JPH10293421A - Magnetic particle powder for magnetic toner and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic particle powder for a magnetic toner, having a negative polarity, a large charge amount, and excellent in dispersibility and wettability in a resin. SOLUTION: On the particle surface, iron (Fe) is replaced by silicon (S).
i) A magnetic particle powder for a magnetic toner to which 0.1 to 5.0% by weight of a silicon compound is attached and which has a charge amount of −60 to −10 μc / g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic particle powder for a magnetic toner used for one-component development such as an electrophotographic method, an electrostatic recording method and an electrostatic copying method, and a method for producing the same. More particularly, the present invention relates to a magnetic particle powder suitable for a magnetic toner used in a developing method using a digital latent image and a method for producing the same.

[0002]

2. Description of the Related Art In a conventional developing method of a dry copying machine such as an electrophotographic method, an electrostatic recording method, and an electrostatic copying machine, a magnetic toner having a positive polarity is widely used. I have. The reason why the one-component developing method using these dry copiers is widely used is that image reproducibility is good, maintenance is easy, density control is unnecessary, toner reinforcement is easy, compact and inexpensive developing. This is because the device can be made. In recent years, however, it has become particularly necessary to faithfully reproduce photographs (reproduction of halftones). For halftones expressed by differences in line density, if the line thickness is not always the same, fine line reproduction and gradation The sharpness of image quality, including tonality, resolution, image density, etc., becomes a problem. As a method that satisfies the above advanced requirements such as reproduction of gradation and resolution, and reproduces the same halftone stably,
The copier itself has been replaced with the conventional analog system, and one using a digital latent image has been developed, and the latent image has been written more minutely than ever. Laser printers (LBP) and digital printers (PP)
C) and the like. These are selenium (Se), amorphous silicon (a-Si), and a positively charged organic photoreceptor (OP
C) and the like, and since the surface polarity of these is positive, the magnetic toner used is a negative toner. However, the magnetic powder particles used in these magnetic toners generally have a positive polarity in many cases. In order to use them as raw materials for a negative magnetic toner, a charge control agent must be used in the production of the magnetic toner. In addition, there is a problem that the polarity and the strength (charge amount) of the magnetic toner must be controlled to be negative. In a general method of manufacturing a magnetic toner, a predetermined amount of a magnetic particle powder, a binder resin, a charge control agent, a colorant, and the like are mixed and melt-kneaded in a toner manufacturing process, and the resulting mass is dried and jet-milled. After pulverization (pulverization method) by a mechanical pulverization means such as described above, it is usual to classify the particles into particles having a predetermined particle size. At this time, in order to manufacture the negative magnetic toner, the polarity and the charge amount are controlled to appropriate values by using a charge control agent such as a metal complex salt or an azo dye.
However, the conventional magnetic toner has a particle shape and a surface state,
The properties of the powder surface and the interaction between the powders are regarded as problems. For example, in a state where the magnetic particle powder and the binder resin are kneaded, the wettability of the resin to the magnetic powder particles (the binding force between the magnetic particle powder and the resin) and the dispersion state in the resin are poor (aggregation). When pulverized by the above-mentioned pulverizing means, the magnetic particles are often separated and pulverized (destructive cutting) at the boundary between the surface of the magnetic particle powder and the part between the resins. Also,
If the magnetic powder is manufactured using magnetic particles having poor dispersibility and wettability in the resin, the filling rate of the magnetic powder material per magnetic toner particle is not uniform, and as a result, the magnetic action of the magnetic toner varies. And the disadvantage of deteriorating the developing characteristics. Furthermore, the fractured and cut surface of the magnetic toner pulverized by the pulverization method has severe irregularities, which deteriorates the fluidity of the magnetic toner. This causes lack of sharpness in image quality, including characteristics, resolution, copy density, and the like. Therefore, for the purpose of improving the fluidity of the magnetic toner, it is common practice to treat the pulverized magnetic toner in a hot air oven and melt the surface of the magnetic toner to form a spherical shape. . By performing such a process, the fluidity of the magnetic toner itself is improved, but since the magnetic toner is manufactured by controlling the polarity and the charge amount to appropriate values with a charge control agent, the dye as a charge control agent is used. The structure is complicated, poor in stability, the processing temperature conditions during heat kneading, mechanical shock, more decomposed or deteriorated such as friction, the phenomenon that the charge controllability is reduced, the outer part of the negative toner and Due to the large amount of the conventional positive magnetic particle powder on the surface portion and the unevenness of the thickness of the resin coating layer, the mixing ratio of the opposite polarity magnetic toner and the weakly charged toner particles increases. Further, it is known that the smaller the particle size, the more effective it is to improve the image quality and make the magnetic toner excellent in fine line reproducibility and gradation. It is necessary to further increase the mixing ratio of the oppositely-polarized magnetic toner and the weakly-charged toner particles. It is a major cause of lowering. Therefore, as a magnetic toner required to faithfully reproduce a photograph by a one-component developing method,
It can respond to the demand for fine latent images, fine line reproducibility and gradation with small particle size, and can respond to high speed, and can also meet severe demands for high performance such as high image quality and high quality. Research and development of magnetic toners having a small particle diameter and negative polarity have been intensively studied and developed, but none of them have been satisfactory.

[0003]

An object of the present invention is to provide a magnetic particle powder having a negative polarity, a large charge amount, and excellent dispersibility and wettability in a resin, and a method for producing the same.

[0004]

Means for Solving the Problems The present inventors have studied the interaction between powders, such as the particle shape and surface state, the dispersion state of the particles, and the properties of the powder surface, which are required for the negative polarity magnetic toner. Of the pH of sodium silicate, the amount of silicon (Si) attached, and the charging polarity, in order to solve the disadvantages of (1) and (2) to achieve the production of magnetic particle powder for magnetic toner having negative polarity. Has properties suitable for negative polarity magnetic toner, good wettability of resin to magnetic powder particles (binding force between magnetic particle powder and resin) and good dispersion state in resin,
The present inventors have found a method for producing a magnetic particle powder having a negative polarity, and have completed the present invention. That is, according to the present invention, 0.1 to 5.0% by weight of a silicon compound as silicon (Si) is attached to iron (Fe) on the particle surface, and the charge amount is −60 to −10 μc /.
g, a magnetic particle powder for a magnetic toner,
Further, after the magnetite (Fe ₃ O ₄ ) particle powder is converted into an alkaline suspension having a pH of 12 or more, a water-soluble silicon compound is added, and then the pH is adjusted to 8 or less, and the silicon compound is added to the surface of the magnetic particle powder. A method for producing magnetic particle powder for a magnetic toner, which is characterized in that the powder is attached. The silicon (Si) used in the present invention is used in the form of a silicon (Si) compound, for example, silicates such as Na ₂ SiO ₃ and Na ₂ SiO ₅ , hydroxides such as Si (OH) ₄ and SiO 2 Oxides such as _2, etc., can be mentioned, and are not particularly limited thereto, and may be any as long as they are water-soluble when the pH of the aqueous solution is 12 or more.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a magnetic particle powder according to the present invention will be described in detail. That is, generally, magnetic particle powder is obtained by mixing a ferrous salt aqueous solution and an alkaline aqueous solution while replacing the inside of a wet stirring oxidation reaction tank having a gas vent tube with nitrogen. After heating the suspension containing the iron colloid to 70-100 ° C, it is manufactured by switching from nitrogen to an oxygen-containing gas such as air, and blowing the gas, followed by filtration, washing, drying, crushing, etc. by a conventional method. It is manufactured through a process. The shape of the particles generated by such a wet reaction becomes an n-hedral, irregular, or spherical shape depending on the type and amount of the alkaline solution used for neutralization.

After completion of the reaction for forming magnetic particles by the above method, a water-soluble silicon compound (for example, sodium silicate (Na ₂ O.nSiO ₂ )) is added to an alkaline suspension having a pH of 12 or more.
After adding silicon (Si) in an amount of 0.1 to 5.0% by weight with respect to iron (Fe) and stirring and mixing for a while, the pH value of the target region (pH 8 or less, preferably By adjusting the pH to 5 or less and attaching a silicon component to the surface of the magnetic particles, the magnetic particles that normally should have positive polarity will exhibit negative polarity. If the pH is not adjusted to this region, the magnetic particles have positive polarity.
In order to increase the amount of negative charge of the magnetic particle powder obtained as described above, the amount of silicon on the surface of the magnetic particle powder may be increased. At this time, in order to increase the amount of silicon attached to the sodium silicate, sodium silicate is added to the alkaline suspension having a pH of 12 or more after the reaction, and the mixture is stirred and mixed for a while. Mn ²⁺ , Co ²⁺ , Zn ²⁺ , Ni
²⁺ , Mg ²⁺ , Cu ^2+, etc.), water-soluble pigment dispersant, coupling agent, etc., alone or in combination of two or more, and further stirred and mixed. Silicon may be co-precipitated and deposited on the surface of the magnetic particle powder by adjusting the pH value of the target region with an aqueous solution. Further, the amount of use thereof is not particularly limited. In this way, a silicon component is attached to the surface of the magnetic particle powder,
Thereafter, the product of the present invention is processed through a process such as filtration, washing, drying, and pulverization by a conventional method, and the produced magnetic particle powder becomes a magnetic particle powder having negative polarity.

The charge amount of the magnetic particle powder of the present invention is -60 to-
10 μc / g, preferably −50 to −15 μc / g,
Since it is more preferably −50 to −20 μc / g, when used for a magnetic toner, the outer portion and the surface portion of the magnetic toner have a negative charge polarity and are magnetic powders having a large charge amount. High developing characteristics can be continuously and stably obtained without increasing the polarity and weakly charged toner particles, and high-quality image characteristics can be obtained. In this case, the charge amount is-
If it is 10 μc / g or more, the desired charge amount cannot be obtained on the developer carrying member, the sharpness of the image is deteriorated from the beginning, and the image density is thin and fogged because the image density is lower than the appropriate range. . In addition, when it is less than −60 μc / g, the charge amount of the developer is accumulated by repeatedly performing image formation, and the charge amount of the developer is further increased. In particular, there is a problem that the image density gradually decreases in a low humidity and low temperature environment.

The method for measuring the charge amount of the magnetic particle powder of the present invention is as follows. That is, using a blow-off powder charge measuring device manufactured by Toshiba Chemical Company, first, Cu-
97.0g of ferrite carrier of Zn and 3.0g of magnetic particle powder
(Content 3%), and rotated at 110 rpm for 5 minutes. 0.2 g of the debbed mixture was weighed correctly, and nitrogen gas 1 kg / cm
The charge amount at 10 seconds and 30 seconds was measured at a pressure of ² .

In the state where the magnetic particle powder and the binder resin are kneaded, the magnetic powder is contained in an amount of 30 to 80% by weight based on the whole magnetic toner. If the wettability of the resin to the magnetic particle powder (the binding force between the magnetic particle powder and the resin) or the state of dispersion in the resin is poor, the magnetic toner characteristics are deteriorated as described above. The fluidity was measured with a powder tester manufactured by
It was converted to the weight per minute (g / min). However, since the fluidity is also higher than that of the conventional product, even if it is a small particle size toner that is required for higher performance and higher quality, Since no magnetic powder particles having a positive polarity are used inside the magnetic toner, the outer peripheral portion and the surface portion of the magnetic toner contain magnetic particles having a large negative charge and a large charge amount, and the resin coat layer Influences such as uneven thickness, processing temperature conditions during hot kneading of dyes as charge control agents, mechanical shock,
Decomposition or deterioration due to friction, etc., even if the phenomenon that the charge controllability decreases occurs, the manufacturing process management becomes easy because the mixing ratio of reverse polarity or weakly charged toner particles does not increase, and wettability and Because of the excellent dispersibility, the magnetic action of each magnetic toner becomes uniform. As a result, even if the content is increased, a clear copied image can be obtained without causing chargeability, image density, fog, and toner scattering. In addition, since magnetic toner can be made to have a small particle size,
Follows fine latent images, fine line reproducibility and gradation, and
It is possible to provide a magnetic toner that can cope with high speed and meet strict requirements such as high performance such as high image quality and high quality.

The dispersibility of the magnetic particles having negative polarity of the present invention in a resin and the evaluation of the magnetic toner were evaluated by the following methods. That is, 40 parts by weight of magnetic powder, 59 parts by weight of a polyester resin (manufactured by Kao Atlas Co., Ltd., molecular weight: about 5000) as a binder resin, and carbon black (Mitsubishi Chemical Corporation)
, MA-100), 1 part by weight, mixed thoroughly with a Henschel mixer, melt-kneaded with a heated twin-screw mixer, cooled and solidified, and then averaged with a jet mill type pulverizer and classifier. After obtaining a negative polarity magnetic toner having a thickness of 10 μm, the magnetic distribution of the magnetic toner was measured by the following brush scattering method using an improved development box of a commercially available one-component copying machine. did. With the brush scattering method, when the rotation speed of the mag roller is variably improved and the charge amount of the magnetic toner is fixed, the rotation speed is increased to increase the rotation speed so that the toner with a weak magnetic force (the content of the magnetic material is small)
Is blown off by centrifugal force. This is a method of measuring the dispersibility of the magnetic powder in the magnetic toner by measuring the amount of the toner and the magnetism of the toner.

In other words, the brush scattering method utilizes the fact that when the dispersibility of the magnetic powder particles in the resin is poor, the magnetic forces of the individual magnetic toners are different, so that the magnetic toner having a weak magnetic force is sputtered quickly. It is a measurement method. Further, the measurement of toner scattering is performed by PARTICLE COUNTER (K) manufactured by RION Corporation.
Attach the suction pipe of the (C-03 light scattering type particle counter) to the upper part of the two-component developing box, put the magnetic toner in the box, rotate the mag roller violently, and centrifugal force by the rotation causes the toner in the box to The dust particles were sucked from the scattering atmosphere, and the particle diameter and the number of the magnetic toner were measured. As a result, the amount of scattering (dust) of the magnetic toner was very small.

As a result of various measurements using the above measurement method, it was found that the magnetic particle powder of the present invention had a wettability with the resin (kneaded with the binder resin for magnetic toner). And the dispersion state in the resin is good.
The content and filling rate of the magnetic particles are uniform, and the magnetic toner has a small particle size but the opposite polarity, and the mixing ratio of the weakly charged toner particles is extremely small. Quality, copy quality, resolution,
Improve image quality characteristics, including image density, and
Since there is no toner scattering, problems such as an offset phenomenon and in-machine contamination can be prevented, and a clear copy image was obtained without deteriorating image characteristics.

Further, due to the demand for higher performance of magnetic toners used in various electrophotographic systems in recent years, the characteristics required of magnetic particles are those having good dispersibility (the toner characteristics are uniform). It is required that the saturation magnetization is large (good transportability of the magnetic toner), the residual magnetization is low (good transferability), and the blackness is large (good image density). Since the magnetic particle powder has a polyhedral shape (spherical shape), it has good dispersibility,
Magnetic particle powder having a small coercive force (Hc) due to small shape magnetic anisotropy, a small residual magnetization (σr) and a large saturation magnetization (σs). The particle size distribution of the body is preferably 0.5 μm or less, and if it exceeds 0.5 μm, the coercive force (Hc) becomes too small, and the remanence (σr) further decreases and the dispersibility is improved. If the content is decreased and the content of the magnetic particle powder is increased, poor fixing occurs, image quality and transferability deteriorate, and overall characteristics deteriorate. Therefore, it is preferably 0.4 to 0.15 μm,
Particularly preferably, the thickness is 0.3 to 0.20 μm. 0.15
If it is less than μm, the holding force (Hc) becomes too large,
As a result, the residual magnetization (σr) further increases, so that the magnetic particle powder easily agglomerates and becomes difficult to disperse in the binder resin. The resolution cannot be obtained. Further, when determining the particle size, it is necessary to set the particle size in an appropriate range that sufficiently satisfies the demand for high performance required for the one-component magnetic toner produced by each production.

[0014]

Hereinafter, a method for producing magnetic particle powder of the present invention will be described.
The present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. First, the method for producing the magnetic particle powder for a magnetic toner used in the present invention will be described in detail. First, pure water 4 was added while a nitrogen gas was passed through a 15-liter stirred oxidation reaction vessel having a gas vent tube.
Then, 1.23 liters of 3.33 mol / l aqueous solution of ferrous salt was added, and 2.8 liters of 2.0 mol / l aqueous sodium carbonate solution were added.After stirring and mixing for 30 minutes, 2.0 mol / l of caustic was added. Soda solution 2.
After adding 0 liter to make the whole liquid volume, 90 ° C with stirring
And air of 1 liter / min is aerated for 8 hours.
The resulting product was filtered, washed, dried and pulverized.

The shape of the magnetic powder particles was confirmed by a scanning electron microscope (SEM) photograph of Akashi Seisakusho Co., Ltd.
The number of particles on the surface of the particles was determined by measuring the number of each particle with a particle size of 100 in the enlarged photograph (the number of surfaces visible at this time was counted, and the back side was considered the same). After the SEM photograph is enlarged with a copy machine, a parallel line of a predetermined width is drawn, and the particle diameter (horizontal Feret diameter) of 150 particles on the line is visually measured, and the particle diameter is divided by the magnification. 0.23μm
The magnetic properties were measured using a vibrating sample magnetometer (Toei Kogyo VSH-1).
5KOe (Oersted)
Is 60 Oe (Oersted), the saturation magnetic flux density (σs) is 86.5 emu / g, and the residual magnetic flux density (σ
r) 5.5 emu / g. The specific surface area was 5.8 m ² / g as a result of measurement with a fully automatic surface area measuring device, Multi Soap, manufactured by Yuasa Ionics Co., Ltd.

Examples 1 to 4 A sodium silicate aqueous solution was added to a reaction-completed slurry solution having a polyhedral particle shape and a PH value of 12 or more, which was obtained by the reaction method described in detail in the method for producing magnetic particle powders in Examples. Was added to Fe ₃ O ₄ at 1.25: 2.5: 5.0: 10.0 wt%, and 15
The mixture was stirred and mixed for 0.5 min, and a 0.5 N aqueous hydrochloric acid solution was added to the above reaction vessel at a rate of 10 ml / min by a metering pump to adjust the pH to 8.0.
Table 1 shows the processing conditions and the evaluation results obtained by filtering, washing, drying, and pulverizing the sample adjusted to ~ 5.0, and examining the charge amount, electric resistance, and fluidity. As shown in Table 1, iron (F
It was confirmed that when the content of silicon (Si) increased with respect to e), the charge amount of the negative polarity increased.

Comparative Examples 1-2 The addition of the aqueous sodium silicate solution to the slurry slurry having a polyhedral particle shape and having a pH value of 12 or higher and used in Examples 1-4 was stopped, and the final pH values were adjusted to 8.0 and 5.0. As a result of performing the same treatment as described above, no negative polarity was exhibited.

Table 1 shows the processing conditions and evaluation results at this time.

[0019]

[Table 1]

Examples 5 to 9 An aqueous solution of sodium silicate was added to a slurry solution having a polyhedral particle shape having a pH value of 12 or more and having a polyhedral particle shape used in Examples 1 to _4, of which 2.5 wt% was added to Fe ₃ O ₄ , After stirring and mixing for 15 minutes, divalent metal ions (Mn ²⁺ , Co ²⁺ , Zn) are used for the purpose of increasing (coprecipitation) the amount of silicon attached to the sodium silicate.
²⁺ , Ni ²⁺ , Mg ²⁺ , Cu ^2+, etc.) and an aqueous solution of a pigment dispersant and a coupling agent, and further stirred and mixed for 15 minutes. The pH value was adjusted to 5.0 with a metering pump, and filtration, washing, drying, and pulverization were performed. As shown in Table 2, when a divalent metal ion or the like, a water-soluble pigment dispersant or a coupling agent is added, the content of silicon (Si) with respect to iron (Fe) tends to increase, and the charge amount It was also confirmed that it increased. Also,
Examples of the divalent metal ion source include sulfates, chlorides, and nitrates thereof.

Comparative Examples 3 and 4 In Examples 5 to 9 except that the addition of the aqueous solution of sodium silicate was stopped, the polarity of the magnetic particles was changed from positive to negative as a result of performing the same treatment as described above. Did not. Table 2 also shows the processing conditions at this time and the evaluation results. As shown in the above examples, in each of the reaction-completed slurry solutions, the sodium silicate aqueous solution was neutralized with hydrochloric acid to make the PH value an acidic side, and then filtered, washed, dried, and crushed, and the charge amount was measured. As a result, a magnetic particle powder exhibiting negative polarity is obtained. To increase the charge amount, it is sufficient to increase the amount of silicon in the outer portion and the surface portion of the magnetic particle powder. Silicon or a coupling agent may be added to coprecipitate silicon.

[0022]

[Table 2]

Claims (2)

[Claims] 1. The method according to claim 1, wherein the surface of the particle is made of silicon (S)
i) A magnetic particle powder for a magnetic toner, characterized in that 0.1 to 5.0% by weight of a silicon compound is adhered thereto and the charge amount is −60 to −10 μc / g. 2. After the magnetite particle powder is converted into an alkaline suspension having a pH of 12 or more, a water-soluble silicon compound is added, and then the pH is adjusted to 8 or less to adhere the silicon compound to the surface of the magnetic particle powder. A method for producing a magnetic particle powder for a magnetic toner, comprising: