JPH01227163A - Color toner for electrophotography - Google Patents

Abstract

PURPOSE:To obviate decrease of an electrostatic charge quantity and to form the toner having excellent printing characteristics by coating the same resin as a binder resin physically onto the toner. CONSTITUTION:The color toner and the powder of the binder resin constituting said toner are mixed and agitated at a high speed to electrostatically stick the powder of the binder resin onto the color toner; thereafter, such impact force as to bring the toner and powder into contact with a plate at a high speed is applied to the mixture and the powder of the binder resin is thermally melted by such impact energy, by which the resin covering is executed. The control of the coating film thickness is possible by changing the grain size and mixing ratio of the color toner and the binder resin powder at this time. The deterioration in the electrostatic chargeability by a change in the bond state which arises at the time of dissolving the binder resin by using a solvent is averted if the coating is executed by such physical method. Since the coating resin and the binder resin are of the same kind, the adhesive strength is high and the exfoliation thereof does not arise.

Description

[Detailed Description of the Invention] [Summary] With regard to color toners used in electrophotography, the purpose of this invention is to create color toners that do not reduce the amount of charge and have excellent printing properties. A binder resin powder having a particle size smaller than that of the color toner and made of the same material is electrostatically adhered to the surface of a color toner prepared by dispersing a charge control agent and a charge control agent, and then thermally melted to form a surface coating. to compose color toner for electrophotography.

[Industrial application field]

The present invention relates to the practical use of color toners that do not have a decrease in the amount of charge and have excellent printing properties.

Electrophotographic technology is widely used in copying machines, but is also actively used in information devices such as printers and facsimile machines.

The printing process of an electrophotographic printer is to uniformly charge the surface of a photocondrum coated with a photoconductive insulator using corona discharge, and then turn it on and off in response to an electrical signal. Light is applied to the photoconductive insulator to create an electrostatic latent image, and toner is applied to the latent image to form a visible image.

In this process, the toner is a colored fine particle made by dispersing a colorant in a synthetic resin, and is supplied to a magnetic roll together with magnetic powder called a carrier, and the carrier is magnetically attracted to form a magnetic brush and rotate once. The carrier and toner rub against each other and are charged to opposite polarities, creating a magnetic developer.

Next, the ear of the magnetic brush rubs the surface of the photocondrum on which the electrostatic latent image is located, so that only the toner is separated and adhered by electric attraction, and the electrostatic latent image is developed.

The toner image created in this way is electrostatically transferred onto the recording paper by applying an electric field from the back side of the recording paper in the transfer section, and then heat and pressure are applied to the toner image in the fixing unit to transfer the toner image onto the recording paper. The record is completed by fusing it to the

Next, a magnetic developer consisting of two components, a carrier and a toner, is made of iron (Fe) with an average particle size of about 100 μm as a carrier.
powder, ferrite (γ-Fe, 0.) powder, magnetite (
Magnetic powder such as Fe+0*) powder or magnetic powder coated with resin is used.

The toner used is a non-magnetic insulating powder obtained by dispersing a colorant in a binder resin made of natural or synthetic resin and pulverizing the mixture to an average particle size of about 10 μm.

[Conventional technology]

As mentioned above, color toners have colorants dispersed in a binder resin made of natural or synthetic resin.
Binder resins include styrene-acrylic, thermoplastic polyester, and thermoplastic epoxy.

Thermoplastic resins such as acrylic resins, polyamide resins, vinyl polymers, and copolymer resins made by combining a plurality of these monomers are used.

Therefore, when used as a conventional two-component developer, color toners contain a larger amount of colorant than black toners in order to improve color development.

Therefore, when printing continuously, the colorant is likely to bleed out onto the surface of the magnetic carrier, resulting in a decrease in the amount of charge and a transfer failure.

As a method for solving this problem, a method is known in which the surface of the toner is coated with a resin different from the binder resin of the toner.

For example, a thermoplastic epoxy resin is often used as the binder resin, and a polymethyl methacrylate (abbreviated as PMMA) resin is coated thereon.

However, when the binder resin and the coating resin are different, the compatibility is poor and the coating resin is likely to peel off.

In addition, a spray drying method is used as a coating method, in which a resin solution dissolved in a solvent is sprayed, but dissolution changes the dielectric properties of the resin film, deteriorating the charging property, and it is difficult to control the film thickness. There were problems such as the resin-coated color toners tending to aggregate together during the solvent drying process.

[Problem to be solved by the invention]

As mentioned above, color toners are prone to elution of the colorant during use, so they need to be coated with a resin. The challenge is to cover it.

[Failure to solve the problem]

The above problem is solved by electrostatically attaching a binder resin powder made of the same material and having a smaller particle size than the color toner to the surface of a color toner made by dispersing a colorant and a charge control agent in a binder resin. This problem can be solved by using color toners that are heat-fused and surface-coated.

[Effect]

In the present invention, the same resin as the binder resin is physically coated on the toner.

That is, the color toner and the binder resin powder constituting it are mixed and stirred at high speed, the binder resin powder is electrostatically deposited on the color toner, and then it is collided with a plate at high speed. An impact force is applied, and the impact energy thermally melts the binder resin powder to form a resin coating.

At this time, the coating thickness can be controlled by changing the particle size and mixing ratio of the color toner and the binder resin powder.

Applying the coating using this physical method avoids deterioration in chargeability due to changes in the bond state (for example, breaking of crosslinks) that occur when the binder resin is dissolved using a solvent, and also prevents the bonding between the coating resin and the binder. Since it is the same type of resin, the adhesive strength is strong (no peeling occurs).

The toner used has an average particle size of about 10 μm, but experiments have shown that the particle size of the binder resin powder coated thereon is in the range of 0.05 to 5 μm, preferably 0.05 μm. It is preferable to use one with a diameter of 1 to 2 μm.

〔Example〕

Example 1: The method for producing a color toner was as follows: Epoxy resin (Evicron 119L Dainippon Ink Industries)...94 parts by weight Cold azo pigment (colorant, Lionol Red CP-
A + Toyo Ink) ... 5 parts by weight of quaternary ammonium salt (charge control agent, Tp-302, Odogaya Chemical Co., Ltd.) ... 1 part by weight was melted and kneaded, then pulverized and classified to produce a color toner with an average particle size of 11 μm. made.

Next, the above-mentioned epoxy resin (Epicron 1191), which is a binder resin for this color toner, was crushed and classified to produce a resin powder having an average particle size of 1 μm.

Next, 100 parts by weight of the color toner and 10 parts by weight of the resin powder were mixed and stirred using a Henschel mixer (FM-10B, manufactured by Mitsui Miike Seisakusho Engineering) to electrostatically adhere the resin powder to the surface of the color toner.

This mixture was then mixed in a centrifugal mixer (Mechanomill MM).
IO, Okada Seiko) for mixing, and the surface of the color toner and the resin powder were thermally fused and coated on the surface of the color toner.

The color toner and ferrite (γ-
A carrier (FezOi) with an average particle diameter of 100 μm
KBN-100 (Hitachi Metals) was stirred using a ball mill to prepare a magnetic developer.

Using this magnetic developer, 100,000 sheets were continuously printed, and the charge amount at the initial stage and after 10B sheets was both 10 μC/g, with no change, and good printing characteristics could be maintained.

Example 2: A color toner was prepared in exactly the same manner as in Example 1 except that polyester resin (NE2150. Kao) was used as the binder resin, and a magnetic developer was prepared by stirring and mixing with the same toner as in Example 1. .

As a result of continuous printing of 100,000 sheets using this magnetic developer, good prints with no background fog were obtained, but the amount of charge increased from the initial 10 μC/g to 15 μC/g. was.

Comparative Example 1: A color toner was prepared in the same manner as in Example 1, except that the surface of the color toner was not coated with a resin, and the toner was stirred with the same carrier as in Example 1 to prepare a magnetic developer.

When continuous printing is performed using this, the initial charge amount is 10 μC.
However, after printing about 3,000 sheets, the charge amount decreased to 2 μC/g, and fogging occurred.

Comparative Example 2 A toner was prepared in the same manner as in Example 1, except that the surface of the toner was coated with a binder resin by the varnish spray dry method, and a magnetic developer was prepared by stirring with the same carrier as in Example 1.

When continuous printing is performed using this, the initial charge amount is 10μC/
g decreased to 0 μC/g after printing about 2000 sheets, and printing became impossible.

〔Effect of the invention〕

As described above, by carrying out the present invention, it is possible to prevent the elution of the colorant during continuous printing, and there is no decrease in the amount of charge.
Color toners with excellent printing properties can be obtained.

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Claims (1)

[Claims] After electrostatically depositing a binder resin powder made of the same material and having a smaller particle size than the color toner on the surface of a color toner made by dispersing a colorant and a charge control agent in a binder resin, heat is applied. A color toner for electrophotography characterized by being melted and surface coated.