JP2500672B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention

[0001]

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 improved magnetic characteristics and electromagnetic conversion characteristics, high durability and good surface property. It is a thing.

[0002]

2. Description of the Related Art In recent years, a magnetic recording medium, particularly a magnetic recording medium for video, is required to have a high reproduction output for short-wavelength recording, and is made finer and has a higher magnetic force than ever before. The tendency for magnetic powder to be used is increasing. However, the magnetic powder is finely divided and /
Alternatively, the higher the magnetic force, the stronger the cohesive force, and as a result, the dispersibility and surface properties required for high reproduction output of short wavelength recording are not satisfied. As a method for improving these properties, for example, a method of using a surfactant as a dispersant, or a method of increasing the content of hydrophilic groups such as -OH group and -COOH group in the binder are used. Is proposed. However, in the former method, since the surfactant used has a low molecular weight, the presence of the surfactant in the coating film causes defects such as deterioration of physical properties, powder falling, blooming due to aging, and the like. Further, in the latter method, although such an improvement in characteristics is slightly recognized, satisfactory dispersibility is not obtained particularly for the fine magnetic particles.

Conventionally used binders for magnetic recording media include vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl propionate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers and the like. Examples thereof include vinyl chloride binders. Especially vinyl chloride
Vinyl acetate-vinyl alcohol copolymers are widely used because OH of vinyl alcohol contributes to the dispersion of magnetic powder and active hydrogen of OH reacts with an isocyanate compound to form a crosslinked structure in a coating film. Has been done. However, even a magnetic recording medium using such a binder is not sufficient in terms of magnetic properties, electromagnetic conversion properties and durability, and a binder capable of further improving such properties has been demanded.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a magnetic recording medium having improved magnetic and electromagnetic conversion characteristics, high durability and good surface property.

The binder used in this invention has the general formula:

Embedded image wherein R is —CH ₃ or —CH ₂ CH ₃ ; X is a hydrophilic group containing —SO ₃ M and (CH ₂
CH) ₁ to -O- bonded to the CH group in -SO ₃
M is an alkylene group _{(- (CH 2) n -} ) and those bonded via an -O- (CH ₂₎ in _n -SO ₃ M (wherein,
n is a positive integer and is preferably 1 to 18, M can be represented by H, Li, Na or K); i is 200 to 800; j is 0 to 20
0; l (el) is 1 to 200; m is 1 to 1
00; k is not 0 and k + 1 is 200
It is a compound represented by the following. In addition, in the said general formula, each component of a compound is conveniently described so that it may be arranged in order regularly. But actually,
As a matter of course, each component may be regularly and repeatedly arranged at a fixed ratio or randomly, other than the case shown by the general formula. Further, in the above general formula, for example, the groups R may be the same or different in one molecule. Even if each R in one molecule has a methyl group and an ethyl group as different groups, the total number of acid vinyl ester components may be within the range represented by the above general formula. Also, X
However, hydrophilic groups represented by the above general formula and different in M may be used in combination.

In the compound represented by the above general formula, the vinyl chloride component contributes to the strength of the medium in order for the compound to be used as a binder of a magnetic recording medium and exhibit a desired effect. If the vinyl chloride component is too small, the desired strength of the medium cannot be obtained, and
If it is too large, the solubility in the solvent will deteriorate.

The vinyl alcohol component contributes to the dispersibility of the magnetic powder due to its hydrophilicity. To further enhance the dispersibility, a part of the OH group is a hydrophilic group represented by X. Is very effective. If this hydrophilic group is too much, the moisture resistance is rather deteriorated, which is not preferable. The equivalent weight (molecular weight) per functional group X is preferably about 200 to 50,000. If the equivalent weight is too small, the hydrophilicity becomes too strong and there is a problem in terms of compatibility with other binders to be mixed and moisture resistance. If the equivalent weight is too large, the effect becomes insufficient.

Further, the maleic acid component is considered to contribute to the dispersibility. If the amount is too small, the effect of adding the maleic acid component will be small, and if it is too large, it will be more than that. It will not contribute to the improvement of dispersibility. Further, the vinyl acetate and / or vinyl propionate component is effective for increasing the solubility of the vinyl chloride component and improving the flexibility, but when these components are too much,
On the contrary, the strength is lowered, which is not preferable. Further, these vinyl acetate component and vinyl propionate component may be present in combination in one molecule.

The compound represented by the above general formula used as a binder in the present invention is usually a copolymer having no vinyl component having a hydrophilic group represented by X in the above general formula, such as vinyl chloride. -Maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl propionate It can be produced from a maleic acid-vinyl alcohol copolymer or the like. In this case, the proportion of the vinyl alcohol component is preferably about 0.5% by weight to 20% by weight. The copolymer as the starting material can be produced by a usual method.

The compound represented by the above general formula using the above-mentioned starting material can be obtained, for example, by adding the compound represented by the general formula: YR ₁ -X to the OH group of the vinyl alcohol component of the starting material.
₁ {wherein Y represents a halogen atom, R ₁ represents an alkylene group having, for example, 1 to 18 carbon atoms, and X 1
₁ is -SO ₃ M (wherein M has the same meaning as above)
Can be produced by reacting a compound represented by Of the compounds Y—R ₁ —X ₁ , the reaction is shown below, using Cl— (CH ₂ ) ₂ —SO ₃ Na as an example.

[0011]

Embedded image Even when other compounds are used, the desired compound can be produced by the similar reaction. This reaction is carried out in an organic solvent such as dimethyl sulfoxide or dimethylformamide in the presence of an amine such as pyridine, triethylamine or picoline, or a dehydrochlorinating agent such as an epoxy compound such as ethylene oxide or propylene oxide.

In the present invention, when the compound represented by the above general formula is used as a binder, it is preferable to blend and use a polyurethane resin, a polyester resin, an AB resin or the like which is said to impart flexibility. In this case, as the cross-linking agent, for example, an isocyanate compound (for example, a bifunctional aromatic isocyanate compound such as 4,4′-diphenylmethane diisocyanate or tolylene diisocyanate, a bifunctional aliphatic isocyanate compound such as hexamethylene diisocyanate, and the like, for example, By using a trifunctional isocyanate obtained by the reaction with trimethylolpropane or the like, a magnetic recording medium having a magnetic layer having a desired effect can be obtained.

In the present invention, the magnetic powder usable in the magnetic layer is γ-Fe ₂ O ₃ , and the γ-Fe ₂ O ₃ and Fe ₃
Mixed crystals with O ₄ , cobalt-doped γ-Fe ₂ O ₃ or Fe ₃ O ₄ , CrO ₂ , barium ferrite, other ferromagnetic alloy powders (eg Fe-Co, Co-Ni, F
e-Co-Ni, Fe-Co-B, Fe-Co-Cr-
B, Mn-Bi, Mn-Al, Fe-Co-V), iron nitride and the like. Aluminum oxide, chromium oxide, silicon oxide, etc. can be added to the magnetic layer as a reinforcing agent, and squalane as a lubricant, carbon black as an antistatic agent, and lecithin as a dispersant can also be added.

The constituent material of the magnetic layer may be dissolved in an organic solvent to prepare a magnetic coating material, which may be coated on the base. And as the solvent of the magnetic paint, ketones (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone), alcohols (for example, methanol, ethanol, propanol and butanol), esters (for example, methyl acetate, ethyl acetate). , Butyl acetate, ethyl lactate, glycol acetate and monoethyl ether), glycol ethers (eg ethylene glycol dimethyl ether, ethylene glycol monoethyl ether and dioxane), aromatic hydrocarbons (eg benzene, toluene and xylene), aliphatic Hydrocarbons (eg hexane and heptane), nitropropane and the like. The base on which the magnetic paint is applied is non-magnetic and includes polyester (eg, polyethylene terephthalate), polyolefin (eg, polypropylene), cellulose derivative (eg, cellulose triacetate and cellulose diacetate), polycarbonate, polyvinyl chloride, polyimide, It may consist of polyamides, polyhydrazides, metals (eg aluminum and copper), paper and the like.

[0015]

EXAMPLES The present invention will be described below with reference to examples and comparative examples. Example A compound represented by the following structural formula was synthesized from a vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer according to a conventional method.

Embedded image

Next, a magnetic paint having the following composition was prepared. Set formed amount (parts by _{weight) Co-γ-Fe 2 O} 3 100 The above compound 15 polyurethane resin (manufactured by Nippon Polyurethane Industry Co., Ltd.: N-2304) 10 Carbon black 5 lubricant 2 abrasive 5 ethyl ketone 100 methyl isobutyl ketone 60 Toluene 60 The magnetic coating composition having the above composition is mixed for 48 hours in a ball mill, and then 5 parts by weight of an isocyanate compound (Desmodur L manufactured by Bayer Co.) is mixed to give a polyester film having a thickness of 15 μm and a dry thickness of about 6 μm. After coating, after surface treatment with super calendar treatment,
A magnetic recording tape was prepared by cutting into a 1/2 inch width.

Comparative Example In the above-mentioned Examples, except that a vinyl chloride-vinyl acetate-maleic acid copolymer (VMCH manufactured by Union Carbide Co.) was used in place of the binder according to the present invention. A magnetic recording tape was similarly prepared.

The following table shows the results of measuring various characteristics of the magnetic recording tape obtained above. Table Example Comparative Example Bm (Gauss) 1350 1150 Br / Bm 0.85 0.79 Powder drop [Note 1] -0.5 -1.5 Y-S / N (dB) [Note 2] +1.50 [Note 1] As for the degree of powder falling, the state of powder falling on the running system (guide roll, etc.) after running the tape is deducted by the deduction method (-5 (bad) to
(Good)). [Note 2] Y-S / N indicates the S / N ratio of a sample recorded black-and-white image and reproduced.

From the above results, it has been found that the magnetic recording tape according to the present invention is superior in all characteristics as compared with the magnetic recording tape according to the above-mentioned comparative example.

In the above-mentioned examples, --O-(CH ₂ ) ₂ --SO ₃ Na was used as the hydrophilic group represented by X. The other hydrophilic group described in the above-mentioned --O-(CH ₂ ) ₂
Even when it is used as a hydrophilic group represented by X instead of —SO ₃ Na, the same results as in the above-mentioned examples are obtained.

[0021]

In the present invention, the polymer used as the binder has a hydrophilic group containing a group as described above in its vinyl alcohol component, so that the dispersibility of the magnetic powder is remarkably improved. In addition to improving the magnetic-electromagnetic conversion characteristics of the magnetic recording medium, the magnetic powder is bound even through the binder and the hydrophilic base, so the detachment of the magnetic powder is reduced, resulting in level fluctuations, output attenuation, clocking, etc. The durability and surface property of the medium due to the powder falling off are significantly improved.

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C08F 218/04 MLF C08F 218/04 MLF (56) Reference JP-A-57-128711 (JP, A) JP-A-53-51705 (JP, A) JP-A-54-143117 (JP, A) JP-A-54-157603 (JP, A) JP-A-54-28603 (JP, A) JP-A-52-49003 (JP , A)

Claims (1)

(57) [Claims] (1) A general formula: {In the formulas, R represents a -CH ₃ or -CH ₂ CH _3; X is -O- (CH ₂₎ in _n -SO ₃ M (wherein, n is a positive integer, M is H, Li, Na Or K); i is 2
0 to 800; j is 0 to 200; l (el) is 1 to 200; m is 1 to 100; k is not 0 and k + 1 (ell) is 200 or less} A magnetic recording medium, wherein the compound represented is used in a magnetic layer.