WO2008075805A1

WO2008075805A1 - Method for preparing toner and toner prepared by same

Info

Publication number: WO2008075805A1
Application number: PCT/KR2006/005558
Authority: WO
Inventors: Jong Chull Park; Mi Sun Kim; Kyung Hyun Baek; Jin Gyu Park
Original assignee: Cheil Industries Inc.
Priority date: 2006-12-19
Filing date: 2006-12-19
Publication date: 2008-06-26
Also published as: KR100833580B1

Abstract

The present invention provides a method of preparing a toner, the method comprising the steps of: providing a polymer latex; forming toner particles by aggregation-coalescence of colorants, charge control agents and wax with said polymer latex in the presence of a phosphorus -containing dispersant; and cooling, separating and drying the toner particles.

Description

METHOD FOR PREPARING TONER AND TONER PREPARED

BY SAME

Technical Field

[1] The present invention relates to a method of preparing a toner. More particularly, the present invention relates to a method of preparing a toner, which enables control of the morphology of the particles and adjustment to a uniform particle size distribution, enables the toner to have improved durability so as to prevent picture inferiority, and simplifies the process by introducing a phosphorus -containing dispersant during an aggregation-coalescence process. The present invention also relates to a toner prepared by the foregoing method.

[2]

Background Art

[3] In the field of electrophotography or electrostatic recording, developers visualizing an electrostatic image or electrostatic latent image mainly include two-component developers consisting of a toner and carrier particles and one-component developers substantially consisting of a toner only. The one-component developers include magnetic one-component developers with magnetic material and non-magnetic one- component developers without magnetic material. The use of non-magnetic one- component developers including a color toner in printers is rapidly growing. When a toner suitable for a developing system using a non-magnetic one-component developer is designed, suitable organic or inorganic particles such as fumed silica are used as external additives so as to enhance the fluidity of the toner.

[4] Non-magnetic one-component developing systems using toner particles treated by external addition usually exhibit problems of toner scattering caused by poor static electricity and lack of toner durability. Most of all, lack of toner durability results in soft blocking in that a toner adheres to the doctor blades and filming in that a toner adheres to OPC. This is the biggest problem in designing a non-magnetic one- component developer. Generally, this type of toner is colored particles obtained by dispersing a colorant, such as carbon black, a charge control agent and organic and inorganic dyes in a binding resin.

[5] Methods for preparing a toner are broadly divided into pulverization methods and polymerization methods. In pulverization methods, the toner is obtained by mixing synthetic resin, colorant, and optionally other additives, pulverizing after melt- mixing, and then sorting for obtaining desired particle size. This pulverization method is referred to as a "break-down method" because it grinds melt-mixed big particles to micro sized particles functioning as a toner.

[6] In polymerization methods, a polymerizable monomer composition is prepared by homogenously dissolving or dispersing polymerizable monomers, colorant, polymerization initiators, and optionally various additives such as a cross-linking agent and an antistatic agent. Subsequently the polymerizable monomer composition is dispersed in a water-based dispersing medium using a mixer so as to form fine droplet particles of the polymerizable polymer composition. Then the temperature is raised and suspension polymerization is performed to obtain colored polymer particles with desired size.

[7] An image forming apparatus such as an electronic photographic apparatus or an electrostatic recording apparatus forms an electrostatic latent image by exposing an image on a uniformly charged photoreceptor, makes a toner image by adhering toner to the electrostatic latent image, transcribes the toner image to a transfer material, and subsequently fixes the unfixed toner image to the transfer medium by heating, pres- surization and so on. In the fixation, generally, the transfer material with the toner image passes between a fixing roll and a pressing roll and the toner is melt-fixed to the transfer material by heating and pressing.

[8] Images formed by an image forming apparatus such as an electrophotocopier should satisfy requirements of high precision and accuracy. Conventionally, a toner manufactured by pulverization was mainly used for an image forming apparatus. In the pulverization method, colored particles with a broad particle size range are likely formed. Therefore in order to obtain satisfactory developing properties, it is necessary to narrow the range of the particle size distribution by sorting the pulverized products. However, when manufacturing a toner suitable for electrophotography or electrostatic latent image, it is difficult to precisely control particle size or particle size distribution in conventional melt-mixing and grinding methods. Also, when preparing a small particle size toner, toner preparation yield is low due to the sorting process. In addition, changes or adjustments to toner design to obtain desirable charging and fixing properties are limited. Accordingly, polymerized toners, in which the size of particles is easy to control and which do not need to undergo a complex manufacturing process such as sorting, have come into the spotlight recently.

[9] Manufacturing a toner by polymerizing methods enables one to obtain polymerized toner having a desired particle size and particle size distribution without grinding or sorting.

[10] Recently, emulsion aggregation has been adopted in the polymerization of toner, in which it is easy to control the shape and size of toner. The emulsion aggregation adopts a core-shell structure formed by encapsulation which introduces a shell in order to minimize the adverse effect of toner components, such as dyes, wax and charge control agents. Although emulsion aggregation has an advantage in that control of the shape of the particles is easier than with suspension polymerization, in practice to control both the shape and size of the particles simultaneously is sometimes difficult and thus it may cause a poor image such as from poor cleaning. In particular, lowering the molecular weight of latex for low temperature fixation may cause other problem such as soft blocking. Also, introducing an additional process to form a core-shell structure may deteriorate the distribution of particle sizes by inducing sticking between desirable sized particles.

[11] Accordingly, the present inventors have developed a method of preparing a toner, which method is simple. With the method, it is easy to control the morphology of particles and to adjust to a uniform particle size distribution in aggregation-coalescence. Further the prepared toner has improved durability so that it is free of image inferiority such as from soft blocking.

[12]

Disclosure of Invention Technical Problem

[13] An object of the present invention is to provide a method of preparing a toner, which method simplifies the manufacturing process and reduces production cost by manufacturing a toner without a separate manufacturing step for a shell latex.

[14] Another object of the present invention is to provide a method of preparing a toner, in which it is easy to control the morphology of the particles.

[15] Yet another object of the present invention is to provide a method of preparing a toner, in which it is possible to provide uniform particle size distribution.

[16] Still another object of the present invention is to provide a method of preparing a toner with improved durability.

[17] Still another object of the present invention is to provide an image forming apparatus and an image forming method having improved properties of particle size distribution and image quality by using the toner according to said preparing method.

[18] The objects and other advantages may be achieved by the present invention which will be discussed below.

[19]

Technical Solution

[20] The method of preparing a toner of the present invention comprises the steps of providing a polymer latex; forming toner particles by aggregation-coalescence of colorants, charge control agents and wax with said polymer latex in the presence of a phosphorus -containing dispersant; and cooling, separating and drying said toner particles. [21] In exemplary embodiments of the invention, the step of forming toner particles may further comprise the step of controlling ionic strength by adding an inorganic salt or an electrolyte.

[22] In embodiments, the phosphorus-containing dispersant may be used in an amount of

0.01 to 5 parts by weight based on 100 parts by weight of total aggregated dry solid.

[23] The phosphorus-containing dispersant may be sodium hexametaphosphate, sodium pyrophosphate, sodium metaphosphate and sodium tripolyphosphate.

[24] Another aspect of the invention provides a toner prepared by the foregoing process.

[25] Another aspect of the invention provides an image forming method. The method comprises the steps of electrifying a photoreceptor; forming a latent image on the photoreceptor by exposing said electrified photoreceptor to light; forming a toner image by contacting the foregoing toner with said latent image on the photoreceptor; transcribing said toner image from the photoreceptor to a final image receptor; fixing the toner on said final image receptor by heating said final image receptor with the transcribed toner image and softening/melting the toner; and removing the remaining toner from said photoreceptor.

[26] Another aspect of the invention provides an image forming apparatus comprising means for electrifying a photoreceptor; means for exposing the electrified photoreceptor to form a latent image on said photoreceptor; developing means for contacting the foregoing toner with the latent image on the photoreceptor to form a toner image; means for transcribing said toner image from the photoreceptor to a final image receptor; means for fixing the toner image on the final image receptor by heating the final image receptor with the transcribed toner image to soften or to melt the toner; and cleaning means for removing the remaining toner from the photoreceptor.

[27]

Advantageous Effects

[28] The present invention provides a toner preparing method, an image forming method and an image forming apparatus, which enable control of the morphology of the particles and adjustment to uniform particle size distribution in aggregation-coalescence, enable the toner to have improved durability so as to prevent picture inferiority such as from soft blocking, and simplify the manufacture method of toner, by introducing a phosphate salt to the surface of the toner particles in the aggregation-coalescence containing at least one colorant, charge control agent, wax and polymer latex.

[29] Simple changes and modifications of the present invention can be easily carried out by those who are ordinarily skilled in the art, and the changes and modifications are deemed to be with the scope of the present invention. [30]

Best Mode for Carrying Out the Invention

[31] The present invention relates to a method for producing toner, in particular chemically polymerized toner (CPT). The above method comprises the steps of preparing polymer latex; forming toner particles by aggregation-coalescence of at least one colorant, charge control agents and wax with said polymer latex in the presence of a phosphorus-containing dispersant; and cooling, separating and drying the coalesced toner particles. Each step of the method will be discussed below in detail.

[32]

[33] Preparing polymer latex

[34] The method according to the present invention comprises a step of preparing polymer latex.

[35] The polymerizable monomer which can be used to prepare polymer latex is, for example, at least one selected from styrenic monomer such as styrene, vinyl toluene andα-methyl styrene; acrylic acid, methacrylic acid; (metha)acrylic acid derivatives such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dimethylaminoethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexylmethacrylate, dimethylaminoethyl- methacrylate, acrylonitrile, methacrylonitrile, acrylamide and methacrylamide; ethylenic unsaturated monoolefin such as ethylene, propylene and butylene; halogenated vinyl such as vinyl chloride, vinylidene chloride and vinyl fluoride; vinyl ester such as vinyl acetate and vinyl propionate; vinyl ether such as vinyl methyl ether and vinyl ethyl ether; vinyl ketone such as vinyl methyl ketone and methyl isopropenyl ketone; and a nitrogen containing vinyl compound such as 2- vinyl pyridine, 4-vinyl pyridine and N- vinyl pyrrolidone. Preferably, the weight average molecular weight of the latex particle is from 10,000 to 300,000.

[36] In the present invention, the monomeric composition of the polymer latex particle may be preferably a styrene- acrylic copolymer containing about 60~80 parts by weight of styrene and about 20 to about 40 parts by weight of butylacrylate. The polymerized latex particles may be used in an amount of about 70 to 95 parts by weight of the total dry solid of the aggregation-coalescence step.

[37]

[38] Aggregation-coalescence of polymer latex

[39] In this step, the aggregation-coalescence of the latex particles prepared as above with colorants, charge control agents and wax is carried out in the presence of a phosphorus -containing dispersant. [40] A carbon black or an aniline black may be used as the colorant for a black toner. A nonmagnetic toner according to the present invention is easily used to prepare color toners. For color toners, a carbon black may be used as a black colorant, and a colored colorant comprises one or more selected from yellow, magenta, and cyan colorants.

[41] Examples of the yellow colorant may include condensation nitrogen compounds, isoindolinone compounds, anthraquine compounds, azo metal complex, or allyl imide compounds. Specifically, C.I. pigment yellow 12, 13, 14, 17, 62, 74, 83, 93, 94, 95, 109, 110, 111, 128, 129, 147, 168, 180, or the like can be used as the yellow colorant.

[42] Examples of the magenta colorant include condensation nitrogen compounds, anthraquine, quinacridon compounds, basic lake pigments, naphthol compounds, ben- zoimidazol compounds, thioindigo compounds, or perylene compounds. Specifically, C.I. pigment red 2, 3, 5, 6, 7, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 166, 169, 177, 184, 185, 202, 206, 220, 221, 254, or the like can be used as the magenta colorant.

[43] Examples of cyan blue colorant include copper phthalocyanine compounds and derivative thereof, anthraquine compounds, or basic lake pigments. Specifically, C.I. pigment blue 1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, 66 or the like can be used as the cyan colorant.

[44] These colorants can be used can be used alone or in combination with one another, and the colorant may be selected based on color, chroma, brightness, weatherability, dispersibility in toner, and the like.

[45] The amount of the colorant may be 0.1 to 20 parts by weight based on 100 parts by weight of the polymerizable monomer. The content of the colorant may be an amount sufficient to color the toner. The coloring effect is not sufficient when the content of the colorant is less than 0.1 parts by weight, while it is not possible to obtain sufficient frictional electric charge. Since the preparation cost of the toner increases when the content of the colorant is more than 20 parts by weight, this is not preferable.

[46] Any suitable wax which provides a desirable characteristic to the final toner compound may be used. The wax may include, but is not limited thereto, polyethylenic wax, polypropylenic wax, silicon wax, paraffinic wax, ester wax, carnauba wax and metallocene wax, for example. The melting point of the wax may be preferably in the range of about 50 to about 150 ⁰C. The amount of wax may be in the range of about 1 to about 10 parts by weight, preferably in the range of about 2 to about 8 parts by weight based on 100 parts by weight of the monomer mixture.

[47] The wax component physically adheres to the toner particles, but does not covalently bond with the toner particles. The wax is fixed on the final image receptor at a low fixation temperature and enables the toner to have superior final image durability and an antiabrasion property by preventing the toner from adhering to the fixing roller, a so-called "hot offset", by functioning as a release agent. In one embodiment of the present invention, high-purity solid fatty acid ester can be used as the wax. For example, polyolefins with low molecular weight such as low molecular weight polyethylene, low molecular weight polypropylene and low molecular weight polybutylene and the like; paraffin wax; multi functional ester compounds and the like are used. It is preferable that the wax used as a releasing agent is a multi functional ester compound prepared from a reaction of tri- or higher functional alcohols and carboxylic acids.

[48] The alcohol with three or more of functional groups, for example, includes aliphatic alcohols such as glycerin, pentaerithritol, pentaglycerol, and the like; cycloaliphatic alcohols such as chloroglycitol, quercitol, inositol, and the like; aromatic alcohols such as tris(hydroxymethyl)benzene and the like; sugars such as D-erythrose, L-arabinose, D-mannose, D-galactose, D-fructose, L-rhamnose, sacharose, maltose, lactose, and the like; and sugar alcohols such as erythrite, D-trehalose, L-arabite, adonitol, xylitol, and the like.

[49] The carboxy acid, for example, includes aliphatic carboxylic acids such as acetic acid, butyric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, myristic acid, stearic acid, margaric acid, arachidic acid, cerotic acid, merichisinic acid, eicosenoic acid, valeric acid, sorbic acid, linolic acid, linolenic acid, behenic acid, tetrolic acid, xymenic acid, and the like; cycloaliphatic carboxylic acids such as cyclohexane carboxylic acid, hexahy- droisophthalic acid, hexahydroterephthalic acid, 3,4,5,6-tetrahydrophthalic acid, and the like; and aromatic carboxylic acids such as benzoic acid, troic acid, cumic acid, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, trimellitic acid, hemimellitic acid, and the like.

[50] The charge control agent may be introduced to enhance charge-up rate and stability of charge. Especially, it is preferable to use a charge control agent having substantially no solubility in an aqueous medium. The charge control agent may be, for example, a salicylic acid compound containing a metal, such as zinc or aluminum; a metal complex of an aromatic carboxylic acid such as dialkyl salicylate, naphthoic acid, or dicarboxylic acid; a boron complex of bisdiphenylglycolic acid; a silicate compound, calixarenes and the like. More particularly, zinc dialkyl salicylate or borobis(l,l-diphenyl-l-oxo-acetyl) potassium salt may be used. The charge control agent can be used in an amount of 0.1 to 7 parts by weight.

[51] In the present invention, a phosphate salt is introduced during the aggregation to attach the phosphate salt to the surface of the particles with a median cumulative volume in the range of 4~10 D. Then, toner particle which contains phosphorus on its surface can be prepared by adjusting pH. In embodiments, a strong acidic environment of pH 2~3 is maintained for about 30 minutes. After forming a coating layer which contains phosphorus on the surface of the toner particles, the aggregation-coalescence solution may be cooled to about 60 ⁰C, followed by separating and drying. As used herein, the median cumulative volume refers to the diameter of the 50' sized particle, provided there are 100 particles, and is indicated as "D50".

[52] The phosphorus-containing dispersant may be a phosphate salt compound. The phosphate compound useful in the present invention may be one selected from sodium hexametaphosphate, sodium pyrophosphate, sodium metaphosphate, and sodium tripolyphosphate. In the present invention, the amount of P-containing dispersant introduced into the aggregation may be in the range of about 0.01 to about 5 parts by weight based on 100 parts by weight of the total aggregated solid. Because it is possible to control the particle size distribution and morphology of the particles independently using this phosphate compound, it is easier to design the toner's particle size distribution and morphology. Also, due to the strong binding between phosphate and the surface of the particles, the durability of the toner can be improved.

[53] An aggregation rate can be controlled by adjusting pH and ionic strength. The size and shape of a toner can be controlled by controlling reaction conditions, such as temperature, heating time, stirring rate, and the like.

[54] In exemplary embodiments of the invention, the latex particles comprising the colorant, the charge control agent and the wax can be aggregated by adjusting pH or adding an inorganic salt, for example, sodium salt such as NaCl, Na SO and Na CO , or magnesium salt such as MgCl and MgSO at the initial stage of aggregation. In case of the black toner, other color salts such as FeSO , Fe (SO ) and the like may be used.

[55] In the aggregation, if the pH increases by adding an alkali, surfaces of the particles are changed to have negative charges, or positive charges are relatively less occupied on the particle surfaces. The change of the particle surfaces into the negative charges are mainly caused by the existence of macro monomer chains chemically bonded to the surfaces, a sulfate group of an initiator such as potassium persulfate (KPS), and an acid group used as a co-monomer.

[56] If the particles have high negative charge value, i.e., a high pH or a high zeta potential value, the aggregation does not proceed actively because of increasing repulsive force. On the contrary, if the pH or the zeta potential value is low, the dispersion stability of the particle may decrease, thereby irregular aggregation having non-uniform particle size distribution or non- aggregation may occur. If the concentration of the electrolyte or the inorganic salt is higher than a critical coagulation concentration, the electrostatic repulsion is compensated and then the aggregation proceeds rapidly by Brownian motion of the latex particles. If the concentration is lower than a critical coagulation concentration, the coagulation will occur slowly.

[57] In the aggregation step, the size of particles may be enlarged by ionic strength and collision among the particles. In the present invention, the step of aggregation may further comprise the step of controlling ionic strength by adding the electrolyte or the inorganic salt.

[58] In exemplary embodiments of the invention, the polymer latex can be aggregated at a temperature of Tg or less. In exemplary embodiments of the invention, the polymer latex can be aggregated by being heated at a temperature of Tg or more. When the polymer latex is aggregated at a temperature of Tg or less, the aggregation process may simultaneously proceed with the aggregation and/or coalescence at a temperature of Tg or more. Above the temperature of Tg of latex, the Gibbs free energy of the latex particle may increase, so that toner with a smooth surface can be obtained. It is also possible to control the shape of the particles based on temperature conditions.

[59]

[60] Cooling. Separation. Drying and External addition of the toner particles

[61] The morphological difference of the toner particles results from the interfacial tension and rheology of the particles. After obtaining desired size and shape of the particles, the toner particles are cooled at a temperature of Tg or less, separated through filtration, and dried. External additives such as silica are externally added to the dried toner. Finally the toner usable for electrophotographic development of laser printer, photocopier and the like can be obtained by controlling the electrified charge.

[62]

[63] Image forming using the toner

[64] The method for forming an image using the toner prepared by aforementioned manner comprises the steps of electrificating, exposing to light, developing, transcribing, fixing, cleaning, and removing charge.

[65] In the electrificating step, the photoreceptor can be typically charged positively or negatively by means of a corona or electrifying roller, the electrifying means.

[66] In the exposing to light step, the optical system as an exposing means, typically a laser scanner or diode arrangement, selectively discharges the electrified surface of the photoreceptor in an imagewise manner corresponding to a target image formed on the final image receptor, and forms the latent image. Electromagnetic irradiation referred to as "light" may include laser irradiation, infrared irradiation, visible light, and UV irradiation.

[67] In the developing step, the toner particles with desirable charge generally contact with the latent image on the photoreceptor. Typically, an electrically-biased developer having the same potential polarity as the toner is used as a developing means. The toner particles move to the photoreceptor, adhere selectively to the latent image by static electricity, and then form the toner image on the photoreceptor.

[68] In the transcribing step, the toner image is transcribed to the final image receptor through a transcribing means. Sometimes, an intermediate transcribing element can be used to effect the transcription of the toner image from the photoreceptor to the final image receptor.

[69] In the fixing step, the toner image on the final image receptor is heated to soften or melt the toner particles, and fixed on the final image receptor by means of the fixing means.

[70] In the cleaning step, the remaining toner on the photoreceptor is removed by the cleaning means.

[71] Finally, in the removing charge step, the charge of the photoreceptor may be exposed to light of a specific wavelength band to be lowered to a substantially uniform low level, so the remaining materials of the original latent image may be removed. Then, the photoreceptor shall be prepared for the next image forming cycle.

[72] The present invention will be discussed in detail in the following examples, and the following examples are to illustrate, but not to limit the scope of the appended claims.

[73]

Mode for the Invention

[74] Examples

[75]

[76] Example 1

[77] 407 g of de-ionized water, carbon black (Mogul-L, manufactured by Cabot), wax

(Esterwax, WE-3 and WE-8) and 246 g of styrene-acryl copolymer latex were put into IL reactor and stirred by using a plate impeller at 150 rpm for 10 minutes. After stirring, pH was adjusted to 10 and MgCl solution of 0.05M was injected. Then, the aggregation-coalescence was conducted for 4 hours with raising the temperature up to 85 ⁰C. Thereafter, sodium hexametaphosphate (SHMP) of 0.10 wt% of dry solid was injected and pH was adjusted to 2. Then, the solution was stirred for 30 minutes, cooled, filtrated and dried to obtain toner particles. Dried toner particles have 6.5 D of D50. Respectively 1.0 wt% and 0.5 wt% of fumed silica R-812S and RY-50 (manufactured by Degussa) were externally added to the toner particles by a hansel mixer.

[78]

[79] Example 2

[80] Toner particles were produced in the same manner as in Example 1 except that phosphate salt, 0.5 % of sodium tripolyphosphate (STPP) was used, and the aggregation-coalescence was conducted for 6 hours. Dried toner particles have 9.2 D of D50.

[81] [82] Comparative Example 1 [83] 407 g of deionized water, carbon black (Mogul-L, manufactured by Cabot), wax (Esterwax, WE-3 and WE-8) and 246 g of styrene-acryl copolymer latex were put into IL reactor and stirred by using a plate impeller at 150 rpm for 10 minutes. After stirring, pH was adjusted to 10 and MgCl solution of 0.05M was injected. Then, the aggregation-coalescence was conducted for 4 hours with raising the temperature up to 85 ⁰C. Thereafter, 0.5 % of sodium silicate was injected and pH was adjusted to 2. Then, the solution was stirred for 30 minutes, cooled, filtrated and dried to obtain toner particles. Dried toner particles have 6.5 D of D50. Respectively 1.0 wt% and 0.5 wt% of fumed silica R-812S and RY-50 (manufactured by Degussa) were externally added to the toner particles by a hansel mixer.

[84] [85] Comparative Example 2 [86] Toner particles were produced in the same manner as in Example 1 except that the phosphate salt was not added. Dried toner particles have 7.5 D of D50.

[87] [88] The kinds and contents of the phosphate salt used in aggregation-coalescence of examples and comparative examples and the results are shown in table 1.

[89] [90] Table 1

[91] [92] In the above table: [93] © : No soft blocking (line occurrence in images) occurred up to 5,000 sheets in image evaluation.

[94] O : No soft blocking occurred up to 5,000 sheets in image evaluation. [95] Δ : No soft blocking occurred up to 3,000 sheets in image evaluation.

[96] x: No soft blocking occurred within 1,000 sheets in image evaluation.

[97] CV. (coefficient of variation): standard variation of total particle size distribution/ average particle diameter.

Claims

[1] A method of preparing a toner, which comprises the steps of: providing a polymer latex; forming toner particles by aggregation-coalescence of colorants, charge control agents and wax with said polymer latex in the presence of a phosphorus- containing dispersant; and cooling, separating and drying said toner particles.

[2] The method of claim 1, wherein the step of forming toner particles further comprises the step of controlling ionic strength by adding an inorganic salt or an electrolyte.

[3] The method of claim 1, wherein said phosphorus-containing dispersant is used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of total aggregated dry solid.

[4] The method of claim 1, wherein said phosphorus-containing dispersant is selected from the group consisting of sodium hexametaphosphate, sodium pyrophosphate, sodium metaphosphate and sodium tripolyphosphate.

[5] A toner prepared by any one of claims 1 to 4.

[6] An image forming method comprising the steps of: electrifying a photoreceptor; forming a latent image on the photoreceptor by exposing said electrified photoreceptor to light; forming a toner image by contacting the toner according to Claim 5 with said latent image on the photoreceptor; transcribing said toner image from the photoreceptor to a final image receptor; fixing the toner on said final image receptor by heating said final image receptor with the transcribed toner image and softening/melting the toner; and removing the remaining toner from said photoreceptor.

[7] An image forming apparatus comprising: means for electrifying a photoreceptor; means for exposing the electrified photoreceptor to form a latent image on said photoreceptor; developing means for contacting the toner according to Claim 5 with the latent image on the photoreceptor to form a toner image; means for transcribing said toner image from the photoreceptor to a final image receptor; means for fixing the toner image on the final image receptor by heating the final image receptor with the transcribed toner image to soften or to melt the toner; and cleaning means for removing the remaining toner from the photoreceptor.