JPS63144416A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease head wear and to obtain excellent running performance and durability by using a carbon black of a thermal black type having 60-200mmu average grain size as an essential component of nonmagnetic powder in a back layer and further, incorporating both a fatty acid ester and modified silicone oil therein. CONSTITUTION:The carbon black of the thermal black type having 60-200mmu average grain size is used as the essential component of the nonmagnetic powder in the back layer and further, the fatty acid ester and modified silicone oil are incorporated therein. The fatty acid ester to be used is preferably 1 or >=2 kinds of the alkyl or alkoxyalkyl ester of fatty acids of 10-22C in terms of lubricity and compatibility with a binder. The modified silicone oil is preferably 1 or >=2 kinds of the oils contg. at least one kind of polar groups such as epoxy group, amino group, carboxyl group and hydroxyl group in the molecular structure thereof in terms of adequate lubricity and the compatibility with the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks used in audio and video equipment or computers. The present invention relates to magnetic recording media with excellent properties.

BACKGROUND OF THE INVENTION In recent years, each of the above-mentioned magnetic recording media has become suitable for high-density recording, and for this purpose, the trend has been to shorten the recording wavelength, narrow the recording track width, and reduce the thickness of the recording medium. As a result, the playback output, S
Electromagnetic conversion characteristics such as N ratio 9 frequency characteristics are generally disadvantageous. As a countermeasure to this problem, methods have been adopted such as pulverizing the magnetic powder and using a highly smooth non-magnetic support to further improve the surface properties of the magnetic layer. However, if the above measures are taken alone, the surface properties of both the front and back sides of the recording medium will increase, resulting in an increase in the coefficient of friction on both sides, which will be disadvantageous in terms of running performance and durability.In order to solve these problems, For high-performance magnetic tapes such as those mentioned above, it has already been proposed to provide a back coat layer (hereinafter referred to as back layer) containing a filler dispersed in a binder on the opposite surface of the support from the magnetic layer surface. (For example, Japanese Patent Application Laid-Open No. 50-6305,
JP-A-52-37406, JP-A-57-5032
Publication No. 7, JP-A-57-135432, JP-A-5
Publication No. 8-222436 (2%), Publication No. 167846/1984, etc.).

Furthermore, in addition to the above-mentioned role, this back layer may be formed for the purpose of improving the antistatic properties of the magnetic recording medium or imparting light-shielding properties. The purpose of preventing static electricity is to reduce the adhesion of substances that cause dropouts due to static electricity on the magnetic recording medium.The purpose of providing light-shielding properties is to detect the end of the tape and the position of the disk by reducing the light transmission of the magnetic recording medium itself. The objective is to reduce malfunctions of the optical sensor used when detecting by the rate. In order to improve the above problems, carbon black powder is generally used as a filler for the back layer (for example,
No. 131403, Japanese Patent Application Laid-open No. 10908/1983,
JP-A No. 52-25603.

JP-A-55-28507, JP-A-57-1118
No. 28, JP-A No. 59-5428, JP-A No. 59-Sho.
Problems that Patent Publication No. 58626, Japanese Unexamined Patent Publication No. 60-10417, and other publications attempt to solve However, conventional carbon black-containing back layers generally have a coating film that is easily scraped, and the coating film does not have sufficient electrical conductivity. In order to provide light shielding properties and running characteristics, a considerable amount of carbon black must be mixed into the back layer.
As a result, the smoothness of the coating film decreases, and in magnetic recording media rolled up into rolls or stacked in sheets, the unevenness of the bank layer is reflected on the surface of the magnetic layer, impairing the surface properties of the magnetic layer. As a result, problems such as deterioration of the electromagnetic conversion characteristics of the magnetic layer medium tend to occur.

Means for Solving the Problems In order to solve the above problems, the present invention provides a magnetic layer on one main surface of a non-magnetic support, and a non-magnetic powder in a binder on the other main surface. In a magnetic recording medium provided with a dispersed back layer, a thermal black type carbon black having an average particle diameter of Sowμ to 200 mμ is used as the main component of non-magnetic powder in the back layer, and fatty acid ester and modified By containing silicone oil, a magnetic recording medium can be obtained which has not only improved conductivity and light-shielding properties but also improved runnability and durability.

Effect The present invention has the above-described structure, which significantly improves the dispersibility of carbon black and the long-term lubrication stability of the coating film.
The purpose is to obtain a back layer having desired characteristics without impairing the electromagnetic conversion characteristics of the magnetic layer medium. Furthermore, it has been found that the magnetic recording medium provided with the back layer according to the present invention is effective in reducing wear on the magnetic head that comes into contact with the magnetic layer. This is thought to be due to the effect of the lubricant component on the surface of the back layer being transferred to the surface of the magnetic layer, since the magnetic layer and back layer on the non-magnetic support come into close contact with each other during the manufacture of magnetic recording media. .

The carbon black used in the present invention preferably has an average particle diameter in the range of 60 to 200 mμ. When the average particle size is less than 60 mμ, the effect of lowering the friction coefficient becomes poor and the coating film coefficient increases. Moreover, if it exceeds 200 mμ, the smoothness of the coating film will be impaired. Further, the carbon black used in the present invention is preferably a thermal type carbon black having a substantially spherical shape without a struttle structure because it can be easily uniformly dispersed in the binder and has a large effect of lowering the coefficient of friction.

The carbon black used in the present invention is added as a main component of non-magnetic powder in the back layer, and its addition ratio is preferably 30 to 70 parts by weight per 100 parts by weight of the back layer. Addition ratio of carbon black is 3
If it is less than 0 parts by weight, the friction coefficient of the coating film will be high, and it will be difficult to satisfy the required electrical conductivity and light shielding properties. On the other hand, if the proportion of carbon black added exceeds 7Q parts by weight, the strength of the coating film will drop significantly. In addition to the above-mentioned carbon black, as a non-magnetic powder component in the back layer, a relatively small amount of high hardness powder, e.g. Al2
O3+Cr2O3+TiO2, etc. may be used in combination.

As the fatty acid ester used in the present invention, from the viewpoint of lubricity and compatibility with the binder, it is preferable to use one or more alkyl or alkoxyalkyl esters of fatty acids having 10 to 22 carbon atoms. If the fatty acid has less than 10 carbon atoms, the lubricating effect is poor and desired properties cannot be obtained. On the other hand, those with a carbon number greater than 22 have poor compatibility with binders and solubility in organic solvents, making them unsuitable in terms of paint production or film performance (excessive pluming, blocking properties, etc.). becomes. The total carbon number of the alkyl or alkoxy

The modified silicone oil used in the present invention contains epoxy groups and amino groups in its molecular structure from the viewpoint of appropriate lubricity and compatibility with fatty acids and binders.

It is preferable to use one or more types containing at least one type of polar group such as a carboxyl group or a hydroxyl group. If silicone oil does not have the above-mentioned functional groups in its structure or if unmodified silicone oil is used, it lacks compatibility with binders and fatty acids, and the lubricity of the coating film cannot be sufficiently increased over a long period of time. Therefore, a bank layer with excellent wear resistance cannot be obtained.

The amounts of fatty acid ester and modified silicone oil used in the present invention added to the back layer are 0.5 to 6 parts by weight and 0.05 to 0 parts by weight, respectively, per 100 parts by weight of the back layer coating.
．． Preferably it is in the range of 5 parts by weight. If the amount of fatty acid ester is less than 0.61 parts by weight, long-term lubrication stability cannot be obtained even when used in combination with modified silicone oil, and if it exceeds 6 parts by weight, the coating film becomes brittle and the fatty acid esters stand out. This is undesirable because excessive pluming (pluming) may result in a decrease in running stability of the magnetic medium. If the amount of modified silicone oil is less than 0.05 part by weight, long-term lubrication stability cannot be obtained even when used in combination with the fatty acid.
If the amount exceeds 5 parts by weight, the silicone oil will be excessively embossed and the running stability of the magnetic medium will likely deteriorate.

Unlike the structure of the present invention, a back layer obtained by mixing only fatty acid ester or modified silicone oil with a carbon blank that satisfies the above conditions cannot sufficiently increase the lubricity of the coating film over a long period of time. A back layer with excellent stability and abrasion resistance cannot be obtained.

The binder for the back layer used in the present invention is not particularly limited, and any binder that is excellent in adhesiveness to the non-magnetic support, fractional property of carbon black, and abrasion resistance of the coating film can be used.

For example, polyurethane resin.

Thermosetting types that combine polyisocyanate compounds with thermoplastic resins such as polyester resins, cellulose resins, vinyl chloride copolymer resins, etc., and radiation-sensitive unsaturated double bonds. It is possible to use a radiation-curable type that combines a resin (compound) having the following.

Embodiments Hereinafter, embodiments of the present invention will be specifically explained using a videotape as an example. It should be noted that all parts of components mentioned in the examples indicate parts by weight.

(Example 1) Preparation of paint for magnetic layer; Ferromagnetic CO gold-containing-Fe203 polyurethane resin [manufactured by Nippon Polyurethane Co., Ltd., N2304]
)...Mark 10 parts Nitrocellulose resin [manufactured by Asahi Kasei Co., Ltd., another 5-%]...
...10 parts α-A1203 powder [average particle size=Q, 3/rm]...
...... 4 parts carbon black [average particle size = 50 mμ] ...
・・・ 4 parts myristic acid ・・・・・・・・・ 2
Butyl stearate ・・・・・・・・・
1 part mixed organic solvent [MEK/) toluene/cyclohexanone = 2:2:1:] 30
0 parts The above composition was cross-dispersed using a pressure kneader and a sand grinder, and then 6 parts of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed. A paint for the magnetic layer was prepared by filtration through a 1 μm filter.

Preparation of paint for back layer; Carbon black fatty acid ester [amyl myristate]...
... 1 part fatty acid ester [phthyl hehenate] 1 part modified silicone oil Epoxy group content - 1,3 polyurethane resin [manufactured by Nippon Polyurethane Co., Ltd., N3022]
'] ・・・・・・15 part 2) 0
Cell O-Sm Fat C manufactured by Asahi Kasei Co., Ltd., BTH-%]...
...15 parts mixed organic solvent (MEK/toluene/cyclohexanone)
2:2:1) ・・・・・・・・・300
After mixing and dispersing the above composition in a ball mill and taking out the kneaded product, 10 parts of a polyisocyanate compound [Coronate L, manufactured by Nippon Polyurethane Co., Ltd.] was added to the kneaded product, and the mixture was stirred and mixed with a high-speed stirrer. A paint for the back layer was prepared by filtering through a filter with a pore size of 3 μm.

Next, the above-mentioned magnetic paint was applied onto a 14 μm thick polyester film, subjected to magnetic field orientation and drying treatment, followed by mirror polishing treatment using a super calender roll, and then heat treatment to form a raw fabric roll having a 5 μm thick magnetic layer. I got it. The above-mentioned back layer paint was applied to the surface opposite to the magnetic layer on this raw roll, dried, and then heat-treated to a thickness of 0.8 μm.
A back layer of m was formed. This was cut to a width of 1.5 inches to create a videotape sample (250 m long).

(Examples 2-3 and Comparative Examples 1-3) Fatty acid ester in the back layer paint of Example 1.

A videotape sample was prepared in exactly the same manner as in Example 1, except that the type and amount of modified silicone oil were as shown in Table 1.

(Example 4) Preparation of paint for back layer; Carbon black fatty acid ester [butoxyethyl stearate]...
... 1 part modified silicone oil 0.2 parts urethane acrylate resin [manufactured by Japan Synthetic Rubber Co., Ltd., 53s
111 ......3 parts vinyl chloride/vinyl acetate/vinyl alcohol copolymer (manufactured by Nissin Chemical Industries, Ltd., TAs) mixed organic solvent (MEK/toluene/cyclohexanone = 2:2: 1〕・
...300 parts of the above composition were mixed and dispersed in a ball mill to remove contaminants, and then filtered through a filter with an average pore size of 3 μm to prepare a back layer paint.

Next, the above coating material for the back layer was applied to the surface of the raw fabric roll obtained in Example 1 opposite to the magnetic layer.

Drying, then accelerating voltage 165 kV, absorption line pattern 5
The back layer was cured by electron beam irradiation under the conditions of M r a d (back layer thickness 0.8 μm).
.

This was cut into % inch width videotape samples (250 mm).
m length) was created.

(Comparative Example 4) The same procedure as in Example 1 was carried out except that the type of carbon black in the back layer paint of Example 4 was changed to Channel Black XC-72 (average particle size = 29 mμ) manufactured by Cabot Corporation. A videotape sample was made.

(Example 5) Preparation of paint for back layer: Carbon black 60 parts Fatty acid ester [butyl laurate] 1 part modified silicone oil ...0.2 parts polyurethane resin [manufactured by Nippon Polyurethane Co., Ltd., N3022]
] 20 parts Nitrocellulose resin [manufactured by Asahi Kasei Co., Ltd., BTH-%]
...20 parts mixed organic solvent (MEK/toluene/cyclohexanone,
=2:2:1) ......300 parts The above composition was mixed and dispersed in a ball mill and the kneaded product was taken out, followed by 10 parts of a polyisocyanate compound (Coronet L) manufactured by Nippon Polyurethane Co., Ltd. was added to the kneaded material, mixed with a high-speed stirrer, and filtered through a filter with an average pore size of 3 μm to prepare a paint for the back layer.

Next, the above coating material for the back layer was applied to the surface of the raw fabric roll obtained in Example 1 opposite to the magnetic layer.

After drying, the above-mentioned back layer paint was applied, dried, and then heat treated to form a back layer with a thickness of 0.8 μm.

This was cut into % inch width videotape samples (2so
m length) was created.

(Comparative Example 5) The modified silicone oil in the back layer paint of Example 5 was changed to non-modified silicone oil as shown in Table 1.
A videotape sample was prepared in exactly the same manner as in Example 1.

(Hereafter, white) Table 1 (Note) ■ - Toren Ricoh Co., Ltd. 5F8411; Epoki Hakuyaku - t3chi ■ - Toren Ricoh - 43F8418;
Carboxy field mist t5chi■-Tore silicone spelling 5
F8427 ;Gasakechi approx. 3*1-ta%■-)-Register!
I:r-7741! Is F 8417; 7 Mi 4-
tMk-o, 5%■-Toren Ricoh 4 9H200
;Non-modified silicone oil The following evaluation tests were conducted on the videotape samples obtained in each of the above Examples and Comparative Examples.

(1) Surface roughness The surface roughness of the magnetic layer and the back layer was measured using a Talistesop stylus type surface roughness meter manufactured by Taylor Hoffmann. The value was obtained by calculating the root mean square of the peak height on the roughness chart (Reference: National Technical Report
lReport)vol, 28 A3June
1982 p. 520).

(2) Video S/N VH8 system VTR (manufactured by Matsushita Oki Sangyo, NV-ssoo
), and the specified luminance signal (SO
% white level signal) was recorded at the optimal recording current of the reference tape, the ratio of the signal to noise contained in the demodulated signal during playback was measured using a video color noise meter, and compared with that of the reference tape in odB. It is.

(3) Number of Dropouts Using the same VTR as in (2), momentary dropouts (15μ, 1edB) of the video playback signal were observed with a dropout counter, and the average value per minute was shown.

(4) Head wear @) Using the same VTR, the amount of wear on the magnetic head was measured when each sample tape was repeatedly run 100 times (26° C., 60% RH).

(5) Using the same VTR as the tape running tension run (2), the entry tension (T1) and exit tension (T2) during running of each sample tape were measured, and the value was calculated as T2/T1.

Table 2 shows the evaluation test results for each sample tape.

(Cram school x 1 red stand) Effects of the invention As is clear from the table above, a magnetic layer is formed on one main surface of the non-magnetic support, and non-magnetic powder is contained in a binder on the other main surface of the non-magnetic support. In a magnetic recording medium provided with dispersed back layers, thermal black type carbon black having an average particle size of 80 mμ to 200 mμ is used as the main component of the non-magnetic powder in the bank layer, and fatty acid ester is further used. By the structure of the present invention in which both a magnetic head and a modified silicone oil are contained, a magnetic recording medium with excellent electromagnetic characteristics, little head wear, and excellent repeated running stability can be obtained.

Although the above embodiment has been explained using a videotape sample as an example, it goes without saying that the present invention can be applied to other magnetic recording media such as audio tapes, magnetic disks, and magnetic cards.

Claims (3)

[Claims] (1) A magnetic recording medium in which a magnetic layer is provided on one main surface of a non-magnetic support, and a back coat layer made of non-magnetic powder dispersed in a binder is provided on the other main surface,
The main component of the non-magnetic powder in the back coat layer is 60 mμ ~
A magnetic recording medium characterized in that it is a thermal black type carbon black having an average particle size of 200 mμ, and further contains a fatty acid ester and a modified silicone oil. (2) The magnetic recording medium according to claim 1, wherein the fatty acid ester is an alkyl or alkoxyalkyl ester of a fatty acid having 10 to 22 carbon atoms. (3) The magnetic recording medium according to claim 1, wherein the modified silicone oil contains at least one of an epoxy group, an amino group, a carboxyl group, and a hydroxyl group in its molecular structure. .