JPS5975261A - Method for making plural copies - Google Patents

Abstract

PURPOSE:To obtain copies having good image quality, by developing an electrostatic latent image with a toner having dielectric constant at a specified value or lower in repeating development and transfer using only one electrostatic latent image once formed on a charge retaining material to obtain plural sheets of copies. CONSTITUTION:When an electrostatic latent image is developed, a developed toner image is formed on the electrostatic latent image. At that time, charge is generated in the toner layer in accordance with the electrostatic capacity by electrostatic induction from the electrostatic latent image. A part or the total amt. of this charge is simultaneously consumed when the developed toner is consumed from the development step to the transfer step, and as a result, charge of the electrostatic latent image is attenuated. In the case of making plural copies, such consumption of charge of the latent image is repeated with respect to the same one image, and therefore, it is presumed that this is one of the factors deteriorating the electrostatic latent image. Such transfer of charge from the latent image to the toner layer becomes smaller, as the electrostatic capacity of the toner layer becomes smaller, that is, the dielectric constant of the toner becomes smaller, and to satisfy the requirements of practicable image quality, the dielectric constant must be reduced to <=3.5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-sheet copying method in which an electrostatic latent image once formed on a charge retaining member is repeatedly developed and transferred to obtain a plurality of copies.

Various such multi-sheet copying methods have been proposed in the past, but these methods tend to cause image density to decrease and characters and lines to become thinner as the number of copies is increased. As a countermeasure to prevent this, a method of using a developer suitable for multiple copying has been proposed, but in both of these methods, the carrier of the dry two-component developer is made to have high resistance to retain charge during development. The purpose is to reduce deterioration of an electrostatic latent image on a member, such as a photoreceptor. However, when the resistance of the carrier is increased, the resistance of the developer increases and the edge effect becomes stronger, so when making multiple copies using this kind of developer, original images of characters and fine lines are maintained to some extent, but solid The density of the image becomes extremely low in the center, and in the end, only the edges of the solid image remain, resulting in an image that is not suitable for practical use.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a method for copying multiple copies with good image quality over a plurality of copies.

In the present invention, when an electrostatic latent image once formed on a charge retention member is repeatedly developed and transferred to obtain a plurality of copies, a toner for developing the electrostatic latent image is provided.
It is characterized by using a material having a dielectric constant of 8.5 or less.

The present invention will be explained in detail below.

First, the inventor of the present invention prototyped various dry two-component developers by combining a carrier and a toner, and developed the various types.

A test was conducted on the agent. As a result, it has been found that the multi-sheet copying characteristics are always good when the same toner is used even when carriers are different, or vice versa. We thought that the cause of this was the leakage of latent image charge during development, as has been said in the past, and measured the resistance of the developer, but no correlation with the resistance of the developer was found.

Therefore, considering that the above cause was due to the toner alone rather than the developer, the physical properties of various toners were measured and their multi-sheet copying characteristics were compared. As a result, it was found that there is a strong correlation between the multi-sheet copying property and the dielectric constant of the toner, and that toners with a low dielectric constant have good multi-sheet copying properties.

Next, a detailed explanation will be given using a specific example.

Table 1 shows the dielectric constants of the five toners A-E used in the experiment.

Table 1 The dielectric constant of each of the above toners is as follows: Toner 2,859
Powder sample compactor for fluorescence
A toner pellet was created by compressing and molding to a diameter of 40 mm, and the dielectric properties of the toner pellet were measured using a dielectric loss measuring device (model TT'1.S-10T manufactured by Ando Electric Co., Ltd.) at a frequency of IHzVC. The measurement was performed using a measuring electrode Fi with a diameter of 88 mm without using a guard electrode.

Next, use iron oxide powder and Nj, -Znn thread elite as a carrier to adjust the toner concentration. , 8vrt4 dry two-component developers were prepared, and the resistance of each developer was measured.

The results are shown in Table 2.

The resistance measurement of the second expression image agent was performed using the retention function used in the experiment described later, that is, the fj1 once formed on the charge retention member.
A magnetic brush developing device in a copying machine that has the ability to obtain multiple copies by repeatedly developing and transferring a latent image, and which develops an electrostatic latent image using a magnetic brush developing device. In an arrangement similar to that of the member, an aluminum drum is used instead of the charge holding member, a voltage of 160 V is applied between the aluminum drum and the non-magnetic sleeve of the magnetic brush developing device, and the developing device is developed in the magnetic brush developing device. It was calculated from the current value after stirring the agent for 10 minutes.

Each of these developers is used in a copying machine having the above-mentioned retention function to perform retention copying, and a surface electrometer (Model 244, manufactured by Monroe Co., USA) is installed inside the copying machine.
) was also incorporated to measure the surface potential of the charge retention member. Table 2 above shows the surface potential retention rate after 20 retention copies.

As is clear from Tables 1 and 2, even when iron oxide powder or ferrite with different resistances is used as a carrier, the lower the dielectric constant of the toner, the smaller the decrease in the surface potential of the charge retention member. . In addition, when comparing the copy images obtained by retention copying, it was found that even after copying multiple copies of toner with a low dielectric constant, an image almost the same as that of the first copy was obtained, but with toner with a high dielectric constant, an image was obtained after copying several copies. The density decreased and only images with blurred characters were obtained.

Further, the developer using a ferrite carrier produced an image with an edge effect, but the developer using an iron oxide powder carrier produced a solid image with high image density.

The quality of the above-mentioned multi-copy image is related to the electrostatic latent image potential of the charge retention member, and in order to satisfy practical image quality, the potential retention rate when copying multiple copies should be 70 or more, preferably 75. It is more than necessary.

In the present invention, in order to satisfy this condition, a toner having a dielectric constant of 8.5 or less, preferably 8.2 or less is used.

For comparison, we measured the dielectric constant of ordinary copying machine toner that is generally used in the market and performs only one development and transfer for the same latent image. (manufactured by Xerox) is 4.
, 2. The toner for Ricopy FT-4060 (manufactured by Ricoh Co., Ltd.) is 8.9, and the toner for RheoDry 45ol (manufactured by Toshiba) is 8.6, both of which are lower than the dielectric constant of the toner used in the present invention. It was also big.

The relationship between the dielectric constant of the toner described above and the multi-sheet copying characteristics is considered to be as follows. That is, when an electrostatic latent image is developed, a developing toner is deposited on the electrostatic latent image.

One layer is formed, and at this time, charges are generated in the developing toner layer by electrostatic induction from the electrostatic latent image according to its capacitance. In principle, this is known as an equivalent circuit in which a charged capacitor is connected in series with another capacitor. In this way, the charge induced in the developing toner layer by electrostatic induction is partially or completely consumed when the developing toner is consumed from the developing process to the transfer process, and as a result, the electrostatic latent image is It is thought that the charge is attenuated. When copying multiple sheets, this kind of latent image charge consumption is repeated for the same latent image, so
This is considered to be one of the factors that deteriorate the electrostatic latent image.

This transfer of charge from the electrostatic latent image to the toner layer is related to the stability of the toner layer, and the smaller the capacitance, that is, if the thickness of the toner layer is the same, the dielectric constant of the toner increases. It is thought that the smaller the value, the smaller the amount of charge movement, and therefore the smaller the attenuation of the charge due to electrostatic charge. Therefore, it goes without saying that the toner is not limited to those used as a dry two-component developer (toner and carrier), but the same applies to toner used as a dry-component developer. As is clear from the above, in the present invention, when an electrostatic latent image once formed on a charge retaining member is repeatedly developed and transferred to obtain a plurality of copies, the electrostatic latent image has a dielectric constant of 8. Since development is performed using toner of .5 or less, it is possible to obtain copies with good image quality over a plurality of sheets.

Claims (1)

[Claims] 1. When obtaining multiple copies by repeatedly developing and transferring an electrostatic latent image once formed on a charge retaining member, the toner used to develop the electrostatic latent image has a dielectric constant of 8.5 or less. A multiple copying method characterized by using.