JP2814141B2 - 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 conventional examples, USP 3,866,574 and 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. With 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 like. In particular, the jumping development method is a method in which the toner carrier and the latent image carrier are moved in the developing area which is the closest part of the toner carrier to the latent image carrier. 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. . (Japanese Unexamined Patent Publication No. 60-73647, etc.) 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: 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 (reverse developing side bias component) The developing side bias component is the potential of the latent image on the latent image holding member as V _S (polarity is Positive), and refers to the portion a in FIG. 4 when the polarity of the toner used is negative, and the reverse-developing side bias component refers to the 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. .

In the case of the conventional example described above, in the case of this developing method, the developing side bias voltage is large, so that the developability of the solid latent image (high potential area) is high, while the reverse developing side bias in the low potential area is large, so 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.

Further, it is characterized in that the developing device used in such a developing method can be made very small with a simple configuration. For example, in high-speed machines, there is room around the photoreceptor, so several developers of other colors are arranged to change the color with one touch, or copy the writing of pages and characters using laser light simultaneously with analog light. At the same time, there is an advantage that the operation can be easily performed.

However, this developing method is characterized by a simple, light and small developing unit. Conversely, the toner used in this method has better image quality and durability unless the charged state is better due to environmental stability than conventional toner. ,
Stability cannot be obtained. That is, the performance of the toner is often directly reflected in the performance of the system. Further, since copiers are moving toward higher speeds, toners must be highly satisfied with high resolution, high speed development, and high durability.

Research and development of toners have been earnestly performed to meet these demanding requirements. Among the materials used for the magnetic toner, the magnetic substance particularly has a content of 20 to 70% by weight based on the whole toner, and thus greatly affects the performance of the toner.

Here, as seen in JP-A-58-189646,
It has been shown that a magnetic toner containing a magnetic powder having an FeO content of 16 to 25% by weight can obtain a high electrostatic image development efficiency and a good transfer efficiency, and can obtain a stable and sufficient image. . However, as copiers have been moving toward higher speeds in recent years, the above magnetic toners containing 16 to 25% by weight of FeO have high resolution, high speed development, and high durability. I cannot be satisfied enough. Further, when the magnetic toner is applied to a high-speed machine, it is difficult to appropriately control the toner charge amount in a low-temperature and low-humidity environment, and an excessive increase in the toner charge amount causes a decrease in image density and a background stain. Often. In addition, as one method of suppressing an excessive increase in the charge amount, there is a method of increasing the number of magnetic substances. However, in this method, the fixing property tends to be deteriorated. In some cases, it is only a symptomatic treatment.

Various methods and apparatuses have been developed for fixing the toner image to a sheet such as paper in the final step of the above-described electrophotographic method, but the most common method is a pressure roller heating method using a heat roller. is there.

In the pressure heating method using a heating roller, fixing is performed by allowing the toner image surface of the sheet to be fixed to pass through the surface of the heat roller having a surface having releasability with respect to the toner under pressure. In this method, since the surface of the heat roller and the toner image of the sheet to be fixed come into contact with each other under pressure, the heat efficiency at the time of fusing the toner image onto the sheet to be fixed is extremely good, and the fixing can be performed quickly. And is very effective in high speed electrophotographic copiers.

In such a fixing method, use of a binder resin containing an acid component in order to improve fixability has been disclosed in JP-A-55-134861.
No. pp. 139 to 163. However, the toner using such a binder resin is susceptible to environmental fluctuations such as insufficient charging under high humidity and excessive charging under low humidity.
Further, sufficient developability such as fog and image density may not be obtained.

On the other hand, an acid anhydride has a function of improving the chargeability, and is disclosed in JP-A-59-13 as an example in which a resin containing an acid anhydride is applied.
No. 9053, JP-A-62-280758, and the like. These methods employ a method of diluting a polymer having acid anhydride units at a high density into a binder resin. With these methods,
It is necessary to uniformly disperse the acid anhydride-containing resin in the binder resin. If the resin is not dispersed well, the toner particles become non-uniformly charged, which adversely affects developability such as fogging. In these methods, the negative chargeability is high, which is not preferable for a positively chargeable toner.

Therefore, dispersing and diluting the units of the acid anhydride into the polymer chains in the binder resin by copolymerization can solve the problem of dispersion and provide toner particles with uniform chargeability. Examples of this are disclosed in JP-A-61-123856 and 61-123856.
There are JP-A-123857 and the like, and these toners have good fixing properties, anti-offset properties, and developability.

However, when such a toner is applied to a high-speed machine or the like under a low humidity, the toner may be excessively charged, resulting in fog and a decrease in density.

This is because the units of the acid anhydride in the binder resin used in these toners are uniformly dispersed, but the amount thereof is large.

[Means and Actions for Solving the Problems] According to the present invention, an electrostatic holding member for holding an electrostatic image and a toner holding member for holding a magnetic toner on the surface are arranged at a certain gap in a developing section. An image forming method in which the magnetic toner is conveyed to the developing unit while regulating the magnetic toner to a thickness smaller than the gap on the toner carrier, and developing is performed while applying an alternating electric field to the toner in the developing unit. 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 set to the reverse developing side voltage. The magnetic toner contains 12% by number or more of magnetic toner particles having a particle size of 5 μm or less, and 33% by number or less of magnetic toner particles having a particle size of 8 to 12.7 μm. 1 A magnetic toner having a particle size distribution of not more than 2.0% by volume and having a volume average particle diameter of 4 to 10 μm, wherein the magnetic toner has at least a binder resin and a magnetic oxidizing agent; The magnetic iron oxide has an FeO content of 25 to 30% by weight, the binder resin has an acid anhydride group, and the acid anhydride of the binder resin has The total acid value (A) of the entire binder resin measured by hydrolysis of the group is 2 to 100 mgKOH / g, and the total acid value (B) derived from the acid anhydride group is less than 6 mgKOH / g; The ratio of the total acid value (B) derived from the acid anhydride group (B) to the total acid value (A) of the entire binder resin [(B) / (A)] × 100 is 6
The present invention relates to an image forming method characterized by being 0% or less.

In the AC electric field at the time of development, the developing bias electric field is increased without changing the frequency of the alternating bias, and the application time of the developing bias electric field is shortened. Since the method of controlling the duty ratio of the alternating bias, which extends the application time, is used, the toner particles having a size of 5 μm or less, which is an essential component for improving the image quality on the sleeve, are effectively fly back and forth. And both high density and reduction of fog can be achieved.

In the case of the magnetic toner, the content of FeO in the magnetic iron oxide is set to 25 to 30% by weight, and the total amount of the total acid measured by hydrolyzing an acid anhydride group contained in the binder resin is measured. Value (A) is 2 to 100 mgKOH / g, the total acid value (B) derived from the acid anhydride group is less than 6 mgKOH / g, and the total acid value (B) derived from the anhydride group is less than 6 mgKOH / g. By using a binder resin in which the ratio [(B) / (A)] × 100 of the entire binder resin to the total acid value (A) × 100 is 60% or less, it is possible to prevent the toner charge amount from excessively increasing in a low humidity environment. As a result, it is possible to obtain a magnetic toner capable of maintaining an appropriate charge amount for a considerably long period of time and maintaining a constant image density for a long period of time. In particular, when applied to a high-speed copying machine, the fixing property can be improved.

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

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

The present inventors have studied using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm in order to see the relationship between the toner particle size and the developability in the developing bias. This is because when a constant developing-side voltage (approximately 1000 V) is applied between the toner carrier and the latent image carrier (approximately 250 μm) in a pulsed manner, the toner starts to adhere to the latent image carrier (image after transfer and fixing). To make the image density 1.0 or more.) The pulse width and the particle size distribution of the toner are observed. That is, the surface potential of the latent image holding member is kept constant, the latent image is developed by changing the pulse width, the developed toner particles on the latent image holding member are collected, and the toner particle size distribution is measured. 8μ
It was found that there were many magnetic toner particles having a particle size of not more than m, and more magnetic particles having a particle size of not more than 5 μm. It was also found that as the pulse width was further reduced, the number of magnetic toner particles of 5 μm or less increased.

That is, it can be seen that the smaller the particle size of the toner, the earlier the time to reach the latent image holding member. Therefore, when the developing-side bias is applied, by setting the developing electric field to be high and for a short time, toner particles having a small particle diameter can be selectively developed.

In addition, when the reverse developing side bias is applied, the peeling electric field is set to be low and set for a long time, so that large toner particles or toner particles having a low charge amount that cannot reach the latent image holding member during the developing side bias (the moving speed is slow). To the toner carrier over time. At this time, the toner particles having a small particle size in the image area on the latent image carrier are hardly peeled off due to a strong mirroring power and a low peeling electric field, but are scattered to the non-image area due to scattering or the like. The adhered toner particles having a small charge amount (fog toner particles) have a weak mirroring power, and are pulled back onto the toner carrier by a peeling electric field.

In general, as the particle size of the toner particles decreases, the surface area per unit volume increases, so that the charge amount per unit weight increases. From such a fact, it is considered that one of the causes that the toner particles having a small particle size are likely to fly is a large charge amount.

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

However, in such a developing method, if a large amount of toner particles having a large particle diameter or insufficiently triboelectrically charged toner particles are contained in the magnetic toner on the toner carrier, these particles remain without being developed. At the same time, the frictional charging of other toner particles is hindered, resulting in a vicious cycle, a change in the particle size distribution of the magnetic toner, and deterioration in image quality.

On the other hand, using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm, the surface potential on the photoreceptor is changed this time, and from a large development potential contrast in which a large number of toner particles are easily developed, to a half tone, A latent image with a changed surface potential on the photoreceptor was developed to a small development potential contrast in which only a few toner particles were developed. The developed toner particles on the photoreceptor were collected, and the toner particle size distribution was measured. It was found that the following magnetic toner particles were many, and in particular, many were 5 μm or less. In other words, when magnetic toner particles having a particle size of 5 μm or less, which are most suitable for development, are smoothly supplied to the development of the latent image on the photoreceptor, the toner is faithful to the latent image and does not protrude from the latent image, and is truly reproducible And excellent images can be obtained.

On the other hand, with respect to the particle size, in the magnetic toner of the present invention, 5
One feature is that the number of magnetic toner particles having a particle size of not more than μm is 12% by number or more. Conventionally, in a magnetic toner, it has been difficult to control the charge amount of magnetic toner particles of 5 μm or less, and the charge tends to be excessive. For this reason, the toner particles having a size of 5 μm or less have a strong reflection force on the developing sleeve and the like, and adhere to the sleeve surface, hinder the triboelectric charging of other particles, generate poorly charged toner particles, reduce roughness, and reduce density. In some cases, it was thought that aggressive reduction was necessary.

However, studies by the present inventors have revealed that magnetic toner particles having a size of 5 μm or less are essential components for forming high-quality images.

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

Further, in the magnetic toner of the present invention, 8 to 12.7 μm
One of the features is that the number of particles in the range is 33% by number or less. This is related to the need for the presence of magnetic toner particles having a particle size of 5 μm or less, as described above. The magnetic toner particles having a particle size of 5 μm or less strictly cover the latent image and have an ability to faithfully reproduce the latent image. However, in the latent image itself, the electric field intensity at the peripheral edge portion is higher than that at the central portion, so that the toner particles may be thinner inside the latent image than at the edge portion, and the image density may appear to be light. In particular, magnetic toner particles of 5 μm or less have a strong tendency. However, we have found that toner particles in the range of 8 to 12.7 μm
It has been found that this problem can be solved and further clarified by containing 33% by number or less. That is,
It is considered that the toner particles having a particle size in the range of 8 to 12.7 μm have a moderately controlled charge amount with respect to the magnetic toner particles having a particle size of 5 μm or less. Supplied to the small inner side, a uniform developed image is formed by compensating for the small amount of the toner particles on the inner side with respect to the edge portion, and as a result, a sharp image with excellent resolution and gradation at high density Is provided.

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

The present inventors have studied the state of the particle size distribution of 5 μm or less and found that there is a state of existence of the fine powder most suitable for achieving the object as shown by the above formula. That is,
For a certain N value of 12 ≦ N ≦ 60, a large N / V indicates that the particles widely include particles of 5 μm or less, and a small N / V indicates that the particles have a particle diameter of about 5 μm. It is understood that the abundance of particles is high, indicating that there are few particles with a particle size smaller than that, and when N is in the range of 12 to 60, the value of N / V is in the range of 2.1 to 5.82. If the above relational expression is further satisfied, good fine line reproducibility and high resolution can be achieved.

Further, for magnetic toner particles having a particle size of 16 μm or more, the content is preferably set to 2.0% by volume or less, and as small as possible.

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

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, it has been found that magnetic toner particles of 5 μm or less are essential components for stabilizing the volume average particle diameter of the magnetic toner on the sleeve during image formation and durability.

Since the magnetic toner particles 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. The appropriate presence of fine magnetic toner particles, which was conventionally considered unnecessary, contributes to the closest packing of the toner in development and contributes to the 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 copying, the particle size distribution changes and the image quality tends to deteriorate.

The binder resin used in the toner of the present invention has an acid value, and the total acid value (A) measured by hydrolyzing an acid anhydride group is 2 to 100 mgKOH / g, preferably 5 to 100 mgKOH / g. ~ 70
mgKOH / g, and more preferably 5 to 50 mgKOH / g.

When the total acid value (A) is less than 2 mgKOH / g, it is difficult to obtain good fixability in a low-temperature environment. A phenomenon occurs in which the toner is fixed and the fixing roller is contaminated by the toner. If it exceeds 100 mgKOH / g, the chargeability of the toner cannot be controlled.

Components that give an acid value include a carboxyl group and an acid anhydride group, and these functional groups have a large effect on the chargeability of the toner. For example, when there is a carboxyl group in the polymer chain, there is a weak negative charge imparting ability. However, as the density of the carboxyl group increases, the hydrophilicity increases, and the electric charge is released to the water in the air.

On the other hand, acid anhydride groups have the ability to impart negative charge, but do not have the ability to release charge. Binder resins having these functional groups are preferred for negatively charged toners because they are negatively charged,
Depending on the selection of the charge control agent, it can be used for a positively chargeable toner. In other words, if the charge-controlling ability of the charge control agent overcomes the charge-giving ability of the functional group, these functional groups will only release charge.

Therefore, the ratio of these functional groups is important for stabilizing the chargeability of the toner. That is, the carboxyl group functions to release electric charges and also to provide charging.

On the other hand, the acid anhydride group works particularly effectively only for imparting chargeability. When a large number of carboxyl groups are present, charge release is increased, the charge amount of the toner becomes insufficient, and it becomes difficult to obtain a sufficient image density. This tendency becomes remarkable under high humidity.

On the other hand, when a large number of acid anhydride groups are present, the charge amount of the toner becomes excessive and fog is increased, and this tendency is enhanced particularly under low humidity, causing a decrease in image density.

Therefore, by providing these functional groups in an excessive ratio, it is possible to balance the application and release of the charge, stabilize the chargeability of the toner, and minimize the influence of environmental changes on the chargeability. It becomes possible.

That is, charging is imparted in the presence of an acid anhydride group, and charge is released in the presence of a carboxyl group to prevent overcharging.

In order to achieve the above object, the binder resin of the present invention has the following features.

First, the total acid value (B) derived from the acid anhydride group is 6 mgKOH / g
, And preferably 1.6 to 2.6 mgKOH / g, as described in Synthesis Examples described later. When the amount is 6 mgKOH / g or more, the toner is liable to be excessively charged, and the density may be reduced under low humidity and fogging may occur.

Further, the total acid value (B) derived from the acid anhydride group is not more than 60% (preferably 50% or less, more preferably 40% or less) of the total acid value (A) of the whole binder resin. Preferably, it is 5 to 12% as described in Synthesis Examples described later. If it exceeds 60%, the application and release of electric charge will not be balanced, and the ability to apply electric charge will win,
It becomes easy to be overcharged.

In addition, when an acid anhydride group is used as a constituent, the absorption peak derived from the acid anhydride (about 17
50cm around ^{-1 ~1850cm -1)} is that for which it is recognized. When the toner is present to this extent, sufficient triboelectric charging stability of the toner can be obtained.

The absorption of carbonyl of the acid anhydride appears on the higher wave number side than that of the ester acid, so that its existence can be confirmed.

The magnetic iron oxide having an FeO content of 25 to 30% by weight used in the toner of the present invention has a high blackness as a black pigment and has an effect of stabilizing the toner charge amount in order to maintain an appropriate electric resistance. It has the effect of improving the image density and improving the fog rank on the image in terms of developability.

Here, as described above, when the magnetic iron oxide having an FeO content of less than 25% by weight is used for the toner, the toner charge amount can be appropriately adjusted particularly in a low-temperature and low-humidity environment when considering application to a high-speed machine. This makes it difficult to control, and cannot sufficiently cope with a decrease in image density due to an excessive increase in the toner charge amount and a stain on the background.

Further, when a magnetic iron oxide having an FeO content of more than 30% by weight is used for the toner, the charge amount of the toner is reduced particularly in a high humidity environment, and the image density is reduced.

From the above, the FeO content in the magnetic iron oxide was reduced to 25 to 30% by weight.
By using the binder resin as described above, it was possible to prevent the toner charge from excessively increasing in a low humidity environment, and to obtain a magnetic toner capable of maintaining an appropriate charge for a considerably long period of time. It has also been found that the fixability can be improved, particularly when applied to a high-speed copying machine.

Although the inventors have not been able to explain this phenomenon clearly, the balance between the release and accumulation of electric charge at the micro interface on the surface of the toner particles is balanced, and the individual toner particles can be uniformly charged. I think that the situation may be the cause.

Here, the toner of the present invention and FeO were measured by a charge amount distribution measuring device E-Spurt Analyzer (manufactured by Hosokawa Micron).
The distribution state of the charge amount per unit weight of the comparative toner having the same formulation as the toner of the present invention except that the content was less than 25% by weight was measured. FIG. 5 shows the measurement results. Hereinafter, the charge amount per unit weight of the magnetic toner is expressed as q / m (μc / g).

In the present invention, whether the charge amount distribution (q / m distribution) of the magnetic toner is sharp or broad is determined by:
The judgment is made based on A and B (existence width of q / m) shown in FIG. The smaller the existence width of q / m (μc / g), the sharper the charge amount distribution (q / m distribution) of the magnetic toner.

In FIG. 5, A = 27 (μc / g), B = 48 (μc / g)
The charge distribution (q / m distribution) of the toner of the present invention was much sharper than that of the comparative toner, indicating that the charge state of each toner particle was uniform.

Conventionally, in a copying machine having a mechanism in which toner is supplied from a toner hopper to a developing device in accordance with a remaining amount of toner in the developing device, a toner is newly supplied from the hopper to the charged toner around the sleeve of the developing device. Is supplied, the charge amount of the toner becomes non-uniform, and the image density may temporarily decrease. In the toner of the present invention, as shown in FIG. 5, since the charge amount distribution is sharp, the above-described temporary decrease in image density did not occur.

Thus, by applying a magnetic toner having a specific particle size distribution containing a specific binder resin and magnetic iron oxide,
It is possible to faithfully reproduce even the fine lines of the latent image formed on the photoreceptor, and is excellent in the reproduction of halftone dots and dot latent images such as digital, and has excellent gradation and resolution. Give the picture. 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 particular, when applied to a high-speed machine, the fixing roller is not contaminated by the toner during continuous running, and the fixing property is improved in a low-temperature environment and the toner charge amount is excessively increased in a low-humidity environment. It is possible to obtain a toner capable of maintaining a constant image density for a long period of time while also preventing the occurrence of a decrease in image density.

Since the magnetic toner of the present invention contains a specific binder resin and magnetic iron oxide, the charged state of each toner particle is uniform and an appropriate charge amount can be maintained for a long period of time.

Therefore, in the developing method of the present invention, in the alternating electric field during development, the developing bias electric field is increased without changing the frequency of the alternating bias, and the application time of the developing bias electric field is shortened. The method uses the method of controlling the duty ratio of the alternating bias, in which the development side bias electric field is kept low and the application time is lengthened, so that the magnetic toner of the present invention, in which the charged state of each toner particle is uniform, can effectively fly back and forth. Excellent in exercising.

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. 6 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. 6, reference numeral 1 denotes a latent image carrier (so-called photosensitive member) such as a rotating drum type in a transfer type electrophotographic method, and an insulator such as a rotary drum type in a transfer type electrostatic recording method, and an electrofax. 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 sleeve 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 thickness of each portion substantially uniform 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 is 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 developing area A is always supplied with the toner thin layer T of the sleeve 22. _One surface rotates, and the copying process is repeated.

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, and the charge amount of the toner gradually increases, so that the electrostatic force (cloning force) with the sleeve increases, and the flying force of the toner to the latent image holding member 1 is reduced. Weakens, stays near the sleeve, hinders 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.

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 fly toner of 5 μm or less which tends to collect near the sleeve, 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, the visual pattern is disturbed, the gradation property and the line reproducibility are deteriorated, and it is easy to cause a drop in the image.

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, it is an essential component to improve the image quality on the sleeve by sufficiently strengthening the developing side bias electric field. This is consistent with the effective reciprocating flight of toner particles having a size of 5 μm or less, thereby preventing the toner particles from adhering to the sleeve surface. That is, the image density is hardly reduced.

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. First 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.

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.

The magnetic iron oxide used in the present invention is obtained by neutralizing iron sulfate (FeSO ₄ ) with caustic soda (NaOH) to obtain Fe (OH) ₂ , adjusting the pH to 12 to 13 by alkali adjustment, and then oxidizing with steam and air to remove magnetite. Obtain a slurry. In the subsequent drying step, FeO in the magnetic iron oxide can be controlled by controlling the drying temperature and the drying time using a warm air dryer. After drying is completed, the powder is crushed to obtain magnetite powder.

Here, the measurement of FeO in the magnetic iron oxide is performed according to the following procedure. 1.000 g of magnetic iron oxide is put into a 500 ml beaker, 50 ml of deionized water is added, and 20 ml of special grade sulfuric acid is further added to completely dissolve the magnetic iron oxide.

Next, 100 ml of deionized water was added, and further MnSO ₄ , H ₂ SO ₄ and
After adding 10 ml of a mixed solution of MnSO ₄ composed of H ₃ PO ₄ (molar ratio 0.3: 2.0: 2.0) to make a total of 180 ml, 10 ml is collected and titrated with a 0.1N KMnO ₄ solution.

And FeO contained in 1.000 g of magnetic iron oxide by the following formula
(%).

As the binder resin used in the magnetic toner of the present invention, a binder resin having a total acid value of 2 to 100 mgKOH / g measured by the following method among known binder resins for toner can be used.

The qualitative and quantitative determination of the functional group in the binder resin in the present invention is, for example, a method using infrared absorption spectrum, acid value measurement of JIS K-0070, hydrolysis acid value measurement (total acid value measurement) and the like. It is listed as.

For example, in the case of infrared absorption, an absorption peak derived from anhydride carbonyl appears at around 1780 cm ^-1 , so the presence of an acid anhydride is confirmed.

In the acid value measurement of JIS K-0070 (hereinafter referred to as JIS acid value), about 50% of the theoretical value of the acid anhydride is measured (the acid anhydride has an acid value as a dicarboxylic acid).

On the other hand, in the measurement of the total acid value, it is measured almost as a theoretical value. Therefore, the difference between the total acid value and the JIS acid value is about 50% of the theoretical value, and the acid anhydride is measured as a dibasic acid. Therefore, the total acid value derived from the acid anhydride per 1 g is determined.

As a specific example, when monooctyl maleate is used as the acid component, a copolymer of monooctyl maleate and maleic anhydride is first synthesized by solution polymerization. By measuring the JIS acid value and total acid value (A) of this copolymer, the total acid value (B) derived from the anhydride can be determined. When this copolymer is further dissolved in a monomer and subjected to suspension polymerization, the ring is partially opened. By measuring the JIS acid value and total acid value (A) of the binder resin thus obtained, the total acid value (B) derived from the remaining anhydride is determined, and the total acid value of the entire binder resin is determined. (A)
The ratio of the total acid value (B) derived from the anhydride in the content is determined.

In the present invention, the total acid value is determined as follows. Dissolve 2 g of sample resin in 30 ml of dioxane,
To this, pyridine 10ml, dimethylaminopyridine 20ml,
3.5 ml of water is added, and the mixture is refluxed for 4 hours while stirring. After cooling, the acid value obtained by neutralization titration with 1 / 10N KOH.THF solution using phenolphthalein as an indicator is defined as the total acid value.

Preparation of 1 / 10N KOH-THF solution is performed as follows. KOH1.5
g was dissolved in about 3 ml of water, and 200 ml of THF and 30 ml of water were added thereto, followed by stirring. Add a small amount of methanol if the solution has separated after standing, and add a small amount of water if the solution is turbid to obtain a uniform and transparent solution, and standardize with a 1 / 10N HCl standard solution.

As the toner binder resin, a known toner binder resin can be used. For example, a styrene-based copolymer of styrene such as a styrene-maleic acid ester copolymer and another vinyl-based monomer or the like can be used alone or in combination.

In the binder resin of the toner, unsaturated dibasic acids such as maleic acid, citraconic acid, dimethylmaleic acid, itaconic acid, alkenylsuccinic acid and anhydrides thereof; fumaric acid, metaconic acid, dimethylfumaric acid; , Anhydride monomers. Further, monoesters of the above unsaturated dibasic acids. Α, β-unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid and anhydrides thereof; anhydrides between the α, β-unsaturated acids and anhydrides with lower fatty acids; These anhydride monomers. It must have a structure such as alkenyl malonic acid, alkenyl glutanic acid, arenyl adipic acid and anhydrides and monoesters thereof. Among these, it is particularly preferable to have a structure of a monoester of α, β-dibasic acid having a maleic acid, fumaric acid or succinic acid structure.

In the present invention, a charge control agent can be used if necessary, and a conventionally known negative or positive charge control agent is used.

Today, charge control agents known in the art include:

The following substances control the toner to be negatively charged.

For example, an organometallic complex, a chelate compound is effective and a monoazo metal complex as described above, an acetylacetone metal complex,
There are aromatic hydroxycarboxylic acids and aromatic dicarboxylic acid-based metal complexes. Other examples include aromatic hydroxycarboxylic acids, aromatic mono- and polycambonic acids and their metal salts, anhydrides, esters, and phenol derivatives such as bisphenol.

The following substances control the toner to be positively charged.

Modified products such as nigrosine and fatty acid metal salts. Onium salts such as quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate, and analogs thereof such as borophonium salts, lake pigments thereof, and triphenylmethane dyes And these lake pigments (phosphor tungstic acid,
Phosphomolybdic acid, phosphotungsten molybdic acid, tannic acid, lauric acid, gallic acid, phyllocyanide,
Metal salts of higher fatty acids; diorganotin oxides such as dibutyltin oxide, dioctyltin oxide and dicyclohexyltin oxide; Dibutyltin borate, dioctyltin borate,
Diorganotin borates such as dicyclohexyl tin borate. These can be used alone or in combination of two or more. Among these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

In the toner of the present invention, it is preferable to add fine silica powder in order to improve charging stability, developability, fluidity, and durability.

The silica fine powder used in the present invention has a specific surface area by nitrogen adsorption measured by the BET method of 30 m ² / g or more (particularly 50 to 400 m
² / g) gives good results. Toner 100
It is preferable to use 0.01 to 8 parts by weight, preferably 0.1 to 5 parts by weight of silica fine powder based on parts by weight.

In addition, the silica fine powder used in the present invention may contain, if necessary, a silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oils, a silane coupling agent, a functional group for the purpose of hydrophobicity, charge control, and the like. It is also preferred that the silane coupling agent is treated with a treating agent such as a silane coupling agent or another organosilicon compound, or in combination with various treating agents.

As other additives, for example, abrasives such as cerium oxide, silicon carbide, and strontium titanate, among which strontium titanate is preferable. Alternatively, for example, a fluidity-imparting agent such as titanium oxide and aluminum oxide, particularly a hydrophobic agent is preferable. A small amount of an anti-caking agent or a conductivity-imparting agent such as carbon black, zinc oxide, antimony oxide, or tin oxide, or white and black fine particles of opposite polarity can also be used as a developability improver.

For the purpose of improving the releasability at the time of fixing with a hot roll, a wax-like substance such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sazol wax, and paraffin wax is added in an amount of 0.5 to 100% by weight of the binder resin. Addition of about 10% by weight to the toner is also a preferred embodiment of the present invention.

In the magnetic toner of the present invention, metals such as iron, cobalt and nickel or aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony,
Magnetic materials such as alloys of metals such as beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium and mixtures thereof may be used in combination.

These ferromagnetic substances preferably have an average particle size of about 0.1 to 2 μm, preferably about 0.1 to 0.5 μm. The amount of the ferromagnetic substance contained in the toner is preferably about 20 to 200 parts by weight per 100 parts by weight of the resin component.
Parts by weight, particularly preferably 40 to 1 to 100 parts by weight of the resin component.
50 parts by weight is good.

In addition, the magnetic characteristics when 10 Ke is applied have a coercive force of 20 to 150 e.
Desirably, the saturation magnetization is 50 to 200 emu / g and the residual magnetization is 2 to 20 emu / g.

Colorants that can be used in the toner of the present invention include any suitable pigments or dyes. Toner colorants are well known and include pigments such as carbon black, aniline black, acetylene black, naphthol yellow, hansa yellow, rhodamine lake, alizarin lake, bengara, phthalocyanine blue, and indanthrene blue. These are used in an amount necessary and sufficient to maintain the optical density of the fixed image, and 0.1 to 20 parts by weight, preferably 2 to 10 parts by weight, per 100 parts by weight of the resin is good. A dye is further used for the same purpose. For example, there are azo dyes, anthraquinone dyes, xanthene dyes, methine dyes, etc.
The addition amount is preferably up to 20 parts by weight, preferably 0.3 to 3 parts by weight.

To prepare the toner for developing an electrostatic image according to the present invention, a binder resin, a metal salt or a metal complex, a pigment or dye as a colorant, a magnetic substance, a charge control agent as necessary, and other additives After thoroughly mixing with a mixer such as a Henschel mixer or a ball mill, melting, kneading and kneading using a hot kneading machine such as a heating roll, kneader or extruder to dissolve the metals in the resin, The toner according to the present invention can be obtained by dispersing or dissolving the compound pigments, dyes, and magnetic substances, and solidifying by cooling, followed by pulverization and classification.

Further, if necessary, desired additives are sufficiently mixed with a mixer such as a Henschel mixer to obtain the toner for developing an electrostatic image according to the present invention.

In the present invention, the charge amount of the toner layer on the carrier was determined using a so-called suction-type Faraday 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 obtained by measuring the charge amount accumulated in the inner cylinder electrostatically shielded from the outside.

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

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 12 types of line images under appropriate copying conditions with a magnifying glass, and determine the resolution value with the number of images (lines / mm) where fine lines are clearly separated. I do.

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

In the present invention, the measurement of the charge amount distribution of the magnetic toner is performed by:
As described above, the distribution state of the charge amount per unit weight was measured by the charge amount distribution measuring device E-Spurt Analyzer (manufactured by Hosokawa Micron). FIG. 5 shows an example of the measurement result.

Hereinafter, the charge amount per unit weight of the magnetic toner is q / m
(Μc / g). In the present invention, whether the charge amount distribution (q / m distribution) of the magnetic toner is sharp or broad is determined by A and B (existing width of q / m) shown in FIG. . The smaller the width of q / m (μc / g), the smaller the charge amount distribution (q / m distribution) of the magnetic toner.
Is sharp.

In the examples and comparative examples, the measurement of the charge amount distribution (q / m distribution) of the magnetic toner was performed immediately before and after the start of the copy test in a low-temperature and low-humidity environment.

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples.
This does not limit the invention in any way.

First, 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) The developing bias power supply to which the alternating bias electric field having the waveform shown in FIG.

This alternating electric field has a peak to peak of 1400 V, a frequency of 2,000 Hz, and a duty ratio of 20%.
It was used as a developing bias power supply.

(Waveform Example 2) The developing bias power supply 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 2000 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 1400 V, a frequency of 2,000 Hz, and a duty ratio of 35%.
It was used as a developing bias power supply.

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

This alternating electric field has a peak to peak of 1400 V, a frequency of 2000 Hz, 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 1400 V, a frequency of 2,000 Hz, and a duty ratio of 50%.
It was used as a developing bias power supply.

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

First, a synthesis example of the binder resin used in the present invention will be described.

Synthesis Example 1 The above compound was added dropwise to 200 parts by weight of xylene heated to the reflux temperature over 4 hours. Further, the polymerization was completed under xylene reflux (138 to 144 ° C), and xylene was removed while heating to 200 ° C under reduced pressure. The resin thus obtained is referred to as resin A.

Next, using resin A 0.12 polyvinyl alcohol partially saponified in the above mixture
170 parts by weight of water in which the above parts were dissolved were added and stirred vigorously to obtain a suspension dispersion. The suspension dispersion was added to a reactor filled with 50 parts by weight of water and purged with nitrogen, and a suspension polymerization reaction was performed at a reaction temperature of 80 ° C. for 8 hours. After completion of the reaction, the resultant was washed with water, dehydrated and dried to obtain a resin B.

Synthesis Example 2 Resin C was obtained in the same manner as in Synthesis Example 1 using the above compound.

Resin D was obtained in the same manner as in Synthesis Example 1 using the above mixed liquid.

Synthesis Example 3 The above compound was added dropwise to 200 parts by weight of xylene heated to the reflux temperature over 4 hours. Further, the polymerization was completed under xylene reflux (138 to 144 ° C), and xylene was removed while heating to 200 ° C under reduced pressure. The resin thus obtained is referred to as a resin E.

Total oxidation of the above binder resin (A), JIS acid value, acid anhydride,
Table 1 shows the total acid value (B) derived and the ratio of the resin to the total acid value (A) [(B) / (A)] × 100.

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

Production Example 14 0.8 M FeSO ₄ aqueous solution 1 in the three-necked flask of ₄
And 0.85M caustic soda aqueous solution 1
Oxidize at about 70 ° C. while blowing steam and oxygen. The obtained black powder is washed with water, and the drying temperature is 130 ° C.
After 10 minutes (initial drying condition) and drying temperature 80
C. for 2 hours (late drying conditions) to obtain a magnetic iron oxide powder containing 26.1% by weight of FeO.

Production Example 2 Initial drying conditions were 130 ° C. for 10 minutes in Production Example 1.
Except that the temperature was kept at 0 ° C. for 15 minutes and the latter drying condition was 80 ° C. for 2 hours, the same operation as in Production Example 1 was carried out.
A magnetic iron oxide powder containing 5.4% by weight was obtained.

Production Example 3 Production was carried out in the same manner as in Production Example 1 except that the drying conditions were changed to 65 ° C. for 15 minutes.
A magnetic iron oxide powder containing 1% by weight was obtained.

Production Example 4 Production was carried out in the same manner as in Production Example 1 except that the drying conditions were changed to 70 ° C. for 10 hours.
A magnetic iron oxide powder containing 2% by weight was obtained.

Comparative Production Example 1 Production was performed in the same manner as in Production Example 1 except that the drying conditions were changed to 130 ° C. and 1.5 hours.
A magnetic iron oxide powder containing 3.0% by weight was obtained.

Comparative Production Example 2 The drying conditions in Production Example 1 were changed to 75 ° C. for 18 hours,
Except that after leaving for 50 hours at 0 ° C. and then for 15 hours in an H ₂ atmosphere, the same operation as in Production Example 1 was performed,
A magnetic iron oxide powder containing 0.5% by weight was obtained.

Table 2 summarizes the drying conditions and the FeO content of the magnetic iron oxide.

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

Production Example 1 of Toner 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 3 shows the particle size distribution of the magnetic toner.

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

 This toner is referred to as toner 1.

Production Example 2 of Toner A magnetic toner having a particle size distribution shown in Table 3 was obtained in the same manner as in Production Example 1 of a toner using the above-mentioned materials, and hydrophobic dry silica (BET ²⁰⁰ m ² / g) was added to 100 parts by weight of the magnetic toner.
Parts by weight were mixed with a Henschel mixer.

 This toner is referred to as toner 2.

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

Production Example 4 of Toner In the same manner as in Toner Production Example 2 using the above materials, Toner 4 having a particle size distribution shown in Table 3 was obtained.

Toner Production Examples 5 and 6 The particle size distribution shown in Table 3 was obtained in the same manner as in Toner Production Example 1 except that the coarsely crushed product obtained in Toner Production Example 1 was used and the fine pulverization classification conditions were changed. Toner 5 and toner 6 were obtained.

Toner Production Example 7 Resin E was used instead of Resin B used in Toner Production Example 1.
The toner 7 having the particle size distribution shown in Table 3 was obtained in the same manner as in Production Example 1 of the toner except for using.

Toner Production Example 8 Instead of resin B used in toner production example 1, resin E
Except that the magnetic iron oxide of Comparative Production Example 1 was used instead of the magnetic iron oxide used in Production Example 1 of the toner.
A toner 8 having a particle size distribution shown in Table 3 was obtained in the same manner as in Production Example 1 of the toner.

Toner Production Example 9 Instead of resin B used in toner production example 1, resin E
And the magnetic iron oxide of Comparative Production Example 2 was used instead of the magnetic iron oxide used in Production Example 1 of the toner.
A toner 9 having a particle size distribution shown in Table 3 was obtained in the same manner as in Production Example 1 of the toner.

The evaluation of fixability was performed according to the following procedure.

The fixability was evaluated by leaving the evaluation machine overnight in a low-temperature and low-humidity environment (15 ° C, 10%). A copy image was taken and the 200th copy image was used for evaluation of fixability. Evaluation of fixability is about 100 g of image reciprocating 10 times with silbon paper
Rubbing with load, image peeling, decrease in reflection density (%)
Was evaluated.

Image formation in Examples and Comparative Examples of the present invention was carried out at room temperature and normal humidity (23.5 ° C., 60%) by Canon copier NP-8580.
The test was performed under low and low humidity (15 ° C, 10%) and high temperature and high humidity (32.5 ° C, 85%) environmental conditions.

In a normal temperature and normal humidity (23.5 ° C., 60%) environment, all the toners used in Examples and Comparative Examples were subjected to a copy test of 100,000 sheets.
An image with high image quality was obtained.

Table 4 shows the results of a 100,000-sheet copy test performed in a low-temperature, low-humidity (15 ° C., 10%) environment.

Examples 1 to 7 As is clear from Table 4, low temperature and low humidity environment (15 ° C, 10%)
Also obtained good results.

Comparative Example 1 An example using a binder resin in which the ratio of the acid value (B) derived from an anhydride to the total acid value (A) of the binder resin is 85% was used. %), White stripes appear on the image from around 1000 sheets, and the image density decreases at the same time.
It was 1.09. Further, the toner charge amount on the sleeve near 15,000 sheets was as high as −29.8 μc / g, and an excessive increase in the charge amount occurred.

Comparative Example 2 A binder resin in which the ratio of the acid value (B) derived from an anhydride to the total acid value (A) of the binder resin was 85%, and a magnetic iron oxide having a ferrous oxide content of 23% were used. As an example, when the endurance was continued in a low temperature and low humidity environment (15 ° C, 10%), 6000
From the vicinity of the sheet, white streaks appeared on the image, and the image density was reduced at the same time. The image density near 10,000 sheets was 1.04. The charge amount of the toner on the sleeve near 10,000 sheets was as high as -31.1 μc / g, and the charge amount was excessively increased.

Comparative Example 3 A binder resin in which the ratio of the acid value (B) derived from an anhydride to the total acid value (A) of the binder resin was 85%, and a magnetic iron oxide having a ferrous oxide content of 30.5% were used. As an example, when the endurance was continued in a low temperature and low humidity environment (15 ° C, 10%), 700
At around the 0th sheet, white streaks appeared on the image and at the same time the image density decreased, and at around the 8000th sheet, the image density became 1.01. The toner charge on the sleeve near 8000 sheets is-
As high as 32.3 μc / g, an excessive increase in the charge amount occurred. In addition, when durability was maintained in a high-temperature, high-humidity (32.5 ° C, 85%) environment, the charge amount on the sleeve decreased from around 8000 sheets,
Further, the transfer efficiency of the toner to the paper also decreased, and the image density decreased. The image density near 10,000 sheets was 1.01.

Comparative Example 4 The image was good, but the toner consumption was large.

Comparative Example 5 Although the image was good at the beginning, the image quality gradually deteriorated as the copying was repeated, the fine line reproducibility became unstable, and the resolution decreased.

Comparative Example 6 This is an example in which a developing bias having a duty ratio of 50% was used, but tailing was observed, and the gradation property and the resolution were inferior.

[Effects of the Invention] The present invention provides a magnetic iron oxide having a specific particle size distribution and a ferrous oxide content of at least 25 to 30% by weight in a magnetic iron oxide and an acid anhydride contained in a binder resin. Total acid value (A) of 2 to 100 mgKOH / g measured by hydrolysis of
And the total acid value (B) derived from the acid anhydride group is 6 mgKOH
/ g, and the ratio of the total acid value (B) derived from the acid anhydride group (B) to the total acid value (A) of the entire binder resin [(B) / (A)] × 100 is 60% or less. This is an image forming method in which a magnetic toner made of a resin is carried and development is performed using an asymmetric developing bias, so that the following excellent effects are exhibited.

(1) High image density, excellent fine line reproducibility, and excellent gradation
Clear, high-quality images without fog can be obtained over a long period of time.

(2) Even under low humidity, the image density is high, and clear high-quality image without fog can be obtained.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of an alternating bias voltage waveform, FIG. 2 shows a schematic diagram of flying adhesion of toner, FIG. 3 shows a schematic diagram of an alternating bias voltage waveform, and FIG. FIG. 5 is a graph showing the distribution of the charge amount of the toner used in the present invention and the comparative toner, FIG. 6 is a schematic explanatory view of the developing device, and FIGS. 7 to 11 are alternating bias voltages. FIG. 3 shows a schematic diagram of a waveform. T: toner, T _1: toner thin 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: direct current Bias applying means 1 ... Latent image holder, 21 ... Hopper 22 ... Toner carrier, 23 ... Magnetic roller 24 ... Doctor blade

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhisa Akashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masaki Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 9/08-9/087

Claims (3)

(57) [Claims] An electrostatic holding member for holding an electrostatic 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 in which the toner is regulated to a thickness smaller than the gap and conveyed to the developing unit and developed while applying an alternating electric field to the toner in the developing unit, the alternating electric field comprises a DC voltage and an asymmetric alternating voltage, and the DC bias voltage is The developing-side voltage component of the alternating 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 magnetic toner contains 12% by number or more of magnetic toner particles having a particle size of 5 μm or less, contains 33% by number or less of magnetic toner particles having a particle size of 8 to 12.7 μm, and contains magnetic toner particles having a particle size of 16 μm or more. 2.0 % By volume, and has a particle size distribution in which the volume average particle diameter of the magnetic toner is 4 to 10 μm. The magnetic toner contains at least a binder resin and magnetic iron oxide, The FeO content in the binder resin is 25 to 30% by weight, the binder resin has an acid anhydride group, and the binder resin is obtained by hydrolyzing the acid anhydride group of the binder resin. A total acid value (A) of 2 to 100 mgKOH / g, a total acid value (B) derived from the acid anhydride group of less than 6 mgKOH / g, and a total acid value derived from the acid anhydride group; (B) / (A)] × 100 is the ratio of the value (B) to the total acid value (A) of the entire binder resin.
An image forming method characterized by being 0% or less. 2. The method according to claim 1, wherein the total acid value (B) derived from the acid anhydride group is
2. The image forming method according to claim 1, wherein the amount is 1.6 to 2.6 mgKOH / g. 3. The ratio [(B) / (B) / (B) / total acid value (A) of the entire binder resin of the total acid value (B) derived from the acid anhydride group.
3. The image forming method according to claim 1, wherein (A)] × 100 is 5 to 12%.