JPH02284152A - Negatively charged magnetic developer - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a developer for developing electrostatic images in electrophotography, electrostatic recording, electrostatic printing, and the like.

More specifically, the present invention relates to a negatively charged magnetic developer which is uniformly and strongly negatively charged in a direct or indirect electrophotographic development method, and which visualizes a digital negative electrostatic image by reversal development to produce a high quality image.

[Background technology]

2. Description of the Related Art Electrophotographic systems generally use a method in which a document image is exposed to light and a latent image carrier is exposed to the reflected light to obtain a latent image. In this method, the reflected light from the original is directly used as an image signal, so the potential of the electrical latent image changes continuously (hereinafter referred to as an analog latent image).

In contrast, recently, a method has been commercialized in which the reflected light of the original is converted into an electrical signal, the signal is processed, and then exposure is performed based on the signal. This method allows for easier magnification and reduction at higher magnifications than the analog latent image method, and allows the image signal to be taken into a computer and output together with other information. Although it has many versatile uses as mentioned above, if the image signal is handled as analog, the amount of signal will be enormous, so digital processing is required to divide the image into pixel units (hereinafter referred to as dots) and determine the exposure amount for each pixel. becomes.

When a latent image is digitized, each dot needs to be developed accurately compared to an analog latent image, and therefore a developer that can faithfully develop pixels at a high development rate is required.

In the case of developing a digital latent image, compared to an analog latent image, the deviation of the surface potential of the latent image during formation is large, and the potential difference between the developer conveying section and the latent image carrier such as a photosensitive drum is small. It is also necessary to carry out development in some areas.

The developability of the developer becomes particularly important in images where images and non-images are repeated for each dot.

Therefore, if a developer developed as an analog latent image developer is used in a digital latent image system, especially the above-mentioned image
In a printing pattern where a non-image is repeated for each dot, the development of each dot is insufficient, resulting in the dots becoming smaller or not being developed at all, resulting in the overall image density becoming lighter and characters becoming blurred. Tend.

This phenomenon becomes remarkable in a developer containing a magnetic toner containing a magnetic material (hereinafter referred to as magnetic developer), which tends to have a small amount of developer charge.

This is thought to be because in the magnetic developer, there are parts where the magnetic material is exposed on the surface of the magnetic toner particles, and the surface that can contribute to charging is small. Because it changes depending on the amount of magnetic material,
The distribution of developer charge amount is wider than that of other developers. Therefore, when a magnetic developer is used in a digital latent image system, characters are likely to become blurred due to the accumulation of magnetic toner particles with a low triboelectric charge in the developer, and an improvement is desired.

Furthermore, in recent years, as image forming devices such as electrophotographic copying machines have become widespread, their uses have expanded to a wide variety of uses, and the requirements for their image quality have become stricter. Copying images such as general documents and books In today's world, it is required to reproduce extremely fine and faithful characters, even the smallest characters, without being crushed or cut off.In particular, when the latent image on the photoreceptor of an image forming device is 100 μm or less, In the case of line images, conventional developers generally have poor fine line reproducibility, and the clarity of line images is still insufficient.Furthermore, recently, image forming devices such as electrophotographic printers that use digital image signals , a latent image is formed by a collection of dots with a constant potential, and solid areas, halftone areas, and light areas are expressed by changing the density of the dots.However, the toner particles do not adhere to the dots faithfully, When toner particles protrude from the dots, there is a problem in that the toner image cannot have gradation that corresponds to the ratio of the dot densities of the black and white areas of the digital latent image.

Furthermore, when improving resolution by reducing dot size in order to improve image quality, it becomes more difficult to reproduce latent images formed from minute dots, resulting in poor resolution, poor gradation, and poor sharpness. This tends to result in images lacking in detail.

Further, although the image quality is good initially, as printing continues, the image quality may deteriorate. This phenomenon is thought to occur because as printouts continue, only toner particles that are easily developed are consumed first, and toner particles that are less developable accumulate and remain in the developing 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, and according to the studies of the present inventors, it is difficult to uniformly “glue” the latent image with this particle size, and toner with a particle size of 5 μm or less is 30% by number or less, and 5% by number is 20 μm or more, which means that the particle size distribution is broad, which also tends to reduce uniformity. In order to form clear images using such coarse toner particles with a broad particle size distribution, it is necessary to thicken the toner particles (by overlapping them to fill the gaps between the toner particles and increase the apparent appearance). There is also a problem in that it is necessary to increase the image density, and the amount of toner consumption required to achieve a predetermined image density increases.

Furthermore, in JP-A-54-72054, a non-magnetic toner having a sharper distribution than the former is proposed, but the particle size of medium weight particles is coarse, 8.5 to 11.0 μm, and There is still room for improvement as a toner in terms of resolution.

In JP-A No. 58-129437, the average particle size is 6 to 6.
A non-magnetic toner has been proposed in which the particle size is 10 μm and the maximum number of particles is 5 to 8 μm, but the number of particles of 5 μm or less is as small as 15% or less, and images that lack sharpness tend 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. In view of stricter requirements such as performance, resolution, and suitability for reversal development, this is not sufficient and further improvements are required.

Furthermore, compared to conventional toners, the toner of the present invention contains considerably more fine powder of 5 μm or less, although it is controlled by means such as classification and heat treatment. As a result, due to the difference in developability due to the difference in particle size, the developer selectively accumulates near the surface of the developer carrier, and the original developer forms a layer on top of it, so that the appropriate amount of charge necessary for development can be obtained. This causes so-called developer carrier memory, in which there is a difference in density between the part where the fine powder layer is formed and the normal part.

In particular, in -component magnetic developers, the amount of magnetic material contained in each fine powder toner particle tends to be smaller than the amount of magnetic material contained in toner of an appropriate particle size, and
- Since the amount of charge is higher than that of the developer particles, the adhesion to the developer carrier is stronger due to the reflection force, and the memory phenomenon of the carrier becomes more pronounced. In addition, in negatively chargeable developers, negatively chargeable hydrophobic fine silica powder is generally used, which is also one of the reasons for promoting toner carrier memory.

The phenomenon of carrier memory refers to the phenomenon of image formation as shown in section 4 of FIG. 1c of the accompanying drawings. For example, when developing the wide image 2 shown in FIG. 1b after developing the image 1 shown in FIG. As shown in FIG. 1C, the image density of the portion 4 of No. 2 is lower than that of other image areas. Note that when the developer carrier makes one revolution to develop image 2, the developer corresponding to the width on the developer carrier is consumed, so the portion 3 after one revolution (length!) is Image density becomes uniform.

Regarding the addition of fine resin particles to the developer, it has been proposed to add fine polymer resin particles smaller than toner particles, as seen in JP-A-60-186854, etc., although the effects are different. When a developer was prepared in the same manner and examined, it was found that although some effect on the memory of the developer carrier was observed in the initial stage, the effect disappeared when a durability test was conducted.

In addition, when we investigated the charging properties of resin particles, we found that no effect was observed when the toner and tribocharges were of the same polarity with respect to iron powder, and that even when the polarities were opposite, a specific tribocharge amount was highly effective. ing. Although the effects are different, Japanese Patent Application Laid-Open No. 61-25058 discloses that fine particles of opposite polarity (for example, silica particles that are negatively charged for positively chargeable toner) and fine particles of the same polarity (for example, positively charged for positively chargeable toner) are used. It has been proposed to add silica fine particles). Regarding this, when a developer was similarly prepared and examined, it was found that it had some effect on the memory of the developer carrier, but the image density was also low.

Additionally, as the durability progresses, particles that appear to be of reverse polarity accumulate in some parts of the cleaner, causing damage to the photoreceptor.
There are still points to be improved.

Recently, the reliability of copying machines and page printers has improved, and there has been a demand for clearer and higher quality images. Furthermore, when considering not only line copying but also graphics and design-related applications, there has been a long-awaited need for a developer that overcomes the above-mentioned phenomena.

[Purpose of the invention]

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

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

A further object of the present invention is to provide a negatively charged magnetic developer whose performance does not change due to environmental changes.

A further object of the present invention is to provide a negatively charged magnetic developer with excellent transferability.

A further object of the present invention is to provide a negatively charged magnetic developer that can provide high image density with low consumption.

A further object of the present invention is to provide a negatively charged magnetic developer capable of forming toner images with excellent resolution, gradation, and fine line reproducibility in an image forming apparatus using digital image signals. .

A further object of the present invention is to provide a negatively charged magnetic developer which can be formed uniformly with a developer layer on a developer carrier and which does not cause developer carrier memory.

Another object of the present invention is to provide an image forming method capable of forming images with little fog (and high image density) using a negatively charged magnetic developer.

More specifically, the present invention provides a magnetic toner having at least a binder resin and a magnetic powder, which contains 17 to 60 number % of magnetic toner particles having a particle size of 5 μm or less, and 6.
Magnetic toner particles having a particle size of 35 to 10.08 μm are contained in an amount of 5 to 50% by number, magnetic toner particles having a particle size of 12.7 μm or more are contained in an amount of 2.0% by volume or less, and the volume average of the magnetic toner is The particle size is 6 to 8 μm, and the group of magnetic toner particles of 5 μm or less is represented by the following formula % [In the formula, N represents the number % of magnetic toner particles having a particle size of 5 μm or less, and ■ represents the number of particles of 5 μm or less. It represents the volume % of magnetic toner particles having a diameter, and k represents a positive number from 4.6 to 6.7. However, N represents a positive number from 17 to 6o. ] 100 parts by weight of an insulating magnetic toner having a particle size distribution satisfying A) 0.1 to 1 weight 1 part and -100 to -35
A negatively charged magnetic toner containing 0.6 to 1.6 parts by weight of hydrophobic silica fine powder (B) having a tribocharge amount of oIic/g in an amount equal to or greater than that of A. .

The magnetic toner of the present invention having the above particle size distribution is capable of faithfully reproducing even the fine lines of a latent image formed on a photoreceptor, and is capable of faithfully reproducing halftone dots and digital dot latent images. Provides images with excellent reproduction and excellent gradation and resolution. Furthermore, it maintains high image quality even when copying or printing is continued, and even in the case of high-density images, it is possible to perform good development with less toner consumption than conventional magnetic toner, making it economical and This also has the advantage of reducing the size of the copying machine or printer itself.

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

That is, one of the characteristics of the magnetic toner of the present invention is that magnetic toner particles having a particle size of 5 μm or less account for 17 to 60% by number. Conventionally, magnetic toner has a diameter of 5 μm.
The following magnetic toner particles are difficult to control the amount of charge, impair the fluidity of the magnetic toner, scatter toner and stain the machine, and cause image fog, so they must be actively reduced. It was considered necessary.

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, using a magnetic toner with a particle size distribution ranging from 0.5 μm to 3071 m, the surface potential on the photoreceptor can be changed from a large development potential contrast where a large number of toner particles are easily developed, to a halftone, to a very small A latent image was developed by changing the surface potential on the photoconductor to a small development potential contrast where only toner particles were developed, and the developed toner particles on the photoconductor were collected and the toner particle size distribution was measured, and the result was 8 μm or less. It was found that there were many magnetic toner particles with a diameter of 5 μm or less, and in particular, there were many 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%. As mentioned above, this is related to the necessity of the presence of magnetic toner particles with a particle size of 571 m or less.
Magnetic toner particles with a particle size of 5 μm or less have the ability to strictly cover a latent image and reproduce it faithfully, but the electric field strength at the edges around the latent image itself is higher than at the center.
As a result, toner particles tend to adhere more tightly inside the latent image than at the edges, and the image density may appear to be thinner.

In particular, magnetic toner particles with a diameter of 5 μm or less have a strong tendency to do so. However, we found that 6.35-10.08
It has been found that this problem can be solved and further clarity can be achieved by containing 5% to 50% of toner particles in the μm range. That is, 6.35 to 10.08
This is thought to be due to the fact that toner particles in the particle size range of μm have a suitably controlled amount of charge compared to magnetic toner particles with a particle size of 5 μm or less. A uniformly developed image is formed by supplementing the lack of adhesion of the inner toner particles to the edge areas, and as a result, a sharp image with high density and excellent resolution and gradation is provided. It is something that

Furthermore, for particles with a particle size of 5 μm or less, the number %
(N) and volume % (V), N/V-0,05N+
One of the characteristics of the magnetic toner of the present invention is that the magnetic toner of the present invention satisfies the following relationship: k (4.6≦≦6.7; 17≦N≦60). This range is shown in FIG. 4, and the magnetic toner of the present invention having a particle size distribution that satisfies this range as well as 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/
A small v value is understood to indicate that the abundance of particles around 5 μm is high (and that there are few particles with a smaller particle size), and the N/V value is 1.6 to 5.85. If N is within the range, N is in the range of 17 to 60, 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 12.7 μm or more be 2.0% by volume or less, and as small as possible.

The magnetic developer 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.
60% by number (preferably 25 to 60% by number, more preferably 30 to 60% by number. If the number of magnetic toner particles with a particle size of 5 μm or less is less than 17%, There are few magnetic toner particles that are effective for image quality, and in particular, as toner is used by continuing to print out, the effective magnetic toner particle component decreases.
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 it exceeds 60% by number, magnetic toner particles tend to aggregate with each other, resulting in toner particles larger than the original particle size, resulting in rough image quality, lowering resolution, or causing the edges of the latent image to The density difference between the area and the inside becomes large, and the image tends to look hollow.

In addition, particles in the range of 6.35 to 10.08 μm are 5 to 5
It is good that it is 0% by number, preferably 8 to 40% by number.
is good. If the number is more than 50%, the image quality deteriorates, and more development than necessary occurs, that is, too much toner is applied, the reproducibility of dirty lines decreases, and the amount of toner consumed increases.

On the other hand, if it is less than 5% by number, high image density cannot be obtained (
It becomes. In addition, between the number% (N%) of magnetic toner particles having a particle size of 5 μm or less and 1% by volume (7%), N/V=-0
, 05N+, and indicates a positive number in the range of 4.6≦ and ≦6.7. Preferably 4.6≦≦6.2, more preferably 4.6≦≦5.7. As shown above, 17≦N≦80, preferably 25≦N≦60, more preferably 30≦N≦60.

When k<4.6, 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, achieves the closest packing of toner during development and contributes to the formation of uniform images without roughness. In particular, by uniformly filling in thin lines and image contours, visual sharpness is further enhanced. That is, when k<4.6, 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<4.6, which is disadvantageous in terms of yield and toner cost.

In addition, when k<6.7, due to the presence of more fine powder than necessary,
(As you continue to print out images, the image density tends to decrease.

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. It is thought that then.

In addition, magnetic toner particles with a particle size of 12.70 μm or more are
．． It is preferably 0% by volume or less, and more preferably 1% by volume.
．． 0 volume% or less, more preferably 0.5 volume%
It is as follows. If it is more than 2.0% by volume, it will hinder fine line reproduction. In addition, the volume average diameter of the magnetic toner is 6 to 8.
μm, and this value cannot be considered separately from each of the components mentioned above. Volume average particle size 6
For applications with digital latent images with a high image area ratio, such as graphic images, if the size is less than μm, the amount of toner on the transfer paper is small (and the problem of low image density tends to occur. For the edge part in the latent image,
It is thought that this is due to the same reason as the reason why the internal concentration decreases. When the volume average particle diameter exceeds 8 μm, the resolution of minute spots of 100 μm or less is not good and there is a lot of scattering in non-image areas. Also, although the printout is good at first, the image quality tends to deteriorate with continued use.

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 TA.
- An interface (manufactured by Nikkaki) that outputs the number distribution and volume distribution using the n-type (manufactured by Coulter) and CX-1
A personal computer (manufactured by Canon) is connected, and a 1% Na (,j!) aqueous solution is prepared using primary sodium chloride as the electrolytic solution.The measurement method is as follows:
150 mji! Add 0.1 to 5 ml of a surfactant as a dispersant, preferably an alkylbenzene sulfonate, and further add 2 to 20 mg of the measurement sample. 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 TArI type. The distribution was measured and the values according to the invention were determined therefrom.

The true density of the magnetic toner of the present invention is 1.45 to 1.8 g.
/ crrd, more preferably 1.55 to 1.75 g/crrr. Within this range, the magnetic toner of the present invention having a specific particle size distribution is
The reversal development method in the presence of a magnetic field is most effective in terms of high image quality and durability stability. If the true density of the magnetic toner is less than 1.45, the weight of the magnetic toner particles themselves is too light, which tends to cause fogging during reversal development, crushing of fine lines due to too much toner particles, scattering, and deterioration of resolution. . In addition, if the true density of the magnetic toner is higher than 1.8, the image density will be low and the image will lack sharpness, such as broken thin lines, and the magnetic force will also be relatively large, so the toner spikes will become long or branched. In this case, when the digital latent image is developed, the image quality is likely to be disturbed, resulting in a rough image.

The true density of magnetic toner can be measured by several methods, but in this application, when measuring fine powder, the following method is adopted as an accurate and simple method.

A cylinder made of stainless steel with an inner diameter of 10 mm and a length of about 5 cm, and an outer diameter of about 10 m that can be inserted tightly into it.
m.

A disk (A) with a height of 5 mm and a piston (B) with an outer diameter of about 10 mm and a length of about 8 cm are prepared. Place the disk (A) at the bottom of the cylinder, then about 1 g of the sample to be measured, and gently push the piston (B). A force of 400 kg/crrr was applied to this using a hydraulic press, and the product was compressed for 5 minutes and taken out. Weigh the compressed sample (
wg) The diameter of the compressed sample (D
cm) and height (L cm ), and calculate the true density using the following formula.

In order to obtain even better development characteristics, the magnetic toner of the present invention has a residual magnetization σ of 1 to 5 emu/gs, preferably 2
〜4.5 emu/g, and the saturation magnetization σ is 20 to 40
emu/g, and the coercive force He preferably satisfies the magnetic properties of 40 to 100 nisted (0,) (in both cases, the measured magnetic field is I KOe).

In addition, in negatively charged magnetic toner, the degree of toner carrier memory tends to deteriorate as the volume particle size becomes smaller. It has been found that a satisfactory developer can be obtained by incorporating fine resin particles (A) having a negative chargeability and fine silica particles having a negative chargeability (B) in a negatively chargeable magnetic toner in an amount such that B≧A.

The positively chargeable resin fine particles used in the present invention preferably have a triboelectric charge amount of +50 μc/g to +35 μc/g. If less than +5 μC/g is added, the addition effect will be small (and the effect of suppressing the memory of the toner carrier will be small, and the image density will likely decrease. Also, if the amount is more than +350 μC/g, the addition effect will be small). This causes a marked deterioration in fluidity, which results in a decrease in density when images are produced repeatedly.

The amount of triboelectric charge of positively charged resin particles is measured as follows. That is, 0.2 g of resin fine particles and 200-300 g of resin particles left overnight in an environment of 25° C. and 250-60% RH.
Carrier iron powder that is not coated with resin and has a main particle size in the mesh (for example, EFV200/3 manufactured by Nippon Iron Powder Co., Ltd.)
00) 99.8g and approximately 200c, c under the above environment
After mixing for 60 minutes in an aluminum pot with a volume of Measure.

The positively charged resin fine particles used in the present invention have an average primary particle diameter of 0.03 to 1.0 μm, preferably 0.05 to 0.5 μm.

If the particle size is less than 0.03 μm, some of the toner particles are controlled to be positively charged, resulting in increased fog.

In addition, particles larger than 1.0 μm tend to separate from the surface of the toner particles (they aggregate with the toner and are developed in the reverse area, causing black spot fog).

For measurement of average particle size, Coulter Counter N4
(manufactured by Nikikaki Co., Ltd.) in a state in which it is dispersed in a solvent using ultrasonic waves. Alternatively, the measurement may be performed using a CAPA-5000 model (manufactured by Horiba, Ltd.). In addition, substantially monodispersed particles obtained by polymerization or the like may be measured by scanning micrographs (SEM images) at a magnification of 7,500 to 10,000 times.

The amount of the main chargeable resin fine particles used in the present invention is 0.05 to 1.0 parts by weight, preferably 0.1 to 0.8 parts by weight, based on 100 parts by weight of the toner. It is used in an amount equal to or less than the amount added. 0
．． When the amount is less than 0.5 parts by weight, the effect on the memory of the toner carrier is small, and when it exceeds 1.0 parts by weight, the image density does not decrease, and the same is true when the amount exceeds the amount of silica fine particles added.

Further, the positively chargeable resin fine particles used in the present invention are preferably spherical, and specifically, the resin fine particles have a ratio of the short axis to the long axis (long axis/breadth axis) of 1.0 to 1.02. is excellent in suppressing or preventing the toner carrier memory phenomenon.

The positively chargeable resin fine particles used in the present invention are produced by an emulsion polymerization method, a spray drying method, or the like.

From the point of view of particle shape retention, the resin of positively charged resin particles is GP.
Weight average molecular weight by C chromatodulam method is 10.00
0 to 200,000 is good. Examples of the resin fine particles of the present invention include methyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, N-methyl-N-phenylethyl methacrylate, diethylaminoethyl methacrylamide, dimethylaminoethyl methacrylamide, 4-vinylpyridine,
- Using resin particles copolymerized with vinyl monomers such as vinylpyridine or mixtures of these monomers.

In order to impart positive chargeability to the resin particles, a method of polymerizing monomers using a nitrogen-containing polymerization initiator may be used,
Alternatively, a method of polymerizing a monomer composition containing a nitrogen-containing vinyl monomer may be used.

Further, in order to exhibit the effects of the spherical fine particles having a particle size within the range of the present invention, it is necessary that the degree of aggregation of the toner of the present invention is 70% or less. If it exceeds 70%, the movement of toner within the developing device will be significantly impaired, resulting in uneven solid black density and a decrease in image density.

The solid black density unevenness referred to here is a phenomenon that occurs because toner aggregates are generated in the developing device, resulting in areas where the toner coating on the sleeve is thin.In extreme cases, areas where the toner is not coated occur. This results in white streaks, and this phenomenon is remarkable in the toner having the particle size distribution of the present invention. This is because the black fine powder having the particle size distribution of the present invention has a large specific surface area and has strong electrostatic aggregation.

The above-mentioned degree of agglomeration was measured using a powder tester manufactured by Hosokawa Micron Co., Ltd. and a three-stage sieve in which a 200-mesh sieve, a 100-mesh sieve, and a 60-mesh sieve were sequentially stacked. As a measuring method, approximately 2g of powder made of toner or developer was placed on a 60-mesh sieve on the upper stage of a three-stage sieve, a voltage of 2.5V was applied to the powder tester, and the powder was passed through the three-stage sieve for 40 seconds. The weight of the powder remaining on the 60-mesh sieve is
g, and the weight b of the powder remaining on the 100 mesh sieve.
g and the powder ffi remaining on the 200 mesh sieve.
The degree of aggregation is calculated from the following formula from cg.

Therefore, the specific electrical resistance of spherical resin particles is 106 to 109Ω.
- Must be cm. Specific electrical resistance is 106Ω
- If a toner particles lower than cm is used, the amount of charge on the toner particles will be significantly reduced, especially in a high temperature and high humidity environment, resulting in a decrease in image density.

Furthermore, if a material with a specific electrical resistance higher than 109 Ω・Cm is used, the fluidity of the toner will be significantly deteriorated, and the movement of the toner in the developing device will be poor (resulting in uneven solid black density and a decrease in image density. Significant at low temperature and low humidity.

The electrical resistivity (volume resistivity) in the present invention is measured, for example, using the apparatus shown in FIG. In the same figure, 41
42 is a pedestal, and 42 is a suppressing means, which is connected to a hand press and has a pressure gauge 43 attached thereto. 44 has a diameter of 3.10
Sample 45 is placed in a 0 cm hard glass cell. 4
6 is a brass press ram, diameter 4.266 cm,
Area 14.2857 Crrl' 047 is a stainless steel push rod, radius 0.397 cm, area 0.49
At 6 ci, pressure from press ram 46 is applied to sample 45.

48 is a brass base, 49 and 50 are Bakelite insulating plates. 51 is a resistance meter connected to the press ram 46 and the stand 8, and 52 is a dial gauge.

In the device shown in Figure 4, the hand press has a hydraulic pressure of 20 kg/
When a pressure of cr rrr is applied, the sample has a weight of 576 kg/
cn (pressure is applied. The resistance is read from the resistance meter 51, multiplied by the cross-sectional area of the sample, and divided by the height of the sample read from the dial gauge 52 to determine the volume resistivity.

It is essential that the spherical resin particles be positively charged, and the particles may be subjected to surface treatment if necessary. Surface treatment methods include iron, nickel, cobalt, copper, zinc,
Methods of surface treatment of metals such as gold and silver by vapor deposition or plating methods, methods of fixing the above metals, magnetic materials, metal oxides such as conductive zinc oxide, etc. by ion adsorption or external addition, pigments or A triboelectrically chargeable organic compound such as a dye or a polymer resin may be supported by coating or external addition.

The magnetic developer of the present invention includes at least hydrophobic silica fine powder, positively charged resin fine particles, and insulating magnetic toner,
It has a BET specific surface area of 1.8 to 3.5 i/g by nitrogen gas adsorption method, a triboelectric charge of -10 to -20 μC/g, and a true specific gravity of 1.45 to 1.8 g/cm.

If the BET specific surface area of the developer of the present invention determined by the nitrogen gas adsorption method is less than 7 g, it will take time to obtain a sufficient amount of charge for development on the developer carrier, and the initial density will be low and fog will occur. There will be many images. Also 3,5rd/g
If it is larger, the mirroring force with the sleeve becomes thicker, resulting in a decrease in development rate and, as a result, a decrease in image density.

To measure the BET specific surface area in the present invention, QUANT
It was determined by the BETI point method using a specific surface area meter Autosorb I manufactured by AC'HROME.

Further, the true specific gravity of the developer of the present invention is 1.45 to 1.8 g/c.
rd, and if it is less than 1.45, fogging is likely to occur in a developing method in which an AC bias is applied in a magnetic field, and the line width becomes thick, resulting in poor resolution.

Examples of the binder resin for the magnetic toner of the present invention include monopolymers of styrene and its substituted products such as polystyrene and polyvinyltoluene; styrene-propylene copolymers, styrene-vinyltoluene copolymers, and styrene-vinylnaphthalene copolymers. combination, styrene-methyl acrylate copolymer,
Styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer,
Styrene-ethyl methacrylate copolymer, styrene-
Butyl methacrylate copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene - Styrenic copolymers such as maleic acid copolymers and styrene-maleic acid ester copolymers;
Polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin , paraffin wax, carnauba wax, etc. can be used alone or in combination.

Further, as coloring materials that can be further added to the magnetic toner according to the present invention, conventionally known carbon black, copper phthalocyanine, iron black, etc. can be used.

As the magnetic fine particles contained in the magnetic toner of the present invention, a substance that is magnetized by being placed in a magnetic field is used, such as powder of a ferromagnetic metal such as iron, cobalt, or nickel, or magnetite, γ-Fe2O3° ferrite. Alloys and compounds such as can be used.

These magnetic fine particles preferably have a BET specific surface area of 2 to 20 rrr/g, particularly 2.5 to 12
rd/g, and preferably a magnetic powder having a Mohs hardness of 5 to 7. The content of this magnetic powder is preferably 70 to 120 parts by weight per 100 parts by weight of the binder resin. Further, the toner of the present invention may contain a charge control agent if necessary, and a negative charge control agent such as a metal complex salt of a monoazo dye; a metal complex salt of salicylic acid, alkyl salicylic acid, dialkyl salicylic acid, or naphthoic acid is used. .

The above-mentioned charge control agent (one that does not function as a binder resin) is preferably used in the form of fine particles. In this case, the number average particle size of this charge control agent is specifically:
The length is preferably 4 μm or less (more preferably 371 m or less).

When internally added to the toner, such a charge control agent is added in an amount of 0.1 to 20 parts by weight (or even 0.1 to 20 parts by weight) per 100 parts by weight of the binder resin.
．． 2 to IO parts by weight) is preferably used.

Further, the magnetic toner according to the present invention has a volume resistivity of 1 o
It is preferable that the resistance is leΩam or more, particularly 10'2 Ωcm or more, from the viewpoint of triboelectric charge and electrostatic transferability. The volume resistivity mentioned here is 100kg/crr for toner? It is defined as the value calculated from the current value after 1 minute has elapsed after the application of an electric field of 100 V/cm.

The negatively chargeable silica fine particles used in the present invention have a tribocharge amount of 1100 μc/g to 130 μc/g. In addition, the BET specific surface area determined by nitrogen adsorption method is 70 to 300 d/g, and the average particle size is 5 m.
It is preferable to use a material corresponding to μ to 30 mμ.

If the amount of tribocharge is less than 1100 μC/g, the amount of tribocharge of the developer itself is reduced, and the humidity characteristics are deteriorated. Also, if a material exceeding -300 p c/g is used, the memory of the developer carrier will be promoted.1. In addition, it is easily affected by silica deterioration, etc. (which impedes the durability characteristics.
If it is finer than 00rrr/g, it will not be effective when added to the developer.If it is coarser than 7゜rd/g, there is a high probability of its existence as a free substance, and it is likely to cause black spots due to uneven silica concentration and aggregates. .

The tribo value of negatively charged silica fine particles is measured by the following method. That is, 0.2 g of silica fine powder left overnight in an environment of 25°C and 950% to 60% RH and 200 to 30%
Carrier iron powder that is not coated with resin and has a main particle size of 0 mesh (for example, EFV200/
300) 9.8g and approximately 50c, c under the above environment
Mix thoroughly (hand shake up and down approximately 50 times for approximately 20 seconds) in a polyethylene wide-mouth bottle having a volume of .

Next, as shown in FIG. 3, 0.5 g of the mixture is placed in a metal measuring container 32 with a 400 mesh screen 33 at the bottom and a metal lid 34 is placed. Measurement container 32 at this time
Weigh the entire weight and let it be W+(g).

Next, using the suction device 31 (which has a small portion in contact with the measurement container 32 (both are insulators), suction is performed from the suction port 37, and the air volume control valve 36 is adjusted to raise the pressure of the vacuum gauge 35 to 250 mm.
Let it be Hg. In this state, sufficient suction is performed to suction and remove the toner. The potential of the electrometer 39 at this time is V (volt)
shall be. Here, 38 is a capacitor, and the capacitance is C
(μF). In addition, the weight of the entire measurement container after suction is measured and is defined as W2 (g). The amount of triboelectric charge of this toner (μ
c/g) is calculated as shown below.

As the silica fine particles used in the present invention, both so-called dry silica produced by vapor phase oxidation of a silicon halide compound or dry silica called fumed silica, and so-called wet silica produced from water glass etc. can be used. It is preferable to use dry silica, which has fewer silanol groups on the surface and inside and has no production residue. In addition, for dry silica, it is also possible to obtain a composite fine powder of silica and other metal oxides by using other metal halogen compounds such as aluminum chloride or titanium chloride together with silicon halogen compounds in the manufacturing process. Also encompasses.

Further, the silica fine particles used in the present invention are preferably hydrophobically treated. For the hydrophobization treatment, a conventionally known hydrophobization method is used, and it is imparted by chemical treatment with an organosilicon compound that reacts with or physically adsorbs the silica fine powder. A preferred method is to treat fine silica powder produced by vapor phase oxidation of silicon or a halogen compound with an organosilicon compound after or simultaneously with the silane coupling agent.

Examples of such treatment agents include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane,
Allyl phenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate , vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyljethoxysilane,
Hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3 diphenyltetramethyldisiloxane, and siloxane units having 2 to 40 siloxane units per molecule, one each for the terminally located unit. S of
Examples include dimethylpolysiloxane containing a hydroxyl group, an alkyl group, or an alkoxy group bonded to i. These can be used alone or in a mixture of two or more.

The water wettability of silica in the present invention is measured as follows. 200m! ! Add 0.1 sample to the separating funnel.
Collect ion exchange water LoomI! Add using a graduated cylinder. Add this to Turbula Shaker Mixer T2
Shake for 10 min at 9 rpm in a c-type.

After leaving the separating funnel for 10 minutes, 20 to 30
After extracting ml, the sample was separated into a 10 mm cell, and the turbidity of the water layer was measured using a colorimeter using ion-exchanged water as a blank (wavelength: 500 nm).The transmittance % with respect to the blank was taken as the water wetness.

If the water wettability of the silica fine powder is 60% or less, image density fluctuations are likely to occur under high temperature and high humidity conditions.

Further, the applied amount of these silica fine particles is 0.6 to 1.6 parts by weight based on 100 parts by weight of toner to exhibit the effect, and it is particularly preferable to add 0.6 to 1.4 parts by weight. A developer exhibiting W conductivity and excellent stability can be provided. Regarding the preferred form of addition, it is preferable that 0.7 to 1.4 parts by weight of the treated silica fine powder be attached to the surface of the toner particles based on the weight of the developer.

The developer of the present invention may further contain other additives, such as Teflon, lubricants such as zinc stearate, fixing aids (such as low molecular weight polyethylene), or conductive additives, as long as they do not have a substantial adverse effect. A metal oxide such as tin oxide may be added as an agent.

In producing the toner of the present invention, the constituent materials are thoroughly kneaded using a heat kneader such as a hot roll, a niegu, or an extruder, and then mechanically crushed or classified, or the materials are mixed in a binder resin solution. A method of producing a toner by dispersing and then spray drying, or a polymerization method of obtaining a toner by mixing a specified material with a monomer to constitute a binder resin to form an emulsified suspension and then polymerizing the resulting toner. , each method can be applied.

Although the toner of the present invention can be applied to various developing methods, the following developing methods are preferred.

Here, an example of a developing process to which the present invention can be applied will be explained. FIG. 2 shows a cross-sectional view of one embodiment of the developing process. In the figure, an electrostatic image holder (photosensitive drum) has a photosensitive layer 5 and a conductive substrate 11, and moves in the direction of the arrow. The non-magnetic cylinder, which is the developer carrier 6, rotates in the developing section so as to move in the same direction as the surface of the electrostatic image carrier. Inside the non-magnetic cylinder 6,
The multipolar permanent magnets are arranged so as not to rotate. The one-component insulating magnetic developer 10 in the developing device 8 is applied onto a non-magnetic cylindrical surface, and by friction between the cylindrical surface and the toner particles,
Gives the toner particles a tribocharge. Furthermore, a magnetic doctor blade 9 made of iron is placed close to the cylindrical surface (with an interval of 50 μm).
By arranging the toner layer to face one magnetic pole position of a multipolar permanent magnet, the thickness of the toner layer can be reduced (~500 μm) (~500 μm).
[mu]m to 300 [mu]m) and is uniformly regulated to form a developer layer thinner than the gap between the electrostatic image holder and the developer carrier in the developer. By adjusting the rotational speed of the cylinder 6, the surface speed and preferably the internal speed of the developer layer are made to be substantially equal to, or close to, the speed of the electrostatic image holding surface. As the magnetic doctor blade 9, a permanent magnet may be used instead of iron to form opposing magnetic poles. Further, an alternating current bias or a pulse bias may be applied by the bias means 14 between the developer carrier 6 and the electrostatic image holding surface in the developing section. This AC bias has an f of 200 to 4000 Hz.

It is sufficient if Vl)p is 500 to 3000V.

In this developing step, a nonmagnetic cylinder 6 containing a multipolar permanent magnet was used to stably hold the one-component magnetic developer on the developer carrier. Further, in order to form a thin and uniform developer layer, a doctor blade 9 made of a thin magnetic plate or a permanent magnet is arranged close to the surface of the cylinder 6.

When a magnetic doctor blade is used in this way, opposing polarity is formed between the magnetic poles of the permanent magnet contained in the developer carrier, and the toner particle chains are forced between the doctor blade and the developer carrier. This is advantageous in controlling the thickness of the developer layer in other parts of the developer carrier, for example, in the development part facing the electrostatic image surface. Further, by imparting such forced movement to the developer, the developer layer becomes more uniform, and a thin and uniform toner layer formation is achieved.

Moreover, since the distance between the doctor blade and the sleeve can be set wide, it is also effective in preventing the destruction and aggregation of toner particles. When the toner particles are transferred in the developing area, they are transferred to the electrostatic image side by the action of the electrostatic force of the electrostatic image holding surface and the alternating current bias or pulse bias. Further, instead of the doctor blade 9, an elastic blade made of an elastic material such as silicone rubber may be used to control the thickness of the developer layer by pressing, and apply the developer onto the developer carrier. .

In the image forming apparatus shown in FIG. 2, the photosensitive layer 5 charged by the primary charger 13 is exposed to light from a predetermined light source. Since the toner of the present invention tends to cause electrostatic adhesion and electrostatic aggregation, the developer 10 in the developing device 8 is stirred by a stirring rod and sequentially supplied to the sleeve. The electrostatic charge image is developed by the developer on the sleeve of the developing device 8, and the toner image on the photosensitive layer 5 is transferred to the transferred transfer material 20 from the charging device 1.
Corona transfer is performed by step 5. Transfer material 2 with toner image
0 is separated from the electrostatic holder by a separation belt 12,
The toner image is fixed via a separation roller 21 and a conveyance roller 18 by a heat-pressure fixing device including a heating roller 16 and a pressure roller 17. After the toner image has been transferred, the remaining developer on the electrostatic image holder is removed by a cleaning blade 16, and the image forming process is sequentially repeated.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but these are not intended to limit the present invention in any way. All parts in the following formulations are parts by weight.

Example 1 Styrene/n-butyl acrylate/divinylbenzene copolymer 10
0 parts by weight (copolymerization ratio 85/14.5 10.5 weight average molecular fiMw = 240,000) magnetite (average particle size 0.2μ
m) 100 parts by weight chromium complex of monoazo dye 0.6 parts by weight low molecular weight polypropylene
4 parts by weight After mixing the above ingredients well in a blender, 1
The mixture was kneaded using a twin-screw kneading extruder set at 30°C. At this time, if the humidity setting is too high, the toner tends to fog. The obtained kneaded material was cooled and coarsely pulverized using a cutter mill, then finely pulverized using a pulverizer using a jet stream, and the obtained pulverized powder was classified using a fixed wall type wind classifier. A classified powder was produced. Furthermore, the obtained classified powder was rigorously classified and removed at the same time to remove ultra-fine powder and coarse powder using a multi-division classification device (elbow jet classifier manufactured by Hakusan Mining Co., Ltd.) that utilizes the Coanda effect. A black fine powder (negatively charged insulating magnetic toner) (A) was obtained.

The obtained black fine powder was negatively charged with respect to the iron powder carrier, and the particle size measured with the aforementioned Coulter counter TAn type is shown in Table 1. For reference, a classification process using a multi-segment classifier is schematically shown in FIG. 5, and a cross-sectional perspective view (stereoscopic view) of the multi-segment classifier is shown in FIG.

An emulsion copolymer containing methyl methacrylate units as a main component (average diameter: 0.000 parts) is added to 100 parts of the negatively chargeable black fine powder.
07 μm1 Tribocharge amount + 100 μc/g % Sphericity approximately 1.0, Contains nitrogen-containing compound, Specific electrical resistance value 3
X 10'Ω/cm, T g 110'C)
and 0.8 part of hydrophobic silica (average diameter 12
mμ, BET specific surface area 200 d/g dry silica was hydrophobized with hexamethyldisilazane and silicone oil, tribocharge amount -280 μc/g % water wettability 9
8%) and mixed with a Henschel mixer to obtain a one-component negatively charged magnetic toner.

The degree of cohesion of the toner was 55%.

The toner was evaluated using a laser beam printer shown in FIG. 1 of the accompanying drawings. The evaluation method is to print out consecutive LOO sheets using the manuscript shown in Figure 1a, then print out the manuscript shown in Figure 1b, and compare the images in Figure 1c,
3.3a and 4 were evaluated using the average value of five measurements each.

In the laser beam printer used, a negatively charged OPC photosensitive drum was used, the gap between the sleeve and the blade was 240 μm, the closest gap between the sleeve and the photosensitive drum was 27'Oμm, and an AC bias was applied at 1500 Vp.
A toner image was generated by a reversal development method while applying p, 1400 Hz and a DC bias of -450 V to the sleeve. The evaluation results are shown in Table 2.

Further, the fine line reproducibility was evaluated by the reproducibility of a digital latent image with a width of 50 μm.

The multi-division classifier used in this example and the classification process using the classifier will be explained with reference to FIGS. 5 and 6. In FIGS. 5 and 6, the multi-segment classifier 101 has side walls having shapes indicated by 122 and 1.24, and a lower wall having a shape indicated by 125. are respectively Naifetsu-type classification edges 117.
118, the classification edge 117. 118, the classification zone is divided into three parts. A raw material supply nozzle 116 that opens into the classification chamber is provided at the lower part of the side wall 122,
A Coanda block 126 is provided which is bent downward in the direction of extension of the bottom tangent of the nozzle to draw an elongated arc.

The upper wall 127 of the classification chamber is provided with a knife-shaped edge 119 toward the bottom of the classification chamber, and a tube 114 that opens into the classification chamber at the top of the classification chamber. 115 is provided.

Also popular tube 114. 115 includes first and second gas introduction adjusting means 120, 121 such as dampers, and a static pressure gauge 128.
゜129 is provided. At the bottom of the classification chamber are discharge pipes 111 each having a discharge port opening into the chamber corresponding to each fractionation area. 112. ．． 113 is provided.

The classified powder is introduced into the classification area from the supply nozzle 116 under reduced pressure, and moves in a curved line 130 due to the Coanda effect of the Coanda block 126 and the action of the high-speed air flowing in at that time, and is moved into the coarse powder 111, coarse powder 111, The powder was classified into black fine powder (magnetic toner) 112 and ultrafine powder 113 having a predetermined volume average particle size and particle size distribution.

Example 2 The same procedure as in Example 1 was carried out except that the amount of magnetite was 80 parts by weight, the particle size of the black fine powder was the particle size distribution of B in Table 1, and the amount of hydrophobic silica was 0.6 parts by weight. Table 2 shows the results.
Shown below.

The degree of aggregation of this toner was 45%.

Example 3 Positively chargeable resin fine particles mainly composed of methyl methacrylate units, average diameter 0.3 μm, ribocharge amount +3
30μc/gs Sphericity approximately 1.0, Specific electrical resistance value 9
．． 0x10'Ω"am, weight average molecular weight 60,000,
The same procedure as in Example 1 was carried out except that emulsion copolymer fine particles having physical properties of Tgl of 14°C were used. The results are shown in Table 2.

The degree of aggregation of this toner was 46%.

Example 4 As positively charged resin particles, an emulsion copolymer of methyl methacrylate (average diameter 0.2 μm, tribocharge amount +280
μc / gs Sphericity approximately 1.0, specific electrical resistance value 7
10'Ω'cm, weight average molecular weight 45,000, Tg
The same procedure as in Example 1 was performed except that llOoC) was used.

The evaluation results are shown in Table 2.

The degree of aggregation of the toner in this example was 40%.

Comparative Example 1 Example 1 except that positively chargeable resin fine particles were not used.
I did the same thing. The evaluation results are shown in Table 2.

The degree of aggregation of the toner in this example was 75%.

Comparative Example 2 Positively charged resin particles are 1.3 μm and triboelectric charge is +15
The same procedure as in Example 1 was performed except that the concentration was 0 μc/g.

The evaluation results are shown in Table 2.

The degree of aggregation of the toner in this example was 82%.

Comparative Example 3 Specific electrical resistance of positively chargeable resin particles is 7×10”Ω・c
m.

The same procedure as in Example 3 was conducted except that the amount of triboelectric charge was +500 μc/g. The evaluation results are shown in Table 2.

The degree of aggregation of the toner in this example was 94%.

Comparative Example 4 The amount of magnetite was set to 60 parts by weight, the particle size of the black fine powder was set to particle size distribution C in Table 1, the positively charged resin fine particles used in Example 3 were set to 0.4 parts by weight, and the amount of hydrophobic silica was set to 60 parts by weight. 0.4
The same procedure as in Example 1 was carried out except that the parts by weight were changed. The evaluation results are shown in Table 2.

The degree of aggregation of the toner in this example was 73%.

Table 3 shows the physical properties of the magnetic developer used on each side.

[Brief explanation of drawings]

1a, 1b, and 1c are diagrams illustrating a developer carrier memory, FIG. 2 is a diagram illustrating an embodiment of an image forming apparatus to which the present invention can be applied, and FIG. 1 shows a schematic diagram of an apparatus for measuring the triboelectric charge amount of silica fine particles used in the present invention. FIG. 4 is a diagram schematically showing an apparatus for measuring the volume resistance of a sample. In the accompanying drawings, FIG. 5 shows an explanatory view of the classification process using the multi-part classification means, FIG. 6 shows a schematic cross-sectional perspective view of the multi-part classification means, and FIG. 7 shows the classification process using the multi-part classification means.
FIG. 3 is a diagram showing the range of the content ratio of particles having a particle size of μm or less. 101...Multi-division classification device, 111...Coarse powder,
112...Powder having a predetermined particle size, 113...Fine powder, 126...Coanda block

Claims (2)

[Claims] (1) In a negatively charged magnetic toner having at least a binder resin and a magnetic powder, magnetic toner particles having a particle size of 5 μm or less are contained in an amount of 17 to 60% by number, and 6.35 to 10% by number.
．． 5 to 50% by number of magnetic toner particles having a particle size of 0.08 μm are contained, 2.0% by volume or less of magnetic toner particles having a particle size of 12.70 μm or more are contained, and the volume average diameter of the magnetic toner is 6 to 50% by number. 8 μm, and the group of magnetic toner particles with a diameter of 5 μm or less is represented by the following formula N/V=-0.05N+K [where N represents the number percent of magnetic toner particles with a particle size of 5 μm or less, and V represents the number of particles with a particle size of 5 μm or less. It shows the volume % of magnetic toner particles having a diameter, and K shows a positive number from 4.6 to 6.7. However, N represents a positive number from 17 to 60. ] Negatively charged magnetic toner 100 having a particle size distribution satisfying
0.1 to 1 part by weight of positively chargeable resin particles (A) having an average particle diameter of 0.03 to 1.0 μm and a specific electrical resistance of 10^8 Ω·cm to 10^9 Ω·cm, based on the weight part; and -100
Negatively charged magnetic material characterized by containing 0.6 to 1.6 parts by weight of hydrophobic silica fine powder (B) having a tribocharge amount of -300 μc/g in an amount equal to or more than A. developer. (2) The magnetic developer according to claim (1), wherein the positively chargeable resin particles are spherical particles having a triboelectric charge amount of +50 to +350 μc/g.