JPH02238468A - Developing method - Google Patents

Abstract

PURPOSE:To ensure image density freed of background fog and stable against a large number of copying cycles by rotating a magnet roll together with a developing sleeve and specifying a doctor gap to regulate the mapping of a magnetic brush. CONSTITUTION:When a developer 7 comprising a silicone-coated ferrite carrier and a positively chargeable toner passes through the doctor gap a, pressure is applied to the developer 7 by narrowing the gap a in <=0.8mm triboelectrification between the carrier and the toner increases and triboelectrification amount is enhanced. Since the developing sleeve 4 and the magnet roll 3 are both rotatable, shear is caused in the developer 7 on the sleeve 4 and the developer 7 is fully stirred, and it is improved in fluidity, so it can easily pass through the narrow gap a, thus permitting occurrence of background fog to be prevented, and correct triboelectrification to be maintained during a large number of copying cycles and accordingly, superior images to be obtained for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing method in an electrophotographic copying machine.

[Conventional technology]

Traditionally, ferrite carriers have lower true specific gravity and can have higher electrical resistance than iron powder carriers.
It has advantages such as the ability to arbitrarily design magnetic properties, the ability to obtain a spherical carrier, and good fluidity, so it is often used as a carrier for dry two-component developers. However, non-coated ferrite carriers suffer from the phenomenon that toner adheres to the carrier when making multiple copies.
There is a problem in that so-called spent occurs, which significantly shortens the life of the developer. Therefore, a resin-coated ferrite carrier is generally used in which the surface of the carrier is coated with a resin. Silicone resin, styrene resin, acrylic resin, fluororesin, etc. have been proposed as materials for this resin coating, and among them, silicone coated ferrite carrier coated with silicone resin has the best spent resistance. It has been confirmed in combination with However, this silicone ferrite carrier with excellent spent resistance has no problem when combined with a negatively chargeable toner due to the triboelectricity peculiar to its silicone resin surface, but when combined with a positively chargeable toner, However, there was a problem in that it was not possible to apply a sufficient amount of electrical charge, and soil burrs occurred from the initial stage.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned problems, and even when a silicone coated ferrite carrier is combined with a positively chargeable toner, it imparts a sufficient amount of triboelectric charge to the toner, does not cause blurring, and can print a large number of sheets. It is an object of the present invention to provide a developing method that provides stable image density even in copying.

[Means to solve the problem]

The present invention uses a dry two-component developer consisting of a silicone coated carrier and a positively charged toner to form a magnetic brush on the outer peripheral surface of a developing sleeve containing magnetotrol, and the magnetic roll and the developing sleeve rotate together. death,
Doctor gap 0. This developing method is characterized in that the magnetic brush is set to 8 m or less to restrict the bristling of the magnetic brush.

A developing device constituting the developing method of the present invention will be described below based on the drawings.

FIG. 1 shows an example of a developing device constituting the present invention. A developing device 2 is installed across a developing gap b from a photoreceptor l rotating in the direction of arrow A in the figure, and rotates in the direction of arrow B. The developer sleeve 4 includes a developing sleeve 4 that rotates in the direction of the arrow C and includes a magnetic roll 3, a developer stirring roller 5, and a doctor blade 6 placed across a doctor gap a to regulate the layer thickness of the developer 7. ing.

The characteristic feature of the developing method of the present invention is that the Doctor Gasop a is 0.00%.
The goal is to keep it below 8u+. That is, by narrowing the doctor gap a to 0.8 or less, when the developer 7 consisting of a silicone-coated ferrite carrier and a positively chargeable toner passes through the doctor gap a, pressure is applied to the developer 7, causing it to form a silicone-coated ferrite carrier. The frictional charging ability with the positively chargeable toner increases, and the amount of charge increases.

Another feature of the developing method of the present invention is that both the developing sleeve 4 and the magnet roll 3 are rotatable. In that case, there is no particular restriction on the direction of rotation of both, but it is preferable that the magneso roll 3 is rotated clockwise as shown in FIG. 1, and the developing sleeve 4 is rotated in the opposite direction. If the number of sleeves 4 is 1, it is preferable that the number of magnet rolls 3 is within the range of 2 to 50. By doing this, the developer 7 on the developing sleeve 4 is coated with sure, the silicone-coated ferrite carrier and the positively charged toner are sufficiently stirred, and the fluidity of the developer 7 is improved, so the narrow It becomes possible to easily pass through the doctor gap a.

In addition, in the present invention, as mentioned above, Dr. Ganop a is
．． It is preferable to set the development gap b to 0.8+n or less because setting it to 8 fins or more will shorten the spikes of the magnetic brush. In this way, the developing gasop b is 0. By setting the thickness to 8 mm or less, the magnetic brush of the developer with short spikes can be brought into good contact with the photoconductor 1, and a clear image can be obtained.

Next, the developer constituting the developing method of the present invention will be explained.

The developer constituting the developing method of the present invention comprises a silicone coated ferrite carrier and a positively chargeable toner. The silicone-coated ferrite carrier is a ferrite core made of metal oxides such as zinc, manganese, copper, etc. and trivalent iron oxide coated with, for example, room-temperature curing silicone resin. In this case, the electrical resistance of the silicone-coated ferrite carrier is preferably 10'3 Ω·cm or more, and if the electrical resistance is less than 10+3 Ω·1, the first
Because the gap between the photoreceptor 1 and the developing sleeve 4 shown in the figure, that is, the developing gap b, is narrow, the photoreceptor 1 and the developing sleeve 4
The electric field strength between the carrier and the carrier becomes stronger, and carrier lifting (carrier adhesion) becomes more likely to occur. Moreover, it is preferable that the average particle diameter of the silicone-coated ferrite carrier is 20 to 70 μm. If the average particle diameter is less than 20 μm, the mass of the silicone-coated ferrite carrier becomes lighter;
The potential due to the bias of the photoreceptor is stronger than the magnetic force between the silicone coated ferrite carrier and the magnet roll 3, and the carrier tends to rise onto the photoreceptor l. When the average particle diameter exceeds 70 μm, the carrier particle diameter is large, making it difficult for the developer to pass through the doctor gap a.

On the other hand, the positively chargeable toner is not particularly limited, but for example, styrene acrylic copolymer resin, polystyrene-ptadiene copolymer resin, polyester resin, polyamide resin, etc. are used as the binder resin, and as the colorant, Nigrosine dyes or quaternary ammonium salts are used as charge control agents such as carbon black, and other additives such as lubricants, abrasives, fixing agents, etc., such as polytetrafluoroethylene powder, It is obtained by mixing low molecular weight polypropylene, etc., melting and kneading, cooling, and then crushing and classifying.

〔Example〕

Next, the present invention will be specifically explained using examples.

It should be noted that the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 Using the developing device shown in FIG. 1, a continuous copy durability test of 300,000 sheets was conducted under the following conditions and developer.

<Developer conditions> Preparation of developer> ○ Toner Mix the above-mentioned ingredients, melt and knead them in a roll mill, cool them, coarsely crush them in a hammer mill, finely crush them in a supersonic jet mill, and then classify. A toner having an average particle size of 12 μm was obtained.

○ Carrier Silicone resin manufactured by Shin-Etsu Chemical Co., Ltd. was dissolved in toluene, a non-coated ferrite carrier was placed in the silicone solution, and the silicone resin was applied and dried several times to form a coating with an average particle size of 45μ and an electrical resistance. l
A silicone-coated ferrite carrier having a Ql of 3Ωl or more was obtained.

A developer was prepared by mixing 7 parts by weight of the toner with 100 parts by weight of the silicone-coated ferrite carrier.

Example 2 <Preparation of developer> O toner The above-mentioned ingredients were mixed, melted and kneaded in a roll mill, cooled, coarsely pulverized in a hammer mill, finely pulverized in a supersonic jet mill, classified, and averaged. A toner with a particle size of 12 μm was obtained.

0 Carrier A silicone resin manufactured by Shin-Etsu Chemical Co., Ltd. was dissolved in toluene, a non-coated ferrite carrier was placed in the silicone solution, and coating was performed by applying and drying the silicone resin several times to obtain a silicone-coated ferrite with an average particle size of 60μ. I got a career.

A developer was prepared by mixing 7 parts by weight of the toner with 100 parts by weight of the silicone coated ferrite carrier. The developer was subjected to a continuous copy durability test of 300,000 sheets using the developing device under the conditions of the developing device of Example 1. Comparative Example 1 A continuous copying durability test was conducted on 300,000 copies under the following conditions. The above-mentioned ingredients were mixed, melt-kneaded in a roll mill, cooled, coarsely pulverized in a hammer mill, finely pulverized in a supersonic jet mill, and classified to obtain a toner having an average particle size of 12 μm. A developer was prepared by mixing 7 parts by weight of the toner with 100 parts by weight of an acrylic coated ferrite carrier manufactured by Dowa Iron Powder Co., Ltd. The developer was subjected to a continuous copy durability test of 300,000 sheets using a developing device under the conditions of the developing device of Example 1.

Comparative Example 2 Using the same developer as in Example 1, developing device Comparative Example 3 Using the same developer as in Example 1, using the developing device under the following conditions, continuous A copy durability test was conducted on 300,000 copies.

Table 1 shows the evaluation results of the continuous copy durability test for the developing method of the present invention based on Examples 1 to 2 and the comparative developing method based on Comparative Examples 1 to 3 as described above. The image density in the table was measured using a Macbeth reflection densitometer, and the soil strength was evaluated visually.

As is clear from the evaluation results in Table 1, the developing method according to the present invention yielded good results for all evaluation items. [Effects of the Invention] As explained above, the developing method of the present invention prevents the occurrence of burr from the initial stage due to insufficient charge amount, which is a drawback of developers made of silicone-coated ferrite carrier and positively chargeable toner. Furthermore, since an appropriate amount of charge can be maintained over a long period of time in the number of copies to be made, good images can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a developing device applied to the developing method of the present invention. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 2... Developing device, 3... Magnet roll, 4... Developing sleeve, 5... Developer stirring roller, 6... Doctor blade, 7... Developer , a... Doctor gap, b... Development gap Patent applicant Tomogawa Paper Mills Co., Ltd.

Claims (1)

[Claims] A magnetic brush is formed on the outer peripheral surface of a developing sleeve containing a magnetic roll using a dry two-component developer consisting of a silicone-coated ferrite carrier and a positively chargeable toner, and the magnetic roll and the developing sleeve rotate together,
A developing method characterized in that a doctor gap is set to 0.8 mm or less to restrict bristling of the magnetic brush.