JP2525446B2 - Polyester film for magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film for a magnetic recording medium.

[Prior Art] As a polyester film for magnetic recording media, a film in which inert inorganic particles are contained in polyester is known (for example, JP-A-62-164733).

[Problems to be Solved by the Invention] However, the above-mentioned conventional polyester film for a magnetic recording medium has a video software (produced by applying a magnetic layer, a calendering step, or dubbing a completed video tape or the like). The video work is recorded and fixed on a package medium, duplicated / produced, and the friction between the roll and the film that comes into contact with the process speed increases.
The drawback is that the film is abraded and scratched, which has become a problem. In recent years, video tapes are often used by recording video works for the above video software from the beginning. In this case, with the above-mentioned conventional video tape, when dubbing (recording and copying) from the master tape at high speed in the "step of recording a video work",
The problem is that the S / N (signal / noise ratio, image quality parameter) is greatly reduced and the image quality is degraded.
On the other hand, some high-grade magnetic recording media, especially tapes, are back-coated in order to reduce the friction coefficient of the base film and impart the running property. However, recently, in order to reduce the cost of the tape, the direction of not applying a back coat is being considered. However, the conventional polyester film for a magnetic recording medium has a drawback that when the surface of the base film is made smooth in order to reduce the deterioration of image quality during dubbing, the coefficient of friction becomes large and the running property becomes poor.

The present invention solves the above problems, is excellent in scratch resistance of the film at high speeds (hereinafter referred to as scratch resistance), has less deterioration in image quality during dubbing (hereinafter referred to as excellent dubbing resistance), and is used as a tape. It is an object of the present invention to provide a film having excellent running property (hereinafter referred to as running property) when it is subjected to the following conditions.

[Means for Solving the Problems] The present invention is a film containing a composition composed of polyester and inert inorganic particles as a main component, wherein the ratio of Rp and Ra on at least one side of the film, Rp / Ra (unit: Both n
m) is 4 to 25, and heat shrinkage stress S in the longitudinal direction at 90 ° C
(Unit is kg / mm ² ) and average surface roughness of 10 points on at least one side
The product Rz · S of Rz (unit is nm) is in the range of 0.5 to 21.5,
The present invention also relates to a polyester film for a magnetic recording medium, which has a heat shrinkage stress in the longitudinal direction at 60 ° C. of 0.09 kg / mm ² or less.

The polyester in the present invention is ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy)
At least one structural unit selected from ethane-4,4'-dicarboxylate and ethylene 2,6-naphthalate units is a main constituent. However, other components may be copolymerized within a range not hindering the present invention, preferably within 15 mol%.

The type of the inert inorganic particles in the present invention is not particularly limited, silica due to colloidal silica, synthetic calcium carbonate, α-alumina, rutile type titanium dioxide,
The thermal type carbon black and titanium nitride are particularly preferable because the scratch resistance, the dubbing resistance, and the running property are further improved. In the case of colloidal silica, an ion exchange method, an alkoxide method and the like are known as a manufacturing method, but the alkoxide method is particularly preferable because scratch resistance, dubbing resistance and running property are further improved.

The shape of the inert inorganic particles in the present invention is not particularly limited, but a substantially spherical shape is particularly preferable because scratch resistance, dubbing resistance, and running property are further improved. The film of the present invention may use internally precipitated particles in combination. The internally deposited particles in the present invention are particles formed by binding at least one compound of calcium compound, magnesium compound and lithium compound added at the time of polyester polymerization and the polyester constituent component. Incidentally, the internal precipitation particles of the present invention, within the range not impairing the object of the present invention, phosphorus element and a trace amount of other metal components, for example, zinc, cobalt, antimony, germanium,
Titanium and the like may be included.

The average particle size and content of the inert inorganic particles are not particularly limited, but when the internal particles are not used together, the inorganic particles of 0.2 to 0.6 μm are used at 0.3 to 1.0% by weight, particularly 0.4 to 0.7% by weight, and the internal particles are used together. If 0.5-1.0μm inorganic particles 0.01-0.15
Scratch resistance, dubbing resistance, in the range of wt%,
It is particularly desirable because the running property is further improved.

The film of the present invention comprises the above composition as a main component, but may be blended with other polymers within a range not impairing the object of the present invention, and may also be an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber. Inorganic or organic additives such as nucleating agents may be added to the extent that they are usually added.

The film of the present invention is a film in which the above composition is biaxially oriented. In non-oriented or uniaxially oriented film,
Scratch resistance, dubbing resistance, and running performance are poor, which is not preferable. The thickness direction refractive index ratio indicating the degree of the orientation is not particularly limited, but is 0.935 to 0.975, preferably,
When it is in the range of 0.940 to 0.970, scratch resistance, dubbing resistance, and running property are further improved, which is particularly desirable.

The film of the present invention needs to have an Rp / Ra ratio (unit: nm) of at least one side of 4 to 25, preferably 6 to 20, and more preferably 9 to 15. If the Rp / Ra ratio (both in nm) on both sides of the film is greater than the above range, dubbing resistance will be poor, and conversely, if it is small, running performance will be
It is not preferable because the scratch resistance becomes poor. Also,
When the Rp / Ra ratio on both surfaces is within the above range, the dubbing resistance is further improved, which is particularly desirable.

The film of the present invention has a product Rz · S of 0.5 to 21.5, which is the product of the heat shrinkage stress S in the longitudinal direction at 90 ° C. (unit: kg / mm ² ) and the 10-point average surface roughness Rz (unit: nm) of at least one side. , Preferably 1.0 to 17.5, more preferably 2.5 to 13.0. If the above Rz · S is smaller than the above range, the running property and scratch resistance will be poor, and conversely if it is large, the dubbing resistance will be poor, such being undesirable. When both sides have Rz and the heat shrinkage stress S in the longitudinal direction at 90 ° C. in the above range, the dubbing resistance is further improved, which is particularly desirable.

The film of the present invention needs to have a heat shrinkage stress in the longitudinal direction at 60 ° C. of 0.09 kg / mm ² , preferably 0.06 kg / mm ² or less. If the heat shrinkage stress in the longitudinal direction at 60 ° C. is larger than the above range, the dubbing resistance becomes poor, which is not preferable. The lower limit of the heat shrinkage stress in the longitudinal direction at 60 ° C. is not particularly limited, but usually about 0 kg / mm ² is a manufacturing limit.

The film of the present invention is particularly desirable because when both sides have Rp of 60 to 190 nm, preferably 70 to 160 nm, more preferably 80 to 150 nm, the dubbing resistance, scratch resistance, and running performance are further improved.

The film of the present invention has an average spacing of surface protrusions on both sides.
20 μm or less, preferably 15 μm or less, more preferably
When it is 12 μm or less, dubbing resistance, scratch resistance and running property are further improved, which is particularly desirable.

The inert inorganic particles of the film of the present invention are particularly preferable because the scratch resistance and the running property are further improved when the crystallization acceleration coefficient dΔTcg is in the range of 3 to 20 ° C., particularly 5 to 15 ° C.

In the film of the present invention, the effective space volume of the surface protrusions on both sides is 1 × 10 ^{3 to} 5 × 10 ⁵ , preferably 5 × 10 ^{3 to} 3 × 1.
When it is in the range of 0 ⁵ , the running property, the dubbing resistance and the scratch resistance are further improved, which is desirable, and the winding shape when used as a video tape is improved, which is particularly desirable.

The film of the present invention has a refractive index in the width direction of 1.655 to 1.700,
Particularly, in the range of 1.675 to 1.700, scratch resistance is further improved, which is desirable.

The film of the present invention is more excellent in running property, scratch resistance, and dubbing resistance when the standard deviation of the projection height distribution is 40 to 150 nm, particularly 50 to 120 nm, and further 60 to 110 nm for both surface projections. Therefore, it is desirable.

The thickness of the film of the present invention is not particularly limited, but may be 6.5 to 2
When the thickness is 5 μm, particularly in the range of 8 to 20 μm, the running property, scratch resistance and dubbing resistance are further improved, which is desirable.

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

First, as a method of incorporating inert inorganic particles into a predetermined polyester, it may be added before polymerization, during polymerization, or after polymerization, but it is mixed with ethylene glycol which is a diol component of polyester in the form of a slurry. The method of adding in a dispersed manner is effective in satisfying the Rz · S, Rp / Ra ratio, Rp in a desired range, and the standard deviation of the protrusion height distribution of the present invention. In addition, this slurry at 0.5
~ Heat treatment for 3 hours before use, or 0.5 to 20% by weight of ammonium phosphate salt based on the amount of particles and /
Alternatively, the method of adding polyvinylpyrrolidone is effective in obtaining the crystallization promoting coefficient in the desirable range of the present invention.
Further, the slurry is sufficiently stirred using a medium such as glass beads to disperse the inorganic particles, and high precision filtration, preferably an absolute filtration precision by the Coulter counter method of 0.5.
The particle diameter distribution of the inert inorganic particles is standard deviation σ (μm) and average particle diameter d (μ
The ratio of m), σ / d, is set to 0.6 or less, preferably 0.4 or less, so that Rz · S and Rp / Ra ratio of the present invention and R in a desirable range are set.
It is effective to obtain the standard deviation of p and the height distribution of protrusions. As a method of adjusting the content of the inorganic particles, a method of diluting a high-concentration master pellet, preferably a master pellet having a particle concentration of 1 to 5% by weight during film formation is within the scope of the present invention.
It is effective for obtaining Rz · S and Rp / Ra ratio. In addition, the intrinsic viscosity of this master pellet, by adjusting the copolymerization component, the difference between the glass transition point Tg and the cold crystallization temperature Tcc (Tcc-Tg), Δ
Tcg, 55 ~ 85 ℃, kept at 60 ~ 80 ℃ sometimes, and to make it larger than ΔTcg of the polyester that does not substantially contain inorganic particles to dilute it, Rz of the present invention.
It is extremely effective in obtaining S, Rp / Ra ratio, Rp in a desired range, and standard deviation of projection height distribution. As the copolymerization component in this case, an isophthalic acid component and a cyclohexanedimethanol component are preferable.

The following method is effective as a method for generating the internally precipitated particles when the internally precipitated particles are used in combination. That is, (1) a process of polycondensation through direct esterification of a predetermined dicarboxylic acid and ethylene glycol, or (2) a polycondensation through a transesterification reaction of dimethyl ester of a predetermined dicarboxylic acid with ethylene glycol. In the process, it is produced by adding at least one of a calcium compound, a magnesium compound, a manganese compound and a lithium compound soluble in glycol, and preferably an acid and / or ester compound of phosphorus. Examples of calcium, magnesium, manganese, and lithium compounds that can be used here include inorganic acid salts such as halides, nitrates, and sulfates, organic acid salts such as acetates, oxalates, and benzoates, hydrides, and oxides. Most preferred are glycol-soluble compounds such as compounds, but two or more kinds may be used in combination. As the phosphorus compound, one or more of phosphate, phosphorous acid, phosphonic acid and their esters and partial esters are used.

Thus, after sufficiently drying the pellets containing the inert inorganic particles, it is supplied to a known melt extruder, 270 ~ 330 ℃
Is extruded into a sheet from a slit-shaped die and cooled and solidified on a casting roll to produce an unstretched film. In this case, when extruded into an unstretched film,
The ratio of die slit gap / unstretched film thickness is 5 to 30,
Rz in the range of the present invention is preferably in the range of 8 to 20.
・ S, Rp / Ra ratio, effective for obtaining heat shrinkage stress at 60 ℃. Further, it is within the scope of the present invention to install a filter having a filtration accuracy represented by a 95% cut-off particle size of 1 to 5 μm, preferably 1 to 3 μm in the polymer channel during extrusion.
It is extremely effective in obtaining Rz · S, Rp / Ra ratio, Rp in a desired range, and standard deviation of projection height distribution.

Next, this unstretched film is biaxially stretched and biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, first use the sequential biaxial stretching method of stretching in the longitudinal direction, then in the width direction,
Stretching in the longitudinal direction is divided into three stages or more, and the total stretch ratio is 3.
The method performed at 5 to 4.5 times is Rz · S, Rp / Ra within the scope of the present invention.
It is effective to obtain the ratio, the heat shrinkage stress at 60 ° C, the desired range of Rp, and the standard deviation of the protrusion height distribution. For the longitudinal stretching temperature, the first stage (polymer glass transition temperature −10
C.) to (glass transition point of polymer + 10.degree. C.).
Rp / Ra ratio, heat shrinkage stress at 60 ℃, R in desired range
It is effective to obtain the standard deviation of p and the height distribution of protrusions. The longitudinal stretching speed is preferably in the range of 5,000 to 50,000% / min. As a stretching method in the width direction, a method using a stenter is generally used. A suitable stretch ratio is 3.0 to 5.0 times. The stretching speed in the width direction is preferably in the range of 1000 to 20000% / min. Next, this stretched film is heat-treated. In this case, the heat treatment temperature is 170 to 200 ° C., particularly 170 to 190 ° C., and the time range of 0.5 to 60 seconds is effective for obtaining Rz · S and heat shrinkage stress at 60 ° C. within the range of the present invention. Further, at the time of heat treatment, stretching in the width direction by 1.05 to 1.3 times, particularly 1.05 to 1.2 times is performed by the Rp / Ra ratio in the range of the present invention, Rz · S, heat shrinkage stress at 60 ° C., projection interval in a desirable range, It is effective in obtaining an effective space volume. Further, it is effective to obtain the heat shrinkage stress at Rz · S and 60 ° C. in the range of the present invention by gradually cooling the film after heat-treating it, preferably at a cooling rate of 2 ° C./sec or less. . Further, the winding tension at the time of winding the film is 8 kg / m or less, preferably 5 kg / m or less, and more preferably 3 kg / m.
It is effective for obtaining heat shrinkage stress at 0 ° C.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Center line average surface roughness Ra, center line depth Rp, 10-point average surface roughness Rz, average interval Sm of protrusions Sm Measurement was performed using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 20 measurements was taken as the value.

・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measuring length: 1 mm ・ Cutoff value: 0.08 mm In addition, center line average surface roughness Ra, center line depth Rp, 10 point average surface roughness Rz, The definition of the average spacing Sm of the protrusions is, for example,
It is described in "Measurement and Evaluation Method of Surface Roughness" by Jiro Nara (General Technology Center, 1983).

(2) Average Particle Size of Inorganic Particles This is a volume average diameter measured by a centrifugal sedimentation method (using CAPA500, Horiba, Ltd.) in which inorganic particles are dispersed in ethanol.

(3) Standard deviation of particle size distribution The particle size distribution obtained by the above method was calculated by approximating the normal distribution by the least squares method.

(4) Content of inorganic particles 0.9 liter of polyester and 1.0 liter of 0-chlorophenol were added and heated at 120 ° C. for 3 hours, and then ultracentrifuge 55P-72 manufactured by Hitachi Koki Co., Ltd. was used for 40 minutes at 30,000 rpm. Centrifugation is performed, and the obtained particles are dried in vacuum at 100 ° C. When a fine particle corresponding to a polymer is observed when the fine particles are measured by a scanning differential calorimeter, 0-chlorophenol is added to the fine particles, and the mixture is heated and cooled, and then centrifuged again. When no dissolution peak is observed, the fine particles are made into particles. Usually, two centrifugation operations are sufficient. The content of the inorganic particles is defined as the ratio (% by weight) to the total weight of the particles thus separated.

(5) Glass transition point Tg, cold crystallization temperature Tcc It was measured using DSC (Differential Scanning Calorimeter) II type manufactured by Perkin Elmer. The DSC measurement conditions are as follows.
That is, 10 mg of a sample is set in a DSC device, dissolved at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected.
The temperature was further raised, and the crystallization exothermic peak temperature from the glass state was set as the cold crystallization temperature Tcc. Here, the difference between Tcc and Tg (Tcc−Tg) is defined as ΔTcg.

(6) Crystallization acceleration coefficient (unit: ° C) The ΔTcg (I) of the polyester containing 1% by weight of the inert particles and the ΔTcg (II) of the polyester having the same viscosity after removing the inert particles were measured by the above-mentioned method. , ΔTcg
Difference between (II) and ΔTcg (I) [ΔTcg (II) -ΔTcg
(I)] was used as the crystallization acceleration coefficient.

(7) Refractive index The sodium D line (589 nm) was used as a light source, and the refractive index was measured using an Abbe refractometer. Methylene iodide was used as the mount solution, and measurement was performed at 25 ° C. and 65% RH.

(8) Refractive index ratio in the thickness direction A non-oriented (amorphous) film prepared by the above-described method, in which the biaxially oriented film has a refractive index in the thickness direction (A) and is melt-pressed and then rapidly cooled into water at 10 ° C. The refractive index (denoted as B) in the thickness direction was measured, and A / B was defined as the refractive index ratio in the thickness direction.

(9) Standard deviation of the height distribution of the surface protrusions The film surface of a two-detector scanning electron microscope [ESM-3200, Elionix Co., Ltd.] and a cross-section measuring device [PMS-1, Elionix Co., Ltd.] The height measurement value of the protrusions when the height of the flat surface of 0 is scanned and sent to the image processing device [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct the film surface protrusion image on the image processing device. Next, the equivalent circle diameter is calculated from the area of each protrusion obtained by binarizing the protrusion portion in this surface protrusion image, and this is made the average diameter of the protrusion. In addition, the highest value among the binarized individual projection portions is set as the height of the projection, and this is obtained for each projection. This measurement is repeated 500 times in different places, and the height distribution of the measured protrusions is regarded as a normal distribution (normal distribution centered on a point having a height of 0), and the minimum is 2
The standard deviation of the height distribution was determined by multiplication. The magnification of the scanning electron microscope is selected to be a value between 1000 and 8000 times.

(10) Heat shrinkage stress The film is formed into a tape having a width of 10 mm and a length of 100 mm, and the tape is heated in a heating furnace at a heating rate of 10 ° C / minute.
At this time, the heat shrinkage force at each temperature of the tape was measured by a U gauge attached to one end, and the heat shrinkage stress was calculated by dividing the tape by the cross-sectional area of the tape.

The temperature at the start of temperature rise is 30 ° C, and the initial stress at this time is
It was 0.12 kg / mm ² .

(11) Filtration accuracy (95% cut-off particle size) The cut rate measured using a Coulter counter is 95.
% Particle size, 95% filtration accuracy (unit μ
m).

(12) Effective space volume of surface protrusions Kosaka Laboratory's high-precision thin film step measuring device ET-10 was used, and the tip radius of the stylus was 0.5 μm, the cutoff was 0.08 mm, the measurement length was 1.0 mm, the vertical magnification was 200,000 times, and the horizontal magnification was 2000. The surface roughness curve of the film is measured in fold. A peak count level is set every 0.005 μm in parallel above the average line (center line) of this roughness curve.
When there is a point that intersects the above peak count level one or more times between two points where the curve intersects the average line,
This is defined as one peak, and the number of peaks is determined between the measurement lengths. For each peak count level, the number of peaks is determined, and the number of peaks determined for the n-th peak count level from the average line is defined as PC (n). When the peak count level at which the number of peaks becomes zero for the first time during the measurement length is m-th from the average line, the effective space volume Φ is The average value of 50 measurements taken at different locations is used.

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

That is, η _SP / C = [η] + K [η] ² · C where η _SP = (solution viscosity / solvent viscosity) −1, and C is the solvent
Dissolved polymer weight per 0.9 ml (g / 100 ml, usually 1.2),
K is the Huggins constant (0.343). Also, solution viscosity,
The solvent viscosity was measured using an Ostwald viscometer.

(14) Scratch resistance (when running at high speed) A film (1/2 inch width) is repeatedly run on a metal guide using a high speed tape running tester (running speed 1000 m / min, running frequency 50 passes) . At this time, the scratches in the film were observed with a microscope. If there were almost no scratches, it was judged that the scratch resistance was good. If there were 5 scratches or more per film width, it was judged that the scratch resistance was poor. Here, the metal guide diameter is 6 mmφ, the material is SUS (surface roughness 0.2S), and the winding angle is 180 °.

(15) Dubbing resistance A magnetic coating composition having the following composition is applied to a film by a gravure roll, magnetically oriented, and dried. Further, after calendering at a temperature of 70 ° C. and a linear pressure of 200 kg / cm with a small test calender device (steel roll / nylon roll, 5 steps), curing is performed at 70 ° C. for 48 hours. The above raw tape was slit into 1/2 inch to prepare a pancake.

(Composition of magnetic paint) ・ Co-containing iron oxide (BET value 50m ² / g): 100 parts by weight ・ S-REC A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight ・ Nipporan 2304 (Nippon Polyurethane Polyurethane) Elastomer: 10 parts by weight-Coronate 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 From this pancake (I), a length of 250 m is embedded in a VHS cassette half to make a cassette tape, and a VTR for household use is used for this tape to produce a TV test waveform generator made by Shibasoku. TG7 / U706) records 100% chroma signal, and from the reproduced signal, Shibasoku color video noise measuring instrument (925D
The chroma S / N was measured in / 1) and was designated as A. In addition, a pancake (I) is produced by using a magnetic tape transfer type video software high-speed printing system (for example, a Sprinter manufactured by Sony Magnescale Co., Ltd.) from the master tape recording the same signal as the above.
After dubbing, the length of 250 m was incorporated into the VHS cassette half to make a cassette tape, and the chroma S /
N was measured in the same manner as above and designated as B. The decrease in chroma S / N (AB) due to this dubbing process
When it was less than 4.0 dB, the dubbing resistance was good, and when it was 4.0 dB or more, the dubbing resistance was poor.

(16) Runnability Using the tape runnability tester TBT-300 (manufactured by Yokohama System Laboratory Co., Ltd.), the above tape was run in an atmosphere of 20 ° C. and 60% RH, and the initial friction coefficient μK was Calculated from the formula (film width was 1/2 inch).

μK = 0.733log (T ₂ / T ₁ ) where T ₁ is the inlet tension and T ₂ is the outlet tension. The guide diameter is 6mmφ, the guide material is SUS27 (surface roughness 0.2S),
The winding angle is 180 ° and the running speed is 3.3cm / sec.

When the above μK was 0.20 or less, the running property was determined to be good, and when it exceeded 0.20, the running property was determined to be poor. 0.20 of this μk value
Is a critical point of whether or not sufficient running characteristics can be obtained when used as a video tape.

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

Examples 1 to 4 and Comparative Examples 1 to 5 Ethylene glycol slurries containing several types of inorganic particles having different average particle diameters, standard deviations of particle diameter distribution and average particle diameter ratio were prepared. These ethylene glycol slurries were treated under different heat treatment conditions, then transesterified with dimethyl terephthalate, and then polycondensed to obtain particles of 1
Particle master pellets of polyethylene terephthalate containing wt% were made. At this time, the degree of polymerization of these master pellets and the ratio of the copolymerization components were adjusted to prepare particle master pellets as shown in Table 1. These particle master pellets were mixed with pellets of ΔTcg of polyethylene terephthalate shown in Table 1 containing substantially no inorganic particles and adjusted to a predetermined concentration. These mixed pellets were dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours, then fed to an extruder and melt-extruded at 300 ° C.
Various ratios of the thickness of the unstretched film were changed, and the film was wound around a casting drum having a surface temperature of 30 ° C. and cooled and solidified to form an unstretched film by using the electrostatically applied casting method. At this time, several filters were made by inserting filters having different filtration accuracy between the extruder and the die.

This unstretched film was stretched 4.0 times in the longitudinal direction. At this time, the number of stages of stretching and the temperature of the first stage were variously changed for stretching. This stretching was performed by the difference in the peripheral speed of the roll, and the average stretching speed was 20000% / min. This uniaxially stretched film was stretched 4.0 times in the width direction using a stenter. At this time, the temperature was 100 ° C. and the speed was 5000% / min. While stretching 0.95 to 1.05 times in the width direction (0.95 to 1.00
Heat treatment was performed at 180 ° C. for 5 seconds, and the cooling rate was changed to obtain various biaxially oriented films. The extrusion discharge rate was adjusted so that the film thickness was all 15 μm.
The scratch resistance, running resistance and dubbing resistance of these films are as shown in Table 2. When the film characteristics are within the range of the present invention, the scratch resistance, running resistance and dubbing resistance are excellent. However, if not, a film having both running property and dubbing resistance could not be obtained. In the experimental examples in Table 2, the film table,
On the back the surface parameters were the same.

Example 5 An ethylene glycol slurry of colloidal silica having an average particle size of 0.6 μm and a ratio (σ / d) of the standard deviation σ of the particle size distribution to the average particle size d of 0.58 was prepared. These ethylene glycol slurries were heat-treated at 190 ° C. for 1.5 hours, transesterified with dimethyl terephthalate, and then polycondensed to prepare polyethylene terephthalate particle master pellets containing 1% by weight of silica particles derived from colloidal silica. . At this time, adjust the degree of polymerization of the master pellet,
Tcg was set to 65 ° C.

On the other hand, 100 parts by weight of dimethyl terephthalate and 62 parts by weight of ethylene glycol are subjected to a transesterification reaction by a conventional method using 0.06 parts by weight of calcium acetate as a catalyst, and the product is 0.04 parts by weight of antimony trioxide, 0.07 parts by weight of lithium acetate and acetic acid. Add 0.04 parts by weight of calcium, followed by
After adding 0.02 part by weight of phosphorous acid and 0.1 part by weight of trimethyl phosphate, polycondensation was carried out to obtain a polyester containing 0.35 part by weight of internally deposited particles (based on 100 parts by weight of polyester) (ΔTcg at 50 ° C. there were). The particle master pellets and polyester containing internally precipitated particles were mixed to adjust the silica content to 0.03% by weight. These mixed pellets were dried under reduced pressure (3 Torr) at 180 ° C for 3 hours, then fed to an extruder and melt-extruded at 300 ° C, the electrostatic slit casting method with a die slit gap / unstretched film thickness ratio of 10. Casting with a surface temperature of 30 ° C
It was wound on a drum and cooled and solidified to prepare an unstretched film. At this time, a film having a filtration accuracy of 2.5 μm was put between the extruder and the die to form a film.

This unstretched film was stretched 4.5 times in the longitudinal direction. At this time, the number of stretching stages was 3, the temperature of the first stage was 80 ° C, and the second to third stages were 90 ° C. This stretching was performed by the difference in the peripheral speed of the roll, and the average stretching speed was 20000% / min. This uniaxially stretched film was stretched 4.0 times in the width direction using a stenter. At this time, the temperature was 100 ° C. and the speed was 5000% / min. Furthermore, while stretching 1.05 times in the width direction, it is heat-treated at 180 ° C for 5 seconds and cooled at a cooling rate of 2 ° C / second to obtain a thickness of
A biaxially oriented film of μm was obtained. The scratch resistance, running property and dubbing resistance of this film are as shown in Table 2, and the scratch resistance, running property and dubbing resistance were excellent. In other cases, a film having both running property and dubbing resistance could not be obtained, and the surface parameters were the same on the front and back of the film.

[Effects of the Invention] In the present invention, the surface roughness parameter of the film, the heat shrinkage stress, and the relationship thereof are devised on both sides of the raw material surface and the film forming method, and are combined into a specific range.
It was a film that was both scratch-resistant even when running at high speeds, and had the drivability that would make it possible to make tapes that would not deteriorate in image quality even when dubbed, as well as runnability when used as magnetic tape. Even if the film is not easily scratched, the film processing speed can be increased in each application. The use of the film of the present invention as a magnetic recording medium is not particularly limited, but it is particularly useful for video tapes, particularly for high-speed processing steps and for video tapes for video software produced by dubbing. Further, among the films of the present invention, the surface parameter of only one side of the film is within the range of the present invention, it is necessary to use the surface having the surface parameter within the range of the present invention as the running surface (non-magnetic surface).

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display area B29L 7:00 B29L 7:00

Claims (1)

(57) [Claims] 1. A film comprising a composition composed of polyester and inert inorganic particles as a main component, wherein the ratio of Rp to Ra on at least one side of the film, Rp / Ra (both units are n
m) is 4 to 25, and heat shrinkage stress S in the longitudinal direction at 90 ° C
(Unit is kg / mm ² ) and average surface roughness of 10 points on at least one side
The product Rz · S of Rz (unit is nm) is in the range of 0.5 to 21.5,
A polyester film for a magnetic recording medium, which has a heat shrinkage stress in the longitudinal direction at 60 ° C. of 0.09 kg / mm ² or less.