JP2010079010A - Developing device - Google Patents

Abstract

To provide a developing device capable of sufficiently scraping off toner remaining on a developing roller after development with a supply roller, thereby preventing a ghost phenomenon.
A developing roller disposed opposite to an electrostatic image carrier having an electrostatic latent image, for conveying and developing toner to the electrostatic image carrier, and a supply roller for supplying the toner to the developing roller The surface of the supply roller is made of an elastic foam material, and when the supply roller is driven to rotate, the load at the contact portion between the supply roller and the developing roller exceeds 0.125 N / cm.
[Selection] Figure 1

Description

  The present invention relates to a developing device, and more particularly, to a developing device that can obtain a good image without causing a ghost phenomenon.

  Electrophotographic image formation is generally performed by developing and visualizing an electrostatic charge image with toner and transferring the toner image obtained by development onto a sheet. As a developing method used for such image formation, the layer thickness of the toner on the developing roller supplied by the supply roller is regulated by a doctor blade, and the toner is charged by friction between the toner and the doctor blade and the developing roller. There is a non-magnetic one-component development method for developing an electrostatic latent image on a body drum.

  In order to obtain a good image in the nonmagnetic one-component development method, it is necessary to form a toner layer having a uniform thickness on the surface of the developing roller. For this purpose, a design is realized that is realized by an appropriate combination of the shape of the doctor blade, the material of the developing roller and the supply roller, the diameter, the stirring rod, and the bias value.

On the surface of the developing roller immediately after the electrostatic latent image on the photosensitive drum is developed with toner, except for the case of a solid image, the portion where the toner layer is thin and the toner layer is not used at all. There are still parts.
In such a non-uniform thickness of the toner layer on the developing roller, in the next step, when the developing roller comes into contact with the supply roller, a portion of the thick toner layer is scraped off to obtain a substantially uniform thickness. Is done.

At the same time, toner is supplied to the surface of the developing roller by the supply roller, regulated to a uniform toner thickness by the doctor blade, and again used for developing the electrostatic latent image on the photosensitive drum.
By the way, when the unevenness of the toner layer remains on the developing roller due to insufficient scraping by the supply roller, the toner is supplied by the supply roller, and this toner is also used in a subsequent process in which the thickness is regulated by the doctor blade. The non-uniformity of the layer is not corrected, and is used for the development of the electrostatic latent image on the next photosensitive drum in the state of the non-uniform toner layer. Therefore, uneven toner layer steps in the image, that is, an inverted version of the previous image, appear like a ghost.

Conventionally, in order to avoid such a ghost phenomenon, conditions such as cell density, hardness, and diameter of the elastic foam material constituting the surface of the supply roller are changed, and the optimum values of these conditions are determined while verifying the image. However, what remains an important factor remains unknown.
For example, Patent Document 1 solves the problem of reducing the stress on the toner, improving the toner scraping function, and continuously supplying the external additive by defining the elastic characteristics of the foamed elastic portion constituting the surface of the supply roller. A developing device has been proposed.

JP 2007-293119 A

  The present invention has been made in view of the above circumstances, and a developing device capable of making a non-uniform toner layer remaining on a developing roller after development uniform by a supply roller, thereby preventing a ghost phenomenon. The purpose is to provide.

  In order to solve the above-described problems, an embodiment of the present invention includes a developing roller that is disposed to face an electrostatic image carrier having an electrostatic latent image and that conveys and develops toner on the electrostatic image carrier, and the toner The surface of the supply roller is made of an elastic foam material, and when the supply roller is driven to rotate, the load at the contact portion between the supply roller and the development roller is 0.125 N A developing device characterized by exceeding / cm is provided.

In such a developing apparatus, the load can be set to a value exceeding 0.125 N / cm by controlling the cell density and / or thickness of the elastic foam material.
A bias voltage higher than the developing roller by −200 V or more can be applied to the supply roller. Further, the rotation direction of the developing roller and the rotation direction of the supply roller can be a counter direction.

  According to the present invention, it is possible to provide a developing device capable of making a non-uniform toner layer remaining on a developing roller after development uniform by a supply roller, thereby preventing a ghost phenomenon.

Hereinafter, embodiments of the present invention will be described.
A developing device according to an embodiment of the present invention is disposed to face an electrostatic image carrier having an electrostatic latent image, and transports and develops toner on the electrostatic image carrier, and the toner is transferred to the electrostatic image carrier. And a supply roller that supplies the developing roller. The surface of the supply roller is made of an elastic foam material, and when the supply roller is driven to rotate, the load at the contact portion between the supply roller and the developing roller exceeds 0.125 N / cm.

  As described above, when the load at the contact portion between the supply roller and the development roller exceeds 0.125 N / cm, the toner remaining on the development roller after development is scraped off by the supply roller that is driven to rotate, and has a uniform thickness. It is said. As a result, even when toner is newly supplied from the supply roller, a toner layer having a uniform thickness is formed on the developing roller. Formation of a toner layer with a non-uniform film thickness is prevented by the lamination of the non-uniform toner layer remaining on the developing roller after development and the newly supplied toner.

  On the other hand, when the load at the contact portion between the supply roller and the development roller is 0.125 N / cm or less, the toner remaining on the development roller after development is not sufficiently scraped by the supply roller, and after development, Due to the lamination of the non-uniform toner layer remaining on the developing roller and the newly supplied toner, a non-uniform toner layer is formed, and a ghost phenomenon occurs.

  In order to set the load at the contact portion between the supply roller and the developing roller to a value exceeding 0.125 N / cm, the cell density of the elastic foam material on the surface of the supply roller, the thickness, the diameter of the supply roller, the diameter of the development roller, the supply roller And the distance between the center of the developing roller and the like may be adjusted as appropriate. In particular, a load exceeding 0.125 N / cm can be obtained by appropriately adjusting the cell density and / or thickness of the elastic foam material on the surface of the supply roller.

As an adjustable range of the characteristics of such a supply roller, the cell density of the elastic foam material is 40 cells / inch to 150 cells / inch, and the thickness of the elastic foam material is 2 to 3 mm.
Since the supply roller supplies toner to the developing roller by a potential difference with the developing roller, the elastic foam material constituting the surface of the supplying roller needs to have conductivity. Therefore, the electrical resistance of the elastic foam material is desirably 1 × 10 ^{4 to} 5 × 10 ⁵ Ω.

Specific examples of the elastic foam material include conductive urethane sponge rubber and conductive silicone rubber.
FIG. 1 is a sectional view showing a developing device 1 according to an embodiment of the present invention. The developing device 2 of the developing device 1 includes a toner cartridge 5 including an upper toner hopper 3 and a lower toner hopper 4, and a developing unit 7 having an exterior frame 6.
Inside the developing unit 7, a developing roller 8, a supply roller 9 for supplying toner to the developing roller 8, a doctor blade 10 for regulating the layer of toner supplied on the developing roller 8 to a certain thickness, and developing An agitating member 11 for agitating the toner in the portion 7 is provided.

Further, the photosensitive drum 21, the cleaner 22, and the charging roller 23 are integrally incorporated with the developing device 2 inside the exterior frame 6 as a drum unit portion 24. The drum unit 24 constitutes a developing drum unit together with the developing unit 7 of the developing device 2. The photosensitive drum 21 is usually formed by uniformly depositing an organic photoconductor on the surface of a conductive metal roller, and the metal roller portion is grounded.
The charging roller 23 has a white printing state charging potential (a uniformly applied initializing potential, a method of applying with a positive polarity and a method of applying with a negative polarity by a high voltage power source (not shown). High voltage) is applied to the photosensitive drum 21. By applying this charging potential, the photosensitive layer on the peripheral surface of the photosensitive drum 21 is uniformly charged to a negative high potential of, for example, −650 V (volts). The photosensitive layer thus charged is then selectively exposed according to image information by an optical writing head (not shown) having a laser light source or an LED light source. By this exposure, a negative low potential portion whose potential is attenuated to about −70 V is formed on the surface of the photosensitive drum 21, and the electrostatic potential is generated by the low potential portion of −70 V and the previously charged high potential portion of −650 V. A latent image is formed.

The toner cartridge 5 contains a non-magnetic one-component toner.
A developing bias of −350 V, for example, is applied to the developing roller 8 from the high voltage power supply 31. Further, a supply bias larger than the developing bias applied to the developing roller 8 by −200 V or more is applied to the supplying roller 9 from another high-voltage power supply 32. Then, a doctor bias of −300 V to −600 V is applied to the doctor blade 10 from another high-voltage power supply 33 in the same manner as described above.
The toner adheres to the surface of the developing roller 8 due to a potential difference between the developing roller 8 and the supply roller 9, and is regulated to a certain thickness by the doctor blade 10. It is charged to a weak negative potential by the high voltage potential and adheres to the surface of the developing roller 8 with a certain thickness.

  The supply roller 9 is formed by forming an elastic foam material, for example, a conductive urethane foam layer around the core metal. When the supply roller is driven to rotate, the load at the contact portion between the supply roller and the developing roller is 0.125 N / The thickness and cell density of the conductive urethane foam layer are adjusted to exceed cm. As a result, the toner remaining on the surface of the developing roller 8 after development is scraped off by the contact with the supply roller to form a uniform toner layer, and new toner is applied to the developing roller 8 by the supply roller. Then, a toner layer having a uniform thickness is formed on the developing roller 8 and is used for the next development.

  This is thought to be due to the following phenomenon. When the supply roller 9 is driven to rotate, the elastic foam material of the supply roller 9 is crushed at the contact portion between the developing roller 8 and the supply roller 9, and a load that opposes the developing roller 8 is generated due to the collapse. When the cell density, thickness, etc. of the elastic foam material are adjusted so that the load exceeds 0.125 N / cm, and the amount of collapse of the elastic foam material of the supply roller is set, the surface of the developing roller 8 by the sufficient supply roller 9 is sufficient. The residual toner scraping effect is obtained, and as a result, a good image without ghost is obtained.

Since the developing roller 8 and the supply roller 9 rotate in the counter direction, the effect of scraping the residual toner on the surface of the developing roller 8 by the supply roller 9 is more fully exhibited.
The developing roller 8 conveys the toner to a portion facing the photosensitive drum 21 while rotating. At the facing portion between the developing roller 8 and the photosensitive drum 21, a potential difference of −280 V is formed between the low potential portion of the −70 V electrostatic latent image and the developing roller 8. That is, the low potential portion of the electrostatic latent image forms a positive polarity potential relative to the developing roller 8.

  Due to the electric field due to this potential difference, the non-magnetic toner charged to the negative polarity is transferred to the positive potential electrostatic latent image low potential portion of the photosensitive drum 21 to form a toner image. The toner image is transported to a facing portion between the photosensitive drum 21 and a transfer roller (not shown) by the rotation of the photosensitive drum 21 and is subjected to transfer.

  The cleaner 22 includes a cleaning blade 26 that contacts the peripheral surface of the photosensitive drum 21 and a conveying screw 25. The cleaning blade 26 removes the waste toner remaining on the peripheral surface of the photosensitive drum 7, and the conveyance screw 25 passes the removed waste toner through the conveyance screw 25 b disposed on the upper left exterior frame 6 a of the exterior frame 6. Then, the toner is sent to the waste toner collection bag 27 via the conveying screw 25c in the waste toner storage pipe 28 disposed in the upper toner hopper 3.

  The lower toner hopper 4 is provided with an agitator 29 for agitating the internal toner at the center, and a seal member 30 is interposed between the lower opening and the opening of the developing unit 7. Has been. The toner inside is supplied to the developing unit 7 through the opening of the lower partition wall by the rotation of the accommodation pipe 28.

Examples Hereinafter, examples of the present invention will be shown, and the present invention will be described more specifically.
Three types of elastic foam materials A to C having different hardnesses and cell densities shown in Table 1 below were wound around a core metal having a diameter of 7 mm, and seven supply roller samples (samples 1 to 7) were made as an experiment. Samples 1 to 5 are samples according to Examples 1 to 5, and Samples 6 and 7 are samples according to Comparative Examples 6 and 7.

サンプル１〜７に用いた弾性発泡材料とサンプルの径を下記表２に示す。

The elastic foam materials used for Samples 1 to 7 and the sample diameter are shown in Table 2 below.

一方、図２に示すように、（株）島津製作所製オートグラフＡＧＳ−Ｊを用いて、供給ローラの弾性発泡材料の弾性を測定した。なお、弾性の測定値は、供給ローラサンプルの軸方向１ｃｍ幅において、上方から力を加えた場合の表面の弾性発泡材料の収縮による負荷（Ｎ／ｃｍ）である。その結果を図３に示す。

On the other hand, as shown in FIG. 2, the elasticity of the elastic foam material of the supply roller was measured using an autograph AGS-J manufactured by Shimadzu Corporation. The measured value of elasticity is a load (N / cm) due to shrinkage of the elastic foam material on the surface when a force is applied from above in the axial direction of 1 cm width of the supply roller sample. The result is shown in FIG.

From FIG. 3, the elasticity of the elastic foam material A (samples 1 and 2) is the largest, the elasticity of the elastic foam material B (samples 3 to 5) is medium, and the elasticity of the elastic foam material C (samples 6 and 7). Is the lowest.
The performance of the samples 1 to 7 as a supply roller was evaluated by printing using a printer N3500 manufactured by Casio Computer Co., Ltd. The various conditions of the printer at that time are shown below.

Printing speed: 24ppm and 40ppm
Bias voltage: The set voltage of N3500 is not changed.
Development roller / supply roller linear speed ratio: N3500 setting is not changed.
Development roller / feed roller rotation direction: counter direction The evaluation results are shown in Table 3 below. In the table below, “◯” indicates that a ghost does not occur and the image has a good image quality, and “x” indicates that a ghost has occurred.

上記表３から、弾性の大きい弾性発泡材料Ａ及びＢを用いたサンプル１〜５（実施例１〜５）について、良好な画像性が得られることがわかる。
ゴースト画像は、上述したように、感光体ドラムの静電潜像印字後の現像ローラ表面上の残留トナーを供給ローラが掻き落とせるかどうかにかかっており、掻きとりが不十分な場合、ゴーストが発生する。供給ローラのこの掻きとり能力は、現像ローラと供給ローラの相対速度、接触部における弾性発泡材料の負荷、現像ローラ・供給ローラ間バイアスに依存すると考えられる。

From Table 3 above, it can be seen that good image quality is obtained for Samples 1 to 5 (Examples 1 to 5) using elastic foam materials A and B having high elasticity.
As described above, the ghost image depends on whether the supply roller can scrape off the residual toner on the surface of the developing roller after the electrostatic latent image is printed on the photosensitive drum. appear. This scraping ability of the supply roller is considered to depend on the relative speed between the development roller and the supply roller, the load of the elastic foam material at the contact portion, and the bias between the development roller and the supply roller.

  As described above, the effect of the bias between the developing roller and the supply roller on the scraping ability is tested without changing the bias of N3500. Therefore, the supply roller is set to maintain a potential difference of −200 V with respect to the development roller. It has become. Since the toner used in N3500 is a negatively charged toner, the force due to the electric field applied to the toner due to this potential difference is the direction of the toner from the supply roller to the developing roller, which is a potential difference that makes it difficult to scrape off. Therefore, when the potential difference is larger than −200 V, the scraping effect is slightly increased. However, since this bias plays a role such as toner supply to the developing roller, it cannot actually be raised or lowered more than -200V.

  Next, the effect of the relative speed on the scraping ability will be examined. The image quality was evaluated at two printing speeds of 24 ppm and 40 ppm. As is clear from the evaluation results in Table 3, there is no difference in the generation of ghosts. Obviously, the relative speed is higher at 40 ppm than at 24 ppm (development roller supply roller relative speed at 24 ppm = 277 mm / sec, relative speed at 40 ppm = 460 mm / sec), and there should be no difference in ghosting. Therefore, it is considered that the influence of the relative speed in scraping off the residual toner is small.

  Next, the load on the elastic foam material and the printing result at the contact portion between the supply roller and the developing roller will be examined. Since the N3500 DS is used as it is and the test is performed by rearranging the samples of the trial supply roller, the amount of collapse of the elastic foam material of the supply roller at the contact portion between the developing roller and the supply roller can be obtained. From the amount of collapse and the measurement result of the elasticity of the elastic foam material by the autograph AGS-J shown in FIG. 3, the load generated by the collapse of the elastic foam material of the supply roller at the contact portion was obtained. The results are shown in Table 4 below in comparison with the printing results.

上記表４から、負荷が０．１２５Ｎ／ｃｍを越えるサンプル１〜５（実施例１〜５）は、現像ローラの残留トナーの掻きとり効果が十分であり、ゴースト画像が発生していないことがわかる。これに対し、負荷が０．１２５Ｎ／ｃｍ以下であるサンプル６、７（比較例６，７）は、現像ローラの残留トナーの掻きとり効果が不十分であり、ゴースト画像が発生している。

From Table 4 above, Samples 1 to 5 (Examples 1 to 5) having a load exceeding 0.125 N / cm are sufficiently effective in scraping off the residual toner on the developing roller, and no ghost image is generated. Recognize. On the other hand, Samples 6 and 7 (Comparative Examples 6 and 7) having a load of 0.125 N / cm or less have an insufficient effect of scraping the residual toner on the developing roller, and a ghost image is generated.

It is a figure which shows the developing device which concerns on one Embodiment of this invention. It is a figure which shows the method of measuring the elasticity of an elastic foam material. It is a characteristic view which shows the relationship between the displacement of a sample, and load.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Developing device, 2 ... Developing device, 3 ... Upper toner hopper, 4 ... Lower toner hopper, 5 ... Toner cartridge, 6 ... Exterior frame, 7 ... Developing part, 8 ... Developing roller, 9 ... Supply roller, 10 ... Doctor Blade 11, stirring member 21, photosensitive drum 22, cleaner 23, charging roller 24, drum unit section 25, 25 b, 25 c conveying screw 26, cleaning blade 27, waste toner collection bag 28 Waste toner storage pipe, 29... Agitator, 30... Seal member, 31, 32, 33.

Claims (4)

  A developing roller disposed opposite to an electrostatic image bearing member having an electrostatic latent image, for conveying and developing toner to the electrostatic image bearing member, and a supply roller for supplying the toner to the developing roller; The developing device according to claim 1, wherein a surface of the supply roller is made of an elastic foam material, and a load at a contact portion between the supply roller and the developing roller exceeds 0.125 N / cm when the supply roller is driven to rotate.   The developing device according to claim 1, wherein the load is set to a value exceeding 0.125 N / cm by controlling a cell density and / or a thickness of the elastic foam material.   The developing device according to claim 1, wherein a bias voltage that is −200 V or more higher than that of the developing roller is applied to the supply roller.   The developing device according to claim 1, wherein the rotation direction of the developing roller and the rotation direction of the supply roller are counter directions.

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