JPH02287458A - Negatively chargeable magnetic developer - Google Patents

Abstract

PURPOSE:To enable a high-speed copying machine to be used by incorporating magnetic toner particles specified in the particle diameter distribution, a fine inorganic powder having a BET specific surface area of 40 - 400m<2>/g by adsorption of nitrogen, and a ferroelectric substance having a BET specific surface area of 0.5 - 30m<2>/g. CONSTITUTION:The negatively chargeable insulating magnetic toner contains the magnetic toner particles of <=5mum diameter in an amount of 17 - 80 number %, those of 6.35 - 12.7mum diameter in an amount of 5 - 50 number %, and those of >=16mum diameter in an amount of <=2.0 volume %, and it has a volume average particle diameter of 4.5 - 9mum, and the particle diameter distribution of the magnetic toner particles of <=5.0mum diameter satisfies expression I in which N is the number % of the magnetic toner particles of <=5mum diameter, V is the volume 5% of them, k is a positive number of 4.5 - 6.5, and N is that of 17 - 80, and the toner comprises the magnetic toner particles and the fine inorganic powder having a specific surface area of 40 - 400m<2>/g, and the ferroelectric substance having that of 0.5 - 30m<2>/g, thus permitting the obtained developer to be used for high-speed copying machines.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a negatively charged developer for visualizing electrostatic latent images in image forming methods such as electrophotography and electrostatic recording, and particularly to a developer for use in high-speed copying machines. The present invention relates to a negatively chargeable developer suitable for.

[Background technology]

2. Description of the Related Art In recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, their uses have expanded to a wide variety of uses, and demands on their image quality have become stricter.

When copying images such as general documents and books, it is required to reproduce extremely finely and faithfully, without being crushed or cut off, even down to the minute characters. especially,
When the latent image on the photoreceptor of an image forming apparatus is a line image with a diameter of 100 μm or less, fine line reproducibility is generally poor, and the sharpness of the line image is still not sufficient.

Furthermore, with the recent rapid streamlining of office work, there is an increasing demand for high-speed copying machines that can make a large number of copies in a short period of time. The quality required for high-speed copying machines is to improve image durability so that the good image quality obtained at the initial stage of copying remains unchanged even after copying a large number of copies, and to improve high-speed copying. Even in the case of large-scale copying, it is desired to improve the scattering resistance of the developer so as not to contaminate the charging wire installed in the copying machine.

Up to now, several developers have been proposed for the purpose of improving image quality. Japanese Patent Publication No. 51-3244
The publication proposes a non-magnetic toner intended to improve image quality by regulating particle size distribution. In the toner,
The toner mainly has a particle size of 8 to 12 μm, which is relatively coarse (according to the studies conducted by the present inventors, it is difficult to uniformly “glue” the latent image with this particle size, and The particle size distribution is broad, which tends to reduce uniformity due to the characteristics that the particle size is 30% or less and the particle size of 20 μm or more is 5% or less. In order to form a clear image using a toner with a large and broad particle size distribution, it is necessary to increase the apparent image density by stacking the toner particles thickly (overlapping them to fill the gaps between the toner particles). Another problem is that the amount of toner consumption required to produce a predetermined image density increases.

Furthermore, in JP-A-54-72054, a non-magnetic toner having a sharper distribution than the former has been proposed, but the size of particles with intermediate weight is coarse (8.5 to 11.0 μm). As a high-resolution toner, there is still room for improvement.

In JP-A No. 58-129437, the average particle size is 6 to 6.
10 μm, and a non-magnetic toner in which the maximum number of particles is 5 to 8 μm has been proposed, but the number of particles of 5 μm or less is 15%.
There is a tendency for images with less sharpness to be formed.

According to studies conducted by the present inventors, it has been found that toner particles of 5 μm or less have the main function of clearly reproducing the outline of a latent image and densely applying the toner to the entire latent image.

In particular, in the electrostatic latent image on the photoreceptor, the electric field strength is higher at the edge part than the inside due to the concentration of electric lines of force.
The quality of the toner particles that collect in this area determines the sharpness of the image quality.

According to studies conducted by 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. Patent No. 4,299,900, 20
A jumping development method using a developer having 10 to 50% by weight of magnetic toner of ~35 μm has been proposed. In other words, the magnetic toner is triboelectrically charged, a toner layer is evenly and thinly applied on the sleeve, and the toner particle size is optimized to improve the environmental resistance of the developer. However, fine line reproduction is difficult. Considering even more stringent requirements such as image quality and resolution, this is not sufficient and further improvements are required.

In addition, with the aim of improving toner properties,
Many proposals have been made to add a third substance to the toner.

JP-A No. 60-32060 proposes that two types of inorganic fine powders having different surface areas are added to the toner to prevent the toner from adhering to the photoreceptor and to prevent the photoreceptor from being poorly charged.

Further, Japanese Patent Laid-Open No. 54-2130 proposes a toner that can develop electrostatic latent images of either positive or negative polarity using a magnetic toner consisting of a coating material, magnetic powder, and ferroelectric material. However, the rotation speed of the outer circumference of the sleeve is 400 cm/s.
By using toner with a fine particle size in high-speed copying machines that exceed EC, we can achieve clear images, high image quality, and high durability. These proposals are not sufficient to prevent contamination caused by fine powder, and high-speed,
In the era of high-quality copying, new technology is required.

[Purpose of the invention]

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

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

A further object of the present invention is to provide a magnetic developer whose performance does not change even after long-term use.

A further object of the present invention is to apply a magnetic developer that does not contaminate the charging wire even during mass copying using 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 a developer carrier for developing an electrostatic image carrying a developer on its surface is 400 mm/sec or more. In the negatively charged magnetic developer containing at least negatively charged insulating magnetic toner, the negatively charged insulating magnetic toner contains 17 to 80 number % of magnetic toner particles having a particle size of 5 μm or less; 5 to 50 number % of magnetic toner particles having a particle size of ~12.7 μm are contained, and 2.0% of magnetic toner particles having a particle size of 16 μm or more are contained.
It is contained in a volume percent or less, and the volume average particle size of the magnetic toner is 4.
．． 5 to 9 μm, and the group of magnetic toner particles of 5 μm or less is represented by the following formula % [In the formula, N indicates the number % of magnetic toner particles having a particle size of 5 μm or less, and ■ has a particle size of 5 μm or less. It represents the volume % of magnetic toner particles, and k represents a positive number from 4.5 to 6.5. However, N represents a positive number from 17 to 80. ] It has a particle size distribution that satisfies the following, and BET due to nitrogen adsorption
Inorganic fine powder with a specific surface area of 40 to 400rd/g and BE
The present invention relates to a negatively charged magnetic developer containing a ferroelectric substance having a T specific surface area of 0.5 to 30 rrr/g. Furthermore, the inorganic fine powder and ferroelectric substance contained in the developer are determined by the following formula [where Sw 1 is the BET specific surface area of the inorganic fine powder (cr
rf/g), 3w2 is the BET specific surface area of the ferroelectric material (
c+rr/g), W represents the weight (g) of the inorganic fine powder contained in the developer, and W2 represents the weight (g) of the ferroelectric substance contained in the developer. This invention relates to a negatively charging developer for high-speed copying machines that satisfies the following.

The magnetic developer of the present invention is capable of faithfully reproducing the latent image formed on the photoreceptor, down to the fine lines, and maintains high image quality even when copying or printing is continued, and Even in the case of mass copying, it is possible to perform good development without charging wire contamination.

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

That is, one feature of the magnetic developer of the present invention is that the number of magnetic toner particles having a particle size of 5 μm or less is 17 to 60%. Conventionally, in magnetic toner, magnetic toner particles of 5 μm or less are difficult to control the amount of charge, impair the fluidity of the magnetic toner, and are a component that scatters the toner and contaminates the machine, further causing image fogging. As a component, it was thought necessary to actively reduce it.

However, according to studies conducted by the present inventors, it has been found that magnetic toner particles of 5 μm or less are an essential component for forming high-quality images.

For example, changing the surface potential on the photoreceptor using a magnetic toner having a particle size distribution ranging from 1.5 μm to 30 μm,
Developing a latent image by changing the surface potential on the photoreceptor, from a large development potential contrast in which a large number of toner particles are easily developed, to a halftone, to a small development potential contrast in which only a few toner particles are developed,
When the developed toner particles on the photoreceptor were collected and the toner particle size distribution was measured, it was found that there were many magnetic toner particles with a diameter of 8 μm or less, and particularly a large number of magnetic toner particles with a diameter of 5 μm or less. In other words, when magnetic toner particles with a particle size of 5 μm or less, which is the most suitable for development, are smoothly supplied to develop the latent image on the photoreceptor, the latent image is faithful to the latent image, does not protrude from the latent image, and true reproducibility is achieved. This is an excellent image changer.

Further, in the magnetic toner of the present invention, 6.35 to 12
．． One of the characteristics is that the number of particles in the range of 7 μm is 5 to 50%. This is related to the necessity of the presence of magnetic toner particles with a particle size of <5 μm or less, as described above.
Magnetic toner particles with a particle size of μm or less have the ability to strictly cover the latent image and reproduce it faithfully, but in the latent image itself,
The electric field strength at the surrounding edges is higher than that at the center (therefore, the inside of the latent image has more toner particles than the edges).
The image may become fainter and the image density may appear lighter. In particular, magnetic toner particles with a diameter of 5 μm or less have a strong tendency to do so.

However, we found that 6.35-12.7 μm
It has been found that this problem can be solved and further clarity can be achieved by containing toner particles in the range of 5% to 50% by number. In other words, this is thought to be because toner particles in the particle size range of 6.35 to 12.7 μm have a suitably controlled amount of charge compared to magnetic toner particles with a particle size of 5 μm or less, but the edge of the latent image The toner is supplied to the inner side, where the electric field strength is lower than the edge area, to compensate for the lack of adhesion of the inner toner particles to the edge area, and a uniform developed image is formed, resulting in high density, resolution and gradation. It provides excellent sharp images.

Furthermore, for particles with a particle size of 5 μm or less, the number %
(N) and volume % (v), N/V = -0,04
N+k (However, 4.5≦≦6.5; 17≦N≦
Another feature of the magnetic toner of the present invention is that it satisfies the following relationship: 80). This range is shown in FIG. 2, and the magnetic toner of the present invention having a particle size distribution that satisfies this range along with other characteristics can achieve excellent developability.

While studying the state of particle size distribution of 5 μm or less, the present inventors found that there is a state of existence of fine powder most suitable for achieving the purpose as shown in the above formula. In other words, for a certain value of N, a large N/V means that 5 μm
It shows that it contains a wide range of particles, including N/
It is understood that a small v value indicates that the abundance of particles around 5 μm is high and that there are few particles with a particle size smaller than that, and the value of N/V is in the range of 1.3 to 5.82. When N is within the range of 17 to 80 and the above relational expression is further satisfied, good fine line reproducibility and high resolution can be achieved.

Further, it is preferable that the amount of magnetic toner particles having a particle size of 16 μm or more is 2.0% by volume or less, and is as small as possible.

The magnetic toner of the present invention solves the conventional problems and can withstand the recent strict demands for high image quality by adopting a concept completely different from the conventional viewpoint.

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

Magnetic toner particles with a particle size of 5 μm or less account for 17 to 17 of the total number of particles.
It is preferably 80% by number, preferably 25 to 60% by number, and even more preferably 30 to 55% by number. When the number of magnetic toner particles with a particle size of 5 μm or less is 17% or less, there are few magnetic toner particles effective for high image quality, and especially as the toner is used for continuous copying or printing, the effective magnetic toner particles become less effective. As the components decrease, the balance of the particle size distribution of the magnetic toner as shown in the present invention deteriorates, and the image quality gradually deteriorates.

In addition, if the content is 80% or more, strong agglomeration of magnetic toner particles tends to occur (toner particles with a particle size larger than the original size result in rough image quality, lowering resolution,
Or, the density difference between the edge part and the inside of the latent image becomes large,
The image tends to look hollow.

In addition, particles in the range of 6.35 to 12.7 p.m.
The content is preferably 50% by number, preferably 15 to 45% by number. If the number is more than 50%, the image quality deteriorates, and more development than necessary occurs, that is, too much toner is applied, leading to an increase in toner consumption.

On the other hand, if it is less than 5% by number, it becomes difficult to obtain high image density. In addition, between the number% (N%) and volume% (7%) of magnetic toner particles with a particle size of 5 μm or less, N/V=-0
, 04N+, and indicates a positive number in the range of 4.5≦ and ≦6.5. Preferably 4.5≦≦6.0, more preferably 4.5≦≦5.5. As shown above, 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 size smaller than 5.0 μm is small, resulting in poor image density, resolution, and sharpness. The presence of an appropriate amount of fine magnetic toner particles, which were conventionally thought to be unnecessary, contributes to achieving close packing of toner during development and forming a uniform image without roughness. In particular, by uniformly filling in thin lines and image contours, visual sharpness is further enhanced. That is, when k < 4.5, these properties are inferior due to the lack of this particle size distribution component.

From another point of view, in terms of production, it is necessary to cut a large amount of fine powder by classification or the like in order to satisfy the condition of k<4.5, which is disadvantageous in terms of yield and toner cost.

Furthermore, when k > 6.5, the image density tends to decrease as copying is continued due to the presence of more fine powder than necessary. This phenomenon occurs when excessive fine powder magnetic toner particles with more charge than necessary adhere to the developing sleeve and prevent the normal magnetic toner from being carried and charged on the developing sleeve. Conceivable.

Further, it is preferable that the magnetic toner particles having a particle size of 16 μm or more be 2.0% by volume or less (more preferably 1.0% by volume or less, still more preferably 0.5% by volume or less.2 If the amount is more than 0% by volume, it not only hinders fine line reproduction, but also causes coarse toner particles of 16 μm or more to protrude on the thin layer surface of toner particles developed on the photoreceptor during transfer. The delicate adhesion between the photoreceptor and the transfer paper via the toner layer is made irregular.
This causes fluctuations in transfer conditions and is a cause of defective transfer images. In addition, the volume average diameter of the magnetic toner is 4.5~
9 .mu.m1, preferably 5 to 8.5 .mu.m, and this value cannot be considered separately from each component mentioned above. If the volume average particle diameter is 4.5 μm or less, in applications with a high image area ratio such as graphic images, the amount of toner on the transfer paper is small (and the problem of low image density tends to occur.This is explained earlier. This is thought to be due to the same reason as the reason why the internal density decreases in the edge part of the latent image.If the volume average particle diameter is 9 μm or more, the resolution is not good (and at best the resolution is not good at the beginning of copying. and image quality deterioration is likely to occur.

The particle size distribution of toner can be measured by various methods.
In the present invention, a Coulter counter was used.

In other words, the measuring device is Coulter Counter-T.
Using A-II type (manufactured by Coulter), an interface (manufactured by Nikkaki) and CX that outputs number distribution and volume distribution
-1 Connect a personal computer (manufactured by Canon),
As the electrolytic solution, a 1% NaCl aqueous solution is prepared using primary sodium chloride. As a measurement method, the electric field aqueous solution 100~
A surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant in 150 mf of 0.1 to 5 mj! In addition, 2 to 20 mg of the measurement sample is added. The electrolytic solution in which the sample was suspended was dispersed for about 1 to 3 minutes using an ultrasonic disperser, and the particle size of the particles was 2 to 40 μ based on the number of particles, using a 100 μ aperture as an aperture using the Coulter counter TAII type. The distribution was measured and the values according to the invention were determined therefrom.

On the other hand, the magnetic toner with the particle size used in the present invention has a volume average particle size of 9 μm or more (the magnetic toner has a high level of charge and tends to aggregate easily, and as the particle size becomes finer, the surface area increases). It is essential to add an appropriate fluidizing agent, and by using the inorganic fine powder with a BET specific surface area of 40 to 400 c rd / g due to nitrogen adsorption used in the present invention, fluidity is improved and the charging of the magnetic toner is improved. It has the effect of adjusting the amount and improving the image quality of the copied image.

Here, the BET specific surface area of the inorganic fine powder is 40 rd/g
If the value is smaller than , the fluidity of the entire toner deteriorates regardless of the amount added, making it impossible to form a uniform toner layer over the entire sleeve. On the other hand, the BET specific surface area is 40
If the value is larger than 0d1g, the inorganic fine particles will aggregate with each other 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 with a BET specific surface area of 0.5 to 30 I/g, contamination of the charging wire by inorganic particles is not observed (and the copied image does not deteriorate due to gluttonous copying). The mechanism by which this effect is obtained can be thought of as follows: When a large number of copies are made using a high-speed copying machine, the long-term high-speed rotation of the sleeve causes the inorganic fine powder that has adhered to the toner surface to gradually spread to the toner surface. On the other hand, the high dielectric substance exists in a polarized state near the toner, and the liberated inorganic 4 fine powder is attracted by the ferroelectric substance before scattering inside the copying machine, and becomes a ferroelectric substance. It is thought that the inorganic fine powder is adsorbed onto the surface of the body material, thereby preventing contamination of the charging wire.

Here, the BET specific surface area of the ferroelectric particles is 0.5 rd/
If the value is smaller than 30d/g, the image obtained by copying will be noticeably rough, while if the value is larger than 30d/g, the ferroelectric substance will scatter into the copying machine along with inorganic particles, contaminating the charging wire. .

In addition, the inorganic fine powder and ferroelectric substance used in the present invention are expressed by the following formula (% formula %) where Sw I is the BET specific surface area of the inorganic fine powder (c
rd/g), 8w2 indicates the BET specific surface area (cm/g) of the ferroelectric material, Wl is the weight (g) of the inorganic fine powder contained in the developer, and W2 is the weight (g) of the inorganic fine powder contained in the developer. The weight (g) of the ferroelectric material is shown. ], there will be no image deterioration due to high-speed mass copying, and no charging wire contamination due to scattering of inorganic fine powder will be observed; however, if the value of the above formula is smaller than 15, the toner's fluidity will be As a result, when a copy image is produced using a copying machine, the image becomes noticeably rough.

- On the other hand, if the value of the above formula exceeds 300, the ferroelectric substance cannot completely adsorb the inorganic fine powder released from the toner surface, and the free inorganic fine powder exists, resulting in
As a result, inorganic fine powder scatters inside the copying machine, causing contamination of the charging wire.

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

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

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

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

For example, monopolymers of styrene and its substituted products such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers , styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-methyl chloromethacrylate copolymer, styrene-
Acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile- Styrenic copolymers such as indene copolymers; polyvinyl chloride, phenolic resin, naturally 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, coumaroindene resin, petroleum resin, etc. can be used.

In the heating and pressure roller fixing method in which little 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. be. Toners that are fixed with less thermal energy usually tend to block or cake during storage or in a developing device, so these problems must also be taken into consideration. The physical properties of the binder resin in the toner are most responsible for these phenomena, but according to the research of the present inventors, reducing the content of magnetic material in the toner causes the toner image to become weaker on the toner image supporting member during fixing. Although the adhesion of the toner to the toner is improved, offset is more likely to occur, and blocking or caking is also more likely to occur. Therefore, when using the heated pressure roller fixing method in which little oil is applied in the present invention, the selection of the binder resin is more important. Preferred binding materials include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of comonomers for the styrene monomer in the styrenic copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylate. acids, monocarboxylic acids having a double bond such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrinitrile, acrylamide, etc., or substituted products thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids with double bonds and substituted products thereof such as methyl maleate, dimethyl maleate, etc.; vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc.; e.g. ethylene, propylene, butylene, etc. vinyl monomers such as ethylene olefins; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; More than one is used.

As the crosslinking agent, compounds having two or more polymerizable double bonds are mainly used, such as aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; for example, ethylene glycol diacrylate,
Carboxylic acid esters having two double bonds such as ethylene glycol dimethacrylate and 1,3-butanediol dimethacrylate; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfone; and three or more vinyl Compounds having groups can be used alone or as a mixture.

Examples of the inorganic fine powder used in the present invention include magnesium oxide and silicate fine powder. Among them, silicic acid fine powder is particularly preferred, and silicic acid 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 the thermal decomposition oxidation reaction of silicon tetrachloride gas in an oxyhydrogen flame, and the basic reaction formula is as follows.

5iCj' 4+2H2+02→SiO2+4HC1 Also, in this manufacturing process, for example, a composite fine powder of silica and other metal oxides can be obtained by using other metal halide compounds such as aluminum chloride or titanium chloride together with a silicon halide compound. are also possible and inclusive.

On the other hand, various conventionally known methods can be applied to the wet manufacturing method. For example, the decomposition of sodium silicate with an acid can be expressed using a general reaction formula (the reaction formula is omitted below): Na 20.X5iO2+HCj! +H20-+S
iO2・nH20+NaCf Other methods include decomposition of sodium silicate with ammonium salts or alkali salts, generation of alkaline earth metal silicate from sodium silicate and decomposition with acid to form silicic acid, and ionization of sodium silicate solution. There are methods such as using exchange resin to produce silicic acid, and using natural silicic acid or silicate.

As the silicic acid fine powder referred to herein, any of anhydrous silicon dioxide (silica) and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate can be used.

Furthermore, the surface of these silicic acid fine powders 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.

Moreover, the following compounds are exemplified as the ferroelectric substance used in the present invention.

(Tartrate-based ferroelectric material) Rochelle acid NaKC2H406・4H20 Lithium ammonium tartrate LiNH4C4H406・
H2O, etc. (phosphate ferroelectric) Potassium dihydrogen phosphate KH2PO4 Cesium dihydrogen phosphate CsH2Po 4, etc. (oxygen octahedral group ferroelectric or its solid solution) Barium titanate
BaTi03 Strontium titanate 5tTiO3
Potassium niobate KNbO3 Sodium tantalate NaTa03 Lead titanate-lead zirconate solid solution Pb (TiZr) 03 Strontium chromate-strontium tantalate solid solution Sr (Cr
, Ta) C3 Potassium titanate-strontium titanate solid solution (K
, Sr) TiO3 (sulfate-based or selenate-based ferroelectric substance) guanidine aluminum sulfate hexahydrate C (Nl2) 3Al (SO4)2.6H20 guanidine-aluminum selenate C (NH*) sAl (Se04)2 Further, it is preferable to use the magnetic toner of the present invention by adding a charge control agent to the toner particles. By using a charge control agent, it is possible to more clearly separate functions for improving image quality in each particle size range.

Negative charge control agents that can be used in the present invention include:
For example, metal complexes or salts of monoazo pigments, salicylic acid,
Mention may be made of metal complexes or salts of alkylsalicylic acids, dialkylsalicylic acids, or naphthoic acids.

It is more preferable to use the above-described charge control agent (which does not function as a binder resin) in the form of fine particles.

The magnetic toner of the present invention may contain additives, if necessary. As the colorant, conventionally known dyes and pigments can be used.

In addition, in order to improve mold releasability during hot roll fixing, waxy substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, Sasol wax, paraffin fuchs, etc.
It is also one of the preferred embodiments of the present invention to add about 5 wt% to the magnetic toner.

Furthermore, the magnetic toner of the present invention may also serve as a colorant, but it contains a magnetic material. The magnetic materials contained in the magnetic toner of the present invention include iron oxides such as magnetite, γ-iron oxide, ferrite, and iron-rich ferrite;
Metals such as cobalt, nickel, or combinations of these metals with metals such as aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium. alloys and mixtures thereof.

To prepare the magnetic toner for developing electrostatic images according to the present invention, magnetic powder, vinyl or non-vinyl thermoplastic resin, pigment or dye as a coloring agent, charge control agent, and other additives are used as necessary. etc. are thoroughly mixed using a mixer such as a ball mill, and then melted, kneaded, and kneaded using a heat kneader such as a heated roll, niegu, or extruder to make the resins compatible with each other, and the pigment or dye is mixed inside. The magnetic toner according to the present invention can be obtained by dispersing or dissolving the toner, cooling and solidifying it, and then pulverizing and strictly classifying it.

Example 1 (Nippon Steel Mining Co., Ltd. Elbow Jet Classifier) was used to strictly classify and remove ultrafine powder and coarse powder at the same time to determine the volume average particle size.

A negatively charged insulating magnetic toner A of 6.5 μm was obtained. Tables 1 and 2 show data obtained by measuring the obtained negatively charged insulating toner A using a Coulter Counter TA type with an aperture of 100 .mu.m as described above.

The above materials were mixed using a blender (after mixing, they were kneaded using a 2-tsumugi kneading extruder set at 150°C. The resulting kneaded material was cooled, coarsely ground using a cutter mill, and then finely ground using a jet stream. The finely ground powder was pulverized using a pulverizer, and the resulting pulverized powder was classified using a fixed-wall wind classifier to produce classified powder.Furthermore, the obtained classified powder was passed through a multi-division classifier using the Coanda effect. The above substances were mixed in a Henschel mixer to form a component-based negatively charged magnetic developer.

The prepared one-component developer was put into the developing device shown in FIG. 1 of the attached drawings, and a development test was conducted. The developing conditions will be explained with reference to FIG. -Component magnetic developer 11
is a rotational speed of the outer circumference in the direction of arrow 16 of 550 cm/sec.
It is applied in a thin layer via the magnetic blade 12 onto the surface of the stainless steel cylindrical sleeve 13 rotating at c.
The gap between the blade 12 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 the fixed magnet 15 generates a magnetic field of 1000 Gauss in the vicinity of the sleeve surface in the development area adjacent to the photoconductive layer 14 having an organic photoconductive layer having a negatively charged latent image. is forming.

Photosensitive drum 14 and sleeve 1 rotating in the direction of arrow 17
The closest distance of No. 3 was set to approximately 300 μm. Note that 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 has a thickness of approximately 75 to 150 μm.
The magnetic toner had a layer thickness of about 95 μm in height in the development area.

The negatively charged latent image formed on the photosensitive drum 14 was developed by flying the one-component developer 11 having a positively charged tripo charge. Performed the image output test 50,000 times in a row,
50,000 toner images were generated.

The results are shown in Table 3.

Example 2 The above substances were mixed in a Henschel mixer to form a -component developer, and then evaluated in the same manner as in Example 1. As shown in the table, we were able to obtain stable, clear, and high-quality images.

Example 3 Conducted. As shown in Table 3, stable, clear, high-quality images could be obtained.

Example 4 Negatively chargeable insulating magnetic toner B (particle size distribution shown in Table 2) was obtained using the above materials in the same manner as in Example 1.

Further, the above substances were mixed in a Henschel mixer to form a one-component developer, and then evaluated in the same manner as in Example 1. As shown in Table 3, stable, clear, high-quality images could be obtained.

Example 5 The above materials were mixed in a Henschel mixer to form a -component developer, and then evaluated in the same manner as in Example 1.
Using the same method as in Example 1, negatively charged insulating magnetic toner C (particle size distribution is shown in Table 2) was obtained.

moreover We were able to obtain high-quality images.

Comparative Example 1 A negatively charged insulating magnetic toner D (the viscosity distribution is shown in Table 2) was obtained using the same materials and method as those shown in Example 1.

The above substances were mixed in a Henschel mixer to form a one-component developer, and then evaluated in the same manner as in Example 1. As shown in Table 3, stable, clear, high-quality images could be obtained.

Example 6 The above substances were mixed in a Henschel mixer to form a one-component developer, and then evaluated in the same manner as in Example 1. The results are as shown in Table 3. The above-mentioned substances were mixed in a Henschel mixer to form a -component developer, which was stable and clear. After that, evaluation was performed in the same manner as in Example 1. As shown in Table 3, the charging wire was severely contaminated (the image after 50,000 sheets was of a very poor quality). When this charging wire was observed with a scanning electron microscope, it was confirmed that fine silica powder was attached. .

Comparative Example 2 A negatively charged insulating magnetic toner E (the viscosity distribution is shown in Table 2) was obtained using the same materials and method as those shown in Example 5.

The above substances were mixed in a Henschel mixer to form a -component developer, and then evaluated in the same manner as in Example 1. As shown in Table 3, the results showed that the image was noticeably rough, which was problematic in practice.

[Brief explanation of drawings]

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

Claims (2)

[Claims] (1) Contains at least a negatively charged insulating magnetic toner that is applicable to a developing method in which the rotation speed of the outer periphery of a developer carrier for developing an electrostatically charged image carrying a developer on its surface is 400 mm/sec or more. In the negatively charged magnetic developer, the negatively charged insulating magnetic toner contains 17 to 80 number % of magnetic toner particles having a particle size of 5 μm or less, and 6.35 μm or less.
5 to 5 magnetic toner particles having a particle size of ~12.7 μm
A group of magnetic toner particles containing 0% by number, containing 2.0% by volume or less of magnetic toner particles having a particle size of 16 μm or more, and having a volume average particle size of 4.5 to 9 μm and 5 μm or less. is the following formula N/V=-0.04N+k [wherein, N represents the number % of magnetic toner particles having a particle size of 5 μm or less, and V represents the volume % of magnetic toner particles having a particle size of 5 μm or less. , k represents a positive number from 4.5 to 6.5. However, N represents a positive number from 17 to 80. ] It has a particle size distribution that satisfies the following, and BET by nitrogen adsorption
Inorganic fine powder with a specific surface area of 40 to 400 cm^2/g,
A negatively charged magnetic developer characterized by containing a ferroelectric substance having a BET specific surface area of 0.5 to 30 m^2/g. (2) The content ratio of the inorganic fine powder and ferroelectric particles is expressed by the following formula Sw_1×W_1/SW_2×W_2=15 to 300
[In the formula, Sw_1 is the BET specific surface area (cm
^2/g), Sw_2 indicates the BET specific surface area (cm^2/g) of the ferroelectric material, W_1 is the weight (g) of the inorganic fine powder contained in the developer, and W_2 is the weight (g) of the inorganic fine powder contained in the developer. The weight (g) of the ferroelectric material contained is shown. ] A negatively charged magnetic developer according to claim (1), which satisfies the following.