JPH0756690B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium used for, for example, a video tape, an audio tape, and the like. More specifically, it has a good dispersion state of ferromagnetic powder, The present invention relates to a magnetic recording medium having excellent conversion characteristics and running durability.

[Prior Art and Problems Thereof] A magnetic recording medium basically comprises a non-magnetic support and a magnetic layer containing a ferromagnetic powder, and is formed by providing a magnetic layer on the non-magnetic support. There is.

The magnetic layer is generally composed of a ferromagnetic powder dispersed in a binder.

In the magnetic recording medium having such a structure, particularly in the magnetic recording medium for VTR, in recent years, for example, an 8 mm width standard, which is narrower than the conventional 1/2 inch width standard, has appeared and is becoming widespread. Under such circumstances, there is a strong demand for high-density recording, and a magnetic recording medium having higher performance, that is, a magnetic recording medium excellent in electromagnetic conversion characteristics and running durability is desired.

Therefore, finely divided ferromagnetic powder has come to be used for the purpose of improving the electromagnetic conversion characteristics of the magnetic recording medium. The finely divided ferromagnetic powder is dispersed in the magnetic layer. It has a problem of poor sex.

As a solution to this problem, for example, a magnetic recording medium using a specific resin having a specific negative functional group as a binder has been proposed (JP-A-59-5423 and JP-A-59-5423).
-5424, 59-8127, etc. reference. However, in these magnetic recording media, although the dispersion state of the ferromagnetic alloy powder is certainly good and the electromagnetic conversion characteristics are improved, the binder formed by introducing a specific negative functional group is a magnetic layer. Since the surface of the magnetic recording medium is smoothed, the friction coefficient of the magnetic layer is increased, and for example, a phenomenon in which the magnetic recording medium sticks to the magnetic head, so-called mu loading, easily occurs, or the rigidity of the magnetic layer decreases, and the magnetic recording medium is repeatedly run. In this case, a new problem in running durability occurs that the edge breakage of the magnetic recording medium and the head clogging easily occur.

That is, in a magnetic recording medium containing a binder having a specific negative functional group introduced, there is still room for improvement in the mechanical properties of the magnetic layer, and it cannot be said that the running property and durability are sufficient. I want to.

On the other hand, as a magnetic recording medium with improved electromagnetic durability and running durability, for example, a magnetic recording medium having a magnetic layer containing two types of carbon blacks having different average primary particle diameters has been proposed ( JP 59-54
26, 59-223937, etc. ).

However, this magnetic recording medium has a problem that although the running durability is improved, the electromagnetic conversion characteristics are not sufficiently improved.

The present invention has been made based on the above circumstances.

An object of the present invention is to provide a magnetic recording medium in which the dispersion state of the ferromagnetic powder in the magnetic layer is good, the electromagnetic conversion characteristics are excellent, and the runnability and durability are improved.

[Means for Solving the Problems] In order to solve the problems, the inventors of the present invention have earnestly studied and, as a result, have found that a ferromagnetic powder containing cobalt-containing iron oxide and a specific functional group having a negative functional group are contained. A magnetic recording medium containing a binder containing a vinyl chloride resin and polyurethane having a glass transition temperature within a specific range and two kinds of carbon black having different average primary particle diameters in a magnetic layer is magnetic. The present invention has been achieved by finding that the dispersion state of the ferromagnetic powder in the layer is good, and that the electromagnetic conversion characteristics and running durability are also excellent.

That is, the constitution of the present invention is a magnetic recording medium comprising a non-magnetic support and a magnetic layer containing a ferromagnetic powder and a binder, wherein the ferromagnetic powder contains cobalt-containing iron oxide, The binder contains a vinyl chloride resin having a negative functional group and a polyurethane having a glass transition temperature in the range of −30 ° C. to 10 ° C., and in the magnetic layer, the average primary particle diameter is 11 μm to 25 μm. And a second carbon black having an average primary particle size in the range of 30 to 45 mμ.

The non-magnetic support and the magnetic layer constituting the magnetic recording medium of the present invention will be described below.

(Non-magnetic support) Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate. A plastic such as polycarbonate may be used. further
It is also possible to use metals such as Cu, Al and Zn, glass, various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.), and the like.

The form of the non-magnetic support is not particularly limited, and a tape,
It may be a sheet, a card, a disc, a drum, or the like, and various materials can be selected and used depending on the form and as needed.

The thickness of the non-magnetic support is usually in the range of 3 to 100 μm, preferably 5 in the case of tape or sheet.
Within the range of 50 μm. In the case of a disc or a card, it is usually in the range of 30 to 100 μm.
Further, in the case of a drum shape, it can be formed into a shape corresponding to the recorder to be used, such as a cylindrical shape.

A back coat layer may be provided on the surface (back surface) of the non-magnetic support, on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing charging, and preventing transfer.

An intermediate layer (for example, an adhesive layer) may be provided on the surface of the non-magnetic support on which the magnetic layer is provided for the purpose of improving the adhesiveness between the magnetic layer and the non-magnetic support.

(Magnetic Layer) The magnetic layer is provided on the non-magnetic support.

The magnetic layer is a layer formed by dispersing the ferromagnetic powder in a binder.

The ferromagnetic powder contains cobalt-containing iron oxide.

Examples of the cobalt-containing iron oxide include Co-containing γ-
Fe ₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, Co-containing FeO _x (4/3 <x <3
/ 2) Powder and the like.

The specific surface area of the ferromagnetic powder by the BET method is 20 m ² / g or more,
It is preferably 20 to 80 m ² / g. If this specific surface area is less than 20 m ² / g, the S / N ratio of the magnetic recording medium may decrease.

The shape of the ferromagnetic powder is not particularly limited, and for example, a needle-shaped, spherical, or ellipsoidal shape can be used.

One of the important points in the present invention is that the binder has a vinyl chloride resin [hereinafter, simply referred to as resin (A)] having a negative functional group. ] And the glass transition temperature is -30 ~
Polyurethane within the range of 10 ° C. [Hereinafter, sometimes referred to simply as resin (B). ] And are included.

The resin (A) has a function of improving the dispersion state of the ferromagnetic powder in the binder of the magnetic recording medium of the present invention.

Examples of the negative functional group in the resin (A), the _{example, -SO 3 M, -OSO 2 M} , -COOM, and (Wherein, M represents a hydrogen atom, one of lithium and sodium, M ¹ and M ² are each a hydrogen atom, is either lithium, potassium, sodium and the alkyl group. The M ¹ and M ² may be different from each other or may be the same.) And the like.

The resin (A) can be obtained, for example, by modifying a vinyl chloride resin and introducing the negative functional group.

Specifically, a vinyl chloride resin, for example, _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OSO 2 M, Cl-CH 2 COOM, (However, M, M ¹ and M ² have the same meanings as described above.) And the like, and can be obtained by condensing a compound having a negative functional group and chlorine in the molecule by a dehydrochlorination reaction.

Examples of the vinyl chloride resin include vinyl chloride-
Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-
Examples thereof include a vinyl propionate-vinyl alcohol copolymer, a vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, a vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer and the like.

For example, when a metal sulfonate group is introduced into the vinyl chloride resin to form the resin (A), the vinyl alcohol OH group contained in the above copolymer and the above Cl
--CH ₂ CH ₂ SO ₃ M, Cl--CH ₂ CHOSO ₂ M and the like of a sulfonic acid metal salt containing chlorine in a polar solvent such as dimethylformamide and dimethylsulfoxide, for example, pyridine, picoline, triethylamine and the like. The dehydrochlorination reaction may be carried out in the presence of a dehydrochlorination agent such as an amine salt, an epoxy compound such as ethylene oxide or propylene oxide.

Among the resins (A), vinyl chloride copolymers are preferable.

The vinyl chloride-based copolymer can be obtained by copolymerizing a vinyl chloride monomer, a copolymer monomer containing an alkali salt of sulfonic acid or phosphoric acid, and, if necessary, another copolymerizable monomer. Since this copolymer is based on vinyl synthesis, it is easy to synthesize,
In addition, 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),
Particularly, potassium is preferable in terms of solubility, reactivity, yield and the like.

Examples of the 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₎ such as ₂ CH ₂ SO ₃ M and the like.

As the _{phosphate, CH 2 = CHCH 2 OCH 2} CH (OH) CH 2 -O-PO 3 M 3 Y 1 CH 2 = CHCONHC (CH 3) 2 CH 2 -O-PO 3 M 3 Y 2 CH ₂ ═CHCH ₂ O (CH ₂ CH ₂ O) _m POMX ² [wherein M represents an alkali metal,
R represents an alkyl group having 1 to 20 carbon atoms, Y ¹ represents a hydrogen atom, M, or CH ₂ ═CHCH ₂ OCH ₂ CH (OH) CH ₂ —, Y ² represents a hydrogen atom, M and CH ₂ CH = CONHC (CH ₃ ) ₂ CH ₂ −, and X ¹ is Represents either OH or OM, X ² represents CH ₂ ═CHCH ₂ O (CH ₂ CH ₂ O _m , OH or OM, and m and n are positive numbers from 1 to 100). Further, as the copolymerizable monomer to be copolymerized as necessary, for example, various vinyl esters, vinylidene chloride,
Acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various acrylic acid esters,
Methacrylic acid ester, ethylene, propylene, isobutene, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, maleic acid ester and the like can be mentioned.

The binder in 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 molecular weight regulator, polymerization initiator, and monomer addition or continuous addition can be applied as necessary.

The amount of the acid group salt-containing monomer in the binder is preferably 0.01 to 30 mol%. If the amount of the salt-containing monomer is too large, the solubility in a solvent may be poor and gelation may easily occur. On the other hand, if the amount of the salt-containing monomer is too small, desired properties may not be obtained.

The vinyl chloride-based copolymer preferably further contains an epoxy group or a hydroxyl group.

By the way, the conventional vinyl chloride-based copolymer has been, for example, a copolymer of the following monomer units.

[However, j, k and l represent integers. However, here, it is considered that the CH ₃ CO—O— group is unlikely to contribute to the crosslinking reaction with the curing agent or the like.

Therefore, in the present invention, instead of CH ₃ CO, It is preferable to contain an epoxy group such as

Specifically, the resin of the combination of the following units can be illustrated.

[However, q, r and s have the same meanings as described above, and t
Is an integer. Z is a monomer unit part containing an alkali metal salt of a sulfo group or a phospho group. The molecular weight of the resin (A) is usually 5,000 to 80,000, preferably 10,000 to 30,000. If this molecular weight exceeds 80,000, the viscosity of the magnetic coating will increase beyond the allowable range,
When used as a magnetic recording medium, the friction coefficient of the magnetic layer may be increased or the workability during production may be deteriorated. On the other hand, when the molecular weight is less than 5000, in the step of applying the magnetic coating material onto the non-magnetic support and then curing it with a curing agent, unreacted portions are generated, and low molecular weight components remain. It may deteriorate the physical properties of the coating film.

The mixing ratio of the resin (A) is usually 5 to 30 parts by weight, preferably 10 to 20 parts by weight, based on 100 parts by weight of the ferromagnetic powder. If the mixing ratio is less than 5 parts by weight, the dispersion state of the ferromagnetic powder in the magnetic layer may be deteriorated, and electromagnetic conversion characteristics, running properties and durability of the magnetic recording medium of the present invention may be deteriorated. On the other hand, even if the amount is more than 30 parts by weight, the effect commensurate with the increase in the blending amount may not be obtained.

The polyurethane [resin (B)] acts to improve the mechanical strength and durability of the magnetic layer in the magnetic recording medium of the present invention, and the smooth friction of the surface of the magnetic layer realized by the resin (A). It has the effect of preventing the coefficient from rising.

The glass transition temperature (Tg) of the resin (B) is usually -30.
It is in the range of ℃ to 10 ℃. If the glass transition temperature (Tg) is less than -30 ° C, the rigidity of the magnetic layer itself may be lowered, and the running durability may not be sufficiently improved.

On the other hand, when the temperature exceeds 10 ° C, so-called calenderability (easiness of being applied to a calendar) is lowered, and the surface smoothing treatment may be difficult.

The resin (B) can be obtained, for example, by reacting an isocyanate with a diol.

Examples of the isocyanate used to obtain the resin (B) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate and hexamethylene diisocyanate. , Tetramethylene diisocyanate,
3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,3-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane , 1,4
-Diisocyanate methylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate dicyclohexylmethane, isophorone diisocyanate and the like.

Examples of the diol used to obtain the resin (B) include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexane. Diol,
Neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol And so on. Further, tri and tetraols such as trimethylol ethane, trimethylol propane, glycerin and pentaerythritol can be used together.

The mixing ratio of the resin (B) is usually 1 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the ferromagnetic powder. If the blending ratio is less than 1 part by weight, the effect of reducing the surface roughness of the magnetic layer is not sufficiently exerted, and the calenderability is insufficiently improved, and the electromagnetic field of the magnetic recording medium of the present invention is reduced. The conversion characteristics and running durability may not be sufficiently improved. On the other hand, if the amount is more than 20 parts by weight, the dispersibility of the ferromagnetic powder in the magnetic layer may not be sufficiently improved.

One of the important points in the present invention is that the magnetic layer contains two kinds of carbon blacks having different average primary particle diameters, that is, the first carbon black and the second carbon black. .

The first carbon black has a function of reducing the friction coefficient of the magnetic layer in the magnetic recording medium of the present invention to improve running durability.

The average primary particle size of the first carbon black is 11 to 25 m.
It is in the range of μ. If the average primary particle size is less than 11 mμ, the dispersibility of the ferromagnetic powder in the magnetic layer may be reduced. On the other hand, when it exceeds 25 mμ, the surface roughness of the magnetic layer increases, which may lead to deterioration of electromagnetic conversion characteristics.

The second carbon black has a function of improving the dispersion state of the ferromagnetic powder in the magnetic layer of the magnetic recording medium of the present invention and reducing the friction coefficient.

The average primary particle size of the second carbon black is 30 to 45 m.
It is in the range of μ. When the average primary particle size is less than 30 mμ, the dispersibility of the ferromagnetic powder in the magnetic layer is reduced, the friction coefficient of the magnetic layer is increased, and the running durability may not be sufficiently improved. On the other hand, if it exceeds 45 mμ, the surface of the magnetic layer may be roughened and the electromagnetic conversion characteristics may be deteriorated.

The mixing ratio of the first carbon black and the second carbon black in the magnetic layer is a weight ratio of (second carbon black) :( first carbon black), and is usually (99: 1) to It is in the range of (30:70), preferably in the range of (99: 1) to (60:40).

In the present invention, the binder may contain other resin components in addition to the resin (A) and the resin (B).

The other resin component has an average molecular weight of about 10,000-200.
Resins within the range of 000 can be used.

Specifically, for example, urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative. (Example: cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubber binders, phenol resin, epoxy resin,
Urea resin, melamine resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol and high molecular weight diol compound And mixtures thereof.

These resins are, for _{example, -SO 3 M, -COOM, -PO} (OM
¹ ) ₂ [wherein M represents a hydrogen atom or an alkali metal, and M ¹ represents any ^one of a hydrogen atom, an alkali metal and a hydrocarbon residue. ] And the like may contain a hydrophilic polar group.

In the present invention, the durability of the magnetic layer is improved by adding a polyisocyanate-based curing agent to the binder together with the resin (A) and the resin (B) and, if necessary, the other resin component. be able to.

Examples of the polyisocyanate curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name; manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (trade name; manufactured by Bayer Co., Ltd.). ), Etc., or urethane prepolymers containing isocyanate groups at both ends, such as those conventionally used as curing agents, and those that are polyisocyanates that can be used as curing agents. can do.

The amount of the curing agent used is usually 5 to 80 parts by weight based on the total amount of the binder.

The mixing ratio of the ferromagnetic powder and the binder (including the hardener when the hardener is used) in the magnetic layer is usually 1 part by weight of the binder per 100 parts by weight of the ferromagnetic powder. ˜200 parts by weight, preferably 1 to 50 parts by weight. If the blending amount of the binder is too large, the blending amount of the ferromagnetic powder may be effectively lowered, and the recording density of the magnetic recording medium may be lowered. If it is too small, the strength of the magnetic layer may be lowered to reduce the magnetic recording medium. The running durability of may decrease.

In the magnetic recording medium of the present invention, in the magnetic layer, the resin (A) and the resin (B), if necessary, these and other resin components, and the above curing agent, a lubricant,
It may contain an abrasive and an antistatic agent.

Examples of the lubricant include solid lubricants such as silicone oil, carbon black, graphite, carbon black graft polymer, molybdenum disulfide, and tungsten disulfide; silicone oil, modified silicone compounds, fatty acids and fatty acid esters, and the like.

These may be used alone or in combination of two or more.

The amount of the lubricant used is usually 0.05 to 10 parts by weight based on 100 parts by weight of the ferromagnetic powder.

Examples of the abrasive include inorganic powders such as aluminum oxide, titanium oxide (TiO, TiO ₂ ), silicon oxide (SiO, SiO ₂ ), silicon nitride, chromium oxide and boron carbide, and benzoguanamine resin powder, melamine resin powder and phthalocyanine. Organic powders such as compound powders may be mentioned.

The average particle size of the abrasive is usually in the range of 0.1 to 1.0 μm.

The amount of the abrasive compounded is usually in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.

Examples of the antistatic agent include graphite, carbon black, tin oxide-antimony oxide-based compounds, tin oxide-titanium oxide-antimony oxide-based compounds, conductive powders such as carbon black graft polymer; natural surfactants such as saponin; Nonionic surfactants such as alkylene oxide type, glycerin type and glycidol type; higher alkyl amines, quaternary pyridines, other heterocycles,
Cationic surfactants such as phosphonium and sulfonium: Anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group: Sulfuric acid and phosphoric acid of amino acids, aminosulfonic acids, aminoalcohols Examples include amphoteric surfactants such as esters.

These may be used alone or in combination of two or more.

The compounding amount of the antistatic agent is usually 0.5 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.

Note that the lubricant, antistatic agent, etc. do not have only a single action, but for example, one compound may act as a lubricant and an antistatic agent.

Therefore, the above classification in the present invention shows the main effects, and the effects of the classified compounds are not limited by the effects shown in the classification.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.

(Production Method) In the magnetic recording medium of the present invention, the magnetic layer forming components such as the ferromagnetic powder and the binder are kneaded and dispersed in a solvent to prepare a magnetic coating material, and the obtained magnetic coating material is then applied to the non-magnetic support. It can be produced by coating on the surface and drying.

As the solvent used for kneading / dispersing the magnetic layer forming components,
For example, ketone systems such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone: alcohol systems such as methanol, ethanol, propanol and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol. Esters such as monoacetate; ethers such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chloride. Halogenated hydrocarbons such as phosphorus and dichlorobenzene can be used.

In kneading the composition of the magnetic paint components, the ferromagnetic powder and the other magnetic paint components are simultaneously or individually added to the kneader. For example, first, the ferromagnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and the kneading is further continued to obtain a magnetic paint.

For kneading and dispersing, various kneaders can be used. Examples of this kneader include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disperkneader, a high-speed mixer, a homogenizer, and an ultrasonic wave. Examples include a disperser.

The coating liquid of the magnetic layer-forming component thus prepared is coated on the non-magnetic support by a known method.

Examples of coating methods that can be used in the present invention include gravure roll coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, squeeze coating, kiss coating and fantin coating. And so on.

The thickness of the magnetic layer thus coated is usually 0.5 to 20 μm as a dry thickness.

In this way, after applying the magnetic layer forming component, magnetic field orientation treatment is carried out in the undried state, if necessary, and surface smoothing treatment is usually carried out using a super calender roll or the like.

Then, by cutting into a desired shape, a magnetic recording medium can be obtained.

The magnetic recording medium of the present invention is cut into a long shape, for example, as a magnetic tape such as a video tape or an audio tape, or cut into a disk shape.
It can be used as a floppy disk or the like. Further, like a normal magnetic recording medium, it can be used in a card shape, a cylindrical shape, or the like.

EXAMPLES Next, examples and comparative examples of the present invention will be shown to more specifically describe the present invention. In the examples and comparative examples described below, "part" means "part by weight".

(Example 1) Using a ball mill, a magnetic layer composition having the following composition was prepared.
After being dispersed by mixing and dispersing for 48 hours, 5 parts of a polyisocyanate compound was added to and mixed with this dispersion to prepare a magnetic coating material.

Co-containing γ-Fe ₂ O ₃ powder 100 parts α-Al ₂ O ₃ 7 parts 1st carbon black (average primary particle size 20 mμ) 5 parts 2nd carbon black (average primary particle size 40 mμ) 5 parts Resin (A ) 20 parts Resin (B) (glass transition temperature 0 ° C.) 10 parts Fatty acid 3 parts Fatty acid ester 1 part Polyisocyanate 10 parts Methyl ethyl ketone 150 parts Toluene 150 parts Table 1 for the above resin (A) and resin (B) The compounds shown outside the column were used.

Thickness of the obtained magnetic paint so that the dry thickness is 4 μm
It was coated on a 15 μm polyethylene terephthalate film.

Then, after removing the solvent under heating, a surface was smoothed by applying a super calendar, and slit into a predetermined width to produce a video tape.

Various characteristics of this video tape were measured.

The results are shown in Table 2.

In addition, each characteristic was measured as follows.

Surface roughness of magnetic layer before and after calendering: The surface roughness of the magnetic layer sample before and after calendering was measured with a roughness analyzer [“SE-3FK” manufactured by Kosaka Laboratory). (Cut-off value 0.25 mm) RF output: Output at the time of reproduction with a 100% white signal was obtained in comparison with the tape of Example 1 with the tape of Example 1 as a reference.

Rumi S / N; using a noise meter (Shibasoku)
Using the tape of Example 1 as a reference, the S / N difference of the sample at 100% white signal was determined in comparison with the tape of Example 1.

Chromer S / N; noise meter (manufactured by Shibasoku Co., Ltd.) was used, and the difference in S / N of the sample in the chroma signal was determined in comparison with the tape of Example 1 with the tape of Example 1 as a reference.

Friction coefficient; MSC tape running tester [Yokohama System Co., Ltd.]
Manufactured by the manufacturer] under the conditions of a tape speed of 3.3 m / sec and a tape tension of 20 g.

(Example 2, Comparative Examples 1 to 7) In the above Example 1, the compounds shown in Table 1 were used in place of the carbon black, resin (A) and resin (B) used in Example 1 to obtain magnetic properties. A video tape was produced in the same manner as in Example 1 except that the paint was prepared, and various properties of the obtained video tape were measured.

The results are shown in Table 2.

(Evaluation) As is clear from Table 2, in the magnetic layer of the magnetic recording medium of the present invention, the surface roughness before calendering is small. That is, it is understood that the magnetic recording medium of the present invention is superior in the dispersibility of the ferromagnetic powder in the magnetic layer as compared with the magnetic recording medium of the comparative example. Moreover, this good dispersibility is developed in a short time. It is considered that this is due to the action of the first carbon black, the second carbon black and the resin (A) in the present invention.

Further, in the magnetic layer of the magnetic recording medium of the present invention, the surface roughness of the magnetic layer after the calendering treatment is small, and the calenderability and so-called calenderability are improved. It is considered that this is due to the action of the polyurethane [resin (B)] in the present invention.

In the magnetic recording medium of the present invention, the surface roughness of the magnetic layer can be made smaller than that of the conventional magnetic recording medium due to the above-mentioned improvement of the calenderability, so that the electromagnetic conversion characteristics are excellent.

Further, in the magnetic recording medium of the present invention, it can be seen that the friction coefficient of the magnetic layer is small and the running durability is improved. It is considered that this is due to the action of the second carbon black in the present invention.

EFFECTS OF THE INVENTION According to the present invention, (1) the magnetic layer contains a first carbon black and a second carbon black each having a specific average primary particle size, and a specific functional group having a negative functional group. Since it contains a binder containing a resin and polyurethane having a specific glass transition temperature, Co having good magnetic properties is contained.
Excellent dispersibility of iron oxide contained, (2) Therefore, so-called calenderability is improved, so that the surface roughness of the magnetic layer can be reduced, and (3) As a result, excellent electromagnetic conversion characteristics and running durability are achieved. It is possible to provide a high performance magnetic recording medium having various advantages such as excellent.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support.
The ferromagnetic powder contains cobalt-containing iron oxide, the binder contains a vinyl chloride resin having a negative functional group and a polyurethane having a glass transition temperature in the range of -30 ℃ ~ 10 ℃, and The magnetic layer contains a first carbon black having an average primary particle size of 11 mμ to 25 mμ and a second carbon black having an average primary particle size of 30 to 45 mμ. And a magnetic recording medium.