JPH03101741A - Developer for developing electrostatic charge - Google Patents

Abstract

PURPOSE:To prevent the degradation of the quality of a developer after the lapse of long-term preservation by incorprating a magnetic toner contg. specific magnetic particles and inorg. fine powder treated with a silicone oil or silicone varnish into the developer. CONSTITUTION:The magnetic toner contg. the magnetic particles having >=0.35g/cm<2> bulk density and the inorg. fine powder treated with the silicone oil or silicone varnish are incorporated into the developer. The bulk density of the magnetic material can be underastood to indirectly indicate the existence amt. of the aggregates of the magnetic particles, i.e., dispersibility. The many aggregates exist in the magnetic material and the sufficient dispersibility in the binder resin is not obtained when the bulk density of the magnetic material is <0.35g/cm<2>. The use of the magnetic material having >=0.35/cm<2> bulk density is, therefore an essential requirement. Thus, the degradation of the quality of the developer after the lapse of the long-term resting and preserving is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developer for developing electrostatic images in image forming methods such as electrophotography, electrostatic recording, and electrostatic printing.

[Prior Art] Conventionally, as an electrophotographic method, U.S. Patent No. 2,297,6
A number of methods are known, as described in Japanese Patent Publication No. 91, Japanese Patent Publication No. 42-23910, Japanese Patent Publication No. 43-24748, etc.; forming an electrical latent image on the photoreceptor by means of;
Then, the latent image is developed using a developer, transferred to a transfer material such as paper as necessary, and then fixed by heat, pressure, heat and pressure, solvent vapor, etc. to obtain a copy.
The developer remaining on the photoreceptor without being transferred is cleaned by various methods, and the above-described steps are repeated.

In recent years, such copying devices have begun to be used not only as office copy machines for copying original documents, but also as printers for computer output or personal copy machines for individuals. There are also a wide variety of methods.

Therefore, smaller size, lighter weight, higher speed, and higher reliability are being strictly pursued, and machines are being constructed of simpler elements in various respects. As a result, the performance required of a one-component developer that can simplify and downsize the developing device configuration has become more advanced, and unless the performance of the developer can be improved, better machines will not be possible. It's coming. However, one-component developers generally have little chance of being charged due to friction, and since the developer particles contain magnetic powder, their charge retention is weak. This has resulted in various problems such as insufficient image density, fogging on white backgrounds, and unsatisfactory high-temperature properties.

Further, if such a developer is left unattended for a long period of time, the developer deteriorates over time, and the problems caused by the chargeability become even more pronounced.

The problem of developer storage stability or deterioration over time is especially important when using a cartridge system that integrates a photoreceptor, developer, cleaning device, etc. from a maintenance-free perspective suitable for personal use. Depending on the situation, this is likely to become an even more important issue in the future.

On the other hand, many patents and other technical documents have conventionally described the addition of a charge control agent in order to obtain stable triboelectrification of a developer.

However, while the addition of a charge control agent contributes to the charging stability of the developer, little consideration has been given to the storage stability of the developer when left for a long period of time and its deterioration over time.

[Problems to be Solved by the Invention] The present invention was made in view of the above-mentioned drawbacks, and its purpose is to maintain the initial characteristics without deterioration even after long-term storage. An object of the present invention is to provide a developer for developing an electrostatic image.

Still another object is to provide a developer for developing electrostatic images in which the triboelectric charge between developer particles and between the developer and a developer carrier such as a sleeve is stable, and the triboelectric charge distribution is sharp and uniform. It's about doing.

Still another object is to provide a developer for developing electrostatic images that reproduces stable images that are not affected by changes in temperature and humidity.

Still another object is to provide a developer for developing electrostatic images that can maintain its initial characteristics even when the developer is used continuously for a long period of time.

[Means and effects for solving the problem] The present inventors,
In order to simultaneously achieve the above objectives, various materials were studied from various angles. As a result, the bulk density is 0
．． It has been found that this can be achieved by an electrostatic image developer characterized by containing a magnetic toner containing magnetic particles of 35 g/cm" or more and inorganic fine powder treated with silicone oil or silicone varnish. .

The developer of the present invention has the above-mentioned structure, so that
Extremely resistant to deterioration when left or stored for long periods of time.

From the above, it has been found that the developer according to the present invention always provides good image formation without impairing the initial characteristics.

The present inventors believe that the reason why the developer according to the present invention exhibits the above effects is as follows. That is,
It is estimated that since magnetic particles are uniformly dispersed and contained in the developer, good charging characteristics can be maintained without deteriorating the surface properties of the developer.

Generally, the binder resin in a developer is subjected to various external pressures during the production of developer particles, and a part of the energy is stored as strain in the internal structure of the particles. This phenomenon is particularly noticeable if uniform dispersion of magnetic particles is not achieved.In areas rich in magnetic particles, the proportion of binder resin decreases, and the local viscoelasticity decreases, causing the magnetic particles and binder to decrease. Microstructural defects such as craze cracks and microvoids are also likely to occur at the resin interface.

In general, such microscopic structural defects in the binder resin are alleviated by shifting to a state of lower free energy due to the movement of segments, which are units of thermal motion of the polymer material. Particularly, the mobility of segments on the particle surface is large, and its change becomes obvious due to a phenomenon such as a decrease in the particle surface area within a certain time scale. At this time, if an additive such as a fluidity imparting agent is present on or near the developer surface, the adhesion state of the additive will be significantly changed. The present inventors estimate that deterioration of the developer over time, such as destabilization of charging characteristics and deterioration of fluidity, is caused by such changes in the surface of the developer.

In the case of negatively chargeable developers, fluidity-imparting agents that exhibit strong negative chargeability, such as hydrophobic colloidal silicate force, are often added, and therefore the triboelectricity of the additives is controlled. By increasing the triboelectric charge amount of the developer, it contributes to maintaining good charging characteristics. Therefore, the deterioration of the surface properties of the developer as described above has a particularly large effect.

On the other hand, the addition of inorganic fine powder treated with silicone oil makes it possible to simultaneously provide fluidity and stabilize chargeability, as seen in many patents and technical documents. However, unlike silane coupling agent treatment which uses chemical bonds, this silicone oil treatment is of a surface coating type, and therefore oil seeps into the developer surface and contaminates it. Oil contamination on the developer surface not only affects the surface chargeability of the developer, but also reduces the viscosity of the contaminated portion of the binder resin and promotes an increase in segment mobility. accelerates the deterioration of the In addition, in areas rich in binder resin,
As the proportion of the magnetic material decreases, the viscoelasticity increases locally, so the degree of freedom of the segment is large, and the above-mentioned phenomenon is particularly likely to occur.

Therefore, in order to prevent deterioration of the developer over time, it is necessary to uniformly disperse and contain magnetic particles in the developer to minimize changes in the surface properties of the developer. This is especially necessary when using inorganic fine powder treated with silicone oil. Among these, it is particularly effective in preventing deterioration over time of negatively chargeable developers.

The bulk density of the magnetic material can be understood to indirectly indicate the amount of aggregates of magnetic particles, that is, the dispersibility.

The bulk density of the magnetic material is 0. If it is less than 35 g/am", there are many aggregates in the magnetic material, and sufficient dispersibility in the binder resin cannot be obtained. This causes the magnetic particles to be unevenly distributed in the binder resin. Defects are likely to occur in the microstructure of the developer, causing deterioration of the developer over time.

In order to obtain good dispersion of magnetic particles in the developer, the bulk density should be 0. It is essential to use a magnetic material with a density of 35 g/cm' or more, preferably 0.5 g/cm' or more.

In the present invention, the bulk density of a magnetic material refers to a value measured according to JIS (Japanese Industrial Standard) K-5101.

The magnetic material contained in the developer according to the present invention is 10,000
Under a magnetic field of 0e, the coercive force (
Hc), more preferably 800e or less. It can be understood that the coercive force of a magnetic particle is dominated by magnetocrystalline anisotropy and shape anisotropy, and indirectly defines its surface shape. That is, as the magnetic material becomes crystalline, the coercive force increases and the magnetic particles have sharply uneven surfaces on their surfaces. When a developer containing magnetic particles having such an uneven surface on its surface is used in the present invention, microstructural defects are likely to occur near the interface between the magnetic particles and the binder resin. Therefore, it is preferable to reduce the coercive force of the magnetic particles and make the surface substantially curved. However, the coercive force may show a value of 1000e or less even when the magnetic particles form an aggregate, so even in this case, the bulk density is 0. 35g/c
m” or more.

Furthermore, the magnetic material contained in the developer according to the present invention is 10
10 emu/g or less under a magnetic field of 000 0e,
It is preferable to use magnetic particles having a residual magnetization Car of preferably 7 emu/g or less. When the residual magnetization of the magnetic material exceeds 10 emu/g, the magnetic agglomeration of the magnetic particles becomes large and they tend to exist as aggregates in the developer, and as mentioned above, this uneven distribution of magnetic particles causes the deterioration of the developer over time. This is not desirable.

The magnetic properties of the magnetic material are, for example, V manufactured by Toei Kogyo Co., Ltd.
This refers to the value measured by SMP-1.

The developer according to the present invention has a triboelectric charge and is therefore substantially electrically insulating. Specifically, it is preferable that the resistance value when a voltage of 100 V is applied under a pressure of 3.0 Kg/c is 10"Ω·crn or more. The spherical magnetic body according to the present invention is binder resin 100
30 to 150 parts by weight (preferably 40 to 150 parts by weight)
100 parts by weight).

If it is less than 30 parts by weight, the conveyance of the magnetic developer on a developer carrier such as a sleeve will be insufficient. When the amount exceeds 150 parts by weight, the insulation properties and heat fixing properties of the magnetic developer deteriorate.

The magnetic material according to the present invention is preferably produced by a wet method using ferrous sulfate as a raw material, and a divalent metal compound such as manganese or zinc is mixed with 0.00%. Preferably, it is formed from magnetite or ferrite containing 1 to 10% by weight.

The magnetic material contained in the developer according to the present invention may be subjected to a crushing treatment, if necessary. As a means used to crush the magnetic material, a mechanical crusher equipped with a high-speed rotor for crushing powder, and
An example is a pressure disperser equipped with loaded rollers for dispersing or crushing powder. When crushing aggregates of magnetic particles using a mechanical crusher, the impact force from the rotor is likely to be excessively applied to the primary particles of the magnetic particles, causing the primary particles themselves to be destroyed. Fine powder of magnetic particles is likely to be generated. Therefore, when a magnetic material that has been crushed by a mechanical crusher is used as a raw material for a developer, there is a large amount of fine powder of magnetic particles, which not only makes it difficult to uniformly disperse the magnetic particles, but also binds the binder resin. Defects are likely to occur in the microstructure inside, which has an adverse effect on the deterioration of the developer over time.

On the other hand, a pressurized dispersion machine equipped with a loaded roller such as a Fredmill is preferable in terms of the efficiency of disintegration of magnetic particle aggregates and the suppression of the production of fine powder magnetic particles.

The particle size of the fine powder used in the present invention is preferably in the range of 0.001 to 2μ, particularly 0.001μ to 2μ. 005~0.2μ
is preferred.

The inorganic fine powder used in the present invention is preferably a group 3 or group 4 metal oxide, such as silicic acid, alumina, titanium oxide, etc. Particularly preferred is silicic acid fine powder.

The silicic acid fine powder preferably used in the present invention can be either the so-called dry method produced by vapor phase oxidation of a silicon halide compound or the so-called wet silica produced by fumed silicate. There are few silanol groups inside, and Na20, SO3
``First-class dry-processed silica with no manufacturing residue is preferred.

In addition, for dry silica, it is also possible to obtain a composite fine powder of silica and other metal oxides by using other metal halide compounds such as aluminum chloride or titanium chloride together with silicon halide compounds in the manufacturing process. These are also included.

By applying the silicone oil of the silicic acid fine powder used in the present invention to the surface of the silicic acid fine powder, the silanol groups can be completely covered and hidden, and the moisture resistance is dramatically improved.

The silane coupling agent used in the present invention has the general formula RmS i Yn R: alkoxy group or chlorine atom m: 1 to 3, integer n: 3 to 1, and typically includes dimethyldichlorosilane, trimethyl Chlorsilane, allyldimethylchlorosilane, hexamethyldisilazane, allyl phenyldichlorosilane, benzyldimethylchlorosilane, vinyltriethoxysilane, γ-methacryloxyprobyltrimethoxysilane, vinyltriacetoxysilane, divinylchlorsilane, dimethylvinyl Examples include chlorsilane. The above-mentioned silane coupling agent treatment of the silicic acid fine powder can be carried out by a dry process in which a vaporized silane coupling agent is reacted with the silicic acid fine powder made into a cloud by stirring, or by dispersing the silicic acid fine powder in a solvent. The treatment can be carried out by a generally known method such as a wet method in which a silane coupling agent is reacted dropwise.

The amount of silicone oil or silicone varnish solid content to be treated in the present invention is preferably 1 to 35 parts by weight, more preferably 2 to 30 parts by weight, based on 100 parts by weight of the fine powder. The reason for limiting the above processing amount is that if the silicone oil processing amount is too small, the result will be the same as silane coupling agent treatment alone, and the moisture resistance will not improve and the fine powder will absorb moisture under high humidity, resulting in high quality copies. Images cannot be obtained. Furthermore, if the amount of silicone oil treated is too large, the above-mentioned fine powder aggregates are likely to form, and free silicone oil is also formed, so it is difficult to improve the fluidity when applied to a developer. There are disadvantages such as not being able to do so.

As the silicon varnish for fine powder treatment used in the present invention, known materials can be used. For example, K made by Shin-Etsu Silicone Co., Ltd.
R-251. Examples include, but are not limited to, KR-112 and the like.

As a method for silicone varnish treatment, the same known techniques as for oil treatment can be used.

Further, it is more preferable that the inorganic fine powder used in the present invention is first treated with a silane coupling agent and then treated with silicone oil or silicone varnish.

Generally, with silicone oil treatment alone, a large amount of silicone oil is required to cover the surface of the inorganic fine powder, which tends to cause aggregates of fine powder during treatment, and when applied to a developer, the fluidity of the developer may deteriorate. Therefore, it is necessary to be careful about the silicone oil treatment process. Therefore, in order to prevent aggregation of inorganic fine powder while maintaining good moisture resistance, it is better to treat inorganic fine powder with a silane coupling agent and then with silicone oil to fully demonstrate the treatment effect of silicone oil. It means that it can be done.

Ultimately, it is desirable that the treated inorganic fine powder be hydrophobized so that the degree of hydrophobization is 60% or more, more preferably 90% or more. If the degree of hydrophobicity is less than this, high-quality images cannot be obtained due to moisture adsorption of the inorganic fine powder under high humidity.

For the degree of hydrophobicity of the inorganic fine powder in the present invention, a value measured by the following method is used. Of course, other measurement methods can also be applied while referring to the measurement method of the present invention.

Pour 10 liters of ion-exchanged water into a sealed 200 mj) separating funnel.
Add 0mf and 0.1g of sample and shake at 9Orpm using a shaker (Yuichi Bra shaker mixer T2C type).
Shake for 0 minutes. After shaking, leave it to stand for 10 minutes, and after the silica powder layer and water calendar are separated, the lower water layer is heated to 20~30n+
1! Collect the sample, place it in a 10 mm cell, and measure the transmittance at a wavelength of 500 nm using blank ion-exchanged water containing no inorganic fine powder as a reference, and use the transmittance value as the degree of hydrophobicity of the inorganic fine powder. It is.

In addition, the application amount of these inorganic fine powders is 10
The effect is exhibited when it is added in an amount of 0.01 to 20 parts by weight relative to 0 parts by weight, and an excellent developer can be provided when it is added more preferably in an amount of 0.1 to 3 parts by weight. Regarding the preferred form of addition, it is preferable that the treated inorganic fine powder is attached to the surface of the developer particles.

Examples of the binder resin for the magnetic toner of the present invention include monopolymers of styrene and its substituted products such as polystyrene and polyvinyltoluene; styrene-propylene copolymers, styrene-vinyltoluene copolymers, and styrene-vinylnaphthalene copolymers. Union. Styrene-methyl acrylate copolymer.
Styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene- Butyl methacrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer. Styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isobrene copolymer, styrene-maleic acid copolymer, Styrenic copolymers such as styrene-maleate ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polybropylene, polyvinyl butyral.
Polyacrylic acid resin, rosin, modified rosin, tempel resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, paraffin wax, carnauba wax, etc. can be used alone or in combination.

A charge control agent, a coloring agent, and a fluidity modifier may be added to the developer as necessary, and the charge control agent and fluidity modifier are mixed (externally added) with the developer particles and used. It's okay. Charge control agents include metal-containing dyes, nigrosine, etc., conventionally known dyes and pigments can be used as coloring agents, and fluidity modifiers include colloidal silica, fatty acid metal salts, and the like. In addition, for the purpose of increasing the amount, calcium carbonate,
A filler such as finely divided silica can also be incorporated into the developer in an amount of 0.5 to 20% by weight. Furthermore, it prevents developer particles from coagulating with each other and improves their fluidity. In addition, for the purpose of increasing the amount, a fluidity improver such as fine Teflon powder may be added, and for the purpose of improving mold release properties during hot roll fixing, low molecular weight polyethylene, low molecular weight polypropylene,
0.5 to 5% by weight of waxy substances such as microcrystalline wax, carnauba wax, and Sasol wax.
You can also add degrees.

[Examples] The basic structure and features of the present invention have been described below, and the method of the present invention will be specifically explained based on Examples. However, this does not limit the embodiments of the present invention in any way. Parts mean parts by weight.

The above mixture is melt-kneaded with a twin-screw extruder heated to 140°C, the cooled mixture is coarsely pulverized with a hammer mill, the coarsely pulverized material is pulverized with a jet mill, and the resulting finely pulverized powder is The powder was classified to obtain negatively charged magnetic particle classified powder-1 (negatively charged magnetic toner) having a volume average particle size of 12 mm.

4 The above ingredients were prepared in the same manner as in Production Example 1 to prepare magnetic particle classified powder-2 (
A negatively charged magnetic toner) was obtained.

4 Bulk density of the plate 0.42g/Cm' (Hc=990e,
Magnetic particle classified powder-3 (negatively charged magnetic toner) was obtained in exactly the same manner as in Production Example 1 except that ar = 8.3 emu/g) was used.

Salmon Imiyu bulk density 0.31g/cm” (Hc= 109 0
Magnetic particle classified powder-4 (negatively charged magnetic toner) was obtained in exactly the same manner as in Production Example 1, except that a magnetic material of e, a r = 10.6 emu/g) was used. Aerosil #2, a fine silicic acid powder with a specific surface area of 200 m2/g
00 (manufactured by Nippon Aerosil Co., Ltd.) was treated with 20 parts of hexamethyldisilazane (HMDS), and then treated with 10 parts of dimethyl silicone oil KF-96 100cs (manufactured by Shin-Etsu Chemical Co., Ltd.) diluted with a solvent. After drying, heat treatment was performed at approximately 250°C to obtain a hydrophobic degree of 99.
% of treated silicic acid fine powder was obtained. 0.4 part of this treated silicic acid fine powder was added to 100 parts of the magnetic particle classified powder-1 (6fi toner) and dry mixed in a Henschel mixer to prepare a developer.

(1) Test 1. (Actual photocopying test under room temperature conditions) A photocopying test of this developer was carried out on an electrophotographic copying machine rFC-5.
A modified machine (manufactured by Canon Inc.) was used. As shown in Figure 1, this modified machine uses a negatively charged organic photosensitive drum, and the surface potential (maximum potential) of the organic photosensitive drum during charging is -700V, and the distance between the photosensitive member and the developing sleeve in the developing space is -700V. The gap (Dsd) is 270 pm, and the gap (Dsb) between the tip of the regulating blade and the developing sleeve is 240 pm.
#Lm, M1 stone body is a fixed type, the magnetic flux density on the surface of the developing sleeve is set to 800 Gauss, and the thickness of the developer layer on the sleeve is set to 80p. m, AC bias 1.800Vp
A copy image was obtained by reverse development by applying p, 1400 Hz and a DC bias of -450 V to the sleeve, and the following items were each evaluated. The results are summarized in Table 1 below.

■Image density using "Macbeth reflection densitometer" (manufactured by Macbeth),
The relative density of a white background portion with an original density of 0.0 with respect to a copied image was measured.

(2) Fog Density The worst value of image blur was determined by using a "Macbeth Reflection Densitometer" (manufactured by Macbeth Co., Ltd.) as a relative density with respect to a white background area where the density of the original was 0.0. Note that the white background inversion density was set to 0.0.

Note that "image blurring" refers to a phenomenon in which developer is scattered on a white background area (non-image area).

(2) Image Quality Copied images were visually judged from five points: image scattering, image missing, image fading, image unevenness, and sharpness. The evaluation is "X" if it is poor and has practical problems, "△" if it is slightly poor but at a practical level, "○" if it is good, and "0" if it is very good. ”.

"Image scattering" refers to the phenomenon in which the developer scatters around the edges of the image, "image missing" refers to the phenomenon in which part of the image is missing, and "image blurring" refers to the phenomenon in which the image has band-like shading. "Image unevenness" refers to a phenomenon in which differences appear in images, and "image unevenness" refers to a phenomenon in which differences in shading occur in images.

(2) Test 2 (live-action test after being stored for 6 months) A live-action test was performed after the developer was stored for 6 months at room temperature, and the above items were evaluated.
The deterioration of the developer over time was evaluated. The results are summarized in Table 1 below.

History of Blood Immunization Treat 100 parts of yusilicate fine powder Aerosil #200 with 10 parts of dimethyl silicone oil KF-96 100cs (manufactured by Shin-Etsu Chemical Co., Ltd.) diluted with a solvent, and after drying, heat treat at 250°C to make it hydrophobic. A treated silicic acid fine powder with a purity of 93% was obtained. This treated silicic acid fine powder was added to 100 parts of magnetic particle classified powder-2 (magnetic toner) of Production Example 2.
Add 0.6 parts and dry mix with a Henschel mixer,
After preparing the developer, it was evaluated and studied in the same manner as in Example 1. The results are shown in Table 1 below.

Silicic acid fine powder Aerosil #3 with a specific surface area of 300m”/g
00 100 parts olefin modified silicone oil KF-
415 (manufactured by Shin-Etsu Chemical Co., Ltd.) was treated in the same manner as in Example 2 to obtain treated silicic acid fine powder with a degree of hydrophobicity of 99%.

This treated silicic acid fine powder was used as magnetic particle classified powder-3 of Production Example 3.
(Magnetic toner) 0.6 part was added to 100 parts and dry mixed in a Henschel mixer to prepare a developer, and then evaluated and studied in the same manner as in Example 1.

The results are shown in Table 1 below.

Member A 100 parts of silicic acid fine powder Aerosil #200 was treated with 15 parts of fluorine-modified silicone oil FL-too 450cs (manufactured by Shin-Etsu Chemical Co., Ltd.) in the same manner as in Example 2 to obtain a hydrophobic degree of 95.
% of treated silicic acid fine powder was obtained. 0.8 parts of this treated silicic acid fine powder was added to 100 parts of magnetic particle classified powder-2 (magnetic toner) of Production Example 2, and the mixture was dry mixed in a Henschel mixer to prepare a developer. Evaluate as in Example 1,
investigated. The results are shown in Table 1 below.

Silicic acid fine powder Aerosil #1 with a specific surface area of 130 m”/g
30 (manufactured by Nippon Aerosil Co., Ltd.) and 5 parts of α-methylstyrene modified silicone oil KF-410 (manufactured by Shin-Etsu Chemical Co., Ltd.) were treated in the same manner as in Example 2 to obtain treated silicic acid fine powder with a degree of hydrophobicity of 94%. Obtained. 1.0 part of this treated silicic acid fine powder was added to 100 parts of magnetic particle classified powder-2 (Mi-based toner) of Production Example 2, and the mixture was dry mixed in a Henschel mixer to prepare a developer. Evaluation in the same manner as in Example 1,
investigated. The results are shown in Table 1 below.

Comparative group Added 0.5 part of the treated silicic acid fine powder of Example 2 to 100 parts of magnetic particle classified powder-4 (magnetic toner) of Production Example 4,
After preparing a developer by dry mixing using a Henschel mixer, evaluation and study were carried out in the same manner as in Example 1. The results are shown in Table 1 below.

(The following is a blank space) [Effects of the Invention] As explained above, the present invention provides that when a developer contains inorganic fine powder treated with silicone oil or silicone varnish, the developer has a bulk density of 0. ．． 35g/cm3
By containing the above-mentioned magnetic particles, the toner has stable and uniform charging properties and can perform development faithful to the latent image. That is,
Even after long-term storage, it does not deteriorate, maintains its initial characteristics, and provides stable image quality. In addition, there is no rise in image density and high image density can be obtained from the beginning.
Clear image quality without fogging can be maintained even when the image forming process is performed many times.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a schematic cross-sectional view of a developing device to which the magnetic developer of the present invention can be preferably applied. 1... One-component magnetic developer 2... Blade 3... Sleeve Table 1 4... Photosensitive drum 5... Fixed magnet 6... Bias application means

Claims (1)

[Claims] A developer for developing electrostatic images characterized by containing a magnetic toner containing magnetic particles having a bulk density of 0.35 g/cm^3 or more and inorganic fine powder treated with silicone oil or silicone varnish. .