JPH0386706A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having high reliability even under high-temperature and high-humidity conditions by using a laminated film containing an oriented film of a styrene polymer having a syndiotactic structure and specified physical property values as a base film. CONSTITUTION:A single-layer film of an oriented film of a styrene polymer (especially with a residual Al component <=3000ppm, a residual Ti component <=10ppm and a residual styrene monomer <=7000ppm) having a syndiotactic structure or a laminated film containing the oriented film 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 mus of 0.3-1.0, desirably 0.3-0.9 (especially desirably in the range of the coefficient of static friction of the surface opposite to the layer on which a magnetic layer is formed), a surface roughness Ra of 0.001.0.05mum, most suitably 0.001-0.04mum and a coefficient of humidity linear expansion of 5X10<-5>/%RH. A magnetic layer is formed on at least either surface of this film to obtain a magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more specifically, it has excellent slip properties, smoothness, dimensional stability against temperature and humidity, etc., and is suitable for use in magnetic tapes, magnetic disks, magnetic drums, etc. This invention relates to magnetic recording media useful for magnetic cards and the like.

[Prior art and problems to be solved by the invention] Conventionally, polyethylene terephthalate (
PET) film supports coated with a magnetic layer are widely used. However, PET film has poor water resistance and may be hydrolyzed under high temperature and high humidity, making it unusable in some cases. Further, the glass transition temperature of PET is 60 to 70°C, and when used at higher temperatures, elongation tends to occur, so reliability is not necessarily sufficient.

On the other hand, in recent years, magnetic recording media have tended to have higher densities, and demands for their reliability have increased. Vapor deposition is one method for increasing the density, but PET films lack heat resistance and have problems such as oligomer precipitation.

By the way, the styrenic 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. , is expected to have a variety of uses.

Therefore, the inventors of the present invention have conducted intensive research to develop a magnetic recording medium that is highly reliable even under harsh conditions such as high temperatures and high temperatures, using this styrene polymer mainly having a syndiotactic structure.

[Means to solve the problem]

As a result, a stretched film of the above-mentioned styrenic polymer or its composition or a laminated film containing the stretched film, which has a magnetic layer on a base film whose coefficient of linear expansion and coefficient of static friction are within a certain range, is as follows. It was discovered that this material can be used as a magnetic recording medium suitable for the purpose. The present invention was completed 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 present invention provides a magnetic recording medium having a magnetic layer on at least one side of a base film having a linear expansion coefficient of 5X10-'/°C or less and a static friction coefficient of 0.3 or more and 1.0 or less.

In the present invention, a single layer film made of the above-mentioned stretched film or a laminated film containing the stretched film is used as the base film of the magnetic recording medium. Further, this base film has a linear expansion coefficient of 5 x 10-5/°C or less, preferably 4 x 10-5/°C or less, and
The static friction coefficient μs of this base film is 0.3
-1.0, preferably 0.3-0.9. This static friction coefficient μs defines the surface condition of the base film, and it is particularly desirable that the static friction coefficient μs of the surface of the base film on the side opposite to the magnetic layer forming side be within the above range.

Further, there is no particular restriction on the surface roughness Ra of this base film, but it is preferable that the surface roughness Ra of at least one side thereof is 0.001 to 0.05 um.
In particular, 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 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 the 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 obtained by blending inorganic fine particles into a styrene polymer mainly having a syndiotactic structure, especially 0.001 μm of inorganic fine particles with an average particle size of 0.01 to 3 μm.
-1% by weight of the composition is heated and melted, extruded, solidified by cooling, heated, stretched, and heat treated to form a stretched film. As a result, an easily slippery single-layer film with smooth and roughened surfaces on both sides can be obtained, which is made only of this stretched film.

(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 styrenic polymer of n+ or less, or a composition containing this styrene polymer as a main component (however, it does not contain inorganic fine particles) is heated and melted, coextruded, cooled and solidified,
Two or more types of stretched films are formed in a laminated state by heating, stretching, and heat treatment. As a result, an easily smooth multilayer (laminated) film having one side that is ultra-smooth and the other side that is roughened can be obtained.

(3) Styrenic polymer mainly having a syndiotactic structure, especially residual aluminum content of 3000 ppm
Hereinafter, a high-purity styrenic polymer with a residual titanium content of 10 ppm or less and a residual styrene monomer of 7000 ppn+ 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.

By forming a layer of a resin M parabolite containing a resin capable of surface roughening or inorganic ultrafine particles on at least one side during the stretching and heat treatment process by laminating, coating, vapor deposition, etc. An easily smooth multilayer film with one side ultra-smooth and the other side 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 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, as for the type, quantity, 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, especially in tapes, the layer having the rough surface may be used as a back 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 2 to 500
In μm, the linear expansion coefficient is 5 x 10-S/'C or less.

The static friction coefficient μs is 0.3 to 1.0, and according to method (1), the surface roughness Ra on both sides is 0.005 to 0.05 μm,
According to methods (2) and (3), both smooth and rough surfaces are obtained, and the surface roughness of each surface is between 0.005 and 0.
．． 05 μm and 0.001 to 0.04 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 μm is suitable for magnetic tapes, a film of 20 to 150 μm is suitable for magnetic disks, and a film of 100 to 500 μm 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 positioned in opposite directions, and its toughness can be determined by nuclear magnetic resonance (C-NMR) method using carbon isotopes.
It is quantified by Toughness measured by 13C-NMR is the proportion of a plurality of consecutive structural units, for example, in the case of two units, it is a diad.

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 having a mainly syndiotactic structure as used in the present invention is usually 75% or more, preferably 85 % or more, or 30% or more in terms of racemic pentads, preferably 50% or more.

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), poly(acenaphthylene), etc. Poly(halogenated styrene) includes poly(chlorostyrene), poly(bromostyrene), poly(
fluorostyrene), etc. In addition, examples of poly(alkoxystyrene y) include poly(methoxystyrene) and poly(ethoxystyrene). Among these, particularly preferred styrenic polymers include polystyrene, poly(p-methylstyrene), and 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 weight average molecular weight (Mw)/number average molecular weight (Mn
) is preferably 1.5 or more and 8 or less. In addition, this styrenic polymer mainly having a syndiotactic structure is
It has much better heat resistance than conventional styrene-based polymers with an active structure.

The styrenic polymer mainly having a syndiotactic structure constituting the above-mentioned stretched film (particularly the film having an ultra-smooth surface) may be of the type described above, but in particular, if the residual aluminum content is 3000 ppmg or less, the styrene polymer mainly has a syndiotactic structure. Preferably, the titanium content is 10 ppm or less and the residual styrene monomer content is 7000 ppm or less. In particular, the residual aluminum content is 11,000 ppm or less, the residual titanium content is 7 ppm or less, and the residual styrene monomer content is 50 ppm or less.
00 ppm or less is 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 the specification of Japanese Patent Application No. 7466/1986).
Or ■ method by deashing and washing, that is, JP-A-62-
A styrenic monomer 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. In this method, the polymer is deashed using a solution of an acid or alkali dissolved in an appropriate solvent, and then washed with an appropriate solvent.

In this way, a styrenic polymer with a syndiotactic structure with a low residual aluminum content and a low residual titanium content can be obtained by the method (1) or (2). The styrene monomer content is 7000 ppm 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 styrenic polymer dried under reduced pressure using method (2) is degassed in an extruder and at the same time is made into a molding material (bullet). . 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 material of the stretched film has a smooth rough surface.
A composition in which inorganic fine particles are mainly contained in a styrenic polymer having a syndiotactic structure, in particular, inorganic fine particles with an average particle size of 0.0 to 3 μm are added to the above styrenic polymer.
．． This is a composition containing 001 to 1% by weight. Although this composition is a styrene polymer, it does not necessarily have to be as highly purified as mentioned above, and may be prepared by the method described in JP-A-62-187708 and the like. ) with inorganic fine particles or by precipitating them during polymerization. Here, the inorganic fine particles are group IA, II
Group A, Group IVA, Group VIA, Group ■A, Group ■.

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

hydroxide, sulfide, nitride, halide 8 carbonate,
Acetate, phosphate, phosphite 1 Shows 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 fluoride.

Calcium titanate, strontium titanate.

Barium carbonate, #! IIA group element compounds such as barium J acid, barium sulfate, barium phosphite, IVA group element compounds such as titanium dioxide (titania), -titanium oxide, titanium nitride, zirconium dioxide (zirconia), -zirconium oxide, 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, nB group element compounds such as zinc oxide and zinc acetate, argonium oxide (alumina)
, aluminum hydroxide, aluminum fluoride, 11rB group element compounds such as aluminosilicate (alumina silicate, kaolin, kaolinite), silicon oxide (silica, silica gel) 9 graphite, carbon, graphite, glass, etc.
Group B element compounds, carnalite, kainite.

Examples include natural particles such as mica and bilosite.

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, and more preferably 0.01 to 3 μm.
．． 01-1 μm, the content in the composition is 0.001-1% by weight, preferably 0.001-0.6% 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. Furthermore, if the content of inorganic fine particles in the composition is less than 0.001% by weight, the effect of improving slipperiness will be insufficient, and if the content is more than 1% by weight, it may be 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 constituting the base film of the present invention further 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, boria compounds 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 50 to 2 when the purpose is gloss.
Weight%, if the purpose is to control surface properties, 0.001~
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.

To form the base film of the magnetic recording medium of the present invention,
The method described above may be used, but the operations from heating and melting to heat setting will be specifically explained 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 tandem type with a -shaft is preferred. Note that impurities and foreign matter can be removed by using a suitable mesh in the extruder. In particular, when producing a stretched film with a smooth surface, the mesh is preferably 100 meshes or more, most preferably 400 meshes or more.

When using these meshes here, considering the pressure resistance 9 strength of the mesh itself, the above-mentioned or lower counts may be added to the front and back. Moreover, the shape of the mesh can be appropriately selected and used, such as a flat plate or a cylindrical shape.

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. 5×106 dyne/cn 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. Various types of refrigerant can be used in this case, such as gas, liquid, and metal rolls! Wear.

When using a metal roll or the like, methods such as an air knife, air chamber touch roll, and electrostatic printing 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 preform for drawing, preferably in the range of 20''C to the 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 stretched uniaxially or biaxially. In the case of biaxial stretching, it may be stretched simultaneously in the longitudinal and transverse directions, or it may be stretched sequentially in any order. Further, the stretching may be performed 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 these may be appropriately selected or combined. The stretching temperature may generally be set between the glass transition temperature and melting point of the preform.

In addition, the stretching speed is usually 1×10 to 1×10’%/min,
Preferably I x 103 to 1 x lOS%/min.

In addition to the stretched film obtained by stretching under the conditions described above, it also has dimensional stability and heat resistance at high temperatures.

In cases where in-plane strength balance of the film is required, 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 under tension, relaxation, or limited shrinkage at a temperature between the glass transition temperature and melting point of the film, preferably 100°C below the melting point. In the temperature range from low temperature to just before the melting point, 0
．． This may be done by holding for 5 to 120 seconds. Note that this heat fixing can be performed two or more times under different conditions within the above range. Moreover, this heat fixation may be performed under an inert gas atmosphere such as argon gas or nitrogen gas.

The base film of the present invention obtained in this manner has a linear expansion coefficient 1 surface roughness Ra and a static friction coefficient μs within the ranges described above. In addition, this base film can be made into 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 base film, and includes an undercoat layer,
A back coat layer or a top coat layer can also be formed. Each of these layers is formed on both sides or all or part of one side of the base film.

Furthermore, there are various types of magnetic materials that can be used as materials for the magnetic layer, such as Go, Co-0, and Co-Cr.

Co-V, Co-Ni, Co-P, Co-rFezO
x.

Co-N1-P, Co-N1-N, Co-N1-W.

Co-Ni-Pt, CoN1(Cr)/Cr, Fe
.

Fe-0, Fe-Ag+ rFezo8. Fe-Co
.

Ni, Crag, etc. can be listed.

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 the operating conditions may be appropriately selected according to conventional methods.

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 to 1 μm for vapor deposition and sputtering
In the case of 1 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, cellulose systems such as nitrocellulose and cellulose acetobutyrate, condensation polymer systems such as saturated polyester, polyurethane boria ξ-d, and epoxy, synthetic rubber systems such as butadiene-acrylonitrile copolymers, and Examples include inorganic polymers such as phosphazene, 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 (7.5 g) of copper sulfate pentahydrate (CuSOn' 5H20) was placed in a glass container with an internal volume of 500 mm and replaced with argon.
1 mol), 200 rd toluene, and 24 d (2501 mol) 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-N
The above-mentioned high magnetic field component (i.e., −〇, 1 to −
0.5 ppm) was 43%.

On the other hand, 100 parts of purified styrene monomer was added with dry process silica (
Add 0.4 part of Anilosyl TT-600 (primary particle diameter: 40 mμ) manufactured by Degutsusa ■ and mix in a cylindrical container using a T, K homomixer L type (manufactured by Tokushu Kika Kogyo). Stirring resulted in a styrene mixture. At this time, 0.05 parts by weight of calcium stearate was added.

In a reaction vessel with an internal volume of 2j2, the styrene mixture 11 prepared as described above, 5 mmol of the contact product obtained as described above as aluminum atoms, 5 mmol of triisobutylaluminum, and pentamethylcyclopentadienyl titanium trimethoxide. 90 using 0.025 mmol
The polymerization reaction was carried out at ℃ for 5 hours. After the reaction is complete, the product is decomposed with a methanol solution of sodium hydroxide to decompose the catalyst component.
After repeated washing with methanol, it was dried to obtain 308 g of a polymer.

The weight average molecular weight of this polymer was determined by gel perminication at 135°C using 1,2.4-trichlorobenzene as a solvent.
As measured by John chromatography, it was 389,
000 and weighted average.

The molecular weight/number average molecular weight was 2.64. Furthermore, it was confirmed by melting point and I3C-NMR measurements that this polymer was polystyrene with a syndiotactic structure.

This polymer was dissolved in 1.2.4-)lichlorobenzene 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, this styrene polymer was heated at 150°C for 2 hours.
Dry under reduced pressure. 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. The pellets contain 700 ppm of styrene monomer with a crystallinity of 35%.
It contained.

(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 417.000. Weight average molecular weight/number average molecular weight is 2.54.1! Content is 75
ppm+, and the Ti content was 2 ppm+.

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

Reference example 2 (manufacture 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 ai. 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 110°C2 at a stretching speed of 6000%/min while changing the circumferential speed of each roll. Subsequently, the film was stretched 3 times in the transverse direction using a tenter at 120° C. and at a stretching rate of 6000%/min.

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 linear expansion coefficient of this film 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 mm, and the static friction coefficient was determined according to ASTM D.
-1984B. 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 performed at 330°C using a device equipped with a T-die at the tip of the extruder. Other than the above, 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) Styrenic polymer pellets 50/150/40
The styrenic polymer pellets of Reference Example 1 (1) were melt-extruded using an in-line tandem single-screw extruder as the main extruder containing a 0/150150 mesh, and a double extruder.

(4) 6 Using the styrene polymer pellets of Example 1 (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 with a syndiotactic structure obtained in Example 1 of JP-A-1-95113 (9.4 mol% divinylbenzene units,
Ethylbenzene unit 5.0 mol% 1 weight average molecular weight 36
A 0.5 wt% chloroform solution of 0.000> was prepared, and 0.5 wt% of dry method silica (particle size of Aerosil 7T-600 secondary particles manufactured by Tegutsusa ■) was added to this solution based on the styrene-divinylbenzene copolymer. 40mμ)
was added and mixed uniformly in a cylindrical container using a Homojiki Kisser L type (Tokushu Kika Kogyobu) 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 obtained film are shown in the table.

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

(6) The inorganic fine particles used were silica (silica) with an average particle size of 4 μm (
A styrenic polymer was prepared in the same manner as in Reference Example 1 (1), except that it was used as Jiruton AMT-40 (manufactured by Suirikagaku Kogyo ■), and then in the same manner as in 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 the base film obtained in the same manner as in Reference Example 2 (1) was subjected to corona discharge treatment, and then C.

A target consisting of 80% by weight and 80% by weight of Ni2O was created, and by using this target, approximately 30
A Co--Ni magnetic thin film having a thickness of 0.00 mm was formed.

At this time, the distance between the target and the film is 60 μm.
, plate voltage! , 9 kV, plate current 160
mA, argon pressure 1. IXIO-”tmHg.

Carefully slit this tape to the same width as the VH3 video tape, disassemble the commercially available tape, and replace only the tape.
Created a videocassette.

The slipperiness of this tape was evaluated based on the coefficient of static friction. The coefficient of static friction of this tape was good and equal to that of the base film.

Further, the VH3-video cassette tape produced was recorded and played back using a home video recording device. At this time, as an indicator of reliability, we observed the recording and repeating conditions under room temperature conditions and under high temperature and humidity conditions of 85°C and 75% RH. Under both conditions, there was almost no change, and the image was in good condition with no disturbance. Ta.

Example 2 One side of a base film obtained in the same manner as in Reference Example 2 (1) was subjected to corona discharge treatment and coated with a magnetic paint. The composition of this magnetic paint is 45 parts by weight of γ-F e O3 magnetic powder, vinyl chloride-vinyl acetate copolymer (U, C
, C, manufactured by VAGH) 17 parts by weight, acrylonitrile-butadiene copolymer (N 143 manufactured by Nippon Zeon Co., Ltd.)
2J) 3.5 parts by weight, 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, and 4 parts by weight of carbon black. The thickness of the magnetic layer after drying is 3μ
It was m.

The same procedure as in Example 1 was carried out using this tape. The results are shown in the table.

Example 3 After corona discharge treatment was applied to both sides of the base film obtained in the same manner as in Reference Example 2 (2), magnetic layers were provided on both sides in the same manner as in Example 1. After appropriately polishing both sides of this film, it was cut out to the same size as a commercially available 5-inch floppy disk. Furthermore, this disk was placed in a commercially available floppy disk to create a floppy disk. The static friction coefficient of the film with the magnetic layer was investigated in the same manner as in Example 1. Further, using the prepared floppy disk, the 5AVE and LOAD conditions were examined using NECPC-9801F under room temperature conditions and high temperature conditions, and both were found to be good.

Example 4 The same procedure as in Example 1 was carried out except that a magnetic layer was provided on the smooth 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 same procedure as in Example 1 was carried out except that a magnetic layer was provided on the smooth 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 same procedure as in Example 1 was carried out 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 A film obtained in the same manner as in Reference Example 2 (6) was prepared in the same manner as in Example 1, except that a magnetic layer was provided on one side of the film. The results are shown in the table.

Comparative Example 3 The same procedure as in Example 1 was carried out 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 same procedure as Example 1 was carried out except that a polyethylene phthalate (PET) film (Tetron N512 μm manufactured by Tijin Co., Ltd.) was used. The results are shown in the table.

(Hereinafter in the margin) [Effects of the Invention] The magnetic recording medium of the present invention obtained in a ridged manner has excellent slip properties and smoothness, and also has excellent dimensional stability against temperature and humidity.

Therefore, the magnetic recording medium of the present invention can be applied to various magnetic tapes, magnetic disks, M! It can be suitably used for magnetic drum 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. 1. A magnetic recording medium having a magnetic layer on at least one side of a base film in which the ratio is 0.3 or more and 1.0 or less. (2) The magnetic recording medium according to claim 1, wherein the stretched film is composed of a styrenic 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 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 magnetic recording medium according to any one of claims 1 to 3, which is a laminate having layers.