JPH04103018A - Magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape used in audio/video equipment or computers.

BACKGROUND OF THE INVENTION Magnetic recording media are increasingly becoming more densely packed year by year. As a result, it is necessary to reduce recording and reproducing losses in the short wavelength region, and measures are being taken to further reduce the gap between the magnetic head and the magnetic recording medium. That is, making the surface of the magnetic recording medium highly smooth, making the magnetic powder finer, etc.

On the other hand, recording and playback times are becoming longer, and magnetic tapes that are thinner than conventional magnetic tapes are being commercialized.

However, when magnetic recording media are manufactured using such measures, the following problems occur. That is, by pulverizing the magnetic powder used in the magnetic layer of a magnetic recording medium, the light-shielding property of the magnetic layer is reduced. This is due to the fact that the particle size of the magnetic powder is smaller than the wavelength of visible light, and the thickness of the magnetic layer is thinner. When the light-shielding property of a magnetic recording medium decreases, the following problems arise. For example, VH5
In the VTR system, detection of the beginning and end of the tape is realized by reading the difference in light transmittance between the leader tape and the magnetic tape. In such a VTR, if the light-shielding property of the magnetic tape falls below a specified value, the start and end ends will not be detected properly, and the tape will no longer run, rendering it of no practical value.

In order to solve this problem, non-magnetic pigments with high light-shielding properties, such as carbon black, are added to the magnetic layer in order to improve the light-shielding properties of the magnetic layer. However, the magnetic recording medium manufactured by this method has a reduction in reproduction output or an increase in noise in terms of electromagnetic conversion characteristics, resulting in a reduction in the performance most necessary for a magnetic recording medium.

Problems to be Solved by the Invention As magnetic powder becomes finer, the light-shielding properties of the magnetic layer decrease. m
When a non-magnetic pigment with high light-shielding property is added to the magnetic layer, the light-shielding property is improved, but the IIT magnetic conversion characteristics are lower than when no non-magnetic pigment is added.

That is, it is not possible to obtain a magnetic recording medium that has good magnetic conversion characteristics and excellent light shielding properties.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention forms a layer containing iron carbide on a non-magnetic support, and further a layer containing a ferromagnetic material thereon. It is a magnetic recording medium.

According to the present invention, with the above structure, since iron carbide with high light-shielding property is contained between the layer containing a ferromagnetic material and the non-magnetic support, The ferromagnetic material here may be any of the Co-containing iron oxide magnetic powder used in conventional coated magnetic recording media, metal magnetic powder, CrO2, etc. Due to the miniaturization of magnetic powder, the light-shielding property of the magnetic powder becomes a practical problem when the specific surface area of the magnetic powder is 40 bo/g or more.

In addition, the size of iron carbide must be determined taking into account the light transmittance of the entire magnetic recording medium, but the average particle size is 0.1~
1.0 μm is desirable. The shape of iron carbide may be either acicular or granular. If it is less than 0.1 μm, there is a risk that the light-shielding property will be insufficient, and if it is more than 1.0 μm, the surface of the coating layer will become rough.
When coated on top of this, it often deteriorates the surface smoothness and may deteriorate electromagnetic conversion characteristics. There are two methods for forming a coating film on a non-magnetic support: a method in which an iron carbide-containing layer is applied and dried, and then a ferromagnetic material is applied thereon and dried, and a ferromagnetic material is applied immediately after the iron carbide-containing layer is applied. There is a method of applying and drying, but either method is acceptable.

The content of iron carbide may be an amount sufficient to satisfy the light transmittance specified by the equipment in which the magnetic recording medium is used, but is preferably 75 to 100% by weight. 75%
Below that, the light-shielding property may be insufficient. When the total thickness of the magnetic recording medium is specified, it is necessary to pay attention to the thickness of the iron carbide-containing layer. Further, regarding a device that utilizes the light-shielding property of a magnetic recording medium for detecting a starting edge and a bond edge, a 900-copy magnetic tape will be described as an example. It should be noted that all values of component ratios given in Examples are in parts by weight.

Example 1 1. Preparation of paint A Iron carbide powder average particle size 02 μm Polyurethane IFIA fat Vinyl chloride-vinyl acetate copolymer methyl ethyl ketone cyclohexanone toluene 2. Preparation of paint B Co-containing r-Fe208 Magnetic iron oxide powder average particle size Length =01 μm 100 parts 10 parts 10 parts 100 parts 100 parts 100 parts 100 parts Specific surface area = 45 po/g Coercive force 9000e Polyurethane resin Vinyl chloride-vinyl acetate copolymer Aluminum oxide powder Average particle size 0.2 μm Methyl ethyl ketone cyclohexanone Toluene 10 parts 10 parts 5 parts 100 parts 50 parts 100 parts Next, the above paint A was applied to a thickness of 1.5 μm on a 14 μm thick polyester film, oriented and dried, and then paint B was further applied to the coated surface of paint A to a thickness of 2 μm. Coating at .0 μm, orientation,
The surface of the magnetic layer was subjected to surface treatment using a dry zero-order super calender roll to obtain a wide jumbo roll having a total thickness of two layers of 3.5 μm. This was cut into 1/2 inch width to produce a videotape.

Example 2 A videotape was produced in the same manner as in Example 1 except that the particle size of iron carbide in paint A of Example 1 was 0.8 μm.

Example 3 A videotape was produced in the same manner as in Example 1 except that the coating thickness of paint A was 1.0 μm and the coating thickness of paint B was 2.5 μm.

Comparative Example 1 In Example 1, a videotape was produced in the same manner as in Example 1 except that Coating #JA was not applied and only Coating B was applied to a thickness of 3.5 μm.

Comparative Example 2 The particle size of iron carbide in paint A of Example 1 was 0.05 μm,
A videotape was produced in the same manner as in Example 1 except for the above.

Comparative Example 3 A videotape was produced in the same manner as in Example 1 except that the particle size of iron carbide in paint A was 1.5 μm.

Comparative Example 4 Iron carbide in paint A of Example 1 was 50 parts, and the other parts were as in Example 1.
A videotape was made in the same manner.

Table 1 shows the S/N, light transmittance, and magnetic layer surface roughness after tape production.
/N is a VH3 type VTR (NV-G manufactured by Matsushita Electric Industrial)
21), and the specified luminance signal (
50% white level signal) was recorded at the optimal recording current on 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 as OdB. It is.

(2) Light i! The i pass rate is 900 using a charging spectrophotometer.
The light transmittance in nm was measured. The display is in %.

(3) Surface roughness was measured using a stylus type surface roughness meter,
The 10-point average roughness Rz was determined from the Japanese Industrial Standard (Jl5) B2O21 "Surface Roughness".

Table 1 Effects of the Invention As detailed above, according to the present invention, by forming a layer containing iron carbide between a nonmagnetic support and a ferromagnetic material,! Since a magnetic recording medium can be obtained that satisfies magnetic conversion characteristics and light shielding properties at the same time, its practical value is great.

Name of agent: Patent attorney Haruaki Ogata and two others As is clear from Table 1, the magnetic tape obtained in the above manner has almost the same S/N ratio as the conventional product, and has high light transmission. Because the rate is low,! It can be said that it satisfies magnetic conversion characteristics and light shielding properties at the same time. In the above embodiment, a magnetic tape was described, but it goes without saying that the present invention is applicable not only to magnetic tape but also to other magnetic recording media such as magnetic sorting.

Claims (3)

[Claims] (1) A magnetic recording medium characterized in that a layer containing iron carbide is formed on a nonmagnetic support, and a layer containing a ferromagnetic substance is further formed thereon. (2) The magnetic recording medium according to claim (1), wherein the ferromagnetic material is Co-containing iron oxide or CrO_2 with a specific surface area of 40 m^2/g or more. (3) The magnetic recording medium according to claim (1), which has a transmittance of 900 nm light of 1% or less.