JPS6354177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method and apparatus using a one-component developer.

A developing method using a one-component magnetic toner is attracting attention as a method to solve the drawbacks of conventional two-component developing methods. When transferring images to other areas, a development occurs in which the edges of the image are disturbed. This is thought to occur because the toner itself is electrically conductive and repels each other due to the high electric field during transfer. In order to solve this problem, that is, to reduce the influence of the electric field, attempts have been made to make the toner highly resistive, but even if the transfer is satisfactory, the original development is insufficient. This is obvious if the system uses an originally conductive toner and develops by electrostatic induction due to latent image charges. To compensate for this drawback, effective methods of increasing the amount of toner supplied, in other words, the amount of toner that comes into contact with the latent image, include increasing the number of rotations of the developing roll and reducing the distance between the latent image and the surface of the developing roll. Although methods have been adopted in which the developing electric field is strengthened, there is a limit to the increase in the number of revolutions of the developing roll, and as the number of revolutions increases, toner may become floating. Furthermore, if the distance between the latent image and the developing roll is made small, the gap through which the toner layer passes becomes smaller, which not only causes toner to accumulate between the nips, but also causes the toner to spill from the side of the roll. As it grows, it exhibits stains in the background of the image, a decrease in density, and unfavorable development.

In order to prevent such toner accumulation, for example, Japanese Patent Application Laid-open No. 52-146642, No. 53-135639, No. 53-
Although the device has been devised as seen in No. 135640,
Not only does this complicate the apparatus, but also the developing performance cannot be sufficiently satisfied, and there is a limit to the copying speed.

Furthermore, an attempt has been made in Japanese Patent Laid-Open No. 52-140339 to improve the developability by utilizing this toner accumulation. However, this method was also unsatisfactory as the image quality deteriorated significantly when a large number of copies were made.

An object of the present invention is to provide a magnetic brush developing method and an apparatus therefor which solve all of the above-mentioned drawbacks, increase copying speed without increasing toner movement speed, and improve image quality, especially in low density areas. The objective is to obtain copies with excellent developability and continuous tone reproducibility.

An object of the present invention is to form a magnetic brush of one-component magnetic toner on a developing roll having a non-magnetic sleeve and a magnet disposed inside the developing roll, and to transfer the magnetic brush to an electrostatic layer formed on a recording medium. In a magnetic brush development method in which development is performed by rubbing against an image, a toner regulating member is provided in front of the narrowest portion formed by the developing roll and the recording body, and a toner regulating member is provided between the developing roll, the recording body, and the regulating member. This can be achieved by a magnetic brush development method characterized in that an amount of toner in excess of the amount required for development is supplied to the area and the toner is forcibly compressed.

The present invention will be explained in detail below.

As shown in FIG. 2, the developing roll 2 has a rotating magnet 21 and a non-magnetic sleeve 22 fixed to its outer periphery. is formed on the non-magnetic sleeve 22.

By rotating the magnet 21 clockwise, the toner is conveyed counterclockwise. The transported toner enters a space created by a regulating member 5 provided between the hopper 3 and the recording medium 1, the developing roll 2, and the recording medium 1. The space between the regulating member 5 and the developing roll 2 is relatively narrow, and since the transported toner is continuously supplied, the toner accumulates and is forcibly compressed to form the compressed toner section 7. During the repeated development process, a certain amount of toner remains. This compressed toner portion 7 is connected to the narrowest part formed by the recording medium 1 and the developing roll 2, and the toner that has passed through this narrowest part forms a magnetic brush again.

The compressed toner section 7 must always maintain a constant amount of toner during the development process, which is repeated many times, and must also be in a forcibly compressed state. The object of the present invention cannot be achieved if toner accumulates naturally or accumulates due to the weight of the toner and the rotational force of the recording medium and developing roll. Toner is continuously supplied to the space surrounded by the recording body 1, the developing roll 2, and the regulating member 5 by the rotational force of the magnet 21, and this space is saturated with toner and becomes forcibly compressed. The purpose of the present invention can be achieved at this time. Therefore, in order to form the compressed toner section 7, the recording medium 1, the developing roll 2, and the regulating member 5 that form this space must be arranged in a fixed manner (that is, without moving back and forth or left and right). . Further, the amount of toner supplied to the compressed toner section 7 must be in excess of the amount required for development.

The electrostatic latent image on the recording medium 1 is developed and visualized by coming into contact with the compressed toner portion 7 and the magnetic brush. The visualized toner image is subsequently transferred to a transfer material such as paper and fixed to form a copy.

The copies developed in this way are relatively insulating.
When a one-component magnetic toner of 10 ⁸ Ωcm to 10 ¹⁴ Ωcm is used, good image quality can be obtained and the copying speed can also be increased.

Next, the present invention will be explained in further detail based on the accompanying drawings.

FIG. 1 shows a conventional magnetic brush developing device using one-component magnetic toner. FIG. 3 shows the effect of toner accumulation. Figure 3-a shows the relationship with background (BKG) concentration.
Figure 3-b shows the relationship between the image density and the original density of 0.7. Figure 3-c shows the relationship between the line thickness of the copied image and 100% indicates a line thickness that is 1:1 with the line of the original. The amount of accumulated toner is expressed as a comparative value because it changes depending on the process speed and the electrical resistance value of the toner used, but it has a proportional relationship with the electrical resistance value. That is, the amount increases with toner having a high electrical resistance value. In FIG. 1-a, the recording medium 1 rotates in the direction of the arrow, and the developing roll 2 is arranged relative to it. The developing machine includes a fixed sleeve 22, a magnet 21 having a plurality of mutually opposing magnetic poles that rotate in the direction of the arrow, and a hopper 3 for replenishing the one-component magnetic toner 4 from above. A part of the hopper 3 also has the function of controlling the thickness of the toner layer. FIG. 1-a shows a state where the toner storage amount is 0, and the broken line indicates that the layer has a thickness approximately equal to the distance between the surface of the recording medium and the developing roll 2. That is, the surface of the photosensitive material and the toner are in a very weak contact state. The state of the toner reservoir is such that toner exists between the photosensitive material and the developing roll, as shown in section 9 of Figure 1-b.
This shows a state in which toner is not transported in the direction of the arrow by the magnetic roll. To explain the influence of toner accumulation with reference to FIG. 3, toner accumulation does not stain the image background area up to a certain state, but when the condition is exceeded, staining rapidly occurs. The reason for this is that up to a certain state, the toner holding magnetic force exerted on the toner by the magnet prevails, but after that state the holding magnetic force becomes inferior to the electrostatic attraction, causing adhesion to non-image areas ( Figure 3-a). Next, in relation to image density, when the accumulation is zero, the contact time with the latent image is extremely short, and as the accumulation grows, the contact time is extended and sufficient development is achieved. I understand. However, if this time is too long, the latent image charge begins to leak through the toner to the developing roll, resulting in a decrease in image density (Figure 3-b). The same reason can be considered for the thickening and thinning of the lines (Figure 3-c).
Looking at the mechanism by which stagnation occurs, one of the reasons is that there is an imbalance between the space between the recording medium and the developing roll and the amount of toner supplied from the hopper. The second problem is that the conveyance force of the developing roll is weak. However, even if these conditions are satisfied, it is inevitable that the amount of retention will vary depending on the density of the image to be developed. That is, when many copies are made of the same document, image areas and non-image areas are limited, and an uneven accumulation amount occurs in the axial direction of the developing roll due to the distribution of toner consumption. Furthermore, a phenomenon similar to the above occurs even in one copy, although it is minute. More than that, there is an unavoidable phenomenon that has been confirmed by the inventors of the present invention. This phenomenon is that irrespective of the image potential, when a non-image area potential exists, toner accumulation occurs. Even if the sensitive material and the developing roll are rotated for a long time in an uncharged state or in a state where a bias potential is applied to the developing roll and there is virtually no developing electric field, stagnation does not occur, but there are cases where the developing roll cannot be developed. In the presence of even a small potential or charge, the stagnation will gradually grow. As described above, the inventors of the present invention have closely observed the mechanism by which stagnation occurs and the influence of the degree of stagnation, and by analyzing the results, they have discovered the following fact. That is, to explain with reference to FIG. 3, 3-a, 3-
From Figures b and 3-c, if it is possible to control the amount of accumulation between accumulation states 1 and 2, it is possible to not only ignore the influence of accumulation, but also to improve the image quality. It is a guess that it will be. Therefore, when an image was formed by applying about 1 to 2 stagnation to the developing machine, the best image quality as expected was obtained. However, although it is possible to copy a small number of copies, a large number of copies will result in deterioration in image quality. Various techniques related to this have been proposed, such as moving the developing device away from the recording medium at an appropriate time or closing the spike control blade 8 to shut down toner supply. As can be seen, this was not appropriate because it caused changes in image density, etc.

In other words, if stagnation is simply caused, even if good copies can be obtained for the first few copies, when a large number of copies are made, image density will drop, lines will become thinner, etc.

Therefore, the inventor of the present invention created a configuration as shown in FIG. That is, the regulating member 5 is disposed close to the recording body side end of the hopper to the extent that it does not come into contact with the recording body as much as possible. The material of the regulating member is suitably non-magnetic. Here, a phosphor bronze material with a thickness of 1 mm is used.

Toner is supplied to a space surrounded by the hopper 3, the recording medium 1, and the developing roll 2, so that a certain amount of toner is always retained. Furthermore, the toner is supplied in excess of the amount of toner required for development, so that the toner is forcibly compressed and accumulated.

As is clear from the above description, the fixed amount of toner accumulation here means that the amount of toner accumulation does not change during repeated development steps, and furthermore, it means that the amount of toner accumulation does not change during repeated development steps. This also means that uneven amounts of toner will not accumulate in the axial and rotational directions of the developing roll.
In addition, the amount of toner supplied to the reservoir is determined by the amount of toner necessary to form a visible image on the recording medium, the amount of toner that does not contribute to development and remains on the developing roll, and the amount of toner that accumulates in the reservoir due to the toner's own weight. The amount of toner supplied is larger than the total amount of toner supplied, and the term "excessive amount of toner" means this.

When making multiple copies with this configuration,
All of the copies obtained had a constant image quality, and the image quality was also very excellent in terms of image density, background density, line reproducibility, continuous gradation reproducibility, etc.

Such a result is due to the effect of the present invention, which forcibly compresses the toner by supplying an amount of toner in excess of the amount required for development to the area formed by the developing roll, the recording medium, and the toner regulating member, that is, 1. Development. time is extended.

2. The packing density of the toner increases at the portion (nip) where the toner held on the developing roll starts contacting with the recording medium until the contact is broken, thereby facilitating electrostatic induction.

3. The amount of charged toner in the nip increases and the starting voltage for development is lowered.

4. Due to the increase in packing density, an effect (scavenging effect) occurs in which fine toner particles that become mechanically and electrostatically adhered dirt (particularly background dirt) are scraped off during the initial stage of development (the beginning of nipping).

This is thought to be due to the following effects.

As shown in Figure 4, the amount of accumulated toner is
When expressed as the distance l from the point of contact between the recording medium and the developing roll to the point P' on the surface of the recording medium corresponding to the tip of the regulating member, the optimum amount of accumulated toner was as follows.

That is, Sensitive material (Se type) potential, Image 800V, BKG.100V Process speed (Surface movement speed of sensitive material) 100mm/sec Magnet rotation speed 500rpm Sensitive material - development roll space 1mm The toner used is ¹⁰⁸ with a particle size of 5 to 30 μm. ^~ 10Ω.cm
(electrical resistance when 100 V is applied) under the condition of one-component magnetic toner, when the value of l was varied between 3 mm and 30 mm and a large number of copies were made for each, it was found that when l was small, When l is large, lines become thinner and image density decreases, and when l is large, lines become thicker.
There was a tendency for stains to occur in the background area.

The optimum l range was 5 mm to 20 mm.

However, this range depends on the sensitive material potential, process speed,
It is relatively determined by the number of rotations of the developing roll, etc., and is not limited to this range. Further, other effects found from various observations made under the above conditions with l=1.2 mm will be described. First of all, as mentioned in 1 of the effect of retention, the development time is extended, but under these conditions, only the process speed was changed from 150 mm to 200 mm/sec, but there was no change in image density. I couldn't help it. In other words, under the initial conditions, a document with a density of 0.7 will have a density of 1.2.
was reproduced in , but remained the same even when the speed was increased.
Next, when the number of revolutions of the developing roll was increased with no accumulation, the relationship shown in Figure 5 existed in the past (for the original density of 0.7), but under these conditions, only the number of revolutions was increased to 500 to 2000 rpm. When it was shaken, it was found that it did not depend on the rotation speed as shown in Figure 6. The rising curve can be considered as the time for the accumulation to grow. If it is allowed to accumulate from the beginning, it will look like the broken line.

Therefore, from these facts, by allowing a certain amount of toner to accumulate from the beginning, the correlation between the process speed and the developing machine conditions, that is, the toner supply amount can be virtually ignored. Next, as a second effect, as shown by the solid line in Figure 7, the development characteristics of conventional one-component magnetic toners have very high contrast, and the low density area is steep, so stains in the background area of the image are suppressed. This resulted in the drawback of poor low-density reproducibility. However, in the case of the present invention, as shown by the broken line, the contrast is relatively soft and the reproducibility in the low density region is improved. This is considered to be a synergistic effect of 3 and 4 mentioned in the retention effect. Furthermore, as a third effect, this was also thought to be due to accumulation, but perhaps due to toner collision in the developing nip, floating toner is generated in that area, which further damages the upper optical system components and charging equipment. Although there was a phenomenon in which the corotron was contaminated and the image deteriorated, it was found that by providing the regulating member 5, this phenomenon was greatly reduced. Analyzing the causes of this effect, as shown in the sketch from the top in Figure 8, one reason is that the accumulation is covered mechanically, and the floating toner T is first electrostatically removed by the regulating member. 5
It is considered that the force that is captured by the developer and then returned to the reservoir by the conveyance force due to the magnetic force of the developing roll under the regulating member 5 is constantly acting, exerting an effect similar to a kind of air curtain in this part. Furthermore, the fourth effect is that conventionally, controlling the amount of toner supplied to prevent accumulation is complicated, and the regulation blade 8 in FIG.
The distance between the developing roll surface 2 and the developing roll surface 2 is extremely small, and the setting of parallelism in the axial direction of the developing roll is strict, so precision is required for the blade member, but in the case of the present invention, retention is forcibly applied. Because of this, there is virtually no value in existence. Furthermore, as the toner accumulation grows, once accumulation and compression reach saturation, no more supply is carried out from the hopper, so the amount of toner supplied from the hopper does not need to be strictly determined, and on the contrary, the opening of the hopper can be made wider. It also has this effect. Fifth
As an effect of this, since contact of the toner with the outside is substantially cut off, the effects of moisture absorption and the like of the toner due to long-term standstill can be reduced.

The regulating member 5 may have a shape other than the above-mentioned plate shape, for example, as shown in FIG. 9. In FIG. 9-a, the regulating member is in the form of a roll, and is disposed between the recording medium 1, the developing roll 2, and the toner hopper 3. This roll-shaped regulating member 51 is preferably made of a non-magnetic material, and it is even more preferable to make it of a relatively elastic material such as rubber or foam rubber, since it can be provided in contact with the recording medium. When provided in contact with the recording medium, the roll-shaped regulating member 51 is arranged to be rotatable.

Further, in FIG. 9-b, the side wall of the toner hopper is used as a regulating member.

In addition to these, various other regulating members can be considered. In other words, it is sufficient that the structure is such that a constant amount of toner is always accumulated in the space surrounded by the recording medium, the developing roll, and the toner hopper during the repeated developing process.

Further, as the recording material used in the present invention, an electrophotographic photoreceptor or an electrostatic recording material in which a photosensitive layer is formed on a conductive support can be used, and a photoreceptor in which a surface insulation layer is further provided on the photosensitive layer can be used. It is more preferable to form an electrostatic latent image by the process of primary charging, secondary charging with a polarity opposite to the primary charging, and image exposure, and then develop it by the developing method of the present invention.

That is, the electrostatic latent image formed by this process has no charge on the surface of the surface insulating layer, so that charge leakage does not occur and the developability is further improved.

As described above in detail, the magnetic brush developing method and device according to the present invention have been developed in the search for a method to remove or eliminate toner accumulation, which is the cause of image quality deterioration and image quality fluctuation.
The inventors of the present invention reversed this and were able to achieve this by actively causing stagnation, and were able to demonstrate excellent developability with an extremely simple ^{configuration} . Even when an insulating toner such as 10 ¹⁴ Ωcm was used, good developability was exhibited. This facilitates subsequent transfer and provides various favorable ramifications, such as the fact that the transfer paper does not necessarily require insulation treatment.

[Brief explanation of the drawing]

Figures 1a and b are of the conventional method, and Figure 2 is of the present invention.
FIG. 3 is a cross-sectional view schematically showing a magnetic brush developing device. Figures 3a, b, and c are graphs showing the effects of toner accumulation. FIG. 4 is an explanatory diagram of the developing device of the present invention, and FIGS. 5 to 7 are graphs showing the state of copying. FIG. 8 is a schematic diagram of the apparatus of the present invention viewed from above. Figures 9a and 9b are schematic sectional views showing other embodiments of the device of the present invention. Codes in the figure: 1...recording body; 2...developing roll;
3...Hopper; 4...One-component magnetic toner; 5...
... Regulating member; 6... Magnetic brush; 7... Compressed toner portion; 8... Ear standing control blade; 21... Magnet; 22... Non-magnetic sleeve; 51... Roll-shaped regulating member.

Claims (1)

[Claims] 1. A magnetic brush of one-component magnetic toner is formed on a developing roll having a non-magnetic sleeve and a magnet disposed inside the developing roll, and the magnetic brush is caused to rub against an electrostatic latent image formed on a recording medium. In the magnetic brush development method, a toner regulating member is provided in front of the narrowest part formed by the developing roll and the recording body, and a toner regulating member is provided in the area formed by the developing roll, the recording body, and the regulating member necessary for development. A magnetic brush developing method characterized in that the toner is forcibly compressed by supplying an excessive amount of toner.