FIELD OF THE INVENTION 
       [0001]    The present invention relates to toners for electrostatic image development used in electrophotographic image formation and in particular to a toner for electrostatic image development, containing a pigment of C.I. Pigment Red 209. 
       BACKGROUND OF THE INVENTION 
       [0002]    Recently, image formation of an electrophotographic system, using a toner for electrostatic image development (hereinafter, also denoted simply as a toner) can perform full-color printing as well as mono-chromatic printing, as typified by conventional document preparation. Such a full-color image forming apparatus, which can prepare prints of the number of required sheets for on-demand printing without making any printing plate, has become mainly employed in the field of short-run printing, as described in, for example, JP-A No. 2005-15724 (hereinafter, the term, JP-A refers to Japanese Patent Application Publication). 
         [0003]    When preparing full-color prints of catalogs or for advertisement using a toner, the toner used therein requires color reproducibility to obtain an image faithful to the original image. Namely, in full-color image formation, toner images of yellow, magenta and cyan are superimposed to reproduce the targeted color image and such color toners on which attainment of faithful color reproduction is based are required to achieve superior color reproducibility. 
         [0004]    Recently, there has been studied expansion of color gamut of a color toner to achieve printing in a broader color gamut than that of standard color of conventional printing. 
         [0005]    There have been also studied a variety of colorants to achieve expansion of color gamut of a color toner and enhanced color reproduction. As one of them was made study of colorant used for a magenta toner. Typical colorants for a magenta toner include, for example, a quinacridone pigment. A toner using such a quinacridone pigment, which exhibits excellent lightfastness, has been widely employed. However, a toner using a quinacridone pigment exhibited lowered chroma and reduced lightness, producing problems such as color contamination. Further, such a toner using a quinacridone pigment resulted in excessive variation of lightness with adhered amount and there still remained a problem in color reproduction when a development amount fluctuated with variation of humidity. 
         [0006]    Accordingly, there was studied a technique in which a quinacridone pigment was used in combination with other pigments instead of its single use to achieve enhanced chroma, as set forth in, for example, JP-A No. 2007-286148, in which there was described the use of quinacridone pigments such as C.I. Pigment Red 122, 192 and 202, and C.I. Pigment Violet 19. 
         [0007]    Further, there was also proposed its use in combination with other pigments, for example, a combination use of a quinacridone pigment and a naphthol pigment, as set forth in JP-A No. 2006-267741 and the use of a quinacridone pigment in combination with an anthraquinone pigment, as described in JP-A No. 2006-154363. 
         [0008]    In these techniques, however, quinacridone pigments slightly supplemented the inherent high lightfastness of the quinacridone pigment itself but could not achieve enhancements of chroma, lightness and lightfastness, making it difficult to maintain stable color in use over a long duration. Thus, there were problems such that a toner using above-described quinacridone pigments as a colorant could not exhibit high chroma capable of expanding color gamut of the toner to achieve printing in a broader color gamut than that of standard color of conventional printing, and making it difficult to maintain stable lightfastness over a long duration. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the invention to provide a toner for electrostatic image development to obtain a high chroma full-color image exhibiting clear color without color contamination and achieving enhanced lightfastness. 
         [0010]    One aspect of the invention is directed to an electrophotographic toner used for electrostatic image development comprising a resin and a colorant, wherein the colorant comprises a pigment of C.I. Pigment Red 209. 
         [0011]    Another aspect of the invention is directed to a full-color toner kit comprising at least four toners comprised of a yellow toner comprising a yellow colorant and a resin, a magenta toner comprising a magenta colorant and a resin, a cyan toner comprising a cyan colorant and a resin and a black toner comprising a black colorant and a resin, wherein the magenta colorant comprises a pigment of C.I. Pigment Red 209. 
         [0012]    Further, another aspect of the invention is directed to an image forming method comprising performing image formation by using at least four toners comprised of a yellow toner comprising a yellow colorant and a resin, a magenta toner comprising a magenta colorant and a resin/a cyan toner comprising a cyan colorant and a resin and a black toner comprising a black colorant and a resin, wherein the magenta colorant comprises a pigment of C.I. Pigment Red 209. 
         [0013]    The toner relating to the invention has achieved formation of a high chroma full-color image without color contamination and the formed toner image has realized stable lightfastness over a long duration. 
         [0014]    It has also become feasible to obtain a monochromatic color toner image of excellent chroma and lightness without color contamination so that a secondary color formed by the toner of the invention exhibits clear color. 
         [0015]    Further, enhanced tints have made it feasible to reproduce clearer red than that of printing standard color. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0016]      FIGS. 1  illustrates an example of an image forming apparatus in which toners relating to the invention are usable. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The present invention relates to a toner for electrostatic image development containing at least a resin and a colorant and in particular to a toner for electrostatic image development, exhibiting excellent color which makes it feasible to fit the hue angle of the toner to color reproduction of a photographic image and also resulting in stable lightfastness. 
         [0018]    As a result of extensive study of novel colorants in place of commonly known quinacridon pigments, it was found that the use of a novel pigment of C.I. Pigment Red 209 rendered it possible to overcome the problems of the invention. A pigment of C.I. Pigment Red 209 used in the toner of the invention has come into being as an effect of the invention, which is presumed to be ascribed to such a characteristic that even when dispersed in a toner resin such as an acryl resin or polyester resin, the pigment does not give rise to a broad absorption, compared to conventional magenta pigments. Specifically, a toner containing a pigment of C.I. Pigment Red 209 results in reduced absorption in the line wing on the long wavelength side of its absorption spectrum, ranging from 550 to 600 nm, as compared to toners containing conventional magenta pigments, which is presumed to be attributed to the substituting position of chlorine atoms. As a result, the red component of reflected light is markedly increased, while the blue component is substantially equivalent to that of toners containing conventional magenta pigments, whereby advantageous effects of the invention have been achieved. 
         [0019]    C.I. Pigment Red 209 refers to Color Index Generic Names. Examples of a commercially available pigment of C.I. Pigment Red 209 include Fast Red EG (produced by Clariant Japan Co., Ltd.) 
         [0020]    A pigment of C.I. Pigment Red 209 is a colorant which is superior in transparency and also in light fastness. Herein, the C.I. Pigment Red 209 refers to Color Index Generic Names. The use of the foregoing colorant in a toner relating to the invention has enabled achievement of broadly stable color reproduction, as compared to conventional toner images or images obtained by use of printing ink. 
         [0021]    A pigment of C.I. Pigment Red 209 usable in the invention (which is hereinafter also denoted simply as C.I. Pigment Red 209) is dispersed in a toner preferably in the form of particles exhibiting a number average primary particle size of from 100 to 300 nm. In the invention, when observing a 1000-fold magnified transmission electron micrograph of a section of a toner particle to determine the Feret&#39;s diameter of colorant particles, the number average primary particle size of colorant particles is defined as the arithmetic average diameter of colorant particles when observing ten toner particles. 
         [0022]    C.I. Pigment Red 209 is contained in a toner preferably in an amount of from 1 to 10% by mass of the toner and more preferably from 3 to 7% by mass in terms of optimization of chroma and lightness. 
         [0023]    There may be added other magenta colorants known in the art, such as a copper phthalocyanine in addition to C.I. Pigment Red 209 to prepare a magenta toner. Such known colorants are added preferably in an amount of less than 50% by mass of C.I. Pigment Red 209. 
         [0024]    In the invention, constitution of plural chromatic toners can realize a full-color toner kit which renders it feasible to form a full-color toner image. Namely, a full-color toner kit constituted of at least four toners of a magenta toner comprised of at least colorants including C.I. Pigment Red 209 and a resin, a yellow toner comprised of at least a yellow colorant and a resin, a magenta toner comprised of at least a magenta colorant and a resin and a black toner comprised of at least a black colorant and a resin enables formation of full-color images. 
         [0025]    There will be described colorants used for toners constituting a full-color toner kit relating to the invention. Examples of a colorant used for a black toner include carbon black, a magnetic material and titanium black. Specific examples of carbon black include channel black, furnace black, acetylene black, thermal black and lamp black. Examples of a magnetic material include ferromagnetic metals of iron, nickel, cobalt and the like and alloys containing these metals; compounds of ferromagnetic metals such as ferrite and magnetite; and alloys which contain no ferromagnetic metal but exhibit ferromagnetism upon a thermal treatment. Examples of such an alloy exhibiting ferromagnetism upon a thermal treatment include so-called Heusler&#39;s. alloy of manganese-copper-aluminum or manganese-copper-tin; and chromium dioxide. 
         [0026]    Examples of a yellow colorant used for a yellow toner include dyes such as C.I. Solvent Yellow 19, ibid 44, ibid 77, ibid 79, ibid 81, ibid 82, ibid 93, ibid 98, ibid 103, ibid 104, ibid 112 and ibid 162; and pigments such as C.I. Pigment Yellow 14, ibid 17, ibid 74, ibid 93, ibid 94, ibid 138, ibid 155, ibid 180 and ibid 185. A mixture of these dyes or pigments may also usable. Of these, C.I. Pigment Yellow 74 is preferred. 
         [0027]    Examples of a cyan colorant used for a cyan toner include C.I. Pigment Blue 15:3. 
         [0028]    The number average primary particle size of a colorant dispersed in a toner, depending on the kind of a colorant, is preferably from 10 to 200 nm. The number average primary particle size can be determined from a transmission electron micrograph of the toner section obtained similarly to the manner described in the C.I. Pigment Red 209. 
         [0029]    Similarly to the foregoing C.I. Pigment Red 209, these colorants are each added in an amount of from 1 to 10% by mass, and preferably from 2 to 8% by mass. Coloring power of a toner may be sufficient when added at not less than 1% by mass, and a colorant may not leave a toner or not be attached to a carrier when added at not more than 10% by mass, adversely affecting the charging property of a toner. 
         [0030]    The use of a full-color toner kit which is comprised of at least four toners of a magenta toner containing a C.I. Pigment Red 209, a yellow toner, a cyan toner and a black toner enables to form excellent full-color toner images. 
         [0031]    There will be further described particle size of the toner of the invention. 
         [0032]    The toner relating to the invention comprises toner particles, which preferably exhibit a volume-based median diameter (also denoted simply as D50v) of not less than 3 μm and not more than 8 μm. The use of a toner exhibiting a volume-based median diameter falling within the foregoing region enables faithful reproduction of fine-dot images, for example, at a level of 1200 dpi (dpi: the number of dots per inch or 2.54 cm). 
         [0033]    The minute particle size level at a volume-based median diameter falling within the minute particle size enables to obtain a highly precise photographic image in which a dot image constituting the photographic image is equivalent to or more than a high-precision printed image. Specifically, in on-demand printing in which orders for several hundreds to several thousands sets are often received, high image quality prints with high-precision photographic images can be delivered to a user. 
         [0034]    The volume-based median diameter (D50v) of toner particles can be determined using COULTER MULTISIZER 3 (Beckmann Coulter Co.), connected to a computer system for data processing. 
         [0035]    The measurement procedure is as follows: 0.02 g of toner particles are added to 20 ml of a surfactant solution (for example, a surfactant solution obtained by diluting a surfactant containing neutral detergent with pure water to a factor of 10) and dispersed by an ultrasonic homogenizer to prepare a toner dispersion. Using a pipette, the toner dispersion is poured into a beaker having ISOTON II (produced by Beckman Coulter Co.) within a sample stand, until reaching a measurement concentration of 5 to 10%. The measurement count was set to 2,500 to perform measurement. Then aperture diameter of MULTISIZER 3 was 50 μm. 
         [0036]    The toner of the invention preferably exhibits a coefficient of variation (CV value) of volume-based particle size distribution of not less than 2% and not more than 21%, more preferably not less than 5% and not more than 15%. The coefficient of variation (also denoted simply as CV value) of volume-based particle size distribution represents a degree of variance of particle size distribution, based on volume and defined as below: 
         [0000]        CV  value (%)={(standard deviation of volume-based particle size distribution)/[median diameter ( D 50 v ) of volume-based particle size distribution]}×100 
         [0037]    A low value indicates a sharper particle size distribution and means that the particle size tends to be uniform. Uniform particle size enables more precise reproduction of fine-dot images or fine lines, as is essential in digital image formation. Printing a photographic image with uniform-sized toner particles results in photographic images of high image quality at a level equivalent to or higher than an image prepared by printing ink. 
         [0038]    The toner of the invention preferably exhibits a softening temperature (also denoted simply as Tsp) of from 70 to 110° C., and more preferably from 70 to 100° C. Colorants used in the toner of the invention are stable, causing no change in spectrum even when affected by heat. A softening point falling within the foregoing range can reduce effects of heat applied to the toner in fixing. Accordingly, image formation is performed without relying on a colorant, so that it is expected to, develop broad stable-color reproduction. 
         [0039]    A toner of a softening point falling within the foregoing range enables fixing a toner image at a lower temperature than the prior art, rendering it feasible to perform image formation friendly to environments at reduced power consumption. 
         [0040]    The softening point of a toner can be controlled by the following methods, singly or in combination. Thus, (1) the kind or the composition of monomer used for resin formation is adjusted; (2) the molecular weight of a resin is controlled by the kind or the amount of a chain-transfer agent; (3) the kind or amount of a wax is controlled. 
         [0041]    The softening point of a toner may be measured by using, for example, Flow Tester CFT-500 (produced by Shimazu Seisakusho Co., Ltd.). Specifically, a sample which is molded to a 10 mm high column, is compressed by a plunger at a load of 1.96×10 6  Pa with heating at a temperature rising rate of 6° C./min and extruded from a 1 mm long nozzle, whereby, a curve (softening flow curve) between plunger-drop and temperature is drawn. The temperature at which flowing-out is initiated is defined as the fusion-initiation temperature and the temperature corresponding to 5 mm drop is defined as the softening temperature. 
         [0042]    There will be described a method of preparing the toner of the invention. 
         [0043]    The toner of the invention is comprised of particles containing at least a resin and a colorant (hereinafter, also denoted as colored particles). The colored particles constituting the toner of the invention are not specifically limited but can be prepared according the convention methods for preparing toners. More specifically, preparation is feasible by applying, for example, a so-called grinding method for preparing a toner through kneading, grinding and classification or a preparation method of a polymer toner in which a polymerizable monomer is polymerized with controlling the shape or size of particles to achieve particle formation (for example, emulsion polymerization, suspension polymerization, or polyester elongation). 
         [0044]    When preparing the toner of the invention through a grinding method, kneading is performed with maintaining a temperature at not more than 130° C. When kneading a mixture at a temperature not exceeding 130° C., heating action applied to the mixture does not tend to cause variation in the coagulation state of a colorant, rendering it easy to maintain uniform colorant coagulation. It is a concern that variation in the coagulation state causes variations in color of the prepared toner, leading to color contamination. 
         [0045]    Next, there will be described resin and wax constituting the toner of the invention, with reference to examples. 
         [0046]    Resins usable for the toner of the invention are not specifically limited but are typically polymers formed by polymerization of polymerizable monomers which are called vinyl monomers. A polymer constituting a resin usable in the invention is constituted of a polymer obtained by polymerization of at least one polymerizable monomer, which is a polymer prepared by using vinyl monomers singly or in combination. 
         [0047]    Specific examples of a polymerizable vinyl monomer are below:
   (1) styrene or styrene derivatives:   
 
         [0049]    styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-phenylstyrene, p-ethylstyrene, 2;4-dimethylstyrene, p-t-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, and p-n-dodecylstyrene;
   (2) methacrylic acid ester derivatives:   
 
         [0051]    methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-propyl methacrylate, iso-butyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate and dimethylaminoethyl methacrylate;
   (3) acrylic acid ester derivatives:   
 
         [0053]    methyl acrylate, ethyl acrylate, iso-propyl acrylate, n-butyl v, t-butyl acrylate, iso-butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate and phenyl acrylate;
   (4) oletins:   
 
         [0055]    ethylene, propylene and isobutylene;
   (5) vinyl esters:   
 
         [0057]    vinyl propionate, vinyl acetate and vinyl benzoate;
   (6) vinyl ethers:   
 
         [0059]    vinyl methyl ether and vinyl ethyl ethert
   (7) vinyl ketones:   
 
         [0061]    vinyl methyl ketone, vinyl ethyl ketone and vinyl hexyl ketone;
   (8) N-vinyl compounds:   
 
         [0063]    N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone;
   (9) others:   
 
         [0065]    vinyl compounds such as vinylnaphthalene and vinylpyridine; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide. 
         [0066]    There may also usable polymerizable monomers containing ionic-dissociative group, as a vinyl monomer, and including, for example, those having a side chain containing a functional group such as a carboxyl group, a sulfonic acid group or a phosphoric acid group. 
         [0067]    Specific examples include carboxyl group containing monomers such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, monoalkyl maleate, monoalkyl itaconate; sulfonic acid group containing monomers such as styrenesulfonic acid, allylsulfosuccinic acid, 2-acrylamido-2-methylpropanesulfonic acid; and phosphoric acid group containing monomers such as acid phosphooxyethyl methacrylate. 
         [0068]    Further, a cross-linked resin can be obtained using poly-functional vinyl compounds. Examples of such poly-functional vinyl compounds include divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentylglycol dimethacrylate and neopentylglycol diacrylate. 
         [0069]    Resins usable in the invention include a polyester resin obtained by polycondensation of an acid anhydride or a polyvalent carboxylic acid having at least two carboxyl groups and a polyvalent alcohol having at least two hydroxyl groups. Specific examples of a polyvalent carboxylic acid include aliphatic dicarboxylic acids such as citric acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glucuronic acid, succinic acid, adipic acid, sebacic acid, n-dodecylsuccinic acid, n-dodecylsuccinic acid and n-dodecenylsuccinic acid; alicyclic dicarboxylic acids such as hexanedicarboxylic acid and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid. Specific examples of a polyvalent alcohol include aliphatic diols such as 1,2-propanediol, 1,3-propanediol, 1,4 -butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, and 1,4-butenediol; aromatic diols such as an alkylene oxide adduct of bisphenol A; and polyols such as glycerin, pentaerythritol, trimethylolpropane, and sorbitol. These polyvalent alcohols may be combined. 
         [0070]    The content of a resin contained in the toner relating to the invention is preferably from 60 to 95% by mass, and more preferably from 70 to 90% by mass. 
         [0071]    Waxes usable in the toner of the invention are those known in the art. Examples thereof include:
   (1) polyolefin wax such as polyethylene wax and polypropylene wax;   (2) long chain hydrocarbon wax such as paraffin wax and sasol wax;   (3) dialkyl ketone type wax such as distearyl ketone;   (4) ester type wax such as carnauba wax, montan wax, trimethylolpropane tribehenate, pentaerythritol tetramyristate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, trimellitic acid tristearate, and distearyl meleate; and   (5) amide type wax such as ethylenediamine dibehenylamide and trimellitic acid tristearylamide.   
 
         [0077]    The melting point of a wax usable in the invention is preferably 40 to 125° C., more preferably 50 to 120° C., and still more preferably 60 to 90° C. A melting point falling within the foregoing range ensures heat stability of toners and can achieve stable toner image formation without causing cold offsetting even when fixed at a relatively low temperature. The wax content of the toner is preferably in the range of 1% to 30% by mass, and more preferably 5% to 20%. 
         [0078]    There may be incorporated, in the process of preparing the toner of the invention, inorganic organic microparticles having a number-average primary particle size of 4 to 800 nm as an external additive to prepare the toner. 
         [0079]    Incorporation of an external additive results in improved fluidity or electrostatic property or achieves enhanced cleaning ability. The kind of external additives is not specifically limited and examples thereof include inorganic microparticles, organic microparticles and a sliding agent, as described below. 
         [0080]    There are usable commonly known inorganic microparticles and preferred examples thereof include silica, titania, alumina and strontium titanate microparticles. There may optionally be used inorganic microparticles which have been subjected to a hydrophobilization treatment. 
         [0081]    Specific examples of silica microparticles include R-976, R-974, R-972, R-812 and R-809 which are commercially available from Nippon Aerosil Co., Ltd.; HVK-2150 and H-200 which are commercially available from Hoechst Co.; TS-720, TS-530, TS-610, H-5 and MS-5 which is commercially available from Cabot Co. 
         [0082]    Examples of titania microparticles include T-805 and T-604 which are commercially available from Nippon Aerosil Co. Ltd.; MT-100S, MT-100B, MT-500BS, MT-600, MT-600SJA-1 which are commercially available from Teika Co.; TA-300SI, TA-500, TAF-130, TAF-510 and TAF-510T which as commercially available from Fuji Titan Co., Ltd.; IT-S, IT-OB and IT-OC which as commercially available from Idemitsu Kosan Co., Ltd. 
         [0083]    Examples of alumina microparticles include RFY-C and C-604 which are commercially available from Nippon Aerosil Co., Ltd.; and TTO-55, commercially available from Ishihara Sangyo Co., Ltd. 
         [0084]    Spherical organic microparticles having a number-average primary particle size of 10 to 2000 nm are usable as organic microparticles. Specifically, there is usable styrene or methyl methacrylate homopolymer or their copolymers. 
         [0085]    There are also usable lubricants, such as long chain fatty acid metal salts to achieve enhanced cleaning ability or transferability. Examples of a long chain fatty acid metal salt include zinc, copper, magnesium, and calcium stearates; zinc, manganese, iron, copper and magnesium oleates; zinc, copper, magnesium, and calcium palmitates; zinc and calcium linolates; zinc and calcium ricinolates. 
         [0086]    Such an external additive or lubricant is incorporated preferably in an amount of 0.1 to 10.0% by weight of the total toner. The external additive or lubricant can be incorporated by using commonly known mixing devices such as a turbuler mixer, a HENSCHEL MIXER, a Nauter mixer or a V-shape mixer. 
         [0087]    The toner of the invention is usable as a two-component developer comprised of a carrier and a toner, or a single-component developer comprised of a toner alone. 
         [0088]    The use of the toner of the invention as a two-component developer enables full-color printing by using a tandem system image forming apparatus as described later. 
         [0089]    Magnetic particles used as a carrier of a two-component developer can use commonly known materials, e.g., metals such as iron, ferrite and magnetite and alloys of the foregoing metals and metals such as aluminum or lead. Of these, ferrite particles are preferred. The volume-average particle size of a carrier of a carrier is preferably from 15 to 100 μm. and more preferably from 25 to 80 μm. 
         [0090]    When used as a nonmagnetic single-component developer without a carrier to perform image formation, a toner is charged with being rubbed or pressed onto a charging member or the developing roller surface. Image formation in a nonmagnetic single-component development system can simplify the structure of a developing device, leading to a merit of compactification of the whole image forming apparatus. Therefore, the use of the toner of the invention as a single-component developer can achieve full-color printing in a compact printer, making it feasible to prepare full-color prints of superior color reproduction even in a space-limited working environment. 
         [0091]    There will be described image formation using the toner of the invention. First, there will be described image formation using the toner of the invention as a two-component developer. 
         [0092]      FIG. 1  illustrates an example of an image forming apparatus in which the toner of the invention is usable as a two-component developer. 
         [0093]    In  FIG. 1 ,  1 Y,  1 M,  1 C and  1 K each designate photoreceptors;  4 Y,  4 M,  4 C and  4 K each designate a developing means;  5 Y,  5 M,  5 C and  5 K each designate primary transfer rollers as a primary transfer means;  5 A designates a secondary transfer roller as a secondary transfer means;  5 Y,  6 M,  5 C and  5 K each designate cleaning means; the numeral  7  designates an intermediate transfer unit; the numeral  24  designates a thermal roll type fixing device; and the numeral  70  designates an intermediate transfer material. 
         [0094]    This image forming apparatus is called a tandem color image forming apparatus, which is, as a main constitution, composed of plural image forming sections  10 Y,  10 M,  10 C and  10 B, an intermediate transfer material unit  7  as a transfer section including an endless belt form of a transfer belt, paper feeding and conveying means  22 A to  22 D to convey recording member P and heated roll-type fixing device  24  as a fixing means. Original image reading device SC is disposed in the upper section of image forming apparatus body A. 
         [0095]    Image forming section  10 Y to form a yellow image as one of different color toner images formed on the respective photoreceptors comprises drum-form photoreceptor  1 Y as the first photoreceptor; electrostatic-charging means  2 Y, exposure means  3 Y and developing means  4 Y which are disposed around the photoreceptor  1 Y; primary transfer roller  5 Y as a primary transfer means; and cleaning means  6 Y. 
         [0096]    Image forming section  10 M to form a magenta image as one of different color toner images formed on the respective photoreceptors comprises drum-form photoreceptor  1 M as the second photoreceptor; electrostatic-charging means  2 M, exposure means  3 M and developing means  4 M which are disposed around the photoreceptor  1 M; primary transfer roller  5 M as a primary transfer means; and cleaning means  6 M. 
         [0097]    Image forming section  10 C to form a cyan image as one of different color toner images formed on the respective photoreceptors comprises drum-form photoreceptor  1 C as the third photoreceptor; electrostatic-charging means  2 Y, exposure means  3 C and developing means  4 C which are disposed around the photoreceptor  1 C; primary transfer roller  5 C as a primary transfer means; and cleaning means  6 C. 
         [0098]    Image forming section  10 K to form a black image as one of different color toner images formed on the respective photoreceptors comprises drum-form photoreceptor  1 K as the fourth photoreceptor; electrostatic-charging means  2 K, exposure means  3 K and developing means  4 K which are disposed around the photoreceptor  1 K; primary transfer roller  5 K as a primary transfer means; and cleaning means  6 K. 
         [0099]    Intermediate transfer unit  7  of an endless belt form is turned by plural rollers has intermediate transfer material  70  as the second image carrier of an endless belt form, while being pivotably supported. 
         [0100]    The individual color images formed in image forming sections  10 Y,  10 M,  10 C and  10 K are successively transferred onto the moving intermediate transfer material ( 70 ) of an endless belt form by primary transfer rollers  5 Y,  5 M,  5 C and  5 K, respectively, to form a composite color image. Recording member P of paper or the like, as a final transfer material housed in paper feed cassette  20 , is fed by paper feed and conveyance means  21  and conveyed to secondary transfer roller  5 A through plural intermediate rollers  22 A,  22 B,  22 C and  22 D and resist roller  23 , and color images are transferred together on recording member P. The color image-transferred recording member (P) is fixed by heat-roll type fixing device  24 , nipped by paper discharge roller  25  and put onto paper discharge tray outside a machine. 
         [0101]    After a color image is transferred onto recording member P by secondary transfer roller  5 A, intermediate transfer material  70  which separated recording member P removes any residual toner by cleaning means  6 A. 
         [0102]    The primary transfer roller  5 K is always compressed to the photoreceptor  1 K. Other primary rollers  5 Y,  5 M and  5 C are each the photoreceptors  1 Y,  1 M and  1 C, respectively, only when forming color images. 
         [0103]    Secondary transfer roller  5 A is compressed onto intermediate transfer material  70  only when recording member P passes through to perform secondary transfer. 
         [0104]    Housing  8 , which can be pulled out from the apparatus body (A) through supporting rails  82 L and  82 R, is comprised of image forming sections  10 Y,  10 M,  10 C and  10 K and the intermediate transfer unit ( 7 ) of an endless belt form. 
         [0105]    Image forming sections are arranged vertically in a line Intermediate transfer material unit  7  of an endless belt form is disposed on the left side of photoreceptors  1 Y,  1 M,  1 C and  1 K, as indicated in  FIG. 2 . Intermediate transfer material unit  7  comprises the intermediate transfer unit ( 7 ) of an endless belt form which can be turned via rollers  71 ,  72 ,  73 ,  74  and  76 , primary transfer rollers  5 Y,  5 M,  5 C and  5 K and cleaning means  6 A. 
         [0106]    The image forming sections  10 Y,  10 M,  10 C and  10 K and the intermediate transfer unit  7  are pulled out of the body A by pulling the housing  8 . 
         [0107]    In the process of image formation, toner images are formed on photoreceptors  1 Y,  1 M,  1 C and  1 K, through electrostatic-charging, exposure and development, toner images of the individual colors are superimposed on the endless belt form, intermediate transfer material ( 70 ), transferred together onto recording member P and fixed by compression and heating in heat-roll type fixing device  24 . After completion of transferring a toner image to recording member P, intermediate transfer material  70  cleans any toner remained on the intermediate transfer material by cleaning device  6 A and then goes into the foregoing cycle of electrostatic-charging, exposure and development to perform the subsequent image formation. 
         [0108]    The image forming method in which the toner relating to the invention is used as a non-magnetic single component developer can be realized by use of an image forming apparatus in which the afore-described two component developing device is replaced by a single component developing device. 
         [0109]    A fixing method which is feasible in the image forming method relating to the invention is not specifically limited and is responsible a fixing system known in the art. Such a fixing system known in the art may be any one of a roller fixing system comprised of a heating roller and a pressure rollers a fixing system comprised of a heating roller and a pressure belt, a fixing system comprised of a heating belt and a pressure roller and a belt fixing system comprised of a heating belt and a pressure belt A heating system may be any one of a halogen lamp system, IH fixing system and the like. 
       EXAMPLES 
       [0110]    The embodiments of invention will be specifically described with reference to examples but the invention is by no means limited to these. 
       Preparation of Developer 
     Example 1 
     Preparation of Toner 1 by Kneading/Grinding Method 
       [0111]    The toner constitution described below was placed in a HENSCHEL MIXER (produced Mitsui-Miike Kogyo Co., Ltd.) and mixed with stirring at a blade-circumferential speed of 25 m/sec for 5 min. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Polyester resin* 
                 100 mass parts 
               
               
                   
                 C.I. Pigment Red 209 
                  5 mass parts 
               
               
                   
                 Releasing agent (pentaerythritol 
                  6 mass parts 
               
               
                   
                 tetrastearate) 
               
               
                   
                 Charge controlling agent (boron 
                  1 mass part 
               
               
                   
                 dibenzylic acid) 
               
               
                   
                   
               
               
                   
                 *condensation product of bisphenol A/ethylene oxide adduct, terephthalic acid and trimeritic acid having a weight average molecular weight of 20,000 
               
             
          
         
       
     
         [0112]    The mixture was kneaded by a biaxial extrusion kneader and discharged at a temperature of 125 to 128° C. The kneaded mixture was roughly ground by a hammer mill, further ground by a turbo-mill (produced by TURBO KOGYC Co., Ltd.) and was subjected to a fine powder classification treatment by an air classifier employing Coanda effect to obtain colored particles having a volume-based median diameter of 5.5 μm. 
         [0113]    Next, to the foregoing colored particles were added external additives described below and subjected to an external treatment in a HENSCHEL MIXER to obtain Toner 1. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Hexamethylsilane-treated silica (average 
                 0.6 mass parts 
               
               
                   
                 primary particle size of 12 nm) 
               
               
                   
                 n-octylsilane-treated titanium oxide 
                 0.8 mass parts 
               
               
                   
                 (average primary particle size of 24 nm) 
               
               
                   
                   
               
             
          
         
       
     
         [0114]    The external treatment in HENSCHEL MIXER was conducted under conditions of a stirring blade circumferential speed of 35 m/sec, a treatment temperature of 35° C. and a treatment time of 15 min. Thus, Toner 1 was prepared. 
         [0115]    It was proved that toner particles of the thus prepared toner 1 exhibited a volume-based median diameter of 5.5 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 20.8% and a softening temperature of 109.4° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 286 nm. 
       Example 2 
     Preparation of Toner 2 by Emulsion Coagulation Method 
     (1) Preparation of Particular Colorant Dispersion 1: 
       [0116]    11.5 parts by mass of sodium n-dodecylsulfate was placed in 160 parts by mass of deionized water and dissolved with stirring to prepare an aqueous surfactant solution. To the aqueous surfactant solution was gradually added 40 parts by mass of C.I. Pigment Red 209 and the foregoing composition was slowly added and dispersed by using CLEARMIX W-motion CLM-0.8 (produced by M Technique Co.) to obtain colorant microparticle dispersion 1. 
         [0117]    Colorant microparticle 1 contained in the foregoing colorant microparticle dispersion 1 exhibited a volume-based median diameter of 98 nm. The volume-based median diameter was measured by using MICROTRAC UPA-150 (produced by HONEYWELL Corp.) according to the following conditions:
       Sample refraction index: 1.59   Sample specific gravity: 1.05 (equivalent converted to spherical particle)   Solvent refraction index: 1.33   Solvent viscosity: 0.797 (30° C.), 1.002 (20° C.)   Zero-point adjustment: adjustment was made by adding deionized water to a measurement cell.       
 
       (2) Preparation of Core Resin Particle 1: 
       [0123]    Resin particles used to form a core (denoted as core resin particle 1) having a multilayer structure was prepared by the steps of 1st polymerization, 2nd polymerization and 3rd polymerization. 
         [0000]    (a) 1st polymerization: 
         [0124]    Into a reaction vessel fitted with a stirrer, a temperature sensor, a condenser and a nitrogen gas-introducing device was added 4 parts by mass of anionic surfactant (Formula 1) together with 3040 parts by mass of deionized water to prepare an aqueous surfactant solution. 
         [0000]      C 10 H 21 (OCH 2 CH 2 ) 2 SO 3 Na   Formula 1: 
         [0125]    To the foregoing aqueous surfactant solution was added a polymerization initiator solution of 10 parts by weight of potassium persulfate (KPS) dissolved in 400 parts by weight of deionized water and after the temperature was raised to 75° C., a monomer solution which was comprised of compounds as below was dropwise added to the reaction vessel over 1 hr. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Styrene 
                 532 mass parts 
               
               
                   
                 n-Butyl acrylate 
                 200 mass parts 
               
               
                   
                 Methacrylic acid 
                  68 mass parts 
               
               
                   
                 n-Octylmercaptan 
                 16.4 mass parts  
               
               
                   
                   
               
             
          
         
       
     
         [0126]    After completing addition of the monomer solution, the reaction mixture was heated with stirring at 75° C. for 2 hrs. to perform polymerization (1st polymerization) to obtain resin particles. The obtained resin particles were designated as particulate resin A1. The weight-average molecular weight of the particulate resin A1 was 16,500. 
         [0000]    (b) 2nd polymerization: 
         [0127]    To a flask fitted with a stirrer was added a mixed monomer solution of compounds describe below and subsequently 93.8 parts by weight of paraffin wax HNP-57 (produced Nippon Seiro Co., Ltd.) as a releasing agent was added and dissolved with heating at 90° C. to prepare a monomer solution. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Styrene 
                 101.1 mass parts  
               
               
                   
                 n-Butyl acrylate 
                 62.1 mass parts 
               
               
                   
                 Methacrylic acid 
                 12.3 mass parts 
               
               
                   
                 n-Octylmercaptan 
                 1.75 mass parts 
               
               
                   
                   
               
             
          
         
       
     
         [0128]    An aqueous surfactant solution was prepared by dissolving 3 parts by mass of the foregoing anionic surfactant in 1560 parts by mass of deionized water and heated at 98° C. To this aqueous surfactant solution was added the foregoing particulate resin A 1  in an amount of 32.8 parts by mass (equivalent converted to solids), and the paraffin wax-containing monomer solution described above was added and was dispersed for 8 hrs. using a mechanical stirrer having a circulation pass, CLEARMIX (produced by M Technique Co.). There was thus prepared an emulsified particle dispersion comprised of emulsion particles having a dispersion particle size of 340 nm. 
         [0129]    Subsequently, to the foregoing emulsified particle dispersion was added a polymerization initiator solution of 6 parts by mass of potassium persulfate dissolved in 200 parts by mass of deionized water. This reaction mixture was heated at 98° C. for 12 hrs. to undergo polymerization (2nd polymerization) to prepare resin particles. The thus prepared resin particles were designated as particulate resin A2. The weight-average molecular weight of the particulate resin A2 was 23,000. 
         [0000]    (c) 3rd polymerization: 
         [0130]    To the particulate resin A2 obtained in the 2nd polymerization step was added a polymerization initiator solution of 5.45 parts by mass of potassium persulfate dissolved in 220 parts by mass of deionized water and a mixed monomer solution composed of the following compounds was dropwise added to the reaction vessel at 80° C. in 1 hr. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Styrene 
                 293.8 mass parts 
               
               
                   
                 n-Butyl acrylate 
                 154.1 mass parts 
               
               
                   
                 n-Octylmercaptan 
                  7.08 mass parts 
               
               
                   
                   
               
             
          
         
       
     
         [0131]    After completing addition, the reaction mixture was heated with stirring for 2 hrs. to undergo polymerization (3rd polymerization). After completing polymerization, the reaction mixture was cooled to 28° C. to obtain core resin particle 1. The weight-average molecular weight of the core resin particle 1 was 26,800. 
       (3) Preparation of Shell Resin Particle: 
       [0132]    Resin particles used for shell (denoted as shell resin particle 1) were prepared similarly to the 1st polymerization of the foregoing core resin particle 1, provided that the composition of the monomer solution used in the 1st polymerization was changed as below. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Styrene 
                 624 mass parts 
               
               
                   
                 2-Ethylhexyl acrylate 
                 120 mass parts 
               
               
                   
                 Methacrylic acid 
                  56 mass parts 
               
               
                   
                 n-Octylmercaptan 
                 16.4 mass parts  
               
               
                   
                   
               
             
          
         
       
     
       (4) Preparation of Toner 2 
       [0133]    Toner 2 was prepared according to the procedure below. 
         [0000]    (a) Formation of core: 
         [0134]    Into a reaction vessel fitted with a stirrer, a temperature sensor, a condenser and a nitrogen gas introducing device was placed the following composition: 
         [0000]                                                Core resin particle   420.7 mass parts                 (equivalent converted to solid)           Deionized water   900 mass parts           Colorant particle dispersion 1   200 mass parts                        
The interior of the reaction vessel was adjusted to 30° C. and the pH was adjusted to 8-11 with an aqueous 5 mol/L sodium hydroxide solution.
 
         [0135]    Subsequently, further thereto, an aqueous solution of 2 parts by mass of magnesium chloride hexahydrate dissolved in 1000 parts by weight of deionized water was added at 30° C. for 10 min. After allowed to stand for 3 min., the mixture was heated to 65° C. in 60 min. to perform coagulation. Using MULTISIZER 3 (Coulter Co.), the dispersion was measured as such with respect to coagulated particle size and when coagulated particles reached a volume-based median diameter of 5.5 μm, there was added an aqueous solution of 40.2 parts by mass of sodium chloride dissolved in 1000 parts by mass of deionized water to terminate coagulation. 
         [0136]    After terminating coagulation, ripening was conducted at 70° C. for 1 hr. to allow fusion to continue, whereby core 1 was prepared. The average circularity of the core 1, which was measured by FPIA 2100 (produced by SYSTEX Co. Ltd.), was 0.912. 
         [0000]    (b) Formation of shell: 
         [0137]    Next, to the foregoing solution maintained at 65° C. was added 96 parts by mass of shell resin particle 1. Further thereto, an aqueous solution of 2 parts by mass of magnesium chloride hexahydrate dissolved in 1000 parts by mass of deionized water was added in 10 min. and the reaction mixture was heated to 70° C. and stirred for 1 hr. Thus, the shell resin particle 1 was melted onto the surface of the core 1 and ripening was carried out for 20 min to form a shell. 
         [0138]    Thereafter was added an aqueous solution of 40.2 parts by mass of sodium chloride dissolved in 1000 parts by mass to terminate shell formation. The reaction mixture was cooled to 30° C. at a cooling rate of 8° C./min. The colored particles thus formed were filtered off and repeatedly washed with deionized water of 45° C., and dried with hot air of 40° C. to prepare colored particle 2 having a shell on the core surface. 
         [0000]    (c) External additive treatment: 
         [0139]    The colored particle 2 was added with the following external additives and subjected to an external treatment with stirring in a HENSCHEL MIXER to prepare toner 2. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Hexamethylsilane-treated silica (average 
                 0.6 mass parts 
               
               
                   
                 primary particle size of 12 nm) 
               
               
                   
                 n-Octylsilane-treated titanium oxide 
                 0.8 mass parts 
               
               
                   
                 (average primary particle size of 24 nm) 
               
               
                   
                   
               
             
          
         
       
     
         [0140]    The external treatment in a Henschel mixer was conducted under conditions or a stirring blade circumferential speed of 35 m/sec, a treatment temperature of 35° C. and a treatment time of 15 min. Thus, toner 2 was prepared. 
         [0141]    It was proved that toner particles of the thus prepared toner 2 exhibited a volume-based median diameter of 5.8 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 17.5% and a softening temperature of 97.1° C. From electron-microscopic observation or colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 255 nm. 
       Comparative Example 1 
     Preparation of Comparative Toner 1 
       [0142]    Comparative toner 1 was prepared similarly to Example 1, provided that C.I. Pigment Red 209 was replaced by copper phthalocyanine. The kneaded mixture was discharged at a temperature of 124 to 129° C. 
         [0143]    It was proved that toner particles of the thus prepared comparative toner 1 exhibited a volume-based median diameter of 5.6 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 21.6% and a softening temperature of 110.5° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 424 nm. 
       Comparative Example 2 
     Preparation of Comparative Toner 2 
       [0144]    Comparative toner 2 was prepared similarly to Example 2, provided that C.I. Pigment Red 209 was replaced by C.I. Pigment Red 122. 
         [0145]    It was proved that toner particles of the thus prepared comparative toner 2 exhibited a volume-based median diameter of 5.9 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 18.9% and a softening temperature of 98.7° C. From electron-microscopic observation of colorant particles dispersed in the toner, particles, the number average primary particle size of the colorant particles was proved to be 432 nm. 
       Preparation of Yellow Toner 1 
       [0146]    Yellow toner 1 was prepared similarly to Example 1, provided that C.I. Pigment Red 209 was replaced by C.I. Pigment Yellow 74. 
         [0147]    It was proved that toner particles of the thus prepared yellow toner 1 exhibited a volume-based median diameter of 5.5 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 21.8% and a softening temperature of 109.1° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number-average primary particle size of the colorant particles was proved to be 294 nm. 
       Preparation of Yellow Toner 2 
       [0148]    Yellow toner 2 was prepared similarly to Example 2, provided that C.I. Pigment Red 209 was replaced by C.I. Pigment Yellow 74. 
         [0149]    It was proved that toner particles of the thus prepared yellow toner 2 exhibited a volume-based median diameter of 5.9 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 18.1% and a softening temperature of 98.0° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 293 nm. 
       Preparation of Cyan Toner 1 
       [0150]    Cyan toner 1 was prepared similarly to Example 1, provided that C.I. Pigment Red 209 was replaced by C.I. Pigment Blue 15:3. 
         [0151]    It was proved that toner particles of the thus prepared cyan toner 1 exhibited a volume-based median diameter of 5.4 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 20.3% and a softening temperature of 109.3° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 355 nm. 
       Preparation of Cyan Toner 2 
       [0152]    Cyan toner 2 was prepared similarly to Example 2, provided that C.I. Pigment Red 209 was replaced by C.I. Pigment Blue 15:3. 
         [0153]    It was proved that toner particles of the thus prepared cyan toner 2 exhibited a volume-based median diameter of 5.8 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 18.5% and a softening temperature of 98.4° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 247 nm. 
       Preparation of Black Toner 1 
       [0154]    Black toner 1 was prepared similarly to Example 1, provided that C.I. Pigment Red 209 was replaced by Carbon Black: Mogul L. 
         [0155]    It was proved that toner particles of the thus prepared black toner 1 exhibited a volume-based median diameter of 5.6 μm, a coefficient of variation (CV value) of volume-based particle size distribution of 19.8% and a softening temperature of 109.8° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 276 nm. 
       Preparation of Black Toner 2 
       [0156]    Black toner 2 was prepared similarly to Example 2, provided that C.I. Pigment Red 209 was replaced by Carbon Black: Mogul L. 
         [0157]    It was proved that toner particles of the thus prepared black toner 2 exhibited a volume-based median diameter of 5.8 μm a coefficient of variation (CV value) of volume-based particle size distribution of 19.8% and a softening temperature of 99.6° C. From electron-microscopic observation of colorant particles dispersed in the toner particles, the number average primary particle size of the colorant particles was proved to be 222 nm. 
       Preparation of Developer 
       [0158]    Each of the foregoing Toners 1 and 2, Comparative toners 1 and 2, Yellow toners 1 and 2, Magenta toners 1 and 2, and Black toners 1 and 2 was mixed with a ferrite carrier which was covered with methyl methacrylate and cyclohexyl methacrylate resin and exhibited a volume average particle size of 50 μm to prepare Developers 1 and 2, Comparative developers 1 and 2, Yellow developers 1 and 2, Cyan developers 1 and 2, and Black developers 1 and 2, each having a toner content of 6%. 
       Evaluation 
       [0159]    Evaluation was conducted by using a commercially available composite printer, bizhub Pro C500 (produced by Konica Minolta Business Technologies Inc.) into which a developing device having combined developers was loaded. 
         [0160]    Such combined developers are as follows. 
         [0000]    Inventive developer 1:
       Developer 1/Yellow developer 1/Cyan developer 1/Black developer 1
 
Inventive developer 2:
   Developer 2/Yellow developer 2/Cyan developer 2/Black developer 1
 
Comparative developer 1:
   Comparative developer 1/Yellow developer 1/Cyan developer 1/Black developer 1
 
Comparative developer 2:
   Comparative developer 2/Yellow developer 2/Cyan developer 2/Black developer 2       
 
         [0165]    Using four kinds of developers described above, evaluation was conducted as below. 
         [0000]    Color reproduction: 
         [0166]    A full-color image obtained by using the foregoing developers was evaluated with respect to range of color reproduction of a full-color image. Thus, solid images (2 cm×2 cm) of yellow (Y), magenta (M), cyan (C), and, as the secondary color, red (R), Blue (B) and green (G) were each formed by using the foregoing developers under an environment at a temperature of 20° C. and a humidity of 50% RH, the color gamut thereof was represented in a*b* coordinates and the area (color gamut area) was measured. The color reproduction range was represented by a relative value, based on the area constituted of a color gamut of Y/M/C/R/G/B obtained by comparative developer 1 being 100. A color gamut area was 120 or more and markedly increased color gamut, as compared to conventional printing standard color, which was also confirmed in the sensory examination and consistent from person to person. Evaluation results are as follows:
       Inventive developer 1: color gamut are=122   Inventive developer 2: color gamut are=126   Comparative developer 1: color gamut are=100   Comparative developer 2: color gamut are=102
 
As is apparent from the foregoing results, the use of the inventive developers 1 or 2 achieved a larger color gamut area than the use of comparative developer 1 or 2. Thus, the use of the toner of the invention achieved expansion of color gamut.
       
 
       Lightfastness: 
       [0171]    A magenta image of 10 cm×10 cm was prepared by each of the foregoing inventive developer 1, inventive developer 2, comparative developer 1 and comparative developer 2. Subsequently, using XENON WEATHER METER 1-XL 75, the thus prepared images were exposed to light under 70,000 lux of a xenon lamp for 480 hrs. to determine a rate of variation in reflection density between before and after exposure. The rate of variation in reflection density between before and after exposure is defined as below: 
         [0000]      Rate of variation (%)=[(reflection density before exposure)−[(reflection density after exposure)]×100/(reflection density before exposure) 
         [0172]    The rate of variation in density between before and after exposure is as follows:
       Inventive developer 1: rate of variation=0.1%   Inventive developer 2: rate of variation=0.1%   Comparative developer 1: rate of variation=8.7%   Comparative developer 2: rate of variation=8.7%       
 
         [0177]    As can be seen from the foregoing results, it was proved that lightfastness of images formed by use of the inventive developers 1 and 2 of the invention was superior to those obtained by use of the comparative developers 1 and 2. 
       Variation of Lightness 
       [0178]    A magenta toner image was formed by development using each of the inventive developers 1 and 2, and comparative developers 1 and 2 under the developing condition at a toner amount of 2.3 g/m 2  in an atmosphere (1) of 25° C. and 90% RH. The thus formed magenta toner image was measured with respect to lightness, which was denoted as lightness (1). A magenta image was also formed in the same manner as the foregoing, except that the atmosphere (1) was changed to an atmosphere (2) of 25° C. and 10% RH and the thus formed magenta toner image was also measured with respect to lightness, which was denoted as lightness (2) Results thereof are shown below. 
         [0000]                                        Rate   Lightness (1)   Lightness (2)   Variation                   Developer 1 (Inv.)   56.2   62.5   11.2       Developer 2 (Inv.)   53.8   60.5   12.4       Developer 1 (Comp.)   46.4   57.8   24.5       Developer 2 (Comp.)   46.3   58.5   26.4                    
The variation rate of lightness was defined as below
 
         [0000]      Variation Rate (%)={[lightness (2)−lightness (1)]/lightness (1)}×100 
         [0179]    Further, when printing was continuously conducted using the magenta developer 1 or 2 of the invention to prepare sheets of print, no scattering of toner occurred in the interior of the machine, and enhanced durability and superior maintenance capability of the developer were achieved. On the contrary, when the comparative developers 1 and 2 were each evaluated under the same conditions, toner scattering occurred and lightness of magenta color was unstable when 200,000 sheets were printed. Thus, it was proved that there were marked differences in durability and maintenance capability of a developer between the inventive and comparative developers.
An electrophotographic toner for electrostatic image development which is capable of obtaining a high chroma full-color image exhibiting clear color without color contamination and achieving enhanced lightfastness is disclosed, comprising a resin and a colorant, wherein the colorant comprises a pigment of C.I. Pigment Red 209. There are also disclosed a full-color toner kit and an image forming method by use of the toner.