JPH06263982A - Thermoplastic polyurethane resin composition - Google Patents

Abstract

PURPOSE:To obtain a resin composition, comprising a prescribed amount of an organotin compound, etc., in a specific thermoplastic polyurethane, excellent in uniform dispersibility and high filling properties and useful as binders, etc., for magnetic recording media. CONSTITUTION:This resin composition comprises (B) 10-1000ppm organotin compound such as dibutyltin dilaurate and/or tertiary amine such as triethylamine in (A) a thermoplastic polyurethane, obtained by reacting (i) a polyester polyol having 500-2000 average molecular weight and containing an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid at (5/95) to (90/10) molar ratio of (aromatic dicarboxylic acid)/(aliphatic dicarboxylic acid) in an acidic component with (ii) a low-molecular diol having <500 molecular weight and (iii) an organic diisocyanate such as tolylene diisocyanate and having 10-1000 equiv./10<6>g metallic sulfonate group per polymer and 1200-3000 equiv./10<6>g urethane group concentration per polymer.

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 composition which is excellent in dispersibility of fine magnetic particles and which can be packed at high density and is useful as a binder for magnetic recording media.

[0002]

Conventionally, as binders for magnetic recording media, ethyl cellulose, nitro cellulose, polyvinylidene chloride resin, vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, polymethacrylic acid methyl resin, Vinylidene chloride-methyl methacrylate copolymers, polyurethane resins, epoxy resins, polyester resins and the like have been used.

However, data tapes for computers,
At present, the performance is not sufficient for applications requiring high performance such as floppy disks and video tapes. In particular, in recent years, high grade has been accelerated in video tape applications, and there is a demand for a magnetic recording medium capable of high density recording for recording and reproducing clear sound and images.

As a measure for increasing the density, magnetic particles have been made finer and the magnetic force has been increased, and there is an increasing tendency to increase the packing density of the magnetic powder in the magnetic layer. However, with the increase in the specific surface area due to the fine particles of the magnetic powder as described above and the increase in the cohesive force due to the increase in the magnetic force, the conventional binder as described above does not have a sufficient dispersing function for the magnetic powder and the dispersion Although the function has been entrusted to the dispersant such as a phosphoric acid compound, in a system in which the dispersant is mixed with the binder, the durability of the magnetic layer is adversely affected, such as the occurrence of bleeding, in the case of long-term use.

In order to solve the above problems, a hydrophilic polar group such as a sulfonic acid group, a hydroxyl group, a carboxyl group or a phosphoric acid group is introduced into the binder to improve the affinity with the magnetic powder and to have a high dispersion function. Binders with are proposed. (Japanese Patent Publication No. 58-41565, Japanese Patent Laid-Open No. 57-92422)
No. 59-30235 and No. 59-1546.
No. 33, No. 60-15473, No. 60-20
Among these, a binder containing a sulfonic acid group is most promising because it has the best dispersibility of the magnetic powder.

[0006]

However, the above-mentioned binder containing a sulfonic acid group is expensive and is generally produced by solution polymerization using a known organic solvent as a reaction medium. Therefore, the product shape is liquid (varnish), and the solid content as an active ingredient is only a part of the product. Therefore, when the product is transported, the transportation cost is high, and there is a safety problem because the combustible organic solvent is transported in the coexistence. In addition, since the reaction solvent used for solution polymerization becomes the solvent for the magnetic coating material, a solvent suitable for the solvent recovery device at the time of manufacturing the magnetic recording medium must be used as the reaction solvent. It is difficult to produce a binder by changing

For the above reasons, a solid binder for a magnetic recording medium is desired, and Japanese Patent Publications No. 58-8053, No. 61-231050 and Japanese Examined Patent Publication No. 3-1364.
No. 8, etc., it is proposed that the magnetic powder has uniform dispersibility.
No solid-state binder for magnetic recording media has been obtained which satisfies high filling properties, that is, low porosity and high surface smoothness during coating. The present inventors have found that a specific thermoplastic polyurethane resin composition is promising as a solid binder for magnetic recording media, and have completed the present invention.

[0008]

That is, the present invention provides a polyester polyol having an average molecular weight of 500 to 2000, wherein the ratio of aromatic dicarboxylic acid and aliphatic dicarboxylic acid in the acid component of the polyester polyol is a molar ratio. (Aromatic dicarboxylic acid) / (Aliphatic dicarboxylic acid)
A thermoplastic polyurethane obtained by reacting a polyester polyol having a molecular weight of 5/95 to 90/10 with a low molecular diol having a molecular weight of less than 500 and an organic diisocyanate, wherein the polymer contains a metal sulfonate group at 10 ˜1000 equivalent / 10 ⁶ g, and the concentration of urethane groups in the polymer is 1500 to 100
It is a thermoplastic polyurethane having an amount of 3000 equivalents / 10 ⁶ g, and an organotin compound and / or a tertiary amine compound having a catalytic function for a urethanization reaction is added to the thermoplastic polyurethane in an amount of 10 to 1000 p / s based on the thermoplastic polyurethane.
It is a thermoplastic polyurethane resin composition characterized by containing pm.

The average molecular weight of the polyester polyol which is a raw material of the thermoplastic polyurethane resin in the present invention is 5
Must be between 00 and 2000. Average molecular weight is 50
When it is less than 0, the thermoplastic polyurethane resin loses flexibility and is not practical. Further, when the average molecular weight exceeds 2000, the melt viscosity of the polyester polyol itself increases and the fluidity decreases, making it difficult to manufacture and also increasing the crystallinity of the polyester polyol forming the soft segment of the thermoplastic polyurethane and dissolving it in a solvent. Sex decreases.

In the polyester polyol according to the present invention, the ratio of the aromatic dicarboxylic acid and the aliphatic dicarboxylic acid in the acid component, which is the constituent component, is a molar ratio of (aromatic dicarboxylic acid) / (aliphatic dicarboxylic acid) = 5/95. ~
90/10, preferably 30/70 to 70/30. When the ratio is less than 5/95, the obtained thermoplastic polyurethane resin becomes soft and, for example, in the case of pellets, so-called "blocking" occurs in which the pellets stick to each other, which is not practical in terms of production and handling of products. Further, if the concentration of the urethane group of the thermoplastic polyurethane is increased to prevent this blocking and the thermoplastic polyurethane resin itself is hardened, blocking can be prevented, but on the contrary, the solubility in the solvent is lowered, or even if dissolved in the solvent, it is used in combination. Compatibility with other resins such as vinyl chloride resin decreases, and as a result, high dispersion and high filling of magnetic powder cannot be realized.

On the other hand, if the above ratio exceeds 90/10, the rigidity of the polyester polyol itself increases and the high softening point,
In addition to the high viscosity making it difficult to manufacture the thermoplastic polyurethane resin, the solvent solubility of the obtained thermoplastic polyurethane resin and the compatibility with other resins decrease, and thus high dispersion and high filling of the magnetic powder cannot be realized.

As the aromatic dicarboxylic acid constituting the polyester polyol used in the present invention, terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalic acid and the like are used. In addition, p-oxybenzoic acid, p-
Aromatic oxycarboxylic acids such as (hydroxyethoxy) benzoic acid, and tri- and tetra-aromatic carboxylic acids such as trimellitic acid and pyromellitic acid can also be used in combination. On the other hand, as the aliphatic dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and the like are used. Further, as described later, an aromatic or aliphatic dicarboxylic acid having a sulfonic acid metal base can also be used.

As the glycol component, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-
Hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-
Examples include trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, bisphenol A ethylene oxide adduct and propylene oxide adduct, hydrogenated bisphenol A ethylene oxide adduct and propylene oxide adduct. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination.

The low molecular weight diol used in the present invention includes ethylene glycol, 1,4-butanediol, 1,
6-hexanediol, propylene glycol, 1,3
-Propanediol, 1,5-pentanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, 1,4-bis (2-hydroxyethoxy) ) Benzene and the like. These low molecular diols may be used alone or in combination of two or more.

Examples of the organic diisocyanate used in the thermoplastic polyurethane resin of the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate and hexamethylene. Diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-
Biphenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5-naphthalene diisocyanate, p
-Xylene diisocyanate, m-xylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane,
4,4'-diisocyanate dicyclohexane, 4,
4'-diisocyanate dicyclohexyl methane, isophorone diisocyanate, etc. may be mentioned.
They may be used alone or in combination of two or more.

The thermoplastic polyurethane resin in the present invention may contain the metal sulfonate group in an amount of 10 to 1000 equivalents / 10 ⁶ g per polymer. If the metal sulfonate base per polymer is less than 10 equivalents / 10 ⁶ g, the dispersion of the magnetic particles will be poor and a high packing property cannot be obtained. Further, the metal sulfonate base per polymer is 1000 equivalents / 1
If it exceeds 0 ⁶ g, the solubility of the thermoplastic polyurethane resin in a solvent becomes poor, resulting in a lack of practicality.

The thermoplastic polyurethane resin in the present invention is obtained by reaction with a polyester polyol, a low molecular weight diol and an organic diisocyanate, and any component may contain a metal sulfonate group, but the polyester polyol is preferable. Some or all of these have a metal sulfonate group.

The polyester polyol having a metal sulfonate base is preferably a dicarboxylic acid having a part of its acid component having a metal sulfonate base. Further, the dicarboxylic acid having the metal sulfonate group may be either an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid.

Examples of the dicarboxylic acid component containing a metal sulfonate group include 5-sodium sulfoisophthalic acid,
There are 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid and the like. The copolymerization amount of these dicarboxylic acid components containing a metal sulfonate group is 0.
It is 5 mol% or more, preferably 1 to 50 mol%, but the molar ratio of the aromatic dicarboxylic acid and the aliphatic dicarboxylic acid in this case is (aromatic dicarboxylic acid) / (aliphatic dicarboxylic acid) = 5/95. To 90/10, preferably 30/7
Must be 0-70 / 30.

The polyester polyol containing the metal sulfonate group may be one kind or two or more kinds. Moreover, you may use together with the polyester polyol which does not have a metal sulfonate base. However, even in this case, the molar ratio of the aromatic dicarboxylic acid to the aliphatic dicarboxylic acid in the acid component of the total polyester polyol is (aromatic dicarboxylic acid) / (aliphatic dicarboxylic acid) = 5/95 to 9
It should be 0/10, preferably 30/70 to 70/30.

The urethane group concentration of the thermoplastic polyurethane resin in the present invention should be 1200 to 3000 equivalents / 10 ⁶ g per polymer. The urethane group concentration is represented by the following equation when 4,4′-diphenylmethane diisocyanate (hereinafter abbreviated as MDI) is used as the organic diisocyanate. Urethane group concentration = {(MDI charge amount / total raw material charge amount) ÷
125} × 10 ⁶ (equivalent / 10 ⁶ g)

When the urethane group concentration is less than 1200 equivalent / 10 ⁶ g, the thermoplastic polyurethane resin obtained becomes soft and blocking between pellets is remarkable, which is not practical in terms of production and handling. Also, 3000 equivalents /
When the amount exceeds 10 ⁶ g, blocking is lost, but the solvent solubility of the resin and the compatibility with other resins are reduced, and as a result, high dispersion and high filling of the magnetic powder cannot be realized.

The method for producing the thermoplastic polyurethane resin in the present invention can be carried out by a known method such as a bulk polymerization method in which all raw materials are rapidly mixed and the mixture is heated and polymerized in a conveyor belt form, a uniaxial or multiaxial extractor. A melt polymerization method in which polymerization is performed while kneading can be used. The desirable blending ratio in this case is NC of organic diisocyanate.
O group / total O of polyester polyol and low molecular weight diol
H group = 0.5 to 1.5, preferably 0.8 to 1.2.

The thermoplastic polyurethane resin composition in the present invention must contain an organotin compound and / or a tertiary amine compound in an amount of 10 to 1000 ppm, preferably 50 to 500 ppm, based on the thermoplastic polyurethane.
More preferably, these compounds have a catalytic function for the urethanization reaction. Generally, the production method of thermoplastic polyurethane is a bulk polymerization method or a melt polymerization method as described above, but the molecular weight at this stage is not sufficiently high, and a curing step by solid-state polymerization is further performed in order to further increase the molecular weight. I need. However, this solid-state polymerization has a slow reaction rate, and in the case of no catalyst, a long curing time is required, resulting in poor productivity. Further, when a magnetic coating material is produced by using this resin as a binder, the reactivity with the polyisocyanate which is a curing agent is remarkably slowed without a catalyst, and curing is not sufficiently achieved. For the above reasons, the inclusion of an organotin compound and / or a tertiary amine compound having a catalytic function for the urethanization reaction is extremely preferable. When the content of the organotin compound and / or the tertiary amine compound having a catalytic function for the urethanization reaction is less than 10 ppm, the effect of addition cannot be obtained as expected. Further, when the content exceeds 1000 ppm, the reaction rate in the polymerization step of the thermoplastic polyurethane and the curing reaction step with the polyisocyanate becomes too fast, or a side reaction occurs to form a gel-like lump, which is not good. Cause of.

The organotin compound and tertiary amine compound having a catalytic function for the urethanization reaction used in the present invention may be known compounds, and preferred organotin compounds include dibutyltin dilaurylate, dibutyltin diacetate,
Examples thereof include dibutyltin thiocarboxylate, dibutyltin dimaleate, dibutyltin mercaptide, dioctyltin mercaptide and dioctyltin thiocarboxylate. Preferred tertiary amine compounds include triethylamine, N, N'-dimethylcyclohexylamine,
N, N, N ', N'-tetramethylethylenediamine,
N, N, N ', N ", N" -pentamethyldiethylenetriamine, triethylenediamine, N, N'-dimethylpiperazine, 1,2-dimethylimidazole, N-methylmorpholine, dimethylaminoethanol, bis (2-
Dimethylaminoethyl) ether and the like can be mentioned. These organotin compounds and tertiary amine compounds may be used alone or in combination of two or more.

A known method may be used as a method for incorporating the organotin compound and / or the tertiary amine compound into the thermoplastic polyurethane, but it is preferable to use a polyester polyol, a low molecular weight diol and an organic diisocyanate during the production of the thermoplastic polyurethane. It is preferable to add an organic tin compound and / or a tertiary amine compound to any of the raw materials and polymerize the raw material so that the raw material is contained in the thermoplastic polyurethane resin.

The thermoplastic polyurethane resin composition of the present invention can be used in any desired shape such as pellets, flakes, sheets, etc. However, considering the solubility in a solvent in the paint manufacturing process, the specific surface area of the resin is Pellets that are wide and easy to dissolve are desirable.

The thermoplastic polyurethane resin composition of the present invention comprises a plasticizer such as dibutyl phthalate, triphenyl phosphate, dioctylsulfo-sodium succinate, t-butylphenol-polyethylene ether, ethylnaphthalene-sodium sulfonate as required. Lubricyl succinate Zinc stearate, soybean oil lecithin, silicone oil and other lubricants and various antistatic agents, substituted benzotriazoles and other UV absorbers, phenol derivatives and other antioxidants, and carbodiyl and other hydrolysis inhibitors Lubricants such as agents and higher fatty acid metal salts can also be added.

As the binder for the magnetic recording medium according to the present invention, other polyurethane resins which are usually used together with the thermoplastic polyurethane resin composition of the present invention, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, nitro are used. Cellulose and other fibrous resins, polyester resins, epoxy resins, phenoxy resins, thermosetting resins such as acrylonitrile-butadiene copolymers or reactive resins and unsaturated prepolymers such as urethane acrylic type, polyester acrylic type, or poly As the functional monomer, an electron beam or ultraviolet curable resin of urethane acrylic type, phosphoric acid ester acrylic type, aryl type or the like can be used in combination.

The fine powder magnetic particles used in the present invention include γ-Fe ₂ O ₃ and Cr having a spinel structure.
O _2, cobalt ferrite _{(CoO, Fe 2 O 3)} , cobalt adsorbed iron oxide, it can be ferromagnetic Fe-Co-Ni alloy or the like is exemplified.

The thermoplastic polyurethane resin composition according to the present invention comprises a paint, an adhesive, a sealing agent, a waterproofing agent, a flooring material, artificial leather, a fiber treating agent, an elastic fiber, a cushioning material, in addition to the binder for the magnetic recording medium. It can be used for seats, belts, films, rolls, gears, solid tires, anti-vibration materials, tubes, backing materials, shoe soles and the like.

[0032]

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Incidentally, "part" in Examples and Comparative Examples
Is "parts by weight" unless otherwise specified. The reduced viscosity of the thermoplastic polyurethane resin was measured at 30 ° C. in a phenol / tetrachloroethane (6: 4 weight ratio) mixed solvent.

(1) Synthesis Example of Polyester Polyol Containing Metal Sulfonate Base In a reaction vessel equipped with a thermometer, a stirrer and a condenser for distillation, 43500 parts of terephthalic acid, 39300 parts of isophthalic acid and 114600 parts of adipic acid are placed. 7400 parts of 5-sodium sulfoisophthalic acid (hereinafter abbreviated as ISN), 42600 parts of ethylene glycol, 87900 parts of neopentyl glycol, 62100 parts of 1,4-cyclohexanedimethanol, 6.0 parts of tetrabutyl titanate. After charging, the esterification reaction was carried out at 180 to 230 ° C. for 5 hours, and then the reaction system was heated to 30 minutes for 5
The pressure was reduced to mmHg, and the temperature was raised to 240 ° C during this period. Furthermore, the polycondensation reaction was performed at 0.3 mmHg and 240 ° C. for 10 minutes. The OH value of the obtained polyester is 79.3 mg.
The number average molecular weight was 1414 in KOH / g. Its composition was as follows from NMR analysis and the like. Terephthalic acid 2
0 mol%, isophthalic acid 18 mol%, 5-sodium sulfoisophthalic acid 2 mol%, adipic acid 60 mol%, ethylene glycol 35 mol%, neopentyl glycol 35 mol%, 1,4-cyclohexanedimethanol 30
Mol%.

Polyester polyols (A) and (B) shown in Table 1 were obtained by the same production method.

(2) Evaluation of dispersibility of magnetic powder Thermoplastic polyurethane resin composition 12 parts Vinylite VAGH (manufactured by UCC) 18 parts Co-containing γ-Fe ₂ O ₃ 120 parts Methyl ethyl ketone 135 parts Toluene 135 parts

After the mixture having the above composition was kneaded for 5 hours using a paint shaker, 12 parts of polyisocyanate Coronate-L (manufactured by Nippon Polyurethane Co.) as a curing agent was further added and further mixed for 30 minutes. The obtained magnetic coating material was applied onto a polyethylene terephthalate film having a thickness of 50 μm using a doctor blade having a gap of 50 μm, and a curing reaction was carried out at 60 ° C. for 20 hours while removing the solvent by drying. The uniform dispersibility of the magnetic powder, the filling rate and the surface smoothness of the obtained magnetic coating film were evaluated as follows.

Uniform dispersibility: Measured and evaluated by the surface gloss of the magnetic coating film. Filling ratio: The magnetic coating film was dipped in silicone oil, and the porosity of the magnetic coating film was evaluated based on the impregnated amount of silicone oil. Surface smoothness: The surface roughness of the magnetic coating film was measured with a stylus meter and evaluated.

(3) Evaluation of Curability of Thermoplastic Polyurethane Resin Composition A coating film was prepared in the same manner as in the above evaluation of dispersibility except that vinylite VAGH and Co-containing γ-Fe ₂ O ₃ were not contained.
Dip the obtained film in methyl ethyl ketone,
The degree of cure was evaluated by setting the weight fraction of the undissolved content of the original film as a gel fraction.

Example 1 The polyester polyol (A), MDI, and propylene glycol shown in Table 1 were treated at 100 ° C. and 50 ° C., respectively.
Stored in a storage tank at 25 ° C, and the polyester polyol (A) was reacted with dibutyltin dilaurylate at 20% per polymer after reaction.
It was added so as to have a content of 0 ppm, and the inside of the storage tank was stirred. After stirring for about 30 minutes, a gear pump was used to feed the liquid at the following feed amount, and the liquid was fed into a twin-screw extruder (L / D = 40) with a screw diameter of 30 mm and the final resin temperature was 230 ° C.
The thermoplastic polyurethane was continuously melt-polymerized while kneading under the following temperature conditions. Polyester polyol (A): 108.7 parts / minute Propylene glycol: 5.8 parts / minute MDI: 36.0 parts / minute

The thermoplastic polyurethane resin in a molten state is discharged in a strand form from the die part of the twin-screw extruder, water-cooled by a cooling bath, pelletized by a strand cutter, and then the pellets are air-fed to the Nauta mixer (Hosokawa Micron). (Made by company) continuously, after filling 50,000 parts of pellets, 10 parts of calcium stearate (0.02 weight% with respect to a polymer) was added, and 60
The mixture was dried and cured for 30 hours with stirring at ℃ under a nitrogen stream to obtain a pellet-shaped thermoplastic polyurethane resin composition. The obtained thermoplastic polyurethane resin composition had a metal sulfonate content of 65 equivalent / 10 ⁶ g, a urethane group concentration of 1900 equivalent / 10 ⁶ g, and a reduced viscosity (η _sp
/ C) was 1.32. When the obtained thermoplastic polyurethane resin composition is dried and cured (60 ° C.)
But there was no blocking.

The surface gloss, porosity and surface roughness of the magnetic coating film using this resin composition are 9 as shown in Table 2.
Good values of 1, 21.0% and 0.023 μm were obtained. In addition, the gel fraction was 75%, indicating good curability.

Examples 2 to 7 A thermoplastic polyurethane resin composition was prepared in the same manner as in Example 1 except that the raw material composition, urethane group concentration, type and content of organotin compound or tertiary amine compound were changed as shown in Table 2. I got a thing. The obtained thermoplastic polyurethane resin composition did not block even in an atmosphere of 60 ° C., and the surface gloss, porosity, surface roughness and gel fraction of the magnetic coating film using these resins are as shown in Table 2. All obtained good values.

Comparative Example 1 A thermoplastic polyurethane resin composition was prepared in the same manner as in Example 1 except that the composition ratio was changed so that the urethane group concentration was 1190 equivalent / 10 ⁶ g. I got a thing. The surface gloss, porosity and surface roughness of the magnetic coating film using this resin composition are good as shown in Table 2, but the pellets of the resulting thermoplastic polyurethane resin composition are 6
It was extremely blocked in an atmosphere of 0 ° C. and was difficult to handle. The gel fraction was also low at 30%.

Comparative Example 2 A thermoplastic polyurethane resin composition was prepared in the same manner as in Example 1 except that the composition ratio was changed so that the urethane group concentration was 3200 equivalent / 10 ₆ g. I got a thing. The resulting thermoplastic polyurethane resin composition was methyl ethyl ketone / toluene (1 /
It was insoluble in the mixed solvent.

Comparative Example 3 A thermoplastic polyurethane resin having the same composition as in Example 1 was obtained in the same manner as in Example 1 without adding dibutyltin dilaurate. The surface gloss, porosity and surface roughness of the magnetic coating film using this resin are good as shown in Table 2 and do not block even in an atmosphere of 60 ° C., but the gel fraction is 5% and almost no curing reaction occurs. Was not in progress.

Comparative Example 4 A thermoplastic polyurethane resin composition was obtained in the same manner as in Example 1 except that the amount of dibutyltin dilaurylate added was changed to 1200 ppm. When this resin composition was used, the gel fraction was 96%, but gel lumps frequently occurred in the coating film, which was not practical.

Comparative Example 5 (D) in Table 1 (the aromatic / aliphatic molar ratio of the acid component was 2/98) was used as the polyester polyol, and 3-methyl-1,5-pentanediol was used as the chain extender. A thermoplastic polyurethane resin composition was obtained in the same manner as in Example 1 with a composition ratio such that the urethane group concentration was 2820 equivalent / 10 ⁶ g. The surface gloss, porosity surface roughness and gel fraction of the magnetic coating film using this resin composition obtained good values as shown in Table 2, but the obtained thermoplastic polyurethane resin composition pellets also at room temperature. Blocking was remarkable and handling was difficult.

Comparative Example 6 A thermoplastic polyurethane resin composition was obtained in the same manner as in Example 1 except that (E) in Table 1 (not containing a metal sulfonate group) was used as the polyester polyol. As shown in Table 2, the surface gloss, porosity, and surface roughness of the magnetic coating film using this resin composition were poor.

[0049]

[Table 1]

[0050]

[Table 2] In Table 2, PG is propylene glycol and MPG
Is 2-methyl-1,3-propanediol, MPD is 3-methyl-1,5-pentanediol, DBTDL
Indicates dibutyltin dilaurylate, TEA indicates triethylamine, and the curing condition for measuring the gel fraction after curing is 60 ° C. for 20 hours.

[0051]

By using the thermoplastic polyurethane resin composition of the present invention, it becomes possible to obtain a binder for a magnetic recording medium which is excellent in dispersibility of magnetic particles at low cost, and as a result, at low cost. A high-density magnetic recording medium can be obtained, which greatly contributes to the industry.

Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location G11B 5/702 7215-5D (72) Inventor Yo Imata 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd. Company Research Institute

Claims (1)

[Claims] 1. An average molecular weight of 500 to 2000,
A polyester polyol having a molar ratio of aromatic dicarboxylic acid and aliphatic dicarboxylic acid in the acid component of (aromatic dicarboxylic acid) / (aliphatic dicarboxylic acid) = 5/95 to 90/10, and a molecular weight of less than 500. A thermoplastic polyurethane obtained by reacting a low-molecular diol and an organic diisocyanate, wherein the polyurethane has a metal sulfonate group of 10 to 1000 equivalents / 10 ⁶ g per the polymer, and a urethane group concentration per the polymer. A thermoplastic polyurethane having an amount of 1200 to 3000 equivalents / 10 ⁶ g, wherein the thermoplastic polyurethane contains an organotin compound and / or a tertiary amine compound in an amount of 10 to 1000 ppm based on the thermoplastic polyurethane. Resin composition.