JPH0789237B2 - Image forming method and image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a step of developing an electrostatic latent image formed by an electrophotographic method, an electrostatic printing method, an electrostatic recording method or the like using a magnetic toner. The present invention relates to an image forming method and an image forming apparatus therefor.

[Prior Art] Conventionally, as a developing method using a one-component magnetic toner, a developing method using a conductive magnetic toner disclosed in US Pat. No. 3,909,258 is known.

However, in such a developing method, the toner needs to be essentially conductive, and the conductive toner transfers the toner image on the latent image carrier to the final image supporting member (for example, plain paper).
It was difficult to transfer by using an electric field.

A novel developing method that solves the above problems in the developing method using a one-component conductive magnetic toner is proposed in JP-A-55-18656 and JP-A-55-18659. In this developing method, an insulating magnetic toner is uniformly applied onto a cylindrical toner carrier having a magnet inside, and the toner is opposed to the latent image carrier without contacting it, and the latent image carrier is developed.
As a method of forming the toner layer on the toner carrier, there is a method of using a coating blade at the outlet of the toner container.
For example, as shown in FIG. 1, a blade 24 made of a magnetic material is provided at a position facing one magnetic pole N1 of a fixed magnet 23 incorporated in a toner carrier 22, and a magnetic force line between the magnetic pole and the magnetic blade is provided. To make the toner stand up along the edges, and by cutting this at the edge of the blade tip, the action of magnetic force is utilized,
It controls the thickness of the toner layer (see, for example, JP-A-54).
-See 43037 publication).

At the time of development, a low-frequency alternating voltage is applied between the toner carrier and the base conductor of the latent image carrier, and the toner is reciprocated between the toner carrier and the latent image carrier to prevent ground fog. It is excellent in reproduction of tonality, and good development is possible without thinning of image edges. In this developing method, the toner is an insulator, so electrostatic transfer is easy.

In FIG. 1, reference numeral 21 is a developing device containing toner T, 1 is a latent image holding member such as a photosensitive drum in electrophotography and an insulating drum in electrostatic recording.

In such a developing method, the following problems are important. Problem: To uniformly coat a toner carrier with a magnetic toner. Problem: To efficiently and uniformly triboelectrically charge a magnetic toner. Attempts have been made to solve the problems in a compatible manner.

In order to solve the problem, a method for uniformly coating a toner carrier with a magnetic toner has been proposed in JP-A-57-66455. This is shown in FIG. 1. As a toner carrier, the surface of the toner carrier is sandblasted with irregular particles to form an irregular rough surface in an irregular shape. It is a developing device that can maintain a good toner coat state for a long period of time without unevenness. The surface of the toner carrier has a mode in which innumerable minute cuts or projections are formed in random directions over the entire surface of the toner carrier.

However, in a developing device using a toner carrier having such a specific surface state, depending on the applied magnetic toner, deterioration of the developability such as fog and density decrease is observed. This is because particles with poor charging are generated in the magnetic toner particles,
It is caused by a decrease in the charge amount of the toner layer.

Furthermore, tailing, scattering, and instability in reproducing fine lines may occur.

In order to improve the triboelectric charge imparting ability of the toner carrier to the magnetic toner, there has been proposed a method of making the surface of the toner carrier smoother. However, with such a method, it has been found that the toner coat of the magnetic toner may become non-uniform, unevenness may occur in the visible image, and a good image may not be expected.

Japanese Patent Application is a method to solve both problems and problems at the same time.
It is proposed in Japanese Patent Publication No. 63-46882. This is a toner carrier shown in FIG. 1, which is capable of uniformly forming a toner coat for a long period of time by using a magnetic toner having a specific particle size distribution and the surface of which is subjected to a blast treatment with regular particles. .

Further, generally, in the one-component developing method, when image formation is repeated, toner having a small particle size adheres to the surface of the toner carrier due to the mirroring force due to the high charge amount, and frictional charging of other toner particles occurs. In some cases, toner particles that do not have sufficient charge amount are increased, resulting in a decrease in density. Such a phenomenon is particularly likely to occur under low humidity.

Such a phenomenon is promoted when the toner on the toner carrier is not consumed (for example, the white background portion of the image), and the image density is reduced. On the other hand, when the toner is consumed from such a state (for example, the black portion of the image), this phenomenon is alleviated, and the density gradually recovers.

Therefore, when an image is formed from a state where the toner carrier has a consumed portion (image portion) and an unconsumed portion (non-image portion), a difference in density on the image (that is, high density in the consumed portion, unconsumed portion) At low concentrations).

Hereinafter, such a phenomenon will be referred to as a carrier memory. Considering the mechanism of formation of the carrier memory, the toner carrier memory is eliminated by toner consumption. That is, the toner is reduced with each revolution of the toner carrier. Therefore, when this phenomenon is light, the memory on the image disappears once, but when it is heavy, it may appear many times repeatedly.

According to the study by the present inventors, the toner carrier subjected to the blast treatment with the regular particles is superior to the toner charge imparting ability to the toner carrier subjected to the blast treatment with the irregular particles, and the toner charging ability is improved. Is advantageous in that the above phenomenon is sufficiently exhibited, but in some cases, excessive charging may occur, and the above-mentioned phenomenon tends to occur easily.

The alternating electric field used for developing the one-component toner is proposed in US Pat. No. 3,866,574, US Pat. No. 3,890,929, and US Pat. No. 3,893,418.

It is proposed that a gap is provided between the latent image carrier and the toner (toner carrier), and an asymmetric AC pulse bias is applied to these to control the flight of the high-resistance one-component toner. A schematic diagram of the waveform at that time is shown in FIG. As described above, in order to prevent the toner from adhering to the non-image portion, the developing method in which the absolute value of the alternating bias voltage is kept low and the developing-side voltage is made small may not obtain sufficient image density.

Other alternating electric fields include those proposed in the impression developing method (USP 3405682 specification, etc.) and the jumping developing method (JP-A-55-18656-18659 etc.). In particular, in the jumping developing method, the toner is transferred to the toner carrier and the latent image by the AC bias voltage applied between the toner carrier and the latent image carrier in the developing area which is the closest portion between the toner carrier and the latent image carrier. It reciprocates with respect to the holding body, and finally, selectively moves and adheres to the surface of the latent image holding body according to the latent image pattern to be visualized. These have a duty ratio of 50% and the developing side time and the reverse developing side time are the same (3rd
See figure).

In the case of this developing method, since the developing side bias voltage is large,
While the developability of the solid latent image (high potential area) is high, the reverse development side bias of the low potential area is large, so the developed toner tends to be excessively stripped off and an image having no gradation is likely to be formed.

In addition, the allowable range for setting the voltage (DC component and AC (V _pp & frequency)) is narrow. In other words, if you try to increase the concentration by adjusting the voltage (lowering the DC component or raising the AC component). Soil on the background (white background fogging) will occur. Increasing the AC frequency is effective for white background fog, but the reproducibility of characters and lines is poor (thin).

However, in some patents relating to the jumping developing method, the duty ratio of the alternating bias voltage applied between the toner carrier and the latent image carrier is controlled according to the remaining amount of the developer in order to adjust the image density. (JP-A-60-73647, etc.).

As a means for improving the above-mentioned two developing methods, when a developing side bias is applied, the developing electric field is increased and the developing side time is set to a short time so that the image density is high and gradation is obtained, and fog You will get an image that does not exist.

However, when it is repeatedly used in the image forming method using such a developing method, the image quality may deteriorate due to a decrease in image density, an increase in fog, or a deterioration in resolution and line reproducibility. It was

At this time, the particle size distribution of the toner in the developing unit was measured, and it was found that the particle size distribution changed compared to the initial stage, and the deterioration of the image quality was due to the selective development of the toner.

[Problems to be Solved by the Invention] An object of the present invention is to uniformly coat a toner carrier with a magnetic toner in a developing method as described above and to evenly coat the magnetic toner on the toner carrier without excess or deficiency. The present invention provides an image forming method and an image forming apparatus that solve the problem of stable charging simultaneously for a long period of time and make the flight of magnetic toner more efficient.

A further object of the present invention is to provide an image forming method and an image forming apparatus capable of obtaining a high-definition image with high image density, excellent fine line reproducibility and gradation, and clear images of high quality for a long period of time.

Still another object is to provide an image forming method and an image forming apparatus which prevent or reduce the carrier memory.

Still another object is that the image density is high even under low humidity,
An image forming method and an image forming apparatus capable of obtaining a clear high-quality image without fog.

[Means and Actions for Solving the Problems] In the present invention, an electrostatic image holding member holding an electrostatic charge image and a toner holding member holding a magnetic toner on the surface are arranged in a developing unit with a certain gap. In the image forming method, in which the magnetic toner is regulated on the toner carrier to a thickness smaller than the gap and conveyed to the developing unit, and the toner is developed while applying an alternating electric field to the toner in the developing unit, the toner carrier is It has a surface that has been blasted with irregular particles and at the same time or on it, or a surface that has been blasted with regular particles. It is applied to the carrier to form an alternating bias electric field between the toner carrier and the electrostatic image carrier, and the alternating bias electric field is the developing side voltage component and the reverse developing side voltage component. The developing-side voltage component is equal to or greater than the reverse-developing-side voltage component, and the developing-side voltage component is applied for a shorter time than the reverse-developing-side voltage component. Contains 12% by number or more of magnetic toner particles having a particle size of 8 to 12.7 μm, contains 33% by number or less of magnetic toner particles having a particle size of 8 to 12.7 μm, and contains 2.0% by volume or less of magnetic toner particles having a particle size of 16 μm or more The magnetic toner has a particle size distribution in which the volume average particle size is 4 to 10 μm.

Further, according to the present invention, an electrostatic image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on its surface are arranged in the developing unit with a certain gap, and the magnetic toner is placed on the toner carrier. In an image forming apparatus in which an electrostatic charge image is developed while being regulated to have a thickness smaller than the above-mentioned gap to a developing unit and applying an alternating electric field to the toner in the developing unit by a bias applying unit, the toner carrier is The surface is subjected to a blast treatment with regular particles and, at the same time or on it, a surface subjected to a blast treatment with regular particles, or a surface subjected to a blast treatment with regular particles, the bias applying means is provided with a DC bias in the developing section. An asymmetric AC bias is applied to the toner carrier to form an alternating bias electric field between the toner carrier and the electrostatic image carrier, and the alternating bias electric field is the developing side. Pressure component and reverse development side voltage component, the development side voltage component is equal to or larger than the reverse development side voltage component, and the application time of the development side voltage component is shorter than the application time of the reverse development side voltage component. The magnetic toner contains 12 number% or more of magnetic toner particles having a particle size of 5 μm or less, and 33 number% or less of magnetic toner particles having a particle size of 8 to 12.7 μm, The present invention relates to an image forming apparatus characterized by containing magnetic toner particles having a particle diameter of 16 μm or more in an amount of 2.0% by volume or less, and having a particle size distribution in which the volume average particle diameter of the magnetic toner is 4 to 10 μm.

Since the surface of the toner carrier is roughened by a regular blasting process, the toner carrier according to the present invention is a toner carrying a magnetic toner in comparison with a toner carrier having a completely smooth surface. The performance of uniformly coating the toner on the carrier is excellent.

It is also excellent in the ability to impart triboelectric charge to magnetic toner.

Since the asymmetric developing bias is used in the alternating electric field at the time of development, it is excellent in effectively flying the toner, and it is possible to achieve both high density and reduction of fog.

The magnetic toner has a volume average particle size of 4 to 10 μm and has a specific particle size distribution. Therefore, even if the toner carrier of the present invention is used, the toner coat layer is prevented from becoming excessively thick, and therefore, A toner coat can be formed uniformly over a long period of time without causing toner coat unevenness.

Further, it is effectively developed by the asymmetric developing bias.

As a result, it is possible to obtain a clear and high-quality image with high image density, excellent fine line reproducibility and gradation, no fog, and high quality.

The present invention achieves this object by providing an image forming method capable of having not only the magnitude of the alternating bias electric field but also the application time t and a triboelectric charge amount suitable for the developing bias to be controlled on the toner holder. It is said that the developing-side bias electric field is increased without changing the frequency of the alternating bias, the application time of the developing-side bias electric field is shortened, and accordingly, the reverse developing-side bias electric field is suppressed to be low and the application time is lengthened. The method of controlling the duty ratio of the alternating bias is used.

In the present invention, the developing-side bias component is a component having a polarity opposite to that of the latent image potential of the latent image carrier with respect to the potential of the toner carrier, and a component having the same polarity as the polarity of the toner. On the other hand, the reverse developing side bias component is a component having the same polarity as the latent image potential of the latent image holding member with respect to the potential of the toner carrier, and a component having a polarity opposite to the polarity of the toner.

For example, in the asymmetrical AC bias shown in FIG. 4, negative polarity toner is used for positive polarity latent image potential, and the potential of the toner carrier is used as a reference (the potential of the toner carrier is zero). The portion is the developing side bias component, and the portion b is the reverse developing side bias component. The magnitudes of the developing side bias component and the reverse developing side bias component are V _a and V _b , respectively.
It is indicated by the absolute value of.

Further, in the present invention, the duty ratio in the alternating bias electric field is defined by the following formula.

Wherein, t _a polar component in the direction of shifting to the toner latent image holder side in one period of the alternating bias electric field polarity is periodically changed in the positive and negative alternating (constituting the developing side bias component a) The application time is shown, and t _b is the application time of the polar component (which constitutes the reverse development side bias component b) in the direction of separating the toner from the latent image carrier side. The present invention will be specifically described below. Further, the toner carrier is hereinafter referred to as a sleeve.

The sleeve in the present invention has a surface having irregularities formed by a plurality of ball field trace depressions, and a blast treatment method using regular particles can be used as a method for obtaining the surface state. As the regular particles, for example, various hard spheres having a specific particle diameter and made of metal such as stainless steel, aluminum, steel, nickel and brass, or various hard spheres such as ceramic, plastic and glass beads can be used.

The sleeve of the present invention can also be obtained by further performing blast treatment with regular particles on a surface having random irregularities formed by blast treatment with irregular particles.

It is also possible to use a blasting method in which irregular particles and regular particles are used at the same time.

Any abrasive grains can be used as the irregular particles.

By blasting the surface of the sleeve with the regular particles having a specific particle diameter, it is possible to form a plurality of spherical trace depressions having substantially the same diameter R.

In the present invention, the diameter R of the plurality of spherical dents on the surface of the sleeve is preferably 20 to 250 μm, and it is not preferable that the diameter R is less than 20 μm because contamination by components in the magnetic toner increases. On the other hand, if the diameter R exceeds 250 μm, the uniformity of the toner coat on the sleeve decreases, which is not preferable. As a regular particle, the surface is substantially curved, and the major axis /
Spherical or spheroidal particles having a ratio of minor axis of 1 to 2 (preferably 1 to 1.5, more preferably 1 to 1.2) are preferable. Therefore, it is preferable that the regular particles used for the blast treatment of the sleeve surface have a diameter (or major axis) of 20 to 250 μm.

The pitch P and the surface roughness d of the unevenness of the sleeve surface which has been subjected to the blast treatment with the regular particles are measured by using a fine surface roughness meter (sales agency, Taylor Hobson Co., Kosaka Laboratory, etc.) on the surface of the sleeve. The surface roughness d is based on 10-point average roughness (RZ) “JIS B 0601”.

A straight line parallel to the average line of the reference length l extracted from the cross-section curve and passing through the third peak from the highest and the third trough from the deepest are two micrometer intervals ( μm). The standard length l = 0.25 mm. The pitch P is obtained as follows by counting the protrusions having a height of 0.1 μ or more with respect to the recesses on both sides as one ridge and the number of ridges within the reference length 0.25 mm. .

[250 (μ)] / [Number of peaks (μ) included in 250 (μ)] In the present invention, the pitch P of the irregularities on the surface of the blasting sleeve formed by the regular particles is preferably 2 to 100 μ, and P is less than 2 μ. In that case, contamination of the sleeve by the components in the magnetic toner increases, which is not preferable. On the other hand, if P exceeds 100 μ, the uniformity of the toner coat on the sleeve decreases, which is not preferable. The surface roughness d of the unevenness of the sleeve surface is
0.1 to 5 μm is preferable, and when d exceeds 5 μm,
In the system in which an alternating voltage is applied between the sleeve and the latent image carrier to cause the magnetic toner to fly from the sleeve side to the latent image surface for development, the electric field is concentrated on the uneven portion and the image is disturbed. It is not preferable because it tends to occur. Conversely, d is 0.1μ
If it is less than 1, the uniformity of the toner coat on the sleeve is deteriorated, which is not preferable.

Further, when the blasting treatment with the irregular particles and the blasting treatment with the regular particles are used together, it is necessary to leave moderate roughness due to the irregular particles and to blunt sharp fine projections.

Therefore, it is preferable that the blasting treatment with the irregular-shaped particles and the blasting treatment with the regular-shaped particles be repeated.

Further, it is preferable that the regular blast particles are larger than the irregular blast particles, particularly preferably 1 to 20 times, and more preferably 1.5 to 9 times.

Further, it is also preferable to make at least one of the processing time and the collision force of the treated particles smaller than that of the irregular shaped particle blast when performing the over-strike treatment with the regular particles.

In addition, the inventors of the present invention have studied the roughened state of the sleeve surface and its performance and found the following.

Hereinafter, the surface blasted with irregular particles is referred to as sleeve A, the particle blasted with regular particles is referred to as sleeve B, and the combination of the above two blast treatments is referred to as sleeve C. Schematic views of the roughened state are shown in FIG. 5 (sleeve A), FIG. 6 (sleeve B), and FIG. 7 (sleeve C).

In terms of sleeve toner coat stability, sleeve A,
The sleeve C is excellent, and the sleeve B is slightly inferior depending on the toner and the usage. It is considered that this is because one of the factors is that the sleeve surface having a sharper surface has a higher carrying ability.

In terms of the ability of the sleeve to impart triboelectric charge to the toner,
The sleeves B and C are excellent, and the sleeve B is particularly excellent. This is because the smoother sleeve surface effectively triboelectrically charges the toner.

Therefore, the toner on the sleeves B and C is uniformly triboelectrically charged, and can stably have a sufficient amount of charge.

However, conversely, depending on the toner or the usage condition, excessive charging may result in a decrease in density and a phenomenon of toner carrier memory, and the risk is higher in the sleeve B, and in the case of the sleeve B, due to excessive charging. Toner coat unevenness may occur.

As described above, the sleeves B and C have a good balance of toner coat stability and triboelectrification imparting ability, and the sleeve C is particularly good.

By the way, in the magnetic toner, the toner particles are coated on the toner carrier in a state that the ears (the magnetic toner particles form a toner chain by the magnetic field) are formed.

Further, at the time of development, the toner particles do not fly one by one, but fly while maintaining the state of the spikes to some extent.
Therefore, when the latent image is visualized, the effect of the shape of the spikes appears on the image quality. That is, when there are long ears or thick ears, image defects such as tailing, splattering, and crushing appear, and resolution and fine line reproducibility are reduced.

In forming the ears, the charge amount of the toner particles, the particle size, etc. act as the main factors. For example, when the toner particles are uniformly and sufficiently charged, the length and thickness of the spikes are uniform, and the image quality is improved.

Further, the magnetic toner used in the present invention, which has a particle size distribution, has a thin ear, a short ear, a (ear condition), and a dense (the following density indicates the density of the ear per unit area). Since it is formed, it is effective in improving the image quality.

On the other hand, if the toner particles are non-uniformly charged, that is, particles that are poorly charged occur, they not only cause fog but also disturb the formation of the ears, and ears such as long, short, thick and thin ears are mixed. As a result, the image quality is degraded.

Further, when the toner particles are not sufficiently charged and the charge amount of the entire toner becomes low, in addition to the disturbance of the ears, the toner particles become sparse and a high image density cannot be expected. On the contrary, if the toner particles are excessively charged, particles that do not form ears adhere to the surface of the sleeve, or the ears become abnormally dense, resulting in uneven toner coating.

In the case of the sleeve A, since the surface thereof is sharp, the toner particles are less likely to come into contact with the sleeve, particles of poor charging are generated, the ears are easily disturbed, and the image quality is adversely affected. In addition, the rising of the charge amount of the toner particles is slow, the ears become sparse, and the initial density may be low or fog may occur. The low condition may continue. From this point of view, it is extremely rare that the toner coating failure occurs due to excessive charging in the sleeve A, and the stability of the toner coating can be obtained in this respect as well.

However, in the case of the sleeve B and the sleeve C, since the surfaces thereof are smooth, the contact charging between the toner particles and the sleeve can be efficiently performed, and the charging of the toner can be uniformly and sufficiently charged, and the ears are also uniform and dense. , High image quality can be obtained.
Further, the charge amount of the toner particles rises quickly, and a high-density fog-free image can be obtained from the initial stage. On the other hand, although the toner has an excellent triboelectrification-providing ability, it may cause the toner to be excessively charged, which is the case in the case of the magnetic toner of the present invention. If it is not consumed during development, it will stick around the sleeve,
The decrease in concentration and the memory of the carrier as described above will occur.

Further, in the case of the sleeve B, the triboelectric charge imparting ability is particularly large, the degree of triboelectric charging of the toner particles is large, the above-mentioned adverse effects are likely to occur, and the toner particles are locally adhered, resulting in abnormally dense ears. Sleeve coat unevenness may occur, but this tends to occur when there are many particles of 16 μm.

That is, in the case of the sleeve C, the sharp fine protrusions due to the irregular particle blast are blunted by the regular particle blast, so that the surface state becomes smoother, the charge imparting ability is also improved, and the toner is efficiently supplied. Triboelectric charging can be performed. Furthermore, since the roughness due to irregular particle blast remains, the toner transporting ability is maintained, uniform toner coating can be performed, and excessive triboelectric charging can be suppressed, and the adverse effects due to excessive charging can be reduced (image density reduction, carrying Body memory) and prevention (uneven toner coat).

Therefore, the effect of promoting high image quality of the magnetic toner of the present invention is achieved by making the formation of the ears on the toner carrier more uniform.

In the magnetic toner according to the present invention, the volume average particle size is 4
One of the features is that it is -10 μm. The sleeve (sleeve B) according to the present invention has a surface having a specific unevenness due to a plurality of spherical trace depressions. The performance of uniformly coating the magnetic toner on the sleeve is obtained by sandblasting with irregular particles. Compared with the sleeve with irregular surface (Sleeve A), the volume average particle size is 11 μm
When using a toner exceeding the above range, the experimental result obtained was slightly inferior under a specific environment. When a magnetic toner having a volume average particle size of more than 11 μm is applied to a developing device having a sleeve A, a sleeve B, and a sleeve C under a specific environment of a temperature of 15 ° C. or less and a humidity of 10% or less, idle rotation is performed. The weight M / S of the toner layer per unit area on the sleeve is 1.6 to 2.3 m for sleeve B.
In g / cm ^2, with the sleeve C, 1.0 to 2.0 mg / cm ^2, a 0.6~1.5mg / cm ² in the sleeve A, thick toner coat sleeves B, continuing further prolonged idling, the sleeve B Then, it was confirmed that toner coat unevenness might occur.

However, according to the study by the present inventors, although the reason is not always clear, the same experiment was conducted using a magnetic toner having a volume average particle diameter of 4 to 10 μm. When the upper M / S was 0.7 to 1.5 mg / cm ² , it was found that the toner coat thickness could be suppressed to a low level, and as a result, even after idling continued for a long time, sleeve coat unevenness did not occur, and toner coat We have found that reducing the thickness is extremely effective for uniforming the toner coat over a long period of time.

Therefore, with the magnetic toner of the present invention, the sleeve B can obtain the same toner coat stability as the sleeve C. However, when a toner having a large charge amount was used, the toner coat stability of the sleeve B was slightly inferior to that of the sleeve C.

The present inventors conducted a study using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm in order to see the relationship between the toner particle size and the developability in the developing bias. This is because when a constant developing-side voltage (about 1000 V) is applied between the toner carrier and the latent image carrier (about 250 μm) in pulses, toner begins to adhere to the latent image carrier (image after transfer and fixing). Make the image density 1.0 or more.) Check the pulse width and toner particle size distribution. That is, the latent image carrier was kept constant in potential, the pulse width was varied to develop the latent image, and the developed toner particles on the latent image carrier were collected and the toner particle size distribution was measured. It was found that there are many magnetic toner particles below and more magnetic toner particles of 5 μm or less. Further, it was also found that when the pulse width is further reduced, the number of magnetic toner particles of 5 μm or less increases.

That is, it can be seen that the smaller the particle size of the toner, the sooner the toner reaches the latent image carrier. Therefore, when the developing-side bias is applied, the developing electric field is set high and the toner particles having a small particle size can be selectively developed by setting the developing electric field for a short time.

Further, when the reverse developing side bias is applied, the stripping electric field is set low and for a long time, so that large toner particles that could not reach the latent image holding member during the developing side bias or toner particles having a low charge amount (moving speed is slow). Is firmly returned to the toner carrier over time. At this time, the toner particles having a small particle size in the image area on the latent image carrier are
Almost no peeling occurs due to strong mirroring power and low stripping electric field, but toner particles with a small amount of electrostatic charge (fogging toner particles) attached to non-image areas due to scattering etc. have weak mirroring power. Therefore, it is pulled back onto the toner carrier by the stripping electric field.

Further, in general, when the particle size of the toner particles is small, the surface area per unit volume is large, so that the charge amount per unit weight is large. From this, it is considered that one of the causes that the toner particles having a small particle diameter easily fly is that the charge amount is large.

As described above, by the developing method using the developing bias, which is a feature of the present invention, gradation can be obtained, and an image with high image density and no fog can be obtained.

However, in such a developing method, when a large amount of toner particles having a large particle size or toner particles having insufficient triboelectric charging are contained in the magnetic toner on the toner carrier, these particles remain without being developed. At the same time, the frictional electrification of other toner particles is hindered, which causes a vicious cycle, which causes a change in the particle size distribution of the magnetic toner and causes deterioration in image quality.

On the other hand, using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm, this time the surface potential on the photoconductor is changed,
From a large development potential contrast where a large number of toner particles are easily developed to a halftone, to a small development potential contrast where only a few toner particles are developed, develop a latent image with the surface potential changed on the photoconductor,
When the developed toner particles on the photoconductor were collected and the toner particle size distribution was measured, it was found that there were many magnetic toner particles having a particle size of 8 μm or less, and particularly 5 μm or less. That is, when the magnetic toner particles having a particle diameter of 5 μm or less, which is most suitable for development, are smoothly supplied to the development of the latent image on the photoconductor, they are faithful to the latent image and do not protrude from the latent image and are truly reproducible. You will get an excellent image of.

On the other hand, regarding the particle size, in the magnetic toner of the present invention,
One feature is that the magnetic toner particles having a particle diameter of m or less are 12% by number or more. Conventionally, it is 5 for magnetic toner.
The magnetic toner particles having a particle size of μm or less were difficult to control the charge amount and were easily overcharged. For this reason, the toner particles of 5 μm or less have a strong mirroring force on the developing sleeve or the like, and stick to the surface of the sleeve to hinder triboelectric charging of other particles.
It has been considered necessary to actively reduce toner particles that are not properly charged, which may cause roughness and decrease in density.

However, according to the study by the present inventors, it was found that magnetic toner particles having a particle size of 5 μm or less are an essential component for forming a high quality image.

In the developing method of the present invention, toner particles having a particle size of 5 μm or less are efficiently ejected, so that sticking to the sleeve surface can be prevented.

One feature of the magnetic toner of the present invention is that the number of particles in the range of 8 to 12.7 μm is 33% by number or less. This is related to the necessity of the presence of magnetic toner particles having a particle size of 5 μm or less, as described above, and the magnetic toner particles having a particle size of 5 μm or less have the ability to exactly cover the latent image and faithfully reproduce it. However, in the latent image itself, the electric field strength of the peripheral edge portion is higher than that of the central portion, so that the inside of the latent image has thinner toner particles than the edge portion,
The image density may appear light. In particular, the magnetic toner particles of 5 μm or less have a strong tendency. However, the present inventors have found that by containing toner particles in the range of 8 to 12.7 μm in an amount of 33% by number or less, this problem can be solved and further sharpened. That is, 8 to 12.7
It is considered that the toner particles in the range of the particle size of μm have an appropriately controlled charge amount with respect to the magnetic toner particles of the particle size of 5 μm or less. It is supplied to compensate for the small amount of toner particles inside the edge portion to form a uniform developed image, and as a result, a sharp image having excellent resolution and gradation at high density is provided. It is something.

12-60% by number for particles with a particle size of 5 μm or less
When the volume average particle size is 7 to 10 μm, N / V = −0.04N + k (however, 4.5 ≦ k ≦ 6.5; 12 ≦ N) between the number% (N) and the volume% (V). It is also preferable that the magnetic toner of the present invention satisfies the relationship of ≦ 60). The magnetic toner of the present invention having a particle size distribution satisfying this range can achieve more excellent developability.

The present inventors, while examining the state of the particle size distribution of 5 μm or less, found that there is a state of presence of fine powder that is most suitable for achieving the purpose as shown by the above formula. That is, 12 ≦
For a certain N value of N ≦ 60, a large N / V means that particles with a size of 5 μm or less are widely included, and a small N / V means that particles with a size of 5 μm or less are included. It is understood that it has a high abundance rate and that there are few particles with a particle size smaller than that, and when N is in the range of 12 to 60, N /
When the value of V is in the range of 2.1 to 5.82 and the above relational expression is further satisfied, good fine line reproducibility and high resolution are achieved.

For magnetic toner particles having a particle size of 16 μm or more,
It is preferably 2.0% by volume or less and as small as possible.

The constitution of the toner of the present invention will be described in detail.

It is preferable that the magnetic toner particles having a particle diameter of 5 μm or less account for 12% by number or more of the total number of particles, preferably 12-60% by number, and more preferably 17-50% by number. When the number of magnetic toner particles having a particle size of 5 μm or less is 12% by number or less, there are few magnetic toner particles effective for high image quality. Particularly, as the toner is used by continuing copying or printing, the effective magnetic toner particles are effective. The components are decreased, the balance of the particle size distribution of the magnetic toner as shown in the present invention is deteriorated, and the image quality is gradually deteriorated. Further, when it is 60% by number or more, the magnetic toner particles are likely to aggregate with each other, resulting in a toner lump having a particle size larger than the original particle size, resulting in a rough image quality, a reduction in resolution, or a latent image edge. In some cases, the difference in density between the inner part and the inner part becomes large, and the image may appear to be hollow.

According to the study by the present inventors, it was found that the magnetic toner particles of 5 μm or less are essential components for stabilizing the volume average particle diameter of the magnetic toner on the sleeve during image formation and durability.

Since the magnetic toner particles with a particle size of 5 μm or less, which is most suitable for development, are consumed when performing image development durability, and if this amount is small, the volume average particle size on the sleeve gradually increases, and M / S increases and tends to make uniformization of the sleeve coat difficult.

Further, the particles in the range of 8 to 12.7 μm are preferably 33% by number or less, and more preferably 1 to 33% by number. 33 pieces%
When the amount is larger, the image quality is deteriorated, and more development than necessary is required.
That is, the toner is excessively overloaded, resulting in an increase in toner consumption. On the other hand, if it is 1% by number or less, it may be difficult to obtain a high image density. Further, the number% (N%) and volume% (V
%), There is a relationship of N / V = −0.04N + k, and 4.5 ≦
Indicates a positive number in the range of k ≦ 6.5. Preferably 4.5 ≦ k ≦ 6.0
Is. As shown above, 12 ≦ N ≦ 60, and the volume average particle size at this time is 7 to 10 μm.

When k <4.5, the number of magnetic toner particles having a particle size smaller than 5.0 μm is small, and the image density, resolution and sharpness tend to be poor. The proper presence of fine magnetic toner particles, which has been conventionally considered unnecessary, contributes to close packing of toner in development and formation of a uniform image without roughness. In particular, by evenly filling the fine lines and the outline of the image, the sharpness is visually enhanced. That is, when k <4.5, these properties tend to be inferior due to the lack of the particle size distribution component.

From another point of view, also in terms of production, the conditions such as classification become stricter in order to satisfy the condition of k <4.5, which is also disadvantageous in terms of yield and toner cost. When k> 6.5, the presence of fine powder more than necessary causes the particle size distribution to become unbalanced during repeated copying, resulting in an increase in the toner cohesion and ineffective triboelectric charging, which results in poor cleaning. May cause fogging.

In addition, magnetic toner particles having a particle size of 16 μm or more are 2.0% by volume.
The amount is preferably below, more preferably 1.0% by volume or less, and further preferably 0.5% by volume or less. 2.0
When the content is more than the volume%, not only does it hinder the reproduction of fine lines, but also rough toner particles of 16 μm or more are prominently present on the thin layer surface of the toner particles developed on the photoconductor during transfer, so that the toner layer The delicate contact state between the photosensitive member and the transfer paper via the irregularity causes irregular transfer conditions, which causes a defective transfer image.

Further, in the image forming method of the present invention, toner particles having a particle size of 16 μm or more cannot fly onto the latent image holding member unless they have a sufficient charge amount, and a large amount of them remain on the toner holding member, which causes a change in particle size distribution. In many cases, the frictional electrification of the toner particles is impaired, the developing ability is deteriorated, and the shape of the spikes is disturbed, which causes deterioration of image quality.

Contrary to magnetic toner particles having a particle size of 5 μm or less, magnetic toner particles having a particle size of 16 μm or more are relatively hard to be consumed even when the image forming durability is performed. Since the volume average particle diameter gradually increases, M / S on the sleeve increases, which is not preferable.

In the present invention, the volume average diameter of the magnetic toner is 4 to 10 μm.
m, preferably 4 to 9 μm, and this value cannot be considered in isolation from the above-mentioned constituent elements. If the volume average particle diameter is 4 μm or less, the problem that the toner amount on the transfer paper is small and the image density is low is likely to occur in applications such as graphic images having a high image area ratio. It is considered that this is due to the same reason as the reason why the internal density is lowered with respect to the edge portion in the latent image described above. If the volume average particle diameter is 10 μm or more, the resolution is not good, and at the beginning of copying, if it is used continuously, the particle size distribution is changed and the image quality is likely to deteriorate.

The magnetic toner of the present invention having a specific particle size distribution can faithfully reproduce even a fine line of a latent image formed on a photoconductor, and reproduces a dot latent image such as a halftone dot and a digital image. It also provides an image excellent in gradation and resolution. In addition, high image quality can be maintained even when copying or printing is continued, and even in the case of high-density images, good development can be performed with less toner consumption than conventional magnetic toner, which is economical. Also, it has an advantage in downsizing of the copying machine or the printer body.

In the developing method applied to the magnetic toner of the present invention, the above effects can be more effectively exhibited.

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

That is, as a measuring device, Coulter Counter TA-I
An I-type (manufactured by Coulter) is used, an interface (manufactured by Nikkaki) that outputs a number distribution and a volume distribution, and a CX-1 personal computer (manufactured by Canon) are connected. % NaCl aqueous solution is prepared. For example, ISOTON-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, a surfactant as a dispersant in the electrolytic aqueous solution 100 to 150 ml,
Preferably, 0.1 to 5 ml of alkylbenzene sulfonate is added, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is dispersed by an ultrasonic disperser for about 1 to 3 minutes,
According to the Coulter Counter TA-II type, 100 μ aperture is used as the aperture, and the number is 2 based on the number.
The particle size distribution of the ~ 40μ particles was measured and the value according to the invention was then determined.

The apparatus that has undergone the developing step in the present invention is given as a specific example, and this is shown in FIG. 1 to describe the constitution of the present invention in more detail, but this does not limit the present invention in any way.

In FIG. 1, reference numeral 1 is a rotary drum type latent image carrier (so-called photoconductor) in the transfer type electrophotographic method, a rotary drum type insulator in the transfer type electrostatic recording method, or an electrofax. Latent image carrier such as photosensitive paper in the method and electrostatic recording paper in the direct electrostatic recording method, an electrostatic latent image is formed on the surface by a latent image forming process device or the same process mechanism not shown in the figure. , Are moving in the direction of the arrow.

Reference numeral 2 is the whole number of the developing device, 21 is a hopper containing toner, 22 is a rotating cylinder (hereinafter referred to as sleeve) as a toner carrier (developer layer supporting member), and a magnetism generating means 23 such as a magnetic roller is provided therein. Built in.

In the drawing, the sleeve 22 has a substantially right half circumferential surface exposed in the hopper 21 and a substantially left half circumferential surface exposed to the outside of the hopper for bearing support.
A doctor blade 24, which is driven to rotate in the direction of the arrow, is a toner applying member disposed on the upper surface of the sleeve 22 with its lower side edge portion being close to the upper surface, and 27 is a stirring member for the toner in the hopper.

The axis of the sleeve 22 is substantially parallel to the generatrix of the latent image carrier 1, and the sleeve 22 closely opposes the surface of the latent image carrier 1 with a small gap α.

The surface moving speeds (peripheral speeds) of the latent image carrier 1 and the sleeve 22 are substantially the same, or the peripheral speed of the sleeve 22 is slightly higher. An alternating bias voltage applying means S is provided between the latent image carrier 1 and the sleeve 22.
_The DC voltage and the AC voltage are superimposed and applied by ₀ and the DC bias voltage applying means S ₁ .

Thus, the substantially right half peripheral surface of the sleeve 22 is constantly in contact with the toner pool in the hopper 21, and the toner in the vicinity of the sleeve surface acts as a magnetic adhesion layer on the sleeve surface by the magnetic force of the magnetism generating means 23 in the sleeve and also as an electrostatic charge. It is attached and held by force. When the sleeve 22 is rotationally driven, the toner layer adhered to the sleeve surface passes through the position of the doctor blade 24 and is layered as a thin toner layer T ₁ having a substantially uniform thickness at each portion. The toner is charged mainly by frictional contact between the sleeve surface accompanying the rotation of the sleeve 22 and the toner in the toner pool in the vicinity thereof, and the toner thin layer surface of the sleeve 22 is one surface of the latent image holding member as the sleeve rotates. It rotates to the side and passes through the developing area A which is the closest portion between the latent image carrier 1 and the sleeve 22. In the course of this passage, the toner in the toner thin layer on the sleeve 22 surface flies by the direct current and the alternating electric field due to the direct current and the alternating voltage applied between the latent image carrier 1 and the sleeve 22 and the surface of the latent image carrier 1 in the developing area A. And the surface of the sleeve 22 reciprocate. Finally, the toner on the sleeve 22 side selectively moves and adheres to the surface of the latent image carrier 1 according to the potential pattern of the latent image, and toner images T ₂ are sequentially formed.

The sleeve surface on which the toner is selectively consumed after passing through the developing area A is re-supplied by being re-rotated to the toner reservoir of the hopper 21, and the developing area A always has a thin toner layer of the sleeve 22. The T ₁ surface rotates and the copying process is repeated.

By the way, as one of the problems in the case where such a developing method (one-component non-contact developing method) is adopted, there is a case where the developing property lowering phenomenon occurs due to an increase in the adhesive force of toner near the sleeve surface. In other words, the rotation of the sleeve 22 causes the toner and the sleeve to be constantly in contact with each other, and the electrostatic charge (Coulomb force) with the sleeve is increased by gradually increasing the charge amount of the toner, and the flight force of the toner to the latent image carrier 1 is increased. Is weakened, stays in the vicinity of the sleeve, inhibits triboelectrification of other toner, and deteriorates developability. This occurs due to low humidity and repeated copying processes. The carrier memory described above also results from a similar mechanism. In the sleeve used in the present invention, triboelectrification is efficient, and the triboelectrification ability of the toner is exerted by sufficiently giving the electrification amount of the toner on the toner carrier, which is effective in improving the developing property. It tends to cause a phenomenon.

Now, the force that causes the toner to fly from the sleeve to the latent image carrier 1 must be accelerated so that it can reach the latent image surface sufficiently by the AC bias electric field. Toner weight is m
The power is given by = m. Roughly, if the charge of the toner is q, the distance from the sleeve is d, and the alternating bias electric field is The reaching force of the toner to the latent image surface is determined by the balance between the electrostatic attraction force with the sleeve and the electric field force.

Here, in order to fly the toner of 5 μm or less that tends to collect near the sleeve, the electric field may be increased. However, simply increasing the developing-side bias voltage causes the toner particles to fly to the latent image side regardless of the latent image pattern, and toner particles having a particle size of 5 μm or less have a strong tendency to cause fog on the ground. Further, the background fogging can be prevented by increasing the reverse developing bias voltage, but when a large alternating bias electric field is applied between the latent image carrier 1 and the sleeve 22, discharge is directly generated between the latent image carrier 1 and the sleeve 22, It significantly disturbs the image quality.

Further, as the reverse developing bias voltage is increased, not only the non-latent image portion but also the toner developed in the latent image pattern is stripped off, and the mirror image power on the latent image holding member is relatively weak.
The toner particles of 12.7 μm are removed, the toner sticking in the latent image portion becomes worse, the visible image pattern is disturbed, and the gradation and line reproducibility are deteriorated, so that the voids are likely to occur.

From the above results, it is necessary to cause the toner in the vicinity of the sleeve to fly and reciprocate while the alternating bias electric field is not increased so much and the reverse developing bias voltage is kept low.

Therefore, the present invention achieves this object by providing an image forming method capable of providing not only the magnitude of the alternating bias electric field but also the triboelectric charge amount on the toner carrier that is suitable for the application time t and the developing bias to be controlled. did. That is, the developing-side bias electric field is increased without changing the frequency of the alternating bias, the developing-side bias electric field is applied for a shorter time, and accordingly, the reverse developing-side bias electric field is suppressed to be lower and the applying time is increased. The method of controlling the duty ratio of the alternating bias was used.

Here, the “duty ratio of the AC bias electric field” is defined by the following equation.

a: The application time of the electric field component of the polarity in the direction in which the toner is transferred to the latent image holding member side in one cycle of the alternating current bias in which the electric field polarity alternately changes positively and negatively. At this time, the DC bias electric field is removed.

b: Conversely, the application time of the electric field component of the polarity in the direction of separating the toner from the latent image carrier side.This method is an essential component for improving the image quality on the sleeve by sufficiently strengthening the developing side bias electric field. This coincided with effective reciprocating flight of certain toner particles of 5 μm or less, and it was possible to prevent the toner particles from adhering to the sleeve surface. That is, it becomes difficult to reduce the image density and cause the carrier memory.

Further, even if the reverse developing side bias electric field is suppressed low, on the contrary, by applying for a sufficiently long time, a force to separate the excess toner adhering to other than the latent image pattern from the latent image holding body 1 is obtained, and the background fog is prevented. it can.

At this time, since the bias electric field on the reverse developing side is kept low, the toner particles of 8 to 12.7 μm, which is an essential component for toner adhesion, are not stripped off. 8th as an example
The figure shows the waveform of the alternating bias voltage used in the present invention.

That is, even if the reverse developing side bias electric field is weak, the effective value of the force of separating from the latent image holding member becomes the same by lengthening the time. Moreover, since the toner image developed into the latent image pattern is not disturbed, it is possible to obtain good image quality with gradation.

By the way, the sleeve used in the present invention has excellent triboelectrification imparting ability and uniformly charges the magnetic toner of the present invention. Therefore, good developing property can be obtained by the developing alternating electric field of the present invention. Therefore, a high-density image without fog can be obtained, and high image quality excellent in gradation, resolution, and fine line reproducibility can be obtained.

That is, toner particles of 5 μm or less are efficiently consumed by the bias on the developing side to achieve high image quality, and even the sleeve of the present invention does not stick to the vicinity of the sleeve, and image density reduction, toner carrier memory, etc. are less likely to occur. Also 8 ~ 12.7
The same can be said for the toner particles of μm, which are sufficiently developed by the developing bias to achieve high density and gradation, and are not stripped off by the latent image holding member by the reverse developing bias. No gaps or line distortions will occur.

Further, with the developing bias of the present invention, when the ears fly and the tips of the ears come into contact with the latent image carrier, toner particles near the tips, particles with a small particle size, or particles with a large charge amount are reflected by the mirroring force. The particles adhere to the latent image holder and are visualized, but the particles at the rear end of the ears or particles with a low charge amount are pulled back onto the toner carrier by the reverse developing bias, and the shape of the ears is destroyed. In the direction, the tailing due to the effect of the ears and the scattering are reduced, but with the sleeve and the magnetic toner of the present invention,
The effect is great because the ears are originally formed in a uniform and small state.

Further, since the magnetic toner having a specific particle size distribution on the sleeve having the specific surface of the present invention is successively supplied to the latent image by the developing side bias of the present invention, there is no shortage of toner. .

According to the present invention, the developing side bias electric field of the alternating bias electric field is strong and the toner in the vicinity of the sleeve can fly, so that the toner having a large electric charge in the vicinity of the sleeve is more strongly developed into the latent image pattern. Therefore, it can be strongly adhered to a weak latent image pattern by the electrostatic force of toner having a high charge amount, and can be developed with good resolution having an edge effect in terms of image, and is an effective component for realizing high image quality. Magnetic toner particles having a particle size of 5 μm or less can be effectively used to obtain remarkably good image quality.

In the developing method used in the present invention, the gap between the sleeve 22 and the latent image holding member 1 is 0.3 mm in the embodiment, but 0.1 mm to 0.5 mm is sufficient for the developing method according to the present invention. It can be developed.

As compared with the conventional developing method, the developing side bias becomes larger, so that the result can be developed even if the gap between the sleeve 22 and the latent image carrier 1 is large.

If the absolute value of the alternating bias voltage is 1.0 kV or more, a satisfactory image can be obtained. Further, considering the leak to the latent image carrier, the absolute value of the alternating bias voltage is preferably 1.0 kV or more and 2.0 kV or less. However, it is no wonder that this leak also fluctuates due to the gap between the sleeve 22 and the latent image carrier 1.

Next, the alternating bias frequency is preferably 1.0 kHz to 5.0 kHz. When the frequency is 1.0 kHz or less, the gradation is improved, but it is difficult to eliminate the background fog. In the low frequency region where the number of reciprocating motions of the toner is small, the pressing force of the toner against the latent image holding member by the developing-side bias electric field becomes too strong even in the non-image part, and the toner peeling force by the reverse developing-side bias electric field also causes It is considered that this is because the toner attached to the non-image area cannot be completely removed. When the frequency is 5.0 kHz or higher, a bias electric field on the reverse developing side is applied before the toner sufficiently contacts the latent image holding member, resulting in a marked decrease in developability. That is, the toner itself cannot respond to the high frequency electric field.

Particularly, according to the present invention, the frequency of the alternating bias electric field is 1.5 kHz.
Showed optimum image quality at 3 kHz.

Finally, the duty ratio that satisfies the alternating bias electric field waveform of the present invention may be less than about 50%, but considering image quality, it is preferable that 10% ≦ duty ratio ≦ 40%. When the duty ratio exceeds 40%, the above-mentioned drawbacks become noticeable,
The effect of the present invention on higher image quality is weakened. If the duty ratio is less than 10%, the alternating bias electric field response of the toner itself, which has been described above, deteriorates and the developability deteriorates. Particularly, the optimum value of the duty ratio is 15% ≦ duty ratio ≦ 35%.

Further, as the alternating bias waveform, a rectangular wave, a sine wave, a sawtooth wave, a triangular wave, or the like can be applied.

Examples of the binder resin used for the magnetic toner in the present invention include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3, Four
-Dichlorostyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonyl Styrene and its derivatives such as styrene, pn-decylstyrene and pn-dodecylstyrene; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; unsaturated polyenes such as butadiene; vinyl chloride, Vinyl halides such as vinylidene chloride, vinyl bromide and vinyl bromide; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate. , Isobutyl methacrylate, n-octyl methacrylate, Dodecyl tacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate,
Methacrylic acid esters such as phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, acrylic Acrylic acid esters such as dodecyl acid, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; vinyl methyl ketone,
Vinyl ketones such as vinyl hexyl ketone and methyl isopropenyl ketone; N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone; vinyl naphthalenes; acrylonitrile, methacrylonitrile, acrylamide Acrylic acid or methacrylic acid derivative such as; vinyl compound derivative having a carboxyl group such as acrylic acid, methacrylic acid, maleic acid, fumaric acid; half ester such as maleic acid half ester, fumaric acid half ester; maleic anhydride, Homopolymers and copolymers containing monomer components made of vinyl compounds such as maleic acid esters and fumaric acid ester derivatives; polyester, polyurethane, epoxy resin, polyvinyl butyral, rosin, modified Jin, terpene resins, phenol resins, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, haloparaffin, paraffin wax; by itself or mixed to be used.

Of these, a styrene resin, an acrylic resin, and a polyester resin are particularly preferably used as the binder resin in consideration of the developing characteristics.

The binder resin as described above is more preferably a polymer cross-linked with a cross-linking agent as exemplified below, in consideration of offset resistance as a toner.

Aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, etc .; Diacrylate compounds linked by an alkyl chain such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-
Butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, and acrylates of the above compounds replaced by methacrylate; alkyl chains containing ether linkages Tethered diacrylate compounds, such as diethylene glycol diacrylate, triethylene glycol diacrylate,
Tetraethylene glycol diacrylate, polyethylene glycol # 400 diacrylate, polyethylene glycol # 600 diacrylate, dipropylene glycol diacrylate, and any of the above compounds in which the acrylate is replaced by methacrylate; a chain containing an aromatic group and an ether bond Bonded diacrylate compounds, for example, polyoxyethylene (2) -2,2-bis (4-hydroxyphenyl) propane diacrylate, polyoxyethylene (4) -2,2-bis (4-hydroxyphenyl) Propane diacrylate and those obtained by replacing the acrylate of the above compounds with methacrylate; further, polyester type diacrylate compounds, for example,
Product name MANDA (Nippon Kayaku) is listed. As the polyfunctional cross-linking agent, pentaerythritol acrylate, trimethylol ethane triacrylate, trimethylol propane triacrylate, tetramethylol methane tetraacrylate, oligoester acrylate, and those obtained by replacing the acrylate of the above compounds with methacrylate; Lucyanurate, triallyl trimellitate, etc. are listed.

These crosslinking agents are based on 100 parts of other monomer components,
It is preferable to use about 0.01 to 5 parts (more preferably about 0.03 to 3 parts).

Among these cross-linking agents, those which are preferably used in the resin for toner from the viewpoint of fixing property and anti-offset property, are linked by a chain containing an aromatic divinyl compound (particularly divinylbenzene), an aromatic group and an ether bond. Diacrylate compounds may be mentioned, and it is particularly desirable that at least one of them is contained in the binder resin.

Further, as the binder resin for the toner which is particularly subjected to the pressure fixing method, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acid, polyamide resin, It is preferable to use a polyester resin or the like alone or in combination.

The magnetic material contained in the magnetic toner of the present invention includes magnetite, maghematite, iron oxide such as ferrite, and iron oxide containing other metal oxides; metals such as Fe, Co, Ni, or these metals. And Al, Co, Cu, Pb, Mg, Ni, Sn, Zn,
Alloys with metals such as Sb, Be, Bi, Cd, Ca, Mn, Se, Ti, W, V,
And mixtures thereof.

These ferromagnetic materials have an average particle size of 0.1 to 2 μm,
Coercive force 20 to 150e Saturation magnetization 5
0-200emu / g (preferably 50-100emu / g), remanent magnetization 2
-20emu / g is preferable.

Further, the magnetic toner of the present invention is preferably used by internally or externally adding a charge control agent to the toner. As the positive charge control agent used in the present invention, known ones can be used. Examples thereof include modified products of nigrosine and its fatty acid metal salt, quaternary ammonium salt, diorganotin oxide, diorganotin borate, etc., alone or in combination of two or more. Can be used in combination. Among these, nigrosine type and quaternary ammonium salts are particularly preferably used.

Also, the general formula A homopolymer of a monomer represented by or a copolymer with a polymerizable monomer such as styrene, acrylic acid ester, and methacrylic acid ester as described above can be used as a positive charge control agent. It also functions as (a part or all of) the resin.

On the other hand, as the negative-charge controlling agent used in the present invention, known ones can be used, for example, carboxylic acid-induced low and its metal salt,
The alkoxylates, organometallic complexes, chelate compounds and the like can be used alone or in combination of two or more. Among these, acetylacetone metal complex, salicylic acid metal complex, naphthoic acid metal complex, and monoazo metal complex are particularly preferably used.

In the toner of the present invention, any suitable pigment or dye can be used as a colorant, if necessary.

Further, the toner of the present invention may be mixed with an additive, if necessary. Examples of such additives include Teflon,
Lubricants such as polyvinylidene fluoride and fatty acid metal salts; Abrasives such as cerium oxide, strontium titanate and silicon carbide; colloidal silica, alumina, silicone oil, various modified silicone oils, silane coupling agents, silanes having functional groups. There are flowability-imparting agents such as silica and alumina treated with a coupling agent, anti-caking agents; conductivity-imparting agents such as carbon black tin oxide; and fixing aids such as low molecular weight polyethylene.
Further, for the purpose of improving releasability at the time of heat roll fixing, a wax-like substance such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, and sol wax is added to the toner of the present invention in an amount of 0.5 to 0.5%.
It is also possible to add about 5% by weight.

In the production of the toner according to the present invention, the toner constituent materials as described above are thoroughly mixed by a ball mill or other mixing machine, then well kneaded by using a heat kneader such as a heat roll kneader or an extruder, and after cooling and solidification. The method of obtaining the toner by mechanical pulverization and classification is preferable, and the method of obtaining the toner by spray-drying after dispersing the constituent materials in the binder resin solution; or the binder resin should be constituted. Polymerization method toner production method in which a predetermined material is mixed with a monomer to form an emulsion suspension, and then the mixture is polymerized to obtain a toner;
Alternatively, in a so-called microcapsule toner including a core material and a shell material, a method in which a predetermined material is contained in the core material or the shell material, or both of them can be applied.

In the present invention, the charge amount of the toner layer on the carrier is determined by using the so-called suction type Faraday cage method. In this suction type Faraday cage method, the outer cylinder is pressed against the toner carrier to suck all the toner on a certain area on the carrier, and the toner is collected by the filter of the inner cylinder and the toner carrier increases from the weight increase of the filter. The weight of the toner layer per unit area above can be calculated. At the same time, this is a method in which the amount of charge on the toner carrier can be determined by measuring the amount of charge accumulated in the inner cylinder that is electrostatically shielded from the outside.

In the present invention, the fine line reproducibility was measured by the following method. That is, an image obtained by copying an original document of a fine line with a width of 100 μm accurately under appropriate copying conditions is used as a measurement sample, and using a Luzex 450 particle analyzer as a measuring device, a line width is displayed by an indicator from an enlarged monitor image. Measure. At this time, since the measurement position of the line width has unevenness in the width direction of the thin line image of the toner, the average line width of the unevenness is used as the measurement point. From this, the fine line reproducibility value (%) is calculated by the following formula.

In the present invention, the resolution is measured by the following method. That is, it is a pattern consisting of 5 thin lines with the same line width and spacing, and 2.8,3.2,3.6,4.0,4.5,5.0,
5.6, 6.3, 7.1, 8.0, 9.0, 10.0 Create an original image that is drawn as if there were one. An image obtained by copying the original document with these 10 types of line images under appropriate copying conditions,
Observe with a magnifying glass, and use the number of images (lines / mm) in which fine lines are clearly separated as the value of resolution.

The larger this number is, the higher the resolution is.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. All parts in the following formulations are parts by weight.

First, the sleeve used in the image forming apparatus used for image formation of the present invention will be described.

Production Example 1 The surface of a cylindrical stainless sleeve (SUS 304) with a diameter of 32 mm (SUS 304) having a magnet inside was treated as amorphous particles with # 400.
Using Al ₂ O ₃ (particle size: 35 to 45 μm), a blast treatment was performed under the conditions of a spray nozzle diameter of 7φ, a distance of 150 mm, an air pressure of 3.5 kg / m ² , and a spray time of 60 seconds. This is sleeve 1.

FIG. 5 is a diagram schematically showing a cross-sectional view of the surface of the sleeve.

Production Example 2 The surface of the sleeve used in Production Example 1 was treated with # 30 as shaped particles.
Blasting was performed under the same conditions as in Production Example 1 using 0 (53 to 62 μm) glass beads (true spherical particles having a ratio of major axis / minor axis of substantially 1.0). This is sleeve 2.

The diameter R of the depressions on the surface of the sleeve was 53 to 62 μm, the pitch P of the irregularities was 33 μm, and the surface roughness d was 2.0 μm.

FIG. 6 is a diagram schematically showing a cross-sectional view of the surface of the sleeve.

Manufacture Example 3 Manufacture Example 1 except that the surface of the sleeve 1 obtained in Manufacture Example 1 uses glass beads (true spherical particles) of # 100 (150 to 180 μm) as shaped particles and the air pressure is 3.0 kg / m ^2. Blast treatment was performed under the same conditions as above. This is the sleeve 3.

FIG. 7 is a diagram schematically showing a cross-sectional view of the surface of the sleeve.

Manufacture Example 4 As in Manufacture Example 1 except that the surface of the sleeve 1 obtained in Manufacture Example 1 was made of # 200 (70 to 90 μm) glass beads (spherical particles) as regular particles and the spraying time was 30 seconds. Blast treatment was performed under the same conditions. This is the sleeve 4.

Production Example 5 The surface of the sleeve used in Production Example 1 was treated with # 10 as regular particles.
Blasting was performed using 0 (150 to 180 μm) glass beads (true spherical particles) under the conditions of an air pressure of 4.0 kg / m ² and a blowing time of 45 seconds. This is the sleeve 5.

The diameter R of the depressions on the surface of the sleeve was 150 to 180 μm, the pitch P of the irregularities was 52 μm, and the surface roughness d was 2.2 μm.

Production Example 6 The surface of the sleeve 1 obtained in Production Example 1 was subjected to a blast treatment under the same conditions as in Production Example 1 with the regular particles (# 300) used in Production Example 2. This is the sleeve 6.

An image forming apparatus used for image formation of the present invention will be described. The outline is the above-mentioned device (FIG. 1), and the specifications are as follows.

A selenium photosensitive drum is used as the latent image carrier 1, the gap α between the latent image carrier 1 and the toner carrier 22 is 0.3 mm, the distance between the toner carrier 22 and the doctor blade 24 is 0.25 mm, the magnet strength of the magnetic roller 23 is strong. It is N ₁ pole 1000gaus on the sleeve surface.
s, S ₁ pole 1000 gauss, N ₂ pole 750 gauss, S ₂ pole 550 gauss.
The copying speed is 50 sheets per minute for A4 size paper.

The developing bias power source used in the image forming apparatus for image formation according to the present invention will be described with reference to the waveform of the alternating electric field.

(Waveform Example 1) The developing bias power source capable of applying the alternating bias electric field having the waveform shown in FIG.

This alternating electric field has a peak-to-peak 1400 V frequency of 2000 Hz and a duty ratio of 20%, and a DC voltage of +200 V is superimposed on it.
It was used as a developing bias power source.

(Waveform Example 2) The developing bias power source capable of applying the alternating bias electric field having the waveform shown in FIG.

This alternating electric field was a peak-to-peak 1400 V frequency 2000 Hz, an alternating voltage with a duty ratio of 30%, and a DC voltage of +200 V superimposed on it.

(Waveform Example 3) The developing bias power source capable of applying the alternating bias electric field having the waveform shown in FIG.

This alternating electric field has a peak-to-peak 1400 V frequency of 2000 Hz and a duty ratio of 35%, and a DC voltage of +200 V is superimposed on it.
It was used as a developing bias power source.

(Waveform Example 4) The developing bias power source capable of applying the alternating bias electric field having the waveform shown in FIG.

This alternating electric field has a peak-to-peak 1400 V frequency of 2000 Hz and a duty ratio of 30%, and a DC voltage of +200 V is superimposed on it.
It was used as a developing bias power source.

(Waveform Example 5) The developing bias power source capable of applying the alternating bias electric field having the waveform shown in FIG.

This alternating electric field has a peak-to-peak 1400 V frequency of 2000 Hz and a duty ratio of 50%, and a DC voltage of +200 V is superimposed on it.
It was used as a developing bias power source.

Next, the magnetic toner used for image formation of the present invention will be described.

Toner Production Example 1 After thoroughly mixing the above materials with a blender, they were kneaded with a twin-screw kneading extruder set at 150 ° C. The obtained kneaded product was cooled, coarsely pulverized by a cutter mill, then finely pulverized by a fine pulverizer using a jet stream, and the finely pulverized powder obtained was classified by a fixed wall type air classifier. A classified powder was produced. Furthermore, the obtained finely divided powder is rigorously classified with a multi-division classifier (Elbowjet classifier manufactured by Nittetsu Mining Co., Ltd.) using the Coanda effect to simultaneously remove black fine powder (magnetic toner). Obtained. The particle size distribution of this magnetic toner is shown in Table 1.

0.6 part of hydrophobic dry silica (BET specific surface area 300 m ^{2 /} g) was added to 100 parts of the obtained black fine powder magnetic toner, and mixed with a Henschel mixer.

This toner is designated as Toner 1.

Toner Production Example 2 Using the above materials, a magnetic toner having the particle size distribution shown in Table 1 was obtained in the same manner as in Toner Production Example 1.
Add 0.8 parts of hydrophobic dry silica (BET 200m ² / g) to 0 parts,
Mixed with a Henschel mixer.

This toner is designated as Toner 2.

Toner Production Example 3 Toner 3 having the particle size distribution shown in Table 1 was obtained in the same manner as in Toner Production Example 1 using the above materials.

Toner Production Example 4 Using the above materials, a toner 4 having a particle size distribution shown in Table 1 was obtained in the same manner as in Toner Production Example 2.

Toner Production Examples 5 and 6 Using the coarsely crushed product obtained in Toner Production Example 1, the particle size distribution shown in Table 1 was obtained in the same manner as in Toner Production Example 1 except that the fine pulverization and classification conditions were changed. Toner 5 and Toner 6 were obtained.

Tables 2 and 3 show the image forming forms in Examples and Comparative Examples of the present invention, and the results of a copying test of 10,000 sheets in each image forming form are shown in Tables 3 and 4. Show. Table 3 shows the results of the image density and the state of the toner carrier, and Table 4 shows the results of the image evaluation.

[Examples 1 to 8] As is clear from Tables 3 and 4, images with high image quality were obtained. Similarly, good results were obtained at 15 ℃ and 10% RH.

However, in Example 5, a slight toner coat unevenness was observed in the non-image area, but it did not appear on the image.

[Comparative Example 1] This is an example in which an irregular-shaped particle blasting sleeve was used, but the initial density was low and tailing was observed. Further, it was slightly inferior to Example 3 in terms of gradation and fog.

[Comparative Example 2] This is an example in which a developing bias with a duty ratio of 50% is used, but tailing and a carrying memory are seen, and the gradation and resolution are inferior to those in Example 1.

[Comparative Example 3] Although the image was a good image, the characters were crushed due to excessive overprinting, and the toner consumption was large.

[Comparative Example 4] Although the image was good in the initial stage, the image quality gradually deteriorated as copying was repeated, the trailing was conspicuous, the fine line reproducibility became unstable, and the resolution fell.

[Advantages of the Invention] The present invention is an image forming method and an image forming apparatus in which a magnetic toner having a specific particle size distribution is carried on a toner carrier having a specific surface shape, and development is performed using an asymmetric developing bias. Therefore, it has the following excellent effects.

(1) The magnetic toner is uniformly coated on the toner carrier to uniformly charge the toner particles on the toner carrier without excess or deficiency, and the state of the spikes is uniform, thin, short, and dense. The image forming method and the image forming apparatus enable the flying and the efficient flight to promote high image quality.

(2) An image forming method and an image forming apparatus which have a high image density, are excellent in fine line reproducibility and gradation, and can obtain a clear, high-quality image without fog for a long period of time.

(3) An image forming method and an image forming apparatus for preventing or reducing the carrier memory.

(4) An image forming method and an image forming apparatus capable of obtaining a clear and high-quality image with high image density even in low humidity and without fog.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a developing device, and FIGS.
FIGS. 8 to 12 are schematic diagrams of alternating bias waveforms, FIG. 4 is an explanatory diagram of bias components, and FIGS. 5 to 7 are schematic diagrams of roughness of the sleeve surface. . T ...... toner, T ₁ ...... thin toner layer T ₂ ...... toner image, A ...... developing area α ...... latent image bearing member and the toner carrying member gap S ₀ ...... alternating bias applying means S ₁ ...... DC Bias applying means 1 ... Latent image holder, 21 ... Hopper 22 ... Toner carrier, 23 ... Magnetic roller 24 ... Doctor blade

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kuniko Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masayoshi Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP 62-70865 (JP, A) JP 57-66455 (JP, A) JP 60-73647 (JP, A) JP 1-222154 (JP, A) JP-A-59-33459 (JP, A) JP-A-1-112253 (JP, A)

Claims (2)

[Claims] 1. An electrostatic image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on its surface are arranged in the developing section with a certain gap, and the magnetic toner is placed on the toner carrier. In an image forming method in which the toner is regulated to a thickness smaller than the gap and conveyed to a developing unit, and the toner is developed in the developing unit while applying an alternating electric field, the toner carrier is subjected to a blasting treatment with amorphous particles, and at the same time, Alternatively, it has a surface blasted with regular particles or a surface blasted with regular particles on it, and in the developing section, a DC bias and an asymmetric AC bias are applied to the toner carrier to form a toner carrier. An alternating bias electric field is formed between the electrostatic image holder and the electrostatic bias electric field. The alternating bias electric field has a developing side voltage component and a reverse developing side voltage component, and the developing side voltage component is the reverse developing side. The magnetic component is equal to or larger than the pressure component, and the application time of the voltage component on the developing side is shorter than the application time of the voltage component on the reverse developing side, and the magnetic toner contains 12% by number or more of magnetic toner particles having a particle diameter of 5 μm or less. Containing 33% by number or less of magnetic toner particles having a particle diameter of 8 to 12.7 μm, containing 2.0% by volume or less of magnetic toner particles having a particle diameter of 16 μm or more, and having a volume average particle diameter of 4 to 4 An image forming method having a particle size distribution of 10 μm. 2. An electrostatic image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on its surface are arranged in the developing unit with a constant gap, and the magnetic toner is placed on the toner carrier. In an image forming apparatus in which an electrostatic charge image is developed while being regulated to a thickness smaller than the gap and conveyed to a developing unit, and an alternating electric field is applied to the toner in the developing unit by a bias applying unit, the toner carrying member has an irregular shape. The blasting means has a surface blasted with particles and at the same time or on the surface blasted with fixed particles, or a surface blasted with fixed particles. An alternating bias is applied to the toner carrier to form an alternating bias electric field between the toner carrier and the electrostatic image carrier. And a reverse development side voltage component, so that the development side voltage component is equal to or larger than the reverse development side voltage component, and the application time of the development side voltage component is shorter than the application time of the reverse development side voltage component. The magnetic toner contains 12% by number or more of magnetic toner particles having a particle size of 5 μm or less, 33% by number or less of magnetic toner particles having a particle size of 8 to 12.7 μm, and 16 μm or more. An image forming apparatus comprising: a magnetic toner particle having a particle size of 2.0 volume% or less and having a particle size distribution in which the volume average particle diameter of the magnetic toner is 4 to 10 μm.