Defoamers for aqueous media

Details Defoamers for aqueous media Defoamers for aqueous media

2002-02-05

2003-04-22

Metzmaier, Daniel S. (Department: 1712)

Colloid systems and wetting agents; subcombinations thereof; pro

Continuous liquid or supercritical phase: colloid systems;...

Primarily organic continuous liquid phase

C516S020000, C516S123000, C516S124000, C516S131000, C564S058000, C564S059000, C564S061000, C564S073000

Reexamination Certificate

active

06552092

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to defoamers for aqueous media, comprising as hydrophobic solids critically influencing the defoaming certain urea derivatives which acquire the properties requisite for their particular activity as defoamers by crystallization from a clear melt dispersed homogeneously in the carrier medium.
2. Related Art
In many industrial processes, and especially when working in aqueous media, it is necessary to suppress, or prevent entirely, the unwanted formation of foam during the preparation or processing operations. This can be achieved by adding what are known as antifoams or defoamers, which even when used at very low concentrations upward of about 0.001% by weight are able to prevent or destroy unwanted foams. Examples of such prior art defoamers are silicone oils, mineral oils, hydrophobic polyoxyalkylenes, long-chain alcohols, and also mixtures of these products with one another and emulsions thereof. To reinforce the activity, it is common to add hydrophobic solids in amounts of from 0.1 to 10% by weight, which specifically promote dewetting processes on foam lamellae and therefore very actively assist in foam collapse. Suitable hydrophobic solids are appropriate silicas, metal stearates, polyolefins, and waxes.
The use of urea and urea derivatives as additives to defoamer formulation is also known per se.
European Patent No. EP-A-0 115 585, which corresponds to U.S. Pat. No. 4,696,761, describe ureas which are prepared in situ in an organic carrier medium at relatively low temperatures and which have defoaming properties for aqueous media. They are obtained by combining preferably equivalent amounts of isocyanates and amines in the organic carrier medium in question at temperatures below the melting point of the reaction product.
This gives urea derivatives of the general formula
R=alkyl C
4
-C
30
R′=single chemical bond; alkylene C
2
-C
12
, mono- to dinuclear aryl radicals which have additional alkyl groups C
1
-C
9
on the aryl radical; cycloalkylene
R″=H, alkyl C
1
-C
24
R′″=H, —CH
3
x=0.5.
It is expressly emphasized that when heated beyond their melting point, or when prepared at above their melting point, the ureas possess only an insignificant defoaming action. This is correlated with the formation of monodisperse or micellar structures during the in situ formation of the urea derivatives.
A disadvantage here is that, as a result of the in situ formation of the urea derivatives in accordance with the procedure described in EP-A-0 115 585, it is necessary to resort to carrier media which cannot react with amines and in particular not with isocyanates either. For example, the hydroxy-functional polyoxypropylenes well-known to the skilled worker as carrier media for defoamers, and hydroxy-functional polyoxyalkylene-polysiloxanes as well, are rejected on account of their hydroxyl functionality. It is true that, in principle, the reaction of an amine with an isocyanate is clearly preferred over the reaction of a hydroxy compound with an isocyanate, in respect of the reaction rate; however, and especially in the presence of the amines, which are known to be catalysts for the nucleophilic addition of hydroxy compounds onto isocyanates, hydroxy compounds react as well to uncontrollable extents and so result in urea derivatives which it is difficult, if possible at all, to crystallize. This would of course directly affect the activity of the resulting urea derivatives and would result at least in results that are difficult if not impossible to reproduce in the context of their use as defoamers.
BRIEF SUMMARY OF THE INVENTION
This invention provides a composition for defoaming aqueous media, comprising as defoamers urea derivatives of the formula I
where
R
1
—is a hydrocarbon radical or a hydrocarbon radical and one nitrogen atom or a hydrocarbon radical and one carbonyl group,
R
2
—is a hydrogen atom or a hydrocarbon radical,
R
3
—is a hydrogen atom or a hydrocarbon radical,
R
4
—is an organic radical, and
n—is from 0 to 5; in the form of solid particles, which are obtained by crystallization from a clear homogeneous melt dispersed in a carrier medium.
This invention also provides a process for preparing a solid particle urea derivative of the formula I
where
R
1
—is a hydrocarbon radical or a hydrocarbon radical having one nitrogen atom or a hydrocarbon radical having one carbonyl group,
R
2
—is a hydrogen atom or a hydrocarbon radical,
R
3
—is a hydrogen atom or a hydrocarbon radical,
R
4
—is an organic radical, and
n—is from 0 to 5;
comprising the steps of
(a) heating the urea derivative solution in a first carrier media above the melting points of said urea derivative to form a homogeneous solution and
(b) mixing the homogeneous solution of step (a) with a second carrier media having a temperature of less than 25° C.
DETAILED DESCRIPTION OF THE INVENTION
It has surprisingly now been found that, for the preparation of defoamer formulations containing urea derivatives as hydrophobic solids, the above-described in situ preparation of such urea derivatives below their melting point is neither necessary nor advantageous and that, instead, by means of controlled melting and recrystallization processes, it is possible to prepare defoamer formulations having improved properties and which, indeed, through the methodical variation of melting and recrystallization conditions, permit custom-tailored property profiles. By preparing the urea derivatives separately it is also possible, if required, to use exclusively carrier media which on account of their potential reactivity with respect to amines and/or isocyanates, because of the side reactions described above, are not amenable to precipitative crystallization in the manner described in EP-A-0 115 585. These include, for example, hydrophobic polyoxyalkylenes and organomodified siloxanes, which may also contain hydroxy functions.
This procedure is specifically successful even with urea derivatives which are explicitly described in EP-A-0 115 585 and which therefore, in accordance with the prior art, in the case of the process described in this patent, should no longer show any extraordinary activity in defoamer formulations. Such urea derivatives are easy to prepare from the corresponding isocyanates and amines.
The invention therefore provides compositions for defoaming aqueous media, comprising as defoamers urea derivatives of the formula I
where
R
1
—is a hydrocarbon radical, preferably having 4 to 30 carbon atoms, or a hydrocarbon radical, preferably having 4 to 24 carbon atoms, and one nitrogen atom or a hydrocarbon radical, preferably having 4 to 30 carbon atoms and one carbonyl group,
R
2
—is a hydrogen atom or a hydrocarbon radical, preferably having 1 to 24 carbon atoms,
R
3
—is a hydrogen atom or a hydrocarbon radical, preferably having 1 to 24 carbon atoms,
R
4
—is an organic radical, preferably having 2 to 30 carbon atoms, and
n—is from 0 to 5; in the form of solid particles, which are obtained by crystallization from a clear homogeneous melt dispersed in a carrier medium.
Preferred compositions are those in which R
1
is a hydrocarbon radical having 4 to 24 carbon atoms, R
2
is a hydrogen atom, R
3
is a hydrogen atom, and R
4
is a hydrocarbon radical having 2 to 24 carbon atoms.
Preference is further given to those compositions of the invention in which R
1
is the organic radical
where R
5
is a hydrocarbon radical having 1 to 18 carbon atoms, R
2
and R
3
are a hydrogen atom, and R
4
is a hydrocarbon radical having 2 to 24 carbon atoms.
In addition, those compositions of the invention comprising as defoamers urea derivatives in which R
1
is the organic radical
where R
6
is an organic radical having 2 to 30 carbon atoms,
R
2
and R
3
are a hydrogen atom, and R
4
is a hydrocarbon radical having 2 to 24 carbon atoms, and compositions comprising as defoamers urea derivatives in which R
1
is a hydrocarbon radical having 2 to 24 carbon atoms, R
2
and R
3
are a hydrogen atom,

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