| 摘要 |
The thickening agent in the composition comprises a mixture of MgO and/or Mg(OH)2 and one or more lithium salts. The thickening agent inhibits viscosity build-up for about 24-48 hours and then gives a rapid increase in viscosity. The thickening agent thus allows extension in the pot-life of the unsaturated polyester and gives rapid viscosity build up after the initial period of inhibition. Fibrous reinforcements can thus be precoated with the low viscosity resin composition which will thus properly wet the fibres, whilst the resin coating will rapidly lose its tack as viscosity rapidly increases and so facilitate storage and handling of the precoated fibres. The use of preforms can thus be eliminated as well as the necessity of coating irregular-shaped preforms with a liquid resin. The preferred lithium salts are inorganic, particularly the halides. the nitrite and nitrate. Less effective are the sulphate, phosphate, acetate. and hydroxide. The amount of MgO and/or Mg(OH)2 used is pref. 1-2% and the amount of the lithium salt is pref. 0.1-1% both based on the weight of the unsaturated polyester resin. The thickening agent can be added before the resin is applied to a substrate, e.g. a glass fibre mat, and before, during or after incorporation of the usual peroxide catalyst, e.g. MEK peroxide or benzoyl peroxide. |
