JPH03126042A - Magnetic toner - Google Patents

Abstract

PURPOSE:To obtain a magnetic toner capable of forming an image superior in durability, high in density, and free from fog on white background in the case of applying a developing method using developing bias by using a magnetic toner specified in size distribution and triboelectrifiability. CONSTITUTION:The magnetic toner contains particles of <= 5mum particle diameter in >= 12 number %, particles of 8 - 12.7mum particle diameter in <= 33 number %, and particles of >= 16mum particle diameter in <= 2 volume % and it has a volume average particle diameter of 4 - 10mum. The triboelectrified amount of the toner and the volume average particle diameter on a toner carrying body satisfy expression I, in which R is the volume average particle diameter of the magnetic toner, and Q is its absolute value of the triboelectrified amount, thus permitting the obtained magnetic toner to be superior in durability, high in density, and free from fog on white background.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a developing method that includes a step of developing an electrostatic latent image formed by electrophotography, electrostatic printing, etc. using magnetic toner. The present invention relates to a magnetic toner used in a magnetic toner.

[Prior art] ■A representative example of the prior art is USP 3,866.
574 and USP 3,890,929 and USP 3
, No. 893, 418.

A proposal has been made to provide a certain gap between a latent image carrier and a toner carrier (toner) and apply an asymmetric alternating current pulse bias to them to control the flight of high-resistance component toner.

A schematic diagram of the waveform at that time is shown in FIG. In terms of content, the gap between the latent image carrier and the toner carrier is 5 Qum to 500a.
m (preferably 50 to 180 μm), frequency is 1
．． 5 K ~ l0KI (Z (preferably 4 ~ 8 K
Hz), development time is toμsec≦TA≦200μs
ec (preferably 30μsec≦TA≦200μ5e
c) Stripping time is 100 μsec≦T0≦500
μsec (preferably looμsec≦0≦18
0μ5ec), development voltage is VA, Q -150V,
The stripping voltage is VD≧400V. -vA≦80
0 V (preferably -150≦vA≦-200V and 400≦vO≦450V). This method prevents flying toner particles from adhering to non-image areas and improves gradation and line reproducibility. Examples of the latent image development method using the above-mentioned schematic % formula (%) shown in FIG. In particular, the jumping development method is a method in which toner is developed by an AC bias voltage applied between the toner carrier and the latent image carrier in the development region where the toner carrier and the latent image carrier are closest to each other. It reciprocates between the developer carrier and the latent image holder, and is finally selectively attached to the surface of the latent image holder in accordance with the latent image pattern, and is visualized. These duty ratios are 50%, and the development side time and the reverse development side time are the same (see FIG. 3).

However, some of the patents related to the jumping development method control the duty ratio of the AC bias voltage applied between the toner carrier and the latent image carrier according to the remaining amount of developer in order to adjust the image density. . (Unexamined Japanese Patent Publication No. 60-7364
7 Publication etc.) Here, "duty ratio of AC bias electric field"
is defined as below.

a: Application time of an electric field component (developing side bias component) having a polarity in the direction of transferring toner to the latent image carrier side in one cycle of an AC bias in which the electric field polarity changes periodically between positive and negative.

At this time, the DC bias electric field is removed.

b = Application time of an electric field component with a polarity in the direction of separating the toner from the latent image carrier side (reverse development side bias component). Also, the development side bias component refers to the latent image potential of the latent image carrier v3 (the polarity is positive). ), and the polarity of the toner used is negative, and the part a in FIG. 4 is referred to as the bias component, and the opposite phenomenon side bias component is the part b in FIG. 4.

As in conventional example (■), a developing method in which the absolute value of the alternating bias voltage is kept low in order to prevent toner from adhering to non-image areas, and the developing side voltage is further reduced, may not be able to obtain sufficient image density. be.

Regarding the above conventional example (■), in this development method, the development side bias voltage is large, so the developability of the solid latent image (high potential area) is high, but the reverse development side bias in the low potential area is large, so the development There is a tendency that excessive toner is removed, resulting in an image with no tonality.

Furthermore, the permissible range for setting the voltage (OC and AC: (V□ & frequency)) is narrow. That is, when attempting to increase the density by adjusting the voltage (lowering the DC component or increasing the AC component, etc.), background stains (white background fog) occur. Increasing the frequency of AC is effective for eliminating fog on white backgrounds, but the reproducibility of letters and lines becomes poor (fine).

As a means of improving the above two developing methods, when applying a bias on the developing side, the developing electric field is increased and the developing side time is set to a short time, thereby achieving high image density and gradation, and eliminating white background fog. You can now obtain images without

However, if an image forming method using such a development method is repeatedly used, the image quality may deteriorate due to a decrease in image density, an increase in white background fog, or a deterioration in resolution and line reproducibility. there were.

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

Additionally, in general, when image formation is repeated in the -component development method, toner with small particle size adheres to the surface of the toner carrier due to mirroring force due to its high charge amount, and friction with other toner particles occurs. Charging may be inhibited, and the number of toner particles that cannot be sufficiently charged may increase, causing a decrease in density. Such a phenomenon is particularly likely to occur under low humidity.

Such a phenomenon is accelerated when the toner on the toner carrier is not consumed (for example, in a white area of the image), resulting in a decrease in image density. On the other hand, from this state, toner is consumed (for example, in black areas of the image), and this phenomenon is alleviated and the density gradually recovers.

Therefore, the toner carrier has a consumed part (image part) and an unconsumed part (
When an image is formed in the presence of a non-image area, a difference in density occurs on the image (that is, a high density in the consumed area and a low density in the unconsumed area).

Such a phenomenon will be referred to below as carrier memory. Considering the mechanism of formation of this toner carrier memory, the toner carrier memory is eliminated by toner consumption, that is, it is reduced with each rotation of the toner carrier. Therefore, this phenomenon In light cases, the memory on the image disappears once, but in severe cases, it may reappear many times.

Therefore, in order to obtain good durability, environmental characteristics, and excellent image quality in the magnetic toner used in the present invention, the particle size distribution of the magnetic toner and the amount of triboelectric charge on the toner carrier are important. It was found that this is a significant factor.

[Problems to be Solved by the Invention] An object of the present invention is to provide a magnetic toner that solves the above-mentioned problems and is used in a developing method using an asymmetric developing bias.

Another object of the present invention is to provide a magnetic toner which is excellent in durability, has high image density even when used continuously for a long period of time, and stably provides images without white background fog.

Still another object is to provide a magnetic toner that provides images with rich gradation, excellent resolution, and fine line reproducibility.

Still another object is to provide a magnetic toner that stably provides images with high image density even under low humidity.

[Means and effects for solving the problems] The present invention arranges a latent image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on its surface with a certain gap in a developing section. , an image forming method in which magnetic toner is regulated to a thickness thinner than the gap on a toner carrier and conveyed to a developing section, and a DC voltage and an asymmetrical alternating voltage are applied between the toner carrier and the latent image carrier. In this case, the developing side voltage component of the alternating bias voltage including DC is set to be the same as or larger than the reverse developing side voltage component (stripping voltage component), and the application time of the developing side voltage is made longer than that of the reverse developing side voltage. In a magnetic toner having at least a binder resin and magnetic powder used in a developing method of small size, the magnetic toner contains 12% or more by number of magnetic toner particles having a particle size of 5 pm or less;
Magnetic toner particles having a particle size of ~12.7 gm are contained at 33% by number or less, magnetic toner particles having a particle size of 16H or more are contained at 2% by volume or less, and the volume average particle size of the magnetic toner is 4~12.7 gm. 10 pm, and the amount of triboelectric charge of the magnetic toner particles on a toner carrier and the volume average particle diameter of the magnetic toner satisfy the following general formula (1).

2 (μc/g) +0.5 (μc/g) R≦Q
(pc/g)≦20 (Fu/g) +0.5 (Cod/g)
R... (1) The present inventors investigated the relationship between the toner particle size and the developability in the development bias.
A study was conducted using a magnetic toner having a particle size distribution over pm. This is between the toner carrier and the latent image carrier (approximately 25
When a constant developing side voltage (approximately 1000 V) is applied in a pulsed manner at 0 pm), toner begins to adhere to the latent image carrier (the image density should be 1.0 or higher in the image after transfer and fixing). ) It looks at the pulse width and toner particle size distribution. That is, the surface potential of the latent image carrier was kept constant, the pulse width was varied to develop the latent image, the developed toner particles on the latent image carrier were collected, and the toner particle size distribution was measured. It was found that there were many magnetic toner particles with a diameter of 8 μm or less (in addition, there were many magnetic toner particles with a diameter of 5 pm or less. Furthermore, as the pulse width was further reduced, the number of magnetic toner particles with a diameter of 51 zm or less increased (findings were also obtained). It was done.

In other words, it can be seen that the toner with a smaller particle size reaches the latent image carrier faster.

Therefore, when applying bias on the developing side, the developing electric field is set to a high level (,
By setting the time to a short time, toner particles having a small particle size can be selectively developed.

Also, when applying bias on the reverse development side, the stripping electric field is set to a low level (
By setting the time to a long time, large toner particles or toner particles with a low charge (moving speed is slow) that could not reach the latent image carrier during the development side bias are firmly returned to the toner carrier over time. . At this time, toner particles with a small particle size in the image area on the latent image carrier are
Due to the strong reflection force and low stripping electric field,
However, toner particles with a small amount of charge (fogged toner particles) that adhere to non-image areas due to scattering or the like have a weak mirroring force, so they are pulled back onto the toner carrier by the stripping electric field.

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

However, in such a development method, if a large number of toner particles with a large particle size are contained in the magnetic toner, these particles tend to become toner particles with a small electrical charge (they remain without being developed, and the toner particles are The magnetic toner on the carrier gradually grows in size, causing image quality deterioration.

Furthermore, if the amount of charge of the magnetic toner is too small, the above-mentioned phenomenon will be promoted, and even if there are few large particles, image quality will deteriorate.

On the other hand, if the amount of charge of the magnetic toner is too large, small particles will remain on the toner carrier, changing the particle size distribution and causing image quality deterioration.

On the other hand, using a magnetic toner with a particle size distribution ranging from 0.54 tn to 30 μm, this time we changed the surface potential on the photoreceptor, from a large development potential contrast where a large number of toner particles are easily developed, to halftone, and A latent image was developed with the surface potential on the photoreceptor changed to a small development potential contrast where only a few toner particles were developed, and the developed toner particles on the photoreceptor were collected and the toner particle size distribution was measured. It has been found that there are many magnetic toner particles with a diameter of 8 pm or less (in particular, there are many magnetic toner particles with a diameter of 5 μm or less. In other words, 5#Lm is the most suitable for development.
When magnetic toner particles with the following particle diameters are smoothly supplied to develop the latent image on the photoreceptor, the latent image is faithful to the latent image, does not protrude from the latent image, and an image with truly excellent reproducibility can be obtained. be.

On the other hand, regarding the particle size, in the magnetic toner of the present invention, 5P
One of the characteristics is that magnetic toner particles having a particle size of m or less account for 12% or more by number. Conventionally, in magnetic toner, it is difficult to control the amount of charge of magnetic toner particles of 5 μm or less, and the charge tends to be excessively charged. For this reason, toner particles of 5 pm or less have a strong mirroring force on the developing sleeve, etc. (and stick to the sleeve surface, inhibiting the frictional charging of other particles, generating toner particles with insufficient charging, causing roughness and a decrease in density. It was thought that it was necessary to proactively reduce the risk of oxidation.

However, according to studies conducted by the present inventors, it has been found that magnetic toner particles of 51 or less are an essential component for forming high quality images.

In the developing method of the present invention, toner particles of 5 pm or less are efficiently flown, so that it is possible to prevent them from sticking to the surface of the sieve.

In addition, in the magnetic toner of the present invention, 8 to 12.7 p.
One of the characteristics is that the number of particles in the range m is 33% or less by number. As mentioned above, this is related to the necessity of the presence of magnetic toner particles with a particle size of 5 ILm or less, and 5 pm or less.
Magnetic toner particles with the following particle sizes have the ability to cover the latent image closely and reproduce it faithfully, but the electric field strength at the edges around the latent image itself is higher than at the center, so The toner particles may adhere more thinly inside the edges than at the edges, and the image density may appear thinner.Especially when using 5H
The following magnetic toner particles have a strong tendency to do so.

However, the present inventors have found that by containing toner particles in the range of 8 to 12.7 pm in an amount of 33% by number or less, this problem can be solved and further clarity can be achieved. That is, toner particles with a particle size in the range of 8 to 12.7 pm are different from magnetic toner particles with a particle size of 5 μm or less.
This is thought to be due to the appropriately controlled amount of charge, but the toner is supplied to the inner side of the latent image where the electric field strength is lower than the edge area, compensating for the lack of adhesion of the inner toner particles to the edge area, resulting in uniform development. An image is formed, and as a result, a sharp image with high density and excellent resolution and gradation is provided.

Regarding particles with a particle size of 5 pm or less, if the number % is 12 to 60 and the volume average particle diameter is 7 to 10 μm, the difference between the number % (N) and the volume % (V) is N/V It is preferable that the magnetic toner of the present invention satisfies the following relationship: =-0.04N + k (4.5≦≦6.5; 12≦N≦60). The magnetic toner of the present invention having a particle size distribution satisfying this range can achieve better developability.

While studying the state of particle size distribution of 5 Pm or less, the present inventors found that there is a state of existence of fine powder most suitable for achieving the purpose, as shown by the above formula. That is, 1
For a certain value of N (2≦N≦60), a large N/V means that particles of 5 μm or less are widely included, and a small N/V means that particles around 5 μm are included. It is understood that this indicates that the existence rate of particles is high and there are few particles with a smaller particle size, and when N is in the range of 12 to 60, the value of N/V is 2.1 to 5.82. When the above relationship is within the range and the above relational expression is further satisfied, good fine line reproducibility and high resolution can be achieved.

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

The structure of the toner of the present invention will be explained in detail.

It is preferable that magnetic toner particles having a particle size of 5 pm or less account for 12% by number or more of the total number of particles (preferably 12 to 60% by number, and more preferably 17 to 50% by number.
If the number of magnetic toner particles with a particle size of m or less is 12% or less, there are few magnetic toner particles effective for high image quality, and especially as the toner is used for continuous copying or printing, the effective magnetic toner particles decrease. As a result, the balance of the particle size distribution of the magnetic toner as shown in the present invention deteriorates, and the image quality gradually deteriorates.
If it is more than 60% by number, magnetic toner particles tend to aggregate with each other, resulting in toner agglomerates larger than the original particle size, resulting in rough image quality, lowering resolution, or forming edges of latent images. There may be a large difference in density between the inside and the image, resulting in a hollow-looking image.

According to studies conducted by the present inventors, it has been found that magnetic toner particles of 5 μm or less are an essential component for stabilizing the volume average particle diameter of the magnetic toner on the sleeve during image printing.

When performing image printing durability, a large amount of magnetic toner particles with a particle size of 5 μm or less, which is the most suitable for development, is consumed.If this amount is small, the volume average particle size on the sleeve gradually increases, This tends to increase M/S and make uniformity of the sleeve coat difficult.

Further, it is preferable that the number of particles in the range of 8 to 12.7 pm is 33% by number or less, preferably 1 to 33% by number.

When the amount is more than 33% by number, the image quality deteriorates and more development than necessary occurs, that is, too much toner is applied, leading to an increase in toner consumption.

On the other hand, if it is less than 1% by number, it is difficult to obtain a high image density (sometimes it may become so). Between, N
There is a relationship that /V=-0,04N+, and 4.5≦≦
Indicates a positive number in the range of 6.5. Preferably 4,5≦ and ≦6
．． It is 0. As shown above, 12≦N≦60, and the volume average particle size in this case is 7 to 10 μm.

When k<4.5, the number of magnetic toner particles having a particle size smaller than 5.0 pm is small, and the image density, resolution, and sharpness tend to be poor. Conventionally, the presence of fine magnetic toner particles, which were often thought to be unnecessary, is important in development.
It achieves the closest packing of toner and contributes to the formation of uniform images without roughness. In particular, by uniformly filling in thin lines and image contours, visual sharpness is further enhanced. That is, when k<4.5, these properties tend to be inferior due to the lack of this particle size distribution component.

From another point of view, in terms of production, conditions such as classification will become stricter in order to satisfy the condition of k<4.5, which will be disadvantageous in terms of yield and toner cost. Also, k>6.
5, due to the presence of more fine powder than necessary, the balance of the particle size distribution is lost as copying is continued, the degree of agglomeration of the toner increases, and frictional charging is not performed effectively, resulting in poor cleaning and fogging on white backgrounds. This may occur.

Further, the amount of magnetic toner particles having a particle size of 16 pm or more is preferably 2.0% by volume or less, more preferably 1.0% by volume or less, and still more preferably 0.5% by volume or less. If the amount is more than 2.0% by volume, it not only hinders fine line reproduction, but also causes coarse toner particles of 16 Pm or more to protrude on the thin layer surface of toner particles developed on the photoreceptor during transfer. , the delicate contact state between the photoreceptor and the transfer paper via the toner layer is irregular,
This causes fluctuations in transfer conditions and is a cause of defective transfer images.

Furthermore, in the developing method of the present invention, toner particles of 16 pm or more cannot fly onto the latent image carrier unless they have a sufficient amount of charge.
A large amount of toner remains on the toner carrier, causing changes in particle size distribution, inhibiting triboelectric charging of other toner particles, reducing developing ability, and often causing image quality deterioration.

The volume average diameter of the magnetic toner of the present invention is 4 to IOpm, preferably 4 to 9pm, and this value cannot be considered in isolation from each of the components mentioned above. If the volume average particle diameter is 4 μm or less, problems such as a small amount of toner on the transfer paper (and low image density) tend to occur in applications where the image area ratio is high, such as graphic images.

This is considered to be due to the same reason as the reason why the density inside the edge portion of the latent image decreases as described above.

If the volume average particle diameter is 10 pm or more, the resolution is not good (or the copying is good at the beginning), but with continued use, the particle size distribution changes and the image quality tends to deteriorate.

The magnetic toner of the present invention, which has a specific particle size distribution, can faithfully reproduce down to the fine lines of the latent image formed on the photoreceptor, and can reproduce halftone dots and digital dot latent images. It provides images with excellent gradation and resolution. Furthermore, it is possible to maintain high image quality even when copying or printing is continued, and to perform good development with less toner consumption than conventional magnetic toners even in the case of high-density images. It also has advantages in terms of economy and miniaturization of the main body of the copying machine or printer.

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

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

In other words, the measuring device is Coulter counter TA.
- An interface (manufactured by Nikkaki) that outputs the number distribution and two volume distributions using the n-type (manufactured by Coulter) and CX-t
A personal computer (manufactured by Canon) is connected, and the electrolyte is approximately 1% NaC using primary sodium chloride! Prepare an aqueous solution. For example, l5OTON■-■ (Coulter)
(manufactured by Scientific Japan) can be used. As a measurement method, the electrolytic aqueous solution is 100 to 150mj! A surfactant, preferably an alkylbenzene sulfonate (0.1 to 5 mj), is added therein as a dispersant, and 2 to 20 mg of a measurement sample is added thereto. The electrolyte in which the sample was suspended was dispersed in an ultrasonic disperser for about 1 to 3 minutes, and then
With the counter TA-n type, the aperture is 100
Using a μ aperture, the particle size distribution of particles of 2 to 40 μ on a count basis was measured and the values according to the invention were determined therefrom.

The structure of the present invention will be described in more detail with reference to a specific example of an apparatus for carrying out the developing step in the present invention, which is shown in FIG. 1, but this is not intended to limit the present invention in any way.

In Figure 5, 1 is a latent image carrier (so-called photoreceptor) such as a rotating drum type in transfer type electrophotography, an insulator such as a rotating drum type in transfer type electrostatic recording method, and an electrofax. An electrostatic latent image is formed on the surface of a latent image carrier such as a photosensitive paper in a method or an electrostatic recording paper in a direct electrostatic recording method using a latent image forming process device or a process mechanism not shown in the figure. , is moving in the direction of the arrow.

2 is the general code of the developing device, 21 is a hopper containing toner, 22 is a rotating cylindrical body (hereinafter referred to as sleeve) as a toner carrier (developer layer supporting member), and magnetism generating means 23 such as a magnetic roller is inside. It is built-in.

In the drawing, the sleeve 22 is supported by bearings with its approximately right half circumferential surface exposed inside the hopper 21 and its approximately left half circumferential surface exposed outside the hopper, and is rotated in the direction of the arrow. A doctor blade 27 is a toner applying member disposed close to each other, and 27 is a toner stirring member in the hopper.

The axis of the sleeve 22 is substantially parallel to the generatrix of the latent image holder 1, and the sleeve 22 faces the latent image holder 1 closely with a small gap α therebetween.

The moving speed (peripheral speed) of each surface of the latent image holding member 1 and the sleeve 22 is -, or the circumferential speed of the sleeve 22 is slightly faster. Further, a DC voltage and an AC voltage are applied in a superimposed manner between the latent image holding member 1 and the sleeve 22 by an alternating bias voltage applying means S0 and a DC bias voltage applying means S1.

The substantially right half circumferential surface of the sleeve 22 is in constant contact with the toner pool in the hopper 21, and the toner near the sleeve surface forms a magnetic adhesion layer on the sleeve surface due to the magnetic force of the magnetism generating means 23 in the sleeve, and also generates static electricity. Adhesion is maintained by force.

When the sleeve 22 is rotationally driven, the toner layer adhering to the sleeve surface passes through the position of the doctor blade 24 and is layered as a thin toner layer T1 having a substantially uniform thickness at each portion. The toner is mainly charged by frictional contact between the sleeve surface and the toner in the toner pool in the vicinity as the sleeve 22 rotates. The developing area portion A, which is the closest portion between the latent image holder 1 and the sleeve 22, rotates to the side.
pass through. During this passing process, the toner in the thin toner layer on the side of the sleeve 22 is blown away by the DC and AC electric fields caused by the DC and AC voltages applied between the latent image carrier 1 and the sleeve 22, and is blown away from the surface of the latent image carrier 1 in the development area A. and the sleeve 22 surface. Finally, the toner image T2 is sequentially formed by selectively transferring and adhering to the surface of the toner image holder on the sleeve 22 side in accordance with the potential pattern of the latent image.

The sleeve surface, on which toner has been selectively consumed after passing through the development area A, is rotated again to the toner reservoir of the hopper 21 and is resupplied with toner. The layer T1 surface is rotated and the copying process is repeated.

By the way, one of the problems when such a developing method (one-component non-contact developing method) is adopted is that developing performance may be deteriorated due to increased adhesion of toner near the sleeve surface. In other words, due to the rotation of the sleeve 22, the toner and the sleeve constantly come into contact and friction, and the amount of charge on the toner gradually increases (as a result, the electrostatic force (Coulomb force) with the sleeve increases, and the toner is transferred to the latent image carrier 1. The flying force is weakened and the toner stays near the sleeve, inhibiting the frictional charging of other toners.
This is a phenomenon that causes a decrease in developability. This occurs due to low humidity or repeated copying processes. A similar mechanism also results in the carrier memory described above.

Now, the force that causes the toner to fly from the sleeve to the latent image holder 1 must be able to reach the latent image surface sufficiently by the AC bias electric field (acceleration a must be applied. The weight of the toner must be m
The force f is given by 12m-a. The charge of the toner is q, the distance from the sleeve is d, and the alternating bias electric field is expressed.The force of the toner to reach the latent image surface is determined by the balance between the electrostatic attraction force with the sleeve and the electric field force. Ru.

Here, in order to fly away toner of 5 μm or less that tends to collect near the sleeve, the electric field may be increased. However, simply increasing the bias voltage on the development side is not related to the latent image pattern (toner particles with a particle size of 5 pm or less tend to fly toward the latent image side), and white background fog becomes a problem.

Furthermore, by increasing the reverse development bias voltage (white background fogging can be prevented, but by applying a thicker alternating bias electric field between the latent image carrier 1 and the sleeve 22, discharge occurs directly between the latent image carrier 1 and the sleeve 22). occurs, significantly disturbing the image quality.

In addition, if the reverse development bias voltage is too large, it will strip off not only the non-latent image area but also the toner developed in the latent image pattern, resulting in a relatively weak mirroring force on the latent image holder.
Toner particles of 12.7 pm are removed, the developed image pattern is also disturbed, toner adhesion in the latent image area becomes poor, gradation and line reproducibility deteriorate, and areas such as missing areas are likely to occur. .

From the above results, it is necessary to make the toner near the sleeve fly and reciprocate by not increasing the alternating bias electric field too much and by keeping the reverse development side bias voltage low.

Therefore, in the present invention, a magnetic toner that can have a triboelectric charge on a toner carrier that is compatible with a developing method that controls not only the magnitude of the alternating bias electric field (and the application time), but also has a particle size distribution. The main purpose has been achieved, that is,
The bias electric field on the development side is increased without changing the frequency of the alternating bias, and the application time of the bias electric field on the development side is shortened (while the reverse bias electric field on the reverse development side is suppressed (suppressed) and the application time is lengthened. A method of controlling the duty ratio of alternating bias voltage was used.

Here, the "duty ratio of AC bias electric field" is defined as in the following formula.

a: Application time of an electric field component having a polarity in the direction of transferring toner toward the latent image carrier in one period of an AC bias in which the electric field polarity changes periodically between positive and negative. At this time, the DC bias electric field is removed.

b: On the contrary, the application time of the electric field component with the polarity in the direction that separates the toner from the latent image carrier side. This is an essential component in order to improve the image quality on the sleeve by making the bias electric field on the developing side sufficiently strong by using this method. This is consistent with the ability to effectively fly and reciprocate toner particles of a certain size of 5 μm or less, and prevents them from adhering to the sleeve surface.

In other words, image density reduction and carrier memory are less likely to occur.

Furthermore, even if the bias electric field on the reverse development side is suppressed to a low level, by applying it for a sufficiently long time, a force is obtained to separate excess toner adhering to areas other than the latent image pattern from the latent image holder 1, thereby preventing white background fog. can.

At this time, the bias electric field on the reverse development side is low (suppressed), so toner particles of 8 to 12.7H, which are essential components for toner paste, are not stripped off.
The figure shows the waveform of the alternating bias voltage used in the present invention.

In other words, even if the bias electric field on the reverse development side is weak, the time is long (as a result, the effective value of the force separating it from the latent image carrier remains the same. Moreover, it does not disturb the toner image developed into the latent image pattern. Therefore, it was possible to obtain good image quality with gradation.

By the way, if the magnetic toner is similarly charged on the toner carrier within the range of general formula (1), preferably within the range of general formula (2), good developability can be obtained. By using this method, images of excellent quality can be obtained. However, at this time, magnetic toner particles with a diameter of 16 μm or more may be insufficiently charged and are not subjected to development, which may cause a change in particle size distribution, so it is necessary to limit the amount to 2% by volume or less.

4 (pc/g) +0.5 (pc/g) R≦Q
(pc/g)≦18 (μc/g) +0.5 (pc
/g) R-(2) Also, if Q<2+0.5R,
Magnetic toner particles of 8 to 12.7 μm are stripped from the latent image carrier by the bias on the reverse development side, resulting in poor toner adhesion, which tends to cause hollow spots and line disturbances.Flight of toner particles also decreases. Therefore, it becomes difficult to obtain sufficient image density, and the image quality tends to be poor.

On the other hand, when Q>20+0.5H, it becomes difficult for magnetic toner particles of 5 μm or less to fly even with the bias on the developing side in the present invention, and the high image quality that is the effect of magnetic toner of 5 μm or less cannot be achieved. It disappears. Furthermore, it tends to accumulate on the toner carrier and inhibits triboelectric charging of other toner particles, resulting in deterioration of developing ability, resulting in decreased image density, carrier memory, roughness, and white background fog.

Here, if the toner particles of 16 pm or more exceed 2% by volume, it may be considered to increase the amount of charge of the toner in order to prevent selective development.

In this case, since the number of particles with a large particle size increases, not only the high image quality aimed at by the present invention cannot be achieved, but also
Lines, crushed letters, and scattering may occur due to excessive application.

Furthermore, it becomes difficult to prevent toner particles with a particle size of 5 pm or less from sticking to the toner carrier, and the developing bias of the present invention may also cause image density reduction in carrier memory.

According to the present invention, the developing side bias electric field of the alternating bias electric field is strong (the toner near the sleeve can also fly, so the toner with a large amount of charge near the sleeve is more strongly developed into a latent image pattern. Therefore, a weak latent image pattern Magnetic toner with 5H or less is an effective ingredient for achieving high image quality, as it can be strongly attached due to the electrostatic force of toner with a high charge amount, and it can develop images with good resolution and edge effects. Particles can be used effectively and significantly better image quality can be obtained.

In the developing method used in the present invention, the gap between the sleeve 22 and the latent image holder 1 was set at 0.3 mm in the embodiment, but in the developing method according to the present invention, the gap was set at 0.3 mm. sufficient development is possible.

Since the bias on the development side is larger than in the conventional development method, development is possible even if the gap between the sleeve 22 and the latent image holder 1 is large.

The absolute value of the alternating bias voltage is 1. If the voltage is above OkV, a sufficiently satisfactory image can be obtained. Furthermore, if leakage to the latent image holder is taken into consideration, the absolute value of the alternating bias voltage is 1.
It is desirable to have a voltage of 2.0 kV or more and 2.0 kV or more. however,
It goes without saying that this leak also varies depending on the gap between the sleeve 22 and the latent image holder l.

Next, the alternating bias frequency is from 1.0kHz to 5.0kHz
z is preferred. When the frequency is 1.0 kHz or less, gradation becomes better, but it becomes difficult to eliminate white background fog. This is because in the low frequency region where the number of toner reciprocating movements is small, even in non-image areas, the force of pressing the toner against the latent image carrier due to the bias electric field on the developing side is strong (too much), and the force of stripping the toner due to the bias electric field on the reverse developing side causes This is thought to be because the toner adhering to the non-image area cannot be completely removed.When the frequency exceeds 5.0 kHz, the bias electric field on the reverse development side is applied before the toner has sufficiently contacted the latent image carrier. As a result, the developability is significantly reduced.In other words, the toner itself becomes unable to respond to the high-frequency electric field.

In particular, according to the invention, the frequency of the alternating bias electric field is 1.5
Optimum image quality was shown between kHz and 3 kHz.

Finally, the duty ratio that satisfies the alternating bias electric field waveform of the present invention should be approximately less than 50%, but when image quality is also considered, it is preferable that the duty ratio be 10%≦duty ratio≦40%. When the duty ratio exceeds 40%, the above-mentioned drawbacks become noticeable, and the effect of the present invention on further improving image quality is weakened. When the duty ratio is less than 10%, the alternating bias electric field responsiveness of the toner itself as described above deteriorates, resulting in a decrease in developability. In particular, the optimum value for the duty ratio is 15%.
≦Duty ratio≦35%.

Further, as the alternating bias waveform, waveforms such as a rectangular wave, a sine wave, a sawtooth wave, and a triangular wave can be applied.

Examples of the binder resin used in the magnetic toner of the present invention include styrene, O-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-
Phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, Styrene and its derivatives such as p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene, isobutylene, etc. ; Unsaturated polyenes such as butadiene; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and concentrated vinyl; Vinyl esters such as vinyl acetate, vinyl propionate, and vinyl benzoate; Methyl methacrylate, methacrylate Ethyl acid, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, methacrylic acid Methacrylic acid esters such as diethylaminoethyl; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate , acrylic acid esters such as 2-chloroethyl acrylate, and phenyl acrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone; vinylnaphthalenes; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide; Vinyl compound derivatives having a carboxyl group such as acrylic acid, maleic acid, and fumaric acid; half esters such as maleic acid half ester and fumaric acid half ester; vinyl derivatives such as maleic anhydride, maleic ester, and fumaric ester derivatives; Monopolymers and copolymers containing monomer components consisting of compounds; polyester, polyurethane, epoxy resin, polyvinyl butyral, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum Resin, haloparaffin, paraffin wax, etc. can be used alone or in combination.

Among these, styrene resins, acrylic resins, and polyester resins are particularly preferably used as the binder resin in consideration of development characteristics.

In consideration of the offset resistance of the toner, the binder resin as described above is more preferably a polymer crosslinked with a crosslinking agent as exemplified below.

Aromatic divinyl compounds, such as divinylbenzene, divinylnaphthalene, etc.; diacrylate compounds linked with an alkyl chain, such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1
．． 4-butanediol diacrylate, 1,5-bentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, and the above compounds in which the acrylate is replaced with methacrylate; alkyl containing an ether bond Chained cyacrylate compounds, such as diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol #400 diacrylate, polyethylene glycol #600 diacrylate, dipropylene glycol diacrylate, and Those in which the acrylate in the above compounds is replaced with methacrylate; diacrylate compounds connected by a chain containing an aromatic group and an ether bond, such as polyoxyethylene (2)-2,2
-bis(4-hydroxyphenyl)propane diacrylate, polyoxyethylene(4)-2,2-bis(4-
hydroxyphenyl) propane diacrylate, and
Examples of the above compounds in which the acrylate is replaced with methacrylate; furthermore, polyester type diacrylate compounds, such as the trade name MANDA (Nippon Kayaku), are listed. Examples of polyfunctional crosslinking agents include pentaerythritol triacrylate, trimethylolethane triacrylate, trimethylolpropane triacrylate,
Examples include tetramethylolmethanetetraacrylate, oligoester acrylate, and compounds obtained by replacing the acrylate of the above compounds with methacrylate, nitriallyl cyanurate, triallyl trimellitate, and the like.

These crosslinking agents are used in an amount of about 0.01 to 5 parts (even about 0.03 to 3 parts) per 100 parts of other monomer components.
It is preferable to use

Among these crosslinking agents, aromatic divinyl compounds (especially divinylbenzene), which are linked by chains containing aromatic groups and ether bonds, are preferably used in toner resins from the viewpoint of fixing properties and anti-offset properties. diacrylate compounds, and it is particularly desirable that at least one of these two be contained in the binder resin.

In addition, examples of binder resins for toners particularly used in pressure fixing systems include low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acids, polyamide resin, It is preferable to use polyester resin or the like alone or in combination.

The magnetic materials contained in the magnetic toner of the present invention include iron oxides such as magnetite, maghematite, and ferrite, and iron oxides including other metal oxides; Fe, Co, and Ni.
or these metals and AR, Go,
Cu, Pb, Mg, Ni, Sn, Zn, S
b, Be.

Bi, Cd, Ca, Mn, Se, Ti, W
, alloys with metals such as V, and mixtures thereof.

These ferromagnetic materials have an average particle size of about 0.1 to 2 pm, and a magnetic property with a coercive force of 20 to 150 when IOK Oe is applied.
0e saturation magnetization 50 to 200 emu/g (preferably 5
0-10100e/g), residual magnetization 2-20emu/
H is desirable.

Further, in the magnetic toner of the present invention, a charge control agent is preferably added internally or externally to the toner so as to obtain a triboelectric charge amount suitable for the developing method. As the positive charge control agent used in the present invention, known ones can be used. For example, nigrosine and its modified products with fatty acids, fatty acid metal salts, etc., quaternary ammonium salts, diorganotin oxide, diorganotin borate, etc. alone or in combination. Can be used in combination of more than one species. Among these, nigrosine type and quaternary ammonium salts are particularly preferably used.

In addition, a monopolymer of the monomer represented by the general formula or a copolymer with a polymerizable monomer such as styrene, acrylic ester, or methacrylic ester as described above can be used as a positive charge control agent. In some cases, it also functions as (a part or all of) a binder resin.

On the other hand, known negative charge control agents can be used in the present invention, such as carboxylic acid derivatives and metal salts thereof,
Alkoxylates, organometallic complexes, chelate compounds, etc. can be used alone or in combination of two or more. Among these, acetylacetone metal complexes, salicylic acid metal complexes, naphthoic acid metal complexes, and monoazo metal complexes are particularly preferably used.

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

Furthermore, additives may be mixed into the toner of the present invention as required. Examples of such additives include Teflon,
Polyvinylidene fluoride, lubricants such as fatty acid metal salts, abrasives such as cerium dioxide, strontium titanate, silicon carbide, etc.; coroiglusilica, alumina, or silicone oil, various modified silicone oils, silane coupling agents, silane cups with functional groups. Fluidity imparting agents such as silica and alumina treated with ring agents, anti-caking agents; conductivity imparting agents such as carbon black and tin oxide;
Alternatively, there may be a fixing aid such as low molecular weight polyethylene. In addition, in order to improve the releasability during hot roll fixing, waxy substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, and Sasol wax may be added to the toner of the present invention at 0°5 to It is also possible to add about 5% by weight.

In manufacturing the toner according to the present invention, the toner constituent materials as described above are thoroughly mixed using a ball mill or other mixer, then thoroughly kneaded using a heat kneader such as a hot roll kneader or an extruder, and after cooling and assimilation. Preferably, the toner is obtained by mechanical pulverization or classification; another method is to obtain the toner by dispersing the constituent materials in a binder resin solution and then spray drying; Polymerization toner production method in which a monomer is mixed with a predetermined material to form an emulsified suspension and then polymerized to obtain a toner: Alternatively, in a so-called microcapsule toner consisting of a core material and a shell material, the core material or the shell material , or a method in which a predetermined material is contained in both of these can be applied.

In the present invention, the charge amount of the toner layer on the carrier was determined using the so-called attraction 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 in a filter in the inner cylinder. The weight of the top toner layer can be calculated. At the same time, this method allows the amount of charge on the toner carrier to be determined by measuring the amount of charge accumulated in an inner cylinder that is electrostatically shielded from the outside.

In the present invention, fine line reproducibility was measured by the following method. In other words, an image of an original manuscript with thin lines exactly 100 μm in width was copied under appropriate copying conditions as a sample for measurement, and a Luzex 450 particle analyzer was used as the measuring device to measure the line width using an indicator from the enlarged monitor image. Perform measurements. At this time, since the line width measurement position has irregularities in the width direction of the fine line image of the toner, the average line width of the irregularities is taken as the measurement point. From this, the value (%) of fine line reproducibility is calculated using the following formula.

2 rishi length fJjl 1llf+ IIUUIAm1
In the present invention, resolution was measured by the following method. In other words, it is a pattern consisting of five thin lines with equal line width and spacing, and 2.8.3.2.3.6 within 1 mm.
．． 4.0.4.5.5.0.5.6.6.3゜7.1.
8. The original image drawn as if there were 0 lines (
Ru. The number of images with clearly separated thin lines (lines/mm) is obtained by observing the images obtained by copying the original document with these 10 types of line images under appropriate copying conditions using a magnifying glass.
Let be the value of resolution. The larger this number, the higher the resolution.

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

Further, FIG. 9 shows the relationship between the volume average particle diameter of the magnetic toner of the present invention and the amount of charge on the toner carrier.

Example 1 The following magnetic toner copying test was conducted using an image forming apparatus having a developing device equipped with the selenium photosensitive drum described above.

Incidentally, the waveform of the alternating bias voltage used in this example is shown in FIG. (Duty ratio: 20%) The above materials were thoroughly mixed in a blender, and then kneaded in a twin-screw kneading extruder set at 150°C.

The obtained mixed material was cooled, coarsely pulverized with a cutter mill, and then finely pulverized with a pulverizer using a jet stream.
The resulting finely pulverized powder was classified using a fixed wall type wind classifier to produce classified powder. Furthermore, the obtained classified material is strictly classified and removed at the same time to remove ultrafine powder and coarse powder using a multi-division classifier that utilizes the Coanda effect (Nippon Steel Mining Co., Ltd.'s Elbow Jet Classifier) to obtain black fine powder (61F1 toner). I got it. Table 1 shows the particle size distribution of this magnetic toner.

To 100 parts of the obtained black fine powder magnetic toner, 0.6 part of hydrophobic dry silica (fBET specific surface area: 300 m''7 g) was added and mixed in a Henschel mixer.

This magnetic toner was used in the image forming apparatus described above for 10,000 yen.
Table 2 shows the results of 0 copies and the volume average particle diameter on the toner carrier, and also shows the amount of charge of the toner on the toner carrier measured during the test.

As is clear from Table 2, it has excellent resolution and fine line reproducibility,
Images with high image density without white background fog were stably obtained, and no carrier memory occurred. Also 15℃, 10%
Similarly good results were obtained under RH.

Example 2.3 A particle size distribution as shown in Table 1 was obtained by changing the amount of magnetic material, charge control agent, and silica added instead of the magnetic toner used in Example 1, and controlling the fine grinding and classification conditions. A copying test was conducted in the same manner as in Example 1 except that the toner was used. The results are shown in Table 2, and stable and clear images were always obtained. Furthermore, 15℃, lo%RH
Similar results were obtained in the copy test below.

Example 4 Table 1 shows the particle size distribution of a magnetic toner obtained using the above materials in the same manner as in Example 1.

Table 2 shows the results of the same copying test as in Example 1 using this toner.However, as a developing bias power source, the alternating bias voltage waveform (duty ratio 3
0%) was used.

As is clear from this table, images of excellent quality can be obtained.
Similar results were obtained at 15° C. and 10% RH.

Examples 5 and 6 A particle size distribution as shown in Table 1 was obtained by changing the amount of magnetic material, charge control agent, and silica added instead of the magnetic toner used in Example 4, and controlling the pulverization and classification conditions. A copying test was conducted in the same manner as in Example 4 except that the toner was used. The results are shown in Table 2.Although stable, high-quality images were always obtained, in Example 5, the memory of the carrier was lighter than the toner carrier. Similar results were also obtained in a copying test at 15° C. and 10% RH.

Example 7 The alternating bias voltage waveform is shown in FIG. 8 (duty ratio 3
5%), and the same copying test as in Example 1 was conducted except that a developing bias power source was used. The results are shown in Table 2.

In this case, similar to Example 1, good results were obtained.

Comparative Example 1 The alternating bias voltage waveform is shown in Fig. 3 (duty ratio 5
A copying test was carried out in the same manner as in Example 1, except that a developing bias power source (0%) was used. The results are shown in Table 2.
Compared to Example 1, the gradation was inferior, the resolution and line reproducibility were slightly inferior, and some white background fog was observed. Memory on the toner carrier was also observed.

Comparative Example 2 A copying test was conducted in the same manner as in Example 1 except that a toner having a particle size distribution as shown in Table 1 was used from the coarsely crushed product obtained in Example 1 by controlling the crushing and classification conditions. . The results are shown in Table 2. Initially, a good image was obtained, but after repeated copying, the image gradually became rough and the resolution and fine line reproducibility became poor.

Comparative Example 3 Table 1 shows the particle size distribution of a magnetic toner obtained using the above materials in the same manner as in Example 1, and Table 2 shows the results of a copying test conducted in the same manner as in Example 1.

The image density was low due to hollow areas, and the line thickness was not stable.

Comparative Example 4 Table 1 shows the particle size distribution of a magnetic toner obtained using the above materials in the same manner as in Example 1.

Table 2 shows the results of a copying test conducted using this toner in the same manner as in Example 1.

Good images were obtained initially, but after repeated copying, a decrease in density was observed, and memory on the carrier also occurred.

Furthermore, in a copying test conducted at 15° C. and 10% RH, this tendency became more pronounced.

(The following is a blank space) [Effects of the Invention] Since the present invention is a magnetic toner having a specific particle size distribution and triboelectric charge, it exhibits excellent effects similar to the case when applied to a developing method using an asymmetric developing bias. It is something.

(1) It is a magnetic toner that has excellent durability, has high image density, and provides images without fogging on white backgrounds.

(2) It is a magnetic toner that is rich in gradation, has excellent resolution and fine line reproducibility, and provides high-quality images.

(3) It is a magnetic toner that does not cause a decrease in image density even under low humidity.

[Brief explanation of the drawing]

Fig. 1 shows a schematic diagram of the alternating bias voltage waveform, Fig. 2 shows a schematic diagram of flying toner adhesion, Fig. 3 shows a schematic diagram of the alternating bias voltage waveform, and Fig. 4 explains the bias component. FIG. 5 shows a schematic explanatory diagram of the developing device,
Figures 6 to 8 show schematic diagrams of alternating bias voltage waveforms, and Figure 9 is a graph plotting the volume average particle diameter of magnetic toner and the target amount (μc/g) on the toner carrier. FIG. T...Toner T1...Toner thin layer T2
...Toner image A...Development area α...Gap between latent image carrier and toner carrier So...Alternating bias application means Sl...DC bias application means 1...Latent image support 21 ...Hopper 22...
・Toner carrier 23...magnetic roller 24...
doctor blade

Claims (1)

[Scope of Claims] A latent image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on the surface are arranged with a certain gap in a developing section, and the magnetic toner is placed on the toner carrier. The thickness is regulated to be thinner than the gap, and the toner is conveyed to the developing section, and a DC voltage and an asymmetrical alternating voltage are applied between the toner carrier and the latent image carrier, and the developing side of the alternating bias voltage including the direct current bias voltage is applied. Convert the voltage component to the reverse development side voltage component (stripping voltage component)
In a magnetic toner having at least a binder resin and magnetic powder used in a developing method in which the voltage is the same as or larger than the voltage on the developing side and the application time of the developing side voltage is smaller than that of the reverse developing side voltage, the magnetic toner has: Magnetic toner particles containing 12% or more by number of magnetic toner particles having a particle size of 5 μm or less, containing 33% or less by number of magnetic toner particles having a particle size of 8 to 12.7 μm, and having a particle size of 16 μm or more is contained in an amount of 2% by volume or less, and the volume average particle size of the magnetic toner is 4 to 1.
0 μm, and the amount of triboelectric charge of the magnetic toner particles on the toner carrier and the volume average particle diameter of the magnetic toner are expressed by the following general formula (
A magnetic toner characterized by satisfying 1). 2(μc/g)+0.5(μc/g)R≦Q(μc/g
)≦20(μc/g)+0.5(μc/g)R...(
1) Indicates a real number such that 4≦R≦10, R represents the volume average particle diameter of the magnetic toner, and Q represents the absolute value of the amount of triboelectric charge of the magnetic toner on the toner carrier.