Improvements in or relating to balls

A golf ball half shell is moulded (see Division B5) from a polyurethene pre-polymer, that is the starting material prior to curing. The prepolymers are prepared by reacting an organic polymer containing hydroxyl groups with an organic polyisocyanate or polyisothiocyanate. Examples of such organic polymers include polyesters, polyethers and polyesteramides, all of which must, however, contain residual isocyanate-reactive groups. Examples of suitable polyesters include polyethylene glycol adipate, polyethylene glycol sebacate, polypropylene glycol adipate and also copolyesters. Examples of suitable polyethers include polyglycols from propylene oxide and tetrahydrofuran. Polyisocyanates which may be used include naphthalene diisocyanates, tolylene diisocianates and diphenyl methane diisocyanates. Poly-urethane pre-polymers which may be used include Registered Trade Mark "Adiprene" L.167, which is prepared from polytetrahydrofuran and tolylene diisocyanate. Curing is effected by means of cross-linking agents e.g. a substance containing at least two active hydrogen atoms per molecule such as diols and diamines. The polyurethane pre-polymer/cross linking agent mixture may be admixed with mineral oils, fillers and colouring materials. In the example of the process given titanium dioxide (anatase) was dried at 140 DEG C. for 1 hour. On cooling to room temperature in a closed container the titanium dioxide was mixed with twice its weight of methylene bis (orthochloranilene) (MOCA), as a cross-linking agent, and the mixture milled for 24 hours. The mixture was then heated in an evacuated vessel to 140 DEG C. to remove dissolved gases, the mixture being subsequently stored in an oven at 110 DEG C. in a sealed container. 30 parts of the mixture at 110 DEG C. were stirred with 100 parts of Adiprene L.167. After moulding of the ensuing mixture, the mixture was cured for 10 minutes between platen heated to 105 DEG C. and 100 DEG C. under pressure, the mould then being brought to room temperature in about 7 minutes. The mould was then transferred to an insulated box containing solid carbon dioxide, the mixture being taken from the mould when its temperature had fallen to about -12 DEG C. and stored in a metal container surrounded by solid carbon dioxide. The mixture was finally cured between platen at 100 DEG C. for 15 minutes under pressure, the mixture being then cooled to room temperature again in about 7 minutes. The final curing time was varied, a resulting property