JPS5870428A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the surface properties and electromagnetically converting characteristics by incroporating a flat abrasive and flat graphite powder into the magnetic layer. CONSTITUTION:To composition consisting chiefly of needlelike magnetic powder, a binder and a solvent are added flat abrasive particles composed of a platelike crystals of TiO2, alpha-Fe2O3, SiO2, Cr2O3 or other oxide, nitride, carbide or silicide and flat graphite powder, and they are well mixed, dispersed, applied to a nonmagnetic support, oriented and dried obtain a magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and an object of the present invention is to provide a magnetic recording medium with excellent surface properties and electromagnetic conversion characteristics.

Magnetic recording media include magnetic tapes, magnetic sheets, magnetic cards, magnetic disks, magnetic drums, etc., and have been used in audio, video, and computer applications, and have seen exciting developments in recent years.

Each of these recording media is suitable for high-density recording, and as the recording wavelength becomes even shorter, sensitivity and frequency characteristics become disadvantageous. Therefore, magnetic recording media with excellent surface properties are required to reduce air gap loss. is desired.

In magnetic recording media in which a magnetic layer is formed by coating a magnetic coating on a non-magnetic support, the following method is generally used to improve the surface properties of the medium.

In the entire manufacturing stage of magnetic paint, which consists of magnetic powder that is generally acicular in shape, a binder, and other additives and solvents that are added as necessary, it is used to improve dispersibility without destroying the magnetic particles. Knead. Next, the magnetic paint obtained in this way is coated on a non-magnetic support such as a polyester film, and when it is necessary to arrange the individual acicular magnetic particles in one direction, until dry. Apply an orientation magnetic field to the coated film and dry it. Next, in order to further improve the surface properties of the magnetic film thus obtained, a calendering device is used to perform surface processing.

In conventional magnetic recording media manufactured by such a method, the trend is to make the surface of the magnetic layer increasingly smooth in order to prevent deterioration of the sensitivity one-frequency characteristic due to air gap loss. In particular, in the case of video tapes, the surface quality is comparable to that of magnetic particles, abrasives, and inorganic pigments such as antistatic carbon black.
No matter how much the surface treatment by a calendering device is improved, the surface properties of the magnetic layer cannot be reduced to less than the maximum particle size among the above-mentioned inorganic pigments. In general, inorganic pigments that inhibit this improvement in surface properties include carbon black, which is an abrasive and an antistatic agent, and granular powders with a diameter of 0.2 to 1 μm are used for each.

As a result of intensive research on the above points, the present invention uses flat, high-hardness fine particles as an abrasive and flat graphite powder as a crushed antistatic agent, resulting in much better surface properties on magnetic surfaces than before. This is based on the discovery that a magnetic recording medium with excellent electromagnetic conversion characteristics was obtained.

That is, the present invention uses flat high-hardness fine particles as an abrasive and flat graphite powder as an antistatic agent in a composition consisting of acicular magnetic powder, a binder, and other additives and solvents added as necessary. In addition, this is sufficiently mixed and dispersed to form a magnetic coating liquid, and this magnetic coating liquid is applied onto a non-magnetic support, oriented, and dried. By subjecting this dried magnetic film to surface treatment using a calender, a magnetic recording medium with extremely excellent surface properties is provided.

The abrasive made from flat powder used in the present invention includes high-hardness fine powder of plate-like crystals made of oxides, nitrides, carbides, and silicides, either alone or in combination. TtOa-Ffl, 03.
There are plate-shaped powders such as SiO2 and Cr2O3. It is effective that the particle size of the flat abrasive particles and flat graphite used is 0.2 to 1 μm, and the thickness is about half or less.

When such flat high-hardness fine particles are used as an abrasive and flat graphite powder is used as an antistatic agent, each flat particle that appears on the surface of the magnetic layer becomes almost parallel to the magnetic surface after being coated and calendered. It is thought that the magnetic layers are arranged in a straight line, further improving the surface of the magnetic layer.

Hereinafter, a method for manufacturing a magnetic recording medium according to the present invention will be explained using a magnetic tape as an example.

The acicular magnetic powder may be any of magnetic iron oxide, chromium dioxide, metal magnetic powder, and the like. To this magnetic powder, an abrasive made of the above-mentioned flat fine powder, flat graphite powder, a binder, and a lubricant 9 a dispersing agent added as necessary;
A plasticizer and the like are added and thoroughly mixed and dispersed with a solvent to produce a magnetic paint having a desired component ratio.

As the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and the like can be used alone or in combination.

Lubricants include higher fatty acids, higher fatty acid esters, silicone oil-based lubricants, and fluorine oil-based lubricants. As a dispersant, the above-mentioned lubricants have this function, but lecithin, metal soap, etc. may also be used.

As the dispersing machine, a ball mill, a vibration mill, a sand mill, a desilver, an attritor, a high-speed mill, a xer kneader, etc. are used, and these may be used in combination.

The magnetic paint thus obtained is applied onto a support such as a polyester film. The coating method may be any of a doctor blade method, a gravure method, a reverse roll method, and the like.

Immediately after application, a smoother, wire smoother, film smoother, etc. can be used to further improve the smoothness of the coating film.

After that, before drying the coating film, a magnetic field orientation device is used to align the magnetic powder in the coating film in one direction, and the coating film is passed through an appropriate magnetic field. The strength of the magnetic field applied at this time varies depending on the coercive force of the magnetic powder, but is preferably about 2 to 4 times the coercive force. Magnets include permanent magnets and electromagnets. After the orientation treatment is performed in this way, it is dried to remove the solvent.

In order to further smoothen the surface of the magnetic layer of the coated and dried wide magnetic film, surface treatment is performed using a super calender roll. The surface properties of the calender roll at this time have a great influence on the electromagnetic conversion characteristics of the magnetic tape, but the conditions at this time are a temperature of 60 to 100°C and a pressure of 50 to 40°C.
00%/cm and a speed of 20 to 200 m/';j are preferred.

Next, the wide magnetic film that has been surface-treated in this way is cut into a predetermined width, and at this time, it is desirable to achieve full width accuracy and minimize width fluctuations without causing one-sided stretching.

During the final product assembly process, make sure that the tape surface is free from dust and other deposits that could cause dropouts.

The magnetic tape obtained as described above has a magnetic layer with better surface properties than conventional tapes and excellent electromagnetic conversion characteristics.

The gist of the present invention is not limited to the magnetic tape described above.
Needless to say, it can be applied to magnetic recording media such as magnetic sheets and magnetic cards.

Hereinafter, the present invention will be specifically explained based on examples.

It should be noted that all parts in the component ratios described in the Examples indicate parts by weight.

(Example 1) CO-containing magnetic iron oxide powder 100 parts Average particle size Length - 0.4 μm Acicularity ratio - 1 W Coercive force - 65000 Polyurethane resin 20 parts (manufactured by Nippon Polyurethane Co., Ltd. N-3113) Vinyl chloride-vinyl acetate co Polymer 6 parts (VAGH manufactured by UCC) Oblate titanium oxide (TiO2) powder 2 parts Average particle size Width - 0.58 m Length - 0.1 μm Oblate graphite powder 4 parts Average particle size Width - 0.3 μm Length Size = 0.06μm Lecithin 2 parts Methyl ethyl ketone (MEK) 100 parts Methyl inbutyl ketone (MIBK) 100 parts Toluene
After mixing and dispersing 100 parts of the above composition in a ball mill for 48 hours, 4 parts of hardener (Coronet L) was added and the resulting kneaded product was filtered through a filter having an average pore size of 3 μmf to prepare a magnetic coating liquid.

Next, this magnetic coating solution was coated on a polyester film with a total thickness of 16 μm, dried, and then rolled using a super calender roll (at a temperature of 9 μm).
The magnetic layer was surface-treated under the conditions of 0° C. and a pressure of 350 KP/crn, and then cut into pieces of a predetermined width to produce a magnetic tape.

(Comparative Example 1) In the composition of Example 1, granular carbon black (particle size 5011 m2) was used instead of the flat graphite powder.
A magnetic tape was produced in the same manner as in Example 1 except that F was used.

(Comparative Example 2) A magnetic tape was prepared in the same manner as in Example 1 except that in the composition of Comparative Example 1, granular titanium oxide powder (particle size 0.5/#1) f was used instead of the flat titanium oxide powder. Created.

(Example 2) CO-containing magnetic iron oxide powder 100 parts Average particle size Length - 0.4 μm 0 Acicularity ratio - 1! /l Coercive force = 650 oe Polyurethane resin 20 parts (Desmocol 176 manufactured by Bayer) Vinyl chloride-vinyl acetate copolymer 6 parts (VAGH manufactured by UCC) Oblate α-hematite (α-Fe203) powder 2 parts Average Particle size Width - 0,571?71 Thickness = 0.
1 part 1 m Oblate graphite powder 4 parts Average particle size Width - 0,37 itn Thickness 0,051 parts m Lecithin 2811 Methyl ethyl ketone (MEK) 100 parts Methyl isobutyl ketone (CMIBK) 100 parts Toluene
After mixing and dispersing 100 parts of the composition in a ball mill for 48 hours, hardener (Coronet)
L) The kneaded product obtained by adding 4 parts was mixed with an average pore size of 3/jm.
A magnetic coating solution was prepared by filtering the magnetic coating solution through a filter having the following properties.

A magnetic tape was produced in the same manner as in Example 1.

(Comparative Example 3) In the composition of Example 2, granular carbon black (particle size 70 μm)ffi was used instead of the flat graphite powder.
A magnetic tape was produced in the same manner as in Example 2 except for the following.

(Comparative Example 4) In the composition of Comparative Example 3, granular α-hematite powder (particle size 0.3 μm) was used instead of the flat α-hematite powder.
A magnetic tape was produced in the same manner as in Example 2 except for using the same method as in Example 2.

Surface roughness of the magnetic surface of each sample above and video 4
The characteristics of are shown in the table below.

(Left below) In the table, (1) surface roughness measurement of the magnetic layer is determined by Ran k , Ta
The measurement was carried out using a TaQ, ystep surface roughness meter (LPF; 25 Hz) manufactured by yR, or Hobson.

(2) Video Hoku records the brightness signal (50 gray level signal) from a television signal generator with a commercially available video tape recorder, plays it back, and measures the noise of the playback signal with a video color noise meter. Values were determined based on the level of Comparative Example 2.

3 As is clear from Table 3, the magnetic recording medium containing the abrasive made of flat fine powder according to the present invention and the antistatic agent made of flat graphite powder is different from the conventional granular abrasive or granular antistatic agent. The surface properties of the magnetic layer are better than those using inhibitors, and the electromagnetic conversion characteristics are clearly superior.

Claims (1)

[Claims] A magnetic recording medium comprising a magnetic layer provided on a non-magnetic support, wherein the polarized magnetic layer contains an abrasive made of flat fine powder and an antistatic agent made of flat graphite powder. magnetic recording media.