JP3758195B2 - Development bias determination method for image forming apparatus - Google Patents

Description

但し、ε_t ：トナーの比誘電率， ρ：トナーの体積電荷密度
σ_m ：感光ドラム上の表面電荷， σ₀ ：感光ドラムの誘導電荷
【００２６】
まず、式（１０）に着目すると、電界Ｅ_O は感光ドラムの一様帯電電位（非露光部の電位）Ｖ_S と現像バイアス電圧Ｖ_b の差である逆バイアス電圧に比例するため、逆バイアス電圧が小さくなると、電界Ｅ_o も弱くなり、トナーが電界から受ける静電力Ｆ_e が小さくなってかぶりが発生し易くなる。また式（１０）において、現像ローラ硬度Ｈが大きくなると、くわえ込み力Ｆ_r は小さくなり、かぶりが起こり易くなる。
【００２７】
さらに、トナー比電荷ｑ／ｍについては、ｑ／ｍが小さくなると右辺第１項が大きくなり、逆にｑ／ｍが大きくなっても右辺第２項が大きくなる。つまり、かぶりを除去するための逆バイアス電圧（Ｖ_S −Ｖ_B ）を最小にするｑ／ｍが存在することになる。そこで、かぶりに大きな影響を及ぼすトナー比電荷と逆バイアス電圧の関係について検討する。
【００２８】
ここで、かぶりのマージン拡大として取り扱っている現像ローラ硬度の影響を除外して考えると、式（１０）は次式のように書き換えることができる。

式（１１）は、かぶり発生の逆バイアス電圧があるトナー比電荷で最小値を取ることを示している。さらに、式（１１）より、かぶりが発生するトナー比電荷Ｔ_p を求めると次式となる。
【００２９】

そこで、各種感光体を用いた場合のトナー比電荷Ｔ_p と逆バイアス電圧（Ｖ_S −Ｖ_B ）との関係について検討する。
【００３０】
結果を図３に示す。本図のデータはＯＰＣ感光体の静電容量の値を用いて式（１２）より求めた計算値である。本図より、有機感光体の場合には、トナー比電荷７〜３５μｃ／ｇにおいて、逆バイアス電圧を７０Ｖとするとかぶりが発生しないことが分かる。これが逆バイアス電圧の下限値となる。なお、計算に使用した各パラメータの値は次の通りである。
【００３１】
トナー粒子径 ｒ_t ＝６μｍ トナー層の比誘電率 ε_t ＝２．２
トナー密度 δ＝１１１０kg／ｍ³ トナー層厚 ｄ_t ＝２４μｍ
トナー層の充填率 β＝０．６ トナー供給能 θ＝２．０
感光体膜厚 ｄ_P ＝２５μｍ 感光体の比誘電率 ε_p ＝３．０
トナーと感光体間の機械的付着力 Ｆ_a ＝４．２×１０^-8Ｎ
転写電荷量 σ_c ＝３２０μｃ／ｍ²
付着トナー量Ｍ＝８ｇ／ｍ² （現像濃度１．３）
かぶり濃度を求めるときの想定逆バイアス電圧Ｖ_S −Ｖ_B ＝１００Ｖ
【００３２】
次に、逆バイアス電圧の上限値について検討する。逆バイアス電圧の上限は、現像領域において、現像ローラ表面からトナーに電荷が注入され、トナーの正規の極性電荷に代わって逆極性の電荷量を持つトナーができ、これが感光体表面の背景部の電位に引かれて背景部に付着するかぶりが発生しない値となる。
【００３３】
そこで、現像バイアス電圧を変化させたときのかぶり濃度を図４に示す。本図より、逆バイアス電圧の上限値を３５０Ｖに設定すれば、電荷注入によるかぶりは発生しないことが分かる。さらに、上述した逆バイアス電圧の下限値もほぼ実験値と一致している。
【００３４】
本発明が適用される画像形成装置（モノクロ方式）の構造概要を図５に示す。図中、１０２はコロナ帯電器、１０３は１成分現像器、１０４はコロナ転写器、１０５はクリーナ、１０６は定着器である。現像器１０３は、現像ローラ１０７と、現像ローラ１０７上のトナー層厚を規制するブレード１０８と、現像ローラ１０７上のトナーを回収して新しいトナーを供給するリセットローラ１０９と、現像ローラ１０７に向けトナーを搬送するパドル１１０と、現像器内のトナーを均一にならずアジテータ１１１とを備えている。
【００３５】
記録に際しては、感光ドラム１０１を図５に矢印で示す時計方向に回転させ、その表面を、コロナ帯電器１０２により一様に帯電させた後、図示しない露光手段により所定のパターンで露光する。これにより、該表面には静電潜像が形成され、該静電潜像は現像ローラ１０７により現像されてトナー像となる。記録紙１２０は、上記トナー像形成とタイミングをとって転写部１１２に送られ、ここで、コロナ転写器１０４による記録紙１２０へのトナー像転写が行われる。
【００３６】
その後記録紙１２０は定着部に送られ、ここで、定着器１０６によるトナー像定着が行われる。定着完了後、記録紙１２０は図示しないスタッカに排出される。また、転写完了後の感光ドラム１０１の表面はクリーナ１０５により清掃され、除電器１１３により除電される。
【００３７】
【発明の効果】
以上述べたように、本発明によれば、現像バイアス電圧の最適化により、かぶりの発生を抑えて印字濃度を安定化することができ、良好な印字を実現することが可能になる。
【図面の簡単な説明】
【図１】本発明の実施例の接触現像の原理説明図である。
【図２】本発明の実施例の現像時にトナーに働く力説明図である。
【図３】本発明の実施例のトナー比電荷と逆バイアスの関係説明図である。
【図４】本発明の実施例の逆バイアス電圧とかぶりの関係説明図である。
【図５】本発明が適用される画像形成装置の構造概要を示す側面図である。
【図６】従来方式の電子写真プロセスの概要図である。
【図７】非磁性一成分現像方式の概要説明図である。
【符号の説明】
１００ トナー
１０１ 感光ドラム（像担持体）
１０７ 現像ローラ
Ｖ_S 非露光部の電位
Ｖ_B 現像バイアス電圧
Ｖ_L 露光部の電位[0001]
[Industrial application fields]
The present invention relates to a developing bias determination method for a non-magnetic one-component developing type image forming apparatus using electrophotographic technology.
[0002]
In recent years, with the rapid development of the information industry, various information systems have been developed, and there is an increasing demand for output machines (printers) suitable for them, and various printers have been commercialized.
[0003]
[Prior art]
Generally, the recording method is divided into an impact method and a non-impact method. While the impact method has advantages such as small size, low price, and maintenance-free, it has a problem in terms of noise. On the other hand, the non-impact method includes a serial method and a page method. The serial method has advantages such as small size and low price, but the thermal transfer method has the problem that the recording speed is slow, and the inkjet method has the problem that clogging occurs.
[0004]
As for the page system, the electrophotographic system is cited as a representative, and there are advantages such as high-speed printing and high printing quality, but it is considered that there is a problem in cost reduction and downsizing of the equipment due to the complicated process. It was. However, recent electrophotographic printers are becoming smaller and less expensive, and are now entering the area of impact printers. Next, an outline of this electrophotographic process will be described.
[0005]
In this process, the photoreceptor is rotated and a uniform charge layer is formed on the surface thereof by printing a high voltage on the discharge wire. Next, an electrostatic latent image corresponding to the image signal is formed on the surface by an exposure process. The electrostatic latent image is visualized with a developer made of charged colored particles called toner (toner image formation). The toner image is usually fixed to the transfer material (recording paper) by heat and pressure after transfer.
[0006]
This electrostatic latent image development method is roughly divided into one-component development and two-component development. In the case of two-component development, the developer used is composed of toner and carrier, and the toner and carrier are triboelectrically charged by mechanical agitation to impart charge to the toner. However, in the case of the two-component development method, it is necessary to always keep the toner density constant, and there is a problem that stable control is difficult.
[0007]
On the other hand, the one-component development system develops the toner alone without mixing with the carrier, and contains magnetic powder in the toner for conveying the toner on the developing roller and supplying the toner to the developing unit. Some use non-magnetic toner. Recently, in consideration of colorization, development of a color printer using a non-magnetic toner has attracted attention.
[0008]
[Problems to be solved by the invention]
By the way, in the conventional development system, the development is performed in a state where the toner supply amount is saturated. An overview of this type of electrophotographic process is shown in FIG. In this case, the toner adhesion amount M on the photosensitive drum (image carrier) 1 is the intensity of the latent image formed on the photosensitive member 1 (development bias voltage V _B -light irradiation portion potential V _L ), toner specific charge T _P. It depends on the size. That is, the development bias voltage is a factor that determines the toner adhesion amount (print density). In FIG. 6, 2 is a developing roller, 3 is a carrier, 4 is toner, V _S is a potential of a non-exposed portion, and V _s −V _B is a reverse bias voltage.
[0009]
However, since the latent image intensity and the specific charge of the toner change due to environmental changes, the toner adhesion amount also changes, and there is a problem that the density and resolution of the printing deteriorate. Therefore, we have proposed a developing method in which toner adhesion is always constant with respect to environmental changes (Japanese Patent Application No. 3-156644, filed on June 27, 1991). This method will be described with reference to FIG. Reference numeral 5 denotes a blade for regulating the toner layer thickness.
[0010]
In this method, the toner adhesion amount can be uniquely determined by the amount of toner conveyed to the developing unit because a very thin and uniform toner layer can be formed on the developing roller 2. The toner adhesion amount M is expressed by the following equation.
M = 2r _t δρn (v _d / v _p )
r _t: Toner radius [delta]: toner filling rate [rho: Toner Density n: toner layer number on the developing roller v _p: photosensitive drum peripheral speed v _d: developing roller peripheral speed [0011]
For this reason, a stable toner adhesion amount can be obtained because it does not depend on the latent image intensity and the toner specific charge which are easily changed with respect to environmental fluctuations. Further, the developing bias voltage in this developing method is set to a sufficiently large value in order to provide a margin for fluctuations in the surface potential of the photoconductor and toner charge amount due to environmental changes.
[0012]
However, depending on whether the developing bias is large or small, it becomes a fogging factor. This will be described in detail. The fog is greatly affected by the reverse bias voltage described above with reference to FIG. When the reverse bias voltage is large, reverse polarity charges are injected into the toner, and the reversely charged toner adheres to the background portion of the print and becomes fogged.
[0013]
Also, when the reverse bias voltage is small, the repulsive force of the normally charged toner on the background of printing with the photosensitive member becomes small, and the toner adheres to the background of printing and fog occurs.
[0014]
An object of the present invention is to provide an image forming apparatus that realizes printing without fogging by setting a developing bias voltage to an optimum value.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, an image in which an electrostatic latent image is formed by an electrostatic potential difference generated between a non-exposed portion where image light is not exposed and an exposed portion where image light is exposed is formed. And a developing roller to which a toner for developing the electrostatic latent image is attached to the surface and a developing bias voltage is applied between the image bearing member and the image bearing member. Non-magnetic one-component development that takes a sufficiently large electrostatic latent image and determines the amount of toner to be formed on the image carrier based on the amount of toner supplied to the developing unit between the image carrier and the developing roller the image forming apparatus of a system, the developing bias voltage V _B which determines the reverse bias voltage is - - (developing bias voltage V _B the non-exposed portion potential V _S) (developing bias voltage exposed portion potential) at which a latent image intensity and , Development area with increasing reverse bias The lower limit is the value at which fog does not occur due to reverse polarity charge injection to the toner, and the upper limit is the value at which fog does not occur due to a decrease in the repulsive force of the charged toner on the image carrier due to a decrease in reverse bias. when setting, the upper limit of the developing bias voltage V _B, the following equation
| V _s −V _B |> [{F _b − (Ar / 6D ² ) (1 + A / 6πD ³ H)} /
{(4/3) πr ³ δ (q / m)}] [(d / ε _d ) + (X / ε _t )]
+ {Βδ (q / m) X ² / 2ε ₀ ε _t }
Where F _b : mechanical adhesion, ε ₀ : vacuum dielectric constant,
ε _t : relative permittivity of toner, ε _d : relative permittivity of image carrier,
X: layer thickness of toner layer, d: thickness of photosensitive layer of image carrier,
r: toner radius, δ: toner particle density,
β: filling rate of toner layer, q / m: specific charge of toner,
A: HAMAKER constant D: closest distance between toner and developing roller,
H: Hardness of developing roller
It is set as the characteristic characterized by determining by .
[0016]
[Action]
As described above, since the development bias voltage is optimized by setting the upper and lower limits, the occurrence of fogging can be suppressed and the print density can be stabilized. That is, good printing can be obtained.
[0017]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0018]
In the present invention, a developing roller in which a developing bias voltage is applied between an image carrier on which an electrostatic latent image is formed and toner for developing the electrostatic latent image is attached to the surface and the image carrier. And is applied to an electrophotographic apparatus in which the amount of toner adhering to the image carrier is uniquely determined by the amount of toner supplied from the developing roller to the image carrier, and realizing printing without fogging It is an object.
[0019]
In order to achieve this object, the development bias voltage for determining the reverse bias voltage (development bias voltage-exposure portion potential) and (non-exposure portion potential-development bias voltage) is the development portion accompanying the increase of the reverse bias. The lower limit is the value at which fog does not occur due to reverse polarity charge injection to the toner, and the upper limit is the value at which fog does not occur due to a decrease in the repulsive force of charged toner on the image bearing member due to a decrease in reverse bias. Set. Next, the reverse bias voltage is calculated from the model diagram of FIG. 1, and the optimum condition in which fog does not occur is examined.
[0020]
In FIG. 1, when the photosensitive drum (image carrier) 101 and the toner 100 are considered as a dielectric, and the developing roller 107 is considered as a resistor, the following equation is established.
−∫ ₀ ^d (σ _o / ε _o ε _d ) dy−∫ _d ^{d + x} [{σ ₀ + σ _m + ρ (y−d)} // ε _o ε _t ] dy = V _B (1) )
However, ε _o : constant ε _d : photosensitive drum relative permittivity y: distance d: photosensitive layer thickness x: gap between photosensitive drum and developing roller ₀ ^d : integral of _{0 to} ^d _ｄ ^{d d + x} : 0 Integration of (d + x)
From equation (1), the dielectric charge σ _o of the photosensitive drum is
σ _o = {− (Xε _d / dε _t ) V _S −V _B − (ρX ² / 2ε _o ε _t )} / {(d / ε _o ε _d ) + (X / ε _o ε _t )} (2)
However, V _S is the photosensitive drum surface potential and is expressed by the following equation.
V _S = (σ _m d / ε _o ε _d ) (3)
[0022]
The electric field E ₁ acting on the surface of the photosensitive drum is expressed by the following equation.
E ₁ = (σ _o + σ _m ) / ε _o …………………………… (4)
By substituting equation (2) into equation (4) and replacing ρ with q / m, the following equation is obtained.
E ₁ = [V _S −V _B − {βδ (q / m) X ² } / 2ε _o ε _t ] / {(d / ε _d ) + (X / ε _t )} (5) )
[0023]
Here, the force acting on the toner particles during development will be examined. As shown in FIG. 2, a mechanical adhesion force F _b acts on the toner particles in addition to the electrostatic force F _e received from the electric field E _o and the force F _r that the developing roller holds the toner. To force the respective conditions that the head does not occur is when the sum of the force F _r Komu addition the electrostatic force Fe is greater than the mechanical adhesion force F _b, the following equation.
F _e + F _r > F _b ……………………………………… (6)
[0024]
Furthermore, in order to clarify what kind of factor each force is, each force was formulated.
F _e = (q / m) E ₁ · δ · (4/3) πr ³ (7)
F _r = (Ar / 6D ² ) (1 + A / 6πD ³ H) (8)
Where r: toner radius, δ: toner particle density q / m: toner specific charge, A: HAMAKER constant (1 × 10 ⁻¹⁹ )
D: closest distance between toner and developing roller, H: hardness of developing roller
Assuming that the mechanical adhesion force F _b is a constant value determined by the force pressing the developing roller against the photosensitive member, the following equation is obtained.
F _b = const ……………………………………… (9)
Substituting Equation (5), Equation (7), Equation (8), and Equation (9) into Equation (6) yields the following equation.

Where ε _{t is} the relative dielectric constant of the toner, ρ is the volume charge density of the toner σ _m is the surface charge on the photosensitive drum, and σ _{0 is} the induced charge on the photosensitive drum.
First, paying attention to equation (10), the electric field E _O is proportional to the reverse bias voltage, which is the difference between the uniform charging potential (non-exposed portion potential) V _S of the photosensitive drum and the developing bias voltage V _b , and therefore, the reverse bias When the voltage is reduced, the electric field E _o is also weakened, and the electrostatic force F _e received by the toner from the electric field is reduced, so that fog is likely to occur. In the formula (10), the developing roller hardness H is increased, narrowing added force F _r becomes small, easily occurs the head.
[0027]
Further, regarding the toner specific charge q / m, when q / m decreases, the first term on the right side increases, and conversely, even if q / m increases, the second term on the right side increases. That is, q / m that minimizes the reverse bias voltage (V _S −V _B ) for removing the fog exists. Accordingly, the relationship between the toner specific charge and the reverse bias voltage that greatly affects fogging will be examined.
[0028]
Here, when the influence of the developing roller hardness handled as the fogging margin expansion is excluded, Expression (10) can be rewritten as the following expression.

Expression (11) shows that the reverse bias voltage for generating fog takes a minimum value with a certain toner specific charge. Further, when the toner specific charge T _{p at} which fog occurs is obtained from the equation (11), the following equation is obtained.
[0029]

Therefore, the relationship between the toner specific charge T _p and the reverse bias voltage (V _S −V _B ) when various photoconductors are used will be examined.
[0030]
The results are shown in FIG. The data in this figure is a calculated value obtained from equation (12) using the capacitance value of the OPC photoreceptor. From this figure, it can be seen that in the case of an organic photoreceptor, fogging does not occur when the reverse bias voltage is 70 V at a toner specific charge of 7 to 35 μc / g. This is the lower limit value of the reverse bias voltage. In addition, the value of each parameter used for calculation is as follows.
[0031]
Toner particle diameter r _t = 6 μm Toner layer dielectric constant ε _t = 2.2
Toner density δ = 1110 kg / m ³ Toner layer thickness d _t = 24 μm
Filling rate of toner layer β = 0.6 Toner supply ability θ = 2.0
Photoreceptor film thickness d _P = 25 μm Relative permittivity of the photoreceptor ε _p = 3.0
Mechanical adhesion between the toner and the photosensitive member F _a = 4.2 × 10 ^-8 N
Transfer charge amount σ _c = 320 μc / m ²
Adhering toner amount M = 8 g / m ² (development density 1.3)
Assumed reverse bias voltage V _S −V _B = 100V when calculating fog density
[0032]
Next, the upper limit value of the reverse bias voltage will be examined. The upper limit of the reverse bias voltage is that the charge is injected from the surface of the developing roller into the toner in the developing area, and a toner having a reverse polarity charge amount is generated instead of the normal polarity charge of the toner, and this is the background area of the photoreceptor surface. It is a value that does not generate fog that is attracted to the potential and adheres to the background.
[0033]
Accordingly, FIG. 4 shows the fog density when the developing bias voltage is changed. From this figure, it can be seen that if the upper limit value of the reverse bias voltage is set to 350 V, fogging due to charge injection does not occur. Furthermore, the lower limit value of the reverse bias voltage described above also substantially coincides with the experimental value.
[0034]
An outline of the structure of an image forming apparatus (monochrome system) to which the present invention is applied is shown in FIG. In the figure, 102 is a corona charger, 103 is a one-component developing device, 104 is a corona transfer device, 105 is a cleaner, and 106 is a fixing device. The developing device 103 is directed toward the developing roller 107, a blade 108 that regulates the toner layer thickness on the developing roller 107, a reset roller 109 that collects toner on the developing roller 107 and supplies new toner, and the developing roller 107. A paddle 110 that conveys the toner and an agitator 111 that does not make the toner in the developing unit uniform are provided.
[0035]
In recording, the photosensitive drum 101 is rotated clockwise as indicated by an arrow in FIG. 5, and the surface thereof is uniformly charged by the corona charger 102 and then exposed in a predetermined pattern by an exposure unit (not shown). Thereby, an electrostatic latent image is formed on the surface, and the electrostatic latent image is developed by the developing roller 107 to become a toner image. The recording paper 120 is sent to the transfer unit 112 in synchronization with the toner image formation, and here, the toner image is transferred to the recording paper 120 by the corona transfer device 104.
[0036]
Thereafter, the recording paper 120 is sent to the fixing unit, where the toner image is fixed by the fixing device 106. After the fixing is completed, the recording paper 120 is discharged to a stacker (not shown). Further, the surface of the photosensitive drum 101 after completion of the transfer is cleaned by the cleaner 105 and discharged by the charge remover 113.
[0037]
【The invention's effect】
As described above, according to the present invention, by optimizing the developing bias voltage, it is possible to suppress the occurrence of fogging and stabilize the print density, thereby realizing good printing.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of contact development according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of force acting on toner during development according to the exemplary embodiment of the present invention.
FIG. 3 is an explanatory diagram of a relationship between a toner specific charge and a reverse bias according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram of the relationship between reverse bias voltage and fogging according to the embodiment of the present invention.
FIG. 5 is a side view showing an outline of the structure of an image forming apparatus to which the present invention is applied.
FIG. 6 is a schematic diagram of a conventional electrophotographic process.
FIG. 7 is a schematic explanatory diagram of a non-magnetic one-component development system.
[Explanation of symbols]
100 Toner 101 Photosensitive drum (image carrier)
107 Development roller V _S Unexposed portion potential V _B Development bias voltage V _L Exposed portion potential

Claims (1)

An image carrier on which an electrostatic latent image is formed;
A developing roller for developing the electrostatic latent image,
The amount of toner formed on the image carrier is determined by taking a sufficient size of the electrostatic latent image on the image carrier and supplying the toner conveyed to the developing unit between the image carrier and the developing roller. In the development bias determination method of the non-magnetic one-component development type image forming apparatus to be determined ,
A developing bias voltage V _B which determines the reverse bias voltage is - (developing bias voltage V _B the non-exposed portion potential V _S), - (developing bias voltage exposed portion potential) at which a latent image intensity and
The lower limit is a value that does not cause fogging due to reverse polarity charge injection to the toner in the developing part due to an increase in reverse bias,
When setting the upper limit to a value at which fog does not occur due to a decrease in the repulsive force of the charged toner on the image carrier due to a decrease in reverse bias,
The upper limit of the development bias voltage V _B is given by
| V _s −V _B |> [{F _b − (Ar / 6D ² ) (1 + A / 6πD ³ H)} /
{(4/3) πr ³ δ (q / m)}] [(d / ε _d ) + (X / ε _t )]
+ {Βδ (q / m) X ² / 2ε ₀ ε _t }
Where F _b : mechanical adhesion, ε ₀ : vacuum dielectric constant,
ε _t : relative permittivity of toner, ε _d : relative permittivity of image carrier,
X: layer thickness of toner layer, d: thickness of photosensitive layer of image carrier,
r: toner radius, δ: toner particle density,
β: filling rate of toner layer, q / m: specific charge of toner,
A: HAMAKER constant D: closest distance between toner and developing roller,
H: Hardness of developing roller
And determining the developing bias of the image forming apparatus.

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