JPH0632866A - Thermoplastic polyurethane - Google Patents

Abstract

PURPOSE:To obtain a thermoplastic polyurethane excellent in dispersibility of fine particle-like magnetic particles and useful as a binder for magnetic recording media. CONSTITUTION:This thermoplastic polyurethane has a sulfonic acid metal salt of 10-1000 equivalent/106g based on the polymer and has >=1000 poise and <=20000 melting viscosity of the polymer at 200 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic polyurethane which is excellent in dispersibility of fine magnetic particles 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 binder for a solid magnetic recording medium is desired, and the present inventors are promising a specific thermoplastic polyurethane as a binder for a solid magnetic recording medium. After finding out that, the present invention has been achieved.

[0008]

That is, according to the present invention, a metal sulfonate base is added in an amount of 10 to 1000 equivalents / 10 per polymer.
^A thermoplastic polyurethane having ⁶ g and a melt viscosity of the polymer at 200 ° C. of 1,000 poise or more and 20,000 poise or less.

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 high molecular weight diol, a low molecular weight diol and a polyisocyanate, and any component may contain a metal sulfonate group, but it is preferably high. It is preferable that part or all of the molecular diol has a metal sulfonate base. In order to obtain the thermoplastic polyurethane of the present invention, as described above, the polymeric diol (which is preferably a metal sulfonate-containing base).
It is preferred that the low molecular diol, polyisocyanate, and polyisocyanate be the main components of the reactive component. Examples of the low molecular weight diol include those exemplified below as the glycol component, but especially 1,4 butanediol, 1,6-hexanediol, neopentyl glycol, 1,3-propanediol, 1,5-pentanediol, etc. Is.

Further, as the polymer diol having a metal sulfonate group, a polyester polyol having a metal sulfonate group is particularly desirable. The polyester polyol having a metal sulfonate group comprises a carboxylic acid component having no metal sulfonate group, a glycol component and a dicarboxylic acid component having a metal sulfonate group.

Examples of the carboxylic acid component having no metal sulfonate base include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, p- (hydroxyethoxy).
Aromatic oxycarboxylic acids such as benzoic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid, and tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid Is mentioned.

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-pentanediolane 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.

As the dicarboxylic acid component containing a metal sulfonate group, 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.

The polymer diol containing the metal sulfonate group may be one kind or two or more kinds. Also, polymeric diols having no metal sulfonate base, such as ordinary polyester diols and polyether diols,
You may use together with a polycarbonate diol, a castor oil derivative, a tall oil derivative, and another hydroxyl group-containing compound.

The polyisocyanate used in the thermoplastic polyurethane resin of the present invention includes 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and p-.
Phenylene diisocyanate, diphenyl methane diisocyanate, m-phenylene diisocyanate, 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 dicyclohexylmethane, isophorone diisocyanate and the like, but if necessary, 2,4
It is also possible to use a small amount of 4'-triisocyanate-diphenyl, benzenetriisocyanate or the like.

The melt viscosity of the thermoplastic polyurethane resin of the present invention at 200 ° C. is 1000 poise or more, 2
Must be 000 poise or less. Melt viscosity is 1
When it is less than 000 poise, when it is dissolved in a solvent and made into a varnish, the dispersibility of the magnetic particles is excellent, but the coating film forming ability of the resin is insufficient, and the performance in terms of durability and surface lubricity is poor. descend. On the other hand, when the melt viscosity exceeds 20,000 poise, the dispersibility is lowered and the paint viscosity is increased, which may cause problems in the mixing, transfer and coating steps in the production of the magnetic paint, which is not practical.

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 in a conveyor belt to perform polymerization, a single-screw or multi-screw extruder. A melt polymerization method in which polymerization is performed while kneading can be used. The desirable blending ratio in this case is NCO of polyisocyanate.
Groups / all OH groups of high molecular weight diol and low molecular weight diol = 0.
It is 5 to 1.5, preferably 0.8 to 1.2.

Further, a catalyst can be used if necessary in the production of the thermoplastic polyurethane resin in the present invention. Examples of the catalyst include nitrogen-containing compounds such as triethylamine and triethylenediamine, and organometallic compounds such as dibutyltin dilaurylate and tin octylate.

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

The thermoplastic polyurethane resin in the present invention may optionally contain a plasticizer such as dibutyl phthalate and triphenyl phosphate, dioctyl sulfo-sodium succinate, t-butylphenol-polyethylene ether, ethylnaphthalene-sodium dilauryl sulfonate. Zinc natestearate, soybean oil lecithin,
Lubricants such as silicone oil, various antistatic agents, ultraviolet absorbers such as substituted benzotriazoles, antioxidants such as phenol derivatives, and hydrolysis inhibitors such as carbodiimides can also be added.

When the polyurethane according to the present invention is used as a binder for a magnetic recording medium, it is used together with the thermoplastic polyurethane resin of the present invention, other commonly used polyurethane resins, vinyl chloride-vinyl acetate copolymers and ethyl ether. Fiber-based resins such as cellulose and nitrocellulose, 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 As the type or polyfunctional monomer, an electron beam or ultraviolet ray curable resin such as urethane acryl type, phosphoric acid ester acryl type or aryl type can be used in combination.

The fine non-magnetic particles used at this time include γ-Fe ₂ O ₃ , CrO ₂ , cobalt ferrite (CoO, Fe ₂ O ₃ ) having a spinel structure, cobalt adsorbed iron oxide, and ferromagnetic Fe-Co. A Ni-based alloy or the like can be given.

The thermoplastic polyurethane resin according to the present invention includes paints, adhesives, sealing agents, waterproofing agents, flooring materials, artificial leather, fiber treating agents, elastic fibers, cushioning materials, sheets, in addition to binders for magnetic recording media. It can be used for belts, films, rolls, gears, solid tires, stretch-proof materials, tubes, packing materials, shoe soles and the like.

[0025]

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. Further, the melt viscosity of the thermoplastic polyurethane resin was measured by using Shimadzu's advanced flow tester CFT-500C, load: 50 kg.
/ Cm ² , die size φ1mm x 100mm, 200 ° C
It was measured at.

(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, 497 parts of adipic acid, 31 parts of 5-sodium sulfoisophthalic acid, 1, 6-hexanediol 578
Part, neopentyl glycol 218 parts, and tetrabutyl titanate 0.02 parts were charged, the esterification reaction was carried out at 180 to 230 ° C. for 5 hours, and then the reaction system was depressurized to 5 mmHg over 30 minutes, while raising the temperature to 240 ° C. Warmed. Furthermore, the polycondensation reaction at 0.3 mmHg and 240 ° C is 1
It was performed for 0 minutes. The OH number of the obtained polyester is 5
The number average molecular weight was 7.2 at 1 mgKOH / g.

(2) Evaluation of dispersibility of magnetic powder Thermoplastic polyurethane resin 12 parts Vinylite VAGH (manufactured by UCC) 18 parts Co-containing γ-Fe ₂ O ₃ 120 parts Methyl ethyl ketone 90 parts Toluene 90 parts Cyclohexanone 90 parts

The mixture having the above composition was kneaded for 5 hours using a paint shaker, 12 parts of Coronate-L (manufactured by Nippon Polyurethane) was further added, and the mixture was 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 the solvent was removed by drying. The surface gloss of the obtained magnetic coating film was measured and the dispersibility was evaluated.

Example 1 In a reaction vessel equipped with a dry nitrogen inlet and a stirrer, 50 parts of a sulfonic acid metal group-containing polyol and Polylite OD.
50 parts of -X-688 (manufactured by Dainippon Ink and Chemicals), 6 parts of neopentyl glycol (NPG), and 2 parts of 1,6-hexanediol (HD) were added, and the mixture was stirred at 150 ° C. When the mixed solution becomes a uniform melt, the temperature is lowered to 80 ° C and 4,4'-
Diphenylmethane diisocyanate (MDI) 29.
Add 7 parts and mix rapidly for 1 minute. The obtained mixed solution was poured onto a Teflon vat and polymerized in an inert oven blown with nitrogen at 190 ° C. for 1 hour, and then 8
Post cure was carried out at 0 ° C. for 24 hours. The thermoplastic polyurethane resin thus obtained had a metal sulfonate group content of 47 equivalents / 10 ⁶ g and a melt viscosity at 200 ° C. of 2
It was 000 poise. The surface gloss of the magnetic coating film using this thermoplastic polyurethane resin was 92.

Examples 2 to 5 Thermoplastic polyurethane resins were obtained in the same manner as in Example 1 except that the amounts of raw materials charged were changed as shown in Table 1. The content of the metal sulfonate group and the melt viscosity at 200 ° C. of the obtained thermoplastic polyurethane resin were as shown in Table 1. Further, the surface gloss of the magnetic coating film using these thermoplastic polyurethane resins is as shown in Table 2, and good results were obtained in all cases.

[Table 1] The subscripts in Table 1 indicate the following. 1) Dainippon Ink and Chemicals Polylite OD-X-688
(Mn = 2000) 2) Neopentyl glycol 3) 1,6-hexanediol 4) 4,4'-diphenylmethane diisocyanate

[0031]

[Table 2] Comparative Example 1 A thermoplastic polyurethane resin containing no metal sulfonate group was obtained in the same manner as in Example 1 except that only Polylite OD-X-688 was used as the polymer diol and the charged amount was changed as shown in Table 1. . The melt viscosity of the obtained thermoplastic polyurethane resin at 200 ° C. was 1800 poise. The surface gloss of the magnetic coating film using this thermoplastic polyurethane resin was 26.

Comparative Example 2 A thermoplastic polyurethane resin was obtained in the same manner as in Example 1 except that the amount of raw material charged was changed as shown in Table 1. The obtained thermoplastic polyurethane resin had a metal sulfonate group content of 47 and the equivalent weight / 10 ⁶ g, and the melt viscosity at 200 ° C. was 30,000 poise. The surface gloss of the magnetic coating film using this thermoplastic polyurethane resin was 60.

[0033]

By using the thermoplastic polyurethane resin 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 a low cost, and as a result, it is possible to obtain a high density at a low cost. A magnetic recording medium can be obtained, which is a major contribution to the industry.

Claims (1)

[Claims] 1. A metal sulfonate base is used in an amount of 1 per polymer.
0 to 1000 equivalents / 10 ⁶ g and of 20 of the polymer
Melt viscosity at 0 ° C is 1000 poise or more, 2000
Thermoplastic polyurethane with 0 poise or less.