CA1191767A - High efficiency antifoam compositions - Google Patents

Abstract

HIGH EFFICIENCY ANTIFOAM COMPOSITIONS

A B S T R A C T

An antifoam composition is described comprising a polydiorganosiloxane oil, a finely divided hydrophobic solid having a surface area of from 50 to 1000 square meters per gram and a siloxane-oxyalkylene black copolymer surfactant.

S P E C I F I C A T I O N

Description

HIGH EF~ICIENCY ANTIFOAM
COMPOSITIONS
BACKGROUND OE` THE INVENTION
1. Field of the Invention The present invention relates to polydiorganosiloxane-based antifoam compositions and to their use in the reduction of foaming in aqueous liquids.

2. DescriPtion of the Prior Art U.S. Patent No. 4,076,648 discloses self-dispersible antifoam compositions. The self-dispersible antifoam compositions of said patent comprise a lipophllic nonionic surface actlve agent~ which may be a siloxane-oxyalkylene blocX
copolymer, homogeneously dispersed in a non-emulsified diorganosiloxane antifoam agent, which may consist of a finely divided inorganic filler in a diorganopolysiloxane oil. All of the antifoam compositions specifically disclosed by said patent are based upon a polydiorganosiloxane `~

:11869 -I

oil having a 25~C viscosity of 500 centistokes. Said patent teaches, in its generic de.scriptions, that polydiorgano-siloxane oils having ?5C viscosities of from 5 ~o 3000 centistokes are preerred and that such vils having viscosities of up to 100,000 may be utilized. Since apparently only th 500 centistoke oil was ac~ually tested, the implication seems to be that the polydiorganosiloxane oil viscosity is not a significant factor, and that such oils having higher viscosities, ~ up eo 100,000 centistokes, would provide antifoam c~mpositions more or less equivalent in effect to those based on the 500 centistoke oil.

SUMMARY OF_THE INVENTION
Applicants have found, quite unexpectedly, that unlike 500 centistoke polydiorganosiloxane oil-based anti-foam compositions such as those described in U.S. Patent No. 4,076,648, antifoam compositions based upon polydiorgano siloxane oils having viscositles in the range of from 5000 to 30,000 centistokes at 25~C are unexpectedly efficient eve in such difficult-to-defoam aqueous systems as those which contain high concen~rations of ionic surfactants and those which are very ~iscous, systems in which the 500 centis~oke oil-based antifoam compositions are not particularly efficient, The high efficiency antifoams of the present invention comprise a polydiorganosiloxane oil having a visc08ity of from 5000 to 30,000 centis~okes ae 25C, a flnely divided hydrophobic solid having a surface area of from SO to 1000 square meters per gram, and a siloxane-oxyalkylene block copolymer surfac~ant having a hydrophilic-'7 11869-~

lipophilic balance (~LB) of from 4 to 14.
DESCRIPTION OF THE PREFERRED EMBODIM~NTS
The antifoam compositions of ehe present invention are especially effective in foaming systems containing high concentrations of ionic ~urfactants (near, at, or above the critical micelle concentraeion). Under such conditions, the antifoam compositions of U.S. Patent No. 4,076,648 are much less effective than are those described and claimed herein.
This new antifoam contains three basic ingredients and can be prepared in the manner shown below:

A ~ B shear C (1) C + D controlled sheas X (2) X ~ F + H2O emulsification Y (3) In above Equation (1), A is a silicone oil (i.e.
a liquid diorg~nosiloxane polymer) which can be of any of the well-known eypeS heretofore employed in the preparationof antifoam compositions. The polymers generally have hydro carbon groups having from 1 to 18 carbon atoms, e.~ alkyl, aryl, alkaryl, aralkyl and the like, bonted to silicon in the ratio of about 1.8 to about 2.2 hydrocarbon groups per silicon atom. Mos~ preferably, the hydrocarbon group is methyl and the basic unit of the polymer is the dimethyl-~iloxane uni~ which constitutes at least 65 mol percent and preferably at least 97.0 mol percent or more of the siloxane polymes. Other units can be presented, such as trimethyl-~loxane uni~ which can be presented in amounts of less than 1 mole percent of the polymer such that ~he resulting vis-cosity will be 5000 to 30,000 centistokes, In addition,

3-'7~j'7 the polymer can contain still other units, such as, monomethylsiloxane units and unsubstituted siloxane units, i.e., Si02, in minimum amounts of less than 10 mol percent a~d preferably below 0.2 mol percent of the siloxane polymer. Preferred diorganosiloxane polymers are the trimethylsiloxy endblocXed dlmethylsiloxane polymers having the formula:
Me3SiO(Me2SiO)nSiMe3 (I) wherein Me design&tes the methyl group and n is an integer. The diorganosiloxane polymers according to the present invention have a viscosity in the range of about 5000 to about 30,000 centistokes measured at 25C. Especially preferred are dimethylslloxane polymers having a viscosity in the range of about 10,000 to 30,000 centistokes at 25C. Thus the value of the integer n is such that the siloxane polymer possesses a viscosity within the range indicated. For example, when n is about 750, the viscosity is about 10,000 centistokes at 25C.
In above Equation (1), B is a hydrophobic finely divided inorganic filler which can be of any type normally employed ln making antifoams.
Powdered alumina and titania are suitable but the hydrophobic solid is conveniently fumed silica or precipitated silica with an average particle si~e of about 200A, resulting in a surface area of 325 square meters per gram. The surface of these inorganic solids can be rendered hydrophobic by treating them with organic or organosilicon compounds having at least one of the functional groups such as -OH, -SH, -NH~, -NHR, -NR2, and -NR3 which are capable of interacting with the inorganic flller surfaces. Typically one can employ disilox3nes or siloxane ~, 3~

such as hexamethyldisilazane, octadecyl trichlorosilane, allyl trichlorosilane, dialkyl dichlorosilane, alkyl monochlorosilane, alkyl trialkGxysilane, dia]kyl dialkoxysilane, trialkyl-monoalkoxysilane, or primary, secondary, tertiary or quaternary alkyl or alkylether amines where the alkyl groups can have 1-18 carbon atoms preferably 1-8 for silicone compounds and 8-14 for organic amine compounds. A typical process for making hydrophobic filler particles consists of tumbling fine silica, which can be either precipitated or fumed or combination of both, with the appropriate hydrophobizing reagent and suitable amounts of alcohol/water mixture. The tumbled product is then heated in an oven at moderate temperatures for two hours. The preparation of suitable hydrophobic solids is found e.~. in U.S.
Patents Nos. 2,802,850, 3,~34,288, 3,649,588, and 3,953,487.
In above Equations (1~ and (2), Compound C
is an intermediate product which is obtained by blending the silicone oil A with the hydrophobic inorganic filler B. The blending is done to obtain a homogeneous mixture of B with A, and can be done at any convenient temperature, e ~. from 20C to 150C, preferably at room temperature. For highly viscous mixes, elevated temperature mixing may be desirable for ease of operation. The relative amounts of B to A can vary from 1 to 20 percent by welght, and is preferably about 3%.
In above Equation ~2), the sur~actant D
should be such that its mixing with C will impart the following properties to the antifoam: (a~
improve the 'L~ ''7~j~7 spreading power of the droplet over the foam bubble, (b~ reduce the ionic foaming surfactant adsorption onto the antifoam drop so as to minimi~e the repulsive force during its transport to the bubble sur~ace and (c) improve the stability of the antifoam droplet against coalescene. To serve these functions the sur~actant should have hydrophobic (or lipophilic) groups, preferably silicone groups such as (CH3)3SiO-, -(CH3~2SiO-, or -CH3(R)SiO-, which ~ill be compatible with the silicone oil phase and hydrophilic nonionic groups such as polyoxyethylene groups which are soluble or compatible with the aqueous foaming solution used.
The surfactant D according to this invention is a block copolymer. The term "block copolymer" is used herein to denote a material wherein at least one section ("block") of the molecule is composed of recurring monomeric units of one type and a~ least one other section ~"block") of the molecule composed of recurring monomeric units of a different type.
The different sections of blocks in the molecule can be arranged in any configuration (e.g., AB, ABA, branched or cyclic). Thus the term block copolymers as used herein includes graft copolymers. The block copolymers used in this invention can be discrete chemical compounds. Usually 9 however, the block copolymers are mixtures of various discrete block copolymer species. The block copolymers are usually mixtures due, at least in part, to the fact that tha siloxane and polyoxyalkylene reactants used to produce the block copolymers are themselves ~ ~t~

~1869-1 usually mi~tures. Sultable block copolymers include hydrolyzable and non-hydrolyzable blocX copolymers.
The ratio of hydrophobic to hydrophilic groups in the block copolymer surfactants of this lnvention should be such that the resulting compound should not be highly soluble in elther of the phases. Such compounds will have hydrophilic-lipophilic balance numbers of 4 to 14. Said hydrophilic-lipophilic balance, hereinafter re~erred to as HLB, is a measure of the balance of the size and strength of the hydrophilic (water-loving or polar) and the lipophilic (oll-loving or non-polar) groups of a surface active agent. The HLB of a surface active agent is related to its solubility and a surface active agent having a low HLB will tend ~o be oil-soluble, while one having a high HLB will tent to be water-solu~le. The types of structures which will satisfy the requirements of this invention include compounds of the formula:
R f R ~ ~ R ~ R
R-Si-O- Si-O _ Si-O -Si-R (II) R ~ R ~ 1 ~ R ~ m R
where each R is an alkyl groups with 1-18 carbon atoms and preferably is a methyl group, R contains polyalkoxy groups which can be either polyoxyethylene or poly(oxyethylene-oxypropylene) mixtures and is preferably linked to the silicon atom by a carbon-silicon bond, and 1 and m ~re such that the resulting compounds are liquid, possess the desired HLB value, and exhibit only limited solubility in either of ~he phases (antifoam and aqueous solution). The art of making these compounds ' '`b 7 7~;~

already exlsts. It is described e.~. in U.S.
Patents Nos. 2,834,748, 2,917,840, 3,398,104, 3,402,192, 3,507,815, and 3,741,917. Typical examples o~ such surfactants are:

HLB
Me3SlO(Me2S10)20(MeS10)3 2SlMe37.6 (III) C3H6(0C2H4)70CH3 Me3SlO(Me2S10)20(MeS10)3 2SlMe3 13.0 (IV) ~3H6(oc2H4)lg(oc3H6)l4H9 Me3SlO(Me2S10)37(MeS10)3SlMe3 7.3 (V) C3H6(0c2~4)7ocH3 These surfactants can be blended with the composition C at anywhere from 1-20 percent by weight, preferably about 10%.
In above Equations (2) and (3), X is a semi-finished product obtained after controlled blending of the intermedlate composition C with the surfactant D. It has been found that excessive mixing At this stage is deleterious to product performance. This product itself can be used as an antifoam. HoweYer, its utility and performance can be signiEicantly improved by successive processing.
In above Equation (3), F is a surfactant or a surfactant mixture used to emulsify X in water.
Typically, it can be polyoxyethylene alcohols, available commercially 8S BrijTM, sorbitan fatty acid esters, available commercially as SpanTM, polyoxyethylene acids, .

available commercially as MyrjTM~ ethoxylated Cll - Cl5 alcohols with three to lS moles of ethylene oxides, available commercially as TergitolTM, or mixtures thereof.
In above Equation (3), Y is a final product which is an emulsion containing 50-99% water. The emulsification is carried out in such a manner that the particles emulsified generally have a particle size of from about 7 to about 20 microns and preferably from 9 to ll microns. Emulsifying techniques are well known to those skilled in the art and it is thus merely necessary to carry out simple experiments to arrive at the desired particle sizes. An advantageous method, for example, is to employ suitable stirring speeds, these being dependent on the nature of the composition to be emulsified. The particles are present in statistical distribution (Gauss distribution) with a variation coefficient of from lO to 15% less, the variation coefficient defining the distance of each turning point of the Gauss distribution curve from its peak in percent of the peak value.
The product Y when compared with known silicone antifoams performs significantly better, particularly in foaming systems containing high foaming surfactant concentrates and/or containing ionic foaming surfactants, such as potassium oleate, sodium dodecyl sulfate, or odecyl amines.
Particularly in foaming systems containing ionic surfactants the performance of the state-of-the-art silicone antifoams may be significantly inhibited due to the interaction between antifoam droplets and the ionic foaming surfactant. These interactions, which ~L:L~'7~

Y1869-l are dependent on the concentration and the nature of the foaming surfactants, result at least in par~ from sur-fsctant ad~orption and the consequent development of sur-face charge on the antifoam as well as foam bubble surface.
Significall~ build-up of surface charge tends to inhibit the antifoam transport ~o the similarly charged foa~
bubble. That i5, the electrical repulsive force causes the antifoam action to become less efficient. In such systems only those antifoams will perform effectively which are capable of either minimizing or overcoming the repulsive forces. The product Y proved to be highly effective also even in several highly viscous system such as 5-10% aqueous ~olutions of polyvinyl alcohol (8~-90% hydrolyzed~.
~ ne embodiment of this in~en~ion is a process, for reducing foaming in an aqueous liquid having a viscosity of at least 100 centistokes at 25C and havin~ a tendency to foam, which comprises forming a mixture of said liquid and an antifoam compositio~ which comprises a polydiorganosiloxane oil having a viscosity in the range of 5,000 to 30,000 centistokes at 25C, 1 ~0 parts by weight per 100 parts by weight of the oil of a finely divided hydrophobibic solid having a surface area of from 50 to 1,000 ~quare meters per gram, and 1-20 part~ by weight per 100 parts by weight of the oil and ~olid together of a siloxasle-oxyalkylene block copolymer ~urfactant havlng a hydrophilic-lipophilic balance in ~he range of 4 to 14.
The following examples illustrate the pre-7~i~7 parations, the dimethylpolysiloxane oils utilized correspond to Formula I above wherein n ls varied to result in oils having different viscosities. (The abbreviation "ctks" refers to centistokes measured st 25C.~ The terminology "hydrophobic silica"
refers ~o a product derived from a fumed silica based which is over 99.8% pure SiO~ and in which the hydrophilic hydroxyl groups which normally populate the silica surface are replaced with trimethylsiloxy groups. The product is commercially available as Tullanox 500TM (BET surface area: 245 m21gm. The polysiloxane-oxyalkylane block copolymer surfactant is the one depicted in Formula III above.

; - lOa-~ ~t3 ~7~j~7 Hydrophobic silica, 4.5 grams, ls mixed with dimethylpolysiloxane oil having a viscosity of 10,000 cstks, 145.5 grams, in a laboratory size dough mixer at medium speed for 15 minutes. Then polysiloxane-oxyalkylane block copolymer surfactant, 16.67 grams, is added to the mixture and mixlng is continued for 10 minutes. The resulting composition can be used )~er se as an antifoaming agent.

The product of preparative Example 1 is emulsified as ~ollows: a mixture of sorbitan mono-stearate, commercially available as Span 600, polyoxyethylene stearate, commercially available as Myrj 52 S, and water in a 1.7:1.3:3.0 weight ratio is prepared by first dissolving the polyoxyethylene stearate in the appropriate amount of water at 60C
and stirring in slowly the sorbitan stearate to obtain a homogeneous mixture. The mixture is added to the product of Preparative Example 1 in a dough mixer and the composition ls mixed at medium speed for 15 mlnutes. Then, whlle mixing continues, water is slowly added. The resulting product is diluted with water to give a 10~ by weight active antlfoam emulsion, weight-average particle si~e 9.5 micrometers.

Hydrophobic silica, 2.25 grams, is mixed with dime~hylpolysiloxane oil having a viscosity of 10,000 cstks, 72.75 grams, for 10 minutes. The product is then mixed with polyslloxane-oxyalkylane !~

.'7~i7 11869-l block copolymer surfRctant, 8.33 grams, Eor 10 minutes. The resulting composition was diluted 10-fold using Dimethyl Carbitol (1,5-dimethoxydiethylether) solvent.

REPARATIVE EXAMPLES S~IOWI~G VARIATIONS IN
MIXING TIMF.S
Hydrophobic silica, A, 4.5 grams, is mixed with dimethylpolysiloxane oil having a viscosity of 10,000 cstks, B, 145.5 grams, in a dough mixer at medium speed for varying periods of time. Then polysiloxane-oxyalkylane block copolymer surfactant, D, 16.67 grams, is added to the mixture and mixing is continued for varying periods of time.

Preparative Time Mixing Time Mixing Example No. A+B (min.) AB+D (min.)

4 5 10 The product of Preparative Example 8 is emulsified by the procedure described in Preparative Example 2.

PREPARATIVE EXAMPLE ~3 Hydrophobic silica, 4.5 grams, is mixed with dimethylpolysiloxane oil having a viscosity of 10,000 cstks, 145.5 grams, in a dough mixer at medium speed for 10 minutes. Then polysiloxane-oxyalkylane block copolymer surfactant, 8.33 grams, is added to the mixture and mixing is continued for 10 minu~es.

11869-l The resulting composit~on is emulsified by the procedure described in Preparative Exam~le 2, providing a produc~
w~th a weight-average particle size of 10.0 micrometers.

.
Hydrophobic silica, 4.5 grams, i6 mixed with dimethylpolysiloxane oil having a viscosity of

5,000 c3tks, 145.5 grams, in ~ dough mixer at medium speed for 10 minutes. Then polysiloxane-oxyalkylene block copolymer surfaceant, 16.7 grams, is added to the mixture and mixing ~s continued for 10 minutes.
The resulting composi~ion is emulsified by ~he procedure described in Preparative Exanple 2.

Hydrophobic silica, 4.5 grams, is mixed with dimethylpoly^iloxane oil having a viscosity of 30,000 cstks, 145.5 grams, in a dough mixer at medium speed for 10 minutes. Then polysiloxane-oxyalkylene block copolymer surfactant, 16.67 grams, is added to the mixture and mixing is continued for 10 minutes.
The resulting composition is emulsified by the procedure described in Preparative Example 2, providing a product with a weight-average particle size of 10.3 micrometers.
~LEND TECHNOLOGY
.
In the follswing preparative examplec, various novel high vi3cosi~y antifoams of our inven~ion are blended with ~ low viscosity an~ifoams in order to make a more versatile antifoam composition. The blends of Preparati~e Examples 17 and 19 fall within the scope of the present in~ention. The low viscosity antifoam is pre-pared by mixlng dimethylpolysiloxane oil of 500 cstks ViscoRity with 3% by weight of fumed fine silica, heating t 11869-~

150C for two hours, and cooling to room temperature.
P_ PARATIVE EXAMPLE 16 Hydrophobic silica, 6.0 grams, is mix~d with dimethylpolysiloxane oil having a viscosity of 10,000 cstks, 194 grams, in a dough mixer at medium speed for 5 minutes. Then the low viscosity antifoam mentioned above, 100 grams, is added to the mixture and mixing is continued for 10 minutes, resulting in a dimethyl-polysiloxane oil ~iscosity of 4470 cstks. Then poly-siloxane-oxyalkylene block copolymer surfactant, 33.4 grams, is added to the mixture and mixing is con~inued for 10 minutes. The resulting composition is emulsified by the procedure described in Preparative Examle 2, providing a product with a weight-average particle ~ize of 8.6 micrometers.
P~
Hydrophobic silica, 7.2 grams, is mixed with dimethylpolysiloxane oil havin~ a viscosity of 10,000 cstks, 232.8 grams, in a dough mixer at medium speed for 5 minu~es. Then the low viscosity antifoam mentioned above 6Q grams, is added to the mixture ant nixing is continuing for 10 ~lnutes, resulting in a dimethylpolysiloxane oil ~iscosity of 6300 cstks. Then polysiloxaneoxyalkylene block copolymer surfactant, 33.4 grams, ~s added to the mixture and mixing is continued for 10 minutes. The resulting composition is emulsified by the procedure des-cribed in Preparative Example 2, providing a product with a weight-average particle size of 10.5 micrometer~.

.
The emulsion prepared by applying the pro--11869-l cedure deseribed in preparative example 2 to the low viscosity antifoam mentioned above is mixed with the emulsion product of Preparative Example 12 in the pro-portion of 4:1, resultin~ in a polydimethylsiloxane oil YiSCosity of 1$08 centistokes.

The emulsion prepared by ~pplying the procedure described in Preparaeive Example 2 to ehe low viscosity antifoam mentioned above is mixed with the emulsion pro-duct of Preparative Example 12 in the proportion of 1:4, resulting in a polydimethylsiloxane oil viscosity of 6300 centistokes.
The following examples establish the criticality of, and unexpectedly improved rPsults due to, the various parameters recited in the appended claims.
~~IFOAM TEST PROCEDURE
. _ The antifoam tests were conducted by mixing 250 ml of foaming solution with appropria~e concentrations of antifoam. The term "concentra~ion of antifoam" refers, in all the tests described here,~o the weight concent-ration of silicone oil/silica mixtuse in the total foaming solution. The aforementioned mixture a course glass frit (20-60 millimicron average pore size) under a constant gas flow rate in a 1000 milliliter graduated glass cylinder.
The rise of foam as a fun~ion of foaming time is recorded.
The mixin~ of the antifoam with the foaming solution was accompli6hed by the use of a wrist action mixer. The control of antifoam/foaming solu~ion mixing intensity and time has been found to be oE critical importance. Therefore, these parameters were kept constant. Furthermore, to obtain a high degree of reproducibility, it is i~portant to clean the glass frit and glassware thoroughly such that they are well wetted by the foaming solutions. For this purpose it is important to clean the frit and glassware, before each experiment, with basic sodium hydroxide solution and the chromic acid followed by thorough washing with distilled water. The glass frit is always kept soaking in distilled water until used. Under the above stated conditions, from a foaming system consisting of 0.5% sodium dodecyl sulfate in water and in the absence of any antifoam, one can obtain a foam volume of 1000 milliliters in 100 seconds.
Linear increase in the foam volume with foaming time, even in the presence of antifoam, is typical of a well-dispersed antifoam. The rate of foam rise at constant air flow rate can be represented as:
dF/dt = K
where F is the foam volume at time t, and K is the rate constant, a function of aeration rate, type, and amount of antifoam present~
Under the conditions of constant aeration, one can define antifoam efficiency, N , as:
N Ko/K
where Ko and K are the foaming rates without and with antifoam present, at a constant aeration rate.

Thus, N = 1 means either the absence of an antifoam or total ineffectiveness of the antifoam while N =

i7 11869-l 20, for example, means a 20-fold increase in the time the would be required to generate the same foam volume in the presence oE antifoam, or that the presence of antifoam will reduce the foaming rate by a factor of 20. In other words, the higher the value of N obtained for a given antifoam the bet~er will it be considered. The efficiency factor N has been found to be extremely useful in characterizing the performance of an antifoam in a particular system.
The foaming systems utilized in the tests which follow can be categorized as normal, ionic, and viscous. All employ commercially available foaming agents. They are aqueous solutions of:
Normal Ter~itolTMl5-S-9 (ethoxylated Cll -Cl5 alcohols - 9 moles ethylene oxide), available from Union Carbide Corporation.
National Aer-O-Foam 3% Re~ular (fire fighting foam - protein based), available from National Foam System, INc.
Ionic Sodium Dodecyl Sulfate, available 98 +
pure from E.M. Laboratories, Inc.
Potassium Oleate, available as Green Soap, 70% active in ethanol, from Eli Lilly and Co.
Palmolive Dishwashin~ Liquid, available from Colgate-Palmolive Co.
Viscous GelvatolTM20/60 (partially hydrolized polyvinyl acetate - 7.5% polyvinyl alcohol), available from Monsanto ElvanolTM50/42 (partially hydrolized polyvinyl 7~i~7 11869-l acetate - 5.0% polyvinyl alcohol), available from DuPont.
Our experiments with mixing times gave the following results in 0.5% sodium dodecyl sulfate systems:

Product of Antifoam Efficiency, N, Prep. Ex. No.at 200 Ppm Conc. Antifoam 8.5

6 9.6

7 15.8

8 ]6.5

9 11.0 The results suggest that (1) in the first step, mixing time is not very critical as long as sufficient time of mixing is given, and (2) in the second step, excessive mixing is deleterious to product performance and, under these conditions, 10 minutes mixing is optimum.

COMPARISON WITH
LOW VISCOSITY ANTIFOAMS
In order to demonstrate the criticality to our invention of the silicone oil viscosity range, the following compositions were prepared:
An antifoam composition (Af-17N) was prepared by mixing 72.75 grams of dimethylpolysiloxane oil (500 cstks) with 2.25 grams of 3~ by weight ~umed fine silica for 10 minutes followed by heating at 150 for two hours and slowly cooling to room temperature. The product was then mixed with 8.33 grams of polysiloxane-oxyalkylane .'~.

'7 block copolymer sur~actant ~or 10 minutes. The mixture was diluted 10-fold using Dimethyl Carbitol solvent.
An antifoam composition (Af-18N) was prepared by mixing 72.75 grams of dimethylpolysiloxane oil (500 cstks) with 2.25 grams of hydrophobic silica for 10 minutes. The product was then mixed with 8.33 grams of polysiloxane-oxyalkylane block copolymer surfactant for 10 minutes. The mixture was diluted 10-fold using Dimethyl Carbitol solvent.
Two antifoam compositions, Af-20N(a) and Af-20N(b), were prepared as follows. 3% by ~eight fumed fine silica in dimethylpolysiloxane oil (500 cstks) were mix heated at 150C for two hours, and slowly cooled to room temperature. 12.0 grams of this product was mixed with 108.0 grams of Dimethyl Carbitol. The solvent Dimethyl Carbitol (DMC) effectively dissolves dimethylpolysiloxane oil and leaves silica in suspension. The silica was separated from this dispersion by centrifugation for 100 minutes (to give complete separation). The residue, which is a hydrophobic silica, was redispersed in two separate fluids (a) 1:9 dimethylpolysiloxane oil (500 cstks)/Dimethyl Carbitol mixture and (b) 1:9 dimethylpolysiloxane oil (10,000 cstks)JDimethyl Carbitol mixture, to yield 3%
(wt/wt) silica based on the dimethylpolysiloxane oil. The suspensions were ~urther mixed with polysiloxane-oxyalkylane ~lock copolymer surfactant to obtain 10% wtlwt surfactant with respect to the dimethylpolysiloxane oil.

EfÇiciency, N, Antifoam Systems in 0.5% Sodium (200 ppm in DMC) Dodecyl Sulfate Af-17N Low viscosity 1.6 (5% Surfactant) Af-18N Low viscosity 9.6 Prep.Ex.3 High viscosity 45.0 Af-20N(a~ Low viscosity 1.6 Af-2ON(b) High viscosity 21.0 The above results clearly indicate that the use of high viscosity silicone oil yields a superior product. They also indicate [compare Af-20N(b)]
with Prep. Ex.3) that the nature of the hydrophobic silica can have some effect on antifoam performance.
To study further the effect of silicone oil viscosity on antifoam performance, the products of Preparative Examples 8 (10,000 cstks, unemulsified) and 12 (10,000 cstks, emulsified) were compared to the product of the preparation described in Preparative Example 15 before the emulsification step, 15N (30,000 cstks, unemulsified), the product of Preparative Example 15 (30,000 cstks, emulsified), as well as to products prepared similarly utilizing polydimethylsiloxane oils of 100~ 500, and 1000 centistokes. The unemulsified products were diluted 10-fold with Dime~hyl Carbitol. The results were as follows:

Antifoam Efficiency (N) in 0.5% Sodium DodecYl Sulfate Through DMC Emulslon Oil ViscositY (cstks~ (400 Ppm) (200 ppm2 100 2.7 500 7.0 2.0 1000 10.0 10.5 5400 21.33

10,000 200.0 43.0 30,000 200.0 45.0 EFFECT OF SILOXANE-OXYALKYLENE BLOCK COPOLYMER
SURFACTANT CONCENTRATION ON ANTIFOAM PERFORMANCE
In order to demonstrate the effect of ~he polysiloxane-oxyalkylene block copolymer surfactant on antifoaming efficiency, the performances of the following products were compared: (a) the product of Preparative Example 12, which contains 10~
surfactant, (b) the product of Preparative Example 13, which contains 5% surfactarlt, and (c) a product prepared by mixing 145.5 grams of dimethylpolysiloxane oil having a viscosity of 10,000 cstks with 4.5 grams of hydrophobic sllica in a dough mixer at medium speed for 10 minutes, followed by mixing for an additional 10 minutes, and then emulsifying by the procedure described in Preparative Example 2. Product ~c) contains 0%
surfactant. All three of these antifoam emulsions were tested at 200 parts per million.

7~3'~

11869-l ANTIFOAM FFFICIENCY (N) Foaming 0% Sur-5% Sur- 10% Sur-System factantfactant factant 0.5% Sodium Dodecyl Sulfate 1.9 13.0 36.4 0.5% Potassium Oleate Soap 4.4 8.9 9.0 0.5% Tergitol 15-S-9 2.5 3.2 4.0 10% Eire Eighting Foam 16.8 38.4 53.0 0.5% Dishwashing Liquid 4.8 13.9 18.0 COMPARAT _E EXAMPLE 5 Ihe products of Preparative Example 1 and of Preparative Example 2 were compared to a product prepared by first mixing dimethylpolysiloxane oil of 500 cstks viscosity with 3% fumed fine silica, then heating to 150C for two hours and cooling to room temperature, and then emulsifying by the procedure described in Preparative Example 2.
ANTIFOAM EFEICIENCY
AT 400 PPM ANTIFOAM CONC.

Foaming Reference System Product PreP. Ex. 2 _rep. Ex. 1 0.5% Sodium Dodecyl Sulfate 1.88 200 192 0.5% Potassium Oleate Soap 2.51 74 0.5% Dishwashing Liquid 5.8513.7 (~

118~9-]

AT 600 YPM ANTIFOAM CONC.
Foaming Reference System roduct Prep Ex. 2 7.5~ Gelvatol 140 200 5.0% Elvanol 62 116 The product of Preparative Example 2 was compared to a product prepared by mixing dimethyl-polysiloxane oil of 500 cstks viscosity with 37O
fumed fine silica, then heating to 150C for two hours and cooling to room temperature, and then emulsifying by the procedure described in Preparative Example 2.

ANTIFOAM EFFICIENCY (N) AT DIFFERENT ANTIFOAM CONC.

Foaming SystemReference Product Prep. Ex. 1 ~_ ppm ppmppm 0.5% Sodium Dodecyl Sul-fate 1.9 9.545 >200 0.5~/O Potassium Oleate Soap 2.5 13 13 75 0.5% Dishwashing Liquid 6.5 >20030 >200 ANTIFOAM PERFORMANCE IN DIFFERENT
FOAMING SYSTEMS
The products of Preparative Examples 12, 16, and 17 were compared to an antifoam prepared by mixing dlmethylpolysiloxane oil of 500 cstks viscosity with 3% fumed fine silica, heating to 150C for two hours, cooltng to room temperature, and emulsifying by the procedure described in Preparative Example 2.

~ 7Ç~t~ 69-1 ANTIFOAM EFFICIENCY (N) (200 PPm~

Foaming Prep. Prep. Prep.
System ReÇerence Ex. 16 Ex. 16 Ex. 12 0.5% Sodium Dodecyl Sulfate 1.8 4.6 9.9 36.4 0.5% Potassium Oleate Soap 2.1 6.2 10 9 0.5% Dishwashing Liqllid 4.0 11 18 18 10% E`ire Eighting Foam 200 120>200 53 0.5% l'ergitol 15-S-9 - 17 12 4.0 The reference antifoam was also compared to the product of Preparative Example 12 in viscous systems.

ANTIFOAM EFFICIENCY (N) (400 PPm) Foaming Systems Reference Prep. Ex. 12 7.5% Gelvatol (300 cstks) 140 200 5.0% Elvanol (48 cstks) 62 116 The reference antifoam was also compared to the products of Preparative Examples 12, 18, and 19, with the ollowing results:

ANTIFOAM EFFICIENCY (N) (400 ppm) Foaming Prep. Prep. Prep.
SYStem Reference Ex. 18 Ex. l9 Ex. 20 0.5% Sodium Dodecyl Sulfate 2.5 82 200 200 10% Fire Fighting Foam 200 200 200 200 ;7 The difference in foaming activity are especially significant in the difficult to defoam systems involving sodium dodecyl sulfate~ potassium oleate soap, and dishwashing liquid.
ALTERNATE PR PARATIONS
While the Preparative Examples given above demonstrate the preferred method for making the antifoam compositions of ~he invention, they can be made in other ways. The following examples demonstrate other mixing procedures:
A = 87.3 parts by weight dimethylpolysiloxane oil (10,000 cstks) B = 2.7 parts by weight hydrophobic silica D = 10.0 parts by weight polysiloxane-oxyalkylene block copolymer surfactant I. A+B+D are mixed simultaneously for 25 minutes II. A+D are mixed for 10 minutes, then B is mixed in for 15 minutes III. D+B are mixed for 10 minutes, then A is mixed in for 15 minutes Products I - III were compared to the product of Preparative Example I. Their antifoam efficiencies N are determined in two different standard foaming systems at the concentrations indicated.

Foamin~ SYStemS Product (Antifoam ~onc. in ppm) N
0.5% Sodium I(375)4~.0 II(380)40.0 Dodecyl Sulfate III(371)23.7 Prep. Ex.
I(360)80.0 10% Fire Fight- I(272)10.6 II(250)8 ing Foam III(280)10 Prep.
Ex.I(253)16.5 '7~i7 The results indicate that, while alternate methods of preparation do lead to a composition with significant antifoaming characteristics, more efficient antifoaming action is achieved with compositions prepared by the preferred method.
Various modifications and variations of this invention will be apparent to workers skilled in the art. It is to be unders~ood that such modifications and variations are to be included within the purview of this application and the spirit of the appended claims.

Claims (13)

WHAT IS CLAIMED IS:

1. An antifoam composition which comprises a polydiorganosiloxane oil having a viscosity in the range of 5,000 to 30,000 centistokes et 25°C, 1 - 20 parts by weight per 100 parts by weight of the oil of a finely divided hydrophobic solid having a surface area of from 50 to 1,000 square meters per gram, and 1 - 20 parts by weight per 100 parts by weight of the oil and solid together of a siloxane-oxyalkylene block copo-lymer surfactant having a hydrophilic-lipophilic balance in the range of 4 to 14.

2. An antifoam composition as defined in claim 1 in which the oil is a polydimethylsiloxane having a viscosity in the range of 5,000 to 30,000 centistokes at 25°C, the solid is a hydrophobic silica having a surface area of at least 50 square meters per gram, and the surfactant is a siloxane-oxyethylene block copolymer having a hydrophillc-lipophilic balance in the range of 4 to 14.

3. An antifoam composition as defined in claim 2 in which the polydimethylsiloxane oil has a viscosity of approximately 10,000 centistokes at 25°C, the hydrophobic silica has a surface area of approxi mately 245 square meters per gram, and the siloxane-oxyethylene block copolymer surfactant has a hydro-philic-lipophilic balance of approximately 7.6.

4. An antifoam composition as defined in claim 2 in which the polydimethylsiloxane oil is present in about 87.3 parts by weight, the hydrophobic silica is present in about 2.7 parts by weight, and the siloxane-oxyethylene block copolymer surfactant is present in about 10.0 parts by weight, all per 100.0 parts by weight of the composition.

5. An antifoam composition as defined in claim 1 which contains water and an emulsifying agent.

6. An antifoam composition as defined in claim 5 in which the emulsifying agent is selected from the group consisting of polyoxyethylene alcohols, sorbitan fatty acid esters, polyoxyethylene acids, ethoxylated C11 - C15 alcohols with 3 to 15 moles of ethylene oxides, and mixtures thereof.

7. An antifoam emulsion which comprises 50 - 99% water into which an antifoam composition as defined in claim 1 has been dispersed by means of an emulsifying agent.

8 An antifoam emulsion as defined in claim 7 wherein the emulsifying agent comprises a mixture of sorbitan monostearate and polyoxyethylene stearate.

9. An antifoam composition in which 1 - 20 weight % of a siloxane-oxyalkylene block copolymer having a hydrophilic-lipophilic balance in the range of 4 - 14 has been blended with a homogeneous mixture of 1 - 20 weight % of a finely divided hydrophobic solid having a surface area of from 50 to 1,000 square meters per gram and 99 - 80 weight % of a polydiorganosiloxane oil having a viscosity in the range of 5,000 to 30,000 centistokes at 25°C.

10. An antifoam emulsion in which the anti-foam composition as defined in claim 9 has been dispersed in a major amount of water by means of an emulsifying agent.

11. A process for reducing foaming in aqueous liquids having a tendency to foam which comprises forming a mixture of said liquid and a composition as defined in claim 1.

12. A process as claimed in claim 11 wherein said aqueous liquid contains an ionic surfactant which increases the tendency of the liquid to foam and which is present in an amount close to or above its critical micelle concentration.

13. A process as defined in claim 11 wherein said aqueous liquid has a viscosity of at least 100 centistokes at 25°C.