Multi-piece solid golf ball

1. A multi-piece solid golf ball comprising a solid core, a cover, at least one intermediate layer situated therebetween, and a plurality of dimples on a surface of the ball, wherein the solid core has a diameter of from 34 to 38.7 mm, a deflection when compressed under a final load of 130 kgf from an initial load of 10 kgf of from 3.5 to 6.0 mm, a Shore D hardness at a center of the core of from 20 to 38, a Shore D hardness in a region 5 mm to 10 mm from the core center of from 23 to 41, a Shore D hardness 15 mm from the core center of from 28 to 46, and a Shore D hardness at a surface of the core of from 37 to 62; the intermediate layer is composed primarily of a material obtained by mixing under applied heat:

100 parts by weight of a resin component of (a) from 95 to 50 wt % of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random copolymer and/or a metal salt thereof, (b) from 0 to 20 wt % of an olefin-unsaturated carboxylic acid random copolymer and/or a metal salt thereof, and (c) from 5 to 50 wt % of a thermoplastic block copolymer composed of a crystalline polyolefin block and a polyethylene/butylene random copolymer,

(d) from 5 to 170 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of from 280 to 1500, and

(e) from 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups within components (a) and (d);

the intermediate layer material has a Shore D hardness of from 35 to 60 and has a Shore D hardness difference with the surface of the solid core of within ±10; the cover is formed primarily of polyurethane, has a thickness of from 0.5 to 1.5 mm, and has a Shore D hardness of from 53 to 65 which is higher than the intermediate layer hardness, the Shore D hardness difference therebetween being from 6 to 15; the overall ball has a deflection, when compressed under a final load of 130 kgf from an initial load of 10 kgf, of from 2.9 to 5.0 mm; and the number of dimples is from 250 to 400 and the sum of the dimple trajectory volumes VT (total dimple trajectory volume TVT) obtained by multiplying the volume of each dimple by the square root of the dimple diameter is from 640 to 800.

2. The multi-piece solid golf ball of claim 1 , wherein the intermediate layer material has a melt flow rate (MFR) of from 5 to 30 g/10 min.

3. A multi-piece solid golf ball comprising a solid core, a cover, at least one intermediate layer situated therebetween, and a plurality of dimples on a surface of the ball, wherein the solid core has a diameter of from 34 to 38.7 mm, a deflection when compressed under a final load of 130 kgf from an initial load of 10 kgf of from 3.5 to 6.0 mm, a Shore D hardness at a center of the core of from 20 to 38, a Shore D hardness in a region 5 mm to 10 mm from the core center of from 23 to 41, a Shore D hardness 15 mm from the core center of from 28 to 46, and a Shore D hardness at a surface of the core of from 37 to 62; the intermediate layer is composed primarily of a material obtained by mixing under applied heat:

100 parts by weight of a resin component of (a) from 95 to 50 wt % of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random copolymer and/or a metal salt thereof, (b) from 0 to 20 wt % of an olefin-unsaturated carboxylic acid random copolymer and/or a metal salt thereof, and (c) from 5 to 50 wt % of a thermoplastic block copolymer composed of a crystalline polyolefin block and a polyethylene/butylene random copolymer,

(d) from 5 to 170 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of from 280 to 1500, and

(e) from 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups within components (a) and (d);

the intermediate layer has a thickness of from 1.0 to 2.5 mm; the intermediate layer material a Shore D hardness difference with the surface of the solid core of within ±10; the cover is formed primarily of polyurethane, has a thickness of from 0.5 to 1.5 mm, and has a Shore D hardness higher than the intermediate layer hardness, the Shore D hardness difference therebetween being from 6 to 15; the cover and the intermediate layer have a combined thickness of from 1.5 to 3.5 mm; and the overall ball has a deflection, when compressed under a final load of 130 kgf from an initial load of 10 kgf, of from 2.9 to 5.0 mm; and the number of dimples is from 250 to 400 and the sum of the dimple trajectory volumes VT (total dimple trajectory volume TVT) obtained by multiplying the volume of each dimple by the square root of the dimple diameter is from 640 to 800.

4. The multi-piece solid golf ball of claim 3 , wherein the intermediate layer material has a melt flow rate (MFR) of from 5 to 30 g/10 min.

5. A multi-piece solid golf ball comprising a solid core, a cover, at least one intermediate layer situated therebetween, and a plurality of dimples on a surface of the ball, wherein the solid core has a diameter of from 34 to 38.7 mm, a deflection when compressed under a final load of 130 kgf from an initial load of 10 kgf of from 3.5 to 6.0 mm, a Shore D hardness at a center of the core of from 20 to 38, a Shore D hardness in a region 5 mm to 10 mm from the core center of from 23 to 41, a Shore D hardness 15 mm from the core center of from 28 to 46, and a Shore D hardness at a surface of the core of from 37 to 62; the intermediate layer is composed primarily of a material obtained by mixing under applied heat:

100 parts by weight of a resin component of (a) from 95 to 50 wt % of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random copolymer and/or a metal salt thereof, (b) from 0 to 20 wt % of an olefin-unsaturated carboxylic acid random copolymer and/or a metal salt thereof, and (c) from 5 to 50 wt % of a thermoplastic block copolymer composed of a crystalline polyolefin block and a polyethylene/butylene random copolymer,

(d) from 5 to 170 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of from 280 to 1500, and

(e) from 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups within components (a) and (d);

the intermediate layer has a thickness of from 1.0 to 2.5 mm; the intermediate layer material has a Shore D hardness of from 35 to 60; the cover is formed primarily of polyurethane, has a thickness of from 0.5 to 1.5 mm, and has a Shore D hardness of from 53 to 65; the cover and the intermediate layer have a combined thickness of from 1.5 to 3.5 mm; and the overall ball has a deflection, when compressed under a final load of 130 kgf from an initial load of 10 kgf, of from 2.9 to 5.0 mm; and the number of dimples is from 250 to 400 and the sum of the dimple trajectory volumes VT (total dimple trajectory volume TVT) obtained by multiplying the volume of each dimple by the square root of the dimple diameter is from 640 to 800.

6. The multi-piece solid golf ball of claim 5 , wherein the intermediate layer material has a melt flow rate (MFR) of from 5 to 30 g/10 min.

7. A multi-piece solid golf ball comprising a solid core, a cover, at least one intermediate layer situated therebetween, and a plurality of dimples on a surface of the ball, wherein the solid core has a diameter of from 34 to 38.7 mm, a deflection when compressed under a final load of 130 kgf from an initial load of 10 kgf of from 3.5 to 6.0 mm, a Shore D hardness at a center of the core of from 20 to 38, a Shore D hardness in a region 5 mm to 10 mm from the core center of from 23 to 41, a Shore D hardness 15 mm from the core center of from 28 to 46, a Shore D hardness at a surface of the core of from 37 to 62 and a Shore D hardness difference of 5 to 30 between the surface and the center; the intermediate layer is composed primarily of a material obtained by mixing under applied heat:

100 parts by weight of a resin component of (a) from 95 to 50 wt % of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random copolymer and/or a metal salt thereof, (b) from 0 to 20 wt % of an olefin-unsaturated carboxylic acid random copolymer and/or a metal salt thereof, and (c) from 5 to 50 wt % of a thermoplastic block copolymer composed of a crystalline polyolefin block and a polyethylene/butylene random copolymer,

(d) from 5 to 170 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of from 280 to 1500, and

(e) from 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups within components (a) and (d);

the intermediate layer has a thickness of from 1.0 to 2.5 mm; the intermediate layer material has a Shore D hardness difference with the surface of the solid core of within ±10; the cover is formed primarily of polyurethane, has a thickness of from 0.5 to 1.5 mm, and has a Shore D hardness higher than the intermediate layer hardness, the Shore D hardness difference therebetween being from 6 to 15; the cover and the intermediate layer have a combined thickness of from 1.5 to 3.5 mm; and the overall ball has a deflection, when compressed under a final load of 130 kgf from an initial load of 10 kgf, of from 2.9 to 5.0 mm; and the number of dimples is from 250 to 400 and the sum of the dimple trajectory volumes VT (total dimple trajectory volume TVT) obtained by multiplying the volume of each dimple by the square root of the dimple diameter is from 640 to 800.

8. The multi-piece solid golf ball of claim 7 , wherein the intermediate layer material has a melt flow rate (MFR) of from 5 to 30 g/10 min.