Process for the preparation of polyurethane particles containing a filler

Abstract

This invention relates to a method for preparing a polymer incorporated into a solid, comprising the following steps: I) providing an aqueous polymer dispersion comprising crystalline polyurethane particles having an average particle size of ≤ 500 nm and further comprising inorganic particles; II) storing the dispersion of step I) at a temperature of ≤ 0°C until a precipitate forms; III) separating the precipitate of step II); and IV) removing water from the precipitate separated in step III), thereby obtaining a dehydrated precipitate. The invention also relates to solid particulate compositions obtainable by the method and the use of said compositions as building materials in additive manufacturing processes, as coatings, adhesives, or as rubbers.

Description

[0001] This invention relates to a method for preparing a polymer incorporated into a solid, comprising: I) providing an aqueous polymer dispersion comprising polymer particles having an intensity-based harmonic mean particle size (Z-mean) of ≤ 500 nm hydrodynamic diameter as determined by dynamic light scattering; II) storing the dispersion of step I) at a temperature ≤ 0°C until a precipitate forms; III) separating the precipitate of step II); and IV) removing water from the precipitate separated in step III), thereby obtaining a dehydrated precipitate. The invention also relates to solid particulate compositions obtainable by the method and the use of said compositions as building materials in additive manufacturing processes, as coatings, or as adhesives.

[0002] Polymer dispersions can be modified with particulate dispersions of inorganic particles in water, such as silica dispersions, and the resulting mixture is typically applied to a substrate. After the liquid component evaporates, a dry film is obtained, with the added inorganic particles embedded within the film. A disadvantage of this approach is that the mixture may not be storage stable, and it can only be obtained in liquid form. Furthermore, when starting with a liquid formulation, the thickness of the applied coating or adhesive layer is limited.

[0003] US 2008 / 171208 A1 relates to adhesives based on aqueous dispersions and surface-passivated isocyanate particles, and potentially reactive coatings, films, and powders made from such dispersions. The adhesive is prepared from an aqueous composition comprising: a) a dispersed polymer having isocyanate reactive groups; b) at least one dispersed, surface-passivated aliphatic solid polyisocyanate having a softening temperature ≥ 40°C; c) a compound of one or more elements of Groups 5 and 6 of the periodic table, wherein the particular element has an oxidation state of at least +4; and d) optionally additional additives and auxiliaries.

[0004] US 2008 / 171208 A1 discloses storing dispersion "2" (comparative) and dispersion "4" (according to the invention in US 2008 / 171208 A1) in a refrigerator at -5°C for 24 hours, resulting in the precipitation of polymer as coarse solid particles. The formulation is then heated to room temperature and the precipitated polymer is separated from the supernatant by filtration. The polymer is then dried under mild conditions and ground in a jet mill under cooling to a d50 particle size of approximately 100 μm. It should be noted that the presence of fillers such as silica is not disclosed in this publication.

[0005] US 2013 / 245163 A1 describes a method for preparing an aqueous composition, particularly a silica-based aqueous dispersion, and a method for preparing an adhesive or coating formulation using the aqueous composition as a component, and a method for preparing an adhesive layer and using the composition to bond a substrate coated on one or both sides by spray application.

[0006] WO 2019 / 158599 A1 discloses a method for applying a fusible polymer above its decomposition temperature. In the experimental section, it is described that certain Dispercoll® U-shaped polyurethane dispersions were frozen at -18°C for 12 hours, followed by filtration of the precipitate, drying, sieving, and extrusion into filaments.

[0007] US 6,451,963 B1 relates to a method for coagulating PU dispersions, the resulting coagulated products, and the use of the coagulated PU dispersions. Reactive or post-crosslinkable PU dispersions are suitable as PU dispersions for use in the methods according to this invention. The methods disclosed include the preparation of films, coatings, and partial or complete impregnation of nonwovens, knitted fabrics, or other fabrics for reinforcement purposes from a variety of different materials. In particular, a method for coagulating a post-crosslinkable dispersion is disclosed, comprising precipitating the post-crosslinkable dispersion by heat treatment between 50 and 120°C, and forming a stable, at least partially crosslinked, polyurethane or gel.

[0008] US 2016 / 280809 A1 describes a continuous or semi-continuous freeze coagulation method for aqueous polymer dispersions, wherein the method includes a freezing step and a solid-liquid separation step, and is further characterized in that it includes a further step of incorporating water and / or water vapor between the freezing step and the solid-liquid separation step.

[0009] US 2012 / 101216 A1 discloses a method for producing polymer solids without an auxiliary emulsifier from a polymer latex (dispersion), wherein a polymer dispersion with an initial pH greater than 9 is set to a pH of 6 to 9 by adding gaseous carbon dioxide, and the polymer dispersion is then coagulated by shearing and / or freezing.

[0010] US 2003 / 088045 A1 relates to the use of isocyanate-free aqueous polyurethane dispersions having a solid content of ≥ 30% by weight and a solvent content of ≤ 10% by weight in formulations of crack sealing coating systems. The use may be for a) primers, floating screeds, floor coatings, spray coatings, and / or sealants, preferably on primer-coated building surfaces, b) roof coatings or paints, and c) sealing of open or underground mines. According to this disclosure, the disclosed polyurethane dispersions are not only more environmentally friendly and easier to use, but also provide partially improved product properties for the corresponding crack sealing coating systems, such as mechanical properties (tensile strength, tensile strength, elongation at break), UV resistance, and color stability. Some examples include Silitin® Z 89 (a mixture of silica, quartz, and kaolinite).

[0011] GB 2269179 A discloses a method for preparing a toner composition, comprising dissolving a polymer and optionally a pigment in an organic solvent; dispersing the resulting solution in an aqueous medium containing a surfactant or a mixture of surfactants; stirring the mixture under optional heating to remove the organic solvent, thereby obtaining suspended particles with a volume diameter of about 0.05 micrometers to about 2 micrometers; subsequently homogenizing the resulting suspension containing the optional pigment in water and a surfactant; and subsequently agglomerating the mixture by heating, thereby providing toner particles with an average particle volume diameter of about 3 to about 50 micrometers, and preferably about 3 to about 21 micrometers, when the pigment is present.

[0012] US 2004 / 058268 A1 discloses a toner method involving mixing a colorant dispersion and a metal oxide with a latex emulsion consisting of a polymer, water, and an anionic surfactant, adding a cationic coagulant, then heating the mixture to a temperature substantially below the glass transition temperature (Tg) of the latex polymer particles to provide toner-sized aggregates consisting of polymer pigments and dyes, heating substantially above the Tg of the polymer, and separating the resulting product.

[0013] EP 1783170 A1 discloses a thermoplastic molding composition. This thermoplastic molding composition is made from a graft copolymer and a thermoplastic polymer. The graft copolymer is made from a soft, elastomer-like particulate graft substrate with a glass transition temperature below 0°C, obtained by emulsion polymerization of a single conjugated diene or a conjugated diene with a small amount of a mono-olefinic unsaturated monomer or at least one C1-C18 alkyl acrylate or a mixture thereof, grafted thereon with a vinyl aromatic monomer and acrylonitrile, and optionally another mono-olefinic unsaturated monomer. An aqueous latex of the graft copolymer is mixed with a dispersion of finely granulated inert material in an aqueous medium. For the dispersion step of the finely granulated inert material in the aqueous solution, a salt of an amphiphilic polymer is used.

[0014] GB 2128623 A discloses a method for coagulating and dehydrating polymer latex by comprising the following steps: (a) freezing the latex to coagulate polymer particles therefrom; (b) thawing the resulting coagulated material and free water; and (c) separating the free water from the coagulated material. This method is reportedly particularly suitable for latex grafted with polybutadiene.

[0015] US 3,228,905 A discloses a latex containing dispersed single particles comprising aggregated butadiene polymers in which single particles of inorganic reinforcing pigments are entrained, the aggregated particles being formed by the aggregation of dispersed butadiene polymer particles and the entrainment of reinforcing pigment single particles by the aggregated butadiene polymer particles during aggregation to form new, larger dispersed butadiene polymer particles.

[0016] WO 92 / 13027 A2 discloses fine polymer particles and polymer-encapsulated particles formed by dissolving a polymer in a selective solvent, lowering the solution temperature, and / or adding a non-solvent for the polymer to cause the polymer to precipitate from the solution. Particulate materials may be included during solution formation to encapsulate the polymer particles as they precipitate from the solution. Two homopolymers are placed in a solution with a selective solvent, such that one polymer precipitates first and remains suspended therein, while the other polymer subsequently precipitates from the remaining solution to encapsulate the first polymer particles, forming core / shell polymer particles. Pigments, liposomes, and other particulate materials can be encapsulated by the polymer, and the polymer and the encapsulated particles are identical in size and morphology.

[0017] EP 2289981 A2 discloses a method for incorporating dyes into latex particles using supercritical fluid microencapsulation technology to achieve improved dispersion of colorants and increased color gamut in latex.

[0018] The object of this invention is to provide a widely applicable method for incorporating particulate materials into polymers, wherein the final product is a filled polymer solid.

[0019] Therefore, a method for preparing a polymer incorporated into a solid includes: I) Provide an aqueous dispersion comprising polymer particles having an intensity-based harmonic average particle size (Z-average) of ≤ 500 nm as measured by dynamic light scattering; II) Store the dispersion from step I) at a temperature ≤ 0°C until a precipitate forms; III) Separate the precipitate from step II); IV) Remove water from the precipitate separated in step III) to obtain a dehydrated precipitate.

[0020] The dispersion of step I) further comprises inorganic particles, and the polymer is crystalline polyurethane.

[0021] It has been unexpectedly discovered that, in the method according to the invention, the precipitated polymer also contains inorganic particles. These inorganic particles are thus incorporated into the polymer material. Therefore, a simplified method for compounding polymers with particulate fillers without heating the polymer and adding inorganic particles to the molten polymer is disclosed.

[0022] The aqueous dispersion provided in step I) may be based on a commercially available polymer dispersion to which inorganic particles have been added. The polymer particles dispersed in the aqueous phase have an intensity-based harmonic mean particle size (Z-mean) of ≤ 500 nm hydrodynamic diameter as measured by dynamic light scattering. A preferred mean particle size is ≥ 10 nm to ≤ 350 nm, and more preferably ≥ 20 nm to ≤ 250 nm. The dispersion may also contain conventional additives, such as emulsifiers. Furthermore, the dispersion may have an acid, base, or buffer system to set the pH to a desired level. A pH of 4 to 10 is preferred. Finally, water-soluble electrolytes such as metal halogens, oxides, or carbonates may be added to influence electrostatic properties, such as the zeta potential of the polymer or inorganic particles.

[0023] When providing the aqueous dispersion of step I), an aqueous dispersion of inorganic particles may be added to the aqueous polymer dispersion. The aqueous dispersion of inorganic particles may have a pH of ≤ 6 or ≥ 8.

[0024] In step II) of this method, the dispersion containing inorganic particles is stored at 0°C or lower until a precipitate forms. This precipitate contains polymer particles as well as inorganic particles. Step II) can be performed simply but efficiently by storing the polymer dispersion with added inorganic particles in a cylinder in a walk-in freezer or commercial refrigeration facility.

[0025] Separation step III) is used to remove most of the aqueous phase and obtain a (wet) precipitate for further processing. Common methods for separating solids from liquids can be used. The residual aqueous phase may have a solid content of ≤ 5% by weight, preferably ≤ 2% by weight, more preferably ≤ 1% by weight, and most preferably ≤ 0.5% by weight.

[0026] Step IV) is a drying step that further reduces the water content of the precipitate. This can produce free-flowing powder or granules. Drying can be carried out by heating, treating with dry air and / or applying a vacuum, as well as by vacuum and / or dry extrusion.

[0027] It should be emphasized that steps III) and IV) can be performed sequentially within the same operation. For example, vacuum filtration of the precipitate will implement steps III) and IV), wherein the filter cake is blotted dry on the filter and then washed with a low-boiling-point non-solvent (“non-solvent” means that the short-term (e.g., 1 hour) absorption is less than 10% by weight of the solvent) such as ethanol or isooctane, and then the precipitate is further retained on the filter for a predetermined time.

[0028] Inorganic particles may be present in the dispersion of step I) in an amount of ≥ 1 wt% to ≤ 50 wt% based on the total weight of the precipitated and dried dispersion. Preferably, the content is ≥ 2 wt% to ≤ 30 wt%, more preferably ≥ 3 wt% to ≤ 25 wt%.

[0029] In one embodiment of the invention, the inorganic particles have an intensity-based harmonic average particle size (Z-average) of ≤ 100 nm hydrodynamic diameter as measured by dynamic light scattering. The preferred average particle size is ≥ 1 nm to ≤ 80 nm, and more preferably ≥ 5 nm to ≤ 60 nm.

[0030] In a further embodiment of the present invention, the method further includes: V) Grind the dehydrated precipitate from step IV) into particles with a number-based average particle size of ≤ 500 μm as measured by optical microscopy.

[0031] The preferred average particle size after grinding is ≥ 10 μm to ≤ 250 μm, and more preferably ≥ 20 μm to ≤ 150 μm. Examples of grinding methods are dry grinding and cryogenic grinding. A suitable temperature should be below the melting point; preferably ≤ 40°C below the melting point, and more preferably below the glass transition temperature of the polymer material. The grinding in step V) can be carried out at a temperature of ≥ -190°C to ≤ 40°C.

[0032] The grinding process in step V) can also be carried out in a repeated process between grinding rollers with continuously decreasing gap sizes until the desired particle size is obtained.

[0033] In another embodiment, the grinding process in step V) is carried out in a conventional ball mill. Alternatively, the grinding process in step V) is carried out in a conical mill, pin mill, or other commonly used powder mills and grinders.

[0034] In a further embodiment of the invention, the dispersion of step I) has a polymer solids content of ≥20% to ≤60% by weight based on the total weight of the dispersion. Preferably, it has a polymer solids content of ≥30% to ≤55% by weight based on commercially available polymer dispersions.

[0035] In a further embodiment of the invention, step II) is performed at a temperature of ≥ -40°C to ≤ -8°C.

[0036] In a further embodiment of the invention, step III) includes a filtration step and / or a decantation step. Decantation is preferred. Although decantation will yield a fairly wet separated precipitate, it is very easy to operate and can be performed at a different location than in step IV) of the dewatering process. Therefore, most of the aqueous phase can be removed very cost-effectively, and the separated precipitate from a combination of several steps III) can be transferred to the more energy-intensive step IV).

[0037] In a further embodiment of the invention, step IV) is performed at a temperature ≤ 2°C. The temperature is preferably ≤ 0°C. This can be performed in the case of a freeze-drying step.

[0038] In a further embodiment of the invention, the dehydrated precipitate of step IV) has a water content of ≥ 0.1 wt% to ≤ 5 wt% based on the total weight of the dehydrated precipitate. Preferably, it has a water content of ≥ 0.1 wt% to ≤ 2 wt%.

[0039] In a further embodiment of the invention, the dehydrated precipitate of step IV) has an inorganic particle content of ≥ 2% to ≤ 50% by weight based on the total weight of the dried precipitate. Preferably, the particle content is ≥ 5% to ≤ 30% by weight.

[0040] Examples of suitable polyurethane polymers include anionic hydrophilic polyurethanes, cationic hydrophilic polyurethanes, and nonionic hydrophilic polyurethanes. Polyurethanes lacking internal hydrophilic groups can be emulsified by adding an external emulsifier to the dispersion. Preferred emulsifiers are those based on nonionic polyethylene glycol.

[0041] Also suitable is a linear polyester polyurethane, which is produced by reacting a) a polyester diol having a molecular weight greater than 600 and optionally b) a diol with a molecular weight of 62 to 600 g / mol as a chain extender with c) an aliphatic diisocyanate, while adhering to an equivalent ratio of hydroxyl groups of components a) and b) to isocyanate groups of component c) of 1:0.9 to 1:0.999, wherein component a) consists of at least 80 by weight of a polyester diol with a molecular weight of 1500 to 3000 based on (i) adipic acid and (ii) 1,4-dihydroxybutane and / or neopentyl glycol.

[0042] Further preferably, component c) comprises IPDI and HDI. Also preferably, the alkane diol b) is selected from: 1,2-dihydroxyethane, 1,3-dihydroxypropane, 1,4-dihydroxybutane, 1,5-dihydroxypentane, 1,6-dihydroxyhexane, or a combination of at least two of these, in an amount of up to 200 hydroxy equivalents based on component a).

[0043] The polyurethane may also contain urea groups and is therefore also considered a polyurethane / polyurea compound.

[0044] The polyurethane is of the crystalline type, meaning it is at least partially crystallized after the dispersion is dried. The degree of at least partial crystallinity of the material can be established by the presence of a melting peak measured by differential scanning calorimetry (DSC) (secondary heating at a rate of 20 K / min). The melting peak of the polyurethane material is preferably at a temperature of 20°C or higher, more preferably 50°C or higher.

[0045] In a further embodiment of the invention, the polymer in the dispersion of step I) has a number-average molecular weight Mn of ≥ 30,000 g / mol, as determined by gel permeation chromatography. This is particularly preferred in the case of polyurethane polymers. Polymers with such high molecular weights are typically only processed into stable dispersions when low solids content is the target. This is irrelevant in the method according to the invention, since the material will precipitate anyway. Therefore, the method according to the invention expands the range of materials that can provide particulate inorganic matter.

[0046] In a further embodiment of the present invention, the particles in the dispersion of step I) are selected from: silicon dioxide, titanium dioxide, aluminum oxide, titanium nitride, tungsten nitride, tungsten carbide, carbon black, graphene, carbon nanotubes, metals, sheet silicates, clay containing organic cations, non-white metal oxides, or a mixture of at least two of the above particle types.

[0047] In a further embodiment of the invention, the dispersion of step I) is free of solid polyisocyanates and / or elements of Groups 5 and 6 of the periodic table, wherein the specific element has an oxidation state of at least +4. The term "free of" means that technically unavoidable impurities may be present in the dispersion. However, this embodiment does not include the intentional addition of such substances. For example, "free of" may mean that the concentration of the relevant substance is less than 1 ppm.

[0048] A further aspect of the invention is a solid particulate composition which can be obtained by the method according to the invention and wherein the particles of the composition comprise a matrix of crystalline polyurethane, wherein the number-based average particle size of the composition, as measured by optical microscopy, is ≤ 10 mm, and wherein inorganic particles are embedded within the matrix, the embedded particles having a number-based average particle size of ≤ 1000 nm, as measured by electron microscopy.

[0049] In a further embodiment of the composition, the particles of the composition have a long axis representing the maximum size of each particle and a short axis representing the minimum size of each particle, these dimensions being measured by optical microscopy, the average ratio of the long axis length to the short axis length being ≥ 1:0.01 to ≤ 1:1 (preferably ≥ 1:0.05 to ≤ 1:0.5), and the number-based average particle size being measured by optical microscopy being ≤ 10 mm.

[0050] A further aspect of the invention is the use of the compositions according to the invention as building materials in additive manufacturing processes, as coatings, as adhesives, or as rubbers. Examples of additive manufacturing or 3D printing processes include extrusion-based methods such as fused deposition modeling (FDM) or freeform fabrication (FFF), and powder-based methods such as selective laser sintering (SLS) and selective laser melting (SLM).

[0051] Examples of coating applications include application in the form of hot melt, hot melt foil, hot melt powder, or in the form of a solution of the material in a solvent such as acetone, methyl ethyl ketone, (cyclo)hexane, (iso)heptane, (iso)octane, toluene, dichloromethane, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, butyl acetate, or mixtures thereof.

[0052] Examples of rubber applications include use as a rubber compounding material for blending with other components such as oils, stabilizers, other fillers, and crosslinking agents in standard rubber mixing equipment, and use as a rubber material after vulcanization at a temperature of ≥ 120°C, preferably ≥ 130°C, and more preferably ≥ 140°C. Example

[0053] The invention is further described with reference to the following embodiments, but is not intended to be limited thereto.

[0054] method Room temperature (RT) was 23°C. Unless otherwise specified, all percentages are based on weight percentages of total weight. Rheological parameters (G', G'') were measured using a plate / plate oscillating viscometer according to ISO 6721-10 at 60°C and an angular frequency of 1 / s. Further measurements were taken every 30 seconds as the temperature decreased at 4 K / min until a temperature of 20°C was reached. At 20°C, the temperature was held constant for 60 minutes, with measurements taken every 30 seconds.

[0055] polymer dispersions Polymer dispersion A is a crystalline polyester polyurethane / urea aqueous dispersion for adhesive applications, with a pH of 6.8, a glass transition temperature (DSC, 20 K / min) of -50°C, a melting temperature (DSC, 20 K / min) of 49°C, and a solid content of approximately 50% by weight.

[0056] Polymer dispersion B is a crystalline polyester polyurethane / urea aqueous dispersion for adhesive applications, with a pH of 6.9, a glass transition temperature (DSC, 20 K / min) of -51°C, a melting temperature (DSC, 20 K / min) of 49°C, and a solid content of approximately 50% by weight.

[0057] Polymer dispersion C is a crystalline polyester polyurethane / urea aqueous dispersion for adhesive applications, with a pH of 7.1, a glass transition temperature (DSC, 20 K / min) of -48°C, a melting temperature (DSC, 20 K / min) of 50°C, and a solid content of approximately 50% by weight.

[0058] Polymer dispersion Y is an amorphous aliphatic polyester polyurethane aqueous dispersion with a pH of 7.0, a glass transition temperature (DSC, 20 K / min) of -4℃, and a solid content of approximately 50% by weight.

[0059] Polymer dispersion Z is a non-crystalline anionic polycarbonate polyurethane aqueous dispersion with a pH of 7.5, a glass transition temperature of -36℃ (DSC, 20 K / min), and a solid content of approximately 40%.

[0060] The polymers of dispersions A, B, and C are linear polyester polyurethanes with terminal hydroxyl groups, prepared by reacting a) a polyester diol having a molecular weight of 1500 to 3000 g / mol and b) a diol chain extender with c) an aliphatic diisocyanate. Component a) contains a polyester diol with a molecular weight of 1500 to 3000 g / mol, component b) is 1,4-dihydroxybutane, and component c) is IPDI and HDI.

[0061] silica suspension Silica suspension D is an aqueous colloidal suspension of amorphous silica with a solid content of about 30% by weight, an average particle size of about 9 nm, and a pH of 10.4.

[0062] Silica suspension E is an aqueous colloidal suspension of amorphous silica with a solid content of about 50% by weight, an average particle size of about 55 nm, and a pH of 9.1.

[0063] Preparation of further polymer dispersions containing silica The dispersion mixture was prepared by mixing 500 mL of polymer dispersion with the desired amount of silica suspension in a stirring cup and stirring at 100 rpm for 5 minutes. The weight percentage of silica dispersion content was based on the total weight of the polymer dispersion / silica dispersion mixture. 100 g of the resulting mixture was taken and the flow time was determined using a DIN 4 cup of freshly prepared mixture and the mixture after storage at room temperature for 56 days. If the flow time increased by more than 30% or particles, coagulation, or sediment were observed, the mixture was classified as "unstable".

[0064] Another 10 grams of the freshly prepared mixture was poured into a 10 cm diameter Teflon cup and dried at 60°C for 1 day until a firm dry film was obtained. The film was then removed and subjected to rheological examination in a plate / plate oscillating rheometer. These experiments are denoted as "dry".

[0065] Another 300 g of the freshly prepared mixture was transferred to a 500 mL plastic screw-cap bottle and stored at -18 °C for 48 hours, followed by thawing at room temperature for 24 hours. After thawing, the resulting coarse polymer suspension was filtered through 10 μm filter paper, and the polymer residue was dried to constant weight in a rotary evaporator at a water bath temperature of 40 °C and a pressure of 20 mbar. A solid material was obtained. Based on the solids initially present in the polymer dispersion and silica suspension, the residual solids content in the filtrate, determined by gravimetric analysis after drying at 125 °C for 1 hour, was less than 2% by weight. These experiments are referred to as "precipitated".

[0066] Table 1, with entries 1 to 27, records the results of rheological tests on materials obtained from polymer dispersions and polymer dispersions containing silica. "*" indicates a comparative example. Silica content is expressed as solids content calculated from the parent suspension.

[0067] Analysis of rheological data shows that the amount of inorganic particles introduced via freeze-coagulation / precipitation exhibits similar modulus modification (reinforcing effect) to standard dry film materials. This reinforcing behavior is typically associated with well-distributed fillers. It is concluded that a highly homogeneous mixture of inorganic filler particles within the polymer has been achieved in the method according to the invention. This avoids the need for temperature- and energy-intensive mixing processes and enables the efficient introduction of fillers with high surface areas at low mixing energies.

[0068] Further comparative examples (28* and 29*) were conducted using dispersions Y and Z and 10% by weight of silica suspension D, respectively.

[0069] In the system of polymer dispersion Y and silica suspension D, the precipitate of polymer and silica particles after thawing was observed to be a solid rubber-like block, which could not be further processed. In the system of polymer dispersion Z and silica suspension D, since the system remained liquid after the process, no precipitation of polymer and silica particles was observed after freezing, thawing, and filtration.

Claims

1. A method for preparing a polymer incorporated into a solid, comprising: I) Provide an aqueous dispersion comprising polymer particles having an intensity-based harmonic average particle size (Z-average) of ≤ 500 nm as measured by dynamic light scattering; II) Store the dispersion from step I) at a temperature ≤ 0°C until a precipitate forms; III) Separate the precipitate from step II); IV) Remove water from the precipitate separated in step III) to obtain a dehydrated precipitate, wherein the dehydrated precipitate has an inorganic particle content of ≥ 2% to ≤ 50% based on the total weight of the dehydrated precipitate. Its features The dispersion of step I) further comprises inorganic particles having an intensity-based harmonic mean particle size (Z-mean) of ≤ 100 nm hydrodynamic diameter as measured by dynamic light scattering. Furthermore, the polymer is crystalline polyurethane.

2. The method according to claim 1, further comprising: V) Grind the dehydrated precipitate from step IV) into particles with a number-based average particle size of ≤ 500 μm as measured by optical microscopy.

3. The method according to any one of claims 1 to 2, wherein the dispersion of step I) has a polymer solid content of ≥ 20% to ≤ 60% by weight based on the total weight of the dispersion.

4. The method according to any one of claims 1 to 2, wherein step II) is carried out at a temperature of ≥ -40°C to ≤ -8°C.

5. The method according to any one of claims 1 to 2, wherein step III) comprises a filtration step and / or a decantation step.

6. The method according to any one of claims 1 to 2, wherein step IV) is performed at a temperature ≤ 2°C.

7. The method according to any one of claims 1 to 2, wherein the dehydrated precipitate of step IV) has a water content of ≥ 0.1% by weight to ≤ 5% by weight based on the total weight of the dehydrated precipitate.

8. The method according to any one of claims 1 to 2, wherein the polymer in the dispersion of step I) has a number-average molecular weight Mn of ≥ 30000 g / mol as determined by gel permeation chromatography.

9. The method according to any one of claims 1 to 2, wherein, The inorganic particles in the dispersion of step I) are selected from silicon dioxide, titanium dioxide, aluminum oxide, titanium nitride, tungsten nitride, tungsten carbide, carbon black, graphene, carbon nanotubes, metals, sheet silicates, clay containing organic cations, non-white metal oxides, or mixtures of at least two of the above particle types.

10. The method according to any one of claims 1 to 2, wherein the dispersion of step I) does not contain solid polyisocyanates and / or elements of Groups 5 and 6 of the periodic table, wherein said elements have an oxidation number of at least +4.

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