JPH0355823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a dry developer comprising a carrier and a toner used in electrophotography.

In electrophotography, an electrostatic latent image formed on a photoreceptor is developed with a developer, and then transferred and fixed onto a transfer sheet as required. As the developer used here, a two-component dry developer consisting of toner and carrier is conventionally known.
This is because toner particles that are triboelectrically charged to the opposite polarity to the carrier particles are held on the surface of relatively coarse carrier particles, and when they flow down or cascade onto the surface of the photoreceptor during development, they are The electrostatic force in the latent image area overcomes the bonding force between the carrier particles and the toner particles, and the toner particles adhere to the latent image to form a visible toner image. The developer is repeatedly used for long-term copying while replenishing toner consumed by development.

Therefore, during long-term use, the carrier must always triboelectrically charge the toner to a desired polarity and a sufficient amount of charge. However, in conventional developers, a toner film is formed on the carrier surface due to mechanical impact caused by collision between particles or collision between particles and a developing machine, or heat generated by these, resulting in so-called spent state.
The charging properties of the carrier deteriorate over time, necessitating replacement of the entire developer.

In order to prevent such spent formation, methods of coating the carrier surface with various resins have been proposed, but no satisfactory method has yet been obtained. For example, a carrier coated with a styrene-methyl methacrylate copolymer or a mixed resin of this copolymer and a silicone resin has excellent charging characteristics, but the critical surface tension of the surface is relatively high, and after repeated copying, Spent formation occurs and its life as a developer is not very long. In addition, since the carrier coated with tetrafluoroethylene polymer has a low surface tension, it is difficult for the toner to become spent, but since the tetrafluoroethylene polymer is located at the most negative side in the triboelectrification series, the toner can be used as a negative electrode. It cannot be used when attempting to be charged sexually. Furthermore,
Carriers coated with silicone resin alone without a mixture of styrene-methyl methacrylate copolymer have been tried because of their low surface tension, but when silicone resin-coated carriers are mixed with conventional toner, the toner is sufficiently charged. The current situation is that it cannot be put into practical use.

The object of the present invention is to solve these conventional drawbacks, and in particular, it is an object of the present invention to provide a long-life electrophotographic dry developer capable of uniformly and negatively charging toner to a sufficient amount. .

Through extensive research by the present inventors, we have discovered that in an electrophotographic dry developer consisting of a carrier and a toner, the carrier surface is coated only with a silicone resin represented by the following general formula, and the toner contains an organic solvent-soluble metal. It has been found that by incorporating a complex salt type monoazo dye, the above-mentioned conventional drawbacks can be solved at once and the object of the present invention can be achieved.

R: hydrogen atom, halogen atom, hydroxy group, methoxy group, _C1-4 lower alkyl group, or phenyl group To explain the present invention in more detail, the silicone resin used in the present invention is a commercially available silicone resin having the general formula above. Examples include straight silicone resins such as baking type and room temperature curing type. For example, Shin-Etsu Chemical's
KR271, KR255, KR152 and Toray silicone products
These are SR2400, SH840, SR2406, etc.

Although the silicone resin itself has the same level of charge series as non-coated carriers such as triiron tetroxide, its charge imparting ability is low when used as a developer by mixing known toners, and the toner is not sufficiently charged. cannot be charged and is not practical. however,
When the organic solvent-soluble metal complex type monoazo dye is mixed into the toner, the toner can be negatively charged to a charge amount of 20 to 30 μc.

In the present invention, the carrier core material for coating the silicone resin includes sand, cobalt, iron, copper, nonmetallic materials such as copper, zinc, aluminum, brass, etc., and metals having an average particle size of 50 to 1000μ, preferably 100 to 500μ. Conventionally used materials are widely used. As a coating method with silicone resin, the resin may be dissolved in a solvent and applied to the surface of the core material.

Metal complex salt type monoazo dye refers to a complex salt obtained by chemically bonding a metal to a monoazo dye molecule, and is a 1:1 type in which one metal atom is bonded to one dye molecule, or a two-dye molecule. Although there are 2:1 type and 3:1 type complex salts in which one metal thickener is bonded, 2:1 type complex salts are particularly preferred in the present invention. Examples of metal atoms include Cr, Co, Cu, and Fe, and Cr and Co are preferably used.

Specific examples are as follows.

Examples of commercially available metal complex monoazo dyes include ValiFast manufactured by Orient Chemical Co., Ltd.
Black #3804, Spilon manufactured by Hodogaya Chemical
Examples include BlackBH and Zapon Fast Red GE manufactured by BASF. These are polystyrene, polyacrylic acid ester, polyvinyl chloride, polyvinyl acetate, and
Toner particles may be prepared by kneading with a binder resin such as an epoxy resin or a polyester resin, and carbon black.

Phenol resin, xylene resin, petroleum resin,
Sulfonamide/formaldehyde resins, active agents such as fluorine-based surfactants, dyes with highly electronegative functional groups such as CISolvent Blue25 and CIVat Violet, and finely powdered silica are known. However, even if these are mixed into a toner and used in combination with the silicone resin-coated carrier of the present invention, sufficient charging cannot be obtained and there is a practical problem.

Hereinafter, the present invention will be explained by giving examples.

Example 1 A coating solution was prepared according to the following recipe.

Silicone resin (Toray Silicone SR2406)
100 parts by weight Toluene 1500 parts by weight 5 kg of oxidized iron powder with an average particle size of 100μ was placed in a rotating disc type fluidized bed particle coating device, and while fluidized, the coating solution with the above formulation was sprayed under heating at 80°C and applied. The dried coating was taken out from the coating device, placed in a constant temperature bath, and heated at 200° C. for 2 hours to cure the silicone film.

On the other hand, use a mixture of the following formulation as a toner formulation.
Kneaded under heat on this roll, cooled, crushed and classified,
Make toner of 5 to 20μ.

Polystyrene (Etsuso D-125) 100 parts by weight Metallic dye (Hodogaya Chemical Spiron Black
BH) 5 parts by weight Carbon black 5 parts by weight The above toner and carrier have a toner concentration of 2wt.
% of the developer. The amount of charge on the toner was measured using the blow-off method.
It was found that the charge was 25 μc/g, indicating that it was negatively charged. Ricoh copiers use this developer.
I conducted a continuous copy test with the FT6400, and measured the amount of charge after copying 100,000 sheets, and it was -20μc/g.
There was almost no deterioration, and the image quality remained the same as the initial version.

Example 2 Silicone resin (Shin-Etsu Chemical KR271) from which a coating liquid with the following formulation was prepared
100 parts by weight Toluene 1500 parts by weight A silicone resin-coated carrier was obtained in the same manner as in Example 1, and a toner and developer having the following formulations were produced. The charge amount was -15 μc/g. Polymer (Sanyo Kasei Hymer SBM73) 100 parts by weight Metal-containing dye (dye example 1) 2 parts by weight Carbon black 10 parts by weight Using this developer, a continuous copy test was conducted with a Ricoh copier FT6400, and 100,000 sheets were printed. The amount of charge after copying was -14 μc/g, which was almost unchanged, and the image quality was also the same as the initial one.

Comparative Example: In place of the metal-containing dye in the toner of Example 1
When the same amount of CISolvent Blue 25 was added to produce a toner and the developer was adjusted, the amount of charge was as low as -5 μc/g, and when a continuous copying test similar to Example 1 was performed, there was extremely high background smudge and it was of no practical value. It was hot.

Claims (1)

[Scope of Claims] 1. An electrophotographic dry developer comprising a carrier and a toner, in which the coating layer resin on the surface of the carrier consists only of a silicone resin represented by the following general formula, and the toner contains an organic solvent-soluble metal. A dry developer for electrophotography characterized by containing a complex salt type monoazo dye. R: hydrogen atom, halogen atom, hydroxy group,
Methoxy group, _C1-4 lower alkyl group or phenyl group.