JP2605464B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium used for audio equipment, video equipment, or a computer.

2. Description of the Related Art The recording wavelength has been shortened due to the improvement of image quality of video equipment or the emergence of digital audio (DAT) equipment. Ferromagnetic powders used in these magnetic recording media have also been reduced to fine particles for the purpose of improving electromagnetic conversion characteristics. If the ferromagnetic powder becomes fine particles, the durability (still life, powder adhesion to the magnetic head, etc.) of the magnetic layer of the magnetic recording medium tends to deteriorate. Improvements in binder resins, lubricants, abrasives, etc. have been made to improve durability. Aluminum oxide, chromium oxide, red iron oxide and the like are used as abrasives, and their particle diameter is about 0.2 μm to 0.7 μm.

Problems to be Solved by the Invention As described above, fine particles of ferromagnetic powder cause a decrease in durability of a magnetic recording medium.
Additives such as lubricants and abrasives are being studied. Above all, the effect of the abrasive is great, and various studies have been made on the type, particle diameter, addition amount, and the like. If the amount of the abrasive is increased, the durability such as the still life is improved, but a problem occurs in that the wear amount of the magnetic head increases. The wear of the magnetic head increases as the hardness, particle diameter, and amount of the abrasive increase.

In addition, it is necessary to reduce the surface roughness of the magnetic layer in order to reduce the gap loss at the time of short wavelength recording and improve the electromagnetic conversion characteristics with the increase in the recording density. Therefore, it is desirable to reduce the particle size of the abrasive added to the magnetic layer.

Generally, the size of these abrasive particles is larger than that of the ferromagnetic powder, so that the orientation of the ferromagnetic powder is hindered and the magnetic properties such as the squareness ratio and the saturation magnetic flux density are reduced. As a result, the electromagnetic conversion characteristics are reduced.

In addition to the above-mentioned problems, the use of alloy heads (such as amorphous heads) has recently increased in proportion to use of metal tapes. In particular, when these heads are used in combination with a metal tape, the head is seized due to metal-metal friction and electromagnetic conversion characteristics are reduced. This head burn-in is affected by the use environment and is a phenomenon that often occurs in a low-temperature and low-humidity environment. In recent years, the usage environment has been diversified due to the spread of a camera-integrated video tape recorder, and it is necessary to satisfy the characteristics in all environments.

Head burn-in does not occur in magnetic recording media using iron oxide-based magnetic powders, which are more abrasive than metal-based magnetic powders. When metal-based magnetic powders are used, it is necessary to consider an abrasive to enhance the abrasion of the magnetic layer when using metal-based magnetic powders become.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium which is excellent in electromagnetic conversion characteristics, running durability, and the like without causing excessive wear and seizure to a magnetic head by optimizing the abrasiveness of a magnetic layer. It is.

Means for Solving the Problems The present invention has an average particle size of 0.
The ferromagnetic powder used for the magnetic layer is a needle-like particle having a major axis diameter of 0.2 μm or less, in which fine particles α-aluminum oxide of 05 to 0.15 μm are added in an amount of 6 to 15 parts by weight based on 100 parts by weight of the ferromagnetic powder. Magnetic powder or barium ferrite.

These abrasives have a specific particle size range, and can solve the above-mentioned problems.

For example, since the particle diameter is within a specific range, the polishing power and the number of abrasive particles are well balanced. That is, since the particles are fine particles, the polishing force is small and the wear amount of the head does not increase. Further, since the particles are fine particles, the number of abrasive particles contained in a unit volume is very large, and they are present evenly on the surface of the magnetic layer coating film, so that the coating film strength is improved and durability such as still life can be improved.

In addition, the surface of the coating film of the magnetic layer has an appropriate head cleaning property, and it is possible to improve the burn-in of the head which has been caused by the combination of the metal tape and the alloy head.
Further, problems such as deterioration of the roughness of the magnetic layer surface and disturbance of the orientation of the ferromagnetic powder due to the small particle size can be solved.

Such a problem becomes more remarkable as the ferromagnetic powder becomes finer, and becomes a serious problem when the major axis diameter of the acicular magnetic powder is 0.2 μm or less.

Barium ferrite magnetic powder also has a similar problem.

The magnetic recording medium of the present invention is obtained by adding fine particles α-aluminum oxide having a particle diameter of 0.05 to 0.15 μm to a magnetic layer containing a needle-shaped magnetic powder or a barium ferrite magnetic powder having a major axis diameter of 0.2 μm or less. .

Fine particles α- within a specific particle diameter range characterized by the present invention
By adding aluminum oxide, durability can be improved without increasing head wear, and a magnetic recording medium having excellent electromagnetic conversion characteristics excellent in magnetic layer surface roughness, magnetic characteristics and magnetic head cleaning properties can be obtained.

Examples Hereinafter, examples of the present invention will be described.

Non-magnetic support Polyethylene terephthalate film Thickness 10 μm Composition of magnetic paint Magnetic powder 100 parts by weight Carbon black (MA-7B: manufactured by Mitsubishi Kasei Kogyo) 3 parts by weight Abrasive (α-Al ₂ O ₃ ) Vinyl chloride vinyl acetate copolymer resin (VAGH: manufactured by UCC) 10
Parts by weight Polyurethane resin (N-2304: manufactured by Nippon Polyurethane)
0 parts by weight Myristic acid 2 parts by weight Stearic acid 1 part by weight n-butyl stearate 2 parts by weight Isocyanate 4 parts by weight The magnetic powder and abrasive used in Examples and Comparative Examples are as follows.

(Magnetic powder) Magnetic powder A: Ferromagnetic alloy powder (major axis diameter 0.16 μm, Hc = 1500 Oe) Magnetic powder B: Ferromagnetic alloy powder (major axis diameter 0.24 μm, Hc = 1500 Oe) Magnetic powder C: Co-containing magnetic oxidation Iron powder (Long axis diameter 0.18μm, Hc = 85
0Oe) Magnetic powder D: Barium ferrite magnetic powder (plate diameter 0.05μm, Hc
= 1100 Oe) (Abrasive (α-Al ₂ O ₃ )) Abrasive A: average particle size 0.1 μm Abrasive B: average particle size 0.05 μm Abrasive C: average particle size 0.2 μm Abrasive D: average particle size 0.4 Production method of μm magnetic paint A mixed solvent of methyl ethyl ketone / toluene / cyclohexanone (weight ratio 3/3/1) is added to a mixture obtained by removing the lubricant and curing agent from the composition of the above magnetic paint to obtain an appropriate viscosity.
The magnetic powder was sufficiently kneaded and dispersed by using a twin-screw extruder as a kneader and a sand mill as a disperser. Thereafter, a lubricant and a curing agent were added so as to have the above composition, the solid content ratio was adjusted to 30% by weight with a mixed solvent, and the mixture was filtered through a 1 μm filter to prepare a magnetic coating material for coating.

(Example using ferromagnetic alloy powder as magnetic powder) Example 1 A polyethylene terephthalate film was subjected to a corona treatment, and then 100 parts by weight of magnetic powder A and 6 parts by weight of abrasive A were applied by the above method. Apply the prepared magnetic paint, orient, dry, calender, and heat cure (60 ° C for 24 hours) to form a magnetic layer with a thickness of 3 µm. On the opposite surface, apply a back coat layer mainly composed of carbon black after drying. 0.7 thick
It was applied and formed to a thickness of μm. This was slit to 1/2 inch width to obtain a magnetic tape sample No. 1 for video.

Example 2 A magnetic paint was prepared by changing only the amount of the abrasive of Example 1 to 10 parts by weight, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 2. .

Example 3 A magnetic paint was prepared by changing only the amount of the abrasive of Example 1 to 15 parts by weight, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 3. .

Example 4 A magnetic paint was prepared by changing the abrasive of Example 1 to Abrasive B, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 4.

Comparative Example 1 A magnetic paint was prepared by changing only the amount of the abrasive in Example 1 to 20 parts by weight, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 5. .

Comparative Example 2 A magnetic paint was prepared by changing the abrasive of Example 1 to abrasive C, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 6.

Comparative Example 3 A magnetic paint was prepared by using only 10 parts by weight of the abrasive of Comparative Example 2, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 7.

Comparative Example 4 A magnetic coating material was prepared by changing the abrasive of Example 1 to abrasive D, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 8.

Comparative Example 5 A magnetic paint was prepared by changing the magnetic powder of Example 2 to magnetic powder B, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 9.

Comparative Example 6 A magnetic paint was prepared by changing the abrasive of Comparative Example 5 to Abrasive B, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 10.

Comparative Example 7 A magnetic paint was prepared by changing the abrasive of Comparative Example 5 to Abrasive C, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 11.

(Example using magnetic iron oxide powder as magnetic powder) Example 5 A magnetic paint was prepared by changing the magnetic powder of Example 2 to magnetic powder C, and a magnetic layer and a back coat layer were formed in the same manner as in Example 1. And a magnetic tape sample No. 12 was obtained.

Comparative Example 8 A magnetic paint was prepared by changing the abrasive of Example 5 to abrasive D, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 13.

(Example using barium ferrite as magnetic powder) Example 6 A magnetic paint was prepared by changing the magnetic powder of Example 2 to magnetic powder D, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1. A magnetic tape sample No. 14 was obtained.

Example 7 A magnetic paint was prepared by changing the magnetic powder of Example 4 to magnetic powder D, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 15.

Comparative Example 9 A magnetic paint was prepared by changing the abrasive of Example 6 to Abrasive D, and a magnetic layer and a back coat layer were provided in the same manner as in Example 1 to obtain a magnetic tape sample No. 16.

The surface roughness, C / N, still life, and head wear of the magnetic layer were measured for the above samples No. 1 to No. 13.

Surface roughness of magnetic layer: The surface roughness of the magnetic layer surface was measured using a non-contact three-dimensional surface roughness measuring device TOPO-3D manufactured by WYKO, USA.

Measurement of C / N: The C / N of the test tape was measured at 7 MHz ± 1 MHz using a VHS video tape recorder (Model NV-FS900, manufactured by Matsushita Electric Industrial Co., Ltd.). In addition, the measurement of the sample prepared using ferromagnetic alloy powder and barium ferrite was performed by appropriately adjusting the recording current.

Still life: Using a VHS video tape recorder (manufactured by Matsushita Electric Industrial Co., Ltd., model NV-FS900), continuous playback was performed in still mode, and the time until the playback signal dropped 6 dB of the recording signal was measured ( Under -10 ° C environment).

Head wear: Using a VHS video tape recorder (Model NV-FS900, manufactured by Matsushita Electric Industrial Co., Ltd.), running each test tape for 100 passes in an environment of 40 ° C and 80% RH (3.3 cm /
Seconds), a test was performed, and the wear amount of the head was measured thereafter.

Table 1 shows the results of the examples using the ferromagnetic alloy powder as the magnetic powder.

From the results in Table 1, the ones with a specific amount of abrasive in a specific particle size range (Samples 1, 2, 3, 4) were compared with those with a large abrasive particle size (Samples 6, 7, 8). Excellent characteristics are obtained in terms of surface roughness, C / N, and head wear.

Further, as the amount of the abrasive added increases, the still life is prolonged, but the C / N and surface properties deteriorate, and the amount of head wear increases (samples 1, 2, 3, and 5).

If the head wear amount is small, head clogging is likely to occur, and if the head wear amount is large, the life of the head is shortened.
1010 μm). For this purpose, it is understood that the amount of the abrasive having a specific particle size range according to the present invention must be 6 to 15 parts by weight (6 parts by weight and
From the amount of head wear with 20 parts by weight added (Sample 1,
5)).

On the other hand, if the abrasive has a large particle diameter, adding 10 parts by weight of the abrasive cannot provide satisfactory characteristics (Sample 7).

If the major axis diameter of the magnetic powder is large, even if the particle size of the abrasive is changed, the characteristics will not be significantly improved (samples 9 and 1).
0,11). This is presumably because the magnetic powder is too large to improve the coating properties such as the surface properties only by changing the abrasive.

The abrasive of the present invention has a fine magnetic powder (major axis diameter 0.18).
(μm or less) shows a remarkable effect.

Table 2 shows the results of Examples using magnetic iron oxide powder as the magnetic powder.

Similar to the case of using ferromagnetic alloy powder, when magnetic iron oxide powder was used, the surface properties and C / N were improved in the case of using a specific abrasive as compared with those having a large abrasive particle size. (Samples 12, 13).

Table 3 shows the results of the examples using barium ferrite as the magnetic powder.

The barium ferrite magnetic powder used was a fine particle with a plate diameter of 0.05 μm, so the effect of the abrasive was remarkably exhibited, and the surface properties, C / N, and head wear were greatly improved (samples 14, 15). , 16).

Effect of the Invention By adding a specific amount of fine particles of α-aluminum oxide having a particle diameter in a specific range, which is a feature of the present invention, durability can be improved without increasing head wear, and the magnetic layer surface roughness and magnetic characteristics can be improved. Further, it is possible to realize a magnetic recording medium which is excellent in magnetic head cleaning property and excellent in electromagnetic conversion characteristics and suitable for high-density recording.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Akira Kisoda 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (72) Inventor Nobuyuki Aoki 1006 Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-248318 (JP, A)

Claims (2)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of a ferromagnetic powder and a binder formed on a non-magnetic support,
The ferromagnetic powder contained in the magnetic layer is a needle-shaped magnetic powder having a major axis diameter of 0.2 μm or less, and has an average particle size of 0.
05-0.15μm fine particles α-aluminum oxide ferromagnetic powder
A magnetic recording medium comprising 6 to 15 parts by weight per 100 parts by weight. 2. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is barium ferrite.