JP2749867B2 - Negatively chargeable magnetic developer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a negatively chargeable developer for visualizing an electrostatic latent image in an image forming method such as electrophotography and electrostatic recording, and particularly to a high-speed copier. And a negatively chargeable developer suitable for:

(Background technology)

2. Description of the Related Art In recent years, as image forming apparatuses such as electrophotographic copiers have become widespread, their uses have been diversified, and 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 very finely and faithfully without crushing or breaking even fine characters. 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.

Further, recently, with the rapid rationalization of office work, a demand for a high-speed copying machine capable of mass copying in a short time is increasing. As the quality required for high-speed copying machines, high image quality obtained at the beginning of copying is improved even after copying a large number of sheets.
Further, in high-speed copying and large-volume copying, it is desired to improve the scattering resistance of the developer so as not to contaminate a charging wire or the like installed in the copying 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 main component is a toner having a particle size of 12 μm, which is relatively coarse. According to the study of the present inventors, it is difficult to achieve “density” on a latent image with a particle size of 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. In order to form a clear image using such a coarse toner particle and a toner having a broad particle size distribution, it is necessary to fill the gap between the toner particles by thickly overlapping the toner particles. There is also a problem that it is necessary to increase the image density, and the amount of toner consumption required to obtain a predetermined image density increases.

Also, 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.

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 to the entire latent image. In particular, in the electrostatic latent image on the photoreceptor, due to the concentration of lines of electric force, the contoured edge portion has a higher electric field intensity 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.

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 reproducibility of fine lines and resolution, it is not sufficient, and further improvements are required.

Many additions of a third substance to a toner have been proposed for the purpose of improving various properties of the toner.

Japanese Patent Application Laid-Open No. 60-32060 proposes adding two types of inorganic fine powders having different surface areas to a toner to prevent fusion of the toner to a photoconductor and poor charging of the photoconductor.

Japanese Patent Application Laid-Open No. Sho 54-2130 proposes a toner capable of developing an electrostatic latent image of either positive or negative polarity by using a magnetic toner comprising a coating agent, a magnetic powder, and a ferroelectric substance.
However, in high-speed copiers where the rotation speed of the outer periphery of the sleeve exceeds 400 mm / sec, the use of toner with a fine particle diameter achieves clear images, high image quality and high durability, and further prevents the scattering of inorganic fine powder. However, these proposals are not enough to prevent contamination and prevention by inorganic fine powder such as a charging wire for corona charging, and new technologies are required in the era of high-speed, high-quality copying.

[Object of the invention]

An object of the present invention is to provide a magnetic developer which solves the above problems.

It is a further object of the present invention to provide a magnetic developer having high image density, excellent fine line reproducibility, and excellent gradation.

It is a further object of the present invention to provide a magnetic developer which does not change its performance over a long period of use.

Still another object of the present invention is to apply a magnetic developer which does not contaminate a charged wire even in a large-scale copying by a high-speed copying machine.

[Summary of the Invention]

More specifically, the present invention is applied to a developing method in which the rotation speed of the outer periphery of the developer carrier for developing an electrostatic image carrying the developer on the surface is at least 400 mm / sec. In a negatively-chargeable magnetic developer containing an insulating magnetic toner, the negatively-chargeable insulating magnetic toner contains 17 to 80% by number of magnetic toner particles having a particle size of 5 μm or less, and a particle size of 6.35 to 12.7 μm 5 of magnetic toner particles having
Magnetic toner particles having a particle size of 16 μm or more are contained at 2.0% by volume or less, and the volume average particle diameter of the magnetic toner is 4.5 to 9 μm, and a group of magnetic toner particles having a particle size of 5 μm or less is represented by the following formula: [Wherein N represents the number% of magnetic toner particles having a particle size of 5 μm or less, V represents the volume% of the magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.5 to 6.5. Show. Here, N indicates a positive number of 17 to 80. Having a particle size distribution that satisfies, and a BET specific surface area by nitrogen adsorption of 40 to 400 m ² g inorganic fine powder, and a BET specific surface area of 0.5
A negatively chargeable magnetic developer containing up to 30 m ² / g of ferroelectric substance. Inorganic fine powder further contained in the developer,
The ferroelectric substance has the following formula [Wherein Sw ₁ is the BET specific surface area (m ² / g) of the inorganic fine powder, Sw ₂
Indicates the BET specific surface area (m ² / g) of the ferroelectric substance, W ₁ is the weight (g) of the inorganic fine powder contained in the developer, and W ₂ is the ferroelectric substance contained in the developer. Indicates the weight (g) of the substance. And a negatively chargeable developer for high-speed copying machines that satisfies the following.

The magnetic developer of the present invention can faithfully reproduce even a fine line of a latent image formed on the photoreceptor, and retains high image quality even when copying or printing out, and Even when performing large-volume copying, good development without contamination of the charged wire can be performed.

The reason why such effects are obtained in the magnetic developer of the present invention is not necessarily clear, but is presumed as follows.

That is, in the magnetic developer of the present invention, the magnetic toner contains 17 to 60% by number of magnetic toner particles having a particle size of 5 μm or less.
Is one feature. Conventionally, magnetic toner particles having a particle size of 5 μm or less have difficulty in controlling the charge amount or impair the fluidity of the magnetic toner.
In addition, as a component that scatters toner and soils the machine,
It has been considered that a component that causes image fogging needs to be actively reduced.

However, according to the study of the present inventors, it has been found that magnetic toner particles of 5 μm or less are essential components for forming high-quality image.

For example, using a magnetic toner having a particle size distribution ranging from 1.5 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 image is faithful to the latent image and is truly reproduced without protruding from the latent image. An image with excellent properties can be obtained.

Further, in the magnetic toner of the present invention, 6.35 ~ 12.7μ
One feature is that the number of particles in the range of m is 5 to 50% 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 surrounding edge portion is higher than that of the central portion, and therefore,
The inside of the latent image may have a smaller amount of toner particles 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 found that this problem can be solved and made clearer by including 5 to 50% by number of toner particles in the range of 6.35 to 12.7 μm. That is, toner particles having a particle size in the range of 6.35 to 12.7 μm
It is considered that the toner has a moderately controlled charge amount with respect to the magnetic toner particles having a particle size of m or less. A uniform developed image is formed by compensating for the small amount of particle adhesion, and as a result, a sharp image with high resolution and excellent gradation is provided at a high density.

Further, for particles having a particle size of 5 μm or less, N / V = −0.04N + k between the number% (N) and the volume% (V).
(However, one of the characteristics is that the magnetic toner of the present invention satisfies the relationship of 4.5 ≦ k ≦ 6.5; 17 ≦ N ≦ 80).
FIG. 2 shows this range, and together with other features, the magnetic toner of the present invention having a particle size distribution satisfying this range can achieve excellent developability.

The present inventors have studied the state of the particle size distribution of 5 μm or less and found that there is a state of existence of the fine powder most suitable for achieving the object as shown by the above formula. In other words, for a given value of N, a large N / V means that 5 μm
It indicates that the following particles are widely contained, and N / V
Is small, it is understood that the abundance of particles around 5 μm is high, and that particles having a particle size smaller than 5 μm are small, and the value of N / V is in the range of 1.3 to 5.82; and N is
When the ratio is in the range of 17 to 80 and the above relational expression is further satisfied, good fine line reproducibility and high resolution are achieved.

Further, for magnetic toner particles having a particle size of 16 μm or more, the content is preferably set to 2.0% by volume or less, and as small as possible.

By a completely different idea from the conventional viewpoint, the magnetic toner of 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 17 to
It is preferably 80% by number, preferably 25 to 60% by number, and more preferably 30 to 55% by number. When the number of magnetic toner particles having a particle size of 5 μm or less is less than 17% 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. Ingredients decrease,
As shown in the present invention, the balance of the particle size distribution of the magnetic toner deteriorates, and the image quality gradually decreases. On the other hand, if it exceeds 80% by number, a strong cohesion state between the magnetic toner particles is likely to occur and the toner mass becomes larger than the original particle size, resulting in rough image quality, lowering the resolution, or reducing the latent image edge. The density difference between the part and the inside becomes large, and the image tends to be slightly hollow.

The particle size in the range of 6.35 to 12.7 μm is preferably 5 to 50% by number, and more preferably 15 to 45% by number. If the content is more than 50% 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 5% by number, it becomes difficult to obtain a high image density. Further, there is a relationship of N / V = -0.04N + k between the number% (N%) and the volume% (V%) of the magnetic toner particle group having a particle diameter of 5 μm or less, and 4.5 ≦ k ≦ 6.5.
Indicates a positive number in the range. Preferably, 4.5 ≦ k ≦ 6.0, more preferably 4.5 ≦ k ≦ 5.5. As indicated earlier, 17
≦ N ≦ 80, preferably 25 ≦ N ≦ 60, more preferably 30
≤N≤55.

When k <4.5, the number of magnetic toner particles having a particle diameter smaller than 5.0 μm is small, and the image density, resolution, and sharpness are poor. The appropriate presence of fine magnetic toner particles, which was conventionally considered unnecessary, contributes to the closest packing of the toner in development and contributes to the formation of a uniform image without roughness. In particular, by uniformly filling the fine lines and the contours of the image, the sharpness is further enhanced visually.
That is, when k <4.5, these properties are inferior due to the lack of the particle size distribution component.

From another aspect, in production, it is necessary to cut a large amount of fine powder by classification or the like to satisfy the condition of k <4.5, which is disadvantageous in terms of yield and toner cost.
When k> 6.5, the presence of more fine powder than necessary
As the copying operation is repeated, the image density tends to decrease. Such a phenomenon occurs when excessive fine magnetic toner particles having an unnecessary charge are charged and adhered to the developing sleeve, thereby impeding normal magnetic toner from being carried on the developing sleeve and applying charge. Conceivable.

The content of the magnetic toner particles having a particle diameter of 16 μm or more is preferably 2.0% by volume or less, more preferably 1.0% 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 made irregular, causing fluctuations in the transfer conditions and causing poor transfer images. The volume average diameter of the magnetic toner is 4.5 to 9 μm, preferably 5 to 8.5 μm, and this value cannot be considered separately from the above-mentioned components. If the volume average particle diameter is less than 4.5 μm, in applications having a high image area ratio such as a graphic image, there is a problem that the amount of toner deposited on the 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 9 μm or more, the resolution is not good, and if the use is continued at the beginning of copying, the image quality is likely 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.

That is, as a measuring device, a Coulter counter is used.
Interface (manufactured by Nikkaki) and CX-1 that output the number distribution and volume distribution using TA-II type (manufactured by Coulter)
A personal computer (manufactured by Canon Inc.) is connected, and a 1% aqueous solution of NaCl is prepared using primary-grade sodium chloride as an electrolytic solution. As a measuring method, a surfactant as a dispersant, preferably 0.1 to 5 ml of an alkylbenzene sulfonate is added to the electric field aqueous solution of 100 to 150 ml, and a measurement sample of 2 to 20 mg is further added.
Add. The electrolyte in which the sample is suspended is
Disperse for 3 minutes, and use the Coulter Counter TA I
Using a type I, a particle size distribution of particles of 2 to 40 μ was measured on the basis of the number by using a 100 μ aperture as an aperture, and then a value according to the present invention was obtained.

On the other hand, the magnetic toner having a particle size used in the present invention has a higher charge amount and tends to aggregate more than conventionally known magnetic toners having a volume average particle size of 9 μm or more, and the smaller the particle size, the larger the surface area. The addition of a fluidizing agent is essential, and by using an inorganic fine powder having a BET specific surface area of 40 to 400 m ² / g by nitrogen adsorption used in the present invention, the fluidity is improved and the charge amount of the magnetic toner is further reduced. This has the effect of adjusting and improving the image quality of the copied image.

Here, if the BET specific surface area of the inorganic fine powder is less than 40 m ² / g, the fluidity of the entire toner deteriorates regardless of the added amount, and it is impossible to form a uniform toner layer on the entire sleeve. Become. On the other hand, if the BET specific surface area is greater than 400 m ² / g, the inorganic fine particles aggregate to form large secondary aggregated particles, making it impossible to maintain a good charge amount of the toner.

On the other hand, by adding a high dielectric substance having a BET specific surface area of 0.5 to 30 m ² / g, contamination of the charged wire by the inorganic fine particles is not observed, and the copied image is not deteriorated by mass copying. The mechanism by which this effect is obtained can be considered as follows. When mass copying is performed by a high-speed copying machine, the inorganic fine powder attached to the toner surface is gradually released from the toner surface due to the high-speed rotation of the sleeve for a long time. On the other hand, the high dielectric substance exists in a polarized state near the toner and is attracted by the ferroelectric substance before the released inorganic fine powder scatters inside the copying machine,
It is considered that the inorganic fine powder is adsorbed on the surface of the ferroelectric substance to prevent contamination of the charged wire.

Here, when the BET specific surface area of the ferroelectric particles is smaller than 0.5 m ² / g, the image obtained by copying is noticeably rough, while when the BET specific surface area is larger than 30 m ² / g, the ferroelectric particles together with the inorganic fine particles are used. Body material scatters into the copier, contaminating the charged wires.

The inorganic fine powder and the ferroelectric substance used in the present invention are represented by the following formula: [Wherein Sw ₁ is the BET specific surface area (m ² / g) of the inorganic fine powder, Sw ₂
Indicates the BET specific surface area (m ² / g) of the ferroelectric substance, W ₁ is the weight (g) of the inorganic fine powder contained in the developer, and W ₂ is the ferroelectric substance contained in the developer. Indicates the weight (g) of the substance. Is satisfied, there is no image deterioration due to high-speed mass copying, and furthermore, no charged wire contamination due to scattering of inorganic fine powder is observed, but when the value of the above expression is smaller than 15, the flow of toner When a copy image is produced by a copying machine, the image becomes noticeably rough. On the other hand, when the value of the above equation exceeds 300, the inorganic fine powder released from the toner surface cannot be completely adsorbed by the ferroelectric substance, and the inorganic fine powder in the released state exists, and as a result, the Inorganic fine powder is scattered, causing contamination of the charged wire.

Further, the addition amount of the inorganic fine particles is preferably from 0.2 to 3 parts by weight, particularly preferably from 0.5 to 2 parts by weight based on the total weight of the toner.

Further, the addition amount of the ferroelectric substance is preferably 0.1 to 10 parts by weight, particularly preferably 0.5 to 5 parts by weight based on the total weight of the toner.
Parts by weight.

As a method of adding the inorganic fine particles and the ferroelectric substance, there is a method of mixing with the toner particles by mechanical shearing force.

As the binder resin used in the magnetic toner of the present invention,
In the case of using a heat and pressure roller fixing device having a device for applying oil, the following binder resin for toner can be used.

For example, polystyrene, poly-p-chlorostyrene,
Styrenes such as polyvinyltoluene and their substituted homopolymers; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene -Methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone Styrene copolymers such as copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally-modified phenolic resins, and naturally-modified maleic resins Acid resin, Acrylic Resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, wheel of fortune resin, Kumaroinden resins, and petroleum resins.

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 problems. is there. These problems must be taken into account at the same time, because toners that fix with less heat energy tend to block or casing during storage or in a developer. 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. The adhesion of the toner to the toner is improved, but 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 the comonomer 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 methacrylic acid. Acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, a monocarboxylic acid having a double bond such as acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like and their substituted products; for example, vinyl chloride, vinyl acetate,
Vinyl esters such as vinyl benzoate; ethylenic 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 and the like; for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate Double bonds such as 1,3-butanediol dimethacrylate, etc.
Carboxylic acid esters; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfone; and compounds having three or more vinyl groups are used alone or as a mixture.

Examples of the inorganic fine powder used in the present invention include magnesium oxide and silicic acid fine powder. Among them, fine silica powder is particularly preferable, and fine silica powder produced by a dry method and a wet method can be used.

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 an oxyhydrogen flame, the basic reaction formula is as follows.

SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl Also, in this manufacturing process, by using another metal halide such as aluminum chloride or titanium chloride together with the silicon halide, a composite of silica and another metal oxide can be obtained. It is also possible to obtain fine powders, which are also included.

On the other hand, as a method of producing by a wet method, various conventionally known methods can be applied. For example, decomposition of sodium silicate with an acid, as shown by a general reaction formula (hereinafter, the reaction formula is abbreviated), Na ₂ O.XSiO ₂ + HCl + H ₂ O → SiO ₂ .nH ₂ O + NaCl In addition, ammonium salts or alkalis of sodium silicate Decomposition with salts, after producing an alkaline earth metal silicate from sodium silicate, a method of decomposing with an acid to produce silicic acid, a method of transforming sodium silicate solution into silicic acid with ion exchange resin, natural silicic acid or There is a method using a silicate.

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

Further, the surface of these fine silica particles may be subjected to an organic treatment such as a coupling treatment, an oil treatment, or a treatment with a fatty acid or a metal salt thereof.

Examples of the ferroelectric substance used in the present invention include the following compounds.

(Tartrate-based ferroelectric) Roscilic acid NaKC ₂ H ₄ O ₆・ 4H ₂ O Lithium ammonium tartrate LiNH ₄ C ₄ H ₄ O ₆・ H ₂ O etc. (Phosphate-based ferroelectric) Potassium dihydrogen phosphate KH ₂ PO ₄ Cesium dihydrogen phosphate CsH ₂ PO ₄ etc. (Oxyoctahedral ferroelectric or solid solution thereof) Barium titanate BaTiO ₃ Strontium titanate SiTiO ₃ Potassium niobate KNbO ₃ Sodium tantalate NaTaO ₃ Lead titanate - lead zirconate solid solution Pb (TiZr) O ₃ strontium chromate - strontium tantalate solid solution Sr (Cr, Ta) c ₃ potassium titanate - strontium titanate solid solution (K, Sr) TiO ₃ (sulfate salt or selenate Guanidine aluminum sulfate hexahydrate C (NH ₂ ) ₃ Al (SO ₄ ) ₂ .6H ₂ O Guanidine aluminum selenate C (NH ₂ ) ₃ Al (SeO ₄ ) ₂ For magnetic toner It is preferable to use a charge control agent in the toner particles. By using the charge control agent, it is possible to further clarify the function separation for high image quality for each particle size range.

Examples of the negative charge control agent that can be used in the present invention include metal complexes or salts of monoazo pigments, and metal complexes or salts of salicylic acid, alkylsalicylic acid, dialkylsalicylic acid, or naphthoic acid.

The above-described charge control agent (having no action as a binder resin) is more preferably used in the form of fine particles.

The magnetic toner of the present invention may optionally contain additives. Dyes conventionally known as colorants,
Pigments can be used.

In addition, wax-like substances such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, and paraffin wax are used for the purpose of improving the releasability at the time of hot roll fixing.
Addition of about 5 wt% to the magnetic toner is also a preferred embodiment of the present invention.

Further, the magnetic toner of the present invention may also serve as a colorant, but contains a magnetic material. Examples of the magnetic material contained in the magnetic toner of the present invention include iron oxides such as magenetite, γ-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.

To prepare a magnetic toner for developing an electrostatic image according to the present invention, a magnetic powder and a vinyl-based, non-vinyl-based thermoplastic resin, a pigment or dye as a colorant, if necessary, a charge control agent,
After thoroughly mixing other additives with a mixer such as a ball mill, melting, kneading and kneading using a hot kneader such as a heating roll, a kneader, an extruder to make the resins compatible with each other. A magnetic toner according to the present invention can be obtained by dispersing or dissolving a pigment or dye in the mixture, and performing cooling and solidification followed by pulverization and strict classification.

Example 1 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 by using a fine pulverizer using a jet stream, and the obtained finely pulverized powder was classified by a fixed wall type air classifier to classify. A powder was produced. Further, the obtained classified powder is strictly classified and removed simultaneously by a multi-division classifier utilizing a Coanda effect (an elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) to simultaneously remove the fine powder and coarse powder.
A negatively chargeable insulating magnetic toner A of 5 μm was obtained. Tables 1 and 2 show data obtained by measuring the obtained negatively chargeable insulative toner A using a Coulter Counter TA II having an aperture of 100 μ as described above.

further The above substances were mixed with a Hensiel mixer to form a one-component negatively chargeable magnetic developer.

The prepared one-component developer was charged into a developing device shown in FIG. 1 of the attached drawings, and a development test was performed. The developing conditions will be described with reference to FIG. One-component magnetic developer 11
A magnetic blade 12 on the surface of a stainless steel cylindrical sleeve 13 rotating at a rotational speed of 550 mm / sec on the outer periphery in the direction of arrow 16.
The gap between the sleeve 13 and the blade 12 was set to about 250 μm. The sleeve 13 has a fixed magnet 15 as a magnetic field generating means, and a magnetic field of 1000 gauss is fixed in the vicinity of the sleeve surface in a developing area close to the photosensitive solar drum 14 having an organic photoconductive layer having a negatively charged latent image.
15 has formed. Photosensitive drum rotating in the direction of arrow 17
The closest distance between the sleeve 14 and the sleeve 13 was set to about 300 μm.
A bias of 2000 Hz / 1350 Vpp, which is a combination of an AC bias and a DC bias, was applied between the photosensitive drum 14 and the sleeve 13 by the bias applying means 18. The one-component developer layer on the sleeve 13 had a layer thickness of about 75 to 150 μm, and in the development area, the magnetic toner formed ears about 95 μm in height.

The negatively charged latent image formed on the photosensitive drum 14 was developed by flying a one-component developer 11 having a positively charged triboelectric charge. The image forming test was continuously performed 50,000 times, and 50,000 toner images were generated. The results are shown in Table 3.

The evaluation method of the evaluation items shown in Table 3 is described below.

Image jumping: Thin horizontal lines of 100 μm width were imaged at 300 μm intervals, enlarged with a loupe, inspected for the state of toner scattered between the horizontal thin lines, and evaluated in three steps.

：: There is almost no scattering of toner between the horizontal thin lines.

Δ: There is some scattering of toner between the thin horizontal lines.

X: toner scattered much between horizontal thin lines.

The image was rough: thin horizontal lines having a width of 100 μm were imaged at 300 μm intervals, the horizontal thin lines were enlarged with a loupe, and the degree of unevenness of the outline of the horizontal thin lines was observed.

：: The contour of the horizontal thin line has little unevenness and the contour is not rough.

Δ: The contour of the horizontal thin line is slightly uneven, and the contour is rough.

×: The outline is so rough that the outline of the horizontal thin line cannot be recognized.

Charging wire contamination: The center of the charging wire for charging the photosensitive drum after 50,000 images has been output is attached to lens cleaner paper (dusper pa).
per), the surface of the lens cleaner paper was visually inspected for dirt, and evaluated on a three-point scale.

：: The dirt on the lens cleaner paper is small.

Δ: Stain is recognized on the lens cleaner paper.

X: The lens cleaner paper is very dirty.

Example 2 After mixing the above substances with a Hensiel mixer to form a one-component developer, the mixture was charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As shown in Table 3, stable and clear high-quality images were obtained.

Example 3 The above materials were used in the same manner as in Example 1 to obtain a negatively chargeable insulating magnetic toner B (particle size distribution is shown in Table 2).

further The above substances were mixed with a Hensiel mixer to form a one-component developer, which was then charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As shown in Table 3, stable and clear high-quality images were obtained.

Example 4 After mixing the above substances with a Hensiel mixer to form a one-component developer, the mixture was charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As shown in Table 3, stable and clear high-quality images were obtained.

Example 5 Using the above materials, a negatively chargeable insulating magnetic toner C (particle size distribution is shown in Table 2) was obtained in the same manner as in Example 1.

further After mixing the above substances with a Hensiel mixer to form a one-component developer, the mixture was charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As shown in Table 3, stable and clear high-quality images were obtained.

Example 6 After mixing the above substances with a Hensiel mixer to form a one-component developer, the mixture was charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As shown in Table 3, stable and clear high-quality images were obtained.

Comparative Example 1 Negatively-chargeable insulating magnetic toner D (viscosity distribution is shown in Table 2) using the same material and method as those shown in Example 1.
I got

The above substances were mixed with a Hensiel mixer to form a one-component developer, which was then charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As a result, as shown in Table 3, the stain on the charging wire was so bad that the image after 50,000 sheets of durability was at a very bad level. Observation of the charged wire with a scanning electron microscope confirmed that silica fine powder had adhered.

Comparative Example 2 Negatively-chargeable insulating magnetic toner E (viscosity distribution is shown in Table 2) using the same material and method as those shown in Example 5.
I got

The above substances were mixed with a Hensiel mixer to form a one-component developer, which was then charged into a developing device shown in FIG. 1 and evaluated under the same conditions as in Example 1. As shown in Table 3, the image was noticeably rough and had a problem in practice.

[Brief description of the drawings]

In the accompanying drawings, FIG. 1 is a schematic sectional view of a developing device to which the negatively chargeable magnetic developer of the present invention is applied, and FIG. It is a figure which shows the range of a content ratio. 11 One-component magnetic developer 13 Developer carrier (sleeve) 14 Photoconductor drum

Claims (2)

(57) [Claims] At least a negatively chargeable insulative magnetic toner applied to a developing method in which a rotation speed of an outer periphery of a developer carrier for developing an electrostatic image carrying a developer on a surface is 400 mm / sec or more. A negatively-chargeable magnetic developer containing 17 to 80% by number of magnetic toner particles having a particle diameter of 5 μm or less, and 6.35 to 12.7 μm.
5 to 50% by number of magnetic toner particles having a particle diameter of m, 2.0% by volume or less of magnetic toner particles having a particle diameter of 16 μm or more, and a volume average particle diameter of the magnetic toner of 4.5% or less.
The magnetic toner particles having a particle size of 5 μm or less are represented by the following formula: [Wherein N represents the number% of magnetic toner particles having a particle size of 5 μm or less, V represents the volume% of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number from 4.5 to 6.5. . Here, N indicates a positive number of 17 to 80. And an inorganic fine powder having a BET specific surface area of 40 to 400 m ² / g by nitrogen adsorption and a BET specific surface area of 0.1
A negatively chargeable magnetic developer containing a ferroelectric substance of 5 to 30 m ² / g. 2. The content ratio of the inorganic fine powder and the ferroelectric particles is represented by the following formula: [Where Sw ₁ is the BET specific surface area (m ² / g) of the inorganic fine powder, Sw ₂
Indicates the BET specific surface area (m ² / g) of the ferroelectric substance, W ₁ is the weight (g) of the inorganic fine powder contained in the developer, and W ₂ is the ferroelectric substance contained in the developer. Indicates the weight (g) of the substance. The negatively chargeable magnetic developer according to claim 1, which satisfies the following.