Process for preparing an aqueous emulsion with narrow droplet si

Details Process for preparing an aqueous emulsion with narrow droplet si Process for preparing an aqueous emulsion with narrow droplet si

1999-03-04

2000-12-12

Wu, David W.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

524804, 526 87, 526 82, 526207, 526208, 526212, C08F 222, C08J 303

Patent

active

06160061&

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for preparing emulsions with a controlled and variable droplet size, of an oily material comprising a highly water insoluble, relatively low molecular weight organic substance or mixtures of such substances, and of mixtures of such highly water insoluble substance(s) with one or more slightly water soluble substances. In particular it relates to the formation of emulsions with a relatively narrow droplet size distribution, even with relatively large average droplet sizes. The emulsions prepared according to the present invention may subsequently be used for the preparation of polymer dispersions, from which polymer particles may be recovered.
Conventional methods for the preparation of emulsions of more or less water insoluble organic liquids comprise the use of effective homogenization equipment. Such emulsions are generally the object of degradation which may take place by two mechanisms. Droplets which come in contact of one another may flocculate, i.e., pass over into greater accumulation, which may be followed by coalescence. This form of degradation may be hindered by use of effective emulsifiers providing layers at the droplet surface which give an effective electrical or sterical hindrance to the aggregation. Another type of degradation which may be predominant with relatively small droplets is degradation by diffusion which is due to that the solubility of a certain material in a small drop in a continuous phase is higher than of the same material in a larger drop. Therefore a slightly water soluble material will diffuse from small droplets to larger droplets so that a steadily more coarse dispersion is formed. This degradation assumes that the dispersed phase has a certain solubility in the continuous phase. However the degradation will be effected relatively fast even with materials with a relatively low solubility in the continuous phase, in the order of 0.1 to 0.01 gram per liter.
It has been described in the literature that one may form stable emulsions of slightly water soluble materials by having dissolved in the slightly water soluble compound a small amount of a highly water insoluble compound in the order of 1-2% based upon the amount of the slightly water soluble compound. In this case one experiences that after a small amount of the slightly water soluble compound has been transported from small to larger droplets, the emulsion is stable because the driving force for a further transport of the slightly water soluble compound becomes balanced by a concentration potential in the opposite direction. In Norwegian Patents 139.410 and 140.932 there is described a method where an aqueous emulsion of slightly water soluble compounds is prepared in a two-step process. In the first step a finely divided emulsion in water of a highly water insoluble compound or mixtures of such compounds is prepared by an effective homogenization, and in the next step the slightly water soluble compounds are allowed to diffuse into the droplets formed in the first step, to form emulsions of the slightly water soluble compounds which in case they are monomers may be polymerized by an initiator which may be water soluble or oil soluble and in the latter case introduced in the different ways discussed above. In Norwegian Patent 145.164 there is also described a similar process where the highly water insoluble compound is an initiator. The success of these methods where one homogenizes the organic compounds in pure water is often dependent upon an effective homogenization which gives very small droplets. This method of preparing latexes has the great advantage that one only has to homogenize the highly water insoluble compound which normally makes up only about 1% of the monomer added in the next step. The mentioned Norwegian patents describe the use of the method for production of PVC latexes. In this case the droplets of the highly water insoluble compounds ("substance I") have a diameter of about 0.03 to 0.2 .mu.m. After absorption of vinyl chloride and polymerization one

REFERENCES:
patent: 4113687 (1978-09-01), Ugelstad
patent: 4563510 (1986-01-01), Ugelstad

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