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] The present invention relates to the control of the particle size, morphology, and triboelectric charging of metal oxide-polymer composite particles.

Background Art

[0002] The formation of 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 reflects a charge pattern, i.e., information to be transferred to the 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, e.g., paper; fixing the image on the substrate; and removing residual electrostatic charge and cleaning residual toner particles from the photoreceptor drum to prepare the photoreceptor surface for the next cycle.

[0003] Toner for use in electrophotography and electrostatic printing contains a binder resin and a colorant, and may further contain a charge control agent, an anti-offset agent, and other additives. To improve the selected properties of the toner particles, including fluidity, transferability, adhesiveness, and cleaning characteristics, external additives for the toner, such as metal oxide particles, are often combined with the toner particles. Various external additives may be used in one toner composition to improve various properties of the toner. For example, some additives may be selected to improve the chargeability, i.e., triboelectric chargeability. Others may be selected to improve the cleaning performance or moisture resistance. Naturally, it is preferable that a toner additive optimized for one function does not adversely affect the functions imparted by various additives.

[0004] One function imparted by the toner additive is maintenance of fluidity and spacing. When toner particles adhere to each other, the toner particles do not flow well; the additive acts to reduce aggregation of the toner powder. Additive particles tend to be hard. On the other hand, toner is formed from a softer polymer. Agglomeration of the resulting toner particles is detrimental to both the operation of the electrophotographic apparatus and the quality of printing. In practice, when manufacturers have tried to reduce the energy required to create the printed pages, they have switched to softer polymers (e.g., polymers with a lower Tg) to reduce the amount of heat required to fix the toner to the substrate. However, hard additive particles may become embedded in the softer 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 rate 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 into and limited drop-off from the toner particles. Here, it is desirable to further manipulate the roughness, shape, and particle size of the metal oxide composite particles to improve the free-flow performance of the metal oxide composite particles and to manipulate their triboelectric charging characteristics and refractive index. SUMMARY OF THE INVENTION

[0005] In one aspect, 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 hydrophobization 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 to 75 mm and an average RTA of at least 0.06, such as 0.06 to 0.019, 0.08 to 0.015 or 0.08 to 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 hydrophobization 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 to 150 nm and an average RTA of at least 0.06, such as 0.06 to 0.019, 0.08 to 0.015 or 0.08 to 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 coarseness greater than 1.22, such as 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 by a second hydrophobizing agent. The metal oxide-polymer composite particles may contain at least 15% metal oxide.

[0008] The bifunctional component may have 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, and R 2is an alkyl linker having the general formula C n H 2n , where n ranges 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 ranges from 2 to 10. The first hydrophobization 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, and 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 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 hydrophobization 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 portion 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 charging of the toner under LL conditions is at least 10% greater than the triboelectric charging of a toner comprising a control metal oxide-polymer composite in which a monofunctional component has been replaced by a bifunctional component. Both the monofunctional component and the bifunctional component may contain a silane group. The monofunctional component may have the formula (OR 1 ) 4-z SiR 4 z wherein R 1 is methyl or ethyl, z is 1 or 2, and R 4 is a branched or unbranched C1-C10 alkyl group. The solubility of the monofunctional component may be from 10 to 0.06 g / L, preferably from 9 to 0.03 g / L, more preferably from 8 to 0.1 g / L, and most preferably from 7 to 0.5 g / L.

[0012] In another aspect, a method of manufacturing composite particles comprises preparing an aqueous dispersion comprising metal oxide particles and a first hydrophobizing system comprising a bifunctional component and a monofunctional component, the aqueous dispersion in which 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 the surface, wherein the polymer matrix of the metal oxide-polymer composite particles is a polymer or copolymer of the first hydrophobizing system; and a drying step of drying the metal oxide-polymer composite particles to form a powder.

[0013] The method further comprises, before or after the drying step, treating the metal oxide-polymer composite particles with a second hydrophobizing agent to produce hydrophobized metal oxide-polymer composite particles. Both the monofunctional component and the bifunctional component may contain a silane group. The monofunctional component may have the formula (OR 1 ) 4-z SiR 4 z wherein R 1 is methyl or ethyl, z is 1 or 2, and R 4 is a branched or unbranched C1-C10 alkyl group. The bifunctional component has the formula [R3 3-x (OR 1 ) x SiR 2 may have Q, 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 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 dispersion may further contain one or more of styrene, a substituted or unsubstituted acrylate or methacrylate monomer, an olefin monomer, a vinyl ester or acrylonitrile. The solubility of the monofunctional component may be from 10 to 0.06 g / L, preferably from 9 to 0.03 g / L, more preferably from 8 to 0.1 g / L, and most preferably from 7 to 0.5 g / L.

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

[0015] The first hydrophobization system may further comprise a monofunctional component covalently bonded to the metal oxide particles, such as silane. 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 monofunctional component has the formula (OR 1 ) 4-z SiR 4 z , where R 1is methyl or ethyl, 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.

[0016] The volume-weighted median particle size D50 of the first group and the second group may have a ratio of about 40:1 to about 1.5:1. The width of the volume-weighted particle size distribution, as described by the ratio D75 / D25, for the first group and the second group may have a ratio of 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, such as 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 may have an average roughness P 2 / 4πS, where P is the perimeter of the image of the metal oxide-polymer composite particles and S is the area of the particle image, and both P and S are determined from a transmission electron micrograph. The polymer matrix may include polymers of styrene, unsubstituted or substituted acrylates or methacrylates, olefins, vinyl esters, and acrylonitrile, as well as copolymers and mixtures of the foregoing. The composite particles can be disposed on the surface of toner particles to form a toner composition.

[0017] In another aspect, a method for producing metal oxide-polymer composite particles is an aqueous dispersion including a first hydrophobization 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 hydrophobization system has the formula [R 3 3-x (OR 1 ) x SiR 2Contains a bifunctional component having Q, where x is 1, 2 or 3, and R 1 is methyl or ethyl, and R 2 is an alkyl linker having the general formula C n H 2n where n is from 1 to 10, and 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; a preparation step of preparing an aqueous dispersion; a step of keeping the dispersion warm for a predetermined time; a step of adding a radical initiator to the dispersion; a forming step of making a chemical group of a first hydrophobization system part of the polymer, thereby forming metal oxide-polymer composite particles; and a step of drying the metal oxide-polymer composite particles to obtain a powder.

[0018] The method may further include a step of treating at least a part of the metal oxide particles with a second hydrophobizing agent, and the treatment step can be carried out before the preparation step of the metal oxide-polymer composite particles or after the forming step. The first hydrophobization system may further include a monofunctional component having the formula (OR 1 ) 4-z SiR 4 z where R 1 is methyl or ethyl, 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 a C1-C10 branched or unbranched alkyl, halogen, C1-C10 alkyl ether, methoxy, ethoxy or hydroxy. The D50 of the first group and the second group may have a ratio of about 40:1 to about 1.5:1. The ratio D75 / D25 for the first group and the second group may have a ratio of about 40:1 to about 1.1:1. The mass ratio of the first group to the second group may be from 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 part of each group of metal oxide particles may protrude inwards and outwards 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 true density of the metal oxide-polymer composite particles is about 30% to about 90% of the true density of the metal oxide when measured by the helium pycnometer method. 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 may have an average roughness P 2 / 4πS may be.

[0020] It is understood that the foregoing general description and the following detailed description are merely exemplary and explanatory and are intended to provide further explanation of the claimed invention.

[0021] The present invention will be described with reference to a plurality of figures of the drawings.

Brief Description of the Drawings

[0022]

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Figure 9

Mode for Carrying Out the Invention

[0023] In one embodiment, the production of metal oxide-polymer composite particles using a first hydrophobization system comprising a bifunctional component and an alkyl-based monofunctional component results in particles that can increase the triboelectric charging of the toner 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, for example 40 - 70 nm or 40 - 65 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, improve the free-flow properties of the toner 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 the anti-blocking property in the toner composition while improving the free flow with respect to smoother spacer particles.

[0026] In another embodiment, the toner composition includes toner particles mixed with a powder including metal oxide-polymer composite particles including 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 hydrophobization system including 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 protrude in and out of a polymer matrix that is a polymer or copolymer of the first hydrophobization system. Such a mixture of two or more groups of metal oxide particles enables the manipulation of the particle size, particle coarseness, and shape of the resulting composite particles, as shown in FIG. 1A. In FIG. 1A, combinations of the first group of metal oxide particles 10 with larger metal oxide particles 12 or smaller metal oxide particles 14 enable 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 shows the weight ratio of metal oxides (10, 12, and 14) to matrix material 16.

[0027] Metal oxide particles suitable for use in the present invention include silica, alumina, ceria, molybdenum oxide, titania, zirconia, zinc oxide, magnetite (Fe 3 O 4 ) and various forms of Fe 2 O 3It includes iron oxides, niobium oxides, vanadium oxides, tungsten oxides, tin oxides, clays, or mixtures or mixed oxides of any two or more of these, but is not limited thereto. For use as an external additive for toner, typically, the metal oxide particles contain at least one of silica, alumina, and titania, such as 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 specific metal oxide, such as silica particles, may have a bimodal or multimodal particle size distribution. Of course, 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 particles of two different particle sizes are used, their volume-weighted median particle sizes D50 may have a ratio of about 40:1 to about 1.5:1, such as about 35:1 to about 2:1, about 25:1 to about 2.5:1, about 20:1 to about 3:1, about 15:1 to about 4:1, or about 10:1 to about 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 the particle sizes corresponding to the peaks of the particle size distribution may be similar to those described above. Alternatively or in addition, two or more metal oxide particles may have similar D50 while having different shapes. Alternatively or in addition, different metal oxide particles may have similar D50, but their particle size distributions may have different widths. One indicator of the width of the particle size distribution is the ratio D75 / D25, which is the ratio of the particle size at which 75% of the particles are smaller in volume to the particle size at which 25% of the particles are smaller in volume. The ratio of the widths of the particle size distributions may be from 40:1 to 1.1:1 for two different particle sizes when measured by D75 / D25.

[0029] Suitable particles include, but are not limited to, precipitated, colloidal, and pyrogenic metal oxide particles. The 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 manufactured using prior art techniques and are often formed from an aqueous medium under the influence of high salt concentration, acid, or other aggregating agents by aggregation of the desired particles. The metal oxide particles are filtered, washed, dried, and separated from the residues of other reaction products by prior art techniques known to those skilled in the art. The precipitated particles are often aggregated in the sense that many primary particles aggregate with each other to form somewhat spherical aggregated clusters. Non-limiting examples of commercially available precipitated metal oxides include the Hi-Sil® products of PPG Industries, Inc. and the Zeosil® products available from Evonik Corporation.

[0031] The production of fumed metal oxides is a well-documented process that involves the hydrolysis of a suitable feedstock vapor (e.g., aluminum chloride for fumed alumina or silicon tetrachloride for fumed silica) in a flame of hydrogen and oxygen. Slightly spherical molten particles are formed in the combustion process, and the particle size can be varied through control of the process parameters. These molten globules, also referred to as primary particles, fuse together by undergoing collisions at their points of contact to form branched three-dimensional chain-like aggregates. The formation of aggregates is thought to be irreversible as a result of the fusion between primary particles. During cooling and collection, the aggregates can undergo further collisions that result in some mechanical entanglement to form agglomerates. These agglomerates are thought to be loosely bound by van der Waals forces and can be redispersed, i.e., deagglomerated, by suitable dispersion in a suitable medium. Mixed or cofumed metal oxide particles can also be produced using prior art known to those skilled in the art, including, for example, the prior art described in British Patent Application Publication No. 2296915 to Ettlinger et al., the entire specification of which is incorporated herein by reference.

[0032] Alternative metal oxide morphologies can be obtained using the methods disclosed in U.S. Pat. Nos. 4,755,368, 6,551,567, and 6,702,994, U.S. Patent Application Publication No. 2011 / 0244387, 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, 2012, pp. 179-182, the entire contents of which are incorporated by reference. Typically, these methods result in metal oxide particles having low structure and small surface area. Many of these particles are pyrophoric, i.e., they are produced in a flame. Other methods for producing pyrophoric particles are disclosed, for example, in Kodas and Hampden-Smith, Aerosol Processing of Materials, Wiley-VCH, 1998. Suitable pyrophoric metal oxides for use in the composite particles provided herein are small, e.g., having a volume average diameter of less than 200 nm.

[0033] Colloidal metal oxide particles are often non-aggregated, individually separated (primary) particles, typically spherical or substantially spherical in shape, but may have other shapes (e.g., having a substantially elliptical, square or rectangular cross-section). Colloidal metal oxides are commercially available or can be prepared by known methods from various starting materials (e.g., wet process type metal oxides). Typically, colloidal metal oxide particles are produced in a manner similar to that of precipitated 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 silicate solution having a pH of about 9 to about 11, and the silicate anions undergo polymerization to yield separated silica particles having a desired particle size in the form of an aqueous dispersion. Typically, colloidal metal oxide starting materials can be utilized as sols, which are dispersions of colloidal metal oxides in a suitable solvent, and in many cases, the suitable solvent is water alone, or water with a co-solvent and / or stabilizer. For example, "Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range" by Stoeber et al., Journal of Colloid and Interface Science, 26, 1968, pp. 62 - 69, "Silica Nucleation, Polymerization, and Growth Preparation of Monodispersed Sols" by Akitoshi Yoshida, Colloidal Silica Fundamentals and Applications, pp47 - 56 (edited by H.E. Bergna & W.O. Roberts, CRC Press: Boca Raton, Florida, 2006), and "The Chemistry of Silica" by Iler, R.K., p866 (John Wiley & Sons: New York, 1979) See alsoNon-limiting examples of commercially available colloidal metal oxides suitable for use in the present invention include SNOWTEX® products from Nissan Chemical, LUDOX® products available from W.R. Grace & Co., NexSil™ and NexSil A™ series products available from Nyacol Nanotechnologies, Inc., Quartron™ products available from Fuso Chemical, and Levasil® products available from AkzoNobel.

[0034] The colloidal metal oxide particles may have a (volume weighted) median particle size D50 of from about 5 to about 300 nm, such as from about 5 to about 10 nm, from about 10 to about 20 nm, from about 20 nm to about 30 nm, from about 30 to about 50 nm, from about 50 to about 70 nm, from about 70 to about 100 nm, from about 100 nm to about 125 nm, from about 125 nm to about 150 nm, from about 150 nm to about 175 nm, from about 175 nm to about 200 nm, from about 200 nm to about 225 nm, from about 225 nm to about 250 nm, from about 250 nm to about 275 nm or from about 275 nm to about 300 nm. Of course, 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 from about 1.5 to about 3, such as from about 1.5 to about 1.8, from about 1.8 to about 2.1, from about 2.1 to about 2.5, from about 2.5 to about 2.8 or from about 2.8 to about 3. The particle size is measured by disc centrifuge photosedimentation analysis or transmission electron microscopy according to the dispersion of the particles described in the examples below.

[0035] In one embodiment of manufacturing composite particles, the metal oxide particles are treated with a first hydrophobization system. The first hydrophobization system may include one or more hydrophobizing components. Preferably, the first hydrophobization system includes at least one bifunctional component, such as silane, having a first reactive group capable of covalently or non-covalently bonding to the metal oxide particles, and a second reactive group capable of being incorporated into the polymer of the metal oxide-polymer composite particles. In certain embodiments, the bifunctional component has a molecular weight less than 300. "Hydrophobic" metal oxide particles, as the term is used herein, include varying the level or degree of hydrophobicity. The degree of hydrophobicity imparted to the metal oxide particles varies depending on the type and amount of the treating agent used. Hydrophobic metal oxide particles for use according to the present invention may have, for example, from about 15% to about 85% of the available metal oxide surface's reacted hydroxyl groups, such as from about 25% to about 75% or from about 40% to about 65% of the available metal oxide surface's reacted hydroxyl groups, or percentages within any range bounded by any two of the upper endpoints. When a second hydrophobizing agent is used as discussed below, it reacts to form a covalent or non-covalent bond with a portion of the hydroxyl groups on the surface of the metal oxide.

[0036] 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 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 from 2 to 10. The first hydrophobization system has the 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, where 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 from 10 to 0.06 g / L, preferably from 9 to 0.03 g / L, more preferably from 8 to 0.1 g / L, and most preferably from 7 to 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 is a branched or unbranched C1-C10 alkyl group. R 4 When is a branched or unbranched C1-C10 alkyl group, the triboelectric charging of the metal oxide-polymer composite particles is higher compared to when other R 4 groups are used, or when no monofunctional component is used at all. For example, the magnitude of the triboelectric charging of a toner using the above metal oxide-polymer particles as an external additive under low temperature / low humidity (LL) conditions is at least 10%, for example up to 45%, for example 12% - 42%, 15% - 40%, 17% - 37%, 20% - 35%, 23% - 32% or 25% - 30% higher than that of a toner having metal oxide-polymer composite particles containing no monofunctional component. Alternatively or in addition, the magnitude of the triboelectric charging of such a toner under high temperature, high humidity (HH) conditions is at least 9%, for example up to 33%, for example 12% - 30%, 15% - 28% or 17% - 25% higher than that of a toner having metal oxide-polymer composite particles containing no monofunctional component. Typically, the triboelectric charging under both HH and LL conditions changes with the addition of an alkyl-containing monofunctional component, and the change in triboelectric charging under HH and the change under LL can be any combination of ranges selected from the above list.

[0039] In addition, at least a part of the metal oxide particles can be treated with a second hydrophobizing agent either before or after treatment with the first hydrophobizing system, or after the formation of the metal oxide-polymer composite particles, in which case only the exposed surface of the metal oxide particles is treated. Preferred agents for use as the second hydrophobizing agent are silazane compounds, siloxane compounds and silane compounds, and silicone fluids having some solubility in water, with or without a co-solvent. A mixture of two or more agents can be used. Preferably, the silicone fluid for use as the second hydrophobizing 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 selected from the group consisting of branched and straight-chain alkyl, alkenyl, C 1 ~C 30 branched and straight-chain alkyl, alkenyl, C 3 ~C 10 cycloalkyl and C 6 ~C 10 aryl, and R’’ is a branched or straight-chain alkyl of C 1 ~C 10 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.

[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] represented by, R 7 and R 8 are independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, aryl and aryloxy; R 9 is hydrogen, (CH 2 ) r CH 3 (where r is an integer from 0 to 3), C(O)(CH 2 ) r CH 3 (where r is an integer from 0 to 3), C(O)NH 2 , C(O)NH(CH 2 ) r CH 3 (where r is an integer from 0 to 3) and C(O)N[(CH 2 ) r CH 3 (CH 2 ) s CH 3 (where r and s are integers from 0 to 3); R 10 is represented by the formula [(CH 2 ) a (CHX) b (CYZ) c , X, Y and Z are independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, aryl and aryloxy, and a, b and c are integers from 0 to 6 satisfying the condition that (a + b + c) is equal to an integer from 2 to 6. The cyclic silazane is of the formula: [Chemical formula] may be a 5- or 6-membered ring having, R 11 is represented by the formula [(CH 2 ) a (CHX) b (CYZ) c , X, Y and Z are independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, aryl and aryloxy, and a, b and c are integers from 0 to 6 satisfying the condition that (a + b + c) is equal to 3 or 4.

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

[0042] Alternatively or in addition, the metal oxide particles can be treated using the dimethylsiloxane copolymers disclosed in U.S. Patent Publication No. 2011 / 0244382, the content of which is incorporated herein by reference. Exemplary dimethylsiloxane copolymers have the formula:

Chemical formula

[0043] Alternatively or in addition, the second hydrophobizing agent may be a charge modifier. Any of the charge modifiers disclosed in U.S. Patent Publication No. 2010 / 0009280, the contents of which are incorporated herein by reference, can be used here. Exemplary charge 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). Charge modifiers containing nitro groups should be used after the copolymer to post-treat the metal oxide particles, as the hydrogenated groups may reduce the nitro groups.

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

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

[0046] The polymer used in the metal oxide-polymer composite particles may be the same as or different from the polymer or copolymer of the first hydrophobization system. That is, if the first hydrophobization 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 bifunctional component is not a polyether. Instead or in addition, the polymer of the bifunctional component is a polymer of acrylate or methacrylate. Instead or in addition, a crosslinking agent or a different monomer that can copolymerize with end groups can be used for the bifunctional component. Suitable monomers that can be used to produce the metal oxide-polymer composite particles include substituted and unsubstituted vinyl and acrylate (including methacrylate) monomers, and other monomers that polymerize 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 a mixture to form a copolymer. Exemplary crosslinking agents include divinyl end-type of bifunctional components (e.g., silanes substituted by vinyl groups) or other well-known vinyl crosslinking agents, such as divinylbenzene and ethylene glycol dimethacrylate. Instead or in addition, the copolymer or crosslinking agent can react with silane. For example, a silanol-terminated siloxane polymer or the copolymer of the above formula (1) can be used in combination with the first hydrophobization system. The comonomer or crosslinking agent can be added simultaneously or at a different time from the first hydrophobization system. The amount of the crosslinking agent can be adjusted to control the degree of crosslinking in the final polymer.

[0047] The metal oxide-polymer composite particles can be produced by creating a dispersion of metal oxide particles in a fluid comprising a first hydrophobization system, an optional monomer, and an aqueous phase. Polymerization of the polymerizable species of the organic phase results in the composite particles. In one exemplary procedure, in an aqueous medium, such as in water having an optional co-solvent, such as an alcohol, such as isopropyl alcohol, a first hydrophobization system, an optional comonomer, a crosslinking agent, and metal oxide particles are used in a ratio of about 0.5:40, such as 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 in terms of mass (polymerizable species / metal oxide) to prepare an emulsion or a mixture. The total amount of the metal oxide particles and the polymerizable species relative to the total amount of the solvent may be about 5 wt% to about 45 wt%, such as 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 about 8.0 - 10 and the dispersion is stirred for between 1 - 3 h (typically) while maintaining the temperature at 25 - 60 °C. Following the stirring, an initiator is introduced at a level of about 0.1 - about 4 wt% relative to the monomer, for example at levels of about 0.1 - about 0.5%, about 0.5% - about 1%, about 1% - about 1.5%, about 1.5% - about 2%, about 2% - about 2.5%, about 2.5% - about 3%, about 3% - about 3.5% or about 3.5% - about 4%. The initiator can be introduced as a powder or as a solution in ethanol, acetone or other water-miscible solvents. Suitable initiators include, but are not limited to, oil-soluble azo or peroxide thermal initiators such as 2,2'-azobis(2-methylpropionitrile) (AIBN), benzoyl peroxide, tert-butyl peracetate and cyclohexanone peroxide. Various suitable initiators are available from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). The initiator can dissolve in the monomer prior to the introduction of the metal oxide and can partition between the monomer and the aqueous phase. The resulting solution is held at 65 - 95 °C for 4 - 6 h with stirring. The resulting slurry can be dried overnight at 100 - 130 °C and the remaining solid ground to form a powder. Other methods of separating the particles from the liquid can also be used to dry the particles. If a second hydrophobizing agent is added after the formation of the metal oxide-polymer composite, it is introduced prior to the drying step. For example, a second hydrophobizing agent may be added and the slurry is further stirred while being held at 60 - 75 °C for 2 - 4 h.

[0049] Those skilled in the art in this field recognize that, in addition to the particle size and shape of two or more groups of metal oxide particles and their ratios to each other in the reaction mixture, changes in such solid loading in the mixture or emulsion, the ratio of polymer and metal oxide, the pH of the aqueous phase, and the holding temperature affect the morphology of the composite particles. In practice, for a given diameter of metal oxide-polymer composite particles, significant changes in the metal oxide particle size and the solid loading in the mixture or emulsion can be used to adjust the shape and particle coarseness of the composite particles. In certain embodiments, the composite particles have metal oxide particles disposed within the composite particles, i.e., completely within the polymer phase, as well as metal oxide particles protruding from the surface. In these embodiments, the metal oxide particles contribute to the mechanical strengthening of the composite particles and increase the compressive strength of the composite particles.

[0050] The degree of surface treatment of the metal oxide by the first hydrophobization system can be controlled by adjusting the pH and temperature of the starting solution. The adsorption rate of the bifunctional component and any monofunctional component to the metal oxide particles (which can then adsorb following the formation of siloxane bonds between the surface and each component) can also be controlled by the choice of leaving group in the silane-based bifunctional or monofunctional component; for example, ethoxy tends to hydrolyze more slowly than methoxy.

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

[0052] Regardless of the particle size distribution of the metal oxide particles, the roughness of the metal oxide-polymer composite particles can be adjusted by changing the reaction conditions. Generally, for example, increasing the pH of the reaction mixture by adding ammonium hydroxide or using a base-stabilized metal oxide dispersion increases the particle roughness or RTA. Decreasing the solid loading in the reaction medium also increases the particle roughness 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 can be from about 1:20 to about 20:1 by mass, such as 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 particles 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 in the polymer portion of the composite particles. Alternatively or in addition, at least a portion of the metal oxide particles may be partially embedded in the polymer portion of the composite particles, i.e., a portion of the metal oxide particles protrudes in and out 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%, such as 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 and the ratio of the particle size distribution (described as D75 / D25) or median particle size D50 of one or more groups of metal oxide particles.

[0055] The metal oxide-polymer composite particles may be round. Depending on the degree to which the metal oxide particles are exposed on the surface of the composite particles, the round particles need not be spherical and are typically understood to have a "bumpy" surface. Instead, the use of two groups of metal oxide particles having a large particle size difference also results in the formation of non-equiaxed particles. Such particles combine an irregular shape with a high particle roughness.

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

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

[0058] The particle roughness is P 2It can be calculated as / 4πS (John C. Russ, The Image Processing Handbook, CRC Press, 4th edition, 2002). FIG. 1B illustrates that the particle roughness can be considered as the ratio of the area of the virtual circle 24 having the same perimeter length as the perimeter 26 of the particle 28 to the area of the actual particle. The roughness of an ideal spherical particle is 1.0. However, the particle roughness of spherical particles with a rough surface may significantly exceed 1. The particle roughness is particularly sensitive to roughness and surface texture at a very fine scale. Since the formula for particle roughness includes both the perimeter and the image area, the particle roughness further indicates the deviation of the particle shape from a spherical shape, especially. For example, the particle roughness for an ellipse having axes 1 and 2 is 1.19, and for an ellipse having axes 1 and 3 is 1.51. Therefore, the particle roughness increases with an increase in surface roughness and an increase in the deviation of the particle shape from a spherical shape. 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 the 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 outer shell 30 around the image of the particle and determine the area C inside the outer shell, called the "hull area". The convex outer shell is a curved convex that shows the boundary of the surface surrounding the entire particle. It is created by moving a pair of parallel lines until they just touch the outside of the particle image. Then, the angle of the parallel lines is changed, and the process is repeated until the entire path of the convex outer shell is defined. As shown in Figure 1B, the convex outer shell is similar to a rubber band stretched around the particle. The relative trough area (RTA) is defined by (C - S) / S, where S is the particle image area. The value of RTA increases with an increase in the protrusions from the surface. The RTA of a perfect sphere, ellipse, or any outer shell object is 0. The RTA of typical non-aggregated colloidal silica is about 0.01. The average RTA of metal oxide-polymer composite particles may be from 0.01 to about 0.19, such as from about 0.03 to about 0.15, from about 0.05 to about 0.13, or from about 0.07 to about 0.11. To promote the free flow of the toner, preferably, the average RTA is greater than 0.06 or 0.08, such as from 0.06 to 0.13. The average RTA is measured using the images of at least 100 particles, preferably at least 500 particles. Of course, using more particle images provides higher sensitivity and facilitates the discrimination of different particle morphologies.

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

[0061] Alternatively or additionally, the metal oxide-polymer composite particles may have a (volume weighted) median particle size or particle diameter D50 of from 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 centrifugal photosedimentation analysis.

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

[0063] To improve the anti-blocking property and prevent toner particles from adhering to each other, preferably, the metal oxide-polymer composite particles have a D50 of 100 to 150 nm, such as 105 to 150 nm or 110 to 150 nm, an average RTA of at least 0.06 or at least 0.08, such as 0.06 to 0.019, 0.08 to 0.015 or 0.08 to 0.13, and instead of or in addition, an average particle roughness of at least 1.22, such as at least 1.25 or at least 1.3, such as 1.25 to 1.60 or 1.70 or 1.22 to 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 is improved, weakening the effect of the increased size and optimizing the composite particles to maintain the anti-blocking property and the free-flow performance.

[0064] Preferably, the metal oxide-polymer composite particles have a density lower than the inherent density of the metal oxide itself (for example, silica has an inherent density of 2.2 g / cm 3 and titanium dioxide has a density of 3.6 g / cm 3 . For example, the inherent density of the composite particles can 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 inherent density of the metal oxide contained therein. The density can be measured by the helium pycnometer method. In some embodiments, by using metal oxide particles of different particle sizes in the composite, the particle size and shape of the composite particles can be changed while maintaining the desired density. Maintaining the desired density enables those skilled in the art to reduce or maintain the 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 an external additive for both conventional toners and chemical toners. Conventional toners can be prepared by mixing and heating, in a conventional melt extrusion apparatus and associated equipment, many known methods, such as resins, pigment particles, optional charge enhancing additives, and other additives. Conventional equipment for dry blending of powders can be used to mix or blend carbon black particles with a resin. Other methods include spray drying and the like. Generally, after the formulation of pigments and other raw materials with a resin, mechanical attrition and classification are carried out to provide toner particles having a desired particle size and particle size distribution. Chemical toners, also known as chemically prepared toners, are manufactured in the liquid phase; generally, resin particles are formed in the presence of a colorant. For example, processes have been developed in which a 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 a pigment in at least one monomer. Further, a pigment / polyester resin dispersion is prepared, combined with water, and then the solvent is evaporated.

[0066] For both conventional toners and chemically prepared toners, the metal oxide-polymer composite particles can be combined with toner particles in the same manner 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 the metal oxide-polymer composite particles with toner particles having a suitable particle size in a blender. Alternatively or in addition, the metal oxide-polymer composite particles can be dry blended with the toner particles to form core-shell composite particles using a Henschel or other suitable mixer, such as the mixers described in U.S. Patent Nos. 9,470,993, 9,500,970, 9,575,425, JP 2019-095616 A, 2018-045006 A, or 2018-036596 A, to combine them with the toner for use as an external additive. Alternatively, a dispersion of the metal oxide-polymer composite particles can be combined with the toner particles by a wet blending method, such as the method disclosed in WO 2014 / 153355. For example, the toner can be sonicated with the dispersion of the composite particles until a well-mixed dispersion is obtained. The toner particles having the metal oxide-polymer particles disposed or distributed on the surface of the toner particles can then be recovered from the dispersion, for example, by vortexing and drying, or by other methods of recovering the particles from the dispersion. Alternatively or in addition, the metal oxide-polymer composite particles can be combined with the toner simultaneously with other external additives, such as additional 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 of ordinary skill 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 of ordinary skill 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 toners. Typically, fumed silica and other inherently hydrophilic materials are rendered hydrophobic for use as toner additives.

[0067] In certain embodiments, the metal oxide-polymer composite particles constitute from about 0.5 wt% to about 7 wt% of the toner composition, such as from about 0.5 wt% to about 1 wt%, from about 1 wt% to about 1.5 wt%, from about 1.5 wt% to about 2 wt%, from about 2 wt% to about 2.5 wt%, from about 2.5 wt% to about 3 wt%, from about 3 wt% to about 3.5 wt%, from about 3.5 wt% to about 4 wt%, from about 4 wt% to about 4.5 wt%, from about 4.5 wt% to about 5 wt%, from about 5 wt% to about 5.5 wt%, from about 5.5 wt% to about 6 wt%, from about 6 wt% to about 6.5 wt% or from about 6.5 wt% to about 7 wt% of the toner composition. The metal oxide-polymer composite particles can be distributed on the surface of the toner particles. Preferably, the surface coverage by the metal oxide-polymer composite particles is from about 10% to about 90% of the toner surface, such as 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%. A suitable surface coverage of the metal oxide-polymer particles on the toner depends on other materials further used as external additives, such as inorganic particles or polymer particles, and on the properties and composition of the toner and any carrier or developer 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 of the distribution of the composite particles on the toner, when measured by scanning electron microscope observation as described in U.S. Patent Application Publication No. 2015 / 0037719, the content of which is incorporated herein by reference, is less than 0.40, such as less than 0.30, such as from 0.05 to 0.15, from 0.10 to 0.20 or from 0.15 to 0.25.

[0068] Preferably, the metal oxide-polymer composite particles exhibit a low level of drop-off, which can improve the durability of the toner and improve print quality over long printing times. The retention of the composite particles on the toner particles depends in part on the composition of the toner, but surrogate tests can be used to compare the performance of the metal oxide-polymer composite particles with that of metal oxide particles of comparable particle size and shape. For example, tests similar to those described in U.S. Patent Application 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 using a Henschel mixer or other fluidized 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 the surface) during the development cycle of an electrophotographic process. The mechanical strength of the particles can be evaluated by formulating a chemical toner using the composite particles. The toner / particle formulation is then mixed with a carrier, such as a silicone-coated Cu-Zn ferrite carrier (particle size of 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% to about 90% and rotated in a stirrer called a three-dimensional mixer that can move the mixing container rhythmically with three-dimensional movement. The mixing container is moved at a rotational speed of about 50 to about 70 revolutions / min at a volume about 6 to about 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 three-dimensional mixer from Glen Mills. After a specified time, the sample is analyzed by SEM. If the composite particles have sufficient mechanical strength, the composite particles will not flatten or deform during mixing. Any flattening or deformation appears 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 min of mixing is less than 25%, preferably less than 20%, for example less than 10%.

[0070] Alternatively or in addition, the metal oxide-polymer composite particles can be used as a cleaning aid. The functions and methods of using the cleaning aid are discussed in U.S. Patent No. 6,311,037, the content of which is incorporated herein by reference. Briefly, after the image is printed, an elastic blade removes excess toner from the photoreceptor. The abrasive particles can facilitate more complete removal of the excess toner, which otherwise would transfer to subsequent copies and result in a "shadow" effect where faint images from previous copies appear in one or more subsequent copies. Generally, currently, two different types of particles are used as cleaning aids. Ground or precipitated inorganic particles (e.g., metal oxides, nitrides, carbides) have a hardness and shape suitable for abrasive cleaning applications. However, they have a broad particle size distribution. Larger particles may scratch the surface of the photoreceptor, and smaller particles may be less than the clearance between the cleaning blade and the photoreceptor. Colloidal silica has a uniform particle size but has limited cleaning ability due to its smooth surface. The metal oxide-polymer composite particles combine the advantages of both these particles - the metal oxide-polymer composite particles not only have an irregular surface interrupted by hard abrasive metal oxide particles but also have a narrow particle size distribution. The metal oxide-polymer composite particles for use as a cleaning aid can be incorporated into the toner formulation or may be contained in a separate storage container, and the metal oxide-polymer composite particles are transported from the storage container to the drum of the copying machine near the cleaning blade.

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

[0072] The metal oxide-polymer composite particle powder can be pulverized or milled, or can be classified by, for example, sieving, filtration, air classification or other methods known to those skilled in the art as described in JP-A-2018-036596. The degree of aggregation of the metal oxide-polymer composite particle powder is less than 70%, for example less than 60%, 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 type vibrator (Showa Sokki Co., Ltd). Sieves with openings of 38 μm (400 mesh), 75 μm (200 mesh) and 150 μm (100 mesh) are stacked in order from the bottom of the vibration table of the powder tester. The measurement is carried out at 23 °C and 60% relative humidity (RH). The vibration amplitude of the vibration table is adjusted in advance so that the displacement value of the digital display type vibration meter is 0.60 mm (from peak to peak). The metal oxide-polymer composite particles are equilibrated at 23 °C and 60% RH for 24 h, and then 5.0 g is weighed and placed in the 150 μm sieve at the top stage of the powder tester. The sieve is vibrated for 30 s, and then the mass of the composite particles remaining on each sieve is measured, and the degree of aggregation is calculated based on the following formula. Degree of aggregation (%) = {(sample mass (g) on the sieve with an opening of 150 μm) / 5 (g)} × 100 + {(sample mass (g) on the sieve with an opening of 75 μm) / 5 (g)} × 100 × 0.6 + {(sample mass (g) on the 38 μm mesh sieve) / 5 (g)} × 100 × 0.2

[0073] Metal oxide-polymer composite particles can form toner in combination with toner particles. Conventional toner can be prepared by mixing and heating resin, pigment particles, optional charge enhancing additives and other additives in conventional melt extrusion equipment and related facilities by many known methods. Conventional equipment for dry blending of powders can be used to mix or blend carbon black particles with resin. Other methods include spray drying and the like. Generally, after compounding of pigments and other raw materials with resin, mechanical friction and classification are carried out to provide toner particles having a desired particle size and particle size distribution. Chemical toner, also known as chemically prepared toner, is manufactured in a liquid phase; generally, resin particles are formed in the presence of a colorant. For example, a process has been developed in which a 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 a pigment in at least one monomer. Further, a pigment / polyester resin dispersion is prepared, combined with water, and then the solvent is evaporated.

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

[0075] The present invention is further clarified by the following examples which are intended to be merely illustrative in nature.

Examples

[0076] To prepare samples for TEM, the particles in the aqueous dispersion were diluted with ethanol and sonicated for 10 min using a probe sonicator. Sufficient dilution and dispersion are required 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 at an accelerating voltage of 80 kV on a JEOL JEM-1200 EX Microscope. Typically, the resolution of the images was set to 2 nm / pixel for an image size of 2048 pixels × 2048 pixels. First, any non-uniform background of the image, if present, was calibrated using ImageJ software available from the National Institutes of Health, then the noise of the image was reduced and the contrast was enhanced using a suitable digital filter. The image was then segmented into two images with separated images of each individual particle. The particle size and shape of each particle were determined using the ImageJ particle analyzer and then combined to obtain the distribution of the shape and particle size of all the particles in the sample, excluding aggregates containing multiple primary composite particles. The values of SF-1, particle roughness, and RTA for the composite particles below are the averages from measurements of at least 500 particles; the values for colloidal silica are the averages from measurements of at least 100 particles.

[0077] To prepare samples for disk centrifugal photosedimentation analysis, a 0.05 wt% dispersion of the composite particles was prepared in reverse osmosis water containing 0.05 wt% Triton X-100 surfactant in a 15 mL glass vial. This was stirred for 20 min using a SMT UH-50 homogenizer with an output of 50 watts at 90% power using 3 mm along a 136 mm titanium tip placed 0.5 mm from the bottom of the vial.

[0078] To combine the toner with the composite particles, a silica-polymer composite particle was mixed with a black polyester chemical toner having a particle size of about 8 μm from Sinonar Corp. using an IKA M 20 Universal mill to achieve a total surface coverage rate of 30%. To prevent the toner from overheating and melting, it was carried out with a 15 s cooling period after three 15 s pulses.

[0079] The surface coverage rate C of the toner was calculated using the following relationship: C = [w / (100% - w)] × [(ρ t ×d t ) / (π×ρ a ×d a )] × [(√3) / 2], where w is the wt% of the additive, and ρ t , d t , ρ a , d a are the density (ρ) and diameter (d) of the toner and additive particles, respectively. The additive particle size was measured by disc centrifuge photosedimentation analysis (CPS), and the density of the additive was measured by the helium pycnometer method. The density of the toner was estimated to be 1.2 g / cm 3 , and the particle size was 8 μm.

[0080] The developer was prepared by mixing 2 parts by weight of the formulated toner with 98 parts of Cu-Zn ferrite carrier (carrier particle size 60 - 90 μm, Powdertech Co., Ltd.) coated with silicone resin. The developer was placed under the conditions of 30 °C and 80% relative humidity for several hours (corresponding to HH (high temperature / high humidity) conditions), or under the conditions of 18 °C and 20% RH (corresponding to LL (low temperature / low humidity) conditions). After being placed under the above conditions, triboelectrostatic charging was developed by rotating the jar containing the developer at 185 rpm for 30 min on a roll mill. The tribocharging 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 min using an air jet of about 20 psi. The electrostatic charging of the toner remaining in the Faraday cage carrier was measured by a potentiometer incorporated in the Vertex tester, and the mass of the blown-off toner was determined as the difference in the weights of the Faraday cage before and after blow-off.

[0081] The aggregation rate of the toner was measured using a Hosokawa PT-X powder tester. 2 g of the toner mixed with the additive was placed on the top sieve of a stack of three sieves (with mesh openings of 75, 45, and 25 μm), and the sieves were vibrated at an amplitude of 1.0 mm and a frequency of 50 - 60 Hz for 20 s. The aggregation rate was calculated according to the formula: Aggregation rate % = (M t / M init )+(M m / M init )×0.6+(M b / M init )×0.2×100%, where M t , M m and M b are the weights of the toner remaining on the top, middle, and bottom sieves, respectively, when the vibration stops, and M init 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 the composite particles by replacing larger ST-O40 colloidal silica with smaller ST-O colloidal silica. For Example 1A, a 3000 mL four-neck round-bottom flask equipped with an overhead stirring motor, condenser, and thermocouple above was filled with 909 mL of deionized water, 257 g of an 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 a 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 h. 2,2’-Azobisisobutyronitrile (further abbreviated as AIBN, CAS#78-67-1, Mw = 164.2) was added, and the temperature was raised to 80 °C in 30 min. After maintaining at 80 °C for 90 min, the reaction mixture was cooled to 65 °C and filtered through a 200-mesh screen to remove fragments of the clot. 23 g of 1,1,1,3,3,3-hexamethyldisilazane (HMDZ) was added to the mixture, and the reaction was continued at 65 °C for an additional 5 - 8 h. Then, the reaction mixture was transferred to a Pyrex tray and dried at 120 °C overnight.

[0083] Examples 1B to 1D were prepared according to the same procedure as described for Example 1A. The only difference is that a mixture of ST-O40 silica and ST-O silica (12 nm diameter, Nissan Chemical) is used (the silica is added sequentially to the reaction flask). Table 1 below contains information on the amounts of chemicals used. Using this method, particles having the median particle sizes described in the table below (as measured by disk centrifugal photosedimentation analysis) can be prepared. The change in particle size does not necessarily significantly change the particle roughness or RTA. For example, using the process of Example 1A, particles having an average SF-1 of 141 to 146, an average particle roughness of 1.29 to 1.32, and an average RTA of 0.092 to 0.097 can be prepared. Using the process of Example 1B, particles having an average SF-1 of 147 to 152, an average particle roughness of 1.27 to 1.30, and an average RTA of 0.090 to 0.096 can be prepared. Figures 2A and 2B show how 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 an increase in the 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 reagent amounts in Table 2 below to produce particles having the median particle sizes 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 arrow in Figure 3B points to the 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 with Irregular Shapes and Relatively Smooth Surfaces The process of Example 1 is used with ST-OL silica (particle size of 45 - 50 nm) instead of the silica described in Example 1 and at 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 with Irregular Shapes and Large Surface Roughness The process of Example 1, except without the addition of ammonium hydroxide, is carried out using Ludox AS-40 silica (WR Grace, 22 nm particle size, 40% solids in dispersion) instead of the silica described in Example 1, at a monomer-silica ratio of 2, and at a solids concentration of 5.4% in the reaction mixture, to produce particles such as those shown in FIGS. 5A and 5B. Using the process of this example, particles having an average SF-1 of 144 to 162, an average particle roughness of 1.49 to 1.65, and an average RTA of 0.108 to 0.142 can be prepared.

[0087] Example 5: Synthesis of Composite Particles Having Spherical Shapes and Various Surface Roughnesses A) The process of Example 1 can be carried out using ST-O40 silica and at a monomer-silica ratio of 3 to produce particles having a median particle size D50 of 115 to 140 nm, such as those shown in FIGS. 6A and 6B. Using the process of this example, particles having an average SF-1 of 116 to 119, an average particle roughness of 1.19 to 1.22, and an average RTA of 0.038 to 0.042 can be prepared.

[0088] B) The process of Example 1 can be carried out using ST-O silica and at a monomer-silica ratio of 1.25 to produce particles having a median particle size D50 of 45 to 70 nm, such as those shown in FIGS. 6C and 6D, but having a particle roughness considerably larger than that of the particles of Example 5A. 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 to 140, an average particle roughness of 1.22 to 1.25, and an average RTA of 0.079 to 0.086 can be prepared.

Table 3

[0089] Example 6 - Comparative Example 1 TEM images of spherical colloidal silica having a smooth particle surface, i.e., MP-1040 colloidal silica (Nissan Chemical Inc.), were collected 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 an alkylsilane as a monofunctional component in combination with a bifunctional component of a first hydrophobization system to increase the triboelectric charging of silica-polymer composite particles. For Examples 7A and B, 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 about 9.3. A mixture of 4.9 g of either a) 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 over 1 h and held at the same temperature for 1.5 h. Then 0.1 g of AIBN is added, the temperature is raised to 80 °C, and held for 1.5 h. 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 h. 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 milled in an IKA mill.

[0091] For Example 7C, a solution of 45 g of ST-O40 silica in 160 g of deionized water is stirred at room temperature and then 0.48 g of 5N ammonium hydroxide is added to bring the pH to about 9.3. A mixture of 11.5 g of diisopropyldimethoxysilane (DIPDMS) and 11.5 g of MPS is added all at once. The temperature is then raised to 40 °C over 1.5 h and held at the same temperature for 2 h. The temperature is then raised to 60 °C and the mixture is kept warm for 45 min. Then 0.5 g of AIBN is added, the temperature is raised to 75 °C and held for 2 h. The reaction mixture is cooled to 65 °C and then 4.3 g of hexamethyldisilazane is added and the mixture is kept warm at 65 °C for 6 h. 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.

[0092] Using these methods, samples formulated into toner at a coating rate of 30%, such as the samples in Table 4 below, can be produced. The column "Hydrophobicity" indicates that the sample does not wet at a methanol concentration lower than the stated ratio in a methanol-water solution, i.e., the material floats on the surface. In contrast, using the process of Example 1A, composite particles can be produced that can be used to produce toner having triboelectric charging under LL conditions of -52 to -50 and triboelectric charging under HH conditions of -22.5 to -21.5. This result shows that the use of alkylsilane in addition to MPS increases triboelectric charging, while the use of aromatic phenylsilane does not significantly increase triboelectric charging.

Table 4

[0093] Example 8 - Increase in particle roughness The method of Example 1, except without the addition of ammonium hydroxide, was used with Ludox AS-30 silica (WR Grace, 12 nm, 30% solids loading in dispersion) and Ludox AS-40 silica, using amounts of silica dispersion and water adjusted to maintain the solids loading and monomer-silica ratio to produce metal oxide-polymer composite particles having the characteristics in the table below (Table 5). Ludox silica was stabilized with ammonium hydroxide to raise the pH of the reaction mixture and increase the roughness of the resulting composite particles.

Table 5

[0094] Example 9 - Positively Charged Composite Particles Particles having the characteristics described in Examples 1A and 5B were further treated with cyclic silazane. 300 g of composite particle powder was placed in a 1 gallon Nalgene bottle and sprayed with a mixture of 4.3 g or 5.5 g of cyclic silazane each having the formula:

Chemical formula

[0095] Example 10 - Comparative Example As described in U.S. Patent No. 7811540, HMDZ was used with ST-XL and ST-YL silica (surface areas 60 m 2 and 45 m 2, Nissan Chemicals, Inc.) is processed to produce hydrophobic particles having about 10 molecules of HMDZ per 1 nm 2 of silica surface. As described in U.S. Patent No. 8455165, the same silica is treated with HMDZ and the cyclic silazane described in Example 9 to produce hydrophobic particles having 5 - 10 molecules of HMDZ and about 1.6 molecules of cyclic silazane per 1 nm 2 of silica surface. Before use in Example 11, the resulting powder was milled in an IKA A11 laboratory mill (IKA Corporation).

[0096] Example 11 - Agglomeration Rate Measurement Particles having the compositions and morphologies 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 having a particle size of 115 nm, an SF - 1 of 111, an average particle roughness of 1.23 and an average RTA of 0.0256) were made into toners having a coating amount selected from 15%, 30 - 32% and 45%. The agglomeration rate of the toners was measured in three ways.

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

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

[0099] The foregoing description of the preferred embodiments of the invention has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

1. Powder-form silica-polymer composite particles comprising a plurality of metal oxide particles and a polymer matrix, wherein the silica particles are surface-modified by a first hydrophobization system comprising a bifunctional component, through which the silica particles are covalently bonded to the polymer matrix; the polymer of the polymer matrix is a polymer or copolymer of the bifunctional component; and the silica-polymer composite particles have a 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, the composite particles.

2. The composite particles according to claim 1, wherein the composite particles have an average particle roughness greater than 1.

22.

3. The composite particles according to claim 1 or 2, wherein at least a part of the surface of the silica-polymer composite particles is modified by a second hydrophobizing agent.

4. The composite particles according to any one of claims 1 to 3, wherein the silica-polymer composite particles contain at least 15% metal oxide.

5. 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 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 2 to 10. The composite particles according to any one of claims 1 to 4.

6. The composite particles according to any one of claims 1 to 5, wherein the first hydrophobization system further comprises a monofunctional component covalently bonded to the silica particles.

7. wherein the monofunctional component has the formula (OR 1 ), 4-z SiR 4 z , 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 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. The composite particle according to claim 6.

8. A toner composition comprising the silica-polymer composite particles according to any one of claims 1 to 7 disposed on the surface of toner particles.

9. A toner composition comprising the silica-polymer composite particles according to claim 6 or 7 disposed on the surface of toner particles, wherein the triboelectrification of the toner under high temperature / high humidity (HH) conditions is at least 9% greater than the triboelectrification of a toner comprising a control silica-polymer composite in which the monofunctional component is replaced by the bifunctional component.

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