Electrophotographic toner

Abstract: Disclosed is a process in which a spherical electrophotographic toner containing a colorant and having a particle size suitable for the electrophotography is directly formed in the polymerization process for formation of a binder resin. If a reaction medium capable of dissolving a monomer but incapable of dissolving a formed polymer is used and polymerization is carried out in the presence of a radical polymerization initiator in the state where the monomer, the colorant and other additives are dissolved or dispersed in the reaction medium, an electrophotographic toner having a desired particle size is obtained. According to this process, the particle size of the colored resin is stably controlled to 1 to 30 µm suitable for a toner in the polymerization process, and the particle size distribution is very sharp.

Description: The present invention relates to a process in which a spherical electrophotographic toner containing a colorant and having a particle size in a range suitable for a toner is directly prepared in the polymerization process for formation of a binder resin. Furthermore, the present invention relates to an electrophotographic toner which is excellent not only in the flowability but also in various photographic characteristics. In the electrophotographic process, a toner is used for visualizing an electrostatic image. Toner particles are composed of a composition comprising a binder resin and, incorporated therein, a colorant and other additives such as a charge controlling agent, and have a particle size adjusted to a certain level, for example, 1 to 30 µm. A resin having desirable electroscopic property and binding property, for example, a styrene resin, is used as the binder resin, and carbon black or other organic or inorganic coloring pigment is used as the colorant. A most typical process for the production of an electrophotographic toner comprises melt-kneading a binder resin as described above with a colorant, cooling and pulverizing the molten composition and classifying the pulverized composition to recover a fraction having a certain particle size. The yield of the toner obtained through pulverization and classification is low and a large equipment is necessary for these operations. Accordingly, the manufacturing cost of the toner is very high. Moreover, the shape of the obtained particles is irregular and the flowability of the toner is generally low, and the toner is defective in that blocking is readily caused. Various trials have been proposed to prepare toners directly in the polymerization process for formation of a binder resin. According to a typical instance, in a water-insoluble monomer is dissolved a polymerization initiator soluble in the monomer, additives such as a colorant are added to the solution, the resulting composition is suspended under high-speed shear stirring into an aqueous solution comprising an appropriate dispersant, for example, a water-soluble polymer, an inorganic powder and a surface active agent, and the suspension is subjected to polymerization to form colored polymer particles. According to this suspension polymerization process, however, the particle size of the final toner is determined by the state of suspension of the monomer composition in water, and the particle size distribution of the toner particles is very broad and readily influenced by the state of throwing of the monomer composition into water or by the stirring condition, and it is very difficult to obtain a toner uniform in the particle size. Furthermore, according to this suspension polymerization process, in general, only coarse particles having a size of scores of µm to several mm are formed, and particles having a size of 1 to 30 µm, suitable for a toner of a developer, can hardly be obtained. Of course, it is possible to reduce the particle size of the formed toner if the amount incorporated of the dispersant is increased. However, in this case, the dispersant is contained in the toner and the toner becomes sensitive to the moisture, and the electrophotographic characteristics are readily degraded. A particular post treatment is necessary to eliminate this disadvantage, and the step number is increased and the process cannot be practically worked. A so-called emulsion polymerization is known as the process for preparing polymer particles having a relatively uniform particle size. This emulsion polymerization process, however, is defective in that the obtained particles are too fine and have a particle size smaller than 1 µm and the step of removing the emulsifier after the polymerization is necessary. Therefore, according to this process, it is difficult to obtain a colored resin for a toner directly in the polymerization process. Furthermore, there is known a process in which a styrene type or acrylic monomer having a polar group such as an amino group or a hydroxyl group and a colorant are subjected to suspension polymerization in the presence of an acid-soluble inorganic compound and the formed suspension is treated with an acid to obtain a toner composed of colored polymer fine particles (see Japanese Patent Publication No. 51-14895). This process, however, is defective in that a troublesome operation of dissolving and removing the inorganic compound becomes necessary and a part of the monomer is polymerized in the state dissolved in the aqueous phase at the dispersing and polymerizing steps to form as by-products fine polymer particles having a size smaller than 1 µm, as in the so-called emulsion polymerization. It is a primary object of the present invention to provide a process for the preparation of an electrophotographic toner, in which a colored resin having a particulate structured suitable for use as the toner and being substantially free of a factor inhibiting electrophotographic characteristics of the toner can be directly prepared in the polymerization process for formation of the resin. Another object of the present invention is to provide a process for the preparation of a toner, in which in the polymerization process for formation of a colored resin, the particle size of the colored resin is controlled to 1 to 30 µm, suitable for the toner, and uniform particle size distribution can be maintained. Still another object of the present invention is to provide an electrophotographic toner to which a good chargeability is efficiently given by using a small amount of a charge-controlling agent, and a process for the preparation of this toner. In accordance with the present invention, there is provided a process for the preparation of an electrophotographic toner, which comprises dispersing core particles comprising a binder resin and a colorant dispersed therein and (i) a radical-polymerizable monomer (B) having a charge-controlling functional group or (ii) a mixture of monomer (B) with a monomer constituting the binder resin or (iii) a mixture of monomer (B) with a monomer (C) wherein monomer (C) is capable of being swollen with the binder resin in a reaction medium capable of dissolving said monomer but incapable of dissolving the binder resin and the resultant polymer and polymerizing the dispersion in the presence of a radical polymerization initiator such that a layer of a polymer or copolymer of the monomer having a charge-controlling functional group is produced on the surface of the colored resin particles. According to this process there is obtainable an electrophotographic toner comprising particles having a core comprising a binder resin derived from a monomer (A) and having a colorant dispersed therein, and a layer composed of a polymer derived from a monomer (B) having a charge-controlling functional group or a copolymer of said monomer (B) and either the monomer (A) constituting said binder resin or a monomer (C) wherein monomer (C) is capable of being swollen with the binder resin, said layer being chemically or physically bonded to the surface of the core. According to the process of the present invention, core particles comprising a binder resin and a colorant dispersed in the binder resin (hereinafter referred to as "colored resin particles") and a monomer (B) having a charge-controlling group or a mixture of said monomer (B) with a monomer constituting the binder resin or a monomer (C) capable of being swollen with the binder resin are dispersed in a reaction medium, the dispersion is subjected to radical polymerization, and a solvent capable of dissolving the monomer and incapable of dissolving the formed polymer is used as the reaction medium. Polymerization advanced in a solution is generally called solution polymerization, and in this solution polymerization, the formed polymer is dissolved in the solvent. On the other hand, in the process of the present invention, the formed polymer is not dissolved in the solvent, that is, the reaction medium. In this point, the polymerization of the present invention is distinguished from the solution polymerization. In the polymerization process, the polymerization of the monomer is initiated in the solution phase or in the surface layer of the dispersed colored resin particles, and the formed polymer or growing polymer chain is precipitated on the surfaces of the dispersed colored resin particles. Especially when the monomer (C) is co-present with the monomer (B), since the monomer (C) is readily absorbed in the dispersed colored resin particles, the polymerization is more smoothly and efficiently advanced on the surface layer of the colored resin particles. In this case, it sometimes happens that growth of the chain of the monomer (B) or the monomers (B) and (C) is caused by so-called graft polymerization. Thus, according to the embodiment (ii) of the present invention, a charge-controlling layer composed of the polymer of the monomer (B) or the monomers (B) and (C) can be formed effectively and tightly on the core of the colored resin. In fact, at least 50%, especially at least 80%, of the used monomer can be converted to a covering layer bonded to the surface of the core, and the amount of the polymer separated from the core particles is very small. The electrophotographic toner obtained according to this process is characterized in that a thin layer of a charge-controlling polymer composed of the monomer (B) or the monomers (B) and (C) is chemically or physically bonded to the surface of a core composed of colored resin particles. In this toner, since the charge-controlling monomer (B) is selectively included in the surface portions of the toner particles, high charge-controlling and chargeability-imparting effects can be efficiently attained with a much smaller amount of the monomer (B) than in the conventional toners. In fact, if the monomer (B) is used in such a small amount as 0.01 to 10% by weight, especially 0.1 to 5% by weight, based on the colored resin, a satisfactory chargeability can be imparted, which will become apparent from the examples given hereinafter. Furthermore, since the charge-controlling polymer is polymeric and is different from a low-molecular-weight compound such as a surface active agent or a dye, the layer of this polymer is tightly bonded to the colored resin core, and therefore, even if the toner is used for a long time, the charging characteristics are not sensitive to the moisture and stable electrophotographic characteristics can always be obtained. In order to include the charge-controlling monomer in the toner according to the suspension polymerization, it is necessary that the charge-controlling monomer should be present in oil drops of the binder resin-constituting monomer, and hence, the kind of the monomer to be used is strictly limited. On the other hand, an optional charge-controlling monomer can be selectively included in the surfaces of the colored resin particles without such limitation. If certain colored resin particles are prepared and the kind of the monomer (B) to be precipitated on the surfaces of the colored resin particles is changed, toners having either negative or positive charging characteristics can be optionally obtained. This is another prominent advantage attained by the present invention. Moreover, by making the expensive charge-controlling agent present locally on the surfaces of the toner particles and thus including the monomer into the polymer layer, the manufacturing cost of the toner can be greatly reduced. The charge-controlling monomer (B) alone may be used for the polymerization or used in combination with other monomer for the polymerization. In the case where the charge-controlling monomer (B) has a good compatibility with the colored resin particles, the monomer (B) alone may be used, but in the case where the monomer (B) is poor in the compatibility with the binder resin, the monomer (B) is used in combination with the binder resin-constituting monomer or a monomer capable of being swollen with the binder resin, whereby a layer of a charge-controlling copolymer bonded tightly to the surface of the core can be formed. Colored Resin Particles The colored resin particles may be prepared according to an optional granulation method such as a kneading pulverization granulation method, a spray-drying granulation method or a suspension polymerization method. Binder Resin A thermoplastic resin having fixing and electroscopic properties can be used as the binder resin. For example, there are preferably used homopolymers and copolymers of vinyl aromatic monomers, acrylic monomers, vinyl ester type monomers, vinyl ether type monomers, diolefin type monomers and mono-olefin type monomers, though resins that can be used are not limited to these polymers. Monomers exemplified below as the radical-polymerizable monomer (A) are used. A styrene resin, an acrylic resin and a styrene-acrylic copolymer resin are preferred. Radical-Polymerizable Monomer (A) The monomer (A) is radical-polymerizable and a polymer formed from this monomer has fixing and electroscopic properties required for a toner. At least one monomer having an ethylenic unsaturation is used so that the above-mentioned conditions are satisfied. For example, monovinyl aromatic monomers, acrylic monomers, vinyl ester type monomers, vinyl ether type monomers, diolefin type monomers and mono-olefin type monomers are preferably used. As the monovinyl aromatic monomer, there can be mentioned monovinyl aromatic hydrocarbons represented by the following formula: wherein R 1 stands for a hydrogen atom, a lower alkyl group or a halogen atom, and R 2 stands for a hydrogen atom, a lower alkyl group, a halogen atom, an alkoxy group, an amino group, a nitro group, a vinyl group or a carboxyl group, such as styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene, o-, m- and p-chlorostyrenes, p-ethylstyrene, sodium styrene-sulfonate and divinylbenzene. These monomers may be used singly or in the form of mixtures of two or more of them. Furthermore, there can be mentioned acrylic monomers represented by the following formula: wherein R 3 stands for a hydrogen atom or a lower alkyl group, and R 4 stands for a hydrogen atom, a hydrocarbon group having up to 12 carbon atoms, a hydroxyalkyl group, a vinyl ester group or an aminoalkyl group, such as acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, ethyl β-hydroxyacrylate, propyl γ-hydroxyacrylate, butyl δ-hydroxyacrylate, ethyl β-hydroxymethacrylate, propyl γ-aminoacrylate, propyl γ-N,N-diethylaminoacrylate, ethylene glycol dimethacrylate and tetraethyelne glycol dimethacrylate, vinyl esters represented by the following formula: wherein R 5 stands for a hydrogen atom or a lower alkyl group, such as vinyl formate, vinyl acetate and vinyl propionate, vinyl ethers represented by the following formula: wherein R 6 stands for a monovalent hydrocarbon group having up to 12 carbon atoms, such as vinylmethyl ether, vinylethyl ether, vinyl-n-butyl ether, vinylphenyl ether and vinylcyclohexyl ether, diolefins represented by the following formula: wherein R 7 , R 8 and R 9 each stand for a hydrogen atom, a lower alkyl group or a halogen atom, such as butadiene, isoprene and chlororprene, and monoolefins represented by the following formula: wherein R 10 and R 11 each stand for a hydrogen atom or a lower alkyl group, such as ethylene, propylene, isobutylene, butene-1, pentene-1 and 4-methylpentene-1. In order to uniformalize the particle size in the colored resin particles, it is preferred that the radical-polymerizable monomer be capable of dissolving the formed polymer therein. For this purpose, a monovinyl aromatic monomer, especially styrene, an acrylic monomer or a mixture thereof is preferably used. Colorant A pigment or dye (hereinafter referred to as "coloring pigment") is used as the colorant for coloring the toner. As preferred examples of the coloring pigment, there can be mentioned black pigments such as carbon black, acetylene black, lamp black and aniline black, yellow pigments such as chrome yellow, zinc yellow, cadmium yellow, yellow iron oxide, Mineral Fast Yellow, nickel titanium yellow, naples yellow, Naphthol Yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG and Tartrazine Yellow Lake, orange pigments such as chrome orange, molybdenum orange, Permanent Orange GTR, Pyrazolone Orange, Vulcan Orange, Indanthrene Brilliant Orange RK, Benzidine Orange G and Indanthrene Brilliant Orange GK, red pigments such as red iron oxide, cadmium red, red lead, mercury cadmium sulfide, Permanent Red 4R, Lithol Red, Pyrazolone Red, Watchung Red calcium salt, Lake Red D, Brilliant Carmine 6B, eosine lake, Rhodamine Lake B, alizarin lake and Brilliant Carmine 3B, violet pigments such as manganese violet, Fast Violet B and Methyl Violet Lake, blue pigments such as prussian blue, cobalt blue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue, metal-free Phthalocyanine Blue, partially chlorinated Phthalocyanine Blue, Fast Sky Blue and Indanthrene Blue BC, green pigments such as chrome green, chromium oxide, Pigment Green B, Malachite Green Lake and Fanal Yellow Green G, white pigments such as zinc flower, titanium oxide, antimony white and zinc sulfide, and extender pigments such as baryte powder, barium carbonate, clay, silica, white carbon, talc and alumina white. As the magnetic pigment, there are known tri-iron tetraoxide (Fe 3 O 4 ), di-iron trioxide (γ-Fe 2 O 3 ), zinc iron oxide (ZnFe 2 O 4 ), yttrium iron oxide (Y 2 Fe 5 O 12 ), cadmium iron oxide (CdFe 2 O 4 ), gadolinium iron oxide (Gd 3 Fe 5 O 12 ), copper iron oxide (CuFe 2 O 4 ), lead iron oxide (PbFe 12 O 19 ), neodium iron oxide (NdFeO 3 ), barium iron oxide (BaFe 12 O 19 ), magnesium iron oxide (MgFe 2 O 4 ), manganese iron oxide (MnFe 2 O 4 ), lanthanum iron oxide (LaFeO 3 ), iron powder (Fe), cobalt powder (Co) and nickel powder (Ni). In the present invention, fine powders of these known magnetic pigments may be used. The weight ratio of the colorant to the binder resin may be changed in a broad range, and it is generally preferred that this weight ratio be in the range of from 1/100 to 20/100, especially from 3/100 to 10/100. It is preferred that the particle size of the colored resin particles be 3 to 30 µm, especially 5 to 20 µm. The shape of the particles is not particular critical, and spherical and irregular shapes may be adopted. Reaction Medium According to the present invention, an organic solvent capable of dissolving the monomer (A) but incapable of dissolving the formed polymer thereof is used as the reaction medium. In order to avoid bad influences of the solvent left in the toner, it is preferred that the organic solvent be easily volatile. The solvent actually used should be determined according to the kinds of the monomer and the polymer thereof. Alcohols, cellosolves, ketones and hydrocarbons are generally preferred. Mixtures of two or more of these solvents, or mixtures of these solvents with other compatible organic solvents or water may be used. As the alcohol, there can be mentioned lower alcohols such as methanol, ethanol and propanol. As the cellosolve, there can mentioned methylcellosolve and ethylcellosolve. As the ketone, there can be used acetone, methylethyl ketone and methylbutyl ketone. As the hydrocarbon, there can be used n-hexane, n-heptane and cyclohexane. Polymerization Initiator A polymerization initiator soluble in a liquid mixture of the monomer and reaction medium is used. For example, there can be mentioned azo compounds such as azobisisobutyronitrile and peroxides such as cumene hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, benzoyl peroxide and lauroyl peroxide. Moreover, combinations of ionizing rays such as γ-rays and accelerated electron beams or violet rays with photosensitizers may be used. Monomer (B) Having Charge-Controlling Functional Groups The same monomers as mentioned above with respect to the embodiment (i) are used as the monomer (B). As the monomer (C) to be used in combination with the monomer (B), binder resin-constituting monomers as mentioned above are used, and moreover, monomers different from the binder resin-constituting monomer but capable of being swollen with the binder resin may be used. For example, a styrene type monomer has a swelling property with not only polystyrene but also an acrylic resin, and a copolymer comprising this monomer is especially suitable for attaining the objects of the present invention. Additives Also in the preparation process of the embodiment (ii), additives desirable to be contained in the toner may be incorporated into the starting composition prior to the polymerization. For example, a parting agent such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, a wax or a silicone oil may be added so as to impart an offset-preventing effect to the toner. Polymerization In the second embodiment (ii) of the present invention, the colored resin particles are dispersed in the reaction medium, and the charge-controlling monomer (B) or a mixture of the monomer (B) and comonomer (C) is dissolved in the reaction medium and the polymerization is initiated. The amount charged of the colored resin particles is 0.1 to 100% by weight, especially 1 to 50% by weight, based on the reaction medium. The amount charged of the monomer (B) is 0.01 to 10% by weight, especially 0.1 to 5% by weight, based on the reaction medium. When the comonomer (C) is used in combination with the monomer (B), the amount of the comonomer (C) is less than 100 times the amount of the monomer (B). The amount of the polymerization initiator such as an azo compound or a peroxide may be a catalytic amount, and it is generally preferred that the amount charged of the polymerization initiator be 0.1 to 10% by weight based on the charged monomer. Known polymerization temperature and time may be adopted, and it is generally preferred that the polymerization be carried out at a temperature of 40 to 100°C for 1 to 50 hours. Stirring of the reaction mixture may be such gentle stirring that homogeous reaction is advanced as a whole. In order to prevent inhibition of the polymerization by oxygen, the reaction atmosphere may be replaced by an inert gas such as nitrogen. All of the monomer and polymerization initiator may be charged at a time, or parts of them may be first added and the remainders may be charged afterward stepwise or continuously. Since the reaction product is obtained in the form of particles having the above-mentioned particle size, the formed particles are filtered, washed with the above-mentioned solvent if necessary and dried to obtain colored particles for a toner. According to need, the colored particles for a toner are sprinkled with carbon black, hydrophobic silica or the like to obtain a final toner. In the preparation process of the embodiment (i), according to need, a dispersion stabilizer may be used as in the first embodiment (i). The present invention will now be described in detail with reference to the following examples that by no means limit the scope of the invention. Example 1 Colored resin particles (a) having an average particle size of 10 µm were obtained by melt-kneading, pulverizing and classifying 100 parts by weight of a styrene/n-butyl methacrylate copolymer, 7 parts by weight of carbon black and 1.5 parts by weight of a polyolefin wax. A composition shown in Table 1 (run No. 1, 2 or 3), which comprised the colored resin particles (a), was charged in a separable flask having a capacity of 1 ℓ, and reaction was carried out at 65°C in a nitrogen current with stirring at 150 rpm for 5 hours to complete polymerization. When the obtained polymer was observed by an optical microscope, it was found that the polymer was composed of black particles having a uniform particle size of about 10 µm and uncolored fine particles were not substantially present. The polymer was separated by filtration and dried under reduced pressure to obtain a toner. The polarity of each of the toners obtained in this example was negative, as shown in Table 5 illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-211) by using these toners, a clear image having no fog was obtained in each case. Run No. 1 Run No. 2 Run No. 3 colored resin particles (g) 108.5 108.5 108.5 methanol (mℓ) 450 450 450 distilled water (mℓ) 50 50 50 styrene (g) 1 5 20 sodium styrene-sulfonate (g) 0.1 1 5 benzoyl peroxide (g) 0.01 0.06 0.25 Example 2 A separable flask having a capacity of 1 ℓ was charged with a composition shown in Table2 (run No. 4, 5 or 6), which comprised the colored resin particles obtained in Example 1 and reaction was carried out at 65°C in a nitrogen current with stirring at 150 rpm for 5 hours to complete polymerization. When the formed polymer was observed by an optical microscope, it was found that the polymer was composed of black particles having a uniform particle size of about 10 µm and uncolored fine particles were not substantially present. The polymer was separated by filtration and dried under reduced pressure to obtain a toner. The polarity of the toner was positive as shown in Table 5 illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-15) charged with this toner, a clear image having no fog was obtained. Run No. 4 Run No. 5 Run No. 6 colored resin particles (g) 108.5 108.5 108.5 methanol (mℓ) 450 450 450 styrene (g) 1 5 20 dimethylaminoethyl methacrylate quaterenary compound (g) 0.1 1 5 azobisisobutyronitrile (g) 0.01 0.06 0.25 Example 3 A sufficiently stirred mixture comprising 96 parts by weight of styrene, 4 parts by weight of divinylbenzene, 5 parts by weight of carbon black and 1 part by weight of azobisisobutyronitrile was added to 500 parts by volume of distilled water containing, dissolved therein, 20 parts by weight of partially saponified Poval (having a saponification degree of 88%) and 1 part by weight of sodium dodecylsulfate, and the mixture was stirred at 3000 rpm for 10 minutes by using a homogenizing mixer (supplied by Tokushu Kika Kogyo) and charged in a separable flask having a capacity of 1 ℓ. Reaction was carried out at 70°C for 8 hours in a nitrogen current with stirring at 150 rpm to complete polymerization. The formed polymer was separated by sedimentation, washed sufficiently, dried under reduced pressure and classified to obtain colored resin particles (b) having an average particle size of 10 µm. Then, a separable flask having a capacity of 1 ℓ was charged with 105 g of the colored resin particles (b), 450 mℓ of methanol, 50 ml of distilled water, 1 g of sodium styrene-sulfonate, 10 g of styrene and 0.1 g of azobisisobutyronitrile, and reaction was carried out at 65°C for 5 hours in a nitrogen current with stirring at 150 rpm to complete polymerization. When the formed polymer was observed by an optical microscope, it was found that the polymer was composed of black particles having a uniform particle size of about 10 µm and uncolored fine particles were not substantially present. The polymer was separated by filtration and dried under reduced pressure to obtain a toner. The polarity of the toner was negative as shown in Table 5 illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-211) charged with this toner, a clear image having no fog was obtained. Example 4 A separable flask having a capacity of 1 ℓ was charged with 105 g of the colored resin particles (b) obtained in Example 3 , 450 mℓ of methanol, 50 mℓ of distilled water, 2 g of diethylaminoethyl methacrylate quaternary compound, 10 g of styrene and 0.1 g of azobisisobutyronitrile, and reaction was carried out at 65°C for 5 hours in a nitrogen current with stirring at 150 rpm to complete polymerization. When the formed polymer was observed by an optical microscope, it was found that the polymer was composed of black particles having a uniform particle size of about 10 µm and uncolored fine particles were not substantially present. The polymer was separated by filtration and dried under reduced pressure. The polarity of the toner was positive as shown in Table illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-15) charged with the obtained toner, a clear image having no fog was obtained. Comparative Example 1 Three toners (runs Nos.7 through 9) having an average particle size of 10 µm were prepared by melt-kneading, pulverizing and classifying compositions shown in Table 3. The polarity of each toner was negative as shown in Table 5 illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-211) by using these toners, a clear image having no fog was obtained in case of the toner of run No. 9, but slight fogging was observed in images formed by using the toners of runs Nos. 7 and 8. Run No. 7 Run No. 8 Run No. 9 styrene/n-butyl methacrylate copolymer resin (g) 100 100 100 carbon black (g) 7 7 7 polyolefin wax (g) 0.1 0.1 0.1 styrene/sodium styrene sulfonate copolymer (5/1) (g) 0.6 6 30 Comparative Example 2 Three toners (runs Nos. 10 through 12) having an average particle size of 10 µm were prepared by melt-kneading, pulverizing and classifying compositions shown in Table The polarity of each toner was positive as shown in Table5 illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-15) by using these toners, a clear image having no fog was obtained in case of the toner of runs Nos. 10 and 11. Run No. 10 Run No. 11 Run No. 12 styrene/n-butyl methacrylate copolymer resin (g) 100 100 100 carbon black (g) 7 7 7 polyolefin wax (g) 0.1 0.1 0.1 styrene/dimethylaminoethyl methacrylate quaternary compound copolymer resin (5/1) (g) 0.6 6 30 Comparative Example 3 A sufficiently stirred mixture comprising 96 parts by weight of styrene, 4 parts by weight of divinylbenzene, 1 part by weight of acid-phosphoxyethyl methacrylate, 5 parts by weight of carbon black and 1 part by weight of azobisisobutyronitrile was added to 500 parts by volume of distilled water containing, dissolved therein, 20 parts by weight of partially saponified Poval (having a saponification degree of 88%) and 1 part by weight of sodium dodecylsulfate, and the mixture was stirred at 3000 rpm for 10 minutes by using a homogenizing mixer (supplied by Tokushu Kika Kogyo) and charged in a separable flask. Reaction was carried out at 70°C in a nitrogen current with stirring at 150 rpm for 8 hours to complete polymerization. The polymer was separated by filtration, sufficiently washed, dried under reduced pressure and classified to obtain a toner having an average particle size of 10 µm. The polarity of the toner was negative as shown in Table 5 illustrating the results of the measurement of the charge quantity according to the blow-off method. The charge quantity of this toner was smaller than that of the toner of Example 3 When the copying operation was carried out in a copying machine (Mita DC-211) charged with this toner, slight fogging was observed in the obtained image. Comparative Example 4 A sufficiently stirred mixture comprising 96 parts by weight of styrene, 4 parts by weight of divinylbenzene, 2 parts by weight of diethylaminoethyl methacrylate quaternary compound, 5 parts by weight of carbon black and 1 part by weight of azobisisobutyronitrile was added to 500 parts by volume of distilled water containing, dissolved therein, 20 parts by weight of partially saponfied Poval (having a saponification degree of 88%) and 1 part by weight of sodium dodecylsulfate, and the mixture was stirred at 3000 rpm for 10 minutes by using a homogenizing mixer (supplied by Tokushu Kika Kogyo) and charged in a separable flask. Reaction was carried out at 70°C in a nitrogen current with stirring at 150 rpm for 8 hours to complete polymerization. The polymer was separated by filtration, sufficiently washed, dried under reduced pressure and classified to obtain a toner having an average particle size of 10 µm. The polarity of the toner was positive as shown in Table 5 illustrating the results of the measurement of the charge quantity according to the blow-off method. When the copying operation was carried out in a copying machine (Mita DC-15) charged with the toner, slight fogging was observed in the obtained image. Charge Quantity (µC/g) Example 1 Run No. 1 - 11 Run No. 2 - 18 Run No. 3 - 25 Example 2 Run No. 4 + 10 Run No. 5 + 13 Run No. 6 + 17 Example 3 - 15 Example 4 + 10 Comparative Example 1 Run No. 7 - 6 Run No. 8 - 9 Run No. 9 - 15 Comparative Example 2 Run No. 10 + 1 Run No. 11 + 5 Run No. 12 + 10 Comparative Example 3 - 9 Comparative Example 4 + 6

Claims: A process for the preparation of an electrophotographic toner, which process comprises dispersing core particles comprising a binder resin having a colorant dispersed therein and (i) a radical-polymerizable monomer (B) having a charge-controlling functional group or (ii) a mixture of monomer (B) with a monomer (A) constituting the binder resin or (iii) a mixture of monomer (B) with a monomer (C) wherein monomer (C) is capable of being swollen with the binder resin in a reaction medium capable of dissolving the monomer but incapable of dissolving the binder resin and the resultant polymer and polymerizing the dispersion in the presence of a radical polymerization initiator such that a layer of polymer or copolymer of the monomer having a charge-controlling functional group is produced on the surface of the coloured resin particles. A process according to claim 1, wherein the radical-polymerizable monomer (B) is used with the monomer constituting the binder resin or the monomer (C). A process according to claim 2, wherein the amount of the monomer (C) is less than 100 times the amount of the monomer (B) used. An electrophotographic toner, obtainable by a process according to any one of the preceding claims, comprising particles having a core comprising a binder resin derived from monomer (A) and having a colorant dispersed therein, and a layer composed of a polymer derived from monomer (B) having a charge-controlling functional group or a copolymer derived from monomer (B) and either monomer (A) or monomer (C) capable of being swollen with the binder resin, said layer being chemically or physically bonded to the surface of the core. An electrophotographic toner, according to claim 4, in the form of spherical particles of uniform size, wherein the binder resin is composed of a mixture comprising a resin component I derived from radical-polymerizable monomer (A) convertible to a fixing thermoplastic resin and a copolymer resin component II derived from the monomer (A) and the radical-polymerizable monomer (B) having a charge-controlling functional group, the repeating units derived from monomer (B) being present in an amount of 0.1 to 10 mole% based on the repeating units derived from monomer (A), 30 to 99 mole% of the repeating units derived from monomer (A) being present in the resin component I and 1 to 70 mole% of the repeating units derived from monomer (A) being present in the resin component II.

Inventors: MATSUMOTO TSUNETAKA, OKUBO MASAYOSHI, TOKUNO TOSHIRO, MATSUMOTO, TSUNETAKA, OKUBO, MASAYOSHI, TOKUNO, TOSHIRO
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1986
Main classification: G03G9
IPC codes: G03G9