JP2503221B2 - Developer for electrostatic image - Google Patents

Description

TECHNICAL FIELD The present invention relates to a developer used to visualize an electrostatic charge image formed on the surface of an image carrier.

[Conventional technology]

The electrostatic image developing agent is used in electrophotography, electrostatic printing, electrostatic recording, etc., but the developing principle is essentially the same in all methods.

For example, in electrophotography, the surface of a photoreceptor such as selenium, zinc oxide, or an organic photoconductor is uniformly charged, and then exposed to form an electrostatic charge image. Iron powder, ferrite powder, etc. are formed on the electrostatic charge image. Of the magnetic particles of the carrier and the toner of the insulating colored resin powder are mixed (in the case of regular development, the toner is triboelectrically charged in the opposite polarity to the electrostatic image) to develop. To do. Then, this is fixed, or the transfer sheets are overlapped and an electric field is applied from the back surface of the transfer sheet to transfer the image, and then the image is fixed. The toner remaining on the surface of the photoconductor after the transfer is removed by a cleaning member such as a blade or a fur brush.

In such an image forming method, in order to stably obtain a high-quality image, it is necessary that the triboelectric charge amount of each toner particle be uniform and that the charge amount be stable. Therefore, in a normal two-component developer, a charge control agent is added inside the toner particles, but it is not always possible to obtain a uniform and stable charge amount. It is considered that this is due to the formation of a toner film on the surface of the carrier (referred to as spent toner) or the formation of a thin layer of toner on the surface of the photoconductor (referred to as filming).

In order to solve such a problem, it is usually performed to add a small amount (several weight% or less) of magnetic oxide particles such as magnetite (Fe ₃ O ₄ ) to the toner. Further, it has been proposed to add composite metal oxide particles having a saturation magnetization of 10 emu / g or less to the surface or inside of the toner particles. (See JP-A-62-2272) [Problems to be Solved by the Invention] However, by adding a small amount of Fe ₃ O ₄ or complex metal oxide particles with low saturation magnetization to the toner, the charge amount of the toner is increased. Although the homogenization and stabilization of the toner are considerably improved, they are insufficient in terms of preventing toner scattering and background fog.

Therefore, an object of the present invention is to provide a developer for electrostatic charge images in which toner scattering and background fog are small and a high quality image can be obtained.

[Means for solving problems]

The developer for electrostatic charge image of the present invention is a developer comprising a magnetic carrier and a toner containing a binder resin and a colorant, and has a toner concentration in the range of 2 to 10% by weight. It is characterized by containing 1 to 30% by weight of magnetic metal oxide particles having a diameter of 1 μm or less and having a saturation magnetization in the range of 10 to 40 emu / g and having a specific composition.

The toner constituting the developer according to the present invention has a saturation magnetization of 10 to 40 em with a fixing resin and a colorant as essential components.
It is necessary to include magnetic metal oxide particles with magnetic properties such as in the u / g range. By adding the magnetic metal oxide particles to the toner, the charge amount of each toner particle can be made uniform and the charge amount of the toner can be stabilized over a long period of time, and further, it is possible to prevent toner scattering and ground fog. Is also effective. If the saturation magnetization value is less than 10emu / g, there is no effect.On the other hand, if the saturation magnetization value is more than 40emu / g, the magnetic attraction force of the magnet roll that constitutes the developing roll increases the force attracted onto the non-magnetic sleeve. Becomes
Image density decreases. The saturation magnetization is a value measured by a vibrating sample magnetometer (VSM-3 manufactured by Toei Industry Co., Ltd.) in a maximum magnetic field of 10 kOe. The average particle size of the magnetic metal oxide particles is less than 1.0 μm in order to uniformly disperse the particles in the toner.

As such magnetic metal oxide particles, specifically, soft ferrite having a composition represented by the following formula may be used.

[MeO] _x [Fe ₂ O ₃ ] _100-x Here, Me is any one of Ni + Zn, Mg + Zn, Cu + Zn, or Li + Zn, and x is in the range of 45 to 80 mol%.

The magnetic metal oxide particles are produced, for example, by the following method. First, the above oxides or carbonates of metals and iron oxide (Fe ₂ O ₃ ) are mixed at a predetermined ratio, and the resulting mixture is mixed with 800
It is calcined at a temperature of up to 1000 ° C. and then ground into particles with a particle size of 1 μm or less. This pulverized powder may be used, but if necessary, the pulverized powder may be fired at a temperature not higher than the crystal growth temperature. When firing at a crystal growth temperature or higher, re-grinding is performed to obtain magnetic metal oxide particles having a predetermined particle size.

In the present invention, the toner, together with the metal oxide particles,
It contains a binder resin and a colorant as essential components.

As the binder resin, one or more known resins can be appropriately selected and used according to the fixing method. For example, in the case of the heat roll fixing method, one or more kinds of styrene-acrylic copolymer, styrene-butadiene copolymer, epoxy resin, polyester resin and the like can be used.

Examples of the colorant include carbon black, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black and rose bengal. it can. These colorants need to be contained in a sufficient amount to form a visible image with a sufficient density, and are usually added in an amount of 1 to 20% by weight based on the total amount of the toner.

Further, a charge control agent can be added to the toner in order to impart a predetermined chargeability to the toner. As the charge control agent, a nigrosine dye having a positive charging property, based on it, a reaction product of an aliphatic monobasic acid and / or a dibasic acid, a reaction product of a nigrosine dye and a carboxyl group-containing resin, triphenyl Examples include metal-containing complexes such as methane dyes, piperazine polymers, and Cr-containing azo dyes having negative charging characteristics. The appropriate amount of the charge control agent added is in the range of 0.1 to 10% by weight based on the total amount of the toner. The toner charge amount is preferably in the range of 5 to 30 μc / g in absolute value when measured by the blow-off method (using Toshiba Chemical's TB-200 type). If the charge amount is less than 5 μc / g, the toner may scatter,
If fog occurs on the ground and is more than 30 μc / g, the developability is deteriorated.

The toner of the present invention can be manufactured, for example, as follows. Raw materials such as a resin, a colorant, and magnetic metal oxide particles are dry preliminarily mixed, kneaded by heating with a kneader or the like, and then cooled and solidified. Then, it is pulverized by a jet mill and classified by a zigzag classifier to obtain a toner having an average particle size of 3 to 30 μm. When the average particle size is less than 3 μm, the developability is deteriorated, and the fog of the image increases, and when it exceeds 30 μm, the graininess of the image becomes severe. It is preferably in the range of 10 to 20 μm.

The developer of the present invention is obtained by mixing toner and magnetic carrier. As the magnetic carrier, various known ones,
For example, iron powder, magnetite powder, or soft ferrite powder such as Ni-Zn ferrite, Cu-Zn ferrite, and Mn-Zn ferrite can be used. These powders are
It may be used as it is, or the surface may be coated with a resin for the purpose of adjusting the chargeability of the carrier.
Further, the resistance of the carrier is preferably in the range of 10 ³ to 10 ¹³ Ω · cm as a measured value when powder is filled in an insulating cell having a gap between electrodes of 5 mm and a voltage of DC 100 V is applied between the electrodes. If the resistance of the carrier is less than 10 ¹³ Ω · cm, carrier adhesion is likely to occur, and if it exceeds 10 ¹³ Ω · cm, the developability is lowered and the image density is lowered. It is preferably 10 ⁶ to 10 ¹⁰ Ω · cm.

The mixing ratio of the toner and the carrier is 2 to the toner concentration.
A range of 10% by weight is preferable. When the toner concentration is less than 2% by weight, carrier adhesion occurs, and when it exceeds 10% by weight, toner scattering and background fog increase.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples,
The invention is not limited to these examples.

Example 1 Raw materials were mixed in a predetermined ratio and calcined at 900 ° C. for 1 hour,
Then, it was wet-ground to an average particle size of 0.8 μm. The obtained pulverized powder is baked at a temperature of 1200 ° C for 5 hours, and the average particle size is 0.8μ again.
m was wet pulverized and then dried to obtain a ferrite powder. This ferrite powder has a molar ratio of 10% NiO and 10% ZnO.
70%, Fe ₂ O ₃ has a composition of 20%, and its saturation magnetization is 12 emu.
It was / g.

25% by weight of this ferrite powder, 60 parts by weight of styrene-acrylic copolymer (Haimer SBM70 manufactured by Sanyo Kasei), 3 parts by weight of low molecular weight polypropylene (Viscor 550P manufactured by Sanyo Kasei), 10 parts by weight of carbon black (# 50 manufactured by Mitsubishi Kasei). , 2 parts by weight of negatively charged dye (Bontron E81 manufactured by Orient Chemical Co., Ltd.) was dry-premixed, kneaded by heating with a kneader, cooled and solidified, then pulverized by a jet mill, and then classified by a zigzag classifier to obtain an average particle size of 12 μm. Toner (saturation magnetization 3emu / g, charge amount -20μc / g) The above toner and ferrite carrier (Hitachi Metal KBN
-100 and a particle size of 74 to 144 μm) were mixed to prepare a developer having a toner concentration of 5% by weight.

A commercially available electronic copying machine (Konishi Roku U-Bi
x 3000 machines, but the development gap was changed to 1.5 mm and the doctor gap was changed to 1.2 mm), the image was evaluated, and the image density was 1.40 and the resolution was 6.3 lines / mm. . In addition, a continuous copy test confirmed that clear images could be obtained up to 100,000 sheets.

Comparative Example 1 A toner was prepared under the same conditions as in Example 1 except that the ferrite powder was not contained and the styrene-acrylic copolymer was 85 parts by weight.

Using this toner, a developer was prepared under the same conditions as in Example 1 and image evaluation was carried out. As a result, background fog was observed at an image density of 1.51 and a resolution of 3.6 lines / mm.

Comparative Example 2 Example 1 except that the content of the ferrite powder was 35 parts by weight and the content of the styrene-acrylic copolymer was 60 parts by weight.
A toner was prepared under the same conditions as described above. The saturation magnetization of the obtained toner was 4.2 emu / g.

Using this toner, a developer was adjusted under the same conditions as in Example 1 and image evaluation was carried out. As a result, a good image with an image density of 1.38 and a resolution of 45 lines / mm was obtained, but the toner fixability deteriorated. did.

Example 2 An Mg-Zn ferrite powder was obtained under the same conditions as in Example 1 except that the type and blending amount of raw materials were changed. This ferrite powder has a molar ratio of 25% MgO, 45% ZnO and 30% Fe ₂ O _3.
%, And its saturation magnetization was 25 emu / g.

The content of the ferrite powder is 15 parts by weight, styrene-
A developer was adjusted under the same conditions as in Example 1 except that the content of the acrylic copolymer was changed to 70 parts by weight, and image evaluation was performed. The image density was 1.41 and the resolution was 6.3 lines / mm. No good quality images were obtained.

Example 3 A Cu-Zn ferrite powder was obtained under the same conditions as in Example 1 except that the type and blending amount of raw materials were changed. This ferrite powder has a molar ratio of 10% CuO, 50% ZnO and 40% Fe ₂ O _3.
%, And its saturation magnetization was 32 emu / g.

5 parts by weight of the above ferrite powder, styrene-
A developer was prepared and image evaluation was performed under the same conditions as in Example 1 except that the content of the acrylic copolymer was 80 parts by weight. The obtained image had a density of 1.40, a resolution of 6.3 lines / mm, and was of good quality without background fog. The results of the continuous copy test also showed clear images up to 100,000 sheets.

Example 4 Li-Zn ferrite powder was obtained under the same conditions as in Example 1 except that the type and blending amount of raw materials were changed. This ferrite powder has a molar ratio of 20% LiO, 40% ZnO and 40% Fe ₂ O _3.
%, And its saturation magnetization was 40 emu / g.

3 parts by weight of the above ferrite powder, styrene-
A developer was prepared under the same conditions as in Example 1 except that the content of the acrylic copolymer was 82 parts by weight, and image evaluation was performed. The obtained image had a density of 1.46, a resolution of 6.3 lines / mm, and was of good quality with no background fog. Also, the results of continuous copying tests showed that clear images were obtained up to 100,000 sheets.

Example 5 A developer was prepared under the same conditions as in Example 1 except that an iron powder carrier was used in place of the ferrite carrier, and the development gap was 3.0 mm and the doctor gap was 3.0 mm. The image was evaluated under the conditions. The resulting image is
It had a density of 1.46 and a resolution of 6.3 lines / mm, and was clear without background fog. Also, in the result of the continuous copy test, clear images were obtained up to 30,000 sheets.

Comparative Example 3 Mn-Zn ferrite powder was obtained under the same conditions as in Example 1 except that the type and blending amount of raw materials were changed. This ferrite powder has a molar ratio of 20% MnO, 35% ZnO and 45% Fe ₂ O _3.
%, And its saturation magnetization was 48 emu / g.

The content of the ferrite powder is 1 part by weight, styrene-
A developer was prepared under the same conditions as in Example 1 except that the content of the acrylic copolymer was 84 parts by weight, and image evaluation was performed. The obtained image had a density of 1.42 and a resolution of 6.3 lines / mm, and background fog was recognized.

 Table 1 shows the results of the above Examples and Comparative Examples.

It can be seen from the above table that a clear image without background fog can be obtained by using a toner containing 1 to 30% by weight of a magnetic powder having an Os of 10 to 40 emu / g and a carrier.

[Effects of the Invention] As described above, according to the present invention, since a developer is prepared using a toner containing metal oxide particles having a specific saturation magnetization, a clear image without background fog can be obtained.

Claims (1)

(57) [Claims] 1. A developer for electrostatic image comprising a magnetic carrier, a toner containing a hinder resin and a colorant, wherein the toner concentration is in the range of 2 to 10% by weight.
An electrostatic charge image having an average particle size of 1 μm, having a saturation magnetization in the range of 10 to 40 emu / g, and containing 1 to 30% by weight of a magnetic metal oxide having a composition represented by the following formula. Developer. _{(MeO) 100-x (Fe} 2 O 3) x where, Me is either Ni + Zn, Mg + Zn, Cu + Zn or Li + Zn. x = 45-80 mol%