JPH04176016A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a recording reproduction characteristic over a wide range from a short to long wavelength areas by using an acrylic resin with a specified range of molecular weight which contains a polar group such as OH group or carboxylic group as resin binder together with a polyurethane resin. CONSTITUTION:A resin binder contains an acrylic resin with a molecular weight of 1,000-10,000 which has 0.1-1.0m mol/g of at least one polar group selected from among a hydroxyl group, a carboxylic acid group, a phosphate group, a sulfonate group or a metal base thereof, an amino group and an ammonium group and a polyurethane resin. With such as arrangement, the resin binder has surface finishing performance and running durability excellent in a magnetic layer and/or in a back coat layer. This presents substantial saturated magnetization in the case of the magnetic layer and contributes to a reduction in jitter in the case of the back coat layer. Thus, an excellent recording/reproduction output can be obtained not only in a long wavelength area but also in a short wavelength area.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic recording medium that has excellent short wavelength recording characteristics and is capable of high density recording.

(Prior Art) In general, coating-type magnetic recording media are made of γ-Fe2O3, γ-Fe2O3,
It is obtained by applying ferromagnetic powder such as CrO2, Go-7-Fe203, or iron powder together with a resin binder to form a magnetic layer.

In recent years, there has been a demand for higher recording density in such magnetic recording media, and in order to meet this demand, it is necessary to reduce the particle size of the magnetic powder, and to increase the packing density of the magnetic powder in the magnetic layer, the so-called backing ratio. (filling rate) increases;
Attempts have been made to smooth the surface of the magnetic layer to reduce the spacing loss with the head.

On the other hand, in order to improve the running properties of the magnetic recording medium, a back coat layer is formed on the back surface of the magnetic layer. That is, it is also known that a back coat layer containing, for example, dispersed carbon fine particles is formed on the back side of the magnetic layer to appropriately roughen the surface, thereby lowering the coefficient of friction and ensuring the required runnability. ing.

Furthermore, as a magnetic powder for high recording density magnetic recording media, some of the Fe atoms are replaced with atoms such as C01TI, and the coercive force is 200 mm, which allows recording and reproduction with a normal recording and reproduction head.
It was controlled to a range of ~20,000e, and the particle size was 0.2
It is also known that ultrafine hexagonal ferrite powders such as sub-μm Ba ferrite are more suitable. In other words, this type of ultrafine hexagonal ferrite powder consists of hexagonal plate-shaped crystals, and in addition to its very small particle size, it also has an axis of easy magnetization perpendicular to the plate surface, making it suitable for high-density magnetic recording. It is suitable for

(Problem to be solved by the invention) By the way, in order to obtain excellent characteristics particularly for recording short wavelength signals in a magnetic recording medium using the ferromagnetic powder,
It is necessary to highly disperse the magnetic powder, improve the surface smoothness of the magnetic layer, and increase the saturation magnetization (M s ) as much as possible. However, since ultrafine hexagonal ferrite powder such as Ba ferrite has a small saturation magnetization, there is a limit in terms of sufficiently improving short wavelength recording characteristics.

In addition, one way to increase the saturation magnetization of the magnetic recording layer is to increase the filling rate of magnetic powder, but it is difficult to balance the durability of the coating film with the electromagnetic conversion characteristics, and it is difficult to achieve a satisfactory result. The current situation was that this was not the case.

Furthermore, in order to improve the surface smoothness of the magnetic layer, high dispersibility of the magnetic powder is required, but dispersion tends to become more difficult as the particles become finer.

In order to improve the dispersibility, it may be considered to improve the resin binder, but even if satisfactory dispersion could be achieved, there was a problem that the running durability of the medium would be insufficient.

Furthermore, in order to improve the dispersibility of magnetic powder, it has been conventionally done to add various dispersants.
When the amount of dispersant is increased, bleeding occurs, and there is a problem in that friction properties and durability deteriorate.

On the other hand, the back coat layer formed on the back surface of the magnetic layer to ensure runnability also causes the following problems. That is, when the surface of the magnetic layer is made smoother for the purpose of improving the recording density, there is a problem in that the protrusions of the back coat layer are transferred to the magnetic layer and the surface of the magnetic layer is roughened. Here, in order to form the back coat layer smoothly, it is necessary to make the particle size of the dispersed carbon particles finer. However, the finer the carbon particles become, the more difficult it becomes to uniformly disperse them.

Furthermore, attempts have been made to improve the dispersibility of carbon particles by improving the resin binder, but this has not yet ensured sufficient running durability of the magnetic recording medium. Also,
Various dispersants are added to improve the above-mentioned dispersibility, but if a dispersant that provides sufficient dispersibility is added or blended, smearing will occur and the friction properties and durability will deteriorate. There's a problem.

The present invention was made to solve these problems, and it improves the durability without impairing the dispersibility or filling rate of ferromagnetic powder, and provides wide-band recording and reproducing characteristics from short wavelengths to long wavelengths. The purpose of the present invention is to provide a magnetic recording medium that has excellent running properties and is capable of high-density recording.

[Structure of the Invention] (Means for Solving the Problems) A magnetic recording medium according to the first invention includes a magnetic layer formed by dispersing ferromagnetic powder in a resin binder on a non-magnetic substrate surface. In the magnetic recording medium, the resin binder has a content of 0.1 to 1. Om mat/g
hydroxyl group and 0.1 to 1. On+ mol/g of a carboxylic acid group, a sulfonic acid group, a sulfonic acid group, or a metal base thereof, an amino group and an ammonium group, and a molecular weight of ioo
.

-10,000 acrylic resin and polyurethane resin.

A magnetic recording medium according to a second aspect of the present invention is a magnetic recording medium in which a back coat layer is formed on the back surface of a magnetic layer formed by dispersing ferromagnetic powder in a resin binder on a non-magnetic substrate surface, and the back coat layer is formed on the back surface of the magnetic layer. The resin binder of the coating layer is 0.1 to 1.
oi ll1 ol/g of hydroxyl groups and 0.1 to 1. Om
an acrylic resin having a molecular weight of 1,000 to 50,000 and having at least one polar group selected from mol/g of a carboxylic acid group, a phosphoric acid group, a sulfonic acid group, or a metal base thereof, an amino group, and an ammonium group;
It is characterized by containing a polyurethane resin.

(Function) In the magnetic recording medium of the present invention, an acrylic resin containing an OH group and a polar group such as a carboxyl group and having a molecular weight within a predetermined range is used together with a polyurethane resin as a resin binder. The polar groups of the resin are easily adsorbed onto the surface of the ferromagnetic powder and carbon particles, and the dispersibility of the ferromagnetic powder and carbon particles is significantly improved. The formed magnetic layer or backcoat layer not only exhibits good surface properties, but also has excellent runnability and durability, so it has excellent functionality in terms of low jitter and short wavelength recording characteristics. Demonstrated.

(Example) First, the structure of the magnetic recording medium according to the present invention will be explained in detail.

In the present invention, the ferromagnetic powder includes γ-Fe2O3,
Acicular ferromagnetic powders such as CrO2, Co7Fe203, Fe powder, and hexagonal ferrite powder can be used, and -hexagonal ferrite powder is particularly suitable.

The hexagonal ferrite powder may be M type (magnetobrambite type) or W type hexagonal Ba ferrite, Sr ferrite, PB ferrite, Ca ferrite, or a solid solution thereof, or an ion substituted product represented by the following formula. etc. can be mentioned.

MaO・nt(Pe+−x ML ) 20 s )(
In the formula, Ha represents any one element selected from Bas Sr and Cas Pb, and Mb is 00% Zn.
s N1% CLI% Mg, Mn, In, Ti,
Sn, Ge, Zr, Hf, V, Nb, S
b.

At least 2 selected from Ta, Cr, MO5ν
Represents various elements, one of which is Nb. n is 5.
Represents a number from 4 to 6.0. ) More specifically, as the hexagonal ferrite powder used in the present invention, a part of Fe atoms, which are constituent elements of uniaxial hexagonal ferrite crystals such as Ba ferrite, are mixed with divalent metal and pentavalent metal. Substituted with Nb, which is a metal, and further substituted with 0.05 to 0.5 Sn per chemical formula.
Those substituted with atoms are suitable, and the amount of substitution of these elements is such that the coercive force value is in the range of 200 to 20,000e.

Here, among the substitutional elements, the divalent metal mainly acts to reduce the coercive force of the hexagonal ferrite to an appropriate range, and the pentavalent metal Nb acts to increase the saturation magnetization. Further, Sn, which is a tetravalent metal, acts to reduce changes in the temperature characteristics of coercive force.

In place of this Sn atom, a Tj atom having the same valence may be used.

In such hexagonal ferrite, divalent metal (H
z) and the appropriate amount of substitution of the pentavalent metal (Mv) is Mll
It depends on the combination of and M, or 1 of Mll
The amount of substitution per chemical formula is approximately 0.5 to 1.2. Then, the relationship between the amounts of substitution of these substitution elements is determined, for example, by M
Looking at type Ba ferrite, the chemical formula of its substituted product is BaFe+2- (x+r (+Zl)M x
M Vy (MIVI)019 (x, y, z
are the substitution amounts per chemical formula of HzlMv and Mlv, respectively. ), MzlMv and MIV
The valences are divalent, pentavalent, and tetravalent, respectively, and the substituted Fe atom is trivalent, so when valence compensation is considered, the relationship y-(xz)/2 holds true. In this way, the amount of substitution of M is uniquely determined from the amount of substitution of Mll and the amount of substitution of MIV.

In the present invention, the acrylic resin used as the resin binder for the magnetic layer and/or backcoat layer contains monomers containing heptamers and hydroxyl groups (OI groups) for forming the molecular skeleton, and polar groups such as carboxyl groups. It can be obtained by copolymerization of the monomers contained therein.

Here, the monomers for forming the skeleton include methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, hexyl methacrylate, lauryl methacrylate, methyl acrylate,
Examples include acrylic acid esters such as ethyl acrylate, butyl acrylate, oligoester acrylates mainly having ester bonds, urethane acrylates having a polyurethane main chain, and epoxy acrylates having an epoxy resin skeleton.

Monomers containing polar groups such as OH groups and carboxyl groups and amino groups include 2-hydroxyethyl methacrylate, glycidyl methacrylate, N-N' diethyl methacrylate, diethylaminomethyl methacrylate, diethylaminoethyl methacrylate, acrylamide, acrylonitrile, and the like. .

The acrylic resin contains OH in its molecular skeleton in order to contribute to the curing reaction with isocyanate and melamine, increase the degree of crosslinking of the coating film (magnetic layer), and improve its hardness.
The group is contained in a proportion of 0.1 to 1.011 mol/g. OH group content is 0.1 m mol/g
If the content is less than 1.0 a mol/g, no effect can be obtained from the introduction, whereas if the content exceeds 1.0 a mol/g, crosslinking of the polyurethane resin added at the same time will be inhibited, which is not preferable.

Furthermore, at least one polar group selected from a carboxyl group, a sulfonic acid group, a phosphoric acid group, or a metal base thereof, an amino group, and an ammonium group has a molecular weight of 1000
~10,000 (50,000) acrylic resin molecular skeleton contains 0.1 to 1. It should be contained at a ratio of Oi + 11 ol/g. The reason why the content of these polar groups is limited to the above range is that the content of polar groups per acrylic resin molecule adsorbed on the surface of ferromagnetic powder, carbon powder, etc. is at least 0.5 and maximum 5. This is to ensure complete adsorption.

As a result of the acrylic resin molecules being completely adsorbed to the surface of the ferromagnetic powder, the finely divided magnetic powder and powder such as carbon are well dispersed, and at the same time, the bond between the magnetic powder and the powder such as carbon and this resin is improved. It becomes strong,
Improves running durability.

Further, problems such as bleeding are also resolved.

Furthermore, in the present invention, the molecular weight My of the acrylic resin containing the 01 (group, etc.) is preferably from 1000 to 1000 when used as a resin binder for the magnetic layer.When the molecular weight of the resin is less than 1000, , bleeding due to the dispersant will similarly occur, and on the other hand, if the molecular weight exceeds 1000[1], it will be difficult to disperse the magnetic powder in the resin, which is undesirable.This is particularly preferred in order to obtain sufficient dispersion. Molecular weight is 2000-8
000 range.

On the other hand, the molecular weight My of the acrylic resin containing OH groups is preferably 1,000 to 50,000 when used as a resin binder for a back coat layer.

If the molecular weight of the resin is less than IO[10, bleeding due to the dispersant will similarly occur, whereas if the molecular weight exceeds 50,000, carphone powder (fine particles) will occur.
This makes it difficult to disperse into the resin, which is not preferable. In order to obtain particularly sufficient dispersion, the preferred molecular weight is 2000 to 5.
The range is 0000.

In the present invention, the polyurethane resin used together with the acrylic resin as a resin binder is a mixture of a polybasic acid or polyhydric alcohol and a polybasic acid or polyhydric alcohol into which a polar group such as a sulfonic acid group has been introduced. It can be obtained by carrying out a condensation reaction.

Here, monomers having these groups or polybasic acids or polyhydric alcohols used in the production of polyurethane resins containing sulfonic acid groups or their metal bases include, for example, vinyl sulfonic acid, vinylbenzenesulfonic acid, -Acrylamido-2-methylpropanesulfonic acid or vinyl heptamine containing these metal bases
Examples include polybasic acids or polyhydric alcohols represented by and.

Monomers used in the production of polyurethane resins having phosphoric acid groups or their metal bases, amino groups, or ammonium groups include vinyl monomers, polybasic acids, or polyhydric alcohols having the respective polar groups. .

Furthermore, the polyhydric alcohol copolymerized with the vinyl monomer having a polar group such as a sulfonic acid group includes 1,
There are 4-butanediol, 1,6-hexamethylene diol, cyclohexanediol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, etc. Similarly, polybasic acids include:
Examples include terephthalic acid, isophthalic acid, adipic acid, sebacic acid, oxalic acid, succinic acid, geltaric acid, pimelic acid, pyromellitic acid, speric acid, and azelaic acid.

The blending ratio of these polyurethane resins and the acrylic resin is 10 to 200 parts by weight, more preferably 10 to 1 part by weight, of the acrylic resin per 100 parts of the polyurethane resin.
00 parts by weight. Increasing the blending amount of acrylic resin increases the dispersion effect and improves the fluidity of the paint, but
Excessive addition tends to make the coating film brittle and reduce the effectiveness of calendering, etc.

In addition, these resin binders contain polyamine-based or polyisocyanate curing agents to increase the mechanical strength and durability of the coating film through crosslinking when it is coated on a non-magnetic substrate together with ferromagnetic powder. A series of compounds are added. Examples of polyamine compounds include tolylene diamine (TDA), 4.4''-diaminodiphenylmethane (MDA), and 4.4°-diamino-
Examples include 3,3'-dichlorodiphenylmethane. In addition, examples of polyisocyanate compounds include toluene diisonenate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (HDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPD).
I) Adducts of trimethylolpropane and water such as xylylene diisocyanate (XDf) and isocyanurates are used. Furthermore, as a hardening agent,
1,4-diisocyanatocyclohexane, 1,3-
Bis(α.

α dimethyl isocyanatomethyl)benzene (TMXD
I), isocyanate methylmethylcyclohexyl isocyanate (IMcI), etc. can also be used.

Furthermore, a lubricant, an abrasive, or a conductivity imparting agent such as carbon black may be added to the components constituting the magnetic coating film, if desired. Here, lubricants include fatty acid or fatty acid alkyl ester, silicone,
Fluorinated silicone-based, fluorinated hydrocarbon-based compounds,
Alternatively, a mixture thereof can be used. In addition, as abrasives, Ti(h), Cr2O3, Al103
, SiC5Zr(h) and other inorganic powders having a Mohs hardness of 5 or more are suitable.

It is desirable that the amount of additives added to these magnetic layers be as small as possible; for example, the amount of lubricant is 4 parts by weight or less, The amount of the abrasive is 6 parts by weight or less, and the amount of carbon black is 3 parts by weight or less.

In forming the magnetic layer of the magnetic recording medium according to the present invention, the ferromagnetic powder, the resin binder, and, if necessary, the various additives described above, are mixed into a compound such as toluene, xylene, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, or nitropropane. Mix thoroughly with an organic solvent to make a magnetic paint. Next, a curing agent such as a polyisocyanate compound is added to the resulting paint, which is applied onto a non-magnetic substrate such as a polyester film, polycarbonate film, or polyimide film, subjected to orientation treatment and drying treatment, and then calendered to the paint film. It can be produced by performing a smoothing process according to.

Note that, if necessary, a conductive primer layer may be formed on the substrate, and a paint may be applied thereon to form the magnetic layer.

On the other hand, in the magnetic recording medium according to the present invention, the back coat layer has the above-mentioned acrylic resin-polyurethane resin-
If necessary, a reinforcing agent and a lubricant may be added to the carbon particulate system. As a reinforcing agent, for example, Ti (
Inorganic powders having a Mohs hardness of 5 or more are suitable, such as h, Cr2O3, Al103, SiC, and ZrO2. Further, if desired, hard resins such as nitrocellulose and salt-vinyl acetate resin may be added. Furthermore, examples of the lubricant include fatty acid or fatty acid alkyl ester compounds, silicone compounds, fluorinated hydrocarbon compounds, or mixtures thereof.

Therefore, the formation of this back coat layer involves thoroughly mixing the acrylic resin-polyurethane resin-carbon particulate system and various additives added as necessary with a solvent, and then adding a curing agent such as a polyisocyanate compound. In addition, by using conventional coating methods such as gravure coater, reverse row coater, comma coater, etc.,
can be formed.

Specific examples of the present invention will be described below.

Example I Co-Ti-Nb substituted Ba ferrite powder 100 parts by weight Acrylic resin (My: 7000, 4 parts by weight OH group amount + 0.8 mmol/g, amino group amount:
0.6 m mol/g) Polyurethane resin (containing 8 parts by weight of sulfonic acid group, My
: 15000, sulfonic acid group amount: 0.5nm
ol/g) Toluene/cyclohexanone 180 parts by weight (1/2
Mixed solution) Alumina (average particle size 0.3 μm) 3 parts by weight Stearic acid (lubricant) 2 parts by weight After the above materials were mixed, they were further mixed and dispersed for 2 hours using a sand grinder. Next, to 100 parts by weight of the obtained magnetic paint, 3 parts by weight of coronated polyisocyanate (Product 22 (manufactured by Nippon Polyurethane Co., Ltd.)) was added, and then a reverse coater was used to coat the pigment/resin binder under 10/100. 2 on the polyester film having a coating layer.
．． The film was applied to a thickness of 5 μm and subjected to a magnetic field (strength + 4 KOe) perpendicular to the film while the film was still wet.
It was dried while passing through the inside. Thereafter, the dried coating film was cured at 40° C. for 3 days, and then cut into 1/2 inch widths to produce magnetic tapes.

Example 2 Co-Tj-Nb substituted Ba ferrite powder 100 parts by weight Acrylic resin (My: 4000, 6 parts by weight OH
Base amount: 0.6s of/g, phosphate group amount: 0.5
m mol/g) Polyurethane resin (aliphatic, 8 parts by weight My: 1
0000, amino group amount: 0.4m mol/g
) Toluene/cyclohexanone 180 parts by weight (l/
2 mixed solution) Alumina (average particle size 0.3 μm) 3 parts by weight Stearic acid (lubricant) 2 parts by weight The above materials were mixed and dispersed to prepare a magnetic paint in the same manner as in Example 1. Next, the obtained paint was applied to a thickness of 2 μm on a polyester film surface-treated by corona discharge, and then passed through a magnetic field perpendicular to the film surface in the same manner as in Example 1. A magnetic tape was prepared by drying the magnetic tape.

Example 3 Co-Ti-Nb substituted Ba ferrite powder 100 parts by weight Acrylic resin (My: 3000, 8 parts by weight OH
Base weight: 0.2a+11ot/g', carboxyl group weight: 0.7m mol/g) Polyurethane resin (containing 8 parts by weight of sulfonic acid sodium group, My: 10000, sulfonic acid group weight: 0)
．． 5+a mol/g) Toluene/cyclohexanone 180 parts by weight (1/2 mixed solution) Alumina (average particle size 0.3 μm) 3 parts by weight Stearic acid (lubricant) 2 parts by weight The above materials were mixed and dispersed, and the Example A magnetic paint was prepared in the same manner as in Example 1. The resulting paint was then applied onto a plasma surface-treated polyester film to a thickness of 2 μm.
A magnetic tape was produced in the same manner as in Example 1.

Example 4 In the case of Example 1, the same procedure was carried out except that the acrylic resin and polyurethane resin shown below were used, respectively.
A magnetic tape was made.

Acrylic resin Mw + 3,500, OH group amount + 0.5 m mol
/g, sulfonic acid group amount: 0.3m sol/g
, Blend l: 6 parts by weight Polyurethane resin My: 10.000, Carboxyl group weight: 0.6I
IIIlo1/g1 Amount: 8 parts by weight Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1, except that 2 parts by weight of lecithin was used as a dispersant instead of the acrylic resin.

Comparative Example 2 Magnetic A tape was made.

Comparative Example 3 In the case of Example 4, vinyl chloride vinyl acetate copolymer resin (Mw: 15.
000, amount of sulfonic acid group: 0.2m mol/g
) A magnetic tape was produced in the same manner as in Example 4, except that a magnetic tape was used.

Table 1 shows the results of measuring the surface properties, filling rate (saturation magnetization), running durability, and recording/reproducing output of the magnetic tapes of Examples 1 to 4 and Comparative Examples 1 to 3.

Since the same magnetic powder was used in both Examples and Comparative Examples, the filling rate was expressed as the saturation magnetization value, and the running durability was expressed as the number of times the tape recorder was run until the output decreased by 1 dB. Further, the recording/reproduction output is shown as the Y signal output when recording at a frequency of 7M)12.
(Left below) Table 1 Surface roughness Saturation Travel Recording/reproduction example Magnetization Durability 8-force RIIl
ax 1.1m eIlu/CC times dBl
0.02 175 150 +
2.02 0.024 178 14111
+1.53 0.015 170
155 +2.54 [), 02 1
73 150 +2.0 Comparative Example 1 0.025 175 93 02
0.03 185 55 -
1.03 0.037 180 30
-1.0 Example 5 Co-Tf-Nb substituted Ba ferrite powder 100 parts by weight Vinyl acetate resin 4 parts by weight Polyurethane resin 8 parts by weight Toluene/cyclohexanone 180 parts by weight (112 mixed solution) Alumina (average particle size 0 .3 μm) 3 parts by weight Stearic acid (lubricant) 2 parts by weight After the above materials were mixed, they were further mixed and dispersed for 2 hours using a sand grinder. Next, to 100 parts by weight of the obtained magnetic paint, 3 parts by weight of coronated polyisocyanate (Product 22 (manufactured by Nippon Polyurethane Co., Ltd.)) was added, and then a reverse coater was used to coat the pigment/resin binder under 10/100. 2 on the polyester film having a coating layer.
, 5 μm thick and calendered to form a magnetic layer.

On the other hand, a back coat agent was prepared using the following composition and method. That is, carbon black 100 parts by weight acrylic resin (My: 10000, 30 parts by weight OH group amount: 0.8 m 11o1/g 1 amino group amount: 0.
6+a mol/g) Polyurethane resin (My: 20,000.70 parts by weight Sulfonic acid group amount: 0.5 Il1 mol/g) Stearic acid (lubricant) 2 parts by weight MEK/Cyclohexanone 1,000 parts by weight (112 mixed solution) were sandwiched. After mixing and dispersing with a grinder, coronate and add 10 parts by weight of polyisocyanate (trade name: manufactured by Nippon Polyurethane Co., Ltd.), apply it with a gravure coater to the back side of the polyester film on which the magnetic layer has been formed. After forming the coating layer, the tape was cut into a width of 1 inch to produce a magnetic tape.

Example 6 Carbon black 100 parts by weight Acrylic resin (My: 3000, 40 parts by weight OH group amount:
0.6m mol/g, phosphate group amount: 0.501
mol/g) Polyurethane resin (My: 50000.60 parts by weight Amino group amount: 0.4 m mol/g) Stearic acid (lubricant) 2 parts by weight MEK/Cyclohexanone 1000 parts by weight (1/2 mixed solution) Back In addition to selecting the composition of the coating agent as above,
A magnetic tape was produced in the same manner as in Example 5.

Example 7 Carbon black 100 parts by weight Acrylic resin (My: 5000, 30 parts by weight OH group amount + 0.2 m mol/g -Carboxyl group amount:
0.7m mol/g) polyurethane resin (My:
30000.70 parts by weight Sulfone group amount: 0.5m
mol/g) Nitrocellulose 3
0 parts by weight Stearic acid (lubricant) 2 parts by weight M
EK/cyclohexanone 1000 parts by weight (1
12 mixed solution) In addition to selecting the composition of the back coating agent as above,
A magnetic tape was produced in the same manner as in Example 5.

Example 8 Carbon black 100 parts by weight Acrylic resin (My: 7000, 10 parts by weight OH group amount:
0.5w aol/g, sulfone group amount: 0.3
m a+ol/g) Polyurethane resin (My:
30000.60 parts by weight carboxyl group Ji + 0
．． 5111mol/g) Salt vinyl acetate
30 parts by weight stearic acid (lubricant) 2
Part by weight MEK/cyclohexanone 1000 parts by weight (1/2 mixed solution) Other than selecting the composition of the back coating agent as above,
A magnetic tape was produced in the same manner as in Example 5.

Comparative Example 4 In the case of Example 5, a magnetic tape was produced by forming a back coat layer with a back coat agent using lecithin as a dispersant instead of the acrylic resin.

Comparative Example 5 In the case of Example 5, a back coat layer was formed using a back coat agent using an acrylic resin containing no amino groups and a molecular weight MW 100 O instead of the 0)1 group and the acrylic resin containing an amino group. , produced a magnetic tape.

Comparative Example 6 Carbon black 100 parts by weight Acrylic resin (My Near 000, 40 parts by weight OH group amount:
0.5m mol/g - Sulfone group amount: 0.3m
mol/g) Salt vinegar 1:' (MW: 15000,
60 parts by weight Sulfone group amount: 0.3 mm
ol/g) Stearic acid (lubricant) 2 parts by weight MEK/Cyclohexanone 1000 parts by weight (
1/2 mixed solution) Other than selecting the composition of the back coating agent as above,
A magnetic tape was produced in the same manner as in Example 5.

For the magnetic tapes of Examples 5 to 8 and Comparative Examples 4 to 6, the surface properties, friction coefficients, durability, and amount of jitter of the back coat layers were measured, and the results are shown in Table 2.

In addition, the surface property was determined using the 10-point average roughness Rz, and the friction coefficient was the value after 100 bus runs under high temperature and high humidity.
(Left below) Table 2 Surface roughness Friction Durability Jitter example μm
Coefficient times μ5ec5 0.23
0.25 )200 0.096 0.25
0.27 >200 0.107 0
．． 20 0.23 >200 0.088
0.22 0.27 )200 0.
09 Comparative Example 4 0.40 0.42 170 0.
175 0.35 0.45 150
0.156 0.42 0.50 50
0.20 In the above example, an acrylic resin and a polyurethane resin containing the required amount of OH groups and polar groups such as carboxyl groups and having a molecular weight within a predetermined range are used as the resin binder of the magnetic layer or back coat layer. Although the recording medium is illustrated as an example, it is of course possible to use a resin binder for both the magnetic layer and the back coat layer without any problem.

[Effects of the Invention] As is clear from the above description, the magnetic recording medium of the present invention has extremely uneven surface properties and running durability in the magnetic layer and/or back coat layer, and In the case of a layer, it exhibits a large saturation magnetization, and in the case of a back coat layer, it contributes to reducing jitter and exhibits a sharp recording and reproducing output not only in a long wavelength region but also in a short wavelength region.

Applicant: Toshiba Corporation Agent: Patent Attorney Su Yamasa -

Claims (2)

[Claims] (1) A magnetic recording medium comprising a magnetic layer formed by dispersing ferromagnetic powder in a resin binder on a non-magnetic substrate surface, wherein the resin binder contains 0.1 to 1.0 mmol/g of hydroxyl groups. and 0.1 to 1.0 mmol/g of carboxylic acid group,
phosphoric acid group, sulfonic acid group, or these metal bases,
At least one polar group selected from an amino group and an ammonium group and a molecular weight of 1000 to 10000
A magnetic recording medium comprising an acrylic resin and a polyurethane resin. (2) A magnetic recording medium in which a back coat layer is formed on the back surface of a magnetic layer formed by dispersing ferromagnetic powder in a resin binder on the surface of a non-magnetic substrate, and the resin binder of the back coat layer is 0.0. At least one selected from 1 to 1.0 mmol/g of hydroxyl group, 0.1 to 1.0 mmol/g of carboxylic acid group, phosphoric acid group, sulfonic acid group, or metal base thereof, amino group, and ammonium group.
1. A magnetic recording medium comprising an acrylic resin having a molecular weight of 1,000 to 50,000 and a polyurethane resin.