Method for preparing large hollow particles

Abstract

Described herein is a method of making hollow latex particles having a volume average particle diameter greater than 1 µm and a particle burst level of less than 50%. Also described are hollow latex particles made thereby and articles containing the hollow latex particles.

Description

[0001] This application claims priority and interest in U.S. Provisional Application No. 63 / 600,859, filed November 20, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to a method for preparing hollow latex particles with a volume average particle size greater than 1 μm and a particle blowout level of less than 50%, the hollow latex particles prepared thereby, and articles comprising said hollow latex particles. Background Technology

[0003] Hollow latex particles, also known as hollow latex granules, are widely used in coatings and coating applications. Methods for preparing hollow latex particles using multi-stage emulsion polymerization have 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. Typical methods involve preparing highly acidic seed latex particles (also known as swellable particles), subsequently encapsulating the seeds with a hydrophobic shell, and then neutralizing and swelling the encapsulated seed latex polymer with an alkali to form hollow latex particles. However, most of the methods disclosed in the prior art are suitable for producing hollow latex particles with a particle size of less than 1 μm (e.g., about 0.4 μm) for use as a light-blocking agent to replace titanium dioxide (TiO2) in coating applications.

[0004] It has been found that hollow latex particles with larger particle sizes (e.g., >1 μm) are useful in some coating applications. For example, hollow particles with a particle size greater than 1.5 μm are used in the undercoat of thermal paper manufacturing to provide thermal insulation properties, thereby improving print quality. A technical challenge encountered in producing large hollow particles with a particle size >1 μm is the formation of a large number of broken and / or fragmented hollow particles, also known as particle bursting. High levels of particle bursting negatively impact the effective porosity of the final hollow particles, thus impairing desired properties such as thermal insulation. Particle bursting is a unique technical challenge associated with the preparation of hollow latex particles with a particle size greater than 1 μm, particularly in the case of 1.5 μm hollow particles, whereas particle bursting is generally absent when preparing hollow particles smaller than 1 μm. WO 22 / 189290 discloses a method for preparing hollow latex particles with an average particle size of 1.6 μm. However, particle bursting is severe and undesirable.

[0005] This invention describes an improved method for preparing large-sized hollow latex particles with a particle size greater than 1 μm (e.g., 1.5 μm) and a low particle bursting level, which addresses the aforementioned challenges. Summary of the Invention

[0006] One aspect of the present invention is a method for producing hollow latex granules, comprising: i) Prepare core latex particles through the polymerization reaction of one or more olefinically unsaturated monomers, then ii) By reacting the nuclear latex particles with the following substances during the polymerization reaction, swellable particles are formed: (A) 5-45% by weight of one or more olefinic unsaturated monomers containing acid functional groups, wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (B) 1-90% by weight of one or more nonionic olefinically unsaturated monomers, wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (C) 1-55% by weight of one or more hydrophobic nonionic olefinic unsaturated monomers, which have lower water solubility than (B), wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (D) Optionally, one or more nonionic surfactants, and (E) At least 0.01% by weight of one or more anionic surfactants, Subsequently, iii) By treating the swollen particles with one or more olefinically unsaturated monomers during the polymerization reaction, a first layer is formed that partially or completely encapsulates the swollen particles, and then... iv) Optionally, a second layer is formed by treating the swellable particles containing the first layer with one or more olefinically unsaturated monomers during the polymerization reaction, thereby partially or completely encapsulating the swellable particles, and then... v) Add a swelling agent to generate hollow latex particles with a volume average particle size greater than 1 μm. The polymerization reactions in steps i), ii), iii), and iv) are emulsion polymerization reactions, and The particle bursting level of the hollow latex particles is less than 50%.

[0007] Another aspect of the present invention is hollow latex particles prepared by the method described herein.

[0008] Another aspect of the present invention is a plurality of hollow latex particles prepared by the method described herein, wherein the particle bursting level of the particles is less than 50%.

[0009] Another aspect of the invention is an article comprising a composition containing the hollow latex particles described herein.

[0010] Another aspect of the invention is paper, coatings, inks, adhesives, or cosmetics comprising a coating composition containing hollow latex particles as described herein.

[0011] Another aspect of the invention is the use of the hollow latex particles described herein in thermal applications (e.g., in thermal printing processes, such as in a base coat applied during the manufacture of thermal paper) or in coating compositions. Attached Figure Description

[0012] The following figures illustrate specific embodiments of the invention and are not intended to limit the scope of the invention described herein in any other way.

[0013] Figure 1 A method for preparing hollow particles is shown: starting with core particles, then forming intermediate swellable particles, and subsequently converting them into hollow particles with a large volume average particle size (>1 µm).

[0014] Figure 2 A-2F shows a comparison of the particle bursting levels of samples AF.

[0015] Figure 3 A comparison of bursting levels is shown between hollow latex particles prepared by the method of the present invention and hollow latex particles prepared by the method described in WO 2022 / 189290 A1. Detailed Implementation

[0016] Hollow latex granules

[0017] A method for preparing monodisperse large (volume average particle size > 1 μm) hollow latex particles with low particle bursting level is described. In one embodiment, the method includes multi-stage emulsion polymerization, wherein (i) core latex particles are prepared by emulsion polymerization of one or more olefinically unsaturated monomers, then (ii) intermediate swellable particles encapsulating the core latex particles are formed by emulsion polymerization, wherein the swellable particles comprise one or more olefinically unsaturated monomers with acidic functional groups, one or more nonionic olefinically unsaturated monomers, one or more hydrophobic nonionic olefinically unsaturated monomers with lower water solubility than nonionic monomers, one or more anionic surfactants, and optionally one or more nonionic surfactants, then (iii) a first layer of fully encapsulated swellable particles is formed by treating the swellable particles with one or more olefinically unsaturated monomers in the polymerization reaction, then (iv) optionally, a second layer of fully encapsulated swellable particles is formed by treating the swellable particles containing the first layer with one or more olefinically unsaturated monomers in the polymerization reaction, then (v) a conventional swelling agent is added to generate hollow latex particles with a volume average particle size greater than 1 μm and a particle bursting level of less than 50%.

[0018] Hollow latex particles prepared by the method of the present invention typically comprise a hollow interior and a shell surrounding the hollow interior, but one or more additional layers may exist between the shell and the internal voids of each particle. In one embodiment, the volume-average particle size of the hollow latex particles is greater than 1 µm and not greater than 10 µm, for example greater than 1 µm and not greater than 8 µm, for example greater than 1 µm and not greater than 6 µm, for example 1.1 µm to 5 µm, for example 1.2 µm to 4 µm, for example 1.3 µm to 3 µm.

[0019] In one embodiment, the particle bursting level of the hollow latex particles is less than 50%, for example less than 40%, for example less than 30%, for example less than 20%, for example 0 to less than 50%, for example 0 to 40%, for example 0 to 30%, for example 5 to less than 50%, for example 5 to 40%, for example 5 to 30%, for example 10 to less than 50%, for example 10 to 40%, for example 10 to 30%.

[0020] The hollow latex particles prepared by the method of this invention can be characterized as a "non-film-forming" component or additive. "Non-film-forming" means that the hollow latex particles will not form a film at or below ambient temperature; in other words, they will only form a film at temperatures above ambient temperature. For the purposes of this specification, ambient temperature is considered to be in the range of 15°C to 45°C. Therefore, for example, when incorporated into an aqueous coating composition, applied to a substrate, and dried or cured at or below ambient temperature, the hollow latex particles will not form a film. In one embodiment, the hollow latex particles remain as discrete particles in the dried or cured coating.

[0021] The shape of hollow latex particles is not particularly restricted. Although the particles are usually approximately spherical, other shapes such as oblong, elliptical, or teardrop shapes are also possible.

[0022] Nuclear latex particles

[0023] In one embodiment, the volume average particle size of the nuclear latex particles is greater than 100 nm and not greater than 500 nm, for example greater than 100 nm and not greater than 400 nm, for example greater than 100 nm and not greater than 350 nm, for example 110 nm to 500 nm, for example 110 nm to 400 nm, for example 110 nm to 350 nm.

[0024] In one embodiment, the latex particles are not particularly limited in composition and are prepared by emulsion polymerization of one or more olefinically unsaturated monomers, such as various C1-C4 monomers. 30Alkyl methacrylates (e.g., methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, n-decyl methacrylate, n-dodecyl methacrylate, tetradecyl methacrylate, lauryl methacrylate, oleyl methacrylate, palmitate methacrylate, and stearyl methacrylate), and various olefinic unsaturated monomers with hydrophilic functional groups (such as carboxyl groups or certain other types of ionizable functional groups) (e.g., methacrylic acid, itaconic acid, fumaric acid, etc.). Lemon acid, vinyl phosphate, polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate phosphate, polyoxyethylene allyl ether phosphate, sulfoethyl (meth)acrylate, aryl sulfonic acid or sulfuric acid, (meth)acrylamidoethane sulfonic acid or sulfuric acid, methacrylamide-2-methylpropane sulfonic acid or sulfuric acid), isobornyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, 1-naphthyl (meth)acrylate, ethoxyethyl (meth)acrylate, ethyl maleate, dimethyl fumarate, ethyl itaconic acid, styrene, α-methylstyrene, vinyltoluene, dimethyl... Vinyltoluene, vinylnaphthalene, 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, poly(propylene glycol) (meth)acrylate, and crosslinking monomers, including but not limited to divinylnaphthalene, allyl (meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,2-butanediol di(meth)acrylate. 1,3-Butanediol di(meth)acrylate, 1,4-Butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dodecane di(meth)acrylate, cyclohexanediethanol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tricyclodecanediethanol diacrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, diallyl phthalate, trimethylolpropane tri(meth)acrylate, triethanolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and combinations thereof. In one embodiment, the core latex particles are prepared by emulsion polymerization of C1-C8 alkyl methacrylates (e.g., methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate) and (meth)acrylic acid.

[0025] Swellable granules

[0026] In one embodiment, the volume average particle size of the swellable particles is 300 to 2,000 nm, for example 300 to 1,500 nm, for example 300 to 1,000 nm, for example 300 to 800 nm, for example 300 to 700 nm.

[0027] In one embodiment, the weight ratio of swellable particles to nuclear latex particles is 5:1 to 200:1, for example 5:1 to 100:1, for example 10:1 to 100:1, for example 10:1 to 75:1.

[0028] The swellable particles are prepared by treating the nuclear latex particles in an emulsion polymerization reaction with the following substances: (i) one or more olefinic unsaturated monomers containing acidic functional groups (monomer A); (ii) one or more nonionic olefinic unsaturated monomers (monomer B); (iii) one or more hydrophobic nonionic olefinic unsaturated monomers with lower water solubility than monomer B (monomer C); (iv) optionally, one or more nonionic surfactants; and (v) one or more anionic surfactants.

[0029] (i) Monomer (A)

[0030] The amount of monomer (A) is 5-45% by weight, for example 10-45% by weight, for example 10-40% by weight, for example 10-35% by weight, for example 15-40% by weight, for example 15-35% by weight, for example 20-40% by weight, for example 20-35% by weight, where the weight percentage is relative to the total weight of monomers (A), (B) and (C).

[0031] In one embodiment, monomer (A) comprises one or more of the following: acrylic acid, methacrylic acid, acryloxypropionic acid, (meth)acryloyloxypropionic acid, itaconic acid, aconitic acid, maleic acid or maleic anhydride, fumaric acid, crotonic acid, monomethyl maleate, monomethyl fumarate, monomethyl itaconic acid, vinyl phosphate, (meth)allyl phosphate, phosphate of polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate, polyoxyethylene allyl ether phosphate, sulfoethyl (meth)acrylate, aryl sulfonic acid or sulfuric acid, (meth)acrylamidoethane sulfonic acid or sulfuric acid, methacrylamido-2-methylpropane sulfonic acid or sulfuric acid, etc.

[0032] In one embodiment, monomer (A) comprises at least one of methacrylic acid and acrylic acid.

[0033] (ii) Monomer (B)

[0034] The amount of monomer (B) is 1-90% by weight, for example 5-90% by weight, for example 5-80% by weight, for example 10-90% by weight, for example 10-80% by weight, for example 10-70% by weight, for example 10-60% by weight, for example 15-90% by weight, for example 15-80% by weight, for example 20-80% by weight, for example 20-70% by weight, for example 30-80% by weight, for example 40-70% by weight, where the weight% is relative to the total weight of monomers (A), (B) and (C).

[0035] In one embodiment, monomer (B) comprises one or more of the following: vinyl aromatic monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, or vinyltoluene; olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide; and (C1-C2) acrylic acid. 20 )alkyl esters or (C 3- C 20 Alkenyl esters, such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, benzyl methacrylate, lauryl methacrylate, alkenyl methacrylate, palmitate methacrylate, stearyl methacrylate, etc.

[0036] In one embodiment, monomer (B) comprises methyl methacrylate.

[0037] (iii) Monomer (C)

[0038] The amount of monomer (C) is 1-55% by weight, for example 1-45% by weight, for example 1-35% by weight, for example 1-25% by weight, for example 1-15% by weight, for example 5-50% by weight, for example 5-40% by weight, for example 5-30% by weight, for example 5-25% by weight, for example 5-15% by weight, where the weight% is relative to the total weight of monomers (A), (B) and (C).

[0039] In one embodiment, monomer (C) comprises (depending on the specific monomer constituting monomer (B), given that monomer (C) is required to be a nonionic olefinic unsaturated monomer with lower water solubility than monomer (B)) one or more of the following: vinyl aromatic monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, or vinyltoluene; olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide; (meth)acrylic acid (C1-C1) 20 )alkyl esters or (C3-C 20Alkenyl esters, such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, benzyl methacrylate, lauryl methacrylate, alkenyl methacrylate, palmitate methacrylate, stearyl methacrylate, etc.

[0040] In one embodiment, monomer (C) comprises at least one of butyl acrylate, styrene, and butyl methacrylate.

[0041] (iv) Nonionic surfactants

[0042] Nonionic surfactant is an optional component. When present, the amount of nonionic surfactant is at least 0.01 wt%, for example, at least 0.05 wt%, for example, at least 0.1 wt%, for example, at least 0.5 wt%, for example, at least 1 wt%, for example, at least 1.5 wt%, for example, 0.01-10 wt%, for example, 0.01-5 wt%, for example, 0.01-3 wt%, for example, 0.1-10 wt%, for example, 0.1-5 wt%, for example, 1-10 wt%, for example, 1-5 wt%.

[0043] 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 oxide-propylene oxide (EO-PO) block copolymers, and alkyl polysaccharides and mixtures thereof.

[0044] Specific examples of suitable nonionic surfactants include, but are not limited to, tert-octylphenoxyethyl polyethoxyethanol, dodecyloxyethylene polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol, polyethylene glycol 2000 monooleate, ethoxylated castor oil, fluorinated alkyl esters and alkoxylates, polyoxyethylene sorbitan monolaurate, sucrose monococarboxylate, di(2-butyl)phenoxyethylene polyethoxyethanol, hydroxyethyl cellulose polybutyl acrylate graft copolymer, dimethylsiloxane polyalkylene oxide graft copolymer, poly(ethylene oxide) poly(butyl acrylate) block copolymer, propylene oxide and ethylene oxide block copolymer, 2,4,7,9-tetramethyl-5-decyn-4,7-diol ethoxylated with 30 moles of ethylene oxide, N-polyoxyethylene lauramide, N-lauryl-N-polyoxyethyleneamine, polyethylene glycol dodecyl sulfide and mixtures thereof.

[0045] In one embodiment, the nonionic surfactant comprises at least one of a straight-chain fatty alcohol ethoxylate, a branched fatty alcohol ethoxylate, an ethoxylated monoalkylphenol, an ethoxylated dialkylphenol, and an ethoxylated trialkylphenol.

[0046] (v) Anionic surfactants

[0047] Based on the total weight of monomers (A), (B), and (C), the amount of anionic surfactant is at least 0.01 wt%, for example, at least 0.05 wt%, for example, at least 0.1 wt%, for example, at least 0.5 wt%, for example, at least 1 wt%, for example, at least 1.5 wt%, for example, 0.01-10 wt%, for example, 0.01-5 wt%, for example, 0.01-3 wt%, for example, 0.01 to 1 wt%, for example, 0.1-10 wt%, for example, 0.1-5 wt%, for example, 1-10 wt%, for example, 1-5 wt%.

[0048] Examples of suitable anionic surfactants include, but are not limited to, alkylbenzene sulfonic acids, alkaline earth metal alkylbenzene sulfonates, sulfonated fatty acids, sulfonated olefins, sulfonated diphenyl ethers, sulfosuccinates, fatty alcohol sulfates, alkylphenol sulfates, alkyl polyethylene glycol ether sulfates, fatty alcohol ether sulfates, fatty alcohol phosphates, alkylphenol phosphates, alkyl polyethylene glycol ether phosphates, alkyl polyalkylene oxide phosphates, fatty alcohol ether phosphates, and mixtures thereof.

[0049] Specific examples of suitable anionic surfactants include, but are not limited to, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, potassium stearate, sodium dioctyl sulfosuccinate, sodium dodecyl diphenyl ether disulfonate, nonylphenoxyethyl poly(I)ethoxyethyl ammonium sulfate, sodium styrene sulfonate, sodium dodecyl allyl sulfosuccinate, sodium or ammonium salts of ethoxylated nonylphenol phosphate, sodium octylphenol-3-sulfonate, sodium cocoyl sarcosinate, sodium 1-alkoxy-2-hydroxypropyl sulfonate, α-olefins (C 14 -C 16 Sodium sulfonate, hydroxyalkanol sulfate, N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinate tetrasodium, N-octadecylsulfosuccinate disodium, alkylamide polyethoxysulfosuccinate disodium, ethoxylated nonylphenol sulfosuccinate half ester disodium, and tert-octylphenoxyethoxypolyethoxyethyl sulfate sodium salt.

[0050] In one embodiment, the anionic surfactant comprises at least one of sulfate, sulfosuccinate, sulfonate, and disulfonate.

[0051] Polymerization reaction

[0052] The method of the present invention includes a multi-stage emulsion polymerization process. The method includes forming swellable latex particles comprising at least one hydrophilic monoolefinically unsaturated monomer polymer, at least one intermediate shell, and a shell comprising an outer shell polymer. The multi-stage emulsion polymer particles may be contacted with a swelling agent (e.g., an alkali) capable of swelling the swellable latex particles, particularly in the presence of water.

[0053] In a specific implementation, the method involves: i) Prepare core latex particles through the polymerization reaction of one or more olefinically unsaturated monomers, then ii) By reacting the nuclear latex particles with a combination of monomers (A), (B), and (C) described herein, an anionic surfactant, and optionally a nonionic surfactant, swellable latex particles are formed, and then... iii) By treating the swollen particles with one or more olefinically unsaturated monomers in the polymerization reaction, a first layer is formed that partially or completely encapsulates the swollen particles, and then... iv) Optionally, by treating the swellable particles containing the first layer with one or more olefinically unsaturated monomers in the polymerization reaction, a second layer is formed that partially or completely encapsulates the swellable particles, and then... v) Add a swelling agent to generate hollow latex particles with a volume average particle size greater than 1 μm and a particle bursting level of less than 50%.

[0054] In one embodiment, all polymerization reactions associated with the preparation of hollow latex particles from nuclear latex particles and swellable particles are emulsion polymerization reactions.

[0055] In one embodiment, all encapsulated polymers partially or completely encapsulate the swellable particles.

[0056] In one implementation, all encapsulating polymers completely encapsulate the swellable particles.

[0057] Multistage emulsion polymer particles may include one or more intermediate encapsulating polymer layers. The intermediate encapsulating polymer partially or completely encapsulates the swellable particles. Each encapsulating polymer layer may be partially or completely encapsulated by another encapsulating polymer layer. Each encapsulating polymer layer can be prepared by emulsion polymerization in the presence of swellable particles or swellable particles encapsulated by one or more encapsulating polymers. The intermediate encapsulating polymer layer can act as a compatibility layer between other layers of the multistage emulsion polymer particles, sometimes referred to as a connecting layer or bonding coating; for example, the intermediate encapsulating polymer layer can help the shell adhere to the swellable particles. The intermediate encapsulating polymer layer can also be used to modify certain properties of the final hollow latex particles.

[0058] At least one intermediate encapsulating polymer may contain one or more hydrophilic monoene-bonded unsaturated monomers and one or more nonionic monoene-bonded unsaturated monomers as polymerization units. Hydrophilic monoene-bonded unsaturated monomers and nonionic monoene-bonded unsaturated monomers used to prepare swellable particles can also be used to prepare such intermediate encapsulating polymers. However, typically, intermediate encapsulating polymers contain a lower proportion of hydrophilic monomers than swellable particle polymers, resulting in less swelling upon contact with a swelling agent. Other intermediate encapsulating polymers may contain nonionic monoene-bonded unsaturated monomers as polymerization units and little or no hydrophilic monoene-bonded unsaturated monomers, for example, less than 10% by weight, less than 5% by weight, or less than 3% by weight. The intermediate encapsulating polymer may also contain crosslinking agents, such as alkylene glycol diacrylates and dimethacrylates, such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, propylene glycol diacrylate, and triethylene glycol dimethacrylate; 1,3-glycerol dimethacrylate; 1,1,1-trimethylolpropane dimethacrylate; 1,1,1-trimethylolethane diacrylate; pentaerythritol trimethacrylate; 1,2,6-hexanetriacrylate; sorbitol pentamethacrylate; methylenebisacrylamide; methylenebisacrylamide; divinylbenzene; vinyl methacrylate; vinyl bar Soybean esters; vinyl acrylates; vinyl acetylene; trivinylbenzene; triallyl cyanurate; divinyl acetylene; divinyl ethane; divinyl sulfide; divinyl ether; divinyl sulfone; diallyl cyanamide; ethylene glycol divinyl ether; diallyl phthalate; divinyl dimethylsilane; glycerol trivinyl ether; divinyl adipate; dicyclopentenyl (meth)acrylate; dicyclopentenyl oxy (meth)acrylate; unsaturated esters of dicyclopentenyl ether diol; allyl esters of α,β-unsaturated mono- and dicarboxylic acids with terminal vinyl unsaturation, including allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconic acid, etc.

[0059] The outer shell is a polymer, which may, for example, comprise a thermoplastic polymer. The glass transition temperature (Tg) of the outer shell polymer is above ambient temperature, typically at least 60°C, for example at least 70°C, for example at least 80°C, or for example at least about 90°C. The Tg of the outer shell polymer may, for example, be from 60°C to 140°C. While the outer shell polymer may be a homopolymer, it is more typically a copolymer comprising repeating polymeric units of two or more different monomers, particularly olefinically unsaturated monomers, such as those capable of being polymerized by free radical polymerization. A further characteristic of the outer shell polymer is that it contains one or more different types of functional groups, particularly reactive, polar, chelating, and / or heteroatom-containing functional groups. These functional groups can be varied and selected as needed to modify certain properties of the hollow latex particles, such as the wet adhesion, scrub resistance (washability), stain resistance, solvent resistance, and tack resistance of the coating composition comprising the hollow latex particles. For example, the functional groups may be selected from 1,3-dione, amino, urea, and urea functional groups and combinations thereof. Suitable 1,3-diketone functional groups include acetoacetate functional groups, which may correspond to the general formula —OC(═O)CH2C(═O)CH3. Suitable amino functional groups include primary, secondary, and tertiary amine groups. Amino functional groups may exist in heterocyclic forms. Amino functional groups may be, for example, oxazoline rings. Other types of functional groups useful in this invention include, for example, hydroxyl (—OH), silane (e.g., trialkoxysilyl, —Si(OH)3), phosphate esters (e.g., PO3H and its salts), fluorocarbons (e.g., perfluoroalkyl such as trifluoromethyl), polyethers (e.g., polyoxyethylene, polyoxypropylene), and epoxy (e.g., glycidyl) functional groups. 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. Functional groups may be reactive; for example, functional groups may participate in reactions as electrophiles or nucleophiles. Functional groups, or combinations of functional groups that are spatially adjacent to each other, may have complexing or chelating capabilities.

[0060] Functional groups can be introduced into the shell polymer in various ways. In one embodiment, the functional groups are introduced into the shell polymer during polymer formation, for example, through the polymerization of one or more polymerizable monomers with the desired functional groups (hereinafter referred to as "functionalized monomers"). Such polymerization can be carried out as copolymerization, in which one or more functionalized monomers copolymerize with one or more non-functionalized monomers. The monomers with functional groups described herein can be added at any stage of multi-stage emulsion preparation, provided that the polymer with such functional groups is at least partially or completely present in the shell polymer of the particles after swelling.

[0061] For example, the shell polymer can be a copolymer of a vinyl aromatic monomer (e.g., styrene) and a radically polymerizable olefinically unsaturated monomer containing a functional group (e.g., 1,3-diketone, amino, urea, urea, hydroxyl, silane, fluorocarbon, aldehyde, ketone, phosphate ester, or polyether functional group). This 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 can be varied as needed to impart specific properties to the resulting shell polymer. Typically, the copolymer contains 0.1 to 10 wt% of a functionalized radically polymerizable olefinically unsaturated monomer. Such copolymers may also contain 80-99.9 wt% of a vinyl aromatic monomer (e.g., styrene) and 0-10 wt% (e.g., 0.1-10 wt%) of an alkyl (meth)acrylate (e.g., methyl methacrylate).

[0062] Radical-polymerizable olefinically unsaturated monomers may contain (meth)acrylate (i.e., acrylate or methacrylate) groups or (meth)acrylamide (i.e., acrylamide or methacrylamide) groups. These (meth)acrylate and (meth)acrylamide groups can participate in radical copolymerization with vinyl aromatic monomers. Allyl groups can also be used to provide polymerizable unsaturated sites.

[0063] For example, imidazolium ketone (meth)acrylate monomers such as 2-(2-oxo-1-imidazolyl)ethyl (meth)acrylate and N-(2-(2-oxo-1-imidazolyl)ethyl (meth)acrylamide can be used as comonomers. Other functionalized, free radical polymerizable olefinic unsaturated monomers suitable for the practice of this invention include, but are not limited to, acetoacetoxy (meth)acrylates (e.g., acetoacetoxyethyl methacrylate, AAEM), allyl acetoacetate, derivatized methacrylamides (e.g., methyl oxalyl diacetone (meth)acrylamide), and aminoalkyl (meth)acrylates (including diacetoacetoxy meth)acrylates. Alkyl and monoalkyl aminoethyl (meth)acrylates), and olefinically unsaturated polymerizable aziridinyl monomers (as described in U.S. Patent No. 3,719,646, the entire contents of which are incorporated herein by reference). Other suitable radical-polymerizable olefinically unsaturated monomers containing useful functional groups include hydroxyethyl vinyl urea methacrylate (HEEUMA) and aminoethyl vinyl urea methacrylate (AEEUMA). Radically polymerizable olefinically unsaturated monomers may contain multiple functional groups on each monomer molecule; for example, monomers may contain two or more urea and / or urea groups on each molecule, such as US The compounds described in 6,166,220 (the entire contents of which are incorporated herein by reference for all purposes) are included. Illustrative examples of specific free radical polymerizable olefinic unsaturated monomers suitable for use as functionalized monomers in this invention include, but are not limited to, aminoethyl acrylates and methacrylates, dimethylaminopropyl acrylates and methacrylates, 3-dimethylamino-2,2-dimethylpropyl-1-acrylates and methacrylates, 2-N-morpholinoethyl acrylates and methacrylates, 2-N-piperidinylethyl acrylates and methacrylates, N-(3-dimethylaminopropyl)acrylamide and methacrylamide, N-(3-dimethylamino-2,2-dimethylpropyl)acrylamide and methacrylamide, N-dimethylaminomethylacrylamide and methacrylamide, N-(4-morpholinomethyl)acrylamide and methacrylamide, etc. Alkenyl imidazole, vinylpyrrolidone, N-(2-methacryloyloxyethyl) ethylidene, N-(2-methacryloyloxyacetamide ethyl)-N-, allyl alkyl ethylidene, N-methacrylamide methyl urea, N-methacryloyl urea, 2-(1-imidazolyl) ethyl methacrylate, 2-(1-imidazolin-2-one) ethyl methacrylate, N-(methacrylamido) ethyl urea, glycidyl (meth) acrylate, hydroxyalkyl (meth) acrylate (such as 2-hydroxyethyl (meth) acrylate), γ-(meth)acryloyloxypropyltrialkoxysilane, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, ethylene glycol (meth) acrylate phosphate, polyethylene glycol (meth) acrylate, polyethylene glycol methyl ether (meth) acrylate, diethylene glycol (meth) acrylate, and combinations thereof.

[0064] The free radical initiator suitable for the monomer polymerization used in the preparation of multi-stage emulsion polymer particles can 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 this application include, but are not limited to, hydrogen peroxide, tert-butyl peroxide, alkali metal persulfates such as sodium persulfate, potassium persulfate and lithium persulfate, ammonium persulfate, and mixtures of such initiators with reducing agents. The amount of initiator may be, for example, 0.01 to 3% by weight, such as 0.5 to 3% by weight, such as 0.1 to 3% by weight, such as 1 to 3% by weight, based on the total weight of monomers (A), (B) and (C).

[0065] In some embodiments, a redox polymerization initiator system is used. In a redox radical initiation system, the reducing agent can be used in combination with the oxidizing agent. Reducing agents suitable for aqueous emulsion polymerization include sulfites (e.g., alkali metal metabisulfites, bisulfites, and hyposulfites). In some embodiments, sugars (such as ascorbic acid and isoascorbic acid or alkali metal (iso)ascorbic acid salts) can also be suitable reducing agents for aqueous emulsion polymerization.

[0066] In a redox system, the amount of reducing agent may be, for example, 0.01 to 3 wt%, such as 0.5 to 3 wt%, such as 0.1 to 3 wt%, such as 1 to 3 wt%, based on the total weight of monomers (A), (B) and (C).

[0067] Oxidizing agents (also known as oxidizing reagents) include, but are not limited to, hydrogen peroxide and ammonium or alkali metal persulfates, perborates, peracetic acids, peroxides and percarbonates, as well as water-insoluble oxidizing agents such as benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide, tert-butyl hydrogen peroxide, 2,2'-azobisisobutyronitrile, tert-amyl hydrogen peroxide, tert-butyl peroxyneodecanate and tert-butyl peroxypentanate. The amount of oxidizing agent may be, for example, 0.01 to 3% by weight, such as 0.5 to 3% by weight, such as 0.1 to 3% by weight, such as 1 to 3% by weight, based on the total weight of monomers (A), (B) and (C).

[0068] Free radical polymerization temperatures typically range from about 10°C to about 110°C. In the case of persulfate systems, the temperature can range from about 60°C to about 100°C. In redox systems, the temperature can range from about 30°C to about 100°C, for example, from about 30°C to about 60°C, or from about 30°C to about 45°C. The type and amount of initiator can be the same or different in the various stages of multi-stage polymerization.

[0069] Suitable swelling agents are typically bases, including volatile bases such as ammonia, ammonium hydroxide, and volatile lower aliphatic amines such as morpholine, trimethylamine, and triethylamine, carbonates, bicarbonates, etc. Fixed or permanent bases, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, zinc ammonium complexes, copper ammonium complexes, silver ammonium complexes, strontium hydroxide, barium hydroxide, etc., may also be used. Solvents, such as ethanol, hexanol, octanol, and Texanol® solvents, as well as those described in US 4,594,363, may be added to aid the penetration of the fixed or permanent base. In some embodiments, the swelling agent is ammonia or ammonium hydroxide. Alkali metal hydroxides such as sodium hydroxide are preferred due to their lack of volatile emissions. The swelling agent may be in the form of an aqueous liquid or gaseous medium containing a volatile base. The composition of the shell and any intermediate encapsulation layers may be selected to allow for permeability to the swelling agent at ambient temperature or moderately elevated temperatures. In one embodiment, the swelling agent is contacted with the multi-stage emulsion polymer particles at a temperature slightly below the glass transition temperature of the shell polymer. For example, the contact temperature can be 5 to 20°C, or 10 to 30°C, or 5 to 40°C lower than the Tg of the outer shell polymer.

[0070] When multi-stage emulsion polymer particles are treated with an alkaline swelling agent (permeable to the intermediate shell layer of the multi-stage emulsion polymer particles) in the presence of the shell polymer monomer, the hydrophilic component of the swellable particles swells. In one embodiment of the invention, the hydrophilic component of the swellable particles is acidic (pH less than 6). Treatment with an alkaline swelling agent in the presence of the shell polymer monomer neutralizes the acidity and raises the pH of the hydrophilic component to greater than 6, or at least about 7, or at least about 8, or at least about 9, or at least about 10, or at least about 11, thereby causing swelling through the hydration of the hydrophilic component of the core. The swelling or expansion of the swellable particles may involve the incorporation of the peripheral portion of the swellable particles into the inner pores of a layer immediately adjacent to the core (e.g., the shell or intermediate encapsulation layer), and the partial enlargement or bulging of the adjacent layer and the entire particle.

[0071] The weight ratio of swellable particles to shell is typically in the range of, for example, 1:5 to 1:20 (e.g., 1:8 to 1:20, 1:8 to 1:15, 1:10 to 1:20). To reduce the dry density of the final hollow latex particles, the amount of shell relative to the amount of core should generally be reduced; however, there should be enough shell to ensure that the core is still encapsulated.

[0072] The methods previously described in the art for producing hollow latex particles are applicable to the present invention, provided that the methods are modified to employ swellable particles prepared by reacting core latex particles with: (i) one or more olefinically unsaturated monomers containing acidic functional groups (monomer A); (ii) one or more nonionic olefinically unsaturated monomers (monomer B); (iii) one or more hydrophobic nonionic olefinically unsaturated monomers (monomer C) with lower water solubility than monomer B; (iv) optionally, one or more nonionic surfactants; and (v) one or more anionic surfactants. Previously known methods that can be modified in this way may include, for example, the methods described in US 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, the entire contents of which are incorporated herein by reference for all purposes. For example, particles according to the invention can be prepared by incorporating the functional monomers described herein into the particle shells of the following examples: (1) Examples 0-14 of US 4,427,836, (2) Examples 0-12 of US 4,468,498, (3) Examples 1-4 of US 4,594,363, (4) Examples 1-19 of US 4,880,842, (5) Examples 1-13 of US 4,920,160, (6) Examples 1-7 of US 4,985,469, (7) Examples 1-7 of US 5,216,044, (8) Examples 1-8 of US 5,229,209, and (9) Examples 1-50 of US 5,273,824.

[0073] practicality

[0074] Upon observation, the hollow particles of the present invention have thermal insulation properties, and therefore can be used as a component in thermal applications that require the creation of thermal insulators or thermal barriers.

[0075] One exemplary application is reducing the energy required in the thermal printing process during thermal paper manufacturing. In one embodiment, the hollow particles of the present invention are present in a base coat applied during the thermal paper manufacturing process, wherein the thermal paper is paper coated with a thermal layer that discolors upon exposure to heat. Incorporating hollow particles into the base coat allows the thermal paper to produce higher quality prints compared to thermal paper with a base coat containing hollow particles. However, prior to this invention, producing hollow particles with a volume average particle size of approximately 1.5 μm and a low level of particle bursting (i.e., particles that are broken, fragmented, or otherwise damaged) has been challenging. Medium to high levels of particle bursting (e.g., greater than 50%, greater than 60%, greater than 70%, greater than 80%) can negatively impact the performance of the hollow particles as a thermal insulator.

[0076] In one embodiment, hollow latex particles as described herein are present in the coating composition.

[0077] In one embodiment, the paper, coating, ink, adhesive, or cosmetic comprises a coating composition containing hollow latex particles as described herein.

[0078] Aspects of the present invention

[0079] Aspect 1. A method for preparing hollow latex particles, comprising: i) Prepare core latex particles through the polymerization reaction of one or more olefinically unsaturated monomers, then ii) By reacting the nuclear latex particles with the following substances during the polymerization reaction, swellable particles are formed: (A) 5-45% by weight of one or more olefinic unsaturated monomers containing acid functional groups, wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (B) 1-90% by weight of one or more nonionic olefinically unsaturated monomers, wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (C) 1-55% by weight of one or more hydrophobic nonionic olefinic unsaturated monomers, which have lower water solubility than (B), wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (D) Optionally, at least 0.01% by weight of one or more nonionic surfactants, and (E) At least 0.01% by weight of one or more anionic surfactants, Subsequently, iii) By treating the swollen particles with one or more olefinically unsaturated monomers during the polymerization reaction, a first layer is formed that partially or completely encapsulates the swollen particles, and then... iv) Optionally, a second layer is formed by treating the swellable particles containing the first layer with one or more olefinically unsaturated monomers during the polymerization reaction, thereby partially or completely encapsulating the swellable particles, and then... v) Add a swelling agent to generate hollow latex particles with a volume average particle size greater than 1 μm. The polymerization reactions in steps i), ii), iii), and iv) are emulsion polymerization reactions, and The particle bursting level of the hollow latex particles is less than 50%.

[0080] Aspect 2. The method of aspect 1, wherein the volume average particle size of the hollow latex particles is greater than 1 µm and not greater than 10 µm, for example greater than 1 µm and not greater than 8 µm, for example greater than 1 µm and not greater than 6 µm, for example 1.1 µm to 5 µm, for example 1.2 µm to 4 µm, for example 1.3 µm to 3 µm.

[0081] Aspect 3. The method as described in aspect 1 or aspect 2, wherein the hollow latex particles are approximately spherical.

[0082] Aspect 4. The method of any one of Aspects 1 to 3, wherein the particle bursting level of the hollow latex particles is less than 50%, for example less than 40%, for example less than 30%, for example less than 20%, for example between 0 and less than 50%, for example between 0 and 40%, for example between 0 and 30%, for example between 5 and less than 50%, for example between 5 and 40%, for example between 5 and 30%, for example between 10 and less than 50%, for example between 10 and 40%, for example between 10 and 30%.

[0083] Aspect 5. The method of any one of Aspects 1 to 4, wherein the volume average particle size of the nuclear latex particles is greater than 100 nm and not greater than 500 nm, for example greater than 100 nm and not greater than 400 nm, for example greater than 100 nm and not greater than 350 nm, for example 110 nm to 500 nm, for example 110 nm to 400 nm, for example 110 nm to 350 nm.

[0084] Aspect 6. The method of any one of Aspects 1 to 5, wherein the amount of monomer (A) is 5-45% by weight, for example 10-45% by weight, for example 10-40% by weight, for example 10-40% by weight, for example 10-35% by weight, for example 15-40% by weight, for example 15-35% by weight, for example 20-40% by weight, for example 20-35% by weight, relative to the total weight percentage of monomers (A), (B) and (C).

[0085] Aspect 7. The method of any one of Aspects 1 to 6, wherein monomer (A) comprises one or more of the following: acrylic acid, methacrylic acid, acryloyloxypropionic acid, (meth)acryloyloxypropionic acid, itaconic acid, aconitic acid, maleic acid or maleic anhydride, fumaric acid, crotonic acid, monomethyl maleate, monomethyl fumarate, monomethyl itaconic acid, vinyl phosphate, (meth)allyl phosphate, phosphate of polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate, polyoxyethylene allyl ether phosphate, sulfoethyl (meth)acrylate, aryl sulfonic acid or sulfuric acid, (meth)acrylamidoethane sulfonic acid or sulfuric acid, methacrylamido-2-methylpropane sulfonic acid or sulfuric acid, etc.

[0086] Aspect 8. The method of any one of Aspects 1 to 7, wherein the monomer (A) comprises at least one of methacrylic acid and acrylic acid.

[0087] Aspect 9. The method of any one of Aspects 1 to 8, wherein the amount of monomer (B) is 1-90% by weight, for example 5-90% by weight, for example 5-80% by weight, for example 10-90% by weight, for example 10-80% by weight, for example 10-70% by weight, for example 10-60% by weight, for example 15-90% by weight, for example 15-80% by weight, for example 20-80% by weight, for example 20-70% by weight, for example 30-80% by weight, for example 40-70% by weight, relative to the total weight percentage of monomers (A), (B) and (C).

[0088] Aspect 10. The method of any one of Aspects 1 to 9, wherein the monomer (B) comprises one or more of the following: vinyl aromatic monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, or vinyltoluene; olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide, (meth)acrylic acid (C1-C2) 20 )alkyl esters or (C 3- C 20 Alkenyl esters, such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, benzyl methacrylate, lauryl methacrylate, alkenyl methacrylate, palmitate methacrylate, stearyl methacrylate, etc.

[0089] Aspect 11. The method of any one of Aspects 1 to 10, wherein the monomer (B) comprises methyl methacrylate.

[0090] Aspect 12. The method of any one of Aspects 1 to 11, wherein the amount of monomer (C) is 1-55% by weight, for example 1-45% by weight, for example 1-35% by weight, for example 1-25% by weight, for example 1-15% by weight, for example 5-50% by weight, for example 5-40% by weight, for example 5-30% by weight, for example 5-25% by weight, for example 5-15% by weight.

[0091] Aspect 13. The method of any one of Aspects 1 to 12, wherein monomer (C) is a nonionic olefinic unsaturated monomer with lower water solubility than monomer (B), and comprises one or more of the following: vinyl aromatic monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, or vinyltoluene; olefins such as ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide; (C1-C2) acrylic acid. 20 )alkyl esters or (C 3- C 20 Alkenyl esters, such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, benzyl methacrylate, lauryl methacrylate, alkenyl methacrylate, palmitate methacrylate, stearyl methacrylate, etc.

[0092] Aspect 14. The method of any one of Aspects 1 to 13, wherein the monomer (C) comprises at least one of butyl acrylate, styrene and butyl methacrylate.

[0093] Aspect 15. The method of any one of Aspects 1 to 14, wherein the polymerization reaction comprises one or more nonionic surfactants, relative to the total weight percentage of monomers (A), (B) and (C), wherein the amount of the one or more nonionic surfactants is at least 0.01 wt%, for example at least 0.05 wt%, for example at least 0.1 wt%, for example at least 0.5 wt%, for example at least 1 wt%, for example at least 1.5 wt%, for example at most 10 wt%, for example 0.01-10 wt%, for example 0.01-5 wt%, for example 0.01-3 wt%, for example 0.1-10 wt%, for example 0.1-5 wt%, for example 1-10 wt%, for example 1-5 wt%.

[0094] Aspect 16. The method of any one of Aspects 1 to 15, wherein the nonionic 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 alkyl polysaccharides, and mixtures thereof.

[0095] Aspect 17. The method of any one of Aspects 1 to 16, wherein the nonionic surfactant includes, but is not limited to, tert-octylphenoxyethyl polyethoxyethanol, dodecyloxyethylene polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol, polyethylene glycol 2000 monooleate, ethoxylated castor oil, fluorinated alkyl esters and alkoxylates, polyoxyethylene sorbitan monolaurate, sucrose monococarboxylate, di(2-butyl)phenoxyethylene polyethoxyethanol, hydroxyethyl cellulose polybutyl acrylate graft copolymer, dimethylsiloxane polyalkylene oxide graft copolymer, poly(ethylene oxide) poly(butyl acrylate) block copolymer, propylene oxide and ethylene oxide block copolymer, 2,4,7,9-tetramethyl-5-decyn-4,7-diol ethoxylated with 30 moles of ethylene oxide, N-polyoxyethylene lauramide, N-lauryl-N-polyoxyethyleneamine, polyethylene glycol dodecyl sulfide and mixtures thereof.

[0096] Aspect 18. The method of any one of Aspects 1 to 17, wherein the nonionic surfactant comprises at least one selected from linear fatty alcohol ethoxylates, branched fatty alcohol ethoxylates, ethoxylated monoalkylphenols, ethoxylated dialkylphenols, and ethoxylated trialkylphenols.

[0097] Aspect 19. The method of any one of Aspects 1 to 18, wherein the amount of the anionic surfactant is at least 0.01 wt%, for example at least 0.05 wt%, for example at least 0.1 wt%, for example at least 0.5 wt%, for example at least 1 wt%, for example at least 1.5 wt%, and at most 10 wt%, for example 0.01-10 wt%, for example 0.01-5 wt%, for example 0.01-3 wt%, for example 0.01 to 1 wt%, for example 0.1-10 wt%, for example 0.1-5 wt%, for example 1-10 wt%, for example 1-5 wt%.

[0098] Aspect 20. The method of any one of Aspects 1 to 19, wherein the anionic surfactant includes, but is not limited to, alkylbenzene sulfonic acids, alkaline earth metal alkylbenzene sulfonates, sulfonated fatty acids, sulfonated olefins, sulfonated diphenyl ethers, sulfosuccinates, fatty alcohol sulfates, alkylphenol sulfates, alkyl polyethylene glycol ether sulfates, fatty alcohol ether sulfates, fatty alcohol phosphates, alkylphenol phosphates, alkyl polyethylene glycol ether phosphates, alkyl polyalkylene oxide phosphates, fatty alcohol ether phosphates, and mixtures thereof.

[0099] Aspect 21. The method of any one of Aspects 1 to 20, wherein the anionic surfactant includes, but is not limited to, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, potassium stearate, sodium dioctyl sulfosuccinate, sodium dodecyl diphenyl ether disulfonate, nonylphenoxyethyl poly(I)ethoxyethyl ammonium sulfate, sodium styrene sulfonate, sodium dodecyl allyl sulfosuccinate, sodium or ammonium salts of ethoxylated nonylphenol phosphate, sodium octylphenol-3-sulfonate, sodium cocoyl sarcosinate, sodium 1-alkoxy-2-hydroxypropyl sulfonate, α-olefin (C 14 -C 16 Sodium sulfonate, hydroxyalkanol sulfate, N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinate tetrasodium, N-octadecylsulfosuccinate disodium, alkylamide polyethoxysulfosuccinate disodium, ethoxylated nonylphenol sulfosuccinate half ester disodium, and tert-octylphenoxyethoxypolyethoxyethyl sulfate sodium salt.

[0100] Aspect 22. The method of any one of Aspects 1 to 21, wherein the anionic surfactant comprises at least one of sulfate, sulfosuccinate, sulfonate and disulfonate.

[0101] Aspect 23. The method of any one of Aspects 1 to 22, wherein all polymerization reactions related to the preparation of hollow latex particles from core latex particles and swellable particles are emulsion polymerization reactions.

[0102] Aspect 24. The method of any one of Aspects 1 to 23, wherein all encapsulated polymers partially or completely encapsulate the swellable particles.

[0103] Aspect 25. The method of any one of Aspects 1 to 24, wherein all encapsulating polymers completely encapsulate the swellable particles.

[0104] Aspect 26. The method of any one of Aspects 1 to 25, wherein the weight ratio of the swollen particles to the nuclear latex particles is 5:1 to 200:1, for example 5:1 to 100:1, for example 10:1 to 100:1, for example 10:1 to 75:1.

[0105] Aspect 27. The method of any one of Aspects 1 to 26, wherein the hollow latex particles are non-film-forming.

[0106] Aspect 28. Hollow latex particles prepared by the method described in any one of Aspects 1 to 27.

[0107] Aspect 29. Use of a plurality of hollow latex particles prepared by any one of aspects 1 to 27 in thermal applications (e.g., in thermal printing processes, such as in a base coat applied during the manufacture of thermal paper) or in compositions.

[0108] Aspect 30. An article comprising a composition containing a plurality of hollow latex particles prepared by any one of aspects 1 to 27.

[0109] Aspect 31. The article of aspect 30, wherein the article is paper, coating, ink, adhesive or cosmetic.

[0110] Aspect 32. The method of aspect 1, wherein step (ii) comprises 0.01-10% by weight of one or more nonionic surfactants relative to the total weight % of monomers (A), (B) and (C).

[0111] Aspect 33. The method of aspect 1, wherein step (ii) comprises 0.01-1 wt% of one or more anionic surfactants relative to the total wt% of monomers (A), (B) and (C).

[0112] experiment

[0113] Dynamic light scattering (DLS)

[0114] Volume average particle size (Mv) and number average particle size (Mn) were measured by dynamic light scattering using a Microtrac Nanotrac UPA150.

[0115] Scanning transmission electron microscopy (STEM) characterization

[0116] The morphology of the hollow particles was finally characterized in STEM mode using a Thermo Scientific™ Helios 5Hydra UX DualBeam microscope.

[0117] Determination of burst level

[0118] Bursting particles refer to hollow particles that exhibit a fractured or fragmented morphology under a microscope. Representative bursting particles are... Figure 3The hollow particles shown are circled and marked. To determine the bursting level, only particles with a diameter within 10% of the average particle size are counted, and at least 50 particles are counted. Specifically, the number of broken or fragmented hollow latex particles relative to all visible hollow latex particles is visually counted under a microscope. The bursting percentage is calculated using the following formula:

[0119] Example

[0120] nuclear particles

[0121] The core particles were prepared by emulsion polymerization of a specified amount of methyl methacrylate and methacrylic acid in a reactor at a temperature of 85-93°C. The volume average particle size of the core particles was 155 nm.

[0122] Intermediate swellable particles - Example 1 of the present invention

[0123] The intermediate swellable particles were prepared using seed emulsion polymerization with core particles as seeds. The monomer mixture used for the intermediate swellable particles contained methyl methacrylate, methacrylic acid, and butyl methacrylate. The surfactant used in the synthesis was a combination of alkyl diphenyl ether disulfonate and linear fatty alcohol ethoxylate, wherein the active amounts of alkyl diphenyl ether disulfonate and linear fatty alcohol ethoxylate were 0.5 wt% and 1.8 wt%, respectively, based on the total weight of the monomers used in the synthesis.

[0124] Intermediate swellable particles - Comparative Example 1

[0125] The intermediate swellable particles were prepared using seed emulsion polymerization with core particles as seeds. The monomer mixture used for the intermediate swellable particles contained methyl methacrylate and methacrylic acid. The surfactant used in the synthesis was a combination of alkyl diphenyl ether disulfonate and linear fatty alcohol ethoxylate, wherein the active amounts of alkyl diphenyl ether disulfonate and linear fatty alcohol ethoxylate were 0.5 wt% and 1.8 wt%, respectively, based on the total weight of the monomers used in the synthesis.

[0126] Intermediate swellable particles - Comparative Example 2

[0127] The intermediate swellable particles were prepared using seed emulsion polymerization with core particles as seeds. The monomer mixture used for the intermediate swellable particles contained methyl methacrylate, methacrylic acid, and butyl methacrylate. The surfactant used in the synthesis was an alkyl diphenyl ether disulfonate, wherein the active amount of the alkyl diphenyl ether disulfonate was 0.5% by weight based on the total weight of the monomers used in the synthesis.

[0128] Intermediate swellable particles - Comparative Example 3

[0129] The intermediate swellable particles were prepared using seed emulsion polymerization with core particles as seeds. The monomer mixture used for the intermediate swellable particles contained methyl methacrylate, methacrylic acid, and butyl methacrylate. The surfactant used in the synthesis was a linear fatty alcohol ethoxylate, wherein the active amount of the linear fatty alcohol ethoxylate was 1.8 wt% based on the total weight of the monomers used in the synthesis.

[0130] Final hollow particles

[0131] The final hollow particles are obtained from intermediate swellable particles through a multi-stage process. First, a pre-emulsified mixture containing methyl methacrylate (MMA), methacrylic acid (MAA), and butyl methacrylate (BMA) is added to a reactor containing the intermediate swellable particles at a temperature of approximately 75°C to approximately 85°C to form a first intermediate layer on the swellable particles. Next, another pre-emulsified mixture containing styrene (STY) and divinylbenzene (DVB) is added to the reactor at a temperature of approximately 75°C to approximately 85°C to form a second intermediate layer on the latex particles. The reaction temperature is raised to approximately 90°C to 95°C and held for a predetermined time to form a shell. A polymerization initiator is then added to the reactor to reduce the monomer content to less than 0.5% monomer (based on the weight of the multi-stage emulsion polymer particles). Subsequently, a sodium hydroxide solution is introduced into the reactor to neutralize the intermediate swellable particles. Finally, styrene is added to the reactor to swell the latex particles, thereby forming the final hollow particles.

[0132] discuss

[0133] Figure 1 An embodiment of the preparation of hollow particles using the method of the present invention is shown: starting with core particles, then forming intermediate swellable particles, and subsequently converting them into hollow particles with a larger particle size (>1 µm).

[0134] Table 1 describes the properties of the exemplary intermediate swellable particles of the present invention and comparative examples. Comparative Example 1, containing only MMA and MAA as polymerizable monomers, could not form stable intermediate swellable particles, as evidenced by severe latex aggregation during synthesis. Therefore, Comparative Example 1 was unsuitable for subsequent conversion into hollow particles. Surprisingly, incorporating hydrophobic monomers into the intermediate swellable particles resulted in the desired particle size, good particle size distribution, and low levels of filterable material (<0.1 wt%) after synthesis (as demonstrated in Example 1 and Comparative Example 2 of the present invention). Therefore, these intermediate swellable particles were selected for conversion into the final hollow particles.

[0135] Table 1. Properties of exemplary intermediate swellable particles

[0136] Table 2 describes the DLS particle size characterization of the final hollow particles converted from the selected intermediate swellable particle examples. All final hollow particles exhibit a large volume-average particle size. Figure 2 A-2F shows a comparison of scanning transmission electron microscopy (STEM) images of the final hollow particles prepared from intermediate swellable particles at 25,000x magnification: (A) Example 1 of the present invention; (B) Comparative Example 2; and (C) Comparative Example 3; and a comparison of STEM images of the final hollow particles prepared from intermediate swellable particles at 10,000x magnification: (D) Example 1 of the present invention; (E) Comparative Example 2; and (F) Comparative Example 3. Surprisingly, it was observed that the final hollow particles prepared from Comparative Example 2 (containing only anionic surfactants)... Figure 2 Comparative Example 3 (containing only nonionic surfactants) and 2E) Figure 2 Hollow particles prepared using C and 2F exhibited a high level of particle bursting. In contrast, hollow particles prepared using embodiments of the present invention comprising a combination of anionic and nonionic surfactants showed a low level of particle bursting. Figure 2 (A and 2D). As summarized in Table 2, the particle bursting levels of the two comparative examples are both greater than 50%, while the particle bursting level of the embodiments of the present invention is less than 40%. The hollow particles prepared by the embodiments of the present invention also exhibit high porosity, such as... Figure 2 This is evidenced by the thin shell (i.e., the dark outer layer of the particle) and large voids (i.e., the light gray area inside the particle) in A and 2D.

[0137] Table 2. Properties of the final hollow particles

[0138] Combined Table 1 and Figure 2 The results of A-2F demonstrate the importance of incorporating both hydrophobic monomers and nonionic and anionic surfactants into intermediate swellable particles when preparing large hollow particles (volume average particle size > 1 μm) with good morphology and low bursting levels.

[0139] The invention described herein is intended to cover not only the individual aspects or exemplary embodiments of the invention, but also combinations of all aspects and embodiments.

Claims

1. A method for preparing hollow latex particles, comprising: i) Prepare core latex particles through the polymerization reaction of one or more olefinically unsaturated monomers, then ii) By reacting the nuclear latex particles with the following substances during the polymerization reaction, swellable particles are formed: (A) 5-45% by weight of one or more olefinic unsaturated monomers containing acid functional groups, wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (B) 1-90% by weight of one or more nonionic olefinically unsaturated monomers, wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (C) 1-55% by weight of one or more hydrophobic nonionic olefinic unsaturated monomers, which have lower water solubility than (B), wherein the percentage by weight is relative to the total weight of monomers (A), (B) and (C). (D) Optionally, at least 0.01% by weight of one or more nonionic surfactants relative to the total weight% of monomers (A), (B) and (C), and (E) At least 0.01% by weight of one or more anionic surfactants relative to the total weight% of monomers (A), (B) and (C), Subsequently, iii) By treating the swollen particles with one or more olefinically unsaturated monomers during the polymerization reaction, a first layer is formed that partially or completely encapsulates the swollen particles, and then... iv) Optionally, a second layer is formed by treating the swollen particles containing the first layer with one or more olefinically unsaturated monomers during the polymerization reaction, thereby partially or completely encapsulating the swollen particles, and then... v) Add a swelling agent to generate hollow latex particles with a volume average particle size greater than 1 μm. The polymerization reactions in steps i), ii), iii), and iv) are emulsion polymerization reactions, and The particle bursting level of the hollow latex particles is less than 50%.

2. The method of claim 1, wherein the volume average particle size of the nuclear latex particles prepared in step i) is greater than 100 nm and not greater than 500 nm.

3. The method of claim 1, wherein the volume average particle size of the swellable particles formed in step ii) is from 300 nm to 2,000 nm.

4. The method of claim 1, wherein the volume average particle size of the hollow latex particles generated in step v) is greater than 1 μm and not greater than 10 μm.

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

6. The method of claim 1, wherein the olefinic unsaturated monomer (B) in step ii) comprises methyl methacrylate.

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

8. The method of claim 1, wherein the anionic surfactant comprises at least one selected from sulfate, sulfosuccinate, sulfonate, and disulfonate.

9. The method of claim 1, wherein step ii) comprises one or more nonionic surfactants, and the one or more nonionic surfactants comprise at least one of the following: linear fatty alcohol ethoxylates, branched fatty alcohol ethoxylates, ethoxylated monoalkylphenols, ethoxylated dialkylphenols, and ethoxylated trialkylphenols.

10. The method of claim 1, wherein the encapsulation in steps ii), iii) and iv) is a complete encapsulation.

11. The method of claim 1, wherein the number of olefinic unsaturated monomers present in the polymerization reactions of steps i), ii)(A), ii)(B), ii)(C), iii), and iv) is two or more.

12. Hollow latex particles prepared by any one of claims 1 to 11.

13. A plurality of hollow latex particles prepared by the method of any one of claims 1 to 11, wherein the particle bursting level is less than 50%.

14. The plurality of hollow latex particles as described in claim 13, wherein the particle bursting level is less than 40%.

15. A composition comprising a plurality of hollow latex particles as described in claim 13.

16. An article comprising the composition of claim 15.

17. Use of the plurality of hollow latex particles as described in claim 13 in thermal applications.

18. The method of claim 1, wherein step (ii) comprises 0.01-10% by weight of one or more nonionic surfactants relative to the total weight % of monomers (A), (B) and (C).

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

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