JP2002042327A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium in which surface property and film strength of a nonmagnetic layer are improved, which has superior electromagnetic conversion characteristics and durability and which can be formed into a thin film, required for high recording density. SOLUTION: The magnetic recording medium has a nonmagnetic layer formed through application of a nonmagnetic coating material, prepared by dispersing at least nonmagnetic powder and carbon black in a binder on at least one surface of a nonmagnetic supporting body, and has a magnetic layer with <=0.5 μm dry film thickness prepared by dispersing ferromagnetic powder in a binder, on at least one surface of a nonmagnetic supporting body. The magnetic layer is applied after the nonmagnetic coating material has been dried, calendered and hardened, and the ultramicro hardness of the nonmagnetic layer is <=30×10-5 N/μm2 before hardening and >=40×10-5 N/μm2 after hardening. The nonmagnetic layer satisfies the relation expressed by formula (I): 200<=(BET specific surface area (m2/g) of carbon black × weight of the carbon black (g) + BET specific surface area (m2/g) of the nonmagnetic powder × weight of the nonmagnetic powder (g))/weight of the binder (g)<=400, where BET specific surface area is obtained by BET method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having improved electromagnetic conversion characteristics and durability such as head adhesion.

[0002]

2. Description of the Related Art In recent years, digitalization of magnetic recording media has been advanced for the purpose of releasing signal deterioration due to repeated copying. Further, the recording density is also required to be higher because the amount of recording data increases. From this point of view, it has been practically used to use finer metal magnetic powder having a high saturation magnetic flux density or hexagonal plate-like barium ferrite powder as the magnetic powder used for the magnetic recording medium.

In order to increase the recording density, it is necessary to consider the thickness loss and the self-demagnetization loss of the medium. From such a viewpoint, it is desired to reduce the thickness of the magnetic layer. However, when the thickness of the magnetic layer is reduced, the surface properties of the support are reflected on the surface of the magnetic layer, so that the electromagnetic conversion characteristics are deteriorated. For this reason, it has been conventionally proposed to provide a nonmagnetic layer using, for example, a thermosetting resin as an undercoat on the surface of a support, and to provide a magnetic layer via the nonmagnetic layer. However, there has been a problem that the conventional nonmagnetic layer has insufficient durability.

When a nonmagnetic layer and a magnetic layer are coated on the surface of a support, a method of forming the magnetic layer after coating and drying the nonmagnetic layer is used. In this case, the problem that the surface property of the non-magnetic layer deteriorated occurred.

To solve such a problem, Japanese Patent Laid-Open Publication No.
JP-A-3-191315 and JP-A-63-191318 disclose a nonmagnetic layer in which a nonmagnetic powder is dispersed in, for example, a thermoplastic resin binder, and the nonmagnetic layer is laminated on the nonmagnetic layer. A method is disclosed in which a coating solution for each layer is applied in a wet state by applying a coating solution for each layer, thereby improving the electromagnetic conversion characteristics, durability and head wear. However, these methods have a problem that the undulation at the interface between the nonmagnetic layer and the magnetic layer is increased, which leads to output fluctuation. In order to solve the above problem, Japanese Patent Application Laid-Open Nos. 8-241515 and 8-263826 disclose a non-magnetic layer in which non-magnetic powder is dispersed in a binder. A method of applying a magnetic layer after drying, calendering, and curing has been proposed.

[0006]

However, in magnetic recording media such as digital recording video tapes and floppy (registered trademark) disks, as the recording density increases, the demand for thinner magnetic layers increases. A non-magnetic layer having good surface properties and high physical properties has been required, and has been disclosed in the above-mentioned JP-A-8-241515 and JP-A-8-26382.
No. 6, the non-magnetic layer has insufficient coating film strength, so that satisfactory results cannot always be obtained due to head adhesion, electromagnetic conversion characteristics, and the like.

Accordingly, an object of the present invention is to provide a magnetic recording medium which can enhance the surface properties and coating strength of a non-magnetic layer, have excellent electromagnetic conversion characteristics and durability, and can sufficiently respond to the demand for thin films accompanying higher recording densities. Is to provide.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, separately determined the ultra-micro hardness before and after the hardening of the non-magnetic layer. By providing a predetermined relationship between the non-magnetic powder, carbon black, and the binder therein, a magnetic recording having smooth surface properties, excellent durability and electromagnetic conversion characteristics, which has been extremely difficult to achieve conventionally. They have found that a medium can be obtained, and have completed the present invention.

That is, the magnetic recording medium of the present invention has a non-magnetic layer in which at least one surface of a non-magnetic support is coated with a non-magnetic paint obtained by dispersing at least a non-magnetic powder and carbon black in a binder. In a magnetic recording medium having a magnetic layer having a dry thickness of 0.5 μm or less formed by dispersing a ferromagnetic powder in a binder, the magnetic layer is dried and calendered. The non-magnetic layer has an ultra-fine hardness before curing of 30 × 10 ⁻⁵ N / μm ² or less, and an ultra-fine hardness after curing of 40 × 10 ^−5. N / μm ²
The following formula (I) is applied between the non-magnetic powder, carbon black and the binder in the non-magnetic layer: 200 ≦ (BET specific surface area of carbon black (m ² / g) × weight of carbon black (g)) + BET specific surface area of nonmagnetic powder (m ² / g) × weight of nonmagnetic powder (g)) / weight of binder (g) ≦ 400 (I) (where BET is the value of the specific surface area by the BET method) ) Is established. When a plurality of types of carbon black or non-magnetic powder are used, the same calculation as that of the molecule of the formula (I) may be performed for each carbon black or non-magnetic powder.

In the present invention, the center line average roughness Ra of the non-magnetic layer after curing is preferably 5.5 nm or less, and the shape of the non-magnetic powder is preferably acicular.

The binder in the non-magnetic layer comprises a radiation-curable resin and a polyfunctional radiation-curable monomer or oligomer, and the polyfunctional radiation-curable monomer or oligomer is added to 100 parts by weight of the radiation-curable resin. It is preferable to include 10 parts by weight or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail. In the present invention, the non-magnetic layer applied on at least one surface of the non-magnetic support needs to have an ultrafine hardness before curing of 30 × 10 ⁻⁵ N / μm ² or less, and is preferable. Is 25 × 10 ⁻⁵ N / μm ² or less. The microhardness is 30 × 10 ^- for exceeds ⁵ N / ^{μm 2} calendering processability is lowered, sufficient surface can not be obtained.

On the other hand, this non-magnetic layer is
Super micro hardness 40 × 10^-FiveN / μm ^TwoThat is all
Required, preferably 45 × 10^-FiveN / μm^TwoAbove
is there. Ultra-micro hardness after curing is 40 × 10^-FiveN / μm^TwoNot yet
If it is full, the hardness of the coating film is insufficient, and the polishing of the magnetic layer
Insufficient capacity or soft coating film may cause
Transfers due to protrusions on the coating surface, rubber, etc. are likely to occur,
This degrades the electromagnetic conversion characteristics.

Here, the ultra-micro hardness used in the present invention is an ultra-micro hardness tester (ENT-1 manufactured by Elionix Inc.).
100), and a value obtained from the indentation displacement of the coating film when a load is applied and unloaded under a low load of 9.8 × 10 ⁻⁵ N using a diamond triangular indenter.

Further, in the present invention, at least the following formula (I) is satisfied between the nonmagnetic powder, carbon black and the binder in the nonmagnetic paint in which the nonmagnetic powder and carbon black are dispersed in the binder. (BET specific surface area of carbon black (m ² / g) × weight of carbon black (g) + BET specific surface area of nonmagnetic powder (m ² / g) × weight of nonmagnetic powder (g)) / weight of binder ( g) ≦ 400 (I) (where BET is the value of the specific surface area by the BET method), preferably the following formula (II): 230 ≦ (BET specific surface area of carbon black (m ² / represented by g) × weight of carbon black (g) + BET specific surface area of the nonmagnetic powder (m ² / g) × non-magnetic powder weight (g)) / weight of binder (g) ≦ 350 (II) It is necessary that the engagement is established. If the parameter value of the formula (I) is less than 200, the resin does not become sufficiently hard even when cured, and conversely, if it exceeds 400, the electric resistance of the nonmagnetic layer increases and the surface property of the nonmagnetic layer deteriorates. Come. The parameter value of the hardness after curing was 40.
Even if it is larger than 0, the value hardly changes, and it has little meaning.

In order to design the ultra-micro hardness of the non-magnetic layer to the above value before and after curing, a thermosetting resin can be used as a binder component. The mold monomer or oligomer is preferably contained in an amount of at least 10 parts by weight, more preferably at least 15 parts by weight, based on the radiation-curable resin 100.

It should be noted that, even when a thermosetting resin using an ordinary isocyanate-based curing agent is used, the ultra-micro hardness value before and after the hardening of the nonmagnetic layer can be satisfied. The surface property and the electromagnetic conversion characteristics are inferior to those of a radiation-curable resin that can be cured online, because the resin is easily cured.

When the amount of the polyfunctional radiation-curable monomer or oligomer is less than 10 parts by weight based on 100 parts by weight of the resin, the increase in hardness after curing is reduced. On the other hand, the upper limit is not particularly specified, but the amount is not limited. If the amount is too large, the coating film may become brittle, so it is preferable to suppress the amount to 40 parts by weight or less.

In the present invention, examples of the radiation-curable resin usable for the nonmagnetic layer include vinyl chloride resins, polyurethane resins, polyester resins, epoxy resins, phenoxy resins, fiber resins, polyether resins, and polyvinyl alcohol resins. Among them, vinyl chloride resins and polyurethane acrylate resins are typical, and it is preferable to use a mixture of both.

Such a radiation-curable vinyl chloride resin is
It is synthesized by radiation-sensitive modification of vinyl chloride resin as a raw material. As the raw material vinyl chloride resin, those having a vinyl chloride content of 60 to 95% by weight, particularly preferably 60 to 90% by weight, are preferable. Such vinyl chloride resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride- Vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-maleic acid copolymer, vinyl chloride-
Vinyl acetate-vinyl alcohol-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth)
There are acrylate-allyl glycidyl ether copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-allyl glycidyl ether copolymer and the like. Particularly, copolymers of vinyl chloride and a monomer containing an epoxy (glycidyl) group are used. preferable. The average degree of polymerization is 100 to 900.
Is more preferable, and more preferably 100 to 600.

The raw vinyl chloride resin having such a hydroxyl group or a carboxylic acid group is thereafter subjected to radiation-sensitive modification. As a method of modifying a thermosetting vinyl chloride resin into an electron beam curing resin, a resin having a hydroxyl group or a carboxylic acid group is reacted with a compound having a (meth) acryl group and a carboxylic anhydride or a dicarboxylic acid. Ester modification, tolylene diisocyanate (TDI) and 2-hydroxyethyl (meth) acrylate (2-HE)
Urethane modification which reacts a reactant (MA) with a reactant (MA) is well known, but has at least one ethylenically unsaturated double bond and one isocyanate group in one molecule, and has a urethane bond. Use of a monomer having no in the molecule (for example, 2-isocyanateethyl methacrylate), to obtain a coating film which does not become brittle even when the content ratio of the vinyl chloride resin is increased, and has excellent dispersibility and surface properties. Can be.

Also, the polyurethane acrylate resin is
Generally, it is obtained by reacting a hydroxy group-containing resin or a hydroxy group-containing acrylic compound with a polyisocyanate-containing compound. Examples of the hydroxy group-containing resin include polyalkylene glycols such as polyethylene glycol, polybutylene glycol, and polypropylene glycol, alkylene oxide adducts of bisphenol A, various glycols, and polyester polyols having a hydroxyl group at a molecular chain terminal. Among these, a polyurethane acrylate resin obtained by using a polyester polyol as one component is preferable.

The carboxylic acid component of the above-mentioned polyester polyol includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, and p- (hydroxyethoxy).
Aromatic oxycarboxylic acids such as benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as dodecanedicarboxylic acid, fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, hexahydrophthalic acid, etc. Unsaturated fatty acids and alicyclic dicarboxylic acids,
Tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid can be mentioned.

The glycol components of the polyester polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and neopentyl glycol. , Diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adducts such as bisphenol A and propylene oxide adduct, hydrogenated bisphenol A Examples include ethylene oxide and propylene oxide adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination. Examples of the polyester polyol include lactone-based polyester diols obtained by ring-opening polymerization of lactones such as caprolactone.

The hydroxy group-containing acrylic compound used in the polyurethane acrylate resin includes residues such as acrylic acid, acrylic ester, acrylic amide, methacrylic acid, methacrylic ester, and methacrylamide (an acryloyl group or a methacryloyl group). ). Specific examples of these hydroxy group-containing acrylic compounds include mono (meth) acrylates of glycols such as ethylene glycol, diethylene glycol and hexamethylene glycol, and mono (meth) acrylates of triol compounds such as trimethylolpropane, glycerin and trimethylolethane. And mono (meth) acrylates of polyols having 4 or more valences such as di (meth) acrylate, pentaerythritol, dipentaerythritol,
Di (meth) acrylate, tri (meth) acrylate,
Hydroxy group-containing acrylic compounds such as glycerin monoallyl ether and glycerin diallyl ether are preferred. These acrylic double bonds must be present in the binder molecule in at least one or more, preferably 2 to 20.

Examples of the polyisocyanate used for the polyurethane acrylate resin include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, biphenylmethane diisocyanate, m-phenylene diisocyanate, and hexamethylene diisocyanate. , Tetramethylene diisocyanate, 3,3'-dimethoxy 4,4'-biphenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl 4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, , 4 'diisocyanate-diphenyl ether, 1,5-naphthalenediisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate Over preparative methylcyclohexane, 1,4-diisocyanate methylcyclohexane,
4,4′-diisocyanatodicyclohexane, 4,
Diisocyanate compounds such as 4'-diisocyanate cyclohexylmethane and isophorone diisocyanate, or 7 mol% or less of 2,4
Triisocyanate compounds such as trimer of tolylene diisocyanate and trimer of hexamethylene diisocyanate.

On the other hand, aside from the above-mentioned method of synthesizing the radiation-curable urethane, a thermosetting polyurethane resin may be used as a raw material in the same manner as the vinyl chloride resin, and this may be subjected to radiation-sensitive modification.

The radiation-curable monomer or oligomer which can be used in the present invention includes those having an epoxy group at the terminal and those having a double bond, and preferably those having a double bond at the terminal. It is desirable that the number of such double bonds is two or more, more preferably three or more per molecule.
Examples include a methacryl group, an allyl group, and a vinyl group. Among them, an acryl group and a methacryl group are particularly preferable. The radiation-curable monomer or oligomer may be added either after the preparation of the coating or during the dispersion during the preparation of the coating. Such a radiation-curable monomer or oligomer is not particularly limited, but is preferably neomer PM-201, neomer TA-5.
05, Neomer DA600 (manufactured by Sanyo Chemical Co., Ltd.), Aronix M-309, Aronix M-450, Aronix M-1600, Aronix M-1960, Aronix M-6300, Aronix M-7100 (Toa Gosei Chemical Co., Ltd.) ) And the like.

The radiation that can be used in the present invention includes electron beams, γ-rays, β-rays, and ultraviolet rays.
Preferably, it is an electron beam. In addition, the irradiation amount is 1 to 1
0 Mrad is preferable, and more preferably 3 to 7 Mrad.
And the irradiation energy (acceleration voltage) is 100 kV
It is better to do the above. In addition, irradiation of radiation, coating,
It is desirable to perform it after drying and before winding, but it may be performed after winding.

In the present invention, the non-magnetic layer contains at least a non-magnetic powder and carbon black. The non-magnetic powder is preferably a fine needle-like non-magnetic powder. Has the effect of filling the projections of the base and improving the surface properties of the magnetic layer. When the shape of the non-magnetic powder is granular or spindle-shaped, the filling property of these non-magnetic powders is too high, so that the film becomes already hard before calendering, and the workability by the calender is inferior. Surface property is worse than that of acicular nonmagnetic powder. The particle diameter of the acicular non-magnetic powder is preferably 0.3 μm or less in short axis diameter, and if it exceeds 0.3 μm, the surface properties of the non-magnetic layer deteriorate. Such non-magnetic powders include, but are not limited to, α-iron oxide, goethite, and titanium oxide.

The BET specific surface area of such acicular nonmagnetic powder is 30 to 80 m ² / g, preferably 40 to 70 m ² / g.

The carbon black used together with the above-mentioned acicular nonmagnetic powder has a function of lowering the surface electric resistance of the magnetic layer and a function of retaining a lubricant added to the coating film. I have. It also has the effect of filling the protrusions of the base and improving the surface properties of the magnetic layer as in the case of the acicular nonmagnetic powder.
The carbon black that can be used is not particularly limited, but preferably has an average particle size of about 10 nm to 80 nm. Examples of such carbon black include known ones such as furnace carbon black, thermal carbon black, and acetylene black. Further, a single system or a mixed system may be used.

[0033] BET specific surface area of these carbon black is 50~500m ² / g, preferably 60~250m ² /
g. The proportion occupied by the carbon black is 5% by weight to 100% by weight, preferably 10% by weight, based on the acicular nonmagnetic powder.
１００100% by weight. If the amount is less than 5% by weight, there arise problems that the holding power of the added lubricant decreases, the surface electric resistance of the magnetic layer increases, and the light transmittance increases. On the other hand, if it exceeds 100% by weight, the thixotropy of the paint becomes high, and the handling of the paint becomes poor. Carbon black that can be used in the present invention, for example,
"Carbon Black Handbook" (edited by Carbon Black Association)
Can be referred to.

In the non-magnetic layer, in addition to the acicular non-magnetic powder and the above-mentioned carbon black, other non-magnetic powders may be used in combination as an abrasive, for example, α-alumina, Cr
₂ O ₃ , Ce ₂ O _{3 and the} like can be used, but not limited thereto.

Further, it is preferable that the nonmagnetic layer in the present invention contains a lubricant in addition to the above materials. Lubricants that can be used include higher fatty acids, higher fatty acid esters,
Known materials such as paraffin and fatty acid amide can be used.

The thickness of the non-magnetic layer may be appropriately determined depending on the surface roughness of the non-magnetic support and the required characteristics of the medium, but is generally 0.5 to 3.0 μm. In order to further exploit the advantages of the nonmagnetic layer, the thickness is preferably 0.8 μm or more. In addition, the center line average roughness Ra of the non-magnetic layer after curing is Ra
Is preferably 5.5 nm or less. This value is 5.5
If it exceeds nm, the surface properties of the magnetic layer provided thereon are poor, and the electromagnetic conversion characteristics are deteriorated.

As the ferromagnetic powder used for the magnetic layer in the present invention, a conventionally known material can be used.
₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing γ-
Oxide fine powders such as Fe ₃ O ₄ , CrO ₂ , barium ferrite, strontium ferrite, Fe, Co, Ni
And fine metal powders such as alloys thereof.

These magnetic powders may be appropriately selected according to the type of medium to be applied.
Metals such as o and Ni or fine powders of alloys thereof are preferable. Further, those containing a rare earth element containing Y as an additive element are also preferable. Also, the coercive force may be arbitrarily adjusted to the existing or under development drive system.

In the present invention, the dry thickness of the magnetic layer is 0.5 μm or less, and the electromagnetic conversion characteristics and durability are improved under such thinning to realize high recording density.

As the nonmagnetic support used in the present invention, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN);
Known films such as polyolefins, polyamide, polyimide, polyamideimide, polysulfone cellulose triacetate, and polycarbonate can be used.

In the case of a magnetic tape, a back coat may be provided in addition to the non-magnetic layer and the magnetic layer. The back coat layer is provided for preventing the magnetic layer from being charged for improving running stability. The back coat layer preferably contains 30 to 80% by weight of carbon black. If the content of carbon black is too small, the antistatic effect tends to decrease, and the running stability tends to decrease. Also, since the light transmittance is likely to be high, there is a problem in a method of detecting the end of the tape by a change in the light transmittance. On the other hand, if the content of carbon black is too large, the strength of the back coat layer decreases, and running durability tends to deteriorate. Any carbon black may be used as long as it is commonly used, and the average particle size is preferably about 5 to 500 nm.

As the binder used in the magnetic layer and the back coat layer of the present invention, a thermoplastic resin, a thermosetting or reactive resin, an electron beam-sensitive modified resin, or the like is used. Is appropriately selected and used in accordance with the process conditions.

As a method of applying the non-magnetic layer and the magnetic layer, a wet-on-dry coating method in which the non-magnetic layer is applied and the magnetic layer is applied after the non-magnetic layer is dried is adopted. With the wet-on-dry coating method, there is no disturbance at the interface between the non-magnetic layer and the magnetic layer, as seen in the wet-on-wet coating method in which the magnetic layer is coated while the non-magnetic layer is in a wet state. An excellent magnetic layer can be obtained. As a coating means in the wet-on-dry coating method, various known coating means such as a gravure coat, a reverse roll coat, and a die nozzle coat can be used.

After the magnetic layer applied on the non-magnetic layer is dried, calendering is performed as a surface smoothing treatment. Rolls for such calendering treatment include epoxy, polyester, nylon, polyimide, polyamide, polyimide amide. A combination of a heat-resistant plastic roll (such as one into which carbon, metal, or another inorganic compound is kneaded) and a metal roll (combination of three to seven steps) can be suitably used.
The processing temperature is preferably 70 ° C. or higher, more preferably 90 ° C. or higher. The linear pressure is preferably 2000 N /
cm or more, more preferably 2500 N / cm or more, and the processing speed is preferably in the range of 20 m / min to 900 m / min. The magnetic recording medium of the present invention can be more favorably obtained at a temperature of 100 ° C. or higher and a linear pressure of 250 kg / cm or higher.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Example 1 <Non-magnetic layer coating material 1> 80 parts by weight of α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DPN-250BW) (average short axis diameter = 23 nm, BET comparison area = 55 m ² / g) Carbon black (Mitsubishi Chemical Corporation: # 850B) 20 parts by weight (Average particle size = 16 nm, BET specific surface area = 200 m ² / g, DBP oil absorption = 70 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd. Co., Ltd .: HIT60A) 5 parts by weight (average particle size = 0.18 μm, BET comparison area = 12 m ² / g) Electron beam-curable vinyl chloride copolymer 20 parts by weight (polymerization degree = 300, polar group: OSO) ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 8 parts by weight (Mn = 25000, polar group: sodium phosphinate = 1 / molecule) Trifunctional acrylic monomer (manufactured by Sanyo Chemical Industry Co., Ltd.) : Neo Over TA505) 5.6 parts Methyl ethyl ketone 120 parts Toluene 120 parts by weight Cyclohexanone 60 parts by weight

After the above composition was kneaded, it was dispersed in a sand grinder mill. Next, the following additives and solvents were added to adjust the viscosity, and Non-magnetic Paint 1 was prepared. Butyl stearate 1 part by weight Stearic acid 1 part by weight Methyl ethyl ketone 40 parts by weight Toluene 40 parts by weight Cyclohexanone 40 parts by weight

<Magnetic Paint 1> 100 parts by weight of metal magnetic powder (Hc = 144.6 kA / m, σs = 130 Am ² / kg, BET specific surface area = 57 m ² / g, average major axis length = 0.10 μm) Vinyl-based copolymer (manufactured by Zeon Corporation: MR110) 10 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) SO ₃ Na-containing polyurethane resin 7 parts by weight (Mn = Α-Al ₂ O ₃ (HIT82 manufactured by Sumitomo Chemical Co., Ltd.) 12 parts by weight (average particle size = 0.12 μm, BET specific surface area = 20 m ² / g) Myristic acid 2 parts by weight Methyl ethyl ketone 90 parts by weight Toluene 90 parts by weight Cyclohexanone 120 parts by weight

After the above composition was kneaded, it was dispersed in a sand grinder mill. Next, the following additives and solvents were added to adjust the viscosity, and Magnetic Coating 1 was prepared. Butyl stearate 1 part by weight Stearic acid 1 part by weight Methyl ethyl ketone 110 parts by weight Toluene 110 parts by weight Cyclohexanone 160 parts by weight

<Coating for Backcoat Layer> 80 parts by weight of carbon black (Conductex SC average particle size = 20 nm, BET specific surface area = 220 m ² / g, manufactured by Columbian Carbon Co.) 1 part by weight of carbon black (manufactured by Columbian Carbon Co., Ltd.) : Sevacarb MT average particle size = 350 nm, BET specific surface area = 8 m ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo KK: TF100, average particle size = 0.1 μm) 1 part by weight vinyl chloride-vinyl acetate -Vinyl alcohol copolymer 65 parts by weight (monomer weight ratio = 92: 3: 5, average degree of polymerization = 420) polyester polyurethane resin (Toyobo Co., Ltd .: UR-8300) 35 parts by weight methyl ethyl ketone 260 parts by weight toluene 260 Parts by weight cyclohexanone 260 parts by weight

After the above composition was kneaded, it was dispersed in a sand grinder mill. Next, the following additives and solvents were added to adjust the viscosity. 1 part by weight of stearic acid 1 part by weight of myristic acid 2 parts by weight of butyl stearate 210 parts by weight of methyl ethyl ketone 210 parts by weight of toluene 210 parts by weight of cyclohexanone

First, the non-magnetic paint 1 was extruded onto a 6.1 μm thick PET film, and was applied by a die nozzle method so that the dry film thickness was 2.0 μm. Then, drying temperature 1
After drying at 00 ° C, temperature 100 ° C, linear pressure 3000N / cm
, And then electron beam irradiation (5
Mrad) to produce a nonmagnetic layer raw material. Next, Coronate L (Nippon Polyurethane Industry Co., Ltd.)
4 parts by weight), 1 part by weight to 100 parts by weight of the backcoat paint, and extrude the magnetic paint 1 on the non-magnetic layer raw material so that the dry film thickness becomes 0.25 μm by a die nozzle method. , And orientation was performed, and the coating film was dried at a drying temperature of 100 ° C. Then, the temperature is 100 ° C and the linear pressure is 300
Calendar processing was performed at 0 N / cm. Next, a back coat paint was extruded on the base surface opposite to the magnetic layer, and was applied by a die nozzle method so as to have a dry film thickness of 0.5 μm, thereby producing a raw roll.

After leaving this roll at room temperature for 24 hours,
After curing in a heating oven at 0 ° C for 24 hours,
It was cut into a 2.7 mm width and assembled into a DLT cassette to obtain a magnetic tape sample.

Example 2 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amount of the following compounding agent was changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 14.6 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 6.3 parts by weight (Mn = 25000) , Polar group: sodium phosphinate = 1 / molecule) Trifunctional acrylic monomer (TA505, manufactured by Sanyo Chemical Industries, Ltd.) 4.2 parts by weight

Example 3 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amount of the following compounding agent was changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 13.0 parts by weight (polymerization degree = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 5.5 parts by weight (Mn = 25000) , Polar group: sodium phosphite = 1 / molecule) 3.7 parts by weight of trifunctional acrylic monomer (manufactured by Sanyo Chemical Industries, Ltd .: TA505)

Example 4 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amount of the following compounding agent was changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 23.3 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 10.0 parts by weight (Mn = 25000) , Polar group: sodium phosphinate = 1 / molecule) 6.7 parts by weight of trifunctional acrylic monomer (manufactured by Sanyo Chemical Industries, Ltd .: TA505)

Example 5 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amount of the following compounding agent was changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 21.2 parts by weight (polymerization degree = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 9.1 parts by weight (Mn = 25000) , Polar group: sodium phosphite = 1 / molecule) Trifunctional acrylic monomer (manufactured by Sanyo Chemical Industries, Ltd .: TA505) 3.0 parts by weight

Example 6 In the non-magnetic layer coating material 1 of Example 1, a pentafunctional acrylic monomer (Neomer DA600: Sanyo Chemical Industry Co., Ltd.) was used instead of the trifunctional acrylic monomer (Neomer TA505).
A magnetic tape sample was prepared in the same manner as in Example 1 except that the same amount was used.

Comparative Example 1 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amount of the following additives was changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 11.6 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 5.0 parts by weight (Mn = 25000) , Polar group: sodium phosphite = 1 / molecule) trifunctional acrylic monomer (manufactured by Sanyo Chemical Industries, Ltd .: TA505) 3.3 parts by weight

Comparative Example 2 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amount of the following compounding agent was changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 29.2 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 12.5 parts by weight (Mn = 25000) , Polar group: sodium phosphinate = 1 / molecule) Trifunctional acrylic monomer (TA505, manufactured by Sanyo Chemical Industries, Ltd.) 8.3 parts by weight

Comparative Example 3 In the non-magnetic layer coating material 1 of Example 1, acicular α-Fe ₂ O _{3 was used.}
(Toda Kogyo Co., Ltd .: DPN-250BW) was converted to granular α
A magnetic tape sample was prepared in the same manner as in Example 1 except that Fe ₂ O ₃ (manufactured by Sakai Chemical Industry Co., Ltd .: FRO-3, average particle size = 30 nm, BET = 45 m ² / g) was used.

COMPARATIVE EXAMPLE 4 In the non-magnetic layer coating material 1 of Example 1, acicular α-Fe ₂ O
₃ Spindle-shaped α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DPN-250BW) (C-9, manufactured by Sakai Chemical Industry Co., Ltd., average short axis diameter = 30 nm, BET = 50 m ² / g) A magnetic tape sample was prepared in the same manner as in Example 1 except that the sample was changed to.

Comparative Example 5 A magnetic tape sample was prepared in the same manner as in Example 1 except that the trifunctional acrylic monomer was not included in the non-magnetic layer coating material of Example 1, and the amount of the following additives was changed. Electron beam-curable vinyl chloride copolymer 23.3 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 10.0 parts by weight (Mn = 25000) , Polar group: sodium phosphite = 1 / molecule)

Comparative Example 6 A magnetic tape sample was prepared in the same manner as in Example 1 except that the amounts of the following additives were changed in the non-magnetic layer coating material 1 of Example 1. Electron beam-curable vinyl chloride copolymer 22.2 parts by weight (degree of polymerization = 300, polar group: OSO ₃ K = 1.5 / molecule) Electron beam-curable polyurethane resin 9.5 parts by weight (Mn = 25000) , Polar group: sodium phosphinate = 1 / molecule) Trifunctional acrylic monomer (TA505, manufactured by Sanyo Chemical Industries, Ltd.) 1.6 parts by weight

With respect to the above samples, the following items were measured and evaluated. (1) Ultra-micro hardness of coating film before and after curing of non-magnetic layer (2) Surface roughness after curing of non-magnetic layer (3) Surface roughness of tape sample (4) Electromagnetic conversion characteristics (5) Head adhesion (6) Error rate

The respective measuring methods and evaluation methods are as follows. (Measurement method of ultra-micro hardness) It was measured under the following conditions. Measuring device: Ultra-fine indentation hardness tester manufactured by Elionix (ENT-1100 (Ver. 3, 0)) Measurement sample preparation method: The measurement sample was attached to a dedicated sample table using Aron Alpha, and left at room temperature for 12 hours or more.

(Measurement Method of Surface Roughness) The center line average roughness (Ra) was measured under the following conditions. Measuring device: Taly step system manufactured by Taylor Hobson Co., Ltd. Measurement condition: Filter condition 0.18-9 Hz Probe 0.1 × 2.5 μm Special stylus Probe pressure 1.96 × 10 ^-5 N Measurement speed 0.03 mm / sec Measurement 500 μm long

(Electromagnetic conversion characteristics) Quantum DL
The output of 5.33 MHz was measured using a T4000 drive, and the value of the reference tape was converted to 100%. 100 ± 15% was accepted. (Error rate) Using a Quantum DLT4000 drive, it was stored for 5 days in an environment of 50 ° C. and 80% RH, and the error rates before and after storage were measured (unit: number of errors / MB). A case where the error rate after storage was 5 times or more that before storage or the value of the error rate became 0.10 or more was regarded as NG. (Head adhesion) After storing the tape sample in an environment of 40 ° C. and 80% RH for 5 days, Quantum DLT40
Using a 00 drive, the head was run for 1,000 passes, and the adhesion of the head after running was checked with an optical microscope having a magnification of 100 times.
The evaluation is as follows. With head adhesion: × Without head adhesion: を The results obtained are shown in Tables 1 and 2 below.

[0068]

[Table 1]

[0069]

[Table 2] 1) Ratio of acrylic monomer to total electron beam-curable resin (excluding acrylic monomer) in nonmagnetic layer coating material 2) (BET specific surface area of carbon black (m ² / g) × weight of carbon black in nonmagnetic layer) (G) + BET specific surface area of nonmagnetic powder (m ² / g) × weight of nonmagnetic powder (g)) / weight of binder (g)

[0070]

According to the present invention, it is possible to provide a magnetic recording medium having smooth surface properties, excellent durability and electromagnetic conversion characteristics, which have been extremely difficult to achieve conventionally.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Doi 1-13-1, Nihonbashi, Chuo-ku, Tokyo FDT term in TDK Corporation (reference) 5D006 BA19 CA01 CA04 CA05

Claims (4)

[Claims] A ferromagnetic powder is provided on at least one surface of a non-magnetic support via a non-magnetic layer coated with a non-magnetic paint obtained by dispersing at least a non-magnetic powder and carbon black in a binder. A magnetic recording medium having a magnetic layer having a dry thickness of 0.5 μm or less dispersed in a binder, wherein the magnetic layer is applied after drying, calendering, and curing the applied nonmagnetic paint. And
The ultrafine hardness of the nonmagnetic layer before curing is 30 × 10 ⁻⁵ N /
μm ² or less and ultra-hard hardness after curing of 40 × 10 ⁻⁵
N / μm ² or more, a non-magnetic powder in the non-magnetic layer,
The following formula (I) is provided between the carbon black and the binder: 200 ≦ (BET specific surface area of carbon black (m ² / g) × weight of carbon black (g) + BET specific surface area of nonmagnetic powder (m ² / g)) × weight of nonmagnetic powder (g)) / weight of binder (g) ≦ 400 (I) (where BET is the value of the specific surface area by the BET method). Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the nonmagnetic layer has a cured center line average roughness Ra of 5.5 nm or less. 3. The magnetic recording medium according to claim 1, wherein the shape of the nonmagnetic powder is acicular. 4. The binder in the non-magnetic layer comprises a radiation-curable resin and a polyfunctional radiation-curable monomer or oligomer, and the polyfunctional radiation-curable monomer or oligomer is added to 100 parts by weight of the radiation-curable resin. The magnetic recording medium according to claim 1, wherein the magnetic recording medium contains at least 10 parts by weight.