JP2769915B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a process of developing an electrostatic latent image formed in 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.

[Prior art] As a conventional example, USP 3,866,574, USP
3,890,929 and USP 3,893,418.

It has been proposed to provide a gap between the latent image holding member and the toner carrier (toner), apply an asymmetrical AC pulse bias to these, and control the flight of the high-resistance one-component toner. FIG. 1 shows a schematic diagram of the waveform at that time. In detail, the gap between the latent image holding member and the toner holding member is 50 μm to 500 μm.
m (preferably 50-180 μm), frequency 1.5K-10KHz
(Preferably 4 to 8 KHz), development time is 10 μsec T _A 200
μsec (preferably 30 μsec T _A 200 μsec), stripping time 100 μsec T _D 500 μsec (preferably 100 μsec
T _D 180μsec), developing voltage V _A -150 V, stripping voltage V _D 400V, and V _D -V _A 800V (preferably -150VV _A
It is -200V and 400VV _D 450V) and the like. By this method, flying adhesion of toner particles to a non-image portion is prevented, and gradation and line reproducibility are improved. FIG. 2 shows the above schematic diagram.

As a latent image developing method using a high-resistance one-component developer (volume resistance of 10 ¹⁰ Ωcm or more), an impression developing method (US
P 3405682, etc.), a jumping development method (JP-A-5
5-18656 to 18659), and the jumping development method is particularly useful in a developing area which is the closest part between the toner carrier and the latent image holder. The toner is reciprocated between the developing carrier and the latent image carrier by the AC bias voltage applied to the toner, and finally is selectively transferred to and adhered to the surface of the latent image carrier according to the latent image pattern, thereby visualizing the image. Is done. These duty ratios are 50%, and the development time and the reverse development time are the same (see FIG. 3).

However, in the patent relating to the jumping development method, there is a method in which the duty ratio of an AC bias voltage applied between the toner carrier and the latent image carrier is controlled in accordance with the remaining amount of the developer in order to adjust the image density. . Here, the “duty ratio of the AC bias electric field” is defined as in the following equation.

a: An application time of an electric field component (developing-side bias component) having a polarity in a direction in which the toner is transferred to the latent image holding member side in one cycle of an AC bias in which the electric field polarity periodically changes alternately between positive and negative. At this time, the DC bias electric field has been removed.

b: Application time of an electric field component (reverse developing side bias component) having a polarity in the direction of separating the toner from the latent image holding member.

The development-side bias component refers to the portion a in FIG. 4 when the latent image potential of the latent image holding member is V _S (polarity is positive) and the polarity of the toner used is negative. The side bias component refers to a portion b in FIG.

With a developing method in which the absolute value of the alternating bias voltage is kept low to prevent toner from adhering to the non-image area and the developing voltage is further reduced as in the conventional example, a sufficient image density may not be obtained. .

Regarding the above conventional example, in the case of this developing method, the developing side bias voltage is large, so that the developing property of the solid latent image (high potential area) is high. The excess toner tends to be stripped off, resulting in images without gradation.

Also, the allowable range for setting the voltage (DC component and AC (V _pp & frequency)) is narrow. That is, adjust the voltage (lower DC
If you try to increase the density, for example, by increasing the amount of orAC), background contamination (white background fog) will occur. Increasing the AC frequency is effective for white background fog, but the reproducibility of characters and lines is poor (thin).

As a means for improving the above two developing methods, by increasing the developing electric field when the developing side bias is applied and setting the developing side time to a short time, the image density is high, gradation is obtained, and white background fog is obtained. Images can be obtained.

However, if the image forming method using such a developing method is repeatedly used, the image quality may be deteriorated due to a decrease in image density, an increase in white background fog, or a decrease 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 to be different from the initial value, and it was found that the deterioration of the image quality was due to the selective development of the toner.

In general, in the one-component developing method, when image formation is repeated, toner having a small particle size is deposited on the surface of the toner carrier.
Due to the mirroring power due to the high charge amount, the toner particles may adhere and hinder the triboelectric charging of other toner particles, increasing the number of toner particles not having a sufficient charge amount and causing a decrease in density. Such a phenomenon is particularly likely to appear under low humidity.

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

Therefore, if an image is formed in a state in which a consuming part (image part) and an unconsumed part (non-image part) are present on the toner carrier, a difference in density on the image (that is, a high density in the consuming part, At low concentration).

Such a phenomenon is hereinafter 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 memory is reduced for each rotation of the toner carrier. Therefore, when this phenomenon is light, the memory on the image is lost at one time, but when this phenomenon is heavy, it may appear repeatedly.

For this reason, a method of improving the smoothness of the surface of the toner carrier, improving the circulation of the toner on the toner carrier and improving the replacement of the toner on the toner carrier can be considered, but the smoothness of the surface of the toner carrier is considered. In this case, a new problem arises in that the toner is charged.

In order to solve the above-mentioned problem, it is necessary to consider conditions under which the toner is uniformly charged and the toner is effectively developed.

[Problems to be Solved by the Invention] An object of the present invention is to provide a developing method as described above in which a magnetic toner is uniformly coated on a toner carrier and the magnetic toner is uniformly and uniformly formed on the toner carrier. An object of the present invention is to provide an image forming method which can solve the problem of stable charging at the same time for a long period of time and makes flying of the magnetic toner more efficient.

Another object of the present invention is to provide a high image density, fine line reproducibility,
An object of the present invention is to provide an image forming method which is excellent in gradation and has no fogging and can obtain a clear, high-quality image for a long period of time.

Still another object is to provide an image forming method for preventing or reducing carrier memory.

Still another object is to provide an image forming method capable of obtaining a clear, high-quality image with high image density and no fog even under low humidity.

[Means and Actions for Solving the Problems] According to the present invention, an electrostatic image holding member for holding an electrostatic image and a toner holding member for holding a magnetic toner on the surface are arranged with a certain gap in a developing section. And controlling the magnetic toner on the toner carrier to a thickness smaller than the gap, transporting the magnetic toner to the developing unit, and developing the toner while applying an alternating electric field to the toner in the developing unit. And the asymmetrical alternating voltage, the developing side voltage component of the alternating bias voltage including the DC bias voltage is equal to or larger than the reverse developing side voltage component (stripping voltage component), and the application time of the developing side voltage is reversed. The FeO content of the magnetic iron oxide contained in the magnetic toner is 30 to 40% by weight based on the iron element in the magnetic iron oxide. When the sulfuric acid aqueous solution of magnetic iron oxide is used, x is the dissolution rate of iron element (% by weight) × 100, and y is the content rate (% by weight) of Fe ^{2+ in} the dissolved iron element × 100. When 0 <x ≦ 30, y ≦ 33.3, y ≧ 0.26x + 16.0
A magnetic toner containing a magnetic iron oxide and a binder resin in a range satisfying both formulas, wherein the magnetic toner contains 12% by number or more of magnetic toner particles having a particle size of 5 μm or less, and 8 to 12.7 μm 33% by number or less of magnetic toner particles having a particle size of 2.0% by volume or less, and has a particle size distribution in which the volume average particle size of the magnetic toner is 4 to 10 μm. An image forming method characterized by the following.

Since the image forming method of the present invention uses an asymmetric developing bias in an alternating electric field during development, it is excellent in effectively flying toner, and can achieve both high density and reduction of fog. it can.

The distribution of FeO (Fe ²⁺ ) in the surface layer of the magnetic iron oxide contained in the magnetic toner according to the present invention has the effect of relaxing the charge unique to FeO at the microscopic interface. And contributes to uniform charging, so that the toner coat layer on the toner carrier can be uniform and stable against various environments.

Further, since the volume average particle diameter is 4 to 10 μm and the toner has a specific particle size distribution, the toner coat layer in the toner carrier is prevented from being excessively thick. Thus, a uniform toner coat can be formed.

Further, the image is effectively developed by the asymmetric development bias.

As a result, this is an image forming method which has a high image density, is excellent in fine line reproducibility and gradation, has no fog, and can obtain a clear and high quality image for a long period of time.

 Hereinafter, the present invention will be described specifically.

In the magnetic toner used in the image forming method of the present invention, the FeO content of the magnetic iron oxide contained in the magnetic toner is 30 to 40% by weight based on the iron element, and is preferably
32-38% by weight is good.

If the amount is less than 30% by weight, excessive accumulation of triboelectric charge of the toner under low humidity cannot be alleviated.
As the FeO component remains on the particle surface, the charge leakage effect increases, and sufficient charge retention ability as toner cannot be maintained.

The magnetic iron oxide used in the magnetic toner of the present invention, the iron element dissolution rate when the magnetic iron oxide using aqueous H ₂ SO ₄ (wt%) × 100 x, Fe in the dissolved iron element ^{2 +} Content ratio (% by weight) x 100, y = 0 <x ≤ 30 It is important to satisfy

The content of Fe ²⁺ existing when the iron element dissolution rate is up to 30% by weight indicates the content of FeO in the surface layer of the magnetic iron oxide.

A toner using a magnetic iron oxide exceeding the range of the formula (a-1) impairs moisture resistance due to an excessive FeO component, significantly lowers resistance, and increases the tendency that the effects intended by the present invention cannot be sufficiently exhibited. .

On the other hand, when the amount exceeds the range of the expression (a-2), the amount of FeO present in the surface layer is small, so that the effect of reducing the charge amount cannot be expected.

In the present invention, the iron element dissolution rate (x) and the Fe ²⁺ content rate (y) are calculated as follows.

About 25 g of the magnetic powder slurried with deionized water is added to a 5 l beaker together with the deionized water while washing with about 805 ml of deionized water.

Next, while maintaining the temperature at about 50 ° C. and the stirring speed at about 200 rpm, about 6952 ml of special grade H ₂ SO ₄ is added to start dissolution.
At this time, the magnetic iron oxide concentration is about 5 g / l, and the H ₂ SO ₄ aqueous solution is about 5 N. From the start of dissolution, 20 ml is sampled every 10 minutes until the whole is dissolved and clear, passed through a 0.1 µ membrane filter, and the filtrate is collected.

10 ml of the filtrate is quantified for iron by plasma emission spectroscopy (ICP).

 The dissolution rate of iron element is calculated by the following equation.

The content of Fe ²⁺ in each sample is 10 ml
Approximately 100 ml of ion-exchanged water is added thereto, and the mixture is titrated with an N / 10 · KMnO ₄ aqueous solution. A blank test is performed in parallel, and the ratio (% by weight) of Fe ^{2+ to} the iron element can be determined by the following equation.

For the measurement of the FeO content based on the iron element, 1 g of magnetic iron oxide is placed in a 500 ml beaker, 50 ml of deionized water is added, and 20 ml of special grade sulfuric acid is added to completely dissolve the magnetic iron oxide. Then add 100 ml of deionized water and titrate with 0.1 N KMnO ₄ solution.

The specific gravity (% by weight) of FeO to the iron element is determined by the following equation.

* Quantified by ICP.

The number of magnetic toner particles having a particle diameter of 5 μm or less is preferably 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. When the number of magnetic toner particles having a particle size of 5 μm or less is less than 12% by number, the amount of magnetic toner particles effective for high image quality is small. In particular, as the toner is used by continuing copying or printing out, the effective magnetic toner particles are effective. The amount of the component decreases, the balance of the particle size distribution of the magnetic toner as shown in the present invention deteriorates, and the image quality gradually decreases. On the other hand, if the content exceeds 60% by number, the magnetic toner particles tend to aggregate with each other, resulting in a toner mass larger than the original particle size, resulting in rough image quality, reduced resolution, or an edge portion of the latent image. In some cases, the density difference between the image and the inside becomes large, and the image may be slightly hollow.

According to the study of the present inventors, magnetic toner particles of 5 μm or less are essential components for stabilizing the volume average particle diameter of the magnetic toner on a toner carrier (hereinafter referred to as a sleeve) during image formation and durability. It turned out to be.

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

The number of particles in the range of 8 to 12.7 μm is preferably 33% by number or less, more preferably 1 to 33% by number. If the content is more than 33% by number, the image quality is deteriorated and the development is performed more than necessary, that is, the toner is excessively applied, which leads to an increase in toner consumption. On the other hand, if it is less than 1% by number, it may be difficult to obtain a high image density. The number% (N%) and the volume% of the magnetic toner particles having a particle size of 5 μm or less
(V%), there is a relationship of N / V = −0.04N + k, and 4.
Indicates a positive number in the range of 5 ≦ k ≦ 6.5. Preferably 4.5 ≦ k ≦
6.0. As described 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 diameter smaller than 5.0 μm is small, and the image density, resolution, and sharpness tend to be poor. Excessive presence of fine magnetic toner particles, which was conventionally considered unnecessary, contributes to the closest packing of the toner in development and contributes to formation of a uniform image without roughness. In particular, by uniformly filling the fine lines and the contours of the image, the sharpness is further enhanced visually. 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, in terms of production, the conditions such as classification tend to be strict to satisfy the condition of k <4.5, which is disadvantageous in terms of yield and toner cost. Also, k> 6.5
Then, due to the presence of fine powder more than necessary, the balance of the particle size distribution is lost while repeated copying is continued, the cohesion of the toner is increased, and triboelectric charging is not effectively performed, resulting in poor cleaning and fogging. Sometimes.

The content of the magnetic toner particles having a particle diameter of 16 μm or more is preferably 2.0% by volume or less, more preferably 1.0% by volume.
Or less, more preferably 0.5% by volume or less.
When the content is more than 2.0% by volume, not only does it hinder the reproduction of fine lines, but also in the transfer, coarse toner particles of 16 μm or more protrude from the thin layer surface of the toner particles developed on the photoreceptor. The delicate state of contact between the photoreceptor and the transfer paper via the layer is made irregular, causing fluctuations in the transfer conditions and causing poor transfer images.

Further, in the image forming method of the present invention, if the toner particles having a size of 16 μm or more do not have a sufficient charge amount, they cannot fly on the latent image holding member, remain in large amounts on the toner holding member, change the particle size distribution, In many cases, the frictional charging of the toner particles is inhibited, the developing ability is reduced, and the shape of the spikes is disturbed, thereby causing deterioration of image quality.

On the other hand, magnetic toner particles having a particle diameter of 16 μm or more, unlike magnetic toner particles having a particle diameter of 5 μm or less, are relatively difficult to be consumed even when image-forming durability is performed. Since the volume average particle diameter is gradually increased, M / S on the sleeve is undesirably increased.

In the present invention, the volume average diameter of the magnetic toner is 4 to 10 μm.
m, preferably 4 to 9 μm, which cannot be considered separately from the above-mentioned components. When the volume average particle diameter is less than 4 μm, in applications having a high image area ratio such as a graphic image, there is a problem that the amount of applied toner on transfer paper is small and the image density is low. This is considered to be due to the same reason as described above for lowering the density inside the edge portion of the latent image. If the volume average particle size exceeds 10 μm, the resolution is not good, and if the use is continued at the beginning of the transfer, the particle size distribution changes and the image quality tends 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 photoreceptor, and reproduce a dot latent image such as a halftone dot and a digital image. To provide an image which is excellent in gradation and resolution. Furthermore, high image quality can be maintained even when copying or printing out is continued, and even in the case of high-density images, good development can be performed with less toner consumption than conventional magnetic toners. In addition, there is an advantage in downsizing 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.

Although the particle size distribution of the toner can be measured by various methods, in the present invention, the measurement was performed using a Coulter counter.

In other words, the Coulter Counter TA is used as a measuring device.
-An interface (manufactured by Nikkaki) that outputs the number distribution and volume distribution and a CX-1 personal computer (manufactured by Canon) are connected using Type II (manufactured by Coulter), and the electrolyte is approximately 1% sodium chloride. Prepare 1% NaCl aqueous solution. For example, ISOTON-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, a surfactant as a dispersing agent, preferably an alkylbenzene sulfonate in 0.1 to 5 ml of the electrolytic aqueous solution 100 to 150 ml is used.
ml and then 2 to 20 mg of the measurement sample. The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the Coulter Counter TA-II was used, and a 100 μ aperture was used as an aperture. The particle size distribution was measured and the values according to the invention were determined therefrom.

A specific example of an apparatus that has performed the developing step in the present invention is shown in FIG. 5, and the configuration of the present invention will be described in more detail. However, this does not limit the present invention in any way.

In FIG. 5, reference numeral 1 denotes a latent image holding member (so-called photosensitive member) such as a rotating drum type in a transfer type electrophotographic method; a rotating drum type or the like in a transfer type electrostatic recording method; Electrostatic latent image is formed on the surface of a latent image holding member such as a photosensitive paper according to the method or an electrostatic recording paper according to the direct electrostatic recording method by a latent image forming process device or a process mechanism not shown in the drawing. Is moving in the direction of the arrow.

Reference numeral 2 denotes the overall reference number of the developing device, reference numeral 21 denotes a hopper containing toner, and reference numeral 22 denotes a rotating cylindrical body (hereinafter, referred to as a sleeve) as a toner carrier (developer layer supporting member). Is built in.

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, and is supported by a bearing. Is a doctor blade as a toner application member which is disposed close to, 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 is closely opposed to the surface of the latent image carrier 1 with a small gap α.

The surface moving speeds (peripheral speeds) of the latent image holder 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 between the latent image holding member 1 and the sleep 22;
By S ₀ and the DC bias voltage applying means S _1, a DC voltage and an AC voltage is superimposed is applied.

Thus, the substantially right half peripheral surface of the sleeve 22 is always in contact with the toner reservoir in the hopper 21, and the toner near the sleeve surface contacts the sleeve surface with the magnetic force of the magnetism generating means 23 in the sleeve as a magnetic adhesion layer, Adhered and held by force. Sleeve 22 is advice service as a thin layer toner layer T ₁ of the respective portions substantially uniform thickness in the process of adhering toner layer when driven rotating the sleeve surface passes through the doctor blade 24 position. The toner is charged mainly by frictional contact between the sleeve surface with the rotation of the sleeve 22 and the toner in the toner reservoir near the sleeve, and the thin toner layer surface of the sleeve 22 is brought into contact with the surface of the latent image holding member 1 with the rotation of the sleeve. And passes through the developing area A, which is the closest part between the latent image holding member 1 and the sleeve 22. During this passage, the toner of the thin toner layer on the side of the sleeve 22 flies by the DC and AC electric fields generated by the DC and AC voltages applied between the latent image holder 1 and the sleeve 22, and the surface of the latent image holder 1 in the developing area A And the sleeve 22 reciprocate. And finally the toner image T ₂ are sequentially formed by selectively transition adhere according to the potential pattern of the latent image to the toner latent image bearing member 1 surface of the sleeve 22 side.

The sleeve surface on which the toner has been selectively consumed after passing through the developing area A receives the toner re-supply by re-rotating into the toner reservoir of the hopper 21, and the toner thin layer of the sleeve 22 is always supplied to the developing area A. T ₁ side is rotated, repeatedly copying step is performed.

By the way, such a developing method (one-component non-contact developing method)
As one of the problems in the case of adopting the method, there is a case where a phenomenon in which the developing property decreases due to an increase in the adhesive force of the toner near the sleeve surface occurs. In other words, the rotation of the sleeve 22 causes the toner and the sleeve to always come into contact friction with each other, and as the amount of charge of the toner gradually increases, the electrostatic force (Coulomb force) with the sleeve increases, and the flying force of the toner to the latent image holding member 1 Weakens and stays near the sleeve, hinders the triboelectric charging of other toner,
This is a phenomenon that causes a decrease in developability. This occurs due to low humidity or repetition of the copying process. Further, the above-described carrier memory is generated from the same mechanism. In the sleeve used in the present invention, triboelectric charging is efficient, the toner on the toner carrier is sufficiently charged, the triboelectric charging ability of the toner is exhibited, and the effect of improving the developing property is improved. It tends to cause phenomena.

The force for causing the toner to fly from the sleeve to the latent image holding member 1 must be accelerated by an AC bias electric field so that the toner can sufficiently reach the latent image surface. The force is given by = m ·, where m is the weight of the toner. If the charge of the toner is q, the distance from the sleeve is d, and the alternating bias electric field is The force of the toner reaching 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 cause toner of 5 μm or more that easily collects near the sleeve to fly, the electric field may be increased. But,
Simply increasing the developing-side bias voltage causes the toner particles to fly to the latent image side irrespective of the latent image pattern, and toner particles having a size of 5 μm or less have a strong tendency to cause background fog.
Further, ground fog can be prevented by increasing the reverse development bias voltage, but when a large alternating bias electric field is applied between the latent image holding member 1 and the sleeve 22, discharge is directly generated between the latent image holding member 1 and the sleeve 22, The image quality is significantly disturbed.

Also, when the reverse developing bias voltage is increased, not only the non-latent image portion but also the toner developed into the latent image pattern is peeled off, and the reflection power on the latent image holding member is relatively weak.
The toner particles having a size of about 12.7 μm are removed, the toner adhesion of the latent image portion is deteriorated, and the visible image pattern is disturbed.

From the above results, it is necessary to cause the toner in the vicinity of the sleeve to fly and reciprocate without increasing the alternating bias electric field so much and keeping the reverse developing side bias voltage low.

Therefore, the present invention achieves the above object by providing an image forming method that can have not only the magnitude of an alternating bias electric field but also an application time t and a triboelectric charge amount suitable for a developing bias to be controlled on a toner carrier. did. In other words, the developing bias electric field is increased without changing the frequency of the alternating bias, the application time of the developing bias electric field is shortened, and accordingly, the reverse developing bias electric field is suppressed low, and the application time is increased. A method of controlling the duty ratio of the alternating bias was used.

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

a: The application time of the electric field component of the polarity in the direction of transferring the toner to the latent image holding member side in one cycle of the AC bias in which the electric field polarity alternately changes positively and negatively. At this time, the DC bias electric field has been 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 holding member side.

By using this method, the developing side bias electric field is sufficiently strengthened, so that the toner particles of 5 μm or less, which is an essential component for improving the image quality on the sleeve, are effectively fly and reciprocated. To prevent adhesion to That is, it is difficult to lower the image density and to generate the carrier memory.

Furthermore, even if the reverse development side bias electric field is kept low,
Conversely, by applying the voltage for a sufficiently long time, a force for separating excess toner adhering to portions other than the latent image pattern from the latent image holding member 1 can be obtained, and the background fog can be prevented.

At this time, since the reverse-developing-side bias electric field is kept low, toner particles of 8 to 12.7 μm, which are essential components for the toner application, are not stripped. Sixth 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 separating from the latent image holding member is the same by increasing the time even if the bias electric field is weak. In addition, since the toner image developed into the latent image pattern is not disturbed, good image quality with gradation is obtained.

By the way, the sleeve used in the present invention is excellent in triboelectric charging ability and uniformly charges the magnetic toner of the present invention, so that good development properties can be obtained by the developing alternating electric field of the present invention. Accordingly, an image having a high density without fog can be obtained, and a 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 developing-side bias to achieve high image quality, and the sleeve of the present invention does not adhere to the vicinity of the sleeve. 8-12.7
The same can be said for the μm toner particles. The toner is sufficiently developed by the developing-side bias to achieve high density and gradation, and is not stripped by the latent image holding member by the reverse-developing side bias. There is no dropout or line disturbance.

Further, with the developing-side bias of the present invention, when the spike flies and the tip of the spike comes into contact with the latent image holding member, toner particles near the tip, small-sized particles, and large-charged particles are reflected by the mirror. The particles adhere to the latent image holding member and are visualized, but the particles at the rear end of the ear or particles having a low charge amount are pulled back onto the toner carrier by the reverse developing side bias,
Although the shape of the ear is destroyed and the tailing and scattering caused by the ear are reduced, the effect of the sleeve and the magnetic toner of the present invention is great because the ear is originally formed in a uniform and small state.

Further, the magnetic toner having the specific particle size distribution on the sleeve having the specific surface of the present invention is supplied to the latent image one after another by the developing side bias of the present invention, so that the toner is not insufficiently supplied. .

According to the present invention, since the developing bias electric field of the alternating bias electric field is strong, the toner near the sleeve can also fly,
The toner having a large charge amount near the sleeve is more strongly developed into a latent image pattern. Therefore, it can strongly adhere to the weak latent image pattern due to the electrostatic force of the toner with a high charge amount, and can develop images with good edge effect and high resolution, and is an effective component for realizing high image quality. Some 5 μm
The following magnetic toner particles can be effectively used, and extremely good image quality can be obtained.

In the developing method used in the present invention, the gap between the sleeve 22 and the latent image holding member 1 was set at 0.3 mm in the embodiment, but from 0.1 mm to 0.5 mm is sufficient for the developing method according to the present invention. Development is possible.

Since the developing-side bias is larger than in the conventional developing method, it is possible to develop even if the gap between the sleeve 22 and the latent image holding member 1 is large.

If the absolute value of the alternating bias voltage is 1.0 kV or more, a sufficiently satisfactory image can be obtained. Further, considering the leakage to the latent image holding member, the absolute value of the alternating bias voltage is 1.0 kV.
Above, 2.0kV or less is desirable. However, this leak naturally varies depending on the gap between the sleeve 22 and the latent image holding member 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. This is because in the low frequency region where the number of reciprocating movements of the toner is small, the pressing force of the toner against the latent image holding member due to the developing bias electric field becomes too strong even in the non-image area, and the toner is stripped off by the reverse developing bias electric field. This is probably because the toner attached to the non-image area cannot be completely removed. When the frequency is 5.0 kHz or more, a bias electric field on the reverse development side is applied before the toner sufficiently contacts the latent image holding member, and the developability is significantly reduced. That is, the toner itself cannot respond to the high-frequency electric field.

In particular, according to the present invention, the frequency of the alternating bias electric field is 1.5 k.
The optimum image quality was shown from Hz to 3kHz.

Lastly, the duty ratio that satisfies the alternating bias electric field waveform according to the present invention may be less than approximately 50%, but in consideration of image quality, the duty ratio is preferably 10% and 40%. When the duty ratio exceeds 40%, the above-described drawbacks become noticeable, and the effect of the present invention for further improving image quality is weakened. If the duty ratio is less than 10%, the above-described alternating bias electric field response of the toner itself is deteriorated, and the developability is reduced. Particularly, the optimum value of the duty ratio is 15% ≦ duty ratio ≦ 35%.

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

Examples of the binder resin used for the magnetic toner in the present invention include styrene, o-mer styrene, m-mer styrene, p-mer styrene, p-methoxy styrene and p-methoxy styrene.
-Phenylstyrene, p-chlorostyrene, 3,4-dicrostyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, Styrene such as pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene and derivatives thereof; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene Unsaturated vinylenes such as butadiene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; methyl methacrylate, methacrylic acid Ethyl acrylate, propyl methacrylate, n-butyl methacrylate, methacrylate Methacrylates such as isobutyl acrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate; methyl acrylate , Ethyl acrylate, n-butyl acrylate, isobutyl acrylate,
Propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate,
Acrylic esters such as 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 pyrrole;
N-vinyl compounds such as vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone; vinylnaphthalenes; acrylic or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide; acrylic acid, methacrylic acid, maleic acid, and fumaric acid A vinyl compound derivative having a carboxyl group; a half ester such as maleic acid half ester and fumaric acid half ester; a maleic anhydride, a maleic acid ester, a fumaric acid ester derivative; Polymers, copolymers: polyester, polyurethane, epoxy resin, polyvinyl butyral, rosin, modified rosin, terpene resin,
Phenol resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, haloparaffins, paraffin waxes and the like can be used alone or in combination.

Among them, styrene resins, acrylic resins, and polyester resins are particularly preferably used as the binder resin in consideration of the development 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 the offset resistance as a toner.

Aromatic divinyl compounds, for example, divinylbenzene,
Divinylnaphthalene and the like; diacrylate compounds linked by an alkyl chain, for example, 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 with methacrylates; alkyl chains containing ether linkages 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 the like Compounds in which acrylate is replaced with methacrylate; diacrylate compounds linked by a chain containing an aromatic group and an ether bond, for example, polyoxyethylene ( ) -2,2-bis (4-hydroxyphenyl) propane diacrylate, polyoxyethylene (4) -2,2-bis (4-hydroxyphenyl) propane diacrylate, and acrylates of the above compounds as methacrylates Substitutes; further, polyester-type diacrylate compounds, for example,
The brand name MANDA (Nippon Kayaku) is listed. As the polyfunctional crosslinking agent, pentaerythritol triacrylate,
Trimethylol ethane triacrylate, trimethylol propane triacrylate, tetramethylol methane tetraacrylate, oligoester acrylate, and acrylates of the above compounds replaced with methacrylate; triallyl cyanurate, triallyl trimellitate; Can be

These crosslinking agents are preferably used in an amount of about 0.01 to 5 parts (more preferably, about 0.03 to 3 parts) based on 100 parts of the other monomer components.

Among these crosslinking agents, those which are preferably used in the toner resin from the viewpoint of fixability and anti-offset property include an aromatic divinyl compound (particularly, divinylbenzene), a chain containing an aromatic group and an ether bond. Diacrylate compounds, and it is particularly desirable that at least one of the two is contained in the binder resin.

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

The magnetic iron oxide contained in the magnetic toner of the present invention has an average particle diameter of about 0.1 to 2 μm, and has a magnetic property at 10 ke applied of a coercive force of 20 to 150 e and a saturation magnetization of 50 to 200 emu / g (preferably 50 to 200 emu / g).
~ 100 emu / g) and those having a residual magnetization of 2-20 emu / g are desirable. It is preferable that the magnetic toner contains 40 to 150 parts by weight of magnetic iron oxide based on 100 parts by weight of the binder resin.

In the magnetic toner of the present invention, it is preferable to use a charge control agent internally or externally added to the toner. As the positive charge control agent used in the present invention, known agents can be used, for example,
Modified products of nigrosine and fatty acid metal salts thereof, quaternary ammonium salts, diorganotin oxide, diorganotin borate, and the like can be used alone or in combination of two or more. Of these, nigrosine and quaternary ammonium salts are particularly preferably used.

Also, the general formula Or a copolymer with a polymerizable monomer such as ethylene, acrylate or methacrylate as described above can be used as the positive charge control agent. It also has a function as (part of or all of) the resin.

On the other hand, as the negative charge control agent used in the present invention, known agents can be used. For example, a carboxylic acid derivative and a metal salt thereof, an alkoxylate, an organic metal complex, a chelate compound and the like 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, if necessary, any appropriate pigment or dye can be used as a colorant.

Further, an additive may be added to the toner of the present invention as needed. Such additives include lubricants such as, for example, Teflon, polyvinylidene fluoride, metal salts of fatty acids;
Abrasives such as cerium oxide, strontium titanate, silicon carbide; colloidal silica, alumina, or silicone oil, various modified silicone oils, silane coupling agents, silica treated with a silane coupling agent having a functional group, alumina, etc. Fluidization imparting agents, anti-caking agents; conductivity imparting agents such as carbon black and tin oxide; and fixing aids such as low molecular weight polyethylene. Further, for the purpose of improving the releasability at the time of hot roll fixing, low molecular weight polyethylene, low molecular weight polypropylene,
A wax-like substance such as microcrystalline wax, carnauba wax and sasol wax can be added to the toner of the present invention in an amount of about 0.5 to 5% by weight.

In producing the toner according to the present invention, the above-mentioned toner constituent materials are sufficiently mixed by a ball mill or other mixer, then kneaded well using a heat kneader of a hot roll kneader or an extruder, and cooled and solidified. A method of obtaining a toner by mechanical pulverization and classification is preferable. Alternatively, a method of obtaining a toner by dispersing a constituent material in a binder resin solution and spray-drying; or forming a binder resin A polymerized toner manufacturing method in which a predetermined material is mixed with a monomer to form an emulsified visual solution and then polymerized to obtain a toner; or, in a so-called microcapsule toner comprising a core material and a shell material, a core material or a shell material Or a method in which both of them contain a predetermined material; and the like.

In the present invention, the charge amount of the toner layer on the carrier was determined using a so-called suction Faraday cage method.
In the 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, collected by a filter of the inner cylinder, and the toner carrier is increased from the weight increase of the filter. The weight of the toner layer per unit area above can be calculated. At the same time, the charge amount on the toner carrier can be determined by measuring the charge amount accumulated in the inner cylinder shielded by electrostatic droplets from the outside.

In the present invention, the resolution was measured by the following method. That is, a pattern consisting of five fine 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 it were there. Observe an image obtained by copying the original manuscript with these 10 line images under appropriate copying conditions with a magnifying glass, and determine the resolution value with the number of images (lines / mm) in which fine lines are clearly separated. I do.

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

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples.
This does not limit the invention in any way. All parts in the following formulations are parts by weight.

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

(Waveform Example 1) A developing bias power supply to which an alternating bias electric field having a waveform shown in FIG.

This alternating electric field has a peak to peak of 1400V, a frequency of 2000Hz, and a duty ratio of 20%.
It was used as a developing bias power supply.

(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 obtained by superimposing a DC voltage of +200 V on an alternating voltage having a peak to peak of 1400 V, a frequency of 2,000 Hz, and a duty ratio of 30%, and was used as a developing bias power supply.

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

This alternating electric field has a peak to peak of 1400V, a frequency of 2000Hz and a duty ratio of 35%.
It was used as a developing bias power supply.

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

This alternating electric field has a peak to peak of 1400V, a frequency of 2000Hz, and a duty ratio of 30%.
It was used as a developing bias power supply.

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

This alternating electric field has a peak to peak of 1400V, a frequency of 2000Hz and a duty ratio of 50%.
It was used as a developing bias power supply.

 Next, a production example of the magnetic iron oxide according to the present invention will be described.

Production example Dissolve 53 kg of FeSO ₄ in 50 l of water, then heat with steam, 40 ° C
While maintaining the above, a solution having an iron concentration of 2.4 mol / l is prepared and oxidized at about 70 ° C. while blowing air.

The obtained slurry is washed with water and dried to obtain a magnetic iron oxide. To control the content and distribution of FeO in the magnetic iron oxide, the oxidation time, the oxidation temperature, the drying time, the drying temperature, and if necessary Then, magnetic iron oxide was produced by reduction under an H ₂ atmosphere as shown in Table 1 (physical properties are shown in FIG. 11).

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

After the above materials were mixed well in a blender, they were kneaded with a biaxial kneading extruder set at 150 ° C. The obtained kneaded material was cooled, coarsely pulverized by a cutter mill, and then finely pulverized using a fine pulverizer using a jet stream, and the obtained finely pulverized powder was classified by a fixed wall type air classifier. A classified powder was produced. Furthermore, the ultrafine powder and the coarse powder are simultaneously strictly classified and removed by a multi-segment classification device (Nippon Mining Co., Ltd. Elbow Jet Classifier) using the Coanda effect to obtain black fine powder (magnetic toner). Obtained. Table 2 shows the particle size distribution of the magnetic toner.

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

 This toner is referred to as toner 1.

In the same manner as in Production Example 1 of the toner using the above materials, the second
A magnetic toner having a particle size distribution shown in the table was obtained, and 0.8 part of hydrophobic dry silica (BET ²⁰⁰ m ² / g) was added to 100 parts of the magnetic toner and mixed with a Henschel mixer.

 This toner is referred to as toner 2.

In the same manner as in Production Example 1 of the toner using the above materials, the second
Toner 3 having the particle size distribution shown in the table was obtained.

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

Production Example 5 of Toner The particle size distribution shown in Table 2 was obtained in the same manner as in Production Example 1 of the toner except that the magnetic iron oxide of Production Example 5 was used instead of the magnetic iron oxide of Production Example 1 in Production Example 1 of the toner. Was obtained.

Production Example 6 of Toner The particle size distribution shown in Table 2 was obtained in the same manner as in Production Example 1 of Toner except that the magnetic iron oxide of Production Example 1 was used instead of the magnetic iron oxide of Production Example 1. Was obtained.

Toner Production Example 7 Toner 7 having the particle size distribution shown in Table 2 in the same manner as in Toner Production Example 1 except that the finely crushed product obtained in Toner Production Example 1 was used and the fine pulverization classification conditions were changed. I got

Embodiments of image formation in Examples and Comparative Examples of the present invention,
Table 3 shows the results of a copy test of 10,000 sheets in each image forming mode.

Examples 1 to 6 As is clear from Table 3, images with high image quality were obtained. Similarly, good results were obtained at 15 ° C. and 10% RH.

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

Comparative Examples 1 and 3 Comparative Example 1 has a small content of FeO in the magnetic iron oxide (weight ratio of the magnetic iron oxide to the iron element) in the magnetic toner. The image density was lower than that of Example 1, and the fog and gradation were slightly inferior.

Comparative Example 2 This is an example in which the distribution of FeO in the magnetic iron oxide in the magnetic toner is remarkably large on the core side of the magnetic iron oxide. The image density was lower than that of Example 1, and the image density and the fog under 15 ° C. and 10% RH were noticeable.

Comparative Example 4 Although the image was a good image, character collapse due to excessive gluing was observed, and the toner consumption was large.

Comparative Example 5 Although the image was good at the beginning, the image quality gradually deteriorated with repeated copying, the gradation was poor, and the resolution was lowered.

Comparative Example 6 This is an example in which a developing bias having a duty ratio of 50% was used. However, tailing and carrying memory were observed, and were inferior in gradation and resolution as compared with Example 1.

[Effects of the Invention] The present invention is an image forming method in which a toner containing a specific magnetic iron oxide and having a specific particle size distribution is carried on a toner carrier and is developed using an asymmetric developing bias. Therefore, the following excellent effects are exhibited.

(1) The magnetic toner is uniformly coated on the toner carrier, and the toner particles on the toner carrier are uniformly and stably charged without excess or shortage, and the state of the spikes is uniform, thin, short, and dense. This is an image forming method for causing the image to fly efficiently and promote high image quality.

(2) An image forming method which has a high image density, is excellent in fine line reproducibility and gradation, and has no fog and can obtain a clear, high-quality image for a long time.

(3) An image forming method for preventing or reducing carrier memory.

(4) This is an image forming method capable of obtaining a clear, high-quality image with high image density and no fog even under low humidity.

[Brief description of the drawings]

FIGS. 1, 3, and 6 to 10 show schematic diagrams of alternating bias waveforms, FIG. 2 shows a schematic diagram of flying adhesion of toner, and FIG. 4 shows an explanatory diagram of bias components. FIG. 5 is a schematic explanatory view of a developing device, and FIG. 11 is a graph showing characteristics of a magnetic iron oxide obtained in a production example. T: toner, T ₁ : thin toner layer T ₂ : toner image, A: developing area α: gap between latent image holder and toner carrier 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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Umino 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Masaki Uchiyama 3-30-2, Shimomaruko, Ota-ku, Tokyo Canon Inside the corporation

Claims (1)

(57) [Claims] An electrostatic image holding member for holding an electrostatic charge image and a toner holding member for holding a magnetic toner on the surface are arranged at a fixed gap in a developing section, and the magnetic toner is placed on the toner holding member. In an image forming method of controlling the thickness to be smaller than the gap and transporting the toner to the developing unit, and developing the toner while applying an alternating electric field in the developing unit, the alternating electric field is formed by a DC voltage and an asymmetrical alternating voltage;
The developing side voltage component of the alternating bias voltage including the DC bias voltage is equal to or larger than the reverse developing side voltage component (stripping voltage component), and the application time of the developing side voltage is shorter than that of the reverse developing side voltage. The FeO content of the magnetic iron oxide contained in the magnetic toner is 30 to 40% by weight based on the iron element in the magnetic iron oxide, and the iron element dissolution when sulfuric acid of the magnetic iron oxide is used Where x is the percentage (% by weight) × 100 and y is the percentage (% by weight) of Fe ^{2+ in} the dissolved iron element × 100, 0 <x ≦ 30 (A) a magnetic toner containing at least a magnetic iron oxide and a binder resin in a range satisfying the expression, wherein the magnetic toner contains 12% by number or more of magnetic toner particles having a particle diameter of 5 μm or less; Particle size distribution containing 33% by number or less of magnetic toner particles having a particle size of 12.7 μm, 2.0% by volume or less of magnetic toner particles having a particle size of 16 μm or more, and a volume average particle size of the magnetic toner of 4 to 10 μm. An image forming method, comprising: