JPS63184764A - Carrier for electrophotographic developer and production thereof - Google Patents

Abstract

PURPOSE:To obtain a low-cost lightweight carrier for an electrophotographic developer having superior characteristics and a long service life by dispersing a nonmagnetic oxide phase comprising one or more among Si, Ca, Al, Mg, Fe, V, Sb, Sn, Pb, Cu and Mn in a magnetite (Fe3O4)-base matrix phase. CONSTITUTION:Hematite-base iron oxide is mixed with nonmagnetic oxide powder comprising one or more among Si, Ca, Al, Mg, Fe, V, Sb, Sn, Pb, Cu and Mn, and only the hematite in the mixture is converted into magnetite by baking in an inert atmosphere to obtain a carrier for an electrophotographic developer. The proper amt. of the nonmagnetic oxide component to be mixed with the iron oxide is 10-40wt.% in case where the oxide phase is finely dispersed. In case of deposition on the grain boundaries, the proper amt. is 0.01-10wt.%. Thus, performance comparable to that of a ferrite carrier is obtd. at a lower cost. Since the carrier of this invention is light in weight, it has low stirring resistance and the size of a copying machine can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an electrophotographic developer, specifically a developer for an electrophotographic copying machine.
The present invention relates to a carrier for a component magnetic brush developer and a method for manufacturing the same.

(Prior Art) Iron powder and ferrite have conventionally been used as carriers for two-component magnetic brush developers for electrophotography.

Since the carrier is required to have a high specific resistance of about 10 6 to 10 I 5 Ω·ω, the iron powder carrier is used by oxidizing the surface or coating it with a resin. Such an oxidized layer on the surface is easily abraded by friction and impact caused by stirring during use as a developer, and the adhesion between the iron powder and the resin coating is often insufficient and peeling is likely to occur. Therefore, the disadvantage of iron powder carriers is that they cannot withstand long-term use.

Another factor that affects the lifespan of the carrier is toner filming. The important role of the carrier during development is to impart a uniform frictional charge to the toner and transport it to the latent image area of the photoreceptor. However, when the carrier and toner repeatedly collide with each other due to agitation of the developer, In addition, some of the toner particles destroyed by the impact may adhere to the carrier surface to form a film. This type of development is called toner filming. When toner filming occurs, the carrier's ability to triboelectrically charge toner decreases, resulting in insufficient toner conveying ability and a decrease in image density. The agitation resistance during development is involved in the occurrence of toner filming. When the stirring resistance increases, the pressure at the time of collision between the carrier and the toner increases, making toner filming more likely to occur. Therefore, in order to extend the life of the carrier, it is necessary to lower the stirring resistance. Since the iron powder carrier has a high specific gravity, the stirring resistance is large and toner filming is likely to occur. Therefore, from this point of view as well, it can be said that iron powder carriers cannot withstand long-term use.

In addition, the saturation magnetization of iron powder carrier is about 200 emu/g, but if a carrier with such high saturation magnetization is used, the strength of the magnetic brush during development becomes excessive, making the developed toner image hard. Sweeping with a brush often leaves so-called brush marks on the copy screen.

(Problems to be Solved by the Invention) In order to eliminate these drawbacks of iron powder carriers, ferrite carriers such as those disclosed in Japanese Patent Publication No. 56-52305 have been used. In addition to being a chemically stable oxide with high resistivity and uniform internally, ferrite carriers are lightweight at approximately 2.5 g/c+n'' compared to the apparent density of iron powder carriers, which is approximately 4.5 g/cm3. Therefore, it is characterized by long life, and has a saturation magnetization of 40 to 60 en+.
It is about U/g, there are no brush marks on the copy print,
It is characterized by high resolution. However, as seen in Japanese Patent Publication No. 56-52305 and Japanese Patent Application Laid-open No. 58-171059, this ferrite carrier has problems in terms of cost because it contains expensive metals such as nickel, manganese, and copper. There is. A carrier using magnetite, which is a material similar to ferrite and is inexpensive, is also disclosed in JP-A-60-458, but although magnetite carriers are lightweight and have a long life, they require resin coating due to their low resistivity. However, due to the high saturation magnetization of approximately 92 emu/g, the strength of the magnetic brush becomes excessive, resulting in the formation of brush marks.

The present invention eliminates the drawbacks of magnetite carriers such as low resistivity and high saturation magnetization, and is also lightweight and has a long life.
The object of the present invention is to provide a carrier for an electrophotographic developer that is inexpensive and has excellent properties, and a method for producing the same.

(Means for Solving the Problems) The electrophotographic developer carrier of the present invention contains Si in a matrix mainly composed of magnetite (Fe+0*).

Ca, At, Mg+ Fe+ L Sb+ Sn,
It is characterized in that a non-magnetic oxide phase consisting of one or more of pb, Cu, and Mn is scattered therein. At this time, the term "scattering" is a concept that includes grain boundary precipitation, surface precipitation, and the like.

Further, the method for producing a carrier for an electrophotographic developer of the present invention includes adding St, Ca, AI, Mg+Fe+V, to iron oxide powder containing hematite (F13103) as a main component.
One or two of Sb, Sn+Pb, Cu, Mn
Mix and granulate non-magnetic oxide powder consisting of seeds or more, and sinter at a temperature of 1000 in an inert atmosphere with an oxygen concentration of 5 vol% or less.
It is characterized in that only hematite is reduced to magnetite by heat treatment at a temperature of 1400°C to 1400°C.

(Function) Such Si + Ca, 8L Mg, Fe, V,
Sb, Sn.

Due to the presence of the oxide nonmagnetic phase consisting of one or more of Pb, Cu, and Mn, the saturation magnetization per unit weight of the carrier particles as a whole is about 92e of magnetite.
It decreases from mu/g to about 30 to 80 en+u/g.

Also, St+ Ca, AI+ Mg, Fe+ v,
sb, Sn, Pb, Cu.

The oxide nonmagnetic phase consisting of Mn also has high electrical resistance, so by being finely dispersed or existing at grain boundaries or on the surface, it finely divides the electrical conduction path by magnetite, reducing the specific resistance of the carrier to about the same as that of the magnetite carrier. 10
Increase from 4Ω to 10h to 10'2Ω/1 degree.

Also, 5to2. Cab, AltOs+ Mgo,
VzOs+ 5bzO3゜Snug, pbo, C
Non-magnetic phases such as ub and MnO have a specific gravity of about 2.6 to 4.
0g/cm3, and about 5.2g/c- of magnetite.
3, the apparent density of the carrier for electrophotographic developer of the present invention is 1.8 to 2.2 g/cm', which is approximately 2.5
It is lighter than a ferrite carrier with a g/cI of 113,
Toner filming does not occur, and high quality copy images can be maintained for a long time.

(Example) The carrier for an electrophotographic developer of the present invention contains iron oxide mainly consisting of hematite and Si, Cat AI+ Mg+
It is obtained by mixing nonmagnetic oxide powders consisting of one or more of Fe, ν+Sb+Sn, pb, Cu, and Mn, firing in an inert atmosphere, and reducing only hematite to form magnetite. The specific manufacturing method will be described below.

Si, Ca, AI+ with a particle size of 0.1 to 10 μm to iron oxide mainly composed of hematite with a particle size of 0.1 to 10 μm
MLFe, V, Sb, Sn, Pb, Cu,
A non-magnetic oxide powder consisting of one or more types of Mn is preferably added in a range of 0.01 to 40 wtX, dispersed in water with a dispersant added, and wet-pulverized using an attritor mill, a ball mill, etc.・Mix to obtain slurry. Among the non-magnetic oxide powders, kaolinite, silica sand, clays, silica powder, alumina powder, etc. are suitable as the St 2 , Car Al source, and each oxide is suitable as the other metal source. Suitable dispersants include ammonium hexametaphosphate, ammonium hyrophosphate, ammonium polycarboxylate, and the like. A binder is added to the resulting slurry, which is dried and granulated using a spray dryer. Polyvinyl alcohol is used as a binder in an amount of 0.1 to 1 tχ.

By firing the granulated raw material in an inert atmosphere, only hematite is reduced to magnetite while leaving non-magnetic phases such as SiO□, Cab, and AlgO+ intact.
It is sintered to form a structure in which a nonmagnetic phase is dispersed in magnetite or exists at grain boundaries or on the surface. At this time, Sing,
In order to prevent hematite or reduced magnetite from reacting with non-magnetic phases such as Cab and Al2O5, it is necessary to set the firing temperature to 1400° C. or lower. In addition, as a result of subsequent experiments, it was found that in order to obtain the saturation magnetization required as a carrier, it is important to sufficiently reduce hematite, and the firing temperature should be at least 1000°C or higher. . Therefore, the firing temperature range is 100
The temperature is 0 to 1400°C. An inert gas such as nitrogen or argon is used for the firing cloud atmosphere, but if necessary, 5 volχ
By mixing up to a certain amount of oxygen into the atmosphere, the reduction rate of hematite can be controlled to lower the saturation magnetization. In this case, if the oxygen concentration exceeds 5 vol.chi., hematite will not be sufficiently reduced, and the saturation magnetization required as a carrier will not be obtained.

The amount of the non-magnetic component to be mixed with the iron oxide is preferably 10-40-tχ when the oxide phase is finely dispersed, and 0.01-tχ when it is sufficient to cause grain boundary precipitation.
~10wtχ is suitable.

In addition, when the non-magnetic oxide phase mentioned above is finely dispersed and the oxide phase has a high melting point, the sinterability is lower than that of a carrier consisting only of magnetite, resulting in crystal grains. Since the growth of oxides is suppressed, it is preferable to add an oxide having a low melting point among the oxides mentioned above in order to compensate for this sinterability.

In this case, the low melting point oxide is Cub, Vt08s
5btosSnO*+PbO is suitable. The appropriate amount of addition is 0.1 to 5 wtχ, especially 1.0 to 2 wtχ.
．． Owtχ is optimal.

SJJLL Iron oxide recovered from steel pickling waste (average particle size 0.8μ
Samples 1 to 4 were prepared by adding the non-magnetic components shown in Table 1 to hematite 99.42).

Table 1 1) After premixing the raw materials pulverized with an atomizer to an average particle size of 3 μm using a Henschel mixer, 30 kg of water and 150 g of polycarboxylic acid ammonium salt as a dispersant (0
. After drying and granulating the obtained slurry with a spray dryer, it was classified with a sieve and 88-1
The particles having a particle size of 25 μm were fired in a nitrogen atmosphere using an alumina container.The firing temperature was kept at 1350°C for 5 hours, and then cooled in the furnace. The properties of the obtained carrier are shown in Table 2.

Table 2 5 wt.chi. of a commercially available styrene-acrylic copolymer resin toner was added to this carrier to prepare a developer, and a photocopying test was conducted using a commercially available copying machine (medium-speed machine using a non-coated ferrite carrier). As a result of the test, good image density and resolution were obtained, and there was no deterioration in image quality even after copying 80,000 sheets. When the carrier after 80,000 copies was collected and observed under an electron microscope, no toner filming had occurred.

11'i Addition amount of silicon oxide (SiO□) and calcium oxide (Cab) to 20 kg of hematite is 5 iOz/Ca.
O = 1/1 (weight ratio) and the amount added is 100g, 200
g, 300g, 400g.

500g, 700g, 1000g, 1200g,
Mix 2000g, add a dispersant, and make a slurry concentration of 50wt! It was made into a slurry. Next, milling is performed using an attritor, PVA is added as a binder,
Granulation and drying were performed using a spray dryer. Thereafter, firing was performed at 1300° C. for 3 hours in nitrogen gas with controlled oxygen concentration.

In addition, as a comparative example, additives (SiO□ and Cab)
An electrophotographic carrier was manufactured under the same conditions as in the previous example, except that only hematite was used without adding. Thereafter, the magnetic properties (saturation magnetization), electrical resistance (specific resistance), and charge amount of the obtained carrier were measured.

The results are shown in Table 3.

We also conducted live-action tests using these carriers. Live-action test: toner concentration 5W for 1 kg of carrier
The developer was adjusted so that tχ was obtained, and the experiment was carried out using a commercially available copying machine. As a photocopying test, image density and resolution were measured using an image analysis device, as well as the presence or absence of the gabbing phenomenon and the number of copies that could be made without deterioration of image quality. The results of image characteristics are shown in Table 4.

As a result, when a conventional ferrite carrier was used, development defects occurred after approximately 45,000 copies, whereas with the carrier according to the present invention, clear copies of 5000 copies or more were obtained in all cases. Further, when the carrier according to the present invention was used, the surface condition of the carrier particles after the actual photographic test was examined, and it was found that there was no change in surface smoothness and no toner filming phenomenon occurred.

Plan 1±1 In addition to iron oxide, oxide VzOs+ 5nOz+ 5bz
O:+, PbO+MgO, with a composition containing 2wtχ of MnO alone, and made into spherical particles according to a conventional method. Thereafter, baking treatment was performed at 1250° C. for 3 hours in an atmosphere with an oxygen concentration of 0.1 volχ to obtain an electrophotographic carrier. Table 5 shows the properties of the obtained carrier for electrophotography. In Table 5, the amount of charge was determined by mixing and adjusting a commercially available toner and carrier in a rotary mill and measuring the value of the carrier by blow-off.

An electrophotographic carrier was obtained in the same manner as in Example 3 using two or more of the oxides shown in Table 5. Table 6 shows the combinations and the characteristics of the obtained carriers.

Table 6 (Effects of the Invention) As explained in detail above, the electrophotographic developer carrier of the present invention has a longer life and higher resolution than the iron powder carrier, and compensates for the drawbacks of the limagnetite carrier that require resin coating.
It provides the same performance as ferrite carriers at a lower cost. In addition, the carrier for electrophotographic developer of the present invention is lighter than the ferrite carrier, which was conventionally lightweight as a carrier for two-component magnetic brush development, so it has less stirring resistance and allows for the miniaturization of copying machines. It is something to do.

Claims (1)

[Claims] 1. Si, Ca, Al, Mg, Fe, V, Sb,
A carrier for an electrophotographic developer, characterized in that a nonmagnetic oxide phase consisting of one or more of Sn, Pb, Cu, and Mn is scattered therein. 2. Si, Ca, Al, Mg, Fe, V, Sb, S to iron oxide powder whose main component is hematite (Fe_2O_3)
By mixing and granulating non-magnetic oxide powder consisting of one or more of n, Pb, Cu, and Mn, and heat-treating at a firing temperature of 1000°C to 1400°C in an inert atmosphere with an oxygen concentration of 5 vol% or less. , a method for producing a carrier for an electrophotographic developer in which only hematite is reduced to magnetite.