JP2011172930A - Multiple-piece golf ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple-piece golf ball that generates a high spin decay rate in a case in which an initial spin rate at the time that the golf ball is struck is high and generates a low spin decay rate in a case in which the initial spin rate is low, thereby increasing the travel distance of the golf ball even in both cases in which the initial spin rate is either high or low. <P>SOLUTION: The multiple-piece golf ball 1 includes a core 10 positioned at the center of the golf ball; an intermediate layer 20 surrounding the core; a cover 30 further surrounding the intermediate layer; and at least one high specific gravity member 40 having a higher specific gravity than the core, the intermediate layer, and the cover. The high specific gravity member 40 is arranged such that the moments of inertia Ix, Iy, and Iz of the golf ball with respect to each of the three axes x-axis, y-axis, and z-axis that intersect orthogonally at the center of the golf ball, the two moments inertia Ix and Iy are substantially the same, and the remaining one moment of inertia Iz is greater than the two moments of inertia Ix and Iy, the difference being at least approximately 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multi-piece golf ball.

  There are many factors that influence the flight distance of a golf ball, but among them, three of the ball initial speed, launch angle, and spin amount are regarded as very important. Among these, the spin of the ball is an indispensable element for raising the golf ball and extending the flight distance. However, if the amount of spin is too large, the ball will blow up or the ball run after dropping will be shortened, and the flight distance will not be extended. The spin amount is the largest in the initial stage when the golf ball is launched, and gradually decreases, that is, attenuates during the flight of the golf ball.

  Japanese Patent Application Publication No. 2002-515808 discloses that a golf ball having a low spin rate is used to increase the moment of inertia of a golf ball on a cover layer outside the core of the golf ball for the purpose of providing a golf ball with a low spin rate. Thus, it is disclosed to provide a non-continuous region of weighted material and to make the region of weighted material visible to the outside of the golf ball.

  Japanese Patent Publication No. 2002-536136 discloses a Rihle compression rate of at least 75 in order to increase the moment of inertia of a golf ball in order to provide a golf ball with a low spin rate for a player with low skill level. A soft core and a hard cover with a Shore D hardness of at least 65 disposed around the core, the cover comprising at least one region of weighted material and at least of a material less dense than the weighted material. A golf ball including one region is disclosed.

Special Table 2002-515808 JP 2002-536136 A

  However, although these documents disclose that the amount of spin can be reduced by increasing the moment of inertia of the golf ball, the relationship between the initial spin amount and the decay rate of the initial spin amount during the flight of the golf ball Not disclosed. When the initial spin amount is large, the spin rate attenuation rate during flight is increased to obtain a desired spin amount. However, when the initial spin amount is small, the spin rate attenuation rate during flight is high. Can not extend the flight distance.

  Therefore, the present invention increases the spin rate attenuation when the initial spin amount of the golf ball is large, and decreases the spin rate decay rate when the initial spin amount is small. An object of the present invention is to provide a multi-piece golf ball capable of extending a flight distance regardless of whether the amount is large or small.

  In order to achieve the above object, a multi-piece golf ball according to the present invention further surrounds a core located at the center of the golf ball, an intermediate layer surrounding the outside of the core, and an outer side of the intermediate layer. A cover, and at least one high specific gravity member having a specific gravity higher than that of the core, the intermediate layer, and the cover, wherein the high specific gravity member has three axes orthogonal to each other at the center of the golf ball as an x axis, y If the axes and the z-axis are Ix, Iy, and Iz, and the moment of inertia of the golf ball with respect to each axis is Ix, Iy, Iy is substantially the same, Iz is greater than Ix and Iy, and Ix, Iy, and Iz It arrange | positions so that a difference may be 3 or more.

  The high specific gravity member may be one or plural. The specific gravity of the high specific gravity member is preferably 2 or more. The high specific gravity member preferably contains a metal or a metal compound.

  As described above, according to the present invention, at least one high specific gravity member having a specific gravity higher than that of the core, the intermediate layer, and the cover is selected from the inertia moments Ix, Iy, and Iz with respect to the three axes of the golf ball. When the spin amount at the initial stage of launching the golf ball is large by arranging so that Iz is larger than Ix and Iy and the difference between Ix and Iy and Iz is 3 or more. A multi-piece golf ball that increases the spin rate attenuation rate and lowers the spin rate attenuation rate when the initial spin rate is low, thereby extending the flight distance regardless of whether the initial spin rate is high or low Can be provided.

1 is a plan sectional view showing an embodiment of a multi-piece golf ball according to the present invention. It is side surface sectional drawing of the multi-piece golf ball shown in FIG. FIG. 2 is a side view of an intermediate layer of the multi-piece golf ball shown in FIG. 1. It is a plane sectional view showing another embodiment of a multi-piece golf ball concerning the present invention. It is side surface sectional drawing of the multi-piece golf ball shown in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a multi-piece golf ball according to the present invention will be described with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The attached drawings give priority to understanding the present invention and are not drawn to scale.

  As shown in FIGS. 1 and 2, the multi-piece golf ball 1 of this embodiment includes a core 10 located at the center of the ball, an intermediate layer 20 surrounding the outside of the core, and an outside of the intermediate layer. A cover 30 is mainly provided. Also, assuming that the three axes orthogonal to each other at the center of the golf ball 1 are an x-axis, a y-axis, and a z-axis, the center of the ball is on the plane including the two axes, in FIG. 1 and FIG. An annular high specific gravity member 40 centering on the center is disposed.

  In the golf ball of the present invention, two inertia moments Ix, Iy of the golf ball inertia moments Ix, Iy, Iz with respect to the three axes orthogonal to each other at the center of the golf ball are substantially the same, and the remaining moments One inertia moment Iz is larger than the two inertia moments Ix and Iy, and the difference between them is 3 or more. With such a configuration, when the golf ball 1 is hit so that the x-axis or the y-axis becomes the rotation axis of the back spin, the moments of inertia Ix and Iy are small, so the attenuation rate of the spin amount during flight is Get higher. Therefore, for example, when the initial spin amount is large, the spin amount during the flight is reduced to an appropriate range, and the flight distance can be extended. On the other hand, when the golf ball 1 is struck so that the z-axis becomes the rotation axis of the backspin, the moment of inertia Iz is large, so the rate of attenuation of the spin amount during the flight is low. Therefore, for example, when the initial spin amount is small, the spin amount during the flight is maintained in an appropriate range, and the flight distance can be extended.

  The difference between the inertia moments Ix, Iy and the inertia moment Iz is preferably 4 or more, more preferably 5 or more, and still more preferably 6 or more. On the other hand, if the difference between the moments of inertia Ix, Iy and the moment of inertia Iz is too large, the initial performance such as the initial spin amount may vary depending on the direction of the golf ball at the time of launch, etc. Is preferably 24 or less, more preferably 23 or less, and even more preferably 22 or less.

  The inertia moment Iz is preferably 120 or less, more preferably 118 or less, and still more preferably 116 or less. On the other hand, the moments of inertia Ix and Iy are preferably 50 or more, more preferably 52 or more, and still more preferably 54 or more.

  As described above, the golf ball 1 is provided with the high specific gravity member 40 having a specific gravity higher than that of the core 10, the mid layer 20, and the cover 30 so that the moments of inertia Ix, Iy, and Iz of the three axes have the relationship described above. ing. The core 10, the intermediate layer 20, the cover 30, and the high specific gravity member 40 will be described in detail below.

  The core 10 is shown as a solid core in FIG. 1, but is not limited thereto, and may be a hollow core or a foamed core formed with a foaming agent. Although the specific gravity of the core 10 is not limited to this, For example, 14 or less are preferable and 13.5 or less are more preferable. Although the minimum of the specific gravity of the core 10 is not limited to this, 0.3 or more are preferable and 0.4 or more are more preferable. As a material for forming the core 10, for example, a base rubber as a main component and optionally a rubber composition containing a co-crosslinking material, an initiator, a filler, a foaming agent, an anti-aging agent, and an organic sulfur compound are used. be able to. Further, as a main component, a thermoplastic elastomer, an ionomer resin, or a mixture thereof can be used instead of the base rubber.

  As the base rubber, rubber (thermosetting elastomer) can be widely used. For example, polybutadiene rubber (BR), styrene butadiene rubber (SBR), natural rubber (NR), polyisoprene rubber (IR), polyurethane rubber (PU), butyl rubber (IIR), vinyl polybutadiene rubber (VBR), ethylene propylene rubber (EPDM), nitrile rubber (NBR), and silicone rubber can be used, but are not limited thereto. As the polybutadiene rubber (BR), for example, 1,2-polybutadiene, cis 1,4-polybutadiene, or the like can be used.

The polybutadiene preferably has a Mooney viscosity (ML _{1 + 4} (100 ° C.)) of 30 or more. 35 or more is more preferable, 40 or more is more preferable, 50 or more is still more preferable, and 52 or more is most preferable. As an upper limit, 100 or less is preferable, 80 or less is more preferable, 70 or less is further more preferable, and 60 or less is still more preferable.

The Mooney viscosity referred to in the present invention is an industrial viscosity index (JIS-K6300) measured with a Mooney viscometer, which is a kind of rotational plasticity meter, and ML _{1 + 4} (100 ° C). M represents Mooney viscosity, L represents a large rotor (L-type), 1 + 4 represents a preheating time of 1 minute, and a rotor rotation time of 4 minutes, and the measurement was performed at 100 ° C.

  Further, the molecular weight distribution Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of polybutadiene is preferably 2.0 or more, more preferably 2.2 or more, and further preferably 2.4 or more. 6 or more is still more preferable. The upper limit is preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and still more preferably 3.4 or less. When Mw / Mn is too small, workability may be reduced, and when Mw / Mn is too large, resilience may be reduced.

  The polybutadiene may be synthesized using a Ni or Co catalyst or may be synthesized using a rare earth element-based catalyst. In particular, the polybutadiene is preferably synthesized using a rare earth element-based catalyst. A well-known thing can be used. For example, a catalyst comprising a combination of a lanthanum series rare earth element compound, an organoaluminum compound, an alumoxane, a halogen-containing compound and, if necessary, a Lewis base can be used.

  In the present invention, in particular, the use of a neodymium-based catalyst using a neodymium compound as a lanthanum series rare earth element compound is superior in polybutadiene rubber having a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds. Specific examples of these rare earth element-based catalysts are described in JP-A No. 11-35633, which is incorporated herein by reference. The thing which is suitable can be mentioned.

  When butadiene is polymerized in the presence of a rare earth element-based catalyst, a solvent may be used, bulk polymerization or gas phase polymerization may be performed without using a solvent, and the polymerization temperature is usually −30 ° C. to 150 ° C., preferably Can be 10-100 degreeC.

  The polybutadiene may be obtained by reacting a terminal modifier with the active terminal of the polymer subsequent to the polymerization using the rare earth element-based catalyst. Specific examples of the terminal modifier and the method of reacting are, for example, cited in Japanese Patent Application Laid-Open No. 11-35633, Japanese Patent Application Laid-Open No. 7-268132, which are incorporated herein by reference. Examples and methods described in JP-A-2002-293996 can be mentioned.

  The polybutadiene is preferably blended in the rubber base material in an amount of 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and most preferably 90% by weight or more. The upper limit of the blending ratio of polybutadiene is preferably 100% by weight or less, more preferably 98% by weight or less, and still more preferably 95% by weight or less. By blending polybutadiene within this range, a golf ball having good resilience can be obtained.

  Further, the above-described rubber other than polybutadiene can be blended in combination with polybutadiene as long as the object of the present invention is not impaired. Particularly preferred rubbers for combined use are styrene butadiene rubber, natural rubber, polyisoprene rubber, ethylene propylene diene rubber and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Although it does not limit to this as a co-crosslinking material, For example, it is preferable to use (alpha), (beta)-unsaturated carboxylic acid or its metal salt. Examples of the α, β-unsaturated carboxylic acid or a metal salt thereof include acrylic acid, methacrylic acid, and zinc salts, magnesium salts, and calcium salts thereof. The blending of the co-crosslinking material is not limited to this, but is preferably 5 parts by weight or more, and more preferably 10 parts by weight or more, with 100 parts by weight of the rubber base material. Further, the amount of the co-crosslinking material is preferably 70 parts by weight or less, and more preferably 50 parts by weight or less.

  The initiator is not limited to this, but an organic peroxide is preferably used. The blending of the initiator is not limited to this. For example, the rubber base is 100 parts by weight, preferably 0.10 parts by weight or more, more preferably 0.15 parts by weight or more, and further 0.30 parts by weight or more. preferable. Moreover, the amount of the initiator is preferably 8 parts by weight or less, and more preferably 6 parts by weight or less.

  As the filler, in order to increase the specific gravity of the core 10, it is preferable to use a metal or a metal compound having a specific gravity of 2 or more. Examples of such metals or metal compounds include silver, gold, cobalt, chromium, copper, iron, germanium, manganese, molybdenum, nickel, lead, platinum, tin, titanium, tungsten, zinc, zirconium, barium sulfate, and oxidation. Zinc, manganese oxide, and the like can be used, but are not limited thereto. The filler is preferably in powder form. The blending of the filler is not limited to this, but for example, 100 parts by weight of the rubber base material, 5 parts by weight or more is preferable, 10 parts by weight or more is more preferable, 15 parts by weight or more is further preferable, 25 parts by weight or more Is most preferred. Moreover, 1000 weight part or less is preferable, as for the mixing | blending of a filler, 980 weight part or less is more preferable, and 960 weight part or less is still more preferable.

  Examples of the foaming agent include, but are not limited to, azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, p-toluenesulfonyl hydrazide, p, p′-oxybis (benzenesulfonylhydrazide), hydrogen carbonate Sodium or the like can be used. The blending of the foaming agent is not limited to this, but, for example, 5 parts by weight or more is preferable and 100 parts by weight or more is more preferable with 100 parts by weight of the rubber substrate. Further, the blending amount of the foaming agent is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less.

  The core 10 has a substantially spherical shape. The outer diameter of the core 10 is preferably 40 mm or less, more preferably 39 mm or less, and still more preferably 36 mm or less. The lower limit of the outer diameter of the core 10 is preferably 4 mm or more, more preferably 5 mm or more, further preferably 6 mm or more, still more preferably 7 mm or more, and most preferably 8 mm or more.

  The core 10 is not limited to the single layer configuration shown in FIG. 1 and can include a plurality of layers. For example, the core may have a two-layer structure including a center core positioned at the center of the golf ball and a core layer surrounding the center core. When the core has a multilayer structure, the thickness of the core layer is preferably 0.8 mm or more, more preferably 1.0 mm or more, and further preferably 1.4 mm or more. Further, the upper limit of the thickness of the core layer is preferably 10 mm or less, more preferably 8 mm or less, still more preferably 6 mm or less, and even more preferably 3 mm or less. For the center core and the core layer, the core materials described above can be used.

  The specific gravity of the intermediate layer 20 is not limited to this, but is preferably 0.2 or more, more preferably 0.3 or more, and still more preferably 0.4 or more. The specific gravity of the intermediate layer 20 is preferably 1.2 or less, more preferably 1.1 or less, and still more preferably 1.08 or less. The material of the intermediate layer 20 is not limited to this, but a thermosetting elastomer, a thermoplastic elastomer, an ionomer resin, or a mixture thereof can be used.

  Examples of the thermosetting elastomer include, but are not limited to, polybutadiene rubber (BR), styrene butadiene rubber (SBR), natural rubber (NR), polyisoprene rubber (IR), polyurethane rubber (PU), butyl rubber (IIR), Vinyl polybutadiene rubber (VBR), ethylene propylene rubber (EPDM), nitrile rubber (NBR), and silicone rubber can be used.

The polybutadiene preferably has a Mooney viscosity (ML _{1 + 4} (100 ° C.)) of 30 or more. 35 or more is more preferable, 40 or more is more preferable, 50 or more is still more preferable, and 52 or more is most preferable. As an upper limit, 100 or less is preferable, 80 or less is more preferable, 70 or less is further more preferable, and 60 or less is still more preferable.

The Mooney viscosity referred to in the present invention is an industrial viscosity index (JIS-K6300) measured with a Mooney viscometer, which is a kind of rotational plasticity meter, and ML _{1 + 4} (100 ° C). M represents Mooney viscosity, L represents a large rotor (L-type), 1 + 4 represents a preheating time of 1 minute, and a rotor rotation time of 4 minutes, and the measurement was performed at 100 ° C.

  Further, the molecular weight distribution Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of polybutadiene is preferably 2.0 or more, more preferably 2.2 or more, and further preferably 2.4 or more. 6 or more is still more preferable. The upper limit is preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and still more preferably 3.4 or less. When Mw / Mn is too small, workability may be reduced, and when Mw / Mn is too large, resilience may be reduced.

  The polybutadiene may be synthesized using a Ni or Co catalyst or may be synthesized using a rare earth element-based catalyst. In particular, the polybutadiene is preferably synthesized using a rare earth element-based catalyst. A well-known thing can be used. For example, a catalyst comprising a combination of a lanthanum series rare earth element compound, an organoaluminum compound, an alumoxane, a halogen-containing compound and, if necessary, a Lewis base can be used.

  In the present invention, in particular, the use of a neodymium-based catalyst using a neodymium compound as a lanthanum series rare earth element compound is superior in polybutadiene rubber having a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds. Specific examples of these rare earth element-based catalysts are described in JP-A No. 11-35633, which is incorporated herein by reference. The thing which is suitable can be mentioned.

  When butadiene is polymerized in the presence of a rare earth element-based catalyst, a solvent may be used, bulk polymerization or gas phase polymerization may be performed without using a solvent, and the polymerization temperature is usually −30 ° C. to 150 ° C., preferably Can be 10-100 degreeC.

  The polybutadiene may be obtained by reacting a terminal modifier with the active terminal of the polymer subsequent to the polymerization using the rare earth element-based catalyst. Specific examples of the terminal modifier and the method of reacting are, for example, cited in Japanese Patent Application Laid-Open No. 11-35633, Japanese Patent Application Laid-Open No. 7-268132, which are incorporated herein by reference. Examples and methods described in JP-A-2002-293996 can be mentioned.

  The polybutadiene is preferably blended in the rubber base material in an amount of 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and most preferably 90% by weight or more. The upper limit of the blending ratio of polybutadiene is preferably 100% by weight or less, more preferably 98% by weight or less, and still more preferably 95% by weight or less. By blending polybutadiene within this range, a golf ball having good resilience can be obtained.

  Further, the above-described rubber other than polybutadiene can be blended in combination with polybutadiene as long as the object of the present invention is not impaired. Particularly preferred rubbers for combined use are styrene butadiene rubber, natural rubber, polyisoprene rubber, ethylene propylene diene rubber and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Examples of the thermoplastic elastomer include, but are not limited to, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and polyolefin-based thermoplastic elastomers.

  Although not limited to this as ionomer resin, what uses the following (a) component and / or (b) component as a base resin can be used. Moreover, the following (c) component can be arbitrarily added to this base resin. The component (a) is an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and / or a metal salt thereof, and the component (b) is an olefin-unsaturated carboxylic acid binary random copolymer and The metal salt (c) component is a thermoplastic block copolymer having a polyolefin crystal block and a polyethylene / butylene random copolymer.

  The weight average molecular weight (Mw) of the olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ternary random copolymer and / or metal salt thereof constituting the component (a) is preferably 100,000 or more, more preferably Is 110,000 or more, more preferably 120,000 or more. As an upper limit, Preferably it is 200,000 or less, More preferably, it is 190,000 or less, More preferably, it is 170,000 or less. The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the copolymer is preferably 3.0 to 7.0.

  The component (a) is a copolymer containing an olefin, and examples of the olefin in the component (a) include those having 2 or more carbon atoms and an upper limit of 8 or less, particularly 6 or less. Specific examples include ethylene, propylene, butene, pentene, hexene, heptene, octene and the like, and ethylene is particularly preferable.

  Examples of the unsaturated carboxylic acid in component (a) include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and acrylic acid and methacrylic acid are particularly preferred.

  Examples of the unsaturated carboxylic acid ester in the component (a) include lower alkyl esters of the unsaturated carboxylic acid described above, and specifically include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate. , Methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and the like, and butyl acrylate (n-butyl acrylate, i-butyl acrylate) is particularly preferable.

  The random copolymer of component (a) can be obtained by random copolymerizing the above components according to a known method. Here, the content (acid content) of the unsaturated carboxylic acid contained in the random copolymer is usually 2% by weight or more, preferably 6% by weight or more, and more preferably 8% by weight or more. The upper limit is 25% by weight or less, preferably 20% by weight or less, and more preferably 15% by weight or less. If the acid content is low, the resilience may be reduced, and if it is high, the processability of the material may be reduced.

  The metal salt of the copolymer of component (a) can be obtained by partially neutralizing acid groups in the random copolymer of component (a) described above with metal ions.

  Here, examples of metal ions for neutralizing acid groups include ions such as Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, and Pb. Preferably, Na, Li, Each ion such as Zn, Mg, and Ca is preferably used, and more preferably Zn ion. The degree of neutralization of the random copolymer of these metal ions is not particularly limited, but is usually 5 mol% or more, preferably 10 mol% or more, particularly 20 mol% or more. As an upper limit, it is 95 mol% or less normally, Preferably it is 90 mol% or less, Especially 80 mol% or less. If the degree of neutralization exceeds 95 mol%, moldability may be reduced. When the amount is less than 5 mol%, it is necessary to increase the amount of the inorganic metal compound as the component (e), which may be disadvantageous in terms of cost. Such a neutralized product can be obtained by a known method. For example, for the random copolymer, the metal ion formate, acetate, nitrate, carbonate, bicarbonate, oxide, water It can be obtained by introducing a compound such as an oxide and an alkoxide.

  Specific examples of the olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ternary random copolymer constituting the component (a) include "Nucleel AN4318", "AN4319", "AN4311" (Mitsui, And DuPont Polychemical Co., Ltd.). Specific examples of the metal salt of the olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ternary random copolymer include trade names “Himilan AM7316”, “AM7331”, “1855”, “1856”. (Mitsui / DuPont Polychemical Co., Ltd.) and trade names “Surlin 6320”, “Same 8120” (DuPont, USA) and the like.

  The weight average molecular weight (Mw) of the olefin-unsaturated carboxylic acid binary random copolymer and / or metal salt thereof constituting the component (b) is preferably 100,000 or more, more preferably 110,000. As mentioned above, More preferably, it is 120,000 or more. As an upper limit, Preferably it is 200,000 or less, More preferably, it is 190,000 or less, More preferably, it is 170,000 or less. The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the copolymer is preferably 3.0 to 7.0.

  The proportion of the component (b) copolymer in the entire base resin is 0 to 20% by weight. A preferred lower limit is 1% by weight or more. The upper limit is preferably 17% by weight or less, more preferably 10% by weight or less, still more preferably 8% by weight or less, and particularly preferably 5% by weight or less.

  (B) Specific examples of the olefin-unsaturated carboxylic acid binary random copolymer constituting the component include trade names “Nucrel 1560”, “Same 1525”, “Same 1035”, etc. (Mitsui / DuPont Polychemicals) ). Specific examples of the metal salt of the olefin-unsaturated carboxylic acid binary random copolymer include trade names “Himilan 1605”, “Same 1601”, “Same 1557”, “Same 1705”, “Same 1706” (Mitsui -DuPont Polychemical Co., Ltd.) and trade names "Surlin 7930", "Same 7920" (manufactured by DuPont, USA).

  As the thermoplastic block copolymer having a polyolefin crystal block and a polyethylene / butylene random copolymer as the component (c), for example, a crystalline polyethylene block (E) as a hard segment and a relatively random combination of ethylene and butylene as a soft segment And a block copolymer having a structure such as an E-EB system or an E-EB-E system having a hard segment at one or both ends as a molecular structure. Preferably used.

  The thermoplastic block copolymer having these (c) polyolefin crystal block and polyethylene / butylene random copolymer can be obtained, for example, by hydrogenating polybutadiene. The polybutadiene used for the hydrogenation has a 1,4-polymerized portion having a 1,4-linkage of 95 to 100% by weight as a block in the butadiene structure. Polybutadiene having a bond of 50 to 100% by weight, more preferably 80 to 100% by weight, is preferably used. That is, a polybutadiene in which 1,4-bonds occupy 50 to 100% by weight, more preferably 80 to 100% by weight, and polybutadiene having 95 to 100% by weight of 1,4-bond portions in a block form is preferable. Used.

  The E-EB-E thermoplastic block copolymer is a 1,4-polymer rich in 1,4-bonds at both ends of the molecular chain, and 1,4-bonds and 1,2-bonds in the middle. What is obtained by hydrogenating polybutadiene mixed with is preferable. Here, the amount of hydrogenation in the hydrogenated product of polybutadiene (passing ratio of double bonds to saturated bonds in polybutadiene) is preferably 60 to 100%, more preferably 90 to 100%. If the amount of hydrogenation is too small, deterioration such as gelation may occur in the blending process with an ionomer resin or the like. In addition, when a golf ball is formed, there may be a problem with the hit durability as the intermediate layer.

  In a block copolymer having an E-EB-based or E-EB-E-based structure in which a hard segment is at one or both ends as a molecular structure, preferably used as a thermoplastic block copolymer, the amount of hard segment is 10 It is preferably ˜50% by weight. If the amount of the hard segment is too large, the object of the present invention may not be achieved effectively due to lack of flexibility, and if the amount of the hard segment is too small, a problem may occur in the formability of the blend.

  The melt index of the thermoplastic block copolymer at 230 ° C. and a test load of 21.2 N is preferably 0.01 to 15 g / 10 min, more preferably 0.03 to 10 g / 10 min. If it is out of the above range, problems such as weld, sink, and short circuit may occur during injection molding. The surface hardness of the thermoplastic block copolymer is preferably 10-50. If the surface hardness is too small, the durability of the golf ball upon repeated hitting may be reduced. On the other hand, if the surface hardness is too large, the resilience of the blend with the ionomer resin may decrease. The number average molecular weight of the thermoplastic block copolymer is preferably 30,000 to 800,000.

  Commercially available products can be used as the thermoplastic block copolymer having the polyolefin crystal block and polyethylene / butylene random copolymer as described above, and examples thereof include Dynalon 6100P, 6200P, and 6201B manufactured by Nippon Synthetic Rubber Co., Ltd. In particular, Dynalon 6100P is a block polymer having a crystalline olefin block at both ends, and can be suitably used in the present invention. These olefinic thermoplastic elastomers may be used alone or in a combination of two or more.

  Furthermore, about the material of the intermediate | middle layer 20, 5-100 weight part of fatty acid or its derivative (s) of molecular weight 280-1500 are used as (d) component with respect to 100 weight part of resin components (a)-(c) mentioned above. As the component (e), 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing the acid group in the components (a), (b) and (d) can be mixed. .

  Component (d) is a fatty acid having a molecular weight of 280 or more and 1500 or less, or a derivative thereof, which contributes to improving the fluidity of the heated mixture, and has a very small molecular weight as compared with the components (a) to (c), It contributes to a significant increase in the melt viscosity of the mixture. Further, the fatty acid (derivative) in the component (d) has a molecular weight of 280 or more and 1500 or less and contains a high content of acid groups (derivatives), so that the resilience loss due to addition is small.

  Even if the fatty acid of component (d) or a derivative thereof is an unsaturated fatty acid (derivative) containing a double bond or a triple bond in the alkyl group, a saturated fatty acid in which the bond in the alkyl group is composed of only a single bond ( It is recommended that the number of carbon atoms in one molecule is usually 18 or more and 80 or less, particularly 40 or less as the upper limit. If the number of carbon atoms is small, the heat resistance is poor, the content of acid groups is too high, and the desired fluidity cannot be obtained due to the interaction with the acid groups contained in the base resin. Therefore, the fluidity may be lowered and the material may be difficult to use.

  Specific examples of the fatty acid (d) include stearic acid, 12-hydroxystearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, lignoceric acid, and the like. Arachidic acid, behenic acid, and lignoceric acid can be preferably used.

  Examples of the fatty acid derivative of component (d) include those obtained by substituting protons contained in the acid group of the fatty acid. Examples of such fatty acid derivatives include metal soaps substituted with metal ions. Examples of metal ions used for the metal soap include Li, Ca, Mg, Zn, Mn, Al, Ni, Fe, Cu, Sn, Pb, Co, and the like, and in particular, Ca, Mg, and Zn. Each ion is preferred. Fe ions may be divalent or trivalent.

  Specifically, as the fatty acid derivative of the component (d), magnesium stearate, calcium stearate, zinc stearate, 12-hydroxy magnesium stearate, 12-hydroxy calcium stearate, zinc 12-hydroxy stearate, magnesium arachidate, arachidin Calcium oxide, zinc arachidate, magnesium behenate, calcium behenate, zinc behenate, magnesium lignocerate, calcium lignocerate, zinc lignocerate, etc. Magnesium arachidate, calcium arachidate, zinc arachidate, magnesium behenate, calcium behenate, zinc behenate, magnesium lignocerate Um, calcium lignoceric acid, can be preferably used zinc lignocerate.

  The component (d) is usually 5 parts by weight or more, preferably 8 parts by weight or more, more preferably 20 parts by weight or more, and still more preferably 40 parts by weight or more with respect to 100 parts by weight of the base resin. The upper limit is usually 100 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, and still more preferably 70 parts by weight or less.

  In the use of the above-described components (a) and / or (b), a known metal soap-modified ionomer (US Pat. No. 5,31,857, which is incorporated herein by reference) U.S. Pat. No. 5,306,760, WO 98/46671, etc.) can also be used.

  The component (e) is a basic inorganic metal compound that can neutralize the acid groups in the components (a), (b), and (d). As mentioned in the conventional example, only the components (a), (b) and (d), particularly only the metal-modified ionomer resin (for example, only the metal soap-modified ionomer resin described in the above-mentioned patent publication) are heated and mixed. As shown below, fatty acid is generated by an exchange reaction between metal soap and unneutralized acid groups contained in the ionomer. This generated fatty acid has low thermal stability and is easily vaporized at the time of molding, so it not only causes molding defects, but when the generated fatty acid adheres to the surface of the molded product, the adhesion of the coating is significantly reduced. Cause. The component (e) is blended in order to solve such a problem.

  As described above, the heating mixture used in the present invention contains, as the component (e), a basic inorganic metal compound that neutralizes the acid group contained in the components (a), (b), and (d) as an essential component. As a blend. (E) In the blending of the components, the acid groups in the components (a), (b) and (d) are neutralized, and due to the synergistic effect of the blending of these components, the thermal stability of the heated mixture is increased, Good moldability is imparted and contributes to resilience as a golf ball.

  The component (e) is a basic inorganic metal compound capable of neutralizing the acid groups in the components (a), (b) and (d), and is preferably a monoxide or a hydroxide. Is recommended and has high reactivity with the ionomer resin and does not contain organic substances in the reaction by-product, so that the neutralization degree of the heated mixture can be increased without impairing the thermal stability.

  Here, as metal ions used for the basic inorganic metal compound, for example, ions such as Li, Na, K, Ca, Mg, Zn, Al, Ni, Fe, Cu, Mn, Sn, Pb, Co, etc. Examples of inorganic metal compounds include basic inorganic fillers containing these metal ions, specifically, magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, sodium hydroxide, sodium carbonate, calcium oxide, hydroxide Calcium, lithium hydroxide, lithium carbonate and the like can be mentioned, but as described above, monoxide or hydroxide is preferable, and magnesium oxide or calcium hydroxide having high reactivity with ionomer resin is preferably used. it can.

  (E) A component is 0.1-10 weight part normally with respect to 100 weight part of said base resins. As a lower limit, Preferably it is 0.5 weight part or more, More preferably, it is 1 weight part or more. The upper limit is preferably 5 parts by weight or less, more preferably 3 parts by weight or less.

  The heating mixture used in the present invention is composed of the components (a) to (e) as described above, and is intended to improve thermal stability, moldability, and resilience, but is used in the present invention. It is recommended that all of the heated mixtures be neutralized at least 70 mol%, preferably at least 80 mol%, more preferably at least 90 mol% of the acid groups in the mixture. a), (b) When only the fatty acid (derivative) and the fatty acid (derivative) are used, the exchange reaction which becomes a problem can be suppressed more reliably, the generation of fatty acid can be prevented, the thermal stability is remarkably increased, and the molding It can be a material having good rebound characteristics and significantly increased resilience compared to conventional ionomer resins.

  Here, in the neutralization of the heating mixture of the present invention, the acid group of the heating mixture is a transition metal ion and an alkali metal and / or alkaline earth metal ion in order to more reliably achieve a high degree of neutralization and fluidity. It is recommended that the transition metal ions have a weaker ionic cohesion than alkali (earth) metal ions, so some of the acid groups in the heated mixture are neutralized and fluidity Can be significantly improved.

  In the present invention, various additives can be further added to the above heated mixture as necessary, for example, fillers, pigments, dispersants, anti-aging agents, ultraviolet absorbers, light stabilizers and the like. Can be added. In addition to the above essential components, various non-ionomer thermoplastic elastomers can be blended in order to improve the feeling at the time of impact. Examples of such non-ionomer thermoplastic elastomers include styrene-based thermoplastic elastomers. , Ester-based thermoplastic elastomers, urethane-based thermoplastic elastomers, and the like, and the use of styrene-based thermoplastic elastomers is particularly preferable.

  As a method for preparing the heated mixture, for example, an internal mixer such as a twin screw extruder, Banbury, kneader or the like is used, and the heating and mixing conditions are, for example, mixed while heating at 150 to 250 ° C. The method for forming the intermediate layer using the heated mixture is not particularly limited, and can be formed by, for example, injection molding or compression molding. When the injection molding method is employed, a method of introducing the above material into the mold after a solid core prepared in advance at a predetermined position of the injection mold can be employed. Further, when the compression molding method is adopted, a method of making a pair of half cups with the above-mentioned material, pressing the core directly or through an intermediate layer with this cup, and heating in a mold can be adopted. In addition, when carrying out pressure heating molding, as molding conditions, the conditions of 120-170 degreeC and 1 to 5 minutes are employable.

  In addition to the main components of the rubber, thermoplastic elastomer, and ionomer resin described above, a filler or a foaming agent can be optionally added to the intermediate layer 20. Examples of the filler include, but are not limited to, barium sulfate, titanium oxide, zinc oxide, and tungsten. The filler is preferably in powder form. The blending of the filler is not limited to this, but for example, the main component is 100 parts by weight, preferably 5 parts by weight or more, more preferably 20 parts by weight or more, and further preferably 25 parts by weight or more. Moreover, 1000 weight part or less is preferable, as for the mixing | blending of a filler, 980 weight part or less is more preferable, and 960 weight part or less is still more preferable.

  Examples of the foaming agent include, but are not limited to, azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, p-toluenesulfonyl hydrazide, p, p′-oxybis (benzenesulfonylhydrazide), hydrogen carbonate Sodium or the like can be used. The blending of the foaming agent is not limited to this, but for example, the main component is 100 parts by weight, preferably 2 parts by weight or more, and more preferably 3 parts by weight or more. Further, the blending amount of the foaming agent is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less.

  Although the thickness of the intermediate | middle layer 20 is not limited to this, 1 mm or more is preferable, 2 mm or more is more preferable, and 3 mm or more is still more preferable. The thickness of the intermediate layer 20 is preferably 15 mm or less, more preferably 13 mm or less, and even more preferably 11 mm or less. In addition, although the intermediate | middle layer 20 showed the single layer in FIG. 1, it is not limited to this, It can also be made into two or more layers.

  Although the specific gravity of the cover 30 is not limited to this, 0.91 or more is preferable and 0.93 or more is more preferable. Further, the specific gravity of the cover 30 is preferably 1.3 or less, and more preferably 1.2 or less. The material of the cover 30 is not limited to these, but an ionomer resin, a polyurethane-based thermoplastic elastomer, a thermosetting polyurethane, or a mixture thereof can be used.

  Although the thickness of the cover 30 is not limited to this, 0.2 mm or more is preferable and 0.4 mm or more is more preferable. Further, the thickness of the cover 30 is preferably 4 mm or less, more preferably 3 mm or less, and still more preferably 2 mm or less.

  The high specific gravity member 40 has a higher specific gravity than any of the core 10, the intermediate layer 20, and the cover 30 described above. Although the specific gravity of the high specific gravity member 40 is not limited to this, 2 or more are preferable from a viewpoint of a freedom degree, 2.5 or more are more preferable, and 4 or more are still more preferable. On the other hand, if the specific gravity of the high specific gravity member 40 is too high, it is difficult to achieve a predetermined moment of inertia in the manufacturing process only by arranging the high specific gravity members slightly unevenly. The specific gravity is preferably 22 or less, and more preferably 20 or less. As the high specific gravity member 40 having such a specific gravity, it is preferable to use a metal composition.

  The metal composition can include a metal or a metal compound. Examples of the metal or metal compound include, but are not limited to, silver, gold, cobalt, chromium, copper, iron, germanium, manganese, molybdenum, nickel, lead, platinum, tin, titanium, tungsten, zinc, zirconium, sulfuric acid Barium, zinc oxide, manganese oxide, or the like can be used.

  The metal composition may contain a binder in order to form the metal or metal compound powder into a predetermined shape. As the binder, it is preferable to use rubber or a thermosetting resin, and the same material as the base rubber described above can be used. When the binder is used, the blending ratio of the metal or metal compound powder is preferably 200 parts by weight or more, more preferably 250 parts by weight or more, still more preferably 350 parts by weight or more, and 400 parts by weight with respect to 100 parts by weight of the base rubber. Part or more is most preferable. The blending ratio of the metal or metal compound powder is preferably 2000 parts by weight or less, more preferably 1900 parts by weight or less, still more preferably 1600 parts by weight or less, and most preferably 1500 parts by weight or less.

  Moreover, since the high specific gravity member 40 can expect a sound insulation effect when the transmission loss of the material in the high sound region of 1000 to 4000 Hz is large, the high specific gravity member 40 has a transmission loss of 10 db or more in the 1000 to 4000 Hz region. Preferably, it is 15 db or more, more preferably 30 db or more. The upper limit of the transmission loss is preferably 60 db or less, more preferably 55 db or less, and even more preferably 40 db or less.

  In FIG. 1 and FIG. 2, an annular high specific gravity member 40 centering on the center of the golf ball 1 is arranged on the xy plane, but the position and number of the high specific gravity members 40 are three axes. The inertia moments Ix, Iy, and Iz are not limited to this as long as the relationship of Ix = Iy ≦ Iz−3 is satisfied. For example, as shown in FIGS. 4 and 5, on the xy plane, four high specific gravity members 40a to 40d are arranged at the vertexes of a square whose center of gravity is the center of the golf ball 1, The above relationship can be satisfied. Note that the number of the high specific gravity members 40 is not limited to this, and can be two, four, six, eight, ten, twelve, twenty, and the like. They can be arranged at the vertices of regular polygons such as quadrangle, regular hexagon, regular octagon, regular decagon, regular dodecagon, regular icosahedron. The upper limit of the number of high specific gravity members 40 is not particularly limited, but is preferably 600 or less, and more preferably 500 or less.

  Further, the thickness of the sheet-like or plate-like high specific gravity member 40 is preferably 0.01 mm or more, more preferably 0.02 mm or more, further preferably 0.09 mm or more, and most preferably 0.10 mm or more. On the other hand, if the high specific gravity member 40 becomes too thick, the deflection hardness of the golf ball becomes high and the hitting sound of the golf ball becomes uncomfortable, so the thickness of the high specific gravity member 40 is 2.0 mm or less. Is preferably 1.75 mm or less, more preferably 0.75 mm or less, and most preferably 0.5 mm or less.

  The shape of the high specific gravity member 40 is a planar annular sheet shape or plate shape in FIGS. 1 and 2, but is not limited to this as long as it satisfies the relationship of the moment of inertia described above. For example, by providing a plurality of high specific gravity members 40 as described above, the shape of the high specific gravity member 40 can be a spherical shape, a conical shape, a polygonal pyramid such as a triangular pyramid or a quadrangular pyramid, or a polyhedron such as a regular tetrahedron or a regular hexahedron. You can also Further, when the high specific gravity member 40 is a sheet or plate, the shape of the high specific gravity member 40 can be a plane triangle or a plane polygon such as a plane square in addition to a plane ring.

  Depending on the arrangement of the high specific gravity material 40, when a golf ball is hit, the initial performance such as the spin rate, the initial speed, and the launch angle may change depending on the hit location of the ball. However, by adjusting the material, shape, and hardness of the high specific gravity member 40, the difference in the initial performance depending on the hitting position of the ball can be reduced. By allowing the ball to exhibit uniform initial performance at any hitting point, a stable shot can be realized with a short shot such as an approach around the green or a bunker shot.

  The ratio of the volume of the high specific gravity member 40 to the total volume of the golf ball 1 is not particularly limited as long as it satisfies the above-described relationship of the moment of inertia, but is preferably 0.001% or more, for example, 0.005% or more. Is more preferably 0.01% or more, still more preferably 0.05% or more, and most preferably 0.1% or more. Further, the volume ratio is preferably 12.5% or less, more preferably 12% or less, further preferably 11.5% or less, and most preferably 11% or less.

  As shown in FIGS. 1 and 2, when the high specific gravity member 40 is disposed on the outer peripheral surface of the intermediate layer 20, as shown in FIG. 3, in order to fit the high specific gravity member 40 into the intermediate layer 20, A recess 22 having the same dimensions as the high specific gravity member 40 is formed. The method for forming the intermediate layer 20 having the depressions 22 is not limited to this. For example, a method of injection molding the intermediate layer material by inserting a core into an inner spherical mold having protrusions on the inner surface, FIG. As shown in FIG. 3, there is a method in which an intermediate layer material is preformed in the shape of a half cup having a recess 22, and two of these are made and bonded to a core. When the high specific gravity member 40 is arranged in the region of the core 10, a core having a recess for fitting the high specific gravity member 40 can be formed by using the core material in the above method.

  The intermediate layer 20 may be formed so as to have a space not filled with a material. Such a space may be, for example, a space having the same shape as the depression 22 shown in FIG. 3 or a hole-like space penetrating the intermediate layer 20, but is not limited thereto. By providing a space in the mid layer 20, instead of arranging the high specific gravity member 40, the mid layer 20 can be reduced in weight and the weight of the entire golf ball 1 can be maintained. A space can be provided in the intermediate layer 20 by adding a foaming agent to the material of the intermediate layer 20. As the foaming agent, the above-mentioned foaming agents can be used. The blending of the foaming agent is not limited to this, but for example, the main component is 100 parts by weight, preferably 2 parts by weight or more, and more preferably 3 parts by weight or more. Further, the blending amount of the foaming agent is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less.

  A plurality of dimples 32 are formed on the surface of the cover 30. The number of dimples 32 on the entire surface of the golf ball 1 is preferably 200 or more, more preferably 250 or more, and still more preferably 300 or more. The upper limit of the number of dimples 32 is preferably 500 or less, more preferably 450 or less, still more preferably 430 or less, and even more preferably 410 or less. By setting the number of dimples 32 within this range, the golf ball 1 can easily receive lift, and in particular, the flight distance by the driver can be increased.

  Regarding the dimple occupancy rate, specifically, the ratio (SR value) of the total dimple area defined by the surface edge of the plane surrounded by the edge of the dimple to the ball ball area assuming that there is no dimple, 60% or more is preferable, 65% or more is more preferable, and 68% or more is still more preferable from the point which can fully exhibit aerodynamic characteristics. The upper limit of the dimple occupation ratio is not limited to this, but is preferably 90% or less, more preferably 85% or less, and still more preferably 80% or less.

Further, a value V _{0 obtained} by dividing the spatial volume of the dimple below the plane surrounded by the edge of each dimple by the cylindrical volume having the plane as the bottom surface and the maximum depth of the dimple from the bottom surface as a height is: From the viewpoint of optimizing the trajectory of the ball, 0.35 or more is preferable. The upper limit of V ₀ is not particularly limited, for example, it is preferably set to 0.80 or less. Further, the VR value occupying the volume of the ball sphere assuming that the dimple volume formed downward from the plane surrounded by the edge of the dimple does not exist is preferably 0.6% or more, and 0.65% The above is more preferable, and 0.7% or more is still more preferable. The upper limit of the VR value is preferably 1.0% or less, and more preferably 0.9% or less.

  A plurality of types of dimples 32 having different diameters and / or depths can be formed. The number of types of dimples is preferably 3 or more, more preferably 4 or more, and still more preferably 5 or more. The upper limit of the types of dimples is preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less. By setting the type of dimple within this range, it is easy to increase the surface occupancy rate of the dimple and the flight distance can be improved.

  The shape of the dimple 32 can be a planar circular shape, a planar noncircular shape, or a combination thereof. In the case of a planar circular shape, the average diameter is preferably 2.8 mm or more, more preferably 3.5 mm or more, and still more preferably 3.8 mm or more. The upper limit of the average diameter is preferably 5.0 mm or less, preferably 4.6 mm or less, and more preferably 4.3 mm or less. The average depth of the dimples 32 is preferably 0.120 mm or more, more preferably 0.130 mm or more, and further preferably 0.140 mm or more from the viewpoint of obtaining an appropriate trajectory. The upper limit of the average depth is preferably 0.185 mm or less, more preferably 0.180 mm or less, and still more preferably 0.174 mm or less.

  The average diameter is an average value of the diameters of all the dimples, and the average depth is an average value of the depths of all the dimples. In many cases, golf balls are painted, and the dimple diameter and depth are measured with the dimples coated with paint. The dimple diameter is measured by measuring the width of the gap between the land portion, which is the surface of the golf ball on which no dimples are formed, and the surface where the dimples are depressed. The depth of the dimple is measured by measuring the vertical distance from the center position to the bottom surface of the dimple when a virtual plane circle is drawn connecting the points where the dimple contacts the land.

  As described above, in the present invention, the spin moment attenuation during the flight of the golf ball 1 is achieved by making the moments of inertia Ix, Iy, and Iz with respect to the three axes satisfy the relationship of Ix = Iy ≦ Iz−3. The rate is made different between when the x-axis or y-axis is the backspin rotation axis and when the z-axis is the backspin rotation axis. When the golf ball 1 is hit so that the z-axis becomes the rotation axis of the back spin, the spin rate attenuation rate is preferably 0.9% or more, more preferably 1.0% or more, and even more preferably 1.1%. It is desirable to design so that it becomes the above. When the golf ball 1 is hit such that the x-axis or y-axis is the rotation axis of the back spin, the spin rate attenuation rate is preferably 20% or less, more preferably 15% or less, and even more preferably 7% or less. It is desirable to design as follows.

  Golf balls having the configurations shown in Table 1 were produced, and tests for measuring the moment of inertia and the flight distance of the golf balls were performed. The test results are shown in Table 1. Table 2 shows the blends A to E of the core material shown in Table 1. The composition F to I (% by weight) of the intermediate layer, core layer and cover materials is shown in Table 3, and the composition J to L (% by weight) of the high specific gravity member is shown in Table 4. Further, in any of the golf balls of Examples 1 to 3 and Comparative Example 1, the high specific gravity member has an outer diameter of 40.7 mm, an inner diameter of 39.7 mm, a width of 2. The one having an annular shape of 5 mm was used. A recess having a width of 2.5 mm and a depth of 1 mm was formed around the intermediate layer to accommodate the high specific gravity member. The depression was arranged so as to be symmetric with respect to the plane including the z axis. The bottom surface of the dent was provided with an R that is concentric with the outer peripheral spherical surface of the intermediate layer. Further, R was provided on the center-side surface of the high specific gravity member so as to coincide with the bottom surface of the depression, and R similar to the outer peripheral spherical surface of the intermediate layer was provided on the outer surface of the high specific gravity member.

BR730 is cis 1,4-polybutadiene manufactured by JSR Corporation and used as a base rubber.
Zinc diacrylate is manufactured by Nippon Shokubai Co., Ltd.
Perhexa C-40 was 1,1-bis (tert-butylperoxy) cyclohexane (40% dilution) manufactured by NOF Corporation and used as an initiator.
Zinc oxide is manufactured by Sakai Chemical Industry.
The organic sulfur compound is pentachlorothiophenol zinc salt.
Nocrack NS-6 was 2,2′-methylenebis (4-methyl-6-tert-butylphenol) manufactured by Ouchi Shinsei Chemical Co., Ltd., and was used as an antioxidant.

High Milan 1605 is an ionomer resin manufactured by Mitsui DuPont Polychemicals.
Dynalon 6100P is a hydrogenated polyolefin thermoplastic elastomer manufactured by JSR.
Polytail H is a polyolefin polyol manufactured by Mitsubishi Chemical Corporation.
Behenic acid is manufactured by Nippon Oil & Fats.
Calcium hydroxide is manufactured by Shiroishi Kogyo.

Hylamin 1557 is an ionomer resin manufactured by Mitsui DuPont Polychemicals.
Hylamin 1855 is an ionomer resin manufactured by Mitsui DuPont Polychemicals.
Barium sulfate 300 is manufactured by Sakai Chemical Industry.

High Milan 1706 is an ionomer resin manufactured by Mitsui DuPont Polychemicals.
The foaming agent is an ADCA master batch made by Otsuka Chemical.

Pandex T8295 is a polyurethane thermoplastic elastomer manufactured by DIC Bayer Polymer.
Pandex T8290 is a polyurethane thermoplastic elastomer manufactured by DIC Bayer Polymer.
Hytrel 4001 is a thermoplastic polyetherester elastomer manufactured by Toray DuPont.
The polyisocyanate compound is 4,4′-diphenylmethane diisocyanate.

Tungsten is manufactured by Nippon Tungsten Co., Ltd. (powder form).
BR730 is cis 1,4-polybutadiene manufactured by JSR.
LIR410 is a liquid isopropylene rubber manufactured by Kuraray.
Sulfur Z is sulfur (powder shape) manufactured by Tsurumi Chemical Co., Ltd.

  The moment of inertia of the golf ball was measured using a moment of inertia measuring machine (M01-005 manufactured by INERTIA DYNAMICS INC). This measuring machine calculates the moment of inertia of a golf ball from the difference between the period of vibration when the golf ball is placed on the jig of the measuring machine and the period of vibration when the golf ball is not placed.

  The golf ball flight distance test was performed using a launcher (UBL manufactured by Automated Design Corporation), when the ball initial velocity was 59 m / s, and the initial spin amount was 2000 rpm and the x axis when the z axis was the spin axis. Alternatively, when the y-axis was struck so as to be the spin axis, it was performed under conditions of 3000 rpm and a launch angle of 11 degrees. The flight distance results in Table 1 are represented by the distance (m) extended in each example with the flight distance of Comparative Example 2 as a reference. UBL is a device that places two pairs of drums on the top and bottom, puts belts on the upper and lower drums, rotates them and inserts the balls between them to hit the balls under desired conditions. is there.

  As shown in Table 1, in the golf ball of Example 1 using a high specific gravity member with a specific gravity of 9.60, the inertia moment Iz on the z axis was 7 larger than the inertia moments Ix and Iy on the x axis and the y axis. Therefore, in comparison with the golf ball of Comparative Example 2 in which the moment of inertia of any axis is the same, when the initial spin amount is hit under a condition of 2000 rpm, the z-axis becomes the spin rotation axis. When the flight distance was increased by 3.2 m and the initial spin amount was as high as 3000 rpm, the flight distance was increased by 2.3 m by making the x or y axis the spin rotation axis.

  In the golf ball of Example 2 using the high specific gravity member having a specific gravity of 4.97 and a relatively lower specific gravity than that of Example 1, the z-axis inertia moment Iz is 3 than the x-axis and y-axis inertia moments Ix and Iy. Therefore, when the initial spin rate was 2,000 rpm less than that of the golf ball of Comparative Example 2, the flight distance was increased by 2.3 m by making the z axis the spin rotation axis. In addition, when the initial spin rate was 3,000 rpm, the flight distance was increased by 0.3 m by making the x axis or y axis the spin rotation axis.

  Since the golf ball of Example 3 having a core having a plurality of layers including a core layer having a low specific gravity used the high specific gravity member similar to that of Example 1, the difference in the moment of inertia was increased by 8; Compared to golf balls, when the initial spin rate is 2,000 rpm, the z-axis becomes the spin rotation axis, so that the flight distance is increased by 3.2 m and the initial spin rate is as high as 3000 rpm. When hitting under the condition, the flight distance was increased by 2.3 m by making the x axis or y axis the spin rotation axis.

The golf ball of Comparative Example 1 using a high specific gravity member having a specific gravity of 2.77 and a lower specific gravity than those of Examples 1 to 3 had a difference of only one moment of inertia. In comparison, when the initial spin amount was 2,000 rpm, the flight distance was increased by 0.9 m because the z axis was the spin rotation axis, but the initial spin amount was 3,000 rpm. In this case, even if the x-axis or y-axis becomes the spin rotation axis, the flight distance does not increase.

Claims (5)

A multi-piece golf ball,
A core located at the center of the golf ball;
An intermediate layer surrounding the outside of the core;
A cover that further surrounds the outside of the intermediate layer;
And at least one high specific gravity member having a specific gravity higher than that of the core, the intermediate layer, and the cover, wherein the high specific gravity member has three axes orthogonal to each other at the center of the golf ball as an x axis, a y axis, and a z axis. Assuming that the moment of inertia of the golf ball with respect to each axis is Ix, Iy, Iz, Ix and Iy are substantially the same, Iz is greater than Ix and Iy, and the difference between Ix and Iy and Iz is 3 A golf ball arranged as described above.   The golf ball according to claim 1, wherein the number of the high specific gravity members is one.   The golf ball according to claim 1, wherein there are a plurality of the high specific gravity members.   The golf ball according to claim 1, wherein the high specific gravity member has a specific gravity of 2 or more. The golf ball according to claim 1, wherein the high specific gravity member includes a metal or a metal compound.

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