JPS6313055A - Developer for electrostatic development - Google Patents

Abstract

PURPOSE:To obtain a high-quality image by specifying the resistance to be possessed by a ferrite carrier, incorporating a nonconductive black dye or black pigment together with a coloring agent into a toner and specifying the relative dielectric constant thereof. CONSTITUTION:The ferrite carrier to be used is constituted of the complete mixture composed of a metal oxide of Ni, Zn, Mg, Cu, Li, Ba, V, Cr, Ca, etc., and tervalent iron oxide. The ferrite carrier having >=1X10<7>OMEGA.cm volume resistivity is used in terms of the image quality, more particularly, image density. The toner to be used is particles of 10-20mum average grain size prepd. by dispersing the coloring agent into the fixing resin. The relative dielectric constant of the toner is required to be specified to <=2.2 as the properties of the toner. The resistance of the toner increases and the improved environmental resistant stability and stabilized image quality of the toner are obtd. if the relative dielectric constant is small. The high-quality image is, therefore, obtd. regardless of environmental conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developer for electrostatic development comprising a ferrite carrier, a toner containing a fixing resin and a colorant.

[Conventional technology]

Developers for electrostatic development are used in electrophotography, electrostatic printing, electrostatic recording, etc., but the development 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 light to form an electrostatic latent image, and a magnetic carrier and toner, which is an insulating colored fine powder, are Development is performed using a developer mixed with, for example, a magnetic brush method.

The developer is charged with a predetermined polarity due to friction between the toner and the carrier. The developed toner image is transferred onto a transfer sheet such as plain paper and fixed thereon to obtain a final image.

In the above-mentioned so-called two-component developer, an iron powder carrier is used as a carrier, and usually one whose surface has been oxidized is often used in order to stabilize triboelectric charging characteristics. However, with long-term use, this iron powder carrier has the disadvantage that a toner film is formed on the particle surface or oxides on the particle surface are lost, resulting in a large change in resistance and unstable triboelectric charging characteristics. There is. As a result, image density decreases and fog increases.

Therefore, in order to eliminate such drawbacks, for example,
Ferrite carriers have been proposed and put into practical use as disclosed in Japanese Patent Application Laid-open No. 52305, Japanese Patent Application Laid-open Nos. 172060/1980 and 76756/1982. Compared to iron powder carriers, this ferrite carrier has the advantages of being chemically stable and having less resistance change during use, being soft and having a low reliable feed torque, and having low saturation magnetization, making it possible to form a soft magnetic brush. .

Further, the toner used together with the carrier contains a fixing resin and a colorant as essential components, and other components such as a release agent and a charge control agent are added as necessary. In normal copying, in order to obtain a black image, carbon or black is used as a coloring agent, as described in, for example, Japanese Patent Publication No. 52-3304, Japanese Patent Publication No. 60-10617, and Japanese Patent Application Laid-open No. 53-33151. It is common to use

[Problem that the invention seeks to solve]

However, when toner containing carbon black is used, the following problems occur.

Since a normal carbon blank is hydrophilic, the volume resistance of the toner decreases when the carbon blank absorbs moisture at high temperatures. Therefore, there is a problem that the image quality changes depending on the environmental conditions. Furthermore, carbon blanks are electrically conductive, and from the viewpoint of image density, carbon blanks are usually
Since the content is about 15% by weight, the developability is good, but there is a problem that the contrast of the image becomes high.

Furthermore, there is a problem that the load control agent is adversely affected, and the amount of triboelectric charge of the toner becomes unstable, resulting in a lack of stability in image quality.

Therefore, an object of the present invention is to solve the above-mentioned problems and
An object of the present invention is to provide a developer for electrostatic development that has good environmental stability and can stably obtain high-quality images.

[Means for solving problems]

The electrostatic developer of the present invention includes a ferrite carrier,
The ferrite carrier is composed of a fixing resin and a toner containing a colorant, and the ferrite carrier has a volume resistivity of 1 x 107 Ωcm or more, and the toner contains a substantially non-conductive black dye or black pigment as a colorant, and has a comparatively It is characterized by a dielectric constant of 2.2 or less.

First, the ferrite carrier used in the present invention is made of Ni
, Zn, Mn, Mg, Cu, Li, Ba,
It is composed of a complete mixture of oxides of metals such as V, Cr, and Ca and trivalent iron oxides, and is a soft magnetic material with a crystallographic structure of spinel, perovskite, hexagonal, garnet, or orthoferrite. characterized.

In terms of image quality and sometimes image density, in the present invention, 1×10'Ω
- It is necessary to use a ferrite carrier having a volume resistance of 1 or more. Also, among the carrier physical properties, saturation magnetization (σ
, ) is preferably in the range of 40 to 90 emu/g. σ is 40
If it is less than emu/g, even if the magnetic force of the developing magnet roll is strengthened (more than 850 G on a non-magnetic sleeve), the roll will separate and the carrier will easily adhere to the surface of the photoreceptor, while σ is 90 emu If it is larger than /g, the conveying force is too strong and the toner is likely to be deformed or destroyed, and the ears of the magnetic brush become hard, resulting in poor reproducibility of intermediate tones. Further, the average particle diameter of the carrier is preferably in the range of 40 to 150 μm. The smaller the particle size, the larger the specific surface area, which increases the maximum toner concentration, improves durability, and improves image quality, so it is preferably 150 μm or less, but if it is smaller than 40 μm, carrier adhesion to the photoreceptor surface tends to occur. Become.

Such a ferrite carrier is manufactured, for example, as follows.

First, a metal oxide and iron oxide (FezO+) are mixed in a predetermined ratio, calcined at a temperature of 800 to 1000°C for several hours, and then ground to a size of several μm or less. Next, the pulverized powder is fog-dried in a heated atmosphere, with a binder added if necessary, to obtain spherical particles. and spherical particles at 1) 00~1300℃
After sintering at a temperature of

Next, the toner used in the present invention is particles having an average particle size of 1° to 201) m, which are obtained by dispersing a coloring agent in a fixing resin. The fixing resin is appropriately selected depending on the fixing method (oven, flash, heat roll, pressure). For example, in the case of a heat roll fixing toner, epoxy resins, polyester resins, styrene resins such as styrene-butadiene copolymers, styrene-acrylic copolymers, and mixed resins thereof can be used.

A semiconductive or insulating black coloring agent is used instead of the commonly used carbon blank. Examples of such colorants include metal-containing dyes, nigrosine dyes, black dyes such as aniline black, and black pigments. The content of the colorant is preferably in the range of 3 to 10% by weight. If it is less than 3% by weight, sufficient image density cannot be obtained, and if it exceeds 10% by weight, the fluidity of the toner will decrease.

The toner of the present invention may contain the following components in addition to the above essential components.

When used in a heat roll fixing method, it is desirable to add a known release agent to enhance the offset prevention effect. As the mold release agent, aliphatic resins such as polyalkylene can be used, but low molecular weight polyolefins having - of 10,000 or less, such as low molecular weight polypropylene and/or low molecular weight polyethylene, are preferred. The amount added is preferably in the range of 1 to 5% by weight. If the amount added is less than 1% by weight, the effect will be small, and if it exceeds 5% by weight, the fluidity of the toner will decrease.

A known charge control agent can be added for the purpose of controlling the charge characteristics of the toner. Examples of positive charge control agents include nigrosine dyes, reaction products based on the same with aliphatic basic acids and/or dibasic acids, reaction products of nigrosine dyes and carboxyl-containing resins, triphenylmethane dyes, etc. can be mentioned. Examples of negative charge control agents include metal-containing azo dyes. The amount of charge control agent added is 1~
A range of 5% by weight is preferable. If it is less than 1% by weight, the charge control effect will be small, and if it exceeds 5% by weight, the fluidity and aggregation resistance of the toner will decrease.

Hydrophobic silica fine powder may be added to the surface and/or inside of the toner in order to improve the fluidity of the toner and the rigidity resistance to the photoreceptor. The amount added is preferably in the range of 0.1 to 5% by weight.

Further, part of the fixing resin may be replaced with inorganic fine powder such as calcium carbonate. If the amount added is small, there will be no effect,
If the amount is too large, the image characteristics will deteriorate, so the range of 1 to 10% by weight is preferable.

A toner made of the above-mentioned components is manufactured, for example, as follows. First, the raw materials are premixed using a mixer such as a ball mill or a super mixer, melted and kneaded using a mixer such as a kneader, and then cooled and solidified.

Next, it is pulverized with a pulverizer such as a jet mill, and then classified into a predetermined particle size.

As for the physical properties of the toner thus obtained, it is necessary that the dielectric constant is 2.2 or less. In general, the relative permittivity tends to decrease (increase) as the resistance increases (decreases). That is, when the relative dielectric constant of the toner is small, the resistance of the toner is high, the environmental stability of the toner is improved, and the image quality is stabilized. In order to obtain such an effect, it is necessary to make the toner substantially free of conductive substances. Also, the average particle size of toner is
A range of 5 to 15 μm is preferable. If it is smaller than 5 μm, fog becomes large, and if it exceeds 15 μm, the image becomes rough.

The developer of the present invention is prepared by mixing the above-described ferrite carrier and toner, and the toner concentration is 3 to 10% by weight.

In the present invention, various physical properties of the carrier and toner are measured as follows.

The resistance of the carrier is determined by filling cells with circular electrodes (25flφ) facing each other with a gap of 51, and
This is a value measured under a DC electric field of 200 V/(to) with a load of 1 kg. The magnetic properties of the carrier are values measured using a vibrating sample magnetometer (VSM a type manufactured by Toei Kogyo). The amount of charge of the toner is 5 parts by weight of toner and 9 parts by weight of carrier.
5 parts by weight, and a commercially available plow-off charge measuring device (
Toshiba Chemical TB200 type) blowing pressure 1.0 kg
/ crA, the value measured after 25 seconds of blowing. The relative dielectric constant of toner is determined by covering the bottom with a conductive electrode.
Weighed 3 to 5 g of the sample into a cell with an inner diameter of 42 mm and whose sides were covered with an insulator with a thickness of 31 mm and a height of 5 mm, and placed it between the opposing electrodes of a Q meter (Yokogawa Electric Corporation QM-102A model). , is a value measured at a frequency of 100kHz.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

Male Jl Raw L Styrene-acrylic copolymer (Sanyo Chemical SBM60
0) 87 parts by weight, 3 parts by weight of low molecular weight polypropylene (Viscol 550P manufactured by Sanyo Chemical Co., Ltd.), 3 parts by weight of black dye (Black BY manufactured by Orient Chemical Co., Ltd.), 2 parts by weight of charge control agent (Bontron 554 manufactured by Orient Chemical Co., Ltd.), CaCO5 (Nitto Co., Ltd.) A toner (NIL 1 ) having a particle size of 5 to 25 μm was produced using 5 parts by weight of NS#2500 (manufactured by Funka Kogyo). The charge amount of this toner was -25 μc/g, and the dielectric constant was 2.18.

The above toner and a ferrite carrier (Hitachi Metals KBN-100) with a volume resistivity of 1 x 101) Ωcm and a particle size of 74 to 149 μm are mixed so that the toner concentration is 5% by weight, and a developer ( A-1) was adjusted.

Also, instead of black dye, carbon black (manufactured by Mitsubishi Kasei #
The composition was the same as above except that 44) was used, and the particle size was 5 to 2.
A 5 μm toner (N[12) was produced. The charge amount of this toner was -27 μc/g, and the dielectric constant was 2.28. A developer (A-2) was prepared using this toner under the same conditions as above.

(a) 20°C using a commercially available electrophotographic copying machine (0-Bix3000m manufactured by Konishiroku Co., Ltd.) using each of the above-mentioned developers.
A continuous copy test was conducted under two types of environmental conditions: , 50% R, H, and (b) 30° C., 80% R, H.

Table 1 shows the image evaluation results after copying 50,000 sheets.

Table 1 shows that when developer A-1 is used, high quality images can be obtained even under high temperature and high humidity environmental conditions. On the other hand, when using A-2 developer,
It can be seen that although good images can be obtained under ambient conditions of room temperature and room temperature, the reproducibility of halftones deteriorates under environmental conditions of high temperature and high humidity.

Four types of toners shown in Table 2 were manufactured by changing the blending amounts of each component in the tlhl) toner of Example 1.

Developers (A-3 to A-6) were prepared using the above toner and the ferrite carrier of Example 1 under the same conditions as in Example 1.

Image evaluation was performed in the same manner as in Example 1 using these developers. The results are shown in Table 3.

Table 3 Table 3 shows that when the developers (A-3 to A-5) whose black dye content is within the range of the present invention are used, images that are stable against environmental conditions can be obtained.

However, a developer with a high content of black dye (A-6)
If you use , the image quality will deteriorate.

Ni-Zn ferrite carrier (C-1) with a main volume resistance of 6X10&Ω・C, M with a volume resistance of 3X107Ω・■
g - A Zn-based ferrite carrier (C-2) and a Cu-Zn-based ferrite carrier (C-3) having a volume resistivity of 1×10I0Ω・■ were prepared and mixed with 1IIllll toner of Example 1 in the same manner as in Example 1. Three types of developer (A-7
-A-9) were adjusted.

Image evaluation was performed in the same manner as in Example 1 using these developers. The results are shown in Table 4.

Table 4 From Table 4, it can be seen that when the developer (A-7) containing a ferrite carrier with a low volume resistivity is used, the image quality deteriorates; , A-9), it can be seen that high quality images can be obtained.

〔Effect of the invention〕

According to the present invention, since a toner and a ferrite carrier that do not substantially contain conductive particles are used, it is possible to stably obtain high-quality images regardless of environmental conditions.

Claims (2)

[Claims] (1) In an electrostatic developer comprising a ferrite carrier and a toner containing a fixing resin and a colorant, the ferrite carrier has a resistance of 1×10^7 Ωcm or more, and the toner has a resistance of 1×10^7 Ωcm or more, and the toner has a resistance as the colorant. A developer for electrostatic development, comprising a non-conductive black dye or black pigment, and having a relative dielectric constant of 2.2 or less. (2) The developer for electrostatic development according to claim 1, wherein the toner contains 3 to 10% by weight of a colorant.