JP2866673B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly, to a magnetic tape, a magnetic disk, a magnetic drum, and a magnetic recording medium having excellent slipperiness, smoothness, and dimensional stability against temperature and humidity. The present invention relates to a magnetic recording medium useful for a magnetic card and the like.

[Problems to be solved by conventional technology and invention]

Conventionally, a magnetic recording medium in which a magnetic layer is coated on a polyethylene terephthalate (PET) film support has been widely used. However, the PET film has poor water resistance, may be hydrolyzed at high temperature and high humidity, and may not be usable. In addition, the glass transition temperature of PET is 60 to 70 ° C., and elongation or the like is apt to occur when used at a higher temperature, and the reliability is not always sufficient.

On the other hand, in recent years, the density of magnetic recording media has tended to increase, and demand for reliability thereof has increased. As one means for increasing the density, there is an evaporation method. However, the heat resistance of the PET film is insufficient, and there are problems such as oligomer precipitation.

By the way, the styrenic polymer mainly having a syndiotactic structure recently developed by the group of the present inventors is a polymer having excellent heat resistance, water resistance and dimensional stability as compared with PET, and having less oligomers. Various applications are expected.

Therefore, the present inventors have conducted intensive studies to develop a magnetic recording medium having high reliability under severe conditions such as high temperature and high humidity by using the styrenic polymer having a syndiotactic structure. .

[Means for solving the problem]

As a result, a stretched film of the styrene-based polymer or the composition thereof or a laminated film including the stretched film, wherein the linear expansion coefficient and the static friction coefficient having a magnetic layer in a certain range of the base film, It has been found that the magnetic recording medium is suitable for the purpose. The present invention has been completed based on such findings.

That is, the present invention mainly relates to a stretched film of a styrenic polymer having a syndiotactic structure or a composition thereof or a laminated film containing the stretched film, having a coefficient of linear expansion of 5 × 10 ⁻⁵ / ° C. or less and a coefficient of static friction. Is 0.3
A magnetic recording medium having a magnetic layer on at least one side of a base film that is not less than 1.0 and a surface roughness Ra of the base film on the side on which the magnetic layer is formed is 0.001 μm or more and 0.05 μm or less. is there.

In the present invention, a single-layer film composed of the above-described stretched film or a laminated film including the stretched film is used as the base film of the magnetic recording medium. The base film has a coefficient of linear expansion of 5 × 10 ⁻⁵ / ° C. or less, preferably 4 × 10 ⁻⁵ / ° C. or less, and the coefficient of static friction μs of the base film is 0.3 to 1.0 ,Preferably
0.3 to 0.9. The coefficient of static friction μs defines the surface condition of the substrate film. In particular, the coefficient of static friction μs of the surface of the substrate film opposite to the side on which the magnetic layer is formed is desirably in the above range.

In addition, the surface roughness Ra of the base film is not particularly limited, but at least one surface roughness Ra is,
It is preferably 0.001 to 0.05 μm, particularly 0.001 to 0.
04 μm is optimal. In particular, it is desirable that the surface roughness Ra of the base film on the side on which the magnetic layer is formed be within the above range.

In addition, about the humidity expansion coefficient of the base film,
Although there is no particular limitation, it is preferably 5 × 10 ⁻⁵ /% RH or less.

There are various methods for producing such a base film of the magnetic recording medium of the present invention, and specifically, the following three methods (1) to (3) can be exemplified.

(1) A composition mainly comprising a styrene polymer having a syndiotactic structure and inorganic fine particles, particularly a composition comprising 0.001 to 1% by weight of inorganic fine particles having an average particle diameter of 0.01 to 3 μm. Heat melting, extrusion, cooling solidification,
Heat, stretch and heat-treat to form a stretched film. As a result, a smooth single-layer film in which the screen composed of only the stretched film is smooth and roughened is obtained.

(2) The composition used in the above (1) and a styrene polymer having a syndiotactic structure, particularly, a residual aluminum content of 3000 ppm or less, a residual titanium content of 10 ppm or less, and a residual styrene monomer of 7000 ppm or less And heat-melting, co-extrusion, cooling and solidification, heating, stretching, and heat-treating a high-purity styrene-based polymer or a composition containing this styrene-based polymer as a main component (but not containing inorganic fine particles). Two or more stretched films are formed in a laminated state. Thereby, a smooth multi-layer (laminated) film having one surface super-smooth and the other surface roughened can be obtained.

(3) Styrene-based polymer having a syndiotactic structure, particularly, the residual aluminum content is 3000 ppm or less,
Residual titanium content is 10 ppm or less and residual styrene monomer is 7
Process of heating and melting, extruding, cooling and solidifying, heating, stretching, and heat-treating a styrene polymer having a high purity of 000 ppm or less or a composition containing this styrene polymer as a main component (but not containing inorganic fine particles). By forming a layer made of a resin or a resin composition containing inorganic ultrafine particles on at least one surface thereof by laminating, coating or vapor-depositing, one surface thereof is super smooth. A smooth multilayer film having one surface roughened can be obtained. At this time, the layer made of the resin composition may be stretched as necessary.

Here, as the resin used for lamination, a styrene-based polymer having a syndiotactic structure or various blend resins can be mainly used, but a resin having a high melting point or softening point is preferable. The type, amount, and particle size of the inorganic fine particles contained in the other resin may be the inorganic fine particles described below.

The method of laminating is not particularly limited, but the productivity is good if the method of dissolving and applying these other resins and other resin compositions besides the co-extrusion method is incorporated in the stretched film manufacturing process.

Here, particularly in a tape, the layer having the rough surface may be used as a back coat layer, and the magnetic layer is mainly provided on the opposite super smooth surface side.

The stretched film thus obtained has a thickness of 2 to 500
μm, linear expansion coefficient 5 × 10 ⁻⁵ / ° C or less, static friction coefficient μs 0.
According to the method (1), the surface roughness Ra of both surfaces is 3 to 1.0.
According to the methods of (2) and (3), both the smooth surface and the smooth surface are combined, and the surface roughness is 0.005 to 0.05 μm and 0.001 to 0.04 μm, respectively. . It is more preferable that the coefficient of humidity expansion is 5 × 10 ⁻⁵ /% RH or less.

Regarding the film thickness, a film of 2 to 20 μm is suitable for a magnetic tape, a film of 20 to 150 μm is for a magnetic disk, and a film of 100 to 500 μm is suitable for a magnetic card.

Using these films, a magnetic recording medium is prepared.If necessary, a film having improved surface adhesiveness by corona treatment or the like may be used.In addition, an adhesive layer is provided in advance on the side on which the magnetic layer is provided. May be.

By the way, the styrene polymer having a predominantly syndiotactic structure used as the film material refers to a stereochemical structure having a predominantly syndiotactic structure,
That is, it has a three-dimensional structure in which phenyl groups and substituted phenyl groups, which are side chains, are alternately located in opposite directions with respect to the main chain formed from carbon-carbon bonds, and has a tacticity of nuclear magnetism due to isotope carbon. It is quantified by the resonance method ( ^13C -NMR method). Tacticity measured by the ¹³ C-NMR method is the abundance ratio of a plurality of continuous structural units, for example, dyad in the case of two, triad in the case of three, 5
The styrene polymer having a syndiotactic structure referred to in the present invention is usually 75% or more, preferably 85% or more as a racemic diad, or a racemic pentad. so
Polystyrene, poly (alkylstyrene), poly (halogenated styrene), poly (alkoxystyrene), poly (vinylbenzoate) having a syndiotacticity of 30% or more, preferably 50% or more, A coalescent and a mixture thereof, or a copolymer containing these structural units is referred to. Here, poly (alkylstyrene) includes poly (methylstyrene), poly (ethylstyrene), poly (propylstyrene), poly (butylstyrene), poly (phenylstyrene), poly (vinylnaphthalene), and poly (vinylstyrene). Vinyl (styrene)) and poly (acenaphthylene). Poly (halogenated styrene) includes poly (chlorostyrene),
Examples include poly (bromostyrene) and poly (fluorostyrene). Examples of poly (alkoxystyrene) include poly (methoxystyrene) and poly (ethoxystyrene). Of these, particularly preferred styrene polymers include polystyrene, poly (p-methylstyrene), poly (m-methylstyrene), poly (p-tert-butylstyrene), poly (p-chlorostyrene), and poly (p-chlorostyrene). m-chlorostyrene), poly (p-fluorostyrene), and a copolymer of styrene and p-methylstyrene (JP-A-62-187708).

Further, as the comonomer in the styrenic copolymer, in addition to the styrenic polymer monomer as described above, olefin monomers such as ethylene, propylene, butene, hexene, and octene; diene monomers such as butadiene and isoprene; and cyclic diene monomers. Examples include polar vinyl monomers such as methyl methacrylate, maleic anhydride, and acrylonitrile.

The molecular weight of the styrenic polymer is not particularly limited, but is preferably 10,000 to 3,000,000, more preferably 50,000 to 1,500,000. Where the weight average molecular weight is 10,000
If it is less than 100%, stretching cannot be performed sufficiently. Further, the molecular weight distribution is not limited in its width and may be any of various types. However, the weight average molecular weight (Mw) / number average molecular weight (Mn) is preferably 1.5 or more and 8 or less. In addition,
The styrene-based polymer mainly having a syndiotactic structure has much better heat resistance than a conventional styrene-based polymer having an atactic structure.

The styrenic polymer mainly having a syndiotactic structure constituting the above-mentioned stretched film (especially, a film having an ultra-smooth surface) may be any one as described above. Titanium content is less than 10ppm and residual styrene monomer is 7000p
Those below pm are preferred. In particular, those having a residual aluminum content of 1000 ppm or less, a residual titanium content of 7 ppm or less, and a residual styrene monomer of 5000 ppm or less are optimal.

There are various methods for producing such a high-purity styrene-based polymer, and for example, it is as follows. First, in order to keep the residual aluminum content and the residual titanium content within the above ranges, a method of producing a styrenic polymer using a highly active catalyst (see Japanese Patent Application No. 63-7466).
Alternatively, a method using deashing and washing, that is,
No. 7708, etc., a styrene-based monomer obtained by polymerizing a styrene-based monomer using a group IV organometallic compound and an alkylaluminoxane such as methylaluminoxane as a catalyst component, and then obtaining a styrene-based polymer having a syndiotactic structure. Coalescing,
This is a method in which deashing is performed with a solution in which an acid or alkali is dissolved in a suitable solvent, and the resultant is washed with a suitable solvent.

In this manner or by the above method, a styrene-based polymer having a syndiotactic structure with a low residual aluminum content and a low residual titanium content can be obtained. Your body will be less than 7000 ppm.

Method for Drying the Styrenic Polymer under Reduced Pressure Here, when drying under reduced pressure, it is efficient to set the drying temperature to be equal to or higher than the glass transition temperature of the polymer.

Method for degassing the styrene-based polymer by an extruder The styrene-based polymer obtained by drying under reduced pressure by the above-mentioned styrene-based polymer or the above method is degassed by an extruder, and is simultaneously formed into a molding material (pellet). Here, the extruder is preferably provided with a vent, and a single-screw or twin-screw extruder may be used.

Through such treatment, a styrene-based polymer having a high purity syndiotactic structure with little residual aluminum, residual titanium and residual styrene-based monomer can be obtained.

On the other hand, the constituent material of the stretched film having a smooth rough surface is mainly a composition containing inorganic fine particles in a styrene-based polymer having a syndiotactic structure, in particular, an average particle size of 0.01 to 3 μm in the styrene-based polymer. Inorganic fine particles
It is a composition containing 0.001-1% by weight. The composition may be a styrene-based polymer (however, it is not necessarily required to have the high purity as described above, and may be prepared according to the method described in JP-A-62-187708). Or precipitated during polymerization.
Here, the inorganic fine particles refer to IA group, IIA group, IVA group, VIA group.
Oxides, hydroxides, sulfides, nitrides, halides, carbonates, acetates, phosphates of Group IV, VIIA, VIII, IB, IIB, IIIB, IVB elements, Shows phosphites, organic carboxylate, silicate, titanate, borate and their hydrated compounds, composite compounds centered on them, and natural mineral particles.

Specifically, group IA element compounds such as lithium fluoride, borax (sodium borate hydrate), magnesium carbonate, magnesium phosphate, magnesium oxide (magnesia), magnesium chloride, magnesium acetate, magnesium fluoride,
Magnesium titanate, magnesium silicate, magnesium silicate hydrate (talc), calcium carbonate, calcium phosphate, calcium phosphite, calcium sulfate (gypsum), calcium acetate, calcium terephthalate, calcium hydroxide, calcium silicate, calcium fluoride, titanium Group IIA element compounds such as calcium phosphate, strontium titanate, barium carbonate, barium phosphate, barium sulfate, barium phosphite, titanium dioxide (titania), titanium monoxide,
Group IVA element compounds such as titanium nitride, zirconium dioxide (zirconia) and zirconium oxide; Group VIA element compounds such as molybdenum dioxide, molybdenum trioxide and molybdenum sulfide; Group VII A element compounds such as manganese chloride and manganese acetate; Group VIII element compounds such as cobalt chloride and cobalt acetate; Group IB element compounds such as cuprous iodide; Group IIB element compounds such as zinc oxide and zinc acetate; aluminum oxide (alumina); aluminum hydroxide; , Aluminosilicate (alumina silicate, kaolin, kaolinite) and other Group IIIB element compounds, silicon oxide (silica, silica gel), graphite, carbon, graphite, glass, etc.
IV Group B element compounds, particles of natural minerals such as kernalite, kainite, mica (mica, kinunmo), and virose ore.

The average particle size of the inorganic fine particles used in the present invention is not particularly limited, but is preferably 0.01 to 3 μm, more preferably 0.01 to 3 μm.
〜1 μm, the content in the composition is 0.001-1% by weight, preferably 0.001-0.6% by weight. Where the average particle size is 0.01
If it is smaller than μm, dispersion may be difficult due to secondary agglomeration of particles, and if it is larger than 3 μm, smoothness may be reduced. On the other hand, if the content of the inorganic fine particles in the composition is less than 0.001% by weight, the effect of improving the slip property is insufficient, and if the content is more than 1% by weight, stretching with a thin material may be difficult.

In addition, the above-mentioned inorganic fine particles are effective components in achieving the object of the present invention. However, as long as the object of the present invention is not impaired, fine particles of other types or other particle sizes, inorganic fillers, and the like are used. May be included.

The inorganic fine particles used in the present invention are contained in the final molded product (film), but there is no limitation on the method of including them.
For example, a method of adding or precipitating the styrene-based monomer in an arbitrary step during the polymerization and a method of adding the styrene-based monomer in an arbitrary step of melt-extrusion may be mentioned.

Among them, particularly in the present invention, a method of adding the above-mentioned inorganic fine particles as a slurry at an arbitrary stage of the polymerization process is preferable from the viewpoint of preventing secondary aggregation of the particles.

In order to effectively disperse these fine particles, a dispersant, a surfactant and the like may be used.

The material used for the stretched film constituting the base film of the present invention may further include an antioxidant, an antistatic agent, and the like, as long as the object of the present invention is not impaired, in consideration of moldability, mechanical properties, surface properties, and the like. An agent, a flame retardant, an inorganic filler, and another resin may be appropriately compounded.

Here, there are various resins as other resins. For example, the styrene-based polymer having an atactic structure, the styrene-based polymer having an isotactic structure, and polyphenylene ether are the styrene-based polymers having a syndiotactic structure. It is easy to be compatible with coalescence, is effective in controlling crystallization when preparing a preform for stretching, improves stretchability thereafter, easily controls stretching conditions, and provides a film with excellent mechanical properties. Obtainable. Among them, when a styrenic polymer having an atactic structure and / or an isotactic structure is contained, a styrene-based polymer having a syndiotactic structure is preferably used. The content ratio of these compatible resin components may be 70 to 1% by weight, particularly preferably 50 to 2% by weight. Here, when the content ratio of the compatible resin component is more than 70% by weight, heat resistance and the like, which are advantages of the styrene-based polymer having a syndiotactic structure, are not preferable. Examples of the incompatible resin include polyolefins such as polyethylene, polypropylene, polybutene and polypentene; polyesters such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate; polyamides such as nylon-6 and nylon 6,6; and polyphenylene sulfide. Polythioether, such as polycarbonate, polyarylate, polystyrene, polyetheretherketone, polyethersulfone, polyimide, vinyl halide polymers such as Teflon, acrylic polymers such as polymethylmethacrylate, and the above-mentioned phases such as polyvinylalcohol. Except for the soluble resin, it corresponds to all, and further includes a crosslinked resin containing the above-mentioned compatible resin. Since these resins are incompatible with the syndiotactic-structured styrene-based polymer of the present invention, if they are contained in small amounts, they can be dispersed like islands in the syndiotactic-structured styrene-based polymer. , Give a good gloss after stretching,
It is effective for improving the surface slip property. The content ratio of these incompatible resin components is 50 for gloss.
~ 2% by weight, 0.001 ~
5% by weight is preferred. When the temperature used as a product is high, it is preferable to use a relatively heat-resistant incompatible resin.

The base film of the magnetic recording medium of the present invention can be formed by the method as described above, and the operation from heat melting to heat fixing performed at this time is specifically described as follows. is there.

First, the above-mentioned molding material is usually extruded (or co-extruded) to obtain a preform for stretching (film, sheet or tube). In this molding, it is common to heat-melt the above molding material into a predetermined shape using an extruder, but without heating and melting the molding material, molding in a softened state. Is also good. The extruder used here may be either a single-screw extruder or a twin-screw extruder, and may or may not have a vent, but a single-screw in-line tandem type is preferred. In addition, if an appropriate mesh is used for the extruder, impurities and foreign substances can be removed. In particular, when preparing a stretched film having a smooth surface, the mesh is preferably 100 mesh or more, and most preferably 400 mesh or more. Here, when these meshes are used, the following counts may be added before and after considering the pressure resistance and strength of the mesh itself. The shape of the mesh can be appropriately selected and used, such as a flat plate shape or a cylindrical shape.

In addition, the extrusion conditions are not particularly limited and may be appropriately selected according to various situations.Preferably, the temperature is selected in a range from the melting point of the molding material to a temperature 50 ° C. higher than the decomposition temperature, and the shear stress is determined. 5 × 10 ⁶ dyne / cm ² or less. The die to be used includes a T-die, a ring die and the like.

After the extrusion molding, the obtained preform for stretching is cooled and solidified. Various refrigerants such as gas, liquid, and metal roll can be used as the refrigerant at this time. When using metal rolls, air knives, air chambers, touch rolls,
According to a method such as electrostatic imprinting, it is effective for preventing thickness unevenness and waviness.

The temperature of cooling and solidification is usually in the range of 0 ° C. to a temperature 30 ° C. higher than the glass transition temperature of the preform for stretching, preferably 20 ° C.
C to the glass transition temperature. The cooling rate is 200
３3 ° C./sec.

Next, the cooled and solidified preform is uniaxially or biaxially stretched. In the case of biaxial stretching, the film may be stretched simultaneously in the machine direction and the transverse direction, but may be sequentially stretched in any order. The stretching may be performed in one step or may be performed in multiple steps.

Here, there are various stretching methods, such as a tenter method, a method of stretching between rolls, a method of bubbling using gas pressure, and a method of rolling, and these may be appropriately selected or combined and applied. The stretching temperature may generally be set between the glass transition temperature and the melting point of the preform. The stretching speed is usually 1 × 10 to 1
× 10 ⁵ % / min, preferably 1 × 10 ³ to 1 × 10 ⁵ % / min. When a stretched film obtained by stretching under the above-mentioned conditions requires further dimensional stability at high temperatures, heat resistance and strength balance in the film plane, it is preferable to further heat-fix. The heat setting can be carried out by a commonly used method. However, the stretched film is stretched, relaxed or restricted in a contracted state, and has a glass transition temperature to a melting point of the film, preferably 100 ° C. lower than the melting point. What is necessary is just to hold | maintain in the temperature range just before a melting point from the temperature for 0.5 to 120 seconds. The heat setting can be performed twice or more with the conditions changed within the above range.
The heat fixing may be performed in an atmosphere of an inert gas such as an argon gas or a nitrogen gas.

The thus obtained substrate film of the present invention has a linear expansion coefficient, a surface roughness Ra and a static friction coefficient μs in the above-mentioned ranges. In addition, this base film can be in various forms such as a tape shape, a disk shape, and a card shape.

The magnetic recording medium of the present invention has at least one magnetic layer formed on the above-mentioned substrate film, but may have an undercoat layer, a backcoat layer or a topcoat layer formed thereon. Each of these layers is formed on all or a part of both surfaces or one surface with the base film as the center.

Further, there are various kinds of magnetic materials as a material of the magnetic layer, for example, Co, Co-O, Co-Cr, Co-V, Co-Ni, Co-P, Co-.
γFe ₂ O ₃ , Co-Ni-P, Co-Ni-N, Co-Ni-W, Co-Ni-Pt, C
oNi (Cr) / Cr, Fe, Fe-O, Fe-Ag, γFe ₂ O ₃ , Fe-Co, Ni, CrO
_{2 and the} like can be listed.

In order to form a magnetic layer on a base film using this magnetic material, various methods such as coating, vapor deposition, sputtering, and plating may be used, and operating conditions and the like may be appropriately selected according to a conventional method.

The thickness of the magnetic layer is not particularly limited, but is generally 0.
The thickness is from 0.01 to 10 μm, particularly from 0.5 to 10 μm in the case of coating, from 0.01 to 1 μm in the case of vapor deposition or sputtering, and from 0.1 to 5 μm in the case of plating.

Examples of the resin for the binder used in the coating include a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl acetate partially saponified copolymer, and a vinyl chloride-vinyl acetate copolymer.
Vinylidene chloride copolymer, vinyl copolymers such as vinyl chloride-acrylonitrile, vinyl butyral, and vinyl formal; fibrous systems such as nitrocellulose and cellulose acetobutyrate; polycondensation systems such as saturated polyester, polyurethane polyamide and epoxy; butadiene -Synthetic rubbers such as acrylonitrile copolymers and inorganic high polymers such as polyphosphazenes may be mentioned, and a crosslinking agent such as an isocyanate compound may be used.

The surface of the magnetic recording medium of the present invention thus obtained may be polished to prevent wear of the magnetic head.

〔Example〕

 Next, the present invention will be described in more detail based on examples.

Reference Example 1 (1) Preparation of Styrenic Polymer Molding Material (Polymer Composition) Containing Inorganic Fine Particles Copper sulfate pentahydrate (CuSO ₄ .5H ₂ O) was placed in a glass container having an inner volume of 500 ml and purged with argon. 17.8 g (71 mmol), 200 ml of toluene and 24 ml (250 mmol) of trimethylaluminum were added and reacted at 40 ° C. for 8 hours. Thereafter, toluene was further distilled off from the solution obtained by removing the solid portion under reduced pressure at room temperature to obtain 6.7 g of a contact product. Its molecular weight measured by freezing point depression method was 610. The high magnetic field component of the above according to the ¹ H-NMR measurement (i.e., -0.1
(-0.5 ppm) was 43%.

On the other hand, 0.4 parts of dry silica (anilosil TT-600 manufactured by Degussa Co., Ltd. (having a primary particle diameter of 40 mμ)) was added to 100 parts of purified styrene monomer, and TK homomixer L was added.
Using a mold (manufactured by Tokushu Kika Kogyo Co., Ltd.), the mixture was stirred in a cylindrical container to obtain a styrene mixture. At this time, 0.05 parts by weight of calcium stearate was added.

A styrene mixture 1 prepared as described above, 5 mmol of the contact product obtained as described above as aluminum atoms, 5 mmol of triisobutylaluminum, 5 mmol of triisobutylaluminum, pentamethylcyclopentadienyl titanium trimethoxide were placed in a reaction vessel having an internal volume of 2. 5 at 90 ° C using 0.025 mmol
The polymerization reaction was performed for an hour. After completion of the reaction, the product was decomposed with a methanol solution of sodium hydroxide to decompose the catalyst component, washed repeatedly with methanol, and dried to obtain 308 g of a polymer.

The weight average molecular weight of this polymer measured by gel permeation chromatography at 135 ° C. using 1,2,4-trichlorobenzene as a solvent was 389,000, and the weight average molecular weight / number average molecular weight was 2.64. Was. Further, the polymer was confirmed to be a polystyrene having a syndiotactic structure by the melting point and ¹³ C-NMR measurement.

This polymer was dissolved in 1,2,4-trichlorobenzene at 130 ° C., filtered and the silica content in the polymer was determined.
It was 4 wt%. Further, this solution was dropped on a slide glass, observed with a microscope, and the average particle diameter of silica was determined to be 0.08 μm.

Further, the styrene polymer was dried at 150 ° C. for 2 hours under reduced pressure. The resulting powder was extruded at 300 ° C. using a device having a capillary at the tip of a vented twin-screw extruder, and after cooling, cut into pellets. The pellet was crystallized while being stirred by hot air. The pellet contained 700 ppm of styrene monomer at a crystallinity of 35%.

(2) Preparation of styrenic polymer molding material containing no inorganic fine particles A styrenic polymer was produced in the same manner as in (1) above, using a styrene monomer containing no fumed silica. The obtained polymer had a weight average molecular weight of 417,000, a weight average molecular weight / number average molecular weight of 2.54, an Al content of 75 ppm, and a Ti content of 2 pp.
m.

This styrene-based polymer was formed into pellets in the same manner as in the above (1). The crystallinity of the pellet was 30% and the styrene monomer content was 800 ppm.

Reference Example 2 (Production of Stretched Styrenic Polymer Film) (1) Using a molding material obtained as in Reference Example 1 (1), using a device in which a T-die was attached to the tip of a series tandem extruder. It was melt extruded at 330 ° C. The shear stress at this time was 1.5 × 10 ⁵ dyne / cm ² . This melt-extruded sheet was brought into close contact with a cooling roll at 63 ° C. by electrostatic imprinting, and was cooled and solidified. The cooling rate at this time is 130μ at an average of 55 ° C / sec.
m of a sheet for stretching was obtained. Change the peripheral speed of each roll between the rolls at 110 ° C,
The film was stretched three times at a stretching speed of 6000% / min. Subsequently, the film was stretched three times in the transverse direction using a tenter at 120 ° C. and a stretching speed of 6000% / min. Further, the film was stretched 1.5 times in the longitudinal direction at 130 ° C. and 2000% / min while being fixed in the transverse direction with a tenter. This film is fixed on a tenter and slightly relaxed.
Heat treatment was performed for 0 seconds.

The resulting film was 12 μm thick. The linear expansion coefficient of this film was measured at 0 ° C to 90 ° C. Furthermore, the surface roughness conforms to JIS B-0601, with a cutoff value of 0.08 mm,
The coefficient of static friction was measured according to ASTM D-1984B. The properties of the resulting film are shown in the table.

(2) The lip opening of the T-die is set to 4 times, and the redraw ratio is set to
The procedure was the same as in Reference Example 2 (1), except that the magnification was 1.3 times. The properties of the resulting film are shown in the table.

(3) Using the crystallized styrene-based polymer pellets of Reference Example 1 (1) and Reference Example 1 (2), melt co-extrusion was performed at 330 ° C. using an apparatus equipped with a T-die at the tip of an extruder. Except for this, the procedure was the same as in Reference Example 2 (1). The properties of the resulting film are shown in the table. At this time, Reference Example 1 (2)
The styrene polymer pellets of 50/150/400/150/50 mesh are put in series tandem single screw extruder of main extruder,
The styrene polymer pellet of Reference Example 1 (1) was melt-extruded with a double extruder.

(4) In the same manner as in Reference Example 2 (1), except that the styrene-based polymer pellets of Reference Example 1 (2) were used and a 50/150/400/150/50 mesh was placed in the extruder. A stretched film was prepared. The film was corona treated. Next, a styrene-divinylbenzene copolymer having a syndiotactic structure (9.4 mol% of divinylbenzene units, 5.0 mol% of ethylbenzene units, and a weight average molecular weight of 360,000) obtained in Example 1 of JP-A-1-95113 was used. A 0.5 wt% chloroform solution is prepared, and to this solution is added 0.5 wt% of styrene-divinylbenzene copolymer by dry process silica (Aerosil TT-600 manufactured by Tegutsusa Co., Ltd .: primary particles having a particle size of 40 mμ). Then, using a homomixer L type (manufactured by Tokushu Kika Kogyo Co., Ltd.), the mixture was uniformly mixed in a cylindrical container to obtain a slurry solution.
This slurry solution was applied to the above film using a bar coater, and dried at 250 ° C. for 10 seconds. The properties of the resulting film are shown in the table.

(5) Reference Example 2 except that no heat treatment was performed
Same as (1).

(6) A styrene-based polymer was prepared in the same manner as in Reference Example 1 (1) except that the inorganic fine particles used were silica having an average particle size of 4 μm (Silton AMT-40 manufactured by Mizusawa Chemical Industry Co., Ltd.). After the preparation, it was the same as Reference Example 2 (1).

(7) A film was prepared from the styrene polymer material of Reference Example 1 (2) in the same manner as in Reference Example 2 (1).

Example 1 One side of a base film obtained in the same manner as in Reference Example 2 (1) was subjected to a corona discharge treatment, followed by 80% by weight of Co, Ni2
A target of 0% by weight was prepared, and a Co-Ni-based magnetic thin film having a thickness of about 3000 mm was formed by the RF sputtering method using the target.

At this time, the distance between the target and the film was 60 mm, the plate voltage was 1.9 kV, the plate current was 160 mA, and the argon pressure was 1.1 × 1.
It was 0 ^-2 mmHg.

Carefully slit this tape to the same width as the VHS-video tape, disassemble the commercial tape, replace only the tape,
I made a video cassette.

The slip property was evaluated from the coefficient of static friction of this tape.
The coefficient of static friction of this tape was as good as that of the base film.

The created VHS-video cassette tape was recorded and played back by a home video recorder. At this time, the recording / reproducing condition was observed under room temperature conditions and high temperature and high humidity conditions of 85 ° C. and 75% RH as an index of reliability. Under both conditions, there was almost no change, and the image was not disturbed and good. .

Example 2 One side of the base film obtained in the same manner as in Reference Example 2 (1) was subjected to a corona discharge treatment, and a magnetic paint was applied.
The composition of this magnetic paint was as follows: γ-FeO ₃ magnetic powder 45 parts by weight, vinyl chloride-vinyl acetate copolymer (UCC VAG)
H) 17 parts by weight, 3.5 parts by weight of an acrylonitrile-butadiene copolymer (N1432J manufactured by Zeon Corporation), 1.5 parts by weight of polyisocyanate (Coronate L manufactured by Nippon Polyurethane)
50 parts by weight of methyl isobutyl ketone, 50 parts by weight of toluene,
4 parts by weight of carbon black. The thickness of the dried magnetic layer was 3 μm.

The same operation as in Example 1 was performed using this tape. The results are shown in the table.

Example 3 After performing corona discharge treatment on both surfaces of the base film obtained in the same manner as in Reference Example 2 (2), magnetic layers were provided on both surfaces in the same manner as in Example 1. After appropriately polishing both sides of the film, the film was cut into the same size as a commercially available 5-inch floppy. Furthermore, this disk was put in a commercially available floppy jacket to make a floppy disk. The coefficient of static friction of the film having the magnetic layer was examined in the same manner as in Example 1. Also, using the floppy that was created, change the status of SAVE and LOAD to NE
Using CPC-9801F, it was found that both were good under room temperature conditions and high temperature and high humidity conditions.

Example 4 The procedure of Example 1 was repeated, except that a magnetic layer was provided on the smooth surface side of the film obtained in the same manner as in Reference Example 2 (3).
The results are shown in the table.

Example 5 The procedure of Example 1 was repeated, except that a magnetic layer was provided on the smooth surface side of the film obtained in the same manner as in Reference Example 2 (4).
The results are shown in the table.

Comparative Example 1 The procedure of Example 1 was repeated, except that a magnetic layer was provided on one side of the film obtained in the same manner as in Reference Example 2 (5). The results are shown in the table.

Comparative Example 2 The procedure of Example 1 was repeated, except that a magnetic layer was provided on one side of the film obtained in the same manner as in Reference Example 2 (6). The results are shown in the table.

Comparative Example 3 The procedure of Example 1 was repeated except that a magnetic layer was provided on one side of the film obtained in the same manner as in Reference Example 2 (7). The results are shown in the table.

Comparative Example 4 The procedure of Example 1 was repeated, except that a polyethylene terephthalate (PET) film (Tetron NS 12 μm manufactured by Teijin) was used. The results are shown in the table.

[Effect of the Invention] The magnetic recording medium of the present invention obtained as described above has excellent slipperiness and smoothness, and also has excellent dimensional stability against temperature and humidity.

Therefore, the magnetic recording medium of the present invention can be suitably used for various magnetic tapes, magnetic disks, magnetic drums, magnetic cards, and the like.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 7:00 C08L 25:00

Claims (3)

(57) [Claims] 1. A stretched film of a styrene polymer having a syndiotactic structure or a composition thereof or a laminated film containing the stretched film, having a coefficient of linear expansion of 5 × 10 ⁻⁵ / ° C. or less and a coefficient of static friction Has a magnetic layer on at least one side of the substrate film is 0.3 or more and 1.0 or less, and the surface roughness Ra of the substrate film on the magnetic layer forming side is
A magnetic recording medium having a size of 0.001 μm or more and 0.05 μm or less. 2. The magnetic recording medium according to claim 1, wherein the stretched film is mainly composed of a styrene polymer composition having a syndiotactic structure containing inorganic fine particles. 3. A layer comprising a predominantly syndiotactic styrene polymer composition containing inorganic fine particles, and a predominantly syndiotactic styrene polymer containing no inorganic fine particles or a composition thereof. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a laminate having a layer composed of: