JP5598178B2 - Weather resistant polyester film - Google Patents

Description

  The present invention relates to a weather resistant polyester film suitable for use in a high temperature and high humidity environment or outdoors. More specifically, the present invention relates to a weather-resistant polyester film that has excellent hydrolysis resistance and can maintain durability over a long period of time.

  Polyester films are excellent in mechanical properties, thermal properties, and chemical resistance, and are used in various applications. In particular, films mainly composed of polyethylene terephthalate have been used in various applications such as industrial applications, packaging applications, and printing applications. However, when a polyester film is used under high temperature and high humidity, hydrolysis of ester bond sites in the molecular chain occurs, resulting in a problem that the mechanical strength is reduced. is there.

  It is known that the hydrolysis of polyester proceeds faster as the carboxyl end concentration (acid value) of the polyester molecular chain is higher. Until now, in order to improve the hydrolysis resistance of polyester, various studies have been made to keep the carboxyl terminal concentration (acid value) of the film resin low. (Patent Documents 1 and 2).

  In addition, a polyester having a relatively high molecular weight (relatively high intrinsic viscosity) is used in order not to greatly reduce the mechanical strength even if the deterioration has progressed to some extent. (Patent Documents 3, 4, 5, 6).

JP 2007-150084 A JP 2007-204538 A JP 2002-134770 A JP 2002-26354 A JP 2006-270025 A JP 2008-31680 A

  The proposed film is improved in hydrolysis resistance as compared with a normal polyester film due to the improved resin composition. However, when the film is used for a long period of time in a harsh usage environment, these films sometimes break early, unlike the initial assumption.

  In view of the above problems, an object of the present invention is to provide a weather-resistant polyester film that has hydrolysis resistance and can maintain durability over a long period of time.

  The present inventor examined the occurrence of breakage that occurred earlier than expected as described above, and found that this was caused by differences in strength and elongation in the film plane. In the case where there is variation in the strength and elongation of the film within the plane of the film, the deterioration of the polyester proceeds, and the breakage of the film proceeds starting from the low elongation portion. Therefore, it was considered that the original weather resistance of the polyester having a carboxyl terminal concentration (acid value) cannot be expressed.

  Therefore, in order to maintain durability over a long period of time, not only the carboxyl end concentration (acid value) is lowered by modifying the resin composition and the molecular weight is increased, but also the difference in strength and elongation in the film surface is reduced. Was considered necessary.

  That is, the present inventor senses that not only the polyester resin composition but also the mechanical property difference caused by the polyester stretching affects the long-term weather resistance of the polyester, and produces a polyester film by a specific stretching method. The present inventors have found a surprising effect of exhibiting excellent hydrolysis resistance as a weather-resistant polyester film, and have achieved the present invention.

That is, this invention is a biaxially-oriented polyester film, Comprising: It is a weather resistant polyester film which satisfy | fills the following structural requirements (1)-(4).
(1) The carboxyl end concentration is 25 eq / ton or less with respect to the polyester (2) The intrinsic viscosity (IV) of the film is 0.60 to 0.90 dl / g (3) JIS-C-2318-1997 For breaking strength (TS) measured according to 3.31 (tensile strength and elongation), the measured value in the longitudinal direction (MD direction) is TS (MD), and the measured value in the transverse direction (TD direction) is TS (TD) is set, and ΔTS defined by the following formula is 10 MPa or less.
ΔTS = | TS (MD) −TS (TD) |
(4) For the breaking elongation (TE) measured in accordance with JIS-C-2318-1997 5.3.31 (tensile strength and elongation), the measured value in the machine direction (MD direction) is TE ( MD), the measured value in the horizontal direction (TD direction) is TE (TD), and ΔTE defined by the following formula is 10% or less.
ΔTE = | TE (MD) −TE (TD) |
Furthermore, the present invention is the weather resistant polyester film obtained by the simultaneous biaxial stretching method.

The weather resistant polyester film of the present invention has good hydrolysis resistance and excellent long-term durability.
Therefore, it is also useful as a base film for solar cell members used outdoors (for example, a base film for solar cell back surface sealing) and a heat ray shielding film for automobile glazing.

  The weather-resistant polyester film of the present invention is a film composed of a polyester resin, and mainly contains at least one of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component. Among these polyester resins, polyethylene terephthalate is most preferable from the balance between physical properties and cost. Polymerization of polyethylene terephthalate (hereinafter simply referred to as PET) includes direct polymerization of terephthalic acid and ethylene glycol and, if necessary, other dicarboxylic acid components and diol components directly, and dimethyl ester of terephthalic acid (required) Depending on the method, any production method such as a transesterification method in which a transesterification reaction of ethylene glycol (including other diol components as necessary) and ethylene glycol (including other dicarboxylic acid methyl esters) can be used.

As the catalyst for preparing the polyester, conventionally known Mn, Mg, Ca, Ti, Ge, Sb, Co compound, aluminum compound, phosphorus compound, antimony compound and the like can be used.
In particular, it is advantageous for the suppression of thermal oxidation degradation to have a low metal content, and it is preferable to ensure a polymerization activity by using a small amount of an aluminum compound and a phosphorus compound as a promoter together. Further, the phosphorus compound preferably has a phenol moiety. A phosphorus compound containing a phenol moiety is particularly preferable because it has an effect of suppressing degradation of polyester that decomposes under a radical mechanism under oxygen. In order to enhance this function, it is preferable that the phenol moiety has a hindered phenol skeleton that is sterically and electronically stabilized and expresses more radical trapping ability.

  The composition containing the dicarboxylic acid component and the glycol component includes a stabilizer, a pigment, a dye, a nucleating agent, a filler, an ultraviolet absorber, an antioxidant, an antibacterial agent, and an antistatic agent, depending on the final use of the polyester. Additives such as lubricants and mold release agents can be contained.

  It is important for the weather resistant polyester film of the present invention that the carboxyl end concentration is 25 eq / ton or less with respect to the polyester to obtain high hydrolysis resistance. The weather resistant polyester film preferably has a carboxyl terminal concentration of 20 eq / ton or less, more preferably 18 eq / ton or less, still more preferably 15 eq / ton or less, and more preferably 13 eq / ton. It is particularly preferable that it is not more than 10 eq / ton. When this value is larger than 25 eq / ton, hydrolysis resistance is lowered, and sufficient durability can be exhibited, and early deterioration tends to occur. In addition, the measurement of the carboxyl terminal density | concentration of polyester can be measured by the titration method mentioned later or NMR method.

  The weather resistant polyester film of the present invention preferably has an intrinsic viscosity (IV) value of 0.60 to 0.90 dl / g in order to obtain high heat resistance and hydrolysis resistance, more preferably 0. .62 to 0.85 dl / g, more preferably 0.65 to 0.8 dl / g. When the intrinsic viscosity is lower than 0.60 dl / g, the hydrolysis resistance and heat resistance are not sufficient, and when it is higher than 0.90 dl / g, the back pressure in the melting process is increased. This is not preferable because the thermal deterioration is promoted due to the deterioration of the heat resistance and shear heat generation. In order to improve the hydrolysis resistance of the film, it is desirable to increase the intrinsic viscosity. However, when the intrinsic viscosity is increased, the back pressure in the melting process may increase, and the productivity of the film may decrease. In this invention, since it has the balanced film physical property as mentioned later, even if the intrinsic viscosity of polyester is in the said range, long-term durability can be maintained.

  In order to make the carboxyl end concentration of the polyester film within the above range, it is preferable that the carboxyl end concentration of the polyester chip used as the raw material resin is less than 25 eq / ton. Moreover, in order to make the intrinsic viscosity (IV) of a polyester film into the said range, it is preferable that the intrinsic viscosity (IV) of the polyester chip used as raw material resin shall be 0.60 dl / g or more. The carboxyl terminal concentration and intrinsic viscosity (IV) of the polyester chip can be adjusted to the above ranges by appropriately selecting the polymerization conditions of the resin. For example, production equipment factors such as the structure of the esterification reaction apparatus, composition ratio of dicarboxylic acid and glycol in the slurry supplied to the esterification reaction tank, esterification reaction temperature, esterification reaction pressure, esterification reaction time, etc. What is necessary is just to set reaction conditions or solid-state polymerization conditions etc. suitably. Furthermore, it is preferable to control the moisture content of the polyester chip or to control the resin temperature in the melting step. It is also a preferred method to block the carboxyl terminal of the polyester with an epoxy compound or a carbodiimide compound. In addition, although the one where the carboxyl terminal density | concentration of a polyester film is smaller is preferable, it considers that 0.5eg / ton is a minimum from the point of productivity.

  As described above, the present inventors have found that the film breakage that occurs earlier than expected due to long-term use in a high-temperature and high-humidity environment is due to the difference in film physical properties within the film plane. When there is a difference in breaking strength or breaking elongation in the film plane, the mechanical strength decreases at approximately the same rate as hydrolysis progresses, so the difference in breaking strength and breaking elongation in the initial state is relatively large. It becomes. Therefore, the balance of the mechanical strength in the film plane is lost due to the deterioration of the film, and the film is damaged from a relatively weak portion. Therefore, in order to improve the durability of the film, it is preferable not only to modify the polyester resin composition, but also to have a good balance between the breaking strength and the breaking elongation, which have an important effect on the mechanical strength, particularly the film breakage, in the film plane. .

The weather resistant polyester film of the present invention has a measured value in the MD direction of TS measured at rupture strength (TS) measured according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation). The measured value in the (MD) and TD directions is TS (TD), and ΔTS defined by the following formula is preferably 10 MPa or less, more preferably 5 MPa or less. The MD direction is the same as the longitudinal direction and the winding direction of the film, the TD direction is the same as the lateral direction of the film, and the MD direction and the TD direction are in an orthogonal direction.
ΔTS = | TS (MD) −TS (TD) |

The weather resistant polyester film of the present invention has a measured value in the MD direction with respect to the elongation at break (TE) measured in accordance with JIS-C-2318-1997 5.3.31 (tensile strength and elongation). TE (MD) and the measured value in the TD direction are TE (TD), and ΔTE defined by the following formula is preferably 10% or less, and more preferably 5% or less.
ΔTE = | TE (MD) −TE (TD) |

  Since the weather resistant polyester film of the present invention has a good balance of mechanical strength as described above, it can retain excellent hydrolysis resistance. The weather resistant polyester film of the present invention has an elongation at break (RTE) at 192 hours of 105 ° C., 100% RH, 0.03 MPa, which is an evaluation of hydrolysis resistance, in both the MD direction and the TD direction. Preferably it is 75% or more, More preferably, it is 80% or more, More preferably, it is 85% or more, More preferably, it is 90% or more. Furthermore, the elongation at break (RTE) at 400 ° C. under 105 ° C., 100% RH and 0.03 MPa is preferably 5% or more, more preferably 10% or more in both the MD direction and the TD direction. By being in such a range, the weather-resistant polyester film of the present invention can maintain high durability that can withstand long-term use outdoors.

  The weather resistant polyester film of the present invention has a good balance of mechanical properties as initial properties in the MD direction and the TD direction. For this reason, even when deterioration under high temperature and high humidity progresses, there is little difference in mechanical properties between the MD direction and the TD direction, and film breakage can be reduced. 105%, 100% RH, 0.03 MPa under 192 hours and 400 hours, the difference in fracture elongation retention in MD direction and TD direction (ΔRTE = | RTE (MD) −RTE (TD) |) is 10% The following is preferable, and 5% or less is more preferable.

  The breaking strength (TS) of the weather-resistant polyester film of the present invention is preferably 100 MPa or more, more preferably 120 MPa in both the MD direction and the TD direction. When the value of the breaking strength (TS) is less than the lower limit, it is difficult to achieve the strength as a film. Moreover, it is preferable that the breaking elongation (TE) of the weather-resistant polyester film of this invention is 120% or more in both MD direction and TD direction, and it is more preferable that it is 150% or more. When the value of the elongation at break (TE) is less than the above lower limit, the impact resistance of the film is lowered and the film is easily broken. In order to control the breaking strength (TS) and the breaking elongation (TE) within the above ranges, it is preferable to appropriately control the orientation of the film, the intrinsic viscosity of the polyester resin, and the thickness of the film.

  The polyester film of the present invention needs to be a biaxially oriented polyester film from the viewpoint of durability and mechanical strength. In the case of a biaxially oriented polyester film, a melting step for melting the polymerized polyester chip in an extruder, a film forming step for forming an unstretched film by extruding a molten resin from the extruder, a stretching step for stretching the unstretched film, And it is desirable to manufacture by passing through the heat setting process which heat-processes the stretched film. Next, the manufacturing method of the weather resistant polyester film of this invention is demonstrated in detail.

  In the melting step, the polyester chip is supplied to a melt extruder, heated to a temperature equal to or higher than the polymer melting point, and melted. At this time, it is preferable to use a sufficiently dried polyester chip in order to suppress an increase in the carboxyl end concentration during film production. The water content of the polyester chip used is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 30 ppm or less. As a method for drying the polyester chip, a known method such as drying under reduced pressure can be used.

  The maximum temperature of the polyester resin in the extruder is preferably 280 ° C. or higher, preferably 285 ° C. or higher, and more preferably 290 ° C. or higher. By raising the melting temperature, the back pressure at the time of filtration in the extruder is lowered, and good productivity can be achieved. Moreover, the maximum temperature of the polyester resin in the extruder is preferably 320 ° C. or less, and more preferably 310 ° C. or less. When the melting temperature is increased, the thermal degradation of the polyester proceeds, the carboxyl terminal concentration of the polyester increases, and the hydrolysis resistance may decrease.

  In the film forming step, a polyester resin is melt-extruded and formed into a sheet shape from a T-die on a cooling rotary roll to create an unstretched film. In this case, for example, by applying the technique described in Japanese Patent Publication No. 6-39521 and Japanese Patent Publication No. 6-45175, high-speed film formation is possible. Moreover, it is good also as a laminated | multilayer film by a co-extrusion method, using a some extruder, assigning various functions to an inner layer and an outer layer.

  In the case of producing a biaxially oriented polyester film, a sequential biaxial stretching method in which uniaxial stretching is performed in the longitudinal direction or the transverse direction and then stretching in the orthogonal direction, a simultaneous biaxial stretching method in which stretching is performed simultaneously in the longitudinal direction and the transverse direction, and Although a method using a linear motor can be adopted as a driving method for simultaneous biaxial stretching, it is preferable to use a simultaneous biaxial stretching method from the viewpoint of the present invention.

  A film stretched in the biaxial direction ideally has an orientation equal to the plane direction. However, in the sequential biaxial stretching method that is usually performed, the film tends to be oriented in the direction of the stretching axis in the subsequent stage, and a difference in mechanical strength within the film surface due to a difference in orientation tends to occur. Therefore, by adopting the simultaneous biaxial stretching method, the balance of the mechanical strength in the film plane can be more suitably maintained.

  When a simultaneous biaxial stretching machine is used, the preferred stretching temperature is 85 ° C to 115 ° C. When the stretching temperature (maximum temperature) exceeds 115 ° C., uniformity such as film thickness accuracy may be lowered. On the other hand, when the stretching temperature (maximum temperature) is less than 85 ° C., breakage may occur during the process, making it difficult to stably form the film. A more preferable stretching temperature is 95 ° C to 105 ° C.

  In the biaxial stretching in the present invention, both longitudinal and lateral stretching are desirably performed at a stretching speed of 10% / second or more, more preferably 30% / second or more, and still more preferably 40% / second or more. Since the orientation strength of the film is increased by increasing the stretching speed, the film breaking strength at the initial value can be increased, and the hydrolysis resistance can be suitably improved. Here, the stretching speed represents the deformation rate of the film per unit time on the basis of the dimensions of the unstretched film, and the stretching speed in the MD direction (longitudinal direction) and TD direction (transverse direction) ( (Unit:% / second) is defined by the following formula, respectively.

MD direction stretching speed (% / second) = Acceleration during film running (m / second / second)
÷ Speed of unstretched film (m / sec) × 100

TD direction stretching speed (% / sec) = width change rate per second (m / sec)
÷ Unstretched film width (m) x 100

  When the maximum stretching speed in any one of the MD direction and the TD direction is less than 10% / second, the orientation of the film becomes weak, so that sufficient hydrolysis resistance is not exhibited.

  On the other hand, the upper limit of the stretching speed is not limited, but if the stretching speed is increased more than necessary, the film becomes unreasonably stretched, and in the production of films on an industrial scale, film productivity is reduced or excessive capital investment is required. This is not preferable. Therefore, in the present invention, the maximum stretching speed between the start of stretching and the end of stretching is preferably 500% / second or less, and more preferably 400% / second or less.

  When a higher degree of thermal dimensional stability is required as a weather resistant polyester film, it is desirable to perform a longitudinal relaxation treatment. As a method of the longitudinal relaxation processing, a known method can be used. For example, a method of performing longitudinal relaxation processing by gradually narrowing the clip interval of the tenter (Japanese Patent Publication No. 4-028218), Then, a method of performing a relaxation treatment by inserting a razor at the end and avoiding the influence of the clip (Japanese Patent Publication No. 57-54290) can be used.

  The thickness of the obtained weather-resistant polyester film is preferably 10 to 500 μm, more preferably 15 to 400 μm, and still more preferably 20 to 250 μm. If it is less than 10 μm, there is no waist and it is difficult to handle. On the other hand, if it exceeds 500 μm, the handling property is lowered and the handling becomes difficult.

  The polyester film of the present invention may be a single layer or a multilayer. Moreover, as long as it exists in the range with the effect of this invention, each of these layers can contain various additives in a polyester resin as needed.

  Moreover, in order to provide various functions such as adhesiveness, insulation, and scratch resistance, the surface of the polyester film may be coated with a polymer resin by a coating method. Moreover, it is good also as a slippery polyester film by making a coating layer contain an inorganic and / or organic particle only from a transparency point. Furthermore, an inorganic vapor deposition layer or an aluminum layer can be provided to provide a water vapor barrier function.

  In addition, the weather resistant polyester film of the present invention preferably has irregularities formed on the film surface in order to improve handling characteristics such as slipperiness, runnability, wear resistance, and winding property. The kind and content of inert particles added to the polyester for imparting slipperiness are not particularly limited, but include metal oxides such as silica, titanium dioxide, talc, and kaolinite, calcium carbonate, calcium phosphate, Examples thereof include particles inert to the polyester resin, such as metal salts such as barium sulfate or heat-resistant polymer particles.

  The weather resistant polyester film of the present invention has good hydrolysis resistance and excellent long-term durability. Therefore, it is suitable for an application that is used for a long time under a severe use environment such as high temperature and high humidity or outdoors. For example, it is also useful as a base film for solar cell members such as a base film for solar cell backside sealing, a base film for electrical insulation used in various motors, a heat ray shielding film for window coverings and glazing for automobiles, etc. is there.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples from the first. In addition, the evaluation method used in each Example and the comparative example is demonstrated below.

(1) Breaking strength (TS), elongation at break (TE)
Measured according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation). A film specimen having a width of 10 mm and a length of 190 mm was sampled from the MD direction (longitudinal direction, film winding direction) and TD direction (lateral direction, direction perpendicular to the MD direction). The film test piece was set in a tensile tester (ORIENTEC Co., Tensilon RTC-125A), and stretched at a distance between chucks of 100 mm and a take-off speed of 200 mm / min in an environment of a temperature of 23 ° C. and a humidity of 65% RH, and fractured. Stress and elongation of the film were measured, and breaking strength (MPa) and breaking elongation (%) were determined.

(2) Evaluation of hydrolysis resistance (retention rate at break (RTE))
As the hydrolysis resistance evaluation, HAST (Highly Accelerated Temperature and Humidity Stress Test) standardized in JIS-60068-2-66 was performed. The equipment was EHS-221 manufactured by ESPEC CORP. Under the conditions of 105 ° C., 100% RH, and 0.03 MPa.
The film was cut into a width of 70 mm and a length of 190 mm from the MD direction and the TD direction, and the film was placed using a jig. Each film was placed at a distance where it did not touch. The treatment was performed for 192 hours and 400 hours under the conditions of 105 ° C., 100% RH, and 0.03 MPa. A sample having a width of 10 mm was taken from each film, and the breaking elongation before and after the treatment was described in (1) according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation). It measured by the method and calculated the elongation at break (RTE) according to the following formula.
RTE (%) = [(breaking elongation after treatment (MPa)) / (breaking elongation before treatment (MPa))] × 100

ΔRTE was determined by the following equation for the RTE measured by the above method, with the RTE in the MD direction being RTE (MD) and the RTE in the TD direction being RTE (TD).
△ RTE = | RTE (MD) −RTE (TD) |

(3) Intrinsic viscosity of polyester (IV)
The polyester was dissolved using a 6/4 (weight ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane and measured at a temperature of 30 ° C.

(4) Method for measuring carboxyl terminal concentration Preparation of sample The polyester is pulverized, vacuum dried at 70 ° C. for 24 hours, and then weighed in a range of 0.20 ± 0.0005 g using a balance. The weight at that time is defined as W (g). A sample weighed with 10 ml of benzyl alcohol is added to a test tube, the test tube is immersed in a benzyl alcohol bath heated to 205 ° C., and the sample is dissolved while stirring with a glass rod. Samples with dissolution times of 3 minutes, 5 minutes, and 7 minutes are designated as A, B, and C, respectively. Next, a new test tube is prepared, and only benzyl alcohol is added and processed in the same procedure, and samples when the dissolution time is 3 minutes, 5 minutes, and 7 minutes are designated as a, b, and c, respectively.
B. Titration Titration is performed using a 0.04 mol / l potassium hydroxide solution (ethanol solution) whose factor is known in advance. Phenol red is used as the indicator, and the titration (ml) of the potassium hydroxide solution is determined with the end point being changed from yellowish green to light red. Samples A, B, and C are titrated as XA, XB, and XC (ml). The titration amounts of samples a, b, and c are Xa, Xb, and Xc (ml).
C. Calculation of carboxyl terminal concentration Using the titration amounts XA, XB and XC for each dissolution time, the titration amount V (ml) at a dissolution time of 0 minutes is determined by the least square method. Similarly, titration volume V0 (ml) is obtained using Xa, Xb, and Xc. Subsequently, the carboxyl terminal concentration was calculated | required according to following Formula.
Carboxyl terminal concentration (eq / ton) = [(V−V0) × 0.04 × NF × 1000] / W
NF: factor of 0.04 mol / l potassium hydroxide solution W: sample weight (g)

(5) Moisture content of the polyester chip Using a moisture content measuring device (VA-05 type, manufactured by Mitsubishi Kasei Co., Ltd.), heat was applied to the chips 1 to 2 g at 230 ° C. for 10 minutes, and the moisture contained in the chip. Is evaporated and the moisture content is measured.

Example 1
(1) Preparation of polycondensation catalyst solution (preparation of ethylene glycol solution of phosphorus compound)
After adding 2.0 liters of ethylene glycol to a flask equipped with a nitrogen introduction tube and a cooling tube at room temperature and normal pressure, while stirring at 200 rpm in a nitrogen atmosphere, Irganox 1222 (Ciba 39) represented by -200 g of Specialty Chemicals) was added. Further, 2.0 liters of ethylene glycol was added, the temperature was raised by changing the jacket temperature setting to 196 ° C., and the mixture was stirred under reflux for 60 minutes from the time when the internal temperature reached 185 ° C. or higher. Thereafter, the heating was stopped, the solution was immediately removed from the heat source, and the solution was cooled to 120 ° C. or less within 30 minutes while maintaining the nitrogen atmosphere. The mole fraction of Irganox 1222 in the obtained solution was 40%, and the mole fraction of the compound whose structure changed from Irganox 1222 was 60%.
(Preparation of aqueous solution of aluminum compound)
After adding 5.0 liters of pure water to a flask equipped with a cooling tube at room temperature and normal pressure, 200 g of basic aluminum acetate was added as a slurry with pure water while stirring at 200 rpm. Further, pure water was added so as to be 10.0 liters as a whole, and the mixture was stirred at room temperature and normal pressure for 12 hours. Thereafter, the jacket temperature was changed to 100.5 ° C., the temperature was raised, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature reached 95 ° C. or higher. Stirring was stopped and the mixture was allowed to cool to room temperature to obtain an aqueous solution.
(Preparation of ethylene glycol mixed solution of aluminum compound)
After adding an equal volume of ethylene glycol to the aqueous aluminum compound solution obtained by the above method and stirring for 30 minutes at room temperature, the internal temperature is controlled to 80 to 90 ° C., and the pressure is gradually reduced to reach 27 hPa while stirring for several hours. Water was distilled off from the system to obtain an ethylene glycol solution of an aluminum compound at 20 g / l. The peak integration value ratio of ²⁷ Al-NMR spectrum of the obtained aluminum solution was 2.2.

(2) Esterification reaction and polycondensation A high-speed stirrer is provided in the transfer line from the third esterification reaction tank to the first polycondensation reaction tank, comprising three continuous esterification reaction tanks and three polycondensation reaction tanks. 0.75 parts by mass of ethylene glycol with respect to 1 part by mass of high-purity terephthalic acid was continuously supplied to a slurry preparation tank. The prepared slurry is continuously supplied, the first esterification tank has a reaction temperature of 250 ° C. and 110 kPa, the second esterification reaction tank has 260 ° C. and 105 kPa, the third esterification reaction tank has 260 ° C. and 105 kPa, and the second ester A polyester oligomer was obtained by continuously adding 0.025 parts by mass of ethylene glycol to the chemical reaction tank. The oligomer is continuously transferred to a continuous polycondensation apparatus comprising three reaction tanks, and the ethylene glycol solution of the aluminum compound and the ethylene glycol solution of the phosphorus compound prepared by the above method in an in-line mixer installed in the transfer line. Are continuously added while stirring with an agitating mixer so as to be 0.015 mol% and 0.036 mol% as aluminum atoms and phosphorus atoms with respect to the acid component in the polyester, respectively. Is 265 ° C., 9 kPa, medium-term polycondensation reaction tank is 265-268 ° C., 0.7 kPa, final polycondensation reaction tank is 273 ° C., 13.3 Pa, and polycondensation is IV 0.620 dl / g, carboxyl end concentration is 12.5 eq / Ton PET was obtained.

  The obtained PET resin is solid-phase polymerized at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus to produce a polyester chip having an IV of 0.750 dl / g and a carboxyl terminal concentration of 5.0 eq / ton. did.

(3) Film formation Polyethylene terephthalate pellets and silica particles having an average particle diameter (electron microscopic method) of 1.0 μm were adjusted to 0.06% by mass with respect to PET, and dried under reduced pressure (1 Torr) at 135 ° C. for 10 hours. Thereafter, the resin was supplied to an extruder, and the maximum resin temperature up to the extruder melt section, kneading section, polymer tube, gear pump, and filter was 290 ° C., and the polymer tube thereafter was 285 ° C., and the sheet was extruded from a die. Further, the resin temperature of the flat die was set to 285 ° C. In addition, as a result of measuring the moisture content of the PET pellet extracted at the entrance of the extruder, the moisture content was 18 ppm. The extruded resin was wound around a casting drum having a surface temperature of 30 ° C. and cooled and solidified to produce an unstretched film.

  Next, the unstretched film was preheated with hot air at 100 ° C. for 40 seconds, and then simultaneously biaxially stretched 3.0 times in the longitudinal and lateral directions at a constant stretching speed of 50% / second. Next, heat treatment was performed with hot air at 220 ° C. for 10 seconds, and the mixture was cooled to room temperature to prepare a weather resistant polyester film having a thickness of 50 μm. The characteristics of the obtained polyester film are shown in the table.

(Example 2)
Except that the draw ratio in the longitudinal and transverse directions was 3.5 times, a film was formed in the same manner as in Example 1 to produce a weatherable polyester film having a thickness of 50 μm. The characteristics of the obtained polyester film are shown in the table.

(Example 3)
Except that the stretching speed in the longitudinal and lateral directions was 100% / second, a film was formed in the same manner as in Example 1 to produce a weatherable polyester film having a thickness of 50 μm. The characteristics of the obtained polyester film are shown in the table.

Example 4
Except that the stretching speed in the longitudinal and transverse directions was set to 300% / second, film formation was performed in the same manner as in Example 1 to produce a weatherable polyester film having a thickness of 50 μm. The characteristics of the obtained polyester film are shown in the table.

(Example 5)
The solid phase polymerization time was adjusted, and a film was formed in the same manner as in Example 4 except that a PET resin having an IV of 0.720 dl / g and a carboxyl terminal concentration of 10.0 eq / ton was used. A weather-resistant polyester film was prepared. The characteristics of the obtained polyester film are shown in the table.

(Comparative Example 1)
An unstretched film obtained by the same production method as in Example 1 was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.2 times in the longitudinal direction with a roll group having a difference in peripheral speed, and uniaxially oriented. A PET film was obtained. Subsequently, the film was stretched 4.0 times in the width direction at 130 ° C. with a tenter, heat-set at 220 ° C., and further relaxed in the width direction at 200 ° C., and a weather-resistant polyester having a thickness of 50 μm. A film was prepared. The characteristics of the obtained polyester film are shown in the table.

(Comparative Example 2)
A biaxially stretched PET film having a thickness of 50 μm is obtained by performing film formation in the same manner as in Comparative Example 1 except that the stretch ratio in the longitudinal direction is 2.8 times and the stretch ratio in the width direction is 4.5 times. It was. A weather-resistant polyester film having a thickness of 50 μm was prepared. The characteristics of the obtained polyester film are shown in the table.

  The weather resistant polyester film of the present invention has good hydrolysis resistance and excellent long-term durability. Therefore, it is suitable for an application that is used for a long time under a severe use environment such as high temperature and high humidity or outdoors. For example, it is also useful as a base film for solar cell members such as a base film for solar cell backside sealing, a base film for electrical insulation used in various motors, a heat ray shielding film for window coverings and glazing for automobiles, etc. is there.

Claims (2)

A biaxially oriented polyethylene terephthalate film, weather resistant polyethylene terephthalate film satisfying the following configuration requirements (1) to (4).
(1) The carboxyl end concentration is 25 eq / ton or less with respect to polyethylene terephthalate. (2) The intrinsic viscosity (IV) of the film is 0.60 to 0.90 dl / g. (3) JIS-C-2318-19975. For breaking strength (TS) measured according to 3.31 (tensile strength and elongation), the measured value in the longitudinal direction (MD direction) is TS (MD), and the measured value in the transverse direction (TD direction) is Let TS (TD), and ΔTS defined by the following formula is 10 MPa or less. ΔTS = | TS (MD) −TS (TD) |
(4) With respect to the breaking elongation (TE) measured in accordance with JIS-C-2318-19997.3.31 (tensile strength and elongation), the measured value in the machine direction (MD direction) is TE (MD ), The measured value in the horizontal direction (TD direction) is TE (TD), and ΔTE defined by the following formula is 10% or less. ΔTE = | TE (MD) −TE (TD) | The weather-resistant polyethylene terephthalate film according to claim 1, obtained by a simultaneous biaxial stretching method.