NANOPARTICLE DISPERSIONS

Abstract

A method for preparing a dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, the method comprising continuously mixing: at least one solution or slurry containing a reactant precursor for the solid organic dye or pigment in an organic or other solvent with the liquid carrier in a counter current mixing reactor whereby to obtain reaction of the reactant precursor and formation of the solid organic dye or pigment as a dispersion of nanoparticles in the liquid carrier and solvent mixture; optionally, removing unreacted reactant precursor and/or by-product from the dispersion when present; and optionally, concentrating the dispersion.

Claims

1: A method for preparing a dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, the method comprising continuously mixing: at least one solution or slurry containing a reactant precursor for the solid organic dye or pigment in an organic or other solvent with the liquid carrier in a counter current or concurrent mixing reactor whereby to obtain reaction of the reactant precursor and formation of the solid organic dye or pigment as a dispersion of nanoparticles in the liquid carrier and solvent mixture; optionally, removing unreacted reactant precursor and/or by-product from the dispersion when present; and optionally, concentrating the dispersion.

2: A method according to claim 1, wherein the at least one solution or slurry and/or the liquid carrier contains a wetting agent and/or a dispersant.

3: A method according to claim 1, further comprising adding a wetting agent and/or a dispersant to the dispersion.

4: A method according to claim 1, wherein the method provides a dispersion of nanoparticles of median (Z) diameter between 100 nm to 300 nm, for example, between 100 nm and 150 nm.

5: A method according to claim 1, wherein the method provides a dispersion having unimodal polydispersity.

6: A method according to claim 1, wherein the method provides a solid content of the dispersion of solid organic dye or pigment greater than 5.0 wt/wt % and less than 15 wt/wt % of the dispersion.

7: A method according to claim 1, wherein the method provides a dispersion having a dynamic light scattering (DLS) polydispersity index between 0.1 and 3.0.

8: A method according to claim 1, wherein the method comprises controlling one or more of nanoparticle size, and polydispersity by selection in the or each organic or other solvent, the liquid carrier, the concentration of reactant precursors in the or each solution or slurry and/or in the liquid carrier, the temperature and pressure of the or each solution or slurry and/or liquid carrier, the residence times of the or each solution or slurry and/or the liquid carrier, and the ratio of the flow rates of the or each solution or slurry and the liquid carrier in the reactor.

9: A method according to claim 1, wherein the liquid carrier comprises water.

10: A method according to claim 9, wherein the organic solvent is one or more of ethyl acetate, ethanol, methanol, diethyl ether, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, acetone, ethylene glycol, propylene glycol and isopropyl alcohol.

11: A dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, obtained or obtainable by the method of claim 1.

12: A dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, wherein the nanoparticles consist essentially of the solid organic dye or pigment.

13: A dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, wherein the nanoparticles consist essentially of the solid organic dye or pigment and a wetting agent for the nanoparticles.

14: A dispersion according to claim 11, comprising less than 5 wt/wt % of a dispersant.

15: A dispersion according to claim 11, having a solid content of nanoparticles greater than 3 wt/wt % and less than 20 wt/wt %.

16: A dispersion according to claim 11, which has unimodal polydispersity.

17: A dispersion according to claim 11, wherein the nanoparticles have median (Z) diameter between 100 nm and 300 nm, for example, between 100 nm and 150 nm.

18: A dispersion according to claim 11, wherein the liquid carrier comprises water.

19: An ink concentrate for digital inkjet printing, comprising the dispersion of claim 11.

20: A cosmetic paste, comprising the dispersion of claim 11.

Description

[0096] The present invention will now be described in more detail with reference to the following Examples and the accompanying drawings in which:

[0097] FIG. 1 is a schematic illustration of a counter current reactor, described in International Patent Application WO 2005/077505 A2, which is suitable for carrying out the method of the present invention;

[0098] FIG. 2 is a scheme outlining the synthesis and dispersion of Pigment Blue 15 in the reactor of FIG. 1 according to one embodiment of the method of the present invention;

[0099] FIG. 3 shows graphs obtained by dynamic light scattering (DLS) from dispersions prepared (a) by suspending Pigment Blue 15 obtained from the reactor according to one embodiment of the method of the present invention in deionised water and (b) a commercially available Pigment Blue 15 in deionised water;

[0100] FIG. 4 shows FT-ATR infra-red spectra of Pigment Blue 15 obtained from the reactor according to one embodiment of the method of the present invention and a commercially available Pigment Blue 15; and

[0101] FIG. 5 is a powder X-ray diffraction pattern of the Pigment Blue 15 obtained from the reactor according to one embodiment of the method of the present invention.

[0102] Referring now to FIG. 1, a counter current mixing reactor, generally designated 10, comprises a first inlet 11 and an outlet 12 in which a second inlet 13 is diametrically opposed to the first inlet 11 and disposed in the first inlet 11. The first inlet 11 and the second inlet 13 are co-axial with one another and the second inlet 12 provides a nozzle 14 in the shape of a conical funnel 15.

Synthesis of Copper (II) Phthalocyanine (CuPC; Pigment Blue 15)

[0103] A proof-of-concept study examined the preparation of copper (II) phthalocyanine (Pigment Blue 15) by synthesis from the reactant precursors phthalonitrile and copper (II) nitrate hydrate (see FIG. 2) in a counter current mixing reactor as shown in FIG. 1 of laboratory scale.

[0104] In one experiment, an upward flow of a solution of copper (II) nitrate hydrate in methanol (0.03 M) and a downward flow of a solution of phthalonitrile in methanol (MeOH) containing sodium methoxide (NaOMe; 5 wt %) was arranged in the reactor using positive displacement pumps with 1:1 flow ratio at total (upward) flow rate 20 ml/min.

[0105] Prior to the mixing, the reactor was heated to a temperature of 200° C. and during the mixing the pressure within the reactor was maintained at 17.2 MPa using a back-pressure regulator.

[0106] The dark green to brown dispersion of copper (II) phthalocyanine exiting the reactor was collected and centrifuged to provide a dark blue pellet in yellow to green supernatant.

[0107] The pellet was removed from the supernatant, washed consecutively with water and tetrahydrofuran. After drying in an oven, a dark blue powder of copper (II) phthalocyanine (CuPC) was obtained.

Dispersions of the Synthesised Copper (II) Phthalocyanine

[0108] A dispersion of copper (II) phthalocyanine in water was prepared by the addition of deionised water containing a dispersant (Disperbyk 190) to the powder obtained above with stirring.

[0109] A sample was prepared from the dispersion for analysis by Dynamic Light Scattering (DLS) Spectroscopy by filtering through a 5.0 micron filter.

[0110] The filtered sample was analysed at 25° C. in a 10 mm cuvette using a Malvern Instruments Nano ZS particle sizer fitted with a back-scattering detector at 173° with an incident laser source (He—Ne laser with wavelength 632.8 nm).

[0111] A CONTIN algorithm was used to deconvolute the scattered light signal and give a size distribution. The analysis assumed a continuous phase of pure water (viscosity=0.8872 cP; refractive index=1.330) for the measurement settings. The z-average size of the nanoparticles was taken from the raw cumulants data fit from the DLS instrument.

[0112] FIG. 3 shows the DLS spectrum (a) obtained for the dispersion and a DLS spectrum (b) obtained from a sample of a dispersion of commercially available Pigment blue 15 (Sigma-Aldrich) prepared in the same way.

[0113] As may be seen, the dispersions are unimodal and the Z-average (˜median) particle size of the nanoparticles are respectively ˜265 nm and ˜310 nm. The DLS polydispersity index of each sample was determined as 0.228 and 0.305 respectively.

[0114] These dispersions, which are stable at standard room temperature and pressure, strongly suggest that dispersions of copper (II) phthalocyanine directly obtained from the reactor will be stable when a wetting agent and/or dispersant is present.

Infra-Red Spectrum of the Synthesised Copper (II) Phthalocyanine

[0115] An infra-red spectrum of the powder from the reactor was obtained by Fourier Transform Attenuated Total Reflectance (FT-ATR) infra-red spectrometry using a Perkin Elmer 100 FT-IR spectrometer equipped GRAMS/AI software. A diamond crystal was used and absorptions were recorded at a constant crystal pressure over 16 scans in the wavelength range 600 cm.sup.−1 to 4000 cm.sup.−1.

[0116] The spectrum 17, shown in FIG. 4, is in excellent agreement (especially in the region from 500 cm.sup.−1 to 1700 cm.sup.−1) with an infra-red spectrum 16 obtained under similar conditions from commercially available Pigment blue 15 (Sigma-Aldrich).

Powder XRD Pattern of Synthesised Copper (II) Phthalocyanine

[0117] A powder X-ray diffraction (XRD) pattern was obtained from the powder using a Bruker AXS D8 X-ray diffractometer (Coventry, UK) with wavelength 0.154 nm, Cu source, voltage 40 kV and filament emission 40 mA. The 2θ scanning range was 5° to 90° and 0.02° steps were used at 1 second time counter. The scatter slit and the receiving slit were set at 0.2° and 0.1° respectively. Data were measured at room temperature in flat-plate geometry from powders pressed into a Macor ceramic holder. Data analysis was performed using the Philips incl. Diffraction Technology Traces software.

[0118] FIG. 5 shows the X-ray diffraction pattern 18 obtained as compared to a library X-ray diffraction pattern 19 for the alpha polymorph of copper (II) phthalocyanine.

[0119] As may be seen, the pattern is in good agreement with the library pattern suggesting that the powder obtained from the reactor is predominantly crystalline and of the alpha form.

[0120] The presence of other peaks in the pattern suggests that the beta polymorph (and amorphous form) may also be present. It is envisaged, therefore, that selection in the parameters controlling nanoparticle size may also provide control over the crystalline form of the nanoparticles and, in particular, whether a single polymorph (alpha or beta) is obtained.

[0121] These studies clearly point to a method comprising tandem synthesis and precipitation of nanoparticle dispersions of a pigment in a counter current mixing reactor.

[0122] The size and polydispersity index of the dispersions are expected (on the basis of precipitation studies of disperse dyes described in our co-pending international patent application PCT/GB2018/053411) to be sensitive to, and controlled by, the selection of parameters such as ratio of flow rate of the organic solvent with the liquid carrier as well as selection of organic solvent and liquid carrier.

[0123] The present invention provides, therefore, a single, continuous process for the synthesis of stable dispersions of an organic pigment or an organic dye with desired nanoparticle size and encapsulation of the nanoparticles. It also provides a single, continuous process for the synthesis of solid organic compounds with desired nanoparticle size.

[0124] The processes are suitable for large scale production and environmentally responsible because they avoid the need for the large amounts of energy and solvent that are necessary for large scale milling.

[0125] The present invention may also allow the preparation of nanoparticle dispersions or nanoparticles of organic dyes or pigments which cannot be milled effectively (for example, Disperse Red 55). It may, therefore, provide access to stable dispersions of solid organic dyes or pigments which are not presently obtainable. It may further provide access to new polymorphs of the crystalline organic dyes or pigments.

[0126] Note that the nanoparticle diameters specified herein are references to diameters which may be determined by, or calculated from, DLS or the dispersions in accordance with ISO 22412:2017. The solid contents specified herein are references to solid contents which may be determined by drying in accordance with ISO 3251:2008.

[0127] Note also that the nanoparticles of the present invention are not comprised or reliant on an oil-in-water emulsion but are instead comprised by the solid organic dye or pigment or by the solid organic dye or pigment encapsulated (at least in part) by a water soluble surfactant.

[0128] Note further that the methods of the present invention may find general applicability to the preparation of nanoparticle dispersions and nanoparticles of other solid organic compounds including pharmaceutical actives, pharmaceutical additives, pharmaceutical excipients, organometallic dopants or emitters useful in organic light emitting diodes (OLEDs) and organometallic catalysts useful in catalytic convertors and in organic synthesis.