WO2010012407A1

WO2010012407A1 - Modified additives for suppressing dust formation

Info

Publication number: WO2010012407A1
Application number: PCT/EP2009/005311
Authority: WO
Inventors: Ralf Thiel; Klaus Busam; Friedhelm Ferlings
Original assignee: Ashland Licensing And Intellectual Property Llc.
Priority date: 2008-07-29
Filing date: 2009-07-22
Publication date: 2010-02-04

Abstract

The invention relates to a solid particulate mixture containing (i) polymer particles comprising a water-soluble or water-swellable polymer and (ii) coated auxiliary particles comprising a core and a coating, wherein the core comprises a multicarboxylic acid or a salt thereof and the coating comprises an oily material comprising a mineral oil or a vegetable oil, wherein the coating covers at least a portion of the surface of the core, and wherein the coated auxiliary particles have an average diameter within the range of from 10 to 10,000 μm, methods for the production thereof and its use.

Description

Modified additives for suppressing dust formation

FIELD OF THE INVENTION

The invention is concerned with the suppression of dust formation in the course of the manufacture and handling of solid particulate mixtures. The invention relates to coated auxiliary particles, their production and use. Further, the invention relates to a solid particulate mixture comprising said coated auxiliary particles, its production and use.

BACKGROUND PRIOR ART

Various industries, such as detergent manufacturing, pharmaceutical manufacturing, agrochemical manufacturing, and personal care manufacturing include compositions comprising active ingredients that tend to form dust due to physical forces encountered during handling and blending operations.

For example, certain solid products require the addition of auxiliary additives, e.g., in order to increase storage stability, processability, and the like. For example, it is known to add solid acids or bases to polymer particles, such as polymer granules, in order to adjust the pH value thereby increasing the storage stability of said polymer particles.

Depending on the type of polymer, the addition of solid auxiliary additives may have further advantages. In particular, when the polymer particles tend to release malodorous substances, such as ammonia, solid acids that are capable of binding the ammonia may be added thereby reducing unpleasant odors.

Many solid additives are rather fragile and break into smaller particles when exposed to mechanical forces, for example during conveying, filling, mixing, etc. Such particles do not have a sufficient hardness to withstand the mechanical impact that is caused, e.g., by a mixer, extruder and the like. The further crushing due to said mechanical impact shifts the particle size distribution towards smaller particles and thus, the content of particles having comparatively small diameters increases, i.e., the granular material is transformed into a powder.

Powdery materials tend to form fine solid airborne particles, i.e., dusts. The formation of airborne dusts is closely related to health and environmental hazards. Various parameters such as particle size distribution, concentration and composition of the particles determine the hazard and toxicity of the respective dusts.

Depending on the material, airborne dusts may be explosive (mill dust explosion) and, therefore, explosion prevention measures are required when handling such materials.

A further problem with dust formation is that dust can cause health problems and allergic reactions. Inhaled dusts reaching the upper and lower respiratory tracts may endanger health leading to diseases of the airways such as bronchitis, pneumonia, asthma, lung cancer, airway obstruction and the like. Thus, handling of particulate materials such as storing, conveying, filling, mixing etc. may require occupational health and safety measures, in particular when the powdery material contains harmful substances, such as toxic compounds, acids, bases, and the like (cf. F. Hamelmann et al. Methods for Characterizing the Dustiness Estimation of Powders. Chem. Eng. Technol. 2004, 27, 844-847).

Still further, powder particles have a greater surface area compared to that of the original granular material. The greater surface area may alter the properties of the additive with respect to its reactivity, stabilizing properties, bulk density, etc. As a result, the quality of the granulate material may decline owing to decreased storability and processability.

Furthermore, the handling of particulate materials, which leads to airborne dust in the ambient air of the workplace, may lead to defective condition of products (impurities).

In an effort to protect the auxiliary additive and reduce dust formation, additives have been formulated with various compounds including binders, coating agents, bleach- scavenging agents, and various encapsulating agents. Numerous techniques have been developed to produce these formulations including prilling, extrusion, spheronization, drum granulation, and fluid bed spray coating. (See e.g. US 4,106,991 ; US 4,242,219; US 4,689,297; US 5,324,649; and US 7,018,821 ).

There is a demand for particulate materials, in particular for granular products, which do not tend to form airborne dusts upon manufacture and further processing.

Methods to prevent the formation of airborne dusts are known in the prior art. For example, it is known to add liquids, such as oils, to the particles in the course of exposing them to mechanical forces, e.g. in a homogenizer, in order to bind the dust that is formed.

WO 2008 / 025652 A relates to polyamine-coated superabsorbent polymer particles having an improved relationship between fluid absorbance and fluid permeability.

EP 1 741 775 A relates to core shell polymer particles comprising a core and a shell, wherein the shell and the core each comprise a polymer containing at least one ethylenically unsaturated group such as α,β-mono-ethylenically unsaturated mono- and dicarboxylic acids and the core additionally contains a benefit agent such as a sugar polyester or a mineral or vegetable oil.

EP 1 731 142 A relates to a delivery device for the delayed release of an active agent in the gastrointestinal tract. Said device comprises a core and two coatings, the shell containing the active agent. The outer coating comprises a hydrophobic substantially water-insoluble polymer such as a (meth)acrylate (co)-polymer (i.e. Eudragit®) or ethylcellulose.

WO 2005 / 027890 A relates to modified release pharmaceutical compositions and describes i.e. coated core compositions containing modafinil wherein the core can have one or more coatings. One of the coating layers may include a plasticized enteric polymer such as esters of cellulose (i.e. hydroxy-propylmethylcellulose HPMC). A second layer may include a mixture of a plasticized water dispersible enteric polymer and a water insoluble polymer. JP 2002-212211 A relates to polymeric particles having a core and shell portions for hair cosmetics. The core is formed by polymerization of hydrophobic monomers such as lauryl methacrylate and the shell is formed by polymerization of hydrophilic monomers bearing a reactive unsaturated group.

DE 101 06 567 A1 relates to an aqueous primary dispersion, containing dispersed and/or emulsified solid and/or liquid polymer particles and/or dispersed solid core- shell particles. The core/shell particles result from the graft copolymerization of organic solids and monomers.

FR 2 774 994 A relates to composite particles containing an active substance. These particles contain both a core including an organic polymer in which a hydrophobic material is dispersed and an external coating containing a metal or silicon oxide or hydroxide as well as an intermediate layer between the core and the outer coating containing an alkali earth metal hydroxide.

EP 0 542 133 A relates to microcapsules with a solid core obtainable by suspension polymerization of a vinyl monomer such as styrene or different (meth)acrylates, a bi- or polyfunctional monomer such as di- or polyvinyl monomers (i.e. di- or triacrylates) and other monomers such as acrylic acids. For the microcapsulation process inorganic or organic solids such as pigments can be applied.

WO 92 / 20771 A relates to polymeric particulate compositions comprising particles having a substantially anhydrous core, a layer of hydrophobic oil around the core and a shell of polymer around the oil layer. The core contains a hydrophobic matrix polymer which can be prepared from any ethylenically unsaturated monomer and contains an active ingredient such as an enzyme.

However, adding oil to a particulate mixture in a homogenizer causes agglutination, even if the oil is sprayed, i.e. added in form of small droplets. Agglutination in turn can be avoided by increasing the efficiency of the homogenizer, e.g., by enhancing the stirring speed of the mixer, enhancing the revolution velocity of the extruder, and the like. However, increasing the homogenizer efficiency also causes an increase of mechanical impact which in turn leads to further pulverization of the particles. In consequence, more oil is needed in order to bind the powder and increasing the amount of oil leads to an increased agglutination.

Thus, there is a demand for a method which allows for homogenizing a mixture of a particulate material without causing agglutination and without forming substantial amounts of airborne dust.

SUMMARY OF THE INVENTION

A first aspect of the invention relates to a solid particulate mixture containing

(i) polymer particles comprising a water-soluble or water-swellable polymer and

(ii) coated auxiliary particles comprising a core and a coating, wherein the core comprises an auxiliary substance, preferably a multicarboxylic acid or a salt thereof, and the coating comprises an oily material, preferably comprising a mineral oil or a vegetable oil, wherein the coating covers at least a portion of the surface of the core, and wherein the coated auxiliary particles have an average diameter within the range of from 10 to 10,000 μm.

It has been surprisingly found that the solid particulate mixture according to the invention has a very low tendency to form dusts and thus, upon manufacturing and handling, the concentration of detrimental airborne particles is very low.

The coated auxiliary particles comprise a coating of an oily material and said oily material prevents dust formation when exposing the coated auxiliary particles to mechanical forces, e.g., when homogenizing a mixture of said coated auxiliary particles with polymer particles.

In consequence, the solid particulate mixture according to the invention displays a significantly decreased risk of forming explosive dusts and the health risk for workers handling the solid particulate mixture according to the invention is significantly decreased. Therefore, the solid particulate mixture according to the invention decreases the requirements for explosion prevention measures and occupational health and safety measures. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration of a preferred embodiment of the method for the manufacture of the solid particulate mixture according to the invention including the method for the manufacture of the coated auxiliary particles according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the invention relates to a solid particulate mixture containing (i) polymer particles comprising a water-soluble or water-swellable polymer and (ii) coated auxiliary particles comprising a core and a coating, wherein the core comprises an auxiliary substance, preferably a multicarboxylic acid or a salt thereof, and the coating comprises an oily material, wherein the coating covers at least a portion of the surface of the core, and wherein the coated auxiliary particles have an average diameter within the range of from 10 to 10,000 μm. The polymer particles are preferably uncoated.

In a preferred embodiment, the relative weight ratio of the polymer particles to the coated auxiliary particles, which are present in the solid particulate mixture according to the invention, is preferably ≤ 1100:1 , more preferably ≤ 600:1 , still more preferably ≤ 400:1 , and in particular < 200:1. In another preferred embodiment, the relative weight ratio of the polymer particles to the coated auxiliary particles is within the range of from 1000:1 to 1 :1 , more preferably of from 500:1 to 2:1 , still more preferably of from 250:1 to 5:1 , yet more preferably of from 200:1 to 10:1 , most preferably of from 150:1 to 15:1 , and in particular of from 100:1 to 20:1.

In a preferred embodiment of the solid particulate mixture the coated auxiliary particles comprise none of the components of the polymer particles and vice versa.

The solid particulate mixture according to the invention contains coated auxiliary particles having an average diameter within the range of from 10 to 10,000 μm. Preferably, the coated auxiliary particles have an average diameter of < 6,000 μm, preferably of < 4,500 μm, more preferably of < 3,500 μm, still more preferably of < 2,000 μm, and in particular of ≤ 1 ,500 μm. In a preferred embodiment, the coated auxiliary particles have a diameter of from 10 to 5,500 μm, preferably of from 20 to 5,000 μm, more preferably of from 30 to 4,000, still more preferably of from 40 to 3,000 μm, and in particular of from 50 to 2,500 μm.

Methods for measuring the average diameter of particles are known to the person skilled in the art, such as mesh analysis, microscopy, electron microscopy or light scattering. Preferably, the average particle size of the particles is determined by mesh analysis, preferably according to DIN ISO 66165.

Preferably, the pure coated auxiliary particles have a bulk density of 0.77±0.25 g/cm³, more preferably 0.77±0.20 g/cm³, still more preferably 0.77±0.15 g/cm³, yet more preferably 0.77±0.10 g/cm³, most preferably 0.77±0.05 g/cm³, and in particular 0.77±0.02 g/cm³. Bulk density is the mass of many particles of the material divided by the volume they occupy. The volume includes the space between particles as well as the space inside the pores of individual particles. The skilled person knows how to measure the bulk density of a solid. In this regard it can be referred to, e.g., ISO 1068:1975, Plastics - Homopolymer and copolymer resins of vinyl chloride - Determination of compacted apparent bulk density, Distributed through American National Standards Institute (ANSI), 2007.

Preferably, the solid particulate mixture contains at most 25 wt.-%, more preferably at most 21 wt.-%, still more preferably at most 16 wt.-%, most preferably at most 11 wt.- %, and in particular at most 6.0 wt.-% of coated auxiliary particles, based on the total weight of the solid particulate mixture.

The coated auxiliary particles according to the invention comprise a core and a coating.

For the purpose of the specification, the term "core" preferably refers to the central part of the coated auxiliary particles usually having different physical and/or chemical properties from the surrounding (coating). Preferably, the core is an agglomerate of solid materials (e.g. crystals, crystallites, amorphous solids, and the like) including the auxiliary substance, preferably multicarboxylic acid or salt thereof. The core may assume any regular or irregular shape, symmetric or unsymmetric, spherical, ellipsoid or arbitrary, in form of solid bodies, pieces, fragments, beads, beadlets, spherules, granules, pellets, globules, and the like.

For the purpose of the specification, the term "agglomerate" refers to any solid material that is gathered into a ball, mass, or cluster. Typically, an agglomerate is clustered or growing together, but not coherent.

The core of the coated auxiliary particles comprises an auxiliary substance, preferably multicarboxylic acid or salt thereof. The core may also contain more than one auxiliary substance, e.g. two, three or four auxiliary substances. For the purpose of the specification, the term "auxiliary substance" preferably refers to any solid additive that may be employed for any purpose, e.g., in order to increase storage stability and/or processability of the polymer particles, bind malodorous substances, and the like.

In a preferred embodiment, the pure auxiliary substance exhibits a hardness of at most 7 or at most 6.5, preferably of at most 6 or at most 5.5, more preferably of at most 5 or at most 4.5, still more preferably of at most 4 or at most 3.5, and in particular at most 3 or at most 2.5 according to the Mohs hardness scale. The skilled person knows how to measure the hardness of a solid according to the Mohs hardness scale. In this regard it can be referred to, e.g., American Federation of Mineralogical Societies, "Mohs Scale of Mineral Hardness".

In another preferred embodiment, the pure auxiliary substance, preferably multicarboxylic acid or salt thereof, exhibits an absolute hardness of at most 200, preferably of at most 150, more preferably of at most 120, still more preferably of at most 100, and in particular of at most 70. The skilled person knows how to measure the absolute hardness of a solid. In this regard it can be referred to, e.g., H. Chandler, Hardness Testing, ASM International; 2nd edition, 1999.

Preferably, the pure auxiliary substance, preferably multicarboxylic acid or salt thereof, has a bulk density of 0.77±0.25 g/cm³, more preferably 0.77±0.20 g/cm³, still more preferably 0.77±0.15 g/cm³, yet more preferably 0.77±0.10 g/cm³, most preferably 0.77±0.05 g/cm³, and in particular 0.77±0.02 g/cm³.

Preferably, the auxiliary substance, preferably multicarboxylic acid or salt thereof, has a molecular weight within the range of from 50 to 500 g/mol, more preferably 75 to 450 g/mol, still more preferably 100 to 400 g/mol, yet more preferably 125 to 350 g/mol, most preferably 150 to 300 g/mol and in particular 175 to 250 g/mol.

Preferably, the auxiliary substance, preferably multicarboxylic acid or salt thereof, has a density within the range of from 1.1 to 2.2 g/cm³, more preferably 1.2 to 2.1 g/cm³, still more preferably 1.3 to 2.0 g/cm³, yet more preferably 1.4 to 1.9 g/cm³, most preferably 1.5 to 1.8 g/cm³ and in particular 1.6 to 1.7 g/cm³.

Preferably, the auxiliary substance, preferably multicarboxylic acid or salt thereof, has a melting point within the range of from 150±50°C, more preferably 150±40°C, still more preferably 150±30°C, yet more preferably 150±20°C, most preferably 150±10°C, and in particular 150±5°C.

Preferably, the auxiliary substance is water-soluble. Preferably, at 20⁰C the water solubility of the auxiliary substance is within the range of from 130±40 g/100 ml, more preferably 130±30 g/100 ml, still more preferably 130±20 g/100 ml, yet more preferably 130±15 g/100 ml, most preferably 130±10 g/100 ml, and in particular 130±5 g/100 ml.

In a preferred embodiment, the auxiliary substance is a multicarboxylic acid or a salt thereof.

For the purpose of the specification, the term "multicarboxylic acid" preferably refers to organic acids having at least two carboxylic acid groups. Preferably, the auxiliary substance is a multicarboxylic acid having two carboxylic acid groups (dicarboxylic acid) or three carboxylic acid groups (tricarboxylic acid).

The multicarboxylic acid may be unsaturated or saturated; aliphatic or aromatic; linear, branched or cyclic; and/or unsubstituted or substituted. Suitable substituents may be alkyl, halogen, amino and/or hydroxy. The multicarboxylic acid is preferably substituted with at least one hydroxy group (hydroxymulticarboxylic acid). Within the group of hydroxymulticarboxylic acids, the hydroxytricarboxylic acids are preferred.

Preferred dicarboxylic acids are selected from the group consisting of oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, citraconic acid, mesaconic acid, adipic acid, muconic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and terephthalic acid.

Preferred tricarboxylic acids are selected from the group consisting of cis-aconitic acid, trans-aconitic acid, tricarba Hylic acid, citric acid, isocitric acid, homocitric acid, 1- carboxyglutamic acid, 4-oxalmesaconic acid, trimellitic acid, trimesic acid, and agaric acid. Citric acid is particularly preferred.

Salts of multicarboxylic acids include the alkali metal salts, such as sodium and potassium; the alkaline earth metal salts, such as calcium and magnesium; transient metal salts, such as zinc, copper, iron; ammonium salts, and the mixtures thereof. The multicarboxylic acid comprises at least two carboxylic acid groups. Optionally, one or more or all of the carboxylic acid groups may be present as salts, i.e., all carboxylic acid groups may be protonated, or some carboxylic acid groups may be protonated while others are present as salts, or all carboxylic acids groups may be present as salts.

The core of the coated auxiliary particles may also comprise mixtures of multicarboxylic acids as auxiliary substance, e.g., a mixture of structurally different dicarboxylic acids, a mixture of at least one dicarboxylic acid and at least one tricarboxylic acid, or a mixture of structurally different tricarboxylic acids, and the corresponding salts, respectively. When the core comprises a mixture of multicarboxylic acids, it contains preferably at least one tricarboxylic acid and/or at least one hydroxytricarboxylic acid, more preferably citric acid and at least another multicarboxylic acid.

In a preferred embodiment, the core of the coated auxiliary particles only contains a single multicarboxylic acid, more preferably only a single hydroxymulticarboxylic acid, still more preferably only a single hydroxytricarboxylic acid, and most preferably only citric acid, or a salt thereof. In a particularly preferred embodiment, the core of the coated auxiliary particles essentially consists of citric acid or a salt thereof.

Preferably, the core of the coated auxiliary substance contains at least 75 wt.-%, more preferably at least 79 wt.-%, still more preferably at least 84 wt.-%, most preferably at least 89 wt.-%, and in particular at least 94 wt.-% of auxiliary substance, preferably citric acid, based on the total weight of the core of the coated auxiliary particles. In a particularly preferred embodiment, the core essentially consists of the auxiliary substance, preferably of citric acid.

Preferably, the coated auxiliary particles contain at least 75 wt.-%, more preferably at least 79 wt.-%, still more preferably at least 84 wt.-%, most preferably at least 89 wt.- %, and in particular at least 94 wt.-% of auxiliary substance, preferably citric acid, based on the total weight of the coated auxiliary particles.

Preferably, the solid particulate mixture according to the invention contains at most 25 wt.-%, more preferably at most 21 wt.-%, still more preferably at most 16 wt.-%, most preferably at most 11 wt.-%, and in particular at most 6.0 wt.-% of auxiliary substance, preferably citric acid, based on the total weight of the solid particulate mixture. In a preferred embodiment, the solid particulate mixture according to the invention contains 0.1 to 20 wt.-%, more preferably 0.5 to 15 wt.-%, still more preferably 1.0 to 10 wt.-%, most preferably 1.5 to 6.0 wt.-%, and in particular 2.0 to 4.0 wt.-% of auxiliary substance, preferably citric acid, based on the total weight of the solid particulate mixture.

The surface of the core of the coated auxiliary particles is at least partially covered with a coating comprising an oily material. In this context, the expression "covered with a coating" shall include any coverage, protection, lamination, lining, casing, deposit, film, overlay, plating, tarnish, shield, and the like.

Preferably, the coating has an average thickness of at least 1.0 nm, more preferably at least 2.0 nm. Preferably, the coating covers at least 1 %, more preferably at least 10%, still more preferably at least 25%, yet more preferably at least 50%, most preferably at least 75% and in particular at least 90% of the mean surface area of the core. The skilled person knows how to measure the mean surface area of the core and its mean degree of coverage. For example, the surface area of the core may be investigated by photoelectron spectroscopy (UPS, XPS), microscopy or electron microscopy.

The coating may comprise one or more layers. Preferably, however, the coating comprises a single layer only. Preferably, the coating comprising the oily material is the outer coating of the coated auxiliary particles. In a particularly preferred embodiment, the coated auxiliary particles consist of a core and a coating comprising a single layer which comprises the oily material.

Preferably, the coating contains at least 75 wt.-%, more preferably at least 79 wt.-%, still more preferably at least 84 wt.-%, most preferably at least 89 wt.-%, and in particular at least 94 wt.-% of oily material, preferably white oil, based on the total weight of the coating of the coated auxiliary particles. In a particularly preferred embodiment, the coating essentially consists of the oily material, preferably of white oil.

Preferably, the coated auxiliary particles contain at most 25 wt.-%, more preferably at most 21 wt.-%, still more preferably at most 16 wt.-%, most preferably at most 11 wt.- %, and in particular at most 6.0 wt.-% of oily material, based on the total weight of the coated auxiliary particles. In a preferred embodiment, the auxiliary substance, preferably white oil, contains preferably 0.1 to 20 wt.-%, more preferably 0.5 to 15 wt.-%, still more preferably 1.0 to 10 wt.-%, most preferably 1.5 to 6.0 wt.-%, and in particular 2.0 to 4.0 wt.-% of oily material, based on the total weight of the coated auxiliary particles.

Preferably, the solid particulate mixture contains at most 10 wt.-%, more preferably at most 5.0 wt.-%, still more preferably at most 2.5 wt.-%, yet more preferably at most 1.0 wt.-%, most preferably at most 0.5 wt.-%, and in particular at most 0.1 wt.-% of oily material, based on the total weight of the solid particulate mixture. Oily materials are known to the person skilled in the art. For the purpose of the specification, the term "oily material" preferably refers to a hydrophobic (lipophilic) composition containing oil or essentially consisting of oil. In this regard, the term "oil" preferably refers to any substance that is in a viscous liquid state at ambient temperatures or slightly warmer, and is both hydrophobic (substantially immiscible with water) and lipophilic (substantially miscible with other oils). Oils include compound classes with otherwise unrelated chemical structures, properties, and uses, including vegetable oils, petrochemical oils, and volatile essential oils. Oil is a nonpolar substance. Preferably, oils are not polymeric.

Preferably, the oily material comprises or essentially consists of a component having a boiling point at atmospheric pressure of at least 150⁰C, more preferably at least 175°C, still more preferably at least 200⁰C, yet more preferably at least 225°C, most preferably at least 250⁰C and in particular at least 275°C.

Preferably, the oily material has a density at 20⁰C of 0.860±0.50 g/cm³, more preferably 0.860±0.40 g/cm³, still more preferably 0.860±0.30 g/cm³, yet more preferably 0.860±0.20 g/cm³, most preferably 0.860±0.10 g/cm³ and in particular 0.860±0.05 g/cm³. Preferably, the density is measured according to DIN 51757.

Preferably, the oily material has a refractive index at 20°C of 1.466±0.400, more preferably 1.466±0.300, still more preferably 1.466±0.200, yet more preferably 1.466±0.100, most preferably 1.466±0.050, and in particular 1.466±0.025.

Preferably, the oily material is characterized by a carbon distribution, preferably according to ASTM D2140, of any of embodiments Ai to A₈:

Ca (aromatic carbon), Cn (naphthene ring carbon), Cp (paraffin chain carbon)

Preferably, the oily material has a viscosity at 20°C of 55±30 mm²/s, more preferably 55±25 mm²/s, still more preferably 55±20 mm²/s, yet more preferably 55±15 mm²/s, most preferably 55±10 mm²/s, and in particular 55±5 mm²/s. Preferably, the viscosity is measured according to DIN 515 562.

Preferably, the oily material comprises or essentially consists of a component selected from the group consisting of fatty oils (e.g., vegetable oil, animal oil), essential oils, mineral/ petrochemical oils (e.g., white oil), and synthetic oils (e.g., silicone oil).

Examples of vegetable oils include soybean oil, palm oil, rapeseed oil, sunflower oil, peanut oil, cottonseed oil, palm kernel oil, olive oil, corn oil, hazelnut oil, linseed oil, rice bran oil, safflower oil, sesame oil, castor oil, coconut oil, canola oil and ben oil. Examples of animal oils include fish oil. Examples of essential oils include rose oil, lavender oil, orange oil and lime oil. Examples of mineral oils and petrochemical oils include hydrocarbons (e.g. C14-C₄₀), alkanes and alkenes, cyclic paraffins, and white petrolatum (petroleum jelly, i.e., hydrocarbons with carbon numbers mainly higher than 25). Examples of synthetic oils include hydrocarbons and silicone oils.

Preferably, the oily material comprises white oil (white petrolatum). In a particularly preferred embodiment, the oily material comprises white oil. Preferably, said white oil has a density at 15°C of at least 0.200 - 1.600 g/ml, more preferably 0.600 - 1.200 g/ml, still more preferably 0.700 - 0.980 g/ml, most preferably 0.780 - 0.900 g/ml and in particular 0.820 - 0.860 g/ml. Methods for measuring the density are known to the skilled person. Preferably, the density is measured according to DIN 51 757.

Preferably, the flashpoint of the oily material is at least between 50-285⁰C, more preferably between 100-235⁰C, still more preferably between 130-205°C, most preferably between 150-185⁰C and in particular between 165-175°C. Methods for measuring the flash point are known to the skilled person. Preferably, the flash point is measured according to DIN ISO 2592.

Preferably, the oily material has a vapor pressure at 2O⁰C which is at least <1.0 hPa, more preferably <0.6 hPa, still more preferably <0.4 hPa, most preferably <0.2 hPa and in particular <0.1 hPa. Preferably, the kinematic viscosity of the oily material at 40⁰C is at least 0.1-20 mm²/s, more preferably 4-16 mm²/s, still more preferably 6-14 mm²/s, most preferably 8-12 mm²/s and in particular 9-11 mm²/s according to DIN 51562. Preferably, the kinematic viscosity at 20⁰C is at least 0.1-40 mm²/s, more preferably 5-35 mm²/s, still more preferably 10-30 mm²/s, most preferably 15-25 mm²/s and in particular 18-22 mm²/s. Methods for measuring the kinematic viscosity are known to the skilled person. Preferably, the kinematic viscosity is measured according to DIN 51562.

In a particularly preferred embodiment, the coated auxiliary particles comprise a core, which is formed by an agglomerate of citric acid, and an at least partial coating of white oil, wherein the white oil preferably covers at least 1 %, more preferably at least 25%, still more preferably 50%, most preferably at least 70%, and in particular at least 90% of the surface area of the citric acid core.

Preferably, the relative weight ratio of the auxiliary substance to the oily material is within the range of from 1000:1 to 1 :1 , more preferably of from 500:1 to 2:1 , still more preferably of from 250:1 to 5:1 , yet more preferably of from 200:1 to 10:1 , most preferably of from 150:1 to 15:1 , and in particular of from 100:1 to 20:1.

In a preferred embodiment, the core and/or coating of the coated auxiliary particles does not contain a polymer. In another preferred embodiment, the coated auxiliary particles do not contain any enzymes.

The solid particulate mixture according to the invention contains polymer particles. Preferably, the polymer particles are not coated with an oily material, more preferably not coated at all.

Preferably, the solid particulate mixture contains at least 75 wt.-%, more preferably at least 79 wt.-%, still more preferably at least 84 wt.-%, most preferably at least 89 wt.- %, and in particular at least 94 wt.-% of polymer particles, based on the total weight of the solid particulate mixture.

Preferably, the polymer particles according to the invention have an average diameter of ≤ 10,000 μm, preferably of ≤ 5,000 μm, more preferably of ≤ 3,000 μm, still more preferably of ≤ 2,000 μm, and in particular of ≤ 1 ,000 μm. In a preferred embodiment, the polymer particles have an average diameter of from 100 to 5,000 μm, preferably of from 100 to 4,000 μm, more preferably of from 100 to 3,000 μm, still more preferably of from 100 to 2,000 μm, and in particular of from 100 to 1 ,000 μm.

In a preferred embodiment, the polymer particles do not contain cellulose.

The polymer particles comprise a water-soluble or a water-swellable polymer.

For the purpose of the specification the term "water-swellable" preferably refers to the increase in volume of polymer particles associated with the uptake of water (cf. D. H. Everett. Manual of Symbols and Terminology for Physicochemical Quantities and Units. Appendix II, Part I: Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Pure & Applied Chemistry 1972, 31, 579-638). The swelling behavior of polymers may be measured at different temperatures and pH values in water. The swollen weights of the polymers are determined at intervals, after removal of the surface water, until equilibrium swelling is attained. The percent swelling is preferably calculated by the following equation: %swelling = 100 * [(W_t - W₀) / W₀], where W₀ is the initial weight and W_t the final weight of the gel at time t (cf. I. M. El- Sherbiny et al. Preparation, characterization, swelling and in vitro drug release behaviour of poly[Λ/-acryloylglycine-chitosan] interpolymeric pH and thermally- responsive hydrogels. European Polymer Journal 2005, 41, 2584-2591 ).

The water-swellable polymers according to the invention may display a %swelling of at least 2.5%, preferably of at least 5.0%, more preferably of at least 7.5%, still more preferably of at least 10%, most preferably of at least 15%, and in particular of at least 20% measured in demineralized water at 20 ⁰C and pH 7.4 in phosphate buffer after equilibrium swelling is attained.

Preferably, the polymer particles contain at least 75 wt.-%, more preferably at least 79 wt.-%, still more preferably at least 84 wt.-%, most preferably at least 89 wt.-%, and in particular at least 94 wt.-% water-swellable or water-soluble polymer, based on the total weight of the polymer particles. In a preferred embodiment, the polymer particles essentially consist of water-swellable or water-soluble polymer.

The polymer particles according to the invention comprise at least one polymer, more preferably at least two polymers, still more preferably at least two structurally different polymers. The polymers may be, e.g., homopolymers or copolymers.

For the purpose of the specification, the term "polymer" preferably refers to a material composed of macromolecules containing >10 monomer units (cf. G. P. Moss et al. Glossary of Class Names of Organic Compounds and Reactive Intermediates Based on Structure. Pure & Applied Chemistry 1995, 67, 1307-1375). For the purpose of the specification, the term "copolymer" preferably refers to a polymer derived from more than one species of monomer. Copolymers that are obtained by copolymerization of two monomer species are termed bipolymers, those obtained from three monomers terpolymers, those obtained from four monomers quaterpolymers, etc. (cf. A. D. Jenkins et al. Glossary of Basic Terms in Polymer Science. Pure & Applied Chemistry 1996, 68, 2287-2311 ).

Preferably, the water-soluble or water-swellable polymer is a non-ionic, anionic, cationic, or amphiphilic polymer. Preferably, the water-soluble or water-swellable polymer is derived from ethylenically unsaturated monomers, preferably from acrylic acid derivatives, such as acrylic acid, acylic acid esters, acrylic acid amides, acrylonitrile, and the like.

For the purpose of the specification, the term "non-ionic polymer" refers to an uncharged material composed of macromolecules containing >10 monomer units, wherein at least one monomer is a non-ionic monomer of general formula (I) as defined below.

The non-ionic polymers may be homopolymers, which comprise non-ionic monomer units as the only monomer component. Further, the non-ionic polymers may be also copolymers, i.e. bipolymers, terpolymers, quaterpolymers, etc., which comprise at least two structurally different non-ionic monomers as the only monomer components. Still further, the non-ionic polymers may be also copolymers, i.e. bipolymers, terpolymers, quaterpolymers, etc. preferably prepared from at least one non-ionic monomer and at least one uncharged amphiphilic monomer as the only monomer components, provided that the weight ratio of the non-ionic monomer units to the uncharged amphiphilic monomer units is >1.0.

Compounds of the following general formula (I) can be used as non-ionic monomers for manufacturing the water-soluble or water-swellable polymers:

wherein

R¹ stands for hydrogen or methyl, and

R² and R³ stand, independently of each other, for hydrogen, alkyl with 1 to 5 carbon atoms, or hydroxyalkyl with 1 to 5 carbon atoms.

The non-ionic monomers (meth)acrylamide, N-methyl(meth)acrylamide, N- isopropyl(meth)acrylamide or N₁N substituted (meth)acrylamides such as N, N,- dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-methyl-N- ethyl(meth)acrylamide or N-hydroxyethyl(meth)acrylamide are preferably used for manufacturing the water-soluble or water-swellable polymers according to the invention. The non-ionic monomer acrylamide is more preferably used.

For the purpose of the specification, the term "cationic polymer" refers to positively charged material composed of macromolecules containing >10 monomer units, wherein at least one monomer is a cationic monomer of general formula (II) as defined below.

Compounds of the following general formula (II) can be used as cationic monomers for manufacturing the water-soluble or water-swellable polymers according to the invention:

wherein

R¹ stands for hydrogen or methyl,

Z¹ stands for O, NH or NR⁴, wherein R⁴ stands for alkyl with 1 to 4 carbon atoms, and

Y stands for one of the groups

wherein

Y⁰ and Y¹ stand for alkylene with 2 to 6 carbon atoms, optionally substituted with hydroxy groups,

Y², Y³, Y⁴, Y⁵, and Y⁶, independently of each other, stand for alkyl with 1 to 6 carbon atoms, and

Z^" stands for halogen, acetate or methyl sulfate.

Protonated or quaternized dialkylaminoalkyl(meth)acrylates or dialkylaminoalkyl- (meth)acrylamides with Ci to C₃-alkyl or Ci to C₃-alkylene groups are preferably used as cationic monomers for manufacturing the water-soluble or water-swellable polymers according to the invention. The methyl chloride-quaternized, ethyl chloride- quaternized, propyl chloride-quaternized, or isopropyl-quaternized ammonium salts of N,N-dimethylaminomethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminomethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, N₁N- dimethylaminomethyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylamide and/or N,N-dimethylaminopropyl(meth)acrylamide are more preferably used. Instead of the alkyl chlorides (i.e., methyl chloride, ethyl chloride, propyl chloride, and isopropyl chloride), the corresponding bromides, iodides, sulfates, etc. may also be used for the quatemization of said N,N-dialkylaminoalkyl(meth)acrylate and N₁N- dialkylaminoalkyl(meth)acrylamide derivatives.

In a preferred embodiment of the invention, the polymer particles of the solid particulate mixture comprise cationic copolymers containing cationic monomer units selected from ADAME-Quat (quatemized N,N-dimethylaminoethyl acrylate) and DIMAPA-Quat (quatemized N,N-dimethylaminopropyl acrylamide) as well as non- ionic monomer units selected from acrylamide and methacrylamide.

The cationic polymers may be homopolymers, which preferably comprise cationic monomer units as the only monomer component. Further, the cationic polymers may be also copolymers, i.e. bipolymers, terpolymers, quaterpolymers, etc., which comprise, e.g., at least two structurally different cationic monomer units or cationic as well as non-ionic monomer units.

In a preferred embodiment, the cationic polymers contain at least 10 wt.-%, more preferably at least 25 wt.-%, still more preferably at least 50 wt.-%, most preferably at least 75 wt.-%, and in particular 100 wt.-% of cationic monomer units.

In another preferred embodiment, the cationic polymers contain 10-100 wt.-%, more preferably 15-90 wt.-%, still more preferably 20-80 wt.-%, most preferably 25-70 wt.- %, and in particular 30-60 wt.-% of cationic monomer units.

For the purpose of the specification the term "anionic polymer" refers to a negatively charged material composed of macromolecules containing >10 monomer units, wherein at least one monomer is an anionic monomer as defined below.

The anionic polymers may be homopolymers, which preferably comprise anionic monomer units as the only monomer component. Further, the anionic polymers may be also copolymers, i.e. bipolymers, terpolymers, quaterpolymers, etc., which comprise, e.g., at least two structurally different anionic monomers or anionic and non-ionic monomer units. The following anionic monomers can be used for manufacturing the water-soluble or water-swellable anionic polymers:

- olefinically unsaturated carboxylic acids and carboxylic acid anhydrides, in particular acrylic acid, methacrylic acid, itaconic acid, crotonic acid, glutaconic acid, maleic acid, maleic anhydride, fumaric acid and the water-soluble alkali metal salts thereof, alkaline earth metal salts thereof, and ammonium salts thereof

- olefinically unsaturated sulfonic acids, in particular aliphatic and/or aromatic vinylsulfonic acids, for example vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, acrylic and methacrylic sulfonic acids, in particular sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy- 3-methacryloxypropylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid, and the water-soluble alkali metal salts thereof, alkaline earth metal salts thereof, and ammonium salts thereof

- olefinically unsaturated phosphonic acids, in particular, for example, vinyl- and allyl-phosphonic acid and the water-soluble alkali metal salts thereof, alkaline earth metal salts thereof, and ammonium salts thereof

- sulfomethylated and/or phosphonomethylated acrylamides and the water-soluble alkali metal salts thereof, alkaline earth metal salts thereof, and ammonium salts thereof.

The anionic monomers are preferably selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, glutaconic acid, maleic acid, maleic anhydride, and fumaric acid. More preferably, the anionic monomers are selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, and crotonic acid. The water-soluble alkali metal salts of acrylic acid and in particular potassium acrylate are most preferred according to the invention.

In a preferred embodiment, the anionic polymers contain at least 10 wt.-%, more preferably at least 25 wt.-%, still more preferably at least 50 wt.-%, most preferably at least 75 wt.-%, and in particular 100 wt.-% of anionic monomer units. In another preferred embodiment, the anionic polymers contain 10-100 wt.-%, more preferably 15-90 wt.-%, still more preferably 20-80 wt.-%, most preferably 25-70 wt.- %, and in particular 30-60 wt.-% of anionic monomer units.

For the purpose of the specification, the term "amphiphilic polymer" preferably refers to a charged, preferably positively charged, or uncharged material composed of macromolecules containing >10 monomer units, wherein the monomer units possess both a hydrophilic and a hydrophobic group (cf. D. H. Everett. Manual of Symbols and Terminology for Physicochemical Quantities and Units. Appendix II, Part I: Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Pure & Applied Chemistry 1972, 31, 579-638). The amphiphilic polymers according to the invention comprise at least one amphiphilic monomer of general formulae (III) or (IV) as defined below.

Compounds of the following general formulae (III) or (IV) can be used as amphiphilic monomers for manufacturing the water-soluble or water-swellable polymers according to the invention:

wherein

Z¹ stands for O, NH or NR⁴, wherein R⁴ stands for hydrogen or methyl,

R¹ stands for hydrogen or methyl,

R⁵ and R⁶ stand, independently of each other, for alkyl with 1 to 6 carbon atoms,

R⁷ stands for alkyl, aryl and/or aralkyl with 8 to 32 carbon atoms,

R⁸ stands for alkylene with 1 to 6 carbon atoms, and

Z^" stands for halogen, pseudohalide ions, methyl sulfate or acetate; or

wherein

Z¹ stands for O, NH or NR⁴, wherein R⁴ stands for alkyl with 1 to 4 carbon atoms,

R¹ stands for hydrogen or methyl,

R⁸ stands for alkylene with 1 to 6 carbon atoms,

R⁹ stands for alkylene with 2 to 6 carbon atoms, and

R¹⁰ stands for hydrogen, alkyl, aryl, and/or aralkyl with 8 to 32 carbon atoms, and

n stands for an integer between 1 to 50.

The conversion products of (meth)acrylic acid or (meth)acrylamide with polyethylene glycols (10 to 40 ethylene oxide units) that have been etherified with fatty alcohol are preferably used as amphiphilic monomers for manufacturing the water-soluble or water-swellable polymers according to the invention.

For the purpose of the specification the term "pseudohalide ions" preferably refers to certain ions such as azide, thiocyanate, and cyanide, which resemble halide ions in their chemistry (cf. G. P. Moss et al. Glossary of Class Names of Organic Compounds and Reactive Intermediates Based on Structure. Pure & Applied Chemistry 1995, 67, 1307-1375).

The amphiphilic polymers may be homopolymers, which comprise amphiphilic monomer units as the only monomer component. Further, the amphiphilic polymers may be also copolymers, i.e. bipolymers, terpolymers, quaterpolymers, etc., which comprise at least two structurally different amphiphilic monomers as the only monomer components. The amphiphilic polymers may be also copolymers, i.e. bipolymers, terpolymers, quaterpolymers, etc. preferably prepared from at least one amphiphilic monomer.

The solid particulate mixture according to the invention may contain polymer particles, which preferably comprise at least one non-ionic polymer, preferably as the only polymer component; or at least one amphiphilic polymer, preferably as the only polymer component; or at least one anionic polymer, preferably as the only polymer component; or at least one cationic polymer, preferably as the only polymer component.

The polymer particles may comprise two or three structurally different amphiphilic polymers as the only polymer components, two or three structurally different non- ionic polymers as the only polymer components, two or three structurally different anionic polymers as the only polymer components, or two or three structurally different cationic polymers as the only polymer components.

Further, the solid particulate mixture according to the invention may contain polymer particles that preferably comprise at least two polymers independently selected from the group consisting of non-ionic polymers, amphiphilic polymers, anionic polymers and cationic polymers.

Still further, the solid particulate mixture according to the invention may contain polymer particles that preferably comprise a mixture of at least three polymers selected from the group consisting of non-ionic polymers, amphiphilic polymers, anionic polymers and cationic polymers.

In a particularly preferred embodiment, the polymer particles contain at least one polymer A and/or at least one polymer B as defined here below.

Polymer A is preferably high-molecular with an average molecular weight (M_w) of ≥ 1.0x10⁶ g/mol, as measured by the GPC method. Polymer B is preferably a low- molecular polymer with an average molecular weight (M_w) of at most 500,000 g/mol, more preferably of at most 400,000 g/mol, still more preferably of at most 300,000 g/mol, most preferably of at most 200,000 g/mol, as measured by the GPC method. Thus, it is preferred that the average molecular weight of polymer A is greater than the average molecular weight of polymer B. The ratio of the average molecular weights of polymer A to polymer B may be at least 4.0, preferably at least 10, more preferably at least 20, still more preferably at least 25, most preferably at least 30, and in particular at least 40.

In a particularly preferred embodiment, the polymer particles comprise at least one water-soluble or water-swellable polymer A and/or at least one water-soluble or water-swellable polymer B as the only polymer components, wherein the water- soluble or water-swellable polymer A as well as the water-soluble or water-swellable polymer B are preferably both cationic or both anionic.

The preparation of the water-soluble and water-swellable polymers is known to the person skilled in the art. For example, the polymers according to the invention may be prepared by polymerization techniques according to the procedures described in WO 2005/092954, WO 2006/072295, and WO 2006/072294.

Depending on the procedure used for the preparation of the water-soluble or water- swellable polymers, the respective polymer products may comprise further substances such as polyfunctional alcohols, water-soluble salts, chelating agents, free-radical initiators and/or their respective degradation products, reducing agents and/or their respective degradation products, oxidants and/or their respective degradation products, etc.

In a preferred embodiment, the content of particles in the solid particulate mixture according to the invention, which have an average diameter of below 10 μm, is at most 40 wt.-%, more preferably at most 30 wt.-%, still more preferably at most 20 wt.- %, most preferably at most 15 wt.-% and in particular at most 10 wt.-% based on the total weight of the solid particulate mixture.

In another preferred embodiment, the content of particles in the solid particulate mixture according to the invention, which have an average diameter of below 15 μm, is at most 40 wt.-%, more preferably at most 30 wt.-%, still more preferably at most 20 wt.-%, most preferably at most 15 wt.-% and in particular at most 10 wt.-% based on the total weight of the solid particulate mixture.

In still another preferred embodiment, the content of particles in the solid particulate mixture according to the invention, which have an average diameter of below 20 μm, is at most 40 wt.-%, more preferably at most 30 wt.-%, still more preferably at most 20 wt.-%, most preferably at most 15 wt.-% and in particular at most 10 wt.-% based on the total weight of the solid particulate mixture.

In yet another preferred embodiment, the content of particles in the solid particulate mixture according to the invention, which have an average diameter of below 25 μm, is at most 40 wt.-%, more preferably at most 30 wt.-%, still more preferably at most 20 wt.-%, most preferably at most 15 wt.-% and in particular at most 10 wt.-% based on the total weight of the solid particulate mixture.

It has been surprisingly found that the solid particulate mixture according to the invention has a very low tendency to form dust and, thus, the concentration of airborne particles in the ambient air is comparatively low when handling the solid particulate mixture according to the invention.

In a preferred embodiment, the dust number, which is applied as a measure for the formation of airborne particles when handling the solid particulate mixture, the dust number is at most 30, at most 25 or at most 20, more preferably at most 18, at most 16 or at most 16, still more preferably at most 14, at most 12 or at most 10, yet more preferably at most 9, at most 8 or at most 7, most preferably at most 6, at most 5 or at most 5, and in particular at most 4, at most 3 or at most 2.

In another preferred embodiment, the dust number is within the range of from 2.1 to 5.0, more preferably of from 2.6 to 4.8, still more preferably of from 3.1 to 4.6, most preferably of from 3.3 to 4.4, and in particular of from 3.6 to 4.0.

In yet another preferred embodiment, the dust number is within the range of from 1.0 to 5.0, more preferably of from 1.2 to 4.8, still more preferably of from 1.4 to 4.6, most preferably of from 1.6 to 4.4, and in particular of from 1.8 to 4.0. The dust number is preferably measured by means of an automated analyzer: A feed funnel, which contains the sample, is opened automatically to begin the measurement and the sample falls into the dust reservoir. The measurement is preferably realized by means of a laser beam: dust formation causes an attenuation of the laser beam. This attenuation is observed in a certain period of time, detected on a scale from 0-100% and saved as a series of dust values. The dust number is the sum of the start value (0.5 seconds) and the dust value after 30 seconds. Suitable devices for measuring the dust number are commercially available. Preferably, the dust number is measured on a Dustview device that is commercialized by the firm Palas^®.

A second aspect of the invention relates to the coated auxiliary particles as defined above. Therefore, the preferred embodiments concerning the coated auxiliary particles that have been described in connection with the solid particular mixture according to the invention shall also apply to the coated auxiliary particles according to the invention.

Preferably, the coated auxiliary particles

- have an average diameter within the range of from 10 to 10,000 μm, preferably 20 to 5,000 μm, more preferably of from 30 to 4,000, still more preferably of from 40 to 3,000 μm, most preferably of form 45 to 2,750 μm, and in particular of from 50 to 2,500 μm, and

- comprise a core and a coating, wherein

• the core comprises a solid agglomerate of an auxiliary substance including a multicarboxylic acid or a salt thereof, preferably citric acid, and the coating comprises an oily material including a mineral oil, preferably white oil, or a vegetable oil,

• the coating covers at least a portion of the surface of the core and

• the relative weight ratio of the auxiliary substance to the oily material is within the range of from 1000:1 to 10:1 , more preferably of from 500:1 to 10:1 , still more preferably of from 250:1 to 10:1 , most preferably of from 150:1 to 10:1 , and in particular of from 100:1 to 10:1.

A third aspect of the invention relates to a method for the manufacture of the coated auxiliary particles described supra comprising the step of (a) contacting the solid agglomerate with the oily material.

The solid agglomerate may be contacted with the oily material by any for of treatment, e.g., by spraying, pouring, bathing, dipping, and the like. The duration of the treatment depends on the individual circumstances.

The oily material, which is preferably white oil, is preferably sprayed onto the solid agglomerate of the auxiliary substance, preferably citric acid, to prepare at least partially coated auxiliary particles.

In a preferred embodiment of the method according to the invention the oily material, preferably white oil, is sprayed onto a solid agglomerate, preferably of citric acid, until at least 1 %, more preferably at least 25%, still more preferably at least 50%, most preferably at least 70%, and in particular at least 90% of the surface area of the core is covered with coating of the oily material, e.g. white oil. It is especially preferred that the oily material, which is preferably white oil, is sprayed onto the solid agglomerate of the auxiliary substance, which is preferably citric acid, until at least 95% or even at least 99% of the surface area of the auxiliary particles is covered with oily material.

It is preferred that the oily material, preferably white oil, is sprayed onto a fluidized bed of a solid agglomerate of the auxiliary substance, which is preferably citric acid.

Fluidization may be achieved by conventional means that are known to the person skilled in the art. For example, step (a) may be performed in a drop-though fluidizer or a blow-through fluidizer. Examples include spray fluidizers, disc fluidizers, swirl fluidizers and the like.

The oily material may be contacted with the solid agglomerate of the auxiliary substance as such, or the oily material may be dissolved in a suitable solvent prior to contacting the solid agglomerate of the auxiliary substance. Preferably, the solvent is capable of dissolving the oily material but not the auxiliary substance. If a solvent is used, the solvent preferably has a comparatively low boiling point, e.g. below 100⁰C.

In a preferred embodiment of the method according to the invention the agglomerates of the auxiliary substance (i.e. the cores of the coated auxiliary particles) are supplied to a fluidizer where the agglomerates of the auxiliary substance are fluidized. The oily material is then supplied through a feeding line to a jet that is connected to the fluidizer. The oily material is sprayed through the jet onto the agglomerates of the auxiliary substance (cores) that are fluidized in the fluidizer. The degree of coating can be adjusted inter alia by regulating the feed rate of the oily material and the condition in the fluidizer (e.g., turbulence, temperature, feed rate of agglomerates, etc.) (cf. Figure 1 ).

A fourth aspect of the invention relates to the coated auxiliary particles obtainable by the method for the manufacture of coated auxiliary particles described above.

A fifth aspect of the invention relates to a method for manufacturing the solid particulate mixture according to the invention comprising the step of (b) mixing the polymer particles with the coated auxiliary particles.

The mixing of the polymer particles with the coated auxiliary particles can be performed by use of conventional mixers or homogenizers such as roll mixers, shaking mixers, shear mixers or compulsory mixers, or in a fluidized bed.

The tendency of dust formation during the mixing (homogenizing) of the coated auxiliary particles and the polymer particles is significantly reduced.

In a preferred embodiment of the method according to the invention in step (a) the solid agglomerate of the auxiliary substance, preferably multicarboxylic acid or salt thereof, is contacted (coated) with the oily material and thereafter, in step (b) the thus obtained coated auxiliary particles are mixed with the polymer particles. It is particularly preferred that steps (a) and (b) are not performed simultaneously. It has been surprisingly found that contacting the auxiliary substance, preferably multicarboxylic acid or salt thereof, with the oily substance in the absence of the polymer particles and mixing the thus obtained coated auxiliary particles with the polymer particles subsequently, is advantageous because inter alia, agglutination can be suppressed.

The solid particulate mixture according to the invention can be used as flocculant or stabilizer. Thus, a sixth aspect of the invention relates to the use of the solid particulate mixture according to the invention as flocculant or stabilizer.

Figure 1 displays a preferred embodiment of the method for the manufacture of the solid particulate mixture according to the invention. The agglomerates of the auxiliary substance (i.e. the cores of the coated auxiliary particles) are delivered by a dosing unit (1), e.g. an overhead traveling crane that is equipped with a balance. Said agglomerates are supplied to a conveyor belt (3) through a funnel (2). Conveyor belt (3) continuously transports the dosed agglomerates to a fluidizer (8) where the agglomerates of the auxiliary substance are fluidized. The oily material is supplied from storage tank (4) by a pump (5) to a dosing unit (6). From dosing unit (6) the oily material is supplied through a feeding line (7) to jet (7a) that is connected to the fluidizer (8). The oily material is sprayed through jet (7a) onto the agglomerates of the auxiliary substance (cores) that are fluidized in the fluidizer (8). The degree of coating can be adjusted inter alia by regulating the feed rate of the oily material through feeding line (7) and the condition in the fluidizer (8) (e.g., turbulence, temperature, feed rate of agglomerates, etc.). The thus obtained coated auxiliary particles leave the fluidizer through feeding line (9) and enter homogenizer (10), where they are mixed with the polymer particles that are introduced into the homogenizer through feeding line (11). The thus obtained homogenized solid particulate mixture can then be supplied by means of a conveyor belt (12) and a feeding line (13) to, e.g., a storage tank (not shown).

The following examples further illustrate the invention but should not be construed as limiting its scope. EXAMPLES

Comparative Examples C-1 , C-2, C-3 and C-4 (citric acid without coating and absence of citric acid at all, respectively) (Table 1 ):

Citric acid without coating was mixed with polymer Praestol 857BS (C-1 and C-3). The resulting mixture was homogenized. Samples were taken after different mixing times (30 min or 60 min) to measure the dust formation. The dust number of Praestol 857BS alone (without any addition of citric acid) was also measured after the same mixing times for reasons of comparison (C-2 and C-4).

Table 1

The dependence of dust formation of citric acid on the mechanical impact caused by the mixer becomes directly evident from Table 1.

Inventive Examples 1-1 , I-2. I-3 and I-4 (coated citric acid) (Table 2):

Citric acid was coated with white oil prior to mixing with Praestol 857BS. A certain amount of citric acid was conveyed from a storage tank to a fluidizer. White oil was sprayed from a storage tank via a pump and a dosing unit to the citric acid (mixing time less than 5 min) and the resulting coated citric acid was continuously fed to the homogenizer containing Praestol 857BS in a flying flux process in the desired amount. Different amounts of white oil from 2 to 6% (referred to the amount of citric acid) were applied (1-1 to I-4). Table 2

^*refers to the amount of citric acid

Table 2 clearly shows a decreased dust formation of citric acid upon coating prior to mixing with Praestol 857BS on mechanical impact which is up to 16 times less compared to citric acid without coating.

Agglutination

Table 3 shows a statistical analysis concerning the decrease of agglutination to demonstrate the advantage of the invention:

Table 3

Claims

1. A solid particulate mixture containing

(i) polymer particles comprising a water-soluble or water-swellable polymer and

(ii) coated auxiliary particles comprising a core and a coating, wherein the core comprises a multicarboxylic acid or a salt thereof and the coating comprises an oily material comprising a mineral oil or a vegetable oil, wherein the coating covers at least a portion of the surface of the core, and wherein the coated auxiliary particles have an average diameter within the range of from 10 to 10,000 μm.

2. The mixture according to claim 1 , wherein the multicarboxylic acid is citric acid.

3. The mixture according to claim 1 or 2, wherein the pure multicarboxylic acid or salt thereof exhibits a hardness of at most 7 according to the Mohs hardness scale.

4. The mixture according to any of the preceding claims, wherein the water-soluble or water-swellable polymer is an anionic or cationic copolymer.

5. Coated auxiliary particles having an average diameter within the range of from 10 to 10,000 μm and comprising a core and a coating, wherein

the core comprises a solid agglomerate of a multicarboxylic acid or a salt thereof and the coating comprises an oily material including a mineral oil and/or a vegetable oil,

wherein the coating covers at least a portion of the surface of the core and wherein the relative weight ratio of the multicarboxylic acid to the oily material is within the range of from 1000:1 to 10:1.

6. The particles according to claim 5, wherein the multicarboxylic acid is citric acid.

7. A method for the manufacture of the coated auxiliary particles according to claim 5 or 6, comprising the step of

(a) contacting the solid agglomerate with the oily material.

8. The method according to claim 7, wherein the oily material is sprayed onto the solid agglomerate.

9. The method according to claim 8, wherein the solid agglomerate is fluidized.

10. A method for manufacturing the solid particulate mixture according to any of claims 1 to 4 comprising the step of

(b) mixing the polymer particles with the coated auxiliary particles.

11. The method according to claim 10, which encompasses the method according to any of claims 7 to 9.