JPS60263321A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder and to improve the electromagnetic characteristic, wear resistance, etc. of a magnetic recording medium by providing a magnetic layer contg. the magnetic powder having a specific value or above of the specific surface area by a BET method and sorbic acid compd. selected from sorbic acid and the deriv. and salt thereof to said medium. CONSTITUTION:The magnetic layer contg. the fine magnetic powder having >=30m<2>/g specific surface area by the BET method and the sorbic acid compd. of >=1 kind selected from the sorbic acid, the deriv. thereof such as sorbic acid ester and sorbic acid amide and the metallic salt of Na, K, Ca, Al, Ti, etc. of the sorbic acid is formed on a substrate. The sorbic acid compd. is incorporated into the magnetic layer in such a manner that the entire weight thereof is within a 0.1-5pts.wt. range with respect to 100pts.wt. the magnetic powder. The dispersibility of the magnetic powder into the binder resin is thus improved and the magnetic recording medium which is free from output fluctuation, has high reproduced output and S/N ratio, has excellent wear resistance, etc. and good video characteristic and is suitable for high-density recording is thus obtd.

Description

[Detailed Description of the Invention] [Technical Field and Objectives] The present invention relates to a magnetic recording medium using fine magnetic powder, and an object of the present invention is to have good dispersibility of the fine magnetic powder and to improve electrical properties. An object of the present invention is to provide a magnetic recording medium that has excellent wear resistance and wear resistance.

[Background technology]

In recent years, in magnetic recording media such as video tapes, playback output, SN ratio, etc. have been improved in order to obtain clear image quality and clear sound quality, especially in response to high-density recording such as video tape recorders. Improvements are expected. For this reason, the magnetic powder used in magnetic recording media is usually made into fine particles by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film and drying it. is advanced and BE
Specific surface area by T method is 30rr! The use of very fine magnetic powder with a particle size of 1.2 g or more has been carried out.

However, this type of fine magnetic powder usually has a hydrophilic surface, and it is difficult to disperse it well in the lipophilic binder resin as it is. The amount increases, the viscosity of the magnetic coating material increases, and the shearing force efficiency of the dispersion machine decreases, resulting in a decrease in dispersibility, making it impossible to sufficiently improve reproduction output, signal-to-noise ratio, etc.

Therefore, in order to improve the dispersibility of this type of magnetic powder,
Saturated or unsaturated fatty acids having a hydrophilic group at one end of the molecule and a lipophilic group at the other end are mixed into magnetic paints as a dispersant (Japanese Patent Publication No. 18221-1982, Japanese Patent Publication No. 18221-1989, However, these saturated or unsaturated fatty acids have a weak bonding force with magnetic powder, and it has not yet been possible to sufficiently improve the dispersibility of especially fine magnetic powder in binder resin. However, it is not possible to sufficiently improve reproduction output, signal-to-noise ratio, etc. by using fine magnetic powder. Furthermore, the magnetic layer formed using this type of fine magnetic powder is easily scratched when it comes into violent sliding contact with the magnetic head, reducing its wear resistance. Fillers have been added to the magnetic layer to improve wear resistance, but the dispersibility of these fillers is even worse than that of this type of magnetic powder. The agent cannot be dispersed sufficiently well, and it is difficult to improve the surface smoothness of the magnetic layer and sufficiently improve the electromagnetic conversion characteristics.

[Summary of the invention]

f In view of the current situation, this invention is particularly effective for dispersing fine magnetic powder with a specific surface area of 30%/g or more in a binder resin by the BET method, and is effective for dispersing fillers such as Cr2O3 and A1□03. As a result of conducting various studies on compounds having both lipophilic and hydrophilic groups, we surprisingly found that sorbic acid, sorbic acid derivatives, and sorbic acid metal salts have particularly excellent dispersion ability. At least one sorbic acid-based compound selected from sorbic acid, sorbic acid derivatives, and sorbic acid metal salts has a specific surface area of 30r+ (including fine magnetic powder of 7 g or more) as determined by the BET method. By incorporating it into the magnetic layer, the dispersibility of this type of fine magnetic powder in the binder resin is sufficiently improved, and the dispersibility of the filler used at the same time is also improved, resulting in improved electromagnetic characteristics and wear resistance. It has sufficiently improved characteristics.

The reason why sorbic acid, sorbic acid derivatives, and sorbic acid metal salts have such remarkable dispersion ability has not yet been clearly elucidated, but considering their unique chemical structure, By having a conjugated double bond, the electron density is localized within the molecule,
Functionality is increased due to increased polarizability, and ■Double bonds both have a trans (trans-trans) structure, so the functional group is located at the outermost end of the molecule, resulting in statistical , Geometrically, the functional groups tend to be unevenly distributed on the surface of the dispersant, and 2) sorbic acid and sorbic acid metal salts have 6 carbon atoms, and sorbic acid derivatives usually have 12 or less carbon atoms; It is presumed that the melting point is 3, which makes it easy to mix into the binder resin in order to impart good fluidity to the paint.

The sorbic acid used in this invention has the chemical formula CH
A compound represented by 3CH=CHCH=C, HCOOH, which has a conjugated double bond in the molecule, both of which are trans, has a relatively small molecular weight, and adheres well to the surface of magnetic powder. It also has good compatibility with the binder resin. Therefore, when this sorbic acid is contained in the magnetic layer, the dispersibility of fine magnetic powder with a specific surface area of 30 rrr/g or more by the BET method in the binder resin is sufficiently improved, and at the same time, the sorbic acid contained in the magnetic layer is The dispersibility of the filler is also improved,
A magnetic recording medium with sufficiently improved reproduction output and S/N ratio, excellent electromagnetic conversion characteristics, and excellent wear resistance can be obtained.

Further, as the sorbic acid derivative used in this invention, for example, methyl ester of sorbic acid C3H
2COocH3, ethyl ester C5H7COOC2H
5, propyl ester JL/C3H2COOC3H2, butyl ester c5H7c00C4H,, 7 mido C5H,
CONH2, Nitori Jl/C5H, CN, 7 Nilide C5
H, CONHCfIH5, phenylhydrazide c5H,
C0NHNHC,I(, etc. are mentioned as suitable ones, and like the above-mentioned sorbic acid, these sorbic acid derivatives also have a conjugated double bond in the molecule, both of these double bonds are trans, and the molecular weight is is relatively small, adheres well to the surface of the magnetic powder, and has good compatibility with the binder resin.Therefore, when these sorbic acid derivatives are included in the magnetic layer, the above-mentioned sorbic acid is also used. The same effect is obtained, and the dispersibility of fine magnetic powder with a specific surface area of 30 m/g or more by the BET method in the binder resin is sufficiently improved, and at the same time, the dispersibility of the filler contained in the magnetic layer is improved. It is possible to obtain a magnetic recording medium with improved reproduction output and S/N ratio, excellent electromagnetic conversion characteristics, and excellent abrasion resistance.

Further, the sorbic acid metal salt used in the present invention is a compound represented by the general formula % (where M is a metal), and has a similar structure in the molecule as the sorbic acid and sorbic acid derivatives described above. It has a conjugated double bond, both of these double bonds are trans, and its molecular weight is relatively small.
It adheres well to the surface of the magnetic powder and is compatible with the binder resin. Therefore, when these sorbic acid metal salts are contained in the magnetic layer, the same effect as when using the above-mentioned sorbic acid and sorbic acid derivatives can be obtained, and the BET
The dispersibility of fine magnetic powder with a specific surface area of 30rd/g or more in the binder resin by method f is sufficiently improved,
At the same time, the dispersibility of the filler contained in the magnetic layer is improved, the reproduction output and the S/N ratio are sufficiently improved, and a magnetic recording medium with excellent electromagnetic conversion characteristics and excellent wear resistance is obtained. Specific examples of such metal sorbic acid salts include sodium salt, potassium salt, lithium salt, copper salt, magnesium salt, calcium salt,
Examples include strontium salts, barium salts, zinc salts, cadmium salts, aluminum salts, tin salts, lead salts, titanium salts, and zirconium salts, all of which are preferably used.

Such sorbic acid, sorbic acid derivatives, or sorbic acid metal salts can be added directly when preparing magnetic paints, or dissolved in a suitable solvent such as alcohol or ether, and the solution obtained by this dissolution can be added. Add it when preparing the magnetic paint, or immerse the magnetic powder in this solution to pre-treat the surface of the magnetic powder.
This magnetic powder is used to cleave the magnetic paint, and it is incorporated into the magnetic layer by applying it onto a substrate and drying it. In particular, sorbate metal salts are water-soluble and easily dissolve in water, so if magnetic powder is immersed in an aqueous solution of sorbate metal salts, the surface treatment of the magnetic powder can be carried out extremely easily. There is no danger associated with immersion. Furthermore, magnetic powder that is normally produced in an aqueous solution can be surface-treated in this metal sorbate salt aqueous solution immediately after washing with water, and the surface treatment of the magnetic powder with the metal sorbate can be easily and quickly performed.

The content of such sorbic acid, sorbic acid derivative, or sorbic acid metal salt in the magnetic layer is preferably within the range of 0.1 to 5% by weight based on the magnetic powder in the magnetic layer. If it is too small, the desired effect will not be obtained,
If there is too much, there is a risk of bleed-out.

Sorbic acid, sorbic acid derivatives, and sorbic acid metal salts contained in the magnetic layer may be used alone or in combination of two or more.
It may also be used in combination with other dispersants, such as saturated fatty acids, unsaturated fatty acids, phosphoric acid esters, lecithin, metal soaps, etc.

The specific surface area according to the BET method used in this invention is 30%/
For example, r-Fe
203 powder, Fe5Q4 powder, γ-Fe203 powder and F
Intermediate compound powder of e3O4 powder, Co-containing r-Fe20
3 powder, Co-containing Fe3O4 powder, CrO2 powder, (x
Various fine magnetic powders having a specific surface area of 30 i/g or more by the conventionally known BET method, such as -Fe powder, CO powder, Fe--Ni powder, Fe4N powder, and barium ferrite powder, are widely included.

In addition, conventional binder resins include vinyl chloride-vinyl acetate copolymers, cellulose resins, butyral resins, polyurethane resins, polyester resins, epoxy resins, polyether resins, and isocyanate compounds. Any of the binder resins listed above can be used.

Examples of organic solvents include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and tetrahydrofuran and dioxane. Solvents suitable for melting the binder resin to be used, such as ether solvents, may be used alone or in a mixture of two or more without particular limitation.

In addition, various additives commonly used in magnetic paints,
For example, a lubricant, an abrasive, an antistatic agent, etc. may be added as appropriate.

Further, a bank coat layer may be provided on the back side of the magnetic recording medium such as a magnetic tape, which is opposite to the magnetic layer, if necessary.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Co-containing rFe2O3 powder 100 parts by weight (specific surface area 40 rrr/g by BET method) i Nitrocellulose (H1/2 Eve, 16
% solution) Carbon blank (average particle size 4.5〃23mμ) cx-Fe203 (granular, average particle size 5.0〃particle diameter 1.0
μ) Cr203 (average particle size 1.O#) 0.8 //A1
203 (average particle size 0.4 μ) 2.0 Zinc stearate 0.5 Cyclohexanone 90 Toluene 90 After dispersing this composition with a high-speed stirrer for 2 to 5 hours,
2.0 parts by weight of sorbic acid was added, and then mixed and dispersed using a sand mill. Next, polyurethane resin (20
% solution) 40 parts by weight trifunctional low molecular weight isocyanate compound (75% solution) n-butyl stearate 1 myristic acid 2 cyclohexanone 40 toluene 40 3 were added in the appropriate order, After mixing and dispersing with a high-speed stirrer,
The magnetic paint was cleaved by passing it through a 1μ filter. This magnetic paint was applied onto a 13 μm thick polyester film to a dry thickness of approximately 5 μm, dried, calendered, and then cut to a predetermined width to make a videotape.

Example 2 A videotape was produced in the same manner as in Example 1, except that the amount of sorbic acid used in the preparation of the magnetic coating material in Example 1 was changed from 2.0 parts by weight to 0.5 parts by weight.

Example 3 A videotape was made in the same manner as in Example 1, except that the amount of sorbic acid used in the preparation of the magnetic paint was changed from 2.0 parts by weight to 5.0 parts by weight.

Example 4 Videotape 4 was prepared in the same manner as in Example 1, except that the same amount of n-butyl sorbate was used in place of sorbic acid in the preparation of the magnetic paint in Example 1.

Example 5 A videotape was made in the same manner as in Example 1, except that in the preparation of the magnetic paint in Example 1, the same amount of potassium sorbate was used instead of sorbic acid.

Example 6 In the preparation of the magnetic paint in Example 1, 50 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (20% solution) was used in place of nitrocellulose, and the amount of polyurethane resin used was 40 parts by weight. A videotape was made in the same manner as in Example 1, except that the amount was changed from 1 part to 35 parts by weight.

Comparative Example 1 A videotape was made in the same manner as in Example 1 except that sorbic acid was omitted in the preparation of the magnetic paint in Example 1.

Comparative Example 2 A videotape was produced in the same manner as in Example 1, except that the same amount of lauric acid was used in place of sorbic acid in the preparation of the magnetic paint in Example 1.

For each magnetic tape obtained in each Example and each Comparative Example, the surface roughness of the magnetic layer, RF specific output chroma output, video SN ratio, color SN ratio, still characteristics, and head wear amount were tested using the following methods. .

<Surface Roughness of Magnetic Layer> The center line average roughness (Ra) of the videotape was calculated using a stylus type surface roughness meter.

<RF ratio output A 50% white video signal was recorded and reproduced on a video tape using a VH3 type VTR, and the level of the FF modulated reproduction signal was measured using an oscilloscope and expressed as a relative value with respect to the reference tape.

<Chroma output> A VH3 system VTR was used to record and play back a single color chroma signal on a videotape, and the level of the playback signal of the low frequency converted color signal was measured using an oscilloscope and expressed as a relative value with respect to the reference tape. .

<Video SN ratio>: 50% on videotape using VH3 system VTR
A white video signal was recorded and reproduced, the noise of the reproduced signal was measured using a color video noise measuring device, and the SN ratio was calculated and expressed as a relative value with respect to the reference tape.

<Color SN ratio> Using a VH3 system VTR, record and play back a one-color chroma signal on a videotape, measure the AM noise of the playback signal with a color video noise measuring device, calculate the SN ratio, and compare it with the reference tape. Shown as a value.

Still Characteristics Using a VH3 VTR, a videotape was played back in still mode, and the time required for the playback output level to drop by 5 dB from the initial value was measured.

<Head wear amount> A video tape was run 100 times using a VH3 type VTR in an environment of 40° C. and 80% RH, and then the head wear amount of the video head was measured.

The table below shows the results.

18 (Effects of the Invention) As is clear from the above table, the magnetic tapes obtained by the present invention (Examples 1 to 6) have a higher surface area of the magnetic layer than conventional magnetic tapes (Comparative Examples 1 and 2). The magnetic recording medium obtained by the present invention has small roughness, high RF output, chroma output, video SN ratio, and color SN ratio, long still characteristic time, and low head wear. It can be seen that it has good dispersibility, good surface smoothness of the magnetic layer, high output, high S/N ratio, excellent electromagnetic conversion characteristics, and excellent wear resistance.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. A magnetic material having a magnetic layer containing magnetic powder having a specific surface area of 30 rrf/g or more by the BET method and at least one sorbic acid compound selected from sorbic acid, sorbic acid derivatives, and sorbic acid metal salts. recoding media