JP3097160B2 - Biaxially oriented laminated polyester 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 polyester film, and more particularly to a film which can form desired fine projections on the surface without adding particles and is optimally used as a base material of a magnetic medium.

[0002]

2. Description of the Related Art A biaxially oriented polyester film, for example, a biaxially oriented polyester film which can be used as a base material of a magnetic medium, has fine protrusions formed uniformly on its surface, lowers the friction coefficient and is hardly scraped off. As such a biaxially oriented polyester film, a film in which a polyester contains substantially spherical silica particles derived from colloidal silica is known (for example, JP-A-59-17162).
No. 3).

[0003]

However, in the case of the film containing the above-mentioned inorganic particles, the processing speed of the film processing step, particularly, the step of coating / calendering and winding the magnetic layer in a magnetic medium application, the step of incorporating the cassette, and the like. As a result, the film surface, especially a film surface having minute irregularities, is easily shaved off by a contacting roll or guide. Further, in the conventional apparatus, the image quality, that is, S / N (signal /
Noise ratio) was also insufficient.

The present invention focuses on such a problem and, when used as a magnetic medium, ensures high image quality at the time of dubbing, that is, good electromagnetic conversion characteristics (hereinafter referred to as excellent in electromagnetic conversion characteristics) while maintaining high speed. A biaxially oriented laminated polyester film whose purpose is to make it difficult for the film surface to be scraped off in the processing step (hereinafter referred to as excellent in high-speed shaving properties), and that it can be achieved by a novel method instead of the conventional method involving particles. The purpose is to provide.

[0005]

According to the present invention, there is provided a biaxially oriented laminated polyester film according to the present invention, wherein at least one surface layer of the biaxially oriented laminated polyester film has at least one layer. 70 to 99.5 parts by weight of a polyester and 0.5 to 30 parts by weight of a liquid crystalline polyester which melts at a molding temperature of the thermoplastic polyester, and a dispersion diameter d of the liquid crystalline polyester in the film is 0.05 to 5 μm; The dispersion standard has a relative standard deviation of 1.2 or less, and the ratio d / t of the dispersion diameter d of the liquid crystalline polyester to the layer thickness t of the layer is 0.05 or more and 5 or less.

First, the polyester film of the present invention must have a laminated structure of at least two layers. If there are two or more layers, three or four layers may be used. However, in the case of a film having a single-layer structure, it is difficult to form desired surface projections due to the dispersed liquid crystalline polyester described later, and it is not possible to satisfy the high-speed shaving property and the electromagnetic conversion characteristics intended in the present invention.

Next, the polyester film of the present invention comprises:
It is necessary that at least one of the above-mentioned layers constituting this is biaxially oriented. It is particularly preferable that all the layers in the laminated structure of two or more layers are biaxially oriented. If all the layers are non-oriented or uniaxially oriented, the properties of the present invention cannot be satisfied.

[0008] The polyester constituting the present invention is not particularly limited, but ethylene terephthalate, ethylene α, β
It is particularly preferred when at least one structural unit selected from -bis (2-chlorophenoxy) ethane-4,4'-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.

The polyester film of the present invention contains a liquid crystalline polyester in at least the outermost layer on one side. This liquid crystalline polyester has a very good affinity for the base polyester compared to conventional additive inorganic particles, etc.
It is difficult to form a gap between the liquid crystalline polyester and the base polyester. That is, in the present invention, the liquid crystalline polyester refers to a material that melts at the molding temperature of the base polyester, and the melted liquid crystalline polyester is dispersed in a spherical shape in the base polyester film, as if it were added particles. It acts as a surface protrusion instead of a particle. Therefore, when such a dispersed liquid crystalline polyester is present in the thin outermost layer laminated film, uniform minute projections are formed on the surface of the laminated film by the dispersed liquid crystalline polyester. In addition, since the liquid crystalline polyester has an extremely good affinity for the base polyester as described above, the formed fine protrusions are extremely difficult to be scraped off, and a surface morphology excellent in high-speed scraping properties can be obtained.

In addition, such a liquid crystalline polyester is
As a method of dispersing and adding to the base polyester, a method of blending and melt-extruding these polyesters is used. In particular, by blending and melt-extruding with a vented twin-screw kneading extruder, dispersion of the liquid crystalline polyester is performed. The properties are uniform and fine. Therefore, uniform fine projections are formed on the surface of the outermost layer, and the electromagnetic conversion characteristics are significantly improved as well as the high-speed cutting property, which is more preferable.

The above-mentioned liquid crystalline polyester is mainly composed of a parahydroxyoxybenzoic acid residue unit, which is copolymerized with an ethylene terephthalate unit, a parahydroxyoxybenzoic acid residue unit and 2-oxynaphthalene-6-hydroxyl. Carboxylic acid residue units, parahydroxyoxybenzoic acid residue units, 4-4′-dihydroxybiphenyl residue units and terephthalic acid residue units, parahydroxyoxybenzoic acid residues Unit, 9,10-dihydro-9-oxa-10- (2 ′,
5'-dihydroxydiphenyl) phosphaphenanthrene-10-oxide residue units and terephthalic acid residue units (and further isophthalic acid residue units). The liquid crystalline polyester is preferably one that softens or forms a molten liquid crystal phase at the molding temperature of the base polyester.

The mixing ratio of the liquid crystalline polyester to the base thermoplastic polyester in the liquid crystalline polyester-containing layer is such that the liquid crystalline polyester is 0.5 to 30 parts by weight, preferably the thermoplastic polyester is 70 to 99.5 parts by weight. The liquid crystalline polyester needs to be 1 to 20 parts by weight based on 80 to 99 parts by weight of the plastic polyester. When the content of the liquid crystalline polyester is less than this ratio, the effect of forming the surface projections by the dispersed liquid crystalline polyester becomes thin, and improvement in high-speed scraping properties and electromagnetic conversion characteristics cannot be expected. On the other hand, when the ratio of the liquid crystalline polyester is larger than the above ratio, the ratio of the base polyester becomes too small, the strength of the film layer itself is reduced, and the high-speed scraping property is reduced.

The dispersion diameter d of the liquid crystalline polyester in the film layer is 0.05 to 5 μm, preferably 0.1 to 5 μm.
It needs to be 3 μm. If the dispersion diameter is smaller than the above range, projections are less likely to be formed on the film layer surface, and if the dispersion diameter is larger than the above range, coarse projections and irregularities in the height of the projections may be increased, resulting in high-speed scraping and electromagnetic properties. Both conversion characteristics are degraded.

The relative standard deviation of the dispersion diameter d is 1.
It must be 2 or less, preferably 1.1 or less. If it is larger than this value, the variation in the height of the surface projections formed of the liquid crystalline polyester becomes large, and both the high-speed scraping property and the electromagnetic conversion property are reduced.

Further, the ratio d / t of the dispersion diameter d of the liquid crystalline polyester to the laminated thickness t of the liquid crystalline polyester-containing layer.
Should be 0.05 or more and 5 or less, preferably 0.07 or more and 4 or less. When d / t is less than the above range,
The variation in the height of the protrusions formed on the surface is large, so that the electromagnetic conversion characteristics are reduced. Above the above range, the thickness of the film layer with respect to the dispersed liquid crystalline polyester is too thin, so that the holding power of the liquid crystalline polyester is reduced or the surface projections formed by the liquid crystalline polyester are easily scraped off, and the high-speed scraping property is reduced. I do.

Regarding the height of the protrusions on the surface of the outermost layer formed of the liquid crystalline polyester, the relative standard deviation of the protrusion height distribution is preferably 1.2 or less. If the value is larger than this value, undesirable coarse projections are present, and the portion is likely to be scraped off, thereby deteriorating high-speed shaving properties and possibly deteriorating electromagnetic conversion characteristics.

The outermost layer portion of the biaxially oriented laminated polyester film of the present invention may simultaneously contain external particles and internal precipitation type particles in addition to the above-mentioned liquid crystalline polyester. Is preferably not increased so as not to deteriorate high-speed shaving properties and electromagnetic conversion characteristics.

In the film of the present invention, other kinds of polymers may be blended as long as the object of the present invention is not impaired, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, etc. May be added to the extent that the organic additives are usually added.

Further, when the polymer IV of the layer containing the liquid crystalline polyester of the biaxially oriented laminated polyester film of the present invention is in the range of 0.4 to 0.9, the high-speed scraping property is further improved, so that it is particularly preferable. preferable. Further, when the difference of the polymer IV from the layer containing no liquid crystalline polyester is within 0.1, it is very preferable because the high-speed scraping property is further improved.

Next, a method for producing the film of the present invention will be described. First, as a method of incorporating the liquid crystalline polyester into the base polyester, for example, the molten liquid crystalline polyester is blended with the thermoplastic polyester, melt-extruded, and pelletized or filmed, the liquid crystalline polyester becomes spherical in the thermoplastic polyester. Be dispersed. It is more preferable to use a vented twin-screw extruder for blending and melt extrusion, since the dispersion diameter of the liquid crystalline polyester becomes uniform and fine. As a method of adjusting the content of the liquid crystalline polyester, a high-concentration master is prepared by the above-described method, and the master is diluted with a polyester substantially free of the liquid crystalline polyester at the time of forming a film to thereby adjust the content of the liquid crystalline polyester. The method of adjusting is effective.

Next, a polyester film having a laminated structure of two 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 more extruders, two or more layers of a manifold or a merging block (for example, a merging block having a square merging portion), at least one layer is a layer containing a liquid crystalline polyester in a predetermined ratio. Laminate, extrude two or more layers of sheets from the die, cool with a casting roll to make 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, using a sequential biaxial stretching method in which stretching in the longitudinal direction and then in the width direction is performed first, 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) Dispersion diameter and relative standard deviation of the molten liquid crystalline polyester in the film The film containing the molten liquid crystalline polyester was formed into an ultra-thin section having a thickness of 1000 mm perpendicular to the film surface, and the transmission electron microscope (for example, JEOL Ltd.) JEM-1200EX) was used to observe the molten liquid crystalline polyester dispersed in the film, the circle equivalent diameter of the molten liquid crystalline polyester was determined for 100 visual fields, and the average was defined as the dispersed diameter of the molten liquid crystalline polyester. When external particles or the like are used in combination, the measurement is carried out by using XMA or the like as necessary and distinguishing the molten liquid crystalline polyester of the present invention from the particles. The distribution of the dispersion diameter for the 100 visual fields was regarded as a normal distribution, and the standard deviation of the dispersion diameter was determined by approximation by the least square method.

(2) Relative standard deviation of the height of surface protrusions A scanning electron microscope with two detectors [ESM-3200,
Elionix Co., Ltd.] and a cross section measuring device [PMS-1,
Elionix Co., Ltd.] and the image processing device [IBAS2000, Carl Zeiss Co., Ltd.]
To reconstruct the film surface projection image on the image processing apparatus. Next, a circle-equivalent diameter is determined from the area of each projection obtained by binarizing the projection portion on the surface projection image, and this is defined as the average diameter of the projection. 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 is repeated 500 times in different places, and the average projection height and standard deviation are obtained for the measured projections, and the relative standard deviation is calculated.
The magnification of the scanning electron microscope is selected between 1000 and 8000 times.

(3) Polymer IV The measurement was carried out at 25 ° C. using o-chlorophenol as a solvent.

(4) Thickness of the outermost layer The thickness of the outermost layer is determined by observing a cross section of the film or using a thin film step measuring device.

(5) High-speed scalability A single-blade is pressed at an angle of 90 ° to a film obtained by slitting a film into a 1 / 2-inch wide tape, and the film is pushed in by 0.5 mm and run for 200 m (speed: 250 m / min, tension: 10
0 g). The adhering height of the powder shaved on one blade was read with a microscope, and the shaved amount (μm) was determined. This shaving amount is 200μ
When it is less than m, the abrasion resistance is good, and when it exceeds it, the abrasion resistance is poor.

(6) Electromagnetic Conversion Characteristics A magnetic paint having the following composition is applied to a 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.
The raw tape was slit into 1/2 inch to prepare 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: 100 parts by weight Vinyl chloride / vinyl acetate copolymer: 10 parts by weight Polyurethane elastomer: 10 parts by weight Polyisocyanate: 5 parts by weight Lecithin: 1 part by weight Methyl ethyl ketone : 75 parts by weight-Methylisobutyl ketone: 75 parts by weight-Toluene: 75 parts by weight-Carbon black: 2 parts by weight-Lauric acid: 1.5 parts by weight Using a home VTR on this tape, using a TV test waveform generator A 100% chroma signal was recorded, and the chroma S / N was measured from the reproduced signal using a color video noise measuring instrument. Comparative Example 1 was set as a reference value (0 dB).

[0029]

Next, embodiments of the present invention will be described based on examples. Example 1 (Table 1) 50 parts by weight of a liquid crystalline polyester-containing pellet and 50 parts by weight of a polyethylene terephthalate pellet not containing a liquid crystalline polyester were mixed and supplied to a vented twin-screw extruder 1 at 280 ° C. Dissolved (Polymer I). Further, another extruder 2 was prepared, and 100 parts by weight of pellets containing no liquid crystalline polyester were added at 180 ° C.
And dried under reduced pressure (3 Torr) for 3 hours and fed to an extruder to dissolve at 290 ° C. (Polymer II). After each of these two polymers is subjected to high precision filtration, the two
In the layer confluence block, polymer II was laminated on the base layer and polymer I was laminated on the one-sided layer, extruded into a sheet shape from a fishtail-type die, and then applied to the surface using an electrostatic application casting method. The film was wound around a casting drum at a 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 content of the liquid crystalline polyester in the laminated portion was 3 parts by weight, the dispersion diameter was 0.5 μm, and the relative standard deviation of the dispersion diameter was 0.5.
5. The ratio d / t between the dispersion diameter d and the lamination thickness was 1.5.

When the electromagnetic conversion characteristics of this film were measured, it was +3.0 dB. In addition, high-speed scraping is 85
(Μm). As described above, when the properties of the liquid crystalline polyester contained in the laminated portion are within the range of the present invention, it is possible to obtain a film having both good electromagnetic conversion properties and high-speed shaving properties.

Examples 2 to 5 and Comparative Examples 1 to 6 (Table 1) Biaxially oriented polyester films were prepared in the same manner as in Example 1, but the presence or absence of the liquid crystalline polyester in the outermost layer and the liquid crystalline polyester were determined. When each of the above characteristics was not within the range of the present invention, it was not possible to obtain a film having both good electromagnetic conversion characteristics and high-speed cutting properties.

[0033]

[Table 1]

[0034]

According to the biaxially oriented laminated polyester film of the present invention, a liquid crystalline polyester having a very high affinity for the base polyester is dispersed in at least one thin layer outermost layer portion. Thus, uniform and hard-to-cut projections can be formed on the surface of the layer, and a desired surface roughness form can be obtained. In addition, excellent electromagnetic conversion characteristics for a magnetic medium can be exhibited.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-144421 (JP, A) JP-A-61-78863 (JP, A) JP-A-2-77431 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B32B 1/00-35/00 G11B 5/73

Claims (2)

(57) [Claims] 1. A biaxially oriented laminated polyester film having a laminated structure of at least two or more layers, wherein at least one layer is formed of a thermoplastic polyester of 70 to 99.
5 parts by weight and 0.5 to 30 parts by weight of a liquid crystalline polyester which is melted at the molding temperature of the thermoplastic polyester, and the dispersion diameter d of the liquid crystalline polyester in the film is 0.05 to 5 μm. A biaxially oriented laminated polyester film, wherein the standard deviation is 1.2 or less, and the ratio d / t of the dispersion diameter d of the liquid crystalline polyester to the laminated thickness t of the layer is 0.05 or more and 5 or less. 2. The biaxially oriented laminated polyester film according to claim 1, wherein the relative standard deviation of the projection height of the film surface of the liquid crystalline polyester-containing layer is 1.2 or less.