JPH0344819A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having high dispersibility, smoothness (calendering property) and high durability by incorporating a polyisocyanate compd. and a binder having at least one OH group at both ends of the molecule which is produced by the reaction of a specified polyurethane and specified compd. CONSTITUTION:The binder (C) having at least one OH group at both ends of the molecule is produced by the reaction of polyurethane resin (A) having at least one isocyanate group at each molecular end and >=0 deg.C glass transition temp.(Tg), and a compd. (B) having at least one OH group at each molecular end and <=-30 deg.C glass transition temp. (Tg). This binder (C) and a polyisocyanate compd. (D) are incorporated to prepare the binder. Thereby, the obtd. magnetic recording medium has high dispersibility, smoothness and high durability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability.

[Conventional technology]

Magnetic tape, which is a general-purpose magnetic recording medium, is made of long sleeve acicular ferromagnetic powder of 1 μm or less with appropriate additives (dispersants, lubricants, etc.).
Magnetic paint is created by dispersing it in a binder solution along with antistatic agents (antistatic agents, etc.), and then applying this to polyethine terephthalate film (non-magnetic support).

The properties required of binders for magnetic recording media include dispersibility, filling properties, and orientation of the ferromagnetic powder, durability of the magnetic layer, abrasion resistance, heat resistance, smoothness, and adhesion to nonmagnetic supports. etc., and binders play 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. Copolymers, nitrocellulose, cellulose acetate butyrate, epoxy resins, acrylic resins, etc. are used.

Among these resins, polyurethane resin has higher toughness and strength compared to other resins due to intermolecular hydrogen bonding caused by urethane bonds.
Although properties such as wear resistance are excellent, they are not necessarily satisfactory.

Furthermore, conventional adipate-type or caprolactone-type polyurethane resins alone have poor properties such as blocking resistance, heat resistance, and running stability. For this reason, polyurethane resin and nitrocellulose or vinyl chloride
A mixed system with a vinyl acetate copolymer is particularly used. However, in terms of properties such as durability, abrasion resistance, and running stability, they are still insufficient in fields that require high performance, such as video tapes, computer tapes, and floppy disks.

Polyisocyanate compounds are used as curing agents to improve the durability, abrasion resistance, etc. of magnetic recording media. Various polyurethane resins are being developed for the purpose of increasing their curability with polyisocyanate compounds and improving the durability, abrasion resistance, etc. of magnetic recording media.

For example, a method in which an isocyanate-terminated prepolymer is used and a trifunctional or higher-functional low molecular weight compound such as glycerin, trimethylolpropane, or pentaerythritol is used as part or all of the chain extender, or an epoxy group is introduced into a polyurethane resin. It is known to introduce a hydroxyl group into a side chain using a special method or a raw material, such as a method of ring-opening a group to generate a hydroxyl group.

However, these polyurethane resins have problems such as gelation sometimes occurring during production and the number of production steps being increased. The biggest problem when using these polyurethane resins as a binder for ferromagnetic powder in magnetic recording media is that polyurethane resins have traditionally had a disadvantage of poor dispersibility of ferromagnetic powder; The more you improve it, the bigger it will become.

In magnetic recording media, in order to improve the S/N ratio (signal/noise ratio) and increase the recording density ratio, finer ferromagnetic powder is packed into the magnetic layer and highly oriented or dispersed like metal particles. Measures are being taken such as using ferromagnetic powder, which is difficult to achieve.

At present, conventional polyurethane resins cannot satisfy these requirements for magnetic recording media.

In this way, with conventional polyurethane resins, the more the curing properties with polyisocyanate used as a curing agent are improved in order to improve the abrasion resistance and durability of magnetic recording media, the more the dispersibility of magnetic particles decreases. , S/N of magnetic recording medium
Unable to meet demands for improved ratio and higher recording density.

Therefore, in order to eliminate these drawbacks, it is recommended to use a polyurethane resin that has high reactivity with the hardening agent and good dispersibility of the ferromagnetic powder as a binder component in the magnetic layer.
has been done. That is, JP-A No. 62-226418 discloses a polymer having a molecular weight of 500 to 50, which is obtained by copolymerizing an isocyanate-terminated prepolymer with 1 to 20 mol% of a trifunctional or higher functional polycarboxylic acid or polyol based on the acid component or alcohol component.
A magnetic recording medium comprising a polyurethane resin reacted with a branched polyester polyol of 0.00 is disclosed. However, since both the isocyanate-terminated prepolymers and polyester polyols have large molecular weights and high glass transition temperatures (T9), their reactivity with curing agents is still insufficient.

[Purpose of the invention]

An object of the present invention is to provide a magnetic recording medium that has extremely high dispersibility, smoothness (calender durability), and high durability.

[Structure of the invention]

The above object of the present invention is to provide a magnetic recording medium provided with a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, wherein the binder has at least one isocyanate group at both ends. , a polyurethane (A) having a glass transition temperature (Tg) of O'C or higher, and at least one OH group at both ends, and a glass transition temperature (Tg) of -30°C
Achieved by a magnetic recording medium characterized by containing a binder (C) having at least one OH group at both ends obtained by reacting the following compound (B) and a polyisocyanate compound (D). can.

That is, the present invention uses polyurethane (A) having a Tg of 0°C or more and a polar group in the main chain to increase the mechanical strength of the binder and improve durability.
By bonding a compound (B) containing an OH group of 130"C or less, a polyurethane (C) having an OH group that is reactive with a highly mobile curing agent is obtained, and this binder is a polyisocyanate. By strongly reacting with (D), a magnetic recording medium with good dispersibility, excellent smoothness, and high durability can be obtained.

The polyurethane (A) having a Tg of 0'C or more and a polar group has a weight average molecular weight of 11,000 to 10,000, preferably 40,000 to 60,000, and a polar group of 1503M, -0503M,
PO3Mz, O, POO20-C00 gate, -N
R,, -NR3X (where M represents hydrogen, an alkali metal, or an ammonium group, R represents an alkyl group, and X represents a halogen atom) is preferred. Furthermore, an epoxy group, O
It is preferred that H groups are present, the amount of these polar groups being from I x 10-' to 50 x 10-' equivalents per gram of polymer, preferably from 2 x 10-5 to 20 x 10-' equivalents.

Such polyurethane (A) can be produced as follows, and specific examples thereof are as follows.

Polyurethane is synthesized by reacting a polyol containing a polar group, such as polyester polyol, polyether polyol, or polycarbonate polyol, with an organic diisocyanate compound and a low-molecular-weight diol as a chain extender. At this time, a polyurethane having isocyanate terminals can be obtained by adjusting the molar ratio of the polyol, diol, and diisocyanate compound.

The polar group-containing polyol can be prepared by a known method such as that described in JP-A-62-226418.

The polyurethane (A) used in the present invention has a Tg of 0°C
It is characterized in that it is the above and that the terminal is an isocyanate group. When Tg is at the 0°C end, the curability is high, but the overall mechanical strength is low and durability cannot be improved. Further, the terminal isocyanate group is a functional group for bonding the compound (B) described later.

The compound (B) of the present invention having a Tg of -30°C or less and having branches has a molecular weight of 300 to 1500, 3 or more OH groups per molecule, 1 to 5 branches, and a skeleton with a Tg of -30°C.
Hydrocarbons, polyesters, and polyethers having a temperature of 0°C or less are preferred.

If the Tg exceeds 130°C or the molecular weight is less than 300, the mobility of the branched chain to which the decreases and durability decreases. Therefore, in order to increase the mobility of the 10H group bonded to the end without reducing the Tg of the central portion of the polyurethane and its strength, and to improve the curability, compounds within the above range are preferred.

The polyurethane of the binder (C) of the present invention can be obtained by reacting the polyurethane (A) and the compound (B) in a conventional manner.

In the magnetic recording medium of the present invention, the content of the polyurethane in the binder is 10 to 70% by weight based on the total binder.
and preferably 15 to 40% by weight. If the content of the polyurethane in the binder is less than the above range, runnability and durability will be poor, and if it is higher than the above range, run problems such as head stains are likely to occur.

The polyisocyanate which is a component of the binder of the magnetic recording medium of the present invention is a compound having two or more isocyan i-+-a in the -molecule. Such polyisocyanates include, for example, tolylene diisocyanate),
4. Isocyanates such as 4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, 0-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and combinations of these isocyanates and polyalcohols. Examples include reaction products and polyisocyanates produced by condensation of these isocyanates. The above polyisocyanates are, for example, available from Nippon Polyurethane Industries Co., Ltd.
HL, Coronate EH, Coronate 2030, Coronate) 2031, Coronate 2036, Coronate 3015
, Coronate 3041, Coronate 2014, Millionate MR, Millione) MTL, Daltosec 1350
, Gertsec 21f 0. Dalto Sesoku 2280, Takenate D-102, Takenate D-11ON, Takenate D-200, Takenate D from Takeda Pharmaceutical Co., Ltd.
-202, Sumidur-N from Sumitomo Bayer Ltd.
75, Desmodule from West German Bayer, Desmodule L, Desmodule IL, Desmodule N,
Desmodur HL is sold by Dainippon Ink and Chemicals Co., Ltd. under trade names such as Burnock-D850 and Parnock D802.

The content of the polyisocyanate in the binder is such that the total number of isocyanate groups (-NC○) in the polyisocyanate is 2 to 100 times the total number of hydroxyl groups in the polyurethane in the binder, preferably The amount is preferably 5 to 50 times, particularly preferably 10 to 30 times. If the content of polyisocyanate in the binder is less than the above range, sticking of the magnetic recording medium,
Driving characteristics deteriorate due to clogging, guide pole dirt, etc.
The electromagnetic conversion characteristics also deteriorate, and if the amount exceeds the above range,
The running durability of stills, etc. may deteriorate.

As the binder for the magnetic recording medium of the present invention, other binders may be used in combination with the above-mentioned bowrethane. Other binders that can be used in combination are not particularly limited, and known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof, which are conventionally used as binders for magnetic recording media, can be used. can.

The polyurethane is 10 to 70% by weight based on the total binder.
It is preferable that the amount of the binder that can be used in combination is 20 to 60% by weight, and the amount of polyisocyanate is 10 to 50% by weight.

The above-mentioned thermoplastic resin has a softening temperature of 150°C or less and an average molecular weight of about 10,000 to 300,000, for example,
Vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer,
Acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer Polymer, urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, Examples include cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, and various synthetic thermoplastic resins. It will be done. Among these thermoplastic resins, vinyl chloride (co)polymerization-resistant, vinylidene chloride (co)polymers, and nitrocellulose are preferred.

In addition, the above-mentioned thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and its molecular weight becomes extremely large when heated after coating and drying, such as phenol resin. , phenoxy resin,
Epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, l mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer Examples include mixtures of polymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and mixtures thereof. Among these resins, phenoxy resins and epoxy resins are preferred.

-0POJz, -C00M, NRi, NRs
It is preferable to have a polar group such as X, an epoxy group, or a -0H group (where M is hydrogen, an alkali metal, or an ammonium group, R is an alkyl group, and X is a halogen atom).

The amount of the polar group is 1 x 10 to 50 x per 1 g of polymer.
IO-'This 1F, better < Ha2 x IO-'
~20xlO-' equivalents.

Particularly preferred binders that can be used in combination are polar group-containing vinyl chloride resins, such as rMR-110J (Nippon Zeon containing 5O3NB) and rlooFD.

(phosphoric acid containing: electrochemical), rMPR-TAO.

(Amine-containing: 8 Shin Kagaku), etc. This combination improves dispersibility.

The orientation ratio of the ferromagnetic powder and the binder in the magnetic layer of the magnetic recording medium of the present invention is preferably 15 to 35 parts by weight, particularly 20 to 30 parts by weight of the binder per 100 parts by weight of the ferromagnetic powder. . If the blending ratio of the binder is less than the above range, the running durability of the magnetic recording medium will deteriorate, and if it is more than the above range, the packing density of the ferromagnetic powder will become low, making it difficult to achieve the desired electromagnetic characteristics. There is a tendency for the coefficient of friction to increase.

The ferromagnetic powder used in the magnetic layer of the magnetic recording medium of the present invention may be any conventionally known ferromagnetic powder as long as it has a crystallite size of 450 Å or less. For example, T-oxide Iron-based ferromagnetic powder, cobalt-containing T-iron oxide-based ferromagnetic powder, ferromagnetic metal or alloy fine powder, iron nitride-based ferromagnetic powder, barium ferrite, strontium ferrite, etc. are used. In particular, ferromagnetic powders such as ferromagnetic metal or alloy powders are preferred.

There are no particular restrictions on the non-magnetic support in the present invention,
Those commonly used can be used. Examples of materials forming the non-magnetic support include various synthetic resin films such as polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, boria trimide, and bolyide, and metals such as aluminum electromagnetic and stainless steel foils. One example is foil.

The thickness of the nonmagnetic support is also not particularly limited, but is generally 2.5 to 100 μm, preferably 3 to 80 μm.

The magnetic recording medium of the present invention has the same structure as a conventionally known magnetic recording medium, except that the binder in the magnetic layer is specified as described above, so the technology can be used as appropriate. can.

For example, when manufacturing the magnetic layer of the magnetic recording medium of the present invention, ferromagnetic fine powder and a binder, an organic or inorganic filler,
Carbon black, dispersant, antistatic agent, il, liT
Known additives (materials) such as abrasives and abrasives are kneaded with a solvent to form a magnetic paint.

The above-mentioned filler is not particularly limited, and for example, the average particle size is in the range of 0.01 to 0.8 μm, preferably 0.06 to
Commonly used particulate fillers in the 0.4 μm range can be used. Examples of the above fillers include graphite, tungsten disulfide, boron nitride, calcium carbonate,
Examples include particles of aluminum oxide, iron oxide, titanium dioxide, magnesium oxide, zinc oxide, calcium oxide, lithopone, and talc, which can be used alone or in combination.

As the carbon black, furnace black, thermal paste, color pigment, acetylene black, etc. can be used. The properties of carbon black include an average particle size of 5 to 1000 mμ (electron microscope), a nitrogen adsorption specific surface area of 1 to 800 bo/g,
pH is 4-11 (JIS K6221), dibutyl phthalate oil absorption is 10-800/100g (JIS K6221)
K6221) is preferred. Regarding the size of carbon black, carbon black of 5 to 100 mμ is used for the purpose of lowering the surface electrical resistance of the coating film, carbon black of 50 to 100 μm is used for the purpose of suppressing the strength of the coating film, and carbon black of 50 to 100 μm is used for the purpose of reducing the surface electrical resistance of the coating film. Finer particles of carbon black (100 mμ or less) are used for smoothing to reduce spacing loss, and coarser particles of carbon black (less than 100 mμ) are used to roughen the surface and lower the coefficient of friction.
50 mμ or more). Fine particle carbon black and coarse particle carbon black may be used together. Also,
Carbon black whose surface is partially graphitized or grafted can also be used.

Examples of dispersants include fatty acids having 10 to 22 carbon atoms (e.g.
caprylic acid, capric acid, lauric acid, myristic acid,
palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, stearolic acid), the above fatty acids and alkali metals (e.g. lithium, sodium, potassium) or alkaline earth metals (e.g. magnesium, calcium, barium). ), esters of the above-mentioned fatty acids and compounds in which part or all of the hydrogen atoms of the compounds have been replaced with fluorine atoms, amides of the above-mentioned fatty acids, fatty acid acholine, higher alcohols, polyalkylene oxide alkyl phosphoric acids When using two dispersions, which may include known dispersants such as esters, alkyl phosphates, alkyl borates, sarcosinates, alkyl ether esters, trialkyl polyolefin oxy quaternary ammonium salts and lecithin, is 0°05 to 2 per 100 parts by weight of bonding used.
It is used in a range of 0 parts by weight.

Examples of antistatic agents include conductive fine powders such as carbon blank and carbon blank graft polymer; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin and glycidol; higher alkyl amines. cationic surfactants such as quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, phosphoniums or sulfoniums;
Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester groups, and phosphoric ester groups; Examples include amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols. be able to. When the above-mentioned conductive fine powder is used as an antistatic agent, it is used in an amount of, for example, 0.2 to 20 parts by weight per 100 parts by weight of the binder, and when a surfactant is used, it is used in an amount of 0.2 to 20 parts by weight. It is used in a range of 1 to IO parts by weight.

Examples of lubricants include the above-mentioned fatty acids, higher alcohols, fatty acids consisting of monobasic fatty acids with 12 to 20 carbon atoms, such as butyl stearate, and sorbitan oleate, and monohydric or polyhydric alcohols with 3 to 20 carbon atoms. esters,
In addition to mineral oils, animal and vegetable oils, olefin low polymers, α-olefin low polymers, known lubricants and plastic lubricants such as silicone oil, graphite fine particles, molybdenum disulfide fine particles, and Teflon fine particles can be mentioned. . The amount of lubricant added can be arbitrarily determined according to known techniques.

As the abrasive material, for example, Ti1t, TiO, ZnO1
CaO, 5nOz, S+02, cr-Fe203,
Cr, 03, tx-81203ZnS, Mo
5z, BaSO4, Ca5Oa, MgC01, BN
, SiC, and the like. These inorganic fillers may be used alone or in combination of two or more. The abrasive is 0 per 100 weight of binder.
．． 01 to 50 parts by weight.

There are no particular restrictions on the solvent used during kneading, and solvents commonly used for preparing magnetic paints can be used.

There is no particular restriction on the kneading method, and the order of addition of each component can be set as appropriate.

For the preparation of magnetic coatings, conventional kneading machines are used, such as two-roll mills, three-roll mills, ball mills, pebble mills Szegvari attritor, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, disper kneaders, high-speed mixers. -, homogenizers, ultrasonic dispersers, and the like.

Note that the above-mentioned additives such as dispersants, antistatic agents, and lubricants are not described with the limitation that they have only the effects described above; It is also possible that it acts as an agent or an antistatic agent. Therefore, it goes without saying that the effects of compounds etc. exemplified by the above classifications are not limited to those listed in the above classifications, and when using substances that have multiple effects, the amount of is preferably determined by considering the action and effect of the substance.

In addition, detergent dispersants, viscosity index improvers, pour point depressants,
Foam stoppers and the like can also be added.

The magnetic paint thus prepared is applied onto the aforementioned non-magnetic support. Coating can be performed directly onto the non-magnetic support, but it can also be applied onto the non-magnetic support via an adhesive layer or the like.

Examples of coating methods on non-magnetic supports include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating,
reverse roll coat, transfer roll coat,
Methods such as gravure coating, kiss coating, cast coating, spray coating, and spin cording can be used, and methods other than these can also be used.

In this way, the magnetic paint can be manufactured so that the thickness of the magnetic layer after drying is generally in the range of about 0.5 to 10 μm, particularly 1.5 to 7.0 μm.
It is applied in a range of m.

The magnetic layer coated on the non-magnetic support is then treated to orient the ferromagnetic powder and then dried. Furthermore, after surface smoothing treatment is performed as necessary, the material is cut into a desired shape.

A known back layer may be provided on the surface of the nonmagnetic support on which the magnetic layer is not provided.

〔Effect of the invention〕

The present invention uses polyurethane (A) having a Tg of 0°C or more and a polar group in the main chain to increase the mechanical strength of the binder, improve durability, and improve the dispersibility of the ferromagnetic powder. , and by bonding an OH group-containing compound (B) with a Tg of 30°C or less to both ends, a polyurethane (C) having an OH group at the end that easily reacts with a highly mobile curing agent can be obtained. , this binder is polyisocyanate C
By strongly reacting with D), a magnetic recording medium with good dispersibility, excellent smoothness, and high durability can be obtained.

That is, since the OH group is added to the end of the polyurethane main chain, the dispersibility of the ferromagnetic powder is not reduced due to polar groups, and the compound (B) reacted at the end has a low Tg and a moderate side chain length. Because of its high mobility, it is possible to obtain a smooth magnetic layer with high calenderability, and its reactivity with polyisocyanate is high, resulting in improved durability. Furthermore, since the Tg of the polyurethane main chain is as high as 0°C or higher, the strength of the entire coating film is high and the durability is high.

〔Example〕

Next, Examples and Comparative Examples of the present invention will be shown.

On each side, "parts" refer to "parts by weight."

The polyurethane used in each example and comparative example was
Using the ingredients shown in Table 1, using the conventional method ("synthetic polymer")
Volume V, pages 309-369, Asakura Shoten, June 1, 1971.
It was synthesized according to the following publication (published on the 5th).

Aiminami Gokuri fatigued ferromagnetic Fe-Ni alloy powder (crystallite size 250, pH 9) 100 parts carbon black (average particle size 40 nm, oil absorption 160 d/100 g) α-Azz O.

(Average particle size 200 nm) Stearic acid Oleic acid Isoamyl stearate Butyl stearate Methyl ethyl ketone Toluene Cyclohexanone 2 parts 5 parts 1 part 1 part 1 part 200 parts 50 parts 50 parts Among the above coating liquid formulations, polyisocyanate compound, stearic acid After removing oleic acid, the mixture was dispersed in a ball mill for 50 hours, and then the remaining composition was added and stirred to prepare a magnetic layer coating solution.

The surface of a 10 μm thick polyethylene terephthalate base (non-magnetic support) was coated, oriented in a magnetic field using a cobalt magnet, dried in an atmosphere at a temperature of 100°C for 1 minute, calendered, and heated at 60°C for 4 days. After heat treatment,
8III11 videotape samples were created by slitting them into 8 widths. The results obtained are shown in Table 2.

Name of polyurethane basic skeleton 1.4-BD=1.4-butanediol AA -adipic acid MDT -diphenylmethane diisocyanate-TDI
=Tolylene diisocyanate 1.6-HD=1. 6-hexanediol NPC = neopentyl glycol IPDI - isophorone diisocyanate HMDI = hexamethylene diisocyanate PA = phthalic acid compound (B) (a): CH3Cl1zC[Cll0COCI71
13501113): Cll:+CIbC[C1
1zO(CHzCHzO+ sH) 3(C) Nido C113C1I□C[CII□O(CC1hC11zC
O-CHzCH2OCII□CHzO)-ztll s
111 0 (d); C11゜CH*CII□C[(CIl□QC(C!lz) ac
OOctI□CCl1. O←3H131 C113 As is clear from the results in Tables 1 and 2, the use of the polyurethane compound of the present invention not only provides both high electromagnetic conversion characteristics and durability, but also prevents calendar roll staining during the manufacturing process. be able to.

Claims (3)

[Claims] (1) In a magnetic recording medium provided with a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, the binder has at least one isocyanate group at both ends, and the glass transition temperature is (Tg) has a polyurethane (A) of 0°C or higher and at least one OH group at both ends,
Compound (B) with a glass transition temperature (Tg) of -30°C or lower
1. A magnetic recording medium comprising a binder (C) having at least one OH group at both ends obtained by reacting with the polyisocyanate compound (D) and a polyisocyanate compound (D). (2) The magnetic recording medium according to claim 1, wherein the binder further contains a polar group-containing vinyl chloride copolymer. (3) The polar group is -SO_3M, -OSO_3M, -
PO_3M_2, -OPO_3M_2, -COOM, -
Claim (1), characterized in that it is at least one of NR_2, -NR_3X (where M represents hydrogen, an alkali metal, or an ammonium group, R represents an alkyl group, and X represents a halogen atom); or (2) Magnetic recording medium.