JPH0812519B2 - Electrostatic image development method - Google Patents

Description

The present invention relates to a method for developing an electrostatic charge image formed on the surface of an image carrier, and particularly to the use of a developer comprising a magnetic carrier and a magnetic toner. , A method of developing by a magnetic brush method.

[Conventional technology]

When developing an electrostatic charge image formed on the surface of an image carrier, a magnetic brush method is generally used. As a developer used for magnetic brush development, there are many two-component developers in which a magnetic carrier and a non-magnetic toner are mixed. On the other hand, there is also a method of using a one-component developer composed of resin and magnetic powder as the developer. In the former method using a two-component developer, although an image having good image density and resolution can be obtained, there is a problem that reproducibility of halftone is inferior. On the other hand, in the latter method using the one-component developer, there are problems that the charge cohesive development of the toner is caused as the toner charge amount increases, and the development is insufficient due to the lack of toner on the sleeve. As means for solving these problems, there has been proposed a developer in which a magnetic carrier and a magnetic toner are mixed, as described in JP-A-59-162563 and JP-A-59-216149, for example. It is said that the advantages of both the two-component developer and the one-component developer are used together.

[Problems to be Solved by the Invention]

In the method of developing an electrostatic charge image using the developer in which the magnetic carrier and the magnetic toner are mixed as described above, both of the advantages of the method of using the two-component type developer and the one-component type developer are obtained. However, when the coercive force of the magnetic toner is low, or when the content of the magnetic powder in the magnetic toner is small, the image becomes unclear. In order to solve this problem, it is necessary to increase the triboelectric charge amount of the magnetic toner in order to adhere the magnetic toner to the electrostatic charge image in a large amount in the developing area. However, in order to improve the triboelectric charge amount, for example, when a large amount of a charge control agent is added, there is a problem that the fixability is deteriorated, and there is also a problem that the magnetic toner adheres to the non-image area to increase the background fog. Coexist.

The present invention solves the above problems existing in the prior art, increases the charge amount of the magnetic toner, and develops an electrostatic charge image capable of obtaining an image having high density and high resolution without inducing background fog. The purpose is to provide a method.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a magnetic carrier is formed on a non-magnetic sleeve which forms an electrostatic charge image on the surface of an image carrier, is arranged to face the surface of the image carrier, and has a magnetic field generating member therein. And a magnetic toner are mixed to supply a developer, and the electrostatic charge image is developed by rubbing the surface of the image carrier with a magnetic brush formed on the non-magnetic sleeve. A magnetic toner having 1 to 20% by weight of magnetic toner having the same polarity as the magnetic carrier and 80 to 99% by weight of magnetic toner having the opposite polarity to the magnetic carrier is used, and a low-frequency AC bias voltage is applied to the magnetic toner. We adopted the technical means of applying and developing.

As the magnetic carrier used in the present invention, known carriers can be used, but from the viewpoint of image quality, magnetite or soft ferrite (Ni-Zn system, Mg-Zn system, Cu-Zn system, Ba-Ni-Zn system, etc.)
A carrier containing iron oxide consisting of is preferred.

The particle size of the magnetic carrier is 20 to 200 μm (preferably 50 to 150 μm) as the average particle size, similar to the usual two-component developer.
It is better to set the range.

The electric resistivity of the magnetic carrier is preferably 10 ⁶ to 10 ¹² Ω · cm because it has an electrode effect.

Further, the saturation magnetization of the magnetic carrier is preferably 40 to 70 emu / g. If it is less than 40 emu / g, carrier adhesion will occur in the image area in the developing area, which is not preferable. on the other hand
When it exceeds 70 emu / g, the carrying force becomes excessive and an unreasonable force acts on the magnetic toner, which is inconvenient.

Next, the magnetic toner used in the present invention is magnetic powder,
A fixing resin, a charge control agent, a coloring pigment, a dye, a fluidity modifier, a resistance adjusting agent, etc. are mixed to form a particle size of 5 to 25 μm, but the magnetic powder content is 10 to 75% by weight. Preferably. That is, when the content of the magnetic powder is less than 10% by weight, the saturation magnetization of the magnetic toner is significantly lowered, the magnetic toner is easily separated from the sleeve, and the magnetic toner is scattered, which is inconvenient. On the other hand, if the content of the magnetic powder exceeds 75% by weight, the fixing property is deteriorated, which is not preferable.

The electric resistivity of the magnetic toner is preferably 10 ¹³ Ω · cm or more in an electric field of DC 4 kV / cm in order to secure transferability. The amount of triboelectrification of the magnetic toner by the blow-off method is preferably 5 to 20 μc / g in absolute value in order to secure developability when the polarity is opposite to that of the magnetic carrier. If the triboelectrification amount is less than 5 μc / sec, the image density is lowered, while if it exceeds 20 μc / g, the background fog is increased, which is inconvenient.

Next, the fixing resin to be contained in the magnetic toner may be appropriately selected according to the fixing method (for example, JP-A-57-97545).
(See the official gazette). As an example, in the case of the heat roll fixing method,
Examples thereof include styrene / acrylic copolymers, styrene / butadiene copolymers, polyester resins, epoxy resins and mixed resins thereof.

As the magnetic powder, alloys or compounds containing ferromagnetism elements such as ferrite, magnetite, etc., such as iron, cobalt, nickel, etc. can be used, but the average particle size is about 0.1 to 3 μm in order to be contained in the toner. The thing of is desirable. Since the coercive force of the toner is substantially determined by the coercive force of the magnetic powder, the coercive force of the toner can be adjusted by changing the type of the magnetic powder.

The following are mentioned as said additive.
As the charge control agent, a nigrosine dye having a positive charge characteristic, a metal-containing (Cr) azo dye having a negative charge characteristic, and the like are generally used. Carbon black is generally used as a resistance adjuster. Hydrophobic silica is often used as a fluidity modifier. If the addition amount of these is too large, the fixing property of the toner is impaired, so the content is generally set to 10% by weight or less.

The developer used in the present invention is adjusted by mixing a carrier and a toner, and the mixing ratio (toner density) of the toner is adjusted.
It is desirable to set 10 to 90% by weight. If the toner concentration exceeds 90% by weight, the toner tends to scatter, and the amount of spent toner increases. On the other hand, if the toner concentration is less than 10% by weight, the sharpness of the image becomes less and dust and blurring occur.
The toner concentration is appropriately determined according to the developing conditions, etc., but the preferable range is 20 to 60% by weight, and the more preferable range is 20 to 60% by weight.
50% by weight.

In the present invention, the magnetic toner charged to the same polarity as the magnetic carrier is contained in an amount of 1 to 20% by weight based on the entire magnetic toner. However, the magnetic toner that should contribute to development, that is, charged to the opposite polarity to the magnetic carrier. The magnetic toner is added for the purpose of improving the triboelectric charge amount of the magnetic toner. If the content is less than 1% by weight with respect to the total amount of the magnetic toner, the effect of improving the triboelectric charge amount is insufficient. On the other hand, if it exceeds 20% by weight, the amount of the magnetic toner attached to the non-image area increases and the background fog is generated. It is not desirable because it will occur.

It is desirable that the developer be conveyed at least by rotating the sleeve in order to prevent magnetic agglomeration of the carrier. Alternatively, the sleeve and the permanent magnet roll may be rotated in the same direction or in opposite directions.

The development gap should be 1.0 mm or less to secure the contact width between the magnetic brush and the photoconductor, but 0.3 mm or more is desirable for the magnetic brush to softly contact the photoconductor.
The preferred range is 0.4 to 0.6 mm. The doctor gap may be set according to the development gap.

In the present invention, the maximum magnetic property of the developer is 5 k0e using a vibrating sample magnetometer (VSM-3 manufactured by Toei Industry Co., Ltd.).
Shall be measured in the magnetic field of.

〔Example〕

FIG. 1 is a sectional view of a main part showing a developing device according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a toner tank, which contains magnetic toner 2. At the bottom of the toner tank 1, a permanent magnet roll 3 having NS magnetic poles on its surface is provided, a sleeve 4 is provided coaxially with the permanent magnet roll 3, and both are provided rotatably relative to each other. The sleeve 4 is formed in a hollow cylindrical shape using, for example, stainless steel or other non-magnetic material. Next, 5 is a photoconductor, which is provided rotatably in the direction of the arrow via the sleeve 4 and the developing gap D. A bias voltage source 6 is connected to the sleeve 4, and is applied in order to prevent the magnetic toner charged with the same polarity as the carrier from adhering to the electrostatic charge image and causing fog on the ground. A low-frequency AC voltage with a frequency of 2 kHz or less is desirable as the bias voltage.

With the above configuration, when the permanent magnet roll 3 and the sleeve 4 are rotated in the opposite directions, the magnetic toner 2 stored in the toner tank 1 passes through the doctor gap d and is agitated by the sleeve 4. Thus, the surface of the photoconductor 5 is rubbed by forming a magnetic brush with the magnetic poles on the surface of the permanent magnet roll 3. Therefore, the electrostatic image formed on the surface of the photoconductor 5 can be developed.

 Next, a more detailed description will be given with reference to specific experimental examples.

Ferrite carrier 60% by weight (KBN-100 manufactured by Hitachi Metals, particle size 70 to 140 μm) Magnetic toner (A) 28 to 40% by weight (ρ = 10 ¹⁵ Ω · cm, TEC = -18 μc / g) Magnetic toner (B) 12 to 0% by weight In this case, the magnetic toner (A) is charged with the opposite polarity to the magnetic carrier and contributes to the development, while the magnetic toner (B) is charged with the same polarity as the magnetic carrier and the magnetic toner (A) is charged. (A) contributes to the improvement of the triboelectric charge amount,
Only by changing the polarities of the charge control agents, the constituent materials and physical properties are made the same. First, the magnetic toner (A) is manufactured as follows.

Styrene-acrylic copolymer 46 wt% (Fujikura Kasei Mw = 22 × 10 ⁴ ) Magnetite 50 wt% (Toda Kogyo EPT500) Polypropylene 3 wt% (Sanyo Kasei Viscole 550P) Negative charge control agent 1 wt% ( Orient Chemical Co., Ltd. Bontron E81) The above ingredients were kneaded at 200 ° C, cooled and solidified, pulverized, and added with 0.5 parts by weight of silica (Nippon Aerosil R972), and heat treated at 120 ° C and classified. , Particle size 5
The magnetic toner (A) having a particle size of up to 20 μm was used.

Next, the magnetic toner (B) was prepared in the same manner except that a positive charge control agent (Bontron N.01 manufactured by Orient Chemical Co., Ltd.) was used instead of the negative charge control agent in the magnetic toner (A).

The magnetic toners (A) and (B) produced as described above were mixed in various proportions, mixed with the ferrite carrier to prepare a developer, and image evaluation was performed. First, an OPC drum (outer diameter 40 mm, peripheral speed 100 mm / sec (clockwise)) having a negative charging polarity is used as the photoconductor 5, uniformly charged to −650 V, and then dividedly exposed by a semiconductor laser to electrostatically charge the surface. Formed an image. As the developing device, a permanent magnet roll 3 having an outer diameter of 18 mm, 8-pole symmetrical magnetization, a surface magnetic flux density of 650 G (on the sleeve 4) and a stainless sleeve 4 having an outer diameter of 20 mm were used. Here, the developing gap D = 0.4 mm and the doctor gap d = 0.3 mm were set, the sleeve 4 was rotated clockwise at 150 rpm, and the permanent magnet roll 3 was rotated counterclockwise at 900 rpm. The sleeve 4 has a bias voltage of -600V DC and 1kV AC.
(V _pp , f = 800 Hz) was applied. After development, it is transferred to plain paper by a corona transfer device (+ 4.5kV), and a fixing force is obtained by a heat roll coated with PFA resin and a silicone rubber roll.
It was fixed under the conditions of 1.0 kg / cm and fixing temperature of 180 ° C. The table below shows the results of image evaluation based on image density, resolution, and background fog. The magnetic toner (A) in the table
The relative content of (B) is shown in ().

As is clear from the table, in No. 1, since the amount of the magnetic toner (B) charged in the opposite polarity to the regular charging polarity is large, the background fog occurs. That is, the result is that the magnetic toner charged to the opposite polarity adheres to the non-image portion. On the other hand, in No. 5, since the magnetic toner (B) does not exist at all, the charge amount is insufficient and the image density is low. On the other hand, in Nos. 2 to 4, since the magnetic toner (B) charged in the opposite polarity is contained in an appropriate amount, a high-density image can be obtained without causing background fog.

[Advantages of the Invention] Since the electrostatic image developing method of the present invention has the above-described configuration and operation, it is possible to increase the charge amount of the magnetic toner, and to induce high density and high density without causing background fog. There is an effect that an image having a resolution can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part showing a developing device according to an embodiment of the present invention. 3: permanent magnet roll, 4: sleeve.

Claims (3)

[Claims] 1. An electrostatic charge image is formed on the surface of an image carrier, the magnetic carrier and the magnetic toner are mixed on a non-magnetic sleeve which is arranged to face the surface of the image carrier and has a magnetic field generating member therein. In the electrostatic charge image developing method of developing the electrostatic charge image by rubbing the surface of the image carrier with a magnetic brush formed on the non-magnetic sleeve, the magnetic toner having the same polarity as the magnetic carrier. 1 to 20% by weight and 80 to 99% by weight of magnetic toner having a polarity opposite to that of the magnetic carrier
An electrostatic charge image developing method characterized by using a magnetic toner obtained by mixing and a magnetic toner, and developing by applying a low-frequency AC bias voltage to the magnetic toner. 2. The electrostatic image developing method according to claim 1, wherein the magnetic carrier is formed of ferrite powder. 3. The electrostatic image developing method according to claim 1, wherein the AC bias voltage is 2 kHz or less.