JP6303193B2 - Multi-piece golf ball - Google Patents

Description

  The present invention relates to a multi-piece golf ball, and more particularly to a multi-piece golf ball having a center formed from a thermoplastic resin composition.

  Conventionally, a cured product of a rubber composition has been used as a core or center of a golf ball. Recently, it has been studied to mold the core or center using a thermoplastic resin that can be injection molded.

For example, Patent Document 1 includes at least one layer manufactured from a polymer composition, the water vapor transmission rate (MVTR) of the polymer composition is 8 g-mil / 100 in ² / day or less, and the polymer A golf ball is disclosed wherein the composition has a highly neutralized acid polymer.

  Patent Document 2 discloses (a) an inner core layer formed from a first HNP (highly neutralized acid polymer) composition, and the first HNP composition has a Shore D hardness of Having a highly neutralized ethylene / acrylic (or methacrylic) acid / alkyl acrylate (or alkyl methacrylate) copolymer of 55 or less and (b) an outer core produced from the second HNP composition A second HNP composition having a Shore D hardness of 45 or more and having a highly neutralized ethylene / acrylic (or methacrylic) copolymer; (c) a cover And a golf ball having a Shore D hardness of the first HNP composition smaller than the Shore D hardness of the second HNP composition is disclosed.

  Patent Document 3 discloses a golf ball having a core and a cover, and having an overall diameter of 3.56 cm (1.40 inches) to 4.22 cm (1.66 inches), and a diameter of 0.318 cm ( A center having a surface hardness of 70 Shore C or more and a specific gravity of 0.50 g / cc to 1.20 g / cc, and a surface hardness of 0.125 inch to 1.91 cm (0.750 inch). A golf ball comprising an outer core layer that is smaller than the surface hardness of the center and has a specific gravity substantially the same as the specific gravity of the center is disclosed.

  In Patent Document 4, in a multi-layer golf ball having a center, a cover layer, and at least two intermediate layers between the center and the cover, the value of the total restitution coefficient of each subassembly of the golf ball is included in the subassembly. Less than the value of the total coefficient of restitution of the next outer layer plus, the center has a highly neutralized thermoplastic copolymer of ethylene and an α, β-unsaturated carboxylic acid, and the acid is A multilayer golf ball is disclosed that is 100% neutralized with a salt of an organic acid, a cation source, or a suitable base of the organic acid.

  Patent Document 5 is formed in a multilayer structure of four or more layers comprising a core, an envelope layer that covers the core, an intermediate layer that covers the envelope layer, and a cover that covers the intermediate layer. In the solid golf ball, the core is mainly made of a thermoplastic resin or a thermoplastic elastomer, and has a diameter of 3 to 18 mm and a Shore D hardness of 15 to 50, and the envelope layer is mainly made of a thermoplastic resin or a thermoplastic elastomer. A solid golf ball is disclosed which is made of a material and has substantially the same Shore D hardness at the boundary surface between the envelope layer and the intermediate layer.

  Patent Document 6 includes the following (A) to (C) components, (A) ionomers, (B) diene polymers, thermoplastic polymers, and one or more selected from the group consisting of thermosetting polymers. A golf ball material comprising a resin composition and an (C) thermoplastic resin composition having an acid group as essential components is disclosed.

  In Patent Document 7, (a) the weight average molecular weight (Mw) is 40,000 to 80,000, and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 5.0 to 8. An olefin-unsaturated carboxylic acid copolymer and / or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer, or a metal neutralized product thereof, and (b) a weight average molecular weight (Mw) of 120. An olefin-unsaturated carboxylic acid copolymer and / or an olefin having a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 6.0 to 9.5 An unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer, or a metal neutralized product thereof, (c) an organic acid or a metal salt thereof, and (d) an acid group in the components (a) to (c) above. To neutralize more than 70 mol% Basic containing an inorganic metal compound, the golf ball material is disclosed, wherein the Shore D hardness of the resin mixture is 30 to 50.

  In Patent Document 8, (a) the weight average molecular weight (Mw) is 120,000 to 200,000, and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 4.3 to 6. An olefin-unsaturated carboxylic acid copolymer and / or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer, or a metal neutralized product thereof, and (b) a weight average molecular weight (Mw) of 120. An olefin-unsaturated carboxylic acid copolymer and / or an olefin having a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 6.8 to 9.5 An unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer, or a metal neutralized product thereof, (c) an organic acid or a metal salt thereof, and (d) an acid group in the components (a) to (c) above. Neutralize more than 70 mol% Basic containing an inorganic metal compound, the golf ball material, characterized by a Shore D hardness of the resin mixture is 30 to 55 have been disclosed for.

  In Patent Document 9, (a) the weight average molecular weight (Mw) is 120,000 to 200,000, and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 4.0 to 7. An olefin-methacrylic acid copolymer and / or an olefin-methacrylic acid-unsaturated carboxylic acid ester copolymer, or a metal neutralized product thereof, and (b) a weight average molecular weight (Mw) of 150,000 to 220 Olefin-acrylic acid copolymer and / or olefin-acrylic acid-unsaturated carboxylic acid having a weight average molecular weight (Mw) and number average molecular weight (Mn) ratio of 5.5 to 8.5. Acid ester copolymer or metal neutralized product thereof, (c) organic acid or metal salt thereof, and (d) neutralize 70 mol% or more of acid groups in components (a) to (c) above Basic inorganic gold Containing compound, the golf ball material is disclosed, wherein the Shore D hardness of the resin mixture is 30 to 60.

JP 2007-130473 A JP 2008-264554 A JP 2009-165824 A JP 2011-87958 A JP 2001-17575 A JP 2007-622 A JP 2011-78774 A JP 2011-78775 A JP 2011-78776 A

  As described above, it has been studied to mold the core or center using a thermoplastic resin that can be injection-molded. However, the performance of these golf balls is not yet satisfactory, and further improvement in performance is required. It has been.

  The present invention has been made in view of the above circumstances, and is a golf ball formed by molding a center using a thermoplastic resin composition, and has a low spin rate on driver shots and a high spin rate on approach shots. An object is to provide a golf ball.

  The multi-piece golf ball of the present invention is a multi-piece golf ball having a center and an enveloping layer of n layers (n is a natural number of 3 or more) covering the center, the material hardness of the center (Shore D hardness) ) Is H0, and the envelope layers formed in order from the center side are the first envelope layer, the second envelope layer, the third envelope layer, the fourth envelope layer,... The (n-1) th envelope layer, the nth envelope. Layer (outermost layer), and when the material hardness (Shore D hardness) is H1, H2, H3, H4... Hn-1, Hn, H1 <H0 <Hn-1 is satisfied. Is formed from a thermoplastic resin composition, and the first envelope layer is formed from a rubber composition.

  The multi-piece golf ball of the present invention has an appropriate hardness distribution by being configured as described above. By having an appropriate hardness distribution, the spin rate on the driver shot decreases and the spin rate on the approach shot increases.

  The center preferably has a diameter of 5 mm or more and 25 mm or less. The multi-piece golf ball of the present invention has a center having a small diameter. Therefore, it can have many envelope layers and can provide hardness distribution in an envelope layer.

  The center material hardness H0 (Shore D hardness) is preferably 5 or more and 60 or less. The center of the multi-piece golf ball of the present invention has a low hardness. As a result, the difference in hardness from the outside of the golf ball increases, and the spin rate on driver shots decreases.

  The material hardness H1 (Shore D hardness) of the first envelope layer is preferably 3 or more and 40 or less. The difference in hardness (H0−H1) between the material hardness H0 (Shore D hardness) of the center and the material hardness (Shore D hardness) of the first envelope layer is preferably 1 or more and 57 or less.

  The thermoplastic resin composition comprises at least an ionomer resin, a thermoplastic olefin copolymer, a thermoplastic styrene elastomer, a thermoplastic polyester elastomer, a thermoplastic polyurethane elastomer, a thermoplastic polyamide elastomer, and a thermoplastic acrylic elastomer as a resin component. What contains 1 type is preferable. As the ionomer resin, a ternary ionomer resin can be suitably used.

  According to the present invention, a multi-piece golf ball formed by molding a center using a thermoplastic resin composition, which has a low spin rate on a driver shot and a high spin rate on an approach shot is obtained. .

1 is a schematic cross-sectional view showing the structure of a golf ball of the present invention.

  The multi-piece golf ball of the present invention is a multi-piece golf ball having a center and an enveloping layer of n layers (n is a natural number of 3 or more) covering the center, the material hardness of the center (Shore D hardness) ) Is H0, and the envelope layers formed in order from the center side are the first envelope layer, the second envelope layer, the third envelope layer, the fourth envelope layer,... The (n-1) th envelope layer, the nth envelope. Layer (outermost layer), and when the material hardness (Shore D hardness) is H1, H2, H3, H4... Hn-1, Hn, H1 <H0 <Hn-1 is satisfied. Is formed from a thermoplastic resin composition, and the first envelope layer is formed from a rubber composition.

(1) Structure of Golf Ball The present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the structure of the multi-piece golf ball of the present invention. In the multi-piece golf ball of the present invention, a center C and an n-layer envelope layer (n is a natural number of 3 or more) covering the center are formed. Here, the envelope layers formed in order from the center side are the first envelope layer 1, the second envelope layer 2, the third envelope layer 3, the fourth envelope layer 4,... The (n-1) th envelope layer n-1. The n-th envelope layer n has a material hardness (Shore D hardness), H1, H2, H3, H4... Hn-1, Hn. The nth envelope layer constitutes the outermost layer. The n is a natural number of 3 or more, more preferably a natural number of 4 or more, preferably a natural number of 10 or less, and more preferably a natural number of 9 or less. If the number of envelope layers is three or more, it becomes easy to impart an appropriate hardness distribution to the envelope layers. On the other hand, if the number of envelope layers is too large, the moldability of the envelope layers is reduced. In addition, the reinforcing layer (adhesive layer) provided in order to improve the adhesiveness between the coating film and the surrounding layer is not included in the surrounding layer. The coating film and the reinforcing layer (adhesive layer) and the envelope layer have different film thickness ranges. The film thickness of the coating film and the reinforcing layer (adhesive layer) is usually 50 μm or less.

  In the multi-piece golf ball of the present invention, the material hardness H1 (Shore D hardness) of the first envelope layer adjacent to the center is smaller than the center material hardness H0 (Shore D hardness). The difference in hardness (H0−H1) between the material hardness H1 of the first envelope layer and the material hardness H0 of the center is preferably 1 or more in Shore D hardness, more preferably 2 or more, still more preferably 4 or more, 57 or less is preferable, more preferably 53 or less, and still more preferably 50 or less. This is because, if the hardness difference (H0−H1) between the material hardness H1 of the first envelope layer and the material hardness H0 of the center is within the above range, the driver spin rate is further reduced.

  In the multi-piece golf ball of the present invention, the material hardness Hn-1 (Shore D hardness) of the n-1th envelope layer is larger than the center material hardness H0 (Shore D hardness). The hardness difference ((Hn-1) -H0) between the material hardness Hn-1 of the n-1th envelope layer and the material hardness H0 of the center is preferably 5 or more, more preferably 7 or more in Shore D hardness. More preferably, it is 10 or more, 75 or less is preferable, More preferably, it is 70 or less, More preferably, it is 65 or less. If the hardness difference ((Hn-1) -H0) between the material hardness Hn-1 of the n-1th envelope layer and the material hardness H0 of the center is within the above range, an outer-hard / inner-soft structure is obtained, and the driver spin This is because the amount is further reduced.

  The center material hardness H0 is preferably a Shore D hardness of 5 or more, more preferably 6 or more, and even more preferably 7 or more. If the material hardness of the center is less than 5 in Shore D hardness, it may become too soft and the resilience may decrease. The material hardness of the center is preferably 60 or less in Shore D hardness, more preferably 45 or less, and still more preferably 30 or less. This is because if the material hardness exceeds 60 in Shore D hardness, it becomes too hard and the feel at impact tends to decrease. In the present invention, the material hardness H0 of the center is a slab hardness measured by molding a thermoplastic resin composition constituting the center into a sheet shape.

  The center has a diameter of preferably 5 mm or more, more preferably 7 mm or more, further preferably 10 mm or more, preferably 25 mm or less, more preferably 22 mm or less, and still more preferably 20 mm or less. This is because if the diameter of the center is 5 mm or more, the amount of driver spin is further reduced. On the other hand, if the diameter of the center is 25 mm or less, the approach spin amount is difficult to decrease.

  When the center has a diameter of 5 mm to 25 mm, the amount of compressive deformation (the amount by which the center contracts in the compression direction) from when the initial load 98N is applied to when the final load 1275N is applied is preferably 1.5 mm or more. Preferably it is 1.7 mm or more, More preferably, it is 2.0 mm or more, 5.0 mm or less is preferable, More preferably, it is 4.7 mm or less, More preferably, it is 4.5 mm or less. When the amount of compressive deformation is 1.5 mm or more, the feel at impact is better, and when it is 5.0 mm or less, the resilience is better.

  The material hardness H1 of the first envelope layer is preferably 3 or more in Shore D hardness, more preferably 4 or more, still more preferably 5 or more, preferably 40 or less, more preferably 37 or less, and still more preferably 35 or less. It is. This is because if the material hardness H1 of the first envelope layer is within the above range, the amount of driver spin is further reduced.

  The material hardness H2 of the second envelope layer is preferably 3 or more in Shore D hardness, more preferably 4 or more, still more preferably 5 or more, preferably 50 or less, more preferably 45 or less, and still more preferably 40 or less. It is. This is because if the material hardness H2 of the second envelope layer is within the above range, the amount of driver spin is further reduced.

  The material hardness Hn-1 of the n-1th envelope layer is preferably 45 or more in Shore D hardness, more preferably 47 or more, further preferably 50 or more, preferably 80 or less, more preferably 77 or less, Preferably it is 75 or less. This is because if the material hardness Hn-1 of the n-1th envelope layer is within the above range, an outer-hard / inner-soft structure is obtained, and the amount of driver spin is further reduced.

The material hardness of the first envelope layer to the (n-1) th envelope layer is preferably Shore D hardness and satisfies the following relational expression (1).
H1 <H2, H3, H4,..., Hn-3, Hn-2, Hn-1 (1)
That is, the multi-piece golf ball of the present invention preferably has the softest material hardness of the first envelope layer. This is because the amount of driver spin is further reduced by making the material hardness of the first envelope layer the softest.

The material hardness of the first envelope layer to the (n-1) th envelope layer is preferably Shore D hardness and satisfies the following relational expression (2).
H1 <H2 <H3 <H4 <... <Hn-3 <Hn-2 <Hn-1 (2)
When the material hardness of the first envelope layer to the (n-1) th envelope layer satisfies the above relational expression, the golf ball has an outer-hard / inner-soft structure, and a golf ball with a low spin rate on driver shots is obtained. A golf ball with a low spin rate on a driver shot has a large flight distance.

The surface hardness (shore) of each layer (first envelope layer, second envelope layer, third envelope layer, fourth envelope layer,... N-1 envelope layer) of the sphere in which the envelope layer is formed in order from the center side. When the D hardness is S1, S2, S3, S4... Sn-1, the surface hardness preferably satisfies the following relational expression (3).
S1 <S2 <S3 <S4 <... <Sn-3 <Sn-2 <Sn-1 (3)
When the surface hardness (Shore D hardness) from the first envelope layer to the (n−1) -th envelope layer satisfies the above relational expression, the golf ball has an outer-hard / inner-soft structure, and golf with a low spin rate on driver shots A ball is obtained. A golf ball with a low spin rate on a driver shot has a large flight distance.

  The hardness difference ((Hn-1) -H1) between the material hardness Hn-1 of the n-1th envelope layer and the material hardness H1 of the first envelope layer is preferably a Shore D hardness of 5 or more, more preferably It is 10 or more, more preferably 15 or more, and 77 or less is preferable, More preferably, it is 70 or less, More preferably, it is 65 or less. If the hardness difference ((Hn-1) -H1) between the material hardness Hn-1 of the (n-1) th envelope layer and the material hardness H1 of the first envelope layer is within the above range, the amount of driver spin is further reduced. Because it does.

  The material hardness Hn of the nth envelope layer (outermost layer) is preferably Shore D hardness of 5 or more, more preferably 7 or more, further preferably 10 or more, preferably 55 or less, more preferably 53 or less, Preferably it is 50 or less. This is because, if the material hardness Hn of the nth envelope layer is within the above range, the spin rate of the approach shot becomes higher.

  The thickness of each layer from the first envelope layer to the (n-1) th envelope layer is not particularly limited, but is preferably 0.1 mm or more, more preferably 0.2 mm or more, further preferably 0.3 mm or more, and preferably 15 mm or less. , 13 mm or less is more preferable, and 10 mm or less is more preferable.

  The thickness of the nth envelope layer (outermost layer) is preferably 2.0 mm or less, more preferably 1.6 mm or less, still more preferably 1.2 mm or less, and particularly preferably 1.0 mm or less. When the thickness of the nth envelope layer (outermost layer) is 2.0 mm or less, the resilience and feel at impact of the obtained golf ball become better. The thickness of the n-th envelope layer (outermost layer) is preferably 0.1 mm or more, more preferably 0.2 mm or more, and still more preferably 0.3 mm or more. If the thickness of the nth envelope layer (outermost layer) is less than 0.1 mm, the molding of the nth envelope layer (outermost layer) may be difficult, and the durability and resistance of the nth envelope layer (outermost layer) may be reduced. Abrasion may be reduced.

  When the multi-piece golf ball of the present invention has a diameter of 40 mm to 45 mm, the amount of compressive deformation (the amount of contraction in the compression direction) when the final load 1275N is applied from the state where the initial load 98N is applied is 2.0 mm or more. More preferably, it is 2.2 mm or more, it is preferable that it is 4.0 mm or less, More preferably, it is 3.5 mm or less. A golf ball having a compression deformation amount of 2.0 mm or more does not become too hard and has a good shot feeling. On the other hand, when the amount of compressive deformation is 4.0 mm or less, the resilience increases.

  Specific examples of the multi-piece golf ball of the present invention include a 5-piece golf ball and a 6-piece golf ball.

(2) Materials The center of the multi-piece golf ball of the present invention is formed from a thermoplastic resin composition, and the first envelope layer adjacent to the center is formed from a rubber composition. The second envelope layer to the nth envelope layer may be formed from either a thermoplastic resin composition or a rubber composition, but are preferably formed from a thermoplastic resin composition. This is because it becomes easy to form the second envelope layer to the nth envelope layer.

  First, the thermoplastic resin composition used in the present invention will be described. The (A) resin component contained in the thermoplastic resin composition is not particularly limited as long as it is a thermoplastic resin. Examples of the thermoplastic resin include thermoplastic resins such as ionomer resins, thermoplastic olefin copolymers, thermoplastic polyurethane resins, thermoplastic polyamide resins, thermoplastic styrene resins, thermoplastic polyester resins, and thermoplastic acrylic resins. Can be mentioned. Among the thermoplastic resins, a thermoplastic elastomer having rubber elasticity is preferable. Examples of the thermoplastic elastomer include thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, thermoplastic styrene elastomers, thermoplastic polyester elastomers, thermoplastic acrylic elastomers, and the like.

(2-1) Ionomer Resin As the ionomer resin, an ionomer resin comprising a metal ion neutralized product of a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms; An ionomer resin comprising a neutralized metal ion of a terpolymer of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester; or a mixture thereof. Can be mentioned.

  In the present invention, “an ionomer resin comprising a metal ion neutralized product of a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms” is simply referred to as “binary ionomer resin”. "Ionomeric resin comprising a metal ion neutralized product of a terpolymer of an olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester" May be simply referred to as “ternary ionomer resin”.

  The olefin is preferably an olefin having 2 to 8 carbon atoms, and examples thereof include ethylene, propylene, butene, pentene, hexene, heptene, octene and the like, and ethylene is particularly preferable. Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid, and acrylic acid or methacrylic acid is particularly preferable. Examples of the α, β-unsaturated carboxylic acid ester include methyl, ethyl, propyl, n-butyl, isobutyl ester and the like such as acrylic acid, methacrylic acid, fumaric acid and maleic acid, and particularly acrylic acid ester. Or a methacrylic acid ester is preferable.

  The binary ionomer resin is preferably a metal ion neutralized product of an ethylene- (meth) acrylic acid binary copolymer. The ternary ionomer resin is preferably a metal ion neutralized product of a ternary copolymer of ethylene, (meth) acrylic acid, and (meth) acrylic acid ester. Here, (meth) acrylic acid means acrylic acid and / or methacrylic acid.

  The content of the α, β-unsaturated carboxylic acid component having 3 to 8 carbon atoms in the binary ionomer resin is preferably 15% by mass or more, more preferably 16% by mass or more, and further more preferably 17% by mass or more. Preferably, 30 mass% or less is preferable, and 25 mass% or less is more preferable. This is because if the content of the α, β-unsaturated carboxylic acid component having 3 to 8 carbon atoms is 15% by mass or more, the resulting component can be easily made to have a desired hardness. Further, if the content of the α, β-unsaturated carboxylic acid component having 3 to 8 carbon atoms is 30% by mass or less, the hardness of the obtained component member is not excessively high, and the durability and feel at impact are good. Because it becomes.

  The neutralization degree of the carboxyl group of the binary ionomer resin is preferably 15 mol% or more, preferably 20 mol% or more, and preferably 100 mol% or less. If the degree of neutralization is 15 mol% or more, the resilience and durability of the resulting golf ball will be good. In addition, the neutralization degree of the carboxyl group of the binary ionomer resin can be obtained by the following formula. Moreover, a metal component may be contained so that the neutralization degree of the carboxyl group in a theoretical ionomer resin may exceed 100 mol%.

  Degree of neutralization of binary ionomer resin (mol%) = 100 × number of moles of neutralized carboxyl groups in binary ionomer resin / total number of moles of carboxyl groups in binary ionomer resin

  Examples of metal ions that neutralize at least part of the carboxyl groups of the binary ionomer resin include monovalent metal ions such as sodium, potassium, and lithium; divalent metals such as magnesium, calcium, zinc, barium, and cadmium. Ions; trivalent metal ions such as aluminum; and other ions such as tin and zirconium.

  A specific example of the binary ionomer resin is exemplified by a trade name “Himiran (registered trademark)” (for example, Himilan 1555 (Na), Himilan 1557 (available from Mitsui DuPont Polychemical Co., Ltd.). Zn), High Milan 1605 (Na), High Milan 1706 (Zn), High Milan 1707 (Na), High Milan AM 7311 (Mg), High Milan AM 7329 (Zn) and the like.

  Furthermore, “Surlyn (registered trademark)” commercially available from DuPont (for example, Surlyn 8945 (Na), Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li), Surlyn 7940 (Li), Surlyn AD8546 (Li)) ”and the like.

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

  As the binary ionomer resin, those exemplified may be used singly or as a mixture of two or more. Na, Zn, Li, Mg, etc. described in parentheses after the trade name indicate the metal species of these neutralized metal ions.

  The bending rigidity of the binary ionomer resin is preferably 140 MPa or more, more preferably 150 MPa or more, further preferably 160 MPa or more, preferably 550 MPa or less, more preferably 500 MPa or less, and further preferably 450 MPa or less. When the bending rigidity of the binary ionomer resin is too low, the spin amount of the golf ball tends to increase and the flight distance tends to decrease. When the bending rigidity is too high, the durability of the golf ball decreases. There is.

  The melt flow rate (190 ° C., 2.16 kg load) of the binary ionomer resin is preferably 0.1 g / 10 min or more, more preferably 0.5 g / 10 min or more, and further preferably 1.0 g / 10 min or more. Yes, it is preferably 30 g / 10 min or less, more preferably 20 g / 10 min or less, still more preferably 15 g / 10 min or less. When the melt flow rate (190 ° C., 2.16 kg load) of the binary ionomer resin is 0.1 g / 10 min or more, the fluidity of the thermoplastic resin composition is improved, and for example, a thin layer can be molded. It becomes. Further, when the melt flow rate (190 ° C., 2.16 kg load) of the binary ionomer resin is 30 g / 10 min or less, the durability of the obtained golf ball becomes better.

  The content of the α, β-unsaturated carboxylic acid component having 3 to 8 carbon atoms in the ternary ionomer resin is preferably 2% by mass or more, more preferably 3% by mass or more, and 30% by mass or less. Is more preferable, and more preferably 25% by mass or less.

  The neutralization degree of the carboxyl group of the ternary ionomer resin is preferably 20 mol% or more, more preferably 30 mol% or more, and preferably 100 mol% or less. If the degree of neutralization is 15 mol% or more, the resilience and durability of the resulting golf ball will be good. In addition, the neutralization degree of the carboxyl group of ionomer resin can be calculated | required by a following formula. Moreover, a metal component may be contained so that the neutralization degree of the carboxyl group in a theoretical ionomer resin may exceed 100 mol%. Degree of neutralization of ionomer resin (mol%) = 100 × number of moles of neutralized carboxyl groups in ionomer resin / total number of moles of carboxyl groups in ionomer resin

  Examples of metal ions that neutralize at least part of the carboxyl groups of the ternary ionomer resin include monovalent metal ions such as sodium, potassium, and lithium; divalent metals such as magnesium, calcium, zinc, barium, and cadmium. Ions; trivalent metal ions such as aluminum; and other ions such as tin and zirconium.

  A specific example of the ternary ionomer resin is exemplified by trade names such as “Himilan (registered trademark)” (for example, Himilan AM7327 (Zn), Himilan 1855 (Zn) available from Mitsui DuPont Polychemical Co., Ltd. ), Himilan 1856 (Na), Himilan AM7331 (Na), etc.). Further, as ternary ionomer resins commercially available from DuPont, “Surlin 6320 (Mg), Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn), Surlyn 9320W (Zn), HPF1000 (Mg ), HPF2000 (Mg), etc.) ”. Examples of the ternary ionomer resins commercially available from ExxonMobil Chemical Co., Ltd. include “Iotech 7510 (Zn), Iotech 7520 (Zn), etc.)”. In addition, Na, Zn, Mg, etc. described in parentheses after the trade name indicate the type of neutralized metal ion. The ternary ionomer resins may be used alone or in combination of two or more.

  The bending rigidity of the ternary ionomer resin is preferably 10 MPa or more, more preferably 11 MPa or more, further preferably 12 MPa or more, preferably 100 MPa or less, more preferably 97 MPa or less, and further preferably 95 MPa or less. When the bending rigidity of the ternary ionomer resin is too low, the spin amount of the golf ball tends to increase and the flight distance tends to decrease. When the bending rigidity is too high, the durability of the golf ball decreases. There is.

  The ternary ionomer resin has a melt flow rate (190 ° C., 2.16 kg load) of preferably 0.1 g / 10 min or more, more preferably 0.3 g / 10 min or more, still more preferably 0.5 g / 10 min or more. Yes, 20 g / 10 min or less is preferable, more preferably 15 g / 10 min or less, still more preferably 10 g / 10 min or less. If the melt flow rate (190 ° C., 2.16 kg load) of the ternary ionomer resin is 0.1 g / 10 min or more, the flowability of the thermoplastic resin composition is good, and a thin envelope layer can be easily molded. Become. Further, when the melt flow rate (190 ° C., 2.16 kg load) of the ternary ionomer resin is 20 g / 10 min or less, the durability of the obtained golf ball becomes better.

  The slab hardness of the ternary ionomer resin is preferably 20 or more in Shore D hardness, more preferably 25 or more, further preferably 30 or more, preferably 70 or less, more preferably 65 or less, and still more preferably 60 or less. It is. If the slab hardness is 20 or more in Shore D hardness, the resulting structural member will not be too soft and the resilience of the golf ball will be good. In addition, when the slab hardness is 70 or less in Shore D hardness, the obtained structural member does not become too hard, and the durability of the golf ball becomes better.

(2-2) Thermoplastic Olefin Copolymer As the thermoplastic olefin copolymer, for example, a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms; And ternary copolymers of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α, β-unsaturated carboxylic acid ester; or a mixture thereof. The thermoplastic olefin copolymer is a nonionic one whose carboxyl group is not neutralized.

  In the present invention, “a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms” is simply referred to as “binary copolymer”, and “olefin and carbon number 3”. The “terpolymer of ˜8 α, β-unsaturated carboxylic acids and α, β-unsaturated carboxylic acid ester” may be simply referred to as “ternary copolymer”.

  As said olefin, the same thing as the olefin which comprises ionomer resin can be mentioned, Especially it is preferable that it is ethylene. The α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and the ester thereof are the same as the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and the ester constituting the ionomer resin. Can be mentioned.

  The binary copolymer is preferably a binary copolymer of ethylene and (meth) acrylic acid. As the ternary copolymer, a ternary copolymer of ethylene, (meth) acrylic acid and (meth) acrylic acid ester is preferable. Here, (meth) acrylic acid means acrylic acid and / or methacrylic acid.

  The content of the α, β-unsaturated carboxylic acid component having 3 to 8 carbon atoms in the binary copolymer or ternary copolymer is preferably 4% by mass or more, more preferably 5% by mass or more. Yes, 30 mass% or less is preferable, More preferably, it is 25 mass% or less.

  The melt flow rate (190 ° C., 2.16 kg load) of the binary copolymer or ternary copolymer is preferably 5 g / 10 min or more, more preferably 10 g / 10 min or more, and further preferably 15 g / 10 min or more. Yes, 1700 g / 10 min or less is preferable, more preferably 1500 g / 10 min or less, still more preferably 1300 g / 10 min or less. When the melt flow rate (190 ° C., 2.16 kg load) of the binary copolymer or ternary copolymer is 5 g / 10 min or more, the fluidity of the thermoplastic resin composition becomes good, and the molding of the constituent members is performed. Becomes easier. Further, when the melt flow rate (190 ° C., 2.16 kg load) of the binary copolymer or ternary copolymer is 1700 g / 10 min or less, the durability of the obtained golf ball becomes better.

  Specific examples of the binary copolymer are exemplified by trade names, for example, trade names “NUCREL® (for example,“ Nucrel N1050H ”,“ Nucrel N2050H ”,“ Nucrel ”from Mitsui DuPont Polychemical Co., Ltd.). N1110H ”,“ Nucleel N0200H ”), an ethylene-methacrylic acid copolymer, an ethylene-acrylic acid copolymer available from Dow Chemical Company under the trade name“ PRIMACOR® 5980I ” Examples include coalescence.

  Specific examples of the ternary copolymer are exemplified by trade names: “Nucrel (registered trademark)” (for example, “Nucrel AN4318” and “Nucrel AN4319”) commercially available from Mitsui DuPont Polychemical Co., Ltd. Trade name "NUCREL" (registered trademark) (for example, "Nuclele AE") commercially available from DuPont, trade name "PRIMACOR (registered trademark) (for example, commercially available from Dow Chemical Company) , “PRIMACOR AT310”, “PRIMACOR AT320”) ”and the like. The binary copolymer or ternary copolymer may be used alone or in combination of two or more.

(2-3) Thermoplastic polyurethane resin and thermoplastic polyurethane elastomer Examples of the thermoplastic polyurethane resin and thermoplastic polyurethane elastomer include thermoplastic resins and thermoplastic elastomers having a plurality of urethane bonds in the main chain of the molecule. The polyurethane is preferably obtained by reacting a polyisocyanate component and a polyol component. Examples of the thermoplastic polyurethane elastomer include trade names “Elastolan XNY85A”, “Elastolan XNY90A”, “Elastolan XNY97A”, “Elastolan ET885”, “Elastolan ET890” manufactured by BASF Japan Ltd. Is mentioned.

(2-4) Thermoplastic styrene-based elastomer As the thermoplastic styrene-based elastomer, a thermoplastic elastomer containing a styrene block can be suitably used. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of the component of the diene block include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more components may be used in combination.

  The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), SBS hydrogenated, SIS hydrogenated and SIBS hydrogenated are included. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

  The content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 10% by mass or more, more preferably 12% by mass or more, and particularly preferably 15% by mass or more. In light of the feel at impact of the obtained golf ball, the content is preferably equal to or less than 50% by weight, more preferably equal to or less than 47% by weight, and particularly preferably equal to or less than 45% by weight.

  The styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and hydrogenated products thereof, and polyolefin. It is. The olefin component in the alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this alloy, the resilience performance of the golf ball is improved. Preferably, an olefin having 2 to 10 carbon atoms is used. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

  Specific examples of polymer alloys include “Lavalon T3221C”, “Lavalon T3339C”, “Lavalon SJ4400N”, “Lavalon SJ5400N”, “Lavalon SJ6400N”, “Lavalon SJ7400N”, “Lavalon SJ8400N”, “Lavalon SJ9400N” manufactured by Mitsubishi Chemical Corporation. And “Lavalon SR04”. Other specific examples of the styrene block-containing thermoplastic elastomer include “Epofriend A1010” manufactured by Daicel Chemical Industries and “Septon HG-252” manufactured by Kuraray.

(2-5) Thermoplastic polyamide resin and thermoplastic polyamide elastomer The thermoplastic polyamide is not particularly limited as long as it is a thermoplastic resin having a plurality of amide bonds (-NH-CO-) in the main chain of the molecule. For example, a product in which an amide bond is formed in the molecule by ring-opening polymerization of a lactam or by reacting a diamine component and a dicarboxylic acid component.

  Examples of the polyamide resin include aliphatic polyamides such as polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, and polyamide 612; poly-p-phenylene terephthale Examples thereof include aromatic polyamides such as amides and poly-m-phenylene isophthalamide. These may be used alone or in combination of two or more. Among these, aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 11 and polyamide 12 are preferable.

  Specific examples of the polyamide resin can be represented by trade names such as “Rilsan (registered trademark) B (for example, Rilsan BESN TL, Rilsan BESN P20 TL, Rilsan BESN P40 TL, Rilsan MB3610, Rilsan MB3610, commercially available from Arkema Co., Ltd.). BMF O, Rilsan BMN O, Rilsan BMN O TLD, Rilsan BMN BK TLD, Rilsan BMN P20 D, Rilsan BMN P40 D, etc.).

  The polyamide elastomer has a hard segment portion and a soft segment portion made of a polyamide component. As a soft segment part of a polyamide elastomer, a polyetherester component or a polyether component can be mentioned, for example. Examples of the polyamide elastomer include a polyether ester amide obtained by a reaction between a polyamide component (hard segment component) and a polyether ester component (soft segment component) composed of polyoxyalkylene glycol and dicarboxylic acid; Examples thereof include polyether amides obtained by a reaction between a segment component) and a polyether (soft segment component) composed of a dicarboxylic acid or a diamine obtained by amination or carboxylation of both ends of polyoxyalkylene glycol.

  Examples of the polyamide elastomer include “Pebax 2533”, “Pebax 3533”, “Pebax 4033”, and “Pebax 5533” manufactured by Arkema.

(2-6) Thermoplastic polyester resin and thermoplastic polyester elastomer The thermoplastic polyester resin is not particularly limited as long as it has a plurality of ester bonds in the main chain of the molecule. For example, dicarboxylic acid and diol are reacted. What is obtained by this is preferable. Examples of the thermoplastic polyester elastomer include a block copolymer having a hard segment made of a polyester component and a soft segment. As a polyester component which comprises a hard segment, aromatic polyester can be mentioned, for example. Examples of the soft segment component include aliphatic polyethers and aliphatic polyesters.

Specific examples of the polyester elastomer include “Hytrel 3548” and “Hytrel 4047” manufactured by Toray DuPont, “Primalloy A1606”, “Primalloy B1600” and “Primalloy B1700” manufactured by Mitsubishi Chemical Corporation. .

(2-7) Thermoplastic (meth) acrylic elastomer As the thermoplastic (meth) acrylic elastomer, a thermoplastic elastomer obtained by copolymerizing ethylene and (meth) acrylic ester can be exemplified. Specific examples of the thermoplastic (meth) acrylic elastomer include “Kuraray (a block copolymer of methyl methacrylate and butyl acrylate)” manufactured by Kuraray Co., Ltd.

  The thermoplastic resin composition comprises at least an ionomer resin, a thermoplastic olefin copolymer, a thermoplastic styrene elastomer, a thermoplastic polyester elastomer, a thermoplastic polyurethane elastomer, a thermoplastic polyamide elastomer, and a thermoplastic acrylic elastomer as a resin component. It is preferable to contain 1 type. It becomes easy to form a component having a desired hardness.

  In the present invention, when an ionomer resin or a thermoplastic olefin copolymer is used as the resin component contained in the thermoplastic resin composition, the thermoplastic resin composition further includes (B) a basic fatty acid metal salt described later. It may contain. (B) By containing a basic fatty acid metal salt, the neutralization degree of an ionomer resin and a thermoplastic olefin copolymer can be increased. By increasing the degree of neutralization, the resilience of the resulting component is increased.

  (B) The basic fatty acid metal salt is obtained by a known production method in which a fatty acid is reacted with a metal oxide or hydroxide, but a general fatty acid metal salt is a metal oxide or hydroxide whose reaction equivalent is a fatty acid. (B) the basic fatty acid metal salt is obtained by adding a metal oxide or hydroxide in excess of the fatty acid and the reaction equivalent, and the metal content of the product, The melting point and the like are different from general fatty acid metal salts.

(B) As a basic fatty acid metal salt, what is shown by following General formula (4) is preferable, for example.
mM ¹ O · M ² (RCOO) ₂ (4)
In the formula (4), m represents the number of moles of the metal oxide or metal hydroxide in the basic fatty acid metal salt represented by the formula (4). m is preferably from 0.1 to 2.0, and more preferably from 0.2 to 1.5. If m is less than 0.1, the resilience of the resulting resin composition may be reduced. If m exceeds 2.0, the melting point of the basic fatty acid metal salt becomes too high, resulting in a resin component. Dispersibility may be difficult. M ¹ and M ² are each preferably a metal belonging to Group 2 or Group 12 of the periodic table. M ¹ and M ² may be the same or different. Examples of the metal belonging to Group 2 include beryllium, magnesium, calcium, strontium, and barium. Examples of metals belonging to Group 12 include zinc, cadmium, and mercury. As the metal of M ¹ and M ² , for example, magnesium, calcium, barium, and zinc are preferable, and magnesium is more preferable.

  In the formula (4), RCOO represents a residue of a saturated fatty acid or an unsaturated fatty acid. (B) Specific examples (IUPAC name) of the saturated fatty acid component of the basic fatty acid metal salt include butanoic acid (C4), pentanoic acid (C5), hexanoic acid (C6), heptanoic acid (C7), and octanoic acid (C8). ), Nonanoic acid (C9), decanoic acid (C10), undecanoic acid (C11), dodecanoic acid (C12), tridecanoic acid (C13), tetradecanoic acid (C14), pentadecanoic acid (C15), hexadecanoic acid (C16), Heptadecanoic acid (C17), octadecanoic acid (C18), nonadecanoic acid (C19), icosanoic acid (C20), heicosanoic acid (C21), docosanoic acid (C22), tricosanoic acid (C23), tetracosanoic acid (C24), pentacosanoic acid (C25), hexacosanoic acid (C26), heptacosanoic acid (C27), octacosanoic acid (C28), nonacosa Acid (C29), triacontanoic acid (C30).

  (B) Specific examples of unsaturated fatty acid components of basic fatty acid metal salts (IUPAC name) include butenoic acid (C4), pentenoic acid (C5), hexenoic acid (C6), heptenoic acid (C7), octenoic acid ( C8), nonenic acid (C9), decenoic acid (C10), undecenoic acid (C11), dodecenoic acid (C12), tridecenoic acid (C13), tetradecenoic acid (C14), pentadecenoic acid (C15), hexadecenoic acid (C16) , Heptadecenoic acid (C17), octadecenoic acid (C18), nonadecenoic acid (C19), icosenoic acid (C20), henicosenoic acid (C21), docosenoic acid (C22), tricosenoic acid (C23), tetracosenoic acid (C24), pentacosene Acid (C25), Hexacosenic acid (C26), Heptacosenic acid (C27), Octacosenic acid (C28), Nonaco Phosphate (C29), and the like triacontene acid (C30).

  (B) Specific examples (common names) of the fatty acid component of the basic fatty acid metal salt include, for example, butyric acid (C4), valeric acid (C5), caproic acid (C6), enanthic acid (C7), caprylic acid (C8) ), Pelargonic acid (C9), capric acid (C10), lauric acid (C12), myristic acid (C14), myristoleic acid (C14), pentadecylic acid (C15), palmitic acid (C16), palmitoleic acid (C16) , Margaric acid (C17), stearic acid (C18), elaidic acid (C18), vaccenic acid (C18), oleic acid (C18), linoleic acid (C18), linolenic acid (C18), 12-hydroxystearic acid (C18) ), Arachidic acid (C20), gadoleic acid (C20), arachidonic acid (C20), eicosenoic acid (C20), behenic acid ( 22), erucic acid (C22), lignoceric acid (C24), nervonic acid (C24), cerotic acid (C26), montanic acid (C28), be mentioned melissic acid (C30).

  (B) The basic fatty acid metal salt is preferably a basic unsaturated fatty acid metal salt. Examples of the unsaturated fatty acid component include oleic acid (C18), erucic acid (C22), linoleic acid (C18), linolenic acid (C18), arachidonic acid (C20), eicosapentaenoic acid (C20), and docosahexaenoic acid (C22). , Stearidonic acid (C18), nervonic acid (C24), vaccenic acid (C18), gadoleic acid (C20), elaidic acid (C18), eicosenoic acid (C20), eicosadienoic acid (C20), docosadienoic acid (C22), pinolene The group consisting of acid (C18), eleostearic acid (C18), mead acid (C20), adrenic acid (C22), sardine acid (C22), nisinic acid (C24), and tetracosapentaenoic acid (C24) It is preferable that it is at least one selected from.

  (B) The basic fatty acid metal salt is preferably a basic fatty acid metal salt having 8 to 30 carbon atoms, and is preferably a basic fatty acid metal salt having 12 to 24 carbon atoms. (B) Specific examples of basic fatty acid metal salts include basic magnesium laurate, basic calcium laurate, basic zinc laurate, basic magnesium myristate, basic calcium myristate, basic zinc myristate, base Basic magnesium palmitate, basic calcium palmitate, basic zinc palmitate, basic magnesium oleate, basic calcium oleate, basic zinc oleate, basic magnesium stearate, basic calcium stearate, basic stearic acid Zinc, basic 12-hydroxy magnesium stearate, basic 12-hydroxy calcium stearate, basic zinc 12-hydroxy stearate, basic magnesium behenate, basic calcium behenate, basic behenine Zinc, and the like. (B) As a basic fatty acid metal salt, basic fatty acid magnesium is preferable, and basic magnesium stearate, basic magnesium behenate, basic magnesium laurate, and basic magnesium oleate are more preferable. The said basic fatty acid can also be used individually or in mixture of 2 or more types.

  (B) The melting point of the basic fatty acid metal salt is not particularly limited. For example, when the metal is magnesium, the melting point is preferably 100 ° C or higher, preferably 300 ° C or lower, more preferably 290 ° C or lower, The thing of 280 degrees C or less is further more preferable. If the melting point is in the above range, the dispersibility in the resin component is improved.

  (B) The content of the metal component of the basic fatty acid metal salt is preferably 1 mol% or more, more preferably 1.1 mol% or more, preferably 2 mol% or less, more preferably 1.9 mol% or less. This is because if the content of the metal component is within the above range, the resilience of the obtained golf ball constituent member is further improved. In addition, content of the metal component of (B) basic fatty acid metal salt means the value which divided the metal amount g contained per 1 mol of metal salts by the atomic weight of the metal, and is represented by mol%.

  The content of the (B) basic fatty acid metal salt in the thermoplastic resin composition used in the present invention is preferably 5 parts by mass or more and more preferably 8 parts by mass or more with respect to 100 parts by mass of the (A) resin component. Preferably, 10 parts by mass or more is more preferable, 100 parts by mass or less is preferable, and 90 parts by mass or less is more preferable. (B) When the content of the basic fatty acid metal salt is 5 parts by mass or more, the resilience of the golf ball constituent member is improved, and when the content is 100 parts by mass or less, golf with an increase in low molecular weight components. It is because the fall of durability of a ball component can be controlled.

  As the resin component constituting the center of the multi-piece golf ball of the present invention, an ionomer resin, a thermoplastic olefin copolymer, a thermoplastic styrene elastomer, or a mixture thereof is preferable. As said resin component, what contains a thermoplastic styrene-type elastomer is preferable. As the thermoplastic styrenic elastomer, an alloy of one or two or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS, and hydrogenated products thereof, and polyolefin is preferable. The content of the thermoplastic styrene-based elastomer in the resin component constituting the center is preferably 5% by mass or more, more preferably 10% by mass or more, preferably 100% by mass or less, and more preferably 80% by mass or less.

The following aspects can be mentioned as a preferable aspect of the resin component which comprises a center.
(1) An embodiment containing an ionomer resin and a thermoplastic styrenic elastomer as a resin component. In a more preferred embodiment, a ternary ionomer resin, one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS, and hydrogenated products thereof, and an alloy of a polyolefin and contains.

(2) An embodiment containing an ionomer resin and a thermoplastic styrene-based elastomer, and further containing a basic fatty acid metal salt in order to increase the degree of neutralization of the ionomer resin. In a more preferred embodiment, a ternary ionomer resin, one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS, and hydrogenated products thereof, and an alloy of a polyolefin and Further, a basic fatty acid metal salt is contained in order to increase the degree of neutralization of the ionomer resin.

(3) An embodiment containing a thermoplastic olefin copolymer and a thermoplastic styrenic elastomer, and further containing a basic fatty acid metal salt in order to increase the degree of neutralization of the thermoplastic olefin copolymer. Examples of the thermoplastic olefin copolymer include a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and / or an olefin and an α having 3 to 8 carbon atoms. , Β-unsaturated carboxylic acid and α, β-unsaturated carboxylic acid ester are preferable, and thermoplastic styrenic elastomers include SBS, SIS, SIBS, SEBS, SEPS, and SEEPS and their water. An alloy of one or more selected from the group consisting of an additive and a polyolefin is preferred.

  The resin component constituting the nth envelope layer (outermost layer) preferably contains an ionomer resin, a thermoplastic polyurethane resin (including a thermoplastic polyurethane elastomer), or a mixture thereof. When the resin component constituting the nth envelope layer (outermost layer) contains an ionomer resin, for example, a golf ball having excellent durability and a large flight distance can be obtained. When the resin component constituting the nth envelope layer (outermost layer) contains a thermoplastic polyurethane resin (including a thermoplastic polyurethane elastomer), a golf ball having excellent shot feel and controllability can be obtained.

  The thermoplastic resin composition used in the present invention can further contain (C) an additive. (C) Examples of the additive include pigment components such as a white pigment (for example, titanium oxide) and a blue pigment, a weight adjusting agent, a dispersant, an anti-aging agent, an ultraviolet absorber, a light stabilizer, a fluorescent material, and a fluorescent whitening. An agent etc. can be mentioned. Examples of the weight adjuster include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

  The content of the white pigment (for example, titanium oxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, with respect to 100 parts by mass of the (A) resin component. 8 parts by mass or less is more preferable. By making the content of the white pigment 0.5 parts by mass or more, concealment can be imparted to the obtained golf ball constituent member. Moreover, it is because durability of the obtained golf ball structural member may fall when content of a white pigment exceeds 10 mass parts.

  The thermoplastic resin composition used in the present invention can be obtained, for example, by dry blending (A) a resin component and (C) an additive. (B) The basic fatty acid metal salt is blended as necessary. Further, the dry blended mixture may be extruded to be pelletized. For dry blending, for example, it is preferable to use a mixer capable of blending pellet-shaped raw materials, and more preferably a tumbler type mixer. For the extrusion, a known extruder such as a single screw extruder, a twin screw extruder, or a twin screw single screw extruder can be used.

The first envelope layer adjacent to the center of the multi-piece golf ball of the present invention is formed from a rubber composition. Further, the second envelope layer to the nth envelope layer may also be formed from the rubber composition. The envelope layer formed from the rubber composition increases the resilience of the resulting golf ball.
Hereinafter, the rubber composition that can be used for the envelope layer of the present invention will be described. Examples of the rubber composition include those containing a base rubber, a crosslinking initiator, a co-crosslinking agent, and a filler.

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

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

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

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

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

  The said crosslinking initiator is mix | blended in order to bridge | crosslink a base rubber component. As the crosslinking initiator, an organic peroxide is suitable. Specifically, dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxy) Organic peroxides such as hexane and di-t-butyl peroxide can be mentioned, and among them, dicumyl peroxide is preferably used. The amount of the crosslinking initiator is preferably 0.3 parts by mass or more, more preferably 0.4 parts by mass or more, and preferably 5 parts by mass or less, more preferably 100 parts by mass of the base rubber. 3 parts by mass or less. If it is less than 0.3 parts by mass, the resulting envelope layer tends to be too soft and the resilience tends to decrease, and if it exceeds 5 parts by mass, the amount of co-crosslinking agent used is set to an appropriate hardness. There is a need to reduce, and the resilience becomes scarce.

  The co-crosslinking agent is considered to have a function of cross-linking rubber molecules by graft polymerization to a base rubber molecular chain. As the co-crosslinking agent, for example, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof can be used. Preferably, acrylic acid, methacrylic acid or a metal salt thereof is used. Can be mentioned. Examples of the metal constituting the metal salt include zinc, magnesium, calcium, aluminum, sodium and the like, and zinc is preferably used because resilience increases.

  The amount of the co-crosslinking agent used is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, and preferably 55 parts by mass or less with respect to 100 parts by mass of the base rubber. More preferably, it is 50 mass parts or less, More preferably, it is 48 mass parts or less. When the amount of the co-crosslinking agent used is less than 10 parts by mass, the amount of the crosslinking initiator must be increased in order to obtain an appropriate hardness, and the resilience tends to decrease. On the other hand, when the usage-amount of a co-crosslinking agent exceeds 55 mass parts, the surrounding layer obtained may become hard too much and there exists a possibility that a shot feeling may fall.

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

  In addition to the base rubber, the crosslinking initiator, the co-crosslinking agent, and the filler, an organic sulfur compound, an anti-aging agent, a peptizer, and the like can be appropriately added to the rubber composition.

  Examples of the organic sulfur compound include thiophenols, thionaphthols, polysulfides, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, thiurams, dithiocarbamates, and thiazoles. Among these, diphenyl disulfides can be suitably used as the organic sulfur compound. Examples of the diphenyl disulfides include diphenyl disulfide; bis (4-chlorophenyl) disulfide, bis (3-chlorophenyl) disulfide, bis (4-bromophenyl) disulfide, bis (3-bromophenyl) disulfide, bis (4- Mono-substituted products such as fluorophenyl) disulfide, bis (4-iodophenyl) disulfide, bis (4-cyanophenyl) disulfide; bis (2,5-dichlorophenyl) disulfide, bis (3,5-dichlorophenyl) disulfide, bis ( 2,6-dichlorophenyl) disulfide, bis (2,5-dibromophenyl) disulfide, bis (3,5-dibromophenyl) disulfide, bis (2-chloro-5-bromophenyl) disulfide, bis (2-cyano Disubstituted compounds such as 5-bromophenyl) disulfide; trisubstituted compounds such as bis (2,4,6-trichlorophenyl) disulfide and bis (2-cyano-4-chloro-6-bromophenyl) disulfide; bis (2 , 3,5,6-tetrachlorophenyl) disulfide and the like; bis (2,3,4,5,6-pentachlorophenyl) disulfide, bis (2,3,4,5,6-pentabromophenyl) Examples include penta-substituted products such as disulfide. These diphenyl disulfides have some influence on the vulcanized state of the rubber vulcanizate and can improve the resilience. Among these, it is preferable to use diphenyl disulfide and bis (pentabromophenyl) disulfide from the viewpoint that a highly repulsive golf ball can be obtained. The compounding amount of the organic sulfur compound is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more and preferably 5.0 parts by mass or less with respect to 100 parts by mass of the base rubber. More preferably, it is 3.0 parts by mass or less.

  The blending amount of the anti-aging agent is preferably 0.1 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the base rubber. Moreover, it is preferable that the compounding quantity of a peptizer is 0.1 to 5 mass parts with respect to 100 mass parts of base rubber.

  The rubber composition can be molded into the envelope layer by kneading the raw materials and molding in a mold.

(3) Manufacturing method of multi-piece golf ball of this invention The said center is obtained by injection-molding a thermoplastic resin composition, for example. Specifically, a thermoplastic resin composition heated and melted at 160 ° C. to 260 ° C. is injected in a mold clamped at a pressure of 1 MPa to 100 MPa in 1 second to 100 seconds, and cooled for 30 seconds to 300 seconds. It is preferable to perform by opening the mold.

  The method for molding the envelope layer made of the rubber composition is not particularly limited. For example, the rubber composition is molded into a half-shell half shell in advance, and the two are used to wrap the center, and 130 ° C. A method of pressure molding at ˜170 ° C. for 5 minutes to 30 minutes can be mentioned. Further, the envelope layer may be formed by injection molding the rubber composition.

  The method of molding the envelope layer made of the thermoplastic resin composition is not particularly limited. For example, the thermoplastic resin composition is molded into a half-shell half shell in advance, and the two are used to form a center. A method of wrapping and press molding at 130 ° C. to 170 ° C. for 1 minute to 5 minutes, or a method of wrapping the center by injection molding of the thermoplastic resin composition directly onto the center is used. The envelope layer of the multi-piece golf ball of the present invention is preferably molded by an injection molding method. This is because the envelope layer can be more easily produced by adopting the injection molding method.

  When molding the envelope layer by injection molding the thermoplastic resin composition on the center, the upper and lower molds for molding have hemispherical cavities, with pimples, and hold pins that allow part of the pimples to advance and retract. It is preferable to use what is also used. Molding of the envelope layer by injection molding can be performed by projecting a hold pin, inserting a center and holding it, and then injecting a heat-melted thermoplastic resin composition and cooling it. .

  When the envelope layer is formed by the compression molding method, the half shell can be molded by either the compression molding method or the injection molding method, but the compression molding method is preferred. The conditions for compression molding the thermoplastic resin composition into a half shell are, for example, -20 ° C or higher and + 70 ° C with respect to the flow start temperature of the thermoplastic resin composition at a pressure of 1 MPa or higher and 20 MPa or lower. The following molding temperatures can be mentioned. By setting the molding conditions, a half shell having a uniform thickness can be molded. As a method for forming the envelope layer using a half shell, for example, a method in which a spherical body is covered with two half shells and compression-molded can be mentioned. As conditions for compression-molding the half shell to form the envelope layer, for example, at a molding pressure of 0.5 MPa or more and 25 MPa or less, the flow start temperature of the thermoplastic resin composition is −20 ° C. or more and + 70 ° C. The following molding temperatures can be mentioned. By setting the molding conditions, an envelope layer having a uniform thickness can be molded.

The molding temperature means the maximum temperature that the surface of the concave portion of the lower mold reaches between the mold clamping and the mold opening. In addition, the flow starting temperature of the thermoplastic resin composition was determined by using a “Flow Tester CFT-500” manufactured by Shimadzu Corporation, a pellet-shaped thermoplastic resin composition, a plunger area: 1 cm ² , DIE LENGTH: 1 mm, DIE DIA. 1 mm, load: 588.399 N, start temperature: 30 ° C., temperature increase rate: 3 ° C./min.

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

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

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples, and all modifications and embodiments without departing from the gist of the present invention are not limited thereto. Included in range.

(1) Material hardness (Shore D hardness)
In the case of the thermoplastic resin composition, a sheet having a thickness of about 2 mm was produced by injection molding. In the case of the rubber composition, it was pressed at 170 ° C. for 25 minutes to produce a sheet having a thickness of about 2 mm. This sheet is stored at 23 ° C. for 2 weeks, and a polymer meter provided with a spring type hardness meter Shore D type defined in ASTM-D2240 in a state where three or more sheets are stacked so as not to affect the measurement substrate and the like. The measurement was made using an automatic rubber hardness tester P1 type.

(2) Compression deformation (mm)
The amount of deformation in the compression direction (the amount by which the core or golf ball shrinks in the compression direction) from when the initial load 98N was applied to the center or golf ball to when the final load 1275N was applied was measured.

(3) Spin amount of approach shot (controllability)
The spin rate (rpm) when an approach shot of about 40 yards from the fairway of the course was hit to 10 testers of handicap 10 or less was measured. The measurement was performed by hitting each golf ball with a CG15 forged wedge (58 °) manufactured by Cleveland Golf. The spin amount (rpm) was measured by taking continuous photographs of the hit golf ball, and the average value of 10 players was taken as the spin amount.

(4) Driver spin rate (rpm)
A golf head swing robot M / C is attached to a metal head W # 1 driver (Dunlop Sports, XXIO S Loft 11 °), hits a golf ball at a head speed of 50 m / sec, and golf immediately after hitting The spin rate of the ball was measured. The measurement was performed 12 times for each golf ball, and the average value was taken as the measured value of the golf ball. The spin speed of the golf ball immediately after hitting was measured by taking continuous photographs of the hit golf ball.

[Production of golf balls]
(1) Preparation of thermoplastic resin composition As shown in Table 1, the blended materials were dry blended, mixed by a twin-screw kneading type extruder, and extruded into cold water in a strand shape. The extruded strand was cut by a pelletizer to prepare a pellet-shaped thermoplastic resin composition. The extrusion conditions were a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D = 35, and the blend was heated to 160-230 ° C. at the die position of the extruder.

The raw materials used in Table 1 are as follows.
High Milan AM7327: manufactured by Mitsui DuPont Polychemical Co., Ltd., zinc ion neutralized ethylene-methacrylic acid-butyl acrylate terpolymer ionomer resin (melt flow rate (190 ° C. × 2.16 kgf): 0.7 g / 10 min, bent (Rigidity: 35 MPa)
Nukurel AN4319: made by Mitsui DuPont Polychemical Co., Ltd., ethylene / methacrylic acid / butyl acrylate copolymer (melt flow rate (190 ° C. × 2.16 kgf): 55 g / 10 min, bending rigidity 21: MPa)
HPF2000: DuPont, magnesium ion neutralized terpolymer ionomer resin (melt flow rate (190 ° C. × 2.16 kgf): 1.0 g / 10 min, flexural rigidity: 64 MPa)
HPF1000: DuPont, magnesium ion neutralized terpolymer ionomer resin (melt flow rate (190 ° C. × 2.16 kgf): 0.7 g / 10 min, flexural rigidity: 190 MPa)
High Milan 1605: Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui DuPont Polychemical Co., Ltd. (melt flow rate (190 ° C. × 2.16 kgf): 2.8 g / 10 min, flexural rigidity: 320 MPa)
High Milan AM7329: Mitsui DuPont Polychemical Co., Ltd., zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin (melt flow rate (190 ° C. × 2.16 kgf): 5 g / 10 min, flexural rigidity: 221 MPa)
Basic magnesium oleate: Nitto Kasei Kogyo Co., Ltd. (metal content 1.7 mol%, in formula (4), M ¹ = M ² = Mg, R = carbon number 17)
Lavalon T3221C: thermoplastic styrene elastomer (SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and one or more selected from the group consisting of these hydrogenated products, and an alloy of polyolefin )
Elastollan XNY84A: BASF Japan Thermoplastic Polyurethane Elastomer Titanium Oxide: Ishihara Sangyo A220

(2) Preparation of rubber composition The materials shown in Table 2 were kneaded to prepare a rubber composition.

The raw materials used in Table 2 are as follows.
Polybutadiene rubber: “BR730 (high cis polybutadiene, cis-1,4-bond content = 96 mass%, 1,2-vinyl bond content = 1.3 mass%, Mooney viscosity (ML _{1 + 4} (100 ° C.)) = 55, molecular weight distribution (Mw / Mn) = 3) ”
Zinc acrylate: “ZNDA-90S”, manufactured by Nippon Distilled Industries
Zinc oxide: Toho Zinc Co., Ltd., “Ginseng (registered trademark) R”
Barium sulfate: Sakai Chemical Co., Ltd. “Barium sulfate BD”
Dicumyl peroxide: NOF Corporation, “Park Mill (registered trademark) D”
Diphenyl disulfide: manufactured by Sumitomo Seika Co., Ltd.

(2) Production of spherical center As shown in Table 4, the obtained pellet-shaped thermoplastic resin composition was injection-molded at 200 ° C. to produce a spherical center. Golf ball No. For the rubber composition No. 11 shown in Table 2, the rubber composition No. A was pressed at 170 ° C. for 25 minutes to form a spherical center.

(3) Production of envelope layer made of rubber composition A half shell was molded from the rubber composition shown in Table 2. The center was covered with two half shells. The center and the half shell were both put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity, and heated at 170 ° C. for 25 minutes to produce an envelope layer composed of a rubber composition. Golf ball no. For No. 11, a two-layer core made of a rubber composition was molded. The properties of the two-layer core are shown in Table 3.

(4) Production of envelope layer made of thermoplastic resin composition The thermoplastic resin composition obtained above was injection-molded at 200 ° C. as shown in Table 4, so that the second envelope layer was changed to n−1. An envelope layer was formed. The nth envelope layer (outermost layer) was formed by compression molding the thermoplastic resin composition obtained above. In compression molding of the half shell, the obtained pellet-shaped thermoplastic resin composition was put in one for each concave portion of the lower mold of the half shell molding die and pressed. The compression molding was performed under the conditions of a molding temperature of 160 ° C., a molding time of 2 minutes, and a molding pressure of 11 MPa. The sphere on which the (n-1) th envelope layer was formed was concentrically covered with two half shells, placed in a mold having a large number of pimples on the cavity surface, and a cover was formed by compression molding. The compression molding was performed under the conditions of a molding temperature of 150 ° C., a molding time of 3 minutes, and a molding pressure of 13 MPa. In the nth envelope layer (outermost layer) after molding, a large number of dimples having a reversed pimple shape were formed. Golf ball no. 1-No. 10 formed 5 envelope layers covering the spherical center.

  The surface of the obtained golf ball main body is sandblasted and marked, and then a clear paint is applied and the paint is dried in an oven at 40 ° C. to obtain a golf ball having a diameter of 42.8 mm and a mass of 45.4 g. It was. The results of evaluating the obtained golf ball are also shown in Table 4.

  From the results of Table 4, a multi-piece golf ball having a center and an enveloping layer of n layers (n is a natural number of 3 or more) covering the center, the material hardness (Shore D hardness) of the center being H0. And the first envelope layer, the second envelope layer, the third envelope layer, the fourth envelope layer,... The (n-1) envelope layer, the nth envelope layer (the outermost layer) Outer layer), and when the material hardness (Shore D hardness) is H1, H2, H3, H4... Hn-1, Hn, H1 <H0 <Hn-1 is satisfied. A multi-piece golf ball formed of a plastic resin composition and having the first envelope layer formed of a rubber composition has a low spin rate on driver shots and a high spin rate on approach shots. As a result, the multi-piece golf ball of the present invention often flies on driver shots and stops well on approach shots.

  The present invention is useful as a golf ball that flies well on a driver shot and stops well on an approach shot.

Claims (5)

A multi-piece golf ball having a center and an enveloping layer of n layers (n is a natural number of 4 to 10) covering the center,
The center material hardness (Shore D hardness) is H0,
The envelope layer formed in this order from the center side, the first envelope layer, the second envelope layer, · · · (n-1) -th surrounding layer, the n surrounding layer (outermost layer), and the material hardness (Shore D hardness) the, H1, H2, · · · Hn -1, when the Hn,
H1 <H0 <Hn-1 is satisfied, and
H1 <H2 <H3 when n = 4, H1 <H2 <H3 <H4 when n = 5, H1 <H2 <H3 <H4 <H5 when n = 6, H1 <H when n = 7 When H2 <H3 <H4 <H5 <H6, n = 8, H1 <H2 <H3 <H4 <H5 <H6 <H7, and when n = 9, H1 <H2 <H3 <H4 <H5 <H6 <H7 < When H8, n = 10, the relationship of H1 <H2 <H3 <H4 <H5 <H6 <H7 <H8 <H9 is satisfied,
The material hardness H0 (Shore D hardness) of the center is 7 or more and 30 or less,
The material hardness H1 (Shore D hardness) of the first envelope layer is 5 or more,
The material hardness H2 (Shore D hardness) of the second envelope layer is 5 or more and 50 or less,
The material hardness Hn-1 (Shore D hardness) of the n-1th envelope layer is 50 or more and 75 or less,
The material hardness Hn (Shore D hardness) of the n envelope layer (outermost layer) is 10 or more and 50 or less,
The hardness difference (H0−H1) between the material hardness H0 (Shore D hardness) of the center and the material hardness H1 (Shore D hardness) of the first envelope layer is 2 or more,
The hardness difference ((Hn-1) -H0) between the material hardness Hn-1 (Shore D hardness) of the n-1th envelope layer and the material hardness H0 (Shore D hardness) of the center is 65 or less,
The hardness difference ((Hn-1) -H1) between the material hardness Hn-1 (Shore D hardness) of the n-1th envelope layer and the material hardness H1 of the first envelope layer (Shore D hardness) is 65. And
The center has a diameter of 10 mm or more and 20 mm or less,
The thickness of each layer from the first envelope layer to the (n-1) th envelope layer is 0.3 mm to 10 mm,
The n-th envelope layer has a thickness of 0.3 mm to 2.0 mm;
The multi-piece golf ball, wherein the center is formed from a thermoplastic resin composition, and the first envelope layer is formed from a rubber composition. The thermoplastic resin composition comprises at least an ionomer resin, a thermoplastic olefin copolymer, a thermoplastic styrene elastomer, a thermoplastic polyester elastomer, a thermoplastic polyurethane elastomer, a thermoplastic polyamide elastomer, and a thermoplastic acrylic elastomer as a resin component. The multi-piece golf ball according to claim 1, comprising one kind. The thermoplastic resin composition contains an ionomer resin,
The multi-piece golf ball according to claim 2 , wherein the ionomer resin is a ternary ionomer resin. The multi-piece golf ball according to any one of claims 1 to 3 , wherein the thermoplastic resin composition contains an ionomer resin and a thermoplastic styrene-based elastomer as resin components. The multi-piece golf ball according to any one of claims 1 to 4 , wherein the second to n-th envelope layers are formed from the thermoplastic resin composition.

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