JPS58195851A - Dry two-component developer - Google Patents

Abstract

PURPOSE:To obtain a developer capable of stably giving copied images of high density over a long term, by using ferrite with low specific resistance as the carrier of a dry two-component developer for an electrophotographic copying machine. CONSTITUTION:A toner and a carrier which are at different positions of the triboelectric charge series are mixed and agitated to obtain a dry two-component developer for developing an electrostatic latent image with the toner charged by friction. At this time, a ferrite carrier with <=about 10<5>OMEGA.cm specific resistance is used as said carrier. The resulting developer can give a high quality image of high density while almost preventing an edge effect under development conditions similar to those for a developer contg. a powdered iron carrier, that is, under proper development conditions having a wide permitted range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry two-component developer used for developing an electrostatic latent image formed on a charge retention member in an electrophotographic copying machine or the like.

Various types of such dry two-component developers are known. For example, in the magnetic brush development method, a dry two-component developer is generally composed of a toner in which a pigment or dye such as carbon black is dispersed in a resin, and an iron powder carrier. The electrostatic latent image is formed by mixing and stirring these toners and carriers using an agent to charge the toner with a polarity opposite to the polarity of the electrostatic latent image to be developed by mutual frictional charging, and applying it to the charge retention member. I'm addicted to toner. In this way, when toner and carrier are mixed and stirred to charge the toner by mutual frictional charging, the mutual frictional charging effect decreases when toner resin adheres to the carrier surface, so the surface type per unit weight is It is preferable to use medium grains which have a large specific surface area, that is, have a small particle size. However, the iron powder carrier commonly used in the magnetic brush development method is difficult to miniaturize, and when it is miniaturized, it oxidizes and produces particles with deteriorated magnetism, which are used as charge retention members during development. There is a problem in that it is resistant to adhesion and deteriorates the quality of developed images.

As a dry two-component developer that solves these problems,
A method using Yaria among ferrites has been proposed. Ferrite carriers are easy to miniaturize due to their manufacturing method, and
Since the chemical composition is stable and the magnetic properties are homogeneous down to the center unlike iron powder carriers, the friction with toner and the effect can be maintained effectively, and therefore it can be used stably for a long period of time. Since the attraction force to the magnetic developing roller can be increased, it is possible to effectively prevent the carrier from adhering to the charge holding member. However, if a conventionally used ferrite carrier is used under the same development conditions as a dry two-component developer with an iron powder carrier, for example in an electrophotographic machine equipped with a magnetic brush developing device, the edge effect may occur. This has the disadvantage that only low-quality images with low development density can be obtained in solid IJMJ images. For this reason, in the past, the developing ability was increased by narrowing the distance between the charge retaining member and the magnetic developing roller, or increasing the potential of the electrostatic latent image, in order to obtain a developed image with the required density. Proper development under these development conditions is 81.1.
ゎ7゜1□io6E4゜ka,A6゜The purpose of the present invention is to solve the above-mentioned various problems and to develop under the same development conditions as when using an iron powder carrier, that is, under appropriate development conditions with a wide tolerance range. An object of the present invention is to provide a dry two-component developer that can stably obtain the required development density over a long period of time.

The present invention provides a dry two-component developer in which toner and carriers located at different positions on a triboelectrification array are mixed and stirred, and the toner is charged by mutual triboelectrification. (c) It is characterized in that it is constructed with a ferrite carrier of 10''Q-ctm or less.

The present inventors believe that when using a ferrite carrier, the above-mentioned edge effect appears strongly and the density of the solid image decreases because the resistivity of the conventionally used ferrite carrier is as high as, for example, 1011Ω・C1l. We have experimentally confirmed that the above-mentioned undesirable phenomenon can be effectively prevented by using a ferrite medium with a low resistivity of less than 10"Ω, and have developed the present invention. Furthermore, even when using a 7-elite carrier with such a low resistivity, there is no drop in the latent image potential when obtaining multiple copies of a single electrostatic II image. It was also confirmed that high-quality uniformity could be obtained over multiple sheets.

The present invention will be described in detail below with reference to the drawings.

First, the present inventors prepared five types of 7-elite carriers A-K, and conducted a mechanical image test on each of them.The zero image test was performed using Se-based electrons rotating in the direction of arrow A, as shown in Figure 1. An electrostatic latent image of p450 volts is formed on the photographic photosensitive drum 1 by a well-known electrophotographic method, and after this is developed with toner using a magnetic brush and a developing device 2, this toner image is transferred to a known bias roller transfer device (not shown). This was done using the Kameko photocopying machine, which transferred the image onto recording paper and then fixed it to make a copy. 7:c magnetic, magnetic, brush developing device @2 has a main developing pole N0 and a plurality of conveying magnetic poles N, , S□.

It is a magnetic sleeve rotating type in which a magnetic developing roller 8 having a magnetic developing roller 8 having a shape of S, , S is fixed, and a non-magnetic sleeve 4 is rotated in the direction of the arrow by approaching the outer circumferential surface of the developing roller 8.
The distance between the non-magnetic sleeve 4 and the electrophotographic drum 1 was set to 411II as in the case of using an iron powder carrier. Further, the ferrite carrier is stored in the developer storage unit, and the toner is stored in the toner hopper 6, so that the toner replenishment roller 7 rotates so that the concentration of cina in the developer 8 is always approximately 8.
% by weight, the toner in the developer storage Se and the Yaria in 7Elite are mixed and stirred by the rotation of the stirring blade 9, and the toner is transferred to the electrophotographic photosensitive drum due to mutual frictional electrification. The charged toner and ferrite carrier are charged with a polarity opposite to that of the electrostatic latent image formed on the non-magnetic sleeve 1, and the amount of conveyance of the charged toner and ferrite carrier due to the rotation of the non-magnetic sleeve is regulated by the doctor blade 10. The developer on the magnetic sleeve 4 is scraped off with a scraper 11.

Table 1 shows the image test results using ferrite materials Yariam-E in winter.

Table 1 Next, the present inventors prepared each A of the above ferrite carriers ~E.
The specific resistance of the sample was measured using the measuring device shown in FIG. This measuring device consists of a cylindrical insulating cell 21 made of poly7tethylene fiber, and a cylindrical portion 2 of this cylindrical insulating cell 21.
Lower part IIE&+28 fixed to the lower part of 2 and circle m part 22
a lower electrode 25 having a weight 24 for loading which is removably installed on the upper part of the lower electrode 25;
and are connected to a DC power source 27 via an ammeter 26.

In this example, the diameters of the lower and upper electrodes 28 and 25 are set to 1
01111. The weights 24 are superimposed 1 to 9, and the ammeter 16 is Kli: ITHLEY's 615 type digital electrometer, and the DC power supply 27 is JHONF.
41 of LU■ company! Uses IB type stabilized DC power supply, lower electrode! 8 and the upper electrode B6 so that the connection @t is 2 periods, the 7-el F carrier 28 is housed in the circle [@11, and while applying voltage, the current value after 1 minute is taken, and the specific resistance ρ is calculated. It was calculated using the following formula. Note that the applied (measured) voltage by the DC m source 8 was 1 volt and 10 volt.

S t However, E: Measured voltage Ill Current value S; Electrode area #Is The table shows the S constant value of the specific resistance of each of the above ferrite carriers to E.

Table 2 Specific Resistivity (Ω-C1l) FIG. 8 plots the results of Tables 1 and 2 above to determine the relationship between specific resistance and image density. As is clear from Figure 8, the picture gj! The density increases as the specific resistance of the ferrite carrier decreases, and in order to obtain an image density of 0.8 or higher, which is considered to be practically necessary, the specific resistance at the measurement voltage lvolts must be approximately 10 using the measuring device shown in Figure 2.
It can be seen that it is sufficient to use a ferrite carrier with a resistance of 5Ω or less.

In addition, using a ferrite carrier with such low resistivity, as shown in Fig. 1, the electrostatic latent image once formed on the photographic photosensitive drum l was repeatedly developed and transferred to obtain multiple copies. It was possible to obtain copies with good image quality and image density over a plurality of sheets without reducing the latent image potential.

In this way, if a 7-element carrier with low resistivity is used as a carrier for a dry component developer, the required development can be achieved under the same development conditions as when using an iron powder carrier, that is, under appropriate development conditions with a wide tolerance range. The developed density can be stably obtained over the printing period, and therefore, when used in an electrophotographic copying machine or the like, it can be easily and inexpensively manufactured.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of the main parts of the electrophotographic copying machine used in the image test. FIG. 3 is a diagram showing the relationship with specific resistance. 1... Electrophotographic photosensitive drum 2... Magnetic brush developing device 8... Magnetic developing roller 4... Non-magnetic sleeve 5
...Developer storage section 6...Toner hopper 7...
- Toner supply roller 8... Developer 9... Stirring blade lO... Doctor blade 11... Scraper 21... M-shaped insulating cell 22... Cylindrical portion 28... Lower electrode 24.・・Sparrow
25... Upper electrode 26... Ammeter
27...DC power supply 28...Ferrite carrier. Figure 2 Figure 3

Claims (1)

[Claims] In a dry two-component developer in which toner and carriers located at different positions on a triboelectrostatic array are mixed and stirred, and the toner is charged by mutual triboelectrification,
A dry two-component developer in which the carrier is a ferrite carrier having a specific resistance of approximately 106Ω or less.