Golf ball

Abstract

To provide a golf ball which extremely reduces deviation of a centroid of a ball, and can enhance rolling (direct advance property) of a ball in putting by a putter.SOLUTION: In a golf ball in which at least one layer of an intermediate layer is formed between a core and a cover, a standard deviation of specific gravity of respective layers of the core, the intermediate layer and the cover is within 0.07, material hardness of the cover is 52 or lower in shore D hardness, a bending amount (mm) when applying a load from an initial load 98 N (10 kgf) to a final load 1,275 N (130 kgf) to the ball is 2.8 mm or lower.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a golf ball in which at least one intermediate layer is formed between a core and a cover, and more specifically, to a golf ball which can exhibit good performance when putting with a putter by optimizing the specific gravity of each layer. [Background technology]

[0002] With regard to the cover layer and mantle layer, which are constituent parts of a golf ball, technology is being developed to make them thinner and multi-layered using injection molding and compression molding in order to improve the feel and reduce the spin rate. With such multi-layering and thinner gauges, uneven gauge (eccentricity) has become an issue. An uneven ball changes the position of the center of gravity, which affects the ball's roll (straightness) when putting with a putter, for example.

[0003] As a technology proposed in the past, there are several patent documents of golf balls with a high moment of inertia. For example, the following patent documents 1 to 3 can be mentioned. These provide a golf ball with a high spin retention rate and good ball rolling with a putter by appropriately blending a specific gravity adjusting material or the like in the outer layer of the golf ball and setting the specific gravity of the outer layer higher than that of the inner layer, thereby increasing the moment of inertia.

[0004] However, the above proposed golf ball has a large difference in specific gravity between the layers, and if any misalignment (eccentricity) occurs between the layers during manufacturing, the center of gravity of the ball will be significantly shifted from the center, resulting in the ball tending to curve and its roll becoming unstable.

[0005] In addition, the applicant has proposed a technology in the previously filed Japanese Patent Application No. 2022-206365 that allows the eccentricity of the core to be easily identified by visual inspection without using an inspection device such as an X-ray imaging device in the manufacturing process of the golf ball by providing a golf ball in which the relationship between the materials and the color tone of both the core and the intermediate layer adjacent to the core is adjusted. However, this technology is intended to make it easy to identify an eccentric intermediate layer, and such an eccentric golf ball has a center of gravity that is shifted from the center, and as with the above prior art, there is a risk that the ball's rolling will become unstable. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-151225 [Patent Document 2] JP 2001-79116 A [Patent Document 3] JP 2012-45391 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide a golf ball in which the deviation of the center of gravity of the ball is extremely small and the ball rolls (straightness) more easily when putting with a putter. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that for a golf ball having at least one intermediate layer formed between a core and a cover, by uniformly setting the standard deviation of the specific gravity of each layer of the core, intermediate layer and cover to within 0.07, setting the Shore D hardness of the material of the cover to 52 or less, and setting the deflection (mm) when the ball is subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) to 2.8mm or less, deviation of the center of gravity of the ball can be greatly reduced, the roll (straightness) of the ball when putted with a putter can be improved, and at the same time, variation in the vertical and horizontal directions when hit with the putter can be suppressed, which has led to the completion of the present invention.

[0009] Accordingly, the present invention provides the following golf ball. 1. A golf ball having at least one intermediate layer formed between a core and a cover, characterized in that the standard deviation of the specific gravity of each layer of the core, intermediate layer and cover is within 0.07, the material hardness of the cover is 52 or less in Shore D hardness, and the deflection (mm) when the ball is subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is 2.8mm or less. 2. If the specific gravity of the core is CM, the specific gravity of the intermediate layer is MM, the specific gravity of the cover is FM, the initial velocity of the core is CV, the initial velocity of a sphere (intermediate layer-covered sphere) obtained by covering the core with the intermediate layer is MV, and the initial velocity of a sphere (ball) obtained by covering the intermediate layer-covered sphere with the cover is FV, ​​then the following formula (1) is obtained: (CM×CV)+(MM×MV)+(FM×FV / FC)>200 ···(1) (However, the initial velocity of the core and the intermediate layer was measured using an initial velocity measuring device of the same type as the USGA's drum rotation type initial velocity meter, and the initial velocity of the ball was measured using a COR type initial velocity meter of the same type as the R&A's.) 1. A golf ball as described above that satisfies the above requirements. 3. The moment of inertia of the ball is 82.5 to 85.0 g cm 2 3. The golf ball according to 1 or 2 above, 4. If the specific gravity of the core is CM, the specific gravity of the intermediate layer is MM, the specific gravity of the cover is FM, the initial velocity of the core is CV, the initial velocity of a sphere (intermediate layer-covered sphere) obtained by covering the core with the intermediate layer is MV, the initial velocity of a sphere (ball) obtained by covering the intermediate layer-covered sphere with the cover is FV, ​​and the moment of inertia of the ball is MOI, then the following formula (2) can be used: (CM×CV / MOI)+(MM×MV)+(FM×FV / FC)>110 ···(2) 3. The golf ball according to claim 1 or 2, which satisfies the above requirement. 5. The specific gravity of all layers of the core, intermediate layer and cover is 1.10 to 1.13 g / cm 3 3. The golf ball according to 1 or 2 above, 6. The golf ball according to 1 or 2 above, wherein the relationship between the specific gravities of the intermediate layer and the cover satisfies the following formula: -0.03≦(specific gravity of mid layer - specific gravity of cover)≦0.03 7. The golf ball according to 1 or 2 above, wherein the material of the intermediate layer contains barium sulfate as a specific gravity adjuster. 8. The golf ball according to 1 or 2 above, wherein the material of the intermediate layer has a Shore D hardness of 60 or more. 9. The golf ball according to 1 or 2 above, wherein the cover is made of a material having a Shore D hardness of 40 or more. Effect of the Invention

[0010] With the golf ball of the present invention, deviation of the center of gravity of the ball is extremely small, improving the roll (straightness) of the ball when putting with a putter, and at the same time reducing variation in the vertical and horizontal directions when hit with a putter. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram for explaining a putting test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will now be described in further detail. The golf ball of the present invention comprises a core, a cover, and an intermediate layer formed therebetween. Each of the above layers will now be described in detail.

[0013] The core can be formed of a single layer or multiple layers. Known rubber materials and various resin materials can be used as the base material for the core. When the core is formed of a rubber material, known base rubbers such as natural rubber or synthetic rubber can be used as the base rubber. More specifically, it is recommended to mainly use polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more of a cis structure. In addition, natural rubber, polyisoprene rubber, styrene butadiene rubber, etc. can be used in combination with the above-mentioned polybutadiene in the base rubber as desired. In addition, polybutadiene can be synthesized using Ziegler catalysts such as titanium-based, cobalt-based, nickel-based, and neodymium-based catalysts, and metal catalysts such as cobalt and nickel.

[0014] The above base rubber may be blended with co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane, etc. Also, commercially available antioxidants and the like may be added as necessary.

[0015] The core can be produced by heat curing the rubber composition containing the above components. For example, the rubber composition is kneaded using a kneading machine such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the molded body is appropriately heated at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, that is, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, to cure the molded body.

[0016] The specific gravity of the core is not particularly limited, but is preferably 1.00 or more, more preferably 1.03 or more, and even more preferably 1.06 or more, and the upper limit is preferably 1.20 or less, more preferably 1.17 or less, and even more preferably 1.14 or less. In order to ensure good flight distance performance when hitting with a driver, the mass of the ball needs to be about 45.0 to 45.6 g, and in this case, if the specific gravity of the core is smaller than the above range, the specific gravity of the intermediate layer and the cover layer needs to be increased, and therefore, the spin performance of the ball may be impaired by adding a specific gravity adjusting material. On the other hand, if the specific gravity of the core is too large, the moment of inertia becomes too small, and the roll with a putter may become poor.

[0017] At least one intermediate layer and a cover may be formed around the core as members that encase the core. When the intermediate layer is made up of two layers, the layers may be referred to as the inner intermediate layer and the outer intermediate layer, from the inside out. The inner intermediate layer may also be referred to as the surrounding layer.

[0018] The intermediate layer is formed of a resin composition. Examples of this resin composition include resin compositions mainly made of resins that have been conventionally used as materials for golf balls. 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. In particular, ionomer resins are preferred in terms of resilience and moldability.

[0019] Various fillers can also be blended into the intermediate layer material as specific gravity adjusters. Suitable fillers include, for example, zinc oxide, titanium oxide, barium sulfate, calcium carbonate, potassium titanate, calcium oxide, magnesium oxide, silica, and ferrite. These may be used alone or in combination of two or more.

[0020] The amount of the specific gravity adjusting material (filler) is not particularly limited, but is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, per 100 parts by mass of the base resin of the intermediate layer. The upper limit of the amount is not particularly limited, but is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too large or too small, the appropriate specific gravity may not be obtained, and the desired effects of the present invention may not be obtained.

[0021] The thickness of the intermediate layer is preferably 0.6 mm or more, more preferably 0.8 mm or more, and even more preferably 1.0 mm or more, with the upper limit being preferably 2.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.3 mm or less. If the intermediate layer is too thin, the ball will have a large amount of spin on a full shot, and the intended flight distance may not be achieved. On the other hand, if the intermediate layer is too thick, the resilience of the ball may be reduced.

[0022] The material hardness of the intermediate layer is not particularly limited, but is preferably 60 or more, more preferably 65 or more, and even more preferably 67 or more in Shore D hardness, with the upper limit being preferably 75 or less, and more preferably 73 or less. The harder the hardness is, the greater the flight distance can be achieved by reducing the spin rate during full shots with an iron (I#6), but if the hardness is too high, there is a risk of the durability against cracking due to repeated impacts decreasing.

[0023] The specific gravity of the intermediate layer is preferably 1.05 or more, more preferably 1.07 or more, and even more preferably 1.09 or more, with the upper limit being preferably 1.25 or less, more preferably 1.20 or less, and even more preferably 1.15 or less. If the specific gravity of the intermediate layer is too low, the durability against cracking due to repeated impacts may be poor. On the other hand, if the specific gravity of the intermediate layer is too high, the resilience of the ball may be low, or the spin rate of the ball may be high during a full shot, resulting in failure to achieve the desired flight distance.

[0024] It is desirable that the relationship in specific gravity between the intermediate layer and the cover satisfies the following formula. -0.03≦(specific gravity of mid layer - specific gravity of cover)≦0.03 The reason for this is that the difference in specific gravity between each layer causes variation in the rolling of the putter (front to back and side to side), so the above ranges are set in order to minimize this variation as much as possible.

[0025] The cover is formed from a resin composition. The resin composition is not particularly limited, but specifically, the cover can be formed using an ionomer resin, a polyurethane thermoplastic elastomer, a thermosetting polyurethane, or a mixture thereof as the main component of the resin composition. In addition to the main component, the cover can also contain other thermoplastic elastomers, polyisocyanate compounds, fatty acids or derivatives thereof, basic inorganic metal compounds, fillers, etc.

[0026] The above-mentioned resin composition can be obtained by mixing the above-mentioned components using various kneading machines such as a kneading type (single-screw or) twin-screw extruder, a Banbury mixer, or a kneader.

[0027] The thickness of the cover is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more, with the upper limit being preferably 2.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.3 mm or less. If the cover is too thin, the abrasion resistance of the ball when hit with a wedge may be poor. On the other hand, if the cover is too thick, the spin of the ball may increase too much, and the desired flight distance may not be achieved.

[0028] The specific gravity of the cover is not particularly limited, but is preferably 1.00 or more, more preferably 1.03 or more, and even more preferably 1.06 or more, and the upper limit is preferably 1.20 or less, more preferably 1.17 or less, and even more preferably 1.14 or less. If the specific gravity of the cover is lower than the above range, the abrasion resistance may be deteriorated due to the blend ratio of the resin used for adjusting the specific gravity. On the other hand, if the specific gravity of the cover is too high, the amount of filler added will be too large, and the resilience may be too low, making it difficult to obtain the desired flight distance.

[0029] It is preferable that the specific gravity of the core, intermediate layer and cover is 1.10 or more and 1.13 or less. By setting the specific gravity of all layers within such a range, a golf ball conforms to the rules of golf and the difference in specific gravity between the layers is minimized, which has the advantage of reducing the variation in rolling with a putter from front to back and side to side.

[0030] The hardness of the cover material is not particularly limited, but is preferably 52 or less, more preferably 47 or less, and even more preferably 45 or less in Shore D hardness, with the lower limit being preferably 40 or more, and more preferably 43 or more. By setting the hardness relatively low, the initial velocity of the ball during putting is less likely to increase, and the variation in putting distance is reduced. Furthermore, within the above range, the harder the hardness is, the greater the distance can be increased by reducing the spin rate during full shots with an iron (I#6).

[0031] The deflection (mm) of the golf ball when subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is 2.8mm or less, preferably 2.5mm or less, and more preferably 2.4mm or less. By setting the deflection to a relatively small value in this manner, the variation in ball distance during putting is reduced. The lower limit of the deflection is preferably 2.2mm or more, and more preferably 2.3mm or more.

[0032] The moment of inertia of the golf ball of the present invention is 82.5 kg cm 2 It is preferable that the resistance is equal to or greater than 83.0 kg cm 2 The upper limit is 85.0 kg cm 2 Here, the moment of inertia employed in the present invention can be calculated by the following formula.

[0033] M = (n / 5880000) × {(r1-r2) × D1 5 +(r2-r3)×D2 5 +r3×D3 5} M: Moment of inertia r1: Core weight D1: Core diameter r2: Middle layer specific gravity D2: (core + mid layer) diameter r3: Cover specific gravity D3: Ball diameter

[0034] That is, the moment of inertia is a calculated value obtained from the diameter (thickness) and specific gravity of each layer, and can be obtained by considering the ball as a perfect sphere. The moment of inertia of a golf ball can be measured using an inertia moment measuring device, such as the "M01-005" manufactured by INERTIA DYNAMICS INC.

[0035] In the present invention, the standard deviation of the specific gravity of each layer constituting the golf ball, that is, the core, intermediate layer and cover, must be within 0.07.

[0036] The above standard deviation is the commonly calculated standard deviation, which is the positive square root of the sum of the squares of the differences between the data values ​​and the average value divided by the total number of data. The difference between the data value and the average value means the deviation, and the squared average of the deviation means the variance, so the standard deviation means the positive square root of the variance.

[0037]

number

[0038] For example, in Example 1 of Table 3, 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 average value of these three data is (1.13 + 1.08 + 1.07) / 3 ≒ 1.0933. Applying this to the above formula, σ = {1 / 3 × (1.13 - 1.0933) 2 +1 / 3×(1.08-1.0933) 2 +1 / 3×(1.07-1.0933) 2} 1 / 2 The value is approximately 0.03.

[0039] The standard deviation of the specific gravity of each layer of the core, intermediate layer and cover is within 0.07, preferably 0.05 or less, and more preferably 0.03 or less. By setting the standard deviation within 0.07, the left-right deviation of the ball during putting is reduced, providing stable putting.

[0040] In the present invention, when the specific gravity of the core is CM, the specific gravity of the intermediate layer is MM, the specific gravity of the cover is FM, the initial velocity of the core is CV, the initial velocity of a sphere obtained by covering the core with the intermediate layer (an intermediate-layer-covered sphere) is MV, and the initial velocity of a sphere (a ball) obtained by covering the intermediate-layer-covered sphere with the cover is FV, ​​the following formula (1) can be used: (CM×CV)+(MM×MV)+(FM×FV / FC)>200 ···(1) (However, the initial velocities listed above are measured using an initial velocity measuring device similar to the USGA's drum rotation initial velocity meter.) It is preferable that the above value of (CM x CV) + (MM x MV) + (FM x FV / FC) is greater than 200, more preferably greater than 203, and even more preferably greater than 206. By setting the value of the above formula to greater than 200 in this manner, the variation in ball distance during putting is reduced.

[0041] Furthermore, in the present invention, when the moment of inertia of the ball is defined as MOI, the following formula (2) is satisfied: (CM×CV / MOI)+(MM×MV)+(FM×FV / FC)>110 ···(2 (However, the initial velocities listed above are measured using an initial velocity measuring device similar to the USGA's drum rotation initial velocity meter.) It is preferable that the above value of (CM×CV / MOI)+(MM×MV)+(FM×FV / FC) is greater than 110, more preferably greater than 113, and even more preferably greater than 115. By setting the value of the above formula to be greater than 110 in this manner, the variation in ball distance during putting is reduced.

[0042] [ About the initial speed of each ball 〕 It is preferable that the relationships among the initial velocity of the core (CM), the initial velocity of the mid layer covered sphere (MV), and the initial velocity of the ball (FV) are set within the following ranges. The initial velocity of the core and the intermediate layer covered ball can be measured using an initial velocity measuring device of the same type as the USGA's drum rotation type initial velocity meter, which is a device approved by the R&A. Specifically, the test is performed in a room with a room temperature of 23.9±2°C, and the ball is hit with a 250 pound (113.4 kg) head (striking mass) at a hitting speed of 143.8 ft / s (43.83 m / s), and the time it takes for the ball to pass a distance of 6.28 ft (1.91 m) is measured to calculate the initial velocity (m / s). In this case, the ball to be measured is conditioned at a temperature of 23.9±1°C for at least three hours. On the other hand, the initial velocity of the ball is a value measured by a COR type initial velocity meter of the same type as that of R&A. Specifically, a COR type initial velocity device manufactured by Hye Precision, USA, is used. As conditions, the air pressure is changed in four stages during measurement, a relational equation between the entrance velocity and COR is constructed, and the initial velocity at an entrance velocity of 43.83 m / s is obtained from this relational equation. The measurement environment of the COR type initial velocity device is a ball that has been temperature-controlled in a thermostatic chamber adjusted to 23.9±1°C for more than three hours, and the measurement is performed at a room temperature of 23.9±2°C. The barrel diameter is selected so that the clearance on one side between the barrel diameter and the outer diameter of the object being measured is between 0.2 and 2.0 mm.

[0043] The initial velocity (CM) of the core is preferably 77.50 m / s or more, more preferably 77.60 m / s or more, and even more preferably 77.70 m / s or more, and the upper limit is preferably 78.10 m / s or less, more preferably 77.90 m / s or less.

[0044] The initial velocity (MV) of the intermediate layer-covered sphere is preferably 77.70 m / s or more, more preferably 77.80 m / s or more, and even more preferably 77.90 m / s or more, with the upper limit being preferably 78.30 m / s or less, more preferably 78.10 m / s or less.

[0045] The initial velocity (FM) of the ball is preferably 77.00 m / s or greater, more preferably 77.10 m / s or greater, and even more preferably 77.20 m / s or greater, with the upper limit being preferably 77.70 m / s or less, and more preferably 77.60 m / s or less.

[0046] If these initial velocities deviate from the above ranges, there may be large vertical variations when hit with a putter.

[0047] A large number of dimples of one or more types may usually be formed on the surface of the cover, and the shape, diameter, depth, number, occupied surface area, etc. of the dimples may be appropriately selected.

[0048] The method for producing a golf ball is not particularly limited, and the ball can be obtained by molding using a known molding method such as injection molding, compression molding, etc. For example, the above-mentioned intermediate layer resin composition is supplied to a core set in the mold of an injection molding machine to produce a covered sphere (intermediate layer-covered sphere) in which the core is covered with an intermediate layer, and then the intermediate layer-covered sphere is set in the mold of another injection molding machine, and the cover resin composition is injected to produce a golf ball covered with a cover.

[0049] A paint layer can be formed on the surface of the cover. In this case, the paint layer is formed from a paint composition. The base resin of the paint composition is not particularly limited, but examples thereof include polyurethane resin, epoxy resin, polyester resin, acrylic resin, and cellulose resin. From the viewpoint of durability of the paint layer, it is preferable to use a two-component curing polyurethane resin. In addition, various additives such as antioxidants, ultraviolet absorbers, light stabilizers, fluorescent agents, and fluorescent brighteners can be blended in appropriate amounts into the paint composition as necessary.

[0050] The method for applying the above-mentioned paint to the surface of the cover is not particularly limited, and any known method can be used, such as electrostatic coating, spray gun coating, brush coating, etc.

[0051] The ball specifications, such as the weight and diameter, of the golf ball of the present invention can be set appropriately in accordance with the Rules of Golf. EXAMPLES

[0052] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0053] [Examples 1 to 5, Comparative Examples 1 to 6] Core compositions were prepared using the rubber blend shown in Table 1, which is common to all of the Examples and Comparative Examples, and then vulcanization was carried out at 150°C for 20 minutes to produce cores. Zinc oxide and zinc acrylate were blended in appropriate amounts to match the specific gravities and deflections shown in Table 3 below, and seven types, A, A', B, B', C, D, and E, were produced.

[0054] [Table 1]

[0055] Details of the above formulation are as follows: Polybutadiene: Product name "BR 01" (manufactured by ENEOS Materials) Organic peroxide: Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) Zinc oxide: Product name "Zinc oxide type 3" (manufactured by Sakai Chemical Industry Co., Ltd.) Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.)

[0056] Formation of the intermediate layer and cover (outermost layer) Next, for each example and comparative example, the intermediate layer resin materials A to D shown in Table 2 were injection molded around the above-mentioned core surface using the injection molding mold described below to form an intermediate layer with a thickness of 1.20 mm and a Shore D hardness of 66 to 68.

[0057] [Table 2]

[0058] Details of the blended ingredients in the above table are as follows. "HiMilan AM7318" Ionomer resin manufactured by Mitsui Dow Polychemicals "Himelen 1706" Ionomer resin manufactured by Mitsui Dow Polychemicals "Trimethylolpropane" manufactured by Tokyo Chemical Industry Co., Ltd. "Barium sulfate" Sakai Chemical Industry Co., Ltd.'s product name "Precipitated Barium Sulfate 300"

[0059] Next, using another injection molding die, three types of urethane resin materials, TPU1, TPU2 and TPU3, were injection molded around the mid layer-covered sphere to form a cover (outermost layer) with a thickness of 0.8 mm and a Shore D hardness of 43 to 50. TPU1, TPU2 and TPU3 are as follows. "TPU1": DIC Covestro Polymer's trade name "Pandex", ether type thermoplastic polyurethane, material hardness (Shore D) "47" "TPU2": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane, material hardness (Shore D) "43" "TPU3": DIC Covestro Polymer's trade name "Pandex", ether type thermoplastic polyurethane, material hardness (Shore D) "50"

[0060] For each example of the golf ball obtained, the difference in specific gravity between the layers, the standard deviation of each specific gravity, the following formulas (1) and (2), the initial velocity of each coated sphere, the amount of deflection of each coated sphere, and the moment of inertia of the ball were calculated, and a putting test was also carried out for each example of the ball. The results are shown in Table 3.

[0061] Deflection of the core, the intermediate layer, and the ball Each covered sphere is placed on a hard plate and the amount of deflection is measured when an initial load of 98N (10kgf) is applied and then a final load of 1275N (130kgf) is applied. The above deflection amounts are measured in a thermostatic chamber at 23.9±1°C for at least three hours and then in a room at 23.9±2°C. A high-load compression tester manufactured by MU Seiki Co., Ltd. is used as the measuring device, and the down speed of the pressure head compressing the core, each layer of covered spheres, or the ball is 10mm / s.

[0062] Core, mid-layer covered sphere and initial velocity of ball Muzzle velocity was measured using a muzzle velocity measuring device that uses the same method as the USGA's drum rotation type muzzle velocity meter, an R&A approved device. The cores, intermediate layers, and covered balls of the ball were conditioned at a temperature of 23±1°C for more than three hours and then tested in a room at room temperature of 23±2°C. Twenty cores, intermediate layers, and covered balls of the ball were each hit twice, and the time it took for them to pass through a distance of 6.28 ft (1.91 m) was measured to calculate the muzzle velocity. This cycle was carried out in approximately 15 minutes.

[0063] Moment of inertia The moment of inertia of the golf ball was measured using an inertia moment measuring machine ("M01-005" manufactured by INERTIA DYNAMICS INC.) This measuring machine calculates the moment of inertia of the golf ball from the difference between the period of vibration when a golf ball is placed on the measuring machine's jig and the period of vibration when no golf ball is placed on it.

[0064] Calculation of the difference and standard deviation of the specific gravity of each layer using formulas (1) and (2) The specific gravity of each layer was calculated from the component mass and component volume of the material of each layer by measuring the outer diameter and weight before and after injection molding. In addition, formula (1) in Table 3 means (CM×CV)+(MM×MV)+(FM×FV / FC), and formula (2) means (CM×CV / MOI)+(MM×MV)+(FM×FV / FC). (CM stands for the specific gravity of the core, MM for the specific gravity of the mid layer, FM for the specific gravity of the cover, CV for the initial velocity of the core, MV for the initial velocity of the mid layer covered sphere, FV for the initial velocity of the ball, and MOI for the moment of inertia of the ball.)

[0065] Putting measurement method The swing width of the putter robot was adjusted and fixed so that the rolling distance was about 5m, and each example ball was hit. The average initial velocity, rolling distance X, and left-right variation Y were measured 10 times at the same target distance, and the standard deviations of X and Y, X(σ) and Y(σ), were defined as the rolling distance (vertical) and left-right (horizontal) deviation, respectively. Figure 1 shows a schematic diagram explaining the putting test. The symbol T indicates the area of ​​the artificial turf, O indicates the hitting point of the putter robot, P indicates the target point, X indicates the rolling distance, and Y indicates the left-right deviation. The conditions of the test equipment are as follows: (Test Equipment) - Head speed of the putter robot when putting: 1.35m / s Artificial Grass Rolling Speed: Set rolling speed to 12 feet on a leveled surface Type of putter: Bridgestone Sports pin-type putter (prototype)

[0066] [Table 3]

[0067] As shown in Table 3, the golf balls of Examples 1 to 6 had a small standard deviation of the specific gravity of each layer, small deviations in the vertical and horizontal distances, and small variations in the vertical and horizontal distances. In contrast, the results for Comparative Examples 1 to 5 are as follows. In Comparative Example 1, the standard deviation of the specific gravity of each layer was large, and therefore the deviation in the vertical distance was large. In other words, the vertical variation was large. In Comparative Example 2, the standard deviation of the specific gravity of each layer was large, and therefore the horizontal distance fluctuated significantly. In other words, the left-right variation was large. In Comparative Example 3, the standard deviation of the specific gravity of each layer was large, so the variation in vertical distance was somewhat large. In Comparative Example 4, the standard deviation of the specific gravity of each layer was large, and therefore the variation in vertical distance was somewhat large. In Comparative Example 5, the ball deflected a lot, so the vertical distance varied greatly, that is, the vertical variation was large.

Claims

1. A golf ball having at least one intermediate layer formed between a core and a cover, characterized in that the standard deviation of the specific gravity of each layer of the core, intermediate layer and cover is within 0.07, the material hardness of the cover is 52 or less in Shore D hardness, and the deflection (mm) when the ball is subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is 2.8 mm or less.

2. Let CM be the specific gravity of the core, MM be the specific gravity of the intermediate layer, and FM be the specific gravity of the cover. Let CV be the initial velocity of the core, MV be the initial velocity of a sphere obtained by covering the core with the intermediate layer (an intermediate-layer-covered sphere), and FV be the initial velocity of a sphere (a ball) obtained by covering the intermediate-layer-covered sphere with the cover. Then, the following formula (1) can be used: (CM×CV)+(MM×MV)+(FM×FV / FC)>200...(1) (However, the initial velocities of the core and the intermediate layer are measured using an initial velocity measuring device of the same type as the USGA's drum rotation type initial velocity meter, and the initial velocity of the ball is measured using a COR type initial velocity meter of the same type as the R&A's.) 2. The golf ball of claim 1, which satisfies the above.

3. The moment of inertia of the ball is 82.5 to 85.0 g cm 2 3. The golf ball of claim 1, wherein

4. Let CM be the specific gravity of the core, MM be the specific gravity of the intermediate layer, and FM be the specific gravity of the cover. Let CV be the initial velocity of the core, MV be the initial velocity of a sphere obtained by covering the core with the intermediate layer (intermediate-layer-covered sphere), and FV be the initial velocity of a sphere obtained by covering the intermediate-layer-covered sphere (ball). Then, MOI is the moment of inertia of the ball, given by the following equation (2): (CM×CV / MOI)+(MM×MV)+(FM×FV / FC)>110...(2) 3. The golf ball according to claim 1, which satisfies the above.

5. The specific gravity of all layers of the core, intermediate layer and cover is 1.10 to 1.13 g / cm 3 3. The golf ball of claim 1, wherein

6. 3. The golf ball according to claim 1, wherein the specific gravity of the intermediate layer and the cover satisfy the following formula: −0.03≦(specific gravity of intermediate layer−specific gravity of cover)≦0.03

7. 3. The golf ball according to claim 1, wherein the material of the intermediate layer contains barium sulfate as a specific gravity adjuster.

8. 3. The golf ball according to claim 1, wherein the intermediate layer has a material hardness of 60 or more in Shore D hardness.

9. 3. The golf ball according to claim 1, wherein the cover is made of a material having a Shore D hardness of 40 or more.

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