METHOD OF MANUFACTURING FILLED POLYURETHANE PARTICLES

Abstract

The present invention relates to a method of manufacturing a solids-incorporating polymer comprising the steps of: I) providing an aqueous polymer dispersion, the dispersion comprising crystallizing polyurethane particles having a mean 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 is formed; III) Isolating the precipitate of step II) and IV) removing water from the isolated precipitate of step III), thereby obtaining a water-depleted precipitate. The invention also relates to a solid particulate composition which is obtainable by the method and the use of the composition as a build material in additive manufacturing processes, as a coating, an adhesive or as a rubber.

Claims

1. A method of manufacturing a solids-incorporating polymer comprising: I) Providing an aqueous dispersion, the dispersion comprising polymer particles having an intensity-based harmonic mean particle size of the hydrodynamic diameter (Z-Average), as determined by dynamic light scattering, of ≤500 nm; II) Storing the dispersion of step I) at a temperature of ≤0° C. until a precipitate is formed; III) Isolating the precipitate of step II) to obtain an isolated precipitate; IV) Removing water from the isolated precipitate of step III), thereby obtaining a water-depleted precipitate; wherein the dispersion of step I) further comprises inorganic particles, and wherein the polymer is a crystallizing polyurethane.

2. The method according to claim 1, wherein the inorganic particles have an intensity-based harmonic mean particle size of the hydrodynamic diameter (Z-Average), as determined by dynamic light scattering, of ≤100 nm.

3. The method according to claim 1, further comprising: V) Grinding the water-depleted precipitate of step IV) into particles with a number-based mean particle size, as determined by optical microscopy, of ≤500 μm.

4. The method according claim 1, wherein the dispersion of step I) has a polymer solids content of ≥20 weight-% to ≤60 weight-%, based on the total weight of the dispersion.

5. The method according to claim 1, wherein step II) is conducted at a temperature of from ≥−40° C. to ≤−8° C.

6. The method according to claim 1, wherein step III) comprises a filtration step and/or a decanting step.

7. The method according to claim 1, wherein step IV) is conducted at a temperature of ≤2° C.

8. The method according to claim 1, wherein the water-depleted precipitate of step IV) has a water content of from ≥0.1 weight-% to ≤5 weight-%, based on the total weight of the water-depleted precipitate.

9. The method according to claim 1, wherein the water-depleted precipitate of step IV) has an inorganic particle content of from ≥2 weight-% to ≤50 weight-%, based on the total weight of dried precipitate.

10. The method according to claim 1, wherein a polymer of the polymer particles in the dispersion of step I) has a number-average molecular weight Mn, determined by gel permeation chromatography, of ≥30000 g/mol.

11. The method according to claim 1, wherein the inorganic particles in the dispersion of step I) comprise silicon dioxide, titanium dioxide, aluminum oxide, titanium nitride, tungsten nitride, tungsten carbide, carbon black, graphene, carbon nanotubes, metals, sheet silicates, clays comprising organic cations, non-white metal oxides, or a mixture of at least two of the aforementioned particle types.

12. The method according to claim 1, wherein the dispersion of step I) is free from solid polyisocyanates and/or elements from subgroups 5 and 6 of the periodic system of elements in which the particular element has an oxidation number of at least +4.

13. A solid particulate composition, obtained by a method according to claim 1, comprising particles, wherein the particles of the composition comprise a matrix of a crystallizing polyurethane, wherein a number-based mean particle of the composition, as determined by optical microscopy, is ≤10 mm, and wherein inorganic particles are embedded within the matrix to form embedded inorganic particles having an number-based mean particle size, as determined by electron microscopy, of ≤1000 nm.

14. The composition of claim 13, wherein the particles of the composition have a major axis representing the largest dimension of each particle and a minor axis representing the smallest dimension of each particle, the dimensions being determined by optical microscopy, wherein the mean ratio of major axis length to minor axis length is from ≥1:0.01 to ≤1:1, and wherein the number-based mean particle size, as determined by optical microscopy, is ≤10 mm.

15. A build material in an additive manufacturing process, a coating, an adhesive or a rubber, comprising the solid particulate composition according to claim 13.

Description

EXAMPLES

[0059] The present invention will be further described with reference to the following examples without wishing to be bound by them.

[0060] Methods

[0061] The room temperature (RT) was 23° C. Unless noted otherwise, all percentages are weight percentages based on the total weight. Rheological parameters (G′, G″) were measured using a plate/plate oscillation viscosimeter according to ISO 6721-10 at 60° C. and an angular frequency of 1/s. Further measurements were taken every 30 seconds with the temperature falling at 4 K/min until a temperature of 20° C. was reached. At 20° C. the temperature was held constant for 60 min and measurements were taken every 30 seconds.

[0062] Polymer Dispersions

[0063] Polymer dispersion A was a crystallizing polyester urethane/urea aqueous dispersion for adhesive applications with a pH of 6,8 with a glass transition temperature of the polymer (DSC, 20 K/min) of −50° C., a melting temperature of the polymer (DSC, 20 K/min) of 49° C. and a solids content of ca. 50 weight-%.

[0064] Polymer dispersion B was a crystallizing polyester urethane/urea aqueous dispersion for adhesive applications with a pH of 6,9, a glass transition temperature of the polymer (DSC, 20 K/min) of −51° C., a melting temperature of the polymer (DSC, 20 K/min) of 49° C. and a solids content of ca. 50 weight-%.

[0065] Polymer dispersion C was a crystallizing polyester urethane/urea aqueous dispersion for adhesive applications with a pH of 7.1, a glass transition temperature of the polymer (DSC, 20 K/min) of −48° C., a melting temperature of the polymer (DSC, 20 K/min) of 50° C. and a solids content of ca. 50 weight-%.

[0066] Polymer dispersion Y was a non-crystallizing aliphatic polyester polyurethane aqueous dispersion with a pH of 7.0 with a glass transition temperature (DSC, 20 K/min) of −4° C. and a solids content of ca. 50 weight-%.

[0067] Polymer dispersion Z was a non-crystallizing anionic polycarbonate ester polyurethane aqueous dispersion with a pH of 7.5 and with a glass transition temperature of −36° C. (DSC, 20 K/min) and a solids content of ca. 40%.

[0068] The polymers of dispersions A, B and C were linear polyester polyurethanes having terminal hydroxyl groups produced by reaction of a) polyester diols having a molecular weight of 1500 to 3000 g/mol and b) diol chain extenters with c) aliphatic diisocyanates. The component a) comprised a polyester diol in the molecular weight range of 1500 to 3000 g/mol, the component b) 1,4-dihydroxybutane and the component c) IPDI and HDI.

[0069] Silica Suspensions

[0070] Silica suspension D was an aqueous colloidal suspension of amorphous silicon dioxide with a solids content of ca. 30 weight-%, a mean particle size of ca. 9 nm and a pH of 10.4.

[0071] Silica suspension E was an aqueous colloidal suspension of amorphous silicon dioxide with a solids content of ca. 50 weight-% a mean particle size of ca. 55 nm and a pH of 9.1.

[0072] Preparation of Polymer Dispersions further Comprising Silica

[0073] Dispersion mixtures were prepared by mixing 500 mL of the polymer dispersion with the desired amount of silica suspension in a stirring cup and stirring at 100 rpm for 5 min. Weight percentages of the silica dispersion content are based on the total weight of the polymer dispersion/silica dispersion mixture. From the resulting mixture 100 g were diverted and the flow time using a DIN 4 cup of the freshly prepared mixture and of the mixture after storing at room temperature for 56 days were determined. The mixture was classified as “instable” if the flow time had increased by more than 30% or particles or coagulate or precipitate were observed.

[0074] Further 10 g of the freshly prepared mixture were poured into a teflon cup with a diameter of 10 cm and dried at 60° C. within one day until a firm, dry film was obtained. The film was removed and rheologically examined in a plate/plate oscillation rheometer. These experiments are denoted “dried”.

[0075] Further 300 g of the freshly prepared mixture were transferred into a 500 mL plastic screw-top bottle, stored for 48 h at −18° C. and subsequently thawed at room temperature for 24 h. After thawing the resulting coarse-grained polymer suspension was filtered through a 10 μm paper filter and the polymer residue was dried to constant weight in a rotary evaporator at 40 ° C. water bath temperature and 20 mbar pressure. A solid material was obtained. The residual solids content in the filtrate was less than 2 weight-%, as determined gravimetrically after drying for 1 h at 125° C. , based on the originally present solids in the polymer dispersion and silica suspension. These experiments are denoted “precipitated”.

TABLE-US-00001 Table 1 with entries 1 to 27 documents the results of rheological testing for material obtained from polymer dispersions and polymer dispersions comprising silica. “*” denotes comparative examples. The silica contents are stated as solid contentcalculated from the parent suspensions. Solid G′ (20° C.) − Stability of non-dried content G′ [Pa] G′ [Pa] G′ [Pa] G′ [Pa] G′ (100° C.) G′(20° C.)/ No. Formulation mixture after 56 d filtrate 100° C. 71° C. 50° C. 20° C. [Pa] G′(100° C.)  1* A dried Stable 7.0E+04 1.7E+05 3.1E+05 7.0E+05 6.3E+05 9.9  2* B dried Stable 2.0E+05 3.8E+05 5.7E+05 1.0E+06 7.9E+05 4.9  3* C dried Stable 5.3E+05 7.0E+05 8.6E+05 1.2E+06 6.3E+05 2.2  4* B with 3% D Stable 2.2E+05 4.2E+05 6.4E+05 1.1E+06 8.4E+05 4.7 dried  5* B with 6% D Stable 2.6E+05 4.9E+05 7.5E+05 1.3E+06 9.9E+05 4.7 dried  6* B with 13% D Stable 5.7E+05 9.9E+05 1.5E+06 2.5E+06 1.9E+06 4.4 dried  7* B with 21% D Instable, flow time 1.8E+06 3.0E+06 4.4E+06 7.5E+06 5.7E+06 4.2 dried increased >30%  8* B with 5% E Stable 2.2E+05 4.0E+05 6.1E+05 1.0E+06 7.9E+05 4.6 dried  9* B with 10% E Instable, flow time 2.8E+05 5.1E+05 7.6E+05 1.3E+06 9.9E+05 4.5 dried increased >30%  10* B with 20% E Instable, flow time 4.4E+05 8.3E+05 1.3E+06 2.1E+06 1.7E+06 4.9 dried increased >30%, sedimentation and coagulation observed  11* B with 30% E Instable, flow time 6.7E+05 1.2E+06 1.9E+06 3.3E+06 2.7E+06 5.0 dried increased >30%, sedimentation and coagulation observed  12* B with 50% E Instable, flow time 5.0E+06 9.3E+06 1.5E+07 2.9E+07 2.4E+07 5.7 dried increased >30%, sedimentation and coagulation observed  13* A precipitated Not determined <1% 7.7E+04 1.8E+05 3.3E+05 6.9E+05 6.1E+05 8.9  14* B precipitated Not determined <1% 2.1E+05 3.8E+05 5.8E+05 9.4E+05 7.3E+05 4.5  15* C precipitated Not determined <1% 5.8E+05 7.8E+05 9.7E+05 1.3E+06 6.9E+05 2.2 16 B with 3% D Not determined <1% 2.1E+05 4.1E+05 6.3E+05 1.1E+06 8.7E+05 5.1 precipitated 17 B with 6% D Not determined <1% 2.4E+05 4.5E+05 6.9E+05 1.1E+06 8.8E+05 4.7 precipitated 18 B with 13% D Not determined <1% 6.8E+05 1.2E+06 1.7E+06 2.8E+06 2.2E+06 4.2 precipitated 19 B with 21% D Not determined <1% 2.8E+06 4.2E+06 5.9E+06 9.5E+06 6.7E+06 3.4 precipitated 20 B with 5% E Not determined <1% 1.9E+05 3.6E+05 5.7E+05 9.8E+05 8.0E+05 5.2 precipitated 21 B with 10% E Not determined <1% 2.4E+05 4.7E+05 7.2E+05 1.2E+06 9.9E+05 5.0 precipitated 22 B with 20% E Not determined <1% 4.2E+05 7.7E+05 1.2E+06 2.0E+06 1.6E+06 4.8 precipitated 23 B with 30% E Not determined <1% 6.7E+05 1.2E+06 1.8E+06 3.2E+06 2.5E+06 4.8 precipitated 24 B with 50% E Not determined <1% 4.2E+06 8.0E+06 1.3E+07 2.3E+07 1.9E+07 5.5 precipitated 25 A with 13% D Not determined <1% 2.3E+05 5.0E+05 9.2E+05 2.1E+06 1.9E+06 9.2 precipitated 26 A with 20% E Not determined <1% 7.2E+04 2.0E+05 4.1E+05 1.0E+06 9.7E+05 14.5 precipitated 27 A with 6% D Not determined <1% 9.5E+04 2.6E+05 5.0E+05 1.2E+06 1.2E+06 13.2 and 10% E precipitated

[0076] An analysis of the rheological data reveals that the amounts of inorganic particles introduced by freeze-coagulation/precipitation perform similarly in modulus modification (strengthening effect) compared to standard dried film materials. This strengthening behavior is commonly associated with a well distributed filler. It is concluded that a highly homogenous mixture of the inorganic filler particles within the polymer has been achieved in the method according to the invention. This circumvents the need for temperature- and energy intensive mixing processes and allows for efficient introduction of fillers with a high surface area at low mixing energies.

[0077] Further comparative examples (28* and 29*) were undertaken with the dispersions Y and Z and 10 weight-% respectively of silica suspension D.

[0078] In the system of polymer dispersion Y and silica suspension D the precipitate of polymer and silica particles after thawing was observed as a solid rubbery-like block that could not be processed any further. In the system of polymer dispersion Z and silica suspension D no precipitation of polymer and silica particles were observed after freezing, thawing and filtration as the systems stayed liquid after the process.