JPS59228664A - Ferrite carrier for development in electrophotography - Google Patents

Abstract

PURPOSE:To reduce humidity dependency of electric resistance extremely by forming the carrier from ferrite particles having specified degree of pore volume. CONSTITUTION:Ferrite particles having <=2.0X10<-2>cm<3>/g pore volume are useful for a carrier for development in electrophotography. Soft ferrite of 1-3 spinel or 2-3 spinel type, magnetite (Fe3O4) or magnetite (gamma-Fe2O3) having above described pore volume may be useful, but(MO)100-x(Fe2O3)x (where x is >=42 mol%, more particulary, 42-90mol%)is preferred.

Description

[Detailed description of the invention] Background of the invention Technical field The present invention relates to a magnetic carrier for electrophotographic development.

More specifically, the present invention relates to a magnetic carrier used particularly in magnetic brush development.

Prior Art and Problems Conventionally, iron powder or so-called ferrite particles are used as they are as magnetic carriers for magnetic brush development for electrophotographic development, but these are coated with a resin before use.

By the way, such a magnetic carrier causes the toner to electrostatically adhere to the toner by frictionally charging the toner, and moves the toner onto the photoreceptor during development.

Therefore, the carrier is required to have uniform triboelectric charging properties and to uniformly pick up and deposit the toner.

In addition, it functions as one electrode in the developing area and serves to make the electric field uniform, and in order to obtain stable images with excellent gradation, the carrier itself has a resistance that depends on the applied voltage. It is required that the resistance be small and that the dependence of the electrical resistance on humidity be small.

Furthermore, in order to be compatible with various copying machines, it is necessary to be able to arbitrarily change the absolute value of the electrical resistance.

By the way, among commercially available carriers, most of the iron powder carriers have a resistance value of 10 6 Ω or less when 1 oov is applied. Furthermore, since an oxide film is formed on the surface, the dependence of the deflection on the applied voltage is extremely large.

For this reason, iron powder carriers are often used with their surfaces coated with a resin, which has the disadvantage that the absolute value of electrical resistance cannot be changed.

On the other hand, as carriers using ferrite particles, US Pat.
No. 29857 and the like disclose examples of soft ferrite particles that are not coated with a resin.

Carriers using these ferrite particles have lower electrical resistance than those coated with resin.
By changing the firing method, it can be changed within a considerable amount of variation.

However, there is a drawback that the electrical resistance is highly dependent on humidity, and the image becomes unstable as the surrounding environment changes.

II. OBJECTS OF THE INVENTION The main object of the present invention is to provide a ferrite carrier for electrophotographic development that exhibits extremely good characteristics, and in particular, has extremely low humidity dependence of electrical resistance.

Such objects are achieved by the invention described below.

That is, the present invention is a ferrite carrier for electrophotographic development characterized by comprising ferrite particles having a pore amount of 2, OX 10 = 7 g or less.

■Specific structure of the invention Hereinafter, a specific configuration of the present invention will be explained in detail.

The ferrite carrier for electrophotographic development of the present invention consists of ferrite particles.

The amount of pores in the ferrite particles is 2. OX 10-
Must be less than 2crn”7g.

When the amount of pores exceeds 2, OX IO "2 crn"/g, moisture is absorbed into the pores under high humidity, and the electrical resistance drops dramatically, making the humidity dependence of resistance critical for practical use. I can't drink sake anymore.

Note that the amount of pores may be measured by the usual mercury intrusion method.

In such a case, more favorable results can be obtained if the amount of pores is 7 g or less.

In addition, the above-mentioned U.S. Patent Nos. 3,839,029 and 391
Specifications such as No. 4181 and No. 392H57 do not disclose such a pore amount, and ferrite particles produced according to the disclosure in the examples of this specification have such a pore amount. It's not a thing.

The composition of ferrite particles having such a pore content may be various, including soft ferrite such as l-3 spinel and 2-3 spinel, magnetite (Fe304), etc.
, magnetite (γ-Fe203), or the like.

However, more preferred is that represented by the following formula.

(MO) (Fe203)x00-x In the above formula, X is 42 mol or more, particularly 42 to 90 mol%.

At this time, the absolute value of electrical resistance changes significantly depending on the firing conditions, and a favorable result is obtained.

In this case, when X is 46.0 to 55.0 mol%, the electrical resistance can be reduced to 1.0% by changing the firing conditions and composition.
05-10 varies within large fluctuations at 2Ω, giving even more favorable results.

Moreover, when X is 46.0 to 55.0 mol%, the voltage dependence of electrical resistance is extremely small, and it is suitable for various copying machines.
Images with excellent gradation can be obtained.

On the other hand, MO is one or more divalent or trivalent metal oxides.

In this case, the MO may be of various types known as soft ferrite, but it is particularly preferable that the main component is a divalent or trivalent metal oxide whose valence does not change.

This is because at this time, the voltage dependence of the electrical resistance becomes extremely small.

Examples of such metal oxides include NfO.

One or more of MgO, ZnO, Al2O3, and Ga203 (7) is suitable.

And especially Nip, NtO+ZnO.

MgO, MgO+ZnO, NiO+MgO.

NiO+ZnO+MgO is preferable.

In these cases, ZnO/NiO has a molar ratio of 0.2 to 3, O, MgO/Nio has a mole ratio of 0.2 to 3.0, and MgO/Zn The molar ratio of O is preferably 0.2 to 3.0.

Furthermore, in addition to these, a total of 8.0 mol% or less (7) range Nite, A1203, Ga203, and even Cub
, Coo, MnO, etc. may be contained.

Such ferrite particles have an average particle size of 10 to 200 gm, more preferably 50 to 150 gm.

If the average particle size is less than 10 pm, when mixed with toner to form a developer, its fluidity will be poor and it will also cause carrier attraction. In addition, the average particle size is 2001Lm
If the magnetic brush exceeds this value, the magnetic brush cannot be formed properly and cannot be put to practical use.

The average grain size of such ferrite particles is 1
It is preferable that it is 0 pLIIn or more.

At this time, moisture resistance is improved.

In addition, the average grain size is 10#Lm or more,
Moreover, more preferable results can be obtained when the particles are not single grains and the average grain size is 1/4 to 1/10 of the average particle diameter.

Such ferrite particles do not have a resin coating on their surfaces.

Such ferrite particles are 15-35, C/
It has a charge amount of g.

Further, its electrical resistance exhibits a value of about 10 6 to 10 12 Ω in the range of 100 to 100 OV, and is small during its fluctuation.

In this case, the measurement of the electrical resistance of the carrier is performed as follows, imitating the magnetic brush development method.

That is, the north pole and the south pole are opposed to each other with an inter-electrode gap of 7 mm. In this case, the surface magnetic flux density of the magnetic pole is 1500
Gauss, the area of the opposing magnetic poles is i.

The size shall be x30mm. Between these magnetic poles, there is an inter-electrode gap of 5 mm.
A non-magnetic parallel plate electrode was placed between the electrodes, and sample 2 was placed between the electrodes.
00mg and held by magnetic force. Then, the resistance may be measured using an insulation resistance meter or an ammeter.

Note that the saturation magnetization of the carrier is 40 to 80 emu
/g.

A magnetic carrier made of such ferrite particles is disclosed in US Pat. No. 3,839,029, Ibid. No. 14181, 39
It is manufactured according to a general procedure such as that described in No. 28857.

That is, first, a corresponding metal oxide is prepared.
Then, after pre-calcining at a predetermined temperature, it is pulverized.

Next, the molten clay and ordinary water are added to form a slurry using, for example, a ball mill, and if necessary, a dispersant, a binder, etc. are added.

Then, it is granulated and dried using a spray dryer.

After that, firing is performed in a predetermined firing atmosphere and firing temperature profile. Firing follows a conventional method.

However, in order to obtain the above amount of pores, (1) When pulverizing, the average particle size should be 1.27 hm or less. (2) When firing, the atmosphere in the heating section and the temperature rising rate must be adjusted. is necessary. Note that the permissible conditions for the atmosphere of the heating section and the heating rate can be easily determined experimentally.

Note that if the equilibrium oxygen partial pressure during firing is reduced, the resistance value is reduced. When the oxygen partial pressure of the firing atmosphere is continuously changed from air to nitrogen atmosphere, the resistance value of the particles changes continuously.

After the firing, the particles are crushed or dispersed and then classified to a desired particle size to produce the magnetic carrier of the present invention.

(2) Specific effects of the invention The magnetic carrier of the invention is combined with a toner to form a developer. In this case, there are no restrictions on the type of toner used and the toner concentration.

Further, in obtaining an electrostatic copy image, there are no particular limitations on the magnetic brush development method, photoreceptor, etc. used, and the electrostatic copy image can be obtained according to a known magnetic brush development method.

(2) Specific Effects of the Invention The magnetic carrier of the present invention has extremely low humidity dependence of electrical resistance, and provides extremely good image stability even when the surrounding environment changes.

Further, if the ferrite composition is of the above formula, the absolute value of the electrical resistance changes significantly depending on the firing conditions, and an optimal image can be obtained depending on various copying machines.

When the amount of Fe2O3 is 46.0 to 55.0 mol%, the dependence of electrical resistance on voltage becomes extremely small, and images with excellent gradation can be produced in various copying machines.

Furthermore, if MO is a divalent or trivalent metal oxide whose valence does not change, such effects will be further improved.

Furthermore, since there is no need to form a film on the surface, durability is also good.

Furthermore, the saturation magnetization is 35 e+w/g or more, and there is little occurrence of so-called carrier attraction, in which carrier adheres to the photoreceptor, or carrier scattering.

Furthermore, there is less toner sticking or adhesion phenomenon called spent, and the carrier is prevented from breaking or being damaged during agitation in the copying machine, resulting in extremely high durability and service life, and extremely less damage to the photoreceptor. It becomes less.

(2) Specific Examples of the Invention The present invention will now be explained in more detail with reference to specific examples.

Example I Nfo 20.5 mol%, ZnO” 30.0 mol%,
Various oxides were prepared so as to have a composition of 49.5 mol % of Fe203, and after calcining in air at 900'C for 2 hours, the mixture was pulverized.

Next, water was added so that the slurry concentration was 60%,
After adding an appropriate amount of a dispersant, the mixture was mixed in a ball mill for 3 hours to form a slurry, and an appropriate amount of a binder was added thereto.

This was granulated and dried using a spray dryer at a temperature of 150°C or higher.

The granules were fired in air or in a predetermined atmosphere using a batch furnace at the maximum temperature shown in Table 1.

Next, this was crushed and classified to obtain various ferrite particles with an average particle size of 60 JLm.

Each ferrite particle was subjected to X-ray diffraction and quantitative chemical analysis, and it was confirmed that it was a spinel structure having the above composition.

The amount of pores and average grain size of the various ferrites obtained are as follows.

455- Next, the electrical resistance of each of these ferrite particles at 30°C
The humidity dependence was measured.

The resistance was measured by magnetically holding 200 mg of particles between parallel plate electrodes spaced apart by 5 mm, and from the current measured with an ammeter.

The results are shown in Figure 1.

From the results shown in FIG. 1, the effects of the present invention are clear.

Example 2 Various oxides were mixed to have the composition shown in Table 2, and 900
After calcining in air for 2 hours, the mixture was pulverized to a predetermined particle size.

Next, water is added so that the slurry degree is 60%,
After adding an appropriate amount of a dispersant, the mixture was mixed in a ball mill for 3 hours to form a slurry, and an appropriate amount of a binder was added thereto.

This was granulated and dried using a spray dryer at a temperature of 150° C. or higher.

Each granule was fired at a maximum temperature of 1320° C. in air or in a predetermined nitrogen-air mixed atmosphere using a batch furnace.

Thereafter, it was crushed and classified to obtain a total of 16 types of ferrite particles with an average particle size of 60 pm.

When each of the obtained ferrite particles was subjected to X-ray diffraction and quantitative chemical analysis, it was confirmed that each particle had a spinel structure and a metal composition corresponding to the blending ratio in Table 2.

In addition, according to the above, ferrite particles having the composition shown in Table 2 were produced according to a known method.

Table 2 4.4024.030.046.0 5.5022.430.047.6 6.6021.530.048.5 7.7020.530.049.5 8.8018.030.052.0 9.9015 .030.055.0 These sample Nos. 4 to 9 and comparative sample No.
, 40-90, pore content, average grain size and R
The rate of change in resistance ΔR (%) when applying 10 OOV at H85% and RH30% is as shown in Table 3 below.

Table 3 41.0XlO' 12 50 5 0.9 12 45 6 1.3 10 60 7 0.4 18 30 8 0.9 14 45 9 0.8 13 40 40 2.4 B 85 50 4.6 4 95 60 3.0 5 95 70 2.8 5 90 80 2.6 5 90 90 2.5 7 80 From the results shown in Table 3, it can be seen that the ferrite carrier of the present invention has extremely low humidity dependence of electrical resistance. Recognize.

Then, 100 to 100O of each obtained ferrite particle
The resistance when V was applied was measured. The resistance was calculated by holding 200 mg of the sample magnetically between parallel plate electrodes spaced apart by 5III m, and from the current measured with an ammeter. The results of samples 4 to 9 are shown in solid lines in FIG. 2.

As a result, it can be seen that a ferrite carrier having an extremely small voltage dependence of resistance can be obtained in the range of 106 to 1O]2 Ω.

Furthermore, in the production of samples 4 to 9, the firing conditions were changed to 30'C! , the following values were obtained when the resistance was measured at 30% RH.

Table 4 Sample Resistance Change Width 4 1Q12~1O11 51011~109 6 1010~108 7 109~107 8 108~106 9108~105 From the results shown in Table 4, the ferrite carrier of the present invention can It can be seen that the absolute value of resistance changes significantly.

Comparative example NiO13,0-T=Nil, ZnO25 mol%, Fe2
Ferrite particles were obtained according to Example 2 by blending various oxides so as to have a composition of 2.0 mol % of O36.

In this case, the firing atmosphere was nitrogen or a nitrogen-air mixed atmosphere, and a total of 7 comparison samples, 21 to 27, were obtained.

The amount of pores in each of these samples lV, 21 to 27 is approximately 3
X 10-2 cm'/g.

The voltage dependence of the resistance measured in the same manner as in Example 2 for each of these samples No. 21 to 27 is shown in FIG. 2 by a broken line.

From the results shown in FIG. 2, the ferrite carriers of the present invention (No. 4 to 9) had a
It can be seen that the voltage dependence of resistance is much smaller than that of .

Example 3 According to Example 1.2, a ferrite carrier having the composition shown in Table 5 below was obtained.

These properties are shown in Table 5.

Note that Table 5 shows the rate of change in resistance (ΔR' C%) when tooV is applied and when 1000V is applied.

From the results shown in Table 5, the effects of the present invention are clear.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams for explaining the present invention in detail. Among them, FIG. 1 is a graph showing the dependence of resistance on applied voltage due to changes in humidity, and FIG. 2 is a graph showing the dependence of resistance on applied voltage as the resistance changes. Applicant TDC Co., Ltd. Agent Patent Attorney Yo Ishii - Fig. 2 1., to ~, 10 ゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゛゜゛゛゛゛゜゛゛゛゜゜゜゜゜゜゜゜ -0 -101 dimensions, ←゜−−− ε 搏 ゛Q, 0＼ Cao ゝ ~ku~ 10 ←Toko←→6→Nipah 81, 615, ? , ゛, 10゛, c2, -semi, 9, 8, ＼6〜 ゛・,. 11, ~゛-゛-゛--~ -1 ゛~-----. 10'>~, Henini,~Ni 泗N04 (Book or 1) No, 5 (Kai Mall) No, 2+ (Comparison) No, 6+ Munamachi No, 23 Cc Hishin Moxibustion) No, 24 (RT Hat No, 25 (Comparison) No. 9 () Mi → 9 To qn Procedural Amendment (Voluntary) July 29, 1982 1. Display of the case 5-7- ν>Nly Ferrite for electrophotographic development in 1975 Career 3: Relationship with the amended person's case Patent applicant's office
Nihonbashi-chome 13-1, Chuo-ku, Tokyo Name
(306) TDC Co., Ltd. Representative Kan Otoshi 4, Agent 171 Address 5-17-11 Nishiikebukuro, Toshima-ku, Tokyo
Goyabe Building 1st floor Telephone: 988-1680 "
2. Scope of Claims" column and "3. Detailed Description of the Invention j, Column 6, Contents of Amendment CI) 12. Scope of Claims" column of the specification will be amended as shown in the attached sheet. (II) The statement in column ``3. Detailed Description of the Invention j'' of the specification is amended as follows. 1) In the 6th line of page 10, rA1203. Ga203j is deleted. 2) No. 10 On page 17-18 lines, fA1203, G
It says a2O3 and even J, so I'll delete it. 3) Amend Table 3 on page 22 as follows. Table 3 Yang. (crn'/g) (#Lm) (%)4
1, 0X10-2 12 50 5 0, 9X10-2 12 45 6 1, 3X10-2 10 60 7 0, 4XIO-2 18 30 8 0, 9X10-2 14 45 9 0, 8XIO-2 13 40 40 2, 4X10-2 8 8550 4, 6X
IO-2 4 9560 3, 0XIO-25
95 7'0 2.8X10-2 5 9080 2, 6
XIO-2' 5 9090 2, 5XIO-2
7 89 and. Claim 1: The amount of pores is 2, O x 10-2 crn”
A ferrite carrier for electrophotographic development, characterized by comprising ferrite particles having a particle size of /g or less. 2. The ferrite particles are 1-3 spinel ferrite,
2-3 The ferrite carrier for electrophotographic development according to claim 1, which is spinel ferrite, magnetite, or magnetite. 3. The ferrite carrier for electrophotographic development according to claim 2, wherein the ferrite particles have a composition represented by the following formula in terms of divalent metal oxide or trivalent metal oxide. (Formula % Formula %) (In the above formula, MO is one or more types of divalent or trivalent metal oxides. Also, X is 42.0 mol% or more.) 4, X
The ferrite carrier for electrophotographic development according to claim 3, wherein is 42 to 90 mol%. 5. The ferrite carrier for electrophotographic development according to claim 4, wherein x is 46.0 to 55.0 mol%. 6. The ferrite carrier for electrophotographic development according to claim 3 or 5, wherein the MO is a divalent or trivalent metal oxide whose valence does not change. 7. The ferrite carrier for electrophotographic development according to claim 6, wherein the MO is one or more of Ni01ZnO and MgO. 8. MO is Nip, NiO and ZnOlMgO
, MgO and ZnO1NiO and MgO5NiO and MgO and ZnO1 or one of these, Cub, Co
8. The ferrite carrier for electrophotographic development according to claim 7, which is an oxide in combination with one or more of MnO and MnO. 9. The ferrite carrier for electrophotographic development according to any one of claims 1 to 8, wherein the pore amount is I x 10'cm'/g. 10. The average particle size of the ferrite particles is lo~200
The ferrite carrier for electrophotographic development according to any one of claims 1 to 9, which is uLm. 11. The average grain size of the ferrite particles is 1
A ferrite carrier for electrophotographic development according to any one of Items 1, 1, and 10 of Claims, wherein the ferrite carrier has a particle diameter of 0 μrn or more. 12. The ferrite carrier for electrophotographic development according to any one of claims 1 to 11, wherein the ferrite particles have no resin coating on their surfaces.

Claims (1)

[Scope of Claims] 1. A ferrite carrier for electrophotographic development, characterized by comprising ferrite particles having a pore content of 2. OX 10"2 cm'/g or less. 2. The ferrite particles are 1-3 spinel ferrite,
2-3 The ferrite carrier for electrophotographic development according to claim 1, which is spinel ferrite, magnetite, or magnetite. 3. The ferrite carrier for electrophotographic development according to claim 2, wherein the ferrite particles have a composition represented by the following formula in terms of divalent metal oxide or trivalent metal oxide. (MO) (F e2 o3 ). 100-! (In the above formula, MO is one or more divalent or trivalent metal oxides. Also, X is 42.0 mol% or more.) 4.
The ferrite carrier for electrophotographic development according to claim 3, wherein is 42 to 90 mol%. 5. The ferrite carrier for electrophotographic development according to claim 4, wherein X is 46,0 to 55,0 mol%. 6. The ferrite carrier for electrophotographic development according to claim 3 or 5, wherein the MO is a divalent or trivalent metal oxide whose valence does not change. 7. MO is Nip, ZnO, MgO1A120
7. The ferrite carrier for electrophotographic development according to claim 6, characterized by one or more of Ga2O3 and Ga2O3. 8. MO is Nip, NiO and ZnO2MgO
, MgO and ZnO, NiO and MgO1NiO, MgO and ZnO1 or one of these, and Al2O
3. The ferrite carrier for electrophotographic development according to claim 7, which is an oxide in combination with one or more of Ga2O3, Cub, Coo, and MnO. 9. The ferrite carrier for electrophotographic development according to any one of claims 1 to 8, which has a pore amount of l x 10-2 cm'/g. 10. The average particle size of the ferrite particles is 10 to 200
The ferrite carrier for electrophotographic development according to any one of claims 1 to 9, which is GM. 11. The average grain size of ferrite particles is lop
The ferrite carrier for electrophotographic development according to any one of claims 1 to 10, wherein the ferrite carrier is at least m. 12. The ferrite carrier for electrophotographic development according to any one of claims 1 to 11, wherein the ferrite particles have no resin coating on their surfaces.