Polydispersant metal oxide nanoparticle dispersion composition

Abstract

The composition includes a plurality of pigment particles including a metal oxide, a first dispersant that is a polymer, and a second dispersant that includes molecules having a lower molecular weight than the first dispersant. The composition may be used in a hardcoat.

Description

[Technical field]

[0001] The present technology relates generally to metal oxide dispersions, and more particularly to metal oxide dispersions stabilized in a polymer matrix. Summary of the Invention

[0002] Polymeric dispersants can be used to stabilize metal oxide dispersions, but excessive levels can adversely affect haze and other properties such as abrasion resistance, weatherability, and formulation viscosity in polymer matrices produced using these dispersions. The techniques of the present disclosure allow the use of low polymeric dispersant levels to stabilize metal oxide dispersions in polymer matrices. In some aspects, these techniques combine polymeric dispersants with low molecular weight dispersants to optimize surface stabilization and coverage of tungsten oxide nanoparticle dispersions.

[0003] In one aspect, the present disclosure provides a composition comprising a plurality of pigment particles comprising a metal oxide; a first dispersant that is a polymer comprising molecules having an average molecular weight equal to or greater than 2000 atomic mass units; and a second dispersant comprising molecules having a maximum molecular weight less than 2000 atomic mass units.

[0004] In another aspect, the present disclosure provides a hardcoat comprising a composition according to the present disclosure.

[0005] In yet another aspect, the present disclosure provides a method for making a pigment dispersion. The method includes dissolving a first dispersant and a second dispersant, which are polymers, in a solvent to form a solution. The first dispersant includes molecules having an average molecular weight of 2000 atomic mass units or more, and the second dispersant includes molecules having a maximum molecular weight of less than 2000 atomic mass units. The method also includes mixing a plurality of pigment particles including a metal oxide in the solution to form a dispersion, and milling the dispersion to a desired particle size.

[0006] In yet a further aspect, the present disclosure provides a method of making a hard coat having pigment particles, the method comprising dissolving a curable binder material in a solvent to form a solution, adding the solution to a dispersion comprising a composition according to the present disclosure, adding one or more additives to the dispersion, coating the dispersion onto a substrate, drying the coating to remove the solvent, and curing the dried coating. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating dispersed pigment particles according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The techniques of the present disclosure allow for the use of low polymeric dispersant levels to stabilize metal oxide dispersions in polymer matrices. In some aspects, these techniques combine polymeric dispersants with low molecular weight dispersants to optimize surface stabilization and coverage of tungsten oxide nanoparticle dispersions.

[0009] Generally, surface stabilizers can be used to stabilize the metal oxide surface and provide dispersibility in solvents, especially organic systems, for example by making the metal oxide surface hydrophilic. Since smaller particles have a higher total surface area compared to using larger particles, more surface stabilizer can be used to adequately cover the particle surface.

[0010] Particularly high levels of dispersants can be used with certain metal oxides, depending on the surface charge and number of hydroxyl groups. In one example, tungsten oxide materials, by having a low surface charge and a small number of hydroxyl groups, can be used with relatively higher loadings of dispersant than other metal oxides. In some known commercial dispersions, the dispersant used can have 2 to 10 times the total weight of the metal oxide nanoparticles in the dispersion. In these existing dispersions, the amount of dispersant used can be described as an excess amount, which may drive the equilibrium to cover the metal oxide surface, especially for tungsten oxide nanoparticles. Some dispersants used with metal oxides include polymeric dispersants with basic anchoring groups such as amines to stabilize acidic particles. The compositions of the present disclosure generally provide a relatively low total weight of dispersant relative to the weight of the metal oxide nanoparticles, compared to existing techniques for producing dispersions, which may improve coating performance.

[0011] The composition of the present disclosure may include a plurality of pigment particles, a first dispersant, and a second dispersant. The second dispersant may have a lower molecular weight in terms of maximum or average molecular weight than the first dispersant. In some embodiments, the first dispersant has an average or minimum molecular weight equal to or greater than a first threshold. In some embodiments, the second dispersant has an average or maximum molecular weight equal to or greater than a second threshold. The plurality of pigment particles may include a metal oxide. In some embodiments, the first dispersant is a polymeric dispersant that may have a high molecular weight. In some embodiments, the second dispersant is a non-polymeric dispersant. In one example, the composition includes a plurality of pigment particles including a metal oxide, a first dispersant that is a polymer, the first dispersant including molecules having an average molecular weight equal to or greater than 2000 atomic mass units, and a second dispersant including molecules having a maximum molecular weight less than 2000 atomic mass units.

[0012] By using a first dispersant and a second dispersant with the pigment particles, the total dispersant usage can be reduced compared to existing compositions that use only one dispersant, especially existing compositions that use high molecular weight polymeric dispersants. The reduced total dispersant usage can improve coating performance. For example, lower total dispersant usage can facilitate lower haze coatings by minimizing the blooming of unbound dispersant to any air interface. In some embodiments, the % haze of a coating produced using the present dispersion can be 15, 10, 5, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, or even 0.4 percent or less. Existing coatings may require more total amount of dispersant to achieve the same % haze. Lower total dispersant usage can also promote higher abrasion resistance, for example, due to higher acrylic resin content and less unbound dispersant acting as a plasticizer. In some cases, lower total dispersant usage can promote better weatherability. Additionally, lower total dispersant usage can reduce formulation viscosity, which can be beneficial in certain applications.

[0013] The compositions of the present disclosure may be used in any suitable application, such as in the manufacture of polymeric hardcoats having pigment particles, or in coating or extrusion layers, such as adhesive layers having pigment particles. Generally, such compositions and hardcoats may be suitable for use in a variety of applications, such as solar control in automotive or building window films, near infrared (NIR) camera readable license plates and traffic signs, fiber laser protection films, among others.

[0014] Any suitable technique may be used to prepare a polymeric hard coat using the composition. In one example, a method of preparing a hard coat having pigment particles includes one or more of the following: dissolving a curable binder material in a solvent to form a solution, adding this solution to a dispersion having any of the compositions of the present disclosure, adding one or more additives to the dispersion, coating the dispersion onto a substrate, drying the coating to remove the solvent, and curing the dried coating.

[0015] The composition can provide dispersed pigment particles. In some embodiments, each pigment particle can be anchored to at least one polymeric first dispersant molecule and at least one second dispersant molecule to form a plurality of dispersed pigment particles. FIG. 1 shows an example of a dispersed pigment particle 10. The dispersed pigment particle 10 includes a pigment particle 12 anchored to one or more first dispersants 14 and one or more second dispersants 16.

[0016] As used herein, "anchoring group" or "anchor group" refers to a functional group on a molecule that can anchor the molecule to a pigment particle.

[0017] Generally, each dispersant can contain at least one anchoring group that is a pigment-affinity anchoring group for the pigment particles used in the composition. Non-limiting examples of anchoring groups include amines, ammonium salts, phosphates, sulfonates, sulfates, carboxylates, phosphonates, and phosphinates.

[0018] The anchoring groups of the dispersants can be classified as cationic, anionic, or nonionic depending on their charge. Charged groups may also be neutralized by counterions. Non-limiting examples of cationic anchoring groups include amines (or polyamines) or ammonium salts. Non-limiting examples of anionic anchoring groups include phosphates, sulfonates, and carboxylates. Non-limiting examples of non-ionic anchoring groups include ethers or esters.

[0019] As used herein, the term "charge" refers to the partial charge on non-carbon atoms of anchoring groups such as N or O. These partial charges can be derived from electron density measured using high resolution X-ray or electron diffraction techniques. Spectroscopic measurements of core electron binding energy shifts and dipole moment measurements also provide information about surface charge. If acidic, the charge of a dispersant can be referred to as the acid number. The acid number can be determined by conventional methods such as titration.

[0020] In some embodiments, the first dispersant and the second dispersant each have an anchoring group, and at least one anchoring group of the first dispersant may have a similar surface charge as at least one anchoring group of the second dispersant when placed in the same solution.

[0021] As used herein, the term "similar surface charge" refers to the surface charge of the anchoring group of a first dispersant being the same as or neutral to the surface charge of the anchoring group of a second dispersant. For example, the first dispersant may have a positive charge and the second dispersant may have a positive or neutral charge.

[0022] Any suitable technique may be used in preparing the composition of the present disclosure. In one example, a method for preparing a pigment dispersion comprising the composition includes one or more of the following: dissolving a first dispersant and a second dispersant, which are polymers, in a solvent to form a solution, mixing a plurality of pigment particles comprising a metal oxide in the solution to form a dispersion, and milling the dispersion to a desired particle size.

[0023] In some embodiments, the present disclosure provides a composition comprising a polymeric dispersant and a low molecular weight dispersant, which may also be described as a surfactant. The polymeric dispersant may be used to provide sufficient separation during high impact milling processes. The low molecular weight dispersant may be used to complement the polymeric dispersant to facilitate surface coverage. The composition may provide improved surface stabilization and coverage of metal oxide nanoparticles, such as tungsten oxide nanoparticles, by, for example, allowing the total dispersant usage to be reduced on a weight basis, especially compared to compositions using only polymeric dispersants.

[0024] The particles in such dispersions can be produced through a ceramic process under reducing conditions (hydrogen partial pressure), so that the primary crystal size is usually several hundred nanometers or more. A high energy media milling process can be applied to reach the desired particle size distribution for the application. For example, distributions in the sub-100 nanometer range are used in many optical applications, such as solar control window films, and have very little or no visible light scattering.

[0025] The composition may be provided in the form of a liquid dispersion or a solid dispersion. The liquid dispersion may include one or more solvents. The solid dispersion may be prepared by removing all the solvents in the liquid dispersion. The solid dispersion may be redispersed in liquid form by adding one or more solvents. The change between the liquid dispersion and the solid dispersion may not significantly change the dispersed pigment particle size.

[0026] As used herein, the term "pigment particles" refers to insoluble particles that are added to change the transmission of solar energy through a material. Pigment particles can be inorganic or organic. In some embodiments, pigment particles selectively scatter light in either the visible or infrared wavelength range, which may be described as non-white in color. In other embodiments, pigment particles, such as titanium dioxide pigment particles, scatter light in both the visible and infrared wavelength ranges, which may be described as white.

[0027] As used herein, the term "dispersed pigment particles" refers to pigment particles fixed in one or more dispersants.

[0028] The pigment particles may include metal oxides. In some embodiments, the metal oxides may include tungsten oxide or mixed valence tungsten oxide. Visible absorbing metal oxides such as cerium oxide, zinc oxide, titanium oxide, tin oxide, manganese oxide, other transition metal oxides or metal oxide pigment nanoparticles (e.g., chromium-iron oxide, spinel oxides (e.g., cobalt aluminate), and iron manganese oxide) may be used. IR absorbing metal oxides such as antimony tin oxide (ATO), indium tin oxide (ITO), aluminum doped zinc oxide, and zinc antimony oxide may also be used.

[0029] Mixed valence tungsten oxides are, for example, WO 2.92 , WO 2.81 , and WO 2.72 Reduced tungsten oxides such as tungsten blue oxide (TBO), or M x WO 3 The tungsten bronze oxides may include tungsten bronze oxides of the type M, where M can be sodium, potassium, cesium, or a number of other metals. Tungsten bronze oxides, such as cesium tungsten oxide (CsWO) or potassium tungsten oxide (KWO), may also be referred to as tungsten oxides or doped tungsten oxides. Mixed-valence tungsten oxides in nanoparticle form generally allow high visible light transmittance and low near-infrared transmittance (or high near-infrared absorptance).

[0030] Dispersants can be used to stabilize particles in solid or liquid dispersions with incompatible solids or liquids. Particles, especially small particles with high surface area, tend to aggregate in the absence of any other charge stabilization mechanism, for example. Dispersants can use steric barriers, electrostatic charges, or electrosteric mechanisms to prevent separation of solid particles.

[0031] The first dispersant may be a polymeric dispersant, which is a polymer having various lipophilic and hydrophilic functional groups attached to the ends of the polymer backbone. Some examples of functional groups of the polymeric first dispersant include polyether, polyester, acrylic, or urethane.

[0032] As used herein, the term "polymeric" describes a molecule that has many repeating subunits. The term "non-polymeric" describes a molecule that does not have many repeating subunits. For example, a polymer molecule can have 10, 20, 30, 50, 100, 200, or even 500 or more repeating subunits.

[0033] The polymeric first dispersant may be a higher molecular weight oligomer or polymer, in some embodiments, the average or minimum molecular weight of the polymeric first dispersant is 1500, 2000, 3000, 4000, 5000, or even 6000 amu or more.

[0034] In some embodiments, the polymeric first dispersant may have a long chain length, hi some embodiments, the chain length may be 15, 20, 25, or even 30 or more carbon-carbon or carbon-heteroatom bonds.

[0035] The polymeric first dispersant may include block copolymers such as diblock, triblock, and brush with acidic, basic, or non-ionic binding groups. Generally, block copolymers are more effective than random copolymers. In some cases, random copolymers may be used and may be more effective.

[0036] Generally, polymeric dispersants with multiple anchoring sites can provide better stability than dispersants with only one anchoring site. Polymeric dispersants can reduce the incidence of dispersant molecules moving to the air interface. Polymeric dispersants can also provide better steric hindrance and steric barrier for high energy media milling process. Polymeric dispersants can be limited by the number of dispersants that are anchored to one particle by steric hindrance, and in some cases, multiple nanoparticles can be anchored to one dispersant particle.

[0037] The first dispersant particle anchoring site can be non-ionic, anionic (usually carboxylic, phosphoric, or sulfonic acids), or cationic (usually amine derivatives). Non-limiting examples of the anchoring groups of the first dispersant include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-polypropylene oxide copolymer (PEO / PPO), polyurethane (PU), polycaprolactone, and polyacrylate.

[0038] In some embodiments, the molecules of the first dispersant may comprise polymer chains, non-limiting examples of which include polyethers, polyesters, polyurethanes, and polyacrylates.

[0039] In some embodiments, the molecules of the first dispersant may include copolymers in the polymer. Non-limiting examples of copolymers in the polymer chain include polyester-polyamine copolymers, polyester-phosphate copolymers, or both. For example, some suitable polyester-polyamine copolymers include SOLPLUS D510 and SOLPERSE M387 (each commercially available from Lubrizol Corporation, Wickliffe, Ohio).

[0040] The second dispersant may be a low molecular weight dispersant. The low molecular weight dispersant may also be described as a small molecular weight surfactant. Such low molecular weight surfactants have been used to stabilize water-oil systems and nanoparticle synthesis. In some embodiments, the average molecular weight or maximum molecular weight of the second dispersant is 2000, 1000, 750, 500, 400, 300, 200, or 150 amu or less.

[0041] In some embodiments, the second dispersant may be a non-polymeric second dispersant. In other embodiments, the second dispersant may be a polymer and have a short length backbone. In one example, the second dispersant may have a maximum or average backbone length of 30, 25, 20, or even 15 or less. In general, when both the first dispersant and the second dispersant are polymeric, the first dispersant has a longer average backbone length than the second dispersant.

[0042] Low molecular weight dispersants may be typical well-defined molecules with a constant mass. Low molecular weight dispersants may have well-defined anchoring groups, such as positively charged quaternary ammonium ions or negatively charged anionic groups such as sulfates, sulfonates, phosphates, etc. The tail of the dispersant may provide solubility in the solvent medium. Low molecular weight may result in more anchoring groups (also described as linking units or head groups) per unit weight, which may result in higher surface coverage per unit weight of the dispersant. Small molecules may also have better mobility and faster binding mechanisms.

[0043] In some existing techniques, low molecular weight dispersants have not been found to be suitable for dispersing nanoparticles by grinding or ball milling approaches: they typically do not have a long enough chain length to form a protective shell to prevent particles from contacting each other during the vigorous milling environment.

[0044] In some embodiments, the second dispersant comprises a molecule having a cationic anchoring group. The cationic anchoring group may comprise a quaternary ammonium salt. Non-limiting examples of molecules having a cationic anchoring group include dodecyltrimethylammonium bromide (DTAB) and dimethyldioctadecylammonium bromide (DODAB), which are examples of quaternary ammonium salts.

[0045] In some embodiments, the second dispersant comprises a molecule having an anionic anchoring group. Non-limiting examples of molecules having an anionic anchoring group include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and dihexadecyl hydrogen phosphate.

[0046] In some embodiments, the second dispersant comprises a molecule having a non-ionic anchoring group. Non-limiting examples of molecules having a non-ionic anchoring group include 2-(methylamino)ethanol (MAE), 3-dimethylamino-1-propanol (DMAP), and 2-[2-(dimethylamino)ethoxy]ethanol (DMAEE).

[0047] In general, comparing dispersants, the first dispersant, which is a polymer, can be described as having a higher molecular weight, a large steric barrier, and some polymeric dispersants have multiple anchoring groups per molecule, providing a more stable average anchoring. The second dispersant, which is a low molecular weight, can be described as having a lower molecular weight, a small steric barrier, only a few anchoring groups per molecule, and less stable surface adsorption.

[0048] Generally, the use of the second dispersant can reduce the total amount of carbon and hydrogen used in the dispersant particles compared to a dispersion using only a long-chain polymeric dispersant. In some embodiments, the weight of the polymeric first dispersant is 50, 40, 30, 25, 20, 15, or even 10 percent or less of the weight of the pigment particles in the composition. In some embodiments, the combined weight of the polymeric first dispersant and the second dispersant is less than 60, 55, 50, 45, 40, 35, 30, 25, 20, or even 15 percent of the weight of the pigment particles.

[0049] The use of a secondary dispersant can reduce the amount of polymeric primary dispersant required to provide a similar milling particle size. In some embodiments, the use of a secondary dispersant can reduce the ratio of total weight of dispersant to weight of pigment particles by at least 20, 30, 40, or even 50 percent compared to using only the polymeric primary dispersant while achieving a similar average particle size.

[0050] As used herein, the term "similar average particle size" refers to one average particle size being within 50, 40, 30, 25, 20, 15, or 10 percent of another average particle size.

[0051] As used herein, the terms "Z-average size" and "average particle size" may be used interchangeably and refer to the harmonic intensity average hydrodynamic particle size in cumulant analysis as defined in ISO 13321 and ISO 22412. Z-average size may be measured using any suitable instrument, such as a ZETASIZER NANO ZS (commercially available from Malvern Instruments Inc, Westborough, MA).

[0052] The suitable size of the dispersed particles produced from the composition can be determined based on the application. In some embodiments, particularly for optical applications, the dispersed pigment particles have an average particle size of 250, 200, 150, 100, 75, or even 50 nanometers or less.

[0053] The pigment particles and the dispersant can be mixed in a dispersion medium or solvent to form a liquid dispersion. Non-limiting examples of the dispersion medium or solvent include water, organic or other alcohols, hydrocarbons or organic solvents, ketones, oils, monomers, oligomers, or any combination thereof. In particular, the solvent can include 1-methoxy-2-propanol (MP), methyl ethyl ketone (or 2-butanone) (MEK), ethylene glycol (EG), or water. An example of an organic alcohol is MP.

[0054] In some embodiments, the selection of molecules for the first and second dispersants may depend at least in part on their respective solubility in the solvent. The solubility of such dispersants in the solvent depends on their chemical structure.

[0055] In some embodiments, various dispersants can be used with water as the solvent. The first dispersant may be a poly(ethylene oxide), a poly(ethylene oxide)-poly(propylene oxide) copolymer, a dispersant commercially available from BYK Additives & Instruments of Wesel, Germany, such as ANTI-TERRA-250, BYK-154, BYK-156, DISPERBYK-183, DISPERBYK-184, DISPERBYK-185, DISPERBYK-191, DISPERBYK-192, DISPERBYK-199, DISPERBYK-2015, or DISPERBYK-2096, a dispersant commercially available from Lubrizol Corporation of Wickliffe, Ohio, such as SOLSPERSE W100, SOLSPERSE W200, SOLSPERSE W320, SOLSPERSE 43000, SOLSPERSE WV400, SOLSPERSE The second dispersant may include one or more of SPAN 43000, or SOLSPERSE 47000, dispersants available from Croda Industrial Chemicals of Edison, New Jersey, such as SPAN 20, SPAN 40, SPAN 60, SPAN 80, TWEEN 20, TWEEN 40, TWEEN 80, or dispersants available from Dow Chemical Company of Midland, Michigan, such as TRITON X-100. The second dispersant may include dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide, dimethyldioctadecylammonium bromide (DODAB), sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, or dihexadecyl hydrogen phosphate.

[0056] In some embodiments, various dispersants can be used with the water-soluble polar organic solvent.The first dispersant can include one or more of the dispersants available from BYK Additives & Instruments, such as DISPERBYK, DISPERBYK-180, DISPERBYK-182, DISPERBYK-2013, DISPERBYK-2055, DISPERBYK-2059, BYKJET-9151 or BYKJET-9152, or the dispersants available from Lubrizol Corporation, such as SOLSPERE 20000, SOLSPERE 27000, SOLSPERE 45000, SOLSPERE 54000, SOLSPERE 65000, SOLSPERE 71000, SOLPLUS D540, SOLPLUS D545 or SOLPLUS D570. The second dispersing agent may include dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide, dimethyldioctadecylammonium bromide (DODAB), sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, or dihexadecyl hydrogen phosphate.

[0057] In some embodiments, various dispersants may be used with less polar organic solvents such as methyl ethyl ketone (MEK) and toluene. The first dispersant may be any dispersant available from BYK Additives & Instruments, such as BYK-W903, BYK-W969, BYK-W985, BYK-W995, BYK-W996, BYK-W9010, BYK-W9011, BYK-W9012, DISPERBYK-111, DISPERBYK-118, BYK-9076, BYK-9077, DISPERBYK-163, DISPERBYK-168, DISPERBYK-184, DISPERBYK-2008, DISPERBYK-2152, DISPERBYK-2155, or any dispersant available from Lubrizol Corporation, such as SOLSPERSE 32000, SOLSPERSE 36000, SOLSPERSE 39000, SOLSPERSE The second dispersant may include one or more of SOLSPERSE 41000, SOLSPERSE 71000, SOLSPERSE 75000, SOLSPERSE76500, SOLSPERSE85000, SOLSPERSE 88000, SOLSPERSE, SOLSPERSE M385, SOLSPERSE M387, SOLSPERSE M388, SOLSPERSE M387. The second dispersant may include 2-(methylamino)ethanol, 3-dimethylamino-1-propanol, or 2-[2-(dimethylamino)ethoxy]ethanol. EXAMPLES

[0058] Compositions of metal oxide dispersions with polymeric and non-polymeric dispersants were prepared and tested for particle size. The dispersions were formulated into coating solutions, applied to films, and dried. The haze and transmittance of the dried coatings were measured.

[0059] These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and elsewhere herein are by weight unless otherwise indicated. The following abbreviations are used herein: nM = nanometers, g / m 2 = grams per square meter, g = grams, °C = degrees Celsius.

[0060] material [Table 1]

[0061] Test Method particle size Particle size distribution was measured using a Zetasizer Nano ZS (Malvern Instruments Inc, Westborough, MA). 173° backscattering mode detection was used. The measurement time was set to automatic mode, allowing the software to determine the time required per run and the number of runs required. The measurement position and attenuation rate were also set to automatic mode. The "General Purpose" model was selected as the software analysis model. The Mark-Houwink A parameter was set to 0.428 and the K parameter was set to 7.67e-05 cm 2 The time was set to 1 / sec. The measurement temperature was set to 25 °C. The solvent viscosity used was 0.43 centipoise for MEK. Due to the low particle concentration, the solvent viscosity was used as the sample viscosity. The samples were first diluted 1:100 to 1:10000 by volume with the same solvent used for milling. Z-average particle size data was reported based on dynamic light scattering theory. Z-average size is the harmonic intensity average hydrodynamic particle size in cumulant analysis as specified in ISO 13321 and ISO 22412. Size distributions were calculated from a two-parameter fit to the correlation data as specified in ISO standard documents 13321:1996 E or ISO 22412:2008.

[0062] Haze and Transmittance Transmittance and haze readings were taken with a BYK haze-gard plus (BYK Instruments USA, Columbia, MD).

[0063] Coating thickness Coating thicknesses were measured using a tec5 AG UV-VIS spectrometer (tec5 USA Inc, Plainview, NY) using an assumed refractive index of 1.49.

[0064] Example - Dispersion The dispersions were processed using a media milling process. The dispersant and solvent were first mixed until completely dissolved, then the pigment powder was slowly charged. The mixed dispersions were milled in a MiniCer (NMC) or LabStar (NLS) laboratory media mill (Netzsch, Exton PA) using 0.2 millimeter Toraycerum yttria stabilized zirconia milling media. Small samples were periodically removed to monitor the milling progress by particle size measurement. Table 2 shows the dispersant formulation (% and ratio calculated for each example), mill type, milling time and resulting particle size.

[0065] Examples E1-E5, CE1-CE2: CsWO / MP / H2O / first dispersant D510 / second dispersant DTAB E1-E2: Nanoparticle dispersion E1 was made using a total of 55% dispersant relative to the particles (D1 / P=50, D2 / P=5). Dispersion E2 was made using a total of 35% dispersant relative to the particles (D1 / P=25%, D2 / P=10%).

[0066] CE1a, CE1b, E3: 1) CE1a dispersion was formulated using only the second dispersant and no first dispersant. The CE1a dispersion was milled for 2 hours to reach submicron particle size, but did not obtain sufficient size reduction. 2) CE1b dispersion was made by adding 10% of the first dispersant (D1 / P=10%) to E3. The CE1b dispersion was milled for an additional 2 hours to obtain further size reduction to less than 400 nm. 3) E3 dispersion was made by adding an additional 10% of the first dispersant to CE1b to reach a total of 35% dispersant (D1 / P=20%, D2 / P=15%). The E3 dispersion was milled for an additional 2 hours to reduce the particle size to less than 100 nm.

[0067] E4: A formulation with a higher pigment concentration (27% of the final dispersion) was milled using a Labstar mill to support formulation evaluation in a precision pilot coater. The final dispersion consisted of 35% dispersant to particle (D1 / P=30%, D2 / P=5%).

[0068] CE2:CsWO / MP dispersions were made using only the first dispersant; approximately 100% of the first dispersant to particle (D1 / P=100%) was required to reach the desired particle size without the second dispersant.

[0069] E5: CsWO / MP dispersion was made with the same first dispersant as E1-E4 and CE1a-CE1b, except the second dispersant was replaced with DODAB (dimethyldioctadecylammonium bromide) instead of DTAB. DODAB is a double-stranded quaternary ammonium molecule. A total of 60% dispersant to particle (D1 / P=50%, D2 / P=10%) was used to reach a particle size of less than 200 nm.

[0070] Examples E6-E7, CE3: KWO / MP / first dispersant D510 / second dispersant DTAB E6: A dispersion was made with a total dispersant to particle ratio of 45% (D1 / P=40%, D2 / P=5%).

[0071] E7: The dispersion was similar to E6 with a total dispersant to particle ratio of 46% but was milled for an extended period to reduce the particle size to below 50 nm.

[0072] CE3: This comparative example required a dispersant to particle ratio (D1 / P) of approximately 100% to reach the desired particle size using only the first dispersant and no second dispersant.

[0073] Examples E8, CE4: CsWO / MEK / first dispersant M387 / second dispersant MAE E8: A second dispersant (MAE) was used, and the amount of the first dispersant was minimized. A total of 55% of the dispersant was used relative to the particles (D1 / P=50%, D2 / P=5%).

[0074] CE4: 100% of the first dispersant, paired with particles (D1 / P) was used.

[0075] Examples E9-E11, CE5: KWO / MEK / first dispersant M387 / second dispersant E9-11: Three KWO / MEK dispersions were made with three different secondary dispersants including MAE for E9, DMAP for E10, and DMAEE for E11. They all used the same primary dispersant. They used 50% primary dispersant on particles (D1 / P=50%) and 5% secondary dispersant on particles (D2 / P=5%).

[0076] CE5: 100% of the first dispersant, paired with particles (D1 / P) was used.

[0077] Examples E12-E13: CsWO / EG / first dispersant D540 / second dispersant E12: Dispersion with SDS as the second dispersant, which consisted of a total of 50% dispersant to particles (D1 / P=40%, D2 / P=10%).

[0078] E13: Dispersion using DHP and DS-10 as the second dispersant, which consisted of a total of 70% dispersant on particles (D1 / P=50%, D2 / P=10%).

[0079] [Table 2]

[0080] [Table 3]

[0081] Example - Hardcoat with E4, E6, CE2, CE3 Dispersions The hardcoat coating solutions included acrylate monomers blended with pigment dispersions, photoinitiators sensitive to UV light, crosslinkers, and slip agents. These solutions were coated onto PET films, dried, and cured. See Table 4 for formulation. The hardcoat solutions were formed in two steps. A premix solution was made by first mixing together equal parts of SR238 monomer, SR295 monomer, and MEK solvent, then adding PZ33 crosslinker at 5.8% by acrylate weight, TEGORAD 2250 slip agent at 0.67% by acrylate weight, and photoinitiators IRGACURE 184 and IRGACURE 819 at 2.4% by acrylate weight, respectively. This monomer premix was then slowly added to the pigment dispersion (E4, E6, CE2, or CE3) under constant mixing to the weight ratios shown in Table 4 below. To facilitate mixing, a solvent blend of 50% MEK and 50% MP was also added, as shown in Table 4. The solution was then mixed for an additional hour.

[0082] The hardcoat coating solution was coated onto a 50 micron thick clear PET film using a precision extrusion die fed using a pressurized vessel controlled by a mass flow meter. The PET had a measured transmission of 93% and a bulk haze of 0.6%. The bulk haze and transmission of the PET were measured by applying a clear liquid with a surface tension low enough to form a continuous layer on both sides of the film before measuring the haze. In this case, the liquid used was 1-methoxy-2-propanol. The coating was dried at an average temperature of 65° C. for 1 minute and then cured at 100% power for 5 seconds in a 600 watt Model I603M UV Cure Chamber (Fusion UV Systems, Gaithersburg MD) under a nitrogen purge. The dispersion pigment loading was calculated. The dried coating thickness, transmission and haze were measured and reported in Table 5.

[0083] [Table 4]

[0084] [Table 5]

[0085] Thus, various embodiments of polydispersant metal oxide nanoparticle dispersion compositions are disclosed. Reference is made herein to a series of accompanying drawings that form a part of this disclosure, at least to those skilled in the art who will appreciate that various adaptations and modifications of the embodiments described herein are within the scope of this disclosure or do not depart from the scope of this disclosure. For example, aspects of the embodiments described herein may be combined with each other in various ways. It is therefore to be understood that within the scope of the appended claims, the claimed invention may be practiced otherwise than as expressly described herein.

[0086] All references and publications mentioned herein are expressly incorporated by reference in their entirety into this disclosure for all purposes, except to the extent that any aspect may directly contradict this disclosure.

[0087] All scientific and technical terms used herein have the meanings commonly used in the art unless otherwise specified. The definitions provided herein are intended to aid in the understanding of certain terms used frequently herein and are not intended to limit the scope of the present disclosure.

[0088] Unless otherwise indicated, all numbers expressing feature sizes, quantities, and physical properties used in the specification and claims can be understood as being modified by either the term "exactly" or "about." Accordingly, unless specifically indicated to the contrary, the numerical parameters set forth in the above specification and appended claims are approximations that can vary, for example, within typical experimental error ranges, depending on the desired properties one of ordinary skill in the art is seeking to obtain using the teachings disclosed herein.

[0089] The term "or" is used generally in its inclusive sense, unless the context clearly indicates otherwise, e.g., "and / or." The term "and / or" refers to one or all of the listed elements or a combination of at least two of the listed elements.

Claims

1. a plurality of pigment particles comprising a metal oxide; a first dispersant that is a polymer comprising molecules having an average molecular weight of 2000 atomic mass units or greater; a second dispersant comprising molecules having a maximum molecular weight less than 2000 atomic mass units; A composition comprising:

2. 10. The composition of claim 1, wherein the second dispersant comprises a non-polymeric second dispersant.

3. The composition of claim 1 , wherein the pigment particles comprise mixed-valence tungsten oxide.

4. The composition of claim 1 , wherein the pigment particles comprise cesium tungsten oxide, potassium tungsten oxide, or any combination thereof.

5. 2. The composition of claim 1, wherein the second dispersant molecules comprise a polymer having a maximum backbone length of 20 or less.

6. 2. The composition of claim 1, wherein the weight of the polymeric first dispersant is less than 50% of the weight of the pigment particles in the composition, and the plurality of pigment particles comprises mixed-valence tungsten oxide.

7. 2. The composition of claim 1, wherein the combined weight of the polymeric first dispersant and the second dispersant is less than 50% of the weight of the pigment particles in the composition, and the plurality of pigment particles comprises mixed-valence tungsten oxide.

8. 10. The composition of claim 1, wherein each pigment particle of the plurality of pigment particles is affixed to at least one polymeric first dispersant molecule and at least one second dispersant molecule to form a plurality of dispersed pigment particles.

9. 2. The composition of claim 1, wherein the anchoring group of the first dispersant has a similar surface charge as the anchoring group of the second dispersant.

10. 10. The composition of claim 9, wherein the first dispersant molecules include anchoring groups including amines, ammonium salts, phosphates, sulfonates, sulfates, carboxylates, phosphonates, and phosphinates.

11. 2. The composition of claim 1, wherein the second dispersant molecules comprise a cationic anchoring group, and the second dispersant molecules comprise dodecyltrimethylammonium bromide (DTAB), dimethyldioctadecylammonium bromide (DODAB), or both.

12. The composition of claim 1 , wherein the molecules of the second dispersant comprise an anionic anchoring group or a non-ionic anchoring group.

13. 10. The composition of claim 1, further comprising a solvent to form a liquid dispersion, wherein the first dispersant molecules comprise a polyester-polyamine copolymer, the second dispersant molecules comprise a quaternary ammonium salt, and the solvent comprises 1-methoxy-2-propanol or 1-methoxypropan-2-ol (MP).

14. A hardcoat comprising the composition of claim 1.

15. 1. A method for making a pigment dispersion, comprising the steps of: dissolving a first dispersant and a second dispersant, which are polymers, in a solvent to form a solution, the first dispersant comprising molecules having an average molecular weight equal to or greater than 2000 atomic mass units and the second dispersant comprising molecules having a maximum molecular weight less than 2000 atomic mass units; mixing a plurality of pigment particles comprising a metal oxide into the solution to form a dispersion; milling the dispersion to a desired particle size.

16. 1. A method for producing a hard coat having pigment particles, comprising: dissolving a curable binder material in a solvent to form a solution; adding said solution to a dispersion comprising the composition of claim 1; adding one or more additives to the dispersion; coating the dispersion onto a substrate; drying the coating to remove the solvent; and curing the dried coating.

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