JP3251660B2 - Biaxially oriented polyester film for magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyester film for a magnetic recording medium.

[0002]

2. Description of the Related Art Biaxially oriented polyester films are widely used as industrial materials. There is a strong desire for something. Further, there is a strong demand for improvement in wear characteristics represented by abrasion of a surface layer and dropping off of particles due to abrasion of a film, and improvement in tape running meandering when used as a base film of a magnetic tape. Furthermore, in the case of high-grade video tape applications, the base film was conventionally used with a back coat applied.However, in order to improve cost, a so-called non-back-coat type high-grade video tape base film is required. These points need to be highly satisfied. Conventionally,
As a means for improving the abrasion resistance, meandering and running properties of a polyester film, there is known a method in which inert fine particles are present in the film and the film surface is appropriately roughened. However, sufficient results have not always been obtained.

[0003] For example, when so-called precipitated particles from a catalyst residue or the like during polyester production are used as fine particles,
Since the precipitated particles are easily broken by stretching, the abrasion resistance and running properties are inferior, and the reuse of the precipitated particles is also difficult. When an inert inorganic compound particle is added to a polyester such as silicon oxide, barium sulfate, titanium dioxide, and calcium phosphate, the particle is not broken or deformed by stretching, and a relatively steep projection can be given. The runnability is improved, but the particle size distribution of the particles is generally wide and the particles easily fall off.For example, when used for video tape, the electromagnetic conversion characteristics often deteriorate and dropouts frequently occur. . To overcome these problems, it has been proposed to use inorganic or organic particles having a sharp particle size distribution. For example, JP-A-62-207356 and JP-A-59-21775.
Japanese Patent Application Publication No. 5 (JP-A) No. 5 discloses an example using monodispersed silicon oxide and crosslinked organic particles by an emulsion polymerization method. However, when silicon oxide particles are used, the hardness of the film is so high that the substrate that the film comes into contact with is easily damaged,
Improvement of abrasion resistance is also insufficient.On the other hand, when crosslinked organic particles are used, not only is there a problem in heat resistance, but also
There is a disadvantage that particles are easily deformed by stretching.

In particular, a so-called non-backcoat type base film for a high-grade video tape is required to have a high running property. Therefore, it is necessary to incorporate a large amount of the above-mentioned particles into the film. Disadvantageous. On the other hand, to solve the problem of wear resistance,
A method has been proposed in which particles having a high hardness, for example, aluminum oxide particles are blended in a base film (for example, Japanese Patent Application Laid-Open No. Hei 1-306220). However,
In the above method, a large amount of aluminum oxide particles must be blended into the base film in order to sufficiently prevent the generation of scratches and abrasion powder of the magnetic tape, and as a result, the following new problems occur. Was found. (1) Aluminum oxide particles are relatively expensive. (2) In the slitting process at the time of film production, the degree of damage to the cutting blade is large, and it is necessary to frequently replace the cutting blade, which lowers the production cost and productivity of the film. If the cutting blade is not replaced frequently, the cutability of the film deteriorates, so that the cut edge is turned up in a streak shape during the slitting process, and mustaches and powder are generated from the cut edge. When such a film is used as a magnetic recording medium,
Electromagnetic conversion characteristics deteriorate or dropout is induced. (3) In the slitting process at the time of magnetic tape processing, the degree of damage to the cutting blade is large, and it is necessary to frequently replace the cutting blade, and the production cost and productivity of the magnetic tape deteriorate. If the cutting blade is not replaced frequently, the cutting properties of the magnetic tape deteriorate. If the cutting property is poor, the cut edge is turned up in a streak shape, and a mustache or powder is generated from the cut edge. When such a phenomenon occurs, white powder adheres to the tape, deteriorating the electromagnetic conversion characteristics and inducing dropout. Therefore, the surface uniformity of the film is excellent, and when it is made into a magnetic tape, generation of abrasion and abrasion powder during running is extremely small, and it has excellent running properties without meandering,
There is a strong demand for polyester films for magnetic recording media having improved raw material cost and slit properties.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and as a result, a specific amount of specific synthetic calcium carbonate particles and aluminum oxide particles has been blended into a laminated film, and the surface of such a film has been mixed. The inventors have found that such an object can be achieved if the roughness and the coefficient of friction satisfy a specific range, and have completed the invention.

That is, the gist of the present invention is a biaxially oriented polyester film obtained by co-extrusion laminating a polyester (A) layer and a polyester (B) layer, and the following formulas (1) to (11) A biaxially oriented polyester film for a magnetic recording medium, characterized by being simultaneously satisfied.

[Number 2] _{0.30 ≦ d a ≦ 0.65 ... (} 1) 0.35 ≦ w a A ≦ 1.00 ... (2) 0.55 ≦ d a + 0.5w a A ≦ 0.95 ... ( ^{_{3) 8d a -w a A ≧}} 1.50 ... (4) 0.005 ≦ d b ≦ 0.50 ... (5) 0.15 ≦ w b A ≦ 1.00 ... (6) w b ≦ 0. 10 (7) 0.009 ≦ Ra ^A ≦ 0.020 (8) 0.002 ≦ Ra ^B ≦ 0.017 (9) 7.0 ≦ Rz ^A / Ra ^A ≦ 15 (10) during ^{_{80 ≦ μ d50 a / μ d1}} a ≦ 1.6 ... (11) [ the above equation, d _a is the average particle size of the (a) layer of synthetic calcium carbonate particles (a) (μm), w a a is the content of the (a) layer of synthetic calcium carbonate particles (a) (wt%), d _b is the average particle size of the (a) layer of aluminum oxide particles (b) (μm), w b a is (a ) content of the aluminum oxide particles (b) in layer (wt%), w _b is oxidized in the entire film Aluminum content of the particles (b) (wt%), Ra ^A
And Rz ^A, respectively (A) layer exposed surface a surface roughness ([mu] m) and ten-point average roughness (μm), Ra ^B is (B)
The surface roughness (μm) and μ _d50 ^A / μ _d1 ^A of the exposed layer represent the ratio of the dynamic friction coefficient of the exposed layer (A) between the initial _stage (first run) and the repeated running (50 th run).

Hereinafter, the present invention will be described in detail. The laminated film referred to in the present invention refers to a film extruded by a so-called co-extrusion method in which all layers are co-melt extruded from a die of an extruder, and stretched and heat-treated. Hereinafter, a three-layer film will be described as a laminated film, but the laminated film is not limited to a three-layer film and may be a multilayer of two or more layers unless the gist of the present invention is exceeded. In the present invention, the polyester constituting each layer of the laminated film is a polyester obtained by using an aromatic dicarboxylic acid or an ester thereof and a glycol as main starting materials, and 80% or more of the repeating structural units are ethylene terephthalate units. Or ethylene-2,6-
Refers to a polyester having a naphthalate unit. Then, other third components may be contained under the conditions that do not deviate from the above range. As the aromatic dicarboxylic acid component,
For example, besides terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-
Oxyethoxybenzoic acid).
As the glycol component, in addition to ethylene glycol,
For example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used.

[0008] To the polyester constituting each layer of the film of the present invention, a stabilizer, a colorant, an antistatic agent, and the like may be appropriately added. Hereinafter, in the present invention, the exposed surface (smooth surface) of the polyester (A) layer is referred to as surface A, and the exposed surface of the polyester (B) layer is referred to as surface B. When the film of the present invention is used as a magnetic tape, a magnetic layer is usually provided on the B side of the film. The layer (B) may be a single layer or a laminate of two or more layers. In particular, in the case of a laminated film of three or more layers having two layers (B), it is preferable to use a low-cost polyester raw material for the intermediate layer. The intermediate layer is not particularly limited, and examples thereof include a recycled polyester and a straight-weight polyester substantially containing no particles. Specific amounts of specific synthetic calcium carbonate particles and aluminum oxide particles are blended in the laminated polyester film of the present invention. First, the calcium carbonate particles used in the present invention will be described. Conventionally, as a method for producing calcium carbonate particles, besides a method of pulverizing and classifying natural calcium carbonate, for example, a method of injecting a carbon dioxide-containing gas into a calcium hydroxide solution and reacting it, a so-called precipitated calcium carbonate particle by a synthetic method is used. Are known. Although the calcium carbonate particles obtained by this synthesis method have a relatively uniform particle size, natural calcium carbonate particles cannot reach a desired particle size distribution. Therefore, in the present invention, synthetic calcium carbonate particles are used, and in particular, synthetic calcium carbonate particles having a uniform particle size distribution are preferably used.

[0009] The particle size distribution of the synthetic calcium carbonate particles (a) used in the present invention is preferably 1.80 or less, more preferably 1.70 or less, and particularly preferably 1.60 or less. If the particle size distribution value exceeds 1.80, the surface roughness of the finally obtained film tends to be non-uniform. As the crystal type of the synthetic calcium carbonate particles (a), three types of calcite type, vaterite type and aragonite type are known, but only in terms of industrial availability and cost advantage. In addition, from the viewpoint that a polyester having good cohesive heat stability, which will be described later, can be obtained, the crystal type of the synthetic calcium carbonate particles (a) used in the present invention is preferably a calcite type. Furthermore, such synthetic calcium carbonate particles can be added as they are to the polyester production process, but reduce the solubility in the reaction system, and dispersibility and
It is particularly preferable to perform a surface treatment in order to improve cohesive heat stability, which is an important property in the present invention. Examples of the surface treating agent also serving as a dispersant include JP-A-59-69426 and JP-A-1-256.
No. 558, a surface treating agent, particularly a polycarboxylic acid or a sodium salt or an ammonium salt thereof is preferably used, and a polyalkylene glycol unit and a polyacrylic acid unit and / or a polyacrylic acid-derived unit are used. Is more preferable. Examples of such a copolymer include a copolymer of polyacrylic acid and polyethylene glycol monomethacrylate, a copolymer of polyacrylic acid and methoxypolyethylene glycol and polypropylene glycol monomethacrylate, or a copolymer of these. Those obtained by neutralizing acrylic acid with ammonia and those obtained by replacing polyacrylic acid soda are exemplified. Usually, it is effective to add these surface treatment agents during the production stage of the particles.

[0010] One important gist of the present invention, the average particle diameter (d _a) and the content of (A) layer (EkiNameraso) in the calcium carbonate particles (a) of the laminated polyester film (w _a ^A) Satisfy the following expressions (1) to (3).

Equation 3] _{0.30 ≦ d a ≦ 0.65 ... (} 1) 0.35 ≦ w a A ≦ 1.00 ... (2) 0.55 ≦ d a + 0.5w a A ≦ 0.95 ... ( in ^{_{3) 8d a -w a a ≧}} 1.50 ... (4) the present invention has an average particle diameter of the synthetic calcium carbonate particles _(a) (d a) is required to be from 0.30~0.65μm is there. Such is less than d _a value 0.30 .mu.m, it is hardly improved running properties and wear resistance of the film, also inferior agglomeration heat stability of the polyester. On the other hand, if the d _a value greater than 0.65 .mu.m, by a so-called smearing, etc., not only would impair the electromagnetic conversion characteristics, in particular the travel meandering film upon the non backcoat type high-grade video tape Little improvement. d _a
The value is preferably in the range of 0.35 to 0.60 μm, and more preferably in the range of 0.38 to 0.55 μm.

[0011] The content of the (A) layer of synthetic calcium carbonate particles (a) of the polyester film of the present invention (w _{a ^A)} is from 0.35 to 1.00 wt%. When the w _a ^A value is less than 0.35% by weight, high-grade video tapes for magnetic recording media satisfying a high level of surface uniformity, running properties, meandering properties, abrasion resistance and the like at the same time, especially non-backcoat type. This is unsuitable because a polyester film suitable for use cannot be obtained. On the other hand, when the w _a ^A value exceeds 1.00% by weight, the surface roughness of the film becomes too high, thereby deteriorating the electromagnetic conversion characteristics. The w _a ^A value is 0.45
0.90% by weight is preferred.

In the polyester film of the present invention, the (d _a +0.5 w _a ^A ) value needs to be in the range of 0.55 to 0.95. If the (d _a +0.5 w _a ^A ) value is less than 0.55, the film is inadequate because the running properties and abrasion resistance of the film are poor. If the value exceeds 0.95, the surface roughness of the film becomes too high, thus deteriorating the electromagnetic conversion characteristics. (D _a +0.5 w _a ^A ) value is
The range is preferably 0.60 to 0.90, more preferably 0.62 to 0.85. In the polyester film of the present invention, (8d _a -w _{a ^A)} value 1.5
0 or more, preferably 1.80 or more, more preferably 2.00 or more. (8d _a -w _{a ^A)} value is 1.5
If it is less than 0, the aggregation of the synthetic calcium carbonate particles in the polyester frequently occurs and becomes coarse, which is not suitable.

As described above, it is necessary to incorporate a large amount of synthetic calcium carbonate particles having a relatively small particle size into the polyester film of the present invention. It has been found that so-called defective products in which calcium carbonate particles are aggregated may occur. When the degree of such agglomeration is large, coarse substances are generated in the polyester film, and as a result, when used as a magnetic recording medium such as a video tape, dropouts occur and electromagnetic conversion characteristics are deteriorated. . Such an aggregation phenomenon is closely related to a change in particle size due to heat treatment. That is, for the synthetic calcium carbonate particles in the polyester, the ratio of the particle diameters before and after the heat treatment, the value of D _a / D _a ′ (after the heat treatment), is 0.6.
It is necessary to be 0 or more, preferably 0.65 or more, more preferably 0.70 or more. This D _a /
When the value of D _a ′ (after heat treatment) is less than 0.60, aggregation of the synthetic calcium carbonate particles in the polyester frequently occurs.

The above D _a represents the average particle size (μm) of the synthetic calcium carbonate particles in the raw material polyester (A) measured by SEM, and D _a ′ (after heat treatment) refers to the polyester (A). 2) shows the average particle size (μm) of the synthetic calcium carbonate particles in the polyester (A) after heat treatment at 280 ° C. for 8 hours under nitrogen. Moreover, such agglomeration heat stability, tend to be better when there is low or the content when the particle diameter of the synthetic calcium carbonate particles containing a large, D _a and content of the feed in the polyester _(A) (U _a ), (8)
d _a −U _a ) value is preferably 1.50 or more,
1.70 or more is more preferable, and 1.90 or more is particularly preferable. Further, the raw material polyester (A) is preferably contained in an amount of 30 to 100% by weight, more preferably 30 to 80% by weight, based on the polyester (A) layer. When the content is less than 30% by weight, characteristics such as surface uniformity, running properties, meandering resistance and abrasion resistance of the film may be inferior.

As the particles contained in the layer (B) of the laminated polyester film of the present invention, the above-mentioned synthetic calcium carbonate particles (a) are preferably used from the viewpoint of ease of recycling and the like. In particular, the content of the synthetic calcium carbonate particles (a) in the outermost layer of the (B) layer is 0.1 w _a ^{A to} 1.0 w
_a ^A weight% is preferable, and more preferably 0.1% by weight.
2w _{a ^A} ~0.8w _{a A%} by weight, particularly preferably 0.25w
is _{a ^A ~0.70w a A} wt%.

The content of the synthetic calcium carbonate particles (a) used in the present invention is preferably as small as possible. That is, the content of the synthetic calcium carbonate particles (a) based on the total polyester is preferably 0.30% by weight or less,
It is more preferably at most 20% by weight, particularly preferably at most 0.15% by weight. Next, the aluminum oxide particles contained in the polyester film of the present invention will be described.
In the layer (A) (easy layer) of the laminated polyester film of the present invention, a specific amount of specific aluminum oxide particles (b) is used in order to highly improve scratch resistance.

(A) Aluminum oxide particles in layer (b)
The average particle diameter d _b of a 0.005 to 0.5 .mu.m, the content thereof is 0.15 to 1.0 wt%. Average particle size d
_{If the b} value is less than 0.005 μm or the content is less than 0.15% by weight, the effect of improving the scratch resistance is too small, and if the average particle size exceeds 0.5 μm or the content is 1.0% by weight.
If it exceeds, the magnetic recording medium is unsuitable because coarse protrusions are formed on the film surface, the surface flatness is impaired, and so-called set-off deteriorates the electromagnetic conversion characteristics of the magnetic recording medium. The average particle size is preferably in the range of 0.01 to 0.1 μm, and the content is preferably in the range of 0.25 to 0.5% by weight, more preferably 0.35 to 0.5% by weight, especially 0.4 to 0.5% by weight.
A range of 2 to 0.5% by weight is preferred. Aluminum oxide particles (b) in the entire laminated polyester film of the present invention
Is 0.10% by weight or less, preferably 0.075% by weight or less, particularly preferably 0.060% by weight or less. If the content exceeds 0.10% by weight, it is necessary to frequently change the cutting blade during the production of the film or the magnetic tape processing step, which is unsuitable because the productivity is deteriorated.

The content of the aluminum oxide particles (b) in the layer (B) is preferably as small as possible in view of the raw material cost. However, a small amount, for example, about 0.07% by weight of aluminum oxide particles may be mixed into the layer (B) by recycling the film. In particular, the content of the aluminum oxide particles (b) in the outermost layer of the layer (B) is 0.1.
It is preferably 50% by weight or less, more preferably 0.10% by weight or less, particularly preferably 0.05% by weight or less, and most preferably 0% by weight. As a method for producing aluminum oxide particles, for example, a thermal decomposition method, that is, a method of flame hydrolysis using anhydrous aluminum chloride as a raw material, or an ammonium alum pyrolysis method, that is, a reaction with sulfuric acid using aluminum hydroxide as a raw material, After that, a method of reacting with ammonium sulfate and calcining as ammonium alum can be exemplified. The primary particle size of aluminum oxide obtained by these methods is usually in the range of 5 to 40 nm, but often 0.5 μm
It is desirable to use it after being appropriately pulverized, since it forms aggregates exceeding the number of aggregates. In this case, the secondary particles may be somewhat aggregated, but the apparent average particle size is 0.5
μm or less is preferable, and 0.1 μm or less is particularly preferable.
The crystal form of the aluminum oxide particles (b) is as follows:
The delta type or the gamma type is more preferable, and the delta type is particularly preferably used, from the viewpoint of improving the wear resistance, the abrasion resistance and the slitting property.

In the present invention, one or more other particles may be used in combination as long as the gist is not exceeded.
However, from the viewpoint of ease of recycling, it is preferably less than the total amount w a A + B of the synthetic calcium carbonate particles used in the laminated polyester film of the present invention (a) (wt%), 0.3 w a A + B weight% or less is more preferable, and 0.1 w a A + B weight% or less is particularly preferable.
0.05w a A + B% by weight is most preferred. Precipitated particles can be mentioned as one of the particles that can be used in combination. The term “precipitated particles” as used herein refers to, for example, those that precipitate in a reaction system by polymerizing a system using an alkali metal or alkaline earth metal compound as a transesterification catalyst by a conventional method. Further, precipitation may be carried out by adding terephthalic acid during the transesterification reaction or the polycondensation reaction. In these cases, one or more phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate, acidic ethyl phosphate, phosphorous acid, trimethyl phosphite, triethyl phosphite, tributyl phosphite, etc. May be present. In addition, even when an esterification step is performed, the inert substance particles can be precipitated by these methods. For example, a polycondensation reaction is carried out in the presence or absence of a phosphorus compound in the presence or absence of an alkali metal or alkaline earth metal compound before or after the end of the esterification reaction. In any case, the precipitated particles in the present invention contain one or more elements such as calcium, lithium, antimony, and phosphorus.

Further, added particles can be used as one of the particles used in combination. The term “added particles” as used herein refers to particles added to the polyester from the outside.Specifically, kaolin, talc, carbon black, molybdenum sulfide, gypsum, barium sulfate, lithium fluoride, calcium fluoride, zeolite, Examples thereof include calcium phosphate, silicon dioxide, and titanium dioxide. Examples of such added particles include heat-resistant fine polymer powder. A typical example of this case is, for example,
A monovinyl compound having only one aliphatic unsaturated bond in the molecule and a compound having two or more aliphatic unsaturated bonds in the molecule as a cross-linking agent, as described in JP-A-9-5216; Can be exemplified, but is not limited thereto, for example, thermosetting epoxy resin, thermosetting phenol resin, thermosetting urea resin, benzoguanamine resin or polytetrafluoroethylene Fluororesin fine powder can also be used.

Incidentally, two or more kinds of synthetic calcium carbonate particles having different average particle sizes may be used. Particularly, in the layer (A) of the laminated polyester film of the present invention, when a small amount of large-particle synthetic calcium carbonate is blended, the winding properties can be improved without impairing the electromagnetic conversion properties and running properties,
preferable. As such a particle size, 1.5 d _{a to} 3.0 d
_a μm is preferred. The particle size of the large particles of synthetic calcium carbonate tend to improve the effect of the wind characteristics 1.5d _a [mu] m smaller than decreases, 3.0d _a [mu] m larger than the electromagnetic characteristics or the running resistance and the like deteriorate There is. The content of the addition (A) layer is preferably in the range of 0.005w _{a ^A} ~0.2w _{a A} wt%, more preferably 0.01w _{a ^A} ~0.1w _{a A} wt%. When the amount of large particles of synthetic calcium carbonate is less than 0.005 w _a ^A wt%, the winding effect of improving characteristics tend to be small, 0.2 w _a ^A greater than the weight percent electromagnetic characteristics or running, etc. May worsen. The particle size distribution value of such large particles of synthetic calcium carbonate is preferably 1.80 or less, more preferably 1.70 or less, and particularly preferably 1.60 or less.

In the production of the polyester containing the synthetic calcium carbonate particles of the present invention, the particles and the additional particles used in combination are preferably added during the polyester synthesis reaction. In particular, it is preferably added after the transesterification or esterification reaction and before the start of the polycondensation reaction. The particles to be added are usually added as a slurry of ethylene glycol.
Processing such as dispersion, classification, and filtration may be performed. The slurry concentration in the added ethylene glycol is 3 to 50% by weight, preferably 10 to 40%. If the particle concentration of the slurry is less than 3% by weight, the use amount of ethylene glycol increases, and the basic unit of ethylene glycol increases. If a slurry having a particle concentration exceeding 50% by weight is added, the dispersibility of the particles may be deteriorated. As a polycondensation reaction catalyst for polyester synthesis, Sb, Ti, Ge, S
A commonly used catalyst such as an n or Si compound is used.

In the laminated film of the present invention, (A)
The thickness ratio of the layer is preferably from 1 to 50%, more preferably from 3 to 30%, particularly preferably from 5 to 25%, based on the whole film. When the thickness ratio of the (A) layer is more than 50%, the slitting property tends to be inferior, and when the thickness ratio of the (A) layer is less than 1%, it may be difficult to control the thickness of the film. Further, in the laminated polyester film of the present invention, the thickness t _A (μm) of the layer (A) is 1.
Preferably _{0d a ~20d a μm, 1.4d a} ~15d
more preferably _a [mu] m, particularly preferably 1.6d _a ~12d _{a μm,} and most preferably 1.8d _a ~9.0d _{a μm.} If t _A is less than 1.0d _a [mu] m, since the thickness control is difficult, there is a tendency that running or wear resistance improving effect is small. On the other hand, if t _A is more than 20d _a [mu] m tend to improving effect and the like of the raw material cost is reduced. The thickness of the film is usually 3 to 20 μm.
, Preferably 7 to 17 µm, particularly preferably 12 to 17 µm.

In the polyester film of the present invention, it is necessary to satisfy the following expressions (8) to (11).

(Equation 4) 0.009 ≦ Ra ^A ≦ 0.020 (8) 0.002 ≦ Ra ^B ≦ 0.017 (9) 7.0 ≦ Rz ^A / Ra ^A ≦ 15 (10) 0.80 ≦ μ _d50 ^A / μ _d1 ^A ≦ 1.6 (11) [In the above formula, Ra ^A and Rz ^A represent the surface roughness (μm) and the ten-point average roughness of the exposed surface of the (A) layer, respectively. μ
m) and Ra ^B are the surface roughness (μ) of the exposed surface of the (B) layer.
m), μ _d50 ^A / μ _d1 ^A represent the ratio of the kinetic friction coefficient of the exposed surface of the layer (A) between the initial _stage (first run) and the repeated running (50 th run). ]

The exposed surface of the layer (A) (easy layer) of the laminated polyester film of the present invention, the surface roughness Ra ^A value of the surface ^A is 0.009 to 0.020 μm, preferably 0.1 to 0.020 μm.
010 to 0.017 μm, more preferably 0.010
０．０１0.015 μm. Ra ^A value is 0.009
If it is less than μm, the running properties and abrasion resistance of the film will deteriorate. On the other hand, when the Ra value exceeds 0.020 μm,
Since the surface roughness of the film becomes too high, the electromagnetic conversion characteristics are impaired due to set-off (transfer to the magnetic layer) or the like.

The exposed surface of the layer (B) of the laminated polyester film of the present invention and the surface roughness Ra ^B value of the surface B (the surface coated with the magnetic layer) are 0.002 to 0.017 μm, preferably 0.007 to 0.017 μm. To 0.015 μm, and more preferably 0.008 to 0.015 μm. When the Ra ^B value is less than 0.002 μm, the base film is poor in slipperiness, and particularly in the magnetic tape processing step, the base film is often scratched, and the electromagnetic conversion characteristics of the magnetic tape deteriorate, It is unsuitable because of poor handling of the film. On the other hand, if the Ra ^B value exceeds 0.017 μm, the electromagnetic conversion characteristics of the magnetic tape deteriorate, which is not preferable. Ra ^A / Ra ^B is 0.2 to 1.0.
Is preferable, 0.3 to 0.9 is more preferable, and 0.5 to 0.9 is preferable.
-0.8 is particularly preferred. Such a range is particularly preferable because the effects of improving the electromagnetic conversion characteristics, running properties, wear resistance, and the like of the finally obtained magnetic tape are increased.

In the film of the present invention, Rz^A / Ra
^A Values range from 7.0 to 15, preferably from 8.0 to 15.
13, more preferably 8.0 to 12. Rz^A /
Ra ^A When the value is less than 7.0, the running property of the film and
The effect of improving wear resistance is small. On the other hand, Rz^A / Ra^A value
Exceeds 15, the effect of improving the meandering property of the film is not sufficient.
It is enough. Furthermore, in the film of the present invention,
A side of (1st time) and repeated running (50th time)
Ratio of dynamic friction coefficient of (smooth surface), μ_d50 ^A/ Μ_d1 ^A The value is 0.
It is in the range of 80 to 1.6, preferably 0.9 to 1.4.
It is. μ_d50 ^A/ Μ_d1 ^A Value less than 0.80 or 1.6
When it exceeds, the running durability of the film is inferior, especially
For non-back coat type high grade video tape
As it does not stand use. Further, the magnetic recording medium of the present invention
In the base film for film, side A of such a film (easy
The smooth surface) consists of a depression around the projection
It is preferable to have a concave-convex unit. That is, the major axis
At least 0.2 μm or more
Film surface area 1mm^Two The number per hit is 1-15,000
Is preferable, and 5-5000 are more preferable. Take
When the number of uneven units is less than one, runnability and surface flatness
The effect of improving the properties tends to be small, and the number of uneven units
If the number exceeds 15,000, wear resistance may deteriorate.
There is.

Further, the refractive index in the thickness direction of the film is preferably set to 1.490 or more. When the refractive index in the thickness direction of the film is 1.490 or more, the adhesiveness to the magnetic layer, running properties, and abrasion resistance can be improved. The refractive index in the thickness direction of the film is preferably 1.4.
92 to 1.505. The film having such physical properties has, for example, a birefringence after longitudinal stretching of 4.0 × 10 ⁻² to 8.
It can be obtained by setting it to about 0 × 10 ⁻² .
The difference (Δn; n _TD −n _MD ) between the refractive index in the width direction (n _TD ) and the refractive index in the longitudinal direction (n _MD ) of the film is 0.02.
When it is 0 or more, it is particularly excellent in cutting properties and is suitable as a base film of a magnetic tape. It is a characteristic when cutting a magnetic tape with a shear cutter or the like. When the cutting property is poor, the cut edge is turned up in a streak shape, and a mustache or powder is generated from the cut edge. When such a phenomenon occurs, white powder adheres to the tape, deteriorating the electromagnetic conversion characteristics and inducing dropout. Δn
Is preferably 0.025 or more, more preferably 0.1.
035 or more, particularly preferably 0.043 or more. Δ
If n is too large, inconveniences such as heat shrinkage will occur, so the upper limit of Δn is preferably set to 0.060.

In the present invention, the intrinsic viscosity of the polyester film is preferably 0.52 to 0.62, more preferably 0.54 to 0.62.
~ 0.59 is more preferred. The lower the intrinsic viscosity, the better the cutability of the film. However, if the intrinsic viscosity is less than 0.52, the film is frequently broken during film formation, which may hinder productivity. On the other hand, when the intrinsic viscosity exceeds 0.62, the effect of improving the cutability of the film may be insufficient. The sum of the longitudinal Young's modulus and the transverse Young's modulus of the film of the present invention is preferably 900 kg / mm ² or more, more preferably 1000 kg / mm ² or more,
Particularly preferred is 1050 kg / mm ² or more. The difference between the Young's modulus in the horizontal direction and the Young's modulus in the vertical direction is 200 kg /
less than mm ^2, more preferably from ^{100~200kg / mm 2, 150~200kg / mm} 2 is particularly preferred. When the Young's modulus of the film satisfies the above conditions, the effects of improving the tape edge damage, durability and cutting properties are increased, which is particularly preferable.

Next, the method for producing the film of the present invention will be specifically described. After preparing a polyester raw material and drying it by a conventional method, it is extruded at 200 to 320 ° C. by a separate extruder, cooled and solidified on a casting drum, and
An amorphous sheet having three or more layers is formed. At this time, it is preferable to use a conventional electrostatic application method because an amorphous sheet having a uniform thickness can be obtained. Next, biaxial stretching heat setting is performed using the amorphous sheet. That is, the film is stretched in the longitudinal direction within the range of 2.5 to 9.0, and then stretched 3.0 times or more, more preferably 3.3 times or more, particularly preferably 3.7 times or more in the horizontal direction. After stretching with
More preferably, after re-stretching in the machine direction at a temperature of 110 ° C. to 180 ° C. by 1.05 to 2.5 times,
Heat treatment is performed at a temperature of 0 ° C, more preferably 210 ° C to 240 ° C. Needless to say, in this case, techniques such as heat setting before re-longitudinal stretching, longitudinal relaxation after re-longitudinal stretching, and longitudinal stretching at a micro-magnification before or after re-longitudinal stretching can be appropriately adopted. In addition, re-stretching may be similarly performed in the lateral direction. Further, various surface treatments or the like may be performed in the film forming process as needed.

In the above stretching step, the longitudinal stretching ratio is 4.
It is particularly preferred that it is in the range of 0 to 9.0 times. As a method for realizing such a high longitudinal stretching ratio, the following method is preferable. That is, the stretching in the longitudinal direction is (A)
The amorphous sheet in the amorphous state has a birefringence of 1.0 × 10 ^{−3 to} 2.5 × 10 ⁻² , more preferably 1.0 × 10 ^−2, at a draw ratio of 1.2 to 4.0 times. The film is stretched longitudinally in one step or multiple steps so as to be 2.5 × 10 ^-2, and (B) a stretching ratio of 1.1 to 1.1 without cooling the film temperature to a glass transition point or lower.
3.5 times and the birefringence is 3.0 × 10 ^{-2 to} 8.0 × 10 ^-2
(C) After the film temperature is cooled below the glass transition point, and (D) the film temperature is heated above the glass transition point, and the film is longitudinally stretched in one or more stages. Preferably, In the polyester film of the present invention, in order to obtain a particularly preferable film strength and birefringence, before heat treatment after longitudinal and transverse stretching, at a temperature of 110 ° C ~ 180 ° C in the longitudinal direction 1.05 ~.
It is particularly preferable to perform 2.5 times re-longitudinal stretching and / or re-lateral stretching.

[0032]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. The measuring methods and definitions of various physical properties and characteristics in the examples are as follows. In the examples and comparative examples, “parts” means “parts by weight”. (1) Average particle size and particle size distribution Centrifugal sedimentation type particle size distribution analyzer (SA-CP manufactured by Shimadzu Corporation)
Integrated volume fraction 5 in equivalent spherical distribution measured by type 3)
0% d ₅₀ value was defined as the average particle diameter. At the same time, the ratio of the diameter d _{25 at} the point of 25% by weight to the diameter d _{75 at} the point of 75% by weight, d ₂₅ / d ₇₅ , integrated from the large particle side, was used as an index of the particle size distribution. The average particle size of the primary particles of the aluminum oxide particles was determined by measuring 100 points by a photographic method using an electron microscope, converting the values into equivalent spheres, and averaging the values.

(2) Average Particle Diameter (D _a ) in Polyester The polyester portion was removed from the polyester containing particles by low-temperature plasma incineration to expose the particles.
The processing conditions were selected such that the polyester was ashed but the particles were not damaged. The exposed particles were observed with a SEM, and the images of the particles were processed with an image analyzer. For observation particles several thousands or more, a number average particle diameter of the particle size of equivalent spherical conversion was D _a. In addition, regarding the aggregated particles, the aggregated particles were converted to equivalent spheres as a single particle, and the particle diameter was determined.

(3) Heat stability of aggregation The polyester containing particles was dried and then heat-treated at 280 ° C. for 8 hours under normal pressure and nitrogen. Next, the average particle size (D _a ′) in the heat-treated polyester was measured. As an indicator of aggregation thermal stability ratio of the average particle size in the polyester before and after the heat treatment, determine the D _a / D _a ', were classified into ranks below.

A: D _a / D _a ′ ≧ 0.70 (very good production stability) C: D _a / D _a ′ <0.60 (production stability is poor and production is difficult) B: 0.60 ≦ D _a / D _a ′ <0.70 (intermediate situation between A and C above)

(4) Intrinsic viscosity of the film: 1 g of the polymer was phenol / tetrachloroethane = 50.
/ 50 (weight ratio) in 100 ml of a mixed solvent.
It was measured at 0 ° C. (5) Refractive index of film Using an Abbe refractometer manufactured by Atago Optical Co., the refractive index in the thickness direction (nα), the refractive index in the width direction (n _TD ) and the refractive index in the longitudinal direction (n _MD ) of the film were measured. It was measured. The refractive index was measured using sodium D line.

(6) Slit property In the film forming process, the end of the film after biaxial stretching and heat fixing is cut with a new stainless steel cutting blade.
After slitting 0000 m, the degree of damage to the cutting blade was visually observed to evaluate the slitting property in the following three ranks. A: There is almost no damage to the cutting blade, and there is no need to replace the slit blade. B: Damage to the cutting blade is apparent, and the slit blade needs to be replaced. C: Intermediate situation between A and C above

(7) Young's Modulus (Tensile Modulus) Tensile Tester Intesco Model 20 manufactured by Intesco Corporation
Using a type 01, a sample film having a length of 300 mm and a width of 20 mm was pulled at a strain rate of 10% / min in a room adjusted to a temperature of 23 ° C. and a humidity of 50% RH. Using the linear portion, Young's modulus (E) was calculated by the following equation. E = Δσ / Δε (where E, Δσ, and Δε are Young's moduli (kg
/ Mm ² ), representing the stress difference due to the original average cross-sectional area between two points on a straight line and the strain difference between the same two points)

(8) Average Roughness and Uniformity of Roughness of Film Surface According to the method described in Japanese Industrial Standard JIS B0601, a surface roughness measuring instrument (SE-
Using 3F), the center line average roughness (Ra) and the maximum height (Rt) were determined. The radius of the stylus used is 2.0μ
m, load is 30mg, cut-off value is 0.08m
m. The smaller Rt / Ra, the more uniform the surface. (9) Number of units of irregularities on the film surface (projections are nuclei and there are dents around the unit) Aluminum is deposited on the (A) side of the film, and the film surface is photographed with a Nikon differential interference microscope. , With a major axis of 0.1 mm per 1 mm ² of total film surface area.
The number of uneven units having a size of 2 μm or more (pieces / mm ² ) was counted.

(10) Running durability (Friction coefficient at initial and repeated running, μ _d1 and μ _d50 ) Fixed hard chrome-plated metal roll (diameter 6 mm, surface roughness 3S)
, The base film surface ((A) surface side) of the magnetic tape is brought into contact at a winding angle (θ) of 135 °, a load of 53 g (T ₂ ) is applied to one end, and the magnetic tape is run at a speed of 3.3 cm / sec. Resistance (T ₁ , g) at the other end is 23 ° C, 50%
The measurement was performed in an RH atmosphere, and the friction coefficient during running (μ _d ) was determined by the following equation. At _{μ d = 0.424 · ln (T} 1/53) the method described above, reciprocating the same location of the base film surface of the magnetic tape, is repeated running, the initial (first time) and the repeating during running (50th ) Is measured, and μ
_d50 / _μd1 was determined.

(11) Number of Coarse Protrusions Aluminum was vapor-deposited on the film surface and measured by a two-beam method using a Nikon Optiphoto interference microscope. The number of projections (projection height of 0.81 μm or more) exhibiting a third or higher order interference fringe at a measurement wavelength of 0.54 μm was measured over an area of 100 cm ² , and was determined as the number of coarse projections.

(12) Winding characteristics The quality of roll misalignment, wrinkling, winding appearance, etc. during the winding operation of the polyester film was comprehensively judged. (13) Wear characteristics Fixed hard chrome fixing pin with a diameter of 6 mm (material SU
S420-J2, finish 0.2S), using a film having a width of 10 mm, and wrapping a 135-degree wrap around the (A) side of the film.
At a speed of 11.4 m / min and an initial tension of 3.
At 200 g, a 200 m film was run for a total of 5000 m, and the amount of abrasion white powder attached to the pins was visually evaluated.
The evaluation was performed for each rank shown below. Rank A: Not attached at all Rank B: Attach a small amount Rank C: Attach a small amount (more than Rank B) Rank D: Attach very much

(14) Magnetic tape properties 200 parts of magnetic fine powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, 10 parts of vinyl chloride-cellulose acetate copolymer, 5 parts of lecithin, 100 parts of cyclohexanone,
After mixing and dispersing 100 parts of methyl isobutyl ketone and 300 parts of methyl ethyl ketone in a ball mill for 48 hours,
A magnetic paint is prepared by adding 5 parts of a polyisocyanate compound,
After this was applied to the (B) side of the polyester film, the coating was magnetically oriented before the coating was sufficiently dried and solidified, and then dried to form a magnetic layer having a thickness of 2 μm. Next, using a five-stage super calender composed of a mirror-finished metal roll and a polyester-based composite resin roll, under the conditions of a roll temperature of 85 ° C., a linear pressure of 250 kg / cm, and a running speed of 80 m / min, Coating film 5
000 m was repeatedly run seven times, and the amount of white powder adhering to the resin roll was visually evaluated and evaluated according to the rank shown below. 〇: Almost no white powder adhered to the resin roll △: Very slight white powder adhered ×: Obviously white powder adhered Next, after slitting the film after calendering to 1/2 inch width, Matsushita The following magnetic tape properties were evaluated at normal speed using an electric NV-3700 video deck.

Electromagnetic conversion characteristics (VTR head output) The VTR head output at a measurement frequency of 4 MHz was measured with a synchroscope and compared with a reference tape (back-coated, high-grade video tape) and evaluated according to the rank shown below. Was done. 〇: Equal to or higher than the reference tape △: Inferior to the reference tape X: Obviously inferior to the reference tape, a video tape recorded with a 4.4 MHz dropout signal that is unpractical The number of dropouts was measured with a dropout counter for about 20 minutes, and the number was converted to the number of dropouts per minute. The measurement was repeated 20 times and compared with a reference tape (high-grade video tape coated with a back coat), and evaluated according to the rank shown below. 〇: equivalent to or higher than the standard tape △: inferior to the standard tape ×: clearly inferior to the standard tape, not practical

(15) Meandering Resistance A video tape was run for 180 minutes using a commercially available VHS type VTR with the unwinding side back tension set to zero. The running state of the tape was observed with the pin immediately before the head cylinder, and the following judgment was made. A: The tape deviates from the prescribed traveling position by less than 0.5 mm during traveling B: The tape deviates from the prescribed traveling position by 0.5 mm or more and less than 2 mm during traveling C: The tape travels by 2 mm or more from the prescribed traveling position Come off

(16) Scratch resistance A magnetic tape slit to a width of 1/2 inch is 6 mm in diameter.
A film is wound around a hard chrome-plated metal pin (finished 3S) at an angle of 135 °, a traveling speed of 3 m / sec and a tension of 50.
g, the base film surface ((A) surface side) of the magnetic tape is 1
It was rubbed twice. Next, about 1000 pieces of aluminum
真空 Vacuum deposited so as to be thick, the amount of scratches was visually observed, and the following judgment was made. Rank 1: The amount of scratches is extremely high. Rank 2: The amount of scratches is high. Rank 3: The amount of scratches is between 2 and 4. Rank 4: The amount of scratches is low.

(17) Cutability The magnetic tape applied in a wide width is cut by a new shear cutter blade to 100-500 m in a width of 1/2 inch, and the state of the cut surface of the magnetic tape is observed with an electron microscope. Was done. 〇: Extremely good with no line-like turning up of the cut surface and no generation of cuttings ×: There are many line-like turning-ups in the cut surface and generation of cuttings △: Intermediate situation between the above △ and X (18) Cutability After the magnetic tape applied in a wide width was cut by a new shear cutter blade at 50,000 m in a 1/2 inch width, the cut surface of the magnetic tape was observed with an electron microscope, and the following judgment was made. 〇: Extremely good with no line-shaped turn-up of the cut surface and no generation of cuttings. X: Many line-shaped turn-ups of the cut-off surface, and generation of chips. △: Intermediate situation between the above △ and X

Example 1 100 parts of dimethyl terephthalate, ethylene glycol
Reaction of 60 parts and 0.09 part of magnesium acetate tetrahydrate
And evaporate methanol while heating.
Perform transesterification and take 4 hours from the start of the reaction
The temperature is raised to 230 ° C, and the transesterification reaction is substantially completed
did. Then, the average particle size is 0.46 μm, and the particle size distribution value d_{twenty five}
/ D₇₅= 1.54 beforehand crushing, classification and
Filter the massive calcite-type calcium carbonate particles
Used, 1.10 parts as ethylene glycol slurry
Was added. The particles used were part of the carboxyl group.
And methoxypoly which are neutralized with ammonia
Ethylene glycol and polypropylene glycol monomer
The copolymer with acrylate is used in an amount of 2% based on the particle.
It has been subjected to surface treatment. Add slurry
Thereafter, 0.03 parts of phosphoric acid and 0.03 parts of antimony trioxide were further added.
4 parts were added and a polycondensation reaction was carried out for 4 hours.
1 polyester (a₁ ) Got. Polyester (a
₁ ) Was heat-treated and the cohesive heat stability was evaluated._a 
/ D _aIs 0.84, which means that the polyester has good cohesive heat stability.
It was confirmed that it was a tell.

In the production of the above polyester (a ₁ ), the average particle size is 0.80 μm, and the particle size distribution value d ₂₅ / d ₇₅ =
1.51, massive calcite-type calcium carbonate particles
Except for using 00 parts, the polyester (a
_A polycondensation reaction was carried out for 4 hours in exactly the same manner as in ₁ ) to obtain a polyester (a ₂ ) having an intrinsic viscosity of 0.60. When the polyester (a ₂ ) was heat-treated and the heat stability of aggregation was evaluated, D _a / D _a ′ was 0.99, confirming that the polyester had good heat stability of aggregation.

In the production of the polyester (a ₁ ), the average particle diameter is 0.0
A transesterification reaction and a polycondensation reaction were carried out in exactly the same manner as above except that 1.50 parts of 3 μm delta-type aluminum oxide was added to obtain a polyester (A) having an intrinsic viscosity of 0.60. Further, except that no calcium carbonate particles were added in the production of the polyester (a ₁ ),
A transesterification reaction and a polycondensation reaction were carried out in exactly the same manner to obtain a substantially particle-free polyester (B) having an intrinsic viscosity of 0.62. Polyester (a ₁ ), polyester (a ₂ ), polyester (A) and polyester (B) were blended at a ratio of 50: 2: 30: 18 (weight ratio), respectively, to obtain a biaxially stretched laminated polyester film ( A) The raw material (1) for the layer was used.

Further, a polyester obtained by blending the polyester (a ₁ ) and the polyester (B) at a ratio of 23:77 (weight ratio), respectively, was used as a raw material for the outer layer (B) of the biaxially stretched laminated polyester film (B). 2). Further, as the raw material (3) of the layer inside the layer (B), polyester (B) is used, and the raw material polyester (1),
After pre-crystallizing (3) and (2) separately,
It is dried by a conventional method, and separated by a separate melt extruder.
Raw material (1) in the layer, raw material (3) in the inner layer of the (B) layer, (B)
Co-extrusion is performed so that the raw material (2) is located on the outer layer of the layers, and a three-layer composite is formed at a thickness ratio of (A) layer / (B) inner layer / (B) layer outer layer = 1: 13: 1. To obtain an amorphous sheet.

The amorphous sheet is first stretched in the longitudinal direction at a film temperature of 112 ° C. by 3.0 times at a film temperature of 112 ° C. by utilizing the peripheral speed difference of the multi-stage nip rolls. The film was stretched 1.5 times at a film temperature of 113 ° C. The birefringence of the first stretched film is 1.5 × 10 ^−2.
And the birefringence of the film after the second-stage stretching is 3.
It was 9 × 10 ^-2 . Then, the obtained film was once
After cooling to 0 ° C., the film was further heated to 98 ° C. and stretched by a factor of 1.2. The birefringence of the obtained vertically stretched film was 6.1 × 10 ^-2 . Next, the longitudinally stretched film is placed in a tenter in the transverse direction at 105 ° C. and 3.95 ° C.
After double stretching, the film was further stretched 1.05 times in the longitudinal direction at 125 ° C., and heat-treated at 220 ° C. to obtain a film having a thickness of 15 μm. The Young's modulus of the obtained film was 430 in the longitudinal direction.
kg / mm ^2, the transverse direction was 620 kg / mm ^2.
The intrinsic viscosity of the film was 0.59. A magnetic layer was applied to the B side of the obtained film to obtain a magnetic tape, and its characteristics were measured.

Example 2 A film was obtained in the same manner as in Example 1 except that the polyester used in Example 1 was used at the contents shown in Table 1 and the properties thereof were evaluated. Comparative Example 1 A film was obtained in the same manner as in Example 1 except that the polyester used in Example 1 was used, the content was as shown in Table 1, and a single-layer film was obtained, and the characteristics were evaluated. Comparative Example 2 In the production of the polyester (a ₁ ) of Example 1, the average particle size was 0.64 μm, the particle size distribution value d ₂₅ / d ₇₅ = 1.73,
A polycondensation reaction was carried out for 4 hours in exactly the same manner as in the polyester (a ₁ ) of Example 1, except that 1.10 parts of massive calcite-type calcium carbonate particles were used.
A polyester (a ₃ ) was obtained. Polyester (a ₃₎
Was heat treated to evaluate the cohesive heat stability, and found that D _a / D
_a ′ was 0.98, and it was confirmed that the polyester had good aggregation heat stability. Using polyester (a ₃ ), polyester (A) and polyester (B), Table 3
And a film was obtained in the same manner as in Example 1 except that the birefringence of the film was 0.005, and the characteristics were evaluated.

Comparative Example 3 In the production of the polyester (a ₁ ) of Example 1, the average particle size was 0.28 μm, the particle size distribution value was d ₂₅ / d ₇₅ = 1.73, and the mass was not subjected to any surface treatment. A polycondensation reaction was carried out for 4 hours in exactly the same manner as in the polyester (a ₁ ) of Example 1, except that 0.90 parts of calcite-type calcium carbonate particles were used.
₄ ) Got it. When the polyester (a ₄ ) was heat-treated and the cohesive heat stability was evaluated, D _a / D _a ′ was 0.33, and the cohesive heat stability was poor. Polyester (a
₄ ) A film was obtained in the same manner as in Example 1 except that the polyester of Example 1 was used, the content was as shown in Table 3, and the birefringence of the film was 0.029, and the characteristics were evaluated.

Comparative Example 4 In the production of the polyester (a ₁ ) of Example 1, 2.00 parts of massive kaolin particles having an average particle size of 0.31 μm and a particle size distribution value d ₂₅ / d ₇₅ = 2.63 were added. Other than using
Exactly the same as the polyester (a ₁ ) of Example 1
A time polycondensation reaction was performed to obtain a polyester (C) having an intrinsic viscosity of 0.62. The polyester (C) was heat-treated, and the aggregation heat stability was evaluated. As a result, D _a / D _a ′ was 0.98, and the aggregation heat stability was good. Polyester (C)
A film was obtained in the same manner as in Example 1 except that the polyester (A) and the polyester (B) of Example 1 were used, the content was as shown in Table 3, and the birefringence of the film was 0.029. The properties were evaluated. The results obtained above are summarized in Tables 1 to 4 below.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

All of the laminated films of the examples satisfying the requirements of the present invention have excellent cohesive heat stability of the raw materials, and therefore are excellent in production stability in such quality aspect, and in view of raw material cost and slit property. And the like, the film surface is uniform, and the running durability, abrasion resistance, scratch resistance and the like are excellent. The films of Examples are suitable as a base film for a magnetic recording medium, and particularly suitable as a non-backcoat type high-grade base film.

[0060]

The film of the present invention is excellent in production stability, raw material cost, etc., and has a uniform fine surface structure in characteristics, especially abrasion resistance,
It has excellent running properties and abrasion resistance, and is very useful as a non-backcoat type high-grade video tape base film and other magnetic recording medium applications, and its industrial value is extremely high.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoji Inagaki 1000 Kamoshita-cho, Midori-ku, Yokohama-shi, Kanagawa Pref. A) JP-A-5-111987 (JP, A) JP-A-4-232611 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A biaxially oriented polyester film in which a polyester (A) layer and a polyester (B) layer are coextruded and laminated, and simultaneously satisfy the following formulas (1) to (11). Biaxially oriented polyester film for magnetic recording media. [Number 1] _{0.30 ≦ d a ≦ 0.65 ... (} 1) 0.35 ≦ w a A ≦ 1.00 ... (2) 0.55 ≦ d a + 0.5w a A ≦ 0.95 ... ( ^{_{3) 8d a -w a A ≧}} 1.50 ... (4) 0.005 ≦ d b ≦ 0.50 ... (5) 0.15 ≦ w b A ≦ 1.00 ... (6) w b ≦ 0. 10 (7) 0.009 ≦ Ra ^A ≦ 0.020 (8) 0.002 ≦ Ra ^B ≦ 0.017 (9) 7.0 ≦ Rz ^A / Ra ^A ≦ 15 (10) during ^{_{80 ≦ μ d50 a / μ d1}} a ≦ 1.6 ... (11) [ the above equation, d _a is the average particle size of the (a) layer of synthetic calcium carbonate particles (a) (μm), w a a is the content of the (a) layer of synthetic calcium carbonate particles (a) (wt%), d _b is the average particle size of the (a) layer of aluminum oxide particles (b) (μm), w b a is (a ) content of the aluminum oxide particles (b) in layer (wt%), w _b is oxidized in the entire film Aluminum content of the particles (b) (wt%), Ra ^A
And Rz ^A, respectively (A) layer exposed surface a surface roughness ([mu] m) and ten-point average roughness (μm), Ra ^B is (B)
The surface roughness (μm) and μ _d50 ^A / μ _d1 ^A of the exposed layer represent the ratio of the dynamic friction coefficient of the exposed layer (A) between the initial _stage (first run) and the repeated running (50 th run).