JPH11258905A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform image by matching the position of a recording body with those of two developing rollers and that of a doctor blade. SOLUTION: Two developing rollers rotating in directions reverse to each other are used so that the moving direction of a first developing roller 41 is set to be reverse to that of a photo-receptive drum 1 and an insulated distance is set to be 0.5-1.5 mm, and the moving direction of a second developing roller 51 is set to be the same direction as that of the photoreceptive drum 1 and the insulated distance is set to be 0.5-1.5 mm, and the first developing roller 41 and the second developing roller 51 are set to be at the position of 30 deg. (±15 deg.) from the center of the photoreceptive drum 1, and a distance between the photoreceptive drum 1 and the doctor blade 6 is set to be 5-15 mm.

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 image forming 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 body, and the latent image is formed by two developing rollers rotating in opposite directions to each other. 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 an image having gradation characteristics of image density or an image photographic printing composed of halftone dots or lines, when importance is placed on the medium / low image density region. Has a problem that the image density is reduced as a whole. 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 solid black portion 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 periphery of the solid black portion 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 is a complex kanji,
However, there are disadvantages such as the difficulty in recognizing the details of characters when printing, etc., the increase in the amount of toner used, the swelling of the printed portion, and the reduction in the commercial value of the 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 having a size of about 3 cm in length and width recorded at a low image density.
FIG. 5B is an example of the cross-sectional view. 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 is 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, it has been 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 uniform and excellent image quality from low image density to high image density.

[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 so as to be located within 0.8 seconds from the optical signal.
Further, the second means of the present invention is characterized in that, in the first means, the first developing roller and the second developing roller are restricted in position by 30 degrees (± 15 degrees) from the center of the recording medium. It is a feature. 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, in the first aspect, 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 characterized by being 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 0 ± 10 degrees before the rotation. It is characterized by being regulated in the range of. 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, the distance formed by the doctor blade and the second developing roller is different.
It is characterized by being restricted to a range of 0.5 mm to 1.5 mm. 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 because the resistance of the magnetic brush, in which the developer composed of the carrier 14 and the toner 15 is formed on the surface of each developing roller, when the magnetic brush contacts the photosensitive drum 1 is kept low. 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 in FIG. 2 is small, the developer cannot contact the photosensitive drum 1 and the development cannot be performed sufficiently. First developing roller 41
When the distance formed by the and the doctor blade 6 is long,
Since the amount of developer passing through the carrier 14 and the toner 15 increases, the photosensitive drum 1 can be sufficiently contacted with the developer. However, the developer does not completely pass between the photosensitive drum 1 and the first developing roller 41, and the developer is stuck. According to an experiment, the load on the motor for driving the first developing roller 41 is increased, and the driving is further stopped. The carrier 4 strongly rubs the surface of the photosensitive drum 1 and damages the photosensitive drum 1 through experiments. This is because it was confirmed. And the second developing roller 5
The distance formed between 1 and the doctor blade 6 is 0.5mm ~
A range of 1.5 mm is desirable. 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 optimum 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, resulting in damage to the photoconductor drum,
Recording becomes impossible. Also, the photosensitive drum 1 and the first
The optimum distance of the insulating layer formed with the developing roller 41 is determined by the photoconductor material (film thickness, dielectric constant, resistance) and the developer material (particle size, particle shape, dielectric constant, resistance). When the charged organic photoreceptor is used, if the optimum distance is long, the developer cannot contact the photoreceptor drum 1 and the development becomes 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. The developer in the developing unit 3 is provided with a pair of screw augers 71 and 7 having a notched blade structure.
The mixture is mixed right and left and back and forth in 2. The screw augers 71 and 72 having the notched blade structure respond to the mixing and stirring.
The effect of mixing and dispersing the toner in the developer and charging the toner is greater than that of a 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 charge latent 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.

The set position of the developing device 3 is as shown in FIG.
Two developing rollers 4 centered on the center of the photosensitive drum 1
When the angle formed between the center positions of 1, 51 is set to 30 degrees (plus or minus 15 degrees), the space can be used efficiently and the whole can be made compact. If it is larger than this, the image quality is deteriorated due to the influence of the dark decay of the photoconductor potential, and if it is smaller than this, the developer conveyance between the first developing roll and the second developing roll is reduced, and it is difficult to arrange the space. become.

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, it has a high recording speed of 20 to 40 cm / s and has 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.

[0017]

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 direction of movement of the first developing roller is opposite to the direction of movement of the recording medium, and the insulation distance between the first developing roller and the recording medium is restricted to a range of 0.5 mm to 1.5 mm. The distance between the 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, and the insulation distance between the second developing roller and the recording medium To
The distance between the second developing roller and the doctor blade is regulated within the range of 0.5 mm to 1.5 mm, and the distance between the recording medium and the doctor blade is regulated within the range of 5 mm to 15 mm. Accordingly, it is possible to provide an image forming apparatus that can obtain excellent image quality.

[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 schematic diagram of a developing roller.

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

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

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

1: photosensitive drum, 2: laser beam, 3: developing device, 41: first developing roller, 51: second developing roller
6: doctor blade, 71, 72: screw auger, 8: feed roller, 91: transport roller, 1
0: scraper, 11: guide plate, 13: catch roller, 14: solid black portion.

Claims (10)

[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. In the image forming apparatus which develops with a two-component magnetic developer having as a main component, the moving direction of the first developing roller in the developing area is opposite to the moving direction of the recording medium, and the first developing roller is The second developing roller is located at a position within 0.2 seconds in time from the signal incident position, and the moving direction of the second developing roller is the same as the moving direction of the recording medium;
An image forming apparatus, wherein a developing roller is regulated within a time range of 0.8 seconds from an incident position. 2. The apparatus according to claim 1, wherein the first developing roller and the second developing roller are positioned at an angle of 30 degrees (± 15 degrees) when viewed from the center of the recording medium. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein an insulation distance between the first developing roller and the recording medium is regulated in a range of 0.5 mm to 1.5 mm. 4. The image forming apparatus according to claim 1, wherein an insulation distance between said recording medium and said second developing roller is regulated in a range of 0.5 mm to 1.5 mm. 5. The distance between the recording medium and a doctor blade
2. The image forming apparatus according to claim 1, wherein the image forming apparatus is restricted to a range of 5 mm to 15 mm. 6. When the position of a line α connecting the center of the first developing roller and the center of the recording medium is 0 degree, the clockwise direction is a positive angle, and the counterclockwise direction is a negative angle. 2. The image forming apparatus according to claim 1, wherein the angle [alpha] formed by the center of the developing magnetic pole is restricted to a range of 0 to 10 degrees. 7. When the position of a line β connecting the center of the second developing roller and the center of the recording medium is 0 degrees, the clockwise direction is a positive angle, and the counterclockwise direction is a negative angle, 2. The image forming apparatus according to claim 1, wherein the angle β formed by the center of the developing magnetic pole is restricted to a range of 0 ± 10 degrees. 8. The image forming apparatus according to claim 1, wherein 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. 9. The image forming apparatus according to claim 1, wherein a distance formed between the doctor blade and the second developing roller is restricted to a range of 0.5 mm to 1.5 mm. 10. The image forming apparatus according to claim 1, wherein a one-component developing method mainly including a magnetic toner is used.