JPH06286089A - Biaxially oriented composite polyethylene naphthalate film for metal thin film magnetic recording medium - Google Patents

Abstract

PURPOSE:To perform higher density recording by utilizing high picture quality of a metal thin film magnetic recording medium and high strength, high heat resistant characteristics of fundamental characteristics of polyethylene-2,6- naphthalate. CONSTITUTION:A biaxially oriented composite film has a layer A made of polyethylene-2,6-naphthalate containing germanium compound and magnesium compound, and a layer B made of polyethylene-2,6-naphthalate containing inactive solid fine particles and laminated on the layer A. The layer A is covered with a coating film in which a discontinuous film or fine particles having a mean particle size of 3nm or more or both exist in such a manner that its surface roughness is 5nm or less. The layer B is formed of polyethylene-2,6- naphthalate containing 0.001-1wt.% of particles having mean particle size of 0.1-0.5mum and a biaxially oriented composite polyethylene naphthalate film for a metal thin film magnetic recording medium has a surface having surface roughness of 25nm or less.

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.
The thing disclosed by the 2-135339 gazette etc. is 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, a blocking phenomenon occurs, and the product cannot be a product. The film surface 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 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 to satisfy this, a method of applying a specific coating agent to the surface of the film to form a discontinuous film structure (Japanese Patent Publication No. 3-80410, JP-A-60-60). -180839, JP-A-60-180838, JP-A-60-180837
JP-A-56-16937, JP-A-58-6822
No. 3, etc.), a composite method in which two kinds of polymers are laminated to form a smooth / rough surface film on the front and back surfaces (Japanese Patent Publication No. 1-2633).
7, JP-A-57-36340, and JP-A-57-3633.
No. 41, Japanese Patent Publication No. 1-26338, and JP-A-57-387.
62, JP-A-57-38763, etc.), a method by low temperature plasma treatment or corona discharge treatment (Japanese Patent Publication No.
No. 3896) has been devised.

In addition, 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.

[0007]

However, the polyethylene-2,6-naphthalate film obtained by the above-described method which is conventionally known can provide good elastic modulus, heat resistance and chemical properties. However, 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-
Good surface properties in naphthalate film production,
It is also an object of the present invention to provide a biaxially oriented composite polyethylene-2,6-naphthalate film for a metal thin film magnetic recording medium, which is easy to handle.

[0009]

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, is a polyethylene-2,6-containing a germanium compound and a magnesium compound.
Layer A made of naphthalate and layer B made of polyethylene-2,6-naphthalate containing inert solid fine particles
A biaxially stretched composite film in which
Is coated with a coating film containing either or both of a discontinuous film and fine particles having an average particle size of 3 nm or more, and a surface roughness of 5
layer B has an average particle size of 0.1 to 0.5.
made of polyethylene-2,6-naphthalate containing 0.001 to 1% by weight of particles having a diameter of 25 μm.
It has a surface of m or less.

The polyethylene-2,6-naphthalate in the present invention is 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 the production of the above-mentioned polymer, the polyethylene-2,6-naphthalate raw material used especially 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 that a magnesium compound is used as a transesterification catalyst and a germanium compound is used as a polycondensation catalyst, and inert solid particles are not added from the outside as much as possible.
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. Also, the addition of external particles is
It should not be added as much as possible because it becomes the nucleus of surface protrusion formation.

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.
Fig. 1 (Photograph of film surface by differential interference microscope: 50
As shown in FIG. 4), a surface structure peculiar to the surface (uneat structure having a wind-like or ripple-like form on the surface) is formed. This means that even if the polycondensation catalyst is replaced with a germanium-based compound in order to eliminate a substance having poor polymer solubility, a unique surface structure is similarly formed.

Even in the case of external particles, it is better not to add it because it is necessary to reduce the poorly soluble substance in the raw material as much as possible.
When 0.08% by weight or less of particles having an average particle size of less than 0.1 μm is added, substantially no unique surface structure is generated,
Fine protrusions are formed. Outside this range, a surface structure peculiar to polyethylene-2,6-naphthalate is formed. However, in the case of external particles, the formation of protrusions is the dominant factor for the surface structure when 0.1% by weight or more of particles having an average particle diameter of 0.2 μm or more is added, probably because the ability to form surface protrusions is high. It cannot be observed because the peculiar surface structure is hidden, but the surface smoothness as a film for a metal thin film magnetic recording medium is lost.

That is, by using a magnesium-based compound and a germanium-based compound and not adding external particles to a polymer that suppresses the formation of internal particles and polymer-insoluble substances, a surface structure peculiar to polyethylene-2,6-naphthalate can be obtained. Generation can be suppressed, and surface properties for a metal thin film magnetic recording medium can be achieved. However, as described above, 0.08% by weight of particles having an average particle size of less than 0.1 μm is used.
When added below, it may be added because it does not form a substantially unique surface structure.

Magnesium compounds used herein include magnesium hydrides, alcoholates, chlorides,
Examples thereof include acetate, carbonate, carboxylate and sulfate. 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.

Examples of the particles include crosslinked polydivinylbenzene, colloidal silica, calcium carbonate, zirconium oxide and aluminum oxide, but are not particularly limited. 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 discontinuous coating applied to the layer A can be obtained by applying a known coating liquid (for example, JP-B-63-57238). The polymer having a discontinuous film forming ability has a molecular weight of 10,000 to 2,000,000, preferably 100,000 to
One million water-soluble polymers 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 film is necessary for improving running property and durability, but the thickness of the discontinuous film 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.

In order to further improve the running property under high temperature and high humidity, it is preferable that fine particles having an average particle diameter of 3 nm or more are present in the discontinuous coating and on the surface thereof at 10 ⁴ to 10 ¹¹ particles / mm ² . 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 S / N ratio of the electromagnetic conversion characteristics deteriorates. Also, 1
Even with an existence density of 0 ⁴ pieces / mm ² , the running performance is not improved,
When it exceeds 10 ¹¹ m / mm ² , of the electromagnetic conversion characteristics of the magnetic surface, the S / N ratio is particularly deteriorated. The shape of the fine particles may be spherical, elliptical, rectangular, cubic, or the like, but spherical particles are particularly suitable.

As the particle type, 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 necessary to improve durability, but one or both may be applied depending on the requirements.

Further, in order to improve the adhesion between the coating film and particles and the surface of the film base, an easily adhesive resin and / or a silane coupling agent may be added.

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 layer A after forming the above coating film is preferably 5 nm or less. More preferably 4 nm
The following are preferred. 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 layer B, the polymer of layer A may be used, or the one obtained by a conventionally known method may be used.

As a method for 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, the unstretched film is uniaxially stretched, a desired coating liquid is applied by a Meyer bar type coating apparatus, dried and then stretched in a direction perpendicular to the previously stretched direction 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 process 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 using a commonly used roll, but as the preheating and stretching rolls, it is preferable to use a roll made of a non-adhesive material such as Teflon or silicon because 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 liquid 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 liquid.
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, longitudinal or width direction,
Further, it may be stretched in the transverse or longitudinal direction.

Next, this 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 According to ASTM-D-882, it was measured at 25 ° C. and 65% RH using an Instron type tensile tester.

(5) Heat Shrinkage A sample film having a width of 10 mm and a length of 250 mm was cut out,
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 slit running tape having a width of ½ inch was used as a tape runnability tester TBT-300 (manufactured by Yokohama System Laboratory Co., Ltd.). It was run in an atmosphere of 20 ° C. and 60% RH, and 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 and T ₂ is the outlet tension. The guide diameter is 6 mmφ, the guide material is SUS27 (surface viscosity 0.2S), the winding 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 influences the handling property and the running property of the tape when processing the film such as a magnetic recording medium.

(8) Output characteristics / heat loss By the continuous vacuum oblique vapor deposition method, Co,
A Ni ferromagnetic metal thin film (Ni = 20 w%, film thickness 1500 angstrom) is formed in the presence of a trace amount 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. The obtained vapor-deposited film is observed, and if the film is discolored in the form of streaks in the longitudinal direction or the film is melted during vapor deposition, it is determined that the heat loss is poor. After that, stearic acid was applied to the surface of the obtained ferromagnetic metal thin film to a concentration of about 10 mg / m ^2, and 8 m
Slit into m width to make a magnetic tape. This tape 50
VT with m length incorporated into Sony high-eight cassette
R cassette tape was used. A Sony VTR (EV-S900) made by Sony is used for this tape, and 100% is obtained by a TV test waveform generator (TG7 / U706) made by Shibasoku.
Chroma signal is recorded and chroma S / N is made from the reproduced signal by Shiba Soku color video noise measuring device (925D / 1).
Was measured.

(9) Durability The tape is 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 at 50,000 times with a scanning electron microscope, and 1
Take 0 photos. From the photograph, the number of particles is counted and converted into particle density per 1 mm ² .

[0053]

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 0.30 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 B-1.

Polymer A-1 was used as the polymer for layer A and vacuum dried at 170 ° C. for 6 hours. On the other hand, as a polymer for layer B, polymers A-1 and B-1 were mixed to obtain a particle concentration of 0.
The raw material adjusted to 2% by weight was vacuum dried at 170 ° C. for 6 hours by another dryer. Each of them was melt-extruded at 295 ° C. with another extruder, and after high-precision filtration, two layers were laminated in the thickness direction in a molten state by using pinol on the die (a thickness ratio of layer A and layer B was 5: 1). A sheet having a slit width of 2 mm was extruded into a sheet shape, wound around a casting drum at 30 ° C. by an electrostatic cast method and cooled and solidified to obtain an unstretched film having a two-layer structure and a thickness of about 133 μm.

This unstretched film was stretched by a silicon roll at a roll surface temperature of 130 ° C. in the longitudinal direction of 4.1.
It was stretched twice. An aqueous dispersion coating solution having the following formulation was applied on the outer surface of Layer A by a Mayer bar coater at 15 mg / m ² and then at 120 ° C.
And dried for 5 seconds. (Prescription) Methylcellulose: 0.2% by weight Water-soluble polyester: 0.3% by weight Colloidal silica: 0.2% by weight (particle size 12 nm)

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

The film obtained has a layer A of 20 nm.
A discontinuous film having a thickness was formed, and 5 × 10 ⁷ fine particles / mm ² were present in the film and on the surface of the film, but the wind ripple structure peculiar to polyethylene-2,6-naphthalate was not formed. The surface roughness was 2.5 nm. Layer B has many surface protrusions based on 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 good surface properties, handling properties, running properties, and durability.

Example 2 In Example 1, the coating liquid formulation was changed to the following. (Prescription) Acrylic resin emulsion: 0.5% by weight (particle size 100 nm) Layer A does not form a discontinuous film, and 5 × 10 ⁶ flat acrylic particles due to deformation during stretching and heat treatment.
mm ² existed, but the airfoil-like structure peculiar to polyethylene-2,6-naphthalate was not formed. The surface roughness was 2.8 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 1, the coating liquid formulation was changed to the following. (Prescription) Methylcellulose: 0.2% by weight Water-soluble polyester: 0.3% by weight In Layer A, a discontinuous film having a thickness of 20 nm was formed, but neither fine particles nor a ripple-like structure was present. The surface roughness was 2.3 nm. Layer B had many surface protrusions based on particles and had a surface roughness of 16 nm. The characteristics are as shown in Table 1, and the surface properties are good, and handling, running,
It was a film with good durability.

Example 4 In Example 1, the particle type of the particle master pellet used in the layer B was changed to spherical silica (the particle concentration and the average particle size were the same), and the layer B was also coated with a coating solution having the following formulation. . (Prescription) Methylcellulose: 0.2% by weight Water-soluble polyester: 0.3% by weight Colloidal silica: 0.2% by weight (particle size 25 nm) In layer A, a discontinuous film having a thickness of 20 nm is formed. Also, although 5 × 10 ⁷ fine particles / mm ² were present on the surface of the film, the airfoil-like structure peculiar to polyethylene-2,6-naphthalate was not formed. The surface roughness is 2.
It was 5 nm. Layer B had a large number of surface protrusions based on silica particles, 6 × 10 ⁶ fine particles due to the discontinuous coating and colloidal silica / mm ² , and had a surface roughness of 19 nm. The respective properties are as shown in Table 1, and the film had good surface properties, handling properties, running properties, and durability.

Example 5 A water sol (particle concentration: 50% by weight) containing colloidal silica particles having an average particle size of 0.09 μm and polymer A-1 were each used in a vent type twin-screw extruder to obtain a high content of 2%. Concentrated particle master pellets were made. This polymer is designated as B-2. The film was formed in the same manner as in Example 1 except that the polymer for the layer A was prepared by mixing the polymers A-1 and B-2 polymer and adjusting the colloidal silica content to 0.05%, and the thickness was 6.5 μm.
m film was obtained.

The film obtained has a layer A of 20 nm.
A discontinuous film having a thickness was formed, 5 × 10 ⁷ fine particles / mm ^{2 were} present in the film and on the surface of the film, and surface protrusions due to colloidal silica particles were also formed. The peculiar wind ripple structure was not formed. The surface roughness was 3.2 nm. Layer B has many surface protrusions based on 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 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. A discontinuous coating having a thickness of 20 nm is formed on layer A, and 5 × 10 5 fine particles are formed in the coating and on the coating surface.
There were ⁷ pieces / mm ^2, but a peculiar structure similar to polyethylene-2,6-naphthalate was formed. As a result, the surface roughness was as rough as 7.5 nm. Layer B had a large number of protrusions formed of particles and had a surface roughness of 16 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. A 20 nm-thick discontinuous film was formed on layer A, and 5 × 1 fine particles were formed in and on the film surface.
Although there existed 0 ⁷ pieces / mm ^2, there was formed a peculiar structure similar to polyethylene-2,6-naphthalate. As a result, the surface roughness was as rough as 6.9 nm. Layer B had a large number of protrusions formed of particles and had a surface roughness of 16 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 having a thickness of 6.5 μm was obtained in the same manner as in Example 1, except that the coating liquid was not applied to the layer A. Layer A
There was neither a discontinuous coating nor particles, and there was no peculiar wind ripple structure. As a result, the surface roughness was as fine as 0.8 nm. Layer B had a large number of protrusions formed by particles and had a surface roughness of 16 nm. Each characteristic is as shown in Table 1,
The film had good surface properties, but was poor in handling property, running property and durability.

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 the layer A, a 20 nm-thick discontinuous film is formed, 5 × 10 ⁷ fine particles / mm ² are present in the film and on the film surface, and a peculiar structure similar to polyethylene-2,6-naphthalate is also formed. There wasn't. As a result, the surface roughness is 2.5n
It was m. Layer B had a large number of projections formed of particles and had a surface roughness of 30 nm. The respective properties are as shown in Table 1, and the film was good in surface property, running property and durability, but poor in heat losing property 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. A discontinuous film having a thickness of 20 nm was formed on both the layer A and the layer B, and 5 × 10 ⁷ fine particles / mm ^{2 were} present in the film and on the surface of the film, and polyethylene-2,6-
The wind-printed surface structure peculiar to naphthalate was not formed. The surface roughness was 2.5 nm. The respective properties are as shown in Table 1, and the film was good in surface property, running property and durability, but poor in handling property.

Comparative Example 6 A water sol (particle concentration: 50% by weight) containing colloidal silica particles having an average particle diameter of 0.15 μm and polymer A-1 were each used in a vent type twin-screw extruder to obtain a high content of 2%. Concentrated particle master pellets were made. This polymer is designated as B-3. The film was formed in the same manner as in Example 1 except that the polymer for the layer A was prepared by mixing the polymers A-1 and B-3 polymers and adjusting the colloidal silica content to 0.1% by weight.
A film of μm was obtained.

The obtained film has a layer A of 20 nm.
A discontinuous film having a thickness is formed, 5 × 10 ⁷ fine particles / mm ² are present in the film and on the surface of the film, and surface protrusions due to colloidal silica particles are also formed.
-A peculiar structure similar to naphthalate was also formed. The surface roughness was 7.2 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 although the surface properties were poor, the film had good handling properties, running properties and durability.

Comparative Example 7 Polymers A-1 and B-1 polymers were mixed to give a particle content of 0.
A film having a thickness of 6.5 μm was obtained in the same manner as in Example 1 except that the raw material adjusted to 15% was used as the polymer for layer A.

The film obtained has a layer A of 20 nm.
A discontinuous film having a thickness is formed, 5 × 10 ⁷ particles / mm ² are present in the film and on the surface of the film, and a large number of surface protrusions due to particles are formed, resulting in a unique pattern of polyethylene-2,6-naphthalate. No structure was observed. The surface roughness was 11 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 although the surface properties were poor, the film had good handling properties, running properties and durability.

[0073]

[Table 1]

[0074]

According to the film of the present invention, sufficient surface properties for a metal thin film magnetic recording medium can be obtained by biaxially orienting polyethylene-2,6-naphthalate containing a specific compound. By handling this film as a composite and providing a specific coating layer, handling property, running property and durability can be obtained. 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 higher density recording.

[Brief description of drawings]

FIG. 1 is a differential interference contrast micrograph (50 times) showing a surface pattern or a rippled surface structure peculiar to a polyethylene-2,6-naphthalate film (drawing-substituting photograph for a thin film).

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Claims (2)

[Claims] 1. A layer A composed of polyethylene-2,6-naphthalate containing a germanium compound and a magnesium compound and a layer B composed of polyethylene-2,6-naphthalate containing inert solid fine particles. In the biaxially stretched composite film, layer A is coated with a coating film in which either or both of a discontinuous film and fine particles having an average particle size of 3 nm or more are present, and has a surface having a surface roughness of 5 nm or less. The layer B is polyethylene-2 containing 0.001 to 1% by weight of particles having an average particle size of 0.1 to 0.5 μm,
A biaxially oriented composite polyethylene naphthalate film for a metal thin film magnetic recording medium, which is composed of 6-naphthalate and has a surface having a surface roughness of 25 nm or less. 2. The average particle diameter of the layer A is 0.1 μm.
The biaxially oriented composite polyethylene naphthalate film for a metal thin film magnetic recording medium according to claim 1, which contains less than 0.08% by weight of inert solid fine particles.