JPH0242452A - Negatively chargeable toner - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a toner used as a developer for developing electrostatic images in electrophotography, electrostatic recording, electrostatic printing, and the like. More specifically, in a direct or indirect electrophotographic development method, a load is applied that is uniformly and strongly negatively charged to visualize a positive electrostatic charge image or visualize a negative electrostatic charge image by reversal development to produce a high quality image. Regarding electrostatic toner.

[Prior Art] Conventionally, as an electrophotographic method, U.S. Patent Section 2.297°69
Specification No. 1, Japanese Patent Publication No. 42-23910 (U.S. Patent Section 3,1388,383), Japanese Patent Publication No. 43-24
A number of methods are known, such as U.S. Pat. No. 748 (U.S. Pat.
After forming an image and then developing the latent image using developer powder (hereinafter referred to as toner) and transferring the toner image to a transfer material such as paper as necessary, heat, pressure, or a pressure heat fixing roller is applied. Alternatively, copies can be obtained by fixing with solvent vapor or the like. In addition, if there is a step of transferring a toner image, 1
Typically, a step is provided to remove residual toner on the photoreceptor.

Development methods for visualizing electrical latent images using toner include, for example, the magnetic brush method described in U.S. Pat. Cascade development method and 2,221,7
Powder cloud method described in US Pat. No. 78, U.S. Pat.
．． A method using conductive magnetic toner described in Japanese Patent No. 909.258 is known.

As toners applied to these developing methods, fine powders in which dyes and pigments are dispersed in natural or synthetic resins have conventionally been used. For example, particles obtained by dispersing a colorant in a binder resin such as polystyrene and pulverizing the particles to about 1 to 30 liters are used as toner. As the magnetic toner, one containing magnetic particles such as magnetite is used. In the case of a system using a so-called two-component developer, the toner is usually mixed with carrier particles such as glass beads and iron powder.

As the charge control agent used in such a dry developing toner, for example, an organic metal complex is generally used, and in particular, those containing Ail, Fa, Zn, or Cr as the central metal are used. These are usually added to thermoplastic resins, heated and melted and dispersed, and then finely ground to adjust the particle size to a standard size before use.

However, these charge control agents are susceptible to mechanical shock, ff
Charge controllability is likely to deteriorate due to friction, changes in temperature and humidity conditions, and the like.

Therefore, when a toner containing these as a charge control agent is used for development in a copying machine, the toner may deteriorate during durability as the number of copies increases.

In order to prevent these problems, it has conventionally been proposed to mix hydrophobic silica in Japanese Patent Publication No. 54-16219 and Japanese Patent Application Laid-open No. 5
These hydrophobic silicas are known from JP-A No. 5-120041 and JP-A No. 59-34539, but these hydrophobic silicas are treated with dimethyldichlorosilane and hexamethyldisilazane, and are not sufficiently hydrophobic. In a harsh high temperature and high humidity environment, the amount of charge decreases due to moisture absorption.

Further, Japanese Patent Application Laid-Open No. 49-42354 discloses a method of treating silica with silicone oil and using it in a toner. In this method, sufficient hydrophobicity can be obtained, but since the silicone oil is a polymeric substance, agglomeration occurs during treatment, resulting in lumps with sizes ranging from 0.1 to several digits. Since these lumps are also negatively charged, they develop in the image area and cause white spots, and friction between particles of silica lumps and toner can cause some toner to be charged to the opposite polarity, causing reverse fog. are doing.

Conventionally, there are three types of processing methods for fine silica powder used for toner: a method in which the processing agent is vaporized and brought into contact with the fine silica powder, and a method in which the processing agent is vaporized and brought into contact with the fine silica powder, and a method in which the fine powder is dispersed by stirring with a high-speed stirrer such as a Henschel mixer. There are two methods: a method of contacting with a processing agent, and a wet processing method of dispersing fine silica powder in a solution of a processing agent and then removing the solvent.

In the wet processing method, wet dispersion of fine silica powder in a solution is insufficient, and aggregation cannot be prevented during solvent removal, resulting in surface-treated silica with many lumps. Furthermore, in the method of stirring with a high-speed stirrer, the resilica fine powder cannot be sufficiently dispersed, and although the amount of bed clumps is lower than in the wet processing method, it cannot be said to be superior. Further, it is virtually impossible to vaporize high molecular weight processing agents such as silicone oil. This aggregation becomes more pronounced as the molecular weight of the processing agent increases, and is significant in treatments with polymeric substances such as dimethyl silicone oil and styrene-n-butyl acrylate. Moreover, it becomes more significant as the amount of processing agent increases.

In addition, in recent years, the demand for multiplex and multicolor copying has increased, and for this reason, it has become necessary to erase the latent images on the drum in designated categories.
The LED and fuse lamp illuminate the drum with light strong enough to prevent the drum potential from dropping any further, giving the drum surface potential VSL of the designated category. Normally, in an electrophotographic copying machine, in order to prevent excess toner from adhering to the bright area (bright area potential VL) of the photoreceptor and causing fog development, the developing sleeve is set at a constant DC bias VDC. The 0 normal inversion fog that is applied is this 1VDc -V.

The value increases as the value of VDCVSLI increases, and the size of these ranges in which fog is allowable is the ability of the toner to prevent fog.

That is, the maximum allowable value of 1Voc -VsLl (inversion fog allowable latitude lV [lc Vst 1I
It can be said that the larger the toner (lax) is, the less fogging the toner has, but conventional toners are not completely satisfactory. In normal copying, it is fine as long as there is no fogging at IVDc -Vl-l, but when erasing the latent image on the drum in a designated category for reduction or multi-color copying, I
It must be a toner that does not fog at VDc - Vst l. In addition, a large IVoc -VSL 1sax also widens the design latitude of the device, and it is desired to develop a toner with a larger 1voc Vst IIaX. Furthermore, as a matter of course, high-speed machines make a larger number of copies than ever before, so toners with higher durability (several 10,000 to several million copies) are required.

As a result of intensive investigation into the above-mentioned problems, the present inventors discovered that silica, which has been conventionally used to improve fluidity and assist chargeability, plays an important role, leading to the present invention.

[Problems to be Solved by the Invention] An object of the present invention is to stabilize the amount of triboelectric charge between toner particles, between toner and carrier 11, or between toner and a toner carrier such as a sleeve in the case of -component development. The object of the present invention is to provide a negatively charged toner which has a sharp and uniform triboelectric charge distribution and can control the charge amount suitable for the developing system used.

Still another object is to provide a toner that can provide clear images without fogging even in multicolor/multiple copying in high-speed machines.

A further object of the present invention is to provide a toner that has excellent impact resistance, does not cause agglomeration, has excellent fluidity, and is durable.

Still another object is to provide a toner that maintains its initial characteristics even when the toner is used continuously for a long period of time, and that causes no increase in fog or density fluctuation.

A further object of the present invention is to provide a toner that does not cause white spots in image areas.

Still another object is to provide a toner that reproduces stable images unaffected by changes in temperature and humidity.

Still another object is to provide a toner with excellent storage stability that maintains its initial characteristics even during long-term storage.

Another objective is to provide bright chromatic toner.

[Means for Solving the Problems] The 4v feature of the present invention is that a negative electrode containing surface-treated silica obtained by dispersing fine silica powder with a high-speed jet air stream and simultaneously contacting it with a treatment agent. It's in sex toner.

Furthermore, the water wettability of the silica contained in the toner of the present invention is 8.
It is effective to have a water wettability of 0% or more (preferably 90% or more) and a water wettability of 50% or more after re-crushing.

Although the silica contained in the toner of the present invention is effective only when treated with a high-speed jet stream, it may also be mixed with a processing agent in advance. It will be even more effective.

As the silica fine powder constituting a component of the developer in the present invention, silica fine powder produced by a dry method or a wet method can be used.

The dry method mentioned here is a method for producing fine silica powder produced by vapor phase oxidation of a silicon halide compound. For example, this method utilizes a thermal decomposition oxidation reaction of silicon tetran1 oxide gas in an oxyhydrogen flame, and the basic reaction formula is as follows.

SiGha+2 H2+ 02→5i02+ 4 HCf
;! In addition, in this manufacturing process, for example, a group for obtaining a composite fine powder of silica and other metal oxides by using alumina chloride 1 or other metal halide compounds such as titanium chloride together with a silicon halide compound is also removable.
These are also included.

Commercially available silica fine powder produced by vapor phase oxidation of a silicon halogen compound used in the present invention includes, for example, those commercially available under the following trade names.

AERO3IL 130 (Japan Aerosil Co., Ltd.) 200 0x50 7-600 0X80 0X170 0K84 Ca-0-3iL (C: ABOT Go, Inc.) S-7 S-75 S-5 H-5 Wacker HDK N 20
V 15 (WACKER-CHEMI
E0M88) N20ED-CFine Si
(Dow Corning, Inc.) Fransal (FranSi1, Inc.) Reolo Seal (
On the other hand, various conventionally known methods can be used to produce the silica fine powder used in the present invention by a wet method.

For example, the decomposition of sodium silicate by an acid can be expressed using a general reaction formula (the reaction formula is omitted below): Na2CIXSi07+HCj) +H20+SiO?
・nToO+NaCl! Other methods include decomposition of sodium silicate with ammonia salts or alkali salts, generation of alkaline earth metal silica-resistant salts from sodium ooate, and then decomposition with acid to produce silicic acid, and methods of converting sodium silicate solution into silicic acid using ion exchange resin. There are methods such as using an acid, and using natural silicic acid or silicate.

The silica fine powder referred to herein may be any of anhydrous silicon dioxide (silica) and silica salts such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate.

Examples of lithographic silica fine powder synthesized by a wet method include those commercially available under the following trade names.

Carplex 112 Nogi Pharmaceutical 21 Pushir
Japan Silica Fine Seal Lucil Nexcil Lului Dotoku Seal.

Vita Shilton.

Stahi Me Shisa I Ro) 1i-sil (High Tokuyama A Taki Hizusawa Chemical Kamishima Chemical Ehime Pharmaceutical Fuji Davison Chemical Seal) Pittsburgh Plate Gla
ssCOl (Pittsburgh Plate Glass) Durosil Fillstoff
-Gesellschaft former torasil (Ultra Marquart) NanosiI (-ynoshir) Hardtaa
n and Ho1den laesch Sil-Stone Ghemische Fabrik Hoesch
5taner Rubber C
o.

(Stoner rubber) Nalc.

(Narco) Nalco Chew, co.

(Narco Chemical) Quso (Kun) Philaclephia Quartz Co
.

(Philadelphia Quartz) Santocell Mon5anto
Chemical Go.

(Monsanto Chemical) Ims i l (Imsil) 111inois Minerals Co.

(Illinois Mineral) Calcium 5ilikat (Calcium Silicate) Chemische Fabrik Hoe
sch K-G (Hiemische Faprikheras) Calsil Fiillstoff-
Fortafil Imperia
l Cheilical Industries,
ta, (Imperial Chemical Industries) Microcal Joseph Cr
osfield & 5onst, ta, (Joseph Crossfield & Thump) Manos i l (?Nosir) Hardman
andnMad AndHo1den Vulkasil Farben
fabrikenBryer, A, G, (7y
) to Lt 77 y Breeken Bayer) Tufknit (tuff =-/to) Durham
Chemicals Ltd.

(Durham Chemicals) Sil Moss White Masonry
Among the silica fine powders mentioned above, the specific surface area due to nitrogen adsorption measured by the BET method is 30 m2/g or more (especially 50 to 400 m2/g).
m2/g) gives good results.

Conventionally, it is known that fine silica powder produced by vapor phase oxidation of a silicon halide compound is added to a developer.

As mentioned above, it is also known to use hydrophobic silica treated with silicone oil or a silane coupling agent, and some of these are in practical use, but there are problems with the treatment method, especially when using a large amount of treatment agent or When treated with a highly viscous processing agent, large and small lumps are generated, resulting in high-speed machines, multiple
In a multicolor copying machine, the value of 1Voc VsLlsax is not sufficient, which limits the latitude of the device design.

In order to solve these problems, the present invention generates a jet stream using high-pressure air to disperse fine silica powder, and at the same time blows a treatment agent into contact with the droplets using a two-fluid nozzle cap to produce surface-treated silica. It was included in the toner.

The air pressure at this time is preferably 1 to 6 kg/cm2.

As for the device used for this treatment, it is sufficient to modify a crusher using a high-speed jet stream, which is conventionally used for crushing toner, and insert a treatment agent droplet spraying device into the crushing section.

However, in this case, since it is difficult to collect with a cyclone, it is preferable to use a Pub filter with good collection efficiency.

Furthermore, by heat-treating the obtained surface-treated silica at a temperature of about 50 to 350°C, it becomes even more stable and uniform.
You can obtain something that has electrical properties.

As the silicone oil used in the treatment of the silica fine powder, silicone oil represented by formula CI) can generally be used.

(Here, R1 and R2 are hydrogen, alkyl group, aryl)
U (or represents an alkoxy group. R3 is a modified group, typified by α-methylstyrene, α-olefin, polyether, alcohol, trifluoroalkyl group, mercapto, glycidyl, carboxyl, etc.).

Further, n is 1 or more, and m is a positive number including O. ) The viscosity of this silicone oil is preferably 100 cps or less at 25°C.

Further, as the organosilicon compound used in the present invention, commonly available commercially available silane coupling agents and disilazane compounds can be used.

Typical examples include dimethyldichlorosilane, trimethylchlorosilane, trimethylethoxysilane, hexamethyldisilazane, and the like.

All of these can be used as a treatment agent for the silica contained in the toner of the present invention, but from the viewpoint of hydrophobicity, treatment with silicone oil or treatment with an organic silicon compound and silicone oil is preferred.

By mixing silica treated with these processing agents in a high-speed jet stream with black fine powder obtained by kneading, crushing, and classifying resin, coloring agent, etc., q1 of toner can be obtained.

Furthermore, L silica may be included during kneading.

The amount of triboelectric charge of the surface-treated silica in the present invention is -100 to -
Preferably it is 200 pC/g.

It is easy for surface-treated silica using conventional treatment methods to fall within the above range of triboelectrification.
The water wettability of the surface-treated silica of the present invention is 80% or more, and even if re-crushing is added, it is 50%.
It will not drop below that.

This decrease in water wettability due to re-crushing is thought to be due to the untreated silica surface being exposed as aggregates of surface-treated silica are broken by re-crushing. It can be said that sex has also improved.

The water wettability of silica in the present invention is measured as follows.

Collect 0.1 g of sample into a 200 mj) separating funnel, and add 100 ml of ion exchange water using a graduated cylinder.

Mix this with a turbo sneaker mixer 12C type at 9 orp.
Shake for 10 min at 0 m. After leaving the separating funnel for 10 min, extract 20-30 mj) from the lower layer, dispense into a 10 mm cell, conduct ion exchange. Use water as a blank, and check the turbidity of the water layer using a colorimeter. 4 (constant wavelength of 500 nm) The transmittance % with respect to the blank is defined as the water wettability.

The amount of triboelectric charge in the present invention is measured at 23.5°C960
An iron powder carrier (Japan Iron Powder EFV 200/30
0) and 2788 in a ratio of 0.5 to 1
．． 5 g was sampled and suctioned with a pressure of 25 cmH2O on a metal 400 mesh screen connected to an electrometer, and based on the state of the sample sample sucked in and its charge amount, the band per medium type 111 was determined. 1 [Depends on the method of determining the amount.

In the present invention, "re-crushing" refers to collecting the finally treated silica by performing jet stream disintegration at an air pressure of 4 kg again without contact with a processing agent. This causes a decrease in the level of symptoms. This water wettability and durability under high temperature and high humidity are closely correlated and are important factors determining toner performance.

Colorants used in the present invention include carbon black, lamp black, iron black, ultramarine blue, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, Rhodamine 6G, Lake 1 Calco Oil Blue, Chrome Yeloquinacridone, and Benzidine Yellow. ,
Any conventionally known dyes and pigments such as rose bengal, triallylmethane dyes, monoazo dyes, disazo dyes and pigments can be used alone or in combination.

The binder resin used in the present invention includes polystyrene,
Homopolymers of styrene and its substituted products such as poly-p-chlorostyrene and polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene 17 coffi polymers, styrene-vinylnaphthalene Copolymers, and styrene-acrylic acid typified by styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers, styrene-methyl acrylate copolymers, styrene-octyl acrylate copolymers, etc. Ester copolymers; also styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, styrene-butyl methacrylate copolymers,
Styrene methacrylate ester copolymers represented by styrene-α-methyl chloromethacrylate copolymers, styrene-acrylonitrile copolymers, styrene-vinyl methyl ether copolymers, and styrene-vinylethyl ether copolymers. , styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-
Styrenic copolymers such as isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid co-ffi polymer, styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride , polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum Examples include resin, chlorinated paraffin, paraffin wax, etc., and they can be used singly or as a mixture.

In particular, as binder resins suitable for pressure fixing, the following may be used singly or in combination.

Polyolefin (low molecular weight 1M polyethylene, low molecular weight T1
1 polypropylene, polyethylene oxide, polytetrafluoroethylene, etc.), epoxy resin, polyester resin, styrene-butadiene copolymer (monomer ratio 5 to 30:95)
~70), olefin copolymers (ethylene-acrylic acid copolymers, ethylene-acrylic ester copolymers, ethylene-methacrylic acid copolymers, ethylene-methacrylic ester copolymers, ethylene-vinyl chloride copolymers) ,
ethylene-vinyl acetate copolymer, ionomer resin),
Polyvinylpyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenol resin, phenol-modified terpene resin.

Further, when the toner of the present invention is used as a two-component developer, it is used in combination with a carrier powder.

All known carriers can be used in the present invention, such as magnetic powders such as iron powder, ferrite powder, and nickel powder, glass beads, etc., and carriers whose surfaces have been treated with resin, etc. Things can be given.

Furthermore, the toner of the present invention can further contain a magnetic material and be used as a magnetic toner. The magnetic materials contained in the magnetic toner of the present invention include iron oxides such as magnetite, hematite, and ferrite; metals such as iron cobalt and nickel;
Examples include alloys of metals such as copper, lead, manesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof.

These ferromagnetic materials preferably have an average particle size of about 0.1 to 2 μl, and are contained in the toner in an amount of about 20 to 200 parts by weight per 100 parts by weight of the resin component, particularly preferably in an amount of about 20 to 200 parts by weight per 100 parts by weight of the resin component. The amount is 40 to 150 parts by weight.

Further, it can be used in combination with a conventionally known charge control agent as long as it does not adversely affect the toner of the present invention.

Furthermore, better results can be obtained with the toner of the present invention when additives are mixed as necessary. Examples of additives include lubricants such as Teflon and zinc stearate, abrasives such as cerium oxide and silicon carbide, flow agents such as colloidal silica and aluminum oxide, anti-caking agents, and carbon black and tin oxide. and fixing aids such as low molecular weight polyethylene.

To prepare the toner for developing an electrostatic image according to Unreleased No. 191, the charge control agent according to the present invention is mixed with a vinyl or non-vinyl thermoplastic resin, a pigment or dye as a coloring agent, a magnetic material as necessary, Additives are thoroughly mixed using a ball mill or other mixer, and then melted, kneaded, and kneaded using a heat kneader such as a heated roll, kneader, or extruder to make the resins mutually dissolve. A toner having an average particle size of 5 to 20 liters can be obtained by dispersing or dissolving a pigment or dye in the toner, cooling and solidifying it, and then crushing and classifying it.

Alternatively, the material can be obtained by dispersing the material in a binder resin solution and then spray-drying it, or by mixing the specified material with the monomers that should constitute the binder resin to form an emulsified suspension and then polymerizing it. A polymerization method for obtaining a toner or a method for producing a so-called capsule toner consisting of a core and a shell can be applied.

[Examples] The present invention will be specifically explained below with reference to Examples, but these are not intended to limit the present invention in any way. Note that all parts in the following formulations are i4iY parts.

Production example 1 BET specific surface area of dry silica fine powder is 200+s2/g
(Aerosil 1200) was used as the treatment base and dimethyl silicone oil (viscosity 25°C) was used as the treatment agent.

100 cps,) is used.

The processing equipment is an improved supersonic jet pulverizer that can spray droplets (for 5 to 20) of a processing solution diluted 4 times with n-hexane from a two-fluid nozzle in the pulverization section. It was used.

At this time, the air pressure was set at 4 kg/cm2, and feed was carried out so that the ratio of the treated body to the treated liquid was 1:0.2.

The collection uses HEPA (High
Efficiency particulate AI
r) 74 Luther was used.

The surface-treated silica thus obtained was heated to 280°C while stirring in a nitrogen-purged stirring tank, and the temperature was increased to 30 m1n.
Silica A was obtained by performing fj% treatment.

Production Example 2 Silica B was obtained in the same manner as in Production Example 1 except that hexamethyldisilazane was used as the treatment agent.

Production example 3 100g of silica fine powder with a specific surface area of 200m27g is added to 1 part of water.
200 g of a 1O% IPA solution of hexamethylene disilazane was added dropwise while stirring and left to stand for several hours. The supernatant liquid was removed, and the resulting slurry was dried and crushed to obtain surface-treated silica. .

This surface-treated silica was heat-treated in the same manner as in Production Example 1 to obtain Silica C.

Production Example 4 100 g of silica fine powder with a specific surface area of 2 oom2/g was placed in a stirring tank purged with nitrogen, maintained at 280°C with stirring, and dimethyl silicone oil (viscosity at 25°C of 100
Silica D was obtained by spraying a treatment solution obtained by diluting cps) 4 times with n-hexane and treating for 30 minutes.

Production Example 5 Silica E was obtained in the same manner as Production Example 1 except that the surface-treated silica D of Production Example 4 was used as the treated 81 body.

Table 1 shows the water wettability and charge amount of silica A-H.

Table 1 Silica A I20 Silica B 110 Silica C80 Silica D I70 Silica E 180 Example 1 100 parts of styrene/butyl methacrylate/maleic acid (80/+515) copolymer (dose average molecular weight MII; approximately 300,000) magnetite
60 parts paper molecular weight polypropylene wax 4 parts tert-butylsalicylic acid Or
Complex Part 3 The materials listed in E were thoroughly mixed in a blender and then kneaded with two rolls heated to 150°C. After the kneaded material was left to cool naturally, it was roughly pulverized with a cutter mill, then pulverized with a pulverizer using a jet stream, and further classified using an air classifier to obtain black fine powder with a number average particle size of 10 JL. Obtained.

A toner was prepared by adding and mixing 4 parts by weight of silica 004 to 100 parts by weight of this black fine powder.

Images of this toner were produced and evaluated using a copying machine manufactured by Canon NP-8570, which is capable of making 70 high-speed copies per minute.

As a result, a clear image without blurring was obtained, and the solid density was 1.40, which was sufficient from the beginning. Further, there was no inversion fog in the VS2 portion, and no white spots were generated in the solid black image.

I made another 100,000 copies, but the solid density was 1.
It was stable at 30, and no deterioration of soil strength or inversion fog was observed.

Furthermore, the environmental conditions were changed to 32.5°C 185% and 15°C, 1
When it was set to 0%, good images were obtained in both cases at room temperature and humidity.

Example 2 The same procedure as Example 1 was carried out except that silica B was used instead of silica A. The results were good except for the slightly lower concentration in an environment of 32.5°C and 985%. No white spots were observed.

Example 3 The same procedure as Example 1 was carried out except that 80 parts of γ iron oxide was used instead of 80 parts of magnetite. The initial density was 1.42, and the density variation up to 100,000 sheets was as small as ±0.08, and good images were obtained. Furthermore, even when the environmental conditions were changed, images as good as those obtained at room temperature and humidity were obtained.

Example 4 The same procedure as in Example 1 was carried out except that a polyester resin (Mn about 5000, Mw about 6o, ooo) was used instead of the styrene/butyl acrylate/maleic acid copolymer. As a result, similar to Example 1, a good image was obtained.

Example 5 The same procedure as Example 1 was carried out except that silica E was used instead of silica A. The initial density is high at 1.38, and the density variation up to 10,000 sheets is small at ±0.05, solid black.

There were no white spots.

Comparative Example 1 When image evaluation was performed in Example 1 without using silica, only images with severe roughness and a lot of ground blur were obtained.

Comparative Example 2 The same procedure as in Example 1 was carried out except that silica C was used instead of silica A. This toner had poor fluidity, and although the image density was as high as 1.41, there was a lot of ground blur and many white spots were seen in the evening area.

Comparative Example 3 The same procedure as in Example 1 was carried out except that silica D was used instead of silica A.

Although the concentration level was not noticeable, there were many white spots in the solid area.

The concentration results are summarized in Table 2.

Table 2 Image density 23.5℃, 60% Initial After 10,000 sheets 1.40 1.30 1.38 1.30 1.42 1.34 1.40 1.35 1.38 1.33 0.68 1 .41 1.42 1.15 1.30 1.25 1.25 1.38 degrees 32.5℃, 85% Initial After 10,000 sheets 1.35 1.33 1.28 1,20 1.40 1. 34 1.31 1.2B 1.37 1.34 1.30 [Effects of the Invention] As explained above, according to the present invention, clear, high-quality images can be obtained over a long period of time.

Claims (3)

[Claims] (1) A negatively chargeable toner containing surface-treated silica obtained by dispersing fine silica powder using a high-speed jet stream and simultaneously bringing it into contact with a processing agent. (2) The water wettability of the surface-treated silica is 80% or more,
The negatively chargeable toner according to claim 1, wherein the water wettability after re-disintegration is 50% or more. (3) The negatively chargeable toner according to claim 1, wherein the processing agent is silicone oil.