Enhanced activated calcium bentonite

Abstract

The invention relates to a layered silicate having a cation exchange capacity in the range of 70 to 130 meq / 100 g, having leachable sodium cations in the range of 65 to 130 meq / 100 g, having leachable magnesium cations in the range of 5 to 65 meq / 100 g, having leachable calcium cations in the range of 15 to 95 meq / 100 g, and wherein the sum of leachable sodium, magnesium and calcium cations is at least equal to the cation exchange capacity, and wherein an aqueous suspension containing 5 % by weight of the layered silicate has a rotational viscosity at 10 rpm of 30 mPas or higher, measured at a temperature of 23 °C.

Description

[0001] ENHANCED ACTIVATED CALCIUM BENTONITE

[0002] The invention relates to a layered silicate having a cation exchange capacity in the range of 70 to 130 meq / 100 g, to a process for preparing the layered silicate, the use of the layered silicate as a rheological additive in an aqueous composition, and to a method of increasing the viscosity of an aqueous composition.

[0003] US 5248641 describes a process for enhancing the aqueous viscosity characteristics of a bentonite clay, wherein the crude bentonite is mixed with water and subjected to shear, followed by drying and adding a bentonite-activating metal salt as a dry blend.

[0004] EP 2367760 A relates to a method for producing a phyllosilicate composition, wherein a phyllosilicate is contacted with an alkali metal salt in an amount between 20 and 50 % of the entire cation exchange capacity of the phyllosilicate, and with sodium carbonate in an amount such that the amount of sodium ion corresponds to between 80 and 120 % of the cation exchange capacity of the phyllosilicate.

[0005] An article by Alther in Applied Clay Science, 1 (1986), 273-284, entitled “The effect of the exchangeable cations on the physico-chemical properties of Wyoming bentonites” suggests that a bentonite with a sodium vs. calcium and magnesium ratio of 60:20:20 will perform better than others with different ratios.

[0006] An Article by Lebedenko and Plee in Applied Clay science, 3 (1988), 1-10, entitled “Some considerations on the ageing of Na2CC>3-activated bentonites” describes the degradation of of Na2CC>3-activated bentonites. The evolution of the Na content during ageing is considered the most important parameter in accounting for the loss of rheological properties. The role of the Mg / Ca ratio is a second order parameter also to be considered.

[0007] The known activated bentonites can be used as additives and thickeners in varying compositions. However, the swelling behavior and the ease of exfoliation is not always satisfactory. There is a need to further improve these properties. Furthermore, for use in combination with hydraulic binders, such as in tile adhesives and mortars, it is often necessary to add organic components to provide additional properties. However, such organic components tend to prolong the setting time of the formulations. There is a need to provide layered silicates which reduce the need for organic components in such formulations. There is also an ongoing need to provide new layered silicates having desirable thickening behavior in aqueous compositions and which are easy to prepare. The invention provides a layered silicate having a cation exchange capacity in the range of 70 to 130 meq / 100 g, having leachable sodium cations in the range of 65 to 130 meq / 100 g, having leachable magnesium cations in the range of 5 to 65 meq / 100 g, having leachable calcium cations in the range of 15 to 95 meq / 100 g, and wherein the sum of leachable sodium, magnesium and calcium cations is at least equal to the cation exchange capacity, and wherein an aqueous suspension containing 5 % by weight of the layered silicate has a rotational viscosity at 10 rpm of 30 mPas or higher, measured at a temperature of 23 °C.

[0008] The layered silicates according to the invention have improved swelling behavior and can be exfoliated easily. This leads to improved thickening properties in aqueous compositions. Furthermore, the layered silicates can be used advantageously as additives in hydraulic binders. In this case, the need to employ additional organic additive components is reduced. When used in aqueous coating compositions, the layered silicates lead to reduced sagging of the paint when applied to vertical surfaces.

[0009] The layered silicate is preferably a modified natural layered silicate comprising calcium interlayer cations. Natural layered silicates are materials which are obtained from clay mines, and which have not been treated or modified, other than by physical methods, such as grinding or sieving to obtain a desired particle size.

[0010] In preferred embodiments, the natural layered silicate is a smectite clay, more preferably a bentonite clay. The different types of bentonites are each named after the respective dominant cation. For industrial purposes, two main classes of bentonite are recognized: sodium and calcium bentonite. Sodium bentonite is the more valuable, but calcium bentonite is more common. As mentioned above, the naming is based on the dominant interlayer cations. In natural bentonites, other cations than the dominant type, namely Mg and Na cations, are typically present as well. In natural calcium bentonite, the molar ratio of Ca:Mg:Na cations may, for example, vary within the range of 60:25:15 to 80:15:5. Furthermore, natural occurring bentonites are typically not available in high purities.

[0011] Typically, they carry amounts of inert minerals as impurities in the mineral.

[0012] Bentonites are natural clay minerals, wherein the major component is montmorillonite. Generally, bentonites contain montmorillonite in the range of 30 to 99 % by weight. The montmorillonites present in bentonites are platelet shaped aluminum-silicates which are stacked on each other. The platelets typically are slightly negatively charged. Therefore, they carry cations in the interlayer between the platelets in order to compensate the negative charges of the layers. Their applications are typically due to their high surface area and platelet like structure which gives them specific advantage in gelling water or solvents or adsorbing specific substances or providing barrier properties. In most of these applications a separation of the platelets into single or small stack platelets is required in order to achieve the best properties. The bentonites can provide this swelling into platelets in case the interlayer cations are single charged, especially if the interlayer cations are sodium or lithium. Bentonite clays which carry mostly divalent cations between their layers as Ca and Mg ions are only slightly swellable and the single platelets of aluminum-silicate cannot be removed from each other in water completely.

[0013] In preferred embodiments, the layered silicate of the invention is a bentonite.

[0014] The natural layered silicate generally has a cation exchange capacity in the range of 70 to 130 meq / 100 g. In preferred embodiments, the cation exchange capacity of the natural layered silicate is at least 75 meq / 100 g, more preferably at least 80 meq / 100 g. Generally, the cation exchange capacity is at most 125 meq / 100 g, preferably at most 120 meq / 100 g. In a further preferred embodiment, the cation exchange capacity is in the range of 80 to 120 meq / 100 g, more preferably 85 to 120 meq / 100g.

[0015] The above values for the cation exchange capacity also apply for the layered silicate of the invention.

[0016] The cation exchange capacity is suitably determined using the copper complex method according to (Ammann, L., Bergaya, F., Lagaly, G., 2005, Determination of the cation exchange capacity of clays with copper complexes revisited. Clay Minerals 40, 441-453)

[0017] The layered silicate of the invention has leachable sodium cations in the range of 65 to 130 meq / 100 g, leachable magnesium cations in the range of 5 to 65 meq / 100 g, and leachable calcium cations in the range of 15 to 95 meq / 100 g.

[0018] The above-mentioned amounts of leachable cations is suitably determined by a method comprising refluxing the treated clay material with an excess of ammonium chloride in water for a period of at least one hour, followed by phase separation, further washing of the solid residue with deionized water, and analysis of the combined liquid phase by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0019] In a preferred embodiment, the layered silicate has leachable calcium ions in the range of 20 to 85 meq / 100 g, even more preferably in the range of 25 to 75 meq / 100 g. It is also preferred that the layered silicate has leachable sodium ions in the range of 70 to 120 meq / 100 g, and even more preferably in the range of 75 to 110 meq / 100 g. In a preferred embodiment, the layered silicate has leachable sodium cations in an amount equal or lower than the cation exchange capacity. Typically, the layered silicate has leachable sodium cations in an amount of 60 % or higher of the cation exchange capacity, preferably the amount of leachable sodium cations is in the range of 60 to 100 % of the cation exchange capacity.

[0020] It is further preferred that the layered silicate has leachable magnesium ions in the range of 10 to 50 meq / 100 g.

[0021] In the layered silicate of the invention, the sum of leachable sodium, magnesium and calcium cations is at least equal to the cation exchange capacity. In typical embodiments, the sum of leachable sodium, magnesium and calcium cations is in the range of 100 to 200 %, preferably 120 to 180 %, of the cation exchange capacity.

[0022] It is generally preferred that the layered silicate of the invention contains a low amount of leachable lithium cations. In typical embodiments, the amount of leachable lithium cations is 5 % or less of the amount of leachable sodium cations, preferably in the range 0 to 3 % of the amount of leachable sodium cations.

[0023] An aqueous suspension consisting of water and 5 % by weight of the layered silicate of the invention has a rotational viscosity at 10 rpm of 30 mPas or higher, measured at a temperature of 23 °C. In typical embodiments, the aqueous suspension has a viscosity of 200 mPas or higher, preferably 250 mPas or higher, and even more preferably 1000 mPas or higher. Generally, the viscosity of the suspension is in the range of 1000 to 6000 mPas, preferably 1500 to 5000 mPas, measured at a rotational viscosity at 10 rpm and at 23 °C.

[0024] The invention further relates to a process for preparing the layered silicate of the invention. The process comprises the steps of i) Providing a natural layered silicate comprising calcium interlayer cations and having a cation exchange capacity in the range of 70 to 130 meq / 100 g, ii) Providing at least one compound having sodium cations as activation agent, iii) Mixing the layered silicate provided in step i) and the compound or compounds provided in step ii) in the presence of water, wherein the water content in the mixture is at least 20 % by weight, for a period of at least 5 minutes, and wherein the compound or compounds having sodium cations are present in an molar amount which is lower than the amount corresponding to the cation exchange capacity of the natural layered silicate, iv) Drying the mixture prepared in step iii) to a water content of 15% by weight or less to obtain a modified layered silicate.

[0025] The natural layered silicate provided in step i) preferably is a natural calcium bentonite, as described above.

[0026] In the second step of the process of the invention, a compound having sodium cations is provided. The compound having sodium cations can be any sodium salt. Examples of suitable sodium salts are sodium halides, such as sodium chloride or sodium bromide, sodium carbonate, sodium hydrogen carbonate, sodium nitrate, sodium sulfate, sodium hydrogen sulfate, sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium formate, sodium acetate, sodium propionate, as well as salts of higher carboxylic acids, sodium citrate, sodium oxalate, as well as sodium salts of sulfonic acids, such as sodium tosylate.

[0027] It is preferred that the compound having sodium cations is provided in the form of an inorganic salts. It is also possible to use mixtures of compounds having sodium cations, for examples mixtures of two or more different compounds having sodium cations.

[0028] The compound having sodium cations is generally provided in an amount so that the amount of sodium cations is lower than the amount corresponding to the cation exchange capacity of the layered silicate provided in step i). Typically, the amount of sodium cations provided corresponds to 20 to 100%, preferably 40 to 80 % of the cation exchange capacity of the layered silicate.

[0029] In the third step of the process of the invention, the layered silicate provided in step i) and the compound or compounds provided in step ii) are mixed in the presence of water. The components can be mixed in any suitable order. It is possible to pre-mix the solid components with water individually, and then combine the aqueous mixtures. Alternatively, the solid components can be pre-mixed and added to water, or water can be added to the pre-mixed solid components. In a further embodiment, the compound having sodium cations is dissolved in water either individually or together, and the aqueous solution is added to the natural layered silicate.

[0030] Water can be used in the form of distilled water, de-ionized water, or tap water.

[0031] The water content in the mixture is at least 20 % by weight, calculated on the total weight of the mixture. In preferred embodiments, the water content is at least 25 % by weight, or at least 30 % by weight. Since the major portion of the water is removed later, it is generally preferred that the water content is at most 60 % by weight, preferably at most 50 % by weight. In particularly preferred embodiments, the water content is in the range of 25 to 45 % by weight, calculated on the total weight of the mixture. In embodiments wherein the drying step iv) of the process is carried out by spray drying, the water content of the mixture may also exceed the above-mentioned values. In this case, the water content of the mixture may be 80 % by weight, or even 95 % by weight. The aqueous mixture generally has the form of an aqueous slurry or of a paste. Mixing can be out using suitable well-known equipment, such as kneaders, blade mixers, or extruders.

[0032] Mixing is carried out for a time sufficient to cause some ion exchange reaction of calcium interlayer cations of the natural layered silicate and sodium cations of the compounds having sodium cations. Generally, mixing is carried out for a period of at least 5 minutes. In typical embodiments, mixing is carried out for a period of at least 10 minutes, preferably at least 15 minutes. Generally, mixing is carried out for a period of at most 120 minutes, preferably at most 90 minutes. In preferred embodiments, mixing is carried out for a period of 20 to 80 minutes.

[0033] The mixing step is generally carried out at ambient temperature, for example in a temperature range of 10 °C to 35 °C. If so desired, mixing can also be carried out at elevated temperature, for example in the range of 36 °C to 80 °C. As the mixing process is generally carried out at atmospheric pressure, the temperature during mixing preferably does not exceed the boiling point of water of 100 °C.

[0034] It is preferred that in the activation agent any compounds having non-sodium alkali cations are present in a low amount or are absent. Generally, compounds having non-sodium alkali cations are present in the activation agent in an amount of 0.0 to 5.0 mol-%, preferably 0.0 to 3.0 mol-%, calculated on the molar amount of sodium cations provided by the compound or compounds having sodium cations.

[0035] In step iv) of the process of the invention, the mixture prepared in step iii) is dried to a water content of 15% by weight or less. The drying step can be carried out immediately after mixing step iii). If so desired, the mixture prepared in step iii) can be allowed to rest for a period of time before drying. That period of time is not particularly limited and is mainly governed by practical consideration of the manufacturing facility, such as the availability of equipment.

[0036] In a further embodiment, the mixture is further treated to reduce the particle size prior to drying, for example with a colloid mill or high-pressure homogenizer or with high temperature steam jet. The drying step can be carried out by any known drying process. Generally, the drying process involves evaporation of water. Evaporation of water can be caused by heating the aqueous mixture in an oven, or by heating while agitating the mixture. In one embodiment, heating and evaporation of water are carried out in an oven. The temperature during can vary in wide ranges. Generally, drying is carried out at temperatures in the range of 60 to 150 °C. If so desired, evaporation of water can be supported by reducing the pressure to below atmospheric pressure. The drying process is carried out for a period sufficient to reduce the water content to a 15 % by weight or less. If so desired, the water content can be reduced to 10 % by weight or less, 8 % by weight or less, or even 5 % by weight or less. Water may even be completely removed during the drying process. However, from an economic perspective and in view of energy consumption, is it generally preferred to dry the treated layered silicate to a water content of 0.1 % or more by weight of water.

[0037] In one embodiment, drying is carried out by spray drying, wherein water is removed from an aqueous slurry by spray drying in a spray drying apparatus to prepare a solid treated layered silicate.

[0038] In a still further embodiment, impurities are removed from the aqueous slurry prior to spray drying. The impurities are mainly present in the aqueous slurry in the form of solid particles or incompletely swollen materials, which can be separated from the aqueous phase by physical separation processes, which are generally known to the skilled person. Examples of suitable separation processes include sedimentation, decantation, flotation, and centrifugation. It is also possible to combine such processes or to carry them out in succession, if so desired.

[0039] The removed impurities include most of the crystalline impurities and low swellable amorphous minerals and low swellable clays. The impurities to be removed typically comprise at least one of feldspar, calcite, mica, quartz, cristobalite, dolomite, and calcium bentonite.

[0040] After the separation step, the aqueous slurry is recovered, and water is removed from the aqueous slurry by spray drying in a spray drying apparatus to prepare the modified natural layered silicate of the invention.

[0041] If so desired, it is possible to disperse the modified natural layered silicate of the invention, dried by a method other than spray drying, in water to prepare an aqueous slurry and to remove impurities as explained above, followed by spray drying.

[0042] The modified natural layered silicate of the invention is highly suitable for controlling the rheology of an aqueous composition. In particular, the modified natural layered silicate of the invention can be readily dispersed in numerous aqueous compositions and causes desirable rheological effects. Therefore, the invention also relates to the use of the modified natural layered silicate of the invention for controlling the rheology of an aqueous composition.

[0043] The invention further relates to a method of increasing the viscosity of an aqueous composition, comprising adding the modified natural layered silicate to an aqueous composition.

[0044] In the above-mentioned use or method, the modified natural layered silicate of the invention is suitably added to the aqueous composition in an amount in the range of 0.05 to 7.00 %, preferably 0.10 to 6.00 % by weight, calculated on the total weight of the aqueous composition.

[0045] When the modified natural layered silicate of the invention is added to an aqueous composition, the viscosity of the aqueous composition generally increases. A higher amount of modified natural layered silicate of the invention generally causes a higher increase of the viscosity. In some embodiments, the addition of the modified natural layered silicate of the invention causes a thixotropic behavior of the aqueous composition.

[0046] The aqueous composition can be any liquid aqueous composition of which the viscosity should be increased, or which should be rendered thixotropic. Aqueous compositions are those in which the main or only liquid diluent used is water. Preferably, aqueous compositions contain less than 35 % by weight, 25 % by weight, 20 % by weight or even less than 10 % by weight of (volatile) organic solvents, based on the total weight of water and organic solvent in the liquid formulation. In some embodiments, aqueous compositions are free of organic solvents. Aqueous compositions may contain water-soluble organic or inorganic compounds, e.g., ionic compounds like salts.

[0047] Examples of suitable aqueous liquid compositions include a coating composition, a (pre-) polymer composition, a pigment concentrate, a ceramic product, a sealant, a cosmetic preparation, an adhesive, a casting compound, a lubricant, an ink, a cleaning agent, a liquid for use in gas- or oil production, a putty, a metal working fluid, a sprayable liquid, like deposition aids used for crop protection, a wax emulsion, a liquid for use in energy storage media like batteries, a liquid for use in electric or electronic components, a casting or potting composition, and a building material.

[0048] The aqueous compositions which are coating compositions or inks can be used in various application fields, like automotive coatings, construction coatings, protective coatings (like marine or bridge coatings), can and coil coatings, wood and furniture coatings, industrial coatings, plastics coatings, wire enamels, foods and seeds coatings, leather coatings (both for natural and artificial leather), color resists (as used for LC displays). Coating materials include pasty materials which typically have a high content of solids and a low content of liquid components, e.g., pigment pastes or effect pigment pastes (using pigments based on aluminum, silver, brass, zinc, copper, bronzes like gold bronze, iron oxide-aluminum); other examples of effect pigments are interference pigments and pearlescent pigments like metal oxide-mica pigments, bismuth oxide chloride or basic lead carbonate.

[0049] The cosmetic compositions can be all kind of aqueous liquid compositions used for personal care and health care purpose. Examples are lotions, creams, pastes like toothpaste, foams like shaving foam, gels like shaving gel and shower gel, pharmaceutical compounds in gel like delivery form, hair shampoo, liquid soap, nail varnish, lipstick, and hair tinting lotions.

[0050] Preferred wax emulsions are aqueous dispersions of wax particles formed of waxes which are solid at room temperature.

[0051] Spraying agents (preferably used as deposition aids) can be equipped with the modified layered silicate of the invention in order to achieve drift reduction. They may for example contain fertilizers or herbicides, fungicides, and other pesticides.

[0052] The formulations used for construction purpose can be materials which are liquid or pasty during handling and processing; these aqueous materials are used in the construction industry and they become solid after setting time, e.g., hydraulic binders like concrete, cement, mortar / plaster, tile adhesives, and gypsum.

[0053] Metal working fluids are aqueous compositions used for the treatment of metal and metal parts. Examples are cutting fluids, drilling fluids (used for metal drilling), mold release agents (mostly aqueous emulsions, e.g., in aluminum die casting and foundry applications), foundry washes, foundry coatings, as well as liquids used for the surface treatment of metals (like surface finishing, surface cleaning and galvanization).

[0054] Lubricants are aqueous compounds used for lubricating purpose, i.e. , used to reduce abrasion and friction loss or to improve cooling, force transmission, vibration damping, sealing effects, and corrosion protection.

[0055] Liquid formulations used for gas and oil production are aqueous formulations used to develop and exploit a deposit. Aqueous drilling fluids or “drilling muds” are preferred examples. An application example is hydraulic fracturing.

[0056] Cleaners can be used for cleaning different kinds of objects. They support the removal of contaminations, residual dirt and attached debris. Cleaners also include detergents (especially for cleaning textiles, their precursors and leather), cleansers and polishes, laundry formulations, fabric softeners, and personal care products. Preferred aqueous compositions include an aqueous coating composition, an aqueous composition comprising a hydraulic binder, an aqueous cleaning composition, and an aqueous personal care composition.

[0057] The above-mentioned aqueous compositions may comprise other ingredients and additives commonly used in aqueous compositions, for example organic co-solvents, crosslinkers, anti-foaming agents, dispersing aids, and UV stabilizers. Although the modified natural layered silicate of the invention provides excellent thickening properties, it is possible to use it in combination with other rheology control agents, if so desired.

[0058] Examples of other rheology control agents include polysaccharides (like cellulose derivatives, guar, xanthan), urea compounds, (poly)amides, polyacrylates (like alkali soluble or swellable emulsions), or associative thickeners (like polyurethane thickeners, aminoplast based thickeners, hydrophobically modified alkali soluble emulsion type thickeners).

[0059] The modified natural layered silicate of the invention can also be used as adsorption agent in certain compositions, for example to absorb undesired impurities. In a still further embodiment, the modified natural layered silicate of the invention can be used as a coagulation agent, for example in the treatment of wastewater.

[0060] Examples

[0061] General methods

[0062] Cation Exchange Capacity

[0063] The cation exchange capacity of layered silicates was determined with the copper complex method according to (Ammann, L., Bergaya, F., Lagaly, G., 2005. Determination of the cation exchange capacity of clays with copper complexes revisited. Clay Minerals 40, 441-453).

[0064] Chemical composition

[0065] The chemical composition of raw calcium bentonite was done by standard ICP-OES after dissolving the bentonite in aqua regia acid mixture. The result of chemical composition of used raw bentonite are listed in table 1. Table 1

[0066] Chemical composition of used raw bentonite types, indicated in % by weight.

[0067] *LOI means weight loss upon heating to 1000°C

[0068] General method for activation of layered silicates

[0069] Calcium bentonite was activated with sodium carbonate in a Werner-Pfleiderer mixer. The activation agent (sodium carbonate) was dissolved in water and then added to the Ca- bentonite. The water content was adjusted to 40 % of the total mixture. The mixture was kneaded for 30 minutes. The treated bentonite was dried at 80 °C and then pulverized. The moisture content in the product was determined and the thickening effect of the product was tested in deionized water. Preparation parameters setting of the examples are listed in Table 2. Comparative Examples 1 and 4 were not treated with an activation agent. The natural calcium bentonites of comparative Examples 1 and 4 were only dried to the indicated water content and pulverized.

[0070] Table 2.

[0071] Preparation parameters setting of the examples.

[0072]

[0073] Comparative Examples are marked by

[0074] Viscosity in water

[0075] An activated-bentonite dispersion in water was prepared at 5 wt% of the activate-bentonite mixed in water for 20 minutes. The viscosity was measured after 1 h storage of the dispersion at 23 °C. The viscosity was measured with a Brookfield rotational viscosimeter at a shear rate of 10 rpm. The viscosity was read after 2 minutes of running time of the measurement. The viscosities of samples are provided in Table 3 in mPas.

[0076] Determination of leachable cations

[0077] For the determination of leachable cations, 1 g of activated bentonite was added to 40 ml of ammonium chloride solution (concentration of 2 wt%) in a centrifuge tube. The mixture was mixed on overhead shaker for 5 hours. The mixture was then centrifuged at 6000 rpm for 10 minutes. The supernatant solution was filtered and collected in a 250 ml glass. The sedimented material was again dispersed in 40 ml of ammonium chloride (2 wt%) and mixed on overhead shaker for 5 hours. The procedure was repeated three times and the supernatant solution was collected in a 250 ml glass. After complete leaching with ammonium chloride three times, the sedimented phase was washed with 40 ml of deionized water: the sedimented phase was dispersed in 40 ml of deionized water and mixed for 5 h on overhead shaker. The mixture was then centrifuged at 6000 rpm for 10 min. The washing step was repeated twice. The leachable cations were determined in the combined aqueous solution by ICP-OES analytical method. The result of leachable cations is listed in table 3. Table 3.

[0078] The cation exchange capacity, total leachable cations, and viscosity in water of activated bentonites Comparative examples are marked by

[0079] Comparative Examples 1 and 4 without sodium ion activation cause no substantial thickening effect when added to water. Comparative Examples 7 and 8 cause a high thickening effect in water. However, when employed in aqueous application systems, like tile adhesive or aqueous paint, comparative Examples 7 and 8 lead to inferior thickening effect, as shown further below.

[0080] The activated bentonite was tested in tile adhesive formulations. Slip was determined according to DIN EN 1308 -2007-11.

[0081] Table 4

[0082] Formulation of tile adhesives

[0083] Table 5

[0084] Result of slip according to DIN EN 1308-2007-11

[0085] Comparative examples are marked by

[0086] Table 5 shows results of the slip of tiles using formulations with and without activated bentonite. The lower the slip value, the better the tile adhesive bonds the tiles to the wall. Example C1 represents a comparative example without bentonite. Comparative Examples C2 and C5 show no improvement over C1 in slip resistance because the non-activated bentonite used has no effect on the rheological properties of the tile adhesive. Comparative Examples C8 and C9, having leachable sodium cations outside the scope of the present invention, show only a minor improvement in slip resistance. Tile adhesive Examples C3, C4, C6 and C7 containing activated bentonites according to the invention exhibit reduced slip. Paint formulations were prepared as summarized in Table 6 below. The amounts of components are indicated in parts by weight.

[0087] Table 6 The paint formulations were applied with a stepped doctor blade Model 421 / S (Erichsen GmbH & Co KG) with 50-500 and 550-1000 pm wet film thickness. The application was done on contrast cards 2801 (BYK-Gardner GmbH) using the automatic applicator byko-drive XL (BYK- Gardner GmbH) with an application speed of 50 mm / s. Directly after application the draw down was hanged up vertical at room temperature until it was dried. After drying the sag resistance was evaluated visually. Table 7 indicates sag resistance as the highest wet film thickness in pm without runner and bulge formation.

[0088] Viscosity curves were measured with a rheometer Physica MCR 301 (Anton Paar). In Table 7 viscosity (Pa.s) is recorded at different shear rates (1 / s), both with ascending and descending shear rate. Table 7: Results of the tested material in paint formulation

[0089]

[0090] It can be concluded that the layered silicate according to the invention provides an improved rheology profile to the aqueous paint formulation. It leads to superior sag resistance and higher viscosity, in particular at low shear, which is relevant for obtaining a good sag resistance.

Claims

Claims1. A layered silicate having a cation exchange capacity in the range of 70 to 130 meq / 100 g, having leachable sodium cations in the range of 65 to 130 meq / 100 g, having leachable magnesium cations in the range of 5 to 65 meq / 100 g, having leachable calcium cations in the range of 15 to 95 meq / 100 g, and wherein the sum of leachable sodium, magnesium and calcium cations is at least equal to the cation exchange capacity, and wherein an aqueous suspension containing 5 % by weight of the layered silicate has a rotational viscosity at 10 rpm of 30 mPas or higher, measured at a temperature of 23 °C.

2. The layered silicate according to claim 1 , wherein the sum of leachable sodium, magnesium and calcium cations is in the range of 100 to 200 % of the cation exchange capacity.

3. The layered silicate according to claim 1 or 2, wherein the layered silicate is a bentonite.

4. The layered silicate according to any one of the preceding claims, wherein an aqueous suspension containing 5 % by weight of the layered silicate has a rotational viscosity at 10 rpm of 250 mPas or higher, measured at a temperature of 23 °C.

5. The layered silicate according to any one of the preceding claims, wherein the layered silicate has leachable calcium ions in the range of 20 to 85 meq / 100 g.

6. The layered silicate according to any one of the preceding claims, wherein the layered silicate has leachable sodium ions in the range of 70 to 120 meq / 100 g.

7. The layered silicate according to any one of the preceding claims, wherein the layered silicate has leachable magnesium ions in the range of 10 to 50 meq / 100 g.

8. The layered silicate according to any one of the preceding claims, wherein the layered silicate has leachable sodium cations in an amount equal or lower than the cation exchange capacity.

9. The layered silicate according to any one of the preceding claims, wherein the layered silicate has leachable sodium cations in an amount of 60 % or higher of the cation exchange capacity.

10. The layered silicate according to any one of the preceding claims, wherein the layered silicate has a cation exchange capacity in the range of 80 to 120 meq / 100 g.

11. A process for preparing the layered silicate according to any one of the preceding claims, comprising i) Providing a natural layered silicate comprising calcium interlayer cations and having a cation exchange capacity in the range of 70 to 130 meq / 100 g, ii) Providing at least one compound having sodium cations as activation agent, iii) Mixing the layered silicate provided in step i) and the compound or compounds provided in step ii) in the presence of water, wherein the water content in the mixture is at least 20 % by weight, for a period of at least 5 minutes, and wherein the compound or compounds having sodium cations are present in an molar amount which is lower than the amount corresponding to the cation exchange capacity of the natural layered silicate, iv) Drying the mixture prepared in step iii) to a water content of 15% by weight or less to obtain a modified layered silicate.

12. The process according to claim 11, wherein in the activation agent compounds having non-sodium alkali cations are present in an amount of 0.0 to 5.0 mol-%, calculated on the molar amount of sodium cations provided by the compound or compounds having sodium cations.

13. The process according to claim 11 or 12, wherein the process comprises the further step of reducing the particle size of the dried mixture obtained in step iv) by milling and / or grinding.

14. Use of the layered silicate according to any one of the preceding claims 1 to 10 as a rheological additive in an aqueous composition.

15. The use according to claim 14, wherein the aqueous composition is an aqueous coating composition.

16. The use according to claim 14, wherein the aqueous composition comprises a hydraulic binder.

17. A method of increasing the viscosity of an aqueous composition, comprising adding the layered silicate according to any one of the preceding claims 1 to 10 to an aqueous composition.

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