JPS6333696B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a magnetic toner for electrostatic charge development used in electrophotography, electrostatic recording, electrostatic printing, etc. Magnetic toner is generally composed of a binder resin, a magnetic material, a resistance adjuster, or a colorant and a fluidizing agent.
Since it is carrierless, there is no need to control the density of the magnetic toner, and the mechanism of the developing device has the advantage of being simple. However, on the other hand, in order to adjust the resistance of the magnetic toner, it is necessary to disperse conductive particles such as carbon black inside the magnetic toner particles or to provide a conductive layer on the surface thereof. Generally, the method for forming a conductive layer is as follows: (a) A conductive layer is formed by mixing and dispersing conductive particles and magnetic toner base particles in a high-temperature air stream, such as in a fluidized drying oven. (b) In a rotating drum, conductive particles and magnetic toner base particles are mixed and dispersed to form a conductive layer. etc. are known. However, in these methods, the magnetic toner base particles and the conductive particles are simply mixed, and the adhesion of the conductive particles to the magnetic toner base particles is insufficient, making it difficult to form a stable conductive layer. At present, it is quite difficult to obtain magnetic toner with a constant resistance value because the amount of processing is small. The magnetic toner in this case has drawbacks such as low image density, frequent occurrence of fogging, and deterioration of image quality. In particular, the above-mentioned drawbacks are noticeable in magnetic roll development using an insulating magnetic roll, such as an alumite-treated aluminum sleeve or a plastic sleeve. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a method for producing magnetic toner that is easy to adjust, has stable quality, has high productivity, and can be processed in large quantities. The purpose is to have a stable and low resistance value (below 9.99 x 10 ⁵ Ω-cm. If the value is 1 x 10 ⁴ Ω-cm or more, fogging will often occur during development, resulting in low image density and low commercial value). and
The present invention provides a magnetic toner that has good fluidity, is less likely to cause fogging even in an insulating magnetic roll development system, and has extremely excellent image quality and image density. Further, in the magnetic roll development system, similarly excellent results are achieved when the sleeve is rotated, the magnet is rotated, and the magnetic sleeve is simultaneously rotated. The present invention uses known high-speed fluidized stirrers (hereinafter referred to as stirring tanks; for example, Super Mixer: manufactured by Kawada Seisakusho, Henschel Mixer: manufactured by Mitsui Miike Seisakusho).
The magnetic toner (hereinafter referred to as
magnetic toner base particles) in a stirring tank at a peripheral speed of 200 m/min to 2000 m/min (peripheral speed 200 m/min).
If the temperature is less than 1, the temperature of the magnetic toner base particles will not rise and the surface of the base particles cannot be softened, and particles smaller than the magnetic toner base particles cannot be firmly attached after adding conductive particles. . Also, 2000
At a circumferential speed exceeding m/min, particles smaller than the magnetic toner base particles adhering to the surface of the magnetic toner base particles peel off, making it impossible to achieve uniform coating. ), the temperature is raised to 45°C to 50°C (above the softening point of the magnetic toner base particles) by high-speed stirring and heat generation between the magnetic toner base particles or between the rotating blade and the tank wall.
This is achieved by adding a resistance modifier (for example, carbon black: Mitsubishi Kasei #44), which is a conductive particle, in a range of 1wt% to 5wt%, and uniformly dispersing and coating it by high-speed stirring again. In addition to the above-mentioned resistance adjusting agent, charge adjusting particles may be appropriately mixed. The melting point and softening point expressed here are:
It is measured by the method shown below. Melting pointer (Meihosha Seisakusho:
Place the magnetic toner base particles in the MP2 type) and gradually raise the temperature to make the surface of the magnetic toner base particles
Pressure is applied using a fine needle, and the temperature at which the surface of the base particle is deformed is measured as the softening point. The melting point is determined by the melting pointer above.
The temperature at which the entire magnetic toner base particles are completely melted is measured as the melting point. There are three methods for fixing magnetic toner onto recording paper: (1) fixing with heat, (2) fixing with pressure, and (3) using a combination of heat and pressure. All three methods exhibit good effects. The present invention will be explained below using examples. Example 1 Epoxy resin (Ciel Chemical, Epicoat
#1004) A toner raw material consisting of 50 parts by weight of iron oxide (Toda Kogyo: Magnetite: EPT-500) was kneaded in a twin-screw kneader, and then crushed to 2 mm in a rotoplex pulverizer <Itoman Engineering Model 8/16>.
The following particles are defined as pin mill < Alpine:
The powder thus obtained was pulverized using a wind classifier <Alpine 100MZR> to a size of 10 to 44μ, and then a high-speed fluid stirring tank <Super Mixer: SMG-20 manufactured by Kawada Seisakusho> After self-heating to 45°C by shearing, a resistance modifier <Mitsubishi Kasei: Carbon Black #44> was immediately added at 2 wt% of the weight of the magnetic toner base particles, and dispersed at 1900 γ pm for 60 seconds to uniformly cover the surface of the magnetic toner base particles. (hereinafter referred to as surface coating). The powder obtained in this way is passed through the wind classifier again.
It was classified into 10-44μ. When the resistance value of this magnetic toner was measured using a cell as shown in FIG. 1, it showed a resistance value of 2.00×10 ³ Ω-cm. Here, in FIG. 1, indicates a copper electrode having a length of 1 cm, a width of 1 cm, and a thickness of 0.03 cm. <The distance between the copper electrodes is 1 cm> indicates a glass cell with inner wall dimensions of length: 1 cm, width: 1.06 cm, and height: 3 cm. <Putting a certain amount of magnetic toner into this cell> indicates a covered conductor connected to. <Connecting to Wheatstone Bridge Terminal> Next, the fluidity was measured using a jig as shown in Figure 2, and it showed a value of 0.6 mm. In Fig. 2, indicates a brass plate with a thickness of 0.15 cm and holes 7 of each size. indicates a ring with an inner diameter of 0.8 cm and a height of 1 cm. <Putting magnetic toner into the main ring> indicates the angle to support the ring. Using such a jig, a ring 5 is placed over each hole 7, and the magnetic toner to be measured is put into the ring 5, and the fluidity is indicated by the diameter of the minimum hole 7 at which the magnetic toner starts to fall through the hole 7. Further measurements of the angle of repose showed it to be 31 degrees. The angle of repose is a measure of the fluidity of powder, and is measured using the Powder Tester (PT
-E type). This magnetic toner was developed by a magnetic roll development method (aluminum sleeve and insulating sleeve, magnet rotation) and heat-fixed, resulting in a homogeneous image with high image density and no fogging phenomenon. . Furthermore, in the magnetic roll development system, excellent results similar to those described above were obtained in the sleeve rotation system and the sleeve and magnet simultaneous rotation system. Next, the same experiment as in Example (1) was repeated five times, and as a result, very stable values of resistance, fluidity, and angle of repose were obtained as shown below. Further, the results after development and fixing were also excellent as in Example (1).

[Table] Comparative Example 1 Magnetic toner base particles obtained in Example 1 600c.c.
was placed in a wide-mouthed polyethylene bottle (No. 1), 2wt% of resistance modifier was added to the magnetic toner base particles, surface coating was performed for 30 minutes using a Sheaker <Toyo Seiki>, and 10 to 44 μm was added using a wind classifier. When we measured the resistance value of this magnetic toner classified into 8
The fluidity that showed ×10 ⁴ Ω-cm was 0.9 mm, the angle of repose was 34
showed degree. Similarly, 2.5% of the magnetic toner base particles obtained in Example 1 were placed in a ball mill pot (No. 5), 2wt% of the weight of the magnetic toner base particles and a resistance modifier were added, and surface coating treatment was performed for 3 hours, followed by air classification. It was classified using a machine at 10 to 44μ. When the resistance value of this magnetic toner was measured, it showed a fluidity of ^0.2 mm and an angle of repose of 35 degrees. The above-mentioned magnetic toners were developed using a magnetic roll development method and heat-fixed. As a result, a conductive roll (aluminum sleeve) produced a uniform image with high image density and no fogging. However, with the insulating magnetic roll, a fogging phenomenon occurred and the image density was low, resulting in an image with low commercial value. Next, the same experiment as in Comparative Example (1) was repeated 5 times each using a sheaker and a ball mill pot.
Resistance, fluidity, and angle of repose showed unstable results as shown below. (Tables 2 and 3) Furthermore, the same results as in Comparative Example 2 were obtained after development and fixing. Sheaker treatment

【table】 ball milling

[Table] Example 2 Styrene resin <Etsuso, Picolastic D-
A magnetic toner was obtained in the same manner as in Example 1 using toner raw materials consisting of 125>40 parts by weight, low molecular weight polypropylene <Sanyo Chemical Co., Ltd.: Viscol 550P> 10 parts by weight, and iron oxide <Toda Kogyo: Magnetite EPT500> 50 parts by weight. Ta. When the resistance value of the obtained magnetic toner was measured,
1.5×10 ³ Ω-cm, fluidity is 0.5 mm, angle of repose
It showed 30 degrees. As a result of developing this magnetic toner using a magnetic roll development method and fixing it using a heat roll, a homogeneous image with high image density and no fogging phenomenon was obtained in both the conductive roll and insulating roll development methods. . Comparative Example 2 A magnetic toner was obtained in the same manner as Comparative Example 2 using the magnetic toner base particles obtained in Example 2.
When the resistance value of the obtained magnetic toner was measured, it was 9×
10 ⁴ Ω-cm, the fluidity was 1.0 mm, and the angle of repose was 35 degrees. Similarly, 2.5 of the magnetic toner base particles obtained in Example 2 were placed in a ball mill pot (No. 5), 2 wt% of the resistance modifier was added to the magnetic toner base, surface coating treatment was performed for 3 hours, and air classification was carried out. The resistance value of this magnetic toner, which was classified by a machine at 10 to 44μ, was 1.5×10 ⁵ Ω-cm.
The fluidity was 1.2 mm, and the angle of repose was 35 degrees. The above-mentioned magnetic toners obtained above were developed using a magnetic roll development method and fixed using a heat roll. As a result, a conductive roll (aluminum sleeve) can produce a homogeneous image with high image density that is unlikely to cause fogging. However, on the insulating magnetic roll, fogging occurred and the image density was low, resulting in an image with low commercial value. Example 3 Polyethylene wax [Mitsui Petrochemical, Hiwax. A magnetic toner was prepared in the same manner as in Example 1 using toner raw materials consisting of 30 parts by weight of 200P], 10 parts by weight of EVA [Mitsui Polychemicals, Evaflex #260], and 60 parts by weight of iron oxide [Magnetite EPT-500, manufactured by Toda Kogyo]. I got it. When the resistance value of the obtained magnetic toner is measured,
The resistance was 1.8×10 ³ Ω-cm, the fluidity was 0.6 mm, and the angle of repose was 31 degrees. As a result of developing this magnetic toner with a magnetic roll and fixing it with a pressure fixing roll, a homogeneous image with high image density and no fog development was obtained in both the conductive roll and insulating roll development systems. . Comparative Example 3 A magnetic toner was obtained in the same manner as Comparative Example 1 using the magnetic toner base particles obtained in Example 3.
When the resistance values of both magnetic toners were measured, those treated with Sheaker showed a resistance value of 7×10 ⁴ Ω-cm;
The fluidity was 1.1 mm and the angle of repose was 35 degrees. The resistance value of the ball milled product is 5×10 ⁵ Ω−
cm, the fluidity was 1.2 mm, and the angle of repose was 35 degrees. The obtained bimagnetic toner was developed with a magnetic roll and fixed with a pressure fixing roll. As a result, on the conductive roll (aluminum sleeve), a homogeneous image with high image density was obtained that was unlikely to cause fogging. In the case of an insulating magnetic roll, a fogging phenomenon occurred, and the image density was low, resulting in an image with low commercial value. As described above, according to the present invention, conductive particles as a resistance adjusting agent are attached to the surface of magnetic toner base particles in a state where the surface is heated from below the melting point to above the softening point by high-speed stirring. In order to be forced to
The conductive particles are uniformly dispersed on the surface of the magnetic toner base particles and are firmly coated. Therefore, a magnetic toner with low resistance, good fluidity, excellent image quality, and stable quality of images with high definition can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a cell for measuring resistance value in each example and comparative example of the present invention, and FIG. 2 is a perspective view of a jig for measuring fluidity in each example and comparative example of the present invention.

Claims (1)

[Claims] 1. At least the surface of the magnetic toner base particles consisting of a binder resin and a magnetic material is heated to a temperature lower than the melting temperature of the magnetic toner base particles and above the softening point by the shearing force of a high-speed fluidized stirrer. After that,
A method for producing a magnetic toner, which comprises again adhering conductive particles to the surface of magnetic toner base particles by the shearing force of a high-speed fluid agitator. 2. Using a high-speed fluidized stirrer, the circumferential speed is 200 m/min or more.
2. The method for producing a magnetic toner according to claim 1, wherein the conductive particles are attached to the surface of the magnetic toner base particles at a speed of 2000 m/min.