JPH0269772A - Resin coated carrier - Google Patents

Abstract

PURPOSE:To increase the power to impart electrostatic charge to the toner in a developer and to facilitate the control of a toner conon. by incorporating fine powder which consists of a resin and a material having nonreactivity and has 3 to 50mum average grain size into this toner and forming the surface to a rugged shape. CONSTITUTION:Ferrite particles having 10 to 200mum average grain size are used as a core material and the surface thereof is coated with the resin. The fine powder which consists of this resin and the material having nonreactivity and has 3 to 50mum average grain size is incorporated into the resin and the surface thereof is formed to the rugged shape. The content of the fine powder in the coating resin is preferably specified to 5 to 80wt.%. The surface area of the resin coated carrier is increased in this way and, therefore, the power to impart the electrostatic charge to the toner in the developer is increased and the ground fogging is suppressed; in addition, the control of the toner concn. is facilitated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a carrier constituting a two-component developer used for development in electrophotography, and particularly relates to a carrier comprising a core material made of ferrite particles coated with a resin. The present invention relates to a resin-coated carrier.

[Conventional technology]

Conventionally, in electrophotography, the surface of a photoreceptor is uniformly charged using, for example, a photoconductive substance, and then an electrostatic image is selectively formed on the surface of the photoreceptor by exposure corresponding to image information. A developer to which a predetermined electrostatic charge has been applied via a triboelectric charging means is brought into contact with the electrostatic charge image, and toner in the developer is adhered onto the electrostatic charge image to form a visualized toner image. Next, this toner image is generally transferred onto recording paper and then fixed using heat or pressure means to obtain a visible image. In this case, the two-component developer consists of a magnetic carrier and a toner, and in order to optimize the amount of charge with the toner and obtain a high-quality image, a resin coated W carrier is used, in which the surface of the carrier is coated with a resin material. used (for example, Japanese Patent Application Laid-open No. 61204643, Japanese Patent Publication No. 62-1827)
(See Publication No. 59, etc.)

[Problem to be solved by the invention]

The conventional resin-coated carrier described above is most commonly formed by, for example, charging the carrier in a fluidized bed furnace and heating it, then spraying a slurry of resin with a solvent to coat the carrier surface, and drying and curing it. It is true. Therefore, the surface of the resin-coated carrier is formed to be smooth, and even when mixed with toner as a developer, the contact area with the toner is reduced.

The ability to charge the toner tends to deteriorate.

Therefore, when the toner concentration increases, the amount of uncharged toner generated increases, and there is a problem that fogging is likely to occur. For this reason, there are problems in that the range of optimal toner density in which problems such as fog do not occur is extremely narrow, and it is difficult to control toner density.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a resin-coated carrier that has a high ability to impart charge to toner in a developer and can easily control toner concentration.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a resin-coated carrier in which a core material is ferrite particles having an average particle diameter of 10 to 200 μm and a resin is coated on the surface of the core material, and the resin is non-reactive with the resin. A fine powder made of a material having an average particle diameter of 3 to 50 μm is contained therein, and one surface is formed into an uneven shape.

A technical method was adopted.

The ferrite particles used in the present invention are ceremonial (MO)
+00-X (F ex o3) Represented by x.

In this case, M is Ba, Ni, Zn, Mg, MnLi, Cu
, V, Cr, and Ca, and X is 55 to 70 mol%.

The ferrite particles composed of the above-mentioned mixture of metal oxide and iron oxide are crystallographically spinel and perovskite hexagonal crystals.

It is a magnetic material with a garnet-5 orthoferrite structure. Note that if X is less than 55 mol%, the saturation magnetization of the ferrite particles becomes small, causing problems such as deterioration of developability and carrier adhesion to the photoreceptor drum, which is not preferable. Moreover, if X exceeds 70 mol %, the saturation magnetization increases and uneven development occurs on one image, which is disadvantageous. The saturation magnetization of the ferrite particles was determined by a vibrating sample magnetometer (Model VSM-3 manufactured by Toei Kogyo Co., Ltd.) at 5000
40 to 80 emu when a magnetic field of 0e is applied
/g is preferable.

The above ferrite particles can be prepared by the following method. First - after mixing the raw materials corresponding to the above composition, they are calcined at a temperature of 900-1000C for 0.5-3 hours. When a carbonate such as BaCO5 is used as a raw material, CO is removed by this calcination and transformed into a metal oxide such as BaO.Next, the above calcined powder is used as a crushing medium using, for example, steel balls. Finely pulverize to an average particle size of about 2 μm or less using a wet pulverizer or the like. The fine powder obtained in this way is heated to 10 to 200% by spray dryer method, for example.
It is granulated to have an average particle size of μm. In addition to the above-mentioned methods, granulation methods include a method in which the powder is rolled and compacted with a binder in a kneader for granulation, an extrusion method, a method in which the powder is aggregated by vibration or spraying with a binder in a fluidized bed, a method in which the powder is granulated using a rotating pan, etc. There is.

For example, pack the powder granulated as above in a sagger pot and
After firing at a temperature of 100 to 1350° C. for 3 to 5 hours, the product is crushed using a crusher or the like and classified to have an appropriate particle size distribution to obtain ferrite particles.

In the present invention, examples of resins that can be coated on ferrite particles include styrene-acrylic copolymers, silicone resins,
There are maleic acid resins, fluororesin polyester resins, epoxy resins, etc., and they can be selected appropriately taking into consideration the electrical resistance, charging characteristics, etc. required of the carrier.

Next, the materials constituting the fine powder to be contained in the coating resin include urethane-based, acrylic-based resins, oxide-based, nitride-based, or carbide-based ceramics, talc, clay, CaCO, etc.

Materials such as inorganic oxides such as kaolin and hentonite can be used; in short, any material that is non-reactive with the coating resin may be used.

The above-mentioned fine powder preferably has an average particle size of 3 to 50 .mu.m, and preferably has a content of 55 to 80 percent in the resin. The fine powder adheres to the surface of the ferrite particles when mixed with the coating resin, forming an uneven surface of the carrier as a whole, but if it is less than the above range, the carrier surface may become uneven. It's difficult.

Therefore, it is inconvenient because it cannot be expected to have an effect of increasing the surface area. On the other hand, if it exceeds the above range, it is undesirable because it tends to peel off from the surface of the ferrite particles, and the liberated fine particles become intervening in the developer, degrading the development performance.

In addition, if the surface of ferrite particles is coated with a resin and fine powder is contained in the resin, the saturation magnetization as a carrier decreases, and carrier adhesion tends to occur during development.

It is preferable to include magnetic powder with an average particle size of 0.1 μm or less in the resin. As the magnetic powder in this case, metals or alloys exhibiting ferromagnetism, such as iron including ferrite and magnetite, cobalt nickel, or compounds containing these elements can be used. If the average particle diameter of the magnetic powder exceeds 0.1 .mu.m, this is not preferable because it will impede the effect of forming the surface of the ferrite particles serving as a carrier into an uneven shape.

Furthermore, it is preferable to treat the surface of the fine particles and/or magnetic powder with a silane coupling agent because this increases the strength against peeling from the surface of the ferrite particles.

When coating the surfaces of ferrite particles with a resin containing the above-mentioned fine powder and magnetic powder, use a suitable organic solvent to dissolve the coating resin (the fine powder is not dissolved; it is dispersed in the solution), ? After coating the powder on the ferrite particles by dipping, spraying, or fluidizing bed method,
What is necessary is just to dry at the temperature of 120-200 degreeC.

In addition to the above-mentioned fine powder, the coating resin may contain an adhesion promoter, a curing agent, a lubricant, a conductive agent, a charge control agent, and the like.

(Function) With the above configuration, the surface of the resin-coated carrier can be made uneven, for example, in the shape of a gold pail.

It can be expected that the surface area will be significantly increased compared to a spherical shape with a smooth surface.

〔Example〕

Raw materials used (11 ferrite particles Hitachi Metals KBN-100 Average particle size: 1008m (2) Fine powder 5iC (3) Clause 1 gender zero minute Intermediate oil made ultrafine particle magnetite Average particle size: 0.01μm (4) Silicone resin Shin-Etsu Chemical type KR250 First, create a diluted solution of silicone resin in an organic solvent.

In this diluted solution, 20 parts by weight of SiC fine powder and 5 parts by weight of magnetic powder were added.
0 parts by weight are uniformly dispersed. In this case, SiC fine powders having different average particle sizes as described later were prepared, and as comparative examples, SiC fine powders containing no SiC fine powder and/or magnetic powder were also prepared. These compounding ratios are shown in Table 1. As the organic solvent, toluene, alcohols, xylene, methyl ethyl ketone, tetrahydrofuran, chloroform and the like can be used alone or in a mixture thereof.

Margin below.

Table 1 (Unit: Weight %) Next, the ferrite particles are degreased and washed with alcohol to make the surface clean, and the diluted solution is sprayed on the ferrite particles while heated to 50 to 150°C. A silicone resin film containing SiC fine powder is formed on the surface.

Note that the organic solvent is quickly volatilized by the above atmosphere, and the film is further solidified by drying at 120 to 200''C, thereby making it possible to obtain a resin-coated carrier.

Next, the toner to be mixed with the resin-coated paint and Yaria will be described.

Raw materials used (1) Styrene-acrylic copolymer 85 parts by weight (Himer SBM600 manufactured by Sanyo Chemical Co., Ltd.) (2) Low molecular weight polypropylene 3 parts by weight (Viscol 550 P manufactured by Sanyo Chemical Co., Ltd.) (3) Charge control agent
2 parts by weight (Orient chemical type Bontron N, 03)
(4) Carbon black 10 parts by weight (manufactured by Mitsubishi Kasei #50) The above-mentioned raw materials were dry-premixed using a ball mill, heat-melted and kneaded using a kneader, cooled and solidified, crushed using a jet mill, etc., and classified into average particles. A positively charged toner having a diameter of 12 μm was prepared.

A developer was prepared by mixing the above toner and the resin-coated carrier so that the toner concentration was 2 to 12% by weight, and a copying test was conducted using a commercially available copy m (SF7300 manufactured by Sharp Corporation). was evaluated. The background fog was evaluated by using ND504DE manufactured by Nippon Denshoku Co., Ltd. and based on the difference in whiteness of the copy paper before and after copying.

The figure shows the relationship between toner density and whiteness difference, which is the result of a copying test. As is clear from the figure, it is natural that the difference in whiteness, that is, the background fog, tends to increase as the toner concentration increases. is large,
This shows that the ground fogging is particularly noticeable. Does this mean that the carrier in the above comparative example does not contain fine powder?

Alternatively, since it contains only fine powder with an extremely small average particle size, the surface of one carrier is relatively smooth.

Therefore, since the contact area with the toner is small, the ability to charge the toner is low, and a large amount of uncharged toner is generated.
It is estimated that the ground cover is large.

On the other hand, in Examples 1 to 3 and Comparative Example 3, fine powder was contained in the resin that coated the carrier, and the carrier surface was formed to have unevenness similar to rice bran. The surface area is larger compared to Examples 1 and 2°4. Therefore, as a result, the contact area with the toner can be increased.
It has a large ability to impart a charge to toner and has the effect of reducing background fog. In other words, by incorporating fine powder with a large average particle size into the resin, it is possible to suppress the increase in background fog that accompanies an increase in toner concentration, resulting in clear images with little background fog over a relatively wide toner concentration range. It is recognized that it is possible to obtain However, Comparative Example 3 has problems as described below.

Next, using the above developer, the toner concentration limit at which carrier adhesion occurs was measured. Table 2 shows the results.

The amount of added magnetic powder and the saturation magnetization value of the carrier are also shown. The saturation magnetization of only the core material that makes up the carrier is 5
7. It was Oemu/g.

Margin below.

Table 2 As is clear from Table 2, in Comparative Examples 3 and 4, since no magnetic powder was contained in the resin, the saturation magnetization of the carrier was lower than that in the case of the core material alone. Therefore, carrier adhesion occurs even though the toner concentration is relatively high as shown in Table 2. Generally, carrier adhesion is more likely to occur when the toner concentration decreases, but this is because the amount of charge between the toner and carrier increases in the low toner concentration region, overcomes the magnetic adsorption force of the developing roll in the developing area, and together with the toner. This is because the carrier is transferred to the surface of the photoreceptor. Therefore, it is necessary that the saturation magnetization to suppress the carrier adhesion is large. Comparatively, in the cases of 3 and 4, since the saturation magnetization value of the carrier is low, the toner concentration limit at which carrier adhesion occurs is a significantly high value.

Next, as another example, resin-coated carriers were created using fine powders of 5i3Na with average particle sizes of 5 μm and 20 μm and ultrafine magnetite particles with an average particle size of 0.01 μm. In this case, the Si, N, and fine powders were treated with a coupling agent consisting of aminopropylmethoxysilane.

The coating resin was the same as the previous example except that a styrene-acrylic copolymer (Himer SBM600 manufactured by Sanyo Kasei) was used.

The toner to be mixed with the resin-coated carrier was the same as in the previous example except that the charge control agent was Bontron E81 manufactured by Orient Chemical Co., Ltd. and a negatively charged toner.

The resin-coated carrier prepared as described above and the toner were mixed in the same manner as described above and a copying test was conducted, and it was confirmed that the toner exhibited good properties in terms of background fogging and prevention of carrier adhesion.

[Effect of the invention] Since the present invention has the structure and operation as described above,
Since the surface area of the resin-coated carrier can be increased, the ability to charge the toner in the developer can be increased, and background fogging can be suppressed, resulting in clear images being obtained over a wide toner concentration range. , it can be expected that the toner concentration can be easily controlled.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between the toner concentration and the difference in whiteness.

Claims (3)

[Claims] (1) In a resin-coated carrier made of ferrite particles with an average particle size of 10 to 200 μm as a core material and coated with a resin on the surface, the resin has an average particle size of 3 to 200 μm and is made of a material that is non-reactive with the resin. A resin-coated carrier characterized by containing fine powder of 50 μm and having an uneven surface. (2) The resin-coated carrier according to claim (1), wherein the resin contains magnetic powder having an average particle size of 0.1 μm or less so that the saturation magnetization value is greater than the value of the core material alone. (3) The resin-coated carrier according to claim 1 or 2, wherein the fine powder and/or magnetic powder is surface-treated with a silane coupling agent.