JPH02306427A - Polyurethane resin binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability, traveling stability, etc., by using CHDM as the diol of a polycarbonate polyol component at the weight of a specific range in a polyurethane resin and simultaneously using an active hydrogen compd. having a hydrophilic polar group. CONSTITUTION:The poly(cyclohexane-1,4-dimethanol carbonate)polyol is used at 20 to 80wt.% as the constituting component of the polycarbonate polyol. The active hydrogen compd. contg. at least >=1 kind of a COOM group, OH group, SO3M group, P=O(OM')2 group, tertiary amino group (where M is hydrogen or alkaline metal, M' is hydrogen, alkaline metal or hydrocarbon group) in one molecule is used as the hydrophilic polar group-contg. active hydrogen compd. Further, a compd. of <=1,000mol.wt. contg. >=2 pieces of hydroxyl groups or amino groups in one molecule is used as a chain extender. The durability at the time of high-speed long-term traveling or long-term preservation is improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a binder for magnetic recording media, and more particularly, the present invention relates to a binder for magnetic recording media, and more particularly, to a magnetic layer formed on a non-magnetic support, the binder has dispersion properties of a specific polyurethane resin binder. This invention relates to a binder for magnetic recording media which has excellent electromagnetic conversion characteristics, etc., and excellent running durability and long-term storage durability.

2. Description of the Related Art In general, magnetic recording media (specifically audio tapes, etc.) used in audio equipment, video equipment, computers, etc.
(used for video tapes, floppy disks, computer data tapes, etc.) is produced by coating a magnetic paint containing magnetic powder and a binder on a non-magnetic support such as polyester film and drying it to form a magnetic layer. can get.

Vinyl chloride resin, polyurethane resin, polyester resin, nitrocellulose resin, epoxy resin, etc. are generally used as the pine mite for forming the magnetic layer of such a magnetic recording medium.

In recent years, with the expansion of uses for magnetic recording media such as audio tapes, video tapes, and data tapes for computers, the required performance has become diverse, and in particular, the demand for high reliability of magnetic recording media has increased. .

Specifically, high-density recording for recording and reproducing clear sound and images, characteristics that can withstand long-term high-speed running or long-term running under high-temperature, high-humidity conditions, and durability and nasal maintenance are particularly required. It is being High density, degree.

As a measure to improve this, there is a growing tendency to make the magnetic powder particles finer and to increase the magnetic force, and to increase the packing density of the magnetic powder in the magnetic layer, the so-called backing density. As the specific surface area increases due to the finer particles of magnetic powder and the cohesive force increases due to the electromagnetic force ratio, dispersion becomes difficult, and conventional binders cannot obtain satisfactory dispersibility and surface properties. It is also difficult to increase the density.

On the other hand, magnetic recording media come into intense contact with magnetic heads, rolls, etc. during recording and playback, which causes the magnetic layer to wear off and fall off, resulting in decreased playback output, fluctuations, noise generation, and increases in drop-outs and clouds. tape noise, poor running performance due to an increase in the coefficient of friction, dirt on the roll due to falling powder, etc.
This may cause the magnetic head to become clogged. Furthermore, the magnetic layer deteriorates during use under high temperature and high humidity conditions or during long-term storage, resulting in the magnetic layer falling off, adhesion of the magnetic layer, etc., and improvements are desired.

By using a highly durable binder system that improves the binder's durability against scratches, abrasion, temperature, humidity, etc., we have improved the durability of magnetic recording media during high-speed long-term running or long-term storage. Polyurethane resins have been proposed, but although they improve the durability of magnetic recording media using conventional binders to some extent, they do not reach a satisfactory level, and they are inferior in terms of dispersibility. As a binder for powder or magnetic powder with high magnetization, its performance is insufficient, and improvements have been desired.

Problem to be Solved by the Invention A binder with high durability and sufficient dispersibility even for finely divided magnetic powder has not been developed, and it is difficult to achieve a certain level of durability in magnetic recording media. , magnetic properties, and electromagnetic conversion properties are required.

Furthermore, it has excellent characteristics that allow it to run at high speeds for long periods of time, to run for long periods of time under high-temperature conditions, and to withstand long-term storage, and has greatly improved dispersibility of magnetic powder and surface properties of the magnetic layer. Improvements to the binder have been requested.

As a result of extensive research and consideration, the present inventors have found that when a polyurethane resin with a specific structure in which a hydrophilic polar base is introduced is used as a binder, it has excellent personnel resistance, and improves the dispersibility of magnetic powder and the surface of the magnetic layer. It was discovered that a magnetic recording medium with significantly improved properties could be obtained, leading to the present invention.Means for solving the problem, that is, the present invention, is to provide a polycarbonate polyol used as a binder for magnetic recording media, a hydrophilic polar group-containing active In a polyurethane resin binder made by reacting a hydrogen compound, a chain extender, and an organic diisocyanate, A) the polycarbonate polyol is a constituent component;
B) The hydrophilic polar group-containing active hydrogen compound contains a COOM group, an OH group, and a 503M group in one molecule. , P=0(OM'
) is an active hydrogen compound containing at least one type of di- or tertiary amino group (where M is hydrogen or an alkali metal, and M' is hydrogen, an alkali metal, or a hydrocarbon group); The binder is characterized by being a compound having a molecular weight of 1000 or less and containing two or more hydroxyl groups or amino groups in one molecule as a chain extender.

The polycarbonate polyol constituting the polyurethane resin of the present invention is obtained by the deethanol condensation reaction of polyhydric alcohol and ethylene carbonate.

The polycarbonate polyol of the present invention has a number average molecular weight of 500 to 3000 and is composed of cyclohexane-1,4-dimetatool (CHDM).
4-dimethanol carbonate) polyol from 20 to 8
Other carbonate polyols include 1,6-hexanediol and diethylene diol as diols.
J col, propylene glycol, 1,4-fucundiol, 3-methyl-1,5-pentanedio-y, 1,
5-bentanediol, neopentyl glycol,
1,8-octanediol, 1,9-nonanediol,
There are aliphatic diols such as 1,10-decane diol,
A preferred diol is 1,6-hexanediol. A polycarbonate diol having a number average molecular weight of 500 to 3,000 obtained by reacting these with ethylene carbonate is used.

As such other polycarbonate diols, the diol components can be used alone or in combination of two or more types.

The polycarbonate diol used in the present invention may be two or more types of polycarbonate diols, or may be a copolymer of CHDM and a diol other than CHDM, containing 20 to 80% by weight as CHDM. . The proportion of polycarbonate diol consisting of CHDM in the polyol is 20 to 80% by weight,
In this case, if it is less than 20% by weight, satisfactory durability cannot be obtained, and if it is more than 80% by weight, the resulting resin will have a high Tg (glass transition point) and become hard and brittle, which is not favorable for running properties. . The preferred range is 30-70% by weight.

-81 The polycarbonate diol used in the present invention has a number average molecular weight of 500 to 3,000, preferably a number average molecular weight of 700 to 2,500. In this case, when the number average molecular weight of the polycarbonate diol becomes smaller than 500,
The resulting polyurethane resin has a high urethane group concentration.
If it is too thick, the resin will have poor flexibility and poor solubility in solvents, making it unsuitable for use as a binder for magnetic recording media. Furthermore, if the number average molecular weight of the polycarbonate diol exceeds 3000, the urethane group concentration of the resulting polyurethane resin becomes too low, resulting in a decrease in the abrasion resistance and heat resistance of the resin, and magnetic recording media using it as a binder have a high abrasion resistance. The properties and heat resistance decrease, making it unsuitable for use as a highly durable binder.

As the hydrophilic polar group-containing compound used in the present invention,
COOM group, OH group, 803M group, p=.

(OM') 2 groups, tertiary amino group (M is hydrogen or alkali metal, M' is hydrogen, alkali metal, or hydrocarbon group) or 225! A compound containing the above-mentioned parent, aqueous polar group in the molecule with 1
It is a diol, diamino, or amino alcohol containing more than one diol, diamino, or amino alcohol. Diols, diamino, or amino alcohols containing these hydrophilic polar groups are used as part of polyhydric alcohols or dicarmenic acids as raw materials for polyester diols, polyester amide diols, etc., which are used in combination to impart hydrophilic polarity to the polyol chain. The groups may also be introduced in the form of side chains.

The content of hydrophilic polar groups in the present invention is 0.001 mmol/g to 0.50 mmol/g for COOM groups.
ol/g.

0.01 mmol/g to 1.0 mmo for OH group
l/g, 0.001 mmol for 803M group
/g ~i, Om mol/g, P = O(OM
') 0.001 m mol/g to 1.0 for 2 units
m mol/g, 0.01 for tertiary amino group. m
Each range is from mol/g to 3.0 mmol/g. If the amount exceeds this range, the viscosity of the polyurethane resin may increase, making the magnetic paint more likely to aggregate, having a negative effect on dispersibility, and causing solvent selectivity. Moreover, durability cannot be obtained.

If the inverse K is less than this range, the ferromagnetic powder will be poorly dispersed, making it impossible to obtain high packing properties of the magnetic particles. Moreover, a satisfactory surface quality cannot be obtained.

Examples of COOM group-containing active hydrogen compounds used in the present invention include COOM group-containing glycols such as 2,
2-dimethylolpropionic acid, 2.2-dimethylolbutyric acid, 2.2-dimethylolvaleric acid, and other reaction products of diamino and acid anhydride, for example, inphorondiamino (IPDA)/phthalic anhydride = 2 /1 (molar ratio)
Compounds having a carboxyl group obtained by the reaction can be mentioned.

An example of an active hydrogen compound having an OH group is one 2
Glycols containing a tertiary OH group include glycerin, an ethylene oxide adduct of glycerin, a propylene oxide adduct of 1,2,6-hexanediocol, and jetanolamino; , 2.3-hydroxy-2-methylpropane, 1,3.5-hydroxy-3-methylpentane, 1
, 2,3,6-hydroxy-2<3-dimethylhexane alone or as a mixture; in addition, N-hydroxyethylethylenediamino, 1,3-diamino-2-propanol, and the like can be mentioned.

Examples of active hydrogen compounds having a 503M group include 1.
Sodium 4-7'tanediol-2-sulfonate, 1
．． 5 such as 4-butanediol-2-sulfone potassium
03M group-containing glycols, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfosuccinic acid and alkyl esters thereof, etc.
Mention may be made of group-containing dicarboxylic acids and esters.

Examples of active hydrogen compounds having two P=O(OM') groups include sodium 2,3-dihydroxybrobylphenylphosphonate, sodium 2,3-dihydroxypropylphenylphosphonate, Potassium bis(2-hydroxyethyl)phosphonate, sodium bis(4-hydroxybutyl)phosphonate, and the like can be mentioned.

Examples of active hydrogen compounds having a tertiary amino group include N
-Methyljetanolamino, N.

Examples include N-jetanolaniline, N,N-dibrobanolaniline, 3-diethylamino-1,2propanediol, and the like.

The chain extender (C) used in the present invention has a molecular weight of 10 or more and has 1-2 or more hydroxyl groups or amino groups in the molecule.
00 or less, such as ethylene glycol, 1,
3-propylene glycol, 1.2-propylene glycol, 1.47"tanediol, 1,5-bentanediol, 1,6-hexanediol, 3-Jf sil-,
5-bentanediol, neopentyl glycol, 1.
8-octanediol, 1,9-nonanediol, diethylene glycol, cyclohexane-1,4-glycol, CHDM or bisphenol A with ethylene oxide or glycols such as propylene oxide adducts, hexamethylene diamino, xylene diamino, IP
Examples include diamino or amino alcohols such as DA monoethanolamino, N,N'-dimethylethylenecyabane, and water that reacts with isocyanate groups to form urea bonds as shown in JP-A No. 61-107531; Urea can also be used as a chain extender. These above-mentioned compounds can be used alone or in the form of mixtures thereof.

Examples of organic diisocyanates used in the present invention include 2.
4-Tolylene diisocyanate, 2゜6-) Li1/
xylene diisocyanate, xylene-1゜4-diisocyanate, xylene-1,3-diisocyanate, 4.4'
-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4°4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate), 3.
3'-dimethyldiphenylmethane-4,4'-diisocyanate=14--), 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1°5 -diisocyanate, 3.3'
- Aromatic diisocyanates such as dimethoxydiphenyl-4,4'-diisocyanate, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophoro/diisocyanate) (I PD I) Hydrogenated diisocyanate , hydrogenated diphenylmethane diisocyanate, alicyclic diisocyanate such as cyclohexane diisocyanate, and the like. These organic diisocyanates may be aromatic, aliphatic, or alicyclic, and are selected depending on the desired physical properties of the resin.

More preferably, alicyclic diisocyanates are selected.

The molar ratios of these components are: hydroxyl group-terminated polycarbonate polyol (2), COOM group, OH group, -8O3 group,
Diol containing one or more hydrophilic polar groups such as P=O(OM') 2 groups, N group (M is hydrogen or an alkali metal, 1M' is hydrogen, and an alkali metal is a hydrocarbon group) , diamino or amino alcohol etc. Q3)
, and the total number of moles of the chain extender (C) and the molar ratio R of the organic diisocyanate (incyanate group/hydroxyl group)
is 0.80-1.05, preferably 0.85-1.00
The binder thus obtained is linear, has hydroxyl groups at both ends, and has a number average molecular weight of 200.
00-130000 preferably 30000-6000
It is a polyurethane resin with a In this case, the molecular weight is 2
If it is less than 000, the dispersibility is excellent, but the coating film-forming ability of the resin is insufficiently sharp, resulting in poor durability and surface smoothness.

When the molecular weight exceeds 130,000, the dispersibility decreases and the viscosity increases, resulting in poor workability in the steps of mixing, transporting, and coating in paint production.

When producing the polyurethane resin according to the present invention, for example, bulk polymerization (solid reaction) method in which the reaction is carried out in a molten state, ketone solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone, ethyl acetate, Ester solvents such as butyl acetate, ether solvents such as dioxane and tetrahydrofuran, glycol ethers known as cellosolve and calpitol, acetic acid glycol ethers such as cellosolve acetate, amide solvents such as dimethylacetamide and dimethylformamide, toluene, When using aromatic hydrocarbon solvents such as xylene, alcohol solvents such as methanol, ethanol, and impropatul alone, it is possible to use a solution polymerization method in which each component is dissolved in a mixed solvent and then reacted. can.

Further, a catalyst and a stabilizer can be used as necessary. Examples of catalysts include nitrogen-containing compounds such as triethylamino and triethylenediamino, organometallic metals such as dibutyltin dilaureate (tin octylate containing DBTDL), and zinc stearate.As stabilizers,
Ultraviolet absorbers such as substituted benzotriazoles, antioxidants such as phenol derivatives, hydrolysis inhibitors, and the like can be added.

In addition to the polyurethane resin of the present invention, if necessary, other polyurethane resins commonly used as binders for magnetic recording media, vinyl chloride-vinyl acetate-based composites, polybutyl butyral-based resins, cellulose-based resins, polyesters, etc. resins, epoxy resins and phenoxy resins, acrylonitrile) thermosetting resins such as IJ sil-tadiene copolymers, or reactive resins and unsaturated prepolymers, such as urethane acrylic types, polyester acrylic types,
Alternatively, as a polyfunctional monomer, an electron beam or ultraviolet curable resin such as a urethane acrylic type, Nisdel phosphate acrylic type, or aryl type can be used in combination.

As the magnetic powder used in the present invention, for example, γ-Fe
Iron oxide magnetic powder such as 2O3, Co-containing 2--Fe2O3, CrO2, hexagonal barinium ferrite fine particles,
and Fe, N4%Co, Fe-Ni-Co alloy,
Fe-Mn-Zn alloy etc. Fe, Ni, Co
Various ferromagnetic powders such as metal magnetic powders whose main ingredients include

In addition to magnetic recording media, the polyurethane resin of the present invention can be used in paints, adhesives, sealants, waterproofing agents, flooring materials, artificial leather, fiber treatment agents, elastic fibers, cushioning materials, sheets, belts, films, and It can be used for gears, solid tires, vibration isolators, tubes, backing materials, shoe soles (microcellular), etc.

Function As described above, by containing a hydrophilic polar group in the resin and using a polyurethane resin as a binder using a polycarbonate polyol consisting of cyclohexane-1,4-dimetatool, it is possible to run at high speeds for long periods of time or at high temperatures. It has excellent durability and can withstand long-term running under high-temperature conditions and long-term storage, and can also significantly improve the dispersibility of magnetic powder and the surface properties of the magnetic layer.

-19-, Examples Next, the present invention will be explained in more detail by Examples, but the present invention is not limited to these Examples.

In addition, "parts" and "chi" in the examples are "parts by weight" and "wt%" unless otherwise specified.

Example 1 Polycarbonate polyol (CH
DM-PCD) number average molecular weight (Mn) 2000 to 400
Polycarbonate polyol (IHG-PCD) consisting of 1.6-hex/glycol, joint average molecular weight 200
16,000 parts of 0, 144 parts of CHDM, and 18 parts of dimethylolpropionic acid (DMPA).

After adding 1100 parts of cyclohexanone and 4 parts of DBTDLto as a urethanization catalyst and mixing at 50°C, IP
464 parts of DI (R=0.98) was added and reacted at 80°C. The viscosity increases with time, so dilute with cyclohexanone and MEK as needed to reduce the total amount of MEK to 2460.
The total amount of cyclohexanone was 369.20 parts (cyclohexanone/MEK=3/2 weight ratio), and a transparent pale yellow liquid was obtained. This polyurethane resin (P
U-1) The solution has a solid content of 30.2% and a viscosity of a000eP.
/25°C, the number average molecular weight is 30,000.

Example 2 CHDM-PCD (Mn=2
000), 1000 copies of HG-PCD (Mn = 20
00) was used, and 0.4 m of S 0sNa group was used.
Polycarbonate polyol (HG-PCD) consisting of sodium 4-7'tanediol-2-sulfonate and 1,6-hexanediol containing mol/g
-8) (Mn=2000) in 60s 1,4-butanediol 90 parts, cyclohexane 1100 parts, DBTDL
Using 14 parts of O, 491 parts of diphenylmethane diisocyanate was added so that R = 0.98, and the reaction was carried out.
Similar to Example 1, cyclohexanone/M'EK was synthesized so that the weight ratio was 372 and the solid content was 30%. A polyurethane resin (PU-2) solution with a final K, solid content of 30.1%, and viscosity of 3200 eP/25° C. was obtained.

Example 3 'In Example 1, CHDM-PCD (Mn=20
00), 1400 copies of HG-PCD (Mn = 2
000), 18 parts of DMPA, HG-
The reaction was carried out using IPDI, CHDM, DBTDL, cyclohexanone, MEK, etc. in the same manner as in Example 1, except that 60 parts of PCD-8 (Mn = 2000) was used, and the solid content was 29.8% and the viscosity was 2850 cP/25. A solution of polyurethane resin (PU-3) at ℃ was obtained.

Example 4 In Example 1, 500 copies of CHDM-PCD (Mn = 1000) and HG-POD S (Mu = 1000)
IPD1. except that 500 parts of CHDM, 144 parts of SDMPA were used, and 11 parts of SDMPA were used. DBTDL, cyclohexanone, MEK, etc. were used in the same manner as in Example 1, and a reaction was carried out to obtain a polyurethane resin (PU-4) solution with a solid content of 30.3% and a viscosity of 3500 cP/25°C.

Example 5 CHDM-PCD (Mn=7QO) in Example 1
1000 copies, 70 copies of HG-PCD (Mn=1000)
Synthesized using 0 part, CHDMf: tsa part, 65 parts of N-methyljetanol amino, and using IPDI, DBTDL, cyclohexanone, MEK, etc. in the same manner as in Example 1, solid content 29.4%, viscosity 2300 cP. Next, a polyurethane resin (PU-5) solution at 25°C was obtained.

Example 6 In Example 1, CHDM PCD (Mn = 2500
), 1000 parts of HG PCD (Mn=1000), 101 parts of CHDM, 80 parts of 3-diethylamino-1°2-propandalicol, and IPD
I.

DBTDL, cyclohexanone, MEK, etc. were used and synthesized in the same manner as in Example 1, and the solid content was 30.5% and the viscosity was 380.
A polyurethane resin (PU-6) solution at 0 cP/25°C was obtained.

Example 7 50 each of CHDM and 1,6-hexane gelicol
polycarbonate polyol (Mn=200
0), 1940 parts of S03Na, 0.4 m mol/
The synthesis was carried out using 60 parts of the same polycarbonate polyol, 58 parts of CHDM, and 16 parts of DMPA, and using IPDI% DBTDL, cyclohexanone, MEK, etc. in the same manner as in Example 1. minute 30.1
%, viscosity 3400cP/25℃ polyurethane resin (P
U-7) Obtain the solution.

Example 8 CHDM and 1,6-hex/glycol at 50% each
% containing polycarbonate polyol (Mn=200
0)t 1940 parts, S OaNa 0.4m yno
l/g and using 60 parts of the same polycarbonate polyol, 58 parts of CHDMt, 18 parts of DMPA, and 65 parts of N-methyljetanol amino, IP
D1. DBTDL, cyclohexanone, MEK, etc. were used and synthesized in the same manner as in Example 1, and a polyurethane resin (PU-8) with a solid content of 29.9% and a viscosity of 2100eP/25°C was obtained.
A solution was obtained.

Example 9 In Example 1, 1000 parts of CHDM-PCD (Mn=2500) and 10 parts of HG-PCD (Mn=1000) were added.
00 part, CI (DM?101m, 2.3'/hi)
Synthesis was carried out using 80 parts of sodium lj-7'o-hyphenylphosphonate and using IPDI, DBTDL, cyclohexanone, MEK, etc. in the same manner as in Example 1, and the solid content was 30.5% and the viscosity was 3800 cP. /25°C polyurethane resin (PU-9) solution was obtained.

Comparative Example 1 KG-PCD (Mn
= 2000) using 2000 parts, using 144 parts of CHDM, reacting using IPDI so that R = 0.98, the solvent composition was the same as Example 1, and the solid content was 30.5%. , a polyurethane resin (comparison-1) solution having a viscosity of 2700 cP/25°C was obtained.

Comparative Example 2 In Comparative Example 1, CHDM PCD (Mn=2000
), 200 copies of HG-PCD (Mn = 2000), 1
It was synthesized using the same raw materials as in Example 1 except that 800 parts were used, and the solid content was 29.7% and the viscosity was 3000 cp/
A polyurethane resin (comparison-2) solution at 25°C was obtained.

Tests were conducted using each resin obtained in the clear film durability evaluation examples and comparative examples.

Clear film creation: Add 10 parts of polyisocyanate (Coronate L: trade name manufactured by Nippon Polyurethane Industries) to 100 parts of resin (each solid content equivalent), and use a knife coater on release paper to obtain a dry film thickness of 100 μm. applied to,
After processing at 60°C for 15 minutes, after processing at 120°C for 30 minutes,
It was cured and dried at 25° C. for 3 days to provide a sample for durability evaluation.

Durability test: A test piece of clear film cut with a JIS No. 4 dumbbell was placed in a constant temperature and humidity chamber at 70°C x 95SRH and left for 5 weeks, and the retention rate of the film's physical properties was determined according to the test method of JIS K-6301. . Table 1 shows the results.
Shown below.

Retention rate: (TB after test <h or EB)/T after test
B (or KB)) Using a polyurethane resin (PU-1), a composition with the following blending ratio was dispersed for 8 hours using a tabletop Saledo grind mill (manufactured by Igarashi Kikai KK), and the resulting magnetic paint was applied onto a 12 μm thick polyethylene terephthalate film. After drying, the coating was coated to a thickness of 5 μm and dried, and the glossiness of each coating was examined (Table 3). In addition, the magnetic paint obtained by dispersing for 8 hours is colonized as polyisocyanate).
-L (manufactured by Nippon Polyurethane Industries) was added as a curing agent to 10 wt% of the polyurethane resin in terms of resin content, mixed for an additional hour, and then placed on a 12 μm thick polyethylene terephthalate film to a thickness of 5 μm after drying. After applying a magnetic field of 2000 Gauss and applying 9 coats, 60
C. for 1 day to obtain a magnetic tape. The results are shown in Table 2.

Compound composition for magnetic recording media Co -r-Fe 203 100 parts Polyurethane resin (PU-1) (resin content) 25 parts Toluene 110 parts M EK 110 parts Cyclohexanone 70 parts Application examples 2 to 8, Comparative examples 1 to 2 Application example 1 Application example 1 The dispersibility and magnetic tape characteristics were evaluated using the same formulation as above.The results are shown in Table 2.

Glossiness: Using a glossy needle on the surface of the obtained magnetic tape, we looked at the reflectance at an incident angle of 60 degrees and a reflection angle of 60 degrees.Friction variation during running = 60°C x 95% RHX Dynamic friction coefficient in a running test within 4 weeks The change in surface properties was measured using a surface property measuring device (HEIDON-14 manufactured by Shinto Scientific Instruments).

Durability = 60° C. x 95% RH

Table 2 Notes for Table 2 ◎: Change rate less than 5 inches ○: Change rate 5% or more and less than 1 degree △: Change rate 10 flat As is clear from the results in Tables 1 and 2, polycarbonate made of CHDM as the polycarbonate polyol A polyurethane resin produced using the same and a magnetic recording medium using the polyurethane resin as a binder for a magnetic layer have excellent dispersibility, durability, and running stability.

Effects of the Invention As is clear from the above explanation, the polyurethane resin of the present invention uses CHDM 20 to 80% as the diol of the carbonate polyol component, and at the same time is an active hydrogen compound having a hydrophilic polar group. By using this, it is possible to improve the dispersibility of the magnetic powder, and when this is used as a binder for the magnetic layer, the durability, running stability, etc. of the magnetic recording medium can be made extremely excellent.

Claims (1)

[Scope of Claims] A polyurethane resin binder prepared by reacting a polycarbonate polyol, a hydrophilic polar group-containing active hydrogen compound, a chain extender, and an organic diisocyanate for use as a binder for magnetic recording media, A) the polycarbonate polyol as a constituent component;
B) The hydrophilic polar group-containing active hydrogen compound contains a COOM group, an OH group, SO_3M group, P=O(OM
')_2 group, an active hydrogen compound containing at least one tertiary amino group (where M is hydrogen or an alkali metal, M' is a hydrogen, alkali metal or hydrocarbon group), and C) A binder characterized in that it is a compound having a molecular weight of 1000 or less and containing two or more hydroxyl groups or amino groups in one molecule as a chain extender.