JP2015070021A - Polyester film for solar battery back sheet, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a polyester film for solar battery back sheet which is superior in concealment and tracking resistance; and a method for manufacturing such a polyester film for solar battery back sheet.SOLUTION: A polyester film for solar battery back sheet satisfies the following requirements (1) to (4): (1) the optical concentration is 1.0 or higher, and L value is 10 or less; (2) the tracking voltage is 330 V or larger; (3) a polyester resin composition constituting the polyester film includes a complex oxide including at least two elements of a group consisting of calcium, manganese and titanium, of which the content is 0.1-5.0 mass% to the total mass of the polyester resin composition constituting the polyester film; and (4) the thickness of the film is larger than 50 μm.

Description

  The present invention relates to a polyester film for a solar battery back sheet excellent in concealability and electrical insulation and a method for producing the same.

  In recent years, solar power generation has attracted attention as a semi-permanent and pollution-free next-generation energy source, and solar cells are rapidly spreading. In a solar cell, a power generation element is sealed with a transparent sealing material such as ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as EVA), a transparent substrate such as glass, and a solar cell back sheet. A resin sheet is bonded together. Sunlight is introduced into the solar cell through the transparent substrate. Sunlight introduced into the solar cell is absorbed by the power generation element, and the absorbed light energy is converted into electrical energy. The converted electric energy is taken out by a lead wire connected to the power generation element and used for various electric devices. Here, the solar cell backsheet is used for the purpose of protecting the power generation element of the solar cell from external influences such as rain.

  Polyester (especially polyethylene terephthalate (hereinafter sometimes abbreviated as PET) or polyethylene-2,6-naphthalenedicarboxylate) resins that are inexpensive and have excellent mechanical properties have been used for solar cell backsheets. .

  In addition, the solar cell is required to be invisible from the outside, such as wiring to the power generation element, from the viewpoint of design. Therefore, high concealability is also required for the solar battery backsheet. In order to improve the concealability of the film, there are a method of whitening the film by adding white particles or the like to the polyester film, and a method of blackening by adding a black pigment or the like. Since a solar cell may be installed on a roof of a house or the like, it is desired to be blackened from the viewpoint of design. Therefore, a polyester film in which carbon black is added to polyester as a black pigment has been proposed (Patent Documents 1 and 2).

JP 2008-56771 A JP2011-119651A

  However, since carbon black has high electrical conductivity, there is a problem in that tracking resistance, which is an index of electrical insulation, is deteriorated by adding carbon black to polyester. Tracking is an evaluation of resistance against the formation of a conductive path on the surface or inside of a solid due to the influence of both electrical stress and contaminants. One of the indexes representing tracking resistance is tracking voltage. A method for measuring the tracking voltage will be described later. As the tracking voltage is higher, the tracking is less likely to occur and the electrical insulation is better. In addition, when carbon black is added to polyester, carbon black becomes the core of crystallization, and the crystallization speed of polyester is increased, so that not only is stretching difficult, but a film using the polyester is placed in a humid heat atmosphere. In such a case, the rate of increase in the crystallinity of the film is high, the film becomes brittle early, and the heat and heat resistance of the film is lowered.

  The method described in Patent Document 1 has a problem that the tracking voltage is lowered by adding carbon black. The method described in Patent Document 2 has a problem that the heat and humidity resistance of the film is lowered and the tracking voltage is lowered by adding carbon black.

  In addition, the film used for the solar battery back sheet is required to satisfy the performance of electrically insulating the power generation element and the outside air for a long period of time, but the films of Patent Documents 1 and 2 are placed in a humid heat atmosphere. In this case, there is a problem that the tracking voltage is greatly reduced.

  In view of the prior art, an object of the present invention is to provide a polyester film for a solar battery back sheet that is excellent in concealability and electrical insulation properties, and further has excellent heat and moisture resistance, and a method for producing the same.

In order to solve the above problems, the present invention has the following configuration. That is, 1. A polyester film for a solar battery back sheet that satisfies the following requirements (1) to (4).
(1) Optical density is 1.0 or more and L value is 10 or less (2) Tracking voltage is 330 V or more (3) The polyester resin composition constituting the polyester film is calcium, manganese, titanium Is a polyester resin composition containing a composite oxide containing at least two kinds of elements in the group consisting of 0.1 to 5.0 mass with respect to the whole polyester resin composition constituting the polyester film. (4) The film thickness is larger than 50 μm. The polyester resin composition constituting the polyester film is a polyester resin composition containing carbon black, and the content thereof is 0.1 to 0.5% by mass with respect to the entire polyester resin composition constituting the polyester film. 1. The polyester film for solar cell backsheets as described in 2.
3. 1. The intrinsic viscosity of the polyester resin constituting the polyester film is 0.65 dl / g or more. Or 2. The polyester film for solar cell backsheets as described in 2.
4). 1. The amount of terminal carboxyl groups of the polyester resin constituting the polyester film is 15 eq / t or less. ~ 3. The polyester film for solar cell backsheets in any one of.
5. When the cold crystallization temperature of the polyester resin composition constituting the polyester film is Tc (° C.) and the glass transition temperature is Tg (° C.), the crystallization parameter ΔTcg calculated by the following formula (i) is 45 ° C. or more and 70 ° C. 1. ~ 4. The polyester film for solar cell backsheets in any one of.
(I) ΔTcg = Tc−Tg
6). It is a manufacturing method of the polyester film for solar cell backsheets which satisfies the requirements of following (1) to (4), Comprising: At least 2 types in the group which consists of calcium, manganese, and titanium to the polyester resin which comprises a polyester film A method for producing a polyester film for a solar battery backsheet, comprising adding a complex oxide containing an element by melt kneading.
(1) Optical density is 1.0 or more and L value is 10 or less (2) Tracking voltage is 330 V or more (3) The polyester resin composition constituting the polyester film is calcium, manganese, titanium Is a polyester resin composition containing a composite oxide containing at least two kinds of elements in the group consisting of 0.1 to 5.0 mass with respect to the whole polyester resin composition constituting the polyester film. (4) The film thickness is larger than 50 μm. The polyester resin composition constituting the polyester film is melt-extruded, and the polyester resin composition after the melt extrusion is subjected to a glass transition temperature of the polyester resin constituting the polyester film of −55 ° C. or higher, and the polyester resin constituting the polyester film. 5. It is cooled and solidified with a drum having a glass transition temperature of −10 ° C. or lower, and then stretched biaxially. The manufacturing method of the polyester film for solar cell backsheets as described in any one of.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film for solar cell backsheets which is excellent in concealability, electrical insulation, and also excellent in heat-and-moisture resistance, and its manufacturing method can be provided.

It is a figure which shows typically the positional relationship of the nozzle at the time of measuring tracking voltage, an electrode, and a measurement sample.

  The polyester constituting the polyester film of the present invention is obtained using a dicarboxylic acid component and a diol component as main raw materials. Here, the main raw material means that 90% by mass or more of all raw materials of the polyester is a dicarboxylic acid component and a diol component. The polyester constituting the polyester film of the present invention may use, as a raw material, a hydroxycarboxylic acid component or a polyfunctional component having a total of 3 or more carboxylic acid groups and hydroxyl groups as long as the effects of the present invention are not impaired.

  Examples of the dicarboxylic acid component used in the present invention include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid Aliphatic dicarboxylic acids such as ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, and the like, terephthalic acid, isophthalic acid, phthalic acid, 1,4- Naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4′-diphenyl dicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfo Isophthalic acid, Fe Toluene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) dicarboxylic acids such as fluorene acids and aromatic dicarboxylic acids, or there may be mentioned an ester derivative thereof is not limited thereto. Also preferred are those obtained by adding oxyacids such as l-lactide, d-lactide, hydroxybenzoic acid, and derivatives thereof, or a combination of a plurality of oxyacids to the carboxy terminus of the dicarboxylic acid component described above. Used. Moreover, these may be used independently or may be used in multiple types as needed.

  Examples of the diol component used in the present invention include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and the like. Aliphatic diols, cycloaliphatic dimethanol, spiroglycol, isosorbide and other alicyclic diols, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4- Examples thereof include, but are not limited to, diols such as hydroxyphenyl) fluorene and aromatic diols, and those in which a plurality of the above diols are linked. Moreover, these may be used independently or may be used in multiple types as needed.

  Moreover, it is preferable that polyester which comprises the polyester film of this invention is polyester which has a terephthalic acid and ethylene glycol as the main structural component from a mechanical characteristic, crystallinity, and a heat-and-moisture resistant viewpoint. The polyester having terephthalic acid and ethylene glycol as main constituents means that the proportion of terephthalic acid constituents in all dicarboxylic acid constituents is 90 mol% or more and 100 mol% or less, and the ratio of ethylene glycol constituents in all diol constituents is It is 90 mol% or more and 100 mol% or less of polyester. The ratio of the terephthalic acid component in the total dicarboxylic acid component is 95 mol% or more and 100 mol% or less, and the proportion of the ethylene glycol component in the total diol component is more preferably 95 mol% or more and 100 mol% or less. . If the proportion of the terephthalic acid constituent component is less than 90 mol% or the proportion of the ethylene glycol constituent component is less than 90 mol%, the mechanical properties may deteriorate, the crystallinity may deteriorate, and the heat and humidity resistance may deteriorate.

  The polyester film of the present invention is required to have an optical density of 1.0 or more (100 μm conversion). If the optical density is less than 1.0, the wiring to the power generation element cannot be concealed, resulting in poor design. More preferably, it is 1.2 or more, More preferably, it is 1.5 or more, Most preferably, it is 2.0 or more.

  In the polyester film of the present invention, it is necessary that the tracking voltage measured by the measurement method described later is 330 V or more. When the tracking voltage is less than 330 V, electrical insulation and tracking resistance are insufficient when used for a solar cell backsheet. The tracking voltage is more preferably 350 V or more, and particularly preferably 355 V or more. The higher the tracking voltage, the better the electrical insulation, and the upper limit is not particularly defined, but it is substantially difficult to produce a polyester film having a tracking voltage higher than 1000V. In addition, since solar cells are used outdoors for a long period of time, the solar cell backsheet is required to maintain high tracking performance even after being exposed to high temperatures and high humidity for a long period of time. Therefore, the polyester film of the present invention preferably has a high tracking property even after being exposed to a high temperature and a high humidity for a long time. The polyester film of the present invention preferably has a tracking voltage of 80% or more before treatment even after a moisture and heat resistance test described later.

  In the polyester film of the present invention, the polyester resin composition constituting the polyester film comprises a composite oxide containing at least two kinds of elements selected from the group consisting of calcium, manganese, and titanium. It is necessary to contain 0.1-5.0 mass% with respect to the whole. By containing a complex oxide containing at least two kinds of elements in the above range from the group consisting of calcium, manganese, and titanium, a polyester film having good tracking resistance and concealment can be obtained. The complex oxide containing at least two elements out of the complex oxide containing at least two elements in the group consisting of calcium, manganese, and titanium preferably has a perovskite structure, and the content of manganese element Is α mol and the content of titanium element is β mol, and when the α / β value is 0.43 ≦ α / β ≦ 999, tracking resistance and concealment can be improved. It is preferable because of excellent film properties. In addition, in this invention, content of the complex oxide with respect to the whole polyester resin composition which comprises a polyester film shall be the addition amount with respect to the whole polyester resin composition which comprises a polyester film.

  The polyester film of the present invention may be a single layer polyester film or a polyester film laminated in two or more layers. A laminated polyester film having at least one layer made of polyester containing a composite oxide containing at least two kinds of elements from the group consisting of calcium, manganese and titanium is also a preferred embodiment of the present invention. A laminated polyester film having at least one layer made of polyester containing carbon black and other known various additives is also a preferred embodiment.

  The thickness of the polyester film of the present invention needs to be larger than 50 μm. When the thickness of the polyester film is 50 μm or less, the concealability is insufficient, and the design properties are insufficient. Further, since the electrical insulation of the polyester film increases according to the thickness of the film, when used for a solar battery back sheet application where high electrical insulation is required over a long period of time, the electrical insulation properties when the film thickness is 50 μm or less. Is insufficient. The thickness of the polyester film is more preferably from 50 μm to 300 μm.

The polyester film of the present invention has a crystallization parameter determined by the following formula (i) when the cold crystallization temperature of the polyester resin composition constituting the polyester film is Tc (° C.) and the glass transition temperature is Tg (° C.). ΔTcg is preferably 45 ° C. or higher and 70 ° C. or lower.
(I) ΔTcg = Tc−Tg
ΔTcg can be used as an index indicating the ease of crystallization of the polyester resin composition. In accordance with JIS K7122 (1999), Tc is heated at a rate of temperature increase of 20 ° C./min from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./min (1st RUN) and held in that state for 5 minutes. Then, it is rapidly cooled to 25 ° C. or lower, and again a 2ndRUN differential scanning calorimetry chart obtained by raising the temperature from 25 ° C. to 300 ° C. at a temperature rising rate of 20 ° C./min (the vertical axis represents thermal energy, The temperature is determined as the temperature of the peak top of the crystallization peak, which is the endothermic peak in the horizontal axis), and Tg is the glass transition temperature obtained by the same method.

  In general, the smaller the value of ΔTcg, the faster the crystallization rate of the polyester resin composition and the lower the heat-and-moisture resistance of the polyester resin composition. And when there exists a coarse aggregate in a polyester resin composition, the value of (DELTA) Tcg falls large.

  Therefore, the value of ΔTcg of the polyester composition constituting the polyester film of the present invention is preferably 45 ° C. or higher and 70 ° C. or lower. By setting ΔTcg within the above range, the crystallization rate of the polyester resin composition in a wet heat atmosphere can be set to an appropriate range, the progress of embrittlement can be suppressed, and the mechanical properties of the polyester resin composition can be reduced. Can be good.

  In the polyester film of the present invention, the intrinsic viscosity of the polyester constituting the polyester film is preferably 0.65 dl / g or more from the viewpoint of tracking resistance, mechanical properties, heat resistance, and moist heat resistance. More preferably, it is 0.65 dl / g or more and 1.0 dl / g or less, and particularly preferably 0.7 dl / g or more and 0.8 dl / g or less. When the intrinsic viscosity is less than 0.65 dl / g, the surface becomes brittle when a voltage is applied, and tracking is likely to occur, and tracking resistance may be reduced. The reason for this is not clear at this time, but it is estimated that when the intrinsic viscosity is less than 0.65 dl / g, low molecular weight components and oligomer components are deposited on the surface when voltage is applied, and tracking is likely to occur. ing.

  The polyester film of the present invention has a terminal carboxyl group content of 15 eq. / T (equivalent / ton) or less is preferable from the viewpoint of heat and humidity resistance. More preferably, 13 eq. / T or less. When the amount of terminal carboxyl groups exceeds 15 eq / t, the heat and humidity resistance is poor, and mechanical properties may be deteriorated particularly when exposed to high temperatures and humidity for a long period of time.

  As a technique for incorporating a complex oxide containing at least two elements out of the group consisting of calcium, manganese and titanium into the polyester resin composition constituting the polyester film of the present invention, in any stage of producing the polyester film A conventionally known method can be used. For example, a compound oxide slurry containing at least two elements of a group consisting of calcium, manganese, and titanium dispersed in ethylene glycol or water is mixed with a polyester raw material to perform an esterification reaction or a transesterification reaction. Or after addition of a compound oxide slurry containing at least two elements of the group consisting of calcium, manganese, and titanium dispersed in ethylene glycol or water after the esterification or transesterification reaction. Good. Further, a polyester raw material constituting the polyester film and a composite oxide containing at least two elements out of the group consisting of calcium, manganese, and titanium may be melt-kneaded using a melt-kneader. Among these, a means for melt-kneading a polyester raw material constituting the polyester film and a composite oxide containing at least two elements out of the group consisting of calcium, manganese, and titanium at the time of melt extrusion of the film is preferable. In addition, a master batch is prepared by melting and kneading a complex oxide containing at least two kinds of elements out of the group consisting of calcium, manganese and titanium at a high concentration in advance in the same polyester as the polyester constituting the polyester film, A master batch method of diluting as necessary is also preferably used. In general, when a single or plural kinds of inorganic compounds are used as additives, the inorganic compounds are aggregated and it is difficult to uniformly disperse them in the film. A master batch in which an additive composed of a single or a plurality of types of inorganic compounds is melt-kneaded in advance is prepared, and the master batch is used to melt-knead with the polyester constituting the film so that the inorganic compound is contained in the film. Is preferable because it can be more uniformly dispersed. Further, it is preferable that the inorganic compound is more uniformly dispersed in the film because not only the film forming property is improved but also the film performance such as concealment property is improved.

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

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

  Examples of the reaction catalyst include conventionally known alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and phosphorus compounds.

  When adopting the masterbatch method as a method of adding a composite oxide containing at least two kinds of elements out of the group consisting of calcium, manganese and titanium, the group consisting of calcium, manganese and titanium in advance in the polyester obtained by the above method Among them, a master batch obtained by melting and kneading a complex oxide containing at least two kinds of elements at a high concentration and the polyester obtained by the above-described method are dried as necessary, and then heated and melted in an extruder to obtain a die. The method of extruding from a sheet onto a cast drum and processing it into a sheet (melt cast method) can be used. When the film of the present invention has a laminated structure, a plurality of extruders are used, and if necessary, the dried raw materials are heated and melted in the respective extruders, and these are joined by a merging device provided between the extrusion device and the die. A method of laminating in a molten state, guiding to a die, and extruding from the die onto a cast drum to process into a sheet is preferably used.

  When a film is produced by the melt casting method, the dried raw material is melt-extruded from the die into a sheet using an extruder, and the surface temperature is (the glass transition temperature of the polyester resin (hereinafter referred to as Tg) -55 ° C.) or more ( On the drum cooled to Tg-10 ° C. or lower) of the polyester resin, it is closely cooled and solidified by static electricity to produce an unstretched sheet. When the polyester resin composition constituting the unstretched sheet contains a complex oxide containing at least two kinds of elements in the group consisting of single or plural kinds of calcium, manganese, and titanium, aggregation of the complex oxides is prevented. From the viewpoint of uniformly dispersing in the film, the surface temperature of the cast drum is preferably within the above range. In general, the molecular chain of polyester has high fluidity near the Tg of the polyester resin. By setting the surface temperature of the cast drum within the above range, the molecular chains of the polyester constituting the unstretched sheet flow and the inorganic compound can be uniformly dispersed in the sheet. More preferably, the surface temperature is (Tg−40 ° C. of polyester resin) or more (Tg−20 ° C. or less of polyester resin). When surface temperature is lower than Tg-55 degreeC of a polyester resin, an additive will not disperse | distribute uniformly. Further, when the surface temperature is Tg-10 ° C. or higher of the polyester resin, the polyester is crystallized on the cast drum and the film forming property is deteriorated.

  When melt extrusion in an extruder, it is preferable to melt in a nitrogen atmosphere, and the time from chip supply to the extruder until it is extruded with a die is better, as a guideline, 30 minutes or less, More preferably, it is 15 minutes or less, More preferably, it is 5 minutes or less from the point which suppresses the increase in the amount of terminal carboxyl groups.

  The polyester film of the present invention can be obtained by biaxially stretching the unstretched film thus obtained. For biaxial stretching, using a longitudinal stretching machine in which several rolls are arranged, stretching in the longitudinal direction using the difference in peripheral speed of the rolls (MD stretching), followed by transverse stretching (TD stretching) by a stenter The polyester film of the present invention is described by taking a sequential biaxial stretching method in which MD stretching is performed after TD stretching, or a simultaneous biaxial stretching method in which MD stretching and TD stretching are performed simultaneously. May be obtained.

  First, the unstretched film is MD stretched. The longitudinal stretching machine comprises a preheating roll, a stretching roll, and a cooling roll, and further comprises a nip roll that cuts the tension and suppresses slipping of the film. In MD stretching, the film running on the stretching roll is pressed with a stretching nip roll at a constant pressure (nip pressure) to sandwich the film, cut the tension, and the next cooling roll of the stretching roll rotates with a difference in peripheral speed. Stretched. The MD stretching temperature is preferably (Tg + 10) to (Tg + 50) ° C., and the stretching ratio of MD stretching is preferably 1.2 to 5.0 times. It cools with the cooling roll group of the temperature of 20-50 degreeC after extending | stretching.

  Next, stretching in the width direction (TD stretching) is performed using a stenter. The stenter is a device that stretches the film between the clips at both ends while holding the both ends of the film with clips, and is stretched into a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone. The wind speed in the preheating zone is preferably 1 to 20 m / s. The stretching ratio of TD stretching is preferably 2.0 to 6.0 times, and the stretching temperature is preferably in the range of (Tg) to (Tg + 50) ° C. After TD stretching, heat setting is performed. In the heat setting treatment, the film is heat-treated in a temperature range of 150 to 240 ° C. while being relaxed under tension or in the width direction. The heat treatment time is in the range of 0.5 to 10 seconds. Then, after cooling in a cooling zone, a film edge can be removed and the polyester film of this invention can be obtained.

[Measurement and evaluation method of physical properties]
(1) Amount of contained metal element Using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Denki Co., Ltd., the amount of metal element contained in the polyester resin composition constituting the polyester film is the polyester constituting the polyester film. It is measured as the content (ppm) relative to the resin composition.

(2) Color tone Based on JIS-Z-8722 (2000), the color tone (L value, a value, b value) of the film is reflected using a spectroscopic color difference meter (SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.). The brightness is measured by The measurement conditions were a C light source, a viewing angle of 2 °, a reflection measurement mode, and a sample measurement diameter of 30 mmφ. For standard matching, an attached standard white plate (X value, Y value, and Z value in the above-described measurement method is 93.67, 95.54, 113.35) was used.

(3) Evaluation of film forming property Count the number of times the film breaks in 1 hour during film formation, A (good) if it is less than 1 time, B 3 times if it is 1 time or more and less than 3 times (normal) The above is evaluated as C (defect).

(4) Tracking voltage Based on ASTM D3638 (2008), it is measured by the following method.

  As a measurement sample, a resin molded to a thickness of 2.5 mm on a 100 mm square is used. When the measurement sample is a film, a film cut into a 100 mm square and having a thickness of 2.5 mm is used. Two electrodes are arranged at an interval of 4.0 mm so as to be in contact with the upper surface of the measurement sample. A nozzle is disposed at a position 35 mm above the midpoint between the two electrodes. While applying a constant voltage between the electrodes, the number of drops when 3.85 Ωcm aqueous ammonium chloride solution is dropped from the nozzle at intervals of 30 seconds and tracking occurs. At this time, the occurrence of tracking means a state in which a current of 0.1 A or more is generated between two electrodes for 0.5 seconds or more. Next, the voltage is changed for convenience, and two voltages that do not exceed 50 drops of ammonium chloride aqueous solution and two voltages that exceed 50 drops are calculated. From these four voltages, a graph of the voltage and the number of drops is formed by a cubic curve, and the voltage when the number of drops becomes 50 drops is obtained as a tracking voltage.

(5) Intrinsic viscosity IV
The polyester resin composition is dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / dl), and the viscosity of the solution at 25 ° C. is measured using an Ostwald viscometer. Similarly, the viscosity of the solvent is measured. Using the obtained solution viscosity and solvent viscosity, [η] (dl / g) is calculated by the following equation (c), and the obtained value is used as the intrinsic viscosity (IV).
(C) ηsp / C = [η] + K [η] ² · C
(Where ηsp = (solution viscosity (dl / g) / solvent viscosity (dl / g)) − 1, K is a Huggins constant (assuming 0.343)).

  In addition, when there is an insoluble matter in the solution in which the polyester resin composition is dissolved, the solution is filtered, and the weight of the filtrate is measured. taking measurement.

(6) Amount of terminal carboxyl group Measured according to the method of Malice under the following conditions (document MJ Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)). 2 g of the polyester resin composition was dissolved in 50 mL of o-cresol / chloroform (weight ratio 7/3) at a temperature of 80 ° C., titrated with a 0.05N KOH / methanol solution, and the amount of terminal carboxyl groups was measured. / Indicated by the value of polyester 1t. In addition, the indicator at the time of titration uses phenol red, and the place where it changed from yellowish green to light red is set as the end point of titration.

  In addition, when there is an insoluble matter in the solution in which the polyester resin composition is dissolved, the solution is filtered, and the weight of the filtrate is measured. taking measurement.

(7) Optical density Measured using an optical densitometer TR-927 manufactured by Macbeth. The same measurement for the same sample is performed five times at random locations, and the average value obtained is converted to a film thickness of 100 μm as the optical density. (The optical density is proportional to the film thickness according to Lambert-Beer's law.)
Concealment is evaluated as follows.
Optical density is 1.5 or more: Optical density A
Optical density is 1.0 or more and less than 1.5: Optical density B
Optical density is less than 1.0: Optical density C
Further, the concealment property is evaluated as follows based on the optical density before the film thickness conversion.
Optical density is 1.5 or more: Concealment ability ○
Optical density is less than 1.5: Concealment property ×
(8) Moisture and heat resistance of the tracking resistance of the film The moisture and heat resistance of the tracking resistance of the film was measured under the conditions of a temperature cooker of 140 ° C. and a relative humidity of 80% using a 100 mm square sample by a pressure cooker manufactured by Tabay Espec. Then, the tracking voltage described in item 5 is measured. Then, the tracking voltage holding ratio after the wet heat resistance test is calculated by the following formula (f).
(D) Tracking voltage retention ratio after wet heat test (%) = tracking voltage after wet heat test (V) / initial tracking voltage (V) × 100
When the tracking voltage holding ratio after moisture and heat resistance is 80% or more;
When the tracking voltage holding ratio after heat and humidity resistance is less than 80%: ×

  [Production of PET-A] From terephthalic acid and ethylene glycol, polymerization was carried out by a conventional method using antimony trioxide as a catalyst to obtain PET-A. The glass transition temperature is 81 ° C., the melting point is 255 ° C., the intrinsic viscosity is 0.65, and the amount of terminal carboxyl groups is 28 eq. / T.

  [Production of PET-B] The obtained PET-A was solid-phase polymerized by a conventional method to obtain PET-B. The obtained PET-B had a glass transition temperature of 82 ° C., a melting point of 255 ° C., an intrinsic viscosity of 0.85, and a terminal carboxyl group content of 11 eq. / T.

  [Production of MB-A] 90 parts by mass of PET-B and 10 parts by mass of additive A (mixed solid solution of calcium carbonate, titanium dioxide and manganese dioxide (MPT-370 manufactured by Ishihara Sangyo Co., Ltd.)) were vented. Then, the mixture was melted and kneaded in the extruder to obtain MB-A.

  [Production of MB-B] 90 parts by mass of PET-B and 10 parts by mass of additive B (carbon black (Mitsubishi Chemical Co., Ltd. # 2600)) were charged into a vented extruder and melted in the extruder. The mixture was kneaded to obtain MB-B.

Example 1
PET-B and MB-A were mixed as shown in the table, put into an extruder heated to an extrusion temperature of 280 ° C., then discharged from a T die, and a casting drum having a surface temperature of 40 ° C. An unstretched film was produced by close contact using an electrostatic application method. Subsequently, the obtained unstretched film was preheated with a heated roll group, then stretched 3.3 times in the longitudinal direction (MD direction) at a temperature of 90 ° C., and then cooled with a roll group at a temperature of 25 ° C. Thus, a uniaxially stretched film was obtained. The both ends of the obtained uniaxially stretched film were stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110 ° C. in the tenter while holding the both ends with clips. Subsequently, a heat treatment was performed for 10 seconds at a temperature of 220 ° C. in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 4% width direction at a temperature of 220 ° C. Next, the film was gradually cooled in a cooling zone and wound up to obtain a biaxially stretched polyester film having a thickness of 50 μm. Each characteristic of the obtained film is shown in the table.

(Examples 2 to 7)
Examples 2 to 7 use PET-B, MB-A, and MB-B, and perform the same procedure as in Example 1 except that the polyester and additive contents and film forming conditions are as shown in the table. An axially stretched polyester film was obtained. Each characteristic of the obtained film is shown in the table. In Example 5 in which carbon black was added, the concealability was good, but the tracking voltage was slightly reduced.

(Example 8)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that PET-A and MB-A were used. Each characteristic of the obtained film is shown in the table. In Example 8 where the intrinsic viscosity of the polyester resin constituting the polyester film was less than 0.65 and the terminal carboxyl group amount was 15 eq / t, the tracking voltage was slightly reduced.

(Comparative Examples 1-7)
Comparative Examples 1 to 7 were the same as in Example 1 except that PET-B, MB-A, and MB-B were used, and the polyester and additive contents and film forming conditions were as described in the table. A biaxially stretched polyester film was obtained. Each characteristic of the obtained film is shown in the table. In Comparative Example 1, the film-forming property was poor, and the film could not be obtained because the film was frequently torn. Therefore, the characteristics could not be evaluated. Comparative Examples 2 and 5 were films inferior in concealability. Comparative Examples 3 and 4 were films with low tracking voltage resistance and poor electrical insulation. The polyester films obtained in Comparative Examples 6 and 7 have an inadequate casting temperature, and thus the casting temperature is not appropriate. Thus, the film-forming property is poor, and the film is frequently broken. I couldn't.

  Since the polyester film of the present invention is excellent in concealment and has a high tracking resistance voltage, it can be suitably used for solar cell backsheet applications.

1: Nozzle 2: Electrode 3: Measurement sample

Claims (7)

A polyester film for a solar battery back sheet that satisfies the following requirements (1) to (4).
(1) Optical density is 1.0 or more and L value is 10 or less (2) Tracking voltage is 330 V or more (3) The polyester resin composition constituting the polyester film is calcium, manganese, titanium Is a polyester resin composition containing a composite oxide containing at least two kinds of elements in the group consisting of 0.1 to 5.0 mass with respect to the whole polyester resin composition constituting the polyester film. (4) The film thickness is greater than 50 μm. The polyester resin composition constituting the polyester film is a polyester resin composition containing carbon black, and the content thereof is 0.1 to 0.5% by mass with respect to the entire polyester resin composition constituting the polyester film. The polyester film for solar cell backsheets of Claim 1. The polyester film for solar cell backsheet according to claim 1 or 2, wherein the polyester resin constituting the polyester film has an intrinsic viscosity of 0.65 dl / g or more. The polyester film for a solar battery backsheet according to any one of claims 1 to 3, wherein the amount of terminal carboxyl groups of the polyester resin constituting the polyester film is 15 eq / t or less. When the cold crystallization temperature of the polyester resin composition constituting the polyester film is Tc (° C.) and the glass transition temperature is Tg (° C.), the crystallization parameter ΔTcg calculated by the following formula (i) is 45 ° C. or more and 70 ° C. It is the following, The polyester film for solar cell backsheets in any one of Claims 1-4.
(I) ΔTcg = Tc−Tg It is a manufacturing method of the polyester film for solar cell backsheets which satisfies the requirements of following (1) to (4), Comprising: At least 2 types in the group which consists of calcium, manganese, and titanium to the polyester resin which comprises a polyester film A method for producing a polyester film for a solar battery backsheet, comprising adding a complex oxide containing an element by melt kneading.
(1) The optical density is 1.0 or more. (2) The tracking voltage is 330 V or more. (3) The polyester resin composition constituting the polyester film is at least selected from the group consisting of calcium, manganese, and titanium. It is a polyester resin composition obtained by containing a composite oxide containing two kinds of elements, and its content is 0.1 to 5.0% by mass with respect to the entire polyester resin composition constituting the polyester film. (4) The thickness of the film is larger than 50 μm The polyester resin composition constituting the polyester film is melt-extruded, and the polyester resin composition after the melt extrusion is subjected to a glass transition temperature of the polyester resin constituting the polyester film of −55 ° C. or higher, and the polyester resin constituting the polyester film. The method for producing a polyester film for a solar battery backsheet according to claim 6, wherein the film is cooled and solidified by a drum having a glass transition temperature of -10 ° C or lower, and then biaxially stretched.

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