JP2933699B2 - Developing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to the technical field of an image forming apparatus using an electrophotographic method, an electrostatic recording method, an ion flow control method, and the like. The present invention is characterized by a developing device which forms an electrostatic latent image on a latent image carrier by an appropriate method, and turns the latent image into a visible image using a high-low anti-one component developer or a two-component developer.

2. Description of the Related Art Conventionally, various development methods have been proposed as a developing method of forming an electrostatic latent image on a latent image carrier and converting the latent image into a visible image using a high-low anti-one-component developer or a two-component developer. , Representative
There is a developing method described in US Pat. Nos. 3,386,974, 3,890,929 and 3,893,418.

In other words, according to this method, a latent image carrier and a donor (developer carrier) are arranged with a certain gap therebetween, and an asymmetrical alternating bias is applied to these, and a high-low anti-one component developer (simply referred to as “toner”) is applied. Has been proposed to control flight. FIG. 10 shows a schematic diagram of the waveform at that time.

Specifically, the gap between the latent image carrier and the donor is 50 μ to 500 μm.
μm (preferably 50-180 μm), frequency 1.5K-10KH _Z
(Preferably 4~8KH _Z), the first phase time T _A 10 .mu.sec ≦ T
_A ≦ 200 μsec (preferably 30 μsec ≦ T _A ≦ 70 μsec), and the second phase time T _D is 100 μsec ≦ T _D ≦ 500 μsec (preferably 10 μsec).
0 μsec ≦ T _D ≦ 180 μsec), and the first phase voltage _VA is V _A ≧ −150
V, the second phase voltage V _D V _D ≧ 400V, is and is and V _D -V _A ≦ 800V (preferably -150V ≦ V _A ≦ -200 and 400V ≦ V _D ≦ 450V).

According to this developing method, flying adhesion of toner particles to a non-image portion is prevented, and gradation and line reproducibility are improved.

Further, as other developing methods, there are developing methods using a high-low anti-one component developer (toner having a volume resistance of 10 ¹⁰ Ωcm or more), an impression developing method (USP3405682, etc.), a jumping developing method (Japanese Patent Laid-Open No. No. 18656-18659).

In particular, in the jumping development method, the toner is applied to the developer carrier by an alternating bias voltage applied between the developer carrier and the latent image carrier in a development area which is the closest portion between the developer carrier and the latent image carrier. And the latent image carrier reciprocally moves, and finally is selectively transferred and adhered to the surface of the latent image carrier according to the latent image pattern to be visualized.

In these developing systems, as shown in FIG.
The duty ratio is 50%, and the development time and the reverse development time are the same. However, Japanese Unexamined Patent Publication No. Sho 60-73647 concerning the above-mentioned jumping development method discloses,
It has been proposed to control the duty ratio of the alternating bias pre-pressure applied between the developer carrier and the latent image carrier according to the remaining amount of the developer.

However, according to the conventional developing method described in U.S. Pat. No. 3,865,574, the absolute value of the alternating bias voltage is reduced to prevent toner from adhering to the non-image area. Since the voltage is reduced, there is a problem that the developing property of the solid latent image is low and the charge variation of the toner is significantly affected.

That is, when the toner coated in a thin layer on the developer carrier, that is, the so-called “development sleeve”, is charged up, the voltage _VA on the first phase side is small, causing a remarkable decrease in density, and conversely, the toner charge is insufficient. As a result, the flying ability of the toner is reduced, resulting in a decrease in density and fogging. FIG. 11 shows the development characteristics.

On the other hand, in the conventional developing method such as the above-mentioned jumping developing method, the developing side bias voltage is large, so that the developability of a solid latent image (high potential area) is high, and it is considered to be somewhat tolerant to toner charge fluctuation. However, in order to reciprocate the toner between the latent image carrier and the developing sleeve, in order to prevent the toner from adhering to the non-image area, the reverse developing side bias voltage is set higher than the developing side bias voltage. In the potential region, the toner developed in accordance with the latent image potential may be peeled off by the action of the peeling electric field. In such a case, an image having no gradation may result, and the reproducibility of the low potential region of the latent image may deteriorate. FIG. 13 shows the developing characteristics. Further, the image may be disturbed by the action of the stripping electric field.

Note that the toner charge amount in FIGS. 11 and 13 indicates a charge amount per unit mass measured by a normal charge measurement method, for example, a blow-off method, and is −1 to −10 μm.
C / g is a toner having a normal distribution in the range of -1 to -10 μC / g with a center at about -6 μC / g. Similarly, -10 to-
20 μC / g means −10 to −20 μC / g around about −15 μC / g.
The toner is normally distributed in the range of g.

Further, in the conventional developing method such as the above-mentioned jumping developing method, a part where only light development is performed even when printing is performed because a non-printed portion (white background) continues, and a dark development is performed because printing is continued. The density unevenness is generated in the portion where the light is applied. According to the experiments and considerations of the present inventors, the mechanism of the ghost formation was found to be deeply related to the layer of fine powder (particle size of 5 to 6 μm or less) formed on the developing sleeve.

That is, there is a clear difference in the particle size distribution of the toner lowermost layer of the developing sleeve between the toner consuming portion and the toner non-consuming portion, and a fine powder layer is formed in the non-consuming portion and the toner lowermost layer. Since the fine powder has a large surface area per volume, the amount of triboelectric charge per mass becomes larger than that of the fine powder having a large particle size, and the fine powder is strongly restrained electrostatically to the developing sleeve by a self-reflective force. For this reason, the toner on the portion where the fine powder layer is formed cannot be sufficiently frictionally charged with the developing sleeve, so that the developing ability is reduced and appears as a sleeve ghost on the image. Such a sleeve ghost is a phenomenon that occurs because the charge of the toner greatly depends on the frictional charge with the developing sleeve together with the formation of the fine powder layer.

In order to solve this problem, when a one-component toner is used, the surface of the developing sleeve has a resin layer containing conductive fine particles having an average particle diameter of about 20 μm and conductive fine particles having a surface lubricating property. The layers have an average volume resistivity
There is a method of providing a thin layer so as to be in the range of 10 ² to 10 ^-6 Ωcm, but in this case, the charge amount of the developer on the developing sleeve is reduced as a whole, so that the density is reduced, rust, fog, letters There is a disadvantage that image reproducibility is deteriorated such as thinning.

Therefore, an object of the present invention is to provide a sufficient density by adhering a sufficient amount of toner to an image area, a halftone part to be well visualized including a low-potential part, a fine line to be reproduced well, and a fog to occur. A developing device that can be removed, always has a good image density, is excellent in gradation, has an edge effect, can reproduce sharp lines, and can obtain extremely excellent image quality. It is to be.

Means for Solving the Problems The above objects are achieved by a developing device according to the present invention.
In summary, the present invention provides a developing device including a developer carrier carrying a developer layer, and applying an oscillating bias voltage to the developer carrier to develop an electrostatic latent image formed on the latent image carrier. In (a), regarding the image portion of the electrostatic latent image, the potential difference between the potential of the electrostatic latent image portion in the energizing phase and the potential of the developer carrier
Maximum value Vu _{1 max} of Vu ₁ is the potential difference between both the reverse biasing phase
Is larger in than the maximum value Vr _{1 max} of vr _1, and oscillating bias voltage time time integral value Iu ₁ potential difference Vu ₁ in the biasing phase of the potential difference Vr ₁ in the reverse bias phase in one period of is greater than the integrated value Ir _1, (b) with respect to the ratio image portion of the electrostatic latent image, the maximum value of the potential difference Vu ₂ between the electrostatic latent image a non-image portion potential on the biasing phase developer carrying member Vu _{2 max} is not less than the maximum value Vr _{2 max} of the potential difference Vr ₂ between the two in the reverse energizing phase, and the potential difference in the energizing phase in one cycle of the oscillation bias voltage.
Vu is the time integral value Iu ₂ of ₂ or less time integration value Ir ₂ of the potential difference Vr ₂ in the reverse biasing phase, further (c) the on the surface of the developer carrying member, a resin layer containing conductive fine particles To provide,
A developing device characterized in that:

According to the developing device of the present invention, in the above configuration, in the energizing phase of the oscillating electric field, a sufficient amount of the developer is supplied not only to a so-called solid portion, but also to a thin line portion and a latent image low potential portion, and Excess developer can be prevented from being removed from these areas in the reverse biasing phase. Nevertheless, a developed image in which fog is sufficiently suppressed can be obtained.

In this specification, the “electrostatic latent image portion” means a maximum potential portion as viewed in absolute value, and the “electrostatic latent image non-image portion” refers to a minimum latent image portion as viewed in absolute value. It means a potential part. Therefore, when the latent image carrier is an electrophotographic photoreceptor, an area where light is not exposed, a so-called dark area potential area is an image area,
Of the image light, a region exposed with the light having the highest intensity, that is, a so-called bright portion potential region is a non-image portion. The toner charged to the polarity opposite to the polarity of the latent image should originally adhere most to the image portion, and it is desired that the toner does not originally adhere to the non-image portion, or if it adheres, the amount is very small.

In any case, the potential region between the image portion and the non-image portion is a halftone region.

Further, in this specification, the “energizing phase” means that a potential (bias voltage) of the developer carrier is applied to the toner in a direction from the developer carrier to the latent image carrier with respect to the potential of the latent image. Means the phase when there is a relationship that gives
It means a phase when the potential (bias voltage) of the developer carrier is in a relationship of giving a toner a force in the direction from the latent image carrier to the developer carrier with respect to the potential of the latent image.

Note that in this specification, the terms “potential” or “potential difference” is used in comparison with an absolute value.

EXAMPLES To avoid complication, the following examples describe the case where the latent image is positive and the toner is negatively charged.

FIG. 1 shows an embodiment in which a developing device according to the present invention is applied to an image forming apparatus based on an electrophotographic method. In this embodiment, the latent image carrier 1 is a cylindrical drum-shaped electrophotographic photosensitive member that rotates in the direction of an arrow, and a photosensitive member in which an amorphous silicon layer is formed as a photosensitive layer on a metal drum that is electrically grounded, for example. Is used.

A charger 3, an image exposure device 4, a developing device 2, a transfer device 5, and a cleaning device 7 are arranged around the photosensitive drum 1. After the transfer, the toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning device 7, and thus the photosensitive drum 1 restored to a clean surface substantially free of toner remains substantially uniformly positively charged by the charger 3. Is charged.
Next, the photosensitive drum 1 is exposed to image light by the exposure device 4 to form an electrostatic latent image. This electrostatic latent image has an image portion potential (dark portion potential V _D ) of, for example, 500 V, and a non-image portion potential (bright portion potential V _L ) of, for example, 50 V. The electrostatic latent image is developed by a developing device 2 described later, and the toner image thus obtained is transferred to a transfer material 6 such as paper by a transfer device 5.

The developing device 2 is a so-called insulating one-component magnetic developer containing no carrier particles (hereinafter referred to as “toner” or “magnetic toner”).
That. A) a container containing T and a base cylinder made of stainless steel, aluminum or the like, supported by the container 21 and rotating at a peripheral speed equal to or higher than the peripheral speed of the photosensitive drum 1 in the direction of the arrow, A non-magnetic cylindrical developer carrier (hereinafter referred to as “developing sleeve”) 22 having a surface layer;
A magnet 23 fixedly arranged inside the developing sleeve 22,
A stirring member 27 for stirring the toner T in the container 21, the developing sleeve 22 has a layer thickness regulating blade 24 for regulating the layer thickness of the toner layer T ₁ for conveying the developing unit A.

According to the present invention, a resin layer containing conductive fine particles is provided on the outer surface of the developing sleeve 22. This conductive particle-containing tree layer has an average volume resistivity in the range of 10 ² to 10 ⁻⁶ Ω · cm, a thickness of between 0.5 μm to 30 μm, and an outermost layer portion having a fine uneven surface. And a conductive fine particle dispersion-containing thin layer having Carbon black and graphite are used as the conductive fine particles, and phenol resin, butyral resin, epoxy resin and the like are used as the resin. Since carbon black is a good conductor, it leaks excessive charge of the toner, and graphite has good fixed lubricating properties, thereby mechanically weakening the strong tendency of the excessively charged toner to adhere to the developing sleeve.

The layer thickness regulating blade 24 is a magnetic member facing the magnetic pole N ₁ of the magnet 23 through the developing sleeve 22, the magnetic toner layer
The thickness of the toner layer is regulated such that the thickness of T ₁ is smaller than the minimum gap α (for example, 250 μm) between the developing sleeve 22 and the drum 1 in the developing section A.

The toner on the developing sleeve 22 flies from the developing sleeve 22 and adheres to the photosensitive drum in the developing section A including the minimum gap between the developing sleeve 22 and the photosensitive drum 1 and the minute section on both sides thereof. That is, the toner is transferred from the developing sleeve 22 to the photosensitive drum 1 by the electric field during the energizing phase, and adheres.
From the developing sleeve 22. Here, the transfer amount and the reverse transfer amount of the toner are different between the image portion and the non-image portion, and the gap between the photosensitive drum 1 and the developing sleeve 22 is enlarged, thereby reducing the electric field strength between the two. The development is completed by weakening. That is, an amount of toner corresponding to the potential of the electrostatic latent image remains on the photosensitive drum 1, and a toner image (visible image) is formed.

The magnet 23 forms a magnetic field in the developing section A, and forms a magnetic pole S ₁ that contributes to reducing toner scattering and fogging, and magnetic poles N ₂ and S ₂ that attract the toner T in the container 21 onto the surface of the developing sleeve 22. Have. The toner mainly obtains a triboelectric charge of negative polarity enough to develop a latent image by friction with the developing sleeve 22.

The developing device 2 includes a power source 2 that constitutes a vibration bias power source.
5, 26 are provided. The power supply 25 generates an alternating voltage having a duty ratio of less than 0.5, and the power supply 26 generates a DC voltage having a value between a bright portion potential and a dark portion potential. Therefore, the developing sleeve
A voltage obtained by superimposing a DC voltage on an alternating voltage is applied to 22 as an oscillation bias voltage. Potential of the image portion of the latent image,
The non-image portion potential is the first peak value V ₁ of the oscillation bias voltage.
When located between the second peak value V _2. Note that the power supply 26 can be omitted.

FIG. 2 shows the developing sleeve 22 when a good result is obtained by developing an electrostatic latent image in which the dark portion potential V _D (image portion potential) is +500 V and the dark portion potential _VL (non-image portion potential) is +50 V. 5 shows a waveform of an applied vibration bias voltage.

This waveform example is a rectangular group having a duty ratio of 0.2, and has a peak value (ie, a latent image non-image portion value peak value) V _{1 in the} energizing phase.
Is -900 V, the peak value of the reverse bias phase (i.e. latent image portion side peak value) V ₂ is + 600V. The power supply 26 is for DC voltage
Generates 300V. And the duration t ₁ of the energizing phase is 100 μs
ec, the duration t ₂ of the reverse biasing phase is 400 μsec.

As will be apparent from Figure 2, with respect to the image portion potential _{V D, Vu 1 max = |} V D -V 1 | = 1400 (V), Vr 1 max = | V D
−V ₂ | = 100 (V), and Iu ₁ = 1400 × t ₁ = 1.4 × 10
⁵ (V · μsec), Ir ₁ = 100 × t ₂ = 0.4 × 10 ⁵ (V · μse
c).

Further, regarding the non-image portion potential _VL , Vu ₂ max = | V _L −V ₁ |
= 950 (V), Vr ₂ max = | V _L -V ₂ | = 550 (V),
Also, Iu ₂ = 950 × t ₁ = 0.95 × 10 ⁵ (V · μ _max ), Ir ₂ = 550
× t ₂ = 2.2 × 10 ⁵ (V · μsec)

That is, for the image portion of the electrostatic latent image, the maximum value Vu _{1 max} of the potential difference Vu ₁ between the potential of the electrostatic latent image portion in the energizing phase and the developing sleeve potential is the potential difference between the two in the reverse energizing phase. is larger in than the maximum value Vr _{1 max} of vr _1, and oscillating bias voltage time integral value Iu ₁ potential difference Vu ₁ in the biasing phase time difference Vr ₁ in the reverse bias phase in one period of Integral value Ir ₁
For the non-image part of the electrostatic latent image, the potential difference between the non-image part of the electrostatic latent image in the energizing phase and the developing sleeve
Potential difference Vr between both maximum values vu _{2 max} of Vu ₂ in reverse biasing phase
₂ is greater than or equal to the maximum value Vr _{2 max} , and the time integral Iu ₂ of the potential difference Vu _{2 in} the energizing phase in one cycle of the oscillation bias voltage is the time integral value Ir of the potential difference Vr ₂ in the reverse energizing phase. _Two
It is as follows.

By the developing device 2 having the above-described configuration, sufficient toner adheres to the image portion to obtain a sufficient density, and the halftone portion is also well visualized including the low potential portion, fine lines are reproduced well, and fog is reduced. Could be removed.

In particular, in the present invention, as described above, unlike the related art, the maximum potential difference between the latent image non-image portion potential and the developing sleeve potential in the energizing phase is larger than the maximum potential difference between the two in the reverse energizing phase. Is also considered great. That is, the toner is strongly urged from the developing sleeve to the photosensitive drum. As a result, a sufficient amount of toner is supplied to the electrostatic latent image portion, a sufficient amount of toner is supplied also to the end of the thin line, and a sufficient amount of toner adheres to the low potential portion.

However, when the toner is strongly urged toward the photosensitive drum, the amount of the toner remaining on the non-image portion increases. That is, fog increases. In order to prevent such fogging, conventionally, the peak-to-peak voltage (peak-to-peak value) of the oscillating voltage is increased to reverse the toner from the photosensitive drum toward the developing sleeve in the reverse biasing phase. The power is also increased, and the toner attached to the non-image area is removed by a strong reverse bias. However, according to this method, not only the toner adhering to the non-image portion but also the toner adhering to the image portion, the thin line portion, and the halftone portion are excessively peeled off, and the reproducibility of the thin line and the low potential portion is removed. Is deteriorated, and the density of the image portion is also reduced.

Therefore, in the present invention, the duty ratio of the oscillating bias voltage is made smaller than 0.5, and the duration of the reverse biasing force is made longer than the duration of the biasing force. In other words, even if the reverse biasing force is relatively weak, by increasing the duration thereof, in other words, the time integral value of the potential difference in the biasing phase
Time integration value Ir ₂ of the potential difference in the reverse biasing phase than iu ₂ by a large, along with fogging toner can be sufficiently removed adhered to the non-image portion, the image portion (including fine line portion), the intermediate An appropriate amount of toner can be adhered and left in each of the adjustment sections (including the low potential section). That is, since the toner adhering to the non-image portion has a weak electrostatic adhesion, even a relatively weak biasing force can be sufficiently removed by applying it for a relatively long time. The toner has an electrostatic adhesion force corresponding to the surface potential of these parts and the halftone part. It will not be removed.

By the way, as one of the problems when such a developing method (one-component non-contact developing method) is adopted, there is a development in which developability is deteriorated due to an increase in adhesion of toner near the surface of the developing sleeve. Generally, this development is called "charging up" of the toner.

That is, the rotation of the developing sleeve 22 causes the toner in the vicinity of the developing sleeve and the developing sleeve to always be in frictional contact, and the charge amount of the toner gradually increases, so that the electrostatic force (cloning force) of the developing sleeve and the photosensitive drum 1 increase. Is a phenomenon in which the toner flying force is weakened, resulting in a decrease in the development density. This occurs due to the low humidity environment and the repetition of the copying process.

The second problem is the development sleeve ghost described above.

When a resin layer containing conductive fine particles is provided on the surface of the developing sleeve 22 in order to solve these problems, the effect of the leak site makes the tribo of the developer on the developing sleeve not only the lower layer (the one closer to the developing sleeve surface) but also The upper layer (the one farther from the surface of the developing sleeve) also decreases, that is, decreases as a whole, and a disadvantage that a desired tribo is difficult to obtain is likely to occur. As a result, the flying ability of the developer is reduced and the developability is deteriorated.

In order to prevent this, the toner on the developing sleeve 22 to which the tribo has not been given yet is held, rotated, and frictionally contacted on the developing sleeve without flying.
It is desirable to wait until sufficient tribo is given to selectively develop. In other words, it is necessary to fly only the developing particles having a sufficient tribo, and to apply a charge to particles smaller than the developing tribo until the tribo increases. This is made possible with the oscillating bias voltage according to the invention.

More specifically, the force for causing the toner to fly from the developing sleeve 22 to the photosensitive drum 1 must be given an acceleration α so that the toner can sufficiently reach the latent image surface by the vibration bias electric field. Assuming that the weight of the toner is m, the force f is = m ·
Given by Assuming that the charge of the toner is q, the distance to the developing sleeve is d, and the vibration bias electric field is E, it can be roughly expressed as follows: = · q− (εε ₀ q ² / d ² ) The force at which the toner arrives at the latent image surface is determined by a balance between the attraction force and the electric field force.

Here, in order to cause the toner near the developing sleeve to also fly, the electric field may be increased. However, simply increasing the bias voltage in the energized phase causes the image to fly to the latent image side irrespective of the latent image pattern, which causes a problem of ground fog. Further, ground fog can be prevented by increasing the bias voltage in the reverse biasing phase. However, when a large vibration bias electric field is applied between the photosensitive drum 1 and the developing sleeve 22, discharge is directly generated between the photosensitive drum 1 and the developing sleeve 22. Occurs, and remarkably disturbs the image quality. Actually, the photosensitive drum 1 and the developing sleeve
When the gap between 22 was experimented with 0.3 mm, the oscillation bias voltage was 2
Leakage occurred above KV.

Also, if the reverse developing bias voltage is increased, not only the non-latent image portion but also the toner developed into the latent image pattern is peeled off. Also, the image quality deteriorates.

From the above results, it is necessary to cause the toner near the developing sleeve to fly and reciprocate while keeping the vibration bias electric field not so large and the reverse developing side bias voltage low.

Accordingly, in the present invention, the duty ratio of the oscillating bias is to increase the developing-side bias electric field and shorten the application time of the developing-side bias electric field. Was used.

In this specification, the “duty ratio” is defined as follows. That is, the oscillation bias voltage is a function of time t.
V _{(t) is} the peak value of the vibration bias voltage
V _1, the value between the latent image portion side peak value V _2, V _S V ₁ and V _2,
In one cycle (t ₁ + t ₂ ) of the oscillation bias voltage, (V _(t) −V _S ) has the same sign as (V ₁ −V _S ) from time 0 to time t ₁ , and time
(V _(t) −V _S ) from t ₁ to time (t ₁ + t ₂ ) is (V ₂ −
V _S ), And

And Thus, the duty ratio is defined by _{t 1 / (t 1 + t} 2).

The duty ratio is 0.2 in FIG. 2 and 0.3 in FIG. 6 described later. In FIG. 6, V _S = 0 (V), t ₁ = 1
50 (μsec) and t ₂ = 350 (μsec).

In any case, in the present invention, an oscillating bias voltage having a duty ratio of less than 0.5 is used.
It is preferably 0.1 or more and 0.4 or less. Duty ratio is
When the value is larger than 0.4, the reproducibility of the fine line is reduced. When the duty ratio is smaller than 0.1, the responsivity of the toner to the oscillating electric field is reduced, and the reproducibility of the gradation region is reduced. Most preferably, the duty ratio is between 0.2 and 0.3.

FIG. 2 shows the waveform of the oscillation bias voltage of the present invention, and FIG. 3 shows the development characteristics. This means that there is a sharp rise in the low-potential latent image portion, which means that it is strong against background fog, and that the developing characteristics from the intermediate potential to the high-potential latent image, which are excellent in gradation, are close to ideal.

In addition, from the viewpoint of preventing charge-up of the toner, the present inventors have proposed that the developing device of the present invention uses two different toner charge amounts.
Similar development characteristics were examined using different types of toners. The charge amount of the toner shown in FIG. 3 is the charge amount per weight of the toner. This experiment uses a negatively charged magnetic toner, and the fact that the initial -10 to -20 μC / g of the toner becomes -1 to -10 μC / g due to the actual high humidity environment or long term suspension of the copying operation It is the result of the model experiment performed based on it.
As a result, as shown in FIG.
It was confirmed that development was possible with almost no influence on the development characteristics even when it changed to -10 μC / g. In other words, by sufficiently increasing the developing-side bias electric field and shortening the application time, it is possible to selectively fly and develop toner having sufficient triboelectricity. This proved to be able to prevent a decline in performance. This suggests that, even when a toner having a lower tribo is used, the higher tribo toner in the toner contributes to the flying as described on the left, and the lower tribo toner shifts to the higher tribo with the rotation of the developing sleeve and contributes to the flying. be able to.

FIG. 5 shows the developing ability of the developing device based on the developing bias waveform having the duty ratio of 50% and the duty ratio of the present invention of 20%.
The relationship between the developing ability of the developing device and the% developing bias waveform is shown. The horizontal axis represents the charge amount of the toner, and the vertical axis represents the layer thickness of the toner transferred to the developed photoconductor on the photoconductor.

The conventional device having a duty ratio of 50% has developability from −1 μC or more. In the developing device of the present invention, developability does not appear unless the temperature exceeds -3 μC. This means that, in the developing device of the present invention, the toner of -3 [mu] C or less cannot fly with a 20% bias waveform, remains on the developing sleeve, and undergoes a tribo-imparting operation on the developing sleeve. -3
When the toner of μC or less becomes −3 μC or less due to the application of the tribo, the toner starts flying for the first time, and developability appears. On the other hand, according to the conventional developing device,
In order to fly even a toner having a low tribo of around 1 μC / g, the image quality is easier to fog, the character reproducibility is inferior, and the image is rougher than the apparatus of the present invention having a 20% bias waveform in image quality.

Specifically, in the present embodiment, the gap between the developing sleeve 22 and the photosensitive drum 1 is 0.3 mm. However, according to the developing method of the present invention, sufficient development is possible in the range of 0.1 mm to 0.5 mm. is there. This is a result of the present invention that the developing side bias is larger than the conventional developing method, so that the developing can be performed even if the gap between the developing sleeve 22 and the photosensitive drum 1 is large. FIG. 4 shows the stability of the image density with respect to the absolute value of the oscillation bias voltage.

From FIG. 4, it was found that even if the toner charge amount fluctuated from -1 to -10 .mu.C / g, a sufficiently satisfactory image could be obtained if the absolute value of the vibration bias voltage was 1.0 KV or more.

Further, considering the leakage to the photosensitive drum, that is, the latent image carrier 1, the absolute value of the vibration bias voltage is desirably 1.0 KV or more and 2.0 KV or less. However, this leak naturally varies depending on the gap between the developing sleeve 22 and the photosensitive drum 1.

Next, the vibration bias frequency, 5.0KH _Z is preferably from 1.0KH _Z. When the frequency is below 1.0KH _Z, but gradation is improved, it is difficult to eliminate fogging. This is because, in a low frequency region where the number of reciprocating movements of the toner is small, the pressing force of the toner against the photosensitive drum 1 by the developing bias electric field becomes too strong even in the non-image area, and the toner is stripped off by the reverse developing side bias electric field. This is probably because the toner attached to the non-image area cannot be completely removed. And
Frequency 5.0KH _Z becomes more than the toner developability will be bias field of reverse development-side is applied is significantly reduced in less sufficient contact with the photosensitive drum 1. That is, the toner itself cannot respond to the high-frequency electric field.

In particular, according to the present invention, the frequency of the oscillating bias electric field is 1.
Optimum image quality was shown from 5KH _Z to 3KH _Z.

Finally, it is sufficient that the duty ratio satisfying the vibration bias electric field waveform of the present invention is less than approximately 50%, but it has been found that 10% ≦ duty ratio ≦ 40% in consideration of image quality. When the duty ratio is 40% or more, the above-mentioned drawbacks are conspicuous and are not very preferable. The effect of the present invention is not so much recognized. When the duty ratio is 10% or less, the above-described vibration bias electric field response of the toner itself is deteriorated, and the developability is reduced. Especially the optimal value of the duty ratio is
20% ≦ duty ratio ≦ 30%.

In this embodiment, the negatively chargeable toner is used, but the positively chargeable toner does not change at all. Further, in this embodiment, a high-low anti-one component magnetic toner is used as a developer, but it is very effective for non-contact development of a high-low anti-non-magnetic one-component toner.
Further, it goes without saying that the present invention can be applied to the reversal developing method.

When copying durability was actually performed using the vibration bias voltage of the present invention, no reduction in density and image quality due to insufficient charge of toner, which had been a problem in the past, was observed.

In the above embodiment, the oscillation bias waveform has been described as a rectangular wave bias waveform. However, another waveform may be used, and FIG. 6 shows another embodiment in which the bias waveform is changed.

FIG. 6 shows a waveform obtained by changing the duty ratio of a normal sine waveform vibration bias. FIG. 7 shows the developing characteristics at this time.

Compared with FIG. 8 of the above example, a good image with excellent gradation was obtained although the developability was slightly inferior.
Further, it can be seen that the toner is strong against the fluctuation of the charge amount of the toner.
In other words, there is a phenomenon in which the rectangular waveform of the developing bias power supply slightly decreases due to the relationship between the impedance and the capacity of the developing device.
The effect is not a problem in the present invention, and it is considered that the latitude of the vibration bias waveform is widened.

The above is an example of the duty ratio control of the sine waveform vibration bias, but it can be sufficiently applied to a vibration bias waveform such as a sawtooth wave and a triangular wave.

The present invention Figure 8, as shown in FIG. 9, a rubber blade, and the thickness above embodiment of the toner layer T ₁ by the elastic blade 28, 29 of the metal plate spring blade or the like is pressed against the developing sleeve 22 The same effect was obtained with a developing device having a configuration in which the thickness is regulated to the same value. In addition, the surface condition of the developing sleeve was effective for the blast surface due to the mirror surface and the irregular shaped particles, and the blast surface due to the granular particles, and was also effective for aluminum and SUS as the developing sleeve material.

Effects of the Invention As described above, the following effects are obtained by using the developing device of the present invention.

(1) Insufficient charge of toner can be prevented, and good image density can always be obtained.

(2) The developability is hardly affected by the change in the charge amount of the toner.

(3) Ideal development characteristics can be obtained, and image quality excellent in background fog and excellent in gradation can be obtained.

(4) Sharp line reproduction with an edge effect becomes possible, and very excellent image quality can be obtained.

(5) The latitude for the vibration bias waveform is wide.

(6) The developing sleeve ghost disappeared.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic image forming apparatus employing a developing device of the present invention. FIG. 2 is a diagram showing a vibration bias waveform in the developing device of the present invention. FIG. 3 is a diagram showing the effect of the present invention. FIG. 4 is a diagram showing the effect of another embodiment of the present invention. FIG. 5 is an explanatory diagram showing the effects of the present invention and the conventional device. FIG. 6 is a diagram showing another vibration bias waveform of the present invention. FIG. 7 is a diagram showing the effect of the developing device of the present invention having the vibration bias waveform of FIG. 8 and 9 are schematic structural views of a developing device according to still another embodiment of the present invention. FIG. 10 is a diagram showing a bias waveform of a conventional developing device. FIG. 11 is a diagram showing the effect of the developing device of FIG. FIG. 12 is a diagram showing a bias waveform of another conventional developing device. FIG. 13 is a view showing the effect of the developing device of FIG.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/06 101 G03G 15/08-15/09

Claims (1)

(57) [Claims] A developer carrying member for carrying a developer layer;
In a developing device for applying an oscillating bias voltage to the developer carrying member to develop an electrostatic latent image formed on the latent image carrying member, (a) an image portion of the electrostatic latent image in an energized phase The maximum value Vu _{1 max} of the potential difference Vu ₁ between the electrostatic latent image portion potential and the developer carrier potential is larger than the maximum value Vr _{1 max} of the potential difference Vr ₁ between the two in the reverse biasing phase, The time integral Iu ₁ of the potential difference Vu ₁ in the energizing phase in _one cycle of the oscillation bias voltage is the time integral value Ir ₁ of the potential difference Vr ₁ in the reverse energizing phase.
(B) For the non-image portion of the electrostatic latent image, the maximum value Vu _{2 max} of the potential difference Vu ₂ between the electrostatic latent image non-image portion potential in the energizing phase and the developer carrier is: It is equal to or greater than the maximum value Vr _{2 max} of the potential difference Vr ₂ between the two in the reverse bias phase, and the time integral value Iu ₂ of the potential difference Vu _{2 in} the bias phase in one cycle of the oscillation bias voltage.
Is not more than the time integral value Ir ₂ of the potential difference Vr ₂ in the reverse biasing phase, and (c) providing a resin layer containing conductive fine particles on the surface of the developer carrying member. Developing device.