JP2918870B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] [0001] The present invention relates to a magnetic recording medium.
More specifically, excellent surface smoothness and magnetic properties
Related to magnetic recording media having dispersibility and durability
It is. [0002] 2. Description of the Related Art Conventionally, as a binder for magnetic recording media.
Widely used for polyester resin, polyurethane resin, etc.
However, ferromagnetic fine powder is dispersed in these resins.
A magnetic recording medium manufactured by placing a substrate on a non-magnetic support
The body has sufficient magnetic powder dispersibility, surface smoothness, and durability
Not. Of these resins, especially polyurethane resins
Has a good aspect of high durability, but is magnetic
Poor affinity for particles, magnetic powder dispersibility, surface smoothness
Inferior. For this reason, magnetic powder dispersion of polyurethane resin
SO to improve the disadvantage of poor_ThreeM groups,
Polarity of COOM group (where M is H, Li, Na or K)
Polyurethane resins each having a single group (Japanese Unexamined Patent Publication No.
5-38693, JP-A-57-92423, JP-A-57-9243
-30235 publications) and tertiary OH groups and SO_ThreeM group, or
SO_ThreePolyurethane with both M and COOM groups
Resins (JP-A-59-108023, JP-A-57-924)
No. 22 publications) were used as binders
Have been. [0004] [Problems to be solved by the invention]
Polyurethane resin developed up to
Affinity and dispersibility are improved, but the effect is indispensable.
It cannot be said that it is enough, and conversely, polyurethane
Polar groups introduced into the resin reduce the mechanical properties of the resin
Therefore, when a magnetic recording medium is manufactured using the resin
The magnetic recording medium cannot exhibit sufficient durability
Can be seen. For this reason, magnetic powder dispersibility, durability
Binder that can fully satisfy all properties and surface smoothness
The emergence of is desired. [0005] [Means for Solving the Problems] The present inventors have proposed the above-mentioned method.
The problem is, that is, a polymer that is excellent in dispersibility of magnetic particles.
Urethane resin has not been obtained, and
With the polyurethane resin obtained, it is absolutely necessary
In light of the fact that satisfactory results have not been obtained,
While maintaining the mechanical properties of polyurethane resin,
Intensive study to improve dispersibility of conductive particles
Polyurethane resin with specific polar group
That the above purpose is achieved by adopting
We have found and completed the present invention. [0006] That is, the present invention relates to a method for preparing a ferromagnetic fine powder and a binder.
Obtained from a magnetic paint obtained by dissolving phenol in an organic solvent
A magnetic recording medium comprising a layer provided on a non-magnetic support.
As a binder, the ammonium of the COOH group
Uses polyurethane resin with at least one salt
To provide a magnetic recording medium characterized by
You. The polyurethane resin used in the present invention is:
If it has the above polar group inside the molecular chain,
Both ends are isocyanate groups, both ends
Are both hydroxyl groups, and one end is an isocyanate
Any of the groups having a hydroxyl group at the other end may be used. or,
The number average molecular weight of the polyurethane resin is 1,000 to 100,00
0 Preferably 5,000 to 50,000. Poliu
If the number average molecular weight of the urethane resin is less than 1000,
Insufficient mechanical properties, friction resistance, and wet heat resistance of the resin
If the number average molecular weight exceeds 100,000,
Although these performances are improved, the dispersion of magnetic powder
Is very inferior in terms of properties.
It is said that it is difficult to make a paint when melting it to make a paint.
Often fall into the situation. Number average molecular weight 5000-50,000
Are particularly required for the polyurethanes of the present invention
Convenient for exhibiting mechanical properties, abrasion resistance and wet heat resistance
It is something. [0008] In the present invention, in the polyurethane molecule
Polyester polyol part is soft segment (soft
Part), consisting of a polyisocyanate and a chain extender.
Is referred to as a hard segment (hard part). In the present invention, a COOH group is used inside a molecular chain.
Of polyurethane resin having ammonium salt
For example, the following methods are available. (1) (a) an organic polyisocyanate, (b)
High molecular weight polyol, (c) COOH group inside the molecular chain
A chain extender having a monium salt is reacted. in this case,
High molecular weight polyols have ammonium salts of COOH groups
What you do not have or what you have. (2) (a) an organic polyisocyanate, (b)
High molecular weight polyol having a COOH group inside the molecular chain, (c)
 Polyurethane having COOH groups obtained by reacting a chain extender
Neutralize the urethane resin with ammonia. In this case, (c)
The chain extender may or may not have a COOH group.
May be. (3) (a) an organic polyisocyanate, (b)
High molecular weight polyol, (c) COOH group inside the molecular chain
Having a COOH group obtained by reacting with a chain extender
Neutralize the urethane resin with ammonia. In this case, (b)
The high molecular weight polyol of may have a COOH group,
It is not necessary to have. In the method of (1), the organic polyisomers of (a)
Hexamethylene diisocyanate as a cyanate
G, lysine diisocyanate, isophorone diisocyanate
, Xylene diisocyanate, cyclohexanediyl
Socyanate, toluidine diisocyanate, 2,4-to
Tolylene diisocyanate, 2,6-tolylene diisocyanate
, 4,4'-diphenylmethane diisocyanate, p-
Phenylene diisocyanate, m-phenylene diisocyanate
Anate, 1,5-naphthylene diisocyanate, 4,4'-
Biphenyl diisocyanate, 3,3'-dimethyl biphenyl
4,4'-diisocyanate, 3,3'-dimethoxybiphe
Nyl-4,4'-diisocyanate, etc.
Examples include hydrogenated products and mixtures of cyanates.
You. Among these, those which are particularly preferably used in the present invention are described.
What can be done is the strength of the produced polyurethane resin
4,4'-diphenylmethane diisocyanate, 2,2
4- and 2,6-tolylene diisocyanate and their
It is a mixture. These organic polyisocyanates are
It is also used in the methods of (2) and (3). In the method (1), the inside of the molecular chain of (c)
A chain extender having an ammonium salt of a COOH group in the general formula [0015] Embedded image (Wherein R represents an alkyl group having 1 to 3 carbon atoms)
Glycol, 1,2-diaminopropio
Acid, diaminobenzoic acids, 3,3'-dicarboxyben
Thidine, 3,3'-carboxy-4,4'-diaminodiphenyl
Aqueous solution such as methane or alcohol such as methanol or ethanol
The amount of COOH groups in the coal solution to completely neutralize the COOH groups in the solution.
Adding ammonia and then removing the solvent
Thus obtained. As the glycol represented by the above general formula,
Is 2,2-dimethylolpropionic acid, 2,2-dimethylol
Butyric acid and 2,2-dimethylolvaleric acid.
For neutralization of these compounds, ammonia gas or ammonium gas is used.
Monia water is used. In the method (1), the reaction of the COOH group
It is also possible to use chain extenders that do not have ammonium salts
it can. (B) in the method of (2), which has a COOH group
As the high molecular weight polyol, the method (1) is described.
Solid glycol or ethylene glycol, trim
Gris such as Tylene glycol and tetramethylene glycol
Coals and adipic acid, sebacic acid, phthalic acid, etc.
Polyester obtained by known dehydration condensation reaction from rubonic acid
Terpolyol or a group represented by the general formula (I)
Recall ethylene oxide and / or propylene oxide
Obtained by the addition of oxides and / or tetrahydrofuran
Polyalkylene ether polyol having COOH groups
And the like. Manufactured polyurethane resin machine
From the viewpoint of the mechanical strength, the high molecular weight polymer used in the present invention
Polyols are particularly preferred as riol.
No. In the method (2), the polyurethane
High molecular weight polyols commonly used in the synthesis of resin
Can also be used in combination. In the method (3), the compound (c) having a COOH group
As the chain extender to be used, COOH described in the method (1) is used.
Glycols or diamines having a group are used. In the method (3), the polyurethane
Chain extender commonly used in the synthesis of resin
be able to. The method used in the methods (1), (2) and (3)
General, commonly used in the synthesis of polyurethane resins
Examples of known high molecular weight polyols include low molecular weight polyols.
Ethylene oxide or propylene
Obtained by adding an alkylene oxide such as
Polyether polyols and polytetramethylene ethers
Glycol, and the like.
Glycol, propylene glycol, 1,4-butanegio
Polyols, phthalic acid, maleic acid,
Malonic acid, succinic acid, adipic acid, terephthalic acid, etc.
A polycondensation product with a polybasic acid and having a hydroxyl group at the terminal
Reester polyols and polycaprolactone polyols
, Polycarbonate polyol, acrylic polyol
, Castor oil, tall oil and the like. or,
Hydroxyl group, amino group, imino group, carboxy
Liquid rubber having an active hydrogen group such as
Mixtures of these can also be used. Of these
Is, in terms of the strength of the manufactured polyurethane resin,
Polyester polyols are high molecular weight polyols.
preferable. The method used in the methods (1), (2) and (3)
General, commonly used in the synthesis of polyurethane resins
Known chain extenders include, for example, ethylene glycol
, 1,2-propylene glycol, 1,3-propylene glycol
Recall, 1,3-butanediol, 1,4-butanediol
, Neopentyl glycol, diethylene glycol,
1,5-pentamethylene glycol, 1,6-hexane glycol
Coal, cyclohexane-1,4-diol, cyclohexyl
San-1,4-dimethanol, bis-β-hydroxyethyl
Low-molecular-weight glycols such as
Diamine, 1,2-propylenediamine, 1,3-propylene
Diamine, 1,4-butanediamine, 1,6-hexanediamine
Amine, 4,4'-methylenebis-2-chloroaniline, 4,
4'-methylenebis-2-ethylaniline, 4,4'-methyl
Bis-diphenylamine, isophoronediamine, 2,4-
Low molecules such as diaminotoluene and 2,6-diaminotoluene
Diamines and mixtures thereof.
You. Polyurethane which can be used in the present invention
The urethane resin has a COOH group as a polar group inside the molecular chain.
In addition to monium salts, SO_ThreeM, COOM (where M is H, Li, Na
Or K), PO (OM ')_Two(However, M 'is H, Li, Na, K,
Amine, ammonia or alkyl), PO (OM ")
(However, M "means H, Li, Na, K, amine, ammonia
Or at least one polar group such as OH)
May be. Introducing these polar groups into the polyurethane resin
to do so, (A) using a high molecular weight polyol having these polar groups
To synthesize polyurethane resin (B) Polyurethane is prepared using these polar group-containing chain extenders.
Synthesizes a tin resin And the like. Of the above high molecular weight polyols, the COOM group
Having the general formula [0028] Embedded image (Wherein R ′ is an alkyl group having 1 to 3 carbon atoms)
The glycols shown, ethylene glycol, trimethyl
Glycos such as ren glycol and tetramethylene glycol
And carbohydrates such as adipic acid, sebacic acid and phthalic acid
Polyester obtained by known dehydration condensation reaction with acid
Polyols can be mentioned, and the general formula (III)
And ethylene oxide and / or
Propylene oxide and / or tetrahydrofuran
Polyalkylene acrylate having a COOM group obtained by addition
Terpolyol and the like can be mentioned. The above general formula
As the glycol represented by (III), 2,2-dimethyloyl
Propionic acid, 2,2-dimethylol butyric acid, 2,2-di
Methylol valeric acid and the like. The chain extender having a COOM group includes
2,2-dimethylolpropionic acid, 2,2-dimethylol
Butyric acid, 2,2-dimethylolvaleric acid, 1,2-diaminopro
Pionic acid, diaminobenzoic acids, 3,3'-dicarboxybe
Ndzine, 3,3'-carboxy-4,4'-diaminodiphenyl
Ethylene and ethylene oxide of these aminocarboxylic acids
Side or propylene oxide adducts and the like.
You. Further, PO (OM ')_TwoAs a chain extender with a group
Is a polyvalent alcohol such as glycerin or trimethylolpropane.
Monophosphate of coal, or in the following general formula (IV)
And the like. [0032] Embedded image (Wherein M ′ is H, Li, Na, K, amine, anne
Monia or alkyl groups, which are different
It may be. R₁', R_Two'Has a substituent or has
Divalent alkylene group or oxyalkylene group
And may be the same or different. Y is hydroxyl or hydrogen
Indicates an atom. l is 0-10, n₁, N_TwoRepresents an integer of 1 to 10
You Specific examples of those represented by the formula (IV) are shown below.
Such a thing is mentioned. [0034] Embedded image As a chain extender having a PO (OM ") group,
Examples thereof include those represented by the following general formula (V). [0036] Embedded image (Wherein M "is H, Li, Na, K, amine, ammo
Near or alkyl group. R₁', R_Two'Has a substituent
Divalent alkylene groups or oxyalkylenes with or without
And may be the same or different. n₁, N_TwoIs
Represents an integer of 1 to 10) Ammonium salt or amine of the compound represented by the formula (V)
Compounds used for forming salts include the following compounds
Ammonia or amines represented by the formula (II) are used
You. [0038] Embedded image (Where R₁, R_Two, R_ThreeAre each independently saturated
Or unsaturated alkyl group, alkanol group, cycloal
Kill group, alkylaryl group, aralkyl group, aryl
Group or hydrogen) As a specific example of the compound represented by the above formula (V)
Is [0040] Embedded image These compounds and their compounds
Salts of the compounds can be used. Also, among the chain extenders having OH groups, primary OH groups
Examples of the chain extender having the formula: N-hydroxyethyl
Ethylenediamine, 1,3-diamino-2-propanol
And chain extenders having a secondary OH group.
Lyserine, glycerin ethylene oxide adduct, 1,
2,6-hexanetriol, 4- [bis (2-hydroxy
Siethyl)]-2-hydroxypentane and diethanol
Propylene oxide adducts of ruamine and the like,
Examples of the chain extender having a tertiary OH group include 1,2,3-
Hydroxy-2-methylpropane, 1,2,3-hydroxy
-2-ethylpropane, 1,2,4-hydroxy-2-methyl
Lobutane, 1,2,5-hydroxy-2-methylpentane,
1,3,5-hydroxy-3-methylpentane, 1,3,6-
Droxy-3-methylhexane, 1,2,3,6-hydroxy
-2,3-dimethylhexane, 1,2,4,6-hydroxy-2,
Simple substance or mixture such as 4-dimethylhexane
It is. The binder in the magnetic recording medium of the present invention.
Conventional polyurethane resin
Known methods, such as thorough mixing of reactants
After mixing, pour the reaction mixture onto a flat plate or vat and heat
Or crushing after cooling, or
Methylformamide, toluene, xylene, benzene,
Dioxane, tetrahydrofuran, cyclohexanone,
Methyl ethyl ketone, methyl isobutyl ketone, acetate
Single or mixed solvent organic solvents such as chill and butyl acetate
It is possible to adopt a production method such as a solution reaction method in which
Wear. At this time, lower the reaction temperature or
Reaction catalyst can be added to shorten the time
You. Specific examples of the reaction catalyst include, for example, triethylene
Diamine, tetramethylethylenediamine, tetramethyl
Amine compounds such as hexanediamine and salts thereof
Or dibutyltin dilaurate, tin octylate,
Organometallic compounds such as lead citrate and manganese octylate
And mixtures thereof. Also poly
Antioxidant to increase urethane resin stability
Agents, UV absorbers, hydrolysis inhibitors, etc. alone or
These can be combined and compounded. Further, in the present invention, a polyurethane resin
In order to improve the durability of the fat, use a suitable hardener
It is also possible to use a cured urethane resin. Curing that can be used in the present invention
As the agent, a low molecular compound having two or more isocyanate groups
Polyisocyanates and low molecular weight polyols
The end of the molecule isocyanate
Compounds having a molecular weight of 150.
Approximately 7000 is preferable. Among these,
Low molecular weight polyisocyanate having two or more isocyanate groups
Anate is preferred. Low molecule having two or more isocyanate groups
The amount of the polyisocyanate is as described in the above method (1).
In addition to those described for (a),
Anisoates, diisomers such as hexamethylene diisocyanate
Of 3 mol of cyanate and 1 mol of trimethylolpropane
Reactants, modified diphenylmethane diisocyanate,
Polyfunctional isocyanates such as polyphenylmethane polyisocyanate
An anate compound can be mentioned. These compounds
Is "Coronate L" from Nippon Polyurethanes, Inc.
"Coronate HL", "Coronate 2030", "Millionone"
Brands such as "Mr. MR" and "Millionate MTL".
"Death module L" from Tomo Bayer Urethane Co., Ltd.
"Death module N", "Death module IL", "De
Smart Module HL ”,“ Death Module R ”,“ Desmo
Joule RF "and other product names from Takeda Pharmaceutical Company Limited
Takenate D-102 "," Takenate D-110N "," Bamboo
Nate D-202 "and the like.
You. In the present invention, the polar group-containing polyurethane
100 parts by weight of resin
5 to 60 parts by weight of a low molecular weight polyisocyanate having a group
In addition, by curing, the mechanical strength of the magnetic layer
Abrasion resistance, heat resistance, wet heat resistance, solvent resistance and
The adhesion can be greatly improved. The above-mentioned polar group used in the present invention
Polyurethane resin having is a generally known polyurethane
Resins and other resins can be used in combination. example
For example, nitrocellulose, acetic acid
Cell of cellulose, cellulose acetate butyrate, etc.
Loose derivative; vinyl chloride / vinyl acetate copolymer, chloride
Vinyl / vinyl acetate / vinyl alcohol copolymer, chloride
Vinyl chloride / vinyl acetate such as vinyl / vinyl acetate / maleic acid copolymer
Fat; vinylidene chloride / vinyl chloride copolymer, vinylidyl chloride
Vinylidene chloride such as den / acrylonitrile copolymer
Fat; Polyester such as alkyd resin and linear polyester
Resin; (meth) acrylic acid / acrylonitrile copolymer
Body, methyl (meth) acrylate / acrylonitrile
Acrylic resin such as coalescing; polyvinyl acetal, polyvinyl
Acetal resins such as nilbutyral; phenoxy resins,
Epoxy resin, polyamide resin, butadiene / acryloyl
Nitrile copolymer, styrene / butadiene copolymer, etc.
No. These resins can be used alone or in combination
Can be The magnetic recording medium of the present invention
Using the polyurethane resin produced by
Binder, ferromagnetic fine powder and additives etc. together with organic solvent
Manufacturing by applying dispersed magnetic paint on non-magnetic support and drying
Is done. At this time, the ratio between the binder and the ferromagnetic fine powder is
10-100 parts by weight of binder per 100 parts by weight of magnetic fine powder
Preferably it is 20 to 50 parts by weight. That is, ferromagnetic fine powder 1
When the amount of the binder is less than 10 parts by weight with respect to 00 parts by weight,
Decreases the bonding strength between the binder and the magnetic powder,
Insufficient abrasion resistance and 100 weight of binder
If the magnetic powder density in the magnetic layer is higher than
The performance of the magnetic recording medium (reproduction output
Etc.) cannot be obtained. Binder for 100 parts by weight of magnetic powder
In particular, when 20 to 50 parts by weight are blended, it is an object of the present invention.
Not only in terms of enhanced mechanical strength and wear resistance,
It is also preferable from the aspect of reproduction output of the magnetic recording medium. Strong magnets that can be used in the present invention
Γ-Fe_TwoO_Three, Γ-Fe_TwoO_ThreeAnd Fe_ThreeO_FourWith
Mixed crystal, Co-modified iron oxide, CrO_Two, Iron, etc., and other iron
It is preferable to use alloy fine powder mainly composed of
Can be. Regarding the shape of these ferromagnetic fine powders,
Any shape such as needle, plate, and sphere can be used
You. The specific surface area of these ferromagnetic fine powders is BET
75m measured by the method^Two/ G or less, but 40
m^Two/ G or less is preferable. Specific surface area of magnetic powder is 75m^Two
/ G, a high playback output cannot be obtained
Alternatively, the strength of the magnetic layer is inferior and the durability is disadvantageous. Magnetic
Specific surface area of conductive powder is 40m^Two/ G or less
Obtaining high playback output while maintaining body durability
This is very preferable in that it can be performed. In the magnetic layer composed of a binder and a ferromagnetic fine powder,
Uses aluminum oxide, chromium oxide, and silicon oxide
It can be added as a toughening agent, dibutyl phthalate,
Plasticizers such as phenyl phosphate, zinc stearate,
Lubricant like silicone oil, soybean oil like lecithin
Various antistatic agents such as powders and carbon black
Etc. can also be added. These materials constituting the magnetic layer are made of organic solvent.
Dissolved in the agent and adjusted as a magnetic paint, which was placed on the support
The magnetic recording medium is manufactured by applying the magnetic recording medium. Magnetic
Acetone, methyl
Ketones such as ethyl ketone, methanol, ethanol, etc.
Alcohols, esters such as ethyl acetate and butyl acetate
System, dioxane, ether system such as tetrahydrofuran,
Aromatic hydrocarbons such as benzene and toluene, hexane, etc.
Aliphatic hydrocarbon solvents. As a support to which the magnetic paint is applied, a non-magnetic
Any material, for example, polyethylene terephthalate
Polyesters such as polyester and polypropylene
Cellulose derivatives such as fins and cellulose triacetate
Body, polycarbonate, polyvinyl chloride, polyimide,
Examples include polyamides and metals such as aluminum.
I can do it. [0054] The polar group-containing polyurethane resin of the present invention
Although the mechanism of action is not always clear,
By changing to ammonium salt, metal and salt in magnetic powder
And a high dispersion effect can be obtained.
Ammonia used for neutralization has two or more isocyanate groups
Reacts with low molecular weight polyisocyanate having
A strong urea bond is formed or the reaction proceeds further,
By forming a cross-linked structure with
It is considered that high durability is obtained. [0055] The present invention will now be described in more detail with reference to the following examples.
As will be apparent, the invention is not limited to only these examples.
Not. In the examples, "parts" means "parts by weight".
Is shown. (Synthesis Example of Polyester Polyol) ・ Polyester polyol (A) Ethylene glycol, tetrame
Tylene glycol, dimethylolpropionic acid and
Molecular weight with one COOH group in the molecular chain from pinic acid
2000 polyester polyols were synthesized. Polyester polyol (B) Hexamethylene glycol,
Pentyl glycol, dimethylol propionic acid and
Adipic acid has two COOH groups inside the molecular chain.
A polyester polyol having a molecular weight of 2000 was synthesized. (Example of Production of Polyurethane Resin) Production Example 1 In a reaction vessel equipped with a thermometer, stirrer, and reflux condenser,
478 parts of ethyl ethyl ketone, 119 parts of cyclohexanone,
234 parts of dimethylene adipate (molecular weight 2000), dimethylo
12 parts of ammonia neutralized product of toluene propionic acid, ethylene glycol
Recall 22 parts, 4,4'-diphenylmethane diisocyanate
132 parts, dibutyltin dilaurate 0.5 parts as catalyst
Was added and reacted at 80 ° C. for 12 hours. Polyurethane obtained
The resin is an ammonium salt of COOH group per polymer molecule.
And its molecular weight was 20000. Production Example 2 In a container similar to that of Production Example 1, 602 parts of methyl ethyl ketone,
67 parts of the polyester polyol (A), polybutylene
Adipate (Molecular weight 2000) 214 parts, ethylene glycol
27 parts, 2,4- and 2,6-toluene diisocyanate mixed
(Weight ratio 80/20) 93 parts, dibutyltin dilla as catalyst
0.5 parts of ureate was added and reacted at 80 ° C. for 15 hours. Next
After cooling the system to room temperature, add 2 parts of 28% ammonia water
Stirred at room temperature for 1 hour. The obtained polyurethane resin is
Having one ammonium salt of COOH group per polymer molecule
And its molecular weight was 12,000. Comparative Production Example 1 As a polyurethane resin without a polar group inside the molecular chain
Prepare "Estan 5715" (BF Goodrich)
Was. Comparative Production Example 2 Ammonium of dimethylolpropionic acid used in Production Example 1
A) In place of the neutralized product, add 11 parts of dimethylolpropionic acid.
The same operation as in Production Example 1 was performed except that the polyurethane resin was used.
Resin was manufactured. Comparative Production Example 3 In a container similar to that of Production Example 1, 566 parts of methyl ethyl ketone,
141 parts of trahydrofuran, polybutylene adipate (min.
261 parts, dimethylolpropionic acid 13 parts,
47 parts of tandiol, 4,4'-diphenylmethane diisocyanate
180 parts, dibutyltin dilaurate as catalyst
0.5 part was added and reacted at 80 ° C. for 10 hours. Then the system
The mixture was cooled to a temperature to obtain a polyurethane resin. Its molecular weight is
 Was 15,000. Comparative Production Example 4 Neutralization operation by adding 28% aqueous ammonia in Production Example 3
The same operation as in Production Example 3 was performed except that the operation was omitted.
A urethane resin was manufactured. Comparative Production Example 5 602 parts of methyl ethyl ketone in the same container as in Production Example 1,
100 parts of the polyester polyol (B) described above, polybutylene
Adipate (molecular weight 2000) 172 parts, butanediol 39
Parts, 2,4- and 2,6-toluene diisocyanate mixture
90 parts by weight (80/20 by weight), dibutyltin dilau as catalyst
0.5 part of the rate was added and reacted at 80 ° C. for 20 hours. Then system
After cooling to room temperature, 4 parts of sodium hydroxide were
Introduce into the urethane solution in 1 hour, then 1 hour at room temperature
While stirring. The resulting polyurethane resin is a COOH-based
The polymer has two lithium salts in one molecule, and the molecule
The quantity was 8000. Embodiment 1 Polyure produced in Production Examples 1-2 and Comparative Production Examples 1-5
The magnetic powder dispersibility of the tin resin was evaluated.
Measure the durability of magnetic disks manufactured using urethane resin
Specified. <Evaluation of magnetic powder dispersibility> -Polyurethane tree of Production Examples 1-2 or Comparative Production Examples 1-5
Fat solution (nonvolatile content 40%) ... 125 parts ・ Γ-Fe_TwoO_Three… 100 copies ・ Methyl ethyl ketone: 278 parts ・ Cyclohexanone: 139 parts After milling the above mixture for 24 hours in a ball mill, the resulting mixture was obtained.
70 micron thick polyethylene terephthalate with magnetic paint
15 μm after coating on substrate film and drying
Coated and dried to become magnetic under an electron microscope (150x)
The surface state of the layer was observed, and the dispersibility of the magnetic powder was evaluated. So
Table 1 shows the results. <Durability Evaluation of Magnetic Disk> -Polyurethane tree of Production Examples 1-2 or Comparative Production Examples 1-5
Fat solution (nonvolatile content 40%): 75 parts ・ Vinylite VAGH (Union Carbide, USA)
Vinyl chloride-vinyl acetate copolymer) 20 parts ・ Γ-Fe_TwoO_Three… 100 copies ・ Carbon black ... 3 parts ・ Lubricant: 2 parts ・ Methyl ethyl ketone… 200 parts ・ Cyclohexanone… 100 parts After the above composition was ground for 24 hours in a ball mill, 10 parts were cured.
Agent (Coronate L, manufactured by Nippon Polyurethane Co.)
After 1 hour of milling, the resulting magnetic paint is
Thickness after drying on ethylene terephthalate base film
And dried and aged so as to be 2 microns. Then,
Cut the film to the specified magnetic disk size and dry
And measure the time it takes for the playback output to drop to 50%.
And the durability was evaluated. The results are shown in Table 1. [0068] [Table 1] [0069] [0070] As specifically shown in the examples,
The polyurethane resin used for the magnetic recording medium of the present invention is a magnetic recording medium.
Unprecedented effects in terms of powder dispersibility and durability
have. This effect is due to the molecular chain of the polyurethane resin.
Due to the introduction of ammonium salt of COOH group inside
This is a remarkable effect compared to conventional polyurethane resin.
It is a fruit. Therefore, the high dispersibility and high durability of the present invention
Magnetic recording media using polyurethane resin is an excellent electromagnetic
The emergence of magnetic recording media with high conversion characteristics and high durability
It is thought that it can answer a desired voice.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-139631 (JP, A) JP-A-59-5423 (JP, A) UK Patent 1076688 (GB, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) C09D 5/23 C09D 175/04-175/12 G11B 5/702

Claims (1)

(57) [Claims] In a magnetic recording medium in which a magnetic layer obtained from a magnetic paint obtained by dissolving a ferromagnetic fine powder and a binder in an organic solvent is provided on a non-magnetic support, a COOH group in a molecular chain is used as a binder as a binder. A magnetic recording medium comprising a polyurethane resin having at least one ammonium salt. 2. The number average molecular weight of the polyurethane resin is 5000 to 50
2. The magnetic recording medium according to claim 1, wherein the number is 000. 3. 3. The magnetic recording medium according to claim 1, wherein the mixing ratio of the polyurethane resin and the ferromagnetic fine powder is from 10 to 100 of the polyurethane resin to 100 of the ferromagnetic fine powder in a weight ratio. 4. 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic fine powder has a specific surface area of 75 m ² / g or less.