JPH0212613A - Binder of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder and to improve the durability and wet heat resistance of the binder by consisting the binder of a specific thermoplastic polyurethane resin and low mol.wt. polyisocyanate having >=2 isocyanate groups. CONSTITUTION:This binder consists of the thermoplastic polyurethane (A) of 20,000-2,000,000mol.wt. having a -PO(OM)2 group (where M is an alkaline metal atom or alkyl group) in the molecular chain and a tertiary hydroxyl group in the position exclusive of both terminals of the main chain and the low mol.wt. polyisocyanate (B) having >=2 isocyanate resin group. This polyurethane resin is incorporated with the -PO(OM)2 group as the side chain to improve the affinity to the magnetic powder and the dispersibility of said powder; in addition, the resin has a large amt. of crosslinking points (hydroxyl groups, etc.) in the main chain and, therefore, the degradation in the reactivity with the isocyanate is lessened and the easy tendency to the formation of network by crosslinking of the resins to each other is obtd. The pigment dispersibility as well as the durability and heat resistance of the binder are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a binder for magnetic recording media. More specifically, the present invention relates to a binder for magnetic recording media that has excellent dispersibility and durability of magnetic powder in a magnetic layer and excellent m1 thermal properties.

(Prior Art and Problems) In recent years, with the expansion of applications such as audio tapes and household VTR tapes, the required performance has also become more diverse. As hardware technology such as 8mm video and DAT%s-VH8 has made remarkable progress, demands on magnetic recording media have become more demanding. In particular, high image quality and high reliability are required during recording and reproduction. Specific examples include a ninth-high recording density that reproduces clear images and sounds, withstands high-speed long-term running under harsh conditions such as high temperatures, and prevents magnetic powder from falling off from the magnetic layer. There are many things that can be mentioned. The important function of the binder is to maintain the characteristics and physical properties of the magnetic layer, and it has excellent dispersibility of the magnetic powder, and provides good electromagnetic properties such as high sensitivity, high 8N ratio, and high CN ratio.
In addition, there is a demand for materials with excellent durability such as abrasion resistance. Various binders have been researched to satisfy these physical properties, and polyurethane has been used as a binder that imparts good wear resistance to the magnetic layer and improves the durability of magnetic recording media. Resin has been proposed.

However, conventional urethane resins cannot sufficiently disperse magnetic powder due to their strong cohesive force. Therefore, materials such as nitrocellulose and vinyl chloride/vinyl acetate copolymers that disperse magnetic powder have been used in combination with polyurethane.

Incidentally, several methods are known for improving the dispersibility of magnetic powder by introducing a polar group into the molecular chain of a binder. For example, JP-A-57-145120 and JP-A-E 58-108031 disclose magnetic recording media using polyurethane resins having tertiary hydroxyl groups as a binder.

However, in the case of magnetic recording media that use highly finely powdered ferromagnetic powder, which has been developed in recent years to improve recording density and electromagnetic characteristics,
The above-mentioned binders cannot sufficiently disperse the magnetic powder. As a result, despite the use of finely divided ferromagnetic powder, the electromagnetic conversion characteristics of the resulting magnetic recording medium are not sufficiently improved, and some of the poorly dispersed magnetic powder falls off from the magnetic layer. This may cause dropouts.

j> On the other hand, JP-A-57-92422 lists -PO(OM)2 groups as functional groups. By introducing this functional it-binder, the dispersibility of magnetic powder is significantly improved. However, polyurethane resins having this functional group have significantly reduced hydrolysis resistance and are inhibited from reacting with isocyanates.

Crosslinking does not proceed and sufficient film strength cannot be obtained.

(Means for Solving the Problems) The present inventors have conducted intensive research to solve the above problems, and as a result, they have completed the present invention. ) 2 groups (where M is an alkali metal atom or an alkyl group), and a tertiary hydroxyl group at positions other than both ends of the main chain, and a molecular weight of 20,000
Pigment dispersibility and durability consisting of a thermoplastic polyurethane resin (A) of ~200,000 and a low molecular weight polyisocyanate (B) having two or more isocyanate groups,
The present invention provides a binder for magnetic recording media that imparts improved properties such as heat and humidity resistance.

The polar groups used in the present invention are -F'O(OM) 2 groups (however, 1M is an alkali metal atom and tea is an alkyl group) and a tertiary hydroxyl group. Normally, if the phosphoric acid compound is completely used, the reactivity of active hydrogen and isocyanate will be significantly impaired.
The crosslinking reaction between the resins does not proceed, reducing the film strength of the reactant. However, the polyurethane resin used in the present invention has two -PO(OM) groups introduced as side chains,
In addition to improving dispersibility by improving the affinity with magnetic powder, it also maintains a large amount of crosslinking points (hydroxyl groups, etc.) in the main chain, reduces reactivity with isocyanate, and is made by crosslinking between resins. Reticulation easily occurs and a tough film can be obtained.

Thermoplastic polyurethane resin (A) used in the present invention
l'i, weight average molecular weight is 20,000 to 200,00
0, preferably 30,000 to 100,000.

In addition, -PO (OM) in the thermoplastic polyurethane resin molecule
) The number of 2 groups per resin is 0.005 or more, preferably 0.05 to 1, particularly preferably 0.1 to 0.5, and the number of tertiary hydroxyl groups is 0.01 or more, preferably 0.0
It is desirable that the number is 5 to 1.ま几、-PO(OM)
Two Mid groups, an alkali metal atom or an alkyl group, preferably Na* as the alkali metal atom
K *Also, as the alkyl group, preferably an ethyl group or a propyl group. That is, the weight average molecular weight is 20,000
Below, the mechanical properties, abrasion resistance, and moist heat resistance of the thermoplastic polyurethane resin are poor, and when it is 200,000 or more, the solution stability of the polyurethane resin deteriorates and the pigment dispersibility also decreases. If the number of -PO(OM) groups in the molecule is less than 0.05, it is difficult to improve pigment dispersibility, and if it is more than 1, the solubility in organic solvents decreases due to increased hydrophilicity. , is not preferable because hydrolysis resistance deteriorates.

Moreover, if the number of tertiary hydroxyl groups in the molecule is 0.01 or less, the moist heat resistance of the urethane after curing is significantly improved.

In addition, both terminals of the thermoplastic polyurethane resin used in the present invention may be an isocyanate group or a hydroxyl group, or one terminal may be an isocyanate group and the other terminal may be a hydroxyl group.

The thermoplastic polyurethane resin (A
) include primary materials.

That is, as organic diisocyanate (Al),
For example, hexamethylene diisocyanate, sulfur diisocyanate, inphorone diisocyanate, xylene diisocyanate, cyclohexane diisocyanate,
Toluidine diisocyanate, 2.4-tolylene diisocyanate, 2.6-) lylene diisocyanate, 4,
4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate
), 15-naphthylene ziisocyanate, and mixtures thereof. Among these, hexamethylene diisocyanate, 4.4'-diphenylmethane diisocyanate, 2.4-tolylene diisocyanate, 2.6
-) lylene diisocyanate and mixtures thereof are preferred.

Polyol (A) containing -PO(OM) 2 groups in its molecular chain
For 2), a phosphoric acid compound represented by the following general formula is used.

HO-R1-N-R2-OH MO-P -OM' R1, R2, R5 are 7 having 1 to 1 carbon atoms A/ =l
l-V 7 group, m and M' represent an alkali metal atom, or t represents an alkyl group having 1 to 10 carbon atoms.

This phosphoric acid compound may be used as it is as a chain extender, or ethylene glycol, 1,2-propylene glycol, 2,3-near ethylene glycol, 1,4-butylene glycol, 2,2-r methyl etc.゜3-7' 9-diol, diethylene glycol, 3-methyl-
A glycol such as 1,5-bentanediol, 1,6-hexamethylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimetatool alone or a mixture thereof and the phosphoric acid compound, succinic acid,
Maleic acid, adipic acid, glutaric acid, pimelic acid, speric acid.

Azelaic acid, sebacic acid, phthalic acid, isophthalic acid,
It can also be used as a polyester polyol with a number average molecular weight of 500 to s, ooo obtained by polycondensation with dibasic acids such as terephthalic acid and hexahydroisophthalic acid, their acid esters, and acid halides. 9, using the phosphoric acid compound as an initiator and having a t-number average molecular weight of 500 to 5,0
It can also be used as a 004 ricazololactone polyol. These polyols are referred to as t (A2).

A triol having 4 to 10 carbon atoms can be used as the polyol (A3) containing 1 & at least 1 tertiary hydroxyl in the molecular chain. For example 1,2,3-hydroxy-2
-Meflupronogun, 1,2,3-hydroxy-2-ethylglopane, 1,2,4-hydroxy-2-methylbutane, 1,2,5-hydroxy-2-methylpentane,
1,3.5-hydroxy-3-methylpentane, 1,3
．． Examples include monomers or mixtures such as 6-hydroxy-3-methylhexane.

These seven polymers may be used as chain extenders: ethylene glycol, 1,2-7'robylene glycol,
2,3-butylene glycol, 1,4-butylene glycol, 2,2-dimethyl-1,3-fcononodiol, diethylene glycol, 3-methyl-1,s-'! Tannediol, 1,6-hexamethylene glycol, 7
Chlohexane-1,4-diol.

Glycol such as cyclohexane-1,4-dimetatool alone or a mixture thereof and the monomer containing the tertiary hydroxyl group, succinic acid, maleic acid.

By polycondensation with dibasic acids such as adipic acid, glutaric acid, pimelic acid, superric acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, hexahydroisophthalic acid, and their acid esters and acid halides. It can also be used as a polyester polyol with a number average molecular weight of 500 to s, ooo. Also, the monomer containing the tertiary hydroxyl group can be used as a polycaprolactone polyol having a number average molecular weight of 500 to 5,000. These polyols (A
3).

Polyols (A4) containing 2 -PO(OM) groups and 1 & tertiary hydroxyl group having 2 or more hydroxyl groups in the molecular chain can be obtained by using together the phosphoric acid compound and the glycol containing the tertiary hydroxyl group. be synthesized. For example, ethylene glycol, 1.2-, "robilene glycol, 2.3-7"
tyrene glycol, 1.4-':' tyrene glycol,
2.2-Dimethyl-1,3-7' lower diol, diethylene glycol, 3-methyl-1,S-hentanediol, 1,6-hexamethylene glycol, cyclohexane-1,4-diol, cyclohexane-1 ,4-
A glycol such as dimethatol alone or a mixture thereof and the phosphoric acid compound and the glycol containing the tertiary hydroxyl group are combined with succinic acid, maleic acid, azopic acid, glutaric acid, pimelic acid, speric acid, azelaic acid, sebacic acid, phthalic acid, etc. Polyester polyols having a number average molecular weight of 500 to 5,000 are synthesized by polycondensation with acids, dibasic acids such as isophthalic acid, terephthalic acid, and hexahydroophthalic acid, their acid esters, and acid halides.

Examples of polyols (A5) having no polar group include polyether polyols, polyester polyols, polycabrolactone polyols, and low molecular weight glycols having a number average molecular weight of 500 to 5,000 terminal hydroxyl groups. Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Moreover, as a polyester polyol, ethylene glycol, 1.2
-Propylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 2,2-dimethyl-1
゜3-f diol, diethylene glycol.

3-methyl-1,5-pentanediol, 1,5-pentamethylene glycol, 1,6-hexamethylene glycol, cyclohexane-1,4-diol.

Glycols such as cyclohexane-1,4-dimetatool alone or in combination with succinic acid, maleic acid,
By polycondensation with dibasic acids such as adipic acid, glutaric acid, pimelic acid, superric acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, hexahydroisophthalic acid, and their acid esters and acid halides. Here are the things you can get. Furthermore, polycabrolactone diols obtained by ring-opening addition polymerization of a lactone such as C-caprolactone in the presence of a glycol or the like are used. As the low molecular weight glycol, the glycols used in the production of the polyester polyols can be used alone or in mixtures. Nine, carbon number 2-10
As the low molecular weight diols, glycols used in the production of the polyester polyols may be used alone or in mixtures. moreover,
Examples include bis7-el/-A, hydroquinone, and the like to which 12 to 4 moles of ethylene oxide or zolopyrene oxide are added.

It is essential that the hydroxyl group in the molecular chain of the polyol is tertiary. Primary and secondary hydroxyl groups have faster reactivity with isocyanates than tertiary hydroxyl groups,
Polymerization of polyurethane causes mesh formation, and the formation of thermoplastic polyurethane resin results in rotation.

Thermoplastic polyurethane resin containing two -PO(OM) groups and a tertiary hydroxyl group in the molecular chain used in the present invention (
A) is an organic diisocyanate (AI).

It is synthesized from the following combination of polyols.

That is, (A2) and (A3), or (A2) and (A4), or (A3) and (A4), or (A4) alone, and if necessary, these polyols are combined with (A5). You may. In addition, the OH/N00 molar ratio of polyol and organic diisocyanate is 0.8571, taking into account impurities (moisture, acid, hydrolytic chlorine, etc.) in each raw material.
．． 00-1.1571.00 preferably 0.95/1
．． 00 to 1.1571.00 is good. If it is outside these ranges, the excellent performances required by the present invention cannot be obtained.

Two IC-PO(OM) groups (
However, if necessary, catalysts and various stabilizers may be used for thermoplastic urethane resins that have a tertiary hydroxyl group (1M is an alkali metal atom or an alkyl group) and a tertiary hydroxyl group at positions other than the ends of the main chain. can.

Examples of catalysts include tertiary amines such as triethylamine and triethylenecyamine, nitrogen compounds such as morpholine and N-methylmorpholine, metal salts such as potassium acetate and zinc stearate, and organometallic compounds such as dibutyltin dilaurate and dibutyltin oxide. etc. The above-mentioned properties of the thermoplastic polyurethane can be significantly improved by incorporating stabilizers against ultraviolet rays such as substituted benzoazoles and stabilizers against thermal oxidation such as phenol derivatives.

Furthermore, the above-mentioned thermoplastic urethane resin can be produced by conventionally known methods. That is, after thoroughly mixing the reactants in the presence of a catalyst if desired, the reaction mixture is poured onto a flat plate or flat surface, heated, cooled, and then crushed. 1 Method of injecting the reaction mixture into an extruder. .

and a manufacturing method such as a solution reaction method in which the reaction is carried out in a single or mixed organic solvent such as dimethylformamide 9, toluene, xylene, benzene, dioxane, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, etc. can be used. As mentioned above, solvents suitable for magnetic coatings, including those for dissolving and diluting solid thermoplastic urethane resins, have an affinity for water.

Examples include toluene, xylene, benzene, etc. with low solubility, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, etc.

In the present invention, the thermoplastic urethane resin is finally used after being subjected to a curing reaction with a curing agent. The curing agent used in this case is optimally a low molecular weight j'' IJ isocyanate.

Examples of the low molecular weight polyisocyanate (B) having two or more isocyanate groups used in the present invention include organic diisocyanates used in the production of the thermoplastic polyurethane resin and low molecular weight polyisocyanates having two or more isocyanate groups (for example, low molecular weight polyisocyanates having two or more isocyanate groups). The molecular weight polyol is converted into a terminal isocyanate group using an isocyanate compound (t compound), and the number average molecular weight is 150 to 7000.
It is of a certain degree. Examples of low molecular weight diisocyanates having two or more isocyanate groups include the following compounds.

Commercially available products of this formula include Burnock@D-750°Crysden@NX (products of Dainippon Ink & Chemicals Co., Ltd.) and Desmodur (products of Sumitomo Bayer).

Coronet) L (Bhon Polyurethane Co., Ltd. product), Takene) D-102 (Takeda Pharmaceutical Co., Ltd. product), etc.

In addition to Maku, Burnock D-950 (manufactured by Inu Nippon Ink Kagaku Kogyo Co., Ltd.), Desmodur R, Desmodur RF (all products of Sumitomo Bayer), etc. can also be used.

/ and 7 Commercial product Burnock D-950 (Dainippon Ink & Chemicals Co., Ltd.)
Co., Ltd. product) Triphenylmethane 4.4', e-triisocyanate CO Commercial product Desmodur R (Sumitomo Bayer AG) The ratio of the thermoplastic urethane resin (A) and low molecular weight polyisocyanate (B) is particularly limited. Although not necessarily, the mechanical strength and abrasion resistance of the urethane resin after curing is preferably improved by adding 3 to 40 parts by weight of the above-mentioned low molecular weight polyisocyanate to 100 parts by weight of the above-mentioned thermoplastic urethane resin. , heat and humidity resistance, solvent resistance, and adhesion to the substrate can be greatly improved.

In addition, if necessary, a thermoplastic urethane resin that is normally used as a binder for a magnetic recording medium made of the above-mentioned thermosetting urethane resin composition obtained in this way may be used.

Commercially available products such as vinyl chloride, vinyl acetate copolymer, cellulose resin, vinyl chloride polymer, polyvinyl butyral resin, thermoplastic polyester resin, vinyl chloride-vinyl propionate copolymer, epoxy resin, and phenoxy resin. Improving the dispersibility of pigments by using them directly together with
It can be used to adjust the hardness of resin, etc.

The magnetic powder that can be used in the binder of the present invention is γ-Fe20.
, γ-F@205 and F.,04 mixed crystal, cobalt r-pulled f'-r-Fe 205 or Fe,04.
CrO2, barium ferrite, and other ferromagnetic alloy powders (
For example, F・-Co, Co-NL, Fe-Co-Ni
, Fe-Co-B, Fe-Co-Cr-B,
Mn-B1.

Examples include Mn-AA, F-Co-V), iron nitride, and the like. It is also possible to add aluminum oxide, chromium oxide, and silicon oxide as reinforcing agents to the binder, as well as squalane as a lubricant, cargen black as an antistatic agent, and V-cytin as a dispersant. In addition, the constituent materials of the binder are dissolved in an organic solvent to prepare a magnetic paint, and this is applied onto the paste. The solvent for the magnetic paint may include ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone), alcohol ( For example, methanol, ethanol, pro9ol.

butanol), esters (e.g. methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate, monoethyl ether), glycol ethers (glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane), aromatic hydrocarbons ( Examples include habenzene, toluene, xylene), aliphatic hydrocarbons (such as hexane and heptane), and nitroprone. The yeast for applying this magnetic food is non-magnetic and is made of polyester (eg, 1m, t? polyethylene terephthalate), ?
Lyolefins (side-lit polyzolopyrene), cellulose derivatives (e.g. cellulose triacetate, cellulose diacetate), polycargonates, polyvinyl chloride, polyimides, polyamides, polyhydrazides, metals (e.g. aluminum, steel).

It may be made of paper or the like.

The thermoplastic urethane resin obtained by the present invention has excellent physical properties such as pigment dispersibility, heat and humidity resistance, abrasion resistance, fluidity, and water elongation. It can also be used for other purposes. Examples include various printing inks, S, adhesives, various paints, conductive resins, and adhesives.

Next, the present invention will be explained with reference to examples, but these are merely embodiments and the present invention is not limited only by the examples.

9. All "parts" in the text indicate weight standards.

(Example) [1f! Synthesis method of urethane resin] Polyester polyol, polycaprolactone polyol, low molecular weight polyol, etc. were charged into a 95-liter stainless steel reaction vessel equipped with a condenser, thermometer, and stirring device, heated to 80°C, and the above polyol and Add 1.5 times the weight of cyclohexanone to the total amount of organic diisocyanates, and mix and stir uniformly.

Furthermore, 100 ppm based on cyclohexanone
After adding dibutyltin dilaurate gold and homogenizing, organic diisocyanate was added and reacted at 90°C. When the viscosity of the polyurethane resin solution reached the target value, methanol in an amount equal to the amount of unreacted isocyanate groups and methyl ethyl ketone in an amount equal to that of cyclohexanone were added to obtain a solution having a urethane resin concentration of 25% by weight.

The molecular weight of a polyurethane resin is determined by the weight average molecular weight in terms of the molecular weight of styrene using a Gruno 9-Miesch chromatography.

[Synthesis Examples 1 to 9 and Comparative Synthesis Examples 1 to 3] Synthesis Examples 1 to 9
And 1 of the polyester diol of Comparative Synthesis Examples 1 to 3, the type of polycabrolactone diol, and the chain extender! Table 1 shows the composition of the II class and the resulting polyurethane resin.

Polycaprolactone polyol (1): Phosphoric acid compound (
1) Polyol polycaprolactone polyol (■): Phosphoric acid compound (U
) t-initiator and ε-ka! Addition polymerization of rolactone results in the following polyol polycaprolactone polyol (II[): 1.3
．． 5-Human 10x-3-methylpentane K Used as an initiator, 6-caprolactone was added and combined to form a constant polyol.Polycaprolactone polyol (1'/): Using ethylene glycol as an initiator, 6-caprolactone was completely added and polymerized to obtain the next polyol phosphoric acid compound. (I): Diisoprovir N. N-bis(2-
and droxyethyl)aminomethylphosphonate phosphoric acid compound (n): N,N-bis(2-hydroxymethyl)aminomethylphosphonate disodium salt [Example Synthesis Examples 1 to 9 and Comparative Synthesis Examples 1 to 3 Polyurethane resin core fi (25%) obtained by 1689
Vinylite VAG) IC manufactured by Union Carbide, USA, vinyl chloride vinyl acetate copolymer) 28 parts cyclohexanone 320 parts Methyl ethyl ketone 700 parts Co-γ-Fe20
3350 parts Carden black 12 parts Lubricant 5 parts Above mixture i
&-After kneading for 48 hours in Rumil, Parnock D-7
50 (manufactured by Dainippon Ink and Chemicals Co., Ltd., low molecular weight - liisocyanate)) was added and kneaded for an additional hour to form a 16 micron thick film after drying on a 10 micron thick polyethylene terephthalate base film. After coating, drying, and calendering, the magnetic recording tape was cut into a predetermined width to prepare a magnetic recording tape.

Dispersibility test - Magnetic tape gloss test The magnetic surface of each magnetic tape before calendering was measured using a digital variable angle gloss meter at an incident angle of 45 degrees and a reflection angle of 45 degrees.

■ Squareness ratio f of the magnetic tape obtained in magnetic tape squareness measurement test VSM (Vlbra
tlnlSample Magn@tm@ter)'
Measured using fx.

Durability test [stiffness of magnetic tape] The stiffness of each of the obtained magnetic tapes was measured using a tape stiffness tester.

Magnetic Tape 0 Moisture Heat Resistance Test Obtained The magnetic tape was wound around a glass tube at 70'C1.
Store it at relative humidity for 500 hours, then leave it at room temperature for 24 hours. After that, unravel all the magnetic layers from the glass tube and evaluate whether there is any stickiness between the magnetic layer and the polyester film tube. 0: No adhesion Δ: Slight adhesion After rotating the roller of the abrasion tester 100 times, the amount of magnetic paint that fell off the magnetic layer was measured.

Gloss, squareness ratio, stiffness, durability of each magnetic tape,
Table 2 shows the measurement results of wear resistance and abrasion resistance.

As is clear from the results in Table 2, -PO(OM)
1. Surface gloss is achieved by using a polyurethane resin containing di- and tertiary hydroxyl groups as a binder for the magnetic layer.

The squareness ratio, stiffness, and durability are improved, and wear resistance is significantly improved. Therefore, it has been confirmed that the dispersibility of magnetic powder, the magnetic properties, durability, and wear resistance of magnetic recording media are significantly improved.

(Effects of the Invention) As is clear from the above description, the molecule used in the present invention contains two -PO(OM) groups and a tertiary hydroxyl group. 161J urethane resin has a high affinity for magnetic powder, so even when highly finely powdered submagnetic powder is used, it has good dispersibility, and the resulting magnetic recording medium has extremely excellent electromagnetic conversion properties. Surface smoothness is also improved.

Nineth, resins can be easily bonded together by reacting with a low molecular weight polyisocyanate containing tertiary hydroxyl groups.
As a result, the durability and abrasion resistance of the resulting magnetic recording medium are dramatically improved.

m-) table Dispersibility luster corner supervisor durability Stiffness [～/10μ 0.79 0.7910.7910.79 Humid heat resistance (adhesion) Abrasion resistance (powder falling) [m9] 1.5 1.4 ○ 0 2.1 2.1 Execution 0.79 example 0.80 0.80 0.79 ratio 0.73 comparison 0.73 example 0.74 1.8 1.8 2.2 3.8 2.0 ×　　　　Δ　　× 4.1. 2.8 15.5

Claims (1)

[Claims] PO(OM)_2 groups in the molecular chain (where M is an alkali metal atom or an alkyl group) and a tertiary hydroxyl group at positions other than both ends of the main chain and a molecular weight of 20,000 to 20
0000 thermoplastic polyurethane resin (A) and a low molecular weight polyisocyanate (B) having two or more isocyanate groups.