JP2692320B2 - Biaxially oriented polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a biaxially oriented polyester film,
The present invention relates to a biaxially oriented polyester film having a laminated film structure suitable as a film for a magnetic recording medium.

[Prior Art] As a biaxially oriented polyester film having improved surface characteristics, a film in which polyester contains substantially spherical silica particles derived from colloidal silica is known (for example, JP-A-59). -171623 publication).

In such a biaxially oriented polyester film, the silica particles contained therein form projections on the surface of the film, thereby lowering the coefficient of friction of the surface to improve handling and running properties, and improve the magnetic properties of magnetic recording media. It is possible to improve the adhesiveness of the layer.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional biaxially oriented polyester film, the contained silica particles are randomly distributed over the entire area in the thickness direction of the film. There is a limit to the increase, and the heights of the protrusions also vary considerably at random. Recently, the following problems have been pointed out due to the unevenness of the protrusion height and the low protrusion density.

When the height of the protrusions on the film surface is non-uniform, the high-height protrusions are easily scraped off, and the film processing step, for example, as the process speed of the magnetic layer coating / calendering step in magnetic recording medium applications increases, The drawback of scratching the film surface by the contacting roll has recently become a problem.

In addition, magnetic recording media applications, especially video tapes, are often used recently for software (produced video works are recorded and fixed on a package medium, duplicated or expanded). For film-based video tapes, S / N for high-speed dubbing (record copying) from the master tape in the process of recording video works
(Signal / noise ratio, parameters of image quality) is greatly reduced, and the image quality deteriorates.

On the other hand, if the projection density on the film surface is low, the effect of improving the slipperiness of the film surface is low, and the effect of improving the handling and running properties cannot be obtained as expected.

Further, not only the above-mentioned biaxially oriented polyester film having surface protrusions formed thereon, but also a normal biaxially oriented polyester film, a wide film is slit into a narrow width (for example, the original width of the magnetic tape) according to the intended use. However, if a large amount of film powder is generated from the end face of the film during slitting, the film powder causes various troubles. Therefore, it is desired to suppress such powder falling from the slit end surface as much as possible.

The present invention forms protrusions of high density and uniform height on the surface of a biaxially oriented polyester film to improve the scratch resistance of the surface (hereinafter referred to as scratch resistance) and image quality by dubbing in magnetic tape applications ( S / N) is prevented from decreasing (hereinafter referred to as dubbing resistance), and at the same time, it is intended to improve the powder falling property during slitting.

[Means for Solving the Problem] A biaxially oriented polyester film of the present invention which meets this object is a film obtained by laminating a film containing polyester A particles as a main component on at least one side of a film containing polyester B as a main component. An axially oriented polyester film, wherein the polyester A laminated film has a thickness of 0.005
.About.3 .mu.m, the average particle size of the particles contained in the laminated film is 0.1 to 10 times the thickness of the laminated film, the content of the particles in the laminated film is 0.5 to 50% by weight, and the polyester A The laminated film layer composition of No. 1 has a intrinsic viscosity smaller than that of the base film layer composition of polyester B.

Further, the above-mentioned object is to achieve the following (2) (3) according to the present invention.
This is also achieved by the biaxially oriented polyester film (4).

(2) A biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, and the surface of the laminated film of polyester A formed by the particles. The average height of the protrusions is 1/3 of the average particle size of the particles.
A biaxially oriented polyester film which is 5 or more and in which the intrinsic viscosity of the laminated film layer composition of polyester A is smaller than the intrinsic viscosity of the base film layer composition of polyester B.

(3) A biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one surface of a film mainly composed of polyester B, and the surface of the laminated film of polyester A formed by the particles. The number of protrusions having a height of 1/3 or less of the average particle diameter of the particles is 70% or less of the total number of protrusions, and
A biaxially oriented polyester film, wherein the intrinsic viscosity of the laminated film layer composition of Polyester A is smaller than the intrinsic viscosity of the base film layer composition of Polyester B.

(4) A biaxially oriented polyester film in which a film containing polyester A and particles as a main component is laminated on at least one surface of a film containing polyester B as a main component, and the laminated film surface of polyester A formed by the particles. The relative standard deviation of the height distribution of the protrusions is 0.6 or less, and the intrinsic viscosity of the laminated film layer composition of polyester A is smaller than the intrinsic viscosity of the base film layer composition of polyester B. Axial oriented polyester film.

In these biaxially oriented polyester films,
Polyester film A layer-containing particles form projections of high density and uniform height on the surface thereof, which improves scratch resistance and dubbing resistance in magnetic tape applications. Polyester film A layer and polyester film B layer By keeping the intrinsic viscosity with
Powder drop characteristics during slitting (hereinafter also referred to as slitting property)
Is improved.

The polyester A in the present invention is not particularly limited, but is preferably ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4 ′.
-When at least one structural unit selected from dicarboxylate and ethylene 2,6-naphthalate units is a main component, the formation of surface projections, scratch resistance, and dubbing resistance in magnetic tape applications are further improved. Is desirable. Further, when the polyester constituting the present invention is crystalline, the scratch resistance and the dubbing resistance are further improved, which is extremely desirable. The crystallinity referred to here means that it is not so-called amorphous, and quantitatively the cold crystallization temperature Tcc in the crystallization parameter is detected, and the crystallization parameter ΔTcg is 150.
It is below ° C. Furthermore, when the heat of fusion (change in enthalpy of fusion) measured by a differential scanning calorimeter shows a crystallinity of 7.5 cal / g or more, the slit property and the scratch resistance are further improved, which is extremely desirable. Further, a polyester containing ethylene terephthalate as a main constituent is particularly preferable because the scratch resistance of the film surface and the dubbing resistance in magnetic tape applications are further improved. In addition, two or more types of polyesters may be mixed or a copolymer may be used within a range not to impair the present invention.

The shape of the particles in the polyester A of the present invention is not particularly limited, but in the case of particles having a particle diameter ratio (particle major axis / minor axis) in the film of 1.0 to 1.3, particularly spherical particles,
Since the height of the protrusions formed on the surface can be easily made uniform and the density can be easily increased, the scratch resistance and the dubbing resistance can be greatly improved.

Further, when the particles in the polyester A of the present invention have a single particle index in the film of 0.7 or more, preferably 0.9 or more, protrusions having a uniform height are easily formed, and the scratch resistance and the scratch resistance of the film surface are improved. Dubbing and slitting properties are further improved, which is particularly desirable.

The type of particles in the polyester A of the present invention is not particularly limited, but as preferable particles for satisfying the above preferable particle characteristics, substantially spherical silica particles derived from colloidal silica, particles formed by a crosslinked polymer (for example, Cross-linked polystyrene). Especially 10% weight loss temperature (measured with a thermogravimetric analyzer Shimadzu TG-30M in nitrogen.
Crosslinked polymer particles having a high degree of crosslinking until the temperature rising rate of 20 ° C / min) reaches 380 ° C or higher are particularly desirable in terms of slit property. In the case of spherical silica originating from colloidal silica, substantially spherical silica having a low sodium content and produced by the alkoxide method is particularly desirable. However, other particles, such as particles of calcium carbonate, titanium dioxide, alumina, etc., can be sufficiently used by appropriately controlling the film thickness and the average particle size.

The thickness of the film layer containing the polyester A as a main component of the present invention is 0.005 to 3 μm, preferably 0.01 to 1 μm, and more preferably 0.03 to 0.8 μm. If the film thickness is smaller than the above range, the slit property and scratch resistance as the laminated film layer cannot be secured, and conversely, if the film thickness is large, surface protrusions of uniform height are formed at high density due to the relationship with the contained particles. Becomes difficult, and dubbing resistance and scratch resistance become poor.

Further, the size of the particles in the present invention, the average particle size in the laminated film containing the particles is 0.1 to 10 times the thickness of the laminated film, preferably 0.5 to 5 times, more preferably
The range is 1.1 to 3 times. If the average particle diameter / laminated film thickness ratio is smaller than the above range, the height of protrusions formed on the surface becomes uneven, and scratch resistance, dubbing resistance,
The slit property becomes poor, and conversely even if it is large, the surface protrusions formed by particles are easily scraped off, scratch resistance,
It is not preferable because the slit property becomes poor.

The average particle size (diameter) of the particles in the polyester A in the film is 0.005 to 3 μm, preferably 0.02 to 0.45 μm.
In the case of the range of μm, scratch resistance, dubbing resistance, and slit property are further improved, which is desirable.

Such particles are contained in the polyester A film in an amount of 0.5 to 50% by weight, preferably 2 to 40% by weight, more preferably 3 to 20% by weight. If it is smaller than this, the film surface projection formation density becomes too low, so good scratch resistance and dubbing resistance can be obtained. Conversely, if it is too high, the proportion of contained particles becomes too high, and the laminated film layer itself becomes brittle. It is not preferable because it becomes too much and scratch resistance and slit property become poor.

The average height of the projections on the surface of the laminated film layer of polyester A formed by the above particles is 1 / 3.5 or more, preferably 1/3 or more, of the average particle diameter of the particles. The surface protrusion having such an average height can be obtained by appropriately selecting and setting the average particle size of the contained particles with respect to the thickness of the laminated film from the above range.

Alternatively, regarding the projections on the surface of the laminated film of polyester A formed by the particles, the number of projections having a height of 1/3 or less of the average particle diameter of the particles is suppressed to 70% or less of the total number of projections. That is, the projections that are too low in height, in other words, the effect of improving scratch resistance is low, and it is possible to prevent the number of projections that deteriorate the slit property from becoming too large.

Furthermore, the relative standard deviation of the height distribution of the protrusions on the surface of the laminated film of polyester A formed by the particles is set to 0.6 or less. That is, the scratch resistance and the dubbing resistance are effectively improved by the uniform projections having the uniform height.

That is, the laminated film layer of the biaxially oriented polyester film of the present invention contains particles having an average particle diameter in the vicinity of the thickness of the film layer or larger. In other words, the ultra-thin laminated film contains fine particles having an average particle diameter near or greater than the film thickness. Therefore, the particles can be substantially concentrated only on the laminated film layer in the thickness direction of the entire biaxially oriented polyester film, and the particles can be distributed. As a result, the particle density in the laminated film can be easily increased, and the density of projections on the film surface formed by the particles can be easily increased. Further, since the particles are contained in the laminated film, the position of the particles is regulated in the thickness direction with respect to the entire biaxially oriented polyester film, and the thickness and the average particle diameter of the laminated film are as described above. However, the height of the surface protrusions formed by the particles is extremely uniform. Therefore, the scratch resistance of the surface of the laminated film is kept high, and the dubbing resistance in magnetic tape applications is improved.

Such a film containing polyester A and particles as main components is laminated on a film containing polyester B as a main component.

Polyester B is the same as polyester A described above, and polyester B and polyester A may be the same or different. The polyester A film layer is laminated on both sides or one side of the polyester B film layer. In other words, the lamination structure is A / B /
The case of A, A / B, but of course, A / B / C in which a C layer having a surface state different from A is provided on the surface opposite to A, or a multilayer structure of more than that may be used. (Where A, B, C
The type of each resin may be the same or different. Also, at least one surface needs to be the A layer. When the magnetic layer is provided, the B layer and the A / B
In the case of the / C configuration, it is preferable to provide it on the smooth surface. Also, as the polyester B, a crystalline polymer is desirable.
Particularly, when the crystallinity parameter ΔTcg is in the range of 20 to 100 ° C., the scratch resistance and the like of the film surface of the polyester B are further improved, which is desirable. As a specific example,
Ethylene terephthalate, ethylene α, β-bis (2-
When at least one structural unit selected from chlorphenoxy) ethane-4,4'-dicarboxylate and ethylene 2,6-naphthalate units is used as a main component, scratch resistance is particularly improved, which is desirable. However, other components may be copolymerized within a range that does not impair the present invention and within a range that does not impair desired crystallinity, preferably within 5 mol%.

Polyester B of the present invention may also be blended with other polymers within a range not to impair the purpose of the present invention, and may contain organic additives such as antioxidants, heat stabilizers, lubricants, and ultraviolet absorbers. It may be added to the extent that it is usually added.

It is not necessary for the film containing polyester B as a main component to contain particles, but the average particle size is 0.007 to 2 μm.
m, especially 0.02 to 0.45 μm, in a very small amount, for example 0.
001 to 0.7% by weight, especially 0.005 to 0.2% by weight, and even 0.00
When the content is 5 to 0.15% by weight, not only the coefficient of friction and scratch resistance are further improved in processing and use, but also the winding shape of the film is improved, which is extremely desirable. The type of particles contained is polyester A
It is desirable to use those which are desirably used for
The types and sizes of the particles contained in the polyesters A and B may be the same or different.

The polyester A containing the particles as described above and the polyester B are laminated by coextrusion, molded into a sheet, and then biaxially stretched to obtain a biaxially oriented polyester film. Lamination by co-extrusion in the present invention means that polyester A and polyester B containing particles are extruded by different extruders and laminated before discharging a laminated sheet from a die. This stack
It may be performed in a die for forming and discharging into a sheet (for example, a manifold), but since the laminated film layer is extremely thin as described above, it is preferably performed in a polymer tube before being introduced into the die. In particular, it is particularly preferable to form the laminated portion in the polymer tube in a rectangular shape, since the laminated portion can be uniformly laminated in the width direction. The molten polymer laminated at the rectangular laminated portion in the polymer tube is widened to a predetermined width in the sheet width direction by the manifold in the die, discharged from the die in a sheet shape, and then biaxially stretched. Therefore, even if the laminated film layer after biaxial orientation is extremely thin, the particle-containing polyester polymer will be laminated in a considerable thickness in the rectangular laminated portion in the polymer tube, so that it can be laminated easily and accurately. it can.

In the biaxially oriented polyester film of the present invention having a laminated structure as described above, the intrinsic viscosity of the laminated film layer composition of polyester A is set to be smaller than the intrinsic viscosity of the base film layer composition of polyester B.
Preferably, the difference in intrinsic viscosity is 0.05 dl / g or more, more preferably 0.07 dl / g or more. By making the intrinsic viscosity have a magnitude relationship in this way, it is possible to efficiently suppress the powder falling from the slit end surface of the film of the polyester B layer, which is the base film layer, at the time of slitting, so that the laminated film as a whole has a powder falling property at the time of slitting. Is improved. That is, as described above, the film surface protrusions of high density and uniform height due to the particles improve scratch resistance and dubbing resistance in magnetic tape applications, while improving the powder falling property at the time of slitting as a whole laminated film. It

In the biaxially oriented polyester film of the present invention having such a laminated film constitution, polyester B is further added.
The difference between the crystallization parameter of the base film layer (1) and the crystallization parameter of the laminated film layer of the polyester A (the former is larger than the latter) is 10 ° C. or more, preferably 15 ° C. or more. By doing so, it becomes possible to further improve the powder falling property at the time of slitting, and it becomes easy to form a desired surface protrusion in the polyester A layer.

Further, in the biaxially oriented polyester film of the present invention, it is preferable that the particle concentration ratio of the particles in the surface layer on the laminated film side including the particles is 0.1 or less. This surface layer particle concentration ratio indicates how the particles forming the film surface protrusions are covered with the thin film of polyester A on the film surface as shown in the measuring method described later, and the particles are substantially covered on the film surface. The higher the degree of direct exposure to the surface, the higher the surface particle concentration ratio, and the higher the degree of surface protrusion formation but the degree of coverage with the polyester A thin film, the lower the surface particle concentration ratio. Since the particles forming the projections are covered with the polyester A thin film, even if the particles are distributed at a high density in the ultra-thin laminated film layer, the particles are still in the laminated film layer, and thus the polyester B. Will be firmly held by the base film layer. Therefore, by setting the surface layer particle concentration ratio to be equal to or less than the above value, the particles are prevented from falling off, and the scratch resistance of the film surface and the powder falling property at the time of slitting are maintained high. Such a surface particle concentration ratio can be achieved by performing lamination by coextrusion. By the way, also by the coating method, it is possible to coat a film having a surface protrusion with the same density as that of the present invention, that is, a film layer of polyester B with a resin layer with an extremely thin thickness and to contain particles in the resin layer. Although it is possible, the surface layer particle concentration ratio is remarkably high (that is, the degree to which particles are substantially directly exposed to the surface is remarkably high), and the surface is extremely fragile as compared with the film of the present invention, and only the slit property is inferior. Absent.

Next, a method for producing the biaxially oriented polyester film of the present invention will be described.

First, as a method of incorporating particles into the polyester A, any of after polymerization, during polymerization, and before polymerization may be used, but a method of kneading a polymer with a vented twin-screw extruder is a surface morphology within the range of the present invention. It is effective for obtaining a film. Further, as a method of adjusting the content of particles, a method of preparing a high-concentration master by the above method and diluting it with a polyester substantially containing no particles at the time of forming a film to adjust the content of particles is known. It is effective for obtaining a film having a surface morphology within the scope of the present invention. Further, a method of adjusting the melt viscosity of the high-concentration master polymer of the particles, the copolymerization component, and the like to keep the crystallization parameter ΔTc g in the range of 30 to 80 ° C. does not cause stretching breakage, and the film having the surface morphology within the range of the present invention. It is effective to get

Thus, after the pellets A containing particles are sufficiently dried, they are fed to a known melt extruder and melted at a temperature not lower than the melting point of the polyester and not higher than the decomposition point, while the other polyester B (type May be the same as or different from the polyester containing particles) is fed to the laminating apparatus as described above, extruded into a sheet from a slit die, and cooled and solidified on a casting roll to obtain an unstretched film. make. That is, 2 or 3
The polyester polymers are laminated using a single extruder, a two or three layer confluence block or die.
In the case of using the merging block method, it is effective to form the laminated portion in a rectangular shape as described above in order to stably produce a film having a surface form within the scope of the present invention, without unevenness in the width direction, and to industrially manufacture the film.

Next, the multilayer unstretched film is biaxially stretched and biaxially oriented. The method of biaxial stretching may be any of simultaneous biaxial stretching and sequential biaxial stretching, but in the case of sequential biaxial stretching in which the film is stretched in the longitudinal direction and width direction in order to stabilize the film having the surface form within the scope of the present invention. Therefore, it is effective for industrial production without unevenness in the width direction. In the case of sequential biaxial stretching, the stretching in the longitudinal direction is divided into two stages, especially three or more stages, at a stretching temperature of 40 to 150 ° C. and a stretching speed of 1000 to 50,000% / min.
The 6-fold method is effective for obtaining a film having a surface morphology within the range of the present invention. The stretching temperature and speed in the width direction are
The range of 60 to 170 ° C. and 1000 to 20000% / min is suitable. The stretching ratio is preferably 3 to 10 times. Further, if necessary, the film can be further stretched in at least one of the longitudinal direction and the width direction. In any case, the point of the present invention is to provide a very thin layer containing particles and then perform stretching of 9 times or more as an area stretching ratio (magnification in the longitudinal direction × magnification in the width direction). Next, this stretched film is heat-treated.
In this case, the heat treatment conditions include relaxation in the width direction, fine stretching, and 140 to 250 ° C. under any of the conditions of constant length, preferably
A temperature of 160 to 220 ° C. for 0.5 to 60 seconds is preferable, but it is preferable to use microwave heating together with the heat treatment because a film having a surface morphology within the range of the present invention can be easily obtained.

A feature of the production method of the film of the present invention is that the film is biaxially stretched after providing a very thin layer containing particles by using a high concentration particle polymer having a specific range of thermal characteristics prepared by a special method. In the film forming process, after uniaxially stretching the film, a method of further coating and stretching, or a laminated film produced by coating a biaxially stretched film is far from the performance of the film of the present invention, and, The film of the present invention is also excellent in cost.

[Method for Measuring Physical Properties and Method for Evaluating Effect] The method for measuring characteristic values and the method for evaluating effect according to the present invention are as follows.

(1) Average particle size of particles Polyester is removed from the film surface by a plasma low temperature ashing method (for example, PR-503 type manufactured by Yamato Scientific Co., Ltd.) to expose the particles. The processing conditions are selected such that the polyester is ashed but the particles are not damaged. This is SEM
Observe with a (scanning electron microscope), connect the image of the particles (light and shade of light produced by the particles) to an image analyzer (for example, QTM900 manufactured by Cambridge Instrument), measure the number of particles, and change the observation location to determine the number of particles. The following numerical processing is performed for 5000 or more particles, and the average particle diameter D thus obtained is taken as the average particle diameter.

D = ΣDi / N Here, Di is the equivalent circle diameter of the particle, and N is the number.

(2) Content of Particles A solvent in which the polyester is dissolved but the particles are not dissolved is selected, the particles are centrifuged from the polyester, and the ratio (% by weight) to the total weight of the particles is defined as the particle content.
In some cases, the combined use of infrared spectroscopy is also effective.

(3) Glass transition point Tg, cold crystallization temperature Tcc, crystallization parameter ΔTc g, melting point Measured using a DSC (Differential Scanning Calorimeter) II type manufactured by Perxielmer. The measurement conditions for DSC are as follows.
That is, 10 mg of a sample is set in a DSC apparatus, melted at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. The quenched sample is heated at a rate of 10 ° C./min, and the glass transition point Tg is detected.
The temperature was further increased, and the crystallization exothermic peak temperature from the glassy state was defined as the cold crystallization temperature Tcc. The temperature was further raised, and the melting peak temperature was taken as the melting point. The difference between Tcc and Tg (Tcc-Tg) is defined as the crystallization parameter ΔTc g.

(4) Average height of surface protrusions and relative standard deviation of height distribution 2 detector type scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] and cross-section measurement device [PMS-1, Elionix Co., Ltd.] The height of the flat surface of the film is 0
The height measurement value of the projection when scanned as is sent to an image processing device [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct the film surface projection image on the image processing device. next,
The equivalent circle diameter is calculated from the area of each protrusion obtained by binarizing the protrusion portion in this surface protrusion image, and this is set as the average diameter of the protrusion. The highest value among the binarized individual projections is defined as the height of the projection, and this is determined for each individual projection. This measurement was repeated 500 times at different locations to determine the number of protrusions, and the average value of the heights of all the measured protrusions was defined as the average height. The standard deviation of the height distribution was determined based on the height data of each projection. The value obtained by dividing the obtained standard deviation by the average value of the heights was defined as a relative standard deviation. The scanning electron microscope has a magnification of 1000-80
Select a value between 00 times. In some cases, the height information obtained using a high-precision optical interference type three-dimensional surface analysis device (TOPO-3D made by WYKO, objective lens: 40 to 200 times, use of a high resolution camera is effective) is used for the above SEM. You may read and use it for the value of.

(5) Surface layer particle densification Using the secondary ion mass spectrum (SIMS), the concentration ratio of the highest concentration element of the particles in the film and the carbon element of the polyester is defined as the particle concentration, and the thickness Perform direction analysis. The ratio A / B between the particle concentration A at the outermost layer particle concentration (point at depth 0) measured by SIMS and the maximum concentration B obtained by further analyzing the depth direction, A / B, was defined as the surface layer particle concentration ratio. The measuring device and conditions are as follows.

Measuring instrument Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany Measuring condition Primary ion species: O ₂ ⁺ Primary ion accelerating voltage: 12KV Primary ion current: 200nA Raster area: 400μm □ Analysis area: Gate 30% Measurement vacuum degree: 6.0 × 10 ⁹ Torr E-GUM: 0.5KV-3.0A (6) Single particle index The cross section of the film is photographically observed with a transmission electron microscope (TEM) to detect particles. When the observation magnification is set to about 100,000, one particle that cannot be further divided can be observed. When the total area occupied by the particles is A and the area occupied by the aggregate in which two particles are aggregated is B, (A-
B) / A is a single particle index. The TEM conditions are as follows: 1 field of view area: 2 μm ² 500 fields of view are measured by changing the location.

・ Device: JEM-1200EX manufactured by JEOL ・ Observation magnification: 100000 times ・ Section thickness: Approximately 1000 Å (7) Particle size ratio In the measurement of (1) above, the average value of the major axis / the average value of the minor axis of each particle. Is the ratio of

 That is, it is obtained by the following equation.

Major axis = ΣD1i / N Minor axis = ΣD2i / N D1i and D2i are the major axis (maximum diameter), minor axis (shortest axis) and N are the total number of the individual particles, respectively.

(8) Thickness of Polyester A Layer in Laminated Film Using secondary ion mass spectrometer (SIMS), the concentration of the element derived from the highest concentration of particles in the film and the carbon element of polyester The ratio (M ₊ / C ₊ ) is the particle concentration,
The depth (thickness) direction is analyzed from the surface of the polyester A layer. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration which once reached a maximum at the depth [I] starts to decrease again. Based on this concentration distribution curve, the depth [II] (here, I
I> I) was taken as the lamination thickness. The conditions are the same as in the measurement method (5).

In addition, when the particles most contained in the film are organic polymer particles, it is difficult to measure by SIMS. Therefore, XPS (X-ray photoelectron spectroscopy), IR
(Infrared spectroscopy) or a confocal microscope
The depth profile of the particle concentration may be measured, and the layer thickness may be obtained by the same method as described above.

(9) Intrinsic viscosity [η] (unit: dl / g) A value calculated from the following formula from the solution viscosity measured at 25 ° C. in orthochlorophenol is used.

That is, ηsp / C = [η] + K [η] ² · C, where ηsp = (solution viscosity / solvent viscosity) -1, C is the solvent
Dissolved polymer weight per 100 ml (g / 100 ml, usually 1.2),
K is the Haggins constant (0.343). Also, solution viscosity,
The solvent viscosity was measured using an Ostwald viscometer.

(10) Scratch resistance The film slit into a tape with a width of 1/2 inch is run on a guide pin (surface roughness: Ra 100 nm) using a tape running tester (running speed 1000 m / Minutes, 10 passes, winding angle: 60 °, running tension: 20g). At this time, observe the wound in the film with a microscope,
Excellent if 2 or less scratches per tape width are less than 2
Less than 10 pieces were judged as good, and 10 or more pieces were judged as bad. Although excellent is desirable, even good is practically usable.

(11) Dubbing resistance A magnetic coating composition having the following composition is applied to a film by a gravure roll, magnetically oriented, and dried. Further, after calendering at a temperature of 70 ° C. and a linear pressure of 200 kg / cm using a small test calender (steel roll / nylon roll, 5 steps), curing is performed at 70 ° C. for 48 hours. The raw tape was slit into 1/2 inch to make a pancake. A length of 250 m from this pancake was incorporated into a VTR cassette to form a VTR cassette tape.

(Composition of magnetic paint) -Co-containing iron oxide (BET value 50 m ² / g): 100 parts by weight-S-REC A (Vinyl chloride / vinyl acetate copolymer manufactured by Sekisi Chemical Co., Ltd.): 10 parts by weight-Nipporan 2304 (Nippon Polyurethane) Polyurethane Elastomer): 10 parts by weight ・ Contonate L (Polyisocyanate made by Nippon Polyurethane): 5 parts by weight ・ Lecithin: 1 part by weight ・ Methyl ethyl ketone: 75 parts by weight ・ Methyl isobutyl ketone: 75 parts by weight ・ Toluene: 75 parts by weight ・ Carbon Black: 2 parts by weight Lauric acid: 1.5 parts by weight A 100% chroma signal is recorded on this tape using a home VTR and a TV test waveform generator (TG7 / U706) made by Shibasoku, and the reproduced signal is used to make Shibasoku colors. Chroma S / N was measured with a video noise measuring device (925D / 1) and was designated as A. The same sample tape (not yet measured) was obtained by measuring the pancake of the master tape recording the same signal as above using a magnetic field transfer type video software high-speed printing system (for example, a Sprinter manufactured by Sony Magnescale Co., Ltd.). Record) Chroma S / D on tape after dubbing to pancake
N was measured in the same manner as above, and was set as B. When the decrease in chroma S / N (AB) due to the dubbing was less than 3 dB, the anti-dubbing property was excellent. When it was 3 dB or more and less than 5 dB, it was judged as good. Although excellent is desirable, even good is practically usable.

(12) Powder dropping characteristics during slitting The film is slit at a speed of 150 m / min using a small slitter for testing. At this time, the black Toray Toraysee (eyeglass wipes) is pressed near the both end faces of the slit film to the extent that it is lightly touched, and 300 m is pulled out. The toraysee after removal was visually observed and judged according to the following criteria.

No powder attached 5 points Some powder attached 3 points Large amount of powder attached 1 point 4 points between 5 points and 3 points and 2 points between 3 points and 1 point ,
A powder with a score higher than 3 was considered to be good.

[Examples] The present invention will be described based on examples.

Examples 1 to 8 and Comparative Examples 1 to 6 Ethylene glycol slurries containing cross-linked polystyrene particles having different average particle diameters, spherical silica particles derived from colloidal silica, etc. were prepared, and the ethylene glycol slurries were heat-treated at 190 ° C. for 1.5 hours. After that, polycondensation was performed, and pellets of polyethylene terephthalate (hereinafter abbreviated as PET) containing a predetermined amount of the particles were prepared by a conventional method.
Polyester A was prepared using these pellets,
By a conventional method, PET containing substantially no particles was produced and designated as polyester B. Each of these polymers
It was dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours. Polyester A
Is fed to the extruder 1 and melted at 310 ° C., polyester B is further fed to the extruder 2 and melted at 280 ° C., and these polymers are combined and laminated before entering the mouthpiece in a combining block having a rectangular laminated portion. Then, the surface temperature is 45
℃ C around a casting drum to cool and solidify,
Two or three layer unstretched films having a polyester A layer on one side were made. At this time, the discharge amount of each extruder was adjusted to adjust the total thickness and the thickness of the polyester A layer. (However, Comparative Example 6 has a single layer A). This unstretched film was stretched 4.5 times in the longitudinal direction at a temperature of 80 ° C. This stretching was performed in four stages with a difference in peripheral speed between two sets of rolls.
This uniaxially stretched film is stretched at a stretching speed of 2000 using a stenter.
Stretched 4.0 times in the width direction at 100 ° C at% / min.
Heat treated at ℃ for 5 seconds, total thickness 15μm, Polyester A
A biaxially oriented laminated film having a layer thickness of 0.03 to 4 μm was obtained. The scratch resistance on the polyester A layer side of this film was evaluated, and the powder falling property at the time of slitting was evaluated.

Next, the dubbing resistance when these films were used as a magnetic tape was evaluated.

Each parameter as the base film is as shown in Table 1, and when these are within the scope of the present invention,
As shown in Table 1, scratch resistance, dubbing resistance, and powder falling characteristics at the time of slitting showed good values, but otherwise, these characteristics could not be combined.

[Effects of the Invention] As described above, when the biaxially oriented polyester film of the present invention is used, the polyester A containing particles is used.
Since the protrusions having a uniform height are formed at a high density on the surface of the layer and the magnitude relationship of the intrinsic viscosity between the polyester A layer and the polyester B layer is defined as a specific relation, excellent scratch resistance is obtained due to the uniform protrusion formation. It is also possible to obtain excellent dubbing resistance when using it for magnetic tape, further absorb the force applied during slitting as a laminated film, and film powder is less likely to occur during slitting. The powder falling property of the laminated film as a whole when slit is significantly improved.

Further, the biaxially oriented polyester film of the present invention is a film made by directly composite laminating by coextrusion without an operation such as coating in the film forming process, and is made during or after the film forming process. Compared with the laminated film, the molecules of the outermost layer are also biaxially oriented, so that besides the above-mentioned characteristics, for example, the surface has much better abrasion resistance, and is advantageous in terms of cost, quality stability, and the like.

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Claims (5)

(57) [Claims] 1. A biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one surface of a film mainly composed of polyester B, wherein the thickness of the laminated film of polyester A is 0.
005 to 3 μm, the average particle diameter of the particles contained in the laminated film is 0.1 to 10 times the thickness of the laminated film, the content of the particles in the laminated film is 0.5 to 50% by weight, and the polyester A biaxially oriented polyester film, wherein the laminated film layer composition of A has an intrinsic viscosity smaller than that of the base film layer composition of polyester B. 2. A biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one surface of a film mainly composed of polyester B, wherein the polyester A formed by the particles is laminated. The average height of the projections on the film surface is the average particle size of the particles.
A biaxially oriented polyester film having a ratio of 1 / 3.5 or more, and an intrinsic viscosity of a laminated film layer composition of polyester A smaller than an intrinsic viscosity of a base film layer composition of polyester B. 3. A biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one surface of a film mainly composed of polyester B, wherein the polyester A formed by the particles is laminated. Regarding the protrusions on the film surface, 1 / of the average particle size of the particles
The number of projections having a height of 3 or more is 70% or less of the total number of projections, and the intrinsic viscosity of the laminated film layer composition of polyester A is smaller than the intrinsic viscosity of the base film layer composition of polyester B. A biaxially oriented polyester film. 4. A biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one surface of a film mainly composed of polyester B, wherein the polyester A formed by said particles is laminated. The relative standard deviation of the height distribution of the protrusions on the film surface is 0.6
A biaxially oriented polyester film, wherein the intrinsic viscosity of the laminated film layer composition of polyester A is smaller than that of the base layer film layer composition of polyester B. 5. The biaxial according to claim 1, wherein the difference between the crystallization parameter of the base film layer of the polyester B and the crystallization parameter of the laminated film layer of the polyester A is 10 ° C. or more. Oriented polyester film.