JPH058429B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic developing method, and more particularly to an electrophotographic developing method using a two-component developer formed by mixing a magnetic carrier and a dry toner. A developing method using a two-component developer is widely used in the field of electrophotography. During development, the developer is mixed and stirred in the developing device, and the mutually frictionally charged state is transported to the electrostatic latent image bearing surface on the photoconductive layer by the rotation of a sleeve or magnet. The toner particles are transferred to the latent image due to the electrostatic attraction between the triboelectric charge of the toner and the electrostatic latent image, and development is performed. Furthermore, when copying a large number of sheets, it is necessary to keep the toner concentration in the developer constant, so a method is used in which only toner is replenished. However, in this two-component developing method, the carrier in the magnetic brush comes into direct contact with the electrostatic latent image, and the charge carrier of the latent image escapes to the developing sleeve, so that a uniform charge is formed on the electrostatic latent image. As a result, brush-like undeveloped areas are formed on the copied image, a so-called brush mark phenomenon, which impairs copy quality. Various proposals have been made as methods for preventing the brush mark phenomenon. For example, there is a method of increasing the toner content in the developer to surround the surface of the carrier with toner to prevent contact between the latent image and the exposed surface of the carrier. Due to the high rate, the entire toner is not uniformly triboelectrically charged, which tends to cause background fogging, and also causes trailing at the trailing edge of the image. Another method is to coat the carrier surface with resin and increase the surface resistance of the carrier to prevent the latent image charge from flowing to the carrier. This causes problems such as limited charge polarity. Furthermore, in the method of using a high-resistance ferrite carrier instead of iron powder, it is necessary to severely limit the development conditions. Carriers have discovered that all of the above-mentioned drawbacks can be solved by using a relatively high-resistance toner as the starting developer and replenishing it with a relatively low-resistance toner when making multiple copies. . The purpose of the present invention is to prevent brush marks, background fogging,
To provide an electrophotographic developing method capable of obtaining high-quality copies with excellent resolution without producing edge effects. Another object of the present invention is to provide a developing method that maintains the initial image density even when copying a large number of sheets and does not cause deterioration in copy quality. That is, in the present invention, a starting developer made of a mixture of a magnetic carrier and a dry toner is brought into contact with an electrostatic latent image bearing surface, and a replenishing toner is added in accordance with the amount of the dry toner consumed for development. In the electrophotographic development method in which replenishment is performed, the overall volume resistance of the dry toner in the starting developer is R ₁ (Ω・cm), and the overall volume resistance value of the replenishment toner is R ₂ (Ω・cm). An object of the present invention is to provide an electrophotographic developing method characterized by the following relationship: 10 ¹³ ≦R ₂ ≦R ₁ /10. In the two-component developing method, the cause of the brush mark phenomenon is as mentioned above.
This is because the latent image charge leaks because the volume resistance of the developer is low overall. Therefore, in the initial stage, the volume resistance of the developer needs to be set high. However, when the toner used in the initial stage is used as replenishment toner when copying a large number of sheets, the resistance of the developer tends to become even higher as the carrier deteriorates. This point will become clearer by referring to FIG. 1, which shows the relationship between copy number and bias current value. In the figure, curve (A) shows the case where a relatively high-resistance toner is used from beginning to end, which is approximately 7 μA at the initial stage.
However, the bias current value decreases rapidly when a large number of copies are made, and decreases to approximately 1.0 μA after 10,000 copies have been made. At this time, the density of the copied image decreases due to the edge effect due to the high resistance, and background fog increases. Similarly, in curve (C) showing the case where toner with relatively low resistance is used throughout, the bias current value decreases as the number of copies increases. At this time, the bias current value shows a high value as a whole, so the image is inevitably susceptible to brush marks. According to the present invention, when the total volume resistance of the dry toner in the starting developer is R ₁ (Ω・cm) and the total volume resistance of the replenishment toner is R ₂ (Ω・cm), 10 ¹³ It is important that the following relationship holds true: ≦R ₂ ≦R ₁ /10 (1). In other words, by setting each toner in the relationship according to the above formula, the occurrence of brush marks can be suppressed in the initial stage, and the bias current value of the developer can be kept stable at all times when copying a large number of sheets (Fig. 1, curve (C)), it is possible to maintain the initial image and obtain copies without deterioration in quality. The reason why the bias current value is kept constant in the first half configuration is not yet clear, but the inventor of the present invention thinks as follows. In the initial stage, the bias current value is determined only by the physical properties of the starting agent. When copying a large number of sheets, the dry toner in the starter agent and replenishment toner are mixed in the developer, and the replenishment toner, which has a small frictional charge with the carrier, is consumed preferentially for development. Dry toner with high resistance always remains in the developing device. At the same time, carriers tend to have higher resistance. In other words, even though the individual amounts or resistance values of replenishment toner, remaining dry toner, and carrier change, due to the condition of equation (1), the resistance of these three is maintained in balance, and the developer This is thought to be because the volume resistance is stabilized as a whole. If the condition of equation (1) is not satisfied, for example
In the case of R ₂ >R ₁ /10, the replenishment toner cannot suppress the development of high resistance of the developer, and an increase in fog density and a decrease in density due to the edge effect are inevitable.
Conversely, when R ₂ <10 ¹³ , the replenishment toner lowers the resistance of the developer too much, causing brush marks to occur. The toner in the starting developer and the replenishing toner used in the present invention can be prepared by means known per se. Examples of resins that promote fixing include known thermoplastic resins such as polystyrene resins, polyamide resins, polyacrylate resins, polymethacrylate resins, polyvinyl chloride resins, and fluorine resins, and thermosetting synthetic resins such as epoxy resins and acrylic resins. Resins, phenolic resins, natural resins such as rosin and gilsonite, and modified products thereof can be used. Further, various coloring agents such as carbon black, chrome yellow, oil red, rose bengal, phthalocyanine blue, nigrosine, fast red, and others can be used as the coloring agent. During production, a pigment such as carbon black is uniformly and uniformly kneaded into a fixing resin medium, and then granulated. In addition, for the purpose of increasing the amount prior to kneading and granulation, fillers such as calcium carbonate and finely powdered silicic acid can be added in an amount of up to 20% by weight based on the total weight of each filler, and the developer is fixed with a heated roll. In this method, offset inhibitors such as silicone oil, low molecular weight olefin resins, various waxes, etc. can be used in an amount of 2 to 15% by weight based on the total weight of each. Further, in applications where the developer is fixed with a pressure roll, a pressure fixing agent such as paraffin wax, various animal/vegetable waxes, fatty acid amide, etc. may be used in an amount of 5 to 30% by weight based on the total amount. In addition, when each toner is brought into the relationship of the volume resistivity of the present invention, by appropriately adjusting the blending amount of a resistance control agent known per se, such as carbon black, conductive metal oxide, etc. Toners with arbitrary resistance can be obtained. Further, the volume resistivity of the toner in the present invention may be as long as the volume resistivity as a whole; for example, even if a mixture of a low-resistance toner and a high-resistance toner is used,
There is no problem as long as the conditions of the present invention are satisfied. The particle size of the toner should be set between 5 and 5, taking into account development characteristics, etc.
20μ is preferred. Iron powder, ferrite, etc. can be used as the magnetic carrier, but in particular, the volume resistance of the entire carrier is
The present invention is more effective when the resistance is 10 ⁶ Ω·cm or less. When developing an electrostatic latent image using the developing method of the present invention, a known two-component developing device can be used. That is, as shown in FIG. 2, a starting material is held on a sleeve 2 containing a magnet 1, a magnetic brush 3 is formed on the sleeve 2,
After both the carrier and the toner are frictionally charged by the stirring mechanism 4 and the amount of developer is regulated by the cutting member 5, the magnetic brush 3 is connected to the latent image holder 6 on the sleeve 2. Developing can be carried out by rubbing one or both of the magnets 1 by rotating them. When copying a large number of sheets, a signal from the detection means 7 that detects the developed toner image and the toner concentration in the developer is used to
By sequentially replenishing the replenishing toner 8 by a toner replenishing roller 10 disposed at the bottom of the hopper 9, the toner density can be kept constant. As described above, the present invention makes it possible to obtain high-quality copies free of brush marks, background fog, and edge effects using a conventional developing device without using a special carrier, and is also effective in copying a large number of sheets. It is also possible to maintain the original image and obtain copies with no deterioration in copy quality. The invention is illustrated by the following example. Toner production example 1 Priorite ACL (styrene-2-ethylhexyl methacrylate copolymer, manufactured by Gutdeyer Co., Ltd.) 100 parts by weight Viscoel 550P (low molecular weight polypropylene, manufactured by Sanyo Chemical Co., Ltd.)
2 Special Black 4 (Carbon Black, manufactured by Degussa) 1 Spiron Black RLH Special (black oil-soluble dye, manufactured by Hodogaya Chemical Co., Ltd.) 3 The above composition was thoroughly mixed in a Henschel mixer and then twin-screw extruded. After melting and kneading in a machine and cooling, it is coarsely ground in a cutting mill. Next, it is finely pulverized using an ultrasonic jet mill, and the resulting finely pulverized product is classified to obtain an average particle size having a particle size distribution of 5 to 20μ.
A black toner of 11.3μ was obtained. Furthermore, to improve fluidity, hydrophobic silica R-972 (manufactured by Nippon Aerosil Co., Ltd.) 0.1% and vapor phase alumina ultrafine particles Al ₂ O ₃ -C were added in a Benciel mixer.
(manufactured by Nippon Aerosil Co., Ltd.) 0.1% was added to the total amount of toner to perform toner surface treatment. The volume resistivity of the obtained toner is 8.9×10 ¹⁴
It was Ω・cm. Toner Production Example 2 Priorite ACL 100 parts by weight Viscoel 550P 2 Special Black 4 6 Spiron Black RLH Special 2 The above composition was prepared in the same manner as in Toner Production Example 1.
A black toner having a particle size distribution of 20μ and an average diameter of 11.4μ was obtained. The volume resistivity of the obtained toner was 5.1×0 ¹³ Ω・
It was cm. Toner Production Example 3 Priorite ACL 100 parts by weight Viscoel 550P 2 Fastret 2BE 7 The above composition was prepared in the same manner as in Production Example 1 to obtain a red toner having an average particle size of 112μ and a particle size distribution of 5 to 20μ. The volume resistivity of the toner was 1.3×10 ¹⁵ Ω·cm. Toner production example 4 Priorite ACL 100 parts by weight Viscoll 550P 2 Fastret 2BE (red monoazo pigment, manufactured by Sanyo Shiki Co., Ltd.) 7 Conductive ZnO particles (manufactured by Honjo Chemical Co., Ltd.) 7 The above composition was prepared in the same manner as in Production Example 1 A red toner with an average particle size of 11.3μ and a particle size distribution of 5 to 20μ was obtained. The volume resistivity value of the toner was 8.1×10 ¹³ Ω·cm. Toner production example 5 Priorite ACL 100 parts by weight Viscoel 550P 2 Special Black 4 2.5 Spiron Black RLH Special 3 The above composition was prepared in the same manner as in the toner production example.
A black toner with an average particle size of 11.5μ with a particle size distribution of 20μ was obtained. The volume resistivity of the obtained toner is 3.6×10 ¹⁴
It was Ω・cm. Toner Production Example 6 Priorite ACL 100 parts by weight Viscoel 550P 2 Special Black 4 13 Spiron Black RLH Special 2 The above composition was prepared in the same manner as in Toner Production Example 1.
A black toner with an average particle size of 11.4μ with a particle size distribution of 20μ was obtained. The volume resistivity of the obtained toner is 3.1×10 ¹²
It was Ω・cm. Example 1 Toner 150 of Production Example 1 as a starting developer
g and 1,500 g of iron powder carrier (EFV200/300, manufactured by Nippon Tetsuko Co., Ltd.), loaded into a two-component dry copying machine (DC-A2, manufactured by Sanda Kogyo Co., Ltd.), and placed in the hopper of the developing device. The toner of Production Example 2 was loaded into the toner and copies were made. The image density, fog density, edge effect, presence or absence of brush marks, and bias current value were measured on the first and 10,000th copy. The results are shown in Table 1. The first image is a clear, high-density image with no edge effects or brush marks, and no fog.
Even after 10,000 images, I was able to obtain an image that was almost the same as the first image. Example 2 A copying test was conducted in the same manner as in Example 1 using the toner of Cutting Example 3 as a starter and the toner of Manufacturing Example 4 as a refill, and a clear red image was obtained. Even after 10,000 images, the image remains the same as the initial image.
The image was clear with high density and no fogging, edge effects, or brush marks. Each measured value is shown in Table 1. Comparative Example 1 A copying test was conducted in the same manner as in Example 1 using the toner of Production Example 1 for starting and replenishing purposes, and the initial image was clear with no fogging, edge effects, or brush marks. It was hot but
After 10,000 sheets, images with noticeable fog, strong edge effects, and lower image density than the initial image were obtained. Each measured value is shown in Table 1. Comparative Example 2 A copying test was conducted in the same manner as in Example 1 using the toner of Production Example 2 for both starting and replenishing toners, and the initial image was found to have high density and fog, with almost no edge effect. However, the brush marks were noticeable. After 10,000 sheets, there was fogging and the brush marks were still noticeable. Each measured value is shown in Table 1. Comparative Example 3 A copying test was conducted in the same manner as in Example 1 using the toner of Production Example 1 for starting and the toner of Production Example 5 for replenishment, but the initial image was the same as that of Example 1. However, after 10,000 copies, the edge effect was noticeable and the image had a slight fog. Each measured value is shown in Table 1. Comparative Example 4 A copying test was conducted in the same manner as in Example 1, using the toner of Production Example 1 as a starter and the toner of Production Example 6 as a refill. The initial images were clear and had no problems, but after 10,000 copies, the brush marks became very noticeable. The results of each measurement are shown in Table 1.

[Table] ○: Does not occur △: Slightly occurs ×: Severely occurs Image density and fog density were measured using a Konishiroku Sakura Decintometer, and edge effects and brush marks were determined by visual judgment. The bias current value was expressed as the current value flowing between the developing sleeve and the photoreceptor when a voltage of 220 V was applied to the developing sleeve.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the number of copies and the bias current value. FIG. 2 shows a sectional view of a developing device using the developing method of the present invention. DESCRIPTION OF SYMBOLS 1... Magnet, 2... Sleeve, 3... Magnetic brush, 4... Stirring mechanism, 5... Ear cutting plate, 6... Image holding member, 7... Detection means, 8... Toner for retention,
9...Hopper, 10...Toner replenishment roller.

Claims (1)

[Claims] 1. Bringing a starting developer made of a mixture of a magnetic carrier and a dry toner into contact with an electrostatic latent image bearing surface,
In an electrophotographic development method in which replenishment toner is supplied according to the amount of the dry toner consumed in development, the overall volume resistance of the dry toner in the starting developer is R ₁ (Ω·cm), An electrophotographic developing method characterized in that the relationship 10 ¹³ ≦R ₂ ≦R ₁ /10 holds true when the overall volume resistance value of replenishment toner is R ₂ (Ω·cm).