Use of grafted polyethersiloxane copolymers for improving the low-temperature stability of antifoams in aqueous dispersions

1. A method of defoaming an aqueous solution or dispersion which comprises of adding an effective amount of a grafted copolymer P based on polyoxyalkylene-polysiloxane block copolymers of the general formula (I)

in which the radical

A is a polyoxyalkylene block of the average formula (II)

[(C 2 H 4-d R′ d O) n (C x H 2x O) r (C 2 H 4-d R″ d O) t ]  (II)

in which

d is from 1 to 3,

n is ≦0,

x is from 2 to 10,

r is ≦0,

t is ≦0,

n+r+t is ≦1,

and

R′ is a monovalent aromatic, optionally substituted hydrocarbon radical,

R″ is a hydrogen radical or a monovalent hydrocarbon radical having 1 to 18 C atoms,

R 1 is an H atom, a monovalent organic linear or branched alkyl radical having the chain length C 1 -C 40 or a carboxyl radical of an optionally branched alkyl or aryl ester,

B is a polysiloxane block of the average formula (III)

in which

R 2 are identical or different and comprise an alkyl radical having 1 to 4 carbon atoms or a phenyl radical and

y has a value from 5 to 200,

m has a value from 2 to 100,

p has a value from 0 to 1 and

q has a value from 0 to 1,

or of the formula (IV)

in which the radicals R 1 , A, B and m, p and q have the abovementioned meaning and

C is a linear or branched alkylene radical having 2 to 20 carbon atoms, to an aqueous solution or dispersion.

2. The method as claimed in claim 1 , wherein, in the formula (II), d is 1, R′ is phenyl and 1≧n<15.

3. The method as claimed in claim 1 , wherein the grafted copolymer P is prepared by free radical graft polymerization of ethylenically unsaturated monomers M in the presence of polyoxyalkylene-polysiloxane block copolymers of the formulae (I) or (IV).

4. The method as claimed in claim 1 , wherein the free radical graft polymerization of ethylenically unsaturated monomers M is carried out in the presence of dihydroxy-functional polyethers of the general formula (VI)

[HO(C 2 H 4-d R′ d O) n (C x H 2x O) r (C 2 H 4-d R″ d O) t H]  (VI)

in which R′, R″, d, n, x, t and r have the meanings stated in claim 1 in the description of the polyoxyalkylene block A.

5. The method as claimed in claim 3 , wherein the amount of the ethylenically unsaturated monomers M, based on the polyoxyalkylene-polysiloxane block copolymers, is from 2 to 500% by weight.

6. The method as claimed in claim 3 , wherein the monomers M are selected from the group consisting of acrylic acid, methacrylic acid, vinyl ethers, vinyl alcohols, vinyl esters, styrene and mixtures and derivatives thereof.

7. The method as claimed in claim 6 , wherein the monomers M comprise derivatives of acrylic acid and methacrylic acid of the general formula (VII)

X—C(0)CR 7 ═CHR 6   (VII)

in which

R 7 and R 6 , independently of one another, are selected from the group consisting of —H, linear C 1 -C 8 -alkyl chains or branched C 1 -C 8 -alkyl chains, methoxy, ethoxy, 2-hydroxyethoxy, 2-methoxyethoxy and 2-ethoxyethyl,

X is selected from the group consisting of the radicals OH, OL, OR 8 , NH 2 , NHR 8 , N(R 8 ) 2 ,

R 8 are linear C 1 -C 40 -alkyl radicals, branched C 3 -C 40 -alkyl radicals, aromatic alkyl radicals or carbocyclic C 3 -C 40 -alkyl radicals, polyfunctional C 6 -C 12 alcohols having 2 to 10 hydroxyl groups, such as ethylene glycol, hexylene glycol, glycerol and 1,2,6-hexanetriol, or alcohol ethers, such as methoxyethanol and ethoxyethanol or polyethylene glycols,

L is a cation selected from the group consisting of Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , NH 4 + , alkylammonium, dialkylammonium, trialkylammonium, tetraalkylammonium and analogous phosphoramine derivatives.

8. The method as claimed in claim 3 , wherein the monomers M are selected from the group consisting of styrene, methylstyrene, tert-butylstyrene, styrene derivatives and mixtures of these monomers.

9. The method as claimed in claim 3 , wherein the monomers M are selected from the group consisting of the vinyl and allyl esters of linear C 1 -C 40 -carboxylic acids, branched C 3 -C 40 -carboxylic acids or carboxylic C 3 -C 40 -carboxylic acids, vinyl acetate, vinyl propionate, vinyl neononanoate, vinyl neoundecanoic acid, vinyl tert-butyl benzoate, vinyl, allyl halides and mixtures of these monomers.

10. The method as claimed in claim 3 , wherein the monomers M are selected from the group consisting of the nitrogen-containing monomers.

11. The method as claimed in claim 10 , wherein the monomers M comprise N,N-dialkylaminoalkyl acrylates and methacrylates and N-dialkylaminoalkylacrylamides and -methacrylamides of the general formula (IX)

in which

R 9 is H or alkyl having 1 to 8 C atoms,

R 10 is H or methyl

R 11 is alkylene having 1 to 24 carbon atoms, optionally substituted by alkyl,

R 12 , R 13 are a C 1 -C 40 -alkyl radical,

Z is nitrogen for x=1 or oxygen for x=0.

12. The method as claimed in claim 10 , wherein the monomers M comprise N-vinylimidazoles of the general formula (VIII)

in which R 14 to R 16 , independently of one another, are hydrogen, C 1 -C 4 -alkyl or phenyl.

13. The method as claimed in claim 1 , wherein the grafted polyoxyalkylene-polysiloxane copolymer is present in a concentration from 0.01 to 20% by weight, based on the total weight of the solution or dispersion.

14. The method as claimed in claim 5 , wherein the amount of the ethylenically unsaturated monomers M, based on the polyoxyalkylene-polysiloxane block copolymers, is from 2 to 200% by weight.

15. The method as claimed in claim 14 , wherein the amount of the ethylenically unsaturated monomers M, based on the polyoxyalkylene-polysiloxane block copolymers, is from 2 to 100% by weight.