Toner additives

The disclosure relates generally to toner additives, and in particular, toner additives that provide desired higher toner charge and low relative humidity (RH) sensitivity. The toner additives comprise titania nanotubes or titania nanosheets in combination with or in place of the commonly used anatase or rutile crystalline titania.

BACKGROUND

The disclosure relates generally to toner additives, and in particular, toner additives that provide desired higher toner charge and low relative humidity (RH) sensitivity. The toner additives comprise titania nanotubes or titania nanosheets in combination with or in place of the commonly used anatase or rutile crystalline titania.

Toners can comprise at least a binder resin, a colorant and one or more external surface additives. The external surface additives can be added in small amounts. Examples of external surface additives include, for example, silica, titanium dioxide, zinc stearate and the like. The properties of a toner are influenced by the materials and amounts of the materials of the toner. The charging characteristics of a toner also can depend on the carrier used in a developer composition, such as, the carrier coating.

Toners having triboelectric charge within the range of about −30 μC/g to about −45 μC/g may be achieved by including smaller-sized silica particles as external additives, for example silica particles having average sizes of less than about 20 nm, such as, for example, R805 (˜12 nm) and/or R972 (˜16 nm) (Evonik, N.J.). However, developability at areas of low toner area coverage degrades over time. That has been attributed to the smaller-sized additives being impacted into the toner surface over time. The problem with smaller-sized additives may be addressed by using larger-sized additives, i.e., additives having a size of about 40 nm or larger such as, for example, RX50 silica, RX515H silica or SMT5103 titania (Evonik, N.J.). However, such toners do not exhibit as high a triboelectric charge and also exhibit charge through.

Thus, there remain problems with providing high charge with good relative humidity (RH) sensitivity of charge to changing environmental conditions for toner compositions. While many toners contain silica as a surface additive to provide high charge, silica is known to be RH sensitive. Hence, it is a goal to provide new toner additives that can improve RH sensitivity while maintaining high charge.

Surface additives also suffer from high additive impaction due to the small primary particle size of 7 to 160 nm. While impaction can be reduced by using larger particle sizes, the larger particle sizes cause the additive to be less adhered to the toner surface which can lead to contamination of other surfaces, such as the photoreceptor and BCR.

Thus, there is a need for new surface additives that can provide high charge, low RH sensitivity, and reduced additive impaction with improved adhesion of the additive to the toner surface.

SUMMARY

The present embodiments provide a toner composition comprising: toner particles comprising a resin and a colorant; and one or more surface additives applied to a surface of the toner particles, the one or more surface additives comprising titania nanotubes, titania nanosheets and mixtures thereof.

In specific embodiments, there is provided a toner composition comprising: toner particles comprising a resin and a colorant; and one or more surface additives applied to a surface of the toner particles, the one or more surface additives comprising titania nanotubes, titania nanosheets and mixtures thereof, wherein the toner composition has a high charge of from about −15 microcoulomb per gram to about −80 microcoulomb per gram and a low relative humidity sensitivity ratio of from about 1 to about 2.

In yet other embodiments, there is provided a developer comprising: a toner composition; and a toner carrier, the toner carrier comprising a carrier core, and a carrier coating disposed over the carrier core, wherein the toner composition comprises toner particles comprising a resin and a colorant, and one or more surface additives applied to a surface of the toner particles, the one or more surface additives comprising titania nanotubes, titania nanosheets and mixtures thereof.

DETAILED DESCRIPTION

The disclosure relates toner additives that provide desired higher toner charge and low relative humidity (RH) sensitivity. The toner additives comprise titania nanotubes (TiNTs) or nanosheets in combination with or in place of the commonly used anatase or rutile crystalline titania. These novel additives comprise tubular or sheets of tubular structures in which the particle may be spherical in one dimension and more linear in other dimensions.

Particulate titania and silica are the two commonly used xerographic toner surface additives. Silica is non-crystalline and has desirable properties of high charge, but suffers from high RH sensitivity, in part because of the high water adsorption of the silica hydroxyl groups. While silica is amorphous, titania has two tetragonal structures, anatase and rutile (i.e., cubic structures that are stretched in one crystalline direction), both characterized by a predominant [101] face, as shown inFIG. 1. These structures of the conventional additives are generally comprised of spherical particles or clumps of spherical particles, while some conventional rutile particulate additives can be comprised of isolated or bundles of acicular shaped crystals.

Particulate titania also is characterized by the [101] face being heavily covered by surface hydroxyl groups. Titania provides lower charge, but also improved RH sensitivity as compared to silica, although titania also has significant RH sensitivity. To address these problems, it has been common in toner developer designs to add both a titania and a silica to get a reasonable compromise for charge and RH sensitivity. However, even this solution has its problems. For example, the inclusion of silica makes it difficult to achieve an RH sensitivity that is anywhere close to the desired value of 1. However, without the silica the charge is too low.

Surface additives also suffer from high additive impaction due to the small primary particle size of 7 to 160 nm. While impaction can be reduced by using larger particle sizes, the larger particle sizes cause the additive to be less adhered to the toner surface which can lead to contamination of other surfaces, such as the photoreceptor and BCR. Thus, primary particles of 7 nm are most sensitive to impaction, while those of 150 nm are least sensitive to impaction but most likely to be lost from the toner particle.

Toner Additives

The present embodiments address the problems faced by conventionally used toner additives. The present embodiments provide a titania nanotube as a toner additive. These titania nanotubes have a different crystalline surface than the commonly produced particulate titania. Modeling has demonstrated that the new titania nanotube is less strongly attracted to water than particulate titania due to a hydroxyl group-free surface which provides higher charging. In embodiments, the nanotubes have a water affinity of from about 0 to about 20 kcal/mole or from about 1 to about 15 kcal/mole or from about 4 to about 15 kcal/mole. In addition, the morphology of the nanotubes—a cylindrical shape—provides a high surface curvature in one dimension that allows the nanotubes to act like a small particle while having a high aspect ratio that increases the area of contact with toner surface which provides reduced impaction. In embodiments, the nanotubes have a surface curvature in one direction and in two dimensions of from about 0.01/nm to about 0.2/nm, or from about 0.02/nm to about 0.1/nm or from about 0.015/nm to about 0.15/nm. In the other direction and dimension the surface curvature is about zero, the nanotube is thus approximately linear in the third dimension. Because developer particles are recycled through many cycles, the many collisions which occur between the toner carrier particles and other surfaces in the xerographic machine cause the toner particles carried on the surface of the carrier particles to be welded or otherwise forced onto the carrier surfaces. The gradual accumulation of impacted toner material on the surface of the carrier, or toner impaction, causes a change in the triboelectric value of the carrier and directly contributes to the degradation of copy quality by eventual destruction of the toner carrying capacity of the carrier. In embodiments, nanosheets, a thin sheet of titania, would tend to sit flat on the surface of the toner particle. Due to the large area on the surface of the toner the nanosheet would be very resistant to impaction into the toner, even more resistant than a nanotube. In embodiments, nanosheets do not provide a substantial surface curvature in any dimension.

Another benefit of the present nanotubes is the increased adhesion of the titania nanotubes to the toner surface which makes it less likely to cause contamination of other xerographic subsystems such as the photoreceptor or bias charge roller (BCR). The pull off force for an additive is proportional to its mass (F=ma), while the adhesion force is proportional to the area in contact and the nature of the chemical interaction—in the absence of specific chemical bonds, the latter will simply be the van der Waal's forces which do not vary very much with material composition. Thus, how well the additive sticks to the surface of the toner will depend mostly on the ratio of the surface area in contact to the mass, for titania additives the surface area to volume, since density is the same for all. Thus, for example, a nanotube of 12 nm diameter and 500 nm length as described below has the same surface area/mass ratio as a 17 nm spherical titania particle. As a result, the titania nanotubes adhere to the toner surface like a small titania. Also, since it is a small radius in one dimension, in terms of properties like toner flow a nanotube acts like a small particle, and thus provides better flow (as cohesion is proportional to the particle radius) than a large particle. However, in terms of additive impaction, the area in contact for a nanotube is equivalent to that of a larger particle. Thus it more difficult to impact the nanotubes. Thus, for impaction, the titania nanotubes above are the equivalent of a 55 nm spherical titania. As the nanotube becomes longer these effects increase. The overall effect is that for charge, flow and adhesion to the toner, nanotubes are expected to act desirably like small particles, but also desirably as large particles for impaction. For nanosheets, the same advantage is expected for both additive impaction and additive adhesion, as expected for the nanotubes, because of their large contact area but small volume due to their thinness. However, because they do not have any substantial curvature, they are not expected to have the same advantage as nanotubes for toner flow.

It is shown that titania nanotubes provide a different crystalline surface than the commonly produced particulate titania. Unlike conventional titania nanoparticle, the surface of the titania nanotubes are typically oxide that is dehydroxylated and not decorated by hydroxyl groups. This reduces the surface polarity and removes a very good binding site for water on the titania surface. Further, it has been shown that the surface that is exposed in titania nanotube is one of the surfaces that has one of the lowest affinities for water of the different possible titania surfaces. Thus, the titania nanotubes have lower RH sensitivity. In embodiments, the toner made from the present embodiments has a RH sensitivity of from about 1 to about 2 or from about 1 to about 1.5 or from about 1 to about 1.3. However, the toner of the present embodiments still maintain a high charge of from about −15 to about −80 microcoulombs/gram or from about −20 to about −70 microcoulombs/gram or from about −20 to about −60 microcoulombs/gram.

Modeling has also shown that the energy gap for charge transfer from the titania nanotube surface is also lower than that for the typical titania surface, due to the lower energy gap and the lower water adsorption. Thus, the charge will be higher.

In the present embodiments, there is provided a toner composition comprising titania nanotubes or titania nanosheets. The toner may be any conventional toner. In embodiments, the toner may also be an emulsion aggregate toner. In embodiments, these titania nanotubes or titania nanosheets are included on the toner surface as toner surface additives. The titania nanotubes or nanosheets are included either in place of or in combination with other conventional toner surface additives, such as for example, particulate silica or titania.

As described above, the nanotubes have structures that may be spherical in one dimension and more linear in other dimensions. The nanosheets have structures that may be formed like platelets or thin flat sheets or aggregations of the same. In embodiments, the nanosheets may have a sheet length of from about 100 to about 2000 nm, or from about 100 to about 1000 nm, or from about 200 to about 500 nm. The nanosheets may have a sheet width of from about 100 to about 2000 nm, or from about 100 to about 1000 nm, or from about 200 to about 500 nm. In further embodiments, the nanosheet may have a thickness of from about 0.5 to about 50 nm, or from about 1 to about 20 nm, or from about 2 to about 10 nm. In embodiments, the ratio of the length to the width of the nanosheet may be from about 1:1 to about 5:1, and the ratio of the area of the sheet, calculated as the width multiplied by the length in nm, divided by the thickness in nm may be from about 500/nm to about 20,000,000/nm.

In embodiments, the titania nanotubes have an average particle diameter of from about from about 5 nm to about 100 nm, or from about 5 to about 50 nm, or from about 6 to about 20 nm. In embodiments, the titania nanotubes have an average particle length of from about from about 50 nm to about 2 microns, or from about 100 nm to about 1 micron, or from about 150 nm to about 500 nm. The surface of the titania nanotube is substantially free of hydroxyl groups. For example, the surface of the titania nanotube has less than 3 hydroxyl groups per nanometer squared of surface, or has from about 0.02 to about 2 hydroxyl groups per nanometer squared of surface, or has from about 0.05 to about 1 hydroxyl groups per nanometer squared of surface. The surface of the titania nanotube or titania nanosheet is also is predominantly of the [001] face, as shown inFIG. 1. In specific embodiments, the surface of the titania nanotube or titania nanosheet comprises from about 1 to about 100 percent, or from about 5 to about 90 percent, or from about 50 to about 100 percent of the [001] face.

In further embodiments, the titania nanotubes or titania nanosheets are used in place of the conventional particulate toner surface additives. In such embodiments, the titania nanotubes or titania nanosheets are present in an amount of from about 0.1 to about 5 wt percent, or of from about 0.5 to about 3 wt percent, or of from about 1 to about 4 wt percent by weight of the total weight of the toner particle. In other embodiments, the titania nanotubes or titania nanosheets are used in combination with the conventional particulate toner surface additives. In such embodiments, the titania nanotubes or titania nanosheets are present in an amount of from about 0.1 to about 5 wt percent, or of from about 0.5 to about 3 wt percent, or of from about 1 to about 4 wt percent by weight of the total weight of the toner particle while the conventional toner surface additives are present in an amount of from about 0.1 to about 5 wt percent, or of from about 0.5 to about 3 wt percent, or of from about Ito about 4 wt percent by weight of the total weight of the toner particle. The conventional toner surface additives are selected from the group consisting of particulate titania, particulate silica and mixtures thereof. The particulate titania may be of anatase or rutile structure.

Emulsion Aggregation Toner

In embodiments, a developer is disclosed including a resin coated carrier and a toner, where the toner may be an emulsion aggregation toner, containing, but not limited to, a latex resin, a wax and a polymer shell.

In embodiments, the latex resin may be composed of a first and a second monomer composition. Any suitable monomer or mixture of monomers may be selected to prepare the first monomer composition and the second monomer composition. The selection of monomer or mixture of monomers for the first monomer composition is independent of that for the second monomer composition and vise versa. Exemplary monomers for the first and/or the second monomer compositions include, but are not limited to, polyesters, styrene, alkyl acrylate, such as, methyl acrylate, ethyl acrylate, butyl arylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate; β-carboxy ethyl acrylate (β-CEA), phenyl acrylate, methyl alphachloroacrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate; butadiene; isoprene; methacrylonitrile; acrylonitrile; vinyl ethers, such as, vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether and the like; vinyl esters, such as, vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate; vinyl ketones, such as, vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; vinylidene halides, such as, vinylidene chloride and vinylidene chlorofluoride; N-vinyl indole; N-vinyl pyrrolidone; methacrylate; acrylic acid; methacrylic acid; acrylamide; methacrylamide; vinylpyridine; vinylpyrrolidone; vinyl-N-methylpyridinium chloride; vinyl naphthalene; p-chlorostyrene; vinyl chloride; vinyl bromide; vinyl fluoride; ethylene; propylene; butylenes; isobutylene; and the like, and mixtures thereof. In case a mixture of monomers is used, typically the latex polymer will be a copolymer.

In embodiments, the first monomer composition and the second monomer composition may be substantially water insoluble, such as, hydrophobic, and may be dispersed in an aqueous phase with adequate stirring when added to a reaction vessel.

The weight ratio between the first monomer composition and the second monomer composition may be in the range of from about 0.1:99.9 to about 50:50, including from about 0.5:99.5 to about 25:75, from about 1:99 to about 10:90.

In embodiments, the first monomer composition and the second monomer composition can be the same. Examples of the first/second monomer composition may be a mixture comprising styrene and alkyl acrylate, such as, a mixture comprising styrene, n-butyl acrylate and β-CEA. Based on total weight of the monomers, styrene may be present in an amount from about 1% to about 99%, from about 50% to about 95%, from about 70% to about 90%, although may be present in greater or lesser amounts; alkyl acrylate, such as, n-butyl acrylate, may be present in an amount from about 1% to about 99%, from about 5% to about 50%, from about 10% to about 30%, although may be present in greater or lesser amounts.

In embodiments, the resins may be a polyester resin, such as, an amorphous resin, a crystalline resin, and/or a combination thereof, including the resins described in U.S. Pat. Nos. 6,593,049 and 6,756,176, the disclosure of each of which hereby is incorporated by reference in entirety. Suitable resins may also include a mixture of an amorphous polyester resin and a crystalline polyester resin as described in U.S. Pat. No. 6,830,860, the disclosure of which is hereby incorporated by reference in entirety.

In embodiments, the resin may be a polyester resin formed by reacting a diol with a diacid in the presence of an optional catalyst. For forming a crystalline polyester, suitable organic diols include aliphatic diols with from about 2 to about 36 carbon atoms, such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol and the like; alkali sulfo-aliphatic diols such as sodio 2-sulfo-1,2-ethanediol, lithio 2-sulfo-1,2-ethanediol, potassio 2-sulfo-1,2-ethanediol, sodio 2-sulfo-1,3-propanediol, lithio 2-sulfo-1,3-propanediol, potassio 2-sulfo-1,3-propanediol, mixture thereof, and the like. The aliphatic diol may be, for example, selected in an amount of from about 40 to about 60 mole percent, in embodiments from about 42 to about 55 mole percent, in embodiments from about 45 to about 53 mole percent (although amounts outside of these ranges can be used), and the alkali sulfo-aliphatic diol can be selected in an amount of from about 0 to about 10 mole percent, in embodiments from about 1 to about 4 mole percent of the resin.

The crystalline resin may be present, for example, in an amount of from about 5 to about 50 percent by weight of the toner components, in embodiments from about 10 to about 35 percent by weight of the toner components. The crystalline resin can possess various melting points of, for example, from about 30° C. to about 120° C., in embodiments from about 50° C. to about 90° C. The crystalline resin may have a number average molecular weight (Mn), as measured by gel permeation chromatography (GPC) of, for example, from about 1,000 to about 50,000, in embodiments from about 2,000 to about 25,000, and a weight average molecular weight (Mw) of, for example, from about 2,000 to about 100,000, in embodiments from about 3,000 to about 80,000, as determined by Gel Permeation Chromatography using polystyrene standards. The molecular weight distribution (Mw/Mn) of the crystalline resin may be, for example, from about 2 to about 6, in embodiments from about 3 to about 4.

Examples of additional diols which may be utilized in generating the amorphous polyester include 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, pentanediol, hexanediol, 2,2-dimethylpropanediol, 2,2,3-trimethylhexanediol, heptanediol, dodecanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, xylenedimethanol, cyclohexanediol, diethylene glycol, dipropylene glycol, dibutylene, and combinations thereof. The amount of organic diol selected can vary, and may be present, for example, in an amount from about 40 to about 60 mole percent of the resin, in embodiments from about 42 to about 55 mole percent of the resin, in embodiments from about 45 to about 53 mole percent of the resin.

Polycondensation catalysts which may be utilized in forming either the crystalline or amorphous polyesters include tetraalkyl titanates, dialkyltin oxides such as dibutyltin oxide, tetraalkyltins such as dibutyltin dilaurate, and dialkyltin oxide hydroxides such as butyltin oxide hydroxide, aluminum alkoxides, alkyl zinc, dialkyl zinc, zinc oxide, stannous oxide, or combinations thereof. Such catalysts may be utilized in amounts of, for example, from about 0.01 mole percent to about 5 mole percent based on the starting diacid or diester used to generate the polyester resin.

Furthermore, in embodiments, a crystalline polyester resin may be contained in the binding resin. The crystalline polyester resin may be synthesized from an acid (dicarboxylic acid) component and an alcohol (diol) component. In what follows, an “acid-derived component” indicates a constituent moiety that was originally an acid component before the synthesis of a polyester resin and an “alcohol-derived component” indicates a constituent moiety that was originally an alcoholic component before the synthesis of the polyester resin.

A “crystalline polyester resin” indicates one that shows not a stepwise endothermic amount variation but a clear endothermic peak in differential scanning calorimetry (DSC). However, a polymer obtained by copolymerizing the crystalline polyester main chain and at least one other component is also called a crystalline polyester if the amount of the other component is 50% by weight or less.

As the acid-derived component, an aliphatic dicarboxylic acid may be utilized, such as a straight chain carboxylic acid. Examples of straight chain carboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,1-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid, as well as lower alkyl esters and acid anhydrides thereof. Among these, acids having 6 to 10 carbon atoms may be desirable for obtaining suitable crystal melting point and charging properties. In order to improve the crystallinity, the straight chain carboxylic acid may be present in an amount of about 95% by mole or more of the acid component and, in embodiments, more than about 98% by mole of the acid component. Other acids are not particularly restricted, and examples thereof include conventionally known divalent carboxylic acids and dihydric alcohols, for example those described in “Polymer Data Handbook: Basic Edition” (Soc. Polymer Science, Japan Ed.: Baihukan). Specific examples of the monomer components include, as divalent carboxylic acids, dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, and cyclohexanedicarboxylic acid, and anhydrides and lower alkyl esters thereof, as well as combinations thereof, and the like. As the acid-derived component, a component such as a dicarboxylic acid-derived component having a sulfonic acid group may also be utilized. The dicarboxylic acid having a sulfonic acid group may be effective for obtaining excellent dispersion of a coloring agent such as a pigment. Furthermore, when a whole resin is emulsified or suspended in water to prepare a toner mother particle, a sulfonic acid group, may enable the resin to be emulsified or suspended without a surfactant. Examples of such dicarboxylic acids having a sulfonic group include, but are not limited to, sodium 2-sulfoterephthalate, sodium 5-sulfoisophthalate and sodium sulfosuccinate. Furthermore, lower alkyl esters and acid anhydrides of such dicarboxylic acids having a sulfonic group, for example, are also usable. Among these, sodium 5-sulfoisophthalate and the like may be desirable in view of the cost. The content of the dicarboxylic acid having a sulfonic acid group may be from about 0.1% by mole to about 2% by mole, in embodiments from about 0.2% by mole to about 1% by mole. When the content is more than about 2% by mole, the charging properties may be deteriorated. Here, “component mol %” or “component mole %” indicates the percentage when the total amount of each of the components (acid-derived component and alcohol-derived component) in the polyester resin is assumed to be 1 unit (mole).

As the alcohol component, aliphatic dialcohols may be used. Examples thereof include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-dodecanediol, 1,12-undecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol and 1,20-eicosanediol. Among them, those having from about 6 to about 10 carbon atoms may be used to obtain desirable crystal melting points and charging properties. In order to raise crystallinity, it may be useful to use the straight chain dialcohols in an amount of about 95% by mole or more, in embodiments about 98% by mole or more.

For adjusting the acid number and hydroxyl number, the following may be used: monovalent acids such as acetic acid and benzoic acid; monohydric alcohols such as cyclohexanol and benzyl alcohol; benzenetricarboxylic acid, naphthalenetricarboxylic acid, and anhydrides and lower alkylesters thereof; trivalent alcohols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, combinations thereof, and the like.

The crystalline polyester resins may be synthesized from a combination of components selected from the above-mentioned monomer components, by using conventional known methods. Exemplary methods include the ester exchange method and the direct polycondensation method, which may be used singularly or in a combination thereof. The molar ratio (acid component/alcohol component) when the acid component and alcohol component are reacted, may vary depending on the reaction conditions. The molar ratio is usually about 1/1 in direct polycondensation. In the ester exchange method, a monomer such as ethylene glycol, neopentyl glycol or cyclohexanedimethanol, which may be distilled away under vacuum, may be used in excess.

Any suitable surfactants may be used for the preparation of the latex and wax dispersions according to the present disclosure. Depending on the emulsion system, any desired nonionic or ionic surfactant such as anionic or cationic surfactant may be contemplated.

Examples of suitable anionic surfactants include, but are not limited to, sodium dodecylsulfate, sodium dodecylbenzene sulfonate, sodium dodecylnaphthalenesulfate, dialkyl benzenealkyl sulfates and sulfonates, abitic acid, NEOGEN R® and NEOGEN SC® available from Kao, Tayca Power®, available from Tayca Corp., DOWFAX®, available from Dow Chemical Co., and the like, as well as mixtures thereof. Anionic surfactants may be employed in any desired or effective amount, for example, at least about 0.01% by weight of total monomers used to prepare the latex polymer, at least about 0.1% by weight of total monomers used to prepare the latex polymer; and no more than about 10% by weight of total monomers used to prepare the latex polymer, no more than about 5% by weight of total monomers used to prepare the latex polymer, although the amount can be outside of those ranges.

Any suitable initiator or mixture of initiators may be selected in the latex process and the toner process. In embodiments, the initiator is selected from known free radical polymerization initiators. The free radical initiator can be any free radical polymerization initiator capable of initiating a free radical polymerization process and mixtures thereof, such free radical initiator being capable of providing free radical species on heating to above about 30° C.

Based on total weight of the monomers to be polymerized, the initiator may be present in an amount from about 0.1% to about 5%, from about 0.4% to about 4%, from about 0.5% to about 3%, although may be present in greater or lesser amounts.

A chain transfer agent optionally may be used to control the polymerization degree of the latex, and thereby control the molecular weight and molecular weight distribution of the product latexes of the latex process and/or the toner process according to the present disclosure. As can be appreciated, a chain transfer agent can become part of the latex polymer.

Chain Transfer Agent

In embodiments, the chain transfer agent has a carbon-sulfur covalent bond. The carbon-sulfur covalent bond has an absorption peak in a wave number region ranging from 500 to 800 cm−1in an infrared absorption spectrum. When the chain transfer agent is incorporated into the latex and the toner made from the latex, the absorption peak may be changed, for example, to a wave number region of 400 to 4,000 cm−1.

Examples of such chain transfer agents also include, but are not limited to, dodecanethiol, butanethiol, isooctyl-3-mercaptopropionate, 2-methyl-5-t-butyl-thiophenol, carbon tetrachloride, carbon tetrabromide and the like.

Based on total weight of the monomers to be polymerized, the chain transfer agent may be present in an amount from about 0.1% to about 7%, from about 0.5% to about 6%, from about 1.0% to about 5%, although may be present in greater or lesser amounts.

In embodiments, a branching agent optionally may be included in the first/second monomer composition to control the branching structure of the target latex. Exemplary branching agents include, but are not limited to, decanediol diacrylate (ADOD), trimethylolpropane, pentaerythritol, trimellitic acid, pyromellitic acid and mixtures thereof.

Based on total weight of the monomers to be polymerized, the branching agent may be present in an amount from about 0% to about 2%, from about 0.05% to about 1.0%, from about 0.1% to about 0.8%, although may be present in greater or lesser amounts.

In the latex process and toner process of the disclosure, emulsification may be done by any suitable process, such as, mixing at elevated temperature. For example, the emulsion mixture may be mixed in a homogenizer set at about 200 to about 400 rpm and at a temperature of from about 40° C. to about 80° C. for a period of from about 1 min to about 20 min.

Any type of reactor may be used without restriction. The reactor can include means for stirring the compositions therein, such as, an impeller. A reactor can include at least one impeller. For forming the latex and/or toner, the reactor can be operated throughout the process such that the impellers can operate at an effective mixing rate of about 10 to about 1,000 rpm.

Following completion of the monomer addition, the latex may be permitted to stabilize by maintaining the conditions for a period of time, for example for about 10 to about 300 min, before cooling. Optionally, the latex formed by the above process may be isolated by standard methods known in the art, for example, coagulation, dissolution and precipitation, filtering, washing, drying or the like.

The latex of the present disclosure may be selected for emulsion-aggregation-coalescence processes for forming toners, inks and developers by known methods. The latex of the present disclosure may be melt blended or otherwise mixed with various toner ingredients, such as, a wax dispersion, a coagulant, an optional silica, an optional charge enhancing additive or charge control additive, an optional surfactant, an optional emulsifier, an optional flow additive and the like. Optionally, the latex (e.g. around 40% solids) may be diluted to the desired solids loading (e.g. about 12 to about 15% by weight solids), before formulated in a toner composition.

Based on the total toner weight, the latex may be present in an amount from about 50% to about 100%, from about 60% to about 98%, from about 70% to about 95%, although may be present in greater or lesser amounts. Methods of producing such latex resins may be carried out as described in the disclosure of U.S. Pat. No. 7,524,602, herein incorporated by reference in entirety.

Various known suitable colorants, such as dyes, pigments, mixtures of dyes, mixtures of pigments, mixtures of dyes and pigments and the like may be included in the toner. The colorant may be included in the toner in an amount of, for example, about 0.1 to about 35% by weight of the toner, from about 1 to about 15% percent of the toner, from about 3 to about 10% by weight of the toner, although amounts outside those ranges may be utilized.

In addition to the polymer resin, the toners of the present disclosure also may contain a wax, which can be either a single type of wax or a mixture of two or more different waxes. A single wax can be added to toner formulations, for example, to improve particular toner properties, such as, toner particle shape, presence and amount of wax on the toner particle surface, charging and/or fusing characteristics, gloss, stripping, offset properties and the like. Alternatively, a combination of waxes can be added to provide multiple properties to the toner composition.

When included, the wax may be present in an amount of, for example, from about 1 wt % to about 25 wt % of the toner particles, in embodiments, from about 5 wt % to about 20 wt % of the toner particles.

Waxes that may be selected include waxes having, for example, a weight average molecular weight of from about 500 to about 20,000, in embodiments from about 1,000 to about 10,000. Waxes that may be used include, for example, polyolefins, such as, polyethylene, polypropylene and polybutene waxes, such as, commercially available from Allied Chemical and Petrolite Corporation, for example POLYWAX™ polyethylene waxes from Baker Petrolite, Wax emulsions available from Michaelman, Inc. and the Daniels Products Company, EPOLENE N-15™ commercially available from Eastman Chemical Products, Inc., and VISCOL 550-P™, a low weight average molecular weight polypropylene available from Sanyo Kasei K. K.; plant-based waxes, such as, carnauba wax, rice wax, candelilla wax, sumacs wax and jojoba oil; animal-based waxes, such as, beeswax; mineral-based waxes and petroleum-based waxes, such as, montan wax, ozokerite, ceresin, paraffin wax, microcrystalline wax and Fischer-Tropsch wax; ester waxes obtained from higher fatty acid and higher alcohol, such as, stearyl stearate and behenyl behenate; ester waxes obtained from higher fatty acid and monovalent or multivalent lower alcohol, such as, butyl stearate, propyl oleate, glyceride monostearate, glyceride distearate, pentaerythritol tetra behenate; ester waxes obtained from higher fatty acid and multivalent alcohol multimers, such as, diethyleneglycol monostearate, dipropyleneglycol distearate, diglyceryl distearate and triglyceryl tetrastearate; sorbitan higher fatty acid ester waxes, such as, sorbitan monostearate, and cholesterol higher fatty acid ester waxes, such as, cholesteryl stearate. Examples of functionalized waxes that may be used include, for example, amines, amides, for example, AQUA SUPERSLIP 6550™ and SUPERSLIP 6530™ available from Micro Powder Inc., fluorinated waxes, for example, POLYFLUO 190™, POLYFLUO 200™, POLYSILK 19™ and POLYSILK 14™ available from Micro Powder Inc., mixed fluorinated, amide waxes, for example, MICROSPERSION 19™ available from Micro Powder Inc., imides, esters, quaternary amines, carboxylic acids or acrylic polymer emulsion, for example JONCRYL 74™, 89™, 130™, 537™ and 538™, all available from SC Johnson Wax, and chlorinated polypropylenes and polyethylenes available from Allied Chemical and Petrolite Corporation and SC Johnson wax. Mixtures and combinations of the foregoing waxes also may be used in embodiments. Waxes may be included as, for example, fuser roll release agents.

Toner Preparation

The toner particles may be prepared by any method within the purview of one skilled in the art. Although embodiments relating to toner particle production are described below with respect to emulsion-aggregation processes, any suitable method of preparing toner particles may be used, including chemical processes, such as suspension and encapsulation processes disclosed in U.S. Pat. Nos. 5,290,654 and 5,302,486, the disclosure of each of which hereby is incorporated by reference in entirety. In embodiments, toner compositions and toner particles may be prepared by aggregation and coalescence processes in which smaller-sized resin particles are aggregated to the appropriate toner particle size and then coalesced to achieve the final toner particle shape and morphology.

In embodiments, toner compositions may be prepared by emulsion-aggregation processes, such as, a process that includes aggregating a mixture of an optional wax and any other desired or required additives, and emulsions including the resins described above, optionally with surfactants, as described above, and then coalescing the aggregate mixture. A mixture may be prepared by adding an optional wax or other materials, which optionally also may be in a dispersion(s) including a surfactant, to the emulsion, which may be a mixture of two or more emulsions containing the resin. The pH of the resulting mixture may be adjusted by an acid (i.e., a pH adjustor) such as, for example, acetic acid, nitric acid or the like. In embodiments, the pH of the mixture may be adjusted to from about 2 to about 4.5. Additionally, in embodiments, the mixture may be homogenized. If the mixture is homogenized, homogenization may be accomplished by mixing at about 600 to about 4,000 revolutions per minute (rpm). Homogenization may be accomplished by any suitable means, including, for example, with an IKA ULTRA TURRAX T50 probe homogenizer.

Following preparation of the above mixture, an aggregating agent may be added to the mixture. Suitable aggregating agents include, for example, aqueous solutions of a divalent cation or a multivalent cation material. The aggregating agent may be, for example, polyaluminum halides, such as, polyaluminum chloride (PAC), or the corresponding bromide, fluoride or iodide, polyaluminum silicates, such as, polyaluminum sulfosilicate (PASS), and water soluble metal salts including aluminum chloride, aluminum nitrite, aluminum sulfate, potassium aluminum sulfate, calcium acetate, calcium chloride, calcium nitrite, calcium oxylate, calcium sulfate, magnesium acetate, magnesium nitrate, magnesium sulfate, zinc acetate, zinc nitrate, zinc sulfate, zinc chloride, zinc bromide, magnesium bromide, copper chloride, copper sulfate, and combinations thereof. In embodiments, the aggregating agent may be added to the mixture at a temperature that is below the glass transition temperature (Tg) of the resin.

The aggregating agent may be added to the mixture to form a toner in an amount of, for example, from about 0.1 parts per hundred (pph) to about 1 pph, in embodiments, from about 0.25 pph to about 0.75 pph.

The gloss of a toner may be influenced by the amount of retained metal ion, such as, Al3+, in the particle. The amount of retained metal ion may be adjusted further by the addition of ethylene diamine tetraacetic acid (EDTA). In embodiments, the amount of retained metal ion, for example, Al3+, in toner particles of the present disclosure may be from about 0.1 pph to about 1 pph, in embodiments, from about 0.25 pph to about 0.8 pph.

The disclosure also provides a melt mixing process to produce low cost and safe cross-linked thermoplastic binder resins for toner compositions which have, for example, low fix temperature and/or high offset temperature, and which may show minimized or substantially no vinyl offset. In the process, unsaturated base polyester resins or polymers are melt blended, that is, in the molten state under high shear conditions producing substantially uniformly dispersed toner constituents, and which process provides a resin blend and toner product with optimized gloss properties (see, e.g., U.S. Pat. No. 5,556,732, herein incorporated by reference in entirety). By, “highly cross-linked,” is meant that the polymer involved is substantially cross-linked, that is, equal to or above the gel point. As used herein, “gel point,” means the point where the polymer is no longer soluble in solution (see, e.g., U.S. Pat. No. 4,457,998, herein incorporated by reference in entirety).

To control aggregation and, coalescence of the particles, in embodiments, the aggregating agent may be metered into the mixture over time. For example, the agent may be metered into the mixture over a period of from about 5 to about 240 min, in embodiments, from about 30 to about 200 min. Addition of the agent may also be done while the mixture is maintained under stirred conditions, in embodiments from about 50 rpm to about 1,000 rpm, in embodiments, from about 100 rpm to about 500 rpm, and at a temperature that is below the Tgof the resin.

The particles may be permitted to aggregate until a predetermined desired particle size is obtained. A predetermined desired size refers to the desired particle size as determined prior to formation, with particle size monitored during the growth process as known in the art until such particle size is achieved. Samples may be taken during the growth process and analyzed, for example with a Coulter Counter, for average particle size. The aggregation thus may proceed by maintaining the elevated temperature, or slowly raising the temperature to, for example, from about 40° C. to about 100° C., and holding the mixture at that temperature for a time from about 0.5 hr to about 6 hr, in embodiments, from about 1 hr to about 5 hr, while maintaining stirring, to provide the aggregated particles. Once the predetermined desired particle size is obtained, the growth process is halted. In embodiments, the predetermined desired particle size is within the toner particle size ranges mentioned above. In embodiments, the particle size may be about 5.0 to about 6.0 μm, about 6.0 to about 6.5 μm, about 6.5 to about 7.0 μm, about 7.0 to about 7.5 μm.

Growth and shaping of the particles following addition of the aggregation agent may be accomplished under any suitable conditions. For example, the growth and shaping may be conducted under conditions in which aggregation occurs separate from coalescence. For separate aggregation and coalescence stages, the aggregation process may be conducted under shearing conditions at an elevated temperature, for example from about 40° C. to about 90° C., in embodiments, from about 45° C. to about 80° C., which may be below the Tgof the resin.

Toners may possess favorable charging characteristics when exposed to extreme RH conditions. The low humidity zone (C zone) may be about 12° C./15% RH, while the high humidity zone (A zone) may be about 28° C./85% RH. Toners of the disclosure may possess a parent toner charge per mass ratio (Q/M) of from about −5 μC/g to about −80 μC/g, in embodiments, from about −10 μC/g to about −70 μC/g, and a final toner charging after surface additive blending of from −15 μC/g to about −60 μC/g, in embodiments, from about −20 μC/g to about −55 μC/g.

Shell Resin

In embodiments, a shell may be applied to the formed aggregated toner particles. Any resin described above as suitable for the core resin may be utilized as the shell resin. The shell resin may be applied to the aggregated particles by any method within the purview of those skilled in the art. In embodiments, the shell resin may be in an emulsion including any surfactant described herein. The aggregated particles described above may be combined with said emulsion so that the resin forms a shell over the formed aggregates. In embodiments, an amorphous polyester may be utilized to form a shell over the aggregates to form toner particles having a core-shell configuration.

Toner particles can have a size of diameter of from about 4 to about 8 μm, in embodiments, from about 5 to about 7 μm, the optimal shell component may be about 26 to about 30% by weight of the toner particles.

Alternatively, a thicker shell may be desirable to provide desirable charging characteristics due to the higher surface area of the toner particle. Thus, the shell resin may be present in an amount from about 30% to about 40% by weight of the toner particles, in embodiments, from about 32% to about 38% by weight of the toner particles, in embodiments, from about 34% to about 36% by weight of the toner particles.

In embodiments, a photoinitiator may be included in the shell. Thus, the photoinitiator may be in the core, the shell, or both. The photoinitiator may be present in an amount of from about 1% to about 5% by weight of the toner particles, in embodiments, from about 2% to about 4% by weight of the toner particles.

Emulsions may have a solids loading of from about 5% solids by weight to about 20% solids by weight, in embodiments, from about 12% solids by weight to about 17% solids by weight.

Once the desired final size of the toner particles is achieved, the pH of the mixture may be adjusted with a base (i.e., a pH adjustor) to a value of from about 6 to about 10, and in embodiments from about 6.2 to about 7. The adjustment of the pH may be utilized to freeze, that is to stop, toner growth. The base utilized to stop toner growth may include any suitable base, such as, for example, alkali metal hydroxides, such as, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, combinations thereof and the like. In embodiments, EDTA may be added to help adjust the pH to the desired values noted above. The base may be added in amounts from about 2 to about 25% by weight of the mixture, in embodiments, from about 4 to about 10% by weight of the mixture. In embodiments, the shell has a higher Tgthan the aggregated toner particles.

Following aggregation to the desired particle size, with the optional formation of a shell as described above, the particles then may be coalesced to the desired final shape, the coalescence being achieved by, for example, heating the mixture to a temperature of from about 55° C. to about 100° C., in embodiments from about 65° C. to about 75° C., which may be below the melting point of a crystalline resin to prevent plasticization. Higher or lower temperatures may be used, it being understood that the temperature is a function of the resins used.

Coalescence may proceed over a period of from about 0.1 to about 9 hr, in embodiments, from about 0.5 to about 4 hr.

After coalescence, the mixture may be cooled to room temperature, such as from about 20° C. to about 25° C. The cooling may be rapid or slow, as desired. A suitable cooling method may include introducing cold water to a jacket around the reactor. After cooling, the toner particles optionally may be washed with water and then dried. Drying may be accomplished by any suitable method, for example, freeze drying.

Carriers

Various suitable solid core or particle materials can be utilized for the carriers and developers of the present disclosure. Characteristic particle properties include those that, in embodiments, will enable the toner particles to acquire a positive charge or a negative charge, and carrier cores that provide desirable flow properties in the developer reservoir present in an electrophotographic imaging apparatus. Other desirable properties of the core include, for example, suitable magnetic characteristics that permit magnetic brush formation in magnetic brush development processes; desirable mechanical aging characteristics; and desirable surface morphology to permit high electrical conductivity of any developer including the carrier and a suitable toner.

Examples of carrier particles or cores that can be utilized include iron and/or steel, such as, atomized iron or steel powders available from Hoeganaes Corporation or Pomaton S.p.A (Italy); ferrites, such as, Cu/Zn-ferrite containing, for example, about 11% copper oxide, about 19% zinc oxide, and about 70% iron oxide, including those commercially available from D.M. Steward Corporation or Powdertech Corporation, Ni/Zn-ferrite available from Powdertech Corporation, Sr (strontium)-ferrite, containing, for example, about 14% strontium oxide and about 86% iron oxide, commercially available from Powdertech Corporation, and Ba-ferrite; magnetites, including those commercially available from, for example, Hoeganaes Corporation (Sweden); nickel; combinations thereof, and the like. In embodiments, the polymer particles obtained can be used to coat carrier cores of any known type by various known methods, and which carriers then are incorporated with a known toner to form a developer for electrophotographic printing. Other suitable carrier cores are illustrated in, for example, U.S. Pat. Nos. 4,937,166, 4,935,326 and 7,014,971, the disclosure of each of which hereby is incorporated by reference in entirety, and may include granular zircon, granular silicon, glass, silicon dioxide, combinations thereof, and the like. In embodiments, suitable carrier cores may have an average particle size of, for example, from about 20 μm to about 400 μm in diameter, in embodiments, from about 40 μm to about 200 μm in diameter.

In some embodiments, the carrier coating may include a conductive component. Suitable conductive components include, for example, carbon black.

There may be added to the carrier a number of additives, for example, charge enhancing additives, including particulate amine resins, such as, melamine, and certain fluoropolymer powders, such as alkyl-amino acrylates and methacrylates, polyamides, and fluorinated polymers, such as polyvinylidine fluoride and poly(tetrafluoroethylene) and fluoroalkyl methacrylates, such as 2,2,2-trifluoroethyl methacrylate. Other charge enhancing additives which may be utilized include quaternary ammonium salts, including distearyl dimethyl ammonium methyl sulfate (DDAMS), bis[1-[(3,5-disubstituted-2-hydroxyphenyeazo]-3-(mono-substituted)-2-naphthalenolato(2-)]chromate(1-), ammonium sodium and hydrogen (TRH), cetyl pyridinium chloride (CPC), FANAL PINK® D4830, combinations thereof, and the like, and other effective known charge agents or additives. The charge additive components may be selected in various effective amounts, such as from about 0.5 wt % to about 20 wt %, from about 1 wt % to about 3 wt %, based, for example, on the sum of the weights of polymer/copolymer, conductive component, and other charge additive components. The addition of conductive components can act to further increase the negative triboelectric charge imparted to the carrier, and therefore, further increase the negative triboelectric charge imparted to the toner in, for example, an electrophotographic development subsystem. The components may be included by roll mixing, tumbling, milling, shaking, electrostatic powder cloud spraying, fluidized bed, electrostatic disc processing, and an electrostatic curtain, as described, for example, in U.S. Pat. No. 6,042,981, the disclosure of which hereby is incorporated by reference in entirety, and wherein the carrier coating is fused to the carrier core in either a rotary kiln or by passing through a heated extruder apparatus.

Conductivity can be important for semiconductive magnetic brush development to enable good development of solid areas which otherwise may be weakly developed. Addition of a polymeric coating of the present disclosure, optionally with a conductive component such as carbon black, can result in carriers with decreased developer triboelectric response with change in relative humidity of from about 20% to about 90%, in embodiments, from about 40% to about 80%, that the charge is more consistent when the relative humidity is changed. Thus, there is less decrease in charge at high relative humidity reducing background toner on the prints, and less increase in charge and subsequently less loss of development at low relative humidity, resulting in such improved image quality performance due to improved optical density.

As noted above, in embodiments the polymeric coating may be dried, after which time it may be applied to the core carrier as a dry powder. Powder coating processes differ from conventional solution coating processes. Solution coating requires a coating polymer whose composition and molecular weight properties enable the resin to be soluble in a solvent in the coating process. That requires relatively low Mwcomponents as compared to powder coating. The powder coating process does not require solvent solubility, but does require the resin coated as a particulate with a particle size of from about 10 nm to about 2 μm, in embodiments, from about 30 nm to about 1 μm, in embodiments, from about 50 nm to about 500 nm.

Examples of processes which may be utilized to apply the powder coating include, for example, combining the carrier core material and resin coating by cascade roll mixing, tumbling, milling, shaking, electrostatic powder cloud spraying, fluidized bed, electrostatic disc processing, electrostatic curtains, combinations thereof and the like. When resin coated carrier particles are prepared by a powder coating process, the majority of the coating materials may be fused to the carrier surface, thereby reducing the number of toner impaction sites on the carrier. Fusing of the polymeric coating may occur by mechanical impaction, electrostatic attraction, combinations thereof and the like.

Following application of the resin to the core, heating may be initiated to permit flow of the coating material over the surface of the carrier core. The concentration of the coating material, in embodiments, powder particles, and the parameters of the heating may be selected to enable the formation of a continuous film of the coating polymers on the surface of the carrier core, or permit only selected areas of the carrier core to be coated. In embodiments, the carrier with the polymeric powder coating may be heated to a temperature of from about 170° C. to about 280° C., in embodiments from about 190° C. to about 240° C., for a period of time of, for example, from about 10 min to about 180 min, in embodiments, from about 15 min to about 60 min, to enable the polymer coating to melt and to fuse to the carrier core particles. Following incorporation of the powder on the surface of the carrier, heating may be initiated to permit flow of the coating material over the surface of the carrier core. In embodiments, the powder may be fused to the carrier core in either a rotary kiln or by passing through a heated extruder apparatus, see, for example, U.S. Pat. No. 6,355,391, the disclosure of which hereby is incorporated by reference in entirety.

In embodiments, the coating coverage encompasses from about 10% to about 100% of the carrier core. When selected areas of the metal carrier core remain uncoated or exposed, the carrier particles may possess electrically conductive properties when the core material is a metal.

The coated carrier particles may then be cooled, in embodiments to room temperature, and recovered for use in forming developer.

In embodiments, carriers of the present disclosure may include a core, in embodiments, a ferrite core, having a size of from about 20 μm to about 100 μm, in embodiments, from about 30 μm to about 75 μm, coated with from about 0.5% to about 10% by weight, in embodiments, from about 0.7% to about 5% by weight, of the polymer coating of the present disclosure, optionally including carbon black.

Thus, with the carrier compositions and processes of the present disclosure, there can be formulated developers with selected high triboelectric charging characteristics and/or conductivity values utilizing a number of different combinations.

Developers

The toner particles thus formed may be formulated into a developer composition. The toner particles may be mixed with carrier particles to achieve a two component developer composition. The toner concentration in the developer may be from about 1% to about 25% by weight of the total weight of the developer, in embodiments, from about 2% to about 15% by weight of the total weight of the developer.

Imaging

The toners can be utilized for electrophotographic processes, including those disclosed in U.S. Pat. No. 4,295,990, the disclosure of which is hereby incorporated by reference in entirety. In embodiments, any known type of image development system may be used in an image developing device, including, for example, magnetic brush development, hybrid scavengeless development (HSD) and the like. Those and similar development systems are within the purview of those skilled in the art.

It is envisioned that the toners of the present disclosure may be used in any suitable procedure for forming an image with a toner, including in applications other than xerographic applications.

Utilizing the toners of the present disclosure, images may be formed on substrates, including flexible substrates, having a toner pile height of from about 1 μm to about 6 μm, in embodiments, from about 2 μm to about 4.5 μm, in embodiments, from about 2.5 to about 4.2 μm.

In embodiments, the toner of the present disclosure may be used for a xerographic print protective composition that provides overprint coating properties including, but not limited to, thermal and light stability and smear resistance, particularly in commercial print applications. More specifically, such overprint coating as envisioned has the ability to permit overwriting, reduce or prevent thermal cracking, improve fusing, reduce or prevent document offset, improve print performance and protect an image from sun, heat and the like. In embodiments, the overprint compositions may be used to improve the overall appearance of xerographic prints due to the ability of the compositions to fill in the roughness of xerographic substrates and toners, thereby forming a level film and enhancing glossiness.

The following Examples are submitted to illustrate embodiments of the disclosure. The Examples are intended to be illustrative only and are not intended to limit the scope of the disclosure. Also, parts and percentages are by weight unless otherwise indicated. As used herein, “room temperature,” refers to a temperature of from about 20° C. to about 30° C.

EXAMPLES

The examples set forth herein below are being submitted to illustrate embodiments of the present disclosure. These examples are intended to be illustrative only and are not intended to limit the scope of the present disclosure. Also, parts and percentages are by weight unless otherwise indicated. Comparative examples and data are also provided.

Synthesis and Characterization of Titania Nanotubes

Synthesis of titania nanotubes (TiNTs) is straightforward from titania nanoparticles. For example synthesis has been reported in Q. Chen, G. Mogilevsky G. W. Wagner, J. Forstater, A. Kleinhammes and Y. Wu, Chemical Physics Letters 48: 134-138 (2009); and G. Mogilevsky, Q. Chen, A. Kleinhammes, Y. Wu, Chemical Physics Letters 460: 517-520 (2008), which are hereby incorporated by reference in their entireties. In the first article, it was concluded that these hydrothermally synthesized titania nanotubes are an air-stable material with a large number of active anatase (001)-like surface sites. In the second article, the synthesis of the nanotubes are discussed. In particular, 4 grams of anatase titanium dioxide nanoparticles (32 nm diameter, commercially available from Aldrich) were combined with 400 mL 10 M NaOH solution, and annealed in a Teflon lined steel autoclave for 72 at 130° C. Subsequently, the material was washed with distilled water and 0.1 M HCl to bring the pH of the material down to 5-6 and to wash out excess sodium. The precipitate was placed in a Pyrex dish and left overnight at 50° C. to dry and was collected for further characterization by various techniques. From acquired TEM data, the titania nanotubes were shown to be multi-walled with inner and outer average diameters are 5-6 nm and 10-12 nm, respectively with each nanotube containing 3-5 layers, and were on the order of 500 nm in length.

Evaluation of Titania Nanotubes—Computer Calculation of Charging Characteristics Including Water Adsorption

To model the electron transfer from the carrier coating resin to the toner additive, a carrier resin silica complex was studied, comprised of a trimer unit of the carrier resin and either a silica or titania surface models.

It is known in the art that in the usual intra-molecular electron transfer, within a single material, the adsorption of sufficient energy from a photon or collision or thermal energy could result in transfer of an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). Since the electron and hole (left when the electron leaves the HOMO) are both on the same molecule, there is no net charge on the molecule. The size of the energy gap determines the amount of energy require to transfer the electron between the orbitals. As shown inFIG. 2, both the carrier resin and toner additive, before they come in contact, have a HOMO and a LUMO and an associated gap. It should be noted that there are also potentially other energy levels above the LUMO (known as LUMO+1, LUMO+2, etc. of increasing energy) and below the HOMO (known as HOMO−1, HOMO−2, etc of decreasing energy). In general, it is possible to transfer an electron from a HOMO-n to a LUMO+m, where n,m≧0 within a material. Note HOMOn=0 is usually written as HOMO, and LUMOm=0 as LUMO for simplicity.

In the computer modeling of the present embodiments, it has been shown that on contact of two materials, such as the toner additive and carrier, a number of different possibilities arise for the location of the HOMO−n and the LUMO+m. Thus, the result of charge transfer has a number of different possibilities. The contact of the two materials may result in the HOMO−n being located on the carrier resin and the LUMO+m on the toner additive. In this situation electron transfer will charge the carrier resin positive and the toner additive negative, as desired for a negative charging toner. This situation, as shown inFIG. 3, is called the forward energy gap. On the other hand, if the LUMO+m is located on the carrier resin and the HOMO−n is on the toner additive electron transfer will charge the toner additive positive and the carrier resin negative, the opposite of what is desired for a negative charging toner. This situation, as also shown inFIG. 3, is called the reverse energy gap. The HOMO and LUMO may be located on just one molecule, as shown inFIG. 2, or could be partially on both molecules. The disposition of these frontier molecular orbitals is a result of the properties of the two materials and their interaction, that interaction also depending on the orientation of the two molecules in contact. In a bulk sample of material, different orientations of the molecules on contact will be obtained randomly. Thus, the overall charge transferred is the sum of these different processes. The important processes for charge transfer will be that of the lowest energy, so in the collection of the modeling data the process is to look at different orientations of contact and identify the lowest energy gap for the forward charge transfer desired (negative toner charge) and the lowest energy gap for reverse charge transfer (positive toner charge). Thus, the modeling shows that for excellent high negative toner charge in charging of toners with toner additives and carriers with a polymeric resin coating, there are two key attributes:1) the minimum energy gap for the forward charge transfer needs to be low2) the minimum reverse energy gap is higher than the forward gap (a negative difference, subtracting 1) from 2)

Table 1 shows the modeling data for electron charge transfer to the toner additive (desirable) to electron charge transfer to polymer (not desirable) for methyl methacrylate (MMA) and dimethylaminoethyl methacrylate (DMAEMA) repeat units as coating materials.

The modeling of polymethyl methacrylate (PMMA) with titania [101] as in anatase predicts a very low energy gap, though titania is not seen to charge higher than silica, it charges lower. The reason is likely that titania has a much higher amount of water on the surface even at low relative humidity, as it is much more polar than the silica surface. Because titania already has a high amount of water on the surface it is relatively RH insensitive, thus the change in water on the surface is much lower than silica. One key for higher charge in titania is to reduce water adsorption, most notably by removing hydroxyl groups from the surface.

Modeling of PMMA charge transfer with the titania [001] which does not have hydroxyl groups, shows an even lower gap to charge transfer of only 1.09 eV. Thus forward charge transfer is very favorable for this surface, which is the face found on the titania nanotube surfaces. Thus, even in the absence of reduced water adsorption, the energy gap predicts the titania nanotube will charge higher than the typical titania surface. The charge transfer can also be analyzed in the presence of water. Calculated HOMO and LUMO electron density distributions of PMMA/(TiO2)36/water cluster demonstrated both PMMA and Water are adsorbed on the [001] surface of the titania nanotubes, (TiO2)36. Even in the presence of water the energy gap is 1.12 eV, much lower than the usual titania, and thus predicted to increase charge.

The water adsorption affinity onto the different surfaces can also be predicted from the modeling as summarized in Table 2.

All the surfaces with Ti—O—Ti groups and no hydroxyl groups will have lower water adsorption than the usual anatase or rutile [101] surface with hydroxyl groups. However, it was discovered that of the Ti—O—Ti surfaces, the [001] surface of titania nanotubes has one of the lowest affinities for water of any of the surfaces, aside from the [010]. Thus, the [001] surface of titania nanotubes is close to the best possible surface that exists in titania for low water adsorption. Both the lack of hydroxyl groups and the nature of the [001] surface thus are expected to result in reduced water adsorption and thus higher charge and low RH sensitivity.

Computer Modeling Procedure

The Anatase cluster (TiO2)36model is constructed by carving the crystal structure unit cell to study the surface effect on electronic properties. Only pure crystal structure (i.e., no saturation of dangling bond) was allowed when generating the Anatase cluster models. Other criteria include neutral cluster, high coordination with all oxygen atoms coordinated to at least two titanium atoms and all titanium atoms coordinated to at least four oxygen atoms. For all substituted methacrylates, a trimer was used to represent the polymer. To distinguish possible effect of C rich and O rich functional group (alkyl/aromatic and acyl) in the polymer, all three acyl groups were designed to coordinate to the same side.

Surface reactivity indices for both PMMA and (TiO2)36cluster were predicted by Fukui functions calculated using density functional theory. A series of initial complexes structures were then generated accordingly for comparison of PMMA approaching different titania surface as shown inFIG. 4. Fukui functions predicted electrophilic (ƒ−), and nucleophilic (ƒ+), maxima of PMMA approach [100], [010], [001] surfaces of /(TiO2)36.

Water adsorption on titania was studied in the same way with PMMA replaced by water. The affinities were calculated by comparing the energy different between complexes and the same for isolated water and titania.

To mimic the surface hydroxyl group of silica model, a one layer cylinder-like silica model was used to design the surface treated silicas with the formula Si12O32H16. In this model, all silicons were in tetrahedral geometry and connected by oxygen. The edge of this cylinder was terminated by two hydroxyl groups to represent the geminal silanols [Si(OH)2], which are typical on the (100) surface of β-cristobalite, identified experimentally on the amorphous silica surface as one of the two types of surface hydroxyl group of untreated silica.

All calculations were performed with the DMol3 module from the Accelrys Materials Studio 4.2 commercial software package. Density functional theory (DFT) was used for the study of surface electronic properties of all models and the coupled toner/carrier complexes. In this study, Perdew's 91 generalized gradient approximation (PW91PW91) were employed as the density functional method. For basis sets, a double numerical basis set with d-polarization functions (DND) was used for all calculations.

The initial structure, optimized structure and electronic properties of adsorbed polymer complexes on the silica were studied. The geometry optimization convergence was achieved when the energy, gradient, and displacement were lower than 2×10-5 Ha, 4×10-3 Ha/Å, and 5×10-3 Å, respectively. Here, Ha is the Hartree Atomic units (au), where 1 au=4.359×10−18Joules.

SUMMARY

The present embodiments provide titania nanotubes as toner additives and in particular as surface toner additives which are advantageous over current rutile and anatase particles. Based on modeling and the structure of these nanotubes, these nanotubes are expected to be higher charging and less prone to water adsorption. Further, these nanotubes are expected to provide the toner flow and adhesion to the toner particle of small titania particles but to reduce impaction as larger additives thus improving toner aging.

Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color or material.

All references cited herein are herein incorporated by reference in their entireties.