JP2821270B2 - Biaxially oriented copolyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to biaxially oriented copolyester films.
More specifically, the present invention relates to a biaxially oriented PENBB film suitable for use as a substrate for a magnetic recording medium capable of obtaining a high quality image and having excellent abrasion resistance.

Biaxially oriented polyester film as a substrate for magnetic recording media such as video tapes and audio tapes,
In particular, PET films are generally used. In order to provide good slip properties to recording media, conventional substrates contain particles that form protrusions on the film surface. The protrusions reduce the coefficient of friction of the film and provide the media with good slip properties. However, there is still a need for improvements in film stiffness (tensile modulus) and mechanical strength that allow the production of thinner films and increase the storage capacity of cassettes made therewith. At the same time, it is desirable that the dimensional stability be further improved.

U.S. Pat. No. 4,720,412 describes a biaxially oriented film having a particular height and number of protrusions and suitable as a substrate for a magnetic recording medium. The film described in this patent is scratched by a roll or guide in contact with the film during the steps of applying a magnetic layer, calendering, or dubbing or recording the finished videotape. It has the disadvantage of being possible. As these steps occur at higher speeds, the problem with scratching becomes more serious. Further, a general magnetic recording tape has a disadvantage that the image quality is deteriorated when dubbing. That is, the S / N ratio (signal / noise ratio) of the dubbed tape is low and unsatisfactory.

Therefore, an object of the present invention is to provide higher scratch resistance even in a high-speed process (hereinafter, referred to as having good scratch resistance), and less image deterioration due to dubbing (hereinafter, having good dubbing property). The purpose of the present invention is to provide a film suitable for a substrate for a magnetic recording medium. In addition, the base film must be dimensionally more stable than common PET films and exhibit improved mechanical strength, especially improved stiffness (tensile modulus).

The present invention relates to a biaxially oriented PEN comprising PENBB and inert particles
A BB film is provided, wherein at least one surface of the film has protrusions formed by the presence of inert particles, and the topography of the surface is provided.
parameter Is 0.1-0.7, and the average distance between adjacent projections is 20 μm or less. Preferably, the surface friction coefficient and surface shape parameters satisfy the following equations (1) and (2): (Where y is the coefficient of friction, β is the average flatness of the protrusions, and σ is the standard deviation of the height distribution of the protrusions.) Similar surface topography is described in EP-A 0 311 426 for PET films.
It is described in.

U.S. Pat.No. 3,008,934 includes 4,4 'as an acid-derived unit.
Copolyesters containing -bibenzoate, and large amounts of other dicarboxylates, including 2,6-naphthaldicarboxylate, have been described. Also, oriented fibers and films made from these copolyesters are described, but no biaxially oriented PENBB films are described or suggested. In particular, improved stiffness (tensile modulus) compared to PET film, MD and TD
No. 3,008,934. These films, which have tensile strength in both of these, as well as heat stability, UV stability, hydrophobicity, dimensional stability and gas impermeability, are not described in U.S. Pat. No. 3,008,934.

The present invention provides a novel biaxially oriented copolyester film suitable for a magnetic recording medium substrate. By using the PENBB film of the present invention as a substrate for a magnetic recording medium, scratching is reduced even in high-speed processing, and the image quality of a dubbing medium is better than that of a conventional medium. Further, the PENBB film does not degrade the magnetic layer formed thereon, and provides the recording medium with good slip characteristics. In addition, the substrate film is dimensionally stable and exhibits improved mechanical strength, especially improved modulus, over conventional polyester films. The latter property allows the use of thinner films, in other words, increases the storage capacity of the cassette. Therefore, an excellent magnetic recording medium can be obtained by using the PENBB of the present invention as a substrate.

The copolyester film of the present invention comprises PENBB and inert particles. The previously mentioned PENBB has at least 3 mole% of the formula Is a copolyester containing a group of

If more than 10 mol% of terephthalic acid-derived groups are present in the copolymer, the content of bibenzoate-derived units is at least 25 mol%. These copolyester films are described in unpublished German patent application P 4224161.8, which is hereby incorporated by reference. PENBB has at least 80 mol% of acid derived units (NBB) consisting of bibenzoate (20-80 mol%, preferably 40-60 mol%) and naphthalate (80-20 mol%, preferably 60-40 mol%) Preferably it is a copolyester. The remaining 20 mol% or less consists of other acid-derived units, which influence, for example, the melting point or crystallization kinetics. The diol derived units of at least 80 mol% -O- (CH ₂₎ that consists of ₂ -O- units preferable. The remaining 20 mol% or less consists of other diol acid units, which also influence, for example, the melting point or the crystallization kinetics. It is also preferred to use hydroxycarboxylic acid derived units, for example those derived from p-hydroxybenzoic acid, instead of small amounts of acid- and / or diol-derived units.

In order to obtain the desired mechanical properties of the biaxially oriented PENBB film, the IV value (logarithmic viscosity number) of the extruded PENBB polymer should be> 0.5 dl / g, preferably> 0.55 dl / g. .

Preferred, but non-limiting, examples of inert particles included in the films of the present invention include essentially spherical silica particles derived from colloidal silica, synthetic calcium carbonate particles, titanium dioxide (rutin) particles, heat-resistant carbon black, and Organic polymer particles, such as crosslinked polymer particles, especially crosslinked styrene-divinylbenzene microspheres. The average diameter d (μm) and the content C (% by weight) of the particles are not limited, but if they satisfy the following formula (3), the scratch resistance is further improved and a better dubbing property is obtained. Further, the average distance between adjacent protrusions required in the present invention can be easily obtained.

0.01 / d ≦ C ≦ 0.45 / d (3) Two or more types of particles may be added to the film. When two or more types of particles having different average diameters are used, the average diameter d in the above formula (3) indicates the entire average diameter of the particles, and the content C in the formula (3) indicates the total content of the particles. .
In the case of calcium carbonate particles and titanium dioxide particles, the preferred range of the average diameter of the particles is 0.2-0.7 μm.

"Non-external" particles may be used as inert particles.
"Non-external" particles are herein defined as the in situ precipitation of at least one compound selected from the group consisting of calcium compounds, magnesium compounds and lithium compounds during the polycondensation of PENBB by adding a binder. Means manufactured particles. It should be noted that phosphorus and trace amounts of other metal components such as zinc, cobalt, antimony, germanium and titanium may be present in the non-external particles in amounts that do not impair the advantageous effects of the present invention. When non-external particles are used with added inert particles, the preferred content of added inert particles is 0.01-3.0% by weight. This is because this amount promotes scratch resistance and good dubbing.

As long as the advantageous effects of the present invention are not impaired, the film of the present invention mainly comprises the above PENBB composition, but other polymers may be incorporated up to 20% by weight. In addition, the films of the present invention may contain inorganic and / or organic additives such as antioxidants, heat stabilizers, lubricants, UV absorbers and crystallization nucleating agents.

The PENBB film of the present invention is a biaxially oriented film.
Non-oriented films and uniaxially oriented films are not preferred because they have poor scratch resistance, do not provide good dubbing properties, and have insufficient mechanical properties for handling tapes.

The film of the present invention has at least one surface on which protrusions are formed due to the presence of inert particles. Surface shape parameter of at least one surface having protrusions Is 0.1-0.7, more preferably 0.15-0.65, even more preferably 0.25-0.62, where β is the average flatness of the protrusions and σ is the standard deviation of the protrusion height distribution. The average flatness of the protrusions and the standard deviation of the height distribution of the protrusions are measured as described later in detail. Surface shape parameters on both sides of the film Is less than the above range, good dubbing properties cannot be obtained. On the other hand, when these are larger than the above ranges, the scratch resistance is reduced.

At least one surface of the film of the present invention has a coefficient of friction y
And surface shape parameters Which satisfies the following equations (1) and (2), preferably (4) and (5), more preferably (6) and (7): If the coefficient of friction on both sides of the film is smaller than the above range defined by the formula (1), good dubbing properties cannot be obtained. On the other hand, if it is larger on both sides than the range defined by equation (2), the scratch resistance decreases.

The average distance between adjacent protrusions on the surface satisfying the formulas (1) and (2) is preferably 20 μm or less, preferably 17 μm or less, and more preferably 15 μm or less. Average interval
If it is larger than 20 μm, the scratch resistance decreases. Although there is no lower limit on the average interval between adjacent projections, it is difficult to form a surface with an interval between projections of less than 1 μm, so about 1 μm is a practical lower limit.

From the viewpoint of scratch resistance, the average distance between adjacent projections having a height of less than 0.08 μm is preferably 10 μm or less, more preferably 8 μm or less, and the average distance between adjacent projections having a height of 0.08-0.5 μm is Preferably 15-150μ
m, more preferably 20-100 μm. It should be noted that the number of protrusions having a height higher than 0.5 μm is preferably less than 5%, more preferably less than 2% of the total number of protrusions.

Furthermore, from the viewpoint of scratch resistance, the difference between the average height of the projections having a diameter of less than 1 μm and the average height of the projections having a diameter of 1 to 8 μm is preferably 0.02 to 0.42 μm, more preferably 0.05 to 0.30. μm. The number of protrusions with a diameter greater than 8 μm is preferably less than 5%, more preferably less than 2%, based on the total number of protrusions.

In order to have good scratch resistance and improved dubbing properties, the R,
(Average surface roughness at 5 places) is preferably 60 to 190 nm, more preferably 70 to 160 nm, and still more preferably 80 to 150 nm.
nm.

In order to further improve the scratch resistance and dubbing properties, the ratio R _p / R _a of at least one surface of the film of the invention (average depth / average surface roughness of center line, R _p and R _a Is preferably 4-25, more preferably 6-20, and even more preferably 9-15.

In order to further improve the scratch resistance and the dubbing property, the effective space volume of the protrusions on at least one surface of the film of the present invention is preferably 1 × 10 ³ −5 × 10 ⁵ , more preferably 5 × 10 ³ −. It is 5 × 10 ⁴ .

To further improve the scratch resistance and dubbing properties, the ratio of the average height (H) in nm (H) to the average diameter (d) of the inert particles on at least one side of the film of the invention (H / d ) Is preferably 0.1-0.5, more preferably 0.1-0.5.
0.4.

In order to further improve the scratch resistance and the dubbing property, the average height of the protrusions on at least one surface of the film of the present invention is preferably 40 to 130 nm, more preferably 50 to 130 nm.
It is 20 nm, even more preferably 50-100 nm.

Although the use of the film of the present invention is not limited,
PENBB films are becoming increasingly popular as substrates for magnetic recording media, especially for video tapes, which are now being increasingly dubbed, which reduces surface scratching during processing. It is useful as a previously recorded videotape. Further, when using the film of the present invention in which only one surface has the above parameters, it is preferable to use the surface having the above parameters as a running surface (ie, in a magnetic recording medium, the surface opposite to the magnetic layer, And in other applications,
Surfaces that have not undergone processing such as printing and layer application).

Next, the method for producing the film of the present invention will be described. However, it should be noted that the manufacturing method is not limited to the method described below.

Inert particles before, during, and after polymerization to form PENBB
Can be added later. Surface shape parameters defined in the present invention Preferably, the inert particles are added to the diol component of PENBB, such as ethylene glycol in a slurry, to obtain a relationship between the coefficient of friction y and the surface shape parameters. In this case, the diol component slurry containing the inert particles is subjected to an absolute filtration accuracy of 0.5 to 4.5 μm, more preferably
It is preferred to filter through a 1.5-3 μm filter. Surface shape parameters defined in the present invention In order to adjust the relationship between the coefficient of friction y and the surface shape parameter, and the content of inert particles to obtain a desired value for the average distance between adjacent protrusions, the content of particles is high. PENB, preferably with a particle content of 1-5% by weight
It is preferred to produce master pellets based on B and then dilute the master pellets during film formation. If the inert particles are essentially spherical silica particles resulting from colloidal silica, the surface shape parameters defined in the present invention To obtain a relationship between the coefficient of friction y and the surface shape parameters, and the average distance between adjacent protrusions, a slurry of a diol component such as ethylene glycol is added at 140-200 ° C, more preferably at 180-200 ° C. It is preferred to heat for minutes to 5 hours, more preferably 1-3 hours. further,
In this case, the surface shape parameters defined in the present invention The relationship between the coefficient of friction y and the surface shape parameters, and to obtain the average distance between adjacent protrusions, maintain the sodium content of the slurry below 0.5% by weight, more preferably below 0.2% by weight, and Preferably, the pH of the slurry is maintained at 7-10. When the inert particles are particles other than silica, such as calcium carbonate and titanium dioxide, the surface shape parameters defined in the present invention To obtain the relationship between the coefficient of friction y and the surface shape parameters, and the average distance between adjacent protrusions, it is preferred to add ammonium phosphate to the slurry in an amount of 0.5-2.0% by weight based on the weight of the particles.

When non-external particles are used, the non-external particles contain, as a binder, at least one compound soluble in glycol selected from the group consisting of calcium compounds, magnesium compounds, manganese compounds and lithium compounds, preferably phosphorus acid and PENBB after direct esterification of dicarboxylic acids and diols with / or ester compounds
It can be generated during the polycondensation or during the polycondensation after transesterification of the alkyl ester of the dicarboxylic acid component with the diol. Preferred calcium, magnesium, manganese and lithium compounds for use herein include mineral salts, soluble in glycols,
Eg halides, nitrates and sulfates; organic acid salts,
Examples include acetates, oxalates and benzoates; hydrides; and oxides soluble in glycols, and mixtures thereof. Preferred examples of phosphorus compounds that can be used here are phosphates, phosphites and phosphonic acids, and their esters and partial esters.

After sufficiently drying a pellet containing a prescribed amount of inert particles (more preferably, a mixture of a master pellet containing a large amount of particles and a PENBB pellet substantially containing no particles), the pellets are fed to an extruder. And extruded from a slot die at a temperature between the melting point (T _m ) and 60 ° C. above the T _m . The sheet is cooled and solidified on a casting roll to obtain a non-oriented amorphous film. Surface shape parameters defined in the present invention To obtain the relationship between the coefficient of friction y and the surface shape parameters, and the average distance between adjacent protrusions, the ratio of the width of the die slit to the heat of the non-oriented film is preferably 5-
30, more preferably 8-20.

Next, the non-oriented film is biaxially oriented by biaxial stretching. Either two or more continuous biaxial stretching steps or a single simultaneous biaxial stretching step may be used. However, the surface shape parameters defined in the present invention To obtain the relationship between the coefficient of friction y and the surface shape parameters, and the average distance between adjacent protrusions, use continuous biaxial stretching, first stretching in the longitudinal direction and then stretching in the transverse direction. It should be noted that is preferred. Although not necessary, the stretching operation may be carried out in three or more stages, preferably four or more stages, in the longitudinal direction so as to obtain a longitudinal stretching ratio of 2.5-5.5. Furthermore, the surface shape parameters defined in the present invention To obtain the relationship between the coefficient of friction y and the surface shape parameters, and the average distance between adjacent protrusions, the first stretching in the machine direction was determined by using the glass transition temperature (T _g ) of PENBB minus 20 ° C and the PENBB. Preferably, the stretching is carried out at a temperature between the glass transition temperature of the polymer plus a temperature of 20 ° C., and the subsequent stretching is performed at a temperature higher than the first stretching. Stretching speed is 5,000-50,000%
/ Min. A tenter is usually used as a transverse stretching method. The stretching ratio in the horizontal method is preferably 2.5 to 5.0 times. The stretching speed in the transverse direction is preferably from 1,000 to 20,000% / min. Biaxial stretching has a birefringence of <0.2, preferably <0.1
And ensure that it is sufficiently isotropic. The birefringence described herein is the absolute value of the difference between the maximum and minimum refractive indices of the film surface, as measured with a common device such as an Abb refractometer, optical bench or compensator.

Next, the film is thermally cured. Thermal curing is preferably carried out 0.5-60 seconds at a temperature between the cold crystallization temperature of PENBB copolyester composition (T _cc) and melting temperature (T _m). During heat curing, the film is stretched laterally to its original length 1.
Stretching 05-1.3 times, especially 1.05-1.2 times, is useful for obtaining the average distance between adjacent projections as defined in the present invention.

Method for Measuring Physical Properties and Method for Evaluating Effects The methods for measuring physical properties and methods for evaluating effects according to the present invention are as follows: (1) Mean diameter of particles PENBB is plasma-treated from a film sample to a film. Excluded by that. The residue is dispersed in ethanol and the volume average diameter of the particles is determined by centrifugation.

(2) Particle content A solvent that dissolves PENBB but does not dissolve the particles, such as a 50/50 mixture of hexafluoroisopropanol and pentafluorophenol, is added to the PENBB film and the mixture is heated to dissolve the copolyester. The resulting mixture is centrifuged, and the resulting particles are washed with a volatile solvent such as acetone and dried in vacuum. The particles are subjected to differential scanning analysis using a DSC (differential scanning calorimeter). PENBB
If a melting peak corresponding to the copolyester is observed, additional solvent is added to the particles and the resulting mixture is heated and then centrifuged. If no melting peak is observed, the remaining particles are separated particles. Two repetitions of centrifugation are usually sufficient. The particle content is defined as the ratio (wt%) of the total weight of the particles thus separated to the total weight of the film.

(3) Glass transition temperature T _g and cold crystallization temperature T _cc Glass transition temperature T _g and cold crystallization temperature T _cc are DSC
Measure as follows: Place a 10 mg sample in a closed pan in DSC and
Melts at a temperature 40 ° C higher than the melting point of ENBB copolyester,
Next, it is quenched in liquid nitrogen. The quenched sample is heated at a rate of 10 ° C./min and the glass transition temperature T _g is measured. Heating is continued from the glassy state until the peak of heat of crystallization is measured. The peak measured in this way is defined as the cold crystallization temperature _Tcc .

(4) Surface roughness R _a , R _z and R _p are measured using a commercially available surface roughness meter under the following conditions: radius of the needle tip: 0.5 μm needle load: 5 mg length of the measuring part 1 mm Cut-off value: 0.08 mm _Ra is measured according to DIN 4768.

R _z and R _p are calculated according to the following formula: R _z = (third highest peak height) − (third deep valley depth) R _p = (highest peak height) − (center line (Value) (5) Effective space volume of the protrusion The surface roughness curve is obtained by the same method as (4). At 5 nm intervals, peaks and centerlines counting parallel levels are superimposed on the surface roughness curve. For each peak whose level is counted, the number of peaks that reach or intersect at the measurement length is measured. For each level n, the number of peaks crossing it is PC (n).
Level m is the first level where PC (m) = O. The effective space volume is defined as: (6) Average height of surface protrusions, standard deviation of height distribution, flatness and diameter Using a scanning electron microscope, the height of protrusions is measured by scanning the film surface. The plane area of the film surface is set to zero. The height of the protrusion thus measured is transferred to the image processing system as a gray value of 256 scales, and the image of the surface protrusion is reconstructed on the image processing system. The radius of the circle is calculated from the area of each protrusion having a scale of 10 or more. This area is obtained by converting the scale into two values. The radius of the circle calculated in this way is defined as the average diameter of the protrusion, d (nm). The highest value of the protrusion portion, each converted by two values, is defined as the height of the protrusion, and this height is measured for each protrusion. This measurement is repeated 500 times in different areas. For protrusions with a height of 200 nm or more, the average height H (nm) and the standard deviation σ (nm) of the height distribution are determined by the least squares regression line, assuming that the protrusion height distribution is Gaussian. Calculate (the Gaussian distribution at the center is a zero height point). The flatness of the projection β is defined as a ratio d / H of the average diameter (d) of the projection to the average height (H) of the projection.

(7) Friction coefficient y Using a commercially available tape running tester, the sample tape is run at 20 ° C. and 60% RH, and the friction coefficient y is calculated according to the following equation: y = (1 / II) 1n (T ₂ / T ₁ ), where T ₁ is the inlet tension and T ₂ is the outlet tension. The diameter of the guide is 6mm, the surface roughness of the material of the guide is 0.2S, the winding angle is IIrad,
The winding speed is 3.3 cm / min.

(8) Logarithmic viscosity number (IV) (expressed in dl / g) Logarithmic viscosity number is calculated from the solution viscosity in pentafluorophenol / hexafluoroisopropanol measured at 25 ° C. according to the following formula: _Where η _rel = (solution viscosity / solvent viscosity) and C is the weight of dissolved polymer per dl (100 ml) of solvent (g / dl, usually 0.1 or 0.2 g / dl). And and solvent viscosities are measured using a Ubbelohde viscometer.

(9) Dubbing A magnetic pigment coating having the following composition is applied to the film with a gravure roll coating machine, the coated magnetic pigment is magnetically oriented, and the coating is dried. Magnetic film at 70 ° C, linear pressure 20
Calendering using a small test calender (steel roll / nylon roll, 5 steps) at 0 kg / cm,
Cure at 70 ° C for 48 hours. 1/2 inch (1.2 inch)
Cut into 5cm) to make bread cake. A 250m long tape is taken from this pancake and set in a video tape recorder (VTR) cassette to produce a VTR tape.

(Composition of magnetic pigment coating, parts by weight) Co-containing F ₂ O ₃ (BET value 50 m ² / g): 100 Vinyl chloride / vinyl acetate copolymer: 10 Polyurethane elastomer: 10 Polyisocyanate: 5 Lecithin: 1 Methyl ethyl ketone: 75 Methyl isobutyl ketone: 75 Toluene: 75 Carbon black: 2 Lauric acid: 1.5 On the tape thus produced, a 100% chroma signal from a commercial television test wave generator is recorded using a hypothetical VTR. The chroma S / N of the reproduced signal is measured using a commercially available color video noise measuring device.
Also, dubbing the puncture of the tape on which the same signal is recorded as described above to another puncture of the same type of tape (without a pre-recorded signal) using a magnetic field recording type high-speed printing system, Then, the chroma S / N of the dubbing tape is measured as described above, and the value is set to B. If the decrease in chroma S / N (AB) due to dubbing is less than 4.0 dB, the tape is considered to have good dubbing properties, and if it is greater than 4.0 dB, the tape is considered to have poor dubbing properties. .

(10) Scratch resistance The above tape is repeatedly run with a commercially available high-speed tape running tester (running speed 800 m / min, running frequency 10
Times). After the test, the film is observed under a microscope to check if a scratch has formed. The film is considered to have high scratch resistance if there are few scratches, and the film is considered to have low scratch resistance if at least three scratches are formed per width of the tape.

The following examples are intended to illustrate the invention without limiting its scope.

Example 1 An ethylene glycol slurry containing colloidal silica having an average diameter of 0.3 μm is prepared. The sodium content of the slurry is adjusted to 0.1% by weight based on the weight of the silica particles. After heating the ethylene glycol slurry at 190 ° C. for 1.5 hours, transesterification is carried out with dimethylnaphthalate / dimethyl4,4′-bibenzoate (50:50 molar ratio). The reaction product is filtered through a filter having an absolute filtration accuracy of 3 μm. The filtered slurry undergoes a polycondensation reaction to produce PENBB master pellets. The polycondensation reaction time is adjusted so that the IV of the polymer is 0.9 dl / g.
In parallel with this, IV is 1.0 dl / g by a general method.
The PENBB pellets are manufactured, and then mixed with the above-mentioned pigments in a ratio such that the silica particle content is 0.5% by weight. The mixed pellets are then depressurized (3 torr)
Then, it is dried at 180 ° C. for 3 hours. The obtained pellets are supplied to an extruder and melted at 310 ° C. The molten polymer is extruded through a slot die and the extruded sheet is heated to the surface temperature.
Fixed by static electricity on a casting drum at 20 ℃ (pi
n) and cool, and solidify the sheet to obtain a non-oriented film. The ratio of the width of the gap of the die slit to the thickness of the non-oriented film is 10. The non-oriented film is stretched in the machine direction to 4.5 times the original length. This orientation is performed in four steps using the difference between the peripheral speeds of the two pairs of rolls. Stretching temperature is 120-1
35 ° C. The uniaxially oriented film thus obtained is then stretched transversely to 4.0 times its original length using a tenter at 130 ° C. at an orientation speed of 2000% / min. The obtained film is thermoset at 250 ° C. for 5 seconds, and at the same time, the film is oriented transversely 1.07 times its original length to obtain a biaxially oriented film having a thickness of 10 μm. The film has excellent scratch resistance and dubbing properties. Both sides of the film have the same parameters. Table 1 shows the improved mechanical and dimensional stability over PET films made by conventional methods.

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI G11B 5/704 G11B 5/704 // B29K 67:00 B29L 7:00 (72) Inventor Chu, A-Won, New Jersey, USA 07869, Randolph, Radoke Road 130 (72) Inventor Flint, John Anthony Lenapi Lane, Berkeley Heights 07922, New Jersey, United States of America 07, 150 Inventor Coumann, Bodo Germany 6258 Runkel 5, Lindenstrasse 5 (56) References JP-A-1-195045 (JP, A) JP-A-55-718 (JP, A)

Claims (10)

(57) [Claims] 1. PENBB, a copolyester consisting essentially of bibenzoate and naphthalate at least 80% of the acid-derived units and having a molar ratio of bibenzoate / naphthalate of 40-60 / 60-40, and inert particles. A biaxially oriented PENBB film comprising at least one layer consisting of:
A biaxially oriented PENBB film having at least one surface with protrusions formed by the presence of inert particles, wherein the average spacing between adjacent protrusions on the surface is less than or equal to 20 μm. 2. A surface shape parameter of a film surface. The biaxially oriented PENBB film according to claim 1, wherein (where β is the average flatness of the projections and σ is the standard deviation of the height distribution of the projections) is from 0.1 to 0.7. 3. The biaxially oriented PENBB film according to claim 1, wherein the surface friction coefficient (y) and the surface shape parameter √ (β / σ) satisfy the following expressions (1) and (2). Where y is the coefficient of friction. 4. The average distance between adjacent projections having a height of less than 0.08 μm is 10 μm or less, the average distance between adjacent projections having a height of 0.08 to 0.5 μm is 15 to 150 μm, and the average of projections having a diameter of less than 1 μm. 3. The biaxially oriented PENB according to claim 1, wherein the difference between the height and the average height of the projections having a diameter of 1 to 8 [mu] m is 0.02 to 0.42 [mu] m.
B film. 5. The biaxially oriented PENBB film according to claim 1, wherein the inert particles are organic polymer particles. 6. The biaxially oriented PENBB film according to claim 1, wherein the inert particles are crosslinked polymer particles. 7. The biaxially oriented PE according to claim 1, wherein the inert particles are crosslinked styrene-divinylbenzene copolymer microspheres.
NBB film. 8. The biaxially oriented PENBB film according to claim 1, wherein the inert particles are inorganic particles. 9. The biaxially oriented PENBB film according to claim 1, wherein the inert particles are selected from the group consisting of colloidal silica, calcium carbonate, titanium dioxide and carbon black. 10. The birefringence is <0.2, and the IV value of PENBB is>
The biaxially oriented PENBB film according to claim 1 or 2, wherein the content is 0.5 dl / g.