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US 11,944,875 B2Granted
Golf balls having cores with increased hardness gradient
AssigneeAcushnet Company
InventorsErin McDermott, Manjari Kuntimaddi, Dennis Britton
Life of this patent
Estimating the term…
Abstract
Golf balls having cores with increased hardness gradients are provided. The cores have an increased “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 the core rubber formulation during the curing process. The resulting golf balls have reduced spin and sufficient impact durability.
Claims17
A golf ball, comprising:
- a dual core comprising an outer core layer disposed over an inner core layer, wherein at least the inner core layer is formed of a rubber composition cured under heat, the rubber composition comprising:
- a base rubber comprising polybutadiene rubber,
- an organic peroxide,
- a cross-linking co-agent comprising a zinc salt of an acrylate, diacrylate, methacrylate, or dimethacrylate,
- calcium sulfate dihydrate in an amount of about 1 phr to about 3.9 phr,
- wherein the inner core layer has a geometric center and an outer surface, each having a hardness, the hardness of the geometric center ranging from about 40 Shore C to about 70 Shore C and the hardness of the outer surface ranging from about 75 Shore C to about 105 Shore C, and
- wherein the hardness of the outer surface is greater than the hardness of the geometric center to define a positive hardness gradient of at least 30 Shore C units;
- and
- a cover layer surrounding the dual core, wherein the cover layer comprises an ionomer, polyurethanes, polyureas, polyurethane-urea hybrids, or copolymers and blends thereof.
6 more elements
A golf ball, comprising:
- a dual core comprising an outer core layer disposed over an inner core layer,
- wherein the outer core layer is formed of a first rubber composition cured under heat, the first rubber composition comprising:
- a base rubber comprising a mixture of polybutadiene rubber and styrene butadiene rubber,
- an organic peroxide, and
- zinc diacrylate,
- wherein the inner core layer is formed of a second rubber composition cured under heat, the second rubber composition comprising:
- a base rubber comprising polybutadiene rubber,
- an organic peroxide,
- zinc diacrylate, and
- calcium sulfate dihydrate in an amount of about 1 phr to about 3.75 phr,
- wherein the inner core layer has a geometric center and an outer surface, each having a hardness, the hardness of the geometric center ranging from about 40 Shore C to about 70 Shore C and the hardness of the outer surface ranging from about 75 Shore C to about 105 Shore C, and the hardness of the outer surface is greater than the hardness of the geometric center to define a positive hardness gradient of 30 Shore C units to 50 Shore C units,
- wherein the amount of calcium sulfate dihydrate and the number of waters of hydration are related to the positive hardness gradient, according to equation (I):
- 2
- ≤
- WRA
- C
- *
- WRA
- WOH
- 1
- -
- 1
- H
- Gr
- ≤
- 1
-
- 5
- (
- I
- )
- where WRAc represents the amount of calcium sulfate dihydrate in parts per hundred;
- HGr represents the positive hardness gradient (Shore C);
- and WRAWOH represents the number of waters of hydration in the calcium sulfate dihydrate;
- an inner cover layer surrounding the dual core, wherein the inner cover layer is formed of an ionomer;
- and
- an outer cover layer disposed about the inner cover layer, wherein the outer cover layer is formed of a polymer selected from the group consisting of polyurethanes, polyureas, polyurethane-urea hybrids, and copolymers and blends thereof.
34 more elements
A golf ball, comprising:
- a dual core comprising an outer core layer disposed over an inner core layer, the inner core layer having a geometric center hardness less than a surface hardness to define a first positive hardness gradient and the outer core layer having an inner surface hardness less than an outer surface hardness to define a second positive hardness gradient,
- wherein the outer core layer and the inner core layer are each formed of a rubber composition cured under heat, the rubber composition comprising:
- a base rubber comprising polybutadiene rubber having a 1,4 cis-bond content of at least 90 percent,
- dicumyl peroxide,
- zinc diacrylate,
- calcium sulfate dihydrate in an amount of about 1 phr to about 3.9 phr, and
- an additive selected from zinc pentachlorothiophenol, zinc oxide, barium sulfate, or combinations thereof, and
- wherein the geometric center hardness is from about 40 Shore C to about 70 Shore C and the surface hardness is from about 75 Shore C to about 105 Shore C, and each of the first positive hardness gradient and the second positive hardness gradient is at least 34 Shore C units;
- an inner cover layer surrounding the core;
- and
- an outer cover layer disposed about the inner cover layer.
8 more elements
Dependencies are inferred from the claim text.