JPS5868232A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the surface properties and electromagnetically converting characteristics by incorporating flat fine powder as an abrasive into the magnetic layer. CONSTITUTION:To a composition consisting of needlelike magnetic powder, a binder and a solvent is added high hardness fine powder composed of platelike crystals of TiO2, alpha-Fe2O3, SiO2, Cr2O3 or other oxide, nitride, carbide or silicide as a flat abrasive, and they are well mixed, dispersed and applied to a nonmagnetic support to obtain a magnetic recording medium. The particle size of the effectively used flat abrasive particles is almost equal to 0.2-1mum size of conventional granular abrasive particles, and the thickness is <=about 1/2 time that of the conventional particles.

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 they have been used for audio, video, and converter applications, and have seen exciting developments in recent years.

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

First, there are magnetic powders and binders that generally have acicular properties.

At the stage of producing a magnetic paint consisting of other additives and a solvent, which may be added as necessary, the magnetic particles are kneaded to improve their dispersibility without destroying them. Next, the magnetic paint obtained in this way is applied onto a non-magnetic support such as a polyester film, and if it is necessary to arrange the individual acicular magnetic particles in one direction, apply the magnetic paint until dry. Apply an orienting magnetic field to the 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 two-frequency characteristics due to air gap loss. In particular, in the case of video tapes, the surface quality is almost the same as the particle size of inorganic pigments such as magnetic particles, abrasives, and carbon blanks for antistatic agents. Even if the particle size is improved, the surface properties of the magnetic layer cannot be reduced below the maximum particle size among the above-mentioned inorganic pigments.

Generally, an abrasive is used as an inorganic pigment that inhibits the improvement of surface properties, and a granular high-hardness powder with a diameter of 0.2 to 1 μm is used for this abrasive.

As a result of intensive research on the above points, the present invention has developed a magnetic recording medium with much better magnetic surface properties and excellent electromagnetic conversion characteristics than before by using flat, high-hardness fine particles as an abrasive. It is based on what we have discovered.

That is, in the present invention, flat high-hardness fine particles are added as an abrasive to a composition consisting of acicular magnetic powder, a binder, other additives added as necessary, and a solvent. The magnetic coating liquid is coated 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 flat abrasive 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. , TiO2°α-Fe2o3. SiO2
There are plate-shaped powders such as , Cr2O3, etc. It is effective that the particle size of the flat abrasive particles to be used is about the same as the size of conventionally used granular abrasive particles, 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, the flat abrasive particles that appear on the surface of the magnetic layer line up almost parallel to the magnetic surface after being coated and calendered, further improving the surface of the magnetic layer. It seems that it is possible to do so.

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, the above-mentioned flat abrasive, binder, lubricant, dispersant, plasticizer, antistatic agent, etc., which are added as necessary, are added and thoroughly mixed and dispersed with a solvent to obtain the desired component ratio. Create a magnetic paint with

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 and higher fatty acid esters.

Fluorinated oil-based or fluorinated oil-based lubricants are available. As a dispersant, the above-mentioned lubricants also have this function (7), but lecithin, metal soap, etc. may also be used.

Examples of antistatic agents include carbon black, graphite, and surfactants.

Dispersion machines include ball mills, vibration mills, sand mills, desilvers, attritors, and high-speed mixers.

A kneader or the like is used, and these may be used in combination.

The magnetic paint thus obtained is applied onto a support such as a polyester film. Application methods include doctor blade method and gravure method.

Any method such as a reverse roll method may be used.

Immediately after coating, 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 manner, 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: temperature 60-100°C2 pressure 50-100°C
400 kf/cm.

A speed of 20 to 200 m/min is preferred.

Next, the wide magnetic film that has been surface-treated in this manner is cut into a predetermined width, and it is desirable to achieve width accuracy without elongation and to reduce width fluctuations.

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 -1o/1 Coercive force = 66008 Polyurethane resin 2 parts (manufactured by Nippon Polyurethane Co., Ltd. N-3113) Vinyl chloride - Vinyl acetate copolymer 5 parts (VAGH manufactured by UCC) Oblate titanium oxide (Ti○) powder 2 parts Average particle size Width = 0.6 μm Thickness = 0.1 μm Lecithin 2 parts Methyl ethyl ketone (MEK) 100 parts Methylene Butyl ketone (MIBK) 10 parts toluene
,. . After mixing and dispersing the above composition in a ball mill for 48 hours, hardener (Coronate L)
A magnetic coating solution was prepared by adding 4 parts of the mixture and filtering it through a filter having an average pore size of 3 μm.

Next, this magnetic coating liquid was coated with a 16 μm thick poly varnish.

After coating and drying on a chill film, the magnetic layer was surface-treated using a super calender roll (temperature: 9°C, pressure: 360 #/cm) and shredded to a predetermined size (d) to produce a magnetic tape.

(Comparative Example 1) A magnetic tape was produced in the same manner as in Example 1 except that granular titanium oxide (particle size: 0.5 μm) was used instead of the flat titanium oxide powder in the composition of Example 1.

(Example 2) Co-containing magnetic iron oxide powder 100 parts Average particle size Length 20.4 μm Acicular ratio -1o/1 Coercive force = etso Oe Polyurethane resin 20 parts (Tesmocol 176 manufactured by Bayer) Vinyl chloride-vinyl acetate Copolymer 5 parts (VAGH manufactured by UCC) Oblate α-hematite (α-F e203) powder 2 parts Average particle size Width = 0.6 μm Thickness = 0.1 μm Lecithin 2 parts 1° Methyl ethyl ketone (MEK) 1oo Part methyl inbutyl ketone (MIBK) 100 parts Toluene After mixing and dispersing the above composition in a ball mill for 48 hours, adding 4 parts of hardener (Coronate L), the resulting kneaded product was filtered through a filter having an average pore size of 3 μm. A magnetic coating solution was prepared.

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

(Comparative Example 2) In the composition of Example 2, granular α-hematite (particle size 0.5 μm) was used instead of the flat α-hematite powder, and the other conditions were exactly the same as in Example 2. was created.

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

(Hereinafter referred to as "Kinshiro") In the table, (1) surface roughness measurement of the magnetic layer is Rank, Tailor
rHobson Talystop surface roughness meter (LP
F; 26Hz).

(2) Video S/N is determined by recording the brightness signal (SO% gray signal) from a television signal generator with a commercially available video tape recorder, playing it back, measuring the noise of the playback signal with a video color noise meter, and comparing it. Values were determined based on the level of Example 1.

As is clear from Table 2, the magnetic recording medium mixed with the abrasive made of the flat fine powder of the present invention has better surface properties of the magnetic layer than those using the conventional granular abrasive, and The conversion characteristics are clearly superior.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer provided on a non-magnetic support, characterized in that the magnetic layer contains an abrasive made of flat fine powder.