JPS59167847A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease coefft. of friction without decreasing S/N in particular and to improve runnability and durability by using a layer consisting of the inorg. powder dispersed in a binder and impregnated therein with silicone oil in constituting the back layer of a magnetic recording medium. CONSTITUTION:A back layer contg. inorg. powder, such as carbon black, graphite, MoS2, SiO2, talc or the like having <=0.8mu average particle size, 0.01- 10wt% silicone oil by the weight of the inorg. powder and a binder resin in a range of 4:1-0.1:1 by weight in the ratio between the inorg. powder and the binder is formed on the base of a magnetic recording medium on the side opposite from the surface provided with a magnetic layer. The back layer is so formed that the surface roughness thereof is <=0.1mu with respect to Ra (average roughness at the centerline) and that the thickness of the layer attains <=1.5mu. Then the transfer of the ruggedness on the back layer to the surface of the magnetic layer when the magnetic medium is wound into a roll or stacked in sheets and the consequent deterioration in the S/N characteristic are obviated and the recording medium having a good running characteristic, good lubricating performance, wear resistance and a long life is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, in particular, it reduces the coefficient of friction without reducing the S/N, improves the running durability, and prevents the edge of the magnetic recording tape from breaking. The present invention relates to an excellent fL'fc magnetic recording tape with little dropout and no scratching of the back surface of the magnetic recording tape.

Generally, in magnetic recording tapes for audio, video, or computers, the surface of the magnetic recording layer is finished to be smooth in order to improve overall sensitivity (particularly output in a high frequency range). However, such smooth magnetic recording tapes are not wound in an orderly manner during winding and unwinding.
It's easy to get into a chaotic situation. When such a magnetic tape is used, running properties deteriorate due to tension fluctuations, etc., and the output fluctuates. Further, the tape is easily deformed and damaged.

In order to prevent this drawback, a magnetic recording tape has been proposed in which a back layer is provided on the side of the support opposite to the magnetic recording layer.

However, the conventionally used back layer is prone to scratching, increase in friction coefficient, and folding of the tape, and as a result, it is easy to cause dropout due to dust, scratches, etc. There is room for improvement.

In general, for the purpose of improving running characteristics and running durability, it has been found that when the entire pack layer is provided, the magnetic recording medium (especially when it is in the form of a tape) may be rolled up or piled up in a sheet form. In this case, it is known that the unevenness of the back layer is transferred to the surface of the magnetic layer, impairing the surface properties of the magnetic layer and impairing the electromagnetic characteristics, especially the S/N characteristics, of the single magnetic layer medium.

S/N characteristics are often degraded because the back layer's running characteristics are considered important, and its surface is rough, but for this reason, it is not possible to store or leave magnetic recording media rolled up or stacked. This is because the unevenness of the back layer is transferred to the surface of the magnetic layer.

An object of the present invention is to provide a magnetic recording medium that does not increase the coefficient of friction and has good running durability.

A further object of the present invention is to provide a magnetic recording medium having a back layer that does not impair the S/N characteristics of the magnetic medium.

The above object of the present invention is to provide a magnetic recording medium having a magnetic layer on the surface of a non-magnetic support and a back layer containing an inorganic powder and a binder on the opposite side. This can be achieved by mixing it into a liquid containing an inorganic powder or overcoating a backing layer containing an inorganic powder and a binder.

The back layer has a surface roughness of 097 or less in Ra and a thickness of Ha! Preferably, it is below μμ.

Examples of the silicone oil used in the present invention include Shin-Etsu Chemical's Silicone Oil KF 2" and Silicone Oil KF 6H".

The amount added is 0.01 to 10% by weight based on the inorganic powder.
, preferably 0,0/~! It is preferable that the amount is within the range of % by weight. If the amount is too large, it is not desirable because the abrasion strength, which is a measure of the durability of the back layer, tends to deteriorate.

Silicone oil is generally viscous and fluid at room temperature and pressure, and has good lubrication performance, which also improves wear resistance.

Along with the silicone oil of the present invention, other lubricants such as
Fatty acids, fatty acid amides, aliphatic alcohols, fluorinated oils, etc. may also be used.

Inorganic powders used in the back layer of the present invention include carbon black powder, graphite, tungsten nitride, molybdenum disulfide, boron nitride, silicon dioxide, calcium carbonate, aluminum oxide, iron oxide, titanium dioxide, magnesium oxide, These include zinc oxide, calcium oxide, lithopone, talc, and stannic oxide.

The average particle size of the inorganic powder used in the present invention is O6t
It is preferably less than μ, particularly preferably θ.

≠μ or less.

As the binder of the present invention, there may be used binders conventionally known in the art, such as thermoplastic resins, thermosetting resins, reactive resins, or mixtures thereof.

Examples of thermoplastic resins include vinyl chloride-vinylacetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. , acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer,
Methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose resin (cellulose acetate butyrate, cellulose dye) acetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amino resins, and various rubber resins.

Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins,
Melamine resin, alkyd resin, acrylic reactive resin,
These include polyincyanates and polyamines.

Among the above, particularly preferred are cellulose resin, thermoplastic polyurethane entomer, and polyisocyanate.
It is an ingredient system.

As the cellulose resin, cellulose derivatives such as nitrocellulose are suitable, and these are useful for imparting heat resistance, toughness, and blocking resistance.

Almost all commercially available thermoplastic polyurethane elastomers can be used. That is, organic dibasic acids such as heptalic acid, adipic acid, trimerized lyluic acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane, hexanetriol, glycerin, and trimethylol. Polyester polyol obtained by reaction with polyhydric alcohols such as ethane and pentaerythritol (tolylene diisocyanate)
, 4',4''-diphenylmethane diisocyanate, hexamethylene diisocyanate, metaxylylene diisocyanate, and other polyester polyurethane resins and polyether polyurethane resins urethanized with polyinsyanate compounds, as well as molecular skeletons represented by general formula (I).

C: +0-4-00C-R1-, C0-) 0ROOC
NH-R2-NHCO=)ga1 [■] However? 7! is an integer from j to ioo, and R is an alicyclic or aromatic compound containing at least 2 M hydroxyalkyl groups having carbon number/~≠4it4. 21 H3 or +CH2+□, n is an integer from ≠ to t.

These molecular weights are j, 0OO-maoo, oo.

Preferably, io, ooo to 200,000 is effective. These polyurethanes are described in Japanese Patent Application Laid-open No. 33
-1.22.23 Publication No. 1.22.23.

Furthermore, as the polyisocyanate, 2. ≠-tolylene diisocyanate, /, J-hexbutylene diisocyanate, triisocyanate (for example, Coronate L manufactured by Nippon Polyurethane Industries, Ltd.), etc. can be used.

The composition ratio of the binder is based on 700 parts by weight of the binder.
Preferably, the cellulose resin is 20.10 parts by weight, the thermoplastic polyurethane distomer is 20 to 10 parts by weight, and the polyisocyanate is io to 10 parts by weight.

The ratio of the inorganic powder to the binder in the back layer used in the present invention is 4t//~0. Can be used within the range of ///.

The back layer of the present invention is selected so as to make the total thickness of the magnetic recording medium (magnetic layer + support + back layer) as thin as possible in order to increase the recording density per unit volume. The thickness of such a back layer is preferably 0.3 to i, sμ.

In the present invention, the surface roughness of the back layer is cutoffO0
Center line average roughness at θ B, a) 0. IOμ
In the following, favorable results are obtained.

According to the present invention, a magnetic recording medium having the characteristics described above can be obtained. That is, in the conventional technique f'L, when the back layer is thinned, the back layer is destroyed (the back layer is scraped when the magnetic recording medium runs), but this drawback does not occur in the present invention. Furthermore, by using an uninvented back layer, the video S/N ratio does not deteriorate even in high-density recording at a recording wavelength of 7.3 microns.

The magnetic recording medium of the present invention is published by JP-A-Sho! λ-1or.

? It can be prepared by following the materials, manufacturing method, etc. described in Publication No. 011.

The magnetic layer of the present invention is made of γ-iron oxide, Co-modified iron oxide, or
It may be one in which ferromagnetic metal powder is dispersed and coated in a binder, or it may be a magnetic metal thin film layer.

Next, examples of the present invention will be described. “Part” in Examples
indicates "parts by weight".

EXAMPLE A magnetic layer containing cobalt-containing γ-iron oxide was provided on the surface of a PET base having a thickness of s/≠μ, and a back layer was provided on the opposite side.

The magnetic layer was provided so that the thickness after drying was jμ. The back layer was provided as follows. A mixture having the following composition was dispersed for 2 hours using a sound hole mill dispersion machine.

CaC0a (average particle size 0.0 lp) 100 parts Nitrocellulose t, o parts Polyurethane (Product name [1"J-2320 parts 0/J Japan Polyurethane @M) Polyester (Product name "Vylon J part promotion j00
Manufactured by J Toyobo ■) Silicone oil (product name rKFJ Shin-Etsu Chemical ff in Table 1) Indicated amount Methyl ethyl ketone 100 parts MIBK
loθ part toluene
ioo part The above composition was added as a dispersion layer and polyisocyanate was added as a hardening agent to prepare a back coat coating solution.
Dry raw material 0. It was coated as a back layer so that it had a thickness of 0.01 to 2.1 μm.

Table 1 Examples A magnetic layer containing cobalt-containing γ-iron oxide was provided on the surface of a polyester (PET) base having a thickness of 4' μm, and a back layer was provided on the opposite side.

The thickness of the magnetic layer after drying! It was provided so that it was .mu.m±O1j .mu.m.

For the back layer, the following mixture was treated using a sand grinder disperser at a liquid flow rate of ' j Ic9/min so that the residence time was to minutes.

Carbon black (average particle size 70mμ) ro part Ca
CO3 (average particle size iomp) 30 parts Polyurethane (Product name "N-230≠" 30 parts manufactured by Nippon Polyurethane) Polyester (Product name "Vylon #! Part j30J
Toyobo Co., Ltd.) 300 parts of methyl ethyl ketone 100 parts of toluene To the above mixture, polyisocyanate (trade name: "Coronate L 7jJ" manufactured by Nippon Polyurethane) was added as a curing agent to the above mixture as a hardening agent, and this was made into a coating solution for back coating, which had a thickness of 0 after drying. It was applied as a pack layer to have a thickness of .5 to -2 μm.

Next, a calendering solution having the following composition was applied onto the surface of the hacking layer, after which it was slit to a width of 772 inches and incorporated into a VHS video cassette.

Example 3 A cobalt magnetic film (C film thickness: 0.2 μm) was completely diagonally deposited on the surface of a polyester (P, ET) base having a thickness of 14 A μm.
A magnetic tape was prepared. As for the evaporation source, an electron beam evaporation source is used, and this is used with Tata.

Fully charged with 5% pure cobalt and vacuum level ×/ 0
Diagonal deposition was performed at -5 Torr so that the incident angle was 70°.

The back layer was obtained in the same manner as in Examples/and λ.

As is clear from Table 3, the back layer and the layer containing silicone oil are as follows:
It can be seen that the practical running tension is low and the nozzle layer shearing (durability) is also excellent.

Claims (2)

[Claims] (1) A magnetic recording medium having a magnetic layer on seven sides of a support and a back layer on the other side, the back layer containing inorganic powder dispersed in a binder, the back layer containing silicone oil. A magnetic recording medium characterized by: (2) The surface roughness of the hack layer is 0. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of /μ or less and a thickness of /,jμ or less.