JP2008030223A - Biaxially stretched polyester film for capacitor, metallized film and film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film for a capacitor, more improved in processability and voltage resistance when used as a capacitor by controlling in specific ranges, the coefficient μsm of static friction parallel to the longitudinal direction of the film, and the coefficient μst parallel to the lateral direction of the film. <P>SOLUTION: When the coefficient of static friction parallel to the longitudinal direction of the film is set at μsm and the coefficient parallel to the lateral direction of the film is set at μst, both of the coefficients μsm and μst of static friction are within a range of 0.40-1.20, and the ratio (μsm/μst) of the coefficient μsm of static friction and the coefficient μst of static friction is 0.70-below 1.05. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polyester film for capacitors having good electrical characteristics, good thickness uniformity, and excellent handling properties. More specifically, the present invention relates to productivity, workability, and withstand voltage. The present invention relates to a biaxially stretched polyester film for capacitors having excellent properties, a metallized film using the same, and a film capacitor.

  Conventionally, a film capacitor using an organic polymer film as a dielectric has been widely used, and in particular, a polyester film and a metal foil are alternately wound or metal is deposited on a polyester film to form an electrode. A technique for obtaining a film capacitor by winding or laminating is known (see Patent Document 1).

  In addition, most of these polyester films for capacitors are roughened by adding inorganic particles or organic particles, etc., and workability, that is, slitting, winding or laminating properties in the film capacitor manufacturing process. Etc. are secured (see Patent Document 2). However, if the surface is roughened by adding particles in order to pursue workability, the characteristics of the film capacitor itself tend to deteriorate.

  In recent years, with the miniaturization of electrical equipment, the demand for miniaturization of film capacitors has also increased. Since the film used under such circumstances is further thinned and the potential gradient applied to the film is increased, the film capacitor may cause a problem of dielectric breakdown.

  In order to solve such problems, a method has been proposed for improving the withstand voltage characteristics of a film capacitor by defining the metal and phosphorus residual amount in the film and setting the surface roughness within a specific range (Patent Document 3). reference).

There is also a proposal to improve the wear resistance in the longitudinal direction by defining the ratio of the Young's modulus of the film and the static friction coefficient in the longitudinal and width directions and making the static friction coefficient in the longitudinal direction larger than the static friction coefficient in the width direction. (Patent Document 4).
JP 63-194318 A JP-A-6-31453 JP-A-9-302111 JP 2000-25107 A

  However, the methods proposed in the above Patent Documents 3 and 4 are not sufficiently satisfactory in the withstand voltage improvement level, and further improvement in withstand voltage and workability has been demanded. Furthermore, in the method proposed in Patent Document 4, the capacitor vapor deposition processing of a thin film with a thickness of 10 μm or less is likely to cause conveyance meandering during the vapor deposition, and also causes a heat loss defect due to width shrinkage on the can drum. There was also. Accordingly, an object of the present invention is to provide a polyester film and a metallized film for a biaxially stretched capacitor that can solve such problems and can improve the workability and withstand voltage particularly when a film capacitor is used.

  Another object of the present invention is to provide a film capacitor having improved withstand voltage characteristics using the above-described biaxially stretched polyester film or metallized film.

  The present inventors have conceived the present invention as a result of intensive studies in order to solve the above problems. In the biaxially stretched polyester film for capacitors of the present invention, when the static friction coefficient parallel to the film longitudinal direction is μsm and the static friction coefficient parallel to the film width direction is μst, the static friction coefficient μsm and the static friction coefficient μst are both 0. A biaxially stretched polyester film for capacitors, characterized in that it is in the range of 40 to 1.20, and the ratio (μsm / μst) of the static friction coefficient μsm to the static friction coefficient μst is 0.70 or more and less than 1.05. is there.

According to a preferred embodiment of the biaxially stretched polyester film for capacitors of the present invention, the film thickness t1 (μm) by the micrometer method and the film thickness t2 (μm) by the weight method satisfy the following formula (1), and the film surface The center line average roughness Ra (nm) satisfies the following formula (2).
t2 ≦ t1 ≦ 1.05 × t2 + 0.25 (1)
20 ≦ Ra ≦ 75 (2)
According to a preferred embodiment of the biaxially stretched polyester film for capacitors of the present invention, the biaxially stretched polyester film for capacitors of the present invention has a film thickness t2 by a weight method in the range of 0.5 to 10.0 μm, and The plane orientation coefficient fn is in the range of 0.155 to 0.180.

  According to a preferred embodiment of the biaxially stretched polyester film for capacitors of the present invention, the biaxially stretched polyester film for capacitors of the present invention is formed and produced by a simultaneous biaxial stretching method.

  According to a preferred embodiment of the present invention, a metallized film having a surface electrical resistance in the range of 1 to 20Ω / □ is prepared by providing a metal film on at least one side of the biaxially stretched polyester film for capacitors of the present invention. However, a film capacitor can be produced using the biaxially stretched polyester film for a capacitor of the present invention or a metallized film thereof.

  According to the present invention, it is possible to obtain a biaxially stretched polyester film for a capacitor and a metallized film, which are excellent in workability in a vapor deposition process, processability in an element process of a film capacitor and withstand voltage. Further, according to the present invention, a film capacitor having improved withstand voltage characteristics can be obtained.

  Hereinafter, the biaxially stretched polyester film for capacitors of the present invention, and the metallized film and film capacitor will be described in more detail.

  The biaxially stretched polyester film for capacitors according to the present invention has a static friction coefficient μsm and a static friction coefficient μst of 0 when the static friction coefficient parallel to the film longitudinal direction is μsm and the static friction coefficient parallel to the film width direction is μst. A polyester film having a ratio between the static friction coefficient μsm and the static friction coefficient μst (μsm / μst) of 0.70 or more and less than 1.05.

  When the static friction coefficient μsm parallel to the film longitudinal direction and the static friction coefficient μst parallel to the film width direction are less than 0.40, the degree of adhesion to the cooling can during deposition processing is poor and heat damage is liable to occur during deposition. Is likely to occur. In addition, after the capacitor element winding process, the pressability of the capacitor element deteriorates. In addition, if the static friction coefficient μsm parallel to the film longitudinal direction and the static friction coefficient μst parallel to the film width direction exceed 1.20, defects are likely to occur during transportation in the vapor deposition process, slit process and capacitor element winding process. It becomes. In particular, in the capacitor element winding process, wrinkles are likely to occur, the interlayer gap is narrow, local interlayer adhesion occurs, and the breakdown voltage tends to decrease due to electric field concentration.

  A more preferable range of the static friction coefficient μsm parallel to the film longitudinal direction and the static friction coefficient μst parallel to the film width direction is in the range of 0.50 to 1.10, and further defects in the vapor deposition process, the slit process, and the capacitor element process. Is improved and a film excellent in processability is obtained.

  Also, if the ratio of the static friction coefficient μsm to the static friction coefficient μst (μsm / μst) is smaller than 0.70, the degree of adhesion to the cooling can during the vapor deposition process will be biased and wrinkles will easily occur when shrinking in the film width direction. , It is easy to cause a defect of film loss. Further, when the ratio (μsm / μst) is 1.05 or more, it is not preferable because it tends to be shifted in the film width direction at the time of adhesion to the cooling can during vapor deposition and causes a margin blur. In particular, when margin accuracy is required, the ratio (μsm / μst) is preferably 0.70 or more and 0.85 or less. By doing in this way, there are no faults, such as a margin blur, and vapor deposition workability improves remarkably.

  A known method can be used as a method for measuring the static friction coefficient. For example, a rectangular sample cut into a length of 10 cm and a width of 7.5 cm in each of the longitudinal direction of the film and the width direction of the film is collected, and the sample A surface / B surface (front surface / back surface) is slipped using a slip tester. It can be measured under conditions of a speed of 15 cm / min, a load of 200 g, a temperature of 23 ° C., and a humidity of 65% RH.

  Here, the technical background of the present invention will be described. In order to improve the vapor deposition processability of the polyester film, it is necessary to control the adhesion between the polyester film surface and the can. In addition, in order to improve the workability of the capacitor element, the ease of slipping during pressing is important, and it is necessary to reduce local interlayer adhesion and residual stress. The coefficient of static friction measured by the slip tester method is an index suitable for expressing the adhesion and slipperiness that are closely related to the vapor deposition processability and the capacitor element processability of the polyester film. It was found that the surface roughness is clearly different. In particular, unlike conventional roughness, by defining the static friction coefficient in the film longitudinal direction (film running direction) and the film width direction in close contact with the can, suitable vapor deposition processability, element processability, and high withstand voltage are obtained. Became possible.

In addition, the biaxially stretched polyester film of the present invention has a tensile strength parallel to the film longitudinal direction, Ex (MPa), and a tensile strength parallel to the film width direction, Ey (MPa). It is preferable that the formula (3b) is satisfied at the same time. Thus, by defining the strength of the polyester film, the film-forming stability, productivity, withstand voltage and workability of the film can be improved.
・ Ex + Ey ≧ 350 (3a)
0.70 ≦ Ex / Ey ≦ 1.35 (3b).

  Here, the longitudinal direction of the film refers to the film running direction, and the width direction of the film refers to a direction perpendicular to the longitudinal direction. Moreover, a well-known method can be used for the measuring method of tensile strength Ex and tensile strength Ey.

  Each of the tensile strength Ex and the tensile strength Ey is preferably 160 or more, and there is little fluctuation in tension on the unwinding and winding side during deposition, and the running property during deposition is stable.

  In the biaxially stretched polyester film for capacitors of the present invention, the film thickness t2 by the weight method is preferably 0.5 to 10.0 μm from the viewpoint of capacitor element size and film formation stability. The film thickness t2 by the weight method is more preferably 0.8 to 5.0 μm, and particularly preferably 1.0 to 3.0 μm.

In the polyester film for capacitors of the present invention, the film thickness t1 (μm) by the micrometer method and the film thickness t2 (μm) by the weight method satisfy the following formula (1), and the center line average of the film surface It is preferable that the roughness Ra (nm) satisfies the following formula (2). Thus, by defining the film thickness and the centerline average roughness, it is possible to improve film formation stability, vapor deposition / element workability, and withstand voltage.
T2 ≦ t1 ≦ 1.05 × t2 + 0.25 (1)
20 ≦ Ra ≦ 75 (2).

Furthermore, by making the above-mentioned centerline average roughness Ra within the range of the following formula (4), the workability and the charged voltage are further improved, and the above-mentioned film thickness t1 and film thickness t2 are represented by the following formula (5). By setting it as the range, when the film is wound up in a roll shape, the amount of air between the film layers is smaller, and the slit processability and the vapor deposition processability are further improved.
・ 25 ≦ Ra ≦ 70 (4)
T2 ≦ t1 ≦ 1.05 × t2 + 0.20 (5)

  In addition, the plane orientation coefficient fn of the biaxially stretched polyester film for capacitors of the present invention is preferably in the range of 0.155 to 0.180 from the viewpoint of withstand voltage. The particularly preferred plane orientation coefficient fn is in the range of 0.160 to 0.180, and the withstand voltage is further improved by defining the plane orientation coefficient fn in this way.

  The biaxially stretched polyester film for capacitors of the present invention preferably has a low content of electrically conductive ions and the like from the viewpoint of insulation resistance and withstand voltage. A metal compound may be added as a catalyst for polymerizing polyester. However, since metal ions are deactivated by phosphorus, the total amount M of metal elements such as Ca, Mg, Li and Mn in the polyester film. The amount of M−P obtained by subtracting the phosphorus amount P from the amount can be used as the index. This metal ion residual amount MP is preferably 200 ppm or less, more preferably 170 ppm or less, and even more preferably 150 ppm or less, from the viewpoints of insulation resistance and voltage resistance.

  Further, the amount of Na element in the polyester film is preferably 4 ppm or less, and more preferably 2 ppm or less. Furthermore, the total amount of Li, Sb, Ca, Mg, and Mn in the polyester film is preferably 100 to 1000 ppm, more preferably 100 to 700 ppm, and the content of chlorine (Cl) is 2 ppm or less. It is easy to obtain a stable film formation without breakage or uneven application, and a polyester film having good insulation resistance and withstand voltage can be suitably obtained.

  The polyester used in the biaxially stretched polyester film for capacitors of the present invention is a polyester mainly composed of aromatic dicarboxylic acid or aliphatic dicarboxylic acid and diol.

  Here, as the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′- Biphenyl dicarboxylic acid, 4,4'-biphenyl ether dicarboxylic acid, 4,4'-biphenyl sulfone dicarboxylic acid, and the like can be used. Of these, terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferably used. Examples of the aliphatic dicarboxylic acid that can be used include adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. These acid components may be used singly or in combination of two or more, and may be partially copolymerized with oxyacids such as hydroxybenzoic acid.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol and 2,2'-bis (4 '-Β-hydroxyethoxyphenyl) propane or the like can be used. Of these, ethylene glycol, 1,4-butanediol and 1,6-hexanediol are preferably used. These diol components may be used alone or in combination of two or more.

  Specific examples of the polyester used in the biaxially stretched polyester film for capacitors of the present invention include, for example, polyethylene terephthalate, a copolymer of ethylene terephthalate and ethylene isophthalate, a copolymer of ethylene terephthalate and ethylene naphthalate, hexa Examples thereof include a copolymer of methylene terephthalate and cyclohexanedimethylene terephthalate and a blend of polyethylene terephthalate and polybutylene terephthalate. From the viewpoint of voltage resistance, long-term heat resistance and stretchability, polyethylene terephthalate and / or polyethylene Polyester mainly composed of naphthalate is preferable.

  The thermal contraction rate of the biaxially stretched polyester film for capacitors of the present invention is 0.5 to 5% in the film longitudinal direction and -1.0 to 2.5% in the film width direction from the viewpoint of withstand voltage. It is preferable. The above heat shrinkage ratio is more preferably 1.0 to 5.0% in the film longitudinal direction and 0 to 2.5% in the film width direction. By setting the heat shrinkage rate within the above range, the adhesion with the can during vapor deposition is improved, and the workability can be improved.

  Next, although the preferable manufacturing method of the biaxially stretched polyester film for capacitors of the present invention is explained, the present invention is not limited to this.

  The polyester used in the present invention can be produced by the following method. For example, a method in which an acid component is directly esterified with a diol component, and then the reaction product is heated under reduced pressure to perform polycondensation while removing excess diol component, or a dialkyl ester as an acid component And a diol component and a transesterification reaction, followed by polycondensation in the same manner as described above. At that time, antimony oxide, germanium oxide, titanium compound and the like can be used as a polymerization catalyst. Furthermore, when a dialkyl ester is used as a raw material as an acid component, an alkali metal, alkaline earth metal and Compounds such as manganese, in particular their acetates can be used.

  If necessary, the polyester used in the present invention may be an organic material such as a coloring inhibitor (phosphorus compound), a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a pigment, a fatty acid ester, and a wax. A lubricant and an antifoaming agent such as polysiloxane can be blended. Furthermore, in order to impart slipperiness, for example, inorganic particles such as clay, mica, titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, acrylic acid polymers, cross-linked polystyrene, and silicone are added. Organic particles or the like as constituent components can also be blended. Moreover, the method by what is called an internal particle formed by deactivating the catalyst etc. which are added at the time of polyester polymerization reaction can also be used.

  In this invention, in order to make a static friction coefficient into the above-mentioned range, while adjusting the surface roughness of a polyester film, it can achieve by adjusting extending | stretching conditions. The stretching method may be either a sequential biaxial stretching method or a simultaneous biaxial stretching method, but a simultaneous biaxial stretching method is preferred. In particular, the stenter simultaneous biaxial stretching method is preferably used from the viewpoint of film formation stability and thickness uniformity.

  In the case of the stenter simultaneous biaxial stretching method, for example, polyester is extruded onto a cast drum by a T-die extrusion method to form an unstretched film, and then stretched simultaneously in the film longitudinal direction and the film width direction. The stretching temperature is preferably between the glass transition temperature (Tg) and the temperature-rising crystallization temperature (Tcc) of the polyester used for stretching. The draw ratio is not particularly limited and is appropriately selected depending on the type of polymer used. A preferable draw ratio is 2 to 8 times in the film longitudinal direction and the film width direction, respectively, and more preferably 3 to 6 times. Moreover, after biaxial stretching, you may re-stretch in a film longitudinal direction or a film width direction, or a film longitudinal direction and a film width direction. In particular, in order to make the coefficient of static friction within the above-mentioned range of the present invention, it is preferable that the total stretching ratio in the film longitudinal direction is 1.30 times or less of the total stretching ratio in the film width direction, and further, re-stretching is performed in the film longitudinal direction. It is preferable that the film is simultaneously stretched by 1.03 to 2.50 times in the direction or the film width direction, or in the film longitudinal direction and the film width direction. In particular, it is preferable to simultaneously stretch the film in the longitudinal direction and the film width direction at the same time as the total stretching ratio in the longitudinal direction by 1.03 to 1.30 times the total stretching ratio in the width direction by simultaneous biaxial stretching. By re-stretching in the direction at 1.03 to 1.30 times, the static friction coefficient can be more easily set within the above-described range of the present invention.

  Further, in the case of simultaneous biaxial stretching, the tensile strength can be easily within a preferred range by stretching 3.5 to 4.8 times at the same time in the vertical and horizontal directions, and the plane orientation coefficient is easily set to 0.155 to 0.00. A range of 180 is also possible.

  Furthermore, in this invention, it is preferable to heat-process the polyester film after biaxial stretching. The heat treatment temperature is preferably 2 to 30 seconds at a film temperature of 180 ° C. to 250 ° C. from the viewpoint of improving the withstand voltage. Subsequent to the heat treatment, the relaxation treatment is preferably performed in the range of 1 to 10%. It is also a preferable method that the polyester film obtained by the heat treatment is once cooled to about room temperature and then aged at a temperature in the range of 40 to 90 ° C. for about 5 seconds to 1 week. By performing aging, the withstand voltage can be further improved. When a metal film is provided on the polyester film surface, aging may be performed after the metal film is provided.

  In the present invention, in order to control the surface roughness of the polyester film, for example, a desired surface can be obtained by adding inert particles in the polyester film. As the inert particles added to the polyester film, for example, inorganic particles such as silica, calcium carbonate, titanium oxide, kaolin, talc and alumina, and organic particles such as crosslinked polystyrene and silicone can be used. The average particle size of the particles to be added is preferably 0.1 to 5 μm, more preferably 0.5 to 2 μm. Further, the amount of particles added is preferably 0.02 to 2%, more preferably 0.05 to 1%. The particles can be added at any stage of the polymer production process, or preferably at the initial stage of the esterification process or transesterification process, and further the polymerization process.

  Further, the additive particles are preferably used as a slurry of a diol component used as a raw material, for example, ethylene glycol, subjected to dispersion by a jet agitator or media dispersion, and further filtered to remove coarse particles. . Further, a dispersant may be added as appropriate. Use of a dispersant improves dispersion and reduces coarse particles, thereby suppressing the occurrence of coarse protrusions on the surface of the polyester film, suppressing the generation of voids around the particles, and adversely affecting insulation resistance and withstand voltage. Is effective in obtaining the preferable surface roughness of the present invention.

  Moreover, when providing a primer layer on a polyester film, particle | grains can be added to a primer layer and desired surface roughness can also be obtained.

  In the present invention, the method for forming a metallized film by providing a metal film on the surface of the polyester film is not particularly limited. For example, an aluminum vapor-deposited film serving as an internal electrode of a film capacitor by depositing aluminum on at least one side of the polyester film The method of providing the metal film is preferably used. At this time, other metal components such as nickel, copper, gold, silver, chromium, and zinc can be deposited simultaneously or sequentially with aluminum. In addition, a protective layer can be provided on the deposited film with oil or the like.

  The thickness of the metal film is preferably in the range of 20 to 100 nm from the viewpoint of electrical characteristics and self-heeling properties of the film capacitor. For the same reason, the surface electrical resistance value of the metal film is preferably in the range of 1 to 20Ω / □. The surface electrical resistance value can be controlled by the type of metal used and the film thickness. Here, the surface electrical resistance can be measured by a known method.

  In the present invention, if necessary, after the metal film is formed, the metallized film can be subjected to an aging treatment at a specific temperature or a heat treatment. Also, a coating such as polyphenylene oxide can be applied to at least one side of the metallized film for insulation or other purposes.

  The metallized film thus obtained can be laminated or wound by a known method to obtain a film capacitor. An example of a preferred method for producing a wound film capacitor is as follows.

  Aluminum is vacuum deposited on both sides of the polyester film. In that case, it vapor-deposits in the stripe form which has the margin part which runs in a film longitudinal direction. Arbitrary single side | surface is prescribed | regulated as a surface, and it deposits by shifting so that the pattern of a surface and a back surface may become alternate. Next, a tape-shaped take-up reel in which a blade is inserted and slit at the center of each vapor deposition section and the center of each margin section on the front surface, with the front surface having a margin on one side and the back surface having a margin on the opposite side. And The obtained reel and one each of the laminated films not having the metal film are overlapped and wound so that the metallized film protrudes from the laminated film in the width direction, and a wound body is obtained. The core material is removed from the wound body and pressed, and the metallicon is sprayed on both end faces to form external electrodes, and a lead wire is welded to the metallicon to obtain a wound capacitor element.

  Film capacitors are used in a wide variety of applications, such as audio, home appliances (TVs, air conditioners, etc.), general noise prevention, automobiles (power windows, wipers, etc.) and power supplies.

  Hereinafter, the present invention will be described based on examples. In the examples, each physical property was measured by the following method.

(1) Static friction coefficient (μsm, μst)
Five rectangular samples each cut into a length of 10 cm and a width of 7.5 cm in the longitudinal direction and the width direction of the film were collected. Sample A surface / B surface (front surface / back surface) is measured under the conditions of a sliding speed of 15 cm / min using a Technone's slip tester, a load of 200 g, a temperature of 23 ° C., and a humidity of 65% RH. The coefficient of static friction was expressed as an average of three samples out of five samples, each of which was removed one by one.

(2) Tensile strength (Ex, Ey)
Five strip samples each cut to a width of 1.0 cm and a length of 20 cm in the longitudinal direction and the width direction of the film were collected. Using a Tensilon tensile tester manufactured by Toyo Sokki, the sample is held at a test length of 10 cm and pulled at a speed of 30 cm / min until the film breaks, and the load-elongation relationship is recorded. The maximum load at that time was defined as the tensile strength, and the tensile strength (Ex, Ey) in each of the longitudinal direction and the width direction of the film was expressed as an average of 5 samples.

(3) Plane orientation coefficient (fn)
According to the method defined in JIS-K7105 (1981 edition), the refractive index in the longitudinal direction, the width direction and the thickness direction was measured using an Abbe refractometer with the sodium D line as a light source (the refractive index in each direction was determined). NMD, nTD, and nZD, respectively). Methylene iodide was used as the mounting solution, and measurement was performed under the conditions of a temperature of 25 ° C. and a humidity of 65% RH, and the plane orientation coefficient fn was calculated by the following equation.
-Planar orientation coefficient fn = (nMD + nTD) / 2-nZD
(4) Film surface roughness (centerline average roughness Ra)
Using a two-dimensional surface roughness meter SE3500 manufactured by Kosaka Laboratory, the surface roughness of the film was measured by the stylus type under the following conditions.
・ Tip tip diameter: 5μR
-Stylus load: 0.7mN
・ Measurement length: 4mm
・ Cutoff value: 0.25mm
When the roughness curve f (x) is obtained under the above conditions, the center line average roughness Ra is given by the following equation.
Ra = (1 / L) .∫ | f (x) | dx
(However, L: measurement length = 4 mm, integration interval: 0 to L).

(5) Film thickness (μm)
A. Micrometer thickness (t1): Ten samples were measured in the width direction and the length direction of the film using a micrometer, and the average value was used.

B. Thickness by weight method (t2): The weight of the measurement sample was measured and obtained from the following calculation formula.
T2 (μm) = film weight (g) / ((film width (m) × film length (m) × density))
(However, the density of polyethylene terephthalate was 1.40).

(6) Deposition processability Aluminum is vacuum-deposited on one side of the polyester film so that the surface resistance is 2Ω / □. At that time, vapor deposition was performed in a stripe shape so as to have a margin portion running in the longitudinal direction (repetition of a vapor deposition portion width of 39.0 mm and a margin portion width of 1.0 mm). The condition of conveyance up to the can during vapor deposition is good. A marginal deviation caused by a deviation in the width direction or the like, and a deviation amount of less than 0.30 mm can be used practically, and is judged as “good”. The above-mentioned marginal deviation of 0.30 mm or more was deemed unusable and was judged as a defective “x”.

(7) Workability in the production of film capacitors (element winding yield)
Aluminum was vacuum-deposited on one side of the polyester film so that the surface resistance was 2Ω / □. At that time, vapor deposition was performed in a stripe shape so as to have a margin portion running in the longitudinal direction (repetition of a vapor deposition portion width of 39.0 mm and a margin portion width of 1.0 mm). Next, a blade was inserted in the center of each vapor deposition section and the center of each margin section, slitted, wound into a tape having a width of 20 mm having a margin of 0.5 mm on the left or right, and made into a reel. Two reels each having a left margin and a right margin were overlapped and wound so that the vapor deposition portion protruded 0.5 mm from the margin portion in the width direction, and wound with a capacitance of about 20 μF. Got. KAW-4NHB manufactured by Minato Seisakusho was used for element winding. The core material was removed from the wound body and pressed as it was at a temperature of 130 ° C. and a pressure of 20 kg / cm ² for 5 minutes. Metallicon was sprayed on both end faces to form external electrodes, and lead wires were welded to the metallicon to obtain a wound type film capacitor element.

  When manufacturing the above film capacitor, visually observe from the beginning of winding to the end of winding, reject those wrinkles and deviations, and indicate the percentage of the number of rejected products as a percentage This was used as an index of workability (hereinafter referred to as element winding yield). The higher the element winding yield, the better. An element winding yield of 95% or more was evaluated as “Excellent”, an element less than 95% as 80% or more was evaluated as “Good”, and an element winding yield of less than 80% was evaluated as “Poor”. Good or better “Δ” is a practical level.

(8) Withstand voltage evaluation Using the film capacitor element obtained by the above method as a sample, using a Kasuga high-voltage DC power supply, applying a voltage while boosting at a rate of 100 V / second, and flowing 10 mA or more It was assumed that dielectric breakdown occurred. The dielectric breakdown voltage was defined as a withstand voltage value obtained by dividing the average value of 50 measurement results by the film thickness. Those with a withstand voltage of 0.350 kv / μm or higher were evaluated as good and evaluated as “good”, and less than 0.350 kv / μm was evaluated as “poor”.

(9) Film-forming stability evaluation Wrinkles and tears of the film were evaluated by visual observation at a film-forming speed of 230 m / min. Evaluation is as follows.

  The case where there was no wrinkle, applied unevenness and tearing on the film was rated as “Good”, and the occurrence of wrinkling, applied unevenness or tearing on the film was visually observed once or twice for 24 hours of film formation. In the case where wrinkles, applied unevenness or tearing of the film was visually observed 3 times or more per 24 hours of film formation, the film was evaluated as defective “x”. Good “Δ” or higher is a practical level at the time of film formation.

(Example 1)
Polyethylene terephthalate was used as the polyester resin. In the polymerization stage of polyethylene terephthalate, 0.10% by weight of agglomerated silica particles having an average particle size of 1.5 μm, ethylene terephthalate, 250 ppm of calcium acetate, 250 ppm of antimony trioxide as a polymerization catalyst, phosphorous acid and dimethylphenylphosphonate, etc. An amount of mixed phosphorus compound of 130 ppm was added by a known method to produce a chip. Agglomerated silica to be added was made into a 10% ethylene glycol slurry, dispersed with a jet agitator, filtered through a filter having an opening of 10 μm, and then added.

  The polyester chip thus obtained was vacuum dried at a temperature of 180 ° C., supplied to an extruder, melted at a temperature of 285 ° C., then discharged from a T-die to form a sheet, and cast with a cooling drum. This sheet was stretched 3.7 times at a temperature of 95 ° C. at the same time in the longitudinal direction of the film and in the width direction of the film with a linear motor type simultaneous biaxial stretching machine at a film forming speed of 230 m / min, and subsequently at a temperature of 235 ° C. After heat treatment, the film was subjected to a relaxation treatment of 2.0% in the film longitudinal direction and 3.0% in the film width direction at a temperature of 170 ° C., the thickness by weight (t2) was 2.70 μm, and the thickness by micrometer (t1) Gave a biaxially stretched polyester film of 2.92 μm. The obtained biaxially stretched polyester film has a surface roughness Ra of 48 nm, a plane orientation coefficient (fn) of 0.168, a static friction coefficient (μsm) parallel to the film longitudinal direction of 0.85, and a film width direction. The coefficient of static friction (μst) parallel to λ was 0.95, and the ratio of μsm / μst was 0.89. In film formation, no unevenness in electrostatic application, wrinkles or tearing was observed during casting, and the film formation property was excellent “◯”.

  Next, aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one side of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a film capacitor. As a result, the vapor deposition processability was satisfactory and excellent, “Excellent”, the element winding yield of the capacitor element was 99%, and the withstand voltage was. It was excellent “◯” at 373 kV. The results are shown in Table 1.

(Example 2)
Using a simultaneous biaxial stretching machine, the film was stretched 3.0 times at 95 ° C at the same time in the film longitudinal direction and the film width direction, and then stretched 1.5 times at the same time in the film longitudinal direction and the film width direction at 170 ° C. Produced a biaxially stretched polyester film in the same manner as in Example 1. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a gravimetric thickness of 2.70 μm and a micrometer thickness of 2.89 μm. The surface roughness (Ra) of the film is 30 nm, and the plane orientation The coefficient (fn) was 0.173, μsm was 1.04, μst was 1.19, and the ratio of μsm / μst was 0.87. In the film formation, no electrostatic application unevenness and wrinkles were observed during casting, but tearing was observed once per 24 hours of film formation, and the film formation property was good “Δ”.

  Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one side of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a film capacitor. As a result, the vapor deposition workability was excellent and excellent “◯” with no marginal deviation, the element winding yield of the capacitor element was 94%, and the withstand voltage was 0.396 kV, which was excellent “◯”. The results are shown in Table 1.

(Example 3)
A biaxially stretched polyester film was produced in the same manner as in Example 1 except that the film was stretched 4.0 times in the longitudinal direction at a temperature of 95 ° C. and then stretched 3.5 times in the width direction at a temperature of 105 ° C. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a weight method thickness of 2.70 μm and a micrometer method thickness of 2.98 μm. The surface roughness (Ra) of the film is 45 nm, and the plane orientation The coefficient (fn) was 0.166, μsm was 0.96, μst was 0.92, and the ratio of μsm / μst was 1.04. In the film formation, no unevenness in electrostatic application, wrinkles, tearing, etc. were observed during casting, and the film formation was good and excellent “◯”.

  Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one surface of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a capacitor. As a result, the deposition processability was good “Δ” with a margin shift of 0.20 mm. Further, the element winding yield of the capacitor element was 97%, the withstand voltage was 0.360 kV, and excellent “◯”. The results are shown in Table 1.

Example 4
The amount of agglomerated silica particles in the polyester chip was 0.15% by weight, and the film was stretched 3.8 times at 95 ° C. at the same time in the film longitudinal direction and film width direction using a simultaneous biaxial stretching machine, and then at a temperature of 170 ° C. A biaxially stretched polyester film was produced in the same manner as in Example 1 except that the film was further stretched 1.05 times in the film width direction. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a gravimetric thickness of 2.00 μm and a micrometer thickness of 2.24 μm. The surface roughness (Ra) of the film is 42 nm, and the plane orientation The coefficient (fn) was 0.170, μsm was 0.61, μst was 0.78, and the ratio of μsm / μst was 0.78. In the film formation, no unevenness in electrostatic application, wrinkles, tearing, etc. were observed during casting, and the film formation property was good and excellent “◯”.

  Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one side of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a capacitor. As a result, the vapor deposition workability was excellent “◯” with no margin shift. The element winding yield of the capacitor element was 99%, and the withstand voltage was 0.380 kV, which was excellent “◯”. The results are shown in Table 1.

(Example 5)
The amount of aggregated silica particles in the polyester chip was 0.15% by weight, and the film was simultaneously stretched 3.8 times in the film longitudinal direction and 3.5 times in the film width direction at a temperature of 95 ° C. with a simultaneous biaxial stretching machine. A biaxially stretched polyester film was produced in the same manner as in Example 1 except that the film was further stretched 1.15 times in the film width direction at a temperature of 170 ° C. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a weight method thickness of 2.00 μm and a micrometer method thickness of 2.24 μm, and the film has a surface roughness (Ra) of 41 nm and a plane orientation. The coefficient (fn) was 0.170, μsm was 0.56, μst was 0.78, and the ratio of μsm / μst was 0.72. In the film formation, no unevenness in electrostatic application, wrinkles, tearing, etc. were observed during casting, and the film formation property was good and excellent “◯”.

  Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one surface of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a capacitor. As a result, the vapor deposition workability was excellent “◯” with no margin shift. The element winding yield of the capacitor element was 99%, and the withstand voltage was 0.381 kV, which was excellent “◯”. The results are shown in Table 1.

(Comparative Example 1)
The amount of agglomerated silica particles in the polyester chip was 0.08% by weight, stretched 5.8 times in the film longitudinal direction at a temperature of 95 ° C., and then stretched 3.5 times in the film width direction at a temperature of 105 ° C. Otherwise, a biaxially stretched polyester film was produced in the same manner as in Example 1. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a weight method thickness of 2.70 μm and a micrometer method thickness of 2.90 μm. The surface roughness (Ra) of the film is 35 nm, and the plane orientation The coefficient was 0.167, μsm was 0.89, μst was 0.81, and the ratio of μsm / μst was 1.10. In the film formation, no unevenness in electrostatic application, wrinkles, tearing, etc. were observed during casting, and the film formation property was good and excellent “◯”.

Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one surface of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a capacitor. As a result, the vapor deposition processability was poor with a margin deviation of 0.30 mm. Further, the element winding yield of the capacitor element was 90%, and the withstand voltage was 0.348 kV, which was a defective “x”. The results are shown in Table 1.
(Comparative Example 2)
The amount of agglomerated silica particles in the polyester chip was 0.03% by weight, and the film was stretched 6.0 times in the longitudinal direction of the film at a temperature of 95 ° C. and then stretched 3.5 times in the width direction of the film at a temperature of 105 ° C. Otherwise, a biaxially stretched polyester film was produced in the same manner as in Example 1. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a weight method thickness of 2.00 μm and a micrometer method thickness of 2.21 μm. The surface roughness (Ra) of the film is 23 nm, and the plane orientation The coefficient (fn) was 0.169, μsm was 1.04, μst was 0.72, and the ratio of μsm / μst was 1.44. In the film formation, no unevenness in electrostatic application or wrinkles at the time of casting was observed, but tearing was observed once for 24 hours of film formation, and the film formation property was good “Δ”.

  Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one surface of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a capacitor. As a result, the vapor deposition processability was poor with a margin deviation of 0.40 mm. Further, the element winding yield of the capacitor element was 78%, and the withstand voltage was 0.334 kV, which was a defective “x”. The results are shown in Table 1.

(Comparative Example 3)
Example 1 except that the film was stretched 3.0 times at a temperature of 95 ° C. at the same time in the film longitudinal direction and the film width direction with a simultaneous biaxial stretching machine, and further stretched 1.7 times in the film width direction at a temperature of 170 ° C. A biaxially stretched polyester film was produced in the same manner as described above. The obtained biaxially stretched polyester film is a biaxially stretched polyester film having a weight method thickness of 2.70 μm and a micrometer method thickness of 2.95 μm, and the surface roughness (Ra) of the film is 53 nm. The orientation coefficient (fn) was 0.169, μsm was 0.54, μst was 0.81, and the ratio of μsm / μst was 0.66. In the film formation, no unevenness in electrostatic application or wrinkles at the time of casting was observed, but tearing was observed 3 times for 24 hours of film formation, and the film formation property was poor “x”.

  Aluminum was vacuum-deposited with an aluminum film thickness of 26 nm on one surface of the obtained biaxially stretched polyester film so that the surface resistance was 2Ω / □, and then wound to obtain a capacitor. As a result, the vapor deposition processability was poor with a margin shift of 0.35 mm. The element winding yield of the capacitor element was 96%, and the withstand voltage was 0.364 kV, which was excellent “◯”. The results are shown in Table 1.

  The biaxially stretched polyester film for capacitors of the present invention has good electrical characteristics, good thickness uniformity, and excellent handling properties, and particularly improves the workability and withstand voltage in the case of film capacitors. This is a biaxially stretched polyester film for capacitors to be obtained. A film capacitor using the biaxially stretched polyester film for capacitors of the present invention has improved withstand voltage characteristics and is useful.

Claims (9)

  When the static friction coefficient parallel to the film longitudinal direction is μsm and the static friction coefficient parallel to the film width direction is μst, the static friction coefficient μsm and the static friction coefficient μst are both in the range of 0.40 to 1.20, and A biaxially stretched polyester film for a capacitor, wherein the ratio (μsm / μst) of the static friction coefficient μsm to the static friction coefficient μst is 0.70 or more and less than 1.05. The film thickness t1 (μm) by the micrometer method and the film thickness t2 (μm) by the weight method satisfy the following formula (1), and the center line average roughness Ra (nm) of the film surface represents the following formula (2). The biaxially stretched polyester film for a capacitor according to claim 1, which is satisfied.
t2 ≦ t1 ≦ 1.05 × t2 + 0.25 (1)
20 ≦ Ra ≦ 75 (2)   The biaxially stretched polyester film for capacitors according to claim 1 or 2, wherein a film thickness t2 by a weight method is in a range of 0.5 to 10.0 µm.   The biaxially stretched polyester film for capacitors according to any one of claims 1 to 3, wherein the plane orientation coefficient fn is in the range of 0.155 to 0.180.   The biaxially stretched polyester film for capacitors according to any one of claims 1 to 4, wherein the film is produced by simultaneous biaxial stretching.   A metallized film comprising a metal film provided on at least one surface of the biaxially stretched polyester film for capacitors according to claim 1.   The metallized film according to claim 6, wherein the surface electric resistance of the metal film is in the range of 1 to 20 Ω / □.   A film capacitor comprising the metallized film according to claim 6 or 7.   A film capacitor formed using the biaxially stretched polyester film for a capacitor according to claim 1.