Polyvinyl alcohol as dispersing aid for mineral dispersions

Abstract

The invention relates to the use of polyvinyl alcohol as a co-dispersant for an aqueous suspension comprising a mineral material selected from the group consisting of alkaline earth metal mineral materials, clays, calcined clays, titanium dioxide and mixtures thereof and a dispersant, and the dispersant being a polyacrylate-containing dispersant. The invention also relates to a method for producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, and to an aqueous suspension obtainable by said method. The invention also relates to a dispersant composition comprising a combination of a dispersant and a co-dispersant, where the dispersant is a polyacrylate-containing dispersant and the co-dispersant is polyvinyl alcohol.

Description

[0001] The present invention relates to the use of polyvinyl alcohol as a co-dispersant for aqueous suspensions comprising a mineral material and a dispersant, a process for producing such an aqueous suspension in combination with said co-dispersant, an aqueous suspension obtainable by said process, the use of said aqueous suspension and a dispersant composition comprising a dispersant in combination with polyvinyl alcohol as a co-dispersant.

[0002] Mineral materials are one of the main components of paints, plastics, paper or paper coating colors. Mineral materials such as calcium carbonate can provide paper and paint quality and agricultural properties improvement, especially for their optical properties.

[0003] For reasons of workability, transportation, storage and drying costs, it is particularly useful to produce the mineral material in the form of a high solids suspension (i.e. a suspension in which the water content is small relative to the total weight of the suspension). Such high solids suspensions generally require the addition of dispersants or grinding aids to maintain suspension stability, pumpability and / or to allow grinding of the suspension.

[0004] However, the presence of dispersants can impair the material properties of the final product, for example, their optical properties can be degraded. Dispersants such as polyacrylates are also non-biodegradable, so for environmental reasons it is desirable to further reduce their use. In addition, dispersants can be a significant cost factor in the production of mineral dispersions.

[0005] EP 0 461 635 A1 relates to polyvinyl alcohol resins that dissolve in high solids aqueous paper coating compositions without external heating. WO 0 134 906 A1 describes multifunctional poly(vinyl alcohol) binders for fine particle size calcium carbonate pigments.

[0006] Therefore, there is a continuing need in the art for alternative aqueous mineral dispersions that solve the aforementioned technical problems.

[0007] Therefore, it is an object of the present invention to provide an aqueous mineral suspension having a high solids content at a workable viscosity. In addition, it is desirable that the aqueous suspension contain a reduced amount of dispersant. The aqueous suspension may also have further improved properties, such as improved long-term stability, improved wet grindability or improved optical properties.

[0008] It would also be desirable to provide aqueous mineral suspensions which are suitable for paper production, especially for paper coating applications, and which can even improve the optical or mechanical properties of the paper substrate.

[0009] Another object of the present invention is to provide additives for aqueous mineral suspensions that can reduce the amount of dispersant required to bring the viscosity of the mineral suspension into a workable range. Furthermore, it is desirable to provide additives that can add additional functionality to aqueous mineral suspensions, such as improved long-term stability, improved wet grindability, or improved optical properties.

[0010] Furthermore, it is an object of the present invention to provide an additive for aqueous mineral suspensions which can be added during the production of said mineral suspension, for example before grinding the mineral material or before precipitation of the mineral material or before or during concentration of the mineral suspension to its final solids content.

[0011] The foregoing and other objects are solved by the subject matter defined herein in the independent claims.

[0012] According to one aspect, there is provided the use of polyvinyl alcohol as a dispersant for an aqueous suspension comprising a mineral material and a dispersant,

[0013] The mineral material is selected from alkaline earth mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof, and the dispersant is a dispersant containing polyacrylate.

[0014] According to another aspect, there is provided a method of producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, comprising the steps of:

[0015] i) providing a mineral material selected from the group consisting of alkaline earth mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof,

[0016] ii) providing a dispersant, wherein the dispersant is a polyacrylate-containing dispersant,

[0017] iii) providing a dispersant, wherein the dispersant is polyvinyl alcohol,

[0018] iv) providing water, and

[0019] v) contacting the mineral material of step i), the dispersant of step ii), the co-dispersant of step iii) and the water of step iv).

[0020] According to yet a further aspect, there is provided a method of producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, wherein the mineral material is precipitated calcium carbonate, and the method comprises the following steps:

[0021] 1) providing a material containing calcium oxide,

[0022] II) providing a dispersant, wherein the dispersant is a polyacrylate-containing dispersant,

[0023] III) providing a dispersant, wherein the dispersant is polyvinyl alcohol,

[0024] IV) preparing milk of lime by mixing water, the calcium oxide-containing material of step I) and the dispersant aid of step III),

[0025] V) carbonating the lime milk obtained in step IV) to form an aqueous suspension of precipitated calcium carbonate, and

[0026] VI) The aqueous suspension obtained in step V) is mixed with the dispersant of step II).

[0027] According to still another aspect of the present invention, there is provided a dispersant composition comprising a combination of a dispersant and a co-dispersant, wherein the dispersant is a polyacrylate-containing dispersant, and the co-dispersant is polyvinyl alcohol.

[0028] According to yet a further aspect of the present invention, there is provided an aqueous suspension obtainable by the process according to the present invention.

[0029] According to yet another aspect of the present invention, there is provided the use of the aqueous suspension according to the present invention in paper applications, packaging applications, polymer applications or water treatment applications.

[0030] Advantageous embodiments of the invention are defined in the corresponding dependent claims.

[0031] According to one embodiment, the polyvinyl alcohol has a degree of hydrolysis of at least 75 mol%, preferably at least 85 mol%, more preferably at least 90 mol%, even more preferably at least 95 mol%, and most preferably at least 98 mol%, and / or the polyvinyl alcohol has an average molecular weight M of 10,000 to 150,000 g / mol, preferably 12,000 to 100,000 g / mol, more preferably 14,000 to 50,000 g / mol, and most preferably 16,000 to 30,000 g / mol. w According to another embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 2 wt.-% or less, preferably in an amount of 0.01 to 1.8 wt.-%, more preferably in an amount of 0.05 to 1.5 wt.-%, even more preferably in an amount of 0.08 to 1 wt.-%, and most preferably in an amount of 0.1 to 0.6 wt.-%, based on the total weight of the aqueous suspension.

[0032] According to one embodiment, the dispersant is a polyacrylate homopolymer, a polyacrylate copolymer or a mixture thereof, and preferably, the dispersant is a polyacrylate homopolymer, preferably at least partially neutralized, preferably at least partially neutralized with sodium ions, potassium ions, lithium ions, ammonium ions, calcium ions and mixtures thereof, more preferably at least partially neutralized with sodium ions, calcium ions or mixtures thereof, and most preferably at least partially neutralized with sodium ions. According to another embodiment, the dispersant has a degree of neutralization of at least 30 mol%, preferably at least 40 mol%, more preferably at least 60 mol%, and most preferably at least 80 mol%, and / or the dispersant has an average molecular weight M of 1000 to 15000 g / mol, preferably 2000 to 12000 g / mol, more preferably 3000 to 11000 g / mol, and most preferably 4000 to 10000 g / mol. w According to yet another embodiment, the aqueous suspension comprises the dispersant in an amount of 3 wt.-% or less, preferably in an amount of 0.01 to 2 wt.-%, more preferably in an amount of 0.05 to 1.5 wt.-%, and most preferably in an amount of 0.1 to 0.8 wt.-%, based on the total weight of the aqueous suspension.

[0033] According to one embodiment, the mineral material is in the form of particles having a weight median particle size d of 0.05 to 100 μm, preferably 0.1 to 50 μm, more preferably 0.15 to 25 μm, even more preferably 0.25 to 10 μm, and most preferably 0.5 to 2 μm. 50 , and / or having a weight-determined top cut particle size d of 0.1 to 200 μm, preferably 0.2 to 100 μm, more preferably 0.3 to 50 μm, even more preferably 0.25 to 20 μm, and most preferably 1 to 4 μm 98 According to yet another embodiment, the aqueous suspension comprises the mineral material in an amount of 10 to 78 wt.-%, preferably 20 to 75 wt.-%, and most preferably 50 to 72 wt.-%, based on the total weight of the aqueous suspension.

[0034] According to one embodiment of the method for producing an aqueous suspension, step v) comprises the following steps: a1) contacting the dispersant of step ii), the auxiliary dispersant of step iii) and the water of step iv), and a2) adding the mineral material of step i) to the mixture obtained in step a1), or b1) contacting the dispersant of step ii) and the auxiliary dispersant of step iii), and b2) adding the mineral material of step i) and the water of step iv) to the mixture obtained in step b1), wherein the mineral material and the water are added separately or in combination, preferably in combination, or c1) contacting the dispersant of step ii), the mineral material of step i) and the water of step iv), and c2) adding the auxiliary dispersant of step iii) to the mixture obtained in step c1), or d) contacting the mineral material of step i), the dispersant of step ii), the auxiliary dispersant of step iii) and the water of step iv simultaneously. According to a further embodiment, the method further comprises a step of grinding and / or dewatering the aqueous suspension during and / or after step v).

[0035] It should be understood that for the purposes of the present invention, the following terms have the following meanings:

[0036] In the meaning of the present invention, a "calcium oxide-containing material" may be a mineral material or a synthetic material having a calcium oxide content of at least 50 wt.-%, preferably 75 wt.-%, more preferably 90 wt.-%, and most preferably 95 wt.-%, based on the total weight of the calcium oxide-containing material.

[0037] In the meaning of the present application, the term "mineral" includes natural or synthetic minerals, fillers and / or pigments, such as calcium carbonate, chalk, dolomite, titanium dioxide and the like.

[0038] "Natural ground calcium carbonate" (GCC) within the meaning of the present invention is calcium carbonate obtained from natural sources such as limestone, marble or chalk, and processed by wet and / or dry processes such as grinding, sieving and / or classifying (e.g. by cyclones or classifiers).

[0039] In the meaning of the present invention, " precipitated calcium carbonate " (PCC) is by carbon dioxide and lime in aqueous, semi-dry or humid environment after reaction precipitation or by the synthetic material obtained by precipitation of calcium ion source and carbonate ion source in water.PCC can be vaterite type, calcite type or aragonite type crystal form.PCC is described in for example EP2447213 A1, EP2524898A1, EP2371766A1, EP1712597A1, EP1712523A1 or WO2013142473A1.

[0040] The "particle size" of a mineral herein is determined by its weight-based particle size distribution d x Description. Among them, the value d xmeans that x wt% of the particles have a particle size less than d x The diameter of the diameter. This means, for example, that d 20 The value is the particle size below which 20% by weight of all particles are smaller than this particle size. 50 The value is the weight median particle size, i.e., 50% by weight of all particles are smaller than this particle size. For the purposes of this invention, particle sizes are specified as weight median particle sizes d unless otherwise indicated. 50 (Weight). By using a Sedigraph from Micromeritics Instrument TM 5100 instrument or Sedigraph TM The particle size is determined using a 5120 instrument. The method and instrument are known to the skilled person and are commonly used for determining the particle size of fillers and pigments. The measurement is carried out in a 0.1 wt. % aqueous solution of Na4P2O7.

[0041] As used herein, the term "polymer" generally includes homopolymers and copolymers, such as block, graft, random and alternating copolymers, and blends and modifications thereof. The polymer may be an amorphous polymer, a crystalline polymer, or a semi-crystalline polymer (i.e., a polymer comprising a crystalline portion and an amorphous portion). Crystallinity is expressed as a percentage and can be determined by differential scanning calorimetry (DSC). Amorphous polymers can be characterized by their glass transition temperature, and crystalline polymers can be characterized by their melting point. Semi-crystalline polymers can be characterized by their glass transition temperature and / or their melting point.

[0042] As used herein, the term "copolymer" refers to a polymer derived from more than one monomeric species. Copolymers obtained by copolymerization of two monomeric species may also be referred to as dimers, those obtained from three monomers as trimers, those obtained from four monomers as tetramers, etc. (see IUPAC Compendium of Chemical Terminology 2014, "copolymer"). Accordingly, the term "homopolymer" refers to a polymer derived from one monomeric species.

[0043] Unless otherwise specified, the "moisture content" of a material refers to the percentage of moisture (i.e., water) that can be desorbed from a sample when heated to 220°C. Moisture content can be measured according to the Karl Fischer coulometric titration method by desorbing water in an oven at 220°C for at least 10 minutes and continuously passing dry nitrogen at 100 mL / min through a Karl Fischer coulometer (Mettler Toledo Coulometric KF Titrator C30, combined with a Mettler Toledo drying oven DO 0337) for at least 10 minutes. A calibration curve using water can be recorded, taking into account a 10-minute nitrogen flow blank without sample.

[0044] The “specific surface area” (in m 2 The total surface area (expressed in m2 / g) of the material can be determined by the Brunauer-Emmett-Teller (BET) method using nitrogen as the adsorption gas and by using a Micromeritics ASAP 2460 instrument. This method is well known to the skilled person and is defined in ISO 9277:2010. Prior to the measurement, the sample is conditioned at 100° C. under vacuum for a period of 30 minutes. 2 Expressed) can be expressed by specific surface area (in m 2 The product of the mass (expressed in g) and the mass of the material (expressed in g) is obtained.

[0045] As referred to herein, a "solution" is understood to be a single-phase mixture of a specific solvent and a specific solute, such as a single-phase mixture of a water-soluble salt and water. Thus, the term "dissolved" as used herein refers to the physical state of a solute in solution.

[0046] A "suspension" or "slurry" within the meaning of the present invention comprises undissolved solids and water and optionally other additives and generally contains a high amount of solids and is therefore more viscous and may have a higher density than the liquid from which it is formed.

[0047] The term "aqueous" suspension refers to a system in which the liquid phase comprises water, preferably consists of water. However, the term does not exclude that the liquid phase of the aqueous suspension comprises a small amount of at least one water-miscible organic solvent selected from methanol, ethanol, acetone, acetonitrile, tetrahydrofuran, and mixtures thereof. If the aqueous suspension comprises at least one water-miscible organic solvent, the liquid phase of the aqueous suspension comprises at least one water-miscible organic solvent in an amount of 0.1 to 40.0 wt.-%, preferably 0.1 to 30.0 wt.-%, more preferably 0.1 to 20.0 wt.-%, and most preferably 0.1 to 10.0 wt.-%, based on the total weight of the liquid phase of the aqueous suspension. For example, the liquid phase of the aqueous suspension consists of water.

[0048] For the purposes of the present invention, the "solids content" of a liquid composition is a measure of the amount of material remaining after evaporation of all solvent or water. If desired, the "solids content" of a suspension within the meaning of the present invention, given in % by weight, can be determined using a moisture analyzer HR73 from Mettler-Toledo (T=160° C., automatic switch-off 3, standard drying) using a sample size of 2-10 g.

[0049] For the purposes of the present invention, the term "viscosity" or "Brookfield viscosity" refers to the Brookfield viscosity. For this purpose, the Brookfield viscosity is measured by means of a Brookfield DV-II+ Pro viscometer at 25°C ± 1°C and 100 rpm using a suitable spindle from the Brookfield RV spindle set and is expressed in mPa·s. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV spindle set that is suitable for the viscosity range to be measured. For example, for a viscosity range of 200 to 800 mPa·s, spindle 3 may be used, for a viscosity range of 400 to 1600 mPa·s, spindle 4 may be used, for a viscosity range of 800 to 3200 mPa·s, spindle 5 may be used, for a viscosity range of 1000 to 2000000 mPa·s, spindle 6 may be used, and for a viscosity range of 4000 to 8000000 mPa·s, spindle 7 may be used.

[0050] Where an indefinite or definite article is used when referring to a singular noun eg “a”, “an” or “the”, this includes a plural of that noun unless something else is specifically stated.

[0051] When the term "comprising" is used in the present description and claims, it does not exclude other elements. For the purposes of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising". If a group is defined below as comprising at least a certain number of embodiments, this should also be understood to disclose a group that preferably consists only of these embodiments.

[0052] Terms such as "capable of obtaining" or "capable of defining" and "obtaining" or "defining" are used interchangeably. For example, this means that, unless the context clearly dictates otherwise, the term "obtaining" is not meant to indicate that, for example, an embodiment must be obtained by, for example, a series of steps following the term "obtaining," although such a limited understanding is always encompassed by the term "obtaining" or "defining" as a preferred embodiment.

[0053] Whenever the terms "including" or "having" are used, these terms are meant to be equivalent to "comprising" as defined above.

[0054] According to the present invention, there is provided the use of polyvinyl alcohol as a dispersant for an aqueous suspension comprising a mineral material and a dispersant, wherein the mineral material is selected from alkaline earth metal mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof, and the dispersant is a polyacrylate-containing dispersant.

[0055] Hereinafter, the details and preferred embodiments of the use of the present invention will be described in more detail. It should be understood that these technical details and embodiments also apply to the method of the present invention, the dispersant composition of the present invention, the aqueous dispersion of the present invention and the inventive use of the dispersion.

[0056] Mineral materials

[0057] According to the present invention, the aqueous suspension comprises a mineral material, wherein the mineral material is selected from the group consisting of alkaline earth mineral materials, clays, calcined clays, titanium dioxide and mixtures thereof.

[0058] According to one embodiment, the mineral material is prepared with a weight median particle size d of 0.05 to 100 μm, preferably 0.1 to 50 μm, more preferably 0.15 to 25 μm, even more preferably 0.25 to 10 μm, and most preferably 0.5 to 2 μm. 50 The particle form exists. TM 5100 instrument or Sedigraph TM 5120 Instrumental evaluation of the median particle size d 50 .

[0059] Additionally or alternatively, the mineral filler may have a weight-determined top cut particle size d of 0.1 to 200 μm, preferably 0.2 to 100 μm, more preferably 0.3 to 50 μm, even more preferably 0.25 to 20 μm, and most preferably 1 to 4 μm. 98 The particle form exists. TM 5100 instrument or Sedigraph TM 5120 Instrument Evaluation Volume Determination of Top Cut Particle Size d 98 .

[0060] Additionally or alternatively, the mineral filler may have a density of 1 to 100 m / s measured using nitrogen and the BET method according to ISO 9277:2010. 2 / g, preferably 5 to 90m 2 / g, more preferably 10 to 80m 2 / g, even more preferably 15 to 70 m 2 / g, and most preferably 17 to 60m 2 It exists in the form of particles with a specific surface area of 1.5 ~ 1.5 g.

[0061] According to one embodiment, the aqueous suspension comprises the mineral material in an amount of 10 to 78 wt.-%, preferably 20 to 75 wt.-%, and most preferably 50 to 72 wt.-%, based on the total weight of the aqueous suspension.

[0062] According to one embodiment, the mineral material is chosen from alkaline earth metal mineral materials.

[0063] The alkaline earth metal mineral material may be selected from alkaline earth metal carbonates, alkaline earth metal phosphates, alkaline earth metal sulfates, alkaline earth metal oxides, alkaline earth metal hydroxides and mixtures thereof. According to a preferred embodiment, the alkaline earth metal mineral material is alkaline earth metal carbonates, alkaline earth metal hydroxides or mixtures thereof.

[0064] According to one embodiment, the alkaline earth metal mineral material is selected from calcium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium hydroxide, magnesium hydroxide and mixtures thereof, preferably the alkaline earth metal mineral material is selected from ground calcium carbonate, precipitated calcium carbonate, dolomite, hydromagnesite, calcium hydroxide, magnesium hydroxide and mixtures thereof.

[0065] Dolomite is a calcium-magnesium carbonate mineral having a chemical composition of CaMg(CO3)2 ("CaCO3·MgCO3"). The dolomite mineral may contain at least 30.0 wt% MgCO3, preferably greater than 35.0 wt%, and more preferably greater than 40.0 wt% MgCO3, based on the total weight of the dolomite.

[0066] Clay refers to small crystalline particles of hydrated silicates, primarily aluminum, sometimes with magnesium and / or iron replacing all or part of the aluminum. The main classes of clay minerals are kaolinite (the main component of kaolin), halloysite, illite, montmorillonite, and vermiculite. Calcined clay can be obtained by heating a source of kaolin to 650°C to 750°C.

[0067] Titanium dioxide can have anatase, rutile, or amorphous structures. Titanium dioxide particles are typically prepared in a chloride process or a sulfuric acid process. In the chloride process, TiCl4 is oxidized to form TiO2 particles. In the sulfuric acid process, sulfuric acid and a titanium-containing ore are dissolved, and the resulting solution is subjected to a series of steps to produce at least one titanium dioxide-containing particle. The titanium dioxide can be substantially pure titanium dioxide or can contain other metal oxides such as silicon dioxide, aluminum oxide, zirconium oxide, etc., preferably silicon dioxide. These other metal oxides can be incorporated into the titanium dioxide particles by co-oxidation or coprecipitation of the titanium compound with other metal compounds during the preparation of the titanium dioxide by the chloride process or the sulfuric acid process.

[0068] calcium carbonate

[0069] According to one embodiment, the alkaline earth metal mineral material is calcium carbonate, optionally in combination with magnesium carbonate, calcium magnesium carbonate, calcium hydroxide, magnesium hydroxide or mixtures thereof.

[0070] According to one embodiment, the calcium carbonate is selected from ground calcium carbonate, precipitated calcium carbonate or mixtures thereof.According to a preferred embodiment, the calcium carbonate is ground calcium carbonate.

[0071] Ground (or natural ground) calcium carbonate (GCC) is understood to be made from naturally occurring forms of calcium carbonate, mined from sedimentary rocks such as limestone or chalk or from metamorphic marble, eggshells or shells. Calcium carbonate is known to exist in three types of crystal polymorphs: calcite, aragonite and vaterite. The most common crystal polymorph, calcite, is considered to be the most stable crystalline form of calcium carbonate. Less common is aragonite, which has a discrete or clustered needle-like orthorhombic crystal structure. Vaterite is the rarest calcium carbonate polymorph and is generally unstable. Ground calcium carbonate is almost entirely a calcite polymorph, which is said to be a rhombohedron. In the meaning of the present application, the term "source" of calcium carbonate refers to the naturally occurring mineral material from which the calcium carbonate is obtained. According to one embodiment of the present invention, ground calcium carbonate is selected from marble, chalk, limestone and mixtures thereof. The source of calcium carbonate may include other naturally occurring components, such as magnesium carbonate, aluminosilicates, etc.

[0072] According to one embodiment of the present invention, GCC is obtained by dry grinding.According to another embodiment of the present invention, GCC is obtained by wet grinding and optionally subsequent drying.

[0073] Typically, the grinding step can be performed using any conventional grinding device, for example, under conditions such that comminution is primarily caused by impact with a second object, i.e., in one or more of the following: a ball mill, a rod mill, a vibrating mill, a roller crusher, a centrifugal impact mill, a vertical bead mill, a grinding mill, a pin mill, a hammer mill, a pulverizer, a shredder, a deblocker, a knife cutter, or other such equipment known to the skilled person. If the mineral material comprising calcium carbonate comprises a wet-ground mineral material comprising calcium carbonate, the grinding step can be performed under conditions such that autogenous grinding occurs and / or by horizontal ball milling and / or other such methods known to the skilled person. The thus obtained wet-processed ground mineral material comprising calcium carbonate can be washed and dehydrated by well-known methods, for example, by flocculation, centrifugation, filtration, or forced evaporation, and then dried. The subsequent drying step can be performed in a single step (such as spray drying) or in at least two steps. Typically, these mineral materials also undergo a beneficiation step (such as flotation, bleaching, or magnetic separation step) to remove impurities.

[0074] According to one embodiment of the present invention, the calcium carbonate comprises one type of ground calcium carbonate.According to another embodiment of the present invention, the calcium carbonate comprises a mixture of two or more types of ground calcium carbonate selected from different sources.

[0075] In the meaning of the present invention, " precipitated calcium carbonate " (PCC) is a synthetic material, usually by precipitation after carbon dioxide and calcium hydroxide react in an aqueous environment or by calcium ions and carbonate ions such as CaCl and NaCO from solution precipitation and obtain.Other possible ways of producing PCC are the lime soda process, or the Solvay process (wherein PCC is the by-product of ammonia production).Precipitated calcium carbonate exists with three main crystalline forms: calcite, aragonite and vaterite, and for each of these crystalline forms, there are many different polymorphs (crystallization states).Calcite has a triangular structure, with typical crystallization states such as scalenoidal face (S-PCC), rhombohedral (R-PCC), hexagonal prism, axial face, colloidal state (C-PCC), cubic and prismatic (P-PCC).Aragonite is an orthorhombic structure, with the typical crystallization states of twin hexagonal prism crystals, and the diverse classification of thin long prisms, scimitars, pointed cones, chisel-shaped crystals, branched trees and coral or worm-like forms. Vaterite belongs to the hexagonal crystal system. The obtained PCC slurry can be mechanically dehydrated and dried.

[0076] According to one embodiment of the present invention, the precipitated calcium carbonate is a precipitated calcium carbonate, preferably comprising aragonite, vaterite or calcite mineralogical crystal forms or mixtures thereof.

[0077] According to one embodiment of the present invention, the calcium carbonate comprises a precipitated calcium carbonate. According to another embodiment of the present invention, the calcium carbonate comprises a mixture of two or more precipitated calcium carbonates selected from different crystalline forms and different polymorphs of precipitated calcium carbonate. For example, at least one precipitated calcium carbonate may comprise a PCC selected from S-PCC and a PCC selected from R-PCC.

[0078] hydromagnesite

[0079] According to one embodiment, the alkaline earth metal mineral material is hydromagnesite, optionally in combination with calcium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium hydroxide, magnesium hydroxide or mixtures thereof.

[0080] Hydromagnesite or basic magnesium carbonate (the standard industrial name for hydromagnesite) is a naturally occurring mineral found in magnesium-rich minerals such as serpentine and altered magnesium-rich igneous rocks, but also as an alteration product of brucite in periclase marble. Hydromagnesite is described as having the formula Mg5(CO3)4(OH)2·4H2O.

[0081] It should be understood that hydromagnesite is a very specific mineral form of magnesium carbonate and occurs naturally as small needle-like crystals or shells of needle-like or blade-like crystals. Furthermore, it should be noted that hydromagnesite is a unique and sole form of magnesium carbonate and is chemically, physically, and structurally distinct from other forms of magnesium carbonate. Hydromagnesite can be readily distinguished from other magnesium carbonates by X-ray diffraction analysis, thermogravimetric analysis, or elemental analysis. Unless specifically described as hydromagnesite, all other forms of magnesium carbonate (e.g., hydromagnesite (Mg2(CO3)(OH)2·3H2O), fulmarite (Mg5(CO3)4(OH)2·5H2O), isohydromagnesite (Mg5(CO3)4(OH)2·5H2O), malachite (Mg2(CO3)(OH)2·0.5H2O), magnesite (MgCO3), dimagnesite (MgCO3·2H2O), pentahydrate magnesite (MgCO3·5H2O) and nesquehonite (MgCO3·3H2O)) are not hydromagnesite within the meaning of the present invention and do not chemically correspond to the above formula.

[0082] In addition to natural hydromagnesite, precipitated hydromagnesite (or synthetic magnesium carbonate) can also be prepared. For example, US Pat. No. 1,361,324, US Pat. No. 935,418, GB Pat. No. 548,197, and GB Pat. No. 544,907 generally describe the formation of an aqueous solution of magnesium bicarbonate (generally described as "Mg(HCO)"), which is then converted to hydromagnesite by the action of an alkali such as magnesium hydroxide. Other methods described in the literature suggest the preparation of a composition containing both hydromagnesite and magnesium hydroxide, wherein the magnesium hydroxide is mixed with water to form a suspension, which is further contacted with carbon dioxide and an aqueous alkaline solution to form a corresponding mixture; see, for example, US Pat. No. 5,979,461.

[0083] It should be understood that the hydromagnesite may be a mixture of one or different types of hydromagnesite. In one embodiment of the present invention, the hydromagnesite comprises, preferably consists of, one type of hydromagnesite. Alternatively, the hydromagnesite comprises, preferably consists of, two or more types of hydromagnesite.

[0084] According to a preferred embodiment, the hydromagnesite is precipitated hydromagnesite.

[0085] Dispersants containing polyacrylates

[0086] In addition to the mineral material, the aqueous suspension according to the invention comprises a dispersant, wherein the dispersant is a polyacrylate-containing dispersant.

[0087] The polyacrylate-containing dispersant may be a polyacrylate homopolymer, a polyacrylate copolymer, or a mixture thereof.

[0088] Polyacrylate homopolymers can be prepared by the polymerization of acrylic acid or methacrylic acid or their salts. Polyacrylate copolymers can be prepared by the polymerization of acrylic acid or methacrylic acid or their salts with at least one nonionic compound selected from the group consisting of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, C1-C5 esters of acrylic acid, C1-C5 esters of methacrylic acid, fumaric acid, itaconic acid, acrylamide, crotonic acid, maleic anhydride, isocrotonic acid, aconitic acid (cis or trans), mesaconic acid, erucic acid, undecylenic acid, angelic acid, canellic acid, hydroxyacrylic acid, acrolein, acrylonitrile, dimethylaminoethyl methacrylate, vinyl pyrrolidone, vinyl caprolactam, ethylene, propylene, isobutylene, diisobutylene, vinyl acetate, styrene, α-methylstyrene, methyl vinyl ketone, and mixtures thereof.

[0089] The C1-C5 ester of acrylic acid and / or the C1-C5 ester of methacrylic acid can be selected from alkyl esters of acrylic acid and / or alkyl esters of methacrylic acid. The alkyl ester may contain other substituents such as hydroxyl and / or sulfonic acid groups. For example, the C1-C5 ester of acrylic acid is selected from alkyl esters of acrylic acid.

[0090] According to one embodiment, the C1-C5 ester of acrylic acid is selected from methyl acrylate, ethyl acrylate, propyl acrylate, hydroxypropyl acrylate, butyl acrylate and amyl acrylate, preferably the C1-C5 ester of acrylic acid is selected from methyl acrylate, ethyl acrylate, propyl acrylate and hydroxypropyl acrylate, and most preferably the ester of acrylic acid is hydroxypropyl acrylate. Additionally or alternatively, the C1-C5 ester of methacrylic acid may be selected from alkyl esters of methacrylic acid. According to one embodiment, the C1-C5 ester of methacrylic acid is selected from methyl methacrylate, ethyl methacrylate, propyl methacrylate, hydroxypropyl methacrylate, butyl methacrylate and amyl methacrylate, preferably the C1-C5 ester of methacrylic acid is selected from methyl methacrylate, ethyl methacrylate and hydroxypropyl methacrylate, and most preferably the ester of methacrylic acid is hydroxypropyl methacrylate.

[0091] According to one embodiment, the polyacrylate homopolymer is prepared by the polymerization of acrylic acid or methacrylic acid or their salts, and / or the polyacrylate copolymer is prepared by the polymerization of acrylic acid or methacrylic acid or their salts with at least one nonionic compound selected from the group consisting of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, C1-C5 esters of acrylic acid, C1-C5 esters of methacrylic acid, fumaric acid, itaconic acid, acrylamide, crotonic acid, maleic anhydride, isocrotonic acid, aconitic acid (cis or trans), mesaconic acid, erucic acid, undecylenic acid, angelic acid, carraconic acid, hydroxyacrylic acid, acrolein, acrylonitrile, dimethylaminoethyl methacrylate, vinylpyrrolidone, vinylcaprolactam, ethylene, propylene, isobutylene, diisobutylene, vinyl acetate, styrene, α-methylstyrene, methyl vinyl ketone and mixtures thereof.

[0092] The polyacrylate homopolymer can be one polyacrylate homopolymer, or a mixture of two or more polyacrylate homopolymers. For example, the polyacrylate homopolymer can be a mixture of two or three polyacrylate homopolymers. Preferably, the polyacrylate homopolymer is one polyacrylate homopolymer.

[0093] The polyacrylate copolymer can be one polyacrylate copolymer, or a mixture of two or more polyacrylate copolymers. For example, the polyacrylate copolymer can be a mixture of two or three polyacrylate copolymers. Preferably, the polyacrylate copolymer is one polyacrylate copolymer.

[0094] In one embodiment of the present invention, the polyacrylate-containing polymer comprises, preferably consists of, a polyacrylate homopolymer or a polyacrylate copolymer. Alternatively, the polyacrylate-containing polymer is a mixture comprising, preferably consisting of, a polyacrylate homopolymer and a polyacrylate copolymer.

[0095] The carboxylic acid functional groups of the polyacrylate-containing polymer may be at least partially neutralized. According to one embodiment, the dispersant has a degree of neutralization of at least 30 mol%, preferably at least 40 mol%, more preferably at least 60 mol%, and most preferably at least 80 mol%. For example, the carboxylic acid functional groups of the dispersant may be at least partially neutralized by any suitable monovalent cation, such as sodium ion, potassium ion, lithium ion, ammonium ion, calcium ion, and mixtures thereof, preferably with sodium ion, calcium ion, or mixtures thereof, and most preferably with sodium ion. According to one embodiment, the carboxylic acid functional groups of the polyacrylate-containing polymer are at least partially neutralized, preferably with at least 30 mol%, preferably at least 40 mol%, more preferably at least 60 mol%, and most preferably at least 80 mol% of a concentration of sodium ion, potassium ion, lithium ion, ammonium ion, calcium ion, and mixtures thereof.

[0096] As used herein, unless otherwise indicated, the term "partially neutralized" means that the polyacrylate-containing polymer still contains unneutralized carboxylic acid functional groups, i.e., free carboxylic acid functional groups are present. In contrast, the term "completely neutralized" means that any carboxylic acid functional groups present in the polyacrylate-containing polymer are neutralized, i.e., free carboxylic acid functional groups are absent. Methods for partially or completely replacing the protons of the carboxylic acid functional groups with monovalent cations are well known, as are methods for determining whether a polymer is partially or completely neutralized.

[0097] According to one embodiment, the dispersant has an average molecular weight M of 1000 to 15000 g / mol, preferably 2000 to 12000 g / mol, more preferably 3000 to 11000 g / mol, and most preferably 4000 to 10000 g / mol. w .

[0098] According to one embodiment, the dispersant is a polyacrylate homopolymer at least partially neutralized with sodium ions. Preferably, the dispersant has a degree of neutralization of at least 30 mol % and an average molecular weight M of 1000 to 15000 g / mol. w According to an exemplary embodiment, the dispersant is completely neutralized with sodium ions and has an average molecular weight M of 4000 to 10000 g / mol. w Polyacrylate homopolymer.

[0099] The dispersant may be provided as an aqueous solution or a solid, and is preferably provided as an aqueous suspension.

[0100] According to one embodiment, the aqueous suspension comprises the dispersant in an amount of 3 wt.-% or less, preferably in an amount of 0.01 to 2 wt.-%, more preferably in an amount of 0.05 to 1.5 wt.-%, and most preferably in an amount of 0.1 to 0.8 wt.-%, based on the total weight of the aqueous suspension.

[0101] polyvinyl alcohol

[0102] According to one embodiment, polyvinyl alcohol is used as co-dispersant for the aqueous suspension comprising the mineral material defined above and the dispersant.

[0103] Polyvinyl alcohol can be prepared by any method known in the art. For example, polyvinyl alcohol can be made by polymerizing vinyl acetate monomer and then hydrolyzing the polyvinyl acetate. Alternatively, commercially available polyvinyl alcohols such as BF-05, BF-04, BF-14, BF-17, BP-04, or BP-05 from Changchun Petrochemical Co., Ltd. can be used.

[0104] The polyvinyl alcohol may be partially or completely hydrolyzed. According to one embodiment, the polyvinyl alcohol has a degree of hydrolysis of at least 75 mol%, preferably at least 85 mol%, more preferably at least 90 mol%, even more preferably at least 95 mol%, and most preferably at least 98 mol%. According to another embodiment, the polyvinyl alcohol has a degree of hydrolysis of 80 to 100 mol%, and more preferably 85 to 99 mol%, for example 85 to 90 mol% or 98 to 99 mol%.

[0105] According to one embodiment, the polyvinyl alcohol has an average molecular weight M of 10,000 to 150,000 g / mol, preferably 12,000 to 100,000 g / mol, more preferably 14,000 to 50,000 g / mol, and most preferably 16,000 to 30,000 g / mol. w .

[0106] The polyvinyl alcohol can be one polyvinyl alcohol, or a mixture of two or more polyvinyl alcohols. For example, the polyvinyl alcohol can be a mixture of two or three polyvinyl alcohols. Preferably, the polyvinyl alcohol is one polyvinyl alcohol.

[0107] The polyvinyl alcohol can be provided in aqueous solution or solid form. According to one embodiment, the polyvinyl alcohol is provided in solid form. For example, the polyvinyl alcohol can be provided in powder form or in the form of particles, beads or pellets. According to one embodiment, the polyvinyl alcohol is provided in powder form and / or pellet form.

[0108] According to one embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 2 wt.-% or less, preferably in an amount of 0.01 to 1.8 wt.-%, more preferably in an amount of 0.05 to 1.5 wt.-%, even more preferably in an amount of 0.08 to 1 wt.-%, and most preferably in an amount of 0.1 to 0.6 wt.-%, based on the total weight of the aqueous suspension.

[0109] According to one embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 2% by weight or less, based on the total weight of the aqueous suspension, and the polyvinyl alcohol has a degree of hydrolysis of at least 75 mol %. According to another embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 2% by weight or less, based on the total weight of the aqueous suspension, and the polyvinyl alcohol has an average molecular weight M of 10,000 to 150,000 g / mol. w According to yet another embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 2 wt.-% or less, based on the total weight of the aqueous suspension, the polyvinyl alcohol having a degree of hydrolysis of at least 75 mol-%, and the polyvinyl alcohol having an average molecular weight M of 10,000 to 150,000 g / mol. w Preferably, the polyvinyl alcohol has a degree of hydrolysis of at least 85 mol%, more preferably at least 90 mol%, even more preferably at least 95 mol%, and most preferably at least 98 mol%.

[0110] According to one embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 0.1 to 0.6% by weight, based on the total weight of the aqueous suspension, and the polyvinyl alcohol has a degree of hydrolysis of at least 75 mol %. According to another embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 0.1 to 0.6% by weight, based on the total weight of the aqueous suspension, and the polyvinyl alcohol has an average molecular weight M of 12,000 to 100,000 g / mol. w According to yet another embodiment, the aqueous suspension comprises polyvinyl alcohol in an amount of 0.1 to 0.6 wt.-%, based on the total weight of the aqueous suspension, the polyvinyl alcohol having a degree of hydrolysis of at least 75 mol-%, and the polyvinyl alcohol having an average molecular weight M of 12,000 to 100,000 g / mol. w Preferably, the polyvinyl alcohol has a degree of hydrolysis of at least 85 mol%, more preferably at least 90 mol%, even more preferably at least 95 mol%, and most preferably at least 98 mol%.

[0111] The inventors of the present invention have surprisingly discovered that the use of polyvinyl alcohol as a co-dispersant in an aqueous mineral material suspension containing a dispersant can further reduce the viscosity of the mineral material suspension. This offers the possibility of reducing the amount of dispersant in the mineral material suspension and / or providing a mineral suspension with a higher solids content within a workable viscosity range. Since dispersants such as polyacrylates tend to negatively affect optical properties, for example, if they are included in paper coatings, the reduction of dispersants can also have a positive effect on the optical properties of such products. Furthermore, it has been found that the addition of polyvinyl alcohol can further improve the optical properties of the mineral material suspension and products containing it, and can, for example, increase light scattering.

[0112] Furthermore, it was found that polyvinyl alcohol can be added during the production of the aqueous mineral material suspension, and thus, additional processing time for addition can be avoided. It was also found that polyvinyl alcohol reduces the viscosity during grinding, and thus, the addition of specific grinding agents can be omitted. Furthermore, it was found that the long-term stability of the aqueous mineral material suspension can be significantly improved.

[0113] According to yet another aspect of the present invention, there is provided a dispersant composition comprising a combination of a dispersant and a co-dispersant, wherein the dispersant is a polyacrylate-containing dispersant, and the co-dispersant is polyvinyl alcohol.

[0114] Additional components

[0115] The aqueous suspensions of the present invention may contain other additives.

[0116] According to one embodiment, the aqueous suspension comprises a cationic homopolymer based on monomer units such as diallyldialkylammonium salts or polyethyleneimine, alkali metal polyphosphates, carboxymethylcellulose or mixtures thereof.

[0117] Additionally, the aqueous suspension may contain preservatives, abrasives, pH stabilizers, pH adjusters, biocides, or mixtures thereof.

[0118] Examples of suitable preservatives are quaternary ammonium salts, peroxides, perchlorates, tributyltin, zinc, biocidal enzymes, biocidal polypeptides, sulfonamides and mixtures thereof.

[0119] According to one embodiment, the aqueous suspension consists solely of a mineral material, a dispersant and a co-dispersant, the mineral material being selected from alkaline earth mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof, wherein the dispersant is a polyacrylate-containing dispersant and wherein the co-dispersant is polyvinyl alcohol.

[0120] Production method

[0121] According to one aspect of the present invention, there is provided a method for producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, wherein the method comprises the following steps:

[0122] i) providing a mineral material selected from the group consisting of alkaline earth metal mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof,

[0123] ii) providing a dispersant, wherein the dispersant is a polyacrylate-containing dispersant,

[0124] iii) providing a dispersant, wherein the dispersant is polyvinyl alcohol,

[0125] iv) providing water, and

[0126] v) contacting the mineral material of step i), the dispersant of step ii), the co-dispersant of step iii) and the water of step iv).

[0127] The mineral material can be provided in any suitable liquid or dry form. For example, the mineral material can be in the form of a powder and / or a suspension. The suspension can be obtained by mixing the mineral material with a solvent, preferably water. The mineral material to be mixed with the solvent and preferably with water can be provided in any form, for example, as a suspension, slurry, dispersion, paste, powder, wet cake or in a compressed or granulated form, and is preferably provided as a powder.

[0128] According to one embodiment, the mineral material is provided in the form of an aqueous suspension, preferably having a solids content of at least 20% by weight, preferably at least 40% by weight, more preferably at least 60% by weight, and most preferably at least 68% by weight, based on the total weight of the suspension. According to another embodiment, the mineral material is provided in the form of an aqueous suspension, preferably having a solids content of 10 to 78% by weight, preferably 20 to 75% by weight, and most preferably 50 to 72% by weight, based on the total weight of the aqueous suspension.

[0129] The dispersant may be provided in the form of an aqueous solution.

[0130] The co-dispersant may be provided in aqueous solution or solid form. According to one embodiment, the co-dispersant is provided in solid form, preferably in powder form, or in the form of particles, beads or granules, and most preferably in powder form or in the form of particles.

[0131] For the purposes of the present invention, any type of water may be provided in process step iv). According to one embodiment, the water is tap water, deionized water, process water or a mixture thereof. Preferably, the water is tap water.

[0132] According to one embodiment, the water of step iv) is provided in combination with the mineral material of step i) and / or with the dispersant of step ii) and / or with the co-dispersant of step iii), preferably, the water of step iv) is provided in combination with the mineral material of step i).

[0133] The contacting step v) can be carried out in any manner known to the skilled person. For example, the contacting of the mineral material of step i), the dispersant of step ii), the co-dispersant of step iii), and the water of step iv) can be carried out under mixing and / or homogenizing and / or particle segmentation conditions. The skilled person will adjust these mixing and / or homogenizing and / or particle segmentation conditions, such as mixing speed, segmentation, and temperature, according to their process equipment.

[0134] Suitable mixing methods are known to those skilled in the art. Examples of suitable mixing methods are shaking, mixing, stirring, agitation, ultrasonic treatment or inducing turbulent or laminar flow by means of components such as baffles or lamina. Suitable mixing equipment is known to those skilled in the art and can be selected from, for example, agitators such as rotor-stator systems, blade stirrers, propeller stirrers, turbine stirrers or anchor stirrers, static mixers such as tubes comprising baffles or lamina. According to an exemplary embodiment of the present invention, a rotor-stator stirrer system is used. The technician will adjust mixing conditions, such as mixing speed and temperature, according to his process equipment.

[0135] Simultaneous mixing and homogenization can be achieved by means of a plowshare mixer. Plowshare mixers operate on the principle of a mechanically generated fluidized bed. Plowshare blades rotate close to the inner wall of a horizontal cylindrical drum and transport the components of the mixture from the product bed into the open mixing space. The mechanically generated fluidized bed ensures intensive mixing of even large batches in a very short time. Choppers and / or dispersers are used to disperse lumps in dry operations. Equipment that can be used in the process of the present invention is available, for example, from Gebrüder GmbH in Germany. Maschinenbau GmbH.

[0136] According to another embodiment of the present invention, method step v) is carried out in a grinding device, preferably in a ball mill, preferably in combination with a cyclone device, which recycles the agglomerates and / or aggregates formed during method step v) back to the inlet of the grinding device. The cyclone device is capable of separating particulate material (such as particles, agglomerates or aggregates) into smaller and larger particulate material fractions based on gravity.

[0137] According to one embodiment, the mineral material particles are divided into smaller particles during method step v). As used herein, the term "dividing" means breaking the particles into smaller particles. This can be performed by grinding, for example, using a ball mill, hammer mill, rod mill, vibrating mill, roller crusher, centrifugal impact mill, vertical bead mill, attritor, pin mill, hammer mill, pulverizer, shredder, de-lumper, or knife cutter. However, any other device capable of dividing the mineral material into smaller particles during method step v) may also be used.

[0138] According to a preferred embodiment, process step v) is carried out under mixing conditions. Thus, in process step v), the mineral material of step i), the dispersant of step ii), the auxiliary dispersant of step iii) and the water of step iv) are mixed.

[0139] Process step v) can be carried out at room temperature, i.e. at a temperature of 20° C.±2° C., or at other temperatures. According to one embodiment, process step v) is carried out at about 25° C. According to one embodiment of the present invention, process step v) is carried out for at least 1 second, preferably for at least 1 minute, for example for at least 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours or 10 hours.

[0140] The components of the aqueous suspension may be contacted in any suitable order.

[0141] According to one embodiment, step v) comprises the following steps:

[0142] a1) contacting the dispersant of step ii), the co-dispersant of step iii) and the water of step iv), and

[0143] a2) adding the mineral material of step i) to the mixture obtained in step a1).

[0144] According to another embodiment, step v) comprises the following steps:

[0145] b1) contacting the dispersant of step ii) and the co-dispersant of step iii), and

[0146] b2) adding the mineral material from step i) and the water from step iv) to the mixture obtained in step b1), wherein the mineral material and the water are added separately or in combination, preferably in combination.

[0147] According to yet another embodiment, step v) comprises the following steps:

[0148] c1) contacting the dispersant of step ii), the mineral material of step i) and the water of step iv), and

[0149] c2) adding the dispersing aid from step iii) to the mixture obtained in step c1). Preferably, the dispersing aid is added in the form of an aqueous solution.

[0150] According to yet another embodiment, step v) comprises the following steps:

[0151] d) simultaneously contacting the mineral material of step i), the dispersant of step ii), the co-dispersant of step iii) and the water of step iv).

[0152] According to one embodiment, the aqueous suspension formed in step v) has a solids content of 10 to 78 wt.-%, preferably 20 to 75 wt.-%, and most preferably 50 to 72 wt.-%, based on the total weight of the aqueous suspension.

[0153] The Brookfield viscosity of the obtained aqueous suspension may be 10 to 5000 mPa·s at 25°C, preferably 50 to 2000 mPa·s at 25°C, more preferably 100 to 1000 mPa·s at 25°C, and most preferably 150 to 800 mPa·s at 25°C.

[0154] According to one embodiment, the method further comprises a step of grinding and / or dewatering the aqueous suspension during and / or after step v).

[0155] The grinding process can be carried out by all techniques and grinders known to those skilled in the art for wet grinding. The grinding step can be carried out using any conventional grinding apparatus, for example, under conditions such that the refining is primarily caused by impact with the second object, i.e., in one or more of the following: a ball mill, a rod mill, a vibrating mill, a centrifugal impact mill, a vertical bead mill, an attritor, or other such equipment known to those skilled in the art. The grinding can be carried out batchwise or continuously, preferably continuously.

[0156] According to one embodiment of the invention, the grinding is carried out at a temperature of 30 to 110° C., preferably 40 to 100° C. Alternatively, the grinding can be carried out at room temperature, ie at a temperature of 20° C.±2° C.

[0157] After grinding, the mineral material may have a weight median particle size d of 0.05 to 100 μm, preferably 0.1 to 50 μm, more preferably 0.15 to 25 μm, even more preferably 0.25 to 10 μm, and most preferably 0.5 to 2 μm. 50 .

[0158] Alternatively or additionally, the aqueous suspension may be dehydrated during and / or after method step v). This may increase the solids content of the suspension. The suspension may be partially or completely dehydrated by filtration, centrifugation, or a thermal separation process. For example, the suspension may be partially or completely dehydrated by a filtration process such as nanofiltration or a thermal separation process such as evaporation at ambient atmospheric pressure or under reduced pressure.

[0159] According to one embodiment, step v) comprises the following steps:

[0160] e1) contacting the dispersant of step ii), the mineral material of step i) and the water of step iv),

[0161] e2) dehydrating the aqueous suspension obtained in step e1), and

[0162] e3) adding the dispersing aid of step iii) to the dehydrated suspension obtained in step e2), preferably in the form of an aqueous solution, and

[0163] e4) optionally dehydrating the suspension obtained in step e3).

[0164] According to one embodiment, the solids content of the aqueous suspension obtained after dehydration is from 55 to 80% by weight, preferably from 60 to 79% by weight, and more preferably from 65 to 78% by weight, based on the total weight of the aqueous suspension.

[0165] According to a further aspect, there is provided a method of producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, wherein the mineral material is precipitated calcium carbonate, and the method comprises the steps of:

[0166] 1) providing a material containing calcium oxide,

[0167] II) providing a dispersant, wherein the dispersant is a polyacrylate-containing dispersant or a mixture thereof,

[0168] III) providing a dispersant, wherein the dispersant is polyvinyl alcohol,

[0169] IV) preparing milk of lime by mixing water, the calcium oxide-containing material of step I) and the dispersant aid of step III),

[0170] V) carbonating the lime milk obtained in step IV) to form an aqueous suspension of precipitated calcium carbonate, and

[0171] VI) The aqueous suspension obtained in step V) is mixed with the dispersant of step II).

[0172] The calcium oxide-containing material of step 1) can be obtained by calcining a calcium carbonate-containing material. Calcination is a heat treatment process applied to the calcium carbonate-containing material to cause thermal decomposition to form calcium oxide and gaseous carbon dioxide. The calcium carbonate-containing material that can be used in this calcination process is selected from the following: precipitated calcium carbonate, minerals containing natural calcium carbonate (such as marble, limestone and chalk) and mixed alkaline earth carbonate minerals containing calcium carbonate (such as dolomite), or calcium carbonate-rich fractions from other sources. Calcium carbonate-containing waste can also be subjected to a calcination process to obtain the calcium oxide-containing material.

[0173] Calcium carbonate decomposes to calcium oxide (commonly known as quicklime) at approximately 1000°C. The calcining step can be carried out under conditions and using equipment known to those skilled in the art. Typically, calcination can be carried out in furnaces or reactors (sometimes referred to as kilns) of various designs, including shaft furnaces, rotary kilns, multiple-hearth furnaces, and fluidized bed reactors.

[0174] The end of the calcination reaction can be determined, for example, by monitoring the density change, the residual carbonate content (for example by X-ray diffraction) or by monitoring the slaking reactivity by conventional methods.

[0175] According to one embodiment of the present invention, the calcium oxide-containing material of step I) is obtained by calcining a calcium carbonate-containing material, which is preferably selected from precipitated calcium carbonate, natural calcium carbonate minerals such as marble, limestone and chalk, mixed alkaline earth carbonate minerals containing calcium carbonate such as dolomite, and mixtures thereof. For reasons of efficiency, the calcium oxide-containing material preferably has a minimum calcium oxide content of at least 75% by weight, preferably at least 90% by weight, and most preferably 95% by weight, based on the total weight of the calcium oxide-containing material. According to one embodiment, the calcium oxide-containing material consists only of calcium oxide.

[0176] The calcium oxide-containing material may consist of only one type of calcium oxide-containing material. Alternatively, the calcium oxide-containing material may consist of a mixture of two or more types of calcium oxide-containing materials.

[0177] The calcium oxide-containing material can be used in the process of the present invention in its original form (i.e. as raw material), for example in the form of smaller and larger pieces. Alternatively, the calcium oxide-containing material can be ground before use. According to one embodiment of the present invention, the calcium oxide-containing material is a material having a weight median particle size d of 0.1 to 1000 μm, and preferably 1 to 500 μm. 50 in the form of particles.

[0178] In process step IV), milk of lime is prepared by mixing water, the calcium oxide-containing material of step I) and the dispersing aid of step III).

[0179] The reaction of the calcium oxide-containing material with water results in the formation of a milky calcium hydroxide suspension, more commonly known as milk of lime. This reaction is highly exothermic and is also known in the art as "lime slaking." According to one embodiment of the present invention, the temperature of the water used in mixing step IV), i.e., the water used to slake the calcium oxide-containing material, is adjusted to a temperature above 0°C and below 100°C. In other words, the water used to slake the calcium oxide-containing material is adjusted to a temperature within which it is in liquid form. Preferably, the temperature of the water used in mixing step IV) is adjusted to a temperature between 1°C and 70°C, more preferably between 2°C and 50°C, even more preferably between 30°C and 50°C, and most preferably between 35°C and 45°C. A skilled person will appreciate that, due to the highly exothermic slaking reaction and / or due to the mixing of materials of different temperatures, the initial temperature of the water need not necessarily be the same as the temperature of the mixture prepared in step IV).

[0180] According to one embodiment, step IV) comprises the following steps:

[0181] A1) mixing the calcium oxide-containing material of step I) with water, and

[0182] A2) adding the dispersing aid of step II) to the mixture of step A1).

[0183] Preferably, process step A2) is carried out after completion of the reaction between the calcium oxide-containing material and water in step I), ie after complete slaking of the lime.

[0184] According to yet another embodiment, step IV) comprises the following steps:

[0185] B1) mixing the dispersant from step III) with water, and

[0186] B2) adding the calcium oxide-containing material of step I) to the mixture of step B1).

[0187] According to yet another embodiment, in step IV), the calcium oxide-containing material of step I), the dispersant aid of step III), and water are mixed simultaneously.

[0188] The dispersant of step III) can be added in one or more portions in step IV). According to one embodiment, the dispersant is mixed with water and the calcium oxide-containing material in step IV) by adding the dispersant in one portion or in two, three, four, five or more portions.

[0189] Method step IV) can be carried out at room temperature, i.e., at a temperature of 20°C ± 2°C, or at an initial temperature of 30 to 50°C, preferably 35 to 45°C. Since the reaction is exothermic, the temperature is generally raised to a temperature of 70°C to 85°C during step IV). According to a preferred embodiment, method step IV) is carried out using mixing, stirring or agitation, for example, using mechanical stirring. Suitable process equipment for mixing, stirring or agitation is known to those skilled in the art. The progress of the aging reaction can be observed by measuring the temperature and / or conductivity of the reaction mixture. It can also be monitored by turbidity control. Alternatively or additionally, the progress of the aging reaction can be visually checked.

[0190] According to one embodiment, the calcium oxide-containing material and water are mixed in a mass ratio of 1:4 to 1:15. According to a preferred embodiment, the calcium oxide-containing material and water are mixed in a mass ratio of 1:5 to 1:9 in step IV).

[0191] According to one embodiment, the milk of lime of step IV) has a solids content ranging from 5 to 25% by weight, preferably from 10 to 20% by weight and most preferably from 10 to 15% by weight, based on the total weight of the milk of lime.

[0192] According to one embodiment, the milk of lime of step IV) has a Brookfield viscosity of 10 to 1000 mPa·s at 25° C., more preferably 20 to 800 mPa·s at 25° C., and most preferably 50 to 600 mPa·s at 25° C. According to one embodiment, the Brookfield viscosity is measured at 100 rpm.

[0193] It is within the scope of the present invention that additional water may be introduced during the slaking reaction in order to control and / or maintain and / or achieve the desired solids content or Brookfield viscosity or temperature of the milk of lime.Process step IV) can be carried out as a batch process, a semi-continuous process or a continuous process.

[0194] In method step V), the lime milk obtained from step IV) is carbonated to form an aqueous suspension of precipitated calcium carbonate. Carbonation is carried out by means and conditions known to those skilled in the art. The introduction of carbon dioxide into the lime milk rapidly results in the formation of carbonate ions (CO3 2- ) formation, and therefore form the required concentration of calcium carbonate. Especially, considering the reaction involved in the carbonation process, the carbonation reaction can be easily controlled. Carbon dioxide dissolves according to its partial pressure, by forming carbonic acid (H2CO3) form carbonate ion, and in this alkaline solution, carbonic acid dissociates into its composition hydrogen ion and carbonate ion. Once the ion product of calcium carbonate is enough greater than the solubility product, calcium carbonate precipitates. Meanwhile, the hydrogen ion of the dissociated hydroxide ion is neutralized. Therefore, the ion product of calcium hydroxide will be less than the solubility product, and it will continue to dissolve. As long as CO2 is bubbled into the solution, this just continues to occur, until all calcium hydroxides are consumed, or are trapped in the calcium carbonate crystal structure. The inventor believes that the method shown in this patent application has significantly minimized the trapping of calcium hydroxide by avoiding nucleation / growth near the calcium hydroxide surface, thereby causing it to be almost completely consumed.

[0195] According to one embodiment of the present invention, in step V), by being fed into the industrial gas of pure gaseous carbon dioxide or the carbonic acid gas that contains at least 10 volume % in the milk of lime, carry out carbonating.Can easily observe the progress of carbonating reaction by measuring specific conductivity, density, turbidity and / or pH.In this respect, the pH of the milk of lime before adding the carbonic acid gas will be greater than 10, is generally 11 to 12.5, and will constantly reduce until reaching approximately 7 pH.Can stopped reaction now.

[0196] The conductivity decreases slowly during the carbonation reaction and drops rapidly to a low level when precipitation is complete. The progress of carbonation can be monitored by measuring the pH and / or conductivity of the reaction mixture.

[0197] According to one embodiment of the present invention, the temperature of the lime milk obtained from step IV) and used in step V) is adjusted to be in the range of 5°C to 95°C. A skilled person will appreciate that, due to the exothermic carbonation reaction and / or due to the mixing of substances with different temperatures, the initial temperature of the lime milk is not necessarily the same as the temperature of the mixture prepared in step IV). According to one embodiment of the present invention, step V) is carried out at a temperature of 5 to 95°C, preferably 30 to 70°C, and more preferably 40 to 60°C.

[0198] Process step V) can be carried out as a batch process, a semi-continuous process, or a continuous process. According to one embodiment, the process of the invention comprising process steps I) to V) is carried out as a batch process, a semi-continuous process, or a continuous process. Process step V) can include any suitable mixing method known to the skilled person, for example any of the mixing methods described above.

[0199] According to one embodiment, the method further comprises a step of dehydrating the aqueous suspension during and / or after step V), as described in more detail above.

[0200] According to a further embodiment, the method according to the invention for producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant may comprise the further step of screening the aqueous suspension after step v) or step VI. Such screening may be performed using any conventional screening means known to the skilled person. Screening may be performed using one or more mesh sizes. Suitable mesh sizes are, for example, 180 μm, 90 μm, 63 μm or 45 μm.

[0201] Aqueous dispersions and applications

[0202] According to a further aspect of the present invention, there is provided an aqueous suspension obtainable by the method according to the present invention.

[0203] According to one embodiment, there is provided an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant,

[0204] wherein the mineral material is selected from alkaline earth metal mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof,

[0205] The dispersant is a polyacrylate-containing dispersant, and

[0206] The dispersant is polyvinyl alcohol.

[0207] The aqueous dispersion comprises:

[0208] a dispersant in an amount of 3% by weight or less based on the total amount of the aqueous suspension,

[0209] a dispersant in an amount of 2% by weight or less based on the total amount of the aqueous suspension, and

[0210] The mineral material is present in an amount of 10 to 78% by weight, based on the total weight of the aqueous dispersion.

[0211] The aqueous suspension obtainable by the method of the present invention can be used in a variety of materials and applications. According to one embodiment of the present invention, the aqueous suspension is used in paper applications, packaging applications, polymer applications, or water treatment applications. According to one embodiment, the aqueous suspension of the present invention is used in a paper coating composition. Thus, a paper coating composition comprising the aqueous suspension according to the present invention is provided. The inventors of the present invention have surprisingly discovered that a paper coating composition comprising the aqueous suspension according to the present invention can improve the optical and / or mechanical properties of a coated paper product, such as a paper substrate or paperboard. Specifically, it has been discovered that the water retention and mechanical surface strength of the paper product can be improved.

[0212] The scope and focus of the present invention will be better understood based on the following examples, which are intended to illustrate certain embodiments of the invention and are non-limiting. Example

[0213] 1. Methods

[0214] Particle size distribution

[0215] The median particle size d is determined by weight measurement using the sedimentation method. 50 (weight), the sedimentation method is the analysis of sedimentation behavior in a gravitational field. TM The measurement was performed at 5120°C. The method and instrument are known to those skilled in the art and are commonly used to determine the particle size distribution of fillers and pigments. The measurement was performed in a 0.1 wt% aqueous solution of Na₄P₂O₇. A high-speed stirrer was used to disperse the sample and ultrasound was applied. The procedure and instrument are known to those skilled in the art and are commonly used to determine the particle size of fillers and pigments.

[0216] 1.2. Viscosity measurement

[0217] The Brookfield viscosities in Examples 1 to 10 were measured using a Brookfield DV-II+ Pro viscometer at 25°C ± 1°C and 100 rpm using an appropriate spindle from the Brookfield RV spindle set and are expressed in mPa·s. A spindle appropriate to the viscosity range to be measured was selected from the Brookfield RV spindle set. For a viscosity range of <200 mPa·s, spindle 2 was used; for a viscosity range of 200 to 800 mPa·s, spindle 3 was used; for a viscosity range of 400 to 1600 mPa·s, spindle 4 was used; and for a viscosity range of 800 to 3200 mPa·s, spindle 5 was used.

[0218] The Brookfield viscosity in Example 11 was measured by a Brookfield DV-III Ultra viscometer at 100 rpm at 24°C ± 3°C using an appropriate spindle from the Brookfield RV spindle set and is expressed in mPa·s. Once the spindle is inserted into the sample, the measurement is started at a constant speed of 100 rpm. The reported Brookfield viscosity value is the value displayed 60 seconds after the start of the measurement. For the viscosity range of 200 to 800 mPa·s, spindle No. 3 is used, for the viscosity range of 400 to 1600 mPa·s, spindle No. 4 is used, and for the viscosity range of 800 to 3200 mPa·s, spindle No. 5 is used.

[0219] 1.3.ACAV viscosity

[0220] ACAV viscosity measurements are performed in an ACAV-2 viscometer. One liter of coating composition is placed in the viscometer's probe chamber and the automatic program is activated. At the end of the measurement, a graph showing the relationship between viscosity and shear rate is obtained. Shear rate is a measure used to describe the flow of a liquid through a channel. More specifically, shear rate is the rate at which the velocity of a fluid under shear changes across its thickness, also known as its velocity gradient. For this application, the ACAV viscosity is taken at a shear rate of 500,000 1 / s.

[0221] 1.4. Water retention rate

[0222] Using AA-GWR water retention meter (GRADEK TM The water retention rate is determined by a water retention meter (DT Paper Science). It consists of a measuring chamber in which a piece of test paper (test blotter) is placed and covered with a perforated plastic sheet (test filter PCTE), where both paper and sheet are commercially available from water retention meter manufacturers.

[0223] 10 mL of the coating composition to be tested is added to the measuring chamber. The AA-GWR device applies a sufficient amount of pressure to the coating composition, causing all or some of the water and water-soluble substances contained in the composition to pass through the perforated plastic sheet and penetrate the test paper. A pressure of 0.5 bar is applied for 90 seconds. The difference in weight between the test paper before and after the test yields a water retention value, which corresponds to the weight of water and water-soluble substances contained in the composition that permeated the test paper during the test. The lower the water retention value, the better the printability of the resulting paper.

[0224] 1.5.pH

[0225] Using the Mettler Toledo Seven Easy pH meter and the Mettler Toledo The Expert Pro pH electrode measures the pH of suspensions or solutions at 25°C. The instrument is first calibrated (by the stepwise method) at three points using commercially available buffer solutions (Sigma-Aldrich, USA) with pH values of 4, 7, and 10 at 20°C. The reported pH value is the endpoint value detected by the instrument (the endpoint is when the measured signal differs by less than 0.1 mV from the average value of the last 6 seconds).

[0226] 1.6. Glossiness

[0227] Paper gloss was measured according to EN ISO 8254-1:2009, TAPPI 75° (%) using an LGDL-05.3-lab instrument (Lehmann Messsysteme GmbH, Germany).

[0228] 1.7. Brightness and UV

[0229] Brightness was measured according to standard ISO 2470-2:2008 using an Elrepho 450 spectrometer (light: D65, viewing angle: 10°, Datacolor, Germany).

[0230] 1.8.PPS roughness

[0231] The paper surface roughness was measured using an L&W PPS tester (Lorentzen & Wettre, Sweden) according to DIN ISO 8791-4 at a pressure of 1.0 mPa using the soft component PPS 1.0 (μm).

[0232] 1.9. Setoff Optical Ink Density

[0233] The offset optical ink density was measured according to the laboratory standard “Wegschlagtest Offset” using the test device “Prüfbau Multipurpose Printability Testing Instrument MZII” (Prüfbau, Germany).

[0234] For the test, the print was countered with a defined counter paper in the second printing unit at a specific time to see how quickly the print is fixed / absorbed in the paper and therefore how quickly the ink transfer to the counter paper will decrease with increasing delay.

[0235] Device settings: Ink unit temperature: 23°C

[0236] Contact pressure: 200N / cm (800N device setting)

[0237] Printing speed: 0.5m / s

[0238] Ink volume: 300mm 3

[0239] Counter time: 15, 30, 60 and 120s

[0240] Printing ink: Test color (Prüfbau, Germany)

[0241] Normkunstdruck APCO II / II (Counter printing paper): 150g / m 2

[0242] Perform the device settings on the test device. Set the timer to 5 seconds. Clamp the opposing paper to the clamping bolts in such a way that it can be easily attached to the print sample carrier after proofing. Place a clean metal printing plate on the second printing unit. Place the print sample carrier with the paper to be tested in front of the first printing unit. Apply ink to the first ink section of the rubber roller and start the dispensing unit. After 30 seconds, place the metal printing plate and ink it for 30 seconds. Place the inked plate on the first printing unit and start it. Start the stopwatch during the start-up release. Use the timer to track the print sample carrier so that the printing process can be stopped immediately.

[0243] Subsequently, the counter paper, along with the printed sample carrier, is inserted into the gap of the second printing unit, and after 15 seconds, a first counterpressure is applied using a lubricating rod. This allows four count times (15, 30, 60, and 120 seconds) to be reproduced consecutively on one print. To prevent possible picking or sticking, the test strip is separated from the counter printing paper immediately after reverse printing. A sample strip is then printed to check the printed image for errors and the required ink quantity. For each subsequent print run, the dispensing unit and printing plate are recolored.

[0244] For evaluation, the prints and various gradations on the opposing paper were punched out into 1.9 x 2.9 cm strips using a punch press and attached to a table with 5 areas ranging from print to reversal time of 120 seconds. To determine the results, the reversed prints were measured using an Epson dual-lens flatbed scanner and the image analysis software "Print Target" (smear module, optical density), and the values obtained are reported as the corresponding reversal times.

[0245] 1.10. Dry Pick

[0246] Dry picking refers to how well a paper resists picking in the absence of dampening solution. Pick resistance, also known as surface strength, refers to how well a paper can withstand forces applied perpendicular to its surface (such as those generated by a sticky ink film during printing) without cracking or picking. Picking can include delamination of paper layers and / or partial or complete removal of the paper coating.

[0247] The dry brushing was measured according to the laboratory standard “Trockenrupfen” using the test device “Prüfbau Multipurpose Printability Testing Instrument MZII” (Prüfbau, Germany).

[0248] Device settings: Ink unit temperature: 23°C

[0249] Contact pressure: 150N / cm (600N device setting)

[0250] Printing speed: 0-3m / s (increasing)

[0251] Ink volume: 200mm 3

[0252] Counter time: 15, 30, 60 and 120s

[0253] Printing inks: Raised test colors (Prüfbau, Germany): No. 1 (low tack), No. 2 (medium tack), and No. 3 (high tack)

[0254] Printing paper: Normkunstdruck APCOII / II 150g / m 2

[0255] Set up the test apparatus. Fill the ink pipette and place the printed sample carrier with the paper to be tested in front of the second printing unit. Apply ink to the first inking section of the rubber roller with a 30-second dispensing time. Then place the blanket printing plate on the roller, and after another 30 seconds, place the inked blanket printing plate on the second printing unit. Using the lubrication rod on the right side of the apparatus, guide the sample carrier under the blanket printing plate until contact is established between the blanket printing plate and the sample at point 0 of the 200 mm print path. Place the blanket printing plate on the printing unit in such a way that any gaps in the blanket lifter do not cause any interruptions in printing over the 200 mm long print path. Once the blanket printing plate is in place on the printing surface, switch on the printing unit drive (speed) and perform the plucking test.

[0256] Depending on the pick strength of the paper, choose the pick test color numbers 1-3 with the appropriate tack. For each test, recolor the dispensing section and blanket printing plate.

[0257] In the fuzzing test with increasing speed, a final speed of 3 m / s corresponds to a pressure distance of 200 mm. The start of fuzzing is the point at which the first fibers or pigment particles on the printed paper strip are lifted or torn from the paper surface. Mark this point on the side with a pencil. Measure the distance from the start of printing to the start of fuzzing and enter it in mm under the corresponding color number in the equation given below. Use the following equation to calculate the start of fuzzing in m / s:

[0258]

[0259] The higher the dry nap value, the better the printability of the paper substrate.

[0260] 1.11. Deltack

[0261] According to the laboratory standard "Messung der The deltack is measured using the "Prüfbau Deltack" (Prüfbau, Germany) testing device "im Offset Druck". The deltack reflects the surface strength of the printed substrate in offset printing and indicates the force with which parts of the substrate (e.g. fibers, pigments, etc.) are torn out of the substrate. For the test, a paper sample is attached to a load cell of a rotating cylinder, which is repeatedly passed through the printing unit until rupture is visible and the force is measured.

[0262] Device Settings:

[0263] Pressure sample carrier: Applicable to substrate (for paper) or 263 μm rubber strip (for cardboard)

[0264] Color volume: 200mm for paper 3 , and for cardboard is 300mm 3

[0265] System temperature: 23°C

[0266] Measuring unit selection: 1

[0267] Printing unit selection: B

[0268] Printing tension: 1000N

[0269] Measurement interval: 4s

[0270] Number of measurement cycles: 20

[0271] Printing speed: 1m / s

[0272] Minimum waiting time: 3s

[0273] Pressure full turn: Activated

[0274] Average value range: 60-160mm

[0275] Secure the paper strip to be tested with tape at both ends, ensuring that the holes from the subsequent punching process are located within the tape area. Use double-sided tape to affix the cardboard strip to be tested to the metal printing plate 63.45. Perform two measurements on each sample. If the results deviate significantly, perform additional replicates to obtain more representative results.

[0276] Place the paper sample to be tested with the corresponding side facing up in the tensile measuring fixture and on the compression sample carrier. Make sure that the sample has not yet triggered the tension on the measuring unit. Use a compression sample carrier to apply the coating on the opposite measuring unit. This ensures that the amount of ink is reduced during the initial printing and is replenished with continuous printing on the printing roller. This results in a more uniform increase in viscosity over time / cycle. Wipe the required amount of ink into the ink distribution system for 30 seconds. Then ink the blanket printing plate for another 30 seconds. After inking, place the printing plate on printing unit B. Apply pressure using the "Start measurement" and "Press 1 / 2 turn" fields. After clicking "Start", the test strip is repeatedly passed through the pressure section under the same settings.

[0277] For measuring cardboard samples, place the rubber strip with the darker side facing up in the tensile measurement fixture and on the pressure sample carrier. Make sure the rubber strip has not yet triggered the tension on the measuring unit. Place the prepared metal printing plate with the cardboard sample to be tested on printing unit B. Apply the required amount of ink to the ink dispensing system for 30 seconds. Then ink the rubber printing plate for an additional 30 seconds. After inking, place the printing plate on printing unit A. Apply pressure using the "Start measurement" and "Press 1 / 2 turn" fields. Apply pressure using the "Start measurement" and "Press 1 / 2 turn" fields. After clicking "Start," the test strip is repeatedly passed through the pressure section with the same settings.

[0278] After each complete rotation, the sample is stopped for a specified time. During this time, the surface is inspected for damage. Any damage detected during the corresponding pass is clearly marked with the letters A-Z and the numbers 1-9. Once damage is confirmed, the measurement is stopped.

[0279] While the sample is in motion, the increasing force curve is observed in the device software so that it can be optimized or adjusted for another strip, if necessary. Generally speaking, the forces (initial and maximum forces) increase with more colors or higher printing speeds. The smaller the measurement interval, the steeper (more gradual) the rise in the force-time diagram, and thus the smaller the force difference obtained with each pass, which yields a more detailed image. Delta is expressed in Newtons, based on a strip width of 5 cm [N / 5 cm].

[0280] 1.12. Bulk

[0281] The formula for bulk is thickness (mm) × basis weight (g / m 2 ) × 1000. Using the values for Thickness and Basis Weight, Bulk can be calculated.

[0282] 2. Materials

[0283] Table 1: Fillers

[0284]

[0285] Table 2: Dispersants

[0286]

[0287]

[0288] Table 3: Polyvinyl alcohol (PVOH)

[0289] PVOH Molecular weight Degree of hydrolysis (mol%) Degree of polymerization PVA 1 18 000-22 000 98-98.8 400-500 PVA 2 22 000-27 000 98-98.8 500 PVA 3 50 000-55 000 >98 1100-1200 PVA 4 75 000-80 000 >98 1700-1800 PVA 5 21 000-27 000 86-89 420-550 PVA 6 27 000-32 000 86-89 550-650 PVA 7 31 000-33 000 69-72 700 PVA 8 9 000-10 000 80 --

[0290] All PVOH grades except PVA 8 were supplied in pellet or powder form by Changchun Petrochemical Co., Ltd. PVA 8 was obtained from Sigma Aldrich.

[0291] Table 4: Materials used in paper coating compositions

[0292]

[0293] 3. Examples

[0294] In the following examples, polyvinyl alcohol was used in the form of a preformulated aqueous solution having a PVOH concentration of 20 wt % based on the total weight of the solution. The 20 wt % PVOH preformulated solution was obtained by dissolving PVOH pellets or powder in water (85-90°C) with stirring until no particles were visible. The preformulated solution was cooled to room temperature and used within one week of preparation.

[0295] In Examples 1-4 and 11, the mineral material was provided in the form of an aqueous suspension having a solids content of approximately 50% by weight. The suspension was further diluted until it could be homogeneously mixed with 0.4-0.5% of a dispersant. This was typically the case at a solids content of 30 to 40% by weight.

[0296] Subsequently, the water was evaporated on a hot plate or using an evaporation device until a concentration of about 68% by weight or about 72% by weight was reached. Additional dispersant was added if necessary. The total amount of dispersant in the final composition is shown in Tables 5 to 7 below.

[0297] In the next step, PVOH is added using the preformulated solution. If a large amount of water is added along with the preformulated PVOH solution, for example if the solids content of the mineral suspension changes by more than 1 wt. %, further evaporation is performed.

[0298] Once the suspension has cooled to room temperature, the viscosity is measured on a Brookfield viscometer using a suitable spindle.

[0299] 3.1. Example 1

[0300] Table 5: Composition and viscosity of the aqueous mineral suspension prepared according to Example 1 (comp.: comparative)

[0301]

[0302] Aqueous mineral material suspensions were prepared by adding 0.5 wt % PVA 1, 0.75 wt % PVA 2, or 0.4 wt % of a mixture of 2 / 7 PVA 1 and 5 / 7 PVA 2 to a 68 wt % suspension of pigment B containing 0.4 wt % or 0.5 wt % dispersant A. In addition, comparative suspensions without PVOH were prepared. The compositions of the tested suspensions are listed in Table 5 above.

[0303] From Table 5 and Figure 1 It can be seen that the viscosity decreases from 3036 mPa s for the pigment B suspension without any PVOH to 105 mPa s for the pigment B suspension containing PVOH (PVA 1) and 110 mPa s for the filler B suspension containing PVOH (PVA 2). The viscosity of the pigment B suspension containing 0.4 wt% dispersant A is too high to be measured without the addition of PVOH. The viscosity of the final suspension (pigment B suspension + mixture of PVA 1 and PVA 2 + dispersant A) is 156 mPa s. In comparison, the 0.75 wt% and 1 wt% dispersant A suspensions without PVOH (pigment B suspension + dispersant A) have viscosities of 1094 mPa s and 85 mPa s, respectively.

[0304] Increasing the amount of dispersant A reduces the viscosity of the suspension of Pigment B. Surprisingly, it was found that the viscosity of the suspension of Pigment B could be reduced to a similar level when PVOH was used and the amount of dispersant A was reduced by at least half. PVOH of different molecular weights could be used, showing that both PVA 1 and PVA 2 worked, as did their combination (mixture).

[0305] 3.2. Example 2 - Longer Chain Length PVOH

[0306] Table 6: Composition and viscosity of the suspension prepared according to Example 2 (comp.: comparative)

[0307]

[0308] Aqueous mineral material suspensions were prepared by adding 0.5 wt% PVA 3 or PVA 4 to a 68 wt% suspension of Pigment A containing 0.5 wt% Dispersant A. In addition, comparative suspensions without PVOH were prepared. The compositions of the tested suspensions are listed in Table 5 above.

[0309] From Table 6 and Figure 2It can be seen that the viscosity decreases from 740 mPa·s for the Pigment A suspension without any PVOH to 332 mPa·s for the Pigment A suspension containing PVOH (PVA 3) and 321 mPa·s for the Pigment A suspension containing PVOH (PVA 4). In comparison, the 1 wt% Dispersant A suspension without PVOH (Pigment A suspension + Dispersant A) has a viscosity of 77 mPa·s.

[0310] In addition, longer chain length PVOH can be used to reduce viscosity, replacing some of the dispersant. This shows that larger filler particle sizes require less dispersant to reduce viscosity. In the case of the coarser particle size of Pigment A, the viscosity is not reduced as much, however, the surprising viscosity-lowering effect of using PVOH is still visible.

[0311] 3.3. Example 3 - Partially Hydrolyzed PVOH

[0312] Table 7: Composition and viscosity of the suspension prepared according to Example 3 (comp.: comparative)

[0313] test# Mineral materials dispersants PVOH Viscosity [m·Pas] 3.1 (comp.) Pigment A 0.5 wt% Dispersant A -- 740 3.2 (comp.) Pigment A 1.0 wt% Dispersant A -- 77 3.3 Pigment A 0.5 wt% Dispersant A 0.5 wt% PVA 5 389 3.4 Pigment A 0.5 wt% Dispersant A 0.5 wt% PVA 6 207

[0314] An aqueous mineral material suspension was prepared by adding 0.5 wt% PVA 4 to a 68 wt% suspension of Pigment A containing 0.5 wt% Dispersant A. In addition, a comparative suspension without PVOH was prepared. The compositions of the tested suspensions are listed in Table 7 above.

[0315] In addition, an aqueous mineral material suspension was prepared by premixing a 20 wt% PVA 6 solution in a 1:1 weight ratio with dispersant A. The PVA 6 dispersant solution was added to the filler A suspension before evaporation to 68% in an amount such that a concentration of 0.5 wt% dispersant A and 0.5 wt% PVA 6 was achieved in the final suspension.

[0316] From Table 7 and Figure 3 As can be seen, the viscosity decreases from 740 mPa·s for the Pigment A suspension without any PVOH to 389 mPa·s for the Pigment A suspension with PVOH (PVA 5). The viscosity in Test #3.4 using the PVOH / dispersant premix was 207 mPa·s. For comparison, the 1 wt% Dispersant A suspension without PVOH (Pigment A suspension + Dispersant A) had a viscosity of 77 mPa·s.

[0317] It shows that larger particle sizes require less dispersant to reduce viscosity. The partially hydrolyzed PVOH used can also be used to replace a portion of the dispersant, although it is not as effective as for smaller particle sizes. In the previous examples, the PVOH was added after the dispersant was added, however, as shown in this example using PVA 6, the PVOH can also be added simultaneously with the dispersant.

[0318] 3.4. Example 4 - Thermal Concentration

[0319] The suspensions obtained from test runs #1.1 to 1.5 of Example 1 were evaporated to a solids content of 72% by weight.

[0320] Depend on Figure 4 It can be seen that the viscosity of (Pigment B suspension + mixture of PVA 1 and PVA 2 + Dispersant A) is 367 mPa·s. In comparison, the 0.5 wt %, 0.75 wt % and 1 wt % Dispersant A slurries without PVOH (Pigment B slurry + Dispersant A) have viscosities of 4290 mPa·s, 351 mPa·s and 278 mPa·s, respectively.

[0321] It has been shown in previous examples that PVOH can be used to reduce the dispersant concentration required to reduce the viscosity of a suspension having a solids content of 68 wt %. This can also be achieved at higher slurry concentrations, as shown in this example at a solids content of 72 wt %.

[0322] 3.5. Example 5 - Magnesium Hydroxide

[0323] A 65 wt% Pigment C suspension was prepared by adding water to Pigment C powder with stirring. For the inventive example (grey line with squares), 0.25 wt% PVOH (PVA 1) was added. Dispersant B was added in increments and the viscosity was measured after each addition. Figure 5 It can be seen that the presence of PVOH reduces the amount of dispersant required to achieve a specific viscosity compared to a suspension without PVOH.

[0324] 3.6. Example 6 - Calcium Hydroxide

[0325] A pre-formulated unstabilized 30 wt% suspension of Pigment D was homogenized with Dispersant C and 0-0.6 wt% PVOH. The PVOH used was PVA 1. Dispersant C was also added in increments with stirring and the viscosity was measured after each addition. Figure 6 It can be seen that the presence of 0.6 wt% PVOH (grey line with diamonds) results in lower viscosity at lower dispersant concentrations compared to the suspension without PVOH.

[0326] 3.7. Example 7 (Pilot Plant Test)

[0327] An aqueous suspension of Pigment A with a solids content of 22.1% by weight was used as the starting material. 0.4-0.8% by weight of Dispersant A (and, if used, 0.5-0.8% by weight of PVA 2) were added (according to the amounts outlined in Table 8 below). The resulting suspension was first dehydrated to a solids content of 55% by weight using an Andritz centrifuge and then to a solids content of 72% by weight using an Epcon evaporator (final slurry).

[0328] The viscosity of the final suspension without PVOH (comparative sample) was 150 mPa·s, while the viscosity of the slurry 3613 / 2 of the present invention containing PVOH was 164 mPa·s, even though the concentration of the dispersant was halved. However, increasing the concentration of PVOH did not further reduce the viscosity. The results of the viscosity measurements are shown in Tables 8 and Figure 7 middle.

[0329] Table 8: Composition and viscosity of the aqueous mineral suspension prepared according to Example 7 (INV = Invention)

[0330] sample Dispersant A [wt%] PVA 2 [wt%] Viscosity [mPa·s] 3613 / 1 0.8 0 150 3613 / 2(INV) 0.4 0.5 164 3613 / 3(INV) 0.4 0.8 180 3613 / 4(INV) 0.8 0.8 216

[0331] 3.8. Example 8 (Pilot Plant Test)

[0332] An aqueous suspension containing a mixture of Pigment E and Pigment F (solids content 76 wt%) and 0.29 wt% of Dispersant D was provided as feed material. Dispersant E and PVOH (if used) were added to the feed material, and the sample was then ground in a 200 L horizontal mill (in the presence of 245 kg of grinding beads with a size of 1.8 to 2.0 mm) until 95 wt% of the pigment had a particle size of less than 2 μm. The ground suspension was treated with 250 ppm of AMP and sieved at 63 μm.

[0333] The results demonstrate that for samples with solids contents up to 72 wt %, PVOH can be added prior to grinding. The results of the viscosity measurements are shown in Tables 9 and Figure 8 Among them Figure 8 The bars in the graph refer to viscosity, and the gray line refers to solid content.

[0334] Table 9: Composition and viscosity of the aqueous mineral suspension prepared according to Example 8 (INV = Invention)

[0335]

[0336] 3.9. Example 9 - Application Test on Lightweight Coated (LWC) Paper

[0337] Table 10: Composition of the coating composition prepared and used in Example 9 (pph: parts per hundred, dry weight; weight % is based on the total weight of dry pigment (except solids content, where weight % is based on the total weight of the suspension))

[0338]

[0339]

[0340] Paper coating trials 1 and 2 were carried out on a pilot coater under the following conditions:

[0341] -Speed: 1400m / min

[0342] -Base paper: 46g / m 2 Commercial LWC substrates containing wood

[0343] - Rigid blade applied, blade thickness: 0.5mm

[0344] -Coating amount: 10.5g / m 2 / side

[0345] -Calendaring speed: 300m / min

[0346] -Line load 300kN / m

[0347] - Temperature: 90℃

[0348] Table 11: Results of Paper Coating Test 1

[0349] Coating composition 1 (Comparison) 5 6 10 Brookfield viscosity 100rpm mPa·s 1120 1095 1140 920 ACAV at 500,000 1 / s mPa·s 77 79 83 98 Water retention rate <![CDATA[g / m 2 ]]> 104 91 68 98 pH 8.8 8.8 8.8 8.8 Glossiness ％ 48.4 48.7 49.0 48.5 Brightness+UV ％ 83.5 84.1 84.5 84.2 PPS roughness μm 1.06 1.02 1.02 1.01 Density of smudged optical ink after 15 seconds 40.5 39.7 40.2 41.1 Dry brushing m / s 0.7 1.1 1.05 1.6 Deltack 0.69 0.80 0.83 0.83

[0350] It can be seen that coating composition 10, which includes the same amount of dispersant as comparative coating composition 1, has higher brightness and significantly improved dry pick and delta (affecting coating strength, resulting in less "picking" during printing) while having good gloss and good roughness.

[0351] Comparison of inventive coating compositions 6 and 10, wherein coating composition 6 has the same amount of dispersant as coating composition 10 but only half the amount, shows slightly higher paper gloss and brightness with similar PPS roughness.

[0352] Comparison of inventive coating compositions 5 and 6, where coating composition 5 contains the same amount of dispersant but only half the amount of PVOH, shows that both compositions exhibit very similar paper properties, both optically and in terms of surface strength.

[0353] Furthermore, the results summarized in Table 11 show that similar Brookfield viscosities and improved water retention can be achieved without the need for rheology modifiers by incorporating PVOH into paper coating compositions (see Coating Compositions 5 and 6). The ACAV high shear viscosity increases as PVOH is introduced into the mineral suspension, and this viscosity increases further as the amount of PVOH increases. Based on these results, Coating Compositions 5 and 6 demonstrate good results.

[0354] Table 12: Results of Paper Coating Trial 2

[0355] Coating composition 1 (Comparison) 3 8 9 Brookfield viscosity 100rpm mPa·s 1120 995 1095 1050 ACAV at 500,000 1 / s mPa·s 77 80 91 81 Water retention rate <![CDATA[g / m 2 ]]> 104 108 70 74 pH 8.8 8.8 8.8 8.8 Glossiness ％ 48.4 51.0 49.5 51.2 Brightness+UV ％ 83.5 83.6 84.8 85.1 PPS roughness μm 1.06 0.97 1.01 0.95 Density of smudged optical ink after 15 seconds 40.5 39.0 39.7 40.0 Dry brushing m / s 0.7 0.35 0.7 1.45 Deltack 0.69 0.66 0.76 0.91

[0356] The results summarized in Table 12 show that by incorporating a PVOH-containing mineral suspension into a paper coating composition, similar surface strength can be achieved despite reducing the amount of latex binder by 1% by weight, based on the total weight of dry pigment (see coating compositions 1 and 8). Furthermore, significantly higher surface strength was achieved despite reducing the amount of starch binder by 1.5% by weight, based on the total weight of dry pigment (see coating compositions 1 and 9). Paper gloss and UV brightness improved as the amount of PVOH incorporated and the total binder amount decreased.

[0357] Furthermore, the results in Table 12 demonstrate that similar Brookfield viscosities and improved water retention can be achieved without a rheology modifier (see coating compositions 1 and 9, and coating compositions 3 and 8), with minimal impact on high shear viscosity.

[0358] 3.10. Example 10 - Application test on cardboard

[0359] Table 13: Composition of the coating composition prepared and used in Example 10 (pph: parts per hundred, dry weight; weight % is based on the total weight of dry pigment (excluding solid content, where weight %

[0360] is based on the total weight of the suspension)

[0361]

[0362] Paperboard coating trials were carried out on a pilot coater under the following conditions:

[0363] Speed: 650m / min

[0364] ■Substrate: 230g / m 2 Commercial folding boxboard (FBB) substrate

[0365] ■Bent blade applied, blade thickness: 0.5mm

[0366] ■Paint amount: 11g / m 2

[0367] Table 14: Comparative test results (comp.: comparison)

[0368]

[0369]

[0370] The results summarized in Table 14 show that by incorporating PVOH into a paper coating composition and reducing the amount of binder by 1% by weight, based on the total weight of dry pigment, similar paper gloss and brightness values can be achieved in the coating composition. The paperboard coated with coating composition 15 even showed a significant improvement in paper gloss, and the paperboards coated with coating compositions 13 and 14 exhibited improved water retention. Furthermore, a slight increase in surface strength was observed.

[0371] Example 11

[0372] An aqueous mineral material suspension was prepared by adding 0.5 wt. % PVA to a 68 wt. % suspension of pigment B containing 0.7 wt. % dispersant A, where the wt. % is based on the total weight of the mineral suspension. In addition, a comparative suspension without PVOH was prepared. The aqueous mineral suspensions listed in Table 15 below were used to prepare the coating compositions summarized in Table 16 below. Table 15: Composition and viscosity of the aqueous mineral suspensions prepared according to Example 11 (comp.: comparative)

[0373]

[0374] Table 16: Composition of the coating composition prepared and used in Example 11 (pph: parts per hundred, dry weight; weight % is based on the total weight of the suspension)

[0375]

[0376]

[0377] Paper coating trials were carried out on a pilot coater under the following conditions:

[0378] -Speed: 20m / min

[0379] -Base paper: 58g / m 2 SappiMagno

[0380] -Bent blade applied, blade thickness: 0.3mm

[0381] -Line load: 700N / m

[0382] -Calendaring temperature: 70℃

[0383] Table 17: Comparative test results (comp.: comparison)

[0384]

[0385] The results summarized in Table 17 show that by incorporating PVOH into the paper coating compositions, improvements in paper gloss, surface roughness, and dry pick were achieved. Coating compositions 17, 18, and 19 also showed improvements in water retention. In addition, coating compositions 17, 18, 19, and 21 exhibited significantly improved deltack.

Claims

1. Use of polyvinyl alcohol as a dispersant for aqueous suspensions comprising a mineral material and a dispersant, wherein the mineral material is selected from alkaline earth metal mineral materials, clays, calcined clays, titanium dioxide and mixtures thereof, and the dispersant is a polyacrylate-containing dispersant.

2. The method according to claim 1 , wherein the polyvinyl alcohol has a degree of hydrolysis of at least 75 mol %, preferably at least 85 mol %, more preferably at least 90 mol %, even more preferably at least 95 mol %, and most preferably at least 98 mol %, and / or the polyvinyl alcohol has an average molecular weight M of 10,000 to 150,000 g / mol, preferably 12,000 to 100,000 g / mol, more preferably 14,000 to 50,000 g / mol, and most preferably 16,000 to 30,000 g / mol. w .

3. The use according to any one of the preceding claims, wherein the aqueous suspension comprises the polyvinyl alcohol in an amount of 2 wt.-% or less, preferably in an amount of 0.01 to 1.8 wt.-%, more preferably in an amount of 0.05 to 1.5 wt.-%, even more preferably in an amount of 0.08 to 1 wt.-%, and most preferably in an amount of 0.1 to 0.6 wt.-%, based on the total weight of the aqueous suspension.

4. The use according to any one of the preceding claims, wherein the dispersant is a polyacrylate homopolymer, a polyacrylate copolymer or a mixture thereof, and preferably the dispersant is a polyacrylate homopolymer, preferably at least partially neutralized, preferably at least partially neutralized with sodium ions, potassium ions, lithium ions, ammonium ions, calcium ions and mixtures thereof, more preferably at least partially neutralized with sodium ions, calcium ions or mixtures thereof, and most preferably at least partially neutralized with sodium ions.

5. The method according to claim 1 , wherein the dispersant has a degree of neutralization of at least 30 mol %, preferably at least 40 mol %, more preferably at least 60 mol %, and most preferably at least 80 mol %, and / or the dispersant has an average molecular weight M of 1000 to 15000 g / mol, preferably 2000 to 12000 g / mol, more preferably 3000 to 11000 g / mol, and most preferably 4000 to 10000 g / mol. w .

6. Use according to any of the preceding claims, wherein the aqueous suspension comprises the dispersant in an amount of 3 wt.-% or less, preferably in an amount of 0.01 to 2 wt.-%, more preferably in an amount of 0.05 to 1.5 wt.-%, and most preferably in an amount of 0.1 to 0.8 wt.-%, based on the total weight of the aqueous suspension.

7. Use according to any one of the preceding claims, wherein the mineral material is in the form of particles having a weight median particle size d of 0.05 to 100 μm, preferably 0.1 to 50 μm, more preferably 0.15 to 25 μm, even more preferably 0.25 to 10 μm, and most preferably 0.5 to 2 μm. 50 , and / or having a weight-determined top cut particle size d of 0.1 to 200 μm, preferably 0.2 to 100 μm, more preferably 0.3 to 50 μm, even more preferably 0.25 to 20 μm, and most preferably 1 to 4 μm 98 .

8. Use according to any one of the preceding claims, wherein the aqueous suspension comprises the mineral material in an amount of 10 to 78 wt.-%, preferably 20 to 75 wt.-%, and most preferably 50 to 72 wt.-%, based on the total weight of the aqueous suspension.

9. A process for producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, comprising the steps of: i) providing a mineral material selected from the group consisting of alkaline earth metal mineral materials, clay, calcined clay, titanium dioxide and mixtures thereof, ii) providing a dispersant, wherein the dispersant is a polyacrylate-containing dispersant, iii) providing a dispersant, wherein the dispersant is polyvinyl alcohol, iv) providing water, and v) contacting the mineral material of step i), the dispersant of step ii), the co-dispersant of step iii) and the water of step iv).

10. The method according to claim 9, wherein step v) comprises the following steps: a1) contacting the dispersant of step ii), the dispersant aid of step iii) and the water of step iv), and a2) adding the mineral material of step i) to the mixture obtained in step a1), or b1) contacting the dispersant of step ii) and the dispersant aid of step iii), and b2) adding the mineral material of step i) and the water of step iv) to the mixture obtained in step b1), wherein the mineral material and the water are added separately or in combination, preferably in combination, or c1) contacting the dispersant of step ii), the mineral material of step i) and the water of step iv), and c2) adding the dispersant aid of step iii) to the mixture obtained in step c1), or d) simultaneously contacting the mineral material of step i), the dispersant of step ii), the co-dispersant of step iii) and the water of step iv).

11. The method according to claim 9 or 10, wherein the method further comprises the step of grinding and / or dewatering the aqueous suspension during and / or after step v).

12. A method for producing an aqueous suspension comprising a mineral material and a combination of a dispersant and a co-dispersant, wherein the mineral material is precipitated calcium carbonate, and comprising the steps of: 1) providing a material containing calcium oxide, II) providing a dispersant, wherein the dispersant is a polyacrylate-containing dispersant, III) providing a dispersant, wherein the dispersant is polyvinyl alcohol, IV) preparing milk of lime by mixing water, the calcium oxide-containing material of step I) and the dispersant aid of step III), V) carbonating the lime milk obtained in step IV) to form an aqueous suspension of precipitated calcium carbonate, and VI) The aqueous suspension obtained in step V) is mixed with the dispersant of step II).

13. A dispersant composition comprising a dispersant in combination with a co-dispersant, wherein the dispersant is a polyacrylate-containing dispersant and the co-dispersant is polyvinyl alcohol.

14. Aqueous suspension obtainable by the process according to any one of claims 9 to 12.

15. Use of the aqueous suspension according to claim 14 in paper applications, packaging applications, polymer applications or water treatment applications.

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