PROCESS FOR THE PREPARATION OF RESIN COMPOSITION COMPRISING ORGANOCLAYS OF IMPROVED DISPERSIBILITY

Abstract: Resin-coating compositions, e.g. unsaturated polyester or epoxy resin compositions, are prepared using an organoclay of improved dispersibility. The organoclay is prepared by suspending a smectite clay in water to form a fluid suspension; treating the suspension with a solution of an inorganic salt, the cation of which has a valency of at least two, the concentration of the salt being such as to flocculate the smectite clay substantially completely; mixing the suspension of the flocculated smectite clay with a quaternary ammonium compound, at least one of the four alkyl groups of which has from 10 to 24 carbon atoms; and dewatering the resultant product.

Description: Field of the Invention This invention relates to organoclays of improved dispersibility in organic media and to their applications in resin compositions, particularly for coating and forming purposes. Background of the Invention An organoclay is an organophilic cation-modified clay derived from a clay mineral, generally of the smectite group, for example a bentonite, montmorillonite, hectorite, saponite or the like, by replacing the inorganic exchangeable cations, which occur in the natural clay mineral, by organic cations, each comprising at least one hydrocarbon radical which has sufficient carbon atoms to render the surface of the cation-exchanged clay hydrophobic. Organoclays have been found to be very useful as thixotropic agents in organic media such as, for example, lubricating greases, oil-based drilling fluids, paints, varnishes, enamels and printing inks. However, an organoclay is, in general, difficult to disperse in an organic medium to form the uniform gel structure which is required to thicken, or to increase the viscosity of, the organic medium. Various means have accordingly been used to improve the dispersiblity of an organoclay in an organic medium, including the use of a polar organic material, such as a low molecular weight alcohol or ketone, as a dispersing aid, and the use of an excess of a specially selected organic cation in the preparation of the organoclay. In Finlayson et al , U.S. Patent No. 4,105,578, an organophilic clay gellant having enhanced dispersiblity in organic systems is disclosed which comprises the reaction product of a methyl benzyl dialkyl ammonium compound wherein the compound contains 20 to 35% alkyl groups having 16 carbon atoms, and 60 to 75% alkyl groups having 18 carbon atoms, and a smectite-type clay having a cation exchange capacity of at least 75 milliequivalents per 100 grams of said clay, and wherein the amount of said ammonium compound is from 100 to 120 milliequivalents per 100 grams of said clay, 100% active clay basis. In Finlayson et al , U.S. Patent No. 4,412,018, an organophilic clay gellant and methods of using and making the same are disclosed, which comprises the reaction product of an organic cation, an organic anion and a smectite-type clay having a cation exchange capacity of at least 75 milliequivalents per 100 grams of said clay, such that an organic cation-organic anion complex is intercalated with the smectite-type clay and the cation exchange sites of the smectite-type clay are substituted with the organic cation. The examples of the patent illustrate the use of the organophilic clay in thixotropic unsaturated polyester compositions and in thixotropic coating compositions. Unsaturated polyester compositions containing various gelling agents are well known. Additionally, it is known that in the preparation of glass fiber laminates of unsaturated polyester and the like, thixotropic gelling agents are used which allow for the ready mixing and spraying of these resins at high shear rates. At low shear rates, however, these gelling agents greatly increase the viscosity of the polyester, thus avoiding the drainage of the resin on vertical surfaces. One of the most widely used gelling agents for unsaturated polyesters was asbestos fibers. Asbestos fibers assisted in producing thixotropic polyesters without significantly affecting resin clarity. However, in the past several years, it has become recognized that the use of asbestos under the usual manufacturing conditions is objectionable, because of its long-term adverse effects on health when inhaled. For this reason, the asbestos gelling agents were replaced by a silica aerogel. When about 1% of silica was dispersed in the resin, it provided effective thixotropy. However, such product is comparatively expensive, and because of low bulk density, presents storage and handling problems. Consequently, the art has turned to the use of organoclays as gelling agents. Conventional organoclays cannot be dispersed in unsaturated polyester solution. They must be predispersed in monomer styrene and the gel subsequently blended with the polyester. This extra stage is expensive and inconvenient. It also limits the amount of organoclay that can be incorporated, to levels which can be physically handled in styrene: above about 8 wt % the gels become unmanageably stiff. Hence there is a need for organoclays which can be stirred directly into polyester solution, like fumed silica. This is demonstrated in the present invention. Summary of the Invention The organoclay employed in the present invention is prepared by a method described in EP-A-0222469 which comprises the following steps: (a) A smectite clay is suspended in water to form a fluid suspension; (b) The aqueous suspension of the smectite clay is treated with a solution of an inorganic salt, the cation of which has a valency of at least two, the concentration of the salt being such as to flocculate the smectite clay substantially completely; (c) The suspension of the flocculated smectite clay is mixed with a quaternary ammonium compound at least one of the four alkyl groups of which has from 10 to 24 carbon atoms; and (d) The product of step (c) is dewatered. In accordance with the present invention, the product of step (d) is combined with an epoxy resin or a dicarboxylic acid/diol polyester having at least 10 olefinic groups per 100 ester groups to form a resin composition. In step (b) the valency of the cation is preferably 3, and most preferably the cation is aluminum. If the valency of the cation is 3 the concentration of the solution of the salt containing the cation is preferably in the range of 0.001 M to 0.02 M. If, however, the valency of the cation is 2 the concentration of the solution of the salt containing the cation must be greater and is preferably in the range from 0.2 M to 2 M. The suspension of the flocculated clay is preferably mixed with the quaternary ammonium compound in proportions such that there are present from 95 to 140 milliequivalents of quaternary ammonium cation per 100 g of dry clay. In step (c) the aqueous suspension of the flocculated smectite clay is preferably mixed with molten quaternary ammonium compound. The quaternary ammonium compound preferably has the general formula: wherein R₁ is a saturated or unsaturated alkyl group having from 10 to 24 carbon atoms, R₂ and R₃, which may be the sme or different, are each a saturated or unsaturated alkyl group having from 1 to 24 carbon atoms or an aralkyl group having from 7 to 10 carbon atoms, R₄ is an alkyl group having from 1 to 6 carbon atoms or an aralkyl group having from 7 to 10 carbon atoms, and X is OH, Cl, Br, NO₂, CH₃SO₄ or CH₃.COO. Examples of such compounds are the benzyl methyl dialkyl ammonium chlorides, the dimethyl dialkyl ammonium chlorides, the benzyl dimethyl alkyl ammonium chlorides, the benzyl trialkyl ammonium chlorides and the methyl trialkyl ammonium chlorides, where the one or more alkyl group represents a mixture of hydrocarbon radicals derived from tallow having from 14 to 20 carbon atoms but in which C₁₈ radicals preferably predominate (a typical analysis of such a mixture of hydrocarbon radicals contained in tallow is: C₁₄ 2.0%; C₁₅ 0.5%; C₁₆ 19.0%; C₁₇ 1.5%; C₁₈ 66.0% and C₂₀ 1.0%). The hydrocarbon radicals may be partially unsaturated as in natural tallow or may be substantially completely saturated as a result of treating the tallow with hydrogen in the presence of a suitable catalyst. It has been found that these organoclays can readily be incorporated in resin compositions containing unsaturated polyester resins or epoxy resins. These organoclays are self-dispersing products for unsaturated polyester/styrene systems and polar organic solvent systems. By means of the present invention, there can be provided a novel thixotropic cross-linkable unsaturated polyester composition which has unique rheological properties, for example, an exceptionally high thixotropic index. Detailed Description The organophilic clays of this invention may be used without the need for a styrene pregel. In particular, polyester compositions may be prepared by mixing the organophilic clay with the final liquid polyester mixture prepared from a liquid unsaturated polyester and unsaturated aromatic monomer. The final polyester compositions can then be cross-linked to produce coatings or glass fiber-reinforced laminates by methods well known in the art. In a typical procedure the liquid unsaturated polyester resin is mixed in conventional apparatus with an unsaturated aromatic monomer to prepare a solution having a solids content between 30 and 80% by weight polyester. The organophilic clays of the invention can then be added to the liquid laminating resin. The unsaturated aromatic monomers of this invention are aromatic compounds to which is bonded one or more ethylenically unsaturated radicals such as a vinyl radical, substituted vinyl radical or an allylic radical. Suitable monomers include styrene,α-methyl styrene, divinyl benzene and allyl benzene. Styrene is preferred due to its effectiveness, wide use and availability. Such monomers are used in cross-linking the polyesters and also act as diluents to reduce viscosity. The unsaturated polyesters useful in preparing the thixotropic compositions of this invention are polyesters of a dicarboxylic acid and a diol having at least 10, and preferably no more than 75 olefin groups per 100 ester groups. The olefinic unsaturation is preferably derived from the carboxylic acid although the diol may be unsaturated. Typical diols are ethylene glycol and propylene glycol. Typical unsaturated acids include maleic acid, fumaric acid. Anhydrides of these acids are also commonly used. Such polyesters are made by conventional techniques of esterification as well known in the art. Generally, polyesters having molecular weights of from 400 to 10,000 and acid numbers in the range of from 0 to 50 mg KOH per gram of resin are useful for preparing the thixotropic composition of this invention. The amounts of organophilic clay gellant used in polyester laminating resins can range from 0.25% to 10%, preferably 0.5 to 4%. Amounts larger than 10% may be employed but are not economical. Practice of the present invention will now be illustrated by the following Examples, which however, are to be considered as merely illustrative of the invention, and not delimitive thereof. The Hegman Gauge referred to in the following examples is used to determine the quality of the dispersion of solid particles in an organic liquid medium, and comprises a polished metal plate provided with a rectangular depression of tapering depth which varies uniformly from zero at one end to 100µm at the other end. A film of the organic liquid composition is spread evenly over the plate and a visual estimate of the coarsest particles present in the composition can be made. If a substantial number of relatively coarse (10 - 100 micrometer) particles are present in the composition a definite "front" will be observed which, when compared with a scale provided alongside the depression, indicates the size of the largest particles present. If only a few particles in the above size range are present these will show up as specks in the depression and may be counted. The particulate solid material in a paint composition should be dispersed to such an extent that no front is visible when a sample of the paint is spread on a Hegman gauge and only a very small number, if any, specks can be seen. Example I Organoclay samples were prepared by the following method. An aqueous suspension of bentonite was prepared by mixing raw Wyoming sodium bentonite in a blunger with sufficient water to form a suspension containing 10% by weight of dry clay. The suspension thus formed was passed through a No. 300 mesh British Standard sieve (nominal aperture 0.053 mm) and the undersize fraction was diluted to about 4% by weight of solids with water and subjected to a particle size separation in an intermittent discharge, continuous centrifuge at a flow rate of 1 litre per min. The fine fraction was then passed through a homogenizer as a pre-treatment to reduce particle size and increase uniformity. To a 500g sample of the homogenized fine fraction, enough water was added to make the organoclay reaction solids 2.3% by weight. To this was then added the calculated weight of aluminum chloride (AlCl₃.6H₂O) which was required to give the desired concentration of aluminum chloride in the suspension. The suspension was then subjected to stirring by means of a paddle mixer for 15 minutes while the suspension was heated to a temperature of 65°C. There was then added to the heated suspension the calculated weight of a mixture of quaternary ammonium compounds and water isopropyl alcohol (in which form the quaternary ammonium compounds are available in commerce) which was required to give the desired loading of quaternary ammonium compounds on dry bentonite. The resultant mixture was then stirred in the paddle mixer for 30 minutes, filtered on a Buchner funnel, washed with hot water and dried for 1 1/2 hours at 60°C in a fluid bed drier. The dry product was then milled to the desired particle size. The various organoclays were prepared according to the above procedure using a mixture of quaternary ammonium compounds comprising 75 mole% dimethyl benzyl hydrogenated tallow ammonium chloride (2MBHT) and 25 mole % dimethyl di(hydrogenated tallow) ammonium chloride (2M2HT), different concentrations of aluminum chloride being used in the preparation of the aqueous suspension of bentonite. Each organoclay was milled to less than 0.250 mm. 1.5% by weight of each dry organoclay composition was incorporated into an unsaturated polyester resin composition using a laboratory stirrer rotating at 3,500 r.p.m. for 15 mins. The resin was a rapid-curing, general-purpose unsaturated polyester resin, marketed by the Scott Bader Company Limited under the trade name "CRYSTIC 196" (CRYSTIC is a Registered Trademark). It is believed to be a co-polymer of ortho-phthalic acid, fumaric acid and propylene glycol, having a number average molecular weight of about 3,000. Cobalt octoate accelerator was added at 0.01% by weight at the end of the mixing time. Crystic 196 as received from Scott Bader is a 70 percent by weight solution of polyester resin in styrene. This is diluted to 54 percent by weight polyester with extra styrene before use. The viscosity of the polyester resin composition containing the organoclay as a gelling agent, was measured using a Brookfield RVT Viscometer at spindle speeds of 0.5 r.p.m., 5 r.p.m. and 50 r.p.m. The data are shown in Table 1. Thixotropic Index ratios are also given. It can be seen from the data in Example I and Table 1 that cross-linkable unsaturated polyester compositions having an unexpectedly high thixotropic index of above about 2.5, preferably above about 3.0 and more preferably at least about 4.0, can be obtained by means of the subject invention.

Claims: A process for preparing a resin composition which process comprises the steps of: (a) suspending a smectite clay in water to form an aqueous suspension; (b) treating said aqueous suspension of the smectite clay with a solution of an inorganic salt, wherein the cation of said inorganic salt has a valency of at least 2, the concentration of the salt in the suspension being such as to flocculate the smectite clay substantially completely; (c) mixing the suspension of the flocculated smectite clay with a quaternary ammonium compound at least one of the four alkyl groups of which has from 10 to 24 carbon atoms; (d) dewatering the product of step (c); and (e) combining the product of step (d) with an epoxy resin or a dicarboxylic acid/diol polyester having at least 10 olefinic groups per 100 ester groups. A process in accordance with Claim 1, wherein the valency of said cation is 3. A process in accordance with Claim 1 or 2, wherein said cation is aluminium. A process in accordance with Claim 1, 2 or 3, wherein the concentration of the solution of the salt containing the cation is in the range of from 0.001 M to 0.02 M. A process in accordance with any one of Claims 1 to 3, wherein the valency of said cation is 2, and wherein the concentration of the solution of the salt containing the cation is in the range of from 0.2 M to 2M. A process according to any preceding claim, wherein the dewatered product of step (c) is dried and milled. A process according to any preceding claim, wherein the quaternary ammonium compound mixed with the aqueous suspension of the smectite clay is molten. A process according to any preceding claim, wherein the quaternary ammonium compound can be represented by the general formula: wherein R₁ is selected from saturated and unsaturated alkyl groups having from 10 to 24 carbon atoms, R₂ and R₃, which may be the same or different, are each selected from saturated and unsaturated alkyl groups having from 1 to 24 carbon atoms and aralkyl groups having from 7 to 10 carbon atoms, R₄ is selected from alkyl groups having from 1 to 6 carbon atoms and aralkyl groups having from 7 to 10 carbon atoms, and X is selected from OH, Cl, Br, I, NO₂, CH₃SO₄ and CH₃.COO. A process according to Claim 8, wherein the quaternary ammonium compound is chosen from benzyl methyl dialkyl ammonium chlorides, dimethyl dialkyl ammonium chlorides, benzyl dimethyl alkyl ammonium chlorides, benzyl trialkyl ammonium chlorides and methyl trialkyl ammonium chlorides in which the one or more alkyl group represents a mixture of hydrocarbon radicals derived from tallow having from 14 to 20 carbon atoms. A process according to any preceding claim, wherein the smectite clay is mixed with the quaternary ammonium compound in proportions such that there are present from 95 to 140 milli-equivalents of quaternary ammonium cation per 100 g of dry clay. A process according to any preceding claim, in which the resin with which the product of step (d) is combined is a dicarboxylic acid/diol polyester having at least 10 olefinic groups per 100 ester groups. A process according to any preceding claim, wherein the resultant resin composition is a coating formulation. A process according to any preceding claim, in which the resultant resin composition is used as an unsaturated polyester/styrene system.

Inventors: GOODMAN, HOWARD
Applicants: ECC INTERNATIONAL LIMITED
Application year: 1986
Main classification: C08K3
IPC codes: C08K3, C04B33, C08L67, C08K9, C01B33, B28C1, C08L101