Multi-piece solid golf ball

1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer and a cover,

wherein the core, envelope layer, intermediate layer and cover have respective surface hardnesses which satisfy the relationship:

core surface hardness>envelope layer surface hardness<intermediate layer surface hardness<cover surface hardness;

the surface hardness of the core and the surface hardness of the envelope layer, expressed in terms of Shore D hardness, satisfy the relationship:

−14≦(envelope layer surface hardness−core surface hardness)≦−5;

the surface hardness of the intermediate layer and the surface hardness of the cover, expressed in terms of Shore D hardness, satisfy the relationship:

5≦(cover surface hardness−intermediate layer surface hardness)≦15;

the ball and a sphere composed of the core covered peripherally by the envelope layer and the intermediate layer (intermediate layer-encased sphere) have respective initial velocities (m/s) which satisfy the relationship:

−1.0 m/s≦(ball initial velocity−intermediate layer-encased sphere initial velocity)≦0 m/s;

the intermediate layer-encased sphere and a sphere composed of the core covered peripherally by the envelope layer (envelope layer-encased sphere) have respective initial velocities (m/s) which satisfy the relationship:

−0.2 m/s≦(intermediate layer-encased sphere initial velocity−envelope layer-encased sphere initial velocity); and

the ball satisfies the relationship:

0.86≦A/B≦0.98,

where A is the deflection (mm) of the ball when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) and B is the deflection (mm) of the intermediate layer-encased sphere when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), and wherein the surface hardness of the envelope layer and the surface hardness of the intermediate layer, expressed in terms of Shore D hardness, satisfy the relationship:

20≦(intermediate layer surface hardness−envelope layer surface hardness)≦30.

2. The multi-piece solid golf ball of claim 1 , wherein the initial velocity (m/s) of the core and the initial velocity (m/s) of the ball satisfy the relationship:

−1.0 m/s≦(ball initial velocity−core initial velocity)≦0 m/s.

3. The multi-piece solid golf ball of claim 1 , wherein the initial velocity (m/s) of the envelope layer-encased sphere and the initial velocity (m/s) of the ball satisfy the relationship:

−0.4 m/s≦(ball initial velocity−envelope layer-encased sphere initial velocity)≦0.4 m/s,

and the initial velocity (m/s) of the core and the initial velocity (m/s) of the ball satisfy the relationship:

−0.8 m/s≦(ball initial velocity−core initial velocity)≦0 m/s.

4. The multi-piece solid golf ball of claim 1 , wherein the envelope layer, the intermediate layer and the cover have respective thicknesses which satisfy the relationships:

envelope layer thickness≦cover thickness, and

intermediate layer thickness≦cover thickness.

5. The multi-piece solid golf ball of claim 1 , wherein the intermediate layer and the cover have respective specific gravities which satisfy the relationship:

cover specific≧gravity intermediate layer specific gravity.

6. The multi-piece solid golf ball of claim 1 , wherein the intermediate layer is formed of a resin composition obtained by blending as essential components:

100 parts by weight of a resin component composed of, in admixture,

(A) a base resin of (a-1) an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer mixed with (a-2) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer in a weight ratio between 100:0 and 0:100, and

(B) a non-ionomeric thermoplastic elastomer

in a weight ratio between 100:0 and 50:50;

(C) from 5 to 80 parts by weight of a fatty acid and/or fatty acid derivative having a molecular weight of from 228 to 1500; and

(D) from 0.1 to 17 parts by weight of a basic inorganic metal compound capable of neutralizing un-neutralized acid groups in components A and C.

7. The multi-piece solid golf ball of claim 1 , wherein the envelope layer is formed of a thermoplastic polyether ester elastomer.

8. The multi-piece solid golf ball of claim 1 , wherein the cover is formed of a resin composition obtained by blending together an ionomer resin and a granular inorganic filler.

9. The multi-piece solid golf ball of claim 1 , wherein the envelope layer has a material hardness, expressed in terms of Shore D hardness, of from 27 to 40.

10. The multi-piece solid golf ball of claim 1 , wherein the intermediate layer has a material hardness, expressed in terms of Shore D hardness, of from 50 to 60.

11. The multi-piece solid golf ball of claim 1 , wherein the initial velocity (m/s) of the core and the initial velocity (m/s) of the envelope layer-encased sphere satisfy the relationship:

−1≦(envelope layer-encased sphere initial velocity−core initial velocity)≦0.

12. The multi-piece solid golf ball of claim 1 , wherein the deflection (mm) of the core and the deflection (mm) of the ball satisfy the relationship:

0.6 mm≦(core deflection−ball deflection)≦1.2 mm,

wherein each of the core deflection and ball deflection is the deflection (mm) of the core and the ball respectively when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).

13. The multi-piece solid golf ball of claim 1 , wherein the deflection (mm) of the core and the deflection (mm) of the envelope layer-encased sphere satisfy the relationship:

−0.6 mm≦(core deflection−envelope layer-encased sphere deflection)≦0.5 mm.

14. The multi-piece solid golf ball of claim 1 , wherein the cover specific gravity and the intermediate layer specific gravity satisfy the relationship:

0.05≦(cover specific gravity−intermediate layer specific gravity).