TW201406526A - Durable polyester film, method for producing same, film for sealing solar cell which is produced using same, and solar cell - Google Patents

Abstract

Provided are: a polyester film which can maintain the durability thereof even under high-temperature/high-humidity conditions, rarely undergoes the occurrence of thickness failure, breakage, internal defects in the film and the like during the process of producing the film, and has excellent productivity; and a method for producing the film. A biaxially oriented polyester film comprising a polyester resin containing 0.1 to 5.0 moles/t inclusive of an alkali metal phosphate salt, wherein the intrinsic viscosity (IV) of the polyester resin that constitutes the film is 0.65 to 0.80 inclusive, the content of a terminal carboxyl group is 20 equivalents/t or less, the content of diethylene glycol is 0.9 to 3.0 mass% inclusive, and the average speed of sound of the film is 2.20 km/sec or more.

Description

Durable polyester film, method for producing the same, and film and solar cell for solar cell packaging using the same

The present invention relates to a polyester film excellent in durability. More specifically, it has a high retention rate in a humidity-resistant environment, and is excellent in productivity and workability of a film, and is particularly useful in outdoor use such as building materials and automobile materials including solar cell packaging films. It is a useful polyester film and a method for producing the same.

The polyester resin is used in various applications in which mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability are excellent. A polyester film obtained by thinning the polyester resin, particularly a biaxially oriented polyester film, is used as a copper clad laminate, a solar cell encapsulating film, or an adhesive tape because of its mechanical properties and electrical properties. Electrically insulating materials such as flexible printed circuit boards, membrane switches, planar heating elements, and flat cables, magnetic recording materials, materials for capacitors, packaging materials, automotive materials, building materials, photographic uses, graphic applications, Various industrial materials such as thermal transfer applications.

Among these applications, in particular, electrical insulating materials (such as solar cell encapsulating films) used outdoors, automotive materials, building materials, and the like are often used in harsh environments for a long time. When used for a long time in such a harsh environment, the polyester resin will be Hydrolysis causes a decrease in molecular weight, and embrittlement progresses, and mechanical properties and the like are lowered. Therefore, in the case where it is used in a severe environment for a long period of time, or in various applications in which moisture is used, durability against moist heat is required. For example, in solar cell packaging applications, in order to reduce the power generation cost by increasing the number of years of durability of the solar cell, it is necessary to improve the moist heat resistance of the polyester film.

Therefore, various studies have been conducted in order to suppress hydrolysis of the polyester resin. For example, a polycondensation catalyst for a polyester resin (Patent Document 1), an epoxy compound (Patent Document 2), and a polycarbodiimide (Patent Document 3) are being studied to improve the heat resistance of the polyester resin itself. Technology. In addition, a method of adding a buffering agent to the polyester resin (Patent Document 4) and a method of introducing a trifunctional component into the polyester resin and improving the moist heat resistance by crosslinking between molecules (Patent Document 5) .

Prior technical literature Patent literature

Patent Document 1 Japanese Patent Laid-Open Publication No. 2010-212272

Patent Document 2 Japanese Patent Laid-Open No. Hei 9-227767

Patent Document 3 Japanese Patent Publication No. 11-506487

Patent Document 4 Japanese Patent Laid-Open Publication No. 2008-7750

Patent Document 5 Japanese Patent Laid-Open Publication No. 2010-248492

However, in the technique of Patent Document 1, hydrolysis resistance is not sufficient. In the techniques of Patent Documents 2 and 3, there is a case where the film is melted and formed into a film. When the gelation progresses, the thickness becomes poor, the filter is clogged, the film is easily broken during the production of the biaxial alignment film, and the problem of the film formation process is not provided, and the problem of the film formation process is not provided. Further, there is a problem that foreign matter remains in the film and the quality is poor. Patent Document 4, which contains a buffering agent in a film, is inferior in durability of a polyester resin, and is produced in a biaxial alignment film as a film forming condition for imparting a necessary molecular property to the film to improve hydrolysis resistance. At the time, problems such as cracking and thickness unevenness are likely to occur, and it is difficult to combine both productivity and hydrolysis resistance. In addition, in the case of having an intermolecular cross-linking structure as in Patent Document 5, although the hydrolysis resistance of the film is improved, the elongation of the film is further lowered, and it is difficult to produce the same as in the case of Patent Document 4. Both sex and hydrolysis resistance. Further, the buffers used in Patent Documents 4 and 5 have a problem that they are easily aggregated at the time of addition, and these aggregates shorten the filter life in the filtration step, and the small aggregates remaining in the unfiltered state become foreign matter and remain in the filter. Because of the inside of the film, there is a problem that the appearance is poor and the yield is deteriorated. In recent years, in order to reduce the cost improvement rate, research is progressing, and the level of demand for reducing foreign matter defects of the film is also increasing. In addition to the improvement of hydrolysis resistance, improvement of foreign matter defects is required.

The object of the present invention is to provide a method capable of maintaining durability even under conditions of high temperature and high humidity in view of the problems of the prior art, and to suppress thickness defects in the film forming step. A polyester film which is excellent in productivity, such as cracking, film internal defects, and the like, and a method for producing the same.

In order to solve this problem, the present invention employs the following means.

[1] A biaxially oriented polyester film comprising a film of a polyester resin containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less, and an intrinsic viscosity of a polyester resin constituting the film (IV) The amount of the terminal carboxyl group is 20 equivalent/t or less, the diethylene glycol content is 0.9% by mass or more and 3.0% by mass or less, and the average ultrasonic conduction velocity of the film is 2.20 km/sec or more.

[2] The biaxially oriented polyester film according to [1], wherein the foreign matter containing a phosphorus element having a long diameter of 100 μm or more contained in the film is 10/1000 cm ² or less.

[3] The biaxially oriented polyester film according to [1] or [2], wherein a ratio of a maximum value to a minimum value of the ultrasonic conduction velocity of the film is 1.00 or more and 1.30 or less.

[4] The biaxially oriented polyester film according to [3], wherein an angle (θ) of a direction in which the ultrasonic conduction velocity of the film exhibits a maximum value and a longitudinal direction of the film is 10° or more and 80° or less.

[5] The biaxially oriented polyester film according to any one of [1] to [4] wherein the long-side shrinkage ratio at a temperature of 150 ° C for 30 minutes is 0.8% or less.

[6] The biaxially oriented polyester film according to any one of [1] to [5] wherein the micro endothermic peak temperature Tmeta (° C.) obtained by differential scanning calorimetry (DSC) is 220° C. or higher. .

[7] The biaxially oriented polyester film according to any one of [1] to [6] wherein the alkali metal element content of the polyester resin: WA (ppm) and phosphorus element content: WP (ppm) The ratio WA/WP is 0.3 or more and 0.7 or less.

[8] The biaxially oriented polyester film according to any one of [1], wherein the polyester resin contains a manganese compound having a manganese element content of 100 ppm or more and 300 ppm or less.

[9] The biaxially oriented polyester film according to any one of [1] to [8] wherein the elongation retention ratio at a temperature of 125 ° C and 100% RH for 72 hours is 50% or more.

[10] A method for producing a biaxially oriented polyester film, comprising: a step of melting and molding a polyester resin containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less into a sheet shape; The long side direction described in (1) to (3) below. The step of extending the width direction and the heat treatment step, and the polyester resin constituting the film has an intrinsic viscosity (IV) of 0.65 to 0.80, a terminal carboxyl group content of 20 equivalent/t or less, and a diethylene glycol content of 0.9% by mass or more and 3.0% by mass. Hereinafter, the average ultrasonic conduction velocity of the film is 2.20 km/sec or more, (1) a step of extending from 3.0% to 4.5 times in the longitudinal direction at an extension speed of 2,000%/sec to 10,000%/sec; and (2) toward the width direction. The film width is extended by 3.5 to 4.5 times, and the film width before the start of the width direction extending step is W0, the film width at the intermediate point of the width direction extending step is W1, and the film width after the width direction extending step is set. In the case of W2, it conforms to the steps of the following formula (A): 60≦100×(W1-W0)/(W2-W0)≦80...(A)

(3) There is an intermediate step between the width direction extending step and the heat treatment step, the temperature of the intermediate step being the temperature of the final section of the width direction extending step: Ts (° C.) and the temperature of the first heat treatment step corresponding to the initial section of the heat treatment step : Temperature between Th (°C), and when the time for passing the film through the intermediate step is Sm (second), it conforms to the step (Th-Ts) / Sm ≦ 50 (B) of the following formula (B).

[11] The method for producing a biaxially oriented polyester film according to [10], wherein the polyester resin containing the alkali metal phosphate is produced in accordance with the following steps (4) to (6): (4) In the polymerization step of synthesizing the polyester resin, an alkali metal phosphate is added; (5) a solution in which the alkali metal phosphate is dissolved or mixed in the diol component, and the concentration of the alkali metal phosphate is 1% by mass or less is added. Or a slurry state; (6) The temperature of the reactant when the alkali metal phosphate is added is 250 ° C or lower.

[12] A film for solar cell encapsulation, which is obtained by using the biaxially oriented polyester film according to any one of [1] to [9].

[13] A solar cell comprising the film for solar cell encapsulation according to [12].

Among them, the invention of the combination of the above [1], [2], [3], and [4], the invention of the above [10], and the combination of the above [10] and [11] particularly exhibit particularly remarkable effects.

According to the present invention, it is possible to provide a polyester film which can have both durability and productivity under high temperature and high humidity and which has few internal defects. The polyester film can be suitably used for an insulating material such as a solar cell encapsulating sheet, a copper clad laminate, an adhesive tape, a flexible printed circuit board, a membrane switch, a planar heating element, or a flat cable, or a capacitor material. The durability of automotive materials and building materials is valued.

[Formation for carrying out the invention]

The polyester film of the present invention comprises a polyester resin containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less, and the terminal carboxyl group of the polyester resin constituting the film is 20 equivalent/t or less. It is necessary to improve the durability under high temperature and high humidity.

A general polyester film is composed of a crystalline polyester, and a crystal portion and an amorphous portion of the polyester are present in the film. In the polyester film obtained by biaxially stretching the crystalline polyester, a portion in which the polyester is crystallized (hereinafter referred to as "alignment crystallization portion") and an amorphous portion are present via alignment. Here, the amorphous portion is considered to have a lower density and a larger average distance between molecules than the crystal portion and the alignment crystal portion. In the case where the polyester film is exposed to a moist heat environment, moisture (water vapor) enters the inside through the molecules of the amorphous portion having a low density, so that the amorphous portion can be plasticized and the mobility of the molecule is improved. In addition, water (water vapor) is a reaction catalyst that uses a proton at the carboxyl end of the polyester to promote molecular mobility. Increase the hydrolysis of the amorphous portion. The hydrolyzed and low molecular weight polyester system further enhances molecular mobility, allowing hydrolysis to proceed and crystallization. By repeating the above results, the embrittlement of the film proceeds, and eventually it becomes a state of cracking even if it is slightly washed.

As described above, it is considered that the hydrolysis reaction proceeds due to the proton of the carboxyl terminal of the polyester as a reaction catalyst. Therefore, the smaller the amount of terminal carboxyl groups in the polyester resin constituting the film, the more the hydrolysis resistance is improved. The amount of terminal carboxyl groups is preferably 15 equivalents/t or less, and more preferably 13 equivalents/t or less. Although the lower limit is not particularly limited, it is substantially difficult to be 1 equivalent/t or less.

Further, since the alkali metal phosphate exhibits ionicity by being separated in the polyester, protons which function as a catalyst for the hydrolysis reaction can be neutralized. As a result, the hydrolysis reaction due to protons can be suppressed, and the moist heat resistance can be improved. Specific examples of the alkali metal phosphate which exhibits such a buffering action include compounds represented by the following chemical formula (I), from the viewpoints of polymerization reactivity of the polyester resin, heat resistance during melt molding, and moist heat resistance. See, particularly preferred examples are potassium dihydrogen phosphate and sodium dihydrogen phosphate.

PO _x H _y M _z . . . Chemical formula (I)

(here, x is an integer of 2 to 4, y is 1 or 2, z is 1 or 2, and M is an alkali metal).

When the content of the alkali metal phosphate of the polyester resin constituting the film of the present invention is less than 0.1 mol/t, sufficient heat and humidity resistance cannot be obtained, and if it exceeds 5.0 mol/t, the alkali is excessive. The metal promotes the decomposition reaction. The alkali metal phosphate content is preferably 0.3 mol/t or more and 3.0 mol/t or less, more preferably 1.0 mol/t or more and 2.0 mol/t. under. Moreover, when the polyester film of the present invention contains 50% by mass or more of a polyester resin containing 0.1 to 5.0 mol/t of the above alkali metal phosphate, it is preferable to maintain the heat and humidity resistance of the film, and further 70 mass. More preferably, it is 90% by mass or more, and particularly preferably 95% by mass or more. In the case of less than 50% by mass, there is a case where the wet heat resistance is deteriorated. Further, the content of the alkali metal phosphate contained in the polyester resin in the present invention is the amount of the alkali metal phosphate added during the synthesis of the polyester resin.

In the polyester resin of the polyester-constituting film of the present invention, the ratio WA/WP of the alkali metal element content WA (ppm) to the phosphorus element content WP (ppm) in the polyester resin is preferably 0.3 or more and 0.7 or less. By adjusting the content within this range, the hydrolysis inhibiting effect of the polyester film can be maintained, and the heat stability can be imparted. Further, when an alkali metal phosphate and phosphoric acid are used in combination as a phosphorus compound, it is particularly preferable because the hydrolysis inhibiting effect can be further enhanced.

In the present invention, the alkali metal phosphate may be added during the polymerization of the polyester or may be added during the melt molding. In that case, it does not matter, and the point of uniform dispersion in the film of the alkali metal phosphate is reduced. When the amount of terminal carboxyl groups at the time of polymerization is added, it is preferably added at the time of polymerization. In the case of adding at the time of polymerization, the addition period may be added from any period between the esterification reaction at the time of polymerization of the polyester or the end of the transesterification reaction until the initial stage of the polycondensation reaction (inherent viscosity is less than 0.3). However, since the alkali metal phosphate is agglomerated by the addition of the alkali metal phosphate and is polymerized by the reaction, a foreign substance containing a phosphorus compound as a main component is generated in the polyester resin. As a result, the filter in the film forming step is closed, the productivity is lowered, and foreign matter remains in the film, which causes problems such as deterioration in appearance and deterioration in insulation performance. Therefore, in the polyester film of the present invention, the foreign matter containing phosphorus having a major axis of 100 μm or more contained in the film is preferably 10 parts/1000 cm ² or less, more preferably 5 pieces/1000 cm ² or less. Good for 3 / 1000cm ² . Although the lower limit of the number of foreign matters is not particularly limited, 0/1000 cm ² is a substantial lower limit.

In order to reduce the amount of the phosphorus-containing foreign matter in the polyester, the alkali metal phosphate is dissolved or mixed with a glycol component such as ethylene glycol in advance, and a solution having a concentration of 1% by mass or less is added. In the case of the slurry state, it is more preferable to set the concentration to 0.5% by mass or less, and to slowly add the diluted solution or slurry over a period of 20 minutes or longer. In addition, when the temperature of the polyester when the alkali metal phosphate is added exceeds 250 ° C, the foreign matter is likely to be generated by the phosphorus compound. Therefore, the temperature of the polyester when the alkali metal phosphate is added is preferably 250 ° C or less. Good for 210 ° C ~ 240 ° C. If the temperature of the polyester when the alkali metal phosphate is added is less than 210 ° C, since the addition period of the alkali metal phosphate is such that the esterification reaction or the transesterification reaction rate is lowered before the esterification reaction or the transesterification reaction, the production is performed. Sexual deterioration becomes poor, and when the period of addition of the alkali metal phosphate is between the end of the esterification reaction or the transesterification reaction until the initial stage of the polycondensation reaction (inherent viscosity is less than 0.3), there is a polyester resin. The dispersibility of the alkali metal phosphate is deteriorated, which is not preferable.

Further, as a method of synthesizing the polyester resin, a method of using a dicarboxylic acid compound as a raw material of a dicarboxylic acid component, and a method of using a dicarboxylic acid a method of an acid ester compound, etc., but in the case where a dicarboxylic acid compound (in the case of polyethylene terephthalate, terephthalic acid) is used as a starting material, there is an acid component derived from a dicarboxylic acid compound. On the other hand, the aggregation of the alkali metal phosphate tends to occur. Therefore, the dicarboxylic acid component is preferably a dicarboxylic acid ester compound (in the case of polyethylene terephthalate, for example, dimethyl terephthalate or the like).

Further, when a dicarboxylic acid compound is used as a raw material, the phosphorus compound can be added by adding the concentration of the alkali metal phosphate to 0.5% by mass or less and the temperature of the polyester in the range of 210 to 230 °C. The formation of foreign matter is suppressed within a practical range. Further, in the transesterification reaction using a dicarboxylic acid ester compound as a raw material, the molar ratio of the diol component to the dicarboxylic acid component (the mass of the diol component (mole) / dicarboxylic acid component) (mole)) The raw material is mixed in a manner of 1.1 to 1.3 times, and the initial temperature of the transesterification reaction is set to a range of 250 to 270 ° C to promote the initial reaction, and the end temperature of the transesterification reaction is set to 220 to 240. In the range of °C, finally, the molar ratio of the diol component to the dicarboxylic acid component (the mass of the diol component (mole) / the mass of the dicarboxylic acid component (mole)) is 1.5 to 2.0 times. When the mixture of ethylene glycol and diethylene glycol is further added to the transesterification reaction, it is preferable because the reactivity can be made good and the productivity of the polyester resin can be improved, and the polyester resin can be easily controlled. The amount of DEG (diethylene glycol) contained is preferably.

As the polycondensation catalyst of the polyester resin of the present invention, a conventional ruthenium compound, ruthenium compound or titanium compound can be used. In the case of using a ruthenium compound and/or a ruthenium compound, the polycondensation reactivity and the solid phase polymerization reactivity are obtained by making the sum of the lanthanum element and the lanthanum element 50 ppm to 500 ppm. It is preferable from the point of view, and further 50 to 300 ppm is preferable from the viewpoint of heat resistance and hydrolysis resistance. When the amount is more than 500 ppm, the polycondensation reactivity and the solid phase polymerization reactivity are improved, but the decomposition reaction at the time of remelting is also promoted. Therefore, the carboxyl terminal group is increased to cause a decrease in heat resistance and hydrolysis resistance. Examples of the ruthenium compound and the ruthenium compound which are suitably used include ruthenium pentoxide, antimony trioxide, and ruthenium dioxide, and they can be used for their respective purposes. For example, an anthracene compound is the most excellent color tone, and a ruthenium compound is excellent in solid phase polymerization reactivity. In consideration of the environmental surface, in the case of manufacturing in a non-ruthenium system, it is preferable that the reactivity of the titanium catalyst in the polycondensation reaction and the solid phase polymerization is good. Further, when a manganese compound is added in the range of 100 to 300 ppm, it is preferred that the hydrolysis resistance is good. This is considered to be because the hydration energy of manganese is high, so that the affinity with water in the polyester film is lowered, so that the hydrolysis reaction becomes difficult to proceed. In the case of less than 100 ppm, the hydrolysis inhibiting effect is insufficient, and when it exceeds 300 ppm, the hydrolysis resistance tends to be deteriorated.

Therefore, in the film of the present invention, the polyester resin constituting the film preferably contains a manganese compound in an amount of 100 ppm or more and 300 ppm or less.

In the present invention, the polyester resin constituting the film has an intrinsic viscosity (IV) of from 0.65 to 0.80, preferably from 0.68 to 0.75. When the intrinsic viscosity (IV) is less than 0.65, the molecular chain is short and the molecular mobility in the heat and humidity resistance environment is likely to increase, and the hydrolysis resistance is easily deteriorated due to an increase in the terminal portion. When the viscosity exceeds 0.80, the viscosity is too high, so that the productivity is deteriorated when the film is formed during film formation, and the thickness unevenness is deteriorated. Also, when manufacturing polyester resin The solid phase polymerization is preferably carried out because the amount of the terminal carboxyl group described above is lowered, and the intrinsic viscosity (IV) is easily adjusted to the above range. In addition, in the molten state in which the polyester resin is melt-formed, the inherent viscosity (IV) of the polyester resin used as the film raw material becomes higher due to hydrolysis and thermal decomposition due to residual moisture. The target value of IV in the polyester resin constituting the film is also high. However, in order to increase the intrinsic viscosity (IV) of the polyester resin of the film raw material, it is necessary to lengthen the time of solid phase polymerization in the production of the polyester resin, increase the amount of catalyst added, and sometimes involve the coloring of the polyester resin. The deterioration of the characteristics. Therefore, the intrinsic viscosity (IV) of the polyester resin of the film raw material is preferably higher than the target value of IV in the polyester resin constituting the film, and the difference is small. The inherent viscosity (IV) of the polyester resin of the film raw material is preferably 0.05 to 0.15 higher than the target value of IV in the polyester resin constituting the film. Before melt-extruding the polyester resin into a film, the amount of moisture in the polyester resin is 50 ppm or less in advance by heating the polyester resin under reduced pressure. The temperature of the polyester resin when the film is formed into a film by extrusion is set to a melting point (Tm) of the polyester resin + 30 ° C or less, and further, the melting time of the resin from the tip end of the extruder to the nozzle is set to be less than 5 minutes, and further In the case of less than 3 minutes, it is possible to suppress hydrolysis and thermal decomposition at the time of melt film formation of the polyester resin, and to reduce the decrease in the intrinsic viscosity (IV), thereby obtaining a polyester film which is stable and has good hydrolysis resistance.

In the present invention, the content of diethylene glycol (DEG) of the polyester resin constituting the film is 0.9% by mass or more and 3.0% by mass or less, preferably 1.0% by mass or more and 2.0% by mass or less. In the present invention, the content of diethylene glycol (DEG) of the polyester resin is determined by the measurement method described later. Seek. In the present invention, the diethylene glycol contained in the polyester resin contains diethylene glycol contained in the polyester resin in a state of being copolymerized with the polyester chain, and is contained in the polyester resin alone. Both diethylene glycol. When the content of diethylene glycol (DEG) is less than 0.9% by mass, the elongation in the film production step is deteriorated, the productivity is lowered due to film breakage, and flashing is likely to occur during the cutting of the processing step. Problems with splitting and so on. In particular, since the film having high hydrolysis resistance has a high internal viscosity (IV) as described above, the stretching tension is also high, particularly in the width direction step of producing a film having a wide film width. In the middle, there is a problem that stress concentrates on the edge of the film (end portion in the film width direction), and the film becomes easily broken. Further, in the film having a low amount of terminal carboxyl groups, intramolecular interaction is weak, and in particular, uniformity of molecular alignment in the central portion and both end portions in the width direction is likely to be deteriorated, cracking during stretching is increased, and film width is increased. The position of the direction and the difference in characteristics become large. By setting the content of diethylene glycol (DEG) in the above range, it is possible to obtain a profile which can impart moderate flexibility to the polyester molecule, is not easily broken, and has improved productivity, and is subjected to punching and the like. A film which is hard to occur, such as cracking and is excellent in workability. In addition, the polyester film of the present invention in which the DEG content in the polyester resin of the polyester film is in the above range is excellent in productivity and workability, and durability (heat and humidity resistance) under high temperature and high humidity. Also good. Since the polyester film of the present invention is excellent in workability, it is possible to adopt a stretching condition in which a conventional film having high hydrolysis resistance is not likely to have a rapid elongation rate as will be described later. The polyester film obtained by using the extension condition can especially make the width direction in the widening film formation The difference in the alignment between the central portion and the end portion and the difference in characteristics due to the misalignment are reduced, the durability (heat and humidity resistance) under high temperature and high humidity is improved, and the difference in characteristics in the width direction can be reduced.

In order to make the amount of diethylene glycol (DEG) in the polyester resin constituting the film within the above range, a method of adding diethylene glycol (DEG) as a diol component in the polymerization of a polyester resin is preferred. . However, since the diethylene glycol component can also be produced as a side reaction component of the ethylene glycol component, in order to stabilize the amount of diethylene glycol (DEG) and set it in the above range, it is necessary to suppress and control the side reaction in the polymerization reaction. ingredient. Therefore, the dicarboxylic acid constituent component is preferably a raw material obtained by esterifying a terminal of a dimethyl terephthalate. For example, in the case where a terminal of a terephthalic acid is used as a raw material of a carboxylic acid as a starting material, a side reaction in which a diol component is allowed to react with each other by a carboxylic acid component is apt to occur. For example, when ethylene glycol is used as the diol component, it is easy to carry out side reactions and produce diethylene glycol (DEG), and a certain amount of diethylene glycol (DEG) component is introduced into the polyester resin. However, it is difficult to control the amount of the side reaction product, and as described above, the foreign matter containing the phosphorus element is easily generated due to the influence of the carboxylic acid component remaining when the alkali metal phosphate used in the present invention is added, Moreover, the amount of foreign matter in the film tends to increase when the polyester film is produced. Further, in the transesterification reaction, a method in which a diol component is not excessively added to a dicarboxylic acid component and a diol component is gradually added in accordance with the reaction, and a preferred method for suppressing a side reaction is used. The diol component is further added at a low temperature of 220 ° C to 240 ° C.

The polyester resin constituting the film of the polyester of the present invention has a polyester having a dicarboxylic acid constituent component and a diol constituent component. Further, in the present specification, the constituent components mean the smallest unit obtainable by hydrolyzing the polyester.

Examples of the dicarboxylic acid constituent component constituting the polyester include malonic acid, succinic acid, glutaric acid, adipic acid, phosphonic acid, sebacic acid, dodecanedioic acid, dimer acid, and An aliphatic dicarboxylic acid such as decadioic acid, pimelic acid, sebacic acid, methylmalonic acid or ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, Cyclohexanedicarboxylic acid, decalin dicarboxylic acid, alicyclic dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene dicarboxylic acid, 1,5- Naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, m-benzene a dicarboxylic acid such as an aromatic dicarboxylic acid such as sodium 5-sulfonate, ethylbenzene dicarboxylic acid, stilbene dicarboxylic acid, phenanthrene dicarboxylic acid or 9,9'-bis(4-carboxyphenyl)nonanoic acid An acid, or an ester derivative thereof, but is not limited thereto. Further, an oxo acid such as 1-lactide, d-lactide or hydroxybenzoic acid, and a derivative thereof may be added as appropriate to the carboxyl terminal of the carboxylic acid component, and a plurality of Oxyacids and the like. Moreover, it is also possible to use these types individually or in a plurality of types as needed.

Further, examples of the diol constituent component constituting the polyester include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-. Aliphatic diols such as butanediol, alicyclic diols such as cyclohexanedimethanol, spiro glycerol, isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzene Methanol, 9,9'-bis(4-hydroxyphenyl)anthracene, aromatic Examples of the diol such as a diol or the like, and a plurality of the diols described above are connected, but are not limited thereto. Moreover, it is also possible to use these types individually or in a plurality of types as needed.

In addition, in the polyester resin to be used in the present invention, the total amount of the carboxyl group (carboxylic acid component) and the number of hydroxyl groups may be three or more, and the epoxy resin may be contained in the total amount of the epoxy resin. Compounds and carbodiimide compounds, An encapsulant of a terminal carboxyl group such as an oxazoline compound. The sum of the number of carboxyl groups (carboxylic acid component) and the number of hydroxyl groups is 3 or more. Examples of the trifunctional aromatic carboxylic acid component include trimesic acid, trimellitic acid, and pyromellitic acid. Examples of the trifunctional aliphatic carboxylic acid constituent component include naphthalene tricarboxylic acid, ethane tricarboxylic acid, propane tricarboxylic acid, butane tricarboxylic acid, and the like, and the number of hydroxyl groups is Examples of the constituent components of 3 or more may, for example, be trihydroxybenzene, trihydroxynaphthalene, trihydroxyindole, trihydroxychalcone, trihydroxyflavone, or trihydroxycoumarin. However, when the total amount of the carboxyl group (carboxylic acid component) and the amount of the hydroxyl group are 3 or more, and the terminal encapsulant is added, the molecular structure in which the molecular chains of the polyester resin are crosslinked is easily formed. As a result, the elongation of the film is deteriorated, and the amount of foreign matter in the film is increased by the gelation, so it should be used as much as possible.

Further, in the polyester resin of the polyester-constituting film of the present invention, the ratio of the aromatic dicarboxylic acid constituent component in the total dicarboxylic acid constituent component in the polyester is 90 mol% or more and 100 mol% or less. good. It is preferably 95% by mole or more and 100% by mole or less. More preferably, it is 98% or more and 100% by mole or less, and particularly preferably 99% by mole or more and 100% by mole%. Hereinafter, it is preferably 100 mol%, that is, all of the dicarboxylic acid constituent components are preferably aromatic dicarboxylic acid constituent components. When it is less than 90% by mole, there is a case where moisture heat resistance and heat resistance are lowered. In the polyester film of the present invention, the ratio of the aromatic dicarboxylic acid constituent component in the all dicarboxylic acid constituent component in the polyester is set to 90 mol% or more and 100 mol% or less. Moist heat and heat resistance.

In the polyester resin of the polyester-constituting film of the present invention, the main repeating unit composed of the dicarboxylic acid constituent component and the diol constituent component composed mainly of the polyester is preferably used, including ethylene terephthalate. Ethylene-2,6-naphthalenedicarboxylate, propylene terephthalate, butylene phthalate, 1,4-cyclohexanedimethyl terephthalate, ethylene-2,6-naphthalene Carboxylates and mixtures thereof. Further, the main repeating unit herein is a total of 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more of the total repeating unit. Further, from the viewpoint of low cost and easier polymerization, and excellent heat resistance, it is preferred to repeat the reaction of ethylene phthalate, ethylene-2,6-naphthalenedicarboxylate, and the like. unit. In this case, in the case where a large amount of ethylene phthalate is used as a repeating unit, a film having a general-purpose moist heat resistance can be obtained more inexpensively, and ethylene-2,6-naphthalenedicarboxylate is used in a large amount as In the case of repeating units, a film which is more excellent in moist heat resistance can be formed.

Further, in the polyester resin of the polyester-constituting film of the present invention, various additives such as an antioxidant, a heat-resistant stabilizer, a weather-resistant stabilizer, an ultraviolet absorber, and an organic slip can be added without deteriorating the properties. Agents, pigments, dyes, organic or inorganic microparticles, fillers, antistatic agents, nucleating agents, crosslinking agents, and the like. Especially in giving In terms of ultraviolet shielding ability, it is preferable that the polyester film contains inorganic particles such as titanium dioxide having high concealing property and an ultraviolet absorber, and in particular, titanium dioxide is used as a solar cell encapsulating film in view of its concealability and reflectance. In this case, it is difficult to see the internal wiring, and in the case of being used as a package film on the back side, it is preferable to reflect the light generated by the power generation to contribute to improvement of power generation efficiency.

Titanium dioxide is a titanium oxide having an anatase type and a rutile type crystal structure. However, compared with an anatase type, a rutile type has a high refractive index because of a dense crystal structure. Therefore, the titanium dioxide used in the present invention is preferably rutile-type titanium oxide from the viewpoint of obtaining a concealing effect by high reflection.

The method for producing titanium dioxide particles mainly includes a sulfuric acid method and a chlorine method. In the sulfuric acid process, by dissolving ilmenite in concentrated sulfuric acid, separating iron into iron sulfate, the solution is hydrolyzed, and titanium is precipitated as a hydroxide. Next, titanium dioxide is obtained by firing the hydroxide in a high-temperature rotary kiln or the like. On the other hand, in the chlorine process, rutile ore is used as a raw material, and chlorine gas and carbon are reacted at a high temperature of about 1,000 ° C to form titanium tetrachloride, and then titanium tetrachloride is separated and oxidized by spraying at a high speed. , titanium dioxide can be obtained. Compared with the sulfuric acid process, the titanium dioxide produced in the chlorine process is synthesized because it is synthesized in a gas phase reaction involving only gas. The vanadium, iron, and manganese have less impurities and can be made into high-purity titanium dioxide. Very good.

Titanium dioxide used in the present invention, in order to suppress photocatalytic activity of titanium dioxide, or to enhance dispersion in a polyester resin Sex, preferably surface treatment. In order to suppress photocatalytic activity, for example, a method of coating a surface with an inorganic oxide such as vermiculite or alumina is mentioned. Further, in order to enhance the dispersibility, for example, a method of surface treatment with a siloxane compound, a polyol, or the like can be mentioned.

The particle size of the titanium dioxide in the present invention is preferably 0.1 μm to 0.5 μm. Since the wavelength at which the light-reflecting ability of the titanium dioxide is maximized is a wavelength of about twice the particle diameter of the titanium dioxide, since the reflection efficiency in the visible light region is improved when the particle diameter of the titanium oxide is within the above range, for example, when it is used as a package film of a solar cell. It is better to increase power generation efficiency. The particle size of titanium dioxide is particularly preferably 0.2 μm to 0.4 μm. When the particle diameter of titanium dioxide is less than 0.1 μm, the titanium oxide particles tend to aggregate and tend to be difficult to disperse, and when it exceeds 0.5 μm, the reflection efficiency in the visible light region tends to decrease. Further, the average particle diameter of the titanium dioxide particles referred to herein is obtained by subjecting the film to ashing treatment, and then observing by a scanning electron microscope (SEM) at a magnification of 20,000 times, and obtaining an average number of particles of 50 observed particles. The value of the path.

The amount of the titanium oxide particles contained in the polyester resin constituting the film of the polyester of the present invention is preferably 2 to 25% by mass, more preferably 3 to 20% by mass. When the amount is less than 2% by mass, the concealability may be insufficient. When the amount is more than 25% by mass, the film may be easily broken and the moist heat resistance may be lowered during stretching. Further, in the polyester film of the present invention, the polyester film is co-extruded in the thickness direction, and one side thereof contains 10 to 25% by weight of titanium oxide particles and serves as a functional layer for blocking ultraviolet rays, and the other side The amount of the medium titanium dioxide particles is 2 to 8% by mass, and is formed by the purpose of maintaining durability in a hot and humid environment. The layer is preferably both high in ultraviolet durability and high in moisture and heat resistance. In this case, when the ratio of the thickness of the layer containing 10 to 25% by weight of the titanium oxide particles to the thickness of the layer containing 2 to 8% by mass of the titanium oxide particles is 1:10 to 1:5, the ultraviolet rays can be more evenly balanced. Durability and high moisture and heat resistance are further preferred. Further, in the case where a titanium-based compound having photocatalytic reactivity is contained in a polyester film, hydrolysis of the polyester film is promoted due to the high activity of the catalyst, and durability in a moist heat environment is lowered. However, the polyester film of the present invention can maintain high moist heat resistance even when a titanium-based compound (titanium-based particles) is contained.

Further, as the ultraviolet absorber which can be used in the present invention, a salicylic acid-based compound, a benzophenone-based compound, a benzotriazole-based compound, a cyanoacrylate-based compound, and a benzo compound are preferably exemplified. a ketone compound, a cyclic imido ester compound, etc., from the viewpoint of dispersibility, benzo Ketone compounds are preferred. These compounds may be used alone or in combination of two or more. It is also possible to use a stabilizer such as HALS and an antioxidant, and it is preferable to use a phosphorus-based antioxidant in combination.

The polyester film of the present invention is a biaxially oriented polyester film. The term "biaxial alignment" as used herein refers to a pattern showing biaxial alignment by wide-angle X-ray diffraction. The biaxially oriented polyester film is generally obtained by extending a polyester sheet in an unstretched state in the longitudinal direction and the width direction of the sheet, followed by heat treatment to terminate the crystal alignment.

The polyester film of the present invention must have an average ultrasonic transmission velocity of 2.20 km/sec or more. Further, the ratio (maximum/minimum value) of the maximum value (km/sec) of the ultrasonic conduction velocity of the film to the minimum value (km/sec) is preferably 1.00 or more and 1.30 or less. Average of the film in the present invention The ultrasonic conduction velocity is a value obtained by measuring the ultrasonic conduction velocity measured by a measurement method described later, based on the longitudinal direction of the polyester film (0°), and measuring from 0° to 180° every 5°. average value. Further, in the present invention, the ratio of the maximum value to the minimum value of the ultrasonic conduction velocity of the film indicates the maximum value of the ultrasonic conduction velocity calculated from the measurement result of the average ultrasonic conduction velocity of the film described above, and the minimum value is divided by the minimum value. Value (maximum/minimum). The ultrasonic conduction velocity of the film is an index relating to the alignment of the polyester chain constituting the polyester film, and it shows that the faster the ultrasonic conduction velocity, the stronger the alignment of the polyester chain in its direction. As described above, in the case where the polyester film is exposed to a hot and humid environment, moisture (water vapor) enters the inside through the molecules of the low-density amorphous portion, so that the amorphous portion can be plasticized to improve the mobility of the molecule. However, since the molecular alignment is strong, the mobility of the amorphous portion is restricted, so that the durability in a hot and humid environment may be improved. Therefore, in the case where the average ultrasonic conduction velocity of the film is less than 2.20 km/sec, the moist heat resistance tends to be deteriorated. The average ultrasonic conduction velocity is preferably 2.25 km/sec or more, more preferably 2.30 km/sec or more. Further, in the case where the ratio of the maximum value to the minimum value of the ultrasonic conduction velocity exceeds 1.30, the difference in the moist heat resistance due to the direction becomes large and the balance deteriorates, especially since the moist heat resistance is weakened in the direction of the minimum value. For the sake of it is not good. The ratio of the maximum value to the minimum value of the ultrasonic conduction velocity is preferably 1.00 or more and 1.25 or less.

In addition, in the conventional position at the center portion in the width direction of the film, the in-plane misalignment is increased due to the arc-shaped bending phenomenon, and the variation in the moist heat resistance is deteriorated. However, by applying, for example, a manufacturing method (longitudinal direction extending method, width direction extending method, width) described later The film of the present invention obtained by the intermediate step between the direction extending step and the heat treatment step may be at a position deviated from the central portion in the width direction of the film (that is, a position at which the deviation of the alignment angle is 10 or more). The difference in the resistance to moist heat performance is reduced in the in-plane direction.

Further, the biaxially oriented polyester film generally has two alignment axes. In the present specification, the alignment axis of the stronger alignment is called the long axis, and the alignment axis of the weaker alignment is called the short axis. Further, in the present invention, the maximum value of the ultrasonic conduction velocity indicates the direction in which the alignment is the strongest in the in-plane of the biaxially oriented polyester film (long-axis direction).

Further, in the present invention, the ultrasonic conduction velocity of the film exhibits an angle (θ) between the direction of the maximum value and the longitudinal direction of the film, and indicates the angle formed by the long axis direction and the longitudinal direction of the film.

Further, in the center portion in the width direction of the intermediate product of the biaxially oriented polyester film which is not cut in the width direction after the production, the alignment axis of the film is usually formed in the longitudinal direction and the width direction in the two directions, and the longitudinal direction Which of the width directions is the long axis and which one is the short axis differs depending on the method of manufacturing the film. When the stretching ratio in the longitudinal direction of the film is higher than the width direction of the film, the long axis of the alignment is the long side direction, and the direction indicating the maximum value of the ultrasonic conduction velocity is also the longitudinal direction of the film. In this case, the angle (θ) is 0° in the central portion in the film width direction, and the longitudinal axis direction is shifted by 10° with respect to the longitudinal direction of the film (for example, in a portion other than the central portion in the film width direction), the angle ( θ) is 10°. On the other hand, when the stretching ratio in the width direction of the film is higher than the longitudinal direction of the film, the long axis of the alignment is the width direction, and the direction showing the maximum value of the ultrasonic conduction velocity is also the width of the film. to. In this case, the angle (θ) is 90° in the central portion in the film width direction, and the longitudinal axis direction is shifted by 10° with respect to the longitudinal direction of the film (for example, in a portion other than the central portion in the film width direction). The angle (θ) is 80°.

Further, in recent years, in order to improve productivity, it is possible to temporarily produce a biaxially oriented polyester film having a wide film width to obtain an intermediate product (intermediate roll), and then cut the intermediate product (intermediate roll) toward the width direction of the film. To obtain a method of several to ten rolls (final product). In the central portion in the width direction of the intermediate product, the angle (θ) when the film is aligned in the longitudinal direction of the film is 0° as described above, and the angle (θ) when the film is aligned in the width direction of the film is 90°, with a deviation. In the central portion (near the end portion) of the polyester film in the width direction, the deviation of the alignment angle is generally caused by the arc-shaped bending phenomenon.

Further, in the case where the alignment in the longitudinal direction of the film is high, the angle (θ) is increased from 0°, and the alignment is high in the film width direction, and the angle (θ) is decreased from 90°. When the alignment angle is deviated and the misalignment between the long axis direction and the short axis direction is large, the difference in characteristics tends to increase due to the direction in the film surface. However, as described above, the biaxially oriented polyester film of the present invention has a deviation of 10° or more, that is, an angle (θ) of 10° or more and 80° or less, and the deviation of the alignment axis is 20°. In the above, that is, the angle (θ) is an end portion in the width direction of 20° or more and 60° or less, as described above, the difference in the ultrasonic conductivity held in the plane is small, that is, the difference in the alignment is small. It can reduce the difference in moisture and heat resistance caused by the direction in the film surface. Therefore, when the angle (θ) of the film is 10° or more and 80° or less, the effects of the present invention are most significantly observed. In addition, when the angle (θ) exceeds 40° and is less than 50°, sometimes It was observed that the elongation of the sheet tends to increase, and the difference in the shrinkage ratio in the oblique direction tends to increase.

The polyester resin constituting the film of the polyester of the present invention preferably has a small endothermic peak temperature (Tmeta) of 220 ° C or more as determined by differential scanning calorimetry (DSC), and can reduce the heat shrinkage rate. The Tmeta system depends on the amount of heat imparted to the film during the heat treatment step. The higher the temperature, the higher the heat treatment. Implemented for a long time. In the manufacturing process of the biaxial alignment film, the heat treatment step is to increase the crystallinity of the polyester molecules in the film by applying heat to the biaxially oriented film, and at the same time as preheating stability and the like, the film The adhesion of the surface is also improved. The Tmeta system is preferably 235 ° C or lower. When the temperature exceeds 235 ° C, the film may be broken due to cracking during heat treatment, and the molecular alignment may be too moderate and the wet heat resistance may be lowered. The method for setting the Tmeta in the above range is not particularly limited, and it is preferred to treat the polyester film at a temperature of from 225 ° C to 240 ° C for 5 seconds or more. In the case where the treatment is carried out at a high heat treatment temperature and when a large amount of the DEG component is contained, the heat and humidity resistance generally decreases as the molecular alignment decreases. However, by applying the production method described later, the alignment of the film can be improved. It is preferable to control the maximum/minimum values of the average ultrasonic conduction velocity and the ultrasonic conduction velocity within the above range.

The polyester film of the present invention has a heat shrinkage ratio in the longitudinal direction of 2.0% or less at a temperature of 150 ° C for 30 minutes, preferably 0.8% or less, more preferably 0.6% or less. In the case where the heat shrinkage rate in the long-side direction is too large, curling may occur at the time of bonding, and a deviation may occur due to a difference in size, and only a small one may be preferable. Long-side heat shrinkage rate Although the limit is not particularly specified, it is substantially difficult to be 0.0% or less. In addition, the heat shrinkage ratio in the width direction at 150 ° C for 30 minutes is preferably 0.0% or more and 1.0% or less, and more preferably 0.0% or more and 0.5% or less from the viewpoint of preventing the width during processing from being shortened. When not only the width direction but also the heat shrinkage rate in the longitudinal direction is mainly treated at a high temperature of 225 ° C or higher in the heat treatment step, the relaxation can be adjusted to the above preferred range in the subsequent heat treatment step to the cooling step. 0.8% or less, in particular, in order to reduce the shrinkage ratio in the longitudinal direction while maintaining the planarity, the method of shortening the gap between the jigs adjacent to the traveling direction of the film at both ends is preferably performed. In order to reduce the heat shrinkage rate to an appropriate value and maintain planarity, it is preferable to carry out the relaxation in the longitudinal direction at a relaxation rate of 1.0% to 2.0% at a temperature of 160 ° C to 200 ° C. In the case where the conventional technique is performed at a high temperature of 225 ° C or higher, the alignment of the film is easily relaxed and the moist heat resistance is lowered, so that it is difficult to achieve both thermal dimensional stability and moist heat resistance. However, by using the technique of the present invention, It can have these characteristics.

The polyester film of the present invention is used for the average ultrasonic wave conduction velocity of the film in the film width direction end portion, particularly in the film width direction end portion of the film (θ) of 10° or more and 80° or less. The method of forming the maximum value/minimum value of the ultrasonic conduction velocity in the above range is preferably achieved by applying the method shown below.

The method for producing a polyester film of the present invention preferably comprises a step of extending from 3.0 to 4.5 times in the longitudinal direction at an elongation speed of from 2,000%/second to 10,000%/second. In order to more efficiently align the polyester molecular chain in the long-side direction, not only the stretching ratio but also the stretching speed is set to The range described is preferred. When the elongation speed in the longitudinal direction is less than 2,000%/second and the stretching ratio is less than 3.0 times, the alignment becomes insufficient, and in the case of more than 10,000%/second and the stretching ratio exceeds 4.5 times, the film is produced. The rupture will increase. Further, the elongation speed in the longitudinal direction is further preferably from 2,500%/sec to 8,000%/sec, particularly preferably from 3,000%/sec to 6,000%/sec. Further, the extension speed referred to herein is expressed by the stretching ratio/extension time (second) × 100. For example, in the case where the circumferential speed difference of the roller is used to extend, the time from the position of the roller leaving the extension starting point to the position of the roller reaching the end point of the extension is measured as the extension time, and from the above formula The child calculates. When the glass transition temperature of the polyester resin is Tg, the film temperature at the time of extending in the longitudinal direction is preferably Tg or more and Tg + 40 ° C or less, more preferably Tg + 10 ° C or more and Tg + 30 ° C or less. . When the longitudinal direction is extended by the above conditions, the molecular alignment in the longitudinal direction can be made uniform, and the influence of the arc bending of the film can be reduced in the width direction extending to the later-described heat treatment step.

The method for producing a polyester film of the present invention has a step of extending 3.5 to 4.5 times in the width direction, and the step of extending the intermediate point in the width direction step is 60 to 80% of the elongation at the end of the width direction extending step. It is better. Here, 60 to 80% of the amount of elongation means that the film width before the start of the width direction extending step is W0, and the film width at the intermediate point of the width extending step is W1, and the width direction extending step is completed. When the film width is set to W2, it conforms to the following formula (A).

60≦100×(W1-W0)/(W2-W0)≦80... Formula (A).

Furthermore, there is an intermediate step between the width direction extending step and the heat treatment step, the ambient temperature of the intermediate step being the ambient temperature of the final section of the width direction extending step: Ts (° C.) and the first heat treatment relative to the initial interval of the heat treatment step Step ambient temperature: temperature between Th (° C.), and the intermediate step is preferably in accordance with the following formula (B) when the time for passing the film is Sm (second). In addition, the ambient temperature of the intermediate step is preferably near the temperature between Th and Ts due to the ease of temperature control, and ((Ts+Th)/2)-20(°C) or more, ((Ts+Th)/2 ) +20 (°C) or less is better. Further, in the intermediate step, since the temperature is unstable due to the inflow of hot air which is partially blown to the film in the stretching step and the heat treatment step, it is preferable to carry out the exhaust treatment to maintain the temperature more stably.

(Th-Ts)/Sm≦50...(B).

Further, the term "heat treatment step" as used herein refers to a step of blowing a heated hot air to a film and heating the film by a heating means such as a radiant heater to perform crystallization. In the heat treatment step, when the melting point of the polyester resin is Tm (° C.), it is preferred to heat the film at a temperature of Tm-80 (° C.) or more and Tm (° C.) or less.

Further, the intermediate step of the present invention is shown in the middle of the width direction extending step and the heat treatment step, without the means for heating the film, and in the longitudinal direction. In the state in which the width of the film is not changed in the width direction, the both ends in the width direction are held, and the conveyance is generally performed. In order to suppress the temperature fluctuation in the intermediate step, it is preferable to surround the periphery with a heat-insulating wall or the like. Further, the ambient temperature in the intermediate step is preferably a temperature between Th and Ts, and is ((Ts+Th)/2)-20 (°C) or more and ((Ts+Th)/2)+20 (°C) or less. For better.

In the production of the biaxially stretched film, in the width direction of the film, in the heat treatment step, the film is stretched in the width direction, and the film on the heat treatment step side is extended in the width direction in the central portion in the width direction in which the film is not held. Indented, so as the end toward the width direction, an arcuate bending phenomenon in which the alignment angle is shifted in the oblique direction occurs. Due to this phenomenon, the difference caused by the direction in which the polyester molecules in the film plane are aligned becomes larger toward the end in the width direction. As described above, the deviation of the molecular alignment is poor due to the influence on the durability of the film in a hot and humid environment. Since the width direction extending step and the intermediate step are carried out, the stretching tension in the width direction is not easily transmitted in the heat treatment step, and deformation of the film alignment axis can be suppressed. In the case where the stretching ratio in the width direction is less than 3.5 times, the amount of stretching at the intermediate point in the step of extending in the width direction is less than 60% of the amount of elongation at the end of the step of extending the width direction, or in (Th-Ts)/Sm When the value exceeds 50, the effect of improving the deformation of the film alignment axis becomes insufficient, and the ratio of the maximum value to the minimum value of the ultrasonic conduction velocity of the film at the end portion in the width direction exceeds 1.30. In the case where the stretching ratio in the width direction exceeds 4.5 times, and the elongation at the intermediate point in the width direction extending step exceeds 80% of the elongation at the end of the width direction extending step, the film at the time of stretching is liable to be broken and productive. Getting worse. Further, regarding the value of (Th-Ts)/Sm, it is preferably less than 40 and more preferably less than 30. Further, the temperature in the step of extending in the width direction is preferably Tg or more and Tg + 40 ° C or less, and more preferably Tg + 10 ° C or more and Tg + 30 ° C or less. In the heat treatment step, when the melting point of the polyester resin is Tm, it is preferable to use Tm-80 ° C or more and Tm -20 ° C or less. The step is preferably Tm-60 ° C or more and Tm -30 ° C or less. Further, the heat treatment step is divided into a plurality of steps, and the method of lowering the temperature Th in the first step with respect to the first interval and increasing the temperature stepwise, while reducing the influence of the arc bending, can be processed at an appropriate heat treatment temperature. It is especially good.

In order to reduce the manufacturing cost of the film, for example, it is necessary to manufacture a biaxially oriented polyester film with a width of a film having a width of more than 2 m, but since the film width is widened, the alignment axis at the end portion in the width direction is inclined, so In the case of a wide film, the above-described manufacturing method is particularly preferable. Further, in the case where the condition of rapid elongation is applied as described above, the load at the time of extending the film generally becomes large, especially in the case where a polyester resin having a high intrinsic viscosity is used in order to maintain durability, there is a film. The problem of increased rupture. However, in the polyester film of the present invention, the amount of diethylene glycol (DEG) in the film can be adjusted to an appropriate amount or the like as described above, and the production can be deteriorated without deterioration in productivity.

Therefore, in the method for producing a polyester film containing a polyester resin, the polyester resin constituting the film has an intrinsic viscosity (IV) of 0.65 to 0.80, a terminal carboxyl group content of 20 equivalent/t or less, and a diethylene glycol content of 0.9. The method for producing a biaxially oriented polyester film having a mass % or more of 3.0% by mass or less and an average ultrasonic transmission velocity of the film of 2.20 km/sec or more is particularly preferable in the following production method.

In other words, the special product has a step of melting a polyester resin (raw material) containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less to form a sheet, and the following (1)~ (3) The long side recorded direction. The step of extending in the width direction and the manufacturing method of the heat treatment step.

(1) a step of extending 3.0 to 4.5 times in the longitudinal direction at an extension speed of 2,000%/second to 10,000%/second; (2) a step of extending 3.5 to 4.5 times in the width direction, and a film before the step of extending the width direction The width is set to W0, the film width at the intermediate point of the width direction extending step is W1, and the film width after the end of the width direction extending step is W2, which conforms to the following formula (A): 60≦ 100×(W1-W0)/(W2-W0)≦80...(A)

(3) There is an intermediate step between the width direction extending step and the heat treatment step, the temperature of the intermediate step being the temperature of the final section of the width direction extending step: Ts (° C.) and the temperature of the first heat treatment step corresponding to the initial section of the heat treatment step : Temperature between Th (°C), and when the time for passing the film through the intermediate step is Sm (second), it conforms to the step (Th-Ts) / Sm ≦ 50 (B) of the following formula (B).

Further, a polyester resin (raw material) containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less is preferably produced in accordance with the following steps (4) to (6).

(4) adding an alkali metal phosphate in the polymerization step of synthesizing the polyester resin; (5) dissolving or mixing the alkali metal phosphate in the diol component, and adding the alkali metal phosphate to a concentration of 1% by mass The following solution or slurry state; (6) The temperature of the reactant when the alkali metal phosphate is added is 250 ° C or lower.

The polyester film of the present invention preferably has a elongation retention ratio of 50% or more when held at a temperature of 125 ° C and a humidity of 100% RH for 72 hours. In the present invention, the elongation retention ratio is 50% or more, and both of the two directions in which the ultrasonic conduction velocity is the largest and the smallest direction are both 50% or more. In the case of using a film, in many cases, force is applied to all directions of the film, and in the case of poor heat and humidity resistance in a specific direction, cracking and cracking of the film may easily occur from the film. Therefore, even in the direction in which the polyester molecular chain having the smallest ultrasonic conduction velocity is aligned in the low direction, that is, the direction in which the moist heat resistance is the most unfavorable, the film having the above-described elongation retention ratio is high in durability. good. More preferably, it is 60% or more, and particularly preferably 70% or more. In the case where the elongation retention ratio is less than 50%, the film may be deteriorated and cracked during use, and there may be a case where cracking is caused.

The thickness of the polyester film of the present invention is preferably 10 μm or more and 500 μm or less, and more preferably 20 μm or more and 300 μm or less. More preferably, it is 25 μm or more and 200 μm or less. In the case where the thickness is less than 10 μm, there is a case where the heat and humidity resistance of the film is excessively lowered. On the other hand, in the case of being thicker than 500 μm, it is difficult to have both moist heat resistance and productivity in the film stretching step.

Next, an example of the method for producing the polyester film of the present invention will be described, but the present invention is not limited to the definition and explanation of the product obtained by the example.

First, an example of the method for producing a polyester resin (polymerization step) includes a first step of performing an esterification reaction or a transesterification reaction, a second step of adding an additive such as an alkali metal phosphate, and the like. In the production method of the third step of the polymerization reaction, a fourth step of the solid phase polymerization reaction may be further added as needed.

In the first step, dimethyl terephthalate as a dicarboxylic acid component is used as a diol component in such a manner that the molar ratio of the diol component is 1.1 to 1.3 times the molar ratio of the dicarboxylic acid component. After mixing a mixture of ethylene glycol and diethylene glycol, a known polymerization catalyst such as antimony trioxide and a manganese-based metal catalyst are added at a temperature of 220 to 270 ° C, and the final diol component and the dicarboxylic acid are used. The molar ratio of the component is subjected to a transesterification reaction while adding a mixture of ethylene glycol and diethylene glycol in a range of 1:1.5 to 1:2.0.

The second step is a step of adding an additive such as an alkali metal phosphate from the end of the transesterification reaction to the intrinsic viscosity of 0.3. The alkali metal phosphate is mixed at a ratio of the ratio of the amount of phosphoric acid and the alkali metal element to the amount of the phosphorus element in the range of 0.3 to 0.7, and is added after diluting to a concentration of 1% by mass or less with ethylene glycol. Further, the pH of the mixed diluent at this time is adjusted to an acidity of 4.0 or more and 6.0 or less, which is preferable from the viewpoint of suppressing generation of foreign matter. In addition, the alkali metal phosphate is preferably added at a temperature of 240 ° C or lower and a addition time of 20 minutes or longer, and is preferably added from the viewpoint of suppressing generation of foreign matter. Further, a method of reducing the number of carboxyl groups of the polyester obtained by the polymerization may be carried out, and a trace amount of an alkali compound such as potassium hydroxide may be added.

In the third step, the polymerization can be carried out by a known method. In order to further reduce the amount of terminal carboxyl groups of the polyester obtained by the polycondensation to a range of 20 equivalent/t or less and to increase the intrinsic viscosity of the polyester, after performing the above polymerization, it is preferred to carry out the fourth step. The temperature above 190 ° C is less than the melting point of the polyester, and so-called solid phase polymerization is carried out by heating under a flow of an inert gas such as a reduced pressure or a nitrogen gas. In this case, after polymerizing the polyester having an intrinsic viscosity of 0.5 or more and 0.6 or less in the third step, the fourth step is preferably carried out by a temperature lower than the melting point of the polyester at 190 ° C or higher, such as a reduced pressure or nitrogen. The inert gas of the like is heated under the flow of the inert gas to carry out solid phase polymerization. When the inherent viscosity of the polyester obtained in the third step is less than 0.5, the sheet is easily cleaved and the morphology becomes non-uniform, and as a result, the polyester obtained by solid phase polymerization in the fourth step may have unevenness in polymerization degree. The situation. Further, when the inherent viscosity of the polyester obtained in the third step is more than 0.6, the thermal deterioration of the third step becomes intense, and as a result, the amount of terminal carboxyl groups of the obtained polyester increases, and hydrolysis resistance at the time of film formation The reason for the decline is not good. By setting the intrinsic viscosity of the polyester obtained in the third step to 0.5 or more and 0.6 or less, a polyester having a uniform intrinsic viscosity can be obtained in a state where the number of carboxyl groups is lowered and maintained in the solid phase polymerization. As a result, hydrolysis resistance can be further improved at the time of film formation.

A method of producing a polyester film using the obtained polyester resin is exemplified.

The polyester resin obtained by the above method was heated under vacuum and dried to have an internal moisture content of 50 ppm or less. The drying degree is preferably 3 kPa or less, and the temperature is 160 ° C or more, and it is preferably dried for 3 hours or more. Then, the dried polyester resin is melted at 260 to 300 ° C in an extruder, and the foreign matter is filtered by a filter, and then extruded into a sheet shape from a T-shaped nozzle, and wound into a surface temperature by electrostatic application casting. A mirror cast drum of 60 ° C was allowed to cool and solidify to obtain an unstretched film. In this step, in order to suppress the hydrolysis of the polyester resin and prevent the inherent viscosity (IV) The decrease in the amount of the terminal carboxyl group and the decrease in the moisture content of the polyester resin supplied to the extruder are as good as possible. Further, the shorter the time from when the resin is extruded from the extruder to the time when the casting drum is touched, the target is 10 minutes or shorter, preferably 5 minutes or shorter, and particularly preferably 3 minutes or shorter.

After preheating the unstretched film by a roll heated to 70 to 100 ° C, it is heated to a temperature of 90 to 120 ° C by using a radiant heater or the like, and extends at an elongation speed of 2,000 to 10,000 % / sec in the longitudinal direction of 3.0 to 300 °. 4.5 times to obtain a uniaxial alignment film. Further, while fixing both ends of the film with a jig, the film is guided to the oven and heated at a temperature of 70 to 150 ° C, and then continuously extended in the width direction by 3.5 to 4.5 times in a heating region of 70 to 150 ° C, followed by 180 ~ The heating zone at 240 ° C is subjected to heat treatment for 5 to 40 seconds, and is subjected to a cooling zone of 100 to 200 ° C to obtain a biaxially oriented polyester film which is crystallographically aligned. Further, in the above heat treatment, a relaxation treatment of 3 to 12% may be carried out as needed. Further, in the extending step in the width direction, the extension amount at the intermediate point of the width direction extending step is 60 to 80% of the elongation at the end of the width direction extending step, and between the width direction extending step and the heat treatment step : There is no means of heating the film, in the long side direction. In the state in which the film size is not changed in the width direction, the intermediate step of carrying the conveyance while maintaining both ends in the width direction, and the temperature change amount (° C.) of the average passage time (second) in the intermediate step is 50° C./sec or less. It is preferable to suppress deformation of the alignment shaft due to arc bending.

In addition, biaxial extension can also use simultaneous biaxial extension. After extending in the direction of the long side and the width, before the heat treatment step, it can also be in the long side direction. Re-expansion in both directions in the width direction, or in either direction Stretch. After cutting the end portion of the obtained biaxially oriented polyester film, the intermediate product is crimped, and then cut into a desired width using a cutter, and then wound into a cylindrical core to obtain a desired length of the poly Ester film roll. Further, in order to improve the curling posture at the time of curling, embossing treatment may be applied to both end portions of the film.

The polyester film of the present invention thus obtained is particularly suitable as a film for solar cell encapsulation because of its high moist heat resistance. In other words, the film for solar cell encapsulation of the present invention is a film for solar cell encapsulation which is obtained by using the biaxial alignment polyester of the present invention. Further, the polyester film of the present invention is used as a package film, which is highly durable and thinner than conventional solar cells. Therefore, the solar cell of the present invention is a solar cell using the film for solar cell encapsulation of the present invention.

[Examples] [Measurement of physical properties]

Hereinafter, the configuration and effects of the present invention will be further specifically described by way of examples. Further, the present invention is not limited to the following embodiments. Before describing each of the examples, various methods for measuring physical properties will be described.

(1) Diethylene glycol (DEG) content

The sample (polyester resin (raw material) or polyester film) 1.0 g was hydrolyzed at 260 ° C with 2.5 mL of monoethanolamine as a solvent. Then, 10 mL of methanol was added and cooled, and after neutralizing with terephthalic acid, the supernatant was subjected to gas chromatography (GC-14A, manufactured by Shimadzu Corporation) to determine the diethylene glycol (DEG) content of the supernatant. . In addition, the added components such as inorganic particles are precipitated into insoluble matter during centrifugation, and the sedimentation component is filtered and heavy. For the measurement, the weight of the sample was subtracted from the weight of the measurement sample, and the measurement of the weight of the sample was performed. Further, a value obtained by using a polyester film as a measurement sample was used as a numerical value of a polyester resin constituting a film.

(2) Intrinsic viscosity (IV)

The measurement sample (polyester resin (raw material) or polyester film) was dissolved in 100 mL of o-chlorophenol (solution concentration C (measurement sample weight / solution volume) = 1.2 g / mL), and the solution was measured using an Oswald viscometer. 25 ° C viscosity. Further, the viscosity of the solvent was measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] was calculated from the following formula (C), and the obtained value was used as the intrinsic viscosity (IV).

Ηsp/C=[η]+K[η] ² . C...式(C)

(Here, η sp = (solution viscosity / solvent viscosity) -1, and K is the Huggins constant (0.343).).

Further, when there is an insoluble matter such as inorganic particles in the solution in which the polyester resin (raw material) or the polyester film is dissolved, the measurement is carried out by the following method.

i) The measurement sample (polyester resin (raw material) or polyester film) was dissolved in 100 mL of o-chlorophenol to prepare a solution having a solution concentration of 1.2 mg/mL. Here, the weight of the measurement sample supplied to o-chlorophenol was taken as the measurement sample weight.

Ii) Next, the solution containing the insoluble matter was filtered, and the weight of the insoluble matter was measured, and the volume of the filtrate after filtration was measured.

Iii) Adding o-chlorophenol to the filtrate after filtration, adjusting (measuring the weight of the sample (g) - the weight (g) of the insoluble matter) / (the volume of the filtrate after filtration (mL) + the volume of the additional o-chlorophenol (mL) )) into 1.2g / 100mL.

(For example, when a concentrated solution having a sample weight of 2.0 g/solution volume of 100 mL is prepared, and the weight of the insoluble matter when the solution is filtered is 0.2 g, and the volume of the filtrate after filtration is 99 mL, 51 mL of o-chlorophenol is added. Adjustment ((2.0g-0.2g) / (99mL + 51mL) = 1.2g / mL))

Iv) iii) using the obtained solution, measuring the viscosity at 25 ° C using an Oswald viscometer, using the obtained solution viscosity, solvent viscosity, calculating [η] from the above formula (C), and using the obtained value as the intrinsic viscosity (IV) ).

(3) The amount of terminal carboxyl groups

The measurement was carried out by the following method according to the method of Maulice (Document M. J. Maurec, F. Huizinga. Anal. Chim. Acta, 22 363 (1960)).

2 g of a measurement sample (polyester resin (raw material) or polyester film) was dissolved in 50 mL of o-cresol/chloroform (weight ratio 7/3) at a temperature of 80 ° C, and titrated with a 0.05 N KOH/methanol solution. The terminal carboxyl group concentration is expressed as the equivalent/polyester 1t value. In addition, the titration indicator indicates the use of phenol red as the end point of the titration when changing from yellowish green to light red. In addition, when there is an insoluble matter such as inorganic particles in the solution in which the polyester resin (raw material) or the polyester film is dissolved, the solution is filtered and the weight of the insoluble matter is measured, and the weight of the insoluble matter is subtracted from the weight of the measurement sample. The resulting value is corrected to determine the sample weight. Further, the value obtained by using the polyester film as a measurement sample was taken as the value of the polyester resin constituting the film.

(4) alkali metal element content

Quantification was carried out by atomic absorption spectrometry (manufactured by Hitachi, Ltd.: polarized Zeeman atomic absorption spectrophotometer 180-80. Flame: acetylene-air).

(5) Phosphorus and manganese content

The measurement was carried out by a wavelength dispersion type fluorescent X-ray analyzer (Model: ZSX100e) manufactured by Rigaku Corporation.

(6) Number of foreign matter containing phosphorus

A sample was taken after the three-wavelength fluorescent lamp was used as a light source, and the foreign matter which was inspected and observed at 1000 cm ² on the film with the transmitted light and the reflected light was marked. Further, at this time, the distance between the light source and the film was adjusted so that the amount of light at the film position became 1000 lux. The obtained foreign matter sample was observed with an optical microscope (magnification: 100 times), and the measurement was made in the direction in which the size of the foreign matter was the largest, and the long diameter of the foreign matter was measured. In addition, a device attached to an energy dispersive X-ray analyzer (EDX) EMAX-7000 (manufactured by Horiba, Ltd.) is used in a scanning electron microscope (SEM) S-4300A (manufactured by Hitachi, Ltd.). Elemental analysis of the foreign matter portion of the foreign matter sample was carried out, and the presence or absence of the phosphorus element was measured, and the number of the foreign matter containing the phosphorus element having a long diameter of 100 μm or more was calculated.

(7) The average ultrasonic conduction velocity of the film, the ratio of the maximum value to the minimum value of the ultrasonic conduction velocity, and the angle at which the ultrasonic conduction velocity exhibits the maximum value and the longitudinal direction of the film (θ) (7-1) Average ultrasonic conduction velocity of the film

A film sample having a width of 300 mm and a length of 300 mm was used, and the SONIC SHEET TESTER SST-250 manufactured by Nomura Co., Ltd. was used as the reference (0°) in the longitudinal direction of the polyester film, and the film was rotated as a shaft. For the sample, the ultrasonic conduction velocity (km/sec) was measured every 5° from 0° to 180°, and the average value of the obtained values was calculated.

(7-2) Ratio of the maximum value to the minimum value of the ultrasonic conduction velocity

The maximum value and the minimum value of the ultrasonic conduction velocity are extracted from the measurement results of the ultrasonic conduction velocity (km/sec) from 0° to 180° obtained by (7-1), and the maximum value of the ultrasonic conduction velocity is obtained. The value divided by the minimum value (maximum/minimum value) is taken as the ratio of the maximum value to the minimum value of the ultrasonic conduction velocity.

(7-3) The angle formed by the direction in which the ultrasonic conduction velocity exhibits the maximum value and the longitudinal direction of the film (θ)

Further, the direction in which the ultrasonic conduction velocity exhibits the maximum value and the angle (θ) formed in the longitudinal direction of the film are calculated. Further, the angle (θ) is an angle at which an acute angle (0° or more and 90° or less) is formed in a direction in which the ultrasonic conduction velocity exhibits the maximum value and an angle formed in the longitudinal direction of the film.

Further, in the following examples and comparative examples, a method of temporarily obtaining a middle roll of a polyester film and then slitting the intermediate roll in the width direction of the film to obtain a plurality of rolls (final product) was employed. Further, in the following examples and comparative examples, the roller (final product) corresponding to the center portion in the width direction of the roll (film) in the intermediate roll, and the end portion in the width direction of the roll (film) of the intermediate roll were respectively The corresponding roller (final product) measures the average ultrasonic conduction velocity of the film, the ratio of the maximum value to the minimum value of the ultrasonic conduction velocity, and the angle formed by the direction in which the ultrasonic conduction velocity exhibits the maximum value and the longitudinal direction of the film ( θ). Moreover, when taking a film sample from the slit film roll (final product), it is taken from the center part of the width direction of a roll (film).

(8) Evaluation of the heat and humidity resistance of the film (stretch retention) (8-1) Evaluation of Moisture and Heat Resistance in the Maximum Direction of Ultrasonic Conduction Velocity

A film sample for measuring the elongation of the strip having a width of 10 mm and a length of 250 mm was prepared so that the direction of the maximum value of the ultrasonic conduction velocity measured in the item (7) was the longitudinal direction.

The prepared sample was subjected to a highly accelerated life test apparatus EHS-221 (manufactured by ESPEC Co., Ltd.) for 72 hours in an environment of a temperature of 125 ° C and a humidity of 100 RH%. The elongation of the film before and after the treatment was measured using a universal tension machine under the conditions of original length (distance between chucks) of 100 mm and tensile speed of 200 mm/min. Further, regarding the elongation, the average value measured by N = 5, respectively. Regarding the obtained film elongation, the value obtained by dividing the elongation after the treatment by the elongation before the treatment was taken as the elongation retention ratio in the maximum direction of the ultrasonic conduction velocity in the moisture heat resistance evaluation.

Further, the elongation retention ratio is 50% or more in the acceptable range, 60% or more is good, and 70% or more is particularly good.

(8-2) Evaluation of Moisture and Heat Resistance in the Minimum Direction of Ultrasonic Conduction Velocity

A film sample for measuring the elongation of the strip having a width of 10 mm and a length of 250 mm was prepared so that the direction of the minimum value of the ultrasonic conduction velocity measured in the item (7) was the longitudinal direction.

Using the prepared sample, the elongation retention ratio was determined in the same manner as in (8-1), and this was taken as the elongation retention ratio in the minimum direction of the ultrasonic conduction velocity in the moisture heat resistance evaluation.

Further, in the following examples and comparative examples, after the intermediate roll of the polyester film was temporarily obtained, the intermediate roll was directed toward the film. A method of slitting in the width direction to obtain a plurality of rolls (final products). Further, in the following examples and comparative examples, the ultrasonic conduction velocity was measured for each of the roller (final product) corresponding to the central portion of the intermediate roller and the roller (final product) corresponding to the most end portion of the intermediate roller. The elongation retention ratio in the maximum direction and the elongation retention ratio in the minimum direction of the ultrasonic conduction velocity. Moreover, when taking a film sample from a film roll (final product), it takes out from the center part of the width direction of a roll.

(9) Thermal shrinkage of the film

A film sample having a width of 300 mm and a longitudinal direction of 300 mm was used. In the center portion of the sample, a pair of marks are formed as the original length (L0) at intervals of 200 mm for the longitudinal direction and the width direction, respectively. The sample was treated in an oven at 150 ° C for 30 minutes, and then cooled to room temperature, and the distance between the pair of marks was measured as the length (L1) after the treatment. Further, the heat shrinkage ratio in the longitudinal direction and the width direction of the film was calculated in accordance with 100 × (L0 - L1) / L0.

Further, in the following examples and comparative examples, a method of temporarily obtaining a middle roll of a polyester film and then slitting the intermediate roll in the width direction of the film to obtain a plurality of rolls (final product) was employed. Further, in the following examples and comparative examples, the heat in the longitudinal direction was measured for each of the rolls (final product) corresponding to the central portion of the intermediate roll and the roll (final product) corresponding to the most end portion of the intermediate roll. Shrinkage and heat shrinkage in the width direction. Moreover, when taking a film sample from a film roll (final product), it takes out from the center part of the width direction of a roll. Moreover, in the following examples and comparative examples, the heat shrinkage ratio in the longitudinal direction obtained by using the roller (final product) corresponding to the central portion of the intermediate roll was calculated and used. The average value of the heat shrinkage ratio in the longitudinal direction obtained by the roller (final product) corresponding to the end portion of the intermediate roll. In the same manner, the heat shrinkage ratio in the width direction obtained by using the roll (final product) corresponding to the center portion of the intermediate roll and the roll (final product) corresponding to the end portion of the intermediate roll are calculated. The average value of the heat shrinkage rate in the width direction.

(10) Penetration optical density

The film penetration optical density of the polyester film was calculated from the incident light beam and the transmitted light beam using an optical densitometer (TR524 manufactured by Macbeth Co., Ltd.) and in accordance with JIS K7605 (1976). In addition, the filter used in the measurement was a Visual filter.

(11) Film forming properties

Use the embodiment. In the conditions of the comparative example, the number of cracks at the time of film formation was converted into a calculated value per day, and it was judged by the following criteria. B or more is a practical range.

S: The rupture per 1 day is less than 1 time; A: The rupture per 1 day is more than 2 times 2 times or less; B: The rupture every 1 day is more than 2 times 3 times or less; C: The rupture every 1 day exceeds 3 times.

(12) Processability (punchability)

Three sheets of the obtained film were stacked, and the mold was cut with a punching cutter, and the cross section was visually observed and judged according to the following criteria. B or more is a practical range.

S: The flash and the hairs are not visible at all; A: The length of the flash and the hairs are 1.3 or less per 0.3m; B: the length of the flash and the hairs are more than one or less than 0.3m per 0.3m; C: the flash and the hair system The length is more than 3 per 0.3m.

(13) Micro endothermic peak temperature (Tmeta)

The film was measured by a differential scanning calorimeter (DSC Q100 manufactured by TA Instruments Co., Ltd.) at a temperature elevation rate of 20 ° C /min in the range of 30 ° C to 280 ° C. The temperature of the minute endothermic peak before the peak of the melting point of the polyester crystal in the differential scanning calorimetry curve obtained by the measurement was defined as Tmeta (° C.). In addition, the Tmeta polyester film appeared after the heat treatment temperature.

Presented in various embodiments. The adjustment method of the resin (raw material) used in the comparative example is used as a reference example.

[Reference Example 1] Modulation of Polyester Resin 1

In the first step, 100 parts by mass of dimethyl terephthalate was mixed with 38.15 parts by mass of ethylene glycol and 0.25 parts by mass of diethylene glycol in a nitrogen atmosphere at a temperature of 260 °C. Then, the temperature was lowered to 225 ° C, 0.068 parts by mass of manganese acetate tetrahydrate and 0.029 parts by mass of antimony trioxide were added, and the mixture was stirred, and while further blooming for 2 hours, 15.9 parts by mass of ethylene glycol and diethylene glycol were gradually added. 0.10 parts by mass of the mixture was distilled off while the methanol was distilled off to complete the transesterification reaction. In the second step, after the end of the transesterification reaction, the temperature of the polyester in the reaction system is set to 225 ° C, and 6.8 parts by mass of ethylene glycol is added to dissolve 0.015 parts by mass of phosphoric acid (1.5 mol/t equivalent) and phosphoric acid. 0.027 parts by mass of sodium hydrogen hydrate (1.5 mol/t equivalent) ethylene glycol solution (concentration of phosphorus compound 0.4% by mass). Connect In the third step, polymerization was carried out under reduced pressure of a final temperature of 285 ° C and a pressure of 13 Pa to obtain a polyester having an intrinsic viscosity of 0.54 and a carboxyl terminal group of 17 equivalent/t. Further, in the fourth step, the obtained polyethylene terephthalate was dried at 160 ° C for 6 hours and crystallized, and then subjected to solid phase polymerization at 230 ° C for 10 hours under reduced pressure of 65 Pa to obtain inherent A polyester having a viscosity (IV) of 0.82, a carboxyl terminal group amount of 9.7 equivalent/t, a diethylene glycol content of 1.20 mass%, a melting point of 260 ° C, and a glass transition temperature of Tg 81 ° C.

[Reference Example 2] Modulation of polyester resin 2~26

A polyester resin was obtained in the same manner as in Reference Example 1 except that the conditions shown in Table 1-1 and Table 1-2 were used. Further, regarding the polyester resin 5, 85.6 parts by mass of terephthalic acid was used instead of 100 parts by mass of dimethyl terephthalate, and for the polyester resins 11 and 12, potassium dihydrogen phosphate was used instead of sodium dihydrogen phosphate 2 hydrate. . Further, regarding the polyester resins 8, 9, and 23, the solid phase polymerization time was adjusted so that the fourth step became the intrinsic viscosity shown in Table 1-1 and Table 1-2. Further, the polyester resin 24 was subjected to solid phase polymerization until the polyester in the third step had an intrinsic viscosity of 0.50 and a carboxyl terminal group of 27 equivalents/t, and then became an intrinsic viscosity of 0.73 in the fourth step.

The results of evaluating the properties of the obtained polyester are shown in Table 1-1 and Table 1-2.

[Reference Example 3] Modulation of polyester resin A containing cerium oxide

5 parts by mass of cerium oxide particles having an average particle diameter of 4.3 μm were kneaded at 290 ° C in a 2-axis extruder to 95 parts by mass of the polyester resin 1 obtained in Reference Example 1 to obtain a cerium oxide-containing polymer. Ester resin A.

[Reference Example 4] Modification of polyester resin B containing rutile-type titanium oxide

50 parts by mass of chlorine rutile-type titanium oxide particles having an average particle diameter of 0.3 μm were kneaded by a 2-axis extruder at 50 °C to 50 parts by mass of the polyester resin 1 obtained in Reference Example 1 to obtain rutile-containing particles. Type 2 titanium dioxide polyester resin B.

[Example 1]

99.5 parts by mass of the polyester resin 1 adjusted in accordance with the reference example and 0.5 parts by mass of the mixture of the cerium oxide-containing polyester resin A were dried at a temperature of 170 ° C for 4 hours under a reduced pressure of 1 kPa. It was supplied to an extruder and melt-extruded at 285 °C.

The stainless steel steel fiber was filtered by a filter having an average mesh opening of 60 μm, and then extruded into a sheet shape by a T-shaped nozzle, and wound into a mirror-casting drum having a surface temperature of 20 ° C by electrostatic application casting. It cools and solidifies. The unstretched film was preheated to 85 ° C by a preheating roll, and then heated to 100 ° C from the upper and lower directions by using a radiant heater and extended in the longitudinal direction at an elongation speed of 3,500%/second by using a peripheral speed difference between the rolls. The film was uniaxially aligned (uniaxially stretched) by cooling to 25 ° C with a cooling roll.

Next, the uniaxially oriented (uniaxially stretched) film was held by a jig, preheated by hot air of 100 ° C in an oven, and then continuously heated in a stretching step at a hot air of 120 ° C while extending 3.8 times in the width direction. Further, the extension in the width direction was set such that the stretching ratio at the intermediate point of the extending step was 3.0 times, and the stretching in the width direction of the intermediate point was 71%. The obtained biaxially oriented (biaxially stretched) film was subjected to an intermediate step and then subjected to a heat treatment step. The first heat treatment was performed with hot air at 200 ° C for 3.5 seconds, and the second heat treatment was performed with hot air at 210 ° C for 3.5 seconds. The third heat treatment system was used. The heat treatment was performed for 7 seconds with hot air at 215 °C. Further, the intermediate step is surrounded by the heat insulating wall, and heating by hot air or the like is not performed, and only the exhaust gas in the step is performed, and the ambient temperature is adjusted to 160 °C. Also, the film passage time of the intermediate step was 3.5 seconds. The film subjected to the heat treatment step was subjected to a relaxation treatment of 5% while cooling from 215 ° C to 100 ° C, followed by cooling to 80 ° C. Next, the film was taken out from the oven, and both ends in the width direction were removed, and then crimped to obtain a thickness of 125 μm , a width of 5.4 m, a heat shrinkage rate of 150 minutes at 150 ° C for 1.6 minutes, and a width of 0.7% in the width direction. Intermediate film intermediate roll. The properties of the obtained polyester film are shown in Table 3-1 and Table 4-1.

Further, the obtained polyester film was cut into a core having an inner diameter of 152.5 mm and an outer diameter of 167 mm by cutting the intermediate roll to a width of 1000 mm × 5 to obtain a polyester film roll. Further, a film obtained by using a polyester film roll corresponding to the center portion in the width direction of the roll (film) in the intermediate roll direction and a polyester film roll corresponding to the end portion in the width direction of the roll (film) of the intermediate roll is used. The characteristics are shown in the table (in the table, "the center portion of the intermediate roll" is measured using a polyester film roll corresponding to the center portion of the intermediate roll. Further, the "intermediate roll end portion" means the use and Measured by the polyester film roll corresponding to the end of the intermediate roll).

The obtained film is a film having high heat and humidity resistance in the center portion and the end portion of the intermediate roll regardless of the direction, and has extremely excellent durability. Moreover, regardless of the film formation used to control the extension conditions of the molecular alignment, the film is not cracked at all, and no flashing occurs at the cutting end face, which is productive. A biaxially oriented polyester film excellent in workability.

[Examples 2 to 27, 29]

A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the raw materials and film forming conditions of Tables 2-1 and 2-2 were applied. The properties of the obtained film are shown in Table 3-1, Table 3-2, Table 4-1, and Table 4-2.

[Example 28]

According to the reference example, a mixture of the adjusted 95 parts by mass of the polyester resin 1 and 5 parts by mass of the rutile-type titanium dioxide-containing polyester resin B was dried at a temperature of 170 ° C for 4 hours under a reduced pressure of 1 kPa. Thereafter, it was supplied to the extruder A and melt-extruded at 285 °C. Further, according to the reference example, a mixture of the adjusted 60 parts by mass of the polyester resin 1 and 40 parts by mass of the rutile-type titanium oxide-containing polyester resin B was subjected to a pressure of 1 kPa under a reduced pressure of 170 ° C under a pressure of 1 kPa. After drying for 4 hours, it was supplied to extruder B and melt-extruded at 285 °C. The molten resin extruded by the extruder A and the molten resin extruded by the extruder B are respectively filtered by a filter having an average mesh size of 60 μm obtained by sintering and compressing stainless steel fibers, and then fed. The block was laminated in two layers in the thickness direction, and then extruded into a sheet shape by a T-shaped nozzle, and wound into a mirror casting drum having a surface temperature of 20 ° C by electrostatic application casting, followed by cooling and solidification. The obtained unstretched sheet was obtained by the same method as in Example 1 to obtain a resin on the side of the extruder A: a resin of the side of the extruder B was laminated in a thickness direction of 6:1 to form a biaxially oriented polyester film. . The properties of the obtained film are shown in Tables 3-2 and 4-2.

[Example 30]

The intermediate roll (intermediate product) was cut and curled into an inner diameter while being formed by a cutter to form a width of 1250 mm × 4 A biaxially oriented polyester film was obtained in the same manner as in Example 1 except for a core of 152.5 mm and an outer diameter of 167 mm. Among the four film rolls obtained, a polyester film roll corresponding to the end of the intermediate roll and a polyester film roll corresponding to the central portion of the intermediate roll (in the film width direction, located in the middle roll) The film properties measured by the polyester film roll next to the polyester film roll at the end are shown in Table 3-2 and Table 4-2.

[Examples 31, 32]

In addition to the raw materials and film forming conditions of Table 2-2, the intermediate roll (intermediate product) has a width of 3.4 m, and the intermediate roll is cut while being cut into an inner diameter of 152.5 by a cutter to form a width of 1000 mm × 3 pieces. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except for a core of mm and an outer diameter of 167 mm. Among the three film rolls obtained, the film properties measured by using the polyester film roll corresponding to the center portion of the intermediate roll and the polyester film roll corresponding to the end portion of the intermediate roll are shown in Table 3-2. Table 4-2.

[Example 33]

In addition to going through the second heat treatment step 225 ° C, the third heat The film subjected to the heat treatment at 235 ° C was subjected to a relaxation treatment of 5% in the width direction at 215 ° C, and then subjected to a relaxation treatment of 1.5% in the longitudinal direction at 200 ° C, followed by cooling to 80 ° C, and the same as in Example 1. A biaxially oriented polyester film was obtained. The properties of the obtained film are shown in Tables 3-2 and 4-2.

[Embodiment 34, 35]

A biaxially oriented polyester film was obtained in the same manner as in Example 33 except that the materials and film forming conditions of Table 2-2 were applied. The properties of the obtained film are shown in Tables 3-2 and 4-2.

[Example 36]

In addition to the raw materials and film forming conditions of Table 2-3, the intermediate roll (intermediate product) was cut by a cutter to form a width of 1250 mm × 4, and the core was curled to a core having an inner diameter of 152.5 mm and an outer diameter of 167 mm. A biaxially oriented polyester film was obtained in the same manner as in Example 33. Among the four film rolls obtained, a polyester film roll corresponding to the end of the intermediate roll and a polyester film roll corresponding to the central portion of the intermediate roll (in the film width direction, located in the middle roll) The film properties measured by the polyester film roll next to the polyester film roll at the end are shown in Table 3-3 and Table 4-3.

[Examples 37, 38]

Except for the raw materials and film forming conditions of Table 2-3, the width of the intermediate roll (intermediate product) was 3.4 m, and the intermediate roll was cut while being formed into a width of 1000 mm × 3 by a cutter to curl into an inner diameter of 152.5 mm. A biaxially oriented polyester film was obtained in the same manner as in Example 33 except for a core having an outer diameter of 167 mm. Among the three film rolls obtained, the film properties measured using the polyester film roll corresponding to the center portion of the intermediate roll and the polyester film roll corresponding to the end portion are shown in Table 3-3 and Table 4 3.

[Example 39]

A laminated biaxially oriented polyester film was obtained in the same manner as in Example 28 except that the materials and film forming conditions of Table 2-3 were applied. The properties of the obtained film are shown in Table 3-3 and Table 4-3.

[Comparative Examples 1 to 11]

A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the raw materials and film forming conditions of Table 2-3 were applied. The properties of the obtained film are shown in Table 3-3 and Table 4-3.

[Comparative Example 12, 13]

A biaxially oriented polyester film was obtained in the same manner as in Example 36 except that the raw materials and film forming conditions of Table 2-3 were applied. Among the four film rolls obtained, a polyester film roll corresponding to the end of the intermediate roll and a polyester film roll corresponding to the central portion of the intermediate roll (in the film width direction, located in the middle roll) The film properties measured by the polyester film roll next to the polyester film roll corresponding to the end portion are shown in Tables 3-3 and 4-3.

[Results]

A polyester resin containing 0.1 to 5.0 mol/t of an alkali metal phosphate is used as a raw material, and the terminal carboxyl group content is 20 equivalent/t or less, the intrinsic viscosity (IV) is 0.65 to 0.80, and the diethylene glycol amount is 0.9 to 3.0. In the polyester film composed of polyester resin in the range of mass %, the result is resistance to moist heat and productivity. The processability was all good. In Comparative Example 1 in which the content of diethylene glycol (DEG) was not more than the above range, film formation could not be carried out stably, and a sample for performing wet heat resistance evaluation and ultrasonic conduction velocity measurement could not be obtained. Reduce the extension ratio of the long side direction and the width direction. In Comparative Example 10, the sample having a reduced crack was obtained, but as a result, the ultrasonic conduction velocity was lowered and the hydrolysis resistance was deteriorated. Further, Comparative Example 2, in which the content of diethylene glycol (DEG) was at least the above range, Comparative Examples 3 to 5 in which the content of the alkali metal phosphate was out of the range, Comparative Examples 6 and 7, and the amount of terminal carboxyl groups in the range in which the intrinsic viscosity was outside the range For Comparative Example 8 outside the range, the results are in a hot and humid environment. Any of the durability or productivity below is deteriorated. In addition, Comparative Example 9 in which the temperature of the polyester in the case where the alkali metal phosphate is added during the polymerization of the polyester resin and the concentration of the alkali metal phosphate in the ethylene glycol are high, the foreign matter containing the phosphorus element in the film is a foreign matter. In addition, Example 5 in which terephthalic acid was used as a starting material for polymerization of a polyester resin, Example 16 in which the polyester temperature was high when an alkali metal phosphate was added, and a phosphate alkali in ethylene glycol. In Example 17, in which the concentration of the metal salt was high, it was found that the amount of the foreign matter containing phosphorus tends to increase in the qualified range.

In the case of the film characteristics, the average value of the omnidirectional ultrasonic conduction velocity is 2.20 km/sec or more, and as a result, the wet heat resistance is good, and the comparative examples 2, 5, 9, 11, 12 which are less than 2.20 km/sec are obtained. 13, is a deterioration in durability when it is resistant to heat and humidity. Furthermore, in the case where the ratio of the maximum value to the minimum value is in the range of 1.00 to 1.30, especially at the end position where the alignment axis is shifted by 10 or more, that is, the angle θ is in the range of 10 to 80 degrees, the position is reduced. The hygrothermal resistance is maintained by the direction, and the heat and humidity resistance can be maintained even in the direction in which the ultrasonic conduction velocity is the smallest, and the result is further improved. Since these have the longitudinal direction extending step, the width direction extending step, and the intermediate step shown in the above [10], even if the end portion of the wide film having a width of 5 m is used as the product portion, the above-mentioned position can be satisfied. Characteristics.

In the viewpoint of thermal dimensional stability, as shown in Examples 33 to 39, the heat shrinkage rate in the longitudinal direction is reduced by heat treatment at a high temperature of 220 ° C or higher and the relaxation treatment in the longitudinal direction. Good characteristics. In addition, in the prior art, when the molecular alignment in the film is moderated at such a high temperature, the moist heat resistance is greatly deteriorated, but the use of the present According to the technique of the present invention, it is possible to maintain a state in which the moist heat resistance is sufficiently high. Therefore, it is possible to combine both durability and thermal dimensional stability which are difficult in the prior art.

Further, in Examples 27, 28, and 39, by including rutile-type titanium oxide, the concealing property of the film and the ultraviolet ray durability are improved, particularly in the case of outdoor use applications such as solar cell encapsulation film use. Further, in Example 28, a layer having a large content of rutile-type titanium oxide in a thickness direction and a small number of laminated layers were formed, even when titanium dioxide having high catalytic activity was contained, especially even as in Example 39. In the case where severe film forming conditions are applied to improve the thermal dimensional stability, high heat and humidity resistance can be maintained, and the result is very good.

In addition, in the table, "MAX" means "the maximum value of the ultrasonic conduction velocity of the film", "MIN" means "the minimum value of the ultrasonic conduction velocity of the film", and "MAX direction" means "the ultrasonic conduction velocity of the film is presented" The direction of the maximum value and the "MIN direction" indicate "the direction in which the supersonic conduction velocity of the film exhibits the minimum value".

Further, the table does not have the characteristics described in the "middle roller center portion" and the "intermediate roller end portion", and the values measured in the "middle roller center portion" and the values measured at the "intermediate roller end portion". the same.

[Industry use possibility]

Since the durable polyester film of the present invention is a film having few internal defects excellent in durability and productivity under high temperature and high humidity, it can be suitably used for a solar cell encapsulating sheet, a copper clad laminate, an adhesive tape, and a flexible film. Printed substrate, diaphragm switch, planar heating element, or flat For electrical insulation materials such as cables, materials for capacitors, materials for automobiles, and construction materials, the use of durability is emphasized.

Claims (13)

A biaxially oriented polyester film comprising a film of a polyester resin containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less, and an intrinsic viscosity (IV) of the polyester resin constituting the film is 0.65 or more and 0.80 or less, the terminal carboxyl group amount is 20 equivalent/t or less, the diethylene glycol content is 0.9% by mass or more and 3.0% by mass or less, and the average ultrasonic conduction velocity of the film is 2.20 km/sec or more. The biaxially oriented polyester film of claim 1, wherein the foreign matter containing a phosphorus element having a long diameter of 100 μm or more contained in the film is 10/1000 cm ² or less. The biaxially oriented polyester film of claim 1 or 2, wherein a ratio of a maximum value to a minimum value of the ultrasonic conduction velocity of the film is 1.00 or more and 1.30 or less. The biaxially oriented polyester film of claim 3, wherein an angle (θ) of the direction in which the ultrasonic conduction velocity of the film exhibits a maximum value and the longitudinal direction of the film is 10° or more and 80° or less. The biaxially oriented polyester film according to any one of claims 1 to 4, wherein the long-side shrinkage ratio at a temperature of 150 ° C for 30 minutes is 0.8% or less. The biaxially oriented polyester film according to any one of claims 1 to 5, wherein the minute endothermic peak temperature Tmeta (° C.) obtained by differential scanning calorimetry (DSC) is 220° C. or more. The biaxially oriented polyester film according to any one of claims 1 to 6, wherein the ratio of the alkali metal element in the polyester resin: WA (ppm) to phosphorus content: WP (ppm) is WA/WP is 0.3. Above 0.7 or less. The biaxially oriented polyester film according to any one of claims 1 to 7, wherein the polyester resin contains a manganese compound having a manganese element content of 100 ppm or more and 300 ppm or less. The biaxially oriented polyester film according to any one of claims 1 to 8, wherein the elongation retention ratio is maintained at 50% or more when held at 125 ° C and 100% RH for 72 hours. A method for producing a biaxially oriented polyester film, comprising: a step of melting and molding a polyester resin containing an alkali metal phosphate of 0.1 mol/t or more and 5.0 mol/t or less into a sheet shape; - (3) the elongation step and the heat treatment step in the longitudinal direction and the width direction, and the polyester resin constituting the film has an intrinsic viscosity (IV) of 0.65 to 0.80 and a terminal carboxyl group content of 20 equivalent/t or less. The diol content is 0.9% by mass or more and 3.0% by mass or less, and the average ultrasonic conduction velocity of the film is 2.20 km/sec or more, and (1) extending to the long side direction at an elongation speed of 2,000%/sec to 10,000%/sec. 4.5 times step; (2) extending 3.5 to 4.5 times in the width direction, and setting the film width before the start of the width direction extending step to W0, and setting the film width at the intermediate point of the width extending step to W1. In the case where the film width after the end of the width direction extending step is W2, it conforms to the following formula (A): 60 ≦ 100 × (W1 - W0) / (W2 - W0) ≦ 80... Formula (A) (3) There is an intermediate step between the width direction extending step and the heat treatment step, the intermediate step having a temperature of width The temperature of the final section of the direction extension step: Ts (°C) and the initial interval corresponding to the heat treatment step The temperature of the first heat treatment step: the temperature between Th (° C.), and when the time for passing the film through the intermediate step is Sm (second), it conforms to the step (Th-Ts) / Sm ≦ 50 of the following formula (B)... Formula (B). The method for producing a biaxially oriented polyester film according to claim 10, wherein the polyester resin containing the alkali metal phosphate is produced in accordance with the following steps (4) to (6): (4) synthesizing the aforementioned polyester In the polymerization step of the resin, an alkali metal phosphate is added; (5) an alkali metal phosphate is dissolved or mixed in the diol component, and a solution or slurry in which the concentration of the alkali metal phosphate is 1% by mass or less is added; (6) The temperature of the reactant when the alkali metal phosphate is added is 250 ° C or lower. A film for solar cell encapsulation which is obtained by using the biaxially oriented polyester film according to any one of claims 1 to 9. A solar cell obtained by using the film for solar cell encapsulation of claim 12.