JPH038009B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium using a specific polyester resin as a binder. Conventionally, various binders for magnetic recording media such as magnetic tapes have been reported. For example, JP-A-54-28603 describes the use of a polyester resin containing a sulfonic acid metal salt with a reduced viscosity of 0.2 or more as a magnetic recording medium, that is, the binder; The use of mixtures of polyester resins with less than 0.2 sulfonic acid groups and thermoplastic and/or thermosetting resins as magnetic recording binders has been reported. That is, in JP-A-Sho, acid components such as terephthalic acid or isophthalic acid,
The properties as a magnetic binder can be improved by further introducing a polycarboxylic acid containing a sulfonic acid group such as sulfonodium isophthalic acid into a polyester resin consisting of a glycol component such as ethylene glycol or neopentyl glycol. It is shown. However, when such conventional binders are used, problems remain because the surface smoothness of the magnetic recording medium is not necessarily sufficient. In other words, insufficient smoothness means that, as home video recorders and audio tape recorders become more widespread, the performance of video tapes and audio tapes, in other words, higher performance is required in various aspects such as image quality, sound quality, and abrasion resistance. This is because the performance of the binder, which plays the role of uniformly and densely filling the magnetic layer coated on the base film of the tape, plays a large role in the performance of the tape, so there are various problems with polyester resin. Therefore, new ideas are needed. However, as a result of extensive research in order to solve this problem, the present inventors have developed a polyester resin in which 0.2 to 10 mol% of a polyhydric alcohol containing a sulfonic acid group is condensed with respect to the total glycol component, and more preferably a nitrogen-containing compound is condensed with the polyhydric alcohol. The present invention has been completed based on the discovery that a magnetic recording medium with very good surface smoothness can be obtained when the polyester resin obtained above is used as a binder. Such remarkable effects of the present invention can be obtained by using a sulfonic acid group-containing polyhydric alcohol in place of the conventional sulfonic acid group-containing polycarboxylic acid as a means for introducing the sulfonic acid group into the polyester resin. be. The structure of the binder of the present invention is completely different from that of conventional sulfonic acid group-containing polyester resins. Hereinafter, the polyester resin used in the present invention will be explained in more detail. The sulfonic acid group-containing polyhydric alcohol used in the present invention is preferably one obtained by reacting an unsaturated polyhydric alcohol with an acidic sulfite to add the acidic sulfite to the unsaturated bond. The reaction is carried out, for example, by heating an unsaturated polyhydric alcohol and an acidic sulfite to about 70°C in the presence of iron oxide. Examples of unsaturated polyhydric alcohols used in the present invention include 3-butene-1,2-diol and 2-butene-1,2-diol.
Olefinic glycols such as 1,4-diol, 2,5-dimethyl-3-hexene-2,5-diol, 1,5-hexadiene-3,4-diol, 2,6-octadiene-4,5-diol Examples include diolefin glycols such as As acidic sulfite, sodium acidic sulfite,
Acidic potassium sulfite and the like are practically used. When producing a polyester resin, the above components are condensed with a polyhydric alcohol and a polyhydric carboxylic acid. Ethylene glycol is a polyhydric alcohol,
diethylene glycol, propylene glycol,
Examples include dipropylene glycol, neopentyl glycol, cyclohexanedimethanol, and pentaerythritol. Examples of polyvalent carboxylic acids include oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, 1, 3-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, phthalic acid, terephthalic acid, isophthalic acid, 2,5-norbornanedicarboxylic acid, 1,4-naphthalic acid, diphenic acid, Saturated carboxylic acids such as 4,4'-oxybenzoic acid, diglycolic acid, thiodipropion, 4,4'-sulfonyl dibenzoic acid, and 2,5-naphthalene dicarboxylic acid are mentioned. If necessary, unsaturated carboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, and citraconic acid may be used in combination. The above carboxylic acid may be in the form of a lower alkyl ester or an acid chloride. The proportion of the sulfonic acid group-containing polyhydric alcohol in the polyester resin must be 0.2 to 10 mol % based on the total glycol component. 0.2
If it is less than mol%, it is difficult to obtain the effects of the present invention, while if it is more than 10 mol%, it has the disadvantage of being difficult to dissolve in general-purpose solvents. By further condensing 0.2 to 10 mol% (proportion in the resin) of a nitrogen-containing compound to the polyester resin used in the present invention, it is possible to further improve the dispersibility of the magnetic particles. A smooth coating film can be obtained. The compound includes (1) general formula H ₂ NR—NH ₂ ,

【formula】

[Formula] or its ring-opened product is used. Here R, R′, R ₁ ,
Both X and X' are the same as above. Nitrogen-containing compounds having the above structure include (1) ethylenediamine, trimethylenediamine, putrescine, cadaverine, hexamethylenediamine,
(2) 2-hydroxyethyl-P-toluidine, 2-
Examples include, but are not limited to, carboxyethyl-P-toluidine, (3) β-propiolactam, γ-butyrolactam, γ-valerolactam, ε-caprolactam, heptolactam, and ring-opened products thereof; One or more of them can be used in combination as appropriate. The magnetic particles used in the present invention include pure iron, γ-
Fe ₂ O ₃ , CrO ₃ , Fe ₂ O ₃ (Co), Fe ₃ O ₄ , Fe ₃ O ₄
(Co), Co―Fe, Co―Ni Co―Ni―Fe, Fe―Ni
-Zn, Fe-Mn-Zn, Co-Ni-Fe-B, Co-
Examples include Ni-P, Fe-Co-Ni-P, etc. The blending ratio of the polyester resin and the magnetic particles is not particularly limited, but the weight ratio is often 1:1 to 1:7. The above components are uniformly mixed with a suitable solvent such as cellosolve acetate, butyl cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, benzene, toluene, xylene, etc., and coated onto the substrate. In this case, crosslinking agents such as isocyanate compounds, epoxy resins and melamine resins, known binders other than the polyester resin of the present invention such as polyesters, ethyl cellulose, nitrocellulose, vinyl chloride-vinyl acetate copolymers, dibutyl phthalate, triphenyl phosphate, etc. A suitable amount of a plasticizer, a lubricant, an antistatic agent, a wetting agent, an anti-grooming agent, etc. may be added. The base material is film, tape, sheet, disk,
It may be a card, a drum, or the like, and various materials are selected depending on the form. For example, when the substrate is in the form of a film or tape, a film or tape made of acetyl cellulose, polyester, polycarbonate, polyvinyl chloride, polypropylene, polyimide, etc. is used. As a means for applying the composition onto the substrate, a doctor knife method, a blade cord method, a reverse roll method, a gravure method, a cast coating method, a spray coating method, etc. are all employed. After the composition is applied onto the substrate directly or via an anchor coat layer, the coating film is subjected to a magnetic field orientation treatment using a solenoid coil or the like while it is still wet, and then dried. The magnetic recording medium thus obtained is used for applications such as magnetic recording tapes, video tapes, tapes for computers and measuring instruments, magnetic cards, and magnetic disks. Next, the magnetic recording medium of the present invention will be further explained by giving an example. Example 1 In a four-neck flask equipped with a thermometer, a stirrer, and a backed column, 0.42 mol of terephthalic acid was added under a nitrogen stream.
0.43 mol of isophthalic acid, 0.15 mol of adipic acid, 0.73 mol of ethylene glycol, 0.75 mol of neopentyl glycol, 0.02 mol of 2-sodiosulfo-1,4-butanediol, 0.1 mol of dibutyltin oxide.
1 part and esterification reaction at 140°C to 220°C with stirring, then 0.1 part of antimony trioxide was added and condensation was carried out at 220°C to 260°C under reduced pressure of 1 torr or less to obtain a polyester resin with [η] of 0.57. Ta. 2-Sodiosulfo for all glycol components
The content of 1,4-butanediol was 1.8 mol%. The performance of the polyester resin as a binder for magnetic tape was evaluated in accordance with the following. Smoothness of coating film: 130 parts of polyester resin, 190 parts of γ-Fe ₂ O ₃ , 290 parts of methyl ethyl ketone, 3 parts of dioctyl sulfonodium succinate, 3 parts of silicone oil,
190 parts of toluene, 100 parts of methyl isobutyl ketone,
60 parts of n-butanol and 8 parts of a 75% solution of an adduct of tolylene diisocyanate and trimethylolpropane (Coronate L manufactured by Nippon Polyurethane Industries Co., Ltd.) were dispersed for 70 hours using a ball mill, and then filtered and defoamed. A magnetic paint was obtained. This magnetic coating was applied onto a 25μ thick polyethylene terephthalate film (stretched product) using the doctor knife method, then oriented in a parallel magnetic field of 1000 oersted, and then dried at 80°C to form a 5μ thick magnetic coating. was formed. The smoothness of this coating film was evaluated by the 60°-60° reflection gloss rate. The results are shown in Table 1. Squareness ratio It is expressed as the ratio Mr/Ms between the saturation magnetization Ms and the residual magnetization Mr of the magnetic hysteresis curve. The results are also shown in Table 1. Control example 1 2-sodiosulfo-1,4- in Example 1
The same experiment as in the same example was carried out except that 5-sodiosulfoisophthalic acid was used in place of butanediol.
The results are shown in Table 1.

[Table] Examples 2 to 4 Experiments were conducted according to Example 1 using polyhydric alcohols containing sulfonic acid groups as shown in Table 2.
The results are shown in Table 2.

[Table] Examples 5 to 7 Example 1 except that 0.02 mol of 2-hydroxyparatoluidine (Example 5), hexamethylene diamine (Example 6), and ε-aminocaproic acid (Example 7) were used in combination. The same experiment as in the same example was conducted. The smoothness was 99.1, 99.3, and 99.5, respectively, and the squareness ratio was 0.86, 0.85, and 0.86, respectively.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium comprising a coating layer made of a polyester resin condensed with 0.2 to 10 mol% of polyhydric alcohol containing a sulfonic acid group based on the total glycol component and magnetic particles on a substrate. 2. Magnetic recording in which a coating layer made of magnetic particles and a polyester resin condensed with 0.2 to 10 mol % of a sulfonic acid group-containing polyhydric alcohol and 0.2 to 10 mol % of a nitrogen-containing compound based on the total glycol component is provided on a substrate. Medium. 3. The magnetic recording medium according to claim 2, wherein the nitrogen-containing compound is a compound represented by the following general formulas (1) to (3). [Formula] or a ring-opened product thereof (where R and R' are alkylene, R ₁ is an alkyl group or an aryl group, and X and X' are a carboxyl group or a hydroxyl group).