Method for preparing large voided particles

Abstract

A process is described for the preparation of voided latex particles having a volume average particle size of greater than 1 µm and a particle blowout level below 50%. The voided latex particles so prepared and articles containing the voided latex particles are also described.

Description

[0001] METHOD FOR PREPARING LARGE VOIDED PARTICLES

[0002] This application claims priority to and benefit of US provisional Application No. 63 / 600,859 filed on November 20, 2023, the contents of which are incorporated herein by reference in their entirety.

[0003] FIELD OF THE INVENTION

[0004] This application is directed to a process for the preparation of voided latex particles having a volume average particle size of greater than 1 pm and a particle blowout level below 50%, voided latex particles prepared produced thereby, and articles containing the voided latex particles.

[0005] BACKGROUND OF THE INVENTION

[0006] Voided latex particles, also known as hollow latex particles, have been widely used in paint and coating applications. The process of making voided latex particles using multistage emulsion polymerization has been disclosed in, for example, US 6,020,435; US 7,943,704; US 10,000,600; US 10,351,689; US 10,442,882; US 11,161,990; US 11,384,126; and US 11,427,728. The typical process consists of preparing a high acid-containing seed latex particle, also known as swellable particle, followed by encapsulating the seed with a hydrophobic shell, and then using a base to neutralize and swell the encapsulated seed latex polymer to form a voided latex particle. However, the process disclosed in the prior arts are mostly suitable for producing voided latex particles with particle size smaller than 1 pm, for example, around 0.4 pm, for use as an opacifier to replace titanium dioxide (TiCh) for paint applications.

[0007] Voided latex particles with larger particle sizes (e.g., >1 pm) have been found useful in several coating applications. For example, voided particles with particle size greater than 1.5 pm are used in the basecoat during the fabrication of thermal papers to provide thermal insulation properties, thus improving printing quality. A technical challenge identified when producing large voided particles with a particle size >1 pm is the significant amount of ruptured and / or broken voided particles formed, also known as particle blowout. A high level of particle blowout negatively impacts the effective void fraction of final voided particles, thus compromising desirable properties such as thermal insulation. Particle blowout is a unique technical challenge associated with making voided latex particles having particle sizes greater than 1 pm, particularly in the case of 1.5 pm voided particles, while in contrast, particle blowout is not typically present when preparing voided particles smaller than 1 pm. WO 22 / 189290 discloses a process of making voided latex particles with an average particle size of 1.6 pm. However, the particle blowout was significant, which was undesired.

[0008] The present invention describes an improved process for preparing large voided latex particles having particle sizes greater than 1 pm, such as, for example, 1.5 pm, with low level of particle blowout that addresses the above identified challenges.

[0009] SUMMARY OF THE INVENTION

[0010] An aspect of the invention is a process of producing voided latex particles comprising: i) preparing a core latex particle by a polymerization reaction of one or more ethylenically unsaturated monomers, followed by ii) forming a swellable particle by reacting the core latex particle with

[0011] (A) 5-45 wt% of one or more ethylenically unsaturated monomers containing an acid functional group, where the wt% is relative to the total wt% of the monomers

[0012] (A), (B) and (C);

[0013] (B) 1-90 wt% of one or more non-ionic ethylenically unsaturated monomers, where the wt% is relative to the total wt% of the monomers (A), (B) and (C);

[0014] (C) 1-55 wt% of one or more hydrophobic non-ionic ethylenically unsaturated monomers having a lower water solubility than (B), where the wt% is relative to the total wt% of the monomers (A), (B) and (C);

[0015] (D) optionally, one or more non-ionic surfactants, and

[0016] (E) at least 0.01 wt% of one or more anionic surfactants, in a polymerization reaction, followed by iii) forming a first layer partially or fully encapsulating the swellable particle by treating the swellable particle with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by iv) optionally forming a second layer partially or fully encapsulating the swellable particle by treating the swellable particle containing a first layer with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by v) adding swelling agents to generate voided latex particles having a volume average particle size of greater than 1 pm, wherein the polymerization reactions in steps i), ii), iii) and iv) are emulsion polymerization reactions, and wherein the voided latex particles have a particle blowout level below 50%.

[0017] Another aspect of the invention is a voided latex particle prepared by a process as described herein.

[0018] Another aspect of the invention is a plurality of voided latex particles prepared by a process as described herein, the particles having a particle blowout level below 50%.

[0019] Another aspect of the invention is an article comprising a composition comprising voided latex particles as described herein.

[0020] Another aspect of the invention is paper, paint, ink, an adhesive or a cosmetic comprising a coating composition comprising voided latex particles as described herein.

[0021] Another aspect of the invention is the use of the voided latex particles as described herein in a thermal application (such as in a thermal printing process, such as in an undercoat applied during the manufacture of thermal paper) or in a coating composition.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following figures represent particular embodiments of the invention and is not intended to otherwise limit the scope of the invention as described herein.

[0024] Figure 1 illustrates a process of making voided particles starting with a core particle, followed by forming an intermediate swellable particle that is subsequently converted into a voided particle with large volume average particle size (>1 pm).

[0025] Figures 2A-2F illustrate a comparison of particle blowout levels for each of Samples A- F. Figure 3 illustrates a comparison of blowout levels between voided latex particles prepared by a process of the present invention and a process as described in WO 2022 / 189290 Al.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] Voided Latex Particles

[0028] A method of producing monodispersed large (volume average particle size > 1 pm) voided latex particles with low levels of particle blowout is described. In an embodiment, the process comprises multi-stage emulsion polymerizations, where (i) a core latex particle is prepared by emulsion polymerization of one or more ethylenically unsaturated monomers, followed by (ii) formation of an intermediate swellable particle by emulsion polymerization that encapsulates the core latex particle, where the swellable particle comprises one or more ethylenically unsaturated monomers containing an acid functional group, one or more non-ionic ethylenically unsaturated monomers, one or more hydrophobic non-ionic ethylenically unsaturated monomers having a lower water solubility than the non-ionic monomer, one or more anionic surfactants, and optionally, one or more non-ionic surfactants, followed by (iii) forming a first layer fully encapsulating the swellable particle by treating the swellable particle with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by (iv) optionally forming a second layer fully encapsulating the swellable particle by treating the swellable particle containing a first layer with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by (v) the addition of conventional swelling agents to generate voided latex particles having a volume average particle size greater than 1 pm and having a particle blowout level below 50%.

[0029] The voided latex particles prepared by the process of the invention generally comprise a hollow interior and an outer shell which encloses the hollow interior, although one or more additional layers may be present between the outer shell and the interior void of each particle. In an embodiment, the voided latex particle has a volume average particle size of greater than 1 pm up to 10 pm, such as greater than 1 pm up to 8 pm, such as greater than 1 pm up to 6 pm, such as from 1.1 pm up to 5 pm, such as from 1.2 pm up to 4 pm, such as from 1.3 pm up to 3 pm.

[0030] In an embodiment, the voided latex particles have a particle blowout level below 50%, such as below 40%, such as below 30%, such as below 20%, such as between 0 to less than 50%, such as between 0 to 40%, such as between 0 to 30%, such as between 5 to less than 50%, such as between 5 to 40%, such as between 5 to 30%, such as between 10 to less than 50%, such as between 10 to 40%, such as between 10 to 30%.

[0031] The voided latex particles prepared by the process of the present invention may be characterized as being a“non-film-forming” component or additive. “Non-film-forming” means that the voided latex particles will not form a film at ambient temperature or below, or stated differently, will only form a film at temperatures above ambient temperature. For the purposes of this specification, ambient temperature is taken as being in the range of 15° C. to 45° C. Thus, for example, when incorporated into an aqueous coating composition, applied to a substrate temperature and dried or cured at ambient temperature or below, the voided latex particles do not form a film. In an embodiment, the voided latex particles remain as discrete particles in the dried or cured coating.

[0032] The shape of the voided latex particles is not particularly limited. While the particles are typically approximately spherical in shape, other shapes, such as oblong, oval or teardrop are also possible.

[0033] Core Latex Particle

[0034] In an embodiment, the core latex particle has a volume average particle size of greater than 100 nm up to 500 nm, such as greater than 100 nm up to 400 nm, such as greater than 100 nm up to 350 nm, such as from 110 nm to 500 nm, such as from 110 nm to 400 nm, such as from 110 nm to 350 nm.

[0035] In an embodiment, the core latex particle is not particularly limited in terms of its composition and is prepared by emulsion polymerization of one or more of ethylenically unsaturated monomers such as various C1-C30 alkyl esters of (meth)acrylic acid (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, tetradecyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate), various ethylenically unsaturated monomers bearing a hydrophilic functional group such as a carboxylic group or some other type of ionizable functional group (e.g., (meth)acrylic acid, itaconic acid, fumaric acid, maleic acid, vinyl phosphate, phosphate esters of polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate, polyoxyethylene allyl ether phosphate, sulfoethyl (meth)acrylate, arylsulfonic or sulfuric acids, (meth)acrylamidoethane- sulfonic or sulfuric acids, methacrylamido-2- methyl propane- sulfonic or sulfuric acids), isobornyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, 1 -naphthyl (meth)acrylate, ethoxy ethyl (meth)acrylate, ethyl maleate, dimethyl fumarate, ethyl methyl itaconate, styrene, a-methyl styrene, vinyl toluene, divinyl toluene, vinyl naphthalene, caprolactone (meth)acrylate, diethylene glycol methyl ether (meth)acrylate, diethylene glycol ethyl ether (meth)acrylate, diethylene glycol butyl ether (meth)acrylate, triethylene glycol methyl ether (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol) (meth)acrylate, crosslinker monomers include but not limited to divinyl naphthalene, allyl (meth)acrylate, , tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, , 1,6-hexanediol di(meth)acrylate, 1,2-butylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dodecyl di(meth)acrylate, cyclohexane dimethanol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, diallyl phthalate, trimethylolpropane tri(meth)acrylate, triethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and combinations thereof. In one embodiment the core latex particle is prepared by emulsion polymerization of C1-C8 alkyl esters of (meth)acrylic acids (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate) and (meth)acrylic acid.

[0036] Swellable Particle

[0037] In an embodiment, the swellable particle has a volume average particle size of 300 to 2,000 nm, such as from 300 to 1,500 nm, such as from 300 to 1,000 nm, such as from 300 to 800 nm, such as from 300 to 700 nm.

[0038] In an embodiment, the weight ratio between the swellable particle to the core latex particle is 5: 1 to 200: 1, such as 5: 1 to 100: 1, such as 10: 1 to 100: 1, such as 10: 1 to 75:1.

[0039] The swellable particle is prepared by treating the core latex particle in an emulsion polymerization reaction with (i) one or more ethylenically unsaturated monomers containing an acid functional group (monomer A); (ii) one or more non-ionic ethylenically unsaturated monomers (monomer B); (iii) one or more hydrophobic non-ionic ethylenically unsaturated monomers having a lower water solubility than monomer B (monomer C); (iv) optionally, one or more non-ionic surfactants; and (v) one or more anionic surfactants.

[0040] (i) Monomer (A)

[0041] Monomer (A) is present in an amount of 5-45 wt%, such as 10-45 wt%, such as 10-40 wt%, such as 10-35 wt%, such as 15-40 wt%, such as 15-35 wt%, such as 20-40 wt%, such as 20-35 wt%, where the wt% is relative to the total wt% of the monomers (A), (B) and (C).

[0042] In an embodiment, monomer (A) comprises one or more of acrylic acid, methacrylic acid, acryloxypropionic acid, (meth)acryloxypropionic acid, itaconic acid, aconitic acid, maleic acid or maleic anhydride, fumaric acid, crotonic acid, monomethyl maleate, monomethyl fumarate, monomethyl itaconate, vinyl phosphates, (meth)allyl phosphate, phosphate esters of polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate, polyoxyethylene allyl ether phosphate, sulfoethyl (meth)acrylate, aryl- sulfonic or sulfuric acids, (meth)acrylamidoethane- sulfonic or sulfuric acids, methacrylamido-2-methyl propane- sulfonic or sulfuric acids and the like.

[0043] In an embodiment, monomer (A) comprises at least one of methacrylic acid and acrylic acid.

[0044] (ii) Monomer (B)

[0045] Monomer (B) is present in an amount of 1-90 wt%, such as 5-90 wt%, such as 5-80 wt%, such as 10-90 wt%, such as 10-80 wt%, such as 10-70 wt%, such as 10-60 wt%, such as 15-90 wt%, such as 15-80 wt%, such as 20-80 wt%, such as 20-70 wt%, such as 30-80 wt%, such as 40-70 wt%, where the wt% is relative to the total wt% of the monomers (A), (B) and (C).

[0046] In an embodiment, monomer (B) comprises one or more of vinyl aromatic monomers such as styrene, a-methyl styrene, p-methyl styrene, t-butyl styrene, or vinyltoluene, olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide, (C1-C20) alkyl or (C3-C20) alkenyl esters of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate and the like. In an embodiment, monomer (B) comprises methyl methacrylate.

[0047] (iii) Monomer (C)

[0048] Monomer (C) is present in an amount of 1-55 wt%, such as 1-45 wt%, such as 1-35 wt%, such as 1-25 wt%, such as 1-15 wt%, such as 5-50 wt%, such as 5-40 wt%, such as 5-30 wt%, such as 5-25 wt%, such as 5-15 wt%, where the wt% is relative to the total wt% of the monomers (A), (B) and (C).

[0049] In an embodiment, monomer (C) comprises, depending on the particular monomer(s) that constitute(s) monomer (B) (in view of the requirement that monomer (C) is a non-ionic ethylenically unsaturated monomer having a lower water solubility than monomer (B), one or more of vinyl aromatic monomers such as styrene, a-methyl styrene, p-methyl styrene, t-butyl styrene, or vinyltoluene, olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide, (C1-C20) alkyl or (C3-C20) alkenyl esters of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2- ethylhexyl (meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate and the like.

[0050] In an embodiment, monomer (C) comprises at least one of butyl acrylate, styrene, and butyl methacrylate.

[0051] (iv) Non-ionic Surfactant

[0052] The non-ionic surfactant is an optional component. When present, the non-ionic surfactant is present in an amount of at least 0.01 wt%, such as at least 0.05 wt%, such as at least 0.1 wt%, such as at least 0.5 wt%, such as at least 1 wt%, such as at least 1.5 wt%, such as 0.01- 10 wt%, such as 0.01-5 wt%, such as 0.01-3 wt%, such as 0.1-10 wt%, such as 0.1-5 wt%, such as 1-10 wt%, such as 1-5 wt%, based on the total weight of the monomers (A), (B) and (C).

[0053] Examples of suitable nonionic surfactants include, but are not limited to, alkyl (e.g., monoalkyl, dialkyl, trialkyl) phenol ethoxylates, polysiloxane polyalkylene oxide copolymers, primary alcohol ethoxylates, fatty alcohol ethoxylates, fatty acid ethoxylates, alkanolamide ethoxylates, fatty amine ethoxylates, ethylene oxi de-propylene oxide (EO-PO) block copolymers and alkylpolyglucosides, and mixtures thereof. Specific examples of suitable nonionic surfactants include, but are not limited to, tert- octylphenoxyethylpoly-ethoxyethanol, dodecyloxypolyethoxyethanol, nony Iphenoxy ethyl - polyethoxyethanol, polyethylene glycol 2000 monooleate, ethoxylated castor oil, fluorinated alkyl esters and alkoxylates, polyoxyethylene sorbitan monolaurate, sucrose monococoate, di(2- butyl)phenoxypolyethoxy ethanol, hydroxy ethylcellulosepolybutyl acrylate graft copolymer, dimethyl silicone polyalkylene oxide graft copolymer, polyethylene oxide)poly(butyl acrylate) block copolymer, block copolymers of propylene oxide and ethylene oxide, 2,4,7,9-tetramethyl- S-decyne-4,7-diol ethoxylated with 30 moles of ethylene oxide, N-polyoxy ethylene lauramide, N-lauryl-N-polyoxy ethylene amine, polyethylene glycol dodecyl thioether and mixtures thereof.

[0054] In an embodiment, the non-ionic surfactant comprises at least one of a linear fatty alcohol ethoxylate, a branched fatty alcohol ethoxylate, an ethoxylated monoalkyl phenol, an ethoxylated dialkyl phenol and an ethoxylated trialkyl phenol.

[0055] (v) Anionic Surfactant

[0056] The anionic surfactant is present in an amount of at least 0.01 wt%, such as at least 0.05 wt%, such as at least 0.1 wt%, such as at least 0.5 wt%, such as at least 1 wt%, such as at least 1.5 wt%, such as 0.01-10 wt%, such as 0.01-5 wt%, such as 0.01-3 wt%, such as 0.01 to 1 wt%, such as 0.1-10 wt%, such as 0.1-5 wt%, such as 1-10 wt%, such as 1-5 wt%, based on the total weight of the monomers (A), (B) and (C).

[0057] Examples of suitable anionic surfactants include, but are not limited to, alkylbenzenesulfonic acids, alkaline earth metal alkylbenzenesulfonates, sulfonated fatty acids, sulfonated olefins, sulfonated diphenyl ethers, sulfosuccinates, fatty alcohol sulfates, alkylphenol sulfates, alkyl polyglycol ether sulfates, fatty alcohol ether sulfates, fatty alcohol phosphates, alkylphenol phosphates, alkyl polyglycol ether phosphates, alkyl polyalkylene oxide phosphates, fatty alcohol ether phosphates and mixtures thereof.

[0058] Specific examples of suitable anionic surfactants include, but are not limited to, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, potassium stearate, sodium dioctyl sulfosuccinate, sodium dodecyldiphenyloxide disulfonate, nonylphenoxyethylpoly(I)ethoxy ethyl sulfate ammonium salt, sodium styrene sulfonate, sodium dodecyl allyl sulfosuccinate, sodium or ammonium salts of phosphate esters of ethoxylated nonylphenol, sodium octoxynol-3-sulfonate, sodium cocoyl sarcocinate, sodium 1 -alkoxy -2 -hydroxypropyl sulfonate, sodium a-olefin (Ci4- Cie)sulfonate, sulfates of hydroxy alkanols, tetrasodium N-(l,2-dicarboxy ethyl)-N- octadecylsulfosuccinamate, disodium N-octadecylsulfosuccinamate, disodium alkylamido polyethoxy sulfosuccinate, disodium ethoxylated nonylphenol half ester of sulfosuccinic acid and the sodium salt of tert-octylphenoxyethoxypolyethoxy ethyl sulfate.

[0059] In an embodiment, the anionic surfactant comprises at least one of a sulfate, a sulfosuccinate, a sulfonate, and a di sulfonate.

[0060] Polymerization Reaction

[0061] The process of the present invention includes a multi-stage emulsion polymerization process. The process includes formation of a swellable latex particle comprising a polymer of at least one hydrophilic monoethylenically unsaturated monomer, at least one intermediate shell, and an outer shell comprising an outer shell polymer. The multi-stage emulsion polymer particles may be contacted with a swelling agent, such as a base, which is capable of swelling the swellable latex particle, particularly in the presence of water.

[0062] In a particular embodiment, the process involves: i) preparing a core latex particle by a polymerization reaction of one or more ethylenically unsaturated monomers, followed by ii) forming a swellable latex particle by reacting the core latex particle with a combination of monomers (A), (B) and (C) as described herein, an anionic surfactant, and optionally, a non-ionic surfactant, followed by iii) forming a first layer partially or fully encapsulating the swellable particle by treating the swellable particle with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by iv) optionally forming a second layer partially or fully encapsulating the swellable particle by treating the swellable particle containing a first layer with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by v) adding swelling agents to generate voided latex particles having a volume average particle size of greater than 1 pm and having a particle blowout level below 50%. In an embodiment, all polymerization reactions related to the preparation of the voided latex particles from the core latex particle and swellable particle are emulsion polymerization reactions.

[0063] In an embodiment, all encapsulating polymers partially or fully encapsulate the swellable particle.

[0064] In an embodiment, all encapsulating polymers fully encapsulate the swellable particle.

[0065] The multi-stage emulsion polymer particles may contain one or more intermediate encapsulating polymer layers. The intermediate encapsulating polymers partially or fully encapsulate the swellable particle. Each encapsulating polymer layer may be partially or fully encapsulated by another encapsulating polymer layer. Each encapsulating polymer layer may be prepared by conducting an emulsion polymerization in the presence of the swellable particle or a swellable particle encapsulated by one or more encapsulating polymers. The intermediate encapsulating polymer layer may function as a compatiblizing layer, sometimes referred to as a tie or tie coat layer, between other layers of the multi-stage emulsion polymer particles; for example, an intermediate encapsulating polymer layer may help adhere the outer shell to the swellable particle. An intermediate encapsulating polymer layer may also serve to modify certain characteristics of the final voided latex particles.

[0066] At least one intermediate encapsulating polymer may contain, as polymerized units, one or more hydrophilic monoethylenically unsaturated monomers and one or more nonionic monoethylenically unsaturated monomers. The hydrophilic monoethylenically unsaturated monomers and the nonionic monoethylenically unsaturated monomers useful for making the swellable particle are also useful for making such an intermediate encapsulating polymer. Generally, however, the intermediate encapsulating polymer contains a lower proportion of hydrophilic monomer than the swellable particle polymer, such that the intermediate incapsulating polymer swells less when contacted with the swelling agent. Other intermediate encapsulating polymers may contain, as polymerized units, non-ionic monoethylenically unsaturated monomer and little or no hydrophilic monoethylenically unsaturated monomer, such as in amounts less than 10 weight %, such as less than 5 weight %, such as less than 3 weight %. Intermediate encapsulating polymers may further include crosslinking agents such as alkylene glycol diacrylates and dimethacrylates, such as, for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate, propylene glycol diacrylate and triethylene glycol dimethylacrylate; 1,3-glycerol dimethacrylate; 1,1,1- trimethylol propane dimethacrylate; 1,1,1 -trimethylol ethane diacrylate; pentaerythritol trimethacrylate; 1, 2, 6-hexane triacrylate; sorbitol pentamethacrylate; methylene bis-acrylamide; methylene bis-methacrylamide; divinyl benzene; vinyl methacrylate; vinyl crotonate; vinyl acrylate; vinyl acetylene; trivinyl benzene; triallyl cyanurate; divinyl acetylene; divinyl ethane; divinyl sulfide; divinyl ether; divinyl sulfone; diallyl cyanamide; ethylene glycol divinyl ether; diallyl phthalate; divinyl dimethyl silane; glycerol trivinyl ether; divinyl adipate; dicyclopentenyl (meth)acrylates; dicyclopentenyloxy (meth)acrylates; unsaturated esters of glycol monodicyclopentenyl ethers; allyl esters of a,P-unsaturated mono- and dicarboxylic acids having terminal ethylenic unsaturation including allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate and the like.

[0067] The outer shell is polymeric and may, for example, comprise a thermoplastic polymer. The outer shell polymer has a glass transition temperature (Tg) above ambient temperature, typically at least 60° C., such as at least 70° C., such as at least 80° C. or such as at least about 90° C. The Tg of the outer shell polymer may be, for example, from 60° C. to 140° C. Although the outer shell polymer may be a homopolymer, more typically it is a copolymer comprising recurring polymerized units of two or more different monomers, especially ethylenically unsaturated monomers such as those capable of being polymerized by free radical polymerization. The outer shell polymer is further characterized by bearing one or more different types of functional groups, particularly reactive, polar, chelating and / or heteroatom-containing functional groups. These functional groups may be varied and are chosen as desired to modify certain characteristics of the voided latex particles, such as the wet adhesion, scrub resistance (washability), stain resistance, solvent resistance and block resistance properties of a coating composition which includes the voided latex particles. For example, the functional groups may be selected from 1,3 -diketo, amino, ureido and urea functional groups and combinations thereof. Suitable 1 ,3-diketo functional groups include acetoacetate functional groups, which may correspond to the general structure — OC(=O)CH2C(=O)CH3. Suitable amino functional groups include primary, secondary and tertiary amine groups. The amino functional group may be present in the form of a heterocyclic ring. The amino functional group may, for example, be an oxazoline ring. Other types of functional groups useful in the present invention include, for example, hydroxyl ( — OH), silane (e.g., trialkoxysilyl, — Si(OH)3), phosphate (e.g., PO3H and salts thereof), fluorocarbon (e.g., perfluoroalkyl such as trifluoromethyl), polyether (e.g., polyoxyethylene, polyoxypropylene), and epoxy (e.g., glycidyl). In one embodiment, the functional group contains a Lewis base such as the nitrogen atom of an amine. In another embodiment, the functional group contains a hydroxyl functional group. The functional group may be reactive; for example, the functional group may be capable of reacting as an electrophile or a nucleophile. The functional group, or a combination of functional groups in proximity to each other, may be capable of complexation or chelation.

[0068] The functional groups may be introduced into the outer shell polymer by different means. In one embodiment, the functional groups are introduced into the outer shell polymer during formation of the polymer, for example by polymerization of one or more polymerizable monomers bearing the desired functional groups (hereinafter “functionalized monomer”). Such polymerization may be carried out as a copolymerization wherein one or more functionalized monomers are copolymerized with one or more non-functionalized monomers. The monomers having functional groups described herein may be added at any stage in the preparation of the multi-stage emulsion provided that polymers bearing such functional groups at least partially or completely reside in the outer shell polymer of the particles after swelling.

[0069] For example, the outer shell polymer may be a copolymer of a vinyl aromatic monomer (e.g., styrene) and a free radical polymerizable ethylenically unsaturated monomer containing a functional group such as a-l,3-diketo, amino, ureido, urea, hydroxyl, silane, fluorocarbon, aldehyde, ketone, phosphate or polyether functional group. The copolymer may contain one or more other additional types of comonomers, such as alkyl (meth)acrylates (e.g., methyl methacrylate). The proportions of different monomers may be varied as may be desired to impart certain characteristics to the resulting outer shell polymer. Typically, the copolymer contains from 0.1 to 10 weight % of free radical polymerizable ethylenically unsaturated monomer(s) containing the functional group(s). Such a copolymer may further comprise 80-99.9 weight % of a vinyl aromatic monomer such as styrene and 0-10 weight % (e.g., 0.1-10 weight %) of an alkyl (meth)acrylate such as methyl methacrylate.

[0070] The free radical polymerizable ethylenically unsaturated monomer may contain a (meth)acrylate (i.e., acrylate or methacrylate) group or a (meth)acrylamide (i.e., acrylamide or methacrylamide) group. Such (meth)acrylate and (meth)acrylamide groups are capable of participating in free radical copolymerization with the vinyl aromatic monomer. Allylic groups may also be used to provide a polymerizable site of unsaturation.

[0071] Imidazolidinone (meth)acrylic monomers such as 2-(2-oxo-l-imidazolidinyl)ethyl (meth)acrylates and N-(2-(2-oxo-l-imidazolidinyl)ethyl (meth)acrylamides may be utilized as comonomers, for example. Other suitable free radical polymerizable ethylenically unsaturated monomers containing functional groups useful in the practice of the present invention include, without limitation, acetoacetoxy(meth)acrylates (e.g., acetoacetoxy ethyl methacrylate, AAEM), allyl acetoacetate, derivitized methacrylamides such as methyloxalated diacetone (meth)acrylamides, aminoalkyl(meth)acrylates (including dialkyl and monoalkyl aminoethyl(meth)acrylates), and ethylenically unsaturated polymerizable aziridinyl monomers (such as those described, for example, in U.S. Pat. No. 3,719,646, incorporated herein by reference in its entirety for all purposes). Other suitable free radical polymerizable ethylenically unsaturated monomers containing useful functional groups include hydroethylethylene urea methacrylate (HEEUMA) and aminoethylethylene urea methacrylate (AEEUMA). The free radical polymerizable ethylenically unsaturated monomer may contain a plurality of functional groups on each monomer molecule; for example, the monomer may bear two or more urea and / or ureido groups per molecule, such as the compounds described in U.S. 6,166,220 (incorporated herein by reference in its entirety for all purposes). Illustrative examples of particular free radical polymerizable ethylenically unsaturated monomers suitable for use in the present invention as functionalized monomers include, but are not limited to, aminoethyl acrylate and methacrylate, dimethylaminopropylacrylate and methacrylate, 3-dimethylamino-2,2- dimethylpropyl-1 -acrylate and methacrylate, 2-N-morpholinoethyl acrylate and methacrylate, 2- N-piperidinoethyl acrylate and methacrylate, N-(3-dimethylaminopropyl)acrylamide and methacrylamide, N-(3-dimethylamino-2,2-dimethylpropyl)acrylamide and methacrylamide, N- dimethylaminomethyl acrylamide and methacrylamide, N-(4-morpholino-methyl)acrylamide and methacrylamide, vinylimidazole, vinylpyrrolidone, N-(2-methacryloyloxyethyl)ethylene urea, N- (2-methacryloxyacetamidoethyl)-N, allylalkyl ethylene urea, N-methacrylamidomethyl urea, N- methacryloyl urea, 2-(I-imidazolyl)ethyl methacrylate, 2-(l-imidazolidin-2- on)ethylmethacrylate, N-(methacrylamido)ethyl urea, glycidyl (meth)acrylates, hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylates, gamma- (meth)acryloxypropyltrialkoxysilanes, N,N-dimethyl(meth)acrylamides, diacetone(meth)acrylamides, ethylene glycol (meth)acrylate phosphates, polyethylene glycol (meth)acrylates, polyethylene glycol methyl ether (meth)acrylates, diethylene glycol (meth)acrylates and combinations thereof.

[0072] Free radical initiators suitable for the polymerization of the monomers used to prepare the multi-stage emulsion polymer particles may be any water soluble initiator suitable for aqueous emulsion polymerization. Examples of free radical initiators suitable for the preparation of the multi-stage emulsion polymer particles of the present application include, but are not limited to, hydrogen peroxide, tert-butyl peroxide, alkali metal persulfates such as sodium, potassium and lithium persulfate, ammonium persulfate, and mixtures of such initiators with a reducing agent. The amount of initiator may be, for example, from 0.01 to 3 percent by weight, such as 0.5 to 3 percent by weight, such as 0.1 to 3 percent by weight, such as 1 to 3 percent by weight, based on the total weight of the monomers (A), (B) and (C).

[0073] In some embodiments, a redox polymerization initiator system is used. In a redox free radical initiation system, a reducing agent may be used in conjunction with an oxidant. Reducing agents suitable for the aqueous emulsion polymerization include sulfites (e.g., alkali metal metabisulfite, hydrosulfite, and hyposulfite). In some embodiments, sugars (such as ascorbic acid and isoascorbic acid or an alkali metal (iso)ascorbate salt) might also be a suitable reducing agent for the aqueous emulsion polymerization.

[0074] In a redox system, the amount of reducing agent may be, for example, from 0.01 to 3 percent by weight, such as 0.5 to 3 percent by weight, such as 0.1 to 3 percent by weight, such as 1 to 3 percent by weight, based on the total weight of the monomers (A), (B) and (C).

[0075] Oxidizing agents (alternatively, oxidants) include, but are not limited to, hydrogen peroxide and ammonium or alkali metal persulfates, perborates, peracetates, peroxides, and percarbonates and a water-insoluble oxidizing agent such as, for example, benzoyl peroxide, lauryl peroxide, t-butyl peroxide, t-butyl hydroperoxide, 2,2'-azobisisobutyronitrile, t-amyl hydroperoxide, t-butyl peroxyneodecanoate, and t-butyl peroxypivalate. The amount of oxidizing agent may be, for example, from 0.01 to 3 percent by weight, such as 0.5 to 3 percent by weight, such as 0.1 to 3 percent by weight, such as 1 to 3 percent by weight, based on the total weight of the monomers (A), (B) and (C). The free radical polymerization temperature typically is in the range of about 10° C. to about 110° C. In the case of the persulfate systems, the temperature may be in the range of about 60° C. to about 100° C. In the redox system, the temperature may be in the range of about 30° C. to about 100° C., such as in the range of about 30° C. to about 60° C., or in the range of about 30° C. to about 45° C. The type and amount of initiator may be the same or different in the various stages of the multi-stage polymerization.

[0076] Suitable swelling agents are generally bases, including volatile bases such as ammonia, ammonium hydroxide, and volatile lower aliphatic amines, such as morpholine, trimethylamine, and triethylamine, carbonates, hydrogen carbonates and the like. Fixed or permanent bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide, zinc ammonium complex, copper ammonium complex, silver ammonium complex, strontium hydroxide, barium hydroxide and the like may also be used. Solvents, such as, for example, ethanol, hexanol, octanol, and Texanol® solvent and those described in U.S. 4,594,363, may be added to aid in fixed or permanent base penetration. In some embodiments, the swelling agent is ammonia or ammonium hydroxide. An alkali metal hydroxide such as sodium hydroxide is preferred for lack of volatile emissions. The swelling agent may be in the form of an aqueous liquid or a gaseous medium containing a volatile base. The compositions of the outer shell and any intermediate encapsulating layers may be selected so as to be permeable to the swelling agent at ambient temperature or at a moderately elevated temperature. In one embodiment, the swelling agent is contacted with the multi-stage emulsion polymer particles at a temperature somewhat less than the glass transition temperature of the outer shell polymer. For example, the contacting temperature may be 5 to 20° C, or 10 to 30° C, or or 5-40° C. less than the outer shell polymer Tg.

[0077] The hydrophilic component of the swellable particle swells when the multi-stage emulsion polymer particles are subjected to a basic swelling agent that permeates the intermediate shells of the multi-stage emulsion polymer particles in the presence of the outer shell polymerizing monomer. In one embodiment of the invention, the hydrophilic component of the swellable particle is acidic (having a pH less than 6). Treatment with a basic swelling agent in the presence of the outer shell polymerizing monomer neutralizes the acidity and raises the pH of the hydrophilic component to greater than 6, or to at least about 7, or to at least about 8, or to at least about 9, or to at least about 10, or to at least about 11 , thereby causing swelling by hydration of the hydrophilic component of the core. The swelling, or expansion, of the swellable particle may involve partial merging of the outer periphery of the swellable particle into the pores of the inner periphery of the layer immediately adjacent to the core (such as the outer shell or an intermediate encapsulating shell) and also partial enlargement or bulging of such adjacent layer and the entire particle overall.

[0078] The weight ratio of the swellable particle to the outer shell may generally, for example, be in the range of from 1:5 to 1 :20 (e.g., from 1 :8 to 1:20, such as from 1 :8 to 1 : 15, such as from 1: 10 to 1:20). To decrease the dry density of the final voided latex particles, the amount of outer shell relative to the amount of core should generally be decreased; however, sufficient outer shell should be present such that the core is still encapsulated.

[0079] Methods previously described in the art for producing voided latex particles may be adapted for use in the present invention, provided the processes are modified with the swellable particle prepared by reacting the core latex particle with (i) one or more ethylenically unsaturated monomers containing an acid functional group (monomer A); (ii) one or more non-ionic ethylenically unsaturated monomers (monomer B); (iii) one or more hydrophobic non-ionic ethylenically unsaturated monomers having a lower water solubility than monomer B (monomer C); (iv) optionally, one or more non-ionic surfactants; and (v) one or more anionic surfactants. Previously known methods subject to such modification may include those described, for example, in U.S. 4,427,836; 4,468,498; 4,594,363; 4,880,842; 4,920,160; 4,985,469; 5,216,044; 5,229,209; and 5,273,824, each of which is incorporated herein by reference in its entirety for all purposes. For example, particles in accordance with the present invention may be made by incorporating the functional monomers described herein into the outer shell of the particles described in the following examples: (1) examples 0-14 of U.S. 4,427,836, (2) examples 0-12 of U.S. 4,468,498, (3) examples 1-4 of U.S. 4,594,363, (4) examples I-IX of U.S. 4,880,842, (5) examples 1-13 of U.S. 4,920,160, (6) examples 1-7 of U.S. 4,985,469, (7) examples 1-7 of U.S. 5,216,044, (8) examples 1-8 of U.S. 5,229,209, and (9) examples 1-50 of U.S. 5,273,824.

[0080] Utility

[0081] The voided particles of the invention were observed to provide thermal insulation properties and would therefore find use as a component in thermal applications where creating a thermal insulator or barrier would be of value. One exemplary use would be in the manufacture of thermal paper to reduce the energy required during the thermal printing process. In an embodiment, the voided particles of the invention are present in an undercoat applied during the manufacture of thermal papers, where thermal paper is paper coated with a thermal sensitive layer that changes color upon exposure to heat. This inclusion of the voided particles in the undercoat enables the thermal papers to produce a higher quality of printing results compared to thermal papers with an undercoat not containing the voided particles. It has been challenging prior to the invention, however, to produce voided particles of roughly 1.5 pm volume average particle size with low level of particle blowout (i.e., ruptured, broken or otherwise damaged particles). Medium to high levels of particle blowout (e.g., greater than 50%, such as greater than 60%, such as greater than 70%, such as greater than 80%) may negatively impact the performance of the voided particles as thermal insulators.

[0082] In an embodiment, the voided latex particles as described herein are present in a coating composition.

[0083] In an embodiment, paper, paint, ink, adhesives or cosmetics comprise the coating composition comprising the voided latex particles as described herein.

[0084] Aspects of the Invention

[0085] Aspect 1. A process of producing voided latex particles comprising: i) preparing a core latex particle by a polymerization reaction of one or more ethylenically unsaturated monomers, followed by ii) forming a a swellable particle by reacting the core latex particle with

[0086] (A) 5-45 wt% of one or more ethylenically unsaturated monomers containing an acid functional group, where the wt% is relative to the total wt% of the monomers (A),

[0087] (B) and (C);

[0088] (B) 1-90 wt% of one or more non-ionic ethylenically unsaturated monomers, where the wt% is relative to the total wt% of the monomers (A), (B) and (C);

[0089] (C) 1-55 wt% of one or more hydrophobic non-ionic ethylenically unsaturated monomers having a lower water solubility than (B), where the wt% is relative to the total wt% of the monomers (A), (B) and (C); (D) optionally, at least 0.01 wt% of one or more non-ionic surfactants, and

[0090] (E) at least 0.01 wt% of one or more anionic surfactants, in a polymerization reaction, followed by iii) forming a first layer partially or fully encapsulating the swellable particle by treating the swellable particle with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by iv) optionally forming a second layer partially or fully encapsulating the swellable particle by treating the swellable particle containing a first layer with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by v) adding swelling agents to generate voided latex particles having a volume average particle size of greater than 1 pm, wherein the polymerization reactions in steps i), ii), iii) and iv) are emulsion polymerization reactions, and wherein the voided latex particles have a particle blowout level below 50%.

[0091] Aspect 2. The process of Aspect 1, wherein the voided latex particle has a volume average particle size of greater than 1 pm up to 10 pm, such as greater than 1 pm up to 8 pm, such as greater than 1 pm up to 6 pm such as from 1.1 pm up to 5 pm, such as from 1.2 pm up to 4 pm, such as from 1.3 pm up to 3 pm.

[0092] Aspect 3. The process of Aspect 1 or Aspect 2, wherein the voided latex particles are approximately spherical in shape.

[0093] Aspect 4. The process of any of Aspects 1 to 3, wherein the voided latex particles have a particle blowout level below 50%, such as below 40%, such as below 30%, such as below 20%, such as between 0 to less than 50%, such as between 0 to 40%, such as between 0 to 30%, such as between 5 to less than 50%, such as between 5 to 40%, such as between 5 to 30%, such as between 10 to less than 50%, such as between 10 to 40%, such as between 10 to 30%.

[0094] Aspect 5. The process of any of Aspects 1 to 4, wherein the core latex particle has a volume average particle size of greater than 100 nm up to 500 nm, such as greater than 100 nm up to 400 nm, such as greater than 100 nm up to 350 nm, such as from 110 nm to 500 nm, such as from 110 nm to 400 nm, such as from 110 nm to 350 nm.

[0095] Aspect 6. The process of any of Aspects 1 to 5, wherein monomer (A) is present in an amount of 5-45 wt%, such as 10-45 wt%, such as 10-40 wt%, such as 10-35 wt%, such as 15-40 wt%, such as 15-35 wt%, such as 20-40 wt%, such as 20-35 wt%, relative to the total wt% of the monomers (A), (B) and (C).

[0096] Aspect 7. The process of any of Aspects 1 to 6, wherein monomer (A) comprises one or more of acrylic acid, methacrylic acid, aery 1 oxy propionic acid, (meth)acryloxypropionic acid, itaconic acid, aconitic acid, maleic acid or maleic anhydride, fumaric acid, crotonic acid, monomethyl maleate, monomethyl fumarate, monomethyl itaconate, vinyl phosphates, (meth)allyl phosphate, phosphate esters of polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate, polyoxyethylene allyl ether phosphate, sulfoethyl (meth)acrylate, arylsulfonic or sulfuric acids, (meth)acrylamidoethane sulfonic or sulfuric acids, methacrylamido-2- methyl propane sulfonic or sulfuric acids and the like.

[0097] Aspect 8. The process of any of Aspects 1 to 7, wherein monomer (A) comprises at least one of methacrylic acid and acrylic acid.

[0098] Aspect 9. The process of any of Aspects 1 to 8, wherein monomer (B) is present in an amount of 1-90 wt%, such as 5-90 wt%, such as 5-80 wt%, such as 10-90 wt%, such as 10-80 wt%, such as 10-70 wt%, such as 10-60 wt%, such as 15-90 wt%, such as 15-80 wt%, such as 20-80 wt%, such as 20-70 wt%, such as 30-80 wt%, such as 40-70 wt%, relative to the total wt% of the monomers (A), (B) and (C).

[0099] Aspect 10. The process of any of Aspects 1 to 9, wherein monomer (B) comprises one or more of vinyl aromatic monomers such as styrene, a-methyl styrene, p-methyl styrene, t-butyl styrene, or vinyltoluene, olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide, (C1-C20) alkyl or (C3-C20) alkenyl esters of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate and the like. Aspect 11. The process of any of Aspects 1 to 10, wherein monomer (B) comprises methyl methacrylate.

[0100] Aspect 12. The process of any of Aspects 1 to 11, wherein monomer (C) is present in an amount of 1-55 wt% , such as 1-45 wt%, such as 1-35 wt%, such as 1-25 wt%, such as 1-15 wt%, such as 5-50 wt%, such as 5-40 wt%, such as 5-30 wt%, such as 5-25 wt%, such as 5-15 wt%, relative to the total wt% of the monomers (A), (B) and (C).

[0101] Aspect 13. The process of any of Aspects 1 to 12, wherein monomer (C) is a non-ionic ethylenically unsaturated monomer having a lower water solubility than monomer (B) and comprises one or more of vinyl aromatic monomers such as styrene, a-methyl styrene, p-methyl styrene, t-butyl styrene, or vinyltoluene, olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide, (C1-C20) alkyl or (C3-C20) alkenyl esters of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate and the like.

[0102] Aspect 14. The process of any of Aspects 1 to 13, wherein monomer (C) comprises at least one of butyl acrylate, styrene, and butyl methacrylate.

[0103] Aspect 15. The process of any of Aspects 1 to 14, wherein the polymerization reaction includes one or more non-ionic surfactants, and the one or more non-ionic surfactant is present in an amount of at least 0.01 wt%, such as at least 0.05 wt%, such as at least 0.1 wt%, such as at least 0.5 wt%, such as at least 1 wt%, such as at least 1.5 wt%, such as up to 10 wt%, such as 0.01-10 wt%, such as 0.01-5 wt%, such as 0.01-3 wt%, such as 0.1-10 wt%, such as 0.1-5 wt%, such as 1-10 wt%, such as 1-5 wt%, relative to the total wt% of the monomers (A), (B) and (C).

[0104] Aspect 16. The process of any of Aspects 1 to 15, wherein the non-ionic surfactant includes, but is not limited to, alkyl (e.g., monoalkyl, dialkyl, trialkyl) phenol ethoxylates, polysiloxane polyalkylene oxide copolymers, primary alcohol ethoxylates, fatty alcohol ethoxylates, fatty acid ethoxylates, alkanolamide ethoxylates, fatty amine ethoxylates, EO-PO block copolymers and alkylpolyglucosides, and mixtures thereof. Aspect 17. The process of any of Aspects 1 to 16, wherein the nonionic surfactant includes, but is not limited to, tert-octylphenoxyethylpoly-ethoxyethanol, dodecyloxypolyethoxyethanol, nonylphenoxyethyl-polyethoxyethanol, polyethylene glycol 2000 monooleate, ethoxylated castor oil, fluorinated alkyl esters and alkoxylates, polyoxyethylene sorbitan monolaurate, sucrose monococoate, di(2-butyl)phenoxypolyethoxyethanol, hydroxyethylcellulosepolybutyl acrylate graft copolymer, dimethyl silicone polyalkylene oxide graft copolymer, polyethylene oxide)poly(butyl acrylate) block copolymer, block copolymers of propylene oxide and ethylene oxide, 2,4,7,9-tetramethyl-S-decyne-4,7-diol ethoxylated with 30 moles of ethylene oxide, N- polyoxyethylene lauramide, N-lauryl-N-polyoxyethylene amine, polyethylene glycol dodecyl thioether and mixtures thereof

[0105] Aspect 18. The process of any of Aspects 1 to 17, wherein the non-ionic surfactant comprises at least one of a linear fatty alcohol ethoxylate, a branched fatty alcohol ethoxylate, an ethoxylated monoalkyl phenol, an ethoxylated dialkyl phenol and an ethoxylated trialkyl phenol.

[0106] Aspect 19. The process of any of Aspects 1 to 18, wherein the anionic surfactant is present in an amount of at least 0.01 wt%, such as at least 0.05 wt%, such as at least 0.1 wt%, such as at least 0.5 wt%, such as at least 1 wt%, such as at least 1.5 wt%, up to 10 wt%, such as 0.01-10 wt%, such as 0.01-5 wt%, such as 0.01-3 wt%, such as 0.01 to 1 wt%, such as 0.1-10 wt%, such as 0.1-5 wt%, such as 1-10 wt%, such as 1-5 wt%, relative to the total wt% of the monomers (A), (B) and (C).

[0107] Aspect 20. The process of any of Aspects 1 to 19, wherein the anionic surfactant includes, but is not limited to, alkylbenzenesulfonic acids, alkaline earth metal alkylbenzenesulfonates, sulfonated fatty acids, sulfonated olefins, sulfonated diphenyl ethers, sulfosuccinates, fatty alcohol sulfates, alkylphenol sulfates, alkyl polyglycol ether sulfates, fatty alcohol ether sulfates, fatty alcohol phosphates, alkylphenol phosphates, alkyl polyglycol ether phosphates, alkyl polyalkylene oxide phosphates, fatty alcohol ether phosphates and mixtures thereof.

[0108] Aspect 21. The process of any of Aspects 1 to 20, wherein the anionic surfactant includes, but is not limited to, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, potassium stearate, sodium dioctyl sulfosuccinate, sodium dodecyldiphenyloxide disulfonate, nonylphenoxyethylpoly(I)ethoxyethyl sulfate ammonium salt, sodium styrene sulfonate, sodium dodecyl allyl sulfosuccinate, sodium or ammonium salts of phosphate esters of ethoxylated nonylphenol, sodium octoxynol-3-sulfonate, sodium cocoyl sarcocinate, sodium 1 -alkoxy-2 - hydroxypropyl sulfonate, sodium a-olefin (Ci4-Cie)sulfonate, sulfates of hydroxyalkanols, tetrasodium N-(l,2-dicarboxy ethyl)-N-octadecylsulfosuccinamate, disodium N- octadecylsulfosuccinamate, disodium alkylamido polyethoxy sulfosuccinate, disodium ethoxylated nonylphenol half ester of sulfosuccinic acid and the sodium salt of tertoctylphenoxyethoxypoly ethoxyethyl sulfate.

[0109] Aspect 22. The process of any of Aspects 1 to 21, wherein the anionic surfactant comprises at least one of a sulfate, a sulfosuccinate, a sulfonate, and a disulfonate.

[0110] Aspect 23. The process of any of Aspects 1 to 22, wherein all polymerization reactions related to the preparation of the voided latex particles from the core latex particle and swellable particle are emulsion polymerization reactions.

[0111] Aspect 24. The process of any of Aspects 1 to 23, wherein all encapsulating polymers partially or fully encapsulate the swellable particle.

[0112] Aspect 25. The process of any of Aspects 1 to 24, wherein all encapsulating polymers fully encapsulate the swellable particle.

[0113] Aspect 26. The process of any of Aspects 1 to 25, wherein the weight ratio of the swellable particle to the core latex particle is 5: 1 to 200: 1, such as 5: 1 to 100: 1, such as 10:1 to 100:1, such as 10: 1 to 75: 1.

[0114] Aspect 27. The process of any of Aspects 1 to 26, wherein the voided latex particles are nonfilm forming.

[0115] Aspect 28. A voided latex particle prepared by the process of any of Aspects 1 to 27.

[0116] Aspect 29. The use of a plurality of voided latex particles prepared by the process of any of Aspects 1 to 27 in a thermal application (such as in a thermal printing process, such as in an undercoat applied during the manufacture of thermal paper) or in a composition

[0117] Aspect 30. An article comprising a composition comprising a plurality of voided latex particles prepared by the process of any of Aspects 1 to 27.

[0118] Aspect 31. The article of Aspect 30, wherein the article is paper, paint, ink, adhesive or a cosmetic. Aspect 32. The process of Aspect 1, wherein step (ii) comprises 0.01-10 wt% of the one or more non-ionic surfactants relative to the total wt% of the monomers (A), (B) and (C).

[0119] Aspect 33. The process of Aspect 1, wherein step (ii) comprises 0.01-1 wt% of the one or more anionic surfactants relative to the total wt% of the monomers (A), (B) and (C).

[0120] Experimental

[0121] Dynamic light scattering (PLS)

[0122] The volume average particle size (Mv) and number average particle size (Mn) were measured using dynamic light scattering using a Nanotrac UPA 150 manufactured by Microtrac.

[0123] Scanning transmission electron microscopy (STEM) characterization

[0124] The morphology of final voided particles was characterized using a Thermo Scientific™ Helios 5 Hydra UX DualBeam microscope under STEM mode.

[0125] Determination of blowout level.

[0126] Blowout particle refers to a voided particle with a ruptured or broken morphology under microscope characterization. Representative blowout particles are identified as being circled in from among the voided particles appearing in Figure 3. To determine blowout level, only the particle that has a particle size within 10 percent of the mean average particle size was included, and at least 50 particles were counted. Specifically, a visual count of ruptured or broken voided latex particles compared to all voided latex particles visible under microscope characterization. The blowout percentage was calculated by following equation:

[0127] # of ruptured or broken voided latex particles Total # of voided latex particles

[0128] EXAMPLES

[0129] Core particle

[0130] The core particle is prepared by emulsion polymerization of a prescribed amount of methyl methacrylate with methacrylic acid in a reactor at a temperature between 85-93°C. The volume average particle size for the core particle is 155 nm. Intermediate swellable particle - Inventive Example 1

[0131] The intermediate swellable particle is prepared using a seeded emulsion polymerization with the core particle as the seed. The monomer mixture used for the intermediate swellable particle comprises methyl methacrylate, methacrylic acid, and butyl methacrylate. The surfactant used in the synthesis is a combination of alkyldiphenyloxide disulfonate and linear fatty alcohol ethoxylates, wherein the active amount of alkyldiphenyloxide disulfonate and linear fatty alcohol ethoxylates is 0.5 wt% and 1.8wt%, respectively, based on the total weight of monomer in the synthesis.

[0132] Intermediate swellable particle - Comparative Example 1

[0133] The intermediate swellable particle is prepared using a seeded emulsion polymerization with the core particle as the seed. The monomer mixture used for the intermediate swellable particle comprises methyl methacrylate and methacrylic acid. The surfactant used in the synthesis is a combination of alkyldiphenyloxide disulfonate and linear fatty alcohol ethoxylates, wherein the active amount of alkyldiphenyloxide disulfonate and linear fatty alcohol ethoxylates is 0.5 wt% and 1.8wt%, respectively, based on the total weight of monomer in the synthesis.

[0134] Intermediate swellable particle - Comparative Example 2

[0135] The intermediate swellable particle is prepared using a seeded emulsion polymerization with the core particle as the seed. The monomer mixture used for the intermediate swellable particle comprises methyl methacrylate, methacrylic acid, and butyl methacrylate. The surfactant used in the synthesis is alkyldiphenyloxide disulfonate, wherein the active amount of alkyldiphenyloxide disulfonate is 0.5 wt%, based on the total weight of monomer in the synthesis.

[0136] Intermediate swellable particle - Comparative Example 3

[0137] The intermediate swellable particle is prepared using a seeded emulsion polymerization with the core particle as the seed. The monomer mixture used for the intermediate swellable particle comprises methyl methacrylate, methacrylic acid, and butyl methacrylate. The surfactant used in the synthesis is linear fatty alcohol ethoxylates, wherein the active amount of linear fatty alcohol ethoxylates is 1.8 wt%, based on the total weight of monomer in the synthesis. Final voided particle

[0138] The final voided particle is converted from the intermediate swellable particle using a multi-stage process. First, a pre-emulsion mixture comprising methyl methacrylate (MMA), methacrylic acid (MAA), and butyl methacrylate (BMA) is added to the reactor containing the intermediate swellable particles at a temperature between about 75°C to about 85°C to form the first intermediate layer on the swellable particle. Next, a different pre-emulsion mixture comprising styrene (STY) and divinyl styrene (DVB) is added to the reactor at a temperature between about 75°C to about 85°C to form a second intermediate layer on the latex particles. The reaction temperature is increased to be in the range of about 90°C to 95 °C for a predetermined amount of time prior to forming the outer shell. Then polymerization initiator is added into the reactor to reduce the amount of monomer present to less than 0.5% monomer based on the weight of the multi-stage emulsion polymer particles. Subsequently, sodium hydroxide solution was introduced into the reactor to neutralize the intermediate swellable particles. Lastly, styrene was added into the reactor to swell the latex particles to form final voided particles.

[0139] Discussion

[0140] Figure 1 shows an embodiment of the inventive process of making voided particles starting with a core particle, followed by formation of an intermediate swellable particle that is subsequently converted into a voided particle with large particle size (>1 pm).

[0141] Table 1 describes the properties of exemplary inventive and comparative intermediate swellable particles. Comparative Example 1 only contains MMA and MAA as polymerizable monomers and was not able to form stable intermediate swellable particles, as evidenced by significant latex coagulation during the synthesis. Therefore, the Comparative Example 1 was not suitable for the subsequent conversion into voided particles. Surprisingly, the incorporation of hydrophobic monomers into intermediate swellable particles yielded desirable particle size, good particle size distribution, and low level of filterables (<0.1 wt%) after completion of the synthesis (as evidenced by Inventive Example 1, and Comparative Example 2). These intermediate swellable particles were thus selected for the conversion into final voided particles. Table 1. Properties of exemplary intermediate swellable particles

[0142] Table 2 describes the DLS particle size characterization of final voided particles converted from the selected intermediate swellable particle examples. All the final voided particles showed large volume average particle size. Figures 2A-2F show scanning transmission electron microscopy comparisons at 25,000X magnification of the final voided particles prepared from intermediate swellable particles: (A) Inventive Example 1; (B) Comparative Example 2; and (C) Comparative Example 3, and also scanning transmission electron microscopy comparisons at 10,000X magnification of the final voided particles prepared from intermediate swellable particles: (D) Inventive Example 1; (E) Comparative Example 2; and (F) Comparative Example 3. It was surprising to observe that the voided particles prepared from Comparative Example 2 with only anionic surfactants (Figures 2B and 2E) and Comparative Example 3 with only non-ionic surfactants (Figures 2C and 2F) showed high levels of particle blowout. In contrast, the inventive example comprising the combination of anionic and non-ionic surfactants yielded voided particles with low levels of particle blowout (Figures 2A and 2D). As summarized in Table 2, both comparative examples showed particle blowout level greater than 50%, while the inventive example showed particle blowout level less than 40%. The voided particles prepared from the inventive example also exhibited high void fraction, as evidenced by 1 thin shell (i.e., the dark exterior layer of the particles) and large voids (i.e., the light grey area inside of the particles) as shown in Figures 2A and 2D.

[0143] Table 2. Properties of final voided particles

[0144] Collectively, the results of Table 1 and Figures 2A-2F demonstrate the importance of incorporating hydrophobic monomers and both non-ionic and anionic surfactants into the intermediate swellable particles when preparing large voided particles (volume average particle size > 1 pm) that exhibit good morphology and low blowout levels.

[0145] The invention as described is intended to cover not only individual aspects or exemplary embodiments of the invention but also combinations of all aspects and embodiments.

Claims

CLAIMS1. A process of producing voided latex particles comprising: i) preparing a core latex particle by a polymerization reaction of one or more ethylenically unsaturated monomers, followed by ii) forming a swellable particle by reacting the core latex particle with(A) 5-45 wt% of one or more ethylenically unsaturated monomers containing an acid functional group, where the wt% is relative to the total wt% of the monomers (A), (B) and (C);(B) 1-90 wt% of one or more non-ionic ethylenically unsaturated monomers, where the wt% is relative to the total wt% of the monomers (A), (B) and (C);(C) 1-55 wt% of one or more hydrophobic non-ionic ethylenically unsaturated monomers having a lower water solubility than (B), where the wt% is relative to the total wt% of the monomers (A), (B) and (C);(D) optionally, at least 0.01 wt% of one or more non-ionic surfactants relative to the total wt% of the monomers (A), (B) and (C), and(E) at least 0.01 wt% of one or more anionic surfactants relative to the total wt% of the monomers (A), (B) and (C), in a polymerization reaction, followed by iii) forming a first layer partially or fully encapsulating the swellable particle by treating the swellable particle with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by iv) optionally forming a second layer partially or fully encapsulating the swellable particle by treating the swellable particle containing a first layer with one or more ethylenically unsaturated monomers in a polymerization reaction, followed by v) adding swelling agents to generate voided latex particles having a volume average particle size of greater than 1 pm, wherein the polymerization reactions in steps i), ii), iii) and iv) are emulsion polymerization reactions, and wherein the voided latex particles have a particle blowout level below 50%.

2. The process according to claim 1, wherein the core latex particle prepared in step i) has a volume average particle size of greater than 100 nm up to 500 nm.

3. The process according to claim 1, wherein the swellable particle formed in step ii) has a volume average particle size of 300 nm to 2,000 nm.

4. The process according to claim 1, wherein the voided latex particle generated in step v) has a volume average particle size of greater than 1 pm up to 10 pm.

5. The process according to claim 1, wherein the ethylenically unsaturated monomer (A) in step ii) comprises at least one of methacrylic acid and acrylic acid.

6. The process according to claim 1, wherein the ethylenically unsaturated monomer (B) in step ii) comprises methyl methacrylate.

7. The process according to claim 1, wherein the ethylenically unsaturated monomer (C) in step ii) comprises at least one of butyl acrylate, styrene, and butyl methacrylate.

8. The process according to claim 1, wherein the anionic surfactant comprises at least one of a sulfate, a sulfosuccinate, a sulfonate, and a disulfonate.

9. The process according to claim 1, wherein step ii) comprises the one or more non-ionic surfactants, and the one or more non-ionic surfactants comprises at least one of a linear fatty alcohol ethoxylate, a branched fatty alcohol ethoxylate, an ethoxylated monoalkyl phenol, an ethoxylated dialkyl phenol and an ethoxylated trialkyl phenol.

10. The process according to claim 1, wherein the encapsulation in steps ii), iii) and iv) is full encapsulation.

11. The process according to claim 1, wherein the number of ethylenically unsaturated monomers present in the polymerization reaction in steps i), ii)(A), ii)(B), ii)(C), iii) and iv) is two or more.

12. A voided latex particle prepared by the process according to any one of claims 1 to 11.

13. A plurality of voided latex particles prepared by the process according to any one of claims 1 to 11, having a particle blowout level below 50%.

14. The plurality of voided latex particles according to claim 13, having a particle blowout level below 40%.

15. A composition comprising the plurality of voided latex particles according to claim 13.

16. An article comprising the composition according to claim 15.

17. Use of the plurality of voided latex particles according to claim 13 in a thermal application.

18. The process according to claim 1, wherein step (ii) comprises 0.01-10 wt% of the one or more non-ionic surfactants relative to the total wt% of the monomers (A), (B) and (C).

19. The process according to claim 1, wherein step (ii) comprises 0.01-1 wt% of the one or more anionic surfactants relative to the total wt% of the monomers (A), (B) and (C).

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