JP2523271B2 - Magnetic recording media - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly to a metal thin film type magnetic recording medium.

2. Description of the Related Art Prior Art and Problems There are active developments of magnetic recording media for video, audio, etc., which have a metal thin film type magnetic layer because of their compactness when formed into a tape and wound.

As the magnetic layer of such a metal thin film type medium, vapor deposition at a predetermined inclination angle with respect to the normal to the substrate, a Co-based film formed by a so-called oblique vapor deposition method, a Co-Ni-based vapor deposition film, or the like, There are various types such as a perpendicular magnetization film made of a Co-Cr-based sputter or vapor deposition film.

In such media, due to downsizing, long-time recording, etc.,
For example, when a thin film having a thickness of 10 μm or less is used, problems occur in terms of running property, occurrence of curl and half stretch, mechanical strength and the like.

Therefore, in order to eliminate these disadvantages, it has been proposed to provide a metal thin film reinforcing layer on the back surface of the film (JP-A-56-16939, JP-A-58-97131, and JP-A-57-78627).
No. 57-37737 etc.).

According to these proposals, the thin metal film as the backing layer improves the Young's modulus of the medium and improves the running property, curl, mechanical strength and the like.

However, in the techniques described in the above-mentioned publications, the optimum Young's modulus design has not been made, output reduction caused by head touch failure, envelope failure, etc. occur, and tape damage such as edge folds and half stretch occurs. This occurs, and further, so-called skew occurs due to storage.

Alternatively, traveling causes cracks in the magnetic layer, scratches in the magnetic layer, increased head wear, and increased dropout.

II Object of the Invention The object of the present invention is to optimize the mechanical strength of a magnetic recording medium using a metal thin film type thin film support, particularly bending rigidity and Young's modulus by forming a predetermined backing layer structure. In addition, it improves head touch, eliminates output drop and envelope defect, eliminates tape damage such as edge fold and half stretch, eliminates skew due to storage, and further improves runnability. In addition, cracks and scratches on the magnetic layer due to running are eliminated, head wear is reduced, and dropout is reduced.

III Disclosure of the Invention Such an object is achieved by the present invention described below.

That is, the first invention has a magnetic layer of a ferromagnetic metal thin film on one surface of a plastic film having a thickness of 10 μm or less, and fine particles having an average particle size of 50 to 5000 Å are arranged on the other surface, There is a lining layer on top of this, and the bending stiffness value of the medium is also
When EI is calculated by the following formula, EI is 3.0 × 10 ^{-3 to} 1.2 ×
The magnetic recording medium is characterized by having a concentration of 10 ⁻² g · cm.

formula (W is the radius ac produced by cutting the magnetic sheet.
Radial displacement d = 0.2πa for a ring-shaped test piece of m and width bcm
Is the load that causes The second invention has a magnetic layer of a ferromagnetic metal thin film on one surface of a plastic film having a thickness of 10 μm or less, and fine particles having an average particle size of 50 to 5000 Å are arranged on the other surface. Then, it has a backing layer on it, and has a backing layer on this backing layer, and when the bending stiffness value EI of the medium is calculated by the following formula,
The magnetic recording medium is characterized by having an EI of 3.0 × 10 ^{−3 to} 1.2 × 10 ⁻² g · cm.

formula (W is the radius ac produced by cutting the magnetic sheet.
Radial displacement d = 0.2πa for a ring-shaped test piece of m and width bcm
Is the load that causes ) Furthermore, the third invention has a magnetic layer of a ferromagnetic metal thin film on one surface of a plastic film having a thickness of 10 μm or less, a surface layer on the magnetic layer, and another surface on the other surface. ,
Fine particles having an average particle size of 50 to 5000 Å are arranged, a backing layer is provided on the backing layer, and a backing layer is provided on the backing layer. When the bending rigidity value EI of the medium is calculated by the following formula, EI is 3.0 × 10 ^-3 ~ 1.2
The magnetic recording medium is characterized by having a ^{density of} × 10 ^-2 g · cm.

formula (W is the radius ac produced by cutting the magnetic sheet.
Radial displacement d = 0.2πa for a ring-shaped test piece of m and width bcm
Is the load that causes Note that none of the above publications matches the flexural rigidity value of the present invention. Slightly close to this, Sample 3 of Example 1 of JP-A-56-16939 describes a composite Young's modulus of 1340 Kg / mm ² , and an estimated bending rigidity value EI of about 2.9 g · cm. Is.

The above-mentioned bending rigidity value range in the present invention is critical, and as will become apparent from the later description, the effect of the present invention cannot be realized if it is out of this range.

IV Specific Configuration of the Invention Hereinafter, the specific configuration of the present invention will be described in detail.

The magnetic recording medium of the present invention has a magnetic layer on a non-magnetic plastic film.

The magnetic layer may be a variety of continuous thin film type ferromagnetic metal thin films.

Ferromagnetic metal thin films include iron, cobalt, nickel and other ferromagnetic metals, or Fe-Co, Fe-Ni, Co-Ni, Fe-
Rh, Fe-Cu, Fe-Au, Co-Cu, Co-Au, Co-Y, Co-L
a, Co-Pr, Co-P, Co-Gd, Co-Sm, Co-Pt, Ni-C
u, Co-Ni-P, Fe-Co-Nd, Mn-Bi, Mn-Sb, Mn-A
Magnetic alloys such as l, Fe-Co-Cr, and Co-Ni-Cr can be cited.

Alternatively, CoCr, Co, which is known as a perpendicular magnetization film,
V, CoNiP, CoP, MnBi, MnAlGe, NdFe, NdCo, CoO, MnS
b, MnCuBi, GdFe, GdCo, PtCo, TbCo, TbFeCo, GdFeC
Any of o, TbFeO ₃ , GdIG, GdTbFe, GdTbFeCoBi, CoFe ₂ O _{4 and the} like may be used.

Then, these magnetic layers may be directly formed on the plastic film by a method such as a vacuum vapor deposition method, a sputtering method, an ion plating method or a plating method, or may be provided via an underlayer.

In this case, in the present invention, Co is an essential component, and C
It is preferably composed of o, Co + Ni, Co + O or Co + Ni + O.

That is, it may be composed of Co alone, or may be composed of Co and Ni.

When Co + Ni, the weight ratio of Co / Ni is preferably 1.5 or more.

Further, O may be contained in addition to Co or Co + Ni. When O is contained, more preferable results can be obtained in terms of electromagnetic conversion characteristics and running durability.

In such a case, the atomic ratio of O / Co (when Ni is not included) or O / (Co + Ni) is 0.6 or less, and preferably 0.15 to 0.5.

On the other hand, in the magnetic layer, Co, Co + Ni, Co + O or Co
Inclusion of Cr in addition to + Ni + O gives even more favorable results.

This is because the electromagnetic conversion characteristics are improved, the output and the S / N ratio are improved, and the film strength is further improved.

In such a case, the weight ratio of Cr / Co (when Ni is not included) or Cr / (Co + Ni) is preferably 0.001 to 0.1.

In this case, the weight ratio of Cr / Co or Cr / (Co + Ni) is 0.00
Even more preferable results are obtained when it is 5 to 0.05.

In such a magnetic layer, other trace components, especially transition metal elements such as Fe, Mn, V, Zr, Nb and T
It may contain a, Mo, W, Ti, Cu, Zn or the like.

Generally, such a Co—Ni-based magnetic layer is preferably an aggregate of particles having a columnar crystal structure inclined with respect to the normal to the main surface of the substrate. Thereby, the electromagnetic conversion characteristics are improved.

In such a case, the particles having a columnar crystal structure are preferably tilted within a range of 20 to 60 ° with respect to the normal line of the main surface of the substrate.

Each columnar crystal particle usually has a length over the entire area in the thickness direction of the magnetic layer, and its minor axis is generally about 50 to 500 °.

Then, Co and Ni, Cr, etc., which are added as necessary, constitute the columnar crystal particles themselves, and when O is added, O is usually mainly present on the surface of each columnar crystal particle mainly as an oxide. Exists in the form of.

Such a Co—Ni based magnetic layer is usually formed by the oblique vapor deposition method.

As the oblique deposition method to be used, a known oblique deposition method may be used, and the minimum value of the incident angle with respect to the normal to the substrate is preferably 30 ° or more.

The vapor deposition conditions and the post-treatment method may be according to known conditions and methods. In this case, effective post-treatment methods include known treatment methods for introducing O into the magnetic layer.

The thickness of such a magnetic layer is usually 0.05 to 0.5 μm, more preferably 0.1 to 0.25 μm in terms of electromagnetic conversion characteristics.

In this case, the magnetic layer may be directly provided on the plastic film, or may be provided on the plastic film via an underlayer.

Also, the magnetic layer is usually formed as a single layer,
Depending on the case, it may be formed by laminating a plurality of layers via an intermediate layer.

Such a magnetic layer is, for example, a polyester film,
It can be formed on various plastic films such as polyamide film and polyimide film by the method described above.

The thickness of the plastic film used in the present invention is 10 μm
The following, preferably 5 to 10 μm, more preferably 6 to 10 μm
m, most preferably 6 to 8 μm.

If the thickness exceeds 10 μm, the objectives of downsizing the medium and recording for a long time cannot be achieved. If this thickness is too thin, the bending rigidity value EI of the medium described below will be too small to fall outside the setting range of the present invention, and problems such as runnability and output reduction will not be solved, and even if a backing layer described below is required. Even if it is made thicker than above and the EI value is within the setting range of the present invention,
In this case, the magnetic surface may be damaged, the head may be worn out more easily, and the output may not be stable.

Fine particles are arranged on the other surface of the plastic film on which the magnetic layer is not provided.

The fine particles to be arranged are 50 to 5000 Å, more preferably 80
It has an average particle size of ~ 2000Å.

If the average particle size exceeds 5000Å, the inconvenience that the electromagnetic conversion characteristics of the medium deteriorates due to the backside transfer to the magnetic surface,
On the other hand, if it is less than 50Å, the running friction coefficient becomes large, the durability running property of the medium deteriorates, and there is a problem that it cannot be put to practical use.

The fine particles may be arranged uniformly on the substrate at a constant density, or may be arranged sparsely and densely with a constant period, and is not particularly limited. In the present invention,
The average arrangement density of the fine particles is preferably 10 ⁵ to 10 ⁹ particles / mm ² , and more preferably 2 × 10 ⁶ to 10 ⁹ particles / mm ² .

When the density is less than 10 ⁵ pieces / mm ² , the running friction coefficient becomes large, the durability running property of the medium deteriorates, and there is a disadvantage that it cannot be put to practical use.

Further, if the density exceeds 10 ⁹ pieces / mm ² , there is an inconvenience that the dropout increases.

The average arrangement density is usually an average value of two or more points in the visual field of about 0.5 μm ^{2 to 1} mm ² .

Further, the height of the protrusions formed on the back surface of the medium due to the disposition of such fine particles is set to about 20 to 5000Å, particularly about 50 to 2000Å.

The fine particles used are generally known as colloidal particles, and include, for example, SiO ₂ (colloidal silica), Al ₂ O ₃ (alumina sol), Cr ₂ O ₃ , Y ₂ O ₃ , CeO ₂ ,
MgO, TiO ₂ , SnO ₂ , Sb ₂ O ₅ , ZnO, Fe ₂ O ₃ , Fe ₃ O ₄ , zirconia, ZrSiO ₄ , CdO, NiO, CaWO ₄ , CaCO ₃ , BaCO ₃ , CoC
O ₃ , BaTiO ₃ , Ti (titanium black), Au, Ag, Cu, Ni,
Fe, various hydrosols, resin particles and the like can be used.
In this case, it is particularly preferable to use an inorganic substance.

These fine particle pigments are, for example, in the case of SiO ₂ , 1) ultrafine particle colloidal solution of silicic acid anhydride (Snowtex, water system, methanol silica sol, Nissan Chemical) 2) ultrafine particle anhydrous silica produced by combustion of purified silicon tetrachloride (Standard product 100Å) (Aerosil, Nippon Aerosil Co., Ltd.) and the like.

Further, the ultrafine particle colloidal solution of 1), and 2)
The ultrafine particulate aluminum oxide produced by the vapor phase method similar to the above, as well as titanium oxide and the above-mentioned particulate pigment may be used.

Such fine particles are used as a coating liquid using various solvents,
This may be coated and dried on a plastic film substrate, or a coating solution to which a resin component such as various aqueous emulsions is added may be coated and dried.

Further, it is possible to provide a gentle protrusion by superimposing it on a fine protrusion based on these fine particles.

The undercoat layer for disposing the fine particles preferably contains a binder component.

In some cases, an undercoat layer may be formed on the substrate before disposing the fine particles.

In such a case, it is particularly preferable that the undercoat layer contains a compound having at least two double bonds sensitive to radiation in one molecule and a crosslinked structure is formed in the undercoat layer by irradiation with radiation.

Since it has two or more radiation-sensitive double bonds,
Of the ionization products generated from the compound itself or the thermoplastic compound used in combination by irradiation, mainly free radicals act as a starting species to act on the double bond of the above compound, causing a so-called radical polymerization reaction. And a complicated mesh-like three-dimensional crosslinked structure is formed. This cross-linking structure improves the solvent resistance of the undercoat layer and reduces the tackiness, and since it is cured while the thermoplastic resin used together in the cross-linking structure is included, problems such as inter-layer adhesion do not occur. . Moreover, in this case, since crosslinking can be introduced by irradiation with radiation immediately after undercoating, it is possible to prevent any winding-shaped interlayer adhesion and deformation due to heat.

As such a compound, a reactive acrylic oligomer or oligoacrylate having two or more double bonds, preferably three or more, is desirable.

Examples of acrylic acid esters and methacrylic acid esters that can be mentioned as specific examples of the acrylic compound include polyacrylates and polymethacrylates of polyhydric alcohols (here, “poly” means diacrylate or higher).

As the polyhydric alcohol, polyethylene glycol,
Polypropylene oxide, polybutylene oxide,
Polycyclohexene oxide, polyethylene oxide, propylene oxide, polystyrene oxide,
Polyoxetane, polytetrahydrofuran, cyclohexanediol, xylylenediol, di- (β-hydroxyethoxy) benzene, glycerin, diglycerin,
Neopensargyricol, trimethylolpropane, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitan, sorbitol, butanediol, butanetriol, 2-ptene-1,4-diol, 2-n-butyl-2-ethyl -Propanediol, 2-butene-1,4-diol, 3-chloro-1,2-propanodiol, 1,4-cyclohexanedimethanol,
3-cyclohexene-1,1-dimethanol, decalin diol, 2,3-dibunim-2-butene-1,4-diol,
2,2-diethyl-1,3, propanediol, 1,5-dihydroxy-1,2,3,4-naphthahydronaphthalene, 2,5-dimethyl-2,5-hexanediol, 2,2-dimethyl- 1,3-
Propanediol, 2,2-diphenyl-1,3-propanediol, dodecanediol, mezoerythritol, 2-
Ethyl-1,3-hexanediol, 2-ethyl-2-
(Hydroxymethyl) -1,3-propanediol, 2-
Ethyl-2-methyl-1,3-propanediol, heptanediol, hexanediol, 3-hexene-2,5-
Diol, hydroxybenzyl alcohol, hydroxyethyl resorcinol, 2-methyl-1,4-butanediol, 2-methyl-2,4-pentanediol, nonanediol, octanediol, pentanediol, 1-phenyl-1,2-entane Diol, propanediol,
2,2,4,4-tetramethyl-1,3-cyclobutanediol,
2,3,5,6-tetramethyl-p-xylene-α, α'-diol, 1,1,4,4-tetraphenyl-1,4-butanediol, 1,1,4,4-tetraphenyl -2-butyne-1,4-
Diol, 1,2,6-trihydroxyhexane, 1,1'-bi-2-naphthol, dihydroxynaphthalene, 1,1'-
Methylenedi-2-naphthol, 1,2,4-benzenetriol, bifnynol, 2,2'-bis (4-hydroxyphenyl) butane, 1,1-bis (4-hydroxyphenyl) cyclohexane, bis (hydroxyphenyl) methane , Catechol, 4-chlororesorcinol, 3,4-dihydroxyhydrocinnamic acid, hydroquinone, hydroxybenzyl alcohol, methylhydroquinone, methyl-2,4,6-trihydroxybenzoate, phloroglucinol, hirogallol, resorcinol, glucose, α -(1-Aminoethyl) -p-hydroxybenzyl alcohol, 2-amino-2-ethyl-
1,3-propanediol, 2-amino-2-methyl-1,3
-Propanediol, 3-amino-1,2-propanediol, N- (3-aminopropyl) -diethanolamine, N, N'-bis- (2-hydroxyethyl) piperazine, 2,2-bis (hydroxymethyl) , 2,2 ', 2 "-Nitrilotriethanol, 2,2-bis (hydroxymethyl)
Propionic acid, 1,3-bis (hydroxymethyl) urea, 1,2-bis (4-pyridyl) -1,2-ethanediol, Nn-butyldiethanolamine, diethanolamine, N-ethyldiethanolamine, 3- Mercapto-1,2-propanediol, 3-piperidino-
1,2-propanediol, 2- (2-pyridyl) -1,
3-propanediol, triethanolamine, α-
(1-aminoethyl) -p-hydroxybenzyl alcohol, 3-amino-4-hydroxyphenyl, sulfone and the like.

Among these acrylic acid esters and methacrylic acid esters, preferred ones are, because of their easy availability,
Ethylene dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol dimethacrylate, dipentaerythritol pentaacrylate, glycerin triacrylate, diglycerin dimethacrylate, 1,3-propanediol acrylate , 1,
2,4-Putanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate, 1,5-pentanediol diacrylate, neopentyl glycol diacrylate, ethylene oxide-added trimethylolpropane triacrylate, and the like.

As acrylamides and methacrylamides that can be used as acrylic compounds, methylenebisacrylamide and methylenebismethacrylamide,
Ethylenediamine, diaminopropane, diaminobutane, pentamethylenediamine, hexamethylene, bis (2-aminopropyl) amine, diethylenetriaminediamine, hebutamethylenediamine, octamethylenediamine, polyamines interrupted by heteroatoms, polyamines having a ring [eg Phenylenediamine, xylylenediamine, β- (4-aminophenyl) ethylamine, diaminobenzoic acid, diaminotoluene, diaminoanthraquinone, diaminofluorene, etc.] and polymethacrylamide.

Also, two or more different addition-polymerizable unsaturated bonds such as N-β-hydroxyethyl-β- (methacrylamido) ethyl acrylate, N, N-bis (β-methacryloxyethyl) acrylamide, allyl methacrylate, etc. The compound having is also suitable as the acrylic compound for the undercoat layer.

Further, as an acrylic compound that can be used, there is a polyester strong polymer having various degrees of polymerization obtained by a reaction of trimethylolpropane monoacrylate, hexanediol and adipic acid. In this case, a diacrylate of an aliphatic polyol such as pentaerythritol or a diacrylate of an alicyclic diglycidyl ether may be used instead of trimethylolpropane monoacrylate. Also, instead of hexanediol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, diethylene glycol,
Dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol,
Ethylene oxide adducts and propylene oxide adducts of bisphenol A, ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like may be used. Trimethylolethane, trimethylolpropane, glycerin,
A small amount of tri- and tetraols such as pentaerythritol may be used together. Further, in place of adipic acid, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid; aromatic oxycarboxylic acids such as p-oxybenzoic acid and p- (hydroxyethoxy) benzoic acid Aliphatic carboxylic acids such as succinic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid may be used.
In this case, when the aromatic carboxylic acid and the aliphatic carboxylic acid are used in combination, the molar ratio thereof is 50/50 to 100/0, and at least 30 mol% of the aromatic carboxylic acid may be terephthalic acid. desirable. A small amount of tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid may be used in combination. The acid component such as adipic acid may be replaced with an aromatic or aliphatic diisocyanate such as tolylene diisocyanate to obtain polyurethane. Further, the molar ratio of the acrylate to the polyol is preferably 80/20 to 10/90 when the acrylate is a monoacrylate and 40/60 to 5/95 when the acrylate is a diacrylate.

These radiation-sensitive compounds may be used by being mixed with a thermoplastic resin such as polyurethane, polyester, rubber (for example, AB) for improving flexibility and adhesiveness. This thermoplastic resin may or may not be acrylic-modified (double bond is introduced). Further, among the radiation-sensitive compound, the active hydrogen group (e.g., -OH, -COOH, -NH ₂₎ those having the thermoplastic resin with a functional group e.g., with -OCN, an -OH or the like at the terminal This reaction product may be used by reacting with polyurethane or a polyester having -OH at the terminal or an acrylonitrile-butadiene-based polymer.

The radiation-sensitive compound used in the undercoat layer may be the above-mentioned acrylic compound or the above-mentioned reaction product. In either case, the molecular weight per acrylic double bond is 200 to 20,000. desirable. That is, the molecular weight is 2
If it is less than 00, the crosslinking reaction proceeds too fast to form a hard and brittle coating film, which is problematic in terms of adhesion and the like. If the molecular weight exceeds 20,000, it becomes difficult to grow the three-dimensional network structure sufficiently.

As the above-mentioned radiation for irradiating the undercoat layer, electron beam, neutron ray, ionizing radiation such as γ ray is used, and its irradiation amount is preferably 1 to 10 Mrad, more preferably 1 to 7 Mrad, and its irradiation energy (acceleration It is recommended that the voltage) be 100 kv or higher. This dose is sufficient to cause the radical reaction described above.

This radiation treatment of the undercoat layer is preferably performed after coating and drying and before winding, but it may be performed after winding.

Further, specifically, the undercoat layer contains 2 (meth) acryloyl groups in one molecule.
More than one, and the number of molecules per (meth) acryloyl group is
It is preferably formed by irradiation with a radiation curable coating material containing one or more oligomers or polymers of 200 or more, and optionally a solvent or a photopolymerization initiator.

Therefore, a coating film having a three-dimensional network structure is formed by radical polymerization.

Further, since it has one or two or more kinds of oligomers or polymers having a molecular weight of 200 or more, there is no large volume shrinkage during the cross-linking curing reaction, there is no curling of the substrate made of a plastic film, good dimensional stability, and good adhesiveness. .

 There is no evaporation and scattering during drying and curing.

Examples of the compound include: I A compound having 2 or more moles of a reaction product of a (meth) acrylic ester monomer having a group having reactivity with an isocyanate group and a polyisocyanate compound, and a compound having two or more hydroxyl groups in a molecule. A reaction product with 1 mol or a reaction product obtained by changing the reactivity of these three members, for example, a bifunctional polyether obtained by adding propylene glycol to propylene glycol (Ateca polyether P-1000 Asahi Denka Co., Ltd.). 1 mol of toluene diisocyanate is reacted with 1 mol, and then 2 mol of 2-hydroxyethyl methacrylate is reacted, and a resin having two acrylic double bonds at the terminal of the molecule, a fleholimer, an oligomer or a telomer is mentioned. You can

Here, as the compound containing one or more hydroxyl groups used, Adeka polyether P-700, Adeka polyether P-1000, Adeka polyether G-1500 (all manufactured by Asahi Denka Co., Ltd.), Polymeg 1000, and Polymeg 650. (These are Quarker Coates Co.) and other polyfunctional polyethers; fibrin derivatives such as nitrocellulose, acetylcellulose and ethylcellulose; some kens having hydroxyl groups such as vinylite VAGH (US Union Carbide) Vinyl chloride-vinyl acetate copolymer; polyvinyl alcohol; polyvinyl formal; polyvinyl butyral; polycaprolactone PCP-0200, polycaprolactone PCP-
Polyfunctional polyester polyols such as 0240, polycaprolactone PCP-0300 (all manufactured by Chisso Corporation); saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, adibic acid, succinic acid, sebacic acid, and ethylene glycol. , Diethylene glycol, 1,4-butanediol,
Ester bond with polyhydric alcohols such as 1,3-butanediol, 1,2-propylene glycol, dipropylene glycol, 1,6-hexane glycol, neobenthyl glycol, glycerin, trimethylolfroban, and Ventaerythritol A saturated polyester resin obtained by
An acrylic polymer containing at least one or more of a hydroxyl group-containing acrylic ester and methacrylic ester can be mentioned.

As the polyisocyanate compound used here, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,4-xylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, hexamethylene diisocyanate,
There are iso-olon diisocyanate, Desmodur L, Desmodur IL (made by West Germany Bayer).

Examples of the monomer having a group that reacts with an isocyanate group and a radiation-curable unsaturated double bond include 2-hydroxyethyl ester of acrylic acid or methacrylic acid, 2
-Hydroxypropyl ester, 2-hydroxyoctyl ester and other esters having a hydroxyl group; Acrylic amide, methacrylic amide, N-methylol acrylate and the like, which has active hydrogen that reacts with isocyanate groups and which contains an acrylic double bond Further, allyl alcohol, maleic acid polyhydric alcohol ester compound, mono- or diglyceride of long-chain fatty acid having unsaturated double bond, etc., and unsaturated double bond having active hydrogen which reacts with isocyanate group and having radiation curability Monomers containing are also included.

II A reaction product of one molecule of a compound containing two or more epoxy groups in a molecule and two or more molecules of a monomer having an epoxy group-reactive group and an electron beam-curable unsaturated double bond, for example, glycidyl methacrylate. A resin or prepolymer in which an acrylic double bond is pentacted in the molecule by reacting acrylic acid with a thermoplastic resin containing an epoxy group obtained by radical polymerization of carboxylic acid, and by ring-opening reaction between a carboxyl group and an epoxy group. Or an oligomer can be mentioned.

Examples of the compound containing two or more epoxy groups in the molecule include homopolymers of acrylic ester or methacrylic ester containing epoxy groups such as glycidyl acrylate and glycidyl methacrylate, or copolymers with other polymerizable monomers; Ebicoat 828, Shrimp coat 100
1, Shrimp Coat 1007, Shrimp Coat 1009 (all manufactured by Shell Chemical Co., Ltd.), and other various types of epoxy resin.

Examples of the monomer having a group that reacts with an epoxy group and a radiation-curable unsaturated double bond include acrylic monomers having a carboxyl group such as acrylic acid and methacrylic acid, methylaminoethyl acrylate, and methylaminomethacrylate. An acrylic monomer having a primary or secondary amino group such as g.

III Compound 1 containing one or more carboxyl groups in the molecule
A reaction product of a molecule and one or more molecules of a monomer having a group reactive with a carboxyl group and a radiation-curable unsaturated double bond,
For example, glycidyl methacrylate is reacted with a thermoplastic resin containing a carboxyl group obtained by solution polymerization of methacrylic acid, and an acrylic double bond is formed in the molecule by ring-opening reaction of a carboxyl group and an epoxy group in the same manner as in Section II. The introduced resin, prepolymer and oligomer can be mentioned.

Examples of the compound having one or more carboxyl groups in the molecule include polyesters having a carboxyl group in the molecular chain or at the terminal of the molecule; radically polymerizable such as acrylic acid, methacrylic acid, maleic anhydride and fumaric acid, and It is a homopolymer of a monomer having a carboxyl group or a copolymer with another polymerizable monomer.

Glycidyl acrylate, glycidyl methacrylate, and the like are examples of the monomer having a group reactive with a carboxyl group and a radiation-curable unsaturated double bond.

A non-reactive solvent is used if necessary. The solvent is not particularly peeled off, but is appropriately selected in consideration of the solubility of the binder and the compatibility. For example, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, ethyl formate, ethyl acetate, esters such as butyl acetate, alcohols such as methanol, ethanol, isopropanol, butanol, toluene,
Aromatic hydrocarbons such as xylene and ethylbenzene, ethers such as isopropyl ether, ethyl ether and dioxane, and furans such as tetrahydrofuran and furfural are used as a single solvent or a mixed solvent thereof.

A lining layer is provided on the surface on which the fine particles are arranged.

The backing layer is preferably a thin film of a single metal such as Al, Cu, W, Mo, Cr and Ti, an alloy containing these, or an oxide thereof.

Among the above metals, it is particularly preferable to use non-magnetic ones. The reason is that, for example, when the backing layer is made of magnetic metal, when the magnetic surface is wound in a magnetized state, the backing layer is magnetized by the leakage flux of the magnetic layer, or the backing layer is magnetized. This is because if the magnetic surface is re-recorded and then rewound, the magnetism of the backing layer disturbs the magnetization state of the magnetic surface, which may cause problems such as increased noise.

The method of forming the lining layer is, for example, vacuum thin film forming method such as vapor deposition, sputtering, ion plating, and various CVs.
A vapor phase growth method such as D or a plating method may be used.

The thickness of the backing layer thus formed is 0.05-1.5μ.
m, more preferably 0.07 to 0.9 μm, and even more preferably 0.07 to 0.7 μm. If this film thickness exceeds 1.5 μm, it exceeds the bending rigidity value range described below, and if it is less than 0.05 μm, it falls below the bending rigidity value range described below, causing the disadvantages described below.

The above-mentioned fine particles are arranged on the back surface of the substrate of the plastic film of the magnetic recording medium of the present invention configured as described above, and fine projections are present on the back surface of the medium.

And, such a protrusion on the back surface of the medium corresponds to the particle diameter and can be observed with an optical microscope, and can not be measured with a stylus type surface roughness meter, but can be observed with a scanning electron microscope. is there.

Such a medium of the present invention has a concentration of 3.0 × 10 ^{−3 to} 1.2 × 10 ⁻² g.
· Cm, more preferably ^{3.5 × 10 -3 ~1.0 × 10 -2} g · cm, and most preferably has a flexural rigidity EI of ^{3.5 × 10 -3 ~8 × 10 -3} g · cm.

 EI is measured as follows.

The measurement is based on y-direction load and diameter change due to loop indentation.

For the measurement, first, with the medium of the present invention, a length of 31.4
Cut out a ribbon-shaped test piece 10 of mm × width 8 mm. Then, as shown in FIG. 1 (a), the double-sided tape 20 is attached at a predetermined position on the flat plate 75, and then one end of the test piece 10 is placed on the double-sided tape 20 with the magnetic surface facing upward. Paste,
Further, as shown in FIGS. 1 (b) and (c), the test piece 10 is bent clockwise in the drawing, and finally the other end of the test piece is attached to the double-sided tape 20 so that the other end is aligned with the one end. ,
Create a ring with radius a and width b. When sticking double-sided tape,
Use double-sided tape that is cut to about 1 mm or less,
The influence of bonding was minimized. In this case, a is 5 mm. Although EI varies depending on the values of a and b, a is fixed to 2 to 5 mm and b is fixed to 3 to 8 mm.

As shown in FIGS. 1 (d) and 1 (e), this ring-shaped test piece 10 is sandwiched between flat plate-shaped plates 71 and 75 and compressed at a constant speed, especially 5 mm / min, and a displacement d = 0.2πa is obtained. Calculate the load bending stiffness EI when it occurs.

The EI is generally different in the longitudinal direction and the width direction of the plastic film wound on the roll before the magnetic layer is formed, and usually has the maximum value in the longitudinal direction. Then, this EI is a value in the tape longitudinal direction.

When such EI is less than 3.0 × 10 ⁻³ g · cm, running stability is deteriorated, a head touch failure is caused, and output reduction and envelope failure are caused. In addition, tape damage such as edge breakage and half stretch occurs. Then, run-up and jitter increase, and skew due to storage increases.

On the other hand, when the EI exceeds 2 × 10 ^-2 g · cm, cracks in the magnetic layer and scratches on the magnetic surface occur due to running. Also,
The amount of head wear increases. And dropouts increase.

The medium of the present invention having such bending rigidity may have only the fine particles and the backing layer arranged on the other surface side of the magnetic layer forming surface.

Alternatively, the backing layer may be further provided on the backing layer.

As the back surface layer, any known material can be used, and various polymer material coatings may be used, and various lubricants may be contained therein. Alternatively, a pigment, an activator or the like may be further contained.

Further, it may be a coating film of various lubricants such as fatty acids, fatty acid esters and silicones, a vapor deposition film or the like.

The back surface layer has a thickness of 2.5 μm or less, particularly about 0.3 to 1.5 μm. At this time, the bending rigidity is almost the same as when the back surface layer is not provided.

By providing such a back surface layer, the runnability is further improved.

Further, in the medium of the present invention, a surface layer may be provided on the magnetic layer to further improve the running property.

As the surface layer, various known ones can be applied, for example, various polymer material coatings, or those containing a lubricant, an antioxidant, a surfactant, inorganic fine particles or the like, or various lubricants. There is a coating film or a vapor deposition film.

 The thickness of the surface layer is about 5 to 300 liters.

It is also possible to further subject the plastic film to various undercoat treatments other than the above, or to form an undercoat layer between the plastic film and the magnetic layer or the backing layer.

According to the present invention, the bending rigidity EI is regulated within a predetermined range,
By providing fine projections on the back surface of the medium, the obtained magnetic recording medium has extremely high running stability, good head touch, and extremely low output drop and envelope defect. Also, the occurrence of tape damage such as edge breakage and half stretch is extremely small. Moreover, the occurrence of skew due to running pits, jitter, and storage is extremely small. Also, there is no reverse shape transfer at the time of winding the roll.

In addition, the occurrence of cracks in the magnetic layer and scratches on the magnetic surface due to running is extremely small, and the amount of head wear is also extremely small. And dropouts are extremely rare.

Such an effect is realized critically only in the above EI range.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail by showing specific examples of the invention.

Example 1 A polyester (PET) film having a thickness shown in Table 1 below was moved along a peripheral surface of a cylindrical cooling can to give O ₂ +.
Ar (volume ratio 1: 1) is flown at a speed of 800 cc / min and the degree of vacuum is 1.0
An alloy of Co80 and Ni20 (weight ratio) is melted in a chamber of × 10 ^-4 Torr, and only a portion with an incident angle of 90 ° to 30 ° is obliquely deposited to form a Co-Ni-O thin film with a thickness of 0.15 μm. did.

A large amount of oxygen was unevenly distributed on the interface with the base and on the surface opposite to the base. Also, the surface opposite to the base was almost entirely covered with oxide.

Hc = 1000 Oe. The average oxygen content in the film is the atomic ratio to Co and Ni. Was 40%.

The back surface of this film was coated with colloidal silica having the average particle size shown in Table 1 (0.003% solution, epoxy acrylate / polycaprolactane = 1/1, solution MEK / toluene = 1/1).

The average arrangement density of the fine particles was 25 × 10 ⁵ particles / mm ² .

Further, an Al backing layer having a thickness shown in Table 1 below was formed on the surface provided with the fine particles by vacuum vapor deposition.

If necessary, add 10% palmitic acid on the Al backing layer.
It was applied to a thickness of 0Å to form a back surface layer.

Furthermore, if necessary, add 25 myristic acid on the magnetic layer.
Å It was applied thickly to form a surface layer.

The following measurements were performed on each of the samples shown in Table 1 below formed in this way.

1) EI (g · cm) The EI in the longitudinal direction of the tape was measured by the indentation method described above.
The sample has a length of 31.4 mm and a width of b8 mm, and a is 5 mm.
And The tester is a stiffene tester (Yokohama System Research Institute Co., Ltd. model number: SFT-700 SD tensile tester)
Was used.

2) Output (dB) Measure the output of center frequency 5MHz and set sample No. 1 to 0dB.
Then, the value was calculated.

3) Output fluctuation (%) After repeatedly running 100 times on a CCD-V8 deck manufactured by Sony Corporation, the output fluctuation was measured using the sample.

When the maximum value of the output in 2) is 100%, the minimum value is%
Displayed in.

4) Envelope variation (%) After repeatedly running 100 times on a CCD-V8 deck manufactured by Sony Corporation, the envelope variation was measured using the sample.

100% maximum envelope width for each sample
The minimum value when was expressed as%.

5) Dropout (units / minute) After repeatedly running 100 times on a CCD-V8 deck manufactured by Sony Corporation, the sample was used to measure the dropout.

 The measurement standard was 15 μsec, 16 dB or more.

6) Head wear (μm) The amount of wear of the head after 100 hours of continuous running was measured 5 times with a CCD-V8 manufactured by Sony Corporation and averaged.

7) Running Naki The tape was run in an atmosphere of 40 ° C and 80% RH, and the presence or absence of pakiness was confirmed. The level difference was judged to be ⊙: none, ∘: almost none, Δ: slightly present, ×: frequent occurrence.

8) Jitter (μsec) After repeatedly running 100 times on a CCD-V8 deck manufactured by Sony Corp., the sample was used, and a jitter meter was connected to the deck used for measuring the head wear.

9) Storage skew (μsec) After storing at 60 ° C. and 80% relative humidity for 10 days, the skew was measured using the deck.

10) Tape damage After repeatedly running 100 times on a CCD-V8 deck manufactured by Sony Corporation, the tape running surface (surface on the magnetic layer forming side) was observed with an optical microscope (x50, x400).

The level difference was judged as ◎ ... almost no damage, ○ ... small damage, △ ... during damage, × ... large damage.

11) Output stability due to durability running on deck After repeatedly running 100 times with CCD-V8 deck manufactured by Sony Corporation, the output stability was measured using the sample. When there is back-side transfer to the magnetic layer, an extreme decrease in output occurs, and the level difference is judged as ⊚ ... almost no decrease in output, ∘ ... small decrease in output, Δ ...

12) Backside sliding surface damage After repeatedly running 100 times on a Sony CCD-V8 deck, using the sample, the backside sliding surface tape damage was observed with an optical microscope (× 50, × 400). I observed.

The level difference was judged as ◎ ... almost no damage, ○ ... small damage, × ... large damage.

 Table 1 shows the results.

From the results shown in Table 1, the effect of the present invention is clear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining a method of measuring a bending rigidity value.

Claims (6)

(57) [Claims] 1. A plastic film having a thickness of 10 μm or less has a magnetic layer of a ferromagnetic metal thin film on one surface, and fine particles having an average particle size of 50 to 5000 A are arranged on the other surface. A magnetic recording medium having a backing layer and having an EI of 3.0 × 10 ^{−3 to} 1.2 × 10 ⁻² g · cm when the bending stiffness value EI of the medium is calculated by the following formula. (W is the radius ac produced by cutting the magnetic sheet.
Radial displacement d = 0.2πa for a ring-shaped test piece of m and width bcm
Is the load that causes ) 2. The magnetic recording medium according to claim 1, wherein the backing layer is a film of a metal or an oxide thereof. 3. The magnetic recording medium according to claim 1, wherein the backing layer has a thickness of 0.05 μm to 1.5 μm. 4. The magnetic recording medium according to any one of claims 1 to 3, wherein the fine particle distribution density is 10 ⁵ to 10 ⁹ particles / mm. 5. A plastic film having a thickness of 10 μm or less has a magnetic layer of a ferromagnetic metal thin film on one surface, and fine particles having an average particle size of 50 to 5000 A are arranged on the other surface. When the bending stiffness value EI of the medium is calculated by the following formula, the EI is 3.0 × 10
^{-3 to} 1.2 × 10 ^-2 g · cm Magnetic recording medium. (W is the radius ac produced by cutting the magnetic sheet.
Radial displacement d = 0.2πa for a ring-shaped test piece of m and width bcm
Is the load that causes ) 6. A plastic film having a thickness of 10 μm or less having a magnetic layer of a ferromagnetic metal thin film on one surface, a surface layer on the magnetic layer, and an average particle size of 50 on the other surface. ~ 5000
Arranged fine particles A, having a backing layer thereon, having a backing layer on the backing layer, when calculating the flexural rigidity EI of the medium by the following equation, EI is 3.0 × 10 ^-3 ~ A magnetic recording medium having a ^{capacity of} 1.2 × 10 ^-2 g · cm. (W is the radius ac produced by cutting the magnetic sheet.
Radial displacement d = 0.2πa for a ring-shaped test piece of m and width bcm
Is the load that causes )