JPH0583966B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording medium, and more particularly, the present invention relates to a magnetic recording medium, and more specifically, the binder component of the magnetic layer has dispersion characteristics mainly formed from a specific polyurethane resin binder.
The present invention relates to a magnetic recording medium that has excellent electromagnetic conversion characteristics, high-speed long-term running durability, and long-term storage durability. 2. Description of the Related Art In general, magnetic recording media used in audio equipment, video equipment, computers, etc. (specifically used in audio tapes, video tapes, floppy disks, computer data tapes, etc.) are made of non-woven media such as polyester film. It is obtained by applying a magnetic paint containing magnetic powder, a binder, etc. onto a magnetic support and drying it to form a magnetic layer. Vinyl chloride resin, polyurethane resin, polyester resin, nitrocellulose resin, epoxy resin, etc. are generally used as binders for forming such magnetic recording media. 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. There is. Specifically, high-density recording for recording and reproducing clear sound and images, high-speed long-term running, and high durability for long-term storage are particularly required. Magnetic recording media come into intense contact with magnetic heads, rolls, etc. during recording and reproduction, which causes the magnetic layer to wear off and fall off, resulting in reductions in reproduction output, fluctuations, etc.
This may cause noise generation, increased dropout,
This may cause an increase in the coefficient of friction, poor running performance due to dirt on the roll due to fallen powder, tape squeal, and clogging of the magnetic head. Furthermore, the magnetic layer deteriorated during long-term storage, sometimes resulting in the defects described above. The magnetic layer contains magnetic powder, binder, lubricant, abrasive, carbon black, dispersant, etc., and the various characteristics of a magnetic recording medium depend on the complex interaction of these, so the occurrence of the above defects is due to the binder. Although it cannot be said that this is the cause, there is a demand for a binder system that has higher durability than the current one, and for improved durability during long-term high-speed running or long-term storage. In polyurethane resins for these improvements, polyurethane resins obtained from polycarbonate polyols containing only carbonate bonds form a tough coating film due to the presence of carbonate groups, and have low tackiness and excellent lubricity. Furthermore, it has excellent durability under high temperature and high room conditions. However, polycarbonate polyol alone has very strong crystallinity, and carbonate bonds are less flexible than ester bonds. Therefore, polyurethane resins containing only carbonate bonds have a high glass transition temperature and low elongation, so they rapidly shrink below room temperature. lose flexibility. In addition, the excellent abrasion resistance and adhesion that it has at room and high temperatures cannot be maintained at low temperatures, resulting in poor running stability at low temperatures, especially when running at high speeds for long periods of time under low-temperature conditions, the magnetic layer may be scratched or worn out. Problems such as falling off of the magnetic layer and an increase in the coefficient of friction due to adhesion of the fallen magnetic layer to the magnetic head, roll, etc. have not resulted in a satisfactory product. Problems to be Solved by the Invention Polyurethane resin is excellent in abrasion resistance, adhesion to other substances, mechanical toughness, weather resistance, etc., and the present inventors have focused on it as a binder for highly durable magnetic recording media. As a result of intensive research on polycarbonate polyols and polyisocyanate systems, they discovered a highly durable magnetic recording medium by using a polyurethane resin with a specific structure as a binder to form the magnetic layer of a magnetic recording medium. It came to this. Means for Solving the Problems That is, the present invention provides a magnetic recording medium in which a magnetic layer consisting mainly of magnetic powder and a binder is formed on a non-magnetic support.
-1) A copolymerized polyol obtained by reacting a carbonate and/or polycarbonate polyol with (A-2) a cyclic ester monomer and/or a polylactone polyol (A-1): (A-
2) is 50% to 95% by weight: 5% to 50% by weight
A magnetic recording medium or a copolymer polyol characterized by containing a polyurethane resin having hydroxyl groups at both ends obtained by reacting (A) a polycarbonate/lactone polyol and (B) an organic diisocyanate in a ratio of As a component (A-
1), (A-2) and (A-3) The present invention relates to a magnetic recording medium using a polyol prepared by adding and reacting an active hydrogen-containing compound. Components for obtaining (A) polycarbonate/lactone polyol that can be used in the present invention include (A-1) carbonate, polycarbonate polyol, (A-2) cyclic lactone monomer, polylactone polyol, (A-
There are those that use the active hydrogen-containing compound of 3) and those that do not. Among these components, the carbonate (A-1) includes dialkyl carbonate, alkylene carbonate, diaryl carbonate, etc. Examples include dimethyl carbonate, diethyl carbonate, di-n-butyl carbonate, di-iso-butyl carbonate, Examples include ethylene carbonate, propylene carbonate, diphenyl carbonate, etc. Further, as the polycarbonate polyol, the above-mentioned carbonates and polyhydric alcohols, for example,
1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,
8-octanediol, 1,9-nonanediol, 2-ethyl-1,6-hexanediol, 2
-Methyl-1,3-propanediol, neopentyl glycol, 1,3-cyclohexanediol, 3-methyl 1,5-pentanediol, 1,
4-Cyclohexanediol, 2,2'-bis-
(4-hydroxycyclohexyl)-propane, p
-xylene diol, p-tetrachloroxylene diol, 1,4-cyclohexanedimethanol, (3(4),8(9)-bis-(hydroxymethyl)-
Tricyclodecane dimethylol, bis-hydroxymethyltetrahydrofuran, di(2-hydroxyethyl)dimethylhydantoin, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, polytetramethylene glycol, thioglycol, trimethylolethane,
trimethylolpropene, hexanetriol,
Particularly preferred are pentaerythritol, etc.
Examples of polyhydric alcohols include 1,6-hexanediol, 3-methyl-1,5-pentanediol,
1,8-octanediol, 1,9-nonanediol, 1,4-cyclohexanediol, 1,4
- Carbon number 6 such as cyclohexanedimethanol
Because the above diols have high boiling points and the formation of by-product cyclic products in the above reaction is small,
These include: The molecular weight of polycarbonate polyol obtained from these carbonates and polyhydric alcohols is
500-5000. The cyclic lactone monomer as component (A-2) for obtaining the polycarbonate-lactone polyol in the present invention is ε-caprolactone,
Examples include alkyl-substituted ε-caprolactone, δ-valerolactone, and alkyl-substituted δ-valerolactone. Moreover, as the polylactone polyol (A-2), the above-mentioned cyclic lactone monomer and (A-1)
Polyhydric alcohols used in the production of polycarbonate polyols are obtained by ring-opening addition reaction of cyclic ester monomers using the alcohols as initiators, such as polyε-caprolactone polyols, polyalkyl-substituted ε - caprolactone polyol,
Examples include poly δ-valerolactone polyol, polyalkyl-substituted δ-valerolactone polyol, and the like. The active hydrogen-containing compound (A-3) that can be used as necessary to obtain the polycarbonate/lactone polyol of the present invention includes the polycarbonate polyol used to obtain the polycarbonate polyol of (A-1). and alcohols. As a method for obtaining a polycarbonate/lactone polyol that can be used in the present invention, (1) 50% to 95% by weight of a polycarbonate polyol and 5% to 50% by weight of a polylactone polyol are mixed with heat to form a carbonate polyol. A method for obtaining a polycarbonate/lactone polyol containing a carbonate group and an ester group obtained by an exchange reaction between an ester bond and a carbonate bond introduced through ring opening of a group to a lactone ring. (2) A carbonate group obtained by reacting 50% to 95% by weight of a polycarbonate polyol and 5% to 50% by weight of a cyclic lactone monomer in the presence of a ring-opening addition reaction catalyst and a lactone ring are introduced through ring opening. A method for obtaining a polycarbonate/lactone polyol containing an ester group. (3) Ring-opening of carbonate group and lactone ring obtained by reacting 50% to 95% by weight of carbonate, 5% to 50% by weight of cyclic lactone momer, and an active hydrogen-containing compound in the presence of a ring-opening addition reaction catalyst. A method for obtaining a polycarbonate/lactone polyol containing an ester group introduced from. (4) There is a method of obtaining a polycarbonate/lactone polyol containing a carbonate group and an ester group introduced from a lactone ring from 50% to 95% by weight of carbonate and 5% to 50% by weight of a polylactone polyol. Commercially available products include Nitsuporan 982 and Nitsuporan 983 (both manufactured by Nippon Polyurethane Industries). The binder in the magnetic recording medium of the present invention is
(A-1) Adding and reacting carbonate and/or polycarbonate polyol and (A-2) cyclic ester monomer and/or polylactone polyol, or (A-1), (A-2)
and (A-3) a copolymerized polyol obtained by adding and reacting an active hydrogen-containing compound (A-1): (A-
2) is 50% to 95% by weight: 5% to 50% by weight
It is a polyurethane resin having hydroxyl groups at both ends obtained by reacting (A) a polycarbonate/lactone polyol and (B) an organic diisocyanate containing a ratio of . In this case, the lactone content of the polycarbonate/lactone polyol is 5% to 50% by weight,
The content is preferably 5% to 30% by weight. If the lactone content exceeds 50% by weight, the durability and lubricity of the magnetic layer under high temperature and high humidity conditions will be poor, while if it is less than 5% by weight, the running stability at low temperatures, especially at high speeds under low temperature conditions, will deteriorate. Long-term running performance becomes poor. Examples of the organic diisocyanate (B) that can be used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
4,4'-didiphenylmethane diisocyanate,
4,4'-diphenyl ether diisocyanate,
2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenyl enylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate,
naphthylene-1,5-diisocyanate, 3,
Aromatic diisocyanates such as 3'-dimethoxydiphenyl-4,4'-diisocyanate, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate,
Examples include alicyclic diisocyanates such as hydrogenated tolylene diisocyanate and hydrogenated diphenylmethane diisocyanate, and aromatic aliphatic diisocyanates such as xylylene-1,3-diisocyanate and xylylene-1,4-diisocyanate. Polyester polyols, polyester amide polyols, polyether polyols, polyether/ester polyols and glycols can be used in combination as necessary. Examples of polyester polyols and polyesteramide polyols that can be used in combination as necessary include succinic acid, adipic acid, sebacic acid, azelaic acid, terephthalic acid, isophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, and their like. dicarboxylic acids, acid esters, acid anhydrides, etc., such as acid esters and acid anhydrides;
Ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-
Butylene glycol, 1,5-pentane glycol, 1,6-hexane glycol, 3-methyl-
1,5-pentane glycol, neopentyl glycol, 1,8-octane glycol, 1,9-
Nonanediol, diethylene glycol, cyclohexane-1,4-diol, cyclohexane-
1,4-dimethanol or bisphenol A
obtained by dehydration condensation reaction with glycols such as ethylene oxide or propylene oxide adducts, diamines such as hexamethylene diamine, xylene diamine, isophorone diamine, monoethanolamine, or amino alcohols alone or in mixtures of two or more. Examples include polyols. or ε-caprolactone, alkyl substituted ε
Examples include polyols such as lactone-based polyester polyols obtained by ring-opening polymerization of cyclic ester (lactone) monomers such as -caprolactone, δ-valerolactone, and alkyl-substituted δ-valerolactone. Furthermore, examples of polyether polyols include polyethylene glycol, polypropylene ether polyol, polytetramethylene ether polyol, and the like. Examples of the polyether/ester polyol include polyols produced from the above-mentioned polyether polyols and the above-mentioned dicarboxylic acids or acid anhydrides. The amount of these polyols used is
It should be kept within 30% by weight. In this case, the amount used must be such that it can maintain excellent durability under high temperature and high humidity conditions, which is a characteristic of polycarbonate/lactone polyols. Further, conditions such as being able to form a tough coating film due to the presence of carbonate groups and maintaining performance with low tackiness and excellent lubricity, and furthermore, vary depending on the type of polyol. In addition, chain extenders used as necessary include ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,
4-butylene glycol, 1,5-pentane glycol, 1,6-hexane glycol, 3-methyl-1,5-pentane glycol, neopentyl glycol, 1,8-octane glycol, 1,
Glycols such as 9-nonanediol, diethylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol or ethylene oxide or propylene oxide adducts of bisphenol A, hexamethylene diamine, xylene diamine, isophorone diamine, mono Examples include diamines such as ethanolamine, N,N'-dimethylethylenediamine, and amino alcohols. Water, urea, etc. that react with other isocyanate groups to form urea bonds can also be used as chain extenders. These above-mentioned compounds can be used alone or in the form of a mixture of two or more. The polyurethane resin in the magnetic recording medium of the present invention, which is substantially linear and has active hydrogen groups at both ends, obtained from these components contains the polycarbonate/lactone polyol (A) and organic diisocyanate (B) as exemplified above as essential components. In order to balance physical properties such as hardness and elongation, polyols other than the polycarbonate/lactone polyol (A) and/or chain extenders may be used as necessary. The molar ratio between these components is the mole of organic diisocyanate (B) relative to the total number of moles of active hydrogen compounds such as (A), the chain extender, and polyols other than the polycarbonate/lactone polyol (A). 0.80-1.05, preferably 0.85-1.00. The polyurethane resin is substantially linear, has active hydrogen groups at both ends, and has a molecular weight of 5000.
~150000 preferably 10000~130000. In this case, if the molecular weight is less than 5,000, the dispersibility is excellent, but the durability and surface smoothness are inferior, and if the molecular weight is greater than 150,000, the dispersibility decreases, which is not preferable. The polycarbonate/lactone polyol (A), which is an essential component of the polyurethane resin used in the present invention, must account for 70% by weight or more, preferably 80% by weight or more of the total active hydrogen compounds used. If it is less than 70% by weight, the durability of the magnetic layer under high temperature and high humidity conditions and surface smoothness are unsatisfactory. When a difunctional or higher functional polyisocyanate is used in combination with the polyurethane resin as a curing agent, a magnetic recording medium can be obtained which has better heat resistance, durability and abrasion resistance than a system in which no curing agent is added. In addition, as the polyisocyanate with two or more functionalities used as a curing agent, there are organic diisocyanates and their polymers (dimer, trimer, carbodiimide-containing polyisocyanate) mentioned as examples of the organic diisocyanate (B) essential component of the polyurethane resin. Furthermore, there are polyisocyanate compounds having isocyanate groups obtained by reacting bifunctional or higher functional polyols with the above-mentioned organic diisocyanates and polymers thereof. These include, for example, Coronate L, Coronate HL, Coronate
2030, Coronate 4048, Coronate 4090, Coronate 4092, Coronate 4400 (all manufactured by Nippon Polyurethane Industries), and the amount thereof should be in the range of 5% to 30% by weight based on the binder. The method for producing the polyurethane resin in the magnetic recording medium of the present invention includes known methods such as a bulk polymerization (solid reaction) method in which the resin is reacted in a molten state, a solution polymerization method, and the like. Solution polymerization methods include ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as dioxane and tetrahydrofuran, and glycol ether solvents known as cellosolve and carbitol. ,
In single or mixed solvents such as acetic acid glycol ethers such as cellosolve acetate, amide solvents such as dimethylacetamide and dimethylformamide, aromatic hydrocarbon solvents such as toluene and xylene, and alcohol solvents such as methanol, ethanol and isopropanol. Each component can be reacted in a dissolved state. When producing the polyurethane resin, a catalyst and a stabilizer can be used as necessary. Examples of the catalyst include nitrogen-containing compounds such as triethylamine and triethylenediamine, and organometallic compounds such as dibutyltin dilaurate, tin octylate, and zinc stearate. As a stabilizer,
Ultraviolet absorbers such as substituted benzotriazoles, antioxidants such as phenol derivatives, hydrolysis inhibitors, and the like can be added. In addition, in the present invention, in addition to the polyurethane resin, if necessary, other polyurethane resins commonly used as binders for magnetic recording media, vinyl chloride-vinyl acetate copolymers, polybutyl butyral resins, cellulose resins, polyesters, etc. resin,
Epoxy resins, phenoxy resins, thermosetting resins such as acrylonitrile-butadiene copolymers, or reactive resins and unsaturated prepolymers can be used in combination. These include, for example, urethane acrylic type, polyester acrylic type,
Alternatively, examples of polyfunctional monomers include electron beam or ultraviolet curable resins such as urethane acrylic type, phosphate ester acrylic type, and aryl type. Examples of the magnetic powder used in the present invention include γ
−Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ and other iron oxide magnetic powders,
CrO ₂ , barium ferrite, and Fe, Ni,
Co, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, etc. Fe,
Examples include various ferromagnetic powders such as metal magnetic powders containing Ni and Co as main components. Effects of the Invention The polyurethane resin used in the magnetic recording medium of the present invention has better solubility in solvents and dispersibility of magnetic powder than binders using conventional carbonate polyols, so it can be easily dispersed and can be used as a magnetic coating material in a short time. It has the advantage of being able to mix This improvement in magnetic powder dispersibility improves magnetic properties (e.g., saturation magnetic flux density (Bm), squareness ratio (Rs)), improves the smoothness of the magnetic layer surface, and further improves electromagnetic conversion properties (e.g., frequency characteristics, (S/N,
C/N) etc. can be improved. In addition, this resin is made by copolymerizing polycarbonate polyol with lactone, which has a low glass transition temperature and excellent water resistance, in a specific range, so it has the characteristics of carbonate, such as film-forming properties, lubricity, and high-temperature, high-humidity conditions. The polyurethane resin, which is obtained from polycarbonate polyol containing only carbonate bonds, maintains excellent durability and has a drawback of running stability at low temperatures, especially when running at high speed for long periods of time under low temperature conditions. It does not stick or wear off, maintains smooth running performance over the entire operating temperature range, and maintains its initial running performance even during long-term storage. As described above, it has excellent effects such as being able to simultaneously satisfy the three requirements of magnetic recording media: magnetic powder dispersibility, surface smoothness of the magnetic layer, and durability of the magnetic layer. Further, the polyurethane resin in the magnetic recording medium of the present invention can be applied as an adhesive for film lamination, an ink binder, a surface treatment agent for plastics, other adhesives, a coating agent, synthetic leather, etc. Examples Hereinafter, the present invention will be described as synthesis examples, comparative synthesis examples, examples,
This will be explained in more detail using comparative examples and the like. "Parts" and "%" in the examples are "parts by weight" and "% by weight", respectively, unless otherwise specified. Synthesis example of polycarbonate/lactone polyolSynthesis example 1 A distillation column equipped with a stainless steel stirring blade and a fractionating column with a reflux condenser with an inner diameter of 18 mm and a height of 300 mm, and a 4-neck glass reaction vessel equipped with a nitrogen introduction tube. , 1080 parts of diethyl carbonate and 1240 parts of 1,6-hexanediol are added, and then 0.03 part of titanium tetrachloride is added as a catalyst. Heat the reaction vessel, 1.
Once 6-hexanediol is dissolved, stirring is started, the internal temperature is maintained at 125°C to 130°C, and the produced ethyl alcohol is distilled out. When the distillation of ethyl alcohol reaches 50% of the theoretical amount, slowly increase the
Raise the temperature to ℃. After reacting at the same temperature for 2 hours,
The degree of vacuum was reduced at a rate of 50 mmHg to 100 mmHg/hour, finally reaching 20 mmHg and maintaining this state for 2 hours, and then raising the internal temperature to 220°C to remove unreacted 1,6
- After distilling off hexanediol, the pressure was returned to normal. 1400 parts of polyol were obtained. Its hydroxyl value was 56.1 and molecular weight was 2000. Then, the obtained polycarbonate polyol
300 parts of a polycaprolactone polyol having a molecular weight of 2000 was added to 700 parts, and an exchange reaction was carried out at 175°C to 185°C for 5 hours to obtain 1000 parts of polyhexane carbonate/caprolactone polyol. The obtained polyol had a hydroxyl value of 55.4 and a viscosity of
It was 1100cSt/75℃. The molecular weight calculated from the hydroxyl value is 2026, and structural analysis by C-NMR, IR, elemental analysis, etc. shows that it is composed of (CH ₂ ) ₆ and (CH ₂ ) ₅ chains with OH groups at both ends, carbonate bonds, and ester bonds. It was confirmed that the polyol was a polyhexane carbonate/caprolactone polyol having repeating polyols and containing carbonate groups and ester groups in a ratio (by weight) of approximately 72:28. Synthesis Example 2 In a reactor similar to Synthesis Example 1, 1190 parts of diphenyl carbonate, 713 parts of 1,6-hexanediol, and tri-iso-propyl titanate as a catalyst were added.
Add 0.1 part and raise the temperature to 210°C over 2 hours to distill off the phenol produced by the reaction. The reaction was carried out at this temperature for 10 hours while a small amount of nitrogen gas was bubbled through to promote the distillation of phenol. Next, at the same temperature, the degree of vacuum was reduced at a rate of 50 mmHg to 100 mmHg/hour, finally reaching 10 mmHg and maintaining this state for 2 hours, and then raising the internal temperature to 220°C to remove unreacted 1,6-hexanediol. After distilling off, the pressure was returned to normal pressure. 850 parts of polyol were obtained.
The obtained polyol had a hydroxyl value of 56.0 and a viscosity of
It was 2400cSt/75℃. The molecular weight calculated from the hydroxyl value is 2004, and structural analysis by C-NMR, IR, elemental analysis, etc. reveals that it is a polycarbonate polyol with OH groups at both ends, a (CH ₂ ) ₆ chain and repeating carbonate bonds. confirmed. Then, the obtained polycarbonate polyol
150 parts of polycaprolactone polyol having a molecular weight of 550 was added to 850 parts, and exchange reaction was carried out at 175°C to 185°C for 5 hours to obtain about 1000 parts of polyhexane carbonate/caprolactone polyol. The obtained polyol had a hydroxyl value of 76.3 and a viscosity of 750 cSt/75°C. The molecular weight calculated from the hydroxyl value is 1470, and according to the same structural analysis as in Synthesis Example 1, it has (CH ₂ ) ₆ and (CH ₂ ) ₅ chains with OH groups at both ends, and repeating carbonate bonds and ester bonds. , and carbonate group: ester group is about
It was confirmed that it was a polyhexane carbonate/caprolactone polyol containing a ratio (weight) of 86:14. Synthesis Example 3 718 parts of diphenyl carbonate, 1185 parts of 1,4-cyclohexanedimethanol, and 0.03 part of titanium tetrachloride as a catalyst were added to the same reactor as in Synthesis Example 1, and the reaction vessel was heated to react with 1,4-cyclohexane dimethanol. Once the methanol has dissolved, start stirring and bring the internal temperature up.
The temperature is maintained at 125°C to 130°C, and the ethyl alcohol produced is distilled off. When the distillation of ethyl alcohol reaches 50% of the theoretical amount, the temperature is slowly raised to 200°C. After reacting at the same temperature for 2 hours, the degree of vacuum was reduced to 50
After reducing the pressure at a rate of mmHg to 100mmHg/1 hour and finally reaching 20mmHg and maintaining that state for 2 hours,
The internal temperature was raised to 220°C to distill off unreacted 1,4-cyclohexanedimethanol, and then returned to normal pressure. 1340 parts of polyol were obtained. The obtained polyol had a hydroxyl value of 143.0, a viscosity of 610 cSt/75°C,
It was hot. The molecular weight calculated from the hydroxyl value is 785, and structural analysis by C-NMR, IR, elemental analysis, etc. shows that it is a polycarbonate with repeating carbonate bonds and residues obtained by removing the OH group from cyclohexanedimethanol, which has OH groups at both ends. It was confirmed that it was a polyol. Then, the obtained polycarbonate polyol
Add 300 parts of caprolactone monomer to 700 parts,
Ring-opening reaction was carried out at 175°C to 185°C for 5 hours using polycarbonate polyol as an initiator to obtain 1000 parts of polycarbonate/caprolactone polyol. The obtained polyol had a hydroxyl value of 98.9 and a viscosity of
It was 850cSt/75℃. The molecular weight calculated from the hydroxyl value is 1135, and the same structural analysis as in Synthesis Example 1 shows that the residue obtained by removing the OH group from cyclohexanedimethanol, which has an OH group at both ends, the (CH ₂ ) ₅ chain, the carbonate bond, and It has repeating ester bonds, and the carbonate group: ester group is about 70:
Polycarbonate containing a ratio (weight) of 30%
It was confirmed that it was caprolactone polyol. Synthesis Example 4 Add 1080 parts of diethyl carbonate, 1240 parts of 1,6-hexanediol, and 0.03 part of titanium tetrachloride as a catalyst to the same reactor as in Synthesis Example 1, heat the reaction vessel, and dissolve the 1,6-hexanediol. Then, start stirring, raise the internal temperature to 125°C to 130°C, and distill out the ethyl alcohol produced. When the distillation of ethyl alcohol reaches 50% of the theoretical amount, the temperature is slowly raised to 200°C. After reacting at the same temperature for 2 hours, the degree of vacuum was reduced to 20 mmHg at a rate of 50 mmHg to 100 mmHg/hour, and this state was maintained for 2 hours, and then the internal temperature was raised to 220°C to remove unreacted 1 , 6-hexanediol were distilled off, and then the pressure was returned to normal pressure. 1400 parts of polyol were obtained. Its hydroxyl value was 56.1, and its molecular weight was 2000. Then, the obtained polycarbonate polyol
Add 300 parts of caprolactone monomer to 700 parts,
Ring-opening reaction was carried out at 175°C to 185°C for 5 hours using polycarbonate polyol as an initiator to obtain 1000 parts of polycarbonate/caprolactone polyol. The obtained polyol had a hydroxyl value of 46.3 and a viscosity of
It was 1500cSt/75℃. The molecular weight calculated from the hydroxyl value is 2420, and according to the same structural analysis as in Synthesis Example 1, it has (CH ₂ ) ₆ and (CH ₂ ) ₅ chains with OH groups at both ends, and repeating carbonate bonds and ester bonds. , and carbonate group: ester group is about
It was confirmed that it was a polycarbonate/caprolactone polyol containing a ratio (by weight) of 72:28. Synthesis Example 5 Add 666 parts of diethyl carbonate, 760 parts of 1,6-hexanediol, and 0.02 part of titanium tetrachloride as a catalyst to the same reactor as in Synthesis Example 1, heat the reaction container, and dissolve the 1,6-hexanediol. Then, start stirring, raise the internal temperature to 125°C to 130°C, and distill out the ethyl alcohol produced. When the distillation of ethyl alcohol reaches 50% of the theoretical amount, the temperature is slowly raised to 200°C. After reacting at the same temperature for 2 hours, the degree of vacuum was reduced at a rate of 50 mmHg to 100 mmHg/hour, and the final state was 20 mmHg.
After maintaining the temperature for a certain period of time, the internal temperature was raised to 220°C to distill off unreacted 1,6-hexanediol, and then the pressure was returned to normal pressure. 900 parts of polyol were obtained. Its hydroxyl value was 124.2, and its molecular weight was 903.5. Then, the obtained polycarbonate polyol
Add 114 parts of caprolactone monomer to 900 parts,
Ring-opening reaction was carried out at 175°C to 185°C for 5 hours using polycarbonate polyol as an initiator to obtain 1014 parts of polyhexane carbonate/caprolactone polyol. The obtained polyol had a hydroxyl value of 109.5 and a viscosity of 250 cSt/75°C. The molecular weight calculated from the hydroxyl value is 1025, and the same structural analysis as in Synthesis Example 1 shows that (CH ₂ ) ₆ and (CH ₂ ) ₅ have OH groups at both ends.
It was confirmed that it is a polycarbonate/caprolactone polyol that has repeating chains, carbonate bonds, and ester bonds, and contains carbonate groups:ester groups in a ratio (weight) of about 90:10. Synthesis Example 6 1080 parts of diethyl carbonate, 1240 parts of 3-methyl-1,5-pentanediol, and 0.03 part of titanium tetrachloride as a catalyst were added to the same reactor as in Synthesis Example 1, and stirring was started immediately to bring the internal temperature to 125 ℃ to 130℃, and distill the produced ethyl alcohol. When the distillation of ethyl alcohol reaches 50% of the theoretical amount, the temperature is slowly raised to 200°C. 2 at the same temperature
After reacting for a time, reduce the vacuum degree to 50mmHg~100mm
After reducing the pressure at a rate of Hg/1 hour and finally reaching 20 mmHg and maintaining that state for 2 hours, the internal temperature was raised to 220°C to distill out unreacted 1,6-hexanediol, and then the pressure was returned to normal pressure. Ta. 1400 parts of polyol was obtained with a hydroxyl value of 55.3 and a molecular weight of 2030.
It was a liquid at room temperature and had a viscosity of 10,500 cSt/25°C. Next, 150 parts of methylvalerolactone polyol with a molecular weight of 2000 was added to 850 parts of the obtained poly3-methyl 1,5-pentane carbonate polyol.
(PMVL) was added and exchange reaction was carried out at 175°C to 185°C for 5 hours to obtain 1000 parts of polycarbonate/methylvalerolactone polyol. The obtained polyol had a hydroxyl value of 56.1 and a viscosity of
1200cSt/75℃, it was a liquid at room temperature. The molecular weight calculated from the hydroxyl value is 2000, and the same structural analysis as in Synthesis Example 1 shows that (CH ₂ ) ₂ CH has OH groups at both ends.
(CH ₃ )(CH ₂ )Carbonate group with repeating lor2 chain, carbonate bond, and ester bond:
It was confirmed that the polyol was a poly3-methyl-1,5-pentane carbonate/methyvalerolactone polyol containing ester groups in a ratio (weight) of about 81:19. Synthesis Example 7 Add 534 parts of ethylene carbonate, 900 parts of 1,6-hexanediol, and 0.03 part of titanium tetrachloride as a catalyst to the same reactor as in Synthesis Example 1, heat the reaction container, and dissolve the 1,6-hexanediol. Then, start stirring, raise the internal temperature to 190°C to 200°C, and distill out the ethylene glycol produced. When the distillation of ethylene glycol reaches 80% of the theoretical amount, the temperature is slowly raised to 220°C. After reacting at the same temperature for 2 hours, the degree of vacuum was reduced at a rate of 50 mmHg to 100 mmHg/hour, finally reaching 20 mmHg and maintaining this state for 2 hours, and then raising the internal temperature to 240 °C to remove unreacted 1 , 6-hexanediol were distilled off, and then the pressure was returned to normal pressure. 1040 parts of polyol were obtained. Then, the obtained polycarbonate polyol
Add 300 parts of caprolactone monomer to 700 parts,
Exchange reaction was carried out at 175°C to 185°C for 5 hours to obtain 1000 parts of polyhexane carbonate/caprolactone polyol. The obtained polyol had a hydroxyl value of 110.0, a viscosity of 300 cSt/75°C, and was a liquid at room temperature. The molecular weight calculated from the hydroxyl value is 1020, and the same structural analysis as in Synthesis Example 1 shows that (CH ₂ ) ₆ has OH groups at both ends,
It was confirmed that it is a polyhexane carbon/caprolactone polyol that has (CH ₂ ) ₅ chains and repeating carbonate bonds and ester bonds, and also contains carbonate groups: ester groups in a ratio (weight) of approximately 72:28. . Synthesis Example 8 666 parts of diethyl carbonate, 760 parts of 3-methyl-1,5-pentanediol, and 0.02 part of titanium tetrachloride as a catalyst were added to the same reactor as in Synthesis Example 1, and the reaction vessel was heated and stirring was started. , the internal temperature is set at 125°C to 130°C, and the produced ethyl alcohol is distilled off. When the distillation of ethyl alcohol reaches 50% of the theoretical amount, the temperature is slowly raised to 200°C. After reacting at the same temperature for 2 hours, the degree of vacuum was reduced to 50
After reducing the pressure at a rate of mmHg to 100mmHg/1 hour and finally reaching 20mmHg and maintaining that state for 2 hours,
Raise the internal temperature to 220℃ to remove unreacted 3-methyl-1,
After distilling off 5-pentanediol, the pressure was returned to normal pressure. 900 parts of polyol were obtained. Its hydroxyl value was 12.5, and its molecular weight was 916.1. Next, 114 parts of caprolactone monomer was added to 900 parts of the obtained polyol, and the mixture was heated at 175°C to 185°C for 5 minutes.
1014 parts of poly 3-methyl-1,5-
A pentane carbonate/caprolactone polyol was obtained. The obtained polyol had a hydroxyl value of 107.5 and a viscosity of 260 cSt/75°C. The molecular weight calculated from the hydroxyl value is 1044, and according to the same structural analysis as Synthesis Example 1, it has OH groups at both ends (CH ₂ ) ₂ C (CH ₃ )
It must be a polycarbonate/caprolactone polyol that has repeating (CH ₂ ) ₂ and (CH ₂ ) ₅ chains, carbonate bonds, and ester bonds, and contains carbonate groups:ester groups in a ratio (weight) of approximately 90:10. It was confirmed. Production Example of Polyurethane Resin Synthesis Example 9 Into a reaction vessel equipped with a thermometer, a stirrer, and an ondenser, 2026.0 parts of the polyhexane carbonate/caprolactone polyol obtained in Synthesis Example 1, 1,4
-18.0 parts of butylene glycol (hereinafter abbreviated as 1,4-BG), methyl ethyl ketone (hereinafter referred to as a solvent)
MEK) 2180 parts and dibutyltin dilaurate (hereinafter referred to as DBTDL) as a urethanization catalyst
After adding 0.4 parts and mixing at 40°C, 297.3 parts of diphenylmethane diisocyanate (hereinafter abbreviated as MDI) was added. The reaction generated heat and the internal temperature reached approximately 80°C, and the viscosity increased over time. Cyclohexanone (hereinafter abbreviated as ANON) was added at appropriate times to dilute the mixture while maintaining this temperature and allowing the reaction to proceed for 7 hours. all
The amount of ANON used was 2180 parts, and a homogeneous and transparent solution was obtained. This polyurethane resin (A) solution has a solid content of 35
%, viscosity 5000cP/25℃, and its molecular weight is
It was 70,000. Synthesis Example 10 In a reaction vessel similar to Synthesis Example 9, 1135 parts of polycyclohexanone-1,4-dimethyl carbonate/caprolactone polyol obtained in Synthesis Example 3, 83.4 parts of neopentyl glycol, 2000 parts of MEK, and
After adding 0.3 parts of DBTDL and mixing at 40°C, 313.0 parts of tolylene diisocyanate (hereinafter abbreviated as TDI) was added. The reaction generated heat and the internal temperature reached approximately 80°C, and the viscosity increased over time. Timely MEK
was added and diluted while maintaining this temperature and reacting for 7 hours. A total of 2840 parts of MEK was added to obtain a homogeneous and transparent solution. This polyurethane resin (B) solution had a solid content of 35%, a viscosity of 15,000 cP/25°C, and a molecular weight of 50,000. Synthesis Example 11 In a reaction vessel similar to Synthesis Example 9, add the polycarbonate/caprolactone polyol obtained in Synthesis Example 8.
1044 parts, 1,4-butylene glycol 27.3 parts,
After adding 2000 parts of MEK and 0.3 parts of DBTDL and mixing at 40°C, 325.0 parts of MDI was added. The reaction generated heat and the internal temperature reached approximately 80°C, and the viscosity increased over time. While diluting by adding MEK and ANONE at appropriate times, the mixture was kept at this temperature and allowed to react for 7 hours. all
MEK and total ANONE were added in amounts of 2,790 parts and 2,790 parts, respectively, to obtain a homogeneous and transparent solution. This polyurethane resin (C) has a solid content of 20% and a viscosity of
The temperature was 1200cP/25°C, and the molecular weight was 75000. Synthesis Example 12 In a reaction vessel similar to Synthesis Example 9, 1025 parts of the polyhexane carbonate/caprolactone polyol obtained in Synthesis Example 5, 118.0 parts of 3-methyl-1,5-pentane glycol, 1000 parts of MEK, 810 parts of toluene,
After adding 0.5 parts of DBTDL and mixing at 40℃, isophorodiisocyanate (hereinafter abbreviated as IPDI) 667.0
Added a section. The reaction generates heat and the internal temperature is approximately 80℃.
℃, and the viscosity was kept constant for 7 hours to form a prepolymer with isocyanate groups at the end. Then, 1160 parts of MEK was added and diluted, followed by isophorone diamine (hereinafter abbreviated as IPDA) 153.3, which became an amine group corresponding to the equivalent weight of isocyanate groups contained. part and 12.3 parts of monoethanolamine (hereinafter abbreviated as MEA)
The urea reaction of IPDI with the amine prepolymer dissolved in 700 parts of MEK caused a rapid increase in viscosity, and after 30 minutes, the isocyanate groups disappeared, yielding a homogeneous and transparent solution. This polyurethane urea resin (D) solution had a solid content of 35%, a viscosity of 5,000 cP/25°C, and a molecular weight of 25,000. Synthesis Examples 13, 14 Molar ratio of IPDA and MEK in Synthesis Example 12: 90:
10 was changed to 95:5 and 70:30, and Synthesis Example 9
We added resins that have a polyurethane urea structure and differ only in molecular weight. The polyurethane urea resin (E) solution with a molar ratio of IPDA and MEK of 95:5 has a solid content of 35%.
Viscosity is 35000cSt/25℃, and its molecular weight is 57000
The polyurethane urea resin (F) solution with a molar ratio of IPDA and MEA of 70:30 has a solid content of 35% and a viscosity of
It was 250cP/25℃ and its molecular weight was 7000. Synthesis Example 15 Put 1025 parts of the polyhexane carbonate caprolactone polyol obtained in Synthesis Example 5 and 35.4 parts of 1,6-hexanediol into a stainless steel beaker, mix gently with a tabletop stirrer and bring to 60°C, then MDI322. 1 part was added and stirred at high speed for 1 minute at 2000 rpm.Then, the reaction mixture was distilled onto a vat heated to 110℃, and the temperature was kept at that temperature for 20 minutes.
The mixture was allowed to stand for a while to complete the reaction. This resin (G) can be easily pelletized with a pelletizer, and MEK/
ANON = 70/30 Easily soluble in solvent, solid content 20
%, the viscosity was 1500cP/25℃. Molecular weight is 85000
It was hot. Synthesis Examples 16 and 17 Comparative Examples 1 and 2 In the same solid reaction as in Synthesis Example 15, poly1,6-hexane carbonate/caprolactone polyol of Synthesis Example 1 and polybutylene adipate (hereinafter abbreviated as PBA), molecular weight 2000, chain 1,4-BG and diisocyanate are used as extenders.
In MDI, 1,4-
Resins (H) to (K) (shown in Table 1) were synthesized in which the ratio of polyols was changed to change the amount of carbonate groups in a system in which BG was fixed at 1.0 mol and MDI was 20 mol. resin
(J) and (K) are comparative examples containing less amount of (A) polycarbonate/lactone polyol, which is an essential component of the polyurethane resin of the present invention. Table 1 shows the amount of preparation and the results of the water resistance test.

【table】

[Table] Numbers indicate the number of moles. → indicates the same as on the left. Water resistance: 100 μm film, physical property retention after 1 month immersion in 80°C hot water 90% or more…◎ 80-90%…○ 60-80%…△ 60% or less…× Synthesis Example 18 Reaction vessel similar to Synthesis Example 9 The polycarbonate/caprolactone polyol obtained in Synthesis Example 7
Add 1020 parts, 1268 parts MEK and 0.2 parts DBTDL at 40℃
25.3 parts of MDI was added. The reaction generated heat and the internal temperature reached approximately 80°C, and the viscosity increased over time. While diluting by adding MEK at appropriate times, the mixture was kept at this temperature and allowed to react for 7 hours. A total of 2350 parts of MEK was added to obtain a homogeneous and transparent solution. This polyurethane resin (R) solution has a solid content of 35%,
The viscosity was 8500cP/25°C, and the molecular weight was 40000. Synthesis Example 19 In a reaction vessel similar to Synthesis Example 9, 1135 parts of the polycyclohexane-1,4-dimethyl carbonate/caprolactone polyol obtained in Synthesis Example 3,
After adding 900 parts of MEK and 0.2 parts of DBTDL and mixing at 40°C, 245.3 parts of MDI was added. The reaction generated heat and the internal temperature reached approximately 80°C, and the viscosity increased over time. While diluting by adding MEK and ANONE at appropriate times, the mixture was kept at this temperature and allowed to react for 7 hours. all
MEK and total ANONE were added in an amount of 1280 parts and 1280 parts, respectively, to obtain a homogeneous and transparent solution. This polyurethane resin (S) solution has a solid content of 35% and a viscosity of
The temperature was 5200cP/25°C, and the molecular weight was 42000. Comparative Synthesis Example 3 Polyhexane carbonate in Synthesis Example 9
Caprolactone polyol (hydroxyl value 55.4, molecular weight 2026, carbonate group/lactone ester group =
Approximately 72/28) PBA (hydroxyl value) instead of 2026.0 parts
56.1) Synthesize in the same manner except that 2000 parts were used,
A homogeneous clear solution was obtained. This polyurethane resin (L)
The solution has a solid content of 35%, a viscosity of 55000cP/25℃,
Its molecular weight was 67,000. Comparative Synthesis Example 4 Diethylene carbonate in Synthesis Example 11 and 3
- Polycarbonate/caprolactone polyol from methyl-1,5-pentanediol and caprolactone monomer (hydroxyl value 107.5, molecular weight 1044, carbonate group/lactone ester group =
90/10) Synthesized in the same manner except that 1250 parts of polycaprolactone polyol (PCL) (hydroxyl value 89.8) was used instead of 1044 parts, and the viscosity was 20% solids.
A polyurethane resin (M) solution at 1300 cP/25°C was obtained.
The molecular weight was 80,000. Comparative Synthesis Example 5 Diethylene carbonate and 3 in Synthesis Example 11
- Polycarbonate/caprolactone polyol from methyl-1,5-pentanediol and caprolactone monomer (hydroxyl value 107.5, molecular weight 1044, carbonate group/lactone ester group =
Synthesized in the same manner except that 1000 parts of polyhexane carbonate polyol (hydroxyl value 112.0) was used instead of 1044 parts (90/10), and the viscosity was 20% solids.
A polyurethane resin (N) solution at 1900 cP/25°C was obtained.
The molecular weight was 83,000. Comparative Synthesis Example 6 Polyhexane carbonate in Synthesis Example 9
Caprolactone polyol (hydroxyl value 55.4, molecular weight 2026, carbonate group/lactone ester group =
Synthesized in the same manner except that 2000 parts of polyhexane carbonate polyol (hydroxyl value 56.1) was used instead of 2026 parts of 72/28), and the solid content was 35% and the viscosity was
A polyurethane resin (O) solution at 5900 cP/25°C was obtained.
The molecular weight was 73,000. Comparative Synthesis Example 7 Polyhexane carbonate/caprolactone polyol from diethylene carbonate, 1,6-hexane glycol, and caprolactone monomer in Synthesis Example 12 (hydroxyl value 109.5, molecular weight 1025, carbonate group/lactone ester group =
Synthesized in the same manner except that 1000 parts of polyhexane carbonate polyol (hydroxyl value 112.2) was used instead of 1025 parts (approximately 90/10), and the solid content was 35% and the viscosity was
A polyurethane urea resin (P) solution at 5900 cP/25°C was obtained. The molecular weight was 23,000. Durability test of clear film Table 2 shows the results of Synthesis Examples 9 to 17 and Comparative Synthesis Examples 1 to 7. Clear film production: Add polyisocyanate (Coronate L) for 10 minutes (in terms of solid content) to 100 parts of resin, coat on release paper using a knife coater to a dry film thickness of 100 μm, and heat at 80°C.
It was cured and dried for 15 min + 120°C x 30 min and used as a sample for durability evaluation.

[Table] Heat resistance test: Measurement of heat resistance properties was carried out by cutting a sample with a JIS No. 4 dumbbell and subjecting it to heat deterioration in a gear oven at 120°C for 300 hours. Hot water resistance test: To measure hot water resistance properties, cut the sample with a JIS No. 4 dumbbell and place it in hot water at 80℃ for 500 minutes.
I left it for a while. TB: Strength at break (Kg/cm ³ ), EB: Elongation at break (%) Evaluation example of magnetic paint and magnetic layer 1 Using the polyurethane resin (A) obtained in Synthesis Example 9, the following compounding ratio was applied. The magnetic coating obtained by dispersing the composition in a tabletop sand glide mill (manufactured by Igarashi Kikai KK) for 8 hours was applied onto a 12 μm thick polyethylene terephthalate film to a thickness of 5 μm, and dried. Magnetic powder dispersibility was determined by gloss and 50x microscopic observation. In addition, Coronate L (manufactured by Nippon Polyurethane Industries) was added as a polyisocyanate to the obtained magnetic paint as a curing agent, and the resin content was 10% based on the total amount of polyurethane resin (A) and VAGH.
In addition, after mixing for another hour, it was applied to a polyethylene terephthalate film with a thickness of 12 μm to a thickness of 5 μm after drying while applying a magnetic field of 200 Gauss, and then left at 60°C for 1 day to coat the magnetic tape. Obtained. The test results are shown in Table 3. Compounding ratio Co-γ-FeO ₃ 100 parts Polyurethane resin (A) (resin content) 15 parts Vinyrite VAGH 10 parts Lecithin 2 parts Lubricant 3 parts Toluene 110 parts MEK 110 parts ANON 70 parts Examples 2 to 11, Comparative Example 1 ~7 Instead of polyurethane resin (A) used in Example 1, Synthesis Examples 10 to 17 Resins B to I, Synthesis Example 18 (R), Synthesis Example
19(S) and the polyurethane resins (J) to (P) obtained in Comparative Synthesis Examples 1 to 7, the dispersibility and magnetic tape properties were tested using the same formulation as in Example 1. The results are shown in Table 3.

[Table] Composition: Magnetic powder/(polyurethane resin + VAGH) =
4/1 Glossiness: Reflection gloss rate was measured from 60 degrees to 60 degrees using a gloss meter (manufactured by UGV-5G Suga Test Instruments). Values in parentheses indicate dispersibility evaluation based on observation results under a 50x electron microscope (good ◎＞○＞△＞×) Dynamic friction coefficient fluctuation rate: low temperature (5℃) and high temperature (60℃)
The dynamic friction coefficient when the vehicle is running is measured using a dynamic friction coefficient measuring device, and the rate of change is shown. (1) Before treatment (2) Durability after treatment: 70°C x 95% RH x 3 weeks Dynamic friction coefficient before and after storage under high temperature and high humidity conditions, low temperature (5°C) running wear amount, and adhesion to base film at 5°C Judging from the test. Adhesion: A 40 g or more B 30-40 g C 30 g or less Table 2 shows that the urethane binder of the magnetic recording medium of the present invention exhibits heat resistance and water resistance properties that are equal to or better than those of the polycarbonate polyol base. Table 3 shows the tape properties, and the glossiness, which is an index of dispersibility, and electron microscopic observation show that the magnetic recording medium of the present invention has better solubility in solvents by using a carbonate/lactone polyol than a carbonate polyol alone. Therefore, it can be seen that it has excellent dispersibility. The coefficient of dynamic friction during storage at high temperature and high humidity hardly changes, and the poor low-temperature properties, which are a drawback of carbonate polyols (Comparative Examples 5 to 7), are not observed, indicating excellent characteristics as a magnetic recording medium.

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is formed on a non-magnetic support, comprising: (A-1) carbonate and/or polycarbonate polyol as a binder component; (A-2) A copolymerized polyol obtained by reacting a cyclic ester monomer and/or a polylactone polyol (A-2)
1): (A-2) is 50% to 95% by weight: 5% by weight
A magnetic recording medium characterized by containing a polyurethane resin having hydroxyl groups at both ends obtained by reacting (A) a polycarbonate/lactone polyol and (B) an organic diisocyanate in a ratio of ~50% by weight. 2. A magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is formed on a non-magnetic support, which contains (A-1) carbonate and/or polycarbonate polyol, and (A-2) cyclic polyol as binder components. A copolymerized polyol obtained by adding and reacting an ester monomer and/or polylactone polyol with (A-3) an active hydrogen-containing compound.
1): (A-2) is 50% to 95% by weight: 5% by weight
A magnetic recording medium characterized by containing a polyurethane resin having hydroxyl groups at both ends obtained by reacting (A) a polycarbonate/lactone polyol and (B) an organic diisocyanate in a ratio of ~50% by weight.