JPH0472362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing magnetic powder for recording media that improves magnetic properties such as saturation magnetization or coercive force. Improvements in the input/output characteristics and frequency characteristics of magnetic recording devices are largely due to the magnetic characteristics (saturation magnetism, coercive force) of the magnetic powder used in magnetic tapes. However, until now, there has been no particular method for further improving the properties of magnetic powder once produced. For example, magnetic powder barium ferrite usually uses Co as a component to control the coercive force.
The one substituted with Ti is used, but the maximum value of saturation magnetization when changing the substitution ratio of Co and Ti is 63±
It is estimated (calculated) to be 1 emu/g (D.
J. De Bitetto, Journal of Applied Physics 35 ,
3482 (1964), the saturation magnetization of normally produced barium ferrite was 57-58. Therefore,
Although it was theoretically expected that further improvements could be made, no suitable method for achieving this was known so far. Therefore, the purpose of the present invention is to further
An object of the present invention is to provide a method for producing magnetic powder for recording media with improved magnetic properties such as saturation magnetization. That is, the present invention is a manufacturing method for a magnetic powder recording medium, characterized in that magnetic powder for a recording medium is subjected to plasma treatment such that the surface of the magnetic powder for a recording medium is in an unmolten state. In the plasma treatment of the present invention, the magnetic powder is brought into contact with plasma or with active species in the plasma without melting the surface of the magnetic powder in a treatment step for improving the magnetic properties of the raw magnetic powder. The magnetic powder for recording media of the present invention, which is plasma-treated in a non-molten state, has improved magnetic properties, and its use improves the input/output characteristics of magnetic recording devices.
It is extremely useful as it can greatly improve frequency characteristics. In particular, if the magnetic powder for recording media is barium ferrite powder, the saturation magnetization among the magnetic properties can be significantly improved by simply contacting active species in plasma. There are no particular restrictions on the method of generating plasma used in the treatment, and microwave discharge plasma, high-frequency discharge plasma, AC glow discharge plasma, DC glow discharge plasma, etc. can be used, but in particular, the method of the present invention shown in the Examples below is applicable. When microwave discharge plasma treatment is performed using the device developed by
It can be processed uniformly and efficiently. Gases for discharge include oxygen; mixed gas of oxygen and rare gases (Ar, He, Ne, Kr, Xe, etc.); mixed gas of oxygen and nitrogen; carbon dioxide; carbon dioxide and rare gases (Ar, Ne, Kr, etc.). , Xe, etc.); mixed gas of carbon dioxide and nitrogen; carbon monoxide; mixed gas of carbon monoxide and rare gas; mixed gas of carbon monoxide and nitrogen; halogenated methane; mixed gas of halogenated methane and rare gas Mixed gas: A mixed gas of halogenated methane and nitrogen is preferred. The treatment can be carried out by placing the powder to be treated directly in the discharge area where plasma is generated and bringing it into contact with the plasma, or by allowing the plasma to flow out of the discharge area and placing the powder to be treated downstream of the flow to form active species. It is also possible to bring them into contact. The former is superior in terms of processing efficiency. Moreover, according to the latter method, temperature rise of the magnetic powder and ion bombardment can be avoided if they are undesirable. In either case, it is desirable to perform the treatment while stirring the powder to be treated in order to perform uniform treatment. The plasma-treated magnetic powder for recording media according to the present invention, particularly barium ferrite, has an increased saturation magnetization, and if the composition, pressure, and treatment time of the discharge gas are appropriately selected, the theoretically estimated maximum The saturation magnetization value is 63±emu/g. Specifically speaking, gas pressure is generally 0.1~
10 Torr, more preferably about 0.5 to 5 Torr.
If it is less than 0.1 Torr, it is often difficult to sustain the discharge stably, and if it exceeds 10 Torr, the plasma tends to converge and uniform processing is difficult. In addition, the gas is preferably a mixed gas of rare gas (especially Ar) and oxygen, especially oxygen/rare gas (partial pressure ratio) of about 0.1.
~1 is good. More specifically, for example, when the total pressure is about 0.5 Torr, the oxygen partial pressure is about 0.045~
0.25 Torr is good, and when the total pressure is about 5 Torr, the oxygen partial pressure is about 0.45 to 2.5 Torr. Hereinafter, the present invention will be specifically explained based on Examples. Example 1 In this example, the apparatus shown in FIGS. 1 to 4 was used. First, the device and its operation will be explained. Figure 1 is a vertical cross-sectional view of the main parts of this device, and Figures 2, 3, and 4 are
They are - sectional view, - sectional view, and - sectional view in the figure. The parts surrounded by broken lines in Fig. 1 are the main components of this device, respectively: 1 is a microwave generation system, 2 is a powder plasma processing system, 3 is a discharge gas supply means, and 4 is an exhaust gas. It is a means. The microwave generation system 1 includes a microwave oscillator (a magnetron in this example) 11 and a waveguide 12 connected to the oscillator for transmitting microwaves. 13 is a three-stub tuber, and 14 is a plunger. The powder plasma processing system 2 consists of a cylindrical container (made of stainless steel in this example) 203 equipped with a discharge gas inlet 201 and an exhaust port 202, and the inside of the container becomes a powder plasma processing chamber 204. ing. This container 203 has the gas inlet 201 and the exhaust port 202 and is hermetically sealed, but an antenna 205 made of a conductive material (in this example, a stainless steel tube) is inserted into the cylindrical container from inside the waveguide 12. It protrudes toward the center. This antenna 205
The protruding portion into the container 203 is hermetically surrounded by a cylindrical body 206 made of a microwave transparent material (quartz in this case). The diameter of the base 206a of the cylinder 206 is increased to increase the strength, and the flange 206b is attached to the base 206a to increase the strength of the container.
It is fixed to the lid part of 03. This cylinder 20
The surfaces of the base and flange portion of 6 are coated with a conductive film (in this case, an Au vapor-deposited film) (not shown),
This conductive film is grounded to provide a shielding effect against macro waves. The left end of the container in Figure 1 is a disk 2 with a hole in the center.
07, a cooling water jacket 208 is provided so as to surround the base 206a of the cylindrical body, and the flange portion 206b of the cylindrical body is attached to the jacket 209.
Fixed by O-rings 21 are provided between the disk 207 and the jacket 208, and between the jacket 208 and the flange portion 206b of the cylinder.
0 and 211 are attached to keep the inside of the container 203 confidential. Cooling water jacket 20
8 is provided to prevent the O-rings 210 and 211 from deteriorating due to heating. The antenna 205 is made of a hollow pipe, and its fixing base 205a is made of an insulating material (quartz in this example), while the antenna body is made of a conductive material as described above. A cooling gas such as N ₂ gas is fed into the antenna pipe from the outside, and the gas flowing out from the tip of the antenna is discharged to the outside through a gap 212 provided at the base of the antenna. The antenna 205 transmits microwaves from the inside of the waveguide 12 into the processing container 203 and generates plasma around it, but inside the horizontally arranged container 203, the powder to be processed is almost cylindrical. The upper half of the cylinder 206 is covered with a gold or aluminum vapor-deposited film (not shown) so that microwaves are reflected and high-concentration plasma is generated below the cylinder 206. Covered. The cylindrical container 203 is equipped with a capacitance manometer 213 in a part thereof, and is further equipped with a stirring means for uniform treatment. That is, a cylindrical stirring tool 214 is provided at the center of the processing container 203 and coaxially therewith. This cylindrical stirring tool 21
4 has an open end 215 and is fixed to a rotary drive shaft 218 at the other end by a stop plate 217 having a narrow hole 216. The other end of the container 203 is covered with a disc-shaped lid 220 having a recess 219 (drive shaft storage housing 222) in the center for accommodating the rotational drive shaft 218.
3 and the lid body 220 are hermetically sealed by a sealing member 221 such as an O-ring. This airtightness is naturally achieved during operation because when the exhaust means 4 is operated to reduce the pressure inside the container 203, a suction force is applied to the lid 220. Recess 2 of lid body 220
19 is a cylindrical housing 22 with a closed end.
2, into which one end of the rotational drive shaft 218 is inserted. The rotational drive shaft 218 is connected to the lid body 2
The lid body 22 is rotatably supported by a bearing 223 provided in the drive shaft storage housing 20 and a bearing 224 provided in the drive shaft storage housing 222.
0 and the drive shaft storage housing 222 at all. The end portion 218a of the rotary drive shaft is made of a ferromagnetic material such as steel, and is rotated using magnetic force as described later. A rotating body 226 in which a plurality of electromagnets or permanent magnets, four permanent magnets 225 in this example are arranged at equal intervals, is arranged around the drive shaft storage housing 222 with a gap 227 in between. The rotating body is rotatably supported (supporting means, not shown) around the drive shaft storage housing in a separate state. 228 is a drive motor, and the power of this motor is transmitted to the rotating body 226 by a belt 229, so that the rotating body 226 can be rotated around the drive shaft storage housing 222. When the rotating body 226 rotates, the magnetic field formed by the four permanent magnets of the rotating body 226 also rotates, which causes the rotary drive shaft 218 to also rotate. That is, in this device, the cylindrical stirring tool 214 is rotated while the inside of the processing chamber is hermetically closed from the outside, thereby stirring the magnetic powder. The inner surface of the cylindrical stirrer 214 is provided with protrusions 230 in some places to increase the stirring efficiency, and has an uneven shape. The discharge gas supply means 3 includes a gas storage cylinder 3
1. A pipe 32 connected to the on-off valve 31a of the cylinder 31, and a gas flow meter 3 provided on the pipe 32.
3 and a needle valve 34. Piping 32 is connected to gas inlet 201 of container 203. Further, the exhaust means 4 connected to the exhaust port 202 of the container 203 includes a pipe 41, a valve 42, and a trap 43.
and an oil rotary pump 44. Next, one method of operating the apparatus will be explained using plasma treatment of magnetic powder as an example. First, the oil rotary pump 44 is operated to exhaust the inside of the processing container 203 to a pressure of 10 ^-3 Torr or less. Next, the discharge gas is passed through the flow meter 33 and the needle valve 3.
4, the gas is supplied from the gas storage cylinder 31 to the processing chamber 204 through the discharge gas inlet 201.
At this time, it is preferable to continue evacuation with the oil rotary pump 44, adjust the pressure in the processing chamber 204 to about 10 ^-1 to 5 Torr, and adjust the gas flow rate to about 30 to 300 c.c./min. The pressure and gas flow rate are adjusted using the needle valve 34 while observing the capacitance manometer 213 and flow meter 33. Next, the microwave oscillator 11 is operated to oscillate microwaves with a frequency of 2450 MHz and a power of 100 to 500 W, which is small enough not to melt the surface of the magnetic powder.
3 and the plunger 14, and the microwave is transmitted into the processing chamber 204 by the antenna 11. Then, plasma is generated around the cylindrical body 206 due to the discharge. At this time, plasma is generated almost entirely within the processing chamber 204;
Due to the Au vapor deposited film covering the upper half of the cylinder 206, particularly high-density plasma is generated near the bottom of the cylinder 206. The active species in the plasma generated in the processing chamber 204 come into contact with the powder 231 placed in the stirring tool 214, and the powder is subjected to plasma treatment. At this time, the cylindrical powder stirring tool 214
is rotated by the power of the motor 228 to agitate the powder. At this time, in order to obtain high stirring efficiency, stirring is performed by placing a stirring piece 232 made of quartz or stainless steel in a stirring tool together with the powder 231 to be treated. Barium ferrite powder (BaOFe10.4Co0.8Ti0.8
O18) was plasma treated. The discharge gas used,
Table 1 shows the discharge power, treatment time, and saturation magnetization after treatment.

【table】

【table】

[Table] Example 2 Using the same apparatus as in Example 1, the same raw material magnetic powder (57.5 emu/g) was subjected to plasma treatment. The discharge gas was a mixed gas of 1.0 Torr of argon and 0.05 to 1.0 Torr of oxygen, and the discharge power was 500 W and the treatment time was 30 minutes. Regarding oxygen partial pressure and saturation magnetization after treatment, Part 5
The results shown in the graph shown in the figure were obtained. Example 3 Using the same apparatus as in Example 1, the same raw material magnetic powder (57.5 emu/g) was subjected to plasma treatment. The discharge gas is a mixed gas of 1.0 Torr of argon and 0.7 Torr of oxygen, and the discharge power is 500W. Processing time 5-75
As a result, the results shown in the graph shown in FIG. 6 were obtained. Example 4 In this example, the apparatus shown in FIG. 7 was used. First, the device and its operating method will be explained. FIG. 7 shows the entire device, showing the main parts in longitudinal section. In the figure, -, -
, - The cross section is exactly the same as in FIGS. 2, 3, and 4. This apparatus includes a plasma generation system 51, a powder treatment system 52 for treating powder with active species generated by the plasma generation system 51, means 53 for supplying discharge gas to the plasma generation system, and a powder treatment system 52 for treating powder with active species generated by the plasma generation system 51. and an exhaust means 54 for reducing the pressure in the body processing system. The discharge gas supply means 53 and the exhaust means 54 are the same as those in the apparatus shown in FIG. The plasma generation system includes a microwave oscillator 55 such as a magnetron, a waveguide 56 connected to the microwave oscillator for transmitting microwaves,
It consists of a discharge tube 57 for generating plasma inside the waveguide, which is arranged to penetrate the waveguide. Discharge tube 57 is typically made of quartz. The waveguide 56 is equipped with a three-stub tuner and a plunger for impedance matching. A water cooling device 58 for cooling the discharge tube 57 is also provided. A pipe from a discharge gas supply means is connected to one end of the discharge tube 57. The powder processing system includes a processing container 60 that is directly connected to the other end of the discharge tube and constitutes a processing chamber 59. The processing container 60 may have an integral structure with the discharge tube 57 and may be made of the same material (quartz), but may also be made of metal such as stainless steel. The processing chamber 60 is an area that accommodates the powder to be processed, and is an area where the plasma generated in the discharge tube 57 is guided, and the magnetic powder is contact-processed with relatively long-lived active species therein. Processing container 6
0 has a substantially cylindrical shape coaxial with the discharge tube 57, and a capacitance manometer 61 is provided at one end thereof. The processing chamber 59 is hermetically sealed except that an exhaust port 62 connected to the exhaust means 54 is provided on the opposite side of the connection side to the discharge tube 57. A cylindrical stirrer 63 having substantially the same structure as the apparatus shown in FIG. 1 is provided inside the container. The exhaust port 62 is provided on the opposite side of the processing chamber from the discharge tube side. This is because the plasma generated in the discharge tube or the flow of active species contained therein needs to flow so as to sufficiently contact the powder disposed in the center of the processing chamber. Next, a procedure for processing powder using the above-mentioned apparatus will be explained. First, the oil rotary pump of the exhaust means 54 is operated to raise the inside of the processing container 59 to 10 ^-3 Torr.
Evacuate to pressure below. Next, the discharge gas is supplied from the gas storage cylinder to the discharge tube 57 via the flow meter and needle valve of the gas supply means 53.
At this time, the exhaust means 54 continues to exhaust the air, and normally,
It is preferable to adjust the pressure in the processing chamber 59 to about 10 ^-1 to 5 Torr and the gas flow rate to about 30 to 300 c.c./min. The pressure and gas flow rate are adjusted using a needle valve while observing the capacitance manometer 61 and flow meter. Next, the microwave oscillator tube 55 is operated to oscillate microwaves with a frequency of, for example, 2450 MHz and a power of 100 to 500 W, impedance matching is performed using the three stub tuber and plunger of the waveguide 56, and the microwave is transmitted into the discharge tube 57. Transmit to. Then,
The discharge gas flowing in the discharge tube 57 is discharged, and plasma is generated. The generated plasma moves along the gas flow from inside the discharge tube 57 to the processing chamber 59, but the short-lived active species disappear shortly after leaving the discharge tube, and only the relatively long-lived active species are processed. It comes into contact with the powder 64 placed in the container. The powder 64 is placed inside the cylindrical stirring tool 63, and the cylindrical powder stirring tool is rotated to stir the powder. At this time, higher stirring efficiency can be obtained by placing a stirring piece 65 made of quartz, stainless steel, etc. in the powder stirring tool together with the powder 64 to be treated. Next, the same barium ferrite as in Example 1 (BaOFe _10.4 Co _0.8 Ti _0.8 O ₁₈ ,
(saturation magnetization: 57.5 emu/g) was subjected to plasma treatment. Table 2 shows the discharge gas used, discharge force, treatment time, and saturation magnetization after treatment.

[Brief explanation of the drawing]

Figures 1 and 7 show the powder plasma processing apparatus used in Example 1 and Example 4, respectively.
Figures 3 and 4 are -, - and - sectional views of Fig. 1, respectively. FIG. 5 is a diagram showing the relationship between oxygen partial pressure and saturation magnetization in Example 2, and FIG. 6 is a diagram showing the relationship between processing time and saturation magnetization in Example 3. DESCRIPTION OF SYMBOLS 1...Microwave generation system, 2...Powder plasma treatment system, 3...Discharge gas supply means, 4...Exhaust means, 203...Cylindrical container, 205...Antenna, 206...Cylindrical body , 214... Cylindrical stirrer, 225... Magnet, 226... Rotating body, 228
... Electric motor, 229 ... Belt, 231 ... Powder, 232 ... Stirring piece, 51 ... Plasma generation system, 52 ... Powder processing system, 53 ... Discharge gas supply means, 54 ... Exhaust means , 57...discharge tube, 6
0... Processing container, 64... Powder, 65... Stirring piece.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A method for producing magnetic powder for recording media, characterized in that the magnetic powder for recording media is subjected to plasma treatment such that the surface of the magnetic powder for recording media is in a non-molten state. 2. The method for producing magnetic powder for recording media according to claim 1, wherein the magnetic powder for recording media is barium ferrite powder.