JPH06289723A - Image forming device - Google Patents

Abstract

PURPOSE:To make the reproducibility of an image satisfactory in development with use of magnetic one-component toner by making the strength of the magnetization of the magnetic one-component toner small and stabilizing a process for imparting a charge to toner. CONSTITUTION:In the image forming device provided with a latent image carrier 10, a latent image forming means forming a latent image on the latent image carrier 10, magnetic toner incorporating a magnetic substance, a developer carrier 1a and a developing device carrying the developer incorporating the magnetic toner and developing the latent image on the latent image carrier 10, the magnetic toner incorporates the magnetic substance composed of a metallic oxide whose magnetization strength in 1KOe (oersted) magnetic field is 10-40emu/g and ferri-diameter in a horizontal direction is 0.05-0.5mum and at least two or more developing carriers 1a are disposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used in an electrophotographic apparatus.

[0002]

[Prior art]

(First invention) Conventionally, as a dry developing method of electrophotography, a method of using a magnetic one-component toner as a developer and a method of using two components of a carrier and a toner are generally well used. The two developing methods using the above-mentioned developer have the following advantages, that is, the one-component developing method can reduce the size of the developing device structure, and the two-component developing method can sufficiently impart the electric charge to the toner. Therefore, it has an advantage that the design allowable range is wide.

However, as can be seen from the fact that the above advantages are in the direction of compensating for the disadvantages of the respective systems, the one-component system is not sufficient in the process of imparting electric charge to the toner, so that the design allowable range of the toner and the developing system is limited. The narrow two-component system has a drawback that the device configuration becomes complicated because the mixed concentration of toner and carrier must be controlled to a constant value.

Further, the copied image by each method is such that the magnetic one-component method uses a chain of toner for developing (generally, "brush").
The resolution in the horizontal direction of the image tends to be worse than that in the vertical direction.
In the latter half of the developed image, a phenomenon called tailing due to the protrusion of the ears tends to occur in the non-image portion, and a rough image tends to occur as compared with the two-component system. On the other hand, in the two-component method, there is a tendency that the sweep trace of the magnetic brush is likely to appear.

(Second invention) Conventionally, a method of using a magnetic one-component toner as a developer as a dry developing method of electrophotography,
A method using two components of a carrier and a toner is generally well used. The two developing methods using the above-mentioned developer have the following advantages, that is, the one-component developing method can reduce the size of the developing device structure, and the two-component developing method can sufficiently impart the electric charge to the toner. Therefore, it has an advantage that the design allowable range is wide.

However, as the above-mentioned advantages tend to compensate for the disadvantages of the respective systems, the one-component system is not sufficient in the process of imparting charge to the toner, and therefore the design allowable range of the toner and the developing system is limited. The narrow two-component system has a drawback that the device configuration becomes complicated because the mixed concentration of toner and carrier must be controlled to a constant value.

Further, in the case of the magnetic one-component method, the copied image by each method is developed while the toner is chained (generally called "brush") at the time of development.
The resolution in the horizontal direction of the image tends to be lower than that in the vertical direction. For example, a phenomenon called tailing due to protrusion of ears is likely to occur in the non-image portion in the latter half of the developed image, and a rough image is generated as compared with the two-component method. Tends to be easy. On the other hand, in the two-component method, there is a tendency that the sweep trace of the magnetic brush is likely to appear.

[0008]

[Problems to be Solved by the Invention]

(First Invention) As described above, one of the disadvantages of the magnetic one-component system is that the charge application process is insufficient, and the other is that the toner contains a magnetic substance. Two points are poor image reproducibility.

As a method of solving the image reproducibility, it is conceivable to make the ears of the toner short and dense, and as a means therefor, it is easy to imagine a method of reducing the ratio of the amount of magnetic material in the toner. Yes, but in general, current development systems rely on the absolute value of the specific charge of the toner,
It is difficult to develop a toner containing a reduced amount of magnetic material for the following reasons.

That is, if the radius of one toner is R, the charge amount is Q, and the density is ρ, the specific charge Q / M of the toner can be expressed as Q / M = 3Q / 4πρR ³ . The density of the magnetic material in the toner of the general magnetic one-component toner is several times higher than the density of the binder resin. Therefore, the toner density ρ decreases as the amount of magnetic material in the toner decreases, and the specific charge increases conversely. As is well known, an increase in specific charge tends to cause a low image density. In particular, as is clear from the above equation, as the toner particle size is reduced, the tendency becomes remarkable.

It is well known empirically that the image quality of a copied image in the magnetic one-component developing system is greatly influenced by the cohesiveness of the toner, and if the cohesiveness becomes strong, image defects such as fog are likely to occur. There is. This fogging phenomenon is caused by thickening of the ears when the cohesiveness of the toner becomes strong, and as a result,
It is qualitatively understood that it is difficult for the toner inside the ears to obtain a charge due to frictional charging with the developer carrying member, that is, the toner is insufficiently charged. . Further, the relationship between the strength of magnetization of the magnetic toner and the shape of the ears is qualitatively understood as follows. That is, when the magnetic toner has a large magnetization intensity, a strong attractive force along the magnetic field direction and a strong repulsive force in the direction perpendicular to the magnetic field are generated between the magnetic toner particles.

Therefore, when the strength of magnetization is high, the ears formed by the magnetic toner become long and rough, and one ear becomes thin, and conversely, when the strength of the magnetization of the magnetic toner is low. This time, the ears become short and dense, and since the binding between the magnetic toners cannot be released, one ears become thick and short, and become agglomerated. Therefore, in the latter case, as described above, the magnetic toner inside the ears becomes insufficiently charged. Therefore, if the ratio of the amount of magnetic material in the toner is simply reduced to shorten the spikes, it is easy to cause image deterioration such as fogging due to toner charge-up or toner charging failure. was there.

Further, in general, the magnetic substance also functions as a coloring agent, and therefore it is easily conceivable that the image density becomes insufficient if the amount of the magnetic substance is reduced as it is.

Further, as a method for shortening and making the toner ears short and dense, a constitution in which an elastic developer layer thickness regulating member is brought into contact with the developer carrying member is considered. However, in the above structure, there is a problem in that the developer layer thickness regulating member of the elastic body is easily worn and lacks durability stability. Therefore, as described above, the layer thickness of the developer of the developer carrying member is regulated in a non-contact state with the developer carrying member, the strength of magnetization of the magnetic toner is reduced, and stable control of charge imparting is performed. Thus, there is still no sufficient magnetic toner and image forming apparatus for improving the image reproducibility.

(Second invention) As described above, the magnetic 1
The two disadvantages of the component system are that the charge application process is insufficient and that the image reproducibility is poor because the toner contains a magnetic material. As a method of solving the image reproducibility, it is conceivable to make the ears of the toner short and dense, and as a means therefor, a method of reducing the ratio of the amount of magnetic material in the toner can be easily imagined. Generally, since the current developing system depends on the absolute value of the specific charge of the toner, it is difficult to develop the toner containing the reduced amount of the magnetic substance for the following reasons.

That is, if the radius of one toner is R, the amount of charge is Q, and the density is ρ, the specific charge Q / M of the toner can be expressed as Q / M = 3Q / 4πρR ³ . The density of the magnetic material in the toner of the general magnetic one-component toner is several times higher than the density of the binder resin. Therefore, the toner density ρ decreases as the amount of magnetic material in the toner decreases, and the specific charge increases conversely. As is well known, an increase in specific charge tends to cause a low image density. In particular, as is clear from the above equation, the tendency becomes more remarkable as the toner particle size is reduced.

It is well known empirically that the image quality of a copied image in the magnetic one-component developing system is greatly influenced by the cohesiveness of the toner, and if the cohesiveness becomes strong, image defects such as fog are likely to occur. There is. This fogging phenomenon is caused by thickening of the ears when the cohesiveness of the toner becomes strong, and as a result,
It is qualitatively understood that it is difficult for the toner inside the ears to obtain a charge due to frictional charging with the developer carrying member, that is, the toner is insufficiently charged. .

The relationship between the magnetic strength of the magnetic toner and the shape of the spikes is also qualitatively understood as follows. That is, when the magnetic toner has a large magnetization intensity, a strong attractive force along the magnetic field direction and a strong repulsive force in the direction perpendicular to the magnetic field are generated between the magnetic toner particles. Therefore, when the magnetization intensity is high, the ears formed by the magnetic toner become long and rough,
Moreover, if one magnetic head becomes thin, and conversely, if the magnetic toner has a small magnetization strength, the magnetic head becomes short and dense this time, and since the coupling between the magnetic toners cannot be released, The ears are thick and short, and they are in an aggregated state. Therefore, in the latter case, as described above, the magnetic toner inside the ears becomes insufficiently charged.

Therefore, when the ratio of the amount of magnetic material in the toner is simply reduced to shorten the ears, deterioration of image quality such as fog due to charge-up of the magnetic toner or defective charging of the magnetic toner occurs. There was a problem that it was easy to cause. Further, in general, the magnetic material also serves as a coloring material, so if the amount of the magnetic material is reduced as it is, it is easily considered that the image density becomes insufficient. Further, as a method for shortening and making the toner ears short and dense, a configuration in which an elastic developer layer thickness regulating member is brought into contact with the developer carrying member is considered. However, in the above structure, there is a problem in that the developer layer thickness regulating member of the elastic body is easily worn and lacks durability stability.

Therefore, as described above, the layer thickness of the developer on the developer carrying member is regulated in a non-contact state with the developer carrying member, and the magnetic substance is magnetically reduced without decreasing the amount of the magnetic material in the magnetic toner. There has not yet been a sufficient magnetic toner and image forming apparatus which can reduce the magnetizing strength of the toner and improve the charging imparting stability and the image reproducibility.

[0021]

[Means and Actions for Solving the Problems]

(First Invention) According to the study by the present inventors, the length of the ears between the length of the ears of the magnetic toner on the developer carrying member in the developing area and the magnetization intensity of the magnetic toner is ∝ It was confirmed that there is a correlation with the magnetic strength of the magnetic toner. Therefore, it was found that if the magnetic strength of the magnetic toner is reduced without reducing the amount of magnetic material in the magnetic toner, it is possible to shorten the length of the brush without changing the weight of the magnetic toner. .

Further, according to the study by the present inventors, the charge amount of the lower layer magnetic toner forming the ears is greater than the charge amount of the upper layer magnetic toner forming the ears. It was found to be high. Further, according to the study of the present inventors, when the number of times or the contact time of the magnetic toner on the upper layer side forming the ears and the developer carrying member is increased, the charging of the magnetic toner becomes stable. It was also found that the ears formed by the magnetic toner tend to be thin.

Further, according to the study by the present inventors, the magnetic toner in the case where the magnetic substance contained in the magnetic toner has a small magnetization intensity without reducing the amount of the magnetic substance in the magnetic toner. In order to improve the charge imparting stability and the image reproducibility during development, it is formed on the developer carrying member in the developing area formed between the latent image carrying member and the developer carrying member. Chain-like aggregate of magnetic toner, that is, the number density of ears is 8 × 10
⁴ lines / cm ² or more, the length of the magnetic toner ears is 180 μ
m or less and the weight average particle diameter of the magnetic toner is γ (μ
m) and the true density is ρ (g / cm ³ ), the amount of the developer on the developer carrier in the developing area is 0.06γρ (mg
/ Cm ² ) It has been found that it is essential to adjust to the above conditions.

Particularly preferably, the number density of ears is 10 × 10.
⁴ lines / cm ² or more, the length of the magnetic toner ears is 160 μm
It has been found that adjusting to m or less is a condition for making the image reproducibility stable and good. Therefore, according to the present invention, a latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, a magnetic toner containing a magnetic material, a developer carrier, and the magnetic toner are provided. An image forming apparatus having a developing device that carries a developer containing the developer on the developer carrier and develops the latent image on the latent image carrier,

The magnetic substance contained in the magnetic toner has a magnetization intensity of 10 to 40 emu / g in a magnetic field of 1 KOe.
The magnetic toner is made of a metal oxide having a horizontal ferret diameter of 0.05 to 0.5 μm, and at least two or more development carriers are arranged, and the magnetic toner is provided between the developer carriers. Is moved to increase the number of contact times or contact time between the magnetic toner on the upper layer side of the ears formed of the magnetic toner and the developer carrying member, thereby increasing the amount of the magnetic material in the magnetic toner. The magnetic strength of the magnetic toner is reduced without decreasing, the process of imparting electric charge to the magnetic toner is stabilized, and the conditions such as the density of the number of ears are stabilized to improve the image reproducibility. is there.

The term "brush" is defined to be about 4γ (μm) above the developer carrying member in the developing region portion with respect to the weight average diameter γ (μm) of the magnetic toner. The aggregate of magnetic toner existing up to is defined as a spike. The density of the number of ears per unit area was defined as the density of the number of ears existing above the developer-carrying member by about 4γ (μm) in the developing area. The method for measuring the number density is as follows. The number density per unit area of the ears existing at the position is determined by focusing an optical microscope with a magnification of 100 at the position of about 4γ (μm) above the developer carrier. It was measured.

Further, the length of the spikes of the magnetic toner is measured by setting the magnification of the optical microscope to 200 times and making the depth of field shallow, and scanning the focus of the microscope upward from above the developer carrier. The length of the spike was measured by measuring the moving distance of the focal portion until the tip of the spike was brought into focus.

The structure of the magnetic toner used in the present invention will be described in more detail below. The range of the strength of magnetization of the magnetic material used in the present invention is 10 to 40 emu / g. 20-40 emu / g is preferable. The magnetic field strength of the magnetic material used here is the value when the magnetic field is 1 KOe. Because the developing device used in the present invention,
Since the magnetic field generated by the magnet disposed inside the developer carrying member is about 1 KOe at the maximum on the surface of the developer carrying member, the strength of the magnetization at the magnetic field of 1 KOe is the magnetic field in the developing device. This is because it is the most suitable value when considering the magnetic characteristics of the toner.

The magnetic force was measured using VSM manufactured by Toei Industry Co., Ltd. The strength of magnetization in a magnetic field of 1 KOe is 10 emu
If it is less than / g, toner scattering becomes a problem, and the transportability is poor and uniform images cannot be obtained. If the magnetization intensity is higher than 40 emu / g, the magnetic toner becomes long and the image reproducibility may be poor, that is, fine line reproducibility and gradation may be poor. The holding power is also related to the image quality. The range of holding power is preferably 50 to 200 Oe. Although the reason is not clear, if the holding power is less than 50 Oe,
Fog on the background portion is likely to occur. If the holding force is greater than 200 Oe, the transportability may be poor, the coating may not be good, and the image quality such as uneven image density may be degraded.

The particle size of the magnetic material is related to the charge amount of the toner, the coloring power and the like. The particle diameter of the magnetic material is indicated by the Feret diameter in the horizontal direction.
The measurement was carried out by magnifying a photograph of a magnetic body of 10,000 times obtained by a transmission electron microscope 4 times to make a photograph of 40,000 times, and randomly selecting 250 magnetic bodies and measuring the diameter thereof. Then, the average particle size is obtained. Average particle size is 0.05 to 0.5
μm. The thickness is preferably 0.08 to 0.4 μm, more preferably 0.1 to 0.4 μm. Average particle size 0.05
If it is less than μm, it is difficult to control the charge and is easily oxidized, resulting in poor handleability. If the average particle size is larger than 0.5 μm, the coloring power is insufficient, and the toner is non-uniformly charged, which may cause fog in the background portion.

When the weight average particle diameter γ of the toner is 7.5 μm or more, the content (% by weight) of the magnetic substance is 30 to 60% by weight. If the amount is less than 30% by weight, there is a problem that the transportability becomes insufficient, image density unevenness or the like occurs, the aggregation of ears becomes difficult to loosen, and fog occurs in the background portion. If it exceeds 60% by weight, the effect of the present invention is reduced and the image reproducibility is deteriorated. When the weight average particle diameter γ of the toner is 7.5 μm or less, the content (% by weight) of the magnetic substance is in the range of {WT = − (10/3) γ + (70 ± 15)}. However, the conditions were such that the problems due to the above-mentioned transportability and aggregation did not occur.

If the charge amount of the toner is not appropriate, a good image cannot be obtained. The charge amount of the toner was determined by the blow-off measurement method. A measuring instrument manufactured by Toshiba Chemical Co. was used.
EFV200 / 300 (manufactured by Nippon Iron Powder Co., Ltd.) was used as a carrier, the toner concentration was 2% by weight, and the mixing time was about 2 minutes. The absolute value of the measured value at this time is preferably 5 to 50 μc / g. It is preferably 5 to 40 μc / g. If it is less than 5 μc / g, the sharpness of the image will be poor and fog in the background will occur. Further, in a high temperature and high humidity environment, a decrease in image density becomes a problem. If it is larger than 50 μc / g, the electrostatic cohesive force becomes large, and the ears are hard to loosen, and the image quality deteriorates. In particular, in a low temperature and low humidity environment, the mirroring power with respect to the toner carrying member becomes larger than necessary, so that the image density is lowered.

The particle size of the toner of the present invention was measured by a TA-II type machine manufactured by Coulter Counter. An aperture of 100 μm is used, and the particle size is a weight average diameter,
The coefficient of change was calculated by dividing the standard deviation of the volume distribution by the volume average diameter and multiplying by 100. As the binder resin for toner,
Homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymers, styrene-vinyl-toluene copolymers and their copolymers; styrene-methyl acrylate Copolymers of styrene and acrylic ester such as copolymers, styrene-ethyl acrylate copolymers, styrene-n-butyl acrylate copolymers; styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate Copolymers, copolymers of styrene and methacrylic acid esters such as styrene-n-butyl methacrylate copolymers; multi-component copolymers of styrene and acrylic acid esters and methacrylic acid esters; other styrene-acrylonitrile copolymers , Styrene-vinyl methyl ether copolymer, styrene Styrene-based copolymerization of styrene and other vinyl-based polymerizable monomers such as butadiene copolymer, styrene-vinyl methyl ketone copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid ester copolymer Combined; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid, phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc. Alternatively, they can be mixed and used.

In particular, as a binder resin for a toner to be subjected to a pressure fixing system, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acid, polyamide resin, Polyester resins and the like can be used alone or in combination. If the polymer, copolymer or polymer blend used contains vinyl aromatic or acrylic monomer represented by styrene in an amount of 40% by weight or more, more desirable results are obtained.

Any suitable pigment or dye can be used as a colorant in the toner. For example, carbon black, phthalocyanine blue, ultramarine, quinacridone,
There are known dyes and pigments such as benzidine yellow. As a method for producing the toner containing the magnetic material used in the present invention, a conventionally known method may be used. That is, the binder resin, the charge control agent, the colorant, the magnetic substance, and the other additives are preliminarily powder-mixed with a Henschel mixer or the like, and then the mixture is kneaded with a roll mixer heated to about 150 ° C. for about 30 minutes and kneaded. The product is obtained, cooled, pulverized, and if necessary classified to obtain a toner composition. If necessary, a fluidity imparting agent, a lubricant, an abrasive, a cleaning aid, a resistance adjusting agent, a charge control agent and the like may be added internally or externally.

(Second Invention) According to a study made by the present inventors, the magnetic strength of the magnetic substance contained in the magnetic toner is reduced without reducing the amount of the magnetic substance in the magnetic toner. In order to improve the stability of charge imparting to the magnetic toner and the image reproducibility during development, the developer carrying in the developing area formed between the latent image carrying body and the developer carrying body is carried. Chain-like aggregates of magnetic toner formed on the body, that is, the number density of ears is 8 × 10 ⁴ / cm ² or more, the length of ears of the magnetic toner is 180 μm or less, and the weight average of the magnetic toner. When the particle size is γ (μm) and the true density is ρ (g / cm ³ ), the amount of the developer on the developer carrier in the developing area is 0.0.
It has been found that it is essential to adjust the conditions to 6γρ (mg / cm ² ) or more.

Particularly preferably, the density of the number of ears is 10 × 10.
⁴ lines / cm ² or more, the length of the magnetic toner ears is 160 μm
It has been found that adjusting to m or less is a condition for making the image reproducibility stable and good. Further, according to the study by the present inventors, the length of the ears is ∝ between the length of the ears of the magnetic toner on the developer carrier in the developing area and the magnetization intensity of the magnetic toner. It was confirmed that there is a correlation with the magnetic strength of the magnetic toner.

Further, in order to stabilize the conditions such as the density of the number of ears, there is provided a means capable of providing a crushing force to the chain-like aggregate of magnetic toner on the developer carrying member,
It is essential to dispose the developer carrier in a non-contact state. According to the study by the present inventors, it has been found that the repulsive force between the toners due to the magnetic force increases in the concentrated portion of the magnetic force lines, and the aggregation of the magnetic toner tends to be released.

Therefore, according to the present invention, a latent image carrier,
A latent image forming means for forming a latent image on the latent image carrier, a magnetic toner containing a magnetic material, a developer carrier having a magnet inside, and a layer of the developer on the developer carrier. A developer regulating member that regulates the thickness of the developer carrier without contacting the developer carrier, and a developer containing the magnetic toner are carried on the developer carrier to develop the latent image on the latent image carrier. In an image forming apparatus having a developing device, the magnetic substance contained in the magnetic toner has a magnetization strength of 10 to 40 em in a magnetic field of 1 KOe.
u / g, a ferrule diameter in the horizontal direction of 0.05 to 0.5 μm, and a magnetic substance made of a metal oxide,

Between the developer regulating member and the developing area formed between the latent image carrier and the developer carrier with respect to the direction in which the developer is carried on the developer carrier. , A magnet having a plurality of magnetic poles is disposed inside the developer carrier,

The chain density of magnetic toner formed on the developer carrying member, that is, the number density of the ears, in the developing area formed between the latent image carrying member and the developer carrying member, 8
× 10 ⁴ lines / cm ² or more, the length of the magnetic toner ears is 1
80 μm or less, and the weight average particle diameter of the magnetic toner is γ
(Μm) and the true density is ρ (g / cm ³ ), the amount of developer on the developer carrier in the development area is 0.06γρ
(Mg / cm ² ) or more, the magnetic strength of the magnetic toner is reduced without reducing the amount of the magnetic substance in the magnetic toner, and the layer thickness of the developer on the developer carrier is reduced. The toner is regulated in a non-contact state with the developer carrier, and the process of imparting a charge to the magnetic toner is stabilized to improve image reproducibility.

The definition of "brush" is that the magnetic toner weight average diameter γ (μm) is about 4γ (μm) or more above the developer carrying member in the developing area of the developer carrying member. The aggregate of the magnetic toner existing up to the point was defined as a spike. The number density of the ears per unit area is about 4 on the developer carrying member in the developing area of the developer carrying member.
It was defined by the number density of panicles existing in the upper part of γ (μm). The method for measuring the number density is about 4 above the developer carrier.
The position of γ (μm) was focused on an optical microscope with a magnification of 100 times, and the density of the number of ears existing at the position per unit area was measured.

Further, the length of the magnetic toner ears is measured by setting the magnification of the optical microscope to 200 times, with a shallow depth of field, and scanning the focus of the microscope upward from above the developer carrying member. Then, the length of the spike was measured by measuring the moving distance of the focal portion until the tip of the spike was brought into focus.

The structure of the magnetic toner used in the present invention will be described in more detail below. The range of the strength of magnetization of the magnetic material used in the present invention is 10 to 40 emu / g. 20-40 emu / g is preferable. The magnetic field strength of the magnetic material used here is the value when the magnetic field is 1 KOe. Because the magnetic field generated by the magnet disposed inside the developer carrier of the developing device used in the present invention is about 1 KOe at the maximum on the surface of the developer carrier, the magnetic field of 1 KOe This is because the strength of magnetization is the most suitable value in consideration of the magnetic characteristics of the magnetic toner in the developing device.

The magnetic force was measured using VSM manufactured by Toei Industry Co., Ltd. The strength of magnetization in a magnetic field of 1 KOe is 10 emu /
If it is less than g, toner scattering becomes a problem, and the transportability is poor and a uniform and good image cannot be obtained. If the magnetization intensity is higher than 40 emu / g, the magnetic toner becomes long and the image reproducibility may be poor, that is, fine line reproducibility and gradation may be poor. The holding power is also related to the image quality.
The range of holding power is preferably 50 to 200 Oe. Although the reason is not clear, if the holding force is less than 50 Oe, fog in the background portion is likely to occur. If the holding force is greater than 200 Oe, the transportability may be poor, the coating may not be good, and the image quality such as uneven image density may be degraded.

The particle size of the magnetic material is related to the charge amount of the toner, the coloring power and the like. The particle diameter of the magnetic material is indicated by the Feret diameter in the horizontal direction.
The measurement was carried out by magnifying a photograph of a magnetic material with a magnification of 10,000 times obtained by a transmission electron microscope by a factor of 4 to obtain a photograph with a magnification of 40,000. Then, 250 magnetic materials were randomly selected and their diameters were measured. This is the average particle size. Average particle size is 0.05-0.5μ
m. The thickness is preferably 0.08 to 0.4 μm, more preferably 0.1 to 0.4 μm. Average particle size 0.05μ
If it is less than m, it is difficult to control the charge and is easily oxidized, resulting in poor handleability. If the average particle size is larger than 0.5 μm, the coloring power is insufficient, and the toner is non-uniformly charged, which may cause fog in the background portion.

The content (% by weight) of the magnetic substance is 30 to 60% by weight. If it is less than 30% by weight, there is a problem that the transportability becomes insufficient, image density unevenness or the like occurs, or the aggregation of ears becomes difficult to loosen, and fog occurs in the background portion.
If it exceeds 60% by weight, the effect of the present invention is reduced and there is a problem that the image reproducibility is deteriorated. When the weight average particle diameter γ of the toner is 7.5 μm or less, the content of the magnetic substance can be derived by the following formula. {WT =-(10/3) γ + (70 ± 15)}

If the charge amount of the toner is not appropriate, a good image cannot be obtained. The charge amount of the toner was determined by the blow-off measurement method. A measuring instrument manufactured by Toshiba Chemical Co. was used.
EFV200 / 300 (manufactured by Nippon Iron Powder Co., Ltd.) was used as a carrier, the toner concentration was 2% by weight, and the mixing time was about 2 minutes. The absolute value of the measured value at this time is preferably 5 to 50 μc / g. It is preferably 5 to 40 μc / g. If it is less than 5 μc / g, the sharpness of the image will be poor and fog in the background will occur.
Further, in a high temperature and high humidity environment, a decrease in image density becomes a problem. If it is larger than 50 μc / g, the electrostatic cohesive force becomes large, and the ears are hard to loosen, and the image quality deteriorates. In particular,
In a low temperature and low humidity environment, the mirroring power with respect to the toner carrying member becomes larger than necessary, so that the image density is lowered.

The particle size of the toner of the present invention was measured by a TA-II type machine manufactured by Coulter Counter. An aperture of 100 μm is used, and the particle size is a weight average diameter,
The coefficient of change was calculated by dividing the standard deviation of the volume distribution by the volume average diameter and multiplying by 100. As the binder resin for toner,
Homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymers, styrene-vinyl-toluene copolymers and their copolymers; styrene-methyl acrylate Copolymers of styrene and acrylic ester such as copolymers, styrene-ethyl acrylate copolymers, styrene-n-butyl acrylate copolymers; styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate Copolymers, copolymers of styrene and methacrylic acid esters such as styrene-n-butyl methacrylate copolymers; multi-component copolymers of styrene and acrylic acid esters and methacrylic acid esters; other styrene-acrylonitrile copolymers , Styrene-vinyl methyl ether copolymer, styrene Styrene-based copolymerization of styrene and other vinyl-based polymerizable monomers such as butadiene copolymer, styrene-vinyl methyl ketone copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid ester copolymer Combined; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid, phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc. Alternatively, they can be mixed and used.

In particular, as a binder resin for a toner which is subjected to a pressure fixing system, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acid, polyamide resin, Polyester resins and the like can be used alone or in combination. More desirable results can be obtained when the polymer, copolymer, or polymer blend used contains 40% by weight or more of a vinyl aromatic or acrylic monomer represented by styrene. Any appropriate pigment or dye can be used as a colorant in the toner. For example, there are known dyes and pigments such as carbon black, phthalocyanine blue, ultramarine blue, quinacridone, and benzidine yellow.

As a method for producing a toner containing a magnetic material used in the present invention, a conventionally known method may be used. That is, a binder resin, a charge control agent, a coloring agent, a magnetic substance, and other additives are previously powder-mixed with a Henschel mixer or the like, and then this is mixed with 15
The mixture is kneaded for about 30 minutes with a roll mixer heated to about 0 ° C. to obtain a kneaded product, which is cooled, pulverized, and if necessary classified to obtain a toner composition. If necessary, a fluidity imparting agent, a lubricant, an abrasive, a cleaning aid, a resistance adjusting agent, a charge control agent and the like may be added internally or externally.

[0052]

【Example】

(First Invention) Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.
The magnetic materials used in the following examples and comparative examples are shown in Table 1.

[0053]

[Table 1]

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a developing device which is an embodiment of the present invention. In the figure, 1a and 2a are sleeves 1b and 2b made of a non-magnetic metal, which is a developer carrier that rotates in the arrow direction.
Is a permanent magnet disposed inside the sleeves 1a and 2a, and 5 is a developer regulating member composed of a magnetic member that regulates the amount of developer on the sleeve 1a which is a developer carrier. It is a magnetic sleeve, and in the present invention,
The magnetic sleeve is arranged in a non-contact state with the developer carrying member.

Here, the non-contact state means a state in which the developer carrier is not in contact with the developer regulating member when the developer is not interposed between the developer carrier and the developer regulating member. It means that it is arranged in. Also, the magnetic sleeve 5
Are arranged such that the distance therebetween is a constant value W with respect to the sleeve 1a. Generally, the distance W is 100 μm to 1
It is set to a value within the range of mm. Further, 9 is a developing device, 3 is a conveying member for conveying the magnetic toner in the developing device 9 toward the sleeve 1a, 10 is a latent image carrier, and 4 is a developing device between the sleeve 2a and the latent image carrier 10. It is a power supply for applying a bias.

According to the developing device having the above-mentioned structure, as shown in FIG.
The toner is regulated to a desired toner layer thickness when it is conveyed in the direction of the arrow on a and passes through the gap between the developer regulating member 5 and the sleeve 1a. Further, the toner T that has passed through the layer thickness regulating portion forms the ears A. The behavior of the toner at the layer thickness regulating portion when the ears A are formed is as follows.

First, consider a plane perpendicular to a straight line connecting the sleeve 1a and the magnetic blade 2 as shown in FIG. When the surface close to the magnetic blade 5 is S1 and the surface close to the sleeve 1a is S2, the width of the magnetic blade 2 is generally narrower than the width of the permanent magnet 1b. Considering the respective magnetic flux densities of the above, the magnetic flux density on the S1 surface becomes larger than the magnetic flux density on the S2 surface. Therefore, the magnetic toner T receives a force in the direction of the arrow in FIG. 3, that is, a force toward the magnetic blade 5 between the sleeve 1 a and the magnetic sleeve 5.

Therefore, as shown in FIG. 4, the magnetic toner T forms the ears B, and the ears are formed from the magnetic blade 5 toward the sleeve 1a. In charging the magnetic toner T, the sleeve 1a and the toner t1 at the tip of the ears formed by the magnetic blade 5 contact each other, so that the toner t1 at the tip is charged. Further, it was found that the toner was conveyed between the sleeve 1a and the magnetic blade 5 as follows.

First, as described above, since the toner t1 at the tip of the brush that comes into contact with the sleeve 1a is charged,
A force in the direction of the sleeve 1a is exerted by the mirroring force, and as a result, a frictional force with the sleeve 1a gives a conveying force in the rotating direction of the sleeve 1a.

Since the toners have a certain amount of cohesive force acting on each other, the toner t2 in contact with the toner t1 also has a conveying force with the intervening cohesive force. Further, similarly, the toner t3 in the upper layer portion also has a carrying force with the cohesive force interposed. However, the magnetic force in the direction of the magnetic blade 5 is also applied to the toner between the sleeve 1a and the magnetic blade 5, as described above. Therefore, when the conveying force applied to the toner overcomes the magnetic force, that is, at the cut line L in FIG. 4, the ears of the toner are torn off, and the toner remaining on the sleeve 1a is conveyed in the rotation direction of the sleeve 1a.

Therefore, of the magnetic toner forming the ears A, the only magnetic toner that can contact the sleeve 1a is the magnetic toner in the vicinity of the sleeve 1a. Contains the toner that has been triboelectrically charged and the toner that has not been triboelectrically charged.
In particular, in the magnetic toner in which the magnetic strength of the magnetic material contained in the magnetic toner used in the present invention is in the above range, the repulsive force between the toner due to the magnetic force is small against the cohesive force between the magnetic toners. Therefore, the ear A becomes thicker, and as a result, a large amount of the toner that is not triboelectrically charged exists in the ear A.

Therefore, according to the present invention, as shown in FIG. 1, the sleeve 2a is disposed so as to face the sleeve 1a, and the magnetic toner is transferred between the sleeve 1a and the sleeve 2a to be formed on the sleeve 1a. The contact probability and contact time between the upper layer of the magnetic toner ears A and the sleeve 2a are increased. Therefore, as shown in FIG. 2, after the transfer between the sleeves, the ears C formed on the sleeve 2a.
The proportion of toner that is not triboelectrically charged inside is smaller than that in the ear A.

Further, according to the present invention, it was also found that when the ratio of the toner which is not frictionally charged in the magnetic toner forming the ears decreases, the ears tend to be thin.
In the configuration of the present invention, the gap between the sleeve 1a and the magnetic blade 5 is about 250 μm. Also, sleeve 1
The distance between a and the sleeve 2a is about 200 μm, and the magnetic toner transfer portion formed by the sleeve 1a and the sleeve 2a is a permanent magnet 1 contained in the sleeve 1a.
The magnetic pole S1 of b and the magnetic pole N3 of the permanent magnet 2b included in the sleeve 2a are opposite to each other so as to have different polarities.

The magnetic flux density of the magnetic poles of the permanent magnets 1b and 2b is preferably 500 G or more in consideration of the transportability of the magnetic toner, and in the present invention, it is about 800 G. Also, the sleeve 1a
The sleeve 2a and the sleeve 2a are cylindrical tubes having the same diameter, and the rotational speeds of the cylindrical tubes are the same. However, the present invention is not limited to this. It is preferable to set the diameter and peripheral speed of the sleeve.

Further, in the structure of the present invention, the developing bias is applied to the sleeve 2a by the power source 4, and
Development bias is Vpp 1,800V, frequency 2,0
It is an AC rectangular wave bias of 00 Hz. The magnetic toner used in the present invention is configured to reduce the magnetic strength of the magnetic toner without reducing the amount of magnetic material in the magnetic toner, that is, the magnetic strength in a magnetic field of 1 KOe is 10 to 4.
It was set to 0 emu / g. In general, a magnetic material having a smaller magnetization intensity than a commonly used magnetic material is used. The magnetic substance contained in the toner includes iron, cobalt, nickel, copper, magnesium, manganese, aluminum,
There are metal oxides containing elements such as silicon. The magnetic material used in the examples of the magnetic toner of the present invention is No. The magnetic substance of No. 1 is spinel type iron oxide obtained by the following synthesis method.

(Synthesis Example) As a reactor, a bubble oxidation type reaction column having an internal capacity of 180 liters was used. Industrial iron sulfate is dissolved in water to prepare 40 liters of a solution having a ferrous iron concentration of 134 g / liter. Separately, 40 liters of a solution having a caustic soda concentration of 182 g / liter was prepared, and the above iron sulfate solution was added thereto with stirring to neutralize the solution so that the residual caustic soda became 5 g / liter. To this was added 50 liters of an industrial zinc hydroxide solution having a pH of 11.3 and a zinc concentration of 40 g / liter to prepare a reaction solution having a ferrous iron concentration of 40 g / liter.

While maintaining the temperature of the above reaction liquid at 80 ° C., oxidizing air was blown at a rate of 10 l / min to carry out the oxidation reaction. The reaction was completed in about 7 hours. Then
This slurry was washed and dried to obtain spinel type iron oxide.
The obtained magnetic material has a horizontal ferret diameter of 0.26 μm, B
ET 8.9 m ² / g, magnetization strength 31.3 emu / g,
The coercive force was 165 Oe, and the residual magnetization was 5.6 emu / g.

Further, the magnetic toner was prepared as follows. Styrene-acrylic copolymer 54.9% by weight Negative charge control agent 0.5% by weight Magnetic substance (magnetic substance obtained in the above synthesis example) 44.4% by weight Release agent 0.2% by weight powder After mixing, the mixture was heat-kneaded with a two-roll mill set at 140 ° C. for about 30 minutes, cooled, and then coarsely pulverized and finely pulverized (jet mill). Further, fine powder and coarse powder were cut by an elbow jet classifier to obtain a toner composition. The particle size of the obtained toner is 8.3 μm in weight average diameter and 30 in coefficient of change.
%Met. Negatively charged colloidal silica is added to this 0.6
Externally added by weight% to obtain a developer.

According to the structure of this embodiment, the amount of the developer per unit area on the developer carrier in the developing area is 0.8.
˜1.0 mg / cm ² , in the developing area formed between the latent image carrier and the developer carrier, the number of chain-like aggregates of the magnetic toner formed on the developer carrier per unit area The density is 8 × 10 ⁴ to 15 × 10 ⁴ lines / cm ² , and the chain-like aggregate of the magnetic toner has a length of 160 μm or less,
Charge application to the magnetic toner was stable and image reproducibility was good.

The magnetic material used in the present invention is not limited to this embodiment, the magnetization intensity in a magnetic field of 1 KOe is 10 to 40 emu / g, and the horizontal ferret diameter is 0.05 μm.
Any magnetic material having a size of m to 0.5 μm may be used.

Further, the gap between the magnetic blade 5 as the developer regulating member and the sleeve 1a used in the present invention is not limited to the above-mentioned constitution, and may be 50 to 1,000 μm. Also, the sleeve 1a and the sleeve 1a. The gap 2a may be a gap that allows the magnetic toner to be transferred between the sleeve 1a and the sleeve 2a, and is preferably 50 to 2,5.
The range may be 00 μm. With the above configuration, it is possible to reduce the intensity of magnetization of the magnetic toner without reducing the amount of the magnetic material in the magnetic toner, and to stabilize the process of imparting charge to the magnetic toner, thus improving the image reproducibility. I was able to do it.

Comparative Example 1 The magnetic material of Example 1 was A toner was prepared in the same manner as in Example 1 except that the magnetic substance of No. 3 was used. The particle size of the obtained toner was 8.3 μm in weight average diameter and 35% in coefficient of change.

This magnetic toner is applied to the developing device shown in FIG. 7, that is, a sleeve 1a made of a non-magnetic metal which is a developer carrying member 1a rotating in the direction of the arrow in FIG.
a permanent magnet disposed inside a, a magnetic blade 5 for regulating the amount of the developer on the developer carrying member composed of a magnetic member arranged in a non-contact state with the developer carrying member, and a developing blade 9 for developing vessel,
An evaluation of a developing device in which 3 is a conveying member for conveying the magnetic toner in the developing device 9 in the direction of the sleeve 1a and 4 is a power source for applying a developing bias to the sleeve is evaluated. However, it cannot be said that the image is more faithful to the latent image as compared with the above embodiment.

The amount of the developer per unit area on the developer carrier in the developing area is 0.8 to 1.0 mg / c.
m ² , the density of the number of magnetic toner ears in the developing area formed between the latent image carrier and the developer carrier is 5 × 10 ^4.
~ 7 × 10 ⁴ / cm ² , the length of the spikes is 200-220μ
It was m. Here, in the permanent magnet 1b arranged in the developing device shown in FIG. 7, the magnetic flux density of the magnetic poles arranged in the vicinity of the developing area of the permanent magnet 1b is 800 G on the sleeve 1a.
The permanent magnet as described above was used.

Comparative Example 2 When the magnetic toner of Example 1 was evaluated in a developing device as shown in FIG. 7, image fogging occurred due to poor charging of the magnetic toner. Further, the amount of the developer per unit area on the developer carrier in the developing area is 0.8 to 1.0 m.
g / cm ² , the length of the ears was 160 μm or less, but the number density of the ears of the magnetic toner in the developing area formed between the latent image carrier and the developer carrier is 5 × 10 ^{4 to} 7 × 1
0 was ⁴ / cm ^2.

Embodiment 2 The present invention is not limited to the magnetic toner of Embodiment 1 described above. A magnetic material was produced in the same manner as in the synthesis example of Example 1 and was spinel-type iron oxide No. A magnetic material of 2 was obtained. The obtained magnetic material has a horizontal ferret diameter of 0.21 μm and BET
The magnetization was 9.3 m ² / g, the magnetization strength was 37.5 emu / g, the coercive force was 76 Oe, and the residual magnetization was 6.3 emu / g. A toner was produced using this magnetic material. The prescription is as follows.

Styrene-acrylic copolymer 49.7% by weight Negative charge control agent 0.5% by weight Magnetic material (magnetic material) 49.6% by weight Release agent 0.2% by weight Weight average diameter 6.2 μm, change coefficient 35
%Met.

Negatively-charged colloidal silica was added to 0.9
Externally added by weight% to obtain a developer. When this magnetic toner and the developing device of Example 1 were used, the amount of developer per unit area on the developer carrier in the developing region was 0.63 to 0.
85 mg / cm ² , in the developing area formed between the latent image carrier and the developer carrier, the number density per unit area of the chain assembly of the magnetic toner formed on the developer carrier is 10 × 10 ⁴ to 18 × 10 ⁴ lines / cm ² , and the length of the chain-like aggregate of the magnetic toner was 140 μm or less, the charge application to the magnetic toner was stable, and the image reproducibility was good.

Example 3 In the above example, two developer carrying members were used.
The present invention is not limited to the configuration of the above-described embodiment, but is not limited to FIG.
As shown in, a sleeve 12a having a permanent magnet 12b therein may be arranged between the sleeve 1a and the sleeve 2a. In the configuration of the present invention, the sleeves are rotated in the same direction as indicated by arrows in FIG. 5, but the present invention is not limited to this.

Further, in the constitution of the present invention, the peripheral speeds of the respective sleeves are set to be the same, but the present invention is not limited to this, and according to the characteristics of the developer to be used,
It is preferable to set the diameter and peripheral speed of each sleeve.

Further, the sleeve 1a used in the present invention
And sleeve 12a, sleeve 12a and sleeve 2
The gaps of a are each set to about 200 μm, but the present invention is not limited to this and may be a gap allowing the transfer of the magnetic toner between the sleeves, preferably 50 to 2,5.
The range may be 00 μm. By using the developing device of this configuration and the magnetic toner of Example 1, the magnetization intensity of the magnetic toner can be reduced without reducing the amount of magnetic material in the magnetic toner, and the process of applying charge to the magnetic toner can be performed. It became possible to stabilize the image and improve the image reproducibility.

Embodiment 4 In the above embodiments, a permanent magnet is included inside each sleeve, but the present invention is not limited to the configuration of the above embodiment, and as shown in FIG. , A sleeve 12a containing a magnetic member 13 inside, and a permanent magnet 1 inside.
b and 2b are arranged between the sleeve 1a and the sleeve 2a, respectively, and a part of the magnetic member 13 is a permanent magnet 1b.
One of the magnetic poles of the permanent magnet 2b, and a part of the magnetic member 13 facing one of the magnetic poles of the permanent magnet 2b, and the magnetic poles of the permanent magnets facing the magnetic member 13 are different from each other. It may be arranged so that it becomes a pole. By using the developing device of this configuration and the magnetic toner of Example 1, the magnetization intensity of the magnetic toner can be reduced without reducing the amount of magnetic material in the magnetic toner, and the process of applying charge to the magnetic toner can be performed. It became possible to stabilize the image and improve the image reproducibility. (Second invention)

Embodiment 1 Hereinafter, one embodiment according to the present invention will be described with reference to the drawings. FIG. 8 is a cross-sectional view of a developing device that is an embodiment of the present invention. In the figure, 1a is a sleeve made of a non-magnetic metal, which is a developer carrier that rotates in the direction of the arrow, 2 is a magnetic blade that regulates the amount of developer on the developer carrier that is composed of a magnetic member, and 10 is a latent image carrier. The body is a photosensitive drum. Again 1
b is the developer regulating member 2, the latent image carrier 10, and the developer carrier 1 with respect to the transport direction of the developer on the developer carrier.
a is a permanent magnet disposed inside the developing sleeve 1a, which has a plurality of magnetic poles, which is a feature of the present invention, between the developing region and the developing region formed between the developing device 1a and a developing device. Denoted at 3 is a carrying member for carrying the magnetic toner in the developing device 9 toward the developing sleeve 1a.

According to the developing device having the above-described structure, as shown in FIG. 9, the magnetic toner T in the developing container 9 is conveyed in the direction of the arrow on the developing sleeve 1a and the gap between the magnetic blade 2 and the developing sleeve 1a. When it passes through, the toner is regulated to a desired toner layer thickness. In addition, the toner T that has passed through the layer thickness regulating portion is
Form ears A. Further, among the toners that form the ears A when passing through the layer thickness regulating portion, the toners that may come into contact with the developing sleeve 1a, the magnetic blade 2 and the like acquire a charging charge by frictional charging.

Therefore, in the layer thickness regulation of the developer according to the above-mentioned method, generally, the above-mentioned frictionally charged toner and the above-mentioned non-frictionally charged toner are mixed in the brush A after passing through the developer regulating member. In particular, in the magnetic toner used in the present invention, in which the magnetic strength of the magnetic substance contained in the magnetic toner is in the above range, the repulsive force between the toners due to the magnetic force against the cohesive force between the magnetic toners. Is considered to be small, the ears A become thicker, and as a result, there are many toners that are not frictionally charged in the ears A. According to the study of the present invention, it has been found that the repulsive force between the toners due to the magnetic force increases at the concentrated portion of the magnetic force lines, and the aggregation of the magnetic toner tends to be released.

Therefore, in the present invention, between the magnetic blade 2 which is the developer regulating member and the developing area,
By disposing a plurality of magnetic poles and arranging a plurality of magnetic flux concentration portions, the aggregation of the ears A is released, and the magnetic toner contained in the ears A is exposed on the surface of the ears A. ,
The exposed toner can come into contact with the developing sleeve 1a when being conveyed on the developing sleeve 1a.
Therefore, in the developing area, the bristle B formed on the developing sleeve 1a is thinner than the bristle A, and the proportion of toner that is not frictionally charged in the bristle B is smaller than that in the bristle A. Become.

In the present invention, the gap between the developing sleeve 1a and the developer regulating member 2 is about 300 μm.
Further, in the structure of the present invention, the developing bias is applied to the developing sleeve 1a by the power source 4, and the developing bias is Vpp 1,400V and frequency 2,000 Hz.
The AC rectangular wave bias of

Further, in the structure of the present invention, at least one of the magnetic poles of the permanent magnet 1b arranged in the developing sleeve 1a is arranged in the vicinity of the developer regulating member 2, and at least 1 is formed. The poles are arranged near the developing area. Further, in the structure of the present invention, two magnetic poles S1 and N2 are arranged between the magnetic pole N1 arranged near the magnetic blade 2 and the magnetic pole S2 arranged near the developing area. Further, with respect to the strength of magnetization of the magnetic toner used in the present invention, the effect of solving the aggregation of the magnetic toner due to the concentration of magnetic force lines at the magnetic pole portion can be expected to be expected to be caused by the developer regulating member and the developing region. The magnetic flux density of each magnetic pole arranged between the magnetic poles was 400 G or more. Therefore, in this configuration, N1 to S
The magnetic flux density of each magnetic pole of two poles was set to 800G.

The magnetic toner used in the present invention has a structure in which the magnetic strength of the magnetic toner is reduced without reducing the amount of magnetic material in the magnetic toner. That is, the strength of magnetization in a magnetic field of 1 KOe was set to 10 to 40 emu / g. In general,
A magnetic material having a smaller intensity of magnetization than a magnetic material that is normally used is used. Examples of the magnetic substance contained in the toner include metal oxides containing elements such as iron, cobalt, nickel, copper, magnesium, manganese, aluminum and silicon. The magnetic substance used in the examples of the magnetic toner of the present invention is spinel-type iron oxide obtained by the synthesis method as shown below.

(Synthesis Example) As a reactor, a bubble oxidation type reaction tower having an internal capacity of 180 liters was used. Industrial iron sulfate is dissolved in water to prepare 40 liters of a solution having a ferrous iron concentration of 134 g / liter. Separately, 40 liters of a solution having a caustic soda concentration of 182 g / liter was prepared, and the above iron sulfate solution was added thereto with stirring to neutralize the solution so that the residual caustic soda became 5 g / liter. To this was added 50 liters of an industrial zinc hydroxide solution having a pH of 11.3 and a zinc concentration of 40 g / liter to prepare a reaction solution having a ferrous iron concentration of 40 g / liter. While maintaining the temperature of the reaction solution at 80 ° C., oxidizing air was blown at a rate of 10 l / min to carry out the oxidation reaction. The reaction was completed in about 7 hours. Next, this slurry was washed and dried to obtain spinel type iron oxide. The obtained magnetic material has a horizontal ferret diameter of 0.25.
μm, BET 8.8 m ² / g, magnetization strength 31.5 em
u / g, coercive force 170 Oe, remanent magnetization 5.7 emu / g
Met.

The magnetic toner was prepared as follows. Styrene-acrylic copolymer 54.9% by weight Negative charge control agent 0.5% by weight Magnetic substance (magnetic substance obtained in the above synthesis example) 44.4% by weight Release agent 0.2% by weight powder After mixing, the mixture was heat-kneaded with a two-roll mill set at 140 ° C. for about 30 minutes, cooled, and then coarsely pulverized and finely pulverized (jet mill). Further, fine powder and coarse powder were cut by an elbow jet classifier to obtain a toner composition. The particle size of the obtained toner was 8.5 μm in weight average diameter and the coefficient of change was 30%. 0.6% by weight of negatively chargeable colloidal silica was externally added to this to obtain a developer.

According to the constitution of this embodiment, the amount of the developer per unit area on the developer carrier in the developing area is 0.
8 to 1.0 mg / cm ² per unit area of the chain aggregate of the magnetic toner formed on the developer carrying member in the developing area formed between the latent image carrying member and the developer carrying member. The number density is 8 × 10 ^{4 to} 14 × 10 ⁴ lines / cm ² , and the length of the chain-like aggregate of the magnetic toner is 160 μm or less, so that the charge application to the magnetic toner is stable and the image reproducibility is good. there were.

The magnetic material used in the present invention is not limited to this embodiment, the magnetization intensity in a magnetic field of 1 KOe is 10 to 40 emu / g, and the horizontal ferret diameter is 0.05 μm.
Any magnetic material having a size of m to 0.5 μm may be used. Further, the developer regulating member 2 and the developing sleeve 1a used in the present invention.
The gap is not limited to the above configuration, but is 50 to 1,00.
It may be 0 μm. With the above configuration, it is possible to reduce the intensity of magnetization of the magnetic toner without reducing the amount of the magnetic material in the magnetic toner, and to stabilize the process of imparting charge to the magnetic toner, thus improving the image reproducibility. I was able to do it.

Example 2 The present invention is not limited to the magnetic toner of Example 1 above. A magnetic substance was produced in the same manner as in the synthesis example of Example 1 to obtain spinel iron oxide. The obtained magnetic material has a horizontal ferret diameter of 0.20 μm, BET of 9.4 m ² / g, magnetization strength of 37.8 emu / g, coercive force of 78 Oe, and residual magnetization of 6.
It was 4 emu / g. A toner was produced using this magnetic material. The prescription is as follows.

Styrene-acrylic copolymer 49.7% by weight Negative charge control agent 0.5% by weight Magnetic substance (the magnetic substance) 49.6% by weight Release agent 0.2% by weight Weight average diameter 6.1 μm, change coefficient 34
%Met. Negatively charged colloidal silica is added to this 0.9
Externally added by weight% to obtain a developer. When this magnetic toner and the developing device of Example 1 were used, the amount of developer per unit area on the developer carrier in the developing area was 0.65 to 0.
85 mg / cm ² , in the developing area formed between the latent image carrier and the developer carrier, the number density per unit area of the chain assembly of the magnetic toner formed on the developer carrier is 10 × 10 ^{4 to} 17 × 10 ⁴ lines / cm ² , the length of the chain-like aggregate of the magnetic toner was 140 μm or less, the charge application to the magnetic toner was stable, and the image reproducibility was good.

Embodiment 3 The present invention is not limited to the structure of the above embodiment, but two or more poles are provided between the magnetic pole N1 arranged near the magnetic blade 2 and the magnetic pole S2 arranged near the developing area. It suffices that the magnetic poles of S1 and S2 are arranged as shown in FIG.
Similar effects were obtained even when the poles were arranged and the magnetic flux density of each was set to 600G. By using the developing device of this configuration and the magnetic toner of Example 1, it is possible to stabilize the charge application to the magnetic toner and to perform image reproducibility.

[0096]

【The invention's effect】

(First Invention) As described above, according to the configuration of the present invention, it is possible to reduce the magnetization intensity of the magnetic one-component toner and to stabilize the process of imparting charge to the toner. It has become possible to improve the image reproducibility in the development using the component toners.

(Second Invention) As described above, according to the configuration of the present invention, it is possible to reduce the strength of magnetization of the magnetic one-component toner and to stabilize the process of imparting charge to the toner. The image reproducibility in the development using the magnetic one-component toner can be improved.

[0098]

[Brief description of drawings]

 (First invention)

FIG. 1 is a sectional view of a developing device that is a first embodiment of the present invention.

FIG. 2 is an explanatory view of the behavior of the magnetic toner in the vicinity of the developer carrier in the present invention.

FIG. 3 is an explanatory diagram of a magnetic flux density in a developer regulating section.

FIG. 4 is an explanatory diagram of toner behavior in a developer regulating section.

FIG. 5 is a sectional view showing a second embodiment of the present invention.

FIG. 6 is a sectional view showing a third embodiment of the present invention.

FIG. 7 is a sectional view showing an example of a conventional technique.

[0099]

[Explanation of symbols]

1a, 2a, 12a are sleeves 1b, 2b, 12b are permanent magnets arranged in the sleeves 3, toner conveying member 4, developing bias power source 5, developer regulating member 9, developing device 13 , The magnetic member T disposed in the sleeve is toner

(Second invention)

FIG. 8 is a sectional view of the developing device according to the first embodiment of the present invention.

FIG. 9 is an explanatory view of the behavior of the magnetic toner in the vicinity of the developer carrier in the present invention.

FIG. 10 is another embodiment of the present invention.

[0101]

[Explanation of symbols]

 1a is a developing sleeve 1b is a permanent magnet disposed inside the developing sleeve 2 is a developer regulating member 3 is a toner conveying member 4 is a developing bias power source T is a toner

Claims (9)

[Claims] 1. A latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, a magnetic toner containing a magnetic material, a developer carrier, and a developer containing the magnetic toner. And a developing device that develops the latent image on the latent image carrier, wherein the magnetic toner has a magnetization intensity of 10 to 10 in a magnetic field of 1 KOe (Oersted). An image containing 40 emu / g and a magnetic material made of a metal oxide having a ferret diameter in the horizontal direction of 0.05 to 0.5 μm, and at least two or more of the development carriers are provided. Forming equipment. 2. The image forming apparatus according to claim 1, wherein the developer carrying members are arranged so that the developer can move between at least two or more developer carrying members. 3. The number density of chain aggregates of magnetic toner formed on the developer carrier is 8 × 10 ⁴ in a developing area formed between the latent image carrier and the developer carrier. Book/
cm ² or more, the length of the chain-like aggregate of the magnetic toner is 180 μm or less, the weight average particle diameter of the magnetic toner is γ (μm), and the true density is ρ (g / cm ³ ), the development is performed. The image forming apparatus according to claim 1, wherein the amount of the developer on the developer carrier in the area is 0.06γρmg / cm ² or more. 4. The image forming apparatus according to claim 1, wherein a magnet is arranged inside at least one developer carrying member. 5. The image forming apparatus according to claim 1, wherein when the weight average particle diameter of the toner is 7.5 μm or more, the content of the magnetic substance in the magnetic toner is 30 to 60% by weight. 6. When the magnetic substance content in the magnetic toner is WT and the weight average particle diameter of the toner is γ (μm), WT = − (10/3) γ + (70 ± 15) γ ≦ 7.5 The image forming apparatus according to claim 1, wherein: 7. A latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, a magnetic toner containing a magnetic material, and a developer carrier having a magnet provided therein. Development in which a developer regulating member for regulating the layer thickness of the developer on the developer carrying member and a developer containing the magnetic toner are carried on the developer carrying member to develop the latent image on the latent image carrying member. And a magnetic toner having a magnetization intensity of 1 KOe in a magnetic field of 1 KOe.
0-40 emu / g, horizontal ferret diameter 0.05-
The developer regulating member, the latent image bearing member, and the developer bearing member containing a magnetic substance composed of a metal oxide having a thickness of 0.5 μm in the transport direction of the developer on the developer bearing member. A magnet having a plurality of magnetic poles between the latent image carrier and the developer carrier, and a magnet having a plurality of magnetic poles is disposed between the latent image carrier and the developer carrier. In the formed developing area, the number density per unit area of the chain assembly of magnetic toner formed on the developer carrying member is 8 × 10.
⁴ pieces / cm ² or more, the length of the chain assembly of the magnetic toner is 180 μm or less, the weight average particle diameter of the magnetic toner is γ (μm), and the true density is ρ (g / cm ³ ). , The developer amount per unit area on the developer carrier in the developing area is 0.06γρ
(Mg / cm ² ) or more, the image forming apparatus. 8. The magnetic substance content of the magnetic toner is 30 to 6.
The image forming apparatus according to claim 1, wherein the image forming apparatus is 0% by weight. 9. When the magnetic substance content in the magnetic toner is WT and the weight average particle diameter of the toner is γ (μm), WT = − (10/3) γ + (70 ± 15) γ ≦ 7.5 The image forming apparatus according to claim 1, wherein: