Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1993-03-17
1994-05-24
Jagannathan, Vasu S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525252, 525258, 525281, 525302, 525308, 525309, 524504, C08F26504, C08L 5100, C08K 512
Patent
active
053149661
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the preparation of a finely divided vinyl chloride graft copolymer and to the use of the process product as viscosity-reducing agent for plastisols or as flatting agent for thermoplastic resins and plastisols.
In DE-A 3,132,890, the preparation of a finely divided vinyl chloride graft copolymer grafted onto an ethylene/vinyl acetate copolymer is described. In this reaction, the graft copolymer is prepared after dissolving the ethylene/vinyl acetate solid resin present in the absence of emulsifier and is suitable in particular for use as viscosity-reducing agent in plastisols. The disadvantage of this method is the complicated dissolution of solid resin, which on top of everything can lead to inhomogeneities with respect to the graft copolymer composition.
In DE-A 3,544,235, a plastisol composition is described which contains a finely divided, crosslinked vinyl chloride graft copolymer grafted onto an ethylene/vinyl acetate copolymer for reducing the viscosity and for flatting. This graft copolymer is also prepared by the suspension polymerization process, in which the ethylene/vinyl acetate solid resin is dissolved in monomeric vinyl chloride before the start of the polymerization.
DE-A 3,803,036 describes the preparation of a vinyl chloride graft copolymer with crosslinked polybutyl acrylate as the graft base. The elastomer content is up to 65% by weight; the vinyl chloride is grafted on only after the polybutyl acrylate has coagulated. It is not possible to prepare finely divided vinyl chloride graft copolymers by this method; coarse polymer particles of irregular shape are formed.
The object of the invention was to develop a process for the preparation of a finely divided vinyl chloride graft copolymer which is suitable for use as viscosity-reducing agent or flatting agent, while avoiding the abovementioned disadvantages.
The invention relates to a process for the preparation of a finely divided vinyl chloride graft copolymer having an average particle size of 20 to 30 .mu.m by the suspension polymerization process in the presence of monomer-soluble free radical initiators and further conventional additives, such as buffer substances or emulsifiers, characterised in that the graft monomer is polymerized in the presence of 1.0 to 5.0% by weight, relative to the graft monomer content, of an alkyl acrylate polymer which is initially introduced in an aqueous emulsion having a solids content of 30 to 60% by weight, and 0.1 to 1.0% by weight, relative to the graft monomer content, of a cellulose ether having a methoxy content of 15 to 25% and a hydroxypropyl content of 3 to 10% and having a viscosity of 30 to 150 mPa.s according to ASTM D 2363, which is initially introduced or metered in after addition of the graft monomer.
To prepare the vinyl chloride graft copolymer, the polyalkyl acrylate emulsion is initially introduced together with the water, the free radical initiators and, if appropriate, the buffer substances and further customary additives. The graft monomer is then metered in. The protective colloid can be initially introduced or it can be metered in after addition of the graft monomer. The polymerization is carried out at a temperature of 50.degree. to 80.degree. C., preferably 55.degree. to 70.degree. C. At a drop in pressure of 1 to 5 bar, preferably 3 to 5 bar, the polymerization is stopped by distilling off the unreacted vinyl chloride. After degassing, the product is freed from water in a centrifuge and dried.
Uncrosslinked homopolymers or crosslinked copolymers of alkyl acrylates having C.sub.2 - to C.sub.8 -alkyl radicals are used as the graft base. Examples of these are polyethyl acrylate, polybutyl acrylate and poly(2-ethylhexyl) acrylate. Alkyl acrylate copolymers used are those containing 0.1 to 1.0% by weight, relative to the alkyl acrylate content, of ethylenically polyunsaturated comonomers which have a crosslinking action. Examples of these are vinyl and allyl esters of unsaturated C.sub.3 - to C.sub.8 -monocarboxylic acids, such as allyl methacrylate; mono
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Grauer Peter
Ober Ludwig
Jagannathan Vasu S.
Wacker - Chemie GmbH
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