JPH0619594B2 - Carrier material for electrostatic image development and method of manufacturing the same - Google Patents

Description

The present invention relates to an electrostatic image developing carrier material and a method for producing the same.

B. Prior Art As a two-component developing method in electrophotographic copying, a cascade developing method and a magnetic brush developing method are well known.
That is, a visible image is formed by attaching toner particles using a carrier as a carrier to an electrostatic charge image or an electrostatic latent image formed on a photoreceptor by charging and exposure, and transferring this to paper or other support. , Is a method of fixing.

At present, iron powder carriers generally put into practical use are classified into the following two types according to their external shapes. One is that it has an irregular shape whose shape is indefinite,
The other one has a spherical shape or a granular shape close to a spherical shape. When each of these is used as a developer, the following drawbacks are recognized. That is, a carrier having an irregular shape whose shape is not fixed (1) is likely to cause "cracks" or "chips" in the process of transporting the developer, which damages the surface of the photoconductor, resulting in image deterioration. Aggravate.

(2) The fluidity of the developer is poor, which causes the deterioration of the copying function.

It has the drawback of

On the other hand, a spherical carrier or a granular carrier close to a sphere has (1) a small effective surface area and low toner supply efficiency.

(2) Since the apparent density is large and the filling weight per unit volume is large, there are drawbacks that the deterioration of the developer is accelerated and the torque applied to the developing roller in the process of conveyance becomes large.

In addition, Japanese Patent Publication No. 53-40092 discloses 50 to 100 μm.
Nodular carriers having an average particle size distribution in the range of are disclosed. That is, this knot-shaped carrier is a fine powder of iron or nickel, an inorganic substance such as sodium silicate, or a styrene-acrylic copolymer or polyvinyl chloride is used as a binder to be spheroidized and dried, for example, at around 125 ° C. After that, when an inorganic material is used as a binder, it is further sintered at 1250 to 1300 ° C to prepare a nodular carrier. It is described that the developer carrier thus prepared has improved triboelectrification characteristics, durability and other image characteristics when used as a developer. However, the development carrier described in the above publication is highly sintered only when an inorganic binder is used,
Its density is 4.43 to 6.41 g / cc, which is considerably high, which is not desirable when considering high durability.

On the other hand, in Japanese Examined Patent Publication No. 55-40863, since the raw iron powder is sintered, pulverized and classified, it becomes an irregular shaped iron powder carrier,
Due to the shape anisotropy, the magnetic flux density is high in the developing magnetic field and the ears are hard, and the solid portions (solid black portions) are likely to have crevices (toner peeling portions).

Further, the ferrite carrier described in Japanese Patent Publication No. 56-52305 has a low saturation magnetization, and when the carrier particles are made smaller in size, carrier adhesion occurs, causing scratches on the photoconductor and the cleaning blade. Has the drawback of significantly shortening its durability.

C. Object of the Invention The present invention has been made in view of the above circumstances.
The first purpose thereof is to eliminate the above-mentioned drawbacks of the carrier having an irregularly shaped irregular shape and the spherical or near-spherical granular carrier, and to make full use of their merits, that is, it is apparently almost the same. It is to provide a carrier material that is spherical and has excellent fluidity, transportability, and durability, and that has no carrier adhesion and high development efficiency.

The second object of the present invention is to have a large number of irregularities on the surface of the particle, which has a large specific surface area, despite being substantially spherical.
It is to provide a carrier material having excellent toner supply efficiency. Further, since the irregularities on the particle surface can be arbitrarily changed by polishing or the like, it is possible to select the effective surface area over a wide range.

Still another object of the present invention is that although it is spherical, it has a low apparent density, and therefore the filling weight per unit volume can be reduced, so that it has an effective feature from the standpoint of material saving, and the manufacturing method is simple. And to provide an inexpensive carrier material.

Another object of the present invention is to provide a method for effectively producing the carrier material as described above.

D, constitution of the invention and its action and effect The above-mentioned object of the present invention is obtained by sintering a slurry consisting of fine iron powder and an organic binder, the appearance constituted by a fine powder aggregate mainly composed of fine iron powder It is achieved by a carrier material for electrostatic image development, which is a substantially spherical powder, the surface of which is polished.

According to the present invention, since the spherical carrier material is mainly composed of an aggregate of fine iron powder particles, it has a large number of pores inside the spherical carrier material, and the carrier particle surface has fine particles on a smooth surface. Are arranged in an innumerable manner, so innumerable irregularities are observed. For this reason, it is possible to obtain a carrier that is spherical, yet has a small apparent density and a large effective area. The presence of pores inside the particles (porosity is preferably 20 to 30%) or the presence of irregularities on the particle surface, which is one of the characteristics of the spherical carrier material of the present invention, relates to the production method of the present invention described later. The explanation and the accompanying pictures will also make it clear.

Further, in the present invention, since the surface of the fine powder aggregate particles constituting the carrier material is polished, the specific surface area of the particles, the apparent density, the fluidity can be set in a desired range, the resulting image quality, durability Is significantly improved, and carrier adhesion, damage to the photoconductor and cleaning blade, etc. can be prevented.

In the present invention, the above-mentioned “apparently spherical powder” is defined as a powder having a shape factor of 5.8 × 10 ⁻² or more and less than 8.0 × 10 ⁻² . Here, the shape factor is defined as the value obtained by dividing the projected area of one carrier by the square of the projected perimeter of the carrier.
× becomes 10 ^-2 or more, and 8.0 × 10 ^-2 true sphere.

The carrier material of the present invention includes, in addition to the outwardly spherical powder composed of a myriad of fine iron powders, a myriad of fine iron powders and metal fine powders (eg Ni) or metal oxides (eg alumina). It may be iron or an iron-based carrier for electrostatic image development, which is obtained by polishing the surface of an apparently spherical powder composed of aggregates.

Further, when forming a set of fine iron powder or a mixed powder of fine iron powder and metal fine powder or metal oxide, using a polymer and an organic substance (hereinafter, referred to as an organic binder) as a binder,
If the sintering is performed, the organic binder is evaporated and removed by the sintering, which is effective in reducing the weight of the carrier material. The average particle size of the fine iron powder to be used is preferably 10 μm or less, 0.1 μm or more, particularly 5 μm or less, 0.5 μm or more, and 400 to 1200 ° C. in a non-oxidizing atmosphere during sintering. It is preferable to sinter at 900 to 1050 ° C. If the sintering temperature is less than 400 ° C, insufficient sintering tends to occur.

The fine metal powder may be made of nickel, manganese, copper, chromium, cobalt, zinc or the like. In addition to alumina, the above metal oxide may be silica, titanium oxide, calcium oxide, or the like. These are preferably mixed in a weight ratio of 5 to 20% with respect to the fine iron powder, and more preferably 10 to 15%.

In order to produce the carrier material of the present invention, a step of atomizing a slurry mainly composed of fine iron powder and an organic binder and drying, and the dry powder thus obtained are sintered in a non-oxidizing atmosphere. It is desirable to adopt a method of manufacturing a carrier material for electrostatic image development, which comprises a step and a step of polishing the surface of this sintered product.

In particular, after making fine iron powder or a mixed powder of fine iron powder and metal powder or metal oxide into a slurry of water and an organic binder, or an organic solvent and an organic binder, jet spray or a high-speed rotating disk surface. Atomized, dried in the air while staying, and collected, and then 400-120 in a non-oxidizing atmosphere.
It is desirable to sinter at 0 ° C. and further polish the surface. That is, 30 to 70% by weight of fine iron powder having an average particle size of 0.1 to 10 μm in water or an organic solvent such as alcohol or ketone.
Mix and suspend to make a slurry. Further, 0.5 to 5% by weight of polyvinyl alcohol, saccharides or various plastics are added and mixed as a binder into this slurry.
This slurry is compressed and sprayed from a nozzle, or dropped onto a disk rotating at a high speed and sprayed by centrifugal force to obtain droplets of 10 to 1000 μm. The droplet becomes spherical due to surface tension while flying in the air. Next, while the spherical droplets are staying in the air, hot air at an appropriate temperature is introduced to evaporate and remove water or organic solvent in the droplets, and the droplets are collected by falling. Spherical iron powder of 10 to 1000 μm in which fine iron powder is hardened with an organic binder as powder is obtained. Furthermore, when this spherical iron powder is sintered at a temperature of 400 to 1200 ° C. in a high-temperature firing furnace in a non-oxidizing atmosphere, the organic binder evaporates, and strong sintering occurs between the fine iron powder particles, Spherical iron powder reaches sufficient strength as a carrier.

Further, in the production process of the present invention, fine iron powder and water or an organic solvent, by mixing other metal powder or an oxide thereof in a slurry consisting of an organic binder, they are evenly distributed among iron powder particles. A spherical carrier interspersed with is obtained. The magnetic force, electric resistance, etc. can be freely adjusted depending on the type and amount of the metal powder or their oxides to be added, and such a manufacturing method enables a wider range of support for the various properties required as a carrier. It is what

In the above, as the usable organic binder, polyvinyl alcohol, polyester derived from saturated or unsaturated fatty acid, alkyl cellulose, acrylic resin, butyral resin, epoxy resin or the like can be used, and the dispersion effect and the binding effect can be obtained. Polycarboxylic acid salts, naphthalene sulfonates, and lignin sulfonates having both of the above are preferable.

Examples of the organic solvent for the slurry include alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, and the like.

E, Examples Hereinafter, the present invention will be described in more detail with reference to Examples.
The following examples can be variously modified based on the technical idea of the present invention.

Example 1. 20 kg of fine iron powder having an average particle size of 3 μm, 10 kg of water and 300 g of polyvinyl alcohol are mixed by stirring, and the resulting slurry is dripped onto a disk rotating at 5000 rpm, and the temperature of the droplets during spray flight is 160 ° C.
Was blown and dried to obtain 19.5 kg of spherical iron powder (Sample A).

Separately, 20 kg of fine iron powder having an average particle size of 5 μm, 15 kg of water, and 400 g of polyvinyl alcohol were mixed with stirring to obtain a slurry.
It was dropped on the disk surface rotating at 000 rpm, and the same operation as in Sample 1 was performed to obtain 19.5 kg of spherical iron powder (Sample B).

Separately, 20 kg of fine iron powder with an average particle size of 3 μm was added to 10 kg of acetone.
kg, 200 g of cellulose acetate were added, and the slurry was stirred and mixed, introduced into a diaphragm pump, compressed to a pressure of 10 kg / cm ² , and injected into the atmosphere at 30 ° C from a nozzle having a fine orifice to produce spherical iron powder 19.5. kg was obtained (Sample C).

The samples A, B, and C were sieved to 100 to 200 mesh, and 12.7 kg of the sample A, 10.7 kg of the sample B, and 13.6 kg of the sample C were obtained. Next, each of these in a hydrogen gas stream
Sintering was performed at 1000 ° C. for 60 minutes. The three kinds of samples thus obtained were further surface-polished by a high-speed rotary polishing machine, and samples A, B, and
Corresponding samples 1, 2, and 3 were obtained from C, and the following characteristics were confirmed for these and shown in Table 1. The iron powder for comparison is an irregular iron powder and a commercially available spherical carrier iron powder having the same particle size, which is not according to the present invention.

As is clear from Table 1, the spherical iron powder according to the present invention has the characteristics that are apparently required to be irregularly shaped in terms of apparent density and specific surface area, and has the characteristics of spherical powder in terms of fluidity. You can see that they are satisfied enough.

Example 2. Sample No. 1 according to the present invention shown in Table 1 was processed by a high-speed rotary polishing machine while changing the processing degree, and the respective properties are shown in Table 2. From this table, it can be seen that the powder characteristics can be variously changed depending on the degree of polishing.

As described above, the carrier iron powder according to the present invention, and the iron-based carrier in which the iron powder is provided with another metal or oxide, has the advantage of irregularly shaped powder and spherical powder used for electrostatic image development. It turned out to be an excellent career with both. Further, as a manufacturing method, for example, fine iron powder of 1 to 10 μm, or other fine metal or an oxide thereof is arranged on the fine iron powder, and water, an organic solvent, and a slurry composed of a binder are sprayed into the air. Mainly making a spherical powder while staying, it is possible to combine various raw materials and to produce a wide composition range and particle size range.

Further, for the atomization of the slurry, a disk rotating at a high speed or a spray jet is used, which is more efficient than an ordinary inclined rotation type pelletizer, and the yield of fine particles of a desired size can be improved. is there.

Example 3. An average 10 μ toner produced by using each carrier shown in Table 1, 100 parts by weight of polyester resin and 10 parts by weight of carbon black, and a hydrophobic Sio ₂ (R-
972) 0.8% is mixed to prepare a developer having the following toner concentration, and electrophotographic copying material "U-BIX5000" (manufactured by Konishi Rokusha Kogyo Co., Ltd.) is used, and the distance between the sleeve and the drum is 2.5 mm.
The image density and solid black uniformity were evaluated by setting the distance between the series blades to 2.0 mm.

In addition, Table 3 shows the results of a durability test conducted by a continuous long run of 30,000 copies using the copying machine.

As described above, the carrier according to the present invention had a high Dmax and gave a high quality image without crispness, and the image quality and Q / M did not change even up to 30,000 copies, which was good.

Example 4. Image evaluation and durability test were performed in the same manner as in Example 1 using each carrier shown in Table 2. The results are shown in Table-4.

As described above, the carrier according to the present invention has significantly higher durability than the carrier without polishing. Also, a large amount of spent toner was detected in the carrier without polishing.

[Brief description of drawings]

The drawing is a photomicrograph (magnification: 375) showing the particle shape of carrier particles according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Nomori Inventor Hiroyuki Nomori 2970 Ishikawa-cho, Hachioji-shi, Tokyo Inside Konishi Rokusha Shinkogyo Co., Ltd. Industry Co., Ltd. (72) Inventor Shoichi Takeuchi 7 No. 7 Tsukiko Sakae-cho, Okayama City, Okayama Prefecture Dowa Iron & Powder Co., Ltd.

Claims (2)

[Claims] 1. An externally spherical powder, which is obtained by sintering a slurry of fine iron powder and an organic binder, and which is mainly composed of a fine powder aggregate of fine iron powder and has a surface of A carrier material for electrostatic image development characterized by being polished. 2. A step of atomizing and drying a slurry mainly composed of fine iron powder and an organic binder, a step of sintering the dry powder thus obtained in a non-oxidizing atmosphere, and this sintering. And a step of polishing the surface of the object.