JP2837671B2 - Developer for electrostatic latent image - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dry developer for developing an electrostatic image, and more particularly, to a developer for an electrostatic latent image composed of a mixture of two kinds of magnetic toners having different average particle diameters. About.

(Prior art)

Many methods for developing (developing) an electrostatic latent image are known, and one of them is a one-component magnetic toner developing method including only a magnetic toner. In this method, the magnetic toner is held on a magnet provided in a conductive and non-magnetic carrier sleeve, and the magnetic toner is carried on an electrostatic latent image by a relative movement between the sleeve and the magnet. In this method, a conductive path is formed between the conductive backing member of the image carrier, the sleeve, and the magnetic toner, and a charge having a polarity opposite to that of the latent image is induced in the magnetic toner for development.

The conductive magnetic toner used in this developing method is one in which the surface of toner particles is made more electrically conductive than a core portion thereof as proposed in, for example, US Pat. No. 3,639,245.

According to such a developing method, there is an advantage that a uniform image can be obtained because the toner density is constant regardless of how much copying is performed. However, on the other hand, there is a disadvantage that it is difficult to electrostatically transfer a toner image developed using such a conductive magnetic toner onto another recording medium (such as paper).

It has also been proposed to increase the electric resistance of the magnetic toner in order to eliminate this drawback, but in this case, on the contrary, the developability is impaired, and a developer satisfying both the developability and the transferability characteristics is not suitable. Not yet developed.

Therefore, the present inventors have previously developed high electric resistance magnetic toner particles containing magnetic fine powder dispersed therein as a developer having excellent developability and transferability, and a volume average particle size smaller than the volume average particle size of the toner particles. A developer for electrostatic latent images comprising a mixture with conductive magnetic particles having the following formula (JP-A-56-142540).

The case of developing using the proposed developer will now be described with reference to the drawings. FIG. 1 schematically shows the development principle.

FIG. 1A is a schematic cross-sectional view at the time of development, and shows a case where an electrostatic latent image 3 formed on a photoconductive layer having a conductive backing 1 or a dielectric layer 2 is developed. High electric resistance magnetic toner particles 5a are placed on the conductive non-magnetic sleeve 4.
And a conductive magnetic particle 5b. The developer 5 is carried to a latent image developing position by the relative movement of the sleeve 4 and the magnet 6. In this state,
Electric charges of the opposite polarity to the latent image charges are guided from the sleeve 4 to the conductive magnetic particles 5b and are partially accumulated in the high electric resistance magnetic toner particles 5a close to the latent image, whereby the electrostatic latent image is transferred to the magnetic toner particles 5a. And the conductive magnetic particles 5b are sucked and developed.

FIG. 1 (B) is a schematic view of a developed state. The developed image is composed of both the magnetic toner particles 5a and the conductive magnetic particles 5b. However, since the conductive magnetic particles 5b have a larger attractive force to the magnet 6 per unit weight, the developed image Is preferentially attached to the latent image. Further, the developed image of FIG. 1B is carried to a transfer step, and a transfer recording medium such as plain paper is superimposed on the developed image and transferred by electrostatic means such as corona discharge. In this step, the high-resistance magnetic toner particles 5a are preferentially transferred, but a part of the conductive magnetic particles 5b is transferred to the magnetic toner particles 5a by a weak adsorption force with the magnetic toner particles 5a. Is done.

Since such a developer proposed by the present inventors does not need to charge toner particles by friction with a magnetic carrier as in a conventional two-component magnetic brush developing method,
This has the advantage that the developing device can be miniaturized and has stability against temperature changes during development. However, this developer has a disadvantage that the mixed components are unevenly distributed with running and an abnormal image (white spot, white band, etc.) is generated.

Further, there is also known a developer in which fine powder having the same polarity as the latent image charge polarity is mixed with the developer in relation to the developing sleeve on the triboelectric series (JP-A-56-161552).
No.). However, such a developer also agglomerates and becomes unevenly distributed as the magnetic particles in the developer continue running, causing white spots,
There is a disadvantage that an abnormal image such as a white band is easily generated. In addition, there is a disadvantage that the developing ability is reduced by running, and an abnormal image such as a solid white trailing edge is easily generated.

〔Purpose〕

The present invention provides a developer for an electrostatic latent image which does not show an abnormal image (white spots, white bands, solid white trailing edge, etc.).

〔Constitution〕

The present invention relates to a high electric resistance magnetic toner particle containing a magnetic fine powder (hereinafter also referred to as "magnetic toner particle 5a" for convenience).
And a conductive magnetic particle having a volume average particle diameter smaller than the volume average particle diameter of the magnetic toner particles 5a (hereinafter also referred to as “conductive magnetic particles 5b” for convenience). Further, the conductive magnetic particles 5b are characterized by comprising a magnetic core material and a conductive coating layer.

By the way, the present inventors have confirmed that the above object can be achieved by modifying the conductive magnetic particles in the developer proposed in JP-A-56-142540. The present invention has been made based on this.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The first important point in the developer of the present invention is to make the average particle size of the conductive magnetic particles 5b smaller than that of the magnetic toner particles 5a. If the conductive magnetic particles are larger than the magnetic toner particles, the smaller magnetic toner particles will cover the periphery of the conductive magnetic particles, and if the conductive magnetic particles become larger, the magnetic attraction force to the magnet 6 will decrease. Since the conductive magnetic particles become stronger, the conductive magnetic particles are just removed from the electrostatic latent image, and white spots called image color omissions are observed. This development is also a development that occurs in the transfer step because the conductive magnetic particles are not easily transferred electrostatically.

On the other hand, it is not preferable that the conductive magnetic particles 5b are too small. That is, if the particle diameter is too small, the fine conductive magnetic particles are strongly adsorbed around the magnetic toner particles 5a by Van der Waals force, and the conventional conductive magnetic toner particles having the magnetic toner particles 5a conductive around the magnetic toner particles 5a. And the electrostatic transferability is deteriorated.

For this reason, the volume average particle diameter of the conductive magnetic particles 5b is preferably about 1/5 to 4/5 of that of the magnetic toner particles 5a, and more preferably about 3/10 to 2/3. That is. The volume average particle size is a value measured by a coulter counter.

The conductivity of the conductive magnetic particles 5b in the present invention is defined as having a volume electric resistance of 10 ⁹ Ωcm or less, and the high electric resistance of the magnetic toner particles 5a is defined as having a volume electric resistance of 10 ¹² Ωcm or more.

When running for a long time using conventional conductive magnetic particles, when the electric resistance is 10 ⁵ to 10 ⁹ Ωcm, the phenomenon of trailing white spot appears, and when the electric resistance is 10 ³ Ωcm or less, the conductive magnetic particles Cohesion occurs and an abnormal image such as a white stripe is generated. Similarly, the electric resistance is larger than 10 ³ Ωcm and 10 ⁵
When it is smaller than Ωcm, both the trailing white spots and white stripes are generated, and a region satisfying both is not obtained.

The developer of the present invention aims to solve such inconveniences,
As the conductive magnetic particles 5b, those obtained by forming a conductive coating layer on the surface of a core material are employed. The electrical resistance of the core material here is 10 ⁵
To 10 ⁹ Ωcm, and the conductive coating layer is preferably 10 ⁵ Ωcm or less.

The material of the core material of the conductive magnetic particles 5b is selected from magnetizable materials, for example, metals such as Fe, Ni, Co, and Mn, alloys or oxides of these metals, and particularly magnetite (Fe ₃ O ₄ ), Γ-hematite (γ-Fe ₂ O ₃ ), ferrite (Zn ferrite, Mn ferrite, etc.) and the like are desirable.

In addition, as a coating material (conductive coating layer material) of the conductive magnetic particles 5b, any substance having a resistance of 10 ⁵ Ωcm or less can be selected from magnetic and non-magnetic. Specifically, carbon black, conductive polymer, Examples include tin oxide, antimony oxide, conductive titanium oxide, gold, silver, copper, nickel, and Fe ₂ O ₅ .

Although it is not yet clear why good results are obtained when such conductive magnetic particles 5b are used in combination with the magnetic toner particles 5a, it is considered as follows. That is, when a developing electric field is generated between the developer 5 on the sleeve 4 and the photoconductive layer or the dielectric layer 2, the developer 5
Is charged and then developed, which causes a time delay before actual development occurs. At this time, the lower the resistance of the developer, the quicker the developer is charged, and as a result,
Prevents trailing white spots. In addition, since the resistance of the core material is relatively high, charges accumulated in the conductive magnetic particles 5b remain, and aggregation of the conductive magnetic particles 5b hardly occurs, and it is considered that white stripes, white spots, and the like do not occur.

Therefore, the volume electric resistance of the conductive magnetic particles 5b of the present invention is desirably 10 ⁴ Ωcm or more. Therefore, it is advantageous to use the conductive magnetic particles 5b having a volume electric resistance of 10 ⁴ to 10 ⁹ Ωcm.

The measurement of volume electric resistance is performed by placing 1 ml of magnetic toner particles 5a or conductive magnetic particles 5b in a cylindrical container whose surface is made of an electrode having an inner diameter of 20 mm and whose side wall is made of an insulating material. It can be calculated by placing an electrode plate weighing less than 20 m and weighing 100 g, allowing it to stand for 1 hour, applying a DC voltage of 100 V between the electrodes, and measuring the current value one minute after the application.

Furthermore, in the developer of the present invention, the conductive magnetic particles 5b have a saturation magnetic moment in the range of 25 to 75 emu / g,
In addition, it is advantageous to use the magnetic toner particles 5a having a magnetic moment larger than the saturation magnetic moment.

The saturation magnetic moment of the conductive magnetic particles 5b is 75 emu /
If it is larger than g, the conductive magnetic particles tend to magnetically aggregate, and agglomerates of the conductive magnetic particles tend to be generated. Similar to the case where the conductive magnetic particles become large, the aggregated conductive magnetic particles have a large magnetic attraction to the magnet 6 as the aggregates become large and are removed from the electrostatic latent image, thereby causing white spots (white spots). ) Occurs. Further, if the mass becomes larger and becomes larger than the doctor gap 7a, the magnetic cohesive force is so strong that it is difficult to pass through the doctor gap 7a, and finally the doctor gap is closed, and the developer cannot be supplied to the developing sleeve. Generate a band. Conversely, if the saturation magnetic moment is less than 25 emu / g, the conductive magnetic particles tend to separate from the sleeve due to the centrifugal force, which causes problems such as contamination inside the machine.

On the other hand, if the saturation magnetic moment of the conductive magnetic particles 5b becomes smaller than the saturation magnetic moment of the magnetic toner particles 5a, the conductive magnetic particles will preferentially adhere to the latent image, but the conductive magnetic particles Therefore, it is difficult to perform electrostatic transfer, and the image density after transfer is reduced.

The saturation magnetic moment referred to here is the applied magnetic field 5KOe measured by a vibrating sample magnetometer (VSM-P7 type) manufactured by Toei Industry Co., Ltd.
It is the value in.

The high electric resistance magnetic toner particles 5a used in the present invention may be conventionally known ones, and are essentially composed of a polymer substance and a magnetic fine powder, and if necessary, a coloring agent, a flow modifier and the like are added. You. Examples of the high-molecular substance include a styrene resin, an acrylic resin, a vinyl resin, an epoxy resin, a polyester resin, a phenol resin, a polyurethane resin,
There are natural resins, celluloses, etc.
A powder having a particle diameter of 1 μm or less of a metal such as Fe, Ni, Co, or Mn or an oxidizable material of an oxide or an alloy of these metals is used. Examples of the colorant include dyes and pigments such as carbon black, aniline black, crystal violet, rhodamine B, malachite green, nigrosine, copper phthalone anine, and azo dye. Other wax,
Fatty acids or fatty acid metal salts, silica powder, zinc oxide powder and the like can be added.

Further, in the developer of the present invention, it has been confirmed that the magnetic toner particles 5a tend to be triboelectrically charged to a polarity opposite to the polarity applied to the transfer recording paper in the electrostatic transfer process, the transfer efficiency is better, Therefore, nigrosine, monoazo dyes, zinc hexadecyl succinate, alkyl esters or alkylamides of naphthoic acid, nitrohumic acid, N, N'-tetramethyldiaminebenzophenone, N, N'-tetramethylbenzidine, triazine, metal complexes of salicylic acid, etc. It is preferable to add a highly polar substance called a charge control agent in this field.

In the developer of the present invention, in relation to the material of the developing sleeve, the development start voltage can be increased by adding fine powder having the same polarity as the electrostatic dyeing image on the triboelectric series to the developer. Can increase the degree of margin against background contamination.

 Next, examples will be described. All parts are parts by weight.

Example 1 (Preparation of magnetic toner particles 5a) Styrene-nBMA copolymer 100 parts Carbon black 2 parts Orient Spirit Black AB (manufactured by Orient Chemical Co.) 2 parts Magnetite (particle size: about 0.2 μm) A mixture consisting of 50 parts Is heated and kneaded by a hot roll, cooled and then crushed and classified to have a volume average particle size of about 20 μm and an electric resistance of 5 × 10 ¹⁴
Ωcm, magnetic toner particles 5a with a saturation magnetic moment of 29 emu / g
Was made.

(Preparation of Conductive Magnetic Particles 5b) Styrene-nBMA copolymer 20 parts Magnetite (particle size: about 0.2 μm) 30 parts Carbon black 2 parts A mixture consisting of 2 parts was heated and kneaded, cooled, pulverized and classified to obtain a volume average particle diameter. Magnetic particles of about 7 μm, electric resistance of 5 × 10 ⁷ Ωcm, saturation magnetic moment of 53 emu / g were obtained, and 100 parts of these magnetic particles and 2 parts of carbon black having an electric resistance of 2 Ωcm were added and mixed to form conductive magnetic particles. Was. At this time, the resistance of the conductive magnetic particles was 3 × 10 ⁶ Ωcm.

Next, 85 parts of magnetic toner particles (5a), 15 parts of conductive magnetic particles (5b) and 0.5 part of titanium oxide were added to prepare a developer.

Using this developer, a negative electrostatic latent image formed on the OPC photoreceptor by ordinary electrophotography is developed by a developing device having an aluminum developing sleeve shown in FIG. When 200,000 copies were run using a copying machine which transferred and heat-fixed while giving a corona discharge, a clear image was obtained without blank spots, white bands, and background stains on the solid rear end.

Comparative Example 1 A developer was prepared and a running test was carried out in the same manner as in Example 1, except that particles not coated with carbon were used instead of the conductive magnetic particles 5b of Example 1.

In this case, a clear image was obtained without any background stain on the initial image. However, when the number of sheets exceeded 150,000 sheets, a solid white trailing edge occurred.

Example 2 (Preparation of Magnetic Toner Particles 5a) Styrene-MMA copolymer 100 parts Spiron black (TOH made by Hodogaya Chemical Co., Ltd.) 1 part Magnetite (particle diameter: about 0.2 μm) A mixture consisting of 100 parts was the same as in Example 1. To produce magnetic toner particles 5a having a volume average particle diameter of about 12 μm, an electric resistance of 3 × 10 ¹³ Ωcm, and a saturation magnetic moment of 43 emu / g.

(Preparation of Conductive Magnetic Particles 5b) Zn-based ferrite of about 5 μm was baked at 250 ° C. for 40 minutes to obtain magnetic particles having an electric resistance of 7 × 10 ⁸ Ωcm and a saturation magnetic moment of 60 emu / g. And electroless plating was performed to form a nickel layer having a thickness of about 0.5 μm to form conductive magnetic particles 5b. At this time, the electric resistance of the conductive magnetic particles was 5 × 10 ⁶ Ωcm.

Next, 80 parts of magnetic toner particles (5a), 20 parts of conductive magnetic particles (5b) and 1.0 part of hydrophobic silica were added and mixed to prepare a developer.

Using this developer, 300,000 copies of a positive electrostatic latent image formed by a normal electrophotographic method using a Se photoreceptor were developed, transferred and thermally fixed in the same manner as in Example 1. However, a clear image was obtained without any solid white trailing edge, white band, and background stain.

Comparative Example 2 Example 5 was repeated except that Mn-Zn ferrite (saturation magnetic moment: 60 emu / g, electric resistance: 6 × 10 ⁵ Ωcm) particles of about 5 μm were used instead of the nimmel-plated conductive magnetic particles 5b of Example 2. In the same manner as in Example 2, a developer was prepared and a running test was performed.

In this case, a clear image was obtained without any background stain on the initial image, but from around 150,000 sheets, trailing white spots and white stripes occurred.

Example 3 (Preparation of Magnetic Toner Particles 5a) Styrene-2-ethylhexyl acrylate copolymer
100 parts Polypropylene 5 parts Stearyl dimethyl benzyl ammonium chloride
A magnetic toner having a volume average particle diameter of about 11 μm, an electric resistance of 7 × 10 ¹² Ωcm, and a saturation magnetic moment of 40 emu / g was prepared by treating a mixture consisting of 3 parts of Zn ferrite (particle diameter: about 0.5 μm) in the same manner as in Example 1. Particle 5a was made.

(Preparation of Conductive Magnetic Particles 5b) Approximately 4 μm of γ-Fe ₂ O ₃ (electrical resistance 7 × 10 ⁹ Ωcm, saturation magnetic moment 65 emu / g) particles are reduced in a hydrogen atmosphere to reduce the surface of the conductive magnetic particles 5b. Was made. At this time, the electric resistance of the conductive magnetic particles 5b was 6 × 10 ⁵ Ωcm.

75 parts of the magnetic toner particles (5a), 25 parts of reduced conductive magnetic particles (5b) and alumina oxide (primary particle diameter of about 0.02 μm)
m) 0.5 part was added and mixed to prepare a developer.

Using this developer, a running test was carried out in the same manner as in Example 1. As a result, a clear image was obtained even after 300,000 sheets without any white trailing edge, white band and background stain.

〔effect〕

As is clear from the description of the examples, according to the use of the developer of the present invention, both the developability and the transferability are excellent, and the image has no background stain, and furthermore, the magnetic properties of the conductive magnetic particles are reduced. It is possible to prevent the occurrence of uneven distribution, and it is possible to prevent the occurrence of white spots, white bands, and solid white trailing edges due to running.

[Brief description of the drawings]

1 (A) and 1 (B) are partially enlarged sectional model views for explaining the action of toner particles of the developer of the present invention. FIG. 2 is an explanatory view of the operation of the apparatus using the toner of the present invention. DESCRIPTION OF SYMBOLS 1 ... Conductive backing 2 ... Electrostatic latent image carrier 3 ... Electrostatic latent image 4 ... Conductive non-magnetic sleeve 5 ... Developer, 5a ... High electric resistance magnetic toner 5b ... Conductivity Magnetic particles, 6 ... magnet 7 ... doctor, 7a ... doctor gab

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Tanaka 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Tomoge Hagiwara 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 Inside Ricoh Co., Ltd. (56) References JP-A-57-185050 (JP, A) JP-A-61-189562 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/083

Claims (1)

(57) [Claims] 1. A developer comprising a mixture of high electric resistance magnetic toner particles containing magnetic fine powder and conductive magnetic particles having a volume average particle size smaller than the volume average particle size of said toner particles, A developer for an electrostatic latent image, wherein the conductive magnetic particles comprise a magnetic core material and a conductive coating layer.