JP2882500B2 - Magnetic recording media - Google Patents

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 such as a magnetic tape and a magnetic disk. More specifically, the present invention relates to a magnetic recording medium using a polyurethane resin having excellent properties as a binder for a magnetic layer provided on a nonmagnetic support.

[0002]

2. Description of the Related Art A magnetic tape as a general-purpose magnetic recording medium is prepared by dispersing acicular magnetic particles having a major axis of 1 μm or less together with a suitable additive (dispersant, lubricant, antistatic agent, etc.) in a binder solution. It is made by making a magnetic paint and applying it on a polyethylene terephthalate film.

[0003] The properties required for the binder of the magnetic recording medium include the dispersibility, filling property, and orientation of the magnetic particles, durability of the magnetic layer, abrasion resistance, heat resistance, and adhesion to the non-magnetic support. The binder plays 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 and the like are used.

[0004]

SUMMARY OF THE INVENTION In magnetic recording media, S /
In order to improve the N ratio (signal / noise ratio) and increase the recording density, the magnetic layer is highly filled with finer magnetic particles and highly oriented, and the surface of the magnetic layer is smoothed.
Alternatively, measures have been taken such as the use of hardly dispersible magnetic particles such as metal particles and barium ferrite particles. Therefore, a binder having better dispersibility is required.
In addition, a binder having better running durability is required to make the surface of the magnetic layer smooth.

[0005] In addition, the requirements for these magnetic recording media are:
As the level of magnetic recording technology in recent years has increased, the situation has become more severe, and the current situation is that conventional polyurethane resins cannot be satisfied. In view of the above circumstances, it is an object of the present invention to provide a magnetic recording medium which is excellent in dispersibility of magnetic particles and has excellent durability in simultaneous running.

[0006]

Means for Solving the Problems The present inventors have found that the lower the urethane bond concentration in the polyurethane resin, the higher the dispersibility of the magnetic powder and the lower the porosity of the magnetic layer. However, a decrease in the urethane bond concentration of the polyurethane resin deteriorates characteristics such as toughness and abrasion resistance, which are peculiar to the polyurethane resin, so that the running durability required for the magnetic recording medium cannot be satisfied. Then, as a result of further intensive studies, the present invention has been reached. That is, the present invention relates to a magnetic recording medium in which a magnetic coating material in which a ferromagnetic powder is dispersed in a binder is applied on a non-magnetic support, wherein a high molecular weight polyol having a molecular weight of 500 to 10,000 is used as a component of the binder. A hydroxyl group-terminated polyurethane resin comprising a component (A), a diisocyanate compound (B), and a low molecular weight compound (C) having a molecular weight of less than 500 having two or more functional groups which react with isocyanate in one molecule as required;
The polyurethane resin comprises a high-molecular-weight polyol component (A) comprising a low Tg polyol component (a1) having a glass transition temperature of -20 ° C or lower and a high Tg polyol component (a2) having a glass transition temperature of 20 ° C or higher. Ingredient (a
1) and the high Tg polyol component (a2) in a weight ratio of 10:
90 to 70:30, and the urethane bond concentration in the polyurethane resin is 500 to 1,50 per ton of resin.
The terminal of the resin is a low Tg polyol component (a1) or a low molecular weight compound (C), and when the terminal is a low molecular weight compound (C), the low molecular weight compound (C) is A magnetic recording medium characterized by being bonded to the low Tg polyol component (a1) via the diisocyanate compound (B).

The polyurethane resin of the present invention is intended to improve the decrease in running durability caused by the decrease in the urethane bond concentration by using a specific high molecular polyol component and the structure of the polyurethane resin.

The polyurethane resin used in the present invention has a glass transition temperature of -2 as the high molecular weight polyol component (A).
A low Tg polyol component (a1) having a temperature of 0 ° C. or less and a high Tg polyol component (a2) having a glass transition temperature of 20 ° C. or more are used in combination. When the glass transition temperature of the low Tg polyol component (a1) used exceeds -20 DEG C., the reactivity with the general-purpose curing agent at the end of the polyurethane resin is insufficient, and the effect of the present invention cannot be obtained. Ingredient (a2
If the glass transition temperature of (2) is less than 20 ° C., characteristics such as toughness and abrasion resistance of the polyurethane resin deteriorate.

The high molecular weight polyol component (a1) having a glass transition temperature of -20 ° C. or lower used in the production of the polyurethane resin used in the present invention includes aliphatic polyester polyol mainly composed of aliphatic dicarboxylic acid component, Alternatively, polycaprolactone-polyol, polyether-polyol and the like can be mentioned. Examples of the high-molecular-weight polyol component (a2) having a glass transition temperature of 20 ° C. or more include aromatic polyester-polyol mainly composed of an aromatic dicarboxylic acid component and aromatic polyester-polyol. And polyester diesters in which a lactone component is added to an aromatic polyester polyol, and the like.

More specifically, the aromatic polyester polyol contains terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalic acid, 2,6
-Naphthalic acid, 4,4'-diphenyldicarboxylic acid,
Examples thereof include aromatic dicarboxylic acids such as 4,4'-diphenyl ether dicarboxylic acid, and aromatic oxycarboxylic acids such as p-oxybenzoic acid and p- (hydroxyethoxy) benzoic acid. Aliphatic polyester polyols include, as dicarboxylic acid components, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid, and have a glass transition temperature of -20 ° C.
The aromatic dicarboxylic acid, aromatic oxycarboxylic acid and the like described above may be used within a range not exceeding.

The glycol components of both polyester polyols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4
-Butanediol, 1,5-pentanediol, 1,6
-Hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4
-Trimethyl-1,3-pentanediol, cyclohexanedimethanol, ethylene oxide adduct and propylene oxide adduct of bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A and propylene oxide adduct, and the like.

The dicarboxylic acid component and glycol component other than those described above include 5-sodium sulfoisophthalic acid,
-Potassium sulfoisophthalic acid, sodium sulfoterephthalic acid, 2-sodium sulfo-1,4-butanediol, 2,5-dimethyl-3-sodium sulfo-2,
Those containing sulfonic acid metal salts such as 5-hexanediol are raised, and sulfonic acid metal bases of polyurethane resins made from polyester polyols obtained by copolymerizing these are used as inorganic powders such as magnetic powder, abrasives, and carbon black. This has the effect of significantly improving dispersibility.

The hydrophilic polar group which can be introduced into the polyurethane resin other than the sulfonic acid metal base includes a —COOM group,
-OH group, -P = O (OM ') ₂ group, tertiary amino group, quaternary
Examples include an ammonium group, a sulfobetaine group, and the like (M is hydrogen or an alkali metal, and M 'is hydrogen, an alkali metal, or a hydrocarbon group).

Some of the raw materials for the above-mentioned polyester polyols include a trifunctional or higher functional compound such as trimellitic anhydride, glycerin, trimethylolpropane, pentaerythritol, etc. And the like may be used within a range that does not impair the characteristics.

The polycaprolactone / polyol component includes ε-caprolactone polyadduct, and the polyether / polyol component includes polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like.

The high molecular weight polyol component (A) of the polyurethane resin used in the present invention has a molecular weight of 500 to 10,000.
0, preferably 500 to 5,000
It is. If the molecular weight is less than 500, the urethane bond concentration becomes too high, and the dispersibility and low-temperature properties of the magnetic powder deteriorate. If the molecular weight exceeds 10,000, properties such as toughness and abrasion resistance peculiar to the polyurethane resin deteriorate. . Further, a high molecular weight polyol component (A) of the polyurethane resin used in the present invention.
Is a low Tg polyol component (a1) having a glass transition temperature of -20 ° C or lower and a high Tg polyol component (a2) having a glass transition temperature of 20 ° C or higher in a weight ratio of 10:90 to 70: 3.
0, preferably in the range of 15:85 to 60:40. When the content of the high Tg polyol component (a2) is less than 30%, the mechanical properties of the polyurethane resin are deteriorated, and the properties such as toughness and abrasion resistance are deteriorated.
If it exceeds 90%, the low Tg polyol component (a1) used at the terminal end becomes insufficient and the effect of the present invention cannot be obtained.

The diisocyanate compound (B) used in the production of the polyurethane resin used in the present invention includes 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene Diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate,
2,6-naphthalenediisocyanate, 3,3′-dimethyl-4,4′-biphenylenediisocyanate, 4,
4′-diphenylene diisocyanate, 4,4′-diphenyl ether diisocyanate, 1,5-naphthalene diisocyanate, m-xylylene diisocyanate,
1,3-diisocyanatomethylcyclohexane, 1,
4-diisocyanatomethylcyclohexane, 4,4 '
-Cyclohexylmethane diisocyanate, isophorone diisocyanate and the like.

The low molecular weight compound (C) having two or more functional groups in one molecule which reacts with an isocyanate having a molecular weight of less than 500, which is used as required in the production of the polyurethane resin used in the present invention, is used for controlling the urethane group concentration in the polyurethane. Available to A low molecular weight compound having three or more functional groups that react with isocyanate in one molecule is effective for improving the reactivity with a general-purpose curing agent. Specific compounds include linear glycols such as ethylene glycol, 1,3-propylene glycol, 1,6-hexanediol, cyclohexane dimethanol, xylylene glycol, diethylene glycol, triethylene glycol, and ethylene oxide adducts of bisphenol A. , Propylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,2,4-trimethyl-1,3-pentanediol, bisphenol A
Branched glycols such as propylene oxide adducts of N, N
Amino alcohols such as methylethanolamine, monoethanolamine and diethanolamine; polyols such as trimethylolpropane, glycerin, pentaerythritol and dipentaerythritol; and ε-caprolactone adducts to one of these polyols.

The polyurethane resin used in the present invention is characterized in that the urethane bond concentration (urethane bond content) is in the range of 500 to 1500 equivalents per ton of resin.
It is preferably in the range of 800 to 1200 equivalents per ton of resin. The urethane bond causes a strong interaction between the resins due to the hydrogen bond, and as the urethane bond concentration increases, the toughness and abrasion resistance of the resin improve, but the dispersibility of the magnetic particles tends to decrease. Urethane bond concentration of 50
If it is less than 0, the running durability is remarkably reduced even with the specific raw material and structure used in the present invention, and if it exceeds 1500, the dispersibility of the magnetic powder is reduced.

The terminal of the polyurethane resin used in the present invention is a low Tg polyol component (a1) or a low molecular weight compound (C). When the terminal is a low molecular weight compound (C), the low molecular weight compound (C) is It is bonded to the low Tg polyol component (a1) via a diisocyanate compound.
The end of the polyurethane resin enhances the reactivity with general-purpose hardeners used in magnetic recording media, increases the crosslink density, prevents the toughness of the polyurethane resin from decreasing due to urethane group concentration control, and provides sufficient durability as a magnetic recording medium Can be provided.

The polyaddition reaction method for the polyurethane resin used in the present invention having such a structure is as follows. First, components other than the low Tg polyol component (a1) are reacted with a diisocyanate compound to form an isocyanate-terminated prepolymer, and then the low Tg The polyol component (a1) is further reacted. The high-Tg polyol component (a2) is reacted with a diisocyanate compound until the hydroxyl group disappears to form an isocyanate group terminal, and a predetermined amount of the low-Tg polyol component (a1) in which the isocyanate group remains unreacted is charged. After that, the low molecular weight compound (C) is reacted with the remaining isocyanate group.
After obtaining an isocyanate-terminated prepolymer from the low Tg polyol component (a1) and the diisocyanate compound, the high Tg polyol component (a2) has a high Tg polyol component under the condition that the number of hydroxyl groups is small relative to the NCO group in the isocyanate-terminated prepolymer. After the isocyanate-terminated prepolymer is charged into (a2) and reacted, a low molecular weight compound (C) or a low Tg polyol component (a1) is further reacted. Among these methods, the method is desirable in terms of good workability.

The reaction may be carried out in either a method in which the raw materials are melted or a method in which the raw materials are dissolved in a solution. The molecular weight of the polyurethane resin used in the present invention is preferably in the range of 5,000 to 50,000 in number average molecular weight.
If the molecular weight is less than 5,000, the mechanical strength of the polyurethane resin decreases, and if it exceeds 50,000, the solution viscosity becomes too high, which may make handling difficult. Stannous octylate, dibutyltin dilaurate, triethylamine and the like may be used as a reaction catalyst. 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, other resins may be added for the purpose of controlling flexibility, improving cold resistance, improving durability, and / or the like. It is desirable to mix compounds that react and crosslink. 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, as a curing agent which is a compound which reacts with and crosslinks with a polyurethane resin, there are a polyisocyanate compound, an epoxy resin, a melamine resin, a urea resin and the like, and among them, a polyisocyanate compound is particularly desirable. The magnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe ₂ O ₃ , crystals of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , γ-Fe coated with CrO ₂ and cobalt.
Examples include Fe ₂ O ₃ or Fe ₃ O ₄ , barium ferrite iron carbide, pure iron, and ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni. In particular, the polyurethane resin of the present invention is particularly effective as a magnetic powder having a surface area of 40 m ² / g or more, which is a finely divided magnetic powder, an alloy powder, or a magnetic powder having difficulty in dispersing such as barium ferrite.

In the magnetic recording medium of the present invention, if necessary, a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctyl sulfo sodium succinate, t
-A lubricant such as butyl phenol / polyethylene ether, ethyl naphthalene / sodium sulfonate, dilauryl succinate, zinc stearate, soybean oil lecithin and silicone oil, and various antistatic materials can also be added.

The polyurethane resin used in the present invention includes, as raw material high molecular polyol components (A), a low Tg polyol component (a1) having a glass transition temperature of -20 ° C. or lower and a high Tg polyol component having a glass transition temperature of 20 ° C. or higher ( a2), the urethane bond concentration is in the range of 500 equivalents to 1500 equivalents per ton of resin, and the terminal of the resin is a low Tg polyol component (a1) or a low molecular weight compound (C), and the terminal is In the case of the high molecular weight compound (C), the low molecular weight compound (C) has a low T via a diisocyanate compound.
g It is characterized by being bonded to the polyol component (a1).

In this case, by setting the urethane bond concentration in the polyurethane to a limited range, the dispersibility of the magnetic particles is improved, and the glass transition temperature of the high molecular weight polyol component (A) is as low as −20 ° C. or less. By arranging the Tg polyol component (a1) at the terminal, the reactivity between the polyurethane resin and a general-purpose curing agent used for a magnetic recording medium is increased, and the crosslinking density is increased. Therefore, the toughness of the polyurethane resin by adjusting the urethane bond concentration is increased. It is considered that the lowering can be prevented and sufficient durability can be exhibited as a magnetic recording medium.

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, “parts” means “parts by weight”. The solution viscosity of the polyurethane resin was measured using a solid content of 30% and MEK as the solvent.
/ Toluene = 1/1 (weight ratio) at 25 ° C. The number average molecular weight was measured by gel permeation chromatography using THF as a solvent and converted to standard polystyrene. The glass transition temperature of the high molecular weight polyol component was measured by a differential scanning calorimeter at a heating rate of 20 ° C./min.

The gloss of the magnetic layer of the magnetic tape was measured at 60 ° gloss. The abrasion resistance of the magnetic layer was evaluated by using a commercially available S-VHS video deck, observing the scratches of the magnetic layer after running 100 times at a temperature of 10 ° C. and 40 ° C. during running, and evaluating the degree by the following six grades. 6: Almost no scratching 5: Slightly scratching 4: Slightly scratching 3: Scratching noticeable, not reaching PET film 2: 〃 PET film surface is slightly visible 1: 〃 PET film surface is much visible and magnetic The curability of the magnetic layer was measured as an index of the running durability of the tape. The curability of the magnetic layer was indicated by the extraction rate when the magnetic tape was immersed in MEK at 25 ° C. for 24 hours. The extraction rate was measured by GPC of MEK with the magnetic tape immersed therein, and expressed as a ratio of the extracted weight to the resin on the magnetic tape.

Synthesis Example 1 A sufficiently dried polyester (60 parts) and NPG (1 part) were dissolved in toluene (133 parts), and MDI (13 parts) was added.
The reaction was carried out at 4 ° C. for 4 hours to obtain an isocyanate group-terminated prepolymer. Then, 40 parts of the dried polyester b was added thereto, reacted for 3 hours, and diluted with 133 parts of MEK to obtain a polyurethane resin. Table 1 shows the characteristic values of the polyurethane resin. The amount of isocyanate groups (NCO groups) of the isocyanate group-terminated prepolymer before the polyester b was charged was determined by the total NCO of the MDI of the charged amount.
The amount was 20.9% based on the amount of the base, and unreacted polyester a was not detected from GPC analysis.

Synthesis Example 2 A sufficiently dried polyester (60 parts) was mixed with toluene 13
In 5 parts, 15.5 parts of MDI was added and reacted at 90 ° C. for 5 hours to obtain an isocyanate group-terminated prepolymer. Then, 40 parts of the dried polyester resin d was added thereto, reacted for 3 hours, and diluted with 135 parts of MEK.
A polyurethane resin was obtained. Table 1 shows the characteristic values of the polyurethane resin. The amount of isocyanate groups (NCO groups) of the isocyanate group-terminated prepolymer before the preparation of the polyester c was 31.7% of the total amount of NCO groups of the MDI in the above-mentioned charged amount, and the amount of unreacted products was determined by GPC analysis. Was not detected.

Synthesis Example 3 50 parts of thoroughly dried polyester a
Dissolve in 7 parts, add 15.5 parts of MDI, and add
The reaction was carried out for an hour to obtain an isocyanate group-terminated prepolymer. Add 50 parts of dried polyester b to it,
After further reacting for 2 hours, 2 parts of TMP was added and reacted for another 2 hours, and diluted with 137 parts of MEK to obtain a polyurethane resin. Table 1 shows the characteristic values of the polyurethane resin. In addition, the isocyanate group (NCO group) of the isocyanate group-terminated prepolymer before the introduction of the polyester b
Is 6 parts with respect to the total amount of NCO groups of the MDI of the charged amount.
5%, and 8.4% before the introduction of TMP.

Synthesis Examples 4 to 7 Polyurethane resins were obtained with the raw material compositions shown in Table 1 in the same manner as in the production methods of Synthesis Examples 1 to 3. Table 1 shows the characteristic values of each polyurethane resin, and Table 2 shows the characteristic values of the polyurethane resin.

[0034]

[Table 1]

[0035]

[Table 2]

Comparative Synthesis Example 1 The polyester, NPG and MDI used in Synthesis Example 1 were dissolved in 133 parts of toluene at a time, reacted at 90 ° C. for 5 hours and diluted with 133 parts of MEK to obtain a polyurethane resin. Table 2 shows the characteristic values of the polyurethane resin. In this example, the structure of the polyurethane resin is outside the scope of the claims.

Comparative Synthesis Example 2 A polyurethane resin was obtained in the same manner as in Synthesis Example 2 except that polyester g was used instead of polyester d. Table 2 shows the characteristic values of the polyurethane resin. In this example, the urethane bond concentration is outside the scope of the claims.

Comparative Synthesis Example 3 A polyurethane resin 10 was obtained in the same manner as in Synthesis Example 1 except that 1 part of NPG was changed to 10 parts. Polyurethane resin 1
Table 2 shows characteristic values of 0. In this example, the urethane bond concentration is outside the scope of the claims.

Comparative Synthesis Example 4 Synthesis Example 1 except that polyester b was used instead of polyester a and polyester a was used instead of polyester b
In the same manner as in the above, polyurethane resin 11 was obtained. Table 3 shows the characteristic values of the polyurethane resin 11. In this example, the structure of the polyurethane resin is outside the scope of the claims.

[0040]

[Table 3]

Using the raw material compositions shown in Table 3, polyurethane resins 12 to 14 were obtained in the same manner as in the production methods of Synthesis Examples 1 to 3. Table 3 shows the characteristic values of each polyurethane resin. Comparative Synthesis Example 5
In (Polyurethane resin 12) , the weight ratio of the low Tg polyol component (a1) to the high Tg polyol component (a2) was out of the claims, and Comparative Synthesis Examples 6 and 7 (Polyurethane
In down resin 13, 14) a low Tg polyol component (a1)
The glass transition temperature of the high Tg polyol component (a2) is outside the scope of the claims.

Example 1 Using a polyurethane resin described in Table 1, a composition having the following compounding ratio was dispersed in a ball mill for 24 hours, and then 1 part of stearic acid and 1 part of butyl stearate were used as lubricants. 6 parts of an isocyanate compound Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent, and the dispersion was further continued for 1 hour to obtain a magnetic paint. This is thickness 1
It was applied onto a 2μ polyethylene terephthalate film while applying a magnetic field of 2,000 gauss so that the thickness after drying was 4μ. After aging at 50 ° C for 48 hours,
The magnetic tape was obtained by slitting to 1/2 inch width. Table 4 shows the properties of the obtained magnetic tape.

[0043]

[Table 4]

The ratio of the magnetic powder to the binder in the magnetic tape is 4: 1 by weight, and the ratio of the binder to the hardener is 5: 1 by weight. 30% solution of polyurethane resin 100 parts Ferromagnetic iron oxide powder (Co-γ-Fe ₂ O ₃ -based 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 copies

Examples 2 to 8 Using the binders shown in Tables 1 and 2, magnetic tapes were obtained in the same manner as in Example 1. Table 4 shows the characteristics of each magnetic tape.

Comparative Examples 1 to 8 Using the binders shown in Tables 2 and 3, magnetic tapes were obtained in the same manner as in Example 1. Table 5 shows the characteristics of each magnetic tape.

[0047]

[Table 5] The abbreviations in the table are as follows.

Raw material composition a: Terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / neopentyl glycol / ethylene glycol = 49/49/2/60/40 (molar ratio), molecular weight = 2,500, Tg = 47 ° C b: Bifunctional poly-ε-caprolactone, molecular weight = 2,000, Tg = -35 ° C c: Terephthalic acid / isophthalic acid / 5-sulfosodium isophthalic acid / neopentyl glycol / hexanediol = 50/47/3 / 40/60 (molar ratio), molecular weight = 4000, Tg = 25 ° C.) d: ε-caprolactone adduct of trimethylolpropane, molecular weight = 800, Tg = −39 ° C. e: adipic acid / neopentyl glycol / hexanediol = 100/40/60 (molar ratio), molecular weight = 2,000, Tg = −29 ° C. f Terephthalic acid / isophthalic acid / neopentyl glycol / ethylene glycol = 40/60/50/50 (molar ratio), molecular weight = 2,000, Tg = 50 ° C. g: adipic acid / neopentyl glycol / hexanediol = 100/30 / 70 (molar ratio), molecular weight = 4,000, Tg = −40 ° C. h: terephthalic acid / isophthalic acid / adipic acid / neopentyl glycol / butanediol = 25/25/50/40/60 (molar ratio) Molecular weight = 2,000, Tg = −18 ° C. NPG: neopentyl glycol HPN: neopentyl glycol hydroxypivalate TMP: trimethylolpropane MDI: 4,4′-diphenylmethane diisocyanate TDI: 1,4-tolylene diisocyanate Polymer: vinyl chloride / vinyl acetate Glycidyl methacrylate copolymer (Nippon Zeon Co. Ltd. MR-110 30% solution)

[0049]

The magnetic recording medium using the specific polyurethane resin of the present invention has excellent magnetic layer smoothness and magnetic properties.
In addition, the magnetic layer has excellent wear resistance, and as a result, a magnetic recording medium having both dispersibility and durability can be provided.

────────────────────────────────────────────────── (5) References JP-A-56-127616 (JP, A) JP-A-62-248127 (JP, A) JP-A-64-89020 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G11B 5/702 C09D 5/23 C09D 175/08

Claims (1)

(57) [Claims] 1. A magnetic recording medium in which a ferromagnetic powder is dispersed in a binder and a magnetic paint containing a curing agent that reacts with the binder is applied on a non-magnetic support, wherein the component of the binder is A high-molecular-weight polyol component (A) having a molecular weight of 500 to 10,000, a diisocyanate compound (B), and a low-molecular-weight compound (C) having two or more functional groups which react with isocyanate in one molecule and having a molecular weight of less than 500 if necessary. ), Wherein the high molecular weight polyol component (A) is a polyol component (a1) having a glass transition temperature of -20 ° C or lower and a polyol component (a2) having a glass transition temperature of 20 ° C or higher. And a polyol component (a1)
And the weight ratio of the polyol component (a2) is 10:90 to 7
0:30, the urethane bond concentration in the polyurethane resin is in the range of 500 to 1,500 equivalents per ton of the resin, and the terminal of the polyurethane resin is a polyol component (a1) or a low molecular weight compound (C). When the terminal is a low molecular weight compound (C), the low molecular weight compound (C) is bonded to the low Tg polyol component (a1) via the diisocyanate compound (B). Magnetic recording medium.