JPS61239251A - Method for developing electrostatic latent image - Google Patents

Abstract

PURPOSE:To attain optimum images by setting a maximum potential of the switching DC bias applied to a developing area, the duty ratio, and the periodical grounding time of the DC bias determined with the duty ratio and the frequency to values in prescribed ranges. CONSTITUTION:A photosensitive drum 11 is rotated clockwise, and a non magnetic sleeve 12 is rotated counterclockwise. The nonmagnetic sleeve 12 involves a fixed magnet gathered body 13, and a magnetic blade 14 is arranged above near the sleeve 12. A DC power source 16 is connected to the nonmagnetic sleeve 12 through a switching circuit 15 whose duty ratio is varied by a timer. A maximum voltage Vmax of the DC bias applied to the nonmagnetic sleeve 12, a toner restraining potential Vt of an electrostatic latent image holding surface, a maximum potential Vd of an image part, a periodical power supply time t1 of the DC bias, and a periodical grounding time t2 of the DC bias are set to satisfy 2Vt<=Vmax<=Vd, t1/t2>=0.3, and t2>=0.2msec.

Description

[Detailed Description of the Invention] ``Field of Industrial Application'' The present invention relates to a method for developing an electrostatic latent image using a single-component high-resistance magnetic toner, and more specifically relates to a toner layer supported on a toner carrier. The present invention relates to a developing method in which toner is selectively transferred by the electric field of an electrostatic latent image without directly contacting the electrostatic latent image holding surface.

"Technique of the Prior Application" The present inventor previously discovered that in order to prevent the occurrence of fogging and improve gradation, the present inventors developed a method for creating a static image with a distance greater than the thickness of the toner layer carried on the toner carrier. A developing method is proposed in which a repulsive magnetic field is formed in a developing region between an electrolatent image carrier and a toner carrier, and a switching DC bias is applied to the developing region. (Special application 1982-2097
7) In this type of development method, the toner which is restrained on the surface of the toner carrier due to Van der Waals force or other restraining force is lifted from the surface of the carrier by the repulsive magnetic field, and the image area and the electrostatic holding surface are The switching DC bias is controlled so that both non-image areas move in either direction without reciprocating or reverse transfer, thereby preventing the toner from transferring in the non-image areas while preventing the toner from moving in the latent image area. The toner is transferred only to the image area in accordance with the surface potential, and as a result, the above effect is achieved.

Specifically, the above-mentioned "switching DC bias controlled to move only in one direction without transfer or reverse transfer" refers to the maximum potential of the image area of the electrostatic latent image holding surface (
Although it is stated that it refers to a switching DC pulse with a substantially rectangular waveform that has the same polarity as Vd) and is controlled within the range of formula A') below, as a result of subsequent confirmation experiments, it was set by Formula A'). Within the range, if we focus on the duty ratio, which is the ratio of the periodic conduction time of the switching DC pulse to the periodic grounding time, we find that the duty ratio, the maximum voltage of the DC bias, and the frequency are closely related, and that they are We found that it is necessary to set it within a specific range.

Vt< Vmax ≦Vd...I')Vm
ax: Maximum voltage of DC bias vt: Toner restraint potential on the electrostatic latent image holding surface Vd: Maximum potential at the image area "Problem to be solved by the invention" According to the prior invention, first, in order to prevent background fog, The toner that has once adhered to the non-image area is pulled back (reverse transfer) by a reverse transfer electric field (Vmax - Vt) directed toward the toner carrier, and the amount of pullback is α corresponding to the pullback speed. (Vmax - Vt) and the pullback time t1. Therefore, in a high frequency region, when the duty ratio is set to 1, if the DC bias maximum potential Vmax approaches the toner restraint potential Vt, the toner Unable to pull back sufficiently,
Background fogging may occur. (α is a constant determined by the amount of charge) On the other hand, in order to eliminate the above drawback, if the duty ratio is set to a large periodic energization time tl and a small periodic grounding time t2, the development in the image area will be reversed. concentration decreases.

That is, the transition in the image area mainly depends on α, which corresponds to the transition speed.
(Vd - V5) and the transition time t2 (Vs is the non-image area potential and is generally Ov or a value close to it), so the larger the duty ratio, the more
It is understood that the amount of toner transfer in the image area is reduced.

In order to solve the problems of the prior art, the present invention aims to appropriately select the maximum potential, frequency, and duty ratio of the switching DC voltage to obtain the most favorable developing conditions for obtaining an optimal image. do.

Another object of the present invention is to provide a developing method that can obtain a good image even at a high frequency by controlling the duty ratio of the bias voltage, and that can cope with an increase in the image formation speed. It's about doing.

In order to achieve such technical problems, the present invention provides a maximum potential of the switching DC bias, a duty ratio, and a periodic period of the DC bias determined by the duty ratio and frequency. The maximum voltage Vmax of the DC bias can be increased to a certain voltage or higher by setting the grounding time within the range of formulas A, C, and C below, and in particular, by setting the duty ratio to become smaller in inverse proportion to the higher frequency of the DC bias. and α(Vma
The amount of toner pullback in the non-image area determined by x - Vt) An electrostatic latent image developing method is proposed in which the amount of toner transfer determined by t2 is increased to obtain good image density.

2Vt≦Vmax≦Vd...a) t1
/t2≧0.3...b)t2≧0.2
m5ec -... C) Vmax: Maximum voltage of DC bias Vt: Toner restraint potential of electrostatic latent image holding surface Vd: Maximum potential of image area tl: Periodic energization time of DC bias t2: Periodic grounding time of DC bias Effects The effects of this developing method will be explained based on FIG.

First, Figure 1 ■ shows the maximum voltage Vma to explain the effect described later.
The relationship between the DC bias voltage and the latent image potentials Vd and Vs when x and the duty ratio t1/t2 are changed, respectively, is shown as a time change. This figure shows the mode of toner transfer and countertransference in the image area and non-image area.

First, as can be understood from (A) in the same figure, in the present invention, since Vmax is set to 2Vt, even if the DC bias is set to a high frequency of IKH2 or higher, the pullback speed α (Vmax -Vt) is large, the toner has a pullback speed sufficient to pull back toner even in a high frequency range, and background fogging can be prevented. In this case, 0. Since the pullback time t1 of Of3msec or more is guaranteed, αCVrnax-Vt)
It is possible to obtain a sufficient amount of toner to pull back tl to prevent background fogging.

Also, as understood from Figure 1 (B) ■, Vwax≦
Since the duty ratio (tl/t2) is set to 0.3 or more under the condition of t2≧0.2 ttrsec, the above-mentioned Vmax and Vd do not reverse because it is set to Vd. It is possible to maintain a predetermined amount of transfer in the image area without t2 becoming extremely smaller than tl, and in particular, by setting the duty ratio (tl/t2) to 1.2 or less, good gradation and image quality can be achieved. It is possible to prevent the concentration from decreasing.

That is, if we look at the above effect from the reverse side, (tl/t2)
<0.3, t2<0.2 m5ec and Vma
When x < 2 Vt, reverse transfer is not achieved and fog increases in non-image areas.

Also, t2<0.2 m5ec and (t1/t2)<0
．． In the case of No. 3, the predetermined amount of transfer cannot be maintained, the image density decreases, the smooth effect of the switching DC bias cannot be achieved, and the gradation quality also decreases.

Furthermore, the smooth effect of the switching DC bias in the high frequency region (t1/t2)>1.2 is not achieved, and the gradation and image density are reduced.

Moreover, according to the present invention, by setting the duty ratio tl/t2 to be small in inverse proportion to the increase in the frequency of the DC bias, the frequency can be increased to around 400082 while maintaining good gradation and image density. This makes it possible to increase the development speed to a high speed.

"Example" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example. However, the scope of this invention shall be limited to the electric field strength, magnetic flux density, rotational speed, dimensions, materials, shapes, and relative arrangement of components described in this embodiment unless otherwise specified. It is not intended to be limiting, but is merely an illustrative example.

FIG. 3A shows a schematic structure of a developing device constructed according to the present invention.

11 is a photosensitive drum, 12 is a non-magnetic sleeve containing a fixed magnet assembly 13, and both members 11 and 12 have a gap distance of about 300 JL at the closest position (hereinafter referred to as the development center position C-C). The photoreceptor drums 11 are arranged to face each other so that the non-magnetic sleeve 1
2 are configured to rotate counterclockwise at a constant speed of a peripheral speed of 100 mm#ec.

A magnetic blade 14 is disposed close to the upstream side of the non-magnetic sleeve 12.
A toner layer regulated to the layer thickness of IL is a non-magnetic sleeve 1.
2 and is transported to a development area A (an area where a repulsive magnetic field is formed as described later).

In FIG. 3B, fixed magnets 13a and 13b of the same polarity are arranged adjacent to each other inside the non-magnetic sleeve 12 in the developing area A, and the non-magnetic sleeve 12 and the photosensitive drum 11 are placed adjacent to each other.
A repulsive magnetic field is formed in the area (development area A) sandwiched between the fixed magnets 13a and 13b.

The non-magnetic sleeve 12 also includes a switching circuit 1 whose duty ratio can be varied by a timer (not shown).
A DC power supply 18 is connected through 5, and a square wave pulse is applied to the development area A. The maximum magnetic flux density on the surface of the non-magnetic sleeve 12 of the fixed magnets 13a and 13b is both set to 500 Gauss, and the maximum fall height at the intermediate position between the re-fixed magnets 13a and 13b is 100 to 200 Gauss. Set it like this. The maximum drop height is 100 gauss or less and 200 gauss or less.
This is because it becomes difficult to form a good repulsive magnetic field when the magnetic field exceeds Gauss.

As a result, the height of the toner tip in the development area A where the repulsive magnetic field is formed is approximately 1.5 times that of the toner layer, that is, 1.
It has a height of 50 to 180p, is very close to the photoreceptor drum 11, and the repulsive magnetic field weakens the binding force between the toner particles and between the toner particles and the non-magnetic sleeve 12,
Transfer of the toner 4 becomes easy.

The relative arrangement position of the fixed magnets 13a, 13b and the development center position C-G is determined based on the distance between the maximum magnetic flux lines of each fixed magnet 13a, 13b, and the center line is set in the direction of rotation of Ol and the non-magnetic sleeve 12. In the case where the downstream side is positive, the deviation amount θ of the development center position C-C is within the range of the following equation 2), that is, it is arranged slightly shifted downstream from the center line of the repulsive magnetic field.

O x θ<+(1/2) l ...2) The reason why the fixed magnets 13a and 13b are formed in this way is that the toner 4 tips formed by the repulsive magnetic field are non-magnetic, which transports the toner 4. Since the toner flows downstream due to the rotation of the sleeve 12, the purpose of this flow is to match the position of the tip of the toner tip with the development position.

Now, in such a configuration, the electrostatic latent image potential carried on the photoreceptor on the surface of the photoreceptor drum 11 is approximately 500 V for one image portion,
It is set in the non-image area Ov, and the toner-4 restraint potential is 120.
V (experimental value), a confirmation experiment was conducted as detailed below.

Note that the toner used in this developing device has an average particle size of 9 to 9.
20IL11 Electrical resistivity 1014Ω・C1, relative dielectric constant 2
．． 0 or less, a magnetic coercive force Ha of 50 to 1000e, and a saturation magnetization of 30 to 40 emu/g,
A fluid containing hydrophobic silica is used as a flow aid.

In addition, the paper temperature of the transfer paper itself was 0.06 to 0.08. a) Confirmation of the relationship between reverse transition (background fog) in the non-image area and DC bias voltage, setting the frequency to 2.5 KH2 and the duty. Ratio (tt/12)
The maximum potential of the DC bias was set to 0.3 (t2: 0.3 m5ec) at 200V, 250V,
FIG. 4A shows seven curves showing the relationship between image density and photoreceptor surface potential when set to 300V and 400V, respectively.

In FIG. 4A, when the bias voltage Vmax is 200V, which is smaller than 2Vd, the photoreceptor surface potential is 100 to 120V.
The image density becomes 0.2 or more before and after V, and fogging occurs!
I can understand what is going on. Further, when Vmax is 250 V or more, the image density is around 0.1, and it can be seen that fog does not occur in most cases.

b) Confirm the relationship between DC bias voltage duty ratio (tt/12) and gradation.The frequency is 1.1 KH2, the maximum potential is 350V, and the duty ratio is 10/3 (t2: 0.21 m5e).
c) , E115 (t2: 0.41 m5e
c) 1/2 (t2: 0.61 m5ec) 1/
FIG. 4B shows seven curves showing the relationship between the image density and the surface potential of the photoreceptor when the image density was set at 3 (t2: 0.88 m5ec).

As can be understood from this figure, the duty ratio is 10/3 (
At t2: 0.21 tasec), the γ value rises,
It was confirmed that the fog was large and the gradation was poor.

However, in this embodiment, in the high frequency range of 1.5 KH2 or more, as the duty ratio becomes lower, fogging is prevented and the γ value is lowered, resulting in better gradation and stability of development density. I can understand what is going on.

C) Check the relationship between the periodic grounding time t2 of the DC bias voltage and the gradation. Set the maximum potential to 350v and the duty ratio to 315.
2. Set the frequency to 3.8 KH2 (t2: 0.18
m5ec), 3.0 KH2 (t2: 0.21m
5ec) 2.5 KH2 (t2:0.25m5ec)
FIG. 4C shows seven curves showing the relationship between image density and photoreceptor surface potential when the image density is set to .

As can be understood from this figure, when t2 was 0.16 m5ec, no fogging occurred, but it was confirmed that the overall density decreased.

As a general trend, as the frequency becomes larger (t2 becomes smaller), the image density tends to become lower and the γ value becomes smaller.

Next, change the frequency to 4 KHz and the duty ratio to 3/10 (t
2: Q, 2Q msec), the concentration was able to be recovered as shown in graph A of Fig. 4C.

According to these examples, it can be understood that the effects of the present invention and the examples are consistent and correlated.

"Effects of the Invention" As described above, the present invention overcomes the problems of the prior art, eliminates background fogging in non-image areas, and further stabilizes the developed density in image areas. It is possible to improve the gradation of a good image.

Furthermore, according to the present invention, even if the frequency is increased, by lowering the duty ratio correspondingly, a predetermined toner transfer time can be maintained, and it is possible to support higher speeds without reducing image density. We can provide a developing device that can.

Furthermore, since a switching DC bias is used, the duty ratio can be easily controlled, and these control mechanisms can be made smaller and lower in price.

It has the same effect as the above.

[Brief explanation of the drawing]

2A and 2B schematically show the structure of a developing device constructed according to the present invention, with FIG. 2A being an overall view and FIG. 2B being an enlarged view of essential parts. Figure 1-41 is an explanatory diagram showing the state of electric field strength in the image area and non-image area when the DC bias according to the present invention is applied to the development area, and Figures 3A to 30 are the DC bias and duty ratio. , is a graph diagram showing seven curves when the frequency is changed within the technical range of the present invention. Fig. 1 Toner tear ν ■ No Fig. 2A Fig. 2B Fig. 3A *@ Electric a (V) Fig. 3B

Claims (1)

[Scope of Claims] 1) A repulsive magnetic field is formed in a development area between an electrostatic latent image carrier and a toner carrier that are arranged with a distance greater than the thickness of the toner layer carried on the toner carrier, and In the electrostatic latent image developing method in which a switching DC bias having a potential smaller than the latent image potential of the photoreceptor is applied in the development area, the maximum potential of the switching DC bias, the duty ratio, and the duty ratio and frequency An electrostatic latent image developing method characterized in that the determined periodic grounding time of the DC bias is set within the range of the following formula: 2vt≦Vmax≦Vd...a) t1/t2≧0.3... b) t2≧0.2msec...c) Vmax: Maximum voltage of DC bias Vt: Toner restraint potential on the electrostatic latent image holding surface Vd: Maximum potential of image area t1: Periodic energization time of DC bias t2: DC bias 2) The electrostatic latent image developing method according to claim 1, characterized in that the duty ratio is set to become smaller in inverse proportion to the higher frequency of the DC bias.