JPH09323394A - Biaxially oriented polyester film - Google Patents

Abstract

(57) Abstract: To provide a polyester film having excellent thermal dimensional stability, scratch resistance and curl recovery property, and particularly excellent dubbing characteristics for magnetic recording media. A film obtained by laminating polyester A on at least one side of polyester B, having a longitudinal elastic modulus E (GPa) and a heat in the longitudinal direction when held at a temperature of 80 ° C. for 30 minutes. The shrinkage ratio S (%) satisfies the following formula, and the intrinsic viscosity of the entire film is 0.80 (d
1 / g) or less, further the content of particles in the surface layer of the surface on which the polyester A is laminated is 0.5% by weight or less, and the surface protrusion interval of the surface is 20 μm or less. Oriented polyester film. 0.05E-S ≧ 0.07

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to a biaxially oriented polyester film.

[0002]

2. Description of the Related Art Polyester films are used for magnetic recording media by utilizing their excellent mechanical properties, thermal properties, electrical properties, surface properties, optical properties, heat resistance and chemical resistance. Widely used in various applications such as capacitors and packaging.

[0003] On the other hand, in accordance with the needs for high quality and compactness of these application products, the required characteristics of polyester films are becoming more and more severe.
Among the above applications, particularly for magnetic recording media,
Along with high quality, long-term recording and thinning of the base film due to compactness, further higher elastic modulus and higher strength are desired. In addition to higher recording density, higher thermal dimensional stability Is desired. Furthermore, improvement of abrasion resistance of the film surface and preferable curl recovery,
In addition, for magnetic recording medium applications, polyester films having good skew characteristics and dubbing characteristics are desired.

[0004] Conventional polyester films have the property of shrinking with temperature. As means for reducing the heat shrinkage of the polyester film, heat treatment at a high temperature, relaxation treatment after stretching, or in a state where the film is wound into a roll in an atmosphere of 110 ° C to 130 ° C for 6 hours The above-mentioned treatment method (for example, JP-A-60-1)
No. 03517) and a method in which a film is relatively loosely wound and heat-treated in a heating furnace as it is (for example, Japanese Unexamined Patent Publication No.
No. 98219).

A polyester film containing substantially spherical silica particles derived from colloidal silica is known to form fine projections on the surface for the purpose of improving the abrasion resistance of the film surface. (For example, JP-A-59-171623). Further, a biaxially oriented laminated film in which thin layers containing particles for forming surface projections are laminated is known (for example, JP-A-2-77431).

[0006]

However, the polyester film produced by the above-mentioned conventional technique has the following problems, for example.

When heat treatment is carried out at a high temperature or when relaxation treatment is carried out after stretching, mechanical properties such as elastic modulus are lowered accordingly. When the film is wound into a roll and left in an atmosphere at 110 to 130 ° C. for 6 hours or more, the surface of the roll and the core of the roll have uneven processing. As a result, not only the appearance of the roll film deteriorates, but also the heat treatment time is long, and the productivity is not good. In addition, it is difficult to heat the film by winding the film relatively loosely, and it is difficult to wind a wide and long film loosely.In addition, since an air layer exists between the films, heat conduction between the films is slow. In addition, it takes time to raise the temperature of the entire roll film.

Further, in the conventional polyester film, in order to reduce the coefficient of friction and improve running and handling in the processing step, etc., inert particles different from polyester are added to form surface protrusions. , Voids are easily generated around the particles. When a void is generated, the formed protrusions are easily broken or the contained particles are easily dropped off, and the film surface is easily scraped off by a guide pin or the like during VTR traveling or the like, which causes a problem that powder is generated. . In addition, when the film is stored in a roll state at high temperature and high humidity, there is a problem of curling.

The object of the present invention is to reduce the thermal dimensional stability and heat resistance without lowering the mechanical properties such as elastic modulus, and without requiring a long processing time or installing special equipment. Another object of the present invention is to provide a biaxially oriented polyester film which has excellent mechanical properties and also has excellent abrasion resistance and curl recovery on the film surface.

[0010]

The biaxially oriented polyester film of the present invention for this purpose is a film obtained by laminating polyester A on at least one side of polyester B, and has elastic modulus E (GPa) in the longitudinal direction. And a temperature of 80
The heat shrinkage ratio S (%) in the longitudinal direction when kept under the condition of 30 ° C. for 30 minutes satisfies the following formula, and the intrinsic viscosity of the entire film is 0.80 (dl / g) or less. Is a biaxially oriented polyester film having a surface layer particle content of 0.5% by weight or less and a surface protrusion interval of 20 μm or less.

0.05E-S ≧ 0.07

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS That is, in the biaxially oriented polyester film of the present invention, the elastic modulus E (G
Pa) and the relational expression of the thermal shrinkage S (%) in the longitudinal direction when held at a temperature of 80 ° C. for 30 minutes.
Is 0.07 or more, preferably 0.12 or more, more preferably 0.15 or more, the thermal dimensional stability can be improved without significantly lowering the elastic modulus.

The biaxially oriented polyester film of the present invention preferably has a heat shrinkage ratio in the longitudinal direction of 0.2% or less when kept at a temperature of 80 ° C. for 30 minutes.
It is more preferably 0.15% or less, still more preferably 0.1%.
08% or less, but not particularly limited. When the heat shrinkage is large, for example, when used for a magnetic recording medium, the video signal is recorded on the tape as an oblique track, but the tape expands and contracts (changes in dimension) in the running direction for some reason, which causes the tape to shrink. The length of the track recorded above changes. For this reason, the frequency of the signal changes, or a tracking error occurs during reproduction, and a phenomenon called skew occurs in which distortion occurs on the screen. Further, if the heat shrinkage is large in a polyester film processing step, for example, a magnetic layer coating step for a magnetic recording medium, it is not preferable because wrinkles and poor flatness occur. In addition, the curl amount of the film becomes large when the film is stored in a roll state at high temperature and high humidity. For example, in a magnetic recording medium or the like, the adhesion between the tape and the head becomes poor, and the output decreases. Therefore, it is not preferable.

The biaxially oriented polyester film of the present invention has an elastic modulus of 4 in at least one of the longitudinal and width directions.
It is preferably at least GPa, more preferably 6G
Pa or more, more preferably 8 GPa or more, but not particularly limited. For example, when used for a magnetic recording medium, if the elastic modulus of the base film is insufficient, the magnetic tape stretches due to the tension received from the magnetic head and guide pins during running, which adversely affects the electromagnetic conversion characteristics (output characteristics). give. In a magnetic tape for long-time recording, it is necessary to improve the elastic modulus in at least one direction in order to make the base film thinner.

The biaxially oriented polyester film of the present invention has an intrinsic viscosity of 0.80 (dl / g) or less, preferably 0.60 (dl / g) or less, more preferably 0.55 (dl / g). g) Below. When the intrinsic viscosity is larger than 0.80 (dl / g), it is difficult to improve thermal dimensional stability while maintaining sufficient mechanical properties such as elastic modulus. On the other hand, the intrinsic viscosity is 0.40 (dl /
If it is smaller than g), it is difficult to extrude the film stably because the melt viscosity is too small, so that the intrinsic viscosity is preferably 0.40 (dl / g) or more, but it is particularly limited. Not done.

The biaxially oriented polyester film of the present invention has a surface layer particle content of 0.5% by weight in the laminated portion.
By setting the content to preferably not more than 0.4% by weight, more preferably not more than 0.3% by weight, a film excellent in abrasion resistance and curl recovery can be obtained. When the content of the particles in the surface layer in the laminated portion is more than 0.5% by weight, voids are generated around the particles and the projections are easily broken, and the projections on the film surface are scraped off when traveling on a metal guide or the like. It is easy to get scratches on the surface,
It is not preferable because powder is generated due to shaving and preferable curl recovery property cannot be obtained.

The biaxially oriented polyester film of the present invention has a surface protrusion spacing Sm of 20 μm or less, preferably 15 μm.
By setting the thickness to be less than or equal to μm, more preferably less than or equal to 10 μm, it is possible to obtain a film that is not easily scratched by minute protrusions on the metal surface when traveling on a metal guide or the like. If the protrusion spacing Sm is larger than 20 μm, it is not preferable because it is easily scratched when traveling on a metal guide or the like.

The type of polyester constituting the biaxially oriented polyester film of the present invention is not particularly limited, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, ethylene 2, When at least one structural unit selected from 6 naphthalate units is a main constituent,
Particularly preferred. Among them, a polyester containing ethylene terephthalate as a main component is particularly preferable.
In addition, two or more kinds of polymers may be mixed or a copolymer may be used within a range not to impair the present invention. Further, within the range not hindering the present invention, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment, a dye,
Organic lubricants such as fatty acid esters and waxes may be added to the extent that they are usually added.

The biaxially oriented polyester film of the present invention may be a film obtained by laminating polyester A on at least one side of a film made of polyester B, but the effect of the present invention is further improved in the case of three layers. preferable.

The protrusions on the surface of the laminated polyester A of the present invention are not formed by conventionally known particles, but are formed by the crystals of polyester A. It is preferable in terms of sex. From this viewpoint, the polyester A of the present invention is not particularly limited, but is selected from ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, and ethylene 2,6 naphthalate units. It is particularly preferable when at least one structural unit is the main constituent. Of these, polyesters containing ethylene terephthalate as a main constituent are particularly preferable. Further, in order to form a large number of protrusions in a short heat treatment time, polyethylene terephthalate having a high crystallization rate due to the effect of a crystal nucleating agent is particularly preferable. When the crystallinity index ΔTcg represented by the difference between the cold crystallization temperature Tcc and the glass transition temperature Tg is in the range of 10 to 60 ° C., preferably 20 to 50 ° C., the surface morphology of the present invention is easily obtained and the abrasion resistance It is also preferable because it is even better. In order to enhance the effect of the crystal nucleating agent and obtain a polyester having a small crystallization index ΔTcg, lithium acetate, magnesium acetate, potassium acetate, phosphorous acid, phosphonic acid, phosphinic acid or their derivatives, antimony oxide can be used during transesterification and polymerization. The presence of germanium oxide is effective. A particularly desirable combination is magnesium acetate and phosphonic acid (or a derivative thereof) and antimony oxide, and as the phosphonic acid (or a derivative thereof),
Examples thereof include phenylphosphonic acid and dimethylphenylphosphonate.

Further, in order to increase the mobility of the molecule and obtain a polyester having a high crystallization rate, it is effective to add a small amount of a flexible movable component or copolymerize it. Here, the flexible movable component means a component having a long flexible chain in the main chain and having a high affinity with polyester, or a copolymerizable component,
For example, it means a long-chain aliphatic diol, polyalkylene glycol and the like, and it is particularly effective to use polyalkylene glycol such as polyethylene glycol, polypropylene glycol and hexamethylene glycol.
Above all, a polyethylene glycol having a number average molecular weight of 200 or more and 50,000 or less, preferably 1,000 or more and 40,000 or less, more preferably 2,000 or more and 30,000 or less is used in an amount of 0.01% by weight or more and 15% by weight or less, preferably 0. It is preferably used in the range of 1% by weight or more and 13% by weight or less, more preferably 1% by weight or more and 10% by weight or less.

However, the method for producing the polyester A is not limited to the above. It should be noted that two or more kinds of polyesters may be mixed within a range that does not impair the object of the present invention. Further, it is desirable that the polyester A contains substantially no particles, but it is not particularly limited.

Whether or not the surface protrusions are caused by the crystals of polyester A is caused by forming the protrusions by etching below the target protrusion in the film thickness direction with an appropriate solvent. When the substance remains as an insoluble substance, it is treated as particles added from the outside or particles precipitated internally (I). When there is substantially no insoluble matter remaining, it can be presumed that the substance that forms the protrusion is a fine protrusion (II). Examples of the solvent include phenol / carbon tetrachloride (weight ratio: 6 /
The mixed solvent of 4) is preferably used. By this method, the frequency of I and the frequency of II when the field of view was set to 1 mm ² were calculated.
It is preferable that the value of I / (I + II) is 70% or more. However, the method for determining whether or not the surface protrusions are fine protrusions of polyester A is not limited to the above method, and an appropriate method can be selected.

The intermediate layer (layers other than the outermost layer) of the biaxially oriented polyester film of the present invention, which has a laminated structure of at least three layers or more, is not particularly limited, but may contain particles. The type of particles may be either inorganic particles or organic particles.

The intrinsic viscosity of the intermediate layer of the biaxially oriented polyester film of the present invention, which has a laminated structure of at least three layers or more, is not particularly limited, but is 0.60 (dl / g) or less, preferably 0.55 ( It is preferably dl / g) or less, and more preferably 0.50 (dl / g) or less, because the effect of the present invention is further improved. On the other hand, when the intrinsic viscosity is less than 0.40 (dl / g), it is difficult to stably extrude the film to form a film because the melt viscosity is too small. Therefore, the intrinsic viscosity is 0.40 (dl / g). ) It is preferable that it is the above or more, but it is not particularly limited.

When the intrinsic viscosity of the intermediate layer is lowered, the tear resistance of the entire film becomes small, and the film tends to be broken during film formation or in the magnetic tape processing step, for example. Further, when the tear resistance is reduced, there is an advantage that a so-called "high edge" in which the surface of the film in contact with the cut surface rises when the film is cut is less likely to occur. The preferable laminated thickness for maximizing such an advantage is not particularly limited, but in the laminated structure having three or more layers, at least one outermost layer has a thickness of 20% or less of the total thickness of the film, preferably It is to be 10% or less.

The intrinsic viscosity of the outermost layer portion on at least one side of the biaxially oriented polyester of the present invention, which has a laminated structure of at least three layers or more, is not particularly limited, but is 0.55.
When it is (dl / g) or more, the scratch resistance and dubbing property of the outermost layer are further improved, which is preferable, but when the intrinsic viscosity of the entire film exceeds 0.80 (dl / g), the above high edge preventing effect is obtained. It is not preferable because the dubbing characteristics cannot be obtained.

Although the film thickness of the biaxially oriented polyester film of the present invention is not particularly limited, for example, for a magnetic tape for long-term recording, it is usually 1 to 30 μm, preferably 3 to 20 μm, more preferably 5 to 15 μm. Things are used.

The use of the biaxially oriented polyester film of the present invention is not particularly limited, but it is excellent in thermal dimensional stability, surface abrasion resistance, etc., so that it can be used as a digital magnetic recording tape or a data storage for computers. It is used for magnetic recording media such as products, capacitors, and packaging.

The method for producing the biaxially oriented polyester film of the present invention will be described, but the present invention is not limited thereto. First, using a known melt extruder, it is extruded into a sheet form from a slit die and cooled and solidified on a casting roll to produce an unstretched film. In addition, the laminated film is formed by laminating the polyester in a molten state on the film layers forming the outermost layers and the film layers forming the intermediate layers by using two or more extruders, manifolds or confluence blocks. The sheet is extruded and cooled on 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 channel is effective.

Next, heat treatment is applied to at least one surface of the unstretched film. Here, the unstretched film refers to a state immediately after being extruded from the die and before being cooled and solidified, to a film that is slightly solidified (up to about 2 times) in the uniaxial direction after being cooled and solidified. The purpose of this heat treatment is to increase the crystallinity of the film surface before stretching to a preferable crystallinity, and as the treatment method, (1) crystallize by slowly cooling the high temperature film immediately after extrusion. Method, (2)
There are a method of reheating a film once cooled and solidified to crystallize it, and a method of (3) heat treatment in a state of being slightly stretched in the uniaxial direction. One of these methods can be performed in the film forming process to obtain the target surface morphology, but two or more of these methods can be used in combination in the film forming process. You may.

In order to obtain the surface morphology for this purpose,
Although the method (2) is preferable, the desired surface morphology can be obtained by using the appropriate conditions even if the method (1) or (3) is used. The treatment method of (2) is not particularly limited, but it is a method of heat treatment by winding it around a heating roll, a method of hot air treatment from the opposite surface that comes into contact with the roll in the state wound around the roll, or a roll wound around the roll. There is a method of performing heat treatment with an infrared heater from the opposite surface in contact with, a method of heat treatment with an infrared heater between rolls, a method of heating with a stenter, and the like, but the method is not particularly limited to these. The heat treatment conditions include a temperature of 100 to 240 ° C. and 0.5
It is desirable to perform heat treatment for 100 seconds. More preferably, the heat treatment conditions of 120 to 220 ° C. for 1 to 50 seconds are desirable conditions for efficiently obtaining the target surface morphology in the film forming process.

Further, this unstretched film is biaxially stretched and heat-set by a known method to obtain a biaxially oriented polyester film. During this stretching, the crystals formed near the surface of the film are harder than the amorphous part and are less likely to be deformed, so that protrusions are formed on the surface.

As a stretching method, it is effective to use a longitudinal method first, and then a sequential biaxial stretching in which widthwise stretching is performed. Stretching in the longitudinal direction depends on the glass transition temperature T of polyester.
5000 to 50,000% at high temperature higher than 10g
It is effective to carry out the stretching at a stretching speed of 3 to 6 times at a stretching speed of 1 / minute or divided into several times. The stretching in the transverse direction varies depending on the type of polyester and cannot be generally stated, but at a temperature of 80 to 160 ° C., 1000 to 2
It is preferable to perform the stretching at a stretching speed of 0000% / min and a stretching ratio of 3 to 7 times. If necessary, the biaxially stretched film may be further stretched in at least one direction. In that case, the stretching method is preferably performed at a temperature of 90 to 180 ° C. and a stretching ratio of 1.1 to 2.0. In addition, the constant length heat treatment after stretching is performed at a temperature of 170 to 2
0.5 to 60 at 40 ° C, preferably 180 to 220 ° C
Seconds are preferred. Also, after the fixed length heat treatment, 80
The effect of the present invention is further improved by performing the two-step heat treatment at 150 ° C for 1 to 60 seconds, which is preferable.

[Method of measuring physical properties and method of evaluating effects]
The method for measuring characteristic values and the method for evaluating effects according to the present invention are as follows.

(1) Elastic Modulus According to the method specified in JIS K-7127,
Using a tensile tester manufactured by Toyo Sokki, 25 ° C, 65% RH
Was measured. The sample was cut into a strip having a width of 10 mm and a length of 200 mm in the measurement direction, the initial tensile chuck distance was 100 mm, and the tensile speed was 300 mm / min.

(2) Heat shrinkage ratio Measured according to the method specified in JIS C-2318. However, the oven temperature was 80 ° C. and the holding time was 30 minutes.

(3) Intrinsic viscosity [η] (unit: dl / g) The value calculated from the following formula from the solution viscosity measured at 25 ° C. in o-chlorophenol is used. That is, ηsp / C = [η] + K [η] ² · C, where ηsp = (solution viscosity / solvent viscosity) -1 and C is the weight of dissolved polymer per 100 ml of solvent (g / 100 m
1, usually 1.2), and K is a Haggins constant (assumed to be 0.343). The solution viscosity and the solvent viscosity were measured using an Ostwald viscometer.

(4) Protrusion spacing Sm Measurement was performed using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions were as follows, and the value was determined as the average value of five measurements.

Stylus tip radius: 0.5 μm Stylus load: 5 mg Measurement length: 1 mm Cutoff value: 0.08 mm The definition of Sm is specified in JIS-B-0601.

(5) Content of particles A composition analysis was carried out by the microscopic FT-IR method (Fourier transform microscopic infrared spectroscopy), and the ratio of the peak due to the carbonyl group of the polyester to the peak due to a substance other than the polyester. I asked from. In order to convert the peak height ratio into a weight ratio, a calibration curve was prepared in advance using a sample with a known weight ratio, and the polyester ratio with respect to the total amount of polyester and other substances was determined. In addition, an X-ray microanalyzer was also used as needed. If a solvent that can dissolve the polyester and not the particles can be selected, dissolve the polyester and centrifuge the particles from the polyester.
The weight percentage of particles was determined.

(6) Particle content in the surface layer of the film: A film slit into a tape having a width of 1/2 inch was used, a single-edged blade was vertically pressed against the surface on which the polyester A was laminated, and 0 It is run for 20 cm while being pushed in by 0.5 mm (running tension: 500 g, running speed: 6.7 cm / sec). At this time, the particle content of the scraped material on the surface of the film attached to the tip of the single-edged blade was determined according to the method for measuring the particle content.

(7) Laminate Thickness Using a transmission electron microscope (H-600 manufactured by Hitachi), the film cross section was subjected to an ultrathin section method (R) at an acceleration voltage of 100 kV.
Observe the interface by observing with uO ₄ ) and obtain the laminated thickness. The magnification is usually selected according to the laminated thickness to be judged, and is not particularly limited, but 10,000 to 100,000 times is suitable. Further, after the laminated polymer is peeled off, the laminated thickness can be determined using a thin film step measuring device.

(8) Glass transition point Tg, cold crystallization temperature T
cc, crystallization index ΔTcg It was measured using a DSC (Differential Scanning Calorimeter) type II manufactured by Parking Elma. The measurement conditions of DSC are as follows. That is, 10 mg of a sample is set in a DSC device,
After melting at a temperature of 300 ° C. for 5 minutes, it is quenched in liquid nitrogen. This sample is heated at a rate of 10 ° C./minute to obtain a glass transition point T
g is detected. The temperature was further raised, and the crystallization exothermic peak temperature from the glassy state was defined as the cold crystallization temperature Tcc. The difference between Tcc and Tg (Tcc-Tg) is taken as the crystallization index Δ.
Define as Tcg. As the sample, raw material pellets before film formation may be used, or 10 mg of powder obtained by scraping off the surface layer of the film after film formation with a razor blade may be used.

(9) Scratch resistance The film was slit into a tape having a width of 1/2 inch, and a tape running tester TBT-300D / H type (manufactured by Yokohama System Laboratory Co., Ltd.) was used at 20 ° C. In a 60% RH atmosphere, the film was run at a winding angle of 60 degrees on a guide pin (surface roughness: stainless steel guide pin having a surface roughness Ra of 50 nm) of a video cassette at an inlet tension of 90 g and a running speed of 250 m / min. At this time, the scratches in the film were observed with a microscope and judged according to the following criteria.

Almost no scratches: Slight scratches but few in number: Good scratches in many: Poor It is desirable that good scratches are practically usable.

(10) Dubbing characteristics A magnetic coating composition having the following composition is applied to the film by a gravure roll, magnetically oriented, and dried. In addition, a small test calendar device (steel roll / nylon roll,
(5 stages), temperature: 70 ° C., linear pressure: 200 kg / cm, and then calendaring is performed at 70 ° C. for 48 hours. The above tape raw material was slit into 1/2 inch, and a length of 250 m was incorporated into a VTR cassette to obtain a VTR cassette tape.

(Composition of magnetic paint) Co-containing iron oxide (BET value 50 m ² / g): 100 parts by weight S-REC A (vinyl chloride / vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.): 10 parts by weight Nipporan 2304 ( Polyurethane elastomer made by Nippon Polyurethane): 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

A TV test wavelength generator (TG7 / U706) made by Shibasoku was used for this tape by using a home VTR.
Chroma S is recorded from the reproduced signal by recording a 00% chroma signal and using a Shiba Soku color video noise measuring instrument (925D / 1).
/ N was measured and designated as A. Also, the same sample tape (A) was measured on the pancake of the master tape recording the same signal as above using a magnetic field transfer type video software high-speed printing system (for example, Sprinter manufactured by Sony Magnescale Co., Ltd.). The chroma S / N of the tape after dubbing to the (unrecorded) pancake was measured in the same manner as above and designated as B. From the decrease in chroma S / N (AB) due to this dubbing, the dubbing characteristics were judged according to the following criteria.

Chroma S / N decrease is less than 3 dB: Excellent Chroma S / N decrease is 3 dB or more and less than 5 dB: Good Chroma S / N decrease is 5 dB or more: Poor Good but good, but practically used It is possible.

(11) Curl recovery property A film having a width of 50 mm is wound around a plastic cylinder having a diameter of 50 mm and a width of 70 mm for about 10 rounds and fixed, and left standing at 50 ° C. and 65% RH for 24 hours. . After that, 100 mm is sampled in the longitudinal direction,
Winding on the glass surface, with the inner side facing up, 25 ° C, 65% R
It was left under H for 1 hour, the maximum distance from the flat surface of the glass plate to the film was measured, and the curl recovery property was judged according to the following criteria.

No curl amount recognized: excellent Curl amount less than 1 mm: good Curl amount greater than 1 mm: defective

[0053]

Next, embodiments of the present invention will be described based on examples.

Examples and Comparative Examples Using the catalysts shown in Table 1, polyethylene terephthalate polymerized by a conventional method or a copolymerized polyester having ethylene terephthalate as a main repeating unit was used. When particles are added, the particles are dispersed in ethylene glycol by using glass beads having a diameter of 50 μm as a medium, the glass beads are removed, and then the particles are polymerized with terephthalic acid to obtain polyethylene terephthalate master pellets. It was diluted with polyethylene terephthalate pellets not contained at a predetermined ratio and adjusted to have a predetermined viscosity.

Pellets of polyesters A and B listed in Table 2 were dried at 180 ° C. for 3 hours under reduced pressure (400P).
After a), melt extrusion is performed at 290 ° C. by using two publicly known extruders, and a rectangular confluent block (feed block) for two layers or three layers is used, and the laminated structure shown in Table 2 is used. To form a fused sheet, and the molten sheet is extruded from the T-die die, and the surface temperature is set to 2 by using the electrostatic applied casting method.
It was wound on a metal casting drum at 5 ° C. and cooled and solidified to obtain an unstretched film. At this time, the ratio of the die slit gap / the thickness of the unstretched film was set to 10. The discharge amount of the extruder was adjusted to adjust the total thickness and the thickness of the laminated portion.

When this unstretched film is heat-treated, it is heat-treated under the conditions shown in Table 2 on a known silicone rubber roll, and thereafter the roll is stretched at 95 ° C. at a stretching rate of 2000% / min. After stretching 3.5 times in the longitudinal direction with a known stenter, it is stretched 4.5 times in the width direction at 95% and 10000% / min, and heat-treated at 200 ° C for 5 seconds under a fixed length. In Examples 9 and 10, heat treatment was further performed at 100 ° C. for 5 seconds to obtain biaxially oriented laminated films having the thicknesses shown in Table 2.

The characteristics of each film in the above Examples and Comparative Examples are shown in Tables 3 and 4. In the case of a two-layer film, the protrusion spacing Sm, scratch resistance, and dubbing characteristics on the surface on which the polyester A is laminated were measured.

In the examples, biaxially oriented polyester films satisfying the relationships of the present invention and having excellent thermal dimensional stability, scratch resistance, dubbing characteristics, and curl recovery were obtained, but they were obtained in comparative examples. Some of the biaxially oriented polyester films do not satisfy the relationship of the present invention, and have poor thermal dimensional stability, scratch resistance, dubbing characteristics, and curl recovery.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

[0062]

[Table 4]

[0063]

EFFECTS OF THE INVENTION The biaxially oriented polyester film of the present invention shows the relationship between heat shrinkage and elastic modulus, the range of intrinsic viscosity of the entire film, and the film surface morphology, and thus has excellent thermal dimensional stability and scratch resistance. It was possible to provide a polyester film having excellent durability and curl recovery property, especially for magnetic recording media.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location B29L 9:00 (72) Inventor Takuji Higashioji 1-1-1, Sonoeyama, Otsu City, Shiga Toray Co., Ltd. Shiga Business Inside the hall

Claims (7)

[Claims] 1. A film obtained by laminating polyester A on at least one surface of polyester B, which has a modulus of elasticity E (GPa) in the longitudinal direction and a longitudinal direction when held at a temperature of 80 ° C. for 30 minutes. The heat shrinkage S (%) satisfies the following formula, and the intrinsic viscosity of the entire film is 0.80 (d
1 / g) or less, further the content of particles in the surface layer of the surface on which the polyester A is laminated is 0.5% by weight or less, and the surface protrusion interval of the surface is 20 μm or less. Oriented polyester film. 0.05E-S ≧ 0.07 2. The intrinsic viscosity of the entire film is 0.60 (d
1 / g) or less, The biaxially oriented polyester film of Claim 1 characterized by the above-mentioned. 3. The intrinsic viscosity of the entire film is 0.55 (d
1 / g) or less, The biaxially oriented polyester film of Claim 1 characterized by the above-mentioned. 4. The biaxially oriented polyester film according to claim 1, wherein the projections on the surface on which the polyester A is laminated are projections mainly caused by crystals. 5. A laminated structure having at least three layers, wherein the thickness of at least one outermost layer is 20% or less of the total thickness of the film. Axial oriented polyester film. 6. The intrinsic viscosity of the intermediate layer portion is 0.60 (dl
/ G) or less, the biaxially oriented polyester film according to claim 5. 7. The biaxially oriented polyester film according to claim 5, wherein at least the outermost layer portion on one side has an intrinsic viscosity of 0.55 (dl / g) or more.