JP2001305853A - Electrophotographic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform image by matching a position of a recording medium and two developing rollers, a kind of a magnetic pole in a development and the position of a doctor blade. SOLUTION: This equipment comprises with the two developing rollers mutually rotating in opposite directions being used, the rotating direction of the first developing roller is opposite to the direction of a photo conductor drum with an insulation distance of 0.5 mm-1.5 mm, the rotating direction of the second developing roller is identical to the direction of the photo conductor drum with the insulation distance of 0.5 mm-1.5 mm, the first and the second developing rollers are positioned 30 degrees respectively from a center of the photo conductor drum, a distance between the photoconductor drum and the doctor blade is 5 mm-15 mm, each of the first developing roller and the second developing roller has two magnetic poles in development respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a colored toner image on a transfer material such as paper using an electrophotographic method or an electrostatic recording method. An electrostatic latent image formed on a body is composed of a magnetic carrier and a toner as main components by a first developing roller and a second developing roller which are arranged along a moving direction of the recording body and rotate in opposite directions to each other. The present invention relates to an electrophotographic apparatus for developing with a two-component magnetic developer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic method or an electrostatic recording method, a charge latent image is formed on a photoconductive photoreceptor or a dielectric, which is a recording material, and the latent image is formed by two developing rollers rotating in opposite directions. Japanese Patent Publication No. Sho 54-10869, Japanese Patent Laid-Open Publication No. 1-503811, and Japanese Utility Model Publication No.
No. 15881 and U.S. Pat. No. 4,442,790.

[0003]

However, in the conventional method, in the case of gradation characteristics of image density and printing of an image photograph consisting of halftone dots or lines, when the importance is placed on the medium / low image density range, the image density is not so high. Had the problem of falling. An object of the present invention is to solve the above problems.

FIG. 3 is a view for explaining a solid black image often seen in a conventional electrostatic latent image developing apparatus. FIG. 3A shows a black solid portion 33 having a size of about 3 cm in length and width recorded at a high image density, and FIG. 3B shows an example of a sectional view thereof. The peripheral portion of the solid black portion 33 is raised high by the edge effect. FIG. 4 is an example of characters when FIG. 3 is recorded. At a high image density with a high developing capacity, the lines and points of the characters are also thick and large. This has drawbacks such as difficulty in recognizing character details when printing complex Chinese characters and the like, an increase in the amount of toner used, an increase in the printing portion, and a reduction in the high quality value of a bound document.

FIG. 5 is a diagram for explaining a solid black image recorded at a low image density. FIG. 5A shows a black solid portion 33 having a size of about 3 cm in length and width recorded at a high image density. FIG. 5B is an example of a cross-sectional view thereof. There is a defect that the central portion of the solid black becomes white as compared with FIG. 3A, and it does not rise as high as in FIG. 3B. FIG. 6 shows FIG.
This is an example of characters when "." Is recorded. Defects remain in the solid black as shown in FIG. 5, but the lines and points of the characters are thin and small,
Recognition of details becomes possible.

As a result of various studies on this image defect, the present inventors have found that the insulation distance formed between the first developing roller and the recording medium, the angle formed between the center of the first developing roller and the center of the recording medium, and the like. In addition, the present inventors have found that the insulation distance formed between the second developing roller and the recording medium and the angle formed between the center of the second developing roller and the center of the recording medium are greatly involved. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which solves the above-mentioned drawbacks of the prior art and provides excellent image quality.

[0007]

As a means for solving the above-mentioned problems, a latent image formed on a recording medium such as a photoreceptor or a dielectric is arranged along a moving direction of the recording medium. The first developing roller and the second developing roller are rotated in opposite directions by an image forming apparatus that develops with a two-component magnetic developer containing a magnetic carrier and a toner as main components.

According to the present invention, the first developing roller is located at a position within 0.2 seconds in time from the optical signal, and the moving direction of the second developing roller is the same as the moving direction of the recording medium. It is characterized in that the developing roller is regulated within a time range of 0.8 seconds from the optical signal. Further, the second means of the present invention is the first means, wherein:
The position of the first developing roller and the second developing roller is regulated by 30 degrees (± 15 degrees) from the center of the recording medium. According to a third aspect of the present invention, in the first aspect, an insulation distance between the first developing roller and the recording medium is restricted to a range of 0.5 mm to 1.5 mm. . According to a fourth aspect of the present invention, the first device
In the above means, an insulation distance between the second developing roller and the recording medium is restricted to a range of 0.5 mm to 1.5 mm. According to a fifth aspect of the present invention, in the first aspect, the distance between the recording body and the doctor blade is restricted to a range of 5 mm to 15 mm. According to a sixth aspect of the present invention, in the first aspect, the angle α formed by the center of the developing magnetic pole with respect to a line connecting the center of the first developing roller and the center of the recording medium is:
The rotation is restricted to a range of 0 to 10 degrees before the rotation. According to a seventh aspect of the present invention, in the first aspect, the angle β formed by the center of the developing magnetic pole with respect to a line connecting the center of the second developing roller and the center of the recording medium.
Is characterized by being restricted to a range of 0 ± 10 degrees before rotation. According to an eighth aspect of the present invention, in the first aspect, a distance formed between the first developing roller and the doctor blade is restricted to a range of 0.5 mm to 1.5 mm. It is. According to a ninth aspect of the present invention, in the first aspect, a distance formed by the doctor blade and the second developing roller is 0.5 mm.
It is characterized by being restricted to a range of up to 1.5 mm. According to a tenth aspect of the present invention, in the first aspect, the developing magnetic pole of the first developing roller is set to two magnetic poles. Eleventh of the present invention
In the first means, the developing magnetic pole of the second developing roller is set to two magnetic poles in the first means. The basic structure of the present invention is sufficiently applicable to a one-component developer.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention describes an image forming apparatus for developing a latent electrostatic image formed on a recording body to obtain a toner image in an electrostatic recording method or an electrophotographic method.

FIG. 1 is a configuration diagram around a developing machine of a laser printer according to an embodiment of the present invention. As shown in the figure, the photoconductive photosensitive drum 1 rotates in the direction of arrow A (clockwise). A laser beam (optical writing system) 2 and a developing unit 3 are arranged around the periphery. The uniformly charged photosensitive drum 1 forms an electrostatic charge latent image with the laser beam 2. The charging polarity of the photosensitive drum 1 may be either positive or negative, but is negative here. Subsequently, reversal development is performed by the developing unit 3 to form a negative polarity toner image on the photosensitive drum 1. Exposure may be performed using background lighting for regular development, but the present invention is more effective in the case of reversal development.

Next, the operation of the developing device 3 will be described. First developing roller 41 that rotates in the opposite direction to photosensitive drum 1
And a second developing roller 51 that rotates in the same direction as the photosensitive drum 1 includes a magnet 42 fixed inside,
It has a magnet 52, and the magnetic force of the magnets 42, 52 attracts a two-component magnetic developer mainly composed of a magnetic carrier and a colored toner (magnetic or non-magnetic) to the developing rollers 41, 51, respectively. The first and second developing rollers 41 and 51 are conveyed by the respective rotations, and the developer is brought into contact with the photosensitive drum 1 to develop the charge latent image.

The angles α and β formed by the centers of the developing magnetic poles with respect to the lines connecting the center of the photosensitive drum 1 and the centers of the first and second developing rollers 41 and 51 are 0-clockwise in the first developing roller 41. At 10 degrees, the second developing roller 51 is set at ± 10 degrees. This is to reduce the resistance when the developer composed of the carrier 14 and the toner 15 contacts the magnetic brush formed on the surface of each developing roller and the photosensitive drum 1. The charge polarity of the toner is minus which is the same as the charge polarity of the photosensitive drum 1. The amount of developer transported is determined by the doctor blade 6 and the first and second developing rollers 4.
It is adjusted by the gap of 1,51. The distance formed by the first developing roller 41 and the doctor blade 6 is 0.5 mm
A range of ~ 1.5 mm is desirable. This is the first developing roller 41
When the distance formed by the and the doctor blade 6 is short,
Since the passage amount of the developer composed of the carrier 14 and the toner 15 decreases, the developer cannot contact the photosensitive drum 1,
Development cannot be performed sufficiently. When the distance formed by the first developing roller 41 and the doctor blade 6 is long, the amount of the developer composed of the carrier 14 and the toner 15 increases, and thus the photosensitive drum 1 can be sufficiently contacted. The developer remains between the first developing roller 41 and the first developing roller 41, so that the load on the motor for driving the first developing roller 41 increases, and further the driving is stopped. Rubs strongly,
This is because it has been confirmed by experiments that the photosensitive drum 1 is damaged. The distance formed by the second developing roller 51 and the doctor blade 6 is preferably in the range of 0.5 mm to 1.5 mm. This was confirmed by conducting an experiment similar to that described above.

The first developing roller 41 has a bias power supply 43,
A bias power supply 53 is connected to the second developing roller 51,
In both cases, a negative voltage having the same polarity as that of the toner is applied. At this time, if the distance between the insulating layer formed by the photoconductor drum 1 and the first developing roller 41 is short, a discharge phenomenon occurs beyond the surface layer of the photoconductor, thereby damaging the photoconductor drum and making recording impossible. Will be. The distance between the insulating layers formed by the photosensitive drum 1 and the first developing roller 41 depends on the photosensitive material (film thickness, dielectric constant, resistance) and the developer material (particle size, particle shape, dielectric constant, resistance). However, when the negatively charged organic photoreceptor is used, if the optimum distance is long, the developer cannot contact the photoreceptor drum 1 and the development is insufficient. Therefore, it was confirmed by experiments that the insulation distance was optimally in the range of 0.5 mm to 1.5 mm. Similarly, it has been confirmed by experiments that the distance between the insulating layers formed by the photosensitive drum 1 and the second developing roller 51 is optimally in the range of 0.5 mm to 1.5 mm. The range of these insulation distances is also effective for smoothing the flow of the developer.
Left and right, front and rear are mixed and stirred by a pair of screw augers 71 and 72 having a notched blade structure. The screw augers 71 and 72 having the notched blade structure have a greater effect of mixing and dispersing the toner in the developer and charging the developer than the screw auger having a simple shape. Therefore, when the toner is supplied from the feed roller 8, the toner can be rapidly dispersed in the developer, and the toner can be started up to a predetermined charge amount in a short time. Can be prevented.

The mixed and stirred developer is attracted to a transport roller 91 having a magnet 92 fixed therein,
The developer that has been conveyed and passed through the gap between the doctor blade 6 and the second developing roller 51 develops the latent charge image on the second developing roller 51, and is returned into the developing device 3. The developer regulated by the doctor blade 6 is supplied to the second developing roller 5
The developer that has been attracted and conveyed toward the first side and has passed through the gap between the doctor blade 6 and the first developing roller 41 develops the latent charge image on the first developing roller 41 and passes through the scraper 10 to the developing device 3. Will be returned within. Excess developer regulated by the second developing roller unit is returned to the screw auger unit by the guide plate 11. First and second developing rollers 41 and 5
In the case of the development in the developing unit 1, not only the toner but also the carrier may adhere to the photosensitive drum 1. The carrier is pulled back by a catch roller 13 having a fixed magnet 12 therein. Transported and collected inside. As shown in FIG. 1, the set position of the developing device 3 is set at 30 degrees (plus or minus 15 degrees) with respect to the center of the photosensitive drum 1 as an axis and the center position of the two developing rollers 41 and 51. , Space can be used efficiently and the whole can be compacted. If it is larger than this, the image quality is deteriorated due to the influence of the dark decay of the photoconductor potential. become. The developer composed of the carrier 14 and the toner 15 adsorbed on the developing magnetic pole of the developing roller is formed like two brushes as shown in FIG. In the case of the first developing roller 41, of the two magnetic poles of the developing magnetic pole, the magnetic force on the second developing roller side, that is, the magnetic force of the magnetic pole at which the developer discharged from the doctor blade 6 is first attracted to the developing magnetic pole is the other, that is, The developer discharged from the doctor blade 6 is 1/4/3 of the magnetic force of the magnetic pole adsorbed after the magnetic pole first adsorbed to the developing magnetic pole.
By regulating the flow rate within the range, the flow of the developer becomes smooth. If the magnetic force is reversed, the developer
It becomes impossible to smoothly pass between the two magnetic poles of the developing roller 41, and the developer stays in the space formed by the photosensitive drum 1 and the first developing roller 41, and then the photosensitive drum 1
And the developing roller is no longer driven. In the case of the second developing roller 51, of the two magnetic poles of the developing magnetic pole,
The magnetic force on the first developing roller 41 side, that is, the magnetic force of the magnetic pole at which the developer discharged from the doctor blade 6 first adheres to the developing magnetic pole is the magnetic force on the catch roll side, that is, the developer discharged from the doctor blade 6 is applied to the developing magnetic pole. The magnetic force of the magnetic pole adsorbed after the first magnetic pole is 1-2 /
By regulating the flow rate to the range of 3, the flow of the developer becomes smooth. When this magnetic force is reversed, it becomes impossible for the developer to pass smoothly between the two magnetic poles of the second developing roller 51, and the developer is formed in the space formed by the photosensitive drum 1 and the second developing roller 51. , And thereafter, the photosensitive drum 1 and the developing roll are not driven.

Although the laser printer to which the present invention is applied is a small printer using the photosensitive drum 1 having a diameter of 60 to 100 mm, the recording speed is as high as 20 to 40 cm / s, and from a low image density to a high image density. It is possible to print an image with excellent uniform reproducibility of halftones, which can provide a uniform image without unevenness in the developing direction.

[0016]

According to the present invention, as described above, two developing rollers rotating in opposite directions are used, and the first developing roller and the second developing roller are at 30 degrees (± 15 degrees) from the center of the recording medium. Position, the moving direction of the first developing roller is opposite to the moving direction of the recording medium, the developing magnetic pole of the first developing roller is increased to two poles, and the insulation distance between the first developing roller and the recording medium is set to 0.5. m
m to 1.5 mm, the distance between the first developing roller and the doctor blade is restricted to a range of 0.5 mm to 1.5 mm, and the moving direction of the second developing roller is the same as the moving direction of the recording medium. Therefore, the developing magnetic pole of the first developing roller is increased to two poles, the insulation distance between the second developing roller and the recording medium is regulated within a range of 0.5 mm to 1.5 mm, and the distance between the second developing roller and the doctor blade is reduced.
By regulating the distance between the recording medium and the doctor blade to a range of 5 mm to 15 mm,
An image forming apparatus that can obtain excellent image quality can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram around a developing device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a developing roller and a developer adsorbed on a developing magnetic pole according to the embodiment of the present invention.

FIG. 3 is a view showing a solid black when recording is performed in a high development area in the laser printer.

FIG. 4 is a diagram showing characters when recording is performed in a high development area in the laser printer.

FIG. 5 is a diagram showing solid black when recording is performed in a low development area in the laser printer.

FIG. 6 is a diagram showing characters when recording is performed in a low development area in the laser printer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Laser beam, 3 ... Developer, 4
DESCRIPTION OF SYMBOLS 1 ... 1st developing roller, 51 ... 2nd developing roller, 6 ... Doctor blade, 71, 72 ... Screw auger, 8 ... Feed roller, 91 ... Transport roller, 10 ... Scraper
11: guide plate, 13: catch roller, 14: carrier, 15: toner, 16: solid black portion.

Claims (4)

[Claims] An electrostatic charge latent image formed on a recording medium is transferred to a magnetic carrier and a toner by a first developing roller and a second developing roller which are arranged along a moving direction of the recording medium and rotate in opposite directions to each other. Is developed with a two-component magnetic developer mainly composed of: and the moving direction of the first developing roller is opposite to the moving direction of the recording medium, and the first developing roller is more temporally shifted than the optical signal incident position. At a position within 0.2 seconds, and the moving direction of the second developing roller is the same as the moving direction of the recording medium, and the second developing roller is regulated within a range of 0.8 seconds from the incident position. An electrophotographic apparatus, wherein the first developing roller developing magnetic pole has two magnetic poles. 2. The method according to claim 1, wherein, of the two magnetic poles of the first developing roller, the magnetic force on the side of the second developing roller is regulated to be in a range of 1 to 4/3 of the other magnetic pole. Electrophotographic equipment. 3. The electrophotographic apparatus according to claim 1, wherein the second developing roller has two developing magnetic poles. 4. The magnetic pole on the first developing roller of the two magnetic poles of the second developing roller, wherein the magnetic force on the side of the first developing roller is regulated to be in a range of 1-2 / 3 of the magnetic force on the catch roll side. Item 3. An electrophotographic apparatus according to Item 3.