JPH06285973A - Biaxially orientated composite polyethylene naphthalate film for thin film magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve handling property, running property and durability and also basic characteristics such as high strength, high heat resistance, etc., and thereby to attain higher-density recording by using a biaxially oriented composite film which is constructed of layers A and B having different structures and different average particle sizes, etc. CONSTITUTION:A biaxially oriented composite film prepared by laminating a layer A constituted of polyethylene-2,6-naphthalate containing a germanium compound or the like and a layer B containing inactive particulates. The layer A has a surface structure having a wind-wrought pattern, contains the inactive particulates of an average particle size (x:mum) less than 0.3mum in the amount (y:wt.%) of addition satisfying y<0.12-0.4x and has a surface of a roughness 5nm or below. The layer B contains particles of 0.01-1wt.% of which the average particle size is 0.1-1wt.%, and has a surface of which the roughness is 25nm or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a metal thin film magnetic recording medium, and more specifically to a metal thin film magnetic recording medium having a smooth film surface and excellent handling property, running property and durability. It relates to an axially oriented composite polyethylene-2,6-naphthalate film.

[0002]

2. Description of the Related Art Polyethylene-2,6-naphthalate films are disclosed in Japanese Examined Patent Publication No. 41700/1988 and Japanese Unexamined Patent Publication No.
No. 2,135,339 and the like are conventionally known. The polyethylene-2,6-naphthalate film is superior to the polyethylene terephthalate film in many points such as mechanical strength, heat resistance, and chemical properties, and its use in magnetic recording media is increasing.

In recent years, for high density magnetic recording media, a ferromagnetic metal thin film as a magnetic recording layer is directly used on a non-magnetic support by a physical deposition method such as vacuum deposition or spattering or a plating method without using a binder. The formed ferromagnetic metal thin film magnetic recording medium has been put to practical use. For example, a Co vapor deposition tape (Japanese Patent Laid-Open No. 54-147010), a perpendicular magnetization film made of a Co-Cr alloy (Japanese Patent Laid-Open No. 52-52).
-134706 gazette) etc. are disclosed.

In the conventional coating type magnetic recording medium (magnetic recording medium prepared by mixing magnetic powder in an organic polymer binder and coating it on a non-magnetic support), the thickness of the magnetic layer is as thick as about 2 μm or more. The metal thin film formed by thin film forming means such as vapor deposition, sputtering or ion plating has a very thin thickness of 0.2 μm or less. Therefore, in the metal thin film type magnetic recording medium, the surface state of the non-magnetic support is directly expressed as unevenness on the surface of the magnetic recording layer, which causes noise. Therefore, it is desirable that the surface condition be as smooth as possible.

On the other hand, from the viewpoint of handling such as film formation, winding, and unwinding of the base film, if the film surface is smooth, the slipperiness between the film and the film is poor and a blocking phenomenon occurs, resulting in a product. If not, the surface of the base film is required to be rough.

As described above, the surface of the non-magnetic support is required to be smooth from the viewpoint of electromagnetic conversion characteristics, and it is required to be rough from the viewpoint of handleability.
Therefore, it is necessary to satisfy both of these contradictory properties at the same time.

As a specific method for producing a polyester film aiming at satisfying both of the above properties at the same time, a specific coating agent is applied to the film surface to form a discontinuous film structure (Japanese Patent Publication No. 3-80410). JP-A-60-
No. 180839, JP-A-60-180838, JP-A-60-180837, JP-A-56-16937, JP-A-58-68223) and the like. A composite method for producing a smooth / rough surface film (Japanese Patent Publication No. 1-26373, JP-A-57-36340).
No. 57-341341, JP-B 1-263338
JP-A-57-38762, JP-A-57-3876
No. 3, etc.), a method using low-temperature plasma treatment or corona discharge treatment (Japanese Patent Publication No. 4-3896), and the like.

Further, the raw material polyethylene-2,6-
Examples of the naphthalate composition include catalysts and additives used in transesterification reaction and polycondensation reaction, for example,
Japanese Patent Application Laid-Open No. 2-112411 discloses a method using a manganese compound, an antimony compound and a phosphorus compound.
No. 187501 proposes a method using a calcium compound and a germanium compound.

[0009]

However, the polyethylene-2,6-naphthalate film obtained by the above-mentioned method which has hitherto been known has a good elastic modulus,
Although heat resistance and chemical properties were obtained, the surface smoothness for metal thin film magnetic recording was not sufficient. Even if an attempt is made to form a film having sufficient smoothness by using a raw material in which so-called internal particle precipitation is suppressed as much as possible, a surface structure peculiar to polyethylene-2,6-naphthalate (form with a ripple pattern or a ripple pattern on the surface) It was impossible to achieve sufficient surface smoothness for metal thin film magnetic recording.

Therefore, the present invention relates to polyethylene-2,6-
A biaxially oriented composite polyethylene-2,6-naphthalate film for a metal thin film magnetic recording medium which has a wind-like surface structure but has a good surface property, handling property and running property in the production of a naphthalate film. The purpose is to provide.

[0011]

A biaxially oriented composite polyethylene naphthalate film for a metal thin film magnetic recording medium according to the present invention, which is directed to this object, comprises a polyethylene-2,6-naphthalate containing a germanium compound and a magnesium compound. Is a biaxially stretched composite film in which a layer A consisting of the following components and a layer B consisting of polyethylene-2,6-naphthalate containing inert solid fine particles are laminated. Diameter (x: μm) is 0.3μ
Inert solid fine particles of less than m are contained in an amount (y:% by weight) satisfying the following formula (1), and y <0.12-0.4x (1) and a surface having a surface roughness of 5 nm or less. The layer B is composed of polyethylene-2,6-naphthalate containing 0.001 to 1% by weight of particles having an average particle size of 0.1 to 0.5 μm, and has a surface having a surface roughness of 25 nm or less. It is characterized by being present.

The polyethylene-2,6-naphthalate in the present invention is a polyethylene naphthalate in which 80 mol% or more of its constituent components are ethylene naphthalate. Examples of the polyester copolymer component other than ethylene naphthalate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, 1,4-butylene glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and polytetramethylene glycol, Dicarboxylic acid components such as isophthalic acid, 5-sodiosulfoisophthalic acid, adipic acid, sebacic acid and its ester-forming derivatives, oxycarboxylic acids such as oxybenzoic acid and its ester-forming derivatives and the like can be used. It is not limited to.

The intrinsic viscosity of such polyethylene-2,6-naphthalate is preferably 0.60 or more.
More preferably, 0.63 to 0.75 is good. In order to prevent a defective phenomenon due to tearing during film formation and film handling, 0.60 or more, preferably 0.63 or more is required. If it exceeds 0.75, melt viscosity becomes too high and melt extrusion becomes difficult.

In producing the above polymer, the polyethylene-2,6-naphthalate raw material used for the layer A is the surface on which the metal thin film magnetic recording layer is provided.
Particularly, good surface properties after biaxial stretching are required. It is important to use a magnesium compound as a transesterification catalyst and a germanium compound as a polycondensation catalyst. In the case of a calcium-based compound that is generally used as a transesterification reaction catalyst, it is not suitable from the viewpoint of surface property because it forms so-called internal particles, and a magnesium-based compound should be selected. Further, in the case of an antimony compound generally used in a polycondensation catalyst, the solubility in the polymer is poor, and the surface property deteriorates because it precipitates in the polymer and acts as a nucleus for forming protrusions during film formation, Germanium compounds should be added.

The above fact is a general matter in polyester, but in the case of polyethylene-2,6-naphthalate, a unique phenomenon occurs. That is, even if a transesterification catalyst is made of a magnesium-based compound to prevent the formation of internal particles, polyethylene-2,6-naphthalate is biaxially stretched if a poor polymer-soluble substance is present.
For example, Fig. 1 (Surface photograph by differential interference microscope, magnification:
50 times), as shown in Fig. 50), the surface has a unique surface structure (uneat structure with a wind or ripple pattern on the surface).
Is formed. This is expressed even if the polycondensation catalyst is made to be a germanium-based compound in order to eliminate the poor polymer-soluble substance, but in the present invention, in order to form a strong and unique surface structure, the magnesium-based compound is used. And the germanium compound must be used at the same time. Similarly, in the case of adding external particles, a surface pattern like a wind ripple is developed. Conventionally, it has been said that the surface structure for a metal thin film magnetic recording medium is not sufficient in terms of surface smoothness, but by adding external particles within a specific range, this structure has a surface structure. It has been found that the surface roughness can be maintained as it is while being sufficiently smooth for a metal thin film magnetic recording medium.

That is, a raw material in which a transesterification catalyst is a magnesium compound and a polycondensation catalyst is a germanium compound is used, and the average particle size (x: μm) is less than 0.3 μm, preferably less than 0.2 μm. Sufficient smoothness can be maintained for a metal thin film magnetic recording medium by containing solid fine particles in an amount (y:% by weight) satisfying the following formula (1) and controlling the surface structure and surface roughness of the wind ripple pattern. y <0.12-0.4x (1)

If the particle size and the addition amount are out of the above ranges, a strong wind-like structure is formed and sufficient surface smoothness cannot be obtained for a metal thin film magnetic recording medium. Further, if the particles having an average particle size of 0.2 μm or more are added in an amount of 0.1% by weight or more, probably because of the high ability of forming surface protrusions, the formation of protrusions becomes a controlling factor of the surface structure, and the specific surface structure is Although it cannot be observed because it is hidden, the surface smoothness as a film for a metal thin film magnetic recording medium is lost.

Magnesium compounds used here include magnesium hydrides, alcoholates, chlorides,
Examples thereof include acetates, carbonates, carboxylates and sulfates. The addition amount is preferably 0.01 mol% or more and 0.15 mol% or less based on the lower alkyl ester of dicarboxylic acid as an atom of magnesium. 0.
When it is less than 01 mol%, the transesterification reaction does not proceed sufficiently or the reaction time becomes extremely long, which makes the production substantially impossible. Further, when the amount added exceeds 0.15 mol%, the transesterification reaction is extremely short and it becomes substantially difficult to control the reaction.

Examples of germanium compounds include germanium oxides, organic acid salts, and alkyl or aryl compounds. Specific examples thereof include germanium oxide, germanium tetraacetate, germanium oxalate, germanium tartrate, and tetraphenyl germanium.
The amount of addition is 0.005 mol% or more as a germanium atom with respect to the lower alkyl ester of dicarboxylic acid, and 0.1.
It is preferably 15 mol% or less. When the amount is less than 0.005 mol%, the polycondensation exchange reaction does not proceed sufficiently or the reaction time becomes extremely long, which makes the production substantially impossible. If it is added in excess of 0.15 mol%, the polycondensation exchange reaction will be extremely short and it will be substantially difficult to control the reaction.

Since the polyethylene-2,6-naphthalate raw material used for the layer B is a running surface on which the metal thin film magnetic recording layer is not formed, the running property is rather emphasized. Therefore, a polymer obtained by a conventionally known polymerization method may be used, but it is necessary to add inert solid fine particles to improve the running property according to a conventionally known surface forming means. However, for metal thin film magnetic recording media, particles must not be added unnecessarily in order to prevent heat loss on the cooling can during vapor deposition. 0.001 to particles having an average particle size of 0.1 to 0.5 μm
It is necessary to add 1% by weight and adjust the surface roughness to 25 nm or less. Addition of particles having a particle size of less than 0.1 μm is not preferable because the slippery effect is not exerted and handling properties are poor, and if it exceeds 0.5 μm, heat loss on the can occurs. For the effect of slipperiness and stabilization of the heat loss phenomenon, it is more preferable to use an average particle size in the range of 0.15 μm to 0.35 μm, and to add a surface roughness of 0.05 to 0.5% by weight. It is preferable to adjust the thickness to 15 nm to 23 nm.

The particles include, but are not particularly limited to, crosslinked polydivinylbenzene, colloidal silica, calcium carbonate, zirconium oxide and aluminum oxide. One kind of particles selected from these particles may be used, or two or more kinds of particles may be used in combination.

The thickness ratio of layer A and layer B must be 1.5 μm or more in absolute value of the thickness of layer A. Preferably 3
μm is required. The thickness of the layer B is the total thickness less the thickness of the layer A. Considering the falling property of the fine particles added to the layer B, a thickness of 0.8 times the average particle size or more is required, but it is expensive. It is better to be as thin as possible in terms of the cost of raw material containing fine particles.

The biaxially oriented composite polyethylene-2,6-naphthalate film is obtained by subjecting the above-mentioned polyethylene-2,6-naphthalate to composite melt extrusion according to a conventional method and cooling and solidifying on a casting drum to obtain an unstretched film.
This unstretched film is obtained by uniaxially stretching, applying a desired coating liquid, drying and then stretching and orienting in a direction orthogonal to the uniaxially stretching direction, and heat-setting. Biaxial stretching can be performed by, for example, a sequential biaxial stretching method or a simultaneous biaxial stretching method. If desired, the mechanical strength in the desired direction can be increased by re-stretching in the machine direction or the transverse direction or the machine direction and the transverse direction. You can also

The layer A may be coated with a known discontinuous film by applying a known coating liquid (for example, JP-B-63-57238). As the polymer capable of forming a discontinuous film, a water-soluble polymer having a molecular weight of 10,000 to 2,000,000, preferably 100,000 to 1,000,000 can be used. When the molecular weight is less than 10,000, the film described below becomes soft, the structure retention becomes difficult, and the durability deteriorates. When the molecular weight exceeds 2,000,000, the coating becomes too hard and brittle, and thus the durability also deteriorates. Examples of such water-soluble polymers include polyvinyl alcohol, tragand gum, gum arabic, casein, gelatin, methyl cellulose, hydroxylethyl cellulose, carboxymethyl cellulose and the like.

The discontinuous coating is applied to improve running property and durability, and the thickness of the discontinuous coating is 50 nm or less, preferably 5 to 30 nm. If the thickness exceeds 50 nm, the electromagnetic conversion characteristics of the vapor-deposited thin film, especially the S / N ratio (signal / noise ratio) deteriorates, which is not preferable.

The high temperature and high discontinuous coating in order to further improve the running properties under humidity and an average particle size 3nm or more fine particles to the surface 10 ⁴ to 10 ¹¹ / mm ² be present are preferred. Fine particles of less than 3 nm do not improve the runnability of the deposited thin film surface. If the average particle size exceeds 150 nm, the electromagnetic conversion characteristics, especially the S / N ratio, deteriorate. Further, even in the density of 10 ⁴ / mm ^2, it does not improve the running property, 10 ¹¹
If the number of particles / mm ² is exceeded, the S / N ratio of the electromagnetic conversion characteristics of the magnetic surface deteriorates. The shape of the fine particles may be spherical, elliptical, rectangular, cubic, or the like, but spherical particles are particularly suitable.

As the particle species, inorganic fine particles such as MgO, ZnO, MgCO ₃ , CaCO ₃ , SiO ₂ ,
CaSO ₄ , BaSO ₄ , Al ₂ O ₃ , TiO ₂ and C
An acid salt such as a, Ba, Zn, or Mn can be used. Organic fine particles include acrylic resin, acrylic /
A styrene copolymer resin, a vinyl acetate resin, an acrylic / vinyl acetate copolymer resin, a polystyrene resin, a crosslinked polydivinylbenzene resin, a silicone resin or the like can be used.

These discontinuous coatings and particles have runnability,
It is applied for the purpose of improving durability, but one or both may be applied depending on the requirements. Further, an easily adhesive resin and / or a silane coupling agent may be added to improve the adhesiveness between the coating film and particles and the surface of the film base.

The easily adhesive resin is preferably a combination of a highly polar group and a hydrophobic group in the molecule. As the polar group, those having a hydroxyl group, an acid group, an ether, an ester group, an epoxy group, a sulfonic acid group, a urethane bond, or the like, and an aliphatic chain or an aromatic chain as a hydrophobic portion are preferable, and a polyester ether copolymer or a water-soluble group. A polyester copolymer, a polyester copolymer containing a polyethylene glycol / sulfonic acid alkali metal salt, or the like can be used. Among the polyester copolymers composed of dicarboxylic acid and glycol, those having 5-sodium sulfoisophthalate and diethylene glycol as components are particularly preferable.

The silane coupling agent is an organosilicon monomer having two or more different reactive groups in its molecule, and one of the reactive groups is a methoxy group, an ethoxy group, a silanol group, etc., Another reactive group is a vinyl group, an epoxy group, a methacrylic group, an amino group, a mercapto group and the like. The reactive group is selected to bond with the silicone side chain group or the terminal group, but vinyltrichlorosilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyl Roxypropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxy Silane, γ-aminopropyltriethoxysilane and the like can be used.

The surface roughness of the above-mentioned layer A (the coating surface when a coating film is applied) is preferably 5 nm or less. More preferably, it is 4 nm or less. If it exceeds 5 nm, the electromagnetic conversion characteristics are deteriorated and it becomes unsuitable for a metal thin film magnetic recording medium. Further, the coating film applied to the layer A may be applied to the layer B for further improving the running property.

The Young's modulus of the film of the present invention in the width direction is 60.
It should be 0 kg / mm ² or more, preferably 650 kg / mm ² or more, and more preferably 680 kg / mm ² or more. When the Young's modulus in the width direction is lower than the above range, both tape edge damage and output become defective, which is not preferable. Although not particularly limited, when the Young's modulus in the longitudinal direction of the film is Young's modulus in the width direction of −50 kg / mm ² or less, it is effective for obtaining the effect of the present invention.

The heat shrinkage of the film of the present invention is not particularly limited, but the effect of the present invention is further improved when the heat shrinkage at 150 ° C. in the longitudinal direction of the film is less than 4.0%.

Next, a method for producing the film of the present invention will be described. An example of the method for producing the polyethylene-2,6-naphthalate of the layer A used in the present invention will be described. After supplying dimethyl naphthalene-2,6-dicarboxylate and ethylene glycol to the transesterification reactor, about 220 to 2 in the presence of a magnesium compound as a transesterification reaction catalyst.
The temperature is gradually raised to 50 ° C. over 2 to 8 hours. By-products such as methanol produced by the transesterification reaction are continuously distilled out of the reaction system. Then, after adding a phosphorus compound and a germanium compound, excess ethylene glycol is distilled off to obtain bishydroxyethyl-2,6-naphthalate and its low polymer (hereinafter referred to as BHN).
Then, after transferring this BHN to a polycondensation reactor, the reaction system is gradually heated and decompressed to proceed the polycondensation reaction, and finally the temperature of the reaction system is 280 to 350 ° C. and the degree of vacuum is 1.0 mm.
A polyethylene-2,6-naphthalate is obtained by making it Hg or less. At the stage of polycondensation reaction polyethylene
The intrinsic viscosity of 2,6-naphthalate changes continuously, but the temperature and vacuum degree of the reaction system are controlled so that the intrinsic viscosity becomes 0.2 within 0.1 to 1.5 hours after the initiation of the polycondensation reaction. It is preferable to reach it. Further, solid phase polymerization may be carried out in order to further increase the degree of polymerization of the polymer obtained by liquid phase polymerization.

As the polyethylene-2,6-naphthalate of the layer B, the polymer of the layer A can be used, or the one obtained by a conventionally known method can be used.

As a method of incorporating particles into these polyethylene-2,6-naphthalates, they may be added before polymerization, during polymerization, or after polymerization, but ethylene glycol which is a diol component of polyester. A method of mixing and dispersing in the form of a slurry into a polymer or the like, and a method of mixing particle powder or an aqueous slurry of particles with a polymer using a vent type twin-screw kneading extruder are preferably used.
As a method of adjusting the content of particles, a method of diluting the high-concentration particle master pellet obtained by the above method during film formation and extrusion can also be used.

Next, after thoroughly drying these polyethylene-2,6-naphthalates, the two 26
Each of them is melt-extruded at a temperature of 0 to 330 ° C., laminated in the thickness direction of the polymer with pinol placed directly above the slit-shaped die and discharged from the die. The discharged polymer is kept at 20 ° C to 60 ° C.
An unstretched film is prepared by cooling and solidifying on a casting drum at ℃.

Next, this unstretched film is uniaxially stretched, and if desired, the coating liquid is applied by a Meyer bar type coating device,
After drying, it is stretched in a direction perpendicular to the direction in which it was previously stretched and heat-treated. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. In the case of the simultaneous biaxial stretching method, it is necessary to apply the coating step to the unstretched film before stretching. However, it is preferable to use a sequential biaxial stretching method in which stretching is first performed in the longitudinal direction and then in the width direction.

Stretching in the longitudinal direction is carried out by using a commonly used roll, but as preheating and stretching rolls, a roll made of a non-adhesive material such as Teflon or silicon is used, and the smoothness of the film surface is good. Therefore, the electromagnetic conversion characteristics of the magnetic tape are improved, which is preferable. The stretching temperature is 110 to 160 ° C, preferably 115 to 150
A method of stretching at a temperature of 3.5 to 7 times is used. The stretching may be performed in one stage or in two or more stages. If the stretching ratio is out of this range, uneven stretching, breakage, etc. occur and a film having good properties cannot be obtained.

The coating solution is dried by using a known tenter at a temperature of 80 ° C. to 140 ° C. for 0.5 to 20 seconds, depending on the water content of the coating solution.
It is possible to dry in less than 0.5 seconds,
Not only the desired hot air temperature rises, but also the air velocity increases, so that the coating film is disturbed by the wind and becomes non-uniform. If it exceeds 20 seconds, crystallization of the uniaxially stretched film proceeds, and the film tends to break during the subsequent stretching in the width direction, which is not preferable.

The stretching in the width direction is preferably carried out using a known tenter at a temperature of 100 to 160 ° C. for 3 to 8 times. If the stretching temperature and the stretching ratio deviate from these ranges, uneven stretching, breakage, etc. occur and a film having good characteristics cannot be obtained. The biaxially stretched film may be further stretched in at least one direction, the lengthwise direction or the widthwise direction, or may be further stretched in the widthwise direction or the lengthwise direction.

Next, the stretched film is heat-treated. As a heat treatment condition, it is performed at a constant length of 160 to 230 ° C., preferably 170 to 220 ° C. for 0.5 to 30 seconds. If necessary, the film can be relaxed in the longitudinal direction by a method of utilizing the peripheral speed difference between two or more rolls heated to a temperature equal to or lower than the heat treatment temperature after the heat treatment.

[Measurement Method of Physical Properties and Evaluation Method of Effect] The characteristic values of the present invention are based on the following measurement methods and evaluation criteria.

(1) Judgment of formation of wind-printed protrusions Observed with a differential interference microscope (50 times) and judged by the presence or absence of protrusions in the form of the photograph shown in FIG.

(2) Surface Roughness (Ra) The surface roughness was measured using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 20 measurements was used as the value.・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measurement length: 1 mm ・ Cutoff value: 0.08 mm Ra is defined, for example, by Jiro Nara, "Measurement / Evaluation Method of Surface Roughness". (Comprehensive Technology Center, 1983).

(3) Thickness of discontinuous film The surface on which the discontinuous film is formed is measured with the above-mentioned stylus roughness meter. It is a value obtained by obtaining the average height interval between peaks and valleys on the obtained roughness curve. The measurement is performed at a vertical magnification of 500,000 times or more and a cutoff of 0.08 mm.

(4) Young's modulus Measured at 25 ° C. and 65% RH using an Instron type tensile tester in accordance with ASTM-D-882.

(5) Heat Shrinkage A sample film was cut out with a width of 10 mm and a length of 250 mm,
Two marks are put at intervals of about 200 mm, and the distance is accurately measured (this is Amm. This sample is left in a hot air oven at 150 ° C for 30 minutes under no tension, and then the distance between the marks is measured. Is measured (this is Bmm), and 100 × (A−
B) / A was defined as the heat shrinkage rate.

(6) Handling property As for the handling property, the produced base film has an inner diameter of 6
Using an inch plastic core, with the non-magnetic surface facing outside, slit into a length of 500 mm x 5000 m and roll up. 1 roll like this
Create 0 rolls and count the number of rolls that can be wound well without wrinkles or winding misalignment. If 8 or more out of 10 cannot be wound well, it is determined that the handling property is poor.

(7) Runnability A film obtained by slitting a tape in a width of 1/2 inch using a tape runnability tester TBT-300 type (manufactured by Yokohama System Research Co., Ltd.). The initial friction coefficient was determined by the following formula (the film width was 1/2 inch): μk = 0.733 log (T ₂ / T ₁ ) where T ₁ is the inlet tension, T ₂ is the outlet tension, the guide diameter is 6 mmφ, the guide material is SUS27 (surface viscosity 0.2S), the wrap angle is 180 °, and the running speed is 3.
It is 3 cm / sec. When μk obtained by this measurement was 1.0 or less, the running property was determined to be good, and when it exceeded 1.0, the running property was determined to be poor. This μk is a critical point that affects the handling property and the running property of the tape when processing the film such as a magnetic recording medium.

(8) Output characteristics and heat loss By the continuous vacuum oblique deposition method, Co,
Ni ferromagnetic metal thin film (Ni = 20% by weight, film thickness 1500)
Angstroms) in the presence of trace amounts of oxygen. The oxygen concentration is adjusted so that the oxygen content of the ferromagnetic metal thin film is 5% in terms of the number of atoms with respect to the metal. Got,
When the vapor-deposited film is observed and discolored in a vertical direction in a streak shape or when the film melts during vapor deposition, it is determined that the heat loss property is poor. After that, stearic acid is applied to the surface of the obtained ferromagnetic metal thin film so as to be about 10 mg / m ² and slit to a width of 8 mm to obtain a magnetic tape. A 50 m length of this tape was incorporated into a Sony high-eight cassette to form a VTR cassette tape. SON on this tape
A YV household VTR (EV-S900) was used to record a 100% chroma signal with a Shiba Soku TV test waveform generator (TG7 / U706), and a Shiba Soku color video noise measuring device (925D / Chroma S / N was measured in 1).

(9) Durability The above tape was repeatedly run 1000 times, and judged from the degree of scratches on the magnetic surface. A: No scratch is observed on the tape surface. ◯: A slight scratch is observed on the tape surface, but no strong scratch is observed. X: A strong scratch is recognized on the tape surface. The measurement environment is 25 ° C / 60% RH and 50 ° C / 8.
It is carried out in the state of 0% RH and judged by the worse evaluation result.

(10) Particle Presence Density in Coating Film The film surface was observed with a scanning electron microscope at 50,000 times and 1
Take 0 photos. From the photograph, the number of particles is counted and converted into particle density per 1 mm ² .

[0054]

EXAMPLES Next, the embodiments of the present invention will be explained based on examples. Example 1 After supplying 100 parts of dimethyl naphthalene-2,6-dicarboxylate, 50 parts of ethylene glycol and 0.06 part of magnesium acetate tetrahydrate to an ester exchange reactor equipped with a stirrer, a rectification column and a condenser. The temperature was gradually raised to 180 to 240 ° C., and simultaneously produced methanol was continuously distilled out of the reaction system to carry out the transesterification reaction. The reaction product thus obtained was added with phosphoric acid trimethyl ester 0.02
After adding 5 parts and reacting for 15 minutes, 0.02 part of germanium dioxide was added and reacted for further 5 minutes. Continuously distilling ethylene glycol continuously 2
A polycondensation reaction was carried out by raising the temperature to 90 ° C. and simultaneously reducing the pressure to 0.2 mmHg to obtain a polymer having an intrinsic viscosity of 0.64. This polymer is referred to as polymer A-1.

A water sol (particle concentration: 50% by weight) containing cross-linked polydivinylbenzene particles having an average particle diameter of 0.15 μm and the above polymer were respectively added to a high concentration particle master of 2% by using a vent type twin-screw extruder. Made pellets. This polymer is designated as A-2.

A water sol (particle concentration: 50) containing crosslinked polydivinylbenzene particles having an average particle size of 0.30 μm.
2 wt%) and the above polymer were each made into a 2% concentrated particle master pellet using a vented twin-screw extruder.
This polymer is designated as B-1.

As the polymer for the layer A, a polymer prepared by mixing the polymer A-1 and the polymer A-2 to have a particle concentration of 0.05% by weight was vacuum dried at 170 ° C. for 6 hours. On the other hand, as a polymer for the layer B, the raw materials obtained by mixing the polymers A-1 and B-1 and adjusting the particle concentration to 0.2% by weight are dried with another dryer.
It was vacuum dried at 0 ° C. for 6 hours.

Each of them was melt-extruded at 295 ° C. by another extruder, and after high-precision filtration, two layers were laminated in the thickness direction in a molten state using pinol on the die (thickness ratio of layer A and layer B: 5:
1) and extruded into a sheet from a fish tail type die with a slit width of 2 mm, and at 30 ° C. by an electrostatic applied cast method.
The film was wound around a casting drum of No. 1 and cooled and solidified to obtain an unstretched film having a two-layer structure with a thickness of about 133 μm. This unstretched film was stretched 4.1 times in the longitudinal direction at a roll surface temperature of 130 ° C. using a silicon roll.

Subsequently, this film was stretched 5.0 times at an ambient temperature of 130 ° C. in a tenter and heat-treated at an ambient temperature of 210 ° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 6.5 μm.

In the film obtained, the layer A had a peculiar structure like polyethylene-2,6-naphthalate, and the surface roughness was 2.1 nm. Layer B had many surface protrusions based on particles and had a surface roughness of 16 nm. The properties are as shown in Table 1, and the film had good surface properties, handling properties, running properties, and durability.

Example 2 In Example 1, after being stretched in the longitudinal direction, a coating solution having the following formulation was applied to Layer A with a Mayer bar coater at 15 mg / m ² and then dried at 120 ° C. for 5 seconds. . (Prescription) Methylcellulose 0.2% by weight Water-soluble polyester 0.3% by weight Colloidal silica 0.2% by weight (particle diameter 12 nm) Subsequently, this film was put in a tenter to obtain an ambient temperature of 130.
The film was stretched 5.0 times at 0 ° C. and heat-treated at 210 ° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 6.5 μm.

In the layer A, the surface structure of a wind-print pattern peculiar to polyethylene-2,6-naphthalate is formed, and 2
A 0 nm-thick discontinuous film was formed, and 5 × 10 ⁷ fine particles / mm ^{2 were} present in the film and on the film surface. The surface roughness was 3.5 nm. Layer B had many surface protrusions based on particles and had a surface roughness of 16 nm. The respective properties are as shown in Table 1, and the film had good surface properties, handling properties, running properties, and durability.

Example 3 In Example 2, the coating liquid formulation was changed to the following. (Prescription) Acrylic resin emulsion: 0.4% by weight (particle size 100 nm) A discontinuous film is not formed on layer A, and 4 × 10 ⁶ flat acrylic particles are formed due to deformation during stretching and heat treatment.
mm ² there is wind ripples like structure of polyethylene-2,6-naphthalate specific formation the surface roughness was 3.8 nm. Layer B had many surface protrusions based on particles and had a surface roughness of 16 nm. Each characteristic is as shown in Table 1,
The film had good surface properties, handling properties, running properties, and durability.

Comparative Example 1 A film of 6.5 μm was obtained in the same manner as in Example 1, except that calcium acetate was used instead of magnesium acetate. In Layer A, a strong wind-striped structure peculiar to polyethylene-2,6-naphthalate was formed.
As a result, the surface roughness was as high as 8.0 nm. Layer B has a large number of protrusions formed of particles and has a surface roughness of 16
was nm. The respective properties are as shown in Table 1, and the film had poor surface properties and had good handling properties, running properties, and durability.

Comparative Example 2 A film was formed in the same manner as in Example 1 except that antimony trioxide was used instead of germanium dioxide, and had a thickness of 6.5 μm.
I got a film of. Layer A contains polyethylene-2,6-
A strong wind-striped structure peculiar to naphthalate was formed. As a result, the surface roughness was as rough as 7.6 nm. Layer B
Has a large number of protrusions formed by particles and has a surface roughness of 1
It was 6 nm. The respective properties are as shown in Table 1, and the film had poor surface properties and had good handling properties, running properties, and durability.

Comparative Example 3 A film was formed in the same manner as in Example 1, except that the raw material in which the polymer A-1 and the polymer A-2 were mixed and the particle addition amount was adjusted to 0.15% by weight was used for the layer A. , 6.5 μm film was obtained. In the layer A, a wind ripple structure having a strength peculiar to polyethylene-2,6-naphthalate was formed. As a result, the surface roughness was as high as 7.8 nm. Layer B had a large number of protrusions formed by particles and had a surface roughness of 16 nm. The respective properties are shown in Table 1, and the film was good in handling property, running property and durability, but poor in surface property.

Comparative Example 4 In Example 1, as the polymer for layer B, A-1 and B-
A film having a thickness of 6.5 μm was obtained in the same manner except that 1 raw material was mixed and the particle concentration was changed to 0.4%. In Layer A, a peculiar structure like polyethylene-2,6-naphthalate was formed, and the surface roughness was 2.1 nm. Layer B had a large number of projections formed of particles and had a surface roughness of 30 nm. Each characteristic is as shown in Table 1,
The film was good in surface property, running property and durability, but was poor in heat loss and poor in overall handling property.

Comparative Example 5 In Example 1, the polymer for layer B was made the same as the polymer for layer A, and a substantially monolayer film was formed to obtain a film having a thickness of 6.5 μm. For both layer A and layer B, polyethylene-
The surface roughness was 2.1 nm although it formed a wind-like surface structure peculiar to 2,6-naphthalate. Table 1 shows each characteristic
As shown in (4), the film had good surface property, running property and durability, but poor handling property.

[0069]

[Table 1]

[0070]

When the film of the present invention is used, polyethylene-2,6-naphthalate containing a specific compound is used as a raw material in which external particles in a specific range are added, and biaxially oriented to obtain a metal. Sufficient surface properties are obtained for a thin film magnetic recording medium, and good handling properties, running properties and durability can be obtained by compounding this film and providing a specific coating layer if necessary. As a result, the high image quality of the metal thin film magnetic recording medium and the high strength and high heat resistance characteristics which are the basic characteristics of polyethylene-2,6-naphthalate are utilized to open the way for high density recording.

[Brief description of drawings]

FIG. 1 is a differential interference microscope photograph (magnification: 50 times) showing a wind-striped or rippled surface structure peculiar to a polyethylene-2,6-naphthalate film (drawing-substituting photograph for thin film).

Claims (2)

[Claims] 1. A layer A made of polyethylene-2,6-naphthalate containing a germanium compound and a magnesium compound and a layer B made of polyethylene-2,6-naphthalate containing inert solid fine particles are laminated. In the biaxially stretched composite film, layer A has a surface pattern structure like a wind ripple, and the addition amount of inert solid fine particles having an average particle diameter (x: μm) of less than 0.3 μm that satisfies the following formula (1). (Y: weight%), y <0.12-0.4x (1) and a surface having a surface roughness of 5 nm or less, and the layer B has particles having an average particle diameter of 0.1 to 0.5 μm. A biaxially oriented composite polyethylene na for a metal thin film magnetic recording medium, characterized by comprising 0.002 to 1% by weight of polyethylene-2,6-naphthalate and having a surface having a surface roughness of 25 nm or less. Phthalate fill Mu. 2. The layer A comprises a discontinuous film and an average particle size of 3 n.
The biaxially oriented composite polyethylene naphthalate film for a metal thin film magnetic recording medium according to claim 1, which is coated with a coating film in which either or both of fine particles of m or more are present.