JP2695647B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having excellent electromagnetic conversion characteristics and high luminosity.

[Conventional technology]

In recent years, magnetic recording media have been actively studied for high-density recording and lengthening, and fine-grained ferromagnetic powders and magnetic recording layers, base films, and the like have become thinner. The transmittance tends to increase.

When the light transmittance of the magnetic tape increases, a method of detecting the tape end based on the amount of light transmission, such as the VHS VTR, tends to cause a malfunction, which is a problem. As a countermeasure, it has been proposed to provide an intermediate layer made of carbon black and a binder resin. Although the purpose is different from this, a method has been proposed in which an intermediate layer made of an inorganic oxide powder and a binder resin is provided to increase the Young's modulus of the tape and improve durability.

However, each of the above-mentioned intermediate layers has a disadvantage. In the intermediate layer to which carbon black is added, the dispersibility of carbon black is inferior, and therefore, the surface properties of the obtained intermediate layer are poor, leading to a decrease in electromagnetic conversion characteristics. In addition, when the porosity of the intermediate layer is large and the magnetic recording layer is coated thereon, the solvent in the coating material for the magnetic recording layer penetrates into the voids of the intermediate layer, which may cause uneven application of the magnetic recording layer.

On the other hand, inorganic oxide powders (CaCO ₃ , BaSO ₄ , ZnO, TiO ₂ , S
In the intermediate layer made of a white powder such as iO ₂ or α-Al ₂ O ₃ ) and a binder resin, the Young's modulus of the magnetic recording medium is improved, but does not contribute to the reduction of the light transmittance.

[Problems to be solved by the invention]

The present invention solves the drawback that when the light transmittance of the intermediate layer of the above-mentioned conventional product is reduced, the surface property is reduced, and thus the magnetic recording medium having good electromagnetic conversion characteristics and low light transmittance. The purpose is to provide.

[Means for solving the problem]

In order to solve the above problems, the present inventors have used carbon black and inorganic oxide powder in combination, and studied the mixing ratio and dispersion method.As a result, the amount of carbon black was reduced to the total amount of inorganic oxide powder and carbon black. On the other hand, when used in a weight ratio of 70% or less, preferably 70% to 40%, the dispersibility of carbon black is improved, the surface smoothness of the intermediate layer is improved, and the occurrence of coating unevenness is prevented. The electromagnetic conversion characteristics of the magnetic layer applied to the magnetic recording medium are improved.
In addition, it was found that the light transmittance of the magnetic recording medium was sufficiently reduced.

The dispersibility of carbon black is improved because when the paint for the intermediate layer containing carbon black inorganic oxide powder is dispersed using a dispersing machine, when the amount of carbon black becomes 70% or less based on the inorganic powder, It is presumed that the coating material can efficiently receive stress because the fluidity is dramatically improved and the amount of solvent used during dispersion can be reduced.

Also, the ratio of carbon black to inorganic oxide powder is
The electric resistance of the intermediate layer changes sharply between 50/50 and 30/70,
If / 50 ^{10 6 Ω / cm 2, 40} /60 At ^{10 7 Ω / cm 2, 30} /70 at 10
^It becomes ¹⁰ Ω / cm ² , and when it becomes 30/70, the electrical resistance increases,
The problem is the generation of static electricity. Furthermore, the light transmittance is 35
If the amount of carbon black is less than / 65, a sufficient light shielding effect cannot be obtained.

To produce the magnetic recording medium of the present invention, furnace black, channel black, carbon black such as graphitized carbon black and CaCO ₃ , BaSO ₄ , TiO ₂ ,
Inorganic oxide powder such as α-Al ₂ O ₃ and nitrocellulose as binder resin, vinyl chloride resin containing hydroxyl group, carboxyl group, phosphate group, sodium sulfonate group, polyurethane resin, polyisocyanate, etc. Is applied onto a non-magnetic substrate, and dried, and then a magnetic recording layer is provided thereon and cut into a desired shape. If necessary, a back coat layer may be provided.

〔Example〕

Next, examples of the present invention and comparative examples will be described. In the following examples, “parts” means “parts by weight”.

Examples 1 to 8 and Comparative Examples 1 to 4 As the intermediate layer coating composition, using the fillers shown in Table 1,
A paint having the following composition was prepared.

Fillers shown in Table 1 100 parts Nitrocellulose (1/2 second grade) 27 parts Polyurethane resin 19 parts Polyisocyanate 8 parts Cyclohexanone 100 parts Methyl ethyl ketone 200 parts Toluene 300 parts Using a dispersing machine such as a high-speed disperser or a sand mill. After dispersion, the mixture was passed through a filter having an average pore size of 0.5 μm, and then applied to one surface of a polyester film (about 13 μm in thickness) so that the thickness after drying was about 0.3 to 1.5 μm. Then, a magnetic recording layer having the following composition was provided, and after performing a calendar process, slitting to a 1/2 inch width was performed to produce a video tape.

In Example 9, nitrocellulose as the binder resin in the intermediate layer was replaced with the same amount of vinyl chloride resin (VAGH manufactured by UCC), and the amount of the organic solvent used was changed to cyclohexane, 80 parts, methyl ethyl ketone, 160 parts, toluene, Changed to 240 copies.

Magnetic recording layer composition Co-containing γ-Fe ₂ O ₃ (specific surface area 35 m ² / g) 100 parts Carbon black (average particle diameter 0.025 μm) 4 parts α-Al ₂ O ₃ (average particle diameter 0.4 μm) 4 parts Stearic acid Zinc 0.5 part Nitrocellulose (1/2 second grade) 9 parts Polyurethane resin 8 parts Polyisocyanate 3 parts Myristic acid 2 parts N-butyl stearate 1 part The video tapes prepared in the above Examples and Comparative Examples are shown below. Was evaluated.

Surface roughness: The center line average roughness of the surface of the magnetic layer was measured using a stylus type surface roughness meter.

RF output: An RF signal was recorded at a reference RF recording current, and the reproduction output was indicated by a relative value to a standard tape.

Light transmittance: The video tape was measured with an optical tester VT-1M measuring device manufactured by Victor Company of Japan, Ltd.

Table 2 shows the measurement results of the video tape in each of the examples and the comparative examples.

The magnetic recording media provided with the intermediate layers of Examples 1 to 9 have low surface roughness and high RF output. Also, the light transmittance is low.

〔The invention's effect〕

As described above, a magnetic recording medium including carbon black and an inorganic oxide powder and having an intermediate layer in which the amount of carbon black is 70% or less by weight based on the total amount of the inorganic oxide powder and carbon black is It has low surface roughness, low light transmittance, and excellent electromagnetic conversion characteristics. It is clear that a magnetic recording medium having carbon black in the range of 70 to 40%, in particular, has a large light-shielding property and can provide a magnetic recording medium having extremely excellent electromagnetic conversion characteristics.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-73237 (JP, A) JP-A-62-214513 (JP, A) JP-A-60-20316 (JP, A) JP-A 63-73 317926 (JP, A)

Claims (1)

(57) [Claims] 1. A magnetic recording medium having a magnetic recording layer containing a ferromagnetic powder on a non-magnetic support, wherein the magnetic recording medium contains carbon black and an inorganic oxide powder and the amount of carbon black is the same as that of the inorganic oxide powder and carbon black. A magnetic recording medium, wherein an intermediate layer having a weight ratio of 70% or less based on the total amount is provided between the nonmagnetic support and the magnetic recording layer.