JPH02101628A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To eliminate the possibility of stopping traveling even with a system to detect the end of the double layer magnetic recording medium from the light transmittance thereof and to enhance the electromagnetic conversion of the recording medium by specifying the light transmittance of the recording medium and the required ratio of the light transmittances of the upper and lower layers to specific values. CONSTITUTION:The 1st and 2nd magnetic layers of the lower and upper layers contg. ferromagnetic powder and binder are laminated on a nonmagnetic base, by which the magnetic recording medium is formed. The required light shieldability is obtd. if the light transmittance of the magnetic recording medium is selected to <=1% and the ratio of the light transmittance of the 1st magnetic layer to the light transmittance of the 2nd magnetic layer is selected to <=1/5. The magnetic recording medium with which the possibility of stopping the traveling in parts exclusive of the tape end is eliminated even with the system of detecting the tape end from the light transmittance and which is enhanced in the electromagnetic conversion characteristics is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium having multiple magnetic layers, particularly to a magnetic recording medium for video.

[Conventional technology and its issues]

Recently, magnetic recording media have been widely used as audio tapes, video tapes, computer magnetic tapes, and the like. Magnetic recording media are required to have excellent properties in various properties such as electromagnetic conversion properties and running durability.

For example, as a method for improving electromagnetic conversion characteristics, the coercive force of the ferromagnetic fine powder used has been improved, and in recent years it has become common to use ferromagnetic fine powders with a coercive force of 500 or more.

Further, in order to improve running characteristics such as running durability and running stability, carbon black is included in the magnetic layer. However, since carbon black is a non-magnetic powder, if the amount of carbon black added is increased, the magnetic properties will deteriorate, resulting in a decrease in the dispersibility of the magnetic paint. Therefore, in order to achieve both good electromagnetic conversion characteristics and good running characteristics, it is necessary to strictly select the optimum amount of carbon black added.

In other words, magnetic layers containing carbon black have poor smoothness on the surface of the magnetic layer, so there is a noticeable tendency for electromagnetic conversion characteristics to deteriorate as the amount of carbon black added increases, especially in video tapes that require high-density recording. be. Also in audio tapes, a magnetic layer containing a large amount of carbon black has a reduced filling degree of magnetic particles in the magnetic layer, resulting in deterioration of electromagnetic conversion characteristics in the same manner as described above. However, a magnetic layer that does not contain carbon black has no antistatic effect, resulting in extremely poor durability.

Therefore, as a method for obtaining a magnetic recording medium with excellent durability and good electromagnetic conversion characteristics, Japanese Patent Laid-Open No. 58-200425
There is the following disclosure in the publication.

The magnetic layer consists of two magnetic layers, and only the second magnetic layer (upper layer) contains carbon black, thereby increasing the antistatic effect and improving durability. Further, the first magnetic layer (lower layer) does not contain carbon black, and the electromagnetic conversion characteristics are improved by increasing the filling rate of magnetic particles in the magnetic layer.

Conventionally, carbon black was mixed into the magnetic layer to obtain an antistatic effect, but tape end detection for VHS video tapes, 5-VHS video tapes, 8 mm video tapes, digital audio tapes, etc. is based on light transmittance. Since the videotape is used in various systems, it is necessary to provide a certain level of light-shielding properties to the videotape depending on the system. However, no consideration was given to light shielding properties and electromagnetic conversion characteristics.

With the development of magnetic recording in recent years, in order to meet the demands for higher image quality and higher sound quality, ferromagnetic powder particles have been made finer and magnetic recording media have become more dense. Multilayering with characteristics for sound quality has been considered. In other words, the multilayer structure has the characteristic that it can be manufactured at high density and at low cost because an appropriate ferromagnetic powder can be selected.

However, conventional multilayer tapes have been studied extensively for audio use, but no studies have been conducted on tapes that are compatible with tape end detection and magnetic properties (particularly S/N) required for video tapes. In other words, as an attempt to improve electromagnetic conversion characteristics by multilayering, Japanese Patent Application Laid-Open No. 58-5622
No. 8, JP-A-58-56230, JP-A-58-175
No. 39, JP-A-58-56229, JP-A-61-13
As shown in No. 3024, it is possible to use fine particles of ferromagnetic powder in the upper layer, but if the ferromagnetic powder becomes fine particles, the light-shielding properties of the magnetic layer will be poor and the running will stop. I understand.

Another method of improving electromagnetic conversion characteristics through multilayering is to reduce non-magnetic powder such as carbon black from the lower layer as described above, as shown in Japanese Patent Application Laid-open No. 58-200425. It was found that the light-shielding properties became poor and the vehicle stopped running.

One effective means for imparting light-shielding properties is to include carbon black as described above, but in a multilayer structure, an example in which twice as much carbon black is used in the lower layer as in the upper layer is also disclosed in Japanese Patent Application Laid-Open No. 62-212933. Are known. However, it was found that because the amount of carbon black used was small, sufficient light-shielding properties could not be obtained with only this amount, causing the vehicle to stop running.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium that does not stop running even in a system in which end detection is performed using light transmittance, and has excellent electromagnetic conversion characteristics.

[Means to accomplish the task]

The present invention provides (1) a magnetic recording device in which a first magnetic layer (hereinafter referred to as the lower layer) and a second magnetic layer (hereinafter referred to as the upper layer) containing ferromagnetic powder and a binder are provided in this order on the surface of a non-magnetic support. In the medium, the light transmittance of the magnetic recording medium is 1% or less and the light transmittance of the lower layer is 1% relative to the light transmittance of the upper layer.
75 or less, and (2)
) In the magnetic recording medium comprising a back coat layer provided on the non-magnetic support, the light transmittance of the back coat layer is 50.
% or less.

The object of the present invention is achieved in a multilayer tape by setting the light transmittance of the lower magnetic layer to 175 or less relative to the light transmittance of the upper layer. Preferably, the light transmittance of the lower magnetic layer relative to the light transmittance of the upper magnetic layer is 1710 or less, more preferably 1750 or less. The thickness of the upper layer is 1.5
It is preferably less than μ, more preferably less than 1.0 μ.

The following methods can be used to obtain a magnetic recording medium having the light transmittance of the present invention.

(1) A colored non-magnetic pigment such as carbon black is added to the magnetic layer.

If the lower magnetic layer contains a non-magnetic pigment, and the amount of the non-magnetic pigment relative to the ferromagnetic powder is greater than that of the upper layer, a tape having the light transmittance of the present invention can be easily obtained. Non-magnetic pigments include carbon black, graphite, amber,
Examples include silicon carbide and metal oxides such as chromium oxide, titanium oxide, red iron oxide, and the like. The amount of these non-magnetic pigments contained in the lower layer is 0.5 to 3Q compared to the ferromagnetic powder.
It is wt%.

(2) When the ferromagnetic powder in the magnetic layer is iron oxide, the ratio of divalent iron atoms to trivalent iron atoms in the upper layer ferromagnetic powder is lower than the ratio of trivalent iron atoms in the ferromagnetic powder in the lower layer. A tape having the light transmittance of the present invention can be easily obtained by increasing the ratio of divalent iron atoms to the total amount of divalent iron atoms. The ratio of trivalent iron atoms to divalent iron atoms in the ferromagnetic powder of the lower layer is 1 to 50%, preferably 5 to 50%.

(3) Also, the particle size and crystallite size of the ferromagnetic powder in the lower layer should be larger than that of the ferromagnetic powder in the upper layer, and the specific surface area of the ferromagnetic powder in the lower layer should be smaller than that of the ferromagnetic powder in the upper layer. However, it is easy to obtain a tape having the light transmittance of the present invention. The particle size of the lower layer ferromagnetic powder is 0.3 to 0.1
5μ, crystallite size of 450 to 250 angstroms, and specific surface area of 25 to 50 m'/g.

It is preferable to use these methods (1), (2), and (3) in combination.

In order to obtain better electromagnetic conversion characteristics in the tape having the light transmittance of the present invention, the thickness of the upper layer is preferably 1.5.
It is less than μ, more preferably less than 1.0 μ. When the thickness of the upper layer is set to 1.5 μm or less, the ratio of the upper layer having low light-shielding properties becomes small, making it easier to ensure the light-shielding properties of the entire tape. However, when the thickness of the upper layer is less than 1.5μ, conventional coating methods have the problem of large thickness fluctuations and low productivity. Using a wet-on-wet simultaneous multilayer coating method solves these problems and is more preferable. The tape having the light transmittance of the present invention may have a bank coat layer. The thickness of the back coat layer is 0.2~
It is desirable that the thickness is 1.5μ and that it has a certain degree of light-shielding property, and that the light transmittance of only the back coat layer is 50% or less.

If a back coat layer is provided, the light-shielding property of the magnetic layer may be lower than that without a back coat layer.

[Actions and effects of the present invention]

The magnetic recording medium of the present invention has a light transmittance of 1% or less as a whole, which is a required characteristic since video tapes use light transmittance to detect the end of the tape.

The present invention aims to provide a light-shielding property of 1% or less of this light transmittance through the light-shielding property of the underlying magnetic layer. Specifically, methods (1) to (3) as described above are adopted, but setting the light transmittance of the lower magnetic layer to 175 or less with respect to the light transmittance of the upper layer in this way The goal is to reduce the amount of colored non-magnetic pigments such as carbon black, reduce the Fe''/Fe 3 + ratio of the ferromagnetic powder, and reduce the particle size and crystallite size.
The goal is to increase T. By doing so, the degree of filling of the ferromagnetic powder is increased, and high-density recording with less noise is possible.

In a videotape, the upper layer is for video recording, and because it records short wavelengths, the effect of this high filling and low noise is great.

The father layer is also responsible for recording audio signals. On the other hand, in the lower layer, in order to reduce the light transmittance, a large amount of pigment such as carbon black is added, the Fe''/Fe3+ of the ferromagnetic powder is increased, and the particle size and crystallite size are also increased.
This is achieved by reducing r, but the lower layer is mainly responsible for audio signals (long wavelength range), so even if the filling degree is slightly lower and the noise is slightly larger, the effect is not so great. Therefore, there is no deterioration of electromagnetic conversion characteristics, and there is no need to stop running due to tape end detection, which is required for video tapes.

Preferred embodiments of the present invention are as follows.

(1) The magnetic recording medium according to claim (1), wherein the light transmittance of the lower magnetic layer is 1710 or less with respect to the light transmittance of the upper magnetic layer.

(2) The magnetic recording medium according to claim (1) or (2), wherein the thickness of the uppermost magnetic layer is 1.5 μm or less.

(3) Claim (1) characterized in that the uppermost magnetic layer is provided on the lower magnetic layer while it is in a wet state.
) or the magnetic recording medium described in (2).

[Detailed description of the invention]

The magnetic recording medium of the present invention includes known binders, lubricants,
An abrasive material can be used. Further, as the ferromagnetic powder, ferromagnetic metal fine powder, iron oxide, CO modified iron oxide, barium ferrite, etc. can be used for both the upper layer and the lower layer. These ferromagnetic powders, binders, lubricants, abrasives, solvents, and adjustment methods using these are described in Japanese Patent Publication No. 56-2
No. 6890. The reason why the tape having the light transmittance of the present invention not only does not cause the problem of stopping running in video decks and audio decks, but also has excellent electromagnetic conversion characteristics is considered as follows. In multilayer magnetic recording media, the magnetic properties of the upper layer near the head are more important. This is more noticeable in video, which is recorded at short wavelengths. However, in order to match the tape with the system, it is necessary to make the tape have a light transmittance below a certain level, and for this reason, in the case of a single-layer tape, a light-shielding substance other than ferromagnetic powder is added. However, these are undesirable because they reduce the filling degree of the magnetic layer, resulting in deterioration of electromagnetic conversion characteristics. On the other hand, the above-mentioned problems also occur in multilayer tapes.

In the present invention, the light transmittance of the entire tape can be lowered by ubiquitously distributing a substance having light-shielding properties in the lower layer of the tape. In addition, it is thought that by increasing the thickness ratio of the lower layer to the total layer, it is possible to prevent deterioration of electromagnetic conversion characteristics due to unnecessary addition of light-shielding substances other than ferromagnetic powder to the upper layer, which is essentially in the vicinity of the head. .

The above also applies to the case where a back coat layer having a light shielding property is provided, but the light shielding property of the magnetic layer may be smaller than when there is no back coat layer, and the electromagnetic conversion characteristics are further improved.

The method for measuring the light transmittance was in accordance with the method specified by the standards of each system. For VHS tapes, a Vigter type light transmittance measuring device was used.

EXAMPLES The present invention will be explained in more detail with reference to Examples below. In the examples, "parts" indicate "parts by weight."

Example 1 (upper layer) 100 parts of cobalt metamorphosed iron oxide (Hc
8000e - Specific surface area 40m'/g, particle size 0.1
8 μ, divalent iron atom/trivalent iron atom = 5%, crystallite size 300 angstrom) Vinyl chloride-vinyl acetate-maleic anhydride copolymer, degree of polymerization 300) 10 parts polyurethane resin 7 parts α-alumina
8 parts carbon black (particle size 40 nm) 4 parts stearic acid
After dispersing 300 parts or more of 2 parts butyl stearate and 1 part butyl acetate in a sand mill, 7 parts of polyisocyanate was added to obtain a magnetic paint.

(Lower layer) Cobalt metamorphosed iron oxide 100 parts (Hc
7000e, specific surface area 30 m'/g, particle size 0.
22 μ, divalent iron atom/trivalent iron atom = 10%, crystallite size 400 angstrom) Vinyl chloride - Vinyl acetate -
Maleic anhydride copolymer (degree of polymerization 300) 10 parts Polyurethane resin 7 parts Carbon black (particle size 40 nm) 8 parts Stearic acid
2-part butyl stearate
After dispersing 300 parts or more of 1 part butyl acetate in a sand mill, a polyisocyanade part was added to obtain a magnetic paint.

These two liquids were applied in a wet-on-wet simultaneous multilayer coating method, resulting in an upper layer thickness of 0.8μ and a lower layer thickness of 3.0μ after drying.
It was applied so as to have a thickness of μ, oriented, and then dried. Next, after calendering, it is slit into 1/2 inch pieces.
HS videotape A-1 was obtained.

Example 2 Upper and lower layers of a tape obtained by processing in the same manner as in Example 1 by changing the particle size of the ferromagnetic powder in the upper and lower layers, the ratio of divalent and trivalent iron atoms, the amount of colored pigment, etc. The light transmittance and electromagnetic conversion characteristics are shown in Tables IA-2 to A-10.

Example 3 A-11 was prepared by using 4 parts of carbon black in the lower layer of Example 1 and providing a back coat layer with a thickness of 0.3 μm on the support surface opposite to the magnetic layer.

Comparative Example 1 In Example 1, the thickness of the upper layer was 1.9μ and the thickness of the lower layer was 1.9μ.
A videotape obtained in the same manner except that μ was
It was set to 1.

Comparative Example 2 (Upper layer) 100 parts of cobalt metamorphosed iron oxide (Hc
8000e, specific surface area 40 m”/g, particle size 0.
18μ, divalent iron atom/trivalent iron atom = 5%, crystallite size
(300 angstroms) Vinyl chloride - Vinyl acetate -
Maleic anhydride copolymer (degree of polymerization 300) 10 parts Polyurethane resin 7 parts α-alumina
8 parts carbon black (particle size 4Qnm) 8 parts stearic acid
After dispersing 300 parts or more of 2 parts butyl stearate and 1 part butyl acetate in a sand mill, 7 parts of polyisocyanate was added to obtain a magnetic paint.

(Lower layer) Cobalt metamorphosed iron oxide 100 parts (Hc
7000e, specific surface area 30m, '/g, particle size 0
．． 22 μ, divalent iron atom/trivalent iron atom = 5%, crystallite size 400 t angstrom) Vinyl chloride-vinyl acetate-maleic anhydride copolymer (degree of polymerization 300) 10 parts polyurethane resin 7 parts carbon black (particles) Size 40nm) 4 parts stearic acid
2-part butyl stearate
1 part Butyl acetate 30
After dispersing 0 parts or more with a sand mill, polyisocyanate 7
% was added to obtain a magnetic paint.

These two liquids were applied in a wet-on-wet simultaneous layered manner, resulting in an upper layer thickness of 0.8 μm and a lower layer thickness of 3.0 μm after drying.
It was applied so as to have a thickness of μ, oriented, and then dried. Next, after calendering, it is slit into 1/2 inch pieces.
IIS videotape B-2 was obtained.

Moreover, the one in which the upper layer thickness was 1.9 μm and the lower layer thickness was 1.9 μm was designated as 8-3.

B-4 was obtained in the same manner as in Comparative Example 2 except that the carbon black in the lower layer of Comparative Example 2 was removed.

8-5 was obtained in the same manner as in Comparative Example 2 except that the upper layer carbon black was 1 part, the lower layer carbon black was 2 parts, the upper layer thickness was 1μ, and the lower layer thickness was 3μ. .

(Light transmittance) Hitachi Recording Spectrophoto
Using a mesh meter (Model EPS-37), a mesh was placed on the reference side, the full scale was adjusted, and measurement was performed in a wavelength range from 500 nm to 1500 mm, and the light transmittance at a wavelength of 8000 m was evaluated.

(Stopping Running) Using 10 commercially available video decks, 10 rolls of each sample were run. At this time, the number of windings of the vehicle whose loading was released at the start or just before running was determined.

(Video S/N) Using a Shibaku Noise Meter (925R) and using the reference tape as sample Nα, the difference in S/N ratio was determined. Bypass filter 10 KHz, low pass filter 4
．． Noise levels were measured at 2MHz. VTR used
It is Matsushita NV-8300.

(Color S/N) The measuring device is a noise meter (925R) made by Shibatsu KK.
The test was carried out using a bypass filter of 10 KHz and a low-pass filter of 500 KHz. The VTR used was Matsushita NV-8300. Based on Comparative Example 1 (O
dB) and compared.

As is clear from the table above, it can be seen that the samples of the present invention are superior in both S/N and running stopping performance compared to the comparative samples.

Claims (2)

[Claims] (1) A magnetic recording medium in which a first magnetic layer containing a ferromagnetic powder and a binder and a second magnetic layer are provided in this order on the surface of a non-magnetic support, wherein the optical transmittance of the magnetic recording medium is 1% or less. A magnetic recording medium, wherein the light transmittance of the first magnetic layer is 1/5 or less of the light transmittance of the second magnetic layer. (2) The magnetic recording medium according to claim 1, wherein the non-magnetic support is provided with a back coat layer, and the back coat layer has a light transmittance of 50% or less.