JPH03171148A - Developer for electrostatic charge development - Google Patents

Abstract

PURPOSE:To obtain the developer which improves the density of images by incorporating a spherical toner which is specified in Wadell's operational sphericity and a carrier which is coated with a resin having the surface of low surface energy. CONSTITUTION:The toner to be used is the spherical toner formed by dispersing additives, such as coloring agents, into a binder resin and is the truly spherical toner having the Wadell's operational sphericity ranging 0.95 to 1. The affinity between the toner and the coated carrier is degraded by the resin of the low surface energy even with the toner having the slightly high electrostatic charge sticking to the carrier and the intramolecular force on the coated carrier is decreased and the images are well developed if the carrier is coated with the resin of a silicone system or fluorine system having the low affinity to the toner as the resin of the low surface energy. Thus, the adhesive strength decreases as a whole even when electrostatic attraction force increases. Consequently, the toner is liable to be attracted to the electrostatic latent images formed on a photosensitive drum while having the prescribed electrostatic charge quantity. The image density is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a developer for developing electrostatic images used in image forming apparatuses such as electrophotographic copying machines.

(Prior Art) In an image forming apparatus such as an electrophotographic copying machine, a developer used to visualize an electrostatic latent image formed on a photoreceptor by a dry development method generally contains fine toner particles and a carrier. A bipartite developer is used. Such a two-component developer is used after being uniformly mixed by stirring.

Due to the stirring, the toner is charged by friction with the carrier and adheres to the surface of the carrier. The electrostatic latent image formed on the photoreceptor through the charging and exposure steps is developed with this toner. The obtained toner image is transferred to a support such as transfer paper, and fixed on the support by a fixing means.

In this way, a copy of the original is obtained.

Conventionally, toner is produced by melt-mixing a binder resin and various additives such as colorants, uniformly dispersing the mixture, pulverizing it with a pulverizer, and classifying it with a classifier. toner has been used.

As the carrier, a coated carrier in which a magnetic material such as iron, nickel, cobalt, or ferrite is coated with styrene or acrylic resin has been used.

(Problems to be Solved by the Invention) In order to improve the image quality of copies, it is necessary to select the most suitable carrier for toner. However, conventional carriers are not suitable for spherical toner produced by polymerization methods that have been studied in recent years.
It cannot be said to be optimal for the following reasons. Spherical toner produced by a polymerization method has superior fluidity compared to irregularly shaped toner, so there are more opportunities for frictional contact with the carrier, and the amount of charge tends to increase. Furthermore, when spherical toner comes into contact with the carrier, van der Waals force acts more easily than with amorphous toner, so the adhesion force of the toner to the carrier increases. If the adhesion force becomes too large, the amount of toner that moves to the electrostatic latent image formed on the photoreceptor decreases, causing a problem of insufficient image density.

The present invention is intended to solve the above-mentioned problems, and its purpose is to contain a spherical toner having a practical Wardell sphericity of 0.95 to 1 and a carrier most suitable for this toner. An object of the present invention is to provide a developer for developing electrostatic images that improves the density of images.

(Means for Solving the Problems) The developer for developing electrostatic images of the present invention comprises a spherical toner having a Wardell practical sphericity of 0.95 to 1.0 and a surface coated with a resin having low surface energy. The above object is achieved by containing the carrier.

(Function) The carrier used in the present invention is a coated carrier obtained by coating the surface of a known carrier conventionally used in dry development methods with a resin having a low surface energy. Examples of resins with low surface energy include silicone-based and fluorine-based resins that have low affinity with toner. When this resin is coated on a known carrier as exemplified below, even if the toner is attached to the carrier and has a relatively high charge amount, the toner and the coating will be bonded due to the presence of the resin coated on the carrier, which has a low surface energy. The affinity with the carrier is lowered, and the intermolecular force of the toner against the coated carrier is reduced, resulting in good development. As mentioned above, the adhesion force of the toner to the carrier is mainly a combination of the electrostatic attraction generated by the friction between the toner and the carrier and the intermolecular force between the toner and the carrier. Since the intermolecular force is reduced by the presence of the resin with low surface energy coated on the carrier, the adhesion force as a whole decreases even if the electrostatic attraction increases.

As a result, the toner is easily attracted to the electrostatic latent image formed on the photoreceptor drum while having a predetermined amount of charge.

(Preferred Embodiment of the Invention) As a method for coating the carrier, any known coating method can be used.

Examples of carriers that can be used include glass beads; oxidized or unoxidized iron powder; and magnetic materials such as ferrite, nickel, and cobalt.

The shape of the carrier is preferably spherical, and the particle size is 2
0μlI1-150μm1 especially 50μlI1-120μ
It is desirable that it be in the range of m.

The above ferrite is iron zinc oxide (ZnFezO4
), iron yttrium oxide (Y3 F es O+z),
Cadmium oxide (Cd3Fes0,2), iron copper oxide (C
uFez 04), iron lead oxide (PbFe+z○1,)
, iron manganese oxide (MnFez Oa), iron neodymium oxide (NdFeO,), iron oxide barium (BaFe
+zO 19), magnesium iron oxide (M g F
A set of ferrite particles consisting of one or more types of ferrite particles such as e zO4), lanthanum iron oxide (LaFeO3), etc., is used. In particular, soft ferrite containing one, preferably two or more metals selected from the group consisting of Cu, Zn, Mg, Mn and Ni, such as copper-zinc-magnesium ferrite, is used.

The coated carrier and a spherical toner having a Wardell practical sphericity of 0.95 to 1 are mixed, the toner concentration is adjusted to 2 to 10% by weight, preferably 3 to 8% by weight, and the mixture is mixed with a developer. do.

The toner used in the present invention is a spherical toner in which additives such as colorants are dispersed in a binder resin, which has been conventionally used in dry development methods, and has a Wardell practical sphericity of 0.95. It is a perfectly spherical toner in the range of 1 to 1.

Binder resins used in toner include styrene polymers, acrylic polymers, styrene-acrylic polymers,
Olefinic polymers such as chlorinated polyethylene, polypropylene, ionomers, etc. Vinyl chloride, polyester, polyamide, polyurethane, epoxy resin, diacryl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, phenol resin, rosin-modified phenol resin, xylene resin, rosin-modified maleic acid resin, rosin ester, etc. Various polymers can be mentioned.

These resins are arbitrarily selected depending on the fixing method and other required properties.

Among these, styrene polymers, acrylic polymers, and styrene-acrylic polymers are preferred, and styrene-acrylic polymers are particularly preferred. The weight average molecular weight of these resins is preferably 30,000 to 200,000, particularly preferably 50,000 to 150,000.

One type of polymer or a mixture of two or more types may be used.

As the colorant to be dispersed in the binder resin, known pigments and dyes used in this field can be used.

Furthermore, the above-mentioned toner may be blended with various compounding agents known per se that are used in this field. For example, as an anti-offset agent, various waxes such as low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax; carbon number 4
The above olefin polymers; fatty acid amide; silicone oil, etc. are contained in an amount of 0.5 to 1% per 100 parts by weight of the binder resin.
It is preferably contained in an amount of 5 parts by weight.

Contains the above structural components and has a Wardell practical sphericity of 0
．． A perfectly spherical toner in the range of 95 to 10 liters can be produced efficiently and in a short time by suspension polymerization, but if a perfectly spherical toner in the above range can be obtained,
It can be produced by any polymerization method. For example, it can also be produced by a so-called seed polymerization method in which ultrafine particles of 0.2 to 0.4 μm produced by emulsion polymerization or the like are used as cores and the ultrafine particles are made larger by polymerization to obtain a desired particle size. Further, the polymerization method is not limited to such a polymerization method, and it can also be produced by a so-called spray drying method in which a binder resin and additives such as a coloring agent are dissolved or dispersed in an organic solvent such as toluene and then sprayed and granulated.

A true spherical toner with a Wardell practical sphericity in the range of 0.95 to 1 has good fluidity, so its adhesion to the carrier increases due to frictional charging with the carrier, but when the carrier of the present invention is used, Since the intermolecular force between the toner and the carrier is reduced, the amount of charge on the toner does not decrease, the toner easily separates from the carrier, and the image density does not decrease.

When the carrier of the present invention is used for an irregularly shaped toner,
Since the amount of charge on the toner caused by friction with the carrier decreases, the electrostatic attraction between the toner and the electrostatic latent image is insufficient, and capri and toner scattering are likely to occur in the resulting image.

(Example) Hereinafter, the present invention will be specifically explained based on Examples.

Preparation of toner: 80 parts by weight of styrene, 2 ethylhexyl methacrylate
0 parts by weight, 5 parts by weight of grafted carbon black, 0.8 parts by weight of divinylbenzene as a crosslinking agent, 2 parts by weight of Spiron Black TRH (manufactured by Hodogaya Chemical Co., Ltd., trade name) and 2 parts by weight of Viscol 550P as a charge control agent. The composition was thoroughly dispersed in a bowl. This was added to 2,2゛azobis-2.4dimethylvaleronitrile (A
DVN) was added to an aqueous phase consisting of 400 parts by weight of water, 6 parts by weight of tricalcium phosphate, and 0.05 parts by weight of sodium dodecylbenzenesulfonate.
The mixture was suspended and dispersed in a K homomixer at 11,500 rpm for 10 minutes. This was polymerized at 75°C for 10 hours to complete the reaction.

The obtained polymer was filtered, washed, and dried to obtain a toner.

The obtained toner was mixed with a ferrite carrier shown in Table 1 coated with resins having different surface energies, and the toner concentration was adjusted to 3% to prepare a two-part developer. This developer was applied to an electrophotographic copying machine DC-11I.
C (manufactured by Sanda Kogyo Co., Ltd., trade name) was used to conduct an image output test. The results are shown in Table 2.

(Left below) Table 1 As can be seen from Table 2, when a developer containing a carrier coated with a resin with low surface energy is used,
Clear images with high image density can be obtained.

(Effects of the Invention) Since the carrier used in the present invention is coated with a resin having low surface energy, the intermolecular force between the toner and the carrier is reduced. Therefore, by using this coated carrier, even a perfectly spherical toner can be transferred to the electrostatic latent image formed on the photoreceptor drum without any problem, and the image density will not be reduced. Since the surface of the coated carrier used in the present invention has low affinity with toner, less spent toner adheres to the coated carrier, resulting in a long-life developer.

Furthermore, since the resin used to coat the carrier has low surface energy and is hydrophobic, the resulting developer has excellent moisture resistance.

that's all

Claims (1)

[Claims] 1. A developer for developing electrostatic images containing a spherical toner having a Wardell practical sphericity of 0.95 to 1.0 and a carrier whose surface is coated with a resin having low surface energy.