JP3961758B2 - Image forming method - Google Patents

Description

【００６５】
なお、上記の表１において、ゴーストの欄の「○」印は、形成された画像パタンのハーフトーン領域にゴーストがまったく認められないことを示す。また、「△」印は、ゴーストが現像ロールの一周目にうっすらと認められることを示す。また、「×」印は、ゴーストが現像ロールの一周目にはっきりと認められることを示す。図５は、図４に示した画像パタン１１を形成した際に、ハーフトーンパタン１３の領域中にソリッドパタン１２の残像１４が現れた様子を模式的に示した図である。
【００６６】
そして、上記の表１に示すように、実施例１〜４においては、いずれも、５０００万枚印刷後においても、初期画像の際に比べてトナー帯電量の上昇が少なく、また、ゴーストの発生は認められず良好な画像を維持できた。
特に、実施例２においては、現像電位が５０Ｖと低い割に高い画像濃度が得られた。また、実施例３及び実施例４では、実施例１及び実施例２に比べて画像濃度は低めであるが、低電位での現像電界の設定により、トナーの帯電の変化が少なく安定して画像形成を行うことができた。
【００６７】
これに対して、上記の表１に示すように、比較例１及び比較例２では、いずれもトナー帯電量が増加して、ゴーストも増加した。また、比較例３では、比較例２と比較しても、トナー帯電量の変化が大きく、ゴーストも初期から発生した。
【００６８】
上述した実施の形態においては、本発明を特定の条件で構成した例について説明したが、本発明は、種々の変更を行うことができる。
【００６９】
【発明の効果】
以上、詳細に説明したように、本発明によれば、二成分現像方式でトナーの薄層を形成した後、非接触法により、トナーを静電潜像担持体上の潜像に飛翔させる現像方式において、カブリの発生を回避しつつ、現像の残像（ゴースト）の履歴現象の発生を防ぐことができる。
【００７０】
さらに、キャリアの表面に被覆層を重合形成すれば、極めて高い強度、耐久性を実現することができる。そして、このキャリアを用いれば、キャリアを繰り返し使用しても、キャリアの表面劣化が少なく、現像ロール上に安定した帯電トナー薄層を形成することができる。その結果、静電潜像担持体に正確に現像することが可能となる。さらに、キャリアの耐久性が高いので、現像機器の寿命まで、実質的に、キャリアを交換する必要がなくなる。
【図面の簡単な説明】
【図１】実施形態の画像形成装置の構成を示す模式図である。
【図２】静電潜像担持体の要部拡大図である。
【図３】現像条件と現像特性との関係を示すグラフである。
【図４】画像特性を評価するための画像パターンの模式図である。
【図５】残像が発生した様子を示す模式図ある。
【符号の説明】
１ 磁気ロール
２ 現像ロール
３ 静電潜像担持体
４ キャリア
５ トナー
６ トナー薄層
７ ＡＣ／ＤＣ電源
８ ＤＣ電源
９ 規制ブレード
１０ 磁気ブラシ
１１ 画像パタン
１２ ソリッドパタン
１３ ハーフトーンパタン
１４ 残像
３０ 感光体
３１ 基材
３２ 阻止層
３３ 感光層
３４ 表面保護層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and more particularly, using a two-component developer that charges a non-magnetic toner using a magnetic carrier, The present invention relates to an image forming apparatus that employs a non-contact developing system in which only the toner that has been applied is held on a developing roll and the electrostatic latent image is developed by causing the toner to fly.
[0002]
[Prior art]
Conventionally, the non-contact development method has been studied as a means of one-component development. However, in recent years, as a high-speed image forming apparatus, for example, for a one-drum color superposition method for sequentially forming a plurality of color images on a photoreceptor. Have been studied. In this one-drum color superposition method, it is possible to form a color image with little color misregistration by accurately superimposing toner on a photoconductor, and has attracted attention as a technique suitable for improving the image quality of color.
[0003]
An example of a conventional non-contact developing method is disclosed in US Pat. No. 3,866,574. According to this technique, a thin layer of nonmagnetic toner is formed on a donor roll (development roll), and is placed in a non-contact manner with respect to the photoreceptor, and the toner is allowed to fly to the photoreceptor latent image by an AC voltage.
[0004]
Another example of the conventional non-contact development method is disclosed in US Pat. No. 3,929,098. According to this technique, a developing device is shown in which a two-component developer is advanced to a donor roll using a magnetic roll, and toner is transferred onto the donor roll to form a thin toner layer. In this example, a two-component development method is adopted and a thin layer can be formed on the donor roll. However, when the toner charge becomes high, it becomes difficult to separate the toner on the donor roll, and a strong AC voltage is applied. Application is required. However, the strong AC voltage disturbs the toner thin layer on the photoreceptor, and is not suitable for color superposition.
[0005]
[Problems to be solved by the invention]
However, in the prior art described above, the fluctuation of the post-exposure potential, which is the potential of the photoconductor immediately after exposure, is large depending on the environment. As a result, it is necessary to set the surface potential of the photoconductor high, which inevitably has a developing electric field. It was set high. For this reason, a toner consumption area and a non-consumption area are generated on the developing roll, and a potential difference is easily generated between the toner adhesion state on the roll and the newly supplied toner. As a result, there has been a problem that a phenomenon in which an afterimage (ghost) of the previous developed image appears overlapping the next image, that is, a so-called history phenomenon (memory phenomenon) is likely to occur.
[0006]
Further, in the prior art, generally a negatively chargeable toner is used. For this reason, when the toner is repeatedly exposed to a high electric field, the potential difference between the charging potential of the toner in the development region and the charging potential of the toner in the non-development region tends to increase, particularly in a low temperature and low humidity environment. As a result, the development ghost tends to become remarkable.
[0007]
Therefore, in order to prevent the occurrence of a hysteresis phenomenon, Japanese Patent Application Laid-Open No. 11-231652 discloses a member for scraping off the developing toner on the developing roll and a scraping toner collecting device. However, when the scraping member is provided, a large physical or electrical stress is applied to the toner, which causes deterioration of the toner.
[0008]
Japanese Patent Application Laid-Open No. 3-113474 proposes a so-called powder cloud development method. In this powder cloud development method, an auxiliary electrode made of a wire is provided between a donor roll and a photoreceptor, and a weak alternating voltage is applied to the auxiliary electrode, whereby the developed toner can be overlaid without disturbing the color. it can. However, with this technique, the auxiliary electrode wire is very easily contaminated, and when the wire vibrates, there is a tendency for image degradation to occur.
[0009]
In addition, the 19th edition of the Electrophotographic Society, 2nd issue (1981), pp. 44-51 describes theoretical considerations regarding the formation of a toner thin layer on the developing roll in the touch-down developing method using a two-component developer. However, in the touch-down development method, it is not easy to replace the undeveloped toner and the replenishment toner, and there is a possibility that selective development occurs and developability is lowered.
[0010]
The present invention has been made to solve the above problems, and in a non-contact development type image forming apparatus using a two-component developer, it is possible to suppress the occurrence of an afterimage and form a clear image. The purpose is to provide technology that can
[0011]
[Means for Solving the Problems]
Therefore, according to the image forming method of the present invention, the toner thin layer is formed on the surface by the magnetic roll that generates the magnetic brush by the carrier that charges and holds the toner and the toner supplied from the magnetic brush. Image forming apparatus including a developing roll and a positively charged photosensitive member, and an electrostatic latent image carrier that forms an image by selectively ejecting toner in a thin toner layer according to the electrostatic latent image In forming an image with the apparatus, a toner having a positively charged polarity with a charge amount controlled within a range of 5 to 20 μC / g is used as a toner, the surface potential of the photoreceptor is within a range of 0 to 250 V, and In this method, the post-exposure potential, which is the potential immediately after exposing the photoconductor, is set in the range of 0 to 100V.
[0012]
When the surface potential of the photoconductor is higher than 250V, charging of the toner thin layer formed on the surface of the developing roller increases. As a result, the potential difference from the charged potential of the toner in the non-development area tends to increase. For this reason, the development ghost tends to be remarkable. Therefore, in the present invention, the surface potential of the photoreceptor is in the range of 0 to 250V.
[0013]
When the post-exposure potential is 100 V or less under the condition where the surface potential is in the range of 0 to 250 V, the charge amount of the positively chargeable toner can be easily controlled in the range of 5 to 20 μC / g, and the developability It was found that the occurrence of fog can be suppressed while maintaining the above.
The post-exposure potential can be controlled by exposure energy.
[0014]
According to the second aspect of the present invention, the potential of the developing roll is in the range of 0 to 200 V, the potential difference between the potential of the developing roll and the potential of the magnetic roll is in the range of 100 to 350 V, In this method, an AC voltage having a frequency of 1 to 3 kHz and a peak voltage of 500 to 2000 V is applied between the electrostatic latent image carrier.
[0015]
Thus, according to the present invention, the bias voltage is lowered, and the potential difference between the magnetic roll and the developing roll is set to a predetermined value. As a result, excessive charging of the donor can be suppressed to suppress the occurrence of a residual image, and a clear image can be formed.
[0016]
Further, by lowering the bias voltage, the electrostatic force with which the toner adheres to the developing roll is reduced. As a result, the development residual toner on the developing roll can be efficiently collected on the magnetic roll by the magnetic brush effect due to the peripheral speed difference between the developing roll and the magnetic roll without providing a special device such as a scraping blade. . Then, by collecting the residual toner and supplying new toner to the developing roll, the toner can be easily replaced, so that a thin toner layer of uniform thickness can be formed on the developing roll. The occurrence of image unevenness can be suppressed.
[0017]
In the present invention, the occurrence of afterimages and fogging can be suppressed by setting the potential difference between the magnetic roll and the developing roll to 100 to 350 V based on experiments.
[0018]
Further, according to the present invention, on the basis of an experiment, an AC voltage having a peak voltage of 500 to 2000 V is applied to the electrostatic latent image carrier at a frequency of 1 to 3 kHz, so that the electrostatic latent image carrier is applied to the electrostatic latent image carrier. It is possible to improve the development accuracy and facilitate the collection of the development residual toner on the magnetic roll.
[0019]
Preferably, the thickness of the toner thin layer is 10 to 50 μm.
When the toner thin layer is too thick, it is difficult to fly the toner to the electrostatic latent image carrier. In general, it is difficult to supply a large amount of toner having a thickness of 50 μm or more from the magnetic roll to the developing roll at a time. For this reason, if the thickness of the toner thin layer is 50 μm or more, a difference in density tends to occur during development. Further, if the toner thin layer is too thick, it is difficult to fly all the toner onto the latent image, and a strong ghost may be generated. In addition, if the toner thin layer is too thick when collecting the development residual toner, the development residual toner cannot be completely collected, which may cause a residual image.
[0020]
On the other hand, if the toner thin layer is too thin, it is necessary to increase the rotation speed of the developing roll in order to secure an amount of toner necessary for developing the latent image with sufficient developability. For this reason, the toner thin layer is desirably 10 μm or more.
[0021]
Preferably, the gap between the developing roll and the electrostatic latent image carrier is 50 to 400 μm, more preferably 200 to 300 μm.
If this gap is smaller than 50 μm, fog is likely to occur. On the other hand, if the gap is larger than 400 μm, it is difficult to cause the toner to fly to the electrostatic latent image carrier, and as a result, it is difficult to obtain a sufficient image density. In addition, it becomes a factor that causes selective development.
[0022]
According to a third aspect of the present invention, there is provided a method in which the photosensitive member is constituted by an amorphous silicon photosensitive layer, and the thickness of the photosensitive member is in the range of 10 to 25 μm.
In the present invention, the thickness of the photosensitive member is not only the thickness of the amorphous photosensitive layer portion, but also the thickness from the surface of the substrate of the electrostatic latent image carrier to the outermost surface of the carrier. Refers to
[0023]
When the photoconductor is thinned, the saturation charging potential is lowered and the withstand voltage leading to dielectric breakdown is lowered. On the other hand, when the photoconductor is thinned, the charge density on the surface of the photoconductor at the time of latent image formation is improved and the developability is improved. This property is particularly remarkable when the thickness is 25 μm or less, more preferably 20 μm or less, in an amorphous silicon photoreceptor having a high dielectric constant of about 10. However, if the thickness of the photoreceptor is less than 10 μm, it is difficult to adjust the potential of the photoreceptor, so that so-called black spots and fog are likely to occur, and the saturation charging potential is lowered to ensure the necessary charging potential. Tend to be difficult. Therefore, in the present invention, the thickness of the amorphous silicon photosensitive member is set to 10 to 25 μm.
[0024]
In addition, since the amorphous silicon photoconductor has an extremely low post-exposure potential of 10 V or less, a sufficient potential difference can be obtained even if the surface potential of the photoconductor is set low, which is advantageous in improving developability.
In particular, when the bias voltage (development bias) is set to a low voltage, there is no practical problem even if the saturation charging potential is lowered and the withstand voltage leading to dielectric breakdown is lowered by thinning the photoreceptor. .
[0025]
Preferably, a surface protective layer having a thickness of 0.3 to 5 μm is provided on the surface of the photoreceptor.
The reason is that when the thickness of the surface protective layer is less than 0.3 μm, characteristics such as the saturation charging potential, wear resistance, and environment resistance of the photoreceptor tend to deteriorate. On the other hand, if the thickness of the surface protective layer exceeds 5 μm, it causes deterioration of image quality, and the manufacturing time becomes longer, which is economically disadvantageous.
[0026]
According to a fourth aspect of the present invention, the photoconductor is composed of an organic photoconductor (OPC), and the thickness of the photoconductor is in the range of 25 to 40 μm.
[0027]
When a positively chargeable organic photoreceptor is used, the post-exposure potential can be reduced to 100 V or less by setting the film thickness of the photosensitive layer to 25 μm or more and increasing the amount of charge generation material added. The organic photoreceptor preferably has a single-layer structure since a charge generating material is added.
On the other hand, when the thickness of the photoreceptor is larger than 40 μm, the resolution is lowered.
[0028]
By the way, in the conventional image forming apparatus, when the carrier is used for a long time, the chargeability of the toner changes due to the deterioration of the carrier. For example, when the coating material on the carrier surface is peeled off by 20% or more, the chargeability to the toner changes. As a result, the variation in charging of the toner on the developing roll increases, causing toner scattering and fogging due to charging failure, image contamination and developability are reduced, and so-called selective development or the like occurs.
[0029]
For this reason, in the conventional image forming apparatus, in order to maintain the image quality, it is necessary to replace the deteriorated carrier after being used for a certain period of time. However, the troublesome replacement of the carrier has hindered the spread of non-contact type image forming apparatuses.
[0030]
Therefore, according to the fifth aspect of the present invention, the carrier comprises a carrier core material having magnetism and a coating layer containing a high molecular weight polyethylene resin polymerized on the surface of the carrier core material. ⁸ -10 ¹² This is a method of using a carrier having a resistance value of Ωcm and a saturation magnetization of 60 to 100 emu / g.
[0031]
As described above, the resistance value of the carrier is controlled with a resistance adjusting agent or the like to control the charge as a predetermined value, and the coating layer is polymerized on the surface of the carrier, so that extremely high strength and durability can be realized. it can. If such a carrier is used, even if the carrier is repeatedly used, the surface of the carrier is hardly deteriorated, and a stable charged toner thin layer can be formed on the developing roll. As a result, the electrostatic latent image carrier can be accurately developed. Further, since the durability of the carrier is high, it is not necessary to replace the carrier substantially until the life of the developing device.
[0032]
Preferably, the carrier core material has minute irregularities on the surface, and the coating layer has a weight average molecular weight obtained by polymerizing and growing by introducing ethylene gas after holding the ethylene polymerization catalyst in the irregularities. It is good to form with 50000 or more high molecular weight polyethylene.
[0033]
As described above, a polymerization method for producing a polyethylene resin-coated carrier by treating the surface of the carrier core material with an ethylene polymerization catalyst and polymerizing (generating) ethylene directly on the surface is disclosed in, for example, JP-A-60-106808 or It is described in JP-A-2-187770.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
First, the configuration of the image forming apparatus according to the embodiment will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus includes a magnetic roll 1 having a diameter of 20 mm, a developing roll 2 having a diameter of 20 mm, and an electrostatic latent image carrier 3. The magnetic roll 1 generates a magnetic brush 10 by a carrier 4 that charges and holds the toner 5. A thin toner layer 6 is formed on the surface of the developing roll 2 by the toner 5 supplied from the magnetic brush 10. The electrostatic latent image carrier 3 forms an image by selectively flying the toner of the toner thin layer 6 according to the electrostatic latent image.
[0035]
The electrostatic latent image carrier 3 has a photosensitive member having a thickness of 10 to 25 μm including a photosensitive layer made of amorphous silicon on the surface.
Here, FIG. 2 shows an enlarged view of a main part of the electrostatic latent image carrier 3. As shown in FIG. 2, the electrostatic latent image carrier 3 has a structure in which a blocking layer 32, an amorphous silicon (a-Si) photosensitive layer 33, and a surface protective layer 34 are sequentially laminated on a substrate 31. Have Here, the thickness of the photoconductor 30 refers to the total T of the thicknesses of the blocking layer 32, the photosensitive layer 33, and the surface protective layer 34.
[0036]
The material of the photosensitive layer of the photoreceptor is not particularly limited as long as it is amorphous silicon. Examples of the amorphous silicon include inorganic materials such as a-Si, a-SiC, a-SiO, and a-SiON.
[0037]
Further, the thickness t of the surface protective layer is 0.3 to 5 μm. Moreover, as a material of the surface protective layer 34, it is desirable to use a material having a specific ratio of Si (silicon) to C (carbon) among a-SiC. As such a-SiC, a-Si _(1-X) C _X (0.3 ≦ X <1.0) is preferable, and a-Si _(1-X) C _X (0.5 ≦ X ≦ 0.95) is more preferable. The reason is that such a-SiC is 10 ¹² -10 ¹³ This is because it has a particularly high resistance value of Ω · cm, and an excellent saturation charging potential, wear resistance, and environmental resistance (humidity resistance) can be obtained.
[0038]
In this embodiment, a toner having a positively charged polarity is used as the toner 5. The surface potential of the photoconductor is set in the range of 0 to 250V, and the post-exposure potential immediately after the photoconductor is exposed by the laser scanner or the LED tube is set in the range of 0 to 100V.
[0039]
Further, a power supply unit 7 including a first DC power supply unit 7a for applying a bias voltage Vdc1 of 0 to 200 V and an AC power supply unit 7b is provided between the electrostatic latent image carrier 3 and the developing roll 2. ing. Further, the AC power supply unit 7b applies an AC voltage having a peak voltage Vpp = 500 to 2000V to the electrostatic latent image carrier 3 at a frequency f = 1 to 3 kHz.
Note that the bias voltage is lower than the surface potential of the photoconductor and higher than the post-exposure potential.
[0040]
Further, a second DC power source 8 for applying a voltage Vdc2 to the magnetic roll 1 is provided. Then, the voltages of the first and second DC power supply units 7a and 8 are determined so that the potential difference | Vdc2-Vdc1 | between the potential of the developing roll 2 and the potential of the magnetic roll 1 becomes 100 to 350V. Here, for example, Vdc2 = 250V, Vdc1 = 100V, and | Vdc2−Vdc1 | = 150V may be set.
[0041]
Here, the relationship between the bias voltage Vdc1 and the potential difference | Vdc2−Vdc1 | and the development characteristics will be described with reference to the experimental result graph of FIG. The horizontal axis of the graph in FIG. 3 represents the potential difference | Vdc2−Vdc1 |, and the vertical axis represents the bias voltage Vdc1. As shown in FIG. 3, when the bias voltage Vdc1 is higher than 200V, a ghost is generated. Further, even when the potential difference | Vdc2−Vdc1 | is less than 100V, a ghost is generated.
[0042]
On the other hand, when the potential difference | Vdc2−Vdc1 | becomes higher than 350V, fogging occurs. Therefore, it can be seen from FIG. 3 that if the bias voltage Vdc1 is 0 to 200 V and the potential difference | Vdc2−Vdc1 | is in the range of 100 to 350 V, high quality image quality can be obtained.
[0043]
Referring to FIG. 1 again, at the time of image formation, the toner 5 is charged to an appropriate level while stirring the developer composed of the carrier 4 and the toner 5 held on the magnetic roll 1. The developer forms the magnetic brush 10. The magnetic brush 10 contacts the developing roll 2 with a certain thickness by passing through the regulating blade 9. Here, the gap between the regulating blade 9 and the magnetic roll 1 is set to 0.3 to 1.5 mm. Similarly, the gap between the magnetic roll 1 and the developing roll 2 is set to 0.3 to 1.5 mm. Further, the gap between the developing roll 2 and the electrostatic latent image carrier 3 is 50 to 400 μm, preferably 200 to 300 μm.
[0044]
When the toner thin layer 6 is formed under such a gap and applied voltage conditions, the thickness of the toner thin layer 6 becomes 10 to 50 μm. Then, the process linear velocity of the developing roll 2 is set to 72 mm / s, and the magnetic roll 1 is rotated at a speed three times that speed. As a result, the undeveloped toner and the supplied toner can be easily replaced by the brush effect due to the peripheral speed difference. For this reason, it is possible to suppress the generation of afterimages and to form a clear image.
[0045]
Furthermore, the carrier 4 used in this embodiment is composed of a carrier core material having magnetism and a coating layer containing a high molecular weight polyethylene resin formed by polymerization on the surface of the carrier core material. The carrier core material has minute irregularities on its surface. Further, the coating layer is made of high molecular weight polyethylene having a weight average molecular weight of 50,000 or more obtained by holding an ethylene polymerization catalyst in the unevenness and then introducing and polymerizing ethylene gas.
[0046]
Carrier 4 is 10 ⁸ -10 ¹² It is desirable to have a resistance value of Ωcm and a saturation magnetization of 60 to 100 emu / g. Carrier resistance is 10 ⁸ If it is less than Ω · cm, carrier development or fog may occur, ¹² This is because if it exceeds Ω · cm, there is a risk of image quality deterioration such as a reduction in image density.
In addition, resistance value is electrode area 5cm ² It is preferable to provide a carrier layer having a thickness of 0.5 cm with a load of 1 kg, apply a voltage of 1 to 500 V to the upper and lower electrodes, measure the current value flowing in the bottom, and convert it.
[0047]
Further, the carrier coating layer preferably includes hydrophobic silica, magnetic powder and / or fine particle resin as at least the outermost shell layer.
[0048]
Such a carrier 4 has extremely high strength and durability. When this carrier is used, even when the carrier is repeatedly used, the surface of the carrier is hardly deteriorated, and a stable charged toner thin layer can be formed on the developing roll. As a result, the electrostatic latent image carrier can be accurately developed. Furthermore, since the durability of the carrier is high, it is not necessary to substantially replace the carrier until the life of the developing device.
[0049]
In addition, the electrophotographic developer according to the exemplary embodiment can be obtained by mixing various toners with a carrier. In the present embodiment, a known positively chargeable toner can be used.
[0050]
Such a positively chargeable toner is preferably composed of a resin and a charge control agent (CCA). As the resin, for example, a resin obtained by introducing a monomer such as methyl methacrylate (MMA) into a styrene acrylic copolymer can be used. Moreover, as a charge control agent (CCA), a quaternary ammonium salt, nigrosine, or a triphenylmethane type dye can be used, for example.
[0051]
Such a positively chargeable toner can be produced by a known method such as a suspension polymerization method, a pulverization method, a microcapsule method, a spray drying method, a mechanochemical method, or the like. The charge amount of the positively chargeable toner is controlled to 5 to 20 μC / g by an external additive, a charge control agent (CCA), a resin, a carrier and the like.
[0052]
In the exemplary embodiment, the mixing ratio of the toner is 2 to 40% by weight, preferably 3 to 30% by weight, and more preferably 4 to 25% by weight with respect to the total amount of the carrier and the toner. When the mixing ratio of the toner is less than 2% by weight, the toner charge amount becomes high and sufficient image density cannot be obtained. On the other hand, if the mixing ratio of the toner exceeds 40%, a sufficient charge amount cannot be obtained, so that the toner scatters from the developing roll and contaminates the inside of the copying machine, or the toner is fogged on the screen.
[0053]
Next, in order to evaluate the effects of the present invention, in the following Examples 1 to 4 and Comparative Examples 1 to 3, image formation was performed using the image pattern 11 shown in FIG. In this image pattern 11, a rectangular solid pattern 12 and a halftone pattern 13 wider than the solid pattern 12 are arranged so that the halftone pattern 13 is developed following the solid pattern 12. Here, the density of the halftone pattern 13 is set to 25% of the density of the solid pattern 12.
[0054]
In these examples and comparative examples, an apparatus in which the developing device of the image forming apparatus FS-1750 manufactured by Kyocera Corporation was modified was used. An AC voltage having a frequency of 2 kHz and a peak voltage of 1.4 kV was applied between the photoconductor 30 and the developing roll 2.
[0055]
In the evaluation, the image pattern 11 was changed by changing only the composition of the photoconductor, the surface potential of the photoconductor, the post-exposure potential of the photoconductor, the DC potential (Vdc1) of the developing roll 2 and the DC potential (Vdc2) of the magnetic roll 1. Image formation was performed. The initial image and the image after printing 50000 sheets were evaluated for density, toner charge amount (QM), and afterimage (ghost), respectively.
In measuring the toner charge amount, about 1 cm on the developing roll after printing several sheets. ² The toner thin layer portion of the area of was measured by sucking with a QM meter manufactured by Trek.
[0056]
[Example 1]
In Example 1, the electrostatic latent image carrier 3 provided with the a-Si photosensitive member 30 having a thickness of 15 μm was used in the above-described embodiment. At the time of image formation, the surface potential of the photoconductor 30 is 250 V, the post-exposure potential of the photoconductor 30 is 10 V, the surface potential of the developing roll 2 (Vdc1) is 50 V, and the surface potential of the magnetic roll 1 (Vdc2) is 200 V. .
[0057]
[Example 2]
In Example 2, the electrostatic latent image carrier 3 provided with the a-Si photosensitive member 30 having a thickness of 12 μm was used in the above-described embodiment. At the time of image formation, the surface potential of the photoconductor 30 is 200 V, the post-exposure potential of the photoconductor 30 is 50 V, the surface potential of the developing roll 2 (Vdc1) is 50 V, and the surface potential of the magnetic roll 1 (Vdc2) is 250 V. .
[0058]
[Example 3]
In Example 3, the electrostatic latent image carrier 3 provided with a positively chargeable organic photoreceptor (OPC) having a thickness of 25 μm was used in the above-described embodiment. At the time of image formation, the surface potential of the photoconductor was 250 V, the post-exposure potential of the photoconductor was 90 V, the surface potential (Vdc1) of the developing roll 2 was 100 V, and the surface potential (Vdc2) of the magnetic roll 1 was 300 V.
[0059]
[Example 4]
In Example 4, the electrostatic latent image carrier 3 provided with a positively chargeable organic photoreceptor (OPC) having a thickness of 30 μm was used in the above-described embodiment. At the time of image formation, the surface potential of the photoconductor was 200 V, the post-exposure potential of the photoconductor was 50 V, the surface potential (Vdc1) of the developing roll 2 was 100 V, and the surface potential (Vdc2) of the magnetic roll 1 was 300 V.
[0060]
[Comparative Example 1]
On the other hand, in Comparative Example 1, the electrostatic latent image carrier 3 provided with the a-Si photosensitive member 30 having a thickness of 35 μm was used. At the time of image formation, the surface potential of the photoconductor 30 is 500 V, the post-exposure potential of the photoconductor 30 is 20 V, the surface potential of the developing roll 2 (Vdc1) is 300 V, and the surface potential of the magnetic roll 1 (Vdc2) is 500 V. .
[0061]
[Comparative Example 2]
In Comparative Example 2, the electrostatic latent image carrier 3 provided with a positively charged organic photoconductor (OPC) having a thickness of 20 μm was used. At the time of image formation, the surface potential of the photoconductor was 700 V, the post-exposure potential of the photoconductor was 120 V, the surface potential (Vdc1) of the developing roll 2 was 400 V, and the surface potential (Vdc2) of the magnetic roll 1 was 700 V.
[0062]
[Comparative Example 3]
In Comparative Example 3, an electrostatic latent image carrier 3 provided with a negatively chargeable laminated organic photoconductor (-OPC) having a thickness of 20 μm was used. At the time of image formation, the surface potential of the photoconductor was 700 V, the post-exposure potential of the photoconductor was 120 V, the surface potential (Vdc1) of the developing roll 2 was 400 V, and the surface potential (Vdc2) of the magnetic roll 1 was 700 V.
[0063]
Table 1 below shows the evaluation results of image formation performed under the development conditions of Examples 1 to 4 and Comparative Examples 1 to 3 described above.
[0064]
[Table 1]

[0065]
In Table 1 above, the “◯” mark in the ghost column indicates that no ghost is recognized in the halftone area of the formed image pattern. The “Δ” mark indicates that the ghost is slightly recognized in the first round of the developing roll. The “x” mark indicates that the ghost is clearly recognized on the first round of the developing roll. FIG. 5 is a diagram schematically showing the afterimage 14 of the solid pattern 12 appearing in the area of the halftone pattern 13 when the image pattern 11 shown in FIG. 4 is formed.
[0066]
As shown in Table 1 above, in each of Examples 1 to 4, the increase in the toner charge amount is smaller than that in the initial image even after printing 50 million sheets, and ghosts are generated. Was not recognized and a good image could be maintained.
In particular, in Example 2, a high image density was obtained although the development potential was as low as 50V. In Example 3 and Example 4, the image density is lower than in Example 1 and Example 2. However, by setting the developing electric field at a low potential, there is little change in toner charge and the image is stable. The formation could be done.
[0067]
In contrast, as shown in Table 1 above, in Comparative Example 1 and Comparative Example 2, the toner charge amount increased and the ghost also increased. Further, in Comparative Example 3, the change in the toner charge amount was larger than that in Comparative Example 2, and ghost also occurred from the beginning.
[0068]
In the above-described embodiments, examples in which the present invention is configured under specific conditions have been described. However, the present invention can be variously modified.
[0069]
【The invention's effect】
As described above in detail, according to the present invention, after a thin layer of toner is formed by the two-component development method, development is performed in which the toner is ejected to a latent image on the electrostatic latent image carrier by a non-contact method. In the method, it is possible to prevent the occurrence of a development afterimage (ghost) history phenomenon while avoiding the occurrence of fog.
[0070]
Furthermore, if a coating layer is formed by polymerization on the surface of the carrier, extremely high strength and durability can be realized. When this carrier is used, even when the carrier is repeatedly used, the surface of the carrier is hardly deteriorated, and a stable charged toner thin layer can be formed on the developing roll. As a result, the electrostatic latent image carrier can be accurately developed. Further, since the durability of the carrier is high, it is not necessary to replace the carrier substantially until the life of the developing device.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment.
FIG. 2 is an enlarged view of a main part of the electrostatic latent image carrier.
FIG. 3 is a graph showing the relationship between development conditions and development characteristics.
FIG. 4 is a schematic diagram of an image pattern for evaluating image characteristics.
FIG. 5 is a schematic diagram illustrating a state in which an afterimage is generated.
[Explanation of symbols]
1 Magnetic roll
2 Development roll
3 Electrostatic latent image carrier
4 Career
5 Toner
6 Toner thin layer
7 AC / DC power supply
8 DC power supply
9 Regulatory blade
10 Magnetic brush
11 Image pattern
12 Solid pattern
13 Halftone pattern
14 Afterimage
30 photoconductor
31 Substrate
32 blocking layer
33 Photosensitive layer
34 Surface protective layer

Claims (3)

A magnetic roll for generating a magnetic brush by a carrier for charging and holding toner;
A developing roll having a toner thin layer formed on the surface by the toner supplied from the magnetic brush;
Electrostatic latent image carrying on the surface a positively chargeable amorphous silicon photoreceptor composed of an amorphous silicon photosensitive layer that forms an image by selectively flying the toner of the toner thin layer according to the electrostatic latent image An image forming method by an image forming apparatus comprising a body,
The photoreceptor constituted by the amorphous silicon photosensitive layer has a thickness in the range of 10 to 25 μm,
As the toner, a toner having a positive charging polarity in which the charge amount is controlled within a range of 5 to 20 μC / g,
The surface potential of the photoreceptor before charging and before exposure is in the range of 200 to 250 V, and
An image forming method, wherein a post-exposure potential that is a potential immediately after the photosensitive member is exposed is in a range of 5 to 10V.   The potential of the developing roll is in the range of 0 to 200 V, the potential difference between the potential of the developing roll and the potential of the magnetic roll is in the range of 100 to 350 V, and the developing roll and the electrostatic latent image carrier are 2. The image forming method according to claim 1, wherein an AC voltage having a frequency of 1 to 3 kHz and a peak voltage of 500 to 2000 V is applied therebetween. The carrier is composed of a carrier core material having magnetism and a coating layer containing a high molecular weight polyethylene resin polymerized on the surface of the carrier core material, and has a resistance value of 10 ⁸ to 10 ¹² Ωcm, The image forming method according to claim 1, wherein a carrier having a saturation magnetization of 60 to 100 emu / g is used.

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