JPH04102865A - Developer for electrophotography - Google Patents

Abstract

PURPOSE:To form a high density image even in the case of low contrast by using a two-component developer composed of toner particles and carrier particles with inorg. oxide particles having specified volume resistivity added to the surfaces. CONSTITUTION:A two-component developer is composed of toner particles and carrier particles with inorg. oxide particles having <=10<10> OMEGAcm volume resistivity added to the surfaces. The particle size of the carrier is regulated to 10-500mum and the particle size of the inorg. oxide particles is regulated to 0.05-10% of that of the carrier. Since the inorg. oxide particles having low electric resistance are added to the surface of the carrier, excessive electrification of the toner is inhibited and the movement of electric changes in a contact region to the noncontact surface of the carrier is facilitated. The exchangeability of electric charges is improved, electrification speed is increased and remarkable reduction of the extent of electrification is inhibited even when some toner sticks to the surface of the carrier. Excessive electrification of the toner is inhibited in the early stage of development.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a two-component developer for developing electrostatic latent images in electrophotography, electrostatic recording, electrostatic printing, and the like.

(Prior art) Electrophotography has been widely used in copying machines and printers, and stabilization of the characteristics of the photoreceptor ζ developer in f) f=-t and Q is a key factor in the reliability of these products. A lot of research and development has been carried out as the most important technical element in improving the technology. Among these photoreceptors, organic photoreceptors are attracting attention due to their low cost and stability, but in this case, there is a problem in that when the photoreceptor is charged at a high potential, the photoreceptor is easily destroyed and its life is shortened. Further, with the recent progress in colorization of office documents, a method of developing toners of two or more colors has come to be used by increasing the surface potential of the photoreceptor to multiple values. In such systems, it has become necessary to significantly lower the surface potential of the photoreceptor than in the past.

On the other hand, two-component development mainly consisting of carrier and toner, called magnetic brush development, is used as the mainstream development method, but when the surface potential of the photoreceptor is low as mentioned above, In systems where high electrostatic contrast cannot be obtained, it is necessary to weaken the adhesion force between toner and carrier to some extent when using these two-component development methods. Furthermore, it was necessary to keep the charge amount of the toner at a low value. The reason for this is that the toner must be peeled off from the carrier and attached to the electrostatic image, and if the toner has a high charge, a small amount of toner will neutralize the charge on the electrostatic image, making it impossible for much toner to adhere. can be explained.

However, in order to reduce the charge amount of toner, it is necessary to increase the ratio of toner to carrier, which may result in insufficient triboelectric charging between toners and insufficient contact with carrier, resulting in an increase in toner of opposite polarity. Ta. Further, when the developer is used, the toner adheres to the surface of the carrier, and due to frictional charging between the toner and the carrier, the amount of toner of opposite polarity increases. These opposite polarities result in toner adhesion to the background portion of the photoreceptor, resulting in the problem that the developer cannot be used for a long period of time.

For this reason, there has been a demand for a developer that is always stable with a low charge amount and that does not increase the amount of toner of opposite polarity even after long-term use. In order to obtain a toner that is particularly strong in reproducing low-contrast electrostatic images and has a stable charge amount over a long period of time, for example,
No. 861 and JP-A-62-129866 disclose that by adding and mixing certain inorganic oxides to the toner surface, the electrical properties of these inorganic oxide additives provide long-term stable triboelectric charging properties. Discloses that the toner is obtained.

However, even if these inorganic oxides are added to the toner surface, if the difference between the charge series on the carrier surface and the charge series on the toner surface is large, the amount of triboelectric charging of the toner will be large, and the toner with the desired low charge amount will not be maintained for a long time. I couldn't get it consistently. Furthermore, since the charge exchangeability between the carrier and the toner is poor and the charging speed is slow, when new toner is added, toner with opposite polarity is generated, causing a problem of fogging.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a developer that can be developed at a high density even if the electrostatic contrast 1~ is low, and more specifically, The goal is to find a developer that has a low charge amount, a narrow charge distribution, and is stable even over long periods of use, and to find a method to utilize this developer.

(Means for Solving the Problems) In order to solve the above problems, a two-component developer consisting of carrier particles and toner particles to which inorganic oxide particles are added is used. The material is not particularly limited, and may be an inorganic fine powder that is added to ordinary electrophotographic toner for the purpose of adjusting charge and adjusting powder speed.

These inorganic oxide particles used in the present invention have a volume resistivity of 10
12 Ωcm or less, more preferably 1012
It may be less than Ωcm.

Specifically, titanium oxide, silica, alumina, zinc oxide,
Examples include magnesium oxide, tin oxide, iron oxide, and the like. The particle size is suitably 1 pm or less, more preferably 0.111 m or less.

Further, the inorganic oxide particles used in the present invention may be subjected to surface treatment for the purpose of hydrophobicization, charge adjustment, etc., if necessary.

The carrier used in the present invention can be a carrier used in ordinary electrophotography, but is not particularly limited.

Specific examples include iron powder, various ferrite powders, various magnetite powders, various metal powders, glass beads, and the like. A resin coating layer may be provided on the surface of these materials for the purpose of charge adjustment, etc., if necessary.

Particles obtained by melt-kneading, pulverizing, and classifying a binder resin and magnetic powder, or particles obtained by melt-kneading a binder resin and magnetic powder, spray cooling, and granulation, that is, So-called dispersed carriers are also suitable.

The particle size of the carrier used in the present invention is suitably 10 to 500 pm, more preferably 20 to 20,011 pm.

The toner used in the present invention is not particularly limited, and any chargeable toner that is used in ordinary electrophotography, in which a colorant is dispersed in a binder resin, can be used.

The amount of inorganic oxide particles added to the carrier used in the present invention is suitably 0.01 to 10%, more preferably 0.05 to 5%.

The method of adding the inorganic oxide particles to the carrier surface is not particularly limited and may be any commonly used mixing device.

Specific examples include a V-type blender, cement mixer, paint shaker, Henschel mixer, kneader coder, and the like. The inorganic oxide particles are added before or simultaneously with the addition of the toner when preparing the developer.

(Function) Although the effect of the present invention is not clear, in the present invention, by adding inorganic oxide particles with low electrical resistance to the carrier surface, excessive toner charge can be suppressed. The charged charge in the area easily moves to the carrier surface that is not in contact with it, and the charge exchange performance and charging speed are also improved. It is thought that the decline will be suppressed.

On the other hand, with a developer that does not have inorganic oxide particles attached to the carrier surface, the density increases with low electrostatic contrast, and as the developer is used, the charging speed becomes slow and the charge exchange performance is poor. Therefore, when new toner is added, reverse polarity occurs, resulting in severe fogging.

From the above, it is considered that the use of the developer of the present invention brings about the effect that good images can be obtained with low electrostatic contrast.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these Examples in any way.

(Example 1) 30 parts of styrene l n-phthyl methacrylate 1 to copolymer 70 parts of magnetic powder (EPT-1000, manufactured by Toda Kogyo Co., Ltd.) were kneaded in a pressurized niegu, pulverized in a jet mill, and air classifier. to obtain a kneaded and pulverized carrier with an average particle size of 5011, and further added 0.2 part of titanium dioxide fine powder (P-25, manufactured by Titan Kogyo Co., Ltd.) to 100 parts of this carrier.
Added using flender.

Styrene/n-phthyl methacrylate copolymer, 84 parts Polypropylene wax 5 parts (660P, manufactured by Sanyo Chemical Co., Ltd.) Carbon black 8 parts (R33
Toner 10 with an average particle size of 11p obtained by kneading, pulverizing, and classifying 3 parts of a charge control agent (Bontron N-04, manufactured by Orient Chemical Co., Ltd.)
0 parts, 0.5 parts of silica fine particles (R972, manufactured by Nippon Aerosil Co., Ltd.) were mixed using a Henschel mixer. The carrier and toner obtained by these operations are
The toners were mixed at a ratio such that the toner concentration was 8% by weight to form a developer.

(Example 2) A developer was prepared using the same composition and operation as in Example 1, except that tin oxide (S-1, manufactured by Mitsubishi Metals) was used instead of titanium dioxide as the conductive fine powder added to the carrier. did.

(Example 3) A developer was prepared using the same composition and operation as in Example 1, except that carbon black (BPL, manufactured by Cabot Corporation) was used instead of titanium dioxide as the conductive fine powder to be added as a carrier.

(Comparative Example 1) A developer was prepared using the same composition and operation as in Example 1, except that fine titanium dioxide powder was not added to the carrier.

Next, an image forming system in which the developer of the present invention was evaluated will be described. In this system, when the middle potential part of an electrostatic latent image has three potential parts: a low potential part, a medium potential part, and a high potential part, and the background potential is used, the low potential part and the high potential part are each colored in different colors. This is a two-color image forming system in which the toner is overlaid and developed, and then transferred onto a copying medium at the same time.

The developer of the present invention has an effect regardless of the polarity of the toner, and in this example, since it was used in combination with positively charged black toner, the parameters of the system were set as follows.

An OPC drum for a racer printer with an outer diameter of 84 mm was used as the photoreceptor tram, and was uniformly charged to -800V using a charger. Next, reverse exposure (image area exposure) is performed using a semiconductor laser writing device with an emission wavelength of 780 nm.
to form an electrostatic latent image having a surface potential of -100V in the exposed area and -800V in the non-exposed area, and a developing bias of -65V.
Development was performed using a negatively charged red toner (red developer for FX5030) under 0V. Next, regular exposure (non-image area exposure) is performed using an exposure lamp, and the non-exposed area -700
An electrostatic latent image having a surface potential of -50 V in the exposed area was formed, and development was performed using the developers of Examples 1 to 3 and Comparative Example 1 using a positively charged black toner. At this time, the developing bias was -400V (), and the electrostatic contrast was 300V.
It was V.

When image quality was evaluated using the above process, the results shown in Table 1 were obtained. In other words, in the developers in which metal oxides were added to the toner and carrier surfaces as in Examples 1 to 3, a low charge amount was stably maintained even after 100,000 copies were made, and a low electrostatic contrast of 300V was achieved. Even latent images can be efficiently developed. Furthermore, it has been shown to have excellent developer performance with a long life and no density loss or fogging.

It should be noted that experiments were also conducted with other electrostatic contrasts to apply this developer, and it was found that sufficient use was possible even at 500V or less.

(Effects of the Invention) By carrying out the above invention, excessive toner charging in the initial stage is suppressed, and charge exchangeability and charging speed using a developer are not reduced. As a result, a stable charge amount can be maintained even with a narrow charge distribution and low charge, and a latent image with low electrostatic contrast can be efficiently developed. As a result, a long-life developer and photoreceptor can be provided. In particular, this developer can be used when the electrostatic contrast is low, e.g.
It has the effect of enabling development in the following,
This enables applications such as multicolor systems.

Patent applicant: Fuji Xerox Co., Ltd. Agent
1st grade) Akira Fujio

Claims (1)

[Claims] (1) A two-component developer for developing an electrostatic latent image with low electrostatic contrast, using carrier particles to which inorganic oxide particles having a volume resistivity of 10^1^2 Ωcm or less are added to the surface.