JPS60156067A - Composite carrier for electrophotographic developer - Google Patents

Abstract

PURPOSE:To maintain satisfactorily high image quality and to provide superior developing power by using a composite carrier made of a mixture of a granular carrier with a flat carrier. CONSTITUTION:A composite carrier is made of a mixture of 30-95pts.wt. granular carrier having 10<7>-10<11>OMEGA.cm resistivity with 70-5pts.wt. flat carrier having 10<3>-10<6>OMEGA.cm resistivity. The flat carrier is obtd. by flattening a granular carrier by physical crushing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier for a two-component developer used in electrophotography.

Carriers conventionally used in magnetic brush development include reduced iron powder, electrolytic iron powder, and atomized iron powder.
These are located between the magnetic brush and the photoreceptor and have a certain specific resistance value, and image quality such as image density, fine lines, gradation, and resolution in copying is adjusted by changes in this resistance.

In this case, it is said that the lower the resistance value of the carrier, or in other words, the higher the conductivity, the higher the image density, but the lower the image quality such as fine lines and gradation. When a carrier that has been made to have a high resistance by applying this process is mixed with toner and used as a developer, the electrode effect of the carrier is insufficient during frictional charging between the toner and the carrier.
The toner is retained on the carrier side and the developability is significantly inhibited, resulting in a serious problem of high image quality and insufficient image density.

In short, in the prior art, it has been difficult to achieve both image density and high image quality using a carrier material.

In view of the above circumstances, the present invention was developed as a result of intensive studies from the carrier side in order to maintain sufficiently high image quality and to obtain a two-component developer with excellent developability. The inventors have discovered that an electrophotographic developer having desired properties can be obtained by using a composite carrier in which the following carriers are mixed, and have thus arrived at the present invention.

That is, in the present invention, the resistance value is 10' to IQIIΩ-CI
ll granular carrier and resistance value 103~106 Ω-c
The present invention provides a composite carrier for an electrophotographic developer comprising a mixture of m flat carriers.

In the present invention, the granular carrier of 107 to 10''<n-CI, l, - is iron powder commonly used for electrophotography such as reduced iron powder, electrolytic iron powder, atomized iron powder, etc., and is treated with oxidation treatment and chemical conversion treatment. The resistance value can be controlled within the range of 10' to 1011 Ω-am by surface treatment, resin coating material, and coating thickness.The resin used for resin coating has good adhesion to the underlying iron oxide powder. For example, styrene/acrylic copolymer, fluorine resin,
Examples include epoxy resin, to which conductive fine powder, conductive resin, antistatic agent, etc. may be added in order to control the resistance value. Further, in this case, the granular shape defined as the shape of the carrier refers to a spherical shape, a regular shape close to the spherical shape, or an amorphous shape other than the flat shape described below.

On the other hand, a flat carrier of 103 to 106 Ω-cII+ is obtained by physically crushing a granular carrier to make it flat, and the resistance value is controlled by the degree of oxidation treatment and chemical conversion treatment on the surface of raw iron powder, as with the granular carrier. It can be obtained by selecting resin coating conditions.

Flatness in this case is defined as follows. In other words, regarding the plan view of the particle (Fig. 1) when the carrier particle 1 is stably stationary on a plane as shown in the drawing, the shortest distance between two parallel lines touching the outline is defined as the minor axis α, The maximum distance between it and the parallel line in the right angle direction is taken as the major axis B, and - lucky case view (
As shown in FIG. 2), the distance between the amorphous carrier and the parallel plane parallel to the horizontal plane and in contact with the particle surface was changed from the amorphous carrier to the flat carrier.

The resistance value in the present invention is determined by installing a carrier in an insulating cylinder having a lower electrode, placing an upper electrode on top of the carrier, and applying a DC voltage (usually 1 (10 to 200 Volt I)).

・It is calculated by applying a current value (degree) and reading the current value with a microammeter while the current flowing through the carrier layer is stable.

The mixing ratio of the two types of carriers has a significant influence on the present invention, and is 70 to 5 parts by weight of the flat carrier to 30 to 95 parts by weight of the granular carrier, preferably 70 to 80 parts by weight of the granular carrier. On the other hand, flat carrier 30
~20 parts by weight are mixed in a mixer and subjected to the present invention.

The particle size of the granular carrier and the flat carrier is not particularly limited, but may be 20 (1/3-00 mesh, or 250/
A 400 mesh product is suitable.

Further, there are no particular restrictions on the toner used in combination with the composite carrier of the present invention, and the positively charged toner or negatively charged toner used in ordinary two-component developers can be used as appropriate depending on the polarity of the latent image on the photoreceptor of the copying machine. used.

Since the present invention has the above-mentioned configuration, the high resistance granular carrier improves image quality such as fine line reproducibility and high resolution, and the low resistance flat carrier improves image density, and the functions are separated and roles are shared. So, in the next technology! You can obtain stable high image quality that was previously unavailable.

Example 1 200 parts by weight of trichlorethylene, 10 parts by weight of styrene/acrylic copolymer resin and 4 parts by weight of carbon black were placed in a magnetic ball mill and rotated for 30 minutes to prepare a resin solution for coating a carrier.

100 parts by weight of this resin liquid was put into a fluidized granulation dryer, and 300 parts by weight of trichlorethylene was added thereto, and then 20 parts by weight of oxidized iron powder of 250/400 mesh size was added.
00 parts by weight, mixed the iron powder and resin liquid in a fluidized bed, and then spray-dried it to produce 4.5XIO"Ω-On.
A granular carrier with a resistance value of + was obtained.

On the other hand, by subjecting the oxidized iron powder of 250/400 mesh size to the rolling process as it is, the oblateness is 0', 2'.
-5, resistivity 2.4X IO et al. A low resistance flat carrier of Ω-0111 was obtained.

A composite carrier of the present invention was obtained by uniformly mixing 30 parts by weight of a low-resistance flat carrier with 70 parts by weight of the above-mentioned high-resistance granular carrier using a low-speed mixer.

For 100 parts by weight of this composite carrier, styrene, /
An electrophotographic developer was prepared by mixing 6 parts by weight of a positively charging toner containing an acrylic copolymer as a main component.

In this case, the blow-off charge amount of Toe J-1 is l 4 u
c/g.

When this developer was applied to a PI)C electronic copying machine equipped with an OPC photoreceptor and a hot roll fixing mechanism and copies were made, it was found that the Macbeth reflection density was 1.4 or higher and the reproducibility of fine lines was good. I got the image quality.

Furthermore, it was confirmed that the initial image after 80,000 continuous copies could be maintained as it was, and that the carrier of the present invention had sufficient durability.

Example 2 200 parts by weight of toluene, 10 parts by weight of epoxy resin and 4 parts by weight of carbon black were placed in a magnetic ball mill for 30 parts by weight.
The mixture was rotated for 1 minute to prepare a carrier coating resin.

100 parts by weight of this resin liquid was put into a fluidized granulation dryer, and 300 parts by weight of toluene was added thereto, and then 200 parts by weight of toluene was added.
2,000 parts by weight of oxidized iron powder of 300 mesh was added, and the iron powder and resin liquid were mixed in a fluidized bed, and then spray-dried to obtain a granular carrier having a resistance value of 8.1 x 10 7 Ω-0111.

On the other hand, by applying oxidized iron powder of 200/300 mesh size to the rolling process as it is, the flatness can be reduced to 0.
19. A low resistance flat carrier with a resistivity of 1' and 9XlO'Ω-am was obtained.

A composite carrier of the present invention was obtained by mixing 20 parts by weight of the above granular carrier into a low-resistance flat carrier. An electrophotographic developer was prepared by mixing 6 parts by weight of a positively charging toner containing a styrene/acrylic copolymer as a main component with 100 parts by weight of this composite carrier. In this case, the toner show-off charge amount was 17 uc/g.

When this developer was applied to a PPC electronic copying machine equipped with a ZnO photoreceptor and a heat roll fixing mechanism, it was found that the Macbeth reflection density was 1.4 or higher and the reproducibility of fine line halftone dots was good. I was able to get good image quality. After continuous copying of 100,000 sheets, it was confirmed that the initial image was maintained as it was.

Example 3 The electrophotographic developer prepared in Example 2 was applied to a developing tank of a high-speed printer having a reversal development system using a Se photoreceptor, and continuous printing was performed. It was confirmed that it was possible to stably obtain dark prints over a long period of time.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams showing the shape of a flat carrier, with Figure 1 being a plane view of the carrier, and Figure 2 being a side view of the carrier. l...Carrier particles α...Shortest distance B...Maximum distance 'r...Flat thickness Patent applicant Tomegawa Paper Mills Co., Ltd.

Claims (1)

[Claims] Composite carrier for electrophotographic developer consisting of a mixture of a granular carrier with a resistance value of 07 to 10" Ω-cIn and a flat carrier with a resistance value of 03 to 106 Ω-cm