GB2257709A - Silicone foam control agent - Google Patents

Description

2 -1 3 77 3 j SILICONE FOAM CONTROL AGENT This invention is concerned with

silicone foam control agents and with compositions containing them.

In many aqueous systems which are used e.g. in food processes, textile dying, paper production, sewage treatment and cleaning applications, surface active agents are present either as an unwanted ingredient or as deliberately introduced materials to achieve a certain function. Due to the presence of these surface active agents foam is often is generated. In certain applications, such as in dish washing by hand, this is a welcome effect but in other applications foam generation can lead to unsatisfactory results. This is for example the case in the dyeing of textiles or in the manufacture of paper. In other applications, for example the use of detergent compositions for domestic laundering, the production of foam needs to be controlled rather than avoided. It is important to keep the foam formation to an acceptable level, especially when laundering is performed in automatic front loading washing machines. Excessive foam would cause overflow of the washing liquor onto the floor as well as reduction in the efficiency of the laundering operation itself.

Foam control agents are known in such industries and have been incorporated into for example heavy duty detergent powders for use in automatic washing machines. Silicone foam control agents are regarded as very effective in this application as they can be added in very small quantities and are not affected by e.g. the hardness of water, while traditional foam control compositions, such as soaps, require a certain water hardness for their effectiveness.

The detergent industry is currently going through an important evolution where, due to environmental concern and energy conservation efforts, there is a move towards the use of detergent compositions which will perform adequately at lower laundering temperatures. one way in which this is achieved is by the increase of the surfactant level in the detergent compositions. Anionic surfactants are especially favoured. Unfortunately these surfactants usually create more foam than for example the nonionic surfactants. Since silicone foam control agents do not directly contribute to the cleaning power of a detergent composition it is desirable to keep the addition level of such foam control agents to a minimum. There has therefore arisen a need to develop improved foam control agents for incorporation in detergent compositions.

Silicone foam control agents containing branched siloxanes are known in the art. E.P. patent specification 0 217 501 describes a foam control agent wherein a liquid siloxane component is obtained by mixing 100 parts by weight of a polydiorganosiloxane having triorganosiloxane end-groups, 10 to 125 parts of a polydiorganosiloxane having at least one terminal silanol group and at least 40 silicon atoms and 0.5 to 10 parts of an organopolysiloxane resin comprising monofunctional and tetrafunctional siloxane units in a ratio of from 0.5:1 to 1.2:1, and having at least one silanol group per molecule, and thereafter heating the mixture. The specification describes the need to control the amount of resin used in order to retain a liquid polymer, avoiding a gel structure. This indicates that some branching occurs in the siloxane component of the foam control agent. Although foam control agents, according to E.P. 0 217 501, perform adequately in many applications there is a continuing search for improved foam control agents.

European Patent Application 0 273 448 discloses a foam suppressant composition made by the free radical polymerisation of a polydiorganosiloxane, silica, a pendant vinyl functional silicone oil and a free radical polymerisation initiator such as benzoyl peroxide. This reaction is carried out at elevated temperature, which reaction cannot be guaranteed to be safe. It is also difficult to control this reaction. It is required in the European Application 0 273 448 that the highly viscous reaction product be diluted with a low viscosity polysiloxane in order to form an effective antifoam end product.

The present invention provides a foam control agent which is an improvement over the silicone foam control agent of E.P. 0 217 501 with regard to efficiency. The process is also safer than that used for the manufacture of the silicone antifoam of E.P. 0 273 448. No dilution of a reaction product is required in order to formulate a final foam control agent. This is significant in that it eliminates a costly and time consuming process step in the manufacture of an end product.

The present invention also differs significantly from that described in the prior art. The reagents used are very different from those of E.P. 0 217 501 and although vinyl functional siloxanes are used, as is the case in the European Application 0 273 448, instead of a pendant vinyl functional silicone oil the present invention uses a vinyl endblocked polydiorganosiloxane. Further differences between the present invention and that set forth in E.P.

0 273 448 are the choice of the second reagent and of the catalyst. Where E.P. 0 273 448 utilises a free radical polymerisation initiator such as benzoyl peroxide the instant invention provides for crosslinking with an organo hydrogensiloxane in the presence of a noble metal catalyst.

The use of hydrosilylation per se is not new in the production of foam control agents. U.S. 4,741,861 discloses a silicon based antifoam composition comprising among other ingredients a diorganopolysiloxane terminated at both molecular chain ends with a vinyldiorganosilyl group and a diorganopolysiloxane terminated at both molecular chain ends with a diorganosilyl group. The two types of diorganopolysiloxane are reacted in the presence of a platinum compound to provide a polymer of higher viscosity through chain extension. There is no indication in the prior art that providing a branched polydiorganosiloxane through hydrosilylation would result in improved foam control agents.

The invention provides in one of its aspects a method for preparing a silicone foam control agent which comprises the steps of (A) forming a mixture of a vinyl end-blocked polydiorganosiloxane, a volatile, low viscosity organohydrogensiloxane having at least 3 silicon- bonded hydrogen atoms and a solvent, (B) reacting said mixture in the presence of a noble metal catalyst to make a branched organopolysiloxane and (C) adding to the mixture a finely divided particulate material having a surface rendered hydrophobic by contact with a treating agent.

Vinyl end-blocked polydiorganosiloxanes which are useful in step (A) of the method of the invention have the general formula Vi-[Si(R 2)0] n -Si(R 2)Vi, wherein R denotes an organic group and Vi denotes a vinyl group. The organic group R is preferably a hydrocarbon group of up to 8 carbon atoms, more preferably an alkyl group or an aryl group, e.g. methyl, ethyl, propyl, hexyl or phenyl. It is most preferred that at least 80% of all R groups are methyl groups. The value of n, which denotes an integer, is such that the viscosity of the vinyl end-blocked polydiorganosiloxane is in the range of from 200 to 100,000 mPa.s, more preferably 2000 to 55,000 mPa.s at a temperature of 250C.

In step (A) of a method according to the invention the volatile low viscosity organohydrogensiloxane may be a cyclic or linear material, and may be a mixture including both cyclic and linear organohydrogensiloxanes. suitable cyclic organohydrogensiloxanes include those of the formula (RIHSiO) X in which R' is an alkyl or aryl radical having from 1 to 6 carbon atoms preferably methyl, and x is an integer from 3 to 5. Suitable linear low viscosity volatile organohydrogensiloxanes include those of the general formula W' 3 SiO(RIHSiO) y SiRll 3 where Rf is the same as above, W' denotes either H or R' and y is from 2 to 9, provided there are at least 3 silicon-bonded hydrogen atoms per molecule.

In step (A) of the method according to the invention a solvent is employed which is preferably a polydiorgano siloxane. Suitable polydiorganosiloxane solvents are substantially linear polymers wherein the silicon-bonded substituents are groups R, as defined above. Most prefer ably at least 80% of all silicon-bonded substituents are methyl groups. Most preferred solvents include trimethyl siloxy end-blocked polydimethylsiloxanes having a viscosity of 500 to 12500 mPa.s measured at 250C. The solvents are mainly present to solubilise the branched polydiorgano siloxane made in step (B) of the method of the invention.

The noble metal catalyst for use in step (B) of the method of the invention catalyses the hydrosilylation reaction and -may be selected from a variety of hydrosilylation catalysts known to promote the reaction of vinylfunctional radicals with silicon- bonded hydrogen atoms. Suitable noble metal catalysts include platinum and rhodium-containing compounds and complexes. Platinum catalysts such as platinum acetylacetonate or chloroplatinic acid are representative of these compounds and suitable for use. A preferred catalyst mixture is a chloroplatinic acid complex of divinyltetramethy1disiloxane diluted in dimethylvinylsiloxy endblocked polydimethylsiloxane which may be prepared according to methods described by Willing in U.S. patent No. 3,419,593. Most preferably this mixture contains about 0.6 weight percent platinum.

Hydrosilylation catalysts are well known in the art and the interested reader is referred to the following patents for detailed descriptions regarding their preparation and use: Speier, U.S. Patent No. 2,823,218; Willing, U.S. Patent No. 3,419,359; Kookootsedes, U.S. Patent No. 3,445, 420; Polmanteer et al, U.S. Patent No. 3,697,473; Nitzsche, U.S. Patent No. 3,814,731; Chandra, U.S. Patent No. 3,890,359 and Sandford, U.S. Patent No. 4,123,604. Many of the catalysts known in the art require the reactants to be heated in order for a reaction to occur. When such catalysts are employed this requirement must be taken into consideration.

The branched organopolysiloxane prepared in step (B) of the method according to the present invention has a three dimensional network and preferably has a viscosity of 500 to 500,000 m.Pa.s measured at 250C, more preferably 5000 to 50,000 m.Pa.s. For purposes of foam control agents according to the present invention, the branched organopolysiloxane should most preferably have a viscosity of about 20, 000 m.Pa.s measured at 250C.

When platinum catalysts are used in step (B) of the method of the invention an inhibitor may be required in order to improve the shelf life of the starting materials and to control the viscosity-time profile of the compositions. These inhibitors are also known in the art and include ethylenically unsaturated isocyanurates, such as trialkylisocyanurate, dialkylacetylenedicarboxylates, alkyl maleates, phosphine, phosphites, aminoalkyl silanes, sulphoxides, acrylonitrile derivatives and others. Particular inhibitors preferably used are diethyl fumarate, bis(2-methoxy-l-nethylene)maleate, bis(2- methoxy-i-methylethyl)maleate and similar compounds.

All of these materials are well known in the art and are commercially available products.

In its simplest terms, the reaction for forming the branched three dimensional network organopolysiloxane in step (B) of the method of the present invention can be is characterised as:

Pt -SiCH=CH 2 + HSi - ------ > -SiCH 2 CH 2 si- The reaction may be carried out in any convenient way but we prefer to blend the vinyl endblocked polydiorganosiloxane, volatile low viscosity organohydrogensiloxane, solvent and noble metal catalyst and to carry out the reaction at a temperature of 30 to 1000C preferably 700C. Preferably, the vinyl endblocked polydiorganosiloxane is included in the reactant solution in an amount of from 5 to 20% by weight and the volatile low viscosity organohydrogensiloxane is employed in an amount of from 0.01 to 3%, more preferably 0.04 to 1% by weight of the solution used in step (A). The concentrations of catalyst and inhibitor to be used in the present invention may be determined by routine experimentation. Typically, the effective amount of catalyst should be in a range so as to provide from about 0.1 to 1000 parts per million (ppm) of platinum by - 8 is weight in the compositions of the present invention. As an example, when the preferred catalyst mixture (i.e. the chloroplatinic acid complex of divinyltetramethy1disiloxane containing about 0.6% by weight of platinum) and inhibitor (i.e. bis(2-methoxy-l-methylethyl)maleate) are employed, a ratio by weight of inhibitor to catalyst mixture ranging from zero to about 0.6 provides a suitably wide range of inhibition which is adequate under most practical conditions of manufacture.

A foam control agent according to the present invention preferably also comprises a polyorganosiloxane fluid and advantageously this may be provided by the polydiorganosiloxane solvent employed in the method of preparing the branched polyorganosiloxane.

The finely divided particulate materials used in step (C) of the method of the invention may be any of the known inorganic fillers suitable for formulating foam control agents. Such fillers are described in many patent applications. They include fumed Tio 21 Al 2 0 31 aluminosilicates, zinc oxide, magnesium oxide, salts of aliphatic carboxylic acids, reaction products of isocyanates with certain materials, e.g. cyclohexylamine, alkyl amides, e.g. ethylene or methylene bis stearamide and Sio 2 with a surface area as measured by BET measurement of at least 50 m2/g. Preferred fillers are silica fillers which can be made according to any of the standard manufacturing techniques for example thermal decomposition of a silicon halide, a decomposition and precipitation of a metal salt of silicic acid, e.g. sodium silicate and a gel formation method. Suitable silicas for use in a method according to this invention include therefore fumed silica, precipitated silica and gel formation silica. The average particle size of these fillers may range from 0.1 to 20 A but preferably is from 0.5 to 2.5 g.

- 9 The surface of filler particles is rendered hydrophobic in order to make the foam control agents sufficiently effective in aqueous systems. Rendering the filler particles hydrophobic may be done either prior to or after dispersing the filler particles in the liquid siloxane obtained in step (A) or step (B) of the method of the invention. This can be effected by treatment of the filler particles with treating agents, e.g. reactive silanes or siloxanes, for example dimethyldichlorosilane, trimethylchlorosilane, hexamethyldisilazane, hydroxy-endblocked and methyl-endblocked polydimethylsiloxanes and siloxane resins. Fillers which have already been treated with such compounds are commercially available from many companies, for example Sipernat@ D10 from Degussa. The surface of the filler may alternatively be rendered hydrophobic in situ, i.e. after the filler has been dispersed in the liquid siloxane component. This may be effected by adding to the liquid siloxane component prior to, during or after the dispersion of the filler e.g. during step (A) of the method of invention, the appropriate amount of a treating agent, of the kind described above, and heating the mixture to a temperature above 400C. The quantity of treating agent to be employed will depend for example on the nature of the agent and the filler and will be evident or ascertainable by those skilled in the art. Sufficient should be employed to endow the filler with at least a discernible degree of hydrophobicity. The filler is added to the foam control agents in an amount of about 1 to 15, preferably 3 to 5% by weight.

The invention provides in another of its aspects a foam control agent made by the method of the invention as described above.

The foam control agents of this invention are useful for reducing or preventing foam formation in aqueous systems. Such foam control agents are particularly useful for reducing the foam generated by detergent compositions, especially during laundering operations. The foam control agent may be incorporated in a detergent composition in any of the known ways, for example in emulsion form or in a form wherein it is protected against degradation during for example storage, such as in encapsulated form. Such methods are well known in the art and have been disclosed in a number of patent specifications. The advantage of foam control agents produced by the method of this invention is greatest when the composition is used in a detergent composition which has a high foaming ability.

However, they can also be incorporated in other detergent compositions. Such detergent compositions are known in the art and are described in many patents.

The foam control agents of the invention are therefore particularly useful when incorporated in those detergent compositions where a high level of high foaming surfactants is present, for example anionic surfactants, e.g. sodium dodecyl benzene sulphonate. High levels of anionic surfactants may be used to ensure effectiveness of detergent composition at lower washing temperatures, e.g. 400C.

In yet another aspect of the invention there is provided a detergent composition comprising (1) 100 parts by weight of a detergent component and (2) from 0.05 to 5 parts by weight of a foam control agent according to the invention.

Suitable detergent components comprise an active detergent, organic and inorganic builder salts and other additives and diluents. The active detergent may comprise organic detergent surfactants of the anionic, cationic, non-ionic or amphoteric type, or mixtures thereof. Suit able anionic organic detergent surfactants are alkali metal soaps of higher fatty acids, alkyl aryl sulphonates, for example sodium dodecyl benzene sulphonate, long chain (fatty) alcohol sulphates, olefine sulphates and sulpho nates, sulphated monoglycerides, sulphated ethers, sulpho succinates, alkane sulphonates, phosphate esters, alkyl isothionates, sucrose esters and fluorosurfactants. Suit- able cationic organic detergent surfactants are alkylamine salts, quaternary ammonium salts, sulphonium salts and phosphonium salts. Suitable non-ionic organic surfactants are condensates of ethylene oxide with a long chain (fatty) alcohol or fatty acid, for example C 14-15 alcohol, condensed with 7 moles of ethylene oxide (Dobanol 45-7), condensates of ethylene oxide with an amine or an amide, condensation products of ethylene and propylene oxides, fatty acid alkylol amide and fatty amine oxides. Suitable amphoteric organic detergent surfactants are imidazoline compounds, alkylaminoacid salts and betaines. Examples of inorganic components are phosphates and polyphosphates, silicates, such as sodium silicates, carbonates, sulphates, oxygen releasing compounds, such as sodium perborate and other bleaching agents and zeolites. Examples of organic components are antiredeposition agents such as carboxymethylcellulose (CMC), brighteners, chelating agents, such as ethylene diamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA), enzymes and bacteriostats. Materials suitable for the detergent component are well known to the person skilled in the art, and are described in many text books, for example Synthetic Detergents, A. Davidsohn and B.M. Milwidsky, 6th edition, George Godwin (1978).

is The following examples illustrate the invention. All parts and percentages are expressed by weight unless-otherwise stated.

Example I

Into a reaction vessel there was added 850 grams of 1000 mPa.s trimethylsiloxy endblocked polydimethylsiloxane solvent. To the vessel there was added chloroplatinic acid (H 2 PtC1 6' 6H 2 0) in the amount of 10- 4 moles of platinum per mole of SiH as catalyst and 150 grams of a vinyl endblocked polydimethylsiloxane having a viscosity of 9500 mPa.s. As crosslinking agent there was added to the vessel 0.04% by weight based on the weight of the composition of cyclic and linear organohydrogensiloxanes as a mixture including the tetramer and pentamer. The vessel was heated to 700C and the organohydrogensiloxane crosslinking agent was added to the vessel until the viscosity of the fluid in the vessel reached a viscosity of 2000 mPa.s. A gel-formation silica treated with hexamethyldisilazane was added to the fluid in the vessel in an amount of 5% by weight of fluid. The product in the vessel was used in a detergent antifoam composition and tested for its foam suppression capabilities as described in Example II.

Example II

A conventional automatic washing machine (Miele 427) of the front loading type, having a transparent loading door was loaded with 3.5kg of clean cotton fabric. A wash cycle with a prewash and a main wash (950C) was carried out using one lot of a commercial detergent powder having no foam control agent present, for each of the prewash and the main wash.

Each lot of detergent powder consisted of 100g of a high foaming detergent powder which comprised linear alkyl sulphonate, alkyl dimethylamine oxide, silicate, sodium 1 tripolyphosphate, sodium perborate and sodium sulphate and a foam control agent prepared in accordance with Example I. The door of the washing machine was divided in its height by a scale of from 0 to 100% with 10% intervals. The foam height during the wash cycle was recorded at one minute intervals from the beginning of the wash cycle. The recording was done when the rotation drum of the washing machine was stationary. Higher values indicate a higher foam level and thus a worse performance of the foam control composition. Values between 30 to 40 indicate that there was no foam formed in the wash drum. Values between 120 and 130 indicate that the foam level in the wash drum filled about one-half of the drum. Values of 180 to 240 or above indicate that the foam filled the drum and that the foam overflowed the machine. The test results indicated in Table I show the highest level of foam obtained during the wash cycle.

Table I shows the amount of foam control agent contained in the detergent powders tested. Six different foam control agents were prepared following the procedure set forth in Example I, and these six foam control agents were added to detergent powders in amounts from 0.05 to 0.2 percent by weight based on the total weight of the detergent powder. The foam control agents which were prepared following the procedure in Example I are identified in Table Ia showing the amount of the trimethylsiloxy endblocked polydimethylsiloxane (PDMS) used, along with its viscosity and the amount of the vinyl endblocked polydimethylsiloxane (Vi) used along with its viscosity.

14 - TABLE I Foam Heiqhts Weight % Foam Control Aqent in the Deterqent 0.2 0.13 0.1 0.08 0.06 0.05 Foam Control Aqent (1) 32 33 51 ill 200 200 (2) 39 32 80 92 200 200 (3) 43 40 43 56 81 110 (4) 33 37 68 73 72 125 (.5) 40 31 57 95 200 200 (6) 51 40 60 90 200 200 CA 39 114 129 200 200 200 In Table I the "Comparative Antifoam11 (CA) is a commercially available antifoam formulation which was tested in order to provide a comparison with the antifoam compositions of the present invention. The "Comparative Antifoam11 was a three dimensional gel network made according to the teachings of E.P. 0 217 501.

Table Ia

Foam Control Aqent Composition Aqent PDMS PDMS mPa. s (1) 90 3000 (2) 90 5000 (3) 85 1000 (4) 90 3000 (5) 85 500 (6) 85 500 It should be apparent that the foam control agents the present invention possess characteristics in comparison antifoam products.

vi is 15 9500 from a consideration of Table I prepared in accordance with superior foam suppressing to commercially available vi mPa. s 55000 55000 9500 9500 55000 - It should be noted that the applicant of the herein described present invention considers the method of manufacturing products in accordance with the previously mentioned E.P. 0 273 448 to be of a hazardous nature because of the high temperatures required for polymerisation and the formation of toxic volatile materials such as formaldehyde and volatile flamnables. Therefore no comparative data were generated with the compositions described in the E.P. 0 273 448.

Claims (13)

1. A method for preparing a silicone foam control agent which comprises the steps of (A) forming a mixture of a vinyl end-blocked polydiorganosiloxane, a volatile, low viscosity organohydrogensiloxane, having at least 3 silicon-bonded hydrogen atoms and a solvent; (B) reacting said mixture in the presence of a noble metal catalyst to make a branched organopolysiloxane, and (C) adding to the mixture a finely divided particulate material, having a surface rendered hydrophobic by contact with a treating agent.

2. A -method according to Claim 1 wherein the vinyl end-blocked polydiorganosiloxanes have the general formula Vi-[Si(R 2)01n-S' (R 2)Vi, wherein R denotes an alkyl or aryl group of up to 8 carbon atoms and Vi denotes a vinyl group.

3. A method according to Claim 1 or 2 wherein the viscosity of the vinyl end-blocked polydiorganosiloxane is in the range of from 200 to 100,000 mPa.s at a temperature of 250C.

4. A method according to any one of the preceding claims wherein the viscosity of the vinyl end-blocked polydiorganosiloxane is in the range of from 2000 to 55,000 mPa.s at a temperature of 250C.

5. A method according to any one of the preceding claims wherein the volatile low viscosity organohydrogensiloxane comprises a cyclic polymer of the formula [RIHSi0Jx, wherein Rf is an alkyl or aryl radical having from 1 to 6 carbon atoms, and x is an integer from 3 to 5.

6. A method according to any one of the preceding claims wherein the volatile low viscosity organohydrogensiloxane. comprises a linear polymer having the general formula RI1SiO(R,IHSiO) SiRll, wherein R' is an alkyl or aryl radical 3 y 3 having from 1 to 6 carbon atoms, W' denotes a hydrogen atom or a group R' and y is from 2 to 9.

7. A method according to any one of the preceding claims in which the noble metal catalyst is a platinum containing compound or complex.

8. A method according to any one of the preceding claims wherein the branched organopolysiloxane formed in Step (B) has a viscosity of from 5000 to 50,000 mPa.s.

9. A method according to any one of the preceding claims in which the solvent is a trimethylsiloxy end-blocked polydimethylsiloxane.

10. A method according to Claim 9 wherein the polydimethy siloxane has a viscosity of from 500 to 12,500 mPa.s.

11. A method according to any one of the preceding claims wherein step (B) is carried out at a temperature of from 30 to 1000C.

12. A method according to any one of the preceding claims wherein the vinyl end-blocked polydiorganosiloxane amounts to 5 to 10% by weight and the organohydrogensiloxane to 0.01 to 3% by weight of the mixture of step (A).

13. A method according to any one of the preceding claims wherein the particulate material is a silica having a surface area of at least 50 M2/g and an average particle size of from 0.5 to 2.5g.