JP3291590B2 - Color toner, color developer and image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to electrophotography, electrostatic recording,
The present invention relates to a dry electrophotographic color toner, a color developer, and an image forming method for developing an electrostatic image in electrostatic printing or the like.

[0002]

2. Description of the Related Art It is well known in the art to form and develop an image on the surface of a photoconductive material by electrostatic means.

That is, US Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910, and Japanese Patent Publication No. 43-2
A number of methods are known, such as Japanese Patent No. 4748, but generally, a photoconductive substance is used to form an electric latent image on a photoreceptor by various means, and then the toner is called a toner on the latent image. A toner image corresponding to an electrostatic latent image is formed by attaching an extremely finely pulverized inspection material.

Then, if necessary, the toner is transferred to the surface of an image support such as paper, and then fixed by heating, pressurizing or solvent vapor to obtain a copy. When a step of transferring a toner image is provided, a step for removing residual toner is usually provided.

[0005] A developing method for visualizing an electric latent image by using a toner is described in, for example, a powder cloud method described in US Pat. No. 2,221,776, and US Pat. No. 2,618,55.
No. 2,874,063, a magnetic brush method, and a conductive property described in 3,909,258. A method using a magnetic toner is known.

As a toner applied to these developing methods, a toner obtained by mixing and dispersing a colorant in a thermoplastic resin and then pulverizing the same is used. As the thermoplastic resin, a polystyrene resin is the most common, but a polyester resin, an epoxy resin, an acrylic resin, a urethane resin, or the like is also used. As a coloring agent, carbon black is most widely used, and in the case of a magnetic toner, iron oxide black magnetic powder is often used. In the case of using a so-called two-component developer, the toner is usually glass beads,
It is used by being mixed with carrier particles such as iron powder.

[0007] The toner image on the final copy image forming member such as paper is permanently fixed on the support by heat, pressure or the like. Conventionally, this fixing step has often been performed by heat.

When a step of transferring a toner image is provided, a step for removing residual toner on the photoreceptor is usually provided.

In recent years, the development of monocolor copying to full-color copying in copying machines and the like has been rapidly progressing, and the study and commercialization of two-color copying machines and full-color copying machines have been greatly increased. For example, “Journal of the Society of Electrophotography,” Vol.
22, no. 1 (1983) and "Journal of the Institute of Electrophotography" Vo
l 25, No. 1, P52 (1986).

[0010] However, full color electrophotography which is not practically compared with the real thing like a television, a photograph, and a color print, and which is regarded as a color image which is more beautifully processed than the real thing, is now in practical use. The images are not always satisfactory.

Further, in recent years, the demand for high definition and high image quality of copying machines has been increasing in the market, and in the technical field, attempts have been made to achieve high image quality and color by reducing the particle size of toner. However, as the particle size becomes smaller, the surface area per unit weight increases, and the amount of charged electricity of the toner tends to increase.

As described above, a sine wave or a rectangular wave is superimposed as a DC component and an AC component in a development region for the purpose of preventing image deterioration due to the reduction in toner particle diameter, preventing deterioration in durability, and improving development efficiency. Improvements are being attempted. However, even in such a developing method, a quality sufficient to cope with a change in the triboelectric charge amount due to the environment or durability of the toner has not been obtained, and a stable developing method cannot be achieved without improving the toner. is there.

A number of developers have been proposed for the purpose of improving image quality. JP 5
Japanese Patent Application Laid-Open No. 1-3244 proposes a non-magnetic toner intended to improve the image quality by regulating the particle size distribution. The toner is mainly composed of a toner having a particle size of 8 to 12 μm, and is relatively coarse. According to the study of the present inventors, it is difficult for the toner to have a dense “glue” to a latent image, In addition, from the characteristic that 5 μm or less is 30 number% or less and 20 μm or more is 5 number% or less, there is a tendency that the particle size distribution is broad and the uniformity is lowered.
In order to form a clear image using such a coarse toner particle and a toner having a broad particle size distribution, it is necessary to fill the gap between the toner particles by thickly overlapping the toner particles. There is also a problem that it is necessary to increase the image density, and the amount of toner consumption required to obtain a predetermined image density increases.

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

Japanese Unexamined Patent Publication (Kokai) No. 58-129439 proposes a non-magnetic toner having an average particle diameter of 6 to 10 μm and a maximum number of particles of 5 to 8 μm. However, images with low sharpness tend to be formed.

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

Therefore, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 2-222.
No. 966, toner particles of 5 μm or less
Although a toner containing several percent has been proposed, a considerable improvement in image quality has been achieved by this, but further improved image quality is also desired.

In Japanese Patent Application Laid-Open No. 2-877, 5 μm
The following toner particles containing 17 to 60% by number of toner particles have been proposed. By this, the image quality and image density were certainly stable, but originals with large consumption such as photo originals were continuously printed. In this case, it was also found that without proper development method, the particle size distribution of the toner changed, and it was difficult to always obtain a constant image.

On the other hand, Japanese Patent Application Laid-Open Nos. 51-3238, 58-144839, and 61-20264 disclose the average particle size and particle size distribution of the carrier.
No. 6 publication. JP-A-51-3238 refers to a rough particle size distribution. However, it does not specifically disclose the magnetic properties closely related to the developability of the developer and the transportability in the developing device. Further, all the carriers in the examples are about 80% by weight at 250 mesh or more.
The average particle diameter is also 60 μm or more.

Japanese Unexamined Patent Publication (Kokai) No. 58-144839 discloses only the average particle size, and the amount of fine powder affecting the carrier adhesion to the photoreceptor and the coarse powder affecting the sharpness of the image. It does not mention the amount and does not describe its distribution in detail in consideration of the characteristics of color copying. Further, Japanese Patent Application Laid-Open No. 61-204646 discloses a combination of a copying machine and an appropriate developer as the gist of the invention, and does not specifically describe the particle size distribution and magnetic properties of the carrier. Furthermore, it does not even disclose why the developer is effective in the copying machine.

Japanese Patent Application Laid-Open No. 49-70630 discloses that
Although the description is made with respect to the magnetic force of the carrier, these are based on iron powder having a higher specific gravity than ferrite as a carrier material, and have a high saturation magnetism. Conventionally, these iron powder carriers have been used in many cases. However, since the specific gravity is large, the copying apparatus is liable to increase in weight and the driving torque is overloaded, and the environment is highly dependent.

Further, the ferrite carrier described in Japanese Patent Application Laid-Open No. 58-23032 is for a material having a large number of porous holes, and such a carrier easily generates an edge effect and has low durability. It has been found to be poor and unsuitable as a color carrier.

Until now, a developer capable of continuously copying an image having a large image area with a small amount of developer and satisfying the characteristic characteristic of color copying which does not cause an edge effect even after durability has been desired. I have. Although studies are being made on developers and carriers, most of them have been proposed in consideration of black-and-white copying, and very few have been proposed for full-color copying. In addition, a carrier having an ability to continuously copy an image having an image area of 20% or more, which is almost a solid image, a reduction in edge effect, and an ability to maintain uniformity of image density in one copy is available. Long awaited.

Therefore, the present inventors have disclosed in Japanese Patent Laid-Open Publication No.
No. 80 proposes a carrier having a narrow particle size distribution in which the amount of fine powder and the amount of coarse powder are controlled, thereby achieving a carrier having improved development characteristics.

However, as described above, the demand for high definition and high image quality of the copying machine is increasing in the market, and in this technical field, it is attempted to achieve high image quality color by reducing the particle size of the toner. Attempts have been made, however, as the particle size becomes smaller, the surface area per unit weight increases, and the amount of charge of the toner tends to increase.

As described above, attempts have been made to further reduce the diameter of the carrier for the purpose of preventing the image density from being reduced and the durability from being reduced due to the reduction in the particle diameter of the toner, or improving the development efficiency. However, in such carriers,
Sufficient quality was not obtained to cope with changes in the amount of charge due to toner environment or durability, and good images without high image density, high image quality, fog, carrier adhesion, etc. were obtained without improving the developing method. I can't.

[0027]

SUMMARY OF THE INVENTION An object of the present invention is to provide a color toner and a color developer which are hardly influenced by the environment such as temperature and humidity and have always stable characteristics.

An object of the present invention is to provide a color toner and a color developer having clear image characteristics without fogging and having excellent durability stability.

An object of the present invention is to provide a color developer and an image forming method which can quickly obtain triboelectric charging between a toner and a carrier and have good transportability in a developing device.

[0030]

SUMMARY OF THE INVENTION According to the present invention, there is provided a latent image holding member and a developer carrying member opposed to the latent image holding member, wherein toner is transferred between the latent image holding member and the developer carrying member. After applying a voltage for drawing from the holder to the developer carrier and a voltage for causing the developer carrier to fly from the developer carrier to the latent image holder for T ₁ hour,
For the image portion, the toner is caused to fly, and for the non-image portion, the voltage in the direction in which the toner is pulled back is at least T.
_A color toner developed by a means for applying a time longer than ₁ hour with a color toner and subjected to an image forming method of transferring a toner image formed on an image carrier onto a transfer material, at least a colorant Containing the resin particles and an external additive, the color toner has a weight average particle diameter of 3 to 7 μm, and a toner having a particle diameter of 5.04 μm or less is contained in more than 40% by number, and a particle diameter of 4 μm or less Is contained in an amount of 10 to 70% by number, a toner having a particle diameter of 8 μm or more is contained in an amount of 2 to 20% by volume, and a toner having a particle diameter of 10.08 μm or more is contained in an amount of 6% by volume or less. The present invention relates to a color toner, wherein the external additive contains at least titanium oxide fine particles.

Further, the present invention relates to a two-component color developer for use in the same image forming method as described above, wherein (1) a carrier having a weight-average particle size of 15 to 45 μm and a carrier particle smaller than 22 μm is used. 20%, 3% or less of carrier particles smaller than 16 μm, 2 to 15% of carrier particles of 62 μm or more, 2% or less of carrier particles of 88 μm or more, and an applied magnetic field of 3000 Oe of the carrier. A color comprising: a carrier having a saturation magnetization of 35 to 90 emu / g, a residual magnetization of 10 emu / g or less, and a coercive force of 40 oersted or less; and (2) the color toner described above. It relates to the developer.

The present inventors have conducted intensive studies on the image density, highlight reproducibility, and fine line reproducibility of the color image forming method. As a result, using a color toner having a specific particle size distribution, a DC component as a developing electric field was used. In addition, when superimposing a discontinuous AC component, it was found that high image quality with high image density, highlight reproduction, fine line reproduction, etc. could be achieved, and further, titanium oxide fine particles were included as an external additive. At times, they have found that stable environmental characteristics can be achieved.

The toner having the above-described particle size distribution can faithfully reproduce a latent image formed on a photoreceptor, and is excellent in reproducibility of a halftone dot and a minute dot latent image such as a digital image. In particular, an image excellent in gradation and resolution of a highlight portion is provided. Furthermore, high image quality can be maintained even when copying or printing out is continued, and even in the case of high density images, good development can be performed with less toner consumption than conventional non-magnetic toner. It also has advantages in terms of performance and miniaturization of the copier or printer body.

However, even if the toner is originally excellent in latent image reproducibility, a conventional continuous sine wave or rectangular wave may cause an electric field in a latent image having a small development contrast like a highlight latent image. 1 because of insufficient strength
With a pulse, the ratio of the toner not reaching the latent image holding member increases. That is, under the bias under the above conditions, the toner makes a vibrating motion so as not to reach the latent image holding member from the developer holding member.

However, by applying a specific AC electric field as in the present invention, it is possible to obtain a good highlight image without roughness. That is, in one pulse, the toner oscillates so that the toner does not reciprocate between the developer carrier and the latent image holding member, but thereafter, the surface potential of the latent image holding member and the DC component of the developing bias are changed. When the potential difference Vcont is Vcont <0, the DC component acts to attract the toner toward the developer carrier, and the toner is biased toward the sleeve side. When Vcont> 0, the DC component is latent in accordance with the latent image potential. The toner acts to attract the toner to the image carrier, and an amount of toner corresponding to the latent image potential is biased toward the latent image carrier. Further, when development is performed under such conditions, the toner that has reached the latent image holding member repeats the vibration there and concentrates on the latent image portion. For this reason, the dot shape is made uniform, and a good image without unevenness can be obtained.

As described above, when the latent image is visualized with the developing bias under the above-described conditions, the dropout of the dot does not occur even in the case of the highlight latent image. Further, by repeating the vibration on the latent image holding member, the toner is concentrated on the latent image portion, and the dots are faithfully reproduced one by one. In the two-component developer, the uniformity due to the contact state of the magnetic brush is uniform. A halftone image can be output.

This will be described in more detail. The number of toner particles having a particle size of 4 μm or less is 10 to 70% by number, preferably 15 to 60% by number of the total number of particles. When the toner particles having a particle size of 4 μm or less are less than 10% by number, the amount of non-magnetic toner particles effective for high image quality is small. In particular, as the toner is used by continuing copy or printout, the effective non-magnetic toner The particle component is reduced, and the balance of the particle size distribution of the non-magnetic toner as shown in the present invention is deteriorated, and the image quality may be gradually reduced. This tendency is remarkable especially when combined with the developing system of the present invention.

On the other hand, if the content exceeds 70% by number, toner particles tend to aggregate with each other, and the toner particles tend to become larger than the original particle size, resulting in poor image quality, reduced resolution, or The density difference between the edge portion and the inside of the latent image is increased, and the image tends to be slightly hollow.

The particles having a particle size of 8 μm or more are 2.0 to 20.0 particles.
%, Preferably 3.0 to 18.0% by volume.
Volume% is good. If the content is more than 20.0% by volume, the image quality is deteriorated, and the development is performed more than necessary, that is, the toner is overloaded, which leads to an increase in toner consumption. On the other hand, 2.0
If the amount is less than the volume%, there is a possibility that the image quality may be deteriorated due to a decrease in fluidity regardless of how the toner formulation is devised.

In order to further improve the effects of the present invention, for the purpose of improving the chargeability and fluidity of the toner,
Particles of 5.04 μm or less are larger than 40% by number,
It is necessary that the number of particles having a size of not more than number%, preferably more than 40 number%, not more than 80 number%, and not less than 10.08 μm should be 0 to 6% by volume, preferably 0 to 4% by volume.

Further, the carrier for electrophotography used in the present invention is a carrier having a small average particle size and a uniform small particle size having a uniform particle size and a controlled amount of fine powder and coarse powder. Therefore, the rise of the triboelectric charging property with the toner is also preferably improved. However, the carrier of the present invention has a much larger amount of fine powder than conventionally known carriers, and there is a concern that the carrier may adhere to the latent image holding member during development. In addition to the above, not only does carrier adhesion not occur, but also it is possible to obtain a good highlight image without roughness. The reason for this is not yet clear, but is presumed as follows.

That is, in the case of a conventional continuous sine wave or rectangular wave, if the electric field strength is increased in order to achieve a high image density, the toner and the carrier are reciprocated between the latent image holding member and the developing sleeve integrally. As a result, the carrier strongly rubs against the latent image holding member, and carrier adhesion occurs. This tendency is more remarkable as the amount of the fine powder carrier increases.

However, when a specific AC electric field is applied as in the present invention, the toner or carrier reciprocates between the developer carrier and the latent image carrier in one pulse, so that the subsequent latent image When the potential difference Vcont between the surface potential of the holding member and the DC component of the developing bias is Vcont <0, the DC component acts to fly the carrier from the developer carrier, but the magnetic characteristics of the carrier and the developing area of the magnet roller By controlling the magnetic flux density at Vcont, the carrier adhesion can be prevented, and when Vcont> 0, the force of the magnetic field and the DC component act to attract the carrier to the developer carrying member side, and no carrier adhesion occurs.

On the other hand, in terms of toner, one pulse is the same that the toner oscillates so as not to reciprocate between the developer carrier and the latent image carrier, but thereafter, the surface potential of the latent image carrier and the developing bias Potential difference Vcont with the DC component of
When Vcont <0, the DC component acts to attract the toner toward the developer carrier, and the toner is biased toward the sleeve. When Vcont> 0, the DC component is used to hold the latent image in accordance with the latent image potential. It acts to attract the toner to the body side, and the amount of toner corresponding to the latent image potential is biased toward the latent image holding member. Further, when development is performed under such conditions, the toner that has reached the latent image holding member repeats the vibration there and concentrates on the latent image portion. For this reason, the dot shape is made uniform, and a good image without unevenness can be obtained.

From the above, when the latent image is visualized with the developing bias under the above-described conditions, the dropout of the dot does not occur even in the case of the highlight latent image. Further, by repeating the vibration on the latent image holding member, the toner is concentrated on the latent image portion, and the dots are faithfully reproduced one by one. In the two-component developer, the uniformity due to the contact state of the magnetic brush is uniform. A halftone image can be output.

The weight average particle diameter of the carrier is 15 to 45 μm, and the number of the carrier particles smaller than 22 μm is 1 to 20%, preferably 2 to 15%, more preferably 4 to 12%, and 16 μm Less than 3% of the smaller carrier particles, preferably less than 2%, more preferably less than 1%.

When the abundance of the fine powder exceeds the above-mentioned value, even when combined with the specific developing electric field of the present invention, the adhesion of the carrier and the smooth electrification with the toner are prevented, and the carrier particles smaller than 22 μm are less than 1%. In this case, the magnetic brush becomes sparse, the rise of the toner charge is deteriorated, and toner scattering and fog are caused.

The coarse powder amount of the carrier having a size of 62 μm or more closely correlates with the sharpness of the image, and needs to be 2 to 15%. If it exceeds 15%, the toner carrying ability of the carrier is reduced, the scattering of the toner to the non-image portion is increased, the resolution of the image is reduced, and the highlight reproducibility is reduced. On the other hand, if it is less than 1%, the fluidity of the developer deteriorates, the developer is shifted in the developing device, and a stable image is hardly obtained.

Further, in order to make the effect of the present invention more effective, the apparent density of the carrier is 1.8 to 3.2 g.
/ Cm ³ is preferable. When the apparent density is smaller than the above value, carrier adhesion is likely to occur, and when the apparent density is larger than the above value, the circulation of the developer is deteriorated, so that not only toner scattering and the like are easily generated, but also the image quality is deteriorated earlier. .

The magnetic properties of the carrier are affected by the magnet roller incorporated in the developing sleeve, and greatly affect the developing properties and transportability of the developer.

In the present invention, on a developing sleeve having a built-in magnet roller, the magnet roller is fixed and the developing sleeve is rotated alone to circulate and transport a two-component developer composed of magnetic particles and an insulating color toner. When developing the electrostatic latent image carried on the surface of the electrostatic latent image carrier with the two-component developer, the magnet roller has a five-pole configuration having repulsive poles, and the magnetic flux density in the development area is 600 to When it is 1200 gauss and the saturation magnetization of the carrier is 90 emu / 35 emu / g, color uniformity is excellent in image uniformity and gradation reproducibility.

If the saturation magnetization exceeds 90 emu / g (for an applied magnetic field of 3000 Oersted), a brush composed of a carrier and a toner on a developing sleeve facing an electrostatic latent image on a photoreceptor at the time of development. The spikes are firmly tightened, and the gradation and the reproduction of halftone are deteriorated. On the other hand, if it is less than 35 emu / g, it becomes difficult to hold the toner and the carrier on the developing sleeve well even in combination with the developing method of the present invention, and the problem that the carrier adhesion and the toner scattering are deteriorated occurs. Easier to do.
Furthermore, if the residual magnetization and coercive force of the carrier are too high, good transportability of the developer in the developing device is hindered, and image defects such as blurring and uneven density in a solid image are likely to occur. It will be reduced. therefore,
In order to maintain the developability in color copying, unlike ordinary black-and-white copying, the residual magnetization is 10 emu / g or less.
Preferably 5 emu / g or less, more preferably substantially 0
It is important that the coercive force be 40 Oe or less (3000 Oe, relative to the applied magnetic field), preferably 30 Oe or less, more preferably 10 Oe or less.

In order to make the present invention more effective, an alternating electric field is applied between the latent image holding member and the developer holding member in the developing region of the developer holding member opposed thereto. The voltage at which the toner is attracted from the latent image holder to the developer carrier and the voltage at which the toner flies from the developer carrier to the latent image holder are T _1.
After time application, for the image portion causes the toner to fly, it is necessary to apply at least the above-mentioned time T ₁ longer than the direction of the voltage pull back the toner for non-image portion.

At the same time, the present inventors have conducted intensive studies on stabilization of the chargeability of the color toner for electrostatic charge development. As a result, as an external additive, anatase surface-treated while hydrolyzing the coupling agent in an aqueous system was used. It has been found that the titanium oxide fine particles are extremely effective in terms of stabilizing charging and imparting fluidity.

This cannot be achieved with the generally known hydrophobic silica as a flow improver.

The reason is that the silica fine particles themselves have strong negative chargeability, whereas the titanium fine particles have almost neutral chargeability. Conventionally, it has been proposed to add hydrophobic titanium oxide. However, titanium oxide fine particles originally have a smaller surface activity than silica, and hydrophobicity has not always been sufficiently achieved. In addition, when a large amount of a treating agent or the like is used or a highly viscous treating agent is used, the degree of hydrophobicity is certainly increased, but coalescence of the particles occurs, and the ability to impart fluidity is reduced. The balance between the stabilization and the provision of liquidity has not always been achieved.

On the other hand, although hydrophobic silica is certainly excellent in fluidity-imparting ability, when it is contained in a large amount, on the contrary, due to its strong charging property, it causes electrostatic aggregation and the fluidity-imparting ability is reduced. I will. In this regard, as the amount of titanium oxide increases, the fluidity of the toner improves.

The use of anatase-type titanium oxide has been proposed, for example, in Japanese Patent Application Laid-Open No. Sho 60-112052. However, anatase-type titanium oxide has a small volume resistivity of about 10 ⁷ Ωcm, and When used, the charge leaks particularly quickly under high humidity, which is not always satisfactory in terms of the stabilization of the charge, and needs improvement.

Further, as an example of the toner containing hydrophobic titanium oxide, Japanese Patent Application Laid-Open No. Sho 59-52255 proposes a toner containing titanium oxide treated with alkyl trialkoxysilane. ,
Certainly, although the electrophotographic properties have been improved, the surface activity of titanium oxide is inherently small, resulting in the formation of coalesced particles during processing and uneven hydrophobicity. It was not satisfactory.

The inventors of the present invention have conducted intensive studies on the stability of the chargeability of the toner. As a result, the specific coupling agent was treated while being hydrolyzed in an aqueous system.
The anatase type titanium oxide having a light transmittance of 40% or more at 400 nm and a hydrophobicity of 20 to 98% and a hydrophobicity of 20 to 98% can be subjected to a uniform hydrophobic treatment, and there is no coalescence of particles. They have found that a toner containing titanium is extremely effective in terms of stabilizing charging and imparting fluidity.

That is, in the present invention, the surface treatment is performed while hydrolyzing the coupling agent while mechanically dispersing the anatase type titanium oxide fine particles to have a primary particle size in an aqueous system. It was found that coalescence of the particles hardly occurs, and that a repelling action between the particles due to the treatment works, so that the anatase type titanium oxide fine particles are surface-treated in a substantially primary particle state.

The feature of the present invention is that the surface of the titanium oxide is treated while the coupling agent is hydrolyzed in an aqueous system. At this time, a mechanical force is applied to disperse the titanium oxide fine particles into the primary particles. Since it is added, there is no need to use a coupling agent that generates a gas like chlorosilanes or silazanes, and furthermore, particles that could not be used together in the gas phase have been used so far. Viscous coupling agents can also be used, and the effect of hydrophobization is enormous.

The coupling agent usable in the present invention may be any of a silane coupling agent and a titanium coupling agent. Particularly preferably used is a silane coupling agent of the general formula R _m SiY _n R: Arukookishi group m: 1 to 3 integer Y: alkyl group vinyl group, glycidoxy group, a hydrocarbon group containing a methacrylic group n: 1 Represented by an integer of -3, for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane , Dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane and the like. That.

More preferably, CaH _{2a + 1} -Si (OC _b H _{2b + 1} ) ₃ a = 4 to 12, b = 1 to 3.

Here, when a in the general formula is smaller than 4, the treatment becomes easy, but sufficient hydrophobicity cannot be achieved.
If a is larger than 13, the hydrophobicity is sufficient, but the coalescence of the titanium oxide particles increases, and the ability to impart fluidity is reduced.

On the other hand, if b is larger than 3, the reactivity is lowered and the hydrophobic treatment is not sufficiently performed.

Therefore, in the present invention, a is 4 to 12,
Preferably 4 to 8, b is 1 to 3, preferably 1 to 2.

The treatment amount is 1 to 50% by weight, preferably 3 to 40% by weight, and the degree of hydrophobicity is 20 to 98%, preferably 30 to 90% by weight with respect to 100 parts by weight of titanium oxide.
%, More preferably 40 to 80%.

That is, if the degree of hydrophobicity is less than 20%, the charge amount is greatly reduced due to long-term storage under high humidity, a mechanism for promoting charging on the hard side is required, and the apparatus becomes complicated. If the degree exceeds 98%, even if anatase type titanium oxide having a small volume resistivity is used, it is difficult to control the charging of the titanium oxide itself, and as a result, the toner will be charged up under low humidity.

The particle size is 0.0
1 to 0.2 μ is good. If the particle size is larger than 0.2 μm, toner charging due to poor fluidity becomes non-uniform, resulting in toner scattering and fogging. On the other hand, if it is smaller than 0.01 μm, the toner is easily embedded on the toner surface, and the toner is deteriorated quickly, and the durability is reduced.
This tendency is more remarkable in the sharp-melt color toner used in the present invention. The particle size of the titanium oxide in the present invention was measured by a transmission electron microscope.

In the present invention, as a method for treating titanium oxide, a method in which titanium oxide is mechanically dispersed in an aqueous system so as to have a primary particle size, and the coupling agent is hydrolyzed, is effective. Yes, it is preferable in that no solvent is used.

Another feature of the present invention is that the treated titanium oxide has a light transmittance of 40% or more at a light length of 400 nm.

That is, the titanium oxide used in the present invention has a very small primary particle diameter of 0.2 to 0.01 μm, but when it is actually contained in the toner, it is not necessarily dispersed in the primary particles. It does not mean that it may be present as secondary particles. Therefore, no matter how small the primary particle diameter is, the effect of the present invention is drastically reduced if the effective diameter acting as a secondary particle is large.

However, the lower limit wavelength of 40 in the visible region is 40.
The higher the light transmittance at 0 nm, the smaller the secondary particle diameter, and good results such as sharpness of the projected image of the fluidity imparting ability OHP can be expected.

The reason for selecting 400 nm is the boundary region between ultraviolet and visible light, and it is said that those having a particle size of 以下 or less of the light wavelength are transmitted. Therefore, the transmittance at wavelengths longer than that is naturally large. It is meaningless.

Further, the crystal form of titanium oxide was confirmed by X-ray diffraction to be an anatase type having a lattice constant (a) of 3.78 ° and a lattice constant (b) of 9.49 °.

On the other hand, as a method for obtaining hydrophobic fine-grained titanium oxide, there is also known a method in which volatile titanium alkoxide or the like is oxidized at a low temperature, spheroidized, and surface-treated to obtain amorphous spherical titanium oxide. However, given the high cost of the starting materials and the complexity of the manufacturing equipment,
It does not reach the cost of the present invention.

When combined with the particle size distribution of the toner of the present invention, the titanium oxide of the present invention is preferable. That is, when the particle size of the toner is reduced, the surface area per weight increases, and excessive charging due to rubbing tends to occur. On the other hand, titanium oxide fine particles which can control charging and impart fluidity have a great effect. The content of titanium oxide suitable for the present invention is 0.5
To 2.5% by weight, preferably 0.7 to 2.0% by weight.

The toner according to the present invention may contain a charge controlling agent for stabilizing the charge characteristics. At that time, a colorless or light-colored charge control agent that does not affect the color tone of the toner is preferable. Examples of the negative charge control agent in this case include an organic metal complex such as a metal complex of an alkyl-substituted salicylic acid (for example, a chromium complex or a zinc complex of di-tert-butylsalicylic acid). When the negative charge control agent is blended in the toner, 0.1 to 10 parts by weight based on 100 parts by weight of the binder resin.
It is advisable to add 0.5 parts by weight, preferably 0.5 to 8 parts by weight.

As the colorant used in the present invention, known dyes and pigments such as phthalocyanine blue, indaslen blue, peacock blue, permanent red, lake red, rhodamine lake, Hanza yellow, permanent yellow, benzidine yellow and the like are widely used. can do. The content thereof is 12 parts by weight or less, preferably 0.5 to 9 parts by weight, based on 100 parts by weight of the binder resin so as to reflect sensitively on the permeability of the OHP film.

Additives may be added to the toner of the present invention as needed as long as the properties of the toner are not impaired. Examples of such additives include Teflon, zinc stearate and polyvinylidene fluoride. Lubricants, fixing aids (eg, low molecular weight polyethylene, low molecular weight polypropylene, etc.), and organic resin particles.

In the production of the toner of the present invention, the constituent materials are kneaded well by a hot kneader such as a hot roll, kneader, extruder or the like, and then obtained by mechanical pulverization and classification, or in a binder resin solution. After dispersing a material such as a colorant in the method obtained by spray drying, or
After mixing the predetermined material with the monomer that should constitute the binder resin,
Each method such as a polymerization toner production method of obtaining a toner by polymerizing this emulsion suspension can be applied.

As the binder used in the colorant-containing resin particles of the present invention, various material resins conventionally known as electrophotographic toner binder resins are used.

For example, styrene-based copolymers such as polystyrene, styrene-butadiene copolymer and styrene-acrylic copolymer, and ethylene-based copolymers such as polyethylene, ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer Copolymer, phenolic resin, epoxy resin, acrylic phthalate resin, polyamide resin, polyester resin, maleic acid resin and the like. In addition, the production method of any resin is not particularly limited.

The effect of the present invention is remarkable when a polyester resin having a high negative chargeability is used among these resins. That is, the polyester-based resin has excellent fixability and is suitable for a color toner, but has a strong negative charging ability and tends to be excessively charged. However, when the polyester resin is used in the composition of the present invention, the harmful effects are improved and excellent. A toner is obtained.

In particular, the following equation

[0087]

Embedded image (Wherein R is an ethylene or propylene group, x, y
Is an integer of 1 or more, respectively, and the average value of x + y is 2 to 10. A) a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, phthalic acid) Acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) are more preferred because they have sharp melting properties.

When a two-component developer using a carrier by using the toner of the present invention is used, an electrically insulating resin is used as a coating resin on the surface of the carrier, and is appropriately selected depending on a toner material and a carrier core material. . In the present invention, at least one monomer selected from at least an acrylic acid (or an ester thereof) monomer and a methacrylic acid (or an ester thereof) monomer in order to improve the adhesion to the carrier core material surface. Must be contained.
In particular, when a polyester resin particle having a high negative chargeability is used as the toner material, it is preferable to further form a copolymer with a styrene monomer for the purpose of stabilizing the charge, and the copolymerization weight ratio of the styrene monomer is preferable. Is preferably 5 to 70% by weight.

As the monomer for the coating resin of the carrier core material usable in the present invention, the styrene monomer includes
For example, styrene monomer, chlorostyrene monomer, α
-Methylstyrene monomer, styrene-chlorostyrene monomer and the like. Examples of the acrylic monomer include, for example, acrylate monomer (methyl acrylate monomer, ethyl acrylate monomer, butyl acrylate monomer, octyl acrylate monomer, phenyl acrylate monomer) And methacrylic acid ester monomers (methyl methacrylate monomer, ethyl methacrylate monomer, butyl methacrylate monomer, phenyl methacrylate monomer).

The carrier core material (magnetic particles) used in the present invention includes, for example, metals such as iron, nickel, copper, zinc, cobalt, manganese, chromium, rare earth and the like, and their alloys or oxides, which are not oxidized or surface oxidized. Things can be used.
Also, there is no particular restriction on the manufacturing method.

As the carrier used in the present invention, known materials can be used as long as the gist of the present invention is not impaired.
Examples include metals such as copper, zinc, cobalt, manganese, chromium, and rare earths, and alloys or oxides and ferrites thereof. Preferably, zinc, copper, nickel, ferrite selected from metals of cobalt is preferable in terms of magnetic properties,
Can be used. The method of controlling the particle size distribution may be any method as long as it satisfies the above-mentioned particle size distribution. Preferably, the coarse powder side is controlled by a mesh.

Further, the surface of the carrier can be covered with a resin or the like. As the method, any of a method of dissolving or suspending a coating material such as a resin in a solvent and applying it to adhere to a carrier, and a method of simply mixing with a powder can be applied.

The measurement of the magnetic properties of the carrier was performed using a BHU-60 type magnetization measurement device (manufactured by RIKEN).
Is used.

About 1.0 g of the measurement sample was weighed and the inner diameter was 7 mm.
A cell having a height of φ and a height of 10 mm is packed and set in the above-mentioned apparatus.

The measurement was performed by gradually applying an applied magnetic field to a maximum of 3,000.
Change to 0 Oersted. Next, the applied magnetic field is decreased, and finally a hysteresis curve of the sample is obtained on the recording paper. From this, the saturation magnetization, residual magnetization, and coercive force are obtained.

As a measurement of the particle size distribution of the carrier,
The measurement was performed using an SRA type Microtrac particle size analyzer (Nikkiso Co., Ltd.) in a range of 0.7 to 125 μm.

Next, an example of an image forming apparatus in which non-magnetic one-component development is performed using the toner of the present invention will be described. However, the present invention is not necessarily limited to this. In FIG.
2 shows an apparatus for developing an electrostatic image formed on a latent image holding member. Reference numeral 1 denotes a latent image holding member, and a latent image is formed by an electrophotographic process unit or an electrostatic recording unit (not shown). 2
Denotes a developer carrier, which is formed of a nonmagnetic sleeve made of aluminum, stainless steel, or the like. The non-magnetic one-component color toner is stored in the hopper 3 and is supplied by the supply roller 4 onto the developer carrier. The supply roller 4 also removes the toner on the developer carrier after development. The toner supplied on the developer carrier is uniformly and thinly applied by the developer application blade 5.
The effective contact pressure between the developer coating blade and the developer carrier is 3 to 250 g / cm, preferably 10 to 120 g / cm, as the linear pressure in the sleeve generatrix direction. If the contact pressure is less than 3 g / cm, it becomes difficult to apply the toner uniformly, and the charge amount distribution of the toner becomes broad, causing fogging and scattering. On the other hand, if the contact pressure exceeds 250 g / cm, a large pressure is applied to the toner, so that the toners are undesirably aggregated or pulverized. By adjusting the contact pressure to 3 to 250 g / cm, it becomes possible to loosen the agglomeration peculiar to the small particle size toner, and it is possible to instantly increase the charge amount of the toner. The developer coating blade is preferably made of a material of a triboelectric series suitable for charging the toner to a desired polarity.

In the present invention, silicone rubber, urethane rubber, styrene-butadiene rubber and the like are preferred. Further, it may be coated with a polyamide resin or the like. Use of a conductive rubber or the like is preferable because the toner can be prevented from being excessively charged.

In the system proposed in the present invention in which a thin layer of toner is coated on a developer carrying member by a blade, the thickness of the toner layer on the developer carrying member must be reduced in order to obtain a sufficient image density. It is necessary to make the length of the gap between the developer carrier and the latent image holding body smaller than the gap length, and to apply an alternating electric field to this gap. That is, by applying a developing bias in which an alternating electric field or a DC electric field is superimposed on the alternating electric field between the developer carrier and the latent image carrier by the bias power source 6 shown in FIG. The transfer of the toner onto the body is facilitated, and a higher quality image can be obtained.

The measuring method of the present invention will be described below. (1) Measurement of toner particle size: The particle size distribution can be measured by various methods. In the present invention, the measurement was performed using a Coulter counter.

That is, a Coulter Counter TA-II type (manufactured by Coulter) was used as a measuring device, and an interface (manufactured by Nikkaki) for outputting the number average distribution and volume distribution and a CX-1 personal computer (manufactured by Canon) were connected. The electrolyte is 1% sodium chloride.
% NaCl aqueous solution is prepared. As a measuring method, a surfactant, preferably an alkylbenzene sulfonate, is used as a dispersant in 100 to 150 ml of the electrolytic aqueous solution.
Add 5 ml, and further add 2-20 mg of the measurement sample.
The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and the volume and number of the toner were measured using the Coulter Counter TA-II, using a 100 μm aperture as the aperture. The volume distribution and number distribution of 〜40 μm were calculated. Then, according to the present invention, the weight-average weight average diameter (D
4) (The median value of each channel is taken as a representative value for each channel), the amount of weight-based coarse powder (1
6.0 μm or more), and the number-based fine powder number (5.04 μm or less) determined from the number distribution. (2) Hydrophobicity measurement: The methanol titration test is an experimental test for confirming the hydrophobicity of a titanium oxide fine powder having a hydrophobized surface.

The "methanol titration test" defined herein for evaluating the degree of hydrophobicity of the treated fine titanium oxide powder is carried out as follows. 0.2 g of the test titanium oxide fine powder was added to 50 m of water in a 250 ml Erlenmeyer flask.
Add to l. Methanol is titrated from the burette until all of the titanium oxide is wetted. At this time, the solution in the flask is constantly stirred with a magnetic stirrer. The end point is observed by the suspension of the entire amount of the fine titanium oxide powder in the liquid, and the degree of hydrophobicity is expressed as the percentage of methanol in the liquid mixture of methanol and water at the end point. (3) Transmittance measurement method: * 1 Dainippon Ink Beckosol 1323-60-E
L * 2 Super Nippon Ink Super-Beckamine J-820-
60 * 3 Amirat thinner manufactured by Kansai Paint The above formulation is collected in a 150 cc mayonnaise bottle, and dispersed for 1 hour using a paint conditioner manufactured by Red Devil. 2. After the dispersion, the PET film is coated with a 2 mil doctor blade. 3.2. Is heated at 120 ° C. for 10 minutes to perform baking. 4.3. The transmittance of the sheet is measured by U-BEST 50 manufactured by JASCO Corporation in the range of 320 to 800 nm and compared.

[0103]

EXAMPLE 1 100 parts of a polyester resin obtained by condensing 100 parts of a propoxylated bisphenol and fumaric acid 4 parts of a phthalocyanine pigment 2 parts of a chromium complex of di-tert-butylsalicylic acid were sufficiently premixed with a Henschel mixer. The mixture was melt-kneaded with an axial extruder, cooled, coarsely pulverized to about 1 to 2 mm using a hammer mill, and then finely pulverized by an air jet pulverizer. Further, the obtained finely pulverized product was classified by a multi-segment classification device, and 2 to 8 μm was selected so as to have the particle size distribution of the present invention, thereby obtaining colorant-containing resin particles.

The particles were mixed with hydrophilic anatase-type titanium oxide fine particles (particle size: 0.05 μm, BET: 120 m ² /
g) while mixing and stirring in an aqueous system, while n-C ₄ H ₉ Si
(OCH ₃ ) ₃ is dispersed in an aqueous system, and is added to and mixed with the titanium oxide fine particles while hydrolyzing so that the solid content is 20% by weight so that the particles do not coalesce, and then dried and crushed. The obtained degree of hydrophobicity was 70% and the average particle size was 0.05 μm.
m, titanium oxide having a transmittance of 60% at 400 nm
5% was mixed with a Henschel mixer to obtain a cyan toner.

This cyan toner has a weight average particle diameter of 6.0 μm 4 μm or less 16.5 number% 5.04 μm or less 45.7 number% 8 μm or more 7.3 volume% 10.08 μm or more 1.2 volume% % Met.

The toner having the surface coated with methyl methacrylate-butyl acrylate (75:25) copolymer
u-Zn-Fe-based ferrite particles were added, and the toner concentration was 4
% Of the developer was prepared.

Using this developer, a developing electric field of a commercially available color copying machine (manufactured by CLC500 Canon) is used as a DC electric field to apply a developing contrast of 350 V and a discontinuous AC superimposed electric field shown in FIG. , 23 ℃ / 5
%, 30 ° C./80%, and a durability test of 10,000 sheets was performed.

As a result, a clear image having a stable image density of 1.40 to 1.60 and no fog was obtained.

Example 2 Example 1 was applied except that a discontinuous alternating electric field shown in FIG. 2 was applied.
When image formation was performed in the same manner as described above, the image density was 1.5 to 1.
Although it was slightly higher at 75, a very stable and good image was obtained.

Example 3 Titanium oxide fine particles treated with 15 parts of nC ₁₀ H ₂₅ Si (OCH ₃ ) ₃ (hydrophobicity 70%, average particle size 0.05 μm)
m, 400% transmittance at 400 nm) except that the image was formed in the same manner as in Example 1.
%, The image density decreased, but good results were obtained.

Example 4 A developing device of a commercially available color copying machine (Color Laser Copier 500, manufactured by Canon) was modified as shown in FIG. 4, and 3,000 was used in the same manner as in Example 1 except that no carrier was used.
The image density was 1.45 to 1.60 when images were printed.
And good results were obtained.

Comparative Example 1 An image was formed in the same manner as in Example 1 except that a direct current and a continuous alternating electric field shown in FIG. 3 were applied.
The image density was reduced to 1.25 under / 60%.

Comparative Example 2 An image was formed in the same manner as in Example 1 except that titanium oxide was not used. The image density was reduced to 1.10 at 23 ° C./60% and fog was also reduced. It got worse.

Comparative Example 3 Example 1 was repeated except that titanium oxide fine particles not treated with nC ₄ H ₉ Si (OCH ₃ ) ₃ were used.
When image formation was performed in the same manner as in the above, the image density increased to 1.81 at 30 ° C./80%.

Example 5 Example 1 was repeated except that 4 parts of a chromium complex of di-tert-butylsalicylic acid was used in the colorant-containing resin particles of Example 1.
In the same manner as above, a cyan toner was obtained.

A carrier was mixed with 7 parts of the cyan toner described above in a total amount of 100 parts of carrier A to prepare a developer. This carrier A was a coated ferrite carrier coated with about 1% of methyl methacrylate / butyl acrylate (75/25).

Using the above-mentioned developer, a commercially available color copier (CLC500, manufactured by Canon Inc.) was used.
Built-in 5-pole magnet roller with 60 Gauss)
At 23 ° C./60%. The development condition is V
cont = 350V, Vback = −130V, and the electric field of FIG. 1 was applied as an AC electric field.

As a result, the original chart excellent in highlight reproduction can be faithfully reproduced even after printing for 10,000 sheets.
A good image having an image density of 1.5 to 1.6 was obtained. Further, even during continuous copying, an image without carrier adhesion and density fluctuation was obtained, and the developer density control was good and stable.

Further, when images were similarly extracted at 23 ° C./5% and 30 ° C./80%, good results were obtained.

Example 6 As a toner, a quinacridone pigment was used in place of the phthalocyanine pigment of Example 5, and the weight average particle diameter was 6.26 μm, 44.3 μm or less was 24.3% by number, and 5.04 μm or less was 52.5% by number. When image formation was performed in the same manner as in Example 5 except that toner having a volume of 8 μm or more and 10.9% by volume and 10.08 μm or more and a volume of 1.4% were used, good results were obtained. Was done.

Example 7 Titanium oxide fine particles using 25% by weight of iso-C ₄ H ₉ —Si (OCH ₃ ) ₃ (hydrophobicity: 65%, average particle size: 0.05 μm, light transmittance at 400 nm: 65%) Was obtained in the same manner as in Example 5 except that the toner was used, and image formation was performed in the same manner as in Example 1 in combination with the carrier C shown in Table 1. As a result, good results were obtained.

Example 8 Using the AC electric field shown in FIG. 2, 2.0% of the titanium oxide fine particles of Example 5 was externally added as a toner, and the weight average particle diameter was 5.2 μm. 0.04 μm or less: 78.6 number% 8 μm or more: 3.2 vol% 10.08 μm or more: 0 vol% 6 parts by weight of cyan toner and carrier D in Table 1 in total amount of 10
Example 5 except that it was used in combination to be 0 parts by weight.
When image formation was performed in the same manner, the image density was 1.35 to
Although slightly reduced to 1.45, an image with excellent reproduction of highlights and fine lines was obtained.

Comparative Example 4 When an image was formed in the same manner as in Example 5 except that the AC electric field shown in FIG. 3 was applied, the image density was reduced to 1.27 at 23 ° C./5%. .

Comparative Example 5 9.7 parts by weight of the carrier E shown in Table 1 and 3 parts of the toner of Example 5
23 ° C / 60%
Below, the image density was reduced to 1.21.

When the toner density was increased to 5%, the image density was increased to 1.47, but toner scattering occurred.

Comparative Example 6 When image formation was performed in the same manner as in Example 5 except that titanium oxide was not used, fog was deteriorated at 23 ° C./60%, and toner scattering occurred.

Comparative Example 7 An image was formed in the same manner as in Example 5 except that a magnet roller having a magnetic flux density of 550 gauss in the developing area was used. Carrier adhesion occurred at 23 ° C./60%. Oops.

[0128]

[Table 1]

[0129]

According to the present invention, there is provided an image forming method in which a discontinuous alternating current component is superimposed as a developing electric field in addition to a direct current component.
By using a color toner having a specific particle size distribution, it is possible to obtain an image excellent in highlight reproduction and fine line reproduction in image density. In addition, stable environmental characteristics can be achieved by including titanium oxide fine particles as an external additive.

Further, in a color developer in which the above-mentioned color toner is used in combination with a carrier having the above-mentioned particle size, the rise of the triboelectric charging property with the toner is improved, and the carrier does not adhere.

[Brief description of the drawings]

FIG. 1 is a graph showing the application of a discontinuous AC superposition electric field.

FIG. 2 is another graph showing application of a discontinuous AC superimposed electric field.

FIG. 3 is a graph showing the application of DC and continuous AC superimposed electric fields.

FIG. 4 is a diagram illustrating an example of a developing device.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Ukai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasuhiro Ichikawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-3-100661 (JP, A) JP-A-2-284163 (JP, A) JP-A-62-1151874 (JP, A) JP-A-60-112052 (JP, A A) JP-A-2-281280 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/09 G03G 15/01

Claims (6)

(57) [Claims] 1. A developing region of a latent image holding member and a developer holding member opposed thereto, between the latent image holding member and the developer holding member.
The voltage at which the toner is attracted from the latent image holder to the developer carrier and the voltage at which the toner flies from the developer carrier to the latent image holder are T _1.
After time application, for the image portion causes the toner to fly against the non-image portion, by means of applying longer than the direction of the voltage of at least the above-mentioned time T ₁ for pulling back the toner, color toner a latent image A color toner provided for an image forming method of transferring a toner image formed on an image carrier onto a transfer material, comprising at least colorant-containing resin particles and an external additive. The weight average particle size is 3 to 7 μm,
More than 40% by number of toner having a particle size of 5.04 μm or less is contained, and 1 toner having a particle size of 4 μm or less is contained.
0 to 70% by number, 2 to 20% by volume of a toner having a particle size of 8 μm or more, and 6% by volume or less of a toner having a particle size of 10.08 μm or more. A color toner comprising at least titanium oxide fine particles. 2. The titanium oxide fine particles have an average particle size of 0.0
The color toner according to claim 1, wherein the color toner is an anatase-type titanium oxide fine particle having a light transmittance of 40% or more at 1 to 0.2 µm, a hydrophobicity of 20 to 98%, and 400 nm. 3. The color toner according to claim 1, wherein the titanium oxide fine particles are surface-treated titanium oxide fine particles subjected to a surface treatment while hydrolyzing a coupling agent in an aqueous system. 4. A developing area of a latent image holding member and a developer holding member opposed thereto, between the latent image holding member and the developer holding member.
The voltage at which the toner is attracted from the latent image holder to the developer carrier and the voltage at which the toner flies from the developer carrier to the latent image holder are T _1.
After time application, for the image portion causes the toner to fly against the non-image portion, by means of applying longer than the direction of the voltage of at least the above-mentioned time T ₁ for pulling back the toner, color toner a latent image A two-component color developer for use in an image forming method of developing a toner image formed on an image carrier and transferring the toner image on a transfer material, wherein (1) the weight average particle size is 15 to 45 μm. 1 to 20% of carrier particles smaller than 22 μm, 3% or less of carrier particles smaller than 16 μm, 2 to 15% of carrier particles of 62 μm or more, and 2% or less of carrier particles of 88 μm or more. The carrier has a saturation magnetization of 35 to 90 emu / g with respect to an applied magnetic field of 3000 Oe, a residual magnetization of 10 emu / g or less, and a coercive force of 40 Oe or less. And (2) a toner having at least titanium oxide fine particles as an external additive, a weight average particle diameter of 3 to 7 μm, and a toner having a particle diameter of 5.04 μm or less is contained in an amount of more than 40% by number, 4 μm
10 to 70% by number of a toner having the following particle size, and 2 to 20% by volume of a toner having a particle size of 8 μm or more
A color developer containing a color toner containing 6% by volume or less of a toner having a particle size of 10.08 μm or more. 5. The titanium oxide fine particles have an average particle size of 0.0
5. The color developer according to claim 4, wherein the color developer is titanium oxide fine particles having a particle diameter of 1 to 0.2 μm, a hydrophobicity of 20 to 98%, and a light transmittance at 400 nm of 40% or more. In 6. on the developing sleeve with a built-in magnet roller, to secure the Ma Gunetto roller rotates the developing sleeve, the color developer of two-component system containing at least a carrier and a color toner circulates transport, latent In the developing area of the image carrier and the developer carrier opposed thereto, between the latent image carrier and the developer carrier, a voltage for drawing the toner from the latent image carrier to the developer carrier and the voltage from the developer carrier are applied. the voltage of flying to the latent image bearing member after applying T ₁ times, for the image portion causes the toner to fly against the non-image portion is longer than the direction of the voltage to retract the toner least the aforementioned T ₁ times An image forming method in which a latent image is developed with a color toner by means for applying time, and a toner image formed on an image carrier is transferred onto a transfer material. A configuration having, (2) the magnetic flux density in the developing region is the 600 to 1200 gauss, image forming method comprising (3) using a pump of Claim 4 as the two-component developer, it.