JPS60125924A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has high S/N and is free from scintillation and chipping of a back coat layer by providing the back coat layer consisting of TiO2 having specific particle sizes on the rear of a base. CONSTITUTION:A magnetic layer which is formed by dispersing ferromagnetic metallic or alloy powder in a resin binder or a magnetic layer which is a magnetic layer consisting of a thin ferromagnetic metallic or alloy film and has >=1,000 Oe coercive force and <=0.08mum surface roughness is provided on the front surface of a plastic film base body. A back coat layer formed by dispersing TiO2 having 0.04-0.5mum average particle sizes in a thermosetting resin binder is provided on the rear surface of the base body. The paint for the back coat is prepd. by packing TiO2 at 4:1-1:1 (by weight) in the binder and kneading the mixture composed thereof. The back coat layer is formed on the rear surface of the base by using such paint for the back coat in such a way that the thickness of the coated film is made 0.3-1.5mum and the surface roughness is made 0.05-0.6mum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and particularly to a high-density magnetic recording medium having excellent physical properties and electromagnetic conversion characteristics.

Background of the Invention Conventionally, ferromagnetic powders that have been used as magnetic recording media include γ-Fe2O3, CO-containing -Fe2
031F eB Oa, C'-containing Fe3O4, CrO
There was a second prize. However, the magnetic properties of these ferromagnetic powders, such as coercive force and maximum residual magnetic flux density, are insufficient for high-sensitivity, high-density recording. is not very suitable.

As the requirements for magnetic recording media become stricter, we have developed a system that has characteristics suitable for high-density recording! 7! i! Magnetic powders have been developed or proposed.

Such magnetic powders include Fe)Co, Fe-Co, Fe-
Examples include metals or alloys such as Co-NiXCo-N1, and alloys of these with AI, Cg Sl, etc. A magnetic recording layer using such an alloy powder needs to have a high coercive force and a high residual magnetic flux density for the purpose of high-density recording, and various manufacturing methods or methods are used to make the magnetic powder meet these standards. Alloy composition must be selected.

The present inventor fabricated magnetic recording media using various alloy powders, and found that the specific surface area measured by the BET method was a8rr? /
9, the coercive force of the magnetic layer is 1.000 Qe or more, and the surface roughness of the magnetic layer (TAYLOR-HOB SON
Average value of 20 points measured using the company's 4-tally step method. Cutoff αj7m, stylus force 2tny.

Needle 0. I x 2.5μ was used. (same below) is 0.
It has been found that when o8Pn or less, a magnetic recording medium with a sufficiently low noise level and suitable for high-density short-wavelength recording can be obtained.

On the other hand, magnetic recording media in which a ferromagnetic metal thin film is coated on a plastic base are also used for similar high-density recording purposes.

Electroplating, chemical plating, vacuum deposition, sputtering,
When a method such as ion blating is used, the ferromagnetic metal thin film formed is 100% metal or alloy, so it can have a high recording density. However, when forming a ferromagnetic metal thin film using the above method, the surface roughness can be reduced to about 0.001 μm, but on the other hand, the surface condition of the support strongly influences the surface condition of the ferromagnetic thin film, affecting the electromagnetic conversion characteristics. do.

Moreover, in all of these magnetic recording media, the thickness of the plastic film base made of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, etc. as a support tends to become thinner and thinner. It is being considered.

When the base becomes thin, the media becomes too soft and friction increases, resulting in poor running, winding, and insufficient strength.

Therefore, it became necessary to strengthen the base and improve running performance. Conventionally, some methods of improving runnability include applying a top coat to the magnetic surface, but in this case, the lubricant on the top coat surface is not permanent, or it may stick when stored at high temperatures, causing problems. Become. In addition, since the surface roughness of the magnetic surface has become better, when a top coat is applied, sticking occurs due to the tightness of the winding, which is undesirable.

Conventionally, it has been widely practiced to solve problems such as poor running, curling, and insufficient strength by applying a back coat layer instead of a top coat.

Disadvantages of the Prior Art However, the performance of the conventional magnetic tape with a back coat layer is not always satisfactory, and the following 17
．． iJ issues have been pointed out.

(b) Decrease in SlN by applying a back coat (
(b) Occurrence of shinching phenomenon due to air being drawn in (c) Scraping of the back coat layer) Damage to the tape during loading or unloading operations with long-term magnetic tape (e) Faulty tape winding The present invention is directed to the above-mentioned problems. By solving traditional technical issues, S
A back coat type magnetic recording medium that has a high lN and can prevent cinching phenomenon, abrasion of the packfoot layer, tape damage during loading or unloading operations, and does not cause the tape to fly out or unwind during high-speed winding. The purpose is to provide

DESCRIPTION OF THE INVENTION In order to achieve the above object, the present invention provides a magnetic layer comprising the above ferromagnetic metal or alloy powder dispersed in a resin binder or a ferromagnetic metal or alloy thin film on the surface of a plastic film substrate. A magnetic layer with a coercive force of 1000 Qe or more and a surface roughness (according to the above measurement method) of 0.08μ
It is characterized by providing a magnetic layer with a diameter of less than m, and providing a back coat layer on the back surface of the substrate in which T i 01 with an average particle size of 0.04 to 0.5 μm is dispersed in a thermosetting resin binder. Provided magnetic recording media.

When the magnetic layer is a metal powder or alloy powder dispersed type, the specific surface area of the magnetic powder t, i B E T method is 48 m'/y
The above is preferable because the S/N ratio of the recording medium is improved. However, if it is too large, the binder of the magnetic powder will not be well dispersed in the d fat, and the effect will be saturated. The surface roughness of this type of magnetic layer is preferably 0.08 μm or less, thereby increasing the recording sensitivity at short wavelengths.

In the case of a gold or alloy N model magnetic layer, a surface roughness of 0.08 μm or less can be easily achieved, and a surface roughness of about 0.01 μm is also possible.

As a result of intensive study on the material and particle size of the inorganic pigment used as the filler in the bank coat layer, the inventors found that TIC with an average particle size of α04 to 15 μm.
It has been found that a dispersion of h in a thermosetting resin binder is extremely effective in solving the above-mentioned conventional problems.

In general, the smaller the average particle size of the filler in the backcoat layer, the worse its dispersibility with respect to the binder. If the back coat layer is formed with insufficient dispersion, the back coat layer will have unevenness, and when the magnetic tape is wound overlappingly, the unevenness will be transferred to the magnetic recording layer, resulting in a decrease in S/N.

In addition, if the filler is soft, the repeated running durability will be e<,
The coating layer is scraped away and white powder is generated. Generation of a large amount of white powder is undesirable because it can lead to malfunction of the video tape recorder.

On the other hand, if an inorganic pigment with a relatively large average particle size is filled as a filler, the dispersibility will be good and the S/N will also improve, but if the particle size is too large, the surface roughness of the Notuku coating layer will increase. When the magnetic tape is wound, the unevenness of the bank coat layer is transferred to the magnetic recording layer, resulting in a decrease in S/N. In addition, if the hardness of the inorganic pigment particles becomes too high, the back coat layer will only be scraped and no white powder will be generated. It will be deleted by

TlO2 used as filled inorganic pigment in the present invention
Since the particles are suitably hard particles with a Mohs hardness of about 5 to 7, the reinforcing effect is improved and a back coat layer with excellent repeated running durability can be obtained. Furthermore, T as a filler
Since the hardness of ie is appropriate, it is possible to eliminate the drawback that the guides of video tape recorders and video cassettes are scratched by the back coat layer. Therefore, damage to the tape during loading or unloading is improved, the back coat is no longer scratched due to contact with a kite such as a VTR or video cassette, and no white powder is generated.

In addition, the average particle rise of this TlO2 particle is set to 004 to 0.
．． Since the thickness is 5 μm, the dispersibility is improved and a back coat layer with an appropriate surface roughness can be obtained. This eliminates the drawback that when the magnetic tape is twisted, the unevenness of the back coat J is transferred to the magnetic recording layer, resulting in a decrease in S/N. This improves the S/N and at the same time prevents the occurrence of the scinning phenomenon. is prevented.

To prepare a backcoat paint using this inorganic pigment, TiO2 with the above particle size is mixed with the binder in a ratio of 1:1 to 1.
:1 (!M ratio) and knead. Using this back coat paint, coat the back side of the support pair with a coating thickness of 0.3 to 15 μm1 and a surface roughness of α05 to 0.6 μm.
Apply a back coat so that The thus obtained magnetic tape gave good results that could solve all of the above-mentioned conventional problems.

If the ratio of filler to binder is less than 1:1, it will cause adhesion to the magnetic recording layer and is not suitable.

It is desirable that the thickness of the back coat layer be as thin as possible, but if it is too thin, it will not be possible to obtain a sufficient reinforcing effect.
．． Approximately 3 to 5 μm is appropriate. Furthermore, if the surface roughness of the back coat layer is rougher than 0.6 μm, the unevenness on the surface of the back coat layer will be transferred to the magnetic recording layer, reducing the S/N and reducing the
．． If it is smoother than 1 μm, the surface roughness will increase and cause intercondyles such as running stops, so the surface roughness should be 0.05 to 06 μm.
A range of is appropriate.

As the binder constituting the back coat layer, all thermosetting binders conventionally used in magnetic recording media can be used. In particular, binders containing nitrocellulose, urethane, vinyl chloride-vinyl acetate copolymers, and isocyanates as resin components, or binders containing urethane, vinyl chloride-vinyl acetate copolymers, and isocyanates as resin components are suitable for dispersing the above pigments. ing.

Furthermore, in order to reduce the friction of the back coat layer and improve running properties, silicone oil, fluorine oil, fatty acid,
Fatty acid esters, paraffin, liquid paraffin, surfactants, etc. can be used, but it is particularly preferable to use fatty acids and/or fatty acid esters. Examples of fatty acids include capric acid, lauric acid, myristic acid, palmitic acid,
stearic acid, behenic acid, oleic acid, elaidic acid,
Carbon number 12 such as sulfuric acid, phosphoric acid, stearolic acid, etc.
The above fatty acids (RCOOH, R is an alkyl group having 11 or more carbon atoms), and fatty acid esters include 12 to 12 carbon atoms.
Fatty acid esters consisting of 16 monobasic fatty acids and a monohydric alcohol with 6 to 12 carbon atoms, monobasic fatty acids with 17 or more carbon atoms, and a total of 21 to 12 carbon atoms in the fatty acid. A fatty acid ester consisting of a monohydric alcohol consisting of 23 alcohols, etc. are used.

When using a dispersed magnetic layer, examples of magnetic alloys that can satisfy the above characteristics include Co, Fe-Co, and Fe-Co-N.
1. Co-Ni etc., as well as Cr, AI, 81
A fine powder containing the following ingredients is used. These metal salts are B
Fine powder wet-reduced with a reducing agent such as H4, iron oxide surface
It is a fine powder obtained by dry reduction in H2 gas after being treated with one compound, or a fine powder obtained by evaporating an alloy in low pressure argon, and has an axial ratio of 1:5 to 1:10, and a residual magnetic flux density Br.
= 2,000 to 3,000 Gauss, and satisfies the above coercive force and surface area conditions.

The alloy magnetic powder can be made into a magnetic paint using various binders, but thermosetting resin thread binders and electron beam curing binders are generally preferred, and other additives include dispersants, lubricants, and antistatic agents. can be used in a conventional manner. Since magnetic powder with a BET coating area ratio of 8rrF19 is used, if there is a problem with dispersibility, a surfactant, an organic titanium coupling agent, or the like may be used as a dispersant. As a binder, a binder consisting of vinyl chloride, vinyl acetate/vinyl alcohol copolymer, polyurethane prepolymer and polyisocyanate, or a binder further containing nitrocellulose,
Other known thermosetting binders, or radiation-curing binders containing acrylic yarns sensitive to ionization energy, 2) L bonds, maleic yarn double bonds, etc. as resin groups, etc. can be used.

According to the usual method, the alloy magnetic powder is mixed with a binder, a specified solvent, and various additives to form a magnetic coating, which is applied to a substrate such as a polyester base, and then thermally cured or electron beam cured to form a magnetic film. In the case of a metal or alloy thin film type magnetic layer, the ferromagnetic material is It can be selected from the same materials as the ferromagnetic metal powder described above, and can be manufactured by the vapor deposition, mottled plating, or other methods described above. ) For example, there is a method in which cobalt and nickel are placed in a crucible, evaporated in a vacuum, and then diagonally deposited on the surface of a polyester film.

Examples of the present invention will be described below along with comparative examples.

magnetic layer 1 Various alloy powders were produced by wet reduction method.

These particles are composed of acicular particles with an axis ratio (minor axis/long axis) of 115 to 1/10, residual magnetic flux density of 2000 to 3000 Gauss, coercive force of 1000 to 20000e, and BET surface area ratio of 4.
5~70u? /9. These magnetic powders were mixed in the following mixing ratio in a conventional manner.

Overlapping part F e -Co -Ni alloy powder 100 myristic acid 2 sorbitan tristearate 2 Goim part of polyisocyanate (Desmodur L manufactured by Bayer AG) was added to this mixture to make a magnetic coating, and it was coated on a polyester film with a thickness of 35 μm. It was coated, dried and calendered. Thereafter, a heat curing reaction was carried out at 80° C. for 48 hours.

By adjusting the calendering conditions, various surface roughnesses of 0.02 to α12 μm were obtained.

Magnetic Layer 2 The same magnetic powder as in Magnetic Layer 1 was used to make a mixture of the following formulations.

Overlapping part: pe-Co-N1 alloy powder 100 This mixture was applied to a polyester film to a thickness of 35 μm, dried, calendered, and then cured with an electron beam.

By adjusting the calendering conditions, the surface roughness was set to 102 to 0.12 μm.

Magnetic layer 6 The magnetic layer used was a diagonally evaporated alloy magnetic film of 80% co/cur) and 20% nickel deposited on the surface of the seriethylene terephthalate film to a thickness of about 150 OA by vacuum evaporation. shi).

The surface roughness was 0.01 μm.

EXAMPLE A thick coat layer was formed on the back side of the above-mentioned diester film substrate on which magnetic layers 1, 2, and 5 were formed in the following manner.

After thoroughly kneading and dispersing each of the compositions of batter 1 in a ball mill, a layer of 1.0 μm thick was coated on the back side of the three types of substrates.
Five samples, Samples 1 to 5, were prepared by coating with 100 m, heating and curing, and calendering. In Table 1, the amounts of composition represent the M-ratio relative to 100 parts of inorganic pigment.

Thereafter, it was cut into 1/2 inch width and assembled into a VHS video cassette, and color S/N, shinching, back coat scraping, and scratches during loading or unloading were measured. The measurement results are shown in Table 2 (using magnetic Jf171), Table 3 (using magnetic layer 2), and Table 4 (using magnetic layer 3). In Table 1 and Table 4, Samples 1 and 2 are Examples of the present invention, and Samples 3 to 5 are Comparative Examples. Samples 3 to 5 are comparative examples in which α-Fe20HI Ca COB and Tie with a large particle size of 06 μm were used as amorphous pigments, respectively. The surface roughness of all the magnetic layers of the sample No. 2.6 is 0.08 μm or less, and all of the surface roughness of the back coat layer in Table 4 is Table 1 Tatsu 2 Table 3 Table 4 When we investigated the relationship between the surface roughness of the magnetic surface and the surface roughness of the magnetic surface, we obtained the results shown in Figure 1. From now on, the surface roughness of the back coat layer is 0.6 μm or less, and the surface roughness of the magnetic layer is 0.
It can be seen that it should be less than 0.08μIn. Therefore, the results in Tables 2 to 4 are limited to those that satisfy these surface roughness conditions. Further, regarding the magnetic layer 1.2, the relationship between the BET method surface area of the metal powder and the S/N was investigated, and it was found that 48 rrF/ji or less provides an excellent S/N (in a high frequency region).

Tables 2 and 3 are limited to those that meet this condition.

As is clear from Tables 2 to 4, α-pe is used as an inorganic pigment.
Comparative sample 6 using ,o, is color 8 /N,
Characteristics such as cinching, back coat scraping, and scratches during loading or unloading are relatively good, but friction increases. Comparative sample 4 has large friction, poor color S/N, cinching, and back coat scraping, and large scratches during loading or unloading ◇Comparative sample 5 has low friction, but cinching and
Backcoat wears off and color S/N deteriorates.

On the other hand, samples 1 and 2 of the embodiment according to the present invention are
Compared to Comparative Samples 3 to 5, the force was excellent at 9-8/N, and cinching was less likely to occur. Furthermore, the back coat cannot be removed,
Damage to the magnetic tape due to loading or unseeding IJ is also greatly reduced.

Effects of the Present Invention As described above, the present invention provides a magnetic recording medium having a magnetic recording layer on the surface of the support and a back coat layer on the nose surface. is characterized by having T i ox of 0.04 to 05 μm dispersed in a binder, so the S/N is high,
It is possible to provide an excellent bank coat type magnetic recording medium that can prevent scintching, back coat layer abrasion, and tape damage during loading or unloading operations.

It is a graph showing the relationship between and 8/N.

Claims (4)

[Claims] (1) In a magnetic recording medium in which a magnetic layer consisting of a ferromagnetic alloy powder dispersed in a resin binder or a magnetic layer consisting of a ferromagnetic thin film is adhered to a Plus Deck base, i7'f 17
1E magnetic p-layer has a coercive force of 1oooooe or more and 008μ
m or less, and furthermore, the back surface of the base has an average particle size (Ti of 1'04 to 05 μm).
B? is characterized by being coated with a back coat Jv made by dispersing Q. in a thermosetting binder. magnetic recording medium (2) The back coat layer is filled with the T + 02 and the binder in a km ratio of 4:1 to 1:1. The magnetic recording medium according to item 1. (3) The back coat layer has a coating thickness of α3 to 15
The magnetic recording medium according to claim 1 or 2, characterized in that the magnetic recording medium is formed to have a diameter of μm. (4) The back coat layer has a surface roughness of 0.05 to
Claims 1 and 2 are characterized in that the film is formed to have a thickness of 0.05 μm. -i The magnetic recording medium according to item 3.