JPH0683110A - Developer for electrophotography - Google Patents

Abstract

PURPOSE:To obtain a developer of high image quality in which electrostatic chargeability is satisfied even by a small particle sized toner, a charge controlling agent does not stick to a carrier even at the time of strong stirring by a developing machine and fogging/toner splash are not generated. CONSTITUTION:In a two component developer for electrophotography composed of a mixture of the toner for electrophotography containing at least a fixing resin and the charge controlling agent and a carrier, a volumetric average particle size of the toner particles is <=8mum, an average particle size of the charge controlling agent is <=4mum and an average particle size of the carrier is 50 to 70mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a two-component developer using a powder toner used in electrostatic photography, electrostatic printing, etc.
In particular, it relates to an improvement for improving the charging property and preventing toner scattering / fog.

[0002]

2. Description of the Related Art An electrophotographic copying method is a system for obtaining a hard copy by forming an image by utilizing a photoconductive phenomenon, and the process includes charging, exposing, developing, transferring, fixing and cleaning steps. There is. Among them, in the developing process, the electrostatic latent image formed on the image support is electrostatically attracted with a toner having a polarity opposite to that of the electrostatic latent image, so that the latent image is visualized. Is. This development process is the process that most strongly affects the final copy image,
Therefore, the characteristics of the toner are one of the important factors along with the characteristics of the photoconductor that forms the electrostatic latent image.

The toner contains a fixing resin and a colorant as essential components, and various organic and inorganic materials such as a charge control agent, a conductivity control agent and a release agent are dispersed and mixed in the fixing resin as required. These are fine resin particles, and in the production, the above-mentioned toner materials are mixed, and the mixture is melt-kneaded to uniformly disperse various constituent materials, followed by cooling, crushing and classification to obtain toner particles. Since these toner particles are still insufficient in fluidity, it is widely practiced to sprinkle fine particles of silica or the like. As silica fine particles, hydrophobic silica is used to prevent deterioration of electrical characteristics due to the environment. Is commonly used.

When the above toner is used as a two-component developer, it is generally mixed with a carrier in an appropriate amount and then mixed and stirred to obtain a developer. As a carrier, iron,
Magnetic materials such as ferrite are widely used. Also,
In order to control the charging property and the like, a coated carrier having a carrier surface coated with an acrylic resin, a fluororesin or the like may be used. The role of the carrier is to impart charge to the toner, convey the toner to the developing region, counter electrode effect at the time of development, and the like, and are important factors greatly involved in image formation.

By the way, recently, along with the improvement of image quality, the particle size of toner has been reduced. For the resolution of images and the reproducibility of fine lines, it is not necessary to say that the toner has a small particle size. However, when the toner has a small particle size, a new problem occurs with it. That is, when the toner has a small particle size, the specific surface area increases, so that the ratio of the specific surface area of the toner and the carrier changes, and charging failure occurs.

[0006]

Conventionally, in order to solve this problem, the carrier has been made smaller in particle size. For example, in JP-A-1-223471, JP-A-2-207275, and JP-A-2-281280, small particle size carriers are used to improve image uniformity and gradation. This is because in the case of a toner having a small particle diameter, the specific surface area is larger than that of the conventional toner, and therefore, the carrier is made smaller in particle diameter to increase the carrier specific surface area, so that sufficient charge can be obtained.

However, a developer using a carrier having a small particle size has poor fluidity and causes a problem that an uneven product is generated in the developing device and a sufficient amount of the developer cannot be supplied to the sleeve, or the stirring is not sufficiently performed. However, problems such as poor charging occur. Therefore, in order to improve the fluidity deterioration of the developer using a small particle size carrier, JP-A-58-140753 is used.
In this method, the small particle size carrier and the large particle size carrier are mixed, but even if the fluidity is improved by this method, the large particle size carrier increases the scattering of toner to the non-image area, decreases the resolution, and further increases the carrier particle size. Since the distribution is wide, problems such as non-uniform charging of toner occur.

On the other hand, as a systematic solution, there is a method of increasing the stirring force of the developing device. However, since the toner and the carrier are in strong contact with each other, the charge control agent exposed on the surface of the toner is selectively carried by the carrier. The toner is likely to adhere to the surface of the toner, and the reversely charged toner is likely to be generated, resulting in problems such as fog / toner scattering. The present invention has been made in view of the above circumstances. Even with a toner having a small particle size, the chargeability is satisfied, and the charge control agent does not adhere to the carrier even when the developer is strongly stirred, and the fog is caused. / An object of the present invention is to provide a high-quality developer in which toner scattering does not occur.

[0009]

According to the present invention, in a two-component developer obtained by mixing an electrophotographic toner containing at least a fixing resin and a charge control agent with a carrier, the volume of toner particles is increased. Provided is an electrophotographic developer characterized in that the average particle size is 8 μm or less, the charge control agent has an average particle size of 4 μm or less, and the carrier has an average particle size of 50 to 70 μm.

[0010]

The electrophotographic toner of the present invention has a volume average particle size of 8
The toner particles having a particle size of μm or less are characterized in that the average particle size of the charge control agent is 4 μm or less, which is smaller than the charge control agent generally used. Also, the average particle size of the carrier is 50
.About.70 .mu.m is another salient feature of the present invention.

When the average particle size of the charge control agent is larger than 4 μm, the charge control agent adheres to the carrier remarkably. This is because when the particle size of the charge control agent is large, the contact interface portion between the charge control agent and the binder resin is structurally weak when the toner compounding agent is melt-kneaded and pulverized in the manufacturing stage, and therefore the selective portion is selected from that portion. The charge control agent is easily exposed on the toner surface, and as a result, the charge control agent is easily attached to the carrier surface by stirring in the developing device. It is considered that this causes fog / toner scattering.

In the present invention, the average particle size of the carrier is 5
If it is less than 0 μm, the fluidity of the developer is significantly reduced. Further, when the developer is made to have a large stirring force (torque) to improve the fluidity, the toner is crushed in a carrier having a particle size of 50 μm or less. As a result, the toner fine powder becomes excessive in the developer, and the charging property is significantly reduced,
It becomes difficult to use as a developer for electrophotography. Further, if the average particle size of the carrier is larger than 70 μm, the surface area of the carrier becomes smaller than the surface area of the toner, so that the probability of contact between the toner and the carrier is reduced, resulting in poor charging.

As the charge control agent, any charge control agent known per se and having an average particle diameter of 4 μm or less, for example, Bontron S-44 (manufactured by Orient Chemical Co., Ltd.), nigrosine base (CI 50415), oil black ( CI
26150), oil-soluble dyes such as spirone black, metal-containing azo dyes, metal salts of naphthenic acid, metal salts of alkylsalicylic acid, fatty acids, soaps, resin acid soaps and the like.

As the carrier of the present invention, glass beads, oxidized or unoxidized iron powder, uncoated carrier such as ferrite, or magnetic material such as iron, nickel, cobalt, and ferrite is used as an acrylic polymer or a fluorine-based carrier. A coated carrier coated with a polymer such as a polymer, polyester or modified silicone resin is used. The toner particles according to the present invention are manufactured by blending a binder resin with additives such as a colorant, a charge control agent and a release agent, and granulating the particles to a particle size of 8 μm or less.

A styrene resin, an acrylic resin, a styrene-acrylic resin, a polyester resin, a polyurethane resin, a silicone resin, a polyamide, a modified rosin or the like is used as the binder resin as the toner component. As the colorant, a conventionally known colorant can be used. For example, Mitsubishi Kasei carbon black # 25
Particles having an average primary particle diameter of 40 to 60 nm, such as (registered trademark), are suitable. Other colorants listed below can be preferably used.

Black carbon black such as furnace black, channel black, gas black, oil black, and acetylene black, lamp black, aniline black, white zinc white, titanium oxide, antimony white, zinc sulfide red red iron oxide, cadmium red, lead tin. , Mercury sulfide, cadmium, permanent red 4R, resole red,
Pyrazolone red, watching red calcium salt,
Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B Orange Red Lead Yellow, Molybdenum Orange, Permanent Orange GTR, Pyrazolone Orange, Vulcan Orange, Indanthrene Brilliant Orange RK, Benzidine Orange G, Indanthrene Brilliant Orange GK Yellow Yellow Lead, Zinc Flower, Cadmium Yellow, Yellow Iron Oxide, Mineral Fast Yellow, Nickel Titanium Yellow, Navels Yellow, Naphthol Yellow S, Hansar Yellow G, Hansar Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake Green Chromium Green, Chromium Oxide, Pigme Togulin B, Malachite Green Lake, Final Yellow Green Blue Navy Blue, Cobalt Blue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue Partial Chloride, Farnest Sky Blue, Indanthrene Blue BC, Metal-free Phthalocyanine Blue Purple Manganese Purple, Fast Violet B, methyl violet lake extender pigments include, for example, perlite powder, barium carbonate,
Examples include clay, silica, white carbon, talc, and alumina white.

Examples of the conductive pigment include conductive carbon black and various metal powders such as aluminum powder. Examples of magnetic pigments include iron trioxide (magnetite iron black), iron sesquioxide (γ-Fe2O3), zinc iron oxide (ZnFe2O4), and yttrium iron oxide (Y3Fe5O1).
2), iron cadmium oxide (CdFe2O4), iron oxide gatorium (Gd3Fe5O4), iron oxide copper (CuFe2O)
4), iron oxide lead (PbFe12O19), iron oxide nickel (NiFe2O4), iron oxide neodymium (NdFeO3),
Iron oxide barium (BaFe12O19), iron oxide magnesium (MgFe2O4), iron manganese oxide (MnFe2O)
4), various ferrites such as lanthanum iron oxide (LaFeO3); iron powder, cobalt powder, nickel powder and the like.

Examples of the photoconductive pigment include zinc oxide,
Examples thereof include selenium, cadmium sulfide, selenium, cadmium sulfide, and cadmium selenide. Manufacture of Toner A binder resin, a colorant, a charge control agent, a release agent and the like are mixed and stirred. The mixing and stirring should be carried out under the condition that a low load and a low shearing force act, and generally, it can be carried out by various mixing and stirring devices such as a conical blender, a ribbon blender, a V-type blender, a Nauta mixer, a Henschel mixer, and a ball mill. The mixing and stirring temperature is preferably lower than the glass transition point (Tg) of the binder resin. The required mixing / stirring time varies depending on the type of equipment and the input amount, but is generally in the range of 10 to 300 minutes.

The pre-mixture thus obtained is melt-kneaded by a conventional method, and the kneaded product is pulverized and classified to obtain toner particles. To the toner particles obtained by the above-mentioned production method, for the purpose of improving fluidity and chargeability, a suitable weight part of hydrophobic silica is mixed and dispersed to obtain a powder toner having an average particle diameter of 8 μm or less. As the hydrophobic silica, an alkyl group, an alkylsilyl group, a hydrophobic silica treated with an alkylsilane,
For example, the product name R974 manufactured by Nippon Aerosil Co., Ltd. may be mentioned.

Examples of the fluidity improver used in combination with the above-mentioned hydrophobized silica, or as a single substance or in a combination other than the hydrophobized silica include inorganic fluidity improvers and organic polymer fluidity improvers. To be As inorganic ones, usual vapor phase silica, vapor phase alumina,
Examples include vapor phase titania and alumina-modified vapor phase silica. As the organic polymer fluidity improver, fine particles of an acrylic resin, a styrene resin, or the like produced by an emulsion-free polymerization method or an emulsion polymerization method are used.

The toner thus obtained is mixed with the above carrier to form a developer, and the toner concentration is preferably 1 to 15%.

[0022]

EXAMPLES Hereinafter, the electrophotographic toner of the present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 (Component) Styrene-acrylic polymer 100 parts by weight carbon black 8.5 parts by weight Chromium complex salt dye (charge control agent) 1.5 parts by weight (Orient Chemical's Bontron S-44 4 μm) Low molecular weight polypropylene (released) Molding agent) 2.0 parts by weight The above components are melt-kneaded by a twin-screw extruder, pulverized by a jet mill, and air-classified by a classifier to obtain toner particles having an average particle size of 8 μm, to which hydrophobic silica fine particles are added. A final electrophotographic toner was obtained by mixing and dispersing it in a proportion of 0.3% by weight based on the total amount of the toner.

Then, this toner and a carrier having an average particle size of 50 μm were mixed and stirred to obtain a developer having a toner concentration of 3.5%. Example 2 The same as Example 1 except that the average particle size of the carrier was changed to 70 μm. Comparative Example 1 The same procedure was performed as in Example 1 except that the charge control agent had an average particle size of 6 μm and the carrier had an average particle size of 60 μm. Comparative Example 2 The procedure of Example 1 was repeated, except that the average particle size of the carrier was changed to 40 μm. Comparative Example 3
The same procedure as in Example 1 was carried out except that the average particle size of the carrier was changed to 80 μm. <Evaluation Test> The toner and the developer obtained in each of the examples and the comparative examples were subjected to a copy test on 20,000 sheets using a product manufactured by Mita Kogyo Co., Ltd. (trade name "DC-1670M modified machine"). However,
The original used for the copy test had an area ratio of 15% of black portions including characters and black solid portions. Evaluation was performed according to the following test methods. Each test method is as follows. (1) Measurement of Image Density (ID) Using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.), the densities of the black solid portions of the copied images at the initial stage and after copying 20,000 sheets were measured. Moreover, the following criteria evaluated.

○: 1.35 or more △: 1.3 or more and less than 1.35 ×: less than 1.3 (2) Measurement of fog density (FD) Initial and 20,000 copies using the reflection densitometer The density of the subsequent white part was measured and defined as the fog density. Moreover, the following criteria evaluated.

○: 0.005 or less △: 0.006, 0.007 ×: 0.008 or more (3) Toner scattering 20,000 sheets of toner at the end of copying are visually judged and evaluated according to the following criteria. did.

◯: No toner scattering Δ: Slight toner scattering X: Toner scattering (4) Charge amount The charge amount at the initial stage and after copying 20,000 sheets was measured with a blow-off charge amount measuring device manufactured by Toshiba Chemical Corporation. . (5) Measurement of Adhesion Amount of Charge Control Agent Adhering to Carrier The toner was removed from the developer after copying 20,000 sheets, and the adhesion amount of the charge control agent in the remaining 5 g of the carrier was measured. From the results of Table 1, in Examples 1 and 2, there was no problem in the fluidity of the developer in the developing device and there was no adhesion of the charge control agent to the carrier, so that the chargeability was stable, resulting in fog / It was found that the toner can be prevented from scattering and a high-quality and good image can be obtained even after copying 20,000 sheets, and the developer has a long life.

On the other hand, as in Comparative Example 1.2.3, even if any one of the average particle size of the charge control agent and the average particle size of the carrier is missing, fog, toner scattering, poor charging,
The fluidity of the developer was lowered.

[0028]

[Table 1]

[0029]

According to the present invention, even in a toner having a small particle size of 8 μm or less, the average particle size of the charge control agent is 4 μm or less and the average particle size of the carrier is 50 to 70 μm. There is an advantage that the fluidity and chargeability can be improved and stabilized, and a developer with high image quality and long life can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Yamamura 1-228 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd. (72) Yoshitake Shimizu 1-228 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Co., Ltd. (72) Inventor Takeshi Higuchi 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Co., Ltd. (72) Inventor Katsumi Okamoto 1-228 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Business

Claims (1)

[Claims] 1. A two-component developer comprising a mixture of an electrophotographic toner containing at least a fixing resin and a charge control agent and a carrier, wherein the toner particles have a volume average particle size of 8 μm or less. An electrophotographic developer having an average particle diameter of 4 μm or less and a carrier having an average particle diameter of 50 to 70 μm.