JPS59172121A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the surface smoothness, heat resistance and durability of a magnetic layer and a short wavelength recording characteristic by using a copolymerized polyester resin contg. a specific compd. on one molecule and polyurethane resin in combination as a binder component. CONSTITUTION:A copolymerized polyester resin having a metallic salt of sulfonic acid and nitrogen element contg. compd. on one molecule and a polyurethane resin are incorporated as a binder component in a magnetic layer. The copolymerized polyester resin having the metallic salt of sulfonic acid and nitrogen element contg. compd. in 1mol has an anionic metallic salt of sulfonic acid and cationic nitrogen element contg. compd. in one molecule and therefore the dispersibility and packability of magnetic powder are improved and the surface smoothness of the magnetic layer is improved, by which the short wavelength recording characteristic in particular is improved. If a trifunctional low mol. wt. isocyanate is further incorporated in the magnetic layer, the compd. generates secure cross-linking and bonding by reacting with the amino group in the copolymerized polyester resin and the OH group, etc. that the polyurethane resin possesses and therefore the resistance of the magnetic layer to wear and heat is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and the object thereof is to have excellent dispersibility and filling properties of magnetic powder, and good surface smoothness, heat resistance, and durability of the magnetic layer. An object of the present invention is to provide a magnetic recording medium with improved short wavelength recording characteristics.

Magnetic recording media typically contain magnetic powder, a binder component, and
It is made by applying a magnetic paint consisting of a melt and other necessary ingredients onto a substrate such as a polyester film and drying it. The binder component used in this case has excellent dispersibility and filling properties of the magnetic powder, improves the smoothness of the surface of the magnetic layer, and provides the magnetic recording medium with excellent electrical properties such as a high S/N ratio. It is necessary to select a material with excellent heat resistance and durability.In particular, as in the case of video tapes, the electrical characteristics greatly depend on the smoothness of the magnetic layer surface, and if the surface smoothness of the magnetic layer is poor, the video S/N ratio will decrease. In magnetic recording media where the smoothness of the magnetic layer deteriorates as much as possible, it is desirable to use a binder component that can improve the smoothness of the magnetic layer surface as much as possible.

For this reason, various research and developments have been conducted on binder resins.
For example, a copolyester resin containing a sulfonic acid metal base has been proposed as a material with excellent dispersibility and filling properties of magnetic powder.For example, Kakutani et al., Kobunshi Ronshu, Volume 2, 139 (1981) , Japanese Patent Publication No. 54-28
No. 603, JP-A-56-74830, etc.

However, copolymerized polyester resin containing this type of sulfonic acid metal base has a strong interaction with magnetic powder, so a large amount of adsorption occurs, and when used as a binder component in magnetic paint, the viscosity becomes extremely high. In addition, if the surface of the magnetic powder is alkaline, this type of copolymerized polyester resin has an anionic sulfonic acid metal base, which increases the viscosity of the magnetic paint and deteriorates its fluidity. When doing so, not only various problems occur, but also the dispersibility and filling properties of the magnetic powder are insufficient, and the surface smoothness and durability of the magnetic layer are not very good.

The inventors conducted various studies in view of the current situation, and found that if a copolyester resin containing a sulfonic acid metal salt compound and a nitrogen element-containing compound in one molecule is used in combination with a polyurethane resin as a binder component of the magnetic layer. Since the copolymerized polyester resin used contains an anionic sulfonic acid metal salt compound and a cationic nitrogen element-containing compound in one molecule, the surface of the magnetic powder used is either alkaline or acidic. However, the magnetic paint does not become highly viscous, and the interaction with the magnetic powder is too strong.The fluidity of the magnetic paint is improved, the dispersibility and filling properties of the magnetic powder are improved, and the magnetic layer The surface smoothness of the magnetic layer is also improved, and since the polyurethane resin used in combination has excellent dispersibility of the magnetic powder and good toughness, the dispersibility of the magnetic powder is further improved and the wear resistance of the magnetic layer is also improved. When a trifunctional low molecular weight isocyanate compound is further used in combination with these, the trifunctional low molecular weight isocyanate compound crosslinks with the copolymerized polyester resin, polyurethane resin, etc., resulting in improved heat resistance and abrasion resistance. The present inventors have discovered that a magnetic recording medium can be obtained that has further improved properties, excellent heat resistance and durability, and particularly excellent short wavelength recording characteristics, and has thus come to form the present invention.

The copolyester resin containing a sulfonic acid metal salt compound and a nitrogen element-containing compound in one molecule used in this invention contains 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-
Sulfonic acid metal salt compounds such as sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, 2-sodium sulfo-1,4-butanediol, 2-potassium sulfo-1,4-butanediol, and hexamethylene diamine, trimethylene Diamine, 6-amino-n-caproic acid, 2-amino-4so-caproic acid, ω-aminocaprylic acid, 4-amino-n-fig, 2-hydroxyethyl-p-)luidine, p-aminobenzoylhydrazide, It is obtained by copolymerizing compounds such as 0-aminobenzyl alcohol, ethanolamine, and 111O-diaminodecane, and these are copolymerized singly or in combination of two or more.

To produce this resin, for example, acid components such as adipic acid, isophthalic acid, and terephthalic acid; glycol components such as ethylene glycol and neopentyl glycol;
Add a predetermined amount of a sulfonic acid metal salt compound such as 5-sodium sulfoisophthalic acid, a nitrogen element-containing compound such as hexamethylene diamine, etc. together with other necessary components, and perform an esterification reaction and a polycondensation reaction under reduced pressure. The esterification reaction and the polycondensation reaction may be carried out separately by charging them all at once or in any order.

This type of copolyester resin containing a sulfonic acid metal salt compound and a nitrogen element-containing compound in one molecule differs from the conventional copolymerized polyester resin containing a sulfonic acid metal base, because it contains an anionic sulfonic acid metal salt compound. Because it contains a cationic nitrogen element-containing compound in one molecule, the magnetic paint will not become highly viscous and will not interact with the magnetic powder even if the surface of the magnetic powder is alkaline or acidic. Since the adsorption is moderate and not too strong, the dispersibility and filling properties of the magnetic powder are sufficiently improved, the surface smoothness of the magnetic layer is also improved, and short wavelength recording characteristics in particular are improved.

The polyurethane resin used in combination in this invention has good affinity with the magnetic powder and has excellent dispersibility of the magnetic powder. Therefore, when this polyurethane resin is used in combination, the dispersibility of the magnetic powder is further improved, and the magnetic powder is The surface smoothness of the layer is also improved, and short wavelength recording characteristics are further improved. Furthermore, since this polyurethane resin has good toughness, the wear resistance of the magnetic layer is also improved. As such polyurethane resins, urethane elastomers and urethane prepolymers, which have been widely used in the past, are all suitable, and both polyether and polyester polyurethane resins are preferably used. In particular, polyurethane resins containing OH groups at both ends or in the molecular chain are more preferably used because they have good dispersibility of magnetic powder. Specific examples of such polyurethane resins include Takenate manufactured by Narita Pharmaceutical Co., Ltd. L-1007, Takenate L-2710, Takerac E-551T.

Examples include Takelac E-550, Pandesox T-5201 manufactured by Dainippon Ink and Chemicals, Pandesox T-5250, and Ml (-101 manufactured by Honey Kasei).

The blending ratio of the above-mentioned copolyester resin containing the sulfonic acid metal salt compound and nitrogen element-containing compound in one molecule and the polyurethane resin varies depending on the type of polyurethane resin used, but the weight ratio of the above-mentioned copolyester resin to the polyurethane resin varies depending on the type of polyurethane resin used. It is preferable that the ratio of the polyurethane resin be within the range of 9:1 to 1:9, and if the amount of the copolymerized polyester resin is too little or too much, the desired effect will not be obtained.

Further, the trifunctional low molecular weight isocyanate compound used in combination with the copolymerized polyester resin and polyurethane resin is usually a compound having a trifunctional isocyanate group obtained by reacting 1 mol of triol with 3 mol of diisocyanate. When these types of isocyanate compounds are used in combination, the isocyanate groups of these compounds will cause the amino groups and polyurethane in the copolyester resin containing the above-mentioned sulfonic acid metal salt compound and nitrogen element-containing compound in one molecule. Since it reacts with the OH groups of the resin to form strong crosslinking bonds, the abrasion resistance and heat resistance of the magnetic layer are improved by 10 times. The amount used varies depending on the type of polyurethane resin used together, but it is 1 to 40% of the total amount of binder components.
It is preferable to use the amount within a range of 1% by weight or less, and the abrasion resistance of the magnetic layer will not be sufficiently improved, and if it exceeds 40% by weight, there will be too many cross-links, making the magnetic layer hard and causing surface problems. Reduces calendar effects in processing. Specific examples of such trifunctional low molecular weight isocyanate compounds include Coronate L manufactured by Nippon Polyurethane Industries, Desmodur L manufactured by Bayer, and Takenate DI02 manufactured by Takeda Pharmaceutical Industries.

In addition, vinyl chloride resins, cellulose resins, polyvinyl acecool resins, etc., which are generally used as binder components, may be used in combination, and depending on the application, the properties may be improved by using these binder components in combination. A magnetic recording medium with good quality can be obtained.

Examples of the magnetic powder used in this invention include 7-F
e2O3 powder, Fe3O4 powder, Co-containing 7-Fe2O
3 powder, CO-containing Fe3O4 powder, CrO2 powder and other F
Various conventionally known magnetic powders are widely included, such as metal powders such as e powder, CO powder, CO ferrite powder, and Ba ferrite powder.

In addition, as the organic solvent, cyclohexanone, methyl ethyl ketone, tetrahydrofuran, dioxane, dimethylformamide, etc. may be used alone or in combination;
Alternatively, a mixed solvent of these solvents and methyl isobutyl ketone or toluene may be used.

The magnetic recording medium of the present invention may be manufactured according to a conventional method, for example, by forming a copolymer containing a magnetic powder, a sulfonic acid metal salt compound, and a nitrogen element-containing compound in one molecule on a substrate such as a polyester film. A magnetic paint containing a binder component consisting of a polyester resin and a polyurethane resin, or a binder component further added with a trifunctional low molecular weight isocyanate compound, an organic solvent, and other additives is sprayed or rolled. It can be applied by any means and dried.

11 Next, embodiments of the invention will be described.

Example 1 0.4 mol of terephthalic acid and 210 mol of isophthalic acid were added to a reaction vessel equipped with a temperature needle, a stirrer, a compressor, and a partial reflux condenser.
．． 4 mol, adipic acid 0.19 mol, ethylene glycol 0.49 mol, neopentyl glycol 0.49 mol, 5-sodium sulfoisophthalic acid 0.01 mol, hexamethylene diamine 0.02 mol, and further zinc acetate 0. .01 mole, 0.005 mole of sodium acetate and 0.01 mole of antimony dioxide to give 140-2
React at 20°C, and then at 210-250°C, 1ml/g
A polycondensation reaction was carried out under the following reduced pressure to produce a copolymerized polyester resin having a sodium sulfonate group and an amino group. Using the copolymerized polyester resin obtained in this way, 600 parts by weight of epitaxial Co-containing oxidized iron magnetic powder (acicularity, long axis 0.2μ) having a sodium sulfonate group and 60〃3 amino groups was prepared. Copolymerized polyester resin Pandex T-5250 (large 42μ polyurethane elastomer manufactured by Nippon Ink Chemical Industry Co., Ltd.) Coronate Shikoku Nippon Polyurethane 18 (manufactured by Nippon Kogyo Co., Ltd., trifunctional low molecular weight isocyanate compound) Toluene 400〃Methyl isobutyl ketone 400〃 Composition A magnetic paint was prepared by mixing and dispersing the mixture in a ball mill for 78 hours. This magnetic paint was applied onto a 15 μm thick polyester film to a dry thickness of 5 μm, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape.

Example 2 The composition of the magnetic paint in Example 1 was the same as in Example 1 except that the same amount of Takelac E-551T (polyurethane prepolymer manufactured by Narita Pharmaceutical Co., Ltd.) was used in place of Pandex T-5250. and made magnetic tape.

Example 3 In the composition of the magnetic paint in Example 1, Coronate L was omitted, the amount of copolyester resin having a sodium sulfonate group and an amino group was changed from 60 parts by weight to 70 parts by weight, and Vandex T- A magnetic tape was produced in the same manner as in Example 1 except that the amount of 5250 used was changed from 42 parts by weight to 50 parts by weight.

Comparative Example I A copolymerized polyester resin having only sodium sulfonate groups was produced in the same manner as in Example 1 except that hexamethylene diamine was omitted, and the same amount of this copolymerized polyester resin was used. A magnetic tape was made in the same manner as in 1.

In each of the Examples and Comparative Examples, the viscosity of the magnetic paint used in making the magnetic tape was measured. Furthermore, the surface roughness of the rectangular shape and magnetic layer of the magnetic tapes obtained in each example and comparative example was measured, the heat resistance was further tested, and the output at each frequency was measured to examine the short wavelength recording characteristics. The viscosity of the magnetic paint was measured at 30° C. using an E-type viscosity needle manufactured by Tokyo Keiki Co., Ltd. The sliding speed at this time is 38.45ec-1
The viscosity was determined in mPa-s. In addition, the square shape was measured using a vibrating sample type magnetometer in the usual manner with an applied magnetic field of 10 kG, and the surface roughness was measured using a Tokyo Seimitsu stylus type surface roughness meter with a cutoff of 0.08n and a center line average. Roughness was measured.

Furthermore, the heat resistance test was performed by cutting the obtained magnetic tape into a length of 1.5 m, applying a weight of 1 pupil, and winding it around a glass tube with a diameter of 36 fi at 60°C and 80% I? ) 4 in a constant temperature bath of I
After storing for 8 hours and leaving at room temperature for 24 hours, the tape was unwound from the glass tube and the degree of adhesion between the tape layers was observed. No adhesion was observed (○), and cases where some adhesion was observed ( Δ), adhesive that can hardly be loosened (×)
It was evaluated as Furthermore, the short wavelength recording characteristics are such that the recording frequency is 30 to 8 at a magnetic tape running speed of 4.75 cm/see.
The non-bias saturated recording and reproducing output at 0KI (z) was measured using a Sendust head with a gap length of 0.3μ.

The table below shows the results.

As is clear from the above table, the viscosity of the magnetic paints in Examples 1 to 3 is lower than that of the magnetic paint in Comparative Example 1, and the magnetic tapes obtained in Examples 1 to 3 are lower than those in Comparative Example 1. The magnetic recording medium obtained by this invention has a high squareness, low surface roughness, and high short-wavelength recording/reproduction output compared to magnetic tape, which has good fluidity of magnetic paint and high It can be seen that the dispersibility and filling properties are excellent, and the surface smoothness of the magnetic layer is also good, resulting in improved short wavelength recording characteristics.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing a polyurethane resin and a copolymerized polyester resin having a sulfonic acid metal salt compound and a nitrogen element-containing compound in one molecule as a binder component 2. As a binder component The magnetic recording medium according to claim 1, further comprising a trifunctional low molecular weight isocyanate compound contained in the magnetic layer.