JPH04157617A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electric transducing characteristic and durability by providing a magnetic layer prepared in such a manner that a lower layer of an Mn compound and an upper layer of an Si compound being in specified quantities respectively are applied on the surface of a Co-coated type needle-like gamma-iron oxide powder and a material thus obtained is dispersed in a binder. CONSTITUTION:The surface of magnetic powder is modified by an Mn compound, an Mn hydroxide in particular, and then an Si compound, a hydroxide thereof in particular, is connected thereon. It is desired herein that the Mn component is in the range of 0.05 to 5.0%, preferably 0.1 to 1.0%, by a weight ratio to a Co-connected type needle-like gamma-iron oxide and that the Si component is in the range of 0.05 to 5.0%, preferably 0.1 to 2.0%, by the weight ratio thereto. By making the Mn compound and the Si compound exist on the surface of the magnetic powder in this way, a magnetic recording medium being excellent both in an electromagnetic conversion characteristic and in durability is obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a magnetic recording medium with improved electromagnetic characteristics, durability, and running friction.

[Conventional technology]

In recent years, magnetic recording media used for magnetic recording are moving toward high-density recording, and short wavelength recording is becoming increasingly important. Therefore, the characteristics required for magnetic recording media include high coercive force, high residual magnetic flux density, and smooth surface, and by improving these, electromagnetic conversion characteristics such as recording and reproducing output and S/N ratio can be improved. We have been trying to improve it. In response to this demand, progress has been made in the direction of micronization as a necessary requirement for magnetic powder. However, when magnetic powder becomes fine particles, it has poor dispersibility.
There were negative effects such as a decrease in square orientation and a roughened coating surface, leading to a decrease in electromagnetic conversion characteristics. Furthermore, when the particles become fine particles, the bondability with the resin decreases, resulting in a problem of deterioration of abrasion resistance and durability. Conventionally, measures have been taken to counter this problem, such as increasing the dispersion time, or using a surfactant as a dispersant to improve the wettability of the magnetic powder and resin. Measures have been taken such as mixing abrasive particles that are harder than magnetic particles and adding lubricants.

[Problems to be solved by the invention] However, measures such as lengthening the dispersion time lead to an increase in manufacturing costs, and the use of surfactants as dispersants still does not have sufficient dispersion effect and durability, and does not affect the surface of the coating film. There are still problems such as discharge and deterioration of running properties.Furthermore, it is necessary to mix non-magnetic components to improve IT abrasion resistance, but this not only reduces the coating film filling rate of magnetic powder. This results in problems such as loss of uniform dispersibility, a decrease in the magnetic field, and deterioration of the S/N ratio.
There has been a desire to resolve the tradeoff of deterioration in coating film strength. The purpose of the present invention is to solve these problems. The present invention solves the problems associated with making the magnetic powder into fine particles by changing the surface structure of the magnetic powder without relying on mechanical means or addition of non-magnetic substances. It is known to change the surface structure of magnetic powder. For example, it has been proposed to retain an aluminum compound and/or a silicon compound on the surface of magnetic particles (Japanese Patent Application Laid-open Nos. 13121-1982 and 184920-1982), but these methods mainly improve wear resistance. However, the improvement in dispersibility is not sufficient. It has also been proposed to contain zinc and/or silicon in magnetic particles (Japanese Patent Laid-Open No. 1992-178122).
) is said to improve dispersibility, but it is insufficient. Furthermore, it has been proposed to coat the surface of cobalt-coated magnetic powder with manganese hydroxide and aluminum hydroxide, or manganese hydroxide and zinc hydroxide (Japanese Patent Application No. 1-203226, No. 59-50504) is said to improve coercive force and dispersibility, but both wear resistance and dispersibility are insufficient. [Means for solving the problem] As a result of various studies to obtain a recording medium with excellent electromagnetic characteristics and durability, we first modified the surface of magnetic powder with a Mn compound, especially Mn hydroxide, and then added Si. By depositing a compound, particularly a hydroxide, a magnetic recording medium with excellent electromagnetic characteristics and durability was obtained. However, in order to simultaneously improve electromagnetic conversion characteristics and durability, Mn and S
It has been found that satisfactory characteristics cannot be obtained only when i is within a specific range, and outside this specific range. It has been found that the Mn hydroxide layer is not sufficiently shielded by the Si layer and contributes sufficiently to the fractionality. Therefore, according to the present invention, both durability and dispersibility can be improved. If this order is reversed, the dispersibility will improve, but durability will not be sufficient. The weight ratio of Mn component to Co-coated acicular γ iron oxide is 0.
．． The Si component is in the range of 0.05 to 5.0%, preferably in the range of 0.1 to 1.0%, and the Si component is in the range of 0.05 to 5.0%, preferably 0.1 to 2.0%. It is desired that the If the content of the Mn component is less than 0.05, the electromagnetic characteristics will not improve, and if it is more than 5.0%, the durability will decrease. Also, Si
The weight ratio of the components to Co-coated acicular γ iron oxide is 0.
If it is less than 1%, the durability effect is lost, and if it is more than 2.0%, the dispersibility will be extremely reduced. By making the Mn compound and the Si compound exist on the surface of the magnetic powder as described above, a magnetic recording medium with excellent electromagnetic conversion characteristics and durability was obtained. It is not yet clear what causes this phenomenon. However, the following reasons are assumed. Effects of Mn (1) The Mn compound added to the magnetic powder combines with the Co coating layer on the surface to form a new surface structure. (2) The wettability between the Mn compound present on the surface of the magnetic powder and the resin is improved despite the presence of the S compound, and the dispersibility is improved. Effect of Si (3) Magnetic powder with a Si compound present on its surface has high hardness and provides a polishing effect. (4) The bond between the Si compound and the resin is excellent, and the strength of the magnetic coating film is improved. It can be thought of as follows. Note that the action and effect of the present invention can be further improved by adding a fatty acid ester to the magnetic layer. Next, examples of the present invention will be specifically described in comparison with comparative examples. Here, the Mn compound and the Si compound more specifically refer to a hydroxide or a hydrated oxide. It also preferably contains saturated fatty acids and saturated fatty acid esters having 10 to 20 carbon atoms, which are commonly used to aid in dispersion. These materials are known in the art. As for the binder, it is preferable that at least one of the functional groups -COO)l, -SO, and Na is introduced into the molecular chain of the binder, which is usually introduced in order to improve dispersibility. Examples of resins into which functional groups can be introduced and which are suitable as binders include thermoplastic polymers, thermosetting prepolymers, and the like. Specifically, there are polyurethane resins, polyester resins, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, etc., and cellulose resins may also be added. For the surface-modified Co-adhered acicular γ iron oxide, manganese sulfate, sodium silicate, etc. are added after Co-adhesion, and neutralized and precipitated with sulfuric acid or the like. The present invention will be explained in detail below.

[Explanation of Examples]

A surface-modified Co-adhered acicular γ iron oxide was produced by the following method. Modified example acicular y Few Os (coercive force Hc4050e,
Disperse 100g (specific surface area 34 m2/g, axial ratio 10/1) in a 1 mol/1 NaOH aqueous solution to make a slurry,
While blowing N2 gas into this, 50 ml of 1 mol/l cobalt sulfate aqueous solution and 125 ml of 1 mol/1 ferrous sulfate aqueous solution.
ml was added and stirred at room temperature for 5 hours. Next, 230 g of a wet cake of iron oxide containing Kobaluo obtained by filtering and washing this slurry with water was dispersed in water to make a slurry of 100 g/l, and this slurry was heated to 45°C while blowing N2 gas, and the slurry was heated to 45°C with stirring. Adding an amount of manganese sulfate aqueous solution to obtain the desired amount of Mn, and subsequently adding an amount of sodium silicate aqueous solution to obtain the desired amount of Si while stirring,
Next, dilute sulfuric acid was added to the slurry to neutralize it to pH 7,
Subsequently, the mixture was stirred and aged for 30 minutes. The obtained hydroxide-coated magnetic powder was used in Examples. Example 1 A magnetic paint was prepared as follows. All parts in the component ratios shown are parts by weight. The Mn compound and Si compound are the weight percent of the metal based on the weight of the magnetic powder. Surface modified Co 7 Fe 2 'Oz
100 parts (Mn 0.5wt%S
i O, 5wt%) Coercive force 6S
O 0e Salt vinyl acetate copolymer 12 parts Polyurethane prepolymer 8 parts α-A℃203
3 part carbon
3 parts fatty acid (stearic acid) 2 parts fatty acid ester (butyl stearate) 1 part curing agent (methyl ethyl ketone) 200 parts After dispersing the above composition in a ball mill for 12 hours, polyisocyanate curing agent 15
The paint obtained by adding 50% of
A force S was applied to the polyester film to apply magnetic field orientation. After that, surface treatment (calendering) is performed 1
A videotape was created by slitting the tape to /2' width. Example 2 A videotape was produced in the same manner as in Example 1, except that the amount of Mn in the magnetic paint of Example 1 was changed from 0.5 wt% to O, 1 wt%. Example 3 A videotape was produced in the same manner as in Example 1, except that the amount of Si in the magnetic paint of Example 1 was changed from 0.5 wt% to O.1 wt%. Example 4 A videotape was produced in the same manner as in Example 1, except that the amount of Si in the magnetic paint of Example 1 was changed to 0.3 wt%. Comparative Example 1 A videotape was produced in the same manner as in Example 1, except that magnetic powder without Mn and Si treatment was used in the magnetic paint of Example 1. Comparative Example 2 In the magnetic paint of Example 1, the amount of Si treated was 0.5wt.
A videotape was produced in the same manner as in Example 1, except that the content was changed from % to 0.12 wt%. Comparative Example 3 In the magnetic paint of Example 1, the amount of Mn treated was 0.5wt.
A videotape was produced in the same manner as in Example 1, except that the content was changed from % to 0.12 wt%. Table 1 shows the measurement results of the video tapes of Examples and Comparative Examples. Comparative Example 4 A videotape was produced according to Example 1 except that A1 was used instead of Mn. Comparative Example 5 A videotape was produced according to Example 1 using Zn instead of Mn0 and without using Si.

[effect]

As can be seen from Figure 1, the examples of the present invention show comprehensively superior results compared to the use of Mn and Si alone. Example 1
．． No. 4 was used in a total amount of 1 and 08% by weight, and was extremely excellent overall. Procedural amendment July 26, 1991 Indication of Wataru Fukasawa, Commissioner of the Japan Patent Office 1990 Patent Application No. 281932 Title of the invention Relationship to the case of a person who makes corrections to magnetic recording media Patent applicant Location Chuo-ku, Tokyo 3-13-11 Nihonbashi
11'5 Contents of amendment in the column of detailed description of the invention in the specification to be amended The description is amended as shown in the attached sheet as follows. 1. In the 8th line from the 7th purchase, "Wettability is achieved despite the presence of S compounds" is corrected to "Wettability is achieved despite the presence of Si compounds."

Claims (5)

[Claims] (1) 0.05~ based on Co-coated acicular γ iron oxide
A lower layer of 5.0% by weight of Mn compound and an upper layer of 0.05 to 5.0% by weight of Si compound are coated on the surface of Co-coated acicular γ iron oxide powder and dispersed in a binder. A recording medium provided with a magnetic layer. (2) The magnetic recording medium according to item 1 above, wherein Mn and Si are hydroxides. (3) The magnetic recording medium according to claim 1 or 2, wherein the magnetic layer contains a saturated fatty acid having 10 to 20 carbon atoms and a saturated fatty acid ester. (4) Functional groups -COOH and -S in the molecular chain of the binder
4. The magnetic recording medium according to claim 1, wherein at least one type of O_3Na is introduced. (5) The surface of the Co-adhered acicular γ-iron oxide powder is modified with Mn hydroxide, and then Si hydroxide is applied. At that time, Mn hydroxide and Si hydroxide are Mn and Si are C
0.05 to 5.0 based on the adhering type acicular γ iron oxide powder.
1. A method for manufacturing a magnetic recording medium, which comprises controlling the magnetic iron oxide powder to 0% by weight, and then dispersing the magnetic iron oxide powder in a binder and adhering it to a non-magnetic supporting substrate.