JPS6313056A - Developer for electrostatic development - Google Patents

Abstract

PURPOSE:To obtain a high-quality image which is free from fogging by incorporating a non-conductive black dye or black pigment as a coloring agent into a toner and incorporating <=15wt% magnetic particles therein. CONSTITUTION:The semiconductive or insulating black coloring agent is used as the coloring agent in place of a generally used carbon black into the toner. Such coloring agent is exemplified by black dyes and black pigments such as metal-contg. dyes, nigrosine dyes and aniline black. The content of the magnetic particles in the coloring agent is specified to a <=15wt%, more particularly preferably 3-15wt% range. The satisfactory image density is not obtainable if the content is below 3wt%. The flowability is low if the content exceeds 15wt%. The splashing of the toner is prevented and the fogging is decreased by adding such magnetic particles into the toner. The volumetric resistance is low and the image quality is deteriorated if the amt. of the magnetic particles to be added exceeds 15wt%.

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 Developing is carried out by a magnetic brush method or the like using a developer mixed with the above. The toner is charged to a predetermined polarity due to friction with the carrier before development. The toner image obtained by development is transferred onto a transfer sheet such as plain paper and fixed.
The final image is obtained.

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. 60-172060 and 60-76756. 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, carbon black is used as a coloring agent in order to obtain a black image, 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. is common.

[Problem that the invention seeks to solve]

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

Since a normal carbon blank is hydrophilic, the carbon blank absorbs moisture at high temperatures, reducing the volume resistivity of the toner. Therefore, there is a problem that the image quality changes depending on the environmental conditions. Further, since carbon black is electrically conductive and usually contains about 5 to 15% by weight, the contrast of the image becomes high. Furthermore, the problem arises that the charge control agent is adversely affected, and the amount of triboelectric charge of the toner becomes unstable, resulting in a decrease in the stability of image quality.

Furthermore, toner for two-component developers has the problem that the toner scatters and contaminates the corona wire or adheres to the optical system, resulting in a reduction 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,
A developer comprising a fixing resin and a toner containing a colorant, the toner containing a non-conductive black dye or black pigment as the colorant and containing 15% or less of magnetic particles. .

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, macrogonal, garnet, or orthoferrite. characterized.

In terms of image quality, especially image density, in the present invention 1 x 107Ω
- It is desirable to use a ferrite carrier having a volume resistivity of cm or more. Further, among the carrier physical properties, the saturation magnetization (σ, ) is preferably in the range of 40 to 90 emu/g. σ,
is less than 40 emu/g, even if the magnetic force of the developing magnet roll is strengthened (850 G or more on a non-magnetic sleeve),
The carrier is easily attached to the surface of the photoreceptor when the roll is detached, while σ.

If the toner is greater than 90 emu/g, the conveying force is too strong and the toner is easily deformed or destroyed, and the ears of the magnetic brush become hard, resulting in poor halftone reproducibility. 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 dried in a heated atmosphere with the addition of a binder if necessary to obtain spherical particles. and 1100 to 1300 spherical particles.
It is sintered at a temperature of ℃ and then classified.

Next, the toner used in the present invention is particles having an average particle size of 10 to 20 μm, in which a colorant is dispersed 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.

As the colorant, a semiconductive or insulating black colorant is used instead of the commonly used carbon black. 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 15%. If it is less than 3% by weight, sufficient image density cannot be obtained, and if it exceeds 15% by weight, the fluidity of the toner will decrease.

Further, in the present invention, magnetic particles are contained together with the colorant or in place of a part of the colorant. Magnetic particles include iron, cobalt, including ferrite and magnetite.
Alloys or compounds containing ferromagnetic elements such as nickel, and various alloys that exhibit ferromagnetism after undergoing some kind of treatment such as geothermal treatment are used. Specific examples include magnetite (FezO4), Co-added magnetite, spinel type ferrite, magnet branbite type ferrite, and the like. The magnetic particles are preferably added in the form of fine particles with an average particle size of 0.1 to 3 μm in order to be uniformly dispersed in the toner. The amount added must be 10 times by weight or less, and the preferable range of the amount added is 1 to 6% by weight. By adding such magnetic particles to the toner, toner scattering can be prevented and fogging can be reduced. However, if the amount added is more than 15% by weight, the fixing properties will be lowered and since the magnetic particles are conductive, the volume resistance of the toner will be lowered, resulting in a decrease in image quality. The preferred content of magnetic particles is 10% by weight or less.

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 agglomeration 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%.

Also, part of the fixing resin may be replaced with inorganic fine powder such as calcium carbonate; if the amount added is small, the effect will be lost;
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 kneader 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 desirable that the dielectric constant is 2.2 or less. In general, the relative dielectric constant 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. Further, the average particle size of the toner is preferably in the range of 5 to 15 μm. 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 a cell with circular electrodes (25 mm φ) with 5 gears facing each other, and placing 1 mm between the electrodes.
This is a value measured under a DC electric field of 200 V/(2) with a load of 1 kg applied. The magnetic properties of the carrier can be measured using a vibrating sample magnetometer (
This is a value measured using a VSMa type (manufactured by Toei Kogyo Co., Ltd.). The charge amount of the toner was determined by mixing 5 parts by weight of the toner and 95 parts by weight of the carrier, and using a commercially available blow-off charge measuring device (Model TB200 manufactured by Toshiba Chemical) at a blow pressure of 1.0 kg/c.
tA is a value measured after blowing for 25 seconds. The relative dielectric constant of the toner is determined by weighing 3 to 5 g of a sample into a cell with an inner diameter of 42 mm and covering the bottom with a conductive electrode and the side with an insulator with a thickness of 3 mm and a height of 5 fl. Between the opposing electrodes of the meter (Yokogawa Electric Model QM-102A), 100
This is a value measured at the frequency of kllz.

〔Example〕

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

Example 1 Styrene-acrylic copolymer SBM60 manufactured by Sanyo Chemical Co., Ltd.
0) 88 parts by weight, 2 parts by weight of low molecular weight polypropylene (Viscol 550P manufactured by Sanyo Chemical Co., Ltd.), 2 parts by weight of Dye-1 (Varifast Yellow 3120 manufactured by Orient Chemical Co., Ltd.), Dye-2 (black dye: Bontron 554 manufactured by Orient Chemical Co., Ltd.)
) 3 parts by weight, magnetite (EPT500 manufactured by Toda Kogyo)
Using 5 parts by weight, toner with a particle size of 5 to 25 μm (Kan 1
) was manufactured. The band Mffi of this toner is -21μc
/g.

The above toner and a ferrite carrier (Hitachi Metals K
A developer (A-, 1) was prepared by mixing the developer (BN-100H) so that the toner concentration was 5% by weight.

Also, carbon black (
Same composition as above except that Mitsubishi Kasei #44) was used.
A toner (N112) with a particle size of 5 to 25 μm was produced. The charge amount of this toner was -22 μC/g. A developer (A-2) was prepared using this toner under the same conditions as above.

Using each of the above-mentioned developers, (a) 2
0°C, 50% R, I1. and (b) 30°C, 80% R,
A continuous copy test was conducted under two types of environmental conditions: 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 normal temperature, the reproducibility of halftones and the like deteriorates under environmental conditions of high temperature and high humidity.

Four types of toners shown in Table 2 were produced by changing the amount of Dye-1 added to the 11h1 toner of Example 1.

Table 2 Q Main 1) Composition unit double placement unit Developers (A-3 to A-6) were prepared using the above toner and the ferrite carrier of Example 1 under the same conditions as 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 From Table 3, it can be seen that the developer (A
-3 to A-5), it can be seen that images that are stable under environmental conditions can be obtained. However, it can be seen that when the developer (A-6) containing a large amount of dye is used, the image quality deteriorates.

Example 3 Five types of toners shown in Table 4 were manufactured by changing the amount of magnetite added in the first toner of Example 1.

Table 4 Q main 1)'! Unit of Jl composition: parts by weight Developers (A-7 to A-11) 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 5.

Table 5 Q quality O: Good, △: Slightly poor, ×: Poor From Table 5, fogging occurs when a developer that does not contain magnetite (A-7) is used, but a developer that contains magnetite within the scope of the present invention It can be seen that fog does not occur when (A-8 to A-11) are used. However, when a developer (A-11) with a high magnetite content is used, the image density decreases.

〔Effect of the invention〕

According to the present invention, since a toner containing a non-conductive colorant and magnetic particles and a ferrite carrier are used, high-quality images with good midtone reproducibility and no fogging can be produced even in high-temperature and humid environmental conditions. Obtainable.

Claims (2)

[Claims] (1) A developer for electrostatic development consisting of a ferrite carrier, a toner containing a fixing resin, and a colorant, wherein the toner contains a non-conductive black dye or black pigment as the colorant and contains 15% of magnetic particles. A developer for electrostatic development, characterized in that it contains less than % by weight. (2) The developer for electrostatic development according to claim (1), wherein the colorant is contained in the toner in an amount of 3 to 15% by weight.