JPH08171228A - Toner for developing electrostatic charge image - Google Patents

Abstract

PURPOSE: To keep the surface of an electrifying member in an always clean state and to obtain a toner stably ensuring the desired quantity of electric charges by frictional contact with the electrifying member. CONSTITUTION: A powdery mixture of fine powder subjected to negative triboelectric charge to iron oxide with fine powder subjected to positive triboelectric charge to iron oxide is stuck as a fluidizing agent to the surfaces of base toner particles consisting essentially of a resin binder and a colorant to uniformly coat the toner particles. Fine silica powder obtd. by bonding silane having an electron withdrawing group to silanol groups on the surface of silica may be used as the fine powder subjected to negative triboelectric charge and fine silica powder obtd. by bonding a silane coupling agent having an electron donating group to the surface of silica may be used as the fine powder subjected to positive triboelectric charge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to electrophotography, electrostatic recording,
The present invention relates to an electrostatic charge image developing toner used for developing an electrostatic latent image in electrostatic printing or the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic apparatus, an electrostatic recording apparatus, etc., an electrostatic charge image (latent image) is formed on a photosensitive member using a photoconductive substance by various means, and then this latent image is formed. Is developed using toner, and after the toner image is transferred to a transfer material such as paper, if necessary, it is fixed by heat, pressure, solvent vapor or the like.

The toner used in such an electrophotographic method is colored particles having a particle size of several μm to several tens of μm, and a thermoplastic resin as a binder resin and a colorant such as a pigment or a dye are melt-mixed. It is obtained by pulverizing and classifying the solidified product after uniform dispersion. And in electrophotography,
By mixing this toner with a relatively coarse carrier powder called a carrier, a desired charge is obtained by friction, and by bringing the mixture of the toner and the carrier into contact with the electrostatic image, only the toner particles are electrostatically charged. The latent image is made visible (developed) by being attached to the image (two-component developing method).

Recently, a one-component developing method has been carried out as a method for charging and developing toner without using the above-mentioned carrier. This method forms a thin layer of toner on the surface of the developing roll using a charging blade,
The toner charged by the friction between the roll surface and the charging blade is brought into contact with the electrostatic charge image for development.

By the way, in any of the above-mentioned developing methods, the toner is a partner member such as a carrier, a developing roll or a charging blade (hereinafter referred to as a charging member).
Since they are charged by being brought into contact with the surfaces of the toners, there is a possibility that those surfaces are stained with the toner. When the surface of the charging member is soiled due to the adhesion of toner, the amount of toner charge is drastically reduced as compared with a clean state, and it becomes impossible to obtain a clear developed image.

Therefore, conventionally, as one of the methods for preventing the charging member such as a carrier from being contaminated by the toner, a fine particle substance (for example, colloidal silica) having a particle size of 10 nm to 1 μm called a fluidizing agent is mixed with the toner. And is using it. Incidentally, since the fluidizing agent exists in a state of being attached to the surface of the toner particles, the toner and the charging member are always in contact with each other via the fluidizing agent. Therefore, the contamination of the surface of the charging member with the toner is greatly reduced.

[0007]

However, the addition of such a fluidizing agent has a problem that the charge amount due to friction of the toner is significantly changed. In particular, when the charge polarity of the toner is different from that of the fluidizing agent, the effect of addition is greatest, and the charge polarity of the toner may be reversed. When the toner and the fluidizing agent have the same charge polarity, the fluidizing agent particles that have once adhered to the toner are often desorbed because the adhesion strength of the fluidizing agent particles to the surface of the toner particles is weak. The amount of charge on the toner changed significantly.

Further, since the fluidizing agent has a very small particle size as compared with the toner and has a large adhesion strength to the surface of the charging member, the fluidizing agent particles are likely to cover the surface of the charging member. Further, such a coating phenomenon on the surface of the charging member may have a great influence on the charging property of the toner.

The present invention has been made in order to solve the above-mentioned various problems in addition of a fluidizing agent. The surface of the charging member is always kept clean, and the desired charging is achieved by frictional contact with the charging member. An object of the present invention is to provide a toner for developing an electrostatic charge image, the amount of which can be stably obtained.

[0010]

That is, the electrostatic image developing toner of the present invention is an electrostatic image developing toner comprising powder particles containing at least a binder resin and a colorant,
It is characterized in that fine powder negatively triboelectrically charged with iron oxide and fine powder positively triboelectrically charged with iron oxide are mixed and adhered to the surface.

In the present invention, as the binder resin, a polymer of styrene or a substitution product thereof, which is a thermoplastic resin conventionally used as a binder resin for toner, or an acrylic resin can be used. . Further, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, phenol resin and the like can be used alone or in combination.

As the colorant, fine particles of carbon black are used for black-and-white copying. In the case of color toner, azo pigment, phthalocyanine pigment, anthraquinone,
Known pigments and dyes such as perylene, thioindigo, and dioxazine can be used.

In the present invention, in order to obtain a base toner containing such a binder resin and a coloring agent, a ball mill, a V-type mixer, etc., a charge control agent for controlling these components and a charge are used. After being mixed and dispersed by using, the mixture is heated and melted using a pressure kneader, a roll, etc., and then pulverized and classified. Here, as the means for coarsely pulverizing, for example, a hammer mill, a cutter mill, a jet mill, a roller mill, a ball mill or the like can be used, and as means for further finely pulverizing the coarsely pulverized material, a jet mill, a high-speed rotary pulverizer, etc. Can be used. Further, as a means for classifying the finely pulverized product, an airflow classifier or the like can be used.

In the present invention, as the fluidizing agent to be attached to the surface of the base toner composed of such a binder resin and a colorant, magnesium oxide, zinc oxide, barium oxide, alumina, titanium oxide, silica, oxidation is used. Inorganic compound powder such as zirconium, or powder of organic polymer such as polymethacrylic acid ester, polystyrene, polyvinyl chloride, nylon (polyamide), polytetrafluoroethylene, vinylidene fluoride, etc. as a base material, particle size of 10 nm ~ Use 1 μm.

The fine powders of these inorganic compounds or organic polymers themselves are triboelectrically charged positively or negatively with respect to iron oxide, but nitro groups, halogen groups, sulfone groups, phosphonium groups, Particles having an electron-accepting or withdrawing (acidic) functional group such as a carboxyl group, a cyano group, a silanol group, an alkylsilyl group, or a perfluoroalkyl group-containing alkylsilyl group are particularly strongly negatively charged. And is most suitable as a fine powder that is negatively triboelectrically charged with respect to the iron oxide of the present invention. Such fine powder can be obtained by binding, adsorbing or adhering the above-mentioned organic compound or polymer having an electron-withdrawing group to the surface of the above-mentioned inorganic fine powder or organic polymer fine powder.

The fine powder that is positively triboelectrically charged with iron oxide used in the present invention includes amino groups, alkylamino groups, and
Those having an electron-donating (alkaline) functional group such as a basic ammonium group, an alkylammonium group, an amino group-containing alkylsilyl group, an alkylamino group-containing alkylsilyl group, and an alkylammonium group-containing alkylsilyl group Most suitable. Such fine powder can be obtained by binding, adsorbing or adhering the above-mentioned organic compound or polymer having an electron-donating group to the surface of the inorganic or organic polymer fine powder. The reason for setting the reference contact partner with the fine powder used as the fluidizing agent to iron oxide and setting it as the charging polarity that develops when it makes frictional contact with iron oxide is as follows. That is, since iron oxide is located exactly in the middle on the scale of acidity and basicity viewed from its isoelectric point and exists almost in the middle of the charging train due to frictional contact, it is the most suitable reference contact partner for setting the charging polarity. This is because it is considered desirable.

In the present invention, by changing the mixing fraction of such negatively charged fine powder and positively charged fine powder,
A mixed powder (fluidizing agent) having an arbitrary charge amount can be obtained, and by adhering it to the surface of the base toner to uniformly coat the toner particles, the change in the charge amount of the toner can be suppressed. Here, in order to attach the fluidizing agent to the surface of the base toner, positively and negatively charged fine powder mixed in a desired mixing fraction determined from the charge amount is used together with the base toner in a Henschel mixer having a high-speed propeller or an impact. A method of stirring and mixing with a mixer having a large shearing force such as a mold crusher is adopted.

Further, in the toner of the present invention whose surface is coated with the fluidizing agent composed of positively and negatively charged fine powder, the fine powder particles are exposed on the surface of the toner particles with a probability corresponding to the mixing fraction. Therefore, the electrostatic attractive force acts not only between the charged fine particles and the base toner but also between the charged fine particles whose polarities are positive and negative. Thus, the fluidizing agent used in the present invention contributes to the control of the charge amount of the toner, and even if the positive and negative polar particles move to the charging member side such as the carrier, Since the other polar fine particles remaining on the toner surface are electrostatically attracted, they serve to clean the surface of the charging member.

[0019]

In the toner for developing an electrostatic image according to the present invention, the fine powder that is negatively charged and the fine powder that is positively charged are mixed with the iron oxide that is positioned approximately in the middle of the charging train due to friction. Since they are attached to the surface of the base toner, the electrical effects on the toner of the fine powders having the opposite polarities are canceled out. Therefore, by adding such a fluidizing agent, the charge amount of the toner is hardly changed, the surface of the charging member such as the carrier is kept clean, and the clear image quality is maintained for a long period of time. To be done.

[0020]

Embodiments of the present invention will be described below.

Example 1 Styrene / butyl acrylate copolymer resin (melting point 130
℃) 100 parts by weight, phthalocyanine blue 4 parts by weight, No. 4
After mixing 2 parts by weight of ammonium salt type charge control agent,
Kneading, crushing and classification are carried out by the usual method, and the average particle size is 8 μm.
To obtain a blue base toner of. Further, silica powder (average particle size 10 nm) was treated with a silane coupling agent having an alkyl group containing an amino group (alkylamino group) to obtain a fine powder that was positively charged with respect to iron oxide. Further, the same silica powder (average particle size 10 nm) was treated with chlorotrimethylsilane to obtain fine powder negatively charged with iron oxide.

Next, 100 parts by weight of the base toner was mixed with 1.0 part by weight of the positively charged silica powder and 0.5 part by weight of the negatively charged silica powder, and the mixture was further stirred for 5 minutes with a Henschel mixer to obtain the surface of the base toner. Silica powder was uniformly adhered to the.

After mixing 4 parts by weight of the toner thus obtained with 100 parts by weight of a spherical ferrite powder carrier, a negatively charged electrostatic charge image (latent image) formed on a known organic photoreceptor is developed and transferred. As a result, a clear image was obtained.
Also, the image obtained after repeating this process 50,000 times was a clear image with no deterioration equivalent to the initial image.

Comparative Example 1 A toner was prepared in the same manner as in Example 1 except that the positively charged silica powder was not added and only 1.5 parts by weight of the negatively charged silica powder was added to 100 parts by weight of the base toner. Then, the toner thus obtained was developed in the same manner as in Example 1. As a result, an image with larger fog was obtained as compared with Example 1. Further, the fog increased as the image forming process was repeated, and the image density decreased remarkably after 10,000 times.

[0025]

As described above, in the toner for developing an electrostatic charge image of the present invention, a mixed powder of fine powder positively charged and negatively charged fine powder with respect to iron oxide is used as a fluidizing agent. Since this is adhered to and uniformly coated on the surface of the particles of the base toner, the surface of the charging member such as the carrier can be kept clean, and the toner can have a stable and desired charge amount. Therefore, it is possible to maintain clear image quality for a long period of time without causing deterioration of image quality such as fogging even after continuous copying of tens of thousands of sheets.

[0026]

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Claims (3)

[Claims] 1. A toner for developing an electrostatic charge image comprising powder particles containing at least a binder resin and a colorant, wherein a fine powder negatively triboelectrically charged with iron oxide and a positive triboelectrically charged with iron oxide. A toner for developing an electrostatic charge image, characterized in that the toner is mixed with fine powder to be adhered to the surface. 2. The electrostatic charge image according to claim 1, wherein the fine powder that is triboelectrically charged negatively with respect to iron oxide is a silane having an electron-withdrawing group bonded to a silanol group on the surface of silica. Toner for development. 3. The fine powder, which is positively triboelectrically charged with respect to the iron oxide, has a silica surface bound with a silane coupling agent having an electron-donating group.
The toner for developing an electrostatic image as described above.