JP3532774B2 - Magnetic developer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic one-component developing method used in electrophotography, electrostatic recording, electrostatic printing and the like.
Method magnetic developer. More specifically, it relates to a magnetic developer capable of obtaining good image characteristics even after being left for a long time.

[0002]

2. Description of the Related Art Generally, in electrophotography, an electrical latent image is formed on a photoconductor, the latent image is developed with toner, the toner image is transferred to a transfer material such as paper, and then heated.
It is fixed by a means such as pressure to obtain a copy. Developers used in such an electrophotographic method include a two-component developer composed of a toner and a carrier, and a one-component developer having the properties of the toner and the carrier at the same time. 1
Component developers are further classified into magnetic one-component developers and non-magnetic one-component developers. The two-component developer has transferability, fixability,
Although it has excellent electrophotographic characteristics such as environmental resistance, it requires a toner concentration sensor to control the mixture ratio of toner and carrier, has a short developer life, and has a complicated developer stirring mechanism. There are problems such as becoming
From such a background, a method of using a magnetic toner as a one-component developer has been proposed and put into practical use in recent years in order to make the apparatus small and simple.

The one-component developing method using magnetic toner is
A contact type magnetic one-component developing method in which a developing roller carrying a developer is brought into contact with a photoreceptor having an electrostatic latent image for development, and a constant gap gap is provided between the developing roller and the photoreceptor and There is a non-contact type magnetic one-component developing method of flying and developing the magnetic toner. In the contact-type magnetic one-component developing method, the non-magnetic toner on the developing roller and the photoconductor having the electrostatic latent image come into contact with each other, so that the developing property is good, but on the other hand, the magnetic toner is not only used in the developing device. Since friction also occurs with the photosensitive drum, the mechanical load on the magnetic toner is large. On the other hand, in the non-contact type non-magnetic one-component developing method, the developer is triboelectrically charged only by the layer regulating member, so that the mechanical load on the developer is small, but the non-contact type is not contacted. In general, there is a problem that a sufficient image density cannot be obtained because the amount of the magnetic one-component developer flying from the developing roller to the photosensitive drum is smaller than that of the mold. This problem,
In particular, this is a serious problem when a magnetic one-component developer is put in a developing device adopting a non-contact type one-component developing method and an image is obtained after leaving it for a long time as it is. It is considered that the cause of this problem is that the charge amount of the magnetic one-component developer is remarkably reduced when left standing for a long time. Therefore, conventionally, the amount of the charge control agent contained in the magnetic one-component developer has been increased to prevent a significant decrease in the charge amount, but the charge control agent has poor dispersibility in the binder resin. The developer particles have different contents of the charge control agent, and as a result, developer particles that are difficult to develop are generated, and the particles remain in the developing device, which hinders the flight properties of other developer particles. It was not possible to obtain a sufficient image density.

[0004]

The present invention is a magnetic single component
It is an object of the present invention to provide a magnetic developer which is used in a developing method and can obtain good image characteristics even after being left for a long time.

[0005]

SUMMARY OF THE INVENTION The present invention carries a magnetic developer layer having a desired thickness and a predetermined charge amount provided by a photoreceptor having a negatively charged electrostatic latent image on its surface and a layer regulating member. A magnetic single component which is visualized by causing the magnetic developer of the magnetic developer layer to fly to the photoconductor by disposing the support and the support in a non-contact state at a constant interval in the developing unit. A magnetic developer used in a developing method, wherein the magnetic developer has at least a binder resin, a magnetic powder, a charge control agent and a release agent, and a hydrophobic silica fine powder is adhered to the surface of the toner particles. A magnetic developer characterized in that the hydrophobic silica fine powder has a charge amount of −200 μc / g to −300 μc / g and an area coverage of 80 to 120% on the surface of toner particles. is there.

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a developing device for developing a magnetic developer of the present invention. In the figure, 1 is a photosensitive drum, 2 is a hopper, 3 is a magnetic developer, 4 is a layer regulating member, and 5 is a layer regulating member. A developing roller using an aluminum sleeve having a magnet for carrying a developer, 6 is a developer leakage preventing member, and 7 is a stirrer. In this developing device, an electrostatic latent image is formed on the photosensitive drum 1 by a known electrophotographic method. A magnetic developer 3 is contained in the popper 2. The magnetic developer 3 is carried by the layer regulating member 4 on the developing roller 5 so as to have a constant layer thickness, and the magnetic developer 3 is An electric charge is given by the friction of. The developing roller 5 includes the photosensitive drum 1 and 120 to 30.
The roller 5 is installed with a gap of 0 μm, and a bias of DC or AC voltage is applied to the roller 5. The magnetic developer carried on the developing roller 5 is conveyed by the rotation of the developing roller 5, and the potential difference between the photosensitive drum 1 having an electrostatic latent image and the developing roller 5 causes the photosensitive drum 1 to develop.
Of the electrostatic latent image is visualized in a non-contact manner.

The magnetic developer is one in which fine particles of hydrophobic silica are attached to the surface of toner particles containing at least a binder resin, magnetic powder, a charge control agent and a release agent. The toner particles are particles obtained by appropriately dispersing and containing at least a binder resin, a magnetic powder, a charge control agent and a release agent, and other additives which are added as required by preliminary dispersion, kneading, etc., and pulverizing and classifying. And the volume average particle diameter is in the range of 5 to 20 μm, preferably 5 to 10 μm. As the binder resin,
Thermoplastic resins such as polyester resin, styrene resin, styrene acrylic resin, polyethylene resin, and epoxy resin are used.
You may mix and use 1 or more types. The glass transition temperature of the resin is 55 to 70 ° C, preferably 60 to 65 ° C. As the magnetic powder, magnetite or ferrite powder having a primary average diameter of 0.1 to 0.5 μm is preferable. The amount added is 5 to 300 parts by weight, especially 10 to 100 parts by weight of the binder resin.
200 parts by weight is preferred. Further, it is preferable to use a magnetic powder having a saturation magnetization of 58 emu / g or more at 1 KOe because an image with less background fog can be obtained.

In the present invention, since it is used in a magnetic one-component developing method of a reversal developing system in which a magnetic developer is developed on a photoreceptor having a negatively charged electrostatic latent image on its surface,
As the charge control agent constituting the magnetic developer, a negatively chargeable charge control agent such as an azo metal complex or a complex salt is used. Further, in order to control the chargeability, a quaternary ammonium compound or a positive chargeable charge control agent such as a resin type charge control agent obtained by copolymerizing a functional group may be added. Examples of the releasing agent include natural waxes such as carnauba wax, candelilla wax and montan wax, low molecular weight polypropylene, low molecular weight polyethylene, synthetic hydrocarbon waxes such as Fischer-Tropsch wax and synthetic ester wax. In particular, natural gas-based Fischer-Tropsch wax, which is excellent in low-temperature fixing property and releasing property, is preferable.

The hydrophobic silica fine powder used in the present invention is obtained, for example, by subjecting hydrophilic silica fine powder to a hydrophobic treatment by a known method and then crushing it with a mixer such as a Henschel mixer capable of imparting a high shearing force. It can be obtained by adjusting a desired particle size distribution by using a mechanical or air flow type pulverizer and a classifier. The hydrophobic treatment is performed by using a silane-based and / or titanium-based coupling agent, silicone oil, or the like, and the preferred hydrophobicity is 50 or more in terms of methanol wettability value.

[0010] charge amount of the hydrophobic silica fine powder, - 2
It is necessary to be from 00 to −300 μc / g . When the charge amount is less than -200 μc / g, image characteristics such as image density after being left for a long time deteriorate. The charge amount of the hydrophobic silica fine powder is a value obtained by measuring the friction charge amount (weight mixing ratio = carrier: silica = 99: 1) with a non-coated ferrite carrier, using a blow-off charge amount measuring device manufactured by Toshiba Chemical Corporation. Can be measured. The charge amount of the hydrophobic silica fine powder can be adjusted by changing the type and the treatment amount of the treating agent during the hydrophobic treatment. For example, in order to increase the positive polarity of the hydrophobic silica fine powder, a functional group having a large positive charging property such as an amino group may be introduced into these treating agents.

In the particle size distribution of the hydrophobic silica fine powder, the ratio of particles having a volume-based particle size of 5.04 μm or less is 60% by volume or more, and the ratio of particles having a volume-based particle size of 20.2 μm or less is 90.
It is preferably at least volume%. Volume-based particle size 5.0
If the proportion of particles having a particle size of 4 μm or less is less than 60% by volume, or if the proportion of particles having a volume-based particle size of 20.2 μm or less is less than 90% by volume, scratches are likely to occur on the surface of the photoreceptor, resulting in black spots. Image defects are likely to occur. The particle size distribution of the hydrophobic silica fine powder is measured by a coal tar counter using an aperture of 100 μm. The hydrophobic silica fine powder has a BET specific surface area of 90 to 30.
It is preferably 0 m ² / g, particularly 100 to 200 m ² / g. The hydrophobic silica fine powder having a BET specific surface area of 90 to 300 m ² / g can impart particularly good fluidity to the magnetic developer.

The magnetic developer is fine particles in which the surface of toner particles is coated with a fine powder of hydrophobic silica, and the area coverage of the fine powder of hydrophobic silica on the surface of the toner particles is 80 to 12.
It is 0%. 80% area coverage of hydrophobic silica fine powder
When it is lower, the image characteristics such as the image density after being left for a long time deteriorates, and the storage stability of the magnetic developer also deteriorates. On the other hand, when the area coverage of the hydrophobic silica fine powder is higher than 120%, the fixability of the magnetic developer is deteriorated and offset occurs. The area coverage of the fine particles of hydrophobic silica on the surface of the toner particles is calculated by the following calculation formula.

## EQU1 ## Coverage (%) = (dt × ρt × W × S × 10
0) / [π (100-W) × ρa × da ³ ] where dt is the number of toner particles 50% diameter (cm), da
Is the primary particle size (cm) of the hydrophobic silica fine powder, ρt is the true specific gravity of the toner particles (g / cm ³ ), ρa is the true specific gravity of the hydrophobic silica fine powder (g / cm ³ ), and W is the toner particles The addition amount (% by weight) of the hydrophobic silica fine powder to S, and S indicates the projected area (cm ² ) of the hydrophobic silica fine powder. As is clear from this formula, the area coverage of the hydrophobic silica fine powder on the surface of the toner particles is calculated by determining the particle diameter of the toner particles, the particle diameter of the hydrophobic silica fine powder, the true specific gravity of the toner particles, the hydrophobic silica fine powder. It can be adjusted by arbitrarily changing the true specific gravity and the addition amount of the hydrophobic silica fine powder. The hydrophobic silica fine powder may be attached to the toner particles by mixing and stirring with a mixer such as a Henschel mixer capable of imparting a high shearing force. Further, the hydrophobic silica fine powder and other externally added fine particles may be used in combination. As the externally added fine particles, for example, a hydrophobic titanium oxide having a primary average diameter of 5 to 50 nm, alumina, an acrylic resin having a primary average diameter of 50 to 500 nm,
Examples thereof include fluorine-based and silicon-based resin fine particles, magnetite having a primary average diameter of 0.1 to 0.6 μm, and ferrite.

[0013]

EXAMPLES Example 1 Hereinafter, the present invention will be described in more detail with reference to Examples.
In addition, "part" means "part by weight". The raw materials of the above formulation were mixed with a Henschel mixer (manufactured by Mitsui Miike Industry Co., Ltd.). The temperature of the mixture is set to 120 with a twin-screw kneader.
After melt-kneading at 0 ° C., jet grinding and air flow classification were carried out to obtain toner particles having a volume average particle diameter of 8.5 μm. Next, the following hydrophobic silica fine powder A was coated on the toner particles at a coverage of 95% [dt: 6.40 × 10 ⁻⁴ (cm), da: 0.
018 × 10 ⁻⁴ (cm), ρt: 1.57 (g / c
m ³ ), ρa: 2.30 (g / cm ³ ), W: 1.55
(% By weight), S: 2.53 × 10 ⁻¹² (cm ² )] and mixed with a Henschel mixer to obtain the magnetic developer of the present invention. The hydrophobic silica fine powder A was manufactured by the following method. 4. Hydrophilic silica (dry method) having a BET specific surface area of about 130 m ² / g was treated with silicone oil, and then crushed and collected by an airflow crushing classifier to obtain a volume standard particle size of 5.
A hydrophobic silica fine powder A having a particle size of particles having a particle size of 04 μm or less of 66.4% by volume and a particle ratio of particles having a volume standard particle size of 20.2 μm or less of 93.2% by volume was obtained. The charge amount of this hydrophobic silica fine powder A was -264 μc / g.

[0014] Henschel mixer (Mitsui Miike Industry Co., Ltd.)
Mixed in. The mixture was melt-kneaded with a twin-screw kneader at a set temperature of 120 ° C., and then jet pulverized and air stream classified to obtain toner particles having a volume average particle diameter of 8.5 μm. Next, the toner particles are coated with the following hydrophobic silica fine powder B at a coverage of 95
% [Dt: 6.34 × 10 ⁻⁴ (cm), da: 0.01
8 × 10 ⁻⁴ (cm), ρt: 1.57 (g / cm ³ ),
ρa: 2.10 (g / cm ³ ), W: 1.43 (wt%), S: 2.53 × 10 ^-12 (cm ² )] and mixed with a Henschel mixer to obtain the magnetic property of the present invention. A developer is obtained. The hydrophobic silica fine powder B was manufactured by the following method. B
Hydrophilic silica (dry method) with an ET specific surface area of about 130 m ² / g is treated with silicone oil, and then crushed and collected by an airflow crushing classifier to obtain a volume standard particle size of 5.04μ.
The ratio of particles of m or less is 63.4% by volume, volume standard particle size is 2
A hydrophobic silica fine powder B having a particle size of 0.2% or less and 91.2% by volume was obtained. The charge amount of the hydrophobic silica fine powder B was −231 μc / g.

[0015] Henschel mixer (Mitsui Miike Industry Co., Ltd.)
Mixed in. The mixture was melt-kneaded with a twin-screw kneader at a set temperature of 120 ° C., and then jet pulverized and air stream classified to obtain toner particles having a volume average particle diameter of 8.5 μm. Next, the toner particles are coated with the following hydrophobic silica fine powder A at a coverage of 95
% [Dt: 6.40 × 10 ⁻⁴ (cm), da: 0.01
8 × 10 ⁻⁴ (cm), ρt: 1.57 (g / cm ³ ),
ρa: 2.30 (g / cm ³ ), W: 1.55 (wt%), S: 2.53 × 10 ^-12 (cm ² )] and mixed with a Henschel mixer to obtain the magnetic property of the present invention. A developer is obtained.

Example 4 The hydrophobic silica fine powder A obtained in Example 1 was pulverized and classified,
The ratio of particles having a volume-based particle diameter of 5.04 μm or less is 43.2.
Example 1 except that silica was used in which the volume ratio of the particles having a volume-based particle size of 20.2 μm or less was 92.3% by volume.
A magnetic developer of the present invention was obtained in the same manner as.

Comparative Example 1 Compared to the toner particles obtained in Example 1, a commercially available hydrophobic silica fine powder C (dry method, BET specific surface area of about 125 m ² /
g, dimethyldichlorosilane treatment, volume standard particle size 5.0
The ratio of particles having a particle size of 4 μm or less is 37.1% by volume, the ratio of particles having a volume-based particle size of 20.2 μm or less is 85.3% by volume, and the coverage is 95% [charge: −190 μc / g] [dt: 6.
40 × 10 ⁻⁴ (cm), da: 0.016 × 10 ⁻⁴ (c
m), ρt: 1.57 (g / cm ³ ), ρa: 2.65
(G / cm ³ ), W: 1.58 (% by weight), S: 2.0
× 10 ⁻¹² (cm ² )] was mixed with a Henschel mixer to obtain a magnetic developer for comparison.

Comparative Example 2 The toner particles obtained in Example 1 were covered with the hydrophobic silica fine powder A at a coverage of 70% [dt: 6.40 × 10 ^-4 (c
m), da: 0.018 × 10 ⁻⁴ (cm), ρt: 1.
57 (g / cm ³ ), ρa: 2.30 (g / cm ³ ),
W: 1.15 (wt%), S: 2.53 × 10 ^-12 (c
m ² )] was mixed with a Henschel mixer to obtain a magnetic developer for comparison. Comparative Example 3 The toner particles obtained in Example 1 were coated with the hydrophobic silica fine powder A at a coverage of 125% [dt: 6.40 × 10 ⁻⁴ (c
m), da: 0.018 × 10 ⁻⁴ (cm), ρt: 1.
57 (g / cm ³ ), ρa: 2.30 (g / cm ³ ),
W: 2.03 (% by weight), S: 2.53 × 10 ^-12 (c
m ² )] was mixed with a Henschel mixer to obtain a magnetic developer for comparison.

(Evaluation of Magnetic Developer) The magnetic developers of Examples 1 to 4 and Comparative Examples 1 to 3 are commercially available printers (developing device as shown in FIG. 1 (organic photoreceptor, charging roller and transfer roller). Application) to evaluate the initial image characteristics, and then leave the magnetic developer in the developing device in a high temperature and high humidity environment (35 ° C., 85% RH) for 1 week.
Then, the image characteristics after standing were evaluated. The results are shown in Table 1.
Shown in. The image densities in Table 1 are measured values of solid image densities by a reflection densitometer (RD-914) manufactured by Macbeth.
Fog is a measurement value of a non-image area by a color difference meter (ZE2000) manufactured by Nippon Denshoku Co., Ltd.

[0020]

[Table 1]

As is clear from Table 1, in Examples 1 to 4, the image density and fog did not change much from the initial image even after standing. On the other hand, in Comparative Examples 1 and 2, the image density after standing was low, and in Comparative Example 3, an offset occurred from the beginning, so the evaluation of the image characteristics was stopped. It should be noted that the image density was slightly lower in Example 3 than in Examples 1 and 2, and in Example 4, scratches were generated on the surface of the photoconductor as compared with Examples 1 and 2 while printing a large number of sheets. It was easy. In addition, Examples 1 to 4 and Comparative Examples 1 to
20g of magnetic developer of 3 was put in a polyethylene container, and 45
After storing at 7 ° C. for 7 days, the magnetic developer was taken out from the container and visually evaluated for the aggregation state of the magnetic developer. As a result, there was no problem in Examples 1 to 4 and Comparative Examples 1 and 3, but the magnetic property of Comparative Example 2 Aggregates (lumps) were generated in the developer.

[0022]

The magnetic developer of the present invention does not cause aggregation even after being left for a long period of time, and can maintain a good storage state.
Therefore, an image having a sufficient image density and almost free from fog can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a developing device used in a non-contact type magnetic one-component developing method.

[Explanation of symbols]

1 photoconductor drum 2 hopper 3 Magnetic developer 4 layer regulation member 5 developing roller 6 developer leakage prevention member, 7 stirrer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-289403 (JP, A) JP-A-6-51554 (JP, A) JP-A-9-204062 (JP, A) JP-A-8- 152742 (JP, A) JP 4-80764 (JP, A) JP 7-319201 (JP, A) JP 8-234483 (JP, A) JP 9-179335 (JP, A) JP-A-9-185181 (JP, A) JP-A-9-319139 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/08

Claims (3)

(57) [Claims] 1. A photosensitive member having a negatively charged electrostatic latent image on its surface and a carrier carrying a magnetic developer layer having a desired thickness and a predetermined amount of charge imparted by a layer regulating member are fixed in a developing section. A magnetic developer used in a magnetic one-component developing method in which the magnetic developer in the magnetic developer layer is visualized by flying the magnetic developer on the photoconductor, the magnetic developer being opposed to each other with a space of The magnetic developer is obtained by adhering hydrophobic silica fine powder to the surface of toner particles containing at least a binder resin, magnetic powder, a charge control agent and a release agent, and the hydrophobic silica fine powder is electrically charged. Amount is -200μc / g
In ~-300μc / g, and magnetic developer, wherein the area coverage with respect to the surface of the toner particles is 80 to 120%. 2. The hydrophobic silica fine powder has a particle size distribution of 60% by volume or more of particles having a volume standard particle size of 5.04 μm or less and 90% of particles having a volume standard particle size of 20.2 μm or less.
The magnetic developer according to claim 1, wherein the magnetic developer is at least volume%. 3. The magnetic developer according to claim 1, wherein the releasing agent is a natural gas type Fischer-Tropsch wax.