JPH11110738A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has a magnetic layer in which highly fine magnetic particles with a high coercive force are dispersed with a high dispersibility and is excellent in magnetic characteristics and an abrasion-resistance. SOLUTION: Magnetic material obtained by dispersing ferromagnetic particles in binder is applied to a nonmagnetic supporter. For that purpose, polyurethane resin containing polyester diol which is obtained from sulfonic acid metal base containing aromatic dibasic acid and side chain containing glycol and has a number-averaged molecular weight of not larger than 1000 as one component of raw material is contained as the binder component of the magnetic layer.

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 tape and a magnetic disk having a magnetic layer excellent in dispersibility and filling property of magnetic particles, and excellent in durability and wear resistance. And so on.

[0002]

2. Description of the Related Art Magnetic tapes, which are general-purpose magnetic recording media,
A floppy disk is made by dispersing needle-like magnetic particles having a major axis of 1 μm or less in a binder solution together with additives such as a dispersant, a lubricant, and an antistatic agent to form a magnetic paint, and applying this to a polyethylene terephthalate film or the like. Have been.

[0003] The properties required for the binder of the magnetic layer include the dispersing performance, dispersion stability, filling properties, and orientation of the magnetic particles, and the durability, abrasion resistance, heat resistance, and non-magnetic support of the magnetic layer. And the binder plays a very important role.

Conventionally used binders include vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer, vinyl chloride / vinylidene chloride copolymer, polyurethane resin, polyester resin,
Acrylonitrile-butadiene copolymer, nitrocellulose, cellulose acetate butyrate, epoxy resin, acrylic resin and the like are used.

[0005] Among these resins, polyurethane resins are superior in toughness and abrasion resistance as compared with other resins due to intermolecular hydrogen bonding by urethane bonds, but conventional polyurethane resins have a dispersion property of magnetic particles. Low, various studies have been made to improve this. For example, Japanese Patent Publication No. 58-41565 discloses an improvement in the dispersion performance of magnetic particles.
It is known that the introduction of sulfonic acid metal bases into polyurethanes is effective.

[0006]

In order to improve the image quality of video tapes and to improve the sound quality of audio tapes, the magnetic particles used are highly fine and uniform, and the coercive force is greatly improved. There is a tendency. In response to such demands, the development of metal fine particles is now the mainstream instead of iron oxide-based magnetic particles, which have been the mainstream in the past. As the magnetic particles become finer and the coercive force becomes higher, the conventional binder becomes more difficult to disperse, and it is required that the dispersibility of the magnetic particles with respect to the binder is further increased. In JP-B-58-41565, although the improvement of the dispersing performance of the binder is recognized, it is not always satisfactory.

[0007] In a magnetic recording medium, the magnetic layer is filled with highly refined magnetic particles for high S / N ratio (signal / noise ratio) and high recording density to achieve high orientation. The surface is made smooth. When the magnetic tape is stored in a roll form, the back coat layer is also smooth so that the output of the magnetic tape does not decrease even if the unevenness of the back coat layer is transferred to the magnetic layer.

The smoother the surfaces of the magnetic layer and the back coat layer, the worse the running property and running durability of the magnetic tape, and the better the durability, abrasion resistance, heat resistance, and adhesion to the non-magnetic support. There is a need for a new binder. The conventional binder for the magnetic layer is insufficient for these requirements, that is, a requirement for both excellent dispersion performance and durability. Accordingly, it is an object of the present invention to provide a magnetic recording medium that improves the dispersion performance and filling property of magnetic particles and has excellent durability.

[0009]

Means for Solving the Problems The present inventors have intensively studied a polyurethane resin and have reached the present invention. That is, the present invention relates to a magnetic recording medium in which a magnetic material in which ferromagnetic particles are dispersed in a binder is coated on a non-magnetic support,
As a binder component of the magnetic layer, a polyurethane resin containing a sulfonic acid metal base-containing aromatic dibasic acid and a polyesterdiol having a number average molecular weight of 1,000 or less obtained from a side chain-containing glycol as a raw material is contained. Magnetic recording medium.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A polyester diol containing a metal sulfonate containing only an aromatic dibasic acid containing a metal sulfonate as an acid component is a sulfonate containing an aromatic dibasic acid containing a metal sulfonate as a part of the acid component. Compared to acid metal base-containing polyester diols, it has low solubility in general-purpose solvents such as toluene, MEK, and cyclohexanone, and has low compatibility with other components. can get. As the acid component of the sulfonic acid metal group-containing polyester diol used in the present invention, only the aromatic sulfonic acid metal group-containing aromatic dibasic acid component is used. Examples of the aromatic dibasic acid containing a sulfonic acid metal base include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, and sodium sulfoterephthalic acid, and 5-sodium sulfoisophthalic acid is particularly preferred.

The glycol component of the sulfonic acid metal base-containing polyester diol used in the present invention is a glycol containing a side chain. Preferably, it is a glycol having an ester bond in the molecule. The glycol containing no side chain has low compatibility with other components when polymerizing the polyurethane resin, so that the metal sulfonate base cannot be uniformly introduced into the polyurethane resin. For this reason, the number of components having no metal sulfonate group in the molecule increases, and sufficient dispersion performance cannot be obtained, and the porosity in the magnetic layer also increases. Such a magnetic layer is inferior in running durability and wear resistance. In addition, the side chain-containing glycol having an ester bond in the molecule is further improved in compatibility with other raw materials constituting the polyurethane resin, and the sulfonic acid metal base is introduced without uneven distribution in each urethane molecule. As a result, the dispersion performance of the magnetic particles is improved, so that a magnetic layer having an extremely high filling property can be obtained. As a result, durability and wear resistance are improved. Further, by leaving glycol in the polyester diol containing a metal sulfonic acid group, the solubility of the polyester diol containing a metal sulfonic acid group is improved, and the polyester diol becomes soluble in a solvent such as MEK and toluene.

In the present invention, the side chain-containing glycol component includes 1,2-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2,2-butyl glycol.
Dimethyl-1,3-propanediol, 3-methyl-
1,5-pentanediol, 2,2,4-trimethyl-
1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate, 2-n-butyl-2 -Ethyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3
-Propyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 3-octyl-1,
5-pentanediol, 3-phenyl-1,5-pentanediol and the like. Among them, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl- having an ester bond in the molecule. 3-Hydroxypropanate is most preferred.

The sulfonic acid metal base-containing polyester diol used in the present invention has a number average molecular weight of 1,000 or less. When the molecular weight is 1000 or more, it becomes difficult to uniformly introduce the metal sulfonate base into the polyurethane resin. As a result, components having no metal sulfonate group in the polyurethane resin are increased, and it is not possible to obtain extremely high dispersion performance particularly required for recent metal tapes. In addition, the porosity in the magnetic layer increases due to the decrease in the dispersion performance of the magnetic particles, and the increase in the porosity deteriorates the running durability of the magnetic layer.

Other raw materials for the polyurethane resin used in the present invention are high molecular polyols and glycols. As the polymer polyol, specifically, an aromatic polyester,
Examples thereof include aliphatic polyester, alicyclic polyester, polyether, and polycarbonate. Glycols include ethylene glycol, propylene glycol, 1,
3-propanediol, 1,4-butanediol, 1,
5-pentaneddiol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-
Pentanediol, cyclohexanedimethanol, 2,
2-dimethyl-3-hydroxypropyl-2 ', 2'-
Dimethyl-3-hydroxypropanate, bispheno-
And diol compounds such as ethylene oxide adducts and propylene oxide adducts of ethylene oxide A and ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A. Particularly, neopentyl glycol, 2,2-dimethyl- 3-hydroxypropyl-
2 ', 2'-dimethyl-3-hydroxypropanate is preferred.

The branching having three or more functional groups which react with isocyanate in one molecule is effective for improving the reactivity with a general-purpose curing agent. Specific compounds include polyols such as trimethylolpropane, glycerin, triethanolamine, pentaerythritol and dipentaerythritol, and ε-caprolactone adducts to one of these polyols.

The organic diisocyanate component of the polyurethane resin used in the present invention includes 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p
Phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4 '-Biphenylenediisocyanate, 1,5-naphthalenediisocyanate, 2,6-naphthalenediisocyanate, 3,
3'-dimethyl-4,4'-diisocyanate, 4,
4'-diisocyanatodiphenyl ether, 1,5-
Xylylene diisocyanate, 1,3-diisocyanate
Tomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane, 4,4'-diisocyanatocyclohexane, 4,4'-diisocyanatocyclohexylmethane, isophorone diisocyanate and the like.

The amount of the sulfonic acid metal base in the polyurethane resin used in the present invention is preferably in the range of 5 to 500 equivalents / 10 ⁶ g. When the amount is less than 5 equivalents / 10 ⁶ g, the dispersing performance of the magnetic particles is insufficient. When the amount exceeds 500 equivalents / 10 ⁶ g, the viscosity of the polyurethane resin solution or the magnetic paint becomes high and the handling or the production of the magnetic recording medium becomes difficult. More obstacles. A particularly preferred range is 50 to 200 equivalents / 10 ⁶ g.

The urethane resin in the urethane resin of the present invention has a urethane group concentration of 500 to 4000 equivalent / 10 ⁶ g. If the urethane group concentration is 500 equivalents / 10 ⁶ g or less, the toughness peculiar to the urethane group cannot be obtained. If it is 4000 g / 10 ⁶ g or more, the mechanical properties of the polyurethane resin can be further improved, but the solubility in a general-purpose solvent is reduced, and a high magnetic particle dispersion performance as a binder for a magnetic tape cannot be obtained. .

The polyurethane resin used in the present invention has a molecular weight of 5,000 to 80000, preferably 10,000 to 50,000. If the molecular weight is less than 5000, the mechanical strength is insufficient, and the running durability is poor. Molecular weight 80
If it exceeds 000, the solution viscosity increases, and the workability and the dispersion performance of magnetic particles, abrasives, carbon black and the like deteriorate.

In the present invention, in addition to the polyurethane resin used in the present invention, other resins are added for the purpose of controlling flexibility, improving cold resistance and heat resistance, and / or mixing a crosslinking agent. It is desirable to do. Examples of other resins include a vinyl chloride resin, a cellulose resin, a polyester resin, an epoxy resin, a phenoxy resin, a polyvinyl butyral, an acrylonitrile-butadiene copolymer, and a polyurethane resin other than the present invention. On the other hand, examples of the crosslinking agent include a polyisocyanate compound, an epoxy resin, a melamine resin, a urea resin, an acid anhydride and the like, and among these, a polyisocyanate compound is particularly preferable.

The ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe ₂ O ₃ and γ-Fe
Mixed crystal of ₂ O ₃ and Fe ₃ O ₄ , γ-F coated with cobalt
Examples include ferromagnetic oxides such as e ₂ O ₃ or Fe ₂ O ₄ and barium ferrite, and ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni.

In the magnetic recording medium of the present invention, if necessary, a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctyl sodium sulfosuccinate, t-butylphenol polyethylene ether, sodium ethylnaphthalene sulfonate, dilauryl succinate Lubricants such as zinc stearate, soybean oil lecithin and silicone oil, and various antistatic agents can also be added.

[0023]

The polyurethane resin of the present invention is obtained by using, as one component of a raw material, a polyester diol having a number average molecular weight of 1,000 or less obtained from an aromatic dibasic acid containing a sulfonic acid metal base and a glycol containing a side chain. It has high magnetic particle dispersion performance as a binder for tapes, and as a result, the magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics.

[0024]

The present invention will be specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”. Tables 1 and 2 show the compositions and other characteristics of the polyester diol and polyurethane resin obtained in the following synthesis examples of polyester diol and polyurethane resin and comparative synthesis examples.

The abbreviations in the table are as follows. TPA: terephthalic acid IPA: isophthalic acid OPA: orthophthalic acid DSN: dimethyl 5-sodium sulfoisophthalate BSI: bis (2-sodium sulfoisophthalate)
(Hydroxyethyl) ester EG: ethylene glycol NPG: neopentyl glycol HPN: 2,2-dimethyl-3-hydroxypropyl-
2 ', 2'-dimethyl-3-hydroxypropanate DMH: 2-butyl-2-ethyl-1,3-propanediol MDI: 4,4'-diphenylmethane diisocyanate IPDI: isophorone diisocyanate P-205: Plaxel 205 (poly Caprolactone)
(Manufactured by Daicel Chemical Industries, Ltd.) Number average molecular weight 500 ODX-688: Polylite ODX-688 (aliphatic polyester polyol) (Dainippon Ink & Chemicals, Inc.)
Manufacture) Number average molecular weight 2000 PPG-1000: Sannic PPG-1000 (polypropylene glycol) (manufactured by Sanyo Chemical Industries, Ltd.)
Number average molecular weight 1000

The number average molecular weight of the sulfonic acid metal base-containing polyester diol, polyester diol, and polyurethane resin was measured by gel permeation chromatography in terms of standard polystyrene. The gloss of the magnetic layer of the magnetic tape was measured at 45 degrees. The squareness ratio of the magnetic layer was measured by using a vibrating sample magnetometer, and the squareness ratio in the vertical direction was measured.

For filling the magnetic layer, a magnetic tape (weight W1) precisely weighed in advance was permeated into silicone oil for 30 minutes. After wiping off the silicone oil attached to the surface of the magnetic tape, the weight (W2) was precisely weighed. After wiping the magnetic layer with a solvent, the film was precisely weighed (W3) to determine the weight of the magnetic layer. The weight increase due to silicone oil immersion with respect to the weight of the magnetic layer, that is, (W2-W1) /
(W1-W3) was determined. Since the silicone oil penetrates into the voids of the magnetic layer, the filling rate of the magnetic layer is higher as the weight increase rate (expressed as a percentage) due to the silicone oil immersion is smaller.

The magnetic layer abrasion resistance test was carried out on a commercially available S-VHS video deck, and the magnetic layer was observed to be damaged after running 100 times at a temperature of 40 ° C. during running. 6: Almost no scratching 5: Slight scratching 4: Scratching and noticeable 3: Scratching noticeable, not reaching PET film 2: Scratching noticeable, PET film surface slightly visible 1: Scratching noticeable Many PET film surfaces

Synthetic Example 1 of Polyester Diol 5-Sodium sulfoisophthalic acid dimethyl ester and 2,2-dimethyl-3-hydroxypropyl-2 ',
2'-dimethyl-3-hydroxypropanate in 1: 3
And the unreacted glycol component was left. In a reaction vessel equipped with a thermometer, stirrer and Liebig condenser, 888 parts of dimethyl 5-sodium sulfoisophthalate, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanoate 1836 were added. And 0.2 part of tetrabutoxytitanium were charged and transesterified at 240 ° C. for 5 hours. 100 temperature
The temperature was lowered to ℃ and diluted with 633 parts of toluene to obtain a polyester diol (a) solution (solid content: 80 wt%). The number average molecular weight of the obtained polyester diol (a) is 6
20.

Synthesis Example 2 of Polyester Diol A polyester diol (b) was synthesized in the same manner as in Synthesis Example 1. The number average molecular weight of the obtained polyester diol (b) was 430.

Synthesis Example 3 of Polyester Diol 485 parts of dimethyl terephthalate was placed in a reaction vessel equipped with a thermometer, stirrer, Vigreux tube, and Liebig condenser.
485 parts of dimethyl isophthalate, 372 parts of ethylene glycol, 416 parts of neopentyl glycol and 0.2 part of tetrabutoxy titanium were charged and transesterification was carried out at 200 to 230 ° C. for 4 hours. Then, the temperature was raised to 240 ° C. over 10 minutes, and the pressure was gradually reduced while the reaction was continued for 30 minutes to complete the polymerization. The number average molecular weight of the obtained polyester diol (c) was 2,000.

Synthesis Example 4 of Polyester Diol Dimethyl isophthalate 4 was placed in the same reaction vessel as in Synthesis Example 3.
After 85 parts, 372 parts of ethylene glycol, 416 parts of neopentyl glycol and 0.2 parts of tetrabutoxytitanium were charged and transesterified at 180 to 220 ° C. for 4 hours, 370 parts of phthalic anhydride was added to perform esterification. Then, the temperature was raised to 240 ° C. over 10 minutes, and the pressure was gradually reduced while the reaction was continued for 30 minutes to complete the polymerization. The number average molecular weight of the obtained polyester diol (d) is 1
900.

Comparative Synthesis Example 1 of Polyester Diol Polyester diol (e) was synthesized in the same manner as in Synthesis Example 1. The number average molecular weight of the obtained polyester diol (e) was 1,500.

Comparative Synthesis Example 2 of Polyester Diol Dimethyl terephthalate 4 was placed in the same reaction vessel as in Synthesis Example 3.
85 parts, dimethyl isophthalate 461 parts, 5-sodium sulfoisophthalic acid dimethyl ester 37 parts, ethylene glycol 372 parts, neopentyl glycol 41
6 parts and 0.2 parts of tetrabutoxy titanium
The transesterification was performed at 0 to 230 ° C for 4 hours. Then, the temperature was raised to 250 ° C. over 20 minutes, and the pressure was gradually reduced, and the reaction was carried out for 30 minutes to complete the polymerization. The number average molecular weight of the obtained polyester diol (f) was 2,000.

Comparative Synthesis Example 3 of Polyester Diol A polyester diol (g) was synthesized in the same manner as in Comparative Synthesis Example 2. The number average molecular weight of the obtained polyester diol (g) was 600.

Synthesis Example 1 of Polyurethane Resin 15 parts of polyester diol (a) solution was dissolved in 12 parts of MEK and 10 parts of toluene, and 37 parts of MDI was added.
The reaction was carried out at a temperature of 1 hour. Next, the solution was diluted with 62 parts of MEK and 62 parts of toluene, and 90 parts of polyester diol (c) was added. After reacting at 80 ° C. for 2 hours, 8 parts of neopentyl glycol was added and reacted at the same temperature for 2 hours. After dilution with 98 parts of MEK and 98 parts of toluene, 0.2 part of dibutyltin dilaurate was added as a catalyst and reacted at the same temperature to obtain a polyurethane resin (a). Polyurethane resin
Table 2 shows the molecular weight, sulfonic acid metal base concentration and urethane group concentration of (a).

Synthesis Examples 2 to 7 of Polyurethane Resins Polyurethane resins (b) to (g) were synthesized in the same manner as in Synthesis Example 1. Table 2 shows the molecular weight, the sulfonic acid metal base concentration, and the urethane group concentration of the polyurethane resin.

Comparative Synthesis Example 1 of Polyurethane Resin Polyester diol (f) 100 was placed in a reaction vessel equipped with a thermometer, stirrer, reflux condenser and Liebig condenser.
And 100 parts of toluene were charged and dissolved. Then, 20 parts of toluene was distilled, and the reaction system was dehydrated by azeotropic distillation of toluene and water. After cooling to 60 ° C., 12 parts of MDI was added and reacted at the same temperature for 2 hours. Then, 130 parts of MEK and 50 parts of toluene were added, 0.1 part of dibutyltin dilaurate was added as a catalyst, and the reaction was carried out at 80 ° C. for 5 hours. I got
Table 2 shows the molecular weight, the concentration of the metal sulfonate group and the concentration of the urethane group of the polyurethane resin (H). In this example, the acid component and molecular weight of the sulfonic acid metal base-containing polyester diol fall outside the scope of the present invention.

Comparative Synthesis Example 2 of Polyurethane Resin Polyurethane resin (R) was synthesized in the same manner as in Synthesis Example 1. Table 2 shows the molecular weight, the sulfonic acid metal base concentration, and the urethane group concentration of the polyurethane resin (i). Since this example does not contain any polyester diol containing a metal sulfonate group, it falls outside the scope of the present invention.

Comparative Example 3 of Polyurethane Resin A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was charged with 50 parts of Praxel 205 (manufactured by Daicel Chemical Industries, Ltd.).
7.5 parts of 5-sodium sulfoisophthalic acid bis (2-hydroxyethyl) ester, 15 parts of neopentyl glycol and 320 parts of dimethylacetamide were charged. After dissolving the solid, 65 parts of MDI was added and reacted at 80 ° C. for 5 hours to obtain a polyurethane resin (N). Polyurethane resin
Table 2 shows the molecular weight, the sulfonate metal base concentration, and the urethane group concentration of (u). In this example, the glycol composition of the sulfonic acid metal base-containing polyester diol falls outside the scope of the present invention.

Comparative Synthesis Example 4 of Polyurethane Resin A polyurethane resin (R) was synthesized in the same manner as in Comparative Synthesis Example 3. Table 2 shows the molecular weight, the concentration of the metal sulfonate group and the concentration of the urethane group of the polyurethane resin (R). In this example, the glycol composition of the sulfonic acid metal base-containing polyester diol falls outside the scope of the present invention.

Comparative Synthesis Example 5 of Polyurethane Resin A polyurethane resin (e) was synthesized in the same manner as in Synthesis Example 1. Table 2 shows the molecular weight, the concentration of the metal sulfonate group and the concentration of the urethane group of the polyurethane resin (e). In this example, the molecular weight of the sulfonic acid metal base-containing polyester diol falls outside the scope of the present invention. Since the sulfonic acid metal base-containing polyester diol has low solubility, it did not completely dissolve in the same solvent as in Synthesis Example 1, and the polyurethane resin solution became cloudy and phase-separated one day later.

Comparative Synthesis Example 6 of Polyurethane Resin A polyurethane resin (W) was synthesized in the same manner as in Synthesis Example 1. Table 2 shows the molecular weight, the concentration of the metal sulfonate group, and the concentration of the urethane group of the polyurethane resin (wa). In this example, the glycol component of the sulfonic acid metal base-containing polyester diol falls outside the scope of the claims. Since the sulfonic acid metal base-containing polyester diol has low solubility, it does not completely dissolve in the same solvent as in Synthesis Example 1, and the polyurethane resin solution becomes cloudy and phase-separated one day later.

Comparative Synthesis Example 7 of Polyurethane Resin A polyurethane resin (f) was synthesized in the same manner as in Comparative Synthesis Example 1. Table 2 shows the molecular weight, the concentration of the metal sulfonate group and the concentration of the urethane group of the polyurethane resin (f). In this example, the acid component of the sulfonic acid metal base-containing polyester diol falls outside the scope of the claims.

Example 1 A composition having the following composition ratio was placed in a ball mill and dispersed for 48 hours, and then 1 part of stearic acid and 1 part of butyl stearate were used as a lubricant, and alumina powder was used as an abrasive (average particle size: 0.2 μm). 5 parts, and 6 parts of coronate L of an isocyanate compound (manufactured by Nippon Polyurethane Co., Ltd.) were added as a curing agent, and the dispersion was further continued for 1 hour to obtain a magnetic paint. This was applied onto a 12 μm-thick polyethylene terephthalate while applying a magnetic field of 2,000 gauss so that the thickness after drying would be 4 μm. 1 after aging at 50 ° C for 48 hours
It was slit to a width of 1/2 inch to obtain a magnetic tape. Table 3 shows the properties of the obtained magnetic tape.

Polyurethane resin (a) 30% solution 100 parts Metal powder (BET 58 m ² / g; coercive force (Hc) 1600 Oe) 120 parts Alumina powder (average particle size 0.2 μm) 5 parts Cyclohexanone 100 parts MEK 50 parts Toluene 50 copies

Examples 2 to 7 Using the binders shown in Table 2, magnetic tapes were obtained in the same manner as in Example 1. Table 3 shows the characteristics of each magnetic tape.

Comparative Examples 1-2 A magnetic tape was obtained in the same manner as in Example 1 using the binders shown in Table 2. Table 3 shows the characteristics of each magnetic tape.

Comparative Examples 3 and 4 Since the solvent composition of the binder was different, solvent replacement was carried out, and a magnetic tape was obtained in the same manner as in Example 1 except that the solvent composition of the binder was the same as that of the polyurethane (a). Table 3 shows the characteristics of each magnetic tape.

Comparative Examples 5 and 6 Since the polyurethane resin solution was cloudy, a magnetic tape was obtained in the same manner as in Example 1 using only the supernatant. Table 3 shows the characteristics of each magnetic tape.

Comparative Example 7 A magnetic tape was obtained in the same manner as in Example 1 using the binders shown in Table 2. Table 3 shows the characteristics of each magnetic tape.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

The polyurethane resin which is a binder for the magnetic particles of the magnetic recording medium of the present invention has a remarkably high dispersion performance of highly fine magnetic particles, and has a remarkably good filling property and abrasion resistance of the magnetic layer. Since it is a binder, it is possible to provide a magnetic recording medium having excellent running properties, running durability, electromagnetic conversion characteristics, and the like, which has not been achieved in the past.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic material in which ferromagnetic particles are dispersed in a binder is coated on a non-magnetic support, obtained from an aromatic dibasic acid containing a metal sulfonic acid base and a glycol containing a side chain. A magnetic recording medium comprising a polyurethane resin containing a polyester diol having a number average molecular weight of 1,000 or less as a raw material as a binder component of a magnetic layer. 2. The magnetic recording medium according to claim 1, wherein the side chain-containing glycol is a compound having an ester bond in the molecule.