JP5080039B2 - Biaxially oriented polyester film for automobile drive motors - Google Patents

Description

  The present invention relates to a biaxially oriented polyester film for automobile drive motors. More specifically, it has heat resistance, has a low frequency of delamination, a small amount of oligomer generation, and has excellent performance in hydrolysis resistance and mechanical properties. The present invention relates to a biaxially oriented polyester film for automobile drive motors.

  In recent years, from the viewpoint of environmental problems, there is an increasing demand for automobiles that can replace conventional gasoline engine cars. In particular, hybrid cars that achieve low fuel consumption and low noise by combining a motor with a gasoline engine are in the spotlight. The motor used in this hybrid car is required to have a very high output, the use environment is very severe, and the use is long-lasting. Therefore, the insulation film used in the motor also has high heat resistance and resistance. Hydrolysis and low oligomer properties are required.

  Also in motor films other than automobile drive motors, for example, insulation films for compressor motors such as refrigerators and air conditioners, in recent years, with the downsizing and higher performance of electrical and electronic equipment, heat resistance has been improved. Increasing cases are demanded for improvement in characteristics such as the amount of oligomer extracted from the refrigerant and hydrolysis resistance. For example, according to Patent Document 1, Patent Document 2, etc., a PEN film or the like is used according to a heat-resistant B-type PET film (B-type PET film) obtained by improving the heat resistance of a normal PET film (heat-resistant category E). Yes.

  However, when PET or PEN film, which has been conventionally used as an insulating film, is used as an insulating film for an automobile drive motor, sufficient performance has not yet been obtained in terms of hydrolysis resistance and low oligomer properties. In particular, the PEN film is prone to a phenomenon in which molecular stacking (stacked structure) is delaminated between planes of aromatic rings, which is called delamination (hereinafter, sometimes referred to as delamination) during punching or bending. There was a problem that caused a drop in As a method for improving delamination that occurs when processing a PEN film, for example, a method for suppressing the orientation of the film is used. However, since such a PEN film is not sufficiently oriented, it has poor mechanical properties. there were. In addition, for example, Patent Document 3 discloses a method for reducing the frequency of delamination by devising the temperature and punch curvature at the time of processing the PEN film, but it is necessary to improve the processing apparatus, and the temperature and humidity. It did not show a sufficient effect in winter when the temperature decreased.

  Thus, in order to use a PEN film as an insulating film for an automobile drive motor, it is more excellent in hydrolysis resistance and low oligomer properties than a conventional PEN film, and a special temperature / humidity environment and processing equipment are used during processing. The present situation is that a PEN film excellent in delamination and mechanical properties is desired.

JP 2001-76536 A JP 2002-273844 A JP-A-6-335960

  The object of the present invention is to solve the problems of the prior art, have heat resistance, have low delamination occurrence frequency, low oligomer generation amount, and have excellent hydrolysis resistance and mechanical properties. The object is to provide a biaxially oriented polyester film.

  As a result of intensive studies to solve the above problems, the present inventors have made the delamination characteristics remarkably improved by making the intrinsic viscosity of polyethylene naphthalene dicarboxylate higher than before, and delamination has occurred conventionally. Therefore, even if the film is oriented to the extent that it was in the region to be used, the occurrence of delamination can be suppressed, so the mechanical properties can be improved, and the high viscosity and degree of film orientation make the film hydrolyzed. Therefore, the present invention has been completed by finding that it can be suitably used as an insulating film for an automobile drive motor.

That is, according to the present invention, an object of the present invention is a biaxially oriented polyester film containing polyethylene naphthalene dicarboxylate as a main component, the plane orientation coefficient of the film being 0.254 or less, and the polyester film An automobile having an intrinsic viscosity of 0.65 dl / g or more, a film thickness of 125 μm or more and 400 μm or less, and a film having a heat shrinkage of 1.0% or less in the longitudinal direction and the transverse direction when treated at 150 ° C. for 30 minutes. This is achieved by a biaxially oriented polyester film for a drive motor.

The automobile driving motors biaxially oriented polyester film of the present invention, as a preferred embodiment, it longitudinal and transverse Young's modulus is respectively 5000MPa or more, and this Oh oligomer extraction amount is 0.5 wt% or less It encompasses as well the preferred embodiment which includes at least one of.
In addition, the biaxially oriented polyester film for an automobile drive motor of the present invention can be specifically used for a drive motor application of a hybrid vehicle or an electric vehicle.

  The biaxially oriented polyester film for automobile drive motors of the present invention is suitable as an insulating film for drive motors of hybrid cars and electric cars because it has excellent delamination characteristics and mechanical characteristics, and is also excellent in hydrolyzability and oligomer generation. Can be used.

The present invention will be described in detail below.
<Polyethylene naphthalene dicarboxylate>
The main component of the polyester film in the present invention is polyethylene naphthalene dicarboxylate. Such polyethylene naphthalene dicarboxylate comprises naphthalenedicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a glycol component. Here, “main” means 80 mol% or more of all repeating structural units in the polymer component. In the polyethylene naphthalene dicarboxylate of the present invention, 80% by mole or more of all repeating units are ethylene-2,6-naphthalene dicarboxylate, ethylene-2,7-naphthalene dicarboxylate, ethylene-1,5-naphthalene dicarboxylate. It is preferably at least one selected from the group consisting of rates, particularly ethylene-2,6-naphthalenedicarboxylate. More preferably, 90 mol% or more, particularly preferably 95 mol% or more of all repeating units is ethylene-2,6-naphthalene dicarboxylate, and particularly a substantially single weight of polyethylene-2,6-naphthalene dicarboxylate. It is preferably a coalescence.

  The polyethylene naphthalene dicarboxylate of the present invention may be a polyethylene naphthalene dicarboxylate copolymer having a copolymerization component of 20 mol% or less. When polyethylene naphthalene dicarboxylate is a copolymer, a compound having two ester-forming functional groups in the molecule can be used as a copolymerization component. Examples of such compounds include oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid. Dicarboxylic acids such as acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid; oxycarboxylic such as p-oxybenzoic acid and p-oxyethoxybenzoic acid Acid; or diethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexane methylene glycol, neopentyl glycol, bisphenol sulfone ethylene Emissions oxide adducts, ethylene oxide adducts of bisphenol A, can be used diethylene glycol, dihydric alcohols such as such as polyethylene oxide glycol. These copolymerization components may be used alone or in combination of two or more. Among the copolymer components, isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and p-oxybenzoic acid are used as the acid component, and diethylene glycol and trimethylene are used as the glycol components. Preferred examples include ethylene oxide adducts of glycol, hexamethylene glycol, neopentyl glycol, and bisphenol sulfone.

  The polyethylene naphthalene dicarboxylate may be one in which a terminal hydroxyl group and / or a carboxyl group is partially or entirely blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol, or for example, It may be a copolymer obtained by using a trifunctional or higher functional ester-forming compound such as glycerin and pentaerythritol within a range in which a substantially linear polymer is obtained.

  The constituent component of the polymer in the polyester film of the present invention is mainly composed of a homopolymer or copolymer of polyethylene naphthalene dicarboxylate, but may be a mixture with other polyesters or organic polymers other than polyester. Good. In the case of a mixture, the ethylene naphthalene dicarboxylate unit in the polymer component is preferably 80 mol% or more, more preferably 90 mol% or more, particularly preferably 95 mol% or more of all repeating structural units. As a result, the original properties of the polyethylene naphthalene dicarboxylate film are not extremely lost, and mechanical properties, long-term durability and dimensional stability can be ensured.

  Polyesters that can be mixed with polyethylene naphthalene dicarboxylate or organic polymers other than polyester include polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene 4,4'-tetramethylene diphenyl dicarboxylate, polyethylene-2,7- Naphthalene dicarboxylate, polytrimethylene-2,6-naphthalene dicarboxylate, polyneopentylene-2,6-naphthalene dicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene Polyesters such as dicarboxylate can be mentioned, and among these, polyethylene isophthalate, polytrimethylene terephthalate, polytrimethylene-2,6-naphthalenedicar Kishireto, poly (bis (4-ethyleneoxy) sulfone) -2,6-naphthalene dicarboxylate are preferred. These polyesters or organic polymers other than polyester may be used alone or in combination of two or more.

  The polyethylene naphthalene dicarboxylate of the present invention directly obtains a low polymerization degree polyester by reaction of dicarboxylic acid and glycol, or obtains low polymerization degree polyester by transesterification of lower alkyl ester of dicarboxylic acid and glycol. It can be produced by a method in which a polyester is obtained by further polymerizing a polyester having a polymerization degree in the presence of a polymerization catalyst.

  Examples of the transesterification catalyst used in the transesterification reaction include one or more compounds including sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt. As polymerization catalysts, antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or partial hydrolysates thereof, titanyl oxalate Mention may be made of titanium compounds such as ammonium, potassium titanyl oxalate and titanium trisacetylacetonate.

  When polymerization is carried out via a transesterification reaction, phosphorous such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, triethylphosphonoacetate, orthophosphoric acid, etc. is used to deactivate the transesterification catalyst before the polymerization reaction. A compound can be added, and the content in polyethylene naphthalene dicarboxylate as a phosphorus element is preferably 20 ppm or more and 100 ppm or less from the viewpoint of thermal stability of the polyester.

  The polyethylene naphthalene dicarboxylate of the present invention is chipped after melt polymerization, and is subjected to solid phase polymerization in the range of the glass transition temperature of the polyethylene naphthalene dicarboxylate or higher and the melting point temperature under an inert gas stream such as heating under reduced pressure or nitrogen. The application is particularly preferred for the purpose of increasing the intrinsic viscosity. The solid phase polymerization temperature in the solid phase polymerization process is preferably 225 ° C. or higher and 250 ° C. or lower, more preferably 230 ° C. or higher and 240 ° C. or lower. When the temperature is lower than 225 ° C., the polymerization of polyethylene naphthalene dicarboxylate by solid phase polymerization is difficult to proceed, and when the temperature is higher than 250 ° C., fusion between chips is caused. The time for the solid phase polymerization treatment is preferably 20 hours or longer, and more preferably 30 hours or longer. The upper limit of the solid phase treatment time is not particularly limited, but the polymerization is considerably advanced at 50 hours or longer, and even if the treatment is continued for a longer time, the effect of further increasing the molecular weight is small, and the productivity is reduced. Absent. A known method can be used for the solid-phase polymerization treatment, and either a batch method or a continuous method can be used.

<Additives>
In order to improve the handleability of the biaxially oriented polyester film of the present invention, inert particles or the like may be added within a range not impairing the effects of the invention. Examples of the inert particles include inorganic particles containing elements of Periodic Tables IIA, IIB, IVA, and IVB (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide, etc.), crosslinked silicone resins, Fine particles made of a polymer having high heat resistance such as crosslinked polystyrene and crosslinked acrylic resin particles can be contained. When the inert particles are included, the average particle diameter of the inert particles is preferably in the range of 0.001 to 5 μm, 0.01 to 10% by weight, more preferably 0.05 to 5% by weight based on the total weight of the film. It is preferable to contain in the range of%. In addition, the biaxially oriented polyester film of the present invention may contain a small amount of an ultraviolet absorber, an antioxidant, an antistatic agent, a light stabilizer, and a heat stabilizer as necessary.

<Intrinsic viscosity>
The intrinsic viscosity of the film after forming into a biaxially oriented film is preferably 0.65 dl / g or more, and more preferably 0.67 dl / g or more. There is no particular upper limit for the intrinsic viscosity, but if it exceeds 0.90 dl / g, the torque applied to the screw of the melt extruder becomes very high, making it difficult to use with a normal melt extruder. Here, the intrinsic viscosity of the film represents the intrinsic viscosity of the polymer constituting the film. The upper limit of the intrinsic viscosity of the film after being formed on the biaxially oriented film is more preferably 0.80 dl / g or less, and 0.75 dl / g or less in terms of screw load at the time of film formation. Is particularly preferred.
When the intrinsic viscosity is less than the lower limit, delamination is likely to occur in a region having a high plane orientation coefficient, and the amount of extracted oligomer and hydrolysis resistance are not sufficient as an insulating film for an automobile drive motor. The intrinsic viscosity is a value (unit: dl / g) measured at 35 ° C. using o-chlorophenol as a solvent.

  The intrinsic viscosity of the polyethylene naphthalene dicarboxylate before film formation used in the present invention is 0.70 dl / g or more, more preferably 0.73 dl / g or more. When the intrinsic viscosity of polyethylene naphthalene dicarboxylate before film formation is less than the lower limit, the intrinsic viscosity of the film obtained by biaxial orientation after melt extrusion may not reach the above range.

<Flat orientation coefficient>
The biaxially oriented polyester film of the present invention may be referred to as the longitudinal direction of the film (hereinafter sometimes referred to as the longitudinal direction, the film forming direction or the MD direction) and the lateral direction (hereinafter referred to as the width direction or the TD direction). ) And the refractive index in the thickness direction, the plane orientation coefficient (ns) is 0.254 or less, preferably 0.251 or less. Here, the plane orientation coefficient is represented by a value obtained by calculation according to the following formula (1) using the refractive index of each direction component of the film measured by the Abbe method.
ns = (nMD + nTD) / 2−nZ (1)
(In the formula, nMD represents the refractive index in the MD direction of the film, nTD represents the refractive index in the TD direction of the film, and nZ represents the refractive index in the thickness direction perpendicular to the film surface.)

  The plane orientation coefficient of the film can be said to be an index representing the orientation state of molecular chains in the film. If this value exceeds the upper limit, the mechanical properties increase, but the molecular chain orientation becomes too strong, and delamination tends to occur during punching or bending, leading to a decrease in yield. On the other hand, when the lower limit value of the plane orientation coefficient is less than 0.20, the hydrolysis resistance may decrease because the ratio of amorphous to the film is large. Further, the lower limit value of the plane orientation coefficient is preferably 0.20 or more, more preferably 0.245 or more, from the viewpoint of enhancing the mechanical properties represented by Young's modulus.

  As a specific achievement means for satisfying the upper limit of the plane orientation coefficient of the film, the direction of decreasing the copolymerization amount of polyethylene naphthalene dicarboxylate is preferable, and the heat fixing temperature is kept within a certain range at the same time when the area magnification is performed at a certain magnification or less. It is preferable to carry out with. When a polyethylene naphthalene dicarboxylate homopolymer is used, it is preferable that the area stretching ratio is 9.5 times or less and the heat setting temperature is 225 ° C. or more and less than 250 ° C. Moreover, when using the polyethylene naphthalene dicarboxylate homopolymer, the means for achieving the lower limit of the plane orientation coefficient is preferably performed at an area stretch ratio of 7.0 times or more and a heat setting temperature of 225 ° C. or more and less than 250 ° C. The difference between the longitudinal draw ratio and the transverse draw ratio is preferably 0.3 or less.

<Young's modulus>
The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the machine direction and the transverse direction of 5000 MPa or more, more preferably 5500 MPa or more, and particularly preferably 6000 MPa or more. When the Young's modulus is less than the lower limit, the film does not have a waist, and clogging is likely to occur during automatic insertion into a motor, resulting in a decrease in yield. The upper limit of the Young's modulus is not particularly limited, but at 7000 MPa or more, film cutting may occur frequently in the film forming process, and the degree of orientation becomes too high and delamination tends to occur. The Young's modulus in the machine direction and transverse direction of the film can be adjusted by the magnification during stretching.
Specific means for achieving the lower limit of the Young's modulus can be performed in the same manner as the means for achieving the lower limit of the plane orientation coefficient. The specific means for achieving the upper limit of the Young's modulus can be performed by the same method as the means for achieving the upper limit of the plane orientation coefficient.

<Thickness>
The thickness of the biaxially oriented polyester film of the present invention is preferably 125 μm or more and 400 μm or less, more preferably 150 μm or more and 350 μm or less. If the film thickness is less than the lower limit, the insulation capacity may be insufficient for slot / wedge / phase-to-phase insulation of an automobile drive motor. On the other hand, when the film thickness exceeds the upper limit, delamination tends to occur, and the yield may decrease.

<Oligomer extraction amount>
The biaxially oriented polyester film of the present invention preferably has an oligomer extraction amount of 0.5% by weight or less. The amount of oligomer extracted in the present invention refers to a 38 mm × 38 mm square film that is boiled in 20 cc of xylene at 139 ° C. for 2 hours, slowly cooled, then taken out of the film, and the amount of oligomer in xylene is determined from the absorbance at a measurement wavelength of 240 nm. It is expressed as a value. When the oligomer extraction amount exceeds 0.5% by weight, when the drive motor is immersed in oil and used under high temperature conditions, the problem is that the oligomer extracted from the film is likely to precipitate in the oil, It may not be used as an insulating film for automobile drive motors. The amount of oligomer extraction is preferably less if it is in the range of 0.5% by weight or less, and the lower limit is preferably 0.0% by weight or more.

<Heat shrinkage>
The biaxially oriented polyester film of the present invention has a heat shrinkage ratio of 1.0% or less in the longitudinal direction and the transverse direction after being heat-treated at 150 ° C. for 30 minutes because the use environment of the automobile drive motor becomes high. It is preferable that it is 0.8% or less. When the heat shrinkage rate exceeds the upper limit, the film only in the part that receives heat from the motor windings shrinks and local distortion is likely to occur, and the heat resistance and hydrolysis resistance of the film at that part decreases, resulting in a motor life. May be undesirable for insulating an automobile drive motor.

<Film forming method>
The polyester film of the present invention needs to be a biaxially oriented film. By being biaxially oriented, mechanical characteristics and heat-resistant dimensional stability are good, and it is possible to exhibit sufficient performance for insulation of automobile drive motors.
If the biaxially oriented polyester film of the present invention is biaxially stretched, it can be produced by using a known film forming method. For example, a sufficiently dried polyethylene naphthalene dicarboxylate is melted at a melting point to (melting point +70). ) Extruded at a temperature of 0 ° C., rapidly cooled on a casting drum to form an unstretched film, and then the unstretched film is sequentially or simultaneously biaxially stretched and heat-set. When the film is formed by sequential biaxial stretching, the unstretched film is stretched 2.5 to 4.0 times at 130 to 170 ° C. in the machine direction, and then 2.5 to 4 at 130 to 150 ° C. in the transverse direction with a stenter. It is preferable to stretch the film by 0 times. The area stretch ratio obtained by multiplying the longitudinal stretch ratio and the lateral stretch ratio is 7.0 to 9.5 times, and the difference between the longitudinal stretch ratio and the lateral stretch ratio is preferably 0.3 or less. The heat setting is preferably performed at a temperature of 225 ° C. or more and less than 250 ° C. under tension or limited shrinkage, and the heat setting time is preferably 1 to 1000 seconds. In the case of simultaneous biaxial stretching, the above stretching temperature, stretching ratio, heat setting temperature and the like can be applied. Moreover, you may perform a relaxation | loosening process after heat setting.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Plane orientation coefficient (ns)
Using an Abbe refractometer, the refractive index in the longitudinal direction, the transverse direction and the thickness direction of the biaxially oriented film obtained using sodium D-line (589 nm) as a light source was measured, and the plane orientation coefficient (ns) of the film was expressed by the following formula: Obtained by (1).
ns = (nMD + nTD) / 2−nZ (1)
(In the formula, nMD represents the refractive index in the MD direction of the film, nTD represents the refractive index in the TD direction of the film, and nZ represents the refractive index in the thickness direction perpendicular to the film surface.)

(2) Intrinsic viscosity Measured at 35 ° C. using o-chlorophenol as a solvent (unit: dl / g). The intrinsic viscosity of the film was obtained by sampling a biaxially oriented film.

(3) Young's modulus Using a Tensilon UCT-100 model manufactured by Orientec Co., Ltd., a biaxially oriented film was cut to a sample width of 10 mm and a length of 15 cm in a room adjusted to a temperature of 20 ° C. and a humidity of 50%, and the gap between chucks was 100 mm. The Young's modulus is calculated from the tangent of the rising portion of the load-elongation curve obtained by pulling at a tensile speed of 10 mm / min and a chart speed of 500 mm / min. Note that the Young's modulus in the longitudinal direction is the direction in which the longitudinal direction of the film is measured, and the Young's modulus in the lateral direction is that in which the lateral direction of the film is the measuring direction. Each Young's modulus was measured 10 times and the average value was used.

(4) Film thickness Using a dot-type film thickness meter, the thickness was measured at any 50 locations in the film width direction and at any location near the center of the film width along the longitudinal direction, and a total of 100 locations. Was the film thickness.

(5) Oligomer extraction amount A biaxially oriented film (38 mm × 38 mm) is boiled in 20 cc of xylene at 139 ° C. for 2 hours, slowly cooled, taken out of the film, and the amount of oligomer in the xylene is determined from the absorbance at a measurement wavelength of 240 nm. . Note that a calibration curve was prepared in advance for the relationship between the oligomer concentration and the absorbance. The absorbance was measured using a UV-VIS-NIR spectrophotometer UV-3101PC manufactured by SHIMADZU.

(6) Heat shrinkage ratio The longitudinal direction and the transverse direction of the biaxially oriented film are marked, and a 30 cm long film whose exact length has been measured in advance is placed in an oven set at a temperature of 150 ° C. with no load, After leaving it to stand for 30 minutes, it is taken out, returned to room temperature, and its dimensional change is read. From the length (L ₀ ) before the heat treatment and the dimensional change (ΔL) due to the heat treatment, the thermal contraction rates in the vertical direction and the horizontal direction were obtained according to the following equation (2). The thermal contraction rate in each direction was evaluated with the number of samples n = 5, and the average value was used.
Thermal contraction rate (%) = ΔL / L ₀ × 100 (2)

(7) Delamination (delamination resistance)
A film sample is cut into a size of 80 × 80 mm, and it is lightly folded in two by hand and sandwiched between a pair of flat metal plates, and then pressed with a press machine at a predetermined pressure P1 (kg / cm ² G) for 20 seconds. did. After pressing, the half-folded film sample was returned to the original flat state by hand, and the length (mm) of the whitened portion appeared was measured and totalized. Each of the new film samples was used, and the above measurement was repeated for a press pressure P1 = 2, 3, 4, 5 (kg / cm ² G).
According to the following formula (3), the average value of the total length (mm) of the whitened portion at each press pressure is defined as the ratio (%) of the total crease length (80 mm) as the crease delamination ratio (%). Delamination was evaluated according to the standard.
Crease delamination rate (%) = total length of whitened portion at each press pressure (mm) / (80 mm × 4) × 100 (3)
○: Crease delamination rate of less than 40% △: Crease delamination rate of 40% or more and less than 70% ×: Crease delamination rate of 70% or more

(8) Hydrolysis resistance An environmental test in which a strip-shaped sample piece cut into a length of 100 mm in the longitudinal direction and a width of 10 mm in the transverse direction of the biaxially oriented film was set to 121 ° C., 2 atm, 100% RH (wet saturation). Leave in the plane for 100 hours. The sample piece was suspended using a stainless steel clip. The longitudinal breaking strength of the sample piece taken out after 100 hours was measured, and the hydrolysis resistance was evaluated according to the following criteria for the average value of the number of samples n = 5.
○: Breaking strength 150 MPa or more Δ: Breaking strength 100 MPa or more but less than 150 MPa
X: Breaking strength less than 100 MPa

[Example 1]
100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 60 parts by weight of ethylene glycol, 0.03 part by weight of manganese acetate tetrahydrate as a transesterification catalyst, and 0.25 weight of calcium carbonate particles having an average particle size of 0.5 μm as a lubricant %, 0.06% by weight of spherical silica particles having an average particle diameter of 0.2 μm, and 0.1% by weight of spherical silica particles having an average particle diameter of 0.1 μm are added, and transesterification is performed according to a conventional method. The reaction was allowed to proceed. Each lubricant shows the compounding quantity with respect to film weight. Thereafter, 0.042 parts by weight of triethylphosphonoacetate was added to substantially complete the transesterification reaction. Subsequently, 0.024 parts by weight of antimony trioxide was added, and then a polymerization reaction was carried out in a conventional manner under high temperature and high vacuum, to obtain a chip of polyethylene-2,6-naphthalenedicarboxylate having an intrinsic viscosity of 0.60 dl / g. Got. The PEN chip was filled in a tumbler and dried at 150 degrees for 6 hours while reducing the pressure to 1 mmHg. Thereafter, the temperature in the tumbler was raised to 240 ° C. and held at that temperature for 20 hours, and a solid phase polymerization-treated PEN chip having an intrinsic viscosity of 0.80 dl / g was collected. After drying this solid state polymerization-treated PEN chip at 175 ° C. for 5 hours, it is supplied to an extruder, melted at a melting temperature of 300 ° C., extruded through a die slit, and then on a casting drum set at a surface temperature of 55 ° C. An unstretched film was prepared by cooling and solidification.

  This unstretched film was stretched 3.1 times in the longitudinal direction (longitudinal direction) at 140 ° C. to obtain a uniaxially stretched film. Subsequently, the film is biaxially stretched 3.0 times in the transverse direction (width direction) at 135 ° C, further subjected to heat setting treatment at a heat setting temperature of 245 ° C for 10 seconds, and further contracted by 2% in the width direction at 245 ° C. Re-heat treatment was performed to obtain a biaxially oriented polyester film having a film thickness of 250 μm and wound on a roll. The characteristics of the obtained biaxially oriented polyester film are shown in Table 1. The film had mechanical characteristics and a plane orientation coefficient that can be used for automobile drive motors, was excellent in delamination resistance and hydrolysis characteristics, and had few extracted oligomers.

[Example 2]
After sequential biaxial stretching, the same operation as in Example 1 was repeated except that a heat setting treatment was performed at a heat setting temperature of 235 ° C., and reheat treatment was performed while shrinking 2% in the width direction at 235 ° C., and a film thickness of 250 μm A biaxially oriented polyester film was obtained. The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 1]
The unstretched film of Example 1 was stretched 5.1 times in the longitudinal direction (longitudinal direction) at 140 ° C. to obtain a uniaxially stretched film. Thereafter, the film is sequentially biaxially stretched 4.6 times in the transverse direction (width direction) at 145 ° C., heat-fixed at a heat setting temperature of 245 ° C., and further contracted by 2% in the width direction at 245 ° C. Except for the heat treatment, the same operation as in Example 1 was repeated to obtain a biaxially oriented polyester film having a film thickness of 250 μm. The characteristics of the obtained biaxially oriented polyester film are shown in Table 1. Although the film had a high Young's modulus and was very stiff, the surface orientation coefficient was large, so that the delamination resistance was not sufficient despite the high intrinsic viscosity. In addition, since the heat shrinkage rate is large, it is not sufficient as an insulating film for an automobile drive motor.

[Comparative Example 2]
The unstretched film of the example was stretched 3.5 times in the longitudinal direction (longitudinal direction) at 140 ° C. to obtain a uniaxially stretched film. After that, biaxial stretching is sequentially performed 3.4 times in the transverse direction (width direction) at 145 ° C., heat setting is further performed at a heat setting temperature of 245 ° C., and recontraction is performed while shrinking 2% in the width direction at 245 ° C. Except for the heat treatment, the same operation as in Example 1 was repeated to obtain a biaxially oriented polyester film having a film thickness of 250 μm. The characteristics of the obtained biaxially oriented polyester film are shown in Table 1. Due to the large plane orientation coefficient, the delamination resistance was not sufficient despite the high intrinsic viscosity.

[Comparative Example 3]
A biaxially oriented polyester film having a film thickness of 250 μm was obtained by repeating the same operation as in Example 1 except that the solid phase polymerization treatment time was changed from 20 hours to 5 hours. The properties of the obtained film are shown in Table 1. Since this film does not have a sufficiently high intrinsic viscosity, it has a plane orientation coefficient that satisfies the mechanical properties that can be used for automobile drive motors, but has poor delamination resistance and hydrolysis resistance.

[Comparative Example 4]
A biaxially oriented polyester film having a film thickness of 250 μm was obtained by repeating the same operation as in Example 1 except that the solid phase polymerization treatment step was not performed. The properties of the obtained film are shown in Table 1. Since this film does not have a sufficiently high intrinsic viscosity, it has a plane orientation coefficient that satisfies the mechanical properties that can be used for automobile drive motors, but has poor delamination resistance and hydrolysis resistance.

[Comparative Example 5]
100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, 0.03 part by weight of manganese acetate tetrahydrate as a transesterification catalyst, and spherical silica fine particles having an average particle size of 0.3 μm as a lubricant are polyethylene terephthalate resin compositions Was added so as to contain 0.1% by weight based on the weight of the product and subjected to a transesterification according to a conventional method, and then 0.042 part by weight of triethylphosphonoacetate was added to substantially complete the transesterification. I let you. Subsequently, 0.024 parts by weight of antimony trioxide was added, and then a polymerization reaction was carried out by a conventional method at high temperature and high vacuum to obtain polyethylene terephthalate (PET) having an intrinsic viscosity of 0.60 dl / g. The PET chip was filled in a tumbler and dried at 140 degrees for 4 hours while reducing the pressure to 1 mmHg. Thereafter, the temperature in the tumbler was raised to 235 ° C. and held at that temperature for 20 hours, and a solid-state polymerization-treated PET chip having an intrinsic viscosity of 0.78 dl / g was collected. This solid state polymerization-treated PET chip was dried at 150 ° C. for 3 hours, then supplied to an extruder, melted at a melting temperature of 280 ° C., extruded through a die slit, and then on a casting drum set at a surface temperature of 25 ° C. An unstretched film was prepared by cooling and solidification.

  This unstretched film is stretched 3.1 times in the continuous film-forming direction at 95 ° C. Thereafter, the film is biaxially stretched successively 3.0 times in the width direction at 120 ° C. and further subjected to heat setting treatment at a heat setting temperature of 230 ° C. for 10 seconds to obtain a biaxially oriented polyester film having a film thickness of 250 μm. Rolled up. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film. Although this film was excellent in delamination, its heat stability, oligomer extraction amount, and hydrolysis resistance were not sufficient as an automotive drive motor insulation film.

  Since the biaxially oriented polyester film in the present invention is excellent in delamination properties and mechanical properties, and is excellent in hydrolyzability and oligomer generation, it can be suitably used as an insulating film for drive motors of hybrid vehicles and electric vehicles. it can.

Claims (4)

A biaxially oriented polyester film comprising polyethylene naphthalene dicarboxylate as a main component, the plane orientation coefficient of the film being 0.254 or less, and the intrinsic viscosity of the polyester film being 0.65 dl / g or more , The film thickness is 125 μm or more and 400 μm or less, and the heat shrinkage rate in the machine direction and the transverse direction of the film when treated at 150 ° C. for 30 minutes is 1.0% or less, respectively. Axial-oriented polyester film.   The biaxially oriented polyester film for an automobile drive motor according to claim 1, wherein Young's modulus in the longitudinal direction and the transverse direction are each 5000 MPa or more. The biaxially oriented polyester film for an automobile drive motor according to any one of claims 1 and 2 , wherein an oligomer extraction amount is 0.5% by weight or less. The biaxially oriented polyester film for an automobile drive motor according to any one of claims 1 to 3 , wherein the automobile is a hybrid vehicle or an electric vehicle.