JPH0750351B2 - Development device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Purpose of the invention [Industrial field of application] The present invention relates to a developing device for developing a latent image formed by an electrophotographic method or an electrostatic recording method, and in particular, a developer carrier and an image carrier. The present invention relates to a developing device that develops by applying an alternating electric field (bias) between the two.

[Prior Art] Conventionally, as described in, for example, JP-B-58-32375, JP-B-58-32377, etc., an image carrier by holding a developer in a uniform thin layer on the developer carrier. On the image carrier by causing the developer on the developer carrier to fly to the image carrier by an alternating electric field applied between the developer carrier and the image carrier. A developing device for developing a latent image is known.

FIG. 2 is a sectional view of the developing device described above applied to a copying machine using a drum type photoconductor. Although not shown in the drawing, a charging mechanism, an image exposure mechanism, a transfer mechanism, a cleaning mechanism, which are well-known electrophotographic processes, are provided around the photosensitive drum 6.
A charge removing mechanism and the like are provided.

In the figure, 1 is a hopper containing a developer 2 (one-component toner, two-component toner, or the like), and 3 is a hopper whose part of the peripheral surface is exposed to the outside from an opening 7 of the hopper 1 in the longitudinal direction. A non-magnetic cylinder (hereinafter referred to as a sleeve) as a developer supporting member rotatably attached between the side plates.

Reference numeral 4 denotes a magnet roller which is concentrically and fixedly provided in the sleeve, and has a plurality of magnetic poles N ₁ · N ₂ and S ₁ · S ₂ formed in parallel to the longitudinal direction of the circumferential surface.

Reference numeral 5 designates a blade as a developer layer thickness regulating means attached to the hopper 1 with a gap g1 formed between the sleeve 3 and the sleeve 3, and 6 a latent image holding means rotatably supported by an unillustrated copying machine body in an arrow direction. The photoconductor as described above, in which the sleeve 3 is arranged in parallel with a gap g2. Reference numeral 7 is a developing section, and 8 is a developing bias power source for applying an alternating electric field between the sleeve 3 and the photoconductor 6.

When the sleeve 3 receives a driving force from a driving source (not shown) and rotates in the arrow direction, the developer 2 is restrained on the sleeve by a supporting force such as a magnetic force or an electrostatic force, and the rotation of the sleeve causes an arrow a. And is applied in a fixed layer thickness t by the blade 5. On the surface facing the photoconductor 6, this coating developer electrostatically jumps or expands the gap g2 by an action of an alternating electric field due to the above-mentioned alternating voltage, corresponding to the latent image pattern on the photoconductor, so that the latent image surface is formed. And is used for development.

[Problems to be solved by the invention]

However, conventionally, as the above-mentioned alternating electric field, since the rising speed in the development promoting direction and the falling speed in the development suppressing direction are symmetrical, a latent image formed by a document in which a bold document is mixed as a solid portion and a line portion is formed. When developed, the bold letters become thicker, making it difficult to read the letters.

Therefore, as a result of repeated experiments and studies, the present applicant changed the relationship between the rising speed of the alternating electric field in the development promoting direction and the falling speed of the alternating electric field in the development suppressing direction, and While showing similar image characteristics, we found a phenomenon in which the image characteristics differ for the latent image of the line part.

This phenomenon seems to occur as follows. FIG. 3 is an electric field diagram that acts on the solid portion 9A and the line portion 9B when the alternating electric field is in the development promoting direction and is large, and the electric force lines 10A are open in both the solid portion 9A and the line portion 9B. .

On the other hand, in FIG. 4, the alternating electric field is in the development promoting direction,
And, when it is small, it is an electric field diagram that acts on the solid portion 9A and the line portion 9B.
Although B only wraps around the image background portion, in the line portion B, the ratio of the electric force lines 10B to the image background portion is larger than that of the opened electric force lines 10A.

It is considered that the image characteristics of the line portion with respect to the latent image differ due to the wraparound of the lines of electric force to the image background portion.

It is an object of the present invention to provide a developing device which can obtain a delicate image from a bold document by utilizing the above-mentioned development.

(B) Structure of the Invention [Means for Solving the Problems] In the present invention, the developer is held in a uniform thin layer on the developer carrier and transferred to the supply position to the image carrier, In a developing device that develops a latent image on the image carrier by an alternating electric field formed between the image carrier and the image carrier, the rising speed of the alternating electric field in the development promoting direction is higher than the falling speed in the development suppressing direction. It is a developing device characterized by speeding up.

[Action]

The alternating electric field in the present invention makes the bold portion of the line portion a delicate image by making the rising in the development promoting direction faster than the falling in the development suppressing direction.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a waveform diagram of an alternating electric field, in which the horizontal axis represents time,
The vertical axis represents voltage, and the higher the position, the faster the development, and the lower the position, the lower the development.

The solid line A is an alternating electric field whose rising and falling waveforms are symmetrical,
A broken line B is an alternating electric field having an asymmetrical waveform that rises sharply to the peak on the development promoting side and then slowly falls from the peak.

When the alternate electric field indicated by the alternate long and short dash line B is used, in the solid portion A, as shown in FIG. 4 (A), there is no difference in the direction of the electric force line 10A between the peak of development promotion and the middle thereof. , Shows the same development characteristics, but the development acceleration bias reaches a peak in a short time in the line portion, so the toner has not yet reached the latent image at the peak time, and then the development acceleration bias decreases, As shown in FIG. 4 (B), the lines of electric force 10B wrap around the background portion, so that the developer cannot reach the latent image, and the line portion becomes thin and a delicate image is obtained.

An experimental example in which the developing device of the present invention is applied to an electrophotographic copying machine will be described below. Toner for NP-150Z (one-component magnetic toner) is used as a commercially available developer, a pulse generator is used as the power source for the developing bias, and the frequency f is 1800 Hz and the peak-to-peak voltage V _pp = 1200 V. Shows a sharp rise and then a slow fall, and a DC voltage was superimposed on the alternating electric field of the waveform B shown in FIG. 1, and when developed, the solid part was uniform and the density was high, and the halftone reproduction was good. Moreover, it was possible to obtain a bold image of the line portion as a delicate image.

For comparison, when the development was carried out under the same conditions as in the above experimental example, except that the alternating electric field was symmetrical with the rising and falling in the direction of development promotion shown in FIG. The density was good, and the reproduction of halftone was good, but the image in which the bold characters in the line portion were slightly thicker.

The table below shows the results of copying with the NP-150Z using a Macbeth reflection densitometer using a halftone of 0.3 mm in image density of φ5 mm, a solid black of φ5 mm in image density of 1.1, and a line original.

As described above, according to the present invention, the alternating electric field applied between the developer carrying member and the image carrying member as the developing bias sharply rises with respect to the development promoting direction and with respect to the development suppressing direction. As a result, a delicate image can be obtained from a bold original without changing the image characteristics of the solid image and the halftone image.

[Brief description of drawings]

FIG. 1 is a waveform diagram of an alternating electric field of a developing device according to an embodiment of the present invention, FIG. 2 is a sectional view of the developing device of the present invention applied to a copying machine, FIGS. 3 (A) and (B), and FIG. FIGS. 3A and 3B are explanatory views of lines of electric force acting on development. 2 ... Developer, 3 ... Developer carrier (sleeve), 6 ...
... Image carrier (photoreceptor).

Claims (1)

[Claims] 1. In a developing device for developing by forming an alternating electric field between a developer carrying member carrying a developer and an image carrying member carrying a latent image, a rising speed toward a peak on the development promoting side of the alternating electric field. Is faster than the falling speed from the peak.