JP2782201B2 - Carrier for two-component developer and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a two-component developer carrier that constitutes a two-component developer together with a toner, and a method for producing the same.

[Prior Art] Various methods are described as electrophotography in U.S. Pat. No. 2,976,691, Japanese Patent Publication No. 42-23910, and Japanese Patent Publication No. 43-24748, all of which are described. An electrostatic latent image is formed by irradiating the photoconductive layer with a light image corresponding to the original, and then, on the electrostatic latent image, a coloring fine powder called toner having a polarity opposite to this is attached. The electrostatic latent image is developed, and if necessary, a toner image is transferred to a transfer material such as paper, and then fixed by heat, pressure, solvent vapor, or the like to obtain a copy.

In the step of developing the electrostatic latent image, toner particles charged to a polarity opposite to that of the latent image are attracted by electrostatic attraction and adhered on the electrostatic latent image. The method of developing an image using toner is roughly classified into a method using a so-called two-component developer in which a small amount of toner is dispersed in a medium called a carrier (magnetic brush method,
Cascade method) and a method using a so-called one-component developer using toner alone without using a carrier.

The present invention relates to a carrier constituting such a two-component developer.

In general, carriers constituting a two-component developer are roughly classified into conductive carriers and insulating carriers.

Oxidized or unoxidized iron powder is usually used as the conductive carrier. However, in a developer containing the iron powder carrier as a component, the triboelectrification characteristics with respect to the toner are unstable, and the developer is formed by the developer. Fogging occurs in the visible image. That is, the toner particles adhere to the surface of the iron powder carrier particles with the use of the developer, so that the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectric charging characteristics become unstable. The image density of the visible image decreases and fog increases.

On the other hand, as the insulating carrier, a carrier in which the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, and ferrite is generally coated with an insulating resin is typical. In a developer using this carrier, toner particles are less likely to fuse to the surface of the carrier than in the case of a conductive carrier, and have excellent durability and a long service life. It has the advantage of being suitable.

However, in the ferrite carrier manufacturing process, sintering occurs at grain boundaries between ferrite particles during ferrite firing, and thus a crushing step is indispensable after firing.

For this reason, fragments (ultrafine powder) of the core material generated during the crushing step are mixed in the carrier core material, which causes lots and blurs in the carrier production.

The presence of such fragments (super-differential) hinders the uniformity of the coating of the insulating resin, resulting in non-uniformity and instability of the charge imparting characteristics of the carrier to the toner. The state cannot be achieved.

Furthermore, the presence of the ultrafine powder carrier is liable to have a high triboelectricity, which is opposite to that of the toner itself. There is a drawback that a phenomenon occurs in which a carrier adheres together with the toner and the image is adversely affected.

In recent years, attempts have been made to reduce the particle size of the toner and the carrier in order to improve the resolution, gradation reproducibility and image quality of the image surface obtained with such a two-component developer. That is, instead of a carrier having a large particle size of 80 to 500 μm, 50 μm
Investigations have been made on a developer having a carrier having a small particle diameter of not more than m and a particle diameter of the mixed toner of not more than 10 μm. However, with the decrease in the particle size of the carrier, the problems of carrier adhesion, toner scattering and image fogging due to deterioration of the charge imparting ability of the carrier to the toner have been highlighted.

The problem of carrier adhesion due to the decrease in the particle size of the carrier has been improved by examining the coating agent and coating amount of the carrier and the toner binder, but at present it has not been improved dramatically. is there.

[Problem to be Solved by the Invention] An object of the present invention is to provide a carrier for a two-component developer which is excellent in a property of imparting charge to a toner and does not cause carrier adhesion.

It is a further object of the present invention to provide a method for producing a carrier for a two-component developer, which can provide a carrier having a stable quality as described above.

[Means and Actions for Solving the Problems] The present invention provides an ultrafine powder having a particle diameter of 1/10 or less of the center particle diameter of a carrier core material composed of a ferromagnetic material selected from iron, nickel, cobalt, magnetite and ferrite. After removing
In a two-component developer carrier having a carrier core material surface coated with an insulating resin, the carrier core material has a center particle size of 25 to 100 μm, and particles having a center particle size of ± 10 μm. 70% by weight or more
The present invention relates to a two-component developer carrier having a particle size distribution containing 2% by weight or less of ultrafine powder having a particle size of 1/10 or less of the central particle size.

In addition, the present invention removes ultrafine powder having a particle size of 1/10 or less of the center particle size of a carrier core material composed of a ferromagnetic material selected from iron, nickel, cobalt, magnetite and ferrite by air classification, Having a diameter of 25 to 100 μm, containing 70% by weight or more of particles having a diameter of the central particle diameter of ± 10 μm, and containing 2% by weight or less of an ultrafine powder having a particle diameter of 1/10 or less of the central particle diameter. The present invention relates to a method for producing a carrier for a two-component developer, comprising: after obtaining a carrier core material having a certain particle size distribution, coating the obtained carrier core material surface with an insulating resin to produce a carrier.

In other words, according to the study by the present inventors, ultrafine powder having a center particle size (microtrack particle size measurement method) of 1/10 or less during ferrite baking and crushing of a carrier core material has a high tribo itself and usually has a high triboelectricity. It cannot be completely removed by the sieving being performed, and 2 to 5% by weight of the total amount is mixed.

The mixture of the ultrafine powder in the carrier core material causes the coating of the insulating resin to be non-uniform, and further impedes the high resistance of the carrier.

That is, the tribo-imparting ability of the toner is reduced, and the toner particles cannot be in a good charged state.

Further, when a latent image is formed, the above-described adverse effect of carrier adhesion occurs.

On the other hand, by removing such ultrafine powder, the resin coat of the carrier core material is made uniform, and production and quality can be stabilized.

As a means for removing ultrafine powder, air classification can be removed most efficiently. In terms of cost, the removal of the ultrafine powder by the air classification does not increase the cost because the mixed amount of the ultrafine powder itself is small.

As the material of the carrier core material used in the present invention, a substance which is strongly magnetized in its direction by a magnetic field, for example, a ferromagnetic metal such as ferrite, magnetite, iron, cobalt, nickel or an alloy containing these metals Alternatively, an alloy that does not contain a compound or a ferromagnetic element but becomes ferromagnetic when appropriately heat-treated may be used.

The particle size of these carrier core materials is 25 to 200 μm, preferably the central particle size is 25 to 100 μm and the central particle size is ± 10 μm.
Preferably has a particle size distribution of 70% by weight or more, more preferably 80% by weight or more.

As a method of removing the ultrafine powder of the carrier core material, after sieving, a normal air classifier can be used, and more preferably, a DS classifier that has good productivity and can easily change the classification point is used. Can be.

It is preferable to remove the ultrafine powder of 1/10 or less of the center particle diameter of the carrier core material to 2% by weight or less, more preferably 1% by weight or less of the total amount by using the above air classifier.

The carrier core material obtained by removing the ultrafine powder obtained as described above is subjected to magnetic separation and then coated with an insulating resin.

Although almost any resin can be used as the insulating resin for coating the carrier core material, it is particularly preferable to use the following fluorine-based or silicone-based resin to give a low energy surface.

Fluorine-based resin; polyvinyl fluoride, polyvinylidene fluoride,
Halo-fluoropolymers such as polytrifluoroethylene, polytrifluorochloroethylene, polytetrafluoroethylene, polyfluoropropylene, copolymers of vinylidene fluoride and acrylic monomers, vinylidene fluoride and trifluoroethylene Copolymer of vinylidene and vinylidene fluoride, copolymer of vinylidene fluoride and tetrafluoroethylene, copolymer of vinylidene fluoride and hexafluoropropylene, Fluoroterpolymers, such as terpolymers of fluoroethylene with vinylidene fluoride and non-fluorinated monomers.

Silicone resin: Silicone varnish, alkyd-modified silicone varnish, epoxy-modified silicone varnish, polyester-modified silicone varnish, acrylic-modified silicone varnish, urethane-modified silicone varnish, reactive silicone resin, and the like can be used alone or in combination.

In addition, as a resin to be combined with the above resin, there is a resin composed of the following monomers.

Styrene such as styrene, p-chlorostyrene, p-dimethylamino-styrene and its substituted products; acrylic acid such as methyl acrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, and N, N-dimethylaminoethyl methacrylate Or esters of methacrylic acid; half-esters, half-amides or diesteroids of maleic anhydride; nitrogen-containing vinyls such as vinylpyridine and N-vinylimidazole; vinylacetals such as vinylformal and vinylbutyral; vinyl chloride;
Vinyl monomers such as acrylonitrile and vinyl acetate;
Vinylidene monomers such as vinylidene chloride; ethylene,
It is an olefin monomer such as propylene. In addition, polyester, polycarbonate, polysulfonate, polyamide, polyurethane, polyurea, epoxy resin,
Rosin, modified rosin, terpene resin, phenol resin,
Fatty acid or alicyclic hydrocarbon resin, aromatic petroleum resin,
A homopolymer or copolymer such as a melamine resin, a polyether resin such as polyphenylene oxide, or a thioether resin, or a mixture thereof can be used. Further, the copolymer of the resin, a graft copolymer, any of a block copolymer can be used as the coating method of the carrier of the present invention, dipping method, spray method, fluidized bed method. preferable. Any organic solvent may be used as long as it dissolves or decomposes the resin, but a mixed solvent obtained by combining a good solvent and a poor solvent can also be used.

After coating, it is manufactured through a heat drying and curing process.

As the toner used as a two-component developer in combination with the carrier of the present invention, any chargeable toner usually used in electrophotography, in which a colorant is dispersed in a binder resin, can be used. Further, other additives (charge control agent, fluidity imparting agent, etc.) can be added to the toner as needed.

Examples of the binder resin of the toner used as a two-component developer in combination with the carrier of the present invention include styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene, and a monomer of a substituent thereof; styrene-p-chlorostyrene. Copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer,
Styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate Copolymer, styrene-acryl-aminoacrylic copolymer, styrene-aminoacrylic copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-
Vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene- Styrene-based copolymers such as maleic acid copolymer and styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin , Polyvinyl butyral, polyacrylic acid resin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc., alone or as necessary. It can be used in combination or more.

In the toner, any suitable pigment or dye can be used as a colorant. For example, a known face wash such as carbon black, iron black, phthalocyanine blue, ultramarine, quinacridone, and benzidine yellow is used.

As charge control agents, amino compounds, quaternary ammonium compounds and organic dyes, particularly basic dyes and salts thereof, benzyldimethyl-hexadecyl ammonium chloride, decyl-trimethyl ammonium chloride,
Nigrosine base, nigrosine hydrochloride, safranin γ and crystal violet, a gold-containing monoazo dye, a gold-containing disazo dye, a salicylic acid metal chelate and the like may be added.

The configuration of the toner described above is based on the general mixing-
It may be used for the toner by a pulverization method, and may be used for the wall material and / or the core material of the microcapsule toner.

[Examples] Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

Example 1 A ferrite carrier core material containing Fe ₂ O ₃ , CuO, and ZnO as main components was granulated, dried, and fired. Subsequently, the resultant was crushed and sieved to obtain a carrier core material having a center particle size of 50 μm and particles having a center particle size of ± 10 μm in an amount of 70% by weight or more.

The obtained spherical core material powder was photographed with a scanning electron microscope (SEM) and observed. As a result, many fine particles (ultrafine ferrite powder) having a central particle diameter of 1/10 or less were present. This ultrafine powder was found to be present at 5.0 wt% of the total amount of the carrier core material.

This carrier core material is air-classified and the ultra fine powder is 0.8wt%
Removal. When the spherical core material powder after the air classification was photographed with a SEM and observed, virtually no ultrafine ferrite powder was observed.

The carrier of the present invention was produced by spraying and coating the carrier core material with a coating solution in which a molar ratio of a fluorine-based resin and an acrylic resin was 5: 5 dissolved in methyl ethyl ketone.

The carrier of the present invention is mixed with a negatively chargeable toner externally added to silica having an average particle diameter of 10 to 20 μm comprising a polyester resin, a phthalocyanine pigment, a low molecular weight polypropylene, and a charge control agent to form a developer to produce an image. Was.

As a result, each of the obtained copy images had excellent image quality without fog and without carrier adhesion.

In addition, this developer did not change in the charge amount before and after image durability, and it was found that this developer was also excellent in this respect.

Example 2 In order to examine the production stability of the carrier, several batches of the same carrier as in Example 1 were prepared and the same evaluation was performed.

As a result, the physical properties of this carrier are
It almost disappeared, and it became clear that a good image was obtained as in Example 1.

Particularly, stabilization of the resistance value of the carrier and stabilization of the tribo-imparting ability to the toner were achieved. The carrier current value was measured by the magnet brush method (calculated from the voltage drop due to a 500 V load (see FIG. 1)). As a result, all carrier current values were in the range of 16 to 24 μA (see Table 1).

Comparative Example 1 Comparative study was performed according to Example 1 except that the ultrafine powder (fragment of the carrier core material) was not removed by air classification.

As a result, the obtained image had carrier adhesion.

The charge amount of the developer also became unstable before and after the image production endurance and became unstable.

Comparative Example 2 Several batches of carriers similar to the carrier of Comparative Example 1 were prepared and subjected to the same evaluation.

As a result, the production of this carrier (no removal of ultrafine powder)
The physical properties of the image were greatly fluctuated, and the obtained image evaluations also fluctuated greatly.

In particular, the carrier resistance has a large fluctuation in the decreasing direction,
The result was a lack of stability in carrier manufacturing.

The current value of the carrier was measured in the same manner as in Example 2.
The current value increased, that is, the resistance value tended to decrease, indicating that the carrier coat lacked uniformity (Table 1).
reference).

Here, the method of measuring the carrier current value by the magnet brush method in the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a method of measuring a carrier current value by a magnet brush method. A magnet brush of a carrier is formed on a magnetic sleeve 1 and an interval between aluminum drums 2 is 1 mm.
Then, a voltage of 500 V is applied to the circuit of FIG. At this time, the voltage applied to the circuit including the 1 MΩ resistor is measured by the voltmeter 3, and the current value is calculated from the voltage drop at this time.

Next, the method of measuring the triboelectric charge amount of the toner with respect to the carrier in the present invention will be described in detail with reference to the drawings.

FIG. 2 is an explanatory diagram of the triboelectric charge amount measuring device. 50 at the bottom
A magnetic brush (toner and magnetic particles) on a developer carrier for which the amount of triboelectric charge is to be measured is measured in a metal measuring container 2 having a conductive screen 3 of 0 mesh (which can be appropriately changed to a size that does not allow the passage of carrier particles). ) And the metal lid 4 is closed. At this time, weigh the entire measuring container 2
W ₁ (g). Next, in the suction device 1 (at least a portion in contact with the measurement container 2 is an insulator), the pressure of the vacuum gauge 5 is adjusted to 70 mmHg by adjusting the air volume control valve 6 by suctioning from the suction port 7. In this state, suction is sufficiently performed (about 1 minute) to remove toner by suction. The potential of the electrometer at this time is V (volt)
And Here, 8 is a capacitor whose capacity is C (μ
F). In addition, weigh the entire measurement container after suction.
W ₂ (g). The triboelectric charge amount Q (μc / g) is calculated as in the following equation.

However, the measurement conditions are 23 ° C and 65% RH.

[Effects of the Invention] As described above, according to the present invention, after the ultrafine powder of the carrier core material is removed by air classification, the surface of the carrier core material is coated with an insulating resin, so that the coat is uniform and friction with the toner is improved. An electrostatic image developing carrier having excellent charging characteristics and free from carrier adhesion and fogging can be obtained.

Further, according to the production method of the present invention, a carrier for developing an electrostatic image of stable quality free of Lot.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method of measuring a carrier current value by a magnet brush method, and FIG. 2 is a schematic diagram of a frictional charge amount measuring device.

Claims (3)

(57) [Claims] An ultrafine powder having a particle diameter of 1/10 or less of a central particle diameter of a carrier core material composed of a ferromagnetic material selected from iron, nickel, cobalt, magnetite and ferrite is removed.
In a two-component developer carrier having a carrier core material surface coated with an insulating resin, the carrier core material has a center particle size of 25 to 100 μm, and particles having a center particle size of ± 10 μm. A carrier for a two-component developer, characterized by having a particle size distribution of not less than 70% by weight, and not more than 2% by weight of ultrafine powder having a particle size of 1/10 or less of the central particle size. . 2. The carrier core material particles having the particle size distribution,
2. The two-component developer carrier according to claim 1, wherein the carrier is obtained by removing ultrafine powder of a carrier core material by air classification. 3. An ultrafine powder having a particle diameter of 1/10 or less of a center particle diameter of a carrier core material composed of a ferromagnetic material selected from iron, nickel, cobalt, magnetite and ferrite is removed by air classification. 25 to 100 μm, containing 70% by weight or more of particles having a central particle size of ± 10 μm, and containing 2% by weight or less of ultrafine powder having a particle size of 1/10 or less of the central particle size. A method for producing a carrier for a two-component developer, comprising: obtaining a carrier core material having a particle size distribution; and coating the obtained carrier core material surface with an insulating resin to produce a carrier.