JP2660589B2 - Method for producing polyurethane resin binder for magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a polyurethane resin binder for a magnetic recording medium. More specifically, in a binder used for a magnetic layer formed on a non-magnetic support,
The present invention relates to a method for producing a polyurethane resin binder for a magnetic recording medium having excellent dispersion characteristics and electromagnetic conversion characteristics.

2. Description of the Related Art Generally, magnetic recording media used for audio equipment, video equipment, computers, etc. (specifically, audio tapes, video tapes, floppy disks, data tapes for computers, etc.) are made of non-magnetic materials such as polyester films. Is obtained by applying a magnetic paint containing a magnetic powder and a binder on the support described above and drying to form a magnetic layer.

As a binder for forming a magnetic layer of such a magnetic recording medium, a vinyl chloride resin, a polyurethane resin, a polyester resin, a nitrocellulose resin, an epoxy resin, or the like is generally used.

2. Description of the Related Art In recent years, performance requirements have been diversified as magnetic recording media such as audio tapes, video tapes, and data tapes for computers have been expanded in use. In particular, demands for high reliability of magnetic recording media have been increasing. Specifically, high-density recording for recording and reproducing clear sound and images is particularly required.

As a measure for increasing the density, the magnetic powder is made finer and the magnetic force is increased, and the packing density of the magnetic powder in the magnetic layer, that is, the so-called packing density, tends to increase. With the increase of the specific surface area due to the reduction of the particle size of the magnetic powder and the increase of the cohesive force due to the increase in the magnetic force, dispersion becomes difficult, and satisfactory dispersibility and surface properties cannot be obtained with the conventional binder. It is also difficult to increase the density.

In recent years, it has been proposed to introduce various hydrophilic polar groups in order to improve dispersibility. For example, (a) -SO
₃ M groups, (b) -COOM groups, (c) -P = O (OM ') ₂ groups,
(D) -OH group and (e) tertiary amino group (M is hydrogen or alkali metal, M 'is hydrogen, alkali metal or hydrocarbon group) and the like are considered. However, (a),
In the case of the polar groups (b) and (c), when these polar groups are introduced, the resulting resin may become turbid and may precipitate, separate, etc. over time. Further, the viscosity of the magnetic coating material in which the magnetic powder is dispersed using the same increases with the introduction amount of the polar group, which may make it difficult to manufacture a magnetic recording medium. (D) and (e) have low dispersing power, and even if the amount of polar groups introduced is increased, their performance is insufficient as a binder for micronized magnetic powders or metal magnetic powders having a high magnetization amount. Had been requested.

Problems to be Solved by the Invention The present inventors have conducted intensive studies and studies in order to eliminate the above-mentioned defects, and as a result, a polyurethane resin binder obtained by a production method of introducing a specific hydrophilic polar group has a magnetic property. The present inventors have found that a magnetic recording medium having greatly improved powder dispersibility and magnetic layer surface properties can be obtained, and have reached the present invention.

Means for Solving the Problem The present invention is as follows.

A method for producing a polyurethane resin binder for a magnetic recording medium, comprising reacting the following raw materials to contain 0.001 to 1.0 mmol / g of a quaternary ammonium salt in a polyurethane resin.

(A) a polyol having a number average molecular weight of 500 to 3,000.

(B) a chain extender.

(C) A quaternary ammonium salt-containing compound represented by the general formula (I).

(In the formula, A represents a trivalent hydrocarbon chain having 14 or less carbon atoms.
R _{1 to} R ₃ represent any of an alkyl group having 1 to 10 carbon atoms, an aryl group, a phenyl group, and a benzyl group. And X ^- represents an anion of an organic or inorganic. Y and Z each represent a hydroxyl group or an amino group. ) (D) -COOM group, -OH group, -SO ₃ M group, -P = O (OM ')
₂ group, (.M the M represents a hydrogen or an alkali metal 'is hydrogen, an alkali metal, or a hydrocarbon group.) Tertiary amino groups from compounds containing one of at least 1
Active hydrogen compounds containing a hydrophilic polar group selected from at least one kind.

(E) an organic diisocyanate.

Each component of the polyurethane resin binder used in the present invention will be described.

Examples of the polyol having a number average molecular weight of 500 to 3,000 used in the present invention include polyester polyol, polyesteramide polyol, polyether polyol, polyether / ester polyol, polycarbonate polyol and the like.

Examples of the polyester polyol include, for example, succinic acid, adipic acid, sebacic acid, azelaic acid, terephthalic acid, isophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid or acid esters thereof, and dicarboxylic acids and acid esters such as acid anhydrides・ Anhydride and 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 ethylene oxide of bisphenol A Alternatively, it can be obtained by a condensation reaction with a glycol such as propylene oxide adduct, hexamethylenediamine, xylenediamine, isophoronediamine, monoethanolamine or the like, or an amino alcohol alone or a mixture thereof. Depending on the raw materials used, polyester amide polyols or lactone polyesters obtained by ring-opening polymerization of cyclic ester (lactone) monomers such as ε-caprolactone, alkyl-substituted ε-caprolactone, δ-valerolactone, and alkyl-substituted δ-valerolactone. There are polyester polyols such as polyols.

Examples of the polyether polyol include polyethylene glycol, polypropylene ether polyol, polytetramethylene ether polyol, and the like.

The polyether / ester polyol is produced from the above polyether polyol and the above dicarboxylic acid or acid anhydride.

The polycarbonate polyol is obtained by, for example, a deethanolation condensation reaction of a polyhydric alcohol and diethyl carbonate, a phenol condensation reaction of a polyhydric alcohol and diphenyl carbonate, or an ethylene glycol condensation reaction of a polyhydric alcohol and ethylene carbonate. Such polyhydric alcohols include 1,6-
Hexane glycol, diethylene glycol, propylene glycol, 1,4-butylene glycol, 3-methyl-1,5-pentane glycol, 1,5-pentane glycol, neopentyl glycol, 1,8-octane glycol, 1,9-nonane glycol And the like. Polycarbonate polyols composed of these polyhydric alcohols further include cyclic esters (lactones) such as ε-caprolactone, alkyl-substituted ε-caprolactone, δ-valerolactone, and alkyl-substituted δ-valerolactone.
It can be used as a monomer initiator, and there is a polycarbonate-lactone polyol obtained by ring-opening polymerization of such a lactone monomer.

Examples of the chain extender used in the present invention include enylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,5-pentane glycol, and 1,6-hexane glycol. , 3-methyl-
1,5-pentane glycol, neopentyl glycol,
Glycols such as 1,8-octane glycol, 1,9-nonane glycol, diethylene glycol, cyclohexane-1,4-glycol, cyclohexane-1,4-dimethanol or bisphenol A ethylene oxide or propylene oxide adduct, hexamethylene diamine And diamines such as xylylenediamine, isophoronediamine, monoethanolamine, and N, N'-dimethylethylenediamine, and amino alcohols. In addition, water and urea which react with an isocyanate group and form a urea bond as disclosed in JP-A-61-107531, can also be used as a chain extender. These compounds may be used alone or
It can be used as a mixture of more than one species.

The quaternary ammonium salt-containing compound used in the present invention is represented by the following general formula (I).

(In the formula, A represents a trivalent hydrocarbon chain having 14 or less carbon atoms.
R _{1 to} R ₃ represent any of an alkyl group having 1 to 10 carbon atoms, an aryl group, a phenyl group, and a benzyl group. And X ^- represents an anion of an organic or inorganic. Y and Z each represent a hydroxyl group or an amino group. Examples of the general formula (I) include 4- (3-hydroxy-
2-hydroxymethyl) propyl-N, N-dimethylaniline, 4- (3-amino-2-aminomethyl) propyl-N, N-dimethylaniline, 4- (3-hydroxy-2
-Hydroxymethyl) propyl-N, N-diethylaniline and the like, an alkylhalogen salt, an alkyl paratoluenesulfonate and the like.

The concentration of the aromatic quaternary ammonium salt in the present invention is 0.001 mmol / g to 1.0 mmol / g, more preferably 0.005 mmol / g.
mmol / g to 0.5 mmol / g. When the concentration is 0.001 mmol / g or less, the dispersibility is not sufficient for micronized magnetic powder, predetermined magnetic properties, electromagnetic conversion properties cannot be obtained, and when the concentration is 1.0 mmol / g or more, The resin becomes cloudy and precipitates are generated, and the viscosity of the magnetic paint produced from such a resin increases, which makes it difficult to apply the resin onto a non-magnetic support.

Examples of the active hydrogen compound having a hydrophilic polar group other than the quaternary ammonium salt used in the present invention include a -COOM group, -OH
Group, -SO ₃ M group, -P = O (OM _') containing ₂ group, -N group (M is hydrogen or an alkali metal, M' is hydrogen, an alkali metal or a hydrocarbon group) hydrophilic polar group such as Active hydrogen compounds of diols, dicarboxylic acids, diamines or amino alcohols. These hydrophilic polar group-containing diols, dicarboxylic acids, diamines or amino alcohols may be used as a part of a chain extender, or may be used in combination with a polyhydric alcohol as a raw material such as polyester diol or polyester amide diol. A hydrophilic polar group may be introduced into a polyol chain by using a part or a part of a dicarboxylic acid. Further, during the production of a polycarbonate polyol or a polycarbonate-lactone-based polyol, the above-mentioned hydrophilic polar group-containing polyhydric alcohol is used in combination as a part of the polyhydric alcohol, and the above-mentioned hydrophilic polar group is added to the polycarbonate polyol or the polycarbonate-lactone-based polyol. May be introduced. The polyol having the hydrophilic polar group introduced into the polyol chain in this manner can also be used as an active hydrogen compound containing a hydrophilic polar group other than the quaternary ammonium salt.

Examples of active hydrogen compounds having a -COOM group include -COOM
As the OM-containing glycol, 2,2-dimethylolpropionic acid, sodium 2,2-dimethylolpropionate, 2,2
-Dimethylolbutyric acid, and 2,2-dimethylolvaleric acid,
Further, a reaction product of a diamine and an acid anhydride, for example, a reaction product of isophoronediamine (IPDA) / phthalic anhydride and the like can be mentioned.

Examples of the active hydrogen compound having an -OH group include glycerin, an ethylene oxide adduct of glycerin, a propylene oxide adduct of 1,2,6-hexanetriol and diethanolamine as one secondary OH group-containing glycol. As glycols having a tertiary OH group in the molecule, 1,2,3-hydroxy-2-methylpropane, 1,3,5
-Hydroxy-3-methylpentane, 1,2,3,6-hydroxy-2,3-dimethylhexane or the like alone or as a mixture, and N-hydroxyethylethylenediamine, 1,3-diamino-2-propanol and the like as diamines. I can give it.

Examples of the active hydrogen compound having a —SO ₃ M group include 2-
SO ₃ M group-containing glycols such as sodium sulfo-1,4-butanediol and 2-potassium sulfo-1,4-butanediol, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfosuccinic acid and alkyls thereof SO ₃ M group-containing dicarboxylic acids and esters such as esters.

Examples of active hydrogen compounds having -P = O (OM ') ₂ groups include sodium 2,3-dihydroxypropyl-phenylphosphonate, sodium 2,3-dihydroxypropyl-phenylphosphonate, bis (2- Potassium 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-methyldiethanolamine, N-phenyldiisopropanolamine, N, N-diethanolaniline, N, N-
Dipropanolaniline, 3-diethylamino-1,2-
And propanediol, 4- (3-hydroxy-2-hydroxymethyl) propyl-N, N-dimethylaniline and the like.

These active hydrogen compounds containing a hydrophilic polar group other than the quaternary ammonium salt may be used as a part of a chain extender, or when producing a polycarbonate polyol or a polycarbonate-lactone polyol, a part of a polyhydric alcohol. The above-mentioned hydrophilic polar group-containing polyhydric alcohol is used in combination, and the above-mentioned hydrophilic polar group is contained in a polycarbonate polyol or a polycarbonate-lactone-based polyol. Used as part of a dihydric alcohol or part of a dicarboxylic acid,
It is also possible to introduce a hydrophilic polar group into the polyol chain.

In the present invention, the content of the hydrophilic polar group other than the quaternary ammonium salt, in the -COOM group, 0.001 to 0.50 m
mol / g, the -OH group 0.01~1.0mmol / g, -SO ₃ Na in 0.001
~ 1.0mmol / g, -P = O (OM ') ₂ groups 0.001 ~ 1.0mmo
1 / g, and 0.01 to 3.0 mmol / g for tertiary amino groups. If each of them exceeds this range, the viscosity of the polyurethane resin may increase, and the magnetic paint tends to agglomerate or the viscosity of the magnetic paint increases, which not only adversely affects the dispersibility but also the selection of the solvent. The nature comes to arise. As a result, workability is deteriorated in the steps of mixing, transferring, and applying the paint in the production of the paint.

As the organic diisocyanate used in the present invention,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, any mixture of 2,4-tolylene diisocyanate and 2,6-tolylene 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, 4,4 '
Aromatic diisocyanates such as diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate And aliphatic alicyclic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate and lysine diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate and cyclohexane diisocyanate.
These organic diisocyanates may be aromatic, aliphatic, or alicyclic, but can be selected according to the desired resin properties.

In the present invention, a polyol having a number average molecular weight of 500 to 3,000, which is a component of the polyurethane resin binder, a chain extender, an active hydrogen compound containing a quaternary ammonium salt, and a hydrophilic polarity other than the quaternary ammonium salt Ratio R of the number of moles of all active hydrogen groups of the group-containing active hydrogen compound to the number of moles of all isocyanate groups of the organic diisocyanate
(Isocyanate group / hydroxyl group) can be produced at 0.80 to 1.05, preferably 0.85 to 1.00.

The polyurethane resin binder for a magnetic recording medium obtained in this manner is a polyurethane resin having a linear hydroxyl group at both ends and a number average molecular weight of 10,000 to 130,000, preferably 20,000 to 60,000. In this case, if the molecular weight is less than 10,000, the dispersibility is excellent and advantageous, but the resin film-forming ability becomes insufficient, and the durability, surface lubricity, and powder falling are inferior. If the molecular weight is larger than 130,000, the dispersibility becomes poor and the viscosity becomes large, so that the workability in the steps of mixing, transporting and applying the coating material becomes poor.

Known methods for producing the polyurethane resin according to the present invention include, for example, a bulk polymerization (solid reaction) method of reacting in a molten state, a ketone solvent such as methyl ethyl ketone (hereinafter abbreviated as MEK), methyl isobutyl ketone, cyclohexanone, and acetic acid. Ethyl solvents such as ethyl and butyl acetate; ether solvents such as dioxane and tetrahydrofuran; glycol ethers such as cellosolve and carbitol; glycol ethers such as cellosolve acetate; amide solvents such as dimethylacetamide and dimethylformamide. Can be carried out by a solution polymerization method in which each component is dissolved or dissolved in a solvent alone or in a mixed solvent such as an aromatic hydrocarbon solvent such as toluene and xylene, or an alcohol solvent such as methanol, ethanol and isopropanol. Further, a catalyst and a stabilizer can be used as required.

Examples of the catalyst include nitrogen-containing compounds such as triethylamine and triethylenediamine, and organic metal compounds such as dibutyltin dilaurate (hereinafter abbreviated as DBTDL), tin octylate, and zinc stearate.

Examples of the stabilizer include ultraviolet absorbers such as substituted benzotriazoles, antioxidants such as phenol derivatives, and hydrolysis inhibitors.

Further, together with the polyurethane resin of the present invention, if necessary, other polyurethane resins usually used as a binder for a magnetic recording medium, a vinyl chloride-vinyl acetate copolymer, a polybutyl butyral resin, a cellulose resin, Polyester resin, ethoxy resin, phenoxy resin, thermosetting resin or reactive resin such as acrylonitrile-butadiene copolymer and unsaturated prepolymer, such as urethane acrylic type, polyester acrylic type, or urethane acrylic type as a polyfunctional monomer, An electron beam or ultraviolet curable resin such as a phosphoric acid ester acrylic type or an aryl type can be used in combination.
As the magnetic powder used in the present invention, for example, γ-Fe
₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , etc., iron oxide magnetic powder, CrO ₂ , hexagonal barium ferrite fine particles, and Fe, Ni, Co, Fe
And various ferromagnetic powders such as metal magnetic powders mainly composed of Fe, Ni and Co such as Ni-Co alloys and Fe-Mn-Zn alloys.

The polyurethane resin according to the present invention includes, in addition to magnetic recording media, paints, adhesives, sealing agents, waterproofing agents, flooring materials, artificial leather, fiber treatment agents, elastic fibers, cushioning materials, sheets, belts, films, rolls, and carriers. , Solid tires, anti-vibration materials, tubes, packing materials, shoe soles (microcellular), etc.

As described above, an aromatic quaternary ammonium salt is contained in a polyurethane resin in an amount of 0.001 to 1.0 mmol / g, and a hydrophilic polar group other than the quaternary ammonium salt is obtained. By using the polyurethane resin binder as a binder for a magnetic recording medium, it is possible to obtain a magnetic recording medium having significantly improved dispersibility in magnetic powder and surface properties of a magnetic layer.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.

Example 1 In a reaction vessel equipped with a thermometer, a stirrer, and a condenser,
2500 parts of polybutylene adipate diol having a number average molecular weight of 2500 (hereinafter abbreviated as PBA-2500) and cyclohexane-
288 parts of 1,4-dimethanol (hereinafter abbreviated as CHDM),
Methyl iodide salt of (3-hydroxy-2-hydroxymethyl) -propyl-N, N-dimethylaniline (hereinafter referred to as P
DMAI) (2 parts), glycerin (15 parts), cyclohexanone (2223 parts) (solid content at the time of reaction = 60%), DBTDL (0.05 part) as a urethanization catalyst was added and mixed at 50 ° C., followed by 2,4-toluene diisocyanate / 530 parts (R = 0.96) of a mixture of 2,6-toluene diisocyanate = 80/20 (weight ratio) (hereinafter abbreviated as TDI) was added and reacted at 80 ° C. Since the viscosity increased with time, the mixture was appropriately diluted with cyclohexanone and toluene, and the total amount of the solvent was 7,840 parts, and the final solvent composition was cyclohexanone / toluene = 2/1 (weight ratio) to obtain a transparent pale yellow liquid.

This polyurethane resin solution has a solid content of 29.8% and a viscosity of 37.
The number average molecular weight was 28900 at 50 cP / 25 ° C. The number average molecular weight was determined using a GPC apparatus (HLC-8020, manufactured by Tosoh Corporation) in terms of polystyrene.

Example 2 A polybutylene adipate diol having a number average molecular weight of 1000 (hereinafter abbreviated as PBA-1000) was placed in a reaction vessel similar to that of Example 1.
1000 parts, neopentyl glycol (hereinafter abbreviated as NPG)
312 parts, methyl bromide salt of 4- (3-hydroxy-2-hydroxymethyl) -propyl-N, N-dimethylaniline (hereinafter abbreviated as PDMAB) 32 parts, 2-sodium sulfo-1,4-butanediol (Hereinafter abbreviated as NSBG) is 4
50 parts, 25 parts of N-methyldiethanolamine (hereinafter abbreviated as NMDEA), 1404 parts of cyclohexanone (solid content at the time of reaction = 60%), and 0.05 part of DBTDL as a urethanization catalyst.
After mixing at ℃, 733 parts (R = 0.97) of TDI was added and reacted at 80 ° C. Since the viscosity increased with time, the mixture was diluted with cyclohexanone and MEK as needed to obtain a transparent pale yellow liquid, with a total solvent content of 4970 parts and a final solvent composition of cyclohexanone / MEK = 1/1 (weight ratio). This polyurethane resin solution has a solid content of 30.9%, a viscosity of 2200 cP / 25 ° C., and a number average molecular weight of 2
It was 5100.

Comparative Example 1 In a reaction vessel similar to that of Example 1, 1000 parts of PBA-1000, 1,4
18 parts of butylene glycol (hereinafter abbreviated as 1,4-BG),
After mixing at 50 ° C., 39 parts of bis (6-hydroxyhexyl) dimethylammonium chloride (hereinafter abbreviated as HHMAC), 924 parts of cyclohexanone (solid content at the time of reaction = 60%), and 0.05 part of DBTDL as a urethanation catalyst were added. 4,4'-
Diphenylmethane diisocyanate (MDI)
329 parts (R = 0.98) were added and reacted at 80 ° C. Cyclohexanone and MEK timely as viscosity increases with time
To give a total solvent amount of 4180 parts and a final solvent composition of cyclohexanone / MEK = 1/1 (weight ratio) to obtain a transparent pale yellow liquid. This polyurethane resin solution had a solid content of 25.4%, a viscosity of 1480 cP / 25 ° C., and a number average molecular weight of 20,100.

Comparative Example 2 A polybutylene adipate diol having a number average molecular weight of 2000 (hereinafter abbreviated as PBA-2000) was placed in the same reaction vessel as in Example 1.
2000 parts of CHDM, 288 parts of CHDM, 43 parts of HHMAC, 2007 parts of cyclohexanone (solid content at the time of reaction = 60%), 0.05 part of DBTDL as a urethanization catalyst, and mixing at 50 ° C., followed by isophorone diisocyanate (hereinafter referred to as IPDI). 679 parts (R = 0.9)
7) Added and reacted at 80 ° C. Since the viscosity increases with time, it is appropriately diluted with cyclohexanone and MEK, and the total solvent amount is 7070 parts, and the final solvent composition is cyclohexanone / MEK = 3/2.
(Weight ratio) to obtain a transparent pale yellow liquid.

This polyurethane resin solution has a solid content of 30.1% and a viscosity of 35%.
The number average molecular weight was 33700 at 20 cP / 25 ° C.

 Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Tables 1 and 2.

Evaluation of Magnetic Paint and Magnetic Layer Applied Example 1 Using the polyurethane resin solution obtained in Example 1, a compounding composition for magnetic paint Co-γ-Fe ₂ O ₃ 100 parts Polyurethane resin (resin equivalent) 25 parts Toluene 110 Part MEK 110 parts Cyclohexanone 70 parts The above composition was placed on a tabletop sand grind mill (Igarashi Machinery KK
For 8 hours, and the obtained magnetic paint is 12 μm thick.
Was dried and applied on a polyethylene terephthalate film having a thickness of 5 μm, and the gloss was observed. Table 3 shows the results. A magnetic paint obtained by dispersing for 8 hours, using Coronate-L (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., solid content of 75%) as a curing agent as a polyisocyanate, in terms of resin content of the polyurethane resin solution of Example 1, Add 10 parts per part, mix for another hour, then add 12 parts
After drying on a polyethylene terephthalate film having a thickness of 5 μm and applying a magnetic field of 2000 gauss so as to have a thickness of 5 μm, the film was left at 60 ° C. for one day to obtain a magnetic tape. Table 3 shows the results of the squareness ratio (Br / Bm).

Application Example 2, Application Comparative Examples 1-2 The same as Application Example 1, except that the polyurethane resin solution obtained in Example 2 and Comparative Examples 1-2 was used instead of the polyurethane resin solution used in Application Example 1. The dispersibility and magnetic tape properties were evaluated by the formulation. Table 3 shows the results.

Gloss: The reflectance of the surface of the obtained magnetic tape was measured at an incident angle of 60 ° and a reflection angle of 60 ° using a gloss meter.

Squareness ratio (Br / Bm): Saturation magnetization and residual magnetization were measured using VSM-3 type (manufactured by Toei Kogyo Co., Ltd.).

Abbreviations in Table 1 are as follows.

PBA-2500: Polybutylene adipate diol with a number average molecular weight of 2500 PBA-1000: Polybutylene adipate diol with a number average molecular weight of 1000 PBA-2000: Polybutylene adipate diol with a number average molecular weight of 2000 CHDM: 1,4-cyclohexanedimethanol NPG: Neopentyl glycol 1,4-BG: 1,4-butylene glycol TDI: 2,4-toluene diisocyanate / 2,6-toluene diisocyanate = 80/20 (weight ratio) mixture MDI: 4,4'-diphenylmethane diisocyanate IPDI : Isophorone diisocyanate PDMAI: Methyl iodide salt of 4- (3-hydroxy-2-hydroxymethyl) propyl-N, N-dimethylaniline PDMAB: 4- (3-hydroxy-2-hydroxymethyl) propyl-N, N-dimethyl Aniline methyl bromide salt HHMAC: bis (6-hydroxyhexyl) dimethylammonium chloride Id NSBG: 2- sodium sulfo-1,4-butanediol NMDEA: N- methyldiethanolamine As is clear from the above description, the quaternary ammonium salt contains 0.001 to 1.0 mmol / g, and the method of the present invention of introducing a hydrophilic polar group other than the quaternary ammonium salt. The obtained polyurethane resin binder is
The dispersibility in magnetic powder can be improved, and when this is used as a binder for a magnetic layer, a high-density magnetic recording medium can be obtained.

Continuation of front page (56) References JP-A-1-182374 (JP, A) JP-A-62-28926 (JP, A) JP-A-62-1102420 (JP, A) JP-A-62-28921 (JP, A) JP-A-62-92230 (JP, A) JP-A-2-56719 (JP, A) JP-A-63-138520 (JP, A) JP-A-63-142518 (JP, A) 54-153009 (JP, A) JP-A-55-100157 (JP, A) JP-A-54-130699 (JP, A)

Claims (1)

(57) [Claims] 1. A method for producing a polyurethane resin binder for a magnetic recording medium, comprising reacting the following raw materials to make the polyurethane resin contain a quaternary ammonium salt in an amount of 0.001 to 1.0 mmol / g. (A) a polyol having a number average molecular weight of 500 to 3,000. (B) a chain extender. (C) A quaternary ammonium salt-containing compound represented by the general formula (I). (In the formula, A represents a trivalent hydrocarbon chain having 14 or less carbon atoms.
R _{1 to} R ₃ represent any of an alkyl group having 1 to 10 carbon atoms, an aryl group, a phenyl group, and a benzyl group. And X ^- represents an anion of an organic or inorganic. Y and Z each represent a hydroxyl group or an amino group. ) (D) -COOM group, -OH group, -SO ₃ M group, -P = O (OM ')
₂ group, (.M the M represents a hydrogen or an alkali metal 'is hydrogen, an alkali metal, or a hydrocarbon group.) Tertiary amino groups from compounds containing one of at least 1
Active hydrogen compounds containing a hydrophilic polar group selected from at least one kind. (E) an organic diisocyanate.