JPH01211770A - Electrophotographic developer - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic developer providing sufficiently good picture image, having long life, and having high stability for changes of environmental conditions by using specified two kinds of carrier. CONSTITUTION:A mixture consisting of two kinds of carrier and a toner is used. The first carrier is formed by coating the surface of a core material with a mixture consisting of an acrylic resin and/or a styrene-acrylic resin with an inorganic electric resistance adjusting agent. The second carrier is formed by coating the surface of the core material with a mixture of a silicone resin with an inorganic electric resistance adjusting agent. Thus, a developer having sufficiently high durability, high stability for changes of environmental conditions, and providing picture images of high quality with low load, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a so-called two-component electrophotographic developer that uses a mixture of carrier and toner.

[Conventional technology]

2. Description of the Related Art Conventionally, a two-component developer consisting of toner particles and carrier particles has been used as a developer for developing an electrostatic image formed on a latent image holding surface of an electrophotographic photoreceptor or the like.

This two-component developer is required to have the following performance.

(1) The developer in the developer tank has sufficient fluidity and transportability to stir the toner and carrier.

(2) It must have an appropriate mechanical strength that will not cause the carrier to break even after repeated use, and it must also have durability such that toner does not adhere to the carrier surface.

(3) The developer must have environmental stability in that the electrical properties, physical properties, etc. of the developer are stable against environmental changes such as temperature and humidity.

(4) When a developer is used, the image quality is high, with high image density and no stains in non-image areas called fog.

Note that the above performance is affected not only by the developer but also by equipment aspects such as the development process and development conditions.

[Problem to be solved by the invention]

In response to the above requirements, developers using carriers with core materials such as spherical iron oxide powder and Feray 14 coated with various resins have been proposed, but there are still no developers with sufficient performance. Not obtained. For example, carriers coated with resins such as styrene-methacrylate copolymers and styrene polymers have excellent charging characteristics, but have problems in durability. Further, a carrier coated with a silicone resin having a low surface tension has a problem of low mechanical strength and a decrease in image quality.

[Means to solve the problem]

The inventors of the present invention have conducted intensive studies to solve the problems of the conventional developer described above, and found that by using a specific carrier in combination, the load on the developer is surprisingly small and durability is improved.
-We have discovered that environmental stability is good and high quality images can be obtained, and have arrived at the present invention. Is this the main message?)
Stomach 1, (G) A carrier whose core material surface is coated with a mixture of acrylic resin and/or styrene-acrylic resin and an inorganic electrical resistance regulator, and B) A silicone resin and an inorganic electrical resistance regulator. An electrophotographic developer characterized by comprising a carrier whose core material surface is coated with a mixture of (C) and (C) a toner.

The present invention will be explained in detail below.

The present invention is characterized in that a specific Ω type of carrier is used in combination.

The first carrier is formed by coating the surface of the core material with a mixture of an acrylic resin and/or a styrene-acrylic resin and an inorganic electrical resistance regulator (hereinafter, this carrier is abbreviated as carrier A). The resin used is what is called an acrylic resin, but usually methyl acrylate, ethyl acrylate, n-butyl acrylate, coethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n- - selected from monopolymers of acrylic esters or methacrylic esters such as butyl methacrylate. Further, as the styrene-acrylic resin, a copolymer of styrene and a monomer constituting the acrylic resin is used.

Among these resins, n-butyl methacrylate resin,
Methyl methacrylate resin and styrene-methyl methacrylate copolymer are preferred, and n-butyl methacrylate resin is particularly preferred.

It is sufficient that these resins are essentially composed of monomers such as those mentioned above, but they may also be composed partially of different monomers different from those mentioned above for some other purpose. Of course.

The inorganic electrical resistance adjuster added to the coating resin is used to control the electrical resistance of the carrier. For example, carbon black, graphite, magnetite, conductive metal oxides, etc. can be used, and carbon black, graphite, etc. Preferably, the main component is carbon. The particle size is O, Sμm
The following are suitable:

The amount of the electrical resistance adjuster added is preferably 90 parts by weight or less per 700 parts by weight of the coating resin.

As the core material of the carrier, known materials can be used, such as iron oxide powder, ferrite, etc.

The core material is preferably ferrite, and iron oxide powder has a higher specific gravity and saturation magnetization than ferrite, so the developing torque is high and the stress on the developer is high.
Ferrite is also difficult to use. General formula (MO)
The ferrite represented by m(Fe2Q3)n usually has a spherical shape, and its MO components include CaO, ZnO, and N.
i OlFeOlMnO, MgO, BaO, etc. can be selected from seven or two or more components. Among these,
A magnet with low electrical resistance because it is easy to adjust electrical resistance.

Tite (Fe304) is particularly preferred.

The core material preferably has an average particle size of 70 to 00 μm and is substantially spherical. Observe the core material particles with an electron microscope,
The length in the longitudinal direction (X) and the length in the transverse direction perpendicular to it (
If the ratio of Y) is in the range of X/Y=/ to 2, it can be suitably used as a substantially spherical material.

A known method may be used to coat the core material with resin. Specifically, the resin component is dissolved in a solvent such as methyl ethyl ketone, xylene, methylcyclohexane, toluene, etc., and an electrical resistance regulator is dispersed therein, and the core material is immersed in this to form a coating consisting of the resin and the electrical resistance regulator. Preferred methods include a method in which the core material is formed and then heat treated at a predetermined temperature, a method in which the core material is fluidized in advance, a resin solution containing the entire electrical resistance modifier is sprayed to cover it, and then a heat treatment is performed at a predetermined temperature.

The amount of resin coating the core material is preferably 0.0s to 3 parts by weight per 100 parts by weight of the core material.

The first carrier is formed by coating the surface of the core material with a mixture of silicone resin and an inorganic electrical resistance adjuster (
Hereinafter, this carrier will be abbreviated as carrier B).

Any silicone resin may be used as long as it can be used to cover the carrier, and specifically, straight silicone consisting only of organosiloxane bonds and known silicone resins modified with alkyd, polyester, epoxy, urethane, etc. are used. be able to.

The type and amount of the inorganic electrical resistance adjuster and core material used in carrier B, and the method of coating the carrier can be selected in the same manner as in carrier A.

Note that the coatings of carriers A and B are not limited to the above-mentioned resin and inorganic electrical resistance modifier, but other additives may be added to improve properties.

The mixing ratio of carrier B to carrier A in the electrophotographic developer of the present invention is preferably 50 to 97 to SO to 3 (weight ratio).

Known toners can be used in the present invention. Since the toner used is one that can be charged to a polarity opposite to that of the carrier and the electrophotographic photoreceptor, a negatively charged toner is used when a selenium photoreceptor is used as in the examples described later.

As the binder resin of the toner, styrene resin, styrene-acrylic resin, polyester resin, epoxy resin, etc. can be used, and as the colorant, carbon black, phthalocyanine blue, ultramarine blue, magnetic powder, etc. can be used.

You can.

Furthermore, a fine particle metal oxide as a fluidity improver, a low molecular olefin polymer as a fixability improver, and other additives may be added to the toner.

Toner production can be accomplished by mixing the above-mentioned raw materials in an appropriate blending ratio, kneading with a kneader, etc., cooling, pulverizing, and classifying. If necessary, an external addition step is provided to add one layer of additives to the toner surface. You can.

What is the average particle size of toner? -20 μm is preferred.

Also, the mixing weight ratio of toner and carriers A and B is /~
"θ: 10θ is preferable.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded.

In addition, "parts" in the examples indicate "parts by weight."

Examples/~S Styrene-n-butyl acrylate (monomer
θ: Co θ) Copolymer resin 100 parts Low molecular weight polypropylene 3 parts Carbon blank 7
Chromium-containing dye 2
After cooling, crush and classify the average particle size/
2 Aim black toner, and the toner io.

0.2 part of hydrophobic silica was added externally to obtain a negatively charged toner.

For a core material made of spherical magnetite with a particle diameter of ti-o~/30 Iim, resin 70 of the type shown in Table 1 was used.
0 part and 1S part of fine graphite powder as an electrical resistance adjuster were dispersed in methyl ethyl ketone, spray coated, and heat treated to obtain carriers ae. In addition, the core material is ferrite) (
Carriers f and g were obtained in the same manner except that the weight ratio was changed to Fe203:CuO:Zn○=7θ:/3:15 (weight ratio).
Coating amount of resin etc. on the core material of each carrier: 0.2wt%
).

Next, 15 parts of carrier AgS and 15 parts of carrier B were mixed in the combination shown in Table 2, and this was mixed with the negative charge toner part O to prepare a developer a-et.

Using these developers, copies of A6 size paper were made with an image area ratio of S% using a copying machine equipped with a selenium photoreceptor, and the state at the initial stage of copying and the state after 20,000 copies were observed. The results are shown in Table 1.

Comparative Examples/~3> As shown in Table 1, developers fh were prepared by mixing 700 parts of carrier A or carrier B alone and part of negatively charged toner C.

Using this, each developer was evaluated in the same manner as in Example/~Left. The results are shown in Table 2.

〔Effect of the invention〕

The present invention can provide an electrophotographic developer that has good image properties, long life, and good environmental stability. Therefore, the present invention is extremely useful industrially.

Claims (1)

[Claims] (1) (A) A carrier whose core material surface is coated with a mixture of an acrylic resin and/or a styrene-acrylic resin and an inorganic electrical resistance regulator, (B) a carrier formed by a mixture of a silicone resin and an inorganic electrical resistance regulator. An electrophotographic developer characterized in that the main components are a carrier formed by coating the surface of a core material and (C) a toner.