JPS63198070A - Electrostatic toner - Google Patents

Abstract

PURPOSE:To obtain a superior electrostatic toner free from nonuniformity of the surface of each toner particle, hydrophilicness, and poorness of triboelectrifiability due to lowering of resistivity by coating the surface of each toner particle with specified fine hydrophobic resin particles and other necessary fine particles. CONSTITUTION:Each toner particle is coated by mixing the toner particles having an average particle diameter of 5-20mu with the fine hydrophobic resin particles having an average particle diameter of <=2mu and a volume resistivity of >=10<14>OMEGA.cm at 35 deg.C and <=90% relative humidity alone or together with the other necessary fine particles,such as a charge controller, silica, an abrasive, and a lubricant, or by treating these necessary additives with said fine hydrophobic particles, then mixing them with the toner particles, and forming an average particle diameter of 5-25mu by applying mechanical stress, thus permitting the obtained superior electrostatic toner to be prevented from disclosure of a pigment or dye, or a magnetic powder, and deterioration due to remainder of materials strong in hydrophilicness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an electrostatic toner for dry developing electrostatic latent images in electrophotography, ion flow recording, and the like.

(Prior Art) The method for manufacturing electrostatic toner for dry developing electrostatic images involves dispersing dyes, pigments, magnetic powder, etc. in toner resin by melting and kneading, and then mechanically pulverizing this.

A common method is to obtain it by classification.

However, it has been pointed out that the toner obtained by this method has drawbacks such as being amorphous, making it difficult to obtain a uniform charge, and having poor fluidity.

Further, the consumption of electrical energy required for melting, kneading and pulverization is enormous, and various methods have been proposed for producing toner using methods other than so-called pulverization.

As methods other than the above-mentioned pulverization method, spray drying method, emulsion polymerization method, interfacial polymerization method, suspension polymerization method, etc. are known.

However, since the spray drying method produces a single spherical toner, it provides a uniform charge and good fluidity, but it requires explosion-proof measures and solvent recovery, and the consumption of thermal energy required during drying is high. There are drawbacks such as being bulky and the solvent remaining in the toner after drying, making it difficult to remove.

Therefore, various methods are currently being investigated to generate spherical toner particles in water using emulsion polymerization, interfacial polymerization, suspension polymerization, etc. However, the dispersant and stability of toner particles in water remain on the toner surface. However, it is difficult to remove, and has the disadvantage that it absorbs moisture in the air, lowering the electrical resistance of the toner, making it difficult to copy on plain paper, and making the surface charge uneven.

(Problems to be Solved by the Invention) The present invention attempts to improve toner surface unevenness, hydrophilicity, poor triboelectric charging properties due to decreased resistance, etc. ℃.

A solvent-free method using hydrophobic resin fine particles with an IQI of 4Ω or higher at a relative humidity of 90% or lower (below).

(abbreviated as dry type) coats the toner surface more easily than conventional methods.

The object of the present invention is to obtain an electrostatic toner having excellent properties as described above.

[Structure of the invention]

(Means for solving the problems) The present invention has an average particle size of 2μ or less and a temperature of 35°C.
The hydrophobic resin fine particles (B) having a volume resistivity of 10'4 Ω1 or more at 90% RH were coated on the target toner particles (A) by dry mixing them under mechanical strain. This invention relates to an electrostatic toner with excellent hydrophobicity and insulation on the toner surface.

In the present invention, toner particles (A
), it is also possible to use toner particles produced by a pulverization method, a spray method, or the like.

Remarkable effects can be obtained when toner particles produced by interfacial polymerization, suspension polymerization, emulsion polymerization, or in water are used.

In other words, toner particles manufactured by the pulverization method expose pigments, dyes, magnetic powder, etc. on the fractured surface that occurs during pulverization, which causes problems such as deterioration of environmental resistance, generation of background smearing, and deterioration of the number of printable sheets. cause

Therefore, the above-mentioned problems are solved by coating these with hydrophobic resin fine particles (B) and also by using a small amount of a charge control agent for the purpose of controlling the charge on the toner surface.

Furthermore, toner particles produced by the spray method have pigments, dyes, magnetic powder, etc. floating on the surface during production, and the above-mentioned treatment method solves this problem.

Since the toner particles (A) as described above can be produced without contact with water, the toner particles (A) can easily obtain a resistance value sufficient for dry development.

However, toner particles (A) produced in water using interfacial polymerization method, suspension polymerization method, emulsion type method, etc. have reduced resistance due to residual dispersion stabilizers, surfactants, etc., and dry development is required. It is not easy to obtain a sufficient resistance value.

Therefore, the present invention is particularly effective when the toner particles (A) are toner particles produced in water.

Toner particles produced by interfacial polymerization include pigments, wax,
A lipophilic polymerizable compound is added to an ink made by dispersing magnetic powder, resin, solvent, etc., and this is poured into an aqueous solution containing a dispersion stabilizer and stirred at high speed to form microdroplets. It is obtained by dispersing and polymerizing at the interface between microdroplets and water.9 For example, JP-A-54-76233, JP-A-58-66948, etc. It is said that

Toner particles produced by suspension polymerization are produced by dispersing pigments, waxes, magnetic powders, resins, etc. into microdroplets in an aqueous solution containing a dispersion stabilizer. 2 For example, JP-A-59-152450, JP-A-59-28
164. JP-A-55-50962, JP-A-51-148
95 The subject matter is that which can be obtained in various ways by conventionally known methods.

In addition, various spherical toner particles produced in water, such as toner particles produced by the emulsion polymerization method and toner particles produced by the cooling precipitation method as described above, are targeted.

These toner particles (A) preferably have an average particle size of 5 to 20 microns.

Note that the toner particles (A) are formed by dyes,
There are coloring materials such as R materials, magnetic powders, waxes, resins, etc., and the following are exemplified.

Colorants include zinc yellow, yellow iron oxide, Hansa yellow, disazo yellow, and quinoline yellow.

Permanent Yellow, Permanent Red, Red Garla, Resole Red, Watchan Red Ca salt.

Watchan Red Mn Salt, Pyrazolone Red.

Lake Re, Do C, Lake Red D, Prilliant Carmine 6B, Prilliant Carmine 3B, Dark Blue.

Pigments or oil-soluble dyes such as phthalocyanine blue, metal-free phthalocyanine, titanium oxide, and carbon black can be used.

As the magnetic powder, alloys or compounds of iron such as various ferrites, magnetites, hematites, zinc, cobalt, nickel, manganese, etc. can be used.

These magnetic powders preferably have a spherical to cubic octahedral shape with an average particle diameter of 0.1 to 0.5 microns, and are surface-treated to have good dispersion in the resin solution. hydrophobic treatment.

It may be subjected to silane coupling agent treatment, resin coating treatment, etc.

The wax is used to improve the offset resistance of the toner, and includes polyethylene wax, polypropylene wax, microcrystalline wax, paraffin wax, and oxidized wax.

Examples include vegetable wax, animal wax, mineral wax, etc., and they can be used alone or in combination as required.

Furthermore, in the case of toner produced by a conventional pulverization method, a thermoplastic resin is used as a binder. Resins for toners include polystyrene, styrene-containing copolymers of styrene and acrylic esters, methacrylic esters, acrylonitrile or maleic esters, polyacrylic esters, polymethacrylic esters, and polyesters. , polyamide type.

Examples include polyvinyl acetate-based, epoxy-based, phenol-based, hydrocarbon-based and petroleum-based resins.

These can be used alone or in combination.

As the hydrophobic resin fine particles (B) used in the present invention, a vinyl polymer or a copolymer of two or more vinyl monomers is used.

The hydrophobic resin fine particles (B) are obtained by monopolymerizing the following vinyl monomers.

That is, examples of vinyl monomers include styrene monomers such as styrene, vinyltoluene, 2-methylstyrene, and t-butylstyrene, methyl acrylate, ethyl acrylate, isopropyl acrylate + n-butyl acrylate, and 2-ethylhexyl. Acrylic acid or methacrylic acid alkyl esters such as acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, monobasic acids such as acrylic acid, methacrylic acid, crotonic acid, fumaric acid, Ethylenically unsaturated carboxylic acid monomers such as dibasic acids such as itaconic acid and maleic acid or their anhydrides, N-methylol methacrylamide.

N-substituted (meth)acrylic monomers such as N-butoxymethylacrylamide and N-butoxymethylmethacrylamide, hydroxyl group-containing monomers such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl acrylate; Examples include epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate.

Further, the resin fine particles (B) can be used as long as they are hydrophobic particles with an average particle size of 2 μ or less and a volume resistivity of 1014 ΩG or more at 35° C. and 90% RH. It is desirable that the two particles produced are spherical particles with uniform diameters (sharp particle size distribution).

Even more desirably, one having less influence on hygroscopicity by the residual surfactant on the surface of the resin fine particles, such as JP-A-61-1
4201 or JP-A-58-12
Particles produced by a soap-free emulsion polymerization method such as those shown in No. 7702.59-199703.59-1503 are suitable. but.

Particles obtained by ordinary emulsion polymerization or suspension polymerization may also be obtained by surface treatment to make them hydrophobic.

Further, the resin fine particles (B) are not particularly limited in terms of physical properties as long as they satisfy the above characteristics, but in particular, the glass transition temperature is 4.
It is desirable that the temperature is 5°C or higher, and if it is lower than 45°C, problems tend to occur in storage stability. Further, there is no problem even if a crosslinked resin is used.

In addition, based on 100 parts by weight of toner particles (A).

The hydrophobic resin fine particles (B) are used in an amount of 0.3 to 10 parts by weight. If the amount is less than 0.3 parts by weight, the surface of the toner particles (A) cannot be coated sufficiently, and if it is more than 10 parts by weight, the effect of adding it cannot be obtained.

In the present invention, other necessary fine particles (C) can also be mixed.

Other necessary fine particles (C) include charge control agents, silica, abrasives, lubricants, and the like.

These fine particles (C) are coated on the toner particles (A) together with the hydrophobic resin fine particles (B) or after being mixed with the hydrophobic resin fine particles (B).

Therefore, this fine particle (C) also has a large particle size.

It is necessary to crush it in advance so that the average particle size is 2μ or less.

When the average particle size is 2 μm or more, separation from the coating layer occurs, and the rigidity resistance of the electrostatic toner decreases.

The charge control agent is known per se, and two examples are Eva,
There are dyes such as Huesotschwarz HBN, Nigrosine Base, Brilliant Schwarz, Zabon Schwarz
, Solvent Black 1, 2° 3.5, 7. C,L
Acid black 123.22゜23.2B, 42,
43. Dyes such as oil black (C, 1° 26150), spirone black, naphthenic acid metal salts, fatty acid metal soaps, etc.

The silica is preferably one in which the silanol groups on the 9 surface have been hydrophobized.

Polishing agents include carborundum, alumina, cerium oxide, etc.; lubricants include metal soap powder, polytetrafluoroethylene, and polyvinylidene fluoride.

There are fine particles of polyethylene, styrene-acrylic copolymer resin, etc.

These fine particles (C) are added as necessary, and are added in an amount of 0.5 to 5 parts by weight per 100 parts by weight of the hydrophobic resin fine particles (B).
Effects can be obtained by using 0 parts by weight.

The advantage of this method of dry coating by applying mechanical strain is that it is easier to operate than the conventional wet coating method, and because it does not use organic solvents, it is safe and the process can be simplified. Furthermore, the best characteristics can be obtained by using hydrophobic resin fine particles as the coating material.

In the present invention, the method of mixing the toner particles (A) and the hydrophobic resin fine particles (B) by applying mechanical strain under conditions such that the average particle size is in the range of 5 to 25 μm is as follows:
The conditions are such that the toner particles (A) are not fused into large lumps, or conversely are not pulverized into fine particles due to too large a strain force, and the resin fine particles ( The conditions are such that B) is thermally melted due to the frictional heat generated while adhering.

As a specific method that satisfies both of these conditions, a mortar is used in the laboratory, but this is insufficient for practical use.

In industrial terms, operating conditions for dispersing machines such as attritors, ball mills, and sand mills that have similar effects to mortars.

It can be used by changing the conditions such as the throughput amount 2 dispersion medium so that the above objectives are achieved.

However, in a mortar, it takes several hours to several tens of days.

Even ball mills and sand mills take a long time.

Industrially, it is a mixer in which the powder is moved at high speed with airflow in a fluidized bed state, or a blade that applies impact.

This is a mixer that is equipped with a hammer, etc. Examples of such mixers are the St mill (specially manufactured by Toyo Ink, see Japanese Patent Publication No. 57-43051 for an overview), and the Atomizer-9 free crusher. (-Nara Machinery Manufacturing Co., Ltd.)
, a crusher manufactured by Kawasaki Heavy Industries (KTM-1), etc., and these devices can be used as they are.

Alternatively, it can be used after being modified as appropriate in accordance with the purpose of the present invention. If possible, a closed system with a circulation system is preferable.

Through such a mixing process, the fine resin particles (B) adhere to the surface of the toner particles (A) and are thermally melted, thereby forming the toner particles (
The effect of coating the surface of A) occurs when the toner particles (A) and fine resin particles (B) collide with each other or with a dispersion medium such as wall blades or beads, instantaneously and 2 This is thought to be due to the fact that the temperature is quite high in some parts, and the air flow temperature in the system is close to the glass transition temperature (T) of the resin.
g) In some cases, it may be necessary to rise to a nearby location and cool the system.

The above phenomenon can be understood by observing electron micrographs before and after premixing.

That is, before the mixing treatment, the toner particles (A) with a relatively large particle size distribution and the resin fine particles (B) are in a partially aggregated state, and after the treatment, the surface of the toner particles (A) is smooth. The fine resin particles (B) are hardly visible and are covered with a thin layer of the fine resin particles (B), making the particles difficult to break even during a running test in a copying machine.

It is also observed that the toner particles (A) after the treatment have fewer small particles and have a uniform particle size, and nine irregularly shaped toner particles have rounded corners.

That is, it is considered that the toner particles (A) having a small particle size are sized into particles of a constant size by the mixing process.

Various factors can be considered to obtain the above effects, but according to research by the present inventors, the speed of airflow is the highest, and is preferably several tens of meters/second to several hundred meters/second.

In the present invention, the average particle size of the toner is in the range of several microns to 20 microns, and it is preferable that toner particles with an average particle diameter of 5 microns or less and 25 microns or more are substantially not included. When the amount of toner with a particle size of 5 μm or less increases, fluidity deteriorates and background smear occurs. Furthermore, if the amount of toner larger than 25μ increases, two images will be distorted, reducing the commercial value.

The advantage of dry coating method by applying mechanical strain as mentioned above is that compared to wet coating method,
It is easy to operate, and since no organic solvent is used, it is safe and the process can be simplified.

Furthermore, toner particles produced by interfacial polymerization, suspension polymerization, etc. cannot be coated with organic solvents due to problems such as swelling oil of the elution 1 polymer resin in the capsule. This is because it can be easily processed by the method of the present invention, which does not use organic solvents.

Furthermore, good toner characteristics can be obtained by using hydrophobic resin fine particles as a coating material.

Can be done.

The present invention will be explained below using specific examples. The middle part of the example shows parts by weight.

Example 1 80 parts of styrene-acrylic resin (manufactured by Nippon Carbide Industries, trade name NC-6157), magnetic powder (manufactured by Toda Kogyo ■, trade name NC-6157),
EPT500) 15 parts, carbon black (Cabot, Mogul-L) 2 parts, and low molecular weight polypropylene (Sanyo Chemical, trade name Viscole 550)
P) 3 parts were pre-mixed in a Henschel mixer, melted and kneaded with a two-wheeled extruder, allowed to cool, and the kneaded product was coarsely crushed using an I-type jet mill to a powder with an upper limit particle size of 25μ or less. Toner particles (A1) having an average particle size of about 10 μm were prepared.

100 parts of this resin particle (AI) and styrene-methyl methacrylate copolymer with an average particle size of 0.2μ (glass transition temperature 120℃, 4X1014Ωcm, 35℃, 90%RH
Bottom) 1 part of fine particles (Bl) and a charge control agent pre-pulverized in an automatic mortar (manufactured by Hodogaya Chemical ■, Subiron Black TR)
H) 0.1 part in a super mixer at 250 Orpm.
Premix for 1 minute at a rotation speed of .

Fine resin particles (B1) and a charge control agent were electrostatically attached to the surface of toner particles (A1). Then, this was introduced into Free Mill M-3, and the internal rotation speed was set to 500 rpm. At this time, the air flow velocity in the free mill was about 90 m/sec, and the average residence time of the 9 gL mixture in the system was about 3 seconds. The desired toner was obtained.

The average particle size of this toner particle was 12μ, and there were substantially no particles of 5μ or less and 25μ or more, and no two-classification was required. Further, 0.3 parts of colloidal silica (manufactured by Nippon Aerosil ■, trade name R-972) was mixed with this to 100 parts of toner to prepare a toner sample.

15 parts of this toner and 85 parts of ferrite carrier (manufactured by Nippon Tetsuko ■, trade name F-141-400) were mixed by rotation in a ball mill for 1 hour to prepare a two-component developer, which was then applied to a commercially available copying machine (Matsushita Co., Ltd.). Made by the electrical industry ■.

(Product name: FP-2520), and copies were made continuously on plain paper using a test chart.

In this copying, separation of magnetic powder and exposure to the toner surface is suppressed, so there is no scratching on the photosensitive drum, and toner fixability, charging stability, blocking resistance, and offset resistance are extremely good. Furthermore, in a running image test in which the toner of the present invention was put into a toner replenishment hopper in a copying machine, an image equivalent to the initial image was maintained over 60,000 sheets, and toner replenishment performance was also good.

Comparative Example 1 Using the same raw materials as in Example 1, production was carried out by a conventional method. That is, 0.5 parts of charge control agent (the amount is increased because it is not a surface coating), 80 parts of styrene-acrylic resin.
15 parts of magnetic powder, 2 parts of carbon blank, and 3 parts of low molecular weight polypropylene.

After pre-mixing with a Henschel mixer, this is melted and kneaded with a two-wheeled extruder, allowed to cool, and this kneaded material is coarsely crushed using a type jet mill with an upper limit particle size of 25.
A toner with an average particle size of about 12 μm or less, and a toner of 5 μm or less was obtained. Furthermore, colloidal silica was mixed with this in the same manner as in Example 1 to prepare a toner sample.

When this toner was subjected to the same test as in Example 1, when compared with the toner of the present invention, background stains were observed, and according to a running test, scratches were observed on the photosensitive drum after approximately 5,000 copies. A bridging phenomenon was observed in the replenishment hopper.

Example 2 240 parts of styrene, 60 parts of n-butyl acrylate, T
135 parts of iti powder (triiron tetroxide coated with stearic acid on the surface) and 12 parts of a 60% benzoyl peroxide xylene solution were mixed into a high-speed stirrer TK-Homo mixer (Tokushu Kikaku ■).
It was well dispersed using a commercially available product.

The above dispersion was added to 1500 parts of an aqueous solution of 0.75% polyvinyl alcohol (0H-20, manufactured by Nippon Gosei Chemical Co., Ltd.), and mixed at 10.00 O with an Ultra Homo Mixer (manufactured by Nippon Seiki ■).
High speed stirring was performed at rpm for 3 minutes.

The emulsion obtained by high-speed stirring was placed in a separable flask equipped with a stirrer, temperature needle, condenser, and nitrogen gas introduction tube, and the polymerization reaction was continued at 990°C for 7 hours with low-speed stirring while introducing nitrogen gas. After washing and drying, spherical toner particles with an average particle size of 15 μm were obtained (Comparative Example 2-1 toner).

Next, Comparative Example 2-1 toner was treated with resin fine particles (polymethyl methacrylate-isobutyl methacrylenide copolymer, glass transition temperature 78°C, 1 .0X10”Ω135℃, 90
%RH) and a charge control agent (T-20805 manufactured by Sumitomo Chemical Co., Ltd.) by applying mechanical strain (Example 2).
toner).

Furthermore, for Comparative Example 2-1 toner, the average particle size was 0°4μ.
Fine resin particles (polymethyl methacrylate, glass transition temperature 120°C, 4.0X10I4Ωaa 35°C.

90% RH) and charge control agent (Sviron Black TR
H) was coated by applying mechanical strain in the same manner as above (
Comparative Example 2-2 toner).

Table 1 shows the volume resistivity and adsorbed moisture content of the three toners mentioned above.

Table 1 Note 1) Toner particles are pressurized at 200 kg/cj and have a diameter of 2
A pellet with a thickness of about 3fi and a diameter of 0al is formed. this.

A main electrode (coated with silver paste) with a diameter of 1.0 cm provided with a guard electrode was placed between the electrodes, a DC current of 100 μm was applied, and after the current value stabilized, measurements were taken. What toner is suitable for copying on plain paper?

It is necessary that the volume resistivity determined by this measurement method is 1014 Ωcm or more.

Note 2) Karl Fischer trace moisture measuring device (Mitsubishi Chemical WWModel CA-02), heating temperature 11
5℃.

Nitrogen flow 1300ml N/win.

Example 2 obtained better results than Comparative Examples 2-1 and 2-2.

The sample of Example 2 was subjected to a classification process to obtain a toner having an average particle size of 13 μm from which particles of 5 μm or less and 25 μm or more were removed.

This is colloidal silica (manufactured by Nippon Aerosil ■).

Add 0.3% of product name R-972) and use a commercially available copying machine (
When the unfixed image was printed using Canon (trade name: NP-3002) and fixed using a test heat-pressure fixing roll manufactured by the company, a good image without capri was obtained.

Example 3 An ink-like material as a toner raw material was obtained using a three-roll mill according to the following recipe.

Synthetic wax (Sunwax 131-P manufactured by Sanyo Chemical Industries) 5 parts EVA
(AC-430 manufactured by Allied Chemical) 5 parts petroleum resin (
COHOLEX #2100 manufactured by Toho Oil Resin)
5 parts Dioctyl phthalate 10 parts High boiling point solvent (Hisol 100, manufactured by Nippon Petrochemicals) 20 parts Magnetic powder (triiron tetroxide) (EP7500, manufactured by Toda Kogyo Co., Ltd.) Diphenylmethane diisocyanate (manufactured by Nippon Polyurethane ■, Millionate MR) -2
00) Add 50g of 0.75% polyvinyl alcohol (part name GH-20 manufactured by Nippon Gosei Kagaku ■) aqueous solution 1600g.
After heating to 60°C, 10,000 g of
Stir for 3 minutes at rpn+.

Emulsified. After stopping the stirrer, 180 g of 10% diethylenetriamine aqueous solution was added to the above emulsion and stirred for 3 hours.
Microcapsules were produced by interfacial polymerization reaction. After further filtering and washing with water three times.

It was dried in a vacuum dryer, and the particle size was adjusted in an air classifier to obtain microcapsule toner particles. This is referred to as Comparative Example 3 toner.

In addition, fine resin particles (styrene-methyl methacrylate copolymer resin, glass transition temperature 120°C, 2×1014
Ωcm 35℃, 90% RH) and charge control agent (PN
P-BE (manufactured by Orient Chemical Co., Ltd.) was coated by applying mechanical strain (Example 3 toner).

In addition, fine resin particles (polymethyl methacrylate, polymethyl methacrylate,
Glass transition temperature 125℃, 2X10”Ω035℃, 90
%RH) and charge control agent (Sviron Black TRH
) was coated by applying mechanical strain (Comparative Example 3-
2 toner).

The above three samples were placed in an environment of 35℃ and 90%RH for 2 hours.
After standing for 4 hours, the volume resistivity and adsorbed water content were compared in the same manner as in Example 2. The results are shown in Table 2.

Table 2 Example 3 obtained better results than Comparative Examples 3-1 and 3-2.

The sample of Example 3 was subjected to a classification process to obtain a toner having an average particle size of 18 μm from which particles of 5 μm or less and particles of 40 g or more were removed.

This is colloidal silica (manufactured by Nippon Aerosil ■).

Add 0.3% of product name R-972) and use a commercially available copying machine (
A printing test was conducted using Canon (trade name: NP-3002), and when the unfixed image was fixed using a pressure roll, a good image without capri could be obtained.

Example 4 Microcapsules were produced in the same manner as in Example 3.

To this, 1 part of the same resin fine particles as used in Example 3, 0.
1 part and hydrophobic colloidal silica (Nippon Aerosil■
Co., Ltd., trade name R-972) was coated in the same manner as in Example 3. The above sample was heated to 35℃, 90%
After being left under RH for 24 hours, the volume resistivity and adsorbed water content were compared, and as shown in Table 1, each property was improved compared to Example 3.

Table 3 [Effects of the Invention] Due to the surface treatment of coating the hydrophobic resin fine particles according to the present invention with mechanical strain, there is no reduction in quality due to exposure of pigments, dyes, magnetic powder, etc., or residual substances with strong hydrophilic properties. An excellent electrostatic toner with no electrostatic charge can be obtained.

Claims (1)

[Claims] 1. Toner particles (A) with an average particle size of 5 to 20 μm, an average particle size of 2 μm or less, a volume resistivity of 35° C., and a relative humidity of 90%.
Below, the hydrophobic resin fine particles (B) having a diameter of 10^1^4 Ωcm or more or the hydrophobic resin fine particles (B) and other necessary fine particles (C) are prepared under conditions such that the average particle diameter is in the range of 5 to 25 μm. 1. An electrostatic toner characterized in that the surfaces of toner particles (A) are coated with hydrophobic resin fine particles (B) and other necessary fine particles (C) by mixing them under mechanical strain. 2. The electrostatic toner according to claim 1, wherein the toner particles (A) are spherical fine particles produced by an interfacial polymerization method. 3. The electrostatic toner according to claim 1, wherein the toner particles (A) are spherical fine particles produced by a suspension polymerization method. 4. The electrostatic toner according to claim 1, wherein the hydrophobic resin fine particles (B) are a vinyl polymer produced by soap-free emulsion polymerization. 5. Claim 5, characterized in that the other necessary fine particles (C) are charge control agents with an average particle size of 2μ or less.
Electrostatic toner as described in section. 6. The electrostatic toner according to claim 1, wherein 0.3 to 10 parts by weight of the hydrophobic resin fine particles (B) are used per 100 parts by weight of the toner particles (A). 7. The electrostatic toner according to claim 1, wherein 0.5 to 50 parts by weight of a charge control agent is used per 100 parts by weight of the hydrophobic resin fine particles (B).