JPH056032A - Positively charged developer for electrophotography - Google Patents

Abstract

PURPOSE:To allow the development of electrostatic images or a low electrostatic contrast with high densities by constituting the above developer of a magnetic powder dispersion type carrier and toner which are respectively specific. CONSTITUTION:The toner contg. silica particles subjected to a surface treatment with a quaternary ammonium salt compd. and the carrier of magnetic powder dispersed resin particles subjected to a surface treatment with conductive inorg. oxide particles are simultaneously used. The excellent powder flow property possessed by the silica particles and the positive chargeability and environmental stability by the surface treating agent are made compatible with the toner in this way. The effect of improving the charge exchange property and electrostatic charging speed by the conductive inorg. oxide particle is assured with the carrier. Consequently, the electrostatic charge quantity of the toner is stably maintained even if the charge quantity is lowered. The developer which hardly generates the reverse polarity toner even in spite of the addition of the fresh toner is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positively chargeable developer for electrostatic charge development which is used for development such as electrophotography and electrostatic recording.

[0002]

2. Description of the Related Art The electrophotographic method is widely used in copying machines and printers, and the most important elemental technology for ensuring its reliability is to stabilize the characteristics of the photoconductor and the developer. .. Regarding the photoconductor, an organic photoconductor has recently been attracting attention because of its low cost and stability. However, there is a problem in that the organic photoconductor is easily destroyed when charged at a high potential and has a short life. Further, in recent years, with the progress of colorization of documents in offices, a method has been used in which the surface potential of a photoconductor is multivalued to develop toner of two or more colors. In this method, it is necessary to develop an electrostatic latent image having low contrast.

On the other hand, as a developing method, a magnetic brush developing method using a two-component developer containing a carrier and a toner is mainly used. However, as described above, when the surface potential of the photoconductor is low, or electrostatic charge is applied. In the method in which the contrast cannot be increased, it is necessary to weaken the suction force of the toner and the carrier to some extent. The reason is that the toner attracted to the carrier must be peeled off from the carrier to be attracted to the electrostatic image. Also, if the charge of the toner is high, the charge of the electrostatic image is neutralized with a small amount of toner, and many This is because the toner cannot be attracted to the electrostatic image. But,
In order to reduce the charge amount of the toner, it is necessary to increase the ratio of the toner to the carrier. However, this increase causes the triboelectric charging between the toners and the contact between the toner and the carrier to be insufficient, thereby increasing the reverse polarity toner. Further, as the developer is used, the toner may adhere to the surface of the carrier to increase the reverse polarity toner. These reverse polarity toners cause toner adhesion to the background portion of the photoconductor, and as a result, they hinder the long-term use of the developer.

As described above, there has been a demand for a developer which is always stable with a low charge amount and does not increase the reverse polarity toner even when used for a long time. JP-A-62-129860, JP-A-62-129861, JP-A-62-12986
Japanese Patent Publication No. 6 describes that an inorganic oxide is added to the toner surface in order to obtain a toner having stable triboelectrification for a long period of time and excellent in reproducing an electrostatic image of low contrast. Even with this addition, when the difference between the charge sequence on the carrier surface and the charge sequence on the toner surface is large, the triboelectric charge amount of the toner becomes large, and it is not possible to stably obtain a toner having a desired low charge amount for a long period of time. .. Further, since the charge exchange property between the carrier and the toner is poor and the charging speed is lowered, fogging due to the opposite polarity toner occurs when a new toner is added.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention solves the above problems and provides a positively chargeable developer for electrophotography capable of developing an electrostatic image having a low electrostatic contrast at a high density. Is what you are trying to do. Further, the present invention is intended to provide a developer having a low charge amount and a narrow charge distribution and capable of obtaining a good image for a long period of time.

[0006]

The present invention relates to a positively chargeable developer for electrophotography containing a magnetic powder-dispersed carrier in which magnetic powder is dispersed in a binder resin, and a conductive inorganic oxide. A positively chargeable developer for electrostatic charge development, comprising a magnetic powder dispersion type carrier surface-treated with fine particles and a toner containing silica fine particles surface-treated with a quaternary ammonium salt compound.

[0007]

According to the present invention, by simultaneously using a toner containing silica fine particles surface-treated with a quaternary ammonium salt compound and a carrier of magnetic powder-dispersed resin particles surface-treated with conductive inorganic oxide fine particles, For toner, it is possible to achieve both excellent powder fluidity of silica fine particles, positive chargeability due to surface treatment agent, and environmental stability, and for carrier, charge exchangeability and charging speed due to conductive inorganic oxide fine particles. As a result, it is possible to maintain the stability even when the charge amount of the toner is lowered, and as a result, it is possible to obtain a developer in which reverse polarity toner is less likely to be generated even when new toner is added. It is possible to obtain stable and good image quality over a long period of time even with low electrostatic contrast.

The quaternary ammonium salt compound used in the present invention may be of any type as long as it has a quaternary ammonium salt structure in the molecule. Specifically, the following cations and anions are combined. A compound can be mentioned. That is, as the cation, dimethyldibutylammonium ion, alkylammonium ions such as dimethyldistearylammonium ion, benzyltrimethylammonium ion, benzylammonium ions such as benzyltributylammonium ion, methylpyridinium ion, pyridinium ion such as cetylpyridinium ion And so on. As anions,
Chlorine ion, bromine ion and other halogen ions, paratoluene sulfonic acid, naphthalene sulfonic acid and other sulfonate ions, sulfate ion, nitrate ion and other inorganic acid ions, acetic acid, benzoic acid and other organic acid ions, etc. is there.

The amount of the quaternary ammonium salt compound added is 0.1 to 300%, preferably 0.
It is suitable to be 5 to 150%.

As a method for attaching the quaternary ammonium salt compound to the surface of the silica fine particles, the compound is dissolved in a solvent,
A method in which the solvent is evaporated and the solvent is removed after drying is generally applied on the surface of silica, and specifically, it is preferably treated with an apparatus such as a kneader coater, a spray dryer, a thermal processor, or a fluidized bed. Further, if necessary, it is possible to carry out pulverization and classification after drying.

The primary particle size of the silica fine particles according to the present invention is 40 nm or less, more preferably 20 nm or less. The surface of the silica fine powder according to the present invention is preferably treated in advance with a hydrophobizing agent such as a silane coupling agent or simultaneously treated with the quaternary ammonium salt compound to render it hydrophobic. The amount of silica fine powder added to the toner is 0.05 to 2
0% is preferable, and 0.1 to 5% is particularly preferable.

The toner according to the present invention uses a binder resin such as an ordinary styrene resin, polyester resin, polyamide resin, epoxy resin, etc., and is made of carbon black, magnetic powder, pigment or dye according to a desired color tone. And the like, and if necessary, a charge control agent, a wax and the like can be added, but the present invention is not limited thereto.

The conductive inorganic oxide used for the carrier surface of the present invention is not particularly limited as long as it has a volume resistance of 10 ¹² Ωcm or less, preferably 10 ¹⁰ Ωcm or less.
Specific examples include titanium oxide, silica, alumina, zinc oxide, magnesium oxide, tin oxide, iron oxide and the like. The particle size is appropriately 1 μm or less, preferably 0.1 μm or less. Note that these inorganic oxides may be surface-treated with a hydrophobizing agent or the like, if necessary.
The amount of the inorganic oxide fine particles used in the present invention added to the carrier is 0.01 to 10%, preferably 0.05 to 5%.

The method of adding the inorganic oxide fine particles to the surface of the carrier can be carried out in a usual mixing device and is not particularly limited. Specific examples include a V-type blender, a cement mixer, a paint shaker, a Henschel mixer, and a kneader coater.

The carrier used in the present invention is a dispersion type carrier containing magnetic powder and a binder resin as essential components. The magnetic powder and the binder resin are melt-kneaded and pulverized and classified, or melt-kneaded and then spray-cooled. , Can be obtained by granulating.

As the binder resin for the carrier used in the present invention, all of the general thermoplastic resins can be used, but specifically, styrenes such as styrene and chlorostyrene, ethylene, propylene, butylene, Monoolefins such as isobutylene, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl esters such as vinyl butyrate, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, Α-Methylene aliphatic monocarboxylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate and dodecyl methacrylate, vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether, vinyl methyl ketone, vinyl hexylke Examples thereof include homopolymers or copolymers of vinyl ketones such as vinyl isopropenyl ketone and the like, and particularly representative binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene- Examples thereof include an alkyl methacrylate copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene copolymer, a styrene-maleic anhydride copolymer, polyethylene and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax and the like can be mentioned.

In the carrier core of the present invention, as the magnetic fine particles to be dispersed in the binder resin, all of the usual ferromagnetic fine particles can be used. Specifically, ferric tetroxide, γ
—Iron sesquioxide, various ferrites, chromium oxide, various metal powders and the like can be mentioned. The amount of magnetic particles added is
It is usually about 30 to 95% by weight, preferably 45 to 90% by weight, based on the total amount of the binder resin, and it gives good results. The particle size of the carrier used in the present invention is 10 to 50.
A range of 0 μm, preferably 20 to 200 μm is suitable.

[0018]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. In the following description, all "parts" represent "parts by weight". (Production of Treated Silica A) Dimethyl distearyl ammonium chloride 10 parts Methanol 1000 parts Hydrophobic silica (R972 manufactured by Nippon Aerosil Co., Ltd.) 100 parts The present invention was prepared by dissolving and dispersing the above mixture well, and then removing the solvent in a fluidized bed. To obtain treated silica A. (Production of treated silica B) Tributylbenzylammonium hydroxynaphthalene sulfate 5 parts Methanol 1000 parts Hydrophobic silica (R972 manufactured by Nippon Aerosil Co., Ltd.) 100 parts The above mixture is well dissolved and mixed, and the solvent is removed by a thermal processor, followed by pulverization, Sifted to obtain treated silica B according to the present invention.

(Manufacture of Toner Particles) Styrene / butyl acrylate copolymer (80/20) 100 parts Carbon black (Regal 330 manufactured by Cabot Co., Ltd.) 10 parts Polypropylene wax (Viscole 660P manufactured by Sanyo Kasei Co., Ltd.) 5 parts The above materials are Banbury. After melt-kneading with a mixer, pulverization and classification were carried out to obtain toner particles having an average particle diameter of 11 μm. (Production of Toner 1) Treated Silica A 1 part Toner particles 100 parts The above materials were mixed with a Henschel mixer to obtain Toner 1 according to the present invention. (Production of Toner 2) Treated Silica B 1 part Toner particles 100 parts The above materials were mixed with a Henschel mixer to obtain Toner 2 according to the present invention. (Production of Toner 3) Hydrophobic silica (R972 manufactured by Nippon Aerosil Co., Ltd.) 1 part Toner particles 100 parts The above materials were mixed with a Henschel mixer to obtain a toner 3 for comparison.

(Production of Carrier Particles) Styrene / n-butyl methacrylate copolymer 25 parts Magnetic powder (EPT1000 manufactured by Toda Kogyo Co., Ltd.) 75 parts The above materials are kneaded by a twin-screw extrusion kneader, pulverized and classified to obtain an average particle size. Dispersion type carrier particles having a diameter of 45 μm were obtained. (Production of Carrier 1) The above carrier particles 100 parts Titanium dioxide fine particles (P-25 manufactured by Nippon Aerosil Co., Ltd.) 0.5 part The above materials were mixed with a V blender to obtain a carrier 1 according to the present invention. (Carrier 2) For comparison, the above carrier particles were directly used as Carrier 2
Used as.

Example 1 Toner 1 5 parts Carrier 1 100 parts The above materials were mixed to obtain a developer according to the present invention. [Example 2] Toner 2 5 parts Carrier 1 100 parts The above materials were mixed to obtain a developer according to the present invention. Comparative Example 1 Toner 3 5 parts Carrier 1 100 parts The above materials were mixed to obtain a comparative developer. Comparative Example 2 Toner 1 5 parts Carrier 2 100 parts The above materials were mixed to obtain a comparative developer. (Evaluation of Actual Machine) Using the developers obtained in Examples 1 and 2 and Comparative Examples 1 and 2, Fuji Xerox copier (FX5075)
, The non-exposed portion potential is 550 V, the exposed portion potential is 70
When a continuous copying test was conducted with V and the developing bias potential set to 200 V, the results shown in Table 1 were obtained. That is, it can be seen that the developers of Examples 1 and 2 were excellent in charge retention property, were able to secure a stable solid portion density, and obtained good image quality without fog in the background portion.

[0022]

[Table 1]

[0023]

EFFECTS OF THE INVENTION According to the present invention, by adopting the above-mentioned constitution, it is possible to secure good powder fluidity, positive chargeability and environmental stability at the same time for the toner. The charging speed can be improved, and as a result, it becomes stable even when the charging amount is lowered, and it becomes possible to prevent the generation of reverse polarity toner even when new toner is added, and even with low electrostatic contrast. It became possible to obtain a stable and good image for a long period of time.

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Claims (1)

Claim: What is claimed is: 1. A positively chargeable developer for electrophotography, comprising a magnetic powder-dispersed carrier in which magnetic powder is dispersed in a binder resin, and a toner. A positively chargeable developer for electrostatic charge development, comprising a surface-treated magnetic powder-dispersed carrier and a toner containing silica fine particles surface-treated with a quaternary ammonium salt compound.