JPH08254854A - Magnetic powder for magnetic toner - Google Patents

Abstract

PURPOSE: To obtain magnetic powder excellent in dispersibility in a resin and uniformity of magnetic action by each of toner particles by coating the surface of magnetic powder with a specified wt.% of a titanium coupling agent in regard to the amt. of the magnetic powder. CONSTITUTION: The surfaces of the particles of a powdery magnetic material are coated with a titanium coupling agent to improve the dispersibility of the magnetic material in a bonding resin. The magnetic material used may be polyhedral magnetite as magnetic particles produced by a wet reaction. The produced magnetite particles are post-treated by filtration, washing and dehydration to 30-40% water content by the conventional method, a prescribed amt. of the resultant cake as starting material is put into a mixing-kneading machine and 0.01-5.0wt.% titanium coupling agent is added in accordance with the specific surface area of the particles. They are kneaded, taken out and dried to obtain the objective magnetic powder for a magnetic toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to dispersibility in a binder resin, which is particularly required in the production of small particle size toners for electrophotography, electrostatic recording, electrostatic copying machines and laser printers.
The present invention relates to a magnetic powder for a magnetic toner having excellent uniformity of magnetic action of each toner.

[0002]

2. Description of the Related Art In recent years, a developing method using a one-component magnetic toner has been widely adopted. The reason is that the one-component developing method does not use a carrier, so the device is simpler and adjustment is easier, only the additional supply of magnetic toner is required, and the developing unit is simple. This is because the labor required for the device can be reduced, the device can be made lightweight, the cost can be reduced, and the energy saving of copying can be achieved. Further, with the demand for higher performance and higher quality such as downsizing of the copying machine itself, higher speed of copying, and higher image quality, there is a strong demand for improvement of the characteristics of the toner itself.
The current situation is that no sufficient improvements have been made yet. Generally, a magnetic toner in a one-component developing system is prepared by mixing a predetermined amount of magnetic powder, a binder resin, a charge control agent, a coloring agent, etc.,
It is usual that a lump obtained by melt-kneading is dried, crushed by a mechanical crushing means such as a jet mill, and classified into particles having a predetermined particle size for production. At this time, it is most important for a good toner that the filling rate of the magnetic powder material per magnetic toner is uniform, and if the dispersion of the magnetic powder in the binder resin is poor, the magnetic powder in the magnetic toner is The filling rate is not uniform, and as a result, the magnetic action of each magnetic toner varies, which adversely affects the charge amount, weak charging or reverse polarity occurs, and the developability in the developing region is deteriorated. Further, if the filling rate is not uniform, it may cause coloring unevenness of the image density. In particular, when the toner particle size is made finer with the demand for higher performance and higher quality, dispersion in the binder resin is important, and it is particularly necessary that the magnetic action of each magnetic toner is uniform. Is. Further, in order to increase the speed of copying, it is necessary to fix the magnetic toner to the paper at the lowest possible temperature and quickly. until now,
High-viscosity polymer binder resin was generally used as the resin for the production of magnetic toners, but low-viscosity binder resin with low viscosity tends to be used more frequently as the copy performance becomes higher. Therefore, when the binder resin and the magnetic powder are kneaded, if the viscosity of the resin is high, the mechanical share will be strong, and the dispersion of the magnetic powder will be supplementarily strengthened. The magnetic share is weak, it becomes difficult to disperse the magnetic powder, and the toner is manufactured in the state of being aggregated, so the magnetic action of each magnetic toner becomes uneven, making it difficult to improve the performance and quality of copy image quality. Become.

[0003]

DISCLOSURE OF THE INVENTION The object of the present invention is to provide a magnetic powder material having excellent dispersibility in a resin and uniformity of magnetic action by individual toners, which are important problems in response to the demand for improvement of magnetic toner characteristics. Another object is to provide a magnetic powder for a magnetic toner.

[0004]

Conventionally, as a method for producing magnetic powder for magnetic toner, generally, there are a dry reaction and a wet reaction. In the case of dry reaction, iron oxide is usually used with hydrogen gas.
A general method is to obtain ferric tetroxide by reduction at 250 to 500 ° C. In the case of a wet reaction, it contains a ferrous hydroxide colloid obtained by the reaction between an aqueous ferrous salt solution and an aqueous alkaline solution. A suspension is produced by blowing an oxidizing gas such as air in a temperature range of 70 ° C or higher and 100 ° C or lower, and then filtration,
The product is manufactured through processes such as washing, drying and crushing. In order to improve the dispersibility in the binder resin without deteriorating the properties of the magnetic powder for magnetic toner thus formed, the present invention uses a titanium-based coupling agent on the particle surface of the magnetic powder material. It is coated to improve the dispersibility of the magnetic powder material in the binder resin.

The magnetic powder for magnetic toner of the present invention improves the dispersibility without being affected by the mechanical share due to the viscosity of the binder resin, and makes the filling rate of each magnetic toner particle uniform, and further, the magnetic powder. The adhesive force between the resin and the binder resin is strong, and even during mechanical crushing, there is no separation and cutting at the boundary of the magnetic powder part and the part between the resins, so the magnetic powder does not fly out to the surface of the magnetic toner. Not able to make magnetic toner. When the dispersibility of the magnetic powder itself in the resin is improved, the magnetic action of each toner does not change even if the toner has a small particle size in accordance with the demand for higher performance and higher quality. A clear copy image can be obtained without causing fog or toner scattering.

Examples of the magnetic powder particles used in the present invention include the magnetic powder particles produced by the above-mentioned wet reaction.
An example is polyhedral magnetite. As a post-treatment of reaction-generated magnetite particles, filtration by a usual method,
Using the cake after washing and dehydration (water content: 30-40%) as a raw material, put a predetermined amount in a mixing and kneading machine, and depending on the specific surface area of the magnetic powder particles, 0.01 to 5.0% by weight titanium-based cup. A magnetic powder for a magnetic toner of the present invention can be obtained by adding a ring agent (general formula C ₁₅ H ₄₀ N ₆ O ₄ Ti or C ₈₇ H ₁₁₂ O ₇ Ti), kneading, taking out and drying. At this time, if the addition amount of the coupling agent is less than 0.01% by weight, the surface of the magnetite cannot be uniformly coated, so the desired effect is small. It does not adversely affect the characteristics, but it is not economical. In such a treatment method, it is a general treatment method to dissolve the coupling agent in a solvent in the usual case and add it to the dry magnetic powder product.
Although the magnetic powder of the present invention can be obtained by such a method, the method as described above is preferable. This is because, in the case of the general method, the number of processes requiring heating and re-assembling equipment for the solvent is increased, and the equipment for recovering the solvent and the heating device are required, whereas in the case of the method as described above, the organic solvent is used. This is because without doing so, it is possible to easily obtain a magnetic powder material which is well dispersed and familiar in the magnetic material powder and the binder resin, without a troublesome process and at a low-cost manufacturing facility. Incidentally, the surface treatment with water glass or a silane coupling agent can also improve the dispersion and familiarity between the magnetic powder material and the binder resin, but it should be sufficient to satisfy the intended purpose of the present invention. Don't

The magnetite used in the magnetic toner using the magnetic powder according to the present invention is not particularly limited, but generally has an average particle size of 0.1 μm to 0.7 μm,
The particles are polyhedral particles having a surface number of at least 10 and a specific surface area of 3 to 40 m / g, and are so-called spherical magnetic powders for magnetic toners. This magnetic powder, styrene-acrylic or polyester-based binder resin, and carbon are mixed together in a Henschel mixer, then melt-kneaded in a twin-screw mixer by a conventional method, and then dried. With a machine, a magnetic toner having an average particle size of about 10 μm can be obtained.

[0008]

EXAMPLES The present invention will be described in more detail with reference to the following examples and comparative examples. Reference Example 1 (Production of Polyhedral Magnetite Particles) Pure water 4 while nitrogen gas was passed through a container having a volume of 15 liters
1 liter, add 1.23 liter of 3.33 mol / liter ferrous chloride aqueous solution, then add 2.8 liter of 2.0 mol / liter sodium carbonate aqueous solution, stir and mix for 30 minutes, and then add 2.0 mol / liter caustic soda. Add 2 liters of the aqueous solution to make the total volume, then stir at 90 ° C.
The temperature was raised to 1, and 1 liter / min of air was aerated for 8 hours, and the resulting product was filtered, washed with water, and dried. The obtained product has an average particle size of 0.25 μm and magnetic properties of coercive force of 63
0e, saturation magnetization 86.0emu / g, residual magnetization 7.5emu / g (5KOe)
It was a polyhedral magnetite particle having a specific surface area of 6.1 m ² / g and a particle surface number of 10 or more. Examples 1 to 6 100 g of polyhedral magnetite manufactured as described above (water content: 35%) was charged into a 1 liter kneader and stirred for about 2 minutes, and then a titanium-based coupling agent KR- manufactured by Ajinomoto Co., Inc. ET (general formula C ₅₇ H ₁₁₂ O ₇ Ti) or KR-44 (general formula
C ₁₅ H ₄₀ N ₅ O ₄ Ti) was added in an amount shown in Table 1, mixed and stirred for 5 minutes, taken out, dried at 110 ° C. for 8 hours, and then pulverized with a pulverizer to prepare magnetic powder. Comparative Examples 1 to 3 When the amount of the titanium-based coupling agent was outside the scope of the present invention (Comparative Example 1), and instead of the titanium-based coupling agent, a silane coupling agent (manufactured by Toray Dow Corning Silicone Co., Ltd., Product name SII-6020, (general formula C ₈ H ₂₂ N ₂ O ₅ S
i)) or sodium silicate (manufactured by Fuji Chemical Co., Ltd., product name KD-
Examples 1 to 6 except that 1, (general formula Na ₂ SiO ₃ )) was used.
A magnetic powder was prepared in the same manner as in. For these, various physical properties were evaluated. The results are shown in Table 1. The liquidity evaluation method is as follows. The fluidity of magnetic particle powder is
As pretreatment, the magnetic particle powder pulverized by a pulverizer such as a pulverizer was measured and evaluated by a powder tester device manufactured by Hosokawa Micron Co., Ltd. That is, 30 g of the classified magnetic particle powder was put into a 60-mesh sieve, a stainless funnel was fixed under the sieve, and a constant vibration (amplitude 1 mm) was applied to the sieve. The drop weight of the above magnetic particle powder was divided by the drop time, and the weight per minute was calculated and displayed (g / min). The value measured by this method is 10g
/ Min or more, preferably about 12 g / min or more, the magnetic toner has excellent dispersibility.

[0009]

[Table 1]

Then, the magnetic powders obtained in Examples 1 to 6 were evaluated for dispersibility in a binder resin by the following method. First, 40 parts by weight of the magnetic powder obtained in Examples 1 to 6 whose surface was coated with 0.01 to 5.0% by weight of the titanium-based coupling agent based on the powder, and polyester resin ( Kao Atlas Co., Ltd.
(Molecular weight: about 5000) 59 parts by weight and carbon black (Mitsubishi Chemical Co., Ltd., MA-100) 1 part by weight were thoroughly mixed with a Henschel mixer, and then melt-kneaded with a heating type twin-screw mixer and cooled and solidified. Then, a magnetic toner having an average particle diameter of 12 μm was obtained with a jet mill type pulverizer and a classifier. Using this magnetic toner, a commercially available one-component copying developer box was improved, and the magnetic distribution of the toner was measured by the brush scattering method using this. The content, that is, the filling rate was uniform, and the magnetic characteristics and the charge amount were stable. As a result, the copy image quality and resolution were improved, and clear copy images were obtained without fog or toner scattering. In addition, the brush scattering method here means that when the rotation speed of the mag roller is variably improved and the amount of charge is constant, the rotation speed is increased so that the magnetic force of the magnetic toner attached to the mag roller is increased. It is a method of knowing the amount of magnetite in the toner, that is, the dispersibility in the resin, by ejecting a weak toner (having a low magnetic material content) by centrifugal force and measuring the amount of the ejected toner and the magnetism of the toner. . Here, if the dispersion of the magnetic material powder in the resin is poor, the magnetic force of each toner will be different, and the one having a weak magnetic force (saturation magnetic flux density) will be quickly ejected.

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Claims (1)

[Claims] 1. The surface of the magnetic powder is 0.
A magnetic powder for a magnetic toner, which is coated with 01 to 5.0% by weight of a titanium coupling agent.