JPH09288369A - Toner for developing electrostatic charge image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure superior flowability and triboelectric chargeability and to form a satisfactory high density image having high resolving power and free from fog and toner scattering by incorporating fine silica particles having a specified BET specific surface area and a specified hydrophobic rate into the surfaces of particles. SOLUTION: This toner contains fine silica particles of pH6-8 having 20-50m<2> /g BET specific surface area and >=85% hydrophobic rate in the surfaces of particles. The fine silica particles are fine particles having Si-O-Si bonds and may be produced by any of dry and wet methods but fine silica particles produced by a dry method, especially vapor phase oxidation of a silicon-halogen compd. are preferably used. The deterioration of the triboelectric chargeability and flowability of this toner due to fatigue is not caused even at high humidity when images are repeatedly formed many times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image developing toner (hereinafter also simply referred to as toner) for forming a visible image by electrophotography.

[0002]

2. Description of the Related Art In the electrophotographic method based on the Carlson method, the steps of charging, image exposure, developing, transferring, fixing and cleaning are repeated many times to form an image on a photosensitive member.

Toner applied to such an electrophotographic method is required to have high fluidity and sufficient triboelectrification property. Conventionally, by containing silica fine particles on the surface of the toner, various properties of the toner are ensured. I have to.

However, the silica fine particles usually contain a small amount of functional groups or impurities on the surface,
As a result, the silica fine particles are often hygroscopic and have an unfavorable pH value.

Therefore, when an image is repeatedly formed using the toner containing the silica fine particles, the characteristics of the toner such as fluidity and triboelectricity are deteriorated due to the influence of environmental humidity, and the image is deteriorated. come. Therefore, by setting the hydrophobicity and pH of the surface of the silica fine particles in a desired range, the physical properties of the silica fine particles are improved, and by extension, various characteristics such as fluidity of toner, triboelectrification, humidity resistance and durability are improved. Suggestions for improvement have been made.

For example, Japanese Patent Application Laid-Open No. 55-159450 (Gazette 1) discloses a two-component developer containing a toner containing silica fine particles having a trimethylsiloxyl group on the surface and a pH of 7.5 or more. Proposed. According to the publication 1, it is described that the humidity dependency of the toner is small in the process of repeatedly forming an image, the effect of adding silica fine particles is continued for a long time, and it is also suitable for color electrophotography.

Furthermore, for example, JP-A-2-287364
Japanese Patent Laid-Open Publication No. (Gazette 2) proposes a magnetic toner containing silica fine particles whose surface is made hydrophobic by a silane coupling agent to a degree of hydrophobicity of 30 to 80 and which has a pH value of 7 or more on the surface of the particle. There is. According to the publication 2, the magnetic toner has little environmental dependence in the process of repeatedly forming an image, there is no fusion of the toner on the photoconductor, and a transfer material for the toner image formed on the photoconductor. It is described that the transferability to the is excellent.

Furthermore, JP-A-4-288557 (publication 3) contains a charge control agent having a pH value of 3 to 5 and hydrophobic silica fine particles having a pH value of 3.5 to 4.5 on the particle surface. A two-component type developer containing a toner has been proposed.
According to the publication 3, the toner is capable of stably obtaining a good image without image defects such as insufficient image density, image fog, image dust, and toner scattering in the process of repeatedly forming an image. There is.

[0009]

However, under the present circumstances where the electrophotographic industry is increasingly required to have high image quality and high durability, any one of the toners described in the above publications has fluidity, It is insufficient in various properties such as triboelectrification property, moisture resistance and durability, and further improvement of the above-mentioned respective properties of the toner is demanded.

Further, in response to the diversification of information, a toner color recycling image forming apparatus has been developed for the purpose of developing a digital color image forming apparatus and improving the working environment and reducing the cost. In these image forming apparatuses, further improvement of various characteristics of the silica fine particles and the toner is indispensable.

As a result of earnest studies, the inventors of the present invention have found that it is necessary to set finer conditions for the silica fine particles added to the toner, and completed the present invention.

The present invention has been proposed in view of the above circumstances, and its object is to provide excellent fluidity and triboelectric chargeability even in repeated image formation many times, high resolution, and high resolution. An object of the present invention is to provide a toner capable of obtaining a good image with high density and without fog and toner scattering.

[0013]

The above object of the present invention is achieved by the following constitution.

BET specific surface area of 20 to 50 m ^{2 on the} particle surface
/ G, pH 6 to 8 and silica fine particles having a hydrophobicity of 85% or more are contained in the toner.

The silica fine particles of the present invention will be described below.

(BET Specific Surface Area of Silica Fine Particles) Silica fine particles used in the toner of the present invention are Si-O-Si.
It is a fine particle having a bond, and may be either one produced by a dry method or a wet method, but one produced by a dry method is preferable, and particularly a silica fine particle produced by vapor phase oxidation of a silicon halogen compound. Preferably there is. The silica fine particles may contain, in addition to silicon dioxide, silicates such as aluminum silicate, sodium silicate, calcium silicate, potassium silicate, zinc silicate, and magnesium silicate. Is preferably 85% by weight or more. The silica fine particles added to the toner of the present invention are often composed of agglomerates of fine primary particles, and the particle size of the agglomerates is usually represented by the BET specific surface area. In the present invention, it is an essential requirement that the BET specific surface area of the silica fine particles is 20 to 50 m ² / g. BE of the fine silica particles
If the T specific surface area is less than 20 m ² , the silica fine particles (aggregates) are too large and the adhesion to the toner becomes uneven. Therefore, the fluidity and the triboelectricity of the toner become uneven, which causes an image defect.

When the BET specific surface area of the silica fine particles is larger than 50 m ² , the silica fine particles (aggregates) are too small, and the silica fine particles are gradually buried in the toner surface in the process of repeatedly forming an image. As a result, the fluidity, triboelectric chargeability, and developability of the toner deteriorate, resulting in defective images.

The BET specific surface area of the silica fine particles was calculated by using Flowsorb 2300 manufactured by Shimadzu Corporation
It is measured by the ET one-point method.

The primary particle size of the silica fine particles is preferably 30 nm to 2 μm, more preferably 50 to 100.
nm.

The silica fine particles have a primary particle diameter of 30 nm.
If it is smaller, the silica fine particles are buried in the toner surface in the process of repeatedly forming an image, and the fluidity, triboelectrification property and developability of the toner are deteriorated. When the primary particle diameter of the silica fine particles is larger than 2 μm, the silica fine particles adhere to the toner unevenly, the developability is deteriorated, and a good quality image cannot be obtained.

The primary particle size was obtained by embedding silica fine particles in an ultraviolet-curable embedding resin and curing the particles by irradiating them with ultraviolet light to prepare a thin piece having a thickness of 2000 angstrom by a microtome. Then, it was observed by a transmission electron microscope and obtained by image analysis.

(Hydrophobicization of silica fine particles) In the present invention, it is an essential requirement that the silica fine particles be treated with a hydrophobizing agent to be described later so as to have a hydrophobicity of 85% or more. When the hydrophobicity of the silica fine particles is less than 85%, when an image is formed under high temperature and high humidity, the charge amount tends to be insufficient and image defects are likely to occur.

As a method for measuring the hydrophobicity of silica fine particles, there is the degree of hydrophobicity described in the above-mentioned Publication 3. In this measurement method, after the silica fine particles are mixed and dispersed in water, methanol is added dropwise and mixed to wet the silica fine particles, and the content (%) of the methanol with respect to the mixed solution when the total amount reaches a suspended state. expressed.

However, it has been found that the above-mentioned measuring method has a change in the measured value each time the measurement is performed, the measuring accuracy is poor, and the practicality is poor.

As a result of efforts to improve the measuring method, the present inventors have established a measuring method of the hydrophobicity which can always obtain a stable measured value.

In order to obtain silica fine particles having a desired hydrophobicity, it is achieved by controlling the amount of the hydrophobizing agent to be reacted with the silica fine particles and the reaction time.

The hydrophobic treatment agent for the silica fine particles includes a titanium coupling agent, and examples of the titanium coupling agent include tetrabutyl titanate, tetraoctyl titanate, isopropyl triisostearoyl titanate, isopropyl tridecylbenzene sulfonyl titanate. , Bis (dioctyl pyrophosphate) oxyacetate titanate and the like. Furthermore,
As the silane coupling agent, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane,
γ-methacryloxypropyltrimethoxysilane, N-
β- (N-vinylbenzylaminoethyl) γ-aminopropyltrimethoxysilane hydrochloride, hexamethyldisilazane, methyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, Examples thereof include decyltrimethoxysilane, dodecyltrimethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane and the like.

Further, a polysiloxane treated with an amino-modified silicone oil can also be used. In this example, polysiloxane treated with γ- (2-aminoethyl) aminopropylmethyldimethoxysilane. And so on.

Further, fatty acids and metal salts thereof can also be used, examples of which include undecyl acid, lauric acid,
Long-chain fatty acids such as tridecyl acid, dodecyl acid, myristic acid, pentadecyl acid, stearic acid, heptadecyl acid, arachidic acid, montanic acid, oleic acid, linoleic acid, and arachidonic acid are mentioned, and their metal salts are zinc,
Examples thereof include salts with metals such as iron, magnesium, aluminum, calcium, sodium and lithium.

The hydrophobizing agent is preferably added to the silica fine particles in an amount of 1 to 30% by weight, and more preferably 3 to 20% by weight.

To coat the silica fine particles with a hydrophobizing agent to make them hydrophobic, the silica fine particles are dispersed in a solution of the hydrophobizing agent in a solvent and then filtered or spray-dried. A method of removing the solvent and then curing it by heating, or using a fluidizing bed device, spray-apply a solution of a hydrophobizing agent dissolved in the solvent to silica fine powder, and then heat-dry it to remove the solvent. Then, a method of curing the coating film can be used.

The hydrophobization rate is measured by the following method.

First, 1.0 g of the material (fine silica particles) was sampled in a 200 ml separating funnel, and ion-exchanged water 10
Add 0 ml in a graduated cylinder. Next, the separating funnel was set in a Turbula shaker mixer “TC type” (manufactured by Shinmaru Enterprises Co., Ltd.), and the speed was set to 1 at 90 rpm.
Stir and disperse for 0 minutes. After the dispersion is completed, let stand for 10 minutes,
The obtained dispersion is sampled in a 10 mm cell for a colorimeter to prepare a sample cell, and the ion-exchanged water is sampled to prepare a comparative cell.

A colorimeter "Digital Double Beam Spectrophotometer UV-210 type" was used for the data cell and the comparison cell.
(Manufactured by Shimadzu Corporation), the turbidity of the silica fine particle dispersion layer with respect to the ion-exchanged water when the ion-exchanged water was used as a blank was measured, and the reading value T (%) at this time was taken as the hydrophobicity rate. . The measurement wavelength is 500 nm.

(PH of Silica Fine Particles) In the present invention, it is an essential requirement that the pH of the surface of the silica fine particles added to the toner is 6 to 8.

If the pH of the surface of the silica fine particles is out of the range of 6 to 8, the triboelectric charging property of the toner is deteriorated. That is, when the pH of the silica fine particle surface is less than 6,
The charge polarity of the toner is negatively biased and is easily affected by moisture, and the charge stability becomes poor in a high temperature and high humidity environment. On the other hand, when the surface of the silica fine particles has a pH of more than 8, on the contrary, the negative charging property (in the case of the reversal developing method in which both the photoconductor and the toner are negatively charged) is insufficient, and the charge amount distribution deteriorates. Cause defects.

The pH of the surface of the silica fine particles varies depending on factors such as the number of functional groups formed on the surface when the silica fine particles are produced by the dry method, the type or amount of impurities, and a hydrophobizing agent. Therefore, silica fine particles having a desired pH can be obtained by controlling the various factors.

Regarding the pH of the surface of the silica fine particles, the silica fine particles are mixed and dispersed in a mixed solution of water and alcohol (methanol, ethanol, isopropyl alcohol) 1: 1, and the obtained dispersion is subjected to a pH tester "Instrumen".
t 8417 ”(manufactured by HANNA).

Next, the amount of the silica fine particles contained on the surface of the toner is preferably 0.05 to 5.0% by weight, and particularly preferably 1.0 to 3.5% by weight. 0.05
If it is less than wt%, sufficient fluidity cannot be imparted to the toner. If it is more than 5.0% by weight,
Part of the silica fine particles exist in a state of being separated from the toner, and as a result, the released silica fine particles adhere to and transfer to a carrier, or adhere to a developing sleeve or a blade for scraping off the developer from the developing sleeve. As a result of accumulation, the triboelectric charge amount of the developer is remarkably reduced.

(Structure of Developer) The toner of the present invention contains a binder resin, a colorant and, if necessary, other additives,
The average particle size (volume average particle size) is preferably 1 to 30 μm, more preferably 5 to 20 μm.

The binder resin that constitutes the toner is not particularly limited, and various conventionally known resins can be used.
For example, styrene resin, acrylic resin, styrene-
Acrylic resins, polyester resins, styrene-butadiene resins, epoxy resins and the like can be mentioned.

The colorant constituting the toner is not particularly limited, and various conventionally known materials can be used.
Examples include carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, rose bengal, and the like.

Other additives include, for example, salicylic acid derivatives, azo metal complexes, nigrosine dyes, quaternary ammonium salts, charge control agents such as triphenylmethanes, low molecular weight polyolefins such as polypropylene and polyethylene, carnauba. A fixing agent such as wax may be used. When a one-component magnetic toner is obtained, the colored particles contain magnetic particles as an additive. As the magnetic particles, magnetic particles such as ferrite and magnetite having a number average primary particle diameter of 0.1 to 2.0 μm are used. The amount of the magnetic particles added is 20 to 80% by weight of the toner.

In addition to the fluidizing agent, a higher fatty acid metal salt such as zinc stearate may be added to the toner as a cleaning aid.

The developer in the present invention is used as a two-component developer by mixing a toner and a carrier, or as a one-component developer containing a magnetic toner as a main component. Further, the toner alone may be used as a non-magnetic one-component developer.

As the carrier constituting the two-component developer, an uncoated carrier composed of only magnetic material particles such as iron and ferrite, the surface of the magnetic material particles is fluororesin, silicone resin, styrene resin, acrylic resin, styrene- It may be either a resin-coated carrier coated with an acrylic resin, a polyester resin, an ethylene resin, a rosin-modified resin, a polyamide resin, or the like, or a resin-dispersed carrier obtained by mixing a resin and magnetic powder. The volume average particle diameter of the carrier is preferably 30 to 150 μm.

[0047]

In the toner of the present invention, the silica fine particles contained on the surface of the toner have a BET ratio surface of 20 to 50 m ² / g.
Since it is set to an extremely suitable value, the silica fine particles are less likely to be buried in the toner surface in the process of repeatedly forming an image, and the excellent fluidity of the toner by containing the silica fine particles for a long period of time is obtained. Also, the triboelectric chargeability and the like are maintained. Therefore, the fluctuation of the image density is small, and a high density and clear image can be stably obtained.

Further, since the pH of the silica fine particles contained on the surface of the toner is set to an extremely suitable value of 6 to 8, proper triboelectric charging of the toner is maintained for a long period in the process of repeatedly forming an image. It can be stably maintained, and toner scattering, toner dust, etc. are less likely to occur, and a high-resolution image can be stably obtained.

Furthermore, since the silica fine particles contained on the surface of the toner are set to have a hydrophobicity of 85% or more, there is little environmental dependency of the toner, and there is no deterioration in the charging property of the toner at high temperature and high humidity, and high durability. In addition, high density and high image quality can be stably obtained in the process of repeatedly forming an image over a long period of time.

The effect of the toner containing the fine silica particles having excellent characteristics as described above is effective for all electrophotographic image forming apparatuses, but particularly, for example, a toner recycling type image forming apparatus and non-contact developing. It is remarkably exhibited in a black and white or color image forming apparatus of the type.

That is, when the silica fine particles are buried in the toner surface in the process of repeatedly forming an image using the non-contact developing method, the triboelectric chargeability between the toner and the carrier is deteriorated, and the bond between the toner and the carrier is not formed. Physical coupling due to van der Waals forces is larger than electrostatic coupling.
Therefore, in the non-contact developing method in which the toner adhering to the carrier in the developer is separated from the carrier by the action of the AC electric field and is made to fly toward the photoconductor to develop the electrostatic charge image on the photoconductor, the development is normally performed. This is because it does not proceed and a good image cannot be obtained.

[0052]

EXAMPLES The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited thereto.

(1) Preparation of Hydrophobic Silica Fine Particles Using silicon tetrachloride as a raw material, the temperature and the amount of water required for the hydrolysis of the raw material are controlled to perform high temperature hydrolysis in oxyhydrogen flame,
Twelve kinds of silica fine particles were obtained.

Each of the above 12 kinds of silica fine particles was hydrophobized with hexamethylsilazane to give BE of Table 1.
Seven types of hydrophobic silica fine particles (A1 to A7) having a T specific surface area, pH value and hydrophobicity for Examples and hydrophobic silica fine particles (A8 to A12) for Comparative Examples were obtained.

[0055]

[Table 1]

(2) Preparation of developer (2-1) Preparation of toner 100 parts by weight of polyester resin (Tg 55.1 ° C.),
10 parts by weight of carbon black and 3 parts by weight of polypropylene were mixed, kneaded, ground and classified to obtain an average particle size of 8.5 μ.
m colored particles were obtained. 100 parts by weight of the colored particles and 2.5 parts by weight of each of the 12 kinds of the hydrophobic silica fine particles were mixed by a Henschel mixer "FM-10B" (manufactured by Mitsui Miike Kako Co., Ltd.) and stirred, and then used in Examples. 7 types of toner (T1 to T7) 5 types of toner (T
8 to T12) was obtained.

(2-2) Preparation of carrier 60 g of resin fine particles obtained by copolymerizing styrene and methyl methacrylate at a ratio of 4: 6, and an external magnetic field of 1000 oersted with a specific gravity of 5.0, a weight average particle diameter of 45 μm and 1000 oersted were applied. Then, 1940 g of Cu—Zn ferrite particles having a saturation magnetization of 30 emu / g were charged into a high-speed stirring mixer, and the product temperature was 3
After mixing at 0 ° C. for 15 minutes, mechanical impact force was repeatedly applied for 30 minutes with the product temperature set at 105 ° C., and then cooled to obtain a carrier.

(2-3) Preparation of two-component developer 558 g of the carrier and 42 g of each of the 12 kinds of toners are mixed for 20 minutes by using a V-type mixer and stirred to prepare 7 kinds of toners for the examples. Developers (D1 to D7) and five types of developers (D8 to D12) for comparative examples were obtained.

(Example 1) Using the above-mentioned 12 kinds of developers, the rate of decrease of the charge amount with the change of the environmental humidity of each toner in the developers was measured. Further, the above-mentioned 12 kinds of developers were filled in a copying machine, and a copy test was conducted many times under an HH environment (30 ° C., 80%) and an LL environment (10 ° C., 10%). Durability was measured.

(1) Measurement of decrease rate of toner charge amount At room temperature and normal humidity (20 ° C., 60%) using the V-type mixer
The charge amount Q1 (μC / g) of the toner T1 in the developer D1 obtained by stirring and mixing for 20 minutes below was measured by the blow-off method.

Next, the charge amount Q2 (μC / g) of the toner T1 after the developer D1 was left in an HH environment for 48 hours was measured by the same method, and the charge amount ratio Q2 / Q was measured.
1 was calculated and evaluated based on the following 4 rank evaluation criteria, and the results are shown in Table 2.

⊚: Q2 / Q1 ≧ 0.95 ○: 0.95> Q2 / Q1 ≧ 0.80 Δ: 0.80> Q2 / Q1 ≧ 0.60 x: 0.60> Q2 / Q1 (2) Toner durability test Color copying machine “Knica 7728” (Konica Corporation)
Using a modified machine with the following development conditions.
A patch of 2.0 × 5.0 cm is placed on the platen, the developing device is filled with the developer D1, and a copy test is performed 40,000 times in each of the HH environment and the LL environment, and the patch image per unit area is The change in the toner adhesion amount, the change range of the toner developability, and the environmental difference in the toner developability were measured, and the durability of the toner was evaluated from these.

(2-1) Development Conditions Surface potential of photoconductor: -750V DC bias: -650V AC bias: Frequency 8KHz, Vp-p 1.8KV Pressing regulation force: 10gf / mm Pressing regulation rod: SUS416 (made of magnetic stainless steel) ), Diameter 3 mm Development sleeve: 20 mm Developer layer: 150 mm (2-2) Measurement of change width of developability Using the above-mentioned modified machine filled with the developer D1, 40,000 times under HH environment and LL environment, respectively. Of the copy test, the difference in the toner adhesion amount per unit area of the patch toner image at the initial time and the 40,000th time (ΔHmg / cm
² and ΔLmg / cm ² ) were measured, and these were used as the developer D1.
The change width of the developing property of the toner T1 in the HH environment and the LL environment was used.

(2-3) Measurement of environmental difference in developability As in the case of measuring the range of change in developability, a copy test was performed 40,000 times under HH environment and LL environment, and the above HH environment was measured. The average value of the toner adhesion amount per unit area of the patch toner image in the entire copying process below,
The difference (ΔPmg / cm ² ) from the average value of the toner adhesion amount per unit area of the patch toner image in the entire copying process under the LL environment was measured, and this was used to determine the developing property of the toner T1 in the developer D1. The difference was the environment.

(2-4) Toner Durability Evaluation Under the HH environment and L of the toner T1 in the developer D1
The durability of the toner based on the variation range of the developing property under the L environment and the environmental difference of the developing property under the HH environment and the LL environment of the toner T1 in the developer D1 was evaluated by the following four ranks. Evaluation was made according to the standard, and the results are shown in Table 2.

(2-5) Evaluation Criteria A: The change range of the developability of the toner and the environmental difference of the developability of the toner are within Δ0.10 mg / cm ² , and the color tone of the image is very stable.

B: The change range of the developability of the toner and the environmental difference of the developability of the toner are within Δ0.20 mg / cm ² ,
And the color tone of the image is stable.

C: The change range of the developability of the toner and the environment difference of the developability of the toner are within Δ0.40 mg / cm ² ,
And the color tone of the image is unstable.

D: The change width of the developability of the toner and the environmental difference of the developability of the toner are larger than Δ0.40 mg / cm ² ,
And the color tone of the image is very unstable.

(3) Image quality evaluation test Using the above-mentioned modified machine, a width of 200 is set on the platen at intervals of 200 μm.
A resolving power test chart in which 5 lines with a length of μm and a length of 10 mm are arranged is placed, a developing device is filled with the developer D1 and a copy test is performed, and the obtained copy image is visually and microscopically (500 times). Both were observed and evaluated according to the evaluation criteria of the following 4 ranks, and the results are shown in Table 2.

(3-1) Evaluation Criteria A: No toner dust around the line is observed even with a microscope.

B: Although it cannot be visually inspected, toner dust around the line is observed with a microscope.

C: Toner dust around the line is visually observed.

D: Dust is so intense that it is difficult to distinguish between the lines.

Examples 2 to 7 and Comparative Examples 1 to 5 Example 1 except that developers D2 to D12 were used instead of developer D1.
In the same manner as above, measurement of reduction rate of charge amount of toner in developer, measurement of toner durability and image defect test are performed,
The results are shown in Table 2.

[0076]

[Table 2]

From Table 2, all of the developers for the examples show little decrease in the charge amount of the toner at high humidity, less fatigue and deterioration of the toner during repeated image formation, and high durability. It can be seen that the toner with a small amount of dust during image formation and a high resolution image can be obtained, but the toner for the comparative example is poor in all of the above-mentioned characteristics and is not practical.

[0078]

According to the toner for developing an electrostatic charge image of the present invention, in the process of repeatedly forming an image a number of times, even when the humidity is high, the triboelectric chargeability and fluidity of the toner do not deteriorate due to fatigue and the toner has high durability. Therefore, it is possible to obtain an effect that an image having high density and high resolution can be stably obtained.

Claims (1)

[Claims] 1. A BET specific surface area of 20 to 50 m on the surface of particles.
^{2. A} toner for developing an electrostatic charge image, comprising silica fine particles having a ratio of ² / g, a pH of 6 to 8 and a hydrophobicity of 85% or more.