A golf ball 2 has a core, a mid layer and a cover. This mid layer comprises 10 parts by weight or greater and 70 parts by weight or less of a thermoplastic elastomer containing a styrene block having a material hardness of less than 10, and 30 parts by weight or greater and 90 parts by weight or less of an ethylene-(meth)acrylic acid copolymer based ionomer resin having a material hardness of 50 or greater and 70 or less. Hardness of this mid layer is less than 40, and the thickness is equal to or less than 1.2 mm. This golf ball 2 has seven kinds of dimples (A to G), each having a different diameter. When all the dimples are arranged in decreasing order of the diameter Di, ratio (Dx/Dn) of the mean diameter Dx of the dimples ranking in the top 10% to the mean diameter Dn of the dimples ranking in the bottom 10% is equal to or greater than 1.30. Standard deviation η of diameters of all the dimples is equal to or less than 0.52.
1. A golf ball which comprises a core, a mid layer and a cover,
said mid layer comprising 10 parts by weight or greater and 70 parts by weight or less of a thermoplastic elastomer containing a styrene block having a material hardness of less than 10, and 30 parts by weight or greater and 90 parts by weight or less of an ethylene-(meth)acrylic acid copolymer based ionomer resin having a material hardness of 50 or greater and 70 or less, per 100 parts by weight of the base polymer, wherein said mid layer has a shore D hardness of less than 40, and said mid layer has a thickness of equal to or less than 1.2 mm,
said golf ball having three or more kinds of dimples, each having a different diameter, on the surface thereof,
an occupation ratio of the total area of the dimples in the surface area of a phantom sphere being equal to or greater than 75%,
a ratio Dx/Dn being equal to or greater than 1.30, wherein a mean diameter of the dimples having a diameter ranking in the top 10% of the diameters of all the dimples is defined as Dx and a mean diameter of the dimples having a diameter ranking in the bottom 10% of the diameters of all the dimples is defined as Dn, and
a standard deviation η of diameters of all the dimples being equal to or less than 0.52.
2. The golf ball according to claim 1 , wherein said cover comprises one part by weight or greater and 30 parts by weight or less of a thermoplastic elastomer containing a styrene block having a material hardness of less than 10, and 50 parts by weight or greater and 99 parts by weight or less of an ethylene-(meth)acrylic acid copolymer based ionomer resin having a material hardness of 50 or greater and 70 or less, per 100 parts by weight of the base polymer,
said cover having a hardness of equal to or greater than 55, and
said covering having a thickness of 1.0 mm or greater and 1.8 mm or less.
3. The golf ball according to claim 1 , wherein the mean value of the diameters of all the dimples is equal to or greater than 4.00 mm.
4. The golf ball according to claim 1 , which comprises five or more kinds of dimples, each having a different diameter, on the surface thereof.
5. The golf ball according to claim 1 , wherein the thermoplastic elastomer containing a styrene block has a material hardness of less than 8.
6. The golf ball according to claim 1 , wherein the thermoplastic elastomer containing a styrene block has a material hardness of less than 6.
7. The golf ball according to claim 1 , wherein the thermoplastic elastomer containing a styrene block has a material hardness of less than 2.
8. The golf ball according to claim 1 , wherein the ethylene-(meth)acrylic acid copolymer based ionomer resin has a material hardness of 53 or greater and 67 or less.
9. The golf ball according to claim 1 , wherein the ethylene-(meth)acrylic acid copolymer based ionomer resin has a material hardness of 55 or greater and 65 or less.