JPH0658738B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD AND OBJECT The present invention relates to a magnetic recording medium, and an object of the invention is to provide a magnetic recording medium having excellent dispersibility of magnetic powder and excellent electrical characteristics. is there.

[Background technology]

The magnetic recording medium is usually prepared by coating a magnetic coating material comprising a magnetic powder, a binder component, an organic solvent and other necessary components on a substrate such as polyester film and drying it.
Those with excellent electrical characteristics are required.

Therefore, it is desirable that the magnetic powder used is excellent in dispersibility and can impart excellent electrical characteristics to the magnetic recording medium. However, since the surface of the magnetic powder is usually hydrophilic, it is a lipophilic binder resin as it is. It is difficult to disperse well in it.

Therefore, in order to improve the dispersibility of the magnetic powder, it has been proposed to mix saturated or unsaturated fatty acid having a hydrophilic group at one end of the molecule and a lipophilic group at the other end into the magnetic paint as a dispersant. (Japanese Patent Publication No. 44-18221,
Japanese Patent Publication No. 58-9488). However, the binding force with the magnetic powder was still weak, and the dispersibility of the magnetic powder in the binder resin could not be sufficiently improved.
Further, as the binder resin, a modified polyester obtained by addition reaction of sorbic acid having a conjugated double bond with polyester containing a maleic acid component is used (JP-A-58-58).
No. 57629), the dispersibility of the magnetic powder has been improved, but the dispersibility of the magnetic powder is still insufficient.

[Outline of Invention]

From the present situation, the present inventors have conducted various studies on a group of compounds having both a lipophilic group and a hydrophilic group in order to find a more effective dispersion of the magnetic powder in the binder resin, and as a result, it is surprising. In particular, it was revealed that sorbic acid and sorbic acid derivatives have a particularly excellent dispersing ability. The reason why such sorbic acid and sorbic acid derivative have remarkable dispersive ability has not yet been clearly elucidated, but considering its unique chemical structure, it has a conjugated double bond in the molecule. As a result, the electron density is localized in the molecule, the polarizability is increased, and thus the functionality is enhanced. Moreover, both of the double bonds have a trans (trans-trans) structure. The functional group is statistically and geometrically unevenly distributed on the surface part of the dispersant, and sorbic acid has 6 carbon atoms.
It is presumed that the number of particles and the number of derivatives thereof are usually 12 or less. Therefore, since they have an appropriate melting point, they are easily mixed in the binder resin in order to impart good fluidity to the coating material.

On the other hand, when a modified polyester obtained by addition reaction of sorbic acid having a conjugated double bond to a polyester containing a maleic acid component is used as a binder resin,
When the sorbic acid having a conjugated double bond is added to the polyester, the conjugated double bond is broken, so that it is considered that the dispersibility of the magnetic powder is not sufficiently improved.

Sorbic acid used in this invention has the chemical formula CH.
₃ A compound represented by CH = CHCH = CHCOOH,
The molecular weight is relatively small, and the two double bonds are both trans, which adheres well to the surface of the magnetic powder and is also well compatible with the binder resin. Therefore, when this sorbic acid is contained in the magnetic layer, the dispersibility of the magnetic powder in the binder resin is sufficiently improved, and a magnetic recording medium having excellent electrical characteristics can be obtained.

Examples of the sorbic acid derivative used in the present invention include sorbic acid methyl ester C ₅ H
₇ COOCH ₃ , ethyl ester C ₅ H ₇ COOC ₂ H
₅ , propyl ester C ₅ H ₇ COOC ₃ H ₇ , butyl ester C ₅ H ₇ COOC ₄ H ₉ , amide C ₅ H ₇ CO
NH ₂ , nitrile C ₅ H ₇ CN, anilide C ₅ H ₇ CO
NHC ₆ H ₅ , phenylhydraside C ₅ H ₇ CONHN
HC ₆ H _{5 and the} like are preferred, and these sorbic acid derivatives, like the above-mentioned sorbic acid, have two double bonds both in trans and a relatively small molecular weight,
It adheres well to the surface of the magnetic powder and is also well compatible with the binder resin. Therefore, even when these sorbic acid derivatives are contained in the magnetic layer, the same effect as in the case of using the above-mentioned sorbic acid is obtained, and the dispersibility of the magnetic powder in the binder resin is sufficiently improved. A magnetic recording medium having excellent electrical characteristics can be obtained.

Such sorbic acid or sorbic acid derivative may be added directly during preparation of the magnetic paint, or may be dissolved in an appropriate solvent such as alcohol or ether, and the solution obtained by this dissolution may be added during preparation of the magnetic paint. A method of adding or dipping the magnetic powder in this solution to pre-treat the surface of the magnetic powder, prepare a magnetic coating using this magnetic powder, and apply it to a substrate and dry it. And contained in the magnetic layer. The content in the magnetic layer is
It is preferable to contain it in the range of 0.1 to 10% by weight with respect to the magnetic powder in the magnetic layer. If it is too small, the desired effect cannot be obtained, and if it is too large, bleed-out may occur.

Thus, the sorbic acid and the sorbic acid derivative contained in the magnetic layer may be used alone or in combination of two or more, and may be used in combination with another dispersant, for example, a saturated agent. You may use together with fatty acid, unsaturated fatty acid, fatty acid ester, phosphoric acid ester, lecithin, metal soaps, alcohols, etc.

The magnetic powder used in the present invention is, for example, γ-
Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, intermediate compound powder of γ-Fe ₂ O ₃ powder and Fe ₃ O ₄ powder, Co-containing γ-Fe
₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, CrO ₂ powder, α-Fe powder, Co powder, Fe-Ni powder, Fe ₄
Various conventionally known magnetic powders such as metal powders such as N powder are widely included.

Further, as the binder resin, vinyl chloride-vinyl acetate copolymer, fibrin resin, butyral resin, polyurethane resin, polyester resin, epoxy resin, polyether resin, isocyanate compound, etc. Any of the known binder resins can be used.

Examples of the organic solvent include cyclohexanone, methyl ethyl ketone, ketone-based solvents such as methyl isobutyl ketone, ethyl acetate, ester-based solvents such as butyl acetate, benzene, toluene, aromatic hydrocarbon-based solvents such as xylene,
Solvents suitable for dissolving the binder resin used, such as sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran and dioxane,
There is no particular limitation and they may be used alone or in combination of two or more.

In addition, various additives that are usually used in the magnetic paint,
For example, a lubricant, an abrasive, an antistatic agent, etc. may be appropriately added and used.

〔Example〕

 Next, an embodiment of the present invention will be described.

Example 1 800 parts by weight of γ-Fe ₂ O ₃ powder VAGH (Vinyl chloride-vinyl acetate-produced by UCC, USA)
Vinyl alcohol copolymer) 120 〃 sorbic acid 16 〃 Methyl isobutyl ketone 410 〃 Toluene 410 〃 After mixing and dispersing this composition in a ball mill for 72 hours, Takelac E-551T (Polyurethane resin manufactured by Takeda Pharmaceutical Co., Ltd.) 65 〃 Coronate (manufactured by Nippon Polyurethane Industry Co., Ltd., trifunctional low molecular weight isocyanate compound) 15 〃 was added to form a magnetic paint, which was applied onto a polyester film having a thickness of 11 µm to a dry thickness of about 6 µm.
After drying and calendering, it was cut into a predetermined width to prepare a magnetic tape.

Example 2 γ-Fe ₂ O ₃ powder 800 g sorbic acid 20 g ethanol 500 ml After the above components were dispersed in a homomixer for 5 hours,
A γ-Fe ₂ O ₃ powder in which 16 mg / g of sorbic acid was adsorbed on the surface of the powder particles was obtained by drying, and this γ-Fe ₂ O ₃ powder was used as the γ-Fe ₂ O ₃ powder used in Example 1. Instead, the same amount was used, and a magnetic tape was prepared in the same manner as in Example 1 except that sorbic acid was omitted from the composition of the magnetic paint in Example 1.

Example 3 A magnetic tape was produced in the same manner as in Example 1 except that the amount of sorbic acid used in the composition of the magnetic coating material in Example 1 was changed from 16 parts by weight to 4 parts by weight.

Example 4 A magnetic tape was produced in the same manner as in Example 1 except that the amount of sorbic acid used in the composition of the magnetic coating material in Example 1 was changed from 16 parts by weight to 40 parts by weight.

Example 5 A magnetic tape was produced in the same manner as in Example 1 except that the same amount of sorbic acid-n-butyl sorbate was used in the composition of the magnetic coating material of Example 1.

Example 6 In the same manner as in Example 1, except that the amount of sorbic acid used was changed from 16 parts by weight to 8 parts by weight and 8 parts by weight of lauric acid was newly added in the composition of the magnetic paint in Example 1. I made a tape.

Example 7 In the composition of the magnetic paint in Example 1, γ-Fe ₂
A magnetic tape was produced in the same manner as in Example 1 except that the same amount of Fe ₃ O ₄ powder was used instead of O ₃ powder.

Example 8 In the composition of the magnetic coating material of Example 1, γ-Fe ₂
Instead of the O ₃ powder to make a magnetic tape, except that the Co-containing gamma-Fe ₂ O ₃ powder was used the same amount in the same manner as in Example 1.

Example 9 In the composition of the magnetic coating material of Example 1, γ-Fe ₂
A magnetic tape was produced in the same manner as in Example 1 except that the same amount of α-Fe powder was used instead of the O ₃ powder and the dry thickness of the magnetic layer was changed from about 6 μ to about 4 μ.

Comparative Example 1 A magnetic tape was prepared in the same manner as in Example 1 except that sorbic acid was omitted from the composition of the magnetic paint in Example 1.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that the same amount of lauric acid was used instead of sorbic acid in the composition of the magnetic coating material in Example 1.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 8 except that sorbic acid was omitted from the composition of the magnetic coating material in Example 8.

Comparative Example 4 A magnetic tape was produced in the same manner as in Example 9 except that sorbic acid was omitted from the composition of the magnetic paint in Example 9.

Comparative Example 5 A four-necked flask equipped with a thermometer, a stirrer, and a packed column was charged with 236 parts by weight of terephthalic acid, 253 parts by weight of isophthalic acid, 15 parts by weight of maleic anhydride, 255 parts by weight of ethylene glycol, and 23 parts of neopentyl glycol under a nitrogen stream.
Add 0 parts by weight and 6 parts by weight of zinc acetate to give 180-2
The esterification reaction was carried out at 40 ° C., then 6 parts by weight of antimony trioxide was added and the reaction was carried out at 270 ° C. under a reduced pressure of 0.2 Torr, and the reaction was terminated when the predetermined torque was reached. As a result, a polyester having an OH group in a molecular weight of 15,000 and less than 5 mol% of a maleic acid component was obtained.

Then, the temperature of the above reaction product was set to 200 ° C., maleic anhydride component in the polyester was added with an equimolar amount of sorbic acid, and the mixture was reacted at this temperature for 30 minutes to obtain a modified polyester having a softening point of 135 ° C. (ring and ball type). .

Next, a magnetic tape was prepared in the same manner as in Example 1 except that sorbic acid was omitted from the composition of the magnetic coating material in Example 1 and 120 parts by weight of the modified polyester obtained in place of VAGH was used.

Comparative Example 6 A magnetic tape was prepared in the same manner as in Example 8 except that sorbic acid was omitted from the composition of the magnetic coating material of Example 8 and 120 parts by weight of the modified polyester obtained in Comparative Example 5 was used instead of VAGH. I made it.

Comparative Example 7 A magnetic tape was prepared in the same manner as in Example 9 except that sorbic acid was omitted from the composition of the magnetic coating material of Example 9 and 120 parts by weight of the modified polyester obtained in Comparative Example 5 was used instead of VAGH. I made it.

For each magnetic tape obtained in each example and each comparative example, the coercive force, the residual magnetic flux density, the squareness, and the degree of orientation are measured as magnetic characteristics, and the electromagnetic conversion characteristics are sensitivity (333Hz, 7KHz, 12.5KHz). ) Maximum distortion-free output (333Hz −M.
OL) was measured respectively. However, regarding the sensitivity and MOL in the table, in comparison with the recording and reproducing equalizer due to the different coercive force, in Examples 1 to 7, Comparative Example 1, Comparative Example 2 and Comparative Example 5, Comparative Example 1 was set to 0 dB. The difference is used as a standard. In addition, Example 8 and Comparative Example 6 are Comparative Example 3, and Example 9 and Comparative Example 7 are Comparative Example 4.
Are taken as 0 dB respectively and expressed as the difference between them.

The results are shown in Tables 1 and 2 below.

As is clear from Tables 1 and 2 above, the magnetic tapes obtained in the present invention (Examples 1 to 9) were rectangular and oriented as compared with the conventional magnetic tapes (Comparative Examples 1 to 7). The magnetic recording medium obtained by the present invention has good dispersibility of magnetic powder and excellent magnetic characteristics and electromagnetic conversion characteristics.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing magnetic powder and sorbic acid or a sorbic acid derivative.