PROCESS FOR PREPARING HIGH % SOLIDS INORGANIC HOLLOW PARTICLE DISPERSIONS USING AN INTERFACIAL MINIEMULSION

SOL-GEL REACTION

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a process for preparing high % solids inorganic hollow particle dispersions , more particularly to a process for preparing high % solids inorganic hollow particle dispersions using an interfacial miniemulsion sol-gel reaction and both solvent based and water based silica precusors; and use of the high % solids inorganic hollow particle dispersions in coating compositions. Description of the Related Art

Nanospheres are submicroscopic colloidal systems composed of a solid or liquid core surrounded by a thin polymer or inorganic shell. This solid or liquid core is removed to form hollow nanospheres. Such core- shell systems may be prepared from micro or miniemulsions via

polymerization reaction at the interface of the droplets, the so-called interfacial polymerization reaction. Interfacial polymerization occurs at the interface of two immiscible phases, for example, oil and water, and a thin shell is formed. In the formation of the shell, the monomers are in either oil or water phase to participate in the reaction. Typically, for the

preparation of core-shell nanocapsules via interfacial polymerization, a microemulsion or miniemulsion is first prepared, either water in oil or oil in water, wherein in the former nanocapsules with an aqueous core suspended in oil are formed and in the latter nanocapsules with an oily core suspended in water are formed. Existing processes for the

preparation of high % solids inorganic hollow particle dispersions either use only solvent based precursors and a hard polymer template that result in higher raw material manufacture cost. A need exists for a lower cost process for preparing high % solids inorganic hollow particle dispersions using an interfacial miniemulsion sol-gel reaction. SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure provides a process for making an inorganic hollow particle dispersion through an interfacial miniemulsion sol-gel reaction comprising:

a) providing a mixture of an oil phase comprising at least one non- reactive solvent and at least one solvent-based silica precursor, and a water phase comprising water and at least one surfactant;

b) forming an oil-in-water emulsion by high energy shearing the mixture from step (a) at an energy density of at least about 10 ^Λ 6 J/m ^A 3, in the absence of a catalyst or alcohol cosolvent, to form thin shell hollow silica templates, and wherein the concentration of solvent-based silica precursor is about 0.01 to about 5 wt %, the silica precursor to non- reactive solvent ratio is about 0.002 to about 3, oil to water ratio is about 0.01 to 0.4, and surfactant concentration is about 0.001 wt % to about 5 wt %;

c) initiating a one-step sol-gel reaction to form thin shell silica hollow particles;

d) adjusting the pH of the emulsion to above about 8, by typically adding base;

e) adding at least one water based silica precursor solution to emulsion at constant feeding rate over at least about 1 hour while maintaining the pH of the solution at about 8 by simultaneously

continuously adding acid, or adding all water based silica precursor solution at once and then slowly lowering the pH to about 8 by

continuously adding acid over at least about one hour, wherein the concentration of water based silica precursor is about 0.5 wt% to about 15 wt%, more typically about 1 wt% to about 10 wt%, based on the total weight of the dispersion; and

f) holding the solution for about 0.5 to about 16 hours, at room temperature, more typically at about 20 °C- to about 95 °C, and still more typically at 20 °C- to about 70 °C, with optional stirring, to allow the silica precursor to hydrolyze and condense to form a layer of silica coating on the thin shell hollow silica templates, resulting in a hollow silica having a particle size of less than about 400 nm. Optionally, adding at least one dispersant with a concentration of about 0.1 wt% to about 5 wt% after step d) and again after step e).

By non- reactive solvent we mean that the solvent does not substantially react, more typically does not react, with any of the other components added to the reaction. The non-reactive solvent is compatible with the solvent-based silica precursor.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is the structure of the resulting particles from Example 1 that was analyzed using transmission electron microscopy.

Figure 2 is the structure of the resulting particles from Example 2 that was analyzed using transmission electron microscopy.

Figure 3 is the structure of the resulting particles from Example 3 that was analyzed using transmission electron microscopy.

DETAILED DESCRIPTION OF THE DISCLOSURE

In this disclosure "comprising" is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Additionally, the term "comprising" is intended to include examples encompassed by the terms "consisting essentially of and "consisting of." Similarly, the term "consisting essentially of is intended to include examples encompassed by the term "consisting of."

In this disclosure, when an amount, concentration, or other value or parameter is given as either a range, typical range, or a list of upper typical values and lower typical values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or typical value and any lower range limit or typical value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the disclosure be limited to the specific values recited when defining a range. In this disclosure, terms in the singular and the singular forms "a," "an," and "the," for example, include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to "inorganic hollow particle dispersion", "the inorganic hollow particle dispersion", or "a inorganic hollow particle dispersion" also includes a plurality of inorganic hollow particle dispersions.

The disclosure provides a process for preparing an inorganic hollow particle dispersion at a solids concentration of at least about 2 wt% solids, more typically about 2 wt% to about 10 wt%, still more typically about 2 wt% to about 5 wt%. These inorganic hollow particle dispersions are useful as hiding or opacifying agents in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

These inorganic hollow particles or nanospheres have a particle size of less than about 400nm, more typically about 5 nm to about 400 nm, still more typically about 50 nm to about 300 nm, and most typically about 100 nm to about 250 nm.

The disclosure provides a process for making an inorganic hollow particle dispersion at a solids concentration of at least 2 wt% solids through an interfacial miniemulsion sol-gel reaction using both solvent based and water based silica presusors comprising:

a) providing a mixture of an oil phase comprising at least one non- reactive solvent and at least one solvent-based silica precursor, and a water phase comprising water and at least one surfactant;

b) forming an oil-in-water emulsion by high energy shearing the mixture from step (a) at an energy density of at least about 10 ^Λ 6 J/m ^A 3, in the absence of a catalyst or alcohol cosolvent, to form thin shell hollow silica templates, and wherein the concentration of solvent-based silica precursor is about 0.01 to about 5 wt %, the silica precursor to non- reactive solvent ratio is about 0.002 to about 3, oil to water ratio is about 0.01 to 0.4, and surfactant concentration is about 0.001 wt % to about 5 wt %;

c) initiating a one-step sol-gel reaction to form thin shell silica hollow particles; d) adjusting the pH of the emulsion to above about 8, by typically adding base;

e) adding at least one water based silica precursor solution to emulsion at constant feeding rate over at least about 1 hour while maintaining the pH of the solution at about 8 by simultaneously

continuously adding acid, or adding all water based silica precursor solution at once and then slowly lowering the pH to about 8 by

continuously adding acid over at least about one hour, wherein the concentration of water based silica precursor is about 0.5 wt% to about 15 wt%, more typically about 1 wt% to about 10 wt%, based on the total weight of the dispersion; and

f) holding the solution for about 0.5 to about 16 hours, at room temperature, more typically at about 20 °C- to about 95 °C, and still more typically at about 20 °C- to about 70 °C, with optional stirring, to allow the silica precursor to hydrolyze and condense to form a layer of silica coating on the thin shell hollow silica templates, resulting in a hollow silica having a particle size of less than about 400 nm. Optionally, adding at least one dispersant with a concentration of about 0.1 wt% to about 5 wt% after step d) and again after step e).

The non-reactive solvent may be an alkane, a hydrocarbon oil, aromatic hydrocarbon or halogenated hydrocarbon liquid, more typically alkane or hydrocarbon oil.

The solvent based silica precursor is tetraethyl orthosilicate

(TEOS), tetramethyl orthosilicate (TMOS) tertrapropyl orthosilicate

(TPOS), tetrabutyl orthosilicate (TBOS), tetrahexyl orthosilicate, diethoxydimethylsilane, ethoxytrimethylsilane, methoxytrimethylsilane, trimethoxy(octyl)silane, triethoxy(octyl)silane,

methoxy(dimethyl)octylsilane, or 3-aminopropyl-(diethoxy)methylsilane; more typically tetraethyl orthosilicate (TEOS) or tertrapropyl orthosilicate (TPOS). The concentration of silica precursor is about 2 to about 10 wt %, more typically about 2 to about 7 wt %, still more typically about 2 to about 5 wt %,

The water phase comprises water and at least one surfactant. Some suitable surfactants include cetyltrimethylammonium bromide (CTAB), lauryltrimethylammonium bromide, dodecyltrimethylammonium bromide, octyltrimethylammonium bromide, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), or

dioctylsulfosuccinate , nonionic surfactants such as alkylphenol

polyoxyethylene, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, octylphenol ethoxylates orpoloxamers, more typically SDS, SDBS or CTAB. Some useful commercially available surfactants series include Triton X® manufactured by The Dow Chemical Company, Brij® manufactured by Croda International PLC, or Pluoronic®

manufactured by BASF.

The solvent based silica precursor to non-reactive solvent ratio is about 0.002 to about 6, more typically about 0.002 to about 3; oil to water or water to oil ratio is about 0.01 to about 0.4, more typically about 0.05 to about 0.25; and surfactant concentration is about 0.001 wt % to about 5 wt %, more typically about 0.1 wt% to about 2 wt%, based on the total weight of all components. It is important because the combination of silica precursor to non-reactive solvent ratio, oil to water ratio and surfactant level determine the particle size, hollow or non-hollow particle structure, and allow high % solid hollow silica synthesis. The process is carried out in the absence of a catalyst or alcohol cosolvent.

The mixture in step (a) may be prepared in any glass container or stainless steel reaction vessel .

The mixture of the water phase and oil phase components is then sheared at an energy density of at least about 10 ^Λ 6 J/m ^A 3, more typically about 10 ^Λ 7 J/m ^A 3 to about 5*10 ^Λ 8 J/m ^A 3, to form a mini-emulsion. Some useful means for shearing include an ultrasonic disruptor, high speed blender, high pressure homogenizer, high shear disperser, membrane homogenizer or colloid mill, more typically an ultrasonic disruptor, high speed blender, or a high pressure homogenizer. Typically shearing occurs for a period of about 5 to about 120 minutes depending on amount of emulsion needed to be prepared and desired emulsion size range, more typically about 30 minutes to about 60 minutes. Typically, shearing is accomplished at room temperature. Optionally, a defoamer may be needed to avoid foaming during emulsifying. Some suitable defoamers include BASF's Foamaster®, Dow Corning® 71 and 74 Antifoams.

A one-step sol-gel reaction is then initiated using the mini-emulsion formed in step (b), by allowing the silica precursors to diffuse to the oil/water interface, where they hydrolyze and condense to form a silica shell resulting in silica hollow particles having a particle size of less than about 400 nm being formed. The one-step sol-gel reaction may be initiated at room temperature, more typically about 20 °C to about 95 °C, and still more typically about 20 °C to about 70 °C. Heating may be accomplished using hot plate, heating mantle or any other heating method.

A sol gel reaction or process is a method used for

fabrication of solid metal oxides materials, especially the oxides of silicon and titanium, from small molecules. The process involves conversion of monomers (precursors) into a colloidal solution that later on turns into an integrated network (or gel) of particles or network polymers.

A one-step sol-gel reaction of this disclosure is initiated using the mini-emulsion formed in step (b), by holding it at room temperature or about 20 °C to about 95 °C, more typically about 20 °C to about 70 °C, with or without stirring for several hours to allow the silica precursors to diffuse to the oil/water interface, where they hydrolyze and condense to form a silica shell resulting in silica hollow particles having a particle size of less than about 400 nm being formed. The pH may be typically adjusted to between about 4 and about 10 prior to initiation of the one step sol gel process.

The pH adjustment in step (d) and (e) may be achieved using any reasonable choice of acid or base. Some useful acids include

hydrochloric, acetic acid, nitric acid, butyric acid and citric acid. Some useful bases include sodium hydroxide and ammonium hydroxide.

The concentration of the at least one dispersant that may be used in the optional step after step (d) and (e) is about 0.1 wt% to about 5 wt%. Some suitable dispersants series include Triton X ^® manufactured by The Dow Chemical Company, Brij ^® manufactured by Croda International PLC, BYK® manufactured by BYK Chemie, SILBYK® manufactured by Evonik, or Pluoronic® manufactured by BASF.

The water-based silica precursor in step (e) is sodium silicate, potassium silicate, ammonium silicate or pre-formed silicic acid; more typically sodium silicate or potassium silicate; still more typically sodium silicate. The concentration of water based silica precursor is about 0.5 wt% to about 15 wt%, more typically about 1 wt% to about 10 wt%, based on the total weight of the dispersion. Applications:

These inorganic hollow particle dispersions are useful as hiding or opacifying agents in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture. EXAMPLES

Glossary:

TEOS tetraethyl orthosilicate

CTAB cetyltrimethylammonium bromide

Silbyk-9000 manufactured by Evonik, Essen , Germany

Dispersant

G1640 manufactured by BASF, Ludwiqshafen, Germany

defoamer

Example 1 :

An oily mixture which contained 4.2 g of hexadecane, 16.8 g octane and 21 .0 g TEOS was first prepared, and added to a water solution which contained 420.0 g of water, 0.5 g G1640 defoamer and 4.2 g of CTAB. Emulsification was achieved by high-speed mixer, and stirring at 9,500 rpm for 30 min. After obtaining a stable emulsion, the mixture was left to sit at room temperature overnight, and hollow particles were formed. After forming the hollow silica, the pH of the emulsion was adjusted to 10.2 and then 15 g of sodium silicate solution was added. Next, the emulsion was stirred for half hour and then the pH of the emulsion was slowly lowered to 8.8 by slowly adding 1 M HCI solution over two hours. Finally, the mixture was left sit at room temperature overnight, and then the temperature was raised to 95 °C for another 3 hours to complete the sol-gel reaction. The structure of the resulting particles was analyzed using transmission electron microscopy and is shown in Figure 1 .

Example 2:

An oily mixture which contained 4.2 g of LPA 210, 16.8 g Shell Sol and 5.25 g TEOS was first prepared, and added to a water solution which contains 420.0 g of water, 0.5 g G1640 defoamer and 4.2 g of CTAB. Emulsification was achieved by high-speed mixer, and stirring at 9,500 rpm for 30 min. After obtaining a stable emulsion, the mixture was left to sit at room temperature overnight, and hollow particles were formed. After forming the hollow silica, 4.7 g of Silbyk-9000 dispersant was added and then the pH of the emulsion was adjusted to 10. The mixture was stirred for an hour, and then the temperature was raised to 95 °C. Next, 1 .88 g of sodium silicate solution was added to the emulsion at constant feeding rate over 2 hours while maintaining the pH of the solution at above about 10 by continuously adding acid. Finally, the mixture was stirred at 95 °C overnight to obtain the thicker shell hollow silica. The structure of the resulting particles was analyzed using transmission electron microscopy and is shown in Figure 2.

Example 3:

An oily mixture which contained 4.2 g of LPA 210, 16.8 g Shell Sol and 0.5 g TEOS was first prepared, and added to a water solution which contains 420.0 g of water, 0.5 g G1640 defoamer and 4.2 g of CTAB. Emulsification was achieved by high-speed mixer, stirred at 9,500 rpm for 30 min. After obtaining a stable emulsion, the mixture was left to sit at room temperature overnight, and hollow particle formed. After forming the hollow silica, 14.01 g of Silbyk-9000 dispersant was added and then the pH of the emulsion was adjusted to 9.9. The mixture was stirred for an hour, and then 25 g of sodium silicate solution was added to emulsion at constant feeding rate over 2 hours while maintaining the pH of the solution at about 9 by continuously adding acid. Finally, another 9.34 g of Silbyk- 9000 dispersant was added to the emulsion to prevent the agglomeration of the silica particles. The mixture was let to sit at room temperature overnight. The structure of the resulting particles was analyzed using transmission electron microscopy and is shown in Figure 3.

Example 4. Hiding power performance of the Examples in coatings formulations

Three hollow particles shown in the above examples were tested in an acrylic latex paint formulation. Four formulations were prepared (Table 1 ), one without any hollow silica (control), and three with 5 wt% of materials from Examples 1 -3. Thin coating films were made from the four formulations, and they were compared for hiding power (Scoat), using standard protocols of Kubelka-Munk theory of reflectance (Table 2). It is evident that addition of hollow silica particle provides films with superior hiding power. The hollow particles described above are thus seen as good additives for hiding power improvement.

Formulation Control Example 1 Example 2 Example 3

5 wt% 5 wt% 5 wt%

Rutile ΤΊΟ2 30.84 30.84 30.84 30.84 slurry(76.5wt%)

Acrylic 54.17 51 .63 51 .63 51 .63 emulsion

(45.0wt%)

Defoamer 0.33 0.33 0.33 0.33

Propylene 0.47 0.47 0.47 0.47 glycol

Surfactant 0.48 0.48 0.48 0.48

Water 8.81 8.81 8.81 8.81

Biocide 0.16 0.16 0.16 0.16

Dispersant 0.22 0.22 0.22 0.22

Ammonia 0.1 1 0.1 1 0.1 1 0.1 1

Coalescent 0.86 0.86 0.86 0.86

Rheology 3.25 3.25 3.25 3.25 modifier 1

(20wt%)

Rheology 0.33 0.33 0.33 0.33 modifier II

(17.5wt%)

Test material — 2.54 2.54 2.54

Table 1 . Composition of paint formulations with and without hollow silica particle.

Test Material T1O2 wt% in Total T1O2 PVC ^* Total Hiding dry film pigment wt% [%] pigment power in dry film PVC ^* [%] (Scoat)

Control 46.5 46.5 20.0 20.0 1.00

Ex. 1 , 5wt% 44.9 49.7 14.9 21 .0 1.064

Ex. 2, 5wt% 44.9 49.7 14.9 21 .0 1.051

Ex. 3, 5wt% 44.9 49.7 14.9 21 .0 1.041

Table 2. Dry film PVC and hiding power data from formulations in Table 2. *PVC=pigment volume concentration.