JPH04326361A - Dry developer and its production - Google Patents

Abstract

PURPOSE:To provide such a developer in which magnetic particles isolated from the carrier to the surface are hardly deposit on a photosensitive material. CONSTITUTION:The dry developer consists of a toner and a carrier containing a binder resin and magnetic powder. This carrier consists of particles treated by heating at the temp. lower than the treatment temp. for spherical particles, and the amt. of exposed magnetic powder on the surface of the carrier particles is preferably 1.0-2.0 atomic % calculated as iron element. This developer is prepared by heat treating the carrier containing a binder resin and magnetic powder at the temp. lower than the spherical treatment temp., and then mixing with the toner.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry developer for developing electrostatic latent images and a method for producing the same.

0002

2. Description of the Related Art In electrophotography or electrostatic recording, a dry developer consisting of two components, a carrier and a toner, is generally used as a developer. In a two-component dry developer, frictional charging is generated between the carrier and the toner by stirring within the developing device, giving the toner a charge of opposite polarity to the electrostatic latent image, which is then attached to the latent image. Development is performed. Conventionally, carriers with larger particle sizes than toner (60 to 500 μm) have been used as such developers, but gradation reproducibility is poor and when the ratio of toner to carrier increases, background areas This has the disadvantage that toner tends to adhere to the surface.

[0003] In order to improve this drawback, a small particle size carrier in which magnetic fine particles are dispersed in a binder resin, a so-called carrier for microtoning, has been proposed and put into practical use.

0004

[Problems to be Solved by the Invention] There are various properties required of carriers, but particularly important properties include appropriate charging properties, impact resistance, abrasion resistance, developability, and developer life. be able to. Considering the above required characteristics,
Conventionally used carriers still have problems to be improved, and no fully satisfactory carriers are known. For example, conductive carriers such as iron oxide powder have excellent solid developability, but are inferior in fine line developability, and in order to extend the life of the toner, it is necessary to include a special charge control agent in the toner. On the other hand, coat-based insulating carriers have the disadvantage of being poor in solid reproducibility, although they are excellent in longevity and fine wire reproducibility. In addition, carriers for microtoning are susceptible to problems such as adhesion of magnetic particles released on the carrier and surface to the photoreceptor, high humidity caused by magnetic particles released on the surface, etc.
It has disadvantages such as changes in the amount of charge at low humidity and difficulty in surface treatment, which makes it impossible to dramatically extend the lifespan. Therefore, it is an object of the present invention to solve the above-mentioned problems in the conventional technology, particularly in the case of small particle carriers, and to create a developer in which the magnetic particles liberated on the surface of the carrier are less likely to adhere to the photoreceptor. It is about providing.

[0005]

[Means for Solving the Problems] The present inventors have achieved the above object by heating a carrier containing a binder resin and magnetic powder at a temperature lower than the temperature at which heat treatment is performed for the purpose of spheroidization. The present inventors have discovered that the present invention is possible and have completed the present invention.

[0006] The present invention provides a dry developer comprising a toner and a carrier containing a binder resin and magnetic powder, characterized in that the carrier is particles heat-treated at a temperature lower than the spheronization temperature. . The dry developer of the present invention is
It can be produced by heating a carrier containing a binder resin and magnetic powder at a temperature lower than the spheroidization temperature and then mixing it with a toner.

The present invention will be explained in detail below. Examples of the binder resin for the carrier used in the present invention include polystyrene, polyethylene, polypropylene, polybutene, acrylic resin, methacrylic resin, polyacrylonitrile,
Addition polymer resins such as polyacrylamide, polyacrylic acid, polymethacrylic acid, vinyl acetate resin, vinyl chloride resin, phenol resin, urea resin, melamine resin, polyester resin, polycarbonate resin, polyamide resin,
Examples include condensation type resins such as polyurethane resins and epoxy resins, and copolymers of these monomers.

The carrier magnetic powder used in the present invention preferably has an average particle size of 0.1 to 3 μm. Magnetite, ferrite, as magnetic powder
Fine powders of iron, nickel, chromium dioxide, γ-hematite, cobalt, etc. can be used. Among them, magnetite is preferred because it is inexpensive and can be used stably. The content of the magnetic powder used in the present invention has a great effect on the saturation magnetic flux density of the magnetic carrier, so care must be taken.

[0009] The blending ratio of the binder resin and magnetic powder in the carrier is 20:80 to 70:30 by weight, preferably 20:
A ratio of 80:50 to 50:50 is appropriate. Magnetic powder content is 80
If the amount exceeds % by weight, the binding ability will be poor, the carrier particles will become brittle, and the manufacture of the carrier will become difficult. On the other hand, if it is less than 30% by weight, sufficient magnetism cannot be obtained and transportability deteriorates. In the present invention, carbon black as a conductivity regulator, a charge control agent, etc. may be added to the carrier as necessary.

[0010] The weight average particle size of the carrier of the present invention is 10 to 50 μm, preferably 20 μm in the case of a small particle size carrier.
A range of ~40 μm is suitable. Weight average particle size is 10μ
If the diameter is less than 50 μm, carrier adhesion to the background will occur, and if the diameter is less than 50 μm,
This is because, if it exceeds this, the sharpness of the image will be lost and the image quality will deteriorate. In addition, if the particle size is not small, 50 to 15
A material in the range of 0 μm is used. In that case, the toner concentration may be lower than in the case of small particle size carriers.

[0011] The carrier of the present invention can be prepared by a method in which a binder resin and magnetic powder are melt-kneaded and then pulverized, a spray-dry method in which magnetic powder is dispersed in a binder resin solution dissolved in a solvent and heated and sprayed, or a method in which magnetic powder is melt-kneaded and then crushed. After creating carrier particles by direct polymerization of binder resin monomers in the presence of
It can be produced by heat treatment at a temperature below the spheroidization treatment temperature, that is, below the melting point of the binder resin, preferably at a temperature around the glass transition point of the binder resin.

[0012] The heat treatment of the carrier can be carried out in the same manner as the so-called heat treatment for spheroidization, in which a non-spherical carrier obtained by conventional kneading and pulverization is heat-treated at a temperature near the melting point of its binder resin. However, in the present invention, unlike conventional heat treatment for spheroidization, heating is performed at a temperature lower than the melting point of the binder resin, preferably at a temperature near the glass transition point. By performing such heat treatment, the magnetic powder free on the surface of the particles of the carrier is covered with the binder resin or is bound to the surface of the carrier, and no longer adheres to the photoreceptor. If the heating temperature is higher than the melting point, the magnetic powder exposed on the surface of the carrier particles will be completely covered with the binder resin, and the charge exchangeability with the toner will be poor, maintaining sufficient chargeability. become unable. As a heating means for the heat treatment, for example, a dryer, a hot air fluidized bed, a high frequency heater, etc. are used.

In the present invention, the above heat treatment is preferably carried out so that the amount of magnetic powder exposed on the carrier particle surface is 1.0 to 2.0 atomic % as iron element. As a result, adhesion of free magnetic powder to the photoreceptor is eliminated, and a developer with high charge retention properties can be obtained.

In the present invention, the amount of exposed magnetic powder is measured as follows. Measuring device: X-ray photoelectron spectrometer JP manufactured by JEOL Ltd.
S-80 Measurement conditions: X-ray: Mg/Al twin anode type Mg1253.6eV acceleration 10KV, 30mA Analyzer resolution: 30eV Target photoelectrons: Fe 2p3/2 O 1s C 1s Binding energy Fe 726-706eV O 542-527eV C 294 ~279eV 0.2eV Step: Fe 500ms/step O 200ms/step C 20ms/step data acquisition Integration: 30 times Peak area calculation: Set the straight background, take the area as the number of atoms, and calculate the area/(intake time/ step)/correction factor However, the correction factors are Fe: 6.14, O: 2.28, C: 1.
00 Fe+O+C=100, calculate the percentage of each number of atoms. Sampling method: 15mm x 10mm x 2mm Al
Fill the container with toner and level it out.

The toner used in the developer of the present invention comprises a binder resin, a colorant and, if necessary, a charge control agent. The average particle size of the toner is preferably 5 to 20 μm.

The developer of the present invention is prepared by mixing a heat-treated carrier and a toner. The mixing ratio of toner and carrier is suitably in the range of 2:98 to 30:70, preferably 5:95 to 15:85 in terms of weight ratio. this is. If the toner content is less than 2% by weight, the image density will be insufficient, and if it exceeds 30% by weight, toner scattering and toner adhesion to the background will occur.

[0017]

[Examples] The present invention will be explained below with reference to Examples and Comparative Examples. Example 1 Styrene-n-butyl methacrylate-methacrylic acid copolymer 30 parts by weight (80% by weight of styrene, 5% by weight of methacrylic acid,
Mw=80,000, Tg=90℃) Magnetite

70 parts by weight After melt-kneading the above ingredients, finely pulverize,
Classification was performed to obtain a carrier having an average particle size of 34.5 μm. The obtained carrier was placed in a fluidized bed dryer, the temperature inside the fluidized bed was controlled to 80° C., and heat treatment was performed for about 30 minutes. After the heat treatment and cooling to room temperature, the carrier was taken out.

[0018] Apart from the above carrier, as a toner
Styrene-n-butyl methacrylate-dimethylamino 94 parts by weight
Methacrylate copolymer (copolymerization ratio 65:30:5;
Mw=50,000)
Carbon black

6 parts by weight of the above components were melted and kneaded and then finely pulverized to obtain a toner having an average particle size of 10.5 μm. 92 parts by weight of the carrier and 8 parts by weight of the toner were mixed in a V blender to prepare a developer.

Example 2 A carrier was obtained in the same manner as in Example 1, except that the temperature inside the fluidized bed was kept at 90° C., and a developer was obtained by mixing the carrier with the same toner as in Example 1 in the same ratio.

Comparative Example 1 A carrier was obtained in the same manner as in Example 1, except that the temperature inside the fluidized bed was set at 100° C., and a developer was obtained by mixing it with the same toner as in Example 1 in the same ratio.

Comparative Example 2 A carrier was obtained in the same manner as in Example 1, except that the carrier was not heat-treated, and was mixed with the same toner as in Example 1 in the same ratio to obtain a developer.

Development Test A development test was conducted on the developers obtained in the above Examples and Comparative Examples. That is, a negative electrostatic latent image was continuously developed for each developer using a magnetic brush developing device equipped with a developer stirring device, and the maintenance of image quality was observed. The results are shown in Table 1.

[0023]

[Table 1]

Regarding background fog in Comparative Example 2,
When fog particles were collected from the photoreceptor and analyzed, most of them were found to be magnetic, and based on their particle size, they were found to be magnetic powder. From the above results, it is clear that when the developer of the present invention is used, there is no fogging in the background, clear images with particularly excellent gradation quality can be obtained, and even when 200,000 copies are made, there are no problems. It was confirmed that excellent image quality was maintained.

[0025]

Effects of the Invention: In the dry developer of the present invention, since the carrier is heat-treated at a temperature lower than the spheroidization temperature, it prevents the carrier and free magnetic powder from adhering to the photoreceptor, and can be used for a long time. Can withstand the use of time. Therefore, when the dry developer according to the present invention is used, images of good quality and excellent resolution and gradation can be obtained for a long period of time.

Claims (3)

[Claims] 1. A dry developer comprising a toner and a carrier containing a binder resin and magnetic powder, characterized in that the carrier is particles heat-treated at a temperature lower than the spheronization temperature. agent. 2. The dry developer according to claim 1, wherein the amount of magnetic powder exposed on the surface of the carrier particles is 1.0 to 2.0 at % as iron element. 3. A method for producing a dry developer, which comprises heat-treating a carrier containing a binder resin and magnetic powder at a temperature lower than a spheroidization temperature, and then mixing the carrier with a toner.