JP3157066B2 - Method for adjusting static resistance of carrier for electrophotographic development - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for arbitrarily adjusting the static resistance of a ferrite carrier in a carrier for electrophotography, particularly in a two-component developer.

[0002]

2. Description of the Related Art Among electrophotographic image forming methods for forming and developing an image on the surface of a photoconductive material by electrostatic means, a so-called magnetic brush developing method is disclosed in U.S. Pat. No. 2,874,063.
As described in the above document, a developer consisting of toner and magnetic carrier particles is arranged like a brush, and the magnetic brush is brought into contact with an electrostatic image supporting surface to cause the toner particles to move from the brush to the latent image by electrostatic force. A visible image is formed by the attraction, and the visible image is transferred to paper or another support, and then fixed by heat or the like to complete the process.

As a carrier material used in the magnetic brush method, a material exhibiting ferromagnetism, for example, magnetite,
Various types such as iron powder, alloys containing the elements Co and Ni, and ferrite have been proposed, but ferrite has now become the mainstream.

The one proposed in US Pat. No. 3,929,657 is one of the important ferrite carriers which does not need to be provided with a coating layer of resin or the like to stabilize against humidity.

[0005]

Ferrite carrier of the invention It is an object of said US patent is to set the theoretical stoichiometry near the (MO) and (Fe 2 _{O 3).} For this reason, it has been found that the resistance value itself is high, the obtained image density is low, and the gradation change rate is low.

In order to improve this problem, Japanese Patent Publication No. Sho 62-377
Japanese Patent No. 82 discloses a treatment method in which (Fe ₂ O ₃ ) is set to 54 mol% or more, and furthermore, the resistance value is continuously lowered by adjusting the atmosphere during firing.
This teaches that an arbitrary image can be obtained. However, when (Fe ₂ O ₃ ) is set to 54 mol% or more, it has been found that carrier properties become unstable with respect to humidity, and as a result, a stable image cannot be obtained without resin coating. Further, it is unavoidable that the production cost is high due to the adjustment of the firing atmosphere.

An object of the present invention is to solve such a problem of the prior art and to provide a new processing method capable of arbitrarily adjusting the resistance value of an electrophotographic developing carrier.

[0008]

According to the present invention, a soft ferrite represented by the general formula (MO) _100-X (Fe ₂ O ₃ ) _X is provided.
Particles (where M is Cu, Zn, Fe, Co, N
i, Mn, one or two or more divalent metal element selected from Cd, X is an arbitrary number less than 40 or more 100 and preferably of representative) of any number in the range of 45 to 70 its
The carrier for electrophotographic development used without providing a resin coating layer on the surface of the substrate has a static resistance value of 10 ⁶ Ω ·
As a means for adjusting to an arbitrary value from cm to 10 ¹² Ω · cm , the content of phosphorus or phosphorus oxide in the ferrite is adjusted.
The present invention provides a method for adjusting the static resistance of a ferrite carrier for electrophotographic development without a resin coating layer , comprising the steps of:

[0009] Alternatively, As ₂ O ₃ or Sb ₂ O ₃ may be used instead of or in addition to the above-mentioned phosphorus or phosphorus oxide.
The present invention provides a method for adjusting the static resistance of a ferrite carrier for electrophotographic development, wherein the method is used as a static resistance adjusting means.

[0010]

The soft ferrite represented by the above general formula has P
It has been found that the addition of P has the effect of reducing the static resistance of the ferrite according to the amount of P added. That is, in order to obtain an intended static resistance value, it is sufficient to add an amount of P corresponding thereto. A similar effect is seen in P ₂ O ₅ and As
It was found that it was also found in ₂ O ₃ and Sb ₂ O ₃ .

Therefore, according to the present invention, for example, (Fe
_{Even if 2} O ₃ ) is a soft ferrite that is stable to a humidity of less than 54 mol% (even if X in the formula is less than 54), it can be freely adjusted to an intended static resistance value. For this reason, it is not necessary to secure stability against humidity by resin coating, and a soft ferrite having a low static resistance value can be provided without resin coating. Therefore, the present invention is particularly useful for soft ferrites in which the value of X in the formula is 40 or more and less than 54, more preferably 45 or more and less than 54.

Also, These P, P ₂ O ₅ , As ₂ O ₃ ,
When an appropriate amount of Sb ₂ O ₃ is added to ferrite, the effect of increasing the impact resistance of the ferrite particles is also exerted.

Japanese Unexamined Patent Publication No. 60-227265 discloses an oxide of an element belonging to Group V of the periodic table, such as phosphorus oxide, arsenic oxide, antimony oxide, bismuth oxide or vanadium oxide in a ferrite carrier material having a specific composition. It is described that spherical particles having a smooth surface can be obtained by adding a compound such as the above. The publication also discloses the electrical resistivity when these oxides are added. However, it is no exaggeration to say that there is almost no change in this data compared to the case where no additive was added. As shown in the examples below, the present inventor has found that a drastic decrease in the static resistance value which is completely unexpected or unexpected from the contents of this publication is caused by adjusting the P content (furthermore, Is P ₂ O ₅ , As
Control of the content of ₂ O ₃ and Sb ₂ O ₃ ).

According to the present invention, the static resistance value of the ferrite carrier can be freely and arbitrarily adjusted to a desired value.
This means that a carrier material having the most appropriate static resistance value can be obtained according to the characteristics of the electrophotographic developing machine (copy machine). That is, in order to obtain a good image, a carrier having a static resistance value matching the model is required. According to the present invention, the requirement corresponding to this model can be satisfied without resin coating.

The electrophotographic carrier to which the method of the present invention can be applied is a soft ferrite particle represented by the general formula (MO) _100-X (Fe ₂ O ₃ ) _X (where M is a divalent metal capable of forming soft ferrite) X represents an arbitrary number of 40 or more and less than 100). Cu, Zn, F as divalent metal elements
e, Co, Ni, Mn, Cd and the like . These elements may exist in combination. The value of X, ie, (Fe ₂ O
The mole% of ₃ ) is preferably 40 or more and less than 100,
More preferably, it is 45 or more and less than 70. When X is less than 40, the saturation magnetization decreases, carrier scattering increases, and the raw material cost increases.

The amount of P added for adjusting the static resistance value (further, the amount of P ₂ O ₅ , As ₂ O ₃ , and Sb ₂ O ₃ ) is 0.05 to 5.00% by weight in total, and is more preferably. 0.1 ~
The amount is in the range of 2.0% by weight, and if the amount of addition is increased in this range, the static resistance value continuously decreases according to the increase. If it is less than 0.05% by weight, the effect of lowering the static resistance is small, and if it exceeds 5.00% by weight, the saturation magnetization is reduced and carrier scattering is increased. The adjustment range of the static resistance value varies depending on the composition of the target ferrite, but can range from 10 ⁶ to 10 ¹² Ω · cm at an applied voltage of 100 V.

The carrier particles of the present invention usually have a particle size of 20 to 200.
It has an average particle size of μm and is used without resin coating within the above-mentioned range of static resistance. Static resistance value is 10 ⁶ Ω · c
m, the resolution decreases, and when it exceeds 10 ¹² Ω · cm, the image density decreases. Further, the saturation magnetization .sigma.s of the carrier particles of the present invention is preferably 45 emu / g or more. If it is less than 45 emu / g, a carrier pulling phenomenon in which the carrier adheres to the photosensitive member appears. Of course, the carrier of the present invention may be used after being coated with a resin for the purpose of charge control or the like.

The carrier of the present invention can be manufactured by a general process as described in the aforementioned US Pat. No. 3,929,657. That is, the ferrite component and water are mixed, and a binder and a dispersant are added as necessary.
Then, the mixture is granulated and dried by a spray dryer and classified to a required particle size. Further, firing is performed at a predetermined firing temperature. At this time, the oxygen concentration in the furnace may be the same as the atmosphere. The cake after baking is crushed by a hammer mill or the like, classified into a desired particle size, and used as a carrier.

[0019]

[Example 1] The mixing ratio of Fe ₂ O ₃ = 53 mol% and CuO = 23.5
P was added in an amount of 0, 0.2, 2.0, and 5.0% by weight, respectively, to those having mol% and ZnO of 23.5 mol% to prepare four kinds of compositions. Add 1% binder and water to each 6
After a slurry having a concentration of 0% was obtained, the slurry was pulverized with a wet ball mill and dried with an average particle size of 80 μm using a spray drier. Then, in a firing furnace at 1150 ° C under the atmosphere
And sieved to obtain ferrite particles having an average particle size of 70 μm.

Table 1 shows the physical properties of each ferrite particle. The saturation magnetization was measured by a DC magnetization characteristic measuring device (manufactured by Yokogawa Electric Corporation). The static resistance value was obtained by measuring the resistance when 100 V was applied to 5 g of the sample using an insulation resistance meter. As for the crushing rate, a sample from which 45 μm or less had been removed in advance was placed in a crushing tester (manufactured by Kyoritsu Riko), and after 15 seconds of operation, the occurrence rate of 45 μm or less was measured. The lower the crushing rate, the higher the particle strength.

[0021]

[Table 1]

From the results shown in Table 1, it can be seen that as the amount of P added increases, the static resistance sharply decreases even though there is no large change in the saturation magnetization. In addition, the crushing rate is reduced and the strength is remarkably improved. Therefore, if the relationship between the amount of P added to the ferrite particles and the static resistance value is grasped in advance, the ferrite particles having the intended static resistance value can be obtained by adjusting the P content by using this correlation. Can be.

Each ferrite particle was used as a developing carrier for a general-purpose copier manufactured by Company A and subjected to a real copying test under the conditions of 20 ° C. and 60 RH%.
The 5.0% carrier provided a high-density image.
The carrier having a content of 0% resulted in an image having a low density. In addition, the same actual shooting test was performed at 30 ° C. at 10 ° C. and 85% at 30 ° C.
When the test was carried out while changing the condition of RH%, the P content was 0.1%.
Similar images were obtained for the samples with 2, 2.0 and 5.0%.
This indicates that the carrier material of the present invention is stable against changes in temperature and humidity.

Example 2 P ₂ O ₅ was added in a proportion of Fe ₂ O ₃ = 50 mol%, CuO = 25 mol%, ZnO = 25 mol%, and P ₂ O ₅ was 0, 0.2, ₂ .. Four compositions were prepared by adding 0.5% by weight. After adding 1% of a binder and water to each to obtain a slurry having a concentration of about 60%, dried particles having an average particle diameter of 80 μm were obtained by a spray dryer. Then, the resultant was fired in a firing furnace at 1115 ° C. in the air atmosphere, and then sieved to obtain ferrite particles having an average particle diameter of 70 μm.

The physical properties of each ferrite particle were measured in the same manner as in Example 1, and the results shown in Table 2 were obtained.

[0026]

[Table 2]

From the results shown in Table 2, it can be seen that the static resistance value of the ferrite particles can be arbitrarily adjusted by adjusting the P ₂ O ₅ content. Further, a real-photographing test was performed using the same copying machine under the same temperature and humidity conditions as in Example 1, but the P ₂ O ₅ content was 0.2, 2.0, and 5.0 irrespective of the fluctuation of the temperature and humidity conditions.
% Carrier resulted in a high density image, but P ₂ O ₅
The carrier having a content of 0% resulted in an image having a low density.

Example 3 The mixing ratio of Fe ₂ O ₃ = 63 mol%, MnO = 20.0
Mol%, ZnO = 17.0 mol%, As ₂ O ₃
Was added at 0, 0.2, 2.0, and 5.0% by weight, respectively, to prepare four types of compositions. After adding 1% of a binder and water to each to make a slurry of 60% concentration, it was pulverized by a wet ball mill and dried by a spray drier to obtain dried particles having an average particle diameter of 80 μm. Then, in a firing furnace under atmospheric air 1
After calcination at 200 ° C, sieving and sieving were carried out to obtain an average particle size of 7
0 μm ferrite particles were obtained.

The physical properties of each ferrite particle were measured in the same manner as in Example 1, and the results shown in Table 3 were obtained.

[0030]

[Table 3]

From the results shown in Table 3, it can be seen that the static resistance value of the ferrite particles can be arbitrarily adjusted by adjusting the As ₂ O ₃ content. In addition, a real-photographing test was performed using the same copying machine while changing the temperature and humidity conditions in the same manner as in Example 1, but the As ₂ O ₃ content was 0.2,
The 2.0 and 5.0% carriers produced high density images, while the 0% As ₂ O ₃ carrier produced low density images.

[0032]

[0033]

[0034]

[0035]

[0036]

As described above, according to the present invention, it is possible to easily adjust the static resistance value of an electrophotographic developing carrier comprising soft ferrite particles to an arbitrary value. Moreover, the adjustment of the static resistance value according to the method of the present invention can be performed irrespective of the composition of the soft ferrite, in particular, the mol% of Fe ₂ O ₃ .
It is extremely practical and versatile as compared with the conventional method of changing the composition or changing the firing conditions. For this reason, for example, even for a composition having the highest stability to temperature and humidity (which generally has a high static resistance value), the conventional method of freely adjusting (decreasing) the static resistance value cannot be achieved by the conventional method. The effect is achieved.

Further, when the static resistance is reduced according to the method of the present invention, the crushing rate of the carrier particles is reduced and the strength is improved. Is also advantageous in that it does not affect

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-227265 (JP, A) JP-A-6-110253 (JP, A) JP-A-56-154743 (JP, A) JP-A-63-1988 184764 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 9/107

Claims (4)

(57) [Claims] 1. Soft ferrite particles represented by the general formula (MO) _100-X (Fe ₂ O ₃ ) _X (where M is Cu,
Kind selected from Zn, Fe, Co, Ni, Mn, Cd
Or two or more divalent metal elements, X is 40 or more and 100 or more.
And represents a resin coating on the surface
The carrier for electrophotographic development used without a layer has a static resistance of 10 ⁶ Ω · cm to 10 ¹² Ω when a voltage of 100 V is applied.
A method for adjusting the static resistance of a ferrite carrier for electrophotographic development without a resin coating layer , comprising adjusting the content of phosphorus or phosphorus oxide in the ferrite as a means for adjusting the ferrite carrier to an arbitrary value up to cm. 2. The method according to claim 1, wherein the content of phosphorus or phosphorus oxide is adjusted in the range of 0.05 to 5.00% by weight. _3. Soft ferrite particles represented by the general formula (MO) _100-X (Fe ₂ O ₃ ) _X (where M is Cu,
Kind selected from Zn, Fe, Co, Ni, Mn, Cd
Or two or more divalent metal elements, X is 40 or more and 100 or more.
And represents a resin coating on the surface
The carrier for electrophotographic development used without a layer has a static resistance of 10 ⁶ Ω · cm to 10 ¹² Ω when a voltage of 100 V is applied.
The static resistance of a ferrite carrier for electrophotographic development without a resin coating layer , which comprises adjusting the content of As ₂ O ₃ or Sb ₂ O _{3 in} the ferrite as a means for adjusting to an arbitrary value up to cm. Adjustment method. 4. The content of As ₂ O ₃ or Sb ₂ O ₃ is from 0.05 to
The method according to claim 3, wherein the static resistance is adjusted in the range of 5.00% by weight.