, the amount of the water-releasing agent present in the rubber composition and the hydration number of the water-releasing agent being related to the positive hardness gradient, and being represented by the following formula (I):

number

number

[0010] The polybutadiene rubber may be present in the mixture in an amount of about 80 phr to about 99 phr, and the styrene butadiene rubber may be present in the mixture in an amount of about 1 phr to about 20 phr. In a further embodiment, the organic peroxide is dicumyl peroxide, and the organic peroxide is present in the first rubber composition in an amount less than the amount of the organic peroxide present in the second rubber composition. In yet a further embodiment, the organic peroxide is present in the second rubber composition in an amount of about 0.1 phr to about 3 phr, the zinc diacrylate is present in the second rubber composition in an amount of about 10 phr to 45 phr, and the water release agent is present in the second rubber composition in an amount of about 3 phr. In yet a further embodiment, the inner cover layer is formed from a partially neutralized ionomer, a highly neutralized ionomer, or a combination thereof, and the outer cover is formed from a thermoplastic polyurethane. In yet a further embodiment, the dual core has a diameter of about 35.31 millimeters to about 41.15 millimeters. In other embodiments, the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 34 Shore C units.

[0011] In yet another embodiment, a golf ball is provided, the golf ball including a dual core including an outer core layer disposed over an inner core layer, an inner cover layer surrounding the core, and an outer cover layer disposed about the inner cover layer, the outer core layer and the inner core layer are each formed from a rubber composition cured under heat, the rubber composition including a base rubber including a polybutadiene rubber having a 1,4 cis content of at least 90%, a water-releasing agent including dicumyl peroxide, zinc diacrylate, and a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of about 1 phr to about 3 phr and being an additive selected from zinc pentachlorothiophenol, zinc oxide, barium sulfate, or combinations thereof, the outer core layer and the inner core layer each having a geometric center having a first hardness and an outer surface having a second hardness, the second hardness being greater than the first hardness and defining a positive hardness gradient of at least 34 Shore C units.

[0012] The water release agent may be present in the rubber composition in an amount of about 3 phr. In a further embodiment, the inner cover layer is formed from an ionomer and the outer cover layer is formed from a polymer selected from the group consisting of polyurethanes, polyureas, polyurethane-urea hybrids, and copolymers and mixtures thereof. In yet a further embodiment, the zinc pentachlorothiophenol is present in the rubber composition in an amount of about 0.1 phr to about 3 phr, the zinc oxide is present in the rubber composition in an amount of about 3 phr to about 10 phr, and the barium sulfate is present in the rubber composition in an amount of about 10 phr to about 20 phr. In yet another embodiment, the additive in the rubber composition is a combination of zinc pentachlorothiophenol, zinc oxide, and regrind. In another embodiment, the water release agent is calcium sulfate dihydrate.

[0013] In one embodiment, a golf ball is provided, the golf ball including a solid core having an exterior surface and a geometric center, and a cover layer surrounding the core, the solid core being formed from a rubber composition that is cured under heat, the rubber composition including a base rubber including a mixture of polybutadiene and ethylene-propylene-diene rubber, an organic peroxide including dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and an acrylate, diacrylate, methacrylate, or a methacrylate-based rubber. and a water-releasing agent comprising a metal sulfate hydrate having one to four waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3.9 phr. The geometric center and the outer surface each have a hardness, the hardness of the geometric center being in the range of from about 45 Shore C to about 65 Shore C and the hardness of the outer surface being in the range of from about 80 Shore C to about 100 Shore C, the hardness of the outer surface being greater than the hardness of the geometric center and defining a positive hardness gradient of at least 30 Shore C units.

[0014] In one embodiment, the metal may be an alkaline earth metal. For example, the synergist may be calcium sulfate dihydrate. In a further embodiment, the polybutadiene is present in the mixture in an amount of about 70 phr to about 99 phr, and the ethylene-propylene-diene rubber is present in the mixture in an amount of about 1 phr to about 30 phr. In yet a further embodiment, the solid core has a compression value of about 10 to about 95. In yet a further embodiment, the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr. In yet a further embodiment, the crosslinking coagent is present in the rubber composition in an amount of about 10 phr to about 45 phr.

[0015] In another embodiment, a golf ball is provided, the golf ball including a solid core having an outer surface and a geometric center, an inner cover layer surrounding the core, and an outer cover layer disposed about the inner cover layer, the solid core being formed from a rubber composition cured under heat, the rubber composition including a base rubber including a mixture of two or more polybutadiene rubbers and an ethylene-propylene-diene rubber, an organic peroxide, a crosslinking coagent including zinc diacrylate, and a water-releasing agent including a metal sulfate hydrate having one to four waters of hydration, the water-releasing agent being present in the rubber composition in an amount of about 1 phr to about 3 phr, the geometric center and the outer surface each having a hardness, the hardness of the outer surface being greater than the hardness of the geometric center and defining a positive hardness gradient of 30 Shore C units to 50 Shore C units, the amount of the water-releasing agent present in the rubber composition and the number of waters of hydration of the water-releasing agent being related to the positive hardness gradient, which is represented by the following formula (I):

number

number

[0016] The inner cover layer may comprise an ethylene acid copolymer containing acid groups such that less than 70% of the acid groups are neutralized, and the outer cover layer may comprise a polymer selected from the group consisting of polyurethanes, polyureas, polyurethane-urea hybrids, and copolymers and mixtures thereof. In a further embodiment, the outer cover comprises a thermoplastic polyurethane. In yet a further embodiment, the solid core has a diameter of about 35.31 millimeters to about 41.15 millimeters. In yet a further embodiment, the two or more polybutadiene rubbers are present in the mixture in an amount of about 85 phr to about 95 phr, and the ethylene-propylene-diene rubber is present in the mixture in an amount of about 5 phr to about 15 phr. In a further embodiment, the inner cover layer has a thickness of about 0.25 millimeters to about 3.05 millimeters, and the outer cover layer has a thickness of about 0.10 millimeters to about 2.03 millimeters. In yet a further embodiment, the organic peroxide is present in the rubber composition in an amount of about 0.1 phr to about 3 phr, the crosslinking coagent is present in the rubber composition in an amount of about 10 phr to 45 phr, and the water-releasing agent is present in the rubber composition in an amount of about 3 phr.

[0017] In yet another embodiment, a golf ball is provided, the golf ball including a solid core having an exterior surface and a geometric center, an inner cover layer surrounding the core, and an outer cover layer disposed about the inner cover layer, the solid core being formed from a rubber composition cured under heat, the rubber composition including a base rubber including a mixture of two or more polybutadiene rubbers and an ethylene-propylene-diene rubber, and a water-releasing agent including dicumyl peroxide, zinc diacrylate, calcium sulfate dihydrate, zinc sulfate dihydrate, or a combination thereof, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3 phr and being an additive selected from zinc pentachlorothiophenol, zinc oxide, barium sulfate, or a combination thereof, the geometric center and the exterior surface each having a hardness, the hardness of the exterior surface being greater than the hardness of the geometric center and defining a positive hardness gradient of at least 34 Shore C units.

[0018] In a further embodiment, the water release agent is present in the rubber composition in an amount of about 3 phr. In another embodiment, the additive is a combination of zinc pentachlorothiophenol, zinc oxide, and barium sulfate. In yet a further embodiment, the zinc pentachlorothiophenol is present in the rubber composition in an amount of about 0.1 phr to about 3 phr, the zinc oxide is present in the rubber composition in an amount of about 3 phr to about 10 phr, and the barium sulfate is present in the rubber composition in an amount of about 10 phr to about 30 phr. In yet a further embodiment, the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of 34 Shore C units to 50 Shore C units. In yet a further embodiment, the water release agent is calcium sulfate dihydrate.

[0019] In one embodiment, a golf ball is provided, the golf ball including a solid core having an outer surface and a geometric center, and a cover layer surrounding the solid core, the solid core being formed from a rubber composition cured under heat, the rubber composition including a base rubber made of polybutadiene rubber and a hydrate having 1 to 4 waters of hydration, the water release agent being present in the rubber composition in an amount of from about 1 phr to about 3.9 phr, the geometric center and the outer surface each having a hardness, the hardness of the geometric center being in the range of from about 45 Shore C to about 65 Shore C, the hardness of the outer surface being in the range of from about 80 Shore C to about 100 Shore C, the hardness of the outer surface being greater than the hardness of the geometric center and defining a positive hardness gradient of at least 30 Shore C units, and the cover layer including an ionomer, a polyurethane, a polyurea, a polyurethane-urea hybrid, or copolymers and mixtures thereof.

[0020] The metal may be an alkaline earth metal. For example, the synergist may be calcium sulfate dihydrate. In a further embodiment, the solid core has a diameter ranging from about 35.31 millimeters to about 41.15 millimeters. In yet a further embodiment, the cover layer is formed from an ionomer, a thermoplastic polyurethane, or a castable polyurethane. In yet a further embodiment, the solid core has a compression value of about 10 to about 95. In a further embodiment, the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr.

[0021] In another embodiment, a golf ball is provided, the golf ball including a solid core having an outer surface and a geometric center, an inner cover layer surrounding the core, and an outer cover layer disposed about the inner cover layer, the solid core being formed from a rubber composition cured under heat, the rubber composition including a base rubber made of a polybutadiene rubber having a 1,4 cis content of at least 90%, an organic peroxide, zinc diacrylate, and a water-releasing agent including a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3 phr and being an additive selected from zinc pentachlorothiophenol, zinc oxide, barium sulfate, or combinations thereof, the geometric center and the outer surface each having a hardness, the hardness of the outer surface being greater than the hardness of the geometric center and defining a positive hardness gradient of from 30 Shore C units to 50 Shore C units, the amount of water-releasing agent present in the rubber composition and the number of waters of hydration of the water-releasing agent being related to the positive hardness gradient, which is represented by the following formula (I):

number

number

[0022] The inner cover layer may be formed of a partially neutralized ionomer, a highly neutralized ionomer, or a combination thereof. In a further embodiment, the outer cover is formed of a thermoplastic polyurethane. In yet a further embodiment, the solid core has a diameter of about 35.31 millimeters to about 41.15 millimeters. In yet a further embodiment, the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 36 Shore C units. In yet another embodiment, the inner cover layer has a thickness of about 0.25 millimeters to about 3.05 millimeters, and the outer cover layer has a thickness of about 0.10 millimeters to about 2.03 millimeters. In a further embodiment, the organic peroxide is present in the rubber composition in an amount of about 0.1 phr to about 2.5 phr, the zinc diacrylate is present in the rubber composition in an amount of about 10 phr to about 45 phr, and the water release agent is present in the rubber composition in an amount of about 3 phr.

[0023] In yet another embodiment, a golf ball is provided, the golf ball including a solid core having an exterior surface and a geometric center, an inner cover layer surrounding the core, and an outer cover layer disposed about the inner cover layer, the solid core being formed from a rubber composition cured under heat, the rubber composition consisting of polybutadiene rubber, dicumyl peroxide, zinc oxide, zinc diacrylate, calcium sulfate dihydrate, zinc pentachlorothiophenol, and barium sulfate, the calcium sulfate dihydrate being present in the rubber composition in an amount from about 1 phr to about 3 phr, the geometric center and the exterior surface each having a hardness, the hardness of the exterior surface being greater than the hardness of the geometric center and defining a positive hardness gradient of at least 34 Shore C units.

[0024] The calcium sulfate dihydrate may be present in the rubber composition in an amount of about 3 phr. In a further embodiment, the inner cover layer is formed from an ionomer and the outer cover layer is formed from a polymer selected from the group consisting of polyurethane, polyurea, polyurethane-urea hybrid, and copolymers and mixtures thereof. In yet a further embodiment, the zinc pentachlorothiophenol is present in the rubber composition in an amount of about 0.1 phr to about 3 phr, the zinc oxide is present in the rubber composition in an amount of about 3 phr to about 10 phr, and the barium sulfate is present in the rubber composition in an amount of about 10 phr to about 30 phr. In yet a further embodiment, the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of about 34 Shore C units to about 40 Shore C units. In another embodiment, the polybutadiene rubber has a 1,4 cis content of at least 90%.

[0025] In one embodiment, a golf ball is provided, the golf ball including a multi-layer core including a plurality of core layers, and a cover layer surrounding the multi-layer core, at least one of the core layers being formed from a rubber composition cured under heat, the rubber composition including a base rubber including a polybutadiene rubber, a crosslinking coagent including an organic peroxide and a zinc salt of an acrylate, diacrylate, methacrylate, or dimethacrylate, and a water-releasing agent including a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3. the core layer is present in an amount of 9 phr and formed from the rubber composition has an outer surface and a geometric center, each having a hardness, the hardness of the geometric center being in the range of about 45 Shore C to about 65 Shore C, the hardness of the outer surface being in the range of about 80 Shore C to about 100 Shore C, the hardness of the outer surface being greater than the hardness of the geometric center defining a positive hardness gradient of at least 30 Shore C units; and the cover layer comprises an ionomer, a polyurethane, a polyurea, a polyurethane-urea hybrid, or copolymers and mixtures thereof.

[0026] In one embodiment, the metal may be an alkaline earth metal. In a further embodiment, the multi-layered core includes at least three core layers. In yet a further embodiment, the multi-layered core has a diameter ranging from about 35.31 millimeters to about 41.15 millimeters. In yet a further embodiment, each core layer of the multi-layered core is formed from a rubber composition. In yet a further embodiment, the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr. In yet a further embodiment, the water synergist is calcium sulfate dihydrate.

[0027] In another embodiment, a golf ball is provided, the golf ball including a multi-layered core including a center and at least two core layers formed about the center, an inner cover layer surrounding the multi-layered core, and an outer cover layer disposed about the inner cover layer, wherein at least one of the center or the at least two core layers is formed of a rubber composition cured under heat, the rubber composition including a base rubber including a polybutadiene rubber, an organic peroxide, zinc diacrylate, and a water-releasing agent including a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3 phr, the layers formed from the rubber composition each having a geometric center and an outer surface having a hardness, the hardness of the outer surface being greater than the hardness of the geometric center and defining a positive hardness gradient of from 30 Shore C units to 50 Shore C units, the amount of the water-releasing agent present in the rubber composition and the number of waters of hydration of the water-releasing agent being related to the positive hardness gradient, which is represented by the following formula (I):

number

number

[0028] In one embodiment, each layer of the multi-layered core is formed from a rubber composition. In a further embodiment, the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr. In yet a further embodiment, the zinc diacrylate is present in the rubber composition in an amount of about 10 phr to 45 phr, and the water release agent is present in the rubber composition in an amount of about 3 phr. In yet a further embodiment, the inner cover layer is formed from a partially neutralized ionomer, a highly neutralized ionomer, or a combination thereof, and the outer cover is formed from a thermoplastic polyurethane. In another embodiment, the multi-layered core has a diameter of about 35.31 millimeters to about 41.15 millimeters. In yet a further embodiment, the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 34 Shore C units.

[0029] In yet another embodiment, a golf ball is provided, the golf ball including a multi-layered core including a center and at least three core layers formed about the center, an inner cover layer surrounding the multi-layered core, and an outer cover layer disposed about the inner cover layer, the center and at least one of the core layers being formed from a rubber composition cured under heat, the rubber composition including a base rubber including a polybutadiene rubber having a 1,4 cis content of at least 90%, a water-releasing agent including dicumyl peroxide, zinc diacrylate, and a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3 phr and including an additive selected from zinc pentachlorothiophenol, zinc oxide, barium sulfate, or combinations thereof, the center and core layer formed from the rubber composition each having a geometric center having a first hardness and an outer surface having a second hardness, the second hardness being greater than the first hardness and defining a positive hardness gradient of at least 34 Shore C units.

[0030] In one embodiment, the central portion and at least two core layers are formed from a rubber composition. In a further embodiment, the inner cover layer is formed from an ionomer and the outer cover layer is formed from a polymer selected from the group consisting of polyurethane, polyurea, polyurethane-urea hybrid, and copolymers and mixtures thereof. In yet a further embodiment, the zinc pentachlorothiophenol is present in the rubber composition in an amount of about 0.1 phr to about 3 phr, the zinc oxide is present in the rubber composition in an amount of about 3 phr to about 10 phr, and the barium sulfate is present in the rubber composition in an amount of about 10 phr to about 20 phr. In yet another embodiment, the additive in the rubber composition is a combination of zinc pentachlorothiophenol, zinc oxide, and regrind. In another embodiment, the water release agent is calcium sulfate dihydrate.

[0031] Further features and advantages of the present invention can be seen from the following detailed description, taken in conjunction with the drawings described below. [Brief description of the drawings]

[0032] [Figure 1] 1 is a cross-sectional view of a two-piece golf ball according to one embodiment of the present disclosure. [Diagram 2] 1 is a cross-sectional view of a three-piece golf ball according to one embodiment of the present disclosure. [Diagram 3] 1 is a cross-sectional view of a four-piece golf ball according to one embodiment of the present disclosure. [Figure 4] 1 is a cross-sectional view of a five-piece golf ball according to one embodiment of the present disclosure. [Diagram 5] 1 is a graphical representation of measured spin rates and ball velocities of example and comparative golf balls after being hit with a driver at a first speed. [Figure 6] 11 is a graphical representation of measured spin rates and ball velocities of exemplary and comparative golf balls after being hit with a driver at a second speed. [Figure 7] 1 is a graphical representation of measured spin rates and ball velocities of exemplary and comparative golf balls after being hit with an 8 iron. [Figure 8] 1 is a graphical representation of measured spin rates and ball velocities of exemplary and comparative golf balls after being hit with a 5 iron. [Figure 9] 1 is a graphical representation of measured spin rates and ball velocities of exemplary and comparative golf balls after hits with a half wedge. [Figure 10] 1 is a graphical representation showing the number of breakages for each of exemplary and comparative golf balls after a particular number of hits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present disclosure provides golf balls having a core with an increased hardness gradient. In some embodiments, the present disclosure provides golf balls having a core with a "positive" hardness gradient (or "hard to soft" hardness) in which the outer surface of the core is harder than the center. Without being bound to a particular theory, the inventors of the present disclosure have discovered that an increased "positive" hardness gradient can be achieved by introducing a water release agent into the core rubber compound during the curing process. It is believed that the water released during the curing process promotes the decomposition of the free radical initiator, further promoting radical deactivation and reducing the number of radicals in the center of the core. This in turn results in an increased hardness gradient between the surface and the center of the core. By increasing the hardness gradient from the outer surface to the center of the core, the number of spins of the golf ball can be reduced and sufficient durability can be maintained.

[0034] definition Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art of this disclosure. Terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of this specification, and it will be further understood that they should not be interpreted in an idealized or overly formal sense unless expressly defined as such in this specification. Well-known functions or structures may not be described in detail for conciseness or clarity.

[0035] The terms "about" and "approximately" are generally intended to mean an acceptable degree of error or variation in the quantity measured, given the nature or precision of the measurements. Numerical values ​​given herein are approximations unless otherwise noted, meaning that the term "about" or "approximately" can be inferred when not expressly stated.

[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to also include the plural (i.e., at least one of what the article modifies) unless the context clearly dictates otherwise.

[0037] Terms such as "first," "second," and "third" are used herein to describe various features or elements, but these features or elements should not be limited by these terms. These terms are used only to distinguish one feature or element from another. Thus, a first feature or element described below can be referred to as a second feature or element, and similarly, a second feature or element described below can be referred to as a first feature or element without departing from the teachings of the present disclosure.

[0038] The term "positive hardness gradient" refers to the result of subtracting the hardness value of the innermost part of the part being measured (e.g., the center of a solid core or inner core in a dual core construction) from the hardness value of the outer surface of the part being measured (e.g., the outer surface of a solid core or the outer surface of an inner core in a dual core). For example, if the outer surface of a solid core has a greater hardness value than the center, the hardness gradient is considered a "positive" gradient.

[0039] The term "percentage", also known as "phr", is defined as the number of parts by weight of a particular component present in the mixture per 100 parts by weight of the base rubber component.

[0040] Core Formulation The present disclosure provides golf balls having a core formulation that provides a "positive" hardness gradient increase across the core. In some embodiments, the core formulation of the present disclosure includes a base rubber, a crosslinking agent, a free radical initiator, and a water-releasing agent that can release water into the rubber formulation during the curing process. The core formulation may also optionally include one or more additives, such as metal oxides, metal fatty acids or fatty acids, antioxidants, softening promoters, or fillers.

[0041] Base Rubber The core formulation of the present disclosure includes a base rubber, which in some embodiments may include natural and synthetic rubbers, as well as combinations of two or more thereof. Examples of natural and synthetic rubbers suitable for use as the base rubber include, but are not limited to, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene-propylene-diene (EPDM) rubber, grafted EPDM rubber, styrene-butadiene rubber, styrene block copolymer rubber (e.g., "SI", "SIS", "SB", "SBS", "SIBS", etc., where "S" is styrene, "I" is isobutylene, and "B" is butadiene), polyalkenamers such as polyoctenamers, butyl rubber, halobutyl rubber, polystyrene elastomers, polyethylene elastomers, polyurethane elastomers, polyurea elastomers, metallocene catalyzed elastomers and plastomers, copolymers of isobutylene and p-alkylstyrene, halogenated copolymers of isobutylene and p-alkylstyrene, copolymers of butadiene and acrylonitrile, polychloroprene, alkyl acrylate rubbers, chlorinated isoprene rubbers, acrylonitrile chlorinated isoprene rubbers, and combinations of two or more thereof.

[0042] In some embodiments, the core formulation may include polybutadiene rubber as the base rubber. The polybutadiene rubber may have various combinations of cis and trans bond structures. In one embodiment, the polybutadiene rubber has a 1,4 cis bond content of at least 40%. In another embodiment, the polybutadiene rubber has a 1,4 cis bond content of at least 80%. In yet another embodiment, the polybutadiene rubber has a 1,4 cis bond content of at least 90%. Generally, polybutadiene rubbers with a high 1,4 cis bond content have high tensile strength. The polybutadiene rubber may have a relatively high or low Mooney viscosity.

[0043] Examples of commercially available polybutadiene rubbers that can be used in accordance with the present disclosure include, but are not limited to, BR 01 and BR 1220 available from BST Elastomers, Bangkok, Thailand; SE BR 1220LA and SE BR1203 available from DOW Chemical, Midland, Michigan; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Akron, Ohio; BR 01, 51, and 730 available from Japan Synthetic Rubber (JSR), Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29 MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221 available from Lanxess, Pittsburgh, and LG, Seoul, Korea. BR1208 available from UBE Chemical, Tokyo, Japan; UBEPOL BR130B, BR150, BR150B, BR150L, ​​BR230, BR360L, BR710, and VCR617 available from UBE Corporation, Tokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF, and P30AF, and EUROPRENE BR HV80 available from Polimeri Europa, Rome, Italy; AFDENE 50 and NEODENE BR40, BR45, BR50, and BR60 available from Karbochem (PTY) Ltd., Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR 710S, KBR 710H, and KBR 750 available from Kumho Petrochemical, Seoul, Korea; and Firestone, Akron, Ohio. and combinations of two or more thereof.

[0044] The core formulation may include a single base rubber or a combination of two or more of the above-mentioned rubbers as the base rubber. In an embodiment, the core formulation may include a polybutadiene rubber, such as high cis 1,4 polybutadiene, as the base rubber. In this embodiment, the core formulation may include a combination of two or more types of polybutadiene rubber, such as two or more different types of high cis 1,4 polybutadiene. In a further embodiment, the core formulation may include an EPDM rubber or a grafted EPDM rubber as the base rubber. Also, in a further embodiment, the core formulation may include a combination of polybutadiene rubber and EPDM rubber as the base rubber. For example, the core formulation may combine an EPDM rubber with two or more different types of polybutadiene rubber, such as two or more different types of high cis 1,4 polybutadiene, as the base rubber.

[0045] In some embodiments, the core formulation includes a base rubber in an amount of 100 phr. That is, if more than one rubber component is used in the core formulation as a base rubber, the total weight of each rubber component must total 100 phr. In some embodiments, the core formulation includes a polybutadiene rubber as a base rubber in an amount of 100 phr. In other embodiments, the core formulation includes a polybutadiene rubber and a second rubber component. In this embodiment, the polybutadiene rubber may be used in an amount of about 70 phr to about 99 phr, and the second rubber component may be used in an amount of about 1 phr to about 30 phr. In yet other embodiments, the polybutadiene rubber may be used in an amount of about 85 phr to about 95 phr, and the second rubber component may be used in an amount of about 5 phr to about 15 phr. In some embodiments, the second rubber component is an EPDM rubber.

[0046] The base rubber may be used in the core formulation in an amount of at least about 5% by weight, based on the total weight of the composition. In some embodiments, the base rubber may be used in an amount of about 20% to about 95% by weight. In further embodiments, the base rubber may be used in an amount of about 45% to about 95% by weight. In yet other embodiments, the base rubber may be used in an amount of at least about 50% by weight. In yet further embodiments, the base rubber may be used in an amount of at least about 70% by weight.

[0047] Crosslinking Agent The core formulation contains a reactive crosslinking coagent. Suitable crosslinking coagents include, but are not limited to, metal salts of unsaturated carboxylic acids having 3 to 8 carbon atoms, unsaturated vinyl compounds and polyfunctional monomers (e.g., trimethylolpropane trimethacrylate), phenylene bismaleimide, and combinations thereof. Examples of suitable metal salts include, but are not limited to, one or more metal salts of acrylates, diacrylates, methacrylates, and dimethacrylates, where the metal is selected from magnesium, calcium, zinc, aluminum, lithium, or nickel. In an embodiment, the crosslinking coagent is selected from zinc salts of acrylates, diacrylates, methacrylates, or dimethacrylates. For example, in one embodiment, the crosslinking coagent is zinc diacrylate (ZDA).

[0048] The crosslinking coagent may be present in the core formulation in an amount of about 5 phr to about 50 phr. In some embodiments, the crosslinking coagent may be present in the core formulation in an amount of about 10 phr to about 45 phr. In further embodiments, the crosslinking coagent may be present in the core formulation in an amount of about 15 phr to about 40 phr. In still further embodiments, the crosslinking coagent may be present in the core formulation in an amount of about 20 phr to about 35 phr. For example, in one embodiment, the crosslinking coagent may be present in the core formulation in an amount of about 30 phr. In other embodiments, the crosslinking coagent may be present in the core formulation in an amount of about 35.5 phr.

[0049] Free Radical Initiators The core formulation may contain a free radical initiator selected from an organic peroxide, a high-energy radiation source capable of generating free radicals, or a combination thereof. In some embodiments, the free radical initiator is an organic peroxide. Suitable organic peroxides include, but are not limited to, dicumyl peroxide, n-butyl-4,4-di(t-butylperoxy)valerate, 1,1-di(t-butylperoxy)3,3,5 trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, di-t-amyl peroxide, t-butyl peroxide, t-butyl cumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, di(2-t-butyl-peroxyisopropyl)benzene, dilauroyl peroxide, dibenzoyl peroxide, t-butyl hydroperoxide, dimethyl tertbutyl peroxide mixture, and combinations thereof. In one embodiment, the free radical initiator is dicumyl peroxide, including but not limited to Perkadox® BC available from Akzo Nobel, in another embodiment, the free radical initiator is dimethyl tertbutyl peroxide, including but not limited to Trigonox® 101-50D-PD available from Nouryon.

[0050] The free radical initiator may be present in the core formulation in an amount of about 0.05 phr to about 15 phr. In some embodiments, the free radical initiator may be present in the core formulation in an amount of about 0.1 phr to about 10 phr. In other embodiments, the free radical initiator may be present in the core formulation in an amount of about 0.5 phr to about 6 phr. In still other embodiments, the free radical initiator may be present in the core formulation in an amount of about 1 phr to about 5 phr. In further embodiments, the free radical initiator may be present in the core formulation in an amount of about 1.5 phr to about 3 phr. In yet further embodiments, the free radical initiator is present in the core formulation in an amount of about 0.1 phr to about 2.5 phr. In yet further embodiments, the free radical initiator is present in the core formulation in an amount of about 0.25 phr to about 1.5 phr. For example, the free radical initiator may be present in the core formulation in an amount of about 0.35 phr. In other embodiments, the free radical initiator may be present in the core formulation in an amount of about 0.6 phr. In yet other embodiments, the free radical initiator may be present in the core formulation in an amount of about 1 phr.

[0051] Water synergist The core formulation of the present disclosure includes a water-releasing agent. As used herein, "water-releasing agent" refers to a compound having at least one water molecule that can be released during the curing process. As briefly described above, when the free radical initiator decomposes and generates decomposition heat during the curing of the core, the temperature near the surface of the core remains substantially the same as the temperature of the mold, while the temperature near the center of the core increases due to the accumulation of the decomposition heat of the free radical initiator. Without being bound to any particular theory, it is believed that by adding a water-releasing agent that can release water at a desired curing temperature to the core formulation, the water can promote further decomposition of the free radical initiator and deactivation of the radicals in the center of the core, resulting in a difference in crosslink density and an increase in the hardness gradient between the center and the surface.

[0052] The water syneresis agent of the present disclosure has a moisture content capable of releasing a sufficient amount of water during the curing process to promote decomposition of the free radical initiator and deactivation of the radicals. In some embodiments, the water syneresis agent has a moisture content (in its molecular form) of at least about 5% by weight. In further embodiments, the water syneresis agent has a moisture content ranging from about 5% to about 95% by weight. In yet further embodiments, the water syneresis agent has a moisture content ranging from about 10% to about 90% by weight. In yet further embodiments, the water syneresis agent has a moisture content ranging from about 15% to about 85% by weight. In still further embodiments, the water syneresis agent has a moisture content of at least about 50% by weight. For example, the water syneresis agent has a moisture content of about 50% to 95% by weight.

[0053] In an embodiment, the synergist of the present disclosure may be a metal sulfate hydrate having one or more waters of hydration that may be released during the reaction of the present disclosure. In an embodiment, the metal may be an alkaline earth metal. For example, the metal may be calcium, magnesium, beryllium, strontium, barium, or radium. In an embodiment, the metal of the metal sulfate hydrate is calcium. In another embodiment, the metal of the metal sulfate hydrate is magnesium. In further embodiments, the metal may be a transition metal or a post-transition metal. For example, the metal may be zinc, copper, iron, cobalt, manganese, chromium, nickel, aluminum, zirconium, cadmium, indium, or vanadium. And in further embodiments, the metal may be neodymium or lanthanum. In an embodiment, the metal of the metal sulfate hydrate is zinc.

[0054] The metal sulfate hydrate may have any number of waters of hydration. In certain embodiments, the metal sulfate hydrate may have 0.5-10 waters of hydration. For example, the metal sulfate hydrate may be a hemihydrate, monohydrate, dihydrate, trihydrate, tetrahydrate, pentahydrate, hexahydrate, heptahydrate, octahydrate, nonahydrate, or decahydrate. In further embodiments, the metal sulfate hydrate may have 1-7 waters of hydration. In still further embodiments, the metal sulfate hydrate may have 1-4 waters of hydration. In still further embodiments, the metal sulfate hydrate may have 1-3 waters of hydration. In other embodiments, the metal sulfate hydrate may have 2 waters of hydration. For example, in one embodiment, the metal sulfate hydrate may be a dihydrate. In still further embodiments, the metal sulfate hydrate may be a heptahydrate (i.e., having 7 waters of hydration).

[0055] Examples of suitable metal sulfate hydrates contemplated for use as synergists according to the present disclosure include calcium sulfate dihydrate (CaSO4·2H2O), magnesium sulfate heptahydrate (MgSO4·7H2O), zinc sulfate dihydrate (ZnSO4·2H2O), zinc sulfate heptahydrate (ZnSO4·7H2O), vanadium oxide sulfate hydrate (VOSO4·xH2O), neodymium sulfate hydrate (Nd2(SO4)3·xH2O), laminar oxalate hydrate (LAS) ... Examples of hydrated copper sulfate include, but are not limited to, lanthanum sulfate hydrate (La2(C2O4)3·xH2O), zinc sulfate monohydrate (ZnSO4·H2O), zirconium sulfate hydrate (Zr(SO4)2·xH2O), nickel sulfate heptahydrate (NiSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), aluminum sulfate hydrate (Al2(SO4)3·xH2O), and copper sulfate pentahydrate (CuSO4·5H2O).

[0056] The core formulation may include two or more of any of the above water syneresis agents. For example, the core formulation may include two or more of any of the above metal sulfate hydrates. In some embodiments, the water syneresis agent is present in the core formulation in an amount of about 1 phr to about 15 phr. In other embodiments, the water syneresis agent is present in the core formulation in an amount of about 2 phr to about 10 phr. In yet further embodiments, the water syneresis agent is present in the core formulation in an amount of about 3 phr to about 8 phr. In yet further embodiments, the water syneresis agent is present in the core formulation in an amount of about 5 phr to about 7 phr. In yet further embodiments, the water syneresis agent is present in the core formulation in an amount of about 1 phr to about 4 phr. In yet further embodiments, the water syneresis agent is present in the core formulation in an amount of about 1 phr to about 3.9 phr. In yet still further embodiments, the water syneresis agent is present in the core formulation in an amount of about 1 phr to about 3.75 phr. In yet further embodiments, the syneresis agent is present in the core formulation in an amount of about 1 phr to about 3 phr. For example, in one embodiment, the syneresis agent is present in the core formulation in an amount of about 3 phr.

[0057] Additives Radical scavengers such as halogenated organic sulfur or its metal salt, organic disulfide compounds, or inorganic disulfide compounds may be added to the core formulation of the present disclosure. These compounds may also function as "softening promoters." As used herein, "softening promoter" means any compound or mixture thereof that can make a core 1) softer (having lower compression) at a constant "coefficient of restitution" (CoR) and / or 2) faster (having higher COR at equal compression) when compared to a core similarly prepared without the softening promoter. Examples of halogenated organic sulfur compounds that may be used with the core formulation include, but are not limited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zinc pentachlorothiophenol (ZnPCTP). The use of PCTP and ZnPCTP in the inner core of a golf ball helps to produce a softer and faster inner core. PCTP and ZnPCTP compounds help to increase the elasticity and coefficient of restitution of the core. In some embodiments, the softening accelerator is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyl disulfide, dixylyl disulfide, 2-nitroresorcinol, or combinations thereof. In some embodiments, the softening accelerator may be used in the core formulation in an amount of about 0.1 phr to about 3 phr. In further embodiments, the softening accelerator may be used in the core formulation in an amount of about 0.2 phr to about 1 phr. For example, the softening accelerator may be used in the core formulation in an amount of about 0.3 phr to about 0.35 phr.

[0058] The core formulation of the present disclosure may also include "fillers" that are added to adjust the density and / or specific gravity of the formulation. Suitable fillers include, but are not limited to, polymeric or mineral fillers, metal fillers, metal alloy fillers, metal oxide fillers, and carbonaceous fillers. The fillers may be in any suitable form, including, but not limited to, flakes, fibers, whiskers, fibrils, plates, particles, and powders. Ground rubber regrind, a reclaimed rubber material obtained from discarded rubber golf ball cores, may also be used as a filler. Since a maximum golf ball weight of 45.93 g (1.62 oz) has been established by the United States Golf Association (USGA), the amount and type of filler utilized will depend on the amount and weight of other ingredients in the golf ball.

[0059] Suitable polymer or mineral fillers that may be added to the core formulation include, for example, precipitated hydrated silica, clay, talc, asbestos, glass fiber, aramid fiber, mica, calcium metasilicate, barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide, tungsten carbide, diatomaceous earth, polyvinyl chloride, carbonates such as calcium carbonate and magnesium carbonate. Suitable metal fillers include titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, lead, copper, boron, cobalt, beryllium, zinc, and tin. Suitable metal alloys include steel, brass, bronze, boron carbide whiskers, and tungsten carbide whiskers. Suitable metal oxide fillers include zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide. Suitable particulate carbonaceous fillers include graphite, carbon black, cotton wool, natural bitumen, cellulose wool, and leather fibers. Microballoon fillers such as glass and ceramic, as well as fly ash fillers, may also be used. In an embodiment, the core formulation of the present disclosure includes zinc oxide. Zinc oxide may be used in an amount ranging from about 1 phr to about 15 phr. In an embodiment, zinc oxide may be used in an amount ranging from about 3 phr to about 10 phr, such as about 5 phr. In a further embodiment, the core formulation of the present disclosure includes barium sulfate. Barium sulfate may be used in an amount ranging from about 10 phr to about 30 phr, such as about 12 phr to about 14 phr.

[0060] The core formulation may also include antioxidants to prevent degradation of the elastomer. Additionally, processing aids such as high molecular weight organic acids and their salts may be added to the formulation.

[0061] In some embodiments, the total amount of additives and fillers present in the core formulation may be about 15% by weight or less, based on the total weight of the core formulation. In other embodiments, the total amount of additives and fillers present in the core formulation may be about 12% by weight or less, based on the total weight of the core formulation. In yet other embodiments, the total amount of additives and fillers present in the core formulation may be about 10% by weight or less, based on the total weight of the core formulation. In further embodiments, the total amount of additives and fillers present in the core formulation may be about 8% by weight or less, based on the total weight of the core formulation. In yet further embodiments, the total amount of additives and fillers present in the core formulation may be about 5% by weight or less, based on the total weight of the core formulation.

[0062] Curing of the Core Compound The base rubber, free radical initiator, crosslinking agent, water release agent, filler, and any other materials used to form the core according to the present disclosure may be combined to form a mixture by any type of mixing known to those skilled in the art. Suitable types of mixing include single pass mixing, multi-pass mixing, and the like. A single pass mixing process in which the ingredients are added sequentially is preferred, as this type of mixing tends to increase efficiency and reduce costs of the process. The compound may be cured using any technique known in the art for rubber compositions for golf balls.

[0063] Golf Ball Structure The core formulations of the present disclosure may be used with golf balls of various constructions. In one version shown in FIG. 1, the golf ball of the present disclosure is a two-piece ball 10 with a single core layer 12 and a single cover layer 14. As shown in FIG. 2, in one embodiment, the golf ball 20 includes a core layer 22, an intermediate layer 24, and a cover layer 26. In FIG. 2, the intermediate layer 24 may be considered an outer core layer, an inner cover layer, a mantle or casing layer, or any other layer disposed between the core 22 and the cover layer 26. Referring to FIG. 3, in another embodiment, a four-piece golf ball 30 includes an inner core layer 32, an outer core layer 34, an intermediate layer 36, and an outer cover layer 38. In FIG. 3, the intermediate layer 36 may be considered a casing or mantle layer, or an inner cover layer, or any other layer disposed between the outer core layer 34 and the outer cover of the ball 38. 4, in another version, a five-piece golf ball 40 includes a three-layer core having an inner core layer 42, an intermediate core layer 44, an outer core layer 46, an inner cover layer 48, and an outer cover layer 50. As illustrated herein, golf balls according to the present disclosure can include any number of core layers, intermediate layers, and any combination of cover layers.

[0064] The core formulations of the present disclosure may be used with single-layer cores or multi-layer cores. The core formulations may be used in one or more layers of the core. In one embodiment, the core formulations described herein may be used in a solid core of a golf ball. In another embodiment, the core formulations described herein may be used in a dual core having an inner core (center) and a surrounding outer core layer. In one embodiment, the inner core layer (center) may be formed from the core formulation of the present disclosure, and the outer core layer may be formed from a rubber composition. In another embodiment, the outer core layer may be formed from a core formulation, and the inner core layer may be formed from a rubber composition. In another embodiment, both the inner core layer and the outer core layer may be formed from the core formulation of the present disclosure. In yet another embodiment, the core formulations described herein may be used in a multi-layer core having three or more layers. For example, the center of the core may be formed from the core formulation of the present disclosure, and the other layers of the core may be formed from a rubber composition. In yet another embodiment, two or more layers of the core may be formed from the core formulation of the present disclosure.

[0065] In some embodiments, when the golf ball core is a dual core or multi-layer core, the surrounding outer core layer may be formed from a polybutadiene rubber composition. The rubber composition may contain any of the base rubbers, free radical initiators, crosslinking agents, softening accelerators, additives, and fillers described above, and the composition may be cured using conventional methods described above. In some embodiments, the surrounding outer core layer may include a combination of polybutadiene rubber and styrene butadiene rubber (SBR) as the base rubber. In this embodiment, the polybutadiene rubber may be used in an amount of about 80 phr to about 99 phr, and the SBR may be used in an amount of about 1 phr to about 20 phr. For example, in some embodiments, the surrounding outer core layer may be formed from a rubber composition including polybutadiene rubber, SBR, dicumyl peroxide, regrind, zinc pentachlorothiophenol, zinc diacrylate, and zinc oxide.

[0066] In solid core embodiments, the core may have a diameter ranging from about 35.31 millimeters to about 41.15 millimeters. In some embodiments, the solid core may have a diameter from about 36.83 millimeters to about 40.64 millimeters. In further embodiments, the solid core may have a diameter from about 38.1 millimeters to about 39.37 millimeters.

[0067] In dual core embodiments, the inner core (center) may have a diameter of about 6.35 millimeters to about 38.35 millimeters. In other embodiments, the inner core (center) may have a diameter of about 7.62 millimeters to about 36.83 millimeters. In yet other embodiments, the inner core (center) may have a diameter of about 12.7 millimeters to about 33.02 millimeters. In further embodiments, the inner core (center) may have a diameter of about 19.05 millimeters to about 29.21 millimeters. In yet further embodiments, the inner core (center) may have a diameter of about 22.86 millimeters to about 26.67 millimeters. For example, the inner core (center) may have a diameter of about 25.654 millimeters. The dual core, including the center and the outer core layer, may have a diameter of about 35.31 millimeters to about 41.15 millimeters. In some embodiments, the dual core has a diameter of about 36.83 millimeters to about 40.64 millimeters. In yet a further embodiment, the dual core has a diameter of about 38.1 millimeters to about 39.37 millimeters.

[0068] In some embodiments, one or more intermediate layers may be disposed between the single-layer or multi-layer core and the surrounding cover layer. These intermediate layers may also be referred to as casings or inner cover layers. The intermediate layers may be formed from any material known in the art, including thermoplastic and thermosetting materials. In some embodiments, the intermediate layers are formed from ionomer compositions that include ethylene acid copolymers that contain at least partially neutralized acid groups. Suitable ethylene acid copolymers that may be used to form the intermediate layers are generally referred to as copolymers of ethylene. They include C3-C8 α,β-ethylenically unsaturated mono- or dicarboxylic acids, and optional softening monomers.

[0069] A protective cover layer may be disposed over the core and any intermediate layers. The cover layer of the present disclosure provides the ball with various advantageous mechanical properties, such as, for example, high impact resistance and high shear resistance levels. The golf ball may include one or more cover layers. For example, the golf ball may have a single-layer cover. In other embodiments, the golf ball may have a dual-layer cover including an inner cover layer and an outer cover layer. In yet other embodiments, the golf ball may have a multi-layer cover including an inner cover layer, one or more intermediate cover layers, and an outer cover layer.

[0070] Suitable conventional materials that can be used to form the cover layer include polyurethanes; thermoplastic polyurethanes; polyureas, copolymers, blends and hybrids of polyurethanes and polyureas; olefin-based copolymer ionomer resins (e.g., Surlyn® ionomer resins and DuPont HPF® 1000, HPF® 2000, and HPF® 1035; and HPF® AD 1172 available from DuPont; Iotek® ionomers available from ExxonMobil Chemical Company; Amplify® ionomers of ethylene acrylic acid copolymers available from The Dow Chemical Company; and A. Schulman Clarix® ionomer resins available from Arkema Inc.; polyethylenes including, for example, low density polyethylene, linear low density polyethylene, and high density polyethylene; polypropylene; rubber-toughened olefin polymers; acid copolymers that are not part of an ionomeric copolymer, for example, poly(meth)acrylic acid; plastomers; flexomers; styrene / butadiene / styrene block copolymers; styrene / ethylene-butylene / styrene block copolymers; dynamically vulcanized elastomers; copolymers of ethylene and vinyl acetate; copolymers of ethylene and methyl acrylate; polyvinyl chloride-based resins; polyamides; poly(amide ester) elastomers, and graft copolymers of ionomers and polyamides, including, for example, Pebax® thermoplastic polyether block amides available from Arkema Inc; crosslinked trans-polyisoprene and mixtures thereof; Hytrel® or Ticona Engineering available from DuPont. Polyester-based thermoplastic elastomers, such as RiteFlex® available from Diesel Polymers; polyurethane-based thermoplastic elastomers, such as Elastollan® available from BASF; synthetic or natural vulcanized rubber; and combinations thereof.Polyurethanes, polyureas, and polyurethane-polyurea hybrids are particularly desirable because these materials can be used to make golf balls that have high resilience and a soft feel. The term "polyurethane-polyurea hybrid" is meant to include copolymers and mixtures thereof.

[0071] Ionomer compositions suitable for the cover layer include partially and highly neutralized ionomers (HNPs), including, for example, mixtures of two or more partially neutralized ionomers, mixtures of two or more highly neutralized ionomers, and ionomers formed from mixtures of one or more partially neutralized ionomers and one or more highly neutralized ionomers. For purposes of this disclosure, "HNP" refers to an acid copolymer after at least 70% of all acid groups present in the composition have been neutralized. Preferred ionomers are salts of O / X- and O / X / Y-type acid copolymers, where O is an α-olefin, X is a C3-C8 α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer. O is preferably selected from ethylene and propylene. X is preferably selected from methacrylic acid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid. Methacrylic acid and acrylic acid are particularly preferred. Y is preferably selected from (meth)acrylates, (meth)alkyl acrylates, where the alkyl group has 1 to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl (meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate.

[0072] In some embodiments, the golf balls of the present disclosure may include a single layer cover formed from an ionomer composition, a thermoplastic polyurethane, or a castable polyurethane disposed over a solid core made from a core formulation described herein. In other embodiments, the golf balls of the present disclosure may include a dual layer cover, where an inner cover layer is formed from an ionomer composition and an outer cover layer is formed from a thermoplastic polyurethane or a castable polyurethane disposed over a solid core made from a core formulation described herein.

[0073] In a further embodiment, the golf ball of the present disclosure may include a single layer cover formed from an ionomer composition, a thermoplastic polyurethane, or a castable polyurethane disposed over a dual core, with the inner core (center) made from a core formulation described herein. In a further embodiment, the golf ball of the present disclosure may include a dual layer cover, with the inner cover layer formed from an ionomer composition and the outer cover layer formed from a castable polyurethane disposed over the dual core, with the inner core (center) made from a core formulation described herein.

[0074] In some embodiments, the cover may be a single layer having a thickness of about 0.25 millimeters to about 1.016 millimeters. In other embodiments, the cover may be a single layer having a thickness of about 0.508 millimeters to about 0.889 millimeters. In further embodiments, the cover may be a single layer having a thickness of about 0.635 millimeters to about 0.762 millimeters.

[0075] In further embodiments, the cover includes an inner cover layer and an outer cover layer. The inner cover layer may have a thickness ranging from about 0.25 millimeters to about 3.05 millimeters. In some embodiments, the inner cover layer may have a thickness ranging from about 0.381 millimeters to about 2.03 millimeters. In further embodiments, the inner cover layer may have a thickness ranging from about 0.508 millimeters to about 1.143 millimeters. The outer cover layer may have a thickness ranging from about 0.10 millimeters to about 2.03 millimeters. In other embodiments, the outer cover layer may have a thickness ranging from about 0.25 millimeters to about 1.397 millimeters. In further embodiments, the outer cover layer may have a thickness ranging from about 0.508 millimeters to about 0.889 millimeters. In still further embodiments, the outer cover layer may have a thickness less than about 0.508 millimeters.

[0076] Golf Ball Characteristics Golf balls having cores formed from the core formulations of the present disclosure have advantageous mechanical and playing performance properties. As briefly discussed above, the water-releasing agent in the core formulations of the present disclosure acts as an accelerator for further decomposition and deactivation of radicals in the center of the core during the curing process, resulting in a difference in crosslink density and an increase in hardness gradient between the center and surface of the core. The increase in hardness gradient of the core can reduce the number of rotations (or rotation speed) of a golf ball after it is hit by a club. A ball with a relatively high number of rotations can be difficult to control and can fly shorter distances, especially for recreational players. Golf balls having cores made according to the present disclosure have higher driver speeds off the tee, higher launch angles, and lower driver rotations. Thus, the ball can travel a long distance and the flight path of the ball can be more easily controlled. This speed and control allows players to make better driver shots.

[0077] Core Hardness The center or inner core layer of the golf balls of the present disclosure has a "positive" hardness gradient (i.e., the outer surface of the inner core is harder than its geometric center). The positive hardness gradient of the inner core is defined by hardness measurements taken on the outer surface of the inner core and radially inward toward the center of the inner core. These measurements are typically taken in 2 mm increments, as described in the test methods below.

[0078] In some embodiments, the inner core layer has a geometric center hardness of about 40 Shore C to about 70 Shore C. In other embodiments, the inner core layer has a geometric center hardness of about 45 Shore C to about 65 Shore C. In yet further embodiments, the inner core layer has a geometric center hardness of about 50 Shore C to about 60 Shore C. In yet another embodiment, the inner core layer has a geometric center hardness of about 50 Shore C to about 55 Shore C. For example, in one embodiment, the inner core layer may have a geometric center hardness of about 55 Shore C.

[0079] In a further embodiment, the inner core layer has an outer surface hardness of about 75 Shore C to about 105 Shore C. In one embodiment, the inner core layer has an outer surface hardness of about 80 Shore C to about 100 Shore C. In yet another embodiment, the inner core layer has an outer surface hardness of about 85 Shore C to about 95 Shore C. In yet another embodiment, the inner core layer has an outer surface hardness of about 85 Shore C to about 90 Shore C. For example, in one embodiment, the inner core layer may have an outer surface hardness of about 89 Shore C. In another embodiment, the inner core layer may have an outer surface hardness of about 91 Shore C.

[0080] The inner core layer of the present disclosure may have a positive hardness gradient of at least about 30 Shore C units. That is, the difference between the outer surface hardness and the geometric center hardness of the inner core layer may be at least about 30 Shore C units. In some embodiments, the inner core layer may have a positive hardness gradient of at least about 33 Shore C units. In yet other embodiments, the inner core layer may have a positive hardness gradient of at least about 36 Shore C units. In further embodiments, the inner core layer may have a positive hardness gradient of at least about 40 Shore C units. For example, the positive hardness gradient of the inner core layer may range from about 30 Shore C units to about 50 Shore C units. In other embodiments, the positive hardness gradient of the inner core layer may range from about 30 Shore C units to about 40 Shore C units.

[0081] In embodiments in which the golf ball includes a dual or multi-layer core, the inner core may have a positive hardness gradient and the outer core layer may have a "zero" hardness gradient (i.e., the hardness values ​​of the outer surface of the outer core layer and the inner surface of the outer core layer are substantially the same) or a "negative" hardness gradient (i.e., the outer surface of the outer core layer is softer than the inner surface of the outer core layer). In other embodiments in which the golf ball includes a dual or multi-layer core, the inner core layer and other layers of the core (e.g., the outer core layer) may have a positive hardness gradient.

[0082] Core component relationships In one embodiment, the amount of water synergist and the water of hydration of the water synergist present in the rubber compound used to form the core are related to the hardness gradient of the core according to the relationship shown in Equation I below:

number

number

[0083] In another embodiment, the amount of water synergist and the water of hydration of the water synergist present in the rubber compound used to form the core are related to the hardness gradient of the core according to the relationship shown in Equation II below:

number

number

[0084] In yet another embodiment, the amount of water synergist and the water of hydration of the water synergist present in the rubber compound used to form the core are related to the hardness gradient of the core according to the relationship shown in Equation II below:

number

number

[0085] In yet another embodiment, the amount of water synergist and the water of hydration of the water synergist present in the rubber compound used to form the core are related to the hardness gradient of the core according to the relationship shown in Equation IV below:

number

number

[0086] In a further embodiment, the number of waters of hydration of the water synergist present in the rubber compound used to form the core is related to the hardness gradient of the core according to the relationship shown in Formula V below:

number

number

[0087] In yet another embodiment, the number of waters of hydration in the water synergist present in the rubber compound used to form the core is related to the hardness gradient of the core according to the relationship shown in Formula VI below:

number

number

[0088] In yet another embodiment, the number of waters of hydration in the water synergist present in the rubber compound used to form the core is related to the hardness gradient of the core according to the relationship shown in Formula VII below:

number

number

[0089] compression The cores of the golf balls of the present disclosure exhibit excellent compression values. In some embodiments, cores made from the formulations described herein have compression values ​​of from about 10 to about 95. In other embodiments, cores made from the formulations described herein have compression values ​​of from about 30 to about 85. In yet further embodiments, cores made from the formulations described herein have compression values ​​of from about 45 to about 80. In further embodiments, cores made from the formulations described herein have compression values ​​of from about 60 to about 80.

[0090] Finished golf balls of the present disclosure may have a compression value ranging from about 70 to about 110. In other embodiments, the finished golf balls may have a compression value ranging from about 75 to about 105. In yet other embodiments, the finished golf balls may have a compression value ranging from about 80 to about 100. In further embodiments, the finished golf balls may have a compression value ranging from about 85 to about 95.

[0091] Coefficient of Restitution (CoR) The cores of the golf balls of the present disclosure also exhibit excellent coefficient of restitution (CoR) values. In some embodiments, the overall CoR of the cores of the present disclosure at 125 ft / s is at least about 0.775. In other embodiments, the overall CoR of the cores of the present disclosure at 125 ft / s is at least about 0.780. In further embodiments, the overall CoR of the cores of the present disclosure at 125 ft / s is at least about 0.785. In still further embodiments, the overall CoR of the cores of the present disclosure at 125 ft / s is at least about 0.790. In other embodiments, the overall CoR of the cores of the present disclosure at 125 ft / s is at least about 0.795. In yet other embodiments, the overall CoR of the cores of the present disclosure at 125 ft / s is at least about 0.800.

[0092] The finished golf balls of the present disclosure may have an overall CoR of at least about 0.750. In other embodiments, the finished golf balls of the present disclosure may have an overall CoR of at least about 0.760. In yet other embodiments, the finished golf balls of the present disclosure may have an overall CoR of at least about 0.770. In further embodiments, the finished golf balls have an overall CoR of at least about 0.780. In yet further embodiments, the finished golf balls have an overall CoR of at least about 0.790. For example, the finished golf balls have an overall CoR of at least about 0.800. The superior compression and CoR properties allow players to generate greater ball speeds off the tee and achieve greater distance with their drives.

[0093] Rotational Speed As briefly described above, the increased hardness gradient of the core of the present disclosure can reduce the number of rotations (or rotational speed) of a golf ball after it is hit by a club. Lower rotations after club impact result in straighter shots when the ball is mishit, higher flight efficiency, and longer shot distance. Golf balls of the present disclosure made using cores incorporating the above-mentioned water syneresis agents exhibit lower rotations when compared to golf balls formed using cores without water syneresis agents.

[0094] In some embodiments, the golf ball of the present disclosure has a driver rotation speed of about 2900 revolutions per minute (rpm) or less at a ball speed of about 150 miles per hour (mph). For example, the golf ball of the present disclosure has a driver rotation speed of about 2700 rpm to about 2900 rpm at a ball speed of about 150 mph. In further embodiments, the golf ball of the present disclosure has a driver rotation speed of about 2800 rpm to about 2900 rpm at a ball speed of about 150 mph. In other embodiments, the golf ball of the present disclosure has a driver rotation speed of about 2750 rpm or less at a ball speed of about 183 mph. For example, the golf ball of the present disclosure has a driver rotation speed of about 2500 rpm to about 2750 rpm at a ball speed of about 183 mph. In still further embodiments, the golf ball of the present disclosure has a driver rotation speed of about 2600 rpm to about 2750 rpm at a ball speed of about 183 mph.

[0095] In a further embodiment, the golf ball of the present disclosure has a spin rate of about 7900 rpm or less at a ball speed of about 120 mph when hit with an 8 iron. For example, the golf ball of the present disclosure has a spin rate of about 7500 rpm to about 7850 rpm at a ball speed of about 120 mph when hit with an 8 iron. In yet another embodiment, the golf ball of the present disclosure has a spin rate of about 7600 rpm to about 7850 rpm at a ball speed of about 120 mph when hit with an 8 iron.

[0096] In yet another embodiment, the golf ball of the present disclosure has a spin rate of about 5300 rpm or less at a ball speed of about 136 mph when hit with a 5 iron. For example, the golf ball of the present disclosure has a spin rate of about 4900 rpm to about 5200 rpm at a ball speed of about 136 mph when hit with a 5 iron. In a further embodiment, the golf ball of the present disclosure has a spin rate of about 5000 rpm to about 5200 rpm at a ball speed of about 136 mph when hit with a 5 iron.

[0097] In yet another embodiment, the golf ball of the present disclosure has a spin rate of about 7000 rpm or less at a ball speed of about 53 mph when hit with a half wedge. For example, the golf ball of the present disclosure has a spin rate of about 6700 rpm to about 7000 rpm at a ball speed of about 53 mph when hit with a half wedge. In yet another embodiment, the golf ball of the present disclosure has a spin rate of about 6800 rpm to about 7000 rpm at a ball speed of about 53 mph when hit with a half wedge.

[0098] Working Example The following non-limiting examples illustrate golf balls and golf ball cores that may be made in accordance with the present disclosure. The examples are merely illustrative of preferred embodiments of the present disclosure and are not to be construed as limiting the disclosure, the scope of which is defined by the appended claims.

[0099] Examples 1 and 2: Exemplary Core Formulations for Solid Cores Table 1A below shows an exemplary core formulation for a solid core. As shown in Table 1A, the synergist calcium sulfate dihydrate is used in the core formulation in an amount of 3 phr.

[0100] [Table 1A]

[0101] The cores formed in Examples 1 and 2 were evaluated for compression, surface hardness, center hardness, coefficient of restitution (COR), and hardness gradient according to the following test methods, and the results are shown in Table 1B.

[0102] [Table 1B]

[0103] Example 3: Exemplary dual core core formulations Table 2 below shows an exemplary core formulation for the dual core. As shown in Table 2, the synergist calcium sulfate dihydrate is used in the core formulation for the inner core in an amount of 3 phr.

[0104] [Table 2]

[0105] Example 4: Properties of Cores Formed with Exemplary Core Formulations and Resulting Golf Balls core The core formulations shown below in Table 3 were used to form the solid cores of Examples 4, 5, 6 and the Comparative Example. The formulations were cured using conventional techniques known in the art.

[0106] [Table 3]

[0107] The cores formed in the examples and comparative examples were evaluated for compression, surface hardness, center hardness, coefficient of restitution (COR), and hardness gradient according to the following test methods. The results are shown in Table 4.

[0108] [Table 4]

[0109] As shown in Table 4, the cores formed with the exemplary formulations had an increased hardness gradient compared to the comparative cores. Similarly, the cores formed with the exemplary formulations exhibited better COR and compression than the comparative cores.

[0110] Resulting Golf Ball A cover having an inner cover layer and an outer cover layer is placed on the core of each of the examples and comparative examples to form a golf ball having three layers. The rotation speed and durability performance of the golf ball are evaluated. The rotation speed of each golf ball is measured after hitting with a driver having an initial rotation speed of about 2900 rpm, a ball speed of about 150 mph, an initial rotation speed of 2700 rpm, and an angle of launch of 10 degrees, a driver having an initial rotation speed of about 182 mph, an initial rotation speed of 2700 rpm, and an angle of launch of 10 degrees, an 8 iron, a 5 iron, and a half wedge golf club.

[0111] 5-10 are graphs showing the results of spin and durability performance tests. Specifically, FIG. 5 shows the measured spin and ball speed of each of the exemplary golf balls and the comparative golf balls after being hit by a driver at a ball speed of about 150 mph. FIG. 6 shows the measured spin and ball speed of each of the exemplary and comparative golf balls after being hit by a driver at a ball speed of about 182 mph. FIG. 7 shows the measured spin and ball speed of each of the exemplary golf balls and the comparative golf balls after being hit by an 8 iron. FIG. 8 shows the measured spin and ball speed of each of the exemplary golf balls and the comparative golf balls after being hit by a 5 iron. FIG. 9 shows the measured spin and ball speed of each of the exemplary golf balls and the comparative golf balls after being hit by a half wedge. FIG. 10 shows the number of breakages of each of the exemplary and comparative golf balls after a certain number of hits.

[0112] The results shown in Figures 5-10 indicate that golf balls having cores formed from the exemplary formulations in which a water synergy agent was added to the core during curing exhibited increased ball speed and decreased spin rates than the comparative golf balls in which water was not added to the core. Similarly, as shown in Figure 6, golf balls having cores formed from the exemplary formulations exhibited greater durability than the comparative golf balls.

[0113] Test Method hardness The core center hardness is obtained by the following procedure. The core is gently pressed into a hemispherical holder having an inside diameter approximately slightly smaller than the diameter of the core such that the core is held in place within the hemispherical portion of the holder while simultaneously leaving the geometric center surface of the core exposed. The core is secured within the holder by friction so that it does not move during the cutting and grinding steps, but the friction is not so excessive that distortion of the natural shape of the core occurs. The core is secured such that the parting line of the core is approximately parallel to the top of the holder. The diameter of the core is measured 90 degrees to this orientation before securing. A measurement is made from the bottom of the holder to the top of the core to provide a reference point for future calculations. A rough cut is made slightly above the exposed geometric center of the core using a band saw or other suitable cutting tool to ensure that the core does not move within the holder during this step. The remainder of the core, still within the holder, is secured to the base plate of the surface grinding machine. The exposed "rough" surface is ground to a smooth, flat surface, exposing the geometric center of the core, which can be verified by measuring the height from the bottom of the holder to the exposed surface of the core and verifying that exactly half of the original height of the core measured above has been removed to within 0.10 millimeters. Leaving the core in the holder, the center of the core is located with a center square, carefully marked, and the hardness is measured at the center mark in accordance with ASTM D-2240. Additional hardness measurements at any distance from the center of the core can be made by drawing a line radially outward from the center mark and measuring the hardness at any given distance along the line, typically in 2 mm increments from the center. The hardness at a particular distance from the center should be measured along at least two, and preferably four, radial arms spaced 180° or 90° apart, respectively, and then averaged. All hardness measurements made on a plane passing through the geometric centre are made with the core still in the holder and without disturbing its orientation, so that the test surface is always parallel to the bottom of the holder and therefore also parallel to the properly aligned feet of the durometer.

[0114] The outer surface hardness of a golf ball layer is measured at the actual outer surface of the layer and is derived from the average of multiple measurements taken from opposing hemispheres, with care to avoid measurements at core parting lines or surface defects such as holes or protrusions. Hardness measurements are made in accordance with ASTM D-2240, "Indentation Hardness of Rubber and Plastic by Means of a Durometer." Because of the curved surfaces, care must be taken to ensure that the golf ball or golf ball subassembly is centered under the durometer indenter before a surface hardness reading is obtained. A calibrated digital durometer capable of reading to 0.1 hardness units is used for hardness measurements. The digital durometer should be mounted on the base of an automatic stand with its feet parallel. Durometer weights and attack rates are in accordance with ASTM D-2240.

[0115] As mentioned above, the direction of the hardness gradient of a golf ball layer is defined by the difference in hardness measurements taken at the outer and inner surfaces of a particular layer. The center hardness of the inner core and the hardness of the outer surface of the inner core in a single core ball or outer core layer are easily determined according to the above test procedures. The outer surface of the inner core layer (or any other intermediate core layer) of a dual core ball is also easily determined according to the procedure described herein for measuring the outer surface hardness of a golf ball layer, if the measurement is made before the layer is surrounded by an additional core layer. It may be difficult to determine the hardness of the inner and outer surfaces of any inner or intermediate layer once an additional core layer surrounds the layer of interest. Thus, for purposes of this disclosure, if the hardness of the inner or outer surface of a core layer is required after the inner layer has been surrounded by another core layer, the above test procedure for measuring a point located 1 mm from the interface is used.

[0116] compression As disclosed in Compression by Any Other Name, Science and Golf IV, Proceedings of the World Scientific Congress of Golf (Eric Thain, ed., Routledge, 2002) ("J. Dalton") by Jeff Dalton, compression can be measured using several different methods, including Atti compression, Riehle compression, load / strain measurements at various fixed loads and offsets, and effective modulus. For the purposes of this disclosure, compression refers to the Soft Center Strain Index ("SCDI"). The SCDI is a program modification of a Dynamic Compression Machine ("DCM") that allows for the determination of the pounds required to distort the core 10% of its diameter. The DCM is a device that applies a load to the core or ball and measures the number of inches the core or ball is distorted by at the measured load. A raw load / strain curve that fits the Atti compression scale is generated, resulting in a number that represents the Atti compression. The DCM does this via a load cell attached to the bottom of a hydraulic cylinder that is pneumatically triggered at a fixed speed (typically about 30.48 centimeters per second) toward a fixed core. The cylinder is fitted with an LVDT that measures the distance the cylinder travels during the test time frame. A software-based logarithmic algorithm ensures that no measurements are taken until at least five consecutive load increases are detected during the initial phase of the test. The SCDI is a slight variation of this configuration. The hardware is the same, but the software and outputs change. In the SCDI, that deflection amount, which is the amount of pounds of force times inches required to deflect the core, is 10% of the core diameter. The DCM is triggered, the cylinder deflects the core by 10% of its diameter, and the DCM reports the pounds of force (measured from an attached load cell) required to deflect the core by that amount. The value displayed is a single number in pounds.

[0117] Restitution coefficient COR is determined according to a known procedure, where a golf ball or golf ball subassembly (e.g., golf ball core) is fired from an air cannon at two given velocities, with the velocity of 125 ft / s being used in the calculation. Ballistic light screens are placed between the air cannon and a steel plate at a fixed distance to measure the ball velocity. As the ball travels towards the steel plate, each light screen is activated and the time of the ball at each light screen is measured. This provides an entry passage time that is inversely proportional to the entry velocity of the ball. The ball impacts the steel plate and bounces, thereby passing through a light screen again. As the bouncing ball activates each light screen, the time of the ball at each screen is measured. This provides an exit passage time that is inversely proportional to the exit velocity of the ball. The COR is then calculated as the ratio of the exit passage time of the ball to the entry passage time of the ball (COR=V out / V in =T in / T out ).

[0118] The golf balls described and claimed herein are not limited in scope by the specific embodiments disclosed herein, as these embodiments are intended as illustrative of the aspects of the present disclosure. Any equivalent embodiments are intended to be within the scope of the present disclosure. Indeed, various modifications of the golf balls in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to be within the scope of the appended claims. All patents and patent applications cited in the above text are expressly incorporated herein by reference in their entirety. The section headings herein are provided solely for consistency with the proposals of 37 C.FR §1.77 or to provide an organizational queue. These headings are not intended to limit or characterize the invention described herein. [Explanation of symbols]

[0119] 10 2-piece ball 12, 22 Core layer 14, 26 Cover layer 20 Golf balls 24, 36 Middle class 30 4-piece golf balls 32, 42 Inner core layer 34, 46 Outer core layer 38 Outer cover layer 40 5-piece golf balls 44 Middle core layer 48 Inner cover layer 50 Outer Cover Layer

Claims

1. A golf ball comprising a dual core and a cover layer surrounding the dual core; The dual core is an outer core layer disposed on an inner core layer; At least one of the outer core layer and the inner core layer is formed from a rubber composition cured under heat, the rubber composition comprising: a base rubber containing polybutadiene rubber; an organic peroxide; a crosslinking coagent comprising a zinc salt of an acrylate, diacrylate, methacrylate, or dimethacrylate; a water-releasing agent containing a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of about 1 phr to about 3.9 phr; the layer formed from the rubber composition has an outer surface and a geometric center, each having a hardness, the hardness of the geometric center being in the range of about 45 Shore C to about 65 Shore C, and the hardness of the outer surface being in the range of about 80 Shore C to about 100 Shore C; the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 30 Shore C units; The cover layer comprises an ionomer, a polyurethane, a polyurea, a polyurethane-urea hybrid, or copolymers and mixtures thereof; Golf ball.

2. 2. The golf ball of claim 1, wherein the metal is an alkaline earth metal.

3. 10. The golf ball of claim 1, wherein the inner core layer has a diameter of about 6.35 millimeters to about 38.35 millimeters.

4. 10. The golf ball of claim 1, wherein the dual core has a diameter ranging from about 35.31 millimeters to about 41.15 millimeters.

5. 10. The golf ball of claim 1, wherein the outer core layer and the inner core layer are formed from a rubber composition.

6. 2. The golf ball of claim 1, wherein the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr.

7. 2. The golf ball of claim 1, wherein the syneresis agent is calcium sulfate dihydrate.

8. 2. The golf ball of claim 1, wherein the crosslinking coagent is zinc diacrylate.

9. 10. The golf ball of claim 1, wherein the water release agent is present in the rubber composition in an amount of from about 1 phr to about 3 phr.

10. 10. The golf ball of claim 1, wherein the hardness of the outer surface is greater than the hardness of the geometric center so as to define a positive hardness gradient of at least 34 Shore C units.

11. 10. The golf ball of claim 1, wherein the water release agent is present in the rubber composition in an amount of about 3 phr.

12. A golf ball comprising a solid core and a cover layer surrounding the core, A solid core having an outer surface and a geometric center is formed from a rubber composition cured under heat, the rubber composition comprising: a base rubber containing a mixture of polybutadiene and ethylene-propylene-diene rubber; an organic peroxide containing dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof; a crosslinking coagent containing a zinc salt of an acrylate, diacrylate, methacrylate, or dimethacrylate; a water-releasing agent comprising a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3.9 phr; Equipped with the geometric center and the outer surface each have a hardness; the hardness of the geometric center ranges from about 45 Shore C to about 65 Shore C, and the hardness of the outer surface ranges from about 80 Shore C to about 100 Shore C; the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 30 Shore C units; Golf ball.

13. 13. The golf ball of claim 12, wherein the metal is an alkaline earth metal.

14. 13. The golf ball of claim 12, wherein the polybutadiene is present in the mixture in an amount of from about 70 phr to about 99 phr and the ethylene-propylene-diene rubber is present in the mixture in an amount of from about 1 phr to about 30 phr.

15. 13. The golf ball of claim 12, wherein the solid core has a compression value of about 10 to about 95.

16. 13. The golf ball of claim 12, wherein the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr.

17. 13. The golf ball of claim 12, wherein the syneresis agent is calcium sulfate dihydrate.

18. 13. The golf ball of claim 12, wherein the coagent is present in the rubber composition in an amount of about 10 phr to 45 phr.

19. 13. The golf ball of claim 12, wherein the water release agent is present in the rubber composition in an amount of from about 1 phr to about 3 phr.

20. 13. The golf ball of claim 12, wherein the water release agent is present in the rubber composition in an amount of about 3 phr.

21. 13. The golf ball of claim 12, wherein the rubber composition further contains an additive selected from zinc pentachlorothiophenol, zinc oxide, barium sulfate, or a combination thereof.

22. A golf ball comprising a solid core and a cover layer surrounding the solid core, A solid core having an outer surface and a geometric center is formed from a rubber composition cured under heat, the rubber composition comprising: a base rubber made of polybutadiene rubber; an organic peroxide; a crosslinking coagent containing a zinc salt of an acrylate, diacrylate, methacrylate, or dimethacrylate; a water-releasing agent comprising a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of from about 1 phr to about 3.9 phr; Contains the geometric center and the outer surface each have a hardness; the hardness of the geometric center ranges from about 45 Shore C to about 65 Shore C, and the hardness of the outer surface ranges from about 80 Shore C to about 100 Shore C; the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 30 Shore C units; The cover layer comprises an ionomer, a polyurethane, a polyurea, a polyurethane-urea hybrid, or copolymers and mixtures thereof; Golf ball.

23. 23. The golf ball of claim 22, wherein the metal is an alkaline earth metal.

24. 23. The golf ball of claim 22, wherein the solid core has a diameter ranging from about 35.31 millimeters to about 41.15 millimeters.

25. 23. The golf ball of claim 22, wherein the cover layer is formed from an ionomer, a thermoplastic polyurethane, or a castable polyurethane.

26. 23. The golf ball of claim 22, wherein the solid core has a compression value of about 10 to about 95.

27. 23. The golf ball of claim 22, wherein the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr.

28. 23. The golf ball of claim 22, wherein the syneresis agent is calcium sulfate dihydrate.

29. 23. The golf ball of claim 22, wherein the water release agent is present in the rubber composition in an amount of from about 1 phr to about 3 phr.

30. 23. The golf ball of claim 22, wherein the hardness of the outer surface is greater than the hardness of the geometric center so as to define a positive hardness gradient of at least 34 Shore C units.

31. 23. The golf ball of claim 22, wherein the polybutadiene rubber has a 1,4 cis content of at least 90%.

32. A golf ball comprising a multi-layer core having a plurality of core layers and a cover layer surrounding the multi-layer core, At least one of the multi-layer cores is formed from a rubber composition cured under heat, the rubber composition comprising: a base rubber containing polybutadiene rubber; an organic peroxide; a crosslinking coagent comprising a zinc salt of an acrylate, diacrylate, methacrylate, or dimethacrylate; a water-releasing agent comprising a metal sulfate hydrate having 1 to 4 waters of hydration, the water-releasing agent being present in the rubber composition in an amount of about 1 phr to about 3.9 phr; a core layer formed from the rubber composition having an outer surface and a geometric center, each having a hardness, the hardness of the geometric center being in the range of about 45 Shore C to about 65 Shore C, and the hardness of the outer surface being in the range of about 80 Shore C to about 100 Shore C; the hardness of the outer surface is greater than the hardness of the geometric center, defining a positive hardness gradient of at least 30 Shore C units; The cover layer comprises an ionomer, a polyurethane, a polyurea, a polyurethane-urea hybrid, or copolymers and mixtures thereof; Golf ball.

33. 33. The golf ball of claim 32, wherein the metal is an alkaline earth metal.

34. 33. The golf ball of claim 32, wherein the multi-layer core comprises at least three core layers.

35. 33. The golf ball of claim 32, wherein the multi-layer core has a diameter ranging from about 35.31 millimeters to about 41.15 millimeters.

36. 33. The golf ball of claim 32, wherein each core layer of the multi-layer core is formed from a rubber composition.

37. 33. The golf ball of claim 32, wherein the organic peroxide is dimethyl tertbutyl peroxide, dicumyl peroxide, or a combination thereof, and the organic peroxide is present in the rubber composition in an amount of about 0.25 phr to about 2.5 phr.

38. 33. The golf ball of claim 32, wherein the syneresis agent is calcium sulfate dihydrate.

39. 33. The golf ball of claim 32, wherein the water release agent is present in the rubber composition in an amount of from about 1 phr to about 3 phr.

40. 33. The golf ball of claim 32, wherein the multi-layer core comprises a central portion and at least three core layers formed around the central portion.

41. 41. The golf ball of claim 40, wherein the center and at least two of the core layers are formed from a rubber composition.

42. 33. The golf ball of claim 32, wherein the water release agent is present in the rubber composition in an amount of about 3 phr.

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