JPS6180263A - Electrophotographic binary developer and developing method using it - Google Patents

Abstract

PURPOSE:To ameliorate gradation by using at least 2 kinds of carriers different in electric conductivity and triboelectrifying them with a toner. CONSTITUTION:A charge is generated on each surface by triboelectrifying the toner and the carrier. When the carrier high in conductivity is used, the surface potential generated by triboelectrification is gradually lowered from the initial potential by diffusion into the inside of the carrier or discharging out of the carrier as the time elapses. In the case of the carrier low in conductivity, it is difficult to diffuse the charge or discharge, and the surface potential is not so much lowered. Therefore, when the conductivity of the carrier is high, the toner holding force is weak, and when low, the holding force is storing, thus permitting the distribution width of the toner holding forces to be set wide by using various kinds of carriers different in conductivity.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a two-component developer for electrophotography, particularly.

The present invention relates to a two-component developer using carriers having different toner retention powers and a developing method using the same.

(Prior Art) Charge is applied to the toner of a two-component developer consisting of a toner and a carrier by utilizing triboelectric development between the toner and the carrier.

The toner is charged with a polarity opposite to that of the carrier due to friction with the carrier, and is attached around the carrier mainly due to electrostatic force. This developer consisting of toner and carrier is then used, for example.

A magnetic brush is formed on the developing sleeve and developed in the developing area. Development is carried out by the electrostatic attraction of the electrostatic latent image on the photoreceptor, which is charged to the opposite polarity to that of the toner, and the toner is attracted to and adheres to the latent image charge. At this time, the toner is transferred onto the latent image due to the difference in the strength of the latent image charge and the holding force due to electrostatic attraction between the toner and the carrier. Originally,
The carrier has inherent electrical conductivity, and if sufficient triboelectric charging is achieved, the charges on the toner and the carrier will be constant and the holding force between the toner and the carrier will also be constant. When such toner is used for development, the resulting toner image is formed on the photoreceptor.

It would be impossible to faithfully correspond to latent image charges that differ slightly depending on the shading of the original image. Nevertheless, 1
In conventional developer development, which is a mixture of one type of toner and one type of carrier.

A copied image having a certain degree of gradation is obtained. This is simply due to differences in the amount of charge due to variations in the electrical conductivity of the powder particles of the carrier and an imbalance in the number of times the toner and carrier come into contact during triboelectrification.

Alternatively, it is simply obtained by a difference in electrostatic attraction due to a difference in the distance between the toner and the photoreceptor due to the curved surface of the photoreceptor drum. Therefore, such a negative and uncertain difference in charge amount cannot cope with subtle differences in latent image charge. Therefore, it is not possible to obtain a copied image with image tonality that is faithful to the original.

(Object of the Invention) The object of the present invention is to provide a two-component developer for electrophotography that can provide reproduced images with excellent tonality by setting a wide range of holding power of a carrier for toner, and a developing method using the same. It is about providing.

(Structure of the Invention) Toner and carrier generate charges on their surfaces due to triboelectric charging. When using a carrier with high electrical conductivity,
Over the course of one hour, the charge generated by triboelectric charging diffuses into the carrier or discharges to the outside of the carrier, so that the surface potential becomes lower than the initial potential. In the case of carriers with low electrical conductivity, these diffusions or discharges are difficult to occur and the surface potential does not decrease much.

Therefore, if the electrical conductivity of the carrier is high.

The toner retention force is weak, and the lower the toner retention force, the stronger the toner retention force. Therefore, by using several types of carriers having different electrical conductivities, it is possible to set a wide range of distribution of the holding force for toner. This allows fine control of the transfer of toner to the electrostatic latent image. The present inventors completed the present invention based on the above findings. Therefore, the two-component developer for electrophotography of the present invention includes at least two types of carriers having different electrical conductivities, thereby achieving the above object.

Further, in the developing method of the present invention, the toner of a developer composed of toner and at least two types of carriers having different electrical conductivities is charged to a predetermined polarity, and then the charged toner is charged to a predetermined polarity. transfer onto a photoreceptor having an electrostatic latent image.

This achieves the above objective.

In the present invention, by setting the ratio of the electrical conductivities of the two types of carriers to an order of two or more orders of magnitude, the distribution width of the holding force for toner can be significantly expanded.

The invention is illustrated by the following example. 3 (Example) A developer was prepared by thoroughly mixing and stirring the following ferrite carrier, iron powder carrier, and toner in various proportions, and copies were made using a Mita DC-191 copying machine. Clear images with no brush marks, fog or edge effects were obtained.

(a) Ferrite carrier electrical conductivity: 5.6X10-1''Ω-1cm -
1 Maximum magnetization: 49.8 emu/g, residual magnetization: 0
．． 25 emu/g.

Coercive Crab 3.380e, center particle size: 40μm) Iron powder carrier electrical conductivity: 2.5X10-'Ωcm-' maximum magnetization: 180. Oemu/g, residual magnetization: 15.
Oemu/g.

Coercive Crab 17.300e, center grain size: 40 μm (C
) Toner Hymer SBM-73 (styrenic resin: manufactured by Sanyo Chemical Industries, Ltd.)...87 parts by weight Viscoel 550P (
Low molecular weight polypropylene: Manufactured by Sanyo Chemical Industries)
...5 parts by weight Special Black 4 (Carbon Blasoc: manufactured by Degussa) ...5.5 parts by weight Bontron S-32 (dye: manufactured by Orient Chemical Co., Ltd.)
・1.5 parts by weight The mixture consisting of the above composition was sufficiently melted and cross-dispersed in a heated three-roll mill, taken out and cooled, and then coarsely pulverized to about 2H using a coarse pulverizer (Rotopresso Casoting Mill: manufactured by Alpine). , then supersonic jet mill (NIPPON)
PNEUMATIII: Finely pulverized with MFCCo, LTD) to a particle size of about 10 to 20 μm.

When copies were made using a Mita DC-191 copying machine under the same conditions as in the example using a developer in which the ferrite carrier, iron powder carrier, and toner used in the flame comparison example were well mixed in the following proportions, there was no fogging. However, copies with edge effects, carrier pull, fogging, brush marks, and poor tonality were obtained as shown by the X marks in the table below.

(Hereinafter, blank space) Development sensitivity curves for the above Examples and Comparative Examples are shown in the figure. In the figure, solid lines represent examples of the present invention, and dotted lines represent comparative examples. As is clear from the figure.

It can be seen that in the examples of the present invention, the rise is more gradual than in the developer made of only iron powder carrier and toner (Comparative Example 4), and the developer has excellent gradation and good midtone reproducibility.

(Effects of the Invention) According to the present invention, as described above, by using at least two types of carriers having different electrical conductivities and being triboelectrically charged with the toner, it is possible to widen the distribution of the holding force of the carrier to the toner. .

As a result, a copy image with excellent tonality that is faithful to the original image can be obtained.

[Brief explanation of drawings]

The figure is a diagram showing development sensitivity curves of Examples and Comparative Examples of the present invention. that's all

Claims (1)

[Scope of Claims] 1. A two-component developer for electrophotography containing at least two types of carriers having different electrical conductivities. 2. The two-component developer for electrophotography according to claim 1, wherein the ratio of the electrical conductivities of the two types of carriers is on the order of two or more digits. 3. Charge the toner of a developer composed of toner and at least two types of carriers having different electrical conductivities to a predetermined polarity, and then transfer the charged toner to a photoreceptor having electrostatic latent images of different polarities. A developing method comprising transferring to the top. 4. The developing method according to claim 3, wherein the ratio of the electrical conductivities of the two types of carriers is on the order of two or more digits.