JPS58168058A - Method for developing electrostatic latent image - Google Patents

Abstract

PURPOSE:To obtain a reproduced image good in image density, gradiation, and sharpness, by using a mixture of toners different in amt. triboelectrified with carrier for toner. CONSTITUTION:A toner A and a toner B different in amt. triboelectrified with carrier are uniformly mixed at a constant ratio, contained in a toner replenishing device, and properly fed into a developer vessel, or the toners A, B are contained in each toner replenishing device 30, 35 respectively, and each is fed into the developer vessel 5 by rotation of each toner replenishing roll 32, 37. A mixing ratio of them is optionally selected by controlling the rotation of the rolls 32, 37 in accordance with original density, thus permitting formation of an image good in reproducibility of image density and gradation, and sharpness.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an electrostatic latent image developing method that is put into practical use in electrophotographic copying machines and the like.

Conventional technology In an electrostatic latent image developing method using a so-called two-component developer, a carrier and a toner are mixed at a certain ratio and mutually triboelectrically charged, and an electrostatic latent image carrier is usually formed by a magnetic brush developing device. Develop the electrostatic latent image carried on the surface of.

By the way, it has been found that in such an electrostatic latent image developing method, the following development occurs depending on the difference in the triboelectric charge amount of the toner (triboelectric charge position relative to the carrier).

That is, when a toner with a high amount of triboelectric charge on the carrier is used, the image density decreases, but the gradation reproducibility and edge sharpness are excellent.

On the other hand, when a toner with a low triboelectric charge amount is used, the gradation reproducibility and sharpness are slightly inferior, but the image density is high and the image is high contrast. Furthermore, toner scattering also increases.

Therefore, when reproducing originals with many halftones such as photographs, it is better to use toner with a high triboelectric charge amount, and when reproducing originals with many line images, it is better to use a toner with a low triboelectric charge amount. It is most ideal to use a toner that has both characteristics.

However, at present, only one type of toner is used in the two-component developer, and it is not easy to set the amount of triboelectric charge of the toner so as to satisfy both characteristics. .

On the other hand, in two-component developers, the combination of toner and carrier is extremely important, and if a carrier with new characteristics is developed, a new toner with an appropriate triboelectric charge amount that can be combined with this carrier must be developed. It was also difficult.

Purpose The present invention has been made in view of the above points, and its purpose is to enable image reproducibility that combines the above two characteristics, and to quickly adjust the triboelectric charging characteristics of toner to carriers with various characteristics. An object of the present invention is to provide a method for developing an electrostatic latent image.

Next 1 In order to achieve the above object, the electrostatic latent image developing method according to the present invention uses a two-component developer, but as a toner,
At least two different amounts of triboelectric charge on the carrier
It is characterized in that a mixture of toners of different types and amounts of L is used. That is, by using a mixture of two or more types of toner, the toner exhibits intermediate triboelectric charging characteristics, and it is possible to ensure good image reproducibility of one gradation of image density and sharpness. Further, by changing the mixing ratio of the toner itself, it is possible to use the toner for development as a toner having arbitrary triboelectric charging characteristics.

Embodiments The electrostatic latent image developing method according to the present invention can be roughly divided into two embodiments.

In the first embodiment, at least two types of toner having different amounts of triboelectric charge on the carrier are uniformly mixed in advance at a certain ratio, and the mixed toner is stored in one toner replenishing device to form a developer. This is a method of appropriately replenishing the tank, and this embodiment is used in a conventional developing device. Of course,
A developer prepared by mixing the two or more types of toner and carrier at a constant ratio is stored in the developer tank in advance.

Specifically, 5 parts by weight of A toner with an average particle size of 13 μm and a triboelectric charge amount of 15.5 μC/fj with respect to the magnetic carrier described later, an average particle size of 13 μm, and a triboelectric charge amount of 7.
5 parts by weight of B toner of 5 μC/fi', average particle size 40 μ
90 parts of a magnetic carrier of 1.0 m was mixed and stirred in a ball mill for about 10 hours, and the mixture was placed in a developer tank as a starter developer. Separately, 5 parts by weight of toner A and toner B) are mixed in a ball mill and stored in a toner replenishing device as replenishing toner. Note that the triboelectric charge amount of the toner refers to the charge amount of the toner when mixed and stirred with a carrier, and specifically, it is a value measured by a blow-off method.

Further, it is desirable that the difference in the amount of triboelectric charge between the A toner and the B toner is at least 3 to 5 μC/li'-L.

When 30,000 half-tone original images were copied using a conventional magnetic brush developing device under the above conditions, very stable image reproducibility was achieved, and the image density was 1.1% on the Macbeth value.
4. In terms of gradation reproducibility, it showed 8 stages on Kodak's 20-stage scale. These values are intermediate values when toner A and toner B) are used alone. Incidentally,
When using A toner alone, these values are 1.32.
There are 10 levels, and when B toner is used alone, these values are 1.5.6 levels.

Note that the mixing ratio of toner A and toner B) has a limit of A:n=1:3 to A, B-3: process rate when image quality is taken into account. This is because if the ratio of any one of the toners increases further, the image quality will become equal to the case where the larger toner is used alone.

In addition, toner A and toner B) are both heat-meltable fine powders, consisting of resin, carbon black, and other additives.
It is manufactured by uniformly heating and kneading these and going through a pulverization and classification process. The additives include a charge control agent, and as the charge control agent, chlorinated paraffin, an electron-accepting organic complex such as a monoazo dye metal complex, a phthalocyanine pigment, a quaternary ammonium, a pyridinium salt, etc. are used. By changing the type and amount added, the amount of charge can be adjusted.

Charge polarity can be changed.

Next, a second example will be described.

In the second embodiment, at least two types of toner having different frictional charge positions relative to the carrier are stored in independent toner replenishing devices, and the replenishment amount of each toner can be arbitrarily controlled.

The drawing shows a developing device used for implementing this second embodiment, and roughly shows a developing sleeve (1) installed at a developing position and a magnetic roller (2) built in this developing sleeve (1).
), developer stirring device (20), and toner supply device +3
0), (35). The photoreceptor drum (40) has a Se photoreceptor deposited on its surface.
It is rotated in the direction of arrow (21) at a circumferential speed of 280 rran/sec, and the surface potential of the electrostatic latent image formed in advance is +600V.

The developing sleeve (1) is made of a non-magnetic conductive material such as aluminum and is formed into a cylindrical shape, and is connected to the photosensitive drum (40).
It can be rotated at 55 rpm in the direction of arrow fb in the vicinity of the surface of the substrate, and a developing bias of 71 oov is applied during development. The magnetic roller (2) has an N pole and an S pole magnetized in sequence around its periphery, and is 2200 rP in the direction of the arrow (b1).
It can be rotated by m. That is, the developer is moved in the direction of the arrow (b) by the rotation of the developing sleeve (1) and the magnetic roller (
2) receives a moving force in the direction of the opposite arrow (b1),
As a result, the developing sleeve (1) is moved in the direction opposite to the arrow (b) due to the difference in the moving forces between the two.

As the developer, the same developer as that used in the first embodiment is used. That is, 90 parts by weight of magnetic carrier with an average particle size of 40 μm and an average particle size of 13 μm.

5 parts by weight of toner A having a triboelectric charge amount of 15.5 μC/P and 5 parts by weight of toner B having an average particle size of 13 μm and a triboelectric charge value of 7.5 μC/9 were uniformly mixed and stirred. In this case, toner A and toner B) are negatively charged due to friction with the carrier.

Furthermore, this developing device is surrounded by a casing (5) that functions as a developer storage tank, and above the developing sleeve (1) there is a casing member (7) that constitutes a part of the upper casing (6). 9) and the tip of the upper casing (6), and is supported by the inner peripheral surface (8) of the casing member (7).
is formed in an arc shape that can be contacted by a magnetic brush formed on the developing sleeve (1). Further, at the tip of the casing member (7) and an extension of the arc of the inner peripheral surface (8), an elastic insulating seal member +10 or an elastic insulating seal member +10 is provided so as to be in contact with the photosensitive drum (40). It is being

On the other hand, a casing (5) is located below the developing sleeve (1).
), a toner spill prevention plate (11) fixed to the end of the developing sleeve (1), and a cleaner provided so as to be in contact with the surface of the developing sleeve (1) in the forward direction opposite to the rotational direction and in the reverse direction following the rotational direction, respectively. (12 and toner scraper +13
1. A developer scattering prevention plate (transport blade 1151 that can be rotated in the direction of arrow (C)) is installed.

The developer stirring device (Company) consists of a transport pipe 123+ installed in the axial direction inside the casing (5) and a packet roller. Inside the transport pipe is a rotating shaft around which a 1 μm coil spring is spirally wound. (21) is installed. The packet roller (goods) has buckets (t25) with a concave cross-section installed at equal intervals around the periphery, and a stirring plate attached to the back side of one packet (■).It can be rotated at 5 Qrpm in the direction of the arrow fd). Then, the developer contained in the casing (5) is scooped up in a packet @ and conveyed to a position close to the developing sleeve (1).

The toner supply devices +30) and +351 are installed in parallel on the upper casing (6), and the toner tank +311
The bottom of (36) is open facing the inside of the casing (5), and toner supply rollers @ and ((text) are installed so as to be rotatable in the directions of arrows (e) and (e1), respectively.

The A toner is stored in the toner tank (31), and the B toner is stored in the toner tank cf+1, and is replenished into the casing (5) based on the rotation of the toner supply rollers (31) and (3), respectively. .

The amount of replenishment of A toner and B) toner, in other words, the mixing ratio of replenishment toner is the rotational speed of the toner replenishment roller (■).

It can be selected arbitrarily and independently by controlling the rotation time. Specifically, the operation panel of the copying machine is equipped with a three-level copy density selection switch for document conditions: "Dark,""Normal," and "Light," and the replenishment toner mixture ratio is controlled according to the selection of this switch. A circuit 138) determines the mixing ratio of toner A and toner B), and based on this mixture ratio signal, a toner replenishing roller rotation control circuit (39) controls the toner replenishing roller (support), +
Controls the rotation state of 371. The replenishment toner mixture ratio control circuit (support) controls the B toner mixture ratio from 0 to 100Wt%.
When "Dark" is selected, B toner with a low amount of triboelectric charge is replenished at a high ratio; when "Light" is selected, B toner with a high amount of triboelectric charge is replenished. Make sure that A toner is replenished at a high ratio. Also, when "Normal" is selected, A toner and B) toner are 1:1.
so that it is replenished at a ratio of However, in either case, the total supply of toner A and toner B) is the same, and only the mixing ratio is different.

Hereinafter, in the L configuration, the newly replenished developer with the A toner and B toner whose mixing ratio is determined according to the state of the original to be copied is stirred and mixed by the rotation of the packet roller, and the developer is transferred to the bucket) (25 ) to the position (-Al) affected by the magnetic field of the magnetic roller (2), and this position +Al
From arrow ff on the developing sleeve (1) as a magnetic brush.
) direction, rubs the surface of the photoreceptor drum,
The electrostatic latent image previously formed on the surface is developed. After being subjected to development, the developer is scraped off from the top of the developing sleeve (1) by a scraper (13), and is then scraped off by a transport blade (151).
The rotation of the packet sends it to the bottom of the roller.

Using this developing device and changing the mixing ratio of A toner and B) toner as appropriate depending on the condition of the original image to be copied, a copying experiment was conducted on 30,000 sheets. It showed very stable image reproducibility similar to that of the previous model.

Note that in the second embodiment, the mixing ratio of toner A and toner B) is variable based on the density of the document, but the invention is not limited to this.
For example, it may be variable based on "solid original", "line original", and "halftone original".

Medial malleolus As is clear from the above explanation, the present invention provides a toner that includes:
At least two different amounts of triboelectric charge on the carrier
Since development is performed using a mixture of more than one type of toner, the toner exhibits intermediate friction retention and shape retention properties that were previously unavailable, depending on the mixture ratio, and has good image density, single gradation reproducibility, and sharpness. It is possible to obtain excellent image reproducibility. Furthermore, by changing the mixing ratio of the toner itself, it is possible to use the toner for development as a toner with arbitrary triboelectric charging characteristics.

Therefore, even if a carrier with new characteristics is developed,
By mixing various toners, it is possible to create toners that can be combined with new carriers.

In particular, as shown in the second embodiment, if the mixing ratio is made variable when replenishing two types of toner with different amounts of triboelectric charge, not only is it not necessary to mix the toners in advance,
Image reproducibility that immediately corresponds to the state of the original to be copied can be obtained.

[Brief explanation of drawings]

The drawing is a sectional view of a developing device used for carrying out an embodiment of the electrostatic latent image developing method according to the present invention. (1)...Developing sleeve, (2)...Magnetic roller,
(5)...Casing (developer tank), ■...Developer stirring device, ■. Zheng)... Toner replenishment device, ■, @... Toner replenishment roller, 138)... Replenishment toner mixture ratio control circuit, ■.
...Toner replenishment roller rotation control circuit, f4I...Photosensitive drum. Patent applicant Minolta Camera Co., Ltd. Agent
Patent attorney Hao Aoyama and 2 others

Claims (1)

[Scope of Claims] 1. An electrostatic latent image developing method for developing an electrostatic latent image carried on the surface of an electrostatic latent image carrier using a developer made of a mixture of toner and carrier, comprising: An electrostatic latent image developing method characterized in that the toner is a mixture of at least two types of toners having different triboelectric charge positions relative to the carrier. 2. The electrostatic latent image developing method according to claim 1, wherein the electrostatic latent image is developed by changing the mixing ratio of each toner in the toner mixture.