JP4165859B2 - Strontium titanate fine powder, method for producing the same, and toner for electrostatic recording using the same as an external additive - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fine powder of strontium titanate useful as an external additive for toner for developing an electrostatic latent image for forming a copy image such as a copying machine and a printer using an electrophotographic system.
[0002]
[Prior art]
In recent years, with the demand for high-definition and high-quality electrostatic images obtained by electrophotographic copying machines and printers, high-quality toners with small particle size and high fluidity are used as a developer. Attempts are being made to achieve. However, if the particle diameter of the toner is reduced, the surface area per weight increases, the triboelectric charge increases, the adhesion between the toners increases, and the fluidity decreases.
[0003]
To solve these problems, strontium titanate powder has a characteristic that the charge level is not changed because it is almost neutral and has a high dielectric constant. Is used in large quantities.
[0004]
For example, Japanese Patent Publication No. 3-10312 discloses a titanate represented by strontium titanate having a specific surface area of 1.0 to 6.0 m ² / g and produced by a sintering method. No. 206730 can use hydrophobic strontium titanate with a number average particle size of 80 to 800 nm, and Japanese Patent Application Laid-Open No. 8-227171 can use strontium titanate with a particle size of 10 to 90 nm as an external additive for toner. Is described.
[0005]
[Problems to be solved by the invention]
However, since strontium titanate described in JP-B-3-10312 and JP-A-2000-206730 is produced by mixing titanium oxide or metatitanic acid and strontium carbonate and firing, the particle size is large. In addition, since it includes those having a large particle size, it was not satisfactory as an external additive in finely divided toner. JP-A-8-227171 suggests that strontium titanate having a particle size of 10 to 90 nm can be used as a fluidizing agent. Strontium acid has not yet been produced.
[0006]
Thus, strontium titanate is very useful as an external additive for toner, and the appearance of strontium titanate with fine particles, good particle size distribution, high crystallinity and excellent dispersibility is expected. Yes.
[0007]
Conventionally, various atmospheric pressure heating reaction methods have been proposed as methods for obtaining a perovskite type fine particle powder such as fine particle strontium titanate at a low cost. For example, Japanese Patent Application Laid-Open No. S59-5928 discloses a method in which a hydrolyzate of a titanium compound and a strontium compound are reacted in a strong alkaline aqueous solution to produce ultrafine strontium titanate. Is 100 to 200 mm, and the particle size is too small as an external additive in finely divided toner, and a method for controlling the particle size is not described.
[0008]
Japanese Patent Laid-Open No. 5-58633 discloses a method of controlling the particle size of strontium titanate by changing the reaction conditions by wet reaction of a hydrolyzate of a titanium compound and a strontium compound in the presence of hydrogen peroxide. However, it is uneconomical because the amount of hydrogen peroxide used is as large as 0.1 to 10 in terms of the H ₂ O ₂ / TiO ₂ molar ratio.
[0009]
Japanese Patent Application Laid-Open No. 6-48734 discloses that a strontium compound in a solution state and a titanium compound in a solution state or a slurry state are mixed at a temperature higher than the temperature at which the reaction starts, so that the particle size distribution is 50 nm or less. It is disclosed that narrow crystalline strontium titanate microparticles can be obtained. However, this method requires an in-line mixer to heat the titanium compound and strontium hydroxide to a temperature higher than the reaction temperature in separate tanks, and to mix them both instantaneously and uniformly. It is not industrially preferable.
[0010]
[Means for Solving the Problems]
From such a point of view, the present inventors have provided strontium titanate fine particles, which are suitable as an external additive for a toner that imparts high fluidity to the toner and is excellent in moisture resistance, with a simple particle size distribution. The present invention was completed by intensive studies to develop a method that can be controlled to a desired particle size.
[0011]
That is, the present invention has an average primary particle diameter of 0.02 to 0.3 μm, a value obtained by dividing the quadrature deviation of the primary particle diameter by the average primary particle diameter is 0.20 or less, and such particles The present invention relates to a fine strontium titanate powder characterized by containing rectangular parallelepiped particles. Moreover, the strontium titanate fine powder of the present invention preferably contains cubic particles as such particles. If the average primary particle size is out of the above range, or the value obtained by dividing the quadrature deviation by the average primary particle size exceeds 0.20 even if the average primary particle size is within the range, it is not preferable because it adversely affects various characteristics of the toner.
[0012]
Since the strontium titanate fine powder of the present invention contains rectangular parallelepiped particles having sharp edges, when used as an external additive for toner, it has an excellent polishing effect in addition to the above effects.
[0013]
The strontium titanate fine powder has an average secondary particle diameter of 0.05 to 0.5 μm, and a value obtained by dividing the quadratic deviation of the secondary particle diameter by the average secondary particle diameter is 0.25. The following is preferable because it is extremely effective for charging stability and fluidity of the toner.
[0014]
The particle size and particle size distribution of the strontium titanate fine powder of the present invention can be measured by various methods. In the present invention, the average particle size and particle size distribution were measured by the following methods.
[0015]
First, the average primary particle size is a 50% particle size based on the weight measured by an equivalent circle diameter from a transmission electron micrograph, and the quadrant is a weight basis measured by an equivalent circle diameter from the transmission electron micrograph. Of the difference between the 75% particle size and the 25% particle size.
[0016]
Moreover, an average secondary particle diameter is a 50% particle diameter of the weight reference | standard calculated | required from the volume distribution measured using Microtrac HRA9320-X100 type made from Honeywell, and a quadratic deviation is 75% of the weight reference | standard calculated | required from the volume distribution. It is represented by 1/2 of the difference between the particle size and the 25% particle size. In the measurement method, an interface for outputting a volume distribution is connected to the apparatus and a personal computer, 10 to 30 mg of a measurement sample is added to 50 to 100 mL of a 0.2% sodium hexametaphosphate aqueous solution, and the ultrasonic dispersion device is used for 1 to 3 minutes. The volume distribution of the sample is obtained by the Microtrac HRA.
[0017]
The strontium titanate fine powder of the present invention typically uses a mineral acid peptized product of a hydrolyzate of a titanium compound as a titanium oxide source in a method for producing a perovskite type titanate compound by a normal pressure heating reaction method. In addition, a water-soluble acidic compound is used as a strontium source, and the mixture is reacted by adding an aqueous alkali solution at 50 ° C. or higher.
[0018]
As the titanium oxide source, a mineral acid peptized product of a hydrolyzate of a titanium compound is used. Specifically obtained by sulfuric acid method, SO ₃ content of less 1.0 wt%, preferably a 0.5 wt% or less of the metatitanic acid to adjust the pH with hydrochloric acid to 0.8-1.5 peptization It is preferable to use a strontium titanate fine powder having a good distribution.
[0019]
As the strontium source, strontium nitrate, strontium chloride or the like can be used.
[0020]
As the alkaline aqueous solution, a caustic alkali can be used, but an aqueous sodium hydroxide solution is preferred.
[0021]
In the above production method, factors affecting the particle size of the resulting strontium titanate fine powder include the mixing ratio of the titanium oxide source and the strontium source during the reaction, the concentration of the titanium oxide source at the initial stage of the reaction, and the addition of the aqueous alkali solution. The temperature, the addition rate, and the like can be mentioned, and may be adjusted as appropriate in order to obtain a target particle size and particle size distribution.
[0022]
In order to prevent the formation of strontium carbonate in the reaction process, it is preferable to prevent mixing of carbon dioxide gas such as reaction in a nitrogen gas atmosphere.
[0023]
The mixing ratio of the titanium oxide source and strontium source in the reaction is the molar ratio of SrO / TiO _2, 0.9 to 1.4, preferably from 0.95 to 1.15.
[0024]
The concentration of the titanium oxide source at the initial stage of the reaction is 0.05 to 1.0 mol / L, preferably 0.1 to 0.8 mol / L as TiO ₂ .
[0025]
The higher the temperature at which the aqueous alkali solution is added, the better the crystallinity can be obtained, but a practical range of 50 ° C. to 101 ° C. is appropriate.
[0026]
The addition rate of the alkaline aqueous solution has the most influence on the particle size of the resulting powder. The slower the addition rate, the larger the particle size strontium titanate powder, the faster the addition rate, the smaller the particle size strontium titanate powder. . The addition rate of the alkaline aqueous solution is 0.001 to 1.0 equivalent / h, preferably 0.005 to 0.5 equivalent / h, with respect to the charged raw material, and is appropriately adjusted according to the particle diameter to be obtained. The addition rate of the aqueous alkaline solution can be changed in the middle depending on the purpose.
[0027]
In the strontium titanate fine powder of the present invention, as in the case of silica and titanium oxide, which have been conventionally used as external additives, for adjusting the charge and improving environmental stability, SiO ₂ , Al ₂ O _3, etc. Hydrophobizing agents such as inorganic oxides, titanium coupling agents, silane coupling agents, and silicone oil can be treated, and fine powder of strontium titanate with a primary particle size of 0.02 to 0.3 μm When used as an additive, a hydrophobizing agent treated in an aqueous system is preferable because the dispersibility is even better. Moreover, in the fine powder of strontium titanate of the present invention, if it is fired at a temperature of 300 to 1000 ° C. for improving the crystallinity, the crystallinity is further improved and the environmental stability is further improved.
[0028]
The fine strontium titanate powder of the present invention is used in all electrostatic recording methods of magnetic one-component toner, two-component toner and non-magnetic one-component toner. It can also be used as an external additive for toners produced by pulverization or polymerization. As the binder resin for the toner, any known synthetic resin and natural resin can be used. Specifically, for example, styrene resin, acrylic resin, olefin resin, diene resin, polyester resin, polyamide resin, epoxy resin, silicone resin, phenol resin, petroleum resin, urethane resin, etc. Is mentioned. Further, a toner in which an additive such as a charge adjusting agent or a release agent is added to the binder according to the purpose may be used.
[0029]
The strontium titanate fine powder of the present invention is used by adding 0.3 to 5.0 wt% externally to the toner, and if necessary, known fluidizing agents used in the field of electrophotography, such as silica, oxidation You may use together with 1 type, or 2 or more types, such as titanium and aluminum oxide.
[0030]
Also, two or more strontium titanate fine powders of the present invention having different particle diameters may be used simultaneously.
[0031]
The fine strontium titanate powder of the present invention has an excellent polishing effect in toner external additives, but is also useful as a normal abrasive.
[0032]
The characteristics required for the abrasive include high hardness, particles having a regular shape that is neither needle-shaped nor plate-shaped, and a surface that is not smooth and has a cutting blade. Strontium titanate has a Mohs hardness of 5 to 6 and is not so high. However, since Mohs hardness of flint that has been used for glass polishing for a long time is 6 to 6.5, the level of hardness is not a problem. . The fine strontium titanate powder of the present invention contains cubic particles having sharp edges as described above. Therefore, the strontium titanate fine powder of the present invention can be sufficiently used for Mohs hardness of around 5, such as glass (hardness 5 to 5.5).
[0033]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are given for illustration only and are not intended to limit the scope of the invention.
[0034]
[Example 1]
The metatitanic acid obtained by the sulfuric acid method was subjected to deiron bleaching treatment, 4N aqueous sodium hydroxide solution was added to adjust pH to 9.0, desulfurization treatment was performed, and then neutralized to pH 5.5 with 6N hydrochloric acid, followed by washing with filtered water. . Water was added to the washed cake to make a slurry of 1.25 mol / L as TiO ₂ , and 6N hydrochloric acid was added to adjust the pH to 1.2, followed by peptization. 0.156 mol of this peptized hydrous titanium oxide was collected as TiO ₂ and charged into a 3 L reaction vessel, and an aqueous strontium chloride solution having a SrO / TiO ₂ molar ratio of 1.15 was added to the peptized hydrous titanium oxide slurry. After that, the TiO ₂ concentration was adjusted to 0.156 mol / L, and nitrogen gas was blown in and left for 20 minutes to replace the inside of the reaction vessel with nitrogen gas. Next, while flowing nitrogen into the reaction vessel and further stirring and mixing, the mixed solution of metatitanic acid and strontium chloride was heated to 90 ° C., and then 143 mL of a 2.5N aqueous sodium hydroxide solution was added over 24 hours. Thereafter, stirring was continued at 90 ° C. for 1 hour to complete the reaction. After the reaction, it was cooled to 40 ° C., the supernatant was removed under a nitrogen atmosphere, and the operation of adding 2.5 L of pure water and decanting was repeated twice, followed by washing with Nutsche. The obtained cake was dried in the atmosphere of 110 ° C. for 8 hours. When the final composite was observed with an electron microscope, it was 0.16-0.20 μm particles including cubic particles, and was a single phase of strontium titanate by X-ray diffraction. The average primary particle diameter calculated on the basis of weight using an electron micrograph was 0.17 μm, and the value obtained by dividing the quarter deviation by the average primary particle diameter was 0.13. Moreover, the average secondary particle diameter calculated | required by Microtrac HRA was 0.28 micrometer, and the value which divided the quarter deviation by the average secondary particle diameter was 0.23.
[0035]
[Example 2]
0.626 mol of hydrated titanium oxide that has been desulfurized and peptized as TiO ₂ is sampled and charged into a 3 L reaction vessel, and the chlorinated titanium oxide slurry is chlorinated at a SrO / TiO ₂ molar ratio of 1.15. After the addition of the strontium aqueous solution, the TiO ₂ concentration was adjusted to 0.626 mol / L, nitrogen gas was blown in, and left for 20 minutes to replace the inside of the reaction vessel with nitrogen gas. Next, while flowing nitrogen into the reaction vessel and further stirring and mixing, the mixed solution of metatitanic acid and strontium chloride was heated to 90 ° C., and then 143 mL of a 10N aqueous sodium hydroxide solution was added over 2 hours. Stirring was continued at 90 ° C. for 1 hour to complete the reaction. After the reaction, it was cooled to 40 ° C., the supernatant was removed under a nitrogen atmosphere, and the operation of adding 2.5 L of pure water and decanting was repeated twice, followed by washing with Nutsche. The obtained cake was dried in the atmosphere of 110 ° C. for 8 hours. When the final composite was observed with an electron microscope, it was 0.03-0.05 μm particles including cubic particles, and was a single phase of strontium titanate by X-ray diffraction. The average primary particle size calculated on the basis of weight using an electron micrograph was 0.042 μm, and the value obtained by dividing the quarter deviation by the average primary particle size was 0.14. Moreover, the average secondary particle diameter calculated | required by Microtrac HRA was 0.13 micrometer, and the value which divided the quarter deviation by the average secondary particle diameter was 0.22.
[0036]
[Example 3]
0.626 mol of hydrated titanium oxide that has been desulfurized and peptized as TiO ₂ is sampled and charged into a 3 L reaction vessel, and the chlorinated titanium oxide slurry is chlorinated at a SrO / TiO ₂ molar ratio of 1.15. After the addition of the strontium aqueous solution, the TiO ₂ concentration was adjusted to 0.626 mol / L, nitrogen gas was blown in, and left for 20 minutes to replace the inside of the reaction vessel with nitrogen gas. Next, while flowing nitrogen into the reaction vessel and further stirring and mixing, the mixed solution of metatitanic acid and strontium chloride was heated to 90 ° C. Then, 143 mL of 10N sodium hydroxide aqueous solution was added over 12 hours. Thereafter, stirring was continued at 90 ° C. for 1 hour to complete the reaction. After the reaction, it was cooled to 40 ° C., the supernatant was removed under a nitrogen atmosphere, and the operation of adding 2.5 L of pure water and decanting was repeated twice, followed by washing with Nutsche. The obtained cake was dried in the atmosphere of 110 ° C. for 8 hours. When the final composite was observed with an electron microscope, it was 0.08 to 0.1 μm particles including cubic particles, and was a single phase of strontium titanate by X-ray diffraction. The average primary particle diameter calculated on the basis of weight using an electron micrograph was 0.091 μm, and the value obtained by dividing the quarter deviation by the average primary particle diameter was 0.13. Moreover, the average secondary particle diameter calculated | required by Microtrac HRA was 0.24 micrometer, and the value which divided the quarter deviation by the average secondary particle diameter was 0.18.
[0037]
【The invention's effect】
The fine strontium titanate powder of the present invention is characterized in that it can control the particle size distribution such as the average primary particle size according to the purpose, and has high crystallinity and excellent dispersibility. Therefore, the fine strontium titanate powder of the present invention is suitable as an external additive for toner, and can be used for a toner excellent in high fluidity and environmental stability.
[0038]
[Brief description of the drawings]
1 is an electron micrograph of strontium titanate fine powder produced according to Example 1 at a magnification of 30,000. FIG.
2 is a particle size distribution diagram of primary particle diameters obtained from an electron micrograph of fine strontium titanate powder produced in Example 1. FIG.
3 is a particle size distribution diagram of secondary particle diameters obtained by Microtrac HRA of strontium titanate fine powder produced in Example 1. FIG.

Claims (4)

The average primary particle size is 0.02 to 0.3 μm, the value obtained by dividing the quadratic deviation of the primary particle size by the average primary particle size is 0.20 or less, and rectangular parallelepiped particles are used as such particles. Strontium titanate fine powder characterized by containing. The average secondary particle diameter is 0.05 to 0.5 μm, and the value obtained by dividing the quadratic deviation of the secondary particle diameter by the average secondary particle diameter is 0.25 or less, Item 2. The fine powder of strontium titanate according to item 1. An electrostatic recording toner using the fine strontium titanate powder according to claim 1 as an external additive. An abrasive comprising as a main component the fine strontium titanate powder according to claim 1 or 2.

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