Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-02-28
1999-11-30
Zitomer, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524801, 524802, 524804, 524832, 524845, C08L 2900, C08F 222
Patent
active
059944579
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the preparation of an aqueous polymer dispersion, in which an aqueous dispersion of a polymer which contains at least two monomers A and B which differ from one another, have at least one ethylenically unsaturated group and are incorporated in chemically bonded form is produced, in a manner known per se, so that the total content of monomers which are free, ie. not chemically bonded, and have at least one ethylenically unsaturated double bond (referred to in this publication as content of residual monomers or residual monomer content) in the aqueous polymer dispersion is from >0 to .ltoreq.1% by weight, based on the aqueous polymer dispersion, and this residual monomer content is then reduced by the action of a free radical redox initiator system comprising at least one oxidizing agent and at least one reducing agent.
The present invention furthermore relates to aqueous polymer dispersions resulting when such a procedure is used.
2. Discussion of the Background
Aqueous polymer dispersions are systems which contain polymer particles in disperse distribution as the disperse phase in an aqueous dispersing medium.
As in the case of polymer solutions when the solvent is evaporated, aqueous polymer dispersions have the property of forming polymer films when the aqueous dispersing medium is evaporated, and aqueous polymer dispersions are therefore widely used as binders, for example for surface coatings or for materials for coating leather.
In principle, a person skilled in the art classifies aqueous polymer dispersions as aqueous secondary dispersions and aqueous primary dispersions. The aqueous secondary dispersions are those in the preparation of which the polymer is produced outside the dispersing medium, for example is present in solution in a suitable nonaqueous solvent. This solution is then transferred to the aqueous dispersing medium, and the solvent is separated off, as a rule by distillation, while dispersing is effected. In contrast, aqueous primary dispersions are those in which the polymer is produced in the aqueous dispersing medium itself, directly as the disperse phase.
The common feature of all preparation processes is essentially that monomers which have at least one ethylenically unsaturated group are used for the synthesis of the polymer, or that this synthesis is effected exclusively from such monomers. The incorporation of such monomers having at least one ethylenically unsaturated group is usually carried out by an initiated polymerization reaction, the type of initiation used being determined in particular by the desired performance characteristics of the end product and therefore being adapted to these. For example, ionic or free radical initiation is suitable. However, the incorporation may also be effected by catalytically initiated polymeranalogous reaction. Free radical initiation is particularly frequently used, and the incorporation of the monomers having at least one ethylenically unsaturated group is therefore carried out as a rule by the free radical aqueous emulsion or suspension polymerization method in the case of aqueous primary dispersions and as a rule by the free radical solution polymerization method in the case of aqueous secondary dispersions.
As it is generally uneconomical to attempt to achieve complete conversion while maintaining the actual polymerization reaction conditions which determine the desired properties of the end product, in relation to the incorporation of the monomers having at least one ethylenically unsaturated group, the aqueous polymer dispersions resulting after the end of this main polymerization reaction usually contain free monomers which are not incorporated and have at least one ethylenically unsaturated double bond (this is the case in particular when monomers such as acrylic acid, methacrylic acid or the amides thereof are involved, said monomers having high water solubility). Owing to the high reactivity of the ethylenically unsaturated
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Hartmann Jurgen
Keller Peter
Stanger Bernd
Tschang Chung-Ji
BASF - Aktiengesellschaft
Zitomer Fred
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