JP2013049791A - Method of producing polyester film, backsheet for solar cell, and solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film that shows excellent wet-heat durability, wherein cracks are less likely to occur even after the lapse of long time period under a wet-heat environment.SOLUTION: The polyester film contains: a polyester resin; and two or more terminal blocking agents having number average molecular weights that are different by 4,000 or larger from each other or one another, wherein the tear strength retention at 120°C, at 100% relative humidity after the lapse of 60 hours under a wet-heat environment is 50% or larger.

Description

  The present invention relates to a polyester film and a method for producing the same, a solar cell backsheet, and a solar cell module.

  Generally, a solar cell module has a transparent filling material (hereinafter also referred to as a sealing material) / solar cell element / sealing material / back sheet on a light receiving surface on which sunlight is incident on a glass or a front sheet. It has a structure laminated in this order. Specifically, the solar cell element is generally configured to be embedded in a resin (sealing material) such as EVA (ethylene-vinyl acetate copolymer) and further to be attached with a protective sheet for solar cell. The In addition, it is known that a conventional polyester film, in particular, a polyethylene terephthalate (hereinafter referred to as PET) film is used for the solar cell backsheet.

  However, the protective sheet for solar cells, especially the back sheet for solar cells, which is the outermost layer, is supposed to be placed in an environment that is exposed to outdoor wind and rain for a long period of time, Excellent weather resistance is required.

Here, polyester films such as PET, which are also used as a back sheet for solar cells, have excellent heat resistance, mechanical properties, chemical resistance, and the like. There is still room for improvement from the viewpoint of hydrolyzability. It is known that a polyester film deteriorates due to hydrolysis over a long period of time.
Hydrolysis is known to be accelerated by the catalytic action of the terminal carboxylic acid in the polyester, and as a countermeasure against this, the technology for improving the hydrolysis resistance of the polyester film includes polycarbodiimide that reacts with the terminal carboxylic acid. It is known to use an end capping agent (see, for example, Patent Document 1).

JP 2010-235824 A

However, when the present inventors further tried the method described in Patent Document 1 (a back sheet was prepared using the described polyester film and bonded to a solar cell), cracks occurred after a thermo test corresponding to long-term aging. It was easy to see that the solar cell was liable to break down due to the water that entered.
The present invention aims to solve the above problems. The problem to be solved by the present invention is to provide a polyester film that is resistant to cracking even after long-term aging in a humid-heat environment (hereinafter referred to as “thermo”). Is to provide.

In order to solve the above-mentioned problems, the present inventors have conducted extensive studies and found that the film obtained by the method described in Patent Document 1 has a low tear strength retention after wet heat aging.
In contrast, the present inventors have found a method for producing a polyester film that contains two or more end-capping agents having different number average molecular weights, and can achieve a specific range of tear strength after wet heat aging. As a result of the examination, it was found that the obtained polyester film hardly cracks even after a long period of time in a wet heat environment and exhibits excellent wet heat durability.

The present invention which is a specific means for solving the above-mentioned problems is as follows.
[1] A polyester resin and two or more kinds of end-capping agents having a number average molecular weight of 4000 or more are different, and the retention of tear strength after 60 hours of thermostat at 120 ° C. and 100% relative humidity is 50% or more. Polyester film characterized by
[2] In the polyester film according to [1], the terminal blocking agent is any one of a carbodiimide compound, an oxazoline compound, an epoxy compound, and a carbonate compound, and the low molecular weight sealing of the two types of terminal blocking agents. It is preferable that the molecular weight of the stopper is 1000 to 6000 and the molecular weight of the high molecular weight sealant is 10,000 to 50,000.
[3] In the polyester film according to [1] or [2], the terminal blocking agent is preferably a carbodiimide compound.
[4] In the polyester film according to any one of [1] to [3], the mixing ratio of the two kinds of end-capping agents is 1 as the value of the low molecular weight sealing agent / high molecular weight sealing agent. / 9 to 9/1 (mass ratio) is preferable.
[5] The polyester film according to any one of [1] to [4] preferably has a crystallization parameter Tcg of less than 70 ° C and 30 ° C or more.
[6] The polyester film according to any one of [1] to [5] preferably has an endothermic peak of 0.04 to 1.26 J / g in the range of 80 ° C. to 150 ° C.
[7] The polyester film according to any one of [1] to [6] has a thermal dimensional change of 0.1% or more and 2% or less, and a maximum of the thermal dimensional change measured in all directions. The value obtained by dividing the difference between the value and the minimum value by the average value is preferably 5% or more and 40% or less.
[8] The polyester film according to any one of [1] to [7] has an intrinsic viscosity IV of 0.6 dl / g to 0.9 dl / g and a terminal carboxylic acid amount AV of 20 eq / ton. The following is preferable.
[9] A step of melt-kneading a polyester resin, polyester fine particles having a melting temperature different by 1 ° C. or more and 35 ° C. or less, a terminal sealing agent having a number average molecular weight different by 4000 or more, and a melt-kneaded melt are formed into a film shape. The manufacturing method of the polyester film characterized by including the process, the process of extending | stretching the said film to 2 directions, and the process of heat-setting.
[10] The method for producing a polyester film according to [9] includes a step of winding the film after heat setting, and the temperature of the polyester film before winding is preferably 26 ° C. or higher and 80 ° C. or lower. .
[11] In the method for producing a polyester film according to [9] or [10], the step of stretching the film in two directions includes longitudinal stretching in the film transport direction and lateral stretching in a direction perpendicular to the film transport direction. And forming a film of an aqueous solution on at least one surface of the film so that a moisture coating amount is 0.1 g / m ² or more and 30 g / m ² or less between the longitudinal stretching and the transverse stretching. It is preferable to include.
[12] In the method for producing a polyester film according to any one of [9] to [11], the heat setting temperature is preferably 196 ° C. or higher and 215 ° C. or lower.
[13] A polyester film produced by the method for producing a polyester film according to any one of [9] to [12].
[14] A solar cell backsheet using the polyester film according to any one of [1] to [8] and [13].
[15] A solar cell module using the polyester film according to [1] to [8] and [13] or the solar cell backsheet according to [14].

  The polyester film of the present invention is resistant to cracking even after long-term aging in a wet heat environment and exhibits excellent wet heat durability. Moreover, according to the manufacturing method of the polyester film of this invention, said polyester film of this invention can be manufactured.

Hereinafter, the protective sheet for solar cells of the present invention (hereinafter also referred to as the protective sheet for solar cells of the present invention), the production method thereof, the back sheet for solar cells and the solar cell module using the same will be described in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Polyester film]
The polyester film of the present invention contains two or more kinds of end-capping agents having different number average molecular weights of 4,000 or more, and the retention of tear strength after 60 hours of thermostat at 120 ° C. and 100% relative humidity is 50% or more. It is characterized by.

(Physical properties of polyester film)
(1) Tear strength retention The polyester film of the present invention has a tear strength retention of 50% or more after 60 hours of thermostat at 120 ° C. and 100% relative humidity.
Conventionally, in a normal weather test, changes in tensile strength and elongation before and after thermo were evaluated. On the other hand, by the inventors' investigation, when approaching the form used in the solar cell, a polyester film is attached to a glass plate and a thermo test is performed, in a time earlier than the breaking elongation retention rate of the polyester film alone, It was found that the polyester film was cracked. Although not bound by any theory, polyester film is formed by stretching biaxially and laterally, so the molecules are aligned and strong in the direction along the film (breaking elongation is unlikely to decrease). ), And the interaction between molecules was weak (it was weak against the force to separate the molecules), and it was found that this was the cause of the crack. Then, when the present inventors examined the cause of a crack and the physical property of a polyester film, it turned out that tear strength becomes a parameter | index of the interaction between molecule | numerators and it is highly relevant by generation | occurrence | production of a crack. The tear strength is measured by the force when peeling between molecules. The higher the tear strength, the stronger the interaction between molecules (normally the weather resistance test evaluates changes in tensile strength and elongation before and after the thermo, Since the strength is pulled in the direction of the molecule, the behavior of the molecule breaking directly is observed, so that the measurement principle is fundamentally different from the tear strength test as in the present invention). Specifically, it has been found that the tear strength of the polyester film is less likely to generate cracks over time as the decrease after the endurance test is smaller. Therefore, the higher the ratio of the tear strength after the endurance test / before the endurance test (the tear strength retention rate), the more difficult it is to crack, and the polyester film of the present invention has a tear strength retention rate of 50% or more.
Here, the tear strength retention of the polyester film of the present invention is preferably 65% or more, more preferably 80% or more.
In addition, although the molecular weight of the polyester is reduced by the thermostat, the polyester film hardly affects the tensile direction (because the length of the molecule is slightly shortened), but the intermolecular interaction is extremely low ( (Inherently few interactions are likely to manifest due to a decrease in molecular weight). For this reason, cracks are likely to occur earlier than the elongation at break. In the present invention, it has been found that the tear strength should be used as a measure of the intermolecular interaction (force to peel off the molecule). Japanese Patent Laid-Open No. 2010-235824 mentions “breaking elongation retention” as an index of weather resistance, but this evaluation method is a tensile test, and the tear strength as in the present invention cannot be measured.

(2) Intrinsic viscosity IV
In the polyester film of the present invention, the intrinsic viscosity of the polyester film after film formation is preferably in the range of 0.6 to 0.9 dl / g. More preferably, it is 0.65-0.85 dl / g, More preferably, it is 0.7-0.82 dl / g.
When it is at least the lower limit of this range, the entanglement between the polyester molecules increases, the effect of using the sealant in combination as described above tends to be exhibited, and the tear strength tends to increase. On the other hand, if it is below the upper limit of this range, the initial (before thermo) tear strength will not be too high, and the tear strength retention will be difficult to decrease. Furthermore, the molecular weight is not too large, and even if the mobility of the polyester is lowered, it is not difficult to react with the end-capping agent, and this is preferable because the reduction of entanglement can be suppressed.

(3) Terminal carboxylic acid concentration AV
The terminal carboxylic acid concentration (AV) of the polyester film of the present invention is preferably 20 eq / ton or less, more preferably 2 eq / ton or more and 15 eq / ton or less, and further preferably 3 eq / ton or more and 10 eq / ton or less.
When the AV is above the lower limit of the above range, the terminal carboxylic acid in the polyester decreases, the bulk of the polyester molecule when it reacts with the end-capping agent decreases, and the thermal shrinkage increases to suppress crystal formation. Since it becomes difficult to do, it is preferable. On the other hand, when AV is not more than the upper limit of the preferred range of the present invention, it becomes easy to react with the end-capping agent, and as a result, the reactivity with the polyester molecule does not decrease, and the above-described entanglement effect is sufficiently obtained. It is preferable because it can suppress a decrease in tear strength.

(4) Thermal dimensional change amount The polyester film of the present invention has a thermal dimensional change amount of 0.1% or more and 2% or less, and averages the difference between the maximum value and the minimum value of the thermal dimensional change amount measured in all directions. The value divided by the value is preferably 5% or more and 40% or less.
When a thermostat is applied to a glass plate, the polyester film undergoes a thermal dimensional change (thermal contraction, thermal expansion) in the thermostat, and the polyester film is likely to crack due to the contraction stress. Polyester is usually biaxially stretched in the orthogonal direction, but if one stretch ratio is too large, the orthogonal direction may expand when that direction contracts.
The preferred thermal dimensional change rate of the polyester film of the present invention is 0.1% or more and 2% or less, more preferably 0.15% or more and 1.5% or less, and further preferably 0.2% or more and 1% or less. It is. The thermal dimensional change rate here refers to the average of the thermal dimensional change measured over the entire circumference every 30 ° from the MD direction. When the thermal dimensional change is not more than the upper limit of the range of the present invention, the stress generated on the glass plate is reduced and cracks are hardly generated, which is preferable. On the other hand, if it is at least the lower limit of the range of the present invention, cracks are less likely to occur, which is preferable. This is because the glass plate also expands in the thermostat, so that if the polyester film changes in size, a dimensional difference is less likely to occur between them, and stress is less likely to occur.

Furthermore, the polyester film of the present invention has a thermal dimensional change distribution (a value obtained by dividing the difference between the maximum value and the minimum value of the thermal dimensional change amount measured every 30 ° from the MD direction by the average value in percentage). % To 40%, more preferably 7% to 35%, and still more preferably 10% to 30%. By uniforming the dimensional change over the entire circumference in this way, stress can be dispersed and cracking can be suppressed (uneven thermal shrinkage is caused by shrinkage unevenness, resulting in local concentration of shrinkage stress. Occurs and cracks easily occur). On the other hand, even if the dimensional change is too uniform over the entire circumference (that is, less than the range of the present invention), cracks are likely to occur, which is not preferable. This is because a solar cell is used in a rectangular shape, and if the heat shrinkage is completely uniform, a stress distribution occurs on the contrary (if the solar cell is circular, the distribution of the thermal dimensional change is naturally zero. Is preferred).
When the high molecular weight sealant is bonded to the polyester molecule, the ordered arrangement of the polyester is reduced, so that the crystallinity is lowered and the thermal dimensional change is increased. Low molecular weight sealants reduce the Tg of polyester and increase thermal shrinkage. On the other hand, in this invention, it discovered that a thermal dimensional change amount (heat shrinkage) reduced by mixing a high molecular weight and low molecular weight sealing agent. Although not bound by any theory, it is presumed to be due to the following mechanism. The high molecular weight sealant at the end inhibits the polyester molecules to be aligned and crystallized by stretching. The low molecular weight sealant has a high affinity with a high molecular weight sealant having a similar chemical structure and gathers around the low molecular weight sealant, and the low molecular weight sealant acts as a plasticizer to promote the arrangement of the high molecular weight sealant. As a result, the orientation crystallization of the polyester does not decrease and an increase in heat shrinkage is suppressed. That is, in the polyester film of the present invention, the high molecular weight sealant is preferably the same type as that of the low molecular weight sealant so that higher affinity is expressed.

(5) Endothermic peak The polyester film preferably has an endothermic peak of 0.04 to 1.26 J / g in the range of 80 ° C to 150 ° C. The endothermic peak is more preferably 0.08 to 0.84 J / g, and still more preferably 0.12 to 0.42 J / g.
This endothermic peak reflects the free volume (gap) between the polyester molecules. When DSC measurement is performed while raising the temperature of the polyester, the volume rapidly expands at Tg. However, if the free volume is small, a large energy is required to expand the volume, and an endothermic peak is generated. That is, the endothermic peak increases as the free volume decreases.
The tear strength can be improved by reducing the free volume. This is because polyester molecules are brought close to each other and entanglement (interaction) is improved. Accordingly, if it is less than the present invention, the tear strength is lowered, which is not preferable. When the amount is not more than the upper limit of the above range, the free volume is not too narrow, and polyester molecules slip (slip through) easily occur during the tear test, the molecules are difficult to cut, and the tear strength of the polyester film is reduced. It is suppressed. Such suppression of the reduction in tear strength is likely to be manifested when the molecular weight is reduced by a thermostat, and the tear strength retention rate is unlikely to decrease.

(6) Crystallization parameter Tcg
The polyester film of the present invention preferably has a crystallization parameter Tcg of less than 70 ° C. and 30 ° C. or more. Tcg represents the difference between the crystallization temperature Tc and the glass transition temperature Tg. A smaller value indicates a higher crystallization speed (easy to crystallize). The Tcg is more preferably 65 ° C. or less and 32 ° C. or more, and further preferably 60 ° C. or more and 35 ° C. or more.
In the polyester film of the present invention, the above range (easily crystallized) is preferable in order to promote crystallization and reduce thermal shrinkage. Crystallinity does not fall too much that it is more than the lower limit of the said range, and heat shrink can be made into a preferable range. On the other hand, it is preferable that it is not more than the upper limit value of the above range, since the crystallinity does not increase excessively, it becomes difficult to become brittle, and it is easy to suppress a decrease in tear strength.

(Polyester resin)
The polyester film of the present invention contains a polyester resin.
The polyester resin may be obtained by synthesis and polymerization, or may be obtained commercially.
The polyester resin can be produced according to a conventionally known polyester production method. That is, it is produced by using a dialkyl ester as an acid component, transesterifying it with a diol component, and then heating the product of this reaction under reduced pressure to perform polycondensation while removing excess diol component. can do. Moreover, it can also manufacture by a conventionally well-known direct polymerization method, using dicarboxylic acid as an acid component. As the reaction catalyst, conventionally known titanium compounds, lithium compounds, calcium compounds, magnesium compounds, antimony compounds, germanium compounds and the like can be used. The polyester thus obtained can be further increased in the degree of polymerization by subjecting it to solid phase polymerization, and the carboxyl end group concentration can be reduced. The solid phase polymerization is preferably performed in a dryer at a temperature of 200 ° C. to 250 ° C. under a reduced pressure of 1 torr or less or under a nitrogen stream for 5 to 50 hours.

In the method for producing master pellets of the present invention, the polyester film IV using the master pellets is slightly reduced in IV, and in order to make the intrinsic viscosity IV equal to or more than the above preferred range, the extrusion in the melt film formation is biaxial. Use a kneader. Moreover, it is preferable to perform a solid phase polymerization process in ethylene glycol atmosphere.
Moreover, it is preferable that AV of the polyester film using this master pellet shall be below the said preferable range.

Such an IV value can be adjusted by adjusting the polymerization time during liquid phase polymerization and / or by solid phase polymerization.
Adjustment to AV as described above can be performed by increasing the degree of vacuum during polymerization and suppressing oxidation due to residual oxygen. It is also preferable to perform solid phase polymerization.

  It is preferable that the manufacturing method of the master pellet of this invention includes the esterification process which performs the esterification reaction and / or transesterification reaction for obtaining the polyester film whose intrinsic viscosity IV is the said preferable range using this master pellet.

-Esterification process-
In this invention, the esterification process which provides an esterification reaction and a polycondensation reaction and produces | generates polyester can be provided. In this esterification step, (a) an esterification reaction and (b) a polycondensation reaction in which an esterification reaction product produced by the esterification reaction is subjected to a polycondensation reaction can be provided.

(A) Esterification reaction The polyester that forms the polyester film of the present invention includes (A) malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, Aliphatic dicarboxylic acids such as pimelic acid, azelaic acid, methylmalonic acid and ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid Acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4 ′ -Diphenyl ether dicarboxylic acid, 5- A dicarboxylic acid such as thorium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, aromatic dicarboxylic acid such as 9,9′-bis (4-carboxyphenyl) fluorenic acid, or an ester derivative thereof; Aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, cyclohexanedimethanol, spiroglycol , Cycloaliphatic diols such as isosorbide, aromatic diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9′-bis (4-hydroxyphenyl) fluorene, and the like The diol compound It can be obtained by an esterification reaction and / or a transesterification reaction.

It is preferable that at least one aromatic dicarboxylic acid is used as the dicarboxylic acid component. More preferably, the dicarboxylic acid component contains an aromatic dicarboxylic acid as a main component. The “main component” means that the proportion of aromatic dicarboxylic acid in the dicarboxylic acid component is 80% by mass or more. A dicarboxylic acid component other than the aromatic dicarboxylic acid may be included. Examples of such a dicarboxylic acid component include ester derivatives such as aromatic dicarboxylic acids.
Further, it is preferable that at least one aliphatic diol is used as the diol component. The aliphatic diol can contain ethylene glycol, and preferably contains ethylene glycol as a main component. The main component means that the proportion of ethylene glycol in the diol component is 80% by mass or more.

  The amount of the aliphatic diol (for example, ethylene glycol) used is in the range of 1.015 to 1.50 mol with respect to 1 mol of the aromatic dicarboxylic acid (for example, terephthalic acid) and, if necessary, its ester derivative. Is preferred. The amount used is more preferably in the range of 1.02 to 1.30 mol, and still more preferably in the range of 1.025 to 1.10 mol. If the amount used is in the range of 1.015 or more, the esterification reaction proceeds favorably, and if it is in the range of 1.50 mol or less, for example, by-production of diethylene glycol due to dimerization of ethylene glycol is suppressed, Many characteristics such as melting point, glass transition temperature, crystallinity, heat resistance, hydrolysis resistance, and weather resistance can be kept good.

  In the polyester resin, the proportion of the aromatic dicarboxylic acid constituent component in all the dicarboxylic acid constituent components in the ester is preferably 90 mol% or more and 100 mol% or less. More preferably, it is 95 mol% or more and 100 mol%. More preferably, it is 98 mol% or more and 100 mol% or less, particularly preferably 99 mol% or more and 100 mol% or less, and most preferably 100 mol%, that is, all of the dicarboxylic acid components should be aromatic carboxylic acid components. If it is less than 90 mol%, the heat and moisture resistance and heat resistance may decrease. In the polyester film of the present invention, when the ratio of the aromatic dicarboxylic acid constituent component in all the dicarboxylic acid constituent components in the polyester resin is 90 mol% or more and 100 mol% or less, both heat and moisture resistance and heat resistance can be achieved. It becomes possible.

  The main repeating unit mainly composed of a dicarboxylic acid component and a diol component in the polyester resin is ethylene terephthalate, ethylene-2,6-naphthalenedicarboxylate, propylene terephthalate, butylene terephthalate, 1,4-cyclohexyl. Those composed of range methylene terephthalate, ethylene-2,6-naphthalenedicarboxylate, and mixtures thereof are preferably used. The main repeating unit referred to here is such that the total of the above repeating units is 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more of all repeating units contained in the polyester.

  Furthermore, it is preferable that ethylene terephthalate, ethylene-2,6-naphthalenedicarboxylate, and a mixture thereof are main constituents in that they can be easily polymerized at low cost and have excellent heat resistance. . In this case, when more ethylene terephthalate is used as a structural unit, a cheap and versatile film having heat and heat resistance can be obtained, and more ethylene-2,6-naphthalenedicarboxylate is used as a structural unit. When used, the film can be made more excellent in heat and moisture resistance.

  As other copolymerization components, various dicarboxylic acids or ester-forming derivatives thereof and diols may be copolymerized. Examples of the copolymerizable dicarboxylic acid component include isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenylsulfone dicarboxylic acid and the like can be mentioned. Examples of the alicyclic dicarboxylic acid component that can be copolymerized include 1,4-cyclohexanedicarboxylic acid. Examples of the diol component include ethylene glycol, 1,2-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4′-β-hydroxyethoxyphenyl) propane, etc. And aliphatic, alicyclic, and aromatic diols. These components may be used alone or in combination of two or more.

  The melting point of the polyester resin preferably used is preferably 250 ° C. or higher in view of heat resistance, and preferably 300 ° C. or lower in terms of productivity. If it is in this range, other components may be copolymerized or blended.

  In addition, various known additives such as an antioxidant, an antistatic agent, a crystal nucleating agent, inorganic particles, and organic particles may be added to the polyester resin. In particular, inorganic particles and organic particles are effective for imparting easy lubricity to the film surface and enhancing the handleability of the film.

  The polyester can be produced according to a conventionally known polyester production method. That is, it is produced by using a dialkyl ester as an acid component, transesterifying it with a diol component, and then heating the product of this reaction under reduced pressure to perform polycondensation while removing excess diol component. can do. Moreover, it can also manufacture by a conventionally well-known direct polymerization method, using dicarboxylic acid as an acid component.

  The PET may have different properties depending on the catalyst described later, and one or more selected from a germanium (Ge) catalyst, an antimony (Sb) catalyst, an aluminum (Al) catalyst, and a titanium (Ti) catalyst. PET that is polymerized using two or more types is preferred, and more preferably, a Ti-based catalyst is used.

  Conventionally known reaction catalysts can be used for the esterification reaction and / or the transesterification reaction. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Usually, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at an arbitrary stage before the polyester production method is completed. As such a method, for example, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is or by dissolving it in ethylene glycol or the like.

It is preferable that the manufacturing method of the polyester film of this invention includes the process of preparing the said polyester resin used for melt film forming by the polycondensation reaction using a Ti-type catalyst.
A polyester film containing a polyester resin polycondensed using the Ti-based catalyst is preferable because weather resistance is hardly lowered. Although not bound by any theory, it is presumed that the reason is as follows. The decrease in weather resistance of the weather resistant polyester film depends to some extent on the hydrolysis of the polyester. The polymerization reaction catalyst also promotes a hydrolysis reaction that is a reverse reaction of condensation, while a Ti catalyst has a low effect of the hydrolysis reaction that is a reverse reaction. Therefore, even if the polymerization reaction catalyst remains in the polyester film after film formation to some extent, the polyester resin polycondensed using the Ti-based catalyst is more than the polyester resin polycondensed using another catalyst. Also, the weather resistance can be made relatively high.

  The Ti-based catalyst has a high reaction activity and can lower the polymerization temperature. Therefore, in particular, the thermal decomposition of PET during the polymerization reaction can be suppressed and the generation of COOH can be suppressed. In the polyester film of the present invention, the AV (terminal COOH amount) is adjusted to the above preferable range. Also suitable.

For the synthesis of Ti-based polyester using such a Ti compound, for example, Japanese Patent Publication No. 8-30119, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 397756, and Japanese Patent No. 396226 are disclosed. Japanese Patent No. 3997866, Japanese Patent No. 3996687, Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269538, Japanese Patent No. The methods described in JP 2005-340616 A, JP 2005-239940 A, JP 2004-319444 A, JP 2007-204538 A, Japanese Patent No. 3436268, Japanese Patent No. 3780137, and the like can be applied.
As a result, coloring during polymerization and subsequent coloring during melt film formation are reduced, and yellowishness is reduced compared to conventional antimony (Sb) catalyst-based polyester resins, and germanium catalysts having a relatively high transparency are also obtained. It is possible to provide a polyester resin having a color tone and transparency comparable to a polyester resin and having excellent heat resistance. Further, a polyester resin having high transparency and less yellowness can be obtained without using a color tone adjusting material such as a cobalt compound or a pigment.

  This polyester resin can be used for applications requiring high transparency (for example, optical film, industrial squirrel, etc.), and it is not necessary to use an expensive germanium-based catalyst, so that the cost can be greatly reduced. In addition, since foreign matters caused by the catalyst that are likely to occur in the Sb catalyst system are also avoided, the occurrence of failures and quality defects in the film forming process can be reduced, and the cost can be reduced by improving the yield.

  The polyester thus obtained can be further increased in the degree of polymerization by subjecting it to solid phase polymerization, and the carboxyl end group concentration can be reduced. The solid phase polymerization is preferably performed in a dryer at a temperature of 200 ° C. to 250 ° C. under a reduced pressure of 1 torr or less or under a nitrogen stream for 5 to 50 hours. That is, the polyester pellets are 180 ° C. or higher and 250 ° C. or lower, more preferably 190 ° C. or higher and 235 ° C. or lower, more preferably 195 ° C. or higher and 225 ° C. or lower, 5 hours or longer and 45 hours or shorter, more preferably 10 hours or longer and 40 hours or shorter. It is preferable to prepare a polyester resin that satisfies IV and AV in the above preferred ranges by heat treatment in a nitrogen stream or in vacuum, preferably 14 hours to 35 hours, more preferably 18 hours to 30 hours. These may be performed at a constant temperature or may be performed while fluctuating.

  The molecular weight and molecular weight distribution of the polyester resin are not particularly limited as long as they can be substantially processed, but the weight average molecular weight is usually 10,000 or more, preferably 40,000 or more, and further 80,000. The above is desirable. The weight average molecular weight here refers to the molecular weight in terms of polymethyl methacrylate (PMMA) measured by gel permeation chromatography.

(End sealant)
The polyester film of this invention contains 2 or more types of terminal blockers from which a number average molecular weight differs 4000 or more.

The end-capping agent is an additive that reacts with the terminal carboxyl group of the polyester resin to reduce the amount of terminal carboxyl group of the polyester resin.
Examples of the terminal blocking agent include carbodiimide compounds, oxazoline compounds, epoxy compounds, carbonate compounds, and the like. The polyester film of the present invention preferably contains at least one terminal blocker among an isocyanate compound, a carbodiimide compound and an epoxy compound, and preferably contains two types of carbodiimide compounds. “End-capping agents” may be used alone or in combination.
Conventionally, when a terminal sealing agent is added as in JP 2010-235824 A, when a bulky sealing agent molecule is attached to the terminal of a polyester molecule, a gap between adjacent polyester molecules is widened, and intermolecular interaction is further increased. Tends to decrease, and the tear strength tends to decrease. On the other hand, the addition of sealants having a number average molecular weight of 4,000 or more as in the polyester film of the present invention has an effect of preventing a decrease in interaction between molecules and suppressing generation of cracks.
The difference in the number average molecular weight between the high molecular weight type end capping agent (hereinafter also referred to as high molecular weight capping agent) and the low molecular weight type end capping agent (hereinafter also referred to as low molecular weight capping agent) of the end capping agent is as follows: It is 4000 or more, More preferably, it is 6000 or more, More preferably, it is 10,000 or more. When it is at least the lower limit of this range, the difference between the low molecular weight type and the high molecular weight type becomes clear, and the above effects are easily obtained.

  The number average molecular weight of the high molecular weight sealant is preferably 10,000 or more and 50,000 or less, more preferably 13,000 or more and 40,000 or less, and further preferably 15,000 or more and 30,000 or less. When the molecular weight of the end-capping agent is large (long), it is entangled with other polyester molecules, and there is an effect of improving the intermolecular interaction. In order to exhibit such an effect, a high number average molecular weight of 10,000 or more is preferable. However, when the molecular weight is large, the mobility is low, and the reactivity (sealing ability) with the polyester terminal tends to decrease. If it is below the upper limit of the molecular weight, the mobility (reactivity) of this sealant is unlikely to decrease, and it is easy to react (seal) with the polyester terminal. On the other hand, if it is more than the lower limit value of the molecular weight range, an entanglement effect is exhibited, and the tear strength of the resulting polyester film can be improved.

  The number average molecular weight of the low molecular weight sealant is preferably 1000 or more and 6000 or less, more preferably 1500 or more and 5500 or less, and further preferably 2000 or more and 5000 or less. The sealing agent having a large molecular weight has low end-capping ability and is difficult to seal the polyester end sufficiently. On the other hand, a sealing agent having a small molecular weight has high reactivity and high sealing ability, but does not exhibit the above-described entanglement effect. Therefore, by using a low molecular weight sealant and a high molecular weight sealant in combination, good tear strength can be achieved even after thermostatting. If the molecular weight of the low molecular weight sealant is not more than the upper limit of the above range, the reactivity does not decrease, it is difficult to decrease the molecular weight with a thermo, and the bulk is decreased to increase intermolecular interaction, Tear strength is easy to improve. On the other hand, when the molecular weight falls below the lower limit of the molecular weight range, it is difficult to volatilize during melt film formation, the sealing ability is improved, the molecular weight is hardly lowered by thermo, and the tear strength of the resulting polyester film is likely to be lowered.

  In the present invention, both the high molecular weight sealant and the low molecular weight in the above range may be contained, and besides these, sealants other than the present invention (for example, the molecular weight is less than 1000, more than 6000 and less than 10,000 and less than 50,000). It may be more than that). In addition, each of the low molecular weight sealant and the high molecular weight sealant may be one kind or plural kinds.

In the polyester film of the present invention, the terminal blocking agent is any one of a carbodiimide compound, an oxazoline compound, an epoxy compound, and a carbonate compound, and the molecular weight of the low molecular weight sealing agent among the two types of terminal blocking agents is 1000. It is preferable that the molecular weight of the high molecular weight sealant is 10,000 to 50,000.
In addition, it can detect that a polyester film contains a low molecular weight sealing agent and a high molecular weight sealing material as said terminal blocker by gel permeation chromatography (GPC).
In addition, when a low molecular weight sealing agent and a high molecular weight sealing material having a similar structure are included as the terminal sealing agent, the polyester film has a low molecular weight sealing agent and a high molecular weight sealing material. The presence of a species can also be detected based on the presence of two molecular weight peaks. When the end capping agent is synthesized by a general method, the single end capping agent usually has one molecular weight peak.

  The total addition amount of the high molecular weight sealing agent and the low molecular weight sealing agent (the total of the high molecular weight sealing agent and the low molecular weight sealing agent) is preferably 0.1% by mass or more and 5% by mass or less with respect to the polyester resin. More preferably, they are 0.2 mass% or more and 3 mass% or less, More preferably, they are 0.3 mass% or more and 2 mass% or less. If it is more than the lower limit of this range, the effect of sealing a carboxyl group is sufficient, and the entanglement effect by the said sealing agent is easy to express. On the other hand, if it is below the upper limit of this range, a sealing agent works as a plasticizer, and it is preferable, without reducing tear strength and strength retention. Furthermore, it can also suppress that excess sealing agent acts as a plasticizer between polyester molecules, and falls tear strength.

  In the polyester film of the present invention, the mixing ratio of the two kinds of end-capping agents is preferably 1/9 to 9/1 (mass ratio) as a value of low molecular weight sealing agent / high molecular weight sealing agent. . The mixing ratio of the low molecular weight sealant and the high molecular weight sealant (weight ratio of low molecular weight sealant / high molecular weight sealant) is more preferably 2/8 to 8/2, still more preferably 3/7 to 7/3. Even if it falls below or exceeds this range, the effect of the mixing is hardly exhibited.

  The polyester film of the present invention is preferable because the Tcg can be controlled within a preferable range by using a low molecular weight sealant and a high molecular weight sealant in the above preferable range. The sealing agent bonded to the end of the polyester is bulky, widens the space between the polyester molecules, and the low-molecular unanti-sealing agent acts like a lubricant (plasticizer) in this gap. Promote

[Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄は、それぞれ独立に、炭素数１〜７のアルキル基あるいは水素原子を表す。ｎは繰返し単位数を示す。] Examples of the terminal blocking agent include carbodiimide compounds, oxazoline compounds, epoxy compounds, carbonate compounds, and the like. When added together with the polyester resin during film formation, the effect is higher. A carbodiimide compound is preferably used. Of course, solid phase polymerization and a terminal blocking agent may be used simultaneously. The sealing agent is preferably any one of a carbodiimide compound, an oxazoline compound, an epoxy compound and a carbonate compound, more preferably a carbodiimide compound, and still more preferably a carbodiimide compound having the following structure. This is because carbodiimide has high reactivity and efficiently reacts with the polyester terminal.

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]

The polyester film of the present invention preferably uses two or more types of polycarbodiimide-based end capping agents.
Polycarbodiimide is a compound having a structure (carbodiimide group) represented by (—N═C═N—). For example, an organic isocyanate is heated in the presence of an appropriate catalyst to perform a decarboxylation reaction. Can be manufactured. In the synthesis step in the present invention, a first polycarbodiimide having a number average molecular weight of 1000 to 4000 and a second polycarbodiimide having a number average molecular weight of 18000 or more are used. The number average molecular weight of polycarbodiimide is obtained by dissolving polycarbodiimide powder in a solvent selected from chloroform, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP) and hexafluoroisopropanol (HFIP), and using GPC By measuring the curve of the distribution curve, the number average molecular weight obtained from the polystyrene standard can be used.

  The polycarbodiimide can be selected from compounds obtained by polymerizing aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates and mixtures thereof. Specific examples of the polycarbodiimide include poly (1,6-hexamethylenecarbodiimide), poly (4,4′-methylenebiscyclohexylcarbodiimide), poly (1,3-cyclohexylenecarbodiimide), poly (1,4-cycloheximide). Silenecarbodiimide), poly (4,4′-dicyclohexylmethanecarbodiimide), poly (4,4′-diphenylmethanecarbodiimide), poly (3,3′-dimethyl-4,4′-diphenylmethanecarbodiimide), poly (naphthylenecarbodiimide) ), Poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (tolylcarbodiimide), poly (diisopropylcarbodiimide), poly (methyl-diisopropylphenylenecarbodiimide), poly (1,3,5- Polycarbodiimides such as (riisopropylbenzene) polycarbodiimide, poly (1,3,5-triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide, poly (triethylphenylenecarbodiimide), poly (triisopropylphenylenecarbodiimide), etc. be able to. Further, as a commercial product, “STABAXOL” manufactured by Rhein Chemie Japan Co., Ltd. can be used. Specifically, examples of the first polycarbodiimide include stabuxol P (molecular weight 3000 to 4000, manufactured by Rhein Chemie Japan), LA-1 (molecular weight about 2000, manufactured by Nisshinbo Chemical Co., Ltd.). Examples of the second polycarbodiimide include stavaxol P400 (molecular weight: about 20000, manufactured by Rhein Chemie Japan) and STABILIZER9000 (molecular weight: about 20000, manufactured by Rhein Chemie).

  The polycarbodiimide is preferably a compound obtained by polymerizing aromatic diisocyanate, and is preferably a polycarbodiimide having a unit structure represented by the following general formula (1).

[Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄は、それぞれ独立に、炭素数１〜７のアルキル基あるいは水素原子を表す。ｎは繰返し単位数を示す。]

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]

  Examples of the polycarbodiimide having a unit structure represented by the general formula (1) obtained by polymerizing aromatic diisocyanate include poly (1,3,5-triisopropylphenylene-2,4-carbodiimide), poly (1 , 5-diisopropylphenylene-2,4-carbodiimide) and copolymers thereof can be preferably used.

  The first polycarbodiimide and the second polycarbodiimide include diisocyanate (for example, 2,4,6-triisopropylphenyl 1,3-diisocyanate) and phospholene oxide (for example, 3-methyl-1-phenyl-2- Phosphorene oxide) can be synthesized by heating. The number average molecular weight of polycarbodiimide can be controlled by selecting the amount of each material added and the reaction time.

  Preferred examples of the epoxy compound include glycidyl ester compounds and glycidyl ether compounds.

  Specific examples of the glycidyl ester compound include benzoic acid glycidyl ester, t-Bu-benzoic acid glycidyl ester, P-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, and lauric acid glycidyl ester. , Glycidyl palmitate, glycidyl behenate, glycidyl versatate, glycidyl oleate, glycidyl linoleate, glycidyl linolein, glycidyl behenol, glycidyl stearol, diglycidyl terephthalate, isophthalic acid Diglycidyl ester, phthalic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester Ter, methylterephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecane Examples thereof include diglycidyl diacid, octadecanedicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester. These may be used alone or in combination of two or more.

  Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (β, γ-epoxypropoxy) butane, 1,6-bis (β, γ- Epoxypropoxy) hexane, 1,4-bis (β, γ-epoxypropoxy) benzene, 1- (β, γ-epoxypropoxy) -2-ethoxyethane, 1- (β, γ-epoxypropoxy) -2-benzyl Oxyethane, 2,2-bis- [р- (β, γ-epoxypropoxy) phenyl] propane and 2,2-bis- (4-hydroxyphenyl) propane and 2,2-bis- (4-hydroxyphenyl) Examples thereof include bisglycidyl polyether obtained by reaction of bisphenol such as methane and epichlorohydrin, and these use one kind or two or more kinds. Door can be.

  The oxazoline compound is preferably a bisoxazoline compound, specifically 2,2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline), 2,2 ′. -Bis (4,4-dimethyl-2-oxazoline), 2,2'-bis (4-ethyl-2-oxazoline), 2,2'-bis (4,4'-diethyl-2-oxazoline), 2 , 2′-bis (4-propyl-2-oxazoline), 2,2′-bis (4-butyl-2-oxazoline), 2,2′-bis (4-hexyl-2-oxazoline), 2,2 '-Bis (4-phenyl-2-oxazoline), 2,2'-bis (4-cyclohexyl-2-oxazoline), 2,2'-bis (4-benzyl-2-oxazoline), 2,2'- p-Phenylenebis (2-oxa Phosphorus), 2,2'-m-phenylenebis (2-oxazoline), 2,2'-o-phenylenebis (2-oxazoline), 2,2'-p-phenylenebis (4-methyl-2-oxazoline) ), 2,2′-p-phenylenebis (4,4-dimethyl-2-oxazoline), 2,2′-m-phenylenebis (4-methyl-2-oxazoline), 2,2′-m-phenylene Bis (4,4-dimethyl-2-oxazoline), 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2 -Oxazoline), 2,2'-octamethylenebis (2-oxazoline), 2,2'-decamethylenebis (2-oxazoline), 2,2'-ethylenebis (4-methyl-2-oxazoline) 2,2′-tetramethylenebis (4,4-dimethyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis (2-oxazoline), 2,2′-cyclohexylenebis (2 -Oxazoline) and 2,2'-diphenylenebis (2-oxazoline) and the like. Among these, 2,2'-bis (2-oxazoline) is most preferably used from the viewpoint of reactivity with polyester. Furthermore, as long as the objective of this invention is achieved, the bisoxazoline compound mentioned above may be used individually by 1 type, or may use 2 or more types together.

(Additive for sealant / stabilizer: phosphorus compound)
In the present invention, in addition to the above end-capping agent, it is also preferable to add a compound that suppresses hydrolysis decomposition in the film. In particular, it is preferable to contain a phosphorus compound. Therefore, in this invention, it is preferable that the phosphorus atom weight in the polyester film at the time of measuring with a fluorescent X ray is 200 ppm or more. More preferably, it is 300 ppm or more, More preferably, it is 400 ppm or more. As the phosphorus compound, it is preferable to use one or more phosphorus compounds selected from the group consisting of phosphoric acid, phosphorous acid, phosphonic acid, methyl esters, ethyl esters, phenyl esters, half esters and other derivatives thereof. In the present invention, phosphoric acid, phosphorous acid, phosphonic acid methyl ester, ethyl ester, and phenyl ester are particularly preferable. Moreover, as a method of containing the phosphorus compound, it is preferable to add the phosphorus compound when manufacturing the polyester raw material chip.
If the phosphorus atom is less than the above range, the hydrolysis inhibiting effect is not exhibited, the molecular weight of the polyester film after thermostating tends to decrease, and the tear strength retention rate decreases accordingly, which is not preferable. On the other hand, if the above range is exceeded, phosphoric acid is generated by the decomposition of the phosphorus compound itself, and the resulting H ⁺ promotes the hydrolysis of the polyester, which tends to lower the molecular weight of the polyester film, resulting in a decrease in tear strength retention. It is not preferable.

(Other additives)
When the polyester film of the present invention is used as a back sheet of a solar cell, it is preferable that the polyester film is not easily affected by deterioration due to sunlight. Therefore, a UV (ultraviolet) absorber or a material that reflects UV may be added to the film. Moreover, it is also one of the preferable aspects that the average reflectance of wavelength 400-700nm in the at least one film surface shall be 80% or more. More preferably, it is 85% or more, and particularly preferably 90% or more. By setting the average reflectance at a wavelength of 400 to 700 nm to 80% or more, the deterioration of the film is reduced even when the solar cell using the film of the present invention is used in direct sunlight.

[Production method of polyester film]
The method for producing a polyester film of the present invention includes a step of melt-kneading a polyester resin, polyester fine particles having a melting temperature of 1 ° C. or more and 35 ° C. or less, an end-capping agent having a number average molecular weight of 4000 or more, It includes a step of forming an article into a film, a step of stretching the film in two directions, and a step of heat setting.

(Melting and kneading process)
In the method for producing a polyester film of the present invention, a high molecular weight and low molecular weight sealant are mixed and used as described above. At this time, it is preferable to uniformly mix the high molecular weight sealant and the low molecular weight sealant. Uniform dispersion can be achieved by adding polyester fine particles having different melting temperatures of 1 ° C. or more and 35 ° C. or less, and melt-kneading the polyester and the end-capping agent.
Without being bound by any theory, the polyester fine particles reduce the friction between the pellets of the extruder used for melt kneading and promote smooth kneading. Also, if there is a distribution in the melting temperature of the polyester fine particles, a friction reducing effect is exhibited in a wider range in the barrel (melting at the barrel inlet only in the low temperature body, not acting at the rear of the barrel, but acting at the rear of the barrel only with the high temperature body Only melts at the inlet and does not work at the entrance).
Since the high molecular weight sealant melts on the high temperature side and the low molecular weight sealant melts on the low temperature side, in order to melt all of them smoothly, it is preferable to add polyester fine particles having different melting temperatures. The difference in melting temperature of the polyester fine particles is 1 ° C. or more and 35 ° C. or less, preferably 3 ° C. or more and 30 ° C. or less, more preferably 5 ° C. or more and 25 ° C. or less.

  Polyester fine particles having different melting temperatures can be produced by changing the crystal size, and can be achieved, for example, by performing heat treatment at 150 to 220 ° C. for 1 hour to 50 hours. The higher the heat treatment temperature, the crystal grows, the crystal size increases, and the melting temperature increases. A preferable melting temperature is 230 ° C. to 275 ° C., more preferably 235 ° C. to 270 ° C., and further preferably 240 ° C. to 265 ° C. A preferable melting temperature difference is 1 ° C. or more and 45 ° C. or less, more preferably 3 ° C. or more and 35 ° C. or less, and further preferably 5 ° C. or more and 25 ° C. or less. The melting temperature is obtained by arbitrarily sampling 20 polyester fine particles, placing the sample on a hot stage, measuring the temperature at which the polyester starts melting, and determining the reconsideration temperature and the minimum temperature. If the difference in melting temperature is less than this range, the effect of promoting the mixing is not manifested, and if this range is exceeded, unmelted particles remain, which becomes a stress concentration point and the tear strength tends to decrease (especially the molecular weight of the thermostat). It manifests when it falls).

  The size of the polyester fine particles is 10 μm or more and 1 mm or less, more preferably 30 μm or more and 500 μm or less, and still more preferably 60 μm or more and 300 μm or less.

  A preferable addition amount of the polyester fine particles is 0.01% or more and 5% or less, more preferably 0.1% or more and 3% or less, and further preferably 0.3% or more and 1.5% or less. Below this range, the effect of promoting mixing is not manifested, and the tear strength retention rate tends to decrease. On the other hand, if it exceeds this range, unmelted particles remain and become stress concentration points, and the tear strength tends to decrease (particularly when the molecular weight decreases due to thermo).

(Film formation / extrusion)
The polyester film of the present invention is produced, for example, as follows. First, a raw fabric (unstretched) polyester sheet constituting the polyester film is produced. In order to produce a raw polyester sheet, for example, the polyester pellets, polyester fine particles, and end sealant prepared as described above are melted using an extruder, discharged from a die, and then solidified by cooling. To form.

  In addition, inorganic and organic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet silica, dry type are used to impart easy slipping, abrasion resistance and scratch resistance to the surface of the polyester film. Inorganic particles such as silica, colloidal silica, calcium phosphate, barium sulfate, alumina and zirconia, organic particles containing acrylic acids, styrene resins, thermosetting resins, silicones and imide compounds, and polyester polymerization reaction It is also a preferred embodiment to add particles (so-called internal particles) that are precipitated by the catalyst or the like.

  Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, thermal stabilizers, lubricants, antistatic agents, whitening agents, coloring, as long as the effects of the present invention are not impaired. Agents, conductive agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments and dyes may be added.

  When these additives and terminal blocker are included in the polyester, a vent type twin-screw kneading extruder in which the terminal blocker is directly mixed with PET pellets and heated to a temperature of 270 to 300 ° C. is used. Thus, a method of kneading into PET to form a high-concentration master pellet is effective. A master pellet is a pellet in which an additive (sealant) is dispersed at a high concentration (3 to 10 times the concentration in a film after film formation), and when this is extruded, the sealant is used. Dilute with pellets without addition. When manufacturing the master pellet, the temperature at which only the terminal sealing agent having the lowest melting point is melted in stages from the supply port of the extruder based on the difference in melting point of the terminal sealing agent. A method of gradually increasing the temperature of each barrel in the order of the temperature at which the high end-capping agent is melted and the temperature at which only the polyester resin is melted is also effective from the viewpoint of suppressing the stability and coloring.

Next, after the pellets of the obtained polyester resin composition are dried under reduced pressure for 3 hours or more at a temperature of 180 ° C., a temperature of 265 to 300 ° C. is preferable in a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease. Is supplied to an extruder heated to a temperature of 270 to 285 ° C., extruded from a slit-shaped die, and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramic, sand and wire mesh, in order to remove foreign substances and altered polymers. A preferable pore diameter is 1 μm or more and 100 μm or less, more preferably 5 μm or more and 80 μm or less, and further preferably 10 μm or more and 70 μm or less. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property.
When laminating films, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merging blocks.

(Molding the melt into a film)
The melt (melt) extruded from the extruder in this way is solidified on a casting (cooling) roll to obtain an original fabric (unstretched film). The temperature of the cooling roll is preferably 10 ° C. or more and 60 ° C. or less, more preferably 15 ° C. or more and 55 ° C. or less, and further preferably 20 ° C. or more and 50 ° C. or less. At this time, in order to improve the adhesion between the melt and the cooling roll, an electrostatic application method, an air knife method, a method of forming a water film on the cooling roll, or the like can be preferably used.
Furthermore, in the present invention, when extruding the melt into a cast roll, the linear velocity of the cast roll is preferably 10 m / min or more, more preferably 15 / min to 50 m / min, and even more preferably 18 m / min or more. 40 m / min or less. If it is more than the lower limit of this range, the residence time of resin in an extruder becomes long, and it is preferable that a sealing agent does not thermally decompose easily. On the other hand, if it is below the upper limit of the above range, the shear rate in the extruder is decreased, thereby reducing heat generation and making the sealant difficult to thermally decompose, which is preferable.

(Longitudinal stretching)
Subsequently, the sheet-like material (original fabric) obtained as described above is heat-treated after being stretched biaxially in the longitudinal direction and the width direction. As the stretching method, a sequential biaxial stretching method such as stretching in the width direction after stretching in the longitudinal direction, a simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched using a simultaneous biaxial tenter, etc. A method combining a sequential biaxial stretching method and a simultaneous biaxial stretching method is included.

  Here, an unstretched film is stretched in the film transport direction (hereinafter also referred to as the longitudinal direction and the longitudinal direction) using a circumferential speed difference of the rolls using a longitudinal stretching machine in which several rolls are arranged ( A biaxial stretching method in which MD stretching and longitudinal stretching are performed, followed by stretching in a direction orthogonal to the film conveyance direction (hereinafter also referred to as a transverse direction and a width direction) by a tenter (TD stretching and transverse stretching) will be described.

First, it is preferable to MD-stretch an unstretched film. Further, it is preferable to sufficiently preheat the original fabric before MD stretching. The preheating temperature is preferably 40 ° C. or higher and 90 ° C. or lower, more preferably 50 ° C. or higher and 85 ° C. or lower, and further preferably 60 ° C. or higher and 80 ° C. or lower. Such preheating is performed by passing the raw material on a heating (temperature control) roll. A preferable preheating time is 1 second to 120 seconds, more preferably 5 seconds to 60 seconds, and further preferably 10 seconds to 40 seconds. It is as follows.
MD stretching may be performed in one stage or in multiple stages. When performed in one stage, the glass transition temperature is Tg to Tg + 15 ° C. (more preferably Tg + 10 ° C.), and the preferred draw ratio is 3.0 to 5.0 times, more preferably 3.3 to 4. 5 times, more preferably 3.5 to 4.2 times. It is preferable to cool with a cooling roll group having a temperature of 20 to 50 ° C. after stretching. Below this magnification, oriented crystals cannot be formed sufficiently, tie chain molecules existing between the oriented crystals are difficult to form, and the tear strength decreases. On the other hand, if it exceeds this range, the longitudinal orientation becomes too strong, it is difficult to form entanglement between molecules, and the tear strength tends to decrease, which is not preferable.
When performing longitudinal stretching in multiple stages, the first low-temperature stretching (MD stretching 1) is in the range of (Tg-20) to (Tg + 10) ° C., more preferably in the range of (Tg-10) to (Tg + 5) ° C. Heated with a certain heating roll group, and preferably stretched in the longitudinal direction by 1.1 to 3.0 times, more preferably by 1.2 to 2.5 times, still more preferably by 1.5 to 2.0 times. MD stretching 2 is performed at a temperature higher than the MD stretching 1 temperature (Tg + 10) to (Tg + 50). A more preferable temperature is (Tg + 15) (˜Tg + 30). The preferable draw ratio of MD drawing 2 is 1.2 to 4.0 times, more preferably 1.5 to 3.0 times. The MD stretching ratio of MD stretching 1 and MD stretching 2 is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.5 times, and even more preferably 3.5 to 5 times. .0 times. The ratio between the draw ratios of the first stage and the second stage (second stage / first stage = multistage ratio) is preferably 1.1 to 3, more preferably 1.15 to 2 times, Preferably they are 1.2 times or more and 1.8 times or less. Even if the multi-stage stretching ratio is less than this range, the tear strength tends to decrease as in the case of single-stage stretching, which is not preferable.

(Process for forming an aqueous solution film)
It is preferable to form a film of an aqueous solution after this longitudinal stretching. The aqueous solution film may be water alone, but it is also preferable to add an additive (low molecular weight, high molecular weight component) of 50% by mass or less, more preferably 40% by mass or less, and 30% by mass or less. Thereby, the viscosity of the coating solution is adjusted, the repelling is suppressed, the evaporation rate of water can be suppressed, the diffusion into the film can be promoted, and the effect of the present invention can be promoted.
At the time of coating, corona treatment, glow treatment, flame treatment, UV treatment and the like are preferably performed on the surface of the polyester film on the support of the coating solution.

  A small amount of an organic solvent that dissolves in water may be added as the additive. Examples of such organic solvents include aliphatic or alicyclic alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, and n-butyl alcohol, diols such as ethylene glycol, propylene glycol, and diethylene glycol, methyl cellosorb, Diol derivatives such as ethyl cellosolve propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as methyl acetate, ethyl acetate and amyl acetate, ketones such as acetone and methyl ethyl ketone, amides such as N-methylpyrrolidone Etc. and mixtures thereof may be used, but are not limited to these.

  Further, as a high molecular weight additive, any water-soluble resin can be used. For example, EVA, EVA and ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate A mixture of copolymer (EBA), ethylene-methacrylic acid copolymer (EMAA), ionomer resin, polyester resin, urethane resin, acrylic resin, polyethylene resin, polypropylene resin, polyamide resin, etc. has high affinity with polyester. Preferably used.

  For such coating, various methods such as a bar coating method, a dip coating method, and a curtain coating method can be used. Of these, the bar coating method is preferable.

The molecules are aligned only in the uniaxial direction by longitudinal stretching, and in this state, the interaction between the molecules is extremely weak. In the subsequent lateral stretching, the molecules are aligned in the horizontal direction, but as they are, the molecules facing in the vertical direction and the molecules facing in the horizontal direction are mixed together, and it is difficult to generate entanglement between them.
In order to increase the entanglement between longitudinally oriented molecules and laterally oriented molecules, it is effective to form a water coating film between longitudinal stretching and lateral stretching. As a result, water penetrates into the film and serves as a plasticizer, increasing the mobility of the polyester molecules and increasing the entanglement in the transverse stretching.
It is preferable that 30% or more of the aqueous solution is water, and it is also preferable to add a low molecular weight component or a high molecular weight component to the aqueous solution from the viewpoint of suppressing the water film from repelling on the polyester film. A preferable coating amount is 0.1 g / m ² or more and 30 g / m ² or less, more preferably 0.5 g / m ² or more and 20 g / m ² or less, and further preferably 1 / m ² or more as a coating amount of water. 10 g / m ² or less. If it is more than the lower limit of this range, the said plasticization effect can fully be expressed. On the other hand, if it is below the upper limit of this range, the mobility of the polyester does not increase excessively, slip does not easily occur between molecules, and entanglement can easily be formed. As a result, in any case, the tear strength is hardly lowered, which is preferable. Such a decrease in tear strength is manifested after a thermostat with a reduced molecular weight, so that the tear strength retention rate is less likely to be greatly reduced.
Improvement of molecular mobility by the formation of such a film of an aqueous solution also has an effect of promoting the provision of illegality of heat shrinkage of the film. That is, since the polyester film is usually stretched in two directions of MD and TD, the orientation of one or both becomes strong and the thermal dimensional change rate increases. On the other hand, by increasing the entanglement between molecules as described above in the formation of a film of an aqueous solution, it has the effect of preventing the molecules from being oriented only in MD and TD (that is, because entanglement is formed, TD When molecules are stretched from MD to TD by stretching, they are oriented while dragging surrounding molecules, so there are molecules in the middle of MD to TD orientation, and uniform orientation can be formed). As a result, the thermal dimensional change rate distribution (see the next section) of the present invention can be achieved.
In order to form a film of such an aqueous solution, the aqueous solution may be applied, sprayed, or immersed in the aqueous solution. Among these, the method by coating is preferable, and various methods such as bar coating, gravure coating, curtain coating and the like are used. Of these, bar coating is preferable. This is because even a small amount can be applied accurately. Prior to the formation of the aqueous solution film, the surface is subjected to corona treatment, flame treatment, UV treatment, glow treatment and the like to activate the surface, thereby preventing the aqueous solution film from being repelled.
The step of forming a film of the aqueous solution has an effect of promoting the formation of entanglement as described above, but also has an effect of suppressing heat shrinkage. This is because the flow of molecules is suppressed by entanglement and heat shrinkage (movement of molecules to shrink) is suppressed.
Formation of the aqueous solution film is preferably performed between the longitudinal stretching and the lateral stretching, and at this time, anisotropy also appears in the formation of the entanglement. For this reason, anisotropy is easy to express, so that there are many application amounts of aqueous solution.

(Lateral stretching)
Next, stretching in the width direction is preferably performed using a tenter (sometimes referred to as a stenter). The draw ratio is preferably 3.0 to 5.0 times, more preferably 3.3 to 4.5 times, and still more preferably 3.5 to 4.2 times. The temperature is preferably in the range of (Tg) to (Tg + 50) ° C., more preferably in the range of (Tg) to (Tg + 30) ° C.

(Heat fixing)
In the method for producing a polyester film of the present invention, the film is heat-set (heat treated) after stretching in two directions. The heat setting can be performed by any conventionally known method such as in a tenter, a heating oven, or on a heated roll.
In the method for producing a polyester film of the present invention, the heat setting temperature is preferably 196 ° C. or higher and 215 ° C. or lower.
By setting the heat setting temperature to 196 ° C. or more and 215 ° C. or less, more preferably 198 ° C. or more and 210 ° C. or less, and more preferably 200 ° C. or more and 208 ° C. or less, the tension of molecules due to stretching can be appropriately released and heat shrinkage can be reduced ( Thermal contraction is manifested by the release of molecular tension generated by orientation). Below this range, the mobility of the polyester molecules is so low that tension cannot be released (heat shrinkage is large). On the other hand, when this temperature is exceeded, some of the crystals begin to melt and thermal shrinkage increases. This seems to be because some of the PET crystals begin to melt.
This heat setting is generally performed at a temperature lower than the melting point of the polyester, but in the present invention, heat setting is preferably performed at the temperature as described above. At this time, it is also preferable to achieve relaxation as described above in at least one of the vertical and horizontal directions as described above.

(Take-up)
It is preferable that the manufacturing method of the polyester film of this invention includes the process of winding up the film after the said heat setting. And the film which heat-treated in this way is wound up at the above-mentioned temperature, and the film of this invention is obtained.

In the method for producing a polyester film of the present invention, the temperature of the polyester film before winding is 26 ° C. or more and 80 ° C. or less, and in the range of 80 ° C. or more and 150 ° C. or less, 0.04 J / g or more and 1.26 J / g. It is preferable for developing the following endothermic peak. Although winding tension is applied during winding, this has the effect of reducing the free volume as described above. Therefore, it has the effect of reducing the mobility of the polyester molecules and suppressing the shrinkage of the molecules during heat shrinkage. For this reason, the effect of reducing the free volume is more easily expressed in the TD than in the MD (this is because the polyester molecule moves because the free volume is relaxed, but it is difficult to move when the molecule is stretched and stretched). ). Therefore, by exhibiting the above endothermic peak, anisotropy of heat shrinkage can also be imparted. Reduction of the free volume makes it difficult to dissipate heat by winding it on a roll, and the temperature can be made 26 ° C. or higher and 80 ° C. or higher. That is, it can be achieved by performing a heat treatment at a temperature below the Tg of the polyester. This is because a stable, small free volume can be obtained by imparting a slight thermal mobility to the polyester. When the temperature is lower than the above temperature, the free volume is not small and is not preferable. As a result, the tear strength decreases both above and below the above temperature range, which is not preferable. Thus, the time wound around the roll is preferably 1 day or more, more preferably 3 days or more, and still more preferably 1 week or more.
Such a heat treatment in the vicinity of Tg or lower is preferably wound after increasing the temperature of the film when it is wound around a roll. When heat treatment is performed after winding on a roll, heat is easily transferred to the outside of the roll, but heat is hardly transferred to the inside of the roll, so that the effect of this treatment cannot be fully expressed.

[Back sheet for solar cells]
The solar cell backsheet of the present invention includes the polyester film of the present invention.
The solar cell backsheet of the present invention comprises the polyester film of the present invention described above, and is composed of an easy-adhesive layer, an ultraviolet absorbing layer, a light-reflective white layer, etc. The functional layer may be provided with at least one layer. Since the polyester film described above is provided, stable durability is exhibited during long-term use.

In the solar cell backsheet of the present invention, for example, the following functional layer may be coated on a polyester film after uniaxial stretching and / or biaxial stretching. For coating, a known coating technique such as a roll coating method, a knife edge coating method, a gravure coating method, or a curtain coating method can be used.
Further, surface treatment (flame treatment, corona treatment, plasma treatment, ultraviolet treatment, etc.) may be performed before the coating. Furthermore, it is also preferable to bond together using an adhesive.

-Easy adhesive layer-
The polyester film of the present invention has an easy-adhesive layer on the side facing the sealing material of the battery-side substrate in which the solar cell element is sealed with a sealing agent when constituting a solar cell module. Is preferred. Easy adhesion showing adhesion to an adherend containing a sealing agent (particularly ethylene-vinyl acetate copolymer) (for example, the surface of the sealing agent on the battery side substrate in which the solar cell element is sealed with the sealing material). By providing the property layer, the back sheet and the sealing material can be firmly bonded. Specifically, it is preferable that the easy-adhesive layer has an adhesive force of 10 N / cm or more, preferably 20 N / cm or more, particularly with EVA (ethylene-vinyl acetate copolymer) used as a sealing material.
Further, the easy-adhesive layer needs to prevent the backsheet from peeling off during use of the solar cell module, and therefore, the easy-adhesive layer desirably has high moisture and heat resistance.

(1) Binder The easy-adhesive layer in the present invention can contain at least one binder.
As the binder, for example, polyester, polyurethane, acrylic resin, polyolefin, or the like can be used. Among these, acrylic resins and polyolefins are preferable from the viewpoint of durability. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. The following can be mentioned as an example of a preferable binder.
Examples of the polyolefin include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals, Inc.). Examples of the acrylic resin include Julimer ET-410 and SEK-301 (both manufactured by Nippon Pure Chemical Industries, Ltd.). Examples of the composite resin of acrylic and silicone include Ceranate WSA 1060 and WSA 1070 (both manufactured by DIC Corporation), and H7620, H7630, and H7650 (both manufactured by Asahi Kasei Chemicals Corporation).
The amount of the binder is preferably in the range of 0.05-5 g / m ^2, the range of 0.08~3g / m ² is particularly preferred. The binder amount is more good adhesion is obtained by at 0.05 g / m ² or more, a better surface is obtained by at 5 g / m ² or less.

(2) Fine particles The easy-adhesion layer in the present invention can contain at least one kind of fine particles. The easy-adhesive layer preferably contains 5% by mass or more of fine particles with respect to the mass of the entire layer.
As the fine particles, inorganic fine particles such as silica, calcium carbonate, magnesium oxide, magnesium carbonate, tin oxide and the like are preferably exemplified. Among these, fine particles of tin oxide and silica are preferable in that the decrease in adhesiveness when exposed to a humid heat atmosphere is small.
The particle size of the fine particles is preferably about 10 to 700 nm, more preferably about 20 to 300 nm. By using fine particles having a particle diameter in the above range, good easy adhesion can be obtained. The shape of the fine particles is not particularly limited, and those having a spherical shape, an indefinite shape, a needle shape, or the like can be used.
The addition amount of the fine particles in the easy-adhesive layer is preferably 5 to 400% by mass, more preferably 50 to 300% by mass per binder in the easy-adhesive layer. When the addition amount of the fine particles is 5% by mass or more, the adhesiveness when exposed to a moist heat atmosphere is excellent, and when it is 1000% by mass or less, the surface state of the easy-adhesive layer is better.

(3) Crosslinking agent The easy-adhesion layer in this invention can contain at least 1 sort (s) of a crosslinking agent.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, an oxazoline-based cross-linking agent is particularly preferable from the viewpoint of securing adhesiveness after wet heat aging.
Specific examples of the oxazoline-based crosslinking agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline. 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2′-bis- (2-oxazoline), 2,2′-methylene-bis- ( 2-oxazoline), 2,2′-ethylene-bis- (2-oxazoline), 2,2′-trimethylene-bis- (2-oxazoline), 2,2′-tetramethylene-bis- (2-oxazoline) 2,2′-hexamethylene-bis- (2-oxazoline), 2,2′-octamethylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (4,4′- Methyl-2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene- Bis- (4,4′-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinylnorbornane) sulfide and the like can be mentioned. Furthermore, (co) polymers of these compounds can also be preferably used.
Further, as a compound having an oxazoline group, Epocros K2010E, K2020E, K2030E, WS500, WS700 (all manufactured by Nippon Shokubai Chemical Co., Ltd.) and the like can be used.
The preferable addition amount of the crosslinking agent in the easy-adhesive layer is preferably 5 to 50% by mass, more preferably 20 to 40% by mass per binder of the easy-adhesive layer. When the addition amount of the crosslinking agent is 5% by mass or more, a good crosslinking effect is obtained, and the strength of the reflective layer is not reduced and adhesion failure hardly occurs. I can keep it long.

(4) Additives The easy-adhesive layer in the present invention is added with known matting agents such as polystyrene, polymethylmethacrylate, silica, etc., as well as known surfactants such as anionic and nonionic types, if necessary. May be.

(5) Method for forming easy-adhesive layer As a method for forming the easy-adhesive layer of the present invention, there are a method for bonding a polymer sheet having easy adhesion to a polyester film and a method for coating. It is preferable in that it can be formed with a simple and highly uniform thin film. As a coating method, for example, a known method such as a gravure coater or a bar coater can be used. The solvent of the coating solution used for coating may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.
Moreover, when forming an easily-adhesive layer by application | coating, as described in the manufacturing method of this invention, it is preferable to combine the drying and heat processing of an application layer in the drying zone after heat processing. The same applies to the case where a colored layer and other functional layers described later are formed by coating.

(6) Physical property Although there is no restriction | limiting in particular in the thickness of the easily-adhesive layer in this invention, Usually, 0.05-8 micrometers is preferable, More preferably, it is the range of 0.1-5 micrometers. When the thickness of the easy-adhesive layer is 0.05 μm or more, the required easy adhesion can be easily obtained, and when the thickness is 8 μm or less, the planar shape can be maintained better.
In addition, the easy-adhesion layer in the present invention may have transparency from the viewpoint of not impairing the effect of the colored layer when a colored layer (particularly a reflective layer) is disposed between the polyester film. preferable.

-Colored layer-
The polyester film of the present invention can be provided with a colored layer. The colored layer is a layer arranged in contact with the surface of the polyester film or through another layer, and can be constituted using a pigment or a binder.

  The first function of the colored layer is to increase the power generation efficiency of the solar cell module by reflecting the light that has reached the back sheet without being used for power generation in the solar cell out of the incident light and returning it to the solar cell. is there. The second function is to improve the decorativeness of the appearance when the solar cell module is viewed from the front side. In general, when a solar cell module is viewed from the front side, a back sheet can be seen around the solar cell, and the decorativeness can be improved by providing a colored layer on the back sheet.

(1) Pigment The colored layer in the present invention can contain at least one pigment. The pigment is preferably contained in the range of 2.5 to 8.5 g / m ² . A more preferable pigment content is in the range of 4.5 to 7.5 g / m ² . When the pigment content is 2.5 g / m ² or more, necessary coloring can be easily obtained, and the light reflectance and decorativeness can be adjusted to be more excellent. When the pigment content is 8.5 g / m ² or less, the planar shape of the colored layer can be more favorably maintained.

  Examples of the pigment include inorganic pigments such as titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, ultramarine blue, bitumen, and carbon black, and organic pigments such as phthalocyanine blue and phthalocyanine green. It is done. Among these pigments, a white pigment is preferable from the viewpoint of constituting a colored layer as a reflective layer that reflects incident sunlight. As the white pigment, for example, titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc and the like are preferable.

As an average particle diameter of a pigment, 0.03-0.8 micrometer is preferable, More preferably, about 0.15-0.5 micrometer is preferable. If the average particle size is within the above range, the light reflection efficiency may be reduced.
When a colored layer is configured as a reflective layer that reflects incident sunlight, the preferred addition amount of the pigment in the reflective layer varies depending on the type of pigment used and the average particle size, but cannot be generally stated. preferably to 15 g / m ^2, more preferably about 3 to 10 g / m ^2. When the addition amount is 1.5 g / m ² or more, the required reflectance is easily obtained, and when it is 15 g / m ² or less, the strength of the reflection layer can be kept higher.

(2) Binder The colored layer in the present invention can contain at least one binder. As a quantity in case a binder is included, the range of 15-200 mass% is preferable with respect to the said pigment, and the range of 17-100 mass% is more preferable. When the amount of the binder is 15% by mass or more, the strength of the colored layer can be more favorably maintained, and when it is 200% by mass or less, the reflectance and the decorativeness are lowered.
As a binder suitable for the colored layer, for example, polyester, polyurethane, acrylic resin, polyolefin, or the like can be used. From the viewpoint of durability, the binder is preferably an acrylic resin or a polyolefin. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. Examples of preferred binders include the following.
Examples of the polyolefin include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals). Examples of the acrylic resin include Julimer ET-4
10 and SEK-301 (both manufactured by Nippon Pure Chemical Industries, Ltd.). Examples of the composite resin of acrylic and silicone include Ceranate WSA1060, WSA1070 (both manufactured by DIC Corporation), H7620, H7630, H7650 (both manufactured by Asahi Kasei Chemicals Corporation) and the like.

(3) Additive In addition to the binder and the pigment, a cross-linking agent, a surfactant, a filler, and the like may be further added to the colored layer in the present invention as necessary.

  Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. The addition amount of the crosslinking agent in the colorant is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, per binder of the colored layer. When the addition amount of the crosslinking agent is 5% by mass or more, a good crosslinking effect can be obtained, the strength and adhesiveness of the colored layer can be maintained high, and when it is 50% by mass or less, the coating solution The pot life can be maintained longer.

As the surfactant, a known surfactant such as an anionic or nonionic surfactant can be used. The addition amount of the surfactant is preferably 0.1 to 15 mg / m ² , more preferably 0.5 to 5 mg / m ² . The amount of the surfactant added is 0.1 mg / m ² or more to effectively suppress the occurrence of repelling, and the amount added is 15 mg / m ² or less to provide excellent adhesion.

  Furthermore, a filler such as silica may be added to the colored layer in addition to the above pigment. The addition amount of the filler is preferably 20% by mass or less, more preferably 15% by mass or less per binder of the colored layer. By including the filler, the strength of the colored layer can be increased. Moreover, since the ratio of a pigment can be maintained because the addition amount of a filler is 20 mass% or less, favorable light reflectivity (reflectance) and decorativeness are obtained.

(4) Forming method of colored layer As a forming method of the colored layer, there are a method of pasting a polymer sheet containing a pigment on a polyester film, a method of co-extruding a colored layer at the time of forming a polyester film, a method by coating, and the like. Among these, the method by coating is preferable in that it can be formed with a simple and highly uniform thin film. As a coating method, for example, a known method such as a gravure coater or a bar coater can be used. The solvent of the coating solution used for coating may be water or an organic solvent such as toluene or methyl ethyl ketone. However, from the viewpoint of environmental burden, it is preferable to use water as a solvent.
A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.

(5) Physical property It is preferable that a colored layer contains a white pigment and is comprised as a white layer (light reflection layer). The light reflectance at 550 nm in the case of the reflective layer is preferably 75% or more. When the reflectance is 75% or more, sunlight that has passed through the solar battery cell and has not been used for power generation can be returned to the cell, and the effect of increasing power generation efficiency is high.

  1-20 micrometers is preferable, as for the thickness of a white layer (light reflection layer), 1-10 micrometers is more preferable, More preferably, it is about 1.5-10 micrometers. When the film thickness is 1 μm or more, necessary decoration and reflectance are easily obtained, and when it is 20 μm or less, the surface shape may be deteriorated.

-Undercoat layer-
An undercoat layer can be provided on the polyester film of the present invention. For example, when a colored layer is provided, the undercoat layer may be provided between the colored layer and the polyester film. The undercoat layer can be formed using a binder, a crosslinking agent, a surfactant, and the like.

  Examples of the binder contained in the undercoat layer include polyester, polyurethane, acrylic resin, and polyolefin. In addition to the binder, an epoxy, isocyanate, melamine, carbodiimide, oxazoline, or other crosslinking agent, anionic or nonionic surfactant, silica or other filler may be added to the undercoat layer.

There are no particular restrictions on the method for coating the undercoat layer and the solvent of the coating solution used.
As a coating method, for example, a gravure coater or a bar coater can be used. The solvent may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.

The application may be applied to the polyester film after biaxial stretching or may be applied to the polyester film after uniaxial stretching. In this case, the film may be further stretched in a direction different from the initial stretching after coating. Furthermore, you may extend | stretch in 2 directions, after apply | coating to the polyester film before extending | stretching.
The thickness of the undercoat layer is preferably 0.05 μm to 2 μm, more preferably about 0.1 μm to 1.5 μm. When the film thickness is 0.05 μm or more, the necessary adhesiveness is easily obtained, and when it is 2 μm or less, the surface shape can be favorably maintained.

-Antifouling layer (fluorine resin layer / silicon resin layer)-
The polyester film of the present invention is preferably provided with at least one of a fluorine-based resin layer and a silicon-based (Si-based) resin layer as an antifouling layer. By providing the fluorine-based resin layer or the Si-based resin layer, it is possible to prevent contamination of the polyester surface and improve weather resistance. Specifically, it is preferable to have the fluororesin-based coating layer described in JP2007-35694A, JP2008-28294A, and WO2007 / 063698.
Moreover, it is also preferable to stick together fluorine resin films such as Tedlar (manufactured by DuPont).

  The thicknesses of the fluorine-based resin layer and the Si-based resin layer are each preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 40 μm, still more preferably 1 μm to 10 μm.

[Solar cell module]
The solar cell module of the present invention includes the polyester film of the present invention or the back sheet of the present invention.
The solar cell module of the present invention comprises a solar cell element that converts light energy of sunlight into electric energy, a transparent substrate on which sunlight is incident, and the polyester film (back sheet for solar cell) of the present invention described above. It is arranged and arranged between. A space between the substrate and the polyester film can be configured by sealing with a resin (so-called sealing material) such as an ethylene-vinyl acetate copolymer.

  The members other than the solar cell module, the solar cell, and the back sheet are described in detail in, for example, “Photovoltaic power generation system constituent material” (supervised by Eiichi Sugimoto, Kogyo Kenkyukai, published in 2008).

  The transparent substrate only needs to have a light-transmitting property through which sunlight can pass, and can be appropriately selected from base materials that transmit light. From the viewpoint of power generation efficiency, the higher the light transmittance, the better. For such a substrate, for example, a glass substrate, a transparent resin such as an acrylic resin, or the like can be suitably used.

  Examples of solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, and group III-V such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenide, and II. Various known solar cell elements such as a group VI compound semiconductor can be applied.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the examples shown below. Unless otherwise specified, “part” is based on mass.

<Measurement method>
(1) Retention rate of tear strength: The sample film is cut into 2 cm width (short side) × 10 cm length (long side) in the MD and TD directions, respectively.
-A notch with a length of 5 cm is placed in the center of the short side in parallel with the long knitting direction, and the stress is measured by the following method using a tensile tester. The measurement is performed at 25 ° C. and 50% relative humidity.
(1-1) One end of the cut portion is held by one chuck of the tensile tester and the other end is held by the other chuck.
(1-2) The tensile stress of the chuck is measured at 30 mm / min. As the distance between chucks increases, the stress increases and a flat portion appears. The stress at the flat end is taken as the tear strength, and the average value is obtained by measuring with the number of repetitions n = 3.
(1-3) This measurement is measured by MD and TD, and the average value is taken as the tear strength.
-The tear strength is measured by the above method for the sample before and after the thermo treatment at 120 ° C. and 100% relative humidity for 90 hours, and the sample before the thermo treatment, and the retention rate (%) of the specific described strength is obtained from the following formula.
100 × {(Tear strength before thermo) − (Tear strength after thermo)} / (Tear strength before thermo)

(2) Tcg
-It measures according to [0059] of Unexamined-Japanese-Patent No. 2010-235824.

(3) 10 mg of the endothermic peak sample film appearing in the range of 80 ° C. or higher and 150 ° C. or lower is weighed, placed in an aluminum pan, and loaded into a scanning differential thermal analysis system (DSC). Measurement is performed while raising the temperature up to 300 ° C. at 20 ° C./min.
-The endothermic amount is obtained from the area of the endothermic peak appearing from 80 ° C to 150 ° C (when there are a plurality of peaks, the sum is obtained).

(4) Thermal dimensional change rate, thermal dimensional change distribution ・ The sample is cut every 30 ° from the MD direction for 15 cm × 10 cm (n = 3) for each measurement.
・ After conditioning at 25 ° C. and a relative humidity of 60% for 12 hours or more, a pair of holes is made at intervals of 10 cm, and the distance between the holes is measured using a pin gauge (this is referred to as L1).
-Put the above film under no tension in an air thermostat at 150 ° C and take it out after 30 minutes.
・ After adjusting the humidity for 12 hours or more at 25 ° C. and 60% relative humidity, measure the distance between these holes using a pin gauge (this is referred to as L2).
・ After dividing the absolute value of the difference between L1 and L2 by L2, multiply by 100 to obtain the thermal dimensional change rate (%), and obtain the average value of n = 3 in each direction. Further, this is averaged in all directions to obtain the thermal dimensional change rate. Further, the difference between the maximum value and the minimum value of the thermal dimensional change rate in each direction divided by the average value and expressed as a percentage is defined as the thermal dimensional change rate distribution.

(5) Intrinsic viscosity (IV)
The film was dissolved in orthochlorophenol, and the intrinsic viscosity was obtained from the following formula from the solution viscosity measured at 25 ° C.
ηsp / C = [η] + K [η] ² · C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the dissolved polymer weight per 100 ml of solvent (in this measurement, 1 g / 100 ml), and K is the Huggins constant (0.343). ). The solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

(6) Carboxyl end group concentration (AV)
0.5 g of a film was dissolved in o-cresol and measured by potentiometric titration using potassium hydroxide to obtain the carboxyl end group concentration.

[Synthesis Example 1]
(Polyester polymerization (raw material PET1 / Sb))
To a mixture of 100 parts by mass of dimethyl terephthalate and 60 parts by mass of ethylene glycol, 0.08 parts by mass of calcium acetate and 0.03 parts by mass of antimony trioxide are added, and the mixture is heated and heated by a conventional method to perform a transesterification reaction. It was. Next, the transesterification reaction product was added to 0.16 parts by mass of lithium acetate and 0.14 parts by mass of trimethyl phosphate, and then transferred to a polymerization reaction tank. Next, the reaction system was gradually depressurized while being heated and heated, and polymerization was performed at 290 ° C. under a reduced pressure of 1 mmHg to obtain a polyester (polyethylene terephthalate) having an intrinsic viscosity [η] of 0.52 dl / g. . The polyester is cut into rectangular parallelepipeds each having a side of 2 mm × 4 mm × 4 mm, and the heat treatment time is adjusted at 230 ° C. under a reduced pressure of 0.5 mmHg by using a rotary vacuum polymerization apparatus. A polyester (PET1) was obtained so as to be AV and IV (as described in the table below, PET1 means that it is Sb-based, and in the table below, AV and IV are different between PET1s). is there).

[Synthesis Example 2]
(Polyester polymerization (Ti / PET2))
-Process (A)-
4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed for 90 minutes to form a slurry, which was continuously supplied to the first esterification reactor at a flow rate of 3800 kg / h. Next, an ethylene glycol solution of a citric acid chelate titanium complex ("VERTEC AC-420", manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal is continuously supplied to the first esterification reaction tank. While stirring at an internal temperature of 250 ° C., the reaction was carried out with an average residence time of about 4.3 hours to obtain an oligomer. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. The acid value of the obtained oligomer was 550 eq / ton.

The obtained oligomer was transferred to a second esterification reaction tank and reacted by stirring at a reaction tank temperature of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 180 eq / ton. The inside of the second esterification reaction tank is divided into three zones from the first zone to the third zone. From the second zone, an ethylene glycol solution of magnesium acetate is added, and the amount of Mg added is 75 ppm in terms of element. Then, from the third zone, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the addition amount of P was 65 ppm in terms of element. The ethylene glycol solution of trimethyl phosphate was prepared by adding a 25 ° C. trimethyl phosphate solution to a 25 ° C. ethylene glycol solution and stirring at 25 ° C. for 2 hours (phosphorus compound content in the solution: 3 .8% by mass).
As a result, an esterification reaction product was obtained.

-Process (B)-
The esterification reaction product obtained in the step (A) was continuously supplied to the first polycondensation reaction tank. Next, polycondensation (ester exchange reaction) is carried out with an average residence time of about 1.8 hours while stirring the esterification reaction product at a reaction temperature of 270 ° C. and a reaction tank pressure of 20 torr (2.67 × 10 ⁻³ MPa). It was.
Next, the obtained reaction product was transferred from the first polycondensation reaction tank to the second double condensation reaction tank. Thereafter, the reaction product was stirred in the second double condensation reaction tank at a reaction tank temperature of 276 ° C. and a reaction tank pressure of 5 torr (6.67 × 10 ⁻⁴ MPa), and the residence time was about 1.2 hours. (Transesterification reaction).
Subsequently, the reaction product obtained by the transesterification reaction is further transferred from the second double condensation reaction tank to the third triple condensation reaction tank. In this reaction tank, the reaction tank temperature is 278 ° C. and the reaction tank pressure is 1. While stirring at 5 torr (2.0 × 10 ⁻⁴ MPa), the reaction (transesterification reaction) was performed under the condition of a residence time of 1.5 hours. Carboxylic acid value: 24 eq / ton, IV (intrinsic viscosity): 0.65 dl / G reaction product (polyethylene terephthalate was obtained.

-Step (C)-
The resin was dried at 170 ° C. for 5 hours. Thereafter, the pellets were transferred to a solid phase polymerization tank, and solid phase polymerization was performed at 210 ° C. while flowing N ₂ gas containing 200 ppm of water vapor into the solid phase polymerization tank at a flow rate of 1 Nm ³ / hr per kg of resin. Incidentally, the solid-phase polymerization time, by changing the ethylene glycol (EG) gas concentration blown into N ₂ gas to achieve the Tables 1 to 4, wherein AV, the IV.
The obtained polyester resin was designated as PET2 (as described in the table below, PET2 means Ti-based, and AV and IV may be different between PET2 in the table below).

  In the production of PET1 and PET2, the AV is lowered and the IV is increased by increasing the solid phase polymerization time. In this experiment, it was carried out by changing in the range of 10 hours to 200 hours.

  Further, in the production of PET1 and PET2, the AV can be reduced by increasing the EG gas. Note that IV is not affected. In this experiment, the range was changed from 100 ppm to 400 ppm.

[Production Example 1]
(Preparation of sealant master pellet)
The PET resin (PET1, PET2) solid-phase polymerized by the above method is mixed with a low molecular weight type and a high molecular weight type end-capping agent at a mixing ratio shown in the following table, and a master pellet having an addition amount of 10% by mass is prepared. It was adjusted. The polyester used for the master pellets was the same type as the polyester used when forming the polyester films of the examples and comparative examples described later.
The master pellet was adjusted using a twin screw extruder. That is, PET resin was added from the hopper, and the end-capping agent of the powder was metered in from the hopper using a feeder, and in the case of liquid, it was added and kneaded using a metering pump from the port provided in the twin-screw extruder.
The following end capping agents were used and the types used were listed in the table below.
The kneaded PET resin and the end-capping agent were extruded into strands, and then cooled with water and cut to prepare master pellets.
<Type of sealant>
(1) Carbodiimide sealing agent C1-1: Starbazole P400: Polycarbodiimide, number average molecular weight of about 20,000, manufactured by Rhein Chemie Japan Co., Ltd. C1-2: Starbazole P: Polycarbodiimide, number average molecular weight 3500, Rhein Chemy Japan C1-3: LA-1: polycarbodiimide, number average molecular weight of about 2000, manufactured by Nisshinbo Chemical Co., Ltd.)
C1-4: STABILIZER 9000: polycarbodiimide, number average molecular weight of about 20000, manufactured by Rhein Chemie)
C1-5: Starvacol P100: polycarbodiimide, number average molecular weight of about 10,000, manufactured by Rhein Chemie Japan Co., Ltd.)
C1-6: Stabuxol I: monocarbodiimide, number average molecular weight 450, manufactured by Rhein Chemie Japan Co., Ltd. C1-7: Production Example 1: polycarbodiimide, number average molecular weight of about 900
C1-8: Production Example 2: Polycarbodiimide, number average molecular weight of about 6000
C1-9: polycarbodiimide described in Production Example 1 of [0129] of JP2009-155479A, number average molecular weight of about 1040
C1-10: polycarbodiimide described in Production Example 2 of [0130] of JP2009-155479A, number average molecular weight of about 2060
C1-11: Production Example 3: Polycarbodiimide, number average molecular weight of about 1000
C1-12: Production Example 4: Polycarbodiimide, number average molecular weight of about 9000
C1-13: Production Example 5: polycarbodiimide, number average molecular weight of about 50,000
C1-14: Production Example 6: polycarbodiimide, number average molecular weight of about 60000
C1-15: Production Example 7: polycarbodiimide, number average molecular weight of about 70000
C1-16: Production Example 8: polycarbodiimide, number average molecular weight of about 3150
C1-17: Production Example 9: polycarbodiimide, number average molecular weight of about 45000

In Production Examples 1 to 9, polycarbodiimide was produced as follows.
Production Example 2: 1000 parts of 2,4,6-triisopropylphenyl 1,3-diisocyanate and 10 parts of 3-methyl-1-phenyl-2-phospholene oxide were heated to 120 ° C. over 1 hour Then, the polycarbodiimide of Production Example 3 was synthesized by performing the reaction for 20 hours without changing the temperature. The number average molecular weight (Mn) of the polycarbodiimide obtained from GPC was found to be 1300.
Production Examples 1 and 3-9: The polycarbodiimides of Production Examples 1 and 3-9 were synthesized by the same method while appropriately controlling the addition amount and reaction time.

(1) Other sealant a) Epoxy sealant E-1: EHPE3150 (molecular weight 3150)
B) Glycidyl-based sealant G-1: Compound described in Production Example 4 of [0132] of JP-A-2009-155479 (molecular weight = 10000)
C) Oxazoline-based compound O-1: Compound described in Production Example 3 of [0131] of JP-A-2009-155479 (molecular weight = 10000)

[Examples 1 to 76 and Comparative Examples 1 to 3]
(1) Film formation of polyester film substrate (unstretched film) After drying the above solid-phase polymerization pellets and terminal pellet master pellets using the same to a moisture content of 100 ppm or less, solid-phase polymerization pellets and master pellets And a polyester resin having a different melting temperature described in Tables 1 to 4 below, while extruding, diluting the end sealant, and including an unstretched film containing the total amount of end sealant described in Tables 1 to 4 Obtained. In addition, the addition amount of terminal blocker here refers to the mass% with respect to a polyester resin. For extrusion, a twin screw extruder was used, and melted and kneaded at 280 ° C. in a nitrogen stream, and this melt (melt) was extruded through a gear pump, a filter and a die onto a chill roll to produce an unstretched film.

(2) Longitudinal stretching The obtained unstretched monolayer film was preheated to 75 ° C. with a heated roll group. Thereafter, the film was longitudinally stretched in the film conveying direction at 85 ° C. at the magnifications shown in Tables 1 to 4. Then, it cooled with the roll group of the temperature of 25 degreeC, and obtained the longitudinally uniaxially stretched film.

(3) Aqueous solution application After the longitudinally uniaxially stretched film was subjected to corona treatment, it was applied to one side so as to have the aqueous solution film thickness described in Tables 1 to 4 using a metal ring bar.
(Aqueous solution A)
Coating material 1 (conductive material): Water dispersion of water-insoluble cationic conductive material: “BONDEIP-PM (registered trademark)” (manufactured by Konishi Oil & Fat Co., Ltd., solid content 30%)
Coating material 2 (binder resin): Acrylic resin water dispersion: Methyl methacrylate / ethyl acrylate / acrylic acid / N-methylol acrylamide = 62/35/2/1 (mass ratio) copolymer acrylic resin (glass transition temperature) : 42 ° C.) dispersed in water at a solid content of 10% in the form of particles.
-Coating material 3 (crosslinking agent): Oxazoline group-containing compound aqueous dispersion: "Epocross (registered trademark)" WS-500 (manufactured by Nippon Shokubai Co., Ltd., solid content 40%)
・ Coating material 4 (surfactant): Acetylene diol surfactant: “Orphine (registered trademark)” EXP4051F (manufactured by Nissin Chemical Industry Co., Ltd.)
-Coating raw material 5: Water The addition amount of the coating raw material 1, the coating raw material 2, the coating raw material 3, the coating raw material 4 and the coating raw material 5 in the aqueous solution A is 18 parts by mass, 3 parts by mass, 0.75 part by mass, and 0, respectively. 0.1 parts by mass and 78.15 parts by mass.

(Aqueous solution B)
Coating material 1 (conductive material): Water-insoluble polythiophene-based conductive polymer water dispersion: “Baytron (registered trademark)” P (Bayer / HC Stark (Germany), solid content 1 .2%)
・ Coating material 2 (binder resin): water-insoluble polyester resin: terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalate = 60/30/10 as an acid component and ethylene glycol / diethylene glycol / polyethylene glycol as a diol component = A polyester resin copolymerized with 95/3/2 (glass transition temperature 48 ° C.) dispersed at a concentration of 10% by mass.
Coating material 3 (crosslinking agent): epoxy-based crosslinking agent: polyglycerol polyglycidyl ether-based epoxy crosslinking agent EX-512 (molecular weight about 630) (manufactured by Nagase ChemteX Corporation).
Coating material 4 (surfactant): Acetylene diol surfactant: “Orphine (registered trademark)” EXP4051F.
-Coating material 5: Water The addition amounts of the coating material 1, the coating material 2, the coating material 3, the coating material 4, and the coating material 5 in the aqueous solution B are 41.6 parts by mass, 2.5 parts by mass, and 0.25, respectively. The mass part, 0.1 part by mass and 32.1 parts by mass were set.

(Aqueous solution C)
-Water is added to <Coating agent 1-1> described in [0130] of JP2009-158952A, and the aqueous solution C is treated in the same manner as the aqueous solution A so as to achieve the moisture application amount described in Tables 1-4. Applied.

(Aqueous solution D)
-Water was added to the coating solution described in [0024] of WO2008 / 069024, and the aqueous solution D was applied in the same manner as the aqueous solution A so as to achieve the coating amount of moisture described in Tables 1 to 4.

(4) Transverse stretching After the above-mentioned application to the obtained uniaxially stretched film, the both ends are held by clips and guided to a preheating zone at a temperature of 95 ° C. in the tenter, and continuously heated at a temperature of 100 ° C. In the width direction (TD direction, lateral direction) perpendicular to the film conveying direction, the film was stretched twice by the magnifications listed in Tables 1-4.

(5) Heat setting / relaxation Subsequently, after performing heat setting for 20 seconds at the temperature shown in Tables 1 to 4 in the heat treatment zone in the tenter, the film was subsequently widened at a temperature 10 ° C. lower than the heat setting temperature. It was relaxed (relaxed) by 5% in the direction (TD).

(6) Winding The film after heat fixing and relaxation was wound into a roll, and the time for winding the film around the roll was 30 days.
The physical properties of the polyester film after winding thus obtained are shown in Tables 1 to 4 below. In addition, Comparative Example 2 was obtained by reexamining Example 1 of JP 2010-235824 A, and as a low molecular weight type end-capping agent, according to [0077] to [0078] of JP 2010-235824 A. The polycarbodiimide described in Reference Example 4 was used, and PET pellets having an intrinsic viscosity of 0.85 described in [0072] to [0075] of JP 2010-235824 A were used as PET resins (in the table, “PET3 ”). Example 72 is the polyester film of the present invention formed by using Comparative Example 2 in combination with a high molecular weight type end-capping agent as described in the following table.

(7) Preparation of solar cell backsheet The following (i) reflective layer and (ii) easy-adhesion layer were coated in this order on the surface of the polyester film on the aqueous solution coated surface.

(I) Reflective layer (colored layer)
Various components having the following composition were mixed and subjected to a dispersion treatment for 1 hour using a dynomill type disperser to prepare a pigment dispersion.
<Prescription of pigment dispersion>
・ Titanium dioxide: 39.9 parts (Taipeke R-780-2, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100% by mass)
・ Polyvinyl alcohol: 8.0 parts (PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10%)
・ Surfactant (Demol EP, manufactured by Kao Corporation, solid content: 25%) ・ ・ ・ 0.5 part ・ Distilled water ・ ・ ・ 51.6 parts

Next, using the obtained pigment dispersion, various components having the following composition were mixed to prepare a coating solution for forming a reflective layer.
<Prescription of reflection layer forming coating solution>
-The above-mentioned pigment dispersion ... 71.4 parts-Polyacrylic resin aqueous dispersion ... 17.1 parts (Binder: Jurimer ET410, manufactured by Nippon Pure Chemical Industries, Ltd., solid content: 30% by mass)
Polyoxyalkylene alkyl ether 2.7 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound (crosslinking agent) ... 1.8 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
・ Distilled water: 7.0 parts

The reflective layer-forming coating solution obtained above was applied to each polyester film with a bar coater and dried at 180 ° C. for 1 minute, and (i) a reflective layer (white) with a titanium dioxide coating amount of 6.5 g / m ² Layer).

(Ii) Easy-adhesive layer The components of the following composition are mixed to prepare an easy-adhesive layer coating solution, and this is applied to the binder layer so that the binder coating amount is 0.09 g / m ² (i) It was applied to. Then, it was made to dry at 180 degreeC for 1 minute, and (ii) the easily bonding layer was formed.
<Composition of coating solution for easy adhesion layer>
・ Polyolefin resin aqueous dispersion: 5.2 parts (carboxylic acid-containing binder: Chemipearl S75N, manufactured by Mitsui Chemicals, solid content: 24% by mass)
Polyoxyalkylene alkyl ether 7.8 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound: 0.8 part (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
Silica fine particle aqueous dispersion 2.9 parts (Aerosil OX-50, manufactured by Nippon Aerosil Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 83.3 parts

  Next, on the surface of the polyester film opposite to the side on which the (i) reflective layer and (ii) easy-adhesive layer are formed, the following (iii) undercoat layer and (iv) antifouling layer are placed on the polyester film side: It was coated sequentially.

(Iii) Undercoat layer Various components having the following composition were mixed to prepare a coating solution for an undercoat layer, this coating solution was applied to a polyester film, dried at 180 ° C. for 1 minute, and an undercoat layer (dry coating amount: about 0.1 g / m ² ) was formed.
<Composition of coating solution for undercoat layer>
・ Polyester resin: 1.7 parts (Vaironal MD-1200, manufactured by Toyobo Co., Ltd., solid content: 17% by mass)
Polyester resin 3.8 parts (Sulphonic acid-containing binder: Pesresin A-520, manufactured by Takamatsu Yushi Co., Ltd., solid content: 30% by mass)
Polyoxyalkylene alkyl ether: 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Carbodiimide compound: 1.3 parts (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 91.7 parts

(Iv) Antifouling Layer As shown below, a coating solution for forming the first and second antifouling layers is prepared, and the first antifouling layer coating solution and the second antifouling layer are formed on the undercoat layer. The two layers of antifouling layers were applied in the order of the layer coating solutions.

<First antifouling layer>
-Preparation of coating solution for first antifouling layer-
Components in the following composition were mixed to prepare a first antifouling layer coating solution.
<Composition of coating solution>
Seranaate WSA1070 (manufactured by DIC Corporation) 45.9 parts Oxazoline compound (crosslinking agent) 7.7 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass )
・ Polyoxyalkylene alkyl ether: 2.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Pigment dispersion used in the reflective layer: 33.0 parts ・ Distilled water: 11.4 parts

-Formation of first antifouling layer-
The obtained coating solution was applied onto the undercoat layer so that the binder coating amount was 3.0 g / m ² and dried at 180 ° C. for 1 minute to form a first antifouling layer.

-Preparation of coating solution for second antifouling layer-
Components in the following composition were mixed to prepare a second antifouling layer coating solution.
<Composition of coating solution>
Fluorine-based binder: Obligard (manufactured by AGC Co-Tech Co., Ltd.) ... 45.9 parts Oxazoline compound ... 7.7 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25 mass) %: Crosslinking agent)
・ Polyoxyalkylene alkyl ether: 2.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-The pigment dispersion prepared for the reflective layer ... 33.0 parts-Distilled water ... 11.4 parts

-Formation of second antifouling layer-
The prepared coating solution for the second antifouling layer is applied on the first antifouling layer formed on the undercoat layer so that the binder coating amount is 2.0 g / m ² , and the mixture is applied at 180 ° C. for 1 minute. A second antifouling layer was formed by drying.

  As described above, a solar cell backsheet having a reflective layer and an easy-adhesion layer on one side of the polyester film and an undercoat layer and an antifouling layer on the other side was produced.

(5) Production and Evaluation of Simulated Solar Cell Using the solar cell backsheet produced as described above, an easy-adhesive layer was attached to a glass plate, and thermostatted at 120 ° C. and a relative humidity of 100% for 60 hours. This was put in water at 15 ° C. and rapidly cooled (this facilitates cracking and becomes a forced test). As a result, the number of cracks (cracks) generated in the backsheet was counted and expressed as an occurrence rate (%) with respect to all wiring.

  From the said Tables 1-4, it turned out that the polyester film of this invention has the high retention of the tear strength after 60-hour thermostat at 120 degreeC and relative humidity 100%. It was also found that the simulated solar cell using the polyester film of the present invention was suppressed from cracking after 60 hours of thermostat at 120 ° C. and 100% relative humidity.

Claims (15)

  A polyester resin and two or more end-capping agents having a number average molecular weight of 4000 or more are contained, and the retention of tear strength after 60 hours of thermostat at 120 ° C. and 100% relative humidity is 50% or more. Polyester film. The terminal blocking agent is any one of a carbodiimide compound, an oxazoline compound, an epoxy compound, and a carbonate compound,
The molecular weight of the low molecular weight sealant is 1000 to 6000, and the molecular weight of the high molecular weight sealant is 10,000 to 50,000. The polyester film as described.   The polyester film according to claim 1 or 2, wherein the end-capping agent is a carbodiimide compound.   The mixing ratio of the two kinds of terminal blocking agents is 1/9 to 9/1 (mass ratio) as a value of low molecular weight sealing agent / high molecular weight sealing agent. The polyester film as described in any one of these.   The polyester film according to claim 1, wherein the crystallization parameter Tcg is less than 70 ° C. and 30 ° C. or more.   The polyester film according to claim 1, which has an endothermic peak of 0.04 to 1.26 J / g in a range of 80 ° C. or more and 150 ° C. or less.   The amount of thermal dimensional change is 0.1% or more and 2% or less, and the value obtained by dividing the difference between the maximum and minimum values of the thermal dimensional change measured in all directions by the average value is 5% or more and 40% or less. The polyester film according to any one of claims 1 to 6, wherein:   The polyester according to any one of claims 1 to 7, wherein the intrinsic viscosity IV is 0.6 dl / g or more and 0.9 dl / g or less, and the terminal carboxylic acid amount AV is 20 eq / ton or less. the film. A step of melt-kneading a polyester resin, polyester fine particles having a melting temperature of 1 ° C. or more and 35 ° C. or less, and an end-capping agent having a number average molecular weight of 4000 or more,
Forming a melt-kneaded melt into a film;
Stretching the film in two directions;
The manufacturing method of the polyester film characterized by including the process of heat-setting. A step of winding the film after the heat setting,
The method for producing a polyester film according to claim 9, wherein the temperature of the polyester film before winding is 26 ° C or higher and 80 ° C or lower. The step of stretching the film in two directions is longitudinal stretching in the film transport direction and lateral stretching in the direction orthogonal to the film transport direction,
Forming a film of an aqueous solution on at least one surface of the film between the longitudinal stretching and the lateral stretching so that a moisture coating amount is 0.1 g / m ² or more and 30 g / m ² or less. The manufacturing method of the polyester film of Claim 9 or 10 characterized by the above-mentioned.   The method for producing a polyester film according to any one of claims 9 to 11, wherein the heat setting temperature is 196 ° C or higher and 215 ° C or lower.   The polyester film manufactured by the manufacturing method of the polyester film as described in any one of Claims 9-12.   A back sheet for a solar cell, wherein the polyester film according to any one of claims 1 to 8 and claim 13 is used.   A solar cell module using the polyester film according to claim 1 or claim 13 or the back sheet for solar cell according to claim 14.