JPS5846349A - Method for reversely developing electrostatic latent image - Google Patents

Abstract

PURPOSE:To obtain a reversal toner image small in fog and high in density, by properly setting thickness of a high resistance magnetic toner layer carried on the surface of a toner conveyor, distance between said surface and a recording material surface, and developing bias voltage. CONSTITUTION:An electrostatic latent image 3 formed on the recording layer 2 on the base of a recording material 1 approaches or touches a magnetic brush formed of a magnetic toner 6 on a sleeve during conveyance to attract the toner 6 to the area of the layer 2 free from charge. Potential of the charge of the image 3 is denoted by Vo, and DC bias voltage applied to the conductive sleeve 5 and a regulating plate is denoted by Vb, and a bias voltage source 8 is connected so as to control Vb/Vo to 1/3-2/3 and Vb same to polarity same as that of Vo. The gap G between the layer 2 and the sleeve 5 and the gap g between the sleeve 5 and the plate 7 are regulated so as to be G>g and 0.05>=g>=0.5mm., thus permitting a toner image high in density and low in fog to be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge latent image reversal developing method in electrophotography and electrostatic recording.

In electrophotography or electrostatic recording, there is a one-component magnetic toner method as a method for developing a latent charge image formed on the surface of a recording medium using toner. In the case of a development method in which the toner is charged in advance and the toner is attracted to the charged latent image surface by the Coulomb force between the toner charge and the latent image charge,
It has the advantage of being able to easily transfer toner images onto regular paper. However, single-component magnetic toners have the disadvantage that charging control is difficult and good toner images cannot be obtained. In particular, in the case of a reversal development method in which toner is attracted to an area with no charge, the electric field pattern formed is complex, resulting in a disordered toner image.

FIG. 1 shows a conventional reversal developing device, in which a charge latent image 3 formed on a recording layer 2 on a base 1 of a recording medium is formed by magnetic toner 6 on a sleeve 5 as it moves in the direction of the arrow. It comes into close contact with the magnetic brush and attracts the toner 6 to areas with no (or little) charge. For this purpose, the magnetic toner 6 contains a charge control agent that is charged to the same polarity as the latent image charge 3, and is further selected in a triboelectric charging order with the sleeve 5 and the regulating plate 7. The magnetic toner 6 is conveyed by rotating one or both of the mag roll 4''! or the sleeve 5 to form a magnetic brush, and the regulating plate 7 controls the thickness of the magnetic brush formed on the surface of the sleeve 5. regulate.

When this reversal developing device attempts to obtain a high-density toner image by depositing a sufficient amount of toner 6 on a large area where there is no latent image charge, toner 6 also adheres to the area where latent image charge exists. There is a drawback that fog occurs in the background.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a charge latent image reversal developing method which can produce toner images with high density and less fogging.

In order to achieve this object, the present invention provides a layer of high-resistance magnetic toner supported on the surface of a toner conveying member with a thickness of 0.05 to 0.
At the same time, the gap at the approach point between the surface of the toner conveying body and the surface of the recording medium is maintained larger than the thickness of the toner layer, and a latent charge image is formed between the toner conveying body and the recording body with the same polarity as the latent charge image. It is characterized by applying a developing bias voltage of 173 to 2/3 of the potential.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments. Incidentally, the same reference numerals are given to the same parts as those in the conventional apparatus, some detailed explanations thereof are omitted, and the illustration of toner is omitted.

In FIG. 2, the potential of the latent image charge 3 formed on the recording layer 2 is V. When doing so, the conductive sleeve 5 and the regulating plate 7
1/3 V o l V b ': 2/3
V.

A bias power supply 8 for applying a DC bias voltage Vb of the same polarity as the latent image charge 3 is connected. The gap G between the recording layer 2 and the sleeve 5 and the gap g between the sleeve 5 and the regulating plate 7 are G.
>g, and further 0.05≦g≦0.5
When it is set to rtrm, a toner image with high density and little fogging can be obtained. If G<g, the amount of fog generated increases and is difficult to remove.

The reason why a toner image with high density and little fogging can be obtained with this developing device is considered to be as follows.

Unlike an uncharged one-component magnetic toner or a two-component developer consisting of a carrier and toner, the charged state of a one-component high-resistance magnetic toner is not uniform in the amount of charge on each toner particle, but is widely distributed. Among them, there are particles that have no charge and particles that have a charge of the opposite polarity to the desired polarity. Therefore, when the toner 6 comes into strong contact with the recording layer 2, the toner also adheres to the background area, that is, the area where the latent image charge 3 is present, and fogging occurs. In order to reduce the occurrence of fluff caused by the contact of the toner 6, it is effective to weaken the contact force.
0.05~0.3m, preferably 0.1~0.2+m
Increasing it will give better results. Gap G.

The value of g is experimentally determined from the relationship between the density of the toner image and fog, but it depends on the degree of fog and the amount of toner 6 in the gap G.
The condition of G>g is necessary for smooth flow.

Bias voltage V is required to increase the density of toner image with reversal development.
The larger b is, the better. On the other hand, the fog caused by the toner 6 charged with the same polarity as the latent image charge is less when the bias voltage Vb is small, and the fog caused by the toner 6 charged with the opposite polarity is less when the bias voltage Vb is large. , the fog due to toner 6 which has no charge is the latent image charge 3
is small when the potential vo and the bias voltage Vb are equal.

Taking all of these into consideration, the relationship between the occurrence of the fogging phenomenon and the magnitude of the bias voltage tends to be mutual depending on the charging state of the toner 6. However, the toner 6 that tends to cause fogging has low magnetism and low electrical charge, and is weakly attracted to the sleeve 5 side. Most of these toners 60 tend to be charged to the same polarity as the latent image charge, so that the bias voltage Vb at which the occurrence of fogging phenomenon is reduced overall is the latent image charge potential V. It is at a much lower level.

Specifically, the potential V of the latent image charge 3 varies slightly depending on the development conditions and materials. When the bias voltage Vb was set to 1/3Vo to 2/3V when V was 200 to 1000V, good results were obtained even when using various toners.

This is different from the conventional method in which the optimal bias voltage for a reversal development method using magnetic toner without charge was approximately equal to the potential of the latent image charge.

Another difference is that in the case of a two-component developer, the fog density increases as the bias voltage increases and there is no minimum value.

FIG. 3 shows an experimental example in which selenium was used as the recording layer 2 and the latent image charge potential was V. This is when G>g (
G=0.3m++, g=0.2mm), Vb=300
A good toner image was obtained at v~500v.

The reason why the gap g between the regulating plate 7 and the sleeve 50 is set to 0.05 to 5 degrees is to reduce variations in the amount of charge of the toner 6. Toner particles usually have a diameter of 3 to 30 μm.
When the sleeve 50 passes through the gap g, it is frictionally charged as it moves on the surface of the sleeve 50. At this time, the friction between the toner particles must be minimized, and a uniform layer of toner (magnetic brush) must be formed on the surface of the sleeve 5. The gap g of this reservoir is 0.05-0.5 m, preferably 0.1-0.3 m
It was experimentally confirmed that m. When the gap g is smaller than the above value, the uniformity of the toner layer deteriorates and uneven density occurs, and when it is large, it is difficult to control the amount of charge, resulting in fogging and a decrease in sharpness.

Further, the gap G between the recording layer 2 and the sleeve 5 is less than 1 inch, preferably less than 0.5 rran. This gap G is
This affects toner image formation and fogging characteristics, and when the gap G is large, the electric field weakens and the edge effect and fogging are strengthened.

The bias voltage Vb does not need to be a direct current as long as its average value satisfies the above conditions.

When the surface of the sleeve 5 is covered with an insulating layer having a thickness of 1 to 200 μm, charge injection from the sleeve to the toner 6 is eliminated, thereby reducing the occurrence of fogging. In this case, since there is a possibility that electric charge may accumulate on the surface of the insulating layer, the sleeve 5 is rotated, the electrode conductor is placed in contact with the toner layer, and it is connected to the conductive part of the sleeve 5, and the insulating layer is It is good to release the surface charge. This electrode conductor is preferably installed on the opposite side of the regulating plate 7, but the regulating plate 7 may also be used.

FIG. 4 shows a developing device in which the mag roll 4 is stationary and the sleeve 5 is rotated, and shows the magnetic force distribution characteristics of the developing magnetic pole, which is effective in preventing fogging. The development end side of the recording layer 2 is shown as positive, and by increasing the magnetic force on the development end side, the toner adhering to the background area during the first half of development can be removed and the occurrence of fogging can be further reduced. According to experiments, the angle at which the magnetic force is maximum is preferably about 10 degrees. A similar effect can be obtained even if the developing magnetic pole position of a mag roll with a symmetrical distribution of magnetic force is rotated and fixed by about 10 degrees toward the development end side.

FIGS. 5 and 6 show other embodiments in which the bias voltage application method is changed. The bias voltage vI applied to the regulating plate 7 by the power supply 9 injects charge from the regulating plate 7 into the toner 6 (not shown) to control the charging of the toner and improve image quality. In this case, covering the surface of the sleeve 5 with an insulating layer eliminates charge injection from the sleeve side and is more effective.

In FIG. 6, an AC voltage b is further superimposed by an AC power supply lO, and the developing bias voltage applied to the sleeve 5 is pulsating (vb
+vb) to improve toner movement and increase uniformity and fog prevention effect.

Various embodiments of the present invention have been described above, but in the end, according to the present invention, the thickness of the single layer of high-resistance magnetic toner carried on the surface of the toner conveying body, the gap between the surface of the toner conveying body and the surface of the recording medium, and the developing bias voltage can be adjusted. By setting it appropriately, a high-density reversal toner image with little fogging can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional reversal developing device, FIG. 2 is a schematic diagram of a reversal developing device using the method of the present invention, FIGS. 3 and 4 are characteristic diagrams, and FIGS. 5 and 6 are FIG. 2 is a schematic configuration diagram of a modified reversal developing device. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Recording layer, 3...Latent image charge, 5
...Sleeve, 6...Toner, 7...Regulation plate, Death...Bias power supply.
-1 I Q Wa, -, G Figure 1 Ya 2 Figure 'f33 m Field 4 Figure 1 Angle θ (degrees)

Claims (1)

[Claims] 1. In a charge latent image reversal development method in which a charge latent image on the surface of a recording medium is reversely developed using pre-charged high-resistance magnetic toner carried on the surface of a toner carrier, the thickness of one layer of high-resistance magnetic toner carried on the surface of a toner carrier is The cylinder length is set to 0.05 to 0.5, and the distance at the approach point between the surface of the toner conveying body and the surface of the recording medium is maintained larger than the thickness of one layer of high-resistance magnetic toner,
A charge latent image reversal developing method characterized in that a developing bias voltage having the same polarity as the charge latent image and having a magnitude of 173 to 2/3 of the charge latent image potential is applied between the toner conveying member and the recording member.