JPH0425687B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing cobalt-containing magnetic iron oxide powders having high coercivity and improved dispersibility in various organic binders. In recent years, recording media such as magnetic tapes are required to have increasingly higher performance. The magnetic powder used in this recording medium is required to have a high coercive force and good dispersibility in an organic binder as the density of magnetic recording increases. In order to meet the demand for high coercive force magnetic powder, the use of cobalt-containing magnetic iron oxide powder in which a cobalt-containing iron oxide layer is formed on the surface of γ-Fe ₂ O ₃ has increased in recent years. However, even if these cobalt-containing magnetic iron oxide powders have improved coercive force, they do not wet well with the binder when kneaded with various organic binders to prepare magnetic paints, and since they are magnetic themselves, the mutual magnetic There were drawbacks such as agglomeration, making it difficult to disperse uniformly in the binder, and poor coercive force stability, transfer characteristics, erasing characteristics, etc. Conventionally, as measures to improve dispersibility, (1) a method of loosening agglomerates using mechanical dispersion means (Japanese Patent Application Laid-Open No. 50-22297,
55-157216, 56-10903), but the acicular particles tend to break and cause a decline in magnetic properties.
Moreover, since aggregation starts when this dispersion operation is stopped, the affinity with the binder is not improved. Furthermore, (2) in order to improve the compatibility between the magnetic powder particle surface and the organic binder, there is a method of coating the particle surface with a surfactant or the like as a dispersant before preparing the paint (Japanese Patent Publication No. 53-19120, Japanese Patent Publication No. 54 −
37297, 53-141196, 54-82354, 54-
85397) and (3) the method of adding an organic dispersant during paint preparation (Japanese Patent Application Laid-open No. 55-151068 and No. 55-151069) have also been attempted. In such cases, the dispersant adsorbed to the surface of the magnetic powder particles is released during kneading with the organic binder, and the dispersion effect cannot be sustained.
Even after the tape is made, the release of the dispersant causes a decrease in the strength of the magnetic coating and particles falling off. In addition, especially when treated with an organic dispersant, although the dispersibility of vinyl acetate and vinyl chloride resins is improved, there are problems with resin selectivity, such as less effect with urethane resins, and the functional group of the dispersant. There are drawbacks such as the reaction between the binder and the functional groups of the binder, making it difficult to prepare the paint. On the other hand, in the production of cobalt-containing magnetic iron oxide, many techniques have been proposed that use Mn and V in combination. For example, (1) cobalt and cobalt on the surface of magnetic iron oxide particles.
A method in which Mn and V are reduced and precipitated as metals (Japanese Unexamined Patent Publication No. 48-76097), (2) After coating the surface of magnetic iron oxide particles with a coprecipitate of cobalt and Mn metals,
Methods of heat treatment at higher temperatures or hydrothermal treatment (Japanese Patent Application Laid-open No. 51-35696, 35697, 96097,
96098), (3) Acicular magnetic iron oxide powder together with cobalt ions, Mn ions, Fe ⁺² ions and alkali
Method of wet heating at temperatures between 60℃ and the boiling point
-132799), (4) Add an aqueous solution containing cobalt and iron to a suspension of magnetic iron oxide powder, and add it to a suspension of magnetic iron oxide powder in the presence of an oxidizing agent.
A method of wet heat treatment at a temperature of 80℃ or higher (JP-A-Sho
52−5498), (5) Cobalt and Mn in magnetic iron oxide powder
When coating a metal coprecipitate, there is a method in which an alkali is added twice, before and after the addition of the metal salt (Japanese Patent Laid-Open No. 52-5494). However, method (1) does not improve dispersion even though it improves coercive force and lowers electrical resistance, and methods (2) to (5) suppress pressure demagnetization and heating demagnetization. Even if efforts are made to stabilize or improve magnetic properties, such as these, they do not contribute to improving dispersibility. Further, in (2) JP-A-51-96098, an attempt is made to improve the coercive force, but the degree of improvement is not large and is not satisfactory. As mentioned above, when magnetic iron oxide is coated with cobalt or ferrous iron, a high coercive force can be obtained.
It is known that it adversely affects various stability of coercive force, transfer characteristics, erasing characteristics, etc. In order to avoid this negative effect, the present inventors reduced the amount of cobalt or cobalt and ferrous iron deposited,
Furthermore, when a M ⁿ compound or a V compound was applied,
It has been found that coercive force and various stability of coercive force, transfer characteristics, erasing characteristics, etc. can be improved. Focusing on this point, Mn compounds or conducted repeated studies on the addition position of the V compound. As a result, a cobalt compound or a cobalt compound and a ferrous compound are deposited on the particle surface of magnetic iron oxide powder, and at least one of Mn and V is added to the slurry during or after aging. The method of the present invention was completed based on the knowledge that coercive force and dispersibility can be improved at the same time by adding, neutralizing, and depositing a water-soluble metal compound. That is, the first invention of the present application is to coat the particle surface of magnetic iron oxide powder with a cobalt compound or a cobalt compound and a ferrous compound, and then coat the particle surface with a compound of at least one metal of manganese and vanadium. 1. A method for producing cobalt-containing magnetic iron oxide powder, which comprises depositing a cobalt-containing magnetic iron oxide powder. The second invention is a method for producing cobalt-containing magnetic iron oxide powder, which comprises applying a compound of at least one metal of manganese and vanadium and then heat-treating the powder. The magnetic iron oxide powder used in the method of the present invention includes γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, or γ-Fe ₂ O ₃ powder.
Examples include bertolide compound powder obtained by partial reduction of γ-Fe 2 O 3 in a reducing gas such as hydrogen by an appropriate means, or powder obtained by pre-denaturing γ-Fe ₂ O ₃ with ferrous hydroxide. _-Fe2O3 powder _is preferred. In the method of the present invention, first, a cobalt compound or a cobalt compound and a ferrous compound are deposited on the particle surface of magnetic iron oxide powder. Specifically, this method includes, for example, a method in which magnetic iron oxide powder is dispersed in water or an aqueous alkali solution, a cobalt salt or a cobalt salt and a ferrous salt are added, and an aqueous alkali solution is added if necessary; A method of dispersing the powder in water and adding an alkaline aqueous solution and a cobalt salt or a cobalt salt and a ferrous salt in parallel; a method of dispersing the powder in a cobalt salt or a cobalt salt and a ferrous salt; A method of adding the liquid dropwise into an alkaline aqueous solution, dispersing the powder in water or an alkaline aqueous solution, and sequentially adding (a) a cobalt salt, an alkali aqueous solution if necessary, a ferrous salt, and an alkali aqueous solution if necessary; b) A method of sequentially adding a ferrous salt, an alkaline aqueous solution if necessary, a cobalt salt, and an alkaline aqueous solution if necessary, after neutralizing the ferrous salt with an alkaline aqueous solution outside the system to generate a ferrous compound. Examples include a method of adding a slurry in which the powder is dispersed in an alkaline aqueous solution to a coating suspension obtained by adding a salt. Cobalt compounds or ferrous compounds formed by salts and alkalis include hydrated hydroxides, hydrated oxides, hydrated oxyhydroxides, etc.
The coating amount is preferably 0.1 to 20% by weight of the former as Co, based on the total Fe amount of the magnetic iron oxide powder.
The content of Fe is 0.5 to 10% by weight, and the latter is 0.2 to 30% by weight, preferably 1 to 20% by weight as Fe. Note that a small amount of a compound such as manganese, zinc, nickel, or chromium may be present during this deposition. In the method of the present invention, the reaction temperature during deposition is usually below the boiling point, preferably from room temperature to 60°C. The atmosphere during deposition is preferably non-oxidizing so that the cobalt compound or ferrous compound is not substantially oxidized. It is good to make it bubble. The addition time of the raw materials during deposition varies depending on the deposition method, the molar concentration of OH groups in the reaction solution, the deposition reaction temperature, etc., and cannot be definitively stated, but in general, 5 minutes or more is required. , preferably 10 minutes to 3 hours. The magnetic iron oxide powder slurry on which the cobalt compound or the cobalt compound and the ferrous compound have been deposited is then usually subjected to aging. Aging as used herein refers to an operation in which the material is allowed to stand with stirring or without stirring after being deposited.
In the present invention, at a temperature below the normal boiling point, preferably from room temperature to 60°C, and at a pH around neutrality,
It is desirable to carry out the ripening at a concentration of OH groups of up to about 3 mol/mole, preferably in a range from around neutral PH to a concentration of free OH groups of up to 2 mol/mole/mole. The atmosphere at this time is preferably non-oxidizing as in the case of the deposition described above. Next, in the method of the present invention, Mn and V are added to the slurry during or after aging after adhering the cobalt compound or the cobalt compound and the ferrous compound.
At least one metal water-soluble compound is added and deposited. As a method for depositing this Mn or V metal compound, for example, Mn or V is added to a slurry of magnetic iron oxide powder during or after ripening after the deposition of a cobalt compound, etc. by neutralization. There is a method in which an aqueous solution of a compound that produces a V metal compound is added and neutralized with an alkali to precipitate the Mn or V metal compound on the surface of the powder particles. In this case, it is effective to allow the neutralization reaction to proceed as gradually as possible in order to uniformly contain the Mn or V metal compound. PH of slurry, free OH
The concentration of the group, the rate of addition of the aqueous solution, etc. can be adjusted as appropriate. The metal compound may be applied immediately after the cobalt compound, etc. is applied, but it may also be done after aging for about 30 hours, preferably after aging for 10 minutes to 20 hours. good. The temperature during deposition is usually below the boiling point, preferably from room temperature to 60°C. This deposition is usually carried out from a pH around neutrality to a free OH group concentration of 3 mol/h, preferably
It is preferable that the reaction be carried out within a pH range of around neutrality to a free OH group concentration of up to 2 mol/mole. The atmosphere at this time is preferably non-oxidizing. Examples of the compound of at least one metal of Mn and V to be deposited include hydrated hydroxide, hydrated oxide, and hydrated oxyhydroxide. 0.1 to 10 parts by weight of Mn per 100 parts by weight of powder;
It is preferably 0.5 to 5 parts by weight, while V
The amount is 0.05 to 5 parts by weight, preferably 0.1 to 2 parts by weight. If the amount of the metal compound is too small than the above range, the desired effect will not be obtained, and if it is too large, the effect of improving dispersibility will continue, but the saturation magnetization (δs) will decrease, which is not preferable. The slurry coated with the Mn or V compound is usually aged at a temperature below the boiling point, preferably from room temperature to 60°C for 30 minutes to 10 hours. The atmosphere at this time is preferably non-oxidizing. The slurry treated as described above is usually filtered, washed with water, and then dried to obtain the cobalt-containing magnetic iron oxide powder of the present invention. In this case, the cobalt compound or the Mn compound,
When depositing and ripening the V compound, it is desirable to select a reaction temperature of, for example, 60°C or higher, or to select a free OH group concentration of, for example, 0.1 mol/ or higher.
In the method of the present invention, it is preferable to perform heat treatment after depositing the Mn or V compound. Specifically, for this heat treatment, for example, the adhering slurry is placed in an autoclave at 100 to 250°C, preferably 100 to 250°C.
A method of wet heat treatment at 200℃, the adhered slurry is filtered and washed with water, the wet cake is dispersed in water again to form a slurry, and this slurry is wet heated at 100 to 250℃, preferably 100 to 200℃ in an autoclave. How to process the wet cake at 60~250℃,
Examples include a method in which the wet cake is heat-treated preferably at 60 to 200°C in the presence of water vapor, and a method in which the wet cake is dry-heated at 100 to 300°C, preferably 100 to 200°C. Here, heat treatment in the presence of water vapor refers to heating in the presence of water vapor in a closed container or open tube furnace ( _N2 gas purge), as well as heating in a fluidized bed after drying at a low temperature. There are methods such as bringing heated steam into contact with the
Further, it is also possible to perform a treatment that also serves as pulverization using a high-speed fluid energy mill or the like. The cobalt-containing magnetic iron oxide powder obtained by the method of the present invention has improved magnetic properties such as coercive force and various stability of coercive force, and magnetic tapes made using this powder have improved coercive force. Starting with
Various stability of coercive force, transfer characteristics, erasing characteristics, etc. are improved, and various magnetic characteristics such as squareness ratio and orientation are also significantly improved. In addition, in the method of the present invention, when a Mn compound is used, it is possible to reduce the infrared transmittance of the magnetic tape, so it is useful in applications that require this property, and is advantageous as it can be expected to be used in a wider range of applications. be. Examples 1 to 5 100 g of γ-Fe ₂ O ₃ (coercive force Hc: 411oe, BET specific surface area: 26 m ² /g) was dispersed in 1 part of water to make a slurry, and the slurry was prepared at 40°C while blowing N ₂ gas into the liquid. , 63 ml of 0.85 mol/cobalt sulfate aqueous solution
98 ml of a 0.90 mol/aqueous ferrous sulfate solution was added and stirred, and then a 5 mol/aqueous NaOH solution was added to deposit a cobalt compound and a ferrous compound on the surface of the γ-Fe ₂ O ₃ particles. After that, it was stirred and aged at 40℃ for 3 hours (the pH of the slurry at this time was
It was 8.5). While maintaining the slurry thus obtained at 40°C, an aqueous solution containing a predetermined amount of manganese sulfate and an aqueous NaOH solution slightly in excess of the neutralization equivalent of this salt are added so that the Mn content is as shown in Table 1 below. A manganese compound was deposited by adding . After that, it was stirred at 40℃ for 1 hour (the pH of the slurry at this time was 10.5).
). This slurry was filtered and washed with water, and the resulting wet cake was placed in an autoclave together with water in a separate container, purged with N ₂ gas, sealed, and heated at 130° C. for 6 hours in the presence of steam. After the treatment, it was dried at 120° C. in N ₂ gas to obtain desired cobalt-containing magnetic iron oxide powders (A) to (E). Comparative Example 1 Cobalt-containing magnetic iron oxide powder (F) was obtained in the same manner as in Example 1 except that no manganese compound was applied. The coercive force (Hc) and saturation magnetization (δs) of the above samples (A) to (F) were measured by a conventional method.
The results are shown in Table 1. Further, for each sample, a mixture was prepared according to the mixing ratio of the urethane formulation and the vinyl formulation described below, and the mixture was kneaded in a ball mill to produce a magnetic paint. Next, each magnetic coating material was applied to a polyester film using a conventional method, oriented and dried to produce a magnetic tape having a magnetic coating film of about 9μ. Coercive force (Hc), squareness ratio (Br/Bm),
Orientation (OR) was measured. The results are shown in Table 1. (Urethane formulation) (1) Cobalt-containing magnetic iron oxide powder 24 parts by weight (2) Polyurethane resin 5 (3) PVC-vinyl acetate copolymer 1.2 (4) Dispersant 0.5 (5) Mixed solvent (toluene /MEK/Cyclohexane = 3/3/1) 69.3 〃 (Vinyl formulation) (1) Cobalt-containing magnetic iron oxide powder 25 parts by weight (2) PVC-vinyl acetate-vinyl alcohol copolymer
5.2 〃 (3) DOP (dioctyl phthalate) 1.1 〃 (4) Dispersant 0.5 〃 (5) Mixed solvent (toluene/MEK=1/1)
68.2〃

[Table] Examples 6 to 8 Disperse 100 g of γ-Fe ₂ O ₃ (coercive force (Hc): 379 Oe, BET specific surface area: 33 m ² /g) in 1 part of water to make a slurry, and make a slurry at room temperature (30°C). While blowing _N2 gas into the mixture, add 70 ml of a 0.85 mol/mol cobalt sulfate aqueous solution and 140 ml of a 0.90 mol/ferrous sulfate aqueous solution.
and stirred, then 10 mol/NaOH
An aqueous solution was added to deposit a cobalt compound and a ferrous compound on the surface of the γ-Fe ₂ O ₃ particles. Thereafter, the mixture was stirred and aged at room temperature (30° C.) for the time shown in Table 2 below (the free OH group concentration at this time was 1 mol/mol). The slurry thus obtained was mixed at room temperature (30
℃), 70 ml of a 0.55 mol/manganese sulfate aqueous solution was added to deposit the manganese compound. Thereafter, the mixture was stirred at room temperature (30°C) for 3 hours. This slurry was filtered and washed with water, and the resulting wet cake was treated in the same manner as in Example 1 to obtain the desired cobalt-containing magnetic iron oxide powders (G) to (I). Comparative Example 2 Cobalt-containing magnetic iron oxide powder (J) was obtained in the same manner as in Example 7 except that no manganese compound was applied. Comparative Example 3 100 g of γ-Fe ₂ O ₃ used in Example 6 was added to 1 part of water.
While blowing _N2 gas into the liquid at room temperature (30°C), add 70 ml of a 0.85 mol cobalt sulfate aqueous solution, 140 ml of a 0.90 mol/ferrous sulfate aqueous solution, and a 0.55 mol/manganese sulfate aqueous solution. Add 70 ml of mixed aqueous solution and stir, then add 10 mol/NaOH aqueous solution to obtain γ-Fe ₂ O ₃
A cobalt compound, a ferrous compound, and a manganese compound were deposited on the surface of the particles. Then room temperature (30℃)
Aged by stirring for 3 hours (free OH
The group concentration was 1 mol/). This slurry was filtered and washed with water, and the resulting wet cake was treated in the same manner as in Example 1 to obtain cobalt-containing magnetic iron oxide powder (K). The coercive force (Hc) and saturation magnetization (δs) of the above samples (G) to (K) were measured by conventional methods.
The results are shown in Table 2. Furthermore, for samples (G) to (K), magnetic tapes were prepared in the same manner as above, and each tape was subjected to the usual methods for coercive force (Hc), squareness ratio (Br/Bm), orientation ( OR) was measured. The results are shown in Table 2.

[Table] Example 9 Disperse 100 g of γ-Fe ₂ O ₃ (coercive force (Hc): 401 Oe, BET specific surface area: 29 m ² /g) in 1 part of water to make a slurry, and add it to the liquid at room temperature (30°C). While blowing _N2 gas, 70ml of 0.85mol/cobalt sulfate aqueous solution and 140ml of 0.90mol/ferrous sulfate aqueous solution.
and stirred, then 10 mol/NaOH
A cobalt compound and a ferrous compound were deposited on the surface of the γ-Fe ₂ O ₃ particles by adding an aqueous solution. Thereafter, the mixture was stirred at room temperature (30°C) for 5 hours to ripen (the free OH group concentration at this time was 1 mol/mol). The slurry thus obtained was heated to 60° C. and 47 ml of a 0.59 mol/vanadyl sulfate aqueous solution was added to coat the vanadium compound. Thereafter, the mixture was stirred for 2 hours. This slurry was filtered and washed with water, and the resulting wet cake was placed in an autoclave together with water in a separate container, purged with N ₂ gas, sealed, and heat-treated at 120° C. for 6 hours in the presence of steam. After the treatment, it was dried at 120° C. in N ₂ gas to obtain the desired cobalt-containing magnetic iron oxide powder (L). Comparative Example 4 Cobalt-containing magnetic iron oxide powder (M) was obtained in the same manner as in Example 9 except that the vanadium compound was not deposited. The coercive force (Hc) and saturation magnetization (δs) of the samples (L) and (M) were measured by a conventional method. The results are shown in Table 3. Furthermore, for samples (L) and (M), magnetic tapes were prepared in the same manner as above, and each tape was subjected to the following methods: coercive force (Hc), squareness ratio (Br/Bm), orientation ( OR) was measured. The results are shown in Table 3.

[Table] Example 10 Disperse 100 g of γ-Fe ₂ O ₃ (coercive force (Hc): 399 Oe, BET specific surface area: 34 m ² /g) in 1 part of water to make a slurry, and add it to the liquid at room temperature (30°C). Stir while blowing N ₂ gas, add 42.2 ml of 10 mol/NaOH aqueous solution, and then add 168 ml of 0.90 mol/ferrous sulfate aqueous solution to coat the γ-Fe ₂ O ₃ particle surface with ferrous compound. I arrived. Subsequently, 10 mol/of
Add 143.5ml of NaOH aqueous solution and add 0.85mol/
70 ml of cobalt sulfate aqueous solution was added to coat the cobalt compound. Thereafter, it was aged by stirring at room temperature (30°C) for 3 hours (the free OH group concentration at this time was approximately 1.2
mole/mol). The slurry thus obtained was mixed at room temperature (30
℃), 14 ml of a 0.91 mole manganese sulfate aqueous solution and an NaOH aqueous solution equivalent to neutralizing this salt were added to deposit a manganese compound. Thereafter, the mixture was stirred at room temperature (30°C) for 2 hours (the concentration of free OH groups at this time was about 1.2 mol/). This slurry was filtered and washed with water, and the resulting wet cake was treated in the same manner as in Example 1 to obtain the desired cobalt-containing magnetic iron oxide powder (N). Comparative Example 5 Cobalt-containing magnetic iron oxide powder (O) was obtained in the same manner as in Example 10 except that no manganese compound was applied. Example 11 γ- similar to that used in Example 10 above
Disperse 100g of Fe ₂ O ₃ in 1 part of water to make a slurry,
135.2 ml of a 10 mol/a NaOH aqueous solution was added, and N ₂ gas was blown into the solution at room temperature (30° C.) to create a non-oxidizing atmosphere in the system. On the other hand, a ferrous sulfate aqueous solution (concentration 0.90 mol/
) 140ml under non-oxidizing atmosphere 10mol/
A suspension containing ferrous hydroxide and cobalt hydroxide was prepared by adding 38.2 ml of NaOH aqueous solution to generate ferrous hydroxide, and then adding 63 ml of 0.85 mol/cobalt sulfate aqueous solution (at this time). The concentration of free OH groups in the suspension was 0.1 mol/). This suspension was added to the slurry in a non-oxidizing atmosphere to deposit a ferrous compound and a cobalt compound on the surface of the γ-Fe ₂ O ₃ particles. Thereafter, the mixture was stirred at room temperature (30°C) for 3 hours to ripen (the concentration of free OH groups in the liquid at this time was 1 mol/mol). The slurry thus obtained was mixed at room temperature (30
℃), 14 ml of a 0.91 mol/molar manganese sulfate aqueous solution and an NaOH aqueous solution equivalent to neutralizing this salt were added to deposit a manganese compound. Thereafter, it was stirred at room temperature (30°C) for 2 hours (at this time, the free
OH group concentration was 1 mol/). This slurry was filtered and washed with water, and the resulting wet cake was treated in the same manner as in Example 1 to obtain the desired cobalt-containing magnetic iron oxide powder (P). Comparative Example 6 The same treatment as in Example 11 was carried out in Example 10 except that the manganese compound was not applied.
A cobalt-containing magnetic iron oxide powder (Q) was obtained. The coercive force (Hc) and saturated oxidation (δs) of the above samples (N) to (Q) were measured by conventional methods. The results are shown in Table 4. Furthermore, for samples (N) to (Q), magnetic tapes were prepared in the same manner as above, and for each tape, coercive force (Hc), squareness ratio (Br/Bm), orientation (OR ) was measured. The results are shown in Table 4.

【table】

Claims (1)

[Claims] 1. After coating a cobalt compound or a cobalt compound and a ferrous compound on the particle surface of magnetic iron oxide powder, a compound of at least one metal of manganese and vanadium is further coated. A method for producing cobalt-containing magnetic iron oxide powder. 2. After depositing a cobalt compound or a cobalt compound and a ferrous compound on the particle surface of magnetic iron oxide powder, depositing a compound of at least one metal of manganese and vanadium, and further heat-treating. A method for producing cobalt-containing magnetic iron oxide powder, characterized by: