JP2803771B2 - 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, and more particularly to a biaxially oriented laminated polyester film most suitable for use as a base material of a coating type magnetic recording medium coated with a magnetic paint .

[0002]

2. Description of the Related Art Conventionally, a biaxially oriented polyester film comprising a polyester containing ethylene naphthalate as a main component (for example, JP-A Nos. 62-143938 and 63-60732), and a core layer made of ethylene. Polyester layer containing terephthalate as a main component,
Laminated biaxially oriented polyester film in which the outer layer is a polyester layer containing ethylene naphthalate as a main component (for example, JP-A-63-197463,
No. -14126).

[0003] Polyester films containing ethylene naphthalate as a main component have excellent mechanical strength, especially elastic modulus, which are much higher than those of polyester film containing ethylene terephthalate as a main component, and also have abrasion resistance. It is known to have excellent properties. When these polyester films are used as a magnetic tape, it is effective to improve the slipperiness by forming uniform fine projections on the surface, particularly in order to secure good running properties of the magnetic tape. As a means, it is known that the inclusion of fine particles is effective.

[0004] However, a polyester containing ethylene naphthalate as a main component is in a molten state.
The viscosity is considerably higher than polyester or the like containing ethylene terephthalate as a main component. For this reason, in the process of filtering the molten polyester, if the filtration accuracy is increased, the filtration pressure becomes too high, and there is a problem that high-precision filtration is difficult. If high-precision filtration is not possible, coarse projections may be formed on the surface of the film when polyester containing ethylene naphthalate as a main component constitutes the film. Out increases and is not preferable. Therefore, in the above-mentioned conventional film composed of polyester alone containing ethylene naphthalate as a main component, there is a problem that coarse projections are generated because high-precision filtration cannot be performed, and ethylene naphthalate is mainly used in the core layer of ethylene terephthalate. Even in a film in which a polyester layer as a component is laminated, the lamination thickness is relatively large,
Again, there is a problem that it is difficult to suppress the occurrence of coarse projections on the film surface.

On the other hand, in a conventional biaxially oriented polyester film, as a method of forming uniform fine projections on the surface, for example, a film in which a polyester contains substantially spherical silica particles caused by colloidal silica is used. Known (for example, Japanese Patent Application Laid-Open No. S59-171623)
No.).

However, with an increase in the processing speed of the film processing step, particularly the application of a magnetic layer in the application of a magnetic medium, calendering and winding, and assembling of a cassette, the rolls and guides that come into contact with the film have a film surface, especially minute irregularities. There is a disadvantage that the film surface is easily scraped off. Further, the conventional one has a disadvantage that the image quality, that is, the S / N (signal / noise ratio) is insufficient because the image quality at the time of dubbing decreases due to the increase in dubbing due to high-speed magnetic field transfer or the like.

In order to solve such a drawback, the outermost layer of the laminated film mainly composed of polyethylene terephthalate is made to be a thin layer, and particles having a relatively large particle size are contained in the layer, and the layer thickness and the particle size are reduced. There has been proposed a biaxially oriented laminated film in which minute projections are formed on the film surface by making the particle diameter a specific relationship (Japanese Patent Laid-Open No. 2-77431).

[0008]

SUMMARY OF THE INVENTION The present invention focuses on the high mechanical strength and abrasion resistance of a polyester film containing ethylene naphthalate as a main component, and discloses a method disclosed in Japanese Patent Application Laid-Open No. 2-77431. Focusing on an efficient method for forming microprojections on the surface, while achieving improved strength and wear resistance, the microprojections on the film surface can be further optimized and runnability can be further improved, especially when used for magnetic media. It is an object of the present invention to provide a biaxially oriented laminated film having dropout characteristics.

[0009]

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 layer thickness t (nm) of the outermost layer is 0.2d ≦ t ≦ 10d, and the surface of the film on the outermost layer side has a thickness of 20 nm or more.
The number of height projections is 3 × 10 ³ to 2 × 10 ⁵ / mm ²
And at least one outermost layer is made of a polyester containing ethylene naphthalate as a main component, and the intermediate layer is made of a polyester containing ethylene terephthalate as a main component.

[0010] In the above biaxially oriented laminated film, above
The number of particles having a particle size satisfying the relationship of 0.2d ≦ t ≦ 10d is 3 × 10 ^{3 to} 1.5 × 1.
0 ⁵ / mm ² der Rukoto is preferable.

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 single-layer or two-layer film cannot provide good image quality and good slitting properties.

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.

In the biaxially oriented laminated film of the present invention, at least one outermost layer is made of a polyester mainly composed of ethylene naphthalate, and the intermediate layer is composed of a polyester mainly composed of ethylene terephthalate. That is, a polyester containing ethylene terephthalate as a main component constitutes a core layer, and an outermost layer located on at least one side of the core layer is made of a polyester containing ethylene naphthalate as a main component. Since the polyester having ethylene naphthalate as a main component constitutes the outermost layer on at least one side, the abrasion resistance of the surface thereof is improved, and the mechanical strength, especially the elastic modulus, of the entire laminated film is improved. In addition, since the outermost layer made of polyester containing ethylene naphthalate as a main component is a thin layer, the filtration pressure does not increase so much even with high-precision filtration, and the problem of the occurrence of coarse projections is eliminated by the high-precision filtration. You. Since the polyester layer containing ethylene terephthalate as a main component constitutes the core layer, it is extremely excellent in film forming properties and the like.

As the polyester containing ethylene naphthalate as a main component and the polyester containing ethylene terephthalate as a main component, other components are copolymerized within a range not to impair the present invention, preferably within 30 mol%. You may. The viscosity (IV) of the polyester containing ethylene naphthalate as a main component and the polyester containing ethylene terephthalate as a main component is preferably 0.55 or more. In particular, IV of polyester containing ethylene terephthalate as a main component
Is preferably 0.58 or more.

The polyester containing ethylene naphthalate as a main component is preferably made of polyethylene naphthalate at 80% or more, but is a blend of polyethylene naphthalate and another polyester, or a mixture of polyethylene naphthalate and another polyester. May be composed of a copolymer of Further, other polyesters may be mixed as long as the object of the present invention is not impaired.

In the biaxially oriented laminated film according to the present invention, at least one outermost layer of the biaxially oriented laminated film contains particles, the relationship 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. As described above, by setting the relationship between the particle diameter of the particles and the layer thickness of the outermost layer to the above-described specific relationship, desired fine projections are efficiently formed by the contained particles in the outermost layer of the thin layer.

As described above, fine projections are efficiently formed on the outermost film surface, and the number of projections is 3 × 10 ³ to 2 × 10 ^{5 in the} biaxially oriented laminated film of the present invention.
Pieces / mm ² .

If the number of projections on the surface of the outermost film is smaller 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,
Dropout characteristics of magnetic tape are reduced.

In the outermost layer-containing particles, the number of particles having a particle size satisfying the relationship of the above formula is 3 × 10 ^{3 to} 1.5 × 10 ⁵ particles /
It contained such that mm ^2. The reason why the range of the number of particles is slightly wider than the range of the number of protrusions is that protrusions may be formed due to particles having other particle diameters or transfer influence from the intermediate layer.

If the number of the outermost layer-containing particles having a particle size satisfying the above formula is smaller than the above range, good running properties cannot be obtained, and if the number is larger than the above range, the drop when forming a magnetic tape will be obtained. Out characteristics deteriorate.

In the biaxially oriented laminated film of the present invention, the polyester containing ethylene naphthalate as a main component is used only for the outermost layer of the thin layer, and the intermediate layer serving as the core layer contains ethylene terephthalate as the main component. As a whole, extremely excellent film-forming properties are maintained as a whole of the laminated film. That is,
Both high strength, abrasion resistance and desirable fine surface projections can be achieved without the problem of formation of coarse surface projections, and a desired laminated film can be easily formed.

In the film of the present invention, a different polymer may be blended within a range not to impair the object of the present invention, or an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber 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 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. The film layer constituting the intermediate layer is a polyester containing ethylene terephthalate as a main component. For example, when the film layers constituting both outermost layers are different from each other in the particle content or the polymer constitution, three extruders are used. When the film layers constituting both outermost layers have the same configuration, three extruders can be used to laminate three layers. Then, three or more layers of the sheet are extruded from the 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, it is effective to lower the melting temperature of the extruder for extruding the polymer on the outermost layer laminated portion side by 5 to 10 ° C. than that on the base layer side.

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, a method of performing stretching in two or more stages in the longitudinal direction by using a sequential biaxial stretching method in which stretching in the longitudinal direction is performed first and then in the width direction is performed without obtaining the lamination structure of the present invention. It is effective for The longitudinal stretching is usually performed using a roll, but since preheating and sticking with the stretching roll may lead to the generation of coarse projections, the roll surface material is
Non-adhesive ones (Teflon or silicone rubber) are preferred. Thereby, dropout can be further suppressed. The longitudinal stretching temperature is 80 to 150 ° C, preferably 85 to 150 ° C.
A range of 145 ° C. is desirable. The stretching ratio is 3-6.
Times, preferably 3 to 5.5 times. With such a stretching temperature and a stretching ratio, the effect of suppressing dropout in the case of using a magnetic tape is further increased. When the temperature is higher than the above temperature range or lower than the above stretching ratio, coarse projections are easily generated. The longitudinal stretching speed is 5000 to 1
A range of 00000% / min is preferred. A method using a stenter is generally used as a stretching method in the width direction, and a stretching temperature is 90 to 150 ° C., preferably 95 to 140 °
° C and a draw ratio of 3 to 6 times, preferably 3 to 5 times.
A range of 5 times is appropriate. If the stretching temperature is higher than this, or if the stretching ratio is higher than this, the tear resistance of the film is inferior and the slitting properties may be deteriorated. The stretching speed in the width direction is preferably in the range of 1000 to 20,000% / min. Further, the film that has been biaxially stretched may be further stretched in at least one direction. When re-stretching, the conditions of 90 to 170 ° C. and 1.1 to 2.0 times are preferable. Next, this stretched film is heat-treated. In this case, the heat treatment temperature is 160 to 240 ° C., and the time is 0.5.
A range of ６０60 seconds is preferred. After that, relax
Any value, for example, any value within 10% may be used.

[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 within a 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 and height of projections on the film surface Two-detector scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] and a cross section measuring device [PMS-1, Elionix Co., Ltd.] In step (1), the measured height of the projections when scanning was performed with the height of the flat surface of the film surface set to 0, was sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.]. To construct. 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 at different locations, and a projection having a height of 20 nm or more was determined as the number of projections, and the average value of the measured projections was defined as the average height. The magnification of the scanning electron microscope is selected between 1000 and 8000 times. In addition,
In some cases, a high-precision optical interference type three-dimensional surface analyzer (TOPO-3D manufactured by WYKO, objective lens: 40 to 2)
The height information obtained by using (00 times, use of a high-resolution camera is effective) may be replaced with the SEM value and used.

(4) Running Property (Friction Coefficient μk) Using a tape running property tester SFT-700 (Yokohama System Laboratory Co., Ltd.), a film obtained by slitting a film into a tape having a width of 1/2 inch is used. , 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.

(5) Evaluation of Dropout on Magnetic Tape After recording a signal from a TV test signal generator (Shibasoku TG-7 / 1 type) using a VTR on the tape, 25
100 passes at 120 ° C and 50% RH (120 passes x 100 passes)
I ran. Using a drop-out counter, the tape was picked up as a drop-out having a drop-out width of 5 μsec or more and a reproduction signal attenuation of -16 dB or more. The measurement was performed for 10 volumes, and the number of dropouts per minute was 1
When the number was less than 0, the dropout was good, and when the number was 10 or more, it was bad.

[0031]

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 naphthalenedicarboxylic acid to obtain a polyethylene naphthalate master pellet.

The above master pellet was diluted with polyethylene naphthalate pellets containing no particles at a predetermined ratio, and dried under reduced pressure (3 Torr) at 180 ° C. for 8 hours. Are supplied to an extruder 1 (for example, a vent-type twin-screw kneading extruder) and an extruder 2, and the pellets are supplied at 280 ° C. to 300 ° C.
And dissolved. After high-precision filtration of these polymers, in a three-layer merging block having a rectangular laminated portion, the polyethylene terephthalate polymer is laminated on the intermediate layer portion, and the particle-containing polyethylene naphthalate polymer is laminated on the double-sided surface layer laminated portion. And extruded in a sheet form from a fishtail-type base. Therefore, the three-layer laminated polymer configuration of the present embodiment is polyethylene naphthalate (PEN) / polyethylene terephthalate (PET) / polyethylene naphthalate (PEN). The sheet extruded from the die is wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method to cool and solidify the sheet.
An unstretched film of 0 μm was made. 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 2.2. The number of protrusions on both surfaces is the same, and the number of surface protrusions is 25,000 / mm ^2.
Met. Further, the number of particles having t / d of 0.2 to 10 is 2
It was 2000 pieces / mm ² .

When the running property (coefficient of friction) of this film was measured, it was as good as 0.24. Further, when the drop-out characteristics of the VTR tape made with this film were evaluated, it was good. As described above, when the relationship between the particles contained in the outermost layer laminate and the laminate thickness, the number of particles satisfying the relationship, and the number of surface projections are within the ranges of the present invention, excellent running properties and dropout characteristics are obtained. And the intermediate layer is a polyester containing ethylene terephthalate as a main component, and at least one outermost layer is a polyester containing ethylene naphthalate as a main component (in this embodiment, both outermost layers contain ethylene naphthalate as a main component). Polyester), so the overall strength of the film is high,
High-accuracy filtration can be performed while obtaining abrasion resistance.

Examples 2 to 4 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 size d of the contained particles were determined. / D, the number of surface protrusions, the number of particles having t / d of 0.2 to 10 and the polymer constitution of each film layer were variously changed to prepare various biaxially oriented laminated polyester films. Comparative Example 1 had a polyethylene terephthalate (PET) single-layer film, Comparative Example 2 had a polyethylene naphthalate (PEN) single-layer film, and Comparative Example 3 had a three-layer structure of PEN / PEN / PEN. 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. Yes, and if the polymer configuration of each film layer satisfies the configuration defined in the present invention,
In each case, excellent running properties and good dropout characteristics were obtained (Examples 2 to 4), but in Comparative Examples 1 to 4 which did not satisfy any of them, even if some conditions were within the range of the present invention. Even so, it was not possible to satisfy both the running properties and the dropout characteristics.

[0037]

[Table 1]

[0038]

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 above relationship is set to a specific range, at least one outermost layer is a polyester containing ethylene naphthalate as a main component, and the intermediate layer is ethylene terephthalate. The main component is polyester, so it is difficult to scrape the surface of the laminated film, and it is possible to efficiently form desired projections to obtain a desired surface form, and to obtain excellent dropout characteristics for magnetic media. As well as good runnability when used as a magnetic medium and during processing, and with extremely excellent strength It is possible to obtain the wear resistance.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-207650 (JP, A) JP-A-62-290535 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1/00-35/00 B29C 55/00-55/30

Claims (5)

(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 the thickness of the outermost layer is 20 nm or more.
The number of height projections is 3 × 10 ³ to 2 × 10 ⁵ / mm ²
Wherein the at least one outermost layer is a polyester containing ethylene naphthalate as a main component, and the intermediate layer is a polyester containing ethylene terephthalate as a main component. 2. The method according to claim 1, wherein the number of particles satisfying the above equation is three.
× Ru 10 ³ to 1.5 × 10 ⁵ cells / mm ² der claim 1
Biaxially oriented laminated film of. 3. The biaxially oriented laminated film according to claim 1, wherein the polyester containing ethylene naphthalate as a main component is 80% or more of polyethylene naphthalate. 4. The polyester according to claim 1, wherein the polyester containing ethylene naphthalate as a main component is a blend of polyethylene naphthalate and another polyester.
Biaxially oriented laminated film. 5. The polyester according to claim 1, wherein the polyester containing ethylene naphthalate as a main component is a copolymer of polyethylene naphthalate and another polyester.
Biaxially oriented laminated film.