A golf ball 2 includes a core 4 , an envelope layer 6 positioned outside the core 4 , a mid layer 8 positioned outside the envelope layer 6 , and a cover 10 positioned outside the mid layer 8 . The core 4 includes a spherical center 12 and a core outer layer 14 positioned outside the center 12 . The center 12 has a diameter of 1 mm or greater and 15 mm or less. The difference (H4−H3) between the JIS-C hardness H4 of the core 4 at its surface and the JIS-C hardness H3 of the core outer layer 14 at its innermost portion is equal to or greater than 10. The cover 10 has a Shore D hardness H7 less than 40. The Shore D hardnesses H5, H6 and H7 of the envelope layer 6 , the mid layer 8 , and the cover 10 satisfy that H5>H6≧H7.
1. A golf ball comprising a core, an envelope layer positioned outside the core, a mid layer positioned outside the envelope layer, and a cover positioned outside the mid layer, wherein:
the core includes a center and a core outer layer positioned outside the center;
the core surface JIS-C hardness H4 is greater than the core outer layer JIS-C hardness H3 at its innermost portion by an amount that is equal to or greater than 10; and
the envelope Shore D hardness H5, the mid layer Shore D hardness H6 and the cover Shore D hardness H7 satisfy the following mathematical formula: H5>H6≧H7.
2. The golf ball according to claim 1 , wherein the center has a diameter of 1 mm or greater than 15 mm or less.
3. The golf ball according to claim 1 , wherein the envelope layer has a thickness of 0.5 mm or greater and 2.2 mm or less.
4. The golf ball according to claim 1 , wherein the mid layer has a thickness of 0.1 mm or greater than 1.2 mm or less.
5. The golf ball according to claim 1 , wherein the mid layer Shore D hardness H6 and the cover Shore D hardness H7 satisfy the following mathematical formula: H6>H7.
6. The golf ball according to claim 5 , wherein the hardness H7 is equal to or less than 40.
7. The golf ball according to claim 1 , wherein the center JIS-C hardness H2 at its surface is greater than the center JIS-C hardness H1 at its central point by an amount that is equal to or less than 15.
8. The golf ball according to claim 1 , wherein the envelope layer has a first thickness, the mid layer has a second thickness, and the cover has a third thickness, and wherein the second thickness is no greater than the first thickness, and the second thickness is no greater than the third thickness.
9. A golf ball comprising a core, an envelope layer positioned outside the core, a mid layer positioned outside the envelope layer, and a cover positioned outside the mid layer, wherein:
the core includes a center and a core outer layer positioned outside the center;
the core has a diameter of 28.0 mm or greater and 40.2 mm or less;
the core outer layer JIS-C hardness H3 at its innermost portion is greater than the center JIS-C hardness H2 at its surface by an amount that is equal to or less than 35; and
the envelope layer Shore D hardness H5, the mid layer Shore D hardness H6 and the cover Shore D hardness H7 satisfy the following mathematical formula: H5>H6>H7.
10. The golf ball according to claim 9 , wherein the center JIS-C hardness H2 at its surface is greater than the center JIS-C hardness H1 at its central point by an amount that is equal to or less than 15.
11. A golf ball comprising a core, a mid layer positioned outside the core, a cover positioned outside the mid layer and at least one layer positioned between the cover and the core wherein:
the core includes a center and a core outer layer positioned outside the center;
the core outer layer JIS-C hardness H3 at its innermost portion is greater than the center JIS-C hardness H2 at its surface by an amount that is equal to or less than 35; and
the envelope layer Shore D hardness H5, the mid layer Shore D hardness H6 and the cover Shore D hardness H7 satisfy the following mathematical formula: H5>H6>H7.