Filler for PVC moulding materials - prepd. by heating calcium sulphate di:hydrate with dilute dehydrating acid, washing with water and drying

摘要

Filler (I) for PVC moulding materials (II) is produced by heating finely-divided CaSO4.2H2O (III) with a dehydrating dilute acid (IV) to 50-190 deg.C, washing the mixt. obtd. with water and drying it. Amt. of (IV) used is below 20 (pref. 7-17) wt.% and acid content is 0.5-7 (pref. 1-3) wt.% w.r.t. total mixt. (IV) is sulphuric or phosphoric acid or a mixt. thereof. Mixt. is heated by direct ignition or by rapid heating using indirect heat exchangers with relatively high wall temps., before washing, the heated mixt. is annealed at 80-190 deg.C for 0.3-24 hrs. (III) is gypsum from flue gas desulphurisation. (I) is then coated, pref. with fatty acids and/or metal salts or with a silanising agent. USE/ADVANTAGE - (I) is useful as a filler for (II) (claimed). The process overcomes the disadvantages of prior-art methods for the prodn. of anhydrous CaSO4 filler (i.e. acid-catalysed degradation of PVC due to residual acid, if the dehydrated prod. is not neutralised, or discoloration of mouldings if the acid is neutralised with Ca(OH)2); (I) has a high brightness value and is suitable for use in rigid PVC mouldings for window frames, etc.