GB2103230A

GB2103230A - Aqueous dispersions of organopolysiloxane anti-foam compositions

Info

Publication number: GB2103230A
Application number: GB08219962A
Authority: GB
Inventors: Raymond Boyadjian; Michel Vialle
Original assignee: Rhone Poulenc Specialites Chimiques
Current assignee: Rhone Poulenc Specialites Chimiques
Priority date: 1981-07-15
Filing date: 1982-07-09
Publication date: 1983-02-16
Also published as: EP0071547B1; CH650697A5; IT8222406A0; FR2509624B1; CA1167733A; ES513944A0; GB2103230B; EP0071547A1; JPS6134848B2; FR2509624A1; ES8308705A1; DE3261131D1; JPS5817802A; BE893836A; IT1155360B

Description

1 GB 2 103 230 A 1

SPECIFICATION Aqueous dispersions of organopolysiloxane anti-foam compositions

The present invention relates to pseudo-plastic colloidal aqueous dispersions of organopolysiloxane anti-foam compositions, containing, as a thickener, a polysaccharide resulting from 5 the fermentation of carbohydrates.

Aqueous emulsions and dispersions of organopolysiloxane anti-foam compositions have been known for a number of years; they generally contain surface-active agents and sometimes thickeners.

U.S. Patent 3,423,340 describes emulsions of this type which consist of:

(1) an organopolysiloxane anti-foam composition comprising a dimethylpolysiloxane oil and finely 10 divided silica, (2) surface-active agents comprising polyoxyethyleneated sorbitan monostearate, sorbitan mono- stearate and/or glycerol monostearate, and (3) a thickener comprising sodium ca rboxymethylce 11 u lose.

These emulsions are prepared in 2 steps: the anti-foam composition, the surface-active agents and the thickener are first mixed and this mixture is then dispersed in water by grinding. They have a 15 good anti-foam efficacy but contain large amounts of surface-active agents and are not always very stable on storage; furthermore, they are slightly pseudo-plastic, which requires a certain energy expenditure in order to agitate them. U.S. Patent 4,039,469 describes aqueous emulsions of organopolysiloxane anti-foam compositions prepared by a slightly different process. In fact, it consists in mixing 2 components, one 20 of which is an aqueous solution of a customary thickener, such as carboxymethylce 11 u lose, and the other of which is an aqueous emulsion of an organopolysiloxane anti-foam composition. The latter is obtained in several steps:

0) dissolution of a surface-active agent in water, (H) dispersion of the anti-foam composition in the solution (i), and (M) grinding the dispersion resulting from (ii) until a stable homogeneous emulsion is formed.

Although this process makes it possible to make more reasonable use of industrial installations for the manufacture of anti-foam emulsions, it requires the prior preparation of an aqueous emulsion by grinding, and then handling thereof in order to add it to the aqueous solution of the thickener.

Furthermore, the pseudoplasticity of the aqueous emulsions thus obtained is low and their stability on 30 storage is not perfect; this group of properties needs to be improved further. The present invention aims to overcome the above disadvantages with the aid of aqueous dispersions of organopolysiloxane anti-foam compositions, which dispersions are pseudo-plastic and stable on storage. 35 According to the present invention there are provided aqueous dispersions which comprise the 35 following (the percentages being expressed by weight): (A) 3 to 20% of an organopolysiloxane anti-foam composition, (B) 0 to 5% of one or more nonionic surface-active agents, (C) 0.3 to 2% of a thickener, and a sufficient amount of water to make up to 100%. They are characterised in that the thickener (C) is chosen from polysaccharides obtained by the fermentation of 40 carbohydrates by means of a microorganism of the genus Xanthomonas.

The organopolysiloxane anti-foam composition (A), representing from 3 to 20% and preferably 5 to 15% of the aqueous dispersions according to the invention, generally comprises:

(h) 100 parts of a diorganopolysiloxane oil of the formula R,SiO(R2S'O),, SiR3, in which the symbols R, which are identical or different, represent methyl, ethyl, vinyl or phenyl radicals, at least 45 80% of the radicals being methyl radicals, and the symbol n represents an integral or fractional number such as to provide a viscosity of 20 mPa.s to 50,000 mPa.s at 250C, and (s) 0.05 to 15 parts, preferably 0.8 to 12 parts, of a finely divided silica, the primary particles of which have an average diameter of less than 0. 1 micron.

The oil (h) can be formed of diorganosiloxy units chosen from those of the formulae:

(CH3)2S'01 C1-13(CH,=CH)SiO, CHI(C21-15)SiO, CH3W^)SiO, and W,Hr)2SIO, and of triorganosiloxy blocking units chosen from those of the formulae:

(CH3)3S'00.5' (CHI)2CH,=CHSiO,.,, (CH,,),C,H,SiO().5, WX6H5)2S'00.5' CH3(CH2=CH)C6H5S'O,.5' 60 CH2=CH)(C6H5)2S'00.5 and (C,H5)3S'01.5.

2 GB 2 103 230 A 2 Preferably the oil (h) corresponds to the formula (CH3)3S'O[(CH3)1S'01,,, Si(CH3)3, in which the symbol n' represents an integral or fractional number having a value sufficient to ensure a viscosity of 50 to 5,000 hiPa.s at 251C.

Some oils (h) are marketed by silicone manufacturers; moreover, they can easily be prepared in 5 accordance with the techniques already described (see French Patents 978,058 and 1,025,150).

The silica (s) is most frequently a pyrogenic silica, precipitated silica or silica aerogel. It is usually has a specific surface area which is at least 50 ml/g and which can be as much as, say, 500 m/g. It can be used either as such or after treatment with organosilicon compounds normally used for this purpose, such as silazanes (hexamethyldisilazane, hexamethylcyclotrisilazane), polysiloxanes (octamethylcyclotetrasiloxane, hexamethyidislioxane), chlorosilanes (tri methylch lorosi lane, dimethyl10 vinylchlorosilane, dimethyidichlorosi lane, methylvinyidichlorosi lane) and alkoxysilanes (trimethylmethoxysilane, trimethylethoxysilane, dim ethyid i methoxysi lane).

During this treatment, the abovementioned organosilicon compounds become attached to and/or react with the surface zone of the silica; as a result, this silica can contain up to 40% of its weight, preferably up to 30%, of the organosilicon compounds or their reaction products. 1 The anti-foam composition (A) can be prepared by malaxating the mixture of the oil (h) and the silica (s); this malaxation should ensure homogeneous dispersion of the silica in the oil. A particularly effective process comprises, in a first stage, grinding a premixture of the oil and the silica in a colloid mill and, in a second stage, heating the resulting ground material for a period of 1 to 12 hours at, say, 60-2001C. In another process, the premixture is heated under the same conditions as the ground 20 material and the premixture treated in this way is then passed through a colloid mill.

Organopolysiloxane polymers can be incorporated into the anti-foam composition (A) by simply mixing, the latter having the appearance of a fluid paste. These organopolysiloxane polymers are typically:

-hydroxydiorganopolysiloxane oils of the formula HOR2S'O(R,SiO)n,,H, in which the symbols R, 25 which are identical or different, have the meaning given above for the oils (h), and the symbol n" represents an integral or fractional number having a value sufficient to ensure a viscosity of 10 to 500 mPa.s at 251C.

It is preferred to use the hydroxydi methyl polysi loxa ne oils of the formula HO(CHI)2S'O[(CHI)2S'01,,,,H, in which the symbol n represents an integral or fractional number 30 having a value sufficient to ensure a viscosity of 20 to 250 mPa.s at 250C.

-copolymers consisting of units of the formulae W3S100.5 and SiO, the molar ratio R1,Si00.5 /Si02 of which is from 0.4A to 1.2A, and containing up to 3% of hydroxyl groups bonded to the silicon atom; the symbols R' represent methyl or vinyl radicals; at most one vinyl radical is present per unit of the formula R'3SiOO.5. It is preferred to use copolymers consisting of units (CHISiO,, and S'02, the molar ratio of which is from 0.5A to 1. 1: 1.

-copolymers each form of a di methyl polysi loxa ne chain and of at least one polyoxyalkylene block, the dimethylpolysiloxane chain having a molecular weight of at least 1,000 and the polyalkylene block having a molecular weight of at least 800.

The polyoxyalkylene block is formed of units of the formula OCH2CH, or of a mixture of units of 40 the formulae OCH2CH2 and OCH27-CH, 1 UM, containing at most 50 moi% of units of the formula OCH2-CH. 1 L;p13 At its free end, it contains an alkoxy radical having from 1 to 4 carbon atoms, a hydroxyl radical or an 45 acetoxy radical, and it is joined to the dimethylpolysiloxane chain via an Si-C linkage. The methylsiloxy units containing the polyoxyalkylene block and the abovementioned Si-C linkage are chosen from those of the formulae:

CH3S'0 i G-G and (CH3)1S'00.5 1 (i-U in which the symbol G represents an alkylene group having from 1 to 4 carbon atoms and the symbol Q 50 represents the polyoxyalkylene block. At each of its ends, the di methyl polysiloxa ne chain contains the abovementioned unit 3 GB 2 103 230 A 3 (CH3)2-S'00.5 1 U-U and/or the unit of the formula (CH3)3SiO,.,,.

Specific examples of these compolymers include those corresponding to the formulae below:

11 (CH 3)2 SiO[(CH 3)2 siol 20 Si(CH 3)2 1 1 G-Q U-W with G = -(CH and Q = -(OCH CH CH CH OH 2)3_ 2 2 15 2t CH 3_ 10 H 3 sio Si(CH 3)3 1 G-Q 1 18 with G = -(CH 2Y and Q = -(OCH2 CH 2)25 CH 2 CH 0COCH 3 6 31 20 (CH 3)3 SiOt(CH 3)2 siol 105 The abovementioned organopolysiloxane polymers are added to the anti-foam composition (A) in amounts which are generally fairly small, typically 0. 1 to 10 parts per 100 parts of diorganopolysiloxane oil (h).

The non-ionic surface-active agent (B), which represents at most 5% and preferably from 0.2 to 3% of the aqueous dispersions according to the invention, is suitably chosen from:

fatty acid esters of sorbitol or of its anhydrides, such as sorbitan monostearate, fatty acid esters of polyethylene glycols, such as polyoxyethyleneated stearates, which are very frequently marketed in the form of mixtures of stearic acid monoesters and diesters of polyethylene 15 glycols, having from 7 to 50 units of the formula OCH,CH,, fatty acid esters of sorbitol or of its anhydrides which have reacted with 4 to 25 mols of ethylene oxide, such as polyoxyethyleneated sorbitan monostearate having about 20 units of the formula OCH,Cl-12, and 20 polyoxyethyleneated alkylphenols and polyoxyethyleneated alkylmercaptans, in which the alkyl 20 radical, which is linear or branched, has from 6 to 18 carbon atoms and the number of units of the formula OCH2CH2 is from 3 to 25, such as polyoxyethyleneated nonylphenol having about 6 units of the formula OCH2CH2 and polyoxyethyleneated dodecyimercaptan having about 9 units of the formula OCH2CH2. 25 All these surface-active agents are available on the chemical products market. The thickener (C), which represents from 0.3 to 2% and preferably from 0.5 to 1.5% of the aqueous dispersions according to the invention, is, as already indicated, a polysaccharide obtained by the fermentation of carbohydrates by means of a microorganism of the genus Xanthomonas. These polysaccharides are linear polymers of high molecular weight, generally more than 1 million, resulting from the fermentation, in an aqueous medium, of, for example, glucose, sucrose, Cerelose, fructose, maltose, lactose, soluble starch, potato starch or maize starch.

Phosphorus derivatives and magnesium derivatives are generally added to the fermentation medium. A source of nitrogen should also be present in the medium in the form of organic products (U.S. Patents 3,000,790, 3,271, 267 and 3,355,447 and French Patent 2,414,555) or in the form of inorganic products (U.S. Patent 3,391,060 and French Patent 2,342,339).

Various species of the genus Xanthomonas can be employed for the manufacture of these polysaccha rides, such as Xanthomonas begonlae, Xanthomonas incanae, Xanthomonas pisi and, more especially, Xanthomonas campestris.

The techniques for the manufacture of these polysaccharides have been known for a number of years; those given in the U.S. and French patents mentioned above (for the use of a source of nitrogen) 40 are fairly recent and can therefore be used to advantage. In particular, the technique described in French Patent 2,415,555 makes it possible to obtain polysaccharides which, when dissolved in water, give gels which can easily be filtered.

The process for the preparation of the aqueous dispersions according to the invention is simple to 45 carry out; in fact, it comprises the two steps Eland E2:

E,-formation of a pseudo-plastic colloidal solution by mixing the thickener (C) with water E,7-dispersion of the organopolysiloxane anti-foam composition (A) in the colloidal solution obtained above.

4 GB 2 103 230 A 4 If the surface-active agents (B) are used, they can be introduced, in total:

either during step E,, by simply mixing them with the thickener (C) and the water, or during step E, by dispersing them in the colloidal solution obtained in step E,, together with the anti-foarn composition (A); they can, if desired, be incorporated into composition A beforehand, for example by adding them during the manufacture of this composition A or alternatively by subsequently 5 mixing them with the latter, or during both steps E, and E2, the surface active agent being distributed between them in any proportion.

To obtain the solution prepared in step E,, it suffices to add the thickener (C), in small amounts, to vigorously agitated water; this results in the formation of a pseudo- plastic solution having the appearance of a fluid gel. This gel fluidises under shear but instantly returns to its initial viscosity when the shear stress is removed. Moreover, it possesses a flow threshold, that is to say a minimum shear stress below which no fluidising takes place.

Its viscosity varies according to the concentration of the thickener; for example, it is generally of the order of 2,000 mPa.s at 250C for a concentration of 0.8% of thickener (C) and of the order of 8,000 15 mPa.s at 250C for a concentration of 2%, the viscosity being measured with a Brookfield viscometer at 30 rpm.

However, the concentration of thickener (C) in this pseudo-plastic solution prepared in step E, is not arbitrary; it should be determined according to the amounts, added subsequently, of the anti-foam composition (A) and, if appropriate, of the surface-active agents (B), so as to provide dispersions, 20 according to the invention, containing from 0.3 to 2% of this thickener (C).

Bactericides, such as formaldehyde, can be added during the preparation of the pseudo-plastic solution according to step E,.

Step E. is then carried out; this comprises dispersing the anti-foam composition (A) in the above pseudoplastic solution. This operation can easily be carried out by pouring the composition (A) into the 25 vigorously agitated pseudoplastic solution; the use of a colloid mill is not obligatory.

The dispersion of the invention thus obtained is a relatively concentrated dispersion, since it contains from 3 to 20% of the organopolysiloxane composition (A). Moreover, it possesses the properties of the solution obtained in step E,; thus, it is pseudoplastic and possesses a flow threshold.

Furthermore, it does not change on storage for a period of at least 12 months. By way of indication, its viscosity is typically from 1,500 to 3,500 to mPa.s at 25 'C, for a speed of the Brookfield viscometer of rpm and for an average concentration of the compounds which it contains.

The aqueous dispersions of organopolysiloxane anti-foam compositions containing carboxymethylcellu lose as the thickener are distinctly less pseudoplastic, at the same concentration of thickener, than the aqueous dispersions containing the thickener (C). As a result, it is necessary to expend more energy to agitate them (when they are manufactured, various additives are incorporated therein or they are simply diluted with water) than to agitate the dispersions according to the invention.

Furthermore, they do not possess flow thresholds, which prevents them from keeping in suspension effectively the compounds which they contain.

The dispersions according to the invention can be used in substantially all the industrial operations faced with foaming problems, such as the fermentations resulting from the action of yeasts, bacteria and fungi on the appropriate nutrient media (for example, the fermentation for the preparation of vitamins and antibiotics), the refining of sugar, the processing of juices containing sugar, the preparation of foodstuffs and drinks, dyeing, the sizing and finishing of textile products, the manufacture of paper, the manufacture of adhesives and glues, the manufacture of industrial soaps and 45 detergents, the separation of ores by flotation, the drilling of oil wells, the circulation of hydraulic fluids and of lubricants, and the preparation of synthetic latices.

As they are relatively concentrated, these dispersions can be diluted before use in a weight ratio of diluting water to dispersions from, say, 1 A to 200A, preferably 2:1 to 150:1 or they can be used as such. The dilute solutions are also stable on storage.

The following Example further illustrates the -present invention..

1 Example (1) a) 88.8 parts of water and 0.5 part of a 30% strength by weight aqueous solution of formaldehyde are introduced successively into a reactor equipped with a blade turbine acting as an agitator and rotating at 2,000 rpm, the turbine running during this introduction. 0.7 part of a creamy- 55 white powder marketed under the name Rhodopol 23 (this is a polysaccharide resulting from the fermentation of carbohydrates with the aid of Xanthomonas campestris and is prepared according to the teaching of French Patent 2,414,555) is incorporated into the agitated contents of the reactor in the space of 30 minutes.

The contents of the reactor are agitated for a further 30 minutes after the addition of the powder 60 has ended. This gives a pseudo-plastic colloidal solution having the appearance of a fluid gel. Its viscosity, measured with a model RVT Brookfield viscometer, is 2,650 mPa. s at 251C using a speed of rpm and 395 mPa.s using a speed of 100 rpm. Its flow threshold is 45 dynes/cml.

GB 2 103 230 A 5 b) The colloidal solution prepared under a) is agitated with the turbine rotating at 2,000 rpm, and parts of an anti-foam composition P, prepared as described below under (c), are added thereto in the space of one minute.

The mixture is then agitated for 30 minutes. The anti-foam dispersion obtained has the properties of the solution prepared under (a); it is therefore pseudo-plastic and has the same viscosity value and 5 flow threshold value. These values have not changed after the dispersion has been stored for 12 months in closed glass containers, and the dispersion has not changed in appearance during this period.

W) Another pseudo-plastic anti-foam dispersion is prepared in accordance with the process described under (a) and (b), that is to say with the same anti-foam composition P,; however, in step (a), 10 87.8 parts of water are used in place of 88.8 parts, and, after the introduction of 0.5 part of the formaldehyde solution and before the introduction of 0.7 part of Rhodopol 23, 1 part of a polyoxyethyleneated nonylphenol having about 6 OCH,CH, units, marketed under the name Cemulsol NP 6, is added.

This pseudo-plastic dispersion has a viscosity [measured as described under (afl of 2,600 mPa.s 15 at 251C using a speed of 10 rpm and of 370 mPa.s at 251C using a speed of 100 rpm; its flow threshold is of the order of 45 dynes/cml.

W1) A pseudo-plastic anti-foam dispersion is prepared by following the procedure described under W), that is to say using 1 part of a polyoxyethyleneated nonylphenol in the preparation of step (a).

However, this time, the polyoxyethyleneated nonylphenol consists of 0.5 part of the above polyoxyethyleneated nonylphenol having 6 OCH,CH, units and 0.5 part of a polyoxyethyleneated nonylphenol having 4 OCH,CH, units, marketed under the name Cemulsol NP 4.

This pseudo-plastic dispersion has a viscosity [measured as described under (a)] of 2,850 mPa.s at 251C using a speed of 10 rpm and of 400 mPa. s at 251C using a speed of 100 rpm; its flow threshold is also of the order of 45 dynes/cM2.

1 35 c) Preparation of the anti-foam composition P, parts of an a,co-bis-(tri methylsi loxy)-di methyl polysi loxa ne oil having a viscosity of 100 mPa.s at 250C are introduced into a reactor fitted with an agitator. The agitation is started and 5.5 parts of a pyrogenic silica having a specific surface area of 200 ml/g and an average diameter of the primary particles of 30 millimicrons are added gradually to the oil introduced.

The mixture thus formed is agitated for 1 hour; it is then ground by passing it through a colloid mill, the grinding temperature being between 45 and 50C and the grinding gap being set at 0.25 mm.

The ground mixture fails into another reactor, where it is heated for 4 hours at 1 700C. After the mixture has cooled to about 300C, 2.2 parts of an a,6o-d i-(hydroxy)-di methyl polysi loxa ne oil having a viscosity of 50 mPa.s at 251C and 5.5 parts of a polyoxyethyleneated dodecyimercaptan having 9 OCH,CH2 35 groups are incorporated therein simply by agitation.

The anti-foam composition obtained, which is referred to as P, has the appearance of a pseudo plastic, opaque, pale grey fluid paste; it has a viscosity, measured as described under (a), of 7,500 mPa.s at 250C using a speed of 10 rpm and of 1,050 mPa.s at 250C using a speed of 10 rpm; its flow threshold is 25 dyneS/CM2.

(11) To determine the anti-foam power of the pseudo-plastic dispersions b, W and W', a multipurpose laboratory shaker is used which possesses a vibrating horizontal axle to which metal arms are fixed, at right-angles and horizontally, the ends of which arms possess clamps which open wide enough to grip glass flasks of 250 crn' capacity.

The frequency of the vibrations of the axle is about 250 per minute; the amplitude of each 45 vibration at the point where the flasks are inserted is 5 cm. A defoaming cycle, consisting of a shaking time of 10 seconds and a pause of 60 seconds, can be established by setting an electronic timer.

A foaming solution manufactured by simply mixing the following:

distilled water 1,000 CM3 sodium nonyinaphthalenesulphonate 5 g 50 acetic acid 3 g sodium acetate 7 g is also used.

crn' of the above foaming solution and 50 mg of one of the dispersions b, W or W' are introduced into each glass flask and the shaker is switched on. The time taken by the foam in the flask 55 to disappear is noted during the first defoaming cycle from the time at which shaking stops, that is to say during the pause of 60 seconds; this is the time T, required for the first defoaming.

The total number of defoaming cycles for which the defoaming time is less than or equal to 60 seconds is then noted; this number is referred to as N.

It is found that, with the 3 anti-foam dispersions b, W and W':

1) the time T1 required for the first defoaming is of the order of 3 seconds, and 2) the number of defoaming cycles N is of the order of 25.

6 GB 2 103 230 A 6 By way of comparison, the anti-foam power of the anti-foam composition P, is determined in accordance with the above process. For this purpose, 5 mg of this composition P, and 100 CM3 of the foaming solution used above are introduced into each flask. The first defoaming time T1 and the number of defoaming cycles N are noted and the following values are found:

T1: of the order of 3 seconds N: of the order of 32.

An examination of these results show that the anti-foam power of the composition P, is not degraded when this composition is dispersed in the pseudo-plastic colloidal solution (a), or of the type (a), in order to make the dispersions b, W and W' (the latter each contain 10% of this composition P,, that is to say 5 mg for a 50 mg sample).

Again by way of comparison, a colloidal solution (a'), similar to the solution (a), is produced by replacing the Rhodopol 23 by the same weight of Blanose R 105, which is a ca rboxymethylcel 1 u lose.

This solution W) has a viscosity, measured with a Brookfield viscometer, of 2 mPa.s at 250C using either a speed of 10 rpm or a speed of 100 rpm. It is clear that this solution is not pseudo-plastic.

10 parts of the anti-foam composition P, are added to this solution (al by following the procedure described under (b); the mixture is then agitated for 30 minutes. This gives a dispersion b having the viscosity values of the solution (a').

This dispersion is unstable; in fact, after it has been stored for 10 hours in closed glass containers, it is found that it has become heterogeneous; it has separated into 2 distinct parts. Furthermore, its anti-foam power is determined using the shaker described above and following the process used with 20 the dispersions b, W and C.

The first defoaming time T1 and the number of defoaming cycles N are noted and the following values are found:

T1: of the order of 3 seconds N. of the order of 15.

These results show that the anti-foam power of the dispersion b is inferior to that of the dispersions b, W and b".

Claims

1. An aqueous dispersion comprising, by weight:

A) 3 to 20% of an organopolysiloxane anti-foam composition, B) 0 to 5% of one or more non-ionic surface-active agents, C) 0.3 to 2% of a thickener which is a polysaccharide obtained by the fermentation of carbohydrates using a microorganism of the genus Xanthomonas, and water.

2. An aqueous dispersion according to claim 1 in which the microorganism of the genus Xanthomonas is Xanthomonas bequoniae, Xanthomonas incanae, Xanthomonas pis! or Xanthomonas 35 campestris.

3. An aqueous dispersion according to claim 1 or 2 in which the organopolysiloxane anti-foam composition comprises:

(h) 100 parts of a diorganopolysiloxane oil of the formula R3SiO(R2SiO),, SiR,, in which the symbols R, which are identical or different, represent methyl, ethyl, vinyl or phenyl radicals, at least 40 80% of the radicals being methyl radicals, and the symbol n represents an integral or fractional number such as to provide a viscosity of 20 mPa.s to 50,000 mPa.s at 250C, and (s) 0.05 to 15 parts of a silica, the primary particles of which have an average diameter of less than 0.1 micron.

4. An aqueous dispersion according to any one of claims 1 to 3 which comprises 0.2 to 3% by 45 weight of non-ionic surface-active agent.

5. An aqueous dispersion according to any one of claims 1 to 4 which comprises 0.5 to 1.5% by weight of thickener.

6. An aqueous dispersion according to any one of the preceding claims which comprises 5 to 15% by weight of anti-foam composition.

comprises:

7. An aqueous dispersion according to claim 1 substantially as described in the Example.

8. Process for the preparation of a composition as claimed in any one of claims 1 to 7 which E,-forming a pseudo-plastic colloidal solution by mixing the thickener (C) with water, and 55 E2--dispersing the organopolysiloxane anti-foam composition (A) in the colloidal solution obtained in step E,.

9. Process according to claim 8 in which surface-active agent (B) is introduced during step E, by mixing it with the thickener (C) and the water.

10. Process according to claim 8 in which surface-active agent (B) is introduced during step E, by dispersing it in the colloidal solution obtained in step E,, together with the organopolysiloxane anti foam composition (A), into which it is optionally incorporated beforehand.

7 GB 2 103 230 A 7

11. Process according to claims 9 and 10 in which surface-active agent (B) is introduced during both steps E, and E2.

12. Process according to claim 8 substantially as described in the Example.

13. An aqueous dispersion as defined in claim 1 whenever prepared by a process as claimed in 5 anyone of claims 8to 12.

14. An aqueous dispersion obtained by diluting with water an aqueous dispersion as claimed in any one of claims 1 to 7 and 13, the weight ratio of diluting water to aqueous dispersion as claimed being from 1. 1 to 200: 1.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained