JPH06139548A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To ensure excellent dispersibility and to obtain a magnetic recording medium having satisfactory running property by incorporating polyurethane resin having prescribed characteristics as the component of a binder. CONSTITUTION:When a magnetic layer based on magnetic powder such as gamma-Fe2O3 and a binder is formed on a base material to obtain a magnetic recording medium, polyurethane resin having hydroxyl groups at both terminals and obtd. from long-chain diol, an org. isocyanate and a chain extender having a sulfone bond in each molecule is incorporated as the component of the binder. Polyester diol having 500-5,000 mean mol.wt. may be used as the long chain diol, bis-(2-hydroxyethyl)sulfone as the chain extender and tolylene diisocyanate as the org. diisocyanate. The objective magnetic recording medium excellent in electromagnetic transducing characteristics and surface characteristics of the coating film is obtd.

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 excellent in electromagnetic conversion characteristics and coating film surface characteristics.

[0002]

2. Description of the Related Art A magnetic layer of a magnetic recording medium is basically formed by applying a magnetic coating material composed of magnetic powder, a resin binder and an organic solvent on a support such as a polyester film and drying it. In recent years, with the increase in recording density of magnetic recording media, the magnetic powder used tends to become finer, and a binder having a high degree of dispersibility and runnability is desired. Generally, polyurethane is a useful binder because it has good abrasion resistance, but it cannot be said that polyurethane has particularly good dispersibility and resin surface lubricity. Therefore, a method of incorporating a hydrophilic group into a known polyurethane resin has been proposed for dispersibility (Japanese Patent Application Laid-Open No. 64-72318). However, in this method, while the dispersibility is improved, the solubility of the resin in the solvent is lowered, so that the stability of the magnetic coating material is deteriorated and it is difficult to obtain a sufficient effect. On the other hand, regarding surface lubricity, in order to compensate for this,
Known methods include adding lubricants such as higher fatty acids and higher fatty acid esters (JP-A-56-19525), and adding silicones (JP-A-59-54035). However, even if the lubricity can be improved by this method, it is difficult to improve the scratch resistance because the characteristics of the resin itself largely influence the scratch resistance. It is considered that the scratch resistance can be improved by a method of introducing three or more hydroxyl groups into the polyurethane molecular chain (Japanese Patent Laid-Open No. 55-139634), but the viscosity of the magnetic coating becomes high and the coating process Becomes difficult.

[0003]

DISCLOSURE OF THE INVENTION The present invention overcomes the above-mentioned drawbacks and provides a magnetic recording medium having both excellent dispersibility and stability of a magnetic paint, and having good running properties and scratch resistance. It was made for the purpose.

[0004]

Means for Solving the Problems As a result of earnest research, the present inventors have introduced a sulfone bond having an appropriate polarity into a hard segment in polyurethane, thereby providing excellent dispersibility and stability of a magnetic coating, Moreover, they have found that a magnetic recording medium having a low surface friction resistance and an excellent scratch resistance can be obtained, and completed the present invention.

That is, the present invention provides a magnetic recording medium comprising a support and a magnetic layer mainly composed of magnetic powder and a binder, wherein a long-chain diol, an organic diisocyanate, and a sulfone in the molecule are used as the binder component. A magnetic recording medium comprising a polyurethane resin having hydroxyl groups at both ends obtained from a chain extender having a bond.

Each component constituting the polyurethane resin of the present invention will be described below. Examples of the long chain diol used in the present invention include polyester diols having a number average molecular weight of 500 to 5,000, polyether diols, polycarbonate diols, polyolefin diols, etc. These long chain diols may be used alone or in combination.

As the polyester diol, dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid and phthalic acid, and ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 3- Methyl-1,5-pentanediol,
1,6-hexanediol, neopentyl glycol,
Those obtained by polycondensation reaction with diols such as diethylene glycol, 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol, or ring-opening polymerization of cyclic ester (lactone) monomers such as ε-caprolactam and δ-valerolactone. What can be obtained by doing. Examples of the polyether diol include polyoxyethylene glycol, polyoxypropylene diol, polyoxytetramethylene diol and the like.

As the polycarbonate diol, a dealcoholization condensation reaction of glycols and dialkyl carbonates such as dimethyl and diethyl, a dephenolation condensation reaction of glycols and diphenyl carbonate, or a deethylene glycol condensation reaction of glycols and ethylene carbonate are generally used. Can be obtained by Examples of the glycols include 1,6-hexanediol,
Diethylene glycol, propylene glycol, 1,4
-Polycarbonate using an aliphatic diol such as butanediol, 3-methyl-1,5-pentanediol, neopentyl glycol or an alicyclic diol such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol Examples include diols. Examples of the polyolefin diol include hydroxyl-terminated polybutadiene and hydrogenated products thereof. The preferred long-chain diol is polycarbonate diol from the viewpoint of water resistance.

The chain extender used in the present invention has a molecular weight of 5
The following compounds of 0-400 are mentioned. Specific examples of the chain extender having a sulfone bond in the molecule used in the present invention include bis- (2-hydroxyethyl) sulfone and bis- (4-aminophenyl) sulfone.
Further, in the present invention, a diol containing no sulfone bond,
Chain extenders such as amines, such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,5
-Pentanediol, 1,6-hexanediol, 3-
Use methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hexamethylenediamine, xylenediamine, isophoronediamine, ethylenediamine, monoethanolamine, etc. together. You can

The organic diisocyanates used in the present invention include tolylene diisocyanate and xylylene-
1,4-diisocyanate, xylylene-1,3-diisocyanate, 4,4'-diphenylmethane diisocineate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'- Diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-
4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-
1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3′-dimethoxydiphenyl-4,
Aromatic diisocyanates such as 4'-diisocyanate,
Aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate and lysine diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, cyclohexane diisocyanate and the like can be mentioned.

The polyurethane resin according to the present invention can be obtained by reacting a long-chain polyol, a chain extender and an organic diisocyanate in a solvent or without a solvent by a known method. The equivalent ratio of isocyanate group to active hydrogen group is obtained. (R) is preferably 0.5 to 1.0. It is particularly preferable that the polyurethane resin thus obtained has hydroxyl groups only at both ends and has a number average molecular weight of 5,000 to 80,000.

In the binder of the present invention, in addition to the components of the present invention,
Other polyurethane resins commonly used as binders for magnetic recording media, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, polyvinyl butyral resins, fibrin resins, polyester resins , Epoxy resin, phenoxy resin, COOM group, SO ₃ M group, P═O (OM ′)
A type in which a hydrophilic polar group such as _two groups (M is hydrogen or an alkali metal, M'is hydrogen, an alkali metal or a hydrocarbon group) is introduced can be used in combination. Further, in the binder of the present invention, an organic polyisocyanate compound can be used as a crosslinking agent for the binder resin. Examples thereof include tolylene diisocyanate, xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate, 4,
4'-diphenylmethane diisocineate, 4,4'-
Diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,
3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,
Aromatic diisocyanates such as 3'-dimethoxydiphenyl-4,4'-diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, aliphatic diisocyanates such as lysine diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, Examples thereof include diisocyanates such as aliphatic diisocyanates such as cyclohexane diisocyanate, and biuret bodies, cyclic trimer bodies, modified uretonimine bodies, polymer bodies, adduct bodies such as trimethylolpropane, of these diisocyanates. Specifically, Coronate L and Coronate 304 manufactured by Nippon Polyurethane Industry Co., Ltd.
1, Coronate HL and the like.

The magnetic powder used in the present invention is γ-
Fe ₂ O ₃ , Co-γ-Fe ₂ O ₃ , Co-FeO · F
Magnetic iron oxide powder such as e ₂ O ₃ , CrO ₂ , hexagonal barium ferrite fine particles, and Fe, Ni, Co, Fe-N
i-Co alloy, Fe-Mn-Zn alloy, etc. Fe, Ni, C
Various ferromagnetic powders such as metal magnetic powders containing o as a main component can be used. A particularly preferred magnetic powder has a surface area (BET) of 30.
It is a needle-shaped iron oxide-based magnetic powder of about 50 m ² / g. In the magnetic recording medium of the present invention, if necessary, carbon fine particles as an antistatic agent, fine particles of a non-polar metal oxide as an abrasive, and higher fatty acid, fatty acid ester, fluidized as a lubricant for reducing the friction coefficient. Paraffin, siloxanes and fluorocarbons may be added, and lecithin or the like may be added as a dispersant. Examples of the material of the support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyimides, polyamide imides, polyphenylene sulfides, etc., which are used in the form of tape, film, sheet depending on the application. .

[0014]

EXAMPLES Next, the present invention will be specifically described with reference to synthetic examples and examples, but the present invention is not limited to these examples. In addition, "part" and "%" in a synthesis example and an Example show a "weight part" and "weight%" unless there is particular notice.

Synthetic Example 1 1000 parts of a long-chain diol A [polyester diol consisting of 1,6-hexanediol and isophthalic acid] having a number average molecular weight of 1000 was placed in a reaction vessel equipped with a thermometer, a stirrer and a condenser. Butanediol 18.0
Part, bis- (2-hydroxyethyl) sulfone 44.2
Parts, cyclohexanone 951 parts and dioctyltin dilaurate 0.2 part as a urethanization catalyst were charged.
After mixing at 0 ° C., 364.7 parts of 4,4′-diphenylmethane diisocyanate was added and reacted at 80 ° C. Since the viscosity increases with time, it was diluted with cyclohexanone and methyl ethyl ketone at appropriate times, and it was confirmed by infrared spectrum that the absorption of the isocyanate group at 2275 cm ^-1 disappeared, and a pale yellow transparent liquid was obtained. This polyurethane resin solution has a solid content of 25.0% and a viscosity of 820 cP / 2.
The number average molecular weight was 28,000 at 5 ° C.

Synthesis Example 2 1000 parts of a long chain diol B [polycarbonate diol consisting of 1,6-hexanediol and diethyl carbonate] having a number average molecular weight of 1000 was placed in a reaction vessel equipped with a thermometer, a stirrer and a condenser. Butanediol (18.0 parts), bis- (4-aminophenyl) sulfone (72.7 parts), cyclohexanone (971 parts) and dioctyltin dilaurate (0.2 parts) as a urethanization catalyst were charged and mixed at 50 ° C. and then 4,4′- 366.1 parts of diphenylmethane diisocyanate was added and reacted at 80 ° C. Since the viscosity increases with time, it was diluted with cyclohexanone and methyl ethyl ketone at appropriate times, and it was confirmed by infrared spectrum that the absorption of the isocyanate group at 2275 cm ^-1 disappeared, and a pale yellow transparent liquid was obtained. This polyurethane resin solution has a solid content of 25.1% and a viscosity of 880c.
It was P / 25 degreeC and the number average molecular weight was 29000.

Synthetic Example 3 A synthetic method similar to Synthetic Example 1 was carried out except that bis- (2-hydroxyethyl) sulfone was not added. Table 1 shows the composition and properties of the synthesized polyurethane resin.

Synthesis Example 4 Synthesis was carried out in the same manner as in Synthesis Example 3 except that the sulfonic group-containing polyester polyol was used in combination with the long chain polyol. Table 1 shows the composition and properties of the synthesized polyurethane resin.

Example 1 Using the polyurethane resin solution obtained in Synthesis Example 1, a composition having the following blending ratio was dispersed in a paint shaker (manufactured by Asada Tekko Co., Ltd.) for 5 hours, and Coronate L (Nippon Polyurethane Industry Co., Ltd.) was used as a curing agent. 15 parts of resin content was added to 100 parts of resin content and mixed for 2 hours. The obtained magnetic coating material was immediately applied onto a polyethylene terephthalate film having a thickness of 15 μm so as to have a dry film thickness of 3 μm, immediately passed through a magnetic field of 2000 gauss for orientation treatment, and further dried at 80 ° C. for 4 minutes and further dried. A magnetic tape was obtained by standing still at 60 ° C. for 24 hours. The glossiness, squareness ratio (Br / Bm), surface dynamic friction coefficient, and scratch resistance of the obtained magnetic tape were evaluated. The measurement results are shown in Table 2. Also,
Similarly, a magnetic coating left standing for 12 hours was applied to the film and subjected to orientation treatment, and the glossiness of the obtained magnetic tape was measured to evaluate the dispersion stability. The results are shown in Table 2.

Compounding composition for magnetic recording medium Magnetic powder (Co-γ-Fe ₂ O ₃ , BET = 33 m ² / g) 100 parts Polyurethane resin (resin content) 20 parts MEK 93 parts Toluene 93 parts Cyclohexanone 93 parts

Example 2, Comparative Examples 1 and 2 The polyurethane resin solutions obtained in Synthesis Examples 2 to 4 were used in place of the polyurethane resin solution used in Example 1, and the glossiness was determined in the same manner as in Example 1, The squareness ratio (Br / Bm), dispersion stability, surface dynamic friction coefficient, and scratch resistance were evaluated.
The results are shown in Table 2.

Example 3 The polyurethane resin solution obtained in Synthesis Example 1 and S-REC A (vinyl chloride-vinyl acetate resin, manufactured by Sekisui Chemical Co., Ltd.)
A magnetic tape was prepared from the composition having the following composition by the same method as in Example 1, and the glossiness and the squareness ratio (Br
/ Bm), dispersion stability, surface dynamic friction coefficient, and scratch resistance. The results are shown in Table 3.

Compounding composition for magnetic recording medium Magnetic powder (Co-Fe ₂ O ₃ Fe ₂ O ₃ , BET = 36 m ² / g) 100 parts Polyurethane resin (resin content) 10 parts SLECK A 10 parts MEK 93 parts Toluene 93 Part cyclohexanone 93 parts Coronate 3041 (resin content) 5 parts Example 4, Comparative Examples 3 and 4 Instead of the polyurethane resin solution used in Example 3, the polyurethane resin solutions obtained in Synthesis Examples 2 to 4 were used. With the same formulation as in Example 3, glossiness, squareness ratio (Br / Bm), dispersion stability, surface dynamic friction coefficient, and scratch resistance were evaluated.
The results are shown in Table 3.

[0024]

[Table 1]

[0025]

[0026]

[Table 2]

[0027]

[Table 3]

Evaluation method of Tables 2 and 3 Glossiness: The magnetic surface of the obtained magnetic tape was measured for reflectance at an incident angle of 45 ° and a reflection angle of 45 ° using a glossmeter. Squareness ratio (Br / Bm): The electromagnetic conversion characteristics of the obtained magnetic tape were measured using a vibrating sample magnetometer VSM-3KA type (manufactured by Toei Industry Co., Ltd.). Surface dynamic friction coefficient: The magnetic surface of the obtained magnetic tape was measured for surface dynamic friction coefficient using a surface property measuring device (manufactured by Shinto Kagaku). Scratch resistance: The magnetic surface of the obtained magnetic tape was scratched 20 times using a surface property measuring device (manufactured by Shinto Kagaku),
The surface state was observed and scratch resistance was evaluated. ○ Magnetic surface is hardly scratched △ Magnetic surface is slightly scratched × Magnetic surface is considerably scratched

[0029]

The magnetic recording medium obtained by the present invention is
It is useful as a video tape, audio tape, computer tape, floppy disk, magnetic card, etc., which requires high recording density because of its excellent electromagnetic conversion characteristics and coating surface characteristics.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a support and a magnetic layer mainly comprising magnetic powder and a binder, wherein the binder component is a long-chain diol, an organic diisocyanate,
A magnetic recording medium comprising a polyurethane resin having hydroxyl groups at both ends, which is obtained from a chain extender having a sulfone bond in the molecule. 2. The magnetic recording medium according to claim 1, wherein the chain extender is bis- (2-hydroxyethyl) sulfone or bis- (4-aminophenyl) sulfone.