Composite particles for toner additives

Abstract

To provide composite particles for toner additives.SOLUTION: Metal oxide-polymer composite particles have a median particle size of 40-75 nm or 100-150 nm and an average RTA of at least 0.06. Alternatively or additionally, metal oxide-polymer composites comprise two or more populations of metal oxide particles differing in size, particle size distribution, or shape. Alternatively or additionally, the use of a multicomponent hydrophobizing system including an alkylsilane to fabricate metal oxide-polymer composite particles increases the tribocharge of the composite particles.SELECTED DRAWING: Figure 8A

Description

[Technical Field]

[0001] This invention relates to the particle size, morphology, and triboelectric charging of metal oxide-polymer composite particles. [Background technology]

[0002] Forming an electrophotographic image includes uniformly charging the surface of a photoreceptor drum or belt; exposing the photoreceptor surface to light to form a latent image on the photoreceptor surface that projects a charging pattern, i.e., information to be transferred to an actual image; developing the latent image with electrostatically charged toner particles containing a colorant dispersed in a binder resin; transferring the developed toner onto a substrate, for example, paper; fixing the image onto the substrate; and preparing the photoreceptor surface for the next cycle by removing residual electrostatic charge and washing away any remaining toner particles from the photoreceptor drum.

[0003] Toners for use in electrophotography and electrostatic printing contain a binder resin and a colorant, and may further contain charge control agents, offset inhibitors, and other additives. To improve selected properties of the toner particles, including fluidity, transferability, adhesion, and cleaning properties, toner additives, such as metal oxide particles, are often combined with the toner particles. Various additives may be used in a single toner composition to improve various properties of the toner. For example, several additives may be selected to improve electrostatic properties, i.e., triboelectricity. Others may be selected to improve cleaning performance or moisture resistance. Naturally, it is preferable that a toner additive optimized for one function does not interfere with the functions provided by various additives.

[0004] One function imparted by toner additives is the maintenance of fluidity and spacing. When toner particles adhere to each other, they do not flow well; additives act to reduce the aggregation of toner powder. Additive particles tend to be rigid, while toner is formed from softer polymers. Aggregation of the resulting toner particles is detrimental to both the operation of the electrophotographic device and the quality of the print. In practice, when manufacturers have tried to reduce the energy required to create the printed page, they have switched to softer polymers (e.g., polymers with lower Tg) to reduce the amount of heat required to fix the toner to the substrate. However, rigid additive particles can become embedded in the soft toner particles, reducing the effectiveness of the additive. Increasing the particle size of the additive particles reduces embedding; however, larger particles are also heavier and exhibit a higher percentage of drop-off from the toner particles. Naturally, additive particles that have dropped off the toner cannot provide their function as part of the toner composition. The metal oxide-polymer composite particles described in U.S. Patent No. 9,568,847 act as spacers between toner particles, while exhibiting both limited embedding and limited drop-off within the toner particles. Here, it is desirable to further manipulate the roughness, shape, and particle size of the metal oxide composite particles to improve their free-flow properties and to manipulate their triboelectric properties and refractive index. [Overview of the Initiative]

[0005] In one embodiment, the metal oxide-polymer composite particles in powder form comprise a plurality of metal oxide particles and a polymer matrix; the metal oxide particles are surface-modified by a first hydrophobic system comprising a bifunctional component, through which the metal oxide particles are covalently bonded to the polymer matrix; the polymer of the polymer matrix is ​​a polymer or copolymer of the bifunctional component; the metal oxide-polymer composite particles have a volume-weighted median particle size D50 of 40-75 mm and an average RTA of at least 0.06, e.g., 0.06-0.019, 0.08-0.015, or 0.08-0.13.

[0006] Alternatively, the metal oxide-polymer composite particles in powder form comprise a plurality of metal oxide particles and a polymer matrix; the metal oxide particles are surface-modified by a first hydrophobic system comprising a bifunctional component, through which the metal oxide particles are covalently bonded to the polymer matrix; the polymer of the polymer matrix is ​​a polymer or copolymer of the bifunctional component; the metal oxide-polymer composite particles have a volume-weighted median particle size D50 of 100-150 nm and an average RTA of at least 0.06, e.g., 0.06-0.019, 0.08-0.015, or 0.08-0.13.

[0007] For any of these composite particles, the metal oxide particles may have a unimodal particle size distribution. The composite particles may have an average particle roughness greater than 1.22, for example greater than 1.25, or up to 1.35, 1.60, 1.70, or 1.90. At least a portion of the surface of the metal oxide-polymer composite particles is modified with a second hydrophobic agent. The metal oxide-polymer composite particles may contain at least 15% metal oxide.

[0008] The bifunctional component is given by formula [R 3 3-x (OR 1 ) x ]SiR 2 Q may be 1, 2, or 3, and R 1 is methyl or ethyl, R 2is an alkyl linker having the general formula C n H 2n , where n is from 1 to 10, R 3 is methyl or ethyl, Q is a substituted or unsubstituted vinyl, acrylate ester or methacrylate ester group, provided that when Q is a substituted or unsubstituted vinyl, n is from 2 to 10. The first hydrophobicization system may further include a monofunctional component covalently bonded to the metal oxide particles, such as silane. The monofunctional component may have the formula (OR 1 ) 4-z SiR 4 z , where R 1 is methyl or ethyl, z is 1 or 2, R 4 is a branched or unbranched C1-C10 alkyl group or R 2 Ph, where Ph is an unsubstituted phenyl group or a phenyl group substituted with a C1-C10 branched or unbranched alkyl, halogen, C1-C10 alkyl ether, methoxy, ethoxy or hydroxy.

[0009] Any of the composite particles described above can be disposed on the surface of the toner particles to form a toner composition.

[0010] In another aspect, the toner composition includes toner particles mixed with a powder including metal oxide-polymer composite particles including a plurality of metal oxide particles and a polymer matrix. The metal oxide particles are surface-modified by a first hydrophobicization system including a bifunctional component through which the metal oxide particles are covalently bonded to the polymer matrix and a monofunctional component covalently bonded to the metal oxide particles. At least a part of the surface of the metal oxide-polymer composite particles is modified by a second hydrophobizing agent, and the polymer of the polymer matrix is a polymer or copolymer of the bifunctional component. The tribocharging of the toner under HH conditions is at least 9% greater than the tribocharging of a toner including a control metal oxide-polymer composite in which the monofunctional component is replaced by the bifunctional component.

[0011] Alternatively, or in addition, the triboelectric charge of the toner under LL conditions is at least 10% greater than that of the toner containing a control metal oxide-polymer composite in which the monofunctional component is replaced by a difunctional component. Both the monofunctional and difunctional components may contain silane groups. The monofunctional component is given by formula (OR 1 ) 4-z SiR 4 z It is good to have R 1 is methyl or ethyl, z is 1 or 2, R 4 The C1-C10 alkyl group is branched or unbranched. The solubility of the monofunctional component may be 10-0.06 g / L, preferably 9-0.03 g / L, more preferably 8-0.1 g / L, and most preferably 7-0.5 g / L.

[0012] In another embodiment, a method for producing composite particles includes the steps of: preparing an aqueous dispersion comprising metal oxide particles and a first hydrophobic system comprising a bifunctional component and a monofunctional component, wherein the bifunctional component and the monofunctional component are chemically bonded to the metal oxide particles; adding a polymerization initiator to the aqueous dispersion to form metal oxide-polymer composite particles having metal oxide particles on their surface, wherein the polymer matrix of the metal oxide-polymer composite particles is a polymer or copolymer of the first hydrophobic system; and drying the metal oxide-polymer composite particles to form a powder.

[0013] The method further includes a step of treating the metal oxide-polymer composite particles with a second hydrophobic agent before or after the drying step to produce hydrophobized metal oxide-polymer composite particles. Both the monofunctional and bifunctional components may contain silane groups. The monofunctional component is of formula (OR 1 ) 4-z SiR 4 z It is good to have R 1 is methyl or ethyl, z is 1 or 2, R 4 is a branched or unbranched C1-C10 alkyl group. The difunctional component is of formula [R3 3-x (OR 1 ) x ]SiR 2 Q may be 1, 2, or 3, and R 1 is methyl or ethyl, R 2 is the general formula C n H 2n It is an alkyl linker having n, where n is 1 to 10, and R 3 Q is methyl or ethyl, and Q is a substituted or unsubstituted vinyl, acrylate ester, or methacrylate ester group, provided that when Q is a substituted or unsubstituted vinyl, n is 2 to 10. The dispersion may further contain one or more of styrene, substituted or unsubstituted acrylate or methacrylate monomers, olefin monomers, vinyl esters, or acrylonitrile. The solubility of the monofunctional component may be 10 to 0.06 g / L, preferably 9 to 0.03 g / L, more preferably 8 to 0.1 g / L, and most preferably 7 to 0.5 g / L.

[0014] In another embodiment, metal oxide-polymer composite particles in powder form may comprise a plurality of metal oxide particles and a polymer matrix. The plurality of metal oxide particles comprise at least a first group of metal oxide particles and a second group of metal oxide particles, wherein the first group of metal oxide particles has a different particle size, shape, or particle size distribution from the second group. The metal oxide particles are surface-modified by a first hydrophobic system comprising a bifunctional component, through which the metal oxide particles are covalently bonded to the polymer matrix, and a portion of the plurality of metal oxide particles are embedded in and protruding from the polymer matrix (i.e., at least a portion of the plurality of metal oxide particles may comprise at least a portion of each group of metal oxide particles, with at least a portion of the plurality of metal oxide particles protruding in and out of the polymer matrix), the polymer matrix comprises a polymer or copolymer of the first hydrophobic system, and at least a portion of the surface of the metal oxide-polymer composite particles is modified by a second hydrophobic agent, and the metal oxide-polymer composite particles have an average SF-1 of 110-185 and an average RTA of 0.06-0.19.

[0015] The first hydrophobic system may further contain monofunctional components covalently bonded to the metal oxide particles, such as silane. The bifunctional component is given by formula [R 3 3-x (OR 1 ) x ]SiR 2 Q may be 1, 2, or 3, and R 1 is methyl or ethyl, R 2 is the general formula C n H 2n It is an alkyl linker having n, where n is 1 to 10, and R 3 Q is methyl or ethyl, and Q is a substituted or unsubstituted vinyl, acrylate ester, or methacrylate ester group, provided that when Q is a substituted or unsubstituted vinyl, n is 2 to 10. Monofunctional components are given by formula (OR 1 ) 4-z SiR 4 z It is good to have R 1is methyl or ethyl, z is 1 or 2, R 4 is a branched or unbranched C1-C10 alkyl group or R 2 Ph is defined as an unsubstituted phenyl group or a phenyl group substituted with a C1-C10 branched or unbranched alkyl, halogen, C1-C10 alkyl ether, methoxy, ethoxy, or hydroxyl group.

[0016] The volume-weighted median particle size D50 of the first and second groups may have a ratio of about 40:1 to about 1.5:1. The width of the volume-weighted particle size distribution for the first and second groups, as described by the ratio D75 / D25, may have a ratio of about 40:1 to about 1.1:1. The mass ratio of the first and second groups may be about 1:20 to about 20:1, for example, about 1:15 to about 15:1, about 1:10 to about 10:1, about 1:5 to about 5:1, or about 1:2 to about 2:1. The metal oxide-polymer composite particles may have a volume-weighted median particle size D50 of about 20 nm to about 1000 nm. The metal oxide-polymer composite particles have an average roughness P of about 1.22 to about 1.9. 2 The matrix may have a coefficient of 4πS, where P is the circumference of the image of the metal oxide-polymer composite particle and S is the area of ​​the particle image, both of which are determined from transmission electron micrographs. The polymer matrix may contain polymers of styrene, unsubstituted or substituted acrylates or methacrylates, olefins, vinyl esters and acrylonitriles, and copolymers and mixtures thereof. The composite particles can be arranged on the surface of toner particles to form a toner composition.

[0017] In another embodiment, a method for producing metal oxide-polymer composite particles is an aqueous dispersion comprising a first hydrophobic system in an aqueous medium and at least a first group of metal oxide particles and a second group of metal oxide particles, wherein the first group of metal oxide particles has a different particle size, shape or particle size distribution than the second group, and the first hydrophobic system is of formula [R 3 3-x (OR 1 ) x ]SiR 2It contains a bifunctional component having Q, where x is 1, 2, or 3, and R 1 is methyl or ethyl, R 2 is the general formula C n H 2n An alkyl linker having n 1 to 10, R 3 The process includes: preparing an aqueous dispersion in which is methyl or ethyl, and Q is a substituted or unsubstituted vinyl, acrylate ester, or methacrylate ester group, provided that when Q is a substituted or unsubstituted vinyl, n is 2 to 10; keeping the dispersion warm for a predetermined time; adding a radical initiator to the dispersion; forming a metal oxide-polymer composite particle by making the chemical group of the first hydrophobic system part of the polymer; and drying the metal oxide-polymer composite particle to obtain a powder.

[0018] The method may further include a step of treating at least a portion of the metal oxide particles with a second hydrophobic agent, the treatment step of which can be performed before the preparation step of the metal oxide-polymer composite particles or after the formation step. The first hydrophobic system is given by formula (OR 1 ) 4-z SiR 4 z It may further contain a monofunctional component having R 1 is methyl or ethyl, z is 1 or 2, R 4 is a branched or unbranched C1-C10 alkyl group or R 2 Ph is an unsubstituted phenyl group or a phenyl group substituted with a C1-C10 branched or unbranched alkyl, halogen, C1-C10 alkyl ether, methoxy, ethoxy, or hydroxy. The ratio of D50 of the first group and the second group may be about 40:1 to about 1.5:1. The ratio D75 / D25 for the first group and the second group may be about 40:1 to about 1.1:1. The mass ratio of the first group to the second group may be about 1:20 to about 20:1.

[0019] The emulsion may further contain one or more of styrene, substituted or unsubstituted acrylate or methacrylate monomers, olefin monomers, vinyl esters, or acrylonitrile. At least a portion of each group of metal oxide particles may protrude inward and outward from the polymer matrix. The metal oxide-polymer composite particles may have a volume-weighted median particle size D50 of about 20 nm to about 1000 nm. The intrinsic density of the metal oxide-polymer composite particles is about 30% to about 90% of the intrinsic density of the metal oxide when measured by helium pycnometer. The metal oxide-polymer composite particles may have an average SF-1 of about 110 to about 185 and an average RTA of about 0.06 to about 0.19. The metal oxide-polymer composite particles have an average roughness P of about 1.22 to about 1.9. 2 It may have / 4πS.

[0020] The above general description and the following detailed description are merely illustrative and descriptive, and are intended to provide a further explanation of the claimed invention.

[0021] The present invention will be described with reference to several figures in the drawings. [Brief explanation of the drawing]

[0022] [Figure 1A] This is a schematic diagram illustrating the effect on particle size and roughness when metal oxide particles of different particle sizes are used to produce metal oxide-polymer composite particles according to embodiments of the present invention. [Figure 1B] This is a schematic diagram illustrating several measurements used for characterizing particles using a transmission electron microscope. [Figure 2A] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 2B] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 3A]These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 3B] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 3C] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 4A] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 4B] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 5A] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 5B] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 6A] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 6B] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 6C] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 6D] These are transmission electron microscope images of metal oxide-polymer composite particles manufactured according to multiple embodiments of the present invention. [Figure 7] This is a transmission electron microscope image of colloidal silica. [Figure 8A] This is a set of graphs obtained from statistical modeling of aggregation rates, relating particle size and average additive RTA at an additive coverage rate of 15% model toner. [Figure 8B]This is a set of graphs obtained from statistical modeling of aggregation rates, relating particle size and average additive RTA at an additive coverage rate of 30% in a model toner. [Figure 8C] This is a set of graphs obtained from statistical modeling of aggregation rates, relating particle size and average additive RTA at an additive coverage rate of 45% in a model toner. [Figure 9] This graph shows the change in aggregation with respect to surface coverage for composite particles with different RTAs. [Modes for carrying out the invention]

[0023] In one embodiment, the production of metal oxide-polymer composite particles using a first hydrophobic system comprising a bifunctional component and an alkyl-based monofunctional component results in particles that can increase the triboelectric charge of toners in which they are used as external additives.

[0024] In another embodiment, metal oxide-polymer composite particles having a volume-weighted median particle size D50 of 40-75 nm, e.g., 40-70 nm or 40-65 nm, and an average RTA of at least 0.06, e.g., 0.06-0.019, 0.08-0.015, or 0.08-0.13, improve the free flow properties of toners in which they are used as external additives.

[0025] In another embodiment, metal oxide-polymer composite particles having a volume-weighted median particle size D50 of 100-150 nm, for example 105-150 nm or 110-150 nm, and an average RTA of at least 0.06, for example 0.06-0.019, 0.08-0.015, or 0.08-0.13, can better promote anti-blocking properties in toner compositions while improving free flow with respect to smoother spacer particles.

[0026] In another embodiment, the toner composition comprises toner particles mixed with a powder containing metal oxide-polymer composite particles comprising at least two groups of metal oxide particles having at least different particle sizes, shapes, or particle size distributions, and a polymer matrix. The surface of the metal oxide particles is modified by a first hydrophobic system comprising a bifunctional component, through which the metal oxide particles are covalently bonded to the polymer. At least a portion of the first group of metal oxide particles, the second group of metal oxide particles, or both, protrudes inward and outward from the polymer matrix, which is the polymer or copolymer of the first hydrophobic system. Such mixtures of two or more groups of metal oxide particles allow for manipulation of the particle size, particle roughness, and shape of the resulting composite particles, as shown in Figure 1A. In Figure 1A, combinations of the first group of metal oxide particles 10 with larger metal oxide particles 12 or smaller metal oxide particles 14 allow for the production of metal oxide composite particles 100, 120, and 140 having different particle sizes. Particle 140 is smaller than particle 100, and particle 100 is smaller than composite particle 120. The schematic diagram shows the equim ratio of metal oxides (10, 12, and 14) to the matrix material 16.

[0027] Suitable metal oxide particles for use in the present invention include, but are not limited to, silica, alumina, ceria, molybdenum oxide, titania, zirconia, zinc oxide, magnetite (Fe3O4), and various forms of Fe2O3, iron oxides, niobium oxide, vanadium oxide, tungsten oxide, tin oxide, clay, or mixtures or mixed oxides of any two or more of these. For use as a toner additive, the metal oxide particles typically include at least one of silica, alumina, and titania, e.g., silica and / or titania. The metal oxide particles may have two or more different particle sizes. For example, metal oxide particles with different compositions may have different particle sizes. Alternatively or in addition, particles of a particular metal oxide, e.g., silica particles, may have a bimodal or multimodal particle size distribution. Naturally, mixtures of two different metal oxides having the same or different compositions and two or more different particle sizes, shapes, or particle size distributions can also be used.

[0028] When two particles of different particle sizes are used, their volume-weighted median particle size D50 may have a ratio of approximately 40:1 to approximately 1.5:1, for example, approximately 35:1 to approximately 2:1, approximately 25:1 to approximately 2.5:1, approximately 20:1 to approximately 3:1, approximately 15:1 to approximately 4:1, or approximately 10:1 to approximately 5:1. D50 can be measured by disc centrifuge photosedimentometry or transmission electron microscopy. Alternatively or in addition, the metal oxide particles may have a bimodal or multimodal particle size distribution. The ratio of particle sizes corresponding to the peaks in the particle size distribution may be similar to those described above. Alternatively or in addition, two or more metal oxide particles may have different shapes while having similar D50s. Alternatively or in addition, different metal oxide particles may have similar D50s, but their particle size distributions may have different widths. One indicator of the width of particle size distribution is the ratio D75 / D25, which is the ratio of particles where 75% of the volume are smaller in size to particles where 25% of the volume are smaller in size. When measured using D75 / D25, the ratio of the width of particle size distribution can be between 40:1 and 1.1:1 for two different particle sizes.

[0029] Suitable particles include, but are not limited to, settled, colloidal, and exothermic metal oxide particles. Metal oxide particles can be manufactured using techniques known to those skilled in the art. Exemplary commercially available titania particles include Cerion's TiO-W1215 titania, Nyacol's TiSolB titania, and Cristal ACTiV S5-300B titania. Exemplary commercially available tin oxide particles include Nyacol's Sn15 tin oxide.

[0030] Precipitated metal oxide particles can be produced using prior art, often formed from aqueous media under the influence of high salt concentrations, acids, or other flocculants by aggregation of desired particles. The metal oxide particles are filtered, washed, dried, and separated from the residues of other reaction products by prior art known to those skilled in the art. The precipitated particles are often aggregated, in the sense that many primary particles aggregate with each other, forming somewhat spherical aggregated clusters. Non-limiting examples of commercially available precipitated metal oxides include the Hi-Sil® product from PPG Industries, Inc. and the Zeosil® product available from Evonik Corporation.

[0031] The production of fumed metal oxides is a well-documented process involving the hydrolysis of a suitable supply stock vapor (e.g., aluminum chloride for fumed alumina, or silicon tetrachloride for fumed silica) in a hydrogen and oxygen flame. Approximately spherical molten particles are formed during the combustion process, and the particle size can be varied through control of process parameters. These molten spheres, also called primary particles, fuse together through collisions at their contact points to form branched, three-dimensional chain-like aggregates. Aggregate formation is considered irreversible as a result of the fusion between primary particles. During cooling and collection, the aggregates undergo further collisions, which may result in some mechanical entanglement, to form agglomerates. These agglomerates are loosely bound by van der Waals forces and can be de-aglomerated by suitable dispersion in a suitable medium. Mixed or cofumed metal oxide particles can also be manufactured using prior art known to those skilled in the art, including, for example, the prior art described in the specification of Ettlinger et al., Publication No. 2296915 of the UK Patent Application, which is incorporated herein by reference in its entirety.

[0032] Alternative forms of metal oxides can be obtained using methods disclosed in U.S. Patent Nos. 4,755,368, 6,551,567 and 6,702,994, U.S. Patent Application Publication No. 20110244387, Mueller et al., “Nanoparticle synthesis at high production rates by flame spray pyrolysis,” Chemical Engineering Science, 58, 1969 (2003), and Naito et al., “New Submicron Silica Produced by the Fumed Process,” presented at NIP28, International Conference on Digital Printing Technologies and Digital Fabrication 2012, pp. 179-182, all of which are incorporated by reference. Typically, these methods result in metal oxide particles with low structure and small surface area. Many of these particles are exothermic, i.e., they are produced in a flame. Other methods for producing exothermic particles are disclosed, for example, in Kodas and Hampden-Smith's Aerosol Processing of Materials, Wiley-VCH, 1998. The exothermic metal oxides suitable for use in the composite particles provided herein are small, having, for example, a volume-average diameter less than 200 nm.

[0033] Colloidal metal oxide particles are often unaggregated, individually separated (primary) particles, typically spherical or nearly spherical in shape, but may have other shapes (e.g., with nearly elliptical, square, or rectangular cross-sections). Colloidal metal oxides are commercially available or can be prepared from various starting materials (e.g., wet-process type metal oxides) by known methods. Typically, colloidal metal oxide particles are produced in a similar manner to settled metal oxide particles (e.g., they are aggregated from an aqueous medium), but remain dispersed in an aqueous medium (often water alone, or water with a co-solvent and / or stabilizer). Metal oxide particles can be prepared, for example, from silicic acid derived from an alkaline silicic acid solution having a pH of about 9 to about 11, where the silicate anions undergo polymerization to yield separated silica particles of the desired particle size in the form of an aqueous dispersion. Typically, colloidal metal oxide starting materials can be used as sols, which are dispersions of colloidal metal oxides in a suitable solvent, often water alone, or water with a co-solvent and / or stabilizer. For example, see Stoeber et al., "Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range," Journal of Colloid and Interface Science, 26, 1968, pp. 62-69; Akitoshi Yoshida, Silica Nucleation, Polymerization, and Growth Preparation of Monodispersed Sols, Colloidal Silica Fundamentals and Applications, pp. 47-56 (edited by Hebergna & W.O. Roberts, CRC Press: Boca Raton, Florida, 2006); and Iler, RK, The Chemistry of Silica, p. 866 (John Wiley & Sons: New York, 1979). SeeNon-limiting examples of commercially available colloidal metal oxides suitable for use in the present invention include Nissan Chemical's SNOWTEX® products, WRGrace & Co.'s LUDOX® products, Nyacol Nanotechnologies, Inc.'s NexSil® and NexSil A® series products, Fuso Chemical's Quartron® products, and AkzoNobel's Levasil® products.

[0034] Colloidal metal oxide particles may have a (volume-weighted) median particle size D50 of approximately 5 to approximately 300 nm, for example, approximately 5 to approximately 10 nm, approximately 10 to approximately 20 nm, approximately 20 nm to approximately 30 nm, approximately 30 to approximately 50 nm, approximately 50 to approximately 70 nm, approximately 70 to approximately 100 nm, approximately 100 nm to approximately 125 nm, approximately 125 nm to approximately 150 nm, approximately 150 nm to approximately 175 nm, approximately 175 nm to approximately 200 nm, approximately 200 nm to approximately 225 nm, approximately 225 nm to approximately 250 nm, approximately 250 nm to approximately 275 nm, or approximately 275 nm to approximately 300 nm. Naturally, a mixture of particles with different volume-weighted median particle sizes D50 may contain particles having two or more particle sizes within these ranges. The metal oxide particles may be spherical or non-spherical. For example, the aspect ratio of the metal oxide particles may be about 1.5 to about 3, for example, about 1.5 to about 1.8, about 1.8 to about 2.1, about 2.1 to about 2.5, about 2.5 to about 2.8, or about 2.8 to about 3. The particle size is measured by disk centrifugation or transmission electron microscopy, according to the particle dispersion described in the examples below.

[0035] In one embodiment for producing composite particles, metal oxide particles are treated with a first hydrophobic system. The first hydrophobic system may contain one or more hydrophobic components. Preferably, the first hydrophobic system includes at least one bifunctional component, such as a first reactive group, which can be covalently or non-covalently bonded to the metal oxide particles, e.g., silane, and a second reactive group, which can be incorporated into the polymer of the metal oxide-polymer composite particles. In certain embodiments, the bifunctional component has a molecular weight less than 300. When the term "hydrophobic" is used herein, metal oxide particles involve altering the level or degree of hydrophobicity. The degree of hydrophobicity imparted to the metal oxide particles varies depending on the type and amount of treatment agent used. Hydrophobic metal oxide particles for use according to the present invention may have, for example, about 15% to about 85% of the reacted hydroxyl groups on the available metal oxide surface, for example, about 25% to about 75% or about 40% to about 65% of the reacted hydroxyl groups on the available metal oxide surface, or a percentage in any range linked by any two of the above endpoints. When a second hydrophobic agent is used as discussed below, it reacts to form covalent or non-covalent bonds with a portion of the hydroxyl groups on the metal oxide surface.

[0036] The bifunctional component is given by formula [R 3 3-x (OR 1 ) x ]SiR 2 Q may be 1, 2, or 3, and R 1 is methyl or ethyl, R 2 is the general formula C n H 2n It is an alkyl linker having n, where n is 1 to 10, and R 3 Q is methyl or ethyl, and Q is mercapto, glycidyl, or a substituted or unsubstituted vinyl, acrylate ester, or methacrylate ester group, provided that when Q is a substituted or unsubstituted vinyl, n is 2 to 10. The first hydrophobization system is given by formula (OR 1 ) 4-z SiR4 z may further have a monofunctional component having, z is 1 or 2, and R 4 is a branched or unbranched C1-C10 alkyl group or R 2 is Ph, and Ph is an unsubstituted phenyl group or a phenyl group substituted with C1-C10 branched or unbranched alkyl, halogen, C1-C10 alkyl ether, methoxy, ethoxy or hydroxy. Exemplary agents suitable for use in the first hydrophobization system are (3-acryloxypropyl)trimethoxysilane, isobutyltrimethoxysilane, propyltrimethoxysilane, mercaptopropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, (3-acryloxypropyl)triethoxysilane, 3-methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, (3-acryloxypropyl)methyldimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-butenyltrimethoxysilane, 3-butenyltriethoxysilane, 4-pentenyltriethoxysilane, 4-pentenyltrimethoxysilane, 5-hexenyltrimethoxysilane, 5-hexenylmethyldimethoxysilane, 3-methacryloxypropylmethyldimethylmethoxysilane, diisobutyldimethoxysilane and diisopropyldimethoxysilane, but are not limited thereto. When the metal oxide particles are not silica, di- or tri-functional silanes should be used (i.e., x should be 2 or 3).

[0037] The solubility of the components of the first hydrophobization system may be 10-0.06 g / L, preferably 9-0.03 g / L, more preferably 8-0.1 g / L, and most preferably 7-0.5 g / L. It is theorized that if the solubility of the components of the first hydrophobization system is too high or too low, the components will not form a sufficient emulsion.

[0038] In some embodiments, preferably, R4 R is a branched or unbranched C1-C10 alkyl group. 4 When is a branched or unbranched C1-C10 alkyl group, the triboelectric charging of the metal oxide-polymer composite particles is due to other R 4 The triboelectric charge is higher when the base is used, or when no monofunctional components are used at all. For example, the triboelectric charge of a toner using the aforementioned metal oxide-polymer particles as an external additive can be increased by at least 10%, for example, up to 45%, for example, 12%-42%, 15%-40%, 17%-37%, 20%-35%, 23%-32%, or 25%-30%, compared to a toner having metal oxide-polymer composite particles without monofunctional components. Alternatively or in addition, the triboelectric charge of such a toner under high temperature, high humidity (HH) conditions can be increased by at least 9%, for example, up to 33%, for example, 12%-30%, 15%-28%, or 17%-25%, compared to a toner having metal oxide-polymer composite particles without monofunctional components. Typically, both triboelectric charging under HH and LL conditions change with the addition of alkyl-containing monofunctional components, and the changes in triboelectric charging at HH and LL may be any combination within the range selected from the list above.

[0039] In addition, at least a portion of the metal oxide particles can be treated with a second hydrophobic agent either before or after treatment with the first hydrophobic system, or after the formation of metal oxide-polymer composite particles, in which case only the exposed surfaces of the metal oxide particles are treated. Preferred agents for use as the second hydrophobic agent are silazane compounds, siloxane compounds, and silane compounds, as well as silicone fluids with or without a cosolvent that have some solubility in water. A mixture of two or more agents can be used. Preferably, the silicone fluid for use as the second hydrophobic agent has a number average molecular weight of up to 500. Examples of silane compounds include alkylsilanes and alkoxysilanes. Alkoxysilanes have the general formula R' x Si(OR'') 4-xcomprising a compound having, wherein R’ is a branched-chain and straight-chain alkyl, alkenyl, C3-C 30 cycloalkyl and C6-C 10 selected from the group consisting of aryl, and R’’ is a branched-chain or straight-chain C1-C 10 alkyl, and x is an integer from 1 to 3. When the metal oxide particles do not contain silica, the use of a bifunctional or trifunctional silane or siloxane or silicone fluid as a second hydrophobizing agent provides a better bond than a monofunctional silane. 10

[0040] Non-limiting examples of silane compounds that can be used as the second hydrophobizing agent described herein include trimethylsilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, benzyldimethylchlorosilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-butyltrimethoxysilane, n-octyltriethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane and the like. Similarly, amine-functionalized alkylalkoxysilanes can be used. Non-limiting examples of useful siloxane compounds include octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane and the like. Non-limiting examples of useful silazane compounds include hexamethyldisilazane (HMDZ), hexamethylcyclotrisilazane, octamethylcyclotetrasilazane and the like. For example, HMDZ can be used to cover unreacted hydroxyl groups on the surface of the metal oxide particles. Exemplary hydrophobizing agents also include hexamethyldisilazane, isobutyltrimethoxysilane, octyltrimethoxysilane and cyclic silazanes, such as those disclosed in U.S. Patent No. 5,989,768. Such cyclic silazanes have the formula:

Chemical formula

[0041] Suitable silicone fluids for use as a second treatment agent include both unfunctionalized and functionalized silicone fluids. Depending on the conditions used to surface-treat the metal oxide particles and the individual silicone fluid used, the silicone fluid may exist as a non-covalently bonded coating or covalently bonded to the surface of the metal oxide particles. Non-limiting examples of useful unfunctionalized silicone fluids include polydimethylsiloxane, polydiethylsiloxane, phenylmethylsiloxane copolymer, fluoroalkylsiloxane copolymer, diphenylsiloxane-dimethylsiloxane copolymer, phenylmethylsiloxane-dimethylsiloxane copolymer, phenylmethylsiloxane-diphenylsiloxane copolymer, methylhydrosiloxane-dimethylsiloxane copolymer, hydroxyl-functionalized or hydroxyl-terminated siloxanes, polyalkylene-modified silicones, and similars. For example, functionalized silicone fluids may contain functional groups selected from the group consisting of vinyl, hydride, hydroxyl, silanol, amino, and epoxy. The functional groups may be directly bonded to the silicone polymer backbone, or bonded through intermediate alkyl, alkenyl, or aryl groups.

[0042] Alternatively, or in addition, metal oxide particles can be treated using dimethylsiloxane copolymers disclosed in U.S. Patent Publication No. 2011 / 0244382, the contents of which are incorporated herein by reference. An example of a dimethylsiloxane copolymer is given by formula: [ka] The copolymer contains R1 = -H, -CH3, R2 = -H, -CH3, and R3 = -CH3, -CH2CH3, -CH2CH2CH3, CH2Ar, -CH2CH2Ar, -Ar, -CH2CH2CF3, or -CH2CH2-R f And R f R4 is a C1-C8 perfluoroalkyl group, and R4 is -CH3, -CH2CH3, -CH2CH2CH3, -CH2CH2CF3, or -CH2CH2-Rf And R f R5 is a C1-C8 perfluoroalkyl group, R5 is -CH3, -CH2CH3, -CH2Ar, -CH2CH2Ar, or -Ar, R6 is -H, -OH, -OCH3, or -OCH2CH3, Ar is an unsubstituted phenyl group, or a phenyl group substituted with one or more methyl, halogen, ethyl, trifluoromethyl, pentafluoroethyl, or -CH2CF3 groups, n, m, and k are integers, n≧1, m≧0, and k≧0, and the copolymer has a molecular weight of 208 to about 20000.

[0043] Alternatively, or in addition, the second hydrophobic agent may be a electrostatic modifier. Any of the electrostatic modifiers disclosed in U.S. Patent Publication No. 2010 / 0009280, the contents of which are incorporated herein by reference, may be used herein. Exemplary electrostatic modifiers include, but are not limited to, 3-(2,4-dinitrophenylamino)propyltriethoxysilane (DNPS), 3,5-dinitrobenzamide-n-propyltriethoxysilane, 3-(triethoxysilylpropyl)-p-nitrobenzamide (TESPNBA), pentafluorophenyltriethoxysilane (PFPTES), and 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPES). Because hydrogenation groups may reduce nitro groups, electrostatic modifiers containing nitro groups should be used to post-treat metal oxide particles after copolymerization.

[0044] Alternatively, or in addition to the second hydrophobic agent, the metal oxide particles may be treated with a third hydrophobic agent following the formation of a metal oxide-polymer composite. The third treatment agent may be a silicone fluid or alkylhalosilane having a number average molecular weight greater than 500. The alkylhalosilane has the general formula R' x SiR'' y Z 4-x-y The compound comprises a compound having R' and R'' as defined above, Z is a halogen, preferably chlorine, and y is 1, 2, or 3.

[0045] (When used after the formation of metal oxide-polymer particles,) the interaction between the second hydrophobic agent and / or the third hydrophobic agent and the polymer component of the metal oxide-polymer composite particles allows these agents to further treat the exposed polymer surface of the metal oxide-polymer composite particles.

[0046] The polymer used in metal oxide-polymer composite particles may be the same as or different from the polymer or copolymer of the first hydrophobic system. That is, if the first hydrophobic system contains one or more polymerizable groups, the same material can be simply used to form the polymer. In certain embodiments, the polymer of the difunctional component is not a polyether. Instead or in addition, the polymer of the difunctional component is an acrylate or methacrylate polymer. Instead or in addition, a crosslinking agent or different monomer that can copolymerize at the terminal groups can be used with the difunctional component. Suitable monomers that can be used to produce metal oxide-polymer composite particles include substituted and unsubstituted vinyl and acrylate (including methacrylate) monomers, as well as other monomers polymerized by radical polymerization. Exemplary monomers include styrene, acrylate and methacrylate, olefins, vinyl esters, and acrylonitrile, which are readily available to those skilled in the art, for example, from Sigma-Aldrich (Milwaukee, WI). Such comonomers may also be substituted with C1-C3 alkyl, halogen, and / or hydroxyl groups. Substituted comonomers include, but are not limited to, hydroxypropyl methacrylate, trifluoropropyl methacrylate, and α-methylstyrene. Any of these monomers can be used by themselves or in combination with a crosslinking agent in the copolymer-forming mixture. Exemplary crosslinking agents include divinyl-terminated difunctional components (e.g., silanes substituted with vinyl groups) or other well-known vinyl crosslinking agents, such as divinylbenzene and ethylene glycol dimethacrylate. Alternatively or in addition, the copolymer or crosslinking agent can react with a silane. For example, a silanol-terminated siloxane polymer or the copolymer of formula (1) above can be used in combination with the first hydrophobic system. The comonomer or crosslinking agent can be added simultaneously with or at different times to the first hydrophobic system. The amount of crosslinking agent can be adjusted to control the degree of crosslinking in the final polymer.

[0047] Metal oxide-polymer composite particles can be produced by creating a dispersion of metal oxide particles in a fluid comprising a first hydrophobic system, an optional monomer, and an aqueous phase. Polymerization of polymerizable species in the organic phase yields the composite particles. In one exemplary procedure, an emulsion or mixture is prepared in an aqueous medium, for example, in water with an optional cosolvent, such as an alcohol, such as isopropyl alcohol, using the first hydrophobic system, an optional comonomer, a crosslinking agent, and metal oxide particles in a ratio of about 0.5:40 by mass (polymerizable species / metal oxide), for example, about 1:about 1.5, about 1.5:about 2, about 2:about 3, about 3:about 10, about 15:about 30, or about 10:about 20. The total amount of metal oxide particles and polymerizable species relative to the total amount of solvent may be about 5 wt% to about 45 wt%, for example, about 5 wt% to about 15 wt%, about 15 wt% to about 20 wt%, about 20 wt% to about 30 wt%, about 30 wt% to about 40 wt%, or about 40 wt% to about 45 wt%.

[0048] Optionally, the pH is adjusted to approximately 8.0–10, and the dispersion is stirred while the temperature is maintained at 25–60°C (typically for 1–3 hours). Following stirring, an initiator is introduced at a level of approximately 0.1–4 wt% relative to the monomer, for example, at levels of approximately 0.1–0.5%, 0.5%–1%, 1%–1.5%, 1.5%–2%, 2%–2.5%, 2.5%–3%, 3%–3.5%, or 3.5%–4%. The initiator can be introduced as a powder or as a solution in ethanol, acetone, or other water-miscible solvent. Suitable initiators include, but are not limited to, oil-soluble azo or peroxide thermal initiators, such as 2,2'-azobis(2-methylpropionitrile) (AIBN), benzoyl peroxides, tert-butyl peracetate, and cyclohexanone peroxides. Various suitable initiators are available from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). The initiator can be dissolved in the monomer before the introduction of the metal oxide and can be partitioned between the monomer and the aqueous phase. The resulting solution is kept warm at 65-95°C for 4-6 hours with stirring. The resulting slurry can be dried overnight at 100-130°C, and any remaining solid is pulverized to form a powder. The particles can also be dried using other methods to separate the particles from the liquid. If a second hydrophobic agent is added after the formation of the metal oxide-polymer composite, it is introduced before the drying step. For example, a second hydrophobic agent may be added, and the slurry is further stirred at 60-75°C for 2-4 hours with heating.

[0049] Those skilled in the art will recognize that the particle size and shape of two or more groups of metal oxide particles, as well as their proportions to each other in the reaction mixture, in addition to variations in the amount of such solids in the mixture or emulsion, the ratio of polymer to metal oxide, the pH of the aqueous phase, and the heat retention temperature all affect the morphology of the composite particles. In practice, for a given diameter of metal oxide-polymer composite particles, the shape and particle roughness of the composite particles can be controlled by significant variations in the metal oxide particle size and the amount of solids in the mixture or emulsion. In certain embodiments, the composite particles have metal oxide particles arranged within the composite particles, i.e., metal oxide particles that are completely in the polymer phase, as well as metal oxide particles that protrude from the surface. In these embodiments, the metal oxide particles contribute to the mechanical strengthening of the composite particles and increase their compressive strength.

[0050] The degree of surface treatment of metal oxides by the first hydrophobicization system can be controlled by adjusting the pH and temperature of the starting solution. The adsorption rate of difunctional and any monofunctional components onto metal oxide particles (adsorption can occur after the formation of siloxane bonds between the surface and each component) can also be controlled by the selection of leaving groups in the silane-based difunctional or monofunctional components; for example, ethoxy tends to hydrolyze more slowly than methoxy.

[0051] The particle size and particle size distribution of metal oxide-polymer composite particles can be controlled by adjusting the proportion of metal oxide particles and the relative particle size and / or particle size distribution. To the extent that the particle size of the metal oxide-polymer composite particles is influenced by the particle size of the metal oxide particles, for a given composite particle produced by first metal oxide particles, the particle size of the composite particle can be increased by substituting at least a portion of the first metal oxide particles with second metal oxide particles having a larger diameter. Similarly, substituting at least a portion of the first metal oxide particles with second metal oxide particles having a smaller diameter will decrease the particle size of the resulting composite particle.

[0052] Regardless of the particle size distribution of the metal oxide particles, the coarseness of metal oxide-polymer composite particles can be adjusted by changing the reaction conditions. Generally, increasing the pH of the reaction mixture, for example by adding ammonium hydroxide or using a base-stabilized metal oxide dispersion, increases particle coarseness or RTA. Decreasing the amount of solids loaded in the reaction medium also increases particle coarseness and RTA.

[0053] When a mixture of two groups of metal oxide particles is used, the ratio of the first metal oxide particles to the second metal oxide particles may be about 1:20 to about 20:1 by mass, for example, about 1:15 to about 15:1, about 1:10 to about 10:1, about 1:5 to about 5:1, or about 1:2 to about 2:1. The desired ratio of the first metal oxide particles to the second metal oxide particles can be varied depending on the particle size of the desired composite particle and the particle sizes of the first and second metal oxide particles.

[0054] At least a portion of the metal oxide particles in the composite particles may be entirely embedded within the polymer portion of the composite particles. Alternatively, or in addition, at least a portion of the metal oxide particles may be partially embedded within the polymer portion of the composite particles, i.e., some of the metal oxide particles protrude inward and outward from the polymer matrix. In certain embodiments, when measured for metal oxide particles observable by electron microscopy of at least 200, preferably at least 500, metal oxide-polymer composite particles, the metal oxide particles exposed on the surface of the composite may have a length protruding from the surface of the metal oxide-polymer composite particles of about 0% to about 95%, for example, about 5% to about 90%, about 10% to about 20%, about 20% to about 30%, about 30% to about 40%, about 40% to about 50%, about 50% to about 60%, about 60% to about 70%, about 70% to about 80%, or about 80% to about 90%. The amount of metal oxide particles protruding from the surface of the metal oxide-polymer composite particles can vary depending on the particle size and / or shape of the metal oxide particles, as well as the particle size distribution (described as D75 / D25) or median particle size D50 of one or more groups of metal oxide particles.

[0055] Metal oxide-polymer composite particles can be round. Depending on the extent to which the metal oxide particles are exposed on the surface of the composite particle, rounded particles do not need to be spherical and are typically understood to have a bumpy surface. Alternatively, the use of two groups of metal oxide particles with large particle size differences also results in the formation of non-equalithic particles. Such particles combine an irregular shape with high particle roughness.

[0056] The shape and degree of "bumpiness" or roughness of metal oxide-polymer composite particles can be analyzed by TEM (transmission electron microscopy) evaluation. Conventional image analysis software is used to define the perimeter P of the particle's TEM image. The same software is used to calculate the particle image area S and to determine the maximum Ferret diameter (Dmax) 20 across the particle, measured between two parallel lines 22 tangent to the particle (see Figure 1B). These measurements are suitable for multiple particles, preferably at least 100 particles, more preferably at least 500 particles, in multiple TEM images.

[0057] SF-1 indicates how much the particle shape deviates from a sphere, and 100(πDmax 2 It is calculated as ( / 4S). The SF-1 of an ideal spherical particle is 100. The larger the SF-1, the more the particle shape deviates from spherical. The average SF-1 for composite particles may be approximately 110 to 185, for example, approximately 110 to 125, approximately 125 to 150, or approximately 150 to 185.

[0058] Particle roughness is P 2It can be calculated as / 4πS (John C. Russ, The Image Processing Handbook, CRC Press, 4th edition, 2002). Figure 1B illustrates that grain roughness can be considered as the ratio of the area of ​​a hypothetical circle 24 having the same circumference as the circumference 26 of the particle 28 to the area of ​​the actual particle. The roughness of an ideal spherical particle is 1.0. However, the grain roughness of a spherical particle with a rough surface can be considerably greater than 1. Grain roughness is particularly sensitive to roughness and surface texture at a very fine scale. Since the grain roughness formula includes both circumference and image area, grain roughness further indicates the deviation of the particle shape, especially the deviation of the particle shape from spherical. For example, the grain roughness for an ellipse with axes 1 and 2 is 1.19, and for an ellipse with axes 1 and 3 it is 1.51. Thus, grain roughness increases with increasing surface roughness and increasing deviation of the particle shape from spherical. The average roughness of the metal oxide-polymer composite particles may be 1.15 to 1.9, for example, 1.15 to 1.2, 1.2 to 1.5, 1.5 to 1.7, or 1.7 to 1.9. To improve free flow, the average roughness of the metal oxide-polymer composite particles is preferably greater than 1.22, for example, greater than 1.25.

[0059] Alternatively, or in addition, the same image analysis software can be used to draw a convex hull 30 for the image of the particle and determine the area C inside the hull, called the "hull area". The convex hull is a curved convex that indicates the surface boundary surrounding the entire particle. It is produced by moving a pair of parallel lines until they are just touching the outside of the particle image. The angle of the parallel lines is then changed, and the process is repeated until the entire path of the convex hull is defined. As shown in Figure 1B, the convex hull is like a rubber band stretched around the particle. The relative trough area (RTA) is defined by (CS) / S, where S is the particle image area. The value of RTA increases with increasing protrusion from the surface. The RTA of a perfectly spherical, elliptical, or any hull is 0. The RTA of a typical unaggregated colloidal silica is approximately 0.01. The average RTA of metal oxide-polymer composite particles may be 0.01 to about 0.19, for example, about 0.03 to about 0.15, about 0.05 to about 0.13, or about 0.07 to about 0.11. To promote the free flow of toner, the average RTA is preferably greater than 0.06 or 0.08, for example, 0.06 to 0.13. The average RTA is measured using images of at least 100 particles, preferably at least 500 particles. Naturally, using more particle images provides higher sensitivity and facilitates the distinction between different particle morphologies.

[0060] Preferably, the metal oxide composite particles have an average SF-1 within the range described above or any lower range, and an average RTA within the range described above or any lower range. In addition, they may further have an average particle roughness within the range described above or any lower range. Particles having at least the average SF-1 and average RTA described above can exhibit improved drop-off performance in toner compared to smoother or rounder particles.

[0061] Alternatively, or in addition, the metal oxide-polymer composite particles may have a (volume-weighted) median particle size or particle size D50 of about 20 nm to about 1000 nm. For example, the D50 of the metal oxide-polymer composite particles may be 20 nm to 100 nm, 100 nm to 200 nm, 200 nm to 300 nm, 300 nm to 400 nm, 400 nm to 500 nm, 500 nm to 600 nm, 600 nm to 700 nm, 700 nm to 800 nm, 800 nm to about 900 nm, or 900 nm to 1000 nm. The particle size of the metal oxide composite particles can be measured by disk centrifugation spectroscopy.

[0062] As shown in the examples, toner aggregation increases with increasing particle size and decreases with increasing particle "roughness" as measured by RTA. Toner aggregation is inversely correlated with free flow. To improve the free flow of toner, preferably, the manufactured metal oxide-polymer composite particles have a D50 of 40-75 nm, e.g., 40-70 nm or 40-65 nm, an average RTA of at least 0.06 or at least 0.08, e.g., 0.06-0.019, 0.08-0.015 or 0.08-0.13, and optionally, an average particle roughness of at least 1.22, e.g., 1.25-1.60 or 1.70 or 1.22-1.35. Particles with a D50 smaller than 40 nm are expected to have a stronger tendency to embed in the toner surface, and particle size is inversely correlated with free flow performance.

[0063] To improve anti-blocking properties and prevent toner particles from adhering to one another, preferably, metal oxide-polymer composite particles have a D50 of 100-150 nm, e.g., 105-150 nm or 110-150 nm, an average RTA of at least 0.06 or at least 0.08, e.g., 0.06-0.019, 0.08-0.015, or 0.08-0.13, and instead of or in addition, an average particle roughness of at least 1.22, e.g., at least 1.25 or at least 1.3, e.g., 1.25-1.60 or 1.70, or 1.22-1.35. The free-flow performance of the toner tends to decrease as the size of the external additive increases. However, larger particles can better avoid being embedded in the soft toner surface. As the roughness of the composite particles increases, the free-flow performance improves, and the composite particles are optimized to mitigate the effect of the increased size and maintain anti-blocking and free-flow performance.

[0064] Preferably, the metal oxide-polymer composite particles have an intrinsic density of the metal oxide itself (for example, silica is 2.2 g / cm³). 3 It has an intrinsic density of 3.6 g / cm³, and titanium dioxide is 3.6 g / cm³. 3 The density is less than (having a density of ). For example, the intrinsic density of the composite particles may be about 30% to about 35%, about 35% to about 40%, 40% to about 45%, about 45% to about 50%, about 50% to about 55%, about 55% to about 60%, about 60% to about 63%, about 63% to about 67%, about 67% to about 70%, about 70% to about 73%, about 73% to about 76%, about 76% to about 79%, about 79% to about 82%, about 82% to about 85%, or about 85% to about 90% of the intrinsic density of the metal oxide contained therein. The density can be measured by helium pycnometer. In some embodiments, the particle size and shape of the composite particles can be changed while maintaining the desired density by using metal oxide particles of different particle sizes in the composite. Maintaining a desired density allows a person skilled in the art to reduce or maintain drop-off performance during fixing, maintain other properties of the toner performance, or change the particle morphology without changing its refractive index.

[0065] Metal oxide-polymer composite particles can be used as external additives for both conventional and chemical toners. Conventional toners can be prepared by many known methods, e.g., by mixing and heating resins, pigment particles, optional electrostatic enhancers, and other additives in conventional melt extrusion apparatus and associated equipment. Conventional equipment for dry blending of powders can be used to mix or blend carbon black particles with resins. Other methods include spray drying and similar methods. Generally, pigments and other raw materials are compounded with resins, followed by mechanical friction and classification to provide toner particles with desired particle size and particle size distribution. Chemical toners, also known as chemically prepared toners, are manufactured in a liquid phase; generally, resin particles are formed in the presence of colorants. For example, a process has been developed in which polymer latex is bonded with an aqueous pigment dispersion and agglomerated using a flocculant to form polymer particles. Another process involves aqueous suspension polymerization of a dispersion of pigments in at least one monomer. Furthermore, pigment / polyester resin dispersions have been prepared, bonded with water, and then the solvent has been evaporated.

[0066] For both conventional and chemically prepared toners, metal oxide-polymer composite particles can be combined with toner particles in the same way as conventional additives, such as fumed metal oxides or colloidal metal oxides. For example, a toner composition can be formulated by mixing a suitable amount of metal oxide-polymer composite particles with toner particles having a suitable particle size in a blender. Alternatively, or in addition, metal oxide-polymer composite particles can be combined with toner for use as an external additive by dry-blending the toner particles with core-shell composite particles using a Henschel or other suitable mixer, for example, using a mixer described in U.S. Patent No. 9,470,993, 9,500,970, 9,575,425, JP 2019-095616, 2018-045006, or 2018-036596. Alternatively, dispersions of metal oxide-polymer composite particles can be combined with toner particles by a wet blending method, for example, the method disclosed in International Publication No. 2014 / 153355. For example, the toner can be sonicated together with the dispersion of composite particles until a well-mixed dispersion is obtained. The toner particles, having metal oxide-polymer particles positioned or distributed on their surface, can then be recovered from the dispersion, for example, by vortexing and drying, or by other methods for recovering particles from the dispersion. Alternatively or in addition, metal oxide-polymer composite particles can be combined with toner simultaneously with other external additives, such as further inorganic, composite, or organic particles, or in a separate mixing step. A variety of particles for use as toner external additives are known to those skilled in the art and can be used in combination with one or more of the metal oxide-polymer composite particles provided herein. Exemplary external additives known to those skilled in the art include, but are not limited to, fumed silica, colloidal silica, titania, polymer particles, fatty acid salts, and other external additives suitable for use with toner. Typically, fumed silica and other inherently hydrophilic materials are imparted hydrophobicity for use as toner additives.

[0067] In certain embodiments, metal oxide-polymer composite particles constitute about 0.5 wt% to about 7 wt% of the toner composition, for example, about 0.5 wt% to about 1 wt%, about 1 wt% to about 1.5 wt%, about 1.5 wt% to about 2 wt%, about 2 wt% to about 2.5 wt%, about 2.5 wt% to about 3 wt%, about 3 wt% to about 3.5 wt%, about 3.5 wt% to about 4 wt%, about 4 wt% to about 4.5 wt%, about 4.5 wt% to about 5 wt%, about 5 wt% to about 5.5 wt%, about 5.5 wt% to about 6 wt%, about 6 wt% to about 6.5 wt%, or about 6.5 wt% to about 7 wt%. The metal oxide-polymer composite particles can be distributed on the surface of the toner particles. Preferably, the surface coverage of the metal oxide-polymer composite particles is about 10% to about 90% of the toner surface, for example, 10% to 20%, 15% to 25%, 20% to 30%, 25% to 35%, 30% to 40%, 15% to 80%, 25% to 75%, 30% to 70%, 35% to 65%, 40% to 60%, 45% to 55%, or 10% to 45%. The suitable surface coverage of the metal oxide-polymer particles on the toner depends on the properties and composition of other materials further used as external additives, such as inorganic particles or polymer particles, as well as the toner and any carriers or developers used with the toner. The distribution of the metal oxide-polymer composite particles on the toner can be relatively uniform. For example, the coefficient of variation in the distribution of composite particles to the toner may be less than 0.40, for example less than 0.30, and for example 0.05 to 0.15, 0.10 to 0.20, or 0.15 to 0.25, when measured by scanning electron microscopy observation as described in U.S. Patent Application Publication No. 2015 / 0037719, the contents of which are incorporated herein by reference.

[0068] Preferably, metal oxide-polymer composite particles exhibit a low level of drop-off, which improves toner durability and can enhance print quality over long printing times. While the retention of composite particles to toner particles depends in part on the toner composition, surrogate tests can be used to compare the performance of metal oxide-polymer composite particles with metal oxide particles of corresponding particle size and shape. For example, tests similar to those described in U.S. Patent Publication Nos. 2003 / 0064310, 2010 / 0009282, 2006 / 0240350, and U.S. Patent No. 9568847 can be used.

[0069] The metal oxide-polymer composite particles should have sufficient mechanical strength to be mixed with toner particles by methods typically used by those skilled in the art, for example, by the use of a Henschel mixer or other fluidizing mixer or blender. Preferably, the metal oxide-composite particles have sufficient strength to withstand collisions between toner particles (having metal oxide-polymer composite particles distributed on their surface) during the development cycle of the electrophotographic process. The mechanical strength of the particles can be evaluated by compounding a chemical toner using the composite particles. The toner / particle mixture is then mixed with a carrier, for example, a silicone-coated Cu-Zn ferrite carrier (particle size 30-90 μm) to form a mixture having 2% (w / w) toner. This mixture is then placed in a mixing container at a filling rate of about 70%-90% and rotated in an agitator called a three-dimensional mixer, which can move the mixing container rhythmically in three-dimensional motion. The mixing container is moved at a rotational speed of about 50-70 revolutions / min at a volume of about 6-8 times the volume of the container. Exemplary stirrers include the Turbula mixer available from Willy A. Bachoven AG, the Inversina mixer available from Bioengineering AG, and the dynaMix 3D mixer from Glen Mills. After a specified time, the sample is analyzed by SEM. If the composite particles have sufficient mechanical strength, they will not flatten or deform during mixing. Any flattening or deformation will appear as a change in particle size in the SEM. In a preferred embodiment, the change in diameter of the metal oxide-polymer composite particles after 10 mins of mixing is less than 25%, preferably less than 20%, and for example less than 10%.

[0070] Alternatively, or in addition, metal oxide-polymer composite particles can be used as cleaning aids. The function and method of using cleaning aids are discussed in U.S. Patent No. 6,311,037, the contents of which are incorporated herein by reference. Briefly, after an image is printed, a resilient blade removes excess toner from the photoreceptor. Abrasive particles can facilitate a more complete removal of excess toner; otherwise, the excess toner will transfer to subsequent copies, resulting in a "shadow" effect where a weak image from the previous copy appears in one or more subsequent copies. Generally, two different types of particles are currently used as cleaning aids. Crushed or settled inorganic particles (e.g., metal oxides, nitrides, carbides) have hardness and shape suitable for abrasive cleaning applications. However, they have a wide particle size distribution. Larger particles may scratch the surface of the photoreceptor, while smaller particles may be less than the clearance between the cleaning blade and the photoreceptor. Colloidal silica has a uniform particle size, but due to its smooth surface, it has limited cleaning ability. Metal oxide-polymer composite particles combine the advantages of both these particles—they have an irregular surface interrupted by hard, abrasive metal oxide particles, as well as a narrow particle size distribution. For use as a cleaning aid, metal oxide-polymer composite particles may be incorporated into the toner formulation or contained in a separate storage container, from which the metal oxide-polymer composite particles are transported to the copier drum near the cleaning blade.

[0071] Preferably, the metal oxide-polymer composite particles are in powder form. Preferably, the metal oxide-polymer composite particles exhibit a low moisture content, for example less than about 10 wt%, for example about 0% to about 3%, about 1% to about 4%, about 3% to about 5%, about 5% to about 7%, or about 7% to about 10%, after equilibration at 25°C at a pressure of about 1 atm and a relative humidity of 50%. The moisture content can be measured by drying a 100 mg sample in a glass vial in an oven at 125°C for 30 mins, discharging the sample (for example, briefly, by holding the sample under a Haug One-Point-Ionizer (Haug North America, Williamsville, NY)), and then loading the sample into an instrument for measuring the mass of the sample after incubating it for 20 mins at a selected relative humidity value of 0 to 95%.

[0072] The metal oxide-polymer composite particle powder can be pulverized or milled, or classified by means of, for example, sieving, filtration, air classification, or other methods known to those skilled in the art, as described in Japanese Patent Application Publication No. 2018-036596. The degree of aggregation of the metal oxide-polymer composite particle powder may be less than 70%, for example less than 60%, and for example 10% to 70%, 20% to 60%, 30% to 50%, or 25% to 40%. The degree of aggregation can be measured in a Hosokawa PT-X powder tester equipped with a Digiviblo Model 1332A digital display vibrometer (Showa Sokki Co., Ltd). Sieves with mesh sizes of 38 μm (400 mesh), 75 μm (200 mesh), and 150 μm (100 mesh) are stacked in order from the bottom of the vibrating table of the powder tester. Measurements are performed at 23°C and 60% relative humidity (RH). The vibration amplitude of the vibrating table is pre-adjusted so that the displacement value of the digital display vibrometer is 0.60 mm (peak to peak). The metal oxide-polymer composite particles are equilibrated at 23°C and 60% RH for 24 hours, after which 5.0 g is weighed and placed into a 150 μm sieve at the top stage of the powder tester. The sieves are vibrated for 30 seconds, and then the mass of the composite particles remaining on each sieve is measured to calculate the degree of aggregation based on the following formula. Degree of aggregation (%) = {(Sample mass on a sieve with a mesh size of 150 μm (g)) / 5 (g)} × 100 + {(Sample mass on a sieve with a mesh size of 75 μm (g)) / 5 (g)} × 100 × 0.6 + {(Sample mass on a sieve with a mesh size of 38 μm (g)) / 5 (g)} × 100 × 0.2

[0073] Metal oxide-polymer composite particles can be combined with toner particles to form toner. Conventional toners can be prepared by many known methods, e.g., by mixing and heating resins, pigment particles, optional electrostatic enhancers, and other additives in conventional melt extruders and associated equipment. Conventional equipment for dry blending of powders can be used to mix or blend carbon black particles with resins. Other methods include spray drying and similar methods. Generally, pigments and other raw materials are compounded with resins, followed by mechanical friction and classification to provide toner particles having the desired particle size and particle size distribution. Chemical toners, also known as chemically prepared toners, are manufactured in a liquid phase; generally, resin particles are formed in the presence of colorants. For example, a process has been developed in which polymer latex is combined with an aqueous pigment dispersion and agglomerated using a flocculant to form polymer particles. Another process involves aqueous suspension polymerization of a dispersion of pigments in at least one monomer. Furthermore, pigment / polyester resin dispersions have been prepared, combined with water, and then the solvent has been evaporated.

[0074] Metal oxide-polymer composite particles can offer various advantages to toners in which they are used as external additives. For example, metal oxide-polymer composite particles can complement the performance of other external additives used in combination, such as mixed metal oxides, waxes, fatty acid salts, polymer particles, and other materials typically used to enhance the free flow and triboelectric properties of the final toner product, including but not limited to fumed or sol-gel (colloidal) silica, titania, strontium titanate, and strontium zirconate.

[0075] The present invention is further clarified by the following embodiments, which are intended to be merely illustrative in essence. [Examples]

[0076] To prepare the sample for TEM, particles in an aqueous dispersion were diluted with ethanol and sonicated for 10 minutes using a probe sonicator. Sufficient dilution and dispersion are necessary to ensure that each individual particle is well separated from adjacent particles. For TEM analysis, the suspension was dropped onto a 200-mesh carbon-coated copper grid. TEM images were obtained using a JEOL JEM-1200 EX Microscope at an accelerating voltage of 80 kV. Typically, the image resolution was set to 2 nm / pixel for a 2048 x 2048 pixel image size. First, any non-uniform background in the image, if present, was calibrated using ImageJ software available from the National Institutes of Health, then the image noise was reduced and the contrast was enhanced with a suitable digital filter. The image was then divided into two images, each containing a separate image of an individual particle. The particle size and shape of each particle were determined using the ImageJ particle analyzer and then combined to obtain the shape and particle size distribution of all particles in the sample, excluding aggregates containing multiple primary composite particles. Below, the SF-1, particle roughness, and RTA values ​​for the composite particles are averages from measurements of at least 500 particles; the values ​​for colloidal silica are averages from measurements of at least 100 particles.

[0077] To prepare a sample for disk centrifugation precipitation analysis, a 0.05 wt% dispersion of composite particles was prepared in a 15 mL glass vial in reverse osmosis treated water containing 0.05 wt% Triton X-100 surfactant. This was stirred for 20 mins using an SMT UH-50 homogenizer with a 50 watt output at 90% power, using a 3 mm stirring distance along a 136 mm titanium tip positioned 0.5 mm from the bottom of the vial.

[0078] To combine the toner with composite particles, an IKA M 20 Universal mill was used to mix silica-polymer composite particles with Sinonar Corp.'s black polyester chemical toner having a particle size of approximately 8 μm, achieving a total surface coverage of 30%. To prevent the toner from overheating and melting, the process was carried out with three 15-second pulses followed by a 15-second cooling period.

[0079] The surface coverage C of the toner is given by the following relationship: C = [w / (100%-w)] × [(ρ t ×d t ) / (π×ρ a ×d a ) × [(√3) / 2] is used for calculation, where w is the wt% of the additive, and ρ t d t ρ a d a These are the density (ρ) and diameter (d) of the toner and additive particles, respectively. The additive particle size was measured by disk centrifugal sedimentation (CPS), and the additive density was measured by helium pycnometer. The density of the toner was 1.2 g / cm³. 3 The particle size was estimated to be 8 μm.

[0080] The developer was prepared by mixing 2 parts by weight of compounded toner with 98 parts of Cu-Zn ferrite carrier coated with silicone resin (carrier particle size 60-90 μm, Powdertech Co. Ltd.). The developer was left for several hours at 30°C and 80% relative humidity (corresponding to HH (high temperature / high humidity) conditions) or at 18°C ​​and 20% RH (corresponding to LL (low temperature / low humidity) conditions). After being placed under the above conditions, the jar containing the developer was rotated on a roll mill at 185 rpm for 30 minutes to develop the triboelectric charge. The triboelectric charge was measured using a Vertex T-150 tester from Vertex Image Products, Inc. 1 g of the charged developer was placed in a Faraday cage. Toner blow-off from the carrier was performed for 1 minute using an air jet of approximately 20 psi. The electrostatic charge of the toner remaining in the Faraday cage carrier was measured using a potentiometer incorporated into the Vertex tester, and the mass of the blow-off toner was determined as the difference in weight of the Faraday cage before and after the blow-off.

[0081] The toner coagulation rate was measured using a Hosokawa PT-X powder tester. 2 g of toner mixed with additives was placed on the top sieve of a stack of three sieves (mesh sizes of 75, 45, and 25 μm), and the sieve was vibrated for 20 seconds with an amplitude of 1.0 mm and a frequency of 50-60 Hz. Formula: Coagulation rate % = (M t / M init )+(M m / M init ) × 0.6 + (M b / M init The coagulation rate is calculated according to ) × 0.2 × 100%, where M t M m and M b This is the weight of the toner remaining in the upper, middle, and lower sieves, respectively, when the vibration is stopped. init This is the weight of the initial sample.

[0082] Example 1: Synthesis of composite particles using a mixture of Snowtex O40 (ST-O40) and Snowtex O (ST-O) This example illustrates a gradual decrease in the particle size of composite particles by replacing larger ST-O40 colloidal silica with smaller ST-O colloidal silica. For Example 1A, a 3000 mL four-necked round-bottom flask equipped with a stirring motor, condenser, and thermocouple was filled with 909 mL of deionized water, 257 g of ST-O40 silica dispersion in water (manufactured by Nissan Chemical; particle size ~22 nm, pH ~4.0, concentration ~41 wt%), and 4.56 g of 5 M aqueous ammonium hydroxide solution. The dispersion was stirred for ~5 min and 131 g of 3-methacryloxypropyltrimethoxysilane (MPS, CAS#2530-85-0, Mw=248.3) was added. The temperature was raised to 50°C and the mixture was stirred at 200 rpm for 3 hours. Add 2,2'-azobisisobutyronitrile (also abbreviated as AIBN, CAS#78-67-1, Mw=164.2) and raise the temperature to 80°C over 30 minutes. After maintaining the temperature at 80°C for 90 minutes, the reaction mixture is cooled to 65°C and filtered through a 200-mesh screen to remove any clumps. Add 23 g of 1,1,1,3,3,3-hexamethyldisilazane (HMDZ) to the mixture and continue the reaction for a further 5-8 hours at 65°C. Then transfer the reaction mixture to a Pyrex tray and dry overnight at 120°C.

[0083] Examples 1B to 1D were prepared according to the same procedure as described for Example 1A. The only difference is the use of a mixture of ST-O40 silica and ST-O silica (12 nm diameter, Nissan Chemical) (the silica is added sequentially to the reaction flask). Table 1 below contains information on the amounts of chemicals used. Using this method, particles with the median particle sizes listed in the table below can be prepared (measured by disk centrifugation precipitation analysis). Changes in particle size do not necessarily significantly change particle roughness or RTA. For example, using the process of Example 1A, particles with an average SF-1 of 141-146, an average particle roughness of 1.29-1.32, and an average RTA of 0.092-0.097 can be prepared. Using the process of Example 1B, particles with an average SF-1 of 147-152, an average particle roughness of 1.27-1.30, and an average RTA of 0.090-0.096 can be prepared. Figures 2A and 2B show what kinds of particles incorporating both types of silica particles can be produced using the respective compositions in Examples 1A and 1B described below. [Table 1]

[0084] Example 2: Synthesis of composite particles using Snowtex O40 (ST-O40) and a mixture of ST-O40 and ST-OL This example illustrates the increase in particle size of composite particles by replacing smaller colloidal silica ST-O40 with larger ST-OL silica. The method of Example 1 is used with the amounts of reagents in Table 2 below to produce particles having the median particle size described. Figures 3A-3C illustrate what kinds of particles incorporating both types of silica particles can be produced using the respective compositions of Examples 2A-2C described below. The arrows in Figure 3B point to ST-OL particles. Using the process of Example 2A, particles having an average SF-1 of 128-134, an average particle roughness of 1.24-1.29, and an average RTA of 0.068-0.077 can be prepared. Using the process of Example 2B, particles having an average SF-1 of 132-139, an average particle roughness of 1.23-1.28, and an average RTA of 0.063-0.073 can be prepared. Using the process of Example 2C, particles having an average SF-1 of 140-144, an average particle roughness of 1.27-1.31, and an average RTA of 0.057-0.067 can be prepared. [Table 2]

[0085] Example 3: Synthesis of composite particles having an irregular shape and a relatively smooth surface The process of Example 1 can be used with ST-OL silica (particle size 45-50 nm) instead of the silica described in Example 1, and with a monomer-silica ratio of 1.4 to produce particles having a median particle size D50 of 125-150 nm, such as the particles shown in Figures 4A and 4B. Using the process of Example 3, particles having an average SF-1 of 131-152, an average particle roughness of 1.21-1.36, and an average RTA of 0.045-0.079 can be prepared.

[0086] Example 4: Synthesis of composite particles having irregular shape and high surface roughness The process described in Example 1, except that ammonium hydroxide is not added, can be used with Ludox AS-40 silica (WR Grace, particle size 22 nm, 40% solid in the dispersion) instead of the silica described in Example 1, at a monomer-silica ratio of 2 and a solid concentration of 5.4% in the reaction mixture to produce particles, for example, those shown in Figures 5A and 5B. Using the process of this example, particles having an average SF-1 of 144-162, an average particle roughness of 1.49-1.65, and an average RTA of 0.108-0.142 can be prepared.

[0087] Example 5: Synthesis of composite particles having a spherical shape and various surface roughnesses A) The process of Example 1 can be used with ST-O40 silica and at a monomer-silica ratio of 3 to produce particles having a median particle size D50 of 115-140 nm, such as the particles shown in Figures 6A and 6B. Using the process of this example, particles having an average SF-1 of 116-119, an average particle roughness of 1.19-1.22, and an average RTA of 0.038-0.042 can be prepared.

[0088] B) The process of Example 1 can be used with ST-O silica and a monomer-silica ratio of 1.25 to produce particles having a median particle size D50 of 45-70 nm, but with a particle roughness considerably greater than that of Example 5A, such as the particles shown in Figures 6C and 6D. The amounts of reagents that can be used to produce both the particles of Example 5A and 5B are listed in Table 3 below. Using the process of this example, particles having an average SF-1 of 135-140, an average particle roughness of 1.22-1.25, and an average RTA of 0.079-0.086 can be prepared. [Table 3]

[0089] Example 6 - Comparative Example 1 TEM images were collected of spherical colloidal silica with a smooth particle surface, i.e., MP-1040 colloidal silica (Nissan Chemical Inc.), and parameters describing the particle shape were measured (Figure 7). The average SF-1 was 113, the average particle roughness was 1.15, and the average RTA was 0.030.

[0090] Example 7 This example illustrates the use of alkylsilane as a monofunctional component in combination with a bifunctional component of the first hydrophobicization system to increase the triboelectric charge of silica-polymer composite particles. For Examples 7A and 7B, a solution of 19 g of ST-O40 silica in 68 g of deionized water is stirred at room temperature, and then 0.19 g of 5N ammonium hydroxide is added to bring the pH to approximately 9.3. A mixture of either a) 4.9 g of n-propyltrimethoxysilane (NPTMS) or b) phenyltrimethoxysilane (PTMS) with 4.9 g of MPS is added all at once. The temperature is then raised to 40°C in 1 hour and held at the same temperature for 1.5 hours. Then 0.1 g of AIBN is added, and the temperature is raised to 80°C and held for 1.5 hours. The reaction mixture is cooled to 65°C, and then 2.5 g of hexamethyldisilazane is added, and the mixture is kept warm at 65°C for 3 hours. The resulting precipitate is filtered by suction, washed with deionized water, and dried under vacuum. The resulting cake is dried in an oven at 120°C for several hours, and then ground in an IKA mill.

[0091] For Example 7C, a solution of 45 g of ST-O40 silica in 160 g of deionized water was stirred at room temperature, and then 0.48 g of 5N ammonium hydroxide was added to adjust the pH to approximately 9.3. A mixture of 11.5 g of diisopropyl dimethoxysilane (DIPDMS) and 11.5 g of MPS was added all at once. The temperature was then raised to 40°C over 1.5 hours and maintained at the same temperature for 2 hours. The temperature was then raised to 60°C and the mixture was kept warm for 45 minutes. Then 0.5 g of AIBN was added, and the temperature was raised to 75°C and maintained for 2 hours. The reaction mixture was cooled to 65°C, and then 4.3 g of hexamethyldisilazane was added, and the mixture was kept warm at 65°C for 6 hours. The resulting precipitate was filtered by suction, washed with deionized water, and dried under vacuum. The resulting cake is dried in an oven at 120°C for several hours, and then ground in an IKA mill.

[0092] Using these methods, samples can be prepared for toner formulation with a 30% coverage, such as the samples in Table 4 below. The column “Hydrophobic” indicates that the sample does not wet in a methanol-water solution at methanol concentrations lower than those indicated, i.e., the material floats on the surface. In contrast, the process of Example 1A can be used to produce composite particles that can be used to produce toner having triboelectricity under LL conditions of -52 to -50 and under HH conditions of -22.5 to -21.5. This result shows that the use of alkylsilane in addition to MPS increases triboelectricity, while the use of aromatic phenylsilane does not significantly increase triboelectricity. [Table 4]

[0093] Example 8 - Increase in particle roughness The method described in Example 1, except that it does not involve the addition of ammonium hydroxide, can be used with Ludox AS-30 silica (WR Grace, 12 nm, 30% solid load in the dispersion) and Ludox AS-40 silica, using silica dispersions and water in amounts adjusted to maintain the solid load and monomer-silica ratio, to produce metal oxide-polymer composite particles having the characteristics shown below (Table 5). The Ludox silica is stabilized with ammonium hydroxide to increase the pH of the reaction mixture and increase the coarseness of the resulting composite particles. [Table 5]

[0094] Example 9 - Positively charged composite particles Particles having the properties described in Examples 1A and 5B were further treated with cyclic silazane. 300 g of the composite particle powder was placed in a 1-gallon Nalgene bottle, and the formula was: [ka] It has R 11 The mixture was sprayed with 4.3 g or 5.5 g of cyclic silazane, each of which is -(CH2CH(CH3)CH2-), and 10 mL of 2-propanol. The bottle was tightly sealed and rotated in a rotary mill at approximately 90 rpm for 1 hour. The sealed bottle was left at room temperature overnight, after which the powder was transferred to a Pyrex tray and deammed in a dry air oven at 120°C for 3-4 hours. The use of cyclic silazane treatment allows these composite particles to become positively charged without altering the particle morphology, while leaving the amine groups bound to the particle surface intact.

[0095] Example 10 - Comparative Example As described in U.S. Patent No. 7811540, ST-XL and ST-YL silica (each with a surface area of ​​60 m²) are used with HMDZ. 2 and 45m 2 (Nissan Chemicals, Inc.) processes to 1nm 2Hydrophobic treated particles having approximately 10 molecules of HMDZ per silica surface are produced. The same silica is treated with HMDZ and cyclic silazane as described in U.S. Patent No. 8,455,165, and Example 9 to obtain 1 nm 2 Hydrophobic treated particles are produced that have 5 to 10 molecules of HMDZ and approximately 1.6 molecules of cyclic silazane per silica surface. Prior to use in Example 11, the resulting powder was pulverized in an IKA A11 laboratory mill (IKA Corporation).

[0096] Example 11 - Measurement of aggregation rate Particles having the composition and morphology described in Examples 1A, 2A, 2C, 4, 5B, 8A, 8B, and 9, the particles of Example 10, and CAB-O-SIL TG-C110 colloidal silica (HMDZ-treated silica with a particle size of 115 nm, SF-1 of 111, average particle roughness of 1.23, and average RTA of 0.0256) were used as toners with coverage amounts selected from 15%, 30-32%, and 45%. The aggregation rate of the toners was measured in three ways.

[0097] The JMP software package (version 12.0.1, SAS Institute, Inc.) was used for statistical analysis of the collected data. A linear regression model was used. In the regression model, toner coagulation was the dependent variable, and toner surface coverage, additive particle size, and additive morphology, described as RTA, were independent variables. The model included an intercept, linear terms for toner coverage and particle size, and a quadratic term for RTA. Only statistically significant terms were included with p-values ​​less than 0.05. The model did not show a relationship between surface treatment (i.e., HMDZ / cyclic vs. HMDZ alone) and toner coagulation. There were 100 results used in the model. 2 The percentage was 81.4%, and the significance level in the F-test was <0.0001.

[0098] Using a linear regression model, response surfaces of toner coagulation rate were generated as a function of additive particle size and RTA at toner surface coverage rates of 15%, 30%, and 45% (Figure 8; solid lines are the functions generated by the model; dotted lines on either side indicate confidence limits). The response surfaces show that the lowest coagulation rate is expected when the model toner is mixed with additives having an RTA of 0.060–0.120. The results show that the coagulation rate increases with increasing particle size and decreasing surface coverage rate. Figure 9 shows plots of coagulation rate against surface coverage rate for toners produced using composite particles having the properties described in Examples 2A (dotted line) and 8B (solid line). The average RTA of the samples produced by Example 8B is higher than the average RTA for Example 2A, indicating that increasing RTA decreases coagulation rate and increases free flow.

[0099] The prior description of preferred embodiments of the present invention is provided for illustrative and explanatory purposes only. It is not intended to be exhaustive or to limit the invention to any express form disclosed. Modifications and changes are possible in light of the above teachings or can be obtained from the practice of the invention. The embodiments have been selected and described to illustrate the principles of the invention and the applications of the practice of the invention, so that those skilled in the art may utilize the invention in various embodiments and with various modifications suitable for the individual uses expected. The scope of the invention is intended to be defined by the claims appended herein and their equivalents.

Claims

1. A method for producing composite particles, A step of preparing an aqueous dispersion comprising silica particles and a first hydrophobic system comprising a bifunctional component and a monofunctional component, wherein the bifunctional component and the monofunctional component are covalently bonded to the silica particles; A step of adding a polymerization initiator to the aqueous dispersion to form silica-polymer composite particles, wherein the polymer matrix of the silica-polymer composite particles is the polymer or copolymer of the first hydrophobic system, and at least a portion of the silica particles protrudes inward and outward from the polymer matrix; and Drying process to dry the silica-polymer composite particles to form a powder. A method comprising the above, wherein the composite particles have a volume-weighted median particle size D50 of 40 to 75 nm or 100 to 150 nm, an average relative trough area (RTA) of at least 0.06, and an average SF-1 of 110 to 185.

2. The method according to claim 1, further comprising the step of treating the silica-polymer composite particles with a second hydrophobic agent before or after the drying step to produce hydrophobic silica-polymer composite particles.

3. The aforementioned monofunctional component is given by formula (OR 1 ) 4-z SiR 4 z It has R 1 is methyl or ethyl, z is 1 or 2, R 4 The method according to claim 1 or 2, wherein is a branched or unbranched C1-C10 alkyl group.

4. The bifunctional component has the formula [R 3 3-x (OR 1 ) x SiR 2 Q, where x is 1, 2 or 3, R 1 is methyl or ethyl, R 2 is an alkyl linker having the general formula C n H 2n , n is from 1 to 10, R 3 is methyl or ethyl, and Q is a substituted or unsubstituted vinyl, acrylate ester or methacrylate ester group, provided that when Q is a substituted or unsubstituted vinyl, n is from 2 to 10. The method according to any one of claims 1 to 3.

5. The method according to any one of claims 1 to 4, wherein the dispersion comprises one or more of styrene, substituted or unsubstituted acrylate or methacrylate monomers, olefin monomers, vinyl esters, or acrylonitrile.

Images