JP2000234029A - Production of polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film having excellent quality in high productivity by melting a polyester resin containing metallic elements and a phosphorus element in a ratio in a specified range, extruding the melt from a slit die to form a molten sheet and cooling the molten sheet by insertion into between a charging roll and a cooling medium to adhere a solid film on the cooling medium. SOLUTION: A polyester resin containing metallic elements and a phosphorus element in ratio represented by the formula is melted, and extruded from a slit die to form a molten sheet. The molten sheet is inserted into between a smooth-surfaced charging roll having an applied voltage of 100 V to 10 kV and a cooling medium such as a drum with a hard chromium-plated surface and an inside through which cooling water is circulated to adhere the sheet to the cooling medium to obtain a film. If required, the film is heated to the glass transition point to effect elongation and heat treatment. In the formula, (m), N, L, and P are the number of moles of the alkali metal atoms the number of moles of the alkaline earth metal atoms, the number of moles of a metallic element selected from among Mn, Co, and Zn, and the number of moles of phosphorus element per ton of the polyester resin, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester film, and more particularly, to a method for producing a polyester film having excellent productivity and high-speed castability. The present invention relates to a method for producing a film suitable for a manufactured electric capacitor.

[0002]

2. Description of the Related Art In a conventional method for producing a polyester film, for example, as disclosed in Japanese Patent Publication No. 37-6142, a polyester film melt-extruded from a die is kept at a temperature lower than the glass transition temperature of the polyester resin. A method of applying a static electricity to a cooling medium and bringing the film into close contact with the film and quenching it to obtain an amorphous cast film having a smooth surface, followed by uniaxial stretching or biaxial stretching as necessary.

In Japanese Patent Publication No. Hei 5-18688,
A method of casting by forming a water film in a cooling medium has been proposed.In a sheet manufacturing method called a calendering method, a resin pool called a bank is formed while sandwiching a molten resin between rolls, and a gap between the rolls is formed. The sheet is molded from

[0004]

However, such a method has the following disadvantages.

That is, films used for electric capacitors are required to have high dielectric breakdown voltage and insulation resistance.
A polyester resin having a small ratio M / P between the metal element (M) and the phosphorus element (P) is used. As described above, when the M / P of the polyester resin is as small as 1 or less, even if static electricity is applied to the molten polyester resin, the adhesive force with the cooling medium does not sufficiently appear, and therefore, the gap between the cooling medium and the cast film does not exist. When air or the like is easily trapped and the voltage of static electricity is increased to obtain the maximum adhesion, a discharge phenomenon is apt to occur, and the film has a defect. In the method in which a water film is formed in a cooling medium and cast, water droplet marks are transferred to the film. In the case of a polyethylene terephthalate resin or the like in which a bank cannot be formed stably by a calendar molding method, the casting speed should be 30 m / min or more. Was difficult and productivity was poor.

That is, an object of the present invention is to provide a production method capable of solving the above-mentioned disadvantages of the prior art and obtaining a polyester film excellent in both productivity and quality, particularly a polyester film suitable for an electric capacitor. It is in.

[0007]

Means for Solving the Problems In view of the above-mentioned problems, the present inventors have made intensive studies and found that a polyester film extruded from a die is cast while being sandwiched between a roll having a DC potential difference and a cooling medium. The inventors have found that the above problem can be solved, and have reached the present invention.

That is, according to the method for producing a polyester film of the present invention, after melting a polyester resin, a molten sheet is discharged from a die, and the sheet is cooled while being sandwiched between a charging roll and a cooling medium, and is cooled and solidified on a cooling medium. In producing a cast film, a polyester film satisfying the following formula (1) is used as a polyester resin.

More preferably, in the method of the present invention, the polyester film has a surface temperature on a cooling medium immediately before the molten sheet is grounded, which is higher than the glass transition point Tg and lower than the melting point Tm of the polyester resin. Or, preferably, a method for producing a polyester film characterized by stretching and / or heat-treating the cast film in the method of the present invention described above, or, further preferably, The method of the present invention is a method for producing a polyester film, wherein the produced film is used for an electric capacitor.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

In the present invention, the polyester resin is a high molecular compound having an ester bond in a molecular main chain,
For example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and copolymers thereof can be mentioned. Among them, polyethylene terephthalate, polyethylene naphthalate and copolymers thereof are preferable, and polyethylene terephthalate and copolymers thereof are particularly preferable. Of course, these polyester resins have various additives, such as sliding materials,
Stabilizers, antioxidants, viscosity modifiers, antistatic agents, colorants, pigments, and the like can be used in combination.

The polyester resin used in the present invention comprises:
The above formula (1) is satisfied, and the ratio of the amount of the metal element to the amount of the phosphorus element contained in the polyester resin has a specific range. That is, it is important that the ratio is in the range of 0.4 to 1.2, preferably 0.45 to 1.
1, particularly preferably in the range of 0.5 to 1.0. When the ratio of the amount of the metal element to the amount of the phosphorus element in the formula (1) is less than 0.4, the adhesion between the cast film and the cooling medium is reduced, and the smoothness of the film is deteriorated or the width of the film is changed. And cast cannot be performed stably. On the other hand, when the ratio exceeds 1.2, the film produced is not suitable for use in an electric capacitor because the breakdown voltage and insulation resistance of the film are reduced, and the adhesion between the cast film and the cooling medium is rather increased. However, there is a problem that the smoothness of the film deteriorates and the width of the film fluctuates.

The metal elements and phosphorus elements contained in the polyester resin are mainly derived from catalysts and stabilizers.
As long as the formula (1) is satisfied, they may be added or contained separately. The metal element is selected from an alkali metal, an alkaline earth metal, Co, Mn, and Zn, and particularly preferably an acetate of Li, Mg, Ca, Co, Mn, or Zn. These metal salts are added before esterification or transesterification when used as a catalyst,
If necessary, they may be added after these reactions.
On the other hand, as the phosphorus element, phosphoric acid, phosphorous acid and their esters, alkylphosphonic acid, phenylphosphonic acid, and their esters and derivatives can be preferably used. These phosphorus compounds are preferably added after the esterification reaction and after the transesterification reaction. In the polymerization of polyester, Sb, Ge, Ti, A
1, It is preferable to use a Si compound.

The method for producing a polyester film in the present invention is a method in which a molten polyester resin is extruded from a die, and then the molten sheet is cast while being sandwiched between a charged roll and a cooling medium. According to the method of the present invention, the charge is directly applied to the sheet,
The adhesiveness is better than the conventional electrostatic application casting method, and high-speed casting is possible even with a polyester resin having a small M / P ratio suitable for an electric capacitor. further,
By sandwiching between the roll and the cooling medium, air entrapment between the sheet and the cooling medium, which has been a problem in the conventional high-speed casting method, can be suppressed. Further, according to the method of the present invention, there is no problem of bank formation unlike the calendering method of forming between rolls.

In the method for producing a polyester film of the present invention, a DC voltage may be applied to the roll itself to charge the roll, and the cooling medium may be grounded (grounded). The voltage applied to the roll is preferably 100 V to 10 KV, and a DC positive voltage or a negative voltage is applied to the roll. Further, an electric resistance can be inserted between the ground and the cooling medium in order to limit the value of the current flowing through the molten sheet.

In the present invention, a charge is applied to the sheet by the potential difference existing between the charging roll and the cooling medium and the sheet is brought into close contact with the cooling medium. The surface may be rubbed. In order to prevent this, it is preferable to apply a charge of the same polarity as the roll to the sheet before the molten sheet comes into contact with the roll. The method of applying the electric charge is, for example, to draw a wire between the die and the roll in the sheet width direction and to apply a voltage having the same polarity as the roll to the wire. The electrode for this purpose is not particularly limited, but the wire-like electrode and the tape-like electrode described here can be preferably used.

The manufacturing method of the present invention is characterized in that a voltage is applied directly to the sheet. This method is particularly effective when the electric resistance at the time of melting the resin is large. Therefore, it is particularly effective for, for example, a supercooled extrusion cast. The supercooled extrusion is to perform extrusion in a so-called supercooled state, in which the resin is once melted at a melting point Tm or higher and then cooled to the melting point Tm or lower and the melt crystallization temperature Tmc or higher. Extrusion in such a supercooled state not only has the effect of reducing the thermal decomposition and gelation of the resin, but also has the effect of reducing the generation of low-molecular-weight oligomers, thereby reducing drum contamination and facilitating casting. There is also.

The roll used in the production method of the present invention comprises:
It is necessary that at least a part of the surface is conductive. It is easiest to use a metal roll as the roll, but a roll such as a rubber roll, a ceramic roll, or a Teflon roll that has been subjected to conductive processing may be used. Further, a roll in which a metal portion and a non-adhesive portion such as a fluororesin are mixed on the roll surface may be used. In the case of such a roll, the molten sheet does not easily adhere to the roll, so that roll cooling is not necessarily required.

The surface roughness of the roll is preferably smooth because the roll directly touches the molten sheet. For example, the surface roughness is 1S or less, preferably 0.5S or less. Further, since the roll comes into contact with the molten sheet, its surface temperature increases. For this reason, a roll in which a metal portion and a non-adhesive portion such as fluororesin are mixed on the roll surface described above is preferable. However,
When the entire roll surface is a metal material, it is preferable to cool the inside of the roll and the roll surface to prevent sticking to the sheet. It is necessary to use an insulating refrigerant for cooling the roll, and the roll can be appropriately selected from insulating oils such as silicone oil, cold air, alternative Freon, and the like. The roll surface temperature at this time is preferably lower than the glass transition point Tg of the thermoplastic resin. Further, it is preferable to install a driving device on the roll and follow the speed of the casting drum in order to obtain a sheet having good surface properties, but a metal portion and a non-adhesive portion such as a fluororesin are mixed on the roll surface. If the roll does not require cooling, such as a roll, it may be a free roll.

On the other hand, a cooling medium that can be used in the production method of the present invention is necessary for cooling a molten sheet and obtaining an amorphous sheet. The form is preferably a drum, and it is preferable to circulate cooling water or the like inside the drum to keep the drum surface temperature constant. The drum surface is preferably a metal, for example, a surface having a surface roughness of 0.5 S or less, which is hard chrome plated, is preferred.

According to the manufacturing method of the present invention, since there is a potential difference between the roll and the cooling medium, it is necessary to pay attention to electric discharge and the like. In particular, at least the conductive portion on the roll surface is 10 mm larger than the cast sheet width. It needs to be narrower.
Also, post-processing of cast sheet (for example, stretching)
In some cases, the sheet edge portion needs to be formed thicker than the sheet central portion. In this case, the surface length of the roll itself may be smaller than the cast sheet width. However, in this case, since the film edge does not easily adhere to a cooling medium such as a drum, it is preferable to adhere the film edge portion by another method. For example, a method in which static electricity is selectively applied only to the edge portion, a method in which compressed air is blown to the edge portion to hold it down, and a method in which water or the like is applied only to the drum surface where the edge portion is applied can be adopted.

According to the present invention, a DC voltage is applied to the rolls. The insulating process is performed by using a ceramic bearing on the rotating shaft, covering the rotating shaft with a ceramic sleeve, or inserting an insulating material into the bearing base. In the case where the refrigerant is further circulated, an appropriate insulating method can be adopted depending on the device, such as connection with an insulating pipe made of nylon resin or the like.

In the method for producing a polyester film of the present invention, in addition to the method described above, the surface temperature of the cooling medium immediately before the molten sheet is grounded is maintained at a temperature not lower than the glass transition point Tg and not higher than the melting point Tm of the resin. Thus, the casting speed can be further increased. When the surface temperature of the cooling medium is equal to or higher than the glass transition point Tg, a strong adhesive force is generated between the cast sheet and the cooling medium, and the adhesion between them is improved. Further, the surface temperature of the cooling medium at the portion where the cast film is peeled off is preferably lower than the glass transition temperature Tg of the resin, whereby crystallization of the cast film is suppressed, and subsequent stretching can be performed favorably. Further, since the adhesive strength at the peeling point can be reduced, the peeling becomes easy, and the surface becomes smooth without leaving any peeling marks on the film surface.

As described above, in order to make the surface temperature of the cooling medium at which the molten sheet comes into contact with the ground to be equal to or higher than the glass transition point Tg, and to set the surface temperature of the cooling medium immediately before peeling to be lower than the glass transition point Tg, During the time from the separation from the cooling medium to the contact with the next melt, the surface of the cooling medium is heated from the outside with a strong radiant heat source such as near-infrared, infrared, or far-infrared, and the inside of the cooling medium Can be achieved by circulating a cooling medium, for example, water, having a glass transition point Tg of the resin. Usually, a drum is often used as the cooling medium, but other forms such as a belt may be used.

The temperature of the heat medium passing through the cooling medium is as follows:
Although the temperature is slightly lower than the glass transition point Tg of the thermoplastic resin, but slightly higher than the operating temperature used in the conventional method, the surface temperature when the molten sheet comes into contact is set to the glass transition point Tg or higher. It is preferable because it is possible.
Although the sheet edge is thicker than the sheet central portion, the cast method in which the adhesive force is strong as in the method of the present invention does not cause the sheet edge to crystallize due to insufficient cooling.

The film cast by the method of the present invention can be further subjected to stretching and / or heat treatment as required. Stretching is longitudinal uniaxial stretching, horizontal uniaxial stretching,
It can be carried out by various methods such as sequential biaxial stretching and simultaneous biaxial stretching, and usually a film with good mechanical balance can be obtained by biaxial stretching. Stretching can be performed by a method of performing between rolls having different peripheral speeds or a tenter method in which a sheet is gripped by a clip and the interval between the clips is changed. The stretching ratio is not particularly limited, but it is preferable to stretch in one direction by 2 to 8 times, and more preferably about 3 to 6 times. The stretching may be performed at a temperature of Tg or more. The heat treatment may be performed at a predetermined temperature as needed after stretching, and conditions may be appropriately set according to the required film characteristics.

According to the method for producing a polyester film of the present invention, a high-quality film suitable for an electric capacitor can be produced with high productivity by high-speed casting.

Next, the method for producing a polyester film in the present invention will be described more specifically.

As a raw material, a polyester resin satisfying the formula (1) or a raw material obtained by adding and blending another compound as required, for example, a liquid crystal polymer or another polyester resin, further, silicon oxide, magnesium oxide, calcium carbonate, oxide Raw materials to which inorganic compounds such as titanium, aluminum oxide, cross-linked polyester, cross-linked polystyrene, mica, talc, kaolin, etc., organic compounds such as ethylene bisstearyl amide, ionic polymer compound ionomer, etc. are added, raw materials once melted, Prepare a raw material or the like mixed with the recovered raw material of the sheet of the present invention, and after drying and dewatering, supply to a melt extruder such as a single screw extruder, a twin screw extruder, a vent extruder, a tandem extruder, Under a nitrogen stream or so as to minimize the molecular weight, for example, the intrinsic viscosity [η], as much as possible. Melt-extruding under vacuum.

Of course, the melting temperature is usually higher than the melting point Tm of the polyester resin.
Extrusion can also be carried out in a so-called supercooled state, in which the resin is melted at a temperature not lower than the melting point Tm and then cooled to the melting point Tm or lower and the melt crystallization temperature Tmc or higher. Extrusion in such a supercooled state not only has the effect of reducing the thermal decomposition and gelation of the resin, but also has the effect of reducing the generation of low-molecular-weight oligomers, thereby reducing drum contamination and facilitating casting. There is also. In order to remove foreign substances in the raw material, it is preferable to extrude the molten resin while filtering the molten resin with an appropriate filter, for example, a sintered metal, a porous ceramic, a sand, a wire mesh, or the like.

The positional relationship between the die and the casting drum is not particularly limited, but it is preferable for stable casting to adjust the molten resin sheet so as to be extruded in the vertical direction. Furthermore, the draft ratio when extruding the molten sheet from the die (= the die lip interval / the thickness of the extruded sheet) is preferably 3 or more, more preferably 7 to 20, so that the thickness unevenness is small. It is easy to obtain a sheet with good flatness.

The polyester resin thus melted is extruded from a die.
Casting is carried out so as to be sandwiched between a roll to which a voltage of 0 KV is applied and a casting drum. More preferably,
At this time, the surface temperature of the drum immediately before touchdown of the melt is
By making the glass transition point Tg or higher of the polyester resin and the melting point Tm or lower, and by setting the surface temperature of the drum immediately before peeling to be lower than the glass transition point Tg of the polyester resin, a cast having a stable, strong adhesion, that is, High-speed casting can be performed.

The cast film thus obtained is subjected to a stretching treatment as required. For example, in the case of a sequential biaxial stretching method, the cast film is first heated to Tg or more by a preheating roll, and then longitudinally rolled by rolls having different peripheral speeds. The film is stretched 2 to 8 times in the direction, and the film is cooled by a cooling roll. Next, the film stretched in the longitudinal direction is guided to a tenter-type transverse stretching machine, where both ends of the sheet are gripped by clips, and the film is heated to Tg or more by hot air.
Extend the film horizontally by widening the clips at both ends.
The film is stretched up to 8 times, and if necessary, the film is heat-treated with hot air.

The polyester film thus obtained has a smooth surface, is excellent in uniformity of thickness and quality in the width direction, and has a low ratio of a metal element / phosphorus element as a raw material, so that it can be used for an electric capacitor. It can be preferably used.

[0035]

[Measurement method of physical properties] Next, the measurement method used in the present invention will be described below. 1. Determination of metal element and phosphorus element in polyester resin For determination of metal element, put 2 g of polyester in a crucible,
It was incinerated in an electric furnace, dissolved in hydrochloric acid, and measured by an atomic absorption method. For the determination of the phosphorus element, the polyester was wet-ashed in the presence of sulfuric acid and perchloric acid, and then colored with ammonium molybdate in a sulfuric acid solution to obtain 845.
The absorbance at nm was measured and quantified by a calibration curve. 2. The intrinsic viscosity [η] of the polyester resin was determined at 25 ° C. using o-chlorophenol as a solvent by the following formula.

[Η] = lm [ηsp / c] The specific viscosity ηsp is obtained by subtracting 1 from the relative viscosity ηr. c is the concentration. The unit is expressed in dl / g. 3. Cast adhesion: The case where air or the like was bitten or sagged on the cast drum, or any other casting defect was not visible, was evaluated as ○, and the case where any defect was visible to the naked eye was evaluated as ×. 4. Cast surface properties Light is applied to a cast sheet surface of 10 m ² or more, and the reflected light is visually observed to determine the presence or absence of surface irregularities such as craters. The criteria are as follows.

No irregularities are found on the surface at all. ○ There are irregularities on the surface, but the depth is less than 0.1 μm, which is shallow and disappears by stretching. . Cast Peelability This is the ease of peeling from the cast drum. The criteria are as follows.

What peels spontaneously from the cast: ○ Can be peeled, but when the peeling force is 100 g / cm or more: Δ When peeling is difficult: × 6. Polyester Thermal Characteristics Using a DSC RDC220 model manufactured by Seiko Denshi Kogyo Co., Ltd., 20 mg of polyester was weighed, and heated at 20 ° C.
Quenched when the temperature was raised to 300 ° C. at a rate of 20 ° C./min, and the glass transition point Tg, crystallization exothermic peak temperature Tcc, and melting point Tm were measured while heating again to 300 ° C. at a rate of 20 ° C./min. did. 20 ° C after reaching 300 ° C
/ Minute, and the crystallization exothermic peak temperature Tmc was measured. 7. Insulation resistance 23 of 1000 capacitor samples with 0.1μF
In an atmosphere of 65 ° C. and 65% RH, measured as 1 minute value at an applied voltage of 500 V with a super insulation resistance meter 4329A manufactured by YHP, and a capacitor sample having an insulation resistance of less than 5000 MΩ is judged as defective according to the following criteria. did.

Less than 20 defective products ... ○ 20 or more defective products and less than 50 defective products ... △ 50 or more defective products ... × 8. Withstand voltage 1 for 1000 capacitor samples
The voltage is applied while increasing the voltage at a rate of 00 V / sec, and a voltage (breakdown voltage) when a dielectric breakdown occurs in the capacitor and a current of 5 mA or more flows is measured. The obtained breakdown voltage was converted into a voltage per unit thickness of the polyester film used as the dielectric, and the withstand voltage was calculated as an average value of 1000 samples. In addition, the capacity of the capacitor is large,
When a current of 5 mA or more flows only by the charging current, the current value is set to an appropriate value that can be separated from the charging current and the dielectric breakdown current. In the present invention, a capacitor with a withstand voltage of 450 V / μm or more was accepted.

[0040]

The present invention will be described in more detail by way of examples.

Example 1 (Polymerization of Polyester Raw Material) 86.5 parts by weight of terephthalic acid and 37.2 parts by weight of ethylene glycol were mixed to form a slurry, and the mixture was stirred while the temperature was raised to 230 ° C. to carry out an esterification reaction. Was. After completion of the esterification reaction, the reaction product was transferred to a polymerization apparatus, 0.05 parts by weight of orthophosphoric acid was added, and 0.05 parts by weight of magnesium acetate tetrahydrate was further added.
An ethylene glycol slurry containing 0.002 parts by weight of lithium acetate dihydrate, 0.03 parts by weight of antimony trioxide, and 0.08 parts by weight of synthetic calcium carbonate particles having an average particle diameter of 0.6 μm was added. The pressure in the polymerization apparatus was reduced from normal pressure to 0.5 mmHg over 2 hours, and the temperature of the reaction product was similarly increased from 230 ° C to 290 ° C over 2 hours.
The polymerization reaction was performed as described above, and the polymerization was terminated when the stirring torque of the stirring blade reached a predetermined value. The polymer was discharged from the polymerization apparatus into a water tank in a gut shape, and formed into chips by a cutter. Thus, a polyester resin having an intrinsic viscosity of 0.62, a glass transition point of Tg of 78 ° C, a crystallization temperature of Tcc of 138 ° C, a melting point of Tm of 260 ° C, and a melt crystallization temperature of Tmc of 205 ° C was obtained. M in the polyester chip
When the amounts of g, Li and P were quantified, the metal /
The phosphorus ratio was 0.60. (Film formation of polyester film) PET polymerized earlier
After being dried so that the water content of the resin becomes 20 ppm or less, the resin is supplied to a melt extruder having a screw diameter of 250 mm to be dried.
After melting at 85 ° C., the mixture was filtered through a 10 μm-cut fiber sintered metal filter, filtered, introduced into a T-die die, and extruded into a sheet. The extruded molten sheet has a diameter of 200 mm, a surface length of 800 mm, a surface having a surface roughness of 0.1 S and a surface having a surface roughness of 0.1 s, and a surface having a diameter of 1.5 m having a surface roughness of 0.1 S being hard chrome plated. While sandwiching between the casting drums, casting was performed at a surface speed of the drum and the roll of 100 m / min. At this time, a DC positive voltage of 5 KV was applied to the roll, and the drum was grounded.
A tungsten wire having a diameter of 0.2 mm was stretched between the roll and the die in the film width direction, and a positive voltage of 8 KV was applied to the wire. Cooling water was passed through the drum to set the drum surface temperature to 25 ° C., and a temperature-controlled silicone oil was circulated through the insulated roll to control the surface temperature to 25 ° C. Further, a DC positive voltage of 8 KV was applied to the film edge portion from a needle-shaped electrode to bring the edge portion into close contact.

As a result of casting in this manner,
The cast adhesiveness and cast peelability were good, and the surface properties of the obtained sheet were also good.

The cast sheet thus obtained has a size of 50 μm.
m, a width of 850 mm, an amorphous sheet having small thickness unevenness, excellent flatness, and no surface defects. Subsequently, the extruded sheet is stretched 5 times at a stretching temperature of 98 ° C. with a known roll-type longitudinal multi-stage stretching machine, cooled to Tg or less,
Subsequently, both ends of the longitudinally stretched sheet are guided to a tenter while gripping both ends with clips, stretched 4.3 times in the width direction in a hot air atmosphere heated to a stretching temperature of 100 ° C, and heat-fixed at a constant length at 220 ° C, and 3% relaxed heat fixing was performed in the width direction at 150 ° C., and a biaxially oriented laminated polyester sheet having a thickness of 4 μm was wound up at a high speed of about 500 m / min in a stable state without breaking.

The sheet thus obtained was a sheet having excellent flatness without any surface defects. (Preparation of capacitor) Aluminum was deposited on one surface of the obtained stretched film so that the surface resistance was 2 Ω / □. At this time, vapor deposition was performed in a stripe shape having a margin portion running in the longitudinal direction. Next, a blade is inserted into the center of each vapor deposition section and the center of each margin section and slit.
It was a tape-shaped take-up reel having a total width of 30 mm and a margin of 30 mm.

One of each of the left and right margins of the obtained reel was overlapped and wound to obtain a capacitor element having a capacitance of 0.1 μF. This condenser element was heated at 130 ° C. and a temperature and pressure of 20 kg / cm ² for 5 minutes.
Pressed for minutes. Metallicon is sprayed on both ends to form external electrodes, the lead wire is welded to the metallicon, and the exterior is cured with epoxy resin to form a wound capacitor. The capacitor is subjected to voltage treatment once at 800 V DC for 30 seconds. This was performed once again with the polarity applied to the two lead wires reversed. The characteristics as a capacitor are shown in Table 1 and were good. Table 1 shows the results.

Examples 2, 4, 5 and Comparative Example 1 A polyester resin was polymerized in the same manner and under the same conditions as in Example 1 except that the amounts of magnesium acetate, lithium acetate and orthophosphoric acid were changed when polymerizing the polyester. Then, casting, stretching, and formation of a capacitor were performed in the same manner and under the same conditions as in Example 1. The results are shown in Table 1. When it was within the range of the present invention, the castability was good and the capacitor was excellent.

Example 3 As a raw material, the polyester resin prepared in Example 2 was used.

In addition to the film forming apparatus of Example 2, a near-infrared heater having an output of 60 KW capable of heating a grounded casting drum was installed between the sheet peeling portion and the ground portion of the casting drum. Warm water maintained at 49 ° C. was circulated through the casting drum, and the surface of the drum was heated by a near-infrared heater. In this way 2
A positive voltage of 6 KV was applied to the roll kept at 5 ° C., and the roll was cast as in Example 1. At this time, the drum surface temperature immediately before the sheet was grounded was 91 ° C., and the drum surface temperature at the portion where the sheet was separated was 49 ° C. As a result of casting in this manner, a sheet film excellent in both quality and productivity could be formed. Table 1 shows the results. Comparative Example 2 A sheet was formed in the same manner as in Example 1 except that the voltage applied to the roll was set to 0. The cast adhesion and surface properties were poor, the sheet width also fluctuated greatly, and clips were frequently dislodged in the transverse stretching step. Further, irregularities were present on the surface of the stretched sheet, and both the quality and the productivity were inferior. Table 1 shows the results.

[0049]

[Table 1]

[0050]

The casting speed can be increased by casting a molten polyester film while sandwiching it between a charged roll and a cooling medium, using a polyester raw material having a small metal element / phosphorus element ratio, whereby a film having a smooth surface can be obtained. It can be obtained with good productivity. The film obtained by the method of the present invention is suitable as a film for an electric capacitor.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) B29L 7:00 F term (reference) 4F071 AA44 AH12 BB02 BB06 BB07 BB13 BC01 4F207 AA24 AG01 AH33 AM28 AM30 AR06 KA01 KA17 KK13 KK56 KK66 KL41 KL84 KW41 4F210 AD05 AD08 AG01 AH33 QA02 QA03 QC06 QD13 QD32 QD44 QG01 QG18 4J002 CF041 CF061 FD030 FD200

Claims (7)

[Claims] After the polyester resin is melted, a molten sheet is discharged from a die, the sheet is cooled while being sandwiched between a charging roll and a cooling medium, and the sheet is cooled and solidified on a cooling medium to produce a cast film. A method that satisfies the following formula (1): 0.4 ≦ (m / 2 + N + L) /P≦1.2 Formula (1) m: mole number of alkali metal per ton of polyester resin N: mole number of alkaline earth metal per ton of polyester resin L: polyester Mn, Co, Zn per ton of resin
P: Number of moles of phosphorus element per ton of polyester resin 2. The method for producing a polyester film according to claim 1, wherein a charge having the same polarity as that of the roll is applied to the surface of the melt sheet before the melt sheet comes into contact with the roll. 3. The method for producing a polyester film according to claim 1, wherein the surface temperature of the cooling medium immediately before the molten sheet is grounded is equal to or higher than the glass transition point Tg and equal to or lower than the melting point Tm of the polyester resin. . 4. The method according to claim 1, wherein when the polyester resin cast film solidified and cooled on the cooling medium is peeled off from the cooling medium, the surface temperature of the cooling medium at the peeling point is not more than the glass transition point Tg of the polyester resin. The method for producing a polyester film according to claim 3, wherein 5. The method for producing a polyester film according to claim 1, wherein the width of the current-carrying portion on the roll surface is shorter than the width of the cast film by 10 mm or more. 6. The method for producing a polyester film according to claim 1, wherein the cast film is stretched and / or heat-treated. 7. The produced film is used for an electric capacitor.
The method for producing a polyester film according to any one of the above.