JPH05341575A - Toner for electrophotography - Google Patents

Abstract

PURPOSE:To obtain a toner which can be used for mixing a plurality of toners different in color as it is and the resulting mixed toner by making a material of exposed surface part of each toner substantially the same. CONSTITUTION:The toner contains at least a domain resin composition 4, a matrix resin composition 5 low in miscibility with the domain resin composition 4 and a dispersing assistant 6 having miscibility with the domain resin composition and the matrix resin composition and Izod impact strength higher than that of the matrix resin composition, and the domain resin composition 4 is dispersed through the dispersing assistant 6 in the matrix resin composition 5. In this constitution, a coloring agent 2 is confined into the domain resin composition 4 and the material exposed on the surface is made the same even if the contained coloring agents 2 are different from each other. As a result, the electrification property of each toner is made the same and by mixing a plurality of the toners, the toner having desired color is used as it is without generating fogging or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner obtained by mixing a plurality of toners.

[0002]

2. Description of the Related Art In general, a toner used for electrophotographic copying is obtained by melt-kneading a colorant, a charge control agent and, if necessary, magnetic powder into a resin as a binder, and crushing and classifying the kneaded product. Is obtained by As shown in FIG. 2, the toner thus obtained has a structure in which a colorant (2) and a charge control agent (3) are uniformly dispersed in a resin (1) as a binder. ing. Various color toners such as black toner, cyan toner, magenta toner, and yellow toner are obtained depending on the type of the colorant.

However, in the toner obtained by the conventional toner manufacturing method, some of additives, colorants and charge control agents are exposed on the surface of the toner. It depends on the type.

Therefore, even if conventional toners are mixed by adjusting a desired color by mixing a plurality of colors, for example, the toners of different colors have different chargeability, and the toners having different charge amounts, and thus the uncharged toners are different. Are likely to occur, which may cause fogging and the like. That is, it is not possible to use a toner having a desired color simply by mixing a plurality of conventional off-the-shelf toners.

Therefore, when a toner of a new color is desired, a manufacturing process suitable for the toner composition and constitution is required, and in the conventional toner constitution, the charging characteristic is different depending on the color as described above. However, an experiment for confirming the charging characteristics for each color is required, which requires a great deal of labor, time and cost.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a toner that can be used as it is by mixing a plurality of toners having different colors, and a mixed toner such as this. To aim.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an electrophotographic toner comprising two or more kinds of toners whose surface exposed portions are made of substantially the same material.

The present invention can be achieved by making the material of the surface exposed portion of each color toner substantially the same. Such a toner can be obtained by using the structure shown in FIG. That is, the toner of the present invention is miscible with at least the domain resin composition (4), the matrix resin composition (5) having low miscibility with the domain resin composition, and both of the domain resin and the matrix resin, and has an Izod impact. The domain resin composition contains a dispersion aid having a value higher than that of the matrix resin, and is dispersed in the matrix resin composition through the dispersion aid. With such a configuration, even if the coloring agent to be contained is different, the coloring agent is enclosed in the domain resin composition, and the material exposed on the surface can be the same. With such a configuration, the charging characteristics of each toner can be made the same, and by mixing a plurality of toners,
A toner having a desired color can be used as it is without causing fogging or the like. Further, since it is not necessary to check the charging characteristics for each color, it is possible to develop a toner of a desired color in a very short period.

As the matrix resin of the toner of the present invention, for example, α-olefins (including ethylene) such as ethylene, propylene, butene-1, pentene-1, 4-methylpentene-1, and hexene-1 are used alone. Alternatively, a mutual copolymer, a block, a random or graft copolymer of a majority weight of these α-olefins and another unsaturated compound, or a treatment of halogenation, sulfonation, oxidation, etc. of these homopolymers or copolymers. Olefin polymer such as modified polymer, acrylonitrile, styrene copolymer (A
S resin), polycarbonate, thermoplastic polyester,
Examples thereof include thermoplastic polymers such as polyamide, polystyrene, styrene / butadiene / styrene-block copolymer, polyacrylonitrile, and polymethylmethacrylate, and rubber.

Other unsaturated compounds which can be copolymerized with α-olefin in the above-mentioned olefin polymers include vinyl esters such as vinyl acetate, vinyl silanes such as vinyl trimethoxysilane and vinyl triacetoxy silane, and the above-mentioned examples. And the ethylenically unsaturated monomer other than the α-olefin.

As the thermoplastic polymer used in the present invention, polyester and polystyrene are preferable as the matrix phase.

The polyester preferably used in the present invention is appropriately selected from those generally obtained by polycondensation of a polybasic acid and a polyhydric alcohol.

As the polybasic acid, terephthalic acid,
Aromatic carboxylic acids such as isophthalic acid and trimellitic acid, adipic acid, hexahydroterephthalic acid, succinic acid, n-
Dodecenyl succinic acid, iso-dodecenyl succinic acid, n-
Examples thereof include aliphatic carboxylic acids such as dodecyl succinic acid, n-octyl succinic acid, iso-octyl succinic acid and n-butyl succinic acid, unsaturated carboxylic acids such as maleic acid and fumaric acid, and anhydrides thereof. As the polyhydric alcohol component, ethylene glycol, propylene glycol, 1,4-butanediol, hexamethylene glycol, neopentyl glycol, 2,2,4,4-tetramethylene glycol, glycerin, trimethylolpropane, bisphenol A, Hydrogenated bisphenol A, sorbitol or etherified hydroxyl compounds thereof, such as polyoxyethylene (10) sorbitol, polyoxypropylene (5) glycerin, polyoxyethylene (4) pentaerythritol, polyoxypropylene
Examples include (2,2) -2,2-bis (4-hydroxyphenyl) propane and polyoxyethylene (2) -2,2-bis (4-hydroxyphenyl) propane.

More preferred polyesters are solvent soluble. Amorphous or low crystalline, especially X
The effect is large when the crystallinity by line analysis is less than 5%. The softening point is 40 to 150 ° C., especially 60 to 15
0 ° C., and number average molecular weight of 500 to 3
0000, especially 1000 to 20000, is highly effective.

Polystyrene preferably used in the present invention includes polystyrene or a copolymerization monomer with styrene, for example, unsaturated carboxylic acid such as acrylic acid and methacrylic acid, methyl acrylate, ethyl acrylate and methyl methacrylate, and n methacrylate. In addition to unsaturated carboxylic acid esters such as butyl, dibutyl fumarate, and dioctyl fumarate, maleic anhydride, acid anhydrides such as itaconic anhydride, so-called unsaturated carboxylic acid or its derivative, etc. within a range not exceeding a majority. The thing copolymerized by is used. Among them, the glass transition temperature is 30 to 105 ° C., the number average molecular weight is 1000 to 150,000, and particularly 2000 to 10
Those of 0000 have a great effect.

As the polystyrene used in the present invention, a solvent-soluble one is particularly preferable. These matrix resins need only be present in an amount sufficient to substantially cover the dispersed domain resin component, and thus can be used in a wide range for toner. Therefore, it is generally preferable to use 20 to 99% by weight, more preferably 30 to 95% by weight, based on the toner resin. When the amount is less than the above range, the matrix resin and the domain resin undergo phase inversion, the colorant-containing resin is exposed on the crushed surface, resulting in poor charging, and over-milling is likely to occur, resulting in a wide particle size distribution and poor manufacturing efficiency. On the other hand, if the amount exceeds the above range, the colorant may be poorly dispersed in the matrix resin.

As the domain resin, the same resin as the above-mentioned matrix resin can be used, but a resin whose compatibility is changed by changing the comonomer to be copolymerized and which is not uniformly mixed with each other is used. By doing so, a domain resin can be dispersed in the matrix resin.

The colorant used in the toner of the present invention is dispersed and held in a domain resin, and the domain resin is dispersed in a matrix resin. By holding the colorant dispersed in the domain resin, it is possible to prevent the colorant from being exposed on the toner surface, and to make the material of the surface-exposed portion substantially the same even for toners of different types of colorant. it can.

That is, in the toner composition of the present invention, the matrix resin and the domain resin are resins which are not uniformly mixed with each other, and those having a greater affinity for the colorant to be used act as the domain resin.

The dispersion aid used in the toner of the present invention is
It is a copolymer containing a domain resin component and a matrix resin component. A resin obtained by graft-copolymerizing a monomer containing one of the domain resin and the matrix resin with a monomer forming the other resin is preferable.

The dispersion aid used in the present invention acts to finely disperse the domain resin in the matrix resin, and if it is 1% by weight or more in the toner composition, the dispersed phase becomes sufficiently fine and uniform. It is preferably used in an amount of 3% by weight or more.

The dispersion aid has an Izod impact value of 0.1 kgf · cm / cm or more, preferably 0.2 kgf · cm / cm or more, more preferably 0.4 kgf · cm / than the matrix resin.
Use one that is at least cm. By using such a resin, breakage of the domain resin can be prevented by preferentially causing breakage in the matrix resin phase in the pulverizing step. Therefore, since the colorant remains confined in the domain resin phase, it is possible to prevent the colorant from being exposed on the toner surface. When the Izod impact value is smaller than the above range, the domain resin is likely to be stressed, and thus easily broken. When the domain resin phase is destroyed, the colorant is exposed, and the material of the exposed surface portion cannot be substantially the same.

In the present invention, the Izod impact value is a Mini-max Izot impact tester (Model CS-183; Instrume).
(manufactured by NT Inc.). At the time of measurement, a test piece of 30 × 12 × 2.0 [mm] was produced by press molding (conditions 130 ° C., 60 to 70 kg / cm ² ), and this test piece was provided to the above tester.

Specific examples of the dispersion aid include a method in which the styrene polymer and the vinyl monomer are graft-reacted, a method in which the polymer is dissolved in a solvent and the vinyl monomer is added to the solution to cause a reaction. To dissolve and react the polymer in, to suspend the polymer particles in water, add vinyl monomer to this to impregnate the polymer particles, then react, to dissolve the polymer in vinyl monomer There are a method of reacting the above in a state of being suspended in water as droplets, a method of reacting with a vinyl monomer in a molten state of a polymer, a radiation grafting method and the like. Among them, the preferable method is the above method or. The polymer obtained by the above method contains a matrix resin and a domain resin at the same time, and can be used without separately adding the matrix resin or the domain resin.

In this reaction, a polymerization initiator is usually used. As the polymerization initiator, those generally used for radical polymerization can be used, but the decomposition temperature is 45 to 110 ° C., especially 50 to 105, in view of the temperature of the polymerization reaction.
It is preferable to select from those in the range of ° C. The decomposition temperature as used herein means that the polymerization initiator is added to 0.1 liter in 1 liter of benzene.
It means the temperature at which the decomposition rate of the radical generator reaches 50% when it is allowed to stand for 10 hours after adding a mole.

Specific examples of such an initiator include 2,4-dichlorobenzoyl peroxide (54 ° C.), t
ert-butyl peroxypivalate (56 ° C), O-methylbenzoyl peroxide (57 ° C), bis-3,5,5-
Trimethylhexanoyl peroxide (60 ℃), octanoyl peroxide (61 ℃), lauroyl peroxide
(62 ° C), benzoyl peroxide (74 ° C), tert-butylperoxy-2-ethylhexanoate (74 ° C),
1,1-bis (tert-butylperoxy) -3,5,5-trimethylcyclohexane (91 ° C), cyclohexanone peroxide (97 ° C), 2,5-dimethyl-2,5-dibenzoylperoxyhexane (100 ° C) , Tert-butyl peroxybenzoate (104 ° C.), di-tert-butyl-
Diperoxyphthalate (105 ° C), methyl ethyl ketone peroxide (109 ° C), dicumyl peroxide (1
17 ° C.), and organic peroxides such as dicumyl-tert-butyl peroxide (temperatures in parentheses indicate decomposition temperatures). These can be used together.

The amount of the polymerization initiator used is 0.05 to 30% by weight, preferably 0.1 to 10% by weight based on the vinyl monomer.
It is in the range of% by weight.

In the present invention, the dispersion aid comprises a matrix resin (for example polyester) and a monomer (for example styrene) which can give a domain resin "in situ".
u) ”can also be obtained by graft copolymerization.

The colorant to be contained in the toner is not particularly limited, and known ones such as carbon black, azo dyes, titanium oxide and various dyes and pigments of various colors can be used. Since it is necessary to disperse and fill practically the entire amount of the colorant in the domain resin, a colorant having a greater affinity for the domain resin than for the matrix resin is used.

To the toner constituting the developer of the present invention, a low molecular weight olefin polymer, colloidal silica, a fatty acid, a fatty acid metal salt or the like is added for the purpose of further improving fluidity and releasability. Good.

For the toner of the present invention, the constitution and composition may be selected according to the application, such as a one-component toner or a two-component developer toner used together with a carrier. Basically, the steps described below are used. Can be prepared. Obtained by the steps of obtaining a kneaded product obtained by melt-kneading the domain resin and the colorant, and obtaining a kneaded product obtained by melt-kneading the matrix resin and the charge control agent, which have low miscibility with the domain resin. Kneaded product, a kneaded product obtained in the step of, and a coloring composition obtained by melt-kneading a dispersion aid having miscibility with both the domain resin and the matrix resin and having an Izod impact value higher than that of the matrix resin. The step of obtaining and the kneaded material obtained in the step are pulverized and classified.

Here, since the impact resistance of the dispersion aid phase is set higher than that of the matrix phase, the dispersion aid phase and the domain resin phase are destroyed in the pulverizing step during the production of the toner. Is effectively prevented. Therefore, the destruction occurs only in the matrix resin phase, and the surface of the pulverized product, that is, the surface of the obtained toner is substantially formed only in the matrix resin phase containing the charge control agent. This is because substantially all of the colorant is contained in the domain resin phase,
This is because the stress concentrates on the matrix phase at the time of pulverization and the matrix phase forms the surface phase, so that each color coloring agent in the domain phase is not exposed on the surface. Even if the type and color of the colorant are changed, it is possible to obtain a toner in which the material of the surface exposed portion is substantially the same.

By mixing the toners of the respective colors obtained as described above, a toner mixture of a desired color can be obtained. For example, a red mixed toner can be obtained by mixing a yellow toner and a magenta toner, a green toner can be obtained by mixing a yellow toner and a cyan toner, and a blue toner can be obtained by mixing a magenta toner and a cyan toner. . Further, a metallic tone can be created by mixing a metallic toner. In addition, a mixed toner having a desired color can be obtained by mixing the toners at various ratios.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to the following examples.

[0035]

EXAMPLES Example 1 The domain resin, matrix resin and dispersion aid used in Examples are shown below. Domain resin Styrene / acrylic acid ester copolymer Molecular weight: 53000 Izod impact strength: 0.51 [kgf · cm / cm ² ] Matrix resin Styrene / maleic anhydride copolymer Molecular weight: 10000 Izod impact strength: 0.17 [kgf · cm / cm ² ] Dispersion aid modified styrene polymer Izod impact strength: 0.41 [kgf · cm / cm ² ]

Production Example of Dispersion Aid In an autoclave having an internal volume of 10 liters, 4 kg of water, 80 g of tricalcium phosphate and 0.12 g of sodium dodecylbenzenesulfonate are added to prepare an aqueous medium, to which 8 g of "Nyper B" is added. A liquid dissolved in a mixed liquid of 640 g of styrene and 160 g of n-butyl acrylate was added and stirred.
The matrix resin (styrene copolymer) particles 12
00 g was charged, the inside of the autoclave was replaced with nitrogen, the system temperature was raised to 60 ° C., and the temperature was maintained for 3 hours to impregnate the matrix resin particles with styrene containing the above-mentioned polymerization initiator. Then, "Perbutyl PV" 11.4g
Was added to this suspension system, the temperature in the system was further raised to 65 ° C. and maintained for 2 hours to initiate the polymerization of the surface of the styrene polymer particles. Then, the system temperature was raised to 90 ° C. and maintained for 3 hours to complete the polymerization. After cooling, the contents were taken out and washed with acid and water to obtain 2 kg of a dispersion aid resin.

42 parts by weight of domain resin and coloring agent (Lionol
3 parts by weight of Yellow FG-1310 (manufactured by Toyo Ink Mfg. Co., Ltd.) were melt-kneaded by a twin-screw kneading extruder. Next, 52 parts by weight of the matrix resin and 3 parts by weight of the charge control agent (Bontron E-81; manufactured by Orient Chemical Co.) were melt-kneaded by a twin-screw extruder. 45 parts by weight of the domain resin kneaded product, 55 parts by weight of the matrix resin kneaded product, and 8 parts by weight of a dispersion aid were melt-kneaded by a biaxial kneading extruder to obtain a colored composition.

A part of the colored composition was sandwiched between a slide glass and a cover glass, heat-melted on a hot press to form a thin film, and observed by a transmission optical microscope. As a result, the presence of a colored dispersed phase was observed. The particle size is 0.
The dispersed phase was uniformly and finely dispersed in the matrix. The colorant was not found in the matrix, and the charge control agent was present only in the matrix. Finely pulverize the obtained colored product with a jet mill,
Then, a yellow toner having an average particle diameter of 11 μm was obtained by classification.

Further, a magenta toner and a cyan toner were manufactured by using the following coloring agent melt-kneaded with 42 parts by weight of the domain resin. Magenta Toner Lionol Red 6B FG-4213 (Toyo Ink Manufacturing Co., Ltd.) 3 parts by weight Cyan Toner Lionol Blue FG-7350 (Toyo Ink Manufacturing) 3 parts by weight

When each of the obtained coloring compositions was partially observed by the above-mentioned method, the presence of a similarly colored dispersed phase was observed. The particle size of the dispersed phase is 0.5 to 1.0.
μm, which was uniformly and finely dispersed in the matrix.
No colorant was found in the matrix, and the charge control agent was present only in the matrix.

The obtained colored product was finely pulverized by a jet mill and then classified to obtain magenta toner and cyan toner each having an average particle size of 11 μm.

The above three color toners were put in a mixing machine in the same proportions and mixed to obtain a black toner for full color.

A carrier (F141-300; manufactured by Powder Tech Co., Ltd.) is used so that this toner has a toner concentration of 8%.
When mixed with a full-color copying machine CF-70 (manufactured by Minolta Camera Co., Ltd.) and running 150,000 sheets, a beautiful image without fog was maintained.

Comparative Example 1 Resin as Binder Styrene-maleic anhydride copolymer (same as the resin used as the matrix resin in the above examples) 100 parts by weight Charge control agent Bontron E-81 (manufactured by Orient Chemical Co.) 3 parts by weight Coloring agent Lionol Yellow FG-1310 (manufactured by Toyo Ink Mfg. Co., Ltd.) 3 parts by weight The above materials were melt-kneaded to obtain a colored product. The obtained colored product was finely pulverized by a jet mill and then classified to obtain a yellow toner having an average particle size of 11 μm.

By using the following colorants, magenta toner, cyan toner and black toner having an average particle diameter of 11 μm were obtained. Magenta toner Lionol Red 6B FG-4213 (manufactured by Toyo Ink Manufacturing Co., Ltd.) 3 parts by weight Cyan toner Lionol Blue FG-7350 (manufactured by Toyo Ink Manufacturing Co., Ltd.) 3 parts by weight The colorants of the above three color toners are exposed on the toner surface. Therefore, the material exposed on the surface differs depending on the toner.

The above three color toners were charged into the mixing machine in the same proportion to obtain a full color black toner. The toner (F141-) is used to adjust the toner concentration to 8%.
300; manufactured by Powder Tech Co., Ltd.) and charged into a full-color copying machine CF-70 (manufactured by Minolta Camera Co., Ltd.), and running was performed, but severe fogging occurred from the initial stage, and actual use was impossible.

Example 2 (Red Toner) The yellow toner obtained in Example 1 and the magenta toner were charged into a mixer at the same ratio and mixed to obtain a red toner.

This toner was mixed with a binder carrier (manufactured by Minolta Camera Co., Ltd.) so that the toner concentration was 8%,
When a copying machine EP-5400 (manufactured by Minolta Camera Co., Ltd.) was loaded and 150,000 sheets were run, a beautiful image without fogging was maintained.

Although the example of the red toner has been described in this embodiment, the magenta toner and the cyan toner obtained in the embodiment 1 are mixed to obtain the blue toner, and the cyan toner and the yellow toner are mixed to obtain the green toner. Can be obtained.

Comparative Example 2 The yellow toner and the magenta toner obtained in Comparative Example 1 were charged into a mixing machine at the same ratio to prepare a red toner. This toner was mixed with a binder carrier (manufactured by Minolta Camera Co., Ltd.) so that the toner concentration was 8%, and the copier EP-540 was used.
Although it was loaded into No. 0 (manufactured by Minolta Camera Co., Ltd.) and running, running was impossible due to severe smoldering from the beginning.

Example 3 (Metallic blue toner) 42 parts by weight of the domain resin prepared in Example 1 and 3 parts by weight of a pearl pigment (Iriodin 100 Silver Pearl; manufactured by Merck) were melt-kneaded by a twin-screw extruder. Next, 52 parts by weight of the matrix resin prepared in Example 1 and 3 parts by weight of the charge control agent (Bontron E-81; manufactured by Orient Chemical Co., Ltd.) were melt-kneaded by a biaxial kneading extruder. 45 parts by weight of the above-mentioned domain resin kneaded material and matrix resin kneaded material 55
Parts by weight and 8 parts by weight of the dispersion aid were melt-kneaded by a biaxial kneading extruder to obtain a metallic composition.

A part of this metallic composition was sandwiched between a slide glass and a cover glass, heat-melted on a hot press to form a thin film, and observed by a transmission optical microscope. Presence was observed, the particle size was 40 to 80 μm, and this dispersed phase was uniformly and finely dispersed in the matrix. The pearl pigment was not found in the matrix, and the charge control agent was present only in the matrix.

The obtained metallic product was finely pulverized by a jet mill and then classified to obtain a metallic toner having an average particle size of 100 μm.

The magenta toner, the cyan toner and the metallic toner prepared in Example 1 were charged into a mixer at a ratio of 1: 1: 2 and mixed to obtain a metallic blue toner.

The obtained toner is mixed with a binder carrier (made by Minolta Camera Co., Ltd.) so that the toner concentration becomes 8%, and the mixture is loaded into a copying machine EP-5400 (made by Minolta Camera Co., Ltd.), and 150,000 sheets are run. A beautiful image without fogging was maintained.

Although the metallic blue toner was described in this embodiment, the cyan toner, the yellow toner and the metallic toner prepared in the same manner as in the first embodiment are mixed in the same manner to obtain the metallic green toner, the yellow toner, the magenta toner and the above-mentioned metallic toner. A metallic red toner can be obtained by mixing the metallic toner.

Comparative Example 3 Resin as binder Styrene-maleic anhydride copolymer (same as resin used as matrix resin in the above examples) 100 parts by weight Charge control agent Bontron E-81 (manufactured by Orient Chemical Co.) 3 parts by weight Colorant Iriodin 100 Silver Pearl (manufactured by Merck) 3 parts by weight The above materials were melt-kneaded to obtain a metallic composition. The obtained metallic composition was finely pulverized by a jet mill and then classified to obtain a metallic toner having an average particle size of 11 μm.

The magenta toner, the cyan toner and the metallic toner prepared in Example 1 were charged into a mixer at a ratio of 1: 1: 2 and mixed to obtain a metallic blue toner.

The obtained toner was mixed with a binder carrier (manufactured by Minolta Camera Co., Ltd.) so that the toner concentration was 8%, loaded into a copying machine EP-5400 (manufactured by Minolta Camera Co., Ltd.), and 150,000 sheets were run. However, from the beginning, the fogging was so severe that it was impossible to actually use it.

[0060]

EFFECTS OF THE INVENTION It is possible to obtain a toner of a desired color by mixing toners of a plurality of colors, and it is possible to deal with the demand for a large number of small-quantity toners in a short period of time.

[Brief description of drawings]

FIG. 1 shows a schematic sectional view of a toner of the present invention.

FIG. 2 is a schematic sectional view of a conventional toner.

[Explanation of symbols]

1: Resin as a binder 2: Colorant 3: Charge control agent 4: Domain resin 5: Matrix resin
6: Dispersion aid

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shoichi Tsuge 2-3-13 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka, Osaka International Building Minolta Camera Co., Ltd. (72) Kenzo Toya Azuchi, Chuo-ku, Osaka-shi, Osaka 2-3-3, Machi, Osaka International Building Minolta Camera Co., Ltd.

Claims (1)

[Claims] 1. An electrophotographic toner comprising two or more kinds of toners whose surface exposed portions are made of substantially the same material.