JP2866088B2 - Developer for developing electrostatic images - Google Patents

Description

Description of the Related Art [0002] The present invention relates to an electrostatic image containing a positively chargeable magnetic toner for visualizing an electrostatic latent image in an image forming method such as electrophotography and electrostatic recording. The present invention relates to a developer for development.

[Background Art] In recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, the applications thereof have been diversified, and the requirements for image quality have become strict. 2. Description of the Related Art In copying images such as ordinary documents and books, it is required to reproduce extremely fine and faithfully, even in fine characters, without being crushed or cut off. In particular, when the latent image on the photoreceptor of the image forming apparatus is a line image of 100 μm or less, thin line reproducibility is generally poor, and the line image is not yet sufficiently sharp. Recently, in an image forming apparatus such as an electrophotographic printer using a digital image signal, a latent image is formed by collecting dots of a constant potential, and a solid portion,
The halftone portion and the light portion are expressed by changing the dot density. However, in a state where the toner particles do not adhere to the dots and the toner particles protrude from the dots, it is not possible to obtain the gradation of the toner image corresponding to the dot density ratio of the black portion and the white portion of the digital latent image. There is a problem. Further, when the resolution is improved by reducing the dot size in order to improve the image quality, the reproducibility of a latent image formed from minute dots becomes more difficult, and the resolution and gradation are poor. Images tend to be poor.

Although the image quality is good at the beginning, the image quality may deteriorate while copying or printing out is continued. It is considered that this phenomenon is caused by the fact that only toner particles which are easily developed during the copy or printout are consumed first, and the toner particles having poor developability accumulate and remain in the developing machine.

Heretofore, some developers have been proposed for the purpose of improving image quality. JP-A-51-3244 proposes a non-magnetic toner intended to improve image quality by regulating the particle size distribution. In the toner, 8 to
The toner mainly has a particle diameter of 12 μm, and is relatively coarse. With this particle diameter, it is difficult for the present inventors to closely “glue” the latent image, and the particle diameter of 5 μm or less is 30 μm.
From the characteristic that the particle size distribution is not more than 5% by number when the particle size is 20% or more, the particle size distribution is also broad, which tends to lower the uniformity.

Further, Japanese Patent Application Laid-Open No. 54-72054 proposes a non-magnetic toner having a sharper distribution than the former,
The size of particles having an intermediate weight is as coarse as 8.5 to 11.0 μm, and there is still room for improvement as a high-resolution toner.

In Japanese Patent Application Laid-Open No. 58-1229437, the average particle size is 6 to 10 μm.
Non-magnetic toners having the largest number of particles of 5 to 8 μm have been proposed, but the number of particles of 5 μm or less is as small as 15% by number or less, and an image lacking in sharpness tends to be formed.

Also, in U.S. Pat.No. 4,299,900, 20-35 μm
A jumping development method using a developer having 10 to 50% by weight of a magnetic toner has been proposed. In other words, the toner particle size suitable for frictionally charging the magnetic toner, uniformly and thinly applying the toner layer on the sleeve, and further improving the environmental resistance of the developer has been devised. However, considering stricter requirements such as fine line reproducibility and resolution, it is not sufficient, and further improvement is required. The present inventors have found that the problem is that long spikes (toner particle chains) and disordered spikes of the magnetic toner are present on the sleeve surface in the development area.

According to the study of the present inventors, it has been found that toner particles having a size of 5 μm or less clearly reproduce the outline of the latent image and have a main function of dense toner adhesion on the entire latent image. In particular, in the electrostatic latent image on the photoreceptor, due to the concentration of lines of electric force, the contour edge portion has a higher electric field strength than the inside, and the sharpness of the image quality is determined by the quality of the toner particles collected in this portion. According to the study of the present inventors, it has been found that the amount of particles of 5 μm or less is effective in solving the problem of sharpness of image quality.

On the other hand, in a conventional dry developer, an appropriate charge amount is stably held on the toner particle surface between toner particles, between a toner and a carrier, and between a toner and a sleeve. It is known that silica fine powder is added to a developer in order to prevent contamination of a carrier or the like and further increase transfer efficiency. As the silica fine powder, it is ideal to use a silica fine powder having the same polarity as the chargeability of the toner particles in order to prevent image quality deterioration such as background fog and reverse fog.

However, when a magnetic toner having a small toner particle size as described above is used as a developer, the charge amount per toner particle is large because the unit surface area per unit weight of the toner particle is large. When a silica fine powder exhibiting the above-mentioned chargeability is added, the toner particles become excessively charged, especially during long-term use under high temperature and low humidity, causing problems such as a decrease in image density, roughness, and scattering.

[Problems to be Solved by the Invention] An object of the present invention is to provide a developer which has solved the above-mentioned problems.

An object of the present invention is to provide an appropriate and stable charge controllability over a long period of time, especially under high temperature and low humidity, and high image density.
An object of the present invention is to provide a developer excellent in fine line reproducibility and gradation.

A further object of the present invention is to provide a developer having excellent transferability.

Another object of the present invention is to provide a developer capable of obtaining a high image density with a small consumption.

It is a further object of the present invention to provide a developer having a small change in performance against environmental changes.

[Means and Actions for Solving the Problems] Specifically, the present invention relates to an electrostatic image developing method comprising a positively chargeable magnetic toner containing at least 65 to 110 parts by weight of a magnetic powder per 100 parts by weight of a binder resin. 15 to 50% by number of the positively chargeable magnetic toner particles having a particle diameter of 5 μm or less, and 1 to 50% by number of the positively chargeable magnetic toner particles having a particle diameter of 8 to 12.7 μm. 0.5% by volume or less of positively-chargeable magnetic toner particles having a particle size of 16 μm or more and a volume average particle diameter of 4 to
A positively-chargeable magnetic toner, which has a particle size distribution of 9 μm, and wherein the developer is surface-treated with a silicone oil having a nitrogen atom in a side chain as an external additive;
0.1 to 5 parts by weight per 100 parts by weight, Negatively-chargeable silica fine powder having a functional group is converted into a positively-chargeable magnetic toner
A developer for developing an electrostatic charge image, comprising 0.05 to 4 parts by weight based on 100 parts by weight, wherein the externally added amount of the negatively chargeable silica fine powder is smaller than the externally added amount of the positively chargeable silica fine powder. About.

The magnetic toner of the present invention having the above particle size distribution can be faithfully reproduced up to the fine lines of the latent image formed on the photoreceptor, and can reproduce dot latent images such as halftone dots and digital images. Gives an image which is excellent in gradation and resolution. Furthermore, high image quality can be maintained even when copying or printing out is continued, and even in the case of high-density images, good development can be performed with less toner consumption than conventional magnetic toners. In addition, there is an advantage in downsizing the copying machine or the printer body.

The reason why such an effect is obtained in the magnetic toner of the present invention is not necessarily clear, but is presumed as follows.

That is, in the magnetic toner of the present invention, 5 μm
One feature is that the magnetic toner particles having the following particle diameters are 15 to 50% by number. Conventionally, magnetic toner
m or less, the charge amount is difficult to control, the fluidity of the magnetic toner is impaired, the toner is scattered, and as a component that stains the machine, and further, as a component that causes image fogging, It was considered necessary to reduce.

However, studies by the present inventors have revealed that magnetic toner particles having a size of 5 μm or less are essential components for forming high-quality images.

For example, using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm, the surface potential on the photoreceptor is changed, and from a large development potential contrast in which a large number of toner particles are easily developed, to a halftone, and further, a very small amount. A latent image with a changed surface potential on the photoreceptor was developed to a small development potential contrast where only toner particles were developed, and the developed toner particles on the photoreceptor were collected. The toner particle size distribution was measured. It has been found that there are many magnetic toner particles, especially magnetic toner particles of 5 μm or less. That is, when magnetic toner particles having a particle size of 5 μm or less, which are most suitable for development, are smoothly supplied to the development of the latent image on the photoreceptor, the toner is faithful to the latent image and does not protrude from the latent image, and is truly reproducible. And excellent images can be obtained.

Further, in the magnetic toner of the present invention, 8 to 12.7 μm
One feature is that the number of particles in the range of m is 1 to 33% by number. This is related to the need for the presence of magnetic toner particles having a particle size of 5 μm or less, as described above. The magnetic toner particles having a particle size of 5 μm or less strictly cover the latent image and have an ability to faithfully reproduce the latent image. However, in the latent image itself, the electric field strength of the peripheral edge portion is higher than that of the central portion, and therefore,
In the latent image, the toner particles may be thinner than the edge portion, and the image density may appear light. In particular, magnetic toner particles of 5 μm or less have a strong tendency. However, the present inventors have solved this problem and found that the toner particles can be further sharpened by containing 1% to 33% by number of toner particles in the range of 8 to 12.7 μm. That is, it is considered that the toner particles having a particle size in the range of 8 to 12.7 μm have a moderately controlled charge amount with respect to the magnetic toner particles having a particle size of 5 μm or less. Supplied to the inside with low intensity, the small amount of toner particles on the inside with respect to the edge part is compensated, and a uniform developed image is formed. As a result, sharpness with high density and excellent resolution and gradation is obtained. The image is provided.

For magnetic toner particles having a particle size of 16 μm or more, the content is preferably 0.5% by volume or less, and is preferably as small as possible.

By a completely different idea from the conventional viewpoint, the magnetic toner in the present invention can solve the conventional problems and can withstand recent severe demands for high image quality.

 The configuration of the present invention will be described in more detail.

Magnetic toner particles having a particle size of 5 μm or less have a total particle number of 12 to
It is preferably 60% by number, preferably 15 to 50% by number, and more preferably 20 to 50% by number. When the number of magnetic toner particles having a particle size of 5 μm or less is less than 12% by number, the amount of magnetic toner particles effective for high image quality is small. In particular, as the toner is used by continuing copy or printout, the effective magnetic toner particles are effective. The amount of the component decreases, the balance of the particle size distribution of the magnetic toner as shown in the present invention is deteriorated, and the image quality gradually decreases. If the content exceeds 60% by number, the magnetic toner particles tend to aggregate with each other,
Since the toner mass is larger than the original particle size, the image quality becomes rough, the resolution is reduced, or the density difference between the edge portion and the inside of the latent image is increased, and the image tends to be slightly hollow.

And, as described above, magnetic toner particles of 5 μm or less
When the content is 15 to 50% by number, more preferably 20 to 50% by number, even if copying or printing is continued, the particle size distribution of the magnetic toner does not deteriorate, the image quality does not decrease, and the resolution does not decrease. The density difference between the edge portion and the inside of the latent image becomes smaller.

The particle size in the range of 8 to 12.7 μm is preferably 1 to 33% by number, and more preferably 8 to 28% by number. If the content is more than 33% by number, the image quality is deteriorated and the development is performed more than necessary, that is, the toner is excessively applied, which leads to an increase in toner consumption. On the other hand, if it is less than 1% by number, it becomes difficult to obtain a high image density.

The content of magnetic toner particles having a particle size of 16 μm or more is preferably 2.0% by volume or less, more preferably 0.5% by volume or less. When the content is more than 2.0% by volume, not only does it hinder the reproduction of fine lines, but also in the transfer, coarse toner particles of 16 μm or more protrude from the thin layer surface of the toner particles developed on the photoreceptor. The delicate state of contact between the photoreceptor and the transfer paper via the layer is irregular,
This causes fluctuations in the transfer conditions, and causes a transfer failure image. As described above, when the content of the magnetic toner particles having a particle diameter of 16 μm or more is 0.5% by volume or less, a change in transfer conditions is small, and a transfer failure image is less likely to occur. The volume average diameter of the magnetic toner is 4 to 9 μm, and this value cannot be considered separately from the above-described components. When the volume average particle diameter is less than 4 μm, in applications having a high image area ratio such as a graphic image, there is a problem that the amount of applied toner on transfer paper is small and the image density is low. This is considered to be due to the same reason as described above for lowering the density inside the edge portion of the latent image. If the volume average particle diameter is 10 μm or more, the resolution is not good, and if the use is continued at the beginning of copying, the image quality tends to deteriorate.

Although the particle size distribution of the toner can be measured by various methods, in the present invention, the measurement was performed using a Coulter counter.

In other words, the Coulter Counter TA is used as a measuring device.
Using type II (manufactured by Coulter), connected to an interface (manufactured by Nikkaki) that outputs the number distribution and volume distribution and a CX-1 personal computer (manufactured by Canon), the electrolyte was 1% using primary grade sodium chloride. Prepare an aqueous NaCl solution. As a measuring method, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the aqueous electrolytic solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte in which the sample was suspended was treated with an ultrasonic
Perform a dispersion treatment for minutes, using the Coulter Counter TAII, using a 100μ aperture as an aperture,
The particle size distribution of the particles of 2 to 40 μ was measured on the basis of the number, and the values according to the present invention were determined therefrom.

Further, as a result of extensive studies by the present inventors, silica fine powder having the same polarity as the chargeability of the toner particles was added to the magnetic toner, and at the same time, the toner particles were weighed less than the silica fine powder. The use of a developer to which silica fine powder having a chargeability opposite to that of the toner is added does not cause deterioration of image quality such as background fog and reversal fog,
Even when a large number of copies are made, it has been found that the toner layer on the toner carrier in the developing unit maintains an appropriate and stable charge amount and has an effect of preventing a decrease in image density, roughness, scattering and the like.

In the present invention, the charge amount of the toner layer on the toner carrier in the developing device means the charge amount of the toner layer per unit area on the toner carrier.

In the present invention, the following measuring methods charge amount Q / S measured by (n / cm ²⁾ is provided for in the good 3~11nc / cm ^2, more preferably, 5~10nc / cm ² is good.

When Q / S> 11 (nc / cm ² ), the toner is excessively charged, and the image density is easily reduced, and the image is apt to be rough and scattered.

In the present invention, the charge amount of the toner layer per unit area on the carrier was determined by using a suction Faraday cage method.
In this suction type Faraday cage method, the outer cylinder is pressed against the toner carrier to suck all the toner on a certain area on the carrier, and is electrostatically shielded from the outside when collecting the toner in the filter of the inner cylinder. In this method, the amount of charge per unit area on the toner carrier can be determined by measuring the amount of charge accumulated in the inner cylinder.

As the positively chargeable silica fine powder in the present invention, a silica fine powder produced by a dry method or a wet method and surface-treated so as to exhibit positive chargeability can be used. Alternatively, silica fine powder produced by a wet method may be used in an untreated state as it is or a surface treated so as not to impair the negative charging property.

The dry method referred to here is a method for producing silica fine powder generated by vapor phase oxidation of a silicon halide.
For example, in a method utilizing the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen-hydrogen, the basic reaction formula is as follows.

SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl In this manufacturing process, for example, another metal halide such as aluminum chloride or titanium chloride is used together with a silicon halide to produce a composite fine powder of silica and another metal oxide. It is also possible to obtain and include them.

Examples of commercially available fine silica powder produced by vapor phase oxidation of a silicon halide used in the present invention include, for example, those commercially available under the following trade names.

AEROSIL 130 (Nippon Aerosil) 200 300 380 OX50 TT600 MOX80 MOX170 COK84 Ca-O-SiL (Ca-O-Jill) M-5 (CABOTO (Cabot) Co.) MS-7 MS-75 HS- 5 EH-5 Wacker HDK N20 V-15 (WACKER-CHEMIE (Wacker Kemi) GMBH) N-20E T-30 T-40 D-C Fine Silica (fine silica) (Dow Corning Co.) Fransol (Fransol) (Frandil) On the other hand, as a method for producing the silica fine powder used in the present invention by a wet method, various conventionally known methods can be applied. For example, the decomposition of sodium silicate with an acid is represented by the following general reaction formula.

Na ₂ O ・ XSiO ₂ + HCl + H ₂ O → SiO ₂・ nH ₂ O + NaCl In addition, decomposition of sodium silicate with ammonium salts or alkali salts, formation of alkaline earth metal silicate from sodium silicate, and decomposition with acid Silicate, a method in which a sodium silicate solution is converted into silicate using an ion exchange resin, a method in which natural silicate or silicate is used, and the like.

Silica such as anhydrous silicon dioxide (silica) and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate and zinc silicate can be applied to the silica fine powder here.

Commercially available fine silica powder synthesized by the wet method includes, for example, those commercially available under the following trade names.

Carplex Shionogi Pharmaceutical Niepsil Nippon Silica Tokusil, Fine Seal Tokuyama Soda Vita Seal Takigi Hito Shilton, Shirunex Mizusawa Chemical Starsil Kamijima Chemical Himejir Ehime Pharmaceutical Syroid Fuji Debison Chemical Hi-Sil Pittsburgh Plate Glass.Co. Durosil Ultorasil Fiillstoff-Gesells chaft Marquart Manosil Hardman and Holden Hoesch Chemische Fabrik Hoesch K-G Hesh) Sil-Stone (Seal Stone) Stoner Rubber Co. (Stonener Rubber) Nalco (Nalco) Nalco Chem. Co. (Nalco Chemical) Quso (Kuso) Philadelphia Quartz Co. ( Philadelphia Quartz) Imsil Illinois Minerals Co. Fortafil Imperial Chemical Industries.Ltd. (Imperial Chemical Industries) Microcal Joseph Crosfiels & Sons.Ltd. (Joseph Crossfield and Sands) Minosil (Manosir) Hardman and Holden (Vulkasil) Vulkasil Farbenfabriken Bryer.A.-G. Tufknit Durham Chemicals.Ltd. Sirmos Shiroishi Kogyo Star Trek S Kamishima Chemical Fricosyl Multi-wood fertilizer Of the above silica fine powders, those with a specific surface area of 30 m ² / g or more (particularly 50 to 400 m ² / g) measured by nitrogen adsorption by the BET method give good results. give.

As a specific method of obtaining a positively chargeable silica fine powder,
In the present invention, the above-mentioned untreated silica fine powder is treated with a silicone oil having an organo group having at least one nitrogen atom in a side chain.

In the present invention, the positively chargeable silica refers to a silica having a positive triboelectric charge with respect to an iron powder carrier when measured by a blow-off method.

As the silicone oil having a nitrogen atom in the side chain used for treating the silica fine powder, a silicone oil having at least a partial structure represented by the following formula can be used.

(Wherein, R ₁ represents hydrogen, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, R ₃ and R ₄ represents hydrogen, an alkyl group, or aryl group, R ₅ Represents a nitrogen-containing hetero environment.) The above alkyl group, aryl group, alkylene group, and phenylene group may have an organo group having a nitrogen atom, and substituents such as halogen may be used as long as chargeability is not impaired. May be provided.

In the present invention, the negatively chargeable silica refers to a silica having a negative tribocharge with respect to an iron powder carrier when measured by a blow-off method.

As a method for obtaining a negatively chargeable silica fine powder having a group,
The silica fine powder may be treated with vinyltriethoxysilane or vinyltrimethoxysilane.

The application amounts of these positively chargeable silica fine powder and negatively chargeable silica fine powder are as follows. 0.1 to 5 parts of the positively chargeable silica fine powder per 100 parts by weight of the positively chargeable magnetic toner
Parts by weight, and the negatively chargeable silica fine powder added simultaneously,
0.05 to 4 within the range not exceeding the weight of the positively chargeable silica fine powder
Parts by weight.

As the binder resin used in the magnetic toner of the present invention, when a heating and pressing roller fixing device having an oil application device is used, the following binder resins for toner can be used.

For example, polystyrene, poly-p-chlorostyrene,
Styrene such as polyvinyltoluene and its substituted homopolymer; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic acid ester copolymer, styrene -Α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-
Styrene such as vinyl ethyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer Copolymers: polyvinyl chloride, phenolic resin, natural modified phenolic resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin , Xylene resin, polyvinyl butyral, terpene resin, cumarone indene resin, petroleum resin and the like can be used.

In the heat and pressure roller fixing method in which almost no oil is applied, the so-called offset phenomenon in which a part of the toner image on the toner image support member is transferred to the roller, and the adhesion of the toner to the toner image support member are important issues. is there. Toners that fix with less heat energy tend to block or cake during storage or in a developing unit, and these problems must also be considered at the same time. The physical properties of the binder resin in the toner are most greatly involved in these phenomena. However, according to the study of the present inventors, when the content of the magnetic substance in the toner is reduced, the toner image supporting member is fixed at the time of fixing. Although the adhesiveness of the toner to the toner is improved, offset tends to occur, and blocking or caking tends to occur. Therefore, in the present invention, when using the heating / pressing roller fixing method in which almost no oil is applied, the selection of the binder resin is more important. Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of comonomers for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacryl. Monocarboxylic acid having a double bond such as acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate Dicarboxylic acids having double bonds, such as methyl, methyl maleate, dimethyl maleate, and the like; and vinyl chloride, vinyl acetate,
Vinyl esters such as vinyl benzoate; ethylene olefins such as ethylene, propylene, butylene; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl methyl ether, vinyl ethyl ether; Vinyl monomers such as vinyl isobutyl ether and the like; alone or two or more vinyl monomers are used.

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, for example, an aromatic divinyl compound such as divinylbenzene, divinylnaphthalene, or the like; for example, ethylene glycol diacrylate, ethylene glycol diacrylate, or the like. Double bonds such as methacrylate, 1,3-butanediol dimethacrylate
Carboxylic acid esters; divinyl compounds such as divinylaniline, divinylether, divinylsulfide, and divinylsulfone; and compounds having three or more vinyl groups are used alone or as a mixture.

When the pressure fixing method is used, a binder resin for a pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Coalescent, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin and the like.

In the magnetic toner according to the present invention, a charge control agent is blended with toner particles (internal addition) or mixed with toner particles (external addition).
It is preferable to use them. The charge control agent makes it possible to control the amount of charge optimally according to the development system. In particular, in the present invention, the balance between the particle size distribution and the charge can be further stabilized.

Examples of positive charge control agents include denatured products such as nigrosine and fatty acid metal salts;
Quaternary ammonium salts such as -hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate; diorganotin oxides such as dibutyltin oxide, dioctyltin oxide and dicyclohexyltin oxide: dibutyltin borate, dioctyltin borate and dicyclohexyltin boat These diorganotin borates can be used alone or in combination of two or more. Of these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

Also, the general formula R ₁ : H, CH ₃ R ₂ , R ₃ : a substituted or unsubstituted alkyl group (preferably
A homopolymer of a monomer represented by C _{1 to} C ₄ ): or a copolymer with a polymerizable monomer such as styrene, acrylate or methacrylate as described above can be used as a positive charge control agent. In this case, these charge control agents also function as (all or part of) the binder resin.

The above-mentioned charge control agent (having no action as a binder resin) is preferably used in the form of fine particles. In this case, the number average particle size of the charge control agent is specifically preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the toner, such a charge control agent is preferably used in an amount of 0.1 to 20 parts by weight (more preferably 0.2 to 10 parts by weight) based on 100 parts by weight of the binder resin.

Various additives may be added to the magnetic toner of the present invention internally or externally as necessary. As the colorant, conventionally known dyes and pigments can be used, and usually 0.5 to 20 parts by weight per 100 parts by weight of the binder resin may be used. Other additives include lubricants such as, for example, zinc stearate, abrasives such as cerium oxide and silicon carbide, or fluidity-imparting agents such as colloidal silica and aluminum oxide, anti-caking agents, or carbon black, tin oxide, for example. And the like.

Further, in order to improve the releasability at the time of fixing with a hot roll, a wax-like substance such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sazol wax, paraffin wax, etc. is used.
The addition of about 5% by weight to the magnetic toner is also a preferred embodiment of the present invention.

Further, the magnetic toner in the present invention may also serve as a colorant, but contains a magnetic material. The magnetic material contained in the magnetic toner of the present invention includes magnetite, γ-
Iron oxides such as iron oxide, ferrite, and iron-rich ferrite;
Metals such as iron, cobalt, nickel or these metals and aluminum, cobalt, copper, lead, magnesium,
Examples include alloys with metals such as 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 1 μm, preferably about 0.1 to 0.5 μm. The amount contained in the magnetic toner is 60 to 120 parts by weight per 100 parts by weight of the resin component.
It is 65 to 100 parts by weight, preferably 100 parts by weight of the resin component.

To prepare the positively chargeable magnetic toner used in the present invention, a magnetic powder, a vinyl-based or non-vinyl-based thermoplastic resin, a pigment or dye as a colorant, a charge control agent, and other additives are used as necessary. After thoroughly mixing with a mixer such as a ball mill, using a hot kneader such as a heating roll, a kneader, or an extruder, disperse or disperse the pigment or dye in the resin that has been melted, kneaded, and kneaded to make the resins compatible with each other. After dissolving, solidifying by cooling, and then crushing and strict classification, the magnetic toner according to the present invention can be obtained.

Further, in the magnetic toner of the present invention, fine particles of a fluorine-containing polymer may be internally added or externally mixed. Examples of the fine particles of the fluorine-containing polymer include fine powders of, for example, polytetrafluoroethylene, polyvinylidene fluoride, and the like, and fine powders of a tetrafluoroethylene-vinylidene fluoride copolymer. It is preferable in terms of abrasiveness. When externally added and mixed, the amount of toner
The amount is preferably 0.01 to 2.0 parts by weight, particularly 0.02 to 1.0 part by weight, and preferably 0.5 to 5 parts by weight, particularly 2 to 4 parts by weight, when internally added and mixed.

In particular, in the magnetic toner combining the silica fine powder and the fine powder, the reason is not clear, but stabilizes the state of silica attached to the toner, for example, the attached silica is released from the toner, The effect on toner abrasion and sleeve fouling does not decrease, and the charging stability can be further increased.

[Examples] Hereinafter, the method of the present invention will be specifically described based on examples. However, this does not limit the embodiment of the present invention at all. The names of the examples are parts by weight.

Example 1 100 parts by weight of styrene / butyl acrylate / divinylbenzene copolymer (copolymerization weight ratio: 80 / 19.5 / 0.5, weight average molecular weight: 320,000) Iron trioxide (average particle diameter: 0.2 μm) 80 parts by weight Nigrosine ( 4 parts by weight Low-molecular-weight propylene-ethylene copolymer 4 parts by weight After the above materials were mixed well in a blender, they were kneaded with a biaxial kneading extruder set at 150 ° C. The obtained kneaded material was cooled, coarsely pulverized by a cutter mill, and then finely pulverized using a fine pulverizer using a jet stream, and the obtained finely pulverized powder was classified by a fixed wall type air classifier. A classified powder was produced. Further, the obtained classified powder is strictly classified and removed at the same time by a multi-division classifier utilizing a Coanda effect (an elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) to remove the ultrafine powder and the coarse powder at the same time.
0 μm black fine powder (magnetic toner) was obtained.

Table 1 shows data obtained by measuring the magnetic toner as a positively-charged black fine powder using a Coulter Counter TAII having an aperture of 100 μ as described above.

On the other hand, the temperature was raised to about 250 ° C. while stirring 100 parts by weight of silica fine powder (trade name, Aloesil # 130, specific surface area: about 130 m ² / g, manufactured by Aloesil Co.) synthesized by a dry method as positively chargeable silica fine powder. Silicone oil with amine in the side chain while holding (viscosity 70 cps at 25 ° C, amine equivalent 83
0) 20 parts by weight were sprayed and treated for 10 minutes to prepare positively chargeable silica fine powder A.

While stirring 100 parts by weight of negatively chargeable silica fine powder (Aloesil # 200 synthesized by a dry method, specific surface area of about 200 m ² / g manufactured by Aloesil Co., Ltd.), the temperature was maintained at about 70 ° C., and vinyltriethoxysilane was added. An alcohol diluted solution prepared so as to have a treatment amount of part by weight was added dropwise. The obtained fine powder
Dry at 120 ° C, A negatively chargeable silica fine powder B having a group was prepared. Further, 0.6 parts by weight of positively chargeable silica fine powder A and 0.2 parts by weight of negatively chargeable silica fine powder B were added to 100 parts by weight of the obtained magnetic toner, which is a black fine powder having positive charge, and mixed with a Henschel mixer.
Developer A was used.

The particle size distribution of the developer A was as shown in Table 2. In a high-temperature and low-humidity environment of 30 ° C. and 5% RH, developer A is charged into a commercially available electrophotographic copying machine NP3525 (manufactured by Canon Inc.), and the initial image and the durable image after 5,000 continuous image output tests Generated. Further, the developing device was removed at the initial stage and after 5,000 image output operations, and the charge amount of the toner layer per unit area on the toner carrier was measured.

 Table 3 shows the results.

As is apparent from Table 3, the magnetic toner of the present invention has excellent image density in both the line portion and the large area portion of characters and the like, and has excellent reproducibility and resolution of fine lines. , Maintaining the good image quality at the beginning. Also, the per copy cost was small and the economy was excellent.

The initial and charge amount of the toner layer per unit area on the toner carrying member in the developing device after 5,000 times of image formation tests each 7.5nc / cm ^2, a 8.3nc / cm ^2, while durable Judging from good images at the initial stage and after 5,000 image outputs, it was confirmed that the developer always maintained a proper and stable charge amount, with little increase in charge amount.

Examples 2 to 6 and Reference Examples In the same manner as in Example 1, developers BG having various particle size distributions shown in Table 2 were prepared.

When the same evaluation as in Example 1 was performed using the developing agents B to G, as shown in Table 3, in each case, both the initial image and the 5,000-sheet endurance image stably had a high image density and a clear high image. An image of high quality was obtained, and the increase in the charge amount of the toner layer after running was small and good.

Comparative Example 1 In the same manner as in Example 1, a developer H having a particle size distribution shown in Table 2 was prepared. In the developer H, the volume% of the magnetic toner particles having a particle diameter of 16 μm or more, the number% of the magnetic toner particles having a particle diameter of 8 to 12.7 μm, and the volume average particle diameter of the magnetic toner are all defined in the present invention. And the particle size distribution of the magnetic toner of the present invention is not satisfied. Table 3 shows the results of evaluation using this developer H in the same manner as in Example 1.

The thin line sometimes causes stains which are considered to be caused by agglomerates of toner particles, and the resolution is 4.5 lines / mm. The concentration was low, and it was slightly hollow. Spot-like fog stains also occurred. In addition, image quality was further deteriorated by repeating copying.

Comparative Example 2 Evaluation was performed in the same manner as in Example 1 except that the magnetic toner I shown in Table 2 was used instead of the magnetic toner used in Example 1. The results are shown in Table 3.

Comparative Example 3 Evaluation was performed in the same manner as in Example 1 except that the magnetic toner J shown in Table 2 was used instead of the magnetic toner used in Example 1.

In the development on the drum, although there was some disturbance, the image quality was relatively good, but the transfer was significantly disturbed, and the density was reduced due to poor transfer. In particular, when copying is repeated, defective toner particles remain in the developing machine.
Due to the accumulation, the lowering of the density and the poor image quality were further exacerbated.

Comparative Example 4 Evaluation was performed in the same manner as in Example 1 except that the magnetic toner K shown in Table 2 was used instead of the magnetic toner used in Example 1.

Since the image density was low and the amount of toner on the image edge portion was poor, the outline was unclear and the image lacked sharpness. The resolution and gradation were poor.

Further, by performing the repetitive copying, sharpness, fine line reproducibility, and resolution were further deteriorated.

Comparative Example 5 Evaluation was performed in the same manner as in Example 1 except that the magnetic toner L shown in Table 2 was used instead of the magnetic toner used in Example 1.

As a result, image density, resolution, and fine line reproducibility were all poor. Observation of the toner spike on the sleeve, which is the toner carrier in the developing machine, is long and sparse. Even if it flies over the photoreceptor, the spike is too long, so that the tail of the toner protruding from the latent image The density was low due to the pulling state, the toner scattering state, and the coarseness of the toner particles.

Comparative Example 6 A developer M was prepared in the same manner as in Example 1 except that the negatively chargeable silica fine powder B was omitted. Developer M
The same evaluation as in Example 1 was performed using
As shown in the table, the initial image was good, but in the durable image after the 5,000-time image output test, a decrease in image density and roughness of the halftone portion were observed. Also, the initial and 50
Comparing the charge amount of the toner layer on the toner carrier after the endurance image of 00 sheets, the charge amount was clearly increased after the endurance, and it was recognized that the developer was excessively charged.

Comparative Examples 7 and 8 Same as Example 1 except that the negatively chargeable silica fine powder B was omitted in each of Example 7 and Comparative Example 1, except that developer N and developer O were used, respectively. As shown in Table 3, in all cases, 50
After the durability of 00 sheets, a decrease in the image density and roughness of the halftone portion were observed, and the charge amount of the toner layer on the toner carrier greatly increased after the durability, and excessive charging of the developer was observed.

[Effects of the Invention] As described above in detail, when the developer of the present invention is used, a high-quality image with clear fine lines can be obtained for a long time,
Very useful.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoshi Yoshida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-62-245267 (JP, A) JP-A-58 -117553 (JP, A) JP-A-61-20053 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/083

Claims (3)

(57) [Claims] 1. A developer for developing an electrostatic image having a positively chargeable magnetic toner containing at least 65 to 110 parts by weight of a magnetic powder per 100 parts by weight of a binder resin, wherein the positively chargeable magnetic toner has a particle size of 5 μm or less. 15 positively chargeable magnetic toner particles
1 to 33% by number of positively-chargeable magnetic toner particles having a particle diameter of 8 to 12.7 μm, and 0.5% by volume or less of positively-chargeable magnetic toner particles having a particle diameter of 16 μm or more. The chargeable magnetic toner exhibits a particle size distribution in which the volume average particle diameter is 4 to 9 μm, and the developer is a positively chargeable silica fine powder surface-treated with a silicone oil having a nitrogen atom in a side chain as an external additive. 0.1 to 5 parts by weight based on 100 parts by weight of the positively chargeable magnetic toner, Negatively-chargeable silica fine powder having a functional group is converted into a positively-chargeable magnetic toner
A developer for developing an electrostatic charge image, comprising 0.05 to 4 parts by weight based on 100 parts by weight, wherein the externally added amount of the negatively chargeable silica fine powder is smaller than the externally added amount of the positively chargeable silica fine powder. . 2. The negatively chargeable silica fine powder is obtained by treating the silica fine powder with vinyltriethoxysilane.
The developer for developing an electrostatic image according to the above. 3. The negatively chargeable silica fine powder is obtained by treating the silica fine powder with vinyltrimethoxysilane.
The developer for developing an electrostatic image according to the above.