JPH08137221A - Developing device - Google Patents

Abstract

PURPOSE: To secure sufficient density in a solid image and to obtain excellent line reproducibility without causing fogging in a background part even to the increase of the charge amount of developer while preventing a power source device from getting large and cost from increasing. CONSTITUTION: In a system for impressing developing bias VB obtained by switching DC voltage in a very short cycle; a developing bias impressing means 3 is equipped with a DC voltage source 4, a switching means 5 turning on/off developing bias DC voltage from the voltage source 4 in the very short cycle, and an excess bias component adding means 6 adding an excess bias component ΔVS temporarily exceeding a developing bias set value VS as an absolute value is added to the start point of the rise part of the developing bias DC voltage at the time of on-operation of the switching means 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an electrophotographic copying machine, a printer or the like, which visualizes a latent image on a latent image carrier with a developer, and in particular, switches a DC voltage in a minute cycle. The present invention relates to an improvement in a developing device of the type that applies a developing bias.

[0002]

2. Description of the Related Art Conventionally, as a method of developing an electrostatic latent image, a method of applying various developing biases to a developer carrying member has been known. For example, there is a jumping developing method as disclosed in JP-A-54-51848.
In this developing method, since an alternating electric field is used as the applied developing bias, a direct current voltage on which an alternating current voltage is superimposed is used. Specifically, as shown in FIG. 6, Vh with respect to the non-image portion potential Vh and the image portion potential Vi on the latent image carrier is Vh.
A developing bias having a waveform in which an alternating current component Vac which is a peak-to-peak voltage Vpp is superimposed on a direct current component Vdc located between V and Vi is used.

However, in order to generate the developing bias using the alternating electric field, since the peak-to-peak voltage Vpp of the AC voltage is several kV, it is unavoidable to use the AC generating high-voltage transformer. In addition to the increase in size and cost of the power supply device, there is also a problem that a leak on the latent image carrier easily occurs.

Therefore, as shown in FIG. 7, it is conceivable to use only the DC component Vdc that does not use the AC component Vac for the developing bias. In this case, the developing ability increases in proportion to the magnitude of the developing contrast Vc depending on the developing contrast Vc which is the difference between the DC component Vdc and the image portion potential Vi in absolute value. Therefore, the DC component Vdc is set to the non-image portion potential V
The approach to h is performed.

However, when only the DC component Vdc is used, the development contrast Vc cannot be said to be sufficient, and the solid density (density for a solid image) may be insufficient. In particular, in the case of a non-magnetic one-component developer, a sufficient solid density cannot be obtained unless the developer has a large adhesion to the developing roll (developer carrier) and the development contrast Vc is increased. Further, in the developing area, the flight direction of the developer is one direction from the developing roll to the latent image carrier, and in the magnetic one-component developer, the developer adheres to the latent image in the state of a chain, and therefore blurs around the line. (Scattering phenomenon of toner), tail buzzing (phenomenon in which toner trails toward the rear end in the process direction), and the like occur.

Therefore, if the DC component Vdc is made larger than the non-image portion potential Vh in order to increase the development contrast Vc, naturally the background portion fog increases. Therefore, the development contrast Vc cannot be larger than the difference between the non-image portion potential Vh and the image portion potential Vi in absolute value.

In order to solve such technical problems,
As a method of cheaply putting the developer in the cloud state, FIG.
As shown in FIG. 2, a method of applying a developing bias in which a DC voltage is switched in a minute cycle can be considered. The parameters in the figure are the minimum gap d (μm) between the latent image carrier and the developing roll, the non-image part potential Vh on the latent image carrier, the image part potential Vi, and the maximum voltage value (setting value) Vs of the developing bias. , A switching cycle, that is, a frequency f (Hz), and a ratio a of on time to the sum of on time and off time of switching. When such a developing bias is used, the maximum voltage value Vs of the developing bias shown in the figure is 100 at most.
Since it is 0V, the power supply device does not become large and expensive,
Moreover, there is no problem that a leak occurs on the latent image carrier. Further, since the developer can be put in a cloud state, it is possible to obtain excellent line reproducibility.

[0008]

However, the above conventional techniques have the following technical problems. That is, when the charge amount of the developer increases and the adhesive force to the developing roll is large (for example, when the ambient atmosphere is low temperature and low humidity, or when the triboelectric charging series of the developing roll and the developer are greatly separated), the developing bias With the maximum voltage value Vs of, the toner of the developer cannot be released from the developing roll, and as a result, the cloud is not sufficiently formed, and not only the solid density is lowered but also the line reproducibility is deteriorated. A challenge was found.

The present invention has been made in view of the above technical problems, and on the premise of a method of applying a developing bias in which a DC voltage is switched in a minute cycle, the power supply device can be increased in size and cost. Provided is a developing device capable of ensuring sufficient density in a solid image and obtaining excellent line reproducibility without causing background fog even when the amount of charge of the developer is increased while avoiding. To do.

[0010]

That is, the present invention provides:
As shown in FIG. 1, a latent image carrier 1 is provided with a developer carrier 2 arranged to face the latent image carrier 1, and a developing bias VB is applied to the developer carrier 2 so that the latent image carrier 1 is formed on the latent image carrier 1. In the developing device which develops the electrostatic latent image Z formed on the developing agent G with the developer G on the developer carrying member 2 to form a visible image, the developing bias applying means 3 includes a DC voltage source 4 and A switching means 5 for turning on and off the developing bias DC voltage from the DC voltage source 4 in a short cycle, and a developing bias set value which is an absolute value with respect to the starting point of the rising portion of the developing bias DC voltage when the switching means 5 is on. And an excess bias component adding means 6 to which an excess bias component ΔVS exceeding VS is added.

In such a technical means, the present invention can be applied to both contact development and non-contact development, but non-contact development, which is a development method by flying a developer, is more effective. Further, the rising portion of the developing bias DC voltage of the present invention broadly refers to a changing portion of the developing bias DC voltage when the switching means 5 is turned on, and for example, the developing bias DC voltage is either positive or negative. Even so, the pulse portion generated when the switching means 5 is turned on is called a rising portion.

Further, the excessive bias component ΔVS may be appropriately selected from the viewpoint of promoting the developing property and effectively preventing the leak between the latent image carrier 1 and the latent image carrier 1. When the minimum gap between the carrier 1 and the developer carrier 2 is d (μm), | 1.1 × VS |
It is preferable to satisfy ≦ | VS + ΔVS | ≦ 10d (unit: volt).

[0013]

According to the technical means as described above, in the developing operation process in which the developing bias VB in which the DC voltage is switched in a minute cycle acts, the rising portion of the developing bias VB has the bias setting value Vs, Carrier 2
The developer G is applied with a moving force in the direction of acceleration of development toward the latent image carrier 1 side. However, this moving force alone increases, for example, the amount of charge, and the developer G strongly adhered to the developer carrier 2. In this case, the toner is not separated from the developer carrying member 2. However, in the present invention, the developing bias VB
Since the excessive bias component ΔVs acting in the development promoting direction is temporarily added to the start point of the rising portion of the developer G, the charge amount increases and the developer G strongly adhered to the developer carrier 2.
This toner is also effectively separated from the developer carrying member 2.
As a result, the amount of toner itself flying from the developer carrying member 2 toward the latent image carrying member 1 increases, and the latent image carrying member 2 develops with the developing bias VB in which the DC voltage is switched in a minute cycle. In the two directions of the image carrier 1 and the latent image carrier 1 to the developer carrier 2, the toner of the developer reciprocates in the developing region to form a cloud, and the toner of the necessary developer is a solid latent image. Not only that, it surely adheres to the line latent image.

Further, since the excessive bias component ΔVs has only the action of separating the developer G from the developer carrier 2, it has almost no influence on the average value of the development bias. Therefore, it is possible to variably set the developing bias independently of other parameters (for example, the developing bias setting value VS), and this excess bias component ΔVs is a useful parameter in design.

Further, by setting the above-mentioned excess bias component ΔVs in the optimum range, leakage to the latent image carrier 1 due to the developing bias can be effectively avoided while maintaining the above-mentioned effect of promoting the developing property.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. FIG. 2 shows an embodiment of a magnetic one-component developing device to which the present invention is applied. In the figure, 1
Reference numeral 1 denotes a photoconductive drum (latent image carrier) having a surface made of a negatively charged organic photoconductor, and for example, an entire surface is uniformly charged by a charger (not shown) and then an optical writing unit (see FIG. It is exposed to light (not shown) and carries an electrostatic latent image. At this time, the non-image area is, for example, −300V, and the potential of the image area (exposure portion) 12 of the electrostatic latent image is −45V.

Further, reference numeral 13 is a hopper for accommodating the one-component magnetic toner 14, and the toner 14 contains 40% of magnetic powder. Reference numeral 15 is a magnet roll having a magnetic pattern as shown by N and S in the figure, and a cartridge (not shown)
It is fixed to. 16 is aluminum with a wall thickness of 0.6 m
m conductive sleeve (developer carrier)
And is rotatably supported around the magnet roll 15. In this embodiment, the minimum gap between the sleeve 16 and the photoconductive drum 11 is set to about 100 μm. Further, reference numeral 17 is a toner amount regulating member, and urethane rubber having a thickness of 1.0 mm is used. The toner amount regulating member 17 abuts on the surface of the sleeve 16 at a position on the opposite side of the developing area by about 180 °, and its free end direction is set to face the rotational direction of the sleeve 16. Further, reference numeral 18 is an agitator for stirring and supplying the toner.

Further, the developing bias VB from the bias applying device 20 is applied to the sleeve 16. As shown in FIG. 3, the bias applying device 20 used in this embodiment includes a DC voltage source 21 that outputs a DC voltage having a developing bias setting value Vs (-500 V in this embodiment).
A switching element 22 for turning on and off the developing bias DC voltage from the DC voltage source 21 at a minute cycle set by a timer (not shown), and an excessive bias adding circuit 23.
It consists of and.

Further, in order to investigate the inclination characteristic of the rising portion of the developing bias of the one-component developing device having the above-mentioned constitution, the DC voltage source 2 is added without adding the excessive bias component.
The developing bias setting value according to 1 is Vs = -500 (V),
Further, the switching frequency of the switching element 22 is f = 100.
0 (Hz), the developing bias VB is applied to the conductive sleeve 16 with the ratio of the ON time to the sum of the ON time and the OFF time of the switching element 22 being a = 0.7, and as shown in FIG. There are four kinds of inclinations of the rising part (A: when there is almost no delay in rising, B: when there is a delay of 100 μs in the rising, C: when there is a delay of 200 μs in the rising, and D: 300 when rising.
When the solid latent image and the line latent image (non-image portion potential: −400 V, image portion potential: −55 V under these experimental conditions) were developed, the results shown in Table 1 below were obtained. was gotten.

[0020]

[Table 1]

In Table 1, ∘ indicates an allowable value, Δ indicates an amount that does not reach the allowable value, and x indicates a level of image quality failure.
According to Table 1, as the slope of the rising portion of the developing bias becomes gentle, the solid density decreases, and
It was confirmed that blur was seen in the line image. Therefore, in order to effectively fly the developer, it is understood that a steep rising voltage is required as the developing bias, such as A. Therefore, in this embodiment, a steep slope of the rising portion of the developing bias from the DC voltage source 21 by the switching element 22 is selected (about 10 μs in this embodiment).

Further, when the developing bias waveform (the output end of the varistor 23) was examined in the one-component developing device having the above-mentioned structure, the result as shown in FIG. 5 was obtained. According to FIG. 5, when the switching element 22 is turned on, the excess bias component is superposed on the starting point of the rising portion of the developing bias, and the developing bias temporarily holds the developing bias set value VS (-500 (V) in this embodiment). It is understood that Vos (developing bias setting value Vs + excess bias component ΔVs) is exceeded. In FIG. 5, Vh is a non-image portion potential (-300 (V)) and Vi is an image portion potential (-45 (V)). It is considered that the excessive developing bias portion Vos facilitates the release of the toner, which is the developer, from the sleeve 16 and contributes to the function of promoting the cloud formation of the toner.

In order to confirm such an action, first,
In a normal environment (in this embodiment, the ambient atmosphere is a temperature of 24 degrees,
At a humidity of 24%), the developing bias setting value is Vs =-
500 (V), the switching frequency of the switching element 22 is f = 2000 (Hz), and the ratio of the on time to the sum of the on time and the off time of the switching element 22 is a = 0.
4 and the number of turns N of the transformer in the excess bias circuit 23
By changing P and NQ, the developing bias excess portion V
os is -500 (V), -600 (V), -700
(V), -800 (V), -900 (V), -1000
A solid image and a line image (in this experimental condition, non-image portion potential: -300 (V), image portion potential: -46 (V)) were developed while being changed to (V) and -1100 (V). The results shown in Table 2 were obtained.

[0024]

[Table 2]

In Table 2, ◯ indicates that the value is within the allowable value. According to Table 2, the excessive developing bias portion Vos is -50.
From 0 (V) to -1000 (V), both the solid density and the level of the blur of the line show a good state. However, the developing bias excess portion Vos is -1100.
In the case of (V), a leak on the photoconductive drum 11 is observed, and it cannot be practically used. Therefore,
In a normal environment, the developing bias excess portion Vos (V)
The maximum voltage value of | Vs | ≦ | Vos | ≦ 10d (however, d
(Μm) is the minimum gap between the sleeve 16 and the photoconductive drum 11, which in this example is 100 μm).

Further, such an excessive developing bias portion Vos
When (-500 (V) to -1000 (V)) was applied, when the amount of toner in the non-image area on the photoconductive drum 11 was examined, almost no toner fog was observed.

Next, as a case where the adhesive force of the developer to the sleeve 16 becomes strong, for example, when the ambient atmosphere is 10 degrees Celsius,
Taking a case where the humidity is 20% (low temperature and low humidity) as an example, under the same conditions as described above, the solid image and the line image (in this experimental condition, the non-image Partial potential: -300 (V), image part potential: -46 (V)) was developed, and the results shown in Table 3 were obtained.

[0028]

[Table 3]

In Table 3, ∘ indicates an allowable value, Δ indicates a level slightly deviating from the allowable value, and x indicates an image quality defect level.
According to Table 3, the developing bias excess portion Vos is -600.
Only in the case of (V) to -1000 (V), both the solid density and the level of the blur of the line are in a good state. When the lower limit of the developing bias excess portion Vos was examined, it was confirmed that a good state was exhibited up to −550 (V). Further, when the developing bias excess portion Vos was 1100 (V), a leak on the photoconductive drum 11 was observed, and it was confirmed that it could not be practically used. Therefore, when the adhesive force of the developer to the sleeve 16 is strong, the developing bias excess portion Vos is stably maintained.
In order to bring out the effect of the
The maximum voltage value of (V) is | 1.1 × Vs | ≦ | Vos | ≦ 1
0d (however, d (μm) is the minimum gap between the sleeve 16 and the photoconductive drum 11, and is 100 in this embodiment.
μm), preferably | 1.2 × Vs | ≦ | Vos
It is necessary that | ≦ 10d.

Further, such an excessive developing bias portion Vos
When (-550 (V) to -1000 (V)) was applied, the amount of toner in the non-image area on the photoconductive drum 11 was examined, and almost no toner fog was observed.

Further, the ambient atmosphere was set to be the same as that at the time of low temperature and low humidity, and the minimum gap d between the sleeve 16 and the photoconductive drum 11 was changed to 160, 200, 250 (μm). Similar effects were seen.

In the above-mentioned embodiment, the effect of increasing the adhesive force of the developer to the sleeve 16 due to the change of the ambient atmosphere is shown, but the present invention is not limited to the above-mentioned embodiment, and is not limited to the above-mentioned example. The same applies to the case where a magnetic one-component developer is used, and even if the ambient atmosphere changes, the developer is effectively separated from the developer carrying roll, and stable developing property (solid concentration, line It was confirmed to obtain a blur level).

[0033]

As is apparent from the above description, according to the present invention, in the type in which the developing bias in which the DC voltage is switched in a minute cycle is applied to the developer carrying member, the starting point of the rising portion of the developing bias is set. By adding an excessive bias component, the release of the developer from the developer carrier is positively promoted. Therefore, even when the adhesive force of the developer to the developer carrier is increased,
It is possible to reliably put the developer in the cloud state,
To that extent, not only the concentration of the solids but also the line reproducibility can be remarkably improved.

Further, since the excessive bias component has only the effect of promoting the release of the developer from the developer carrying member,
No increase in toner fog due to excess bias component is seen, and other advantages of the developing device that applies a developing bias that is switched in a short cycle to the developer carrier, for example, to prevent cost reduction of the developing bias power supply Nor.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a developing device according to the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of a developing device to which the present invention is applied.

FIG. 3 is an explanatory diagram showing a specific example of the developing bias applying device according to the embodiment.

FIG. 4 is an explanatory diagram showing a tilt characteristic of a rising portion of a developing bias used in an example.

FIG. 5 is a graph showing a developing bias waveform used in Examples.

FIG. 6 is a graph showing a conventional DC superimposed AC developing bias waveform.

FIG. 7 is a graph showing a conventional DC developing bias waveform.

FIG. 8 is a graph showing a developing bias waveform in which a conventional DC voltage is switched in a minute cycle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Latent image carrier, 2 ... Developer carrier, 3 ... Development bias applying means, 4 ... DC voltage source, 5 ... Switching means, 6
... Excess bias applying means, G ... Developer, Z ... Electrostatic latent image,
VB ... Development bias, Vs ... Development bias set value, ΔVs
… Excessive bias component

Claims (2)

[Claims] 1. A developer carrying member (2) disposed so as to face the latent image carrying member (1), and a developing bias (VB) is applied to the developer carrying member (2). In the developing device which develops the electrostatic latent image (Z) formed on the latent image carrier (1) with the developer (G) on the developer carrier (2) to form a visible image, The bias applying means (3) includes a direct current voltage source (4), a switching means (5) for turning on and off a developing bias direct current voltage from the direct current voltage source (4) in a minute cycle, and an on operation of the switching means (5). An excess bias component adding means (6) for temporarily adding an excess bias component (ΔVS) exceeding the development bias set value (VS) to the starting point of the rising portion of the development bias DC voltage at the time of absolute value. A developing device characterized in that 2. The device according to claim 1, wherein the minimum gap between the latent image carrier (1) and the developer carrier (2) is d (μ
m), | 1.1 × VS | ≦ | VS + ΔVS | ≦
A developing device which satisfies 10d (unit: volt).