JPH0386707A - High density-magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a high density-magnetic recording medium which has high reliability even under high temperature and high humidity conditions, does not curl during vacuum deposition and excels in coercive force by forming a vertical magnetic layer on a base film comprising an oriented laminated film comprising a styrene polymer of a syndiotactic structure and having specified physical property values. CONSTITUTION:An oriented film of a styrene polymer mainly having a syndiotactic structure or its composition or a laminated film containing one or more of such oriented films is used as a base film. This base film should have a coefficient of linear expansion <=5X10<-5>/ deg.C, desirably 4X10<-5>/ deg.C, a coefficient of static friction mum of 0.3-1.0, desirably 0.3-0.9, a heat distortion temperature >=230 deg.C, desirably >=235 deg.C, a surface roughness Ra on at least either surface (especially the layer on which a magnetic layer is formed) of 0.001-0.02mum and a coefficient of humidity expansion desirably <=10<-5>/%RH. A vertical magnetic layer is formed on at least either surface of this film to form a high density- magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-density magnetic recording medium, and more particularly to a high-density magnetic recording medium that is free from curl during deposition and has excellent coercive force.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Polyethylene terephthalate as a magnetic recording medium) (P
ET) A film support coated with a magnetic layer is generally used.

Incidentally, in recent years, there has been an increasing demand for higher density magnetic recording media. In particular, for videotapes, there are various demands such as miniaturization, high image quality, and long recording times.

Although various techniques have been proposed for increasing the density, perpendicular magnetic recording is considered to be promising. This technology involves coating barium ferrite.

Co--Cr sputtering and the like have been proposed.

On the other hand, the stretched film of a styrene polymer mainly having a syndiotactic structure, which was recently developed by the group of the present inventors, has superior heat resistance, water resistance, and dimensional stability compared to PET, and is a polymer with less oligomers. Therefore, various uses are expected. However, none of the conventional stretched films satisfies both the slipperiness and smoothness required for a magnetic recording medium.

Furthermore, when forming a sputtering film of Co--Cr or the like on a conventional PET film, sputtering at high temperatures is required in order to fully develop its magnetic properties. However, PET film inherently has insufficient heat resistance, and sputtering at its upper limit temperature may cause problems such as curling of the PET film on which the sputtered film is formed, or the film surface may deteriorate under high temperature and reduced pressure. There are problems such as oligomer precipitation.

Therefore, the present inventors developed a styrene-based polymer that mainly has a syndiotactic structure, which is highly reliable even under harsh conditions such as high temperatures, does not curl during vapor deposition, and has excellent coercive force. Intensive research was conducted to develop high-density magnetic recording media.

[Means to solve the problem]

As a result, the linear expansion coefficient, static g-friction coefficient μs, heat distortion temperature, and surface roughness Ra of the stretched film made of the above-mentioned styrenic polymer or its composition or the laminated film containing the stretched film are within a certain range. It has been found that a substrate film provided with a perpendicular magnetic layer can be used as a high-density magnetic recording medium suitable for the above purpose. The present invention is based on this knowledge.

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,
The coefficient of linear expansion is 5X10-'/°C or less, the coefficient of static friction μs is 0.3 to 1.0, the thermal deformation temperature is 230°C or more, and the surface roughness Ra of at least one side is 0.001 to 0.0.
The present invention provides a high-density magnetic recording medium in which a perpendicular magnetic layer is formed on at least one side of a base film having a magnetic flux density of 2 am.

As mentioned above, the base film of the magnetic recording medium used in the present invention is a stretched film of a styrenic polymer mainly having a syndiotactic structure, or a stretched film of a composition containing this styrenic polymer as one component, or It is a laminated film containing one or more layers of these stretched films. In addition, this base film has a linear expansion coefficient of 5
10-'/"C or less, preferably 4 x 10-'/"
"C or less, the static friction coefficient μs is 0.3 to 1.0, preferably 0.3 to 0.9, and the heat distortion temperature is 230 ° C.
The temperature is preferably 235°C or higher. Furthermore, the base film has a surface roughness Ra of 0.001 on at least one side.
~0.02 μm, preferably 0.005-0.02 μm
It is. In particular, it is desirable that the surface roughness Ra of the base film on the side where the magnetic layer is formed is within the above range.

The humidity expansion coefficient of the base film is not particularly limited, but is preferably 5X10-'/%RH or less.

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

(1) Mi products made by blending inorganic fine particles into a styrene polymer mainly having a syndiotactic structure, especially inorganic fine particles with an average particle size of 0.01 to 3 μm.
A composition containing i to 1% by weight is heated and melted, extruded, solidified by cooling, heated, and stretched (area magnification of 6 times or more is preferable).
, heat treatment (preferably at 220°C or higher) to form a stretched film. As a result, a single-layer film consisting only of this stretched film and having smooth and smooth surfaces on both sides can be obtained.

(2) The composition used in (1) above and a styrenic polymer mainly having a syndiotactic structure, especially a residual aluminum content of 3000 ppm or less and a residual titanium content of 1
0ppm or less and residual styrenic monomer 7000pp
A high-purity styrene polymer with a purity of less than m or a composition containing this styrene polymer as a main component (however, it does not contain inorganic fine particles) is heated and melted, coextruded, solidified by cooling, heated, stretched, and heat treated. Two or more types of stretched films are formed in a laminated state. As a result, a multilayer (laminated) film with one side ultra-smooth and the other side smooth and rough can be obtained.

(3) A styrenic polymer mainly having a syndiotactic structure, especially a residual aluminum content of 3000 pp-
Hereinafter, a high purity styrenic polymer with a residual titanium content of 10 ppm or less and a residual styrenic monomer content of 7000 ppm or less, or a composition containing this styrene polymer as a main component (however, it does not contain inorganic fine particles) will be used. , heating melting,
Extrusion, cooling solidification, heating.

In the process of stretching and heat treatment, a layer made of a resin capable of surface roughening or a resin composition containing inorganic ultrafine particles is formed on at least one side by laminating, coating, vapor deposition, etc. A multilayer film can be obtained in which one side is ultra-smooth and the other side is smooth and rough. At this time, the layer made of the resin composition may be stretched as necessary.

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

Although there are no particular limitations on the laminating method, productivity is improved if a method of melting and coating other resins or other resin compositions is incorporated into the stretched film manufacturing process in addition to the coextrusion method.

Here, particularly in tapes, the layer having the rough surface may be used as a pack coat layer, and the magnetic layer is mainly provided on the opposite ultra-smooth surface side.

The stretched film thus obtained has a thickness of 3 to 15
0 μm, linear expansion coefficient of 5 x 10-'/”C or less, static friction coefficient μs of 0.3 to 1.0, heat distortion temperature of 230°C
above, and the surface roughness Ra of at least one side is 0.
001 to 0.02 μm. Further, it is more preferable that the humidity expansion coefficient is 5×10 −′/%RH or less.

Regarding the film thickness, a film of 2 to 20 tIm is used for magnetic tape, and a film of 20 to 150. A czm film is suitable for magnetic disks, and a 100 to 500 μm film is suitable for magnetic cards.

These films are used to create magnetic recording media, but if necessary, films whose surface adhesion has been improved by corona treatment etc. may also be used, and an adhesive layer may be provided in advance on the side where the magnetic layer is to be provided. You can leave it there.

By the way, the styrenic polymer mainly having a syndiotactic structure used as the above-mentioned film material has a stereochemical structure mainly having a syndiotactic structure, that is, a side chain with respect to the main chain formed from carbon-carbon bonds. It has a three-dimensional structure in which phenyl groups and substituted phenyl groups are alternately located in opposite directions, and its toughness is determined by nuclear magnetic resonance (C3C-NMR) using carbon isotopes.
It is quantified by Toughness measured by 13C-NMR is the proportion of a plurality of consecutive constituent units, for example, if there are two units, it is a diamond.

In the case of 3 atoms, it can be expressed as triat, and in the case of 5 atoms, it can be expressed as pentad, but the styrenic polymer mainly having a syndiotactic structure as referred to in the present invention is usually racemic diamond with a proportion of 75% or more, preferably 85%. Polystyrene having a syndiotacticity of 30% or more, preferably 50% or more in racemic pentads.

Refers to poly(alkyl styrene), poly(halogenated styrene), poly(alkoxystyrene), poly(vinyl benzoate), hydrogenated polymers thereof, mixtures thereof, or copolymers containing these structural units. do. Note that poly(alkylstyrene) here includes poly(methylstyrene), poly(ethylstyrene),
Poly(propylstyrene), poly(butylstyrene),
Poly(phenylstyrene), poly(vinylnaphthalene)
, poly(vinylstyrene) 9 poly(acenaphthylene), etc. Poly(halogenated styrene) includes poly(chlorostyrene), poly(bromostyrene), poly(bromostyrene), etc.
Examples of poly(alkoxystyrene) include poly(methoxystyrene) and poly(ethoxystyrene). Among these, particularly preferred styrenic polymers include polystyrene, poly(p-methylstyrene), poly(m-methylstyrene), poly(p-tert-butylstyrene) poly(p-
-chlorostyrene), poly(m-chlorostyrene), poly(p-fluorostyrene), and copolymers of styrene and p-methylstyrene (JP-A-62-187708).

Furthermore, as comonomers in the styrene copolymer, in addition to the above-mentioned styrene polymer monomers, olefin monomers such as ethylene, propylene, butene, hexene, and octene, diene monomers such as butadiene and isoprene, cyclic diene monomers, etc. methyl methacrylate,
Examples include polar vinyl monomers such as maleic anhydride and acrylonitrile.

In addition, this styrene polymer has a weight average molecular weight of 10,000 or more and 3,000 or more, although there is no particular restriction on the molecular weight.
0,000 or less is preferred, especially 50,00
The optimum value is 0 or more and 1,500.000 or less. If the weight average molecular weight is less than 10,000, sufficient stretching cannot be achieved. Furthermore, there are no restrictions on the width or narrowness of the molecular weight distribution, and various values can be used, but the weight average molecular weight (Mw)/number average molecular it (M
n) is preferably 1.5 or more and 8 or less. Note that this styrenic polymer mainly having a syndiotactic structure has much better heat resistance than conventional styrenic polymers having an atactic structure.

The styrenic polymer mainly having a syndiotactic structure constituting the above-mentioned stretched film (particularly a film having a smooth surface) may be of the type described above, but especially the one containing residual aluminum and -1-um. It is preferable that the residual aluminum content is 3000 ppm or less, the residual titanium content is 10 ppn+ or less, and the residual styrene monomer is 7000 ppm or less.In particular, the residual aluminum content is 1000 ppn+ or less, the residual titanium content is 7 ppm or less, and the residual styrene monomer is 5000 pp+s. The following are optimal.

To produce such high-purity styrenic polymers,
There are various methods, such as the following. First, in order to suppress the residual aluminum content and the residual titanium content within the above range, there is a method for producing a styrenic polymer using a highly active catalyst (see Japanese Patent Application No. 7466/1983).
Or ■ method by deashing and washing, that is, JP-A-62-
A styrenic polymer with a syndiotactic structure obtained by polymerizing a styrenic monomer using an ordinary IVA group organometallic compound described in Publication No. 187708 and an alkylaluminoxane such as methylaluminoxane as a catalyst component. This is a method of deashing with a solution of acid or alkali dissolved in an appropriate solvent, and washing with an appropriate solvent.

In this way, a styrenic polymer with a syndiotactic structure with a low residual argonium content and residual titanium content can be obtained by the method (■) or (2). , the residual styrene monomer is 7000 pp- or less.

(2) Method of drying the styrenic polymer under reduced pressure When drying under reduced pressure, it is efficient to set the drying temperature to the glass transition temperature or higher of the polymer.

■Method of degassing the above styrenic polymer in an extruder The above styrenic polymer or the styrene polymer dried under reduced pressure using method (■) is degassed in an extruder, and at the same time is made into a molding material (pellet). . Here, the extruder is preferably equipped with a vent, and either a -shaft or twin-screw extruder may be used.

Through such treatment, a highly purified styrenic polymer having a syndiotactic structure with a small residual aluminum content, residual titanium content, and residual styrene monomer can be obtained.

On the other hand, the constituent materials of stretched films and lumens with easy-to-clean rough surfaces are mainly composed of a styrene polymer having a syndiotactic structure containing inorganic fine particles, especially the styrene polymer having an average particle size of 0. The composition contains o, ooi to 1% by weight of inorganic fine particles of 0 to 3 μm. This composition is made of a styrene-based polymer (however, it does not necessarily have to be of high purity as described above,
The method described in the publication, etc. may be used. ) with inorganic fine particles or by precipitating them during polymerization. Here, the inorganic fine particles are group IA, I
Group IA, Group IVA, Group VIA, Group ■A, Group ■.

Oxides of Group IB, Group IIB, Group IIIB, Group IVB elements.

hydroxides, sulfides, nitrides, halides, carbonates,
Shows acetates, phosphates, phosphites, organic carboxylates, silicates, titanates, borates and their hydrated compounds, complex compounds centered on them, and natural mineral particles.

Specifically, lithium fluoride, Group IA element compounds such as borax (sodium borate hydrate), magnesium carbonate, magnesium phosphate, magnesium oxide (magnesia), magnesium chloride, magnesium acetate, magnesium fluoride, magnesium titanate, and silicic acid. Magnesium, magnesium silicate hydrate (talc), calcium carbonate, calcium phosphate.

Calcium phosphite, calcium sulfate (gypsum), calcium acetate, calcium terephthalate, calcium hydroxide,
Calcium silicate calcium octafluoride.

Calcium titanate, strontium titanate.

■ Group A element compounds such as barium carbonate, barium phosphate, barium sulfate, barium phosphite, titanium dioxide (titania), titanium oxide, titanium nitride, zirconium dioxide (
l'lt/A group element compounds such as zirconia), -zirconium oxide, and molybdenum dioxide.

Group VIA element compounds such as molybdenum trioxide and molybdenum sulfide; ■ Group A element compounds such as manganese chloride and manganese acetate; Group ■ element compounds such as cobalt chloride and cobalt acetate;
IB group element compounds such as cuprous iodide, IIB group element compounds such as zinc oxide and zinc acetate, aluminum oxide (alumina), aluminum hydroxide, aluminum fluoride, aluminosilicate (aluminum silicate, kaolin, kaolinite) )
Group 111B element compounds such as silicon oxide (silica, silica gel) 9 graphite, carbon, graphite, glass, etc.
Group B element compounds, carnalite, kainite.

Examples include particles of natural minerals such as mica and villoseite.

The average particle size of the inorganic fine particles used in the present invention is not particularly limited, but is preferably from 0.01 to 3 μm, more preferably from 0.01 to 3 μm.
．． 01-1am, the content in the composition is 0.001-1% by weight, preferably o,ooi-0.6% by weight. If the average particle size is smaller than 0.01 μm, dispersion may become difficult due to secondary aggregation of particles, and if the average particle size is larger than 3 μm, smoothness will decrease. Also, &l
lll If the content of biologically sensitive particles is less than 0.001% by weight, the effect of improving slipperiness will be insufficient;
If the amount is more than % by weight, it may become difficult to stretch thin products.

In addition, although the above-mentioned inorganic fine particles are an effective component in achieving the object of the present invention, other types or particle sizes of fine particles, inorganic fillers, etc. may be used as long as they do not impede the object of the present invention. It may include.

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 containing them. Examples include a method of adding or precipitating the styrenic monomer at any step during polymerization, and a method of adding at any step of melt extrusion.

Among these, particularly in the present invention, the method of adding the above-mentioned inorganic fine particles in the form of a slurry at any stage of the polymerization process is
This is preferable since secondary aggregation of particles can be prevented.

Further, in order to effectively disperse these fine particles, a dispersant, a surfactant, etc. may be used.

The material used for the stretched film that constitutes the base film mentioned above also has moldability and mechanical properties.

In consideration of surface properties, etc., antioxidants, antistatic agents, flame retardants, inorganic fillers, and other resins may be appropriately blended within a range that does not impede the object of the present invention.

There are various types of other resins, such as styrene polymers with an active structure.

Isotactic structure styrenic polymers, polyphenylene ethers, etc. are easily compatible with the syndiotactic structure styrenic polymers mentioned above, and are effective in controlling crystallization when creating preforms for stretching. , it is possible to obtain a film with improved subsequent stretchability, easy control of stretching conditions, and excellent mechanical properties. Among these, when a styrene polymer having an actic structure and/or an isotactic structure is contained, it is preferable to use a monomer similar to the styrene polymer having a syndiotactic structure. In addition, the content ratio of these compatible resin components is 7
The amount may be 0 to 1% by weight, particularly preferably 50 to 2% by weight. If the content of the compatible resin component exceeds 70% by weight, it is not preferable because the advantages of the syndiotactic styrene polymer, such as heat resistance, will be impaired.

Further, examples of the incompatible resin include polyethylene.

Polyolefins such as polypropylene, polybutene, polypentene, and polyethylene terephthalate.

Polyesters such as polybutylene terephthalate and polyethylene naphthalate, polyamides such as nylon-6 and nylon 6.6, polythioethers such as polyphenylene sulfide, and polycarbonates.

Polyarylate, polysulfone, polyether ether ketone, polyether sulfone, polyimide, halogenated vinyl polymers such as Teflon, acrylic polymers such as polymethyl methacrylate, polyvinyl alcohol, etc., all other than the compatible resins listed above are equivalent. Furthermore, crosslinked resins containing the above-mentioned compatible resins can be mentioned. These resins are incompatible with the styrenic polymer having a syndiotactic structure of the present invention, so if they are contained in small amounts, they cannot be dispersed like islands in the styrenic polymer having a syndiotactic structure. It is effective in imparting a suitable gloss after stretching and improving surface slipperiness. The content ratio of these incompatible resin components is 0.0 for the purpose of light control.
01 to 5% by weight is preferred. Furthermore, when the temperature at which the product is used is high, it is preferable to use an incompatible resin that is relatively heat resistant.

The base film of the high-density magnetic recording medium of the present invention may be formed by the method described above, but the operations from heat melting to heat fixation will be specifically explained as follows.
It is as follows.

First, the above-mentioned molding material is usually extruded (or coextruded) to form a preform for stretching (film, sheet, or tube). In this molding, it is common to heat and melt the above-mentioned molding material and mold it into a predetermined shape using an extrusion molding machine, but the molding material is molded in a softened state without being heated and melted. Good too. The extrusion molding machine used here may be either a -shaft extruder or a twin-screw extruder, and may be either with a vent or without a vent, but a -shaft tandem type is preferred.

Note that impurities and foreign matter can be removed by using a suitable mesh in the extruder. In particular, the mesh at this time is preferably 100 mesh or more, and most preferably 400 mesh or more. When using these meshes here, considering the pressure resistance and two-strength of the mesh itself, the above-mentioned or lower counts may be added to the front and back. Further, the shape of the mesh can be appropriately selected and used, such as a flat plate, a cylindrical shape, etc.

The extrusion conditions here are not particularly limited and may be appropriately selected depending on various situations, but preferably the temperature is selected within the range of 50°C higher than the melting point of the molding material to the decomposition temperature, and the shear stress is reduced. 5X106dyne/c4 or less. The die used may be a T-die, an annular die, or the like.

After the above extrusion molding, the obtained preform for stretching is cooled and solidified. As the refrigerant at this time, various types such as gas, liquid 5 metal rolls, etc. can be used.

When using a metal roll or the like, methods such as an air knife, air chamber, touch roll, and electrostatic charging are effective in preventing thickness unevenness and waviness.

The cooling solidification temperature is usually in the range of 0°C to 30°C higher than the glass transition temperature of the acid form for stretching, preferably 2°C.
It is in the range of 0''C to glass transition temperature.

Further, the cooling rate is appropriately selected within the range of 200 to 3°C/sec.

Next, this cooled and solidified preform is uniaxially or biaxially stretched. In the case of biaxial stretching, stretching may be carried out simultaneously in the longitudinal and transverse directions, or sequentially in any order, and stretching may be carried out in one stage or in multiple stages.

The stretching method used here is a method using a tenter.

There are various methods such as stretching between rolls, bubbling using gas pressure, and rolling, and any of these methods may be appropriately selected or combined. In particular, it is preferable to stretch the film between rolls in the MD direction, then stretch it with a tenter in the TD force direction, and then re-stretch it if necessary. Generally, the stretching temperature may be set between the glass transition temperature and the melting point of the preform; however, in the case of sequential or multistage stretching, the first stage should be set at a temperature between the glass transition temperature and the low-temperature crystallization temperature. , the latter stage is preferably at a temperature between the glass transition temperature and the melting point. In addition, the stretching speed is usually 1
×10-1×10S%/min, preferably lXIO3-l
Xl0'%/min.

In cases where the stretched film obtained by stretching under the above conditions is required to have further dimensional stability at high temperatures, heat resistance, and in-plane strength balance of the film, it is preferable to further heat set the film. Heat setting can be carried out by a commonly used method, and the stretched film is heated at a temperature of 0.5 to 120° C. under tension, relaxation, or limited shrinkage at a temperature ranging from 220°C to the melting point. This can be done by holding it for a second. Note that this heat fixing can be performed two or more times under different conditions within the above range.

If the heat setting temperature is too low, sufficient heat resistance will be lost when forming a magnetic layer by vapor deposition, which is not preferable. Also, this heat fixation is done using argon gas.

It may be carried out under an inert gas atmosphere such as nitrogen gas.

The base film of the present invention obtained in this manner has a linear expansion coefficient, a static friction coefficient μs, a heat distortion temperature, and a surface roughness Ra.
is within the range mentioned above. Note that this base film is tape-shaped or disk-shaped.

It can be made into various forms such as a card shape.

The magnetic recording medium of the present invention is formed by forming a perpendicular magnetic layer on at least one side of the base film, but an undercoat layer, back coat N or top coat layer may also be formed.

Each of these layers is formed on both sides or all or part of one side of the base film.

Further, the magnetic material that is the material of the magnetic layer is a magnetic material that can be perpendicularly magnetized, such as Go, Co-0, Co-Cr, Co-
V, Co-Ni, Co-P, Co-Nt-0゜Co-N
1-P, Co-N1-N, Co-N1-W.

CoN1(Cr)/Cr , Ba0 ・I FezOz
etc. can be listed.

Coating, vapor deposition, and sputtering are used to form a perpendicular magnetic layer on a base film using this magnetic material.

Various methods such as plating may be used, and the operating conditions may be appropriately selected according to conventional methods.

In particular, Co-based magnetic materials are produced by vapor deposition or sputtering, B
aO・γFe, 0. It is preferable to form the perpendicular magnetic layer by coating.

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

Examples of binder resins used for coating include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate partially saponified copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile, and vinyl chloride-vinyl acetate copolymer. Butyral.

Vinyl copolymer systems such as vinyl formal, uI trinary systems such as nitrocellulose and cellulose acetobutyrate, condensation polymer systems such as saturated polyester, polyurethane polyamide, and epoxy, synthetic rubber systems such as butadiene-acrylonitrile copolymers, polyphosphazene, etc. Examples include inorganic polymers, and crosslinking agents such as isocyanate compounds may also be used.

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

〔Example] Next, the present invention will be explained in more detail based on examples.

Reference Example 1 (1) Styrenic polymer molding material containing inorganic fine particles (
17.8 g (71 g of copper sulfate pentahydrate (CaSO3-5H!0)
2001d of toluene and 24d (250 mmol) of trimethylaluminum were added, and the mixture was reacted at 40°C for 8 hours. Thereafter, from the solution obtained by removing the solid portion, toluene was further distilled off under reduced pressure at room temperature to obtain 6.7 g of a contact product. The molecular weight of this product was 610 as measured by freezing point depression method. Also, 'H-NMR
The above-mentioned high magnetic field components (i.e. -0, 1 to -0.
5ppm) was 43%.

On the other hand, 95 parts of purified styrene monomer was added with dry process silica (Anirodyl TT-600 (manufactured by Degutsusa) (primary particle diameter 4.
A styrene mixture was obtained by adding 0.4 parts of 0 mμ (0 mμ)) and stirring in a cylindrical container using a homomixer L type (manufactured by Tokushu Kika Kogyo Co., Ltd.). At this time, 0.2 parts by weight of calcium stearate was added.

In a reaction vessel with an internal volume of 21, the styrene mixture 1i prepared as above, 5 trimoles of the contact product obtained above as aluminum atoms, 5ξ trimoles of triisobutylaluminum, and pentamethylcyclopentadienyl titanium trimethoxide. 90°C using 0.025 mmol
After the polymerization reaction was completed for 5 hours, the catalyst component of the product was decomposed with a methanol solution of sodium hydroxide, washed repeatedly with methanol, and dried to obtain 308 g of a polymer.

The weight average molecular weight of this polymer was determined to be 389.0 by Gelper knee chromatography at 135°C using 1,2.4-trichlorobenzene as a solvent.
00, and the weight average molecular weight/number average molecular weight is 2.
It was 64. Furthermore, it was confirmed by melting point and 13C-NMR measurements that this polymer was polystyrene with a syndiotactic structure.

This polymer was dissolved in 1,2,4-trichlorobenzene at 130°C, filtered, and the silica content in the polymer was determined to be 0.4 wt%. Further, this solution was dropped onto a glass slide and observed under a microscope to find out the average particle size of the silica, which was 0.08 μm.

Furthermore, 150'l, t? of this styrene polymer was added. It was dried under reduced pressure for 2 hours. The obtained powder was extruded at 300° C. using a vented twin-screw extruder with a capillary at the tip, cooled, and then cut into pellets. The pellets were crystallized while stirring with hot air. This pellet contains 700p of styrene monomer with a crystallinity of 35%.
It included p+i.

(2) Preparation of styrenic polymer molding material containing no inorganic particles A styrenic polymer was produced in the same manner as in (1) above using a styrene monomer containing no dry silica. The obtained polymer had a weight average molecular weight of 4i7. OOO, weight average molecular weight/number average molecular weight is 2.54. /l content is 75
The ppim and Tt contents were 2 ppm.

This styrene polymer was made into pellets in the same manner as in (1) above. The crystallinity of this pellet was 30%, and the styrene monomer content was 800 ppm. Reference Example 2 (Production of styrenic polymer stretched film) (1
) The molding material obtained as in Reference Example 1 (1) was melt-extruded at 330° C. using an in-line tandem extruder equipped with a T-die at the tip.

The shear stress at this time is 1.5 x 10'dyne/
It was c4. This melt-extruded sheet was brought into close contact with a cooling roll at 63° C. by electrostatic charging, and cooled and solidified.

The cooling rate at this time was an average of 55° C./sec to obtain a stretched sheet of 130 μm. This sheet was stretched 3 times between rolls in the longitudinal direction at a 110"C1 stretching speed of 6000%/min by changing the circumferential speed of each roll. Then, in the transverse direction using a tenter, the sheet was stretched at 120° C. Stretching speed 6000%/
It was stretched 3 times in minutes.

Furthermore, while fixing it horizontally with a tenter, vertically, 13
It was re-stretched to 1.5 times at 0° C. and 2000%/min. This film was fixed in a tenter, slightly relaxed, and heat-treated at 255° C. for 10 seconds.

The resulting film had a thickness of 12 μm. The humidity expansion coefficient of this film was measured in the range of 20% to 80%, and the expansion coefficient was measured at 0°C to 90°C.

Furthermore, the surface roughness was determined according to JIS B-0601 with a cutoff value of 0.08 ani, and the static friction coefficient was determined according to AS
Measured in accordance with TM D-1984B.

The heat distortion temperature of this film was measured using thermal mechanical analysis (TMA). Note that the thermal deformation temperature was the temperature at which the sample length changed by 2%. The properties of the obtained film are shown in the table.

(2) The same procedure as in Reference Example 2 (1) was carried out except that the lip opening degree of the T-die was 4 times and the re-stretching ratio was 1.3 times. The properties of the obtained film are shown in the table.

(3) Using the crystallized styrenic polymer pellets of Reference Example 1 (1) and Reference Example 1 (2), melt coextrusion was carried out at 330°C using a device equipped with a T-die at the tip of the extruder. Other than that, the same procedure as in Reference Example 2(1) was carried out. The properties of the obtained film are shown in the table. In addition, at this time, reference example 1 (2
) 50/150/400 styrenic polymer pellets
The styrenic polymer pellet of Reference Example 1 (1) was melt-extruded using an in-line tandem single-screw extruder as a main extruder containing a /150150 mesh, and a double extruder using a double extruder.

(4) Using the styrene polymer pellet of Reference Example t(2), 50/150/400/150150 was added to the extruder.
A stretched film was prepared in the same manner as in Reference Example 2(1) except that a mesh was added. This film was corona treated. Next, a styrene-divinylbenzene copolymer having a syndiotactic structure obtained in Example 1 of JP-A-1-95113 (9.4 mol% of divinylbenzene units,
Ethylbenzene units 5.0 mol% 9 Weight average molecular weight 36
A 0.5 wt% chloroform solution of 0.000) was prepared, and this solution was added with 0.5 wt% dry process silica (particle size 40 mμ of Aerosil TT-600 secondary particles manufactured by Tegutsusa ■) based on the styrene-divinylbenzene copolymer. ) was added thereto and mixed uniformly in a cylindrical container using a homomixer L type (manufactured by Tokushu Kika Kogyo) to obtain a slurry solution. Apply this slurry solution to the above film using a bar coater,
It was dried at 250°C for 10 seconds. The properties of the obtained film are shown in the table.

(5) Reference example 2 (1) except that no heat treatment was performed.
).

(6) 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 Reference Example 2 Corona treatment was applied to one side of the film of (1), and a 0.1 μm Co-Cr film (Cr20wt%) was applied to that side.
was formed by a vacuum evaporation method. The substrate temperature at this time is 25
Although the temperature was 0°C, no curling of the tape was observed.

The static friction coefficient of the tape after vapor deposition was determined by ASTM D-19.
84, the result was 0.55, indicating good slipperiness. Further, the coercive force Hc after vapor deposition was determined from a magnetization characteristic curve using a vibrating sample magnetometer VSM and was found to be 9000e.

Example 2 Corona treatment was applied to one side of the film of Reference Example 2 (1),
Magnetic paint was applied to that surface. The composition of this magnetic paint is
100 parts by weight of barium ferrite magnetic powder, vinyl chloride
Vinyl acetate copolymer (U, C.

VAGH manufactured by C0) 15 parts by weight, 20 parts by weight of polyurethane, 4 parts by weight of lecithin, 3 parts by weight of stearic acid, 100 parts by weight of methyl isobutyl ketone, 1 part by weight of methyl ethyl ketone.
00 parts by weight, 100 parts by weight of cyclohexanone, and 3 parts by weight of isocyanate.

The thickness of the magnetic layer after drying was 3 μm. This magnetic tape was examined in the same manner as in Example 1. The results are shown in the table.

Example 3 Corona treatment was applied to both sides of the film of Reference Example 2 (2),
The procedure was the same as in Example 1 except that the magnetic material was provided on both sides and the disc shape was used. The results are shown in the table.

Example 4 Corona treatment was applied to one side of the film of Reference Example 2 (3),
A CO-0 film (0.21%) of 0.8 μm was formed on that surface. The formation of this film uses an electron beam to evaporate Co and introduces Ox gas at a deposition rate of about 900 people/sec.
I went there. EPMA was used to analyze the oxygen composition in the film.

This vapor-deposited tape was examined in the same manner as in Example 1. The results are shown in the table.

Example 5 Using the film of Reference Example 2 (4), CoN 1 (Ni
Co-Nt-0 film (0.1 wt%)
The procedure was the same as in Example 4 except that t%) was formed.

The results are shown in the table.

Comparative Example 1 Using the film of Reference Example 2 (5), the substrate temperature was 100°C.
The procedure was the same as in Example 1 except for the following.

The results are shown in the table. Incidentally, it was difficult to form a magnetic layer on the substrate at 250° C. due to shrinkage and curling of the film.

Comparative Example 2 Example 1 except that the film of Reference Example 2 (6) was used.
I did the same thing. The results are shown in the table.

Comparative Example 3 The same procedure as in Example 1 was carried out using a PET film (Tetron N512 μm manufactured by Tijin Co., Ltd.) at a substrate temperature of 200°C. The results are shown in the table. Note that when the magnetic layer is formed at a substrate temperature of 250'C, part of the film is melted.

This was difficult due to elongation, etc.

(The following is a blank space) [Effects of the Invention] The high-density magnetic recording medium of the present invention has no curl during vapor deposition, has excellent coercive force, and has a perpendicular magnetic layer formed at extremely high density. Furthermore, it has excellent slipperiness and smoothness, and also excellent dimensional stability against temperature and humidity.

Therefore, the high-density magnetic recording medium of the present invention can be applied to various magnetic tapes, magnetic disks, and magnetic drums.

It can be suitably used for magnetic cards and the like.

Claims (4)

[Claims] (1) A stretched film of a styrenic polymer or its composition mainly having a syndiotactic structure, or a laminated film containing the stretched film, with a coefficient of linear expansion of 5 x 10^-^5/°C or less, and a coefficient of static friction. μs is 0.3~
1.0, a high-density magnetic material formed by forming a perpendicular magnetic layer on at least one side of a base film having a heat deformation temperature of 230°C or higher and a surface roughness Ra of at least one side of 0.001 to 0.02 μm recoding media. (2) The high-density magnetic recording medium according to claim 1, wherein the stretched film is composed of a styrene-based polymer composition mainly having a syndiotactic structure and containing inorganic fine particles. (3) Claim 1 wherein the surface roughness Ra of at least one side of the base film is 0.001 μm or more and 0.05 μm or less.
Or the high-density magnetic recording medium according to 2. (4) The base film consists of a layer consisting of a styrenic polymer composition with a mainly syndiotactic structure containing inorganic fine particles and a styrenic polymer composition with a mainly syndiotactic structure containing no inorganic fine particles or a composition thereof. The high-density magnetic recording medium according to any one of claims 1 to 3, which is a laminate having layers.