JPH08314201A - Carrier for color developer and two-component type developer formed by using the same - Google Patents

Abstract

PURPOSE: To prevent the degradation in the electrostatic chargeability of carriers after repetitive use, the in-machine splashing of toners by an increase in reverse polarity toners and the degradation in image quality, such as fogging, by coating magnetic particles with a specific resin. CONSTITUTION: The carriers are formed by coating the surfaces of the magnetic particles with the resin. Styrene-acrylic copolymer resins by combinations of >=2 kinds of styrene monomer components, such as styrene and α-methylene aliphat. monocarboxylate ester monomer components α-methylene aliphat. monocarboxylic monomers, methyl methacrylate, are used as the resin for coating. An azo compd. is used as a polymn. initiator at the time of synthesizing the coating resin. Azo-bis isobutyl nitrile, azo-bis isovaleronitrile, etc., are used as the azo compd. The magnetic particles are preferably coated with 0.05 to 5.0wt.% resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for a color developer used in electrophotography and a two-component developer using the carrier.

[0002]

2. Description of the Related Art In recent years, a method of visualizing image information through an electrostatic latent image such as electrophotography has been used in various fields. In electrophotography, an electrostatic latent image is formed on a photoconductor by charging and exposing steps, a developer containing toner is attached to the electrostatic latent image, and then the toner image is transferred to a transfer material such as paper. After that, it is fixed by heating or pressing to form a copied image. As the developer, generally, a one-component type developer made of only a magnetic toner containing a magnetic substance and a two-component type developer made of a non-magnetic toner not containing a magnetic substance and a magnetic carrier are known. ing. The latter two-component developer frictionally charges the toner by mechanically stirring the toner and the carrier, so that the chargeability and charge amount of the toner can be determined by selecting the characteristics of the carrier, stirring conditions, and the like. It is superior to the one-component developer in that it can be appropriately controlled.

As a carrier used for a two-component developer, a coating carrier obtained by coating the surface of magnetic particles with a resin is preferably used because the durability and triboelectric charging property of the carrier can be improved. ing. Styrene / acrylic resins are well known as coating resins. In particular, a carrier coated with a styrene / acrylic resin is often used as a carrier for a color developer because of its high chargeability and charge retention property. However, there have been problems such as toner scattering in the copying machine and image fog while the carrier is repeatedly used, and improvements have been desired. The monomer composition ratio of the coating resin and the monomer species were changed, and addition of an internal additive (carbon black or the like) was studied, but satisfactory results were not obtained.

[0004]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present invention has been made as a result of intensive studies to prevent deterioration of chargeability of a carrier after repeated use and deterioration of image quality such as toner scattering and fogging due to increase of reverse polarity toner. By using an azo compound as the polymerization initiator used in the synthesis of the resin for coating particles, it is possible to obtain a high chargeability of the carrier and further suppress the generation of a reverse polarity toner, which causes the above problems. It is a solution to the problem.

[0005]

The present invention relates to a carrier for a color developer comprising magnetic particles coated with a styrene / acrylic copolymer resin using an azo compound as a polymerization initiator, and a carrier for the same. It is a two-component developer used.

In the present invention, examples of the azo compound which is a polymerization initiator used in the synthesis of the coating resin include azobisisobutyronitrile (AIBN) and azobisisovaleronitrile (AIVN). In the case of an azo compound, it is considered that the decomposition product left by the decomposition of the polymerization initiator remains as the terminal group of the polymer chain, and the polarity and chargeability of the carrier itself are controlled by the degree of polarization of this terminal group. In the case of, the isobutyronitrile group remains in the terminal group, and it is speculated that this strong polarization enhances the chargeability of the carrier.

The following resins can be used as the resin for coating the magnetic particles used in the present invention. Styrene monomer components such as styrene, chlorostyrene and methylstyrene, α-methylene aliphatic monocarboxylic acid monomers such as methacrylic acid and acrylic acid, methyl methacrylate, propyl acrylate and butyl acrylate, 2
-Copolymer resin obtained by combining two or more kinds of α-methylene aliphatic monocarboxylic acid ester monomer components such as ethylhexyl acrylate.

As the magnetic particles used in the present invention, it is possible to use, for example, ferrite powder, magnetite powder or the like composed of elements such as iron powder, nickel, copper, zinc, magnesium and barium. It is preferable that these magnetic core particles have a weight average particle diameter of 10 to 100 μm. 1
If it is less than 0 μm, it tends to scatter, and if it exceeds 100 μm, the image quality tends to be rough.

These magnetic particles have a content of 0.05 to 5.0.
It is preferably coated with the above-mentioned copolymer resin in a weight percentage. If the amount of coating resin is less than 0.05% by weight, the coating effect tends to be insufficient, and if it exceeds 5.0% by weight, coalescence of carriers tends to occur.

The present invention is also a two-component developer using the above-mentioned carrier, and the color toner for the two-component developer includes a colorant, a binder resin, a charge control agent and the like. Is used. As the colorant, a commonly used pigment or dye can be used, and a hydrate cake pigment or the like may be used without any particular limitation. For example, carbon black, iron black, various non-ferrous metal oxides, zinc white, yellow iron oxide, ultramarine,
Dyes / pigments selected from titanium oxide, azo, phthalocyanine, anthraquinone, thioindigo, perinone, perylene, quinacridone, dioxazine, quinophthalone, isoindolinone, benzimidazolone, dodamine , Or nigrosine oil-soluble dye, crystal violet, azo metal complex salt,
Examples thereof include metal complex salt dyes such as balatin dye and orazole dye.

The binder resin may be a thermoplastic resin which is usually used for toners, and in view of transparency, colorless and transparent resin is preferable. Examples thereof include polystyrene, styrene-acrylic acid ester copolymer, styrene-butadiene copolymer, styrene-vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin and the like.

The charge control agents include those classified as dyes and those classified as resins. Specific examples of the toner that imparts a positive chargeability include an igrosine oil-soluble dye, crystal violet, and a quaternary ammonium salt. In addition, as a material that imparts a negative charging property to the toner, a metal complex salt dye such as a balatin dye or an azole dye can be used. Many color toners are negatively charged.

In addition, if necessary, various charge stabilizers, lubricants such as magnetic powders and various waxes, improvement of fluidity of toner,
As a cleaning aid, hydrophobic silica, metal oxides such as alumina and titania, metal salts of higher fatty acids represented by zinc stearate, fine powders of fluoropolymers, and the like can be added.

[0014]

The present invention will be described in more detail based on the following examples.

[Synthesis Example of Resin A Coated with Magnetic Particles] Styrene /
Using methyl methacrylate (40:60) monomer, AIBN was added in an amount of 2% by weight based on the total amount of the monomer,
Solvent polymerization is carried out in a xylene solution, Tg = 70 ° C., number average molecular weight (hereinafter abbreviated as Mn) 20,000, weight average molecular weight (hereinafter abbreviated as Mw) 50,000, Mw / Mn = 2.5 carrier coating resin A Got

[Synthesis example of resin B coated with magnetic particles] Styrene /
Methyl methacrylate (40:60) monomer was used, and benzoylperoxide (BPO) was used as the total monomer.
2% by weight relative to the amount, solvent polymerization is performed in a xylene solution, Tg = 70 ° C., number average molecular weight (hereinafter abbreviated as Mn) 30,000, weight average molecular weight (hereinafter abbreviated as Mw) 60,000, M
A carrier coating resin B having w / Mn = 2.0 was obtained.

Example 1 A coating resin A was made into a resin solution having a solid content of 10%, magnetic particles (spherical ferrite of Cu--Zn--Fe composition having a weight average particle diameter of 45 .mu.m) were applied by dip coating, and the resin coating amount was 0.14. Weight percent carrier was obtained. On the other hand, the color toner is manufactured as follows. Non-linear polyester resin 100 parts by weight Quinacridone pigment 4 parts by weight Bontron E-84 4 parts by weight (negative charge control agent manufactured by Orient Chemical Co., Ltd.) The above composition was melt-kneaded with a twin-screw extruder, and after cooling, with a hammer mill. Coarse crushing, then fine crushing with a collision type crusher,
By classification, a toner having an average particle size of 8 μm was obtained. The obtained toner was mixed with 0.3 part by weight of hydrophobized silica fine particles and 0.6 part by weight of hydrophobized titanium fine particles to prepare a magenta toner. The above carrier and magenta toner
And were mixed so as to have a toner concentration of 4.5% to obtain a developer. The developer was evaluated after 3 minutes of ball milling and after 60 minutes for triboelectric charge and reverse polarity toner ratio. The triboelectrification amount was measured by the blow-off method, and the reverse polarity toner ratio was measured by a charge amount distribution measuring device "E-Spart Analyzer" (manufactured by Hosokawa Micron Co., Ltd.). The mass ratio of the charging toner was calculated. The results are shown in Table 1. Next, using this developer, a plurality of actual copying tests were conducted with a commercial full-color copying machine. The evaluation is also shown in Table 1 for image fogging, toner scattering and durability.

Comparative Example 1 Example 1 except that a carrier is prepared using the coating resin B.
The same evaluation as above was performed, and the results are shown in Table 1.

[0019]

[Table 1]

[0020]

The present invention can provide a durable full-color carrier excellent in image quality and a two-component developer.

Claims (5)

[Claims] 1. A carrier for color developers, characterized in that magnetic particles are coated with a styrene / acrylic copolymer resin using an azo compound as a polymerization initiator. 2. The weight average particle diameter of the magnetic particles is 10 to 100.
The carrier for color developer according to claim 1, wherein the carrier for color developer is μm. 3. The carrier for color developer according to claim 1, wherein magnetic particles are coated with 0.05 to 5.0% by weight of the copolymer resin. 4. The carrier for color developer according to claim 1, which is positively charged. 5. The color according to any one of claims 1 to 4.
A two-component developer using a developer carrier.