JPH05323671A - Production of toner - Google Patents

Abstract

PURPOSE:To obtain electrophotographic toner with which the rise of the toner charge amount is steep when the toner is mixed with a carrier and which causes neither attenuation of the charge amount nor pollution of a carrier by a charge controlling agent even when the toner is mixed with the carrier over a long time and the method for manufacture thereof. CONSTITUTION:The electrophotographic toner is constituted of nucleus particles consisting of the mixture of a fixing resin and a compounding agent for the toner other than a charge control agent and the coating layer of a charge control agent present only on the surface of the nucleus particles and has a specific surface (A) of <=3.3 defined by an equation, A=B/C. In the equation, C is the specific area (m<3>/g) of the toner calculated as a true sphere based on the volume standard median diameter measured by the colter counter method and B is the specific area (m<3>/g) measured by the BET method and a part having an area ratio of >=0.5%, on which the charge controlling agent is distributed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner for electrophotography having a novel particle surface structure and a method for producing the same.

[0002]

2. Description of the Related Art A dry toner used for electrophotography, that is, a toner for a two-component developer, is prepared by mixing a mixture of a fixing resin, a color pigment and a charge control agent, a release agent, and other toner compounding agents with a heat roll or the like. It is manufactured by kneading with, pulverizing the kneaded material, and classifying the material. However, in such a conventional toner, only a small part of the added charge control agent is used for charge control of the toner particles, and there is a problem of low efficiency. As a solution to this drawback, Japanese Patent Laid-Open No. 63-138358 discloses that toner base particles composed of a binder resin and a dye / pigment are mixed with charge control agent particles to attach the charge control agent particles to the surface of the toner base particles. 50 to 300 m / s after the composite particles are formed into the composite particles.
It has been proposed that the charge control agent particles are fixed to the surface of the toner mother particles by applying an impact force in the air flow of ec.

Further, in JP-A-64-18153, a mixture of a thermoplastic resin and a colorant is melted and kneaded and then pulverized to prepare colored mother particles, and then charge control is performed on the mother particles. It is described that a plurality of fine particles are fixed to the surface of the colored mother particles by mixing fine powder mainly containing the agent and the offset preventive agent and applying a compressive force and an impact force to the obtained mixture.

Further, Japanese Patent Application Laid-open No. 2-
JP-A-308262 discloses a step of kneading a fixing resin and a compounding agent for toner other than a charge control agent, pulverizing the kneaded product, and classifying the kneaded material to produce a toner precursor, and the precursor and the charge control agent. Powder of the fixing resin is mixed at a temperature lower than the melting point or softening point of the fixing resin under high shearing force and high compressing force to embed the charge control agent in the form of primary particles on the surface of the precursor particles. The method for producing a toner is described.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above proposal, the charge control agent particles are fixed or embedded only on the surface of the toner mother particles, and the amount of the charge control agent used is higher than that in the conventional internal addition method. It is intended to obtain an effective charge control action while reducing the charge. Further, in the fixing or embedding method described above,
When the toner and the carrier are mixed, the advantage that the charge amount rises more than the charge control agent internally added toner is obtained, but when the mixing with the carrier is continued, the charge amount is considerably higher than that at the initial stage. It was found that the charge control agent was further reduced, and the charge control agent migrated to the surface of the carrier to electrically contaminate the carrier.

Accordingly, an object of the present invention is to provide an electrophotographic toner and a method for producing the same, in which the charge control agent is distributed on the surface of the toner particles, but the above-mentioned drawbacks of the conventional fixing or embedding method toner are eliminated. To provide. Another object of the present invention is that when the toner and the carrier are mixed, the toner charge amount rises rapidly, and even when the toner and the carrier are mixed for a long time, the charge amount is not attenuated, and It is an object of the present invention to provide an electrophotographic toner which does not cause the carrier to be contaminated by a charge control agent and a method for producing the same.

[0007]

According to the present invention, a fixing resin and a compounding agent for toner other than a charge control agent are kneaded, and the kneaded product is crushed and classified to produce precursor particles for toner. ,
The precursor particles and the charge control agent powder are pre-mixed to deposit the charge control agent particles on the surface of the precursor particles, and the pre-mixture is at a temperature lower than the melting point or softening point of the fixing resin,
A method for producing a toner is provided, which comprises applying a shearing / impacting force that causes rounding of precursor particles to form a uniform coating layer of a charge control agent on the surface of the precursor particles.

According to the present invention, it further comprises core particles composed of a mixture of a fixing resin and a compounding agent for toner other than the charge control agent, and a coating layer of the charge control agent existing only on the surface of the core particles. In the electrophotographic toner, the toner has a specific surface area (calculated as a true sphere based on the volume-based median diameter measured by the Coulter counter method, where C is a formula 1) A = B / C. m ² / g) and B is the specific surface area (m ² / g) of the toner measured by the BET method. The specific surface area ratio (A) defined by is less than or equal to 3.3, and in the distribution surface analysis of the charge control agent by an electron probe micro analyzer (EPMA), the portion where the charge control agent is distributed is present. There is provided an electrophotographic toner having an area fraction of 0.5% or more.

[0009]

In the method for producing a toner according to the present invention, toner precursor particles (mother particles) are produced from a fixing resin and a toner compounding agent by a kneading pulverization method, and a charge control agent powder is added to the precursor particles. Premixing and applying shearing / impacting force to this premixing are in agreement with the above-mentioned prior art, but the shearing / impacting force is applied to the premixing to the extent that rounding of precursor particles occurs The remarkable feature is to form a uniform coating layer of the charge control agent on the surface of the body particles. That is, in the conventional fixing or embedding method, a portion where the charge control agent was localized and a portion where the charge control layer was not present were inevitably present on the toner surface. When applying shearing / impact force that causes rounding,
With this rounding, the charge control agent spreads over the entire particle surface, and a uniform coating with the charge control agent is formed.

The degree of rounding, that is, the degree of smoothness of the toner can be evaluated by the specific surface area ratio (A) of the above "Formula 1". The denominator C on the right side of "Equation 1" is calculated from the following formula based on the volume-based median diameter, assuming that the particles are spherical.

During Equation 2] C = 6 / (d · ρ ) equations, d is the volume-based median diameter (m), ρ represents the density of the toner (g / m ^3). The specific surface area (m ² / g) calculated by The molecule B on the right side has a specific surface area (m ² /
g).

Since the toner particles obtained by the kneading and pulverizing method are amorphous and have many irregularities and corners, B is considerably larger than the value of C and the specific surface area ratio (A) is generally 3.3 or more. Is also large. In the present invention, the specific surface area ratio (A) is 3.3 or less, particularly in the range of 2.7 to 3.3 by performing the rounding process after attaching the charge control agent to such toner particles, and most preferably. Is in the range of 2.8 to 3.2. With this rounding treatment, the localization of the charge control agent particles on the surface of the toner particles is eliminated, and a uniform coating due to the presence of charge control is formed on the surface of the toner particles.

The distribution state of the charge control agent on the surface of the toner particles can be measured by surface analysis using an electron probe micro analyzer (EPMA). That is, when the sample is irradiated with an electron beam accelerated to several tens of kv, X-rays having a wavelength peculiar to the constituent elements (complex salt metal contained in the charge control agent), that is, characteristic X-rays are generated. The concentration can be measured from the intensity of this X-ray, and the distribution in the plane direction can be measured by two-dimensionally scanning the electron beam. Since the electron beam penetration depth is about 3 μm, it can be considered that the charge control agent in the toner measured by this method is mainly present on the surface.
By image analysis of the EPMA area chart thus obtained, the area fraction in which the charge control agent is distributed can be determined. According to the present invention, the area fraction of the conventional fixing or embedding method toner can be determined. While it was less than 10%,
This area fraction can be improved to 10% or more, especially 15% or more.

FIG. 1 is a scanning electron micrograph (a magnification of 4000) of a conventional fixing or embedding toner, which has a specific surface area ratio (A) of 3.84. The small particles that adhere to the surface of the large particles are the charge control agent particles. "FIG. 2" is a scanning electron micrograph (a magnification of 4000) of the toner according to the present invention, and the specific surface area ratio (A) of the toner is 3.08. The presence of charge control agent particles can no longer be detected by electron microscopy, in connection with the rounding of the toner particles.

FIG. 3 is an EP of the toner particles of FIG.
It is an MA surface analysis chart, and the white dots correspond to X-rays due to the complex salt metal (Fe) in the charge control agent. In the toner shown in FIG. 1, the charge control agent particles have a localized state (area fraction 9.92).
%) Is confirmed. FIG. 4 is an EPMA surface analysis chart of the toner particles of FIG. 2, and the fact that the charge control agent is uniformly distributed over almost the entire surface of the toner particles (area fraction 31.88%) is understood. To be done.

According to the present invention, the charge control agent forms a uniform coating on the surface of the toner particles so that the charge amount of the toner rises sharply when mixed with the carrier, and the charge when the mixture is mixed for a long time. It offers the advantage that there is little attenuation of the quantity and little carrier contamination.

FIG. 5 is a graph in which the mixing time with the carrier is plotted on the abscissa and the charge amount is plotted on the ordinate for various toners containing a charge control agent, and the curve A is the toner according to the present invention (see FIG. 2 "), curve B is for fixed or embedded toner (" FIG. 1 "), and curve C is for internally added toner. In the fixing or embedding method toner B,
Although the charge amount rises faster than the internally added toner C, when the mixture with the carrier is continued, the charge amount is significantly attenuated. On the other hand, the toner A according to the present invention provides the steepest rise of the charge amount as compared with the toners B and C, and a high level charge amount regardless of the mixing time. Moreover, it becomes clear that the charge amount does not decrease even when the mixing is performed for a long time.

FIG. 6 is a plot of the relationship between the amount of charge attenuation and the amount of transfer of the charge control agent to the carrier. A close inverse correlation is observed between the two and the amount of charge is shown. In the toner of the present invention, it is clear that the charge control agent is present as a coating layer which is strong and has high adhesion. Of course,
With the toner of the present invention, since the particles are rounded, the fluidity is good, and the chargeability of the toner is also extremely excellent, so that there is no toner scattering or fog, and a high-density, high-contrast image can be obtained with excellent development work It also has an excellent advantage that it can be formed with good properties.

[0018]

As the fixing resin used in the present invention, all the resins conventionally used in electrophotographic toners can be used. For example, a thermoplastic resin, an uncured form or a precondensate form can be used. Curable resin with melting point or softening point of 60
Those in the range of to 200 ° C. are used. Suitable examples thereof include, but are not limited to, polystyrene,
Acrylic resins, styrene-acrylic copolymer resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenol resins, petroleum resins, olefin resins and the like.

Examples of the compounding agent for toner other than the charge control agent include a release agent and various pigments. As the releasing agent, various animal and vegetable waxes, mineral waxes, polyethylene waxes, polypropylene waxes and the like are used, and these are generally blended in the toner in an amount of 1 to 5% by weight.

As the pigment, in addition to the color pigment, various pigments conventionally used in toners such as magnetic pigments and conductive pigments can be used. Suitable examples thereof include, but are not limited to: Black pigments Channel black, furnace black, iron black. Yellow pigments Yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral first yellow, nickel titanium yellow, navels yellow, Teftle yellow S, Hansa yellow 10G, benzidine yellow G, quinoline yellow lake, permanene yellow NGG, Tartrazine rake. Orange pigment Red lead yellow molybdenum orange, Permanent orange GTR, Pyrazolone orange, Vulcan orange, Indanthrene brilliant orange RK, Benzidine orange G, Indanthrene brilliant orange GK. Red Pigment Bengal, Cadmium Red, Red Tan, Mercury Cadmium Sulfide, Permanent Orange 4R, Resole Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B.

Purple pigment Manganese purple, fast violet B, methyl violet lake. Blue pigment Navy blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, fast sky blue, indense en blue B
C. Green pigment chrome green, chrome oxide, pigment green B,
Malachite Green Rake, Fanal Yellow Green G. White pigment Titanium dioxide (white titanium), zinc white. Extender pigment Palite powder, barium carbonate, clay, silica, white carbon, talc, aluminum white.

Examples of the magnetic material pigment include iron trioxide (Fe ₃ O ₄ ), iron sesquioxide (γ-Fe ₂ O ₃ ), zinc iron oxide (ZnFe ₂ O ₄ ), and yttrium iron oxide (Y _3).
Fe ₅ O ₁₂ ), cadmium oxide (Gd ₃ Fe ₅ O ₁₂ ),
Iron oxide copper (CuFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O 4
₁₉ ), iron neodymium oxide (NdFeO ₃ ), iron oxide barium (BaFe ₁₂ O ₁₉ ), iron magnesium oxide (MgF
e ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), iron powder (Fe), cobalt powder (Co), nickel powder (Ni), etc. are known.
Also in the present invention, any of these known fine powders of magnetic materials can be used.

These pigments may have multiple functions. For example, carbon black has a function as a black pigment and a function as a conductive pigment. Similarly, iron black (magnetite) has a function as a black pigment and a function as a magnetic pigment. It is preferable that these pigments are present in the toner in an amount of 5 to 15% by weight, particularly 7 to 12% by weight, depending on its use.

The process for producing the toner precursor in the present invention is the same as the process for producing the toner by the conventional pulverization method except that the charge control agent is not added. The particle size of the precursor particles is preferably such that the volume-based median diameter by a Coulter counter is in the range of 5 to 30 μm, particularly 5 to 15 μm. The precursor particles preferably have a specific surface area ratio (A) of 3.3 or more, particularly 3.3 to 4.3 in order to uniformly form the coating of the charge control agent by the rounding treatment. If the specific surface area ratio (A) of the precursor particles is lower than the above range, it tends to be difficult to make the charge control agent coating uniform by rounding, while the specific surface area ratio (A) is too large. When it gets bigger, when rounding
It is observed that the charge control agent is more often incorporated inside the precursor particles, and the amount present on the surface is reduced. The adjustment of the specific surface area ratio (A) in the precursor particles also depends on the pulverization conditions and the type of resin. Generally, the longer the grinding time and the higher the grinding temperature, the smaller the specific surface area ratio (A) tends to be, and the larger the brittleness of the resin, the larger the specific surface area ratio (A) tends to be. It suffices to select conditions that fall within the above range.

As the charge control agent embedded in the toner precursor, any charge control agent conventionally used for toner is used. Examples of the charge control agent include nigrosine dyes, oil blacks, oil-soluble dyes such as spirone black, and naphthenic acid, salicylic acid, octylic acid, higher fatty acids, resin acids of manganese, iron, cobalt, lead, zinc, and cerium. Examples thereof include metal soaps such as metal salts of calcium, nickel and the like, metal-containing azo dyes, pyrimidine compounds, metal chelates of alkylsalicylic acid and the like.
A typical example of the positive charge control agent is an oil-soluble dye, and a typical example of the negative control agent is a metal-containing complex salt dye. These charge control agents are preferably 0.01 to 3% by weight, and more preferably 0.05 to 2% by weight, based on the toner precursor, although they vary depending on the kind. In the present invention, it is a remarkable advantage that a high charge amount can be obtained by using a small amount of charge control agent.

According to the present invention, the toner precursor particles and the charge control agent are premixed using a high shear mixer. In this premixing, the charge control agent fine particles are uniformly sprinkled and attached to the surface of the toner precursor particles, and a Henschel mixer, a homomixer or the like can be used as the high shear mixer. As a matter of course, the temperature used is lower than the melting point or softening point of the fixing resin in the toner precursor, and mixing for about 5 to 90 minutes is suitable.

Then, the premix obtained is subjected to a shearing / impacting force at a temperature lower than the melting point or softening point of the fixing resin to cause the precursor particles to be rounded, so that the surface of the precursor particles is electrically charged. Form a uniform coating of control agent. The shearing / impacting force that causes rounding of sheared particles varies depending on the processing equipment used, but the relationship between the applied energy and the rounded state of particles after processing and the amount of electrification should be calculated in advance. Thus, this condition can be easily determined. Generally, the applied energy is from 0.2 to 10 J (joule) / kg, based on the unit weight of the premix,
Particularly, in the range of 1.0 to 7.0 J / kg, satisfactory results can be obtained. The applied energy can be obtained by subtracting the load energy when the apparatus is operated empty from the load energy when the object to be processed is put into the apparatus and operated.

As the device for applying the shearing / impacting force, any device known per se can be used. For example, an Ongmill manufactured by Hosokawa Micron Co., Ltd. or a hybridizer manufactured by Nara Machinery Co., Ltd. is used. be able to. Generally, the temperature may be room temperature, but of course, when the heat generated during mixing is too large, forced cooling is performed using cooling water, cold air, brine, or conversely, hot water or steam is used for the purpose of shortening the mixing time. Infrared heating, through a heating medium such as
There is no problem even if heating is performed by means such as electric heat.

[0029]

The present invention will be described in the following examples. Evaluation of various properties was performed as follows. <Evaluation method> 1) Charge amount: 3 parts by weight of each toner and 9 ferrite carriers
7 parts by weight were mixed in a 300 ml poly container and measured with a blow-off charge amount measuring device. Rise of charge ○: Rise is fast ×: Rise is slow. Stability ○: Stable at a constant value. X ... unstable. 2) Actual copying test: Using the developer having the above mixing ratio, continuous copying of 20,000 sheets was performed on a copying machine DC-1657 manufactured by Mita Kogyo. The image density of 1.30 or more is good. Background fogging 0.005 or more is good. Toner scattering After 20,000 sheets were actually copied, the inside of the copying machine was examined to evaluate the degree of dirt on the developing device.

Example 1 Styrene-acrylic resin (St / BA / MMA, Tg 68 ° C.) 100 parts by weight carbon black (# 2300, manufactured by Mitsubishi Kasei) 10 parts by weight Polyethylene wax (high wax 200P, manufactured by Mitsui Petrochemical) 2 parts by weight The mixture having the above composition was melt-kneaded by a twin-screw extruder, the obtained kneaded product was cooled, and then the volume average diameter was adjusted to 13.5 μm using a jet mill pulverizer and an Alpine refiner to prepare a precursor. Got the body 100 parts by weight of this precursor and a charge control agent (T
-77, Hodogaya Chemical Co., Ltd.) 1 part by weight was premixed with a Henschel mixer (FB-10B type, manufactured by Mitsui Miike Seisakusho). 50 g of this pre-mixture was put into a surface modifier (Ong Mill, manufactured by Hosokawa Micron Co., Ltd.) and treated at 65 ° C. or lower for 30 minutes to obtain Toner A of the present invention. The total applied energy in this treatment was 2.3 J / kg.

Example 2 Toner D was obtained in the same manner as in Example 1 except that the amount of the charge control agent added was changed to 0.05 part by weight.

Comparative Example 1 100 g of the premixture obtained in Example 1 was charged into a surface reforming machine (Angmill, manufactured by Hosokawa Micron), and 110
The toner B was obtained by treating with G centrifugal force for 60 minutes. At this time, the material temperature was 50 ° C. or lower, and the total applied energy was 0.18 J / kg.

Comparative Example 2 Styrene-acrylic resin (St / BA / MMA, Tg 68 ° C.) 100 parts by weight Carbon black (# 2300, manufactured by Mitsubishi Kasei) 10 parts by weight Polyethylene wax (high wax 200P, manufactured by Mitsui Petrochemical) 2 parts by weight Charge control agent (T-77, Hodogaya Chemical Co., Ltd.) 1 part by weight The mixture having the above composition is melt-kneaded by a twin-screw extruder, and the obtained kneaded product is cooled, and then a jet mill grinder and Using an Alpine classifier, toner particles C having a volume average diameter of 13.5 μm were obtained.

Comparative Example 3 Toner E was obtained in the same manner as in Example 1, except that the amount of charge control agent added was 0.025 parts by weight.

Example 3 Polyester resin (Tg 63 ° C.) 100 parts by weight Carbon black (Printex 85, manufactured by Degussa) 6.5 parts by weight Polyethylene wax (high wax 200P, manufactured by Mitsui Petrochemical Co., Ltd.) 2.0 parts by weight The mixture having the above composition is melt-kneaded by a twin-screw extruder, the obtained kneaded product is cooled, then pulverized by a jet mill pulverizer, and further adjusted by an Alpine classifier so that the volume average diameter becomes 8.0 μm. To obtain a precursor. 100 parts by weight of this precursor and 0.3 part by weight of a charge control agent (Bontron S-34, manufactured by Orient Chemical Industry Co., Ltd.) were premixed with a Henschel mixer. 50 g of the preliminary mixture was put into a surface modifier (Ong Mill, manufactured by Hosokawa Micron Corp.) and treated at 60 ° C. or lower for 20 minutes to obtain a toner F. The total applied energy in this treatment was 2.1 J / kg.

Example 4 100 parts by weight of styrene acrylic resin (St / BA / MMA, Tg 66 ° C.) carbon black (# 2300, manufactured by Mitsubishi Kasei) 8.0 parts by weight polyethylene wax (high wax 200P, manufactured by Mitsui Petrochemical Co., Ltd.) ) 2 parts by weight The mixture having the above composition is melt-kneaded by a twin-screw extruder, the obtained kneaded product is cooled, then pulverized by a jet mill pulverizer, and further, the volume average diameter is made 10 μm by an Alpine classifier. It was adjusted so that a precursor was obtained. 100 parts by weight of this precursor and 0.2 parts by weight of a charge control agent (Spiron Black TRH, Hodogaya Chemical Co., Ltd.) were premixed with a Henschel mixer. 50 g of this pre-mixture was put into a surface reformer (Angmill, manufactured by Hosokawa Micron Co., Ltd.), and the temperature was adjusted to 9 at 65 ° C. or lower.
After processing for 0 minutes, Toner G was obtained. The total applied energy in this treatment was 6.7 J / kg. Example 1
4 and the measurement results of the toner particles of Comparative Examples 1 to 3 are summarized in Table 1.

[0037]

[Table 1] The evaluation results of the above toners are summarized in Table 2.

[0038]

[Table 2]

[0039]

According to the present invention, the shearing / impacting force that causes the precursor particles to be rounded is applied to the pre-mixture of the toner precursor particles and the charge control agent powder to apply the charge control agent powder. By forming a uniform coating, it is possible to obtain a stable toner in which the charge amount rises sharply when mixed with the carrier and the charge amount is not attenuated even when the mixture is mixed for a long time. The excellent effects of the present invention are listed below. 1. The amount of charge obtained with respect to the amount of charge control agent (CCA) used is large and efficient. 2. The charge rises quickly, which is advantageous for toner scattering and background fog. 3. Good charging stability and stable image quality during continuous copying. 4. Excellent charging characteristics can be obtained with a small amount of CCA used. 5. This is a toner manufacturing method in which the chargeability can be controlled to be positive, negative, or arbitrarily large or small simply by changing the CCA type in the final step. 6. Since the chamfering (spheroidization) can be performed at the same time as the coating, the fluidity can be improved.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a conventional fixing or embedding method toner.

FIG. 2 is a scanning electron micrograph of a toner according to the present invention.

FIG. 3 is a PMPA surface analysis chart of the toner particles shown in FIG.

FIG. 4 is a PMPA surface analysis chart of the toner particles shown in FIG.

FIG. 5 shows various toners containing a charge control agent.
3 is a graph in which the horizontal axis represents the mixing time with the carrier and the vertical axis represents the charge amount. Curve A is the toner according to the present invention (FIG. 2), and curve B is the fixed or embedded toner (see FIG. 1). Curve), and the curve C is for the internally added toner.

FIG. 6 is a graph plotting the relationship between the amount of charge attenuation and the amount of charge control agent transferred to carriers.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G03G 9/08 381

Claims (2)

[Claims] 1. A fixing resin and a toner compounding agent other than a charge control agent are kneaded, and the kneaded material is crushed and classified to produce toner precursor particles, and the precursor particles and the charge control agent powder are mixed. Pre-mixing to attach the charge control agent particles to the surface of the precursor particles, and the pre-mixture is subjected to shearing / impact to cause rounding of the precursor particles at a temperature lower than the melting point or softening point of the fixing resin. A method for producing a toner, comprising applying a force to form a uniform coating layer of a charge control agent on the surface of precursor particles. 2. An electrophotographic toner comprising core particles composed of a mixture of a fixing resin and a compounding agent for toner other than the charge control agent, and a coating layer of the charge control agent existing only on the surface of the core particles. The toner has the following formula: A = B / C where C is a toner specific surface area (m ² / g) calculated as a true sphere based on the volume-based median diameter measured by the Coulter counter method. And B is the specific surface area (m ² / g) of the toner measured by the BET method. The specific surface area ratio (A) defined by is less than or equal to 3.3, and in the distribution surface analysis of the charge control agent by an electron probe micro analyzer (EPMA), the portion where the charge control agent is distributed is present. An electrophotographic toner having an area fraction of 0.5% or more.