JPS61239254A - Reversal developing method - Google Patents

Abstract

PURPOSE:To prevent photographic fog and to attain images having high quality by using a pulse voltage which has the same polarity as electrification of a photosensitive body and has a pulse width in a prescribed range as a bias voltage. CONSTITUTION:An electrifier 2, a laser beam 3 which forms a prescribed electrostatic latent image, a reversal development device 4, a transfer device 6, a cleaner 7, a destaticizing lamp 8, etc. are arranged around a photosensitive drum 1. The development device 4 consists of a nonmagnetic sleeve 41, a fixed magnet gathered body 42, a layer thickness control member 43 and a toner vessel 44 and a DC power source 46 is connected to the nonmagnetic sleeve 41 through a switching circuit 45. The pulse voltage whose polarity is equal to that of electrification of the photosensitive drum 1 and waveform width is 0.1-5.0msec and rise is sharp is used as the DC bias given to the nonmagnetic sleeve 41.

Description

Detailed Description of the Invention "Industrial Application Field J This invention relates to a reversal developing method applied to electrophotography and electrostatic recording, and particularly relates to a reversal developing method using a -component high-resistance magnetic toner. .

``Conventional techniques l#J Conventionally, laser beam, optical fiber, LE
2. Description of the Related Art Image forming apparatuses such as printers and facsimile machines that form an uncharged electrostatic latent image on a photoreceptor whose entire surface is charged using an exposure means such as a D or LCD are already known. Furthermore, a microfilm system is already known that uses a positive film to form a similar electrostatic latent image on the photoreceptor.

Unlike electronic copying machines, these devices apply toner charged with the same polarity as the photoreceptor to a negative (uncharged) electrostatic latent image on the photoreceptor formed by the exposure means. In other words, toner is not attached to non-exposed areas that have an electrostatic charge due to electrostatic repulsion, and the toner is transferred only to the electrostatic latent image area that is non-charged. A so-called reversal development method is used.

In this type of development method, it is advantageous to use a single-component magnetic toner from the viewpoint of downsizing the device, stabilizing development, free maintenance, etc., and in particular, it is advantageous to use a high-resistance magnetic toner from the viewpoint of improving transfer efficiency. It is already known that
As a reversal development method using a high-resistance magnetic toner having such a component, there is a magnetic brush development method (in which development is carried out by rubbing a magnetic brush formed on a toner carrier carrying the magnetic toner on the surface of a photoconductor). Japanese Patent Publication No. 58-2705, Japanese Unexamined Patent Publication No. 55-134884, etc.) are known.

However, in this developing method, development is performed by rubbing the toner over almost the entire surface of the photoreceptor, so the toner also adheres to non-exposed areas where electrostatic charges with electrostatic repulsion exist, causing fogging. Moreover, the photoreceptor is abraded due to the above-mentioned rubbing, resulting in a decrease in durability.

In order to eliminate this drawback, a direct current bias voltage or an alternating current bias voltage formed by superimposing an alternating current voltage on the direct current bias voltage is applied to the side of the toner carrier disposed facing the photoreceptor with a predetermined distance between them. A developing method in which toner is transferred from a toner carrier to an electrostatic latent image area of a photoreceptor using a bias voltage (JP-A-54-8!3733, JP-A-55-1348)
f (4, JP-A-58-48349, etc.) exists.

"Problems to be Solved by the Invention" However, the following drawbacks occur in the developing method that applies a DC bias voltage.

(2) That is, the image density in the above development method is generally determined by the difference between the DC bias potential Vd and the latent image surface potential Vw of the photoreceptor. Since the potential Vd must be set below the surface potential vb of the non-exposed part of the photoreceptor, in order to obtain a high-quality image with high contrast, the surface potential vb of the non-exposed part must be made high. As a result, the degree of fatigue of the photoreceptor increases, leading to a decrease in durability.

(■Also, in order to eliminate the above-mentioned drawbacks as much as possible, if the DC bias potential Vd is formed close to the surface potential Vb of the non-exposed part of the photoreceptor, the background density of the exposed document will vary,
Also, due to variations and fluctuations in the non-exposed portion surface potential (b), there is a portion where the DC bias potential Vd becomes higher than the non-exposed portion surface potential vb, and fogging occurs in that portion.

(2) Furthermore, if the same level of potential is continued to be applied to the toner carrier for a long time, the charged polarity of the toner on the toner carrier becomes stronger. When the application of the potential is finished, the toner carrier is strongly charged to the opposite polarity to the toner on the toner carrier, which has a strong charging polarity, and the toner is attracted onto the toner carrier. Therefore, uneven charging naturally occurs in the single layer of toner on the carrier, and if development is performed in this state, fogging may occur, or image blurring or double images may occur due to edge effects.

On the other hand, in the latter developing method (JP-A-54-89733), which uses an alternating bias voltage formed by superimposing an alternating current voltage on a direct current bias voltage having a potential equal to or close to the surface potential vb of the non-exposed area, Although the pulsation effect eliminates the charging unevenness of the toner layer, since the peak side potential of the alternating bias voltage is higher than the non-exposed area surface potential vb, fogging is likely to occur, and what are the disadvantages of (1) and (2) above? Not only is this problem impossible to solve, but since the alternating current voltage is superimposed, the problem becomes a commercial voltage, which reduces safety.

A technical problem to be solved by the present invention is to provide a reversal development method that can obtain high-quality images without causing fogging.

Another object of the present invention is to maintain the potential of the non-exposed portion of the photoreceptor, that is, the charging potential, at a low potential to improve durability.

Another object of the present invention is to prevent uneven charging in a single layer of toner on a carrier and to obtain clear images.

"Summary of the Invention" First, the process leading to the completion of the present invention will be explained step by step.

In the reversal development method in which toner is transferred to the electrostatic latent image portion of the photoreceptor by a bias voltage, the toner is transferred to the electrostatic latent image portion of the photoreceptor because the toner layer carried on the toner carrier and the photoreceptor are in a non-contact state. In order for the toner to transfer from the carrier to the photoreceptor, a finite time consisting of "toner flight speed S x development interval L" is required, and the above flight speed S is determined by the electric field that exists between the development intervals, that is, the bias. It is determined by the difference between the voltage Vbias and the photoreceptor surface potential (Vw or vb). Therefore, even if the bias voltage is constant, if the photoreceptor surface potential (Vw or vb) differs, the flying speed S of the toner will naturally change. will show different values.

Therefore, for example, even if the bias voltage is set to be larger than the non-latent image surface potential (exposure area potential) vb, the application time t of the bias voltage is determined by α(Vbias-Vw)X development interval. If the toner flight time t1 is set to be larger than the toner flight time t1 of the exposed area and smaller than the toner flight time t2 of the non-exposed area determined by α(Vbias-vb) x development interval, toner will not transfer to the exposed area. Even if the toner is not exposed to light, the toner will not be transferred to the non-exposed areas. (The above α is a constant) However, in this case, if the bias voltage is composed of a pulse voltage whose peak value and valley side voltage level are both the same polarity as the charged polarity of the photoreceptor, the bias voltage can be adjusted to the toner polarity and It is possible to maintain the same polarity as the photoreceptor charge polarity, and there is no problem in performing reversal development, and the application time t (pulse width), maximum potential, frequency, etc. Another advantage is that it can be freely and easily set according to the range.

Based on this idea, the present inventor conducted extensive research and repeated experiments, and found that the bias voltage is a pulse having the same polarity as the charged polarity of the photoreceptor and whose waveform has steep rises and falls. It has been found that the above object can be smoothly achieved by using a voltage and setting the pulse width to 0.1 to 5°0 m5ec.

Therefore, according to the present invention, it is possible to lower the surface potential of the non-exposed portion of the photoreceptor below the bias voltage level within the range of the following formula only by using the pulse voltage. The present invention is not limited to the case where the pulse voltage is set to the surface potential of the non-exposed part or higher, but also when the pulse voltage is set to the surface potential of the non-exposed part or lower, the effects described later can be smoothly achieved and are included in the technical scope of the present invention. .

l Vb l > l Vbias/ a l +b
V・-a)■b: Surface potential of the non-exposed part of the photoconductor Vbias: Peak value of pulse voltage 1.52<a<1.88. −20<b<110
In addition, a pulse voltage having the same polarity as the charged polarity of the photoreceptor and whose waveform has steep rises and falls is
Generally, it is formed by a rectangular wave pulse obtained by switching a DC power source (see Figure 1 A), but it is not necessarily limited to this. For example, it can be formed by connecting a rectifier circuit and a clipper circuit to an AC power source. or by connecting a slicer circuit whose lower clip level is set to Ov or a voltage level with the same polarity as the charged polarity of the photoconductor, a substantially trapezoidal pulse voltage whose waveform has steep rises and falls ( (see FIG. 1B) is formed.

Therefore, the pulse voltage simply means that the valley side voltage level is OV.
or has the same polarity as its peak value, regardless of whether the pulse generating power source is an AC power source or a DC power source. In this case, it is natural that the valley side voltage level is preferably lower than the latent image surface potential of the photoreceptor.

Further, as mentioned above, the pulse width of the DC pulse is 0.
1-5.0 m5ec, preferably 0.15-)2ms
It is best to set it within the ec range, but the pulse width should be set within the range of
4 It is easy to determine the relationship between the Tey ratio and the frequency. For example, when the duty ratio of the DC pulse is 50%, the frequency is 100 to 5000H2, preferably 50%.
By setting it to 0 to 3000H2, it is possible to obtain a pulse width within the above range. Of course, the duty ratio does not necessarily need to be set to 50%, and it is possible to change the duty ratio as appropriate in relation to the frequency.

Further, in the present invention, it is preferable that the development interval between the toner carrier and the photoreceptor be larger than the thickness of one layer of toner carried on the toner carrier.

Furthermore, by setting the pulse voltage within the range of the following formula, the potential difference r can be set to a value sufficient to obtain high quality image density.
V bias -Vw J can be taken, and high quality images can be maintained in both solid density and line density.

l Vbiasl > c X l Vw l -d V
2.5 < c < 3.3 , -35 < d < 135 "Effect" According to this invention, the pulse voltage of the above structure that changes periodically as the bias voltage is used as the bias voltage. As a result, there is no risk of space charge being generated between the toner carrier and the developer container, and as a result, uneven charging in the toner layer on the carrier is prevented, and the developed image is Clear images can be obtained without blurring or double images.

Furthermore, in the present invention, in particular, by configuring the pulse voltage with a rectangular wave pulse obtained by switching a DC power supply, the potential, frequency, and duty ratio can be easily changed, and as a result, the behavior of the toner can be regulated. becomes easier,
Optimal images without variations can always be obtained.

Further, according to the present invention, within the range of the above formula (a), the potential vb of the non-exposed part of the photoconductor is adjusted as shown in FIGS.
Even when V bias is set to be smaller than the peak value V bias of the pulse voltage, after the toner is transferred to the exposed area, but before the toner is transferred to the non-exposed area, the pulse voltage quickly becomes lower than the non-exposed area potential vb. Because of this, high-quality images can be obtained without fogging, and the charged potential of the photoconductor can be lowered accordingly, reducing fatigue of the photoconductor, improving durability and safety. can be increased.

Furthermore, since the present invention adopts a configuration in which toner is transferred to the electrostatic latent image area of the photoreceptor using an electric field rather than a magnetic field, a fixed magnetic pole is arranged on the back side of the toner carrier as in magnetic brush development. Although this is not a condition, it is also possible to arrange the fixed magnetic pole at a predetermined position as necessary, or to configure it in combination with a magnetic brush development method.

It should be noted that the present invention further has various effects, which will be further clarified by the following examples.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. It's nothing more than that.

FIG. 2 shows a schematic configuration of an image forming apparatus to which the present invention is applied, in which 1a is the surface of a photoreceptor, and a photoconductive insulating layer is formed on the surface of the photoreceptor drum 1, and the photoreceptor drum 1 is directed in the direction of the arrow. It is configured to be rotatable at a circumferential speed of 100 mm/sea.

Inorganic semiconductors such as selenium, zinc oxide, and amorphous silicon, and organic semiconductors such as polyvinyl carbazole are used for the photoconductive insulating layer, and each has different usage characteristics. It uses a semiconductor and is configured to be positively charged.

Around the photoreceptor drum 1, there is a charger 2 that uniformly charges the photoreceptor surface 1a along the rotation direction, and a charger 2 that dissipates the charge on the photoreceptor surface 1a based on image information. a laser beam 3 that forms a predetermined electrostatic latent image; a reversal developing device 4 that reversely develops the electrostatic latent image; a transfer device 6 that transfers the toner image visualized by the developing device 4 onto a transfer paper 5; A cleaner 7 that removes residual toner after transfer, and a static elimination lamp 8 (eraser) that removes residual charges in non-exposed areas are provided, thereby making it possible to repeat a predetermined image forming cycle.

The developing device 4 includes a non-magnetic sleeve 41 that is arranged at a predetermined distance from the photoreceptor drum 1 and rotates in the direction of the arrow at the same circumferential speed as the photoreceptor drum 1, and a non-magnetic sleeve 41 that is enclosed within the sleeve 41. Fixed magnet assembly 42 and the photoreceptor surface 1a
It is composed of a layer thickness regulating member 43 disposed upstream of the facing position and a toner container 44, and the toner layer thickness is regulated by the development interval (nearest interval) with the photoreceptor drum l and the layer thickness regulating member 43. The development interval is set to be larger than the thickness of the toner layer at the development position.

Further, the non-magnetic sleeve 41 includes a switching circuit 45.
A DC power supply 46 is connected through the switching circuit 45, and a rectangular DC pulse voltage is applied to the non-magnetic sleeve 41 by periodically performing a switching operation using a timer (not shown) attached to the switching circuit 45. It consists of

The toner used in the developing device 4 is a magnetic toner having an average particle size of 8 to 20 ILm, an electrical resistivity of 1014 Ω·cm, a relative permittivity of 2.0 or less, and having positive charging polarity due to triboelectric charging. use.

The results of experiments conducted using such an apparatus are shown below.

■First, in order to investigate the relationship between the pulse width a of the DC pulse voltage, image density, and fog, we set VB to 500V and VW to 28V.
0v, fix the V bias frequency to 150 Hz,
When only the duty ratio was changed in the range of 10 to θO% in 10% increments, the duty ratio was 80% (pulse width a
Fog occurred above 5.5 m5ec).

Next, when the V bias frequency was fixed at 3KHz and only the duty ratio was changed in 10% increments, the image density became less than 1.0 when the duty ratio was less than 20% (pulse width a O, 07m5ec). found.

Therefore, the pulse width of the DC pulse voltage a O, 1 to 5.0 m
! By setting eC1 preferably in the range of 0.15 to 2 m5ec, high quality image density can be obtained without fogging.

■ Estimation of equation (a) showing the relationship between Vbias and vb that allows obtaining an image with no fog, that is, an image with an image density of 0.1 or less in the unexposed area. First, as in (■) above, fix the frequency and duty ratio of Vbias However, when changing vb from 200V to 500V (VW is the same as above), we measured Vbias at which an image with an image density of 0.1 or less in the non-exposed area was obtained, and found that the correlation was 0. It was confirmed that it changes linearly with a probability of 993. (Refer to the imaginary line in Figure 3.The duty ratio is fixed there, and the frequency is varied in the same way as in (■) above.A relational expression between V bias and vb that can obtain a fog-free image is calculated using a statistical method. As a result, it was found that fog-free images could be obtained within the range of formula (a) below.

l Vb l > l Vbias/ a l +b
V...-a) 1.52<a<1.88. -20
<b <110 Therefore, when Vbias is set to, for example, 800v, Vb is approximately 400 to 520V520
If V bias is set, it is possible to set a voltage lower than V bias, and since V bias can be set high, a high quality image with high contrast and no fogging can be obtained.

■For reference, Vb that provides an image density of 1.0 or more
The relationship between the minimum value of ias and the latent image surface potential Vw was confirmed.

First, when the V bias frequency is fixed at 1 KHz, the duty ratio is fixed, and Vw is varied from 50 to 300 V, an image density of at least 1.0 or higher can be obtained in both V bias
When measured, it was confirmed that when Vbias is at least larger than Vv and 250V or more, it changes linearly with a probability of a correlation of 0.89. (-2 on the imaginary line in Figure 3) Furthermore, V bia which can obtain an image density of 1.0 or more by changing the frequency from 100 Hz to 10KH2, respectively.
The range of the minimum value of s was determined using a statistical method. As a result, it was found that when the frequency was 5 KHz (0.1 m5ec) or less, an image density of 1.0 or more could be obtained within the range of the following equation.

Vbias>c X I Vw l -d V≧250
2.5 < c < 3.3, -35 < d < 135 Therefore, if V bias is at least Vw or more and satisfies the above formula, the present invention can be applied smoothly. It turns out it can be done. For example, when the Vw is 180V, good image density can be obtained if the V bias is approximately 320 to 630V or more.

[Brief explanation of drawings]

1A and 1B are graphs showing specific examples of pulse voltage waveforms applied to the present invention, FIG. 2 is a schematic diagram of an image forming apparatus to which the present invention is applied, and FIG. 1 is a graph diagram showing the relationship between pulse voltage and surface potential of a non-exposed area and a latent image area of a photoreceptor, respectively. Figure 1 (A) (0+b!a+bA□J (B) Figure 2 Figure 3 (■)

Claims (1)

[Claims] 1) In a reversal development method in which a one-component high-resistance magnetic toner charged with the same polarity as the charge polarity of the photoreceptor is transferred to an electrostatic latent image area on the photoreceptor by a bias voltage. As the bias voltage, a pulse voltage having the same polarity as the charged polarity of the photoreceptor and whose waveform has steep rises and falls is used, and the pulse width is 0.1 to 5.0 m.
sec. 2) A reversal developing method characterized in that the surface potential of the non-exposed part of the photoreceptor is set below the peak value of the pulse voltage within the range of the following formula. Reversal development method described in item 1 |Vb|>|Vbias/a|+bV Vb: Surface potential of non-exposed portion of photoreceptor Vbias: Peak value of pulse voltage 1.52<a<1.88, -20<b<110