JPS61201258A - Iron powder carrier of binary developer and its preparation - Google Patents

Abstract

PURPOSE:To obtain the iron powder carrier of a binary developer by reducing and oxidizing an iron ore to form a porous iron powder having a resistivity of a specified value or more. CONSTITUTION:The porous iron powder to be used here is obtained by reducing the iron ore with a reducing agent, such as carbon, at about 1,000 deg.C and after treatment including pulverization, oxidizing it at about 800 deg.C. Since oxygen is released by the reduction treatment, such an iron powder is made porous. This powder is low in electric resistivity, and it can be enhanced to a resistivity of >=1X10<8>OMEGA.cm by subjecting it to oxidation treatment in a rotary mill.

Description

[Detailed Description of the Invention] Field of the Invention 1.'1. ′°°・ □ ・・４． φThe present invention relates to an iron powder carrier for a two-component developer. do.

PRIOR ART AND TECHNICAL PROBLEM TO BE SOLVED In the field of electrophotographic devices, so-called magnetic Brush development method is known.2. This is used for stirring developer and 17, electrostatic toner and carrier.

Two-component developers consisting of rear, rear and rear are also well known.

Namely 1. Mutual friction between the toner and the carrier causes the toner to retain a certain polarity of electric charge. By bringing the magnetic brush into contact with the photoreceptor rod/surface having the electrostatic latent image, a toner layer corresponding to the latent image is obtained. , , .

A carrier made of porous iron powder is known as a carrier used in such a developer, but the electrical resistance value of this carrier is generally on the order of 106Ω,
There is a problem that 1'FIL resistance value is low.

In other words, in the low-pressure brush development method, high-concentration toner,
A high electrical resistance value is required to obtain an image. It is. This type of iron powder carrier has a high electrical resistance value.
In order to do this, oxidation treatment such as heating is usually performed. However, when carriers using porous iron powder are subjected to oxidation treatment such as heating, the interior of the iron powder particles is oxidized and the surface of the particles is oxidized because the particles themselves are porous. In order to achieve high resistance, it is necessary to hold the iron powder at a very high temperature, and in this case the iron powder itself melts (
There is an inconvenience that the margin is 1-2.

Therefore, to the best of the knowledge of the present inventors, a carrier for a two-component developer made of porous iron powder having a high electrical resistance value of 3×1[')7Ω or more is not yet known. An object of the present invention is to provide a carrier for a two-component developer made of porous iron powder having a high electrical resistance value, and a method for producing the carrier.

SUMMARY OF THE INVENTION According to the present invention (C), the present invention consists of porous iron powder obtained by reducing and oxidizing iron ore, and contains at least I
An iron powder carrier for a two-component developer is provided, which is characterized by having a resistance value of 8Ω.

According to the present invention, the iron powder carrier for a two-component developer is further characterized in that porous iron powder obtained by reducing and oxidizing iron ore is oxidized in a rotary mill! The manufacturing method is provided 'h-7,).

Structure of the Invention The porous iron powder used in the present invention is produced by reducing iron ore using a reducing agent such as carbon at a temperature of about 1oonC, and after undergoing processing steps such as pulverization, at a temperature of about 800U. It can be obtained by performing oxidation treatment in .

Such iron powder is porous because oxygen is released during the reduction treatment described above (7. The specific surface area measured by the BET method is 1.5 to 2.5 times that measured by the transmission method.
It has a specific surface area of cnf/fl. Furthermore, the electrical resistance of this iron powder is low, about IXI D6 to 2X107Ω, and according to the present invention, by subjecting it to oxidation treatment in a rotary mill, it can be made to have a high resistance of 1×10δΩ or more. shall be taken as a thing.

In this specification, electrical resistance refers to the dynamic electrical resistance of a magnetic brush, and refers to the electrical resistance value dynamically measured under development conditions using a magnetic brush, and refers to the value determined by the following method. That is, an aluminum electrode drum of the same size as the electrophotographic photoreceptor drum is installed in place of the photoreceptor drum, a developer is supplied onto the developing sleeve to form a magnetic brush, and this magnetic brush slides with the electrode drum. This refers to the resistance value calculated by applying a voltage between the sleeve and the drum and measuring the current flowing between them. In the measurement, a voltage of 50 V is applied in the case of a developer consisting of toner and carrier, and a voltage of 20 V is applied in the case of measuring with the carrier alone forming a magnetic brush. It is measured according to the developing conditions of the developing device (for example, the distance between the drum and the sleeve, the moving speed of the magnetic brush, etc.). In other words, it is understood that the resistance value obtained by this measurement is the resistance value immediately equal to the developing device in the copying machine used.

That is, the iron powder is charged into a rotary mill and oxidized by the mutual seating of the powder particles by stirring for one revolution. In this case, the atmosphere 1d air in the rotary mill is sufficient, but it is also possible to use 02 gas (i17) if necessary.

In such rotary agitation, in order to perform the oxidation treatment quickly, the following formula is used: where B is filled into the rotary mill! 7 is the bulk volume of the iron powder, Vo is the internal volume of the rotary mill, and the filling volume ratio (/?V) defined as is generally in the range of 01 to 07, particularly 0.2 to 04. is desirable.

In order to effectively carry out the sweet oxidation treatment, the rotation speed of the rotary mill is determined by the following formula, where D is the inner diameter of the rotary mill (Cm). 〜160chi,
In particular, it is desirable that it be in the range of 80 to 12c1%.1. stomach. When using a rotation speed higher than 160% of this limit rotation speed, centrifugal force forces the iron powder particles against the wall of the rotating mill, reducing stirring efficiency and preventing sufficient oxidation treatment. .

According to the present invention, the stirring process is carried out three times under the above-mentioned rotation conditions.
By carrying out the heating for about 60 to 1200 minutes, an iron powder carrier having a low electrical resistance value (41 x 10'Ω or more) can be obtained.

As the toner used in combination with the iron powder carrier of the present invention, any colored toner having electrostatic property and fixing property can be used, and the binder resin contains a colored pigment, a charge control agent, etc. A granular composition having a particle size of 5 to 60 microns dispersed therein is used. As the resin, a thermoplastic resin or an uncured or initial condensate thermosetting resin is used. Suitable examples include, in order of importance, vinyl aromatic resins such as polystyrene, acrylic resins, polyvinyl acetate,
These include tar resin, polyester resin, epoxy resin, phenol resin, petroleum resin, olefin resin, etc.

As the pigment, one or more of carbon black, cadmium yellow, molybdenum, liven orange, pyrazolone red, fast violet B, phthalocyanine blue, etc. can be used. - As a charge control agent, for example, nigrosine base (c, I5..04.i5)
Oil-soluble dyes such as , oil black (C1, .26150), spirone black, metal salts of nanthenate, fatty acid metal soaps, resin acid soaps, etc. are used as necessary.
5. , In order to obtain a suitable image density with the artist component type developer and I-, it is recommended to use such toner and the above-mentioned iron powder carrier in a weight ratio of 100:6 to 100:11 on a weight basis. Good. This ratio also does not affect the electrical resistance of the magnetic brush of the developer. That is, as the ratio of the iron powder carrier to the iron powder carrier increases, the electric resistance of the magnetic brush of the developer tends to decrease. The optimum ratio between the two is also closely related to the specific surface area of the iron powder carrier and the electrostatic toner. In preferred embodiment 1 of the present invention, the toner concentration (Ct) of the mixture forming the magnetic brush is determined by the following formula, where 5c is the specific surface of the iron powder carrier - Ccl/l: Actual illumination value by transmission method. ri, s
It is the specific surface area of toner Cc, d/? :・Coulter, −
This is the effective specific surface area calculated based on the flat diameter measured using a counter, assuming that the toner is a true sphere, and is the average axial diameter! If we get it now\ゝ(t/crtl), 'St 73(r'-
1) l) ′ccalculated value),” is o, do, 乃4
Developing at a density that satisfies Sol-゛
□First, the third term on the right side of equation (2) S c/(,'
, S t S, g ) is a [term related to the specific surface area of the carrier and the toner, specifically, the specific surface area of the carrier and the toner.
It is a numerical value representing the total surface area of the mixed composition by weight and the proportion of the surface area occupied by the carrier (hereinafter simply referred to as the area occupied by the carrier). -9-
'', J-□ However, 1. In this aspect of the present invention, the electrostatic charge by the two-component developer is When the image is developed, the image improves by 4 degrees, the Caprillo degree decreases,
This results in improved resolution and improved gradation.

Toner concentration (Ct%) and carrier surface area occupancy (S c
/ (St 10S C) + Chi) can be evaluated by finding the ratio of both, that is, "C""S'/ (S t +S C )] coefficient k.

Although this coefficient differs depending on the shape of the iron powder carrier used, in the present invention, this coefficient k is set to 0, 9 as described above.
By setting it in the range of 0 to 1.14, high image density, low Capri density, high resolution, and excellent gradation properties can be obtained, and these characteristics are not limited only at the initial stage of development, but also in the 4 to 1.14 range.
The effect that there is almost no deterioration even after continuous copying of 0,000 sheets is achieved.

According to the present invention, since it is not possible to obtain an iron powder carrier with a very high electrical resistance value, by using this in combination with a commonly used electrostatic toner, it is possible to obtain a stable 1-7 and high concentration. The invention is illustrated by the following examples.

EXAMPLE In order to confirm the actual effect of the present invention, under the conditions described below, it was confirmed how much the resistance increased at what stirring time, and furthermore, the carrier which had been made to have a high resistance was tested under the conditions described below. It was used in a copying machine and its electrophotographic characteristics were observed.

Ball mill■ A ball mill manufactured by Irie Shokai was used. The ball mill container has an inner diameter of 10 m, a length of 10 m, and a capacity of 785.
crl! A stainless steel container was used.

For the experiment, the rotational speed of the ball mill was selected to be 120 r.mu.m, which has the highest stirring efficiency based on experience (-, and the experiment was conducted with a carrier filling rate of 0.4).

Center particle size: 45 μm, irregular rugby ball shape, apparent density: 6.16 zo 101
Porous iron powder resistance value 1 x 10'Ω The resistance value was measured under the following developing area conditions of the copying machine, with an At electrode drum loaded in place of the photoreceptor drum.
2. A voltage of 20V was applied between the drum and the sleeve, and the D-5 resistance of the ferrite carrier was determined from the flowing current value.

Development area conditions Copying speed: Photoreceptor drum rotation speed 16 tv/se
c Development development section resleeve rotation speed 2n / SeQ development magnet strength 1000 Gauss Ear cutting interval 1. OrErn Developing area: Both the photoreceptor and the developing sleeve were rotated clockwise, and the gap between D-5 was fixed at 5 mm.

Experiment The porous iron powder carrier from 1 to above was subjected to rotational agitation treatment under the conditions from 1 to above, and was taken out from the ball mill at regular intervals] 7. Measurement of D-5 resistance 12. Rotating mill agitation time and carrier resistance We investigated the relationship between changes.

The results are shown in Table 1.

As shown in Table 1, as the stirring by the rotary mill progresses, the carrier resistance value also rises, and the solution is almost hydrated at 12 oom.

In addition, the resistance reaches 1080 at 560 m1n, and it is thought that the oxidation of the developer, which causes resistance changes during copying when the developer is put into the actual machine, can be prevented, so it is sufficient to carry out the stirring process under the above conditions for 560 to 1200 minutes. I understand that.

During the main stirring process, the carrier resistance increases by 1, due to friction.
.

X-ray diffraction reveals that carriers 6, 1
An increase in oxides on the surface has been confirmed. from these things,
It is now possible to adjust carrier resistance 1 through non-heat treatment, and it is now possible to create carriers with high resistance, which could not be obtained with porous iron powder. The following copying test was conducted. As a copying device, a commercially available copying machine (DC-191 manufactured by Mita Kogyo Co., Ltd.) was used and set to the following conditions.
・ 1 ・1 ・ ・−15−・5・Pa・.

Photoreceptor: diameter 90ttanAl base and St 70μ
Light source for exposing the photoconductor deposited to a film thickness of 6 m: Halogen lamp Static neutralization light source: No. 2 blade cleaning method Main charging:
Corona charger (15.4&V applied) Transfer, charging: # (16.OKV applied) Close-up speed: Photoreceptor drum rotation speed 16 ryn/s
EC developing section Nisleeve rotation speed variable 23 (7n/sm,
Developing magnetic strength 11] [10 Gauss panicle incision interval 1.01 Developing area: Both the photoreceptor and the developing sleeve are rotated clockwise, and the gap between D-5 is fixed in the order of 1.5.

□Toner (1) Composition'□" , -", 1' 6- (1i) Preparation The mixture consisting of the above composition was thoroughly melted and mixed and dispersed in a heated three-roll mill, and then the kneaded product was taken out, cooled, and coarsely pulverized. The machine (Rotobrex cutting mill: manufactured by Alpine) was used to coarsely grind the sushi to the size of 2 pieces of sushi, and then an ultra high-speed jet mill (NlPP0NPNEUA (ATICMFCC)
(manufactured by LTD) to prepare a toner having a particle size of about 5 to 20 μm.

What should be noted here is that the toner is prepared by repeating classification until the content of fine particles of 5 μm or less becomes substantially zero (in terms of capacity) (hereinafter referred to as fine particle cut toner). This toner had a specific surface area of 4560a/1/f and a volume resistivity of 4.5×10+40(7).

Carrier: Iron powder carrier resistance value with center particle size of 40μm
One with 1 x 10' ohm and one with 2.9 x 10' ohm.

Mix the aforementioned toner and carrier in the ratio of specific surface area□.

The combined mixture is used as developer and 1. was used in the experiment.

In continuous copying tests, untreated powdered iron carriers
As the number of copies increases, the carrier surface becomes oxidized 2, as shown in Figure 2.
Since the resistance as a developer also increases as shown in FIG. 1, it becomes ineffective as a counter electrode, an edge effect occurs, and the image density decreases as shown in FIG.

However, a developer using a carrier that has a high resistance due to the agitation process in a rotary mill shows no change in resistance value during continuous copying (and no change in image density, as shown in Figures 1 and 2). The results were obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the number of copies and image density when a copying test was conducted using the carrier of the present invention and a carrier for comparison. FIG. 2 is a graph showing the relationship between the number of copies and the resistance value of a developer using a carrier of the present invention and a developer using a carrier for comparison.

Claims (2)

[Claims] (1) An iron powder carrier for a two-component developer, which is made of porous iron powder obtained by subjecting iron ore to a reduction-acid treatment, and has a resistance value of at least 1×10^8 Ω. . (2) A method for producing an iron powder carrier for a two-component developer, which comprises oxidizing porous iron powder obtained by reducing and oxidizing iron ore in a rotary mill.