JPH02208824A - Magnetic recording medium with good electromagnetic conversion characteristics and little sliding noise - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with good electromagnetic conversion characteristics in a high frequency range and little sliding noise by specifying the surface roughness Ra of the layer adjacent to the upper most layer of the magnetic recording medium. CONSTITUTION:The magnetic recording medium has a multilayered structure and the layer adjacent to the most upper layer is made to have the surface roughness Ra satisfying Ra<=0.022mum, and more preferably 0.005<=Ra<=0.022mum. To provide the layer adjacent to the most upper layer with the specific roughness, the particle sizes of magnetic powder, antistatic agent and filler are controlled. Thereby, the obtd. medium has good electromagnetic conversion characteristics at high frequency range and little sliding noise even after repeatedly travelled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, magnetic floppy disks, etc., which have good electromagnetic conversion characteristics particularly in high frequencies (high frequency bands), and which can be used repeatedly. The present invention relates to a magnetic recording medium that generates less sliding noise even after running.

[Background of the invention]

In recent years, there has been an increasing demand for high-density recording in magnetic recording media, and in particular, with the demand for higher recording frequencies in video tapes, it has become necessary to perform extremely high-density recording. As a result, magnetic powders with smaller particle sizes have come to be used.

By making the magnetic particles finer and increasing their BET value, the surface of the magnetic layer is smoothed, allowing higher density recording, and improving the electromagnetic wave conversion characteristics of the magnetic recording medium. However, if the surface of the magnetic layer is smoothed in this way, magnetic recording tape,
Particularly, as a result of the increased frictional resistance between the magnetic layer and the magnetic head during the running of the video tape, the magnetic layer of the magnetic recording medium tends to be damaged and the occurrence of sliding noise increases after a short period of use.

In other words, conventionally, improving the electromagnetic conversion characteristics in high frequencies and suppressing the increase in sliding noise after repeated running have been mutually contradictory matters.

[Purpose of the invention]

It is an object of the present invention to correct such conventional drawbacks and provide a magnetic recording medium that has good electromagnetic conversion characteristics in high frequencies and generates less sliding noise even after repeated running. be.

(Structure of the Invention) The object of the present invention can be achieved by the present invention described below.

The present invention provides surface roughness (Ra
) is characterized in that Ra≦0.022 μm.

The layer structure of a magnetic recording medium generally includes a magnetic layer on an undercoat layer, a second magnetic layer on top of it if necessary, and a back layer on the undercoat layer on the opposite side. The undercoat layer is provided to improve the adhesion between the magnetic layer or back layer and the support.

As already mentioned, in order to improve the electromagnetic conversion characteristics, it is necessary to smooth the surface of the magnetic layer.On the other hand, in order to suppress the generation of noise, especially sliding noise, the surface of the magnetic layer must be smoothed. It has to be roughened to some extent. Since it is almost impossible to satisfy these two requirements simultaneously with a single layer, the magnetic layer in the magnetic recording medium of the present invention usually has a multilayer structure of two or more layers.

In the magnetic recording medium of the present invention having such a layer structure, the surface roughness (Ra) of the layer adjacent to the uppermost layer is
However, usually Ra≦0.022 μms, preferably o,
It is necessary to satisfy o o, s≦Ra≦0.022 μm, and by adopting such a layer configuration, the above two requirements can be satisfied at the same time.

Note that, as is well known, the surface roughness (R
a) is a value in μm that is averaged by tracing the surface using the stylus method and using the center line of the obtained surface roughness curve as a reference.

There are various methods for giving the layer adjacent to the top layer the surface roughness specified in the present invention. Examples include methods of adjustment.

If the thickness of the top layer is too thick, the effect of defining the adjacent surface roughness within the above range in the present invention may not be fully developed, so the thickness of the top layer is usually , preferably in the range of 0.1-1.5 μm.

The thickness of the layers other than the top layer is not particularly defined in the present invention, but it is not preferable to make it too thin due to the characteristics of the magnetic recording medium, so it is usually 0.5μ.
It is desirable to make it more than m.

In the production of so-called multilayer magnetic recording media having a layer structure of two or more layers, there are two methods: a method in which multiple layers are provided simultaneously using magnetic paint, and a method in which multiple layers are provided in two or more layers.

The former is a so-called wet multilayer coating method (wet-on coating method).
The latter method is a method of stacking layers one by one through a coating and drying process (wet-on-dry coating method), but the magnetic recording medium of the present invention can be manufactured by either method.

Magnetic recording media are usually made by adding ferromagnetic powder, a hardening agent, a dispersant, an abrasive, a lubricant, a matting agent, an antistatic agent, and an appropriate solvent as necessary to a binder resin. It is manufactured by applying a magnetic coating material obtained by adding and dispersing it onto a support and then drying it.

Examples of the magnetic powder used in the magnetic recording medium of the present invention include γ-Fe, 0. ．． Co-containing γ-Fe, O, or c
O deposition - Co-γ-Fe, O,, like Fe, O,
Fe, 0. ．． Co-containing Fe, O, or Co-coated Fe5
0. CO-γ-F e 20 s +Cry2 like
oxide magnetic materials such as Fe, Ni, and Fe-Ni alloys.

Fe-Co alloy, Fe-Ni-P alloy, Fe-Ni
-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn
alloy, Fe-Co-Ni-Cr alloy, Fe-Co-N
i-P alloy, Co-P alloy, Co-Cr alloy, etc. Fe,
Examples include various ferromagnetic materials such as metal magnetic powder containing Ni and Co as main components.

Si is an additive to these metal magnetic powders.

Elements such as Cu, Zn, Aα+P+Mn*Cr, or compounds thereof may be included. Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

The binder used in the magnetic recording medium of the present invention includes abrasion-resistant polyurethane.

It has strong adhesion to other materials, is mechanically strong to withstand repeated applied forces or bending, and has good abrasion and weather resistance.

In addition to polyurethane, if a cellulose resin, a vinyl chloride (co)polymer, or a polyester (co)polymer is used in combination, the dispersibility of the magnetic powder in the magnetic layer will improve and its mechanical strength will increase. increase

However, if the cellulose resin, vinyl chloride (co)polymer, or polyester (co)polymer is used alone, the layer becomes too hard, but this can be prevented by the presence of the above-mentioned polyurethane.

Furthermore, polymer blends and copolymers of polyurethane and other polymers, such as polyester, are also suitably used.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. The vinyl chloride (co)polymer or polyester (co)polymer described above may be partially hydrolyzed. Preferred vinyl chloride copolymers include vinyl chloride-vinyl acetate copolymers and vinyl chloride-vinyl acetate-vinyl alcohol copolymers.

Preferably, the polyester (co)polymer includes a partial hydrolyzate thereof.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to those of the polyurethane described above, and the stability of the physical properties of the tape over time can be significantly improved.

Furthermore, in addition to the above-mentioned binders, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used (improving the durability of the magnetic layer of the magnetic recording medium of the present invention). To achieve this, magnetic paint can contain various hardening agents.
For example, incyanate can be included. Examples of aromatic incyanates include tolylene diisocyanate (TDI) and adducts of these isocyanates with active hydrogen compounds, and the average molecular weight is lO
A value in the range of 0 to 3,000 is suitable.

Examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

A dispersant is used in the magnetic paint used to form the magnetic layer, and additives such as a lubricant, an abrasive, a matting agent, an antistatic agent, etc. may be included as necessary.

Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. , also negative organic groups (e.g. -COOH)
It is also possible to use salts of polymeric dispersants having . These dispersants may be used alone or in combination of two or more. In addition, as lubricants, silicone oil, gelaphalite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monosalt fatty acid with 12 to 16 carbon atoms, and the number of carbon atoms of the fatty acid are used. Total number of carbon atoms is 2
Fatty acid esters (so-called waxes) consisting of 1 to 23 monohydric alcohols can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

Commonly used abrasives include alumina, σ-alumina, other types of alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (main ingredients: corundum and magnetite). etc. are used. These abrasives have an average particle size of 0.0
A size of 5 to 5 μm is used, particularly preferably 0.1 to 2 μm. These abrasives are binder 100
It is added in an amount of 1 to 20 parts by weight.

As the matting agent, organic powder or inorganic powder may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferred. Powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, α-Fe, 0
．． , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

Antistatic agents include carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; and alkylene oxide compounds. , nonionic surfactants such as glycerin, glycidol, etc.; cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphonium or sulfonium; carboxylic acids, sulfonic acids, phosphoric acids , anionic surfactants containing acidic groups such as sulfate ester groups and phosphate ester groups; amino acids;
Examples include amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above paint or diluting solvents when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, furopanol, and butanol; if methyl and acetic acid. ethyl, butyl acetate,
Ethyl lactate, ethylene glycol monos; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene, and the like can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose diacetate and cellulose triacetate, and polymers such as polyamide and polycarbonate. Metals such as Zn, glass, boron nitride, ceramics such as Si carbide, etc. can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card shape, the diameter is about 30 μm-101, and in the case of a drum shape, a cylindrical shape is used, and the shape is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, trans770-lu coating, gravure coating, kiss coating, and cast coating. , Tin Ray coat, Kistrusion coat, etc. can be used, but are not limited to these.

The magnetic layer coated on the support by such a method is optionally treated to orient the ferromagnetic powder in the layer, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is approximately 500 to 50
It is about 00.0e. Drying temperature is approximately 40-120°C
The drying time is approximately 0.5 to 10 minutes.

Further, the magnetic recording medium of the present invention is manufactured by performing surface smoothing and cutting into a desired shape, if necessary.

Next, the present invention will be explained with reference to examples, but it goes without saying that the present invention is not limited to the following examples.

〔Example〕

Examples 1 to 6 and Comparative Examples 1 to 4 Magnetic paints having the formulations shown in Tables 1 to 4 below were manufactured according to a conventional method.

After the mixture was well dispersed, 5 parts by weight of "Coronate L" manufactured by Nippon Polyurethane Co., Ltd. was added to prepare a magnetic paint.

After kneading the above magnetic paint components and dispersing each component well in the mixture as in the case of the paints in Table 1, add each component to the mixture. A magnetic paint was prepared by adding 5 parts by weight of Coronate L''.

As in the case of the paint in Table 1, the above magnetic paint components were kneaded and each component was well dispersed in the mixture, and then 5 parts by weight of "Coronate L 11" manufactured by Nippon Polyurethane Co., Ltd. was added to form a magnetic paint. was prepared.

The following paint components were kneaded to ensure that each component was well dispersed in the mixture.

Next, the obtained magnetic paint was coated in multiple layers on a polyethylene terephthalate support with various thicknesses of the uppermost layer and the lower layer, and then dried to produce various magnetic recording media.

For each sample thus obtained, the surface roughness (Ra) of the layer adjacent to the top layer, the electromagnetic conversion characteristics of the magnetic recording medium, and the sliding noise were measured.

For each experimental sample, Table 5 shows the results of measuring the surface roughness of the layer adjacent to the top layer and the thickness of the coating layer, and Table 6 shows the results of measuring the electromagnetic conversion characteristics, etc.

As is clear from the results in Table 6, the multilayer tape of the present invention not only has excellent high-frequency characteristics, but also significantly improves sliding noise, which has been unresolved in the past. can.

■Measurement method of characteristics in Examples and Comparative Examples <Y-C
N> (1) Fast forward until the winding thickness of the magnetic recording tape on the winding side becomes approximately 3 mm, and from there record at 6 MHz for 10 minutes. Play this three times. The recording level is set to +20% of the optimum recording level of the comparison tape.

(2) Add 4. to the part where 5 MHz was recorded and played back in (1) above.
A 5° 6.8 MHz signal is recorded for about 3 minutes each. The recording level is set to +20% of the optimum recording level of each comparative tape. The RF reproduction output (referred to as C) and C/N are compared with the values of the comparison tape.

<Sliding noise> (i) Perform playback without running the tape, and measure system noise with a spectrum analyzer.

(u) Play the sample tape for 1 minute and measure the sliding noise with a spectrum analyzer (l pass).

(iii) The sample tape is played back 10 times for 1 minute each, and the sliding noise is measured using a spectrum analyzer.

(lO path) (iv) Using the noise level around 9 MHz as a reference to the system noise (OdB), read the noise values of each of the l path and the lO path.

*All measurements were performed at room temperature of 20±2℃ and relative humidity of 10±2%.
The test is carried out under the following environmental conditions, with the top cover of the VTR removed.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a magnetic recording medium which has good electromagnetic conversion characteristics in a high frequency range and which generates less sliding noise even after repeated running.

Claims (4)

[Claims] (1) A magnetic recording medium comprising multiple layers provided on a non-magnetic support, characterized in that the surface roughness (Ra) of the layer adjacent to the top layer is Ra≦0.022 μm. . (2) The surface roughness (Ra) of the layer adjacent to the top layer is 0.0
Claim No. 05≦Ra≦0.022 μm (
1) The magnetic recording medium described in item 1). (3) The magnetic recording medium according to claim (1) or (2), wherein the top layer has a thickness of 0.1 to 1.5 μm. (4) The magnetic recording medium according to claim (1), (2) or (3), wherein the thickness of the layers other than the top layer is 0.5 μm or more.