Patent Description:
For energy conservation, efforts have been made with copiers and printers that use the electrophotographic method to reduce the amount of heat required by a fixing apparatus, i.e., to improve low-temperature fixability. In addition, for such devices there is demand for increases in the toner cartridge print yield in order to improve maintenance characteristics thereof by reducing the frequency of toner cartridge replacement. Accordingly, there is demand that the toner has, in addition to low-temperature fixability, a durability that provides a high-quality image stably even during long-term use. In addition to these, another demand that is placed on the toner is a storage stability such that the toner is unaffected even by severe environments in which the temperature and humidity undergo sharp variations after production and during transport to consumers.

In order to achieve these simultaneously, a toner with a core/shell structure, in which a shell resin covers the surface of a resin that forms the core of the toner, has been proposed.

<CIT> discloses a toner in which the surface of a toner core particle is coated by a shell layer formed of a resin that contains a unit derived from monomer for a thermosetting resin and a unit derived from a thermoplastic resin.

<CIT> discloses a toner that exhibits both an excellent fixing performance and an excellent storability. In this toner, a shell layer is formed on the surface of a toner core, and in this shell layer, a plurality of concave portions, which each expose the core, are formed.

<CIT> discloses a toner having an excellent storability and an excellent low-temperature fixability. This toner has a plurality of concave portions in the surface of a toner core, and has a shell layer that is present on the surface region of the toner core in both the regions within the concave portions and the regions outside of the concave portions.

However, as a result of investigations by the present inventor, it has been found that with regard to the toner described in <CIT>, because the shell layer covers the entire surface of the toner particle, there is room for improvement in the low-temperature fixability. It has been also found that the ability to retain an external additive may decline during long-term use.

With regard to the toner described in <CIT>, it is thought that the hardness distribution of the toner particle is controlled by the formation, in the shell layer, of a plurality of concave portions that expose the core. However, it has been found that the number of concave portions in the shell layer is insufficient and that there is room for improvement in the low-temperature fixability similarly to the toner described in <CIT>. In addition, <CIT> does not address the storage stability in severe environments in which temperature and humidity undergo sharp variations.

It has been found that the toner described in <CIT> has neither a satisfactory storability nor a satisfactory durability. It has been found that in the toner according to <CIT>, the shell layer is present in both the regions within the concave portions and regions outside of the concave portions, however, the coverage of the toner particle is not uniform and that many regions where the toner core is exposed over a broad range are present. This has been presumed to result in the unsatisfactory storability and unsatisfactory external additive retention. In addition, <CIT> does not address the storage stability in severe environments in which temperature and humidity undergo sharp variations.

Thus, as noted above, there has been a problem with regard to achieving simultaneously a low-temperature fixability, a storability in severe environments, and an excellent durability during long-term use.

The present disclosure has been pursued considering the above problem and provides a toner that exhibits an excellent low-temperature fixability, an excellent storability in severe environments, and an excellent durability, and also provides a method for producing the toner.

The toner of the present disclosure is a toner as specified in claims <NUM> to <NUM>.

The method for producing a toner of the present disclosure is a method for producing a toner as specified in claim <NUM>.

According to the present disclosure, a toner and a method for producing a toner that exhibit an excellent low-temperature fixability, an excellent storability in severe environments, and an excellent durability can be provided.

Unless specifically indicated otherwise, the expressions "from XX to YY" and "XX to YY" that show numerical value ranges refer in the present disclosure to numerical value ranges that include the lower limit and upper limit that are the end points.

The toner of the present disclosure is a toner comprising a toner particle that comprises a toner base particle and an outermost layer present on a surface of the toner base particle, the toner base particle containing a binder resin wherein.

The present inventor carried out investigations and found that when an outermost layer is present on a toner particle, the area where the toner base particle is exposed at the toner particle surface is made small, toner base particle-to-toner base particle contact between toner particles is suppressed, and the storability in severe environments is improved. It was also found that the charging characteristics are improved by increasing the area over which the outermost layer is present on the toner particle surface.

It was also found, on the other hand, that the low-temperature fixability can be impaired when the area over which the outermost layer is present on the toner particle surface is increased. The heat stability of the toner particle assumes an increasing trend when an outermost layer is present on the surface of the toner base particle. Due to this, the outermost layer exercises a large effect on the thermal properties of the toner base particle when the area over which the outermost layer is present on the toner particle surface is increased, and a reduction in the low-temperature fixability exhibited by the toner base particle can then occur.

On the occasion of intensive investigations by the present inventor in order to overcome this phenomenon, the present inventor discovered that, by having the outermost layer of the toner base particle have concave portions, the configuration of the outermost layer and toner base particle at the toner particle surface could be better controlled than heretofore and the severe environment storability could be made to coexist with an excellent low-temperature fixability and durability.

A concave portion in the toner particle surface denotes a region where the toner base particle is exposed or a region where the thickness of the outermost layer becomes thin, and is presumed to function to reduce the area over which the outermost layer is present on the toner particle surface. A novel effect was also found: when concave portions are formed in the toner particle surface, the external additive is then fixed in the concave portions and a trend of stabilization of the charging performance and flowability is then displayed even during long-term use. The present inventor thought that, by controlling the size and number of the concave portions, the severe environment storability could be made to coexist with a suppression of the impairment of the low-temperature fixability, and thus achieved the present disclosure.

More specifically, when T (nm) is an average thickness of the outermost layer in analysis of a cross section of the toner particle as observed with a transmission electron microscope, and.

When "n" represents a number of the concave portions that satisfy formulas (<NUM>) to (<NUM>) below per <NUM><NUM> of the surface of the toner particle, "n" is from <NUM> to <NUM>.

When the number of the concave portions "n" is less than <NUM>, low-temperature fixability is not obtained and storability in severe environments is not obtained. In addition, storability in severe environments is not obtained when the number of the concave portions "n" is larger than <NUM>. From the standpoints of the low-temperature fixability, durability, and storability in severe environments, the number of the concave portions "n" is preferably from <NUM> to <NUM> and is more preferably from <NUM> to <NUM>.

The number of concave portions "n" can be controlled through the concentration of dispersing agent particles that are attached to the toner base particle during formation of the outermost layer and through the heating temperature during formation of the outermost layer. Specifically, the number of the concave portions "n" increases with an increase in the concentration of the dispersing agent particles and with an increase in the heating temperature during formation of the outermost layer.

As provided by measurement of the concave portions in the toner particle surface using a scanning probe microscope (also referred to hereafter as an SPM), the long diameter A of the concave portions is preferably from <NUM> to <NUM> and is more preferably from <NUM> to <NUM>. The short diameter B of the concave portions, as provided by the same measurement, is preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>.

The low-temperature fixability tends to be more improved when the long diameter A of the concave portions is at least <NUM>. The low-temperature fixability also tends to be more improved when the short diameter B of the concave portions is at least <NUM>.

On the other hand, the storability in severe environments tends to be more improved when the long diameter A of the concave portions is not more than <NUM>. The storability in severe environments also tends to be more improved when the short diameter B of the concave portions is not more than <NUM>.

The long diameter A of the concave portions and the short diameter B of the concave portions can be controlled through the long diameter and short diameter of the dispersing agent particles that are attached to the toner base particle when the outermost layer is formed, and the long diameter and short diameter of these dispersing agent particles can be controlled through, for example, the reaction temperature and shear conditions during production of the dispersing agent particles. Specifically, a higher reaction temperature and stronger shear conditions during production of the dispersing agent particles tend to provide a smaller long diameter A and short diameter B of the concave portions.

The following formula is preferably satisfied by the average thickness T of the outermost layer in analysis of the toner cross section as observed with a transmission electron microscope (also indicated by TEM in the following), and by the depth D of the concave portions as obtained by measurement of the concave portions on the toner particle surface, using a scanning probe microscope, from the outermost surface of the outermost layer toward the center of the toner particle.

This D is more preferably from <NUM> × T (nm) to <NUM> × T (nm).

When D is at least <NUM> × T, the area of the toner base particle present in the concave portions is then large, and as a result the low-temperature fixability tends to be more improved. When, on the other hand, D is not greater than <NUM> × T, the concave portions are then not too deep and as a result the occurrence of strain in the surface of the outermost layer and the occurrence of burial of the external additive are suppressed and the durability tends to be more improved.

The concave portion depth D can be controlled, for example, through the concentration of the dispersing agent particles that are attached to the toner base particle when the outermost layer is formed, and through the amount of addition of the material that forms the outermost layer. Specifically, the concave portion depth D assumes an increasing trend as the concentration of the dispersing agent particles increases and as the amount of addition of the material that forms the outermost layer increases.

When "N" represents a number of the concave portions that satisfy both formulas (<NUM>) and (<NUM>) below per <NUM><NUM> of the surface of the toner particle (such concave portions are also referred to in particular as oversized concave portions in the following), "N" is not more than <NUM>. This N is more preferably not more than <NUM>. In addition, the number of the oversized concave portions "N" is preferably at least <NUM>. Any combination of these numerical value ranges may be used.

When the number of the oversized concave portions "N" having a long diameter a greater than <NUM> and a short diameter b greater than <NUM> is not more than <NUM> per <NUM><NUM> of the toner particle surface, toner base particle-to-toner base particle contact in severe environments is suppressed and the storability in severe environments tends to be more improved.

The number of the oversized concave portions "N" having a long diameter a greater than <NUM> and a short diameter b greater than <NUM> can be adjusted through, for example, the concentration of the dispersing agent particles that are attached to the toner base particle during formation of the outermost layer. Specifically, as the concentration of the dispersing agent particles declines, a declining trend is assumed by the number of the oversized concave portions "N" having a long diameter a larger than <NUM> and a short diameter b larger than <NUM>.

The average thickness T (nm) of the outermost layer is preferably from <NUM> to <NUM>.

The durability and the storability in severe environments tend to be more improved when the average thickness T (nm) of the outermost layer is at least <NUM>. The low-temperature fixability tends to be more improved when, on the other hand, the average thickness T (nm) of the outermost layer is not more than <NUM>.

The average thickness T (nm) of the outermost layer can be controlled through, for example, the amount of addition of the material that forms the outermost layer. Specifically, the average thickness T (nm) of the outermost layer assumes an increasing trend as the amount of addition of the material that forms the outermost layer increases.

From the standpoint of achieving coexistence between the low-temperature fixability and the durability and severe environment storability, the average thickness T (nm) of the outermost layer is more preferably from <NUM> to <NUM>.

Outermost Layer: The outermost layer preferably contains a thermoplastic resin. The content of the thermoplastic resin in the outermost layer may be, for example, from <NUM> mass% to <NUM> mass%.

The thermoplastic resin can be exemplified by the following resins: styrenic resins, acrylic resins (for example, acrylate ester polymers and methacrylic acid polymers), olefin resins (for example, polyethylene resins and polypropylene resins), vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, polyester resins, polyamide resins, and urethane resins.

Also usable are copolymers of these resins, i.e., copolymers (for example, styrene-acrylic resins and styrene-butadiene resins) provided by the insertion of a freely selected repeat unit into an aforementioned resin.

The thermoplastic resin preferably includes a styrene-acrylic resin. A copolymer of at least one kind of styrenic monomers and at least one kind of (meth)acrylic monomers is also a preferred embodiment of this styrene-acrylic resin.

For example, styrenic monomers and (meth)acrylic monomers as indicated in the following can be favorably used to synthesize the styrene-acrylic resin.

Favorable examples of the styrenic monomer are styrene, alkylstyrenes (for example, α-methylstyrene, p-ethylstyrene, and <NUM>-tert-butylstyrene), p-hydroxystyrene, m-hydroxystyrene, vinyltoluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, and p-chlorostyrene.

Favorable examples of the (meth)acrylic monomers are (meth)acrylic acid, (meth)acrylonitrile, alkyl (meth)acrylate esters, and hydroxyalkyl (meth)acrylate esters.

Favorable examples of alkyl (meth)acrylate esters are methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isobutyl (meth)acrylate, butyl (meth)acrylate, and <NUM>-ethylhexyl (meth)acrylate.

Favorable examples of the hydroxyalkyl (meth)acrylate esters are <NUM>-hydroxyethyl (meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, and <NUM>-hydroxybutyl (meth)acrylate.

The outermost layer includes a thermosetting resin in another preferred embodiment. The content of this thermosetting resin in the outermost layer may be, for example, from <NUM> mass% to <NUM> mass%.

Favorable examples of the thermosetting resin are melamine resins, urea resins, and glyoxal resins.

The thermosetting resin preferably includes a melamine resin. Melamine resin is, for example, the polycondensate of melamine and formaldehyde, and the monomer used to form a melamine resin is, for example, melamine.

Binder Resin: The binder resin preferably includes a styrene-acrylic resin (more preferably a styrene-alkyl acrylate ester resin). The content of the styrene-acrylic resin in the binder resin may be, for example, from <NUM> mass% to <NUM> mass%.

The same monomers as the styrenic monomers and (meth)acrylic monomers described above for synthesis of the thermoplastic resin in the outermost layer can be suitably used as the monomer for synthesis of the styrene-acrylic resin.

The binder resin includes a polyester resin in another preferred embodiment. The content of the polyester resin in the binder resin may be, for example, from <NUM> mass% to <NUM> mass% or from <NUM> mass% to <NUM> mass%.

The polyester resin can be obtained by the condensation polymerization or cocondensation polymerization of a heretofore known dibasic or at least tribasic carboxylic acid component with a dihydric or at least trihydric alcohol component.

For example, a derivative of the ester (for example, acid halide, anhydride, and lower alkyl ester) may be used as the dibasic or at least tribasic carboxylic acid component. Lower alkyl here means an alkyl group having from <NUM> to <NUM> carbon atoms.

The following, for example, can be used as the dibasic carboxylic acid component: dibasic acids such as succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, malonic acid, and dodecenylsuccinic acid and their anhydrides and lower alkyl esters, and aliphatic unsaturated dicarboxylic acids, e.g., maleic acid, fumaric acid, itaconic acid, and citraconic acid.

For example, <NUM>,<NUM>,<NUM>-benzenetricarboxylic acid and <NUM>,<NUM>,<NUM>-benzenetricarboxylic acid and their lower alkyl esters can be used as the at least tribasic carboxylic acid component.

A single one of these carboxylic acid components may be used by itself or at least two of these may be used in combination.

Preferred examples of the dihydric or at least trihydric alcohol component are diols, bisphenols, and at least trihydric alcohols.

The dihydric alcohol component can be exemplified by the following compounds: alkylene glycols (ethylene glycol, <NUM>,<NUM>-propylene glycol, and <NUM>,<NUM>-propylene glycol), alkylene ether glycols (polyethylene glycol and polypropylene glycol), alicyclic diols (<NUM>,<NUM>-cyclohexanedimethanol), bisphenols (bisphenol A), and alkylene oxide (ethylene oxide or propylene oxide) adducts on alicyclic diols.

The alkyl moiety of the alkylene glycol and alkylene ether glycol may be straight chain or branched. An alkylene glycol having a branched structure can also preferably be used.

The at least trihydric alcohol component can be exemplified by the following compounds: glycerol, trimethylolethane, trimethylolpropane, and pentaerythritol.

A single one of these alcohol components may be used by itself or at least two of these may be used in combination.

As necessary, a monobasic acid such as acetic acid or benzoic acid and a monohydric alcohol such as cyclohexanol or benzyl alcohol may also be used for the purpose of adjusting the acid value or hydroxyl value.

There are no particular limitations on the method for synthesizing the polyester resin, but, for example, a transesterification method or direct polycondensation method, as such or in combination, may be used.

Wax: The toner base particle may contain a wax.

Specific examples are as follows: petroleum waxes as represented by paraffin waxes, microcrystalline waxes, and petrolatum, and derivatives thereof; montan wax and derivatives thereof; hydrocarbon waxes provided by the Fischer-Tropsch method, and derivatives thereof; polyolefin waxes as represented by polyethylene, and derivatives thereof; and natural waxes as represented by carnauba wax and candelilla wax, and derivatives thereof. These derivatives also include oxides and block copolymers and graft modifications with vinyl monomer.

Also usable are alcohols such as higher aliphatic alcohols; fatty acids such as stearic acid and palmitic acid, and their acid amides, esters, and ketones; hardened castor oil and derivatives thereof; plant waxes; and animal waxes.

A single one of these waxes may be used by itself or at least two of these may be used in combination.

Among the preceding, a trend of an enhanced developing performance and transferability is exhibited when a polyolefin, a hydrocarbon wax provided by the Fischer-Tropsch method, or a petroleum wax is used, which is thus preferred.

An oxidation inhibitor may be added to these waxes in a range that does not influence the effects for the toner according to the present disclosure.

The content of the wax is preferably from <NUM> mass parts to <NUM> mass parts per <NUM> mass parts of the binder resin. The melting point of the wax is preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>.

The wax preferably contains an ester compound.

This ester compound can be exemplified by esters between a monohydric alcohol and an aliphatic carboxylic acid or an ester between a monobasic carboxylic acid and an aliphatic alcohol, such as behenyl behenate, stearyl stearate, and palmityl palmitate; esters between a dihydric alcohol and an aliphatic carboxylic acid and esters between a dibasic carboxylic acid and an aliphatic alcohol, such as ethylene glycol distearate, dibehenyl sebacate, and hexanediol dibehenate; esters between a trihydric alcohol and an aliphatic carboxylic acid and esters between a tribasic carboxylic acid and an aliphatic alcohol, such as glycerol tribehenate; esters between a tetrahydric alcohol and an aliphatic carboxylic acid and esters between a tetrabasic carboxylic acid and an aliphatic alcohol, such as pentaerythritol tetrastearate and pentaerythritol tetrapalmitate; esters between a hexahydric alcohol and an aliphatic carboxylic acid and esters between a hexabasic carboxylic acid and an aliphatic alcohol, such as dipentaerythritol hexastearate and dipentaerythritol hexapalmitate; and esters between a polyhydric alcohol and an aliphatic carboxylic acid and esters between a polybasic carboxylic acid and an aliphatic alcohol, such as polyglycerol behenate.

The low-temperature fixability is further enhanced due to the plasticizing effect on the toner particle brought about by the use of these ester compounds. Among the preceding, the wax more preferably contains, from the standpoint of the balance between the durability and low-temperature fixability, an ester compound given by formula (<NUM>) or formula (<NUM>). <CHM>
<CHM>.

In formulas (<NUM>) and (<NUM>), R<NUM> represents an alkylene group having from <NUM> to <NUM> (preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>) carbons and R<NUM> and R<NUM> each independently represent an alkyl group having from <NUM> to <NUM> (preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>) carbons. This alkyl group may be a straight-chain alkyl group or branched alkyl group, but straight-chain alkyl groups are preferred.

Among ester compounds given by formulas (<NUM>) and (<NUM>), ethylene glycol distearate, in which R<NUM> is a C<NUM> alkylene group and R<NUM> and R<NUM> are C<NUM> straight-chain alkyl groups, is more preferred.

The content of the ester compound in the wax is preferably from <NUM> mass% to <NUM> mass% and more preferably from <NUM> mass% to <NUM> mass%. Coexistence between the durability and low-temperature fixability is more readily brought about when the ester compound content in the wax is in the indicated range.

Colorant: The toner base particle may contain a colorant. Known pigments and dyes can be used as the colorant. Pigments are preferred for the colorant from the standpoint of providing an excellent weathering resistance.

Cyan colorants can be exemplified by copper phthalocyanine compounds and derivatives thereof, anthraquinone compounds, and basic dye lake compounds.

Specific examples are as follows: C. Pigment Blue <NUM>, <NUM>, <NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>, <NUM>, and <NUM>.

Magenta colorants can be exemplified by condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds.

Specific examples are as follows: C. Pigment Red <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and C. Pigment Violet <NUM>.

Yellow colorants can be exemplified by condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo-metal complexes, methine compounds, and allylamide compounds.

Specific examples are as follows: C. Pigment Yellow <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Black colorants can be exemplified by carbon black and by black colorants provided by color mixing using the aforementioned yellow colorants, magenta colorants, and cyan colorants to give a black color.

A single one of these colorants may be used by itself or a mixture of at least two of these may be used. These may also be used in solid solution form.

The content of the colorant is preferably from <NUM> mass parts to <NUM> mass parts per <NUM> mass parts of the binder resin.

Charge Control Agents and Charge Control Resins: The toner base particle may contain at least one selection from the group consisting of charge control agents and charge control resins.

A known charge control agent can be used as the charge control agent, wherein a charge control agent that provides a fast triboelectric charging speed and that can maintain a defined and stable triboelectric charge quantity is particularly preferred. When the toner particle is produced by the suspension polymerization method, a charge control agent that exercises little polymerization inhibition and that is substantially free of material soluble in the aqueous medium is particularly preferred.

Charge control agents include charge control agents that control toner to negative charging and charge control agents that control toner to positive charging.

Charge control agents that control the toner to negative charging can be exemplified by monoazo metal compounds; acetylacetone-metal compounds; metal compounds of aromatic oxycarboxylic acids, aromatic dicarboxylic acids, oxycarboxylic acids, and dicarboxylic acids; aromatic oxycarboxylic acids, aromatic monocarboxylic acids, and aromatic polycarboxylic acids and their metal salts, anhydrides, and esters; phenol derivatives such as bisphenol; urea derivatives; metal-containing salicylic acid compounds; metal-containing naphthoic acid compounds; boron compounds; quaternary ammonium salts; calixarene; and charge control resins.

Charge control agents that control toner to positive charging can be exemplified by the following: guanidine compounds; imidazole compounds; quaternary ammonium salts such as tributylbenzylammonium <NUM>-hydroxy-<NUM>-naphthosulfonate and tetrabutylammonium tetrafluoroborate, and their onium salt analogues, such as phosphonium salts, and their lake pigments; triphenylmethane dyes and their lake pigments (the laking agent is exemplified by phosphotungstic acid, phosphomolybdic acid, phosphomolybdotungstic acid, tannic acid, lauric acid, gallic acid, ferricyanides, and ferrocyanides); metal salts of higher fatty acids; and charge control resins.

Among these charge control agents, metal-containing salicylic acid compounds are preferred and metal-containing salicylic acid compounds in which the metal is aluminum or zirconium are particularly preferred.

The charge control resin can be exemplified by polymers and copolymers having a sulfonic acid group, sulfonate salt group, or sulfonate ester group. Polymer having a sulfonic acid group, sulfonate salt group, or sulfonate ester group is particularly preferably a polymer that contains at least <NUM> mass%, as the copolymerization ratio, of a sulfonic acid group-containing acrylamide-type monomer or sulfonic acid group-containing methacrylamide-type monomer, and more preferably is a polymer containing at least <NUM> mass% of same.

The charge control resin preferably has a glass transition temperature (Tg) from <NUM> to <NUM>, a peak molecular weight (Mp) from <NUM>,<NUM> to <NUM>,<NUM>, and a weight-average molecular weight (Mw) from <NUM>,<NUM> to <NUM>,<NUM>. When this is used, preferred triboelectric charging characteristics can be conferred without exercising an influence on the thermal characteristics required of a toner particle. Moreover, because the charge control resin contains a sulfonic acid group, for example, the dispersibility of the charge control resin itself, as well as the dispersibility of, e.g., the colorant, in the polymerizable monomer composition is improved and the tinting strength, transparency, and triboelectric charging characteristics can then be further improved.

A single one of these charge control agents or charge control resins may be used by itself, or at least two of these may be used in combination.

The content of the charge control agent or charge control resin, per <NUM> mass parts of the binder resin, is preferably from <NUM> mass parts to <NUM> mass parts and is more preferably from <NUM> mass parts to <NUM> mass parts.

Inorganic Particles of, e.g., Silica, Used as External Additive: The toner particle as such may be used as a toner, but is often used as toner after optional mixing with, e.g., an external additive, to attach same to the surface.

The presence of silica particles with a number-average particle diameter (D1) for the primary particles of at least <NUM> (preferably at least <NUM>) on the toner surface is preferred. This D1 can be, for example, not greater than <NUM>. Any combination of these numerical value ranges may be used.

The content of the silica particles having a primary particle D1 of at least <NUM>, per <NUM> mass parts of the toner particle, is preferably from <NUM> mass parts to <NUM> mass parts and is more preferably from <NUM> mass parts to <NUM> mass parts.

The flowability and charging performance can be improved by the addition to the toner particle of silica particles as an external additive. In addition, by having the primary particle diameter of the external additive be at least <NUM>, the inorganic particles then become fixed in the concave portions in the outermost layer and a stabilization of the charging performance and flowability is obtained even during long-term use.

Inorganic particles other than the aforementioned silica particles may be present on the toner surface. Such inorganic particles can be exemplified by titanium oxide particles, alumina particles, silica particles having a primary particle diameter of less than <NUM>, and composite oxide particles of the preceding.

The silica particles can be exemplified by the dry silica and fumed silica produced by the vapor-phase oxidation of a silicon halide, and by the wet silica produced from water glass. Dry silica is preferred because dry silica contains little of the silanol group present on the surface and in the interior of silica particles and contains little Na<NUM>O and SO<NUM><NUM>-. The dry silica may be a composite fine particle of silica and another metal oxide as produced by the use in the production process of a silicon halide compound in combination with a metal halide compound such as, for example, aluminum chloride or titanium chloride.

Viewed from the standpoints of the charge quantity on the toner, the environmental stability, the properties in high humidity environments, the developing performance, the transferability, and so forth, hydrophobed silica particles (also referred to as hydrophobic silica) are more preferably used as the silica particles.

The treatment agent for this hydrophobic treatment of the silica particles can be exemplified by unmodified silicone varnishes, variously modified silicone varnishes, unmodified silicone oils, variously modified silicone oils, silane compounds, silane coupling agents, other organosilicon compounds, and organotitanium compounds. A single one of these treatment agents may be used by itself or at least two of these may be used in combination.

Among the preceding, silica particles that have been treated with silicone oil are preferred. A hydrophobic silica provided by the hydrophobic treatment of silica particles with a silane coupling agent and treatment with silicone oil either at the same time as or after this treatment, is more preferred from the standpoints of maintaining a high charge quantity on the toner particle even in high humidity environments and reducing selective development.

The BET retention ratio of the toner, which is measured by the method described below, is preferably from <NUM>% to <NUM>% and more preferably from <NUM>% to <NUM>%.

The durability during long-term use tends to be more improved when the BET retention ratio of the toner is in the range from <NUM>% to <NUM>%. The low-temperature fixability and storability in severe environments can also be further improved.

The BET retention ratio of the toner can be controlled through, for example, the addition of inorganic particles having a primary particle D1 of at least <NUM> and through the attachment conditions for the external additive (temperature, time).

The method for producing the toner contains the following steps.

The production method according to the present disclosure is described in detail in the following.

In accordance with the process in (a) to (c), dispersing agent particles are attached to the surface of the toner base particle, material for formation of the outermost layer is added to the dispersion that contains this toner base particle, and the outermost layer is formed on the surface of the toner base particle. The medium used during formation of the outermost layer is preferably an aqueous medium from the standpoint of preventing the elution of components contained in the toner base particle into the medium.

Dispersing agent particles are attached to the surface of the toner base particle in step (a). The following are examples of methods for attaching the dispersing agent particles to the surface of the toner base particle: addition of the dispersing agent after toner base particles have been mechanically dispersed in the aqueous medium using a device that has a strong stirring capability; addition of toner base particles to an aqueous medium that contains the dispersing agent. Between these, the addition of toner base particles to an aqueous medium containing the dispersing agent is preferred because this enables a uniform dispersion of the toner base particles in the aqueous medium using little power.

For example, a polymeric dispersing agent, surfactant, resin particles, or inorganic particles can be used without particular limitation as the dispersing agent. Among these, the use of inorganic particles is preferred from the standpoints of preventing surface modification of the surface of the toner base particle and bringing about a high level of dispersion of the toner base particle in the medium (particularly an aqueous medium). Particles of an inorganic compound, e.g., sodium phosphate or calcium chloride, can be used as the inorganic particles.

The number-average particle diameter of the dispersing agent particles is preferably from <NUM> to <NUM> and more preferably is from <NUM> to <NUM>. The amount of use of the dispersing agent particles, per <NUM> mass parts of the toner base particle, is preferably from <NUM> mass parts to <NUM> mass parts and more preferably from <NUM> mass parts to <NUM> mass parts.

Due to the uniform dispersion of the dispersing agent particles in the aqueous medium containing the dispersing agent particles, the dispersing agent particles can be attached to the toner base particle surface by introducing the toner base particles and carrying out mechanical mixing with a stirring device.

When the toner base particle is produced by the suspension polymerization method, an aqueous dispersion of toner base particles having dispersing agent particles attached to the surface is produced in the production process, and as a consequence this aqueous dispersion of toner base particles can also be used as such as a toner base particle dispersion. That is, a step of attaching dispersing agent particles to the toner base particle surface can be included in the step of producing toner base particles.

The outermost layer is formed on the toner base particle surface in step (b). For example, an outermost layer can be formed on the toner base particle surface by adding the material of the outermost layer to the toner base particle dispersion.

For example, the aforementioned thermoplastic resins and the aforementioned thermosetting resins can be used as the material of the outermost layer. When a thermoplastic resin is used as the material of the outermost layer, the outermost layer can be formed, for example, by mixing a dispersion of the thermoplastic resin with the toner base particles to attach the thermoplastic resin to the surface of the toner base particles in the aqueous dispersion, and heating. When a thermosetting resin is used as the material of the outermost layer, the outermost layer can be formed by mixing the monomer constituting the thermosetting resin with the toner base particle and developing the reaction at the surface of the toner base particle in the aqueous medium by heating.

The outermost layer covers areas where the dispersing agent particles attached in step (a) are attached and is formed in a film configuration on all or a portion of the toner base particle surface.

The temperature during formation of the outermost layer is preferably from <NUM> to <NUM> and is more preferably from <NUM> to <NUM>. Formation of the outermost layer proceeds well by carrying out formation of the outermost layer in this temperature range.

In step (c), the dispersing agent particles are removed from the toner base particle surface after the outermost layer has been formed. When the dispersing agent particles are inorganic particles, for example, removal from the toner base particle surface can be carried out by dissolving the inorganic particles using acid and subsequently performing filtration. Removal of the dispersing agent particles enables the shape of the dispersing agent particle to be formed into a concave portion shape in the outermost layer.

This is followed as necessary by repeated dispersion in water and filtration to obtain a toner particle having concave portions in the surface.

The methods for measuring the various property values are described in the following.

Method for Measuring Long Diameter of Each of Concave Portions, Short Diameter of Each of Concave Portions, Depth of Each of Concave Portions, and Number of Concave Portions in Toner Particle Surface.

The concave portions in the toner particle surface are observed using a scanning probe microscope (SPM) and the following method.

An SI-DF20 (Al coated back side) from Seiko Instruments Inc. is used for the measurement cantilever and is operated in dynamic force mode. The SPM is used after checking the accuracy in the depth direction pre-measurement using a pattern sample (<NUM> ± <NUM>) for accuracy checking.

Conductive two-sided tape is first applied to the sample stand, and the toner particles are sprayed onto this. The excess toner particles are removed from the sample stand by blowing with air. Using this sample, the toner particle surface is magnified to <NUM> × <NUM> using the SPM (product name: E-sweep, Hitachi High-Tech Science Corporation) and the concave portions in the outermost layer are observed.

After the measurement, tilt correction is performed on the obtained <NUM> × <NUM> measurement data and the mean surface roughness is then calculated. The mean surface roughness means the arithmetic average value, over the <NUM> × <NUM>, of the depth of the concave portions for measurement toward the center of the toner particle from the outermost surface of the outermost layer, and is designated the depth d<NUM> (nm) of the concave portions in the outermost layer in the present disclosure. The depths from d<NUM> to d<NUM> of the concave portions for <NUM> toner particles are determined by this method, and the arithmetic average value of from d<NUM> to d<NUM> is taken to be the depth D (nm) of the concave portions.

The number of concave portions "n" that satisfy formulas (<NUM>) to (<NUM>) and the number of the oversized concave portions "N" are determined as follows. The tilt-corrected measurement data provided by the aforementioned measurement is output; the long diameters a (nm) of the concave portions, the short diameters b (nm) of the concave portions, and the depths d (nm) of the concave portions in <NUM> × <NUM> are surveyed; and the number of concave portions "n<NUM>" that satisfy formulas (<NUM>) to (<NUM>) and the number of oversized concave portions "N<NUM>", in each case per <NUM> × <NUM> of the toner particle surface, are counted. The numbers from n<NUM> to n<NUM> of concave portions satisfying formulas (<NUM>) to (<NUM>) and the numbers from N<NUM> to N<NUM> of oversized concave portions are counted for <NUM> toner particles using this method, and their arithmetic average values are designated the number of concave portions "n" and the number of oversized concave portions "N", respectively.

The long diameter A of the concave portions and the short diameter B of the concave portions are determined as follows. The tilt-corrected measurement data provided by the aforementioned measurement is output; the arithmetic average values of the long diameters of the concave portions and the short diameters of the concave portions per <NUM> × <NUM> of the toner particle surface are determined and are respectively designated the long diameter at of the concave portions and the short diameter b<NUM> of the concave portions. The long diameters from a<NUM> to a<NUM> of the concave portions and the short diameters from b<NUM> to b<NUM> of the concave portions are determined for <NUM> toner particles using this method, and their arithmetic average values are designated the long diameter A of the concave portions and the short diameter B of the concave portions, respectively.

When the concave portions were to be measured on the surface of toner having an external additive attached to the surface, the external additive was removed using the following procedure and the measurements of the concave portions by the methods described above were performed on the resulting toner particles.

A <NUM>% aqueous sucrose solution is prepared by the addition of <NUM> of sucrose (Kishida Chemical Co. ) to <NUM> of deionized water and dissolving while heating on a water bath. <NUM> of this sucrose concentrate and <NUM> of Contaminon N (product name) (a <NUM> mass% aqueous solution of a neutral pH <NUM> detergent for cleaning precision measurement instrumentation, including a nonionic surfactant, anionic surfactant, and organic builder, Wako Pure Chemical Industries, Ltd. ) are introduced into a centrifugal separation tube to prepare a dispersion. <NUM> of the toner is added to this dispersion, and clumps of the toner are broken up using, for example, a spatula.

The centrifugal separation tube is shaken with a shaker for <NUM> minutes at <NUM> strokes per minute (spm). After shaking, the solution is transferred over to a glass tube (<NUM>) for swing rotor service, and separation is performed with a centrifugal separator using conditions of <NUM>,<NUM> rpm and <NUM> minutes.

Satisfactory separation of the toner particles from the aqueous solution is checked visually, and the toner particles separated into the uppermost layer are recovered with, for example, a spatula. The recovered toner particles are filtered using a reduced pressure filter and are then dried for at least one hour in a dryer. The dried product is broken up with a spatula to yield toner particles.

The cross section of the toner particle is observed with a transmission electron microscope (TEM) using the following method.

The toner particles are first thoroughly dispersed in a normal temperature-curable epoxy resin followed by curing for <NUM> days in a <NUM> atmosphere. Thin-section samples with a thickness of <NUM> are sliced from the resulting cured material using a microtome equipped with a diamond blade, and ruthenium staining is performed using a vacuum staining device (Filgen, Inc. The resulting sample is then magnified <NUM>,000X using a TEM (product name: Tecnai TF20XT electron microscope, FEI Company). The thickness (unit: nm) of the outermost layer is measured at four randomly selected locations on a single toner particle.

Examination of the cross section is carried out on <NUM> toner particles using this method, and the arithmetic average value for the total of <NUM> locations is used as the average thickness T (nm).

The weight-average particle diameter (D4) and number-average particle diameter (D1) of the toner, toner particle, and toner base particle (also referred to below as, for example, toner) is determined proceeding as follows.

The measurement instrument used is a "Coulter Counter Multisizer <NUM>" (registered trademark, Beckman Coulter, Inc. ), a precision particle size distribution measurement instrument operating on the pore electrical resistance method and equipped with a <NUM>-µm aperture tube.

The measurement conditions are set and the measurement data are analyzed using the accompanying dedicated software, i.e., "Beckman Coulter Multisizer <NUM> Version <NUM>" (Beckman Coulter, Inc. The measurements are carried out in <NUM>,<NUM> channels for the number of effective measurement channels.

The aqueous electrolyte solution used for the measurements is prepared by dissolving special-grade sodium chloride in deionized water to provide a concentration of <NUM>% and, for example, "ISOTON II" (Beckman Coulter, Inc. ) can be used.

The dedicated software is configured as follows prior to measurement and analysis.

In the "modify the standard operating method (SOMME)" screen in the dedicated software, the total count number in the control mode is set to <NUM>,<NUM> particles; the number of measurements is set to <NUM> time; and the Kd value is set to the value obtained using "standard particle <NUM>" (Beckman Coulter, Inc. The threshold value and noise level are automatically set by pressing the "threshold value/noise level measurement button". In addition, the current is set to <NUM>,<NUM>µA; the gain is set to <NUM>; the electrolyte solution is set to ISOTON II; and a check is entered for the "post-measurement aperture tube flush".

In the "setting conversion from pulses to particle diameter" screen of the dedicated software, the bin interval is set to logarithmic particle diameter; the particle diameter bin is set to <NUM> particle diameter bins; and the particle diameter range is set to <NUM> to <NUM>.

The specific measurement procedure is as follows.

The volume-average diameter of the particles in the thermoplastic resin dispersion is measured using a Zetasizer Nano-ZS (Malvern Instruments Ltd.

A measurement sample is first prepared by diluting the thermoplastic resin dispersion to be measured with water to a solid-liquid ratio of <NUM> mass% (±<NUM> mass%), and this is introduced into a quartz cell, which is installed in the measurement section. The refractive index of the thermoplastic resin and the refractive index and viscosity of the dispersing medium are input for the measurement conditions, and measurement is carried out in the range from <NUM> to <NUM>.

The glass transition temperature (Tg) of, e.g., the toner base particle or outermost layer material, is measured using a "Q1000" differential scanning calorimeter (TA Instruments) in accordance with ASTM D <NUM>-<NUM>.

The melting points of indium and zinc are used for temperature correction in the instrument detection section, and the heat of fusion of indium is used for correction of the amount of heat.

Specifically, a <NUM> sample is exactly weighed out and this is introduced into an aluminum pan; an empty aluminum pan is used for reference. The measurement is run at a ramp rate of <NUM>/min in the measurement temperature range from <NUM> to <NUM>.

In the measurement, heating is carried out to <NUM>, followed by cooling to <NUM> at a ramp down rate of <NUM>/min and then reheating.

The change in the specific heat in the temperature range of from <NUM> to <NUM> is obtained in this second heating process. The glass transition temperature (Tg) is taken to be the point at the intersection between the differential heat curve and the line for the midpoint for the baselines for prior to and subsequent to the appearance of the change in the specific heat.

The BET specific surface area of the toner is measured in accordance with JIS Z <NUM> (<NUM>). The specific measurement procedure is as follows.

A "TriStar <NUM> (Shimadzu Corporation) automatic specific surface area/pore distribution analyzer", which employs a constant-volume gas adsorption method as its measurement principle, is used as the measurement instrument. The "TriStar <NUM> Version <NUM>" dedicated software provided with this instrument is used to set the measurement conditions and analyze the measurement data. A vacuum pump, nitrogen gas line, and helium gas line are connected to the instrument. The value calculated by the BET multipoint method using nitrogen gas as the adsorption gas is used as the BET specific surface area in the present disclosure.

The BET specific surface area is specifically determined as follows.

First, nitrogen gas is adsorbed on the sample (toner) and the equilibration pressure P (Pa) within the sample cell and the amount of nitrogen adsorption Va (mol·g-<NUM>) by the sample are measured at this point. The adsorption isotherm is obtained using the relative pressure Pr, which is the value provided by dividing the equilibration pressure P (Pa) within the sample cell by the saturation vapor pressure of nitrogen Po (Pa), for the horizontal axis and using the amount of nitrogen adsorption Va (mol·g-<NUM>) for the vertical axis. The monomolecular layer adsorption amount Vm (mol·g-<NUM>), which is the amount of adsorption required to form a monomolecular layer on the surface of the sample, is then determined using the BET equation provided below.

Here, C is the BET parameter and is a variable that changes with the type of measurement sample, the type of adsorption gas, and the adsorption temperature.

The BET equation can be rendered as a straight line, with a slope of (C - <NUM>)/(Vm × C) and an intercept of <NUM>/(Vm × C), by using Pr for the X-axis and Pr/Va(<NUM> - Pr) for the Y-axis. This straight line is called a BET plot. <MAT><MAT>.

The value of the slope of this straight line and the value of its intercept can be calculated by plotting the measured values of Pr and the measured values of Pr/Va(<NUM> - Pr) on a graph and generating a straight line by the least-squares method. Using these values, Vm and C can be calculated by solving the aforementioned simultaneous equations for the slope and intercept.

The BET specific surface area S (m<NUM>·g-<NUM>) of the sample is then calculated using the following formula, the Vm calculated as above, and the molecular cross-sectional area of the nitrogen molecule (<NUM><NUM>).

Here, N is Avogadro's number (mol-<NUM>).

The procedure for calculating Vm is described in the following. The procedure for determining Vm using this instrument is carried out according to the "TriStar <NUM> Instruction Manual V4. <NUM>" provided with the instrument, and the measurement is specifically carried out using the following procedure.

The glass sample cell (stem diameter = <NUM>/<NUM> inch, volume = approximately <NUM>) provided with the instrument is thoroughly cleaned and dried and then exactly weighed to determine the tare mass. The sample is introduced into this sample cell using a funnel. The sample amount is adjusted as appropriate in accordance with the specific gravity and particle diameter of the sample; for toner, approximately <NUM> is introduced.

The sample cell loaded with the sample is set in a "Vacuprep <NUM> Pretreatment Apparatus" (Shimadzu Corporation) connected to a vacuum pump and nitrogen gas line and vacuum degassing is continued for about <NUM> hours at <NUM>. This vacuum degassing is performed by gradually degassing while adjusting the valve in order to avoid suctioning sample into the vacuum pump. The pressure in the cell gradually drops as degassing proceeds and approximately <NUM> Pa (approximately <NUM> millitorr) is finally reached. After the completion of vacuum degassing, nitrogen gas is gradually introduced and the interior of the sample cell is returned to atmospheric pressure and the sample cell is removed from the pretreatment apparatus. The mass of this sample cell is exactly weighed and the precise mass of the toner is calculated from the difference from the tare mass. The sample cell is closed with a rubber stopper during weighing in order to prevent the sample in the sample cell from being contaminated with, for example, moisture in the atmosphere.

Measurement of the free space in the sample cell including the connection fixtures is then performed. For the free space, the volume of the sample cell is measured at <NUM> using helium gas; then, after the sample cell has been cooled with liquid nitrogen, the volume of the sample cell is similarly measured using helium gas; and the free space is calculated converting from the difference in these volumes. In addition, the saturation vapor pressure Po (Pa) of the nitrogen is automatically measured separately using the Po tube built into the instrument.

Then, after the interior of the sample cell has been vacuum degassed, the sample cell is cooled with liquid nitrogen while vacuum degassing is continued. After this, nitrogen gas is admitted in stages into the sample cell and the nitrogen molecules are adsorbed to the sample. At this point, the above-described adsorption isotherm is obtained by measurement of the equilibration pressure P (Pa) as required, and this adsorption isotherm is converted to a BET plot. The relative pressure Pr points for data collection are set at a total of six points, i.e., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. A straight line is generated by the least-squares method from the obtained measurement data and Vm is calculated from the slope and intercept of this straight line. Using this value of Vm, the BET specific surface area of the toner is calculated as described above.

Method for Identifying Resin Type for Resin in Outermost Layer.

The type of resin is identified for the resin in the outermost layer using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

The resin type for the binder resin and the structure of the ester wax compound in the wax are identified using nuclear magnetic resonance spectroscopy (<NUM>H-NMR) [<NUM>, CDCl<NUM>, room temperature (<NUM>)] or pyrolysis GCMS.

<NUM> of the toner and <NUM>µL of methylation reagent (<NUM>% methanol solution of tetramethylammonium hydroxide) are added to the Pyrofoil under the aforementioned measurement conditions and analysis is performed.

The number-average primary particle diameter of the external additive is determined using a scanning electron microscope (SEM).

The toner surface is observed using these conditions and the particle diameter of the external additive is determined. This procedure is repeated and the arithmetic average value for <NUM> is determined.

The toner and toner production method according to the present disclosure are more particularly described by the examples provided below. However, these in no way limit the present disclosure. Unless specifically indicated otherwise, "parts" in the examples and comparative examples is on a mass basis in all instances.

<NUM> parts of sodium dodecyl sulfate and <NUM>,<NUM> parts of deionized water were introduced into a beaker fitted with stirrer, and stirring was continued at <NUM> until complete dissolution had occurred to prepare an aqueous solution. The following materials were then mixed to prepare a polymerizable monomer composition.

The temperature of the polymerizable monomer composition was reduced to <NUM>, followed by the admixture of <NUM> parts of tertiary-butyl peroxypivalate as polymerization initiator and introduction into the aforementioned aqueous solution. An emulsion of the polymerizable monomer composition was prepared by exposure for <NUM> minutes (<NUM> second intermittent, maintenance of <NUM>) to ultrasound from a high-output ultrasound homogenizer (VCX-<NUM>).

This emulsion was introduced into a heat-dried four-neck flask; bubbling with nitrogen was performed for <NUM> minutes while stirring the emulsion at <NUM> rpm; and stirring was thereafter carried out for <NUM> hours at <NUM>. To stop the reaction, the emulsion was then air-cooled while being stirred, thus yielding a thermoplastic resin dispersion <NUM> of a styrene-acrylic resin that would provide the outermost layer material. This thermoplastic resin dispersion was then separated at <NUM>,<NUM> rpm for <NUM> hour using a centrifugal separator, and the supernatant was removed. Dispersion with the fresh addition of deionized water and separation with a centrifugal separator was repeated three times, and deionized water was then added to prepare a thermoplastic resin dispersion <NUM> having a solids concentration of <NUM> mass%. The volume-average diameter of the particles in the thermoplastic resin dispersion <NUM> was measured at <NUM>, and the Tg was <NUM>.

A thermoplastic resin dispersion <NUM> was produced proceeding as in the method for producing the thermoplastic resin dispersion <NUM>, but changing the amount of sodium dodecyl sulfate as indicated in Table <NUM> and changing the composition of the polymerizable monomer composition as indicated below. The volume-average diameter of the particles in the thermoplastic resin dispersion <NUM> and Tg are given in Table <NUM>.

A thermoplastic resin dispersion <NUM> was produced proceeding as in the method for producing the thermoplastic resin dispersion <NUM>, but changing, as indicated in Table <NUM>, the amount of sodium dodecyl sulfate in the method for producing thermoplastic resin dispersion <NUM>. The volume-average diameter of the particles in the thermoplastic resin dispersion <NUM> and Tg are given in Table <NUM>.

The following materials were mixed in a reactor fitted with a condenser, stirrer, and nitrogen introduction line and were heated and held at <NUM> while stirring.

A styrene-acrylic resin <NUM> was synthesized by continuously adding <NUM> parts of a <NUM>% xylene solution of t-butyl hydroperoxide dropwise to the system over <NUM> hours and, after cooling, separating and removing the solvent. The weight-average molecular weight Mw was <NUM>,<NUM>, and Tg was <NUM>.

The following materials were mixed in a reactor fitted with a condenser, stirrer, and nitrogen introduction line.

The system was subjected to nitrogen substitution by a pressure-reduction process, after which heating was carried out to <NUM> and a reaction was run for <NUM> hours while introducing nitrogen and removing the produced water. Then, while continuing to stir, the temperature was gradually raised to <NUM> under reduced pressure, and a polyester resin <NUM> was synthesized by reaction for an additional <NUM> hours. The weight-average molecular weight Mw was <NUM>,<NUM>, and Tg was <NUM>.

The following materials were thoroughly mixed using an FM mixer (Nippon Coke & Engineering Co. ), followed by melt-kneading using a twinscrew kneader (Ikegai Ironworks Corporation) set to a temperature of <NUM>.

The resulting kneaded material was cooled and was coarsely pulverized to <NUM> and below using a hammer mill to yield a coarse pulverizate.

A fine pulverizate of about <NUM> was then obtained from the resulting coarse pulverizate using a Turbo Mill from Turbo Kogyo Co. , followed by cutting the fines and coarse powder using a Coanda effect-based multi-grade classifier to obtain the toner base particle <NUM>.

Toner base particle <NUM> had a number-average particle diameter (D1) of <NUM>, a weight-average particle diameter (D4) of <NUM>, and a Tg of <NUM>.

<NUM> parts of sodium phosphate (dodecahydrate) was introduced into <NUM> parts of deionized water in a reactor, and this was held for <NUM> hour at <NUM> while purging with nitrogen.

Stirring was carried out at <NUM>,<NUM> rpm using a T. Homomixer (Tokushu Kika Kogyo Co. While maintaining the stirring, an aqueous calcium chloride solution of <NUM> parts of calcium chloride (dihydrate) dissolved in <NUM> parts of deionized water was introduced all at once into the reactor to prepare an aqueous medium that contained inorganic fine particles as a dispersing agent. <NUM> mol/L hydrochloric acid was introduced into the aqueous medium in the reactor to adjust the pH to <NUM> and provide an aqueous medium <NUM>.

<NUM> parts of toner base particle <NUM> was introduced into aqueous medium <NUM> and dispersion was carried out for <NUM> minutes at a temperature of <NUM> while rotating at <NUM>,<NUM> rpm using a T. Deionized water was added to adjust the toner base particle concentration in the dispersion to <NUM>%, thus providing toner base particle dispersion <NUM>.

Aqueous media <NUM> to <NUM> and toner base particle dispersions <NUM> to <NUM> were produced proceeding as in the method for producing the toner base particle dispersion <NUM>, but changing, as shown in Table <NUM>, the amounts of the sodium phosphate and calcium chloride used for the aqueous medium <NUM> in the method for producing the toner base particle dispersion <NUM>.

Stirring was carried out at <NUM>,<NUM> rpm using a T. Homomixer (Tokushu Kika Kogyo Co. While maintaining the stirring, an aqueous calcium chloride solution of <NUM> parts of calcium chloride (dihydrate) dissolved in <NUM> parts of deionized water was introduced all at once into the reactor to prepare an aqueous medium that contained inorganic fine particles as a dispersing agent. <NUM> mol/L hydrochloric acid was introduced into the aqueous medium in the reactor to adjust the pH to <NUM> and provide aqueous medium <NUM>.

These materials were introduced into an attritor (Nippon Coke & Engineering Co. ) and dispersion was carried out for <NUM> hours at <NUM> rpm using zirconia particles with a diameter of <NUM> to prepare a colorant dispersion in which the pigment was dispersed.

The following materials were then added to this colorant dispersion.

(condensation polymer of terephthalic acid and the <NUM> mol adduct of propylene oxide on bisphenol A, weight-average molecular weight Mw = <NUM>,<NUM>).

This material was then held at <NUM> and a polymerizable monomer composition <NUM> was prepared by dissolving and dispersing to uniformity at <NUM> rpm using a T.

While holding the temperature of aqueous medium <NUM> at <NUM> and the stirrer rotation rate at <NUM>,<NUM> rpm, the polymerizable monomer composition <NUM> was introduced into the aqueous medium <NUM> and <NUM> parts of the polymerization initiator t-butyl peroxypivalate was added. Granulation was performed for <NUM> minutes under these conditions while maintaining <NUM>,<NUM> rpm with the stirrer. Polymerization Step.

The high-speed stirrer was replaced with a stirrer equipped with a propeller impeller and polymerization was carried out for <NUM> hours while maintaining <NUM> and stirring at <NUM> rpm. An additional polymerization reaction was run by raising the temperature to <NUM> and heating for <NUM> hours. Deionized water was added to adjust the toner base particle concentration in the dispersion to <NUM>%, thus yielding toner base particle dispersion <NUM> in which toner base particle <NUM> was dispersed.

A reactor holding <NUM> parts of deionized water was held at <NUM>, after which dilute hydrochloric acid was added to adjust the pH of the aqueous medium to <NUM>. After the pH had been adjusted, the following materials were introduced and dissolution was carried out to obtain aqueous medium <NUM>.

<NUM> parts of toner base particle <NUM> was added to aqueous medium <NUM> and the reactor was stirred for <NUM> hour at a rate of <NUM> rpm. Deionized water was then added to adjust the toner base particle concentration in the dispersion to <NUM>%, thus yielding a toner base particle dispersion <NUM> in which toner base particle <NUM> was dispersed.

A reactor holding <NUM> parts of deionized water was held at <NUM>, after which dilute hydrochloric acid was added to adjust the pH of the aqueous medium to <NUM>. After the pH had been adjusted, the following material was introduced to obtain aqueous medium <NUM>.

Using a mixer (FM-10B Henschel mixer from Nippon Coke & Engineering Co. ), toner base particle <NUM> and acrylic monodisperse particles (MP-<NUM>, Soken Chemical & Engineering Co. , volume-average diameter = <NUM>) were mixed for <NUM> minutes at <NUM>,<NUM> rpm to obtain a toner base particle <NUM>, in which the acrylic monodisperse particles had been preliminarily externally added to the surface of the toner base particle <NUM>.

<NUM> parts of magnesium chloride was introduced into and dissolved in <NUM> parts of deionized water in a reactor, after which holding was carried out for <NUM> hour at <NUM> while purging with nitrogen.

Stirring was carried out at <NUM>,<NUM> rpm using a T. Homomixer (Tokushu Kika Kogyo Co. While maintaining the stirring, an aqueous sodium hydroxide solution of <NUM> parts of sodium hydroxide dissolved in <NUM> parts of deionized water was introduced all at once into the reactor to prepare an aqueous medium containing a dispersion stabilizer. <NUM> mol/L hydrochloric acid was introduced into the aqueous medium in the reactor to adjust the pH to <NUM> and provide aqueous medium <NUM>.

While holding the temperature of the aqueous medium at <NUM> and the stirrer rotation rate at <NUM>,<NUM> rpm, the polymerizable monomer composition <NUM> was introduced into the aqueous medium <NUM> and <NUM> parts of the polymerization initiator t-butyl peroxypivalate was added. Granulation was performed for <NUM> minutes under these conditions while maintaining <NUM>,<NUM> rpm with the stirrer. Polymerization Step.

The high-speed stirrer was replaced with a stirrer equipped with a propeller impeller and a polymerization reaction was run at <NUM> while stirring at <NUM> rpm. After the polymerization conversion had reached approximately <NUM>%, <NUM> parts of methyl methacrylate, as polymerizable monomer for the outermost layer, and <NUM> parts of <NUM>,<NUM>-azobis(<NUM>-methyl-N-(<NUM>-hydroxyethyl)propionamide) (VA086, Wako Pure Chemical Industries, Ltd. ) dissolved in <NUM> parts of deionized water were added while maintaining the same polymerization temperature. The temperature was then raised to <NUM> and a polymerization reaction was run while heating for <NUM> hours. Deionized water was added to adjust the toner base particle concentration in the dispersion to <NUM>%, thus yielding a toner base particle dispersion <NUM> in which toner base particle <NUM> was dispersed.

The system was subjected to nitrogen substitution by a pressure-reduction process, after which heating was carried out to <NUM> and a reaction was run for <NUM> hours while introducing nitrogen and removing the produced water. Then, while continuing to stir, the temperature was gradually raised to <NUM> under reduced pressure, and the polyester resin <NUM> was synthesized by reaction for an additional <NUM> hours. The weight-average molecular weight Mw was <NUM>,<NUM>, and Tg was <NUM>.

The resulting kneaded material was cooled and was coarsely pulverized to not greater than <NUM> using a hammer mill to yield a coarse pulverizate.

Toner base particle <NUM> was obtained proceeding as for toner base particle <NUM>, but without using the ethylene glycol distearate. Toner base particle dispersion <NUM> was then obtained proceeding as for toner base particle dispersion <NUM>.

Toner base particle <NUM> was obtained proceeding as for toner base particle <NUM>, but using <NUM>,<NUM>-hexanediol dilaurate in place of the ethylene glycol distearate. Toner base particle dispersion <NUM> was then obtained proceeding as for toner base particle dispersion <NUM>.

Toner base particle <NUM> was obtained proceeding as for toner base particle <NUM>, but using the ester compound given by CH<NUM>(CH<NUM>)<NUM>COO(CH<NUM>)<NUM>COO(CH<NUM>)<NUM>CH<NUM> in place of the ethylene glycol distearate. Toner base particle dispersion <NUM> was then obtained proceeding as for toner base particle dispersion <NUM>.

The following samples were weighed into a reactor and mixed using a propeller impeller.

The pH of the resulting mixture was then adjusted to <NUM> using a <NUM> mol/L aqueous NaOH solution, and the temperature of the mixture was brought to <NUM> and holding was subsequently carried out for <NUM> hour while mixing using the propeller impeller at <NUM> rpm. Then, while stirring with the propeller impeller, the temperature was raised to <NUM> at a rate of <NUM>/min and holding was carried out for <NUM> hours.

The temperature of the contents was thereafter cooled to normal temperature (approximately <NUM>); the pH was then adjusted to <NUM> with <NUM> mol/L hydrochloric acid and stirring was carried out for <NUM> hour; and filtration while washing with deionized water subsequently yielded a toner particle <NUM> having a styrene-acrylic thermoplastic resin in the outermost layer.

Toner particles <NUM> to <NUM> and <NUM> to <NUM> were produced proceeding as in the Toner Particle <NUM> Production Example, but changing the type of toner base particle dispersion and the type and amount of the thermoplastic resin dispersion in the Toner Particle <NUM> Production Example to that indicated in Table <NUM>.

The temperature of the mixture was then brought to <NUM> and holding was subsequently carried out for <NUM> hour while mixing using a propeller impeller at <NUM> rpm. Then, while stirring with the propeller impeller, the temperature was raised to <NUM> at a rate of <NUM>/min and holding was carried out for <NUM> hours. This was followed by adjusting the pH of the resulting mixture to <NUM> using a <NUM> mol/L aqueous NaOH solution.

The temperature of the contents was thereafter cooled to normal temperature (approximately <NUM>); the pH was then adjusted to <NUM> with <NUM> mol/L hydrochloric acid and stirring was carried out for <NUM> hour; and filtration while washing with deionized water subsequently yielded a toner particle <NUM> having a melamine thermosetting resin in the outermost layer.

<NUM> parts of toner base particle dispersion <NUM> was introduced into a reactor and the temperature was raised to <NUM> at a rate of <NUM>/min while stirring at <NUM> rpm. After the temperature had been raised, stirring was continued for <NUM> hours using conditions of <NUM> and <NUM> rpm. The pH of the resulting mixture was then adjusted to <NUM> using a <NUM> mol/L aqueous NaOH solution.

After the temperature of the contents had then been cooled to normal temperature (approximately <NUM>), filtration and washing were carried out five times to yield a toner particle <NUM> that had a thermoplastic resin and a thermosetting resin in the outermost layer.

Toner particles <NUM> to <NUM> and <NUM> were produced proceeding as in the Toner Particle <NUM> Production Example, but changing the type and amount of the toner base particle dispersion and the production temperature in the Toner Particle <NUM> Production Example to that indicated in Table <NUM>.

<NUM> parts of toner base particle dispersion <NUM> was introduced into a reactor and the temperature was raised to <NUM> at a rate of <NUM>/min while stirring at <NUM> rpm. After the temperature had been raised, stirring was continued for <NUM> hours using conditions of <NUM> and <NUM> rpm. The pH of the resulting mixture was then adjusted to <NUM> using a <NUM> mol/L aqueous NaOH solution. After the temperature of the contents had then been cooled to normal temperature (approximately <NUM>), filtration and washing were carried out five times to yield a toner particle <NUM> that had a melamine thermosetting resin in the outermost layer and that had the pre-externally-added acrylic monodisperse particles fixed to the surface.

The pre-externally-added acrylic monodisperse particles on the toner base particle surface were then removed. The melamine thermosetting resin formed in the outermost layer is tightly fixed to the toner base particle surface, while the pre-externally-added acrylic monodisperse particles are fixed to the surface by a weak force. As a consequence, the pre-externally-added particles can be removed by the application of an external force even after the outermost layer has been formed.

In this instance, toner particle <NUM> was first dispersed in a mixed aqueous solution including a <NUM>% aqueous sucrose solution and a <NUM>% neutral aqueous detergent solution for cleaning precision measurement instrumentation, including a nonionic surfactant and an anionic surfactant. A treatment of shaking <NUM> times in <NUM> minute was then performed using a shaker, after which the thusly treated toner particle <NUM> was dispersed in the aforementioned mixed aqueous solution and was subjected to a treatment in which ultrasound was applied for <NUM> minutes at an electrical output of <NUM> W. After the execution of this treatment, the execution of five cycles of filtration and washing yielded a toner particle <NUM> that had a melamine thermosetting resin in the outermost layer, and from which the acrylic monodisperse particles had been removed.

<NUM> parts of toner base particle dispersion <NUM> was introduced into a reactor and the temperature was raised to <NUM> at a rate of <NUM>/min while stirring at <NUM> rpm. Immediately after the temperature in the reactor reached <NUM> during the temperature ramp up process, the pH of toner base particle dispersion <NUM> was adjusted to <NUM> by adding a <NUM> mol/L aqueous NaOH solution to the reactor. This was followed by continuing to stir for <NUM> hours using conditions of <NUM> and <NUM> rpm.

After the temperature of the contents had then been cooled to normal temperature (<NUM>), five cycles of filtration and washing were carried out to yield a toner particle <NUM> that had a thermoplastic resin in the outermost layer.

The properties of the obtained toner particles <NUM> to <NUM> are given in Table <NUM>.

In Table <NUM>, "Y" in the cells that report the status of occurrence of concave portions indicates that concave portions were formed in the toner particle surface, and "N" in the cells that report the status of occurrence of concave portions indicates that concave portions were not formed in the toner particle surface. In cells other than this, "Y" indicates that the value is within the prescribed range, and "N" indicates that the value is not within the prescribed range.

The external additives indicated below were added to <NUM> parts of toner particle <NUM> and mixing was carried out for <NUM> minutes at a peripheral velocity of <NUM>/s using an FM mixer (Nippon Coke & Engineering Co. ); toner <NUM> was obtained by removing the coarse particles using a mesh with an aperture of <NUM>.

Toners <NUM> to <NUM> and <NUM> to <NUM> were produced proceeding as in the Toner <NUM> Production Example.

The external additive indicated below was added to <NUM> parts of toner particle <NUM> and mixing was carried out for <NUM> minutes at a peripheral velocity of <NUM>/s using an FM mixer (Nippon Coke & Engineering Co. ); toner <NUM> was obtained by removing the coarse particles using a mesh with an aperture of <NUM>.

The following evaluations were performed using toners <NUM> to <NUM>. The results of the evaluations are given in Table <NUM>.

The evaluation methods and evaluation criteria used in the present disclosure are described in the following.

A modified version of an LBP-712Ci (Canon, Inc. ) commercial laser printer was used as the image-forming apparatus.

With regard to the modifications, the potential in charging, transfer, and so forth was made reversible through connection to an external high-voltage power source and image formation was thus made possible with a positive-charging or a negative-charging toner as produced in the present instance. The process speed was also made <NUM>/sec.

A commercial <NUM> (cyan) toner cartridge (Canon, Inc. ) was used as the process cartridge. The product toner was removed from the interior of the cartridge; cleaning with an air blower was performed; and <NUM> of a toner as described above was loaded.

The product toner was removed at each of the yellow, magenta, and black stations, and the evaluations were performed with the yellow, magenta, and black cartridges installed, but with the remaining toner amount detection mechanism inactivated.

For each of the obtained toners <NUM> to <NUM>, approximately <NUM> was introduced into a <NUM>,<NUM>-mL plastic cup, and this was held for <NUM> hours in a low-temperature, low-humidity environment (<NUM>, <NUM>% RH) followed by transition to a high-temperature, high-humidity environment (<NUM>, <NUM>% RH) over <NUM> hours. Holding in the high-temperature, high-humidity environment for <NUM> hours was carried out, followed by transition back to the low-temperature, low-humidity environment (<NUM>, <NUM>% RH) over <NUM> hours. After the toner had been subjected to three cycles of this process, it was removed and inspected for aggregation. A time chart of the heat cycle is given in <FIG>. The results of the evaluation are given in Table <NUM>.

An image with a print percentage of <NUM>% was continuously output in a low-temperature, low-humidity environment with a temperature of <NUM> and a humidity of <NUM>% RH. After each <NUM> prints, a solid image and a halftone image were output and were visually inspected for the presence/absence of the occurrence of vertical streaks caused by toner melt-adhesion to the control member, that is, the occurrence of development streaks. <NUM>,<NUM> prints of the image were ultimately output. The results of the evaluation are given in Table <NUM>.

In addition, in the evaluation of the paper-feed durability, the BET retention ratio was calculated using the following formula-where Vini is the BET specific surface area prior to the evaluation in the paper-feed durability test and Vend is the BET specific surface area after the <NUM>,<NUM>-sheet paper-feed durability test-and was used to evaluate the toner durability.

The fixing unit was detached from the modified LBP-712Ci laser printer (Canon, Inc. Using the loaded toner, an unfixed toner image (<NUM>/cm<NUM>) with a length of <NUM> × width of <NUM> was subsequently formed on image-receiving paper (Office Planner <NUM>/m<NUM>, Canon, Inc. ) at a location <NUM> from the leading edge with respect to the paper feed direction. The detached fixing unit was then modified to enable adjustment of the fixation temperature and process speed. This was used to carry out a fixing test on the unfixed image.

First, with the process speed set to <NUM>/s and the fixing lineal pressure set to <NUM> kgf, and operating in a normal-temperature, normal-humidity environment (<NUM>, <NUM>% RH), the low temperature-side fixing onset point was measured by carrying out fixing of the unfixed image at each temperature starting from an initial temperature of <NUM> and increasing the set temperature sequentially in <NUM> increments.

The criteria for evaluating the low-temperature fixability are given below. The results of the evaluations are given in Table <NUM>.

This low temperature-side fixing onset point is the lowest temperature at which there are three or fewer occurrences of image exfoliation with a diameter of at least <NUM>, when the surface of the fixed image has been rubbed five times at a speed of <NUM>/s using lens-cleaning paper (Dusper K-<NUM>) carrying a load of <NUM> kPa (<NUM>/cm<NUM>). This image exfoliation assumes an increasing trend when a strong fixing has not been executed.

In the table, "*" denotes number of prints to occurrence of development streaks.

Claim 1:
A toner comprising a toner particle that comprises a toner base particle and an outermost layer present on the surface of the toner base particle, the toner base particle containing a binder resin wherein
a plurality of concave portions are formed on the surface of the toner particle, and
when T (nm) is the average thickness of the outermost layer in analysis of a cross section of the toner particle as observed with a transmission electron microscope, and
a (nm) is the long diameter of each of the concave portions determined as described in the description, b (nm) is the short diameter of each of the concave portions determined as described in the description, and d (nm) is the depth of each of the concave portions when the concave portions on the toner particle are measured by using a scanning probe microscope from an outermost surface of the outermost layer toward a center of the toner particle,
when "n" represents the number of the concave portions that satisfy formulas (<NUM>) to (<NUM>) below per <NUM><NUM> of the surface of the toner particle, "n" satisfies formula (<NUM>) below: <MAT> <MAT> <MAT> <MAT>