Resinous microparticles useful in powdery toner for electrophotography

Abstract: Resinous microparticles useful in toner for electrophotography which are made of vinyl resin obtained by emulsion polymerization of at least one α,β-ethylenically unsaturated monomers in the presence of cationic surfactant having an onium salt structure and a polymerization initiator having an amidine or amidine salt structure and whose average particle diameter is in a range of from 0.01 to 1µ, and toner composition comprising toner particles and resinous microparticles as abovementioned are provided.

Description: The present invention relates to resinous microparticles capable of improving the flowability of powders, especially toners to be used in electrophotography, electrostatic recording and the like. More specifically, the invention concerns resinous microparticles having positive charging ability. Among the various methods capable of forming a visible image from an electric latent image or electric signal, the so-called dry-developing process has been widely used because a simple device can be used for carrying out that process safely and the thus obtained image is stable for many copying cycles. However, the toner used in that dry-developing process should possess an excellent flowability in view of the image quality and the cyclic stability of the image. For improving the flowability of the toner, an inorganic powder such as silica, alumina and titanium dioxide powder has heretofore often been applied onto the toner surface. Recently, it has also been adopted to treat the surface of such an inorganic powder with various materials which are capable of improving the moisture absorption of the powder, such as silane coupling agents, silicone oil and various surfactants. Furthermore, there has also been proposed to employ fluorine polymer particles with a uniform diameter (for example in Japanese Patent Publication (unexamined) Sho 61-275768). On the other hand,with the different intention of preventing deficient cleaning, Japanese Patent Publication (unexamined) Sho 60-186851 discloses the addition of resinous microparticles such as acrylic copolymer or styrene/acrylic copolymer to the toner particles. However, when the abovementioned microparticles are used with the intention of giving appropriate flowability to the positive charging toner, it often happens that the charging of said toner is adversely affected, since most of such microparticles are charged negatively instead of positively. Furthermore, at that time, when the particle size is as large as 0.3 µm or more, a larger quantity of resinous particles is required for obtaining the desired flowability and, as a consequence, there arises a trouble that the resinous particles are liable to leave the toner surface and to cause contamination, thereby spoiling the cyclic stability of copied image. When resinous microparticles with an average particle diameter of as small as less than 0.3 µm, prepared by using a surfactant, are used for improving the flowability of the toner, the abovementioned problem is solved, but when the selection of the polymerization initiator is not appropriate, there is a tendency that the resinous microparticles stick together, and thus the desired flowability can hardly be obtained. Such resinous microparticles may also be prepared by using a persulfate polymerization initiator as disclosed in Japanese Patent Publication (unexamined) Nos. Sho 60-186851 and 60-186868. However, when such resinous microparticles are used together with toner particles, the desired positively charging toner can hardly be obtained because the resinous microparticles thus prepared are liable to be negatively charged. It is, therefore, an object of the invention to provide resinous microparticles which have positive charging ability and are capable of providing an appropriate flowability on toner. Another object of the invention is to provide a toner for electrophotography which contains said resinous microparticles and has an excellent flowability. According to the present invention, the aforesaid objects can be attained with resinous microparticles comprising a vinyl resin obtainable by emulsion polymerization of at least one α,β-ethylenically unsaturated monomer, using a cationic surfactant having an onium structure as an emulsifier and a compound having an amidine or amidine salt structure as a polymerization initiator to obtain vinyl resin microparticles having an average particle diameter of 0.01 to 1 µm. Examples of cationic surfactants having an onium salt structure for use in the present invention are alkyl trimethyl amine salts alkyl benzyl trimethyl amine salts, dialkyl dimethyl amine salts, alkyl pyridinium salts and alkyl phosphonium salts. In order to obtain positive charging ability, such surfactants must be of a cationic nature and the specific surfactant and its amount are to be determined by due consideration of its affinity for the monomer used, the emulsion stability during emulsion polymerization and the like. As the polymerization initiator having an amidine or amidine salt structure, the following are advantageously used: azoamidine compounds such as 2,2'-azobis(2-methyl-N-phenylpropionamidine), 2,2'-azobis[N-(4-chlorophenyl)-2-methylpropionamidine], 2,2'-azobis[N-(4-hydroxyphenyl)-2-methylpropionamidine], 2,2'-azobis[N-(4-aminophenyl)-2-methylpropionamidine], 2,2'-azobis[2-methyl-N-(phenylmethyl)propionamidine]dihydrochloride, 2,2'-azobis[2-methyl-N-2-propenylpropionamidine], 2,2'-azobis(2-methylpropionamidine) and 2,2'-azobis[N-(2-hydroxyethyl)-2-methylpropionamidine]; cyclic azoamidine compounds such as 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane], 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane], 2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidine-2-yl)propane], 2,2'-azobis[2-(5-hydroxy-3,4,5,6-tetrahydropyrimidine-2-yl)propane] and 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}; their hydrochlorides, methane sulfonates, p-toluene sulfonates and other amidine salt compounds. Examples of α,β-ethylenically unsaturated monomers for use in the invention are styrene; α-methylene aliphatic monocarboxylic acids or esters thereof such as acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate and butyl methacrylate; N,N-dialkylaminoalkyl(meth)acrylates such as N,N-dimethylaminomethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate and N,N-diethylaminoethyl(meth)acrylate; N,N-dialkylaminoalkyl(meth)acrylamides such as N,N-dimethylaminoethyl(meth)acrylamide, and N,N-dimethylaminopropyl(meth)acrylamide; fluorine containing monomers such as trifluoro acrylate and perfluoro acrylate; and silicon containing monomers. When a carboxyl containing monomer such as acrylic acid, methacrylic acid or vinyl benzoic acid is included as a part of said monomers to be polymerized, the resinous particles thus obtained are specifically useful in the present invention because the cyclic stability of charging of the toner used with said particles is greatly improved. When an amphoionic group containing monomer is included in the resin constituting monomers, there hardly occurs a decrease in developing properties of the toner. This is especially true under high temperature and high humidity conditions. This is believed to be due to the fact that said amphoionic groups will absorb humidity under such conditions and exert a kind of buffer effect avoiding a decrease of the charge control action. Examples of such amphoionic group are groups of the aminosulfonic acid type, the amino-carboxylic acid type or the sulfobetaine type represented by the formula: N-A-SO₃H, N-A-COOH or N-A-SO₃ wherein A represents a linear or branched alkylene having 1 to 6 carbon atoms, a phenylene or a substituted phenylene group. As the monomers having an amphoionic group of the aminosulfonic acid or the amino-carboxylic acid type, mention is made of monomers prepared by the addition reaction of a benzyl halide and an aminosulfonic acid having primary or secondary amino groups (e.g. N-(vinylbenzyl)taurine or N-methyl-N-(vinylbenzyl)taurine; and monomers prepared by the reaction of an oxirane and an aminoacid compound having primary or secondary amino groups (e.g. N-(2-hydroxy-3-allyloxypropyl)taurine, 2-(N-(2-hydroxy-3-allyloxypropyl))taurine or N-(2-hydroxy-3-allyloxypropyl)alanine. Examples of monomers bearing an amphoionic group of the sulfobetaine type (as disclosed in Japanese Patent Publication (unexamined) Sho 53-72090) compounds represented by the formula: wherein R₁₀ represents hydrogen atom or a methyl group, R₁₁ and R₁₂ are the same or different and each represents an alkyl group having 1 to 6 carbon atoms, A₂ is O or NH, and m₁ and n₁ are the same or different and each represents an integer of 1 to 12, and compounds represented by the formula: or wherein R₁₃ is hydrogen atom or a methyl group, R₁₄ is hydrogen atom or an alkyl group having 1 to 3 carbon atoms, m₂ is 0 to 6, n₂ is an integer of 1 to 6, and A₂ has the same meaning as defined above. The present resinous microparticles may be crosslinked when desired. For this end, polyfunctional monomers such as divinyl benzene, ethylene glycol dimethacrylate, neopentyl glycol dimethacrylate and trimellitic triallylate may be used. One or more of the abovementioned monomers may be selected as constituting monomers of the present resinous microparticles depending on the desired properties thereof. However, when 2 or more monomers having different hydrophylic properties are used together, the thus obtained microparticles show excellent cohesion resistance, and hence are particularly preferred. After polymerization, the formed emulsion may be subjected to a drying operation with a hot air drier or a freezing drier, and the resinous microparticles thus obtained can be used directly. However, when the emulsion is purified by using an ion-exchange resin, or an ultrafiltration device prior to drying, far better properties of the resinous microparticles can be expected. For improving the flowability of the toner, the resinous microparticles added should preferably have an average particle diameter of 0.1 µm or less. The particle diameter may be measured by any conventional means such as by direct observation by means of a transmission type electron microscope, or a scanning type electron microscope, or by indirect methods such as light scattering or centrifugal settling. The present resinous microparticles may be added to any of the heretofore known toners. For example, they may be added to a positive charging toner to improve the flowability thereof. Or, they may be added to an ordinary toner without containing any charge controlling agent, thereby giving both flowability and charging properties to the toner. Furthermore, the present resinous microparticles may by added to a negatively over-charged toner to control the charge level, as well as the flowability thereof. The toner per se may be prepared by any conventional means such as by kneading and pulverizing, spray-drying, emulsion polymerization or suspension polymerization. The amount of the present resinous microparticles may vary with the average particle diameter of the toner and the resinous microparticles used. For example, when 0.08 µm resinous microparticles are added to a 12 µm toner, the amount of said resinous microparticles is advantageously selected in the range of 0.01 to 5% by weight, preferably in the range of 0.1 to 3% by weight, calculated on the toner weight. When the amount of resinous microparticles is less than the lower limit, it is impossible to get sufficient effect of the invention, and when the amount of resinous microparticles is more than 5% by weight of the toner weight, there is a tendency that the resinous microparticles detach from the toner surface and contaminate the charge donor such as the carrier, and sub-system members such as the development container. Therefore, the added amount should be determined carefully in due consideration of the particle diameter of the toner and the diameter of the resinous microparticles, and the shape and the surface conditions of the toner and the carrier. The present resinous microparticles may be mixed with the toner by means of either the so-called dry mixing method using Henshel mixer, Super mixer, other high speed mixer or V-type blender, or the wet mixing method wherein the toner is added to an emulsion of resinous microparticles and stirred well. When the glass transition point of the resinous microparticles is higher than that of the toner, storage stability of the toner may be improved. The present resinous microparticles are used alone to improve the flowability of the toner, but if desired, they may be used together with other conventional additives. Both of the cationic surfactant having an onium salt structure and the polymerization initiator having an amidine or amidine salt structure are materials having excellent positive charging characteristics and therefore, according to this invention, it is possible to provide resinous microparticles with excellent positive charging characteristics. Furthermore, when the abovementioned two components are used together at the emulsion polymerization of α,β-ethylenically unsaturated monomers, the thus obtained emulsion is very stable and therefore, can result in hardly cohesive resinous microparticles. Such microparticles are uniformly adhered onto the surface of the powdery toner. When the resinous microparticles are prepared form α,β-ethylenically unsaturated monomers including a carboxyl bearing monomer, the thus obtained microparticles each have the positive charging onium salt and the amidine salt having comparatively high charging speeds, as well as the carboxyl group having comparatively low charging speed. Therefore, when compounded with toner particles, the cyclic stability of positive charging of the thus obtained toner is excellent. When amphoionic groups are present in the resinous microparticles to be compounded with the toner, excellent environmental stability is given to the present toner. Therefore, at the time when the photoconductor having an excess amount of toner remained thereon is subjected to a cleaning operation, even after 50,000 copying operations, there is no fear of cleaning defect with the present toner. Contrary therewith, with a conventional toner an effective cleaning can be expected at the early stage indeed, but after 20,000 to 30,000 copying operations, an amount of toner will remain on the photoconductor imagewisely and cause a ghost image or black stripe on next copies. Under high temperature and high humidity conditions, such defects will appear at a much earlier stage. The invention shall be now more fully explained in the following Examples. Unless otherwise indicated, all parts and percentages are by weight. Example 1 Into a 2 liters separable flask fitted with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel, were placed 230 parts of deionized water and 0.6 part of Cation 300 (alkylbenzyl trimethyl amine salt surfactant, trademark of Sanyo Kasei K.K.) and the mixture was heated to 75°C. To this were added a solution of 0.5 part of initiator V-50 (2,2'-azobis(2-methyl propionamidine)dihydrochloride, trademark of Wako Junyaku K.K.) in 10 parts of deionized water and then dropwise a monomer mixture of 90 parts of methyl methacrylate and 10 parts of styrene in 45 minutes. After completion of said addition, the combined mixture was maintained at 75°C for 4 hours to complete the polymerization reaction. The reaction mixture was then subjected to spray-drying to obtain the resinous microparticles of this invention. Example 2 The same procedures as stated in Example 1 were repeated, except for that the reaction mixture was treated with a ultrafiltration apparatus prior to spray-drying to obtain the purified resinous microparticles. Example 3 Into the similar reaction vessel as used in Example 1, but fitted with two dropping funnels, were placed 220 parts of deionized water and 0.6 part of Cation 300, and the mixture was heated to 75°C. To this was added one half of the solution of 1 part of initiatror V-50 in 20 parts of deionized water. Then, from said two dropping funnels, the remaining half of the initiator solution and a monomer mixture of 90 parts of methyl methacrylate and 10 parts of n-butyl methacrylate were simultaneously and dropwise added in 90 minutes. After completion of said addition, the combined mixture was maintained at 75°C for 2 hours to complete the polymerization reaction. The reaction mixture was then purified by using an ion exchange resin and subjected to spray-drying to obtain the resinous microparticles of this invention. Example 4 The same procedures as stated in Example 1 were repeated, except for changing the amount of initiator V-50 to 1 part and the monomer composition to a mixture of 85 parts of methyl methacrylate, 10 parts of styrene and 5 parts of ethylene glycol dimethacrylate to obtain the resinous microparticles of this invention. Example 5 The same procedures as stated in Example 1 were repeated, except for substituting 1 part of initiator VA-058 (2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane] dihydrochloride, trademark of Wako Junyaku K.K.) for 0.54 part of V-50 to obtain the present resinous microparticles. Example 6 The same procedures as stated in Example 1 were repeated, except for substituting 0.5 part of initiator VA-061 2,2'-azobis[2-(2-imidazolin-2-yl)propane], trademark of Wako Junyaku K.K.) for 0.5 part of V-50 to obtain the present resinous microparticles. Example 7 The same procedures as stated in Example 1 were repeated, except for substituting 1 part of 2,2'-azobis(2-methyl propion amidine)di-p-toluenesulfonate for 0.5 part of V-50 to obtain the present resinous microparticles. Example 8 The same procedures as stated in Example 1 were repeated, except for substituting 1 part of cetylpyridinium chloride for 0.6 part of Cation 300 as cationic surfactant to obtain the present resinous microparticles. Example 9 The same procedures as stated in Example 1 were repeated, except for substituting 3 parts of cetylpyridinium chloride for 0.6 part of Cation 300 as cationic surfactant to obtain the present resinous microparticles. Example 10 Into a similar reaction vessel as used in Example 1, were placed 400 parts of deionized water and 3 parts of Cation 300 (cationic surfactant, alkyl benzyl trimethyl amine, trademark of Sanyo Kasei K.K.) and the mixture was heated to 75°C. To this was added a solution of 0.5 part of initiator V-50 (2,2'-azobis(2-methyl propionamidine)dihydrochloride, trademark of Wako Junyaku K.K.) in 10 parts of deionized water, and then monomer mixture of 90 parts of methyl methacrylate and 10 parts of styrene was dropwise added in 60 minutes. After completion of said addition, the mixture was maintained 5 at 75°C for 2 hours to complete the polymerization reaction. Thus obtained reaction mixture was dried by using a spray-drier to obtain the present resinous microparticles. Example 11 The same procedures as stated in Example 10 were repeated using a monomer mixture of 88 parts of methyl methacrylate, 10 parts of styrene and 2 parts of methacrylic acid to obtain the present resinous microparticles. Example 12 The same procedures as stated in Example 10 were repeated using a monomer mixture of 87 parts of methyl methacrylate, 10 parts of styrene and 3 parts of methacrylic acid to obtain the present resinous microparticles. Example 13 The same procedures as stated in Example 10 were repeated using a monomer mixture of 87 parts of methyl methacrylate, 10 parts of styrene and 3 parts of vinyl benzoic acid to obtain the present resinous microparticles. Example 14 The same procedures as stated in Example 10 were repeated, except for substituting 1 part of cetyl pyridinium chloride for 3 parts of Cation 300 as cationic surfactant and changing the monomer composition to a mixture of 88 parts of methyl methacrylate, 10 parts of styrene and 2 parts of methacrylic acid to obtain the present resinous microparticles. Example 15 Into a similar reaction vessel as used in Example 1, were placed 370 parts of deionized water and 0.6 part of Cation 300 and the mixture was heated to 70°C. To this a solution of 2 parts of 2,2-azobis(2-amidinopropane)dihydrochloride in 20 parts of deionized water was added and the combined mixture was allowed to stand for 5 minutes. Thereafter, 15 parts of the solution of 22 parts of 1-(3-sulfopropyl)-2-vinyl pyridinium betaine dissolved in 198 parts of deionized water and 12 parts of the monomer mixture of 126 parts of styrene, 16 parts of n-butyl methacrylate and 36 parts of n-butyl acrylate were added and after keeping at the same temperature for 10 minutes, the remaining parts of the abovementioned two were dropwise added in 1 hour and the combined mixture was further maintained at the same temperature for 3 hours to obtain an emulsion having a solid content of 25.2%. The average particle diameter of the emulsion particles was 0.07 µm. Said emulsion was then subjected to freeze drying to obtain the present microparticles of acrylic resin containing sulfobetained group, amidino group and ammonium group. Example 16 Into a similar reaction vessel as used in Example 1, were placed 370 parts of deionized water and 0.4 part of Cation 300 and the mixture was heated to 70°C. While maintaining the same temperature, a solution of 1.4 parts of 2,2-azobis(2-amidinopropane)dimethane sulfonic acid in 20 parts of deionized water was added, and after standing for 5 minutes, 15 parts of a solution of 6 parts of N-methyl-N-(vinylbenzyl)taurine in 198 parts of deionized water and 12 parts of the mixture of 152 parts of methyl methacrylate and 42 parts of n-butyl methacrylate were added. After standing for 10 minutes, the remaining parts of the abovementioned two were dropwise added in 1 hour and then the combined mixture was maintained at the same temperature for 3 hours to obtain an emulsion having a solid content of 25.0%, the average particle diameter of the emulsion particles was 0.1 µm. The emulsion was then subjected to freeze drying to obtain the microparticles of acrylic resin having aminosulfonic acid group, amidino group and ammonium group. Example 17 Into a similar reaction vessel as used in Example 1, were placed 350 parts of deionized water and 0.8 part of Cation 300 and the mixture was heated to 75°C. While maintaining the same temperature at 75°C, a solution of 2 parts of 2,2-azobis(2-amidinopropane) in 60 parts of deionized water was added and the mixture was allowed to stand for 5 minutes. Thereafter, a solution of 4 parts of N-(2-hydroxy-3-allyloxypropyl)alanine in 178 parts of deionized water and a monomer mixture of 120 parts of methyl methacrylate, 40 parts of styrene and 36 parts of n-butyl acrylate were simultaneously and dropwise added in 1 hour and the combined mixture was maintained at the same temperature for 3 hours to obtain an emulsion having a solid content of 25.3% and an average particle diameter of 0.08 µm. The emulsion was then subjected to freeze drying to obtain the microparticles of acrylic resin having amino acid group, amidino group and ammonium group. Comparative Example 1 Into a similar reaction vessel as used in Example 1, 900 parts of deionized water were added and the content was heated to 75°C. To this was added 1 part of V-50 dissolved in 10 parts of deionized water and then 20 parts of methyl methacrylate. After stirring for 5 minutes, a monomer mixture of 70 parts of methyl methacrylate and 10 parts of styrene was dropwise added in 45 minutes and the combined mixture was maintained at 75°C for 4 hours to complete the polymerization reaction. The thus obtained mixture was treated as in Example 1 to obtain the comparative resinous microparticles by the so-called soap-free emulsion polymerization method. Comparative Example 2 The same procedures as stated in Example 1 were repeated, except for substituting 0.5 part of potassium persulfate for 0.5 part of initiator V-50 and changing the polymerization temperature to 80°C. In this Example, the formed resin began to agglomerate shortly after the completion of the monomer addition and it was impossible to obtain the desired resinous microparticles. Comparative Example 3 The same procedures as stated in Example 1 were repeated, except for substituting 5 parts of polyoxyethylene nonyl phenol (nonionic surfactant) for 0.6 part of Cation 300 (cationic surfactant) to obtain the comparative resinous microparticles. Comparative Example 4 The same procedures as stated in Example 1 were repeated, except for substituting 1 part of potassium persulfate for 0.5 part of initiator V-50, and a mixture of 4 parts of polyoxyethylene nonyl phenol (nonionic surfactant) and 1 part of sodium lauryl sulfate for 0.6 part of Cation 300 (cationic surfactant), to obtain the comparative resinous microparticles comprising 90 parts of methyl methacrylate, 10 parts of styrene and 4 parts of vinyl pyrrolidone. Experiments (1) The average particle of the resinous microparticles obtained in Examples 1∼17 (except for Example 7) and in Comparative Examples 1, 3 and 4 were determined by using a scanning type microscope. Light scattering method was used for determining the average particle diameter of the resinous microparticles of Example 7. (2) Tribo value: 0.2 part of the resinous microparticles obtained in the respective Example and 100 parts of reduced iron powder carrier (TEFV 2100/300, manufactured by Nippon Iron Powder Co.) were throughly mixed in a ball mill for 1 hour and the blow off tribo value of the resulted mixture was determined. (3) Aerated apparent density: 100 parts of toner prepared by melt-kneading a mixture of styrene-acrylic copolymer and carbon black, pulverizing and sieving and having an aerated apparent density of 0.303 g/cc were mixed well with 1 part of the resinous microparticles obtained in the respective Example, in a Henshel mixer and the aerated apparent density of the resulted toner was determined by using a Powder Tester manufactured by Hosokawa Micron K.K. The test results are shown in Table 1. Average particle diameter (µm) Tribo value (µ C/g) Aerated apparent density (g/cc) Example 1 0.08 +110 0.336 2 0.08 +105 0.346 3 0.08 +190 0.335 4 0.09 +150 0.335 5 0.08 +130 0.338 6 0.09 + 50 0.335 7 0.08 +107 0.341 8 0.1 +160 0.333 9 0.02 +109 0.329 10 0.06 + 85 0.365 11 0.07 + 62 0.358 12 0.07 + 43 0.359 13 0.07 + 27 0.355 14 0.06 + 24 0.360 15 0.07 + 95 0.351 16 0.1 + 88 0.336 17 0.08 +103 0.344 Comp. Ex. 1 0.3 +250 0.299 3 0.1 + 10 0.305 4 0.1 - 50 0.310 As is clear from the test results of Table 1, the present resinous microparticles can give excellent positive charging characteristics and toner fluidity. Example 18 6 parts of the toner employed in Experiment No. 3 and added with the resinous microparticles of Example 1 were mixed with 100 parts of 80 µm iron powder carrier coated with a fluorine-contained resin to give a developing composition. Using the developing composition in a copier SF-8100 (manufactured by Sharp K.K.), continuous copying operations were carried out. Excellent images were obtained up to 20,000 copies. Example 19 Styrene-acrylic resin 100 parts carbon black 8 parts nigrosine 5 parts low molecular weight polypropylene wax 4 parts The abovementioned composition was melt-kneaded in a pressurized kneader, pulverized and sieved to obtain colored particles having an average particle diameter of 12 µm. To 100 parts of the thus obtained colored particles, was mixed 0.5 part of the resinous microparticles of Example 10 by using a Henshel mixer to obtain the present toner composition. Example 20 The procedures stated in Example 19 were repeated, except for substituting 0.5 part of the resinous microparticles of Example 11 for 0.5 part of the resinous microparticles of Example 10 to obtain the present toner composition. Example 21 The same procedures as stated in Example 19 were repeated, except for substituting the same amount of resinous microparticles of Example 12 for the microparticles of Example 10 to obtain the present toner composition. Example 22 The same procedures as stated in Example 19 were repeated, except for substituting the same amount of resinous microparticles of Example 13 for the microparticles of Example 10 to obtain the present toner composition. Example 23 The same procedures as stated in Example 19 were repeated, except for substituting the same amount of resinous microparticles of Example 14 for the microparticles of Example 10 to obtain the present toner composition. Example 24 The same procedures as stated in Example 19 were repeated, except for increasing the amount of resinous microparticles of Example 10 from 0.5 part to 4 parts to obtain the present toner composition. Example 25 The same procedures as stated in Example 19 were repeated, except for substituting 2 parts of the resinous microparticles of Example 14 for 0.5 part of the microparticles of Example 10 to obtain the present toner composition. Example 26 The same procedures as stated in Example 19 were repeated, except for substituting 1 part of the resinous microparticles of Example 15 for 0.5 part of the microparticles of Example 10 to obtain the present toner composition. Example 27 The same procedures as stated in Example 19 were repeated, except for substituting 2 parts of the resinous microparticles of Example 16 for 0.5 part of the microparticles of Example 10 to obtain the present toner composition. Example 28 The same procedures as stated in Example 19 were repeated, except for substituting 3 parts of the resinous microparticles of Example 17 for 0.5 part of the microparticles of Example 10 to obtain the present toner composition. Comparative Example 5 In this Example, the colored particles stated in Example 19 were used as such as toner, without adding the resinous microparticles of Example 10. Comparative Example 6 The same procedures as stated in Example 19 were repeated, except for substituting 0.5 part of alumina (manufactured by Nippon Aerosil K.K. AOC) for 0.5 part of the risinous microparticles of Example 10 to obtain the comparative toner. Comparative Example 7 The same procedures as stated in Example 19 were repeated, except for substituting 0.5 part of Aerosil R972 (manufactured by Nippon Aerosil K.K.) for 0.5 part of the resinous microparticles of Example 10 to obtain the comparative toner. Experiment (4) Aerated apparent densities of the toners obtained in Examples 19∼25 and Comparative Examples 5∼7 were measured by using Powder Tester manufactured by Hosokawa Micron K.K. (5) Each 5 parts of the toner obtained in the respective Example were mixed with 100 parts of iron powder carrier coated with fluorine containing resin. Tribo values of the toner were measured by using Blow off tester manufactured by Toshiba Chemical K.K. at three different stages after elapsing 3, 20 and 60 minutes mixing times. The test results are shown in Table 2. Aerated apparent density (g/cc) Tribo value (µ C/g) 3 min. 20 min. 60 min. Example 19 0.340 +23.0 +26.0 +29.0 20 0.345 +22.0 +22.3 +23.4 21 0.339 +21.5 +22.5 +22.5 22 0.342 +21.0 +22.0 +22.3 23 0.350 +21.0 +21.5 +21.5 24 0.360 +30.0 +34.0 +34.2 25 0.362 +32.0 +32.2 +32.2 Comp. Ex. 5 0.298 +18.0 +22.0 +22.2 6 0.345 + 8.8 +10.5 +12.8 7 0.350 - 2.5 - 0.2 + 2.5 As clearly shown in Table 2, the present toner exhibits excellent flowability and can be electrificated well with positive charge. Furthermore, as is clear from the test results of Examples 20∼23, when the toner is added with microparticles of a resin having carboxyl groups in the molecule, there is only minor change in tribo values at different mixing times and thus, the toner is excellent in cyclic stability of charging. Next, the toner compositions of each of Examples 26~28, Example 19 and Comparative Examples 5∼6 was subjected to mixing in a ball mill under three different atmospheric conditions (i.e. temp. 22°C and relative humidity 55%; temp. 35°C and relative humidity 85%; and temperature 10°C and relative humidity 30%) for 20 minutes and the tribo value was measured each time. The test results obtained are shown in Table 3. Aerated apparent density (g/cc) Tribo value (µ C/g) 22°C 55%RH 35°C 85%RH 10°C 30%RH Example 19 0.340 +26.0 +21.2 +31.1 26 0.347 +25.6 +23.0 +27.4 27 0.351 +27.3 +24.9 +29.0 28 0.355 +29.8 +26.7 +31.3 Comp. Ex. 5 0.298 +22.0 +15.6 +30.2 6 0.345 + 10.5 + 7.0 +14.3 As is clear from the test results shown in Table 3, when the microparticles are composed of a resin having an amphoionic group in its molecule, the present toner added with such resinous microparticles can exhibit excellent atmospheric stability, showing only minor change in the tribo value under different mixing conditions. When continuous copying operations were carried out with these toners, excellent copies were obtained under different atmospheric conditions.

Claims: Resinous microparticles useful in toners for electrophotography comprising a vinyl resin obtainable by emulsion polymerization of at least one α,β-ethylenically unsaturated monomer in the presence of a cationic surfactant having an onium salt structure and a polymerization initiator having an amidine or amidine salt structure, and whose average particle diameter is in the range of 0.01 to 1 µm. Resinous microparticles according to claim 1, wherein a carboxyl group bearing monomer is one of said α,β-ethylenically unsaturated monomers. Resinous microparticles according to claim 1, wherein an amphoionic group bearing monomer is one of said α,β-ethylenically unsaturated monomers. A toner composition for electrophotography containing the resinous microparticles of claim 1, 2 or 3 in an amount of 0.01 to 5% by weight of the total toner weight.

Inventors: HISAJIMA EIO, KASHIHARA AKIO, KIDA KATSUAKI, MARUTA MASAYUKI, YABUUCHI NAOYA, HISAJIMA, EIO, KASHIHARA, AKIO, KIDA, KATSUAKI, MARUTA, MASAYUKI, YABUUCHI, NAOYA
Applicants: NIPPON PAINT CO LTD, NIPPON PAINT CO., LTD.
Application year: 1989
Main classification: G03G9
IPC codes: G03G9, C08F2