JP5029981B2 - Black composite iron oxide particles, electrophotographic toner using the same, and image forming method - Google Patents

Description

  The present invention relates to black composite iron oxide particles containing titanium and iron, particularly containing high-grade FeO and excellent in blackness.

  Black composite iron oxide particles obtained by an aqueous solution reaction, and magnetite particles, which are representative thereof, are widely used as material powders for magnetic toners in electronic copying machines and printers. In such applications, various general development characteristics are required, but in recent years, due to the development of electrophotographic technology, copying machines and printers using digital technology have developed rapidly, and the required characteristics are more advanced. It has become a thing.

The above required characteristics are diverse, but among them, the strong demand for magnetic toner material powder is excellent blackness.
The blackness of magnetite particles widely used for magnetic toner material powder depends mainly on FeO contained, and the higher the content, the better the blackness. For example, Patent Document 1 discloses a magnetic iron oxide containing 25 to 30% by weight of FeO, and Patent Document 2 discloses a magnetic iron oxide containing 30 to 40% by weight of FeO based on an iron element.
Further, Patent Document 3 discloses a magnetite particle having a FeO content of 31 to 35% while having a fine particle size of 0.1 μm or less.

On the other hand, as described above, FeO has a low numerical value due to oxidation in the atmosphere. Therefore, since the blackness does not depend on FeO, the metal oxide component other than FeO has blackness. There are also attempts to prevent deterioration.

Japanese Patent Laid-Open No. 4-130327 JP-A-4-335673 Japanese Patent No. 3464801

As described above, as a means for improving the blackness, attempts have been made to increase the amount of FeO contained as much as possible. However, the content is not only limited by the theoretical value, but also by oxidation in the atmosphere. The numerical value must be low, and as disclosed in Patent Documents 1 and 2, it is at most about 30% by weight with respect to the iron oxide particles. Or even if it is high FeO content, it is the actual condition that only a small particle size product of about patent document 3 is obtained.

  As for means for preventing the deterioration of the blackness with a metal oxide component other than FeO, the metal oxide to be used generally contains heavy metals, and most of the environmentally hazardous substances which are regarded as a problem in recent years are not preferable.

Accordingly, an object of the present invention is to provide black composite iron oxide particles composed of a heavy metal-free iron-based oxide at a level excluding unavoidable inclusions and having high FeO and excellent blackness, which has been difficult with the above-described prior art. There is.

In the present invention, when an alkaline aqueous solution containing tartaric acid or glutamic acid and an aqueous solution containing ferrous salt and titanium salt are mixed, the pH is adjusted to 10.8 to 11.5, and then air is blown in. Black composite iron oxide particles obtained by wet oxidation of Fe ²⁺ at a reaction temperature of 90-100 ° C. ,
And _{Fe 3 O 4 (Fe x Ti} y) z O 4 ( where, x is 0.5 to 3, y is 0.25-1.25, z represents a number of 0.5 to 1.5) In the crystal structure, the content of titanium in the crystal structure is 3 to 12% by weight, and the content of divalent iron in the crystal structure is 31. The object is achieved by providing black composite iron oxide particles having a content of 5 to 36% by weight and titanium substantially uniformly from the center to the surface of the particles.

  The black composite iron oxide particles of the present invention contain a large amount of titanium, have a high FeO content and excellent blackness. Furthermore, since it does not contain heavy metals or carcinogenic substances, safety is high.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The black composite iron oxide particles of the present invention (hereinafter simply referred to as composite iron oxide) are characterized by their high titanium content. The content of titanium in the composite iron oxide of the present invention is 3 to 12% by weight, preferably 4.5 to 10% by weight, and more preferably 4.5 to 7.5% by weight. When the content of titanium is less than 3% by weight, the magnetization of the composite iron oxide becomes high, so that it becomes difficult to use in a place where the influence of the magnetic field is strong. If it exceeds 12% by weight, it becomes difficult to incorporate titanium into the composite iron oxide, and precipitates in the form of TiO _{2 on} the particle surface. As a result, the specific surface area of the particles increases and the environmental dependency deteriorates.

The content of titanium in the composite iron oxide is measured by dissolving the composite iron oxide and quantifying titanium by ICP. In order to make the content of titanium in the composite iron oxide within the above range, for example, the composite iron oxide may be manufactured by a wet method according to the manufacturing method described later.

Composite iron oxide of the present invention, preferably has a crystal structure of _Fe 3 _{O 4} and _{(Fe x Ti y) z O} 4, those having a so-called magnetite and ferrite similar crystal structure is preferred. _{(Fe x Ti y) z O} 4 , a part of the trivalent iron sites in _Fe 3 _{O 4} is intended state are substituted with titanium, has a structure similar to ferrite. However ferrite, since those divalent iron in magnetite is replaced with other divalent metal element, not have a _{(Fe x Ti y) z O} 4 is completely structure of ferrite Absent. The present invention therefore is called _{(Fe x Ti y) z O} 4 of the ferrite similar structure. That is, the above notation indicates that titanium does not exist in the form of TiO ₂ but exists in the state of a complex oxide with iron.

When seen from the results of X-ray diffraction analysis, the in the composite iron oxide of the present invention and it is _Fe 3 _{O 4} and _{(Fe x Ti y) z O} 4, both are present uniformly throughout the particle as a solid solution It is thought that. In _{(Fe x Ti y) z O} 4 in the composite iron oxide of the present invention x is 0.5 to 3, preferably from 1 to 2.5, y is 0.25-1.25, It is preferably 0.5 to 1, z is 0.5 to 1.5, and preferably 0.8 to 1.33. Particularly _preferably, in the _{(Fe x Ti y) z O} 4 is _{(Fe 2.5 Ti 0.5) 1.04 O} 4, (Fe 2 Ti) 0.8 O 4 or _{(FeTi) 1.33} O ₄ It has the structure represented.

_(Fe x _{Ti y)} x in z _{O 4,} y and z can be determined from X-ray diffraction analysis of the composite iron oxide of the present invention. Also can be determined from the weight ratio is also X-ray diffraction analysis of the _Fe 3 _{O 4} in the composite oxide of iron and _{(Fe x Ti y) z O} 4. Fe ₃ O ₄ and the weight ratio of _{(Fe x Ti y) z O} 4, i.e. _{Fe 3 O 4 / (Fe x} Ti y) z O 4 is 0.13 to 6.46, especially from 0.13 to 2. It is preferable that it is 17 from the point which can maintain FeO high and also makes a color (a value, b value) favorable as a result.

In the composite iron oxide of the present invention, titanium is present substantially uniformly from the center of the particle to the surface. Therefore, the composite iron oxide of the present invention is clearly different in titanium distribution from particles in which TiO ₂ is precipitated on the surface of magnetite particles, that is, particles in which titanium is unevenly distributed on the surface. Whether titanium is present almost uniformly from the center of the particle to the surface can be confirmed from the relationship between the degree of dissolution and the amount of titanium eluted by gradually dissolving the particle from the surface.

  In the composite iron oxide of the present invention, the average particle size (Ferret diameter) is preferably 0.15 to 0.5 μm, particularly preferably 0.2 to 0.5 μm. As described in the prior art, it was difficult for the average particle diameter to exceed 0.1 μm, but according to the present invention, the average particle diameter has a general-purpose particle diameter. In this case, the hiding power and coloring power are sufficient, and the performance as a black pigment is improved.

Moreover, the composite iron oxide of the present invention has a small BET specific surface area. Specifically, the composite iron oxide of the present invention has a small BET specific surface area of preferably 3 to 300 m ² / g, more preferably 3 to 20 m ² / g. This is advantageous from the viewpoint of increasing the coloring power of the composite iron oxide of the present invention to improve the performance as a black pigment and the environmental dependency. The composite iron oxide of the present invention having a small BET specific surface area is clearly distinguished from magnetite particles in which TiO ₂ is precipitated on the surface of the particles and the BET specific surface area is large due to this.

Further, the composite iron oxide of the present invention contains a large amount of a titanium component, so that it has a low magnetization compared to general-purpose magnetite. Specifically, the composite iron oxide of the present invention preferably has a saturation magnetization under 79.6 kA / m of 35 to 60 Am ² / kg, and more preferably a saturation magnetization under 79.6 kA / m of 35 to 55 Am. ^The value is as low as ² / kg. This is advantageous in that the inconvenience hardly occurs even when the composite iron oxide of the present invention is used in a place where a magnetic field is strong.

  The particle shape of the composite oxide of the present invention can be various shapes depending on the characteristics required for the composite oxide and specific applications. For example, when it is desired to maintain the high FeO of the composite oxide of the present invention and improve the color (a value, b value), an octahedron may be used. Furthermore, when it is desired to improve both dispersibility and color, a polyhedral shape exceeding octahedron may be used. The particle shape of the composite oxide can be controlled by adjusting various conditions in the production method described later.

  Since the composite oxide of the present invention has the above-described configuration, it has a high FeO content and a high blackness. Specifically, in the measurement of the blackness and hue of powder according to JIS K5101-1991, the L value by a color difference meter is preferably 25 or less, more preferably 22 or less, and the blackness is high. The a value is preferably 0.5 or less, and the b value is preferably 0.5 or less.

For the purpose of improving various properties of the composite oxide of the present invention, various coating treatments may be applied to the surface of the composite oxide. For example, the surface of the composite oxide can be coated with an aluminum compound. Examples of the aluminum compound include Al (OH) ₃ , α-AlO (OH), γ-AlO (OH), and hercinite (FeO · Al ₂ O ₃ ). By applying a coating treatment with these aluminum compounds, the effect of lowering the saturation magnetization at 79.6 kA / m of the composite oxide of the present invention can be expected, and it becomes easier to use in a magnetic field. From this viewpoint, it is preferable to use Al (OH) ₃ , γ-AlO (OH), or hercinite (FeO · Al ₂ O ₃ ) as the aluminum compound.

  The surface of the composite oxide can be coated with a silane coupling agent. As the silane coupling agent, those usually used as a surface treatment agent for iron oxide can be used without particular limitation. For example, usual silane coupling agents, aminosilane coupling agents, vinylsilane coupling agents, and the like can be used. By performing coating treatment with these silane coupling agents, the dispersibility of the composite oxide of the present invention in the resin is improved. As the silane coupling agent, it is particularly preferable to use octyltriethoxysilane, decyltriethoxysilane, octyltrimethoxysilane, and decyltrimethoxysilane from the viewpoint that the particle surface can be uniformly coated.

  Next, a preferred method for producing the composite oxide of the present invention will be described. The composite oxide of the present invention is adjusted to have a pH of 10.8 to 11.5 when an aqueous solution containing ferrous and titanium ions and an alkaline aqueous solution containing tartaric acid or glutamic acid are mixed. It can be produced by performing wet oxidation by blowing air into the aqueous solution, setting the reaction temperature during wet oxidation to 90 to 100 ° C., and the consumption rate of ferrous ions to 4 to 8 g / l per hour.

The feature of this production method is that in the wet oxidation of ferrous salt, tartaric acid or glutamic acid is present in the reaction system, and oxidation of Fe ²⁺ is gradually performed. That is, in the composite oxide of the present invention, it is important to add an aqueous solution containing a ferrous salt and a titanium salt to an alkaline aqueous solution containing tartaric acid or glutamic acid, and then gradually blow-oxidize Fe ²⁺ by blowing air. . By this operation, a large amount of titanium can be taken into the iron oxide particles.

  Tartaric acid or glutamic acid is used in combination with the condition that the reaction pH is controlled to 10.8 to 11.5 and the reaction temperature is increased to 90 to 100 ° C., in addition to the high titanium uptake effect. This is important for making the oxide a high FeO product.

  The ferrous salt is not particularly limited as long as it is a water-soluble salt. For example, ferrous sulfate or ferrous chloride can be used. The titanium salt is not particularly limited as long as it is a water-soluble salt. For example, titanyl sulfate can be used.

  A procedure of a preferred example of this manufacturing method is as follows. First, an alkaline aqueous solution containing tartaric acid or glutamic acid is prepared (this aqueous solution is referred to as solution A). The concentration of tartaric acid or glutamic acid in Solution A is preferably 0.04 to 0.5% by weight, particularly 0.08 to 0.35% by weight. For example, when sodium hydroxide is used as the alkali, the alkali concentration is (sodium hydroxide weight / (water + sodium hydroxide weight)) 9 to 12.5 wt%, particularly 10 to 12.5 wt%. Is preferred. As the alkali, for example, a strong alkali such as sodium hydroxide can be used.

Separately from the solution A, an aqueous solution of ferrous salt (this aqueous solution is called solution B) and an aqueous solution of a titanium salt (this aqueous solution is called solution C) are prepared. The concentration of the ferrous salt in the solution B is 9 to 12.5% by weight, particularly 10 to 12.5% by weight in terms of Fe ²⁺ . On the other hand, the concentration of the titanium salt in the solution C is 4.5 to 10% by weight, particularly 5 to 8.5% by weight in terms of Ti ⁴⁺ .

  Solution B and solution C having the aforementioned concentrations are mixed and stirred. As for the mixing ratio, the ratio of the weight of the solution B to the weight of the solution C (weight of the solution B / weight of the solution C) is preferably 6.5 to 11, particularly 7.2 to 10.

  Next, the mixed solution of the solution B and the solution C is heated to about 35 to 55 ° C., and added to the solution A in a state heated to about 65 to 100 ° C. under the state. Next, an alkali is added to the three mixed solutions to adjust the pH to 10.8 to 11.5. The ratio of the weight of the mixed solution of solution B and solution C to the weight of solution A (weight of the mixed solution of solution B and solution C / weight of solution A) is 0.5 to 1.5, especially 0.6. ~ 1 is preferred.

Under this state, air is blown into the reaction system to perform wet oxidation. At this time, controlling the reaction temperature to be as high as 90 to 100 ° C. is important for making the obtained composite oxide a high FeO product, as described above. It is also important to gradually oxidize Fe ²⁺ . When oxidation is performed rapidly, the hydrolysis reaction of titanium becomes dominant and TiO ₂ is deposited. From this viewpoint, air is blown so that the consumption rate of Fe ²⁺ during wet oxidation is 4 to 8 g / l per hour, and preferably 4 to 6.5 g / l.

  The amount of air blown during wet oxidation may be constant or may vary. For example, the amount of air blown can be relatively increased in the initial stage of wet oxidation, and can be relatively decreased in the subsequent stages. Varying the amount of blowing in this way has the advantage that stirring in a state of high slurry viscosity at the initial stage of the production reaction can be sufficiently performed and particles having a uniform particle size distribution can be produced.

  By performing wet oxidation under such conditions in the presence of tartaric acid or glutamic acid, a large amount of titanium can be taken into the particles, and the resulting composite oxide can be made into a high FeO product.

  By adjusting the pH of the reaction system during wet oxidation and the concentration of tartaric acid or glutamic acid present in the reaction system, the particle shape of the resulting composite iron oxide can be controlled. Specifically, when obtaining octahedral particles, the pH of the reaction system is set to 10.8 to 11.5, and glutamic acid is used, and the concentration is set to about 0.05 to 0.75% by weight. It is preferable. When it is desired to obtain octahedral polyhedral particles, the pH of the reaction system is preferably 10.8 to 11.5, and tartaric acid is used, and the concentration is preferably about 0.05 to 0.25% by weight. . In addition, controlling the reaction pH to 10.8 to 11.5 is important for making the obtained complex oxide a high FeO product as described above.

Wet oxidation is performed until there is no unreacted Fe ²⁺ in the reaction system. After completion of the reaction, the reaction system is neutralized, and then solid-liquid separation is performed to obtain the composite oxide of the present invention. It is not necessary to further heat-treat the obtained composite oxide. Therefore, particle aggregation due to heat treatment does not occur, and as a result, the composite oxide has good dispersibility.

Since the composite oxide obtained in this way contains a large amount of titanium in the particles, its magnetization is lower than that of magnetite usually produced by wet synthesis. Further, since titanium is not deposited on the surface in the form of TiO ₂ or the like, the BET specific surface area of the composite oxide is small. As a result, the composite oxide is excellent in environmental dependency.

  The composite iron oxide of the present invention is suitably used as an electrophotographic toner material powder or a paint black pigment powder. When used as an electrophotographic toner material powder, various images having excellent image characteristics such as image density, resolution, and gradation can be formed by an electrophotographic image forming method.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
(A) Preparation of Solution A 8 kg of sodium hydroxide was added to 60 L of water. To this, 55.3 g of tartaric acid dissolved in 500 mL of warm water was added to obtain a solution A.

(B) Preparation of Solution B Ferrous sulfate was dissolved in 35 L of water to obtain Solution B. The amount of ferrous sulfate added was 4000 g in terms of Fe ²⁺ .

(C) Preparation of Solution C Solution C was obtained by dissolving titanyl sulfate in 5 L of warm water. The amount of titanyl sulfate added was 277 g in terms of Ti ⁴⁺ .

(D) Wet oxidation Solution B and solution C were mixed and heated to 50 ° C. This mixed solution was added to and mixed with the solution A heated to 85 ° C. to obtain a reaction solution. Sodium hydroxide was added to the reaction solution to adjust the pH to 11.0. Under this condition, air was blown into the reaction solution to perform wet oxidation. The amount of air blown was adjusted to 5 L / min and the reaction temperature was 90 ° C. The consumption rate of Fe ²⁺ at this time was 5.8 g / L per hour. After confirming that there was no unreacted Fe ²⁺ , air blowing was stopped. The reaction solution was neutralized to a pH of 6, followed by solid-liquid separation to obtain composite iron oxide.

[Example 2, Comparative Examples 1 and 2]
Implemented except that the types and concentrations of the organic acids contained in the solution A are shown in Table 1, the concentrations of the solutions B and C are the values shown in the table, and the air blowing amount is the value shown in the table In the same manner as in Example 1, composite iron oxide was obtained.

[Performance evaluation]
About the composite iron oxide obtained by the Example and the comparative example, the total Fe amount, FeO amount, and Ti amount were measured with the following method. The results are shown in Table 2. Moreover, the shape and average particle diameter of the obtained composite iron oxide were observed with an electron microscope. The average particle diameter was determined by measuring the ferret diameter. Further, saturation magnetization, BET specific surface area and black L value under 79.6 kA / m were measured by the following methods. These results are shown in Table 2. Furthermore, the result of the X-ray diffraction analysis of the composite iron oxide obtained in Example 1 is shown in FIG.

[Measurement of total Fe amount, FeO amount and Ti amount]
The total Fe amount and Ti amount were obtained by dissolving composite iron oxide and measuring the amounts of Fe and Ti contained in the solution by ICP. The amount of FeO was measured by oxidation-reduction titration using a complex solution of iron oxide in sulfuric acid and a potassium permanganate standard solution.

[Saturation magnetization]
Using a vibrating sample magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd., measurement was performed with an external magnetic field of 79.6 kA / m.

[BET specific surface area]
It was measured with Shimadzu-Micromeritics 2200 type BET meter.

[Black L value]
To 2.0 g of the sample, 1.4 cc of castor oil was added and kneaded with a Hoover type Mahler. After adding 7.5 g of lacquer to 2.0 g of this kneaded sample and further kneading, this was applied onto a mirror-coated paper using a 4 mil applicator. After drying, the color difference was measured with a color difference meter (Tokyo Denshoku Color Analyzer TC-1800 type).

As is clear from the results shown in Tables 1 and 2, the composite iron oxides of the examples have excellent blackness due to FeO being 31.5% by weight or more, and contain Ti. Therefore, there is an advantage that inconvenience hardly occurs even when used in a place with a low magnetization and a strong magnetic field.
On the other hand, the composite iron oxide of the comparative example had low FeO and poor blackness.

2 is a chart showing the results of X-ray diffraction analysis of the composite iron oxide obtained in Example 1. FIG.

Claims (8)

When an alkaline aqueous solution containing tartaric acid or glutamic acid and an aqueous solution containing ferrous salt and titanium salt are mixed, the pH is adjusted to 10.8 to 11.5, and then air is blown to reaction temperature 90 to Black composite iron oxide particles obtained by wet oxidation of Fe ²⁺ at 100 ° C. ,
And _{Fe 3 O 4 (Fe x Ti} y) z O 4 ( where, x is 0.5 to 3, y is 0.25-1.25, z represents a number of 0.5 to 1.5) In the crystal structure, the content of titanium in the crystal structure is 3 to 12% by weight, and the content of divalent iron in the crystal structure is 31. 5 to 36% by weight, and black composite iron oxide particles characterized in that titanium is present substantially uniformly from the center to the surface of the particles.   The black composite iron oxide particles according to claim 1, wherein the average particle size is 0.15 to 0.5 µm. The black composite iron oxide particles according to claim 1 or 2, having a BET specific surface area of 3 to ²⁰ m ² / g. The black composite iron oxide particles according to any one of claims 1 to 3, wherein a saturation magnetization under 79.6 kA / m is 35 to 60 Am ² / kg.   The black composite iron oxide particles according to any one of claims 1 to 4, wherein the surface is coated with an Al compound.   The black composite iron oxide particles according to any one of claims 1 to 5, wherein the surface is coated with a silane coupling agent.   An electrophotographic toner using the black composite iron oxide particles according to claim 1.   An image forming method using an electrophotographic method using the electrophotographic toner according to claim 7.