JP2000051394A - Multi-piece solid core golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball in which multi-piece solid core parts are formed of a rubber composition and by which a ball hit feeling is softened and lowering of repulsion is decreased. SOLUTION: This multi-piece solid core golf ball is so constructed that a solid core 3 of a multi-layer structure formed by covering an inner core 1 with outer cores 2 of one, two or more Layers is coated with a cover 4. The golf ball is characterized in that the diameter of the inner core is 6-18 mm, the JIS-A hardness of the inner core is 70 or less, and tanδ at 30 deg.C is 0.03 or less. Preferably, the JIS-C hardness of the outer core is 60-85, and the inner core is formed by crosslinking the base rubber with a resin cross linking agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an inner core comprising one layer or two layers.
More specifically, the present invention relates to a multi-piece solid core golf ball having a multi-layer solid core having a multi-layered outer core covered with a cover, and more particularly to a multi-piece solid core having an inner core and an outer core made of rubber. It relates to a golf ball.

[0002]

2. Description of the Related Art In recent years, two-piece solid core golf balls having a rubber core covered with a thermoplastic cover containing an ionomer resin have been widely used. This two-piece solid core golf ball has the advantage that amateur golfers have a good flight distance due to its high initial velocity, but gives a hard feel when hit. this is,
This is generally due to high rigidity, and as a result, there is a disadvantage that control is difficult in short shots and approach shots. To get a soft feel at impact,
If the hardness of the core is reduced, the resilience is reduced, and the flying distance, which is an advantage of a two-piece solid golf ball, is impaired.

In order to improve such a drawback, a multi-piece solid core golf ball having two or three or more solid core portions has been proposed. The multi-piece solid core golf ball reduces the hardness of the core of the innermost layer (hereinafter referred to as “inner core”) corresponding to the core to soften the impact, and the core portion excluding the core (hereinafter referred to as “outer core”). It is intended to secure resilience by making it hard.

[0004] However, when both the inner core and the outer core are made of rubber, it is easier to reduce the resilience while lowering the hardness, even if it is easier than in the case of a two-piece golf ball. In fact, the balance of resilience was still inadequate.

For this reason, a multi-piece solid core golf ball has been proposed in which the inner core is made of a rubber core and the outer core is made of a hard thermoplastic resin.

For example, Japanese Unexamined Patent Publication (Kokai) No. 4-244174 discloses a diene rubber having a crosslinked inner core (specifically, cis-
1,4-polybutadiene), the outer core of which is a mixture of an ionomer (Shore D hardness 55-65) and an amide-based thermoplastic elastomer (Shore D hardness 30-40). 40-5
Golf balls covered with about 5 ionomer resin covers have been proposed. JP-A-6-142228 discloses a multi-piece solid core having an inner core made of polybutadiene and an outer core made of a mixture (a Shore D hardness of 30 to 50) of a thermoplastic elastomer and an ionomer with an ionomer resin cover. A constructed golf ball has been proposed.

[0007]

However, a multi-piece solid core golf ball whose outer core is made of a thermoplastic material has a higher impact resistance than a two-piece solid core golf ball made of a solid rubber core. There is a problem that they are weak and have poor shape stability.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a multi-piece solid core golf ball in which a multi-piece solid core portion is made of a rubber composition. Moreover, it is an object of the present invention to provide a golf ball having a soft feel at impact and a small decrease in resilience.

[0009]

Means for Solving the Problems The present inventors have determined not only the hardness of the rubber but also the tan δ for the inner core corresponding to the core.
The present inventors have found that by adjusting the hardness of the rubber core, it is possible to suppress a decrease in resilience due to a decrease in the hardness of the rubber core, and thus completed the present invention.

That is, the multi-piece solid core golf ball of the present invention is a multi-piece solid golf ball having a multi-layer solid core having an inner core coated with one or more outer cores and covered with a cover. The diameter of the inner core is 6 to 18 mm, and the JI of the inner core is
The SA hardness is 70 or less, and ta at 30 ° C.
nδ is not more than 0.03.

[0011] The outer core preferably has a JIS-C hardness of 60 to 85, and the inner core is preferably formed by cross-linking a base rubber with a resin cross-linking agent.

Here, tan δ (loss tangent) refers to a value measured using a viscoelastic spectrometer manufactured by Shimadzu Corporation under the following conditions.

Measurement conditions Specimen: width x length x thickness 4 mm x 30 mm x 2 mm Deformation site length in sample: 20 mm (5 mm at both ends of 30 mm length) Initial strain: 10% (2 mm) Amplitude: 0. 25% (0.05 mm) Frequency: 10 Hz Temperature: 30 ° C. Both JIS-A hardness and JIS-C hardness are JIS.
It is a hardness measured based on 5.2 A spring hardness test and A type C of K6301. Usually, the C type hardness tester is
It is suitable for measuring the hardness of a sample having a hardness of 70 or more in an A-type hardness test.

The JIS-A hardness and the JIS-C hardness have a correlation, and are generally as shown in FIG.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A multi-piece solid golf ball according to the present invention is, as shown in FIG. 2, formed by covering a solid core 3 having a multilayer structure in which an inner core 1 is covered with an outer core 2 with a cover 4. Things.

The core of the golf ball of the present invention is:
JIS-A hardness is 70 or less and ta at 30 ° C.
nδ is 0.03 or less. The reason why the JIS-A hardness is 70 or less (equivalent to 30 or less in JIS-C hardness) is that the lower the hardness of the inner core, the lower the impact force when hitting is generally required. Therefore, the more preferred JIS-
The upper limit of the A hardness is 60 or less. On the other hand, if the JIS-A hardness is too small, the resilience tends to decrease.
A preferred lower limit is 30 degrees or more, more preferably 40 degrees.
Degrees or more.

Tan δ (loss tangent) is the storage elastic modulus E
₁ Modulus of elasticity E for_Two Ratio (E _Two / E₁ ), Viscous
Due to the phase lag caused by the element,
Part of the mechanical energy given is consumed as heat
The ratio of consumed energy to stored energy
I have. Even if the inner core softens, tanδ is small
Reduces energy loss and suppresses a drop in resilience performance.
It is thought that we can control. However, regarding the lower limit of tan δ
Is preferably 0.01 or more due to manufacturing problems.
And more preferably 0.015 or more.

The inner core 1 has a diameter of 6 to 18 mm. 6
If it is less than 18 mm, the effect of reducing the impact force is small, and if it is 18 mm or more, the inner core 1 which is the impact absorbing layer becomes too large, and even if tan δ is small, a decrease in the resilience performance cannot be avoided.

The rubber composition constituting the inner core (rubber composition for the inner core) is not particularly limited as long as it has a JIS-A hardness of 70 or less and a tan δ at 30 ° C. of 0.03 or less. In order to satisfy the requirements, specifically, the following composition is preferable.

The base rubber used in the rubber composition for the inner core may be a rubber having a diene component in the molecule, for example, natural rubber (NR), butadiene rubber (B
R), isoprene rubber (IR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NB
R), ethylene propylene diene terpolymer (EPD)
M), and these may be used alone or in combination of two or more.

As a crosslinking agent for crosslinking the base rubber, only sulfur, a combination of sulfur and a vulcanization accelerator, peroxide, oxime,
A resin cross-linking agent may be used, but a resin cross-linking agent is preferable in order to satisfy the above requirements for hardness and tan δ. Here, examples of the resin crosslinking agent include an alkylphenol-formaldehyde, a brominated alkylphenol-formaldehyde, a phenol resin, and a cumarone resin. Such a crosslinking agent is preferably blended in an amount of about 2 to 20 parts by weight per 100 parts by weight of the base rubber.

The rubber composition for the core includes, for example, a diene rubber, a crosslinking agent, a specific gravity adjuster, a processing aid, an antioxidant and a plasticizer, a dispersant, an ultraviolet absorber, a coloring agent, etc. It is possible to appropriately mix a usual additive compounded in the core material as needed.

The outer core 2 is not particularly limited.
It is preferable to set the SC hardness to 60 to 85. Since the outer core 2 mainly ensures resilience, its lower limit must be 60 or more. Therefore, it may be appropriately selected within the range of JIS-C hardness of 60 to 85. For example, when high rebound is required, JIS-C hardness is preferably 78 to 85, and when low impact is required. Has JI
It is preferable to set the SC hardness to 60 to 80. The outer core 2 is not limited to a single layer, and may have a multilayer structure of two or more layers.
From the viewpoint of production easiness, it is preferable to use one layer.
When the outer core 2 has a multilayer structure, the hardness of the outer core 2 refers to the hardness of the entire outer core.

The outer core 2 preferably has a core diameter of 36.0 to 40.8 mm when covered with the outer core.

The rubber composition constituting the outer core (rubber composition for outer core) which can satisfy the above requirements preferably has the following compounding composition.

The base rubber is preferably a high cis polybutadiene rubber having at least 40, preferably at least 80%, more preferably at least 90% of a diene rubber, especially cis-1,4-polybutadiene rubber. Alternatively, one or more other diene rubbers such as natural rubber, isoprene rubber (IR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR) may be mixed.

Examples of the cross-linking agent include cross-linking agents used in the composition for the core core, that is, sulfur alone, a combination of sulfur and a vulcanization accelerator, peroxides, oximes, and resin cross-linking agents. Among these, it is preferable to use an organic peroxide in combination with an unsaturated carboxylic acid as a co-crosslinking agent.

As the organic peroxide, specifically, dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,5-trimethylcyclohexane, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane, di-t-butyl peroxide and the like can be mentioned. Of these, dicumyl peroxide is preferably used. The compounding amount of the organic peroxide is preferably 0.3 to 5.0 parts by weight based on 100 parts by weight of the base rubber. As the metal salt of the unsaturated carboxylic acid, specifically, a monovalent or divalent monovalent or divalent zinc or magnesium salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms such as acrylic acid or methacrylic acid. Of these, zinc acrylate which imparts high resilience is preferably used. The amount of the metal salt of unsaturated carboxylic acid is 10
It is preferably from 60 to 60 parts by weight, particularly preferably from 20 to 50 parts by weight.

In the composition for the outer core, in addition to the base rubber and the crosslinking agent, specific gravity adjusters such as zinc oxide, barium sulfate, and calcium carbonate; antioxidants; plasticizers; dispersants; ultraviolet absorbers; An ordinary additive such as a disintegrant and a coloring agent, which is blended in the core material for golf balls, can be appropriately blended as needed.

The multi-piece solid core having the above configuration is generally manufactured as follows. First, the inner core rubber composition is heated and press-molded in a mold having a predetermined diameter to form an inner core. The vulcanization condition of the inner core is press temperature 1
It is 10 to 60 minutes at 40 to 180 ° C. On the other hand, an outer core is manufactured using an outer core mold and a core having a predetermined diameter. At this point, the semi-vulcanized outer core may be produced, and the semi-vulcanized condition is 140 to 170 ° C. for 30 seconds to 2 minutes. The multi-piece solid core is manufactured by coating the previously manufactured inner core with a semi-vulcanized outer core and performing heat press molding again. The vulcanization conditions for finishing are 140 to 170 ° C. for 15 to 40 minutes.

The golf ball of the present invention is obtained by covering the multi-piece solid core configured as described above with a cover. The cover may be a single layer or two or more layers.

The type of cover may be either a parata cover or an ionomer cover, but it is preferable to use an ionomer cover because of its excellent strength, and the thickness of the cover is preferably 1 to 3.4 mm.

As the ionomer, an ionomer conventionally used as a cover for two-piece golf in view of high strength and high elasticity, that is, metal ion of α-olefin and α, β-unsaturated carboxylic acid copolymer A neutralized product is preferably used. Examples of metal ions that neutralize the copolymer include monovalent metal ions such as sodium ion, potassium ion, and lithium ion; zinc ions;
Divalent metal ions such as calcium ion, magnesium ion, copper ion, and manganese ion; and trivalent metal ions such as aluminum ion and neodymium ion. Among them, zinc ion is particularly preferred because the binding force of the aggregate of metal ions is large. .

Specific examples of the ionomer include Himilan 1605 (trade name of sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin) and Himilan 1707 (sodium ion-neutralized ethylene-methacrylic acid) manufactured by Du Pont-Mitsui Polychemicals, Inc. Trade name of copolymer ionomer resin), Himilan 1706 (trade name of zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin), Himilan AM7315 (trade name of zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin) ), Himilan AM7317 (trade name of zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin), Himilan 1555 (trade name of sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin) Himilan 1557 (trade name of zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin), Iotech 8000 manufactured by Exxon Chemical Co., Ltd. (trade name of sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin), Iotech 7010 (Trade name of zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin), Surlyn 7930 (trade name of lithium ion neutralized ethylene-methacrylic acid copolymer ionomer resin) manufactured by DuPont, Surlyn 8511 (trade name of zinc ion Japanese ethylene-methacrylic acid copolymer type ionomer resin), Surlyn 8
512 (trade name of sodium ion neutralized ethylene-methacrylic acid copolymer-based ionomer resin), and these may be used alone or in combination of two or more.

The golf ball of the present invention is manufactured by coating the prepared core with the cover as described above. The coating method is a usual injection molding method, and a half cup of the cover is previously formed. For example, a method in which a core is packed therein and subjected to hot press molding is used.

A large number of pits, usually called dimples, are formed on the surface during cover molding, and the product is made into a product by applying a paint finish, a marking stamp, or the like to enhance aesthetics and commercial value.

[0037]

[Example] [Evaluation measuring method] Hardness (JIS-A hardness, JIS-C hardness) 5.2 Spring hardness test A type of JIS K6301,
Measured based on Form C. tan δ Measured using a viscoelastic spectrometer manufactured by Shimadzu Corporation under the following conditions.

Measurement conditions Sample: width × length × thickness 4 mm × 30 mm × 2 mm Deformation site length in sample: 20 mm (5 mm at both ends of 30 mm in length) Initial strain: 10% (2 mm) Amplitude: 0. 25% (0.05 mm) Frequency: 10 Hz Temperature: 30 ° C. Rebound The speed change when a stationary golf ball is hit with a stainless steel cylindrical column at an initial speed of 35 m / s is measured, and the speed and weight of the ball are measured. Was calculated as an index with the coefficient of restitution of Reference Example 3 (standard two-piece golf ball) as 100. A higher index indicates a higher repulsion. Compression (mm) The amount of compression deformation (mm) when a load of 130 kgf was applied was measured based on the amount of deformation when a load of 10 kgf was applied to the manufactured ball. Generally, the smaller the deformation amount, the harder the ball. Impact force The maximum impact force (kg) when the ball is hit at an initial speed of 35 m / s with an acceleration pickup attached to the W # 1 club
f) was measured. A large impact force indicates that the shot feeling is hard. [Preparation of Three-Piece Golf Ball] An inner core having a predetermined diameter is prepared by vulcanizing the composition for core at 180 ° C. for 15 minutes. On the other hand, using an outer core mold having a diameter of 38.5 mm and a core having an outer diameter corresponding to the inner core diameter, the outer core composition was preformed at 160 ° C. for 1 minute to obtain a semi-vulcanized outer core. A nucleus was made. The semi-vulcanized outer core covered the inner core previously prepared, and was vulcanized at 160 ° C. for 25 minutes to produce a two-layer solid core.

Next, an ionomer resin (equivalent mixture of Himilan 1605 and Himilan 1706) was injection-molded and coated on the surface of the two-layer core to produce a ball having a diameter of 42.8 mm and a weight of 45.0-45.4 g. .

With respect to the core and the ball manufactured respectively,
The hardness, tan δ, compression, resilience index, and impact force were measured and evaluated based on the above measurement and evaluation methods. The results are shown together with the composition. [Relationship between Inner Core Hardness and Tan δ and Compression, Rebound, and Impact Force] Table 1 shows the base rubber and the type of cross-linking agent constituting the inner core rubber composition while keeping the rubber compounding composition constituting the outer core constant. By changing the hardness and tan δ as shown in FIG. 1
To 6 were prepared. Further, by changing the degree of cross-linking of the rubber composition for the outer core, the outer core is further hardened so that the golf ball N
o. 7 was produced. In Table 1, BR01 is a butadiene rubber manufactured by Nippon Synthetic Rubber Co., Ltd., and is EPDM505A.
Is ethylene propylene diene 3 manufactured by Sumitomo Chemical Co., Ltd.
EPDM670F is a non-oil extended product of a terpolymer, and EPDM670F is an oil extended product of an ethylene propylene diene terpolymer (manufactured by Sumitomo Chemical Co., Ltd.).
0 parts by weight), and the high blur is a vinyl polyisoprene manufactured by Kuraray Co., Ltd. Tack roll is a resin cross-linking agent (brominated alkylphenol formaldehyde), and DCP is dicumyl peroxide as a cross-linking agent. [S + Accelerator] refers to sulfur and vulcanization accelerator ("Sanseller NS" manufactured by Sanshin Chemical Co., Ltd.)
(Trade name of N-tert-butyl 1,2-benzothiazoyl-sulfenamide)).

The results of measuring the compression, resilience, and impact force of the manufactured golf ball are also shown in Table 1. FIG. 3 shows the relationship between the tan δ of the inner core material and the resilience.
FIG. 4 shows the relationship between the JIS-A hardness of the inner core material and the impact force.
To

As a reference example, the measurement results of compression, resilience and impact force of a two-piece golf ball (Reference Example 1) having a core made of the rubber composition for an outer core shown in Table 1 are also shown in Table 1. Show.

[0043]

[Table 1] As can be seen from Table 1 and FIG. 3, tan δ 0.3 or less,
Preferably, when the hardness is 0.015 or more, even if the hardness is 70 or less, the resilience can be maintained at the same level or more as that of a conventional two-piece golf ball. FIG. 4 shows that JIS-A
When the hardness is 70 or less, the JIS-A hardness and the impact force are not necessarily correlated. By adjusting tan δ, the impact force can be reduced without lowering the hardness (for example, No. .1 is higher in hardness than No. 6, but has a lower impact force). [Relationship Between Inner Core Diameter and Compression, Rebound, and Impact Force] Using a rubber composition for an inner core and a rubber composition for an outer core as shown in Table 2, three-piece golf balls No. Nos. 8 to 12 were produced. Table 2 also shows the results of measuring the compression, resilience, and impact force of the manufactured golf balls.

As a reference example, the results of measurement of compression, resilience, and impact force of a two-piece golf ball (Reference Examples 2 and 3) having a core made of the rubber composition for an outer core shown in Table 2 are also shown.

[0045]

[Table 2] As shown in Table 2, as the diameter of the inner core increases, the compression increases and the impact force decreases, but the resilience also decreases. Therefore, it can be seen that by appropriately selecting the diameter of the inner core, it is possible to balance the resilience and the impact force.

On the other hand, as can be seen from the Reference Example, in the two-piece golf ball, it was difficult to finely adjust the resilience and compression by changing the rubber base material and changing the crosslinking agent to change the resilience and compression.

[0047]

【The invention's effect】 [Brief description of the drawings]

FIG. 1 is a graph showing the relationship between JIS-A hardness and JIS-C hardness.

FIG. 2 is a schematic view showing a configuration of a multi-piece solid core golf ball of the present invention.

FIG. 3 is a graph showing a relationship between tan δ and resilience.

FIG. 4 is a graph showing the relationship between JIS-A hardness and impact force.

[Explanation of symbols]

 1 inner core 2 outer core 3 solid core 4 cover

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 23/26 C08L 23/26

Claims (3)

[Claims] 1. A multi-piece solid core golf ball in which a solid core having a multilayer structure in which an inner core is covered with one or two or more outer cores is covered with a cover, wherein the diameter of the inner core is 6 to 18 mm. The JIS-A hardness of the inner core is 70 or less and 30
A multi-piece solid core golf ball having a tan δ at 0.3 ° C. of 0.3 or less. 2. The outer core has a JIS-C hardness of 60 to 85.
The multi-piece solid core golf ball according to claim 1, wherein 3. The multi-piece solid core golf ball according to claim 1, wherein the inner core is formed by cross-linking a base rubber with a resin cross-linking agent.