JP2001131258A - Thermoplastic polyurethane resin for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid polyurethane resin having a high glass transition temperature and high dispersing performances for magnetic particles. SOLUTION: This thermoplastic polyurethane resin for a magnetic recording medium is obtained by a reaction of starting materials in a molten state and has a glass transition temperature of at least 80 deg.C and a urethane bond group concentration of less than 3,000 equivalents/ton.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic polyurethane resin for a magnetic recording medium, and more particularly, as a binder for a magnetic recording medium such as a magnetic tape and a magnetic disk.
The present invention relates to a thermoplastic polyurethane resin exhibiting excellent durability, abrasion resistance, heat resistance, and excellent dispersibility and filling properties.

[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 1 μm or less together with additives such as dispersants, lubricants and antistatic agents in a binder solution to form a magnetic paint, and applying this to a polyethylene terephthalate film. Have been.

[0003] The properties required for the binder of the magnetic layer include the dispersibility of magnetic particles, the filling property, the orientation, the durability of the magnetic layer, the abrasion resistance, the heat resistance, the adhesion to the non-magnetic support and the like. 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 / butylate , Epoxy resin or acrylic resin is used.

[0005] Among these resins, polyurethane resins are superior in toughness and wear resistance to other resins due to intermolecular hydrogen bonding by urethane bonds. It is known that it is effective to introduce a metal sulfonate group into polyurethane molecules in order to improve the dispersion performance of magnetic powder. (JP-A-54-159603)

In recent years, there has been a strong demand for lowering the cost of raw materials for magnetic tapes and magnetic disks for the purpose of reducing the manufacturing cost of general-purpose video tapes or general-purpose floppy disks. Against this background, the binder resin, which is one raw material component, is shifting from the conventional solution type to the solid type, which is cheaper in production cost and transportation cost, etc.
Nos. 053 and 61-231050, Tokuhei 3
No. 13648 is proposed. Furthermore, the magnetic layer has been made thinner to further reduce costs and improve performance, and it has become necessary to increase the amount of carbon black to lower the light transmittance. Problems such as increase have occurred.

[0007]

The solid type thermoplastic polyurethane resin is obtained by supplying the raw material components to the extruder while maintaining a constant flow rate in a molten state, and reacting them in the molten state. If the melt viscosity of the raw material components is high, it is difficult to control the flow rate, and a stable quality polyurethane resin cannot be obtained. A polyester diol mainly composed of an aromatic dibasic acid is a very useful raw material for designing a binder resin having a high glass transition temperature, which is indispensable for imparting durability to a magnetic recording medium. However, it has a high melt viscosity and is difficult to employ as a raw material component of solid type polyurethane. Therefore, conventionally, when designing a solid type polyurethane resin having a high glass transition temperature, a measure is taken to increase the urethane bonding group concentration with an aromatic diisocyanate compound using a polyester diol mainly composed of an aliphatic dibasic acid. I was

However, when the urethane group bond concentration is increased, the solubility of the obtained polyurethane resin in a general-purpose solvent decreases, and when it is used as a binder for a magnetic recording medium, the dispersibility of magnetic particles deteriorates. there were. Therefore, a solid type polyurethane resin having a high glass transition temperature and high dispersibility for magnetic particles has been demanded.

[0009]

Means for Solving the Problems As a result of intensive studies on a polyurethane resin to achieve the object of the present invention, the present invention has been reached. That is, the present invention relates to a thermoplastic polyurethane resin obtained by reacting raw material components in a molten state, wherein the thermoplastic polyurethane resin has a glass transition temperature of 80 ° C. or more and a urethane binding group concentration of 3000 equivalents / ton. It is intended to provide a thermoplastic polyurethane resin for magnetic recording media, wherein

Conventionally, an aromatic polyester diol having a specific composition having a low melt viscosity is adopted as a raw material component, and further mixed with a low molecular weight diol component having a molecular weight of 300 or less in a molten state and supplied to an extruder. This makes it possible to supply an aromatic polyester diol, which was considered difficult, to an extruder stably while maintaining a constant flow rate.

That is, the polyester diol used for the thermoplastic polyurethane resin is, for example, a glycol component having 10 to 50 mol% of 1,6-hexanediol, a branched diol having a side chain alkyl group and / or an alicyclic ring. It is composed of an aromatic dibasic acid, and is composed of an aromatic dibasic acid having an acid component of 80 mol% or more.

The acid component of the polyester diol used in the present invention has a naphthalene skeleton such as 1,5-naphthalic acid and 2,6-naphthalic acid, as well as terephthalic acid,
Hydrogenated compounds of aromatic dibasic acids such as isophthalic acid, orthophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylethercarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and phthalic anhydride Aliphatic dibasic acids such as alicyclic dibasic acids, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and the like can be mentioned. Of these, isophthalic acid and orthophthalic acid are preferable.

The glycol component of the polyester diol is a straight-chain aliphatic diol having 5 to 12 carbon atoms, preferably 1,6-hexanediol. Other glycols are 1,3-propanediol, 1,2-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, branched glycols such as 2,2-diethyl-1,3-propanediol, 1,4-bis (hydroxymethyl) cyclohexane, hydrogenated Examples include alicyclic glycols such as bisphenol A or its ethylene oxide adduct and propylene oxide adduct. 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. When 1,6-hexanediol is copolymerized in an amount of 10 mol% or more, it has a remarkable effect on lowering the melt viscosity. However, when the copolymerization amount exceeds 50 mol%, when used as a binder for a magnetic recording medium, the dispersibility of the magnetic powder when a high concentration of carbon black is blended decreases. On the other hand, if the copolymerization amount exceeds 50 mol%, the glass transition point temperature is remarkably lowered, and it is impossible to obtain the desired binder resin for a magnetic recording medium having a high Tg and a high dispersibility.

The branched glycol improves the solubility of the resin, and contributes to the improvement of the magnetic powder dispersion performance as a binder resin for a magnetic recording medium.

Further, the alicyclic glycol has an effect of improving the glass transition temperature of the resin.

The dicarboxylic acid component and glycol component other than those described above include 5-sodium sulfoisophthalic acid,
Those containing metal sulfonic acid salts such as potassium sulfoisophthalic acid, sodium sulfoterephthalic acid, 2-sodium sulfo-1,4-butanediol, 2,5-dimethyl-3-sodium-2,5-hexanediol; No. Sulfonate metal bases have the effect of significantly improving the dispersibility of inorganic particles such as magnetic powders, abrasives and carbon black.

The low molecular weight diol having a molecular weight of 300 or less which is blended in the molten state for the purpose of lowering the melt viscosity of the polyester diol includes ethylene glycol,
1,3-propylene glycol, 1,4-butanediol, 1,6-
Hexanediol, cyclohexanedimethanol, xylylene glycol, diethylene glycol, triethylene glycol, linear glycols such as ethylene oxide adduct of bisphenol A, 1,2-propylene glycol, neopentyl glycol, 1,2-butanediol,
3-butanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propylene glycol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2 Branched glycols such as'-dimethyl-3'-hydroxypropanate and bisphenol A propylene oxide adduct, N-
Examples thereof include amino alcohols such as methylethanolamine, monoethanolamine, and diethanolamine, and polyols such as trimethylolpropane, glycerin, pentaerythritol, and dipentaerythritol. Of these, 1,2-propylene glycol, 2,2,4-trimethyl-
1,3-pentanediol and 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3′-hydroxypropanate are preferred.

The molecular weight of the polyester diol used in the polyurethane resin of the present invention is preferably 2,000 or less, more preferably 1,000 or less. Molecular weight 2
If it exceeds 000, the melt viscosity of the polyester diol becomes high, and even if a low molecular weight diol component having a molecular weight of 300 or less is melt-mixed, it is still difficult to stably supply the extruder.

The low molecular weight diol used in the polyurethane resin of the present invention preferably has a molecular weight of 300 or less. 300
When the ratio exceeds the above, an effect of sufficiently lowering the melt viscosity of the mixture when mixed with the polyester diol cannot be obtained. Further, the low molecular weight diol having a molecular weight of 300 or less is not limited to one kind, and may be 2
Mixtures of more than one species are also effective.

The acid component of the polyester diol is at least 80 mol% aromatic dibasic acid. If the aromatic dibasic acid content is less than 80 mol%, the glass transition temperature of the polyurethane resin produced is lowered, and when used as a binder for a magnetic recording medium, sufficient durability cannot be imparted to the recording medium. At that time, by increasing the urethane binding group concentration, it is possible to keep the glass transition temperature of the obtained polyurethane resin high, but the solubility in general-purpose solvents is deteriorated, and it is important as a binder for magnetic recording media. Magnetic powder dispersion performance, which is an excellent performance, is reduced.

The diisocyanate compound used in the production of the polyurethane resin of 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'-biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3 '
-Dimethyl-4,4'-biphenylenediisocyanate, 4,4'-
Diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-
Examples thereof include diisocyanate methylcyclohexane, 4,4'-diisocyanatecyclohexane, 4,4'-diisocyanatocyclohexylmethane, and isophorone diisocyanate.

The polyurethane resin of the present invention preferably has a molecular weight of 5,000 to 80000, more preferably 100
00 to 40000. When 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 dispersibility of magnetic powder, abrasive, carbon black and the like deteriorate.

As a reaction catalyst, stannous octoate, 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.

For the polyurethane resin of the present invention, a method based on melt polymerization is desirable from the recent situation where low cost of general-purpose magnetic tape raw materials is required.

When the polyurethane resin of the present invention is used as a binder resin for a magnetic recording medium, another resin may be added for the purpose of controlling flexibility, improving cold resistance and improving durability, and / or Alternatively, it is desirable to mix a compound that reacts with and crosslinks with the polyurethane resin. Other resins include vinyl chloride resins, polyester resins, polyurethane resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, and the like. On the other hand, examples of the compound that crosslinks with the polyurethane resin include a polyisocyanate compound, an epoxy resin, a melamine resin, and a urea resin.
In particular, among these, a polyisocyanate compound is preferable.

The magnetic particles used together with the polyurethane resin of the present invention include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Cr
O ₂ , γ-Fe ₂ O ₃ or Fe ₃ O ₄ coated with cobalt,
Barium ferrite and Fe-Co, Fe-Co-Ni
Ferromagnetic alloy powder, pure iron and the like.

Further, if necessary, a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctyl sulfo sodium succinate, t-butyl phenol / polyethylene ether, ethyl naphthalene / sodium sulfonate, dilauryl succinate, zinc stearate, A lubricant such as soybean oil lecithin and silicone oil and various antistatic agents can also be added.

(Function) An aromatic polyester diol which has been conventionally considered to be unsuitable as a raw material for a solid type polyurethane obtained by a melt reaction due to a high melt viscosity, such as 1,6-hexanediol as a glycol component is used.
The melt viscosity is reduced by blending 0 mol% or more and 50 mol% or less, and the melt viscosity is significantly reduced by melt blending with a low molecular weight diol having a molecular weight of 300 or less, and supplied to an extruder as a raw material of a solid type polyurethane resin. It was possible to use it. The obtained polyurethane resin of the present invention is mainly composed of an aromatic polyester polyol component, and has both a high glass transition temperature and good solubility in general-purpose solvents such as toluene, MEK, and cyclohexanone. Also, since the melt viscosity of the polyester polyol was low, it was quickly and uniformly mixed with other raw materials, and the supply to the extruder was stable, so the molecular weight distribution was narrow, and as a result, it was used as a binder for magnetic recording media. In this case, good dispersibility of the magnetic particles and carbon black and excellent durability of the magnetic recording medium are exhibited.

[0029]

The present invention will be specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”. Abbreviations in the table and in the text are as follows. OPA: orthophthalic acid IPA: isophthalic acid DSN: dimethyl-5-sodium sulfoisophthalic acid AA: adipic acid NPG: 2,2-dimethyl-1,3-propanediol HPN: 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-Dimethyl-3'-hydroxypropanate CHDM: 1,4-bis (hydroxymethyl) cyclohexane HD: 1,6-hexanediol BD: 1,4-butanediol PG: 1,2-propylene glycol MDI : 4,4'-diphenylmethane diisocyanate

The number average molecular weight of the polyurethane resin is determined by gel permeation chromatography using tetrahydrofuran as a solvent.
(Model: 150C manufactured by Waters), the value in terms of standard polystyrene was measured. The glass transition temperature was determined as Tg at the peak point of the loss elastic modulus (E ″) from the measurement results of the temperature dependence of dynamic viscoelasticity.
Frequency 110 by T-Leospectler DVE-AV
Hz, amplitude 10.0μm, temperature rise condition 4 ℃ / min.
The sample piece was cut into a size of 15 mm × 4 mm and a thickness of 25 μm.

The gloss of the magnetic layer of the magnetic tape was measured at 60 ° gloss. The squareness ratio of the magnetic layer was measured by using a vibrating sample magnetometer (MODEL BHV-50 manufactured by Riken Denshi Co., Ltd.) and the squareness ratio in the direction perpendicular to the coating direction. The wear resistance of the magnetic layer was measured using a commercially available S-VHS VCR at a running temperature of 40.
Observation of scratches on the magnetic layer after 100 times running at 100 ° C. was performed, and the degree was evaluated by the following six grades. 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 Thermoplastic Polyurethane Among the following raw materials, a polyester diol and a low molecular weight diol were melt-mixed and then injected into a twin-screw extruder to react with an organic polyisocyanate. The polyurethane in the molten state was taken out from the nozzle into a strand, cooled, and cut to obtain a solid polyurethane resin in the form of a pellet. Table 1 shows the properties of the obtained resin.

(Raw materials component) Polyester diol ・ Composition (molar ratio) Acid component: isophthalic acid 44 orthophthalic acid 54 5-sodium sulfophthalic acid 2 glycol component: neopentyl glycol 40 1,4-cyclohexane dimethanol 20 1,6- Hexanediol 40 ・ Hydroxyl value (KOHmg / g): 160 ・ Acid value (KOHmg / g): 0.50 Low molecular weight diol ・ 2,2-dimethyl-3-human-dioxyfluoro-2 ′, 2′-dimethyl-3 ′ -Hydroxyfluorocarbonate polyester thiol / low molecular weight diol mixture ratio: 100/25 (weight ratio) Polyester diol / low molecular weight diol mixture melt viscosity (ps, 90 ° C): 6 organic polyisocyanate • 4,4'-diphenylmethane diisocyanate Reaction ratio Isocyanate equivalent / total hydroxyl equivalent: 0.95 (reaction conditions) ・ Extrusion Machine reaction temperature: 170 ° C setting ・ Twin screw rotation speed: 260 rpm

Synthesis Example 2 of Thermoplastic Polyurethane The polyester diol and the low molecular weight diol in the following raw material components were melt-mixed, injected into a twin-screw extruder, and reacted with an organic polyisocyanate. The polyurethane in the molten state was taken out from the nozzle into a strand, cooled, and cut to obtain a solid polyurethane resin in the form of a pellet. Table 1 shows the properties of the obtained resin.

(Raw materials component) Polyester diol ・ Composition (molar ratio) Acid component: orthophthalic acid 96 5-sodium sulfophthalic acid 4 Polychol component: neopentyl glycol 60 1,4-cyclohexanedimethanol 20 1,6-hexanediol 20・ Hydroxy group value (KOHmg / g): 186 ・ Acid value (KOHmg / g): 0.39 Low molecular weight diol ・ 2,2-Dimethyl-3-human-peroxyfluoro-2 ′, 2′-Dimethyl-3′-Horoxy-fluoro Polyester diol / low molecular weight diol mixture ratio: 100/20 (weight ratio) Polyester diol / low molecular weight diol mixture Melt viscosity (ps, 90 ° C): 4 Organic polyisocyanate ・ 4,4'-Diphenylmethane diisocyanate Reaction ratio Isocyanate Equivalent / total hydroxyl equivalent: 0.95 (reaction conditions)-Extruder reaction temperature: 170 ° C setting-Twin screw rotation speed: 260 rpm

Comparative Synthesis Example 1 of Thermoplastic Polyurethane The aromatic dibasic acid in the acid component of the polyester diol was 80%.
The following examples were given as examples of less than mol%. Polyester diol and low molecular weight diol do not melt and mix,
Each was injected into the extruder. The obtained polyurethane resin in a molten state was taken out in the form of a strand as in Synthesis Example 1, cooled, and cut into a pellet. Table 1 shows the properties of the obtained resin.

(Raw materials component) Polyester diol • Composition (molar ratio) Acid component: orthophthalic acid 38 isophthalic acid 30 acid diacid 30 5-sodium sulfophthalic acid 2 glycol component: neopentyl glycol 55 1,6-hexanediol 45 • hydroxyl group Value (KOHmg / g): 138 ・ Acid value (KOHmg / g): 0.36 ・ Polyesterdiol A melt viscosity (ps, 90 ° C.): 7poise Low molecular weight diol ・ 1,4-Phenyldiol polyesterdiol / Low molecular weight diol Ratio: 100/4 (weight ratio) Organic polyisocyanate ・ 4,4'-diphenylmethanediisocyanate Reaction ratio Isocyanate equivalent / total hydroxyl equivalent: 0.95 (reaction conditions) ・ Extruder reaction temperature: 170 ° C setting ・ Two axes Screw rotation speed: 260rpm

Comparative Synthesis Example 2 of Thermoplastic Polyurethane An example in which 1,6-hexanediol exceeds 50 mol% in the glycol component of the polyester diol is shown below. The polyester diol and the low molecular diol B were melt-mixed and injected into a twin-screw extruder to react with the organic polyisocyanate. The polyurethane in the molten state was taken out from the nozzle into a strand, cooled, and cut to obtain a solid polyurethane resin in the form of a pellet. Table 1 shows the properties of the obtained resin. (Raw ingredients) Polyester diol • Composition (molar ratio) Acid component: orthophthalic acid 38 Isophthalic acid 60 5-sodium sulfophthalic acid 2 Polychol component: Neopentyl glycol 30 1,6-hexanediol 70 • Hydroxyl value (KOHmg / g) : 200 ・ Acid value (KOHmg / g) ： 0.41 Low molecular weight diol ・ 2,2-Dimethyl-3-human peroxyfluoro-2 ′, 2′-Dimethyl-3′-Hydroxyfluorophosphate polyester diol / Low molecular weight diol ratio : 100/20 (weight ratio) Polyester diol / low molecular weight diol mixture melt viscosity (ps, 90 ° C): 5poise Organic polyisocyanate • 4,4'-diphenylmethane methane isocyanate Reaction ratio Isocyanate equivalent / total hydroxyl equivalent: 0.95 (Reaction conditions)-Extruder reaction temperature: 170 ° C setting-Twin screw rotation speed : 260rpm

Comparative Example 3 of Thermoplastic Polyurethane An example was given in which the acid component of the polyester diol was mainly composed of an aliphatic dibasic acid, and the glass transition temperature of the polyurethane resin obtained by increasing the urethane bonding group concentration was increased. . The polyester diol and the low molecular diol were each injected into an extruder without melting and mixing. Table 1 shows the properties of the obtained resin. (Raw ingredients) Polyester diol ・ Composition (molar ratio) Acid component: acid diacid 94 5-sodium sulfophthalic acid 6 Polychol component: neopentyl glycol 30 1,6-hexanediol 70 ・ Hydroxy group value (KOHmg / g): 262 ・Acid value (KOHmg / g): 0.44 ・ Polyester diol melt viscosity (ps, 90 ° C.): 2poise Low molecular weight diol ・ 1,2-Fluoropolyethylene glycol polyester diol / Low molecular weight diol ratio: 100/20 (weight ratio) Organic Polyisocyanate • 4,4'-diphenylmethanediisocyanate Reaction ratio Isocyanate equivalent / total hydroxyl equivalent: 0.95 (reaction conditions) • Extruder reaction temperature: 170 ° C setting • Twin screw rotation speed: 260 rpm

[0040]

[Table 1]

Example 1 A composition having the following composition ratio was dispersed in a ball mill for 48 hours, and then 1 part of myristic acid and 1 part of butyl stearate were used as a lubricant, and Coronate L of an isocyanate compound was used as a curing agent (Japan). Polyurethane Industry Co., Ltd.):
6 parts were added and the dispersion was further continued for 1 hour to obtain a magnetic paint.
This is treated with a 12 μm thick polyethylene terephthalate (PE
T) The film was applied while applying a magnetic field of 2,000 Gauss so that the thickness after drying was 4 μm. 50
After aging at 48 ° C. for 48 hours, the tape was slit to a width of イ ン チ inch to obtain a magnetic tape. Table 2 shows the properties of the obtained magnetic tape.

A 30 wt% MEK solution of the polyurethane resin of Synthesis Example 1 36 parts MAG527 solution * 36 parts Cobalt magnetite ** 100 parts Raven 1255 ** 15 parts alumina powder *** Cyclohexanone 42 parts MEK 96 parts Toluene 46 parts * PVC -Based copolymer resin (UCC Co., Ltd.), MEK / toluene: 50/50 30% solution ** ANB170HC Toda Kogyo KK ** Carbon black Colombian Carbon KK ** ** Alumina powder Sumitomo Chemical KP-20

Example 2 A magnetic tape was prepared in the same manner as in Example 1 except that the polyurethane resin of Synthesis Example 2 was used instead of the polyurethane resin of Synthesis Example 1, and the characteristics were evaluated. The results are shown in Table 2.

Example 3 Using the polyurethane resin of Synthesis Example 2 alone without using MAG527, a magnetic tape was produced in the same manner as in Example 1, and the characteristics were evaluated. The results are shown in Table 2.

Comparative Example 1 Using the polyurethane resin of Comparative Synthesis Example 1 in place of the polyurethane resin of Synthesis Example 1, a magnetic tape was produced in the same manner as in Example 1, and the characteristics were evaluated. The results are shown in Table 2.

Comparative Example 2 A magnetic tape was prepared in the same manner as in Example 1 except that the polyurethane resin of Comparative Example 2 was used instead of the polyurethane resin of Synthesis Example 1, and the characteristics were evaluated. The results are shown in Table 2.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1 except that the polyurethane resin of Comparative Synthetic Example 3 was used instead of the polyurethane resin of Synthetic Example 1, and the characteristics were evaluated. The results are shown in Table 2.

[0048]

[Table 2]

[0049]

Conventionally, it has been difficult to obtain a thermoplastic polyurethane resin having a urethane bonding group concentration of 3000 equivalents / ton or less and a glass transition temperature of 80 ° C. or more by a melt polymerization method. This was made possible by melt blending a low molecular weight diol having a molecular weight of 300 or less using the polyester diol having the specific composition of the present invention as a raw material. When used as a binder for magnetic recording media, a magnetic recording medium having both high magnetic powder dispersibility and tape durability can be obtained, and the cost of the binder resin, one of the main raw materials of magnetic tape, has been reduced. Can reduce the manufacturing cost.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C09D 5/23 C09D 5/23 175/04 175/04 F term (Reference) 4J002 CK031 DA086 DE116 FD100 FD170 GS01 4J034 DA01 DB03 DF01 DF16 DF21 HA01 HA07 HC03 HC12 HC13 HC17 HC22 HC46 HC52 HC61 HC64 HC67 HC71 HC73 JA01 JA06 PA03 QA01 QB03 RA16 4J038 DG001 MA13 NA11 NA14 PB11 5D006 BA15

Claims (1)

[Claims] 1. A thermoplastic polyurethane resin obtained by reacting raw material components in a molten state, wherein the thermoplastic polyurethane resin has a glass transition temperature of 80 ° C. or more, and has a urethane binding group concentration of 3000 equivalent / A thermoplastic polyurethane resin for a magnetic recording medium, wherein the thermoplastic polyurethane resin is less than ton.