JPH0258629B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device for developing an electrostatic latent image using insulating magnetic toner.

In development using a one-component developer, it is required to be able to transfer onto ordinary plain paper, and for this purpose a development method using an insulating magnetic toner is desirable. Further, in this method of developing a latent image by charging the insulating magnetic toner, various things are required to keep the developed density stable and to stabilize the image. One of the requirements is that the toner should not be agglomerated. To this end, toner is applied onto the developer support means, the toner is charged, the toner layer and the latent image holding means are placed apart from each other, and the toner on the developer support means is caused to fly up onto the image area of the latent image. A method of developing is also preferred. This is one way to prevent the toner from being compressed and agglomerated between the developer supporting means and the latent image holding means. This method is known as the so-called jumping development method.
9475, US Pat. No. 2,839,400, etc.), non-magnetic toner is used. Also known is a method of developing by applying a high frequency electric field between the developer supporting means and the back surface of the electrostatic latent image holding means (for example, US Pat. No. 3,866,574, US Pat. No. 3,893,418, etc.). However, although various attempts have been made to date, it has been difficult to keep the developer density stable, to always stably coat a uniform toner layer on the developer supporting means, and to prevent the toner from agglomerating.

In addition, in the two-component dry developing method, the strength of the developing magnetic pole corresponding to the developing section of the fixed magnetic roller in the rotating developing sleeve does not have a substantial effect on image quality; however, when using one-component magnetic toner, In the non-contact development method, image quality is greatly affected. For example, if the strength of the developing magnetic pole is too strong, the image may not be developed.

The present invention is intended to solve this problem, and aims to provide a developing device that can obtain good image quality through a non-contact developing method using insulating magnetic toner.

Embodiments of the developing device according to the present invention will be described below. The drawings schematically illustrate one embodiment of the invention. 1 is a CdS photoreceptor whose surface is covered with an insulating film (polyester film 25μ thick). 2 is a conductive cylinder. A well-known method can be applied to form a latent image on the photoreceptor, but for example, after the photoreceptor drum is positively charged with a primary charger, it is charged with a negative secondary corona charge almost simultaneously with the photoimage exposure. Then, a high-contrast electrostatic latent image is obtained by full-surface exposure. The potential of the electrostatic latent image was +500 V in the dark areas of the image and OV in the bright areas. After this electrostatic latent image was developed by the developing device 8, it was transferred to plain paper by corona discharge, and a good fixed copy was obtained.

In detail about the developing device 8, 3 is a non-magnetic developing sleeve having a magnetic roller 4 inside, which rotates at approximately the same circumferential speed in a direction that follows the direction of movement of the electrostatic latent image surface as shown by the arrow. are doing. In the developing section, a developing magnetic pole _S1 is fixedly arranged inside the developing sleeve 3, facing the electrostatic latent image. Reference numeral 5 denotes a developer layer thickness regulating blade for applying the developer 7 to an appropriate thickness on the developing sleeve 3, and is a blade made of a magnetic material. Here, the iron blade was fixed at a distance of 250 μm from the developing sleeve 3. A magnetic pole N ₁ is fixedly arranged inside the developing sleeve 3 so as to face the blade 5 .
The magnetic field of this magnetic pole is concentrated on the magnetic blade 5, and a strong magnetic curtain is formed between the blade 5 and the sleeve 3. As a result, a magnetic toner layer having a thickness thinner than the gap between the magnetic blade 5 and the sleeve 3 is formed as described later.

6 is a hopper, and 7 is an insulating magnetic toner contained therein. In the developing section, the developing device 8 of the developing sleeve 3 is set so that it is located 300 μm away from the electrostatic latent image surface.

The magnetic powder content of the magnetic toner used for development is
If the amount is less than 20% by weight, the amount of magnetic powder contained inside the magnetic toner particles is small, and more toner particles are produced during the crushing process when forming particles. Since the toner layer has poor fluidity during conveyance and is prone to agglomeration, even if the toner layer thickness is controlled by the magnetic blade and the fixed magnetic pole opposed thereto, the toner layer thickness may not be controlled to be sufficiently thin by the magnetic field between the two, or the toner may become agglomerated. If the toner particles pass through the toner, it becomes difficult to form a uniform toner layer. This makes it difficult to obtain good image quality. Therefore, it is necessary to increase the content to 20% by weight or more.

On the other hand, if the content exceeds 60% by weight, the fixing performance deteriorates, and when an alternating bias voltage is applied to the developing sleeve, the toner is finely loosened by the vibration movement of the magnetic toner, resulting in fine-grained image quality. If the magnetic powder content exceeds 60% by weight, the magnetic brush of the magnetic toner will be difficult to collapse in the developing magnetic field, which will impair image quality, which is not preferable. Therefore, it is preferable to maintain the content at 60% by weight or less.

The toner used below was a negative insulating magnetic toner consisting of about 80 parts by weight of styrene resin and about 20 parts by weight of magnetic powder, and had an average particle size of approximately 6 μm. The thickness of the developer layer coated on the developing sleeve 3 was approximately 150 μm, which was thinner than the 250 μm gap between the magnetic blade 5 and the sleeve 3. During development, a developing bias voltage is applied between the developing sleeve 3 and the cylinder 2. Reference numeral 9 denotes a power source for generating this developing bias voltage, which is, for example, an alternating voltage generator described in Japanese Patent Application No. 53-92108. This developing bias voltage has a frequency of 200Hz and a peak value of 800Vpp.
DC voltage +200V is superimposed on the alternating voltage.

The magnetic roller 4 has the above-mentioned developing magnetic pole S ₁ and developer applying magnetic pole N ₁ preferably spaced apart by 90°, and has a magnetic pole separated from the developing magnetic pole by about 90° to collect the developer into the hopper. N ₂ and further,
Then, magnetic pole groups S ₂ , N ₃ ,
Has _S3 .

The strength of the magnetic field of the magnetic pole _N1 of the magnetic roller 4 facing the developer layer thickness regulating blade 5 had a surface magnetic flux density of about 800 Gauss on the surface of the developing sleeve 3.

In the developing section, development was carried out by varying the strength of the developing magnetic pole _S1 fixedly arranged inside the developing sleeve 3 facing the electrostatic latent image. By changing the strength of the developing magnetic pole, the magnetic flux density on the surface of the developing sleeve 3 in the developing section is 0 Gauss, 200 Gauss, 450 Gauss, and 800 Gauss.
The image quality was compared for Gauss, 950 Gauss, and 1000 Gauss. If the strength of the magnetic field on the surface of the developing sleeve 3 in the developing section is approximately 0, toner will fly and adhere excessively to non-image areas, easily causing background fog.
It has been found that with Gauss, it is difficult for the magnetic toner to fly to the image area and almost no development is achieved.
Almost all fog can be removed at 200 Gauss. At 950 Gauss, the development density was somewhat low and the letters became thinner, but an almost good image was obtained. Also, at 450 Gauss and 800 Gauss, the developed density was satisfactory, and good, high quality images with sharp gradation were obtained.

Note that as the particle size of the magnetic toner becomes smaller, it tends to electrostatically stick to the sleeve strongly, making it difficult for it to fly to the latent image holding surface, and the adhesion force of the newly supplied toner to the sleeve increases. This weakens the toner layer, which prevents the formation of a stable toner layer, and when the toner passes through the magnetic field between the magnetic blade and the sleeve, the layer thickness tends to become uneven, deteriorating the image quality.
Such inconvenience can be prevented by setting the average particle size of the magnetic toner to 5 μm or more.

As described above, according to the present invention, the rotating developer supporting means provided opposite to the latent image holding means and the magnetic powder are
Average particle size 5μ containing 20% by weight or more and 60% by weight or less
A means for supplying the above insulating magnetic toner to the developer supporting means, and a layer thickness of the magnetic toner on the developer supporting means that is smaller than the distance between the latent image holding means and the developer supporting means. The thickness regulating means includes a regulating member made of a magnetic material located on the developer side of the developer supporting means, and a regulating member provided on a side opposite to the developer side of the developer supporting means with respect to the regulating member. a second fixed magnetic pole that generates a fixed magnetic field having a magnetic flux density of 200 Gauss or more and 950 Gauss or less on the surface of the developer supporting means in the developing section; Bias application means for applying an alternating bias voltage;
By using an insulating magnetic toner, a developing device equipped with this has the effect of producing high-quality images with stable sharp development density without unpleasant fogging. It can also be transferred to plain paper and provides good image quality. Development using one-component magnetic toner has become possible.

[Brief explanation of the drawing]

The figure is a sectional view showing one embodiment of the developing device according to the present invention. 3...Developer supporting means, 4...Magnetic roller, 5...Thickness regulating means, 6...Developer supply means, 7...Magnetic developer.

Claims (1)

[Scope of Claims] 1. A rotating developer supporting means provided opposite to a latent image holding means, and an insulating magnetic toner containing 20% by weight or more and 60% by weight or less of magnetic powder and having an average particle size of 5μ or more. a means for supplying the developer to the developer supporting means; and a thickness regulating means for regulating the thickness of the magnetic toner layer on the developer supporting means to a layer thickness smaller than the distance between the latent image holding means and the developer supporting means. It's hot,
A thickness having a magnetic regulating member located on the developer side of the developer supporting means, and a first fixed magnetic pole facing the regulating member and provided on the side opposite to the developer side of the developer supporting means. a regulating means; a second fixed magnetic pole that generates a fixed magnetic field having a magnetic flux density of 200 Gauss or more and 950 Gauss or less on the surface of the developer supporting means in the developing section; and a bias application that applies an alternating bias voltage to the developer supporting means. A developing device comprising: means;