Sinterable, finely-divided PVC moulding material - by suspension polymerisation of vinyl chloride, with addn. of emulsion-PVC latex before sepn. from aq. phase

摘要

A process is claimed for the prodn. of a sinterable, finely-divided moulding material (I) based on PVC with K value 55-90, density 400-700 g/dm3 and mean particle size 10-50 microns with 99-30 wt.% below 33 microns, 1-60 wt.% from 33-63 microns, 0-9 wt.% from 63-125 microns and 0-1 wt.% above 125 microns; the process involves homopolymerisation of vinyl chloride (VC), copolymerisation of VC with 0.5-25 wt.% other comonomers or graft copolymerisation of VC with 0.1-5 wt.% of a polymer, in acid aq. suspension in the presence of oil-soluble radical activator(s), suspension stabiliser(s), emulsifier(s) (3-16C alkyl-arylsulphonic acids, 8-16C alkylsulphonic acids or 8-16C monoalkyl sulphates) and possibly other additives; the novelty is that, after at least 70 wt.% of the VC is polymerised but before sepn. of the aq. phase, a latex obtd. by emulsion or microsuspension polymerisation of VC and contg. 0.5-5 wt.% emulsifier(s) is added in an amt. such that the mixt. contains 0.5-8 pts.wt. PVC from the latex w.r.t. 100 pts. wt. PVC from the suspension polymerisation, then the polymer is coagulated, the aq. phase is sepd. and the polymer mixt. is dried. USE/ADVANTAGE - (I) is useful for the prodn. of sintered mouldings, esp. separator plates for electrical cells (claimed). The orocess enables the prodn. of (I) which can be readily processed at low relative humidity without adverse effects on the mechanical properties of the separator plates (contrast prior-art processes, which also use comparatively expensive additives and involve tedious post-treatment with special equipment).