JPH0618066B2 - Magnetic recording medium - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic sheet.

B. 2. Description of the Related Art In recent years, in magnetic recording media, particularly in magnetic recording media for video that requires short wavelength recording, finer particles than ever have been used.
There is an increasing tendency to use magnetic powder with high magnetic force. However, as the magnetic powder becomes finer and the magnetic force becomes higher,
The cohesive force of the individual particles is strengthened, and as a result, the dispersibility and surface smoothness required to obtain a high reproduction output for short wavelength recording and a good S / N ratio cannot be sufficiently satisfied. Further, since such a recording medium is in strong sliding contact with the magnetic head during recording and reproduction, the magnetic coating film is abraded by repeated use, and the magnetic powder contained in the coating film easily falls off, which is an unfavorable result such as clogging of the magnetic head. Give rise to.

Therefore, the particle size distribution of the magnetic powder is adjusted to improve the dispersibility of the magnetic powder in the binder, or a surfactant is used as the dispersant, or a hydrophilic group in the binder, for example, a hydroxyl group, There has been proposed a method of modifying by introducing a phospho group, a sulfo group, a carboxy group or the like to improve the characteristics.

For example, by introducing a sulfonic acid metal salt residue into a polyester resin, JP-A-56-74824 and JP-A-56-74827 disclose that surface smoothness (gloss) and adhesion to a support are improved. 56-13519, 56-74826, 56-74828
No. 56-74829 and the like disclose dispersibility and improvement of filling property relating to interfacial tension. The sulfonic acid metal group-introduced polyester resin, polyurethane resin, nitrocellulose, vinyl chloride-vinyl acetate resin, etc. Many proposals have been made for binder compositions by combining them.

Furthermore, since vinyl chloride resins have high mechanical strength, vinyl chloride-vinyl acetic acid copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-aricronitrile copolymers or vinyl chloride-vinyl acetate-vinyl alcohols. Maleic anhydride copolymers and the like are prized.

The modification of the vinyl chloride resin with a sulfonic acid metal salt residue is disclosed in JP-A-57-44227. First, a vinyl chloride resin containing an OH group and, for example, a chlorine atom and a sulfone in a molecule. Dehydrochlorination is carried out with a compound containing an acid metal salt residue to obtain a modified vinyl chloride resin having a sulfonic acid metal salt residue introduced therein.

As for the vinyl chloride copolymer containing free sulfo group (-SO ₃ H) is where disclosed in JP-A-58-108032.

However, a vinyl chloride-based copolymer obtained from such a polymerizable monomer having a free sulfo group increases the viscosity of the coating when mixed with a magnetic coating, which causes a problem in the process and causes a problem of the medium. It also adversely affects the running performance.

C. Object of the Invention The object of the present invention is not only excellent in dispersibility of magnetic powder, but also good in durability, good lubricity of a magnetic layer and excellent in still image durability, running stability, and S / N. An object is to provide an excellent magnetic recording medium.

D. Structure of the Invention and Effects of the Invention That is, the present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, wherein the binder contains a sulfo group and / or a phosphate group in the form of an alkali metal salt. At least a vinyl chloride copolymer and a urethane resin contained in are used, and the magnetic layer contains at least one fatty acid selected from the following Group A and at least one fatty acid ester selected from the following Group B: The present invention relates to a magnetic recording medium, characterized in that the content (weight) of fatty acid is higher than the content (weight) of the fatty acid ester.

Group A caproic acid caprylic acid capric acid lauric acid myristic acid palmitic acid stearic acid isostearic acid linolenic acid linoleic acid oleic acid elaidic acid behenic acid malonic acid succinic acid maleic acid glutaric acid adipic acid pimelic acid sebacic acid octane dicarboxylic acid 1,12 -Dodecanedicarboxylic acid Group B oleyl oleate isocetyl stearate dioleyl maleate butyl stearate butyl palmitate butyl myristate octyl myristate octyl palmitate amyl stearate amyl palmitate isobutyl oleate stearyl stearate lauryl oleate octyl oleate isobutyl oleate methyl Oleate isotridecyl oleate 2-ethylhexyl stearate methyl steare 2-Ethylhexyl palmitate Isopropyl palmitate Isopropyl myristate Methyl laurate Cetyl-2-ethyl hexalate Dioleyl adipate Diethyl adipate Diisobutyl adipate Diisodecyl adipate According to the present invention, the binder is a sulfo group and / or a phospho group. Since it is contained in the form of an alkali metal salt, the dispersibility of the magnetic powder is improved and the surface smoothness of the magnetic layer is improved. Moreover, since the magnetic layer contains both fatty acid and fatty acid ester, and the content of the former is larger than that of the latter, the defects that occur when used alone are offset while exhibiting the respective characteristics of both. As a result, the lubrication effect can be improved, and still image durability, running stability, S / N ratio, etc. can be improved. In this case, the amount of fatty acid added is preferably 0.2 to 3 parts by weight, more preferably 0.5 to 2.5 parts by weight, based on 100 parts by weight of the magnetic powder. If the amount of fatty acid deviates from this range, the dispersibility of the magnetic powder decreases, and the running property of the medium tends to decrease. If the amount of fatty acid increases, the fatty acid tends to exude or the output tends to decrease. The amount of the fatty acid ester added is preferably 0.1 to 2 parts by weight, more preferably 0.2 to 1.5 parts by weight, based on 100 parts by weight of the magnetic powder. If the amount of ester is less than this range, the effect of improving the running property is poor, and if the amount of ester is too large, the ester exudes or the output is apt to decrease.

The binder according to the present invention, in particular, a vinyl chloride-based copolymer is obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and optionally other copolymerizable monomer. Can be obtained by Since this copolymer is based on vinyl synthesis, it is easy to synthesize, various copolymerization components can be selected, and the characteristics of the copolymer can be optimally adjusted.

The metal of the salt of sulfonic acid or phosphoric acid is an alkali metal (particularly sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

Examples of the above-mentioned copolymerizable monomer containing a sulfonate include CH ₂ ═CHSO ₃ M, CH ₂ ═CHCH ₂ SO ₃ M, CH ₂ ═C (CH ₃ ) CH ₂ SO ₃ M, CH ₂ ═CHCH ₂ OCOCH (CH ₂ COOR) SO
_{3 M, CH 2 = CHCH 2} OCH 2 CH (OH) CH 2 SO 3 M, CH 2 = C (CH 3) COOC 2 H 4 SO 3 M, CH 2 = CHCOOC 4 H 8 SO 3 M CH 2 = CHCONHC (CH ₃₎ include ₂ CH ₂ SO ₃ M.

As the phosphate, CH ₂ ═CHCH ₂ OCH ₂ CH (OH) CH ₂ —O—PO.
^{_{3 MY 1, CH 2 = CHCONHC}} (CH 3) 2 CH 2 -O-PO 3 M
Y ² , _{CH 2 = CHCH 2 O (CH} 2 CH 2 O) mPO 2 MX 2 is above Te at M an alkali metal, R represents an alkyl group having 1 to 20 carbon atoms, Y ¹ is H, M or CH ₂ = CHCH ₂ OC
_{H 2 CH (OH) CH 2} -, Y 2 is H, M or _{CH 2 = CHCONHC (CH 3)} 2 CH
_2- , X ¹ is OH or OM, X ² is CH ₂ ═CHCH ₂ O (CH ₂ CH
₂ O), OH or OM. Also, n is 1 to 100, m
Is an integer of 1 to 100.

As the copolymerizable monomer to be copolymerized as necessary, there are known polymerizable monomers, for example, various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid,
Examples include various acrylic acid esters, methacrylic acid esters, ethylene, propylene, isobutene, butadiene, isoprene, vinyl ethers, aryl ethers, aryl esters, acrylamides, methacrylamides, maleic acid, maleic acid esters and the like.

The binder according to the present invention is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization and bulk polymerization. In any of the methods, known techniques such as a molecular weight modifier, a polymerization initiator and a monomer may be dividedly added or continuously added if necessary.

The amount of the acid group salt-containing monomer in the binder used in the present invention is preferably 0.01 to 30 mol%. When the amount of the salt-containing monomer is too large, the solubility in a solvent is poor and gelation is likely to occur. Further, if the amount of the salt-containing monomer is too small, desired characteristics cannot be obtained.

Particularly, the vinyl chloride-based copolymer as the binder is preferably used in combination with a urethane resin that improves the durability of the magnetic medium.

Urethane resin can be synthesized by the reaction of polyol and polyisocyanate. As usable polyols, organic dibasic acids such as phthalic acid, adipic acid, dimerized linoleic acid and maleic acid, and glycols such as ethylene glycol and diethylene glycol, or trimethylolpropane, hexanetriol, glycerin,
Polyester polyol synthesized by reaction with any two or more polyols selected from polyhydric alcohols such as trimethylolethane and pentaerythritol, or s-caprolactam, a-methyl-1-caprolactam, s- Lactone polyester polyol synthesized from lactams such as methyl-s-caprolactam and γ-butyrolactam, or ethylene oxide,
Examples thereof include polyether polyols synthesized from propylene oxide, butylene oxide and the like.

These polyols are reacted with an isocyanate compound such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and metaxylylene diisocyanate, and thereby urethane-formed polyester polyurethane, polyether polyurethane, or polycarbonate carbonated with phosgene or diphenyl carbonate. Polyurethane is synthesized.

These urethane resins have free isocyanate groups and / or
Alternatively, it may be in the form of a urethane resin or urethane prepolymer containing a hydroxyl group, or may be one not containing these reactive terminal groups (for example, a urethane elastomer).

Since methods for producing polyurethane, urethane prepolymers, urethane elastomers, curing cross-linking methods, etc. are well known, detailed description thereof will be omitted.

Furthermore, various conventionally known resins may be used in combination. The thermoplastic resin used together has a softening temperature of 150 ° C or lower,
Those having an average molecular weight of about 10,000 to 200,000 and a degree of polymerization of about 200 to 2000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester- Acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, acrylic acid ester-styrene copolymer,
Methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride,
Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer Polymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber thermoplastic resins, and mixtures thereof are used.

Further, the thermosetting resin or the reactive resin has a molecular weight of about 200,000 or less in the state of the coating liquid, and the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, a phenol resin, an epoxy resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, an acrylic reaction resin, a mixture of a high molecular weight polyester resin and an isocyanate prepolymer, a methacrylate copolymer and a diisocyanate prepolymer. Examples thereof include a mixture, a mixture of polyester polyol and polyisocyanate, a urea formaldehyde resin, a mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, a polyamine resin and a mixture thereof.

The resin is _{-SO 3 M -, - OSO 3} M, -COO
It may be a resin containing a hydrophilic polar group such as M, —PO (OM ′) ₂ (where M is hydrogen or an alkali metal, M ′ is hydrogen, an alkali metal or a hydrocarbon residue).

The compounding ratio of the vinyl chloride copolymer and the urethane resin usable in the present invention is 90 to 10 parts by weight, more preferably 80 to 20 parts by weight of the vinyl chloride copolymer according to the present invention. Is desirable. If the compounding ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film remarkably deteriorates, and the adhesion to the support also deteriorates. Further, if the above-mentioned mixing ratio is less than 10 parts by weight, the magnetic powder is likely to fall off.

Further, the durability can be improved by further adding a polyisocyanate curing agent to the magnetic coating material containing the binder according to the present invention. Examples of such a polyisocyanate curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (manufactured by Bayer), and the like. Any of those conventionally used as a curing agent such as a trifunctional isocyanate or a urethane prepolymer having an isocyanate group at both ends, and any polyisocyanate usable as a curing agent can be used. The amount of the polyisocyanate-based curing agent used is 5 to 80 parts by weight based on the total amount of the binder.

Next, the above fatty acids used in the present invention may be monobasic or dibasic. Fatty acids having 6 to 30 carbon atoms, and more preferably 10 to 22 carbon atoms are preferable. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Palmitic acid (7) Stearic acid (8) Isostearic acid (9) Linolenic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid (21) Sebacic acid (22) 1,12-dodecanedicarboxylic acid (23) Octanedicarboxylic acid Examples of the above fatty acid ester used in the present invention are as follows.

(1) Oleyl oleate (2) Isocetyl stearate (3) Dioleyl maleate (4) Butyl stearate (5) Butyl palmitate (6) Butyl myristate (7) Octyl myristate (8) Octyl palmitate ( 9) Amyl stearate (10) Amyl palmitate (11) Isobutyl oleate (12) Stearyl stearate (13) Lauryl oleate (14) Octyl oleate (15) Isobutyl oleate (16) Methyl oleate (17) Isotridecyl oleate (18) 2-Ethylhexyl stearate (19) Methyl stearate (20) 2-Ethylhexyl palmitate (21) Isopropyl palmitate (22) Isopropyl myristate (23) Methyl laurate (24) Cetyl-2-ethyl hexalate (25) Georail Adipate (2 6) Diethyl adipate (27) Diisobutyl adipate (28) Diisodecyl adipate FIG. 1 shows a magnetic recording medium according to the present invention, for example, a magnetic tape, which comprises a support 1 and a subbing layer 2 (this layer is necessary). The magnetic layer 3 may not be provided depending on the case.
Are stacked. According to the present invention, the magnetic layer 3 contains the above-mentioned binder, fatty acid, fatty acid ester, and magnetic powder.

The support 1 is preferably provided with a so-called backcoat 4 on the surface opposite to the side on which the magnetic layer is provided for the purpose of preventing electrification and transfer.

As the magnetic powder used for the magnetic layer, particularly as the ferromagnetic powder, γ
-Fe ₂ O _3, Co-containing _{γ-Fe 2 O 3, Fe} 3 O 4, Co -containing Fe ₃ O ₄ and the like iron oxide magnetic powder: Fe, Ni, Co, Fe -Ni-Co alloy, Fe-Mn- Zn
Alloy, Fe-Mi-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-
Various ferromagnetic powders such as Ni—P alloys, Co—Ni alloys, etc., metal magnetic powders containing Fe, Ni, Co, etc. as the main component: CrO ₂ can be mentioned.

In addition to the above, other dispersants, other lubricants, abrasives, antistatic agents, etc. may be added to the magnetic layer.

Other dispersants that can be used in combination include alkali metals (Li, Na, K, etc.) or alkaline earth metals (Mg,
Ca, Ba) metal soap; fluorine-containing compound of the above fatty acid ester; amide of the above fatty acid; lecithin; trialkylpolyolefinoxy quaternary ammonium salt (alkyl has 1 to 5 carbon atoms, olefin has ethylene, Such as propylene) is used. Besides this, carbon number
It is also possible to use higher alcohols of 12 or more, and sulfate ester in addition to these.

Other lubricants that can be used include dialkyl polysiloxane (where alkyl is 1 to 5 carbon atoms), COOR (R = H
Or a dialkyl polysiloxane modified with a C _{1 to} C ₂₀ alkyl group), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms, alkoxy) Has 1 to 4 carbon atoms, phenyl polysiloxane, fluoroalkyl polysiloxane (where alkyl is 1 to 5 carbon atoms)
Silicone oil such as); conductive fine powder such as graphite; inorganic fine powder such as molybdenum disulfide and tungsten disulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α -Olefin polymer; unsaturated aliphatic hydrocarbon that is liquid at room temperature (a compound in which an n-olefin double bond is bonded to the terminal carbon, carbon number about 20); and fluorocarbons can be used.

As abrasives, commonly used materials such as alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite) are used. To be done. These abrasives have a Mohs hardness of 5 or more,
An average particle size of 0.05 to 5 μm is used,
It is particularly preferably 0.1 to 2 μm. These abrasives are added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of magnetic powder.

As the antistatic agent, conductive fine powder such as carbon black and carbon black graft polymer; natural surfactant such as saponin; nonionic surfactant such as alkylene oxide type, glycerin type and glycidol type; higher alkylamines, Cationic surfactants such as quaternary ammonium salts, pyridine and other heterocycles, phosphoniums; anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group and phosphate ester group; amino acids And amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohol, and the like are used. The conductive fine powder is added in an amount of 0.2 to 20 parts by weight, and the surfactant is added in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the magnetic powder. You may add these surfactant individually or in mixture. These are used as antistatic agents, but in some cases, they are used for their purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and coating aid.

Further, the constituent material of the magnetic layer is mixed with an organic solvent to prepare a magnetic coating material, which is coated on a support. The solvent of the magnetic coating material is a ketone (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone). ,
Alcohols (eg methanol, ethanol, propanol, butanol), esters (eg methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether),
Glycol ether (eg ethylene glycol monoethyl ether, ethylene glycol diethyl ether,
Dioxane), aromatic hydrocarbons (eg benzene, toluene, xylene), aliphatic hydrocarbons (eg hexane,
Heptane), nitropropane and the like. The support to which this magnetic coating is applied is polyester (eg polyethylene terephthalate, polyethylene-2,6-naphthalate), polyolefin (eg polyethylene, polypropylene), cellulose derivative (eg cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate). Propionate), polycarbonate, polyvinyl chloride, polyimide, polyamide, polyhydrazide, metal (eg aluminum, copper), paper and the like.

E. EXAMPLES Hereinafter, the present invention will be described with reference to specific examples. The components, ratios, operation sequences and the like shown below can be variously modified without departing from the spirit of the present invention. In the following examples, all "parts" represent "parts by weight".

Example-1 In this example, a vinyl chloride-based copolymer containing the salt was synthesized as follows.

The following composition was charged in a reaction vessel and replaced with N ₂ to cause a reaction.

Methyl isobutyl ketone 86 parts by weight of methyl acetate 280 〃 vinyl chloride 150 〃 vinyl acetate 50 〃 _{CH 2 = CHCH 2 OCOCH (SO} 3 K) CH 2 COOC
₈ H ₁₇ 6 〃 Diisopropyl peroxydicarbonate (polymerization initiator) 2 〃 The above formulation composition was heated to 53 ° C. with stirring, and 9 methyl isobutyl ketone was added to the polymerization initiator 1 in the formulation.
After 15 hours, the mixture was cooled to 30 ° C., the residual vinyl chloride was recovered, and further recovered under reduced pressure. In this way, solid content 32%, viscosity 70
480 parts by weight of a copolymer solution of cps (25 ° C.) was obtained.

The vinyl chloride resin containing the unsaturated compound having an alkali metal salt of a sulfo group as a copolymerization component thus obtained is used as a binder A. Then, the following composition was prepared.

Binder A 15 parts Polyurethane (1,4-butanediol / adipic acid /
Diphenylmethane diisocyanate, Goodrich Estan 5701) 7 parts Co-γ-Fe ₂ O ₃ 100 parts Lecithin 1 part Carbon black 2 parts Chromium oxide 2 parts Fatty acid (oleic acid) 1 part Fatty acid ester (butyl palmitate) 0.5 parts Cyclohexanone 150 parts Methyl ethyl ketone 70 parts Toluene 30 parts After the above ingredients were charged into a ball mill and dispersed, 5 parts of trifunctional isocyanate was added to this paint, which was applied on a support with a reverse roll coater to a thickness of 5 μm and a super calendar. And then slit it into a 1/2 inch width to make a video tape.

Example-2 In Example-1, instead of the binder A, a vinyl chloride resin containing an unsaturated compound having an alkali metal salt of a phospho group as a copolymerization component (in the binder A of Example-1, CH ₂ = CHCH ₂ OCOCH (SO ₃ K) CH ₂ C
0.5 parts by weight of 6 parts by weight of OOC ₈ H ₁₇ are CH ₂ = CH
The same operation as in Example 1 was performed, except that CONHC (CH ₃ ) ₂ CH ₂ OPO ₃ K ₂ was used instead of the one obtained: Binder B).

Example 3 Example 1 was repeated except that fatty acid was used as lauric acid and fatty acid ester was used as oleyl oleate.

Example 4 Example 1 was repeated except that fatty acid was used as myristic acid and fatty acid ester was used as isocetyl stearate.

Example 5 Example 1 was repeated except that the fatty acid was used as palmitic acid and the fatty acid ester was used as butyl stearate.

Example 6 Example 1 was repeated except that stearic acid was used as the fatty acid and butyl myristate was used as the fatty acid ester.

Example 7 The procedure of Example 1 was repeated, except that oleic acid was used as the fatty acid and octyl myristate was used as the fatty acid ester.

Example 8 The procedure of Example 1 was repeated except that behenic acid was used as the fatty acid and fatty acid ester was used as the amyl stearate.

Comparative Example-1 In Example-1, instead of the binder A, an unsaturated compound having a sulfo group. The same operation as in Example-1 was carried out except that a vinyl chloride resin containing B as a copolymerization component (referred to as a binder C) was used.

Comparative Example-2 In Example-1, 1 part of fatty acid and 0.5 of fatty acid ester are used.
The same operation as in Example-1 was performed except that the charged amount of 0.5 part of fatty acid and the charged amount of 1 part of fatty acid ester were used instead of the charged amount of part.

Comparative Example-3 In Example-2, 1 part of fatty acid and 0.5 parts of fatty acid ester are used.
The same operation as in Example-2 was performed, except that the charged amount of 0.5 part of fatty acid and the charged amount of 1 part of fatty acid ester were used instead of the charged amount of part.

Comparative Example-4 In Example-1, instead of 1 part of fatty acid (oleic acid) and 0.5 part of fatty acid ester (butyl palmitate),
Dimethyl silicone oil ((C ₇ H ₁₅ COO) ₂ Si (C
H _{3) 2)} outside using 1.5 parts was carried out in the same manner as in Example -1.

Comparative Example-5 The procedure of Example-1 was repeated, except that the amounts of the fatty acid (oleic acid) and the fatty acid ester (butyl palmitate) were changed to 0.75 parts each.

Comparative Example-6 The procedure of Example-2 was repeated, except that the amounts of the fatty acid (oleic acid) and the fatty acid ester (butyl palmitate) in Example-2 were 0.75 parts each.

Comparative Example-7 In Example-1, 15 parts of VAGH (a vinyl chloride / vinyl acetate / vinyl alcohol copolymer manufactured by Union Carbide Co.) and 7 parts of Estane 5701 were used instead of 15 parts of the binder A and 7 parts of polyurethane. The same procedure as in Example 1 was carried out except that some parts were used.

The characteristics of the above samples are shown in the table below.

From these results, it can be seen that when the magnetic layer is formed according to the present invention, the magnetic powder has excellent dispersibility and the running property of the medium is improved, and therefore magnetic properties and electric properties are excellent.

[Brief description of drawings]

The drawings show an embodiment of the present invention, and FIGS. 1 and 2 are enlarged cross-sectional views of a part of two examples of a magnetic tape. In addition, in the code | symbol shown in drawing, 1 ... non-magnetic support body 2 ... subbing layer 3 ... magnetic layer 4 ... back coat layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08L 75/04 NGG 8620-4J C09D 5/23 PQV 7211-4J G11B 5/708 7215-5D (72 ) Inventor Kazumasa Matsumoto 1-Sakura-cho, Hino-shi, Tokyo Within Konishi Roku Photo Industrial Co., Ltd. (56) Reference JP-A-58-41436 (JP, A) JP-A-60-121514 (JP, A) JP-A-SHO 60-5420 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing magnetic powder and a binder, wherein the binder contains a sulfo group and / or a phosphoric acid group in the form of an alkali metal salt. At least a combination and a urethane resin are used, the magnetic layer contains at least one fatty acid selected from the following Group A and at least one fatty acid ester selected from the following Group B, and the content (weight) of the fatty acid is A magnetic recording medium, characterized in that the content (weight) of the fatty acid ester is higher. Group A caproic acid caprylic acid capric acid lauric acid myristic acid palmitic acid stearic acid isostearic acid linolenic acid linoleic acid oleic acid elaidic acid behenic acid malonic acid succinic acid maleic acid glutaric acid adipic acid pimelic acid sebacic acid octane dicarboxylic acid 1,12 -Dodecanedicarboxylic acid Group B oleyl oleate isocetyl stearate dioleyl maleate butyl stearate butyl palmitate butyl myristate octyl myristate octyl palmitate amyl stearate amyl palmitate isobutyl oleate stearyl stearate lauryl oleate octyl oleate isobutyl oleate methyl Oleate isotridecyl oleate 2-ethylhexyl stearate methyl steare 2-Ethylhexyl palmitate Isopropyl palmitate Isopropyl myristate Methyl laurate Cetyl-2-ethyl hexalate Dioleyl adipate Diethyl adipate Diisobutyl adipate Diisodecyl adipate