WO2012033141A1

WO2012033141A1 - Polyester film for solar cell, and easily adhesible polyester film for solar cell and front sheet equipped with the film

Info

Publication number: WO2012033141A1
Application number: PCT/JP2011/070404
Authority: WO
Inventors: 晃侍伊藤; 池畠　良知; 潤稲垣; 清水　亮; 村田　浩一; 澤崎　真治
Original assignee: 東洋紡績株式会社
Priority date: 2010-09-08
Filing date: 2011-09-07
Publication date: 2012-03-15
Also published as: JP6068802B2; JPWO2012033141A1

Abstract

The purpose of the present invention is to provide: a polyester film for a solar cell, which has excellent hydrolysis resistance and is rarely curled during processing; and an easily adhesible polyester film for a solar cell, which has good hydrolysis resistance and excellent adhesion properties and transparency; and a front sheet produced using the easily adhesible polyester film. This polyester film for a solar cell is characterized in that the lengths of crystals aligned in the lengthwise direction on face (-105) are 50 Å or longer as measured by a wide angle X-ray diffraction method, the film has an MOR value (MOR-C) of 1.0-2.0 when the thickness of the film is deemed as 50 μm, and the film has a density of 1.37-1.40 g/cm³. This easily adhesible polyester film for a solar cell comprises the above-mentioned polyester film for a solar cell and a coating layer that is mainly composed of a urethane resin and a block isocyanate and is formed on at least one surface of the polyester film.

Description

Polyester film for solar cell, easily adhesive polyester film for solar cell, and front sheet using the same

The present invention relates to a solar cell polyester film suitable for a solar cell constituent material such as a solar cell backside sealing sheet and a solar cell protective sheet, and more specifically, for a solar cell that is excellent in hydrolysis resistance and hardly curls during processing. It relates to a polyester film. Moreover, this invention relates to the easily adhesive polyester film for solar cells, and a front sheet using the same. Specifically, when used on the surface of the solar cell in contact with the encapsulant, the easily adhesive polyester film for solar cells having excellent transparency and high transparency even under high temperature and high humidity, and the same It is related with the front seat using.

In recent years, solar cells have attracted attention as an alternative to petroleum energy, which causes global warming, and the demand for solar cells is increasing. A solar cell is a photovoltaic power generation system that directly converts solar energy into electricity. As solar cell elements, semiconductors such as single crystal silicon, polycrystalline silicon, and amorphous silicon, compound-based or organic dyes, and the like are used. Generally, a solar cell element has several packagings for protecting a device over a long period (about 20 years or more) by wiring several to several tens of solar cell elements in series and in parallel. Done and unitized. A unit incorporated in this package is called a solar cell module.

Here, in general, a solar cell module is a heat- and weather-resistant plastic material whose surface to which sunlight is applied is covered with glass, the solar electronic element under the surface is filled with a sealing material, and the back surface is called a back sheet It is the structure protected by the protective sheet which consists of several layer structures, such as these. As the sealing material for filling the solar cell element, an olefin resin such as ethylene / vinyl acetate copolymer resin (hereinafter EVA), polyvinyl butyral resin (hereinafter PVB) or the like is used. Using these sealing materials, a module is manufactured by superposing the glass substrate / sealing material / solar cell element / sealing material / back sheet and then heat-pressing with a vacuum laminator or the like. The sealing material has a role of adhering and fixing the solar cell element, preventing moisture from entering from the outside, and protecting the solar cell element.

Conventionally, it has been common to use glass as a surface protection member of a solar cell module. In recent years, there has been an increasing interest in plastic films such as polyester having flexibility in terms of impact resistance and weight reduction (Patent Documents 1 to 5). Further, as a constituent member of the back sheet for sealing the back surface of the solar cell module, an inexpensive and cost-effective polyester film is used.

However, when a polyester film is used as a solar cell member under high temperature and high humidity for a long time, the ester bond site in the molecular chain is hydrolyzed, resulting in a problem that the mechanical strength is lowered. For this reason, there is a limit to use in high-temperature and high-humidity environments and outdoors. It is known that the hydrolysis of polyester proceeds faster as the carboxyl end concentration (acid value) of the polyester molecular chain is higher. Until now, in order to improve the hydrolysis resistance of polyester, various studies have been made to keep the carboxyl terminal concentration (acid value) of the film resin low (Patent Documents 6 and 7). In addition, polyesters having a relatively high molecular weight (relatively high intrinsic viscosity) are used in order not to greatly reduce the mechanical strength even if the deterioration has progressed to some extent (Patent Documents 8 to 11).

Also, the polyester film constituting the inner layer (the side facing the solar cell element) of the front sheet or the back sheet is required to have adhesiveness with the sealing material. However, the surface untreated polyester film cannot obtain sufficient adhesiveness and is required to be improved. As a method for improving the adhesion of the polyester film, it has been proposed to provide an adhesive layer containing a resin or a crosslinking agent (Patent Documents 12 to 15).

JP 2010-186932 A JP 2007-253463 A JP 2006-261287 A JP-A-11-261085 JP 2000-114565 A JP 2007-150084 A JP 2007-204538 A JP 2002-134770 A JP 2002-26354 A JP 2006-270025 A JP 2008-31680 A JP 2006-152013 A JP 2006-332091 A JP 2007-48944 A JP 2007-136911 A

The film proposed in the above-mentioned patent document shows an improvement in hydrolysis resistance as compared with a conventional polyester film by improving the resin composition. However, when the film is used for a long period of time in a harsh usage environment, these films sometimes break early, unlike the initial assumption. Furthermore, when using a polyester film as a solar cell member, it is used as a laminated body bonded with a sealing material layer or a barrier layer. In recent years, the processing temperature at the time of producing a laminate is increasing due to the improvement in productivity. Therefore, the quality of the laminate may be deteriorated due to curling, wrinkles and the like due to the thermal dimensional stability of the film.

Therefore, in view of the above problems, an object of the present invention is to provide a solar cell polyester film that has excellent hydrolysis resistance and is less likely to curl during processing.

Furthermore, in order to improve the photoelectric conversion efficiency of the solar cell element, high transparency is required for the front sheet used on the front surface of the solar cell. In addition, solar cell modules that are used outdoors under severe environmental conditions are expected to have a lifetime of 20 years or longer. For this reason, not only the initial adhesiveness but also the high adhesiveness of the sealing material easy-adhesive film used as a member must be maintained for a long period of time even under high temperature and high humidity. However, when an easy-adhesion layer containing a cross-linking agent is provided in order to improve the adhesion with the sealing material, the transparency may be lowered.

In addition, various composition types including additives such as a crosslinking agent and an ultraviolet absorber are used for the sealing material from the viewpoint of improving productivity and preventing deterioration. Therefore, various packaging processes have been adopted depending on the sealing material used. For example, in the case of a sealing material that is a standard cure type, after temporary bonding by thermocompression bonding (for example, 5 to 10 minutes at 90 to 130 ° C.), heat treatment (for example, 30 to 50 minutes at 140 to 160 ° C.) is performed. Adhesive conditions that slowly cure the encapsulant are employed. On the other hand, in the case of a fast-cure type sealing material, an adhesive condition is employed in which heat-pressure bonding (for example, 15 to 20 minutes at 140 to 160 ° C.) is performed in a short time to rapidly cure the sealing material. Therefore, it is desirable to have a highly versatile and easy-to-adhere film that can cope with various bonding conditions as well as high versatility that shows the same degree of adhesion to various sealing materials.

Furthermore, components such as front seats and back seats are required to have high durability that can withstand long-term outdoor use. As measures to improve the durability of the polyester film, it has been proposed to keep the carboxyl terminal concentration (acid value) of the polyester resin low, or to use a polyester resin having a relatively high molecular weight (relatively high intrinsic viscosity). ing. However, even if the resin composition is improved, when the film is used for a long period of time in a harsh usage environment, these films may be damaged earlier than originally assumed.

In view of the above problems, an object of the present invention is to provide an easily-adhesive polyester film for solar cells having excellent hydrolysis resistance, excellent adhesion to a sealing material, and high transparency. . More preferably, the present invention provides an easily-adhesive polyester film for solar cells that hardly causes a decrease in adhesion under high temperature and high humidity and has good adhesion to various sealing materials. .

Polyester film for solar cell The present inventors have examined the occurrence of breakage that occurs earlier than expected as described above, and found that this is due to the balance between the in-plane orientation and crystallinity. In other words, it was found that if the balance of orientation and crystallinity is poor, the original weather resistance of the resin cannot be expressed even if the physical properties of the polyester resin such as carboxyl end concentration and intrinsic viscosity are improved. Furthermore, the surprising effect that the hydrolysis resistance outstanding as a solar cell use was exhibited by controlling the orientation and crystallinity of a polyester film was discovered.

Furthermore, as a result of intensive studies by the present inventor, surprisingly, a coating layer is formed from a coating liquid containing urethane resin and blocked isocyanate as main components and adjusting the dissociation temperature of the blocked isocyanate and the boiling point of the blocking agent. As a result, it has been found that the adhesiveness to the sealing material is excellent and high transparency can be maintained. Based on the above findings, we have completed a highly durable polyester film for solar cells and an easily adhesive polyester film for solar cells that have both high durability and high adhesion.

The polyester film for solar cells of the present invention has a length of crystals oriented in the longitudinal direction in the (−105 plane) measured by wide-angle X-ray diffraction method of 50 mm or more, and the MOR value when the film thickness is converted to 50 μm. The value (MOR-C) is 1.0 to 2.0, and the density of the film is 1.37 to 1.40 g / cm ³ . The heat shrinkage rate at 150 ° C. of the film is preferably −1.0% or more and 3.0% or less in both the longitudinal direction and the width direction, more preferably −0.5% or more and 0.5%. It is as follows. The polyester constituting the film is polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof and a phosphorus compound having a phenol moiety, and the carboxyl terminal concentration is 25 eq / ton or less of the polyester, The intrinsic viscosity (IV) of the film is preferably 0.60 to 0.90 dl / g. MOR is an abbreviation for molecular orientation ratio, and MOR-C is an abbreviation for molecular orientation ratio-correction.

The easily adhesive polyester film for solar cells of the present invention has the above-described polyester film for solar cells and a coating layer formed on at least one surface of the polyester film, and the coating layer is mainly composed of a urethane resin and a blocked isocyanate. The dissociation temperature of the said block isocyanate is 130 degrees C or less, and the boiling point of a blocking agent is 180 degrees C or more, It is characterized by the above-mentioned. The urethane resin is preferably a urethane resin containing an aliphatic polycarbonate polyol as a constituent component. In the infrared spectroscopic spectrum of the coating layer, the ratio of the absorbance at the peak near 1460 cm ⁻¹ derived from the aliphatic polycarbonate component (A ₁₄₆₀ ) to the absorbance at the peak near 1530 cm ⁻¹ derived from the urethane component (A ₁₅₃₀ ) ( A ₁₄₆₀ / A ₁₅₃₀ ) is preferably 0.50 to 1.55. The mass ratio of urethane resin to blocked isocyanate (urethane resin / block isocyanate) in the coating solution is preferably 1/9 to 9/1.

The present invention also includes a solar cell front sheet including the above-described easily adhesive polyester film for solar cells.

The polyester film for solar cells of the present invention has good hydrolysis resistance and is less likely to curl during processing. Moreover, the polyester film for solar cells of the present invention can be provided with good productivity. Therefore, it can be suitably applied as a solar cell member.
The easily-adhesive polyester film for solar cells of the present invention has good hydrolysis resistance, excellent adhesion to a sealing material, and high transparency. More preferably, it exhibits strong adhesiveness even under various sealing materials and bonding conditions, and is particularly excellent in adhesiveness (humidity heat resistance) under high temperature and high humidity. Therefore, when the easily adhesive polyester film for solar cells of the present invention is used as a member of a front sheet, high photoelectric conversion efficiency is maintained and adhesiveness with a sealing material is good.

As described above, the present inventor has found that the breakage of the film that occurs earlier than expected due to long-term use in a high-temperature and high-humidity environment is due to the balance between orientation characteristics and crystallinity in the film plane. First, regarding the balance of the orientation characteristics, if there is a difference in the orientation characteristics in the film plane, a difference in the intensity balance in the in-plane direction results. For this reason, as the hydrolysis proceeds, the mechanical strength decreases at a substantially constant speed in each direction (longitudinal direction and width direction), so that the difference in strength balance in the initial state becomes relatively large. Thereby, the deterioration of the film loses the balance of the mechanical strength in the film plane, and the film breaks from a relatively weak portion. Therefore, in order to improve the durability of the film, it is preferable not only to modify the polyester resin composition but also to have a good orientation balance in the film plane. In particular, in a generally performed sequential biaxial stretching method in the longitudinal direction (MD direction) -width direction (TD direction), the orientation tends to remain on the stretching axis in the subsequent width direction (TD direction). Differences in mechanical strength within the film surface due to differences are likely to occur. Therefore, maintaining the orientation characteristics in the longitudinal direction is suitable for controlling the balance of mechanical strength in the film plane.

Next, regarding the crystallinity, when the crystallinity of the entire film increases, the brittleness increases when degradation due to hydrolysis proceeds, and the film breaks easily. On the other hand, when the orientation of the entire film is lowered, the film strength as an absolute value is weakened and the strength as a solar cell member cannot be maintained. Therefore, it is preferable to lower the crystallinity while keeping the orientation high. In the film, polyester crystal forms include oriented crystals having directionality mainly due to stretch orientation and thermal crystals mainly due to heating and cooling. Therefore, by reducing the number of thermal crystals while maintaining the orientation crystal, the balance of crystallinity is controlled by lowering the crystallinity while maintaining high orientation as the whole film, thereby improving the durability of the film. You can plan.

That is, the characteristics of the polyester film for solar cells of the present invention based on the above technical idea are that the length of the crystals oriented in the longitudinal direction in the (−105 plane) measured by wide-angle X-ray diffraction method is 50 mm or more, and the film thickness The MOR value (MOR-C) when converted to 50 μm is 1.0 to 2.0, and the density of the film is 1.37 to 1.40 g / cm ³ .

The length of the crystal oriented in the longitudinal direction on the (−105) plane of the polyester film for solar cells measured by wide-angle X-ray diffraction is 50 mm or more, preferably 53 mm or more, more preferably 54 mm or more. The crystal size in the longitudinal direction (MD direction) on the (−105) plane mainly indicates oriented crystals by stretching in the longitudinal direction (MD direction), and the crystal size depends on the orientation strength. Therefore, when the crystal size of the (−105) plane in the longitudinal direction (MD direction) is in the above range, the film orientation is high and the solar cell member has a specific strength. Further, in the sequential biaxial stretching method in the longitudinal direction (MD direction) -width direction (TD direction) that is generally performed, the orientation tends to remain on the stretching axis in the width direction (TD direction) in the subsequent stage. Differences in mechanical strength within the film surface due to differences are likely to occur. Therefore, maintaining the orientation in the longitudinal direction within the above range is suitable for controlling the balance of the mechanical strength in the film plane. The length of the crystal is preferably 60 mm or less. When the crystal length is larger than 60 mm, stretching in the width direction is difficult, and productivity may be deteriorated due to breakage during film formation. In order to control the crystal size, it is preferable to increase the orientation strength of the film by increasing the stretching ratio or decreasing the stretching temperature.

The polyester film for solar cell has a MOR value (MOR-C) of 1.0 to 2.0, preferably 1.3 to 1.8, more preferably 1 when the film thickness is converted to 50 μm. .4 to 1.7. MOR-C is an index indicating the balance between the film longitudinal direction and the width direction. Controlling the MOR-C of the film within the above range and controlling the orientation balance in the film plane is effective in maintaining mechanical strength and durability in a long-term hydrolysis degradation test. In addition, curling that occurs when the solar cell member is laminated with another functional layer can be suppressed, which is effective in improving adhesion. As a method for bringing MOR-C into the above range, there may be mentioned controlling the ratio of the stretching ratio in the longitudinal direction (MD direction) and the width direction (TD direction) in the stretching step.

The polyester film for solar cells has a film density of 1.370 to 1.400 g / cm ³ , preferably 1.375 to 1.398 g / cm ³ , more preferably 1.380 to 1.395 g / cm ³ . ³ . The density of the film is an index indicating the crystallinity of the entire film. By keeping the film density relatively low in the above range, the film is hardly broken even when deterioration due to hydrolysis proceeds, and durability is maintained. In order to control the film density to the above range while controlling the crystal size of the oriented crystal by stretching orientation to the above range, it is desirable to suppress thermal crystallization. Since the thermal crystal of the film is likely to grow in the heat setting step during film formation, it is preferable to lower the heat setting temperature in order to bring the film density to the above range. In addition, when a film contains the microparticles | fine-particles mentioned later, let the density of the polyester component except these microparticles | fine-particles be a film density.

The above-mentioned polyester film for solar cells exhibits excellent durability by making the above properties highly compatible. That is, the above properties do not contribute independently, and it is important for the excellent hydrolysis resistance of the present invention that they are indispensably combined. The polyester film for solar cells has an elongation retention at 200 ° C., 100% RH, 0.03 MPa, and 200 hours, which is an evaluation of hydrolysis resistance, preferably 65% or more, more preferably 70% or more. It is. By being in such a range, the polyester film for solar cells can exhibit high hydrolysis resistance that can withstand long-term outdoor use.

The solar cell polyester film preferably has a thermal shrinkage rate at 150 ° C. of −1.0% or more in both the longitudinal direction (MD direction and longitudinal direction) and the width direction (TD direction and lateral direction). Preferably, it is −0.5% or more, preferably 3.0% or less, more preferably 2.0% or less, and still more preferably 1.8% or less. In addition, for example, when a more severe low thermal shrinkage rate is required as a solar cell member such as use at high temperature and precision in high temperature processing, the thermal shrinkage rate at 150 ° C. is determined in the longitudinal direction (MD direction, longitudinal direction) and the width direction. Both (TD direction and lateral direction) are preferably −0.5% to 0.5%. Thereby, generation | occurrence | production of the curl etc. at the time of heat processing, such as the time of forming an adhesion layer etc., or a lamination state can be suppressed. Examples of the method for setting the heat shrinkage rate at 150 ° C. in the above range include controlling the stretching conditions or performing longitudinal relaxation treatment and lateral relaxation treatment in the heat setting step.

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

(polyester)
The polyester constituting the polyester film for solar cells is an aromatic dicarboxylic acid or ester thereof such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid, ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol or the like. Polyester produced by polycondensation with glycol. These polyesters are prepared by a method in which an aromatic dicarboxylic acid and a glycol are directly reacted; a method in which an alkyl ester of an aromatic dicarboxylic acid and a glycol are transesterified and then polycondensed; a diglycol ester of an aromatic dicarboxylic acid is subjected to a polycondensation. It can be produced by a method of condensation; This polyester may be a copolymer of the third component, but a homopolymer is preferred from the viewpoint of durability. Representative examples of such polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and the like.

As the polyester polycondensation catalyst, antimony and / or a compound thereof, titanium and / or a compound thereof, germanium and / or a compound thereof, tin and / or a compound thereof, aluminum and / or a compound thereof can be used. In particular, the suppression of thermal oxidative degradation is advantageous when the metal content is low, and it is particularly preferable to use a small amount of aluminum and / or a compound thereof and a phosphorus compound as a promoter to ensure polymerization activity. Further, the phosphorus compound preferably has a phenol moiety. The phosphorus compound containing a phenol moiety has an effect of suppressing polyester degradation that decomposes under a radical mechanism under oxygen. In order to enhance this function, it is preferable that the phenol moiety has a hindered phenol skeleton that is sterically and electronically stabilized and exhibits more radical trapping ability.

Further, after polymerizing the polyester, the thermal stability of the polyester can be further enhanced by removing the catalyst from the obtained polyester or deactivating the catalyst by adding a phosphorus compound or the like.

The degree of heat-resistant oxidation of polyester can be indicated by a thermal stability parameter (TS) represented by the following formula. When exhibiting high thermal stability, the thermal stability parameter (TS) of the polyester is preferably 0.25 or less, more preferably 0.20 or less. By using the polyester in which the TS falls within the above range, the thermal stability in the melting step when the film is produced is excellent, and high durability can be achieved.

TS is calculated by the following method. 1 g of polyester (intrinsic viscosity [IV] _f ) is placed in a glass test tube and vacuum dried at 130 ° C. for 12 hours. Subsequently, after maintaining in a molten state at 300 ° C. for 2 hours under a non-circulating nitrogen atmosphere, the sample is taken out and frozen and pulverized. After it is vacuum dried, the intrinsic viscosity ([IV] _f ) is measured. For example, when the polyester is polyethylene terephthalate, it can be calculated by the following formula.
TS = 0.245 × {[IV] _f ^-1.47- [IV] _i ^-1.47 }

During the polymerization of polyester, dialkylene glycol is by-produced. When the solar cell member is exposed to a high temperature for a long time, the durability may be lowered due to the influence of dialkylene glycol. Taking diethylene glycol as an example of typical dialkylene glycol, the amount of diethylene glycol is preferably 2.3 mol% or less, more preferably 2.0 mol% or less, and even more preferably 1.8 mol% or less. . By making the amount of diethylene glycol within the above range, the heat resistance stability can be improved, and the increase in the carboxyl terminal concentration (the increase in acid value) due to decomposition during drying and molding can be further reduced. Although the amount of diethylene glycol is preferably small, it is produced as a by-product during the esterification reaction of terephthalic acid and the ester exchange reaction of dimethyl terephthalate during polyester production. It is 0 mol%, further 1.2 mol%.

In the present invention, in order to provide durability of the polyester film for solar cells, it is preferable to use a polyester having an intrinsic viscosity of more than 0.60 dl / g as a raw material resin. Moreover, the intrinsic viscosity of the polyester constituting the polyester film for solar cells is preferably 0.60 to 0.90 dl / g, more preferably 0.65 to 0.75 dl / g, and still more preferably 0.68 to 0. 72 dl / g. When the intrinsic viscosity of the film is lower than 0.60 dl / g, the hydrolysis resistance and heat resistance of the film may be inferior. Moreover, when it is higher than 0.90 dl / g, productivity may deteriorate.

The carboxyl terminal of polyester has an action of promoting hydrolysis by autocatalysis. Therefore, it is preferable that the carboxyl terminal density | concentration of the polyester film for solar cells of this invention is 25 eq / ton or less with respect to polyester. When the carboxyl terminal concentration is 25 eq / ton or less, high hydrolysis resistance as a solar cell member can be suitably achieved. The carboxyl terminal concentration is preferably 20 eq / ton or less, more preferably 18 eq / ton or less, and still more preferably 16 eq / ton or less with respect to the polyester. The carboxyl terminal concentration is preferably low, but is preferably 0.5 eq / ton or more from the viewpoint of productivity. In addition, the measurement of the carboxyl terminal density | concentration of polyester can be measured by the titration method mentioned later or NMR method.

In order to set the carboxyl terminal concentration of the polyester film within the above range, the carboxyl terminal concentration of the polyester chip used as the raw material resin is preferably less than 25 eq / ton. Moreover, in order to make the intrinsic viscosity of a polyester film into the said range, it is preferable that the intrinsic viscosity of the polyester chip used as raw material resin shall be 0.60 dl / g or more. Setting the carboxyl terminal concentration and intrinsic viscosity of the polyester chip to the above ranges can be performed by appropriately selecting the polymerization conditions of the resin. For example, production equipment factors such as the structure of the esterification reaction apparatus, composition ratio of dicarboxylic acid and glycol in the slurry supplied to the esterification reaction tank, esterification reaction temperature, esterification reaction pressure, esterification reaction time, etc. What is necessary is just to set reaction conditions or solid-state polymerization conditions etc. suitably. In particular, the solid phase polymerization method can be suitably employed from the viewpoint of productivity. Furthermore, it is preferable to control the moisture content of the polyester chip or to control the resin temperature in the melting step. It is also a preferable method to block the carboxyl terminal of the polyester with an epoxy compound or a carbodiimide compound. Since the film of the present invention has balanced orientation characteristics, good durability can be maintained by setting the carboxyl terminal concentration and intrinsic viscosity of the polyester within the above ranges.

The polyester film for solar cells of the present invention may contain fine particles for the purpose of imparting slipperiness. Examples of the fine particles to be contained include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, and zinc sulfide, but are not particularly limited.

If the particles are added to such an extent that the film has sufficient slipperiness, the transparency of the entire film may be lowered. Therefore, the polyester film for solar cells has a multilayer structure of three or more layers, and it is also a preferable aspect that at least the outermost layer contains inorganic or organic particles for improving slipperiness. Furthermore, in the easily adhesive polyester film for solar cells described later, when high transparency is required, a configuration in which particles are contained only in the coating layer without containing particles in the polyester film serving as a substrate is also preferable.

The fine particles preferably have an average particle size of 0.01 μm or more and 10 μm or less, more preferably 0.05 μm or more and 8 μm or less, and most preferably 0.1 μm or more and 3 μm or less. The average particle size of the fine particles is measured by the following method. Take a picture of the particles with a scanning electron microscope (SEM), and at a magnification such that the size of one smallest particle is 2-5 mm, the maximum diameter of 300-500 particles (between the two most distant points) The average value is defined as the average particle size (number basis).

The content of the fine particles is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less in the polyester resin constituting the outermost layer. When the content of the fine particles is smaller than 0.01% by mass, the film is less slippery, so that scratches are generated due to friction with a roll or the like in the process, and handling property in post-processing is decreased. Absent. Moreover, when content of particle | grains exceeds 5 mass%, there exists a possibility that it may become difficult to control a haze value and film surface roughness in a suitable range.

It is also preferable to add an ultraviolet absorber in the polyester film in order to improve the weather resistance as a solar cell front sheet. In this case, the light transmittance (wavelength 380 nm) of the film is preferably 20% or less, and more preferably 15% or less. Here, the light transmittance is measured in a direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type). In order to exhibit excellent weather resistance, it is preferable that the light transmittance (wavelength 380 nm) is low, but when a large amount of the ultraviolet absorber is added, the ultraviolet absorber may bleed out to the film surface. Therefore, the lower limit of the light transmittance (wavelength 380 nm) is preferably 0.001%.

A known substance can be used as the ultraviolet absorber. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency. Examples of organic ultraviolet absorbers include benzotriazoles, benzophenones, cyclic iminoesters, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. From the viewpoint of durability, benzotriazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

At this time, the concentration of the UV absorber in the master batch is preferably 1 to 30% by mass in order to uniformly disperse the UV absorber and economically blend it. Is preferably low. As a condition for producing the master batch, it is preferable to use a kneading extruder and to extrude at a temperature not lower than the melting point of the polyester raw material and not higher than 290 ° C. for 1 to 15 minutes. Above 290 ° C, the weight loss of the UV absorber is large, and the viscosity of the master batch is greatly reduced. When the extrusion temperature is 1 minute or less, uniform mixing of the UV absorber becomes difficult. At this time, if necessary, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added.

Furthermore, if necessary, other additives can be contained in the polyester. Examples of the additive include a fluorescent brightening agent, an infrared absorbing dye, a heat stabilizer, an antioxidant, a light resistance agent, an antigelling agent, an organic wetting agent, an antistatic agent, and a surfactant. As the antioxidant, aromatic amine type, phenol type and the like antioxidants can be used. As the stabilizer, phosphorous, phosphoric acid ester and other phosphorous, sulfur and amine stabilizers can be used.

The method for producing the polyester film for solar cells of the present invention is arbitrary and is not particularly limited. For example, it can be produced as follows.

The polyester chip obtained by polymerization is melted with an extruder, the resin is extruded from the die into a sheet shape, and taken out with a cooling roll to form an unstretched film. The maximum temperature of the polyester resin in the extruder is preferably 280 ° C or higher, more preferably 290 ° C or higher. By raising the melting temperature, the back pressure at the time of filtration in the extruder is lowered, and good productivity can be achieved. However, when the resin temperature is higher than 310 ° C., the thermal deterioration of the resin proceeds, which is not preferable. Therefore, the maximum temperature of the polyester resin in the extruder is preferably 310 ° C. or less, and more preferably 300 ° C. or less. If the melting temperature is too high, thermal degradation of the polyester proceeds, the carboxyl terminal concentration of the polyester increases, and the hydrolysis resistance may decrease.

Next, a method for stretching the obtained film will be described. In sequential biaxial stretching, the obtained unstretched film is heated with a heated roll or a non-contact heater, and then stretched in the longitudinal direction (roll stretching) between rolls having a speed difference, and then uniaxially stretched with a clip. After both ends are held and heated in an oven, the film is stretched in the width direction and heat-fixed by applying higher heat (tenter stretching).

The draw ratio in the longitudinal direction is preferably 3.0 to 4.5 times, more preferably 3.5 to 3.8 times. The stretching temperature in the longitudinal direction is preferably 90 to 110 ° C. The draw ratio in the width direction is preferably 3.2 to 4.8 times, more preferably 3.5 to 4.5 times. The stretching temperature in the width direction is preferably 120 to 150 ° C. The ratio of the stretching ratio in the longitudinal direction to the stretching ratio in the width direction is preferably (stretching ratio in the longitudinal direction) / (stretching ratio in the width direction) = 0.8 to 1.0. In any case, it is preferable to appropriately control the film so as to obtain the aforementioned predetermined characteristics as a film within the above range.

When the solar cell member requires higher thermal dimensional stability, it is desirable to perform longitudinal relaxation treatment. As a method of longitudinal relaxation processing, a known method can be used. For example, a method of performing longitudinal relaxation processing by gradually narrowing the clip interval of the tenter (Japanese Patent Publication No. 4-028218), A method of performing relaxation treatment by inserting a razor at the end and avoiding the influence of the clip (Japanese Patent Publication No. 57-54290) can be used. Moreover, you may use the method of applying heat off-line and mitigating. The heat shrinkage in the vertical and horizontal directions is preferably in the range of −1.0% to 3.0%, more preferably in the range of −0.5% to 0.5%. If the heat shrinkage is less than -1.0%, the film becomes a problem of deflection during processing. On the other hand, if it is larger than 3.0%, the shrinkage during processing is large and wrinkle-like wrinkles are generated, which is not preferable.

Further, in order to impart various functions such as adhesion, insulation, and scratch resistance, the film surface may be coated with a polymer resin by a coating method. Moreover, it is good also as a slippery polyester film by containing inorganic and / or organic particle | grains only in a coating layer. Furthermore, an inorganic vapor deposition layer or an aluminum layer can be provided to provide a water vapor barrier function.

The coating layer exhibiting easy adhesion is preferably provided by an aqueous coating solution containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Moreover, the coating layer formed from the polyurethane resin and block isocyanate which are mentioned later is also a preferable aspect. Examples of these coating liquids include water-soluble or water-dispersible copolyester resin solutions, acrylic resin solutions, polyurethane resin solutions disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, and the like. Etc. Such a coating layer may be provided after film formation (offline coating method) or during film formation (inline coating method), but from the point of productivity, during film formation. It is preferable to provide it.

The solar cell referred to in the present invention refers to a system that takes in incident light such as sunlight and room light, converts it into electricity, and stores the electricity. Surface protection sheet, high light transmission material, solar cell element, filler layer And a back surface sealing sheet. There are flexible properties depending on the application.

The polyester film for a solar cell of the present invention can be used as a base film (base film) for a back surface sealing sheet, a surface protection sheet, or a bonding material for a flexible electronic member. In particular, it is suitable as a base film for a solar cell backside sealing sheet that requires high durability and long-term thermal stability. The solar cell back surface sealing sheet protects the solar cell module on the back side of the solar cell.

The polyester film for solar cell back surface sealing of the present invention can be used as a solar cell back surface sealing sheet, either alone or in combination. The solar cell backside sealing sheet of the present invention may be laminated with a film having water vapor barrier properties, an aluminum foil or the like for the purpose of imparting water vapor barrier properties. As the barrier film, a polyvinylidene fluoride coating film, a silicon oxide vapor deposition film, an aluminum oxide vapor deposition film, an aluminum vapor deposition film, or the like can be used. These can be laminated on the polyester film for solar cell of the present invention via an adhesive layer or directly, or can be used in the form of a sandwich structure.

Easy-adhesive polyester film for solar cells (coating layer)
The easy-adhesive polyester film for solar cells of the present invention comprises a urethane resin and a blocked isocyanate having a dissociation temperature of 130 ° C. or lower and a blocking agent having a boiling point of 180 ° C. or higher, based on the polyester film for solar cells. It is important to have a coating layer formed from a coating solution as a main component. Here, the “main component” means that it is contained in an amount of 50% by mass or more, more preferably 70% by mass or more as a total solid component contained in the coating solution.

In order to provide easy adhesion, a flexible urethane resin is preferably used. Conventionally, from the point of improving the adhesion of the coating layer, it was considered desirable to introduce a cross-linked structure positively to make a strong coating layer. Therefore, isocyanate may be used as a cross-linking agent, but because of its high reactivity, it reacts with water in an aqueous coating solution to lose cross-linking reactivity or reacts with a urethane resin to produce aggregates. It tends to be easy. Therefore, the so-called pot life is short, and it is difficult to stably apply for a long time. Therefore, an isocyanate having a functional group blocked with a blocking agent that is dissociated by thermal addition may be used. However, due to the influence of the undissociated blocking agent, sufficient adhesion may not be obtained when high adhesion is required.
Further, depending on the type of blocked isocyanate, the transparency of the polyester film may be deteriorated. This is considered to be because minute uneven pinholes are formed on the coated surface when the dissociated blocking agent volatilizes at a high temperature.

As a result of intensive studies by the present inventor, excellent adhesion can be obtained by employing a coating liquid mainly composed of a urethane resin and a blocked isocyanate having a dissociation temperature of 130 ° C. or lower and a blocking agent having a boiling point of 180 ° C. or higher. And found that high transparency and high transparency can be obtained. That is, when the dissociation temperature exceeds the above temperature, it is considered that the dissociation of the blocking agent due to heat addition is insufficient, and a sufficient cross-linked structure cannot be obtained, resulting in a decrease in adhesion, particularly moist heat resistance. Moreover, when the boiling point of a blocking agent is less than the said temperature, it is thought that the blocking agent which remained in the application layer volatilizes by heat addition, and an application | coating external appearance falls.
The structure of the easily adhesive polyester film for solar cells of the present invention is described in detail below.

(Urethane resin)
The urethane resin contains at least a polyol component and a polyisocyanate component as constituent components, and further contains a chain extender as necessary. The urethane resin is a polymer compound in which these constituent components are copolymerized mainly by urethane bonds.

Examples of the polyol component include polyvalent carboxylic acids (for example, malonic acid, succinic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or acid anhydrides thereof and polyhydric alcohols (for example, Reaction of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, neopentylglycol, 1,6-hexanediol, etc.) Polyester polyols, polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol and other polyether polyols obtained from Triol compounds and polyolefin polyols, and acrylic polyols, and the like. Especially, it is preferable to contain the aliphatic polycarbonate polyol which is excellent in heat resistance and hydrolysis resistance in the polyol component which is a structural component of the said urethane resin. From the viewpoint of preventing yellowing due to sunlight, it is preferable to use an aliphatic polycarbonate polyol. In addition, the structural component of these urethane resins can be specified by nuclear magnetic resonance analysis or the like.

When an aliphatic polycarbonate component is included as a constituent component of the urethane resin, from the viewpoint of adhesiveness with the sealing material, the vicinity of 1460 cm ⁻¹ derived from the aliphatic polycarbonate component measured by infrared spectroscopy of the coating layer is used. The ratio (A ₁₄₆₀ / A ₁₅₃₀ ) between the absorbance (A ₁₄₆₀ ) and the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ derived from the urethane component is preferably 0.50 to 1.55.

In the conventional technical common sense, from the point of improving the durability of the coating layer, it was considered desirable to make the coating layer rigid and strong in forming the coating layer. However, in the present invention, by controlling the absorbance by infrared spectroscopy within a certain range in a polyurethane resin containing aliphatic polycarbonate polyol as a constituent component, it exhibits strong adhesion and adhesion under high temperature and high humidity heat. The property can be improved more suitably. Although the mechanism of improving adhesiveness with such a configuration is not well understood, the present inventor thinks as follows.

For example, when packaging a module, thermocompression bonding is performed at a high temperature in a configuration in which a polyester film (coating layer) having a surface protective material / sealing material / coating layer is laminated. Under the present circumstances, stress arises between a polyester film (coating layer) and a sealing material by the thermal contraction of the polyester film at the time of high temperature adhesion. In particular, the generation of such stress can also vary depending on various types of sealing materials and bonding conditions. In particular, in a standard cure type in which a high temperature takes a long time, the stress change accompanying the heat shrinkage of the film becomes large. As a result, it is considered that the stress is not completely relaxed and the adhesiveness with the sealing material is lowered. Furthermore, when such a laminated body is placed under high temperature and high humidity, degradation of the coating layer proceeds due to hydrolysis. As a result, it is considered that the stress cannot be withstood, the sealing material is peeled off, and the adhesiveness under high temperature and high humidity is lowered. Therefore, in order to maintain high adhesion to the sealing material and high adhesiveness under high temperature and high humidity, instead of simply imparting durability by firmly crosslinking the coating layer, heat resistance, It is considered desirable to have a component that retains hydrolysis resistance and to be flexible enough to withstand the stress. However, if it is simply flexible, when it is subjected to high-temperature thermocompression bonding in a short time as in the fast cure type, the sealing material partially dissolved in the coating layer will be eroded, especially the polyester film base after high-temperature and high-humidity treatment. It is considered that the adhesiveness with the material is lowered. Therefore, it is most desirable to make these conflicting characteristics compatible.

In the case where the main component is a urethane resin having an aliphatic polycarbonate polyol as a constituent component and a crosslinking agent, the absorbance (A ₁₄₆₀ ) around 1460 cm ⁻¹ derived from the aliphatic polycarbonate component measured by infrared spectroscopy and the urethane component _By setting the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ derived from 0.50 to 1.55, the above characteristics can be achieved more suitably. That is, the above characteristics can be achieved by coexisting an aliphatic polycarbonate component having hydrolysis resistance and a urethane component exhibiting toughness at a predetermined ratio and further adding a crosslinking agent. Thereby, since the stress due to the thermal contraction of the film at the time of thermal bonding at high temperature can be relieved, strong adhesiveness can be obtained even under various sealing materials and bonding conditions. Moreover, since the heat resistance and hydrolysis resistance are maintained even in a subsequent environment of high temperature and high humidity, the coating layer can be prevented from deteriorating.

Here, the absorbance around 1460 cm ⁻¹ (A ₁₄₆₀ ) is derived from the bending vibration unique to the CH bond of the methylene group contained in the aliphatic polycarbonate component. Therefore, the magnitude of the absorbance (A ₁₄₆₀ ) near 1460 cm ⁻¹ depends on the amount of the aliphatic polycarbonate polyol component constituting the urethane resin present in the coating layer. On the other hand, the absorbance (A ₁₅₃₀ ) in the vicinity of 1530 cm ⁻¹ is derived from the bending vibration specific to the N—H bond contained in the urethane component. Therefore, the magnitude of the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ depends on the amount of the urethane component constituting the urethane resin present in the coating layer. Therefore, these absorbance ratios (A ₁₄₆₀ / A ₁₅₃₀ ) indicate that both components having different characteristics coexist in a specific ratio. In the present invention, the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) is preferably 0.50 to 1.55. The lower limit of the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) is preferably 0.60, and more preferably 0.70. The upper limit of the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) is preferably 1.45, more preferably 1.35, and even more preferably 1.25. When the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) is less than 0.50, the amount of the hard urethane component is excessive, and the stress relaxation of the coating layer is lowered, so that the heat and humidity resistance may be lowered. In addition, when the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) exceeds 1.55, the aliphatic component of the flexible aliphatic polycarbonate is excessively increased, and the strength of the coating layer is lowered. May decrease.

Examples of the aliphatic polycarbonate polyol include an aliphatic polycarbonate diol and an aliphatic polycarbonate triol, and an aliphatic polycarbonate diol can be preferably used. Examples of the aliphatic polycarbonate diol that is a component of the urethane resin include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 3-methyl-1 , 5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,8-nonanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedi Examples thereof include aliphatic polycarbonate diols obtained by reacting one or more diols such as methanol with carbonates such as dimethyl carbonate, diphenyl carbonate, ethylene carbonate, and phosgene.

The number average molecular weight of the aliphatic polycarbonate diol is preferably 1500 to 4000, more preferably 2000 to 3000. When the number average molecular weight of the aliphatic polycarbonate diol is small, the ratio of the aliphatic polycarbonate component constituting the urethane resin is relatively small. Therefore, in order to make the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) within the above range, it is preferable to control the number average molecular weight of the aliphatic polycarbonate diol within the above range. When the number average molecular weight of the aliphatic polycarbonate diol is large, the absorbance (A ₁₄₆₀ ) around 1460 cm ⁻¹ derived from the aliphatic polycarbonate component increases and the aliphatic component increases. The strength after processing may be reduced. When the number average molecular weight of the aliphatic polycarbonate diol is small, a strong urethane component increases, and stress due to thermal shrinkage of the base material cannot be relieved, and adhesiveness may be lowered.

Examples of the polyisocyanate that is a component of the urethane resin include aromatic diisocyanates such as xylylene diisocyanate; alicyclic rings such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis (isocyanatomethyl) cyclohexane. Diisocyanates of formula; aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; or polyisocyanates obtained by adding these compounds in advance with trimethylolpropane or the like in a single or plural form. . When aromatic isocyanate is used, there is a problem of yellowing, which may not be preferable. Moreover, since it becomes a hard coating film compared with an aliphatic type | system | group, it becomes impossible to relieve | moderate the stress by the heat shrink of a base material, and adhesiveness may fall.

Examples of the chain extender include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol; ethylenediamine Diamines such as hexamethylenediamine and piperazine; aminoalcohols such as monoethanolamine and diethanolamine; thiodiglycols such as thiodiethylene glycol; or water. However, when a chain extender having a short main chain is used, the absorbance (A ₁₅₃₀ ) in the vicinity of 1530 cm ⁻¹ derived from the urethane component increases, and the flexibility of the coating layer may decrease. Therefore, a chain extender having a long main chain is preferable. From the viewpoint of imparting flexibility to the coating layer, a chain extender of diol or diamine having a length of 4 to 10 carbon atoms in the main chain is preferable. From these points, 1,4-butanediol, 1,6-hexanediol, hexamethylenediamine and the like are preferable as the chain extender used in the present invention. That is, in order to prevent a decrease in absorbance in the vicinity of 1530 cm ⁻¹ derived from the urethane component, straight chain and high molecular weight materials such as 1,4-butanediol, 1,6-hexanediol, and hexamethylenediamine are preferable.

The coating layer of the present invention is preferably provided by an in-line coating method described later using an aqueous coating solution. Therefore, it is desirable that the urethane resin of the present invention is water-soluble. In addition, said "water-soluble" means melt | dissolving with respect to water or the aqueous solution containing less than 50 mass% of water-soluble organic solvents.

In order to impart water solubility to the urethane resin, a sulfonic acid (salt) group or a carboxylic acid (salt) group can be introduced (copolymerized) into the urethane molecular skeleton. Since the sulfonic acid (salt) group is strongly acidic and it may be difficult to maintain moisture resistance due to its hygroscopic performance, it is preferable to introduce a weakly acidic carboxylic acid (salt) group. Moreover, nonionic groups, such as a polyoxyalkylene group, can also be introduce | transduced.

In order to introduce a carboxylic acid (salt) group into a urethane resin, for example, as a polyol component, a polyol compound having a carboxylic acid group such as dimethylolpropionic acid or dimethylolbutanoic acid is introduced as a copolymer component to form a salt. Neutralize with an agent. Specific examples of the salt forming agent include trialkylamines such as ammonia, trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine and tri-n-butylamine; N such as N-methylmorpholine and N-ethylmorpholine. -Alkylmorpholines; N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine; and the like. These can be used alone or in combination of two or more.

When a polyol compound having a carboxylic acid (salt) group is used as a copolymerization component in order to impart water solubility, the composition molar ratio of the polyol compound having a carboxylic acid (salt) group in the urethane resin is the total poly of the urethane resin. When the isocyanate component is 100 mol%, it is preferably 3 to 60 mol%, more preferably 5 to 40 mol%. If the composition molar ratio is less than 3 mol%, water dispersibility may be difficult. Moreover, when the said composition molar ratio exceeds 60 mol%, since water resistance falls, moist heat resistance may fall.

The glass transition temperature of the urethane resin of the present invention is preferably less than 0 ° C, more preferably less than -5 ° C. When the glass transition temperature is less than 0 ° C., the viscosity is close to that of partially melted olefin resin such as EVA or PVB at the time of pressure bonding, contributing to the improvement of strong adhesion by partial mixing. From the viewpoint of stress relaxation of the layer, it is preferable that suitable flexibility is easily obtained.

In order to improve the adhesiveness after high temperature and high humidity, a crosslinking group may be introduced into the resin itself. A silanol group is preferred from the viewpoint of the stability over time of the coating solution and the effect of improving the crosslinking density.

A resin other than the urethane resin may be contained in order to improve the adhesiveness. For example, a urethane resin, an acrylic resin, a polyester resin, or the like containing polyether or polyester as a constituent component may be used.

(Block isocyanate)
In the present invention, it is necessary to contain a blocked isocyanate having a dissociation temperature of 130 ° C. or lower and a blocking agent having a boiling point of 180 ° C. or higher in the coating solution. The blocked isocyanate can be obtained by reacting a polyisocyanate and a blocking agent. The dissociation temperature and boiling point can be measured by differential thermal analysis.

The dissociation temperature of the blocked isocyanate is 130 ° C or lower, more preferably 125 ° C or lower, and further preferably 120 ° C or lower. In the case of a drying step after application of the coating solution or an in-line coating method, the blocking agent is dissociated from the functional group by heat addition in the film forming step, and a regenerated isocyanate group is generated. Therefore, a crosslinking reaction with a urethane resin or the like proceeds, and the adhesiveness is improved. When the dissociation temperature of the blocked isocyanate is equal to or lower than the above temperature, the dissociation of the blocking agent proceeds sufficiently, so that the adhesiveness, particularly the moist heat resistance is improved. The dissociation temperature is not particularly limited as long as it is room temperature or higher for stabilization of the coating solution, but is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, and further preferably 80 ° C. or higher.

As the blocking agent, a compound having one active hydrogen in the molecule is preferably used. In this case, in order to make the dissociation temperature relatively low as described above, it is preferable to employ a blocking agent capable of obtaining a high electron density. For example, a blocking agent having a heterocyclic ring or a similar structure in the molecule is preferably used.

The boiling point of the blocking agent is 180 ° C or higher, preferably 190 ° C or higher, more preferably 200 ° C or higher, and further preferably 210 ° C or higher. The higher the boiling point of the blocking agent, the lower the volatilization of the blocking agent and the occurrence of fine irregularities on the coated surface in the heat application in the drying process after application of the coating liquid and the film formation process when the in-line coating method is adopted. It is suppressed and the transparency of the film is improved. The upper limit of the boiling point of the blocking agent is not particularly limited, but is about 300 ° C. from the viewpoint of productivity. Since the boiling point is related to the molecular weight, it is preferable to use a blocking agent having a large molecular weight in order to increase the boiling point of the blocking agent. The molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and still more preferably 80 or more.

Examples of the blocking agent having a dissociation temperature of 130 ° C. or lower used for the blocked isocyanate and a boiling point of the blocking agent of 180 ° C. or higher include bisulfite compounds such as sodium bisulfite; 3,5-dimethylpyrazole, 3-methyl Pyrazole compounds such as pyrazole, 4-bromo-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole; malonic acid diester (dimethyl malonate, diethyl malonate, di-n-butyl malonate, di2 malonate) Active methylenes such as -ethylhexyl); triazoles such as 1,2,4-triazole. Of these, pyrazole compounds are preferred from the viewpoints of heat and humidity resistance and yellowing.

The polyisocyanate that is a precursor of the blocked isocyanate is obtained by introducing diisocyanate. Examples of the polyisocyanate include diisocyanate urethane-modified products, allophanate-modified products, urea-modified products, biuret-modified products, uretdione-modified products, uretoimine-modified products, isocyanurate-modified products, and carbodiimide-modified products.

Diisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthylene diene Isocyanate, 1,4-naphthylene diisocyanate, phenylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4 '-Diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiphenyl-4 Aromatic diisocyanates such as 4'-diisocyanate and xylylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, 1,3-bis (isocyanatemethyl) cyclohexane; hexamethylene diisocyanate, 2, Aliphatic diisocyanates such as 2,4-trimethylhexamethylene diisocyanate; From the viewpoints of transparency, adhesiveness, and heat and humidity resistance, aliphatic and alicyclic isocyanates and modified products thereof are preferred. When an aromatic isocyanate is used, there is a problem of yellowing, which may not be preferable for a front sheet that requires high transparency. Moreover, since it becomes a hard coating film compared with an aliphatic type | system | group, it becomes impossible to relieve | moderate the stress by shrinkage | contraction and swelling of a sealing material etc., and adhesiveness may fall.

It is preferable that the blocked isocyanate introduces a hydrophilic group to the precursor polyisocyanate in order to impart water solubility or water dispersibility. Hydrophilic groups include (1) quaternary ammonium salts of dialkylamino alcohols and quaternary ammonium salts of dialkylaminoalkylamines, (2) sulfonates, carboxylates, phosphates, etc. (3) alkoxy groups One end-capped polyethylene glycol, polypropylene glycol and the like can be mentioned. When a hydrophilic site is introduced, it becomes (1) cationic, (2) anionic, and (3) nonionic. Especially, since many water-soluble resins are anionic, the anionic and nonionic thing which can be easily compatible is preferable. In addition, anionic ones are excellent in compatibility with the resin, and nonionic ones do not have an ionic hydrophilic group, so that they are preferable for improving the heat and moisture resistance. In addition, anionic and cationic ones aggregate with the resin or self-aggregate and may affect the transparency and appearance, and among these, nonionic ones are more preferable.

As the anionic hydrophilic group, those having a hydroxyl group for introduction into polyisocyanate and a carboxylic acid group for imparting hydrophilicity are preferable. Examples include glycolic acid, lactic acid, tartaric acid, citric acid, oxybutyric acid, oxyvaleric acid, hydroxypivalic acid, dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, and polycaprolactone having a carboxylic acid group. An organic amine compound is preferable for neutralizing the carboxylic acid group. Examples of the organic amine compound include ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, C1-C20 linear, branched 1, 2 or tertiary amines such as triisopropylamine, tributylamine and ethylenediamine; cyclic amines such as morpholine, N-alkylmorpholine and pyridine; monoisopropanolamine and methylethanol Amine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanol Amine, hydroxyl group-containing amines such as triethanolamine; and the like.

The nonionic hydrophilic group is preferably one having 3 to 50 repeating units of polyethylene glycol, polypropylene glycol having ethylene oxide and / or propylene oxide capped at one end with an alkoxy group, more preferably 5 to 30. When the repeating unit is small, the compatibility with the resin is deteriorated and the haze is increased. When the repeating unit is large, the adhesiveness under high temperature and high humidity may be decreased.

In order to improve the water dispersibility of the blocked isocyanate, nonionic, anionic, cationic, and amphoteric surfactants can be added to the coating solution. Examples of the surfactant include nonionic surfactants such as polyethylene glycol and polyhydric alcohol fatty acid esters; anionic surfactants such as fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, sulfosuccinates, and alkyl phosphates. And cationic surfactants such as alkylamine salts and alkylbetaines; amphoteric surfactants such as carboxylic acid amine salts, sulfonic acid amine salts, and sulfate ester salts.

In addition, the coating solution can contain a water-soluble organic solvent in addition to water. For example, the organic solvent used in the reaction or it can be removed and another organic solvent can be added.

The mass ratio of urethane resin to blocked isocyanate (urethane resin / block isocyanate) in the coating solution is preferably 1/9 to 9/1, more preferably 1/9 to 8/2, and further 2/8 to 6/4. preferable. Moreover, as content of the block isocyanate in the solid component of a coating liquid, 5 to 90 mass% is preferable, More preferably, it is 20 to 80 mass%. When the content of the blocked isocyanate is low, the solvent resistance of the coating layer and the adhesiveness under high temperature and high humidity decrease, and when it is high, the flexibility of the resin of the coating layer decreases, and the high temperature and high temperature Adhesion under humidity decreases. Two or more types of blocked isocyanates may be combined, or two or more types of blocking agents may be combined. In that case, at least one blocked isocyanate must satisfy the provisions of the present invention.

In the present invention, two kinds of crosslinking agents may be mixed in order to improve the strength of the coating layer. Examples of the crosslinking agent to be mixed include melamine, epoxy, carbodiimide, and oxazoline. A carbodiimide type and an oxazoline type are preferable from the viewpoint of the stability over time of the coating solution and the effect of improving the adhesion under high temperature and high humidity treatment. Moreover, in order to promote a crosslinking reaction, a catalyst etc. are used suitably as needed.

(Additive)
In the present invention, particles may be contained in the coating layer. The particles are (1) silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, titanium dioxide, zirconium dioxide, satin white, Inorganic particles such as aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrous halloysite, magnesium carbonate, magnesium hydroxide, (2) acrylic or methacrylic, vinyl chloride, vinyl acetate, nylon, styrene / acrylic, Styrene / butadiene, polystyrene / acrylic, polystyrene / isoprene, polystyrene / isoprene, methyl methacrylate / butyl methacrylate, melamine, polycarbonate, urea, epoxy, urethane Phenolic, diallyl phthalate, and organic particles of a polyester or the like.

The particles preferably have an average particle diameter of 1 to 500 nm. The average particle size is not particularly limited, but is preferably 1 to 100 nm from the viewpoint of maintaining the transparency of the film. The particles may contain two or more kinds of particles having different average particle diameters. The average particle size (on the basis of the number) is obtained by photographing a cross section of the laminated film at a magnification of 120,000 using a transmission electron microscope (TEM), and measuring 10 or more particles present in the cross section of the coating layer. The maximum diameter can be measured and obtained as an average value thereof.

The particle content is preferably 0.5% by mass or more and 20% by mass or less. When the amount is small, sufficient blocking resistance cannot be obtained. In addition, the scratch resistance is deteriorated. When the amount is large, the coating film strength decreases.

The coating layer may contain a surfactant for the purpose of improving leveling properties during coating and defoaming the coating solution. The surfactant may be any of cationic, anionic, nonionic, etc., but is preferably a silicon-based, acetylene glycol-based or fluorine-based surfactant. These surfactants are preferably contained in a range that does not impair the adhesion to the sealing material, for example, in the range of 0.005 to 0.5% by mass in the coating solution.

In order to impart other functionality to the coating layer, various additives may be contained within a range that does not impair the adhesion with the sealing material. Examples of the additive include fluorescent dyes, fluorescent brighteners, plasticizers, ultraviolet absorbers, pigment dispersants, foam suppressors, antifoaming agents, preservatives, and antistatic agents.

In the present invention, as a method of providing a coating layer on a polyester film, a method of coating a polyester film with a coating solution containing a solvent, the urethane resin, the blocked isocyanate and, if necessary, particles, and the like, and drying can be mentioned. Examples of the solvent include organic solvents such as toluene, water, and a mixed system of water and a water-soluble organic solvent. Preferably, water alone or a mixture of a water-soluble organic solvent and water is used from the viewpoint of environmental problems. preferable.

The coating layer is formed by coating a coating solution on at least one surface of the polyester film at any stage of the formed film or the film manufacturing process. In particular, coating (in-line coating method) in a film production process capable of high heat addition for dissociation of the blocking agent is preferable. There is no particular problem even if the coating layer is formed on both sides of the polyester film. The solid content concentration of the resin composition in the coating solution is preferably 2 to 35% by mass, and particularly preferably 4 to 15% by mass.

Any known method can be used as a method for applying the coating liquid to the polyester film. For example, reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, etc. It is done. These methods are applied alone or in combination.

In the case of the in-line coating method, the coating layer is formed by applying the coating solution to an unstretched or uniaxially stretched polyester film, drying it, stretching in at least a uniaxial direction, and then performing a heat treatment.

In the present invention, the thickness of the coating layer finally obtained is preferably 10 to 3000 nm, more preferably 10 to 1000 nm, still more preferably 10 to 500 nm, and particularly preferably 10 to 400 nm. The coating amount of the coating layer after drying is preferably 0.01 to 3 g / m ² , more preferably 0.01 to 1 g / m ² , still more preferably 0.01 to 0.5 g / m ² , and particularly Preferably, it is 0.01 to 0.4 g / m ² . When the coating amount of the coating layer is less than 0.01 g / m ² , the effect on the adhesiveness is almost lost. On the other hand, when the coating amount exceeds 3 g / m ² , the blocking resistance is lowered.

In order for the blocking agent of the blocked isocyanate to be easily dissociated by heat addition, the maximum temperature and heat treatment time in the tenter during heat treatment of the film is preferably 160 ° C. or higher, preferably 1 second or longer, 180 ° C. or higher, 5 seconds or longer. Is more preferable. In order to suitably suppress volatilization of the blocking agent, the maximum temperature in the tenter and the heat treatment time during heat treatment are preferably 250 ° C. or less and 60 seconds or less, and more preferably 240 ° C. or less and 50 seconds or less. In addition, the said heat processing time says the residence time from the heat processing zone in a tenter after extending | stretching to a cooling zone.

In the easily adhesive polyester film for solar cells, the thickness of the polyester film as a substrate is not particularly limited, but is preferably 20 to 500 μm, more preferably 25 to 450 μm, and further preferably 30 to 300 μm. If the substrate thickness is thin, the influence of heat shrinkage is large, and the adhesiveness after the high-temperature and high-humidity treatment may be reduced. If it is thick, it cannot be wound as a roll.

When using the easily adhesive polyester film for solar cells as a front sheet, it is desirable that the transparency of the film is high from the viewpoint of photoelectric conversion efficiency. The haze of the film is preferably less than 5.0%, more preferably less than 4.5%, and still more preferably 4.3% or less.

(Front sheet for solar cells)
The front sheet for solar cells of the present invention comprises the above-mentioned easily adhesive polyester film for solar cells as a constituent member. In particular, it is preferably used for the outermost layer that is in direct contact with the sealing material. With such a configuration, the back sheet for a solar cell of the present invention can exhibit strong adhesion with a sealing material, and exhibits excellent adhesion even under a severe environment over a long period of time. Therefore, it can contribute to moisture proof maintenance and barrier property improvement of the solar cell element.

As an aspect of the solar cell front sheet of the present invention, for example, a configuration such as the above-mentioned easily adhesive polyester film for solar cells / adhesive / metal foil or a film having a metal-based thin film layer / adhesive / hard coat layer, Examples of the configuration include an easily adhesive polyester film for solar cells / adhesive / hard coat layer. Moreover, the structure which has the said coating layer on both surfaces may be sufficient as the said easily-adhesive polyester film for solar cells. In this case, the lamination process can be suitably performed without newly providing an adhesive layer. The coating layer can exhibit good adhesion with a configuration other than the sealing material (for example, a hard coat layer). Here, as the film having a metal foil or a metal thin film layer, a film having a water vapor barrier property can be suitably used.

Examples of the metal include aluminum, tin, magnesium, silver, and stainless steel. Among them, aluminum and silver are preferable because they have a relatively high reflectance and are easily available industrially. The metal layer may be used as a metal foil, or may be laminated as a thin film on a polyester film or the like. As a method of laminating these metals as a thin film, a vacuum deposition method, a sputtering method, an ion plating method, a plasma vapor deposition method (CVD), or the like can be used.

It is also a preferable aspect that an ultraviolet absorber is added to the hard coat layer in order to improve the weather resistance. In addition, providing an antifouling layer, an antireflection layer, or the like as the outermost layer is a preferable aspect in increasing the amount of light incident on the solar cell element and improving the photoelectric conversion efficiency.

Moreover, the easily adhesive polyester film for solar cells of the present invention can also be suitably used as the innermost layer (layer on the side in contact with the sealing material) of the solar cell backsheet.

(Back sheet for solar cell)
The easy-adhesive polyester film for solar cells can be used as a constituent member of a back sheet for solar cells. In particular, it is preferably used for the outermost layer that is in direct contact with the sealing material. With such a configuration, the solar cell backsheet can exhibit strong adhesion to the sealing material, and can exhibit good adhesion even under a severe environment for a long period of time. Therefore, it can contribute to moisture proof maintenance and barrier property improvement of the solar cell element.

Examples of the back sheet for solar cell include, for example, the above-mentioned easily adhesive polyester film for solar cell / adhesive / metal foil or film having a metal thin film layer / adhesive / polyvinyl fluoride film or polyester-based highly durable moisture-proof film. Such a configuration is exemplified. Moreover, the structure which has the said coating layer on both surfaces may be sufficient as the said easily-adhesive polyester film for solar cells. The coating layer of the present invention can exhibit good adhesiveness with configurations other than the sealing material. Here, as the film having a metal foil or a metal thin film layer, a film having a water vapor barrier property can be suitably used.

(Solar cell module)
The solar cell module uses, for example, a solar cell element as a photovoltaic element provided with wiring, a sealing material interposed so as to sandwich the solar cell element, and the solar cell front sheet or back sheet of the present invention. Composed. As the sealing material, an olefin resin such as an ethylene / vinyl acetate copolymer or a polyvinyl butyral resin is preferably used. In particular, since the coating layer of the present invention has such flexibility, it can exhibit good adhesiveness with a sealing material such as an ethylene / vinyl acetate copolymer or a polyvinyl butyral resin.

Sealing materials are classified into a standard cure type that cures by a curing process in an oven provided in a separate line after thermocompression bonding in the laminating process, and a fast cure type that cures inside the laminator in the laminating process. However, either can be applied. In particular, the coating layer of the present invention can exhibit suitable adhesion in any of these types and has high versatility.

As the main component of the sealing material, an olefin resin such as an ethylene / vinyl acetate copolymer or a polyvinyl butyral resin is used. Here, the “main component” means that 50% by mass or more, more preferably 70% by mass or more of the sealing material is contained. For example, a crosslinking agent or a reaction initiator for causing the crosslinking reaction to proceed is added to the sealing material. For example, when thermal crosslinking is performed, 2,5-dimethylhexane-2,5-dihydroxyperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) -3-hexyne, di- Organic peroxides such as t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane are used. When photocuring is performed, a photosensitizer such as benzophenone, methyl orthobenzoylbenzoate or benzoin ether is used. Furthermore, a silane coupling agent may be blended in consideration of adhesion to the glass substrate. For the purpose of promoting adhesion and curing, an epoxy group-containing compound may be blended. Epoxy group-containing compounds include triglycidyl tris (2-hydroxyethyl) isocyanurate, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, acrylic glycidyl ether, 2-ethylhexyl glycidyl ether, etc. A compound is used.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

1. Evaluation method 1-1. Polyester raw material / Intrinsic viscosity of film (IV)
The polyester raw material or film was dissolved using a 6/4 (mass ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane and measured at a temperature of 30 ° C.

1-2. Glass transition temperature Based on JIS K7121, the glass transition start temperature was calculated | required from the DSC curve using the differential scanning calorimeter (The Seiko Instruments company make, "DSC6200").

1-3. The length of the crystal oriented in the longitudinal direction (MD direction) A film laminated to a thickness of about 50 μm or more is used as a sample for X-ray diffraction, and the film is placed on the sample holder of an X-ray diffraction apparatus (manufactured by Rigaku Corporation) A sample was placed so as to measure in a plane perpendicular to the MD direction. While changing the incident angle of X-rays with respect to the width direction of the film, diffraction peaks were observed by the transmission method. At this time, from the diffraction peak at 2θ of about 43 °, the crystal size D (angstrom) in the (−105) plane direction, which is the diffraction crystal plane of the peak, was calculated according to Scherrer's formula and oriented in the MD direction. The length of the crystal.
D = λ / (B−b) cos θ
Here, B: diffraction peak half width (rad), b = 0.12 (rad), λ: Cu Kα ray wavelength (1.5418 Å)

1-4. Film thickness A tape-like sample (5 cm in the horizontal direction x 1 m in the vertical direction) continuous in the vertical direction was collected, and the thickness of 20 points was measured at a 1 cm pitch using an electronic micrometer (manufactured by Seiko EMM Co., Ltd., “Millitron 1240”). And it calculated | required as the average value.

1-5. MOR-C
The film was divided into five equal parts in the width direction, and square samples with a length of 100 mm in the longitudinal direction and width direction were collected at each position. The MOR value of the obtained sample was measured using a microwave transmission type molecular orientation meter (manufactured by Oji Scientific Instruments, “MOA-6004”). The MOR-C value was determined with a thickness correction of 50 μm, and an average value of 5 points was calculated.

1-6. Density of polyester film The density was measured at 25 ° C. using a density gradient tube according to JIS K7112.

1-7. Thermal shrinkage of film at 150 ° C. (HS150)
The film was cut into a size having a width of 10 mm and a length of 250 mm along the direction in which the long side (250 mm) coincided with the longitudinal direction and the width direction, respectively, to prepare a test piece. The test piece was marked with two marks at intervals of about 200 mm, and the distance A between these two points was measured under a constant tension of 5 g. Subsequently, the test piece was left in an oven at 150 ° C. for 30 minutes with no load. The film was taken out of the oven and cooled to room temperature, and then the mark interval B was determined under a constant tension of 5 g, and the thermal shrinkage was determined by the following equation. In addition, the heat shrinkage rate at 150 ° C. of the film is measured at 100 mm intervals in the film width direction, the average value of three samples is rounded off to the third decimal place, and rounded to the second decimal place. The values in the direction with larger values in the longitudinal direction and the width direction were used.
Thermal contraction rate (%) = [(AB) / A] × 100

1-8. Carboxyl terminal concentration (AV)
The film and the raw material polyester resin were measured by the following method.
i. Preparation of sample The film or the raw material polyester resin was pulverized, vacuum-dried at 70 ° C. for 24 hours, and then weighed using a balance so that the range was 0.20 ± 0.0005 g. The mass at this time was defined as W (g). A sample weighed with 10 ml of benzyl alcohol was added to the test tube, the test tube was immersed in a benzyl alcohol bath heated to 205 ° C., and the sample was dissolved while stirring with a glass rod. Samples with dissolution times of 3 minutes, 5 minutes, and 7 minutes were designated as A, B, and C, respectively. Next, a new test tube is prepared, and only benzyl alcohol is added and processed in the same procedure, and samples when the time is 3 minutes, 5 minutes, and 7 minutes are designated as a, b, and c, respectively.
ii. Titration Titration was performed using a 0.04 mol / l potassium hydroxide solution (ethanol solution) whose factor was previously known. The indicator used was phenol red, and the titration (ml) of the potassium hydroxide solution was determined with the end point at which the color changed from yellowish green to light red. Samples A, B, and C were titrated as XA, XB, and XC (ml), and samples a, b, and c were titrated as Xa, Xb, and Xc (ml).
iii. Calculation of carboxyl terminal concentration Titration volume V (ml) at a dissolution time of 0 minutes was determined by the least square method using titration volumes XA, XB, and XC for each dissolution time. Similarly, titration volume V0 (ml) was determined using Xa, Xb, and Xc. Subsequently, the carboxyl terminal concentration was calculated | required according to following Formula.
Carboxyl terminal concentration (eq / ton) = [(V−V0) × 0.04 × NF × 1000] / W
NF: Factor of 0.04 mol / l potassium hydroxide solution

1-9. Diethylene glycol content (DEG)
After 0.1 g of polyester was thermally decomposed at 250 ° C. in 2 ml of methanol, it was quantitatively determined by gas chromatography.

1-10. Hydrolysis resistance i. Sample processing HAST (Highly Accelerated Temperature and Humidity Stress Test) standardized in JIS C-60068-2-66 was performed. The equipment was EHS-221 manufactured by ESPEC Co., Ltd. under the conditions of 105 ° C., 100% Rh, 0.03 MPa.
The film was cut into 70 mm × 190 mm, and the film was placed using a jig. Each film was placed at a distance where it did not touch. The treatment was performed for 200 hours under the conditions of 105 ° C., 100% Rh, 0.03 MPa.

ii. Breaking elongation retention rate The hydrolysis resistance was evaluated by the breaking elongation retention rate. The breaking elongation before and after each treatment was measured according to JIS C 2318-1997 5.3.31 (tensile strength and elongation), and the elongation at break was calculated according to the following formula.
Breaking elongation retention rate (%) = [(breaking elongation after treatment) × 100] / (breaking elongation before treatment)

1-11. Thermal oxidation stability parameter (thermal stability parameter) (TS)
The film ([IV] _i ) was frozen and ground to a powder of 20 mesh or less. This powder was vacuum-dried at 130 ° C. for 12 hours, and 300 mg of the powder was placed in a glass test tube having an inner diameter of about 8 mm and a length of about 140 mm and vacuum-dried at 70 ° C. for 12 hours. Next, [IV] _f1 was measured after dipping in a salt bath at 230 ° C. and heating for 15 minutes under dry air with a drying tube containing silica gel attached to the top of the test tube.
TS was determined as follows. However, [IV] _i and [IV] _f1 indicate IV (dl / g) before and after the heating test, respectively. The freeze pulverization was performed using a freezer mill (Specks Corp., Model 6750). After putting about 2 g of a resin chip or film and a dedicated impactor in a dedicated cell, the cell is set in the apparatus, liquid nitrogen is filled into the apparatus and held for about 10 minutes, and then RATE10 (the impactor is about 1 second per second). Crushed for 5 minutes.
TS = 0.245 {[IV] _f1 ^-1.47- [IV] _i ^-1.47 }

1-12. The haze of the haze film was measured using a turbidimeter (Nippon Denshoku, NDH2000) according to JIS K7136.

1-13. Absorbance measurement by infrared spectroscopy The coating layer was scraped off and a sample of about 1 mg was collected. A pressure was applied to the collected sample to prepare a coating layer sample piece (size: about 50 μm × about 50 μm) molded into a film having a thickness of about 1 μm. Further, a sample piece (blank sample piece) was prepared in the same manner as described above for a PET resin having the same quality as the base film as a blank sample.
The prepared sample piece was placed on a KBr plate, and an infrared absorption spectrum was measured by a microscopic transmission method under the following conditions. The infrared absorption spectrum of the coating layer was determined as a difference spectrum between the infrared spectrum obtained from the coating layer sample piece and the spectrum of the blank sample piece.
Absorbance around 1460 cm ^-1 derived from an aliphatic polycarbonate component (A ₁₄₆₀₎ is 1460 and the value of the absorption peak height having an absorption maximum in the region of ± 10 cm ^-1, the absorbance in the vicinity of 1530 cm ^-1 derived from urethane component (A ₁₅₃₀ ) is the value of the absorption peak height having an absorption maximum in the region of 1530 ± 10 cm ⁻¹ . The baseline was a line connecting the hems on both sides of each maximum absorption peak. The absorbance ratio was determined from the obtained absorbance by the following formula.
(Absorbance ratio) = A ₁₄₆₀ / A ₁₅₃₀

(Measurement condition)
Apparatus: FT-IR analyzer (manufactured by SPECTRA TECH, “IRμs / SIRM”)
Detector: MCT
Resolution: 4cm ^-1
Integration count: 128 times

1-14. After producing the curled back sheet, the film cut out to 10 cm × 10 cm was heated in an oven at 80 ° C. for 10 minutes. The taken back sheet is placed on a flat table, and the maximum value of the raised part is measured. A sample having a lift of 1.0 cm or less was designated as “A”, and a sample having a lift of 1.0 cm or less was designated as “B”.

1-15. Adhesiveness An easily adhesive polyester film for solar cells was prepared by cutting out 100 mm width × 100 mm length and EVA sheet cut out to 70 mm width × 90 mm length. A sample was prepared by stacking with the configuration of film (applied layer surface) / EVA / (applied layer surface) film described below and thermocompression bonding with a vacuum laminator under the following adhesive conditions. The produced sample was cut out to 20 mm width × 100 mm length, and then attached to a SUS plate, and the peel strength between the film layer and the EVA layer was measured with a tensile tester under the conditions described below. The peel strength was determined as the average value of the parts that were stably peeled after exceeding the maximum point. The ranking was based on the following criteria.
A: 100 N / 20 mm or more, or material breakage of film B: 75 N / 20 mm or more, less than 100 N / 20 mm C: 50 N / 20 mm or more, less than 75 N / 20 mm D: less than 50 N / 20 mm

(Sample preparation conditions)
Apparatus: Vacuum laminator (NPC, LM-30 × 30 type)
Pressurization: 1 atm EVA:
A. Standard cure type AI. Sunvik Ultra Pearl PV (0.4μm)
Lamination process: 100 ° C. (vacuum 5 minutes, vacuum pressurization 5 minutes)
Cure process: Heat treatment 150 ° C (normal pressure 45 minutes)
A-II. Mitsui Fabro Solar EVA SC4 (0.4μm)
Lamination process: 130 ° C (vacuum 5 minutes, vacuum pressurization 5 minutes)
Cure process: 150 ° C (45 minutes at normal pressure)
B. Fast cure type BI. Sunvik Ultra Pearl PV (0.45μm)
Lamination process: 135 ° C (vacuum 5 minutes, vacuum pressure 15 minutes)
B-II. Mitsui Fabro Solar Eva RC02B (0.45μm)
Lamination process: 150 ° C. (vacuum 5 minutes, vacuum pressure 15 minutes)

(Measurement condition)
Device: Tensilon (Toyo BALDWIN, RTM-100)
Peeling speed: 200 mm / min Peeling angle: 180 degrees

1-16. Moisture and heat resistance The easy-adhesive polyester film for solar cells was left in a constant temperature and humidity chamber at 85 ° C. and 85% RH for 1000 hours. Next, the film was taken out and allowed to stand at room temperature and humidity for 24 hours. Thereafter, the peel strength was measured by the same method as in (15) above, and ranked according to the following criteria.
A: 100 N / 20 mm or more, or material breakage of film B: 75 N / 20 mm or more, less than 100 N / 20 mm C: 50 N / 20 mm or more, less than 75 N / 20 mm D: less than 50 N / 20 mm

2. 2. Production of PET resin 2-1. Production of PET-I When the temperature of the esterification reactor reached 200 ° C., a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was charged, and trioxide was used as a catalyst while stirring. 0.017 parts by mass of antimony and 0.16 parts by mass of triethylamine were added. Subsequently, the pressure was increased and the pressure esterification reaction was performed under the conditions of a gauge pressure of 3.5 kgf / cm ² and 240 ° C. Thereafter, the inside of the esterification reaction vessel was returned to normal pressure, and 0.071 part by mass of magnesium acetate tetrahydrate and then 0.014 part by mass of trimethyl phosphate were added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by mass of trimethyl phosphate and then 0.0036 part by mass of sodium acetate were added. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, gradually heated from 260 ° C. to 280 ° C. under reduced pressure, and subjected to a polycondensation reaction at 285 ° C.

After completion of the polycondensation reaction, filtration is performed with a filter (manufactured by Naslon, 95% cut diameter is 5 μm), extruded into a strand form from a nozzle, and cooled with cooling water that has been previously filtered (pore diameter: 1 μm or less). , Solidified and cut into pellets. The obtained PET resin (PET-I) had an intrinsic viscosity of 0.620 dl / g, an acid value of 14.5 eq / ton, and contained substantially no inert particles and internally precipitated particles.

2-2. Production of PET-II After pre-crystallization of PET-I at 160 ° C., it was solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C. to obtain a PET resin having an intrinsic viscosity of 0.70 dl / g and an acid value of 10 eq / ton ( PET-II) was obtained.

2-3. Production of PET-III Polyethylene terephthalate masterbatch pellets (inherent viscosity 0.62 dl / g) containing 1000 ppm of irregular-shaped massive silica particles having an average particle size of 2.3 μm were prepared in the same manner as PET-I.

2-4. Production of PET-IV PET-III was pre-crystallized in advance at 160 ° C. and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C. to obtain a PET resin having an intrinsic viscosity of 0.71 dl / g and an acid value of 10 eq / ton ( PET-IV) was obtained.

2-5. Production of PET-V Preparation of polycondensation catalyst solution (1) Preparation of ethylene glycol solution of phosphorus compound To a flask equipped with a nitrogen introduction tube and a cooling tube, 2.0 liters of ethylene glycol was added at room temperature and normal pressure, and then stirred at 200 rpm in a nitrogen atmosphere. Meanwhile, 200 g of Irganox (registered trademark) 1222 (manufactured by Ciba Specialty Chemicals) was added as a phosphorus compound. Further, 2.0 liters of ethylene glycol was added, the temperature was raised by changing the jacket temperature setting to 196 ° C., and the mixture was stirred under reflux for 60 minutes from the time when the internal temperature reached 185 ° C. or higher. Thereafter, the heating was stopped, the solution was immediately removed from the heat source, and the solution was cooled to 120 ° C. or less within 30 minutes while maintaining the nitrogen atmosphere. The mole fraction of Irganox 1222 in the obtained solution was 40%, and the mole fraction of the compound whose structure changed from Irganox 1222 was 60%.

(2) Preparation of aqueous solution of aluminum compound After adding 5.0 liters of pure water to a flask equipped with a cooling tube at room temperature and normal pressure, 200 g of basic aluminum acetate as a slurry with pure water while stirring at 200 rpm added. Further, pure water was added so as to be 10.0 liters as a whole, and the mixture was stirred at room temperature and normal pressure for 12 hours. Thereafter, the jacket temperature was changed to 100.5 ° C., the temperature was raised, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature reached 95 ° C. or higher. Stirring was stopped and the mixture was allowed to cool to room temperature to obtain an aqueous solution.

(3) Preparation of ethylene glycol mixed solution of aluminum compound An equal volume of ethylene glycol was added to the aluminum compound aqueous solution obtained by the above method, and the mixture was stirred at room temperature for 30 minutes. Thereafter, the internal temperature was controlled at 80 to 90 ° C., and the pressure was gradually reduced to reach 27 hPa, and water was distilled off from the system while stirring for several hours to obtain an ethylene glycol solution of an aluminum compound of 20 g / l. The peak integration value ratio of ²⁷ Al-NMR spectrum of the obtained aluminum solution was 2.2.

II. Esterification reaction and polycondensation It consists of three continuous esterification reaction tanks and three polycondensation reaction tanks, and has a high-speed stirrer in the transfer line from the third esterification reaction tank to the first polycondensation reaction tank. A continuous polyester production apparatus equipped with an in-line mixer was used. 1 part by mass of high-purity terephthalic acid and 0.75 part by mass of ethylene glycol were continuously supplied to the slurry preparation tank to prepare a slurry. The prepared slurry is continuously supplied to the esterification reaction layer, the first esterification tank has a reaction temperature of 250 ° C. and 110 kPa, the second esterification reaction tank has 260 ° C. and 105 kPa, the third esterification reaction tank has 260 ° C., 105 kPa. At the same time, 0.025 parts by mass of ethylene glycol was continuously added to the second esterification reaction tank to obtain a polyester oligomer. The oligomer was continuously transferred to a continuous polycondensation apparatus consisting of three reaction vessels. At this time, the ethylene glycol solution of the aluminum compound and the ethylene glycol solution of the phosphorus compound prepared by the above method were added to the in-line mixer installed in the transfer line. In addition, it added continuously, stirring with a stirring mixer so that it might become 0.015 mol% and 0.036 mol% as an aluminum atom and a phosphorus atom with respect to the acid component in polyester, respectively. The initial polycondensation reaction tank is 265 ° C., 9 kPa, the intermediate polycondensation reaction tank is 265-268 ° C., 0.7 kPa, the final polycondensation reaction tank is 273 ° C., 13.3 Pa, and the intrinsic viscosity is 0.630 dl. PET resin (PET-V) having a carboxyl terminal concentration of 10.5 eq / ton was obtained.

2-6. Production of PET-VI Using a rotary vacuum polymerization apparatus, PET-V was subjected to solid phase polymerization at a reduced pressure of 0.5 mmHg at 220 ° C. for various times, with an intrinsic viscosity of 0.72 dl / g and a carboxyl end concentration. Produced a 5.0 eq / ton PET resin (PET-VI).

3. 3. Polyester film for solar cell 3-1. Production Example 1
(Production of film)
A mixture of 50% by mass of PET resin (PET-II) and 50% by mass of (PET-IV) was used as a raw material for the layer (A). 100% by mass of PET resin (PET-II) was used as a raw material for the layer (B). These raw materials were put into separate extruders, mixed and melted at 285 ° C., and then joined in a molten state to form an A / B / A layer using a feed block. At this time, the discharge rate ratio of the A layer and the B layer was controlled using a gear pump. Next, the sheet was extruded onto a cooling drum adjusted to 30 ° C. using a T-die to produce an unstretched sheet.

(Production of biaxially stretched film)
The obtained unstretched sheet was uniformly heated to 75 ° C. using a heating roll, and heated to 100 ° C. with a non-contact heater to perform 3.3-fold roll stretching. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C., stretched to 4.0 times, fixed in width, heat-treated at 215 ° C. for 5 seconds, and further 210% in the width direction at 210 ° C. By relaxing, a polyester film for solar cells having a thickness of 50 μm (A / B / A = 3/44/3 μm) was obtained.

3-2. Production Example 2
A polyester film for solar cells having a thickness of 100 μm (6/88/6 μm) was obtained in the same manner as in Production Example 1 except that the discharge amount and speed were adjusted.

3-3. Production Example 3
The film produced in Production Example 1 was passed through an offline dryer (5-zone temperature control, each zone length 3 m, width 2 m, non-contact, wind speed 7 m / min) at a maximum setting temperature of 170 ° C. and a speed of 30 m / min. In addition, in order to maintain planarity, it processed, controlling line tension, and obtained the polyester film for solar cells.

3-4. Production Example 4
The unstretched sheet obtained by the same method as in Production Example 1 was uniformly heated to 75 ° C. using a heating roll, and heated to 100 ° C. with a non-contact heater to perform 3.3-fold roll stretching. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C., stretched to 4.0 times, fixed in width, and subjected to heat treatment at 215 ° C. for 5 seconds. Further, the film was relaxed by 4% in the width direction at 210 ° C., and both ends of the film were cut at 170 ° C. Next, while the end portion was held with a pinch roll, the speed of the take-up roll was adjusted to perform a longitudinal relaxation treatment to obtain a polyester film for a solar cell.

3-5. Production Example 5
In Production Example 1, a polyester film for a solar cell having a thickness of 50 μm was obtained in the same manner as in Production Example 1 except that the longitudinal draw ratio was 3.7 times and the horizontal draw ratio was 3.8 times.

3-6. Production Example 6
A polyester film for a solar cell solar cell having a thickness of 50 μm was obtained in the same manner as in Production Example 1 except that both layers (A) and (B) were made 100% by mass of polyethylene terephthalate resin (PET-VI).

3-7. Production Example 7
(Preparation of coating solution)
(Polymerization of urethane resin solution containing aliphatic polycarbonate polyol)
In a reaction vessel, 43.75 parts by mass of 4,4-diphenylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, 153.41 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, And 84.00 mass parts of acetone was added as a solvent, and it stirred at 75 degreeC under nitrogen atmosphere for 3 hours. After the temperature of the reaction solution was lowered to 40 ° C., 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. 450 g of water was added, the temperature was adjusted to 25 ° C., and the polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 2000 min ⁻¹ . Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution I having a solid content of 35% by mass. The glass transition temperature of the obtained polyurethane resin was −30 ° C.
(Coating solution)
The following coating agents were mixed to prepare a coating solution.
Water 55.86% by mass
Isopropanol 30.00% by mass
Polyurethane resin solution I 13.52% by mass
0.59% by mass of particles
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

In Production Example 1, the coating solution was applied to one side of a PET film by roll coating on a uniaxially oriented PET film that had been longitudinally stretched, and then dried at 80 ° C. for 20 seconds. In addition, it adjusted so that the application quantity after the final (after biaxial stretching) drying might be 0.15 g / m < ² >. Subsequently, the film was stretched by a tenter in the same manner as in Example 1 to obtain a polyester film for a solar cell having a thickness of 50 μm.

The obtained film 100 mm width × 100 mm length, EVA sheet cut into 70 mm width × 90 mm length was prepared, stacked with the configuration of film (coating layer surface) / EVA / (coating layer surface) film described below, and the following with a vacuum laminator A sample was prepared by thermocompression bonding under the described bonding conditions. The produced sample exhibited good adhesion even after being left in an environment of 85 ° C. and 85% RH for 1000 hours in a high-temperature and high-humidity tank.

Apparatus: Vacuum laminator LM-30 × 30 type, pressurization: 1 atm EVA: Sanbic Ultra Pearl PV (0.4 μm)
Lamination process: 100 ° C. (vacuum 5 minutes, vacuum pressurization 5 minutes)
Cure process: Heat treatment 150 ° C (normal pressure 45 minutes)

3-8. Production Example 8
A 50 μm-thick polyester film for solar cells was obtained in the same manner as in Production Example 1 except that both layers (A) and (B) were changed to 100% by mass of polyethylene terephthalate resin (PET-I).

3-9. Production Example 9
A solar cell having a thickness of 50 μm was produced in the same manner as in Production Example 1 except that the longitudinal draw ratio was 3.0 times, the transverse draw ratio was 4.3 times, and the heat setting temperature in the tenter was 245 ° C. in Production Example 1. A polyester film was obtained.

The evaluation results of the obtained polyester film for solar cells are shown in Table 1.

3-10. Production Example 10
(Manufacture of back sheets for solar cells)
The solar cell polyester film / polyester film (manufactured by Toyobo Co., Ltd., A4300 125 μm) / manufactured example 1 solar cell polyester film was bonded by a dry laminating method to obtain a solar cell backsheet. .
Adhesive for dry lamination Takelac A-315 (Mitsui Chemicals) / Takenate A-10 (Mitsui Chemicals) = 9/1 (solid content ratio)

4). Preparation of urethane resin 4-1. Polymerization of urethane resin A-1 having aliphatic polycarbonate polyol as a constituent component 4,4-dicyclohexylmethane was added to a 4-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer. 43.75 parts by mass of diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, 153.41 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent And stirred at 75 ° C. for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached a predetermined amine equivalent. Next, after the temperature of this reaction liquid was lowered to 40 ° C., 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25 ° C., and stirred and mixed at 2000 min ⁻¹ , the polyurethane prepolymer solution was added and dispersed in water. . Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution (A-1) having a solid content of 35% by mass. The obtained polyurethane resin (A-1) had a glass transition temperature of −30 ° C.

4-2. Polymerization of Urethane Resin A-2 Containing Aliphatic Polycarbonate Polyol As a 4-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 4,4-dicyclohexylmethane 29.14 parts by mass of diisocyanate, 7.57 parts by mass of dimethylolbutanoic acid, 173.29 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 3000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent And stirred at 75 ° C. for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached a predetermined amine equivalent. Next, after the temperature of this reaction liquid was lowered to 40 ° C., 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25 ° C., and stirred and mixed at 2000 min ⁻¹ , the polyurethane prepolymer solution was added and dispersed in water. . Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution (A-2) having a solid content of 35% by mass.

4-3. Polymerization of urethane resin A-3 comprising aliphatic polycarbonate polyol as a constituent component 4,4-dicyclohexylmethane was added to a 4-neck flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer. 43.75 parts by weight of diisocyanate, 11.12 parts by weight of dimethylolbutanoic acid, 1.97 parts by weight of hexanediol, 143.40 parts by weight of polyhexamethylene carbonate diol having a number average molecular weight of 2000, 0.03 parts by weight of dibutyltin dilaurate, and 84.00 parts by mass of acetone was added as a solvent, and the mixture was stirred at 75 ° C. for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached a predetermined amine equivalent. Next, after the temperature of this reaction liquid was lowered to 40 ° C., 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25 ° C., and stirred and mixed at 2000 min ⁻¹ , the polyurethane prepolymer solution was added and dispersed in water. . Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution (A-3) having a solid content of 35% by mass.

4-4. Polymerization of urethane resin A-4 containing aliphatic polycarbonate polyol as a constituent component Polyhexamethylene carbonate diol having a number average molecular weight of 2000 in the water-soluble polyurethane resin (A-1) is changed to polyhexamethylene carbonate diol having a number average molecular weight of 1000. A water-soluble polyurethane resin solution (A-4) having a solid content of 35% by mass was obtained in the same manner except for the change.

4-5. Polymerization of urethane resin A-5 containing aliphatic polycarbonate polyol as a constituent component Polyhexamethylene carbonate diol having a number average molecular weight of 2,000 in water-soluble polyurethane resin (A-1) is changed to polyhexamethylene carbonate diol having a number average molecular weight of 5,000. A water-soluble polyurethane resin solution (A-5) having a solid content of 35% by mass was obtained in the same manner except for the change.

4-6. Polymerization of Urethane Resin A-6 Containing Polyester Polyol Same as above except that polyhexamethylene carbonate diol having a number average molecular weight of 2000 in the water-soluble polyurethane resin (A-1) is changed to a polyester diol having a number average molecular weight of 2000 Thus, a water-soluble polyurethane resin solution (A-6) having a solid content of 35% by mass was obtained.

5. Preparation of blocked isocyanate 5-1. Synthesis of Block Polyisocyanate Crosslinking Agent B-1 A polyisocyanate compound having an isocyanurate structure using hexamethylene diisocyanate as a raw material (Duranate (registered trademark) manufactured by Asahi Kasei Chemicals) in a flask equipped with a stirrer, a thermometer, and a reflux condenser. TPA) 52.21 parts by mass were added. To this, 20.72 parts by mass of polyethylene glycol monomethyl ether (number average molecular weight 1000) was added dropwise and held at 70 ° C. for 5 hours in a nitrogen atmosphere. Thereafter, 27.08 parts by mass of 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) was added dropwise. After measuring the infrared spectrum of the reaction solution and confirming that the absorption of the isocyanate group had disappeared, 25 parts by mass of dipropylene glycol dimethyl ether and 125 parts by mass of water were added, and the mixture was stirred at 30 ° C. at a high speed. A block polyisocyanate aqueous dispersion (B-1) was obtained.

5-2. Synthesis of Block Polyisocyanate Crosslinking Agent B-2 A polyisocyanate compound having a biuret structure using hexamethylene diisocyanate as a raw material (Duranate 24A-100, manufactured by Asahi Kasei Chemicals) 52 in a flask equipped with a stirrer, a thermometer, and a reflux condenser. .54 parts by mass were added. To this, 19.78 parts by mass of polyethylene glycol monomethyl ether (number average molecular weight 1000) was added dropwise and held at 70 ° C. for 5 hours in a nitrogen atmosphere. Thereafter, 27.67 parts by mass of 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) was added dropwise. After measuring the infrared spectrum of the reaction solution and confirming that the absorption of the isocyanate group had disappeared, 25 parts by mass of dipropylene glycol dimethyl ether and 125 parts by mass of water were added, and the mixture was stirred at 30 ° C. at a high speed. A block polyisocyanate aqueous dispersion (B-2) was obtained.

5-3. Synthesis of Block Polyisocyanate Crosslinking Agent B-3 A polyisocyanate compound having an isocyanurate structure using hexamethylene diisocyanate as a raw material (Duranate TPA, manufactured by Asahi Kasei Chemicals) in a flask equipped with a stirrer, a thermometer, and a reflux condenser 66. 04 parts by mass and 17.50 parts by mass of N-methylpyrrolidone were added. 25.19 parts by mass of 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) was added dropwise thereto, and the mixture was kept at 70 ° C. for 1 hour in a nitrogen atmosphere. Thereafter, 5.27 parts by mass of dimethylolpropanoic acid was added dropwise. After measuring the infrared spectrum of the reaction solution and confirming that the absorption of the isocyanate group disappeared, 5.59 parts by mass of N, N-dimethylethanolamine and 132.5 parts by mass of water were added, and the solid content was 40% by mass. A block polyisocyanate aqueous dispersion (B-3) was obtained.

5-4. Synthesis of Block Polyisocyanate Crosslinking Agent B-4 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) of the block polyisocyanate aqueous dispersion (B-1) was converted to diethyl malonate (dissociation temperature: 120). A block polyisocyanate aqueous dispersion (B-4) having a solid content of 40% by mass was obtained in the same manner except that the temperature was changed to 0 ° C. and a boiling point of 199 ° C.

5-5. Synthesis of Block Polyisocyanate Crosslinking Agent B-5 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) of the block polyisocyanate aqueous dispersion (B-1) was converted to methyl ethyl ketoxime (dissociation temperature: 140 ° C.). A block polyisocyanate aqueous dispersion (B-5) having a solid content of 40% by mass was obtained in the same manner except that the boiling point was changed to 152 ° C.).

5-6. Synthesis of Block Polyisocyanate Crosslinking Agent B-6 3,5-Dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) of block polyisocyanate aqueous dispersion (B-3) was converted to methyl ethyl ketoxime (dissociation temperature: 140 ° C.). A block polyisocyanate aqueous dispersion (B-6) having a solid content of 40% by mass was obtained in the same manner except that the boiling point was changed to 152 ° C.).

6). 6. Easy adhesive polyester film for solar cell 6-1. Production Example 11
(1) Adjustment of coating liquid The following coating agent was mixed and the coating liquid was produced.
Water 55.62% by mass
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 11.29% by mass
Block polyisocyanate aqueous dispersion (B-1) 2.26% by mass
Particles 0.71% by mass
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
0.07% by mass of particles
(Silica sol with an average particle size of 450 nm, solid content concentration of 40% by mass)
Surfactant 0.05% by mass
(Silicon, solid content concentration of 100% by mass)

(2) Production of Easy Adhesive Polyester Film for Solar Cell A mixture of 50% by mass of PET resin (PET-II) and 50% by mass of (PET-IV) was used as a raw material for the layer (A). 100% by mass of PET resin (PET-II) was used as a raw material for the layer (B). These raw materials were put into separate extruders, mixed and melted at 285 ° C., and then joined in a molten state to form an A / B / A layer using a feed block. At this time, the discharge rate ratio of the A layer and the B layer was controlled using a gear pump. Next, the sheet was extruded onto a cooling drum adjusted to 30 ° C. using a T-die to produce an unstretched sheet.

The obtained unstretched sheet was uniformly heated to 75 ° C. using a heating roll, and heated to 100 ° C. with a non-contact heater to perform 3.3-fold roll stretching. Next, the coating solution that was allowed to stand at room temperature for 5 hours or more was applied to one side of a uniaxially stretched film obtained by a roll coating method, and then dried at 80 ° C. for 20 seconds. In addition, it adjusted so that the application quantity after the last drying (after biaxial stretching) might be set to 0.15 g / m < ² > (coating layer thickness after drying 150 nm). Further, the film is led to a tenter, heated to 140 ° C., stretched to 4.0 times, fixed in width, subjected to heat treatment at 215 ° C. for 5 seconds, and further relaxed by 4% in the width direction at 210 ° C. 100 micrometer (A / B / A = 6/88 / 6micrometer) The easily adhesive polyester film for solar cells was obtained.

6-2. Production Example 12
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the block polyisocyanate aqueous dispersion was changed to the block polyisocyanate aqueous dispersion (B-5).

6-3. Production Example 13
An easily adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the block polyisocyanate aqueous dispersion was changed to the block polyisocyanate aqueous dispersion (B-6).

6-4. Production Example 14
For a solar cell in the same manner as in Example 1 except that the block polyisocyanate aqueous dispersion was changed to a polyisocyanate aqueous dispersion having an isocyanurate structure (WT30-100, manufactured by Asahi Kasei Chemicals) using hexamethylene diisocyanate as a raw material. An easily adhesive polyester film was obtained.

6-5. Production Example 15
Except having changed the coating liquid into the following, it carried out similarly to manufacture example 11, and obtained the easily adhesive polyester film for solar cells.
Water 58.02% by mass
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 9.47% by mass
Block polyisocyanate aqueous dispersion (B-1) 1.89 mass%
0.59% by mass of particles
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-6. Production Example 16
Except having changed the coating liquid into the following, it carried out similarly to manufacture example 11, and obtained the easily adhesive polyester film for solar cells.
54.75% by mass of water
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 12.99% by mass
Block polyisocyanate aqueous dispersion (B-1) 1.52% by mass
Particles 0.71% by mass
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-7. Production Example 17
Except having changed the coating liquid into the following, it carried out similarly to manufacture example 11, and obtained the easily adhesive polyester film for solar cells.
Water 57.35% by mass
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 8.12% by mass
Block polyisocyanate aqueous dispersion (B-1) 3.79% by mass
Particles 0.71% by mass
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-8. Production Example 18
Except having changed the coating liquid into the following, it carried out similarly to Example 1, and obtained the easily adhesive polyester film for solar cells.
Water 59.95% by mass
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 3.25% by mass
Block polyisocyanate aqueous dispersion (B-1) 6.06% by mass
Particles 0.71% by mass
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-9. Production Example 19
Except having changed the coating liquid into the following, it carried out similarly to manufacture example 11, and obtained the easily adhesive polyester film for solar cells.
60.82% by mass of water
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 1.62% by mass
Block polyisocyanate aqueous dispersion (B-1) 6.82 mass%
Particles 0.71% by mass
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-10. Production Example 20
An easily adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the polyurethane resin was changed to the polyurethane resin (A-2).

6-11. Production Example 21
An easily adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the polyurethane resin was changed to the polyurethane resin (A-3).

6-12. Production Example 22
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the polyurethane resin was changed to the polyurethane resin (A-4).

6-13. Production Example 23
A reester film for solar cells was obtained in the same manner as in Production Example 11 except that the polyurethane resin was changed to polyurethane resin (A-5).

6-14. Production Example 24
An easily adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the polyurethane resin was changed to polyurethane resin (A-6).

6-15. Production Example 25
An easily adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the block polyisocyanate aqueous dispersion (B-1) was changed to the block polyisocyanate aqueous dispersion (B-2).

6-16. Production Example 26
An easily adhesive polyester film for a solar cell was obtained in the same manner as in Production Example 11 except that the block polyisocyanate aqueous dispersion (B-1) was changed to the block polyisocyanate aqueous dispersion (B-3).

6-17. Production Example 27
An easily adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that the block polyisocyanate aqueous dispersion (B-1) was changed to the block polyisocyanate aqueous dispersion (B-4).

6-18. Production Example 28
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that PET resin pellets having an intrinsic viscosity of 0.69 g / dl that practically did not contain particles were used as the PET resin for the outer layer.

6-19. Production Example 29
A solar cell easy-adhesive polyester film was obtained in the same manner as in Production Example 11 except that the base layer thickness of the solar cell easy-adhesive polyester film was changed to 50 μm while keeping the ratio of each layer the same.

6-20. Production Example 30
A solar cell easy-adhesive polyester film was obtained in the same manner as in Production Example 29 except that the base layer thickness of the solar cell easy-adhesive polyester film was changed to 350 μm while maintaining the same ratio of each layer.

6-21. Production Example 31
Except having changed the coating liquid into the following, it carried out similarly to manufacture example 29, and obtained the easily adhesive polyester film for solar cells.
62.82% by mass of water
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 5.67% by mass
Block polyisocyanate aqueous dispersion (B-1) 1.13% by mass
0.35% by mass of particles
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-22. Production Example 32
Except having changed the coating liquid into the following, it carried out similarly to manufacture example 11, and obtained the easily adhesive polyester film for solar cells.
Water 45.9 mass%
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 18.99% by mass
Block polyisocyanate aqueous dispersion (B-1) 3.80 mass%
1.19% by mass of particles
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
Surfactant 0.03 mass%
(Silicon, solid content concentration of 100% by mass)

6-23. Production Example 33
The film produced in Production Example 11 was passed through the film with an offline dryer (5 zone temperature control, each zone length 3 m, width 2 m, non-contact, wind speed 7 m / min) at a maximum setting temperature of 170 ° C. and a speed of 30 m / min. . In addition, in order to maintain flatness, it processed, controlling line tension, and obtained the easily adhesive polyester film for solar cells.

6-24. Production Example 34
An unstretched sheet obtained by the same method as in Production Example 11 was uniformly heated to 75 ° C. using a heating roll, and heated to 100 ° C. with a non-contact heater to perform 3.3-fold roll stretching. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C., stretched to 4.0 times, fixed in width, and subjected to heat treatment at 215 ° C. for 5 seconds. Further, the film was relaxed by 4% in the width direction at 210 ° C., and both ends of the film were cut at 170 ° C. Next, the gripping roll was adjusted while adjusting the speed of the take-up roll while holding the end with a pinch roll to obtain an easily adhesive polyester film for solar cells.

6-25. Production Example 35
In Production Example 11, a solar cell easy-adhesive polyester film was obtained in the same manner as in Production Example 11 except that the longitudinal draw ratio was 3.7 times and the horizontal draw ratio was 3.8 times.

6-26. Production Example 36
An easy-adhesive polyester film for a solar cell solar cell was obtained in the same manner as in Production Example 11, except that both layers (A) and (B) were changed to 100% by mass of polyethylene terephthalate resin (PET-VI).

6-27. Production Example 37
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Production Example 11 except that both layers (A) and (B) were changed to 100% by mass of polyethylene terephthalate resin (PET-I).

6-28. Production Example 38
In Production Example 11, a solar cell easy-adhesive polyester film was obtained in the same manner except that the longitudinal draw ratio was 3.0 times, the transverse draw ratio was 4.3 times, and the heat setting temperature in the tenter was 245 ° C. It was.

6-29. Production Example 39
Manufacture of front sheet for solar cell In Production Example 11, an easy-adhesive polyester film for solar cell was obtained in the same manner except that coating layers were formed on both surfaces of the film. The front sheet for solar cells was obtained by apply | coating and hardening | curing ultraviolet curable acrylate on the single side | surface of the obtained easily adhesive polyester film for solar cells, and forming a hard-coat layer (5 micrometers).

Tables 2 and 3 show the evaluation results of the easily adhesive polyester film for solar cell obtained.

Since the polyester film for solar cells of the present invention is excellent in hydrolysis resistance and processability, it is suitable for a solar cell constituent material such as a solar cell backside sealing sheet and a solar cell protective sheet. Moreover, since the easily adhesive polyester film for solar cells of the present invention has good hydrolysis resistance and is excellent in transparency and adhesiveness, it is used as a base film for solar cell members, particularly solar cell front sheets. Is preferred.

Claims

The length of the crystal oriented in the longitudinal direction in the (−105 plane) measured by wide-angle X-ray diffraction method is 50 mm or more,
When the film thickness is converted to 50 μm, the MOR value (MOR-C) is 1.0 to 2.0,
A polyester film for solar cells, wherein the density of the film is 1.37 to 1.40 g / cm 3 .
The polyester film for solar cells according to claim 1, wherein the film has a thermal shrinkage rate at 150 ° C of -1.0% or more and 3.0% or less in both the longitudinal direction and the width direction.
2. The polyester film for solar cells according to claim 1, wherein the film has a thermal shrinkage rate at 150 ° C. of −0.5% or more and 0.5% or less in both the longitudinal direction and the width direction.
The polyester that makes up the film
Polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof and a phosphorus compound having a phenol moiety,
The carboxyl end concentration is 25 eq / ton or less with respect to the polyester,
The polyester film for solar cells according to any one of claims 1 to 3, wherein the intrinsic viscosity (IV) of the film is 0.60 to 0.90 dl / g.
A polyester film for solar cells according to any one of claims 1 to 4, and a coating layer formed on at least one side of the polyester film,
The coating layer is formed from a coating liquid mainly composed of urethane resin and blocked isocyanate,
The easily adhesive polyester film for solar cells, wherein the dissociation temperature of the blocked isocyanate is 130 ° C or lower, and the boiling point of the blocking agent is 180 ° C or higher.
6. The easily adhesive polyester film for solar cell according to claim 5, wherein the urethane resin is a urethane resin containing an aliphatic polycarbonate polyol as a constituent component.
In the infrared spectroscopic spectrum of the coating layer, the ratio of the absorbance at the peak near 1460 cm −1 derived from the aliphatic polycarbonate component (A 1460 ) to the absorbance at the peak near 1530 cm −1 derived from the urethane component (A 1530 ) ( The easily adhesive polyester film for solar cells according to claim 6, wherein A 1460 / A 1530 ) is 0.50 to 1.55.
The solar cell easy adhesion property according to any one of claims 5 to 7, wherein a mass ratio of the urethane resin to the blocked isocyanate (urethane resin / block isocyanate) in the coating solution is 1/9 to 9/1. Polyester film.
A solar cell front sheet comprising the easily adhesive polyester film for solar cells according to any one of claims 5 to 8.