JP4525116B2 - Method for manufacturing magnetic recording medium - Google Patents

Description

The present invention is a video tape, audio tape, a manufacturing method of a floppy disk, various tape-shaped magnetic recording medium material such as a computer data storage tape.

  In recent years, with the improvement in performance represented by high-vision VTRs and digital VTRs, improvement in characteristics of magnetic recording media has been demanded.

In order to achieve high-density recording of a coating-type magnetic recording medium, metal fine particles are used as the ferromagnetic powder, and the surface of the medium is super-smoothed to minimize the spacing loss and at the same time by recording demagnetization. It is also important to reduce output loss.
Methods for achieving these objects include increasing the coercive force and saturation magnetization of the ferromagnetic powder, making the coercive force distribution of the ferromagnetic powder uniform, imparting perpendicular anisotropy, and reducing the thickness of the magnetic layer.

Among these, the improvement of the ferromagnetic powder is effective as a method for directly improving the output.
With regard to such improvements regarding coercive force and saturation magnetization, the elemental composition of the ferromagnetic powder has been studied, metal fine particles having a coercive force exceeding 160 kA / m, and metal fine particles having a saturation magnetization exceeding 140 Am ² / kg. Has also been developed.
The coercive force distribution reflects the particle size distribution of the ferromagnetic powder, and it has been found that the coercive force distribution is remarkably improved by making the particle size uniform.

Giving perpendicular anisotropy is a technique for increasing the density by perpendicular magnetic recording. In this regard, in the case of a coating-type magnetic recording medium, it is largely due to control of the magnetic orientation of the ferromagnetic powder. For example, when using acicular particles, it has been attempted to subject the coating film to vertical alignment treatment or oblique alignment treatment.
However, since there are problems such as difficulty in orientation control and disturbance of the coating film surface due to orientation, these orientation treatments have not yet become practical.

The thinning of the magnetic layer is considered to be very effective as a method for reducing the self-demagnetization loss.
Here, if the thickness of the magnetic layer is simply reduced to, for example, 1 μm or less, the surface shape of the nonmagnetic support is easily reflected on the surface of the magnetic layer, and it becomes difficult to smooth the surface of the magnetic layer. For this reason, when the magnetic layer is thinned, a so-called multilayer coating type configuration in which a nonmagnetic coating layer (nonmagnetic layer) is interposed between the nonmagnetic support and the magnetic layer is often employed. Yes.
By interposing the nonmagnetic layer in this manner, the thickness is increased between the surface of the nonmagnetic support and the surface of the magnetic layer, and the surface shape of the nonmagnetic support is less likely to appear on the surface of the magnetic layer. Therefore, a thin magnetic layer can be formed with a smooth surface shape.

  Various improvements have been proposed for the multilayer coating type magnetic recording medium as described above. For example, a method of setting the coating thickness of the lower nonmagnetic layer to 0.5 μm to 3.5 μm (for example, see Patent Document 1). ), A method of containing an appropriate amount of carbon black in the lower nonmagnetic layer (see, for example, Patent Document 2), and a method of coating the surface of the nonmagnetic oxide of the lower nonmagnetic layer with an inorganic substance (see, for example, Patent Document 3). ), A method using two or more kinds of nonmagnetic powders having different sizes in the lower nonmagnetic layer (see, for example, Patent Document 4), a method of regulating the standard deviation of the film thickness of the upper magnetic layer within a specific range (for example, And Patent Document 5), and a method of forming the upper magnetic layer with two or more magnetic layers (for example, see Patent Documents 6 and 7) has been reported.

  By the way, in recent years, the use of digital high-definition VTRs in the field of film photography requiring high image quality typified by movies has led to a demand for a large volume of digital video data. Accordingly, it is required to provide a magnetic medium with high output and low noise.

Conventionally, in order to suppress noise and achieve high-density recording, it is necessary to shorten the recording wavelength. For this reason, fine magnetic powder shorter than the recording wavelength is used.
In order to obtain a high output, various proposals for increasing the magnetic characteristics have been made. For example, a ferromagnetic metal powder having a high saturation magnetization is used to improve the magnetic characteristics so as to achieve a high output. (See, for example, Patent Document 8).
In addition, the magnetic powder alone is better as the coercive force Hc and the saturation magnetization σs are higher, and the long axis length, short axis length, and crystallite size are small if they are small in order to improve short wavelength output and reduce noise. There is also a proposal for a technique that defines an appropriate range (see, for example, Patent Document 9).

  In addition, in order to reduce noise, a super-calendar process is used to provide a surface finishing treatment of the magnetic coating film to smooth the coating film surface and reduce the noise ( For example, refer to Patent Documents 10 and 11.)

JP-A 63-187418 JP-A-4-238111 JP-A-5-182177 JP-A-5-274651 Japanese Patent Laid-Open No. 5-298653 JP-A-6-162485 JP-A-6-162489 JP-A-61-37761 Japanese Patent No. 2946262 Japanese Patent Publication No.52-17404 Japanese Patent Publication No. 60-12688

However, in the various technologies proposed in the past as described above, it is considered to support a large capacity, high transfer rate broadcasting station such as an uncompressed digital VTR or a new digital VTR for movie production. However, sufficient electromagnetic conversion characteristics and low noise have not been achieved.
In addition, with higher output, high output heads such as laminated amorphous heads have come to be applied. The problem of down-leveling is becoming more serious.
For this reason, in the future, it will be necessary to design a magnetic paint that can achieve higher output and higher reliability.

Therefore, in the present invention, in view of the conventional situation as described above, even when applied to a large capacity, high transfer rate broadcasting station such as an uncompressed digital VTR or a new digital VTR for movie production, High-power and high-reliability magnetism having a magnetic layer in which magnetic powder of high Hc and high σs is uniformly dispersed in good condition to achieve sufficient electromagnetic conversion characteristics and achieve low noise It was decided to provide a method for manufacturing a recording medium.

In the present invention, a nonmagnetic lower layer formed by dispersing nonmagnetic powder in a binder is formed on a nonmagnetic support , and then a magnetic coating is applied on the nonmagnetic lower layer to form a magnetic layer. will by the magnetic coating, the magnetic powder, by mixing the silane coupling agent, followed by making the first coating material by mixing a binder resin, a hydroxycarboxylic acid to the first coating material Is added to prepare a second coating material, and an isocyanate curing agent is added to the second coating material, and a method for producing a magnetic recording medium is provided.

  According to the present invention, the surface treatment of the magnetic powder is performed by including a silane coupling agent in the magnetic layer, and the dispersion of the magnetic paint is performed by adding hydroxycarboxylic acid in the subsequent process. The magnetic recording medium having a magnetic layer in which the magnetic powder having a higher Hc and higher σs than that of the prior art is dispersed in a uniform and good state can be obtained, and can be used for uncompressed high-definition digital broadcasting. A technology has been established for obtaining a magnetic recording medium with high capacity, high transfer rate, and high reliability.

  Moreover, according to the method of the present invention, first, a coating material is prepared by mixing magnetic powder and a silane coupling agent, and further mixing a binder resin, and adding a hydroxycarboxylic acid to the coating material. As a result, the dispersion state of the magnetic coating material could be reliably improved.

Specific embodiments of the method for producing a magnetic recording medium of the present invention will be described, but the present invention is not limited to the following examples .
A schematic cross-sectional view of an example of a magnetic recording medium is shown in FIG.
The magnetic recording medium 10 has a configuration in which a nonmagnetic lower layer 2 and a magnetic layer 3 are sequentially formed on a nonmagnetic support 1 and a backcoat layer 4 is formed on the side opposite to the magnetic layer forming surface. Have. Hereinafter, each layer will be described.

  As the nonmagnetic support 1, any of those generally used for magnetic recording media can be applied. For example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, cellulose triacetate, cellulose diester Cellulose derivatives such as acetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamideimide, other plastics, metals such as aluminum and copper, light alloys such as aluminum alloys and titanium alloys Examples include alloys, ceramics, single crystal silicon, and the like.

Next, the nonmagnetic lower layer 2 will be described.
The nonmagnetic lower layer 2 is formed by applying a paint in which a nonmagnetic inorganic powder is dispersed in a binder.
As the nonmagnetic inorganic powder, any conventionally known material for forming the underlayer of the coating-type magnetic recording medium can be applied. For example, α-Fe ₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , α- _{FeOOH, CaO, SiO 2, Al} 2 O 3, and calcium carbonate. The shape of these pigments may be acicular or spherical, but the major axis length of the non-ferromagnetic inorganic powder is preferably 0.3 μm or less, particularly 0.02 μm to 0.3 μm. Of these, acicular hematite is preferable.

As the binder for forming the nonmagnetic lower layer 2, the same binder as that for forming the magnetic layer 3 described later can be used.
By forming the nonmagnetic lower layer 2, the surface electrical resistance value can be reduced, and a magnetic recording medium having excellent electromagnetic conversion characteristics and surface properties can be obtained.
In addition, you may add various additives, such as a well-known lubricant, a dispersing agent, an antistatic agent, a rust preventive agent, to the coating material for forming the nonmagnetic lower layer 2 as needed.

  As the solvent for preparing the coating material for forming the nonmagnetic lower layer 2, the same solvents as those for adjusting the magnetic coating material described later can be used, and any conventionally known solvents can be applied. For example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol acetate monoethyl ester, glycol ether solvents such as glycol monoethyl ether and dioxane Solvents, aromatic hydrocarbon solvents such as benzene, toluene and xylene, and organic chlorine compound solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene.

  The coating material for forming the nonmagnetic lower layer 2 is prepared by kneading and dispersing the above-described components together with a solvent. The kneading and dispersing method may be a known method, and is not particularly limited, but a normal kneader such as a continuous biaxial kneader (extruder), a kneader, a pressure kneader, or the like can be applied.

  The nonmagnetic lower layer 2 can be formed by applying a paint by a conventional application method such as gravure coating, extrusion coating, air doctor coating, reverse roll coating, and the like.

Next, the magnetic layer 3 will be described.
The magnetic layer 3 contains a magnetic powder, a binder, an antistatic agent, an abrasive, a lubricant, and other additives. In the present invention, in particular, a silane coupling agent and a hydroxycarboxylic acid are included. It shall be contained.

The magnetic powder will be described.
The magnetic powder constituting the magnetic layer is a Co-containing metal magnetic powder having a coercive force Hc of 200 kA / m or more, a saturation magnetization σs 120 Am ² / kg and a particle size of 100 nm or less, and in particular, acicular Co-containing Fe magnetic powder is preferred.
Thus, by specifying the coercive force Hc and the saturation magnetization σs, it is possible to increase the output of the finally obtained magnetic recording medium.

In order to use the conventional general broadcast station VTR format, the coercive force Hc is 100 kA / m or more, more preferably 105 kA / m or more, which is the lower limit of the coercive force Hc of the conventional format standard. For example, about 120 kA / m is optimal for a digital VTR format such as a digital beta cam and D-2, and about 135 kA / m is optimal for an HDCAM which is a high-vision digital VTR.
However, for high-capacity digital video, it is necessary to make the recording density 3 to 5 times or more of the conventional recording density, and therefore the shortest recording wavelength is 0.2 microns or less, which is half or less of 0.5 μm of HDCAM. For this reason, it is necessary to use fine magnetic powder with higher magnetic energy.
Here, there are two methods of increasing the magnetic energy: a method of increasing the coercive force Hc and a method of increasing the saturation magnetization σs. In particular, high Hc is effective in a short wavelength region of 0.2 μm or less.
The preferred Hc is 210 kA / m to 250 kA / m, although it varies depending on the format used.

Furthermore, an output difference between the output at a wavelength twice or four times the wavelength to be recorded and an output difference between the shortest wavelength, so-called frequency characteristics, becomes a problem in practice. In particular, when the output difference depending on this frequency is large. It is known that the error rate deteriorates.
It has been found that the saturation magnetization σs needs to be 120 Am ² / kg or more in order to improve the frequency dependency. Practically, it has been confirmed that better characteristics can be obtained when the saturation magnetization σs is 130 Am ² / kg or more.
On the other hand, if the saturation magnetization σs exceeds 200 Am ² / kg, the deterioration rate of magnetic properties due to long-term storage in a high-temperature and high-humidity environment after the magnetic tape is deteriorated, the saturation magnetization σs is 120 Am ² / kg. It is desirable to set it as kg or more and 200 Am < ² > / kg or less.

The particle size of the magnetic powder needs to be 100 nm or less, preferably 30 nm to 70 nm, in accordance with the above-described background (short wavelength).
If the particle size is less than 30 nm, sufficient dispersibility cannot be ensured in the binder, and a uniform magnetic paint may not be obtained.

The silane coupling agent will be described.
The silane coupling agent has an effect of improving the adsorbing power of a binder resin, such as a vinyl chloride copolymer or a polyurethane resin, by adsorbing on the surface of the magnetic powder described above or causing a chemical reaction on the surface. . That is, the dispersant improves the dispersibility of the magnetic paint.
Therefore, when preparing a magnetic coating, the silane coupling agent is first mixed with the magnetic powder, and in the subsequent process, the binder resin and other additives are mixed and diluted and dispersed in an organic solvent. And

  Examples of the silane coupling agent include vinyl silane compounds such as vinyl methoxy silane, vinyl triethoxy silane, tris- (2-methoxy ethoxy) vinyl silane, γ-methacryloxy propyl trimethoxy silane, and γ-glycidoxy propyl tri Epoxysilane compounds such as methoxysilane and β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and aminosilanes such as γ-aminopropyltriethoxysilane and N-β (aminoethyl) γ-aminopropylmethyldimethyloxysilane Compounds, mercaptosilane compounds such as γ-mercaptopropyltrimethoxysilane, isocyanate silane compounds such as γ-isocyanatopropyltriethoxysilane, γ-isocyanatopropyltrimethoxysilane, and the like can be used.

The addition amount of the silane coupling agent has a specific surface area of the magnetic powder (BET value), when it is 50m ² / g~80m ² / g is less than 5 parts by weight or more and 1 part by weight by weight relative to 100 parts by weight of the magnetic powder Preferably, the amount is 3 parts by weight or more and 4 parts by weight or less.
If the addition amount of the silane coupling agent is less than 1 part by weight, the dispersibility of the magnetic paint cannot be secured sufficiently, and even if added in a large amount, the dispersibility improving effect is saturated at a certain point. .

Next, the hydroxycarboxylic acid which is a magnetic coating component will be described.
First, the usage of hydroxycarboxylic acid will be described.
In the present invention, the above-described magnetic powder and silane coupling agent are mixed, and then a paint (first paint) in which a binder resin is mixed is prepared, and then hydroxycarboxylic acid is added ( In the step before the second coating) and before application, an isocyanate curing agent is added to prepare a magnetic coating, and the magnetic layer 3 is formed by applying this magnetic coating.

  By using the method as described above, the dispersion state of the magnetic paint can be surely improved. That is, after the dispersion of the first paint is completed, the addition of hydroxycarboxylic acid can prevent the paint from agglomerating, thereby improving the surface properties after application.

Hydroxycarboxylic acid also has the effect of neutralizing the base point on the surface of the magnetic powder and improving the adsorptive power of polar groups of the binder resin, and removal of the binder by adsorption of the isocyanate curing agent to the magnetic powder. Separation can be suppressed.
For this reason, by adding it to the paint in the step before adding the isocyanate curing agent, it is possible to reliably suppress the agglomeration of the paint and to obtain a magnetic paint excellent in applicability. A magnetic recording medium with good output, high output and little noise can be obtained.

  Examples of the hydroxycarboxylic acid include p-hydroxybenzoic acid, 5-hydroxyisophthalic acid, 6-hydroxy-2-naphthoic acid, p-hydroxyphenylacetic acid and other aromatic hydroxycarboxylic acids, citric acid, gluconic acid, lactic acid, Aliphatic hydroxycarboxylic acids such as malic acid, amino acids such as serine, threonine, and tyrosine can be used.

The amount of the hydroxycarboxylic acid added is preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight, with respect to 100 parts by weight of the magnetic powder.
If the amount added is less than 0.5 parts by weight, a sufficient effect cannot be exhibited. If the amount added is too large, a phenomenon (blooming) that oozes out after long-term storage on the surface of the magnetic layer occurs.

Next, the binder will be described.
As the binder, a polyurethane resin containing a tertiary amine is particularly suitable.
This is because the affinity of the functional part (polar part) of the tertiary amine to the magnetic powder surface is improved by the adsorption of the hydroxycarboxylic acid to the magnetic powder.
That is, by making the liquid property on the surface of the magnetic powder acidic, the compatibility with the binder resin having a more basic polar group is improved, and the effect of suppressing the coating aggregation is exhibited.

  As the binder resin, any known material can be used. For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile. Copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylic ester-styrene copolymer Polymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene Emissions copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea - formaldehyde resins, polyvinyl acetal resins, or mixtures thereof, and the like.

  In particular, a polyurethane resin, a polyester resin, an acrylonitrile-butadiene copolymer, etc., which are supposed to impart flexibility, and a cellulose derivative, a phenol resin, an epoxy resin, etc. which are supposed to impart rigidity are desirable.

Next, the antistatic agent will be described.
Carbon black can be applied as the antistatic agent.
Carbon black can refer to, for example, “Carbon Black Handbook (edited by Carbon Black Association)”, and is not limited at all with respect to the type of carbon.

Carbon black has a DBP oil absorption of 30 to 150 ml / 100 g, preferably 50 to 150 ml / 100 g, an average particle size of 5 to 150 nm, preferably 15 to 50 nm, and a specific surface area by the BET method of 40 to 40. 300m ² / g, yet is suitably those which are 100 to 250 m ² / g. The tap density is preferably 0.1 to 1 g / cc, and the pH is preferably 2.0 to 10.
Carbon black having a higher DBP oil absorption has a higher viscosity and remarkably deteriorates dispersibility. On the other hand, when the amount is small, the dispersibility deteriorates, so that the dispersion process takes too much time.
The smaller the average particle diameter of carbon black, the longer the dispersion time, but the better the surface property, and the larger the carbon black, the worse the surface property. Therefore, it is preferable to select 15 to 50 nm.

Examples of the carbon black that satisfies the above-described conditions include, for example, Raven 1250 (particle size 23 nm, BET value 135.0 m ² / g, DBP oil absorption 58.0 ml / 100 g), 1255, manufactured by Columbian Carbon Co., Ltd. (Particle size 23 nm, BET value 125.0 m ² / g, DBP oil absorption 58.0 ml / 100 g), 1020 (particle size 27 nm, BET value 95.0 m ² / g, DBP oil absorption 60.0 ml / 100 g), 1080 (Particle size 28 nm, BET value 78.0 m ² / g, DBP oil absorption 65.0 ml / 100 g), Raven 1035, Raven 1040, Raven 1060, Raven 3300, Raven 450, Raven 780, etc., or CONDUCTEX SC (particle size 20 nm, BET value 220.0m ² / g, DBP oil absorption amount 115 0ml / 100g) any good.
Also, Asahi Carbon Co., Ltd. # 80 (particle size 23 nm, BET value 117.0 m ² / g, DBP oil absorption 113.0 ml / 100 g), Mitsubishi Kasei # 22B (particle size 40 nm, BET value 5.0 m ² / g) , DBP oil absorption 131.0 ml / 100 g), # 20B (particle size 40 nm, BET value 56.0 m ² / g, DBP oil absorption 115.0 ml / 100 g), Cabot Corporation Black Pearls L (particle size 24 nm, BET value 250.0 m ² / g, DBP oil absorption 60.0 ml / 100 g), Black Pearls 800 (particle size 17.0 nm, BET value 240.0 m ² / g, DBP oil absorption 75.0 ml / 100 g), Black Pearls 1000, Black Pearls 1100, Black Pearls 700, Black Pearls 905, or the like may be used.
Further, as carbon having a larger particle diameter, MT carbon (Colombian Carbon Co., particle diameter 350 nm), Thermax MT, etc. can be used.

  As the antistatic agent, known antistatic agents such as natural surfactants, nonionic surfactants, and cationic surfactants can be used in addition to the above-described carbon black.

Next, the abrasive will be described.
Examples of the abrasive include α-alumina, β-alumina, γ-alumina, α-alumina of 90% or more, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, oxide Needle-like α obtained by dehydrating and annealing titanium, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, and magnetic iron oxide Iron oxide and, if necessary, surface-treated with aluminum and / or silica are used alone or in combination.
The particle size of these non-magnetic powders is usually in the range of 0.01 to 2 μm, preferably 0.015 to 1.00 μm, more preferably 0.015 to 0.50 μm. Nonmagnetic powders of different sizes can be combined, or even a single nonmagnetic powder can have the same effect by widening the particle size distribution.
The tap density is 0. It shall be 05-2 g / cc, Preferably it shall be 0.2-1.5 g / cc.
The specific surface area is 1 to 200 m ² / g, preferably 5 to 100 m ² / g, and more preferably 7 to 80 m ² / g.
The crystallite size is in the range of 0.01 to 2 μm, preferably 0.015 to 1.00 μm, more preferably 0.015 to 0.50 μm.
The oil absorption amount using DBP is usually 5 to 100 ml / 100 g, desirably 10 to 80 ml / 100 g, and more desirably 20 to 60 ml / 100 g.
Specific gravity shall be 1-12, preferably 2-8.
The particle shape may be spherical, dice, or plate.
In addition, the nonmagnetic powder used as an abrasive does not necessarily need to be 100% pure, and the surface may be treated with another compound depending on the purpose. At that time, if the purity is usually 70% or more, the effect is not reduced. For example, when titanium oxide is used, it is generally used to treat the surface with alumina.
The ignition loss is desirably 20% or less.
The Mohs hardness of the nonmagnetic powder of the abrasive is preferably 6 or more.

As the abrasive, for example, a known material having a Mohs hardness of 6 or more can be used alone or in combination, with α-alumina, β-alumina, fused alumina, titanium oxide and the like as main components. .
Specific examples of abrasives that can be used in the present invention include UA5600, UA5605, Showa Denko AKP-20, AKP-30, AKP-50, HIT-50, HIT-100, ZA-G1, Nippon Chemical Industry, manufactured by Sumitomo Chemical. G5, G7, S-1, manufactured by Toda Kogyo Co., Ltd. TF-100, TF-120, TF-140, DPN250BX, DBN270BX, Ishihara Sangyo TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO -55S, TTO-55D, FT-1000, FT-2000, FTL-100, FTL-200, M-1, S-1, SN-100, Titanium Industry ECT-52, STT-4D, STT-30D, STT-30, STT-65C, Mitsubishi Materials T-1, Nippon Shokubai NS-O, NS-3Y, NS-8Y, manufactured by Teika T-100S, MT-100T, MT-150W, MT-500B, MT-600B, MT-100F, Sakai Chemical's FINE X-25, BF-1, BF-10, BF-20, BF-1L, BF- 10P, Dowa Mining DEFIC-Y, DEFIC-R, and Titanium Industry Y-LOP.

Next, the lubricant will be described.
A conventionally known material can be applied as the lubricant. For example, higher fatty acid esters, silicone oils, fatty acid-modified silicones, fluorine-containing silicones, or other fluorine-based lubricants, polyolefins, polyglycols, alkyl phosphate esters, and metal salts, polyphenyl ethers, fluorinated alkyl ethers, alkyl carboxylic acids Amine-based lubricants such as amine salts and fluorinated alkyl carboxylic acid amine salts, and alcohols having 12 to 24 carbon atoms (which may be unsaturated or branched, respectively), higher grades having 12 to 24 carbon atoms Any fatty acid can be applied.

Further, as the higher fatty acid ester component, higher fatty esters having 12 to 32 carbon atoms (which may be either unsaturated or branched) may be used. For example, lauric acid, myristic acid, palmitic acid, stearin Acid, isostearic acid, arachidic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid, linolenic acid, etc. methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, pentyl ester, hexyl ester, heptyl Ruester, octyl ester and the like. Specific examples of the compound include butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, butoxyethyl stearate, octyl myristate, isooctyl myristate, butyl palmitate and the like.
The lubricant may be used alone, or a plurality of lubricants may be mixed and applied.

In order to improve durability, the magnetic layer 3 preferably contains an isocyanate curing agent having an average functional group number of 2 or more.
In addition, both the polymeric body of polyisocyanate and the polyol adduct of polyisocyanate can be used. Among them, isocyanurate having a cyclic skeleton which is a trimer of diisocyanate is a more reactive curing agent and has a high durability improving effect.

Examples of isocyanate curing agents include aromatic polyisocyanates and aliphatic polyisocyanates, and adducts of these with active hydrogen compounds are preferred.
Aromatic polyisocyanates include toluene diisocyanate (TDI), 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), p-phenyl diisocyanate, m-phenyl diisocyanate, 1, Examples include 5-naphthyl diisocyanate.
Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, and isophorone diisocyanate (IPDI).
Active hydrogen compounds that form adducts with these include ethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane, glycerin, and the like, with an average molecular weight of 100 Those in the range of ~ 5000 are preferred.

The amount of the curing agent added is generally 0 to 20 parts by weight, preferably 0 to 10 parts by weight, based on the weight ratio of the binder resin.
Theoretically, the amount of the curing agent that is equivalent to the amount of isocyanate equivalent to the active hydrogen in the polyurethane resin composition (or binder resin composition) is sufficient.
However, in the actual production process, since the isocyanate of the curing agent component reacts with moisture or the like, there are many cases where a sufficient effect cannot be obtained only with an amount of isocyanate equivalent to active hydrogen. It is desirable to add a 10% to 50% excess of the curing agent.

  Further, when a curing agent made of polyisocyanate is used, stronger adhesion can be obtained by accelerating the curing reaction at a temperature of 40 ° C. to 80 ° C. for several hours after coating the magnetic paint.

Next, the solvent for adjusting the magnetic paint will be described.
Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and ethyl acetate monoethyl ether, glycol monoethyl ether and dioxane. Examples include glycol ether solvents such as benzene, toluene and xylene, aromatic hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene. .
In addition to the above, conventionally known organic solvents can be used.

Next, a method for forming the magnetic layer 3 will be described.
First, the silane coupling agent is first mixed with the magnetic powder, and in the subsequent step, a binder resin is added and diluted and dispersed in an organic solvent. Subsequently, various additives are added and further diluted and dispersed with an organic solvent to obtain a first paint.
Next, a hydroxycarboxylic acid is added to obtain a second paint, and if necessary, a polyisocyanate curing agent is added to produce a magnetic paint, which is applied onto the nonmagnetic lower layer 2 The magnetic layer 3 can be formed.

  In addition, as a method for adjusting the paint, any known method can be used. For example, a roll mill, a ball mill, a sand mill, a tron mill, a high-speed stone mill, a basket mill, a disper, a homomixer, a kneader, a continuous kneader, an extruder, a homogenizer, and an ultrasonic disperser can be used.

  In the magnetic recording medium of the present invention, a nonmagnetic backcoat layer 4 may be provided on the side opposite to the magnetic layer forming surface. The film thickness of the back coat layer is preferably 0.3 to 1.0 μm.

  In addition, before applying the paint directly on the nonmagnetic support 1, before the corona discharge treatment or the electron beam irradiation treatment on the undercoat layer such as an adhesive layer or on the nonmagnetic support 1, the coating is applied. Processing may be performed.

  As the coating method of the paint, any of conventionally known methods such as air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, gravure coating, transfer roll coating, cast coating, etc. However, the present invention is not limited to these, and a simultaneous multilayer coating method by extrusion coating may be applied.

  Further, the nonmagnetic lower layer 2 and the magnetic layer 3 may be formed by a so-called wet-on-dry method in which respective paints are sequentially applied and dried, and the nonmagnetic lower layer 2 and the magnetic layer 3 are magnetically formed on the nonmagnetic lower layer 2 in a wet state. You may form by the so-called wet-on-wet system which coat | covers the layer 3 in piles.

  The magnetic recording medium of the present invention will be described based on specific experimental results, but the present invention is not limited to the examples shown below.

[Examples 1 to 25], [Comparative Examples 1 and 2]
Based on the composition shown below, a magnetic paint for forming the magnetic layer was prepared.
(Preparation of magnetic layer coating)
Magnetic powder: 100 parts by weight (The average major axis length, coercive force, and saturation magnetization are shown in Tables 1 to 3 below.)
Vinyl chloride copolymer: 10 parts by weight (manufactured by Zeon Corporation, trade name: MR-110)
Polyester polyurethane resin: 8 parts by weight (The structure, molecular weight, and polar group are shown in Tables 1 to 3 below.)
Abrasive: 10 parts by weight (Sumitomo Chemical HIT-50)
Silane coupling agent: Variable (Specific materials and addition amounts are shown in Tables 1 to 3 below.)
Hydroxycarboxylic acid: Variable (Specific materials and addition amounts are shown in Tables 1 to 3 below.)
Polyisocyanate: 4 parts by weight (manufactured by Nippon Polyurethane Co., Ltd., trade name: Coronate L. However, polyisocyanate was mixed immediately before coating.)
Myristic acid: 1 part by weight Butyl stearate: 1 part by weight Methyl ethyl ketone: 80 parts by weight Cyclohexanone: 80 parts by weight Toluene: 80 parts by weight

The magnetic powder and the silane coupling agent are mixed with a planetary mixer, then vinyl chloride and polyurethane resin are added, and appropriately diluted with a mixed solvent of methyl ethyl ketone / cyclohexanone / toluene = 1/1/1 to obtain a solid The mixture was kneaded with three rolls at a rate of 60%.
Thereafter, the pasty paint was diluted with a mixed solvent of methyl ethyl ketone / cyclohexanone / toluene with a disper and dispersed in a sand mill together with other additives to obtain a paint liquid (first paint).
Next, hydroxycarboxylic acid was added to the first coating material, and the mixture was filtered through a 1 μm filter and stirred for 2 hours (second coating material).
And in the process just before application | coating, 4 weight part of polyisocyanate of a hardening | curing agent and 1 weight part of myristic acid were added, and it was set as the magnetic coating material.

Based on the composition shown below, a nonmagnetic paint for forming the nonmagnetic lower layer 2 was prepared.
(Preparation of coating for nonmagnetic underlayer)
α-Fe ₂ O ₃ (hematite): 100 parts by weight Average major axis length: 0.5 μm
Specific surface area: 50 m ² / g by BET method
Vinyl chloride copolymer: 15 parts by weight (manufactured by Zeon Corporation, trade name: MR-110)
Polyester polyurethane resin: 8 parts by weight (isophthalic acid / terephthalic acid / neopentyl glycol-MDI polyurethane molecular weight 25000, polar group: SO ₃ Na = 0.2 wt% contained)
Abrasive: 10 parts by weight (Alumina manufactured by Sumitomo Chemical Co., Ltd .: HIT-50)
Carbon black: 10 parts by weight (Showa Cabot Corporation: BP-L)
Polyisocyanate: 4 parts by weight (manufactured by Nippon Polyurethane Co., Ltd., trade name: Coronate L.
However, the polyisocyanate was mixed immediately before coating. )
Stearic acid: 1 part by weight Butyrate stearate: 1 part by weight Methyl ethyl ketone: 80 parts by weight Cyclohexanone: 80 parts by weight Toluene: 80 parts by weight

The nonmagnetic coating composition described above was kneaded in a kneader, dispersed with a sand mill, and filtered through a filter having a 1 micron aperture.
Immediately before coating, 4 parts by weight of polyisocyanate and 1 part by weight of myristic acid were added to obtain a lower-layer nonmagnetic coating liquid.

Based on the composition shown below, a coating material for forming the backcoat layer 4 was prepared.
(Preparation of paint for forming back coat layer)
Carbon black: 100 parts by weight (average particle size 20 nm)
Carbon black: 5 parts by weight (average particle diameter: 350 nm)
Polyurethane resin: 25 parts by weight (polycarbonate polyol / neopentyl glycol HDI polyurethane,
(Molecular weight 35000, N-methyldiethanolamine = 0.2 wt%)
Nitrocellulose: 15 parts by weight
(Product name: NC-1 / 2H, manufactured by Asahi Kasei Corporation)
Polyisocyanate: 20 parts by weight (manufactured by Nippon Polyurethane Co., Ltd., trade name: Coronate L.
However, the polyisocyanate was mixed immediately before coating. )
Methyl ethyl ketone: 180 parts by weight Cyclohexanone: 180 parts by weight Toluene: 180 parts by weight

  The back coat layer forming material is kneaded with three rolls, then dispersed using a sand mill, added with 20 parts by weight of a polyisocyanate, filtered through a filter having an average diameter of 1 μm, and a back coat layer forming paint. did.

Each paint produced as described above is die-coated to a PEN (polyethylene naphthalate) film having a film thickness of 7.7 μm, a magnetic layer of 0.2 μm, and a nonmagnetic lower layer of 2.5 μm in thickness. The coating was applied by the -on-Wet method, and the back coat layer was further applied with a thickness of 0.7 μm, followed by drying and calendar treatment.
The resulting wide magnetic film was cured and then cut into ½ inch widths to produce video tapes.
This was incorporated into a cassette for Sony HDCAM-SR, and cassette tapes of Examples 1 to 25 and Comparative Examples 1 and 2 were produced.

  The sample tapes of Examples 1 to 25 and Comparative Examples 1 and 2 produced as described above were subjected to measurement and evaluation for each of electromagnetic conversion characteristics, still durability, running durability, blooming, and rust characteristics.

(Measurement of electromagnetic conversion characteristics)
The sample tape was incorporated into an HDCAM-SR cassette, and a digital video signal output at 77.33 MHz and C / N at 76.33 MHz were measured with a Sony HDCAM-SR video recorder (SRW-5000).
In addition, the measured value of Example 21 was set to 0 dB (reference value), and the relative value to this was used as the measured value.
Here, in the measurement of electromagnetic conversion characteristics, it was determined that the characteristics were inferior at −0.5 dB or less than the standard tape, and it was determined that the standards of various formats were not satisfied at −1.0 dB or less.

(Still durability measurement)
The sample tape incorporated in the HDCAM cassette was run in a still mode for 100 minutes in an HDCAM-SR video recorder (SRW-5000) manufactured by SONY in an environment of 5 ° C. and 15% RH. The part was visually observed and evaluated according to the following criteria.
○: Completed for 100 minutes without damage to the tape edge.
Δ: Completed for 100 minutes, but channel condition error occurred.
×: Not running for 100 minutes

(Durability measurement)
Recording and reproduction for 100 hours were performed with an HDCAM-SR video recorder (SRW-5000) manufactured by Sony, and the output waveform of the video signal was measured and evaluated according to the following criteria.
○: Video signal with no output degradation.
Δ: Output deteriorates but recovers or is within -2.0 dB.
X: A head clog occurred.

(Measurement of blooming)
The cassette tape was stored at 60 ° C. for 3 months and then allowed to stand at room temperature for 24 hours. Then, the tape surface was observed with the optical microscope, and the presence or absence of blooming was confirmed.
○: No blooming.
(Triangle | delta): The thing which generation | occurrence | production looks like a spot shape when observed with an optical microscope 50 times.
X: A thing which looks blooming like a spot visually.

(Measurement of rust characteristics)
After evaluating the blooming characteristics, electromagnetic conversion characteristics were measured, output deterioration before and after storage was measured, and evaluated according to the following criteria.
○: Within −0.2 dB Δ: −0.2 dB or more, −0.5 dB or less X: Deterioration of −0.5 dB or more.

  Tables 1 to 1 below show the measurement evaluation results for the magnetic layer compositions, electromagnetic conversion characteristics, still durability, running durability, blooming, and rust characteristics of the sample tapes of Examples 1 to 25 and Comparative Examples 1 and 2. 3 shows.

  In Examples 1 to 5 produced by the method of the present invention, practically sufficient evaluation was obtained for each of the electromagnetic conversion characteristics, still durability, running durability, blooming, and rust characteristics. In Examples 4 and 5 in which the long axis length of the powder was 100 nm or more, the output was slightly lowered and the electromagnetic conversion characteristics were slightly deteriorated because it was not suitable for recording a short wavelength signal.

In Examples 6 to 10, the coercive force Hc and the saturation magnetization σs of the magnetic powder are changed. From these results, the higher the coercive force Hc and the saturation magnetization σs, the better the output. I found out that
Here, in Example 9, although a magnetic powder having a saturation magnetization σs of 200 Am ² / kg was used, output degradation of −0.5 dB was observed after confirmation of blooming characteristics. This is because if the saturation magnetization is too high, the corrosion resistance deteriorates and the rust characteristics deteriorate.

In Examples 11 to 15, the amount of the silane coupling agent added to the magnetic layer was changed. From these results, when the amount was less than 1 part by weight, the output decreased, and 5 parts by weight or more. Then, blooming was found to occur.
From this result, it was found that the addition amount of the silane coupling agent is preferably 1 part by weight or more and less than 5 parts by weight.

In Examples 16 to 19, the amount of hydroxycarboxylic acid added to the magnetic layer was changed. From these results, when the amount was 0.5 parts by weight or less, the output decreased, and 5 parts by weight was reduced. It was found that blooming was observed beyond this.
From this result, it was found that the effective addition amount of hydroxycarboxylic acid is preferably 0.5 parts by weight or more and 5 parts by weight or less.

  In Example 20 and Example 21, the polar group of the urethane binder of the binder was changed. From these results, the tertiary amine-based polar group was compared with the output from the sulfonic acid sodium salt. It has been found that a better effect can be exhibited.

In Examples 22 to 25, all are samples prepared according to the present invention, but these are all about electromagnetic conversion characteristics and still durability, running durability, blooming, and rust characteristics. Evaluation sufficient for practical use was obtained.
In particular, in Examples 24 and 25, extremely fine magnetic powders having an average major axis length of 45 nm and 30 nm were applied, but in these, extremely excellent electromagnetic conversion characteristics could be realized.

  Comparative Example 1 is an example in which hydroxycarboxylic acid was not contained in the magnetic layer, but in this case, the output decreased and the electromagnetic conversion characteristics deteriorated. Further, the still durability was extremely deteriorated, and a practically sufficient evaluation could not be obtained.

  Comparative Example 2 is an example in which the silane coupling agent was not contained in the magnetic layer. In this case, the dispersion of the paint was remarkably deteriorated, and the electromagnetic conversion characteristics were deteriorated. Further, both the still durability and the running durability were extremely deteriorated, and a practically sufficient evaluation could not be obtained.

1 is a schematic sectional view of a magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 2 ... Nonmagnetic lower layer, 3 ... Magnetic layer, 4 ... Backcoat layer, 10 ... Magnetic recording medium

Claims (4)

On the nonmagnetic support, a nonmagnetic lower layer in which nonmagnetic powder is dispersed in a binder is formed, and then a magnetic paint is applied on the nonmagnetic lower layer to form a magnetic layer.
The magnetic coating comprises a magnetic powder, by mixing the silane-coupling agent, followed by making the first coating material by mixing the binding agent resin,
To prepare a second coating material by adding hydroxycarboxylic acid to the first coating material,
Wherein the second coating material, manufacturing method of the magnetic recording medium are those prepared by adding an isocyanate-based curing agent. The magnetic powder in the magnetic layer is
The coercive force Hc is 200 kA / m or more,
Saturation magnetization σs is 120 Am ² / kg or more,
Particle size below 100 nm, manufacturing method of a magnetic recording medium according to the cobalt-containing magnetic metal powder der Ru請 Motomeko 1. The content of the silane coupling agent is 1 part by weight or more and less than 5 parts by weight with respect to 100 parts by weight of the magnetic powder,
The content of the hydroxycarboxylic acid, the relative magnetic powder 100 parts by weight, a method of manufacturing a magnetic recording medium according to 請 Motomeko 1 you and less than 5 parts by weight or more 0.5 part by weight . It said binder in the magnetic layer, manufacturing method of a magnetic recording medium according to 請 Motomeko 1 Ru polyurethane resins der having an amine polar group.

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