JP2000070409A - Multipiece solid golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multipiece golf ball which gives a user good soft feeling in an approach shot or putting and has superior successive hitting resistance and excellent flying properties when fully hit by a driver. SOLUTION: In a multipiece solid ball with a solid core 1, at least one middle layer 2 to cover the core 1, and at least one layer of cover 3 to cover the middle layer 2, the middle layer 2 is formed mainly of thermoplastic resin with 8-35 of Shore D hardness and the cover 3 is formed of a cover material mainly constituted of thermoplastic resin and the Shore D hardness of the cover 3 is higher than that of the middle layer by more than 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-piece solid golf ball having at least a three-layer structure having a solid core, an intermediate layer and a cover. The present invention relates to a multi-piece solid golf ball having continuous hitting durability and an increased flight distance at the time of a full shot with a driver.

[0002]

2. Description of the Related Art Conventionally, two-piece solid golf balls proposed so far have a trajectory called a so-called rod ball for both driver shots and iron shots as compared with thread-wound golf balls. It has the advantage that the total flight distance is increased due to the large number of runs due to the structural characteristics that do not easily cause spin.

[0003] On the other hand, two-piece solid golf balls tend to be harder to stop on the green because of less spin on iron shots than thread wound golf balls, and tend to be inferior in controllability.

[0004] On the other hand, a golf ball is required to have a soft feel at the time of hitting as the flight distance increases, otherwise the commercial value is impaired. In general, thread-wound golf balls have structural characteristics that are softer and provide a better feel when compared to two-piece solid golf balls.

For this reason, it is common practice to soften the ball structure of a two-piece solid golf ball comprising a core and a cover in order to achieve a soft feel when hit.

[0006] However, such a soft type two-piece solid golf ball generally uses a soft core. If the core is too soft, the resilience is reduced, the flying performance is reduced, and the durability is remarkably increased. As a result, not only the excellent flight performance and durability characteristic of the two-piece solid golf ball cannot be obtained, but also the actual use becomes difficult.

Recently, in order to solve such problems, many three-piece solid golf balls having an intermediate layer between a core and a cover have been proposed (Japanese Patent Laid-Open No. 7-2).
4084, JP-A-6-23069, JP-A-4-244174, JP-A-9-10358, JP-A-9-313543 and the like.

However, even in these proposals,
If the cover and the intermediate layer are formed softly, the feeling becomes soft, but the flight distance at the time of a full shot with a driver is reduced. Conversely, when trying to obtain a flight distance, the cover and the intermediate layer must be formed hard, resulting in a reduced hit feeling at the time of approach shot and putting. Golf balls have not yet been obtained, and further improvements have been desired.

The present invention has been made in view of the above circumstances, and provides a multi-piece solid golf ball having at least a three-layer structure including a solid core, an intermediate layer, and a cover, which is very soft and good at the time of approach shot and putting. It is an object of the present invention to provide a multi-piece solid golf ball having a ring, excellent continuous hitting durability, and excellent flight performance at full shot with a driver.

[0010]

Means for Solving the Problems and Embodiments of the Invention As a result of intensive studies to achieve the above object, the present inventor has found that a multi-layer structure having at least a three-layer structure including a solid core, an intermediate layer and a cover is provided. In a piece solid golf ball, while combining a relatively soft core, a very soft intermediate layer, and a relatively hard cover,
By adding an appropriate amount of inorganic filler to the cover, it has a very soft and good feeling during approach shots and putting, as well as excellent continuous hitting durability and excellent flight performance during full shots with a driver. It has been found that a golf ball can be obtained.

That is, in a multi-piece solid golf ball having a solid core, at least one intermediate layer covering the core, and at least one cover covering the intermediate layer, preferably, the solid core is formed of a rubber base material. With a specific gravity of 1.0 to 1.3 and a deformation of 3.0 m when a load of 100 kg is applied to the core.
m or more, and the intermediate layer covering this core is made of a very soft thermoplastic resin having a Shore D hardness of 8 to 35, in particular, (A) a thermoplastic polyester elastomer, and (B) an olefin elastomer. Either a heated mixture obtained by mixing an elastomer and a modified product thereof, and one or more thermoplastic elastomers selected from a styrene-based block copolymer and a hydrogenated product thereof is formed as a main material, or (B ) The main component is a thermoplastic elastomer, and the cover for covering the intermediate layer is made of a relatively hard thermoplastic resin, particularly, having a Shore D hardness of 57.
The above-mentioned ionomer resin is formed as a main material, the cover is formed so that the Shore D hardness of the cover is 25 or more higher than the Shore D hardness of the intermediate layer, and the cover is softened by adding an appropriate amount of an inorganic filler to the cover. Can compensate for the decrease in durability caused by the intermediate layer, and these can act synergistically, have a very soft feeling when approaching shots and putting, and have excellent durability during continuous hitting. It has been found that an unprecedented multi-piece solid golf ball having excellent flight performance at the time of a full shot with a driver can be obtained, and the present invention has been completed.

Accordingly, the present invention provides (1) a multi-piece solid golf ball having a solid core, at least one intermediate layer covering the core, and at least one cover covering the intermediate layer. The intermediate layer is formed mainly of a thermoplastic resin having a Shore D hardness of 8 to 35, and the cover is formed of a cover material mainly containing a thermoplastic resin, and an inorganic filler is added to the cover material. And the Shore D hardness of the cover is the Shore D of the intermediate layer.
A multi-piece solid golf ball having a hardness of at least 25 higher than the hardness, (2) the solid core is formed mainly of a rubber base material, and has a specific gravity of 1.0 to 1.3; The multi-piece solid golf ball according to (1), wherein the deformation amount when a load of 100 kg is applied to the multi-piece solid golf ball is (A) a thermoplastic polyester elastomer and (B) an olefin. Formed from a heated mixture with one or two or more thermoplastic elastomers selected from the group consisting of a thermoplastic elastomer and a modified product thereof, and a styrene-based block copolymer and a hydrogenated product thereof, or the component (B) (1) The multi-piece solid golf ball according to (1) or (2), wherein the multi-piece solid golf ball is formed using the thermoplastic elastomer as a main material. The multi-piece solid golf ball according to (1), (2) or (3), wherein the bar is formed mainly of an ionomer resin and has a Shore D hardness of at least 57, and (5) the thickness of the intermediate layer is 0.2. ~ 5.0m
m, wherein the specific gravity of the multi-piece solid golf ball according to any one of (1) to (4), is 0.8 or more;
(6) The multi-piece solid golf ball according to any one of (1) to (5), wherein the cover has a thickness of 1.0 to 5.0 mm and a specific gravity of 1.0 or more.

Hereinafter, the present invention will be described in more detail.
As shown in FIG. 1, a solid core 1, at least one intermediate layer 2 covering the core 1, and at least one cover 3 covering the intermediate layer 2 are provided.

The solid core 1 can be formed from a rubber composition mainly composed of a base rubber mainly composed of polybutadiene rubber, polyisoprene rubber, natural rubber, and silicone rubber. For this purpose, polybutadiene rubber is preferred. As the polybutadiene rubber, a cis-structure having at least 40% or more of a cis structure can be used.
1,4-polybutadiene is preferred. In the base rubber, natural rubber, polyisoprene rubber, styrene-butadiene rubber, and the like can be appropriately blended with the above-mentioned polybutadiene, but the resilience of the golf ball is improved by increasing the polybutadiene rubber component. Therefore, the rubber component other than polybutadiene is preferably not more than 10 parts by weight based on 100 parts by weight of polybutadiene.

The rubber composition may contain, in addition to the rubber component, a crosslinking agent such as zinc salts of unsaturated fatty acids such as zinc methacrylate and zinc acrylate, magnesium salts and ester compounds such as trimethylpropane methacrylate. Particularly, zinc acrylate can be suitably used because of its high resilience. The amount of these crosslinking agents is preferably 15 to 40 parts by weight based on 100 parts by weight of the base rubber.

The rubber composition usually contains dicumyl peroxide or a mixture of dicumyl peroxide and 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane. Contains a sulfuric acid,
The amount of the vulcanizing agent is 0.1 to 100 parts by weight of the base rubber.
It can be 1 to 5 parts by weight.

The rubber composition may further include, if necessary,
Zinc oxide, barium sulfate or the like can be blended as an antioxidant or a filler for adjusting specific gravity. The blending amount of these fillers is 0 to 130 parts by weight based on 100 parts by weight of the base rubber.

The above-mentioned rubber composition for a core is kneaded using an ordinary kneader (for example, a Banbury mixer, a kneader, a roll, or the like), and the obtained compound is subjected to injection molding or compression molding using a core mold. Can be formed.

The solid core thus obtained is
Its diameter is preferably 25 to 40 mm, more preferably 27 to 39 mm, still more preferably 30 to 38 mm, weight is 10 to 40 g, preferably 15 to 35 g, more preferably 20 to 32 g, and specific gravity is 1. 0-1.
3, preferably 1.03 to 1.28, more preferably 1.06 to 1.25.

The amount of deformation when a load of 100 kg is applied to the solid core is 3.0 mm or more, preferably 3.
2 to 7.0 mm, more preferably 3.4 to 6.5 mm,
More preferably, it is 3.6 to 6.0 mm. If the amount of deformation is less than 3.0 mm, the feeling may be hard, while if it exceeds 7.0 mm, the resilience may decrease.

The core may have a single-layer structure made of one kind of material or a multi-layer structure made up of two or more layers made of different materials.

In the present invention, at least one, preferably one or two intermediate layers 2 are formed around the core 1. The intermediate layer 2 is formed mainly of a very soft thermoplastic resin having a Shore D hardness of 8 to 35.
Thus, by forming an unusually soft intermediate layer between the core and the cover, a very soft and good feeling can be realized during approach shots and putting.

As the thermoplastic resin of the intermediate layer,
(A) a heated mixture of a thermoplastic polyester elastomer and (B) an olefin elastomer and a modified product thereof, and one or more thermoplastic elastomers selected from a styrene block copolymer and a hydrogenated product thereof; Alternatively, the thermoplastic elastomer of the component (B) can be used alone.

Here, the thermoplastic polyester elastomer as the component (A) includes terephthalic acid, 1,4-butanediol and polytetramethylene glycol (PT).
MG) or polypropylene glycol (PPG), a polyetherester-based multi-block having a polybutylene terephthalate (PBT) portion as a hard segment and a polytetramethylene glycol (PTGM) or polypropylene glycol (PPG) portion as a soft segment. Copolymers are preferred.
Specifically, Hytrel 3078, Hytrel 404
7. Commercial products such as Hytrel 4767 (manufactured by Toray DuPont) can be used.

The olefin elastomer of the component (B) includes a copolymer of ethylene and an alkene having 3 or more carbon atoms, preferably a copolymer of ethylene and an alkene having 3 to 10 carbon atoms, or α-olefin. Examples thereof include an olefin, an unsaturated carboxylic acid ester, and a polymerizable monomer containing a carboxyl group or a carboxylic anhydride group. Examples of the olefin elastomer include ethylene-propylene copolymer rubber, ethylene-butene copolymer rubber, ethylene-hexene copolymer rubber, and ethylene-octene copolymer rubber. Further, ethylene-propylene-non-conjugated dienes such as 5-ethylidene norbornene, 5-methylnorbornene, 5-vinyl norbornene, dicyclopentadiene, butene, and the like are added as a third component. -Propylene-butene copolymer rubber, ethylene-ethyl acrylate copolymer resin and the like.

Specific examples of such olefin-based elastomers include "MITUIEPT", "Tuffmer" (manufactured by Mitsui Petrochemical Industries, Ltd.), "ENGAGE" (manufactured by Dow Chemical Japan), and "Dynalon" (Japan). Commercial products such as synthetic rubber) can be used.

Also, modified products of the above-mentioned olefin-based elastomers can be suitably used. Examples of such modified olefin-based elastomers include those obtained by graft-modifying maleic anhydride onto an ethylene-ethyl acrylate copolymer resin. Specifically, commercially available products such as “HPR” (manufactured by DuPont-Mitsui Polychemicals) can be used.

As the styrene-based block copolymer, a polymer whose conjugated diene block is composed of butadiene alone, isoprene alone, or a mixture of isoprene and butadiene is preferred. Further, hydrogenated products of these styrene block copolymers can be suitably used, for example, hydrogenated products of styrene-butadiene-styrene block copolymer, hydrogenated products of styrene-isoprene-styrene block copolymer, and the like. Is mentioned.

Specific examples of the hydrogenated styrene conjugated diene block copolymer include “Dynalon” (manufactured by Nippon Synthetic Rubber Co., Ltd.), “Septon”, “Hibler” (manufactured by Kuraray), and “ Commercial products such as "Toughtec" (manufactured by Asahi Kasei Corporation) can be used.

The intermediate layer of the present invention comprises one or more selected from the group consisting of (A) a thermoplastic polyester elastomer, (B) an olefin elastomer and a modified product thereof, and a styrene block copolymer and a hydrogenated product thereof. A heated mixture of two or more kinds can be formed as a main material. In this case, the mixing ratio of the two is such that the component (A) is 95% by weight or less,
Preferably, (A) / (B) is from 95 to 0/5 to 100% by weight, more preferably from 90 to 5/10 to 95% by weight, even more preferably from 80 to 10/20 to 90% by weight.

As the mixture of the components (A) and (B), commercially available products can be used, and for example, "Primalloy" (manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned.

Further, a thermoplastic elastomer obtained by singly or in combination of two or more kinds selected from the olefin-based elastomer (B) component and its modified product, and the styrene-based block copolymer and its hydrogenated product is used. It can be used as a main material of the intermediate layer.

Incidentally, in addition to the above-mentioned resin component, a weight adjuster, a colorant, a dispersant, and the like can be added to the intermediate layer composition, if necessary.

The method for coating the above-mentioned intermediate layer around the core is not particularly limited, and ordinary injection molding or compression molding can be employed.

The intermediate layer thus formed must have a Shore D hardness of 8 to 35, preferably 9 to 30, more preferably 10 to 29, still more preferably 12 to 27, Most preferably, it is 15 to 24.
If the Shore D hardness is less than 8, the intermediate layer becomes too soft,
The resilience and durability are reduced, making it difficult to use. On the other hand, if the Shore D hardness exceeds 35, the intermediate layer becomes too hard, and the shot feeling at the time of approach shot and putting becomes too hard to achieve the object of the present invention.

The thickness of the intermediate layer is preferably from 0.2 to
It is 5.0 mm, more preferably 0.5 to 4.0 mm, still more preferably 0.7 to 3.5 mm, and has a specific gravity of 0.8 or more, preferably 0.85 to 1.4, more preferably 0.5 to 1.4 mm.
87-1.2, more preferably 0.89-1.15.

Next, a cover 3 is formed around the intermediate layer 2 in at least one layer, preferably one layer or two layers. The cover 3 is formed mainly of a thermoplastic resin having a Shore D hardness of 25 or more than the intermediate layer.

The cover can be formed by using a usual thermoplastic resin as a main material, for example, an ionomer resin,
Examples include polyester-based elastomers, polyamide-based elastomers, styrene-based elastomers, polyurethane-based elastomers, olefin-based elastomers, and mixtures thereof, and ionomer resins are particularly preferred.
Specifically, commercially available products such as “Himilan” (manufactured by DuPont-Mitsui Polychemicals) and “Surlyn” (manufactured by DuPont) can be used. Note that a UV absorber, an antioxidant, a dispersant such as metal soap, or the like can be added to the cover material as needed.

The method of coating the cover around the intermediate layer is not particularly limited, and ordinary injection molding or compression molding can be employed.

In this way, the cover has a Shore D hardness of 5
7 or more, preferably 58 to 70, more preferably 59 to 70
68, more preferably 60 to 65. The hardness of the cover needs to be 25 or more higher in Shore D than the hardness of the intermediate layer, preferably 25 to 50, and more preferably 29 to 45. Hardness difference between cover and middle layer is 25
If less, the cover becomes soft, and the resilience decreases. On the other hand, if it exceeds 50, the difference in hardness becomes too large, and the durability is reduced. In addition, the energy loss is increased, and the flight distance may be reduced.

The thickness of the cover is 1.0 to 5.0 m.
m, preferably 1.2 to 4.0 mm, more preferably 1.3 to 3.0 mm, even more preferably 1.4 to 2.5 m
m.

In the present invention, an appropriate amount of an inorganic filler is added to the above cover. By adding the inorganic filler to the cover in this manner, it is possible to effectively compensate for the decrease in durability due to the very soft formation of the intermediate layer.

In this case, the inorganic filler is added in an amount of 5 to 40 parts by weight, preferably 15 to 38 parts by weight, more preferably 18 to 36 parts by weight, based on 100 parts by weight of the resin component forming the cover. If the amount of the inorganic filler is less than 5 parts by weight, the reinforcing effect may not be obtained, while if it exceeds 40 parts by weight, dispersibility and resilience may be adversely affected.

The average particle size of the inorganic filler is usually 0.1.
It is from 0.1 to 100 µm, preferably from 0.1 to 10 µm, more preferably from 0.1 to 1.0 µm. If the average particle size is too small or too large, the dispersibility at the time of filling will be deteriorated, and the effect of the present invention may not be achieved.

The inorganic filler is not particularly limited, and includes, for example, barium sulfate, titanium dioxide, calcium carbonate, tungsten and the like. One of these may be used alone, or two or more may be used in combination. However, barium sulfate and titanium dioxide are particularly preferred.

When the inorganic filler is added to the cover, the specific gravity of the cover to which the inorganic filler is added is 1.0.
As described above, it is preferably 1.01 to 1.4, more preferably 1.05 to 1.3, and still more preferably 1.1 to 1.2.

It is to be noted that an appropriate amount of an inorganic filler can be added to the intermediate layer, and the durability can be further improved by adding the inorganic filler to both the cover and the intermediate layer. Things.

In this case, the amount of the inorganic filler to be added is 5 to 40 parts by weight, preferably 15 to 38 parts by weight, based on 100 parts by weight of the resin component forming the intermediate layer. The diameter and other conditions are the same as in the case of the cover.

The multi-piece solid golf ball of the present invention has the above structure, and has a relatively soft core, a very soft intermediate layer covering the core, and a relatively hard intermediate layer covering the intermediate layer. By combining the cover with the cover and adding an appropriate amount of an inorganic filler to the cover and further to the intermediate layer, these are combined to achieve an approach shot,
It has a very soft and good feeling when putting, and has excellent continuous hitting durability and excellent flight performance when a full shot is made with a driver.

The golf ball of the present invention has a large number of dimples formed on the surface thereof, and the surface can be subjected to a finishing treatment such as painting and stamping if necessary. The hardness of the entire ball is preferably 2.6 to 5.5 mm, more preferably 2.8 to 4.8 mm in terms of deformation when a load of 100 kg is applied, and the ball diameter and weight are in accordance with the R & A Golf Rules. 42.67m in diameter
m and a weight of 45.93 g or less.

[0051]

According to the present invention, an approach shot,
A multi-piece solid golf ball having a soft and good feeling at the time of putting and having excellent flight performance and excellent continuous hitting durability at the time of a full shot with a driver can be obtained.

[0052]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. The amounts in Tables 1, 2, and 3 are all parts by weight.

[Examples and Comparative Examples] The rubber compositions for cores having the compounding formulations shown in Table 1 were kneaded with a kneader and vulcanized in a core mold at a temperature of 155 ° C for about 15 minutes. Solid cores 1 to 7 and Comparative Examples 1 to 6 were prepared.

An intermediate layer material shown in Table 2 and a cover material shown in Table 3 were formed around the obtained core by injection molding, respectively, to form Examples 1 to 7 and Comparative Examples 1, 2, 4, and 4. 5
A three-piece solid golf ball was created.

The three-piece ball of Comparative Example 3
A pair of half shells are formed in advance using the intermediate layer material shown in Table 2, and the cores are covered with these half shells.
By vulcanizing at 5 ° C. for 15 minutes, a double solid core was prepared, and a cover was formed around the double core by injection molding to prepare the core. Comparative Example 6 is a two-piece golf ball having a core and a cover without an intermediate layer.

Next, regarding the obtained golf ball,
Various characteristics were evaluated by the methods shown below. The results are also shown in Tables 4 and 5. The amount of deformation of the solid core was expressed as the amount of deformation (mm) of the core when a load of 100 kg was applied to the core. Flying performance At a head speed of 45 m / sec (HS45), the club was driven by a driver (# W1) (“PRO230Titan” Loft 10
The degree of carry, the total flight distance, and the spin rate at the time of actual hitting were measured using a degree (manufactured by Bridgestone Sports Co., Ltd.). In addition, the club is designated as a ninth iron (# I9) ("MOD
EL 55-HM "instead of 44 degrees loft (Bridgestone Sports Co., Ltd.)
The amount of spin when actually hitting with ec (HS33) was similarly measured. The club is composed of a driver (# W1), a ninth iron (# I9) and a putter (#P)
The feel when actually hitting using T) was evaluated according to the following criteria. ：: very soft △: normal ×: hard continuous hitting durability The obtained ball was used as a driver (“PRO230Titan”) by a swing robot manufactured by Miyamae.
Loft 10 degrees "(Bridgestone Sports Co., Ltd.)
After hitting repeatedly at a head speed of 45 m / sec (HS45) using, the state of the ball surface was relatively evaluated according to the number of hits according to the following criteria. ○: No problem at all △: Destruction relatively early ×: Early destruction

[0057]

[Table 1] *: BR01 made by Nippon Synthetic Rubber Co., Ltd.

[0058]

[Table 2] * 1: "Hytrel" polyester elastomer manufactured by Toray DuPont * 2: "Pebax" polyamide elastomer manufactured by Atochem * 3: "Primalloy" alloy material mainly composed of a polyester elastomer manufactured by Mitsubishi Chemical Corporation * 4: "HPR" ethylene-ethyl acrylate copolymer resin modified by maleic anhydride grafted by Mitsui / Dupont * 5: "Tuftec" styrene-based elastomer manufactured by Asahi Kasei Corporation * 6: "Himilan" manufactured by Mitsui / Dupont Polychemical Ionomer resin * 7: "Surlyn" ionomer resin manufactured by DuPont

[0059]

[Table 3] * 6: Ionomer resin manufactured by "Himilan" Mitsui / Dupont Polychemicals * 7: Ionomer resin manufactured by "Surlyn" Dupont

[0060]

[Table 4] * 8: Core + middle layer

[0061]

[Table 5] * 8: Core + middle layer

As is clear from the results of Tables 4 and 5, all of the balls of Comparative Examples 1 to 5 had a mid layer having a Shore D hardness of 4
0 or more, the hardness difference between the cover and the intermediate layer is less than 25, and the cover contains only 5.6 parts by weight of titanium dioxide as an inorganic filler, so that the effects of the present invention cannot be exhibited. .

That is, Comparative Example 1 is a three-piece ball of the same type as disclosed in Japanese Patent Application Laid-Open No. Hei 7-24084, in which the flight distance on driver shots is relatively increased, but the feel of the putter is hard and poor.

Comparative Example 2 is a three-piece ball of the same type as disclosed in Japanese Patent Application Laid-Open No. 4-244174, in which the flight distance upon driver shot is reduced and the hit feeling is hard and poor.

Comparative Example 3 is a three-piece ball of the same type as disclosed in Japanese Patent Application Laid-Open No. Hei 6-23069, which has a reduced flight distance when shot with a driver and a hard and inferior hit feeling with any of the driver, 9-iron and putter. It is.

Comparative Example 4 is a three-piece ball of the same type as that of Japanese Patent Application Laid-Open No. 9-10358, in which the flight distance upon driver shot is reduced and the hit feeling is hard and inferior.

Comparative Example 5 is a three-piece ball of the same type as that of Japanese Patent Application Laid-Open No. 9-313643, in which the flight distance on a driver shot is relatively increased, but the hit feeling with a driver is hard and poor.

Comparative Example 6 is a soft two-piece solid golf ball, which has a reduced flight distance on driver shots and a remarkably poor continuous hitting durability.

On the other hand, the three-piece balls of Examples 1 to 7 have a soft and good hit feeling in any of the driver, the 9-iron, and the putter, and the flying distance at the time of a full shot with the driver is remarkable. Increased to
It has excellent continuous impact durability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a multi-piece solid golf ball according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid core 2 Middle layer 3 Cover G Golf ball

Continuing from the front page (72) Inventor Junji Hayashi Inside Bridgestone Sports Co., Ltd. 20 at Onohara, Chichibu City, Saitama Prefecture (72) Inventor Shunichi Kashiwagi 20 at Bridgestone Sports Co., Ltd. 20 at Onohara, Chichibu City, Saitama Prefecture (72) Inventor Akira Kawada Saitama Bridgestone Sports Co., Ltd. 20 Onohara, Chichibu City, Japan

Claims (6)

[Claims] 1. A multi-piece solid golf ball comprising a solid core, at least one intermediate layer covering the core, and at least one cover covering the intermediate layer, wherein the intermediate layer has a Shore D hardness of 8 And the cover is formed of a cover material mainly composed of a thermoplastic resin, and an inorganic filler is added to the cover material, and the Shore D hardness of the cover is adjusted. Is higher than the Shore D hardness of the intermediate layer by 25 or more. 2. The solid core is formed mainly of a rubber base material, and has a specific gravity of 1.0 to 1.3.
2. The multi-piece solid golf ball according to claim 1, wherein the amount of deformation when a load of 100 kg is applied to the solid core is 3.0 mm or more. 3. The intermediate layer is one or two selected from (A) a thermoplastic polyester elastomer, (B) an olefin elastomer and a modified product thereof, and a styrene block copolymer and a hydrogenated product thereof. The multi-piece solid golf ball according to claim 1 or 2, wherein the multi-piece solid golf ball is formed mainly of the above-mentioned heated mixture with the thermoplastic elastomer, or formed mainly of the thermoplastic elastomer of the component (B). 4. The multi-piece solid golf ball according to claim 1, wherein said cover is formed mainly of an ionomer resin, and has a Shore D hardness of 57 or more. 5. The intermediate layer according to claim 1, wherein the intermediate layer has a thickness of 0.2 to 5.0 mm and a specific gravity of 0.8 or more.
Item 8. The multi-piece solid golf ball according to item 1. 6. The cover according to claim 1, wherein the cover has a thickness of 1.0 to 5.0 mm and a specific gravity of 1.0 or more.
Item 8. The multi-piece solid golf ball according to item 1.