Improved activated calcium bentonite

Abstract

The present invention relates to a layered silicate having a cation exchange capacity in the range of 70-130 meq / 100 g, having leachable sodium cations in the range of 65-130 meq / 100 g, having leachable magnesium cations in the range of 5-65 meq / 100 g, having leachable calcium cations in the range of 15-95 meq / 100 g, and having a cation exchange capacity in the range of 70-130 meq / 100 g, having leachable sodium cations in the range of 65-130 meq / 100 g, having leachable magnesium cations in the range of 5-65 meq / 100 g, having leachable calcium cations in the range of 15-95 meq / 100 g, and wherein the sum of the 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 rotary viscosity at 10 rpm of 30 mPas or higher measured at a temperature of 23 DEG C.

Description

[0001] This invention relates to a layered silicate with a cation exchange capacity in the range of 70-130 meq / 100g, a method for preparing the layered silicate, the use of the layered silicate as a rheology modifier in an aqueous composition, and a method for increasing the viscosity of an aqueous composition.

[0002] US 5248641 describes a method for enhancing the aqueous viscosity properties of bentonite, wherein unprocessed bentonite is mixed with water and sheared, then dried and a bentonite-activated metal salt is added as a dry mix.

[0003] EP 2367760 A relates to a method for producing a foli silicate composition, wherein the foli silicate is contacted with an alkali metal salt in an amount of 20-50% of the total cation exchange capacity of the foli silicate and sodium carbonate in an amount such that the amount of sodium ions corresponds to 80-120% of the cation exchange capacity of the foli silicate.

[0004] Alther's article entitled "The effect of exchangeable cations on the physicochemical properties of Wyoming bentonite" in Applied Clay Science, 1 (1986), 273-284 shows that bentonite with a sodium to calcium, magnesium ratio of 60:20:20 performs better than bentonite with other ratios.

[0005] Lebedenko and Plée, in their article "Some Thoughts on the Aging of Na₂CO₃-Activated Bentonite" in Applied Clay Science, 3 (1988), 1-10, describe the degradation of Na₂CO₃-activated bentonite. The change in Na content during aging is considered the most important parameter when taking into account the loss of rheological properties. The Mg / Ca ratio is also a secondary parameter to consider.

[0006] Activated bentonite is known to be used as an additive and thickener in various compositions. However, its swelling behavior and ease of peeling are not always satisfactory. Further improvements to these properties are needed. Furthermore, for use in combination with hydraulic adhesives, such as tile adhesives and mortars, it is often necessary to add organic components to provide additional properties. However, these organic components tend to prolong the setting time of the formulation. There is a need to provide layered silicates that reduce the need for organic components in such formulations. There is also a continued need to provide new layered silicates that exhibit ideal thickening behavior in aqueous compositions and are easy to prepare.

[0007] The present invention provides a layered silicate having a cation exchange capacity in the range of 70-130 meq / 100g, having leached sodium cations in the range of 65-130 meq / 100g, having leached magnesium cations in the range of 5-65 meq / 100g, having leached calcium cations in the range of 15-95 meq / 100g, and wherein the sum of the leached 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 of 30 mPas or higher at 10 rpm when measured at 23°C.

[0008] The layered silicates of the present invention exhibit improved swelling behavior and can be easily peeled off. This results in improved thickening properties in aqueous compositions. Furthermore, layered silicates can be advantageously used as additives in hydraulic adhesives. In this case, the need for additional organic additive components is reduced. When used in aqueous coating compositions, 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 containing interlayer calcium cations. Natural layered silicates are materials obtained from clay minerals that have not been treated or modified except through physical methods such as grinding or sieving to obtain the desired particle size.

[0010] In a preferred embodiment, the natural layered silicate is montmorillonite clay, more preferably bentonite. Different types of bentonite are named according to their respective dominant cations. For industrial purposes, two main categories of bentonite are recognized: sodium-based bentonite and calcium-based bentonite. Sodium-based bentonite is more valuable, but calcium-based bentonite is more common. As mentioned above, the naming is based on the dominant interlayer cation. Other cations of non-dominant types, namely Mg and Na cations, are also commonly present in natural bentonite. In natural calcium-based bentonite, the molar ratio of Ca:Mg:Na cations can vary, for example, from 60:25:15 to 80:15:5. Furthermore, natural bentonite is generally not available in high purity. They typically contain a certain amount of inert minerals as impurities in the mineral composition.

[0011] Bentonite is a natural clay mineral, primarily composed of montmorillonite. Bentonite typically contains 30-99% montmorillonite by weight. The montmorillonite present in bentonite is in the form of stacked, sheet-like aluminosilicates. These sheets are generally slightly negatively charged. Therefore, they contain cations between the sheet layers to counteract the negative charge of these layers. Their applications are often due to their high surface area and sheet-like structure, which gives them unique advantages in gelling water or solvents, adsorbing specific substances, or providing barrier properties. In most of these applications, it is required to separate the sheets into single or small stacked sheets for optimal performance. In the case of monovalent cations between the layers, especially if the interlayer cations are sodium or lithium, bentonite can provide this swelling to the sheets. Bentonite with divalent cations, primarily Ca and Mg ions, in its interlayers swells only slightly, and the single aluminosilicate sheets cannot be completely separated from each other in water.

[0012] In a preferred embodiment, the layered silicate of the present invention is bentonite.

[0013] This natural layered silicate typically has a cation exchange capacity in the range of 70-130 meq / 100g. In a preferred embodiment, the cation exchange capacity of the natural layered silicate is at least 75 meq / 100g, more preferably at least 80 meq / 100g. The cation exchange capacity is typically at most 125 meq / 100g, preferably at most 120 meq / 100g. In a further preferred embodiment, the cation exchange capacity is in the range of 80-120 meq / 100g, more preferably 85-120 meq / 100g.

[0014] The above-mentioned values ​​for cation exchange capacity also apply to the layered silicates of the present invention.

[0015] Cation exchange capacity was appropriately determined using the copper complex method according to (Ammann, L., Bergaya, F., Lagaly, G., 2005, Further exploration of the determination of cation exchange capacity of clay using copper complexes. Clay Minerals 40, 441-453).

[0016] The layered silicate of the present invention has leached sodium cations in the range of 65-130 meq / 100g, leached magnesium cations in the range of 5-65 meq / 100g, and leached calcium cations in the range of 15-95 meq / 100g.

[0017] The above-mentioned amount of leached cations is suitably determined by a method comprising refluxing the treated clay material with an excess of ammonium chloride aqueous solution for at least 1 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).

[0018] In a preferred embodiment, the layered silicate has leached calcium ions in the range of 20-85 meq / 100g, or even more preferably in the range of 25-75 meq / 100g.

[0019] Preferably, the layered silicate has leached sodium ions in the range of 70-120 meq / 100g, and even more preferably in the range of 75-110 meq / 100g. In a preferred embodiment, the amount of leached sodium cations in the layered silicate is equal to or less than its cation exchange capacity. The layered silicate typically has an amount of leached sodium cations of 60% or higher of its cation exchange capacity, preferably in the range of 60-100% of its cation exchange capacity.

[0020] Further preferably, the layered silicate has leached magnesium ions in the range of 10-50 meq / 100g.

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

[0022] Typically, the layered silicate of the present invention contains a small amount of leachable lithium cations. In a typical embodiment, the amount of leachable lithium cations is 5% or less of the amount of leachable sodium cations, preferably in the range of 0-3% of the amount of leachable sodium cations.

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

[0024] The present invention further relates to a method for preparing the layered silicate of the present invention. The method comprises the following steps:

[0025] i) Provides natural layered silicates containing interlayer calcium cations and having a cation exchange capacity in the range of 70-130 meq / 100g.

[0026] ii) Provide at least one compound having a sodium cation as an activator,

[0027] iii) Mixing the layered silicate provided in step i) and one or more compounds provided in step ii) in the presence of water for at least 5 minutes, wherein the water content in the mixture is at least 20% by weight, and wherein the one or more compounds having sodium cations are present in a molar amount less than the amount corresponding to the cation exchange capacity of the natural layered silicate.

[0028] iv) The mixture prepared in step iii) is dried to a water content of 15% by weight or less to obtain a modified layered silicate.

[0029] The natural layered silicate provided in step i) is preferably natural calcium-based bentonite as described above.

[0030] In the second step of the method of the present invention, a compound having a sodium cation is provided. This compound having a sodium cation can be any sodium salt. Examples of suitable sodium salts are sodium halides, such as sodium chloride or sodium bromide, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium sulfate, sodium bisulfate, sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium formate, sodium acetate, sodium propionate, and salts of higher carboxylic acids, sodium citrate, sodium oxalate, and sodium salts of sulfonic acids, such as sodium toluenesulfonate.

[0031] Preferably, the compound having a sodium cation is provided in the form of an inorganic salt. Mixtures of compounds having a sodium cation may also be used, such as a mixture of two or more different compounds having a sodium cation.

[0032] The compound having sodium cations is typically provided in an amount such that the amount of sodium cations is less than the amount corresponding to the cation exchange capacity of the layered silicate provided in step i). The amount of sodium cations provided typically corresponds to 20-100% of the cation exchange capacity of the layered silicate, preferably 40-80%.

[0033] In the third step of the method of the present invention, the layered silicate provided in step i) and one or more compounds provided in step ii) are mixed in the presence of water. These components can be mixed in any suitable order. The solid components can be premixed with water separately, and then these aqueous mixtures can be combined. Alternatively, the solid components can be premixed and added to water, or water can be added to the premixed solid components. In a further embodiment, the compound having a sodium cation is dissolved in water alone or together, and the aqueous solution is added to the natural layered silicate.

[0034] Water can be used in the form of distilled water, deionized water, or tap water.

[0035] The water content in the mixture is at least 20% by weight, calculated based on the total weight of the mixture. In a preferred embodiment, the water content is at least 25% by weight or at least 30% by weight. Since most of the water is subsequently removed, a water content of up to 60% by weight, preferably up to 50% by weight, is generally preferred. In a particularly preferred embodiment, the water content is in the range of 25-45% by weight, calculated based on the total weight of the mixture. In embodiments where the drying step iv) of the method is carried out by spray drying, the water content of the mixture may also exceed the above values. In this case, the water content of the mixture may be 80% by weight or even 95% by weight. The aqueous mixture is typically in the form of an aqueous slurry or paste. Mixing can be carried out using well-known suitable equipment, such as a kneader, paddle mixer, or extruder.

[0036] The mixing is carried out for a time sufficient to cause some ion exchange reaction between the interlayer calcium cations of the natural layered silicate and the sodium cations of the compound having sodium cations. Mixing typically takes place for at least 5 minutes. In a typical embodiment, mixing takes place for at least 10 minutes, preferably at least 15 minutes. Mixing typically takes place for up to 120 minutes, preferably up to 90 minutes. In a preferred embodiment, mixing takes place for 20-80 minutes.

[0037] The mixing step is typically carried out at ambient temperature, for example, in the temperature range of 10-35°C. If desired, mixing can also be carried out at elevated temperatures, for example, in the range of 36-80°C. Since this mixing method is typically carried out under atmospheric pressure, the temperature during the mixing process preferably does not exceed the boiling point of water at 100°C.

[0038] Preferably, the activator contains, or does not contain, any compound having a non-sodium alkali metal cation. The compound having a non-sodium alkali metal cation is typically present in the activator in an amount of 0.0-5.0 mol%, preferably 0.0-3.0 mol%, calculated based on the molar amount of sodium cation provided by the one or more compounds having a sodium cation.

[0039] In step iv) of the method of the present invention, the mixture prepared in step iii) is dried to a water content of 15% by weight or less. The drying step may be performed immediately after the mixing step iii). If desired, the mixture prepared in step iii) may be allowed to stand for a period of time before drying. This period of time is not particularly limited and is mainly determined by practical considerations of the manufacturing equipment, such as equipment availability control.

[0040] In a further embodiment, the mixture is further processed before drying to reduce particle size, for example, by using a colloid mill, a high-pressure homogenizer, or a high-temperature steam jet.

[0041] The drying step can be carried out using any known drying process. This drying process typically involves the evaporation of water. Evaporation of water can be caused by heating the aqueous mixture in an oven or by heating while stirring the mixture. In one embodiment, the heating and evaporation of water are carried out in an oven. The temperature during this process can vary over a wide range. Drying is typically carried out at temperatures in the range of 60-150°C. If desired, the evaporation of water can be supported by reducing the pressure to below atmospheric pressure. The drying process can be carried out for a sufficient time to reduce the water content to 15% by weight or less. If 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 can even be completely removed during the drying process. However, from an economic perspective and considering energy consumption, it is generally preferred to dry the treated layered silicate to a water content of 0.1% by weight or more.

[0042] In one embodiment, drying is carried out by spray drying, wherein water is removed from the aqueous slurry by spray drying in a spray drying apparatus to prepare a treated layered silicate solid.

[0043] In a further embodiment, impurities are removed from the aqueous slurry prior to spray drying. These impurities exist primarily in the form of solid particles or incompletely swollen material in the aqueous slurry and can be separated from the aqueous phase using physical separation methods generally known to those skilled in the art. Examples of suitable separation methods include sedimentation, decantation, flotation, and centrifugation. These methods can also be combined or performed sequentially, if desired.

[0044] The removed impurities include most crystalline impurities, as well as low-swellable amorphous minerals and low-swellable clays. The impurities to be removed typically include at least one of feldspar, calcite, mica, quartz, cristobalite, dolomite, and calcium-based bentonite.

[0045] 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 present invention.

[0046] If desired, the modified natural layered silicate of the present invention, dried by a method other than spray drying, can be dispersed in water to prepare an aqueous slurry and impurities removed as explained above, followed by spray drying.

[0047] The modified natural layered silicates of the present invention are highly suitable for controlling the rheological properties of aqueous compositions. The modified natural layered silicates of the present invention can be readily dispersed in many aqueous compositions and produce desirable rheological effects. Therefore, the present invention also relates to the use of the modified natural layered silicates of the present invention in controlling the rheological properties of aqueous compositions.

[0048] The present invention further relates to a method for increasing the viscosity of an aqueous composition, comprising adding the modified natural layered silicate to the aqueous composition.

[0049] In the above-described uses or methods, the modified natural layered silicate of the present invention is appropriately added to the aqueous composition in an amount in the range of 0.05-7.00% by weight, preferably 0.10-6.00% by weight, based on the total weight of the aqueous composition.

[0050] When the modified natural layered silicate of the present invention is added to an aqueous composition, the viscosity of the aqueous composition typically increases. Larger amounts of the modified natural layered silicate of the present invention typically result in an even greater increase in viscosity. In some embodiments, the addition of the modified natural layered silicate of the present invention induces thixotropic behavior in the aqueous composition.

[0051] The aqueous composition can be any liquid aqueous composition for which its viscosity is to be increased or for which it is to be endowed with thixotropic properties. An aqueous composition is one in which water is used as the primary or sole liquid diluent. Preferably, the aqueous composition contains less than 35%, 25%, 20%, or even less than 10% by weight (volatile) organic solvent based on the total weight of water and organic solvent in the liquid formulation. In some embodiments, the aqueous composition does not contain organic solvent. The aqueous composition may contain water-soluble organic or inorganic compounds, such as ionic compounds like salts.

[0052] Examples of suitable aqueous liquid compositions include coating compositions, (pre)polymer compositions, pigment concentrates, ceramic products, sealants, cosmetic formulations, adhesives, casting compounds, lubricants, inks, detergents, liquids for oil and gas production, putties, metalworking fluids, sprayable liquids such as deposition aids for crop protection, wax emulsions, liquids for energy storage media such as batteries, liquids for electrical or electronic components, casting or encapsulation compositions, and building materials.

[0053] Aqueous compositions of coatings or inks can be used in a wide range of applications, such as automotive coatings, architectural coatings, protective coatings (e.g., marine or bridge coatings), can and roll coatings, wood and furniture coatings, industrial coatings, plastic coatings, enameled wire coatings, food and seed coatings, leather finishing agents (for both natural and artificial leather), and color resists (for liquid crystal displays). Coatings include paste-like materials that typically have a high solids content and a low liquid component content, such as pigment pastes or effect pigment pastes (using pigments based on aluminum, silver, brass, zinc, copper, bronze such as gold bronze, iron oxide-aluminum); other examples of effect pigments are interference pigments and pearlescent pigments such as metal oxide-mica pigments, bismuth oxychloride, or basic lead carbonate.

[0054] Cosmetic compositions can be any type of aqueous liquid composition intended for personal care and health care purposes. Examples include lotions, creams, ointments such as toothpaste, foams such as shaving foam, gels such as shaving gel and shower gel, pharmaceutical compounds in gel delivery forms, shampoos, liquid soaps, nail polish, lipsticks, and hair dyes.

[0055] The preferred wax emulsion is an aqueous dispersion of wax particles formed from wax that is solid at room temperature.

[0056] Sprays (preferably used as deposition aids) can be formulated with the modified layered silicates of the present invention to achieve drift reduction. They may, for example, contain fertilizers or herbicides, fungicides, and other pesticides.

[0057] Formulations used for construction purposes can be materials that are liquid or paste-like during handling and processing; these water-containing materials are used in the construction industry and become solid after a setting time, such as hydraulic adhesives like concrete, cement, mortar / plaster, tile adhesive, and plaster.

[0058] Metalworking fluids are aqueous compositions used to treat metals and metal parts. Examples include cutting fluids, drilling fluids (used for drilling metals), release agents (mostly aqueous emulsions, such as in aluminum die casting and casting applications), casting detergents, casting coatings, and liquids used for surface treatment of metals (such as surface finishing, surface cleaning, and galvanizing).

[0059] Lubricants are water-containing compounds used for lubrication purposes, that is, to reduce wear and friction loss or to improve cooling, force transmission, vibration reduction, sealing effect and corrosion protection.

[0060] Liquid formulations used in oil and gas production are water-bearing formulations used for developing and mining mineral deposits. Water-based drilling fluids, or "drilling mud," are preferred examples. An application example is hydraulic fracturing.

[0061] Cleaning agents can be used to clean various types of objects. They help remove contaminants, residual dirt, and attached debris. Cleaning agents also include detergents (especially for cleaning textiles, their precursors, and leather), cleaning agents and polishes, laundry formulations, fabric softeners, and personal care products.

[0062] Preferred aqueous compositions include aqueous coating compositions, aqueous compositions containing hydraulic binders, aqueous cleaning compositions, and aqueous personal care compositions.

[0063] The above-described aqueous compositions may contain other components and additives commonly used in aqueous compositions, such as organic cosolvents, crosslinking agents, defoamers, dispersants, and UV stabilizers. Although the modified natural layered silicate of this invention provides excellent thickening properties, it can be used in combination with other rheology control agents, if desired.

[0064] Other examples of rheology control agents include polysaccharides (such as cellulose derivatives, guar gum, xanthan gum), urea compounds, (poly)amides, polyacrylates (such as alkali-soluble or alkali-swellable emulsions), or associative thickeners (such as polyurethane thickeners, amino-based thickeners, and hydrophobically modified alkali-soluble emulsion thickeners).

[0065] The modified natural layered silicates of the present invention can also be used as adsorbents in certain compositions, for example, to adsorb unwanted impurities. In a further embodiment, the modified natural layered silicates of the present invention can be used as coagulants, for example, in wastewater treatment.

[0066] Example

[0067] General Method

[0068] Cation exchange capacity

[0069] The cation exchange capacity of layered silicates was determined using the copper complex method according to (Ammann, L., Bergaya, F., Lagaly, G., 2005, Further exploration of the determination of cation exchange capacity of clay using copper complexes. Clay Minerals 40, 441-453).

[0070] Chemical composition

[0071] The chemical composition of the unprocessed calcium-based bentonite was determined by standard ICP-OES after dissolving the bentonite in a mixture of aqua regia. The results of the chemical composition of the unprocessed bentonite used are listed in Table 1.

[0072] Table 1. Chemical composition of the unprocessed bentonite types used, expressed as % by weight

[0073]

[0074] LOI refers to the weight loss when heated to 1000°C.

[0075] General methods for activating layered silicates

[0076] Calcium-based bentonite was activated with sodium carbonate in a Werner-Pfleiderer mixer. The activator (sodium carbonate) was dissolved in water and subsequently added to the calcium-based 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 of the product was determined, and the thickening effect of the product was tested in deionized water. The preparation parameters for the examples are listed in Table 2. Comparative Examples 1 and 4 were not treated with the activator. Only the natural calcium-based bentonite of Comparative Examples 1 and 4 was dried to the indicated water content and pulverized.

[0077] Table 2. Preparation parameter settings for the examples

[0078]

[0079] The comparative scale is marked

[0080] Viscosity in water

[0081] The dispersion of activated bentonite in water was prepared by mixing 5% by weight of activated bentonite in water for 20 minutes. Viscosity was measured after storing the dispersion at 23°C for 1 hour. Viscosity was measured using a Brookfield rotational viscometer at a shear rate of 10 rpm. Viscosity was read after a 2-minute measurement run. The viscosity of the samples is provided in mPas in Table 3.

[0082] Determination of leachable cations

[0083] To determine the leaching cations, 1 g of activated bentonite was added to 40 mL of ammonium chloride solution (2 wt%) in a centrifuge tube. The mixture was stirred on a top-mounted shaker for 5 hours. Then, the mixture was centrifuged at 6000 rpm for 10 minutes. The supernatant was filtered and collected in a 250 mL glass bottle. The precipitate was redispersed in 40 mL of ammonium chloride (2 wt%) and stirred on a top-mounted shaker for 5 hours. This procedure was repeated three times, and the supernatant was collected in a 250 mL glass bottle. After complete leaching with ammonium chloride three times, the precipitate was washed with 40 mL of deionized water: the precipitate was dispersed in 40 mL of deionized water and stirred on a top-mounted shaker for 5 hours. Then, the mixture was centrifuged at 6000 rpm for 10 minutes. The washing step was repeated twice. The leaching cations were determined by ICP-OES analysis in the combined aqueous solution. The results for the leaching cations are listed in Table 3.

[0084] Table 3. Cation exchange capacity, total leached cations, and viscosity in water of activated bentonite

[0085]

[0086] The comparative scale is marked

[0087] Comparative Examples 1 and 4, without sodium ion activation, did not produce a significant thickening effect when added to water. Comparative Examples 7 and 8 produced a high thickening effect in water. However, when used in aqueous applications, such as tile adhesives or water-based paints, Comparative Examples 7 and 8 resulted in poor thickening effects, as further shown below.

[0088] The activated bentonite was tested in tile adhesive formulations. Slip was determined according to DIN EN 1308-2007-11.

[0089] Table 4. Tile adhesive formula

[0090]

[0091] Table 5. Slip results according to DIN EN 1308-2007-11

[0092]

[0093] The comparative scale is marked

[0094] Table 5 shows the slip results for tiles using formulations with and without activated bentonite. Lower slip values ​​indicate better adhesion of the tile adhesive to the wall. Example C1 represents a comparative example without bentonite. Comparative examples C2 and C5 showed no improvement in anti-slip properties compared to C1 because the unactivated bentonite used had no effect on the rheological properties of the tile adhesive. Comparative examples C8 and C9, containing leached sodium cations outside the scope of this invention, showed only minor improvements in anti-slip properties. Examples C3, C4, C6, and C7, containing the activated bentonite of this invention, showed reduced slip.

[0095] Prepare the paint formulation as outlined in Table 6 below. The amounts of each component are shown in parts by weight.

[0096] Table 6.

[0097]

[0098] Paint formulations were applied using a 421 / S type stepped doctor blade (Erichsen GmbH & Co KG) at wet film thicknesses of 50-500 and 550-1000 µm. Application was performed using an automatic applicator, byko-drive XL (BYK-Gardner GmbH), on a comparison chart 2801 (BYK-Gardner GmbH) at a speed of 50 mm / s. Immediately after application, the coated film was hung vertically at room temperature until dry. Sagging resistance was visually evaluated after drying. Table 7 shows sagging resistance as the maximum wet film thickness in µm without runs or blistering.

[0099] Viscosity profiles were measured using a Physica MCR 301 (Anton Paar) rheometer. Viscosities (Pa·s) at different shear rates (1 / s) are recorded using both rising and falling shear rates in Table 7.

[0100] Table 7: Results of the tested materials in paint formulations

[0101]

[0102] The following conclusion can be drawn: the layered silicates of the present invention provide improved rheological properties for waterborne paint formulations. This results in excellent anti-sagging properties and higher viscosity, especially at low shear conditions, which is suitable for achieving good anti-sagging performance.

Claims

1. A layered silicate having a cation exchange capacity in the range of 70-130 meq / 100g, having leached sodium cations in the range of 65-130 meq / 100g, having leached magnesium cations in the range of 5-65 meq / 100g, having leached calcium cations in the range of 15-95 meq / 100g, and wherein the sum of the leached 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 of 30 mPas or higher at 10 rpm when measured at 23°C.

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

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

4. A 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 of 250 mPas or higher at 10 rpm when measured at 23°C.

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

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

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

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

9. A layered silicate according to any one of the preceding claims, wherein the layered silicate has an amount of leaching sodium cations of 60% or more of the cation exchange capacity.

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

11. A method for preparing layered silicates according to any one of the preceding claims, comprising: i) Provides natural layered silicates containing interlayer calcium cations and having a cation exchange capacity in the range of 70-130 meq / 100g. ii) Provide at least one compound having a sodium cation as an activator, iii) Mixing the layered silicate provided in step i) and one or more compounds provided in step ii) in the presence of water for at least 5 minutes, wherein the water content in the mixture is at least 20% by weight, and wherein the one or more compounds having sodium cations are present in a molar amount less than the amount corresponding to the cation exchange capacity of the natural layered silicate. iv) The mixture prepared in step iii) is dried to a water content of 15% by weight or less to obtain a modified layered silicate.

12. The method of claim 11, wherein the compound having a non-sodium alkali metal cation in the activator is present in an amount of 0.0-5.0 mol% based on the molar amount of sodium cation provided by the one or more compounds having a sodium cation.

13. The method of claim 11 or 12, wherein the method comprises an additional step of reducing the particle size of the dried mixture obtained in step iv) by crushing and / or grinding.

14. Use of the layered silicate according to any one of claims 1-10 as a rheology modifier 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 for increasing the viscosity of an aqueous composition, comprising adding a layered silicate according to any one of claims 1-10 to the aqueous composition.

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