JPH06259746A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce the porosity in a magnetic layer by combining specified glycols with specified dibasic acids in polyurethane resin using polyester diol as one of starting materials. CONSTITUTION:A magnetic layer is formed on a nonmagnetic substrate by coating with a magnetic material prepd. by dispersing ferromagnetic powder in a binder to obtain the objective magnetic recording medium. The binder contains polyurethane resin consisting of high molecular polyol having >=500mol. wt. and an org. diisocyanate or further contg. a polyol compd. having <=500mol. wt. At least 50wt.% of the high molecular polyol is polyester diol, >=60mol% of all the glycol components of this polyester diol are branched glycol and alicylic glycol in (20:80)-(80:20) molar ratio and >=80mole% of all the acid components of the polyester diol are an arom. dibasic acid and an alicyclic dibasic acid in (0:100)-(90:10) molar ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a magnetic tape or a magnetic disk which has excellent dispersibility and filling of fine magnetic powder and excellent durability of a magnetic layer. Is.

[0002]

2. Description of the Related Art A magnetic tape, which is a general-purpose magnetic recording medium,
The floppy disk is prepared by dispersing needle-like magnetic particles with a major axis of 1 μm or less in a binder solution together with additives such as a dispersant, a lubricant and an antistatic agent to prepare a magnetic paint, which is applied to a polyethylene terephthalate film. Has been.

Properties required for the binder of the magnetic layer include dispersibility of magnetic particles, packing properties, orientation, magnetic layer durability, abrasion resistance, heat resistance, and adhesion to a non-magnetic support. The binder plays a very important role.

Binders that have been conventionally used include
Vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer, vinyl chloride / vinylidene chloride copolymer, polyurethane resin, polyester resin, acrylonitrile / butadiene copolymer, nitrocellulose, cellulose acetate / butyrate , Epoxy resin, acrylic resin, etc. are used.

Among these resins, polyurethane resin is superior in toughness and abrasion resistance to other resins due to intermolecular hydrogen bond by urethane bond. However, conventional polyurethane resin has a dispersibility of magnetic powder. However, various studies have been conducted to improve this. For example,
One using a urethane resin derived from a polyester polyol containing 2,2-dialkyl-1,3-propanediol (JP-A-2-240177), a polyurethane resin using a polyhydric alcohol having a branched chain (special Kaihei 2-177020).

[0006]

Magnetic particles used to improve image quality in video tapes and to improve sound quality in audio tapes tend to be finer and have a high coercive force to improve recording density. Magnetic particles are used. The finer the magnetic particles and the higher the coercive force, the more difficult the conventional binder is to disperse, and it is required that the dispersibility of the magnetic particles in the binder is higher. JP-A-2-240177, JP-A-2-240177
Improvement in the dispersibility of the binder in 177020 is recognized, but it is not always satisfactory.

Further, in the magnetic recording medium, the magnetic layer is finely filled with finely-divided magnetic particles to improve the S / N ratio (signal / noise ratio) and increase the recording density, and the magnetic layer is highly oriented. The surface is made smooth. The smoother the surface of the magnetic layer is, the worse the running property and running durability of the magnetic tape are, and a binder having good durability, abrasion resistance, heat resistance, and adhesiveness with a non-magnetic support is required. There is. Conventional binders for magnetic layers are insufficient to meet these requirements. Therefore, it is an object of the present invention to improve the dispersibility and filling property of finely divided magnetic particles and to provide a magnetic recording medium having excellent durability.

[0008]

Means for Solving the Problems As a result of diligent studies on a polyurethane resin in order to achieve the object of the present invention, as a result of combining a specific glycol and a dibasic acid in the polyurethane resin containing polyester diol as a raw material, The inventors have found that the dispersion performance of particles and the filling property of the magnetic layer are improved and the porosity in the magnetic layer is reduced, and thus the present invention has been accomplished.

That is, according to the present invention, in a magnetic recording medium in which a magnetic material in which ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, a molecular weight of 5 is used as the binder component of the magnetic layer.
00 or more polymer polyol (A), organic diisocyanate (B), and optionally a polyurethane resin comprising a polyol compound (C) having a molecular weight of 500 or less, and at least 50% by weight of the polymer polyol (A) is a polyester diol. (A ₁ ), 60 mol% or more of the total glycol component of the polyester diol (A ₁ ) is a branched glycol and an alicyclic glycol, and the ratio of the branched glycol and the alicyclic glycol is 20:80 to. 8
It is 0:20 (molar ratio), and 80 mol% or more of all the acid components of the polyester diol (A ₁ ) is an aromatic dibasic acid and an alicyclic dibasic acid. The magnetic recording medium is characterized in that the ratio of the cyclic dibasic acid is 0: 100 to 90:10 (molar ratio).

Examples of the polymer polyol (A) of the polyurethane resin used in the present invention include polyester polyol, polyether polyol, polycarbonate polyol and the like.

At least 50% by weight of the polymer polyol (A) of the polyurethane resin used in the present invention is a polyester diol (A ₁ ) made of a specific raw material, and the glycol component of the polyester diol has a branched chain. Containing one or more branched glycols and alicyclic glycols as essential components, specifically, in the branched glycols, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2, 3-butylene glycol, 2,2-dimethyl-1,3-propanediol, 3-methyl-
1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,2-
Dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-
Hydroxypropanate, 2-normal butyl-2-ethyl
-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 3-octyl-1,5 -Pentanediol, 3-myristyl-1,5-pentanediol, 3-stearyl-1,5-pentanediol, 3-phenyl-1,5-pentanediol, 3- (4-nonylphenyl) -1,5- Pentanediol, 3,3-bis (4-nonylphenyl) -1,5-pentanediol, 2,5-dimethyl-3-sodium sulfo-2,5-hexanediol and the like can be mentioned. 2-dimethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate, 2-normal-butyl-2-ethyl-1,3-propane The diol and 2,2-diethyl-1,3-propanediol are particularly preferred.

Examples of the alicyclic glycol include 1,2-bis (hydroxymethyl) cyclopropane, 1,3-bis (hydroxyethyl) cyclobutane, 1,3-bis (hydroxymethyl) cyclopentane and 1,3-bis. (Hydroxymethyl)
Cyclohexane, 1,4-bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethyl) cyclohexane, 1,4-bis (hydroxypropyl) cyclohexane,
1,4-bis (hydroxyethyl) cycloheptane, 1,4-bis (hydroxymethoxy) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane, 2,2-bis (4-
Hydroxymethoxycyclohexyl) propane, 2,2-bis (4-hydroxyethoxycyclohexyl) propane,
Bis (4-hydroxycyclohexyl) methane, 2,2-bis (4-hydroxycyclohexyl) propane, 3 (4), 8
Examples include (9) -tricyclo [5.2.1.02,6] decane dimethanol. Of these, 1,4-bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane and bis (4-hydroxycyclohexyl) methane are particularly preferable.

The acid component of the polyester diol (A ₁ ) contains an aromatic dibasic acid and an alicyclic dibasic acid as essential components. Specific examples of the aromatic dibasic acid include terephthalic acid and isophthalic acid. , Orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, 3,4-biphenyldicarboxylic acid,
Aromatic dicarboxylic acids such as 4,4'-diphenylmethane dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoterephthale Mention may be made of dicarboxylic acids containing sulfonic acid metal salts such as acids. Among these, terephthalic acid, isophthalic acid, orthophthalic acid and 5-sodium sulfoisophthalic acid are particularly preferable.

The alicyclic dibasic acids include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,
1,4-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2-bis (4-carboxycyclohexyl) methane, 2,2-bis (4-carboxycyclohexyl) propane and the like, Particularly, 1,2-cyclohexanedicarboxylic acid and 4-methyl-1,2-cyclohexanedicarboxylic acid are preferable.

As diol components and carboxylic acid components other than the above, ethylene glycol, propylene glycol,
Aliphatic glycols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol, and sulfonic acid metal salts such as 2-sodium sulfo-1,4-butanediol And aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid are preferred, and ethylene glycol is preferred as the glycol component.

A trifunctional or higher-functional compound such as trimellitic anhydride, glycerin, trimethylolpropane and pentaerythritol is used as a part of the raw material of the polyester diol (A ₁ ) in the organic solvent solubility of polyurethane resin and the coating workability. You may use it in the range which does not impair the characteristics.

The high molecular weight polyol component (A) of the polyurethane resin used in the present invention has a molecular weight of preferably 500 or more, more preferably 500 to 5,000. If the molecular weight is less than 500, the urethane group concentration will be too high and the dispersibility of the magnetic powder and low temperature characteristics will deteriorate. If the molecular weight exceeds 5,000, the characteristics such as toughness and abrasion resistance characteristic of polyurethane resins will deteriorate.

Polyester diol (A ₁ ) of polymer polyol (A) of polyurethane resin used in the present invention
As a component, 60 mol% or more of all glycol components are branched glycol and alicyclic glycol, and the ratio of branched glycol and alicyclic glycol is 20:80 to 80:20.
(Molar ratio), preferably 30:70 to 70:30 (molar ratio). When the content of the branched glycol component is less than 20 mol%, the solvent solubility is poor, and when the content of the branched glycol component exceeds 80 mol%, the mechanical properties of the polyurethane resin are deteriorated and the properties such as toughness and abrasion resistance are deteriorated. .
When the amount of the branched glycol and the alicyclic glycol is less than 60 mol% of the total glycol component, the dispersibility and filling property of the magnetic powder are deteriorated and the effect of the present invention cannot be obtained.

At least 80 mol% of the total acid component of the polyester diol (A ₁ ) is an aromatic dibasic acid and an alicyclic dibasic acid, and the ratio of the aromatic dibasic acid and the alicyclic dibasic acid is Is 0: 100 to 90:10 (molar ratio), preferably 30:
It is used in the range of 70 to 80:20 (molar ratio). Aromatic dibasic acids and alicyclic dibasic acids account for 80 mol% of all acid components
If it is less than the above range, the toughness, abrasion resistance, hydrolysis resistance and the like of the polyurethane resin deteriorate. In addition, the aromatic dibasic acid component is 9
If it exceeds 0 mol%, the effect of the present invention is not observed. Copolymerization of branched glycols, alicyclic glycols, and alicyclic dibasic acids in the polyurethane resin skeleton in the proportions shown in the scope of the claims allows the aggregation of polymer molecules without significantly lowering the glass transition temperature of the resin. It is possible to reduce the energy density. This improves the wettability of the binder polymer molecule to the surface of the magnetic powder in the magnetic paint, and improves the dispersion ability. As a result, electromagnetic conversion characteristics,
And a magnetic layer excellent in durability can be obtained.

Examples of the diisocyanate compound (B) used in the production of the polyurethane resin used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate and m-phenylene. Diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4 '-Diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane, 4,4'-diiso A sulfonates cyclohexane, 4,4'-diisocyanate cyclohexylmethane, isophorone Socia sulfonate, and the like.

A low molecular weight compound having two or more functional groups in one molecule which reacts with an isocyanate (C) having a molecular weight of less than 500, which is optionally used in the production of the polyurethane resin used in the present invention, may be a urethane group concentration in the polyurethane or the like. Available for adjustment. A low molecular weight compound having 3 or more functional groups that react with isocyanate in one molecule is effective in improving the reactivity with a general-purpose curing agent.

Specific compounds include ethylene glycol, 1,3-propylene glycol, 1,6-hexanediol, cyclohexanedimethanol, xylylene glycol, diethylene glycol, triethylene glycol,
Linear glycol such as ethylene oxide adduct of bisphenol A, propylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol,
2,2,4-Trimethyl-1,3-pentanediol, branched glycols such as propylene oxide adduct of bisphenol A, amino alcohols such as N-methylethanolamine, monoethanolamine, diethanolamine, trimethylolpropane, glycerin, penta Examples thereof include polyols such as erythritol and dipentaerythritol, and ε-caprolactone adducts of one of these polyols.

The reaction method may be either a method in which the raw materials are melted or a method in which they are dissolved in a solution.
The number average molecular weight of the polyurethane resin used in the present invention is preferably in the range of 5,000 to 80,000. When the molecular weight is less than 5,000, the mechanical strength of the polyurethane resin is lowered, and when it exceeds 80,000, the solution viscosity becomes too high and it may be difficult to handle.

As a reaction catalyst, stannous octylate, dibutyltin dilaurylate, triethylamine and the like may be used. Further, an ultraviolet absorber, a hydrolysis inhibitor, an antioxidant and the like may be added before, during or after the production of the polyurethane resin.

In the present invention, in addition to the polyurethane resin used in the present invention, for the purpose of adjusting flexibility, improving cold resistance and improving durability, other resin is added and / or a polyurethane resin is used. It is desirable to mix compounds that react and crosslink. Examples of other resins include vinyl chloride resins, polyester resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, and the like.

On the other hand, a compound that crosslinks with the polyurethane resin
As, a polyisocyanate compound, an epoxy resin,
Melamine resin, urea resin, etc. are available.
A lisocyanate compound is preferred. Magnetic recording of the present invention
The magnetic particles used in the magnetic layer of the medium include γ-Fe
₂O ₃, Γ-Fe₂O₃And Fe₃O_FourCrystal of Cr
O₂, Fe coated with cobalt₂O₃Or Fe₃
O_Four, Barium ferrite and Fe-Co, Fe-Co
-Ferromagnetic alloy powder such as Ni, pure iron, etc.
It

Particularly, the finely divided magnetic powder having a surface area of BET of 40 m ² / g or more, alloy powder, or magnetic powder in which barium ferrite or the like is difficult to disperse, and the polyurethane resin of the present invention is particularly effective.

The magnetic recording medium of the present invention may optionally contain a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctyl sulfosodium succinate, t-.
Butylphenol / polyethylene ether, ethylnaphthalene / sodium sulfonate, dilauryl succinate,
Lubricants such as zinc stearate, soybean oil lecithin, silicone oil and various antistatic agents can also be added.

[0029]

In the polyurethane resin used in the present invention, at least 50% by weight of the starting polymer polyol component (A) is the polyester diol (A ₁ ), and 60 mol% or more of the total glycol component of the polyester diol is a branched glycol. And alicyclic glycol, and the ratio of branched glycol to alicyclic glycol is 20:80 to 80:20.
(Molar ratio), wherein 80 mol% or more of all the acid components of the polyester diol are aromatic dibasic acid and alicyclic dibasic acid, and the ratio of aromatic dibasic acid and alicyclic dibasic acid Is 0: 100 to 90:10 (molar ratio).

By branching the polyurethane resin skeleton with a branched glycol, an alicyclic glycol and an alicyclic dibasic acid in the proportions shown in the claims, the glass transition temperature of the resin is maintained at a relatively high level. It is possible to reduce the cohesive energy density of the polymer molecule as it is. As a result, the polymer molecule exhibits good solubility in a mixed solvent such as toluene, mail ethyl ketone, and cyclohexanone generally used in this field, and the molecular size in the solution is widened. In such a state, the wettability of the polymer particles with respect to the surface of the magnetic powder in the solution is improved, and the magnetic powder dispersion ability of the binder polymer molecule is maximized. As a result, a magnetic layer having excellent electromagnetic conversion characteristics and excellent durability can be obtained.

[0031]

The present invention will be specifically illustrated by the following examples. In the examples, "parts" means "parts by weight". The composition, molecular weight, and T of the polyester diol (A ₁ ) used in the following synthetic examples of polyurethane resin and comparative synthetic examples
g is shown in Tables 1 and 2. The abbreviations in the table are as follows. OPA: Orthophthalic acid IPA: Isophthalic acid
TPA: terephthalic acid HOPA: 1,2-cyclohexanedicarboxylic acid HTPA: 1,4-cyclohexanedicarboxylic acid 4 M-HOPA: 4-methyl-1,2-cyclohexanedicarboxylic acid SA: sebacic acid AA: adipic acid NPG: 2, 2-Dimethyl-1,3-propanediol DMH: 2-butyl-2-ethyl-1,3-propanediol HPN: 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-
Dimethyl-3-hydroxypropanate CHDM: 1,4-bis (hydroxymethyl) cyclohexane HBF: Bis- (4-hydroxycyclohexyl) methane EG: Ethylene glycol MDI: 4,4'-diphenylmethane diisocyanate Vinyl chloride copolymer: MEK / toluene = 1 / so that the solid content concentration of MR-110 manufactured by Zeon Corporation is 30%.
It was dissolved in the mixed solvent of No. 1 and used.

The number average molecular weight in the polyurethane resin was measured by gel permeation chromatography using tetrahydrofuran as a solvent, and the value in terms of standard polystyrene was measured. The gloss of the magnetic layer of the magnetic tape was measured at 60 degrees. The squareness ratio of the magnetic layer was measured by using a vibration test magnetometer and measuring the squareness ratio in the vertical direction. The magnetic layer density was determined by measuring the weight and volume of the magnetic layer. The wear resistance of the magnetic layer is S-commercially available.
Put it on a VHS VCR and run it at 10 ° C for 10
After scratching the magnetic layer for 0 times, scratches on the magnetic layer were observed, and the degree was evaluated according to the following 6 grades. 6: Almost no scratch 5: Slightly scratched 4: Slightly scratched and slightly noticeable 3: Scratched and noticeable, not reaching the PET film 2: Scratched and noticeable, PET film surface is slightly visible 1: Scratched and noticeable, Many PET film surfaces can be seen

Synthesis Example 1 100 parts of fully dried polyester a and HPN:
Dissolve 14 parts in 40 parts of toluene and 40 parts of MEK,
DI: 29.5 parts was added and reacted at 80 ° C. for 10 hours,
A polyurethane resin (a) was obtained by diluting with toluene: 128 parts and MEK: 128 parts. Table 3 shows the properties of the polyurethane resin (a).

Synthesis Examples 2 to 6 Polyurethane resins (b) to (f) were obtained with the raw material compositions shown in Table 3 in the same manner as in the production method of Synthesis Example 1. The characteristics of each polyurethane resin are shown in Table 3.

Synthesis Example 7 60 parts of fully dried polyester a: toluene:
Dissolve in 96 parts, add MDI: 29.5 parts, polyester I: 40 parts, HPN: 14 parts and react at 80 ° C. for 10 hours and dilute with toluene: 72 parts, MEK: 168 parts to obtain polyurethane resin (g) Obtained. Polyurethane resin (G)
The characteristics of are shown in Table 3.

Synthesis Example 8 A polyurethane resin (h) was obtained with the raw material composition shown in Table 3 in the same manner as in the production method of Synthesis Example 7. The characteristics of the polyurethane resin (H) are shown in Table 3.

Comparative Synthetic Example 1 Polyester g was used in place of the polyester a used in Synthetic Example 1, and a polyurethane resin (i) was obtained in the same manner as in the manufacturing method of Synthetic Example 1. Table 4 shows the characteristics of polyurethane resin
Shown in. In this example, the ratio of branched glycol to alicyclic glycol is outside the scope of the claims.

Comparative Synthetic Examples 2 to 5 Polyurethane resins (n) to (wa) were obtained with the raw material compositions shown in Table 2 in the same manner as in the production method of Synthetic Example 1. The characteristics of each polyurethane resin are shown in Table 4. In Comparative Synthesis Example 2, the ratio of the branched glycol and the alicyclic glycol is outside the scope of the claims, and in Comparative Synthesis Example 3, the contents of the branched glycol and the alicyclic glycol are outside the scope of the claims. In Comparative Synthesis Example 4, the ratio of the aromatic dibasic acid and the alicyclic dibasic acid is outside the scope of the claims, and in Comparative Synthesis Example 5, the content of the aromatic dibasic acid and the alicyclic dibasic acid is It is outside the scope of claims.

Comparative Synthesis Example 6 A polyurethane resin (f) was obtained with the raw material composition shown in Table 4 in the same manner as in the production method of Synthesis Example 7. Table 4 shows the characteristics of the polyurethane resin (f). In Comparative Synthesis Example 6, the content of the polyester diol (a) with respect to the high molecular weight polyol (A) falls outside the scope of claims.

Example 1 Using the polyurethane resin (a) shown in Table 3, a composition having the following blending ratio was placed in a ball mill and dispersed for 24 hours, and then stearic acid as a lubricant: 1 part, butyl stearate. : 1 part, Coronate L of isocyanate compound
(Manufactured by Nippon Polyurethane Industry Co., Ltd.): 6 parts was added as a curing agent, and the dispersion was continued for 1 hour to obtain a magnetic coating material. On a polyethylene terephthalate film with a thickness of 12μ,
It was applied while applying a magnetic field of 2,000 gauss so that the thickness after drying was 4 μm. After aging at 50 ° C. for 48 hours, it was slit into a 1/2 inch width to obtain a magnetic tape. The characteristics of the obtained magnetic tape are shown in Table 5. 30% solution of polyurethane resin (a) 100 parts Ferromagnetic iron oxide powder (Co-γ-Fe ₂ O ₃ system BET 45 m ² / g) 120 parts Alumina oxide powder (average particle size 0.2 μm) 5 parts Cyclohexanone 100 parts MEK 50 parts Toluene 50 parts

Examples 2 to 8 Using the binders shown in Table 5, magnetic tapes were obtained in the same manner as in Example 1. Table 5 shows the characteristics of each magnetic tape.

Comparative Examples 1 to 8 Using the binders shown in Table 6, magnetic tapes were obtained in the same manner as in Example 1. Table 6 shows the characteristics of each magnetic tape.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

[0049]

INDUSTRIAL APPLICABILITY The magnetic recording medium using the specific polyurethane resin of the present invention has excellent dispersibility and filling property of the magnetic layer, and as a result, excellent smoothness, durability and magnetic characteristics of the magnetic layer, and A magnetic recording medium having excellent wear resistance can be supplied.

Claims (1)

[Claims] 1. Magnetic properties in which a ferromagnetic powder is dispersed in a binder
In a magnetic recording medium in which a material is coated on a non-magnetic support
As a binder component of the magnetic layer,
Child polyol (A), organic diisocyanate (B), and
And, if necessary, a polyol compound having a molecular weight of 500 or less
(C) a polyurethane resin,
At least 50% by weight of Liol (A) is polyester
Diol (A ₁) And the polyester diol (A
₁60% by mole or more of the total glycol component of) is branched grease.
Cole and alicyclic glycol, with branched glycol
The ratio of alicyclic glycol is 20:80 to 80:20 (model
Of the polyester diol (A₁) Total acid
80 mol% or more of the components are aromatic dibasic acids and alicyclic diacids.
Basic acid, the ratio of aromatic dibasic acid and alicyclic dibasic acid
Is 0: 100 to 90:10 (molar ratio)
And a magnetic recording medium.