JP2013248288A - Golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball having excellent flight performance because of an excellent hardness distribution measured by an evaluation method of hardness which has excellent measurement accuracy and can sufficiently evaluate a difference in performance between samples.SOLUTION: A golf ball includes: a spherical core 4 comprising at least one layer; and a cover 12 comprising at least one layer and covering the spherical core 4. About the number N per unit volume of a scatterer wherein a gyration radius Robtained by performing curve fitting with a specific expression to a scattering intensity curve Iobtained by X-ray scattering measurement or neutron beam scattering measurement is 1 nm-100 μm, the number N of an outermost part of a rubber composition/the number N of an innermost part of the rubber composition is ≥2.0.

Description

The present invention relates to a golf ball.

As a method of extending the flight distance of a driver shot golf ball, there are a method using a core having high resilience and a method using a core having a hardness distribution in which the hardness increases from the center of the core toward the surface. The former has the effect of increasing the initial velocity of the golf ball, and the latter has the effect of increasing the launch angle and reducing the spin. A golf ball having a high launch angle and a low spin has a large flight distance.

As a technique using a core having a hardness distribution, in a two-piece golf ball comprising a core formed from a rubber composition containing a base rubber, a co-crosslinking agent and an organic peroxide, and a cover, the core is JIS- In the display with a C-type hardness meter, the center hardness is 1:58 to 73, the hardness is 5 to 10 mm from the center 2:65 to 75, the hardness 15 to 15 mm from the center is 3:74 to 82, and the surface hardness is 4:76 to 84. There is disclosed a two-piece golf ball having a hardness distribution, hardness 2 being substantially constant within a hardness range, and the others satisfying a relationship of 1 <2 <3 ≦ 4 (see Patent Document 1).

On the other hand, in a polymer material such as a rubber composition used for golf balls, hardness is an important physical quantity that affects various properties of the product. For example, in the core of a golf ball that is a rubber product, the hardness Is closely related to resilience performance and spin performance. As a method for measuring the hardness of rubber products, a method based on JIS K6253 is widely known (see Non-Patent Document 1).

However, the measurement method using a JIS hardness meter has a large error and is not satisfactory as measurement accuracy. In addition, when the difference between values for each sample is small, there is a problem that the difference cannot be evaluated with good reproducibility. Furthermore, in such a method, there is no evaluation method for examining the molecular structure in detail.

Therefore, it provides a method for evaluating the hardness of a polymer material that is excellent in measurement accuracy and sufficiently evaluates the performance difference between samples, and has a good hardness distribution obtained by the precise evaluation method, thereby improving flight performance. It is desired to provide an excellent golf ball.

JP-A-6-154357

JIS K6253 “Hardness test method of vulcanized rubber”

The present invention provides a golf ball that solves the above-described problems, has excellent measurement accuracy, has a good hardness distribution measured by a hardness evaluation method that can sufficiently evaluate performance differences among samples, and has excellent flight performance. The purpose is to do.

The present invention relates to a golf ball having a spherical core composed of at least one layer and at least one cover covering the spherical core, wherein at least one layer of the spherical core is formed from a rubber composition. The inertia radius R _g obtained by curve fitting with the following (formula 1) to (formula 5) with respect to the scattering intensity curve I _(q) obtained by X-ray scattering measurement or neutron scattering measurement is 1 nm to The present invention relates to a golf ball in which the outermost number N of the rubber composition / the innermost number N of the rubber composition is 2.0 or more with respect to the number N of scatterers per unit volume of 100 μm.

In the golf ball, the X-ray scattering measurement is preferably a small-angle X-ray scattering measurement, and the neutron scattering measurement is preferably a small-angle neutron scattering measurement, and q represented by (Equation 1) is 10 nm ⁻¹ or less. It is preferable to measure in the region.

In the golf ball, the rubber composition comprises (a) a base rubber, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof as a co-crosslinking agent, (c) In the case of containing only a α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, and (b) a crosslinking initiator, (d) an acid and / or a salt thereof, (E) It is preferable to contain a metal compound.

In the golf ball, the rubber composition preferably contains 0.5 to 30 parts by mass of (d) an acid and / or a salt thereof with respect to 100 parts by mass of the base rubber (a).
Here, it is preferable that carbon number of the said (d) acid and / or its salt is 1-13.
Moreover, it is preferable that the (d) acid and / or salt thereof is a carboxylic acid and / or salt thereof.

In the golf ball, the carboxylic acid and / or salt thereof is preferably a fatty acid and / or a fatty acid salt.
Here, the fatty acid and / or fatty acid salt is preferably a fatty acid zinc salt.

In the golf ball, the rubber composition preferably further contains (f) an organic sulfur compound.
Here, (f) the organic sulfur compound is preferably a thiophenol, a diphenyl disulfide, a thionaphthol, a thiuram disulfide, or a metal salt thereof.

In the golf ball, the rubber composition preferably contains 0.05 to 5 parts by mass of (f) an organic sulfur compound with respect to 100 parts by mass of the base rubber (a).

In the golf ball, the rubber composition contains (a) 100 parts by mass of base rubber, and (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof. It is preferable to contain 15-50 mass parts.

In the golf ball, the rubber composition preferably contains (b) a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent.

The present invention relates to a golf ball having a spherical core composed of at least one layer and at least one cover covering the spherical core, wherein at least one layer of the spherical core is formed from a rubber composition. The inertia radius R _g obtained by curve fitting with the following (formula 1) to (formula 5) with respect to the scattering intensity curve I _(q) obtained by X-ray scattering measurement or neutron scattering measurement is 1 nm to For the number N of scatterers per unit volume of 100 μm, the outermost number N of the rubber composition / the innermost number N of the rubber composition is 2.0 or more. In other words, hardness can be evaluated with high measurement accuracy with small measurement error, and excellent hardness that can accurately evaluate the difference in hardness between different samples that could not be evaluated with good reproducibility by the conventional evaluation method. A golf ball having a good hardness distribution measured using an evaluation method. Therefore, the golf ball of the present invention has a great flight distance on driver shots and has excellent flight performance.

An example of the scattering intensity curve obtained by the SAXS measurement which concerns on one Embodiment of this invention. An example of the scattering intensity curve obtained by the SANS measurement which concerns on one Embodiment of this invention. 1 is an example of a partially cutaway sectional view showing a golf ball according to an embodiment of the present invention.

〔Golf ball〕
The golf ball of the present invention is a golf ball having a spherical core comprising at least one layer and at least one cover covering the spherical core, wherein at least one layer of the spherical core is a rubber composition. A radius of inertia R _g obtained by curve fitting with the following (Expression 1) to (Expression 5) with respect to the scattering intensity curve I _(q) obtained by X-ray scattering measurement or neutron scattering measurement. The number N per unit volume of scatterers having a thickness of 1 nm to 100 μm is such that the outermost number N of the rubber composition / the innermost number N of the rubber composition is 2.0 or more.

By measuring small-angle X-ray scattering or small-angle neutron scattering of a polymer material such as a rubber composition containing metal atoms, the number N of clusters formed by aggregation of metal atoms in the material can be calculated. Then, it has been found that there is a high correlation between the number N of clusters and the hardness, and the hardness increases as N increases. Therefore, by measuring X-ray scattering or neutron scattering of a polymer material, the hardness of the material can be evaluated.

Here, the reason why there is a correlation between the number N of clusters and the hardness is not necessarily clear, but it is considered that the larger the number N of clusters, the closer the clusters are packed, and as a result, the hardness increases. It is guessed.

(Small angle X-ray scattering measurement)
In the present invention, in order to evaluate the hardness of the polymer material, as X-ray scattering measurement, SAXS (Small-angle X-ray Scattering) is used to measure the scattering intensity by irradiating the polymer material with X-rays. Angle: normally 10 degrees or less))) measurement can be suitably employed. In small-angle X-ray scattering, structural information of a substance can be obtained by measuring X-rays that are scattered by irradiating the substance with X-rays, and having a small scattering angle. , Can analyze the regular structure at several nanometer level.

In order to obtain detailed molecular structure information from the SAXS measurement, it is desirable that an X-ray scattering profile with a high S / N ratio can be measured. Therefore, the X-rays emitted from the synchrotron preferably have a luminance of at least 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more. Note that bw represents the band width of X-rays emitted from the synchrotron. Examples of such synchrotrons include beam lines BL03XU and BL20XU of a large synchrotron radiation facility SPring-8 owned by the High Brightness Optical Science Research Center.

The luminance (photons / s / mrad ² / mm ² /0.1% bw) of the X-ray is preferably 10 ¹⁰ or more, more preferably 10 ¹² or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

The number of photons (photons / s) of the X-ray is preferably 10 ⁷ or more, more preferably 10 ⁹ or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

(Small angle neutron scattering measurement)
In the present invention, in order to evaluate the hardness of the polymer material, as a neutron scattering measurement, SANS (Small-Angle Neutron Scattering) is used to measure the scattering intensity by irradiating the polymer material with a neutron beam (scattering angle: normal) 10 degrees or less))) can be suitably employed. In small-angle neutron scattering, the structure information of a substance can be obtained by measuring the small scattering angle among neutrons that are scattered by irradiating the substance with neutron rays. Analyze ordered structures at the nanometer level.

In the SANS measurement, a method using a known magnetic structure or deuteration method can be used. When employing the deuteration method, for example, the polymer material can be swollen with a deuterated solvent, and the polymer material in an equilibrium state in the deuterium solvent can be irradiated with neutrons to measure the scattering intensity. . Here, as the deuterated solvent for swelling the polymer material, deuterated water, deuterated hexane, deuterated toluene, deuterated chloroform, deuterated methanol, deuterated DMSO ((D ₃ C) ₂ S═O ), Deuterated tetrahydrofuran, deuterated acetonitrile, deuterated dichloromethane, deuterated benzene, deuterated N, N-dimethylformamide and the like.

Neutron rays used for neutron scattering measurement such as SANS can be obtained by using a beam line SANS-J of the JRR-3 research reactor owned by the Japan Atomic Energy Agency.

Similar to the SAXS measurement, the neutron flux intensity (neutrons / cm ² / s) of the neutron beam is preferably 10 ³ or more, more preferably 10 ⁴ in that a neutron scattering profile having a high S / N ratio can be obtained. That's it. Although an upper limit is not specifically limited, It is preferable to use the neutron flux intensity below the grade which does not have radiation damage.

(Measurement condition)
In the X-ray and neutron scattering measurement, since the finer molecular structure of the polymer material needs to be measured, the q represented by the above (Formula 1) is 10 nm using the X-ray and neutron beam. It is preferable to measure in a region of ⁻¹ or less. The q (nm ⁻¹ ) region is desirable from the viewpoint that smaller information can be obtained as the numerical value increases. Therefore, the q region is more preferably 20 nm ⁻¹ or less.

X-rays scattered in the SAXS measurement are detected by an X-ray detection device, and an image is generated by an image processing device or the like using X-ray detection data from the X-ray detection device.

Examples of the X-ray detector include a two-dimensional detector (X-ray film, nuclear dry plate, X-ray imaging tube, X-ray fluorescence intensifier tube, X-ray image intensifier, X-ray imaging plate, X-ray CCD. , Amorphous body for X-rays, etc.), a line sensor one-dimensional detector can be used. An X-ray detection device may be selected as appropriate depending on the type and state of the polymer material to be analyzed.

As the image processing apparatus, an apparatus capable of generating a normal X-ray scattering image based on X-ray detection data obtained by the X-ray detection apparatus can be appropriately used.

The SANS measurement can be measured by the same principle as the SAXS measurement. The scattered neutron beam is detected by the neutron beam detection device, and the image is generated by the image processing device using the neutron beam detection data from the neutron beam detection device. Is done. Here, as described above, as the neutron beam detection device, a known two-dimensional detector, a one-dimensional detector, and an image processing device that can generate a known neutron scattering image can be used. Good.

(Method for analyzing scattering intensity curve)
Next, a method for analyzing a scattering intensity curve obtained by X-ray scattering measurement and neutron scattering measurement of a polymer material will be specifically described.
When a SAXS measurement or a SANS measurement is performed on a polymer material including a functional group having a metal atom and having a metal coordination ability, for example, by analyzing the obtained scattering intensity curve by the following method, 1 nm to The number N per unit volume of scatterers having a radius of inertia (R _g ) of 100 μm can be obtained.

With respect to the scattering intensity curve I _(q) obtained by SAXS measurement such as FIG. 1 or the scattering intensity curve I _(q) obtained by SANS measurement such as FIG. Curve fitting is performed using, and the fitting parameter is obtained by the least square method.

By using G among the obtained fitting parameters, the number N of scatterers per unit volume having an inertial radius (R _g ) of 1 nm to 100 μm can be obtained. When obtaining the number N, the difference in electron density or scattering length density between the scatterer and the surrounding matrix material is used. The difference in electron density between the filler such as silica and the rubber material such as butadiene rubber, the scatterer and the surroundings. A known value or a measured value can be used for the difference in scattering length density from the deuterated solvent. Specifically, when X-ray scattering measurement is performed on a rubber material (matrix rubber: natural rubber, butadiene rubber, modified butadiene rubber, etc.) whose scatterer is silica, the electron density difference σ is 3.8 × 10 A value of ²³ (electron · cm ⁻³ ) can be used. Further, when neutron scattering measurement is performed in a deuterated toluene equilibrium swelling state for a polymer material whose scatterer is polybutadiene, for example, the scattering length density difference σ is 5.22 × 10 ¹⁰ (cm ⁻² ). A value can be used. And as above-mentioned, since the correlation of this number N and hardness is high and hardness is so high that N is large, it is thought that N has exerted a big influence on hardness. Accordingly, X-ray scattering measurement such as SAXS and neutron ray scattering measurement such as SANS are performed, and N is obtained by curve fitting using the above (Formula 1) to (Formula 5), thereby polymer materials such as polymer materials. It is possible to evaluate the hardness.

For the scattering intensity curve I _(q) obtained by X-ray scattering measurement or neutron scattering measurement of the rubber composition forming at least one layer of the spherical core, curve fitting is performed by the above (Expression 1) to (Expression 5). resulting inertia radius R _g is the number per unit volume of the scatterer is 1nm~100μm when the N, R _g in the outermost of the number N (outermost of the rubber composition in the golf ball of the present invention a is the number per unit volume of the scatterer N) / the innermost of the number of the rubber composition N (number per unit volume of the scatterer _{R g} is 1Nm～100myuemu in the innermost N) is 1Nm～100myuemu, 2.0 or more. For example, when a spherical core having a single layer structure is formed of the rubber composition, the number N of the surface portions of the spherical core / the number N of the central portions of the spherical core is 2.0 or more, and the spherical core having a multilayer structure is formed. When any layer of the core is formed of the rubber composition, the outermost number N of the layers / the innermost number N of the layers is 2.0 or more.

Since it has such a number distribution of scatterers, that is, a hardness distribution, the amount of driver spin decreases and the flight distance increases. The outermost number N of the rubber composition / the innermost number N of the rubber composition is preferably 2.5 or more, more preferably 3.0 or more.

In the golf ball of the present invention, the rubber composition forming at least one layer of the spherical core is not particularly limited as long as it has the number distribution. For example, (a) base rubber, (b) co-crosslinking agent An α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof, (c) a crosslinking initiator, (d) an acid and / or a salt thereof, and (b) a co-crosslinking agent In the case of containing only an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms, those formed by a rubber composition further containing (e) a metal compound are preferable. By being configured as described above, the degree of the outer-hard / inner-soft structure of the spherical core is increased, so that the spin rate on driver shots decreases and the flight distance increases.

First, (a) the base rubber will be described. (A) As the base rubber, natural rubber and / or synthetic rubber can be used. For example, polybutadiene rubber, natural rubber, polyisoprene rubber, styrene polybutadiene rubber, ethylene-propylene-diene rubber (EPDM) or the like is used. it can. These may be used alone or in combination of two or more. Among these, a high cis polybutadiene having 40% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, which is particularly advantageous for repulsion is suitable.

The high-cis polybutadiene preferably has a 1,2-vinyl bond content of 2% by mass or less, more preferably 1.7% by mass or less, and still more preferably 1.5% by mass or less. If the content of 1,2-vinyl bond is too large, the resilience may be lowered.

The high cis polybutadiene is preferably synthesized with a rare earth element-based catalyst. In particular, the use of a neodymium catalyst using a neodymium compound which is a lanthanum series rare earth element compound has a high content of 1,4-cis bonds. , 1,2-vinyl bond is preferred because a polybutadiene rubber having a low content can be obtained with excellent polymerization activity.

The high-cis polybutadiene preferably has a Mooney viscosity (ML _{1 + 4} (100 ° C.)) of 30 or more, more preferably 32 or more, still more preferably 35 or more, and preferably 140 or less, more preferably 120 or less. More preferably, it is 100 or less, and most preferably 80 or less. The Mooney viscosity (ML _{1 + 4} (100 ° C.)) as used in the present invention is an L rotor according to JIS K6300, with a preheating time of 1 minute, a rotor rotation time of 4 minutes, and a condition of 100 ° C. Measured value.

The high-cis polybutadiene preferably has a molecular weight distribution Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of 2.0 or more, more preferably 2.2 or more, and still more preferably 2. It is 4 or more, most preferably 2.6 or more, and preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and most preferably 3.4 or less. If the molecular weight distribution (Mw / Mn) of the high cis polybutadiene is too small, the workability is lowered, and if it is too large, the resilience may be lowered. The molecular weight distribution was determined by gel permeation chromatography (manufactured by Tosoh Corporation, “HLC-8120GPC”), using a differential refractometer as a detector, column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40 ° C., mobile phase. : Measured under conditions of tetrahydrofuran and calculated as a standard polystyrene equivalent value.

Next, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof will be described. (B) The α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or the metal salt thereof is blended in the rubber composition as a co-crosslinking agent and grafted to the base rubber molecular chain. By polymerizing, it has a function of cross-linking rubber molecules. When the rubber composition used in the present invention contains only an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, the rubber composition contains (e) a metal compound as an essential component. Furthermore, it contains. An α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent is obtained by neutralizing an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal compound in the rubber composition. This is because substantially the same effect as that obtained when an acid metal salt is used can be obtained. In the case where an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and a metal salt thereof are used in combination as the co-crosslinking agent, (e) a metal compound may be used as an optional component.

Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

Examples of the metal constituting the metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include monovalent metal ions such as sodium, potassium and lithium; magnesium, calcium, zinc, barium, cadmium and the like A divalent metal ion; a trivalent metal ion such as aluminum; and other ions such as tin and zirconium. The said metal component can also be used individually or in mixture of 2 or more types. Among these, as said metal component, bivalent metals, such as magnesium, calcium, zinc, barium, cadmium, are preferable. This is because by using a divalent metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms, metal crosslinking is likely to occur between rubber molecules. In particular, as the divalent metal salt, zinc acrylate is preferable because the resilience of the obtained golf ball is increased. The α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof may be used alone or in combination of two or more.

(B) The content of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or the metal salt thereof is preferably 15 parts by mass or more with respect to 100 parts by mass of the base rubber (a), 20 mass parts or more are more preferable, 50 mass parts or less are preferable, 45 mass parts or less are more preferable, and 35 mass parts or less are still more preferable. (B) When the content of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or the metal salt thereof is less than 15 parts by mass, the member formed from the rubber composition has an appropriate hardness. In addition, the amount of the crosslinking initiator (c) described later must be increased, and the resilience of the golf ball tends to decrease. On the other hand, when the content of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or the metal salt thereof exceeds 50 parts by mass, the member formed from the rubber composition becomes too hard, and golf There is a possibility that the hit feeling of the ball is lowered.

(C) A crosslinking initiator is blended in order to crosslink (a) the base rubber component. (C) As a crosslinking initiator, an organic peroxide is suitable. Specifically, the organic peroxide is dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di Examples thereof include organic peroxides such as (t-butylperoxy) hexane and di-t-butyl peroxide. These organic peroxides may be used alone or in combination of two or more. Of these, dicumyl peroxide is preferably used.

(C) As for content of a crosslinking initiator, 0.2 mass part or more is preferable with respect to 100 mass parts of (a) base rubber, More preferably, it is 0.5 mass part or more, Comprising: 5.0 mass Part or less, more preferably 2.5 parts by weight or less. If the amount is less than 0.2 parts by mass, the member formed from the rubber composition tends to be too soft, and the resilience of the golf ball tends to decrease. If the amount exceeds 5.0 parts by mass, the member is formed from the rubber composition. In order to make the member appropriate hardness, it is necessary to reduce the amount of the (b) co-crosslinking agent described above, and there is a possibility that the resilience of the golf ball is insufficient or the durability is deteriorated.

Next, (d) the acid and / or salt thereof will be described. Examples of the acid component of (d) the acid and / or salt thereof used in the present invention include oxo acids such as carboxylic acid, sulfonic acid and phosphoric acid; hydrogen acids such as hydrochloric acid and hydrofluoric acid; Of these, oxo acids are preferred, and carboxylic acids are more preferred. (B) The α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a salt thereof used as a co-crosslinking agent is not included. (D) The acid and / or salt thereof has an action of cleaving a metal bridge formed by a metal salt of (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the center of the core at the time of core molding. It is considered a thing.

The core hardness distribution increases almost linearly from the center of the core toward the surface, and the degree of the outer-hard / inner-soft structure increases, thereby reducing the driver spin rate and improving the flight distance performance. The reason why the core hardness distribution increases almost linearly from the core center to the surface is considered as follows. The core internal temperature at the time of molding the core is high at the core center and decreases toward the core surface. This is because the reaction heat of the cross-linking reaction accumulates in the core center. (D) The acid and / or salt thereof reacts with the metal salt of (b) α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms at the time of molding the core to produce a metal salt of carboxylic acid. . That is, (d) the acid and / or salt thereof exchanges a cation with a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and α, β having 3 to 8 carbon atoms. Cleaving metal bridges with metal salts of unsaturated carboxylic acids. This cation exchange reaction is likely to occur at the core center where the core internal temperature is high, and is less likely to occur toward the surface. In other words, the cutting of the metal bridge is likely to occur at the center of the core and is less likely to occur toward the surface. As a result, the cross-linking density inside the core increases from the core center to the surface, so the core hardness is considered to increase almost linearly from the core center to the surface.

As a result of further investigation, it was found that by adopting (d) an acid and / or a salt thereof, the degree of outer-hard / inner-softness of the spherical core was further increased, and the spin rate on driver shots was reduced. (D) By adopting an acid and / or a salt thereof, the degree of outer-hard / inner-softness of the spherical core is further increased. The reason for this is considered as follows. The acid and / or salt thereof exchanges a cation with a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Breaks metal bridges with metal salts. This action of breaking the metal bridge is considered to be influenced by the number of moles of acid and / or salt thereof added. At the same time, the acid and / or salt thereof acts as a plasticizer for the spherical core. When the blending amount (mass) of the acid to be added and / or its salt is increased, the entire core is softened. This plastic effect is affected by the amount (mass) of the acid and / or salt thereof to be added. In consideration of these actions, the use of an acid and / or a salt thereof having a small carbon number (small molecular weight) compared to the case of using an acid and / or a salt thereof having a large carbon number (large molecular weight). The number of moles to be added can be increased with the same blending amount (mass). That is, the effect of cutting the metal bridge can be enhanced while suppressing the entire spherical core from being softened by the plastic effect.

(D) The acid and / or salt thereof is an aliphatic acid and / or salt thereof as long as it can exchange a metal salt and a cationic component of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. (In the present invention, it may be simply referred to as “fatty acid / fatty acid salt”) or an aromatic acid and / or a salt thereof. When the carbon number is lowered, there are problems such as toxicity and odor. In addition, carbon number is the carbon number of an acid component.

The fatty acid / fatty acid salt may be a saturated fatty acid / saturated fatty acid salt or an unsaturated fatty acid / unsaturated fatty acid salt, but is preferably a saturated fatty acid / saturated fatty acid salt. Specific examples of the fatty acid component of the fatty acid / fatty acid salt include, for example, butyric acid (C4), valeric acid (C5), caproic acid (C6), enanthic acid (C7), caprylic acid (octanoic acid) (C8), pelargon Examples include acid (C9), capric acid (decanoic acid) (C10), and lauric acid (C12). The fatty acid component can be used alone or as a mixture of two or more. As the fatty acid component, caprylic acid (octanoic acid) (C8), pelargonic acid (C9), capric acid (decanoic acid) (C10), and lauric acid (C12) are preferable, caprylic acid (octanoic acid) (C8), Capric acid (decanoic acid) (C10) or lauric acid (C12) is more preferred.

Specific examples of the aromatic acid component of the aromatic acid and / or salt thereof include, for example, benzoic acid (C7), phthalic acid (C8), isophthalic acid (C8), terephthalic acid (C8), hememilitic acid (benzene- 1,2,3-tricarboxylic acid (C9), trimellitic acid (benzene-1,2,4-tricarboxylic acid) (C9), trimesic acid (benzene-1,3,5-tricarboxylic acid) (C9), merophane Acid (benzene-1,2,3,4-tetracarboxylic acid) (C10), planitic acid (benzene-1,2,3,5-tetracarboxylic acid) (C10), pyromellitic acid (benzene-1,2) , 4,5-tetracarboxylic acid) (C10), meritic acid (benzenehexacarboxylic acid) (C12), diphenic acid (biphenyl-2,2′-dicarboxylic acid) (C12), toluic acid Methylbenzoic acid) (C8), xylic acid (C9), prenylic acid (2,3,4-trimethylbenzoic acid) (C10), γ-isoduric acid (2,3,5-trimethylbenzoic acid) (C10), Julylic acid (2,4,5-trimethylbenzoic acid) (C10), β-isoduric acid (2,4,6-trimethylbenzoic acid) (C10), α-isoduric acid (3,4,5-trimethylbenzoic acid) ) (C10), cumic acid (4-isopropylbenzoic acid) (C10), ubitoic acid (5-methylisophthalic acid) (C9), α-toluic acid (phenylacetic acid) (C8), hydroatropic acid (2-phenylpropane) Acid) (C9), hydrocinnamic acid (3-phenylpropanoic acid) (C9), and the like.

Examples of the aromatic acid component substituted with a hydroxyl group, an alkoxy group, or an oxo group include, for example, salicylic acid (2-hydroxybenzoic acid) (C7), anisic acid (methoxybenzoic acid) (C8), cresotic acid ( Hydroxy (methyl) benzoic acid) (C8), o-homosalicylic acid (2-hydroxy-3-methylbenzoic acid) (C8), m-homosalicylic acid (2-hydroxy-4-methylbenzoic acid) (C8), p -Homosalicylic acid (2-hydroxy-5-methylbenzoic acid) (C8), o-pyrocatechuic acid (2,3-dihydroxybenzoic acid) (C7), β-resorcylic acid (2,4-dihydroxybenzoic acid) (C7) ), Γ-resorcylic acid (2,6-dihydroxybenzoic acid) (C7), protocatechuic acid (3,4-dihydroxybenzoic acid) (C7), α-resorci Acid (3,5-dihydroxybenzoic acid) (C7), vanillic acid (4-hydroxy-3-methoxybenzoic acid) (C8), isovanillic acid (3-hydroxy-4-methoxybenzoic acid) (C8), veratrum acid (3,4-dimethoxybenzoic acid) (C9), o-veratormic acid (2,3-dimethoxybenzoic acid) (C9), orthelic acid (2,4-dihydroxy-6-methylbenzoic acid) (C8), m -Hemipic acid (4,5-dimethoxyphthalic acid) (C10), gallic acid (3,4,5-trihydroxybenzoic acid) (C7), syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) ( C9), asaronic acid (2,4,5-trimethoxybenzoic acid) (C10), mandelic acid (hydroxy (phenyl) acetic acid) (C8), vanylmandelic acid (hydroxy (4-hydroxy Roxy-3-methoxyphenyl) acetic acid) (C9), homoanisic acid ((4-methoxyphenyl) acetic acid) (C9), homogentisic acid ((2,5-dihydroxyphenyl) acetic acid) (C8), homoprotocatechuic acid ((3 , 4-dihydroxyphenyl) acetic acid) (C8), homovanillic acid ((4-hydroxy-3-methoxyphenyl) acetic acid) (C9), homoisovanillic acid ((3-hydroxy-4-methoxyphenyl) acetic acid) (C9) ), Homobellatrumic acid ((3,4-dimethoxyphenyl) acetic acid) (C10), o-homobellatrumic acid ((2,3-dimethoxyphenyl) acetic acid) (C10), homophthalic acid (2- (carboxymethyl) benzoic acid) (C9), homoisophthalic acid (3- (carboxymethyl) benzoic acid) (C9), homoterephthalic acid (4- (cal (Boxymethyl) benzoic acid) (C9), phthalonic acid (2- (carboxycarbonyl) benzoic acid) (C9), isophthalonic acid (3- (carboxycarbonyl) benzoic acid) (C9), terephthalonic acid (4- (carboxycarbonyl) Benzoic acid (C9), atrolactic acid (2-hydroxy-2-phenylpropanoic acid) (C9), tropic acid (3-hydroxy-2-phenylpropanoic acid) (C9), mellilotic acid (3- (2- Hydroxyphenyl) propanoic acid) (C9), furoletic acid (3- (4-hydroxyphenyl) propanoic acid) (C9), hydrocaffeic acid (3- (3,4-dihydroxyphenyl) propanoic acid) (C9), hydro Ferulic acid (3- (4-hydroxy-3-methoxyphenyl) propanoic acid) (C10), hydroisoferulic acid (3 (3-hydroxy-4-methoxyphenyl) propanoic acid) (C10), p-coumaric acid (3- (4-hydroxyphenyl) acrylic acid) (C9), umberic acid (3- (2,4-dihydroxyphenyl) Acrylic acid) (C9), caffeic acid (3- (3,4-dihydroxyphenyl) acrylic acid) (C9), ferulic acid (3- (4-hydroxy-3-methoxyphenyl) acrylic acid) (C10), isofera Examples include acid (3- (3-hydroxy-4-methoxyphenyl) acrylic acid) (C10), sinapinic acid (3- (4-hydroxy-3,5-dimethoxyphenyl) acrylic acid) (C11), and the like. .

The cation component of the acid salt may be either a metal ion or an organic cation. Examples of the metal ion include monovalent metal ions such as sodium, potassium, lithium and silver; divalent metal ions such as magnesium, calcium, zinc, barium, cadmium, copper, cobalt, nickel and manganese; aluminum and iron And other ions such as tin, zirconium, and titanium. The cation component of the acid salt is preferably zinc ion. The cationic component may be a single component or a mixture of two or more types.

The organic cation is a cation having a carbon chain. The organic cation is not particularly limited, and examples thereof include organic ammonium ions. Examples of the organic ammonium ion include primary ammonium ions such as stearyl ammonium ion, hexyl ammonium ion, octyl ammonium ion, and 2-ethylhexyl ammonium ion, and secondary such as dodecyl (lauryl) ammonium ion and octadecyl (stearyl) ammonium ion. Ammonium ion; tertiary ammonium ion such as trioctyl ammonium ion; quaternary ammonium ion such as dioctyl dimethyl ammonium ion and distearyl dimethyl ammonium ion. These organic cations may be used alone or in combination of two or more.

(D) As said acid and / or its salt, carboxylic acid and / or its salt are preferable, and C1-C13 is preferable. Fatty acid zinc salts are also preferred. Especially, the metal salt of caprylic acid (octanoic acid) (C8), pelargonic acid (C9), capric acid (decanoic acid) (C10), or lauric acid (C12) is preferable, and caprylic acid (octanoic acid) (C8 ), Capric acid (decanoic acid) (C10) or zinc salt of lauric acid (C12) is more preferred. In addition, carbon number of a C1-C13 carboxylate is carbon number of a carboxylic acid component, for example, in the case of the organic cation salt of carboxylic acid, the carbon number in an organic cation is not included.

(D) The content of the acid and / or salt thereof is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, further preferably 100 parts by mass of the base rubber (a). 1.5 parts by mass or more, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and further preferably 20 parts by mass or less. If the content is too small, (d) the effect of adding an acid and / or salt thereof is not sufficient, and the degree of flexibility of the spherical core may be reduced. Moreover, when there is too much content, there exists a possibility that the hardness of the core obtained may fall entirely and a resilience may fall. The surface of zinc acrylate used as a co-crosslinking agent may be treated with (d) an acid and / or a salt thereof in order to improve dispersibility in rubber. In the present invention, when (d) zinc acrylate surface-treated with an acid and / or salt thereof is used, the amount of (d) acid and / or salt which is a surface treatment agent is the content of component (d) It is not included in the quantity. It is considered that (d) the acid and / or salt thereof used for the surface treatment of zinc acrylate hardly contributes to the cation exchange reaction with (b) the co-crosslinking agent.

When the rubber composition used in the present invention contains only an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, the rubber composition contains (e) a metal compound as an essential component Is further contained. (E) The metal compound is not particularly limited as long as (b) the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms can be neutralized in the rubber composition. (E) Examples of the metal compound include magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, copper hydroxide, and other metal hydroxides; magnesium oxide, calcium oxide. Metal oxides such as zinc oxide and copper oxide; metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate and potassium carbonate. (E) The metal compound is preferably a divalent metal compound, more preferably a zinc compound. This is because the divalent metal compound reacts with the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal bridge. Moreover, a golf ball with high resilience can be obtained by using a zinc compound. These (e) metal compounds may be used alone or in combination of two or more. In addition, what is necessary is just to select suitably content of (e) metal compound according to content of (b) C3-C8 alpha, beta-unsaturated carboxylic acid.

The core rubber composition used in the present invention preferably further contains (f) an organic sulfur compound. In addition to (d) the carboxylate having 1 to 13 carbon atoms, (f) the organic sulfur compound is used in combination with the rubber composition for the core while maintaining the substantially linearity of the core hardness distribution. The degree of the outer-hard / inner-soft structure can be controlled. (F) The organic sulfur compound is not particularly limited as long as it is an organic compound having a sulfur atom in the molecule. For example, a thiol group (-SH) or a polysulfide bond having 2 to 4 sulfur atoms (-S). Organic compound having -S-, -SSS-S-, or -SSS-SS-), or a metal salt thereof (-SM, -SMS-S-, -SM -S-S-, -SSS-SS-, -SMSSS-, etc., where M is a metal atom). (F) The organic sulfur compound is an aliphatic compound (aliphatic thiol, aliphatic thiocarboxylic acid, aliphatic dithiocarboxylic acid, aliphatic polysulfide, etc.), heterocyclic compound, alicyclic compound (alicyclic thiol). , Alicyclic thiocarboxylic acid, alicyclic dithiocarboxylic acid, alicyclic polysulfide, etc.) and aromatic compounds. (F) Organic sulfur compounds include, for example, thiophenols, thionaphthols, polysulfides (such as diphenyl disulfides), thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, thiurams (such as thiuram disulfides), dithiocarbamine Examples include acid salts and thiazoles. From the viewpoint of increasing the hardness distribution of the spherical core, the organic sulfur compound (f) is preferably an organic sulfur compound having a thiol group (-SH) or a metal salt thereof, such as thiophenols, thionaphthols, or These metal salts are preferred. Examples of the metal salt include monovalent metal salts such as sodium, lithium, potassium, copper (I), silver (I), zinc, magnesium, calcium, strontium, barium, titanium (II), manganese (II), Examples thereof include divalent metal salts such as iron (II), cobalt (II), nickel (II), zirconium (II), tin (II) and the like.

Examples of thiophenols include thiophenol; 4-fluorothiophenol, 2,5-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, penta Thiophenols substituted with a fluoro group such as fluorothiophenol; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,4,5-trichloro Thiophenols substituted with a chloro group such as thiophenol, 2,4,5,6-tetrachlorothiophenol, pentachlorothiophenol; 4-promothiophenol, 2,5-dipromothiophenol, 2,4, 5-tripromothiophenol, 2,4,5,6-tetrapromoti Thiophenols substituted with a bromo group such as phenol and pentabromothiophenol; 4-iodothiophenol, 2,5-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5 Examples thereof include thiophenols substituted with an iodo group such as 6-tetraiodothiophenol and pentaiodothiophenol; or metal salts thereof. As the metal salt, a zinc salt is preferable.

Examples of thionaphthols include 2-thionaphthol, 1-thionaphthol, 2-chloro-1-thionaphthol, 2-promo-1-thionaphthol, 2-fluoro-1-thionaphthol, and 2-cyano-1-. Thionaphthol, 2-acetyl-1-thionaphthol, 1-chloro-2-thionaphthol, 1-promo-2-thionaphthol, 1-fluoro-2-thionaphthol, 1-cyano-2-thionaphthol, 1-acetyl -2-thionaphthol or a metal salt thereof can be mentioned, and 1-thionaphthol, 2-thionaphthol, or a zinc salt thereof is preferable.

Examples of the sulfenamide-based organic sulfur compound include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide. Is mentioned. Examples of the thiuram organic sulfur compound include tetramethyl thiuram monosulfide, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, and dipentamethylene thiuram tetrasulfide. Examples of the dithiocarbamate salts include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, copper (II) dimethyldithiocarbamate, dimethyldithiocarbamate Examples thereof include iron (III), selenium diethyldithiocarbamate, and tellurium diethyldithiocarbamate. Examples of thiazole-based organic sulfur compounds include 2-mercaptobenzothiazole (MBT), dibenzothiazyl disulfide (MBTS), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, or cyclohexylamine salt, 2- (2,4-dinitrophenyl) mercaptobenzothiazole, 2- (2,6-diethyl-4-morpholinothio) benzothiazole and the like can be mentioned.

(F) The said organic sulfur compound can be used individually or in mixture of 2 or more types.

(F) The content of the organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and 5.0 parts by mass with respect to 100 parts by mass of the (a) base rubber. Part or less, more preferably 2.0 parts by weight or less. If it is less than 0.05 parts by mass, the effect of adding the (f) organic sulfur compound cannot be obtained, and the resilience of the golf ball may not be improved. On the other hand, if the amount exceeds 5.0 parts by mass, the amount of compressive deformation of the resulting golf ball increases, and the resilience may be reduced.

The rubber composition used in the present invention may contain additives such as pigments, fillers for weight adjustment, anti-aging agents, peptizers, softeners and the like, if necessary. Further, as described above, when the rubber composition used in the present invention contains only an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, the rubber composition contains (e) It is preferable to further contain a metal compound.

Examples of the pigment blended in the rubber composition include a white pigment, a blue pigment, and a purple pigment. As the white pigment, titanium oxide is preferably used. The type of titanium oxide is not particularly limited, but it is preferable to use a rutile type because it has good concealability. Further, the content of titanium oxide is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and preferably 8 parts by mass or less, relative to 100 parts by mass of (a) the base rubber. Preferably it is 5 mass parts or less.

It is also a preferred embodiment that the rubber composition contains a white pigment and a blue pigment. The blue pigment is blended to make white appear vivid, and examples thereof include ultramarine blue, cobalt blue, and phthalocyanine blue. Examples of the purple pigment include anthraquinone violet, dioxazine violet, and methyl violet.

The content of the blue pigment is preferably 0.001 part by mass or more, more preferably 0.05 part by mass or more, and 0.2 part by mass or less with respect to 100 parts by mass of (a) the base rubber. Preferably, it is 0.1 part by mass or less. If it is less than 0.001 part by mass, the bluish color is inadequate and looks yellowish, and if it exceeds 0.2 part by mass, it becomes too blue and the vivid white appearance is lost.

The filler used in the rubber composition is mainly blended as a weight regulator for adjusting the weight of the golf ball obtained as a final product, and may be blended as necessary. Examples of the filler include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. The content of the filler is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, preferably 30 parts by mass or less, and 25 parts by mass or less with respect to 100 parts by mass of the base rubber. More preferred is 20 parts by mass or less. When the filler content is less than 0.5 parts by mass, it is difficult to adjust the weight. When the filler content exceeds 30 parts by mass, the weight fraction of the rubber component tends to be small and the resilience tends to decrease.

The content of the antioxidant is preferably 0.1 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the base rubber (a). Moreover, it is preferable that content of a peptizer is 0.1 to 5 mass parts with respect to 100 mass parts of (a) base rubber.

The rubber composition used in the present invention includes (a) a base rubber, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof, (c) a crosslinking initiator, (D) It can be obtained by mixing and kneading an acid and / or a salt thereof and, if necessary, other additives. The method of kneading is not particularly limited, and for example, a kneading roll, a Banbury mixer, a kneader or the like may be used.

The spherical core of the golf ball of the present invention can be obtained by molding the kneaded rubber composition in a mold. The temperature at which the spherical core is molded is preferably 120 ° C or higher, more preferably 150 ° C or higher, still more preferably 160 ° C or higher, and preferably 170 ° C or lower. When the molding temperature exceeds 170 ° C., the core surface hardness tends to decrease. The pressure during molding is preferably 2.9 to 11.8 MPa. The molding time is preferably 10 to 60 minutes.

The spherical core has a linear approximation curve R ² obtained by a least square method when plotting the hardness measured at 9 points equally divided by 12.5% of the core radius and the distance from the core center. It is preferable that it is 0.95 or more. If R ² is 0.95 or more, increased linearity of the hardness distribution of the core, the driver spin rate is lowered, thereby improving the flight distance performance.

As for the hardness of the spherical core, the JIS-C hardness is measured at 9 points obtained by equally dividing an arbitrary radius of the spherical core at intervals of 12.5%. That is, the distance from the core center is 0% (core center), 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, 100% (core surface) JIS-C hardness is measured at 9 points. Next, a graph is created by plotting the measurement results with the JIS-C hardness measured as described above as the vertical axis and the distance (%) from the core center as the horizontal axis. In the present invention, R ² of a linear approximation curve obtained by the least square method from the plot is preferably 0.95 or more. R ² of the linear approximation curve obtained by the method of least squares indicates the linearity of the obtained plot. In the present invention, if R ² is 0.95 or more, it means that the hardness distribution of the spherical core is substantially linear. A golf ball using a spherical core having a substantially linear hardness distribution has a reduced spin rate on driver shots. As a result, the flight distance of the driver shot increases. R ^{2 of the} linear approximation curve is more preferably 0.96 or more. By increasing the linearity, the flight distance of the driver shot becomes larger.

The hardness difference (Hs-Ho) between the surface hardness Hs and the center hardness Ho of the spherical core is JIS-C hardness, preferably 27 or more, more preferably 28 or more, further preferably 30 or more, and preferably 80 or less, 70 or less is more preferable, and 60 or less is still more preferable. When the hardness difference between the core surface and the core center is large, a golf ball having a high launch angle and a low spin distance can be obtained.

The center hardness Ho of the spherical core is preferably JIS-C hardness of 30 or more, more preferably 40 or more, and further preferably 45 or more. If the central hardness Ho of the spherical core is less than 30 in terms of JIS-C hardness, the spherical core may become too soft and the resilience may decrease. Further, the central hardness Ho of the spherical core is preferably 70 or less in JIS-C hardness, more preferably 65 or less, and further preferably 60 or less. This is because if the center hardness Ho exceeds 70 in JIS-C hardness, the center hardness Ho becomes too hard and the shot feeling tends to decrease.

The surface hardness Hs of the spherical core is JIS-C hardness, preferably 76 or more, more preferably 78 or more, preferably 100 or less, and more preferably 95 or less. By setting the surface hardness of the spherical core to 76 or more in terms of JIS-C hardness, the spherical core does not become too soft and good resilience can be obtained. Further, by setting the surface hardness of the spherical core to JIS-C hardness of 100 or less, the spherical core does not become too hard and a good shot feeling can be obtained.

The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, further preferably 38.8 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, and still more preferably. 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the cover will not be too thick and the resilience will be better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover is not too thin, and the function of the cover is more exhibited.

When the spherical core has a diameter of 34.8 to 42.2 mm, the amount of compressive deformation (the amount by which the center contracts in the compression direction) from when the initial load is 98 N to when the final load is 1275 N is 2.0 mm. The above is preferable, 2.8 mm or more is more preferable, 6.0 mm or less is preferable, and 5.0 mm or less is more preferable. If the amount of compressive deformation is 2.0 mm or more, the feel at impact is better, and if it is 6.0 mm or less, the resilience is better.

The cover of the golf ball of the present invention is formed from a cover composition containing a resin component. Examples of the resin component include an ionomer resin, a thermoplastic polyurethane elastomer marketed by BASF Japan Co., Ltd. under the trade name “Elastollan (registered trademark)”, and a trade name “Pebax (registered trademark)” from Arkema Co., Ltd. , Thermoplastic polyester elastomer marketed by Toray DuPont Co., Ltd. under the trade name “Hytrel®”, and trade name “Lavalon” from Mitsubishi Chemical Co., Ltd. ) "And the like are commercially available.

Examples of the ionomer resin include a resin obtained by neutralizing at least a part of a carboxyl group in a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal ion. And a neutralization of at least a part of a carboxyl group of a terpolymer of an α, β monounsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester, or And mixtures thereof. The olefin is preferably an olefin having 2 to 8 carbon atoms, and examples thereof include ethylene, propylene, butene, pentene, hexene, heptene, octene and the like, and ethylene is particularly preferable. Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid, and acrylic acid or methacrylic acid is particularly preferable. Examples of the α, β-unsaturated carboxylic acid ester include methyl, ethyl, propyl, n-butyl, isobutyl ester and the like such as acrylic acid, methacrylic acid, fumaric acid and maleic acid, and particularly acrylic acid ester. Or a methacrylic acid ester is preferable. Among these, as the ionomer resin, a metal ion neutralized product of an ethylene- (meth) acrylic acid binary copolymer, an ethylene- (meth) acrylic acid- (meth) acrylic acid ester terpolymer, A metal ion neutralized product is preferred.

Specific examples of the ionomer resin are illustrated by trade names, such as “Himilan (registered trademark)” (for example, Himilan 1555 (Na), Himilan 1557 (Zn), Himilan, which is commercially available from Mitsui DuPont Polychemical Co., Ltd.). 1605 (Na), HiMilan 1706 (Zn), HiMilan 1707 (Na), HiMilan AM3711 (Mg), etc., and terpolymer ionomer resins include HiMilan 1856 (Na), HiMilan 1855 (Zn), etc.) ".

Further, ionomer resins commercially available from DuPont include "Surlyn (registered trademark)" (for example, Surlyn 8945 (Na), Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li), Surlyn 7940 (Li), Surlyn AD8546 (Li) and the like, and terpolymers Examples of the ionomer resin include Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn), Surlyn 6320 (Mg), F1000 (Mg), and HPF2000 (Mg)).

Examples of ionomer resins commercially available from ExxonMobil Chemical Co., Ltd. include “Iotek (registered trademark)” (for example, Iotech 8000 (Na), Iotech 8030 (Na), Iotech 7010 (Zn), Iotech 7030 ( Zn) and the like, and examples of the ternary copolymer ionomer resin include Iotech 7510 (Zn) and Iotech 7520 (Zn)).

Note that Na, Zn, Li, Mg, and the like described in parentheses after the trade name of the ionomer resin indicate the metal species of these neutralized metal ions. The ionomer resins may be used alone or in admixture of two or more.

The cover composition constituting the golf ball cover of the present invention preferably contains a thermoplastic polyurethane elastomer or an ionomer resin as a resin component. When an ionomer resin is used, it is also preferable to use a thermoplastic styrene elastomer in combination. 50 mass% or more is preferable, as for the content rate of the polyurethane or ionomer resin in the resin component of the composition for covers, 60 mass% or more is more preferable, and 70 mass% or more is still more preferable.

In addition to the resin component described above, the cover composition includes a pigment component such as a white pigment (for example, titanium oxide), a blue pigment, and a red pigment, a weight adjusting agent such as zinc oxide, calcium carbonate, and barium sulfate, a dispersant, You may contain an anti-aging agent, a ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent whitening agent, etc. in the range which does not impair the performance of a cover.

The content of the white pigment (for example, titanium oxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and 10 parts by mass with respect to 100 parts by mass of the resin component constituting the cover. The following is preferable, and more preferably 8 parts by mass or less. By setting the content of the white pigment to 0.5 parts by mass or more, the cover can be concealed. Moreover, it is because durability of the cover obtained may fall when content of a white pigment exceeds 10 mass parts.

The slab hardness of the cover composition is preferably set as appropriate according to the desired performance of the golf ball. For example, in the case of a distance type golf ball that places importance on the flight distance, the slab hardness of the cover composition is preferably 50 or more, more preferably 55 or more, more preferably 80 or less, and more preferably 70 or less in Shore D hardness. By setting the slab hardness of the cover composition to 50 or more, a golf ball having a high launch angle and a low spin can be obtained in a driver shot and an iron shot, and the flight distance is increased. Further, by setting the slab hardness of the cover composition to 80 or less, a golf ball having excellent durability can be obtained. In the case of a spin-type golf ball where controllability is important, the slab hardness of the cover composition is Shore D hardness, preferably less than 50, preferably 20 or more, and more preferably 25 or more. If the slab hardness of the cover composition is less than 50 in Shore D hardness, on the driver shot, the core of the present invention increases the flying distance and increases the spin rate of the approach shot, which tends to stop on the green. A golf ball is obtained. Moreover, by setting the slab hardness to 20 or more, the scratch resistance is improved. In the case of a plurality of cover layers, the slab hardness of the cover composition constituting each layer may be the same or different as long as it is within the above range.

As a method for molding the cover of the golf ball of the present invention, for example, a hollow shell-like shell is molded from the cover composition, and the core is covered with a plurality of shells and compression molded (preferably, the cover composition And a method in which a hollow shell-shaped half shell is molded from a product and the core is covered with two half shells and compression molded), or a cover composition is directly injection molded on the core.

When the cover is molded by the compression molding method, the half shell can be molded by either the compression molding method or the injection molding method, but the compression molding method is preferred. The conditions for compression molding the cover composition into a half shell include, for example, a pressure of 1 MPa or more and 20 MPa or less and a flow start temperature of the cover composition of −20 ° C. or more and 70 ° C. or less. A molding temperature can be mentioned. By setting the molding conditions, a half shell having a uniform thickness can be molded. As a method for forming a cover using a half shell, for example, a method in which a core is covered with two half shells and compression-molded can be mentioned. As a condition for compression-molding the half shell into a cover, for example, at a molding pressure of 0.5 MPa or more and 25 MPa or less, a flow start temperature of the cover composition is −20 ° C. or more and 70 ° C. or less. A molding temperature can be mentioned. By setting the molding conditions, a golf ball cover having a uniform cover thickness can be molded.

When a cover composition is injection molded to form a cover, it may be injection molded using a pellet-shaped cover composition obtained by extrusion, or it may be used for a cover such as a base resin component or a pigment. The materials may be dry blended and directly injection molded. As the upper and lower molds for forming the cover, it is preferable to use a cover mold having a hemispherical cavity and having a pimple and also serving as a hold pin in which a part of the pimple can advance and retreat. The cover can be formed by injection molding by projecting a hold pin, inserting a core and holding it, then injecting the cover composition and cooling the cover, for example, 9-15 MPa A cover composition heated to 200 to 250 ° C. is poured into a mold clamped with pressure in 0.5 to 5 seconds, cooled for 10 to 60 seconds, and opened.

The cover is usually formed with a depression called a dimple on the surface. The total number of dimples is preferably 200 or more and 500 or less. If the total number of dimples is less than 200, the dimple effect is difficult to obtain. Further, when the total number of dimples exceeds 500, the size of each dimple becomes small and it is difficult to obtain the dimple effect. The shape (plan view shape) of the dimple formed is not particularly limited, and a circular shape; a polygon such as a substantially triangular shape, a substantially square shape, a substantially pentagonal shape, or a substantially hexagonal shape; Alternatively, two or more kinds may be used in combination.

The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and still more preferably 2.0 mm or less. If the cover has a thickness of 4.0 mm or less, the resulting golf ball will have better resilience and feel at impact. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.5 mm or more, still more preferably 0.8 mm or more, and particularly preferably 1.0 mm or more. If the thickness of the cover is less than 0.3 mm, the durability and wear resistance of the cover may decrease. In the case of a plurality of cover layers, the total thickness of the plurality of cover layers is preferably in the above range.

The golf ball body in which the cover is molded is preferably taken out from the mold and subjected to surface treatment such as deburring, washing, and sandblasting as necessary. Moreover, a coating film and a mark can also be formed if desired. The film thickness of the coating film is not particularly limited, but is preferably 5 μm or more, more preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. This is because when the film thickness is less than 5 μm, the coating tends to be worn away by continuous use, and when the film thickness exceeds 50 μm, the dimple effect is reduced and the flight performance of the golf ball is reduced.

When the golf ball of the present invention has a diameter of 40 to 45 mm, the amount of compressive deformation (the amount of contraction in the compression direction) when the final load 1275N is applied from the state where the initial load 98N is applied may be 2.0 mm or more. Preferably, it is 2.4 mm or more, more preferably 2.5 mm or more, most preferably 2.8 mm or more, preferably 5.0 mm or less, more preferably 4.5 mm or less. is there. A golf ball having a compression deformation amount of 2.0 mm or more does not become too hard and has a good shot feeling. On the other hand, when the amount of compressive deformation is 5.0 mm or less, the resilience increases.

The structure of the golf ball of the present invention is not particularly limited as long as it has a spherical core composed of at least one layer and at least one cover covering the spherical core. FIG. 3 is a partially cutaway sectional view showing a golf ball 2 according to an embodiment of the present invention. The golf ball 2 has a spherical core 4 and a cover 12 that covers the spherical core 4. A large number of dimples 14 are formed on the surface of the cover. Of the surface of the golf ball 2, a portion other than the dimples 14 is a land 16. The golf ball 2 includes a paint layer and a mark layer on the outside of the cover 12, but these layers are not shown.

The spherical core may have either a single layer structure or a multilayer structure. In the case of a multilayer structure, the core rubber composition of the present invention may be used in any layer. Further, the cover may have a structure of one or more layers, and may have a single layer structure or a multilayer structure of at least two layers. As the golf ball of the present invention, for example, a two-piece golf ball comprising a spherical core having a single layer structure and a single layer cover disposed so as to cover the spherical core; a spherical core having a multilayer structure and the spherical core; A multi-piece golf ball comprising a single-layer cover arranged to cover; a multi-piece golf ball having a single-layer spherical core and two or more layers of covers arranged to cover the spherical core A multi-piece golf ball having a multi-layered spherical core and two or more cover layers arranged to cover the spherical core; a spherical core and a rubber thread layer provided around the spherical core; and the yarn Examples thereof include a thread-wound golf ball having a cover disposed so as to cover the rubber layer. The present invention can be suitably used for golf balls having any of the above structures.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[Evaluation method of spherical core molded product]
(1) SANS measurement method A plate-like sample (core center sample, core surface sample) having a thickness of about 1 mm was attached to a sample holder in a state of equilibrium swelling with deuterated toluene, and the sample was irradiated with neutron beams at room temperature. The distance from the sample to the detector was 2.5 m, 10 m, and the absolute scattering intensity curve obtained from the focusing lens measurement was combined by the least square method. The combination of the three curves fixed the scattering intensity curve obtained from the measurement with a distance of 2.5 m from the sample to the detector, and shifted the scattering intensity curve obtained from the focusing lens measurement by 10 m. Curve fitting was performed on the obtained scattering intensity curve I _(q) using the above (Formula 1) to (Formula 5), and the fitting parameter G was obtained by the least square method. By using the scattering length density difference σ5.22 × 10 ¹⁰ (cm ⁻² ) of polybutadiene (scatterer, deuterated toluene equilibrium swelling), the scatterer (cluster of inertia radius R _{g 1} nm to 100 μm) per unit volume The number N was determined. With respect to the obtained value of N, the N value of the core surface sample / the N value of the core center sample was determined.

(SANS equipment)
SANS: SANS measuring device attached to beam line SANS-J of JRR-3 research reactor owned by Japan Atomic Energy Agency (measuring conditions)
Neutron beam wavelength: 6.5 mm
Neutron flux intensity of neutron beam: 9.9 × 10 ⁷ neutrons / cm ² / s
Distance from sample to detector: 2.5 m, 10 m (Note that in order to obtain further information on the small angle side, measurement using a focusing lens was performed under the condition of a distance of 10 m from the sample to the detector.)
(Detector)
2-dimensional detector ⁽³ the He two-dimensional detector and the two-dimensional photomultiplier + ^ZnS / 6 LiF detectors)

(2) Core hardness JIS-C hardness measured in the surface part of the spherical core was used as the surface hardness of the core using a spring type hardness meter C type specified in JIS-K 6301, and the spherical core was cut into a hemisphere, The JIS-C hardness measured at the center of the cut surface was taken as the center hardness of the core. From the obtained value, the surface hardness of the core−the center hardness of the core was calculated.

[Manufacture of spherical core molded products]
According to the formulation shown in Table 1, the mixture was kneaded with a Banbury kneader and a roll kneader, and then the kneaded material was press molded at 170 ° C. for 20 minutes to obtain a spherical core molded product of a golf ball.

A cylindrical test piece having a radius of 3 mm and a thickness of 1 mm was cut out from the center of the spherical core molded product and used as a core center sample. Further, a cylindrical test piece having a radius of 3 mm and a thickness of 1 mm was cut out so that the circumferential portion was in contact with the surface of the spherical core molded product, and used as a core surface sample.
The obtained core center sample and core surface sample were evaluated by the SANS measurement method, and the spherical core molded product was evaluated for the core hardness.

[Golf Ball Evaluation Method]
(1) A flying head manufactured by True Temper Co., Ltd. A metal head # W1 driver (XXIO S 11 degrees) was attached, and a spherical core was hit at a head speed of 40 m / sec. Distance (m)) was measured. The measurement was performed 10 times for each golf ball, and the average value was defined as the flight distance of the golf ball. The larger the value, the higher the flight distance performance.

[Production of golf balls]
(1) Preparation of core A rubber composition having the composition shown in Table 1 was kneaded by a kneading roll, and heated and pressed in an upper and lower mold having hemispherical cavities at 170 ° C. for 20 minutes to form a spherical core having a diameter of 39.8 mm. Obtained.

(2) Production of Cover Next, the cover material having the composition shown in Table 2 was extruded by a biaxial kneading type extruder to prepare a pellet-shaped cover composition. Extrusion was performed with a screw diameter of 45 mm, a screw speed of 200 rpm, and a screw L / D-35. The blend was heated to 150-230 ° C. at the die position of the extruder. The obtained cover composition was injection-molded on the spherical core obtained as described above to a thickness of 1.5 mm to produce a golf ball having a spherical core and a cover covering the core. .
The flying distance was evaluated for each manufactured golf ball.

BR730: made by JSR, high cis polybutadiene (cis-1,4-bond content = 96 mass%, 1,2-vinyl bond content = 1.3 mass%, Mooney viscosity (ML _{1 + 4} (100 ° C.)) = 55, molecular weight distribution (Mw / Mn) = 3)
Sunseller SR: Sanshin Chemical Co., Ltd. zinc acrylate (10% by mass stearic acid coating product)
Park mill D: Dicumyl peroxide TN manufactured by NOF Corporation TN: 2-thionaphthol DPDS manufactured by Tokyo Chemical Industry Co., Ltd. Diphenyl disulfide 2,6-DCTP manufactured by Sumitomo Seika Co., Ltd. 2,6-dichlorothiophenol octane manufactured by Tokyo Chemical Industry Co., Ltd. Zinc acid: Made by Mitsuwa Chemicals (purity 99% or more)
Zinc laurate: Made by Mitsuwa Chemicals (purity 99% or more)

High Milan 1605: Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui DuPont Polychemical Co., Ltd. High Milan 1706: Zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin Elastollan XNY97A manufactured by Mitsui DuPont Polychemical Co. BASF Japan thermoplastic polyurethane elastomer

From Table 1, the spherical core molded product of the comparative example has N (core surface) / N (core center) of less than 2.0, whereas the molded product of the example added with zinc octoate or zinc laurate is It was 2.0 or more, and it was clear that the sample had a sufficient hardness distribution. Further, for the molded product of the example, a difference in hardness was hardly observed in the spring type hardness tester, whereas a difference was observed in the SANS measurement. According to this method, it is difficult to evaluate the difference in hardness due to the sample. It became clear that even a thing can measure a minute difference accurately. Further, a good correlation was found between the N value of each spherical core molded product and the flight performance of golf balls made using each rubber composition for the spherical core.

Claims (14)

A golf ball having a spherical core composed of at least one layer and at least one cover covering the spherical core,
At least one layer of the spherical core is formed of a rubber composition;
With respect to the X-ray scattering measurement or scattered obtained by neutron scattering intensity curve _{I (q),} the scattering radius of gyration _{R g} obtained by curve fitting by the following formulas (1) to (5) is 1nm~100μm For the number N per unit volume of the body,
A golf ball having an outermost number N of the rubber composition / an innermost number N of the rubber composition of 2.0 or more.

The golf ball according to claim 1, wherein the X-ray scattering measurement is a small-angle X-ray scattering measurement, and the neutron scattering measurement is a small-angle neutron scattering measurement. The golf ball according to claim 1, wherein q is measured in a region where q represented by (Formula 1) is 10 nm ⁻¹ or less. The rubber composition includes (a) a base rubber, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof as a co-crosslinking agent, (c) a crosslinking initiator, (D) When it contains an acid and / or a salt thereof and (b) contains only an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, it further comprises (e) a metal compound The golf ball according to claim 1, comprising: The golf ball according to claim 4, wherein the rubber composition contains 0.5 to 30 parts by mass of (d) an acid and / or a salt thereof with respect to 100 parts by mass of the base rubber (a). 6. The golf ball according to claim 4, wherein the acid (d) and / or salt thereof has 1 to 13 carbon atoms. The golf ball according to claim 4, wherein the (d) acid and / or salt thereof is a carboxylic acid and / or salt thereof. The golf ball according to claim 7, wherein the carboxylic acid and / or salt thereof is a fatty acid and / or a fatty acid salt. The golf ball according to claim 8, wherein the fatty acid and / or the fatty acid salt is a fatty acid zinc salt. The golf ball according to claim 4, wherein the rubber composition further contains (f) an organic sulfur compound. (F) The golf ball according to claim 10, wherein the organic sulfur compound is a thiophenol, a diphenyl disulfide, a thionaphthol, a thiuram disulfide, or a metal salt thereof. The golf ball according to claim 10, wherein the rubber composition contains 0.05 to 5 parts by mass of (f) an organic sulfur compound with respect to 100 parts by mass of (a) the base rubber. The rubber composition is (b) 15 to 50 parts by mass of (b) α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof per 100 parts by mass of the base rubber. The golf ball according to claim 4, which is contained. The golf ball according to claim 4, wherein the rubber composition contains (b) a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent.

Images