JP2001325711A - Magnetic recording media - Google Patents

Abstract

(57) [Problem] To produce a magnetic recording medium having excellent magnetic properties and good surface properties. SOLUTION: In a magnetic recording medium 10 having a magnetic layer 2 formed by applying a magnetic paint on a non-magnetic support 1, a specific surface area of a magnetic powder of the magnetic paint forming the magnetic layer 2 is 50 to 80. [M ² / g], and the binder contains a polyurethane resin having a tertiary amine as a polar group and a fruit acid having a carboxyl group. The amount of fruit acid added to the binder is 1 to 10 parts by weight based on 100 parts by weight of the magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art Recently, high-definition VTRs and digital V
With high performance represented by TR, demands for improving the characteristics of magnetic recording media have been increasing.

[0003] As high-density magnetic recording progresses, a so-called coating type magnetic recording medium in which a magnetic paint is applied on a non-magnetic support to form a magnetic layer. As shown in the example, the demand for high density recording is increasing year by year.

[0004] Magnetic recording on a conventional magnetic recording medium is as follows.
Mainly, by rotating a rotating drum having a large number of magnetic heads mainly composed of ferrite, amorphous, sendust, etc. on the surface of the magnetic recording medium to increase the relative speed between the magnetic head and the magnetic recording medium, The mechanism that records a lot of information was mainstream. Further, in order to obtain a higher magnetic signal in performing high-density recording, a metal head made of amorphous or the like is particularly used.

However, when the magnetic head mainly composed of sendust, amorphous, or the like, and the magnetic layer surface of the magnetic recording medium formed by the magnetic powder and the binder slide continuously, the magnetic layer surface is slightly reduced. Is oxidized by oxygen in the air and adheres and accumulates on the magnetic head as an oxide or the like, resulting in deterioration of the output obtained from the magnetic head. That is, the accumulated oxides and the like on the magnetic head cause spacing, so that the performance of the magnetic recording medium (magnetic tape) or the magnetic head for obtaining high output cannot be sufficiently brought out.

[0006] In order to solve the above-mentioned problems, the amount of abrasive contained in the magnetic layer is increased, or the surface of the magnetic layer is roughened to improve the frictional force with the magnetic head. A method has been proposed in which the polishing force on the surface of the medium is increased to remove accumulated matter attached to the magnetic head by sliding.

[0007]

However, as described above, when the amount of the abrasive in the magnetic layer is increased, the amount of magnetic powder per unit area of the magnetic layer is relatively reduced, and the magnetic recording medium In this case, there is a problem that the residual magnetic flux density Br of the magnetic characteristics of (1) and (2) decreases to cause a decrease in output. Also, if the magnetic layer contains a large amount of abrasive, sliding between the magnetic recording medium and the magnetic head causes the surface of the magnetic head to be scraped off, resulting in a problem that the life of the magnetic head is greatly shortened.

Further, roughening the surface of the magnetic recording medium increases the amount of spacing between the magnetic recording medium and the magnetic head, thereby causing a problem that output is reduced and noise is increased.

Further, in recent years, there has been an increasing demand for finer magnetic powder in order to cope with short-wavelength recording accompanying the thinning of the magnetic layer.
When the value) is used 50 to 80 [m ² / g] as fine magnetic powder, it becomes difficult to uniformly and sufficiently dispersed in the binder, as a result, the surface roughness of the surface of the magnetic recording medium ( R
There is also a problem that a) becomes worse. In particular, the thickness of the magnetic layer has recently been reduced to 2 [μ
m] The following magnetic recording media have been proposed, but in a magnetic recording medium having such a thin magnetic layer, the state of the surface of the magnetic layer is affected by the state of the surface of the nonmagnetic support. , Further deteriorating the surface properties, resulting in a high C /
It is becoming difficult to secure N.

Therefore, the present inventors have conducted intensive research on a binder used for forming a magnetic layer constituting a coating type magnetic recording medium, and have improved the dispersibility of fine magnetic powder to achieve extremely high surface properties. A good magnetic recording medium was provided.

[0011]

The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer formed by applying a magnetic paint on a non-magnetic support. The paint is composed of at least a magnetic powder and a binder, and the specific surface area of the magnetic powder is 50 to 80.
[M ² / g], and the binder contains a polyurethane resin having a tertiary amine as a polar group and a fruit acid having a carboxyl group. The amount of fruit acid added to the binder is 1 to 1 with respect to 100 parts by weight of the magnetic powder.
It is assumed to be 0 parts by weight.

According to the present invention, in order to obtain a magnetic recording medium with high recording density, even when extremely fine magnetic powder is used, the dispersibility of the magnetic powder in the binder is improved, The surface properties of the magnetic layer were improved, and the output deterioration characteristics of the magnetic recording medium, that is, the durability, were improved.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention is a so-called coating type magnetic recording medium having a magnetic layer formed by applying a magnetic paint on a non-magnetic support. The magnetic paint to be formed is composed of at least a magnetic powder and a binder.
0 to 80 [m ² / g], and the binder contains a polyurethane resin having a tertiary amine as a polar group and a fruit acid having a carboxyl group. The amount of fruit acid in the binder is 1 to 10 parts by weight based on 100 parts by weight of the magnetic powder.

FIG. 1 shows a schematic structure of an example of a magnetic recording medium 10 of the present invention, and a magnetic recording medium and a method of manufacturing the same will be described. However, the magnetic recording medium of the present invention is not limited to the following examples. It is not something to be done.

The magnetic recording medium 10 shown in FIG. 1 has a structure in which a magnetic layer 2 formed by applying a predetermined magnetic paint on a non-magnetic support 1 is formed.

The non-magnetic support 1 is made of, for example, a long (tape) plastic film. For example, a polyethylene terephthalate film can be used. The magnetic recording medium of the present invention has such a shape. However, the present invention is not limited to this, and can be applied to various shapes such as a sheet shape and a drum shape.

As the material of the nonmagnetic support 1, various known materials other than polyethylene terephthalate can be applied. That is, polyesters such as polyethylene naphthalate, polyethylene, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose diacetate, cellulose acetate butyrate, and vinyl resins such as polyvinyl chloride and polyvinylidene chloride. ,
Polycarbonate, polyimide, polyamide imide, other plastics, paper, aluminum, copper and other metals,
The same applies to light alloys such as aluminum alloys and titanium alloys, ceramics, single crystal silicon, and the like.

Next, the magnetic layer 2 formed on the non-magnetic support 1 will be described. The magnetic layer 2 is prepared by a conventionally known method using a magnetic powder, a binder (binder), an abrasive, an antistatic agent, a rust preventive, a curing agent, an organic solvent, and the like described in detail below. Thus, a magnetic paint is prepared, and the magnetic paint is applied to the non-magnetic support 1 to a predetermined thickness to form a magnetic paint. In the magnetic recording medium of the present invention, in order to reduce the thickness of the magnetic recording medium, the thickness of the magnetic layer is preferably formed to be 0.1 to 2.0 [μm].

The preparation of the magnetic paint can be carried out by a known method. Examples thereof include a roll mill, a ball mill, a sand mill, a tron mill, a high-speed stone mill, a basket mill, a disper, a homomixer, a kneader, a continuous kneader, an extruder, and a homogenizer. And kneading and adjustment using an ultrasonic disperser or the like. When the magnetic paint is applied on the non-magnetic support 1, it can be applied directly on the non-magnetic support 1.

Further, an undercoat layer such as an adhesive layer for the purpose of improving adhesiveness, an intermediate layer such as a non-magnetic layer, or the like may be formed on the non-magnetic support layer 1 as appropriate. A fine uneven shape may be formed on the surface, or a pretreatment such as a corona discharge treatment or an electron beam irradiation treatment may be performed on the surface.

A magnetic paint is applied on the non-magnetic support 1,
Methods for forming the magnetic layer 2 include air doctor coating, blade coating, rod coating, extrusion coating,
Any conventionally known method such as an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a gravure coat, a transfer roll coat, a cast coat and the like can be applied, and a simultaneous multilayer structure by extrusion coating may be used. That is, the magnetic layer 1 may have a single-layer structure or a plurality of structures.

Next, the material constituting the magnetic layer 2 of the magnetic recording medium 10 of the present invention will be described in detail. Magnetic layer 2
Are prepared using magnetic powder, a binder, an abrasive, an antistatic agent, a dispersant, a curing agent, a lubricant, and the like.

First, as the material of the magnetic powder used to form the magnetic layer 2, any of conventionally known materials can be used. That is, γ-Fe ₂ O ₃ , Fe ₃ O
₄ or a ferromagnetic iron oxide-based material represented by FeO _x with these intermediate iron oxides, those obtained by adding Co to these iron oxides, and ferromagnetic materials containing Fe, Ni, and Co as main components (75% or more) Any of known ferromagnetic materials such as alloys, barium ferrite, and strontium ferrite can be used.

The magnetic powder used in the magnetic layer 2 of the magnetic recording medium 10 of the present invention is selected to have a specific surface area of 50 to 80 [m ² / g] by the BET method. In order to realize a magnetic recording medium for high-density recording, the demand for finer magnetic powder is increasing, and the specific surface area of the magnetic powder needs to be 50 [m ² / g] or more. In magnetic powders having a specific surface area of less than 50 [m ² / g], that is, relatively coarse magnetic powders,
Since the dispersion with the binder is relatively easy, there is no significance in applying the constitution of the present invention. Further, fine magnetic powder having a specific surface area exceeding 80 [m ² / g] complicates the production process and is not practical. Further, since the fine magnetic powder is fine, dispersibility with a binder is deteriorated.

Also, for the purpose of preventing sintering during reduction,
Alternatively, in order to maintain the shape, in addition to the above magnetic powder, A
Light metal elements such as 1, Si, P, and B may be appropriately contained, or two or more of these may be used in combination.

Next, the binder used to form the magnetic layer 2 constituting the magnetic recording medium 10 of the present invention will be described.

The binder for a magnetic recording medium of the present invention contains a polyurethane resin having a tertiary amine as a polar group and a fruit acid having a carboxyl group. The amount of fruit acid added in the binder was 100% of magnetic powder.
The amount is 1 to 10 parts by weight with respect to parts by weight.

The polyurethane resin having a tertiary amine as a polar group used for the binder can be obtained by copolymerizing a polyol, an isocyanate, and a chain extender (crosslinking agent) having a tertiary amine in the molecule. .

The polyurethane resin used for the binder includes various materials depending on the polyol used as a raw material. Examples thereof include polyester polyurethane resins such as adipate type and polycaprolactone type, polyether polyurethane resin, and polycarbonate type and acrylic type. , Butadiene and the like. Polyols used as raw materials include ethylene glycol (EG), 1,4-
Polyester diols obtained by polycondensation (and transesterification) of low molecular weight diols such as butanediol (BG) and neopentyl glycol with dicarboxylic acids (or diesters thereof) such as adipic acid, phthalic acid and sebacic acid; Various materials such as polylactone diol such as polycaprolactone diol are exemplified, and particularly, polyester polyurethane resin and polyether polyurethane resin are more preferable.

As the diisocyanate compound for synthesizing the polyurethane resin, conventionally known materials can be appropriately used. For example, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,
2,4-toluene diisocyanate, 2,6-toluene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, 4,4′-
Diphenylmethane diisocyanate, 2,4'-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'-diphenylpropanediisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate Such as aromatic diisocyanate, tetramethylene diisocyanate,
Aliphatic diisocyanates such as lysine diisocyanate,
Examples include diisocyanates such as alicyclic diisocyanates such as water-added tolylene diisocyanate, water-added xylene diisocyanate, water-added diphenylmethane diisocyanate, and tetramethyl xylene diisocyanate.

As the tertiary amine to be introduced into the polyurethane resin used as the binder, aliphatic amines, aromatic amines,
Examples thereof include alkanolamines and alkoxyalkylamines. Examples thereof include dimethylamine, diethylamine, diisopropylamine, diisobutylamine, metal ethanolamine, dioctylamine, N-methylaniline, and N-methylaniline.
-Methylbutylamine, N-methylphenylamine, 2
-Methoxyethylamine, di-2-methoxyethylamine and the like. When these tertiary amines are introduced into the polyurethane resin, they may be introduced into the molecular main chain of the polyurethane resin or into the molecular side chains. Note that this 3
The content of the secondary amine is 0.01 [mmol] / ~
It is preferable to be within the range of 0.5 [mmol].

The fruit acid to be added to the binder used in the magnetic recording medium 10 of the present invention generally includes natural fruits, vegetables, cereals, seaweed, etc., fermented miso, soy sauce, sake, wine Name of the main component of sourness contained in beer, vinegar and the like. Specific examples of the fruit acid having a carboxyl group to be added to the binder used for producing the magnetic recording medium of the present invention include malic acid, citric acid, succinic acid, tartaric acid, lactic acid and the like. In addition, these fruit acids can be obtained by a conventionally known method such as an extraction method, a fermentation method, and a synthesis method. In the present invention, the addition amount of the fruit acid is 1 to 1 with respect to 100 [parts by weight] of the magnetic powder.
0 [parts by weight], but if the addition amount is less than 1 [parts by weight], even when applied to the magnetic recording medium of the present invention, a remarkable effect on improvement of the dispersibility of the magnetic powder cannot be confirmed. 10
If it exceeds [parts by weight], the magnetic properties of the magnetic recording medium will be degraded.

The polyurethane resin used as a binder has a hydrophilic group introduced into the molecule at an appropriate ratio in order to improve the resin adsorbability to the ferromagnetic powder and the dispersibility of the ferromagnetic powder. You can also. Examples of the method for introducing a hydrophilic group include sodium sulfonate using a polyester polyol containing sodium-5-sulfoisophthalic acid as a part of a diol component, dimethylolpropionic acid, N-methyldiethanolamine, and 3-diethylamino. There are methods such as carboxylic acid introduction using -1,2-propanediol as a part of the chain extender and tertiary amine introduction.

As a device for producing a polyurethane resin, any of conventionally known devices can be used. For example, a mixing and kneading apparatus such as a reaction vessel equipped with a stirring device, a kneader, a single-screw or multi-screw extrusion reactor, and the like can be used. In order to promptly proceed the reaction, a metal catalyst or an amine-based catalyst usually used in the production of polyurethane may be used as the catalyst.

As the binder, in addition to the polyurethane resin having a tertiary amine as the polar group, conventionally known materials can be appropriately mixed and used. For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer Copolymer, acrylate-vinylidene chloride copolymer, acrylate-acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylate-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride , Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol Fat, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea - formaldehyde resins, polyvinyl acetal resins, or mixtures thereof and the like can be appropriately used.

Examples of the abrasive used when forming the magnetic layer 2 include α-alumina, β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, and α.
-Known materials having a Mohs hardness of 6 or more can be used, such as iron oxide, corundum, diamond, quartzite, garnet, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium oxide, and the like as main components. The materials can be applied alone or in combination of two or more.

As an antistatic agent used for forming the magnetic layer 2 constituting the magnetic recording medium 10, carbon black is mainly used. In addition, a natural surfactant, a nonionic surfactant, Such as cationic surfactants,
Any of conventionally known antistatic agents can be applied. Any conventionally known carbon black can be used. Depending on the production method, carbon black includes acetylene black, furnace black and the like.
AVEN) 1250 can be applied.

The dispersant used for forming the magnetic layer 2 constituting the magnetic recording medium 10 may have 5 to 25 carbon atoms.
Metal soaps, fatty acid esters, fatty acid amides, amines, quaternary ammonium salts, phosphate esters of fatty acids and their alkali metal salts or alkaline earth metal salts,
Any conventionally known dispersant such as borate ester can be used.

As a curing agent used when forming the magnetic layer 2 constituting the magnetic recording medium 10, for example, polyisocyanate is used in an amount of 5 to 30 with respect to 100 parts by weight of the binder.
[Parts by weight] By mixing, the adhesion, rigidity and durability can be improved. However, if the added amount of the polyisocyanate is less than 5 parts by weight with respect to 100 parts by weight of the binder, a sufficient effect as a curing agent cannot be obtained, and also, based on 100 parts by weight of the binder. If added in an amount exceeding 30 parts by weight, the storage properties of the magnetic paint may deteriorate,
The flexibility of the coating film is impaired, the coating film is cut off at the time of cutting, and the durability is deteriorated. For this reason, the addition amount of the polyisocyanate is preferably 5 to 30 parts by weight based on 100 parts by weight of the binder.

Specific examples of the curing agent include aromatic polyisocyanates and aliphatic polyisocyanates, and adducts of these with active hydrogen compounds can be suitably used. As the aromatic polyisocyanate,
Toluene diisocyanate (TDI), 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 4,4'-diphenylmethane diisocyanate (M
DI), p-phenyl diisocyanate, m-phenyl diisocyanate, 1,5-naphthyl diisocyanate, and the like. As the aliphatic polyisocyanate, hexamethylene diisocyanate (HD
I), dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate (IPDI) and the like. Examples of the active hydrogen compound that forms an adduct with these include ethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane, and glycerin. Those having a range of -5000 are preferred.

Further, in the magnetic recording medium 10 of the present invention, a lubricant may be appropriately mixed into the magnetic layer 2, or a lubricant layer may be formed on the magnetic layer 2 as a top coat layer. . As the material of the lubricant, silicone oil, fatty acid-modified silicone, fluorine-containing silicon, or other fluorine-based lubricant polyolefin, polyglycol, alkyl phosphate and metal salt, polyphenyl ether, fluorinated alkyl ether, having 12 to 12 carbon atoms 24
Alcohols (each of which may have an unsaturated structure or may have a branched structure), having 12 to 2 carbon atoms
Amines such as higher fatty acids 4, fatty acid esters (each of which may have an unsaturated structure or a branched structure), alkyl carboxylic acid amine salts, and fluorinated alkyl carboxylic acid amine salts A system lubricant can also be applied. Examples of the above higher fatty acids and fatty acid esters include, specifically, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid Linoleic acid, octyl stearate, isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate, butyl stearate, heptyl stearate and the like. These materials may be used alone or in combination of two or more.

Organic solvents for preparing the magnetic paint include ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, alcohol solvents, ester solvents, ether solvents, hydrocarbon solvents, and halogenated carbon solvents. Any of conventionally known solvents such as a solvent and an aromatic compound solvent such as toluene can be used. The solvent is appropriately selected and applied according to the material of the ferromagnetic powder and the binder.

The magnetic recording medium of the present invention is not limited to the example of the structure shown in FIG. 1. For example, like the magnetic recording medium 20 shown in FIG. The back coat layer 3 may be formed on the main surface opposite to the surface on which the layer 2 is formed. The back coat layer 4 is formed to a thickness of about 0.1 to 2.0 [μm], and more preferably to a thickness of 0.3 to 1.0 [μm]. For producing the magnetic recording medium, any material that is usually used as a material for a back coat layer can be used for the back coat layer 4. For example, solid particles such as inorganic pigments are bonded. The coating material for the back coat layer prepared by dispersing in the agent and kneading with an organic solvent selected according to the type of the binder is applied to the non-magnetic support 1 on the side opposite to the side on which the magnetic layer 2 is formed. It is applied and formed on the side surface.
As the solid particles such as the inorganic pigment for the back coat layer, any conventionally known materials can be used as long as they provide an antistatic effect and a lubricating effect. For example, graphite, carbon black, carbon black graft polymer, tungsten disulfide, molybdenum disulfide, titanium oxide and the like can be mentioned. Each of these solid particles can be used alone or in combination of two or more. Further, as the binder for forming the back coat layer 4, any conventionally known material can be used. That is, if it is conventionally used for forming a back coat layer, a thermoplastic resin,
Any of the thermosetting resins can be appropriately selected and used. In addition, as a material constituting the back coat layer 4, in addition to the solid particles and the binder described above, a dispersant, an abrasive, an antistatic agent, and the like can be appropriately used as additives. As the dispersant, abrasive, and antistatic agent, any materials can be used as long as they are conventionally used materials.

Further, as in a magnetic recording medium 30 shown in FIG. 3, a non-magnetic powder,
The intermediate layer 4 may be formed of a coating material in which a magnetic powder or a mixture of both of them and a binder are mixed.

Hereinafter, the magnetic recording medium of the present invention will be described.
The present invention will be specifically described with reference to Examples and Comparative Examples, but the magnetic recording medium of the present invention is not limited to the following examples.

[Example 1] A magnetic paint used for forming the magnetic layer 2 constituting the magnetic recording medium 10 is manufactured using the following materials. Magnetic powder (specific surface area 55 m ² / g): 100 parts by weight Polyurethane resin having a tertiary amine in a polar group: 20 parts by weight α-Al ₂ O ₃ : 4 parts by weight Carbon black: 1 part by weight Citric acid: 5 parts by weight Methyl ethyl ketone: appropriate amount Toluene: appropriate amount Cyclohexanone: appropriate amount

After kneading the above materials in a continuous kneader,
Dispersed using a sand mill. Next, after adding and mixing 4 parts by weight of polyisocyanate and 1 part by weight of myristic acid, the mixture was filtered through a filter having an average diameter of 3 μm to prepare a magnetic paint.

The magnetic paint prepared as described above was applied to a polyethylene terephthalate resin film having a thickness of 11 μm to a thickness of 1.5 μm, subjected to an orientation treatment, and then dried. After applying the calendar process, 1/2
The sample was cut into [inch] width to prepare a sample magnetic tape.

Example 2 In place of citric acid in [Example 1], 5 [parts by weight] of DL-malic acid was added, and the other conditions were the same as in [Example 1]. Was produced.

Example 3 The applied thickness of the magnetic paint was 0.1
[Μm] to form a magnetic layer. Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

Example 4 The amount of citric acid added in [Example 1] was 1 [part by weight]. Other conditions are
A sample magnetic tape was produced in the same manner as in [Example 1].

Example 5 The amount of citric acid added in Example 1 was 10 parts by weight. Other conditions are
A sample magnetic tape was produced in the same manner as in [Example 1].

Comparative Example 1 In the above [Example 1], a polyurethane resin having a carboxyl group as a polar group was replaced with a polyurethane resin having a tertiary amine as a polar group.
20 parts by weight were used. Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

[Comparative Example 2] In the above [Example 1], fruit acid (citric acid in the above example) was not added, and other conditions were as follows:
A sample magnetic tape was produced in the same manner as in [Example 1].

Comparative Example 3 In the above [Example 1], instead of the polyurethane resin having a tertiary amine as a polar group, a polyurethane resin having a -SO ₃ Na group as a polar group was used.
20 parts by weight were used. Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

Comparative Example 4 The amount of citric acid added was 0.5
A sample magnetic tape was prepared in the same manner as in [Example 1] above except that the amount was [parts by weight].

The characteristics of the magnetic tape of each sample manufactured as described above were evaluated. The evaluation method is
Using a Sony HDW-500 type video tape recorder, a 30-minute long magnetic tape was run 50 times repeatedly, and the value obtained by subtracting the output after running 50 times from the initial output was compared as the initial level down amount. After storing the magnetic tape of each sample at 40 ° C. and 80% humidity for 3 days,
Using a Sony HDW-500 type video tape recorder, a 30-minute long magnetic tape was repeatedly run 50 times, and the level reduction amount was measured. In addition, for each of the magnetic tapes of the respective samples, Susaka Lab.
The center line average roughness Ra was measured with an rfcoder ET-30HK surface profiler and compared.

The results of evaluation of the magnetic tapes of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0059]

[Table 1]

As shown in Table 1 above, the magnetic layer
The specific surface area of the magnetic powder is 50 [m ^Two/ G]
Polyurethane having a tertiary amine as a polar group in the binder
Using a tan resin and a fruit acid having a carboxyl group
The amount of fruit acid added to the magnetic powder 10
0 to 10 parts by weight for 0 parts by weight
Examples 1 to 5
The initial level down amount and the humidity of 40 ° C and 80
%, The level reduction amount after storage for 3 days is -5 [d
B] and the level down amount is low.
Reduced magnetic recording medium with excellent durability
I got the body.

The above [Example 1], [Example 2],
The magnetic tapes of the samples of [Example 4] and [Example 5] also have a relatively low surface roughness (Ra), indicating that these magnetic tapes have extremely good surface properties. . Note that the above [Example 3] is an example in which the thickness of the magnetic layer is 0.1 [μm], but in this example, the thickness of the magnetic layer is the same as that of the sample magnetic tape of the other example. Since the surface property of the magnetic layer is greatly affected by the state of the surface of the non-magnetic support, the surface roughness of the magnetic layer is lower than that of the sample magnetic tape of the other examples. Although the value of Ra) is large, the roughness (Ra) has no problem in practical use as a magnetic tape. However, the surface roughness (R
From the value of a), if the thickness of the magnetic layer is made thinner than 0.1 [μm], the surface properties of the magnetic layer are greatly affected by the state of the surface of the non-magnetic support. Since the surface roughness (Ra) becomes large, it is understood that the thickness of the magnetic layer is preferably formed to be 0.1 [μm] or more.

As shown in [Table 1], a magnetic tape was prepared by using 20 parts by weight of a polyurethane resin having a carboxyl group as a polar group without using a polyurethane resin having a tertiary amine as a polar group. In Example 1), the initial level-down amount and the level-down amount after storage at 40 ° C. and 80% humidity for 3 days were both less than −5 [dB], and sufficient durability was not obtained. By comparing the measurement result of [Comparative Example 1] with the measurement result of [Example 1], the durability of the magnetic recording medium can be improved by using a polyurethane resin having a tertiary amine as a binder as a binder. It was found that it could be improved.
The magnetic tape of Comparative Example 1 had a surface roughness (Ra)
Is larger than those of the magnetic tapes of [Example 1], [Example 2], [Example 4] and [Example 5], and the surface property is inferior. From this, it is possible to improve the dispersibility of fine magnetic powder by using a polyurethane resin having a tertiary amine as a polar group,
It was found that a magnetic recording medium having good surface properties could be obtained.

As shown in Table 1, a magnetic tape was prepared without adding a fruit acid having a carboxyl group as a polar group to the binder [Comparative Example 2]. The amount of level reduction after storage at 80% humidity for 3 days was less than -5 [dB], and sufficient durability was not obtained. By comparing the measurement result of [Comparative Example 2] with the measurement result of [Example 1],
It was found that the durability of the magnetic recording medium can be improved by adding a fruit acid having a carboxyl group as a polar group to the binder. Further, the magnetic tape of [Comparative Example 2] has a surface roughness (Ra) value of the magnetic tape of [Example 1], [Example 2], [Example 4] and [Example 5]. It was found that the surface property was inferior to that of the comparative example. From this, by adding a fruit acid having a carboxyl group as a polar group to the binder, the dispersibility of fine magnetic powder can be improved, and a magnetic recording medium having good surface properties can be obtained. all right.

As shown in Table 1, a magnetic tape was prepared using a polyurethane resin having a —SO ₃ Na group as a polar group without using a polyurethane resin having a tertiary amine as a binder as a binder. In Comparative Example 3],
Good values were obtained for the initial level-down amount and the surface roughness (Ra), but the level-down amount after storage at 40 ° C. and 80% humidity for 3 days was less than -5 [dB]. By comparing the measurement results of [Comparative Example 3] with the measurement results of [Example 1], it is possible to use a polyurethane resin having a tertiary amine as a binder as a binder. As a result, it was found that the level reduction amount after storage of the magnetic recording medium could be reduced, and the durability could be improved.

As shown in Table 1, citric acid was used as a fruit acid having a carboxyl group as a polar group, and a magnetic tape was prepared with the addition amount of 0.5 [part by weight] (Comparative Example 4). In, the initial level down amount and the level down amount after storage at 40 ° C and 80% humidity for 3 days,
All were below -5 [dB], and sufficient durability was not obtained. On the other hand, comparing the measurement result of [Comparative Example 4] with the measurement result of [Comparative Example 2] when no fruit acid having a carboxyl group as a polar group was added, the magnetic tape of [Comparative Example 4] was compared. It was found that the amount of level down was reduced in the case of. However, the fruit acid
[Parts by weight] The measurement result of [Example 1] added and the measurement result of [Example 4] added with 1 [parts by weight] of fruit acid are compared with the measurement results of [Comparative Example 4]. Therefore, in order to sufficiently improve the durability, it is necessary that the addition amount of the fruit acid having a carboxyl group is 1 [part by weight] or more.

The surface roughness (Ra) of the magnetic tape of [Comparative Example 4] was obtained when no fruit acid having a carboxyl group as a polar group was added [Comparative Example 2].
Comparison of the measurement results shows that the magnetic tape of Comparative Example 4 had better surface properties. However, the measurement results of [Example 1] in which 5 [parts by weight] of fruit acid were added, the measurement results of [Example 4] in which 1 [part by weight] of fruit acid was added, and the measurement of [Comparative Example 4] When compared with the results, the surface properties are inferior. From this, in order to sufficiently improve the surface properties, the amount of the fruit acid having a carboxyl group should be 1 [part by weight] or more. is necessary.

As described above, the present invention relates to a so-called coating type magnetic recording medium in which the magnetic powder has a specific surface area of 5%.
Higher density recording is achieved by selecting fine particles in the range of 0 to 80 [m ² / g].
The polyurethane resin having a secondary amine and the fruit acid having a carboxyl group are contained, and the addition amount of the fruit acid is selected from 1 to 10 parts by weight based on 100 parts by weight of the magnetic powder. The dispersibility of the magnetic powder in the agent was improved, and the surface properties of the magnetic layer could be improved.

The thickness of the magnetic layer 2 constituting the magnetic recording medium 10 according to the present invention is set in the range of 0.1 to 2.0 [μm], and the magnetic layer 2 is made thinner than the conventional magnetic recording medium. Also in this case, the specific surface area of the magnetic powder is set to 50 to 80 [m ² /
g], and as a binder,
A polyurethane resin having a tertiary amine as a polar group;
A fruit acid having a carboxyl group is contained, and the addition amount of the fruit acid is selected from 1 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder, thereby improving the surface properties of the magnetic layer. I was able to.

As described above, according to the present invention,
Since the dispersibility of the magnetic powder in the binder is improved, the surface properties of the magnetic layer are improved, thereby reducing the amount of level reduction of the output after a number of runnings. Under the above conditions, the output level reduction amount was able to be suppressed even after long-term storage, and a magnetic recording medium having excellent durability and excellent magnetic properties was obtained.

[0070]

According to the present invention, an extremely fine magnetic powder,
That is, even when a magnetic powder having a specific surface area of 50 to 80 [m ² / g] is used, the dispersibility of the magnetic powder in the binder can be improved, and the magnetic layer formed by applying a magnetic paint can be obtained. Was able to improve the surface properties.

The thickness of the magnetic layer constituting the magnetic recording medium of the present invention is set in the range of 0.1 to 2.0 [μm]. Fine particles having a surface area in the range of 50 to 80 [m ² / g] are selected, and a polyurethane resin having a tertiary amine as a polar group and a fruit acid having a carboxyl group are contained as binders. By setting the amount of the fruit acid to be 1 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder, the surface properties of the magnetic layer could be improved.

Further, according to the present invention, a magnetic recording medium having a magnetic layer having excellent surface properties can be obtained, so that it is possible to reduce the amount of output level reduction after running a predetermined number of times. Even after long-term storage under the above conditions, the amount of level reduction in output could be suppressed to a low level, and a magnetic recording medium having excellent durability and excellent magnetic properties could be obtained.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration diagram of an example of a magnetic recording medium of the present invention.

FIG. 2 shows a schematic configuration diagram of another example of the magnetic recording medium of the present invention.

FIG. 3 shows a schematic configuration diagram of another example of the magnetic recording medium of the present invention.

[Explanation of symbols]

1 non-magnetic support, 2 magnetic layer, 3 back coat layer,
4 Intermediate layer, 10, 20, 30 magnetic recording medium

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // C10M 105/24 C10M 105/24 105/26 105/26 107/44 107/44 C10N 30:00 C10N 30:00 Z 30:04 30:04 40:18 40:18 (72) Inventor Akemi Kumagai 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Hiroyuki Murakami Kita-Shinagawa, Shinagawa-ku, Tokyo 6-chome 7-35 Sony Corporation F-term (reference) 4H104 BB18A BB19A CE11A PA16 4J038 DG051 DG111 DG121 DG131 DG191 DG261 GA09 HA166 JA37 KA08 NA22 PB11 PC08 5D006 BA08 BA09 BA15 BA19 CA01 FA09

Claims (4)

[Claims] 1. A magnetic recording medium having a magnetic layer formed by applying a magnetic paint on a non-magnetic support, wherein the magnetic paint comprises at least a magnetic powder and a binder; Has a specific surface area of 50 to 80 [m ² / g], and the binder contains a polyurethane resin having a tertiary amine as a polar group and a fruit acid having a carboxyl group. A magnetic recording medium characterized in that the acid is added in an amount of 1 to 10 parts by weight based on 100 parts by weight of the magnetic powder. 2. The thickness of the magnetic layer is 0.1 to 2.0.
2. The magnetic recording medium according to claim 1, wherein the thickness is [μm]. 3. An intermediate layer formed by using at least one of nonmagnetic powder and magnetic powder and a binder on the nonmagnetic support, wherein the magnetic layer is formed on the intermediate layer. The magnetic recording medium according to claim 1, wherein a layer is formed. 4. An intermediate layer formed by using at least one of nonmagnetic powder and magnetic powder and a binder on the nonmagnetic support, wherein the intermediate layer is formed on the intermediate layer. The magnetic recording medium according to claim 2, wherein a magnetic layer is formed.