JP2928604B2 - Developing device - Google Patents

Description

The present invention relates to a developing device for visualizing an electrostatic latent image in an electrophotographic apparatus, an electrostatic recording apparatus, or the like.

(Prior Art) As one of the developing methods using a one-component developer, a pressure development method (Impression Deveropment) is known. One of the features of this pressure development method is that toner charged by friction adheres to the surface of a developing roller and is conveyed to a developing area. Therefore, a magnetic material is not required, and there are many advantages such as simplification and downsizing of the device and easy colorization of the toner.

In this pressure development method, the toner adhering to the developing roller is thinned by regulating the transport amount by a toner thin layer forming member called a blade pressed against the developing roller,
Thereafter, the latent image is visualized by approaching or in contact with the photosensitive drum. Therefore, a developing roller having elasticity and conductivity is desired. Therefore, as a developing roller, a roller provided with a conductive layer on an elastic body is mainly used.

However, in such an image forming apparatus, the surface portion of the developing roller deformed by the pressure contact with the photosensitive drum or the blade may reach the developing area without being completely recovered. Omission sometimes occurred. In particular, such a situation often occurs in the first printing after the apparatus is left for a long time, and often occurs when the hardness of the developing roller is reduced due to a rise in the temperature inside the apparatus main body.

(Problems to be Solved by the Invention) As described above, in the conventional developing device using the pressure developing method, the developing process is performed while the deformation of the surface of the developing roller is left. And the like, and the quality of the image is greatly deteriorated.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a developing device capable of obtaining a high-quality image free of defective images such as white spots and density unevenness over a long period of time.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a developing device of the present invention includes a developing roller disposed to face an electrostatic latent image holding member, and a developing roller for the developing roller. And a developer thin layer forming means for forming a developer thin layer on the surface, by bringing the developer thin layer formed on the surface of the developing roller close to or in contact with the electrostatic latent image holding member, In a developing device for visualizing an electrostatic latent image formed on an electrostatic latent image holding member, a developer thin layer forming unit includes a semicircular cross-sectional portion pressed against the surface of the developing roller with the developer thin layer interposed therebetween. If the radius of curvature of the semicircular cross-sectional portion of the pressed portion is R (mm) and the amount of biting of the pressed portion into the developing roller is D (mm), 15 ≦ R / D
It satisfies the relationship of ≦ 500.

(Operation) In the first invention, the optimum radius of curvature of the semicircular cross section of the press contact portion is determined from the amount of bite of the press contact portion of the developer thin layer forming means into the developing roller. It is possible to realize a developing device capable of obtaining a high-quality image without a defective image such as density unevenness over a long period of time.

Further, in the developing device according to the second aspect of the present invention, the distortion of the developing roller due to the pressure contact of the pressure contact portion of the developer thin layer forming means is reduced between the electrostatic latent image holder and the developing roller as long as the above relationship is satisfied. It is possible to cancel by the bite amount, and as a result, it is possible to obtain a high-quality image without defective images such as white spots and density unevenness over a long period of time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing the overall structure of a contact type one-component non-magnetic developing device (hereinafter simply referred to as a developing device) according to an embodiment of the present invention.

As shown in FIG. 1, a developing device 10 includes a non-magnetic toner (hereinafter simply referred to as a toner) as a developer on an electrostatic latent image formed on a surface of a photosensitive drum 11 as an electrostatic latent image holding member. A developing roller 12 for transferring the A to visualize the electrostatic latent image, a toner container 13 containing the toner A, and a mixer 14 for stirring the toner A in the toner container 13
A toner supply roller 15 for supplying the toner A in the toner container 13 to the developing roller 12, and a blade 16 as a developer thin layer forming means for forming a toner thin layer on the surface of the developing roller 12. The main part is configured.

Next, a developing process in the developing device 10 will be described.

The toner A stored in the toner container 13 is
The toner is fed toward the toner supply roller 15 while being agitated by the
Supplied to Here, the toner A is negatively charged by friction with the surface of the rotating developing roller 12 and is electrostatically attracted to the surface of the developing roller 12 to be transported. After this, the developing roller
The toner A adhered to the surface of the developing roller 12 is thinned by regulating the transport amount thereof by the blade
Then, the toner is charged again by friction with the blade 16 and is conveyed as a dense toner layer. Thereafter, the toner A adhered to the surface of the developing roller 12 is transferred onto the electrostatic latent image on the surface of the photosensitive drum 11 by contact with the photosensitive drum 11. Thereby, the electrostatic latent image is visualized. The toner A on the surface of the developing roller 12 that has not been transferred rubs through the recovery blade (mylar film) 17 and returns into the toner container 14.

By the way, in this embodiment, since the reversal developing method using the negatively charged organic photosensitive drum 11 is adopted, a negatively charged toner is used as the toner A, and the blade 16 is used.
The material used is such that the toner A can be easily negatively charged. The surface potential of the photosensitive drum 11 is -550 V, whereas -200 V as a developing bias potential is applied to the metal shaft 12a of the developing roller 12 through a protective resistor. The developing roller 12 rotates at a speed of about 1.2 to 4 times the rotation speed of the photosensitive drum 11 while always having a contact width (developing nip) of about 1 to 4 mm with the surface of the photosensitive drum 11. I have.

If the toner A drops from the developing roller 12 for any reason in the above-described developing process, the inside of the main body device or the transfer paper is stained. Therefore, in this embodiment, a plasticizer which reacts with the toner A and welds the toner A is used. A toner welding member 18 made of a material such as the above is attached to a lower portion of the developing device 10. In addition, even when the developing device 10 is placed upside down, scattering of the toner A can be prevented.

The blade 16 is supported by the apparatus main body by a first blade holder 16a, a spacer 16b, and a second blade holder 16c. 19 is the first blade boulder 16a
And a baffle plate for sandwiching a foam material 20 made of, for example, maltprene with the back surface of the blade 16. By sandwiching the foam material 20 between the baffle plate 19 and the back surface of the blade 16 in this manner, leakage of the toner A from the toner container 13 and vibration of the blade 16 are prevented.

The tip of the blade 16 (tip 162)
The rotating shaft presses the surface of the developing roller 12 with appropriate force
It is constantly urged by a plurality of compression springs 22 with 21 as a fulcrum.

 FIG. 2 is a perspective view showing details of the blade 16.

As shown in the figure, the blade 16 has a thickness of 2 mm made of urethane resin, and a tip of a thin plate spring 161 having a length of 20 mm.
A chip 162 having a semicircular cross-section that is pressed against the surface of the developing roller 12 with toner interposed therebetween is mounted in the longitudinal direction, and a sealing material 163 made of urethane foam or the like is attached to both ends of the thin plate spring 161. ing. Also chip 1
62 is made of urethane resin and has a higher rubber hardness in the JIS-A standard compared to the urethane resin of the thin plate spring 161. Thus, the chip 162 can be pressed against the developing roller 12 with a uniform force over the whole without impairing the elasticity of the thin plate spring 161. Therefore, in this embodiment,
The thin plate spring 161 is made of urethane resin of JIS-A standard 75 mm, and the chip 162 is made of urethane resin of JIS-A standard 50 mm.

Also, a sealing material 163 having a thickness greater than the height of the chip 162 is used.
It is attached to the thin plate spring 161 so as to protrude from the distal end surface of 162. Thus, when the chip 162 is pressed against the surface of the developing roller 12, the outflow of toner from both ends can be reliably sealed. In addition, this sealing material 163
Is mounted so that the end of the thin plate spring 161 is sandwiched between the thin plate springs 161, there is no fear that the thin plate spring 161 will be peeled off even if it receives the conveying pressure of the toner.

Further, in the blade 16 of this embodiment, as shown in FIG. 3, the tip 162 is mounted from a position away from the tip of the thin plate spring 161 by d1. That is, the tip portion of the thin plate spring 161 is used for pressing and positioning when the chip 162 is mounted on the thin plate spring 161 by bonding. This can improve the mounting accuracy of the chip 162 and the accuracy of the tangential direction between the developing roller 12 and the chip 162. Note that if d1 is too large, the pressure due to the flow of the toner may cause formation failure of the toner layer. Therefore, a thickness of about 0.5 mm to 5 mm is appropriate. Desirably, about 0.5 mm to 2 mm is optimal. Further, at both ends in the longitudinal direction of the thin plate spring 161, there are portions where the chip 162 is not mounted. The seal member 163 is attached to this portion. That is, the length Lp of the tip 162 in the longitudinal direction is the thin plate spring 1
That is, it is shorter than the length Lc of 61 by d2 + d3 minutes.
The length of d2 + d3 is required to be at least about 3 mm on one side in consideration of the sealing property. However, if the length is too long, the developing device 10 itself becomes large, so that the length is preferably about 4 to 30 mm, and more preferably about 4 to 20 mm. At this time, the length Lp of the tip 162 is larger than the effective developing width, and the length Lc of the thin plate spring 161 is set to be equal to the width of the developing roller 12 or to be about the side seal (not shown) of the developing roller 12. I do.

Next, the developing roller 12 will be described. FIG. 4 is a perspective sectional view of the developing roller 12.

The characteristic required of the developing roller 12 is “having conductivity and elasticity”. The simplest configuration that satisfies this is, for example, a configuration in which the outer periphery of a metal shaft is covered with a conductive rubber roller.In this embodiment, in order to transport the toner while pressing it against the surface of the developing roller 12, Surface smoothness is required. Therefore, in this embodiment, an elastic layer 12b made of, for example, conductive silicon rubber or urethane rubber is provided on the outer periphery of the metal shaft 12a, and a conductive polyurethane-based conductive layer 12c is provided on the surface of the elastic layer 12b. It has a two-layer structure.

The elastic layer 12b may be a conductive layer or a non-conductive layer. However, a conductive layer is more preferable in consideration of a case where the conductive layer 12c is peeled or damaged. Also, regarding the permanent distortion shown in JIS K6301 during packing or leaving for a long time, if this exceeds 10%, unevenness of the rotation cycle of the developing roller occurs in the image, so the compression distortion of the elastic layer 12b is 10%.
%, Preferably 5% or less. In general, the relationship between rubber hardness and permanent strain tends to be such that the higher the rubber hardness is, the smaller the permanent strain is. The developing roller 12 is a blade
After being deformed by 16, development is performed in direct contact with the photosensitive drum 11, and if the deformation is not substantially recovered before the start of the development, image quality will be degraded.
Therefore, the overall rubber hardness of the developing roller 12 (JIS-A
Standard) is 35 ° or less, the elastic layer 12b is preferably 30 ° or less, and more preferably 30 ° or less and 25 ° or less, respectively.

Further, since the surface of the conductive layer 12c is a surface that comes into contact with the blade 16 and the photoconductor drum 11, the toner A and the photoconductor drum are exposed by exuding a plasticizer, a vulcanizing agent, process oil, and the like.
11 As long as the surface is not contaminated, the maximum surface roughness of the surface is desirably 3 μm or less.
Above that, uneven patterns on the surface tend to appear in the image.

As a method of realizing the smoothness of the conductive layer 12c having a maximum surface roughness of 3 μm or less, a conductive layer 12c having a sufficient thickness is provided on the elastic layer 12b, and a predetermined process is performed by post-processing (polishing). A method of finishing the outer diameter and surface roughness is conceivable,
This method is costly. Therefore, a method of finishing without post-processing is desired. For this purpose, the surface roughness of the elastic layer 12b, the thickness of the conductive layer 12c, and the
The viscosity of the paint to form c must be optimally selected. That is, the lower the viscosity of the paint and the greater the surface roughness of the elastic layer 12b, the larger the thickness of the conductive layer 12c must be. Further, with respect to the paint for forming the conductive layer 12c, the viscosity must be changed by changing the dilution amount of the same paint according to the method of applying the paint on the surface of the elastic layer 12b.

5 to 7 show a typical method of applying the conductive layer paint.

FIG. 5 shows a coating method by spraying, FIG. 6 shows a coating method by dipping, and FIG. 7 shows a coating method by knife edge.

The viscosity of the paint in each method is in the order of spray method <dipping method ≦ knife-edge method, and the film thickness T of the paint necessary for realizing the smoothness of the surface of the conductive layer 12c (maximum surface roughness 3 μm).
(Μm) indicates the maximum surface roughness of the elastic layer 12b as Rz (μm).
Then, it becomes possible if T ≧ 10 × Rz is satisfied in the spray method, and T ≧ 5 × Rz in the dipping method and the knife edge method.

From the above points, in this embodiment, conductive silicon rubber is used as the elastic layer 12b of the developing roller 12, and the conductive layer 1
As 2c, a conductive polyurethane paint is used. The conductive silicone rubber used for the elastic layer 12b is JIS standard
It has a hardness of 28 ° with a K6301 type A hardness tester, and has an elongation of 425%. The outer diameter is 18mm. Further, the electric resistance value of the conductive silicone rubber is obtained by arranging the developing roller 12 in parallel with a stainless steel roller having a diameter of 60 mm so that the contact width becomes 2 mm, and providing a potential difference of 100 V between the metal shafts of the rollers. 3.4 × 10 ³ Ω calculated from the measured current value
・ It was cm. Further, the permanent set was 1.8% as a result of measurement using a measuring method of JIS K6301.

On the other hand, conductive polyurethane paint 10 ³ Ω · c by dispersing conductive carbon particles in the polyurethane resin
A conductive layer having a conductivity of m was employed, and a conductive layer 12c was provided on the surface of the elastic layer 12b by using the paint in the following steps.

First, using a trade name "Sparex DH20Z313" manufactured by Nippon Milactron Co., Ltd. as a conductive polyurethane paint, and diluting a mixed solvent of methyl ethyl ketone (MEK) and tetrahydrofuran (THF) in a 1: 1 ratio. Added. "Sparex DH20Z313" is a solution-type conductive polyurethane paint based on thermoplastic polyurethane. After sufficiently agitating the diluted paint, it is applied by dipping to the surface of the elastic layer 12b washed with a solvent. At this time, the processing material lifting speed is 3.5 mm / se
c. After application, dry in air for about 30 minutes, then
Heat treatment was performed at 00 ° C. for 20 minutes.

By the above steps, the resistance between the metal shaft 12a and the conductive layer 12c is 5 × 10 ³ Ω · cm, and the rubber hardness is JIS standard K6301.
36 mm in A-type hardness tester with a surface roughness of 3 μm Rz
Could be obtained.

Now, such a developing device 10 is mounted on a laser printer, and the image portion potential, that is, the exposed portion potential is -80 V, the non-image portion potential, that is, the unexposed portion potential is -500 V, and the developing bias is-.
When reverse development was performed with the contact width between the photosensitive drum 11 and the developing roller 12 set to 1.5 mm at 20 V, a print sample having an extremely sharp line image with no image fog at 1.4 image density and a uniform solid image without unevenness was obtained. I got it. Further, as a result of a life test of 10,000 sheets, an extremely good image equivalent to the initial image could be obtained even after the life test was completed.

FIG. 8 is a graph showing changes in image density and toner charge amount from the initial stage to 10,000 sheets. Here, a solid image was used for measuring the image density. The charge amount of the toner was measured by using a charge amount measuring device for 10 rotations of the developing roller 12.

From this graph, it can be seen that the image density hardly changes even after the end of 10,000 sheets, and the charge amount hardly changes. Further, when the shape of the chip 162 after 10,000 sheets was visually confirmed, the height of the chip 162 was about 0.5 mm.
Although worn, no change was observed in the shape of the pressure contact surface and the contact width with the developing roller 12.

Next, an experiment was performed in which the radius of curvature of the tip 162 of the blade 16 and the amount of pressurization were changed, and the amount of bite into the developing roller 12 was confirmed. Where the radius of tip 162 is 1.0
mm to 10.0 mm and the amount of pressurization was varied from 250 g to 1000 g.

FIG. 9 is a schematic view of an apparatus for measuring the bite amount. This bite amount measuring device includes a pressing member 91 and the pressing member 91.
Load 92, 92, a laser displacement meter 94 for measuring the displacement of the developing roller 12 using an optical sensor 93, and a digital meter 95 for displaying a value measured by the laser displacement meter 94, and It comprises a recorder 96 for recording the value measured by the laser displacement meter 94. The pressing member 91 is
The tip having the same shape as the tip of the tip 162 is used.

The result of this experiment is shown in FIG. From this result chip 16
The larger the radius of curvature of 2, the larger the developing roller 12 of the chip 162.
It can be seen that the amount of bite into the shell becomes smaller.

FIG. 11 is a graph showing the result of actually performing image extraction under the above-described experimental conditions and confirming the state of the image.

From this graph, assuming that the amount of penetration of the chip 162 into the developing roller 12 is D (mm) and the radius of curvature of the chip 162 is R (mm), a good image is obtained in a range satisfying the relationship of 15 ≦ R / D ≦ 500. Was found to be obtained, and if it exceeded this range, white spots and density unevenness occurred on the solid image, or the image density was reduced.

From the above experimental results, in this embodiment, the radius of curvature of the semicircular cross section of the tip 162 is set to 2.0 mm, and the load of the blade 16 is set to 1
000g. The amount of biting into the developing roller 12 at this time was 90 μm when measured with a biting amount measuring device shown in FIG.
Met.

In addition, the present inventors conducted experiments in which the contact width between the blade 16 and the developing roller 12 and the bite amount were changed, and the effect on the image was confirmed each time.

Here, the contact width and the bite amount between the photosensitive drum 11 and the developing roller 12 were fixed to 3 mm and 0.12 mm, respectively. The contact width and the bite amount were changed by the pressure amount of the blade 16. Further, in this experiment, the radius of curvature of the tip 162 was changed from 2 mm to 4 mm. The contact width between the blade 16 and the developing roller 12 was measured by applying a commercially available ink to the chip 162 and then actually measuring the trace of the ink obtained by pressing the developing roller 12 with the chip 162 with a predetermined load. I went. The measurement of the contact width between the photosensitive drum 11 and the developing roller 12 was performed in the same manner. The amount of bite of the photosensitive drum 11 and the blade 16 into the developing roller 12 was measured by the bite amount measuring device shown in FIG.

 FIG. 12 is a graph showing the experimental results.

From this graph, the contact width between the blade 16 and the developing roller 12 is Sb (mm), the bite amount of the blade 16 into the developing roller 12 is Db (mm), and the contact width between the photosensitive drum 11 and the developing roller 12 is Sp. (Mm), and assuming that the amount of bite of the photosensitive drum 11 into the developing roller 12 is Dp (mm), it is confirmed that a good image can be obtained in a range satisfying a relationship of Sb × Db ≦ Sp × Dp. In the range not satisfying the condition, the pressing mark of the blade 16 was whitened out in the solid image or the halftone image, or the density unevenness occurred.

From the above experimental results, in the present embodiment, the contact width Sp between the photosensitive drum 11 and the developing roller 12 is set to 3 mm, the bite amount Dp of the photosensitive drum 11 into the developing roller 12 is set to 0.12 mm, and the tip 162 The radius of curvature was set to 3 mm, the contact width Sb between the blade 16 and the developing roller 12 was set to 1.5 mm, and the amount of penetration Db of the blade 16 into the developing roller 12 was set to 0.16 mm. Since the blade 16 of this embodiment uses the thin leaf spring 161a, the amount of pressurization obtained from the above experimental results is converted in consideration of the leaf spring constant.

Thus, by satisfying the above relationships, it is possible to realize a developing device capable of obtaining a high-quality image free of defective images such as white spots and density unevenness over a long period of time.

13 and 14 are sectional views showing another embodiment of the blade.

The blade 130 shown in FIG. 13 is configured by adhering a tip 132 of silicon rubber to a tip 132 of a thin plate spring 131 made of phosphor bronze. The angle θ1 of the tip of the tip 132 is 90 °, and the abutment portion with the developing roller has a radius of curvature of 4 mm. In addition, the JIS of chip 132 made of this silicone rubber
-A standard rubber hardness is 50mm and width is 5mm.

The blade 140 shown in FIG. 14 is formed by bonding a tip 142 of a thin plate spring made of stainless steel to a tip 142 made of urethane rubber and having a semicircular cross section at the tip. The tip 142 made of this urethane rubber
The rubber hardness of JIS-A standard is 60 mm.

In addition, a thin leaf spring made of stainless steel or phosphor bronze plate,
It is also effective to mount a chip having a curvature surface along the peripheral surface of the developing roller.

Further, in the above-described embodiment, the blade is supported at the position of “Agenst” with respect to the rotation direction of the developing roller, but may be supported at the position of “With” with respect to the rotation direction.

[Effects of the Invention] As described above, according to the present invention, it is possible to realize a developing device capable of obtaining a high-quality image free of defective images such as white spots and density unevenness over a long period of time.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the overall structure of a developing device according to an embodiment of the present invention, FIG. 2 is a perspective view showing details of a blade in the developing device shown in FIG. 1, and FIG. 3 is a blade shown in FIG. FIG. 4 is a perspective sectional view showing details of the developing roller, FIGS. 5 to 7 are diagrams showing a method of forming a conductive layer of the developing roller, respectively, and FIG. 8 is a developing device shown in FIG. FIG. 9 is a graph showing a result of a life test performed using the image forming apparatus and examining changes in image density and charge amount, and FIG. 9 is a view for explaining a configuration of an apparatus for measuring a bite amount of a photosensitive drum and a blade into a developing roller. FIG. 10 is a graph showing the relationship between the radius of curvature of the tip and the amount of pressure applied to the blade and the amount of bite into the developing roller,
FIG. 11 is a graph showing the relationship between the image radius and the radius of curvature of the chip and the pressure of the blade, and FIG. 12 is a graph showing the relationship between the image amount and the bite amount of the chip into the developing roller and the contact width. 13 and 14 are cross-sectional views showing another embodiment of the blade. 10 Developing device 11 Photoconductor drum 12 Developing roller 16 Blade 161 Thin spring 162 Chip

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/08

Claims (1)

(57) [Claims] An image forming apparatus comprising: a developing roller arranged to face an electrostatic latent image holding member; and a thin developer layer forming means for forming a thin developer layer on a surface of the developing roller. A developing device that visualizes an electrostatic latent image formed on the electrostatic latent image holding member by bringing a thin developer layer formed on the surface close to or in contact with the electrostatic latent image holding member; The thin layer forming means has a pressure contact portion having a semicircular cross-sectional portion pressed against the surface of the developing roller with the developer thin layer interposed therebetween, and the radius of curvature of the semicircular cross-sectional portion of the pressure contact portion is R.
(Mm), the biting amount of the press contact portion into the developing roller is D
(Mm) A developing device characterized by satisfying a relationship of 15 ≦ R / D ≦ 500.