JP2016132726A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film hard to tear when cutting, and hard to be scratched when inserting into a slot.SOLUTION: The biaxially oriented polyester film satisfies the following (1) and (2). (1) The average R1 of a tear resistance Rm in a direction having a maximum refractive index and a tear resistance Rt in a direction making an angle of 90° with respect to the direction having the maximum refractive index is not less than 10 N/mm and not greater than 40 N/mm. (2) The flexure stiffness by a loop stiffness tester at a depth of 7.0 μm from at least one surface layer of the polyester film is not less than 30 μN/5 mm and not greater than 50 μN/5 mm.SELECTED DRAWING: None

Description

The present invention relates to a biaxially oriented polyester film having excellent processability.

  Polyester resins, especially polyethylene terephthalate (hereinafter sometimes abbreviated as PET) and polyethylene 2,6-naphthalene dicarboxylate (hereinafter sometimes abbreviated as PEN) are mechanical properties, thermal properties, chemical resistance, electrical properties, It has excellent moldability and is used for various purposes. Polyester films made from polyester, especially biaxially oriented polyester films, are used for car air conditioners used in solar battery back sheets, water heater motors, hybrid vehicles, etc. due to their excellent mechanical and electrical properties. It is used as various industrial materials such as electric insulation materials for motors and drive motors, magnetic recording materials, capacitor materials, packaging materials, building materials, photographic applications, graphic applications, and thermal transfer applications.

  Among these applications, when used for electrical insulating materials (for example, compressor motors for air conditioners), it is used in an environment where the temperature becomes high as the refrigerant is compressed and expanded. PEN was often used (Patent Documents 1 and 2). However, PEN is hard due to its molecular structure, and if a conventional processing machine is used as it is, when it is molded or inserted into a slot or wedge, shock deformation or cracking occurs, or cleavage occurs during cutting. There is a problem that insulation failure occurs. Further, there is a problem that clogging occurs in the automatic molding machine and the machine stops. Therefore, in order to solve this problem, it has been proposed to introduce a special processing process (Patent Document 3).

Japanese Patent Laid-Open No. 9-300452 JP 2007-99971 A JP-A-6-335960

  However, when a special processing process is introduced, there is a problem that the cost is increased and defective products are generated due to the process, resulting in a decrease in yield. For this reason, the present inventors have studied using a film using PET having excellent heat resistance as described in JP-A-2011-256333 for electrical insulating materials, and the PET film is a PEN film. It has been found that there is a problem in that, since it is more flexible than that in the processing stage, it is easy to be damaged at the time of insertion of the slot, resulting in an insulation failure due to the damage.

  In view of the background of the prior art, an object of the present invention is to provide a biaxially oriented polyester film that is not easily torn at the time of cutting and that is difficult to damage the surface layer when a slot is inserted.

In order to solve the above problems, the present invention has the following configuration. That is,
[I] A biaxially oriented polyester film satisfying the following (1) and (2).
(1) The average R1 ((Rm + Rt) / 2) of the tear resistance Rm in the direction having the maximum refractive index and the tear resistance Rt in the direction forming 90 ° with the direction having the maximum refractive index is 10 N / mm or more and 40 N / mm or less.
(2) The bending stiffness by the loop stiffness tester at a depth of 7.0 μm from at least one polyester film surface layer is 30 μN / 5 mm or more and 50 μN / 5 mm or less.
[II] The biaxially oriented polyester film according to [I] that satisfies the following (3).
(3) | Rt−Rm | is 5 N / mm or more and 30 N / mm or less [III] The number of times until cleaving in the fir test is 100 or more and 1000 or less, as described in [I] or [II] Biaxially oriented polyester film [IV] The biaxially oriented polyester film according to [I] to [III], in which the bending strength FE is 4.0 or more.
[V] The time according to any one of [I] to [IV], wherein the time required for the strength retention rate to be 50% or less is 300 hours or more when placed at 200 ° C. and 0% RH. Biaxially oriented polyester film.
[VI] It consists of three layers of A / B / A, the intrinsic viscosity of the polyester constituting the A layer is 0.50 or more and 0.62 or less, and the intrinsic viscosity of the polyester constituting the B layer is 0.60 or more and 0 The biaxially oriented polyester film according to any one of [I] to [V], which is 80 or less and the intrinsic viscosity of the polyester resin constituting the A layer is lower than the intrinsic viscosity of the polyester resin constituting the B layer.
[VII] The polyester resin comprising the three layers A / B / A has a melting point of 260 ° C. or higher and 300 ° C. or lower and the polyester resin constituting the B layer has a melting point of 240 ° C. or higher and 260 ° C. or lower. The biaxially oriented polyester film according to any one of [I] to [V], wherein the polyester resin constituting the A layer has a higher melting point than the polyester resin constituting the B layer.
[VIII] Three layers of A / B / A, the intrinsic viscosity of the polyester resin constituting the A layer is 0.50 or more and 0.62 or less, and the melting point is 260 ° C. or more and 300 ° C. or less. The intrinsic viscosity of the constituting polyester resin is 0.60 or more and 0.80 or less, the melting point is 240 ° C. or more and 260 ° C. or less, and the intrinsic viscosity of the polyester resin constituting the A layer is the intrinsic viscosity of the polyester resin constituting the B layer. The biaxially oriented polyester film according to any one of [I] to [V], which is lower in viscosity and has a higher melting point of the polyester resin constituting the A layer than the melting point of the polyester resin constituting the B layer.
[IX] The biaxially oriented polyester film according to any one of [VI] to [VIII], wherein the ratio of the sum of the thicknesses of the A layer and the B layer is in the range of 1: 2.5 to 1:10.
[X] The biaxially oriented polyester film according to any one of [I] to [IX], which is used as an insulating member of a motor.

  According to the present invention, a biaxially oriented polyester film having excellent processability can be provided. The film obtained by the present invention provides a biaxially oriented polyester film that reduces the yield during processing even when it is used as an electric insulating member of a motor because it is difficult to tear when cutting and the surface layer is not easily damaged when inserting a slot. can do.

It is the schematic showing the core and insertion hole of a motor.

  Hereinafter, the present invention will be described in detail with specific examples.

The film of the present invention needs to be a biaxially oriented polyester film.
The term “biaxial orientation” as used herein refers to a pattern showing a biaxial orientation pattern by wide-angle X-ray diffraction. A biaxially oriented polyester film can be generally obtained by stretching an unstretched polyester sheet in the sheet longitudinal direction and width direction, and then performing a heat treatment to complete crystal orientation.

  The polyester used in the present invention has a dicarboxylic acid component and a diol component. In addition, in this specification, a structural component shows the minimum unit which can be obtained by hydrolyzing polyester. Examples of the dicarboxylic acid component constituting the polyester include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalon. Aliphatic dicarboxylic acids such as acid, ethylmalonic acid and the like, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene Dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalate Acid, fe Toluene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) dicarboxylic acids such as fluorene acids and aromatic dicarboxylic acids, or there may be mentioned an ester derivative thereof is not limited thereto.

  Examples of the diol component constituting the polyester include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. Aliphatic diols such as cyclohexanedimethanol, spiroglycol, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9′-bis (4-hydroxy Examples include, but are not limited to, diols such as phenyl) fluorene and aromatic diols, and a series of a plurality of the above-mentioned diols.

  Moreover, the polyester film as used in the field of this invention means containing 70 mass% or more of polyester with respect to the whole resin which comprises a film. More preferably, it is 85 mass% or more.

The biaxially oriented polyester film of the present invention must satisfy the following (1).
(1) The average R1 ((Rm + Rt) / 2) of the tear resistance Rm in the direction having the maximum refractive index and the tear resistance Rt in the direction forming 90 ° with the direction having the maximum refractive index is 10 N / mm or more and 40 N / mm or less.

  A general polyester film is composed of crystalline polyester, and there are crystalline and amorphous parts of the polyester in the film. Moreover, in the biaxially oriented polyester film obtained by biaxially stretching such crystalline polyester, there are a portion where the polyester is crystallized by orientation and an amorphous portion. A portion crystallized by orientation has a higher refractive index than an amorphous portion. Therefore, the biaxially oriented polyester film has the maximum refractive index in the longitudinal direction or the width direction that is most oriented. In the portion crystallized by orientation, the molecular chains of the polyester are regularly present in a certain direction. Therefore, the biaxially oriented polyester film has a feature that when an external force is applied, the biaxially oriented polyester film easily tears in the most oriented direction (direction having the maximum refractive index: longitudinal direction or width direction). When biaxially oriented polyester film is used for electrical insulation, it is subject to tearing in the longitudinal direction or width direction when processing the film, because it is processed into a mold or cut while transporting the film. There is. In the biaxially oriented polyester film of the present invention, the tear resistance Rm in the direction having the maximum refractive index and the average R1 ((Rm + Rt) / 2) of Rt in the direction forming 90 ° with the direction having the maximum refractive index is 10N. By setting the thickness to / N or more and 40 N / mm or less, it is possible to prevent the film from being torn during processing, and to be easily cut and to be a film having no cracks or burrs. When R1 is less than 10 N / mm, the film is torn during processing, and when it exceeds 40 N / mm, the film is difficult to cut during cutting and burrs are generated. Preferably it is 20 N / mm or more and 40 N / mm or less, More preferably, it is 30 N / mm or more and 40 N / mm or less, and since a film is hard to tear further and a crack and a burr | flash can be suppressed, it is more preferable.

The value of the tear resistance R1 can be adjusted by, for example, the following method, but the method for obtaining the biaxial polyester film of the present invention is not limited to these.
(1-1) When the biaxially oriented polyester is produced, if the draw ratio is lowered, the orientation of the molecular chain can be relaxed and the tear resistance can be improved (R1 is increased). On the other hand, when the draw ratio is increased, the orientation of the molecular chain is strengthened, so that the tear resistance can be lowered (R1 is lowered).
(1-2) When the molecular chain of the polyester constituting the biaxially oriented polyester film is lengthened, the mobility of the molecular chain is lowered. The tear resistance is high (R1 is high). On the other hand, when the molecular chain of the polyester constituting the biaxially oriented polyester film is shortened, the mobility of the molecular chain is improved. Therefore, even if the molecular chains are stretched at the same stretch ratio, the molecular chains are easily arranged and a crystal structure is easily formed. Therefore, the tear resistance is low (R1 is low). As a method of lengthening the molecular chain of the polyester constituting the biaxially oriented polyester film, a method of increasing the intrinsic viscosity used as a raw material of the film or a method of linking molecular chains with a chain extender can be used. It is not limited to.
(1-3) A method in which a polyester film has a laminated structure, and other resins having different melting points such as polyester, polyamide, polyphenylene sulfide, and polyolefin are laminated and stretched. When laminated with a resin having a melting point higher than that of polyester, it can be stretched at a higher temperature than a film made only of polyester. When stretched under such conditions, the molecular chains are difficult to align and the orientation of the molecular chains is relaxed, so that the tear resistance is high (R1 is high). On the other hand, when laminated with a resin having a melting point lower than that of polyester, it can be stretched at a temperature lower than that of a film made only of polyester. When stretched under such conditions, the molecular chains are easily arranged and a crystal structure is easily formed, so that the tear resistance is low (R1 is low).

Moreover, it is preferable that the polyester film of this invention satisfy | fills following (3).
(3) | Rt−Rm | is 5 N / mm or more and 30 N / mm or less.

  If | Rt−Rm | exceeds 30 N / mm, even if R1 is large, tearing may occur in the longitudinal direction or the width direction during film processing. On the other hand, if | Rt−Rm | exceeds 30 N / mm, the film may be curled, and the film may be easily damaged when the film is inserted into the mold.

  On the other hand, the difference | Rt−Rm | between Rt and Rm is preferably smaller and most preferably 0 from the viewpoint of suppressing the occurrence of tearing in the longitudinal direction or the width direction during film processing. However, a film having a difference | Rt−Rm | of Rt and Rm of less than 5 N / mm has tear resistance in the longitudinal direction and the width direction of the same level. Therefore, depending on the force applied when cutting in a certain direction is required. In some cases, there is a problem that tearing occurs not only in the direction to be cut but also in another direction. Therefore, by setting the difference | Rt−Rm | between Rt and Rm to be 5 N / mm or more, it is possible to improve the workability in the direction of 90 ° in that direction while maintaining the difficulty of tearing in a certain direction. The direction of insertion and cutting according to the process at the time of processing can be selected. | Rt−Rm | is preferably 10 N / mm or more and 25 N / mm or less, and more preferably 15 N / mm or more and 20 N / mm or less.

In order to set | Rt−Rm | to the above value, it is necessary to impart anisotropy to the molecular chain orientation of the polyester film. For example, it can be adjusted by the following method. The method for obtaining the axial polyester film is not limited to these.
(3-1) A method of increasing the difference between the stretching ratio in one direction and the other stretching ratio when producing a biaxially oriented polyester.
(3-2) A method of forming a laminated polyester film obtained by bonding polyester films having different degrees of orientation.
(3-3) The polyester film has a laminated structure of three or more layers, and a polyester having a melting point higher than that of the inner layer is laminated on the surface layer and biaxially stretched, thereby causing a difference in stretching behavior between the surface layer and the inner layer when co-stretched. Anisotropy can be imparted to the orientation of the molecular chain.
(3-4) The polyester film has a laminated structure of three or more layers, and a polyester having a lower intrinsic viscosity than the inner layer is laminated on the surface layer and biaxially stretched, so that there is a difference in stretching behavior between the surface layer and the inner layer when co-stretched. Anisotropy can be imparted to the orientation of the resulting molecular chain.

The biaxially oriented polyester film of the present invention needs to satisfy the following (2).
(2) The bending stiffness by the loop stiffness tester at a depth of 7.0 μm from at least one polyester film surface layer is 30 μN / 5 mm or more and 50 μN / 5 mm or less.

  The bending stiffness by the loop stiffness tester is obtained by a method described later, and serves as an index representing the hardness of the film. Higher values indicate that the film is harder and less likely to be damaged, and lower values indicate that the film is softer and more likely to be damaged. Therefore, the bending stiffness by the loop stiffness tester at a depth of 7.0 μm from the surface layer of the polyester film is an index representing the hardness near the film surface layer. When the bending rigidity at a depth of 7.0 μm from the polyester film surface layer is 30 μN / 5 mm or more, the structure of the film surface layer is hard and rigid, and the durability is improved. Scratches and wrinkles can be prevented from entering the film. The bending rigidity of the film surface layer is preferably 35 μN / 5 mm or more, and more preferably 40 μN / 5 mm. On the other hand, if the bending stiffness at a depth of 7.0 μm from the surface layer of the polyester film exceeds 50 μN / mm, the crease is difficult to be formed during bending.

In order to set the bending rigidity at a depth of 7.0 μm from the surface of the polyester film to the above value, for example, it can be adjusted by the following method, but the method for obtaining the biaxial polyester film of the present invention is not limited thereto.
(2-1) When the biaxially oriented polyester is produced, if the draw ratio is lowered, the orientation of the molecular chain can be relaxed and the bending rigidity can be lowered. On the other hand, when the draw ratio is increased, the orientation of the molecular chain becomes strong and rigid, so that the bending rigidity can be increased.
(2-2) A method in which a polyester film is made into a laminated structure, and resins having different orientations are laminated and stretched can be mentioned. The resin constituting the surface layer is stretched as a resin that is more easily oriented than the resin constituting the inner layer (for example, the resin constituting the surface layer has a shorter molecular chain (lower intrinsic viscosity) than the resin constituting the inner layer, or the surface layer The resin constituting the surface layer is oriented more strongly than the resin constituting the inner layer by making the resin constituting the inner layer a lower melting point than the resin constituting the inner layer and stretching at a low temperature under the conditions of the inner layer. The bending rigidity of the surface layer can be increased.
(2-3) When glass fiber or inorganic particles are contained in the polyester resin composition constituting the polyester film, the bending rigidity can be improved.

  Since the biaxially oriented polyester film of the present invention can improve the yield at the time of cutting or bending using a mold by satisfying the above requirements (1) and (2), the cutting or bending in particular. It can be suitably used for an insulating member of a motor that frequently processes.

  Moreover, it is preferable that the frequency | count until it cleaves in the fir test is 100 times or more and 1000 times or less until the biaxially oriented polyester film of this invention.

  The number of times until cleaving in the fir tree test is determined by the method described later, and is an index representing the brittleness of the film. The higher the value, the tougher and less fragile film, and the lower the value, the more brittle and fragile film. It is preferable to set the number of times until cleaving in the fir test to 100 times or more because flexibility inside the film can be maintained and cleavage can be prevented when the film is cut. Further, the larger the number of times until cleaving in the fir tree test is, the more preferable it is because the cleavage during the cutting process can be suppressed. However, when the film exceeds 1000 times, the mechanical strength may be insufficient. It is more preferably 500 times or more and 1000 times or less, and most preferably 800 times or more and 1000 times or less in order to suppress cleavage during the cutting process.

  In the biaxially oriented polyester film of the present invention, the folding strength FE is preferably 4.0 or more.

  The bending strength FE is obtained by a method described later, and is an index representing the ease of cracking of the film. The higher the value, the more difficult the film is to be broken when folded, and the lower the value, the easier the film is to be broken when folded. By making the folding strength FE of the film 4.0 or more, the film can be prevented from cracking during bending or punching, and the yield can be improved, and more preferably 5.0 or more. On the other hand, if it exceeds 7.0, it may be difficult to make a crease during processing. Therefore, it is preferably 7.0 or less.

  The biaxially oriented polyester film of the present invention comprises three layers of A / B / A, the intrinsic viscosity of the polyester resin constituting the A layer is 0.50 or more and 0.62 or less, and constitutes the B layer. The intrinsic viscosity of the polyester resin is preferably 0.60 or more and 0.80 or less, and the intrinsic viscosity of the polyester resin constituting the A layer is preferably lower than the intrinsic viscosity of the polyester resin constituting the B layer.

  The biaxially oriented polyester film of the present invention comprises three layers of A / B / A, the melting point of the polyester resin constituting the A layer is 260 ° C. or more and 300 ° C. or less, and the melting point of the polyester resin constituting the B layer. The melting point of the polyester resin constituting the A layer is preferably higher than the melting point of the polyester resin constituting the B layer.

  Further, the biaxially oriented polyester film of the present invention comprises three layers of A / B / A, the intrinsic viscosity of the polyester resin constituting the A layer is 0.50 or more and 0.62 or less, and the melting point is 260 ° C. or more. 300 ° C. or less, the intrinsic viscosity of the polyester resin constituting the B layer is 0.60 or more and 0.80 or less, the melting point is 240 ° C. or more and 260 ° C. or less, and the intrinsic viscosity of the polyester resin constituting the A layer is More preferably, it is lower than the intrinsic viscosity of the polyester resin constituting the B layer, and the melting point of the polyester resin constituting the A layer is higher than the melting point of the polyester resin constituting the B layer.

  In general, when the molecular chain orientation of the biaxially oriented polyester film is increased, the bending rigidity is improved, but the tear resistance is lowered. Therefore, by making the polyester film into three layers of A / B / A, a physical property difference can be generated between the surface layer and the inner layer of the film. As a result, bending rigidity is imparted by increasing the orientation of the molecular chains of the polyester that constitutes the surface layer, and flexibility is imparted and tear resistance is imparted by suppressing the orientation of the molecular chains of the polyester that constitutes the inner layer. Can be made.

  If the intrinsic viscosity of the polyester resin constituting the A layer is too low, durability in oil may be reduced when used as an insulating member for a motor. Moreover, when the intrinsic viscosity of the polyester constituting the A layer is too high, lamination unevenness may easily occur when laminated by coextrusion. A preferable range of the intrinsic viscosity of the polyester resin constituting the A layer is 0.53 or more and 0.61 or less. The intrinsic viscosity of the polyester constituting the B layer is 0.60 or more and 0.80 or less, preferably 0.62 or more and 0.78 or less, and the durability is increased by making it higher than the intrinsic viscosity of the polyester resin constituting the A layer. Since tear resistance and workability can be imparted, it can be suitably used as an insulating member for a motor. Moreover, it is preferable that the difference of the intrinsic viscosity of the polyester resin which comprises A layer and the intrinsic viscosity of the polyester resin which comprises B layer is 0.01 or more and 0.30 or less. By setting it as the said range, it can be set as a film with favorable workability and scratch resistance, making film forming property favorable. The difference between the intrinsic viscosity of the polyester resin constituting the A layer and the intrinsic viscosity of the polyester resin constituting the B layer is more preferably 0.03 or more and 0.20 or less, and 0.05 or more and 0.15 or less. More preferably it is.

  Further, if the melting point of the polyester resin constituting the A layer is too high, lamination unevenness may easily occur when the layers are laminated by coextrusion. Further, if the melting point of the polyester constituting the B layer is too low, the durability may be lowered because it may be under high temperature conditions when used as an insulating member for a motor. A preferable range of the melting point of the polyester resin constituting the A layer is 262 ° C. or higher and 295 ° C. or lower. The melting point of the polyester resin constituting the B layer is 240 ° C. or more and 260 ° C. or less, preferably 245 ° C. or more and 260 ° C. or less, and is lower than the melting point of the polyester resin constituting the A layer. Can be suitably used as an insulating member for a motor. Moreover, it is preferable that the difference of the melting point of the polyester resin which comprises A layer and the melting point of the polyester resin which comprises B layer is 5 degreeC or more and 40 degrees C or less. By setting it as the said range, it can be set as a film with favorable workability and scratch resistance, making film forming property favorable. More preferably, it is 5 ° C. or higher and 30 ° C. or lower.

  The biaxially oriented polyester film of the present invention of the present invention comprises three layers of A / B / A, the resin constituting the A layer is a polyphenylene sulfide having a melting point of 270 ° C. or higher and 300 ° C. or lower, You may employ | adopt the structure made into the polyester resin whose melting | fusing point is 240 to 260 degreeC.

  The biaxially oriented polyester film of the present invention preferably has a total film thickness of 100 μm or more and 500 μm or less. When a polyester film is used as an insulating member of a motor, it is exposed to high-temperature oil, and deterioration proceeds from the surface layer of the film. Therefore, by setting the total thickness of the film to 100 μm or more, the amount of polyester decomposed relative to the total amount of polyester constituting the film is small, and deterioration of the entire film can be suppressed. Moreover, when the total thickness of the film exceeds 500 μm, it may be easily broken when the film is bent.

  Moreover, when the biaxially oriented polyester film of the present invention has a laminated structure composed of A / B / A as described above, the ratio of the sum of the thicknesses of the A layer and the thickness of the B layer is 1: 2.5 to 1:10. It is preferable that it is the range of these. By making the ratio of the sum of the thickness of the A layer and the thickness of the B layer 1: 2.5 to 1:10, a film having good workability and scratch resistance can be obtained while improving the film forming property. Is preferable. More preferably, the thickness of the surface layer A is the same, and the ratio of the thickness of the A layer / the thickness of the B layer / the thickness of the A layer is preferably 1: 6: 1 to 1: 15: 1.

  Moreover, when the biaxially oriented polyester film of the present invention is placed under the condition of 200 ° C. and 0% RH (200 ° C. dry heat test), the time required for the strength retention to be 50% or less is 300 hours or more. Preferably there is. More preferably, it is 350 hours or more, More preferably, it is 400 hours or more, Especially preferably, it is 450 hours or more. By setting it as 300 hours or more, when it is used for an application requiring heat resistance (for example, an insulating member application for a motor), it can be a film that maintains its characteristics for a long period of time.

  Next, although an example is given and demonstrated about the manufacturing method of the biaxially-oriented polyester film of this invention, this invention is limited to only the thing obtained by this example, and is not interpreted.

  As a method for obtaining the polyester used in the present invention, a conventional polymerization method can be employed. For example, it can be obtained by subjecting a dicarboxylic acid component such as terephthalic acid or a derivative thereof and a diol component such as ethylene glycol to a transesterification reaction or an esterification reaction by a known method, and then performing a melt polymerization reaction. If necessary, the polyester obtained by the melt polymerization reaction may be subjected to a solid phase polymerization reaction at a temperature lower than the melting point of the polyester.

  Although the polyester film of the present invention can be obtained by a conventionally known production method, the average value of tear resistance Rm and Rt and | Rt−Rm | Since the polyester film made into the range can be obtained stably, it is preferable.

  The polyester film of this invention can use the method (melt cast method) which heat-melts the raw material dried as needed in an extruder, and extrudes it on the cast drum cooled from the nozzle | cap | die, and processes it into a sheet form. As another method, the raw material is dissolved in a solvent, and the solution is extruded from a die onto a support such as a cast drum or an endless belt to form a film, and then the solvent is dried and removed from the film layer to form a sheet. A method (solution casting method) or the like can also be used.

  When the film is produced by the melt casting method, an extruder is used for each layer constituting the laminated polyester film, the raw materials of each layer are melted, and these are melted in a joining device provided between the extrusion device and the die. A method is preferably used in which the layers are laminated, guided to a die, and extruded from the die onto a cast drum and processed into a sheet shape. The laminated sheet is adhered and cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 ° C. or higher and 40 ° C. or lower to produce an unstretched sheet, or the unstretched sheet is further biaxially stretched. A polyester film can be obtained.

  When performing melt extrusion in an extruder, it is better that the time from melting in a nitrogen atmosphere to supplying chips to the extruder and extruding with a die is as short as possible. As a guideline, it is 30 minutes or less, more preferably 15 minutes. Hereinafter, more preferably 5 minutes or less, from the viewpoint of suppressing the increase in the amount of terminal carboxyl groups, and when using a plurality of types of polyester raw material, the polyester is copolymerized by a transesterification reaction in the extruder. It is preferable from the viewpoint of suppression. The amount of the terminal carboxyl group of the resin constituting the polyester film of the present invention is 15 eq. / T (equivalent / t) or less is preferable. The temperature of the extruder at the time of melt extrusion with an extruder is from the viewpoint of suppressing an increase in the amount of terminal carboxyl groups, and when multiple types of polyester raw materials are used, the polyester is copolymerized by a transesterification reaction in the extruder. From the viewpoint of suppressing this, it is preferably less than 300 ° C, more preferably less than 290 ° C.

The obtained unstretched sheet is biaxially stretched under the condition (i).
(I) At a temperature T1n satisfying the following expression (a), the film is biaxially stretched in an area magnification of 6 times or more in the longitudinal direction (MD) and the width direction (TD) of the film.
(A) Tg ≦ T1n ≦ Tg + 30 ° C.
Tg: Glass transition temperature (° C.) of polyester resin as a main constituent
As a method of biaxial stretching, in addition to a sequential biaxial stretching method in which stretching in the longitudinal direction (MD) of the film and stretching in the width direction of the film (direction perpendicular to the longitudinal direction of the film, TD) is performed, the longitudinal direction Examples thereof include a simultaneous biaxial stretching method in which stretching in the direction and the width direction is simultaneously performed.

  When the stretching temperature (T1n) is Tg or less, stretching cannot be performed. Moreover, when T1n is in the above range, it becomes possible to impart orientation to the resin constituting the polyester film.

  Next, in order to complete the crystal orientation of the obtained biaxially stretched film and to impart flatness and dimensional stability, it is 30 seconds or more at a temperature of Tg or more and less than the melting point of the main constituent polyester resin. The polyester film of the present invention is obtained by performing a heat treatment for 2 seconds or less, uniformly cooling, and then cooling to room temperature.

  The film obtained by this invention can improve the yield at the time of a cutting process and bending using a metal mold | die, and can be used suitably especially for the insulating member of the motor which cuts and bends frequently.

[Characteristic evaluation method]
A. Refractive index The refractive index of a film is determined by measuring the refractive index in all directions by the following method. When the refractive index of the film to be measured cannot be measured by the following method, the longitudinal direction of the film is the direction having the maximum refractive index, and the width direction is the direction forming 90 ° with the direction having the maximum refractive index. When the film is substantially square, the direction parallel to any side is the longitudinal direction, and the direction at 90 ° is the width direction.
・ Device: Abbe refractometer 4T (manufactured by Atago Co., Ltd.)
・ Light source: Sodium D line ・ Measurement temperature: 25 ° C.
・ Measurement humidity: 65% RH
Mount solution: methylene iodide, sulfur methylene iodide Melting point of resin (℃)
Using a method based on JIS K-7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. and a disk session “SSC / 5200” for data analysis were used. The measurement was carried out in the following manner.
The sample was weighed in a sample pan by 5 mg, and the sample was heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1st RUN). A 1st RUN differential scanning calorimetry chart (the vertical axis is thermal energy and the horizontal axis is temperature) is obtained. In the differential scanning calorimetry chart of 1stRun, the peak top temperature at the crystal melting peak, which is the endothermic peak, is determined, and this is defined as the melting point (° C.). When two or more crystal melting peaks are observed, the temperature at the peak top with the highest temperature is taken as the melting point.

C. Tear resistance (tearability, tear anisotropy)
A. In the measurement, tear resistance (N / mm) in the direction having the maximum refractive index and the direction forming 90 ° was measured using a digital light load tear tester manufactured by Toyo Seiki Seisakusho. The sample size is 63 mm in the tear direction, 50 mm in the direction perpendicular to the tear direction, 13 mm incision is made in the tear direction, the tear strength (mN) when the remaining 50 mm is torn is read, and the tear is calculated by the following formula Resistance (N / mm) was calculated. The measurement was performed 5 times, and Rt and Rm were calculated by calculating the average value.
Tear resistance (N / mm) = Tear strength (mN) / Sample thickness (μm)
Moreover, average values R1 and | Rt−Rm | were calculated from the obtained Rt and Rm, and tearability and tear anisotropy were evaluated.
(Tearability)
30 <R1 ≦ 40: Tearability S
20 <R1 ≦ 30 (except for S): Tearability A
10 ≦ R1 ≦ 20 (excluding those corresponding to S and A): Tearability B
R1 <10, 40 <R1: Tearing C
S is the best and C is the worst.
(Tear anisotropy)
15 ≦ | Rt−Rm | ≦ 20: Tear anisotropy S
10 ≦ | Rt−Rm | ≦ 25 (except for S): Tear anisotropy A
5 ≦ | Rt−Rm | ≦ 30 (except for S and A): Tear anisotropy B
| Rt−Rm | <5: Tear anisotropy C
| Rt−Rm |> 30: Tear anisotropy C
S is the best and C is the worst.

D. Flexural rigidity (μN / 5mm)
A film having a thickness of 7 μm is cut out from the film surface by a microtome and cut into test pieces having a length of 100 mm and a width of 5 mm. Using a loop step tester manufactured by Toyo Seiki Seisakusho Co., Ltd., a test piece placed in a loop shape was loaded with a load from the tip of the loop, and the loop was crushed in the diameter direction, and the load at that time was measured. . At this time, the loop length was 50 mm, the crushing distance was 20 mm, the measurement was performed 5 times, and the average value was calculated. The bending rigidity (μN / 5 mm) was calculated from the obtained load (mg) using the following formula.
Flexural rigidity (μN / 5mm) = Load (mg) × 9.8
E. Scratch resistance The number of rub tests is measured according to JISK6328 using a Scott-type scoring abrasion tester manufactured by Toyo Seiki Seisakusho. The sample size was measured at a width of 10 mm, a length of 200 mm, a load of 2 kg, a distance between chucks of 30 mm, a stroke distance of 50 mm, and a speed of 120 times / min. The measurement was performed 5 times and evaluated from the average value.
800 ≦ scratch test ≦ 1000: Scratch resistance S
500 ≦ Scratch test <800: Scratch resistance A
100 ≦ Scratch test <500: Scratch resistance B
Scratch test <100: Scratch resistance C
S is the best and C is the worst.

F. Folding strength FE
The test is performed based on JIS P-8115 (1994). The film is cut out to 5 mm × 100 mm so that the direction to be measured becomes the long side, using a folding test machine manufactured by Toyo Seiki Co., Ltd., tension 9.8 N / mm 2, clamp R 0.38 mm, folding angle 135 ° The test is performed at a rotational speed of 175 cpm. A. In this measurement, the test is performed with n = 5 in each of the direction having the maximum refractive index and the direction forming 90 °, and the number of times until the film breaks is measured. Folding strength FE is calculated from the average value N by the following formula, and bendability is evaluated.
FE = logN
G. Intrinsic viscosity IV
The polyester resin is dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / dl), and the viscosity of the solution at 25 ° C. is measured using an Ostwald viscometer. Similarly, the viscosity of the solvent is measured. [Η] (dl / g) is calculated by the following formula using the obtained solution viscosity and solvent viscosity, and the obtained value is used as the intrinsic viscosity (IV).
ηsp / C = [η] + K [η] ² · C
(Where ηsp = (solution viscosity (dl / g) / solvent viscosity (dl / g)) − 1, K is a Huggins constant (assuming 0.343)).

H. Thickness (μm) of each layer of laminated film
The film cross section is cut out with a microtome in a direction parallel to the film width direction. The cross section is observed with a scanning electron microscope at a magnification of 5000 times to determine the thickness ratio of each layer. The thickness of each layer is calculated from the obtained lamination ratio and the above-described film thickness.

I. Scratch resistance The film was cut out so that the film had a length of 40 mm and a width of 20 mm, and then both end portions were folded back by 5 mm in parallel to the width direction to prepare a sample for motor insertion. This sample was inserted into a motor rotor portion as shown in FIG. This insertion operation was repeated, and the number of times S until the film was visually confirmed to be scratched was measured to evaluate the scratch resistance during film insertion. About each side of the film, it implemented 5 times each and evaluated by the average value of a total of 10 times.
1000 ≦ S: Scratch resistance S
600 ≦ S <1000: Scratch resistance A
300 ≦ S <600: Scratch resistance B
S <300: Scratch resistance C
S is the best and C is the worst.

J. et al. Cracking during processing (punchability)
Using a test piece punching machine manufactured by Kobunshi Keiki Co., Ltd., the laminated film is punched into a No. 5 dumbbell shape described in JIS K-6251. The number of sheets M in which the end face is cracked when punching 10 films one by one is counted, and the punchability is evaluated.
0 ≦ M ≦ 2: Punchability S
3 ≦ M ≦ 5: Punchability A
6 ≦ M ≦ 8: Punchability B
9 ≦ M ≦ 10: Punchability C
S is the best and C is the worst.

K. Heat resistance [Strength half-life]
The film is cut into a size of 1 cm × 20 cm so that the long side is parallel to the longitudinal direction and the width direction of the film, respectively, and according to ASTM-D882 (1997), the chuck is 5 cm and the pulling speed is 300 mm / min. Measure the breaking strength when pulled. The number of samples is n = 5, and after measuring in the longitudinal direction and the width direction of the film, the average value thereof is obtained, and this is set as the breaking strength E0 of the film.
Next, the film cut in the same manner is subjected to a dry heat treatment in a gear oven manufactured by Tabai Espec Co., Ltd. under a high temperature condition of a temperature of 200 ° C. and a relative humidity of 0% RH, and then the breaking strength is measured. In addition, it is set as n = 5 and it measures about each of the longitudinal direction of a film, and the width direction, and let the average value be breaking strength E1. Using the obtained breaking strengths E0 and E1, the strength retention is calculated by the following equation. The treatment time was changed by 1 hour, and the time required for the strength retention to be 50% or less was determined.

Strength retention (%) = E1 / E0 × 100
From the time required for the obtained strength retention to be 50% or less, the heat resistance of the film was determined as follows.
When the time required for the strength retention to be 50% or less is 450 hours or more: A
When the time required for the strength retention to be 50% or less is 400 hours or more and less than 450 hours: B
When the time required for the strength retention to be 50% or less is 350 hours or more and less than 400 hours: C
When the time required for the strength retention to be 50% or less is 300 hours or more and less than 350 hours: D
When the time required for the strength retention to be 50% or less is less than 300 hours: E
A to C are good, and A is the best among them.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

  [Production of PET] From terephthalic acid and ethylene glycol, polymerization was carried out by a conventional method using antimony trioxide as a catalyst to obtain PET-α. The obtained PET-α was solid-phase polymerized by a conventional method to obtain PET.

  [Production of PEN] A transesterification reaction was carried out from dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol using manganese acetate as a catalyst. After the transesterification reaction, PEN was obtained by a conventional method using antimony trioxide as a catalyst.

  [Production of polycyclohexylenedimethylene terephthalate (PCHT)] A transesterification reaction was carried out from dimethyl terephthalate and 1,4-cyclohexanedimethanol using manganese acetate as a catalyst. After the transesterification reaction, PCHT was obtained by a conventional method using antimony trioxide as a catalyst.

[Production of polybutylene terephthalate (PBT)]
A transesterification reaction was carried out from dimethyl terephthalate and 1,4-butanediol using manganese acetate as a catalyst. After the transesterification reaction, PBT was obtained by a conventional method using antimony trioxide as a catalyst.

(Examples 1-14)
As the resin constituting the A layer, PEN and PET having the physical properties shown in the table were blended so as to have the ratio shown in the table, vacuum dried at 180 ° C. for 2 hours, and then charged into the extruder 1. Further, as the resin constituting the B layer, PET having the physical properties shown in the table was vacuum-dried at 180 ° C. for 2 hours and then charged into the extruder 2. Each raw material was melted in an extruder, and the resin charged into the extruder 1 was merged by a merger so as to be both surface layers of the film, and extruded into a casting drum shape to produce a laminated sheet having a three-layer structure. Subsequently, the sheet is preheated with a heated roll group, and then stretched at a stretching ratio shown in the table in the longitudinal direction (MD direction) at a temperature of 95 ° C., and then cooled with a roll group at a temperature of 25 ° C. to be uniaxial. A stretched film was obtained. The resulting uniaxially stretched film was stretched at a stretching ratio shown in the table in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110 ° C. in the tenter while holding both ends with clips. Subsequently, a heat treatment was performed for 10 seconds at a temperature of 220 ° C. in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 4% width direction at a temperature of 220 ° C. Next, the film was gradually cooled in the cooling zone and wound up to obtain a laminated polyester film having a lamination ratio and thickness shown in the table. Each characteristic of the obtained film is shown in the table. It was found that the film was excellent in workability such as tearability, tear anisotropy, scratch resistance, scratch resistance, and punchability.

(Examples 15 to 27)
A laminated film was obtained in the same manner as in Examples 1 to 13 except that the resin constituting the A layer was PCHT. Each characteristic of the obtained film is shown in the table. Although the cracking property is slightly inferior to PEN, it was found that the film was excellent in workability such as tearing property, tearing anisotropy, scratch resistance, scratch resistance, and punchability.

(Examples 28 and 29)
PET having the physical properties shown in the table was vacuum-dried at 180 ° C. for 2 hours and then charged into the extruder 1 and melted in the extruder and extruded into a casting drum to produce a single-layer sheet. Next, a single-layer PET film was obtained in the same manner as in Examples 1-13. After applying an epoxy adhesive on both sides of the resulting polyester film and drying it, the polyphenylene sulfide (PPS) film “Torelina” manufactured by Toray Industries, Inc. was layered and cured at 150 ° C. for 1 hour. Thus, a laminated film having a thickness and a lamination ratio shown in the table was obtained. Each characteristic of the obtained film is shown in the table. Although the resistance to cracking and cracking are slightly inferior to those of PEN, it was found that the film was excellent in tearability, tearing anisotropy, scratch resistance, resistance to scratching, cracking, and other workability.

(Example 30)
As the resin constituting the A layer, PEN and PET having the physical properties shown in the table were blended so as to have the ratio shown in the table, vacuum dried at 180 ° C. for 2 hours, and then charged into the extruder 1. Further, as the resin constituting the B layer, PET having the physical properties shown in the table was vacuum-dried at 180 ° C. for 2 hours and then charged into the extruder 2. A laminated film was obtained in the same manner as in Example 1 except that a laminated sheet having a two-layer structure was produced. Each characteristic of the obtained film is shown in the table. It was found that the film was excellent in processability, although it was slightly inferior in tear resistance and scratch resistance.

(Comparative Example 1)
A single film of PEN was obtained in the same manner as in the example. The physical properties of the film are shown in the table. Tear resistance Rt and Rm average R1 is outside the range of 10 to 40 N / mm, resulting in poor tearability, and | Rt-Rm | is also outside the range of 5 to 30 N / mm, resulting in poor tear anisotropy. Met.

(Comparative Example 2)
A PET single film was obtained in the same manner as in the Examples. The physical properties of the film are shown in the table. Since | Rt−Rm | was outside the range of 5 to 30 N / mm, the film was inferior in tearing anisotropy, and was inferior in scratch resistance when the bending rigidity was outside the range of 30 to 50 μN / 5 mm.

(Comparative Example 3)
A PET single film was obtained in the same manner as in the Examples. The physical properties of the film are shown in the table. Since the average R1 of the tear resistances Rt and Rm was outside the range of 10 to 40 N / mm, the film was inferior in tearability, and was inferior in scratch resistance when the bending rigidity was outside the range of 30 to 50 μN / 5 mm.

(Comparative Example 4)
A laminated film was obtained in the same manner as in Example 1 except that the resin constituting the A layer was PBT described in the table. The physical properties of the film are shown in the table. The film was inferior in scratch resistance when the bending stiffness was outside the range of 30 to 50 μN / 5 mm.

Since the polyester film of the present invention is difficult to tear at the time of cutting and the surface layer is not easily damaged at the time of inserting a slot, the yield at the time of cutting or bending using a mold can be improved. It can be suitably used for an insulating member of a motor that is frequently used.

1 Film insertion hole 2 Motor rotor (core)
3 Insertion hole width 4 Insertion hole length

Claims (10)

A biaxially oriented polyester film satisfying the following (1) and (2).
(1) The average R1 ((Rm + Rt) / 2) of the tear resistance Rm in the direction having the maximum refractive index and the tear resistance Rt in the direction forming 90 ° with the direction having the maximum refractive index is 10 N / mm or more and 40 N / mm or less.
(2) The bending stiffness by the loop stiffness tester at a depth of 7.0 μm from at least one polyester film surface layer is 30 μN / 5 mm or more and 50 μN / 5 mm or less. The biaxially oriented polyester film according to claim 1, which satisfies the following (3).
(3) | Rt−Rm | is 5 N / mm or more and 30 N / mm or less. The biaxially oriented polyester film according to claim 1 or 2, wherein the number of times until cleaving in the fir tree test is 100 or more and 1000 or less. The biaxially oriented polyester film according to any one of claims 1 to 3, which has a bending strength FE of 4.0 or more.   The biaxially oriented polyester film according to any one of claims 1 to 4, wherein when it is placed at 200 ° C and 0% RH, the time required for the strength retention to be 50% or less is 300 hours or more. . It consists of three layers of A / B / A, the intrinsic viscosity of the polyester resin constituting the A layer is 0.50 or more and 0.62 or less, and the intrinsic viscosity of the polyester resin constituting the B layer is 0.60 or more and 0.00. The biaxially oriented polyester film according to any one of claims 1 to 5, which is 80 or less and the intrinsic viscosity of the polyester resin constituting the A layer is lower than the intrinsic viscosity of the polyester resin constituting the B layer. The polyester resin comprising the three layers A / B / A has a melting point of 260 ° C. or higher and 300 ° C. or lower, and the polyester resin constituting the B layer has a melting point of 240 ° C. or higher and 260 ° C. or lower. The biaxially oriented polyester film according to any one of claims 1 to 5, wherein a melting point of the polyester resin constituting the B is higher than a melting point of the polyester resin constituting the B layer. A polyester comprising three layers of A / B / A, the polyester resin constituting the A layer having an intrinsic viscosity of 0.50 to 0.62 and a melting point of 260 ° C. to 300 ° C., constituting the B layer The intrinsic viscosity of the resin is 0.60 or more and 0.80 or less, and the melting point is 240 ° C. or more and 260 ° C. or less,
The intrinsic viscosity of the polyester resin constituting the A layer is lower than the intrinsic viscosity of the polyester resin constituting the B layer, and the melting point of the polyester resin constituting the A layer is higher than the melting point of the polyester resin constituting the B layer. Item 6. The biaxially oriented polyester film according to any one of Items 1 to 5. The biaxially oriented polyester film according to any one of claims 6 to 8, wherein the ratio of the sum of the thicknesses of the A layer and the thickness of the B layer is in the range of 1: 2.5 to 1:10. The biaxially oriented polyester film according to any one of claims 1 to 9, which is used as an insulating member for a motor.

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