JPH0367267B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to an electrostatic latent image carrier that develops an electrostatic latent image carried on the surface of an electrostatic latent image carrier with a magnetic developer, specifically, a developer containing magnetic toner. The present invention relates to an image developing method.

Technical background The electrostatic latent image developing method described above uses a developer containing an uncharged magnetic toner which itself is not substantially triboelectrically charged, and a method that uses a developer that includes contact between toners or a developing sleeve or the like. There are two main types: those that use a developer containing a charged magnetic toner that is triboelectrically charged by contact with the toner; here,
Although the former method is advantageous in that the polarity of the electrostatic latent image to be developed does not matter, the latter method is superior in terms of development efficiency, and from a practical standpoint, the latter method is not suitable. There is. However, this latter method has problems such as easy development fog, low contrast of the developed image, and relatively poor image quality of the developed image, and it is currently desired to improve these problems. be.

Incidentally, in connection with these points, the present inventors conducted various experiments and confirmed that the charged magnetic toner has a triboelectric charge amount of 5 μc/g or more with respect to iron powder, and When using magnetic toner that is triboelectrically charged to a polarity opposite to that of the electrostatic latent image to be developed, a magnetic brush developing device having a developing sleeve equipped with a developing magnet inside is used, and an AC is applied to the developing sleeve. It has been found that developing an electrostatic latent image while applying a developing bias suppresses the occurrence of development fog and improves the contrast of the developed image. It has also been found that when an electrostatic latent image is developed while being driven, the image quality of the developed image becomes finer.

However, surprisingly, when the electrostatic latent image is developed while applying the AC developing bias and rotating the developing magnet at the same time, although the above-mentioned improvement is achieved, as shown in FIG. It has been experienced that uneven development occurs in shading. 1st
The figure shows the development of a solid copy image with halftone density (density of about 0.8) obtained by a powder image transfer type electrophotographic copying machine incorporating the magnetic brush developing device MD shown in Fig. 2. The density distribution in the direction (the direction of movement of the photoreceptor drum) is shown, and within the circle represented by (A), the density distribution measured by a microdensitometer is shown by a solid line a. The configuration of the developing device MD will be described in detail later, but when obtaining the copied image, an AC developing bias with a frequency of 400 Hz is applied to the developing sleeve 2, and the magnetic roller 3 rotates at a rotation speed of 1200 rpm. It was being driven.

Among the development unevenness shown in Figure 1, the high-frequency unevenness that appears in the solid line a occurs in a micro region of the size of a toner particle, and cannot be visually identified and can be ignored as development unevenness. Of course,
The low frequency unevenness as shown by the dashed line b is
This appears as a parallel striped pattern in the image, making the developed image or the copied image itself extremely unsightly. It is believed that such low frequency unevenness is caused by the following reasons.

That is, based on the experience of the present inventors, when the above-mentioned development is performed, an alternating electrostatic force due to an AC development bias is applied to the charged toner in the development area.
The alternating magnetic force generated by the rotational drive of the magnetic roller is superimposed on the force that changes instantaneously. It is thought that the developing characteristics of the electrostatic latent image, so to speak, the developing efficiency is changed, and as a result, the low frequency unevenness as described above occurs.

OBJECT OF THE INVENTION An object of the present invention is to solve various problems that occur when developing an electrostatic latent image using a developer containing a charged magnetic toner, without substantially causing low-frequency development unevenness as described above. It's about improving.

Summary of the Invention The summary of the present invention is that, in the electrostatic latent image developing method according to the present invention, when developing an electrostatic latent image using the developer, a developing sleeve to which an AC developing bias is applied; A developing device having a magnetic roller rotatably provided inside is used, and the following formula fe≧P・R/16 R≧37・Vp/P …… …… However, fe: AC developing bias frequency (Hz) P: number of magnetic poles of the magnetic roller R: number of rotations of the magnetic roller (rpm) Vp: speed of movement of the surface of the electrostatic latent image carrier (mm/sec). The conditions of the above formula were derived empirically as a result of numerous experiments conducted by the present inventors, and as long as the above development is performed under conditions where these conditions are satisfied, Even if low-frequency development unevenness occurs, the degree of occurrence is within a substantially negligible range.

Example FIG. 2 shows a magnetic brush developing device MD used in development experiments by the present inventors, and this developing device MD can be used to carry out the electrostatic latent image developing method according to the present invention. . The developing device MD is incorporated in a powder image transfer type electrophotographic copying machine, and in the copying machine, the electrophotographic photosensitive drum 1 is driven to rotate at a circumferential speed of 130 mm/sec in the direction of arrow a. be done. Here, an electrostatic latent image with a potential (+) of 600 V in the image area and a potential (+) of 40 V in the non-image area is formed on the surface of the photoreceptor drum 1. The image is developed by a developing device MD.

The developing device MD includes a non-magnetic developing sleeve 2 made of an aluminum material and having an outer diameter of 31 mm, and a magnetic roller 3 having 8 magnetic poles rotatably provided inside the developing sleeve 2.
The magnetic force of each magnetic pole of the magnetic roller 3 is set so that a magnetic field of 750 Gauss is formed on the circumferential surface of the developing sleeve 2. Note that during electrostatic latent image development, the developing sleeve 2 and the magnetic roller 3 are rotated at a constant rotation speed in the direction of arrow b, and the magnetic developer de is rotated on the circumferential surface of the developing sleeve 2.
is conveyed in the direction of arrow c. Further, the developing sleeve 2 is disposed facing the photosensitive drum 1 with a developing gap of 0.4 mm being maintained to form a developing area between the developing sleeve 2 and the photosensitive drum 1.

In the developing device MD, the developer DE is stored in the developer storage tank 4, and during development, it is magnetically attracted onto the circumferential surface of the developing sleeve 2, and is also subjected to the spike height regulating action by the spike height regulating plate 5. The photoreceptor drum 1 is conveyed in the direction of arrow c while being received by the photoreceptor, and the surface of the photoreceptor drum 1 is rubbed in the development area, thereby developing the electrostatic latent image carried on the surface. Here, the tip edge of the height regulating plate 5 is 0.25 mm relative to the circumferential surface of the developing sleeve 2.
The Hodaka regulation gap is maintained. Note that while the developer de used for development is further conveyed in the direction of arrow c, it is once scraped off from the circumferential surface of the developing sleeve 2 by the mesh-shaped blade plate 6 and passes through the mesh portion of the plate plate 6. Then, it is returned onto the circumferential surface of the developing sleeve 2 again.

By the way, regarding the developing sleeve 2,
AC bias power supply 7 and DC bias power supply 8 are connected, and during development, AC developing bias power of 500Vrms and (+) 100V are applied to the developing sleeve 2.
DC developing biases are applied in a superimposed manner. Note that the voltage value of this DC developing bias is set to a value slightly higher than the potential (+) 40 V of the non-image area of the electrostatic latent image. This is because the surface of the photoreceptor drum is rubbed by the developer de, which may cause a phenomenon in which the potential of the non-image area is increased.

In the electrostatic latent image developing method according to the present invention, the developer has a triboelectric charge amount of 5 μc/g or more on iron powder, and is triboelectrically charged with a polarity opposite to the polarity of the electrostatic latent image to be developed. A developing device including a developing sleeve to which an AC developing bias is applied, and a magnetic roller rotatably provided inside the developing sleeve is used as a developing device, and the above-mentioned, The electrostatic latent image is developed under the conditions of the formula. This not only suppresses the occurrence of development fog and improves the contrast of the developed image, but also makes the quality of the developed image finer and at the same time virtually ignores low-frequency development unevenness that may appear in the developed image. This should be kept to the extent possible.

Here, the amount of frictional charge of the magnetic toner with respect to iron powder is Z200 manufactured by Nippon Tetsuko Co., Ltd. (average particle size approximately 100 μm).
5 parts by weight of the magnetic toner to be measured was mixed with 95 parts by weight of iron powder), and after stirring for 2 hours, a blow-off powder charge measuring device manufactured by Toshiba Chemical Co., Ltd. was used.
It is measured with TB200, and all triboelectric charges shown in this specification were measured in this way.

Note that the magnetic toner contained in the developer is not necessarily limited to one type, and the developer may contain several types of magnetic toner. It is necessary that the magnetic toner always exhibits the amount of triboelectric charge as described above. Further, various additives may be mixed into the developer as necessary. Furthermore, the voltage value, frequency, rotation speed of the magnetic roller, etc. of the AC developing bias can be set arbitrarily within the range that satisfies the conditions of the above formula, and the developing characteristics of the electrostatic latent image can be arbitrarily changed within the range. , it can also be improved.

Hereinafter, among the numerous development experiments conducted by the present inventors, representative ones will be shown as experimental examples to clarify specific embodiments of the electrostatic latent image developing method according to the present invention.

Experimental Example 1 The rotational speed of the developing sleeve 2 and magnetic roller 3 in the developing device MD shown in Fig. 2 was set at 60 rpm, respectively.
1000 rpm and the frequency of AC bias power supply 7.
800 Hz, and using a -component magnetic developer consisting of magnetic toner with an average particle size of 12.5 μm and a triboelectric charge of (-)15 μc/g against iron powder, and supported on the surface of the photoreceptor drum 1. When the electrostatic latent image was developed, a developed image of extremely good quality was obtained. When this developed image was visually observed, no striped development unevenness was observed.

In addition, according to the above formula, the developing sleeve 2
The rotation speed of the is 37×130/8rpm, that is, 601rpm or more, and the frequency of the AC bias power supply is 8×
It is required that the frequency be 1000/16Hz, that is, 500Hz or higher, and this condition is satisfied in the settings of Experimental Example 1. By the way, when performing the above-mentioned development, when the voltage value of the AC bias power supply 7 is changed, if the value is approximately equal to the potential of the image area of the electrostatic latent image to be developed, specifically, It was confirmed that a developed image with good gradation reproducibility could be obtained within the range of 450 to 750 Vrms.

Comparative Experimental Example 1 In the settings of Experimental Example 1, AC bias power supply 7
When an electrostatic latent image is developed by changing only the frequency of It was observed that remarkable striped development unevenness occurred.

Comparative Experimental Example 2 In the settings of Experimental Example 1, when the electrostatic latent image was developed by changing only the rotational speed of the magnetic roller 3, a state in which the condition of the above formula was no longer satisfied, specifically, a rotation speed of 1600 rpm or more was detected. to 1700rpm, also
In any case where the speed was changed from 601 rpm to 500 rpm, it was observed that remarkable striped development unevenness occurred in the obtained developed image.

Experimental Example 2 The diameter of the developing sleeve 2 was reduced to 24.5 mm, and the magnetic force of each magnetic pole of the magnetic roller 3 was strengthened to the extent that a magnetic field of 800 Gauss was formed on the circumferential surface of the developing sleeve 2. practically the second
When an electrostatic latent image was developed using the same developing device as the developing device MD shown in the figure under the same conditions as Experimental Example 1, a developed image of extremely good quality was obtained as in Experimental Example 1. . In addition, comparative experiment examples 1 and 2
When the frequency of the AC bias power supply 7 or the number of rotations of the magnetic roller 3 was changed as shown in the figure, it was observed that remarkable striped development unevenness occurred in the developed image.

Experimental Example 3 When an electrostatic latent image was developed under the same conditions as Experimental Example 1 using the same developing device as the aforementioned developing device MD except that the number of magnetic poles of the magnetic roller 3 was increased to 12 poles, an electrostatic latent image was developed in Experimental Example 1. As in the previous case, a developed image of extremely good quality was obtained. At this time, the AC bias power supply 7
It has been confirmed that if the frequency of the magnetic roller 3 is changed to 700 Hz, or the rotational speed of the magnetic roller 3 is changed to 1100 rpm or 350 rpm, remarkable striped development unevenness occurs in the developed image.

Experimental Example 4 The circumferential speed of the photoreceptor drum 1 was accelerated to 260 mm/sec, and as a developer, only magnetic toner with an average particle size of 13.2 μm and a triboelectric charge amount of (-) 34.5 μc/g with respect to iron powder was used. When an electrostatic latent image was developed under the same conditions as in Experimental Example 3 except that a one-component magnetic developer was used, a developed image of extremely good quality was obtained as in Experimental Example 1. At this time, change the frequency of the AC bias power supply 7 to 700Hz, or change the rotation speed of the magnetic roller 3 to 1100rpm, or
It was confirmed that when the speed was changed to 750 rpm, noticeable striped development unevenness occurred in the developed image.

By the way, using the magnetic developer used in Experimental Example 4, Experimental Examples 1 to 3 and Comparative Experimental Examples 1 and 2
When similar experiments were conducted, the results were almost the same as those shown in the examples above.

Effects of the Invention In the electrostatic latent image developing method according to the present invention, the amount of triboelectric charge on the iron powder is 5 μc/g or more, and the triboelectric charge is opposite to the polarity of the electrostatic latent image to be developed. A developing device is used which includes a developing sleeve to which an AC developing bias is applied, and a magnetic roller rotatably provided inside the developing sleeve. The electrostatic latent image is developed while simultaneously applying an AC developing bias to the sleeve and rotating the magnetic roller.
Not only is it possible to suppress the occurrence of development fog and improve the contrast of the developed image, but also the image quality of the developed image becomes finer. Incidentally, since the electrostatic latent image is developed under the conditions of the above formula, striped low-frequency development unevenness that may appear in the developed image is suppressed to a substantially negligible level.

[Brief explanation of drawings]

Figure 1 is a drawing showing the occurrence of uneven development, Figure 2
The figure is a diagram showing a magnetic brush developing device used in development experiments by the present inventors. MD...magnetic brush developing device, de...magnetic developer, 1...electrophotographic photosensitive drum, 2...developing sleeve, 3...magnetic roller, 7...AC bias power supply.

Claims (1)

[Scope of Claims] 1. An electrostatic latent image developing method in which an electrostatic latent image carried on the surface of an electrostatic latent image carrier is developed with a magnetic developer, the developer being a friction material against iron powder. A developer containing a magnetic toner having a charge amount of 5 μc/g or more and triboelectrically charged to a polarity opposite to that of the electrostatic latent image, and a developing device in which an AC developing bias is applied. A developing device having a sleeve and a magnetic roller rotatably provided inside the developing sleeve is used, and the conditions of the following formula are fe≧P・R/16 R≧37・Vp/P …… However, fe : Frequency of AC developing bias (Hz) P: Number of magnetic poles of the magnetic roller R: Number of rotations of the magnetic roller (rpm) Vp: Moving speed of the surface of the electrostatic latent image carrier (mm/sec) An electrostatic latent image developing method characterized by developing. 2. The electrostatic latent image developing method according to claim 1, wherein in the developing device, the magnetic roller is rotationally driven in a direction opposite to the direction in which the developer is conveyed. 3. The electrostatic latent image developing method according to claim 2, wherein in the developing device, the developing sleeve is rotatably provided and is rotationally driven in the same direction as the magnetic roller.