Dual Core Golf Ball Hardness Gradient Control

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Solution Overview

Problem

Conventional golf ball cores, particularly those with thermoset materials, have limitations in achieving varied properties across the core due to their crosslinked structure, making it difficult to create specific hardness gradients that can affect compression, feel, and spin.

Innovation Solution

A golf ball design incorporating a thermoplastic inner core layer with a negative hardness gradient and a thermoset outer core layer with a positive hardness gradient, utilizing materials like ionomers, diene rubber, and gradient-promoting additives to achieve specific Shore C hardness values and gradients.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a thermoset rubber core is used with conventional curing cycles, then the core achieves basic structural integrity, but the physical properties become highly dependent on variable time/temperature history, creating inconsistent hardness gradients

Engineering Contradiction:

Improveconsistency of physical propertiesVSAvoidhardness gradient control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies parameter changes by systematically varying time/temperature history during the curing cycle to create controlled hardness gradients. Specifically, different curing regimes (e.g., higher temperature for shorter time vs. lower temperature for longer time) are used to achieve different hardness profiles from center to surface, transforming a reliability issue into a controllable manufacturing parameter

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements local quality by creating spatially varying hardness properties within the core. The center region experiences different curing conditions than the surface, resulting in a hardness gradient where the core center has one hardness value and the surface has another. This allows different regions of the same component to have optimized properties for their specific functional requirements

Inventive Principle:

Principle #3Local quality

2Strength

If a hard core is used to increase compression and distance, then the ball achieves greater compression and distance, but the feel becomes too harsh for some golfers

Engineering Contradiction:

ImprovecompressionVSAvoidharsh feel

Core Design Contradiction:

StrengthVSObject-generated harmful factors

Solution Approach 1:

The patent resolves this contradiction by creating local quality variations in hardness. The core center is formulated to be harder to provide compression and distance, while the core surface is formulated to be softer to provide a pleasant feel. This allows the same component to simultaneously deliver both performance characteristics in different regions

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9072944B2Dual core golf ball having a shallow “positive hardness gradient” thermoplastic inner core and a steep “positive hardness gradient” thermoset outer core layer

Publication Date: 2015.07.07 ACUSHNET CO

AI summary

A golf ball includes an inner core layer including a thermoplastic highly-neutralized ionomer formed from a copolymer of ethylene and an α,β-unsaturated carboxylic acid, an organic acid or salt thereof, and sufficient cation source to neutralize the acid groups of the copolymer by 80% or greater. The inner core has a geometric center hardness and a surface hardness to define a first hardness gradient. An outer core layer is disposed about the inner core and is formed from a homogenous thermoset composition. The outer core layer has an interior hardness and an outer surface hardness to define a second hardness gradient. An inner cover layer is disposed about outer core layer and an outer cover layer is disposed about the inner cover layer. A slope of the second hardness gradient is greater than a slope of the first hardness gradient.