JPS62173479A - Developing method - Google Patents

Abstract

PURPOSE:To obtain a visible image which has no color clouding and has high quality stably for a long period of time by using a developer contg. nonmagnetic ceramics and magnetic ceramics. CONSTITUTION:The developer contg. the nonmagnetic ceramics and magnetic ceramics is used in a developing method for making non-contact development of an electrostatic latent image under an alternating bias. Ceramics such as aluminate and steatite which are nonmagnetic and have an insulating characteristic are usable for the nonmagnetic ceramics and ceramics such as magnetite and ferrite having magnetism are usable for the magnetic ceramics. Fluidity is inferior and there is an easier tendency for sticking of the carriers to each other, by which the deteriorated agitation characteristics with the toner is caused if the grain size of the carrier for development is <10mum. On the other hand, the developability is deteriorated as the amt. of the toner to be supplied to a developing space is decreased and the electric field distribution by the developing electrode effect possessed by the carrier chain is roughened if the grain size exceeds 200mum.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a developing method, and more specifically, to a developing method for visualizing an electrostatic latent image formed on an image carrier in electrophotography. .

BACKGROUND OF THE INVENTION As a developing device used for the above-mentioned development, the following type of developing device is widely adopted because it is easy to downsize. That is, a layer of magnetic developer is formed on the surface of the developing sleeve, which serves as a developer transport carrier, by the action of a magnet located on the back side, and the magnetic developer is supplied to the surface of the image carrier, and the image carrier is heated under an alternating electric field. It is a type that attaches to the electrostatic latent image on the top. For color copying, a non-contact developing method is preferred in which the magnetic brush is not brought into contact with the image carrier so as not to destroy the previously developed toner image. Non-contact development is a method in which an alternating current bias is applied to the developer conveying body to form an alternating electric field in the development area without bringing the magnetic brush into contact with the image carrier, causing the toner to fly and adhere to the electrostatic latent image. It is.

The developer used in the above-mentioned development is roughly divided into a one-component developer made of a magnetic toner that has a magnetic substance therein and imparted with magnetism, and a two-component developer made of a non-magnetic toner and a magnetic carrier. Two-component developers do not require the toner to contain a black or brown magnetic material, and can produce toner images with clear colors, and toner charge control is easier than with single-component developers. It is particularly suitable for color copying.

Such magnetic carrier particles are made of metals such as iron, chromium, nickel, cobalt, or compounds or alloys thereof, as in conventional magnetic carrier particles.
For example, triiron tetroxide, γ-ferric oxide, chromium dioxide,
Particles of ferromagnetic or paramagnetic substances such as manganese oxide, ferrite, and manganese-copper alloys are made finer, preferably spherical, or the surfaces of these magnetic particles are preferably coated with styrene resin or vinyl resin. resins, ethyl resins, rosin modified resins, acrylic resins, polyamide resins, epoxy resins, polyester resins, palmitic acid,
Cover it in a spherical shape with fatty acid wax such as stearic acid, or
Or, more preferably, particles of a resin or fatty acid wax containing dispersed magnetic particles are pulverized or granulated and polymerized to preferably form spherical particles, and the resulting particles have a conventionally known average particle diameter. It can be obtained by particle size selection by other means.

An example of developing using a two-component developer using a non-contact development method or a near-contact development method is JP-A-56-144452.
, 57-139761, 59-67565, 5
9-91453, 59-121077, 59-1
54469 and 59-181362.

As a result of repeated studies, the inventors of the present invention found that the above-mentioned conventional developing method using a magnetic carrier has the following drawbacks. That is, (1) The surface properties of the carrier, such as triboelectricity due to oxidation, surface resistance, surface energy, etc., change depending on the environment and mechanical stress, making it difficult to stably obtain a toner image of good quality.

(2) Resin-dispersed carriers made into spheres using resins, etc. have a long life and have a wide range of tolerance for developing conditions, but because they are basically resin powders, they have poor fluidity and do not interact well with toner. As a result, the stirring time required to impart sufficient charge to the toner for development becomes long.

(3) It is difficult to completely avoid adhesion of the carrier to the image bearing member, and this sometimes causes color turbidity in copies. This tendency is seen in reversal development. In reversal development, the non-image area (white background area, which often occupies a large area) on the image carrier has a high charge density, so carriers tend to adhere to the non-image area and the edges of the image area. .

Purpose of the Invention The present invention has been made in view of the above circumstances, and includes:
The object of the present invention is to provide a developing method that does not cause color turbidity and can stably obtain high-quality visible images over a long period of time.

21. Constitution of the Invention The present invention provides a developing method for non-contact developing an electrostatic latent image under an alternating bias, which is characterized by using a developer containing a non-magnetic ceramic and a magnetic ceramic. Pertains to.

E. Examples As the non-magnetic ceramics, non-magnetic and insulating ceramics such as alumina and steatite can be used, and as the magnetic ceramics, magnetic ceramics such as magnetite and ferrite can be used.

First, a preferred embodiment of the developing carrier (hereinafter simply referred to as carrier) based on the present invention will be described.

(1) If the particle size is less than 10 μm, the fluidity will be poor and the carriers will tend to adhere to each other, resulting in a decrease in agitation with the toner. On the other hand, if it exceeds 200 μm, the amount of toner supplied to the development space decreases and the electric field distribution due to the development electrode effect of the carrier chain becomes rough, resulting in a decrease in developability. Therefore, the average particle size is 10-200μm
The thickness is preferably within the range of 20 to 100 μm.

(2) Electrical resistance should preferably be in the range of 10 to 109cm;
It varies depending on the type of ceramic used and the mixing ratio with the magnetic ceramic, and is selected within the above range depending on the development conditions.

The resistivity is determined by placing the particles in a container with a cross-sectional area of 0.50 Cffl, tapping them, applying a load of 1 kg/cJ on the packed particles, and at this time, the carrier particles have a thickness of about IH. This value is obtained by reading the current value when a voltage is applied that creates an electric field of 1000 V/cm between the load and the bottom electrode.

(3) Magnetization characteristics are adjusted by the mixing ratio of magnetic ceramics and non-magnetic ceramics, and are adjusted to 20 to 10% according to the development conditions.
It can be selected and set within a wide range of 100e/g.

(4) Regarding triboelectric charging properties, select a ceramic that charges the toner to a desired polarity depending on the relationship with the toner resin and the charge control agent mixed in the developer. For example, alumina (Aj2z
O3) is positively charged due to frictional charging with the toner resin, and the toner is negatively charged. A reversely chargeable toner can be obtained by adding this carrier and an electron-donating charge control agent such as nigrosine to the toner.

The carrier based on the present invention can be manufactured as follows.

(1) Granulation using a spray dryer For example, a slurry made by mixing non-magnetic ceramic powder and magnetic ceramic powder in a wet process is granulated using a rotating disk type spray dryer, and this is sintered to obtain an average particle size of 10. ~100
Make it a μm powder.

The structure of one carrier particle, as shown in an enlarged view in FIG. Magnetic ceramic powder with a particle size of about 0.1 μm is kneaded with a resin binder such as styrene, acrylic, polyester, etc., and granulated by a crushing granulation method.

The structure of one carrier particle is composed of a non-magnetic ceramic particle 1 and a magnetic ceramic particle 2, as shown in an enlarged view in FIG.

Next, the toner constituting the developer together with the carrier according to the present invention will be explained.

Generally, when the average particle size of toner particles in a two-component developer becomes smaller, the amount of charge qualitatively decreases in proportion to the square of the particle size, and the adhesion force such as van der Waals force becomes relatively large. Therefore, it becomes difficult for the toner particles to separate from the carrier particles, and once the toner particles adhere to the non-image area of the image carrier surface, they cannot be easily removed by rubbing with a conventional magnetic brush, resulting in fogging. It becomes like this.

In the conventional magnetic brush development method, such problems became noticeable when the average particle size of toner particles was 10 IIm or less. The developing method of the present invention solves this problem by performing non-contact development under an oscillating electric field without bringing the image carrier into contact with the developer layer. That is, the toner particles adhering to the developer layer are easily moved away from the developer layer and transferred to the image area and non-image area on the image carrier surface by the electrically applied vibrations, and are also easily separated from the developer layer. and,
Toner particles with a low charge amount hardly migrate to the image area or non-image area, and since they are not rubbed against the surface of the image carrier, they do not adhere to the image carrier due to frictional charging. Toner particles with a particle size of about 1 μm have come to be used.Therefore, it is possible to obtain a clear toner image with good reproducibility by faithfully developing an electrostatic latent image.Furthermore,
Since the oscillating electric field weakens the bond between toner particles and carrier particles, adhesion of carrier particles accompanying toner particles to the image bearing surface is also reduced. In the image area and non-image area, toner particles with a large amount of charge vibrate under an oscillating electric field, and depending on the strength of the electric field, carrier particles also vibrate.
Since the toner particles selectively migrate to the image area on the image carrier surface, adhesion of carrier particles to the image carrier surface is significantly reduced.

On the other hand, as the average particle size of the toner increases, as described above, the roughness of the image becomes noticeable.

Normally, toner with an average particle size of about 20 μm has no practical problem for developing fine lines lined up at a pitch of about 10 lines/dragon with high resolution, but if fine particles with an average particle size of 1 μm or less are used, The resolution has been significantly improved, and it is now possible to produce clear, high-quality images that faithfully reproduce the differences in shading. For the above reasons, the average particle size of toner is 20.
The appropriate condition is 10 μm or less, preferably 10 μm or less.

Further, in order for the toner particles to follow the electric field, it is desirable that the amount of charge of the toner particles be greater than 1 to 3 μC/g (preferably 3 to 100 μC/g). Particularly when the particle size is small, a high amount of charge is required. Also, the resistivity is 10SΩc
It is good if it is I11 or more, preferably 10'3 Ωcm or more.

Such toner can be obtained in the same manner as conventional toner. That is, it is possible to use a toner in which spherical or amorphous nonmagnetic or magnetic toner particles in conventional toners are sorted by an average particle size sorting means. Among these, it is preferable that the toner particles are magnetic particles containing magnetic particles, particularly when the amount of magnetic fine particles is 60 wt.
It is preferable that the amount does not exceed 30 wt %, but in order to obtain color clarity, a small amount of 30 wt % or less is preferable. When the toner particles contain magnetic particles, the toner particles are influenced by the magnetic force of the magnet included in the developer transport carrier, so that the uniform formation of the magnetic brush is further improved. The occurrence of fogging is prevented, and furthermore, toner particles are less likely to scatter. However, if the amount of magnetic material contained is too large, the magnetic force between it and the carrier particles becomes too large, making it impossible to obtain a sufficient development density.
Furthermore, fine magnetic particles appear on the surface of the toner particles, making it difficult to control triboelectrification, making the toner particles more likely to be damaged, and making them more likely to aggregate with carrier particles.

To summarize the above, the preferred toner in the image forming method of the present invention uses the resin described above for the carrier and furthermore, fine particles of magnetic material, to which a coloring component such as carbon and a charge control agent, etc. are added as necessary. The average particle diameter that can be produced by a method similar to a conventionally known method for producing toner particles is 20 μm or less, particularly preferably 10 μm.
It consists of the following particles.

In the image forming method of the present invention, a developer in which the above-described spherical carrier particles and toner particles are mixed in the same proportion as in a conventional two-component developer is preferably used, but this also includes: If necessary, a fluidizing agent to prevent particles from flowing and sliding, a cleaning agent to help clean the surface of the image carrier, etc. are mixed.As fluidizing agents,
Colloidal silica, silicon face, metal soap, nonionic surfactants, etc. can be used, and as cleaning agents, surfactants such as fatty acid metal salts, organic group-substituted silicones, or fluorine, etc. can be used.

The above are the conditions for the developer, and such a developer can prevent color clouding between the mosaic filters. Next, conditions regarding a developer transporting body for forming a developer layer using such a developer to develop an electrostatic image on an image carrier will be described.

The developer carrier used is the same as that used in conventional development methods to which a bias voltage can be applied.
In particular, a structure in which a rotating magnet having a plurality of magnetic poles is provided inside a sleeve on which a developer layer is formed is preferably used. In such a developer conveying body, the developer layer formed on the surface of the sleeve moves in an undulating manner due to the rotation of the rotating magnet, so new developer is supplied one after another, and the developer layer is moved in a wave-like manner. Even if there is some degree of non-uniformity in the layer thickness of the developer layer on the surface of the IJ-b, its influence is sufficiently covered by the above-mentioned wavy undulations so that it does not become a problem in practice. It is preferable that the developer transport speed due to the rotation of the rotating magnet and the rotation of the sleeve is almost the same as or faster than the moving speed of the image carrier. Further, it is preferable that the rotation of the rotating magnet and the rotation of the sleeve are carried in the same direction. Image reproducibility is better in the same direction than in the opposite direction. However, it is not limited to these.

Further, the thickness of the developer layer formed on the developer transport body is preferably such that the adhered developer is sufficiently scraped off by a thickness regulating blade to form a uniform layer.
The gap between the developer conveying member and the image bearing member is several tens to two.
000 μm is preferred. If the surface gap between the developer conveying member and the image bearing member becomes narrower than several tens of micrometers, it will be difficult to form magnetic brush ears that will uniformly develop the gap, and it will also be difficult to transfer sufficient toner particles to the developing area. If the gap greatly exceeds 2000 μm, the opposing electrode effect will decrease and sufficient development density will not be obtained, and the electrostatic image The edge effect, in which more toner adheres to the contour than the center of the image, also increases. in this way,
If the gap between the developer transporter and the image carrier becomes extreme, it will not be possible to make the thickness of the developer layer on the developer transporter appropriate.
Within the range of m, the developer layer can be formed to have an appropriate thickness. Therefore, the gap and the thickness of the developer layer should be adjusted such that the tip of the magnetic brush does not come into contact with the surface of the image carrier with a gap of 10 to 500 μm and is close to the surface of the image carrier under the condition that no oscillating electric field is applied. It is particularly preferable to set the conditions. This is because the toner development of the latent image is prevented from having scratches or fog caused by the rubbing of the magnetic brush.

Furthermore, development under an oscillating electric field is preferably carried out by applying an oscillating bias voltage to the sleeve of the developer carrier. Further, it is preferable to use a bias voltage that is a combination of a direct current voltage that prevents toner particles from adhering to non-image areas and an alternating current voltage that makes it easier for toner particles to separate from carrier particles. However, the present invention is not limited to the method of applying an oscillating voltage to the sleeve or the method of applying a superimposed voltage of DC and AC.

In addition to the magnetic brush method described above, the developing method may be a non-contact developing method in which the image carrier is not rubbed with a developer. The non-contact development method will be explained in specific examples below.

Next, specific examples of the present invention will be described.

The developing device used had the structure shown in Figure 3, and the developer [
)e is conveyed in the direction of the arrow by the magnetic roll 22 rotating in the direction of arrow F and the sleeve 21 rotating in the direction of arrow G.

The thickness of the developer ()e is regulated by the spike regulating blade 23 during transportation.

The spike control blade 23 is made of an elastic metal plate, and the sleeve 21
The thickness of the developer being conveyed is controlled by pressing the surface of the developer.

A stirring screw 24 is provided in the developer reservoir 29 to sufficiently stir the developer [)e, and when the developer De in the developer reservoir 29 is consumed, the toner supply roller 25 is rotated. By rotating, toner T is replenished from the toner hopper 26. And sleeve 2
A DC power supply 27 that applies a developing bias to 1 and an AC electrode 2
8 and a protection resistor R are connected in series. Further, the sleeve 21 and the image carrier 41 are arranged facing each other with a gap d in between, and the toner is held in a non-contact state with respect to the image carrier 41 in the development area E.

In order to obtain a desirable image in color copying, this non-contact state is essential, especially in the second and subsequent development.

The above-mentioned non-contact state means that when there is no potential difference between the sleeve 21 and the image carrier 41 (a state where no developing bias is applied), they are arranged facing each other with a gap d between them, and the developer layer thickness is This means that t is set smaller than the gap d.

By doing this, damage to the toner image already formed on the image carrier 41 can be avoided during the second and subsequent development, and the toner already attached to the image carrier 41 can be removed from the sleeve 21. It is possible to avoid the occurrence of color turbidity due to the toner going backwards and mixing into the subsequent developing device which stores toner of a different color from the toner of the preceding stage.

Fruit 110 - 20% by weight of alumina powder with an average particle size of 1 μm, average particle size of 0
．． 55% by weight of 1 μm magnetite powder and 25% by weight of polyester resin as a binder resin were blended, kneaded, crushed and granulated, and then classified into particle sizes of 20 to 30 μm to obtain a carrier. The specific gravity of this carrier was about 3°O or less.

This carrier has U-B i X1800 (product name)
A toner for a copying machine (a toner containing carbon in polyester resin) was blended so that the toner concentration was 20% by weight, and copying was performed under the following conditions.

The photosensitive layer of the image carrier 41 is made of an organic photoconductive material (OPC), its circumferential speed is 60/see, the gap d is 0, 3, and the developer layer thickness is O, O5, The diameter of the sleeve 21 is 24, and the rotation speed is 200 rpm.
AC bias 600 V r, m, s, 2Ktl
z, DC bias was set to -300V.

The image carrier 41 is charged by a charger (not shown) and exposed to image by an image exposure device (not shown), and its surface potential is set to 1,700V in the black area and -30V in the white area, and this electrostatic latent image is A toner image was formed on the image carrier 41 by reversal development using the developing device 20 shown in FIG. 3, and was copied onto recording paper using a transfer device and a fixing device (not shown) to examine the durability of the carrier.

As a result, the carrier showed a lifespan of more than 100,000 copies, and the copies obtained during that time had no defects such as carrier adhesion, fogging, or color turbidity, and there was only a very slight change in image quality.

The main gap d of the dispensing plate is 1.0, and the developer layer thickness t is 0.3*m.
, the outer diameter of the sleeve 21 is 18 mm, the rotation speed is 200 rpm,
The rotation speed of the magnetic roll 22 was set to 80 rpm, the AC bias was set to 1 K Vr, m, s, 2 KHz, and the DC bias was set to -300 V, and the other conditions were the same as in Example 1. Transferred and fixed.

The obtained copy was of good quality and stable, similar to the copy obtained in Example I above.

As a comparative example, ferrite particles with a diameter of 80 μm were coated with styrene.
When a developer containing a carrier coated with an acrylic polymer and the above-mentioned toner is used, carrier adhesion occurs easily due to its resistance and polarizability, and AC bias stabilizes the photoreceptor surface potential with high precision. It is necessary to take measures such as intentionally lowering the developability by lowering the voltage, which has the disadvantage that the appropriate range of development conditions is extremely narrow compared to the above-mentioned ceramic carrier.

Although the above example is an example in which the present invention is applied to a two-component developer, the present invention is not limited to a two-component developer, but can be applied to a -component developer to replace the magnetic particles contained in the toner with non-magnetic particles. It is also possible to obtain high quality visible images as it is made of ceramics and magnetic ceramics.

As described in detail, the developing method based on the present invention performs non-contact development under alternating bias, so the image bearing member is not rubbed with the developer, and even in color copying. Toners of different colors do not mix with each other, and a previously developed toner image is not destroyed, and a high-quality image without color turbidity or fogging is formed.

In the present invention, since a developer containing non-magnetic ceramics and magnetic ceramics is used in this non-contact development, the surface properties of the developer are stable, the fluidity is good, and the toner is compatible with the toner. The toner is easily charged by friction.

Further, the degree of charging and magnetization can be set to desired values within a wide range by selecting the mixing ratio of both. As a result, while taking advantage of the features of non-contact development, the image quality of the copies obtained by sufficiently charging the toner becomes stable and good. Furthermore, even in reverse development, it is possible to prevent deterioration in image quality due to adhesion of magnetic particles, such as carriers.

[Brief explanation of drawings]

The drawings all show embodiments of the present invention; FIGS. 1 and 2 are enlarged views showing the structure of a carrier, and FIG. 3 is a schematic sectional view of a developing device. In addition, in the symbols shown in the drawings, 1...Alumina (non-magnetic ceramics)
Particles 2...Magnetite (magnetic ceramics) particles 3...Binder resin 20...Developer 21...・Sleeve (developer carrier) 22
......Magnetic roll 24...P & stirring screw 26...
..... Toner hopper 27 ..... DC bias power supply 28 ...
...AC bias power supply 29...Developer reservoir 41...Image carrier E...Development area [) e. ......Developer T......Toner.

Claims (1)

[Claims] 1. A developing method for developing an electrostatic latent image in a non-contact manner under an alternating bias, characterized by using a developer containing a non-magnetic ceramic and a magnetic ceramic.