JP2820176B2 - Biaxially oriented laminated film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented laminated film.

[0002]

2. Description of the Related Art As a biaxially oriented laminated film, for example, a biaxially oriented polyester film, a film in which a polyester contains substantially spherical silica particles originating from colloidal silica is known (for example, see Japanese Patent Application Laid-Open No. H10-163,873). 59
171623).

[0003] However, as the processing speed of the film processing step, especially the application of the magnetic layer in the magnetic medium application, calendering and winding, and the step of assembling the cassette, increases, the film surface, especially minute irregularities, is caused by the contacting rolls and guides. There is a disadvantage that the film surface is easily scraped off (poor in scratch resistance). Also, in the conventional one,
With the speeding up of dubbing by high-speed magnetic field transfer,
To reduce the image quality during dubbing, the image quality, ie, S / N
(Signal / noise ratio) was insufficient.

[0004] In order to solve such a drawback, the outermost layer of the laminated film is made to be a thin layer, and particles having a relatively large particle diameter are contained in the layer thickness. There has been proposed a biaxially oriented laminated film in which minute projections are formed on the film surface so as to be hardly scraped off by making the relationship (JP-A-2-77431).

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art and discloses a technique disclosed in
The technology proposed in Japanese Patent No. 7431 is further improved by further optimizing the fine projections on the film surface to further improve the running property, scratch resistance, and projection breaking strength, and to reduce the image quality when used as a magnetic medium. It is an object of the present invention to provide a biaxially oriented laminated film having good dubbing characteristics (hereinafter, sometimes referred to as excellent electromagnetic conversion characteristics).

[0006]

According to the present invention, there is provided a biaxially oriented laminated film having a laminated structure of at least three layers, wherein particles are contained in at least one outermost layer of the biaxially oriented laminated film. The relationship between the average particle diameter d (nm) of the particles and the thickness t (nm) of the outermost layer is as follows:
0.2d ≦ t ≦ 10d, and the number of protrusions having a height of 20 nm or more on the outermost film surface is 3 × 10 ³
２2 × 10 ⁵ / mm ² , and at least one outermost layer has an intrinsic viscosity higher than that of the intermediate layer.

[0007] In the above biaxially oriented laminated film, above
The number of particles having a particle size satisfying 0.2d ≦ t ≦ 10d is 3 × 1
0 ³ ~1.5 × 10 ⁵ cells / mm ² der Rukoto is preferred
No.

First, the film of the present invention needs to have a laminated structure of at least three layers. If there are three or more layers,
Four or five layers may be used, but a three-layer structure is preferable because the effects of the present invention are further improved. However, a film having a single-layer or two-layer structure cannot satisfy the running properties, scratch resistance, projection breaking strength, and electromagnetic conversion characteristics, and cannot provide good image quality and good dubbing resistance.

Next, in the film of the present invention, it is necessary that at least one of the layers constituting the film is biaxially oriented. It is particularly preferable that all the layers of the three or more layered structure are biaxially oriented. If all the layers are non-oriented or uniaxially oriented, the properties of the present invention cannot be satisfied.

The polymer constituting the biaxially oriented laminated film of the present invention is not particularly limited, but polyester is preferred for use in magnetic media. The polyester is not particularly limited, but ethylene terephthalate, ethylene α,
β-bis (2-chlorophenoxy) ethane-4,4′-
It is particularly preferred when at least one structural unit selected from dicarboxylate and ethylene 2,6-naphthalate units is the main constituent. Among them, a polyester containing ethylene terephthalate as a main component is particularly preferable. 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.

In the biaxially oriented laminated film of the present invention, the outermost layer on at least one surface of the biaxially oriented laminated film first has particles in the relation between the average particle diameter d (nm) of the particles and the layer thickness t (nm) of the outermost layer. Is contained so that 0.2d ≦ t ≦ 10d. If t is smaller than 0.2d, the running property is deteriorated, and if t is larger than 10d, the image quality of a magnetic tape is reduced.

[0012] Mainly due to the outermost layer-containing particles, the number 3 × 10 ³ to 2
× 10 ⁵ protrusions / mm ² are formed.

If the number of protrusions on the outermost film surface is less than the above range, the coefficient of friction increases, and good running properties cannot be obtained. Conversely, if the number of protrusions is larger than the above range, the image quality of the magnetic tape will be reduced, and the scratch resistance will be reduced.

In order to form such projections, the number of particles having a particle size satisfying the relationship of the above equation is 3 × 10 ^{3 to} 1.5 × 1.
Contained such that 0 ⁵ / mm ^2. in this way,
By setting the number of particles having a particle diameter satisfying a specific relationship between the particle diameter of the particles and the layer thickness of the outermost layer in a specific range, first, the desired fine protrusions are efficiently formed on the film surface by the contained particles themselves. Is done. The reason why the range of the number of particles is smaller than the range of the number of protrusions is that the protrusions may be formed by the transfer effect from the intermediate layer or the like.

In the biaxially oriented laminated film of the present invention, the intrinsic viscosities of the respective layers are set so that the intrinsic viscosity of at least one outermost layer is higher than the intrinsic viscosity of the intermediate layer. By making the intrinsic viscosity of the outermost layer portion higher than that of the intermediate layer portion, the scratch resistance of the outermost layer is kept high, and the particles are more firmly retained in the layer, and the projection breaking strength is also improved. Is done.

In particular, the intrinsic viscosity of the entire laminated film is 0.60 or more, and the intrinsic viscosity of at least one outermost layer is higher than the intrinsic viscosity of the intermediate layer by 0.02 or more and less than 0.2. preferable. If the intrinsic viscosity of the entire laminated film is lower than 0.60, the thermal dimensional stability becomes poor, and the skew characteristics of the magnetic recording medium deteriorate. When the difference between the intrinsic viscosity of the outermost layer and the intrinsic viscosity of the intermediate layer is less than 0.02, the scratch resistance of the outermost layer is insufficient. Is too high, and the filter for filtration may be damaged, and the productivity is reduced.

In the film of the present invention, different polymers may be blended as long as the object of the present invention is not impaired, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers and the like may be blended. Organic additives may be added to the extent that they are usually added.

Next, the method for producing the film of the present invention will be described for the case of a polyester film. First, as a method for incorporating particles into the polyester, for example, a method is preferred in which particles are dispersed in a predetermined ratio in the form of a slurry in ethylene glycol, which is a diol component, and this ethylene glycol is polymerized with a predetermined dicarboxylic acid component. When adding particles, for example, if the water sol or alcohol sol obtained during the synthesis of the particles is added without drying once, the dispersibility of the particles is very good, high-speed scraping,
Both electromagnetic conversion characteristics can be improved. A method of directly mixing a water slurry of particles with predetermined polyester pellets, supplying the mixture to a vent-type twin-screw kneading extruder, and kneading the resulting mixture with polyester is also very effective for further improving the effects of the present invention. As a method of adjusting the content and the number of particles, a high-concentration particle master is prepared by the above method, and the particle master is adjusted by diluting it with a polyester substantially containing no particles during film formation. The method is effective.

Next, a polyester film having a laminated structure of three or more layers is formed by using the polyester pellets. The polyester pellets obtained by the above method are mixed at a predetermined ratio, dried, fed to a known extruder for melt lamination, extruded from a slit die into a sheet, and cooled and solidified on a casting roll. At least make an unstretched film. That is, using two or three or more extruders, three or more manifolds or a merging block (for example, a merging block having a square merging portion), a film layer constituting each outermost layer and a film layer constituting an intermediate layer Are laminated, and three or more sheets are extruded from a die and cooled by a casting roll to produce an unstretched film. In this case, a method of installing a static mixer and a gear pump in the polymer flow path is effective. Further, the melting temperature of the extruder for extruding the polymer on the side of the outermost layer lamination portion is set at 5 from the base layer side.
It is effective to lower by -10 ° C.

Next, the unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, using a sequential biaxial stretching method in which stretching in the longitudinal direction and then in the width direction is performed first, the stretching in the longitudinal direction is divided into three or more stages, and the total longitudinal stretching ratio is 3.5 to 6.5 times. The method is particularly preferred. The stretching temperature in the longitudinal direction varies depending on the type of polyester and cannot be unconditionally determined.
It is effective to set the temperature to 30 ° C. and to increase the temperature after the second stage. The longitudinal stretching speed is 5,000 to 50,000% /
A range of minutes is preferred. As a stretching method in the width direction, a method using a stenter is generally used. Stretch ratio is 3.0
A range of up to 5.0 times is appropriate. The stretching speed in the width direction is
The temperature is preferably in the range of 1000 to 20000% / min and the temperature is in the range of 80 to 160 ° C. Next, this stretched film is heat-treated. The heat treatment temperature in this case is 170 to 220 ° C., particularly 1
The temperature is preferably from 80 to 200 ° C. and the time is preferably from 0.2 to 20 seconds.

[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 and number of particles The polymer is removed from the film by a plasma low-temperature ashing method to expose the particles. The processing conditions are selected so that the polymer is ashed but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of SEM is about 2000 to 10000 times, and the visual field in one measurement is appropriately selected from about 10 to 50 μm on one side. The volume average diameter d is obtained from the particle diameter and its volume fraction by the following formula from 5000 particles or more at different observation points. d = Σd _i · Nv _i where d _i is the particle size, Nv _i is its volume fraction. The number of particles is determined from the volume fraction of the particles satisfying the relationship between the layer thickness and the average particle diameter, and is converted into mm ² . If the particles are organic particles or the like and are significantly damaged by the plasma low-temperature incineration method, the following method may be used. The cross section of the film was measured using a transmission electron microscope (TEM).
Observe at a magnification of 100 to 100,000. The thickness of the section of the TEM is about 1000 mm, the measurement is made at 500 places or more at different places, and the volume average diameter d is obtained from the above equation.

(2) Thickness of laminated polyester layer (thickness of outermost layer: t) Using a secondary ion mass spectrometer (SIMS), the highest of the particles in the film in the range of 3000 nm in depth from the surface layer. The concentration ratio (M ⁺ / C ⁺ ) between the element resulting from the particles and the carbon element of the polyester is defined as the particle concentration, and the analysis in the thickness direction is performed from the surface to 3000 nm in depth. 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 has once reached the maximum value starts to decrease again. Based on this concentration distribution curve, the depth at which the surface layer particle concentration was の of the local maximum value (this depth was deeper than the local maximum value) was determined, and this was defined as the lamination thickness. The conditions are as follows. Measurement device Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany Measurement conditions Primary ion species: O ₂ ⁺ Primary ion acceleration voltage: 12 KV Primary ion current: 200 nA Raster area: 400 μm □ Analysis area: Gate 30% Measurement vacuum degree: 6.0 × 10 ^-9 Torr E-GUN: 0.5 KV-3.0 A SIMS is used when organic particles are most contained in the range from the surface layer to the depth of 3000 nm. Is difficult to measure with XPS (X
Line photoelectron spectroscopy), IR (infrared spectroscopy), etc., the same depth profile as described above may be measured to determine the lamination thickness, or the change in particle concentration and polymer The interface can be recognized from the difference in contrast due to the difference, and the lamination thickness can be determined. Further, after the laminated polymer is peeled off, the laminated thickness can be determined using a thin film step measuring device.

(3) Number of protrusions on the film surface A two-detector scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] and a cross section measuring device [PMS-1, manufactured by Elionix Co., Ltd.] The measured height of the projections when scanning with the height of the flat surface set to 0 is sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.], and the film surface projection image is reconstructed on the image processing apparatus. Next, the highest value among the individual projections obtained by binarizing the projections in this surface projection image is defined as the height of the projection, and this is determined for each individual projection. This measurement was repeated 500 times in different places, and the number of protrusions was determined by using protrusions having a height of 20 nm or more as protrusions. The magnification of the scanning electron microscope is selected between 1000 and 8000 times. In some cases, a high-precision optical interference type three-dimensional surface analyzer (WY
KO TOPO-3D, objective lens: 40 to 200
The height information obtained by using (2, the use of a high-resolution camera is effective) may be replaced with the SEM value and used.

(4) Intrinsic viscosity [η] (unit: dl / g) The value calculated from the following equation 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, and C is the solvent
Weight of dissolved polymer per 100 ml (g / 100 ml, usually 1.2), K is the Huggins constant (0.343). Also,
Solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

(5) Image Quality (Chroma S / N) A magnetic paint having the following composition is applied to the film by a gravure roll, magnetically oriented, and dried. In addition, a small test calendar device (steel roll / nylon roll,
5), a calendar treatment is performed at a temperature of 70 ° C. and a linear pressure of 200 kg / cm 2, and then curing is performed at 70 ° C. for 48 hours.
Slit the above tape into 1/2 inch, length 25
A length of 0 m was incorporated into a VTR cassette to form a VTR cassette tape. (Magnetic paint composition) Co-containing iron oxide (BET value 50 m ² / g): 100 parts by weight Eslek A (vinyl chloride / vinyl acetate copolymer manufactured by Sekisui Chemical): 10 parts by weight Nipporan 2304 (manufactured by Nippon Polyurethane) Polyurethane elastomer): 10 parts by weight Coronate L (polyisocyanate manufactured 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 was recorded on this tape by using a home VTR with a Shibasoku TV test waveform generator (TG7 / U706), and the reproduced signal was used as a shivasoku. Chroma S / N was measured with a color video noise measuring instrument (925 D / 1) manufactured by FUJIFILM Corporation.

(6) Running Property (Friction Coefficient μk) A film obtained by slitting the film into a tape having a width of 1/2 inch was used by using a tape running property tester SFT-700 (manufactured by Yokohama System Laboratory Co., Ltd.). , 20 ° C., 60% RH atmosphere, and the initial coefficient of friction was determined by the following equation (film width was １ ／ inch). μk = 2 / πln (T ₂ / T ₁ ) Here, T ₁ is the entrance tension, and T ₂ is the exit tension. The guide diameter is 6 mmφ, the guide material is SUS27 (surface roughness 0.2S), the winding angle is 90 °, and the running speed is 3.
3 cm / sec. When μk obtained by this measurement was 0.3 or less, it was determined that the friction coefficient was good, and when it exceeded 0.3, it was determined that the friction coefficient was poor. This μk is a critical point that affects the handling properties when processing the film for magnetic recording media, capacitors, packaging and the like.

(7) Scratch resistance The film is slit into a tape having a width of 1/2 inch, and a tape running tester TBT-300D / H type (manufactured by Yokohama System Laboratory Co., Ltd.) is used. In a 20 ° C., 60% RH atmosphere, a guide pin of a video cassette (with a surface roughness of 50 nm, R
At t, the tape is wound on a stainless steel guide pin having a surface of 2500 nm in degree and wound at an angle of 60 degrees, a point 90 m from the beginning of the run is sampled, aluminum is deposited, and the amount of scratches is visually determined as follows. The judgment was made based on the standard. No scratches at all ··· Excellent scratches but few in number ··· Good Good with many deep scratches ···

(8) Dubbing resistance A magnetic paint having the following composition is applied to the film by gravure roll, magnetically oriented, and dried. Furthermore, a small test calendar device (steel roll / nylon roll,
5 steps), calendar at temperature: 70 ° C, linear pressure: 200 kg / cm
After the treatment, cure at 70 ° C for 48 hours. The above table
The raw material was slit to 1/2 inch to make a baked cake. A length of 250 m from the baked cake 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 Eslek A (vinyl chloride / vinyl acetate copolymer manufactured by Sekisui Chemical): 10 parts by weight Nipporan 2304 (manufactured by Nippon Polyurethane) Polyurethane elastomer): 10 parts by weight-Connetate 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 was recorded on this tape by using a Shibasoku TV test waveform generator (TG7 / U706) using a VTR for home use. The chroma S / N was measured from the reproduced signal using a Shibasoku color video noise measuring instrument (925 D / 1), and was designated as A. A master table that records the same signals as above
The same sample table as that obtained by measuring A using a magnetic field transfer type video software high-speed printing system (for example, a Sprinter manufactured by Sony Magnescal Co., Ltd.).
The chroma S / N of the tape after dubbing into the baked (unrecorded) baked cake was measured in the same manner as above, and was designated as B. The decrease in chroma S / N (AB) due to this dubbing is 3d
When less than B, the anti-dubbing property was excellent: when it was 3 dB or more and less than 5 dB, it was judged as good, and when it was 5 dB or more, it was judged as poor. Although excellent is desirable, even good is practically usable.

(9) Protrusion Breaking Strength A film obtained by slitting a film into a tape having a width of 1/2 inch is repeatedly run on guide pins using a tape running tester. (Guide material: SUS, surface roughness:
0.3S) A 200 g load was applied to one end of the film, and the film was run for 20 passes at a winding angle of 90 degrees and a running speed of 3.3 cm / sec. Then, the amount of white powder adhering to the guide pins was evaluated. Was observed with a differential interference microscope, and the state of destruction of projections and the state of falling particles was evaluated. Magnification 1
Observation was performed for 10 visual fields at a magnification of 000, and the ratio of the particle dropping portion to the total number of protrusions was excellent (no particle dropping was observed), good (particles were dropped slightly, but the amount of adhered white powder was very small), and poor. (A large number of particles were observed and the amount of adhered white powder was large).

[0030]

Next, embodiments of the present invention will be described based on examples. Example 1 (Table 1) Particles contained in the outermost layer were dissolved in ethylene glycol.
Dispersing 50 μm diameter glass beads as media,
After removing the glass beads, the mixture was polymerized with terephthalic acid to obtain a polyethylene terephthalate master pellet.

The above master pellets are diluted at predetermined ratios with polyethylene terephthalate pellets containing no particles, each is prepared to have a predetermined viscosity, dried at 180 ° C. for 8 hours under reduced pressure (3 Torr), and then extruded. The mixture was supplied to the extruder 1 and the extruder 2 (for example, a vent type twin screw kneading extruder), and was melted at 280 ° C and 290 ° C. These two polymers are each subjected to high-precision filtration, laminated in a three-layer merging block having a rectangular laminated portion, extruded in a sheet shape from a fishtail-type die, and then subjected to an electrostatic application casting method. The film was wound around a casting drum having a surface temperature of 30 ° C., cooled and solidified to form an unstretched film having a thickness of about 160 μm. The draft ratio at this time was 6.5.

This unstretched film is divided into three stages in the longitudinal direction, 1.2 times at 123 ° C., 1.45 times at 126 ° C.,
Each was stretched 2.3 times at 14 ° C. This uniaxial film is divided into two stages in the width direction using a stenter, stretched 3.7 times at 111 ° C. and 1.2 times at 113 ° C., and stretched 200 times at a constant length.
C. for 5 seconds to obtain a film having a thickness of 13 .mu.m. The outermost layer laminated thickness t of the obtained film is 100
At 0 nm, the laminated thickness t of the outermost layer and the average particle size d of the contained particles
And the relationship t / d was 1.5. The number of projections on both surfaces is the same, and the number of projections on the surface is 18000 / mm ^2.
Met. Further, the number of particles having a t / d of 0.2 to 10 is 1
It was 4000 pieces / mm ² . The outermost layer has an intrinsic viscosity of 0.66 dl / g, and the intermediate layer has an intrinsic viscosity of 0.60 d / g.
1 / g. The overall intrinsic viscosity is 0.61 dl
/ G.

When the image quality of the VTR tape made with this film was measured, the chroma S / N was +2.5 dB. The running property (coefficient of friction) of the film was as good as 0.24. Furthermore, when the scratch resistance, the dubbing resistance, and the projection breaking strength were evaluated, all were excellent. As described above, the relationship between the particles contained in the outermost layer laminated portion and the lamination thickness, the number of particles satisfying the relationship, the number of surface protrusions are within the scope of the present invention, and the intrinsic viscosity of each layer is the relationship of the present invention. When the above conditions are satisfied, excellent image quality, running properties, scratch resistance, dubbing resistance, and projection breaking strength can be obtained.

Examples 2 to 5 and Comparative Examples 1 to 4 (Table 1) In the same manner as in Example 1, the thickness t of the outermost layer and the relationship t between the thickness t of the outermost layer and the average particle diameter d of the contained particles were determined. Various biaxially oriented laminated polyester films were prepared in the case where / d, the number of surface protrusions, the number of particles having t / d of 0.2 to 10 and the intrinsic viscosity of each layer were changed. The laminated thickness of the outermost layer, the relationship t / d between the laminated thickness t and the average particle diameter d of the contained particles, the number of surface protrusions, and the number of particles having a t / d of 0.2 to 10 are within the scope of the present invention. When the intrinsic viscosity of each layer satisfies the relationship of the present invention, excellent image quality, running properties, scratch resistance, dubbing resistance, and projection breaking strength were obtained (Examples 2 to 5). ), If any of the requirements, especially the intrinsic viscosity of each layer does not satisfy the relationship of the present invention, even if some other conditions are within the scope of the present invention, image quality, running properties, scratch resistance, All of the dubbing resistance and the protrusion breaking strength could not be satisfied (Comparative Examples 1 to 4).

[0035]

[Table 1]

[0036]

According to the biaxially oriented laminated film of the present invention, the outermost layer on at least one side of the laminated structure of at least three layers satisfies the relationship between the specific particle average particle size and the layer thickness of the outermost layer. As described above, the number of surface protrusions or the number of particles having a particle size satisfying the relationship is set to a specific range, and the relationship between the intrinsic viscosity of the outermost layer and the intermediate layer is specified, so that the surface of the laminated film is not easily shaved. And it is possible to efficiently form desired projections to obtain a desired surface form,
Excellent running properties, scratch resistance, and projection breaking strength can be exhibited, and excellent image quality and anti-dubbing properties for magnetic media can be obtained.

Continuation of the front page (56) References JP-A-3-207651 (JP, A) JP-A-62-290535 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1 / 00-35/00 G11B 5/704 B29C 55/00-55/30

Claims (3)

(57) [Claims] 1. A biaxially oriented laminated film having a laminated structure of at least three or more layers, wherein the outermost layer on at least one side thereof contains particles, and the particles have an average particle diameter d (nm).
And the thickness t (nm) of the outermost layer is 0.2d ≦
t ≦ 10d , and 2 of the film surface on the outermost layer side
The number of protrusions having a height of 0 nm or more is 3 × 10 ³ to 2 × 10 ^3
5 is / mm ^2, further at least one surface of the biaxially oriented laminated film of intrinsic viscosity of the outermost layer portion is equal to or higher than the intrinsic viscosity of the intermediate layer portion. Wherein said 0.2d ≦ t ≦ 10d particle number particle diameter satisfying the ³ × 10 3 ~1.5 × 10 ⁵ cells / mm ² der
The biaxially oriented laminated film according to claim 1 . 3. The intrinsic viscosity of the entire laminated film is 0.60 or more, and the intrinsic viscosity of at least one outermost layer portion is higher than the intrinsic viscosity of the intermediate layer portion by 0.02 or more and less than 0.2. 1 or 2 biaxially oriented laminated film.