Patent Application
20250073537
This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2023-137956 filed in Japan on Aug. 28, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a golf ball in which at least one intermediate layer is formed between a core and a cover. More particularly, the invention relates to a golf ball which, by optimizing the specific gravities of the constituent layers, is able to achieve a satisfactory performance on putts with a putter.
With regard to the cover layer and the intermediate layer serving as structural components of a golf ball, in order to improve the feel of the ball at impact and lower its spin rate, technical advances are being made that reduce the layer thicknesses and create multilayer structures through the use of injection molding or compression molding. With such multilayer structures and smaller layer thicknesses, gage non-uniformity (eccentricity) becomes an issue. In a nonuniform ball, the center of gravity position changes, which affects, for example, rolling of the ball (straightness) on putts with a putter.
The prior art includes a number of patent disclosures on golf balls that have a high moment of inertia. For example, JP-A H10-151225, JP-A 2001-79116 and JP-A 2012-45391 provide golf balls which roll well on shots with a putter because the outside layer of the ball has been set to a higher specific gravity than the inside layer through the suitable addition of a specific gravity modifier or the like to the outside layer, thus increasing the moment of inertia and achieving a high spin retention.
However, owing to the large differences between the specific gravities of the respective layers in these prior-art golf balls, the deviation in the position of the ball center of gravity from the center of the ball increases when eccentricity arises in each layer during production. As a result, the ball has a tendency to curve and rolling of the ball becomes unstable.
Also, the patent applicant has disclosed, in earlier filed Japanese Patent Application No. 2022-206365, that by providing a golf ball in which the relationships between the materials and color tones of the core and the intermediate layer adjoining the core have been calibrated, the eccentricity of the core can be easily distinguished visually even without the use of inspection equipment such as an x-ray imaging device in the golf ball production process. Yet, the purpose of the foregoing art is to be able to easily identify an eccentric intermediate layer; in such an eccentric golf ball, the ball center of gravity position deviates from the center and so, as in the above prior art, rolling of the ball may become unstable.
It is therefore an object of the present invention to provide a golf ball in which the amount of deviation in the ball center of gravity is exceedingly small, increasing the straightness with which the ball rolls on putts with a putter.
As a result of intensive investigations, we have discovered that, in a golf ball having at least one intermediate layer formed between the core and the cover, by uniformly setting the standard deviation in the specific gravities of the respective layers (the core, the intermediate layer and the cover) to 0.07 or less, setting the material hardness of the cover on the Shore D hardness scale to 52 or below and setting the deflection of the ball when compressed under a final load of 1.275 N (130 kgf) from an initial load of 98 N (10 kgf) to 2.8 mm or less, the deviation in the ball center of gravity becomes exceedingly small, the straightness with which the ball rolls on putts with a putter rises and, at the same time, the dispersion in the vertical (longitudinal) and horizontal (left-right) directions when the ball is hit with a putter can be suppressed.
Accordingly, the invention provides a golf ball having a core, a cover and at least one intermediate layer formed therebetween, wherein the core, intermediate layer and cover have respective specific gravities with a standard deviation of 0.07 or less, the cover has a material hardness on the Shore D hardness scale of 52 or less and the ball has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is 2.8 mm or less.
In a preferred embodiment of the golf ball of the invention, letting CM be the specific gravity of the core, MM be the specific gravity of the intermediate layer, FM be the specific gravity of the cover, CV be the initial velocity of the core, MV be the initial velocity of the sphere obtained by encasing the core with the intermediate layer (intermediate layer-encased sphere) and FV be the initial velocity of the ball, which is the sphere obtained by encasing the intermediate layer-encased sphere with the cover, the ball satisfies formula (1) below
[the initial velocity values for the core and the intermediate layer-encased sphere being values measured using an initial velocity instrument of the same type as a USGA drum rotation-type initial velocity tester, and the initial velocity value for the ball being a value measured using a COR-type initial velocity instrument of the same type as a R&A tester].
In another preferred embodiment of the inventive golf ball, the ball has a moment of inertia of from 82.5 to 85.0 g·cm2.
In yet another preferred embodiment, letting CM be the specific gravity of the core, MM be the specific gravity of the intermediate layer, FM be the specific gravity of the cover, CV be the initial velocity of the core, MV be the initial velocity of the sphere obtained by encasing the core with the intermediate layer (intermediate layer-encased sphere), FV be the initial velocity of the ball, which is the sphere obtained by encasing the intermediate layer-encased sphere with the cover, and MOI be the moment of inertia of the ball, the ball satisfies formula (2) below
In still another preferred embodiment, the specific gravities of the core, the intermediate layer and the cover are all from 1.10 to 1.13 g/cm3.
In a further embodiment, the specific gravities of the intermediate layer and the cover satisfy the following relationship:
In a yet further embodiment, the intermediate layer is formed of a material which includes barium sulfate as a specific gravity modifier.
In a still further embodiment, the intermediate layer has a material hardness on the Shore D hardness scale of 60 or more.
In an additional embodiment, the cover has a material hardness on the Shore D hardness scale of 40 or more.
The golf ball of the invention has a center of gravity deviation that is exceedingly small, increasing the straightness with which the ball rolls on putts with a putter. At the same time, the dispersion in the vertical (longitudinal) and horizontal (left-right) directions when the ball is struck with a putter can be suppressed.
The FIGURE is a schematic diagram for explaining the putting test used in the Examples.
The objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the appended diagram.
The golf ball of the invention has a core, a cover and an intermediate layer formed therebetween. Each layer is described in detail below.
The core may be formed as a single layer or as a plurality of layers. A known rubber material or any of various resin materials may be used as the base in the core material. A known base rubber such as natural rubber or synthetic rubber may be used as the base rubber. Specific examples include polybutadiene, with the use of primarily cis-1,4-polybutadiene having a cis structure content of at least 40% being especially recommended. If desired, natural rubber, polyisoprene rubber, styrene-butadiene rubber or the like may be optionally used together with the above polybutadiene in the base rubber. The polybutadiene can be synthesized with a Ziegler catalyst such as a titanium-based, cobalt-based, nickel-based or neodymium-based catalyst, or with a cobalt, nickel or other metal catalyst.
Co-crosslinking agents such as unsaturated carboxylic acids and metal salts thereof, inorganic fillers such as zinc oxide, barium sulfate and calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy) cyclohexane may be included in the above base rubber. Where necessary, a commercial antioxidant or the like may be suitably added.
The core can be produced by vulcanizing/curing the rubber composition containing the above ingredients. For example, production may be carried out by kneading the composition using a mixer such as a Banbury mixer or a roll mill, compression molding or injection molding the kneaded composition using a core mold, and curing the molded body by suitably heating it at a temperature sufficient for the organic peroxide and the co-crosslinking agent to act, i.e., from 100° C. to 200° C., and preferably from 140 to 180° C., for a period of 10 to 40 minutes.
The specific gravity of the core is not particularly limited, although it is preferably at least 1.00, more preferably at least 1.03, and even more preferably at least 1.06. The upper limit is preferably not more than 1.20, more preferably not more than 1.17, and even more preferably not more than 1.14. To maintain a good distance performance on shots with a driver, it is essential to set the ball weight to from about 45.0 g to about 45.6 g. When doing so, if the specific gravity of the core is smaller than the above range, the specific gravity of the intermediate layer or the cover layer must be increased. By including a specific gravity modifier for this purpose, there is a possibility that the spin performance of the ball may be lost. On the other hand, when the core specific gravity is too large, the moment of inertia may become too small, as a result of which rolling of the ball on shots with a putter may worsen.
At least one intermediate layer and a cover can be formed over the core as members encasing the core. In cases where the intermediate layer consists of two layers, these layers are sometimes called, in order from the inside, the inner intermediate layer and the outer intermediate layer. The inner intermediate layer is sometimes referred to by another name: the “envelope layer.”
The intermediate layer is formed of a resin composition, This resin composition is exemplified by resin compositions composed primarily of resins that have hitherto been employed as golf ball materials. Examples of the base resin of the resin composition include ionomer resins, polyester resins, polyurethane resins, polyamide resins, polyolefin resins, olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers. From the standpoint of rebound and moldability, ionomer resins are especially preferred.
Various types of fillers may be included as specific gravity modifiers in the intermediate layer material. Examples of such fillers that may be suitably used include zinc oxide, titanium oxide, barium sulfate, calcium carbonate, potassium titanate, calcium oxide, magnesium oxide, silica and ferrite. One of these may be used alone or two or more may be used together.
No particular limitation is imposed on the amount of the specific gravity modifier (filler) included, although the amount may be set to preferably at least 10 parts by weight, and more preferably at least 15 parts by weight, per 100 parts by weight of the intermediate layer base resin. There is no particular upper limit in the amount included, although the amount is preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 30 parts by weight, per 100 parts by weight of the intermediate layer base resin. When the amount included is too great or too small, a proper specific gravity may not be obtained and the desired effects of the invention may not be achieved.
The intermediate layer has a thickness which is preferably at least 0.6 mm, more preferably at least 0.8 mm, and even more preferably at least 1.0 mm. The upper limit is preferably not more than 2.0 mm, more preferably not more than 1.5 mm, and even more preferably not more than 1.3 mm. When the intermediate layer is too thin, the spin rate of the ball on full shots may rise, as a result of which the intended distance may not be achieved. On the other hand, when the intermediate layer is too thick, the ball rebound may become lower.
No particular limitation is imposed on the material hardness of the intermediate layer, although the hardness on the Shore D hardness scale is preferably at least 60, more preferably at least 65, and even more preferably at least 67. The material hardness is preferably not more than 75, and more preferably not more than 73. As the hardness value becomes higher, an increased distance owing to the lower spin rate of the ball on full shots with an iron (I#6) can be achieved. However, if the material hardness is too high, the durability of the ball to cracking on repeated impact may decline.
The specific gravity of the intermediate layer is preferably at least 1.05, more preferably at least 1.07, and even more preferably at least 1.09. The upper limit is preferably not more than 1.25, more preferably not more than 1.20, and even more preferably not more than 1.15. When the specific gravity of the intermediate layer is too low, the durability to cracking on repeated impact may worsen. On the other hand, when the specific gravity of the intermediate layer is too high, the ball rebound may decrease or the spin rate of the ball on full shots may rise, as a result of which the intended distance may not be attained.
It is desirable for the specific gravities of the intermediate layer and the cover to satisfy the following relationship:
A difference in specific gravity between these layers gives rise to long-short and left-right dispersion in rolling of the ball on shots with a putter, and so the specific gravity difference is set within the above range to minimize such dispersion.
The cover is formed of a resin composition. This resin composition is not particularly limited, although the cover can be formed using an ionomer resin, a polyurethane-based thermoplastic elastomer, a thermosetting polyurethane, or a mixture thereof as the chief ingredient of the resin composition. Aside from the above chief ingredient, other thermoplastic elastomers and also, for example, polyisocyanate compounds, fatty acids or derivatives thereof, basic inorganic metal compounds and fillers may be added to the cover.
The resin composition may be obtained by mixing together the above ingredients using any of various types of mixers, such as a kneading-type single-screw or twin-screw extruder, a Banbury mixer or a kneader.
The cover thickness is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. The upper limit is preferably not more than 2.0 mm, more preferably not more than 1.5 mm, and even more preferably not more than 1.3 mm. When the cover is too thin, there is a possibility that the scuff resistance of the ball when struck with a wedge will worsen. On the other hand, when the cover is too thick, there is a possibility that the spin rate of the ball will rise excessively and that the desired distance will not be attained.
The specific gravity of the cover, although not particularly limited, is preferably at least 1.00, more preferably at least 1.03, and even more preferably at least 1.06. The specific gravity is preferably not more than 1.20, more preferably not more than 1.17, and even more preferably not more than 1.14. At a cover specific gravity smaller than the above range, the scuff resistance sometimes worsens on account of the blending ratio of the resin used for modifying the specific gravity. On the other hand, when the specific gravity of the cover is too large, the amount of filler added may increase and the rebound may become too low, as a result of which the intended distance may not be attained.
The specific gravities of the above core, intermediate layer and cover are preferably all at least 1.10 and not more than 1.13. Setting the specific gravities of all the layers within such a numerical value range has the advantage of giving a golf ball which conforms with the Rules of Golf in addition to which the specific gravity differences among the layers are smallest, resulting in smaller long-short and left-right dispersion in rolling of the ball on shots with a putter.
The cover has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably not more than 52, more preferably not more than 47, and even more preferably not more than 45. The material hardness is preferably at least 40, and more preferably at least 43. By setting the hardness to a relatively low value, the initial velocity of the ball on putts tends to remain low and the dispersion in the putting distance is small. Within this range, a higher hardness enables an increased distance to be achieved on full shots with an iron (I#6) due to a lower spin rate.
The golf ball has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) of 2.8 mm or less, preferably 2.5 mm or less, and more preferably 2.4 mm or less. By thus setting the deflection to a relatively small value, the dispersion in the ball distance on putts becomes smaller. The lower limit in this deflection is preferably at least 2.2 mm, and more preferably at least 2.3 mm.
The golf ball of the invention has a moment of inertia that is preferably at least 82.5 kg·cm2, and more preferably at least 83.0 kg·cm2. The upper limit is preferably not more than 85.0 kg·cm2. The moment of inertia used in the invention can be calculated from the following formula.
The moment of inertia is a value calculated from the diameter (thickness) and specific gravity of each layer, and can be determined by treating the ball as a perfect sphere. The moment of inertia of the golf ball can be measured using a moment of inertia measuring instrument such as the M01-005 from Inertia Dynamics Inc.
In this invention, it is critical for the core, the intermediate layer and the cover serving as structural components of the golf ball to have respective specific gravities with a standard deviation of 0.07 or less.
The above standard deviation is the commonly calculated standard deviation, which is the positive square root of the value obtained by summing the differences between individual data values and the mean raised to the second power and dividing the sum by the total number of data (n). Here, the difference between a data value and the mean is referred to as the “deviation,” and the squared mean of the deviations is referred to as the “variance” or “dispersion.” The standard deviation is thus the positive square root of the variance.
(wherein τ is the standard deviation, Xi is a data value, X0 is the mean, and n is the total number of data).
For example, in Example 1 in Table 3 below, the specific gravity of the core is 1.13, the specific gravity of the intermediate layer is 1.08 and the specific gravity of the cover is 1.07. The mean of these three data is (1.13+1.08+1.07)/3≈1.0933. Plugging this value into the above formula, σ={⅓×(1.13−1.0933)2+⅓×(1.08−1.0933)2+⅓×(1.07−1.0933)2}½≈0.03.
The standard deviation of the specific gravities of the core, the intermediate layer and the cover is 0.07 or less, preferably 0.05 or less, and even more preferably 0.03 or less. By setting the standard deviation to 0.07 or less, the degree of left-right dispersion by the ball during putting decreases, enabling stable putting to be obtained.
Also, in this invention, letting CM be the specific gravity of the core, MM be the specific gravity of the intermediate layer, FM be the specific gravity of the cover, CV be the initial velocity of the core, MV be the initial velocity of the sphere obtained by encasing the core with the intermediate layer (intermediate layer-encased sphere) and FV be the initial velocity of the ball, which is the sphere obtained by encasing the intermediate layer-encased sphere with the cover, it is desirable for the ball to satisfy formula (1) below
Here, the initial velocities are values measured for the respective test spheres using an initial velocity instrument of the same type as a USGA drum rotation-type initial velocity tester. The value of (CM×CV)+(MM×MV)+(FM×FV/FC) above is preferably larger than 200, more preferably 203 or more, and even more preferably 206 or more. By thus setting the value of the above formula larger than 200, the dispersion in the distance of the balls on putts becomes smaller.
Additionally, letting MOI be the moment of inertia of the ball, it is desirable for the ball to satisfy formula (2) below
Here, the initial velocities are values measured for the respective test spheres using an initial velocity instrument of the same type as a USGA drum rotation-type initial velocity tester. The value of (CM×CV/MOI)+(MM×MV)+(FM×FV/FC) is preferably more than 110, more preferably 113 or more, and even more preferably 115 or more. By thus setting the value of the above formula so as to be larger than 110, the dispersion in the distance traveled by the ball on putts becomes smaller.
The initial velocities of the core (CM), the intermediate layer-encased sphere (MV) and the ball (FV) are preferably set within the following respective ranges.
The initial velocities of the core and the intermediate layer-encased sphere can be measured using an initial velocity measuring instrument of the same type as the USGA drum rotation-type initial velocity instrument approved by The Royal & Ancient Golf Club of St. Andrews (R&A). The initial velocity of the test sphere is tested in a room-temperature (23.9±2° C.) chamber by using a 250-pound (113.4 kg) head (striking mass) at an impact velocity of 143.8 ft/s (43.83 m/s), and the time taken for the sphere to traverse a distance of 6.28 ft (1.91 m) is measured and used to compute the initial velocity (m/s). The spheres to be tested are held isothermally at a temperature of 23.9±1° C. for at least 3 hours.
The ball initial velocities are values measured with a COR initial velocity tester of the same type as a R&A tester. Specifically, a COR initial velocity tester manufactured by Hye Precision Products (U.S.A.). At the time of measurement, the air pressure is changed in four stages and measurement is carried out, based on which a formula relating the inbound velocity and the COR is established and the initial velocity at an inbound velocity of 43.83 m/s is determined. Measurement with this COR initial velocity tester is carried out at a room temperature of 23.9±2° C. using a ball that has been held isothermally for at least 3 hours in a thermostatic chamber adjusted to 23.9±1° C. The barrel diameter is selected such that the clearance on one side with respect to the outside diameter of the test object falls in a range of from 0.2 to 2.0 mm.
The initial velocity of the core (CM) is preferably at least 77.50 m/s, more preferably at least 77.60 m/g, and even more preferably at least 77.70 m/g. The upper limit is preferably not more than 78.10 m/s, and more preferably not more than 77.90 m/g.
The initial velocity of the intermediate layer-encased sphere (MV) is preferably at least 77.70 m/s, more preferably at least 77.80 m/s, and even more preferably at least 77.90 m/s. The upper limit is preferably not more than 78.30 m/s, and more preferably not more than 78.10 m/s.
The initial velocity of the ball (FV) is preferably at least 77.00 m/s, more preferably at least 77.10 m/s, and even more preferably at least 77.20 m/s. The upper limit is preferably not more than 77.70 m/s, and more preferably not more than 77.60 m/s.
If these initial velocities fall outside of the above ranges, the dispersion in the vertical direction when the ball is hit with a putter sometimes becomes large.
Numerous dimples of two or more types are generally formed on the surface of the cover. Characteristics of these dimples, such as their shape, diameter, depth, number and surface coverage are suitably selected.
No particular limitation is imposed on the method of manufacturing the golf ball. The golf ball can be obtained using a known molding method such as injection molding or compression molding. For example, the golf ball can be manufactured by feeding the above-described intermediate layer-forming resin composition to an injection molding machine mold in which a core has been set and creating a sphere consisting of the core encased by an intermediate layer (intermediate layer-encased sphere), and subsequently setting the intermediate layer-encased sphere in the mold of another injection molding machine and injecting a cover-forming resin composition into the mold to form the cover.
A paint layer may be formed on the surface of the cover. The paint layer in this case is formed of a paint composition. Examples of the base resin of this paint composition include, but are not particularly limited to, polyurethane resins, epoxy resins, polyester resins, acrylic resins and cellulose resins. From the standpoint of the durability of the paint layer, the use of a two-part curable polyurethane resin is preferred. Where necessary, the coating composition may include suitable amounts of various additives such as antioxidants, ultraviolet absorbers, light stabilizers, fluorescent agents and fluorescent brighteners.
A known method may be used without particular limitation as the method for applying this paint onto the cover surface. For example, electrostatic painting, spray painting or brush painting may be employed.
Ball specifications such as the weight and diameter of the inventive golf ball can be suitably set in according with the Rules of Golf.
The following Examples and Comparative Examples are provided to illustrate the invention, and are not intended to limit the scope thereof.
A core composition common to all of the Examples and Comparative Examples was prepared according to the rubber formulation shown in Table 1, following which the composition was vulcanized at 150° C. for 20 minutes, thereby producing a core. The zinc oxide and zinc acrylate were included in amounts suitable for conforming to the specific gravities and deflections shown in Table 3, thereby producing seven core formulations: A, A′, B, B′, C, D and E.
Details on the above formulations are given below.
Next, in each Example and Comparative Example, using the injection mold described below, intermediate layer-forming resin materials A to D shown in Table 2 were injection-molded over the surface of the above core, thereby forming an intermediate layer having a thickness of 1.20 mm and a Shore D hardness of from 66 to 68.
Details on the compounding ingredients in the above table are provided below.
Next, using another injection mold, three types of urethane resin materials (TPU1, TPU2 and TPU3) were injection-molded over the above intermediate layer-encased sphere, thereby forming a cover (outermost layer) having a thickness of 0.8 mm and a Shore D hardness of from 43 to 50. TPU1, TPU2 and TPU3 were as follows.
The specific gravity difference between layers, the standard deviation of the specific gravities, formulas (1) and (2) below, the initial velocity of each encased sphere, the deflection of each encased sphere and the moment of inertia of the ball were calculated for the resulting golf balls in each Example, and putting tests were carried out using the balls in the respective Examples. The results are shown in Table 3.
The core, intermediate layer-encased sphere or ball is placed on a hard plate and the amount of deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. The amount of deflection is the value obtained by measurement in a 23.9±2° C. room after temperature conditioning the sphere for at least 3 hours at 23.9±1° C. in a thermostatic chamber. The instrument used is a high-load compression tester available from MU Instruments Trading Corp. The downward speed of the pressing head which compresses the core, the respective layer-encased spheres or the ball is set to 10 mm/s.
The initial velocity is measured using an initial velocity measuring instrument of the same type as the USGA drum rotation-type initial velocity tester approved by the R&A. The core, the intermediate layer-encased sphere and the ball are tested in a chamber at a room temperature of 23±2° C. after at least 3 hours of temperature conditioning at 23±1° C. in a thermostatic chamber. Twenty cores, intermediate layer-encased spheres and balls are each hit two times and the time taken for the balls to traverse a distance of 6.28 ft (1.91 m) is measured and used to compute the initial velocity (m/s). This cycle is carried out over a period of about 15 minutes.
The golf ball moment of inertia is measured using a moment of inertia measuring instrument (“M01-005” from Inertia Dynamics Inc.). This instrument measures the moment of inertia of a golf ball from the difference between the period of oscillation when the golf ball is mounted on the instrument platform using a holding fixture and the period of oscillation when the golf ball is not mounted.
The diameters and weights of the respective layers are measured before and after injection molding, and the specific gravities of the layers are computed from the member weights and volumes for the material making up each layer.
Formula (1) in Table 3 refers to (CM×CV)+(MM×MV)+(FM×FV/FC), and formula (2) refers to (CM×CV/MOI)+(MM×MV)+(FM×FV/FC).
Here, CM is the specific gravity of the core, MM is the specific gravity of the intermediate layer and FM is the specific gravity of the cover. CV is the initial velocity of the core, MV is the initial velocity of the intermediate layer-encased sphere and FV is the initial velocity of the ball. MOI is the moment of inertia of the ball.
The swing width of a putter robot is adjusted and set so as to result in a rolling distance of about 5 meters and the balls in each Example are hit. The average initial velocity, rolling distance X and left-to-right dispersion Y when each ball is measured ten times at the same target distance are determined, and the standard deviations X(σ) and Y(σ) for X and Y are respectively treated as the dispersion in the rolling distance (vertical dispersion) and the dispersion in the left-right (horizontal) direction. The Figure is a schematic diagram serving to explain the putting test. In the diagram, T represents a region of artificial turf, O is the striking position by the putter robot, P is the target position, X is the rolling distance, and Y is the width of the horizontal dispersion. The test apparatus conditions are presented below.
As demonstrated by the results in Table 3, each of the golf balls in Examples 1 to 6 had small standard deviations for the specific gravities of the constituent layers and the inconsistencies in the vertical distance and the horizontal distance for each of these balls on putts were small, meaning that the balls had long-short and left-right dispersions that were both small. The findings for the balls in Comparative Examples 1 to 5 were as follows.
In Comparative Example 1, the standard deviation in the specific gravities of the layers was large, as a result of which the inconsistency in the longitudinal distance was large. That is, the longitudinal dispersion was large.
In Comparative Example 2, the standard deviation in the specific gravities of the layers was large, as a result of which the inconsistency in the left-right distance was large. That is, the left-right dispersion was large.
In Comparative Example 3, the standard deviation in the specific gravities of the layers was large, as a result of which the inconsistency in the longitudinal distance was somewhat large.
In Comparative Example 4, the standard deviation in the specific gravities of the layers was large, as a result of which the inconsistency in the longitudinal distance was somewhat large.
In Comparative Example 5, the ball deflection was large, as a result of which the inconsistency in the longitudinal distance was large. That is, the longitudinal dispersion was large.
Japanese Patent Application No. 2023-137956 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-137956 | Aug 2023 | JP | national |
