JPH0261743B2 - - Google Patents

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 the magnetic brush development method include reduced iron powder, electrolytic iron powder, and atomized iron powder. By changing this resistance, image quality such as image density, fine lines, gradation, resolution, etc. in copying is adjusted.

In this case, the lower the resistance value of the carrier, in other words, the higher the conductivity, the higher the image density.
It is said that image quality such as fine lines and gradation is inferior.On the other hand, carriers made of high resistance by applying surface treatment such as resin coating to the surface of iron powder, when mixed with toner and made into a developer, the toner and carrier During frictional charging with the toner, the electrode effect of the carrier is insufficient, and the toner is retained on the carrier side, significantly impairing developability, resulting in a serious problem of high image quality and insufficient image density.

In short, in the prior art, it has been difficult to satisfy 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 present invention was achieved by discovering that an electrophotographic developer having desired characteristics can be obtained by using a composite carrier in which two types of carriers having specific resistance values and shapes are mixed.

That is, the present invention uses a resin-coated iron powder-based granular carrier having a resistance value of 10 ⁷ to ^{10 11} Ω-cm (hereinafter referred to as granular carrier) and an iron powder-based flat carrier having a resistance value of 10 ⁴ to ^{10 7} Ω-cm. (hereinafter referred to as a flat carrier) for an electrophotographic developer.

The granular carrier of 10 ⁷ to 10 ¹¹ Ω-cm referred to in the present invention uses iron powder commonly used for electrophotography such as reduced iron powder, electrolytic iron powder, atomized iron powder, etc., and has been subjected to surface treatment by oxidation treatment, chemical conversion treatment, etc. The resistance value is controlled within the range of 10 ⁷ to 10 ¹¹ Ω-cm depending on the resin coating material and coating thickness. When performing a resin coating, the resin may be one that has good adhesion to the iron oxide base, such as styrene/acrylic copolymer, fluorine resin, Epoquin resin, etc., and can be used to control the resistance value. For this purpose, conductive fine powder, conductive resin, antistatic agent, etc. may be added. Further, in this case, the granular shape defined as the shape of the carrier means 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, flat carriers with a resistance of 10 ⁴ to 10 ⁷ Ω-cm are obtained by physically crushing the iron powder used in granular carriers to make them flat, and the resistance value is controlled by controlling the surface of the raw iron powder, as with granular carriers. It can be obtained by selecting the degree of oxidation treatment, chemical conversion treatment, and resin coating conditions.

Flatness in this case is defined as follows. In other words, as shown in the drawing, the plan view of the carrier particle 1 when it is stably stationary on a plane (the first
), the shortest distance between two parallel lines touching the contour is the shortest axis α, the maximum distance between two parallel lines perpendicular to it is the long axis α, and the particle is parallel to the horizontal plane as shown in the side view (Figure 2). A flat carrier is defined as a regular or irregular carrier whose flatness ratio, that is, the average of T/α+β/2, is 1/2 or less, where the distance between the flat surface and the parallel plane is T.

The resistance value in the present invention is determined by placing a carrier in an insulating cylinder with a lower electrode, placing an upper electrode on top of it, and applying a DC voltage (usually about 100 to 200 Volt).
is applied, and the current value is read with a microammeter when the current flowing through the carrier layer is stable.

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

The particle size of the granular carrier and flat carrier is not particularly limited, but it may be 200/300 mesh used in a normal two-component development system, or
A product with 250 to 400 meshes is suitable.

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

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. Therefore, it is possible to obtain stable high image quality that could not be obtained with conventional techniques.

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 liquid for carrier coating.

Put 100 parts by weight of this resin liquid into a fluidized granulation dryer,
After adding 300 parts by weight of trichlorethylene to this, 2000 parts by weight of oxidized iron powder of 250/400 mesh size was added, and the iron powder and resin liquid were mixed in a fluidized bed and then spray-dried to obtain a 4.5×
A granular carrier with a resistance value of 10 ⁸ Ω-cm was obtained.

On the other hand, by applying oxidized iron powder of 250/400 mesh size to the rolling process as it is, the oblateness is improved.
A flat carrier with a low resistance of 0.25 and a resistivity of 2.4×10 ⁶ Ω-cm was obtained.

For 70 parts by weight of the above high resistance granular carrier,
A composite carrier of the present invention was obtained by uniformly mixing 30 parts by weight of a low-resistance flat carrier using a low-speed mixer.
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 blow-off charge amount of the toner is
It was 14μc/g.

When this developer was applied to a PPC electronic copying machine equipped with an OPC photoreceptor and a hot roll fixing mechanism and copies were made, high image quality with a Macbeth reflection density of 1.4 or higher and good reproducibility of fine lines was obtained. . Furthermore, when 80,000 sheets were continuously copied, the initial image could be maintained as it was, confirming 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 and rotated for 30 minutes to prepare a carrier coating resin.

Put 100 parts by weight of this resin liquid into a fluidized granulation dryer,
After adding 300 parts by weight of toluene to this,
Add 2000 parts by weight of oxidized iron powder of 200/300 mesh, mix the iron powder and resin liquid in a fluidized bed, and then spray dry to obtain a granular carrier having a resistance value of 8.1 x 10 ⁷ Ω-cm. .

On the other hand, by directly applying 200/300 mesh size oxidized iron powder to the rolling process, the oblateness can be improved.
A flat carrier with a low resistance of 0.19 and a resistivity of 1.9×10 ₆ Ω-cm was obtained.

A composite carrier of the present invention was obtained by mixing 20 parts by weight of a low-resistance flat carrier with 80 parts by weight of the above granular 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. The blow-off charge amount of the toner in this case was 17 μc/g.

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

Example 3 The electrophotographic developer prepared in Example 2 was applied to a developing tank of a high-speed printer equipped with a reflection development system using an Se photoreceptor, and continuous printing was performed. Prints with Macbeth reflection density of 1.5 or higher and excellent sharpness were obtained. It was confirmed that this can be obtained stably over a long period of time.

Comparative 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 liquid for carrier coating.

Put 100 parts by weight of this resin liquid into a fluidized granulation dryer,
After adding 300 parts by weight of trichlorethylene to this, 2000 parts by weight of oxidized iron powder of 250/400 mesh size was added, and the iron powder and resin liquid were mixed in a fluidized bed and then spray-dried to obtain a 4.5×
A granular carrier with a resistance value of 10 ⁸ Ω-cm was obtained.

On the other hand, oxidized iron powder of 250/400 mesh size was directly subjected to a rolling process to make the flatness ratio 0.25, and then 2000 parts by weight of the flat oxidized iron powder, 100 parts by weight of the above carrier coating resin liquid, and trichloride were added. A flat carrier having a resistance value of 5×10 ⁷ Ω-cm was obtained by putting 300 parts by weight of ethylene into a fluidized granulation dryer, mixing the iron powder and resin liquid in a fluidized bed, and then spray drying the mixture.

For 70 parts by weight of the above-mentioned high-resistance granular carrier,
A composite carrier for comparison was obtained by uniformly mixing 30 parts by weight of a high-resistance flat carrier using a low-speed mixer.

In this case, 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 the carrier. In this case, the blow-off charge amount of the toner is
It was 22μc/g.

When this developer was applied to a PPC electronic copying machine equipped with an OPC photoreceptor and a hot roll fixing mechanism and copies were made, the Macbeth reflection density was 1.1 and the image density was low.

Comparative Example 2 200 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 liquid for carrier coating.

Put 100 parts by weight of this resin liquid into a fluidized granulation dryer,
After adding 500 parts by weight of trichlorethylene to this, 2000 parts by weight of oxidized iron powder of 250/400 mesh size was added, and the iron powder and resin liquid were mixed in a fluidized bed and then spray-dried to 5x
A granular carrier with a resistance value of 10 ⁶ Ω-cm was obtained.

A composite carrier for comparison was obtained by uniformly mixing 70 parts by weight of the high-resistance granular carrier of Comparative Example 1 with 30 parts by weight of the above-mentioned low-resistance granular carrier using a low-speed mixer.

An electrophotographic developer was prepared by mixing 100 parts by weight of this composite carrier with 6 parts by weight of a positively charging toner containing a styrene/acrylic copolymer as a main component. In this case, the blow-off charge amount of the toner is
It was 15μc/g.

When this developer was applied to a PPC electronic copying machine with an OPC photoreceptor and a hot roll fixing mechanism and copies were made, the Macbeth reflection density was 1.0, the image density was low, and the edge effect was too strong, resulting in a solid black image. There was some unevenness in the image.

Comparative Example 3 70 parts by weight of the low-resistance granular carrier of Comparative Example 2 and 30 parts by weight of the high-resistance flat carrier of Comparative Example 1 were uniformly mixed in a low-speed mixer to obtain a composite carrier for comparison.

An electrophotographic developer was prepared by mixing 100 parts by weight of this composite carrier with 6 parts by weight of a positively charging toner containing a styrene/acrylic copolymer as a main component. In this case, the blow-off charge amount of the toner is
It was 11μc/g.

When this developer was applied to a PPC electronic copying machine with an OPC photoreceptor and a hot roll fixing mechanism and copies were made, the Macbeth reflection density was as high as 1.4 or higher, but fine lines and gradation were poor for practical use. The image quality was poor.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams showing the shape of a flat carrier, with FIG. 1 being a plan view of the carrier, and FIG. 2 being a side view of the carrier. 1...Carrier particle, α...Shortest distance, β...
...Maximum distance, T... Flat thickness.

Claims (1)

[Claims] 1. A composite carrier for an electrophotographic developer comprising a mixture of a resin-coated iron powder-based granular carrier having a resistance value of 10 ⁷ to 10 ¹¹ Ω-cm and an iron powder-based flat carrier having a resistance value of 10 ⁴ to 10 ⁷ Ω-cm.