JPS61158339A - Dry-type developer and electrostatic latent image developing method using same - Google Patents

Abstract

PURPOSE:To obtain a carrier prevented from the rise of electric charge, the reduction of picture density and the generation of spent toner even if the carrier is stirred together with the toner for a long period while increasing the resistance of the carrier by containing the carrier consisting of carrier grains having recessed parts filled with resin on their surfaces. CONSTITUTION:For instance, ferrite or iron can be used as the carrier grains. The carrier grains 1 having recessed parts 3 on their surfaces are sufficiently mixed and stirred together with resin powder 2 having particle size to be entered into the recessed parts at a fixed rate to adhere the resin powder 2 to the surfaces of the carrier grains and their recessed parts. Almost all the resin powder is embedded into the recessed parts of the carrier grains by mixing the carrier grains 1 and the resin powder sufficiently and the resin powder is not almost adhered to the surfaces of the carrier surfaces. Under said status, the carrier grains are heated to melt the resin powder. Polystyrene resin or polyester resin is used as the resin powder as an example, but the kind of the resin is not limited to the example.

Description

DETAILED DESCRIPTION OF THE INVENTION - Industrial Application Field The present invention relates to a dry developer and a method for developing an electrostatic latent image using the developer.

Conventional technology Conventionally, developers for developing electrostatic latent images include cascade development developers using carrier particles such as glass peas and insulating toner particles, and developers using magnetic carrier particles such as iron powder and insulating toner particles. Two-component developers, such as developers for magnetic brush development, are in practical use.

The problem with electrostatic latent image development methods using these developers is that when development is carried out for a long period of time, the toner (spent toner) in the developer fuses to the surface of the carrier particles, reducing the ability of the carrier. As a result, the density of the developed image decreases and fog occurs, making the image unclear.

In order to solve this phenomenon, the particle size of the carrier can be reduced (
For example, it has been proposed to avoid strong contact between particles, e.g. However, in this method, with a low resistance carrier, a phenomenon of charge injection from the developing sleeve to the carrier occurs, and the carrier tends to adhere to the photoreceptor, whereas with a high resistance carrier, on the other hand, the charge leakage effect is reduced. When agitated with toner for a long time, especially in a low humidity environment, the amount of charge increases, causing problems such as a decrease in image density and generation of spent toner. In order to solve the problem caused by this high resistance, it has been proposed to use a binder type carrier in which fine magnetic powder and resin are dispersed, pulverized, and classified as carrier particles. This carrier has an uneven charge distribution due to the mixture of resin parts and magnetic parts on its surface. Therefore, when it comes into contact with toner, charge leaks locally and increases the charge amount. is suppressed.

However, since this binder-type carrier is made by dispersing magnetic powder in a resin, it has the disadvantage that if the amount of resin is increased, the magnetic properties become too weak, and if the proportion of magnetic powder is increased, it becomes brittle. In any case, in order to maintain the strength of the carrier at a practical value, a considerable amount of resin is required.
As a result, the magnetic properties are considerably affected.

Furthermore, Japanese Patent Application Laid-Open No. 57-204560 discloses that the resistance value of an iron oxide carrier increases over time, and the resistance value of a synthetic resin-coated carrier decreases over time. A technique has been proposed to obtain a developer containing a carrier whose resistance value changes little over time by blending the carriers in appropriate proportions. However, in this method, the resin is only partially fused to the surface of the iron oxide, and it is easy to peel off due to friction between the carriers or between the carrier and the toner, and is not necessarily satisfactory. Furthermore, since iron oxide is used in combination, the problem of fusion of spent toner to the surface of carrier particles cannot always be satisfactorily solved.

Problems to be Solved by the Invention In order to solve the above-mentioned problems, the present invention aims to make the carrier high in resistance, yet the amount of charge does not increase even when mixed with the toner for a long time, resulting in a decrease in image density and a problem with spent toner. The purpose is to provide a carrier that does not cause the occurrence of

Means for Solving the Problems The present invention provides a dry developer containing a carrier in which a resin is embedded in the recesses of carrier particles having recesses on the surface, and a method for developing an electrostatic latent image using the developer. provide.

Examples of carrier particles having concave portions on the surface include fine particles of ferrite, iron, and the like.

Conventional ferrites and the like have been used that have virtually no recesses on their surfaces. In the present invention, carrier particles having concave portions are used. In order to form recesses on the surface of ferrite, etc., the quasi-spinelized powder obtained by pre-calcination of the raw metal oxide is crushed in a water bath, and then sintered to grow crystals of primary particles. A method such as forming a recess on the mating surface may be used. Although it is difficult to quantify these four parts, they can be expressed by the degree of crystal growth based on the primary particle diameter of the carrier particles. That is, randomly selected carrier particles were photographed using a scanning electron microscope (500x magnification) at appropriately different locations three times, and carrier particles composed of primary particles of 10μ or more were photographed. The number % of the number of particles can be determined, and the concave portions in the carrier particles can be evaluated from this. The carrier particles used in the present invention preferably have a size of 20 to 70 μm, particularly 20 to 50 μm.

The carrier particles used in the present invention include, for example, ferrite [(NjO)o, 5(ZnO)o, 7(F eto*)
o, ss], iron, etc. can be used.

A resin is embedded in the recesses of carrier particles having recesses on their surfaces. An example of how the resin is embedded is shown in FIGS. 1 to 4.

FIG. 1 shows carrier particles (1) having a recess (3) and resin powder (2) having a particle size that can fit into the recess.

Both are thoroughly mixed and stirred at a constant ratio, and the resin powder (2) is adhered to the surface of the carrier particles and the concave portions thereof, as shown in FIG. When the two are sufficiently mixed, the third
As shown in the figure, most of the resin powder is embedded in the recesses of the carrier particles, with almost no adhesion to the surface thereof. After reaching this state, the carrier particles are heated to melt the resin powder (FIG. 4). As a result, a carrier is obtained in which the molten resin is embedded in four parts of the carrier particles. Further, when the carrier particles and the added resin powder are triboelectrically charged, the resin powder is relatively strong due to Coulomb force and adheres to the concave portions of the carrier particles, so that no particular melting step is required. Therefore, it is possible to obtain a carrier as shown in FIG.゛Resins that can be used in the present invention include, but are not limited to, polystyrene, styrene acrylic resin, acrylic resin, epoxy resin, fluororesin, and polyester resin. For example, as shown in Figure 4, when melting resin powder in a recess, it is necessary to use a thermoplastic resin. There is no need to use thermoplastics. The type of resin used is 0.1-1.0 parts by weight, more preferably 0.4-1.0 parts by weight, per 100 parts by weight of the carrier particles. It is 0 parts by weight.

The average particle size of the carrier obtained in this way is 20 to 70
It is more preferably 20 to 50 μm than 1 μm. In addition, the electrical resistance value is 107Ω・cm or more, more preferably 109Ω
・01 or more (value measured under an electric field of 500V/cm)
It is.

These carriers can be used in conjunction with toners commonly used in conventional electrostatic latent image development methods. Also the third
A component that imparts lubricity to the developer, such as titanium oxide or silica, may be added.

The developer thus obtained can be used in conventionally known electrostatic latent image developing methods.

FIG. 5 shows an outline of an apparatus for developing an electrostatic latent image using the dry developer of the present invention.

As shown in Fig. 5, a magnetic roller (8) with S and N poles sequentially magnetized on the outer periphery is housed coaxially within a developing sleeve (7) formed in a cylindrical shape from a conductive non-magnetic material. A developing sleeve (7) is installed in the opening of the toner supply tank (16) so as to be close to the surface of the photoreceptor drum (6), and the developer is supplied by the rotation of the magnetic roller (8) in the direction of arrow (a). or/
Based on the rotation of the developing sleeve (7) in the direction of the arrow (b), the developing sleeve (7) is conveyed in the direction of the arrow (b) on the outer peripheral surface of the developing sleeve (7).

The height regulating plate (18) is integrally formed on the inner surface of the inclined upper surface of the toner replenishing tank (16), and is installed on the upstream side of the developing area (A) in the developer transport direction. Further, the toner supply tank (16) is partitioned into a developing section and a toner storage section (17) by a first partition plate (9) and a second partition plate (11). The second partition plate (11) is attached to the bottom of the toner replenishing tank (16), and the tip thereof is close to the outer peripheral surface of the developing sleeve (7). The first partition plate (9) is attached to the ceiling of the toner supply tank (16), and its lower end is bent toward the second partition plate (11). ) forms a toner supply slit (lO). Slit (lO
) extends in the axial direction of the developing sleeve within the area covered by the magnetic field of the magnetic roller (8).

Further, between the height regulating plate (18) and the first partition plate (9), there is a vacant space (12) in which a magnetic carrier or a mixture of magnetic carrier and toner is loaded in advance in the developing sleeve (7). It is formed to open only toward the outer peripheral surface. Fin (13) located within this empty space (12)
Place a large number of sheets on the first partition plate (9) and place them in the developing sleeve (
7), and has the function of stirring the magnetic developer in the empty chamber (12) in the axial direction of the developing sleeve (7). Further, magnetic developer spill prevention plates (14) and (15) are installed at the lower end of the toner supply tank (I6) and below the development area (A). Toner spilled from the toner is magnetically attracted by the developer spill prevention plates (14) and (15).

On the other hand, the toner storage section (17) of the toner supply tank (16)
) are provided with a toner supply blade (19) and a toner empty detection plate (21). Toner supply blade (
19) can be driven to rotate at a constant speed in the direction of arrow (d) with the support shaft (20) as a fulcrum, and this rotation conveys the toner toward the slit (10). The toner empty detection plate (21) is rotatable about the support shaft (22), and the toner supply blade (19) rotates in the direction of arrow (d).
It moves upward once it comes into contact with the object, and then moves downward under its own weight after the contact is released.

This downward movement time varies depending on the amount of toner contained. That is, as the amount of toner decreases, the resistance decreases and the downward movement time becomes shorter. Therefore, the toner amount is detected by appropriately measuring this downward movement time with a switching means, and when the toner becomes empty, it is configured to be displayed externally.

Further, a cartridge (24) for replenishing toner is detachably attached to the upper part of the toner supply tank (16). The toner stored in the cartridge (24) in advance is
By pulling out the cartridge lid (25) together with the toner supply tank 1 (23), the storage section (17) is replenished.

Next, the operation of the dry developing device having the above structure will be explained.

First, a starter made of a mixture of magnetic carrier and toner is loaded into the empty chamber (12), and after the device is pre-operated, toner is loaded into the toner storage section (17). At this time, only a magnetic carrier may be loaded into the empty chamber (I2) instead of the starter. In this state, the electrostatic latent image can be developed by this apparatus.

Here, the toner is conveyed in the direction of arrow (b) on the outer peripheral surface of the developing sleeve (7) based on the rotation of the magnetic roller (8) in the direction of arrow (a), and as it passes through the empty chamber (12). The toner is mixed and stirred with a magnetic carrier, and the toner and magnetic carrier are each triboelectrically charged. As a result of this mixing and agitation, the toner and magnetic carrier, which are each component of the developer, are constantly integrated at a constant mixing ratio at this point, and the developing area (A)
A magnetic brush of developer material is formed in the step. The magnetic brush formed here rubs the surface of the photoreceptor drum (6) and develops the electrostatic latent image on the surface into a visible image.

After being subjected to development, the developer remaining on the outer peripheral surface of the developing sleeve (7) reaches the empty chamber (I2) again, where new toner is supplied, mixed and stirred, and then subjected to development again. Ru.

The toner is supplied as follows.

The toner stored in the toner storage portion (I7) is conveyed to the slit (10) side by the rotation of the toner supply vane (19) in the direction of the arrow (d), and is conveyed to the slit (10) side by the rotation of the toner supply blade (19) in the direction of the arrow (a) of the magnetic roller (8). ) The second partition plate (
11) in Figure 5, it rises along the right side and the slit (
10) into the cavity (12). The supply amount corresponds to the amount of toner reduced in the empty chamber (12).

Note that as the developing bias, a DC voltage is applied to the developing sleeve (7) based on a normal method, but an AC voltage may be superimposed on this, or the developing sleeve may be grounded.

The present invention will be explained below with reference to Examples.

Example 1 Each metal oxide, which had been sized in advance to 10μl or less, was prepared as a raw material into Fee's 47: MgO28; ZnO20.
; MnO, l; 4 mol % of CuO is prepared, mixed using a Henschel mixer or ribbon blender, and then pre-calcined at 900°C for 3 hours in a tunnel or kiln. The powder that has undergone a quasi-spinel reaction through pre-calcination is mixed with water, and then milled in a ball mill, vibration mill or attritor for 8 hours.
Grind and finely grind for hours. A binder (P) is added to this aqueous solution.
V A :polyvinyl alcohol) and a dispersant are added in a few percent by weight to form a slurry solution, which is then spray-dried using a fluidized granulation dryer or spray dryer, or into a spherical or irregular shape with an appropriate particle size using a kneader or the like. Granulate into particles. The granulated pellets are fired at 1320°C.
It was fired for 4 hours in an Ip (gas or electric furnace) to promote the sintering reaction, and a ferrite powder composed of appropriate primary particles was created. This was sieved using a vibrating sieve or a gyro sifter, and the desired particle size was obtained by air classification to produce carrier particles.

Usually, carrier particles produced by the above-mentioned method are polycrystalline particles composed of primary particles (unit grains).

The primary particles are generated by sintering of microparticles that have been atomized in the pulverization process, causing a solid phase reaction, and crystal growth.

-The size of the secondary particles depends on the properties of the initial raw material, additives, calcining,
It can be controlled by various conditions such as firing or pulverization.

Due to crystal growth of primary particles during sintering, recesses are created at the bonding surfaces between primary particles. The rate at which the recesses are formed is controlled by the conditions of the formation process described above. It is clear that this depends on the form of the constituent primary particles. What is important for a ferrite carrier to be used in a developer is the surface properties of the carrier particles, but it is difficult to quantify the irregularities of individual carrier particles. Therefore, it was decided to express the degree of crystal growth based on the particle size of the secondary particles constituting the carrier particles. Randomly selected carrier particles were photographed using a scanning electron microscope at 500x magnification in SEM (scanning electron micrograph) images at three different locations, and primary particles of 10 μm or larger were photographed. The number percent of carrier particles constituted by the above was calculated, and this was taken as the crystal growth degree.

The characteristics of the prepared magnesium zinc-based ferrite carrier particles were as follows: Average particle size: 34
μ-apparent density: 2.259/cc Saturation magnetization: 50.2emu/g (l 0KOe)
Electrical resistance value: 9X10”Ω・am (5QOV/C
Shoulder) Crystal growth degree = 33% Place the carrier particles 20, 9 and polyvinylidene fluoride resin powder (average particle size 0.2 μx) 0.08 and 9 obtained above in a 20Q polyethylene container, and rotate at a rotation speed of 30 rpm. at 24
Rotate and stir for hours. When the obtained carrier was observed with an SEM (scanning electron microscope), as shown in FIG. 3, the resin powder was buried in the recesses of the ferrite, and almost no resin powder was attached to the surface. This carrier was heat-treated at 180° C. for 60 minutes to obtain a carrier in which the resin was thermally fused in the ferrite recesses as shown in FIG.

200 parts by weight of the carrier and 100 parts by weight of toner were mixed and filled into the empty chamber (12) of the developing device shown in FIG. More toner replenishment! (16) and operated to maintain the toner content in the empty chamber (12) at 33% by weight.

As a toner, 100 parts by weight of styrene-acrylic copolymer (manufactured by Gutdeyer: PLIORITE AC);
Magnetic fine powder (manufactured by Titan Kogyo Co., Ltd.: MAGETITE)
RB-BL) 80 parts by weight, carbon black (manufactured by Mitsubishi Kasei Corporation: MA# 100) 4 parts by weight, charge control dye (TRH: negatively chargeable dye manufactured by Hodogaya Chemical Co., Ltd.) 2
A magnetic toner having an average particle size of 12 μm and a resistance value of 1014 Ω·cm obtained by melt-mixing parts by weight, cooling, pulverizing, and classifying was used.

The image density (D: image density transferred to paper) was measured when development was performed under the following conditions, and the results are shown in Tables 1 and 2. Table 1 shows the initial image density at 23°C and 1845% and the image density after 500 sheets of continuous copying.
The initial image density at RH is shown.

For comparison, the ferrite of Example 1 was developed in the same manner as above using a carrier that was not treated with resin powder, and the resulting image densities are also shown in Tables 1 and 2.

[Development conditions] Developing sleeve: Diameter 24.5 x shoulder rotation speed 79 rpm Magnetic roller: Number of poles 8 Magnetic flux density 750 Gauss rotation speed 90 Orpm Developing gap (di): 0.45 mm Brush height regulation gap (d2): 0.35 ovth 2 partition plate gap (a): 1.5mm slit width (b):
1.7xm Slit height c): 1. Om shoulder process speed: 112mx/5ec (photosensitive drum peripheral speed) Electrostatic latent image maximum potential: +500V Developing bias: DC +200v AC IK Hz (350V rms) Toner supply blade 2 rotations 60 rpIl1 Table-1 Table-2 Example 2 Each metal oxide, which had been sized in advance to a particle size of 10 μm or less, was used as a raw material in a molar % ratio of FetOs48; ZnO33; N
iO14; blended with CuO5,0, and added Coo to this with 0
．． After adding 2% by weight and mixing in the same manner as in Example 1, it is pre-fired at 900° C. for 2 hours in a pre-sintering furnace. The generated powder is wet-pulverized for 5 hours using a ball mill, a vibration mill, or an attritor to make the powder fine. Add a binder (PVA) and some dispersant to this aqueous solution,
After forming a slurry solution, it is spray-dried using a spray dryer and granulated. This was fired in a gas furnace or an electric furnace at a firing temperature of 1250°C for 4 hours to create a ferrite powder composed of -order particles.

After sizing, the properties of the prepared nickel-zinc ferrite carrier particles were as follows: Average particle size:
56μ Shoulder apparent density: 2.739/CC Saturation magnetization: 52.8emu/g (10KOe) Electrical resistance value: 8XlO'Ω・cm (500V/a
x) Crystal growth degree: 55% Polyvinylidene fluoride resin powder (average particle size 0.2 μm1) 0.16 &
9 was placed in a 2012 plastic container and rotated and stirred at a rotation speed of 30 rpm for 24 hours. As shown in FIG. 3, the obtained carrier had a form in which the resin powder was embedded in the recesses of the ferrite. Example 1 except for using this carrier
When developed in the same manner as above, after continuous copying,
Further, almost no decrease in image density was observed even at low humidity.

Effects of the Invention The carrier used in the present invention has resin partially attached only to the surface recesses, and unlike conventional binder type carriers, there is no significant deterioration in magnetic properties or embrittlement of the carrier.

In addition, even in a low-humidity environment, an abnormal increase in the amount of charge of the toner does not occur, and a decrease in image density due to this does not occur. In addition, in order to control the degree of uneven charging of the carrier, it is sufficient to change the distribution (number, size, etc.) of the recesses on the surface of the carrier particles and/or the amount of resin powder added.
Significant changes in magnetic properties seen in binder-type carriers do not occur.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of carrier particles and resin powder, Figure 2 is a diagram of resin powder adhering to the recesses and surface of carrier particles, and Figure 3 is a carrier particle with resin powder embedded in the recesses of carrier particles. FIG. 4 is a diagram showing a carrier to which the resin is fused, and FIG. 5 is a schematic diagram showing an embodiment of a developing device for carrying out the method of the present invention. (1) Particles for carrier (2) Resin powder (3) Concave part
(4) Fusion resin (6) Photosensitive drum (7)
Developing sleeve (8) Magnetic roller (10) Toner supply slit (12) Empty chamber (16) Toner supply tank (17) ) Toner storage section (19) ) Toner supply vane (A) Developing area Patent applicant Minolta Camera Co., Ltd. Company 1m 11211 Figure 3 41!

Claims (1)

[Scope of Claims] 1. A dry developer containing a carrier formed by carrier particles having recesses on the surface and a resin embedded in the recesses. 2. An electrostatic latent image developing method using a dry developer containing a carrier formed by carrier particles having recesses on the surface and a resin embedded in the recesses.