JPS5988750A - Reversal developing method - Google Patents

Abstract

PURPOSE:To obtain an image having excellent sharpness by providing two magnetic brushes and regulating the density for packing the magnetic toner therein and the speeds of the two brushes and a photosensitive body at prescribed values. CONSTITUTION:The densities for packing a magnetic toner in the developing region of the magnetic brush on the 1st magnetic brush roll (expressed hereunder as the 1st roll) 2 and the 2nd magnetic brush roll 3 are determined respectively at 0.2-0.7. The moving speed Vu of the 1st roll 2 and the moving speed Vl of the 2nd roll 3 are determined respectively 2-7 times of the moving speed Vp of a photosensitive body 1. The ratio Vl/Vu in the moving ratio between the 1st and 2nd rolls 2, 3 is set at 0.5-2. The voltage of the potential equal to the latent image potential in a background part or above is impressed on the roll 2 by a bias power source 7 and a bias voltage of <=0.8 times of the latent image potential in the background part is impressed on the roll 3 by a bias power source 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reversal development method using one-component magnetic toner. -Component There are various developing methods using magnetic toners, but there are two methods: developing with a low-resistance magnetic toner using static induction and transferring it to processed paper, and another method in which electrical charges are applied to insulating magnetic toner using frictional charging, etc. It is broadly divided into methods that apply it and transfer it to plain paper. However, the former method requires the use of processed paper, and the latter method deteriorates over time due to frictional electrification. Therefore, attempts have been made to use magnetic toner with relatively high resistance, apply electric charge to the toner by electrostatic induction, polarization, injection, etc., and perform electrostatic transfer onto plain paper. However, with this method, the image quality, especially the peripheral areas of the group, is distorted and the sharpness is poor.

In addition, the reproducibility of low-density areas and fine lines was poor.◎ In order to overcome this drawback, two developing rolls were used to first over-develop and then to adhere to non-orthogonal areas. Attempts have been made to remove toner and improve the sharpness of r-images and low density reproducibility (Japanese Patent Application Laid-open Nos. 55-73058 and 55-1).
38766 and 56-14268).

Also, an attempt has been made to improve the poor quality of one-plane image peculiar to the reversal phenomenon by using it on two rolls.

As a result of applying the inversion phenomenon, the present inventors found that the conventional
It is sufficient to know about the reversal development method using a book development roll or the development method using two development rolls (hereinafter referred to as the two-stage development method) disclosed in the above-mentioned patent. It was confirmed that it was not possible to obtain the quality of a single artist. In other words, the fog density was high (the image sharpness was low), and the reproducibility of one gradation was also insufficient.Furthermore, in the case of reversal development, a negative original is used, but the contrast of the original varies. Therefore, it is necessary to perform troublesome operations such as changing the phenomenon bias for each document, adjusting the exposure deformation, or adjusting the position of the photoreceptor.

An object of the present invention is to eliminate the drawbacks of reversal development using the two-stage roll development method described above, reduce fog density, and obtain image quality with excellent low density reproducibility and sharpness. The present invention provides a two-stage roll developing method for reversal development. Further, the present invention provides a developing method in which good image quality can be obtained by always setting a constant bias voltage related to the conotrast of an E-magnetic original.

Hereinafter, the inversion present method of the present invention will be explained in detail with reference to the drawing.

First, the current bias voltage applied to the latent image potential level for the inversion phenomenon of negative to positive conversion will be described in detail.

Figure 1 shows the electrostatic potential level and bias voltage application level when performing reversal development using one developing roll. vI is a potential corresponding to the fog density (background density) of a negative original.VBlag
is a bias potential, which has the same polarity as the latent image, and is set approximately 100V lower than the fog density vl.

Therefore, K to develop the density area (artist area) is VBins.
Toner adheres to the contrast of VBK
It will be lit'. However, the fog density and bleed density (referred to as document contrast) of negative originals vary over a fairly wide range. FIG. 2 illustrates the stiffness relationship regarding the original contrast.

The horizontal axis shows the density of negative originals (positive image [urine density)], and the vertical axis shows the fogging density (tenon non-111ii1 quadrant density)
, and the difference between fogging density and non-fogging density is indicated by diagonal lines as contrast. As is clear from this figure, the fog density corresponding to vI ranges over a wide range;
Even if the bias voltage VBlam shown in the figure is set to the optimum value (Vx -100v) assuming a fog density of 1.0,
When reproducing a negative original with low fog density, after one phenomenon,
Fog may occur in the background, or images with different contrasts may appear in the same document [v, ', v□ in Figure 1.
411X), an image with low contrast is not reproduced, resulting in an inconvenient combination.

FIG. 3 is an explanatory diagram of a method of applying a bias voltage in the two-stage roll method. vBK l The drawing on the energy chart is the latent r quadrant potential corresponding to the concentration (corresponding to the positive image 1 quadrant)
, vI is the latent r-quadrant potential corresponding to the fog density (corresponding to the positive non-ambient part), and vl indicates the bias voltage level to be applied to the upper roll. The bias potential V1 applied to the upper roll is Set to a potential higher than the latent (image potential) that has the same polarity as the reservoir potential and corresponds to the maximum fog density of the original (1,0 in Figure 2).Normally 1
．． 0 to 2.0 times, preferably about 1.5 times. Applying a bias V to the upper roll, the first current 1
When you carry out the elephant.

Toner adhesion (indicated by symbol T) occurs over all areas of the negative chart having different contrasts, including the fog density area (positive background area).

The amount of adhesion (actual amount) is determined according to the potential difference with the bias voltage potential applied to the upper roll, that is, the contrast potential (excluded is the density difference).

Figure 4 shows the bias 'rlV f+ applied to the lower roll.
γ■2 is shown. Set the lower roll bias potential to the same polarity as the latent image, and set it to the fog density equivalent to the negative chart'ttc [t7
: VI and EX are set approximately in the middle of the concentration equivalent potential VBK.

Normally, the latent image electric current corresponding to the maximum fog density is 0 of γv1.
．． Set an example before and after 5 times. The toner r image generated by the upper roll is subjected to the next process by the applied bias v2 of the lower roll. As shown by the symbol T, turnip IJ with the north roll.
When removed from the l/1 degree area (corresponding to the positive non-image area), the toner f which adhered to the entire density area is at an image potential level (■2 to V□) higher than the bias voltage v2. is attracted to the lower roll side, and conversely, the bias voltage v2
Developed images at a lower latent image potential level are subjected to electrostatic forces such that they are developed again. However, - attached to the latent f-elements (
- Toner, that is, toner deposited in layers on a recording medium, has a stronger static adhesion (charge amount) in the F layer, and is saturated with latent charge. Since the image density does not increase even if the image time is increased, the effect of the lower roll bias 2 is ultimately due to the toner adhering to the latent image potential level higher than v2. It takes 7J to adsorb the toner to the lower roll side. However, as mentioned above, due to the high and low voltage potential level (in other words, electrostatic contrast), once the toner is fogged, the electrostatic force is weak, so it is easy to remove the toner. However, for the density area indicated by V□', it was confirmed that only the toner in the upper layer was adsorbed to the 7th stage roll side, and the toner in the vicinity of the deepest layer remained attached to the latent image area. .

The image quality obtained by the reversal phenomenon using the two-step roll phenomenon method has low fog density (and shows sufficient painter's density,
Furthermore, the gradation reproducibility is also very excellent.

Figure 5 shows the image quality, upper stage, upper roll bias voltage V1,
This shows the relationship of v2. As is clear from the figure, the bias voltage V and v2hs that satisfy both image density and fog are 1.0 times higher than v1 and the maximum fog density v0 of the Enega disaster, preferably k'! , 1. ．． 5 times or more, ■2
is located approximately midway between the lowest fogging density VBK and the highest fogging density vl, and is 0.8 times or less, preferably 0.5 times or less, than the highest fogging density V0. Furthermore, it is desirable from the viewpoint of gradation reproducibility.

Next, the present invention will be explained in detail with reference to FIG. 6, which is a schematic diagram of an example of a developing device used to carry out the reversal development method of the present invention.

In the figure, 1 is a photoreceptor, which rotates at a constant speed in the direction of the arrow. Reference numeral 2 denotes an upper image roll, and 3 an upper image roll, through which the toner passes under the action of an electrode/trimming member and is evened out to a constant I-thickness. On the other hand, the toner on the upper roll 3 (the toner has been deposited in a single layer on the surface roll in advance) passes through the electrode/trimming member 6 and is evened out to a constant layer thickness, and excess toner is removed from the upper roll. It is configured to be attracted to the roll 2 side. The upper roll and the lower roll move in the directions shown by the arrows, and the bias voltages of the bias voltages 7 and 8 are changed to - respectively.
Applied to the upper stage and upper roll. Although the injection electrode to the feed member is shown to be at the same potential as the phenomenon roll, the injection may be made at the same potential as appropriate. Furthermore, the rotation directions of the upper and lower developing rolls or the toner transport method are not limited to these.

The two-stage roll phenomenon method is basically considered to be a two-stage process of over-effect and excess toner pickup. According to the studies of the present inventors, in order to improve the sharpness of one image and suppress the fog density.

It has been found that the condition of the toner brush of the upper F-stage phenomenon roll and the speed of the roll are important factors. That is,
Regarding the condition of the toner brush, the gap quality is thick (depends on the set value of dP2 (the closest distance between the photoreceptor 1 and the current slag roll 3), and the dT and dPO ratio (dT/dP)).
It is necessary to set the X value in the range of 0.2 to 0.7 for both the upper and lower developing rolls. In particular, the lower toy roll is the same as the upper one.
The developed image developed with the roller is brought into contact with the toner brush again to perform the final repair, so the condition of the toner is very important. This relationship is shown in FIG. 7 for the lower roll. dT2 Figure 7 shows the trimming gap (equivalent to the thickness of the toner brush).
The relationship between the distance dP2 and the distance between the photosensitive drum and the developing roll is plotted. ii $l line A area (dP2≦0
．． 4. dT2≧0.2), toner retention occurs in the image nip and most of the developed image visualized in the upper developing device 5 is scraped away.

In addition, the touch-down method in which the distance between the photoreceptor drum and the developing roll is in contact is at its limit in terms of maintainability. On the other hand, the area indicated by diagonal line B (dP2≧0.4, d
T2≧O, "7 dP2) The phenomenon 1 that is overdeveloped in the 1st stage phenomenon device is the non-image area (background area)
Not only that, but the toner adhering to the low-density image, which has weak adhesion to the latent image, was also picked up, so although the fog density was low, the image quality was poor in low-density reproducibility. . On the other hand, the area indicated by diagonal line C (dT2
(dP2, dP2≧0.2), the friction of the toner brush is weak, so the phenomenon of toner being forced to adhere to the background area is controlled by the bias voltage EE.
It was not possible to pull it back to the roll side again using the image roll, and as a result, only one image with a difference in fog density was obtained. In other words, in order to maintain the reproducibility of low-density images and suppress fog density, it goes without saying that the polarity of the developing bias voltage (or control of the Etna layer potential), the selection of the applied voltage, and the The backing density of the toner (denoted as dT2/dP2) was found to be an important factor.

In order to achieve both of the image characteristics described above, the trimming gap must be within the range shown by straight lines A and A in FIG.

It is necessary to maintain the distance between the photosensitive drum and the developing roll. Experimentally, dT2/dP2 is 0.2-0.7
．． It has been confirmed that a value of preferably 0.25 to 0.35 is appropriate.

Furthermore, the important point here is that, as mentioned above, the backing density of the toner in the egg (in other words, the toner brush) is very soft, and the most advanced toner is developed in the upper roll. (By rubbing the first part lightly, it is possible to prevent the disturbance of the edges of both sides, which is peculiar to one-component development.

It was also found that the speed and speed ratio of the upper and first rolls in two-stage roll development have a very large effect on image quality.This relationship is shown in Figures 6 and 8. 0 In Fig. 6, the upper appearance roll 2 and the Flfl- appearance roll 3 are integrated.
The flow of toner from the toner roll 2 to the upper stage roll 2 is carried out by being magnetically upwardly anodized in the area of the quasi-pole 6 which also serves as a trimmer. Incidentally, the rotation speed of each phenomenon roll can be controlled independently.

The rotational speed of the photoreceptor 10, the rotational speed of the upper developing roll 20, fi ru, and the rotational speed of the lower developing roll 70 are represented by ■, and the directions of rotation are indicated by arrows. In addition, due to the above-mentioned phenomenon, the backing density (dT/dP) of the toner in the image is 0.5 for the roll shown in the upper row. The lower developing roll is 0.3
is set to . The relationship between the rotational speed of the photoreceptor drum l]j and the rotational speed of the phenomenon roll in the second and lower stages, 9.

Experiments were conducted on low density reproducibility, disturbances at the edges of both images, and density, and as shown in Figure 8, the effects of the roll speed and speed ratio on the upper and lower stages were large (influenced) on the image quality and density. In other words, the area (Vu
≦271/'p) was a case where the speed of the two-stage image roll was slow, the density of one stroke was low, and the edge of the first image was disordered. This is because the sliding speed of the toner brush is slow.

The appearance of the phenomenon image is poor (presumably due to low phenomenon efficiency. The area indicated by diagonal line B (7/b < 2 h) is the case where the lower phenomenon image roll speed is slow. Only an image was obtained in which the edges of one image were disturbed and the fog density was high.

On the other hand, the speed ratio of the upper and lower developing rolls (2Q/white)
Regarding the area indicated by the diagonal line C, that is, when the lower roll speed is more than twice that of the upper roll speed, the fog density and the disturbance at both open edges are suppressed, but the low density reproducibility is poor. The only thing I could get was an elephant. In other words, the current 1 of stage F
It is presumed that if the rotation speed of the elephant roll is high, the Sugabe/Ji effect will be emphasized. In addition, in the area indicated by diagonal lines, that is, when the roll speed 4 is 0.5 times or more F compared to the speed 9 of the first upper stage [Sueur's speed 9], low speed reproducibility is satisfied, but fogging occurs. It turned out that only very low-quality paintings with high concentration and disordered edges could be obtained. Furthermore, it has been confirmed that when the speed of each image roll becomes more than 7 times the speed of the photoreceptor drum, the toner on the sleeve becomes poorly conveyed and bald spots occur on the image roll. As a result of further investigation, the fog density was low only within the range indicated by the straight line A and the mouth, and the low density reproducibility was good.
It was discovered that a seven-dimensional image of the edge of a house could be obtained. That is, the developing roll speeds of the upper and F stages are in the range of 2 to 7 times the speed of the photoreceptor drum, and the roll speed ratio of the upper and F stages is 0.5 to 2. Within the range of 0 ((Something turned out to be true.

Regarding the speed and speed ratio of the upper and lower developing rolls,
It was confirmed that there are optimal ranges for each of the two series, but when observing the above effects on the shape of the development gap using a microscope etc., it was found that for the -L corrugated roll, The speed of the toner brush has an influence on the disturbance around the 1st house, especially the protrusion at the rear end of the The reason for this is to remove the toner adhering to the background part and to correct (pick up) the toner r phenomenon that sticks out at the rear end of the house. Therefore, it is assumed that the contact pressure and sliding speed of the magnetic brush are the keys. That is, the start-up force including electrostatic, magnetic, and mechanical forces is proportional to the speed of the brush and the contact pressure (substituted by dT/dP). Since the adhesion force of the developed toner to the latent image is different in the background, low density, and high density areas, the toner adhering to the background area is completely collected by the brush and is attached to the low density area. Since it is necessary to repair only the peripheral area without re-adhering (recovering) the toner i1 to the toner brush, it is necessary to control the speed of the lower roll. It turns out that the ratio is an important parameter.

As mentioned above, trimming/guggag, photoreceptor drum and current 1
It was found that the distance between the image rolls, the speed of the upper one-stage roll, and the quality of the speed ratio inverted image had a large influence (and that there was an optimal range).

By simply using the conventional method, the sharpness of the elephant does not improve even after going through the process of picking up the current toy taste, and
Merely switching the phenolic bias potential results in poor gradation reproducibility and cannot absorb variations in the degree of ca of negative originals.

According to the present invention, the condition of the toner brush of each developing roll in the upper stage and the lower stage, in other words, the phenomenon nig density (expressed as a dT/dP ratio), the speed of each phenomenon roll in the upper stage and T stage, and the speed ratio can be determined. This is the first time that it has been possible to control image sharpness, one-level gradation reproducibility, and anti-fogging IF, and to absorb variations in the contrast of negative originals and improve gradation reproducibility by applying a single-image bias. Since this has become possible, embodiments of the present invention will be described below.

An apparatus 7 as shown schematically in FIG. 6 was used.

Selenium photoreceptor as photoreceptor, resistivity 10 as toner
'5Ωcm (8KV/lym) -component magnetic toner.

As a developing machine, both the 2-stage and 2-stage loaf t are equipped with an 8-pole symmetrical internal magnet (800G) and a non-magnetic cylindrical sleeve (3
7φ, 5US304), the closest distance dT between the electrode trimmer and the developing roll, and the distance between the photoreceptor and the developing roll.
Closest distance dP to elephant roll.

The ratio (ar/dP), the rotational speed r of each roll, and the insulator pressure V were determined as shown in the table below.

Original contrast o, :s~0°9 under the above setting conditions
It was possible to obtain images with high image density and excellent sharpness without fog over a long period of time.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the latent potential level and bias potential in conventional reversal development using one developing roll; Figure 2 is a diagram showing Reenega Harane's latitude;
Figure LX is a diagram showing the relationship between the upper stage phenomenon roll bias' level and the latent 1st phenomenon potential level in the two-stage roll current method,
Figure 4 is the same (a diagram showing the relationship between the F stage phenomenon roll bias potential and the latent image potential level, and Figure 5 is a graph showing the relationship between the applied bias potential and image quality of the upper stage and r stage phenomenon rolls) 6 is a schematic diagram of an example of a two-stage roll development device used in the reversal development method of the present invention, FIG. 7 is a graph showing the relationship between dT and dP for the lower developing roll, and FIG. The figure is a graph showing the relationship between the speeds of the second and lower rolls. Reference numbers in the figure: 1... photoreceptor; 2... upper developing roll; 3...F
Stage development [Elephant roll 4'4... Hopper; 5, 6... Trimming member also used as injection electrode; 7.8... Bias power supply. Fig. 1 Fig. 2 Original parrot] Citrus No. 7 m dp, (mm) Shin 8 Katsui 1st Danguchi ~ 1 Renkang also (Xc)

Claims (1)

[Claims] The electrostatic latent images formed on the photoreceptor are
In a reversal process, the development of magnetic brushes on a first magnetic brush roll and on a second magnetic brush roll is performed using a one-component magnetic toner on a magnetic brush roll and a second magnetic brush roll. The packing density of the magnetic toner in each region is set to 0.2 to 0.7, and the moving speed Vu of the first magnetic brush roll and the moving speed vL of the second magnetic brush roll are respectively set to the moving speed Vp of the photoreceptor. The moving speed ratio (v1/Mu) of the first and second magnetic brush rolls is set to 0.5 to 2, and the first magnetic brush roll has a potential equal to or equal to the potential of the background latent image. A reversal developing method characterized in that a bias voltage higher than that is applied, and a bias voltage lower than 0.8 times the background latent image potential is applied to the second magnetic brush roll.