Examples of the other diol units which may be contained in the polyester resin (I) are those derived from: aliphatic diols having 2 to 10 carbon atoms, e.g. ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 2-methylpropanediol and 1,5-pentanediol; alicyclic diols, e.g.cyclohexanedimethanol and cyclohexanediol; and polyalkylene glycols having a molecular weight of not more than 6