WO2012111437A1

WO2012111437A1 - Golf ball

Info

Publication number: WO2012111437A1
Application number: PCT/JP2012/052320
Authority: WO
Inventors: 美文宮田; 中　裕里; 二宮　徳数; 藤川　良宏; 雅史宇田; 淳之介和田
Original assignee: 美津濃株式会社
Priority date: 2011-02-17
Filing date: 2012-02-01
Publication date: 2012-08-23
Also published as: US20120214614A1; JPWO2012111437A1; TW201238625A

Abstract

The invention addresses the problem of providing a golf ball with excellent scratch resistance and spin performance as well as having good resilience. The ball is provided with a core (3), an intermediate layer (5) formed so as to cover the core (3), an inner cover (7) formed so as to cover the intermediate layer (5), and an outer cover (15) formed so as to cover the inner cover (7). The outer cover (15) comprises a neutralized product containing an ethylene-unsaturated carboxylic acid-alkyl (meth)acrylate terpolymer with a weight average molecular weight (Mw) of 80000 - 500000, and an ethylene-acrylic acid or ethylene-methacrylic acid copolymer with a weight average molecular weight (Mw) of 2000 - 30000. The inner cover (7) also comprises said blended neutralized product.

Description

Golf ball

The present invention relates to a golf ball.

An ionomer resin or a polyurethane resin is generally used as a main component of the material constituting the outer cover which is the outermost layer of the golf ball. Of these, golf balls using polyurethane resin (urethane golf balls) are characterized by superior scratch resistance and spin performance, and are therefore mainly used as golf balls for advanced players and professionals. (For example, refer to Patent Document 1).

JP 2004-97581 A

However, the above-described polyurethane golf ball has a drawback that it has a low rebound and a low initial velocity compared to a golf ball (ionomer golf ball) using an ionomer resin as an outer cover. In order to improve this resilience, a technology to form the outer cover thinly has been developed, but the resilience is still not sufficient compared to the ionomer golf ball, and a technology to form the outer cover thin is necessary. Therefore, there were problems in mass productivity and cost. Therefore, an object of the present invention is to provide a golf ball that has excellent scratch resistance and spin performance and good resilience.

A golf ball according to the present invention includes a core, an intermediate layer formed to cover the core, an inner cover formed to cover the intermediate layer, and an outer cover formed to cover the inner cover The outer cover includes an ethylene-unsaturated carboxylic acid-alkyl (meth) acrylate terpolymer having a weight average molecular weight (Mw) of 80000 to 500,000, and a weight average molecular weight (Mw) of 2000 to The inner cover includes a neutralized product of 30000 ethylene-acrylic acid or ethylene-methacrylic acid copolymer, and the inner cover includes a neutralized product of the outer cover.

According to this golf ball, since the ionomer resin is used for the outer cover, the resilience is superior to those using polyurethane resin. Moreover, since the ionomer resin used for the outer cover is also included in the inner cover, the adhesion between the outer cover and the inner cover can be improved, and as a result, the scratch resistance can be improved. It is possible to improve the resilience by reducing the energy loss of the hitting force by the driver. Further, since the ionomer resin is excellent in resilience, the hardness can be lowered while ensuring resilience, and the spin performance can be improved. The neutralized product may be a mixture of an ethylene-unsaturated carboxylic acid-alkyl (meth) acrylate terpolymer and a copolymer neutralized with a base, or an ethylene-unsaturated product. A copolymer obtained by neutralizing a saturated carboxylic acid-alkyl (meth) acrylate terpolymer may be blended, or an ethylene-unsaturated carboxylic acid- (meth) may be obtained by neutralizing the copolymer. A mixture of alkyl acrylate terpolymers may also be used. Moreover, about the said weight average molecular weight (Mw), it measures by GPC and calculates | requires polystyrene conversion molecular weight distribution.

In the above golf ball, the Shore D hardness of the inner cover is preferably about 62 to 72, more preferably about 64 to 70. Thereby, the followability with respect to a deformation | transformation of an outer cover improves an inner cover, and scratch resistance improves more. The Shore D hardness of the outer cover is preferably about 50 to 57. The Shore D hardness of the inner cover and outer cover is the hardness of the surface with the inner cover formed on the intermediate layer and the surface with the outer cover formed on the inner cover, respectively. Measure and measure the location without dimples on the outer cover. In addition, regarding the Shore D hardness of the core and the intermediate layer, which will be described later, the hardness of the surface where the core is formed and the surface where the intermediate layer is formed on the core are measured. Specifically, the core measures the hardness of the upper end portion on the radially outer side of the rib. However, when the plane of the portion is not sufficiently taken, the hardness of the surface portion of the portion other than the rib of the core may be measured. This is because the temperature and pressure at the time of forming the core are normally applied to the core ribs and portions other than the ribs in the same manner, so that the hardness is equal at the upper end portion of the ribs and the surface portion of the other portions. In addition, with respect to the intermediate layer, a portion without a rib is measured. The surface hardness is measured according to JIS K7215.

The inner cover layer thickness is preferably 0.9 mm to 1.2 mm, and the outer cover layer thickness is preferably 0.9 mm to 1.2 mm. Thus, the outer cover and inner cover layer thicknesses are reduced. As a result, the core and the intermediate layer can be enlarged. This makes it difficult to spin when using the driver, improves resilience, and increases the flight distance. At this time, the diameter of the sphere composed of the intermediate layer and the core is preferably about 37.5 mm to 39.5 mm.

Further, the core includes a spherical main body portion and a plurality of ribs formed on the surface of the main body portion, and the intermediate layer can be configured to be filled in a recess surrounded by the ribs. And by making this rib harder than the intermediate layer, the movable range in which the intermediate layer of the hit part is deformed in the direction along the spherical surface is limited by the rib, so the impact force is in the direction along the spherical surface. Dispersion can be prevented. As a result, the striking force applied to the intermediate layer can be efficiently transmitted to the main body of the core, so that high resilience can be obtained and soft feeling at the time of striking can be obtained.

In addition, by setting the edge angle of the plurality of dimples formed on the surface of the outer cover to 6.2 deg to 7.2 deg, the scratch resistance can be further improved.

According to the present invention, it is possible to provide a golf ball having excellent scratch resistance and spin performance and good resilience.

FIG. 1 is a cross-sectional view showing an embodiment of a golf ball according to the present invention. FIG. 2 is a perspective view showing a core of the golf ball in FIG. FIG. 3 is a view for explaining the edge angle of the dimple of the golf ball according to the present embodiment. FIG. 4 is a perspective view showing another example of the core of FIG. FIG. 5 is a side view of the core of FIG. FIG. 6 is a side view of an essential part showing another example of the core of FIG. FIG. 7 is a side view showing another example of the core of FIG. FIG. 8 is a side view showing another example of the core of FIG. FIG. 9 is a side view showing another example of the core of FIG. FIG. 10 is a view showing an example of a golf ball manufacturing method using the core shown in FIG. FIG. 11 is a view showing another example of a golf ball manufacturing method using the core shown in FIG. FIG. 12 is a cross-sectional view showing another embodiment of a golf ball according to the present invention. FIG. 13 is a cross-sectional view showing a golf ball according to the present invention when hit.

Hereinafter, an embodiment of a golf ball according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, a golf ball 1 according to this embodiment is a multi-piece golf ball in which a core 3 is covered with an intermediate layer 5, an inner cover 7, and an outer cover 15. The diameter of the golf ball 1 needs to be 42.67 mm or more according to the rules (see R & A and USGA). However, in consideration of aerodynamic characteristics and the like, it is preferable to make the ball diameter as small as possible, for example, 42.7 mm to 42.9 mm. Each of the ribs 11 is composed of a rubber composition, and the core 3 is composed of a spherical main body 9 and three ribs (projections) 11 integrally formed on the surface thereof, as shown in FIG. Has been. The ribs 11 are formed on the surface of the body portion 9 and extend along great circles orthogonal to each other. The ribs 11 form eight recesses 13 on the surface of the main body portion 9.

The diameter of the main body 9 is preferably 34.0 mm to 36.0 mm, and more preferably 34.5 mm to 35.5 mm. The height of the rib 11 is preferably 1.5 mm to 2.5 mm, and more preferably 1.75 mm to 2.25 mm. With this size, the core 3 preferably has a surface Shore D hardness of 50 to 60, and more preferably 53 to 58. By setting the hardness of the core 3 within the above range, it is possible to ensure a good feel while ensuring sufficient resilience.

As shown in FIGS. 1 and 2, each rib 11 is formed in a trapezoidal cross section so that its width increases as it goes to the main body 9 side. The width a of the radially outer upper end portion of the rib 11 is preferably 1.5 mm to 2.5 mm, and the width b of the radially inner lower end portion of the rib 11 is 3.0 mm to 6.0 mm. It is preferable to do. Although it may be outside this range, by setting the lower limit of each end of the rib 11 in this way, when filling the intermediate layer 5 at the time of manufacture, filling of the intermediate layer 5 resulting from the pressure of mold clamping The rib 11 can be prevented from being deformed by pressure. As a result, the core 9 can be accurately held at the center of the mold.

The intermediate layer 5 is composed of a rubber composition or an elastomer, covers the surface of the core 3, and has a substantially spherical outer shape. As shown in FIG. 1, the intermediate layer 5 has a layer thickness substantially the same as the height of the ribs 11 and is filled in eight concave portions 13 surrounded by the ribs 11, and the tips of the ribs 11 are exposed from the surface of the intermediate layer 5. is doing. The hardness of the mid layer 5 is preferably lower than the hardness of the core 3 in order to obtain a soft feeling upon impact and to improve the spin performance in the approach. Specifically, the Shore D hardness of the surface of the intermediate layer 5 is preferably 47 to 57, and more preferably 50 to 55. At this time, the hardness of the intermediate layer 5 is preferably about 1 to 6 lower than the hardness of the core 3 in Shore D hardness.

The inner cover 7 is made of an elastomer and covers the tip of the rib 11 and the intermediate layer 5. The layer thickness of the inner cover 7 is preferably 0.7 mm to 1.5 mm, and more preferably 0.9 mm to 1.2 mm. The hardness is preferably 62 to 72, and more preferably 64 to 70, on the surface of the inner cover 7. The flexural modulus of the material of the inner cover 7 is preferably 300 to 500 Mpa, more preferably 350 to 450 Mpa. In addition, the measuring method of a bending elastic modulus is based on JISK7016.

The outer cover 15 is made of an elastomer, covers the inner cover 7, and has predetermined dimples (not shown) formed on the surface thereof. The layer thickness of the outer cover 15 is preferably 0.7 mm to 1.5 mm, and more preferably 0.9 mm to 1.2 mm. The Shore D hardness is preferably 50 to 57, more preferably 51 to 56. The layer thickness of the outer cover 15 is a value obtained by measuring the distance from an arbitrary point on the outermost side in the radial direction where no dimples are formed to an arbitrary point in contact with the intermediate layer along the normal line. Regarding the layer thickness, the total layer thickness of the inner cover 7 and the outer cover 15 is preferably 1.5 mm to 3 mm, more preferably 1.7 mm to 2.4 mm. The outer cover 15 is measured using a viscoelasticity tester (viscoelastic spectrometer) under the conditions of a frequency of 10 Hz, a dynamic strain of 5%, a tensile mode, and a temperature increase rate of 4 ° C./min. (Tan δ) is preferably 0.4 or less. The lower the loss factor (tan δ), the better the resilience and the tendency to increase as the dynamic strain increases. However, even when the dynamic strain is 5%, the loss factor (tan δ) is 0.1 to 0.4. A ball excellent in resilience and spin performance can be realized.

Next, dimples formed on the outer cover 15 will be described. As the dimple shape, a circular shape, various polygonal shapes, an elliptical shape, or the like can be used alone or in combination. For example, in the case of a circular dimple, the diameter can be set to 3.5 mm to 5.0 mm. The number of dimples is preferably 250 to 450. If the number of dimples is too large, the ball trajectory may be lowered and the flight distance may be reduced. On the other hand, if the number of dimples is too small, the trajectory becomes high and the flight distance may be reduced. Further, the area ratio of dimples to the spherical surface of the golf ball is preferably 70% or more, and more preferably 75% or more. The dimple edge angle α is preferably 6.0 degrees to 7.5 degrees, and more preferably 6.2 degrees to 7.2 degrees. By setting it as such a lower limit, it is possible to prevent the lift from becoming too large, and to maintain good flight distance performance. By setting the upper limit, it is possible to maintain good scratch resistance. As shown in FIG. 3, the dimple edge angle α is an arc of the dimple from the intersection R of the straight line L2 and the dimple D, which is offset by 0.015 mm below the straight line L1 connecting both ends of the dimple D, toward the dimple edge. The angle α between the tangent line T drawn along the line L1 and the straight line L1.

Subsequently, materials constituting each member of the golf ball 1 will be described in detail. The core 3 can be manufactured from a known rubber composition containing a base rubber, a cross-linking material, a metal salt of an unsaturated carboxylic acid, a filler, and the like. As the base rubber, natural rubber, polyisobrene rubber, styrene butadiene rubber, EPDM, or the like can be used, but it is particularly preferable to use high cis polybutadiene having 80% or more of cis 1,4 bonds.

As the crosslinking agent, for example, organic peroxides such as dicumyl peroxide and t-butyl peroxide can be used, and it is particularly preferable to use dicumyl peroxide. The amount is 0.3 to 5 parts by weight, preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the base rubber.

As the metal salt of the unsaturated carboxylic acid, it is preferable to use a metal salt of a monovalent or divalent unsaturated carboxylic acid having 3 to 8 carbon atoms such as acrylic acid or methacrylic acid, but zinc acrylate is used. Then, the resilience performance of the ball can be improved, which is particularly preferable. The blending amount is preferably 10 to 40 parts by mass with respect to 100 parts by mass of the base rubber.

As the filler, those usually blended in the core can be used, and for example, zinc oxide, barium sulfate, calcium carbonate, etc. can be used. The blending amount is preferably 2 to 50 parts by mass with respect to 100 parts by mass of the base rubber. Moreover, you may mix | blend an anti-aging agent or a peptizer as needed.

The intermediate layer 5 is composed of a rubber composition or an elastomer as described above, but when composed of a rubber composition, it can be composed of the same components as the core 3 described above.

When the intermediate layer 5 is composed of an elastomer, for example, styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene- Styrenic thermoplastic elastomers such as ethylene-propylene-styrene block copolymer (SEPS); olefinic thermoplastic elastomers with polyethylene or polypropylene as hard segments and butadiene rubber, acrylonitrile butadiene rubber, or ethylene / propylene rubber as soft segments; Vinyl chloride with crystalline polyvinyl chloride as the hard segment and amorphous polyvinyl chloride or acrylonitrile butadiene rubber as the soft segment -Based thermoplastic elastomer; polyurethane-based thermoplastic elastomer with polyurethane as hard segment and polyether or polyester as soft segment; polyester-based thermoplastic elastomer with polyester as hard segment and polyether or polyester as soft segment; polyamide as hard A polyamide-based thermoplastic elastomer having a segment and a polyether or polyester soft segment; an ionomer resin or the like can be used.

The outer cover 15 is preferably made of ionomer resin as a main component. Examples of the ionomer resin include an ethylene-unsaturated carboxylic acid-alkyl (meth) acrylate terpolymer having a weight average molecular weight (Mw) of 80000 to 500,000 and a weight average molecular weight (Mw) of 2000 to 30000. Mention may be made of neutralized products containing ethylene-acrylic acid or ethylene-methacrylic acid copolymers and metal salts. Examples of the metal salt include magnesium hydroxide.

The reason for using such a neutralized product is as follows. That is, a copolymer having a high weight average molecular weight is excellent in physical properties such as resilience and scratch resistance, but has poor moldability. Therefore, a low weight average molecular weight copolymer having good fluidity is blended. These two materials have a similar structure and high compatibility, and by including each of them, a material excellent in moldability, resilience and scratch resistance can be obtained. In addition, by adding a metal salt, the neutralization degree of the carboxylic acid is increased, thereby improving the resilience.

Here, the weight average molecular weight (Mw) in the neutralized product is calculated in terms of polystyrene in GPC (gel permeation chromatography), but the binary copolymer and ternary copolymer are: Since it cannot be measured as it is, the sample is dissolved by adding hydrochloric acid in a xylene-butanol mixed solvent and heating. And what is necessary is just to measure what reprecipitated the solution in methanol.

The neutralized product may be a mixture of an ethylene-unsaturated carboxylic acid-alkyl (meth) acrylate terpolymer and a copolymer, which is neutralized with a metal salt. A copolymer obtained by mixing an unsaturated carboxylic acid-alkyl (meth) acrylate terpolymer neutralized with a metal salt with a copolymer, or a copolymer neutralized with a metal salt may be mixed with an ethylene-unsaturated copolymer. A mixture of a saturated carboxylic acid-alkyl (meth) acrylate terpolymer may be used. The main component of the outer cover 15 is a material that has the largest weight among the materials included in the outer cover 15. For example, the main component of the outer cover 15 is the weight of the entire outer cover 15. As 100% by weight, it is preferable to contain about 60% to 100% by weight. As specific examples of the ionomer resin used as the main component of the outer cover 15, for example, HPC AD1043 manufactured by DuPont or HPC AD1022 can be preferably used. Further, the outer cover 15 may contain other ionomer resin. More specifically, the outer cover 15 may include Hi-Millan 1706, 1605 manufactured by Mitsui DuPont Polychemical Co., Ltd. or Surlyn 9910, 8940, 8150, 8120, 8320 manufactured by DuPont. And so on.

The inner cover 7 preferably contains about 10% to 50% by weight, preferably about 15% to 45% by weight, of the ionomer resin that is the main component of the outer cover 15 described above. In addition, the inner cover 7 also contains an ionomer resin, and examples thereof include an ethylene- (meth) acrylic acid binary copolymer having an acid content of 10% or more. Are Mitsui DuPont's High Milan 1706, 1605, DuPont's Surlyn 9910, 8940, 8150, HPF1000, and HPF2000. Thus, when the inner cover 7 includes the main component of the outer cover 15 in the above range, the adhesion between the inner cover 7 and the outer cover 15 can be improved.

Since the golf ball 1 according to the present embodiment configured as described above uses an ionomer resin instead of a urethane resin as a main component of the outer cover 15, first, the resilience is excellent. High spin performance can be exhibited by lowering the hardness while ensuring resilience due to its excellent properties. Further, since the material of the inner cover 7 contains the main component of the outer cover 15, the adhesion between the outer cover 15 and the inner cover 7 can be improved, and the inner cover can be deformed when hitting. 7 follows and deforms. As a result, the scratch resistance can be improved, and the resilience can be further improved by reducing the energy loss of the striking force by a driver or the like. Further, since the material of the inner cover 7 contains the main component of the soft outer cover 15, the hardness of the inner cover 7 can be lowered, and thereby the spin performance can be improved by the approach. Here, by increasing the diameter of the sphere composed of the core 3 and the intermediate layer 7, it is possible to prevent the resilience performance from being lowered.

Moreover, if the hardness of the inner cover 7 is lowered and the spin performance in the approach is improved as described above, the spin rate increases with a general golf ball even when shot with the driver, and the flight distance performance with the driver. In the present invention, as described below, the core 3 is provided with the rib 11 and the recessed region surrounded by the rib 11 is filled with the intermediate layer 5 in the present invention. Spin can be suppressed by using the restoring force of the rib 11 deformed during the shot.

More specifically, as shown in FIG. 13A, in this golf ball, the intermediate layer 5 is filled in the recessed area surrounded by the ribs 11, so that the ribs 11 are enlarged by the hitting by the club C. Deform. Due to this impact, a stress that generates back spin B acts on the ball itself. When the ball leaves the club C, as shown in FIG. 13B, the deformation of the rib 11 is restored, so that the force F acts in the direction of canceling out the backspin B by this restoration. As a result, the spin is reduced and the jump angle is increased, so that the flight distance can be further extended. In particular, in the present embodiment, the rib 11 is not a mere protrusion, but is configured as a wall surrounding the periphery of the intermediate layer 5, so that the force when the rib 11 is restored depends on the entire wall 5. Acts greatly from the surroundings, and this promotes a force F opposite to the backspin B. Therefore, the backspin amount is reduced and the flight distance can be greatly increased. Such an effect becomes prominent particularly when a club aiming at a flight distance such as a driver is used. In FIG. 13, the current state is represented by a solid line, and the state immediately before is represented by a broken line. Thereby, it is possible to realize both the spin performance in the approach and the flight distance performance in the driver.

By the way, the above-described rib can be formed in various shapes, but from the viewpoint of efficiently forming the intermediate layer at the time of manufacture, it is preferable to form the following notch in the rib. FIG. 4 is a perspective view of the core in which a notch is formed, and FIG. 5 is a cross-sectional view of FIG. As shown in FIGS. 4 and 5, the notch 24 is formed to have a bottom surface 24 a extending along a tangential plane H passing through the intersection point P of the great circle. That is, the notch 24 is formed by cutting the rib 11 by the tangential plane H. By forming the notches 24 in this way, the four recesses 13 arranged around the intersection point P of the great circle communicate with each other. As will be described later, the intermediate layer material is passed through the notches 24 as shown in FIG. 13 can be easily distributed. In this case, as shown in FIG. 6, the plane H1 inclined by 1 ° to 3 ° from the tangential plane H toward the center of the rib 11, that is, the normal n of the main body 9 passing through the intersection P and 91 ° to 93 in plan view. You may make it form the bottom face 24a of the notch part 24 along the plane which makes the angle of (degree). If it does in this way, the said inclination turns into a draft, for example, when a shaping | molding die is comprised from 2 type | molds, an upper mold | type and a lower mold | type, the core 3 can be easily taken out from a shaping | molding die.

Further, when the notch 24 is formed as described above, as shown in FIG. 5, the arc direction of the upper end where the notch 24 is not formed in each arc section S delimited by each intersection P in the rib 11. It is preferable that the length L is 10 mm or more.

Further, as shown in FIG. 7, the notch portion 24 may be formed to have a bottom surface 24 a that passes through the middle of the height direction of the rib 11 and extends along the plane H <b> 2 perpendicular to the normal line n. In this case, in order to smoothly flow the intermediate layer 5 between the recesses 13, the notch 24 is formed by setting the distance D from the upper end of the virtual rib 11 to the bottom surface 24 a to 1.2 mm or more when there is no notch 24. It is preferable to do. Further, the length L is preferably 10 mm or more as described above. Further, in this case, similarly to FIG. 6, the draft 24 can be formed by forming the bottom surface 24a of the notch 24 along a plane which forms an angle of 91 ° to 93 ° with the normal n.

Also, a notch can be provided in the middle of each arc section S of the rib 11. That is, as shown in FIG. 8A, two bottom surfaces 25a extending from one point on the normal line m of the main body 9 passing through the center point Q in the arc direction of the arc section S to the intersection P side on both ends are provided. The notch 25 can also be formed. In this case, it is preferable that the bottom surface 25a and the normal line m form an angle of 45 to 48 degrees when viewed from the front. If it does in this way, as above-mentioned, the core 3 can be easily extracted from a shaping | molding die. However, if the angle is larger than 48 degrees, the length L of the rib in the arc direction is not preferable. In this case, the depth D of the notch 25 is preferably 1.2 mm or more. Although outside this range is possible, by setting the above range, the material for the intermediate layer can be smoothly distributed between the recesses 13. The depth D of the notch 25 refers to the distance from the upper end of the virtual rib 11 to the deepest part of the notch 25 when there is no notch 25.

Alternatively, as shown in FIG. 8B, two planes in which the cutout portion 25 extends from one point on the normal line m of the main body portion 9 passing through the center point Q in the arc direction of the arc section S to the intersection P side on both ends. Can be formed so as to have a side surface 25b along the main body portion 9 and an arc-shaped bottom surface 25c along the main body portion 9. The angle formed between the side surface 25b and the normal line m is 45 ° to 48 ° in plan view in consideration of the draft, as in FIG. 8A. The bottom surface 25c can also be formed so as to pass through an intermediate portion of the rib 11 in the height direction. However, also in this case, the depth D of the notch is preferably 1.2 mm or more. In addition, two or more cutout portions 25 can be provided in the middle portion of the arc section S as long as the shape can be easily removed.

Further, as shown in FIG. 9, the arc section S may have both the notch 24 shown in FIG. 5, FIG. 6, or FIG. 7 and the notch 25 shown in FIG. As shown in FIGS. 8 and 9, the length L (= L1 + L2) of the portion of the arc section S where the notch is not formed is preferably 10 mm or more.

In the above embodiment, the layer thickness of the intermediate layer 5 and the height of the rib 11 are the same, but it is not necessarily the same. For example, the layer thickness of the intermediate layer 5 is made larger than the height of the rib 11. May be. However, it is desirable that the height is slightly higher than the height of the rib 11, for example, within 0.3 mm.

Next, an example of a method for manufacturing the golf ball configured as described above will be described with reference to the drawings. Below, the manufacturing method in the case of forming an intermediate | middle layer with a rubber composition is demonstrated. 10 and 11 are views showing a method for manufacturing a four-piece golf ball having the core shown in FIG.

First, the core is molded. Here, a predetermined amount of unvulcanized rubber composition is placed in a mold. Deploy. This rubber composition is obtained by blending the above-described base rubber, a crosslinking agent, a metal salt of an unsaturated carboxylic acid, a filler, and the like, and kneading them with a kneader such as a panbury mixer or a roll. Then, this rubber composition is press molded at 130 ° C. to 180 ° C. to form the core 3 shown in FIG.

Next, as shown in FIG. 10, the intermediate layer 5 is formed by press molding. As shown in FIG. 10A, the mold for forming the intermediate layer includes an upper mold 43 and a lower mold 45 having a hemispherical recess 41. The recesses 41 of the upper mold 43 and the lower mold 45 are finished with a rough surface in the same manner as the core molding die, and a plurality of concave burrs 49 are formed around the recesses 41.

Then, as shown in FIG. 10A, an unvulcanized rubber composition 61 is inserted into the recess 41 of the lower mold 45, and the rubber composition 61 is disposed on the upper portion of the core 3 formed as described above. The core 3 is disposed between the upper mold 43 and the lower mold 45. Subsequently, as shown in FIG. 10B, the upper die 43 and the lower die 45 are brought into contact with each other, and the rubber composition 61 is fully vulcanized at 130 ° C. to 180 ° C. for 5 minutes to 25 minutes to perform press molding. The intermediate layer 5 is formed.

At this time, the rubber composition 61 disposed in the upper part of the core 3 and the concave part 41 of the lower mold 45 is filled into the concave part 13 while being pressed onto the surface of the core 3. As described above, the adjacent recesses 13 communicate with each other through the notch 24, so that the rubber composition reaches all the recesses and is uniformly filled. In addition, the intermediate | middle layer 5 can also be shape | molded by injection molding, for example using a metal mold | die as shown in FIG. In this case, if there is no notch portion, the rubber composition is not uniformly filled unless gates are provided for all the recesses 13, but by providing the notches 24 in the rib 11 as described above, the

molds

47 and 48 are provided. Even after the core 3 is inserted into the rubber composition, even if the rubber composition is injected from one gate 50, the rubber composition is uniformly filled into the concave portions 13 through the notches 24 in the same manner as described above.

Thus, when the forming of the intermediate layer 5 is completed, the core 3 covered with the intermediate layer 5 is removed from the mold. Subsequently, the inner cover 7 is press-molded or injection-molded on the surface of the intermediate layer 5. Further, when the outer cover is covered on the surface of the inner cover so as to have predetermined dimples by press molding or injection molding, the golf ball according to the present embodiment can be obtained.

Thus, since the notch 24 is formed in the rib 11 and the adjacent recessed part 13 is connected via the notch 24, even if the rubber composition 61 is pressed from any position on the surface of the core 3, all It fills in the recesses 13 of the filler. Therefore, the intermediate layer 5 can be coated on the core 3 by one-step press molding, and as a result, the manufacturing time can be greatly shortened.

In the above description, a method for manufacturing a golf ball having an intermediate layer in which a notch is formed has been described. However, a golf ball having no notch can be manufactured by a substantially similar method. However, when there is no notch, it is necessary to place the material so that each recess is filled with the material of the intermediate layer and press-mold, or in the case of injection molding, it is necessary to provide multiple gates corresponding to each recess There is.

As mentioned above, although one embodiment of the golf ball concerning the present invention was shown, the golf ball concerning the present invention is not limited to this, and various changes are possible unless it deviates from the meaning. For example, in the above embodiment, three ribs are formed along the great circle of the main body, but the form of the ribs is not particularly limited, and the shape, number, and position thereof can be changed as appropriate. That is, it is only necessary to form a recess filled with the intermediate layer by the rib.

Moreover, although the said embodiment demonstrated as what the rib 11 was formed in the core 3, as shown in FIG. 12, the core 3 should be comprised only with the spherical main-body part 9 without forming a rib. You can also.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In addition, this invention is not limited to the following Example. Here, 21 types of golf balls according to examples of the present invention are compared with five types of golf balls according to comparative examples. Each Example and Comparative Example except Example 21 has a shape as shown in FIG. 1, and the golf ball according to Example 21 has a shape as shown in FIG.

Table 1 below shows the shape and material of each golf ball. All of these golf balls were manufactured with a diameter of about 42.70 mm, a weight of about 45.50 g, and a dimple count of 366. The hardness difference in Table 1 is the hardness difference between the core and the intermediate layer, and the total thickness is the total thickness of the inner cover and the outer cover. The diameter of the intermediate layer is the diameter of the intermediate layer including the core. Further, “HPC” means DuPont's Ionomer HPC AD1022, “8940” means DuPont's Surlyn 8940, “8150” means DuPont's Surlyn 8150, and “8320” means DuPont's Surlyn 8320. Moreover, the ratio of each material shows the ratio of weight%.

Table 2 below shows the composition of the material constituting the core of each golf ball, Table 3 shows the composition of the material constituting the intermediate layer of each golf ball, and the numerical values in Tables 2 and 3 indicate parts by mass. ing. Incidentally, as the cis 1,4-polybutadiene in Tables 2 and 3, trade name BR-01 manufactured by Nippon Synthetic Rubber Co., Ltd. was used. In addition, as zinc oxide, manufactured by Hakusuitec Co., Ltd., trade name: baked zinc white, manufactured by Sakai Chemical Industry Co., Ltd. as barium sulfate, trade name: barium sulfate fertilizer, as an anti-aging agent, Kawaguchi Chemical Co., Ltd. Product name Antage W-400 2,2'-Methylene bis- (4-metyhl-6-tert-butyl phenol), zinc acrylate, manufactured by Kawaguchi Chemical Industry Co., Ltd., trade name Actor ZA, Dicumyl As a peroxide, Nippon Oil & Fats Co., Ltd., trade name “Park Mill D” was used. The molding conditions were a mold temperature of 160 ° C. and a crosslinking time of 6 minutes.

Table 4 shows that the golf ball according to each of the examples and the comparative example is No. 1 wood (1W: MP Craft 425 manufactured by Mizuno Co., Ltd., loft angle 9.5 °) by a hitting robot (SHOT ROBO v manufactured by Miyamae Co., Ltd.). Blow using shaft QUAD 6 Butt standard length 45 inches, shaft hardness S) and sand wedge (SW: Mizuno Corporation MP T11, 56 ° nickel chrome plating, shaft dynamic gold Wedge flex length 35.25 inches) The test shows the results of measuring the initial ball speed, flight distance (carry), spin rate, scratch score, and hit feeling. Here, the head speed of No. 1 wood was 43 m / s, and the head speed of the sand wedge was 17 m / s.

Regarding the number of scratched points in Table 4, the surface condition of the ball after the test with the above-mentioned sand wedge was visually confirmed, and a five-step evaluation (1: a striking trace such as a trace where the cover material was peeled off remained) 2: Large crusts / scratches are noticeable on the ball surface 3: Small crusts / scratches are seen on the ball surface 4: Slightly flaws are seen on the ball surface (to be confirmed with the naked eye) 5: Ball 5 people were able to go to the surface. The average value was used as the number of scratches in each example. The higher the score, the more difficult the ball is to be scratched, that is, a ball with good scratch resistance. In addition, a hit feeling test with 5 amateur seniors was performed on the sand wedge. In this hit feeling test, the test subject was evaluated on a five-point scale (1: very hard hit feeling, 2: hard hit feeling, 3: slightly hitting feel, 4: soft hit feeling, 5: very soft hit feeling) The average value is shown in Table 4 as the hit feeling value of each example. The coefficient of restitution was calculated from the ratio of the incident speed and the reflection speed when the ball hits the rigid plate with an air gun at a speed of 43.7 m / s. From the comparison between Examples 1 to 21 and Comparative Examples 1 to 5 shown in Table 4, it can be seen that all of the inner covers containing the main component HPC of the outer cover show good scratch resistance. It was.

DESCRIPTION OF SYMBOLS 1 Golf ball 3 Core 5 Intermediate layer 7 Inner cover 9 Main-body part 11 Rib 13 Recessed part 15 Outer cover

Claims

The core,
An intermediate layer formed to cover the core;
An inner cover formed to cover the intermediate layer;
An outer cover formed to cover the inner cover,
The outer cover comprises an ethylene-unsaturated carboxylic acid-alkyl (meth) acrylate terpolymer having a weight average molecular weight (Mw) of 80,000 to 500,000, and an ethylene-acrylic having a weight average molecular weight (Mw) of 2,000 to 30,000. A neutralized product comprising an acid or an ethylene-methacrylic acid copolymer,
The inner cover is a golf ball including the neutralized product.
The golf ball according to claim 1, wherein the Shore D hardness of the inner cover is 64 to 70.
The inner cover has a layer thickness of 0.9 mm to 1.2 mm,
The golf ball according to claim 1, wherein the outer cover has a layer thickness of 0.9 mm to 1.2 mm.
The core includes a spherical main body and a plurality of ribs formed on the surface of the main body.
The golf ball according to claim 1, wherein the intermediate layer is filled in a recess surrounded by the rib.
The golf ball according to claim 4, wherein the rib has a hardness higher than that of the intermediate layer.
The outer cover has a plurality of dimples formed on the surface,
6. The golf ball according to claim 1, wherein an edge angle of the dimple is 6.2 degrees to 7.2 degrees.