Composition and use

Abstract: A composition of a glycoside and an acrylic copolymer. The blend may be used to prepare aqueous dispersions of a ceramic materials, for example zirconium silicate. Alternatively, aqueous dispersions of fluorine containing polymers, for example polyvinylidene fluoride, may be prepared using the blend. The proportion of glycoside to acrylic copolymer may be 10:1 to 1:10, for example 1:1, by weight.

Description: The present invention relates to suspensions particular, to compositions which can be used to prepare of particulate solids in an aqueous medium. For many applications it is desirable to form dispersions of solids in an aqueous medium. The dispersions thus formed may be used to form coatings of the solid onto a surface. A number of solids are difficult to disperse or, if dispersed, give a dispersion which is unsatisfactory coating of solid onto a surface. It is known to use surface active materials to assist in the formation of the dispersion but even when using surface active materials some solids are difficult to disperse or, if dispersed, give an unsatisfactory coating. This is undesirable, especially when coating a wax former to produce a ceramic mould for the formation of complex metal castings which are suitable for use in the automobile and aerospace industry. Accordingly there remains a need to provide improved materials for the formation of dispersions. We have found that improved dispersing properties can be obtained using a mixture of materials and, in particular, a mixture of specific materials and, in particular, a mixture of specific materials can provide an especially useful effect. US 4678595 discloses a carpet cleaning composition comprising a a surfactant ingredient comprising 5-70 weight percent of a glycoside surfactant and 30-90 weight percent of an anionic surfactant; b a styrene/maleic anhydride copolymer possibly neutralised or partly esterified; and c water. In the following description the symbol "RTM" accompanying a proprietary name indicates that the name is believed to be registered as a trade mark in at least one of the countries designated for this application. According to the present invention there is provided: a suspension of a particulate solid in an aqueous medium, the medium including as a dispersing agent a composition comprising: (A) a glycoside of the formula: R(OG)a where R is a hydrophobic moiety; G is a saccharide group; and a has a value of at least one; and (B) an acrylic polymer which is i at least one acrylic copolymer containing water soluble side chains and not more than 5% by weight of acrylic acid monomer units; and/or ii at least one acrylic copolymer containing no water soluble side chains and comprising from 2 to 10% by weight of acrylic acid monomer units; the weight ratio of (A) : (B) being from 1:20 to 20:1. The group R can be a hydrocarbyl or a substituted hydrocarbyl group. More specifically, the group R can be an alkyl, cycloalkyl, aryl, alkaryl, aralkyl or alkenyl group and is preferably an alkyl group. The group R conveniently contains from 4 to 30 carbon atoms, preferably up to 24 carbon atoms, more preferably from 6 to 18 carbon atoms and especially from 8 to 14 carbon atoms. The group R can be a mixture of different groups, for example a mixture of alkyl groups which contain, on average, 8 to 14 carbon atoms, for example a mixture of alkyl groups containing on average, from 9 up to 10 carbon atoms. The saccharide group G may be derived from fructose, glucose, mannose, galactose, telose, gulose, allose, altrose, idose, arabinose, xylose, lyxose and ribose or from mixtures thereof. The group G is conveniently derived from glucose units and the glycoside is then a glucoside. The value of a is the degree of polymerisation. When a is one, the glucoside is a monoglycoside. Typically the value of a is greater than one and the glycoside is a polyglycoside, a mixture of polyglycosides, a mixture of a monoglycoside and a polyglycoside, or a mixture of a monoglycoside with a mixture of polyglycosides. The value of a is typically at least 1.1, particularly at least 1.2 and especially at least 1.3. The value of a is typically not greater than 8, particularly not greater than 4 and especially not greater than 2. When the glycoside is an alkyl glucoside, the value of a is conveniently between 1 and 2. We have obtained useful resuLts when the glycoside is an alkyl glucoside of the general formula: C n H (2n+1) O(C 6 H 10 O 5 ) b H where: n has a value of 8 to 14, and b has a value of greater than one and not more than two. The glycoside may be one in which the average value of n is from 9 to 13 and particularly is about 10. The value of b is typically at Least 1.3 and not more than 1.9. A particularly useful material of this type is one in which n is from 8 to 11 and has an average value of 10 and b is about 1.35. Hydrocarbyl glycosides are commercially available materials for example as APG 225 (RTM) Glycoside, APG 300 (RTM) Glycoside or as Triton BG 10 (RTM). The acrylic copolymer which is component (B) of the mixture is a copolymer having some surface active characteristics. Thus, the copolymer is either an acrylic copolymer having water soluble side chains or is a product containing acid groups which are capable of salt formation in the presence of one or more bases. The copolymer may contain both water soluble side chains and acid groups. Whilst satisfactory results can be obtained with a copolymer which contains water soluble side chains, we have found that an improvement is obtained if such a copolymer also contains some acid groups. If the copolymer contains water soluble side chains, these very conveniently include oxyethylene units and preferably are polyoxyethylene chains. Such chains may be terminated with a hydroxy group but it is generally preferred that the chain is terminated with an alkoxy group, particularly a methoxy group. The copolymer is preferably a copolymer of an acrylic ester with an acrylic acid, which may have been reacted, for example pre-reacted with a polyoxyethylene glycol or derivative. Hence, a copolymer of this type contains ester groups together with groups which are derived from the reaction of an acid with the polyoxyethylene glycol. (For convenience hereafter the term "ester" will be used to mean the grouping obtained by the reaction of an alcohol, other than a polyoxyethylene glycol, or phenol with a carboxylic acid.) The copolymer preferably also includes some acid groups. The acrylic copolymer may be obtained from acrylic monomers or derivatives of acrylic monomers such as methacrylic monomers, or may be derived from mixtures thereof. Copolymers based on methacrylic monomers are preferred, such monomers including methacrylic acid and esters thereof such as the methyl and butyl esters. Copolymers containing water soluble side chains typically contain at least 50% by weight of units containing the water soluble side chains and not more than 5% by weight of units containing acid groups, the remainder being units containing ester groups. The copolymers typically contain not more than 80% by weight of units containing the water soluble side chains and not less than 20% by weight of units containing ester groups. The acrylic copolymer may, alternatively, be one in which there are no water soluble side chains. Such a copolymer is a copolymer of an acrylic acid monomer with at least one acrylic ester monomer (the terms "acrylic acid monomer" and "acrylic ester monomer" are used herein to include derivatives thereof such as methacrylic acid and esters thereof). Copolymers of this type preferably contain at least 2% by weight of the acid monomer as defined but in general the acid monomer content does not exceed 10% by weight. The remainder of the copolymer is formed of ester groups and may be all the same ester units or a mixture of ester units such as a mixture of methyl and butyl esters. A copolymer of this type is generally essentially insoluble in an aqueous medium, including aqueous base solutions, but is soluble in organic solvents, particularly non-polar organic solvents, for example aromatic solvents such as benzene, toluene, xylene and the like. It is generally preferred that the acrylic copolymer is one containing water soluble side chains in a sufficient quantity to render the whole polymer water soluble. The acrylic copolymer which is component (B) of the mixture is typically a polymer containing the units where R 1 is hydrogen or a hydrocarbyl group; R 2 is hydrogen, a hydrocarbyl group or a group (AO) x R 3 R 3 is hydrogen or a hydrocarbyl group; A is an alkylene group; x is at least one; and at least some of the groups R 2 are hydrgen or (AO) x R 3 . If the groups R 1 , R 2 or R 3 are hydrocarbyl groups they are preferably alkyl groups which contain not more than 24 carbon atoms and particularly are lower alkyl groups containing 1 to 6 carbon atoms, for example a methyl or butyl group. If R 2 is a group (AO) x R 3 , the group A may be ethylene, propylene or butylene and is preferably ethylene. The value of x is typically at least 10 and generally does not exceed 40. The acrylic copolymer typically consists of the units in which the groups R 1 and R 2 can vary. Typically R 1 is hydrogen or methyl or in some units is hydrogen and in other units is methyl. The group R 2 may be hydrogen, a hydrocarbyl group such as methyl or butyl or a hydrocarbyloxy polyoxyethylene group and is typically a combination of at least two such groups. Preferred acrylic copolymers are those in which R 1 is methyl and R 2 is a combination of hydrogen, a methyl or butyl group and a methoxypolyoxyethylene group. The number average molecular weight of the acrylic copolymer is typically at least 1000. The molecular weight of the acrylic copolymer is preferably not so high that a solution thereof has a high viscosity and does not flow readily, for example the solution does not pour easily. Hence, it is preferred that the number average molecular weight does not exceed 10000. In general, the number average molecular weight is at least 2000 and is not more than 6000. The glycoside which is component (A) of the composition typically contains several alcoholic -OH groups and the acrylic copolymer which is component (B) preferably contains some acid groups. On mixing such materials the possibility of reaction is slight provided the mixture is maintained at ambient temperature or a temperature which is only a little above ambient temperature, for example not more than 50°C. It is preferred to avoid any reaction until the composition is used and hence the mixture should be stored at a temperature at which no appreciable reaction occurs. We have found that compositions of surfactants and acrylic polymers as described above can be used to form suspensions or slurries of solids in liquids, more specifically in an aqueous medium. Using the compositions of the present invention it is possible to form suspensions or slurries having improved properties. The solid may be a ceramic material and using the compositions of the present invention it is possible to prepare slurries containing at least 50% and in many instances up to 80%, or more, by weight of solid, the remainder being water. Even at such high levels of solid, the slurry obtained has satisfactory flow properties and can be coated onto a substrate to give a smooth coating which sticks well to the substrate. In contrast, using other mixtures or using the glycoside alone, a smooth surface coating is not obtained and the coating may not adhere satisfactorily to the substrate. Such slurries of ceramic material, for example a zirconium silicate slurry, can be used to prepare moulds for metal casting by coating the slurry on to a wax former. We have found that the effectiveness of the surfactant/acrylic co-polymer composition used in the present invention is dependent on the particular solid being dispersed and that different compositions show different effects depending on the particular solid. The present invention includes aqueous suspensions of organic solids, for example polymeric materials especially those which do not readily form a satisfactory, stable, suspension such as a fluorine-containing polymer. We have obtained aqueous suspensions containing at least 20% by weight of a polymer material, particularly at least 40%, for example 50%, by weight of polyvinylidene fluoride using a composition in accordance with the present invention. In contrast to suspensions containing only one of the components or containing a different mixture of components, the suspensions obtained using the composition of the present invention give no caking or bleeding on being stored for a day and have a low viscosity. If a suitable thickener is added, for example a polysaccharide or a cellulose derivative, the suspension shows no caking and little or no bleeding on being stored for a week. The amount of the surfactant/acrylic copolymer composition used to obtain a suspension is dependent on the components of the suspension. Thus, satisfactory suspensions can be obtained using the composition in an amount of from at least 0.1 up to 10% by weight of the total weight of the suspension. In general the amount of the composition in the suspension is at least 0.25% by weight. The amount of the composition in the suspension generally does not exceed 7.5% by weight. Various aspects of the present invention are described in more detail hereafter in the following, non-limiting examples in which all proportions are by weight unless stated to the contrary. Examples 1 and 2 Slurries based on zirconium silicate were prepared using one or more additives. A surfactant, or a mixture of surfactants, was mixed with a slurry of silica in water containing 30% by weight of silica. In the preparations of Example 1, 2 and Comparative Example E n-hexanol was then added to the mixture whilst continuing to stir. Zirconium silicate and cobalt aluminate were then added to the mixture whilst continuing to stir at 500 r.p.m. The mixture was then subjected to vigorous stirring and shearing for one minute using an Ultra-Turrax mixer operating at 2000 r.p.m. The viscosity of the slurry obtained was then determined. Each slurry was coated onto a wax and a glass plate by dipping the plate in the slurry and allowing the coated plate to dry for at least 30 minutes at ambient temperature. The appearance of the coating was assessed visually. The compositions formed, and the results obtained, are set out in Table One. Ex.or Comp. Ex. Composition - Wt % Visc (mPa.s) Coat Z-1 S-W CA G1 G2 G3 M P1 POE NH A 72 20 8 0.2 - - - - - - 4680 RT B 72 20 8 - 0.2 - - - - - 21530 RT C 72 20 8 - - 0.2 - - - - 6240 R D 72 20 8 - - - 0.2 - - - ND R 1 72 20 8 0.2 - - - 0.2 - 0.3 1880 VSG 2 72 20 8 - 0.2 - - 0.2 - 0.3 4060 VSG E 72 20 8 - - - - 1.0 0.2 0.3 ND RB Examples 3 to 6 The procedure of Examples 1 and 2 was repeated using a different type of zirconium silicate and different additive combination. The results are set out in Table Two, from which it can be seen that the effectiveness of the additives is dependent on the nature of the material being dispersed. The dispersions were coated onto both wax and glass substrates. Ex.or Comp. Ex. Composition - Wt % (d) Visc (mPa.s) Coat Z-2 S-W CA NH P1 P2 G1 G2 G4 M F 72 20 8 0.3 0.2 - - - - - 1400 R G 72 20 8 0.3 1.0 - - - - - 1470 FR 3 72 20 8 0.3 - 0.2 0.2 - - - 1300 VS 4 72 20 8 0.3 0.2 - 0.2 - - - 2340 R 5 72 20 8 0.3 0.2 - - - 0.2 - 4530 FR/S 6 72 20 8 0.3 0.2 - - 0.2 - - 17320 R H 72 20 8 0.3 0.2 - - - - 0.2 2340 R I 72 20 8 0.3 1.0 - - - - 0.2 2800 R Examples 7 to 9 The surface tension of a number of aqueous solutions was measured using a torsion balance (White Electrical Instruments Co.Ltd.) at ambient temperature. The solutions were prepared using distilled water. The results are set out in Table Three. Ex.or Comp. Ex. Additive Surface Tension (mN/m) Additive Concentration (wt.%) Type % 0.01 0.05 0.1 0.2 0.4 0.6 1.0 J G1 100 41 35 31.5 31.5 31.5 31.5 ND 7 G1/P1 70/30 49 42 32.5 31.5 31.5 ND 31.5 8 G1/P1 50/50 52 39.5 35 31.5 31 31.5 31.5 9 G1/P1 30/70 52 44 40 34.5 31.5 31.5 32.5 K P1 100 50.5 51 51 51 ND 46.5 46.5 L ESL 100 46.5 41.5 40.5 40.5 41 40.5 41 M ESL/P1 70/30 ND 44.5 43 42.5 41 41 40 N ESL/P1 50/50 44 40.5 42 40.5 41 41 40.5 O ESL/P1 30/70 58 43 41 41 40.5 41 38.5 Example 10 Aqueous dispersions of polyvinylidene fluoride were prepared as follows: A surfactant, or a mixture of surfactants, was mixed with distilled water. Polyvinylidene fluoride was added as a powder whilst stirring at 300 r.p.m. The mixture was then homogenised for three minutes using an Ultra-Turrax mixer operating at 2000 r.p.m. The slurry obtained was then allowed to stand at ambient temperature for 24 hours and the viscosity and stability of the slurry were then determined. The compositions of the dispersions, and the properties thereof, are set out in Table Four. Ex. or Comp. Ex Composition W Stab Sep Visc (mPa.s) F P1 FNS G1 ETA M P 50 3 - - - - 47 C N ND 10 50 3 - 3 - - 44 NC N 95 Q 50 3 - - 3 - 44 NC N 980 R 50 3 - - - 3 44 C N 78 S 50 - 3 3 - - 44 NC N/T 14040 Examples 11 to 15 The procedure described for Example 10 was repeated with the addition of thickeners to a dispersion having the composition of Example 10 with the exception that the water content was 43.5 parts by weight. The thickener was added to the mixture after adding the polyvinylidene fluoride and before effecting the homogenisation. The amount of thickener, and the properties of the dispersions obtained, are set out in Table Five. Example Thickener Stab Sep Visc (mPa.s) Type Amount (o) 11 NIL NIL C 25 95 12 T1 0.5 NC 0 3120 13 T2 0.5 NC 10 2500 14 T3 0.5 NC 0 3440 15 T4 1.0 NC/F 0 2800

Claims: A suspension of a particulate solid in an aqueous medium, the medium including as a dispersing agent a composition comprising: (A) a glycoside of the formula: R(OG)a where R is a hydrophobic moiety; G is a saccharide group; and a has a value of at least one; and (B) an acrylic polymer which is i at least one acrylic copolymer containing water soluble side chains and not more than 5% by weight of acrylic acid monomer units; and/or ii at least one acrylic copolymer containing no water soluble side chains and comprising from 2 to 10% by weight of acrylic acid monomer units; the weight ratio of (A) : (B) being from 1:20 to 20:1. A suspension as claimed in claim 1 wherein R is a mixture of alkyl groups containing different numbers of carbon atoms. A suspension as claimed in either claim 1 or claim 2 wherein the glycoside is an alkyl glycoside of the general formula: C n H (2n+1) O(C 6 H 10 O 5 ) b H where n is from 8 to 14, and b is greater than one and not more than two. A suspension as claimed in any one of claims 1 to 3 wherein the acrylic polymer contains at least 50% by weight of units containing water soluble side chains, which side chains are polyoxyethylene chains terminated with an alkoxy group. A suspension as claimed in any one of claims 1 to 4 wherein the acrylic copolymer is a polymer containing the units: where R 1 is hydrogen or a hydrocarbyl group; R 2 is hydrogen, a hydrocarbyl group or a group (AO) X R 3 ; R 3 is hydrogen or a hydrocarbyl group; A is an alkylene group; x is at least one; and at least some of the groups R 2 are hydrogen or (AO) x R 3 . A suspension as claimed in any one of claims 1 to 5 which contains from 0.1 to 10% of the composition comprising the glycoside and the acrylic polymer. A suspension as claimed in any one of claims 1 to 5 which contains a ceramic solid or a fluorine containing polymer. A suspension as claimed in claim 7 which contains at least 50% by weight of ceramic solid. A suspension as claimed in claim 7 which contains at least 20% by weight of a fluorine containing polymer. A suspension as claimed in claim 9 which additionally contains a thickener. A process of coating a substrate with a ceramic composition which comprises coating the substrate with a suspension as claimed in claim 8, and subsequently drying the suspension. A process as claimed in claim 11 which comprises preparing a mould for metal casting by coating the suspension on to a wax former.

Inventors: ROGIERS LODEWIJK MARIA, ROGIERS, LODEWIJK MARIA
Applicants: ICI PLC, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1989
Main classification: C08L33
IPC codes: C09D17, C08K5, C04B35, C08L33, B01J13