JP2018202866A - Laminated polyester film - Google Patents

Abstract

To provide a laminated polyester film having high adhesion to a solar battery backside sealing material (EVA) due to excellent wet heat resistance even when placed outdoors for a long period of time.SOLUTION: There is provided a laminated polyester film with at least two layers. At least one of one surface layer (layer A) and other surface layer (layer B) exhibits at least two crystallization peaks in a differential scanning calorimeter (DSC) curve obtained by analyzing with the DSC. The layer having the peak contains a single polyester of 90 wt.% or more based on the whole body of the layer.SELECTED DRAWING: None

Description

  The present invention relates to a laminated polyester film having at least two layers.

In recent years, in consideration of environmental load and safety, a power generation method using renewable resources such as wind power and solar power is attracting attention regardless of thermal power or nuclear power. Among other things, solar power generation is clean energy that does not involve the emission of greenhouse gases such as carbon dioxide, and because it uses relatively compact solar cell modules regardless of installation location, such as wind power generation. The spread is accelerating.
In general, a solar cell module is configured by laminating a cover material, a front side sealing material, a solar cell that performs photoelectric conversion, a back side sealing material, and a back sheet in order from the light receiving surface side.

Among them, the solar cell backsheet is used for the purpose of protecting the power generating element of the solar cell from external influences such as rain, and for efficiently reflecting light to increase the output of the solar cell. is there.
Since the solar cell is used outdoors for a long period of time due to its characteristics, the polyester film used for the solar cell back sheet is required to have high weather resistance, particularly moisture and heat resistance. In general, in order to protect the power generating element of the solar cell from external influences such as rain, a backside sealing made of an ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) is used as a polyester film used for a solar cell backsheet. It is necessary to provide materials. Therefore, the polyester film used for the solar battery back sheet is required to maintain adhesion with EVA for a long period of time.
So far, studies have been made on moisture resistance and high reflectance of polyester films used for solar battery backsheets (Patent Documents 1 and 2).

JP 2014-24319 A JP, 2006-204668, A

  The polyester film for solar battery backsheet is required to have an adhesive property that does not peel off from EVA even if it is installed outdoors for a long period of time. However, the above patent document is insufficient. Moreover, when the reflectance of the polyester film for a solar battery back sheet is high, the solar battery back sheet reflects the sunlight that is not directly incident on the solar battery cell out of the sunlight incident on the solar battery, and the reflection Although it is possible to increase the output of the solar battery by making light incident on the solar battery cell, the above-mentioned patent document does not satisfy the required characteristics for improving the reflectance. For example, in Patent Document 1, a study for improving the adhesion with EVA is made, but there is no description about adhesion maintenance for a long period of time, and Patent Document 2 describes the relationship with EVA after heat and wet heat treatment. Although there are descriptions such as studies on adhesiveness, long-term adhesion maintenance, and module efficiency maintenance, all are inadequate and the means are complicated, such as the need for additives to the surface layer.

  The problem to be solved by the present application is to easily provide a laminated polyester film suitable as a polyester film for a solar battery back sheet, which has excellent heat and moisture resistance and can be kept in close contact with the back surface sealing material even when placed outdoors for a long time. It is to be.

In order to solve the above problems, the present invention has the following configuration.
(1) A DSC that is a laminated polyester film having at least two layers, wherein at least one of one surface layer (layer A) and the other surface layer (layer B) is obtained by differential scanning calorimetry (DSC) measurement A laminated polyester film in which the curve is a layer having at least two crystallization peaks, and the layer having the peak contains a single polyester in an amount of 85% by weight or more based on the entire layer.
(2) At least one peak crystallization peak temperature of the layer having at least two crystallization peaks (first crystallization peak (Tcc-1)) is observed at 138 to 145 ° C., and at least 1 (The second crystallization peak (Tcc-2)) is observed at 120 to 135 ° C., the laminated polyester film according to (1).
(3) The laminated polyester film according to claim 2, wherein the difference between the first crystallization peak (Tcc-1) and the second crystallization peak (Tcc-2) is 5 to 20 ° C.
(4) The laminated polyester film further has a layer (layer C) containing polyester as a main component, the layer C contains a resin a that is incompatible with polyester, and the content thereof is 3 with respect to the entire layer C. The laminated polyester film according to any one of (1) to (3), which is -40% by weight.
(5) The laminated polyester film according to any one of (1) to (4), wherein an average relative reflectance measured from at least one film surface side is 80% or more.
(6) The laminated polyester film according to any one of (1) to (5), wherein the amount of terminal carboxyl groups of the laminated polyester film is 25 eq / t or less.
(7) The laminated polyester film according to any one of (1) to (6), which is used for a solar battery backsheet.
(8) When used in a solar cell having a layer containing an ethylene-vinyl acetate copolymer, the surface layer having the at least two crystallization peaks is used in contact with the layer containing an ethylene-vinyl acetate copolymer (1 The laminated polyester film according to any one of (1) to (7).

ADVANTAGE OF THE INVENTION According to this invention, the laminated polyester film excellent in moisture-heat resistance and excellent in the adhesiveness with a back surface sealing material (EVA layer) is obtained even if it is left outdoors for a long time.

FIG. 1 is a cross-sectional view showing an example of a solar cell using the laminated polyester film of the present invention as a solar cell backsheet.

  Next, embodiments of the laminated polyester film of the present invention will be described in detail.

  The laminated polyester film of the present invention needs to be a laminated polyester film having at least two layers. When one surface layer is the surface layer (A) and the other surface layer is the surface layer (B), functional separation becomes possible and, for example, a base material layer for ensuring high light reflectance between the two (for example, This is necessary because functions such as a layer (C) described later) can be provided.

  If it is a single-layer polyester film, conflicting functions cannot coexist. For example, in order to obtain a high light reflectance, as described later, it is preferable to include a large number of cavities, but when the laminated polyester film of the present invention is used as a polyester film for a solar battery backsheet, If the surface layer on the side to be bonded to the sealant (7 in FIG. 1) contains a large number of cavities, the adhesion is reduced, so that the purpose of protecting the solar cell when the solar cell is incorporated cannot be achieved.

  In the laminated polyester film of the present invention, at least one of one surface layer (layer A) and the other surface layer (layer B) has a crystallization of at least two DSC curves obtained by differential scanning calorimetry (DSC) measurement. It is necessary that the layer has a peak. By using the polyester film of the present invention as a solar cell backsheet by having two crystallization peaks, at least one surface is a laminated polyester film excellent in wet heat resistance and adhesiveness with the EVA layer after wet heat treatment. be able to. On the other hand, when both surfaces have a single crystallization peak, the adhesive strength with the EVA layer after the wet heat treatment is inferior and is not suitable for practical use.

  Further, the layer having at least two crystallization peaks needs to contain a single polyester in an amount of 85% by weight or more based on the entire layer. If the layer having at least two crystallization peaks is less than 85% by weight of a single polyester with respect to the whole layer, the system becomes complicated and the cost becomes high, the stretching becomes unstable, and the oriented crystallization is moderate. Without progressing, the heat and humidity resistance deteriorates and the film-forming properties such as tearing deteriorate. Here, “containing a single polyester of 85% by weight or more with respect to the entire layer” means that one type of polyester is contained by 85% by weight or more with respect to the entire polyester constituting the layer. . As will be described later, one type of polyester may be a homopolyester or a copolyester.

  The polyester resin constituting the laminated polyester film of the present invention is a polymer obtained by condensation polymerization from a diol and a dicarboxylic acid, a hydroxycarboxylic acid, or a derivative thereof. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, and sebacic acid. Examples of the diol include those represented by ethylene glycol, trimethylene glycol, tetramethylene glycol and cyclohexanedimethanol.

  Specific examples of the polyester resin include polyethylene terephthalate, polytetramethylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalenedicarboxylate. It is done. In the present invention, polyethylene terephthalate is particularly preferably used. Various additives such as an antioxidant and an antistatic agent can be added to the polyester resin.

  Although the detailed expression mechanism in which the adhesive force differs depending on whether or not the at least one surface layer has two crystallization peaks is not clear, the present inventors consider as follows.

  A surface layer having at least two crystallization peaks means that there are relatively different environments of crystallinity and hydrophilic functional group amounts such as OH groups and COOH groups in the surface layer. When the adhesion strength with the EVA layer after the wet heat treatment is evaluated, the surface layer adheres to the EVA layer by absorbing moisture in a portion having high hydrophilicity (and / or a portion having low crystallinity). While the force is increased, it is considered that delamination is less likely to occur in a portion with a high degree of crystallinity (and / or a portion with low hydrophilicity) in order to prevent moisture from entering.

  Further, it is considered that at least one surface layer has at least two crystallization peaks because of a difference in crystallinity, hydrolysis from extrusion to cooling, or both. When producing a polyester film by melt film formation, the polyester resin composition constituting the polyester film is melt-kneaded with an extruder and then extruded and cooled and solidified on a cooling drum to obtain an unoriented laminated polyester film In this case, the surface layer side (for example, the surface layer (layer A)) in contact with the cooling drum surface can suppress the promotion of crystallinity. Further, as will be described in detail in the description of the manufacturing process described later, crystallization is further suppressed by the cooling air chamber on the surface opposite to the cooling drum surface. This two types of cooling may be one of the factors that cause the surface layer to have two crystallization peaks. On the other hand, crystallization of the surface layer (for example, (layer B)) located on the surface opposite to the cooling drum surface is not suppressed as compared with the surface layer (layer A). For example, this tendency becomes prominent when a substrate layer described later is included, and the substrate layer includes particles having different thermal conductivities and cavities generated by the particles, and cooling is performed when the surface layers on both sides are compared. There may be differences in efficiency, resulting in at least two crystallization peaks, and a greater temperature difference between the peaks. Therefore, in the single layer film obtained by the usual prescription and manufacturing method, it is considered that the difference of the invention of the present application is observed as one peak without being able to be separated and observed by the measurement method described later.

  In the laminated polyester film of the present invention, the peak top temperature of the crystallization peak of the layer having at least two crystallization peaks is at least one (first crystallization peak (Tcc-1)) of 138 to 145 ° C. It is observed that at least one (second crystallization peak (Tcc-2)) is preferably observed at 120 to 135 ° C. When Tcc-1 is higher than 135 ° C and lower than 138 ° C, and Tcc-2 is higher than 135 ° C and lower than 138 ° C, the effect of increasing the adhesion with the EVA layer after wet heat treatment cannot be obtained sufficiently (Tcc-1 and Tcc-2 may be substantially one peak). Even when Tcc-1 exceeds 145 ° C or when Tcc-2 is less than 120 ° C, the effect of improving the adhesion with the EVA layer after the wet heat treatment may not be sufficiently obtained.

  In the laminated polyester film of the present invention, at least one surface layer preferably has a difference between Tcc-1 and Tcc-2 of 5 to 20 ° C. When the difference between Tcc-1 and Tcc-2 is in the above range, the effect of increasing the adhesion strength with the EVA layer after the wet heat treatment can be obtained particularly remarkably.

  In the laminated polyester film of the present invention, the polyester resin composition constituting the film preferably contains inorganic particles. Examples of inorganic particles contained in the polyester resin composition constituting the polyester film of the present invention include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, and calcium phosphate. Alumina, talc, kaolin, calcium fluoride, and the like can be used. Among these, it is a preferable embodiment to use titanium oxide from the viewpoints of weather resistance and light reflection characteristics.

  Examples of the titanium oxide include crystalline titanium oxides such as anatase titanium oxide and rutile titanium oxide.

  Further, in the laminated polyester film of the present invention, the polyester resin composition constituting the film contains the inorganic particles described above, and the content thereof is 0.5% by weight or more and 5% by weight with respect to the entire polyester composition. The following is preferable. When the content of the inorganic particles of the polyester resin composition constituting the film is less than 0.5% by weight, the ultraviolet resistance is insufficient, so that it cannot be installed outdoors, and the light reflection characteristics are not sufficient. The effect of improving the power generation efficiency may not be sufficiently obtained. On the other hand, if it exceeds 5% by weight, the hydrolysis resistance is deteriorated, and the fine gap generated between the inorganic particles and the polyester is a trigger, and the adhesion with the sealant after the wet heat treatment may be deteriorated. is there. A more preferable concentration is 1.5% by weight or more and 5% by weight or less.

  Moreover, it is preferable that the void content in the cross section of the film calculated | required by the measuring method mentioned later is 4% or more and 40% or less. If the void content is less than 4%, the light reflection characteristics may not be sufficient, and the power generation efficiency of the solar cell may not be improved. On the other hand, if it exceeds 40%, the film-forming property may be deteriorated, the mechanical strength and heat and heat resistance of the film may be deteriorated, and the adhesion after the wet heat treatment may be deteriorated. The method for forming a cavity in the polyester film and the layer for forming the cavity are not particularly limited, but the laminated polyester film of the present invention has polyester as a main component in addition to the surface layer (layer A) and the surface layer (layer B). It is preferable that it is the laminated polyester film which consists of three layers of the layer (layer C) to perform.

  Although the method of making a polyester film contain a cavity is not specifically limited, It can form by comprising a film from the polyester resin composition containing the resin a incompatible with a polyester resin and a polyester resin. In the polyester resin, a resin a that is incompatible with the polyester resin is finely dispersed and stretched (for example, biaxially stretched) to form a cavity around the resin a that is incompatible with the polyester resin. The The cavity formed in the film has a refractive index difference from that of the polyester resin, and light incident at the interface is reflected, so that a high reflectance can be obtained. The content of the incompatible resin a is preferably 3 to 40% by weight with respect to the whole layer C, more preferably 6% to 30% by weight, and still more preferably 8% to 15% by weight. % Or less. It is possible to obtain a high reflectance by increasing the amount of the resin a that is incompatible with the polyester resin, and it is possible to suppress a decrease in mechanical strength and improve productivity by reducing the amount added. Become. As the amount of the resin a that is incompatible with the polyester resin is increased, the number of cavity nuclei and the number of cavity layers increase, so that the reflectance is improved and the output characteristics are improved.

  The resin a incompatible with the polyester resin used in the present invention is not particularly limited as long as it is a resin incompatible with polyester. For example, poly-3-methylphthalene-1, poly-4-methylpentene-1, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, poly Melting point 180 selected from dimethylstyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, amorphous polyolefin, cyclic olefin copolymer resin, etc. Examples thereof include a polymer having a temperature of at least ° C.

Among these, polyolefins, particularly polymethylpentene and cyclic olefins are preferably used. The cyclic olefin copolymer resin is a copolymer composed of ethylene and at least one cyclic olefin selected from the group consisting of bicycloalkene and tricycloalkene.
In order to disperse the incompatible resin a in the polyester resin, it is effective to add a dispersion aid. The dispersion aid is a compound having an effect of promoting dispersion, and the effect is recognized in the following compounds.

  As such a dispersion aid, a thermoplastic polyester elastomer is preferably used. Examples of the dispersion aid include polyalkylene glycols such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, and polypropylene glycol, cyclohexanedimethanol copolymer, ethylene oxide / propylene oxide copolymer, and dodecylbenzenesulfonic acid. Examples include sodium, alkyl sulfonate sodium salt, glycerin monostearate, tetrabutylphosphonium, and paraaminobenzene sulfonate.

  Particularly preferred is polyalkylene glycol, and polyethylene glycol is more preferably used. A copolymer of polybutylene terephthalate and polytetramethylene glycol is also preferably used for improving the dispersibility of the incompatible polymer.

  The addition amount of the dispersion aid is preferably 3% by weight or more and 40% by weight or less with respect to the entire polyester resin composition constituting the layer containing the resin a incompatible with the polyester resin. It is possible to improve the dispersibility of the resin a that is incompatible with the polyester resin by increasing the amount of the dispersion aid added, and use it without damaging the original properties of the film base material by reducing the amount added. can do.

  Such a dispersion aid can be added in advance to the film base polymer to prepare a master polymer (master chip). Regarding the relationship with the optical characteristics, the dispersion diameter is extremely reduced up to the region of 3% by weight to 40% by weight by adding a dispersion aid, so that the number of cavity layers per the same thickness increases and reflection occurs. The rate is improved, contributing to higher efficiency of the solar cell module. In the region where the addition of the dispersion aid is larger than 40% by weight, even if the addition amount is increased, the dispersion diameter may not be reduced, and even if added, there may be no effect.

  The polyester resin composition used in the present invention includes a heat resistance stabilizer, an oxidation resistance stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an organic / inorganic lubricant, Additives such as system / inorganic particles, fillers, nucleating agents, dyes, dispersants, coupling agents, etc. may be blended.

  The laminated polyester film of the present invention preferably has a total film thickness in the range of 38 μm to 500 μm. When the thickness is less than 38 μm, the effects of the reflection performance of the reflection layer and the diffusion performance of the diffusion layer are insufficient, and the performance of improving the power generation efficiency may be insufficient. Moreover, when thickness is thicker than 500 micrometers, productivity will deteriorate, and when using the laminated polyester film of this invention as a solar cell backsheet, the weight of a solar cell backsheet may become heavy. More preferably, it is the range of 125 micrometers-500 micrometers, Most preferably, it is the range of 150 micrometers-500 micrometers.

  The laminated polyester film of the present invention is a laminated polyester film comprising at least two layers, and it is preferable that the layer thickness of at least one surface layer is 12 μm or more. When the layer thickness of the surface layer placed on the solar cell side is 12 μm or more, the ultraviolet light incident from the solar cell side can diffuse the light reflected by the reflective layer, and the power generation efficiency of the solar cell can be increased. It becomes possible. Moreover, when the layer thickness on the side opposite to the solar battery cell is 12 μm or more, it becomes possible to improve the ultraviolet resistance. From the above, it is preferable that both surface layers have a thickness of 12 μm or more from the viewpoint of improving power generation efficiency and ultraviolet resistance. Further, since it is known that the polyester film is gradually reduced by ultraviolet rays or rain and wind, it is more preferably 20 μm or more.

  The polyester resin composition constituting the laminated polyester film of the present invention preferably has an intrinsic viscosity of 0.5 or more and 1.0 or less from the viewpoint of mechanical properties and heat resistance. More preferably, it is 0.7 or more and 0.9 or less.

  Moreover, in the polyester resin composition which comprises the lamination | stacking polyester film of this invention, the amount of terminal carboxyl groups (henceforth a COOH end group amount may be called) is 25 eq. / T (equivalent / ton) or less is preferable from the viewpoint of heat and humidity resistance. More preferably, 14 eq. / T or less.

  When the laminated polyester film of the present invention is used as a solar battery back sheet, the laminated polyester film of the present invention has an average relative reflectance of 80% or more measured from at least one film surface side. It is preferable because power generation efficiency can be improved. When the average relative reflectance is less than 80%, the effect of improving the power generation efficiency of the solar cell module may not be sufficiently obtained.

  As a manufacturing method of the laminated polyester film of the present invention, for example, a manufacturing method (coextrusion method) including a step of feeding raw materials of a surface layer and a base material layer into separate extruders and extruding them from a T-die into a sheet shape, a single film In the laminated polyester film of the present invention, the co-extrusion method described later can be used. Is preferred.

  In the present invention, the above-described method for laminating the base material layer and the surface layer will be specifically described, but the scope of the present invention should not be construed as being limited by the specific examples shown below.

  Use cyclic olefin as resin a which is incompatible with polyester resin, use polyethylene glycol as dispersion aid, and polybutylene terephthalate and polytetramethylene glycol copolymer, mix these with polyethylene terephthalate, and mix well It is made to dry and it supplies to the extruder B heated to the temperature of 270-300 degreeC. Separately, polyethylene terephthalate containing inorganic particles such as titanium oxide is supplied to the extruder A, and the base material layer and the surface layer are laminated by extruding the polymer from the extruder A and the extruder B, respectively, in the T die die. Sheet.

  The sheet thus melted and laminated is closely cooled and solidified by electrostatic force on a drum having a drum surface temperature cooled to 10 to 60 ° C. to obtain an unstretched film.

The laminated polyester film of the present invention is preferably produced, for example, by a production method that satisfies the following (1) to (6).
(1) The method includes a step (casting step) in which a polyester resin composition constituting a polyester film is melt-kneaded with an extruder and then extruded and cooled and solidified on a cooling drum to obtain an unoriented laminated polyester film.
(2) A process of obtaining a uniaxially oriented laminated polyester film by stretching the unoriented polyester film obtained by (1) in the longitudinal direction at a stretching temperature of 70 to 120 ° C. and a stretching ratio of 2.0 to 4.0 times. Including.
(3) The biaxially oriented laminated polyester obtained by stretching the uniaxially oriented laminated polyester film obtained in the step (2) in the width direction at a stretching temperature of 70 to 150 ° C. and a stretching ratio of 3.0 to 4.0 times. Including the step of obtaining a film.
(4) A step of relaxing 0 to 10% in the width direction while heat-treating the biaxially oriented laminated polyester film obtained in the step (3) at 205 to 240 ° C.
(5) including a step (winder step) of winding the biaxially oriented laminated polyester film relaxed in (4) into a roll shape.
Further, it is preferably obtained by a production method satisfying (6) to (7).
(6) In the casting step of (1), the temperature of the cooling drum is Tg−70 ° C. or higher and Tg−30 ° C. or lower of the polyester resin constituting the layer in contact with the cooling drum.
(7) In the casting step of (1), the time of contact with the cooling drum (residence time) is from 20 seconds to 120 seconds.

  Hereinafter, the manufacturing methods (1) to (7) will be described.

  In the laminated polyester film of the present invention, the polyester resin composition constituting the polyester film (surface layer, base material layer) is melt-kneaded with each extruder, then extruded, cooled and solidified on a cooling drum, and unoriented laminated. A coextrusion method for obtaining a polyester film is preferred. This is because in the melt laminating method, the adhesion between the surface layer and the base material layer is weak and easily peeled off.

  In the casting step of (1), when the surfaces that contact the cooling drum are the drum surface (D surface) and the non-drum surface (non-D surface), the drum surface is cooled by the cooling drum, and the non-drum surface is 10 − It is considered that a film that is difficult to tear can be formed by cooling with air at 20 ° C., and further, it can have the two crystallization temperatures as described above. Moreover, it is preferable that the temperature of a cooling drum is the glass transition temperature (henceforth Tg) -70 degreeC-Tg-30 degrees C or less of the polyester resin which comprises a surface layer. By setting the temperature of the cooling drum in the above range, it is possible to proceed to the longitudinal stretching while maintaining the thermal crystallization degree of the polyester resin constituting the unoriented polyester film in an appropriate range. When it is out of the above range, the thermal crystallization degree on the drum surface side does not fall within an appropriate range, which may cause film tearing. The temperature of the cooling drum is preferably Tg−60 ° C. or higher and Tg−35 ° C. or lower, and Tg−55 ° C. or higher and Tg−40 ° C. or lower of the polyester resin constituting the layer in contact with the cooling drum. It is particularly preferred.

  Further, the time of contact with the cooling drum (residence time) is preferably 20 seconds or more and 120 seconds or less. By contacting the cooling drum, the drum surface side transfers the unevenness of the cooling drum, so that the maximum roughness of the drum surface can be reduced to 2 μm or less, and can have the two crystallization temperatures as described above. it is conceivable that. If it is shorter than 20 seconds, the polymer is rapidly cooled, so that thermal crystallization occurs greatly, and the film may be broken after the longitudinal stretching. Moreover, the unevenness | corrugation of a drum cannot fully be transcribe | transferred to a film, and maximum roughness may be unable to be made into the said preferable range. If the cooling drum is in contact with the cooling drum for more than 60 seconds, the drum will be huge or the drum rotation speed will be considerably slow, which is not economical and the thermal crystallization is too small. May cause film tearing. The time of contact with the cooling drum (residence time) is preferably 20 seconds or longer and 60 seconds or shorter, and particularly preferably 25 seconds or longer and 45 seconds or shorter.

  The cooled film is first stretched in the longitudinal direction. At this time, it is preferable to obtain a uniaxially oriented laminated polyester film by stretching at a stretching temperature of 70 to 120 ° C. and a stretching ratio of 2.0 to 4.0 times. Producing in this range is preferable because the durability of the resulting polyester film and the adhesion after wet heat treatment can be improved while maintaining good productivity.

  Stretching in the width direction is guided to a tenter while holding both ends of the film with clips, and stretched 3 to 4 times in a direction perpendicular to the longitudinal direction (width direction) in an atmosphere heated to a temperature of 70 to 150 ° C. It is preferable to do. By setting the stretching temperature and the stretching ratio in the longitudinal direction and the width direction within the above ranges, the occurrence of film breakage or the like can be suppressed, the productivity can be improved, and the EVA adhesion after the wet heat treatment can be improved.

  When a biaxially oriented laminated polyester film is heat treated at 205-240 ° C. and includes a step of relaxing 0-10% in the width direction, it is easy to maintain the surface shape (maximum roughness) formed on the surface layer as it is It becomes.

  It is preferable to include a step of uniformly cooling in the next step, followed by cooling to room temperature and winding. Since the film produced by winding can be transported in large quantities at once, it is economical.

  By using the above-described laminated polyester film of the present invention as a solar battery back sheet, a solar battery having high light reflection characteristics and excellent wet heat resistance and adhesion after wet heat treatment can be obtained. When the laminated polyester film of the present invention is used in a solar battery backsheet of a solar battery having a layer containing an ethylene-vinyl acetate copolymer, the surface layer having at least two crystallization peaks is an ethylene-vinyl acetate copolymer. When it is used so as to be in contact with a layer containing, it is preferable because it maintains high adhesiveness with the back surface sealing material (EVA) of the solar cell even when placed outdoors for a long time. And a solar cell is laminated | stacked in order of the cover material, front side sealing material, a photovoltaic cell, a back side sealing material, and the above-mentioned solar cell backsheet of this invention, and can be heated.

In the present invention, the method of laminating and heating each of the above materials is specifically a method of thermocompression bonding by applying pressure in a temperature environment equal to or higher than the melting point of the sealing material at atmospheric pressure, or a vacuum state. However, from the viewpoint of suppressing the generation of bubbles in the solar cell, it is preferable to pressurize in a vacuum state and perform thermocompression bonding. It is an aspect.
By disposing the diffusion layer between the back-side sealing material and the reflective layer, light that passes through the gap between the solar cells and is reflected by the reflective layer can be more efficiently incident on the solar cells. It becomes possible.

A schematic configuration of the solar cell of the present invention is shown in FIG.
FIG. 1 is a cross-sectional view showing an example of a solar cell using the laminated polyester film of the present invention as a solar cell back sheet when the laminated polyester film of the present invention has a three-layer laminated structure having a surface layer and a base material layer. It is. In the solar cell backsheet 2, the surface layer 7 and the base material layer 8 are laminated, and the surface layer 7 is preferably located on the sealing material 3 side.

  The cover material used by this invention is a material located in the outermost surface of a solar cell, and glass is often used in the part irradiated with sunlight directly. Cover material is transparent to sunlight, mechanically resistant to electrical insulation, snow and wind pressure, weather resistance to acid rain, long-term temperature, humidity and ultraviolet rays, and scratch resistance when sand and solar cells are installed Additionality is required.

  Examples of the sealing material used for the solar cell include EVA, silicone resin, polyurethane, and modified polyolefin. Among these, EVA is preferably used from the viewpoint of weather resistance, adhesion to other members, and member costs. In this application, it aims at the EVA adhesive force which is a main sealing material being high.

Hereinafter, the laminated polyester film of the present invention will be described using examples.
[Methods for measuring physical properties and methods for evaluating effects]
The characteristic value evaluation method and the effect evaluation method are as follows.

(1) The thickness of the polyester film and the thickness of each layer:
The thickness of the polyester film was measured according to JIS C2151: 2006. The polyester film was cut in the thickness direction using a microtome to obtain a section sample. Using a field emission scanning electron microscope (FE-SEM) S-800 manufactured by Hitachi, Ltd., three points were imaged at a magnification of 3000 times, and the average value of the layer thickness was determined from the three points. Measurement was made and the total thickness, which is the sum of the thickness of each layer and the thickness of each layer, was calculated.

(2) Cavity content in the film cross section:
The film was cut in the thickness direction with a microtome, and a cross section of the obtained sample was imaged at three points with a magnification of 3000 times using a Hitachi Field Emission Scanning Electron Microscope (FE-SEM) S-800. The area ratio of the cavity was calculated from the three points of imaging, and the ratio of the area of the entire cavity film in the cross-sectional direction of each layer or each layer was calculated from the average value according to the following formula.
The ratio of the area of the entire hollow film or each layer in the cross-sectional direction = the area of the hollow in the visual field / the entire film or the area of each layer in the visual field.

(3) Amount of terminal carboxyl group (in the table, described as COOH amount)
The amount of terminal carboxyl groups was measured according to the following conditions according to the method of Malice. 2 g of polyester film was dissolved in 50 mL of o-cresol / chloroform (weight ratio 7/3) at a temperature of 80 ° C., titrated with a 0.05N KOH / methanol solution, the amount of terminal carboxyl groups was measured, and equivalent / polyester 1 It is expressed in tons. In addition, the indicator at the time of titration uses phenol red, and the place where it changed from yellowish green to light red is set as the end point of titration.
If there is insoluble matter in the solution in which the polyester composition is dissolved, the solution is filtered and the weight of the filtrate is measured, and the value obtained by subtracting the weight of the filtrate from the weight of the measurement sample is measured. To do. (Document M. J. Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)).
(4) Intrinsic viscosity In 100 ml of orthochlorophenol, a measurement sample (polyester resin (raw material) or polyester film) is dissolved (solution concentration C (measurement sample weight / solution volume) = 1.2 g / ml). The viscosity at 0 ° C. was measured with an Ostwald viscometer. Similarly, the viscosity of the solvent was measured. [Η] was calculated according to the following formula (I) using the obtained solution viscosity and solvent viscosity, and the obtained value was defined as intrinsic viscosity (IV).
ηsp / C = [η] + K [η] ² · C (I)
(Where ηsp = (solution viscosity / solvent viscosity) −1, K is the Huggins constant (assuming 0.343))
In addition, when there existed insoluble matters, such as inorganic particles, in the solution in which the measurement sample was dissolved, the measurement was performed using the following method.
i) A measurement sample is dissolved in 100 mL of orthochlorophenol to prepare a solution having a solution concentration higher than 1.2 mg / mL. Here, let the weight of the measurement sample used for orthochlorophenol be a measurement sample weight.
ii) Next, the solution containing the insoluble matter is filtered, and the weight of the insoluble matter and the volume of the filtrate after filtration are measured.
iii) Adding orthochlorophenol to the filtrate after filtration, (measurement sample weight (g) −insoluble matter weight (g)) / (volume of filtrate after filtration (mL) + volume of orthochlorophenol added) (ML)) is adjusted to 1.2 g / 100 mL.
(For example, when a concentrated solution having a measurement sample weight of 2.0 g / solution volume of 100 mL was prepared, the weight of insoluble matter when the solution was filtered was 0.2 g, and the filtrate volume after filtration was 99 mL Adjust to add 51 mL of orthochlorophenol ((2.0 g-0.2 g) / (99 mL + 51 mL) = 1.2 g / mL))
iv) Using the solution obtained in iii), the viscosity at 25 ° C. is measured using an Ostwald viscometer, and the obtained solution viscosity and solvent viscosity are used to calculate [η] according to the above formula (C). And the obtained value is taken as the intrinsic viscosity (IV).

(5) Film formation stability:
Whether the polyester film can be stably formed was evaluated according to the following criteria.
○: A film can be stably formed for 24 hours or more.
Δ: Film can be stably formed for 12 hours or more and less than 24 hours.
X: Breakage occurs within 12 hours, and stable film formation is not possible. Or a film sufficient for evaluation cannot be obtained.

(6) Power generation improvement rate by modularization:
The flux “HOZAN H722” was applied to the front and back silver electrode portions of the polycrystalline silicon solar cell “Gintech G156M3” with a dispenser, and the length of 155 mm was applied to the front and back silver electrodes. Wiring material “Hitachi Cable Co., Ltd. copper foil SSA-SPS0.2 × 1.5 (20)” cut at 10 mm from one end of the cell on the surface side is the end of the wiring material, and the back side is the surface side And a soldering iron was used to contact the soldering iron from the back surface side of the cell, and the front surface and the back surface were simultaneously soldered to produce one cell string. Next, the longitudinal direction of the wiring material protruding from the cell of the produced 1 cell string and the longitudinal direction of the extraction electrode “copper foil A-SPS 0.23 × 6.0 manufactured by Hitachi Cable, Ltd.” cut into 180 mm are perpendicular to each other. Then, the flux was applied to the portion where the wiring material and the extraction electrode overlapped, and solder welding was performed, and strings with extraction electrodes were produced. At this time, the short-circuit current was measured according to the standard state of JIS C8914: 2005, and the power generation performance of the cell alone was obtained.
Next, the solar cells are set in the lower order as shown in FIG.
-190 mm x 190 mm glass as cover material (3.2 mm thick white plate heat-treated glass for solar cells manufactured by Asahi Glass Co., Ltd.)
-190mm x 190mm ethylene-vinyl acetate as the front side sealing material (Samvik's sealing material 0.5mm thickness)
・ Strings with extraction electrode that evaluated the power generation performance of the cell alone ・ 190mm × 190mm ethylene-vinyl acetate as the back side sealing material (0.5mm thick sealing material manufactured by Sanvik)
・ Polyester film for backsheet to be measured (polyester film with the surface layer on the ethylene-vinyl acetate side and cut into 190mm x 190mm)
Set the set so that it comes into contact with the hot plate of the vacuum laminator from the cover material side, vacuum laminate under the conditions of hot plate temperature 145 ° C, evacuation 4 minutes, press 1 minute and holding time 10 minutes, solar cell Got a module. At this time, the strings with extraction electrodes were set so that the glass surface was on the cell surface side. The obtained solar cell module was subjected to measurement of a short-circuit current measured according to the standard state of JIS C8914: 2005, and set as the power generation performance after modularization.
From the power generation performance of the single cell thus obtained and the power generation performance after modularization, the performance improvement rate by modularization was calculated according to the following formula.
-Power generation improvement rate by modularization (%) = ((power generation performance after modularization / power generation performance of single cell) × 100) −100 (%).

(7) Inorganic particle content The measurement sample is weighed and the weight is m1. The weighed sample is placed on a sample boat, and the sample boat is placed in a muffle furnace and incinerated at 900 ° C. The sample boat is cooled to room temperature in a desiccator and weighed to m ² . The inorganic particle content (% by mass) is calculated by the following formula. This trial is performed five times, and the arithmetic average is taken as the content (% by mass).
(M2-m) / m1 × 100 where m is the weight of the sample boat.

(8) Evaluation of adhesion strength with EVA sheet The adhesion strength with the EVA sheet was measured based on JIS K 6854-2 (1999). An EVA sheet (manufactured by Sanvic Co., Ltd., fast cure type (500 μm thick sheet)) is stacked on the surface layer (layer having at least two crystallization peaks) of the laminated polyester film, and further a semi-tempered glass having a thickness of 3 mm thereon. After being vacuumed using a commercially available glass laminator, press treatment was performed at 135 ° C. under a load of 29.4 N / cm ² for 15 minutes to produce an evaluation sample (pseudo solar cell module sample). A test sample for adhesion strength test was prepared with a test piece having a width of 10 mm and a length of 150 mm. As for the peeling method, the semi-tempered glass and the EVA sheet were held on one side, the base material layer and the surface layer were held on the other side, 180 ° peeling was performed, and the number of measurements was n = 3. The average value of the three measured values was determined as the adhesion strength value as follows.
In addition, when any surface layer did not have the layer which has two crystallization peaks, both surfaces were evaluated and evaluated by the value with the higher adhesion strength.
A: When the adhesion strength is 40 N / 10 mm or more B: When the adhesion strength is 30 N / 10 mm or more and less than 40 N / 10 mm C: When the adhesion strength is 20 N / 10 mm or more and less than 30 N / 10 mm D: Adhesion strength When it is less than 20 N / 10 mm, A to C are good, and A is the best among them.

(9) Adhesion after wet heat test (adhesion strength with EVA sheet after wet heat test)
In the same manner as in (8) above, an evaluation sample (pseudo solar cell module sample) was prepared, and the pressure cooker manufactured by Tabai Espec Co., Ltd. was used for 48 hours under conditions of a temperature of 120 ° C. and a relative humidity of 100% RH. Processed. Then, according to the said (8) term, the adhesive strength with the EVA sheet | seat after a wet heat test was measured, and it determined as follows.
A: When the adhesion strength is 40 N / 10 mm or more B: When the adhesion strength is 30 N / 10 mm or more and less than 40 N / 10 mm C: When the adhesion strength is 20 N / 10 mm or more and less than 30 N / 10 mm D: Adhesion strength When it is less than 20 N / 10 mm, A to C are good, and A is the best among them.

(10) Using an average relative reflectance spectrophotometer U-3410 (manufactured by Hitachi, Ltd.), spectral reflectance in the wavelength range of 400 to 700 nm is measured at intervals of 10 nm, and the average value is average relative reflection. Rate. The number of samples was n = 5, each average relative reflectance was measured, and the average value was calculated. The measuring unit used an integrating sphere (model number 130-0632) with a diameter of 60 mm, and a 10 ° inclined spacer was attached. Moreover, aluminum oxide (model number 210-0740) was used for the standard white plate. In addition, when a film is a laminated | multilayer film, it measures from the polyester layer side of this invention.

(11) Crystallization temperature (peak top temperature of crystallization peak)
In accordance with the method described in JIS K7122 (JIS Handbook 1999 edition), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Electronics Industry Co., Ltd. was used, and a disk session “SSC / 5200” was used for data analysis. The glass transition temperature Tg and the crystallization peak of the polyester resin composition were measured. When there were a plurality of crystallization peaks, the highest temperature side was Tcc-1, and the lowest temperature side was Tcc-2. In the case of the shoulder peak, the temperature at the inflection point was read. In the measurement, the surface layer of the film is first peeled off (if it is not peeled off), 5 mg of this surface layer sample is weighed in a sample pan, and the temperature rise rate is 20 ° C./min. The sample was heated at a rate of temperature rise / minute, held in that state for 5 minutes, then rapidly cooled to 25 ° C. or less, and again heated from room temperature to 300 ° C. at a rate of temperature rise of 20 ° C./minute. . After Tg in the obtained 2ndRun DSC curve (crystallization enthalpy), the temperature at the peak top (and inflection point) of the crystallization peak (and shoulder peak) before the melting peak was defined as the crystallization temperature Tcc.

  Next, the present invention will be described using examples. However, the present invention is not construed as being limited by these examples.

Example 1
(polyethylene terephthalate)
100 parts by weight of terephthalic acid, 57.5 parts by weight of ethylene glycol, 0.03 part by weight of manganese acetate (1.35 mol / t in terms of Mn metal element), 0.03 part by weight of antimony trioxide at 150 ° C. in a nitrogen atmosphere After melting, the temperature was raised to 230 ° C. over 3 hours with stirring, methanol was distilled off, and the transesterification reaction was completed. After the transesterification reaction, 0.005 parts by weight of phosphoric acid (corresponding to 0.52 mol / t in terms of P element) and 0.021 parts by weight of sodium dihydrogen phosphate dihydrate (1.3 mol / t in terms of P element) Equivalent) was dissolved in 0.5 parts by weight of ethylene glycol, and an ethylene glycol solution (pH 5.0) was added. Thereafter, the polymerization reaction was carried out at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr to obtain polyethylene terephthalate having an intrinsic viscosity of 0.52 and a carboxyl group amount of 16 eq / t. The obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours, and then subjected to solid phase polymerization at 220 ° C. and a vacuum degree of 0.3 Torr for 8 hours to obtain an intrinsic viscosity of 0.85 and a terminal carboxyl group amount of 10.2 eq. / T, melting point 255 ° C., glass transition temperature Tg of 82 ° C. Polyethylene terephthalate 1 was obtained.

(Base material layer (layer C))
72.5% by weight of polyethylene terephthalate 1 prepared by the above-described method for the base material and copolymer 1 of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, trade name: “Hytrel” manufactured by Toray Du Pont Co., Ltd.) (Registered trademark)) 9% by weight, copolymer polyethylene terephthalate 1 (PET / CHDM) obtained by copolymerizing 33 mol% of 1,4-cyclohexanedimethanol in all diol units, 9% by weight, as an incompatible polymer 9% by weight of ethylene-norbornene copolymer 1 (COC) having a glass transition temperature Tg of 190 ° C. as a cyclic olefin copolymer and 50% by weight of titanium dioxide having a number average secondary particle size of 0.25 μm as inorganic particles. Dispersed titanium dioxide master chip 1 (titanium dioxide based on the total amount of master chips 0% by weight, the master chip contains only polyethylene terephthalate 1 as a polyester component) 0.5% by weight is adjusted and mixed to form a base material layer, which is dried at 180 ° C. for 3 hours, and then 270 An extruder B heated to a temperature of ˜300 ° C. was charged.

(Surface layer (layer A, layer B))
On the other hand, a titanium dioxide master chip 1 in which 76% by weight of the polyethylene terephthalate 1 prepared as a raw material constituting the surface layer and 50% by weight of titanium dioxide having a number average secondary particle size of 0.25 μm are dispersed as inorganic particles. Is adjusted and mixed with 24% by weight to obtain a surface layer material. This is vacuum-dried at a temperature of 180 ° C. for 3 hours and then charged into the extruder A heated to a temperature of 280 ° C.

(Laminated polyester film)
The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: 12 was laminated through a laminating apparatus so as to be formed into a sheet shape from a T die, and the layer A side was brought into contact with a cooling drum having a surface temperature of 25 ° C. and cooled and solidified for 40 seconds. Meanwhile, the side not in contact with the drum was cooled by applying 15 ° C. air at a wind speed of 20 m / sec. The unstretched film thus obtained was introduced into a roll group heated to a temperature of 85 to 98 ° C., longitudinally stretched 3.4 times in the longitudinal direction, and cooled by a roll group having a temperature of 21 ° C. Subsequently, both ends of the longitudinally stretched film thus obtained were guided to a tenter while being held with clips, and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 120 ° C. . Thereafter, heat setting at a temperature of 200 ° C. is carried out in a tenter, and after uniform cooling, cooling to 25 ° C., winding the surface in contact with the drum when cooled and solidified as a wound outer surface, a polyester film having a thickness of 150 μm Got. The power generation improvement rate by modularization when the obtained polyester film is used as a solar battery back sheet is 8.1%, and the physical properties are as shown in Table 1. The film formation was stable and the adhesion after wet heat treatment was also good.

(Example 2)
Polyethylene terephthalate 1 prepared by the above method is 24.5% by weight, polybutylene terephthalate-polytetramethylene glycol copolymer 1 is 25% by weight, copolymer polyethylene terephthalate 1 is 25% by weight, incompatible As a polymer, 25% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer material, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 136: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were inferior to Example 1. Was at a satisfactory level (Table 1).

Example 3
54.5% by weight of polyethylene terephthalate 1 prepared by the above method, 15% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 15% by weight of copolymerized polyethylene terephthalate 1 are incompatible. 15% by weight of polymethylpentene 1 (PMP, trade name: “TPX” (registered trademark) manufactured by Mitsui Chemicals, Inc.) as a polymer and 0.5% by weight of titanium dioxide master chip 1 as an inorganic particle are mixed and mixed. It was set as the material C, and this was dried at a temperature of 180 ° C. for 3 hours, and then charged into an extruder B heated to a temperature of 270 to 300 ° C. The surface layer material was the same as in Example 1. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 136: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. 1).

(Example 4)
69.5% by weight of polyethylene terephthalate 1 prepared by the above method, 10% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 10% by weight of copolymerized polyethylene terephthalate 1 are incompatible. As a polymer, 10% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 136: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were inferior to Example 1. Was at a satisfactory level (Table 1).

(Example 5)
90.5% by weight of polyethylene terephthalate 1 prepared by the above method, 3% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 3% by weight of copolymerized polyethylene terephthalate 1, incompatible As a polymer, 3% by weight of polymethylpentene 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at 180 ° C. for 3 hours, and then 270 to 300 ° C. An extruder B heated to a temperature was charged. The surface layer material was the same as in Example 1. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 136: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were inferior to Example 1. Was at a satisfactory level (Table 1).

(Example 6)
A base material layer material was prepared in the same procedure as in Example 4, and this was dried at a temperature of 180 ° C. for 3 hours, and then charged into an extruder B heated to a temperature of 270 to 300 ° C. The surface layer material was the same as in Example 1. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 136: It was laminated through a laminating apparatus so as to be 12, formed into a sheet shape from a T die, contacted with a cooling drum having a surface temperature of 25 ° C., and the layer A was cooled and solidified for 20 seconds. Other than that, film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. The film formation stability and EVA adhesion were inferior to Example 1, but at a level with no problem (Table 1). .

(Example 7)
9.5% by weight of polyethylene terephthalate 1 prepared by the above method, 30% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 30% by weight of copolymerized polyethylene terephthalate 1, and incompatible As a polymer, 30% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as that of Example 1 except that 70% by weight of polyethylene terephthalate 1 and 30% by weight of titanium dioxide master chip were used. The polymer supplied to the extruders A and B is A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layer A and the layer B are the same), and the film layer has a thickness ratio of 25: 300: The film was laminated through the laminating apparatus so as to be 25, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were at the same level as in Example 1. (Table 1).

(Example 8)
A base material layer material was prepared by the same procedure as in Example 1, dried for 3 hours at a temperature of 180 ° C., and then charged into an extruder B heated to a temperature of 270 to 300 ° C. The surface layer material was the same as that of Example 1 except that the polyethylene terephthalate 1 was 84% by weight and the titanium dioxide master chip was 16% by weight. The polymer supplied to the extruders A and B is A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 6:26: The film was laminated through the laminating apparatus so as to be 6, and the film was formed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, the film formation stability and EVA adhesion were somewhat in Example 1. It was inferior but no problem level (Table 2).

Example 9
A base material layer material was prepared in the same procedure as in Example 4, and this was dried at a temperature of 180 ° C. for 3 hours, and then charged into an extruder B heated to a temperature of 270 to 300 ° C. The surface layer material was the same as that of Example 1 except that 70% by weight of polyethylene terephthalate 1 and 30% by weight of titanium dioxide master chip were used. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: It was laminated through a laminating apparatus so as to be 12, formed into a sheet form from a T die, and the layer A side was brought into contact with a cooling drum having a surface temperature of 25 ° C. and cooled and solidified for 100 seconds. Otherwise, film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were at the same level as in Example 1 (Table 2).

(Example 10)
69.5% by weight of polyethylene terephthalate 1 prepared by the above method, 10% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 10% by weight of copolymerized polyethylene terephthalate 1 are incompatible. As a polymer, 10% by weight of polymethylpentene 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at 180 ° C. for 3 hours, and then 270 to 300 ° C. An extruder B heated to a temperature was charged. The surface layer material was the same as in Example 1. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were inferior to Example 1. Was at a satisfactory level (Table 2).

(Example 11)
81.5% by weight of polyethylene terephthalate 1 prepared by the above method, 6% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 6% by weight of copolymerized polyethylene terephthalate 1 are incompatible. As a polymer, 6% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as Example 1 except that polyethylene terephthalate 1 was 99% by weight and titanium dioxide master chip was 1% by weight. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 226: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were inferior to Example 1. Was at a satisfactory level (Table 2).

(Example 12)
90.5% by weight of polyethylene terephthalate 1 prepared by the above method, 3% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 3% by weight of copolymerized polyethylene terephthalate 1, incompatible As a polymer, 3% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as that of Example 1 except that 80% by weight of polyethylene terephthalate 1 and 20% by weight of titanium dioxide master chip were used. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 25:60: The film was laminated through the laminating apparatus so as to be 25, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were inferior to Example 1. Was at a satisfactory level (Table 2).

(Example 13)
The surface layer material was the same as in Example 12. The polymer supplied to the extruder A was adjusted to have a thickness of 160 μm, and a film without a base material layer as compared with Example 1 (the layer structure is A / B, and the raw materials constituting the layers A and B are the same) ) When the evaluation was performed, the film formation stability was good and the EVA adhesion after the wet heat treatment was at a level with no problem, but the reflectance was low (Table 2).

(Example 14)
81.5% by weight of polyethylene terephthalate 1 prepared by the above method, 6% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 6% by weight of copolymerized polyethylene terephthalate 1 are incompatible. As a polymer, 6% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were the same as in Example 1. It became a level (Table 2).

(Example 15)
63.5% by weight of polyethylene terephthalate 1 prepared by the above method, 12% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 12% by weight of copolymerized polyethylene terephthalate 1, As a polymer, 12% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, film formation stability and EVA adhesion were the same as in Example 1. It became a level (Table 2).

(Comparative Example 1)
9.5% by weight of polyethylene terephthalate 1 prepared by the above method, 20% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 20% by weight of copolymerized polyethylene terephthalate 1 are incompatible. As a polymer, 50% by weight of polymethylpentene 1 and 0.5% by weight of titanium dioxide master chip 1 are adjusted and mixed to form a base material layer, which is dried at a temperature of 180 ° C. for 3 hours, and then 270 to 300 ° C. An extruder B heated to a temperature was charged. The surface layer material was the same as in Example 1. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: It was laminated through a laminating apparatus so as to be 12 and formed into a sheet form from a T die, and the layer A was brought into contact with a cooling drum having a surface temperature of 25 ° C. and cooled and solidified for 15 seconds. Other than that, film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. As a result, the film formation stability was poor and EVA adhesion after wet heat treatment was low (Table 3).

(Comparative Example 2)
96.5% by weight of polyethylene terephthalate 1 prepared by the above method, 1% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 1% by weight of copolymerized polyethylene terephthalate 1 and incompatible As a polymer, 1% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. The film formation stability was good, but the reflectance was Compared to the examples, the EVA adhesion after wet heat treatment was also low (Table 3).

(Comparative Example 3)
72.5% by weight of polyethylene terephthalate 1 prepared by the above method, 9% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 9% by weight of copolymerized polyethylene terephthalate 1, and incompatible As a polymer, 9% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1 except that 38% by weight of polyethylene terephthalate 1 and 62% by weight of titanium dioxide master chip were used. The polymer supplied to the extruders A and B is A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 50:50: The film was laminated through the laminating apparatus so as to be 50, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. The film formation stability was good, but after wet heat treatment The EVA adhesion was also low (Table 3).

(Comparative Example 4)
72.5% by weight of polyethylene terephthalate 1 prepared by the above method, 9% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 9% by weight of copolymerized polyethylene terephthalate 1, and incompatible As a polymer, 9% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1. The polymer supplied to the extruders A and B becomes A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 3:30: 3 was laminated through a laminating apparatus to form a sheet from a T die, and the layer A was brought into contact with a cooling drum having a surface temperature of 25 ° C. and cooled and solidified for 10 seconds. Otherwise, the film was formed in the same procedure as in Example 1, and the samples were collected and evaluated. The film-forming stability was slightly inferior to that of the desperate example, the reflectance was low, and the EVA adhesion after wet heat treatment was also low. It became low (Table 3).

(Comparative Example 5)
72.5% by weight of polyethylene terephthalate having a larger amount of COOH than polyethylene terephthalate 1 prepared by the above method, 9% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and copolymerized polyethylene terephthalate 1 9% by weight, 9% by weight of an ethylene-norbornene copolymer 1 as an incompatible polymer, and 0.5% by weight of a titanium dioxide master chip 1 are mixed to form a base material layer. After drying for a period of time, it was put into an extruder B heated to a temperature of 270 to 300 ° C. The surface layer material was the same as in Example 1. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: It was laminated through a laminating apparatus so as to be 12 and formed into a sheet form from a T die, and the layer A was brought into contact with a cooling drum having a surface temperature of 25 ° C. and cooled and solidified for 15 seconds. Otherwise, the film was formed in the same procedure as in Example 1, and the samples were collected and evaluated. The film formation stability was good, but the COOH terminal amount of the entire film was 30 eq / t, The EVA adhesion after the heat treatment was also low (Table 3).

(Comparative Example 6)
72.5% by weight of polyethylene terephthalate 1 prepared by the above method, 9% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, 9% by weight of copolymerized polyethylene terephthalate 1, and incompatible As a polymer, 9% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1 except that 60% by weight of polyethylene terephthalate 1 and 40% by weight of titanium dioxide master chip were used. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 12: 126: The film was laminated through the laminating apparatus so as to be 12, and film formation was performed in the same procedure as in Example 1, and samples were collected and evaluated. The film formation stability was good, but after wet heat treatment The EVA adhesion was also low (Table 3).

(Comparative Example 7)
1.5% by weight of polyethylene terephthalate 1 prepared by the above method, 19% by weight of copolymer 1 of polybutylene terephthalate and polytetramethylene glycol, and 19% by weight of copolymerized polyethylene terephthalate 1 are incompatible. As a polymer, 60% by weight of ethylene-norbornene copolymer 1 and 0.5% by weight of titanium dioxide master chip 1 were adjusted and mixed to form a base material layer, which was dried at a temperature of 180 ° C. for 3 hours. It was put into an extruder B heated to a temperature of 300 ° C. The surface layer material was the same as in Example 1 except that polyethylene terephthalate 1 was 70% by weight and titanium dioxide master chip was 30% by weight. The polymers supplied to the extruders A and B are converted into A / C / B (surface layer / base material layer / surface layer, the raw materials constituting the layers A and B are the same), and the film layer has a thickness ratio of 3: 144: 3 was laminated through the laminating apparatus, and the film was formed by the same procedure as in Example 1 except that the film forming property was remarkably low, and an evaluable sample could not be obtained (Table 3). .

Since the polyester film of the present invention is excellent in wet heat resistance and adhesiveness with a sealing material (EVA) after wet heat treatment, it can be suitably used for solar cell backsheet applications.

1: Solar cell 2: Solar cell backsheet 3: Back side sealing material 4: Front side sealing material 5: Cover material 6: Solar cell 7: Surface layer (Back side sealing material (layer containing ethylene-vinyl acetate copolymer) ) Side in contact with
8: Base material layer 9: Surface layer

Claims (8)

A laminated polyester film having at least two layers, wherein at least one of one surface layer (layer A) and the other surface layer (layer B) has at least a DSC curve obtained by differential scanning calorimetry (DSC) measurement. A laminated polyester film which is a layer having two crystallization peaks, and the layer having the peak contains a single polyester in an amount of 85% by weight or more based on the whole layer. As for the peak top temperature of the crystallization peak of the layer having the at least two crystallization peaks, at least one (first crystallization peak (Tcc-1)) is observed at 138 to 145 ° C., and at least one (first crystallization peak). The laminated polyester film according to claim 1, wherein a crystallization peak (Tcc-2) of 2 is observed at 120 to 135 ° C. The laminated polyester film according to claim 2, wherein a difference between the first crystallization peak (Tcc-1) and the second crystallization peak (Tcc-2) is 5 to 20 ° C. The laminated polyester film further has a layer (layer C) containing polyester as a main component, the layer C contains a resin a that is incompatible with the polyester, and the content thereof is 3 to 40 wt. The laminated polyester film according to any one of claims 1 to 3. The laminated polyester film according to any one of claims 1 to 4, wherein an average relative reflectance measured from at least one film surface side is 80% or more. The laminated polyester film according to any one of claims 1 to 5, wherein the amount of terminal carboxyl groups of the laminated polyester film is 25 eq / t or less. The laminated polyester film according to any one of claims 1 to 6, which is used for a solar battery backsheet. When used in a solar cell backsheet of a solar cell having a layer containing an ethylene-vinyl acetate copolymer, the surface layer having at least two crystallization peaks is used in contact with the layer containing an ethylene-vinyl acetate copolymer. The laminated polyester film according to any one of claims 1 to 7.

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