JP2000163736A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium excellent in magnetic characteristics and durability. SOLUTION: When a magnetic layer is formed on a nonmagnetic substrate by coating with a magnetic material prepared by dispersing a ferromagnetic powder in a binder to obtain a magnetic recording medium, a polyurethane resin satisfying the formula b>=0.53a [where (a) and (b) are the reduced viscosities of the resin measured under conditions 1 and 2, respectively] is contained as a binder component of the magnetic layer. The measurement conditions 1 comprise phenol/1,1,2,2-tetrachloroethane (60/40) as a measurement solvent, 4 g/l concentration of a measurement solution and 30 deg.C measurement temperature. The measurement conditions 2 comprise toluene/MEK/ cyclohexanone (30/50/20) as a measurement solvent, and 4 g/l concentration of a measurement solution.

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 having excellent dispersibility and filling property and durability.
The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk having excellent wear resistance.

[0002]

2. Description of the Related Art Magnetic tapes, which are general-purpose magnetic recording media,
Floppy disks are made by dispersing needle-like magnetic particles with a major axis of about 1 μm in a binder solution together with additives such as dispersants, lubricants, and antistatic agents to make a magnetic paint, and applying this to a polyethylene terephthalate film. ing.

[0003] The properties required for the binder of the magnetic layer include the dispersibility, dispersion stability, filling property, orientation, and the like of the magnetic particles.
In addition, the binder plays a very important role, such as durability, abrasion resistance, heat resistance, and adhesion to a non-magnetic support of the magnetic layer.

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 / butylate , Epoxy resin or acrylic resin is used.

[0005] Among these resins, polyurethane resins are superior in toughness and abrasion resistance to other resins due to intermolecular hydrogen bonds by urethane bonds, but conventional polyurethane resins have a dispersing property of magnetic powder. And various studies have been made to improve this. For example,
Those using a urethane resin derived from a polyester polyol containing 2,2-dialkyl-1,3-propanediol (JP-A-2-240177), polyurethane resins using a polyhydric alcohol having a branched chain No. 2-177020).

[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 fine metal particles has now become the mainstream instead of the iron oxide-based magnetic powders that have been the mainstream. As the magnetic particles become finer and the coercive force increases, it becomes more difficult to disperse the magnetic particles with a conventional binder, and it is required that the magnetic particles have higher dispersion performance with respect to the binder. JP-A-2-240177, JP-A-2-240177
Although the dispersibility of the binder in 177020 is improved, 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.

In a recent high-density magnetic recording medium, the magnetic layer is formed by a wet coating together with an undercoat layer in which a non-magnetic pigment is dispersed.
It is applied by an on-wet simultaneous two-layer coating method. When a paint is applied by such a coating method, the rheological stability of the paint is extremely important. Long shaft diameter 0.15
When a ferromagnetic metal powder of μm or less is used, it has been difficult for the conventional binder resin to maintain the dispersion stability of the paint after dispersion. Further, as the surface of the magnetic layer becomes smoother, the friction with the magnetic head increases and the relative running speed of the magnetic tape tends to increase, so that the magnetic layer is required to have sufficient durability more than ever.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyurethane resin which stably disperses finely divided ferromagnetic metal powder having a high coercive force and forms a magnetic layer having excellent durability. As a result of the study, the present invention has been reached. That is, the present invention relates to a magnetic recording medium having a magnetic layer formed by applying a magnetic material in which a ferromagnetic powder is dispersed in a binder on a non-magnetic support, as a binder component of the magnetic layer under the following condition 1. The present invention proposes a magnetic recording medium containing a polyurethane resin, wherein the measured reduced viscosity value a and the reduced viscosity value b measured under the condition 2 satisfy the following relational expression. b ≧ 0.53a Measurement condition 1 Measurement solvent: phenol / 1,1,2,2 tetrachloroethane (weight ratio 60/40) Measurement solution concentration: 4 g / L Measurement temperature: 30 ° C. Measurement condition 2 Measurement solvent: toluene / MEK / cyclohexanone (weight ratio 30/50/20) Measurement solution concentration: 4 g / L Measurement temperature: 30 ° C. The ferromagnetic powder is acicular ferromagnetic metal fine particles having a major axis diameter of 0.15 μm or less. Can be.

[0010] The reduced viscosity value represents the size of the polymer molecule in the measurement solvent, and the larger the numerical value, the larger the molecular size. The phenol / 1,1,2,2, -tetrachloroethane (weight ratio 60/40) mixed solution used in the above measurement condition 1 is a mixed solvent having an extremely high dissolving power. In this mixed solvent, various polyurethane resins are used. It is almost uniformly solvated. The reduced viscosity value measured in the mixed solvent hardly reflects the characteristics of the structure and composition of the individual polyurethane resin, and the measured value changes solely with the molecular weight of the polyurethane resin. That is, even if the polyurethane resins having different structures and compositions have the same molecular weight, the measured values obtained under the measurement condition 1 show almost the same values. On the other hand, the mixed solvent (toluene / MEK / cyclohexanone =
The weight ratio of 30/50/20) is a common solvent for magnetic paints. In this mixed solvent, the solvation state of various polyurethane resins differs depending on the structure and composition of the polyurethane. That is, even if the molecular weights of the individual polyurethane resins are the same, the measured values obtained under condition 2 may show different values.

When the measured value of the reduced viscosity a of the various polyurethane resins under the condition 1 and the measured value b under the condition 2 satisfy the following formula, the polyurethane resin is sufficiently solvated in the magnetic paint, The size has been expanded. Therefore, the major axis size is 0.15 μm due to the steric repulsion effect of the polymer molecules.
The dispersion stability of the following ferromagnetic alloy powder is improved, a magnetic layer having a thin and smooth surface property is formed, and the obtained magnetic recording medium exhibits excellent performance. On the other hand, when the measured values a and b do not satisfy the following relational expression, the steric repulsion effect of the polymer molecules is not sufficiently expected, the dispersion stability of the ferromagnetic alloy powder is poor, and an excellent magnetic recording medium cannot be obtained. b ≧ 0.53a

The relationship between a and b is preferably such that b ≧ 0.5
7a, more preferably b ≧ 0.6a, even more preferably b ≧ 0.63a, and particularly preferably b ≧ 0.63a.
≧ 0.65a. Here, a does not exceed b, preferably b ≦ 0.9a, more preferably b ≦ 0.
8a, more preferably b ≦ 0.75a. Also,
a is preferably 0.9 or less. If b exceeds 0.9a, the viscosity of the magnetic paint at the time of application becomes too high, which may make application difficult.

[0013] The above reduced viscosity condition is satisfied and 0.15 μm
Even when using the following magnetic powder, high dispersibility, filling properties,
For example, a polyurethane resin capable of producing a tape having excellent durability and abrasion resistance can be achieved by combining the following resin design concepts. (1) To optimize the urethane bond concentration range. (2) Separate urethane bonding intervals by a certain amount or more. (3) The cohesive force of the urethane binding portion is increased by, for example, introducing an aromatic component. (4) The space between the urethane bonds is a soft component to enhance the solubility.

Particularly preferably, it can be achieved by combining the following specific components, for example. (1) 80% of all acid components as polyester polyol
At least mol% consists of aliphatic and / or alicyclic dibasic acids,
The polyester polyol (A) having a number average molecular weight of 300 to 800 is used. (2) Use aromatic polyisocyanate (B). (3) If necessary, at least one kind of a branched compound (C) having a molecular weight of less than 300 and having two or more functional groups that react with isocyanate is used. (4) The urethane bond concentration of the polyurethane resin is 4000
Does not exceed equivalent / 10 ⁶ g.

The ferromagnetic metal particles used in the present invention include Fe or Co, Ca, Mg, Zn, Mn, Sr, B
There are alloys with a, Ni, Cu and the like. The major axis diameter of these acicular metal powders is preferably 0.1 μm or less, and 0.15 μm or less.
If it exceeds m, it is not suitable for short-wavelength recording, and the recording density cannot be sufficiently improved. More preferably 0.1 μm or less,
More preferably 0.09 μm or less, particularly preferably 0.08 μm or less, most preferably 0.07 μm or less, when using ferromagnetic metal particles of 0.1 μm or less,
The high dispersibility of the resin of the present invention and the fineness of the magnetic powder combine to provide a magnetic recording tape having high density recording and high durability.

The carboxylic acid component of the polyester polyol (A) of the polyurethane resin used in the present invention includes aliphatic dibasic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, dodecynylsuccinic acid and the like. , 2-cyclohexanedicarboxylic acid, 1,3-
Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2-bis (4-carboxycyclohexyl) methane,
Examples include alicyclic dibasic acids such as 2,2 bis (4-carboxycyclohexyl) propane and aliphatic alicyclic dibasic acids such as dimer acid. Of these, adipic acid, dodecyl succinic acid, 1,2-cyclohexanedicarboxylic acid, and dimer acid are particularly preferred. In addition, 20 of all acid components
An aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or orthophthalic acid, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid,
Examples thereof include dicarboxylic acids containing a metal salt of sulfonic acid such as sodium sulfoterephthalic acid. Among these, 5-sodium sulfophthalic acid is particularly preferred.

It is preferable that the polyurethane resin of the present invention contains a hydrophilic group such as a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group from the viewpoint of dispersibility of magnetic components.
The preferred content of the hydrophilic group is 5 to 500 equivalent / 10 ⁶
g, more preferably 50 to 200 equivalent / 10 ⁶ g. If the amount is less than 5 equivalents / 10 ⁶ g, the dispersibility of the magnetic component may be insufficient. If the amount exceeds 500 equivalents / 10 ⁶ g, the viscosity at the time of coating becomes too high, and handling obstacles increase.

The glycol components include ethylene glycol, propylene glycol, 1,3-propanediol,
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2 , 2-dimethyl-1,3-propanediol,
3-methyl-1,5-pentanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate, 2,2-diethyl-1,3-propanediol, etc. Aliphatic glycol, 1,3-bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethyl) cyclohexane,
1,4-bis (hydroxypropyl) cyclohexane, 1,4-
Bis (hydroxymethoxy) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane, 2,2 bis (4-
Hydroxymethoxycyclohexyl) propane, 2,2-bis (4 hydroxyethoxycyclohexyl) propane,
Bis (4-hydroxycyclohexyl) methane, 2,2-bis
(4-hydroxycyclohexyl) propane, 3 (4), 8 (9)-
Alicyclic glycols such as tricyclo [5.2.1.0 2,6] decane dimethanol are exemplified. Especially in these
2,2-dimethyl-1,3-propanediol, 2,2-diethyl-
1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate and 1,6-hexanediol are preferred. 1,4 bis (hydroxymethyl) cyclohexane. Also, trimellitic anhydride, glycerin,
A trifunctional or higher functional compound such as trimethylolpropane or pentaerythritol may be used within a range that does not impair the properties of the polyester resin such as solubility in an organic solvent and application workability.

As the glycol component of the polyester diol other than the above, those containing a metal sulfonic acid salt such as 2-sodium sulfo-1,4-butanediol and 2-sodium sulfo-1,6-hexanediol are exemplified. .

For example, at least 80 mol% of the total acid component of the polyester polyol (A) of the polyurethane resin used in the present invention is composed of an aliphatic and / or alicyclic monomer, and is an aromatic monomer. Is preferably used in a range of 20 mol% or less. When the amount of the aromatic monomer exceeds 20 mol%, the solubility of the polyurethane resin decreases, and the dispersibility of the magnetic powder decreases. Further, the obtained polyurethane resin has a low elongation at break, so that sufficient toughness cannot be obtained.

The average molecular weight calculated from the hydroxyl value of the polyester polyol (A) is preferably in the range of 300 to 800, more preferably in the range of 300 to 600. If it is more than 800, it is difficult to achieve both the effects of the present invention, that is, the dispersibility of the magnetic powder and the excellent properties of the resin, which lead to the improvement of the durability. That is, when the molecular weight of the polyester polyol A is 800 or more, the copolymerization amount of the compound (C) having a molecular weight of less than 300 increases in order to keep the glass transition temperature of the obtained polyurethane resin at a sufficiently high level. Accordingly, the length of the segment chain formed by repeating the compound C and the aromatic polyisocyanate (B) in one molecule of the polyurethane becomes long. The increase in the number of repeating segment chains of the compound (C) and the aromatic polyisocyanate lowers the solubility of the polyurethane resin and deteriorates the dispersibility of the magnetic powder. Similarly, when the polyester polyol (A) having an average molecular weight of 300 or less is used, the solubility of the obtained polyurethane resin decreases, and the dispersibility of the magnetic powder deteriorates.

As the aromatic polyisocyanate (B) of the polyurethane resin used in the present invention, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, m-phenylene diisocyanate, 3,3'-
Dimethoxy-4,4'-biphenylenediisocyanate, 2,6-
Naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate, etc. Can be Of these, 4,4'-
Diphenylmethane diisocyanate is particularly preferred.

The branched compound C having a molecular weight of less than 300 and having two or more functional groups that react with an isocyanate group in one molecule, which is copolymerized as required in the polyurethane resin used in the present invention, includes 1,2- Propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2,2-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, 2,5-dimethyl-3-sodiumsulfo-2,5-hexanediol and the like, and among these, 2,2-dimethyl-
1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate, 2
-N-butyl-2-ethyl-1,3-propanediol,
2,2-Diethyl-1,3-propanediol is particularly preferred.

These branched compounds (C) contribute to improving the solubility of the polyurethane resin, and can be copolymerized at a high ratio in combination with the polyester polyol (A) and the aromatic polyisocyanate (B). is there. An increase in the copolymerization ratio of the compound (C) leads to an increase in the urethane binding group concentration, and makes the urethane resin more tough. That is, a polyurethane resin having both high solubility and tough mechanical properties in a general-purpose solvent can be obtained.
These characteristics as the urethane resin contribute to high magnetic powder dispersing ability as a binder resin for a magnetic tape and improvement in tape durability.

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

The copolymerization amount of these branched compounds (C) is
The polyurethane resin of the present invention has a urethane bonding group concentration of 40.
It is used in a range not exceeding 00 eq / 10 ⁶ g. When the urethane binding group concentration exceeds 4000 eq / 10 ⁶ g, although the mechanical properties as a polyurethane resin can be further improved, the solubility in a general-purpose solvent is reduced, and the polyurethane resin has a high binder resin for a magnetic tape. Magnetic powder dispersion performance cannot be obtained. The urethane binding group concentration is adjusted according to the copolymerization amount of the branched compound (C) and the molecular weight of the polyester polyol (A).

The polyurethane resin used in the present invention has a number average molecular weight of 5,000 to 80000, preferably 1,000.
Use from 0 to 40000. Number average molecular weight of 50
If it is less than 00, the mechanical strength is insufficient and the running durability is poor.
When the number average molecular weight exceeds 80,000, the solution viscosity increases, and the workability and the dispersibility of magnetic powder, abrasive, carbon black and the like deteriorate. The reaction may be performed in either a method in which the raw materials are melted or a method in which the raw materials are dissolved in a solution.

As a reaction catalyst, stannous octylate, dibutyltin dilaurate, triethylamine and the like may be used. Further, an ultraviolet absorber, a hydrolysis inhibitor, an antioxidant, and the like may be added before, during, or after the production of the polyurethane resin.

In the present invention, in addition to the polyurethane resin used in the present invention, other resins may be added for the purpose of controlling flexibility, improving cold resistance and improving durability, and / or mixing with the polyurethane resin. It is desirable to mix compounds that react and crosslink. Other resins include vinyl chloride resins, polyester resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile-butadiene copolymers, and the like.

On the other hand, compounds that crosslink with the polyurethane resin include polyisocyanate compounds, epoxy resins,
There are melamine resin, urea resin and the like, and among them, polyisocyanate compound is particularly preferable.

In the magnetic recording medium of the present invention, a plasticizer such as dibutyl phthalate and triphenyl phosphate, dioctyl sulfo sodium succinate, t-
Butyl phenol / polyethylene ether, ethyl naphthalene / sodium sulfonate, dilauryl succinate,
Lubricants such as zinc stearate, soybean oil lecithin and silicone oil and various antistatic agents can also be added.

The inorganic fine particles used in the back coat layer of the magnetic recording medium of the present invention include inorganic lubricants such as calcium carbonate, magnesium carbonate, aluminum oxide, chromium dioxide, silicon dioxide and titanium oxide, and carbon black.
And antistatic agents such as tin oxide.

[0033]

The polyurethane resin of the present invention is sufficiently solvated in a magnetic coating material and has an expanded molecular size. Therefore, the dispersion stability of the ferromagnetic alloy powder having a long axis of 0.15 μm or less is improved by the steric repulsion effect of the molecule, and an excellent magnetic recording medium can be obtained.

[0034]

The present invention will be specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”. Tables 1 and 2 show compositions and other characteristics of polyester polyols and polyurethane resins obtained in the following synthetic examples of polyester polyol and polyurethane resin and comparative synthetic examples. The abbreviations in the table are as follows.

TPA: terephthalic acid IPA: isophthalic acid AA: adipic acid DDSA: dodecinylsuccinic acid 4MHOPA: 4-methyl-1,2-cyclohexanedicarboxylic acid DA: dimer acid SA: sebacic acid SIPA: 5-sulfoisophthalic acid NPG: 2 2,2-dimethyl-1,3-propanediol HD: 1,6-hexanediol PG: 1,2-propylene glycol 2MG: 2-methyl-1,3-propanediol ND: 1,9-nonanediol DMH: 2 -Butyl-2-ethyl 1,3-propanediol HPN: 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-
Dimethyl-3-hydroxypropanate CHDM: 1,4-bis (hydroxymethyl) cyclohexane EG: ethylene glycol MDI: 4,4'-diphenylmethane diisocyanate

The hydroxyl value of the polyester polyol (A) was determined as follows. Polyester polyol: 5
0 g was dissolved in a mixed solvent of toluene: 60 g and MEK: 60 g, MDI: 70 g was added, and the mixture was reacted at 80 ° C. for 2 hours. Then, the concentration of the residual isocyanate group in the reaction solution was quantified by titration to obtain a hydroxyl value. The average molecular weight was calculated from the obtained hydroxyl value by the following calculation. Polyester polyol average molecular weight = 1 × 106 × 2 /
Hydroxyl value (eq / 10 ⁶ g)

The number average molecular weight of the polyurethane resin was determined by gel permeation chromatography using tetrahydrofuran as a solvent and a value in terms of standard polystyrene was measured. As for the glass transition temperature (Tg), the temperature at the refraction point of the storage elastic modulus (E ′) was defined as Tg from the measurement results of the temperature dependence of dynamic viscoelasticity. Further, the yield strength, breaking strength, and breaking elongation of the film at 25 ° C. and 70% humidity were measured. 1.5cm ×
Using a 3.0 cm, 30 μm thick sample test piece,
cm / min. The measurement was performed at a pulling speed of.

The gloss of the magnetic layer of the magnetic tape was measured at 45 ° gloss. For the magnetic layer squareness ratio, use a vibration measurement type magnetometer,
The squareness ratio in the vertical direction was measured. The magnetic layer density was determined by measuring the weight and volume of the magnetic layer. The magnetic layer abrasion resistance was measured by applying a commercially available S-VHS VCR to the magnetic layer and observing the magnetic layer after 100 times of running at a temperature of 40 ° C.
The degree was evaluated on the following six levels. 6: Almost no scratching 5: Slightly scratching 4: Slightly scratching 3: Scratching prominent, not reaching PET film 2: Scratching prominent, PET film surface slightly visible 1: Scratching prominent, Many PET film faces are visible

Synthesis Example 1 of Polyester Polyol (A) 555 parts of adipic acid, 53 parts of 5-sodiumsulfoisophthalic acid, and 2,2-dimethyl-1,3-butylamine were placed in a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser. Hydroxypropane 79
0 parts, and tetrabutoxy titanate as a catalyst was added.
Three parts were added. The reaction was carried out at 220 DEG C. for about 8 hours under a stream of N2, and the generated water was distilled off. Then, the pressure was reduced at the same temperature for about 5 minutes to complete the reaction. The hydroxyl value of the obtained polyester polyol (a) was 4850 eq / 10 ⁶ g, and the acid value was 2.5 eq / 10 ⁶ g.

Synthesis Example 2 of Polyester Polyol (A) In the same reaction vessel as in Synthesis Example 1, 292 parts of adipic acid, 426 parts of dodecenylsuccinic anhydride, 106 parts of 5-sodium sulfoisophthalic acid, and 2,2-dimethyl-3- 1632 parts of hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate were charged, and 0.3 part of tetrabutoxytitanate was added as a catalyst. The reaction was carried out at 235 ° C. for about 10 hours under a stream of N ₂ , and the generated water was distilled off. The obtained polyester polyol (b) had a hydroxyl value of 3,400 eq / 10 ⁶ g and an acid value of 5.5 eq / 10 ⁶ g.

Synthesis Example 3 of Polyester Polyol (A)
Table 8 shows the composition, hydroxyl value, average molecular weight calculated from the hydroxyl value, and acid value of the polyester polyols (c) to (h) synthesized by the same method.

Comparative Synthesis of Polyester Polyol (A)
Example 1 A similar reaction vessel as in Synthesis Example 1 was charged with 555 parts of adipic acid and 5-natto.
53 parts of lithium sulfoisophthalic acid and 2,2-dimethyl 1,3-
312 parts of droxypropane, 354 parts of 1,6-hexanediol
And 0.3 parts of tetrabutoxytitanate as a catalyst
Was added. N _Two Reaction at 220 ° C under air flow for about 6 hours,
The generated water was distilled off. Then depressurized at the same temperature for 20 minutes
Then, the polymerization reaction was completed. Polyester polio obtained
(I) has a hydroxyl value of 1140 eq / 10⁶ g, acid value
Was 2.5 eq / 106 g.

Comparative Synthesis Example 2 of Polyester Polyol (A) 555 parts of adipic acid, 53 parts of 5-sodium sulfoisophthalic acid and 720 parts of 2-methyl-1,3-hydroxypropane were charged into the same reaction vessel as in Synthesis Example 1. And 0.3 parts of tetrabutoxytitanate. The reaction was carried out at 220 ° C. for about 8 hours under a stream of N ₂ , and the generated water was distilled off to terminate the polymerization reaction. The hydroxyl value of the obtained polyester polyol (j) is 72.
10 eq / 10 ⁶ g and the acid value was 2.0 eq / 10 ⁶ g.

Comparative Synthesis Example 3 of Polyester Polyol (A) In a reaction vessel similar to that of Synthesis Example 1, 298 parts of terephthalic acid, 409 parts of adipic acid, 53 parts of 5-sodium sulfoisophthalic acid and 2,2-dimethyl 1,3- 291 parts of hydroxypropane and 322 parts of ethylene glycol were added, and 0.3 part of tetrabutoxytitanate was added. The reaction was carried out at 250 ° C. for about 5 hours under a stream of N ₂ , and the generated water was distilled off. Then, the pressure was reduced at the same temperature for 5 minutes to terminate the polymerization reaction. The hydroxyl value of the obtained polyester polyol (k) was 4970 eq / 10 ⁶ g,
The acid value was 5.5 eq / 10 ⁶ g.

Comparative Synthesis Example 4 of Polyester Polyol (A) In a reaction vessel similar to that of Synthesis Example 1, 332 parts of terephthalic acid, 299 parts of isophthalic acid, 53 parts of 5-sodium sulfoisophthalic acid and 2,2-dimethyl 1,3- 291 parts of hydroxypropane and 322 parts of ethylene glycol were charged, and 0.3 part of tetrabutoxytitanate was added. The reaction was carried out at 250 ° C. for about 5 hours under a stream of N ₂ , and the generated water was distilled off. Then, the pressure was reduced at the same temperature for 5 minutes to terminate the polymerization reaction. The hydroxyl value of the obtained polyester polyol (l) is 4760 eq / 10 ⁶
g and the acid value were 2.5 eq / 10 ⁶ g. Table 1 shows the composition, hydroxyl value and acid value of the polyester polyol obtained in Comparative Synthesis Example.

[Table 1]

Synthesis Example 1 of Polyurethane Resin Polyester polyol (a): 100 parts and MEK: 8
The mixture was dissolved in 0 parts and toluene: 80 parts, MDI: 60 parts was added, dibutyltin dilaurate: 0.05 part was added as a catalyst, and the mixture was reacted at 80 ° C. for 5 hours. Then MEK:
The solution was diluted with 180 parts and toluene: 32 parts to obtain a polyurethane resin. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

Synthetic Examples 2 to 4 of Polyurethane Resin Polyurethane resin was synthesized in the same manner as in Synthetic Example 1, and the resin composition, molecular weight and mechanical properties are shown in Table 2.

Synthesis Example 5 of Polyurethane Resin Polyester polyol (a): 100 parts and MEK: 8
0 parts and toluene: 80 parts, MDI: 110 parts were added, and the mixture was reacted at 80 ° C. for 1.5 hours. Then ME
The solution was diluted with 312 parts of K and 88 parts of toluene, and 2,-
30 parts of butyl-2-ethyl-1,3-hydroxypropane were added, 0.1 part of dibutyltin dilaurate was added as a catalyst, and the mixture was reacted at the same temperature for 5 hours to obtain a polyurethane resin. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

Synthesis Examples 6 to 9 of Polyurethane Resin Polyurethane resin was prepared in the same manner as in Synthesis Example 5.
Was synthesized, and the resin composition, molecular weight, and mechanical properties are shown in Table 2.

Comparative Synthesis Example 1 of Polyurethane Resin Polyester polyol (i): 100 parts and MEK: 8
0 parts and toluene: 80 parts, MDI: 29 parts were added, and the mixture was reacted at 80 ° C. for 1.5 hours. Then ME
K: Dilute the solution with 147 parts and toluene: 17 parts to give 2,-
Butyl-2-ethyl-1,3-hydroxypropane: 10 parts was added, dibutyltin dilaurate: 0.3 part was added, and the mixture was reacted at the same temperature for 5 hours to obtain a polyurethane resin 10. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

Comparative Synthesis Example 2 of Polyurethane Resin Polyester polyol (i): 100 parts and MEK: 8
0 part and toluene: 80 parts, MDI: 170 parts was added, and the mixture was reacted at 80 ° C. for 1.5 hours. Then ME
The solution was diluted with 280 parts of K, 280 parts of toluene, and 550 parts of cyclohexanone, and the solution was diluted with 2, -butyl-2-ethyl-.
1,3-Hydroxypropane: 100 parts was added, dibutyltin dilaurate: 0.17 parts was added, and the mixture was reacted at the same temperature for 5 hours to obtain a polyurethane resin 11. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

Comparative Synthesis Example 3 of Polyurethane Resin Polyester polyol (i): 100 parts and MEK: 8
0 parts and toluene: 80 parts, MDI: 320 parts were added, and the mixture was reacted at 80 ° C. for 1.5 hours. Then ME
The solution was diluted with 385 parts of K: 385 parts, 385 parts of toluene, and 930 parts of cyclohexanone.
1,3-Hydroxypropane: 200 parts was added, dibutyltin dilaurate: 0.3 part was added, and reacted at the same temperature for 5 hours to obtain a polyurethane resin 12. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

Comparative Synthesis Example 4 of Polyurethane Resin Polyester polyol (j): 100 parts and MEK: 8
0 parts and toluene: 80 parts, MDI: 124 parts was added, and reacted at 80 ° C. for 1.5 hours. Then ME
The solution was diluted with 100 parts of K, 100 parts of toluene and 360 parts of cyclohexanone, 15 parts of 2,2-dimethyl-1,3-hydroxypropane was added, and 0.1 part of dibutyltin dilaurate was added. The reaction was carried out for 5 hours to obtain a polyurethane resin 13. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

Comparative Synthesis Example 5 of Polyurethane Resin Polyester polyol (k): 100 parts and MEK: 8
0 parts and toluene: 80 parts, MDI: 90 parts was added, and the mixture was reacted at 80 ° C. for 1.5 hours. Then ME
K: 77 parts, toluene: 77 parts, cyclohexanone: 3
The solution was diluted with 14 parts, 2,2-dimethyl-3-hydroxypropyl-2,2'-dimethyl-3-hydroxypropanate: 25 parts was added, and dibutyltin dilaurate: 0.09.
And react for 5 hours at the same temperature.
I got 14. Table 2 shows the molecular weight and mechanical properties of polyurethane resin.
It was shown to.

Comparative Synthesis Example 6 of Polyurethane Resin Polyester polyol (l): 100 parts and MEK: 8
0 parts and toluene: 80 parts, and MDI: 89 parts were added and reacted at 80 ° C. for 1.5 hours. Then ME
K: 77 parts, toluene: 77 parts, cyclohexanone: 3
The solution was diluted with 14 parts, 2,2-butyl-2-ethyl-1,3-hydroxypropane: 20 parts was added, dibutyltin dilaurate: 0.09 part was added, and the mixture was allowed to react at the same temperature for 5 hours. Obtained. Table 2 shows the molecular weight and mechanical properties of the polyurethane resin.

[Table 2]

Measurement of Reduced Viscosity of Polyurethane Resin A Ubbelohde type viscosity tube was used to measure under the measurement conditions 1 and 2. The reduced viscosity was determined by the following calculated value. Reduced viscosity (dl / g) = ((t1 / t2) -1) / 0.
4

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 diameter was 0%). .2 μm): 5 parts, Coronate L of an isocyanate compound as a curing agent (Nippon Polyurethane Industry Co., Ltd.)
): 6 parts were added, and the dispersion was further continued for 1 hour to obtain a magnetic paint. This is placed on a polyethylene terephthalate film having a thickness of 12 μm so that the thickness after drying becomes 4 μm.
The coating was performed while applying a magnetic field of 00 Gauss. 50 ° C, 48
After time aging, the tape was slit to a width of 1/2 inch to obtain a magnetic tape. Table 3 shows the properties of the obtained magnetic tape.

[Table 3]

30% solution of polyurethane resin 50 parts 30% solution of vinyl chloride copolymer * 50 parts Metal powder 120 parts (major axis length 0.08 μm, BET 58 m2 / g; coercive force (Hc) 1600 Oe) Alumina powder (average 5 parts Cyclohexanone 100 parts MEK 50 parts Toluene 50 parts * MR110 manufactured by Zeon Corporation is dissolved in a mixed solvent of MEK / toluene = 50/50 so as to have a solid content concentration of 30%. Using.

Examples 2 to 11 Using the binders shown in Table 3, magnetic tapes were obtained in the same manner as in Example 1. Table 3 shows the characteristics of each magnetic tape.

Comparative Examples 1 to 5 Magnetic tapes were obtained in the same manner as in Example 1 using the binders shown in Table 3. Table 3 shows the characteristics of each magnetic tape.

[0061]

The polyurethane resin of the present invention is excellent in dispersion stability of magnetic powder and mechanical properties of the resin. As a result, by using the polyurethane resin of the present invention, a magnetic material having both excellent magnetic properties and durability can be obtained. Recording media can be supplied.

Claims (2)

[Claims] In a magnetic recording medium having a magnetic layer formed by applying a magnetic material in which a ferromagnetic powder is dispersed in a binder on a non-magnetic support, the binder component of the magnetic layer is measured under the following condition 1. A magnetic recording medium containing a polyurethane resin, wherein the relationship between the a value and the b value satisfies the following relational expression, where a is the reduced viscosity value measured, and b is the reduced viscosity value measured under condition 2. b ≧ 0.53a Measurement condition 1 Measurement solvent: phenol / 1,1,2,2 tetrachloroethane (weight ratio 60/40) Measurement solution concentration: 4 g / L Measurement temperature: 30 ° C. Measurement condition 2 Measurement solvent: toluene / MEK / cyclohexanone (weight ratio 30/50/20) Measurement solution concentration: 4 g / L Measurement temperature: 30 ° C 2. A magnetic recording medium, wherein the ferromagnetic powder according to claim 1 is acicular ferromagnetic metal fine particles having a major axis diameter of 0.15 μm or less.