JPH07160052A - Two-component developer - Google Patents

Abstract

PURPOSE:To provide a two-component developer capable of high quality image development and allowing production at a low price, the complete recovery of a toner residual on the surface of an image carrier, and the application of compact design to a whole device. CONSTITUTION:A carrier made of magnetic grains formed to have a non- spherical shape having a mean diameter between 5 and 100mum, or more preferably between 5 and 50mum, is mixed with a magnetic toner where contained magnetic powder has an unsteady form with the breadth of size distribution equal to or more than 1mum, and grains having a diameter equal to 2mum or less are present by 90% or more, while the magnetic toner being formed to have a mean diameter equal to or less than 10mum and a value of sigmas equal or or less than 50emu/g. Also, the magnetic toner is formed to have a coersive force iHc equal to or less than 50Oe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for developing an electrostatic charge image used in electrophotographic printers, facsimiles and the like, and more particularly to a carrier composed of magnetic particles of small particle size and a magnetic toner. It relates to a two-component developer formed by mixing.

[0002]

2. Description of the Related Art Conventionally, in printers, facsimiles, etc. to which the electrophotographic method is applied, an electrostatic charge image corresponding to information is formed on a photosensitive drum formed in a cylindrical shape, and is provided so as to face the photosensitive drum. A magnetic developer is attracted and conveyed by a developing roll having a permanent magnet member, and a magnetic brush is formed in the developing area, and the electrostatic charge image forming surface on the photosensitive drum is rubbed by the magnetic brush to obtain a toner image. To visualize as. The most general means is to transfer the visualized toner image onto recording paper and then heat fixing.

In this case, since a small amount of toner remains on the photosensitive drum as the image carrier even after the toner image is transferred onto the recording paper, a cleaning device is provided to remove this residual toner. Is normal. Therefore, a space for the cleaning device must be secured around the photoconductor drum, which hinders downsizing of the entire image forming apparatus.

On the other hand, as an example of means for reducing the size of the entire apparatus, the cleaning device is omitted and the toner remaining on the photosensitive drum is collected and the electrostatic charge image is formed in the area where the photosensitive drum and the developing roll face each other. There is a device provided with a so-called development cleaning device for performing visualization together with the above (see, for example, JP-A-4-86878). In such an image forming apparatus without a cleaning device, a magnetic developer formed by mixing toner and a spherical magnetic carrier is used.

[0005]

However, when the magnetic carrier formed in the spherical shape as described above is used, the contact area with the toner is necessarily small because the specific surface area of the magnetic carrier is small. As a result, the triboelectric charge amount of the toner becomes small, the image density is low, and a clear image cannot be formed.

When the particle size of the magnetic carrier is reduced in order to form a fine image, a thin developer layer is formed and a high-resolution and high-quality image can be obtained. As a result of insufficient magnetic holding force against the carrier, carrier scattering increases and contamination near the developing means,
There is a problem in that deterioration of image quality due to carrier adhesion is caused.

Since the magnetic toner constituting the above-mentioned two-component developer contains magnetic powder, the magnetic toner on the image formed on the photosensitive drum rolls due to the rotation of the developing roll. However, there is also a problem in that the image quality is deteriorated due to the possibility of tailing.

Further, since the magnetic toner constituting the conventional two-component developer for high image quality uses magnetic powder having a uniform particle size, that is, a narrow particle size distribution as a raw material, the manufacturing cost must be increased. There is a problem that it does not exist.

FIG. 3 is a diagram showing the particle size distribution of the magnetic powder contained in the magnetic toner. What is shown by the curve b in FIG. 3 is a conventional one, and for example, the particle size distribution is
It is about 0.2 to 0.8 μm. In order to obtain such a uniform particle size, it is necessary to strictly control the manufacturing conditions, and it is clear that the manufacturing cost will inevitably increase.

Further, when development is performed once per one rotation of the photosensitive drum by using the developing cleaner for collecting the toner and visualizing the electrostatic charge image as described above, the toner is recorded on the recording paper. When the residual toner after the transfer of the image is present on the photoconductor drum, the residual toner is not completely collected by the developing cleaning section and remains on the previous electrostatic charge image forming section even after the development. is there.

If the residual toner is poorly collected as described above, there is a problem that the quality of the obtained image is significantly deteriorated. On the other hand, in order to solve such a problem, there is also a system in which a means for developing once every two rotations of the photosensitive drum is used to completely collect the residual toner.
In such a method, there is a problem that the image forming speed is inevitably lowered, and it may not be possible to meet the demand for speeding up information transmission.

The present invention solves the above-mentioned problems existing in the prior art, enables high-quality development, can be manufactured at a low price, and completely collects residual toner on the surface of an image carrier. Moreover, it is an object of the present invention to provide a two-component developer for developing an electrostatic charge image, which enables downsizing of the entire apparatus.

[0013]

In order to achieve the above object, the present invention contains a carrier composed of non-spherical magnetic particles having an average particle size of 5 to 100 μm, preferably 5 to 50 μm. 90% or more of the magnetic powder has an irregular shape and has a particle size distribution width of 1 μm or more and a particle size of 2 μm or less, and an average particle size of 10 μm or less,
A technical means of mixing with a magnetic toner formed to have a σ s of 50 emu / g or less was adopted.

The above magnetic toner has a coercive force iHc of 50 O
e It is preferable to form the following. In the present invention, if the average particle size of the magnetic particles is small, so-called carrier scattering occurs and adheres to the surface of the image carrier, which deteriorates the image quality, which is not preferable. On the other hand, if the particle size is large, the image tends to become rough, which is inconvenient. Therefore, the average particle size of the magnetic particles is 5 to 100 μm, preferably 5 to 50 μm.

The above-mentioned magnetic particles may be any of iron powder such as crushed iron powder, reduced iron powder, etc., ferrite powder, magnetite powder, or magnetic particles dispersed in resin.
The shape is preferably a non-spherical shape such as a polyhedron shape, a polyhedron shape, a scale shape, a flat shape, or an indefinite shape, and has a large specific surface area. However, from the viewpoint of preventing carrier adhesion, it is desirable that the magnetic particles have a saturation magnetization (σs) of 60 emu / g or more.

The developer carrier of the present invention may be formed by coating the surface of the above magnetic particles with a resin material. Such resin materials include styrenes such as P-chlorostyrene and methylstyrene: vinyl halides such as vinyl chloride, vinyl bromide and vinyl fluoride: vinyl acetate, vinyl propionate, vinyl benzoate, vinyl acetate. And other vinyl esters: methyl acrylate, ethyl acrylate, rubutyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate,
3-chloroethyl acrylate, phenyl acrylate, α
-Esters of α-methylene aliphatic monocarboxylic acid such as methyl chloroacrylate and butyl methacrylate: vinyl ethers such as acrylonitrile, methacrylonitrile, acrylamide, vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether: vinyl ethyl Homopolymers or copolymers obtained by polymerizing monomers such as ketones, vinylhexyl ketone, methyl isopropenyl ketone and other vinyl ketones, or other resins such as epoxy resin, silicone resin, rosin-modified phenol formalin resin, cellulose resin, poly Ether resin, polyvinyl butyral resin, polyester resin, styrene-butadiene resin, polyurethane resin, polycarbonate resin, fluororesin such as tetrafluoroethylene, etc. alone or Rend to be able to use.

Of these, styrene-acrylic resin, silicone resin, epoxy resin, styrene-butadiene resin, and cellulose resin are particularly useful. The coated carrier as described above can be produced, for example, as follows. First, the resin is appropriately dissolved, but as the solvent, for example, benzene, toluene, xylene, methyl ethyl ketone, tetrahydrofuran, chloroform, hexane or the like can be used. It is also possible to use the resin as an emaldiene. The resin solution or emulsion is sprayed so as to uniformly coat the surfaces of the magnetic particles. In order to obtain a uniform surface coating, it is preferable to keep the magnetic particles in a fluidized state. It is desirable to use a spray dryer or a fluidized bed for this purpose. The resin solution is sprayed at about 200 ° C or lower, preferably about 100 to 150 ° C.
The atmosphere is used to quickly remove the solvent. In this step, the resin coating is dried. In the case of resin emulsion,
Spraying is performed at room temperature to 100 ° C. to fuse the resin to the surface of the magnetic particles.

Next, when the average particle diameter of the magnetic toner exceeds 10 μm, the resolution is lowered, and 400 which has been recently demanded.
D. P. I. It is not preferable because it cannot be applied to the development of high image quality. However, if the average particle size is too small, the toner tends to scatter, so the average particle size is preferably 3 μm or more.

The coercive force iHc of the magnetic toner is 50 Oe.
When the value exceeds 50emu / g or the saturation magnetization σs exceeds 50emu / g, the magnetic toner on the image formed on the image carrier easily rolls due to the rotation of the developing roll, which may cause tailing, etc. It is not preferable because it causes

The magnetic powders contained to form the above magnetic toner include Ni-Zn, Cu-Zn,
A soft ferrite such as Mn-Zn or Mg-Zn or a non-spherical magnetite can be used. Further, in order to impart a predetermined magnetic characteristic to the magnetic toner, the content of the magnetic powder is appropriately in the range of 10 to 70% by weight.

Next, it is preferable that the particle size of the magnetic powder contained in the magnetic toner is small. That is, if the particles having a large particle size are contained, the content of the magnetic powder in each magnetic toner particle varies in the crushing process in the magnetic toner manufacturing process, resulting in non-uniform magnetic characteristics and poor image quality. It is not preferable because it lowers. Therefore, it is preferable to use a magnetic powder having a particle size distribution such that 90% or more of particles having a particle size of 2 μm or less are present. In addition, if a magnetic powder having a spherical shape and a narrow particle size distribution is used, the cost reduction of the magnetic toner is hindered as described above, so that the magnetic powder has an indefinite shape and a wide particle size distribution (specifically, For this, a magnetic powder having a particle size distribution width of 1 μm or more, eg, curve a in FIG. 3) is preferable.

Such magnetic powder is not a fixed shape such as spherical, hexagonal, or octahedral in the conventional one, but an irregular shape such as soft ferrite polishing powder or crushed powder. Can be used as it is or after being subjected to some sort (classification) as necessary.

The magnetic toner according to the present invention contains the above-mentioned magnetic powder and fixing resin as essential components, and as optional components, a fluidity modifier (hydrophobic silica, inorganic fine particles such as alumina) and a charge control agent ( Known additives such as nigrosine dyes, Cr-containing azo dyes, etc.), release agents (polyalkylenes etc.), colorants (carbon black etc.) may be contained. The fixing resin may be appropriately selected according to the fixing method. For example, in the case of the heat roll fixing method, it is desirable to use styrene resin or polyester resin. The above magnetic toner can be manufactured by a known method such as a pulverizing method, a spray drying method or a suspension polymerization method.

[0024]

With the above construction, the peeling and collecting action of the residual toner of the magnetic brush in the developing and cleaning area can be improved, and even in the image forming means in which the step of cleaning the surface of the image carrier before the electrostatic charge image formation is omitted, The residual toner in the electrostatic charge image forming section can be completely recovered, and a clear and high-quality image can be obtained. The two-component developer of the present invention can of course be used for an image forming method in which the surface of the image carrier is cleaned before electrostatic image formation.

Further, even if a low-grade non-uniform shape is used as the magnetic powder, the variation in the magnetic characteristics of the magnetic toner is small, and a high-quality image can be obtained despite the low cost. .

[0026]

[Examples] First, mild steel scraps are first pulverized, then subjected to steps such as oil baking and beneficiation, followed by nitriding to form brittle primary particles. After crushing the primary particles, the particles are classified to have average particle diameters of 5 μm, 10 μm, 30 μm, 50 μm and 100 μm, respectively.
Iron powder particles of μm and 120 μm were obtained. These iron powder particles were non-spherical with a polyhedral shape and a flat shape, and had a volume resistivity of 4 × 10 ⁵ Ω · cm, and they were used as a developer carrier.

On the other hand, as a comparative example, a developer carrier composed of spherical iron powder particles was prepared in the following manner. That is, after the above primary particles were pulverized, denitrification was performed, the surface was oxidized and reduced, and the particles were classified to obtain a spherical carrier for a developer having an average particle diameter of 30 μm. The volume resistivity of this developer carrier was 8 × 10 ⁵ Ω · cm.

Next, a charge-type magnetic toner was prepared by blending the following raw materials. Styrene-n-butylmethacrylate 50 parts by weight (Mw = 21 × 10 ⁴ , Mn = 1.6 × 10 ⁴ ) Magnetite (iHc = 30Oe) 45 parts by weight Polypropylene (Sanyo Kasei VISCOL 550P) 3 parts by weight Charge control agent (Orient) Chemically manufactured Bontron E-81) 2 parts by weight The raw materials having the above composition are kneaded with a kneader having a heating roller for 30 minutes, cooled, solidified, pulverized and classified to obtain a magnetic toner having a volume average particle diameter of 9 μm. . This magnetic toner has a volume resistivity of 3 × 10 ¹⁴ Ω · cm and a coercive force iH.
c was 30 Oe, and saturation magnetization σs was 36 emu / g. The magnetite contained in the magnetic toner was non-spherical and 100% of particles of 2 μm or less were used.

The volume resistivity is 3.05 mm obtained by improving the dial gauge by collecting several tens of mg of the sample to be measured.
It was filled in an insulating cylinder made of Teflon (trade name) of φ (cross section 0.073 cm ² ) and pressure of 0.1 kgf was applied.
It was calculated by measuring the value for the charged magnetic toner at an electric field of DC4000V / cm and the value for the developer carrier at an electric field of DC200V / cm. A Yokogawa Hewlett-Packard insulation resistance meter (4329A type) was used for the measurement.
The magnetic characteristics of the carrier and the magnetic toner were measured by a vibrating sample magnetometer (VSM-3 manufactured by Toei Industry Co., Ltd.).
The measurement was performed by applying a maximum magnetic field of 10 kOe.

The above carrier for developer and magnetic toner were mixed to prepare a developer having a toner concentration of 30% by weight, and the image was evaluated by the image forming means described below. Next, FIG. 1 is an explanatory view of a main part configuration showing an example of an image forming means in an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an image forming unit, which houses constituent members described later and is integrally provided on the control unit 2. Reference numeral 3 denotes a photosensitive drum, which is formed in a cylindrical shape, has a photosensitive layer (not shown) made of zinc oxide or an organic semiconductor on the outer peripheral surface, and is provided in the image forming unit 1 so as to be rotatable in the arrow direction. Reference numeral 4 is a charger, 5 is a developing cleaner formed as described later, and 6 is a transfer device, which are provided near the outer periphery of the photosensitive drum 3, respectively. Reference numeral 8 denotes a magnet roll, which is rotatably provided on the developing and cleaning device 5 and is formed so as to face the photosensitive drum 3.

Next, a fixing device 9 is provided on the downstream side of the recording paper path 10 of the image forming unit 1 and includes the heating roll 1.
9 and the pressure roll 20 are formed so as to be capable of pressure contact and rotatable. The heating roll 19 and the pressure roll 20 each have an outer diameter of 20 mm and are pressed against each other at a linear pressure of 0.5 kg / cm. The heating roll 19 is provided with a heating element made of an electric resistance material on the outer circumference of a core material made of, for example, aluminum, and a release layer made of, for example, PTFE on the outer circumference thereof.
It is formed by applying about 0 μm. On the other hand, the pressure roll 20 is constituted by applying an outer layer made of, for example, silicone rubber to the outer circumference of a core material made of the same material as the heating roll 19.

With the above configuration, each component in the image forming unit 1 is brought into a driving state or an operating state via the control unit 2, and the laser scanner 16 is made to input information or an electric signal corresponding to an image. Next, the surface of the photosensitive drum 3 is uniformly charged by the charger 4, and the charged surface is irradiated with the laser beam by the electric signal to form an electrostatic charge image. Then, the electrostatic charge image is visualized as a toner image by the magnetic developer attracted and conveyed by the magnet roll 8 in the developing and cleaning device 5, and the transfer device 6 moves the recording paper path 10 to the recording paper (not shown). ) Is transcribed on. The magnetic toner remaining on the photoconductor drum 3 after the transfer is simultaneously removed from the photoconductor drum 3 when the electrostatic charge image is visualized (developed) in the development cleaner 5.

Next, the recording paper carrying the toner image is the fixing device 9
The heat of the heating roll 19 is transmitted to the toner image on the recording paper, the binder resin constituting the magnetic toner is melted,
It is fixed.

FIG. 2 is an enlarged cross-sectional view of the essential parts showing the magnet roll 8 in FIG. In FIG. 2, the magnet roll 8 is made of, for example, a sintered powder magnet material such as hard ferrite, which is integrally molded into a cylindrical shape, or a mixture of ferromagnetic magnet material powder and a binder, which is integrally molded into a cylindrical shape. 21 and a sleeve 22 formed of a non-magnetic material such as an aluminum alloy or stainless steel in a hollow cylindrical shape are provided coaxially.

A plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface of the permanent magnet member 21, and a specific magnetic pole (for example, N pole) is fixed so as to face the photosensitive drum 3. Sleeve 2
By rotating counterclockwise around the permanent magnet member 21, a magnetic developer 2 is attracted to a magnetic developer (not shown) and is conveyed to the photosensitive drum 3.

With the above structure, in the area where the magnet roll 8 and the photosensitive drum 3 face each other, the magnetic brush 23 is formed by the magnetic developer by the magnetic pole N and rubs the surface of the photosensitive drum 3. Therefore, the magnetic toner remaining on the photosensitive drum 3 even after passing through the transfer device 6 shown in FIG. 1 is removed and collected by the magnetic brush 23, and the electrostatic charge image formed on the photosensitive drum 3 is developed. To be done. That is, the magnetic toner in the magnetic developer adheres to the electrostatic charge image to form a visualized toner image.

Next, the result of image formation by the image forming unit 1 shown in FIG. 1 using the developer prepared by mixing the iron powder carrier and the chargeable magnetic toner will be described. First, the photoconductor drum 3 is set to -55 by the charger 4.
It is uniformly charged to 0 V and rotated in the direction of the arrow at a surface speed of 60 mm / sec.

The magnet roll 8 constituting the developing and cleaning device 5 has a sleeve made of SUS304 having an outer diameter of 20 mm and is rotated in the direction of the arrow at 150 rpm. The permanent magnet member 21 shown in FIG. 2 was magnetized with 6 poles, and the surface magnetic flux density on the sleeve 22 was 750G. A bias voltage of -450 V was applied to the sleeve 22, and the doctor gap and the developing gap were set to 0.2 mm and 0.3 mm, respectively. The heat roll fixing after the transfer was performed at a temperature of 180 ° C. and a linear pressure of 1 kgf / cm.

Table 1 is a table showing the results of image formation using the developer prepared as described above.

[0040]

[Table 1]

As is clear from Table 1, in the case of a non-spherical carrier, when the average particle size of the carrier is larger than 100 μm (No. 6), drum scratches occur. The average particle size of the carrier is preferably 50 μm or less from the viewpoint of resolution. On the other hand, when the carrier has a spherical shape (No. 7), the image density is low and the occurrence of background fog is observed.

Next, as the magnetic powder to be contained in the magnetic toner, pulverized powder of Mn-Zn ferrite (particle size distribution: 0.1 to
2.1 μm, peak 1.0 μm, 98% of 2 μm or less
Table 2 shows the results of the same image evaluation as described above using No. 3 carrier in Table 1. The volume resistivity of this magnetic toner is 8 × 10 ¹⁴ Ω · cm,
The coercive force iHc was 0.1 Oe and the saturation magnetization was 32 emu / g.

As the magnetic powder, ground powder of Cu-Zn ferrite (particle size distribution: 0.2 to 2.2 μm, peak 1.2 μm)
m, particles of 2 μm or less 95% or more) and Ba-Ni
-Zn ferrite crushed powder (particle size distribution: 0.1 ~ 2.3μ
m, peak 1.5 μm, 90% or more of particles of 2 μm or less)
Magnetic toner (No. 8-10) and spherical magnetite (average particle size 0.3 μm, iHc = 80 Oe)
Using magnetic toner (No. 11) prepared using
The results of image evaluation similar to the above are also shown in Table 2.
The cost index in the table is 10 for the No. 11 magnetic toner.
It is a value when 0 is set.

[0044]

[Table 2]

As is clear from Table 2, the magnetic toners (No. 8 to 10) containing the non-uniformly shaped magnetic powder are lower in cost than the magnetic toners containing spherical magnetite,
Moreover, high quality images without tailing, background fog and carrier adhesion can be obtained.

In the above embodiments, the developer carrier and the magnetic toner were mixed to give a toner concentration of 30% by weight. In this case, the toner concentration was 10%.
It is good to set it in the range of about 90% by weight, preferably 10 to 40% by weight.

[0047]

Since the present invention has the structure and operation as described above, by using a carrier having a small particle diameter and an aspherical shape, the image quality can be improved and carrier scattering can be prevented. . Further, the peeling and collecting action of the magnetic brush on the residual toner in the developing and cleaning area can be improved, and the residual toner can be completely collected even in the case of image formation in which the cleaning means for the surface of the image carrier or the cleaning step is omitted. it can.

Further, by using the magnetic toner having a relatively low magnetic force, it is possible to prevent the occurrence of tailing or the like due to the rolling of the magnetic toner on the image formed on the image carrier.
Therefore, there is an effect that a clear and high-quality image can be obtained.

Furthermore, since a relatively low grade amorphous magnetic powder can be used, the magnetic toner can be manufactured at a low cost and the cost of the two-component developer can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a main part configuration showing an example of an image forming unit in an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of an essential part showing a magnet roll 8 in FIG.

FIG. 3 is a diagram showing a particle size distribution of magnetic powder.

[Explanation of symbols]

 3 Photoconductor drum 5 Development cleaning device 8 Magnet roll

Claims (2)

[Claims] 1. An average particle size of 5 to 100 μm, preferably 5
A carrier consisting of non-spherical magnetic particles of ˜50 μm, and a magnetic powder contained therein having an irregular shape and a particle size distribution width of 1 μm or more and a particle size of 2 μm or less are present in 90% or more, Average particle size 10 μm or less, σs 50
A two-component developer characterized by being mixed with a magnetic toner formed at an emu / g or less. 2. The two-component developer according to claim 1, wherein the magnetic toner has a coercive force iHc of 50 Oe or less.